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Mike Steele

Senior Principal Oceanographer






Dr. Steele is interested in the large-scale circulation of sea ice and water in the Arctic Ocean. He uses both observed data and numerical model simulations to better understand the average circulation pathways as well as the causes of interannual variations in these pathways. Analysis of ocean observations has focused on the upper layers, which are generally quite cold and fresh.

Dr. Steele has active field programs in which data are collected in the field by his team and others, using aircraft, ships, and autonomous sensors like buoys and profiling floats. He is also involved with efforts to improve computer models of the arctic marine system, via the Arctic Ocean Model Intercomparison Project, AOMIP.

Funding for his research comes from the National Science Foundation, NASA, and the National Oceanic and Atmospheric Agency (NOAA). He is involved with many outreach programs such as lectures to K-12 and college students. Mike Steele began work at the Polar Science Center in 1987.

Department Affiliation

Polar Science Center


B.A. Physics, Reed College, 1981

Ph.D. Geophysical Fluid Dynamics, Princeton University, 1987


North Pole Environmental Observatory

The observatory is staffed by an international research team that establishes a camp at the North Pole each spring to take the pulse of the Arctic Ocean and learn how the world's northernmost sea helps regulate global climate.


Producing an Updated Synthesis of the Arctic's Marine Primary Production Regime and its Controls

The focus of this project is to synthesize existing studies and data relating to Arctic Ocean primary production and its changing physical controls such as light, nutrients, and stratification, and to use this synthesis to better understand how primary production varies in time and space and as a function of climate change.


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.


More Projects

The Arctic Ocean Model Intercomparison Project (AOMIP): Synthesis and Integration

The AOMIP science goals are to validate and improve Arctic Ocean models in a coordinated fashion and investigate variability of the Arctic Ocean and sea ice at seasonal to decadal time scales, and identify mechanisms responsible for the observed changes. The project's practical goals are to maintain and enhance the established AOMIP international collaboration to reduce uncertainties in model predictions (model validation and improvements via coordinated experiments and studies); support synthesis across the suite of Arctic models; organize scientific meetings and workshops; conduct collaboration with other MIPs with a special focus on model improvements and analysis; disseminate findings of AOMIP effort to broader communities; and train a new generation of ocean and sea-ice modelers.


The Impact of Changes in Arctic Sea Ice on the Marine Planktonic Ecosystem- Synthesis and Modeling of Retrospective and Future Conditions

This work will investigate the historical and contemporary changes of arctic sea ice, water column, and aspects of the marine ecosystem as an integrated entity, and project future changes associated with a diminished arctic ice cover under several plausible warming scenarios.


The Fate of Summertime Arctic Ocean Heating: A Study of Ice-Albedo Feedback on Seasonal to Interannual Time Scales

The main objective of this study is to determine the fate of solar energy absorbed by the arctic seas during summer, with a specific focus on its impact on the sea ice pack. Investigators further seek to understand the fate of this heat during the winter and even beyond to the following summer. Their approach is use a coupled sea ice–ocean model forced by atmospheric reanalysis fields, with and without assimilation of satellite-derived ice and ocean variables. They are also using satellite-derived ocean color data to help determine light absorption in the upper ocean.


UpTempO: Measuring the Upper Layer Temperature of the Arctic Ocean

This project aims to measure the time history of summer warming and subsequent fall cooling of the seasonally open water areas of the Arctic Ocean. Investigators will focus on those areas with the greatest ice retreat i.e., the northern Beaufort, Chukchi, East Siberian, and Laptev seas. Their method will be to build up to 10 relatively inexpensive ocean thermistor string buoys per year, to be deployed in the seasonally ice-free regions of the Arctic Ocean. Arctic-ADOS buoy data will be provided to both the research and operational weather forecasting communities in near real time on the International Arctic Buoy Program (IABP) web site.


Seasonality of Circumpolar Tundra: Ocean and Atmosphere Controls and Effects on Energy and Carbon Budgets

Through this project, investigators will characterize the seasonal linkages between the land surface greenness and a suite of land, atmosphere, and ocean characteristics, focusing on the Beringia/ Beaufort Sea, where there have been strong positive increases in the Normalized Difference Vegetation Index (NDVI) over the past 25 years, and the west-central Arctic Eurasia region, where the NDVI trends have been slightly negative. This is a collaborative project led by Howard Epstein at the University of Virginia with Uma Bhatt, Univ. of Alaska, Fairbanks, and Mike Steele, University of Washington.


Changing Seasonality of the Arctic: Alteration of Production Cycles and Trophic Linkages in Response to Changes in Sea Ice and Upper Ocean Physics

This project will investigate future changes in the seasonal linkages and interactions among arctic sea ice, the water column, and the marine production cycles and trophic structure as an integrated system. This is a collaborative project led by Jinlun Zhang with Mike Steele, Univ. of WA, Y. Spitz, Oregon State Univ., C. Ashjian, Woods Hole, and R. Campbell, Univ. of Rhode Island.



Arctic Sea Ice Extent and Volume Dip to New Lows

By mid-September, the sea ice extent in the Arctic reached the lowest level recorded since 1979 when satellite mapping began.

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15 Oct 2012

APL-UW polar oceanographers and climatologists are probing the complex ice–ocean–atmosphere system through in situ and remote sensing observations and numerical model simulations to learn how and why.

Changing Freshwater Pathways in the Arctic Ocean

Freshening in the Canada Basin of the Arctic Ocean began in the 1990s. Polar scientist Jamie Morison and colleagues report new insights on the freshening based in part on Arctic-wide views from two satellite system.

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5 Jan 2012

The Arctic Ocean is a repository for a tremendous amount of river runoff, especially from several huge Russian rivers. During the spring of 2008, APL-UW oceanographers on a hydrographic survey in the Arctic detected major shifts in the amount and distribution of fresh water. The Canada basin had freshened, but had the entire Arctic Ocean?

Analysis of satellite records shows that salinity increased on the Russian side of the Arctic and decreased in the Beaufort Sea on the Canadian side. With an Arctic-wide view of circulation from satellite sensors, researchers were able to determine that atmospheric forcing had shifted the transpolar drift counterclockwise and driven Russian runoff east to the Canada Basin.

Oceanography from Space

In the North Atlantic and Arctic oceans observations by sensors on orbiting satellites are giving oceanographers insight to ocean processes on vast spatial and temporal scales.

1 Dec 2011

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2000-present and while at APL-UW

Validation of satellite sea surface temperature analyses in the Beaufort Sea using UpTempO buoys

Castro, S.L., G.A. Wick, and M. Steele, "Validation of satellite sea surface temperature analyses in the Beaufort Sea using UpTempO buoys," Remote Sens. Environ., 187, 458-475, doi:10.1016/j.rse.2016.10.035, 2016.

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15 Dec 2016


• Blended SST (L4) analyses exhibit very large differences in the Beaufort Sea.
• L4 analyses are evaluated using independent UpTempO buoy observations in 3 regimes.
• High-latitude performance is tested using Taylor diagrams and skill scores.
• Ice masking is assessed and has minimal impact.
• Analysis performance varies with region, but 3 products provide best results.

The phenology of Arctic Ocean surface warming

Steele, M., and S. Dickinson, "The phenology of Arctic Ocean surface warming," J. Geophys. Res., 121, 6847-6861, doi:10.1002/2016JC012089, 2016.

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15 Sep 2016

In this work, we explore the seasonal relationships (i.e., the phenology) between sea ice retreat, sea surface temperature (SST), and atmospheric heat fluxes in the Pacific Sector of the Arctic Ocean, using satellite and reanalysis data. We find that where ice retreats early in most years, maximum summertime SSTs are usually warmer, relative to areas with later retreat. For any particular year, we find that anomalously early ice retreat generally leads to anomalously warm SSTs. However, this relationship is weak in the Chukchi Sea, where ocean advection plays a large role. It is also weak where retreat in a particular year happens earlier than usual, but still relatively late in the season, primarily because atmospheric heat fluxes are weak at that time. This result helps to explain the very different ocean warming responses found in two recent years with extreme ice retreat, 2007 and 2012. We also find that the timing of ice retreat impacts the date of maximum SST, owing to a change in the ocean surface buoyancy and momentum forcing that occurs in early August that we term the Late Summer Transition (LST). After the LST, enhanced mixing of the upper ocean leads to cooling of the ocean surface even while atmospheric heat fluxes are still weakly downward. Our results indicate that in the near-term, earlier ice retreat is likely to cause enhanced ocean surface warming in much of the Arctic Ocean, although not where ice retreat still occurs late in the season.

Modeling the seasonal evolution of the Arctic sea ice floe size distribution

Zhang, J., H. Stern, B. Hwang, A. Schweiger, M. Steele, M. Stark, and H.C. Graber, "Modeling the seasonal evolution of the Arctic sea ice floe size distribution," Elem. Sci. Anth., 4, doi:10.12952/journal.elementa.000126, 2016

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13 Sep 2016

To better simulate the seasonal evolution of sea ice in the Arctic, with particular attention to the marginal ice zone, a sea ice model of the distribution of ice thickness, floe size, and enthalpy was implemented into the Pan-arctic IceOcean Modeling and Assimilation System (PIOMAS). Theories on floe size distribution (FSD) and ice thickness distribution (ITD) were coupled in order to explicitly simulate multicategory FSD and ITD distributions simultaneously. The expanded PIOMAS was then used to estimate the seasonal evolution of the Arctic FSD in 2014 when FSD observations are available for model calibration and validation.

Results indicate that the simulated FSD, commonly described equivalently as cumulative floe number distribution (CFND), generally follows a power law across space and time and agrees with the CFND observations derived from TerraSAR-X satellite images. The simulated power-law exponents also correlate with those derived using MODIS images, with a low mean bias of 2%. In the marginal ice zone, the modeled CFND shows a large number of small floes in winter because of stronger winds acting on thin, weak first-year ice in the ice edge region. In mid-spring and summer, the CFND resembles an upper truncated power law, with the largest floes mostly broken into smaller ones; however, the number of small floes is lower than in winter because floes of small sizes or first-year ice are easily melted away. In the ice pack interior there are fewer floes in late fall and winter than in summer because many of the floes are welded together into larger floes in freezing conditions, leading to a relatively flat CFND with low power-law exponents.

The simulated mean floe size averaged over all ice-covered areas shows a clear annual cycle, large in winter and smaller in summer. However, there is no obvious annual cycle of mean floe size averaged over the marginal ice zone. The incorporation of FSD into PIOMAS results in reduced ice thickness, mainly in the marginal ice zone, which improves the simulation of ice extent and yields an earlier ice retreat.

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Seasonal heat and freshwater cycles in the Arctic Ocean in CMIP5 coupled models

Ding, Y., J.A. Carton, G.A. Chepurin, M. Steele, and S. Hakkinen, "Seasonal heat and freshwater cycles in the Arctic Ocean in CMIP5 coupled models," J. Geophys. Res., 121, 2043-2057, doi:10.1002/2015JC011124, 2016.

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1 Apr 2016

This study examines the processes governing the seasonal response of the Arctic Ocean and sea ice to surface forcings as they appear in historical simulations of 14 Coupled Model Intercomparison Project Phase 5 coupled climate models. In both models and observations, the seasonal heat budget is dominated by a local balance between net surface heating and storage in the heat content of the ocean and in melting/freezing of sea ice. Observations suggest ocean heat storage is more important than sea ice melt, while in most of these models, sea ice melt dominates. Seasonal horizontal heat flux divergence driven by the seasonal cycle of volume transport is only important locally. In models and observations, the dominant terms in the basin-average seasonal freshwater budget are the storages of freshwater between the ocean and sea ice, and the exchange between the two. The largest external source term is continental discharge in early summer, which is an order of magnitude smaller. The appearance of sea ice (extent and volume) and also ocean stratification in both the heat and freshwater budgets provides two links between the budgets and provides two mechanisms for feedback. One consequence of such an interaction is the fact that models with strong/weak seasonal surface heating also have strong/weak seasonal haline and temperature stratification.

