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Craig Lee

Senior Principal Oceanographer

Professor, Oceanography





Research Interests

Upper Ocean Dynamics, Coastal Ocean Processes, Internal Waves, Fronts, Dynamics and Biological Process Interactions


Dr. Lee is a physical oceanographer specializing in observations and instrument development. His primary scientific interests include: (1) upper ocean dynamics, especially mesoscale and submesocale fronts and eddies, (2) interactions between biology, biogeochemistry and ocean physics and (3) high-latitude oceanography.

With partner Dr. Jason Gobat, Lee founded and leads a team of scientists and technologists that pursues a wide range of oceanographic field programs, including intensive studies of the Kuroshio Current, coupled physical–biogeochemical studies such as the recent patch-scale investigation of the North Atlantic spring phytoplankton bloom and studies aimed at quantifying and understanding Arctic change. An important component of this work involves identifying advances that could be achieved through novel measurements and developing new instruments to meet these needs.

The team's accomplishments include autonomous gliders capable of extended operation in ice-covered waters, high-performance towed vehicles and light-weight, inexpensive mooring technologies. The team also pursues K-12 educational outreach and routinely employs undergraduate research assistants. Within the community, Lee provides leadership through service on the science steering committees for several large research programs and by serving on and chairing advisory panels for U.S. Arctic efforts. Lee supports and advises masters and doctoral students and teaches graduate level courses on observations of ocean circulation and instruments, methods and experimental design.

Department Affiliation

Ocean Physics


B.S. Electrical Engineering and Computer Science, University of California, Berkeley, 1987

Ph.D. Physical Oceanography, University of Washington, 1995


The Submesoscale Cascade in the South China Sea

This research program is investigating the evolution of submesoscale eddies and filaments in the Kuroshio-influenced region off the southwest coast of Taiwan.

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26 Aug 2015

Science questions:
1. What role does the Kuroshio play in generating mesoscale and submesoscale variability modeled/observed off the SW coast of Taiwan?
2. How does this vary with atmospheric forcing?
3. How do these features evolve in response to wintertime (strong) atmospheric forcing?
4. What role do these dynamics play in driving water mass evolution and interior stratification in the South China Sea?
5. What role do these dynamics/features have on the transition of water masses from northern SCS water into the Kuroshio branch water/current and local flow patterns?

Salinity Processes in the Upper Ocean Regional Study — SPURS

The NASA SPURS research effort is actively addressing the essential role of the ocean in the global water cycle by measuring salinity and accumulating other data to improve our basic understanding of the ocean's water cycle and its ties to climate.

15 Apr 2015

Lateral Mixing

Small scale eddies and internal waves in the ocean mix water masses laterally, as well as vertically. This multi-investigator project aims to study the physics of this mixing by combining dye dispersion studies with detailed measurements of the velocity, temperature and salinity field during field experiments in 2011 and 2012.

1 Sep 2012

More Projects

Seasonal and Interannual Variability of the Alaska Coastal Current: Long-term, Three-dimensional Observations Using a Telemetering Autonomous Vehicle

The AUV Seaglider is used to study the seasonal and interannual variability in ACC freshwater content and transport, the ACC's role in governing springtime mixed layer evolution over the shelf, the processes controlling temporal and spatial variability in the spring bloom, and the processes that may produce onshore nutrient flux.


Physical and Optical Structures of the Upper Ocean of the Japan/East Sea

This study seeks to understand the processes that control physical and bio-optical variability in the Japan/East Sea including the upper ocean response to strong wintertime atmospheric forcing; watermass formation, subduction and spreading; dynamics of the subpolar front; and to characterize cross-front and cross-shelf bio-optical transitions.


Adriatic Circulation Experiment: Mesoscale Dynamics and Response to Strong Atmospheric Forcing

The Adriatic Sea provides a unique laboratory in which oceanographers can study the ocean's response to atmospheric forcing at small (10 km) lateral scales and investigate the processes that communicate atmospheric forcing events (seasonal winds and freshwater flows) to the ocean interior.


An Observational Array for High-resolution, Year-round Measurement of Volume, Freshwater and Ice Flux Variability in Davis Strait

A coordinated domestic and international effort quantifies the variability of fluxes connecting the Arctic and Atlantic oceans and seeks to understand the role played by the Arctic and sub-Arctic in steering decadal scale climate variability; we will make year-round measurements of volume, liquid freshwater, and ice fluxes across Davis Strait.


Glider Monitoring, Piloting, and Communications System

APL-UW is leading a consortium of glider developers in advanced research and development to improve underwater glider systems for environmental characterizations during naval operation. Improvements include a common command control and display/transfer interface for use across all existing glider designs - the GLMPC system.


Japan/East Sea Data Archive

The Japan/East Sea exhibits many of the dynamical and biological features found in larger oceans, including deep water formation, subduction, boundary inputs, fronts, eddies, and biological zonation. This, combined with the basin's modest size and easy logistics, makes the Japan/East Sea an excellent laboratory for pursuing oceanographic studies with modern instruments and approaches. Building on the work of previous investigations, the Office of Naval Research sponsored an intensive observation and modeling program that explored the sea's physical, chemical, and biological systems. The program's data products, published papers, and reports are now accumulated and presented through one user interface.


A Modular Approach to Building an Arctic Observing System for the IPY and Beyond in the Switchyard Region of the Arctic Ocean

This project will provided for the design, development, and implementation of a component of an Arctic Ocean Observing System in the Switchyard region of the Arctic Ocean (north of Greenland and Nares Strait) that will serve the scientific studies developed for the IPY (International Polar Year), SEARCH (Study of Environmental ARctic Change), and related programs. Specifically, the project will continue and expand two aircraft-based sections between Alert and the North Pole for long-term observation of hydrographic properties and a set of tracers aimed at resolving relative age structure and freshwater components in the upper water column.


Salinity Processes in the Upper-Ocean Regional Study (SPURS)

In conjunction with the new Aquarius satellite mission, which will measure sea surface salinity from space, this project aims to directly measure an annual cycle of upper ocean salinity in the North Atlantic using by high-resolution glider surveys.


North Atlantic Bloom

The phytoplankton of the North Atlantic bloom play a major role in pulling carbon dioxide from the atmosphere and storing it in the ocean. An ambitious collaborative experiment in the North Atlantic near Iceland was led to coincide with the bloom in 2008. The challenge of the experiment was to characterize the bloom's temporal and spatial evolutions of physics, biology, and chemistry over its entire duration.


North Atlantic Bloom - Webinar Series

This dynamic webinar series features the research of scientists from the North Atlantic Bloom (NAB) Experiment and focuses on key concepts in ocean science. The five-part series consists of presentations from NAB scientists, and tells the story of the North Atlantic spring phytoplankton bloom and its role in the ocean ecosystem.



Eddies Drive Particulate Carbon Deep in the Ocean During the North Atlantic Spring Bloom

The swirling eddies that create patches of stratification to hold phytoplankton near the sunlit surface during the North Atlantic spring bloom, also inject the floating organic carbon particles deep into the ocean. The finding, reported in Science, has important implications for the ocean's role in the carbon cycle on Earth: phytoplankton use carbon dioxide absorbed by the ocean from the atmosphere during the bloom and the resulting organic carbon near the sea surface is sequestered in the deep ocean.

27 Mar 2015

Seaglider: Autonomous Undersea Vehicle

APL-UW scientists continually expand Seaglider's hardware/software systems, and sensor packages. First developed for oceanographic research, it is also used by the U.S. Navy to detect and monitor marine mammals. Recently, the manufacture and marketing of Seaglider has been licensed to Kongsberg Underwater Technology, Inc., which will push the vehicle to emerging markets in offshore environmental monitoring for the oil and gas industry.

14 Aug 2013

Marginal Ice Zone (MIZ) Program

An integrated program of observations and numerical simulations will focus on understanding ice–ocean–atmosphere dynamics in and around the MIZ, with particular emphasis on quantifying changes associated with decreasing ice cover. The MIZ measurement program will employ a novel mix of autonomous technologies (ice-based instrumentation, floats, drifters, and gliders) to characterize the processes that govern Beaufort Sea MIZ evolution from initial breakup and MIZ formation though the course of the summertime sea ice retreat.

22 Mar 2013

More Videos


2000-present and while at APL-UW

Stratified Ocean Dynamics in the Arctic: Science and Experiment Plan

Lee, C.M., et al., "Stratified Ocean Dynamics in the Arctic: Science and Experiment Plan," APL-UW TR 1601, Technical Report, Applied Physics Laboratory, University of Washington, Seattle, September 2016, 46pp.

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15 Sep 2016

Vertical and lateral water properties and density structure within the Arctic Ocean are intimately related to the ocean circulation, and have profound consequences for sea ice growth and retreat as well as for propagation of acoustic energy at all scales. Our current understanding of the dynamics governing arctic upper ocean stratification and circulation derives largely from a period when extensive ice cover modulated the oceanic response to atmospheric forcing. Recently, however, there has been significant arctic warming, accompanied by changes in the extent, thickness distribution, and properties of the arctic sea ice cover. The need to understand these changes and their impact on arctic stratification and circulation, sea ice evolution, and the acoustic environment motivate the Office of Naval Research (ONR) Stratified Ocean Dynamics of the Arctic Departmental Research Initiative.

Collaborative observations of boundary currents, water mass variability, and monsoon response in the southern Bay of Bengal

Lee, C.M., S.U.P. Jinadasa, A. Anutaliya, L.R. Centurioni, H.J.S. Fernando, V. Hormann, M. Lankhorst, L. Rainville, U. Send, and H.W. Wijesekera, "Collaborative observations of boundary currents, water mass variability, and monsoon response in the southern Bay of Bengal," Oceanography 29, 102–111, doi:10.5670/oceanog.2016.43, 2016.

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1 Jun 2016

The region surrounding Sri Lanka modulates monsoon-driven exchange between the Bay of Bengal and the Arabian Sea. Here, local circulation impacts the pathways followed by the boundary currents that drive exchange, thereby modulating mixing and water mass transformation. From 2013 to 2016, an international partnership conducted sustained measurements around the periphery of Sri Lanka, with the goal of understanding how circulation and mixing in this critical region modulate exchange between the Bay of Bengal and the Arabian Sea. Observations from satellite remote sensing, surface drifters, gliders, current meter moorings, and Pressure Inverted Echo Sounders capture seasonally reversing monsoon currents off the southern tip of Sri Lanka, trace the wintertime freshwater export pathway of the East India Coastal Current, and document the deflection of currents running along the east coast of Sri Lanka by cyclonic and anticyclonic eddies. Measurements also reveal energetic interleaving, indicative of mixing and stirring associated with these flows. Circulation inferred from satellite remote sensing and drifter tracks sometimes differs from that indicated by in situ sections, pointing to the need for observing systems that employ complementary approaches toward understanding this region.

Radar backscattering changes in Arctic sea ice from late summer to early autumn observed by space-borne X-band HH-polarization SAR

Park, J.-W., H.-C. Kim, S.-H. Hong, S.-Ho. Dang, H.C. Graber, B. Hwang, and C.M. Lee, "Radar backscattering changes in Arctic sea ice from late summer to early autumn observed by space-borne X-band HH-polarization SAR," Remote Sens. Lett., 7, 551-560, doi:10.1080/2150704X.2016.1165881, 2016.

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1 Jun 2016

Melt ponds are believed to play an important role in sea ice dynamics because they accelerate the melting of sea ice in the warmer spring and summer months. Additionally, they are known to absorb solar radiation rather than reflect it as the surrounding sea ice does. However, the size and distribution of melt ponds are highly variable, and thus, the contribution of melt ponds to sea ice melting should differ based on the maturity of the melt pond. Because of the harsh conditions of the Arctic, estimating the actual surface changes via in situ measurements and/or optical remote sensing data is difficult. In this study, we present a high-resolution time-series analysis of the short-term variation of sea ice and melt ponds over the Beaufort Sea using space-borne multispectral and synthetic aperture radar (SAR) images. A KOMPSAT-3 (Korea Multi-Purpose Satellite-3) optical image was used for an initial classification of the surface types, and 15 TerraSAR-X SAR images covering 46 days in the 2014 Arctic summer were used to perform a dense time-series analysis. The surface of the target sea ice was classified into six categories based on spectral characteristics. The temporal variation of the radar backscattering coefficient in each class exhibited a distinct pattern, which was closely related to surface changes. Overall, changes in the radar backscattering coefficient indicated dynamic surface changes, except over pressure ridges. All ice classes showed a two-step decrease in radar backscattering, whereas snow-covered ice surfaces exhibited far fewer changes compared to bare ice surfaces. The surfaces adjacent to ponds showed stronger negative decreases than other classes. The changes in dark melt pond classes presented a complex non-linear decrease, which differed from the stepwise decrease of blue melt ponds. These observations can be used for important modelling studies of surface melting/freezing rates and to infer the variation over large areas using remote sensing data.

More Publications

Global estimate of lateral springtime restratification

Johnson, L., C.M. Lee, and E.A. D'Asaro, "Global estimate of lateral springtime restratification," J. Phys. Oceanogr., 46, 1555–1573, doi:10.1175/JPO-D-15-0163.1, 2016.

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1 May 2016

Submesoscale frontal dynamics are thought to be of leading-order importance for stratifying the upper ocean by slumping horizontal density gradients to produce vertical stratification. Presented here is an investigation of submesoscale instabilities in the mixed layer—mixed layer eddies (MLEs)—as a potential mechanism of frontal slumping that stratifies the upper ocean during the transition from winter to spring, when wintertime forcings weaken but prior to the onset of net solar warming. Observations from the global Argo float program are compared to predictions from a one-dimensional mixed layer model to assess where in the world’s oceans lateral processes influence mixed layer evolution. The model underestimates spring stratification for ~75% ± 25% of the world’s oceans. Relationships between vertical and horizontal temperature and salinity gradients are used to suggest that in 30% ± 20% of the oceans this excess stratification can be attributed to the slumping of horizontal density fronts. Finally, 60% ± 10% of the frontal enhanced stratification is consistent with MLE theory, suggesting that MLEs may be responsible for enhanced stratification in 25% ± 15% of the world’s oceans. Enhanced stratification from frontal tilting occurs in regions of strong horizontal density gradients (e.g., midlatitude subtropical gyres), with a small fraction occurring in regions of deep mixed layers (e.g., high latitudes). Stratification driven by MLEs appears to constrain the coexistence of sharp lateral gradients and deep wintertime mixed layers, limiting mixed layer depths in regions of large lateral density gradients, with an estimated wintertime restratification flux of order 100 W m−2.

An assessment of the Arctic Ocean in a suite of interannual CORE-II simulations. Part II: Liquid freshwater

Wang, Q., et al., including B. Curry and C.M. Lee, "An assessment of the Arctic Ocean in a suite of interannual CORE-II simulations. Part II: Liquid freshwater," Ocean Model., 99, 86-109, doi:10.1016/j.ocemod.2015.12.009, 2016.

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1 Mar 2016

The Arctic Ocean simulated in 14 global ocean-sea ice models in the framework of the Coordinated Ocean-ice Reference Experiments, phase II (CORE-II) is analyzed in this study. The focus is on the Arctic liquid freshwater (FW) sources and freshwater content (FWC). The models agree on the interannual variability of liquid FW transport at the gateways where the ocean volume transport determines the FW transport variability. The variation of liquid FWC is induced by both the surface FW flux (associated with sea ice production) and lateral liquid FW transport, which are in phase when averaged on decadal time scales. The liquid FWC shows an increase starting from the mid-1990s, caused by the reduction of both sea ice formation and liquid FW export, with the former being more significant in most of the models. The mean state of the FW budget is less consistently simulated than the temporal variability. The model ensemble means of liquid FW transport through the Arctic gateways compare well with observations. On average, the models have too high mean FWC, weaker upward trends of FWC in the recent decade than the observation, and low consistency in the temporal variation of FWC spatial distribution, which needs to be further explored for the purpose of model development.

An assessment of the Arctic Ocean in a suite of internal CORE-II simulations. Part I: Sea ice and solid freshwater

Wang, Q., et al., including B. Curry and C.M. Lee, "An assessment of the Arctic Ocean in a suite of internal CORE-II simulations. Part I: Sea ice and solid freshwater," Ocean Model., 99, 110-132, doi:10.1016/j.ocemod.2015.12.008, 2016.

