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Abstract Over recent decades, the West Antarctic Ice Sheet has experienced rapid thinning of its floating ice shelves as well as grounding line retreat across its marine‐terminating glaciers. The transport of warm Modified Circumpolar Deep Water (MCDW) onto the continental shelf, extensively documented along the West Antarctic Peninsula (WAP), and in the Amundsen Sea, has been identified as the key process for inducing these changes. The Bellingshausen Sea sits between the Amundsen Sea and the northern part of the WAP, but its oceanic properties remain remarkably under‐studied compared to surrounding regions. Here, we present observations collected from a hydrographic survey of the Bellingshausen Sea continental shelf in austral summer 2019. Using a combination of ship‐based and glider‐based CTD and lowered ADCP observations, we show that submarine troughs provide topographically steered pathways for MCDW from the shelf break toward deep embayments and ultimately under floating ice shelves. Warm MCDW enters the continental shelf at the deepest part of the Belgica Trough and flows onshore along the eastern side of the trough. Modification of these shoreward‐flowing waters by glacial melt is estimated by calculating meltwater fractions using an optimal multiparameter analysis. Meltwater is found to be elevated at the western edge of both the Latady and Belgica troughs. Meltwater distributions, consistent with other diagnostics, suggest a recirculation in each trough with modified waters eventually flowing westward upon leaving the Belgica Trough. Our results show that the Bellingshausen Sea is a critical part of the larger West Antarctic circulation system, linking the WAP and the Amundsen Sea.
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Cross-Shelf Exchange in Prograde Antarctic Troughs Driven by Offshore-Propagating Dense Water Eddies
Abstract This study examines the link between near-bottom outflows of dense water formed in Antarctic coastal polynyas and onshore intrusions of Circumpolar Deep Water (CDW) through prograde troughs cutting across the continental shelf. Numerical simulations show that the dense water outflow is primarily in the form of cyclonic eddies. The trough serves as a topographic guide that organizes the offshore-moving dense water eddies into a chain pattern. The offshore migration speed of the dense water eddies is similar to the velocity of the dense water offshore flow in the trough, which scaling analysis finds to be proportional to the reduced gravity of the dense water and the slope of the trough sidewalls and to be inversely proportional to the Coriolis parameter. Our model simulations indicate that, as these cyclonic dense water eddies move across the trough mouth into the deep ocean, they entrain CDW from offshore and carry CDW clockwise along their periphery into the trough. Subsequent cyclonic dense water eddies then entrain the intruding CDW further toward the coast along the trough. This process of recurring onshore entrainment of CDW by a topographically constrained chain of offshore-flowing dense water eddies is consistent with topographic hotspots of onshore intrusion of CDW around Antarctica identified by other studies. It can bring CDW from offshore to close to the coast and thus impact the heat flux into Antarctic coastal regions, affecting interactions among ocean, sea ice, and ice shelves. Significance StatementTroughs cutting across the Antarctic continental shelf are a major conduit for the transport of dense shelf water from coastal formation regions to the shelf break. This study describes a process in which clockwise-spinning eddies moving offshore in prograde troughs successively entrain filaments of relatively warm Circumpolar Deep Water from offshore across the entire shelf and into the coastal region. This eddy-induced transport provides a new understanding of the shelf edge exchange process identified in previous studies and a mechanism for further onshore intrusion of the warm Circumpolar Deep Water over parts of the Antarctic shelf. The resultant onshore heat flux could potentially bring a substantial amount of heat from offshore into the coastal region and thus affect ice–ocean interactions through melting sea ice and ice shelves.
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- Award ID(s):
- 2147884
- PAR ID:
- 10528960
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of Physical Oceanography
- Volume:
- 54
- Issue:
- 8
- ISSN:
- 0022-3670
- Format(s):
- Medium: X Size: p. 1613-1631
- Size(s):
- p. 1613-1631
- Sponsoring Org:
- National Science Foundation
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