Loitering of the retreating sea ice edge in the Arctic Seas

Steele, M., and W. Ermold, "Loitering of the retreating sea ice edge in the Arctic Seas," J. Geophys. Res., 120, 7699-7721, doi:10.1002/2015JC011182, 2015.

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1 Dec 2015

Each year, the arctic sea ice edge retreats from its winter maximum extent through the Seasonal Ice Zone (SIZ) to its summer minimum extent. On some days, this retreat happens at a rapid pace, while on other days, parts of the pan-arctic ice edge hardly move for periods of days up to 1.5 weeks. We term this stationary behavior "ice edge loitering," and identify areas that are more prone to loitering than others. Generally, about 20–25% of the SIZ area experiences loitering, most often only one time at any one location during the retreat season, but sometimes two or more times. The main mechanism controlling loitering is an interaction between surface winds and warm sea surface temperatures in areas from which the ice has already retreated. When retreat happens early enough to allow atmospheric warming of this open water, winds that force ice floes into this water cause melting. Thus, while individual ice floes are moving, the ice edge as a whole appears to loiter. The time scale of loitering is then naturally tied to the synoptic time scale of wind forcing. Perhaps surprisingly, the area of loitering in the arctic seas has not changed over the past 25 years, even as the SIZ area has grown. This is because rapid ice retreat happens most commonly late in the summer, when atmospheric warming of open water is weak. We speculate that loitering may have profound effects on both physical and biological conditions at the ice edge during the retreat season.

Interannual variations of light-absorbing particles in snow on Arctic sea ice

Doherty, S.J., M. Steele, I. Rigor, and S.G. Warren, "Interannual variations of light-absorbing particles in snow on Arctic sea ice," J. Geophys. Res., 120, 11,391-11,400, doi:10.1002/2015JD024018, 2015.

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16 Nov 2015

Samples of snow on sea ice were collected in springtime of the 6 years 2008–2013 in the region between Greenland, Ellesmere Island, and the North Pole (82°N – 89°N, 0°W – 100°W). The meltwater was passed through filters, whose spectral absorption was then measured to determine the separate contributions by black carbon (BC) and other light-absorbing impurities. The median mixing ratio of BC across all years' samples was 4 ± 3 ng g-1, and the median fraction of absorption due to non-BC absorbers was 36 ± 11%. Variances represent both spatial and interannual variability; there was no interannual trend in either variable. The absorption Angstrom exponent, however, decreased with latitude, suggesting a transition from dominance by biomass-burning sources in the south to an increased influence by fossil-fuel-burning sources in the north, consistent with earlier measurements of snow in Svalbard and at the North Pole.

Sea ice floe size distribution in the marginal ice zone: Theory and numerical experiments

Zhang, J., A. Schweiger, M. Steele, and H. Stern, "Sea ice floe size distribution in the marginal ice zone: Theory and numerical experiments," J. Geophys. Res., 120, 3484-3498, do:10.1002/2015JC010770, 2015.

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12 May 2015

To better describe the state of sea ice in the marginal ice zone (MIZ) with floes of varying thicknesses and sizes, both an ice thickness distribution (ITD) and a floe size distribution (FSD) are needed. In this work, we have developed a FSD theory that is coupled to the ITD theory of Thorndike et al. (1975) in order to explicitly simulate the evolution of FSD and ITD jointly. The FSD theory includes a FSD function and a FSD conservation equation in parallel with the ITD equation. The FSD equation takes into account changes in FSD due to ice advection, thermodynamic growth, and lateral melting. It also includes changes in FSD because of mechanical redistribution of floe size due to ice ridging and, particularly, ice fragmentation induced by stochastic ocean surface waves. The floe size redistribution due to ice fragmentation is based on the assumption that wave-induced breakup is a random process such that when an ice floe is broken, floes of any smaller sizes have an equal opportunity to form, without being either favored or excluded. To focus only on the properties of mechanical floe size redistribution, the FSD theory is implemented in a simplified ITD and FSD sea ice model for idealized numerical experiments. Model results show that the simulated cumulative floe number distribution (CFND) follows a power law as observed by satellites and airborne surveys. The simulated values of the exponent of the power law, with varying levels of ice breakups, are also in the range of the observations. It is found that floe size redistribution and the resulting FSD and mean floe size do not depend on how floe size categories are partitioned over a given floe size range. The ability to explicitly simulate multicategory FSD and ITD together may help to incorporate additional model physics, such as FSD-dependent ice mechanics, surface exchange of heat, mass, and momentum, and wave-ice interactions.

Seasonal ice loss in the Beaufort Sea: Toward synchrony and prediction

Steele, M., S. Dickinson, J. Zhang, and R. Lindsay, "Seasonal ice loss in the Beaufort Sea: Toward synchrony and prediction," J. Geophys. Res., 120, 1118-1132, doi:10.1002/2014JC010247, 2015.

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1 Feb 2015

The seasonal evolution of sea ice loss in the Beaufort Sea during 1979–2012 is examined, focusing on differences between eastern and western sectors. Two stages in ice loss are identified: the Day of Opening (DOO) is defined as the spring decrease in ice concentration from its winter maximum below a value of 0.8 areal concentration; the Day of Retreat (DOR) is the summer decrease below 0.15 concentration. We consider three aspects of the subject, i.e., (i) the long-term mean, (ii) long-term linear trends, and (iii) interannual variability. We find that in the mean, DOO occurs earliest in the eastern Beaufort Sea (EBS) owing to easterly winds which act to thin the ice there, relative to the western Beaufort Sea (WBS) where ice has been generally thicker. There is no significant long-term trend in EBS DOO, although WBS DOO is in fact trending toward earlier dates. This means that spatial differences in DOO across the Beaufort Sea have been shrinking over the past 33 years, i.e., these dates are becoming more synchronous, a situation which may impact human and marine mammal activity in the area. Retreat dates are also becoming more synchronous, although with no statistical significance over the studied time period. Finally, we find that in any given year, an increase in monthly mean easterly winds of ~1 m/s during spring is associated with earlier summer DOR of 6–15 days, offering predictive capability with 2–4 months lead time.

Seasonality and long-term trend in Arctic Ocean surface stress in a model

Martin, T., M. Steele, and J. Zhang, "Seasonality and long-term trend in Arctic Ocean surface stress in a model," J. Geophys. Res., 119, 1723-1738, doi:10.1002/2013JC009425, 2014.

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1 Mar 2014

A numerical ocean sea-ice model is used to demonstrate that Arctic sea ice retreat affects momentum transfer into the ocean. A thinner and thus weaker ice cover is more easily forced by the wind, which increases the momentum flux. In contrast, increasing open water reduces momentum transfer because the ice surface provides greater drag than the open water surface. We introduce the concept of optimal ice concentration: momentum transfer increases with increasing ice concentration up to a point, beyond which frictional losses by floe interaction damp the transfer. For a common ice internal stress formulation, a concentration of 80–90% yields optimal amplification of momentum flux into the ocean. We study the seasonality and long-term evolution of Arctic Ocean surface stress over the years 1979–2012. Spring and fall feature optimal ice conditions for momentum transfer, but only in fall is the wind forcing at its maximum, yielding a peak basin-mean ocean surface stress of ~0.08 N/m2. Since 1979, the basin-wide annual mean ocean surface stress has been increasing by 0.004 N/m2/decade, and since 2000 by 0.006 N/m2/decade. In contrast, summertime ocean surface stress has been decreasing at –0.002 N/m2/decade. These trends are linked to the weakening of the ice cover in fall, winter and spring, and to an increase in open water fraction in summer, i.e., changes in momentum transfer rather than changes in wind forcing. In most areas, the number of days per year with optimal ice concentration is decreasing.

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.

Diffusive vertical heat flux in the Canada Basin of the Arctic Ocean inferred from moored instruments

Lique, C., J.D. Guthrie, M. Steele, A. Proshutinsky, J.H. Morison, and R. Krishfield, "Diffusive vertical heat flux in the Canada Basin of the Arctic Ocean inferred from moored instruments," J. Geophys. Res., 119, 496-508, doi:10.1002/2013JC009346, 2014.

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1 Jan 2014

Observational studies have shown that an unprecedented warm anomaly has recently affected the temperature of the Atlantic Water (AW) layer lying at intermediate depth in the Arctic Ocean. Using observations from four profiling moorings, deployed in the interior of the Canada Basin between 2003 and 2011, the upward diffusive vertical heat flux from this layer is quantified. Vertical diffusivity is first estimated from a fine-scale parameterization method based on CTD and velocity profiles. Resulting diffusive vertical heat fluxes from the AW are in the range 0.1–0.2 W m-2 on average. Although large over the period considered, the variations of the AW temperature maximum yields small variations for the temperature gradient and thus the vertical diffusive heat flux. In most areas, variations in upward diffusive vertical heat flux from the AW have only a limited effect on temperature variations of the overlying layer. However, the presence of eddies might be an effective mechanism to enhance vertical heat transfer, although the small number of eddies sampled by the moorings suggest that this mechanism remains limited and intermittent in space and time. Finally, our results suggest that computing diffusive vertical heat flux with a constant vertical diffusivity of ~2 x 10-6 m2 s-1 provides a reasonable estimate of the upward diffusive heat transfer from the AW layer, although this approximation breaks down in the presence of eddies.

The great 2012 Arctic Ocean summer cyclone enhanced biological productivity on the shelves

Zhang, J., C. Ashjian, R. Campbell, V. Hill, Y.H. Spitz, and M. Steele, "The great 2012 Arctic Ocean summer cyclone enhanced biological productivity on the shelves," J. Geophys. Res., 119, 297-312, doi:10.1002/2013JC009301, 2014.

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1 Jan 2014

A coupled biophysical model is used to examine the impact of the great Arctic cyclone of early August 2012 on the marine planktonic ecosystem in the Pacific sector of the Arctic Ocean (PSA). Model results indicate that the cyclone influences the marine planktonic ecosystem by enhancing productivity on the shelves of the Chukchi, East Siberian, and Laptev seas during the storm. Although the cyclone's passage in the PSA lasted only a few days, the simulated biological effects on the shelves last 1 month or longer. At some locations on the shelves, primary productivity (PP) increases by up to 90% and phytoplankton biomass by up to 40% in the wake of the cyclone. The increase in zooplankton biomass is up to 18% on 31 August and remains 10% on 15 September, more than 1 month after the storm. In the central PSA, however, model simulations indicate a decrease in PP and plankton biomass. The biological gain on the shelves and loss in the central PSA are linked to two factors. (1) The cyclone enhances mixing in the upper ocean, which increases nutrient availability in the surface waters of the shelves; enhanced mixing in the central PSA does not increase productivity because nutrients there are mostly depleted through summer draw down by the time of the cyclone's passage. (2) The cyclone also induces divergence, resulting from the cyclone's low-pressure system that drives cyclonic sea ice and upper ocean circulation, which transports more plankton biomass onto the shelves from the central PSA. The simulated biological gain on the shelves is greater than the loss in the central PSA, and therefore, the production on average over the entire PSA is increased by the cyclone. Because the gain on the shelves is offset by the loss in the central PSA, the average increase over the entire PSA is moderate and lasts only about 10 days. The generally positive impact of cyclones on the marine ecosystem in the Arctic, particularly on the shelves, is likely to grow with increasing summer cyclone activity if the Arctic continues to warm and the ice cover continues to shrink.

