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  • 1
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    Methane and nitrous oxide distributions across the North American Arctic Ocean during summer 2015 (2017)
    American Geophysical Union
    In:  EPIC3Journal of Geophysical research: Ocean, American Geophysical Union, 122, pp. 1-18
    Details
    Publication Date: 2017-11-12
    Description: We collected Arctic Ocean water column samples for methane (CH4) and nitrous oxide (N2O) analysis on three separate cruises in the summer and fall of 2015, covering a ~10,000 km transect from the Bering Sea to Baffin Bay. This provided a three-dimensional view of CH4 and N2O distributions across contrasting hydrographic environments, from the oligotrophic waters of the deep Canada Basin and Baffin Bay, to the productive shelves of the Bering and Chukchi Seas. Percent saturation relative to atmospheric equilibrium ranged from 30-800% for CH4 and 75-145% for N2O, with the highest concentrations of both gases occurring in the northern Chukchi Sea. Nitrogen cycling in the shelf sediments of the Bering and Chukchi Seas likely constituted the major source of N2O to the water column, and the resulting high N2O concentrations were transported across the Arctic Ocean in eastward-flowing water masses. Methane concentrations were more spatially heterogeneous, reflecting a variety of localized inputs, including likely sources from sedimentary methanogenesis and sea ice processes. Unlike N2O, CH4 was rapidly consumed through microbial oxidation in the water column, as shown by the 13C enrichment of CH4 with decreasing concentrations. For both CH4 and N2O, sea-air fluxes were close to neutral, indicating that our sampling region was neither a major source nor sink of these gases. Our results provide insight into the factors controlling the distribution of CH4 and N2O in the North American Arctic Ocean, and an important baseline data set against which future changes can be assessed.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
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    The rapid response of the Canada Basin to climate forcing : from bellwether to alarm bells (2011)
    Oceanography Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Oceanography Society, 2011. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 24 no. 3 (2011): 146–159, doi:10.5670/oceanog.2011.66.
    Description: Sea ice extent in the Arctic Ocean diminished significantly during the first decade of the 2000s, most particularly in the Canada Basin where the loss of both multiyear and first-year ice was greater than in the other three subbasins. Using data collected during basin-wide surveys conducted from 2003–2010 together with data collected during the 1990s and 2000s at one station in the southern Canada Basin, we investigate the response of the Canada Basin water column to this significant decrease in ice cover. Changes were evident from the surface down to the Atlantic layer: some changes were the result of Beaufort Gyre forcing on regional processes, others were the result of Arctic Ocean atmospheric forcing on a hemispheric scale and large-scale advection. These changes have troubling consequences for the ecosystem.
    Description: We acknowledge support from Fisheries and Oceans Canada, the US National Science Foundation Office of Polar Programs (grant OPP-0424864), and the Canadian International Polar Year office.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
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    The 1995 Georges Bank Stratification Study and moored array measurements (2005)
    Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-25
    Description: The 1995 Geoges Bank Stratification Study (GBSS) was the first intensive process study conducted as part of the U.S. GLOBEC Northwest Atlantic/Georges Bank field program. The GBSS was designed to investigate the physical processes which control the seasonal development of stratification along the southern flank of Georges Bank during spring and summer. Past work suggested that during this period, larval cod and haddock tended to aggregate to the thermocline on the southern flank where higher concentrations of their copepod prey were found. A moored array was deployed as part of GBSS to observe the onset and evolution of sesonal stratification over the southern flank with sufficient vertical and horizontal resolution that key physical processes could be identified and quantified. Moored current, temperature, and conductivity (salinity) measurements were made at three sites along the southern flank, one on the crest, and one on the northeast peak of the bank. Moored surface meteorological measurements were also made at one southern flank site to determine the surface wind stress and heat and moisture fluxes. The oceanographic and meteorological data collected with the GBSS array during January-August 1995 are presented in this report. Meteorological data collected on National Data Buoy Center environmental buoys 44011 (Georges Bank), 44008 (Nantucket Shoals), and 44005 (Gulf of Maine) are included in this report for completeness and comparison with the GBSS southern flank meteorological measurements.
    Description: Funding was provided by the National Science Foundation under Grant Numbers OCE-98-06379 and OCE-98-06445.