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1 Mar 2016

The Arctic Ocean simulated in fourteen global ocean-sea ice models in the framework of the Coordinated Ocean-ice Reference Experiments, phase II (CORE II) is analyzed. The focus is on the Arctic sea ice extent, the solid freshwater (FW) sources and solid freshwater content (FWC). Available observations are used for model evaluation. The variability of sea ice extent and solid FW budget is more consistently reproduced than their mean state in the models. The descending trend of September sea ice extent is well simulated in terms of the model ensemble mean. Models overestimating sea ice thickness tend to underestimate the descending trend of September sea ice extent. The models underestimate the observed sea ice thinning trend by a factor of two. When averaged on decadal time scales, the variation of Arctic solid FWC is contributed by those of both sea ice production and sea ice transport, which are out of phase in time. The solid FWC decreased in the recent decades, caused mainly by the reduction in sea ice thickness. The models did not simulate the acceleration of sea ice thickness decline, leading to an underestimation of solid FWC trend after 2000. The common model behavior, including the tendency to underestimate the trend of sea ice thickness and March sea ice extent, remains to be improved.

Submesoscale streamers exchange water on the north wall of the Gulf Stream

Klymak, J.M., R.K. Shearman, J. Gula, C.M. Lee, E.A. D'Asaro, L.N. Thomas, R.R. Harcourt, A.Y. Shcherbina, M.A. Sundermeyer, J. Molemaker, and J.C. McWilliams, "Submesoscale streamers exchange water on the north wall of the Gulf Stream," Geophys. Res. Lett., 43, 1226-1233, doi:10.1002/2015GL067152, 2016.

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16 Feb 2016

The Gulf Stream is a major conduit of warm surface water from the tropics to the subpolar North Atlantic. Here we observe and simulate a submesoscale (<20 km) mechanism by which the Gulf Stream exchanges water with subpolar water to the north. Along isopycnals, the front has a sharp compensated temperature-salinity contrast, with distinct mixed water between the two water masses 2 and 4 km wide. This mixed water does not increase downstream despite substantial energy available for mixing. A series of streamers detrain this water at the crest of meanders. Subpolar water replaces the mixed water and resharpens the front. The water mass exchange accounts for a northward flux of salt of 0.5–2.5 psu m2 s-1, (large-scale diffusivity O (100 m2 s-1)). This is similar to bulk-scale flux estimates of 1.2 psu m2 s-1 and supplies fresher water to the Gulf Stream required for the production of 18° subtropical mode water.

Greenland freshwater pathways in the sub-Arctic seas from model experiments with passive tracers

Dukhovskoy, D.S., P.G. Myers, G. Platov, M.-L. Timmermans, B. Curry, A. Proshutinsky,
J.L. Bamber, E. Chassignet, X. Hu, C.M. Lee, and R. Somavilla, "Greenland freshwater pathways in the sub-Arctic seas from model experiments with passive tracers," J. Geophys. Res., 121, 877-907, doi:10.1002/2015JC011290, 2016.

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26 Jan 2016

Accelerating since the early 1990s, the Greenland Ice Sheet mass loss exerts a significant impact on thermohaline processes in the sub-Arctic seas. Surplus freshwater discharge from Greenland since the 1990s, comparable in volume to the amount of freshwater present during the Great Salinity Anomaly events, could spread and accumulate in the sub-Arctic seas, influencing convective processes there. However, hydrographic observations in the Labrador Sea and the Nordic Seas, where the Greenland freshening signal might be expected to propagate, do not show a persistent freshening in the upper ocean during last two decades. This raises the question of where the surplus Greenland freshwater has propagated. In order to investigate the fate, pathways, and propagation rate of Greenland meltwater in the sub-Arctic seas, several numerical experiments using a passive tracer to track the spreading of Greenland freshwater have been conducted as a part of the Forum for Arctic Ocean Modeling and Observational Synthesis effort. The models show that Greenland freshwater propagates and accumulates in the sub-Arctic seas, although the models disagree on the amount of tracer propagation into the convective regions. Results highlight the differences in simulated physical mechanisms at play in different models and underscore the continued importance of intercomparison studies. It is estimated that surplus Greenland freshwater flux should have caused a salinity decrease by 0.06–0.08 in the sub-Arctic seas in contradiction with the recently observed salinification (by 0.15–0.2) in the region. It is surmised that the increasing salinity of Atlantic Water has obscured the freshening signal.

Symmetric instability, inertial oscillations, and turbulence at the Gulf Stream front

Thomas, L.N., J.R. Taylor, E.A. D'Asaro, C.M. Lee, J.M. Klymak, and A. Shcherbina, "Symmetric instability, inertial oscillations, and turbulence at the Gulf Stream front," J. Phys. Oceanogr., 46, 197-217, doi:10.1175/JPO-D-15-0008.1, 2016.

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1 Jan 2016

The passage of a winter storm over the Gulf Stream observed with a Lagrangian float and hydrographic and velocity surveys provided a unique opportunity to study how the interaction of inertial oscillations, the front, and symmetric instability (SI) shapes the stratification, shear, and turbulence in the upper ocean under unsteady forcing. During the storm, the rapid rise and rotation of the winds excited inertial motions. Acting on the front, these sheared motions modulate the stratification in the surface boundary layer. At the same time, cooling and downfront winds generated a symmetrically unstable flow. The observed turbulent kinetic energy dissipation exceeded what could be attributed to atmospheric forcing, implying SI drew energy from the front. The peak excess dissipation, which occurred just prior to a minimum in stratification, surpassed that predicted for steady SI turbulence, suggesting the importance of unsteady dynamics. The measurements are interpreted using a large-eddy simulation (LES) and a stability analysis configured with parameters taken from the observations. The stability analysis illustrates how SI more efficiently extracts energy from a front via shear production during periods when inertial motions reduce stratification. Diagnostics of the energetics of SI from the LES highlight the temporal variability in shear production but also demonstrate that the time-averaged energy balance is consistent with a theoretical scaling that has previously been tested only for steady forcing. As the storm passed and the winds and cooling subsided, the boundary layer restratified and the thermal wind balance was reestablished in a manner reminiscent of geostrophic adjustment.

The arctic observing summit 2013

Lee, C., H. Eicken, and M. Jakobson, "The arctic observing summit 2013," Arctic, 68, A04, doi:10.14430/arctic4456, 2015.

15 Dec 2015

Eddy-Kuroshio interaction processes revealed by mooring observations off Taiwan and Luzon

Tsai, C.-J., M. Andres, S. Jan, V. Mensah, T.B. Sanford, R.-C. Lien, and C.M. Lee, "Eddy-Kuroshio interaction processes revealed by mooring observations off Taiwan and Luzon," Geophys. Res. Letts., 42, 8090-8105, doi:10.1002/2015GL065814, 2015.

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16 Oct 2015

The influence and fate of westward propagating eddies that impinge on the Kuroshio were observed with pressure sensor-equipped inverted echo sounders (PIESs) deployed east of Taiwan and northeast of Luzon. Zero lag correlations between PIES-measured acoustic travel times and satellite-measured sea surface height anomalies (SSHa), which are normally negative, have lower magnitude toward the west, suggesting the eddy-influence is weakened across the Kuroshio. The observational data reveal that impinging eddies lead to seesaw-like SSHa and pycnocline depth changes across the Kuroshio east of Taiwan, whereas analogous responses are not found in the Kuroshio northeast of Luzon. Anticyclones intensify sea surface and pycnocline slopes across the Kuroshio, while cyclones weaken these slopes, particularly east of Taiwan. During the 6%u2009month period of overlap between the two PIES arrays, only one anticyclone affected the pycnocline depth first at the array northeast of Luzon and 21%u2009days later in the downstream Kuroshio east of Taiwan.

The LatMix summer campaign: Submesoscale stirring in the upper ocean

Shcherbina, A.Y., et al., including E. D'Asaro, R.R. Harcourt, C.M. Lee, R.-C. Lien, and T.B. Sanford, "The LatMix summer campaign: Submesoscale stirring in the upper ocean," Bull. Am. Meteor. Soc., 96, 1257-1279, doi:10.1175/BAMS-D-14-00015.1, 2015.

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1 Aug 2015

Lateral stirring is a basic oceanographic phenomenon affecting the distribution of physical, chemical, and biological fields. Eddy stirring at scales on the order of 100 km (the mesoscale) is fairly well understood and explicitly represented in modern eddy-resolving numerical models of global ocean circulation. The same cannot be said for smaller-scale stirring processes. Here, the authors describe a major oceanographic field experiment aimed at observing and understanding the processes responsible for stirring at scales of 0.1–10 km. Stirring processes of varying intensity were studied in the Sargasso Sea eddy field approximately 250 km southeast of Cape Hatteras. Lateral variability of water-mass properties, the distribution of microscale turbulence, and the evolution of several patches of inert dye were studied with an array of shipboard, autonomous, and airborne instruments. Observations were made at two sites, characterized by weak and moderate background mesoscale straining, to contrast different regimes of lateral stirring. Analyses to date suggest that, in both cases, the lateral dispersion of natural and deliberately released tracers was O(1) m2 s-1 as found elsewhere, which is faster than might be expected from traditional shear dispersion by persistent mesoscale flow and linear internal waves. These findings point to the possible importance of kilometer-scale stirring by submesoscale eddies and nonlinear internal-wave processes or the need to modify the traditional shear-dispersion paradigm to include higher-order effects. A unique aspect of the Scalable Lateral Mixing and Coherent Turbulence (LatMix) field experiment is the combination of direct measurements of dye dispersion with the concurrent multiscale hydrographic and turbulence observations, enabling evaluation of the underlying mechanisms responsible for the observed dispersion at a new level.

Outside influences on the water column of Cumberland Sound, Baffin Island

Bedard, J.M. S. Vagle, J.M. Klymak, W.J. Williams, B. Curry, and C.M. Lee, "Outside influences on the water column of Cumberland Sound, Baffin Island," J. Geophys. Res., 120, 5000-5018, doi:10.1002/2015JC010811, 2015.

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1 Jul 2015

Cumberland Sound, host to a commercially viable fish population in the deepest depths, is a large embayment on the southeast coast of Baffin Island that opens to Davis Strait. Conductivity, temperature, and depth profiles were collected during three summer field seasons (2011–2013), and two moorings were deployed during 2011–2012. Within the sound, salinity increases with increasing depth while water temperature cools reaching a minimum of -1.49°C at roughly 100 m. Below 100 m, the water becomes both warmer and saltier. Temperature-salinity curves for each year followed a similar pattern, but the entire water column in Cumberland Sound cooled from 2011 to 2012, and then warmed through the summer of 2013. Even though the sound's maximum depth is over a kilometer deeper than its sill, water in the entire sound is well oxygenated. A comparison of water masses within the sound and in Davis Strait shows that, above the sill, the sound is flooded with cold Baffin Island Current water following an intermittent geostrophic flow pattern entering the sound along the north coast and leaving along the south. Below the sill, replenishment is infrequent and includes water from both the Baffin Island Current and the West Greenland Current. Deep water replenishment occurred more frequently on spring tides, especially in the fall of 2011. Although the sound's circulation is controlled by outside currents, internal water modifying processes occur such as estuarine flow and wind-driven mixing.

Towards real-time under-ice acoustic navigation at mesoscale ranges

Webster, S.E., L.E. Freitag, C.M. Lee, and J.I. Gobat, "Towards real-time under-ice acoustic navigation at mesoscale ranges," Proc. IEEE International Conference on Robotics and Automation, 26-30 May, Seattle, WA, 537-544, doi:10.1109/ICRA.2015.7139231 (IEEE, 2015).

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26 May 2015

This paper describes an acoustic navigation system that provides mesoscale coverage (hundreds of kilometers) under the ice and presents results from the first multi-month deployment in the Arctic. The hardware consists of ice-tethered acoustic navigation beacons transmitting at 900 Hz that broadcast their latitude and longitude plus several bytes of optional control data. The real-time under-ice navigation algorithm, based on a Kalman filter, uses time-of-flight measurements from these sources to simultaneously estimate vehicle position and depth-averaged local currents. The algorithm described herein was implemented on Seagliders, a type of autonomous underwater glider (AUG), but the underlying theory is applicable to other autonomous underwater vehicles (AUVs). As part of an extensive field campaign from March to September 2014, eleven acoustic sources and four Seagliders were deployed to monitor the seasonal melt of the marginal ice zone (MIZ) in the Beaufort and northern Chukchi Seas. Beacon-to-beacon performance was excellent due to a sound duct at 100 m depth where the transmitters were positioned; the travel-time error at 200 km has a standard deviation of 40 m when sound-speed is known, and ranges in excess of 400 km were obtained. Results with the Seagliders, which were not regularly within the duct, showed reliable acoustic ranges up to 100 km and more sparse but repeatable range measurements to over 400 km. Navigation results are reported for the real-time algorithm run in post-processing mode, using data from a 295-hour segment with significant time spent under ice.

A simple optical index shows spatial and temporal heterogeneity in phytoplankton community composition during the 2008 North Atlantic Bloom Experiment

Cetinić, I., M.J. Perry, E. D'Asaro, N. Briggs, N. Poulton, M.E. Sieracki, and C.M. Lee, "A simple optical index shows spatial and temporal heterogeneity in phytoplankton community composition during the 2008 North Atlantic Bloom Experiment," Biogeosciences, 12, 2179-2194, doi:10.5194/bg-12-2179-2015, 2015.

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14 Apr 2015

The ratio of two in situ optical measurements — chlorophyll fluorescence (Chl F) and optical particulate backscattering (bbp) —3 varied with changes in phytoplankton community composition during the North Atlantic Bloom Experiment in the Iceland Basin in 2008. Using ship-based measurements of Chl F, bbp, chlorophyll a (Chl), high-performance liquid chromatography (HPLC) pigments, phytoplankton composition and carbon biomass, we found that oscillations in the ratio varied with changes in plankton community composition; hence we refer to Chl F/bbp as an "optical community index". The index varied by more than a factor of 2, with low values associated with pico- and nanophytoplankton and high values associated with diatom-dominated phytoplankton communities. Observed changes in the optical index were driven by taxa-specific chlorophyll-to-autotrophic carbon ratios and by physiological changes in Chl F associated with the silica limitation. A Lagrangian mixed-layer float and four Seagliders, operating continuously for 2 months, made similar measurements of the optical community index and followed the evolution and later demise of the diatom spring bloom. Temporal changes in optical community index and, by implication, the transition in community composition from diatom to post-diatom bloom communities were not simultaneous over the spatial domain surveyed by the ship, float and gliders. The ratio of simple optical properties measured from autonomous platforms, when carefully validated, provides a unique tool for studying phytoplankton patchiness on extended temporal scales and ecologically relevant spatial scales and should offer new insights into the processes regulating patchiness.

Eddy-driven subduction exports particulate organic carbon from the spring bloom

Omand, M.M., E.A. D'Asaro, C.M. Lee, M.J. Perry, N. Briggs, I. Cetinić, and A. Mahadevan, "Eddy-driven subduction exports particulate organic carbon from the spring bloom," Science, 348, 222-225, do:10.1126/science.1260062, 2015.

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26 Mar 2015

The export of particulate organic carbon (POC) from the surface ocean to depth is traditionally ascribed to sinking. Here, we show that a dynamic eddying flow field subducts surface water with high concentrations of nonsinking POC. Autonomous observations made by gliders during the North Atlantic spring bloom reveal anomalous features at depths of 100 to 350 m with elevated POC, chlorophyll, oxygen, and temperature-salinity characteristics of surface water. High-resolution modeling reveals that during the spring transition, intrusions of POC-rich surface water descend as coherent, 1 to 10 km scale filamentous features, often along the perimeter of eddies. Such a submesoscale eddy-driven flux of POC is unresolved in global carbon cycle models but can contribute as much as half of the total springtime export of POC from the highly productive subpolar oceans.