Hydrographic changes in the Lincoln Sea in the Arctic Ocean with focus on an upper ocean freshwater anomaly between 2007 and 2010

De Steur, L., M. Steele, E. Hansen, J. Morison, I. Polyakov, S.M. Olsen, H. Melling, F.A. McLaughlin, R. Kwok, W.M. Smethie, and P. Schlosser, "Hydrographic changes in the Lincoln Sea in the Arctic Ocean with focus on an upper ocean freshwater anomaly between 2007 and 2010," J. Geophys. Res., 118, 4699-4715, doi:10.1002/jgrc.20341, 2013.

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1 Sep 2013

Hydrographic data from the Arctic Ocean show that freshwater content in the Lincoln Sea, north of Greenland, increased significantly from 2007 to 2010, slightly lagging changes in the eastern and central Arctic. The anomaly was primarily caused by a decrease in the upper ocean salinity. In 2011 upper ocean salinities in the Lincoln Sea returned to values similar to those prior to 2007. Throughout 2008—2010, the freshest surface waters in the western Lincoln Sea show water mass properties similar to fresh Canada Basin waters north of the Canadian Arctic Archipelago. In the northeastern Lincoln Sea fresh surface waters showed a strong link with those observed in the Makarov Basin near the North Pole. The freshening in the Lincoln Sea was associated with a return of a subsurface Pacific Water temperature signal although this was not as strong as observed in the early 1990s. Comparison of repeat stations from the 2000s with the data from the 1990s at 65°W showed an increase of the Atlantic temperature maximum which was associated with the arrival of warmer Atlantic water from the Eurasian Basin. Satellite-derived dynamic ocean topography of winter 2009 showed a ridge extending parallel to the Canadian Archipelago shelf as far as the Lincoln Sea, causing a strong flow toward Nares Strait and likely Fram Strait. The total volume of anomalous freshwater observed in the Lincoln Sea and exported by 2011 was close to 110 ± 250 km, approximately 13% of the total estimated FW increase in the Arctic in 2008.

Seasonal to decadal variability of Arctic Ocean heat content: A model-based analysis and implications for autonomous observing systems

Lique, C., and M. Steele, "Seasonal to decadal variability of Arctic Ocean heat content: A model-based analysis and implications for autonomous observing systems," J. Geophys. Res., 118, 1673-1695, doi:10.1002/jgrc.20127, 2013.

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1 Apr 2013

A high-resolution global ocean/sea ice model is used to investigate the modes of Arctic Ocean heat content variability for the period 1968–2007. A rotated empirical orthogonal function analysis is performed on the monthly mean vertically integrated heat content to investigate the mechanisms governing its spatiotemporal variations. In the model, 28% of the heat content variability is driven by the seasonal and interannual fluctuations of the atmospheric heat flux in the seasonally ice free regions. The heat flux variability associated with Atlantic Water advected through Fram Strait drives 31% of the heat content variability. Changes of temperature and circulation drive Fram Strait heat transport variability, and these two effects project on different modes and thus drive heat content variations in different parts of the Eurasian Basin. A second branch of Atlantic Water is modified in the Barents Sea and the variations of the heat flux associated with the Barents Sea water branch penetrating the deep Arctic yield heat content variations in the Eurasian Basin. The effect of the Bering Strait heat flux variations remains limited to the Chukchi Sea. Autonomous observing system may be able to capture the Arctic heat content variability. Sea surface temperature satellite observations combined with temperature profiles of the top 800 m in the deep Arctic covered by sea ice are sufficient to capture most of the variability signal. The results emphasize the crucial need for measurements in the Eurasian Basin.

Synthesis of integrated primary production in the Arctic Ocean: II. In situ and remotely sensed estimates

Hill, V.J., P.A. Matrai, E. Olson, S. Suttles, M. Steele, L.A. Codispoti, and R.C. Zimmerman, "Synthesis of integrated primary production in the Arctic Ocean: II. In situ and remotely sensed estimates," Prog. Oceanogr., 110, 107-125, doi:10.1016/j.pocean.2012.11.005, 2013.

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1 Mar 2013

Recent warming of surface waters, accompanied by reduced ice thickness and extent may have significant consequences for climate-driven changes of primary production (PP) in the Arctic Ocean (AO). However, it has been difficult to obtain a robust benchmark estimate of pan-Arctic PP necessary for evaluating change. This paper provides an estimate of pan-Arctic PP prior to significant warming from a synthetic analysis of the ARCSS-PP database of in situ measurements collected from 1954 to 2007 and estimates derived from satellite-based observations from 1998 to 2007.

Synthesis of primary production in the Arctic Ocean: I. Surface waters, 1954-2007

Matrai, P.A., E. Olson, S. Suttles, V. Hill, L.A. Codispoti, B. Light, and M. Steele, "Synthesis of primary production in the Arctic Ocean: I. Surface waters, 1954-2007," Prog. Oceanogr., 110, 93-106, doi:10.1016/j.pocean.2012.11.004, 2013.

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1 Mar 2013

The spatial and seasonal magnitude and variability of primary production in the Arctic Ocean (AO) is quantified with a pan-arctic approach. We synthesize estimates of primary production (PP), focusing on surface waters (0–5 m), using complementary methods that emphasize different spatial and temporal scales. These methods include (1) in situ observations of 14C uptake mostly and possibly some O2 production reported in units of carbon (in situ PP), (2) remotely sensed primary production (sat-PP), and (3) an empirical algorithm giving net PP as a function of in situ chlorophyll a (in situ Chl-PP). The work presented herein examines historical data for PP collected in surface waters only, as they form the majority of the values of a larger ensemble of PP data collected over >50 years (ARCSS-PP) by many national and international efforts. This extended set of surface and vertically-resolved data will provide pan-Arctic validation of remotely sensed chlorophyll a and PP, an extremely valuable tool in this environment which is so difficult to sample. To this day, PP data in the AO are scarce and have uneven temporal and spatial coverage which, when added to the AO's regional heterogeneity, its strong seasonal changes, and limited access, have made and continue to make obtaining a comprehensive picture of PP in the AO difficult.

Synthesis of primary production in the Arctic Ocean: III. Nitrate and phosphate based estimates of net community production

Cadispoti, L.A., V. Kelly, A. Thessen, P. Matrai, S.Suttles, V. Hill, M. Steele, and B. Light, "Synthesis of primary production in the Arctic Ocean: III. Nitrate and phosphate based estimates of net community production," Prog. Oceanogr., 110, 126-150, doi:10.1016/j.pocean.2012.11.006, 2013.

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1 Mar 2013

Combining nitrate, nitrite and phosphate data from several sources with additional quality control produced a database that eliminates many questionable values. This database, in turn, facilitated estimation of net community production (NCP) in the Arctic Marine System (AMS). In some regions, the new database enabled quantitative calculation of NCP over the vegetative season from changes in nutrient concentrations. In others, useful inferences were possible based on nutrient concentration patterns. This analysis demonstrates that it is possible to estimate NCP from seasonal changes in nutrients in many parts of the Arctic, however, the data were so sparse that most of our estimates for 14 sub-regions of the AMS are attended by uncertainties >50%. Nevertheless, the wide regional variation of NCP within the AMS (~two orders of magnitude) may make the results useful.

The impact of an intense summer cyclone on 2012 Arctic sea ice retreat

Zhang, J., R. Lindsay, A. Schweiger, and M. Steele, "The impact of an intense summer cyclone on 2012 Arctic sea ice retreat," Geophys. Res. Lett., 40, 720-726, doi:10.1002/grl.50190, 2013.

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25 Jan 2013

This model study examines the impact of an intense early August cyclone on the 2012 record low Arctic sea ice extent. The cyclone passed when Arctic sea ice was thin and the simulated Arctic ice volume had already declined ~40% from the 2007–2011 mean. The thin sea ice pack and the presence of ocean heat in the near surface temperature maximum layer created conditions that made the ice particularly vulnerable to storms. During the storm, ice volume decreased about twice as fast as usual, owing largely to a quadrupling in bottom melt caused by increased upward ocean heat transport. This increased ocean heat flux was due to enhanced mixing in the oceanic boundary layer, driven by strong winds and rapid ice movement. A comparison with a sensitivity simulation driven by reduced wind speeds during the cyclone indicates that cyclone-enhanced bottom melt strongly reduces ice extent for about two weeks, with a declining effect afterwards. The simulated Arctic sea ice extent minimum in 2012 is reduced by the cyclone, but only by 0.15 x 106 km2 (4.4%). Thus without the storm, 2012 would still have produced a record minimum.


Timmermans, M.-L., et al., including J. Jackson, M. Steele, and R. Woodgate, "Ocean," In Arctic Report Card, M.O. Jeffries, J.A. Richter-Menge, and J.E. Overland, eds., 42-54 (NOAA Climate Program Office, 2012).

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5 Dec 2012


The 2011 annual wind-driven circulation regime was anticyclonic, supporting continued high volumes of freshwater in the Beaufort Gyre region and consistent with a 2012 shift of the Beaufort Gyre freshwater center to the west.

Sea surface temperatures in summer continue to be anomalously warm at the ice-free margins, while upper ocean temperature and salinity show significant interannual variability with no clear trends.

Oceanic fluxes of volume and heat through the Bering Strait increased by ~50% between 2001 and 2011.

Sea level exhibits decadal variability with a reduced correlation to sea level atmospheric pressure since the late 1990s.

Taking the temperature of the arctic with UMVs

Meinig, C., M. Steele, and K. Wood, "Taking the temperature of the arctic with UMVs," Sea Technol., 53, 23-33, 2012.

1 Sep 2012

Where can we find a seasonal cycle of the Atlantic water temperature within the Arctic Basin?

Lique, C., and M. Steele, "Where can we find a seasonal cycle of the Atlantic water temperature within the Arctic Basin?" J. Geophys. Res., 117, doi:10.1029/2011JC007612, 2012.

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17 Mar 2012

Recent mooring observations in the Arctic Basin suggest the existence of a seasonality of Atlantic Water (AW) temperature. Here the DRAKKAR global ocean/sea-ice model is used to examine the seasonal cycle amplitude of AW temperature within the Arctic Ocean and to investigate the possible mechanisms governing this seasonality. The simulation as well as available mooring data reveals that the amplitude of the AW temperature seasonal cycle is significant only in the Nansen Basin along the continental slope, where AW is primarily advected. In the model, the seasonal cycle of the AW temperature is advected from Fram Strait up to St. Anna Trough and then re-energized by the Barents Sea Branch. This suggests that the seasonal AW temperature signal survives over a finite distance (~1000 km). Interannual changes in the seasonal cycle amplitude can be as large as the mean seasonal cycle amplitude; thus seasonality is difficult to characterize from observations spanning only a short period. The seasonal bias of in-situ observations taken during spring and summer does not induce a large error when considering the interannual-to-decadal variations of AW temperature, because the seasonal cycle accounts for a small or negligible part of AW temperature variability, even near the inflow region.

Changing Arctic Ocean freshwater pathways

Morison, J., R. Kwok, C. Peralta-Ferriz, M. Alkire, I. Rigor, R. Andersen, and M. Steele, "Changing Arctic Ocean freshwater pathways," Nature, 481, 66-70, doi:10.1038/nature10705, 2012.

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5 Jan 2012

Freshening in the Canada basin of the Arctic Ocean began in the 1990s and continued to at least the end of 2008. By then, the Arctic Ocean might have gained four times as much fresh water as comprised the Great Salinity Anomaly of the 1970s, raising the spectre of slowing global ocean circulation. Freshening has been attributed to increased sea ice melting and contributions from runoff, but a leading explanation has been a strengthening of the Beaufort High — a characteristic peak in sea level atmospheric pressure — which tends to accelerate an anticyclonic (clockwise) wind pattern causing convergence of fresh surface water. Limited observations have made this explanation difficult to verify, and observations of increasing freshwater content under a weakened Beaufort High suggest that other factors must be affecting freshwater content.

