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  • Articles  (40)
  • Arctic Ocean  (40)
  • American Geophysical Union  (20)
  • John Wiley & Sons  (20)
  • Irkutsk : Ross. Akad. Nauk, Sibirskoe Otd., Inst. Zemnoj Kory
  • Krefeld : Geologischer Dienst Nordhein-Westfalen
  • Periodicals Archive Online (PAO)
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  • Articles  (40)
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  • 1
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    Sediments in sea ice drive the Canada Basin surface Mn maximum: insights from an Arctic Mn Ocean model (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-02-28
    Description: Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 36(8), (2022): e2022GB007320, https://doi.org/10.1029/2022GB007320.
    Description: Biogeochemical cycles in the Arctic Ocean are sensitive to the transport of materials from continental shelves into central basins by sea ice. However, it is difficult to assess the net effect of this supply mechanism due to the spatial heterogeneity of sea ice content. Manganese (Mn) is a micronutrient and tracer which integrates source fluctuations in space and time while retaining seasonal variability. The Arctic Ocean surface Mn maximum is attributed to freshwater, but studies struggle to distinguish sea ice and river contributions. Informed by observations from 2009 IPY and 2015 Canadian GEOTRACES cruises, we developed a three-dimensional dissolved Mn model within a 1/12° coupled ocean-ice model centered on the Canada Basin and the Canadian Arctic Archipelago (CAA). Simulations from 2002 to 2019 indicate that annually, 87%–93% of Mn contributed to the Canada Basin upper ocean is released by sea ice, while rivers, although locally significant, contribute only 2.2%–8.5%. Downstream, sea ice provides 34% of Mn transported from Parry Channel into Baffin Bay. While rivers are often considered the main source of Mn, our findings suggest that in the Canada Basin they are less important than sea ice. However, within the shelf-dominated CAA, both rivers and sediment resuspension are important. Climate-induced disruption of the transpolar drift may reduce the Canada Basin Mn maximum and supply downstream. Other micronutrients found in sediments, such as Fe, may be similarly affected. These results highlight the vulnerability of the biogeochemical supply mechanisms in the Arctic Ocean and the subpolar seas to climatic changes.
    Description: This work was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC) Climate Change and Atmospheric Research Grant: GEOTRACES (RGPCC 433848-12) and VITALS (RGPCC 433898), an NSERC Discovery Grant (RGPIN-2016-03865) to SEA, and by the University of British Columbia through a four year fellowship to BR. Computing resources were provided by Compute Canada (RRG 2648 RAC 2019, RRG 2969 RAC 2020, and RRG 1541 RAC 2021).
    Keywords: GEOTRACES ; Arctic Ocean ; Trace elements ; Canadian Arctic Archipelago ; Ocean modeling ; Micronutrients
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  • 2
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    Radium inputs into the Arctic Ocean from rivers a basin‐wide estimate (2023)
    American Geophysical Union
    Details
    Publication Date: 2023-03-11
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Bullock, E., Kipp, L., Moore, W., Brown, K., Mann, P., Vonk, J., Zimov, N., & Charette, M. Radium inputs into the Arctic Ocean from rivers a basin‐wide estimate. Journal of Geophysical Research: Oceans, 127(9), (2022): e2022JC018964, https://doi.org/10.1029/2022jc018964.
    Description: Radium isotopes have been used to trace nutrient, carbon, and trace metal fluxes inputs from ocean margins. However, these approaches require a full accounting of radium sources to the coastal ocean including rivers. Here, we aim to quantify river radium inputs into the Arctic Ocean for the first time for 226Ra and to refine the estimates for 228Ra. Using new and existing data, we find that the estimated combined (dissolved plus desorbed) annual 226Ra and 228Ra fluxes to the Arctic Ocean are [7.0–9.4] × 1014 dpm y−1 and [15–18] × 1014 dpm y−1, respectively. Of these totals, 44% and 60% of the river 226Ra and 228Ra, respectively are from suspended sediment desorption, which were estimated from laboratory incubation experiments. Using Ra isotope data from 20 major rivers around the world, we derived global annual 226Ra and 228Ra fluxes of [7.4–17] × 1015 and [15–27] × 1015 dpm y−1, respectively. As climate change spurs rapid Arctic warming, hydrological cycles are intensifying and coastal ice cover and permafrost are diminishing. These river radium inputs to the Arctic Ocean will serve as a valuable baseline as we attempt to understand the changes that warming temperatures are having on fluxes of biogeochemically important elements to the Arctic coastal zone.
    Description: This study was a broad, collaborative effort that would not have been possible without contributions from numerous funding sources, including the National Science Foundation (NSF-0751525, NSF-1736277, NSF-1458305, NSF-1938873, NSF-2048067, NSF-2134865), the NERC-BMBF project CACOON [NE/R012806/1] (UKRI NERC) and BMBF-03F0806A, and an EU Starting Grant (THAWSOME-676982).
    Keywords: Radium isotopes ; Arctic Ocean ; River fluxes
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  • 3
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    Insights into water mass origins in the central Arctic Ocean from in-situ dissolved organic matter fluorescence (2021)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2021. 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: Oceans 126(7), (2021): e2021JC017407, https://doi.org/10.1029/2021JC017407.
    Description: The Arctic Ocean receives a large supply of dissolved organic matter (DOM) from its catchment and shelf sediments, which can be traced across much of the basin's upper waters. This signature can potentially be used as a tracer. On the shelf, the combination of river discharge and sea-ice formation, modifies water densities and mixing considerably. These waters are a source of the halocline layer that covers much of the Arctic Ocean, but also contain elevated levels of DOM. Here we demonstrate how this can be used as a supplementary tracer and contribute to evaluating ocean circulation in the Arctic. A fraction of the organic compounds that DOM consists of fluoresce and can be measured using in-situ fluorometers. When deployed on autonomous platforms these provide high temporal and spatial resolution measurements over long periods. The results of an analysis of data derived from several Ice Tethered Profilers (ITPs) offer a unique spatial coverage of the distribution of DOM in the surface 800 m below Arctic sea-ice. Water mass analysis using temperature, salinity and DOM fluorescence, can clearly distinguish between the contribution of Siberian terrestrial DOM and marine DOM from the Chukchi shelf to the waters of the halocline. The findings offer a new approach to trace the distribution of Pacific waters and its export from the Arctic Ocean. Our results indicate the potential to extend the approach to separate freshwater contributions from, sea-ice melt, riverine discharge and the Pacific Ocean.
    Description: Danish Strategic Research Council for the NAACOS project (grant no. 10-093903), the Danish Center for Marine Research (grant no. 2012-01). C. A. S. has received funding from the Independent Research Fund Denmark Grant No. 9040-00266B. Funding for R.M.W.A. came from the US NSF, Arctic Natural Science program grant 1504469. RG-A has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Grant Agreement No. 839311. ITP93 and part of the work by MH and BR were a contribution to the Helmholtz society strategic investment Frontiers in Arctic Marine monitoring (FRAM). The work of BR is a contribution to the cooperative projects Regional Atlantic Circulation and global Change (RACE) grant #03F0824E funded by the German Ministry of Science and Education (BBMF) and Advective Pathways of nutrients and key Ecological substances in the Arctic (APEAR) grants NE/R012865/1, NE/R012865/2 and #03V01461, part of the Changing Arctic Ocean program, jointly funded by the UKRI Natural Environment Research Council (NERC) and the BMBF. Support for Krishfield was made possible by grants from the NSF Arctic Observing Network program (PLR-1303644 and OPP-1756100).
    Description: 2021-12-27
    Keywords: Arctic Ocean ; CDOM ; DOM ; FDOM ; Fluorescence ; Halocline
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  • 4
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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
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  • 5
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    The transpolar drift as a source of riverine and shelf-derived trace elements to the central Arctic Ocean (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2020. 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: Oceans 125(5), (2020): e2019JC015920, doi:10.1029/2019JC015920.
    Description: A major surface circulation feature of the Arctic Ocean is the Transpolar Drift (TPD), a current that transports river‐influenced shelf water from the Laptev and East Siberian Seas toward the center of the basin and Fram Strait. In 2015, the international GEOTRACES program included a high‐resolution pan‐Arctic survey of carbon, nutrients, and a suite of trace elements and isotopes (TEIs). The cruises bisected the TPD at two locations in the central basin, which were defined by maxima in meteoric water and dissolved organic carbon concentrations that spanned 600 km horizontally and ~25–50 m vertically. Dissolved TEIs such as Fe, Co, Ni, Cu, Hg, Nd, and Th, which are generally particle‐reactive but can be complexed by organic matter, were observed at concentrations much higher than expected for the open ocean setting. Other trace element concentrations such as Al, V, Ga, and Pb were lower than expected due to scavenging over the productive East Siberian and Laptev shelf seas. Using a combination of radionuclide tracers and ice drift modeling, the transport rate for the core of the TPD was estimated at 0.9 ± 0.4 Sv (106 m3 s−1). This rate was used to derive the mass flux for TEIs that were enriched in the TPD, revealing the importance of lateral transport in supplying materials beneath the ice to the central Arctic Ocean and potentially to the North Atlantic Ocean via Fram Strait. Continued intensification of the Arctic hydrologic cycle and permafrost degradation will likely lead to an increase in the flux of TEIs into the Arctic Ocean.
