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Matthew Alkire

Senior Oceanographer

Email

malkire@apl.washington.edu

Phone

206-897-1623

Department Affiliation

Polar Science Center

Education

B.S. Marine Sciences, Richard Stockton College of New Jersey, 2003

M.S. Chemical Oceanography, Florida Institute of Technology, 2005

Ph.D. Oceanography, Oregon State University, 2010

Publications

2000-present and while at APL-UW

Tracing sources of freshwater contributions to first-year sea ice in Svalbard fjords

Alkire, M.B., F. Nilsen, E. Falck, J. Søreide, and T.M. Gabrielsen, "Tracing sources of freshwater contributions to first-year sea ice in Svalbard fjords," Cont. Shelf. Res., 101, 85-97, doi:10.1016/j.csr.2015.04.003, 2015.

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1 Jun 2015

Salinity, δ18O, and total alkalinity were determined from sea ice cores collected from various fjords (Billefjorden, Tempelfjorden, Raudfjorden, Rijpfjorden, and Palanderbukta) around Spitsbergen and Nordaustlandet, Svalbard between February and April 2013. The data were used to determine whether ice cores could be used to quantitatively evaluate contributions of meteoric water (glacial meltwater, river runoff, and precipitation) to the fjords instead of traditional methods that rely on data collected from the water column where brine introduced during sea ice formation can complicate interpretation. The majority of the cores exhibited only small contributions (≤5%) of meteoric water ice compared to that derived from seawater; however, cores collected close to the front of Tunabreen, a tidewater glacier located at the head of Tempelfjorden, contained a significant contribution (36%) of meteoric water ice. The shape of the vertical δ18O profiles, as well as excess total alkalinities (relative to salinity) from the Tempelfjorden cores suggested that the source of this meteoric water was subglacial meltwater discharged from Tunabreen during fall and/or winter. Although cores were also collected close to the front of Nordenskiöldbreen (a tidewater glacier in Billefjorden), these did not exhibit a large meltwater influence. We speculate that the combination of the 2004 surge and subsequent retreat of Tunabreen, combined with the cyclonic circulation pattern of warm Atlantic waters that intruded into the Isfjorden system in mid-January of 2012 might have played a role in the apparently larger meltwater contribution to Tempelfjorden. Increasing Atlantic water temperatures in the West Spitsbergen Current and larger and/or more frequent intrusion of these waters into Isfjorden reduces winter sea ice growth and can thereby aid in the melt of tidewater glaciers (during summer and winter months). These interactions have important implications on glacier flow and deserve further study.

Variability in the meteoric water, sea-ice melt, and Pacific water contributions to the central Arctic Ocean, 2000–2014

Alkire, M.B., J. Morison, and R. Andersen, "Variability in the meteoric water, sea-ice melt, and Pacific water contributions to the central Arctic Ocean, 2000–2014," J. Geophys. Res., 120, 1573-1598, doi:10.1002/2014JC010023, 2015.

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12 Mar 2015

Fourteen years (2000–2014) of bottle chemistry data collected during the North Pole Environmental Observatory were compiled to examine variations in the composition of freshwater (meteoric water, net sea-ice meltwater, and Pacific water) over mixed layer of the Central Arctic Ocean. In addition to significant spatial and interannual variability, there was a general decrease in meteoric water (MW) fractions at the majority of stations reoccupied over the duration of the program that was approximately balanced by a concomitant increase in freshwater from sea-ice melt (SIM FW) between 2000 and 2012. Inventories (0–120 m) of MW and SIM FW computed using available data between 2005 and 2012 exhibited similar variations over the study area, allowing for first-order estimates of the mean annual changes in MW (–389±194 km3 yr-1) and SIM FW (292±97 km3 yr-1) for the Central Arctic region. These mean annual changes were attributed to the diversion of Siberian river runoff to the Beaufort Gyre and the overall reduction of sea ice volume across the Arctic, respectively. In addition to this lower-frequency variability, spatial gradients and interannual variations in MW, SIM FW, and Pacific water contributions to specific locations were attributed to shifts in the Transpolar Drift that advects waters of eastern and western Arctic origin through the study area.

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.

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

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

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1 Jun 2012

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

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.

Sensor-based profiles of the NO parameter in the central Arctic and southern Canada Basin: New insights regarding the cold halocline

Alkire, M.B., K.K. Falkner, J. Morison, R.W. Collier, C.K. Guay, R.A. Desiderio, I.G. Rigor, and M. McPhee, "Sensor-based profiles of the NO parameter in the central Arctic and southern Canada Basin: New insights regarding the cold halocline," Deep-Sea Res. Part I, 57, 1432-1443, doi:10.1016/j.dsr.2010.07.011, 2010.

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1 Nov 2010

Here we report the first optical, sensor-based profiles of nitrate from the central Makarov and Amundsen and southern Canada basins of the Arctic Ocean. These profiles were obtained as part of the International Polar Year program during spring 2007 and 2008 field seasons of the North Pole Environmental Observatory (NPEO) and Beaufort Gyre Exploration Program (BGEP). These nitrate data were combined with in-situ, sensor-based profiles of dissolved oxygen to derive the first high-resolution vertical NO profiles to be reported for the Arctic Ocean.

The focus of this paper is on the halocline layer that insulates sea ice from Atlantic water heat and is an important source of nutrients for marine ecosystems within and downstream of the Arctic. Previous reports based on bottle data have identified a distinct lower halocline layer associated with an NO minimum at about S=34.2 that was proposed to be formed initially in the Nansen Basin and then advected downstream. Greater resolution afforded by our data reveal an even more pronounced NO minimum within the upper, cold halocline of the Makarov Basin. Thus a distinct lower salinity source ventilated the Makarov and not the Amundsen Basin. In addition, a larger Eurasian River water influence overlies this halocline source in the Makarov. Observations in the southern Canada Basin corroborate previous studies confirming multiple lower halocline influences including diapycnal mixing between Pacific winter waters and Atlantic-derived lower halocline waters, ventilation via brine formation induced in persistent openings in the ice, and cold, O2-rich lower halocline waters originating in the Eurasian Basin. These findings demonstrate that continuous sensing of chemical properties promises to significantly advance understanding of the maintenance and circulation of the halocline.

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.

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center
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