Salinity and temperature balances at the SPURS central mooring during fall and winter

Farrar, J.T., L. Rainville, A.J. Plueddemann, W.S. Kessler, C. Lee, B.A. Hodges, R.W. Schmitt, J.B. Edson, S.C. Riser, C.C. Eriksen, and D.M. Fratantoni, "Salinity and temperature balances at the SPURS central mooring during fall and winter," Oceanography, 28, 56-65, doi:10.5670/oceanog.2015.06, 2015.

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1 Mar 2015

One part of the Salinity Processes in the Upper-ocean Regional Study (SPURS) field campaign focused on understanding the physical processes affecting the evolution of upper-ocean salinity in the region of climatological maximum sea surface salinity in the subtropical North Atlantic (SPURS-1). An upper-ocean salinity budget provides a useful framework for increasing this understanding. The SPURS-1 program included a central heavily instrumented mooring for making accurate measurements of air-sea surface fluxes, as well as other moorings, Argo floats, and gliders that together formed a dense observational array. Data from this array are used to estimate terms in the upper-ocean salinity and heat budgets during the SPURS-1 campaign, with a focus on the first several months (October 2012 to February 2013) when the surface mixed layer was becoming deeper, fresher, and cooler. Specifically, we examine the salinity and temperature balances for an upper-ocean mixed layer, defined as the layer where the density is within 0.4 kg m-3 of its surface value. The gross features of the evolution of upper-ocean salinity and temperature during this fall/winter season are explained by a combination of evaporation and precipitation at the sea surface, horizontal transport of heat and salt by mixed-layer currents, and vertical entrainment of fresher, cooler fluid into the layer as it deepened. While all of these processes were important in the observed seasonal (fall) freshening at this location in the salinity-maximum region, the variability of salinity on monthly-to-intraseasonal time scales resulted primarily from horizontal advection.

A framework for prioritization, design and coordination of Arctic long-term observing networks: A perspective from the U.S. SEARCH program

Lee, O., H. Eicken, G. Kling, and C. Lee, "A framework for prioritization, design and coordination of Arctic long-term observing networks: A perspective from the U.S. SEARCH program," Arctic, 68, 5 (Suppl. 1), do:10.14430/arctic4450, 2015.

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1 Jan 2015

Arctic observing networks exist in many countries and often cross international boundaries. We review their status and the development of networked long-term observations as part of a U.S. Arctic Observing System, highlighting major challenges and opportunities for prioritizing observations, designing a network, and increasing coordination. Most Arctic observing activities focus on specific themes and ecosystem services, resulting in a relatively narrow scope of observations for each network. Across all networks there is a need to improve national and international coordination to (1) reduce potential mismatch between identified science needs and outcomes desired by society, (2) link current observing networks to emerging agency and private-sector observing programs across disciplines, and (3) present a stable set of goals and priorities to increase network utility in view of the limited funding resources. We survey the landscape of observing activities and efforts to coordinate them internationally and present a framework for prioritization and coordination based on the activities of the U.S. Study of Environmental Arctic Change (SEARCH). This framework includes a hierarchy of interconnected activities involved in the design and implementation of observing networks. Across the hierarchy, definition of %u201Cactionable%u201D science questions helps drive network design, with priorities set by the breadth and depth of the societal applications or policy requirements that these questions can inform. We present an example of applying this design hierarchy to observations that support policy and management decisions about offshore resource development in the Chukchi Sea.

Multipurpose acoustic networks in the integrated Arctic Ocean observing system

Mikhalevsky, P.N., H. Sagen, P.F. Worcester, A.B. Baggeroer, J. Orcutt, S.E. Moore, C.M. Lee, J. Vigness-Raposa, L. Freitag, M. Arrott, K. Atakan, A. Beszczynska-Moller, T.F. Duda, B.D. Dushaw, J.C. Gascard, A.N. Gavrilov, H. Keers, A.K. Morozov, W.H. Munk, M. Rixen, S. Sandven, E. Skarsoulis, K.M. Stafford, F. Vernon, and M.Y. Yuen, "Multipurpose acoustic networks in the integrated Arctic Ocean observing system," Arctic, 68, 5 (Suppl. 1), doi:10.14430/arctic4449, 2015.

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1 Jan 2015

The dramatic reduction of sea ice in the Arctic Ocean will increase human activities in the coming years. This activity will be driven by increased demand for energy and the marine resources of an Arctic Ocean accessible to ships. Oil and gas exploration, fisheries, mineral extraction, marine transportation, research and development, tourism, and search and rescue will increase the pressure on the vulnerable Arctic environment. Technologies that allow synoptic in situ observations year-round are needed to monitor and forecast changes in the Arctic atmosphere-ice-ocean system at daily, seasonal, annual, and decadal scales. These data can inform and enable both sustainable development and enforcement of international Arctic agreements and treaties, while protecting this critical environment. In this paper, we discuss multipurpose acoustic networks, including subsea cable components, in the Arctic. These networks provide communication, power, underwater and under-ice navigation, passive monitoring of ambient sound (ice, seismic, biologic, and anthropogenic), and acoustic remote sensing (tomography and thermometry), supporting and complementing data collection from platforms, moorings, and vehicles. We support the development and implementation of regional to basin-wide acoustic networks as an integral component of a multidisciplinary in situ Arctic Ocean observatory.

Preliminary results in under-ice acoustic navigation for Seagliders in Davis Strait

Webster, S.E., C.M. Lee, and J.I. Gobat, "Preliminary results in under-ice acoustic navigation for Seagliders in Davis Strait," Proc., OCEANS 2014, 14-19 September, St. John's Newfoundland, doi:10.1109/OCEANS.2014.7003070 (IEEE, 2014).

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14 Sep 2014

This paper presents an under-ice acoustic navigation system developed for Seaglider, a buoyancy-driven autonomous underwater vehicle (AUV), and post-processed navigation results from one of fourteen glider deployments between 2006 and 2014 in Davis Strait. Seagliders typically receive all geolocation information from global positioning system (GPS) signals received while they are at the surface, and perform dead reckoning while underwater. Extended under-ice deployments, where access to GPS is denied due to the inability of the glider to surface, require an alternative source of geolocation information. In the deployments described herein, geolocation information is provided by range measurements from mooring-mounted acoustic navigation sources at fixed, known locations. In this paper we describe the navigation system used in Davis Strait and present navigation results from a six degree-of-freedom Kalman filter using post-processed navigation data.

Global patterns of diapycnal mixing from measurements of the turbulent dissipation rate

Waterhouse, A.F., et al., including M.H. Alford, E. Kunze, T.B. Sanford, and C.M. Lee, "Global patterns of diapycnal mixing from measurements of the turbulent dissipation rate," J. Phys. Oceanogr., 44, 1854-1872, doi:10.1175/JPO-D-13-0104.1, 2014.

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1 Jul 2014

The authors present inferences of diapycnal diffusivity from a compilation of over 5200 microstructure profiles. As microstructure observations are sparse, these are supplemented with indirect measurements of mixing obtained from (i) Thorpe-scale overturns from moored profilers, a finescale parameterization applied to (ii) shipboard observations of upper-ocean shear, (iii) strain as measured by profiling floats, and (iv) shear and strain from full-depth lowered acoustic Doppler current profilers (LADCP) and CTD profiles. Vertical profiles of the turbulent dissipation rate are bottom enhanced over rough topography and abrupt, isolated ridges. The geography of depth-integrated dissipation rate shows spatial variability related to internal wave generation, suggesting one direct energy pathway to turbulence. The global-averaged diapycnal diffusivity below 1000-m depth is O(10-4) m2 s-1 and above 1000-m depth is O(10-5) m2 s-1. The compiled microstructure observations sample a wide range of internal wave power inputs and topographic roughness, providing a dataset with which to estimate a representative global-averaged dissipation rate and diffusivity. However, there is strong regional variability in the ratio between local internal wave generation and local dissipation. In some regions, the depth-integrated dissipation rate is comparable to the estimated power input into the local internal wave field. In a few cases, more internal wave power is dissipated than locally generated, suggesting remote internal wave sources. However, at most locations the total power lost through turbulent dissipation is less than the input into the local internal wave field. This suggests dissipation elsewhere, such as continental margins.

Response of upper ocean currents to Typhoon Fanapi

Hormann, V., L.R. Centurioni, L. Rainville, C.M. Lee, and L.J. Braasch, "Response of upper ocean currents to Typhoon Fanapi," Geophys. Res. Lett., 41, 3995-4003, doi:10.1002/2014GL060317, 2014.

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16 Jun 2014

The response of upper ocean currents to Typhoon Fanapi in fall 2010 was studied using an extensive air-deployed drifter array. Separation of the observations into near-inertial and sub-inertial motions quantified the importance of strong advection by the sub-inertial circulation for the evolution of the cold wake formed by Typhoon Fanapi. The near-inertial currents generated during the storm showed the expected rightward bias, with peak magnitudes of up to 0.6 m/s and an e-folding time of about 4 days for the strong currents within the cold wake. The shear of the near-inertial currents is crucial for the storm-induced cooling and deepening of the mixed layer and such instabilities were here directly observed across the base of th — a dominant process for the wake warming — was found to be noticeably reduced when the near-inertial motions were strongest.

Multiplatform, multidisciplinary investigations of the impacts of modified circumpolar deep water in the Ross Sea, Antarctica

Smith Jr., W.O., et al., including C.M. Lee, "Multiplatform, multidisciplinary investigations of the impacts of modified circumpolar deep water in the Ross Sea, Antarctica," Oceanography, 27, 180-185, doi:10.5670/oceanog.2014.36, 2014.

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1 Jun 2014

In 2010–2011, three projects combined to characterize the temporal and spatial distributions of Modified Circumpolar Deep Water (MCDW) in the Ross Sea using icebreaker-based sampling, gliders, instrumented seals, and hindcasts from a numerical circulation model. The fieldwork clearly identified MCDW throughout the Ross Sea, and the data were used to determine its influence on potential heat and nutrient inputs and biotic distributions. Furthermore, the numerical simulations confirm its apparent trajectory and location. Substantial small-scale variability in oceanographic and biological distributions suggests that such variability may play an important role in biogeochemical cycles. Data from the three projects provide a view of hydrographic variability in the Ross Sea that is impossible to obtain using traditional sampling. Multiplatform investigations are promising approaches to future polar experiments where logistical considerations are of paramount importance.

On the distribution of dissolved methane in Davis Strait, North Atlantic Ocean

Punshon, S., K. Azetsu-Scott, and C.M. Lee, "On the distribution of dissolved methane in Davis Strait, North Atlantic Ocean," Mar. Chem., 161, 20-25, doi:10.1016/j.marchem.2014.02.004, 2014.

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20 Apr 2014

Depth profiles of dissolved methane were measured along three transects of Davis Strait and the northern Labrador Sea in October 2011. Concentrations ranged from 0.2 nmol L-1 (6% saturation) in the remarkably methane depleted Baffin Bay Deep Water to 38.8 nmol L-1 (1057% saturation) in localised subsurface anomalies near the Baffin Island Shelf. These anomalies may be the result of natural gas seepage and this hypothesis is supported by the distribution of potential sea surface oil slicks detected by satellite radar backscatter. In contrast, methane concentrations within the Baffin Island Current 200 km to the south of these anomalies were only slightly above atmospheric equilibrium. Methane was moderately supersaturated in West Greenland Shelf Water (< 200%) with a distribution consistent with a sediment source. These measurements represent the first detailed baseline study of the vertical distribution of dissolved methane in an important Canadian Arctic Archipelago outflow region.

Modulation of Kuroshio transport by mesoscale eddies at the Luzon Strait entrance

Lien, R.-C., B. Ma, Y.-H. Cheng, C.-R. Ho, B. Qiu, C.M. Lee, and M.-H. Chang, "Modulation of Kuroshio transport by mesoscale eddies at the Luzon Strait entrance," J. Geophys. Res., 119, 2129-2142, doi:10.1002/2013JC009548, 2014.

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1 Apr 2014

Measurements of Kuroshio Current velocity at the entrance to Luzon Strait along 18.75°N were made with an array of six moorings during June 2012 to June 2013. Strong positive relative vorticity of the order of the planetary vorticity f was observed on the western flank of the Kuroshio in the upper 150 m. On the eastern flank, the negative vorticity observed was about an order of magnitude smaller than f. Kuroshio transport near its origin is computed from direct measurements for the first time. Kuroshio transport has an annual mean of 15 Sv with a standard deviation of 3 Sv. It is modulated strongly by impinging westward propagating eddies, which are identified by an improved eddy detection method and tracked back to the interior ocean. Eight Kuroshio transport anomalies >5 Sv are identified; seven are explained by the westward propagating eddies. Cyclonic (anticyclonic) eddies decrease (increase) the zonal sea level anomaly (SLA) slope and reduce (enhance) Kuroshio transport. Large transport anomalies of >10 Sv within O(10 days) are associated with the pairs of cyclonic and anticyclonic eddies. The observed Kuroshio transport was strongly correlated with the SLA slope (correlation = 0.9). Analysis of SLA slope data at the entrance to Luzon Strait over the period 1992–2013 reveals a seasonal cycle with a positive anomaly (i.e., an enhanced Kuroshio transport) in winter and spring and a negative anomaly in summer and fall. Eddy induced vorticity near the Kuroshio has a similar seasonal cycle, suggesting that seasonal variation of the Kuroshio transport near its origin is modulated by the seasonal variation of the impinging mesoscale eddies.

Multi-year volume, liquid freshwater, and sea ice transports through Davis Strait, 2004–2010

Curry, B., C.M. Lee, B. Petrie, R.E. Moritz, and R. Kwok, "Multi-year volume, liquid freshwater, and sea ice transports through Davis Strait, 2004–2010," J. Phys. Oceanogr., 44, 1244-1266, doi:10.1175/JPO-D-13-0177.1, 2013.

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1 Apr 2014

Davis Strait is a primary gateway for freshwater exchange between the Arctic and North Atlantic oceans including freshwater contributions from West Greenland and Canadian Arctic Archipelago glacial melt. Data from six years (2004–2010) of continuous measurements collected by a full-strait moored array and concurrent high-resolution Seaglider surveys are used to estimate volume and liquid freshwater transports through Davis Strait, with respective annual averages of –1.6 ± 0.5 Sv and –93 ± 6 mSv (negative sign indicates southward transport). Sea ice export contributes an additional 10 ± 1 mSv of freshwater transport, estimated using satellite ice area transport and moored upward-looking sonar ice thickness measurements. Interannual and annual variability of the net transports are large, with average annual volume and liquid freshwater transport standard deviations of 0.7 Sv and 17 mSv and with interannual standard deviations of 0.3 Sv and 15 mSv. Moreover, there are no clear trends in the net transports over the 6-yr period. However, salinity in the upper 250 m between Baffin Island and mid-strait decreases starting in September 2009, remains below average through August 2010, but appears to return to normal by the end of 2010. This freshening event, likely caused by changes in Arctic freshwater storage, is not apparent in the liquid freshwater transport time series due to a reduction in southward volume transport in 2009–2010. Reanalysis of Davis Strait mooring data from the period 1987–1990, compared to the 2004–2010 measurements, reveals less Arctic outflow and warmer, more saline North Atlantic inflow during the most recent period.

Multiyear volume, liquid freshwater, and sea ice transports through Davis Strait, 2004–10

Curry, B., C.M. Lee, B. Petrie, R.E. Moritz, and R. Kwok, "Multiyear volume, liquid freshwater, and sea ice transports through Davis Strait, 2004–10," J. Phys. Oceanogr., 44, 1244-1266, doi:10.1175/JPO-D-13-0177.1, 2014.