    Description: Funding for Arctic GEOTRACES was provided by the U.S. National Science Foundation, Swedish Research Council Formas, French Agence Nationale de la Recherche and LabexMER, Netherlands Organization for Scientific Research, and Independent Research Fund Denmark. Data from GEOTRACES cruises GN01 (HLY1502) and GN04 (PS94) have been archived at the Biological and Chemical Oceanography Data Management Office (Biological and Chemical Oceanography Data Management Office (BCO‐DMO); https://www.bco-dmo.org/deployment/638807) and PANGAEA (https://www.pangaea.de/?q=PS94&f.campaign%5B%5D=PS94) websites, respectively. The inorganic carbon data are available at the NOAA Ocean Carbon Data System (OCADS; doi:10.3334/CDIAC/OTG.CLIVAR_ARC01_33HQ20150809).
    Description: 2020-10-08
    Keywords: Arctic Ocean ; Transpolar Drift ; trace elements ; carbon ; nutrients ; GEOTRACES]
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  • 6
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    Heat flow in the Western Arctic Ocean (Amerasian Basin) (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2019. 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-Solid Earth 124(8), (2019): 7562-7587, doi: 10.1029/2019JB017587.
    Description: From 1963 to 1973 the U.S. Geological Survey measured heat flow at 356 sites in the Amerasian Basin (Western Arctic Ocean) from a drifting ice island (T‐3). The resulting measurements, which are unevenly distributed on Alpha‐Mendeleev Ridge and in Canada and Nautilus Basins, greatly expand available heat flow data for the Arctic Ocean. Average T‐3 heat flow is ~54.7 ± 11.3 mW/m2, and Nautilus Basin is the only well‐surveyed area (~13% of data) with significantly higher average heat flow (63.8 mW/m2). Heat flow and bathymetry are not correlated at a large scale, and turbiditic surficial sediments (Canada and Nautilus Basins) have higher heat flow than the sediments that blanket the Alpha‐Mendeleev Ridge. Thermal gradients are mostly near‐linear, implying that conductive heat transport dominates and that near‐seafloor sediments are in thermal equilibrium with overlying bottom waters. Combining the heat flow data with modern seismic imagery suggests that some of the observed heat flow variability may be explained by local changes in lithology or the presence of basement faults that channel circulating seawater. A numerical model that incorporates thermal conductivity variations along a profile from Canada Basin (thick sediment on mostly oceanic crust) to Alpha Ridge (thin sediment over thick magmatic units associated with the High Arctic Large Igneous Province) predicts heat flow slightly lower than that observed on Alpha Ridge. This, along with other observations, implies that circulating fluids modulate conductive heat flow and contribute to high variability in the T‐3 data set.
    Description: B.V. Marshall of the U.S. Geological Survey (USGS) was critical to the T‐3 heat flow studies and would have been included as a coauthor on this work if he were not deceased. The original T‐3 heat flow data acquisition program was supported by the USGS and by the Naval Arctic Research Laboratory of the Office of Naval Research. Over the decade of USGS research on T‐3 Ice Island, numerous researchers and technical staff, including B.V. Marshall, P. Twichell, D. Scoboria, J. Tailleur, B. Tailleur, and others, spent months on the island and endured difficult and sometimes dangerous conditions to acquire this data set alongside colleagues from other institutions. Outstanding support from the USGS Menlo Park office, transportation and logistics assistance from other U.S. federal government agencies, Arctic expertise supplied by native Alaskan communities, and collaboration with Lamont researchers made this research program possible. B. Lachenbruch and L. Lawver revived interest in this data set in 2016, and they, along with D. Darby and J. K. Hall, provided ancillary information on T‐3 studies. B. Clarke and M. Arsenault assisted with initial data digitization. We thank M. Jakobsson, R. Saltus, and G. Oakey for providing critical shapefiles and other data and R. Jackson and S. Mukasa for clarification on unpublished information. Reviews by J. Hopper, P. Hart, and W. Jokat improved the manuscript, and V. Atnipp Cross and A. Babb were instrumental in completion of data releases. The USGS's Coastal/Marine Hazards and Resources Program supported C.R. and D.H. between 2016 and 2019, and C.R. used office space provided by the Earth Resources Laboratory at the Massachusetts Institute of Technology during completion of this work. Data in Figure 11 were provided by the U.S. Extended Continental Shelf (ECS) Project. The opinions, findings, and conclusions stated herein are those of the authors and the U.S. Geological Survey, but do not necessarily reflect those of the U.S. ECS Project. Any use of trade, firm, or product name is for descriptive purposes only and does not imply endorsement by the U.S. Government. Digital data, metadata, and supporting plots for T‐3 heat flow, navigation, and radiogenic heat content, along with Lamont gravity and magnetics data, are available from Ruppel et al. (2019), and the original T‐3 expedition report with explanatory metadata can be downloaded from Lachenbruch et al. (2019).
    Keywords: Arctic Ocean ; heat flow ; thermal history ; ice island
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  • 7
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    Analysis of the Beaufort Gyre freshwater content in 2003-2018 (2020)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Proshutinsky, A., Krishfield, R., Toole, J. M., Timmermans, M-L., Williams, W. J., Zimmermann, S., Yamamoto-Kawai, M., Armitage, T. W. K., Dukhovskoy, D., Golubeva, E., Manucharyan, G. E., Platov, G., Watanabe, E., Kikuchi, T., Nishino, S., Itoh, M., Kang, S-H., Cho, K-H., Tateyama, K., & Zhao, J. Analysis of the Beaufort Gyre freshwater content in 2003-2018. Journal of Geophysical Research-Oceans, 124(12), (2019): 9658-9689, doi:10.1029/2019JC015281.
    Description: Hydrographic data collected from research cruises, bottom‐anchored moorings, drifting Ice‐Tethered Profilers, and satellite altimetry in the Beaufort Gyre region of the Arctic Ocean document an increase of more than 6,400 km3 of liquid freshwater content from 2003 to 2018: a 40% growth relative to the climatology of the 1970s. This fresh water accumulation is shown to result from persistent anticyclonic atmospheric wind forcing (1997–2018) accompanied by sea ice melt, a wind‐forced redirection of Mackenzie River discharge from predominantly eastward to westward flow, and a contribution of low salinity waters of Pacific Ocean origin via Bering Strait. Despite significant uncertainties in the different observations, this study has demonstrated the synergistic value of having multiple diverse datasets to obtain a more comprehensive understanding of Beaufort Gyre freshwater content variability. For example, Beaufort Gyre Observational System (BGOS) surveys clearly show the interannual increase in freshwater content, but without satellite or Ice‐Tethered Profiler measurements, it is not possible to resolve the seasonal cycle of freshwater content, which in fact is larger than the year‐to‐year variability, or the more subtle interannual variations.
    Description: National Science Foundation. Grant Numbers: PLR‐1302884,OPP‐1719280, and OPP‐1845877, PLR‐1303644 and OPP‐1756100, OPP‐1756100, PLR‐1303644, OPP‐1845877, OPP‐1719280, PLR‐1302884 Key Program of National Natural Science Foundation of China. Grant Number: 41330960 Global Change Research Program of China. Grant Number: 2015CB953900 Ministry of Education, Korea Japan Aerospace Exploration Agency (JAXA) /Earth Observation Research Center (EORC) Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT) Stanback Postdoctoral Fellowship Russian Foundation for Basic Research. Grant Number: 17‐05‐00382 Presidium of Russian Academy of Sciences HYCOM NOPP. Grant Number: N00014‐15‐1‐2594 DOE. Grant Number: DE‐SC0014378 National Aeronautics and Space Administration Tokyo University of Marine Science and Technology Department of Fisheries and Oceans Canada Woods Hole Oceanographic Institution
    Keywords: Beaufort Gyre ; Arctic Ocean ; Freshwater balance ; Circulation ; Modeling ; Climate change
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  • 8
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    Melt pond conditions on declining arctic sea ice over 1979-2016: Model development, validation, and results (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2018. 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-Oceans, 123(11), (2018): 7983-8003. doi:10.1029/2018JC014298.
    Description: A melt pond (MP) distribution equation has been developed and incorporated into the Marginal Ice‐Zone Modeling and Assimilation System to simulate Arctic MPs and sea ice over 1979–2016. The equation differs from previous MP models and yet benefits from previous studies for MP parameterizations as well as a range of observations for model calibration. Model results show higher magnitude of MP volume per unit ice area and area fraction in most of the Canada Basin and the East Siberian Sea and lower magnitude in the central Arctic. This is consistent with Moderate Resolution Imaging Spectroradiometer observations, evaluated with Measurements of Earth Data for Environmental Analysis (MEDEA) data, and closely related to top ice melt per unit ice area. The model simulates a decrease in the total Arctic sea ice volume and area, owing to a strong increase in bottom and lateral ice melt. The sea ice decline leads to a strong decrease in the total MP volume and area. However, the Arctic‐averaged MP volume per unit ice area and area fraction show weak, statistically insignificant downward trends, which is linked to the fact that MP water drainage per unit ice area is increasing. It is also linked to the fact that MP volume and area decrease relatively faster than ice area. This suggests that overall the actual MP conditions on ice have changed little in the past decades as the ice cover is retreating in response to Arctic warming, thus consistent with the Moderate Resolution Imaging Spectroradiometer observations that show no clear trend in MP area fraction over 2000–2011.