    Keywords: U.S. GLOBEC ; Moored array ; Parizeau (Ship) Cruise PAR94-018 ; Parizeau (Ship) Cruise PAR95-010 ; Endeavor (Ship: 1976-) Cruise EN256 ; Endeavor (Ship: 1976-) Cruise EN259 ; Endeavor (Ship: 1976-) Cruise EN260 ; Endeavor (Ship: 1976-) Cruise EN262 ; Endeavor (Ship: 1976-) Cruise EN269 ; Endeavor (Ship: 1976-) Cruise EN271 ; Endeavor (Ship: 1976-) Cruise EN274 ; Seward Johnson (Ship) Cruise SJ95-04 ; Seward Johnson (Ship) Cruise SJ95-06 ; Seward Johnson (Ship) Cruise SJ95-08
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
    Format: 4846761 bytes
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  • 4
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    Beaufort Gyre freshwater reservoir : state and variability from observations (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 114 (2009): C00A10, doi:10.1029/2008JC005104.
    Description: We investigate basin-scale mechanisms regulating anomalies in freshwater content (FWC) in the Beaufort Gyre (BG) of the Arctic Ocean using historical observations and data collected in 2003–2007. Specifically, the mean annual cycle and interannual and decadal FWC variability are explored. The major cause of the large FWC in the BG is the process of Ekman pumping (EP) due to the Arctic High anticyclonic circulation centered in the BG. The mean seasonal cycle of liquid FWC is a result of interplay between the mechanical (EP) and thermal (ice transformations) factors and has two peaks. One peak occurs around June–July when the sea ice thickness reaches its minimum (maximum ice melt). The second maximum is observed in November–January when wind curl is strongest (maximum EP) and the salt input from the growing ice has not yet reached its maximum. Interannual changes in FWC during 2003–2007 are characterized by a strong positive trend in the region varying by location with a maximum of approximately 170 cm a−1 in the center of EP influenced region. Decadal FWC variability in the period 1950–2000 is dominated by a significant change in the 1990s forced by an atmospheric circulation regime change. The center of maximum FWC shifted to the southeast and appeared to contract in area relative to the pre-1990s climatology. In spite of the areal reduction, the spatially integrated FWC increased by over 1000 km3 relative to climatology.
    Description: The funding for Andrey Proshutinsky, Richard Krishfield, John Toole, and Mary-Louise Timmermans (partial financial support of logistics, hydrographic observations on the board of Canadian icebreaker, and full financial coverage of all mooring instrumentation) was provided by the National Science Foundation (under grants ARC- 0806115, ARC-0631951, and ARC-0806306) and Woods Hole Oceanographic Institution internal funding.
    Keywords: Beaufort Gyre oceanography ; Freshwater balance ; Circulation and water masses
    Repository Name: Woods Hole Open Access Server
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  • 5
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    Rates of summertime biological productivity in the Beaufort Gyre : a comparison between the low and record-low ice conditions of August 2011 and 2012 (2015)
    Elsevier
    Details
    Publication Date: 2022-05-25
    Description: © The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Marine Systems 147 (2015): 29-44, doi:10.1016/j.jmarsys.2014.04.006.
    Description: The Arctic Ocean is changing rapidly as the global climate warms but it is not well known how these changes are affecting biological productivity and the carbon cycle. Here we study the Beaufort Gyre region of the Canada Basin in August and use the large reduction in summertime sea ice extent from 2011 to 2012 to investigate potential impacts of climate warming on biological productivity. We use the gas tracers O2/Ar and triple oxygen isotopes to quantify rates of net community production (NCP) and gross oxygen production (GOP) in the gyre. Comparison of the summer of 2011 with the summer of 2012, the latter of which had record low sea ice coverage, is relevant to how biological productivity might change in a seasonally ice-free Arctic Ocean. We find that, in the surface waters measured here, GOP in 2012 is significantly greater than in 2011, with the mean basin-wide 2012 GOP = 38 ± 3 mmol O2 m− 2 d− 1 whereas in 2011, mean basin GOP = 16 ± 5 mmol O2 m− 2 d− 1. We hypothesize that this is because the lack of sea ice and consequent increase in light penetration allows photosynthesis to increase in 2012. However, despite the increase in GOP, NCP is the same in the two years; mean NCP in 2012 is 3.0 ± 0.2 mmol O2 m− 2 y− 1 and in 2011 is 3.1 ± 0.2 mmol O2 m− 2 y− 1. This suggests that the heterotrophic community (zooplankton and/or bacteria) increased its activity as well and thus respired the additional carbon produced by the increased photosynthetic production. In both years, stations on the shelf had GOP 3 to 5 times and NCP 2 to 10 times larger than the basin stations. Additionally, we show that in 2011, the NCP/GOP ratio is smallest in regions with highest ice cover, suggesting that the microbial loop was more efficient at recycling carbon in regions where the ice was just starting to melt. These results highlight that although satellite chlorophyll records show, and many models predict, an increase in summertime primary production in the Arctic Basin as it warms, the net amount of carbon processed by the biological pump during summer may not change as a function of ice cover. Thus, a rapid reduction in summertime ice extent may not change the net community productivity or carbon balance in the Beaufort Gyre.