Here we use observations to show that during a time of record reductions in ice extent from 2005 to 2008, the dominant freshwater content changes were an increase in the Canada basin balanced by a decrease in the Eurasian basin. Observations are drawn from satellite data (sea surface height and ocean-bottom pressure) and in situ data. The freshwater changes were due to a cyclonic (anticlockwise) shift in the ocean pathway of Eurasian runoff forced by strengthening of the west-to-east Northern Hemisphere atmospheric circulation characterized by an increased Arctic Oscillation index. Our results confirm that runoff is an important influence on the Arctic Ocean and establish that the spatial and temporal manifestations of the runoff pathways are modulated by the Arctic Oscillation, rather than the strength of the wind-driven Beaufort Gyre circulation.

Modeling the formation and fate of the near-surface temperature maximum in the Canadian Basin of the Arctic Ocean

Steele, M., W. Ermold, and J. Zhang, "Modeling the formation and fate of the near-surface temperature maximum in the Canadian Basin of the Arctic Ocean," J. Geophys. Res., 116, doi:10.1029/2010JC006803, 2011.

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12 Nov 2011

A numerical model is used to investigate the time and space extent of the near-surface temperature maximum (NSTM) of the Canadian Basin of the Arctic Ocean over the years 2000%u20132009. The NSTM is formed from local summertime absorption of solar radiation which, in some circumstances, descends through the fall and early winter to form a warm subsurface layer just below the winter mixed layer. We find that winter survival of this layer is confined largely to the Beaufort Gyre of the Canadian Basin, where Ekman convergence and downwelling push the summer warm layer down below the winter mixing depth. In recent years, summer stratification has increased, downwelling has accelerated, and the NSTM has warmed as the sea ice cover in the Beaufort Gyre has thinned. The result is a strengthening NSTM which contained enough heat by the end of winter 2007/2008 to melt about 20 cm of sea ice. Northwest of Alaska the model also simulates a second, deeper temperature maximum layer that forms from advection of saltier summer Pacific water. However, this layer is difficult to adequately resolve and maintain given the model's resolution.

Arctic Ocean warming contributes to reduced polar ice cap

Polyakov, I.V., et al., including M. Steele, "Arctic Ocean warming contributes to reduced polar ice cap," J. Phys. Oceanogr., 40, 2742-2756, doi:10.1175/2010JPO4339.1, 2011.

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1 Dec 2010

Analysis of modern and historical observations demonstrates that the temperature of the intermediate-depth (150–900 m) Atlantic water (AW) of the Arctic Ocean has increased in recent decades. The AW warming has been uneven in time; a local 1C maximum was observed in the mid-1990s, followed by an intervening minimum and an additional warming that culminated in 2007 with temperatures higher than in the 1990s by 0.24C. Relative to climatology from all data prior to 1999, the most extreme 2007 temperature anomalies of up to 1C and higher were observed in the Eurasian and Makarov Basins. The AW warming was associated with a substantial (up to 75–90 m) shoaling of the upper AW boundary in the central Arctic Ocean and weakening of the Eurasian Basin upper-ocean stratification.

Taken together, these observations suggest that the changes in the Eurasian Basin facilitated greater upward transfer of AW heat to the ocean surface layer. Available limited observations and results from a 1D ocean column model support this surmised upward spread of AW heat through the Eurasian Basin halocline. Experiments with a 3D coupled ice–ocean model in turn suggest a loss of 28–35 cm of ice thickness after 50 yr in response to the 0.5 W m-2 increase in AW ocean heat flux suggested by the 1D model. This amount of thinning is comparable to the 29 cm of ice thickness loss due to local atmospheric thermodynamic forcing estimated from observations of fast-ice thickness decline. The implication is that AW warming helped precondition the polar ice cap for the extreme ice loss observed in recent years.

Mechanisms of summertime upper Arctic Ocean warming and the effect on sea ice melt

Steele, M., J. Zhang, and W. Ermold, "Mechanisms of summertime upper Arctic Ocean warming and the effect on sea ice melt," J. Geophys. Res., 115, doi:10.1029/2009JC005849, 2010.

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6 Nov 2010

In this study, we use a numerical sea-ice-ocean model to examine what causes summertime upper ocean warming and sea ice melt during the 21st century in the Arctic Ocean. Our first question is, "What causes the ocean to warm in the Pacific Sector during the summer"? We find that about 80% of total heating over this region comes from ocean surface heat flux, with the remaining 20% originating in ocean lateral heat flux convergence. The latter occurs mostly within a few hundred kilometers of the northwest Alaskan coast. In the summer of 2007, the ocean gained just over twice the amount of heat it did over the average of the previous 7 years. Our second question is, "What causes sea ice to melt in the Pacific Sector during summer"? Our analysis shows that top melt dominates total melt early in the summer, while bottom melt (and in particular, bottom melt due to ocean heat transport) dominates later in the summer as atmospheric heating declines. Bottom melt rates in summer 2007 were 34% higher relative to the previous 7 year average. The modeled partition of top versus bottom melt closely matches observed melt rates obtained by a drifting buoy. Bottom melting contributes about 2/3 of total volume melt but is geographically confined to the Marginal Ice Zone, while top melting contributes a lesser 1/3 of volume melt but occurs over a much broader area of the ice pack.

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.

Arctic sea ice response to atmospheric forcings with varying levels of anthropogenic warming and climate variability

Zhang, J., M. Steele, and A. Schweiger, "Arctic sea ice response to atmospheric forcings with varying levels of anthropogenic warming and climate variability," Geophys. Res. Lett., 37, doi:10.1029/2010GL044988, 2010.

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28 Oct 2010

Numerical experiments are conducted to project arctic sea ice responses to varying levels of future anthropogenic warming and climate variability over 2010–2050. A summer ice-free Arctic Ocean is likely by the mid-2040s if arctic surface air temperature (SAT) increases 4 deg C by 2050 and climate variability is similar to the past relatively warm two decades. If such a SAT increase is reduced by one-half or if a future Arctic experiences a range of SAT fluctuation similar to the past five decades, a summer ice-free Arctic Ocean would be unlikely before 2050. If SAT increases 4 deg C by 2050, summer ice volume decreases to very low levels (10–37% of the 1978–2009 summer mean) as early as 2025 and remains low in the following years, while summer ice extent continues to fluctuate annually. Summer ice volume may be more sensitive to warming while summer ice extent more sensitive to climate variability. The rate of annual mean ice volume decrease relaxes approaching 2050. This is because, while increasing SAT increases summer ice melt, a thinner ice cover increases winter ice growth. A thinner ice cover also results in a reduced ice export, which helps to further slow ice volume loss. Because of enhanced winter ice growth, arctic winter ice extent remains nearly stable and therefore appears to be a less sensitive climate indicator.

Narwhals document continued warming of southern Baffin Bay

Laidre, K.L., M.P. Heide-Jorgensen, W. Ermold, and M. Steele, "Narwhals document continued warming of southern Baffin Bay," J. Geophys. Res., 115, doi:10.1029/2009JC005820, 2010.

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23 Oct 2010

We report on wintertime data collected from Baffin Bay and northern Davis Strait, a major gateway linking the Arctic with the subpolar North Atlantic, using narwhals (Monodon monoceros) as an oceanographic sampling platform. Fourteen narwhals were instrumented with satellite-linked time-depth-temperature recorders between 2005 and 2007. Transmitters collected and transmitted water column temperature profiles from each dive between December and April, where >90% of maximum daily dive depths reached the bottom. Temperature measurements were combined with 15 helicopter-based conductivity-temperature-depth (CTD) casts taken in April 2007 across central Baffin Bay and compared with hydrographic climatology values used for the region in Arctic climate models. Winter temperature maxima for whale and CTD data were in good agreement, ranging between 4.0 deg C and 4.6 deg C in inshore and offshore Baffin Bay and in Davis Strait. The warm Irminger Water was identified between 57 deg W and 59 deg W (at 68 deg N) between 200 and 400 m depths. Whale data correlated well with climatological temperature maxima; however, they were on average 0.9 deg C warmer plus/minus 0.6 deg C (P < 0.001). Furthermore, climatology data overestimated the winter surface isothermal layer thickness by 50–80 m.

Our results suggest the previously documented warming in Baffin Bay has continued through 2007 and is associated with a warmer West Greenland Current in both of its constituent water masses. This research demonstrates the feasibility of using narwhals as ocean observation platforms in inaccessible Arctic areas where dense sea ice prevents regular oceanographic measurements and where innate site fidelity, affinity for winter pack ice, and multiple daily dives to >1700 m offer a useful opportunity to sample the area.

Modeling the impact of declining sea ice on the Arctic marine planktonic ecosystem

Zhang, J., Y.H. Spitz, M. Steele, C. Ashjian, Carin, R. Campbell, L. Berline, and P. Matrai, "Modeling the impact of declining sea ice on the Arctic marine planktonic ecosystem," J. Geophys. Res., 115, doi:10.1029/2009JC005387, 2010.

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8 Oct 2010

We have developed a coupled 3-D pan-Arctic biology/sea ice/ocean model to investigate the impact of declining Arctic sea ice on the marine planktonic ecosystem over 1988–2007. The biophysical model results agree with satellite observations of a generally downward trend in summer sea ice extent during 1988–2007, resulting in an increase in the simulated photosynthetically active radiation (PAR) at the ocean surface and marine primary productivity (PP) in the upper 100 m over open water areas of the Arctic Ocean. The simulated Arctic sea ice thickness has decreased steadily during 1988–2007, leading to an increase in PAR and PP in sea ice-covered areas. The simulated total PAR in all areas of the Arctic Ocean has increased by 43%, from 146 TW in 1988 to 209 TW in 2007; the corresponding total PP has increased by 50%, from 456 Tg C yr-1 in 1988 to 682 Tg C yr-1 in 2007. The simulated PAR and PP increases mainly occur in the seasonally and permanently ice-covered Arctic Ocean. In addition to increasing PAR, the decline in sea ice tends to increase the nutrient availability in the euphotic zone by enhancing air-sea momentum transfer, leading to strengthened upwelling and mixing in the water column and therefore increased nutrient input into the upper ocean layers from below. The increasing nutrient availability also contributes to the increase in the simulated PP, even though significant surface nutrient drawdown in summer is simulated. In conjunction with increasing surface absorption of solar radiation and rising surface air temperature, the increasing surface water temperature in the Arctic Ocean peripheral seas further contributes to the increase in PP. As PP has increased, so has the simulated biomass of phytoplankton and zooplankton.

The Arctic: Ocean [in State of the Climate in 2009]

Proshutinsky, A., et al., including J. Morison, M. Steele, and R. Woodgate, "The Arctic: Ocean [in State of the Climate in 2009]," Bull. Amer. Meteor. Soc., 91, S85-87, 2010.

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1 Jul 2010

This 20th annual State of the Climate report highlights the climate conditions that characterized 2009, including notable extreme events. In total, 37 Essential Climate Variables are reported to more completely characterize the State of the Climate in 2009.

Combining satellite altimetry, time-variable gravity, and bottom pressure observations to understand the Arctic Ocean: A transformative opportunity

Kwok, R., et al., including J. Morison, C. Peralta-Ferriz, and M. Steele, "Combining satellite altimetry, time-variable gravity, and bottom pressure observations to understand the Arctic Ocean: A transformative opportunity," In Proceedings, OceanObs'09: Sustained Ocean Observations and Information for Society (Vol. 2), Venice, Italy, 21-25 September 2009, J. Hall, et al., eds. (ESA Publication WPP-306, doi:10.5270/OceanObs09.cwp.58, 2010).