    Description: We gratefully acknowledge the support of the NASA Cryosphere Program (grants NNX15AG68G, NNX17AD27G, and NNX14AH61G), the Office of Naval Research (N00014‐12‐1‐0112), the NSF Office of Polar Programs (PLR‐1416920, PLR‐1603259, PLR‐1602521, and ARC‐1203425), and the Department of Homeland Security (DHS, 2014‐ST‐061‐ML‐0002). The DHS grant is coordinated through the Arctic Domain Awareness Center (ADAC), a DHS Center of Excellence, which conducts maritime research and development for the Arctic region. The views and conclusions in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the DHS. MODIS‐derived MP area data are available at https://icdc.cen.uni‐hamburg.de/1/daten/cryosphere/arctic‐meltponds.html. MP area fraction statistics derived from MEDEA images are available from http://psc.apl.uw.edu/melt‐pond‐data/. Sea ice thickness and snow observations are available at http://psc.apl.washington.edu/sea_ice_cdr. CFS forcing data used to drive MIZMAS are available at https://www.ncdc.noaa.gov/data‐access/model‐data/model‐datasets/climate‐forecast‐system‐version2‐cfsv2.
    Description: 2019-04-18
    Keywords: Arctic Ocean ; sea ice ; melt ponds ; numerical modeling ; climate variability
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  • 9
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    Deepening of the winter mixed layer in the Canada Basin, Arctic Ocean over 2006-2017 (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2019. 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-Oceans 124(7), (2019): 4618-4630, doi: 10.1029/2019JC014940.
    Description: The Arctic Ocean mixed layer interacts with the ice cover above and warmer, nutrient‐rich waters below. Ice‐Tethered Profiler observations in the Canada Basin of the Arctic Ocean over 2006–2017 are used to investigate changes in mixed layer properties. In contrast to decades of shoaling since at least the 1980s, the mixed layer deepened by 9 m from 2006–2012 to 2013–2017. Deepening resulted from an increase in mixed layer salinity that also weakened stratification at the base of the mixed layer. Vertical mixing alone can explain less than half of the observed change in mixed layer salinity, and so the observed increase in salinity is inferred to result from changes in freshwater accumulation via changes to ice‐ocean circulation or ice melt/growth and river runoff. Even though salinity increased, the shallowest density surfaces deepened by 5 m on average suggesting that Ekman pumping over this time period remained downward. A deeper mixed layer with weaker stratification has implications for the accessibility of heat and nutrients stored in the upper halocline. The extent to which the mixed layer will continue to deepen appears to depend primarily on the complex set of processes influencing freshwater accumulation.
    Description: We gratefully acknowledge J. Toole for helpful conversations. S. Cole was supported by the National Science Foundation under grant PLR‐1602926 and J. Stadler by the Woods Hole Oceanographic Institution Summer Student Fellowship program. Profile data are available via the Ice‐Tethered Profiler program website: http://whoi.edu/itp. SSM/I ice concentration data were downloaded from the National Snow and Ice Data Center.
    Description: 2019-12-22
    Keywords: Arctic Ocean ; Mixed layer ; Freshwater
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  • 10
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    Shelf-basin interactions and water mass residence times in the western Arctic Ocean: Insights provided by radium isotopes (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2019. 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-Oceans 124(5), (2019): 3279-3297, doi: 10.1029/2019JC014988.
    Description: Radium isotopes are produced through the decay of thorium in sediments and are soluble in seawater; thus, they are useful for tracing ocean boundary‐derived inputs to the ocean. Here we apply radium isotopes to study continental inputs and water residence times in the Arctic Ocean, where land‐ocean interactions are currently changing in response to rising air and sea temperatures. We present the distributions of radium isotopes measured on the 2015 U.S. GEOTRACES transect in the Western Arctic Ocean and combine this data set with historical radium observations in the Chukchi Sea and Canada Basin. The highest activities of radium‐228 were observed in the Transpolar Drift and the Chukchi shelfbreak jet, signaling that these currents are heavily influenced by interactions with shelf sediments. The ventilation of the halocline with respect to inputs from the Chukchi shelf occurs on time scales of ≤19–23 years. Intermediate water ventilation time scales for the Makarov and Canada Basins were determined to be ~20 and 〉30 years, respectively, while deep water residence times in these basins were on the order of centuries. The radium distributions and residence times described in this study serve as a baseline for future studies investigating the impacts of climate change on the Arctic Ocean.
    Description: We thank the captain and crew of the USCGC Healy (HLY1502) and the chief scientists D. Kadko and W. Landing for coordinating a safe and successful expedition. We thank the members of the pump team, P. Lam, E. Black, S. Pike, X. Yang, and M. Heller for their assistance with sample collection and for their unfailingly positive attitudes during this 65‐day expedition. We also appreciate sampling assistance from P. Aguilar and M. Stephens, and MATLAB assistance from B. Corlett, A. Pacini, P. Lin, and M. Li. The radium data from the HLY1502 expedition are available through the Biological & Chemical Oceanography Data Management Office (https://www.bco‐dmo.org/dataset/718440) and the radium measurements from the SHEBA, AWS‐2000, and SBI expeditions can be found in the supporting information. This work was funded by NSF awards OCE‐1458305 to M.A.C., OCE‐1458424 to W.S.M., and PLR‐1504333 to R.S.P. This research was conducted with Government support under and awarded by a DoD, Air Force Office of Scientific Research, National Defense Science and Engineering Graduate (NDSEG) Fellowship awarded to L.E.K., 32 CFR 168a.
    Description: 2019-10-26
    Keywords: Radium ; Arctic Ocean ; GEOTRACES ; Chukchi shelf
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  • 11
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    Structure, transport, and seasonality of the Atlantic Water boundary current north of Svalbard: Results from a yearlong mooring array (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2019. 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-Oceans 124(3), (2019): 1679-1698, doi:10.1029/2018JC014759.
    Description: The characteristics and seasonality of the Svalbard branch of the Atlantic Water (AW) boundary current in the Eurasian Basin are investigated using data from a six‐mooring array deployed near 30°E between September 2012 and September 2013. The instrument coverage extended to 1,200‐m depth and approximately 50 km offshore of the shelf break, which laterally bracketed the flow. Averaged over the year, the transport of the current over this depth range was 3.96 ± 0.32 Sv (1 Sv = 106 m3/s). The transport within the AW layer was 2.08 ± 0.24 Sv. The current was typically subsurface intensified, and its dominant variability was associated with pulsing rather than meandering. From late summer to early winter the AW was warmest and saltiest, and its eastward transport was strongest (2.44 ± 0.12 Sv), while from midspring to midsummer the AW was coldest and freshest and its transport was weakest (1.10 ± 0.06 Sv). Deep mixed layers developed through the winter, extending to 400‐ to 500‐m depth in early spring until the pack ice encroached the area from the north shutting off the air‐sea buoyancy forcing. This vertical mixing modified a significant portion of the AW layer, suggesting that, as the ice cover continues to decrease in the southern Eurasian Basin, the AW will be more extensively transformed via local ventilation.
    Description: We are grateful to the crew of the R/V Lance for the collection of the data. The U.S. component of A‐TWAIN was funded by the National Science Foundation under grant ARC‐1264098 as well as a grant from the Steven Grossman Family Foundation. The Norwegian component of A‐TWAIN was funded by the “Arctic Ocean” flagship program at the Fram Centre. The data used in this study are available at http://atwain.whoi.edu and data.npolar.no (Sundfjord et al., 2017). The data from Fram Strait are available at https://doi.pangaea.de/10.1594/PANGAEA.853902
    Description: 2019-08-15
    Keywords: Atlantic Water ; Svalbard branch ; A‐TWAIN ; seasonality ; Arctic Ocean ; Fram Strait branch
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  • 12
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    Inorganic carbon and pCO(2) variability during ice formation in the Beaufort Gyre of the Canada Basin. (2019)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in DeGrandpre, M. D., Lai, C., Timmermans, M., Krishfield, R. A., Proshutinsky, A., & Torres, D. Inorganic carbon and pCO(2) variability during ice formation in the Beaufort Gyre of the Canada Basin. Journal of Geophysical Research-Oceans, 124(6), (2019): 4017-4028, doi:10.1029/2019JC015109.
    Description: Solute exclusion during sea ice formation is a potentially important contributor to the Arctic Ocean inorganic carbon cycle that could increase as ice cover diminishes. When ice forms, solutes are excluded from the ice matrix, creating a brine that includes dissolved inorganic carbon (DIC) and total alkalinity (AT). The brine sinks, potentially exporting DIC and AT to deeper water. This phenomenon has rarely been observed, however. In this manuscript, we examine a ~1 year pCO2 mooring time series where a ~35‐μatm increase in pCO2 was observed in the mixed layer during the ice formation period, corresponding to a simultaneous increase in salinity from 27.2 to 28.5. Using salinity and ice based mass balances, we show that most of the observed increases can be attributed to solute exclusion during ice formation. The resulting pCO2 is sensitive to the ratio of AT and DIC retained in the ice and the mixed layer depth, which controls dilution of the ice‐derived AT and DIC. In the Canada Basin, of the ~92 μmol/kg increase in DIC, 17 μmol/kg was taken up by biological production and the remainder was trapped between the halocline and the summer stratified surface layer. Although not observed before the mooring was recovered, this inorganic carbon was likely later entrained with surface water, increasing the pCO2 at the surface. It is probable that inorganic carbon exclusion during ice formation will have an increasingly important influence on DIC and pCO2 in the surface of the Arctic Ocean as seasonal ice production and wind‐driven mixing increase with diminishing ice cover.
