The Southern Boundary of the Antarctic Circumpolar Current

Oelerich, Ria (2022) The Southern Boundary of the Antarctic Circumpolar Current. Doctoral thesis, University of East Anglia.

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Abstract

Antarctic ice sheet mass loss is a major contributor to global sea level rise. Circumpolar Deep Water, transported by the Antarctic Circumpolar Current (ACC), contributes heat to amplify ice shelf basal melting, when it accesses the Antarctic continental shelf. The Southern Boundary of the ACC provides the closest connection of warm ACC waters to Antarctica. Strong density gradients across the Southern Boundary constitute a frontal jet and modulate the southward heat transport. Mechanisms modulating the poleward transport of heat are poorly understood. This thesis explores two such mechanisms.

Firstly, the frontal structure of the Southern Boundary is investigated with observed hydrographic transects. A global ocean reanalysis is used to identify the interannual and seasonal variability of the Southern Boundary and deep-water temperatures on the Bellingshausen Sea continental shelf. Annual means of potential temperature reveal interannual variability and enable separation into warm and cold regimes with deep-water temperature differences of up to 1°C. The results suggest that the deep-water temperature in the southern Bellingshausen Sea is due to a combination of shelf break heat transport and
surface heat fluxes. Surface heat flux variability is related to the variability of the Amundsen Sea Low and its influence on sea ice extent and local formation of cold, dense water in winter.

Secondly, the variability of the Southern Boundary at the Greenwich Meridian is investigated using ocean gliders and satellite altimetry. It is demonstrated that a cyclonic eddy near the Southern Boundary increases its density gradients and amplifies its frontal jet. Mixing length scales are suppressed across the frontal jet while the eddy is crossing and increase to about 25 km after the eddy has crossed the Greenwich Meridian. This increase supports an increased exchange of water parcels across the Southern Boundary, implying that the ‘barrier’ properties of the Southern Boundary are reduced.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Environmental Sciences
Depositing User:	Chris White
Date Deposited:	26 Jun 2023 09:49
Last Modified:	26 Jun 2023 09:49
URI:	https://ueaeprints.uea.ac.uk/id/eprint/92493
DOI:

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