Distribution of <scp>U</scp>pper <scp>C</scp>ircumpolar <scp>D</scp>eep <scp>W</scp>ater on the warming continental shelf of the <scp>W</scp>est <scp>A</scp>ntarctic <scp>P</scp>eninsula

Couto, Nicole; Martinson, Douglas G.; Kohut, Josh; Schofield, Oscar

doi:10.1002/2017jc012840

Cited by 54 publications

(48 citation statements)

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“…In this part of the section there is evidence of three warm-cored features possessing θ max > 1.7°C, while only one is found toward the southern end of the trough, with θ max < 1.6°C. The horizontal scale of these anomalies, between 5 and 15 km, is consistent with warm eddies observed previously in this region (e.g., Moffat et al (2009);Martinson & McKee, 2012;Couto et al (2017)). A similar gradient is seen when viewed in θ/S space: Profiles near the southern edge of the trough (but away from the open ocean) are generally colder along isopycnals than in the central (and to a lesser extent, the northern) portion of the trough (Figure 3c).…”

Section: Resultssupporting

confidence: 91%

“…Identifying, tracking, and characterizing these individual eddies from observations or model output can be done in a number of ways, including by finding closed contours of SSHA, PV anomalies, or anomalies of hydrographic properties . Eddies on the WAP shelf have been characterized with both hydrographic surveys and moored time series using temperature anomalies and velocity records, when available (Couto et al, 2017;Martinson & McKee, 2012 ;Moffat et al, 2009). Both these methods require making assumptions about the shape of the eddies.…”

Section: Eddy-mediated Export Of Shelf Watermentioning

confidence: 99%

“…A follow-up study using mooring-based observations (Martinson & McKee, 2012) roughly halfway up MT documented an average of around 40 eddies per year from 2007 to 2010, with an average diameter of 8-10 km. More recently, a broad-scale census of these features has been carried out across the WAP shelf by Couto et al (2017). Combining several years of underwater glider surveys conducted from the Palmer Long-Term Ecological Research program, they conclude that 60% of the glider profiles containing UCDW were part of a coherent eddy.…”

Section: Introductionmentioning

confidence: 99%

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The Role of Eddies and Topography in the Export of Shelf Waters From the West Antarctic Peninsula Shelf

et al. 2019

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Oceanic heat strongly influences the glaciers and ice shelves along West Antarctica. Prior studies show that the subsurface onshore heat flux from the Southern Ocean on the shelf occurs through deep, glacially carved channels. The mechanisms enabling the export of colder shelf waters to the open ocean, however, have not been determined. Here, we use ocean glider measurements collected near the mouth of Marguerite Trough (MT), west Antarctic Peninsula, to reveal shelf-modified cold waters on the slope over a deep (2,700 m) offshore topographic bank. The shelf hydrographic sections show subsurface cold features (θ <=1.5°C), and associated potential vorticity fields suggest a significant instability-driven eddy field. Output from a high-resolution numerical model reveals offshore export modulated by small (6 km), cold-cored, cyclonic eddies preferentially generated along the slope and at the mouth of MT. While baroclinic and barotropic instabilities appear active in the surrounding open ocean, the former is suppressed along the steep shelf slopes, while the latter appears enhanced. Altimetry and model output reveal the mean slope flow splitting to form an offshore branch over the bank, which eventually forms a large (116 km wide) persistent lee eddy, and an onshore branch in MT. The offshore flow forms a pathway for the small cold-cored eddies to move offshore, where they contribute significantly to cooling over the bank, including the large lee eddy. These results suggest eddy fluxes, and topographically modulated flows are key mechanisms for shelf water export along this shelf, just as they are for the shoreward warm water transport.Plain Language Summary The glaciers and ice shelves of the West Antarctic Peninsula have been rapidly retreating in the past 50 years, believed to be driven by increasing fluxes of heat from the ocean. While knowledge of the mechanisms that drive this heat from the open ocean onto the continental shelves has improved, our understanding of the counterbalancing flows of shelf waters remains limited. In this study, temperature, salinity, and velocity observations from an underwater autonomous vehicle, alongside numerical model output, are used to elucidate the pathway and mechanisms by which shelf waters are moved into the ocean interior. Small spinning vortices-known as eddies-containing shelf water are periodically generated from dynamical instabilities that derive from the horizontal shear of the flow. These small eddies then move offshore to cool a region of elevated topography near the mouth of Marguerite Trough, a deep glacially carved canyon. Here, cold water accumulates in a larger persistent eddy; satellite observations suggest that this water may ultimately be discharged into the Southern Ocean interior. Given that the topographic conditions of the field site are not unique, eddies and topographic flows are likely key mechanisms that balance the onshore flux of ocean heat in the West Antarctic.