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1 Apr 2014

Davis Strait is a primary gateway for freshwater exchange between the Arctic and North Atlantic Oceans including freshwater contributions from west Greenland and Canadian Arctic Archipelago glacial melt. Data from six years (2004–10) of continuous measurements collected by a full-strait moored array and concurrent high-resolution Seaglider surveys are used to estimate volume and liquid freshwater transports through Davis Strait, with respective annual averages of –1.6 ± 0.5 Sverdrups (Sv; 1 Sv = 106 m3 s-1) and –93 ± 6 mSv (negative sign indicates southward transport). Sea ice export contributes an additional –10 ± 1 mSv of freshwater transport, estimated using satellite ice area transport and moored upward-looking sonar ice thickness measurements. Interannual and annual variability of the net transports are large, with average annual volume and liquid freshwater transport standard deviations of 0.7 Sv and 17 mSv and with interannual standard deviations of 0.3 Sv and 15 mSv. Moreover, there are no clear trends in the net transports over the 6-yr period. However, salinity in the upper 250 m between Baffin Island and midstrait decreases starting in September 2009 and remains below average through August 2010, but appears to return to normal by the end of 2010. This freshening event, likely caused by changes in arctic freshwater storage, is not apparent in the liquid freshwater transport time series due to a reduction in southward volume transport in 2009–10. Reanalysis of Davis Strait mooring data from the period 1987–90, compared to the 2004–10 measurements, reveals less arctic outflow and warmer, more saline North Atlantic inflow during the most recent period.

On the waters upstream of Nares Strait, Arctic Ocean, from 1991 to 2012

Jackson, J.M., C. Lique, M. Alkire, M. Steele, C.M. Lee, W.M. Smethie, and P. Schlosser, "On the waters upstream of Nares Strait, Arctic Ocean, from 1991 to 2012," Cont. Shelf Res., 73, 83-96, doi:10.1016/j.csr.2013.11.025, 2014.

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1 Feb 2014

The Lincoln Sea is a bifurcation point, where waters from the Canadian and Eurasian Basins flow to Nares or Fram Strait. Mechanisms that control which waters are found in the Lincoln Sea, and on its continental shelves, are unknown. Using conductivity-temperature-depth (CTD; from hydrographic and ice-tethered profiler surveys), nutrient, and mooring data with the DRAKKAR global 3-D coupled ocean/sea-ice model, the Lincoln Sea was examined from 1991 to 2012. Although both Pacific and Atlantic waters were observed on the North Ellesmere and North Greenland shelves, Atlantic water was shallower on the North Greenland shelf. Thus, deeper than 125 m, water was warmer and saltier on the North Greenland shelf than the North Ellesmere shelf. Three different water types were identified on the North Ellesmere shelf — waters from the Canadian Basin were observed 1992, 1993, 1996, 2005, and 2012, waters from both the Canadian and Eurasian Basins were observed in 2003, 2004, and 2008, and waters with no temperature minima or maxima below the surface mixed layer were observed in 1991, 2006, 2009, and 2010. Mixing with vertical advection speeds of 1x10-4 m s-1 were observed on the continental slope and this mixing could cause the disappearance of the temperature maxima. Model results suggest that currents on the North Ellesmere shelf were weak (less than 10 cm s-1), baroclinic, and directed away from Nares Strait while currents on the North Greenland shelf were stronger (less than 15 cm s-1), and primarily directed towards Nares Strait. CTD, mooring, and model results suggest that the water advected to Nares Strait is primarily from the North Greenland shelf while water on the North Ellesmere shelf is advected westward.

Subthermocline eddies over the Washington continental slope as observed by Seagliders, 2003–09

Pelland, N.A., C.C. Eriksen, and C.M. Lee, "Subthermocline eddies over the Washington continental slope as observed by Seagliders, 2003–09," J. Phys. Oceanogr., 43, 2025-2053, doi:10.1175/JPO-D-12-086.1, 2013.

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1 Oct 2013

In the California Current System, subthermocline, lenslike anticyclonic eddies generated within the California Undercurrent (CU) are one mechanism for lateral transport of the warm, saline waters of the CU. Garfield et al. established the name "Cuddies" for eddies of this type and hypothesized that they account for a significant fraction of the offshore transport of CU water. This study presents observations of subthermocline eddies collected from a time series of Seaglider surveys in the northern California Current System. Gliders made 46 crossings of subthermocline anticyclones and 17 crossings of subthermocline cyclones over 5.5 yr. Close inspection grouped these into 20 distinct anticyclones and 10 distinct cyclones. Water properties at the core of anticyclonic eddies were similar to those in the core of the CU over the continental slope; these anticyclones are examples of Cuddies. Anticyclonic (cyclonic) eddies had average radii of 20.4 (20.6) km, peak azimuthal current speeds of 0.25 (0.23) m s-1, and average core anomalies of potential vorticity 65% below (125% above) ambient values. Anticyclones contained an order of magnitude greater available heat and salt anomaly relative to background conditions than cyclones on average. Circumstantial evidence of eddy decay through lateral intrusions was found although this was not observed consistently. Observed eddy properties and the geometry of flow over the continental slope were consistent with eddy formation due to frictional torque acting on the CU. Loss of heat and salt from the CU due to subthermocline eddies is estimated to account for 44% of the freshening and cooling of the CU as it flows poleward.

Statistics of vertical vorticity, divergence, and strain in a developed submesoscale turbulence field

Shcherbina, A.Y., E.A. D'Asaro, C.M. Lee, J.M. Klymak, M.J. Molemaker, and J.C. McWilliams, "Statistics of vertical vorticity, divergence, and strain in a developed submesoscale turbulence field," Geophys. Res. Lett., 40, 4706-4711, doi:10.1002/grl.50919, 2013.

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16 Sep 2013

A detailed view of upper ocean vorticity, divergence, and strain statistics was obtained by a two-vessel survey in the North Atlantic Mode Water region in winter 2012. Synchronous Acoustic Doppler Current Profiler sampling provided the first in situ estimates of the full velocity gradient tensor at O(1 km) scale without the usual mix of spatial and temporal aliasing. The observed vorticity distribution in the mixed layer was markedly asymmetric (skewness 2.5), with sparse strands of strong cyclonic vorticity embedded in a weak, predominantly anticyclonic background. Skewness of the vorticity distribution decreased linearly with depth, disappearing completely in the pycnocline. Statistics of divergence and strain rate generally followed the normal and χ distributions, respectively. These observations confirm a high-resolution numerical model prediction for the structure of the active submesoscale turbulence field in this area.

Propagation of internal tides generated near Luzon Strait: Observations from autonomous gliders

Rainville, L., C.M. Lee, D.L. Rudnick, and K.-C. Yang, "Propagation of internal tides generated near Luzon Strait: Observations from autonomous gliders," J. Geophys. Res., 118, 4125-4138, doi:10.1002/jgrc.20293, 2013.

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1 Sep 2013

The vertical isopycnal displacements associated with internal waves generated by the barotropic tidal currents in the vicinity of Luzon Strait are estimated using measurements collected by autonomous underwater gliders. Nearly 23,000 profiles from Seagliders and Spray gliders, collected during 29 different missions since 2007, are used to estimate the amplitude and phase of the linear semidiurnal and diurnal internal waves in this energetic region, particularly in the previously poorly sampled area near the eastern ridge and on the Pacific side of Luzon Strait. The mean and variability of the internal wave field in the upper 1000 m of the water column are described. The phase progression of internal waves as they propagate away from their generation sites is captured directly. The glider-based observations are used to map the mode-1 semidiurnal and diurnal internal wave fields, providing the baroclinic energy flux over a roughly 600 km x 800 km region based strictly on in situ observations.

Transport estimate of the Western Branch of the Norwegian Atlantic Current from glider surveys

Høydalsvik, F., C. Mauritzen, K.A. Orvik, J.H. LaCasce, C.M. Lee, and J. Gobat, "Transport estimate of the Western Branch of the Norwegian Atlantic Current from glider surveys," Deep-Sea Res. I, 79, 86-95, doi:10.1016/j.dsr.2013.05.005, 2013.

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1 Sep 2013

The northernmost limb of the Atlantic Meridional Overturning Circulation (AMOC), so relevant for understanding decadal climate variability, enters the Nordic Seas as the Norwegian Atlantic Current and continues on to recirculate in the Arctic Ocean. The strength of the Eastern Branch of the Norwegian Atlantic Current has been systematically monitored for over 15 years at the Svinøy section off southern Norway, whereas the strength of the Western Branch has not. We therefore used autonomous gliders to monitor and quantify the strength of this broader branch at the Svinøy section, located 500 km downstream from the Iceland–Scotland Ridge, and at the Station Mike section 300 km further downstream. The gliders' diving depth is 1000 m, spanning the warm Atlantic Water. The current encompasses more than warm Atlantic Water; we find that the transport peaks in two distinct temperature ranges, one around 7.5–8°C (Atlantic Water, carrying 7 Sv (1x106 m3/s)) and another around –0.5°C (Norwegian Sea Deep Water, carrying 12 Sv). Contrary to earlier expectations, our results indicate that the Western Branch carries as much water of Atlantic origin (temperature>7.5°C) as the Eastern Branch. It should therefore be included in future monitoring plans for this region.

Observations of the cold wake of Typhoon Fanapi (2010)

Mrvaljevic, R.K., P.G. Black, L.R. Centurioni, Y.-T. Chang, E.A. D'Asaro, S.R. Jayne, C.M. Lee, R.-C. Lien, I.-I. Lin, J. Morzel, P.P. Niiler, L. Rainville, and T.B. Sanford, "Observations of the cold wake of Typhoon Fanapi (2010)," Geophys. Res. Lett., 40, 316-321, doi:10.1002/grl.50096, 2013.

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28 Jan 2013

Several tens of thousands of temperature profiles are used to investigate the thermal evolution of the cold wake of Typhoon Fanapi, 2010. Typhoon Fanapi formed a cold wake in the Western North Pacific Ocean on 18 September characterized by a mixed layer that was >2.5°C cooler than surrounding water, and extending to >80 m, twice as deep as the pre-existing mixed layer. The initial cold wake became capped after 4 days as a warm, thin surface layer formed. The thickness of the capped wake, defined as the 26°C to 27°C layer, decreased, approaching the background thickness of this layer with an e-folding time of 23 days, almost twice the e-folding lifetime of the Sea Surface Temperature (SST) cold wake (12 days). The wake was advected several hundreds of kilometers from the storm track by a pre-existing mesoscale eddy. The observations reveal new intricacies of cold wake evolution and demonstrate the challenges of describing the thermal structure of the upper ocean using sea surface information alone.

Composition and fluxes of freshwater through Davis Strait using multiple chemical tracers

Azetsu-Scott, K., B. Petrie, P. Yeats, and C. Lee, "Composition and fluxes of freshwater through Davis Strait using multiple chemical tracers," J. Geophys. Res., 117, doi:10.1029/2012JC008172, 2012.

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1 Dec 2012

Freshwater transport through Davis Strait can supply additional buoyancy to the deep convection region of the Labrador Sea which influences the strength of the meridional overturning circulation and consequently the global climate. The freshwater contribution from local sea ice meltwater, meteoric water (fluvial, glaciofluvial and precipitation) and the Arctic outflow were quantified using oxygen isotope composition (δ18O), salinity and nutrient relationships in September–October, 2004. Freshwater transported by the Arctic outflow was isolated using a modified nutrient relationship method and further deconvoluted into sea ice meltwater, meteoric water and Pacific water. For the first time, fluxes of individual freshwater components were estimated using observations of the velocity field derived from mooring arrays and geostrophic currents from hydrography. The Arctic outflow dominated in western Davis Strait (>60%) and its influence extended eastward close to the Greenland Slope. The sea ice meltwater fraction was small (<2%) and limited to the surface layer of the central and western Strait. The meteoric water fraction was highest on the Greenland Shelf (>6%) and attributed to glacial meltwater. The freshwater inventory of the 0–100 m layer was equivalent to 7.4 m in western Davis Strait: 8 m from the Arctic outflow and –0.6 m from brine rejection. In eastern Davis Strait, the freshwater inventory was 4 m: 3 m from meteoric water and 1 m from sea ice meltwater. The Arctic outflow contributed 82–99 mSv to the southward freshwater transport about 67–81% of the total; glacial meltwater contributed the largest northward transport of 10–30 mSv.

Marginal Ice Zone (MIZ) Program: Science and Experiment Plan

Lee, C.M., et al., "Marginal Ice Zone (MIZ) Program: Science and Experiment Plan," APL-UW TR 1201, Technical Report, Applied Physics Laboratory, University of Washington, Seattle, October 2012, 48 pp.

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9 Oct 2012

The Marginal Ice Zone (MIZ) intensive field program will employ an array of cutting-edge autonomous platforms to characterize the processes that govern Beaufort Sea MIZ evolution from initial breakup and MIZ formation though the course of the summertime sea ice retreat. Instruments will be deployed on and under the ice prior to initial formation of the MIZ along the Alaska coast, and will continue sampling from open water, across the MIZ, and into full ice cover, as the ice edge retreats northward through the summer. The flexible nature of ice-mounted and mobile, autonomous oceanographic platforms (e.g., gliders and floats) facilitates access to regions of both full ice cover and riskier MIZ regions. This approach exploits the extended endurance of modern autonomous platforms to maintain a persistent presence throughout the entire northward retreat. It also takes advantage of the inherent scalability of these instruments to sample over a broad range of spatial and temporal scales.

Eddy-driven stratification initiates North Atlantic spring phytoplankton blooms

Mahadevan, A., E. D'Asaro, C. Lee, and M.J. Perry, "Eddy-driven stratification initiates North Atlantic spring phytoplankton blooms," Science, 337, 54-58, doi:10.1126/science.1218740, 2012.

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6 Jul 2012

Springtime phytoplankton blooms photosynthetically fix carbon and export it from the surface ocean at globally important rates. These blooms are triggered by increased light exposure of the phytoplankton due to both seasonal light increase and the development of a near-surface vertical density gradient (stratification) that inhibits vertical mixing of the phytoplankton. Classically and in current climate models, that stratification is ascribed to a springtime warming of the sea surface. Here, using observations from the subpolar North Atlantic and a three-dimensional biophysical model, we show that the initial stratification and resulting bloom are instead caused by eddy-driven slumping of the basin-scale north-south density gradient, resulting in a patchy bloom beginning 20 to 30 days earlier than would occur by warming.

Particulate organic carbon and inherent optical properties during 2008 North Atlantic Bloom Experiment

Cetinić, I., M.J. Perry, N.T. Briggs, E. Kallin, E.A. D'Asaro, and C.M. Lee, "Particulate organic carbon and inherent optical properties during 2008 North Atlantic Bloom Experiment," J. Geophys. Res., 117, doi:10.1029/2011JC007771, 2012.

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30 Jun 2012

The co-variability of particulate backscattering (bbp) and attenuation (cp) coefficients and particulate organic carbon (POC) provides a basis for estimating POC on spatial and temporal scales that are impossible to obtain with traditional sampling and chemical analysis methods. However, the use of optical proxies for POC in the open ocean is complicated by variable relationships reported in the literature between POC and cp or bbp. During the 2008 North Atlantic Bloom experiment, we accrued a large data set consisting of >300 POC samples and simultaneously measured cp and bbp. Attention to sampling detail, use of multiple types of POC blanks, cross-calibration of optical instruments, and parallel measurements of other biogeochemical parameters facilitated distinction between natural and methodological-based variability. The POC versus cp slope varied with plankton community composition but not depth; slopes were 11% lower for the diatom versus the recycling community. Analysis of literature POC versus cp slopes indicates that plankton composition is responsible for a large component of that variability. The POC versus bbp slope decreased below the pycnocline by 20%, likely due to changing particle composition associated with remineralization and fewer organic rich particles. The higher bbp/cp ratios below the mixed layer are also indicative of particles of lower organic density. We also observed a peculiar platform effect that resulted in ~27% higher values for downcast versus upcast bbp measurements. Reduction in uncertainties and improvement of accuracies of POC retrieved from optical measurements is important for autonomous sampling, and requires community consensus for standard protocols for optics and POC.

Estimates of net community production and export using high-resolution, Lagrangian measurements of O2, NO3, and POC through the evolution of a spring diatom bloom in the North Atlantic

Alkire, M.B., E. D'Asaro, C. Lee, M.J. Perry, A. Gray, I. Cetinic, N. Briggs, E. Rehm, E. Kallin, J. Kaiser, and A. Gonzalez-Posada, "Estimates of net community production and export using high-resolution, Lagrangian measurements of O2, NO3, and POC through the evolution of a spring diatom bloom in the North Atlantic," Deep Sea Res. I, 64, 157-174, doi:10.1016/j.dsr.2012.01.012, 2012.

