Eddy overturning of the Antarctic Slope Front controls glacial melting in the Eastern Weddell Sea

O A Nøst,Q Zhou,L H Smedsrud,V Tverberg,C Lydersen,M Biuw,K M Kovacs,T Hattermann

doi:10.1029/2011jc006965

O A Nøst, Q Zhou + Show 6 more

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https://doi.org/10.1029/2011jc006965

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Abstract

The Eastern Weddell Sea is characterized by narrow continental shelves and Warm Deep Water (WDW) is located in close proximity to the ice shelves in this region. The exchange of WDW across the Antarctic Slope Front (ASF) determines the rate of basal ice shelf melting. Here, we present a unique data set consisting of 2351 vertical profiles of temperature and salinity collected by southern elephant seals (Mirounga leonina) and a profile beneath the Fimbul Ice Shelf (FIS), obtained via drilling through 395 m of ice. This data set reveals variations in salinity and temperature through winter, and using a conceptual model of the coastal salt budget we quantify the main exchange processes. Our data show that modified WDW, with temperatures below −1.5°C, is advected onto the shelf and into the ice shelf cavities by an eddy overturning of the ASF. The onshore Ekman flux of surface waters during summer is the main source of freshwater that leads to the formation of low salinity shelf waters in the region. The modified WDW that reaches beneath the ice shelves is too cold for basal ice shelf melting to create such low salinity water. A high‐resolution model of an idealized ASF–continental shelf–ice shelf system supports the conclusions from the data analysis. The inflow of WDW onto the continental shelf and into the ice shelf cavity occurs within a bottom boundary layer where the eddy advection in the model is particularly strong, in close agreement with the observed vertical profile of temperature beneath the FIS.

Highlights

[2] Basal melting of Antarctic ice shelves may have significant impacts on the Antarctic ice sheet and global sea level [Pollard and DeConto, 2009], as thinning ice shelves are associated with acceleration of inland ice streams in Antarctica [Shepherd et al, 2002] and Greenland [Holland et al, 2008; Straneo et al, 2010]
The most important heat source for ice shelf basal melting around Antarctica is the warm Circumpolar Deep Water (CDW), which circulates from the continental slope region, across the continental shelf and into ice shelf cavities at many different locations around Antarctica [Fahrbach et al, 1994; Walker et al, 2007; Thoma et al, 2008; Nicholls et al, 2008a; Wåhlin et al, 2010]
[3] In the Eastern Weddell Sea (EWS), Warm Deep Water, (WDW), which is derived from the main mass of CDW around 20°–30°E [Deacon, 1979], is separated from ice shelves by the Antarctic Slope Front (ASF) [Gill, 1973; Fahrbach et al, 1994; Heywood et al, 1998]

Summary

Introduction

[2] Basal melting of Antarctic ice shelves may have significant impacts on the Antarctic ice sheet and global sea level [Pollard and DeConto, 2009], as thinning ice shelves are associated with acceleration of inland ice streams in Antarctica [Shepherd et al, 2002] and Greenland [Holland et al, 2008; Straneo et al, 2010]. Cold surface water is transported onshore within the Ekman layer and dominates the continental shelf, while warmer and more saline WDW is forced downward below the depth of the continental shelf [Sverdrup, 1953; Ohshima et al, 1996; Heywood et al, 1998] Given the potential for melting represented by WDW, direct investigation of both the water masses and dynamic processes on the continental shelf and slope are essential for ocean and climate modeling. Technical details of the data analysis are given in Appendix A

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Results

Discussion

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Conclusion