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  • 1
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    Evolution of the freshwater coastal current at the southern tip of Greenland (2018)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 2127-2140, doi:10.1175/JPO-D-18-0035.1.
    Description: Shipboard hydrographic and velocity measurements collected in summer 2014 are used to study the evolution of the freshwater coastal current in southern Greenland as it encounters Cape Farewell. The velocity structure reveals that the coastal current maintains its identity as it flows around the cape and bifurcates such that most of the flow is diverted to the outer west Greenland shelf, while a small portion remains on the inner shelf. Taking into account this inner branch, the volume transport of the coastal current is conserved, but the freshwater transport decreases on the west side of Cape Farewell. A significant amount of freshwater appears to be transported off the shelf where the outer branch flows adjacent to the shelfbreak circulation. It is argued that the offshore transposition of the coastal current is caused by the flow following the isobaths as they bend offshore because of the widening of the shelf on the west side of Cape Farewell. An analysis of the potential vorticity shows that the subsequent seaward flux of freshwater can be enhanced by instabilities of the current. This set of circumstances provides a pathway for the freshest water originating from the Arctic, as well as runoff from the Greenland ice sheet, to be fluxed into the interior Labrador Sea where it could influence convection in the basin.
    Description: Funding for this project was provided by the National Science Foundation under Grant OCE-1259618.
    Description: 2019-03-11
    Keywords: Boundary currents ; Coastal flows ; Instability ; Ocean circulation ; Potential vorticity ; Transport
    Repository Name: Woods Hole Open Access Server
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  • 2
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    The East Greenland Coastal Current : structure, variability, and forcing (2008)
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Elsevier B.V. , 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Progress In Oceanography 78 (2008): 58-77, doi:10.1016/j.pocean.2007.09.006.
    Description: The subtidal circulation of the southeast Greenland shelf is described using a set of high-resolution hydrographic and velocity transects occupied in summer 2004. The main feature is the East Greenland Coastal Current (EGCC), a low-salinity, high-velocity jet with a wedge-shaped hydrographic structure characteristic of other surface buoyancydriven currents. The EGCC was observed along the entire Greenland shelf south of Denmark Strait, while the transect north of the strait showed only a weak shelf flow. This observation, in conjunction with water mass considerations and other supporting evidence, suggests that the EGCC is an inner branch of the East Greenland Current (EGC) that forms south of Denmark Strait. It is argued that bathymetric steering is the most likely reason why the EGC apparently bifurcates at this location. Repeat sections occupied at Cape Farewell between 1997 and 2004 show that the alongshelf wind stress can have a strong influence on the structure and strength of the EGCC and EGC on timescales of 2-3 days. Accounting for the wind-induced effects, the volume transport of the combined EGCC/EGC system is roughly constant (~2 Sv) over the study domain, from 68°N to Cape Farewell near 60°N. The corresponding freshwater transport increases by roughly 60% over this distance (59 to 96 mSv, referenced to a salinity of 34.8). This trend is consistent with a simple freshwater budget of the EGCC/EGC system that accounts for meltwater runoff, melting sea-ice and icebergs, and net precipitation minus evaporation.
    Description: This work was funded by the National Science Foundation grant OCE-0450658. DS was also partially supported by the Woods Hole Oceanographic Institution Academic Programs Office.
    Keywords: Coastal currents ; East Greenland Current ; Sea ice ; Boundary currents ; Arctic freshwater flux
    Repository Name: Woods Hole Open Access Server
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  • 3
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    The western Arctic boundary current at 152°W : structure, variability, and transport (2010)
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    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 56 (2009): 1164-1181, doi:10.1016/j.dsr2.2008.10.014.