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1 Jun 2012

Budgets of nitrate, dissolved oxygen, and particulate organic carbon (POC) were constructed from data collected on-board a Lagrangian, profiling float deployed between April 4 and May 25, 2008, as part of the North Atlantic Bloom Experiment. These measurements were used to estimate net community production (NCP) and apparent export of POC along the float trajectory. A storm resulting in deep mixing and temporary suspension of net production separated the bloom into early (April 23–27) and main (May 6–13) periods over which ~264 and ~805 mmol C m-2 were produced, respectively. Subtraction of the total POC production from the NCP yielded maximum estimates of apparent POC export amounting to ~92 and 574 mmol C m-2 during the early and main blooms, respectively. The bloom terminated the following day and ~282 mmol C m-2 were lost due to net respiration (70%) and apparent export (30%). Thus, the majority of the apparent export of POC occurred continuously during the main bloom and a large respiration event occurred during bloom Termination. A comparison of the POC flux during the main bloom period with independent estimates at greater depth suggest a rapid rate of remineralization between 60 and 100 m. We suggest the high rates of remineralization in the upper layers could explain the apparent lack of carbon overconsumption (C:N>6.6) in the North Atlantic during the spring bloom.

The subpolar front of the Japan/East Sea. Part III: Competing roles of frontal dynamics and atmospheric forcing in driving ageostrophic vertical circulation and subduction

Yoshikawa, Y., C.M. Lee, and L.N. Thomas, "The subpolar front of the Japan/East Sea. Part III: Competing roles of frontal dynamics and atmospheric forcing in driving ageostrophic vertical circulation and subduction," J. Phys. Oceanogr., 42, 991-1011, doi:10.1175/JPO-D-11-0154.1, 2012.

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1 Jun 2012

The effects of wind stress and surface cooling on ageostrophic vertical circulation and subduction at the subpolar front of the Japan/East Sea are investigated using a nonhydrostatic numerical model. In experiments forced by wind and/or cooling, ageostrophic vertical circulation is enhanced relative to the unforced case. Both surface cooling and wind stress intensify the circulation by enhancing frontogenesis associated with frontal meandering. Winds further strengthen vertical motions by generating internal gravity waves. Downfront winds (i.e., oriented along the frontal jet) transport surface water from the denser to lighter side of the front, causing it to migrate toward the region of higher stratification and enhancing the vertical mixing at the front. This induces outcropping of isopycnals from the middle of the pycnocline along which surface water is subducted. Hence downfront winds enhance subduction down to the middle of the pycnocline, but not beneath. On the other hand, cooling uplifts isopycnals from greater depths to the surface so that it allows for the subduction of fluid to greater depths. In contrast to the vertical circulation, frontal subduction is more intensified by surface cooling than wind stress, because part of wind-forced circulation (e.g., internal gravity wave) does not contribute to subduction. Ageostrophic vertical circulation and frontal subduction are most intense when both wind stress and surface cooling are at play.

The Arctic Ocean in summer: A quasi-synoptic inverse estimate of boundary fluxes and water mass transformation

Tsubouchi, T., S. Bacon, A.C. Naveira Garabato, Y. Aksenov, S.W. Laxon, E. Fahrbach, A. Beszczynska-Möller, E. Hansen, C. M. Lee, and R. B. Ingvaldsen, "The Arctic Ocean in summer: A quasi-synoptic inverse estimate of boundary fluxes and water mass transformation," J. Geophys. Res., 117, doi:10.1029/2011JC007174, 2012.

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31 Jan 2012

The first quasi-synoptic estimates of Arctic Ocean and sea ice net fluxes of volume, heat and freshwater are calculated by application of an inverse model to data around the ocean boundary. Hydrographic measurements from four gateways to the Arctic (Bering, Davis, and Fram Straits and the Barents Sea Opening) completely enclose the ocean, and were made within the same 32-day period in summer 2005. The inverse model is formulated as a set of full-depth and density-layer-specific volume and salinity transport conservation equations, with conservation constraints also applied to temperature, but only in non-outcropping layers. The model includes representations of Fram Strait sea ice export and of interior Arctic Ocean diapycnal fluxes.

The results show that in summer 2005 the transport-weighted mean properties are, for water entering the Arctic: potential temperature 4.49°C, salinity 34.50 and potential density 27.34 kg m-3; and for water leaving the Arctic, including sea ice: 0.25°C, 33.81, and 27.13 kg m-3, respectively. The net effect of the Arctic in summer is to freshen and cool the inflows by 0.69 in salinity and 4.23°C, respectively, and to decrease density by 0.21 kg m-3. The volume transport into the Arctic of waters above ~1000 m depth is 9.2 Sv (1 Sv = 106 m3 s-1), and the export (similarly) is 9.3 Sv. The net oceanic and sea ice freshwater flux is 187 ± 48 mSv. The net heat flux (including sea ice) is 189 ± 37 TW, representing loss from the ocean to the atmosphere.

Autonomous data describe North Atlantic spring bloom

Fennel, L., I. Cetinic, E. D'Asaro, C. Lee, and M.J. Perry, "Autonomous data describe North Atlantic spring bloom," Eos, Trans. AGU, 92, 465, doi:10.1029/2011EO500002, 2011.

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13 Dec 2011

Each spring, increasing sunlight and associated changes in the ocean structure trigger rapid growth of phytoplankton across most of the North Atlantic Ocean north of 30°N. The bloom, one of the largest in the world, is a major sink for atmospheric carbon dioxide and a prototype for similar blooms around the world. Models of the ocean carbon cycle, a necessary component of climate models, need to accurately reproduce the biological, chemical, and physical processes occurring during these blooms. However, a paucity of detailed observations severely limits efforts to evaluate such models.

Circulation and intrusions northeast of Taiwan: Chasing and predicting uncertainty in the cold dome

Gawarkiewicz, G., S. Jan, P.F.J. Lermusiaux, J.L. McClean, L. Centurioni, K. Taylor, B. Cornuelle, T.F. Duda, J. Wang, Y.J. Yang, T. Sanford, R.-C. Lien, C. Lee, M.-A. Lee, W. Leslie, P.J. Haley Jr., P.P. Niiler, G. Gopalakrishnan, P. Velez-Belchi, D.-K. Lee, and Y.Y. Kim, "Circulation and intrusions northeast of Taiwan: Chasing and predicting uncertainty in the cold dome," Oceanography 24, 110-121, doi:10.5670/oceanog.2011.99, 2011.

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5 Dec 2011

An important element of present oceanographic research is the assessment and quantification of uncertainty. These studies are challenging in the coastal ocean due to the wide variety of physical processes occurring on a broad range of spatial and temporal scales. In order to assess new methods for quantifying and predicting uncertainty, a joint Taiwan-US field program was undertaken in August/September 2009 to compare model forecasts of uncertainties in ocean circulation and acoustic propagation, with high-resolution in situ observations. The geographical setting was the continental shelf and slope northeast of Taiwan, where a feature called the "cold dome" frequently forms. Even though it is hypothesized that Kuroshio subsurface intrusions are the water sources for the cold dome, the dome's dynamics are highly uncertain, involving multiple scales and many interacting ocean features. During the experiment, a combination of near-surface and profiling drifters, broad-scale and high-resolution hydrography, mooring arrays, remote sensing, and regional ocean model forecasts of fields and uncertainties were used to assess mean fields and uncertainties in the region. River runoff from Typhoon Morakot, which hit Taiwan August 7%u20138, 2009, strongly affected shelf stratification. In addition to the river runoff, a cold cyclonic eddy advected into the region north of the Kuroshio, resulting in a cold dome formation event. Uncertainty forecasts were successfully employed to guide the hydrographic sampling plans. Measurements and forecasts also shed light on the evolution of cold dome waters, including the frequency of eddy shedding to the north-northeast, and interactions with the Kuroshio and tides. For the first time in such a complex region, comparisons between uncertainty forecasts and the model skill at measurement locations validated uncertainty forecasts. To complement the real-time model simulations, historical simulations with another model show that large Kuroshio intrusions were associated with low sea surface height anomalies east of Taiwan, suggesting that there may be some degree of predictability for Kuroshio intrusions.

Seasonal and mesoscale variability of the Kuroshio near its origin

Rudnick, D.L., S. Jan, L. Centurioni, C.M. Lee, R.-C. Lien, J. Wang, D.-K. Lee, R.-S. Tseng, Y.Y. Kim, and C.-S. Chern, "Seasonal and mesoscale variability of the Kuroshio near its origin," Oceanography 24, 52-63, http://dx.doi.org/10.5670/oceanog.2011.94, 2011

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5 Dec 2011

The Kuroshio is the most important current in the North Pacific. Here, we present historical data and recent observations of the Kuroshio off the coasts of Taiwan and the Philippine Archipelago, with a focus on its origins. Seasonal climatologies from shipboard hydrographic and velocity measurements, and from surface drifters, demonstrate changes in the Kuroshio caused by the monsoon. In particular, seasonal monsoon forcing affects the degree of penetration of the Kuroshio through Luzon Strait. Data from surface drifters and underwater gliders describe its mesoscale variability. Velocities derived from drifters make clear the mesoscale variability associated with the Subtropical Countercurrent east of the Kuroshio. Underwater gliders document mesoscale structure prominent in salinity extrema associated with water masses. The evolution of these water masses as they progress northward near the Kuroshio indicates strong mixing in the region.

Typhoon-ocean interaction in the western North Pacific: Part 1

D'Asaro, E., P. Black, L. Centurioni, P. Harr, S. Jayne, I.-I Lin, C. Lee, J. Morzel, R. Mrvaljevic, P.P. Niiler, L. Rainville, T. Sanford, and T.Y. Tang, "Typhoon-ocean interaction in the western North Pacific: Part 1," Oceanography, 24, 24-31, doi:10.5670/oceanog.2011.91, 2011

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5 Dec 2011

The application of new technologies has allowed oceanographers and meteorologists to study the ocean beneath typhoons in detail. Recent studies in the western Pacific Ocean reveal new insights into the influence of the ocean on typhoon intensity.

High-resolution observations of aggregate flux during a sub-polar North Atlantic spring bloom

Briggs, N., M.J. Perry, I. Cetinic, C. Lee, E. D'Asaro, A.M. Gray, and E. Rehm, "High-resolution observations of aggregate flux during a sub-polar North Atlantic spring bloom," Deep-Sea Res. I, 58, 1031-1039, doi:10.1016/j.dsr.2011.07.007, 2011.

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1 Oct 2011

An aggregate flux event was observed by ship and by four underwater gliders during the 2008 sub-polar North Atlantic spring bloom experiment (NAB08). At the height of the diatom bloom, aggregates were observed as spikes in measurements of both particulate backscattering coefficient (bbp) and chlorophyll a fluorescence. Optical sensors on the ship and gliders were cross-calibrated through a series of simultaneous profiles, and bbp was converted to particulate organic carbon. The aggregates sank as a discrete pulse, with an average sinking rate of ~75 m^2 d^-1; 65% of aggregate backscattering and 90% of chlorophyll fluorescence content was lost between 100 m and 900 m. Mean aggregate organic carbon flux at 100 m in mid-May was estimated at 514 mg C m^2 d^-1, consistent with independent flux estimates. The use of optical spikes observed from gliders provides unprecedented coupled vertical and temporal resolution measurements of an aggregate flux event.

A synthesis of exchanges through the main oceanic gateways to the Arctic Ocean

Beszczynska-Moller, A., R.A. Woodgate, C. Lee, H. Melling, and M. Karcher, "A synthesis of exchanges through the main oceanic gateways to the Arctic Ocean," Oceanography, 24, 82-99, doi:10.5670/oceanog.2011.59, 2011.

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1 Sep 2011

In recent decades, the Arctic Ocean has changed dramatically. Exchanges through the main oceanic gateways indicate two main processes of global climatic importance - poleward oceanic heat flux into the Arctic Ocean and export of freshwater toward the North Atlantic. Since the 1990s, in particular during the International Polar Year (2007-2009), extensive observational efforts were undertaken to monitor volume, heat, and freshwater fluxes between the Arctic Ocean and the subpolar seas on scales from daily to multiyear. This paper reviews present-day estimates of oceanic fluxes and reports on technological advances and existing challenges in measuring exchanges through the main oceanic gateways to the Arctic.

Impact of wind-driven mixing in the Arctic Ocean

Rainville, L., C.M. Lee, and R.A. Woodgate, "Impact of wind-driven mixing in the Arctic Ocean," Oceanography 24, 136-145, doi:10.5670/oceanog.2011.65, 2011.

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1 Sep 2011

The Arctic Ocean traditionally has been described as an ocean with low variability and weak turbulence levels. Many years of observations from ice camps and ice-based instruments have shown that the sea ice cover effectively isolates the water column from direct wind forcing and damps existing motions, resulting in relatively small upper-ocean variability and an internal wave field that is much weaker than at lower latitudes. Under the ice, direct and indirect estimates across the Arctic basins suggest that turbulent mixing does not play a significant role in the general distribution of oceanic properties and the evolution of Arctic water masses. However, during ice-free periods, the wind generates inertial motions and internal waves, and contributes to deepening of the mixed layer both on the shelves and over the deep basins - as at lower latitudes. Through their associated vertical mixing, these motions can alter the distribution of properties in the water column. With an increasing fraction of the Arctic Ocean becoming ice-free in summer and in fall, there is a crucial need for a better understanding of the impact of direct wind forcing on the Arctic Ocean.

Closing the loop: Approaches to monitoring the state of the Arctic Mediterranean during the International Polar Year 2007-2008

Mauritzen, C., et al., including C.M. Lee, "Closing the loop: Approaches to monitoring the state of the Arctic Mediterranean during the International Polar Year 2007-2008," Prog. Oceanogr., 90, 62-89, doi: 10.1016/j.pocean.2011.02.010, 2011.

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1 Jul 2011

During the 4th International Polar Year 2007-2009 (IPY), it has become increasingly obvious that we need to prepare for a new era in the Arctic. IPY occurred during the time of the largest retreat of Arctic sea ice since satellite observations started in 1979. This minimum in September sea ice coverage was accompanied by other signs of a changing Arctic, including the unexpectedly rapid transpolar drift of the Tara schooner, a general thinning of Arctic sea ice and a double-dip minimum of the Arctic Oscillation at the end of 2009. Thanks to the lucky timing of the IPY, those recent phenomena are well documented as they have been scrutinized by the international research community, taking advantage of the dedicated observing systems that were deployed during IPY. However, understanding changes in the Arctic System likely requires monitoring over decades, not years. Many IPY projects have contributed to the pilot phase of a future, sustained, observing system for the Arctic. We now know that many of the technical challenges can be overcome.

Enhanced turbulence and energy dissipation at ocean fronts

D'Asaro, E., C. Lee, L. Rainville, L. Thomas, and R. Harcourt, "Enhanced turbulence and energy dissipation at ocean fronts," Science, 332, 318-322, doi:0.1126/science.1201515, 2011.

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15 Apr 2011

The ocean surface boundary layer mediates air-sea exchange. In the classical paradigm and in current climate models, its turbulence is driven by atmospheric forcing. Observations at a 1-km-wide front within the Kuroshio found the rate of energy dissipation within the boundary layer to be enhanced by 10 to 20 times, suggesting that the front not the atmospheric forcing supplied the energy for the turbulence. The data quantitatively support the hypothesis that winds aligned with the frontal velocity catalyzed a release of energy from the front to the turbulence. The resulting boundary layer is stratified, in contrast to the classically well-mixed layer. These effects will be strongest at the intense fronts found in the Kuroshio, Gulf Stream, and Antarctic Circumpolar Current, key players in the climate system.

Export and mesopelagic particle flux during a North Atlantic spring diatom bloom

Martin, P., R.S. Lampitt, M.J. Perry, R. Sanders, C. Lee, and E. D'Asaro, "Export and mesopelagic particle flux during a North Atlantic spring diatom bloom," Deep Sea Res. I, 58, 338-349, doi: 10.1016/j.dsr.2011.01.006, 2011.