15 Feb 2010

An arctic hydrologic system in transition: Feedbacks and impacts on terrestrial, marine, and human life

Francis, J.A., D.M. White, J.J. Cassano, W.J. Gutowski, L.D. Hinzman, M.M. Holland, M.A. Steele, and C.J. Vorosmarty, "An arctic hydrologic system in transition: Feedbacks and impacts on terrestrial, marine, and human life," J. Geophys. Res., 114, doi:10.1029/2008JG000902, 2009.

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9 Dec 2009

The pace of change in the arctic system during recent decades has captured the world's attention. Observations and model simulations both indicate that the arctic experiences an amplified response to climate forcing relative to that at lower latitudes. At the core of these changes is the arctic hydrologic system, which includes ice, gaseous vapor in the atmosphere, liquid water in soils and fluvial networks on land, and the freshwater content of the ocean. The changes in stores and fluxes of freshwater have a direct impact on biological systems, not only of the arctic region itself, but also well beyond its bounds. In this investigation, we used a heuristic, graphical approach to distill the system into its fundamental parts, documented the key relationships between those parts as best we know them, and identified the feedback loops within the system. The analysis illustrates relationships that are well understood, but also reveals others that are either unfamiliar, uncertain, or unexplored. The graphical approach was used to provide a visual assessment of the arctic hydrologic system in one possible future state in which the Arctic Ocean is seasonally ice free.

The Arctic: Oceans [in State of the Climate in 2008]

Proshutinsky, A., R. Krishfield, M. Steele, et al., "The Arctic: Oceans [in State of the Climate in 2008]," Bull. Amer. Meteor. Soc., 90, S99-102, 2009

1 Aug 2009

Rapid change in freshwater content of the Arctic Ocean

McPhee, M.G., A. Proshutinsky, J.H. Morison, M. Steele, and M.B. Alkire, "Rapid change in freshwater content of the Arctic Ocean," Geophys. Res. Lett., 36, doi:10.1029/2009GL037525, 2009.

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21 May 2009

The dramatic reduction in minimum Arctic sea ice extent in recent years has been accompanied by surprising changes in the thermohaline structure of the Arctic Ocean, with potentially important impact on convection in the North Atlantic and the meridional overturning circulation of the world ocean. Extensive aerial hydrographic surveys carried out in March–April, 2008, indicate major shifts in the amount and distribution of fresh-water content (FWC) when compared with winter climatological values, including substantial freshening on the Pacific side of the Lomonosov Ridge. Measurements in the Canada and Makarov Basins suggest that total FWC there has increased by as much as 8,500 cubic kilometers in the area surveyed, effecting significant changes in the sea-surface dynamic topography, with an increase of about 75% in steric level difference from the Canada to Eurasian Basins, and a major shift in both surface geostrophic currents and freshwater transport in the Beaufort Gyre.

Tracing freshwater anomalies through the air-land-ocean system: A case study from the Mackenzie River Basin and the Beaufort Gyre

Rawlins, M.A., M. Steele, M.C. Serreze, C.J. Vorosmarty, W. Ermold, R.B. Lammers, K.C. McDonald, T.M. Pavelsky, A. Shilomanov, and J. Zhang, "Tracing freshwater anomalies through the air-land-ocean system: A case study from the Mackenzie River Basin and the Beaufort Gyre," Atmos. Oceans, 47, 79-97, doi:10.3137/OC301.2009, 2009.

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1 Mar 2009

Mackenzie River discharge was at a record low in water year (WY) 1995 (October 1994 to September 1995), was near average in WY 1996, and was at a record high in WY 1997. The record high discharge in WY 1997, with above average flow each month, was followed by a record high flow in May 1998, then a sharp decline. Through diagnosing these changing flows and their expression in the Beaufort Sea via synthesis of observations and model output, this study provides insight into the nature of the Arctic's freshwater system.

The low discharge in WY 1995 manifests negative anomalies in P–E and precipitation, recycled summer precipitation, and dry surface conditions immediately prior to the water year. The complex hydrograph for WY 1996 reflects a combination of spring soil moisture recharge, buffering by rising lake levels, positive P–E anomalies in summer, and a massive release of water held in storage by Bennett Dam. The record high discharge in WY 1997 manifests the dual effects of reduced buffering by lakes and positive P–E anomalies for most of the year. With reduced buffering, only modest P–E the following spring led to a record discharge in May 1998. As simulated with a coupled ice–ocean model, the record low discharge in WY 1995 contributed to a negative freshwater anomaly on the Mackenzie shelf lasting throughout the winter of 1995/96. High discharge from July–October 1996 contributed approximately 20% to a positive freshwater anomaly forming in the Beaufort Sea in the autumn of that year. The remainder was associated with reduced autumn/winter ice growth, strong ice melt the previous summer, and positive P–E anomalies over the ocean itself. Starting in autumn 1997 and throughout 1998, the upper ocean became more saline owing to sea ice growth.

Arctic sea ice retreat in 2007 follows thinning trend

Lindsay, R.W., J. Zhang, A. Schweiger, M. Steele, and H. Stern, "Arctic sea ice retreat in 2007 follows thinning trend," J. Climate, 22, 165-176, 2009.

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1 Jan 2009

The minimum of Arctic sea ice extent in the summer of 2007 was unprecedented in the historical record. A coupled ice–ocean model is used to determine the state of the ice and ocean over the past 29 yr to investigate the causes of this ice extent minimum within a historical perspective. It is found that even though the 2007 ice extent was strongly anomalous, the loss in total ice mass was not. Rather, the 2007 ice mass loss is largely consistent with a steady decrease in ice thickness that began in 1987. Since then, the simulated mean September ice thickness within the Arctic Ocean has declined from 3.7 to 2.6 m at a rate of –0.57 m decade-1. Both the area coverage of thin ice at the beginning of the melt season and the total volume of ice lost in the summer have been steadily increasing. The combined impact of these two trends caused a large reduction in the September mean ice concentration in the Arctic Ocean. This created conditions during the summer of 2007 that allowed persistent winds to push the remaining ice from the Pacific side to the Atlantic side of the basin and more than usual into the Greenland Sea. This exposed large areas of open water, resulting in the record ice extent anomaly.

What drove the dramatic retreat of arctic sea ice during summer 2007?

Zhang, J., R. Lindsay, M. Steele, and A. Schweiger, "What drove the dramatic retreat of arctic sea ice during summer 2007?" Geophys. Res. Lett., 35, doi:10.1029/2008GL034005, 2008.

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11 Jun 2008

A model study has been conducted of the unprecedented retreat of arctic sea ice in the summer of 2007. It is found that preconditioning, anomalous winds, and ice-albedo feedback are mainly responsible for the retreat. Arctic sea ice in 2007 was preconditioned to radical changes after years of shrinking and thinning in a warm climate. During summer 2007 atmospheric changes strengthened the transpolar drift of sea ice, causing more ice to move out of the Pacific sector and the central Arctic Ocean where the reduction in ice thickness due to ice advection is up to 1.5 m more than usual. Some of the ice exited Fram Strait and some piled up in part of the Canada Basin and along the coast of northern Greenland, leaving behind an unusually large area of thin ice and open water. Thin ice and open water allow more surface solar heating because of a much reduced surface albedo, leading to amplified ice melting. The Arctic Ocean lost additional 10% of its total ice mass in which 70% is due directly to the amplified melting and 30% to the unusual ice advection, causing the unprecedented ice retreat. Arctic sea ice has entered a state of being particularly vulnerable to anomalous atmospheric forcing.

Did unusually sunny skies help drive the record sea ice minimum of 2007?

Schweiger, A.J., J. Zhang, R.W. Lindsay, and M. Steele, "Did unusually sunny skies help drive the record sea ice minimum of 2007?" Geophys. Res. Lett., 35, doi:10.1029/2008GL033463, 2008.

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30 May 2008

We conduct experiments with an ice-ocean model to answer the question whether and to what degree unusually clear skies during the summer of 2007 contributed to the record sea ice extent minimum in the Arctic Ocean during September of 2007. Anomalously high pressure over the Beaufort Sea during summer 2007 appears associated with a strong negative cloud anomaly. This anomaly is two standard deviations below the 1980–2007 average established from a combination of two different satellite-based records. Cloud anomalies from the MODIS sensor are compared with anomalies from the NCEP/NCAR reanalysis and are found in good agreement in spatial patterns and magnitude. However, these experiments establish that the negative cloud anomaly and increased downwelling shortwave flux from June through August did not contribute substantially to the record sea ice extent minimum. This finding eliminates one aspect of the unusual weather that may have contributed to the record minimum.

Ensemble 1-year predictions of Arctic sea ice for the spring and summer of 2008

Zhang, J., M. Steele, R. Lindsay, A. Schweiger, J. Morison, "Ensemble 1-year predictions of Arctic sea ice for the spring and summer of 2008," Geophys. Res. Lett., 35, doi:10.1029/2008GL033244, 2008.

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22 Apr 2008

Ensemble predictions of arctic sea ice in spring and summer 2008 have been carried out using an ice-ocean model. The ensemble is constructed by using atmospheric forcing from 2001 to 2007 and the September 2007 ice and ocean conditions estimated by the model. The prediction results show that the record low ice cover and the unusually warm ocean surface waters in summer 2007 lead to a substantial reduction in ice thickness in 2008. Up to 1.2 m ice thickness reduction is predicted in a large area of the Canada Basin in both spring and summer of 2008, leading to extraordinarily thin ice in summer 2008. There is a 50% chance that both the Northern Sea Route and the Northwest Passage will be nearly ice free in September 2008. It is not likely there will be another precipitous decline in arctic sea ice extent such as seen in 2007, unless a new atmospheric forcing regime, significantly different from the recent past, occurs.

Seasonal predictions of ice extent in the Arctic Ocean

Lindsay, R.W., J. Zhang, A.J. Schweiger, and M.A. Steele, "Seasonal predictions of ice extent in the Arctic Ocean," J. Geophys. Res., 113, doi:10.1029/2007JC004259, 2008.

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29 Feb 2008

How well can the extent of arctic sea ice be predicted for lead periods of up to one year? The forecast ability of a linear empirical model is explored. It uses as predictors historical information about the ocean and ice obtained from an ice–ocean model retrospective analysis. The monthly model fields are represented by a correlation-weighted average based on the predicted ice extent. The forecast skill of the procedure is found by fitting the model over subsets of the available data and then making subsequent projections using independent predictor data. The forecast skill, relative to climatology, for predictions of the observed September ice extent for the pan-arctic region is 0.77 for six months lead (from March) and 0.75 for 11 months lead (from October). The ice concentration is the most important variable for the first two months and the ocean temperature of the model layer with a depth of 200 to 270 m is most important for longer lead times. The trend accounts for 76% of the variance of the pan-arctic ice extent, so most of the forecast skill is realized by determining model variables that best represent this trend. For detrended data there is no skill for lead times of 3 months or more. The forecast skill relative to the estimate from the previous year is lower than the climate-relative skill but it is still greater than 0.45 for most lead times. Six-month predictions are also made for each month of the year and regional three-month predictions are made for 45-degree sectors. The ice-ocean model output significantly improves the predictive skill of the forecast model.

Arctic Ocean surface warming trends over the past 100 years

Steele, M., W. Ermold, and J. Zhang, "Arctic Ocean surface warming trends over the past 100 years," Geophys. Res. Lett., 35, doi:10.1029/2007GL031651, 2008.