    Description: We thank our funding sources: the National Science Foundation (PLR 1304406, PLR-0856531) and the support of Fisheries and Oceans Canada.
    Keywords: Arctic Ocean ; Canada Basin ; Beaufort Gyre ; Gross production ; Net community production
    Repository Name: Woods Hole Open Access Server
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  • 6
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    Freshwater and its role in the Arctic Marine System : sources, disposition, storage, export, and physical and biogeochemical consequences in the Arctic and global oceans (2016)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Geophysical Research: Biogeosciences 121 (2016): 675-717, doi:10.1002/2015JG003140.
    Description: The Arctic Ocean is a fundamental node in the global hydrological cycle and the ocean's thermohaline circulation. We here assess the system's key functions and processes: (1) the delivery of fresh and low-salinity waters to the Arctic Ocean by river inflow, net precipitation, distillation during the freeze/thaw cycle, and Pacific Ocean inflows; (2) the disposition (e.g., sources, pathways, and storage) of freshwater components within the Arctic Ocean; and (3) the release and export of freshwater components into the bordering convective domains of the North Atlantic. We then examine physical, chemical, or biological processes which are influenced or constrained by the local quantities and geochemical qualities of freshwater; these include stratification and vertical mixing, ocean heat flux, nutrient supply, primary production, ocean acidification, and biogeochemical cycling. Internal to the Arctic the joint effects of sea ice decline and hydrological cycle intensification have strengthened coupling between the ocean and the atmosphere (e.g., wind and ice drift stresses, solar radiation, and heat and moisture exchange), the bordering drainage basins (e.g., river discharge, sediment transport, and erosion), and terrestrial ecosystems (e.g., Arctic greening, dissolved and particulate carbon loading, and altered phenology of biotic components). External to the Arctic freshwater export acts as both a constraint to and a necessary ingredient for deep convection in the bordering subarctic gyres and thus affects the global thermohaline circulation. Geochemical fingerprints attained within the Arctic Ocean are likewise exported into the neighboring subarctic systems and beyond. Finally, we discuss observed and modeled functions and changes in this system on seasonal, annual, and decadal time scales and discuss mechanisms that link the marine system to atmospheric, terrestrial, and cryospheric systems.
    Description: World Climate Research Program-Climate and Cryosphere (WCRP-CliC); Arctic Monitoring and Assessment Program (AMAP) International Arctic Science Committee (IASC); Norwegian Ministries of Environment and of Foreign Affairs; Swedish Secretariat for Environmental Earth System Sciences (SSEESS); Swedish Polar Research Secretariat; NSF Grant Numbers: OCE 1130008, 1249133, AON-1203473, AON-1338948, OCE 1434041; Polar Research Programme of the Norwegian Research Council Grant Number: 226415
    Keywords: Arctic ; Oceans ; Circulation ; Freshwater ; Carbon cycle ; Acidification
    Repository Name: Woods Hole Open Access Server
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  • 7
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    The adjustment of barotropic currents at the shelf break to a sharp bend in the shelf topography (2012)
    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-25
    Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1996
    Description: During January-March, Scotian Shelf water has been observed to flow episodically from the southwestern Scotian Shelf directly across the Northeast Channel to Georges Bank. The possible factors that allow Scotian Shelf water to break the topographic constraint presented by the Northeast Channel and flow directly to Georges Bank are considered. As a simple analog to the flow over the southwestern Scotian Shelf near the Northeast Channel, the adjustment of a barotropic current near a shelf-break to a sharp bend in the shelf topography is studied numerically. For parameters within the oceanographic range, the adjustment to the bend is smooth and steady with no eddies shed at the corner. The vorticity dynamics allow a balance between the vortex stretching in the flow and the curvature in the flow. This is possible since the bend is a right-hand one facing downstream, a similar balance not being possible for a left-hand bend, in which case eddy formation is likely. A simple model of this balance clarifies the vorticity dynamics and provides the scaling rc = √eL/0.765 for any streamline in the flow, where rc is the radius of curvature at the corner, E = u0/fL and L = h0/b, where uo is the initial speed, f the coriolis parameter, h0 the initial depth and b the bottom slope. These results show that other factors such as stratification, wind stress, and time-dependent inflow must play a role in any flow across the Northeast Channel.
    Description: I am very grateful to the US-GLOBEC program for providing the funding for this study (N.S.F. grant OCE-9313671).
