Origin of Circumpolar Deep Water intruding onto the Amundsen and Bellingshausen Sea continental shelves

Abstract

Melting of West Antarctic ice shelves is enhanced by Circumpolar Deep Water (CDW) intruding onto the Amundsen and Bellingshausen Seas (ABS) continental shelves. Despite existing studies of cross-shelf and on-shelf CDW transports, CDW pathways onto the ABS originating from further offshore have never been investigated. Here, we investigate CDW pathways onto the ABS using a regional ocean model. Simulated CDW tracers from a zonal section across 67°S (S04P) circulate along the Antarctic Circumpolar Current (ACC) and Ross Gyre (RG) and travel into ABS continental shelf after 3–5 years, but source locations are shifted westward by ~900 km along S04P in 2001–2006 compared to 2009–2014. We find that simulated on- and off-shelf CDW is ~0.1–0.2 °C warmer in the 2009–2014 case than in the 2001–2006 case together with changes in simulated ocean circulation. These differences are primarily caused by lateral, rather than surface, boundary conditions, implying that large-scale atmospheric and ocean circulations are able to control CDW pathways and thus off- and on-shelf CDW properties.

The Antarctic Slope Current in a Changing Climate

“…At present, modeling and observational capabilities are unable to capture feedbacks between these small‐scale dynamics and the larger‐scale forcing. Adequately representing these small‐scale features in GCMs through physical parameterizations is one approach, but creatively coupling different model types and model domains may also provide additional insight (Nakayama et al, ).…”

“…Finally, the Warm Shelf case is of dynamical interest because over this region the eastward moving flow along the WAP transitions to a westward moving flow associated with the southern boundary of the Ross Gyre (Figure ). The location, variability, and physical processes associated with the initiation of the westward flow, traditionally linked to the ASC, in the Bellingshausen and Amundsen sector remains an open question and may be influenced by nonlocal processes that determine the spatial extent of the Ross Gyre and the intensity of its southern boundary (Armitage et al, ; Dotto et al, ; Nakayama et al, ).…”

“…Eventually, the circulation over the continental shelf brings this warm water into contact with marine‐terminating glaciers of the Antarctic Ice Sheet (AIS). The ASC is a unique feature that responds not only to local changes, for example, the surface wind stress (Gill, ; Stewart & Thompson, ) but also to larger‐scale modes of climate variability, such as El Niño and the Southern Annular Mode (De Rydt et al, ; Nakayama et al, ; Spence et al, ). Shifts in the intensity or position of ASC fronts, or changes to the range of densities that occupy the continental shelf, will therefore exert a strong influence over the heat budget of the Antarctic margins.…”

“…These waters are then entrained into the ASC, where they can be returned to the northern part of the gyre in narrow and frictionally balanced boundary currents. Thus, the ASC may also exhibit characteristics similar to western boundary current systems, and it can be an important mediator of oceanic and atmospheric changes over much broader spatial scales (Nakayama et al, ).…”

Brief communication: A submarine wall protecting the Amundsen Sea intensifies melting of neighboring ice shelves

“…During its transport onto the continental shelf the water mass is transformed into modified CDW (mCDW) by mixing with local water masses. In the Amundsen Sea the large-scale oceanic and atmospheric circulation controls the CDW uplift (Nakayama et al, 2018). It includes the tropic's influence via atmospheric wave trains The Cryosphere Discuss., https://doi.…”