    Description: Research Associate Cory Beatty (University of Montana) prepared the CO2 instruments and helped with the mooring deployments and data processing. Pierce Fix (undergraduate intern, University of Montana) helped with the mass balance modeling. The moorings were designed and deployed by personnel at Woods Hole Oceanographic Institution. Michiyo Yamamoto‐Kawai (University of Tokyo) and Marty Davelaar (Institute of Ocean Sciences; IOS) provided the alkalinity and dissolved inorganic carbon data. We thank the captain, officers, crew, and chief scientists (Bill Williams and Sarah Zimmerman, IOS) of the CCGS Louis S. St. Laurent. The data used in this study are available through the U.S. National Science Foundation (NSF) Arctic Data Center (https://arcticdata.io). This research was made possible by grants from the NSF Arctic Observing Network program (ARC‐1107346, PLR‐1302884, PLR‐1504410, and PLR‐1723308).
    Keywords: Sea ice ; Dissolved inorganic carbon ; Carbon cycle ; Solute exclusion ; Partial pressure of CO2 ; Arctic Ocean
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  • 13
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    Radium isotopes across the Arctic Ocean show time scales of water mass ventilation and increasing shelf inputs (2018)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Geophysical Research: Oceans 123 (2018): 4853-4873, doi:10.1029/2018JC013888.
    Description: The first full transarctic section of 228Ra in surface waters measured during GEOTRACES cruises PS94 and HLY1502 (2015) shows a consistent distribution with maximum activities in the transpolar drift. Activities in the central Arctic have increased from 2007 through 2011 to 2015. The increased 228Ra input is attributed to stronger wave action on shelves resulting from a longer ice‐free season. A concomitant decrease in the 228Th/228Ra ratio likely results from more rapid transit of surface waters depleted in 228Th by scavenging over the shelf. The 228Ra activities observed in intermediate waters (〈1,500 m) in the Amundsen Basin are explained by ventilation with shelf water on a time scale of about 15–18 years, in good agreement with estimates based on SF6 and 129I/236U. The 228Th excess below the mixed layer up to 1,500 m depth can complement 234Th and 210Po as tracers of export production, after correction for the inherent excess resulting from the similarity of 228Ra and 228Th decay times. We show with a Th/Ra profile model that the 228Th/228Ra ratio below 1,500 m is inappropriate for this purpose because it is a delicate balance between horizontal supply of 228Ra and vertical flux of particulate 228Th. The accumulation of 226Ra in the deep Makarov Basin is not associated with an accumulation of Ba and can therefore be attributed to supply from decay of 230Th in the bottom sediment. We estimate a ventilation time of 480 years for the deep Makarov‐Canada Basin, in good agreement with previous estimates using other tracers.
    Description: U.S. National Science Foundation Grant Numbers: OCE‐1458305, OCE‐1458424; US NSF Grant Number: OCE‐1433922
    Keywords: Radium‐228 ; Thorium‐228 ; Arctic Ocean ; Transpolar drift ; GEOTRACES
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  • 14
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    Variability and redistribution of heat in the Atlantic Water boundary current north of Svalbard (2018)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Geophysical Research: Oceans 123 (2018): 6373-6391, doi:10.1029/2018JC013814.
    Description: We quantify Atlantic Water heat loss north of Svalbard using year‐long hydrographic and current records from three moorings deployed across the Svalbard Branch of the Atlantic Water boundary current in 2012–2013. The boundary current loses annually on average 16 W m−2 during the eastward propagation along the upper continental slope. The largest vertical fluxes of 〉100 W m−2 occur episodically in autumn and early winter. Episodes of sea ice imported from the north in November 2012 and February 2013 coincided with large ocean‐to‐ice heat fluxes, which effectively melted the ice and sustained open water conditions in the middle of the Arctic winter. Between March and early July 2013, a persistent ice cover‐modulated air‐sea fluxes. Melting sea ice at the start of the winter initiates a cold, up to 100‐m‐deep halocline separating the ice cover from the warm Atlantic Water. Semidiurnal tides dominate the energy over the upper part of the slope. The vertical tidal structure depends on stratification and varies seasonally, with the potential to contribute to vertical fluxes with shear‐driven mixing. Further processes impacting the heat budget include lateral heat loss due to mesoscale eddies, and modest and negligible contributions of Ekman pumping and shelf break upwelling, respectively. The continental slope north of Svalbard is a key example regarding the role of ocean heat for the sea ice cover. Our study underlines the complexity of the ocean's heat budget that is sensitive to the balance between oceanic heat advection, vertical fluxes, air‐sea interaction, and the sea ice cover.
    Description: Arctic Ocean program at the FRAM-High North Research Centre for Climate and the environment; National Science Foundation (NSF) Grant Number: ARC-1264098; Polish-Norwegian Research Programme Grant Number: POL-NOR/202006/10/2013; Research Council of Norway Grant Number: 276730; Steven Grossman Family Foundation
    Keywords: Atlantic Water ; Arctic Ocean ; Heat flux ; Nansen Basin ; Boundary current ; A‐TWAIN
    Repository Name: Woods Hole Open Access Server
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  • 15
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    Significance of northeast-trending features in Canada Basin, Arctic Ocean (2018)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geochemistry, Geophysics, Geosystems 18 (2017): 4156–4178, doi:10.1002/2017GC007099.
    Description: Synthesis of seismic velocity, potential field, and geological data from Canada Basin and its surrounding continental margins suggests that a northeast-trending structural fabric has influenced the origin, evolution, and current tectonics of the basin. This structural fabric has a crustal origin, based on the persistence of these trends in upward continuation of total magnetic intensity data and vertical derivative analysis of free-air gravity data. Three subparallel northeast-trending features are described. Northwind Escarpment, bounding the east side of the Chukchi Borderland, extends ∼600 km and separates continental crust of Northwind Ridge from high-velocity transitional crust in Canada Basin. A second, shorter northeast-trending zone extends ∼300 km in northern Canada Basin and separates inferred continental crust of Sever Spur from magmatically intruded crust of the High Arctic Large Igneous Province. A third northeast-trending feature, here called the Alaska-Prince Patrick magnetic lineament (APPL) is inferred from magnetic data and its larger regional geologic setting. Analysis of these three features suggests strike slip or transtensional deformation played a role in the opening of Canada Basin. These features can be explained by initial Jurassic-Early Cretaceous strike slip deformation (phase 1) followed in the Early Cretaceous (∼134 to ∼124 Ma) by rotation of Arctic Alaska with seafloor spreading orthogonal to the fossil spreading axis preserved in the central Canada Basin (phase 2). In this model, the Chukchi Borderland is part of Arctic Alaska.
    Description: Funding for this work was provided in part through the Geological Survey of Canada as part of Canada’s UNCLOS Project and through the U.S. Geological Survey as part of the U.S. Extended Continental Shelf project.
    Keywords: Canada Basin ; Tectonics ; Arctic Ocean ; Strike slip ; Seafloor spreading
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  • 16
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    Arctic deep water ferromanganese-oxide deposits reflect the unique characteristics of the Arctic Ocean (2018)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 18 (2017): 3771–3800, doi:10.1002/2017GC007186.
    Description: Little is known about marine mineral deposits in the Arctic Ocean, an ocean dominated by continental shelf and basins semi-closed to deep-water circulation. Here, we present data for ferromanganese crusts and nodules collected from the Amerasia Arctic Ocean in 2008, 2009, and 2012 (HLY0805, HLY0905, and HLY1202). We determined mineral and chemical compositions of the crusts and nodules and the onset of their formation. Water column samples from the GEOTRACES program were analyzed for dissolved and particulate scandium concentrations, an element uniquely enriched in these deposits. The Arctic crusts and nodules are characterized by unique mineral and chemical compositions with atypically high growth rates, detrital contents, Fe/Mn ratios, and low Si/Al ratios, compared to deposits found elsewhere. High detritus reflects erosion of submarine outcrops and North America and Siberia cratons, transport by rivers and glaciers to the sea, and distribution by sea ice, brines, and currents. Uniquely high Fe/Mn ratios are attributed to expansive continental shelves, where diagenetic cycling releases Fe to bottom waters, and density flows transport shelf bottom water to the open Arctic Ocean. Low Mn contents reflect the lack of a mid-water oxygen minimum zone that would act as a reservoir for dissolved Mn. The potential host phases and sources for elements with uniquely high contents are discussed with an emphasis on scandium. Scandium sorption onto Fe oxyhydroxides and Sc-rich detritus account for atypically high scandium contents. The opening of Fram Strait in the Miocene and ventilation of the deep basins initiated Fe-Mn crust growth ∼15 Myr ago.
    Description: National Science Foundation Grant Numbers: 1434493, 1713677; NSF-OCE Grant Number: 1535854
    Description: 2018-05-08
    Keywords: Arctic Ocean ; Ferromanganese deposits ; Rare metals ; Scandium ; Paleoceanography ; Genetic model
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  • 17
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    Sea surface pCO2 and O2 dynamics in the partially ice-covered Arctic Ocean (2017)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2017. 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: Oceans 122 (2017): 1425–1438, doi:10.1002/2016JC012162.