    Description: From August 2002 to September 2004 a high-resolution mooring array was maintained across the western Arctic boundary current in the Beaufort Sea north of Alaska. The array consisted of profiling instrumentation, providing a timeseries of vertical sections of the current. Here we present the first-year velocity measurements, with emphasis on the Pacific water component of the current. The mean flow is characterized as a bottom-intensified jet of O(15 cm s-1) directed to the east, trapped to the shelfbreak near 100 m depth. Its width scale is only 10-15 km. Seasonally the flow has distinct configurations. During summer it becomes surface-intensified as it advects buoyant Alaskan Coastal Water. In fall and winter the current often reverses (flows westward) under upwelling-favorable winds. Between the storms, as the eastward flow re-establishes, the current develops a deep extension to depths exceeding 700 m. In spring the bottom-trapped flow advects winter-transformed Pacific water emanating from the Chukchi Sea. The year-long mean volume transport of Pacific Water is 0.13±0.08 Sv to the east, which is less than 20% of the long-term mean Bering Strait inflow. This implies that most of the Pacific water entering the Arctic goes elsewhere, contrary to expected dynamics and previous modeling results. Possible reasons for this are discussed. The mean Atlantic water transport (to 800 m depth) is 0.047±0.026 Sv, also smaller than anticipated.
    Description: AN was funded by the Swedish Research Council; RP, PF, and DT were funded by grant N00014-02-1-0317 of the Office of Naval Research.
    Keywords: Polar oceanography ; Shelf edge dynamics ; Boundary currents ; Volume transport ; Pacific Water ; Atlantic Water
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  • 4
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    Eddy formation near the west coast of Greenland (2010)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 38 (2008): 1992-2002, doi:10.1175/2008JPO3669.1.
    Description: This paper extends A. Bracco and J. Pedlosky’s investigation of the eddy-formation mechanism in the eastern Labrador Sea by including a more realistic depiction of the boundary current. The quasigeostrophic model consists of a meridional, coastally trapped current with three vertical layers. The current configuration and topographic domain are chosen to match, as closely as possible, the observations of the boundary current and the varying topographic slope along the West Greenland coast. The role played by the bottom-intensified component of the boundary current on the formation of the Labrador Sea Irminger Rings is explored. Consistent with the earlier study, a short, localized bottom-trapped wave is responsible for most of the perturbation energy growth. However, for the instability to occur in the three-layer model, the deepest component of the boundary current must be sufficiently strong, highlighting the importance of the near-bottom flow. The model is able to reproduce important features of the observed vortices in the eastern Labrador Sea, including the polarity, radius, rate of formation, and vertical structure. At the time of formation, the eddies have a surface signature as well as a strong circulation at depth, possibly allowing for the transport of both surface and near-bottom water from the boundary current into the interior basin. This work also supports the idea that changes in the current structure could be responsible for the observed interannual variability in the number of Irminger Rings formed.
    Description: AB is supported by WHOI unrestricted funds, JP by the National Science Foundation OCE 85108600, and RP by 0450658.
    Keywords: Eddies ; Boundary currents ; Quasigeostrophic models ; North Atlantic ; Coastlines
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  • 5
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    Two configurations of the Western Arctic Shelfbreak Current in summer (2012)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 42 (2012): 329-351, doi:10.1175/JPO-D-11-026.1.
    Description: Data from a closely spaced array of moorings situated across the Beaufort Sea shelfbreak at 152°W are used to study the Western Arctic Shelfbreak Current, with emphasis on its configuration during the summer season. Two dynamically distinct states of the current are revealed in the absence of wind, with each lasting approximately one month. The first is a surface-intensified shelfbreak jet transporting warm and buoyant Alaskan Coastal Water in late summer. This is the eastward continuation of the Alaskan Coastal Current. It is both baroclinically and barotropically unstable and hence capable of forming the surface-intensified warm-core eddies observed in the southern Beaufort Sea. The second configuration, present during early summer, is a bottom-intensified shelfbreak current advecting weakly stratified Chukchi Summer Water. It is baroclinically unstable and likely forms the middepth warm-core eddies present in the interior basin. The mesoscale instabilities extract energy from the mean flow such that the surface-intensified jet should spin down over an e-folding distance of 300 km beyond the array site, whereas the bottom-intensified configuration should decay within 150 km. This implies that Pacific Summer Water does not extend far into the Canadian Beaufort Sea as a well-defined shelfbreak current. In contrast, the Pacific Winter Water configuration of the shelfbreak jet is estimated to decay over a much greater distance of approximately 1400 km, implying that it should reach the first entrance to the Canadian Arctic Archipelago.