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29 Jan 2008

Ocean temperature profiles and satellite data have been analyzed for summertime sea surface temperature (SST) and upper ocean heat content variations over the past century, with a focus on the Arctic Ocean peripheral seas. We find that many areas cooled up to –0.5°C per decade during 1930–1965 as the Arctic Oscillation (AO) index generally fell, while these areas warmed during 1965–1995 as the AO index generally rose. Warming is particularly pronounced since 1995, and especially since 2000. Summer 2007 SST anomalies are up to 5°C. The increase in upper ocean summertime warming since 1965 is sufficient to reduce the following winter's ice growth by as much as 0.75 m. Alternatively, this heat may return to the atmosphere before any ice forms, representing a fall freeze-up delay of two weeks to two months. This returned heat might be carried by winds over terrestrial tundra ecosystems, contributing to the local heat budget.

Arctic ocean freshwater changes over the past 100 years and their causes

Polyakov, I.V., V.A. Alexeev, G.I. Belchansky, I.A. Dmitrenko, V.V. Ivanov, S.A. Kirillov, A.A. Korablev, M. Steele, L.A. Timokhov, and I. Yashayaev, "Arctic ocean freshwater changes over the past 100 years and their causes," J. Clim., 21, 364-384, 2008.

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1 Jan 2008

Recent observations show dramatic changes of the Arctic atmosphere–ice–ocean system. Here the authors demonstrate, through the analysis of a vast collection of previously unsynthesized observational data, that over the twentieth century the central Arctic Ocean became increasingly saltier with a rate of freshwater loss of 239 ± 270 km3 decade-1. In contrast, long-term (1920–2003) freshwater content (FWC) trends over the Siberian shelf show a general freshening tendency with a rate of 29 ± 50 km3 decade-1. These FWC trends are modulated by strong multidecadal variability with sustained and widespread patterns. Associated with this variability, the FWC record shows two periods in the 1920s–30s and in recent decades when the central Arctic Ocean was saltier, and two periods in the earlier century and in the 1940s–70s when it was fresher. The current analysis of potential causes for the recent central Arctic Ocean salinification suggests that the FWC anomalies generated on Arctic shelves (including anomalies resulting from river discharge inputs) and those caused by net atmospheric precipitation were too small to trigger long-term FWC variations in the central Arctic Ocean; to the contrary, they tend to moderate the observed long-term central-basin FWC changes. Variability of the intermediate Atlantic Water did not have apparent impact on changes of the upper-Arctic Ocean water masses. The authors' estimates suggest that ice production and sustained draining of freshwater from the Arctic Ocean in response to winds are the key contributors to the salinification of the upper Arctic Ocean over recent decades. Strength of the export of Arctic ice and water controls the supply of Arctic freshwater to subpolar basins while the intensity of the Arctic Ocean FWC anomalies is of less importance. Observational data demonstrate striking coherent long-term variations of the key Arctic climate parameters and strong coupling of long-term changes in the Arctic/North Atlantic climate system. Finally, since the high-latitude freshwater plays a crucial role in establishing and regulating global thermohaline circulation, the long-term variations of the freshwater content discussed here should be considered when assessing climate change and variability.

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.

Observational program tracks Arctic Ocean transition to a warmer state

Polyakov, I., et al. (including M. Steele), "Observational program tracks Arctic Ocean transition to a warmer state," Eos, Trans. AGU, 88, 398, doi:10.1029/2007EO400002, 2007.

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2 Oct 2007

Over the past several decades, the Arctic Ocean has undergone substantial change. Enhanced transport of warmer air from lower latitudes has led to increased Arctic surface air temperature. Concurrent reductions in Arctic ice extent and thickness have been documented. The first evidence of warming in the intermediate Atlantic Water (AW, water depth between 150 and 900 meters) of the Arctic Ocean was found in 1990. Another anomaly, found in 2004, suggests that the Arctic Ocean is in transition toward a new, warmer state [Polyakov et al., 2005, and references therein].

The return of Pacific waters to the upper layers of the central Arctic Ocean

Alkire, M.B., and K.K. Falkner, I. Rigor, M. Steele, and J. Morison, "The return of Pacific waters to the upper layers of the central Arctic Ocean," Deep-Sea Res. I, 54, 1509-1529, doi:10.1016/j.dsr.2007.06.004, 2007.

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1 Sep 2007

Temperature, salinity, and chemical measurements, including the nutrients silicic acid, nitrate, nitrite, ammonium, and phosphate, the oxygen isotopic composition of seawater, and barium concentrations were obtained from the central Arctic Ocean along transects radiating from the North Pole in early spring, 2000–2006. Stations that were reoccupied over this time period were grouped into five regions: from Ellesmere Island, (1) north along 70°W and (2) northwest along 90°W; near the North Pole, (3) on the Amundsen Basin flank and (4) directly over the Lomonosov Ridge; (5) through the Makarov Basin along 170–180°W. These regions had been shown by others to have undergone marked changes in water-mass assemblies in the early 1990s, but our time series tracer hydrographic data indicate a partial return of Pacific origin water within the mixed layer and the upper halocline layers beginning in 2003–2004. Back-trajectories derived from satellite-tracked ice buoys for these stations indicate that the upper levels of Pacific water in the central Arctic in 2004–2006 transited westward from the Bering Strait along the Siberian continental slope into the East Siberian Sea before entering the Transpolar Drift Stream (TPD). By 2004, the TPD shifted back from an alignment over the Alpha-Mendeleev Ridge toward the Lomonosov Ridge, as was characteristic prior to the early 1990s. At most stations occupied in 2006, a decrease in the Pacific influence was observed, both in the mixed layer and in the upper halocline, which suggests the Canadian branch of the TPD was shifting back toward North America. Clearly the system is more variable than has been previously appreciated.

The large-scale energy budget of the Arctic

Serreze, M.C., A.P. Barrett, A.G. Slater, M. Steele, J. Zhang, and K.E. Trenberth, "The large-scale energy budget of the Arctic," J. Geophys. Res., 112, doi:10.1029/2006JD008230, 2007.

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14 Jun 2007

This paper synthesizes a variety of atmospheric and oceanic data to examine the large-scale energy budget of the Arctic. Assessment of the atmospheric budget relies primarily on the ERA-40 reanalysis. The seasonal cycles of vertically integrated atmospheric energy storage and the convergence of energy transport from ERA-40, as evaluated for the polar cap (defined by the 70°N latitude circle), in general compare well with realizations from the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis over the period 1979–2001. However, shortcomings in top of atmosphere radiation, as compared to satellite data, and the net surface flux, contribute to large energy budget residuals in ERA-40. The seasonal cycle of atmospheric energy storage is strongly modulated by the net surface flux, which is also the primary driver of seasonal changes in heat storage within the Arctic Ocean. Averaged for an Arctic Ocean domain, the July net surface flux from ERA-40 of –100 W m-2 (i.e., into the ocean), associated with sea ice melt and oceanic sensible heat gain, exceeds the atmospheric energy transport convergence of 91 W m-2. During winter (for which budget residuals are large), oceanic sensible heat loss and sea ice growth yield an upward surface flux of 50–60 W m-2, complemented with an atmospheric energy convergence of 80–90 W m-2 to provide a net radiation loss to space of 175–180 W m-2.

Effect of vertical mixing on the Atlantic Water layer circulation in the Arctic Ocean

Zhang, J., and M. Steele, "Effect of vertical mixing on the Atlantic Water layer circulation in the Arctic Ocean," J. Geophys. Res., 112, doi:10.1029/2006JC003732, 2007.

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13 Mar 2007

An ice-ocean model has been used to investigate the effect of vertical mixing on the circulation of the Atlantic Water layer (AL) in the Arctic Ocean. The motivation of this study comes from the disparate AL circulations in the various models that comprise the Arctic Ocean Model Intercomparison Project (AOMIP). It is found that varying vertical mixing significantly changes the ocean's stratification by altering the vertical distribution of salinity and hence the structure of the arctic halocline. In the Eurasian Basin, the changes in ocean stratification tend to change the strength and depth of the cyclonic AL circulation, but not the basic circulation pattern. In the Canada Basin, however, the changes in ocean stratification are sufficient to alter the direction of the AL circulation. Excessively strong vertical mixing drastically weakens the ocean stratification, leading to an anticyclonic circulation at all depths, including both the AL and the upper layer that consists of the surface mixed layer and the halocline. Overly weak vertical mixing makes the ocean unrealistically stratified, with a fresher and thinner upper layer than observations. This leads to an overly strong anticyclonic circulation in the upper layer and an overly shallow depth at which the underlying cyclonic circulation occurs. By allowing intermediate vertical mixing, the model does not significantly drift away from reality and is in a rather good agreement with observations of the vertical distribution of salinity throughout the Arctic Ocean. This realistic ocean stratification leads to a realistic cyclonic AL circulation in the Canada Basin. In order for arctic ice-ocean models to obtain realistic cyclonic AL circulation in the Canada Basin, it is essential to generate an upward concave-shaped halocline across the basin at certain depths, consistent with observations.

Water properties and circulation in Arctic Ocean models

Holloway, G., F. Dupont, E. Golubeva, S. Hakkinen, E. Hunke, M. Jin, M. Karcher, F. Kauker, M. Maltrud, M.A.M. Maqueda, W. Maslowski, G. Platov, D. Stark, M. Steele, T. Suzuki, J. Wang, J. Zhang, "Water properties and circulation in Arctic Ocean models," J. Geophys. Res., 112, doi:10.1029/2006JC003642, 2007.

7 Mar 2007

Steric sea level change in the northern seas

Steele, M., and W. Ermold, "Steric sea level change in the northern seas," J. Clim., 20, 403-417, 2007.

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1 Feb 2007

Ocean temperature and salinity data over the period 1950%u20132000 in the Northern Seas, defined here as the North Atlantic Ocean (north of 50°N), North Pacific Ocean (north of 40°N), and Arctic Oceans, are combined to diagnose the steric (i.e., density) contribution to sea level variation. The individual contributions to steric height from temperature (thermosteric height) and salinity (halosteric height) are also analyzed. It is found that during 1950–2000, steric height rose over the study's domain, mostly as a result of halosteric increases (i.e., freshening). Over a shorter time period (late 1960s to early 1990s) during which climate indices changed dramatically, steric height gradients near the Nordic Seas minimum were reduced by 18%–32%. It is speculated that this may be associated with a local slowing of both the Meridional Overturning Circulation and the southward flow through Fram Strait. However, steric height increases in the North Pacific Ocean during this time imply a possible acceleration of flow through the poorly measured Canadian Arctic. Evidence that the Great Salinity Anomaly of the late 1960s and 1970s had two distinct Arctic Ocean sources is also found: a late 1960s export of sea ice, and a delayed but more sustained 1970s export of liquid (ocean) freshwater. A simple calculation indicates that these Arctic Ocean freshwater sources were not sufficient to create the 1970s freshening observed in the North Atlantic Ocean.

Relaxation of central Arctic Ocean hydrography to pre-1990s climatology

Morison, J., M. Steele, T. Kikuchi, K. Falkner, and W. Smethie, "Relaxation of central Arctic Ocean hydrography to pre-1990s climatology," Geophys. Res. Lett., 33, 10.1029/2006GL026826, 2006.

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8 Sep 2006

Upper ocean hydrography in the central Arctic Ocean has relaxed since 2000 to near-climatological conditions that pertained before the dramatic changes of the 1990s. The behavior of the anomalies of temperature and salinity in the central Arctic Ocean follow a first-order linear response to the AO with time constant of 5 years and a delay of 3 years.

Origins of the SHEBA freshwater anomaly in the Mackenzie River delta

Steele, M., A. Porcelli, and J. Zhang, "Origins of the SHEBA freshwater anomaly in the Mackenzie River delta," Geophys. Res. Lett., 33, 10.1029/2005GL024813, 2006.