    Description: Understanding the physical and biogeochemical processes that control CO2 and dissolved oxygen (DO) dynamics in the Arctic Ocean (AO) is crucial for predicting future air-sea CO2 fluxes and ocean acidification. Past studies have primarily been conducted on the AO continental shelves during low-ice periods and we lack information on gas dynamics in the deep AO basins where ice typically inhibits contact with the atmosphere. To study these gas dynamics, in situ time-series data have been collected in the Canada Basin during late summer to autumn of 2012. Partial pressure of CO2 (pCO2), DO concentration, temperature, salinity, and chlorophyll-a fluorescence (Chl-a) were measured in the upper ocean in a range of sea ice states by two drifting instrument systems. Although the two systems were on average only 222 km apart, they experienced considerably different ice cover and external forcings during the 40–50 day periods when data were collected. The pCO2 levels at both locations were well below atmospheric saturation whereas DO was almost always slightly supersaturated. Modeling results suggest that air-sea gas exchange, net community production (NCP), and horizontal gradients were the main sources of pCO2 and DO variability in the sparsely ice-covered AO. In areas more densely covered by sea ice, horizontal gradients were the dominant source of variability, with no significant NCP in the surface mixed layer. If the AO reaches equilibrium with atmospheric CO2 as ice cover continues to decrease, aragonite saturation will drop from a present mean of 1.00 ± 0.02 to 0.86 ± 0.01.
    Description: U.S. National Science Foundation Arctic Observing Network Grant Number: ARC-1107346 and ARC-0856479
    Description: 2017-08-25
    Keywords: Arctic Ocean ; CO2 ; O2 ; Biogeochemistry ; Dynamics ; Carbon cycle
    Repository Name: Woods Hole Open Access Server
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  • 18
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    Subsea ice-bearing permafrost on the U.S. Beaufort Margin : 2. Borehole constraints (2017)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 17 (2016): 4333–4353, doi:10.1002/2016GC006582.
    Description: Borehole logging data from legacy wells directly constrain the contemporary distribution of subsea permafrost in the sedimentary section at discrete locations on the U.S. Beaufort Margin and complement recent regional analyses of exploration seismic data to delineate the permafrost's offshore extent. Most usable borehole data were acquired on a ∼500 km stretch of the margin and within 30 km of the contemporary coastline from north of Lake Teshekpuk to nearly the U.S.-Canada border. Relying primarily on deep resistivity logs that should be largely unaffected by drilling fluids and hole conditions, the analysis reveals the persistence of several hundred vertical meters of ice-bonded permafrost in nearshore wells near Prudhoe Bay and Foggy Island Bay, with less permafrost detected to the east and west. Permafrost is inferred beneath many barrier islands and in some nearshore and lagoonal (back-barrier) wells. The analysis of borehole logs confirms the offshore pattern of ice-bearing subsea permafrost distribution determined based on regional seismic analyses and reveals that ice content generally diminishes with distance from the coastline. Lacking better well distribution, it is not possible to determine the absolute seaward extent of ice-bearing permafrost, nor the distribution of permafrost beneath the present-day continental shelf at the end of the Pleistocene. However, the recovery of gas hydrate from an outer shelf well (Belcher) and previous delineation of a log signature possibly indicating gas hydrate in an inner shelf well (Hammerhead 2) imply that permafrost may once have extended across much of the shelf offshore Camden Bay.
    Description: 2017-05-04
    Keywords: Permafrost ; Arctic Ocean ; Climate change ; Borehole logging ; Gas hydrates
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  • 19
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    Spatial variability of the Arctic Ocean's double-diffusive staircase (2017)
    John Wiley & Sons
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2017. 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: Oceans 122 (2017): 980–994, doi:10.1002/2016JC012419.
    Description: The Arctic Ocean thermohaline stratification frequently exhibits a staircase structure overlying the Atlantic Water Layer that can be attributed to the diffusive form of double-diffusive convection. The staircase consists of multiple layers of O(1) m in thickness separated by sharp interfaces, across which temperature and salinity change abruptly. Through a detailed analysis of Ice-Tethered Profiler measurements from 2004 to 2013, the double-diffusive staircase structure is characterized across the entire Arctic Ocean. We demonstrate how the large-scale Arctic Ocean circulation influences the small-scale staircase properties. These staircase properties (layer thicknesses and temperature and salinity jumps across interfaces) are examined in relation to a bulk vertical density ratio spanning the staircase stratification. We show that the Lomonosov Ridge serves as an approximate boundary between regions of low density ratio (approximately 3–4) on the Eurasian side and higher density ratio (approximately 6–7) on the Canadian side. We find that the Eurasian Basin staircase is characterized by fewer, thinner layers than that in the Canadian Basin, although the margins of all basins are characterized by relatively thin layers and the absence of a well-defined staircase. A double-diffusive 4/3 flux law parametrization is used to estimate vertical heat fluxes in the Canadian Basin to be O(0.1) W m−2. It is shown that the 4/3 flux law may not be an appropriate representation of heat fluxes through the Eurasian Basin staircase. Here molecular heat fluxes are estimated to be between O(0.01) and O(0.1) W m−2. However, many uncertainties remain about the exact nature of these fluxes.
    Description: National Science Foundation Division of Polar Programs
    Description: 2017-08-08
    Keywords: Arctic Ocean ; Double-diffusion ; Atlantic Water
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  • 20
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    Seasonally derived components of the Canada Basin halocline (2017)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 44 (2017): 5008–5015, doi:10.1002/2017GL073042.
    Description: The Arctic halocline stratification is an important barrier to the transport of deep ocean heat to the underside of sea ice. Surface water in the Chukchi Sea, warmed in summer by solar radiation, ventilates the Canada Basin halocline to create a warm layer below the mixed-layer base. The year-round persistence of this layer is shown to be consistent with the seasonal cycle of halocline ventilation. We present hydrographic observations and model results to show how Chukchi Sea density outcrops migrate seasonally as surface fluxes modify salinity and temperature. This migration is such that in winter, isopycnals bounding the warm halocline are blocked from ventilation, while the cool, relatively salty and deeper halocline layers are ventilated. In this way, the warm halocline is isolated by stratification (both vertically and laterally) each winter. Results shed light on the fate and impact to sea ice of the warm halocline under future freshening and warming of the surface Arctic Ocean.
    Description: National Science Foundation Division of Polar Programs Grant Number: 1107623
    Description: 2017-11-26
    Keywords: Arctic Ocean ; Halocline ; Ventilation
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  • 21
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    Subsea ice-bearing permafrost on the U.S. Beaufort Margin : 1. Minimum seaward extent defined from multichannel seismic reflection data (2017)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 17 (2016): 4354–4365, doi:10.1002/2016GC006584.
    Description: Subsea ice-bearing permafrost (IBPF) and associated gas hydrate in the Arctic have been subject to a warming climate and saline intrusion since the last transgression at the end of the Pleistocene. The consequent degradation of IBPF is potentially associated with significant degassing of dissociating gas hydrate deposits. Previous studies interpreted the distribution of subsea permafrost on the U.S. Beaufort continental shelf based on geographically sparse data sets and modeling of expected thermal history. The most cited work projects subsea permafrost to the shelf edge (∼100 m isobath). This study uses a compilation of stacking velocity analyses from ∼100,000 line-km of industry-collected multichannel seismic reflection data acquired over 57,000 km2 of the U.S. Beaufort shelf to delineate continuous subsea IBPF. Gridded average velocities of the uppermost 750 ms two-way travel time range from 1475 to 3110 m s−1. The monotonic, cross-shore pattern in velocity distribution suggests that the seaward extent of continuous IBPF is within 37 km of the modern shoreline at water depths 〈 25 m. These interpretations corroborate recent Beaufort seismic refraction studies and provide the best, margin-scale evidence that continuous subsea IBPF does not currently extend to the northern limits of the continental shelf.
    Description: DOE NETL/NRC Methane Hydrate Fellowship Grant Number: DE-FC26-05NT42248; USGS–DOE Interagency Agreements Grant Number: DE-FE000291 and 0023495
    Description: 2017-05-04
    Keywords: Subsea permafrost ; Gas hydrates ; Multichannel seismic data ; Arctic Ocean
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  • 22
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    The Atlantic Water boundary current north of Svalbard in late summer (2017)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2017. 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: Oceans 122 (2017): 2269–2290, doi:10.1002/2016JC012486.
    Description: Data from a shipboard hydrographic/velocity survey carried out in September 2013 of the region north of Svalbard in the Nansen Basin are analyzed to characterize the Atlantic Water (AW) boundary current as it flows eastward along the continental slope. Eight meridional transects across the current, spanning an alongstream distance of 180 km, allow for a detailed description of the current and the regional water masses. During the survey the winds were light and there was no pack-ice. The mean section reveals that the boundary current was O(40 km) wide, surface-intensified, with a maximum velocity of 20 cm/s. Its mean transport during the survey was 3.11 ± 0.33 Sv, of which 2.31 ± 0.29 Sv was AW. This suggests that the two branches of AW entering the Arctic Ocean via Fram Strait—the Yermak Plateau branch and the Svalbard branch—have largely combined into a single current by 30°E. At this location the boundary current meanders with a systematic change in its kinematic structure during offshore excursions. A potential vorticity analysis indicates that the flow is baroclinically unstable, consistent with previous observations of AW anticyclones offshore of the current as well as the presence of a near-field cyclone in this data set. Our survey indicates that only a small portion of the boundary current is diverted into the Kvitøya Trough (0.17 ± 0.08 Sv) and that the AW temperature/salinity signal is quickly eroded within the trough.