    Description: This work was supported by National Science Foundation GrantsOCE-0726640,OPP-0731928, and OPP-0713250.
    Description: 2012-09-01
    Keywords: Arctic ; Continental shelf/slope ; Boundary currents
    Repository Name: Woods Hole Open Access Server
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  • 6
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    Role of shelfbreak upwelling in the formation of a massive under-ice bloom in the Chukchi Sea (2014)
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 105 (2014): 17-29, doi:10.1016/j.dsr2.2014.03.017.
    Description: In the summer of 2011, an oceanographic survey carried out by the Impacts of Climate on EcoSystems and Chemistry of the Arctic Pacific Environment (ICESCAPE) program revealed the presence of a massive phytoplankton bloom under the ice near the shelfbreak in the central Chukchi Sea. For most of the month preceding the measurements there were relatively strong easterly winds, providing upwelling favorable conditions along the shelfbreak. Analysis of similar hydrographic data from summer 2002, in which there were no persistent easterly winds, found no evidence of upwelling near the shelfbreak. A two-dimensional ocean circulation model is used to show that sufficiently strong winds can result not only in upwelling of high nutrient water from offshore onto the shelf, but it can also transport the water out of the bottom boundary layer into the surface Ekman layer at the shelf edge. The extent of upwelling is determined by the degree of overlap between the surface Ekman layer and the bottom boundary layer on the outer shelf. Once in the Ekman layer, this high nutrient water is further transported to the surface through mechanical mixing driven by the surface stress. Two model tracers, a nutrient tracer and a chlorophyll tracer, reveal distributions very similar to that observed in the data. These results suggest that the biomass maximum near the shelfbreak during the massive bloom in summer 2011 resulted from an enhanced supply of nutrients upwelled from the halocline seaward of the shelf. The decade long trend in summertime surface winds suggest that easterly winds in this region are increasing in strength and that such bloom events will become more common.
    Description: This study was supported by the National Science Foundation under Grant OCE-0959381 (MAS), and by the Ocean Biology and Biogeochemistry Program and the Cryosphere Science Program of the National Aeronautic and Space Administration under Award NNX10AF42G (RSP;KRA). GWKM was supported by the Natural Sciences and Engineering Research Council of Canada. ETB was supported by the U. S. Navy.
    Keywords: Upwelling ; Boundary currents ; Shelf-basin interaction ; Phytoplankton blooms
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  • 7
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    Circulation in the vicinity of Mackenzie Canyon from a year-long mooring array (2020)
    Elsevier
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Lin, P., Pickart, R. S., Fissel, D., Ross, E., Kasper, J., Bahr, F., Torres, D. J., O'Brien, J., Borg, K., Melling, H., & Wiese, F. K. Circulation in the vicinity of Mackenzie Canyon from a year-long mooring array. Progress in Oceanography, 187, (2020): 102396, doi:10.1016/j.pocean.2020.102396.