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1 Apr 2011

Spring diatom blooms are important for sequestering atmospheric CO2 below the permanent thermocline in the form of particulate organic carbon (POC). We measured downward POC flux during a sub-polar North Atlantic spring bloom at 100 m using thorium-234 (234Th) disequilibria, and below 100 m using neutrally buoyant drifting sediment traps. The cruise followed a Lagrangian float, and a pronounced diatom bloom occurred in a 600 km2 area around the float. Particle flux was low during the first three weeks of the bloom, between 10 and 30 mg POC m/d. Then, nearly 20 days after the bloom had started, export as diagnosed from 234Th rose to 360-620 mg POC m2/d, co-incident with silicate depletion in the surface mixed layer. Sediment traps at 600 and 750 m depth collected 160 and 150 mg POC m2/ d, with a settled volume of particles of 1000-1500 mL m2/ d. This implies that 25-43% of the 100 m POC export sank below 750 m. The sinking particles were ungrazed diatom aggregates that contained transparent exopolymer particles (TEP). We conclude that diatom blooms can lead to substantial particle export that is transferred efficiently through the mesopelagic. We also present an improved method of calibrating the Alcian Blue solution against Gum Xanthan for TEP measurements.

Atmospheric and oceanic processes in the vicinity of an island strait

Pullen, J.D., A.L. Gordon, J. Sprintall, C.M. Lee, M.H. Alford, J.D. Doyle, and P.W. May, "Atmospheric and oceanic processes in the vicinity of an island strait," Oceanography, 24, 112-121, doi:10.5670/oceanog.2011.08, 2011.

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1 Mar 2011

In early February 2008, the mean flow through the Philippines' Mindoro Strait reversed. The flow was southward through the strait during late January and northward during most of February. The flow reversal coincided with the period between two Intensive Observational Period cruises (IOP-08-1 and IOP-08-2) sponsored by the Office of Naval Research as part of the Philippine Straits Dynamics Experiment (PhilEx). Employing high-resolution oceanic and atmospheric models supplemented with in situ ocean and air measurements, we detail the regional and local conditions that influenced this flow reversal. High-resolution air-sea simulations captured the flow reversal and agreed with measured currents from two moorings in the vicinity of Mindoro Strait. A short (January 24-27) easterly monsoon surge and a longer (February 9-16) northerly surge were represented in the model as well as in QuikSCAT and underway wind data taken during IOP-08-2. Mesoscale oceanic dipole eddies off Mindoro and Luzon islands were formed/enhanced and subsequently detached during these wind events. The cyclonic eddy in the dipole pair associated with the easterly surge was opportunistically sampled during the IOP-08-1 cruise, and the modeled eddy characteristics were verified using in situ shipboard data. The predominant geostrophic southward flow through the strait was interrupted by a strong and sustained wind-driven (by the northerly surge) flow reversal in early February. Enhanced upper-ocean stratification in winter 2008 due to anomalously high precipitation served to isolate the observed near-surface flow.

Development of a hindcast/forecast model for the Philippine Archipelago

Arango, H.G., J.C. Levin, E.N. Curchitser, B. Zhang, A.M. Moore, W. Han, A.L. Gordon, C.M. Lee, and J.B. Girton, "Development of a hindcast/forecast model for the Philippine Archipelago," Oceanography, 24, 58-69, doi:10.5670/oceanog.2011.04, 2011.

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1 Mar 2011

This article discusses the challenges of developing a regional ocean prediction model for the Philippine Archipelago, a complex area in terms of geometry, bathymetry-dominated dynamics and variability, and strong local and remote wind forcing, where there are limited temporal and spatial ocean measurements. We used the Regional Ocean Modeling System (ROMS) for real-time forecasting during the Philippine Straits Dynamics Experiment (2007-2009) observational program. The article focuses on the prediction experiments before and during the exploratory cruise period, June 6 - July 3, 2007. The gathered observations were not available in real time, so the 4-Dimensional Variational (4D-Var) data assimilation experiments were carried out in hindcast mode. The best estimate of ocean state (nowcast) is determined by combining satellite-derived products for sea surface temperature and height, and subsurface temperature and salinity measurements from several hydrographic assets over a sequential five-day data assimilation window. The largest source of forecast uncertainty is from the prescribed lateral boundary conditions in the nearby Pacific Ocean, especially excessive salt flux. This result suggests that remote forcing and inflows from the Pacific are crucial for predicting ocean circulation in the Philippine Archipelago region. The lateral boundary conditions are derived from 1/12 degree global HYbrid Coordinate Ocean Model (HYCOM) daily snapshots. The incremental, strong-constraint 4D-Var data assimilation successfully decreased temperature and salinity errors of the real-time, nonassimilative control forecast by 38% and 49%, respectively.

Observations of currents and temperature-salinity-pigment fields in the northern Adriatic Sea in winter 2003.

Poulain, P.M., C. Lee, E. Mauri, G. Notarstefano, and L. Ursella, "Observations of currents and temperature-salinity-pigment fields in the northern Adriatic Sea in winter 2003." Bollettino di Geofisica Teorica ed Applicata, 52, 149-174, 2011.

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1 Mar 2011

Satellite (sea surface temperature and chlorophyll concentration) and in-situ data (currents from surface drifters and ADCP; sub-surface temperature, salinity and optical properties measured by a towed-vehicle) are used to describe the circulation features and the distribution of temperature, salinity and chlorophyll pigment in the northern Adriatic Sea in winter 2003, with particular focus on fronts and jets. The horizontal structure and temporal variations of these parameters are qualitatively related to the local wind forcing, to the river runoff and to the bathymetry. Vigorous currents are triggered by predominant northeasterly Bora wind events, including a strong cross-basin jet, south of Istria, associated with a sharp (> 3 C/km) and thin (< 0.5 km) front almost compensated in temperature and salinity and affected by barotropic instabilities. To the north, a cyclonic gyre is evident with a southern limb corresponding to the Po River plume extending offshore to the NE. Cold and pigment-rich, river-influenced waters prevail off the entire Italian coast. South of the Po delta these waters flow southeastwards in a coastal layer with baroclinic instabilities.

Tidally driven exchange in an archipelago strait: Biological and optical responses

Jones, B.H., C.M. Lee, G. Toro-Farmer, E.S. Boss, M.C. Gregg, and C.L. Villanoy, "Tidally driven exchange in an archipelago strait: Biological and optical responses," Oceanography, 24, 142-155, doi:10.5670/oceanog.2011.11, 2011.

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1 Mar 2011

Measurements in San Bernardino Strait, one of two major connections between the Pacific Ocean and the interior waters of the Philippine Archipelago, captured tidal currents that drove vertical mixing and net landward transport. A TRIAXUS towed profiling vehicle equipped with physical and optical sensors was used to repeatedly map subregions within the strait, employing survey patterns designed to resolve tidal variability of physical and optical properties. Strong flow over the sill between Luzon and Capul islands resulted in upward transport and mixing of deeper high-salinity, low-oxygen, high-particle-and-nutrient-concentration water into the upper water column, landward of the sill. During the high-velocity ebb flow, topography influences the vertical distribution of water, but without the diapycnal mixing observed during flood tide. The surveys captured a net landward flux of water through the narrowest part of the strait. The tidally varying velocities contribute to strong vertical transport and diapycnal mixing of the deeper water into the upper layer, contributing to the observed higher phytoplankton biomass within the interior of the strait.

Volume, freshwater, and heat fluxes through Davis Strait, 2004-05

Curry, B., C.M. Lee, and B. Petrie, "Volume, freshwater, and heat fluxes through Davis Strait, 2004-05," J. Phys. Oceangr., 41, 429-436, doi: 10.1175/2010JPO4536.1, 2011.

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1 Mar 2011

Davis Strait volume, freshwater, and heat fluxes estimated from objectively mapped 2004-05 moored array data do not differ significantly from values based on a 1987-90 array but are distributed differently across the strait. The 2004-05 array provided the first year-long measurements in the upper 100 m and over the shelves. The upper 100 m accounts for 39% of the net volume and 59% of the net freshwater fluxes. Shelf contributions are small: 0.4 Sv (volume), 15 mSv (freshwater), and 3 TW (heat) from the West Greenland shelf and -0.1 Sv, -7 mSv, and 1 TW from the Baffin Island shelf. Contemporaneous measurements of the Baffin Bay inflows and outflows indicate that volume and freshwater budgets balance to within 26% and 4%, respectively, of the net Davis Strait outflow. Davis Strait volume and freshwater fluxes nearly equal those from Fram Strait, indicating that both are significant Arctic freshwater pathways.

Calcium carbonate saturation states in the waters of the Canadian Arctic Archipelago and the Labrador Sea

Azetsu-Scott, K., A. Clarke, K. Falkner, J. Hamilton, E.P. Jones, C. Lee, B. Petrie, S. Prinsenberg, M. Starr, and P. Yeats, "Calcium carbonate saturation states in the waters of the Canadian Arctic Archipelago and the Labrador Sea," J. Geophys. Res., 115, doi:10.1029/2009JC005917, 2010.

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23 Nov 2010

Ocean acidification is predicted to occur first in polar oceans. We investigated the saturation state of waters with respect to calcite and aragonite in six sections along an Arctic outflow pathway through the Canadian Arctic Archipelago (CAA) and into the northwestern Atlantic using dissolved inorganic carbon and total alkalinity measurements from 2003 to 2005. The study area, a key region connecting the Arctic and the North Atlantic, includes Smith Sound, Barrow Strait, Baffin Bay, Davis Strait, Hudson Strait, and the Labrador Sea.

The average aragonite in the Arctic outflow was 1.18 plus/minus 0.17 in Barrow Strait and 1.31 plus/minus 0.14 in Smith Sound, with areas where aragonite < 1. The Arctic outflow through the CAA has a high content of Pacific waters, which have a low saturation state. These waters can be traced along the western Baffin Bay to Davis Strait. South of Davis Strait, this outflow is modified by mixing with slope and offshore waters of Atlantic origin and with the outflow from Hudson Strait. Despite the mixing, low saturation state water can still be identified on the southern Labrador Shelf. The aragonite saturation horizon is found at ~150 m in Barrow Strait; at 200 m in Baffin Bay, Davis Strait, and Hudson Strait; and at 2300 m in the Labrador Sea. This study provides baseline data of the saturation states for the waters of the CAA and the northwest Atlantic. It also illustrates the downstream evolution of low saturation state Arctic outflow in the northwest Atlantic.

Analysis of the Arctic system for freshwater cycle intensification: Observations and expectations

Rawlins, M.A., et al., including M. Steele, C.M. Lee, M. Wensnahan, and R. Woodgate, "Analysis of the Arctic system for freshwater cycle intensification: Observations and expectations," J. Clim., 23, 5715-5737, doi:10.1175/2010JCLI3421.1, 2010.

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1 Nov 2010

Hydrologic cycle intensification is an expected manifestation of a warming climate. Although positive trends in several global average quantities have been reported, no previous studies have documented broad intensification across elements of the Arctic freshwater cycle (FWC). In this study, the authors examine the character and quantitative significance of changes in annual precipitation, evapotranspiration, and river discharge across the terrestrial pan-Arctic over the past several decades from observations and a suite of coupled general circulation models (GCMs). Trends in freshwater flux and storage derived from observations across the Arctic Ocean and surrounding seas are also described.

Singing behavior of fin whales in the Davis Strait with implications for mating, migration and foraging

Simon, M., K.M. Stafford, K. Beedholm, C.M. Lee, and P.T. Madsen, "Singing behavior of fin whales in the Davis Strait with implications for mating, migration and foraging," J. Acoust. Soc. Am., 128, 3200-3210, doi:10.1121/1.3495946, 2010.

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1 Nov 2010

Most baleen whales undertake migrations between low-latitude breeding grounds and high-latitude feeding grounds. Though little is known about the timing of their migration from the Arctic, fin whales are assumed to undertake a similar migratory pattern. To address questions about habitat use and migrations, the acoustic activity of fin whales in Davis Strait, between Greenland and Canada, was monitored continuously for two years using three bottom-moored acoustic recorders.

The acoustic power in the fin whale call frequencies peaked in November–December, showing that fin whales are present in Davis Strait much later in the year than previously expected. The closely timed peaks in song activity and conception time imply that not all fin whales migrate south to mate, but rather start mating at high latitudes rather than or before migrating. Singing activity was strongly linked to daylight hours, suggesting that fin whales might feed during the few daylight hours of the late fall and early Arctic winter. A negative correlation between the advancing sea ice front and power in fin whale frequencies indicates that future changes in sea ice conditions from global warming might change the distribution and migratory patterns of fin whales near the poles.

Observations of storm-induced mixing and Gulf Stream Ring incursion over the southern flank of Georges Bank: Winter and summer 1997

Lee, C.M., and K.H. Brink, "Observations of storm-induced mixing and Gulf Stream Ring incursion over the southern flank of Georges Bank: Winter and summer 1997," J. Geophys. Res., 115, doi:10.1029/2009JC005706, 2010.

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7 Aug 2010

High-resolution hydrographic measurements collected along the southern edge of Georges Bank during March and June–July 1997 focused on characterizing processes that drive fluxes of material between the slope and bank. Wintertime sampling characterized changes driven by a strong storm. A Scotian Shelf crossover event produced a ribbon of anomalously fresh water along the bank's southern flank that was diluted during the storm. Comparison of prestorm and poststorm sections shows that over the bank changes in heat and salt inventories are consistent with those expected solely from local surface fluxes. In deeper waters, advective effects, likely associated with frontal motion and eddies, are clearly important. Summertime surveys resolve the development of a massive intrusion of Gulf Stream-like waters onto the bank. East of the intrusion, a thin extrusion of bank water is drawn outward by the developing ring, exporting fresher water at a rate of about 7 x 104 m3/s. A large-amplitude Gulf Stream meander appears to initiate the extrusion, but it quickly evolves, near the bank edge, into a warm core ring. Ring water intrudes to approximately the 80 m isobath, 40 km inshore from the bank edge. The intrusion process seems analogous to the development of Gulf Stream shingles (a hydrodynamic instability) in the South Atlantic Bight. It appears that, once the intruded water is established on the bank, it remains there and dissipates in place. Although the intrusion is an extremely dramatic event, it is probably not actually a major contributor to shelf edge exchanges over a seasonal time scale.

The subpolar front of the Japan/East Sea. Part II: Inverse method for determining the frontal vertical circulation

Thomas, L.N., C.M. Lee, and Y. Yoshikawa, "The subpolar front of the Japan/East Sea. Part II: Inverse method for determining the frontal vertical circulation," J. Phys. Oceanogr., 40, 3-25, doi:10.1175/2009JPO4018.1, 2010.

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1 Jan 2010

An inverse method for inferring vertical velocities from high-resolution hydrographic/velocity surveys is formulated and applied to observations collected at the subpolar front of the Japan/East Sea (JES) taken during several cold-air outbreaks. The method is distinct from vertical velocity inferences based on the omega equation in that the driving mechanism for the ageostrophic flow is inferred rather than assumed and hence is particularly appropriate for application to wind- or buoyancy-forced upper-ocean currents where friction, mixing, inertial/superinertial motions, or higher-order effects can contribute along with shear/strain of the geostrophic flow to force vertical motions.

The inferred vertical circulation at the subpolar front of the JES has amplitudes O(100 m day-1) compared to the 20 m day-1 vertical velocities predicted by the omega equation. Time-dependent, near-inertial motions driven by the winds and modified by the vertical vorticity of the frontal jet appear to be the primary cause of the strong vertical motions. The strongest vertical motions are associated with submesoscale, O(5 km), frontal downdrafts that tend to align with the slanted isopycnal surfaces of the front and advect water with low salinity and high chlorophyll fluorescence down the dense side of the front.

Glider observations of kinematics in a Gulf of Alaska eddy

Martin, J.P., C.M. Lee, C.C. Eriksen, C. Ladd, and N.B. Kachel, "Glider observations of kinematics in a Gulf of Alaska eddy," J. Geophys. Res., 114, doi:10.1029/2008JC005231, 2009.