    Description: National Science Foundation Grant Number: ARC-1264098
    Description: 2017-09-21
    Keywords: Atlantic Water ; Arctic Ocean ; Kvitøya Trough ; Nansen Basin ; Svalbard Branch ; A-TWAIN
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  • 23
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    Dynamics of an idealized Beaufort Gyre : 1. The effect of a small beta and lack of western boundaries (2016)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2016. 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: Oceans 121 (2016): 1249–1261, doi:10.1002/2015JC011296.
    Description: The Beaufort Gyre in the Arctic Ocean differs from a typical moderate-latitude gyre in some major aspects of its dynamics. First, it is located in a basin without a western boundary, which is essential for closing midlatitude circulations. Second, the gradient in Coriolis parameter, β, is small and so the validity of the Sverdrup balance is uncertain. In this paper, we use an idealized two-layer model to examine several processes that are related to these two issues. In a circular basin with closed geostrophic contours in interior, the variability of vorticity in the upper layer is dominated by eddies. But in the time-mean circulation, the main dynamical balance in the basin's interior is between the curl of wind stress and the eddy vorticity fluxes. The torque of friction becomes important along the boundary where the rim current is strong. It is found that the smallness of β has only a relatively small impact in a circular basin without a meridional boundary. The gyre is considerably more sensitive to the existence of a meridional boundary. The time-mean circulation weakens considerably when a peninsula is inserted between the model's center and the rim. (One side of the peninsula is dynamically equivalent to a midlatitude western boundary.) The gyre's sensitivity to β has also increased significantly when a meridional boundary is present. Subsurface ridges have similar effects on the gyre as a boundary, indicating that such topographic features may substitute, to some extents, the dynamical role of a western boundary.
    Description: This study has been supported by the National Science Foundation's Arctic Natural Science Program for J.Y. and A.P. via grant PRL-1107412, and for AP via grants PRL-1313614, PRL-1302884, and PRL-1107277.
    Description: 2016-08-12
    Keywords: Arctic Ocean ; Beaufort Gyre ; Freshwater content ; Beta effect ; Western boundary
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  • 24
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    Sources of dissolved inorganic carbon to the Canada Basin halocline : a multitracer study (2016)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2016. 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: Oceans 121 (2016): 2918–2936, doi:10.1002/2015JC011535.
    Description: We examine the dissolved inorganic carbon maximum in the Canada Basin halocline using a suite of geochemical tracers to gain insight into the factors that contribute to the persistence of this feature. Hydrographic and geochemical samples were collected in the upper 500 m of the southwestern Canada Basin water column in the summer of 2008 and fall of 2009. These observations were used to identify conservative and nonconservative processes that contribute dissolved inorganic carbon to halocline source waters, including shelf sediment organic matter remineralization, air-sea gas exchange, and sea-ice brine export. Our results indicate that the remineralization of organic matter that occurs along the Bering and Chukchi Sea shelves is the overwhelming contributor of dissolved inorganic carbon to Pacific Winter Water that occupies the middle halocline in the southwestern Canada Basin. Nonconservative contributions from air-sea exchange and sea-ice brine are not significant. The broad salinity range associated with the DIC maximum, compared to the narrow salinity range of the nutrient maximum, is due to mixing between Pacific and Atlantic water and not abiotic addition of DIC.
    Description: NSERC; Fisheries and Oceans Canada; US National Science Foundation Office of Polar Programs Grant Number: OPP-0424864; Canadian International Polar Year Office
    Description: 2016-11-04
    Keywords: Arctic Ocean ; Dissolved inorganic carbon ; Nutrients ; Stable isotopes ; Shelf-basin CO2 pump
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    Evolution of the eddy field in the Arctic Ocean's Canada Basin, 2005–2015 (2016)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 43 (2016): 8106–8114, doi:10.1002/2016GL069671.
    Description: The eddy field across the Arctic Ocean's Canada Basin is analyzed using Ice-Tethered Profiler (ITP) and moored measurements of temperature, salinity, and velocity spanning 2005 to 2015. ITPs encountered 243 eddies, 98% of which were anticyclones, with approximately 70% of these having anomalously cold cores. The spatially and temporally varying eddy field is analyzed accounting for sampling biases in the unevenly distributed ITP data and caveats in detection methods. The highest concentration of eddies was found in the western and southern portions of the basin, close to topographic margins and boundaries of the Beaufort Gyre. The number of lower halocline eddies approximately doubled from 2005–2012 to 2013–2014. The increased eddy density suggests more active baroclinic instability of the Beaufort Gyre that releases available potential energy to balance the wind energy input; this may stabilize the Gyre spin-up and associated freshwater increase.
    Description: National Science Foundation Division of Polar Programs Grant Number: 1350046
    Description: 2017-02-03
    Keywords: Arctic Ocean ; Eddies ; Beaufort Gyre
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    Arctic pathways of Pacific Water : Arctic Ocean Model Intercomparison experiments (2016)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    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: Oceans 121 (2016): 27–59, doi:10.1002/2015JC011299.
    Description: Pacific Water (PW) enters the Arctic Ocean through Bering Strait and brings in heat, fresh water, and nutrients from the northern Bering Sea. The circulation of PW in the central Arctic Ocean is only partially understood due to the lack of observations. In this paper, pathways of PW are investigated using simulations with six state-of-the art regional and global Ocean General Circulation Models (OGCMs). In the simulations, PW is tracked by a passive tracer, released in Bering Strait. Simulated PW spreads from the Bering Strait region in three major branches. One of them starts in the Barrow Canyon, bringing PW along the continental slope of Alaska into the Canadian Straits and then into Baffin Bay. The second begins in the vicinity of the Herald Canyon and transports PW along the continental slope of the East Siberian Sea into the Transpolar Drift, and then through Fram Strait and the Greenland Sea. The third branch begins near the Herald Shoal and the central Chukchi shelf and brings PW into the Beaufort Gyre. In the models, the wind, acting via Ekman pumping, drives the seasonal and interannual variability of PW in the Canadian Basin of the Arctic Ocean. The wind affects the simulated PW pathways by changing the vertical shear of the relative vorticity of the ocean flow in the Canada Basin.
    Description: National Science Foundation (NSF). Grant Numbers: PLR-0806306 , PLR-85653100 , PLR-82486400 , PLR-1313614; NASA Advanced Supercomputing (NAS) Division; JPL Supercomputing and Visualization Facility (SVF) Grant Numbers: ARC-0806306 , ARC-85653100 , ARC-82486400; Russian Foundation of Basic Research; Ministry of the Education and Science of the Russian Federation; UK Natural Environment Research Council Grant Number: NE/I028947/
    Keywords: Arctic Ocean ; Beaufort Gyre ; Pacific Water ; Ocean dynamics ; Wind forcing
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    Ecosystem model intercomparison of under-ice and total primary production in the Arctic Ocean (2016)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2016. 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: Oceans 121 (2016); 934–948, doi:10.1002/2015JC011183.
    Description: Previous observational studies have found increasing primary production (PP) in response to declining sea ice cover in the Arctic Ocean. In this study, under-ice PP was assessed based on three coupled ice-ocean-ecosystem models participating in the Forum for Arctic Modeling and Observational Synthesis (FAMOS) project. All models showed good agreement with under-ice measurements of surface chlorophyll-a concentration and vertically integrated PP rates during the main under-ice production period, from mid-May to September. Further, modeled 30-year (1980–2009) mean values and spatial patterns of sea ice concentration compared well with remote sensing data. Under-ice PP was higher in the Arctic shelf seas than in the Arctic Basin, but ratios of under-ice PP over total PP were spatially correlated with annual mean sea ice concentration, with higher ratios in higher ice concentration regions. Decreases in sea ice from 1980 to 2009 were correlated significantly with increases in total PP and decreases in the under-ice PP/total PP ratio for most of the Arctic, but nonsignificantly related to under-ice PP, especially in marginal ice zones. Total PP within the Arctic Circle increased at an annual rate of between 3.2 and 8.0 Tg C/yr from 1980 to 2009. This increase in total PP was due mainly to a PP increase in open water, including increases in both open water area and PP rate per unit area, and therefore much stronger than the changes in under-ice PP. All models suggested that, on a pan-Arctic scale, the fraction of under-ice PP declined with declining sea ice cover over the last three decades.
    Description: NASA Grant Number: NNX13AE81G; the NSF Office of Polar Programs Grant Number: (ARC-0968676, PLR-1417925, PLR-1417677 and PLR-1416920); the NASA Cryosphere Grant Number: (NNX12AB31G); Climate and Biological Response Grant Number: (NNX11AO91G)
    Description: 2016-07-27
    Keywords: Ecosystem modeling ; Sea ice ; Under-ice production ; Phenology ; Primary production ; Arctic Ocean
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    Early ice retreat and ocean warming may induce copepod biogeographic boundary shifts in the Arctic Ocean (2016)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2016. 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: Oceans 121 (2016): 6137-6158, doi:10.1002/2016JC011784.