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4 May 2006

The formation of a low salinity anomaly observed in the southern Beaufort Gyre in fall 1997 is examined, using output from a numerical sea ice – ocean climate model. The anomaly forms from locally reduced fall ice growth and from advection of river water. With regard to the latter, we find anomalous northwestward advection of water from the Mackenzie River delta (MRD) during 1997–1999, which fed a low salinity anomaly that circulated and deepened in the Beaufort Gyre until summer 2002, when it dissipated. The MRD salinity anomaly was especially fresh in 1997 because unusually convergent sea ice the previous summer and fall 1996 suppressed fall ice growth. The model shows a high correlation between advection from the MRD and salinity anomalies in the southern Beaufort Gyre until about 2002, when the correlation weakens as local sea ice melt/growth becomes the dominant forcing.

One more step toward a warmer Arctic

Polyakov, I.V., A. Beszczynska, E.C. Carmack, I.A. Dmitrenko, E. Fahrbach, I.E. Frolov, R. Gerdes, E. Hansen, J. Holfort, V.V. Ivanov, M.A. Johnson, M. Karcher, F. Kauker, J. Morison, K.A. Orvik, U. Schauer, H.L. Simmons, O. Skagseth, V.T. Sokolov, M. Steele, L.A. Timokhov, D. Walsh, and J.E. Walsh, "One more step toward a warmer Arctic," Geophys. Res. Lett., 32, doi:10.1029/2005GL023740, 2005

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9 Sep 2005

This study was motivated by a strong warming signal seen in mooring-based and oceanographic survey data collected in 2004 in the Eurasian Basin of the Arctic Ocean. The source of this and earlier Arctic Ocean changes lies in interactions between polar and sub-polar basins. Evidence suggests such changes are abrupt, or pulse-like, taking the form of propagating anomalies that can be traced to higher-latitudes. For example, an anomaly found in 2004 in the eastern Eurasian Basin took ~1.5 years to propagate from the Norwegian Sea to the Fram Strait region, and additional ~4.5–5 years to reach the Laptev Sea slope. While the causes of the observed changes will require further investigation, our conclusions are consistent with prevailing ideas suggesting the Arctic Ocean is in transition towards a new, warmer state.

Dissolved oxygen extrema in the Arctic Ocean halocline from the North Pole to the Lincoln Sea

Falkner, K.K., M. Steele, R.A. Woodgate, J.H. Swift, K. Aagaard, and J. Morison, "Dissolved oxygen extrema in the Arctic Ocean halocline from the North Pole to the Lincoln Sea," Deep Sea Res. I, 52, 1138-1154, doi:10.1016/j.dsr.2005.01.007, 2005

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30 Jul 2005

Dissolved oxygen (O2) profiling by new generation sensors was conducted in the Arctic Ocean via aircraft during May 2003 as part of the North Pole Environmental Observatory (NPEO) and Freshwater Switchyard (SWYD) projects. At stations extending from the North Pole to the shelf off Ellesmere Island, such profiles display what appear to be various O2 maxima (with concentrations 70% of saturation or less) over depths of 70–110 m in the halocline, corresponding to salinity and temperature ranges of 33.3–33.9 and ~1.7 to ~1.5°C. The features appear to be widely distributed: Similar features based on bottle data were recently reported for a subset of the 1997–1998 SHEBA stations in the southern Canada Basin and in recent Beaufort Sea sensor profiles. Oxygen sensor data from August 2002 Chukchi Borderlands (CBL) and 1994 Arctic Ocean Section (AOS) projects suggest that such features arise from interleaving of shelf-derived, O2-depleted waters. This generates apparent oxygen maxima in Arctic Basin profiles that would otherwise trend more smoothly from near-saturation at the surface to lower concentrations at depth. For example, in the Eurasian Basin, relatively low O2 concentrations are observed at salinities of about 34.2 and 34.7. The less saline variant is identified as part of the lower halocline, a layer originally identified by a Eurasian Basin minimum in "NO," which, in the Canadian Basin, is reinforced by additional inputs. The more saline and thus denser variant appears to arise from transformations of Atlantic source waters over the Barents and/or Kara shelves. Additional low-oxygen waters are generated in the vicinity of the Chukchi Borderlands, from Pacific shelf water outflows that interleave with Eurasian waters that flow over the Lomonosov Ridge into the Makarov Basin and then into the Canada Basin. One such input is associated with the well-known silicate maximum that historically has been associated with a salinity of %u224833.1. Above that (322-depleted.

We propose that these low O2 waters influence the NPEO and SWYD profiles to varying extents in a manner reflective of the large-scale circulation. The patterns of halocline circulation we infer from the intrusive features defy a simple boundary-following cyclonic flow. These results demonstrate the value of the improved resolution made feasible with continuous O2 profiling. In the drive to better understand variability and change in the Arctic Ocean, deployment of appropriately calibrated CTD-O2 packages offers the promise of important new insights into circulation and ecosystem function.

Salinity trends on the Siberian shelves

Steele, M., and W. Ermold, "Salinity trends on the Siberian shelves," Geophys. Res. Lett., 31, doi:10.1029/2004GL021302, 2004.

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24 Dec 2004

We present an analysis of observed long-term (~100 year) salinity trends on the freshwater-dominated Siberian continental shelves. A multiple regression was performed in the White Sea (WS), the Kara Sea (KS), the Laptev Sea (LS), and the East Siberian Sea (ESS). Since 1930, the WS has gained freshwater while the ESS has lost it, consistent with river discharge trends over this period. Over the past 20 years, increases in both river discharge and direct precipitation can explain observed salinity decreases in the WS, but not in the KS. Salinity trends in the LS and ESS indicate that ocean circulation plays a dominate role in these areas, where in recent years freshwater has been diverted eastward along the coast, rather than northward toward the deep ocean.

Dissolved oxygen extrema in the Arctic Ocean halocline from the North Pole to the Lincoln Sea

Falkner, K.K., M. Steele, R.A. Woodgate, J.H. Swift, K. Aagaard, and J. Morison, "Dissolved oxygen extrema in the Arctic Ocean halocline from the North Pole to the Lincoln Sea," Eos Trans. AGU, 85(47), Abstract OS41A-0465, 2004.

15 Dec 2004

Increasing exchanges at Greenland-Scotland Ridge and their links with the North Atlantic Oscillation and Arctic Sea Ice

Zhang, J., M. Steele, D.A. Rothrock, and R.W. Lindsay, "Increasing exchanges at Greenland-Scotland Ridge and their links with the North Atlantic Oscillation and Arctic Sea Ice," Geophys. Res. Lett., 31, L09307, 10.1029/2003GL019304, 2004.

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6 May 2004

A global ice-ocean model shows increasing Atlantic water (AW) inflow at the Iceland-Scotland Ridge (ISR) during 1953–2002. As a result, the Greenland-Iceland-Norwegian (GIN) Sea is gaining more heat and salt from the North Atlantic Ocean, while the latter is being freshened mainly by exporting more salt to the GIN Sea. The exchanges of volume, heat, and freshwater at the Greenland-Scotland Ridge (GSR) are strongly correlated with the North Atlantic Oscillation (NAO) and their positive trend is closely linked to the NAO elevation in recent decades. The model confirms observations of decreasing dense water outflow at the Faroe-Scotland Passage since the 1950s. However, the simulated dense water outflow shows an increase at Denmark Strait, at the Iceland-Faroe Ridge, and at the GSR as a whole, owing to an increase in AW inflow that may cause an increase in AW recirculation and deep water production in the GIN Sea. The increase of the ISR heat inflow since 1965 contributes to continued thinning of the arctic sea ice since 1966. The influence of the heat inflow on arctic sea ice lags 2–3 years, which suppresses ice production even when the NAO temporarily shifts to a negative mode. Because of this delay, the decline of arctic sea ice is likely to continue if the inflow continues to increase and if the NAO does not shift to a sustained negative mode.

Comparing modeled streamfunction, heat and freshwater content in the Arctic Ocean

Steiner, N., G. Holloway, R. Gerdes, S. Hakkinen, D. Holland, M. Karcher, F. Kauker, W. Maslowski, A. Proshutinsky, M. Steele, and J. Zhang, "Comparing modeled streamfunction, heat and freshwater content in the Arctic Ocean," Ocean Modelling, 6, 265-284, doi:10.1016/S1463-5003(03)00013-1, 2004.

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1 Mar 2004

Within the framework of the Arctic Ocean Model Intercomparison Project results from several coupled sea ice–ocean models are compared in order to investigate vertically integrated properties of the Arctic Ocean. Annual means and seasonal ranges of streamfunction, freshwater and heat content are shown. For streamfunction the entire water column is integrated. For heat and freshwater content integration is over the upper 1000 m. The study represents a step toward identifying differences among model approaches and will serve as a base for upcoming studies where all models will be executed with common forcing. In this first stage only readily available outputs are compared, while forcing as well as numerical parameterizations differ.

The intercomparison shows streamfunctions differing in pattern and by several Sverdrups in magnitude. Differences occur as well for the seasonal range, where streamfunction is subject to large variability.

Annual mean heat content, referenced to 0°C, in the Canada Basin varies from –3.5 to +1.8 GJ m-2 among the models, representing both colder and warmer solutions compared to the climatology. Seasonal range is highest in regions with seasonal or no ice cover.

Corresponding freshwater content, referenced to 34.8 ppt, shows differences most obviously in the Beaufort Sea and Canada Basin where maximum values vary between 6 and 24 m for the individual models. Maxima in the seasonal range are related to river inflow.

In the current stage of the project, applied windstress contributes significantly to the differences. However differences due to model resolutions and model parameterizations can already be detected.

Circulation of summer Pacific halocline water in the Arctic Ocean

Steele, M., J. Morison, W. Ermold, M. Ortmeyer, and K. Shimada, "Circulation of summer Pacific halocline water in the Arctic Ocean," J. Geophys. Res., 109, C02027, doi:10.1029/2003JC002009, 2004.

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26 Feb 2004

We present an analysis of Arctic Ocean hydrographic and sea ice observations from the 1990s, with a focus on the circulation of water that originates in the North Pacific Ocean. Previous studies have shown the presence of two varieties of relatively warm "summer halocline water" in the vicinity of the Chukchi Sea, i.e., the relatively fresh Alaskan Coastal Water (ACW) and the relatively saltier summer Bering Sea Water (sBSW). Here we extend these studies by tracing the circulation of these waters downstream into the Arctic Ocean. We find that ACW is generally most evident in the southern Beaufort Gyre, while sBSW is strongest in the northern portion of the Beaufort Gyre and along the Transpolar Drift Stream. We find that this separation is most extreme during the early mid-1990s, when the Arctic Oscillation was at historically high index values. This leads us to speculate that the outflow to the North Atlantic Ocean (through the Canadian Archipelago and Fram Strait) may be similarly separated. As Arctic Oscillation index values fell during the later 1990s, ACW and sBSW began to overlap in their regions of influence. These changes are evident in the area north of Ellesmere Island, where the influence of sBSW is highly correlated, with a 3-year lag, with the Arctic Oscillation index. We also note the presence of winter Bering Sea Water (wBSW), which underlies the summer varieties. All together, this brings the number of distinct Pacific water types in our Arctic Ocean inventory to three: ACW, sBSW, and wBSW.

North Pole Environmental Observatory delivers early results

Morison, J.H., K. Aagaard, K.K. Falkner, K. Hatakeyama, R. Mortiz, J.E. Overland, D. Perovich, K. Shimada, M. Steele, T. Takizawa, and R. Woodgate, "North Pole Environmental Observatory delivers early results," Eos Trans. AGU, 83, 357-361, 2002.