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24 Dec 2009

The depth-radial structure of a Gulf of Alaska (GoA) eddy is investigated using observations from an autonomous winged buoyancy-driven glider, drifters, and satellite altimeters. The eddy formed when Sitka and Yakutat eddies merged in June 2005. Sitka and Yakutat eddies form in the northeastern GoA and travel westward carrying anomalous energy, temperature, and chemical properties. The glider crossed the eddy seven times from mid-August to late October 2005. A temperature maximum, at 130 m depth near the eddy's center, is indicative of coastal water. The strongest azimuthal current is 0.35 m s-1, occurring at 270 m depth and 17.5 km radius. The eddy's Rossby (Burger) number is 0.16 (0.47). Using a model with nonzero constant potential vorticity anomaly only within each depth's radius of strongest current, a function is fit to azimuthal current. The fit explains a large percentage of the current's radial variance, with a squared correlation coefficient of >/=0.9 at the depths of strongest current (270 m) and weakest stratification (360 m). Temporal trends in azimuthal volume transport rate and depth mean potential vorticity are not observed during the glider survey.

Surprising return of deep convection to the subpolar North Atlantic Ocean in winter 2007-2008

Vage, K., R.S. Pickart, V. Thierry, G. Reverdin, C.M. Lee, B. Petie, T.A. Agnew, A. Wong, and M.H. Ribergaard, "Surprising return of deep convection to the subpolar North Atlantic Ocean in winter 2007-2008," Nature Geosci., 2, 67-72, doi:10.1038/ngeo382, 2009

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1 Feb 2009

In the process of open-ocean convection in the subpolar North Atlantic Ocean, surface water sinks to depth as a distinct water mass, the characteristics of which affect the meridional overturning circulation and oceanic heat flux. In addition, carbon is sequestered from the atmosphere in the process. In recent years, this convection has been shallow or non-existent, which could be construed as a consequence of a warmer climate.

Here we document the return of deep convection to the subpolar gyre in both the Labrador and Irminger seas in the winter of 2007–2008. We use profiling float data from the Argo programme to document deep mixing. Analysis of a variety of in situ, satellite and reanalysis data shows that contrary to expectations the transition to a convective state took place abruptly, without going through a phase of preconditioning. Changes in hemispheric air temperature, storm tracks, the flux of fresh water to the Labrador Sea and the distribution of pack ice all contributed to an enhanced flux of heat from the sea to the air, making the surface water sufficiently cold and dense to initiate deep convection. Given this complexity, we conclude that it will be difficult to predict when deep mixing may occur again.

Seaglider observations of blooms and subsurface chlorophyll maxima off the Washington coast

Perry, M.J., B.S. Sackman, C.C. Eriksen, and C.M. Lee, "Seaglider observations of blooms and subsurface chlorophyll maxima off the Washington coast," Limnol. Oceanogr., 53, 2169-2179, doi:10.4319/lo.2008.53.5_part_2.2169, 2008.

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1 Sep 2008

From September 2003 to December 2007, autonomous, underwater Seaglider continuously ran a V-shaped transect off Washington State from about 200-m water depth (i.e., at the break between the shelf and slope) to offshore waters with depths >2700 m. Seaglider visited the offshore vertex at 47°N, 128°W, where our observations concentrated, approximately monthly. Seaglider measured temperature, conductivity, and dissolved oxygen to 1000 m and also recorded chlorophyll a (Chl a) fluorescence and particulate optical backscatter to 150 m.

Distinct interannual variation was documented in timing and depths of winter mixing, transition to a shallow summer pycnocline, and onset of mixed-layer erosion in autumn. Chl a concentrations estimated from fluorescence were directly comparable among the seven laboratory-calibrated sensors used, but their estimates exceeded concurrent, satellite-derived concentrations by a factor of three. Seaglider optical profiles enabled interpretation of satellite imagery by revealing that the apparent autumn bloom after destratification was instead a vertical redistribution of phytoplankton from the subsurface maximum to a depth where they could be observed by satellites. Results of 4 yr of sampling within 25 km of the vertex demonstrate the value of gliders in ocean observing and their capability to carry out multiyear, fully autonomous operations under any sea state. The true power of glider programs will be realized in combination with other measurement platforms, including larger spatial coverage by satellites and more comprehensive biogeochemical measurements from moorings and occasional ship-based sampling.

Acoustic navigation and communications for high latitude ocean research (ANCHOR)

Lee, C.M., and J.I. Gobat, "Acoustic navigation and communications for high latitude ocean research (ANCHOR)," J. Acoust. Soc. Am., 123, 2990, doi:10.1121/1.2932529, 2008.

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1 May 2008

Recent community reports on autonomous and Lagrangian platforms and Arctic observing identify the development of under-ice navigation and telemetry technologies as one of the critical factors limiting the scope of autonomous (e.g. floats, AUVs and gliders) high-latitude measurement efforts. These platforms could provide persistent, high-resolution, basin-wide sampling in ice-covered regions and collect measurements near the critical ice–water interface. Motivated by the dramatic advances in temporal and spatial reach promised by autonomous sampling and by the need to coordinate nascent efforts to develop navigation and communication system components, an international group of acousticians, platform developers, high-latitude oceanographers and marine mammal researchers gathered in Seattle, U.S.A. from 27 February – 1 March for an NSF Office of Polar Programs sponsored Acoustic Navigation and Communication for High-latitude Ocean Research workshop.

Workshop participants summarized the current state of knowledge concerning Arctic acoustics, navigation and communications, developed an overarching system specification to guide community-wide engineering efforts and established an active community and steering group to guide long-term efforts and ensure interoperability between elements developed by disparate teams. This presentation will summarize workshop findings and provide an update on recent developments stemming from the EU DAMOCLES and US NSF Arctic Observing Network programs.

Fresh-water fluxes via Pacific and Arctic outflows across the Canadian polar shelf

Melling, H., T.A. Agnew, K.K. Falkner, D.A. Greenberg, C.M. Lee, A. Munchow, B. Petrie, S.J. Prinsenberg, R.M. Samelson, and R.A. Woodgate, "Fresh-water fluxes via Pacific and Arctic outflows across the Canadian polar shelf," in Arctic-Subarctic Ocean Fluxes, edited by R.R. Dickson, J. Meincke, and P. Rhines, 193-248 (Springer: Dordrecht, 2008).

1 Jan 2008

The arctic freshwater system: Changes and impacts

White, D., et al. (including C. Lee, M. Steele, and R. Woodgate), "The arctic freshwater system: Changes and impacts," J. Geophys. Res., 112, doi:10.1029/2006JG000353, 2007.

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30 Nov 2007

Dramatic changes have been observed in the Arctic over the last century. Many of these involve the storage and cycling of fresh water. On land, precipitation and river discharge, lake abundance and size, glacier area and volume, soil moisture, and a variety of permafrost characteristics have changed. In the ocean, sea ice thickness and areal coverage have decreased and water mass circulation patterns have shifted, changing freshwater pathways and sea ice cover dynamics. Precipitation onto the ocean surface has also changed. Such changes are expected to continue, and perhaps accelerate, in the coming century, enhanced by complex feedbacks between the oceanic, atmospheric, and terrestrial freshwater systems. Change to the arctic freshwater system heralds changes for our global physical and ecological environment as well as human activities in the Arctic. In this paper we review observed changes in the arctic freshwater system over the last century in terrestrial, atmospheric, and oceanic systems.

Introduction to special section: Recent advances in oceanography and marine meteorology of the Adriatic Sea

Lee, C.M., M. Orlic, P.M. Poulain, and B. Cushman-Roisin, "Introduction to special section: Recent advances in oceanography and marine meteorology of the Adriatic Sea," J. Geophys. Res., 112, 10.1029/2007JC004115, 2007.

30 Mar 2007

A climatology of the northern Adriatic Sea's response to bora and river forcing

Jeffries, M.A., and C.M. Lee, "A climatology of the northern Adriatic Sea's response to bora and river forcing," J. Geophys. Res., 112, doi:10.1029/2006JD007907, 2007.

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28 Mar 2007

A new northern Adriatic climatology characterizes salinity and temperature fields associated with response to strong riverine input and bora wind forcing acting on variable ambient stratification. Time series of key forcing variables, specifically Po River discharge and wind velocity in bora pathways, combined with a measure of time-variable ambient stratification, indicate the dominant dynamics (e.g., bora winds acting on an unstratified northern Adriatic or strong Po River outflow into an unstratified basin). These indicators define an averaging scheme which organizes archived temperature and salinity profiles into groupings based on common dynamics, providing climatological characterizations of response to bora forcing and the differing basin responses to strong and weak Po discharge into strong and weak ambient stratification. The resulting maps demonstrate that the offshore penetration of Po waters depends strongly on outflow strength and ambient stratification. The climatology reveals buoyant Po River waters spreading in a surface layer throughout much of the northern basin during periods of strong ambient stratification, with little dependence on outflow strength. In contrast, during unstratified periods, outflow strength determines whether the river waters penetrate into the basin (strong outflow) or remain trapped over the Italian shelf (weak outflow). In addition, separation of oceanographic data into periods of strong bora winds reveals the formation of a freshwater filament in the resulting salinity fields. This feature extends into the open sea, separating two pools of higher salinity water. Significance testing of the mode-maps with climatological averages indicate that the mode-based maps are statistically robust within the 95% confidence interval in areas of energetic mesoscale activity such as those regions subject to direct riverine or wind forcing.

Turbulence in the wintertime northern Adriatic Sea under strong atmospheric forcing

Peters, H., C.M. Lee, M. Orlic, and C.E. Dorman, "Turbulence in the wintertime northern Adriatic Sea under strong atmospheric forcing," J. Geophys. Res., 112, doi:10.1029/2006JC003634, 2007.

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17 Feb 2007

In February 2003, we observed the response of the 40 to 50 m deep northern Adriatic Sea to strong surface forcing by 20 m s-1 winds and 600 W m-2 net upward heat flux resulting from cold bora winds blowing onto a relatively warm sea through gaps in the Croatian mountains. Ocean turbulence throughout the water column was observed with a microstructure profiler and a bottom-mounted, upward-looking, 5-beam, acoustic Doppler current profiler (ADCP). Microstructure-based dissipation rates were close to similarity scaling of the surface wind stress. The surface buoyancy flux, related to the oceanic heat loss, contributed little energy to the turbulence, but led to sustained unstable stratification. The energy-containing range of the turbulence together with the upper end of the inertial subrange, with horizontal scales between a few hundred meters and about 10 m, contained coherent, anisotropic overturning motions aligned with the low-frequency, barotropic ocean currents which carried stress and showed an asymmetry between rare, narrow, faster downdrafts and diffuse, weak updrafts. These motions bear no similarity with Langmuir cells. The turbulence measurements were embedded in surveys of the mesoscale ocean variability. Part of the observations were set in a front a few hundred meters wide with little density contrast. As the bora wind relaxed, the front began to develop a highly stratified "foot" undergoing intense mixing. The paper addresses problems of beam spreading and instrumental noise in ADCPs.

Bora event variability and the role of air-sea feedback

Pullen, J., J.D. Doyle, T. Haack, C. Dorman, R.P. Signell, and C.M. Lee, "Bora event variability and the role of air-sea feedback," J. Geophys. Res., 112, doi:10.1029/2006JC003726, 2007.

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13 Feb 2007

A two-way interacting high resolution numerical simulation of the Adriatic Sea using the Navy Coastal Ocean Model (NCOM) and Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) was conducted to improve forecast momentum and heat flux fields, and to evaluate surface flux field differences for two consecutive bora events during February 2003. (COAMPS is a registered trademark of the Naval Research Laboratory.) The strength, mean positions and extensions of the bora jets, and the atmospheric conditions driving them varied considerably between the two events. Bora 1 had 62% stronger heat flux and 51% larger momentum flux than bora 2. The latter displayed much greater diurnal variability characterized by inertial oscillations and the early morning strengthening of a west Adriatic barrier jet, beneath which a stronger west Adriatic ocean current developed. Elsewhere, surface ocean current differences between the two events were directly related to differences in wind stress curl generated by the position and strength of the individual bora jets. The mean heat flux bias was reduced by 72%, and heat flux RMSE reduced by 30% on average at four instrumented over-water sites in the two-way coupled simulation relative to the uncoupled control. Largest reductions in wind stress were found in the bora jets, while the biggest reductions in heat flux were found along the north and west coasts of the Adriatic. In bora 2, SST gradients impacted the wind stress curl along the north and west coasts, and in bora 1 wind stress curl was sensitive to the Istrian front position and strength. The two-way coupled simulation produced diminished surface current speeds of ~12% over the northern Adriatic during both bora compared with a one-way coupled simulation.

February 2003 marine atmospheric conditions and the bora over the northern Adriatic

Dorman, C.E., et al. (including C.M. Lee), "February 2003 marine atmospheric conditions and the bora over the northern Adriatic," J. Geophys. Res., 111, 10.1029/2005JC003134, 2006.

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9 Dec 2006

A winter oceanographic field experiment provided an opportunity to examine the atmospheric marine conditions over the northern Adriatic. Mean February winds are from a northeasterly direction over most of the Adriatic and a more northerly direction along the western coast. Wind speeds are fastest in jets over the NE coast during bora events and weakest in the mid-northwestern Adriatic. Diurnal air temperature cycles are smallest on the NE coast and largest in the midwestern Adriatic. The maximum sea-air difference is ±10°C on the eastern coast and near zero on the midwestern Adriatic. Boras are northeasterly (from) wind events that sweep off Croatia and Slovenia, bringing slightly colder and drier air over the northern Adriatic. The main bora season is December to March. Winter 2002–2003 was normal for bora events. Synoptic-scale temporal variations are correlated over the northern Adriatic. Fastest Bora winds and highest wind stress over the northern Adriatic is concentrated in four topographically controlled jets. The strongest is the Senj Jet, while the Trieste Jet extends across the entire northern Adriatic. Between each two jets is a weak wind zone. The greatest mean net heat loss is in bora jets in the NE Adriatic, where it was ~438 W m-2 and is weakest in the midwestern northern Adriatic, where it was near zero. Wind stress is concentrated over the NE half of Adriatic in four bora jets, while wind stress is weak in the NW Adriatic. There is significant variation in wind stress mean and standard deviation structure over the northern Adriatic with each bora event.

Aliasing due to sampling of the Adriatic temperature, salinity and density in space

Pasaric, Z., M. Orlic, and C.M. Lee, "Aliasing due to sampling of the Adriatic temperature, salinity and density in space," Estuar. Coast. Shelf Sci., 69, 636-642, doi:10.1016/j.ecss.2006.05.018, 2006.

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1 Sep 2006

High-resolution underway temperature and conductivity measurements collected by R/V Knorr during winter and spring 2003 are used to characterize errors associated with spatial aliasing in the northern and central Adriatic Sea. During winter, 99th percentile temperature, salinity and density errors were 0.62°C, 0.25 and 0.12 kg/m3 (0.25°C, 0.10 and 0.05 kg/m3) for sampling at 10 km (5 km) horizontal resolution, respectively. The corresponding values in spring were 1.31°C, 0.50 and 0.40 kg/m3 (0.93°C, 0.25 and 0.22 kg/m3) for the 10 km (5 km) sample spacing, respectively. The largest errors were associated with energetic regions over the shallow, western Adriatic, in front of the Po River mouth and off the tip of the Istrian peninsula. The deeper eastern basin exhibited smaller errors. The variability of errors in time and space reflected the variability of small-scale density features, characterized by wavelengths as small as 2 km in winter and 1 km in spring and being more pronounced in the western and northern parts of the Adriatic. As these results indicate that errors associated with undersampling can be considerable, they should be taken into account while planning future CTD measurements in the region.

Biological structure and seasonality in the Japan/East Sea

Ashjian, C., R. Arnone, C. Davis, B. Jones, M. Kahru, C.M. Lee, and B.G. Mitchell, "Biological structure and seasonality in the Japan/East Sea," Oceanography, 19, 126-137, 2006.

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1 Sep 2006

The Japan/East Sea (JES) contains several oceanic regions separated by dynamic boundaries. These distinct regions, and the physical features that establish and maintain the boundaries between the regions, have significant impacts on its ocean biology. Until recently, most studies of the biology of the JES have focused on nearshore regions, with few detailed studies of the interior of the JES or the dynamic features that define the different regions. In addition, the classic sampling methods used in previous work have not allowed high-resolution studies of biological-physical interactions associated with key dynamic mesoscale frontal zones, quasi-synoptic surveys of water column and bio- logical structure in three dimensions, or broad-scale description of the seasonal cycles in the different biogeographic regions of the JES.