    Description: Early ice retreat and ocean warming are changing various facets of the Arctic marine ecosystem, including the biogeographic distribution of marine organisms. Here an endemic copepod species, Calanus glacialis, was used as a model organism, to understand how and why Arctic marine environmental changes may induce biogeographic boundary shifts. A copepod individual-based model was coupled to an ice-ocean-ecosystem model to simulate temperature- and food-dependent copepod life history development. Numerical experiments were conducted for two contrasting years: a relatively cold and normal sea ice year (2001) and a well-known warm year with early ice retreat (2007). Model results agreed with commonly known biogeographic distributions of C. glacialis, which is a shelf/slope species and cannot colonize the vast majority of the central Arctic basins. Individuals along the northern boundaries of this species' distribution were most susceptible to reproduction timing and early food availability (released sea ice algae). In the Beaufort, Chukchi, East Siberian, and Laptev Seas where severe ocean warming and loss of sea ice occurred in summer 2007, relatively early ice retreat, elevated ocean temperature (about 1–2°C higher than 2001), increased phytoplankton food, and prolonged growth season created favorable conditions for C. glacialis development and caused a remarkable poleward expansion of its distribution. From a pan-Arctic perspective, despite the great heterogeneity in the temperature and food regimes, common biogeographic zones were identified from model simulations, thus allowing a better characterization of habitats and prediction of potential future biogeographic boundary shifts.
    Description: National Science Foundation Polar Programs Grant Number: (PLR-1417677, PLR-1417339, and PLR-1416920)
    Description: 2017-02-20
    Keywords: Arctic Ocean ; Marine ecosystem ; Climate change ; Biogeography ; Individual-based model ; C. glacialis
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    Inorganic carbon system dynamics in landfast Arctic sea ice during the early-melt period (2015)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2015. 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: Oceans 120 (2015): 3542-3566, doi:10.1002/2014JC010620.
    Description: We present the results of a 6 week time series of carbonate system and stable isotope measurements investigating the effects of sea ice on air-sea CO2 exchange during the early melt period in the Canadian Arctic Archipelago. Our observations revealed significant changes in sea ice and sackhole brine carbonate system parameters that were associated with increasing temperatures and the buildup of chlorophyll a in bottom ice. The warming sea-ice column could be separated into distinct geochemical zones where biotic and abiotic processes exerted different influences on inorganic carbon and pCO2 distributions. In the bottom ice, biological carbon uptake maintained undersaturated pCO2 conditions throughout the time series, while pCO2 was supersaturated in the upper ice. Low CO2 permeability of the sea ice matrix and snow cover effectively impeded CO2 efflux to the atmosphere, despite a strong pCO2 gradient. Throughout the middle of the ice column, brine pCO2 decreased significantly with time and was tightly controlled by solubility, as sea ice temperature and in situ melt dilution increased. Once the influence of melt dilution was accounted for, both CaCO3 dissolution and seawater mixing were found to contribute alkalinity and dissolved inorganic carbon to brines, with the CaCO3 contribution driving brine pCO2 to values lower than predicted from melt-water dilution alone. This field study reveals a dynamic carbon system within the rapidly warming sea ice, prior to snow melt. We suggest that the early spring period drives the ice column toward pCO2 undersaturation, contributing to a weak atmospheric CO2 sink as the melt period advances.
    Description: We acknowledge support from the Polar Continental Shelf Program (PCSP) of Natural Resources Canada, the Natural Sciences and Engineering Research Council of Canada, the Northern Scientific Training Program, Canada Economic Development, and Fisheries and Oceans Canada.
    Description: 2015-11-19
    Keywords: Sea ice ; Carbon cycling ; CO2 ; Brines ; Stable isotopes ; Arctic Ocean
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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
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    Diffusive vertical heat flux in the Canada Basin of the Arctic Ocean inferred from moored instruments (2014)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2014. 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: Oceans 119 (2014): 496-508, doi:10.1002/2013JC009346.
    Description: 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 × 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.
    Description: C. Lique acknowledge support from JISAO and the Program on Climate Change of the University of Washington. J. Guthrie and J. Morison are supported by National Science Foundation grants ARC-0909408 and ARC-0856330. M. Steele is supported by the Office of Naval Researches Arctic and Global Prediction Program, by NSFs Division of Polar Programs, and by NASAs Cryosphere and Physical Oceanography programs. Support for the BGOS program and R. Krishfield was provided by the National Science Foundation (under grants ARC-0806115, ARC-0631951, ARC-0806306, and ARC-0856531) and Woods Hole Oceanographic Institution internal funding. For A. Proshutinsky, this research is supported by the National Science Foundation Office of Polar Programs, awards ARC-1203720 and ARC-0856531.
    Description: 2014-07-22
    Keywords: Arctic Ocean ; Atlantic water ; Mixing
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    The great 2012 Arctic Ocean summer cyclone enhanced biological productivity on the shelves (2014)
    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): 297-312, doi:10.1002/2013JC009301.
    Description: 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.
    Description: This work is supported by the NSF Office of Polar Programs and the NASA Cryosphere Program.
    Keywords: Cyclone effects on biology ; Arctic Ocean ; Ocean mixing
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    Western Arctic Ocean temperature variability during the last 8000 years (2012)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 38 (2011): L24602, doi:10.1029/2011GL049714.
    Description: We reconstructed subsurface (∼200–400 m) ocean temperature and sea-ice cover in the Canada Basin, western Arctic Ocean from foraminiferal δ18O, ostracode Mg/Ca ratios, and dinocyst assemblages from two sediment core records covering the last 8000 years. Results show mean temperature varied from −1 to 0.5°C and −0.5 to 1.5°C at 203 and 369 m water depths, respectively. Centennial-scale warm periods in subsurface temperature records correspond to reductions in summer sea-ice cover inferred from dinocyst assemblages around 6.5 ka, 3.5 ka, 1.8 ka and during the 15th century Common Era. These changes may reflect centennial changes in the temperature and/or strength of inflowing Atlantic Layer water originating in the eastern Arctic Ocean. By comparison, the 0.5 to 0.7°C warm temperature anomaly identified in oceanographic records from the Atlantic Layer of the Canada Basin exceeded reconstructed Atlantic Layer temperatures for the last 1200 years by about 0.5°C.
    Description: J.R.F., T.M.C., and R.C.T. thank support by USGS Global Change Program, G.S.D. thanks support from the USGS Global Change Program and the NSF Office of Polar Programs, A.d.V. thanks support by Fond québécois de la recherché sur la nature et les technologies (FQRNT) and the Ministere du Développement économique, innovation et exportation (MDEIE) of Quebec.
    Description: 2012-06-17
    Keywords: Arctic Ocean ; Atlantic Layer ; Temperature ; Variability
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    Storm-induced upwelling of high pCO2 waters onto the continental shelf of the western Arctic Ocean and implications for carbonate mineral saturation states (2012)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 39 (2012): L07606, doi:10.1029/2012GL051574.
    Description: The carbon system of the western Arctic Ocean is undergoing a rapid transition as sea ice extent and thickness decline. These processes are dynamically forcing the region, with unknown consequences for CO2 fluxes and carbonate mineral saturation states, particularly in the coastal regions where sensitive ecosystems are already under threat from multiple stressors. In October 2011, persistent wind-driven upwelling occurred in open water along the continental shelf of the Beaufort Sea in the western Arctic Ocean. During this time, cold (〈−1.2°C), salty (〉32.4) halocline water—supersaturated with respect to atmospheric CO2 (pCO2 〉 550 μatm) and undersaturated in aragonite (Ωaragonite 〈 1.0) was transported onto the Beaufort shelf. A single 10-day event led to the outgassing of 0.18–0.54 Tg-C and caused aragonite undersaturations throughout the water column over the shelf. If we assume a conservative estimate of four such upwelling events each year, then the annual flux to the atmosphere would be 0.72–2.16 Tg-C, which is approximately the total annual sink of CO2 in the Beaufort Sea from primary production. Although a natural process, these upwelling events have likely been exacerbated in recent years by declining sea ice cover and changing atmospheric conditions in the region, and could have significant impacts on regional carbon budgets. As sea ice retreat continues and storms increase in frequency and intensity, further outgassing events and the expansion of waters that are undersaturated in carbonate minerals over the shelf are probable.
    Description: Funding for this work was provided by the National Science Foundation (ARC1041102 – JTM, OPP0856244-RSP, and ARC1040694- LWJ), the National Oceanic and Atmospheric Administration (CIFAR11021- RHB) and the West Coast & Polar Regions Undersea Research Center (POFP00983 – CLM and JM).
    Description: 2012-10-11
    Keywords: Arctic Ocean ; CO2 fluxes ; Ocean acidification ; Upwelling
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    Surface freshening in the Arctic Ocean's Eurasian Basin : an apparent consequence of recent change in the wind-driven circulation (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. 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 116 (2011): C00D03, doi:10.1029/2011JC006975.
    Description: Data collected by an autonomous ice-based observatory that drifted into the Eurasian Basin between April and November 2010 indicate that the upper ocean was appreciably fresher than in 2007 and 2008. Sea ice and snowmelt over the course of the 2010 drift amounted to an input of less than 0.5 m of liquid freshwater to the ocean (comparable to the freshening by melting estimated for those previous years), while the observed change in upper-ocean salinity over the melt period implies a freshwater gain of about 0.7 m. Results of a wind-driven ocean model corroborate the observations of freshening and suggest that unusually fresh surface waters observed in parts of the Eurasian Basin in 2010 may have been due to the spreading of anomalously fresh water previously residing in the Beaufort Gyre. This flux is likely associated with a 2009 shift in the large-scale atmospheric circulation to a significant reduction in strength of the anticyclonic Beaufort Gyre and the Transpolar Drift Stream.