    Keywords: Ocean currents
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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  • 8
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    The Effect of Sea Ice on Tidal Propagation in the Kitikmeot Sea, Canadian Arctic Archipelago (2021)
    In:  EPIC3Journal of Geophysical Research: Oceans, 126(5), ISSN: 2169-9275
    Details
    Publication Date: 2022-01-31
    Description: The tides in the Kitikmeot Sea, in the southern Canadian Arctic Archipelago, are found to be heavily influenced by seasonal sea-ice formation and blocking in a strait. Data from a moored current profiler in Dease Strait exhibit strong tidal damping during wintertime seasonal sea-ice cover, with 50%– 60% reduction in tidal elevation and 65% reduction in tidal velocities. We used a 3D unstratified barotropic numerical tidal model of the region to show that the observed wintertime tidal damping likely requires both high sea-ice friction and a partial sea-ice blockage in Victoria Strait (VS), the eastern gateway of the Kitikmeot Sea, where tidal-induced ridging causes thick, rough ice to accumulate over its shallow sill. Our analysis of the model shows different dynamics for the M2 and K1 tides. Both tidal constituents are dominated by the Atlantic tides entering through VS. Overall, ∼90% of the M2 tidal energy entering VS does not reach Dease Strait because, in addition to dissipation in VS (∼25%), it is significantly diverted into adjoining bays and around an amphidrome in eastern Queen Maud Gulf (∼65%). In contrast, the smaller K1 tide is less diverted into the subsidiary channels, after ∼20% dissipation in VS and only ∼25% in adjoining bays, it propagates far into the region and is amplified due to resonance in Dease Strait and Coronation Gulf, resulting in larger tidal height than the M2 tide in Coronation Gulf.
    Repository Name: EPIC Alfred Wegener Institut
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  • 9
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    Mechanisms of Pacific Summer Water variability in the Arctic's Central Canada Basin (2015)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Geophysical Research: Oceans 119 (2014): 7523–7548, doi:10.1002/2014JC010273.
    Description: Pacific Water flows northward through Bering Strait and penetrates the Arctic Ocean halocline throughout the Canadian Basin sector of the Arctic. In summer, Pacific Summer Water (PSW) is modified by surface buoyancy fluxes and mixing as it crosses the shallow Chukchi Sea before entering the deep ocean. Measurements from Ice-Tethered Profilers, moorings, and hydrographic surveys between 2003 and 2013 reveal spatial and temporal variability in the PSW component of the halocline in the Central Canada Basin with increasing trends in integrated heat and freshwater content, a consequence of PSW layer thickening as well as layer freshening and warming. It is shown here how properties in the Chukchi Sea in summer control the temperature-salinity properties of PSW in the interior by subduction at isopycnals that outcrop in the Chukchi Sea. Results of an ocean model, forced by idealized winds, provide support to the mechanism of surface ocean Ekman transport convergence maintaining PSW ventilation of the halocline.
    Description: Funding was provided by the National Science Foundation Division of Polar Programs under award 1107623, 1313614, 1107412, 1107277, 1303644, and 0938137 and by Yale University. ICMMG model development was supported by the Russian Fund for Basic Research (14-05-00730A).
    Keywords: Arctic Ocean ; Halocline ventilation ; Pacific Water
    Repository Name: Woods Hole Open Access Server
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  • 10
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    Changes in the arctic ocean carbon cycle with diminishing ice cover (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in DeGrandpre, M., Evans, W., Timmermans, M., Krishfield, R., Williams, B., & Steele, M. Changes in the arctic ocean carbon cycle with diminishing ice cover. Geophysical Research Letters, 47(12), (2020): e2020GL088051, doi:10.1029/2020GL088051.
    Description: Less than three decades ago only a small fraction of the Arctic Ocean (AO) was ice free and then only for short periods. The ice cover kept sea surface pCO2 at levels lower relative to other ocean basins that have been exposed year round to ever increasing atmospheric levels. In this study, we evaluate sea surface pCO2 measurements collected over a 6‐year period along a fixed cruise track in the Canada Basin. The measurements show that mean pCO2 levels are significantly higher during low ice years. The pCO2 increase is likely driven by ocean surface heating and uptake of atmospheric CO2 with large interannual variability in the contributions of these processes. These findings suggest that increased ice‐free periods will further increase sea surface pCO2, reducing the Canada Basin's current role as a net sink of atmospheric CO2.
    Description: This research was made possible by grants from the NSF Arctic Observing Network program (ARC‐1107346, PLR‐1302884, PLR‐1504410, and OPP‐1723308). In addition, M. S. was supported by ONR (Grant 00014‐17‐1‐2545), NASA (Grant NNX16AK43G), and NSF (Grants PLR‐1503298 and OPP‐1751363).
    Keywords: Arctic Ocean ; Ice concentration ; Seawater CO2 ; Interannual variability ; Canada Basin ; Shipboard CO2 measurements
    Repository Name: Woods Hole Open Access Server
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