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1 Aug 2002

Scientists have argued for a number of years that the Arctic may be a sensitive indicator of global change, but prior to the 1990s, conditions there were believed to be largely static. This has changed in the last 10 years. Decadal-scale changes have occurred in the atmosphere, in the ocean, and on land [Serreze et al., 2000]. Surface atmospheric pressure has shown a declining trend over the Arctic, resulting in a clockwise spin-up of the atmospheric polar vortex. In the 1990s, the Arctic Ocean circulation took on a more cyclonic character, and the temperature of Atlantic water in the Arctic Ocean was found to be the highest in 50 years of observation [Morison et al., 2000]. Sea-ice thickness over much of the Arctic decreased 43% in 1958–1976 and 1993–1997 [Rothrock et al., 1999].

Partial recovery of the Arctic Ocean halocline

Boyd, T.J., M. Steele, R.D. Muench, and J.T. Gunn, "Partial recovery of the Arctic Ocean halocline," Geophys. Res. Lett., 29, doi:10.1029/2001GL014047, 2002.

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16 Jul 2002

The evolution during the 1990's of the cold halocline layer (CHL) of the Arctic Ocean is investigated using data from icebreaker and SCICEX submarine cruises. The CHL disappearance and subsequent partial recovery is described along repeated transects through the central Arctic Ocean from the Alpha Ridge to the Nansen Basin. Salinity at the top of the halocline is used as a measure of halocline development, with high salinity corresponding to a poorly developed halocline. In the Nansen, Amundsen, and Makarov basins, upper ocean salinity increased from 1991 to 1998 as the CHL disappeared, then decreased from 1998 to 2000 as it recovered. Salinity was higher over the study region through the 1990's than at any time during the prior 40 year period, hence the 1990's CHL recovery was only partial. Disappearance of the CHL from the Eurasian Basin in the early 1990's was due to a shift from the Laptev to East Siberian seas of the region for seaward flow of low salinity Siberian shelf waters. Ice velocities and sea level pressure fields suggest that the reappearance of the CHL in 1999 corresponded to a shift of this flow back to the Laptev Sea region.

Return of the cold halocline layer to the Amundsen Basin of the Arctic Ocean: Implications for the sea ice mass balance

Bjork, G., S. Soderkvist, P. Winsor, A. Nikolopoulos, and M. Steele, "Return of the cold halocline layer to the Amundsen Basin of the Arctic Ocean: Implications for the sea ice mass balance," Geophys. Res. Lett., 29, 10.1029/2001GL014157, 2002.

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7 Jun 2002

CTD measurements from the Arctic Ocean 2001 expedition reveal that the cold halocline layer (CHL) has returned to the Amundsen Basin at a position close to that found during the Oden'91 expedition. River water from the Siberian shelves formed a strong freshwater front in the Amundsen Basin, extending from the Gakkel Ridge to the Lomonosov Ridge. Furthermore, we show from model computations that the presence of a CHL may increase winter sea ice growth by 0.25 m over one season compared to a case with a non-existing CHL due to increased vertical heat flux from the warm Atlantic water. The difference in sea ice growth is due to a much shallower winter convection with a CHL present, which is not able to reach into the warm Atlantic layer, resulting in a considerably smaller oceanic heat flux.

Multinational effort studies differences among Arctic Ocean models

Proshutinsky, A., M. Steele, J. Zhang, G. Holloway, N. Steiner, S. Hakkinen, D. Holland, R. Gerdes, C. Koeberle, M. Karcher, M. Johnson, W. Maslowski, Y. Zhang, W. Hilber, and J. Wang, "Multinational effort studies differences among Arctic Ocean models," Eos Trans. AGU, 82, 643-644, doi:10.1029/01EO00365, 2001.

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18 Dec 2001

The Arctic Ocean is an important component of the global climate system. The processes occurring in the Arctic Ocean affect the rate of deep and bottom water formation in the convective regions of the high North Atlantic and influence ocean circulation across the globe. This fact is highlighted by global climate modeling studies that consistently show the Arctic to be one of the most sensitive regions to climate change. But an identification of the differences among models and model systematic errors in the Arctic Ocean remains unchecked, despite being essential to interpreting the simulation results and their implications for climate variability. For this reason, the Arctic Ocean Model Intercomparison Project (AOMIP), an international effort, was recently established to carry out a thorough analysis of model differences and errors. The geographical focus of this effort is shown in Figure 1.

Recent environmental changes in the Arctic: A review

Morison, J., K. Aagaard, and M. Steele, "Recent environmental changes in the Arctic: A review," Arctic, 53, 359-371, 2000.

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1 Dec 2000

Numerous recent observations indicate that the Arctic is undergoing a significant change. In the last decade, the hydrography of the Arctic Ocean has shifted, and the atmospheric circulation has undergone a change from the lower stratosphere to the surface. Typically the eastern Arctic Ocean, on the European side of the Lomonosov Ridge, is dominated by water of Atlantic origin. A cold halocline of varying thickness overlies the warmer Atlantic water and isolates it from the sea ice and surface mixed layer. The western Arctic Ocean, on the North American side of the Lomonosov Ridge, is characterized by an added layer of water from the Pacific immediately below the surface mixed layer. Data collected during several cruises from 1991 to 1995 indicate that in the 1990s the boundary between these eastern and western halocline types shifted from a position roughly parallel to the Lomonosov Ridge to near alignment with the Alpha and Mendeleyev Ridges. The Atlantic Water temperature has also increased, and the cold halocline has become thinner. The change has resulted in increased surface salinity in the Makarov Basin. Recent results suggest that the change also includes decreased surface salinity and greater summer ice melt in the Beaufort Sea. Atmospheric pressure fields and ice drift data show that the whole patterns of atmospheric pressure and ice drift for the early 1990s were shifted counterclockwise 40°-60° from earlier patterns. The shift in atmospheric circulation seems related to the Arctic Oscillation in the Northern Hemisphere atmospheric pressure pattern. The changes in the ocean circulation, ice drift, air temperatures, and permafrost can be explained as responses to the Arctic Oscillation, as can changes in air temperatures over the Russian Arctic.

Recent changes in arctic sea ice: The interplay between ice dynamics and thermodynamics

Zhang, J., D.A. Rothrock, and M. Steele, "Recent changes in arctic sea ice: The interplay between ice dynamics and thermodynamics," J. Climate, 13, 3099-3114, 2000.

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1 Sep 2000

It is well established that periods of high North Atlantic oscillation (NAO) index are characterized by a weakening of the surface high pressure and surface anticyclone in the Beaufort Sea and the intensification of the cyclonic circulation in the eastern Arctic Ocean. The response of Arctic sea ice to these atmospheric changes has been studied with a thickness distribution sea-ice model coupled to an ocean model. During a period of high NAO, 1989–96, the model shows a substantial reduction of ice advection into the eastern Arctic from the Canada Basin, and an increase of ice export through Fram Strait, both of which tend to deplete thick ice in the eastern Arctic Ocean and enhance it in the western Arctic, in an uneven dipolar pattern we call the East–West Arctic Anomaly Pattern (EWAAP). From the period 1979–88 with a lower-NAO index to the period 1988–96 with a high-NAO index, the simulated ice volume in the eastern Arctic drops by about a quarter, while that in the western Arctic increases by 16%. Overall, the Arctic Ocean loses 6%. The change from 1987 to 1996 is even larger — a loss of some 20% in ice volume for the whole Arctic. Both the model and satellite data show a significant reduction in ice extent in the eastern Arctic and in the Arctic Ocean as a whole.

There are corresponding changes in open water and therefore in ice growth, which tend to moderate the anomaly, and in lateral melting, which tends to enhance the anomaly. During the high NAO and strong EWAAP period, 1989%u201396, the eastern (western) Arctic has more (less) open water and enhanced (reduced) winter ice growth, so ice growth stabilizes the ice cover. On the other hand, the increased (decreased) open water enhances (reduces) summer melt by lowering (increasing) albedo in the eastern (western) Arctic. The nonlinearity of ice%u2013 albedo feedback causes the increased summer melt in the eastern Arctic to dominate the thermodynamic response and to collaborate with the ice advection pattern to enhance the EWAAP during high NAO.

Sea ice growth, melt and modeling: A survey

Steele, M., and G. Flato, "Sea ice growth, melt and modeling: A survey," The Freshwater Budget of the Arctic Ocean, edited by E.L. Lewis, 549-587 (NATO Advanced Research Workshop Series, Kluwer, Dordrecht, 2000).

15 Jan 2000

In The News

Seattle climate scientists spread word on warming, skip politics

The Seattle Times, Jerry Large

Climate scientists at the University of Washington want to talk more about their work because it and public policy are intertwined. They stick to the science side of the equation, which they want the rest of us to understand better so that we can make informed decisions about climate change.

12 Jan 2017

Cyclone did not cause 2012 record low for Arctic sea ice

UW News and Information, Hannah Hickey

"The Great Arctic Cyclone of August 2012," is thought by some to have led to the historic sea ice minimum reached in mid-September 2013. UW research suggests otherwise.

31 Jan 2013

Study finds arctic cyclone had insignificant impact on 2012 ice retreat

The New York Times, Andrew C. Revkin

A new modeling study by the Applied Physics Laboratory at the University of Washington, replaying last summer%u2019s Arctic Ocean ice conditions with and without the storm, shows that the short-term influence of all that ice churning probably played almost no role in the final ice retreat in September.

31 Jan 2013

More News Items

Arctic sea ice: Claims it has recovered miss the big picture

The Washington Post, Jason Samenow and Brian Jackson

Perhaps you've heard Arctic sea ice extent has fully recovered after nearly setting record low levels in September, 2011. Sea ice extent is a one-dimensional measure of Arctic ice. Sea ice volume, which is estimated each month at the University of Washington, shows levels well below normal.

16 May 2012

Arctic ice hits second-lowest level, US scientists say

BBC News

Sea ice cover in the Arctic in 2011 has passed its annual minimum, reaching the second-lowest level since satellite records began, US scientists say.

16 Sep 2011

NSIDC: Arctic sea ice extent second lowest; NOAA: 8th warmest August globally

Washington Post, James Samenow

While NSIDC's estimate of the minimum extent is second lowest on record, some instruments/algorithms are suggesting a new record low. And University of Washington's estimate for Arctic sea ice volume - which takes into account the ice thickness - is lowest on record.

15 Sep 2011

Arctic sea ice volume reaches record low for second straight year

Washington Post, James Samenow

Arctic sea ice continues a long-term melting trend, setting new record lows for both volume and extent. The University of Washington estimates August sea ice volume was 62% below the 1979-2010 average.

14 Sep 2011

Extent of Arctic summer sea ice at record low level

Christian Science Monitor, Pete Spotts

Researchers at the University of Washington's Polar Science Center note that in 2010 the volume of summer sea ice fell to a record low. Volume takes into account ice thickness, as well as extent.

10 Sep 2011

July Arctic sea ice melts to record low extent, volume

The Washington Post, Jason Samenow

The impacts of a sweltering July extended well beyond the eastern two-thirds of the continental U.S. Both the extent and volume of ice in the Arctic were lowest on record for the month according to data and estimates from the National Snow and Ice Data Center and APL-UW's Polar Science Center.

8 Aug 2011

Narwhals transmit climate data from Arctic seas

Nature News, Lucas Laursen

Marine mammals armed with thermometers return temperature readings from icy Baffin Bay.

28 Oct 2010

Ten climate indicators in new report point to marked warming in last 30 years

UW Today, Sandra Hines

A NOAA climate report just out, that's different from other climate publications because it's based on observed data and not computer models, says 10 climate indicators all point to marked warming during the past three decades.

5 Aug 2010

Arctic sea ice rebounds some in 2009, but still low, new report says

The Oregonian, Scott Learn

Sea surface temperatures in the Arctic this season remained higher than normal, but slightly lower than the past two years, according to data from Oceanographer Mike Steele. The cooler conditions, which resulted largely from cloudy skies during late summer, slowed ice loss compared with the past two years.

7 Oct 2009

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