    Description: Data from a five-mooring array extending from the inner shelf to the continental slope in the vicinity of Mackenzie Canyon, Beaufort Sea are analyzed to elucidate the components of the boundary current system and their variability. The array, part of the Marine Arctic Ecosystem Study (MARES), was deployed from October 2016 to September 2017. Four distinct currents were identified: an eastward-directed flow adjacent to the coast; a westward-flowing, surface-intensified current centered on the outer-shelf; a bottom-intensified shelfbreak jet flowing to the east; and a recirculation at the base of the continental slope within the canyon. The shelf current transports −0.120.03 Sv in the mean and is primarily wind-driven. The response is modulated by the presence of ice, with little-to-no signal during periods of nearly-immobile ice cover and maximum response when there is partial ice cover. The shelfbreak jet transports 0.030.02 Sv in the mean, compared to 0.080.02 Sv measured upstream in the Alaskan Beaufort Sea over the same time period. The loss of transport is consistent with a previous energetics analysis and the lack of Pacific-origin summer water downstream. The recirculation in the canyon appears to be the result of local dynamics whereby a portion of the westward-flowing southern limb of the Beaufort Gyre is diverted up the canyon across isobaths. This interpretation is supported by the fact that the low-frequency variability of the recirculation is correlated with the wind-stress curl in the Canada Basin, which drives the Beaufort gyre.
    Description: The authors are indebted to Fisheries and Oceans Canada for building the logistics for MARES into the at-sea missions of the Integrated Beaufort Observatory. We are grateful to the captain and crew of the CCGS Sir Wilfred Laurier for ably deploying and recovering the MARES array. Marshall Swartz assisted with the cruise preparation logistics. We thank the two anonymous reviewers for their input which helped improve the paper. This project was funded by the US Bureau of Ocean Energy Management (BOEM), on behalf of the National Ocean Partnership Program. The Canadian contribution was supported by the Environmental Studies Research Fund (ESRF Project 2014-02N). MARES publication 003.
    Keywords: Canadian Beaufort Sea ; Mackenzie Canyon ; Boundary currents ; Canyon circulation ; Ice-ocean interaction
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  • 8
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    Mean conditions and seasonality of the West Greenland boundary current system near Cape Farewell (2021)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2020. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 50(10), (2020): 2849-2871, https://doi.org/10.1175/JPO-D-20-0086.1.
    Description: The structure, transport, and seasonal variability of the West Greenland boundary current system near Cape Farewell are investigated using a high-resolution mooring array deployed from 2014 to 2018. The boundary current system is comprised of three components: the West Greenland Coastal Current, which advects cold and fresh Upper Polar Water (UPW); the West Greenland Current, which transports warm and salty Irminger Water (IW) along the upper slope and UPW at the surface; and the Deep Western Boundary Current, which advects dense overflow waters. Labrador Sea Water (LSW) is prevalent at the seaward side of the array within an offshore recirculation gyre and at the base of the West Greenland Current. The 4-yr mean transport of the full boundary current system is 31.1 ± 7.4 Sv (1 Sv ≡ 106 m3 s−1), with no clear seasonal signal. However, the individual water mass components exhibit seasonal cycles in hydrographic properties and transport. LSW penetrates the boundary current locally, through entrainment/mixing from the adjacent recirculation gyre, and also enters the current upstream in the Irminger Sea. IW is modified through air–sea interaction during winter along the length of its trajectory around the Irminger Sea, which converts some of the water to LSW. This, together with the seasonal increase in LSW entering the current, results in an anticorrelation in transport between these two water masses. The seasonality in UPW transport can be explained by remote wind forcing and subsequent adjustment via coastal trapped waves. Our results provide the first quantitatively robust observational description of the boundary current in the eastern Labrador Sea.
    Description: A.P., R.S.P., F.B., D.J.T., and A.L.R. were funded by Grants OCE-1259618 and OCE-1756361 from the National Science Foundation. I.L.B, F.S., and J.H. were supported by U.S. National Science Foundation Grants OCE-1258823 and OCE-1756272. Mooring data from MA2 was funded by the European Union 7th Framework Programme (FP7 2007-2013) under Grant 308299 (NACLIM) and the Horizon 2020 research and innovation program under Grant 727852 (Blue-Action). J.K. and M.O. acknowledge EU Horizon 2020 funding Grants 727852 (Blue-action) and 862626 (EuroSea) and from the German Ministry of Research and Education (RACE Program). G.W.K.M. acknowledges funding from the Natural Sciences and Engineering Research Council.