Intermediate water formation at the Japan/East Sea subpolar front

Lee, C.M., L.N. Thomas, and Y. Yoshikawa, "Intermediate water formation at the Japan/East Sea subpolar front," Oceanography, 19, 54-64, 2006.

1 Sep 2006

An estimate of tidal energy lost to turbulence at the Hawaiian Ridge

Klymak, J.M., J.N. Moum, J.D. Nash, E. Kunze, J.B. Girton, G.S. Carter, C.M. Lee, T.B. Sanford, and M.C. Gregg, "An estimate of tidal energy lost to turbulence at the Hawaiian Ridge," J. Phys. Oceanogr., 36, 1148-1164, doi: 10.1175/JPO2885.1, 2006.

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1 Jun 2006

An integrated analysis of turbulence observations from four unique instrument platforms obtained over the Hawaiian Ridge leads to an assessment of the vertical, cross-ridge, and along-ridge structure of turbulence dissipation rate and diffusivity. The diffusivity near the seafloor was, on average, 15 times that in the midwater column. At 1000-m depth, the diffusivity atop the ridge was 30 times that 10 km off the ridge, decreasing to background oceanic values by 60 km. A weak (factor of 2) spring–neap variation in dissipation was observed. The observations also suggest a kinematic relationship between the energy in the semidiurnal internal tide (E) and the depth-integrated dissipation (D), such that D ~ E1±0.5 at sites along the ridge. This kinematic relationship is supported by combining a simple knife-edge model to estimate internal tide generation, with wave–wave interaction time scales to estimate dissipation. The along-ridge kinematic relationship and the observed vertical and cross-ridge structures are used to extrapolate the relatively sparse observations along the length of the ridge, giving an estimate of 3 ± 1.5 GW of tidal energy lost to turbulence dissipation within 60 km of the ridge. This is roughly 15% of the energy estimated to be lost from the barotropic tide.

Internal tides and turbulence along the 3000-m isobath of the Hawaiian Ridge

Lee, C.M., E. Kunze, T.B. Sanford, J.D. Nash, M.A. Merrifield, and P.E. Holloway, "Internal tides and turbulence along the 3000-m isobath of the Hawaiian Ridge," J. Phys. Oceanogr., 36, 1165-1183, doi: 10.1175/JPO2886.1, 2006.

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1 Jun 2006

Full-depth velocity and density profiles taken along the 3000-m isobath characterize the semidiurnal internal tide and bottom-intensified turbulence along the Hawaiian Ridge. Observations reveal baroclinic energy fluxes of 21 ± 5 kW m-1 radiating from French Frigate Shoals, 17 ± 2.5 kW m-1 from Kauai Channel west of Oahu, and 13 ± 3.5 kW m-1 from west of Nihoa Island. Weaker fluxes of 14 ± 2 kW m-1 radiate from the region near Necker Island and east of Nihoa Island. Observed off-ridge energy fluxes generally agree to within a factor of 2 with those produced by a tidally forced numerical model. Average turbulent diapycnal diffusivity K is (0.5–1) x 10-4 m2 s-1 above 2000 m, increasing exponentially to 20 x 10-4 m2 s-1 near the bottom. Microstructure values agree well with those inferred from a finescale internal wave-based parameterization. A linear relationship between the vertically integrated energy flux and vertically integrated turbulent dissipation rate implies that dissipative length scales for the radiating internal tide exceed 1000 km.

Structure of the baroclinic tide generated at Kaena Ridge, Hawaii

Nash, J.D., E. Kunze, C.M. Lee, and T.B. Sanford, "Structure of the baroclinic tide generated at Kaena Ridge, Hawaii," J. Phys. Oceanogr., 36, 1123-1135, doi:10.1175/JPO2883.1, 2006.

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1 Jun 2006

Repeat transects of full-depth density and velocity are used to quantify generation and radiation of the semidiurnal internal tide from Kaena Ridge, Hawaii. A 20-km-long transect was sampled every 3 h using expendable current profilers and the absolute velocity profiler. Phase and amplitude of the baroclinic velocity, pressure, and vertical displacement were computed, as was the energy flux. Large barotropically induced isopycnal heaving and strong baroclinic energy-flux divergence are observed on the steep flanks of the ridge where upward and downward beams radiate off ridge. Directly above Kaena Ridge, strong kinetic energy density and weak net energy flux are argued to be a horizontally standing wave. The phasing of velocity and vertical displacements is consistent with this interpretation. Results compare favorably with the Merrifield and Holloway model.

Intensification of ocean fronts by down-front winds

Thomas, L., and C.M. Lee, "Intensification of ocean fronts by down-front winds," J. Phys. Oceanogr., 35, 1086-1102, doi:10.1175/JPO2737.1, 2005

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1 Jun 2005

Many ocean fronts experience strong local atmospheric forcing by down-front winds, that is, winds blowing in the direction of the frontal jet. An analytic theory and nonhydrostatic numerical simulations are used to demonstrate the mechanism by which down-front winds lead to frontogenesis. When a wind blows down a front, cross-front advection of density by Ekman flow results in a destabilizing wind-driven buoyancy flux (WDBF) equal to the product of the Ekman transport with the surface lateral buoyancy gradient. Destabilization of the water column results in convection that is localized to the front and that has a buoyancy flux that is scaled by the WDBF. Mixing of buoyancy by convection, and Ekman pumping/suction resulting from the cross-front contrast in vertical vorticity of the frontal jet, drive frontogenetic ageostrophic secondary circulations (ASCs). For mixed layers with negative potential vorticity, the most frontogenetic ASCs select a preferred cross-front width and do not translate with the Ekman transport, but instead remain stationary in space. Frontal intensification occurs within several inertial periods and is faster the stronger the wind stress. Vertical circulation is characterized by subduction on the dense side of the front and upwelling along the frontal interface and scales with the Ekman pumping and convective mixing of buoyancy. Cross-front sections of density, potential vorticity, and velocity at the subpolar front of the Japan/East Sea suggest that frontogenesis by down-front winds was active during cold-air outbreaks and could result in strong vertical circulation.

Transport pathways of the Adriatic: Multi-disciplinary perspectives on a wintertime bora wind event

Lee, C.M., F. Askari, J. Book, S. Camiel, B. Cushman-Roisin, D. Dorman, J. Doyle, P. Flament, C.K. Harris, B.H. Jones, M. Kuzmic, P. Martin, A. Ogston, M. Orlic, H. Perkins, P. Poulain, J. Pullen, A. Russo, C. Sherwood, R.P. Signell, and D. Thaler, "Transport pathways of the Adriatic: Multi-disciplinary perspectives on a wintertime bora wind event," Eos Trans. AGU, 86, 157, 163, 165, 2005.

1 Jun 2005

Cruise Report: DOLCE VITA 1 and 2, 31 January - 24 February and 26 May - 15 June, 2003

Lee, C., and J. Gobat, et al., "Cruise Report: DOLCE VITA 1 and 2, 31 January - 24 February and 26 May - 15 June, 2003," APL-UW TR 0409, February 2005.

28 Feb 2005

An Observational Array for High-Resolution, Year-Round Measurements of Volume, Freshwater, and Ice Flux Variability in Davis Strait: Cruise Report for R/V Knorr 179-05, 22 September - 4 October 2004

Lee, C.M., B. Petrie, J.I. Gobat, V. Soukhovtsev, J. Abiel, K. Van Thiel, and M. Scotney, "An Observational Array for High-Resolution, Year-Round Measurements of Volume, Freshwater, and Ice Flux Variability in Davis Strait: Cruise Report for R/V Knorr 179-05, 22 September - 4 October 2004," APL-UW TR 0408, November 2004

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30 Nov 2004

As part of the Freshwater Initiative sponsored by the National Science Foundation Office of Polar Programs, a team of scientists from the Applied Physics Laboratory of the University of Washington and the Bedford Institute of Oceanography are investigating freshwater exchange through Davis Strait. This 300-km-wide strait sits between Baffin Island and the west coast of Greenland and acts as the gateway for waters passing between the Canadian Arctic Archipelago and the subpolar North Atlantic. In autumn 2004 the R/V Knorr cruise 179-05 undertook the first of three one-year mooring deployments. Six subsurface moorings, one off-axis sound source, eight bottom landers, and two Seagldiers were deployed successfully slightly north of the Davis Strait sill. Four cross-strait hydrographic lines, complete with sampling for chemical tracers, characterized water mass variability from the southern end of Baffin Bay to the northern tip of the Labrador Sea. The moored array will be recovered, serviced, and redeployed annually for a period of at least three years.

Introduction to special section: U.S. GLOBEC: Physical processes on Georges Bank (GLOBEC)

Beardsley, R.C., P.C. Smith, and C.M. Lee, "Introduction to special section: U.S. GLOBEC: Physical processes on Georges Bank (GLOBEC)," J. Geophys. Res., 108, 8000, doi: 10.1029/2003JC002165, 2003

18 Nov 2003

From tides to mixing along the Hawaiian Ridge

Rudnick, D.L., T.J. Boyd, R.E. Brainard, G.S. Carter, G.D. Egbert, M.C. Gregg, P.E. Holloway, J.M. Klymak, E. Kunze, C.M. Lee, M.D. Levine, D.S. Luther, J.P. Martin, M.A. Merrifield, J.N. Moum, J.D. Nash, R. Pinkel, L. Rainville, and T.B. Sanford, "From tides to mixing along the Hawaiian Ridge," Science, 301, 355-357, DOI: 10.1126/science.1085837, 2003.

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18 Jul 2003

The cascade from tides to turbulence has been hypothesized to serve as a major energy pathway for ocean mixing. We investigated this cascade along the Hawaiian Ridge using observations and numerical models. A divergence of internal tidal energy flux observed at the ridge agrees with the predictions of internal tide models. Large internal tidal waves with peak-to-peak amplitudes of up to 300 meters occur on the ridge. Internal-wave energy is enhanced, and turbulent dissipation in the region near the ridge is 10 times larger than open-ocean values. Given these major elements in the tides-to-turbulence cascade, an energy budget approaches closure.

Japan/East Sea intrathermocline eddies

Gordon, A.L., C.F. Giulivi, C.M. Lee, H.H. Furey, A. Bower, and L. Talley, "Japan/East Sea intrathermocline eddies," J. Phys. Oceanogr., 32, 1960-1974, 2002.

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15 Jun 2002

Intrathermocline eddies (ITE) with diameters of 100 km and of thickness greater than 100 m are observed within each of the three quasi-stationary meanders of the Tsushima Current of the Japan/East Sea. Within the ITE homogenous, anticyclonic flowing core, the temperature is near 10°C with a salinity of 34.12 psu. Because of compensatory baroclinicity of the upper and lower boundaries of the ITE core, the ITE has minor sea level expression. The ITE core displays positive oxygen and negative salinity anomalies in comparison to the surrounding thermocline water, indicative of formation from winter mixed layer water along the southern side of the Japan/East Sea subpolar front. The winter mixing layer is then overridden, or slips below, the regional upper thermocline stratification with its characteristic salinity maximum layer. The winter mixed layer off the coast of Korea closely matches the ITE core characteristics, and is considered as a potential source region. Other sources may be present along the southern boundary of the subpolar front, including a frequently observed warm eddy over the western side of Yamato Rise.

Mesoscale eddies, coastal upwelling, and the upper-ocean heat budget in the Arabian Sea

Fischer, A.S., R.A. Weller, D.L. Rudnick, C.C. Eriksen, C.M. Lee, K.H. Brink, C.A. Fox, and R.R. Leben, "Mesoscale eddies, coastal upwelling, and the upper-ocean heat budget in the Arabian Sea," Deep-Sea Res. II, 49, 2231-2264, doi:10.1016/S0967-0645(02)00036-X, 2002.

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4 Mar 2002

Estimation of the terms in the upper-ocean heat budget from a moored array in the central Arabian Sea shows periods when a rough balance between the temperature trend and the horizontal advection of heat exists. Altimetry and sea-surface temperature imagery are used to demonstrate that these episodes of strong horizontal advection are associated with mesoscale features. During the wintertime Northeast (NE) Monsoon these are capped-off mesoscale eddy features generated during the previous summertime Southwest (SW) Monsoon and have little horizontal transport of heat within the mixed layer. During the SW Monsoon the major contribution is strong offshore export of coastally upwelled water in a filament with a strong surface presence. Temperature and salinity properties from the moored array and a SeaSoar survey during the formation of the coastal filament confirm the offshore transport of the upwelled water mass to the site of the moored array, more than 600 km offshore. Estimates of the filament section heat flux are several percent of the total estimated heat flux due to upwelling along the Arabian Peninsula, and remote sensing data show that similar mesoscale variability along the coast is enhanced during the SW Monsoon. This points to the importance of mesoscale-modulated transports in not only the observed heat budget at the moored array, but in the overall upper-ocean heat budget in the Arabian Sea.

The Modular Ocean Data Assimilation System (MODAS)

Fox, D.N., W.J. Teague, C.N. Barron, M.R. Carnes, and C.M. Lee, "The Modular Ocean Data Assimilation System (MODAS)," J. Atmos. Ocean. Technol., 19, 240-252, 2002.

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1 Feb 2002

The Modular Ocean Data Assimilation System (MODAS) is used by the U.S. Navy for depiction of three-dimensional fields of temperature and salinity over the global ocean. MODAS includes both a static climatology and a dynamic climatology. While the static climatology represents the historical averages, the dynamic climatology assimilates near-real-time observations of sea surface height and sea surface temperature and provides improved temperature and salinity fields. The methodology for the construction of the MODAS climatology is described here. MODAS is compared with Levitus and Generalized Digital Environmental Model climatologies and with temperature and salinity profiles measured by SeaSoar in the Japan/East Sea to illustrate MODAS capabilities. MODAS with assimilated remotely sensed data is able to portray time-varying dynamical features that cannot be represented by static climatologies.

The upper-ocean response to monsoonal forcing in the Arabian Sea: Seasonal and spatial variability

Lee, C.M., B.H. Jones, K.H. Brink, and A.S. Fischer, "The upper-ocean response to monsoonal forcing in the Arabian Sea: Seasonal and spatial variability," Deep-Sea Res. II, 47, 1177-1226, 2000.

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16 Mar 2000

Observations from four towed profiler surveys undertaken between December 1994 and October 1995 examine the seasonal and spatial variability of the upper ocean response to the Monsoon cycle in the Arabian Sea. Although observed atmospheric forcing agrees well with modern climatologies, cross-basin patterns of mixed-layer depth and water properties observed in 1994–1995 are not entirely consistent with an upper-ocean response dominated by Ekman pumping. During the winter monsoon, the mixed-layer deepens dramatically with distance offshore. Surface cooling intensifies with offshore distance, and a one-dimensional response dominated by convective overturning could explain observed wintertime mixed-layer depths. Except for waters associated with a filament extending offshore from the Omani coast, mixed-layer depths and water properties show only modest cross-basin contrasts during the Southwest Monsoon. Filament waters differ from surrounding mid-basin waters, having shallow mixed-layers and water properties similar to those of waters upwelled near the Omani coast. In September, following the Southwest Monsoon, waters within 1000 km of the Omani coast have cooled and freshened, with marked changes in stratification extending well into the pycnocline. Estimates of Ekman pumping and wind-driven entrainment made using the Southampton Oceanographic Center 1980–1995 surface flux and the Levitus mixed-layer climatologies indicate that during the Southwest Monsoon wind-driven entrainment is considerably stronger than Ekman pumping. Inshore of the windstress maximum, Ekman pumping partially counters wind-driven entrainment, while offshore the two processes act together to deepen the mixed-layer. As Ekman pumping is too weak to counter wind-driven mixed-layer deepening inshore of the windstress maximum, another mechanism must act to maintain the shallow mixed-layers seen in our observations and in climatologies. Offshore advection of coastally upwelled water offers a mechanism for maintaining upper ocean stratification that is consistent with observed changes in upper ocean water properties. Ekman upwelling will modulate wind-driven entrainment, but these results indicate that the primary mechanisms acting inshore of the windstress maximum are wind-driven mixing and horizontal advection.

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