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Section: Resultssupporting

confidence: 91%

Section: Eddy-mediated Export Of Shelf Watermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Role of Eddies and Topography in the Export of Shelf Waters From the West Antarctic Peninsula Shelf

et al. 2019

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“…The colors correspond to potential temperature ( ) on simulation date 9 October 2012 at a depth of 230 m or at the ocean bed in regions shallower than 230 m. to support relatively strong tidal ellipses and mixing (e.g., Foldvik et al, 1990;MacAyeal, 1984;Robertson, 2001), studies demonstrating that tidal fluctuations can substantially enhance cross-slope exchange have only materialized in the last decade (e.g., Mack et al, 2017;Padman et al, 2009;Wang et al, 2013). Mesoscale eddies can transfer CDW onto the shelf when isopycnals connect the shelf waters to the open ocean, for example, in regions where the ASF is absent (e.g., Couto et al, 2017;Graham et al, 2016;Martinson & Mckee, 2012;Nakayama et al, 2014) or where AABW descends the continental slope (e.g., Stewart & Thompson, 2015a;Thompson et al, 2014). Eddies can also support intrusions of CDW along the ocean bed in regions where there is a pronounced ASF Nøst et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Circum‐Antarctic Shoreward Heat Transport Derived From an Eddy‐ and Tide‐Resolving Simulation

Stewart

Klocker

Menemenlis

2018

Geophysical Research Letters

108

167

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Almost all heat reaching the bases of Antarctica's ice shelves originates from warm Circumpolar Deep Water in the open Southern Ocean. This study quantifies the roles of mean and transient flows in transporting heat across almost the entire Antarctic continental slope and shelf using an ocean/sea ice model run at eddy‐ and tide‐resolving (1/48°) horizontal resolution. Heat transfer by transient flows is approximately attributed to eddies and tides via a decomposition into time scales shorter than and longer than 1 day, respectively. It is shown that eddies transfer heat across the continental slope (ocean depths greater than 1,500 m), but tides produce a stronger shoreward heat flux across the shelf break (ocean depths between 500 m and 1,000 m). However, the tidal heat fluxes are approximately compensated by mean flows, leaving the eddy heat flux to balance the net shoreward heat transport. The eddy‐driven cross‐slope overturning circulation is too weak to account for the eddy heat flux. This suggests that isopycnal eddy stirring is the principal mechanism of shoreward heat transport around Antarctica, though likely modulated by tides and surface forcing.

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“…Part of the heat delivered to the shelf break by eddies and the background mean flow is channeled farther onshore by cross-shelf troughs, pathways that have been most extensively observed in West Antarctica (e.g., Couto et al, 2017;Gunn et al, 2018;Moffat et al, 2009;Nakayama et al, 2013;Walker et al, 2007Walker et al, , 2013Wåhlin et al, 2013Wåhlin et al, , 2016Zhang et al, 2016). Onshore heat transports within these troughs are estimated to be of O(1-10 TW) based on in situ observations Ha et al, 2014;Kalén et al, 2015;Martinson & McKee, 2012;Walker et al, 2007;Wåhlin et al, 2013) and idealized or regional numerical simulations (e.g., Graham et al, 2016;St-Laurent et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

Oceanic Heat Delivery to the Antarctic Continental Shelf: Large‐Scale, Low‐Frequency Variability

2018

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Onshore penetration of oceanic water across the Antarctic continental slope (ACS) plays a major role in global sea level rise by delivering heat to the Antarctic marginal seas, thus contributing to the basal melting of ice shelves. Here the time‐mean (Φmean) and eddy (Φeddy) components of the heat transport (Φ) across the 1,000‐m isobath along the entire ACS are investigated using a 0.1∘ global coupled ocean/sea ice simulation based on the Los Alamos Parallel Ocean Program (POP) and sea ice (Community Ice CodE) models. Comparison with in situ hydrography shows that the model successfully represents the basic water mass structure, with a warm bias in the Circumpolar Deep Water layer. Segments of on‐shelf Φ, with lengths of O(100–1,000 km), are found along the ACS. The circumpolar integral of the annually averaged Φ is O(20 TW), with Φeddy always on‐shelf, while Φmean fluctuates between on‐shelf and off‐shelf. Stirring along isoneutral surfaces is often the dominant process by which eddies transport heat across the ACS, but advection of heat by both mean flow‐topography interactions and eddies can also be significant depending on the along‐ and across‐slope location. The seasonal and interannual variability of the circumpolarly integrated Φmean is controlled by convergence of Ekman transport within the ACS. Prominent warming features at the bottom of the continental shelf (consistent with observed temperature trends) are found both during high‐Southern Annular Mode and high‐Niño 3.4 periods, suggesting that climate modes can modulate the heat transfer from the Southern Ocean to the ACS across the entire Antarctic margin.

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Distribution of Upper Circumpolar Deep Water on the warming continental shelf of the West Antarctic Peninsula

Cited by 54 publications

References 45 publications

The Role of Eddies and Topography in the Export of Shelf Waters From the West Antarctic Peninsula Shelf

The Role of Eddies and Topography in the Export of Shelf Waters From the West Antarctic Peninsula Shelf

Circum‐Antarctic Shoreward Heat Transport Derived From an Eddy‐ and Tide‐Resolving Simulation

Oceanic Heat Delivery to the Antarctic Continental Shelf: Large‐Scale, Low‐Frequency Variability

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