    Keywords: Boundary currents ; Convection ; Deep convection ; Transport ; In situ oceanic observations ; Seasonal cycle
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  • 9
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    Cyclonic Eddies in the West Greenland Boundary Current System (2021)
    American Meteorological Society
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    Publication Date: 2022-05-27
    Description: Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 51(7), (2021): 2087–2102, https://doi.org/10.1175/JPO-D-20-0255.1.
    Description: The boundary current system in the Labrador Sea plays an integral role in modulating convection in the interior basin. Four years of mooring data from the eastern Labrador Sea reveal persistent mesoscale variability in the West Greenland boundary current. Between 2014 and 2018, 197 middepth intensified cyclones were identified that passed the array near the 2000-m isobath. In this study, we quantify these features and show that they are the downstream manifestation of Denmark Strait Overflow Water (DSOW) cyclones. A composite cyclone is constructed revealing an average radius of 9 km, maximum azimuthal speed of 24 cm s−1, and a core propagation velocity of 27 cm s−1. The core propagation velocity is significantly smaller than upstream near Denmark Strait, allowing them to trap more water. The cyclones transport a 200-m-thick lens of dense water at the bottom of the water column and increase the transport of DSOW in the West Greenland boundary current by 17% relative to the background flow. Only a portion of the features generated at Denmark Strait make it to the Labrador Sea, implying that the remainder are shed into the interior Irminger Sea, are retroflected at Cape Farewell, or dissipate. A synoptic shipboard survey east of Cape Farewell, conducted in summer 2020, captured two of these features that shed further light on their structure and timing. This is the first time DSOW cyclones have been observed in the Labrador Sea—a discovery that could have important implications for interior stratification.
    Description: A. P. and R. S. P. were funded by National Science Foundation Grants OCE-1259618 and OCE-1756361. I. L. B. and F. S. were funded by National Science Foundation Grants OCE-1258823 and OCE-1756272. N. P. H. was supported by the Natural Environment Research Council U.K. OSNAP program (NE/K010875/1 and NE/K010700/1). M. A. S. was supported by NSF Grants OCE-1558742 and OPP-1822334.
    Description: 2021-12-08
    Keywords: Boundary currents ; Eddies ; Transport
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  • 10
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    Structure and variability of the shelfbreak East Greenland Current north of Denmark Strait (2017)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 47 (2017): 2631-2646, doi:10.1175/JPO-D-17-0062.1.
    Description: Data from a mooring array deployed north of Denmark Strait from September 2011 to August 2012 are used to investigate the structure and variability of the shelfbreak East Greenland Current (EGC). The shelfbreak EGC is a surface-intensified current situated just offshore of the east Greenland shelf break flowing southward through Denmark Strait. This study identified two dominant spatial modes of variability within the current: a pulsing mode and a meandering mode, both of which were most pronounced in fall and winter. A particularly energetic event in November 2011 was related to a reversal of the current for nearly a month. In addition to the seasonal signal, the current was associated with periods of enhanced eddy kinetic energy and increased variability on shorter time scales. The data indicate that the current is, for the most part, barotropically stable but subject to baroclinic instability from September to March. By contrast, in summer the current is mainly confined to the shelf break with decreased eddy kinetic energy and minimal baroclinic conversion. No other region of the Nordic Seas displays higher levels of eddy kinetic energy than the shelfbreak EGC north of Denmark Strait during fall. This appears to be due to the large velocity variability on mesoscale time scales generated by the instabilities. The mesoscale variability documented here may be a source of the variability observed at the Denmark Strait sill.
    Description: Support for this work was provided by the Norwegian Research Council under Grant Agreement 231647 (LH and KV) and the Bergen Research Foundation under Grant BFS2016REK01 (KV). Additional funding was provided by the National Science Foundation under Grants OCE-0959381 and OCE-1558742 (RP).
    Keywords: Ocean ; Arctic ; Boundary currents ; Currents ; Stability ; Oceanic variability
    Repository Name: Woods Hole Open Access Server
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