    Description: This work was funded by the National Science Foundation Office of Polar Programs Arctic Sciences Section under awards ARC‐0519899, ARC‐0856479, and ARC‐ 0806306.
    Keywords: Arctic Ocean ; Circulation ; Fresh water
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    An unstructured-grid, finite-volume sea ice model : development, validation, and application (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. 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 116 (2011): C00D04, doi:10.1029/2010JC006688.
    Description: A sea ice model was developed by converting the Community Ice Code (CICE) into an unstructured-grid, finite-volume version (named UG-CICE). The governing equations were discretized with flux forms over control volumes in the computational domain configured with nonoverlapped triangular meshes in the horizontal and solved using a second-order accurate finite-volume solver. Implementing UG-CICE into the Arctic Ocean finite-volume community ocean model provides a new unstructured-grid, MPI-parallelized model system to resolve the ice-ocean interaction dynamics that frequently occur over complex irregular coastal geometries and steep bottom slopes. UG-CICE was first validated for three benchmark test problems to ensure its capability of repeating the ice dynamics features found in CICE and then for sea ice simulation in the Arctic Ocean under climatologic forcing conditions. The model-data comparison results demonstrate that UG-CICE is robust enough to simulate the seasonal variability of the sea ice concentration, ice coverage, and ice drifting in the Arctic Ocean and adjacent coastal regions.
    Description: This work was supported by the NSF Arctic Program for projects with grant numbers of ARC0712903, ARC0732084, and ARC0804029. The Arctic Ocean Model Intercomparison Project (AOMIP) has provided an important guidance for model improvements and ocean studies under coordinated experiments activities. We would like to thank AOMIP PI Proshutinsky for his valuable suggestions and comments on the ice dynamics. His contribution is supported by ARC0800400 and ARC0712848. The development of FVCOM was supported by the Massachusetts Marine Fisheries Institute NOAA grants DOC/NOAA/ NA04NMF4720332 and DOC/NOAA/NA05NMF4721131; the NSF Ocean Science Program for projects of OCE‐0234545, OCE‐0227679, OCE‐ 0606928, OCE‐0712903, OCE‐0726851, and OCE‐0814505; MIT Sea Grant funds (2006‐RC‐103 and 2010‐R/RC‐116); and NOAA NERACOOS Program for the UMASS team. G. Gao was also supported by the Chinese NSF Arctic Ocean grant under contract 40476007. C. Chen’s contribution was also supported by Shanghai Ocean University International Cooperation Program (A‐2302‐10‐0003), the Program of Science and Technology Commission of Shanghai Municipality (09320503700), the Leading Academic Discipline Project of Shanghai Municipal Education Commission (J50702), and Zhi jiang Scholar and 111 project funds of the State Key Laboratory for Estuarine and Coastal Research, East China Normal University (ECNU).
    Keywords: Arctic Ocean ; Finite-volume ; Sea ice modeling ; Unstructured-grid
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    Storm-driven mixing and potential impact on the Arctic Ocean (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. 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 109 (2004): C04008, doi:10.1029/2001JC001248.
    Description: Observations of the ocean, atmosphere, and ice made by Ice-Ocean Environmental Buoys indicate that mixing events reaching the depth of the halocline have occurred in various regions in the Arctic Ocean. Our analysis suggests that these mixing events were mechanically forced by intense storms moving across the buoy sites. In this study, we analyzed these mixing events in the context of storm developments that occurred in the Beaufort Sea and in the general area just north of Fram Strait, two areas with quite different hydrographic structures. The Beaufort Sea is strongly influenced by inflow of Pacific water through Bering Strait, while the area north of Fram Strait is directly affected by the inflow of warm and salty North Atlantic water. Our analyses of the basin-wide evolution of the surface pressure and geostrophic wind fields indicate that the characteristics of the storms could be very different. The buoy-observed mixing occurred only in the spring and winter seasons when the stratification was relatively weak. This indicates the importance of stratification, although the mixing itself was mechanically driven. We also analyze the distribution of storms, both the long-term climatology and the patterns for each year in the past 2 decades. The frequency of storms is also shown to be correlated (but not strongly) to Arctic Oscillation indices. This study indicates that the formation of new ice that leads to brine rejection is unlikely the mechanism that results in the type of mixing that could overturn the halocline. On the other hand, synoptic-scale storms can force mixing deep enough to the halocline and thermocline layer. Despite a very stable stratification associated with the Arctic halocline, the warm subsurface thermocline water is not always insulated from the mixed layer.
    Description: This study has been supported by the NASA Cryospheric Science Program and the International Arctic Reseach Center. We benefited from discussion with Dr. A. Proshutinsky. D. Walsh wishes to thank the Frontier Research System for Global Change for their support. The IOEB program was supported by ONR High-Latitude Dynamics Program and Japan Marine Science and Technology Center (JAMSTEC).
    Keywords: Arctic Ocean ; Mixing ; Storm ; Upper ocean
    Repository Name: Woods Hole Open Access Server
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  • 38
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    Pathways of Pacific water across the Chukchi Sea : a numerical model study (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. 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 109 (2004): C03002, doi:10.1029/2003JC001962.
    Description: Pathways of Pacific Water flowing from the North Pacific Ocean through Bering Strait and across the Chukchi Sea are investigated using a two-dimensional barotropic model. In the no-wind case, the flow is driven only by a prescribed steady northward flow of 0.8 Sv through Bering Strait. The resulting steady state circulation consists of a broad northeasterly flow, basically following the topography, with a few areas of intensified currents. About half of the inflow travels northwest through Hope Valley, while the other half turns somewhat toward the northeast along the Alaskan coast. The flow through Hope Valley is intensified as it passes through Herald Canyon, but much of this flow escapes the canyon to move eastward, joining the flow in the broad valley between Herald and Hanna Shoals, another area of slightly intensified currents. There is a confluence of nearly all of the flow along the Alaskan coast west of Pt. Barrow to create a very strong and narrow coastal jet that follows the shelf topography eastward onto the Beaufort shelf. Thus in this no-wind case, nearly all of the Pacific Water entering the Chukchi Sea eventually ends up flowing eastward along the narrow Beaufort shelf, with no discernable flow across the shelf edge toward the interior Canada Basin. Travel times for water parcels to move from Bering Strait to Pt. Barrow vary tremendously according to the path taken; e.g., less than 6 months along the Alaskan coast, but about 30 months along the westernmost path through Herald Canyon. This flow field is relatively insensitive to idealized wind-forcing when the winds are from the south, west or north, in which cases the shelf transports tend to be intensified. However, strong northeasterly to easterly winds are able to completely reverse the flows along the Beaufort shelf and the Alaskan coast, and force most of the throughflow in a more northerly direction across the Chukchi Sea shelf edge, potentially supplying the surface waters of the interior Canada Basin with Pacific Water. The entire shelf circulation reacts promptly to changing wind conditions, with a response time of ~2–3 days. The intense coastal jet between Icy Cape and Pt. Barrow implies that dense water formed here from winter coastal polynyas may be quickly swept away along the coast. In contrast, there is a relatively quiet nearshore region to the west, between Cape Lisburne and Icy Cape, where dense water may accumulate much longer and continue to become denser before it is carried across the shelf.
    Description: Financial support was provided to PW by the Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution (WHOI), the Swedish Foundation for International Cooperation in Research and Higher Education (STINT), and the J. Seward Johnson Fund. Funding for DCC came through a grant from the Coastal Ocean Institute at WHOI.
    Keywords: Arctic Ocean ; Pacific Water ; Chukchi Sea
    Repository Name: Woods Hole Open Access Server
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  • 39
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    Preface to special section on Arctic Ocean Model Intercomparison Project (AOMIP) Studies and Results (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2007. 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 112 (2007): C04S01, doi:10.1029/2006JC004017.
    Description: This research is supported by the National Science Foundation Office of Polar Programs under cooperative agreements (OPP-0002239 and OPP-0327664) with the International Arctic Research Center, University of Alaska Fairbanks.
    Keywords: Modeling ; Arctic Ocean ; Dynamics
    Repository Name: Woods Hole Open Access Server
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  • 40
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    Modeling transport and fate of riverine dissolved organic carbon in the Arctic Ocean (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    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 Global Biogeochemical Cycles 23 (2009): GB4006, doi:10.1029/2008GB003396.
    Description: The spatial distribution and fate of riverine dissolved organic carbon (DOC) in the Arctic may be significant for the regional carbon cycle but are difficult to fully characterize using the sparse observations alone. Numerical models of the circulation and biogeochemical cycles of the region can help to interpret and extrapolate the data and may ultimately be applied in global change sensitivity studies. Here we develop and explore a regional, three-dimensional model of the Arctic Ocean in which, for the first time, we explicitly represent the sources of riverine DOC with seasonal discharge based on climatological field estimates. Through a suite of numerical experiments, we explore the distribution of DOC-like tracers with realistic riverine sources and a simple linear decay to represent remineralization through microbial degradation. The model reproduces the slope of the DOC-salinity relationship observed in the eastern and western Arctic basins when the DOC tracer lifetime is about 10 years, consistent with published inferences from field data. The new empirical parameterization of riverine DOC and the regional circulation and biogeochemical model provide new tools for application in both regional and global change studies.
    Description: I.M.M. and M.J.F. are grateful to National Science Foundation for financial support.
    Keywords: Arctic Ocean ; Ocean circulation ; Biogeochemical processes
    Repository Name: Woods Hole Open Access Server
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