Date of Award

2024

Degree Type

Thesis

Degree Name

Master of Science in Oceanography

Specialization

Physical Oceanography

Department

Oceanography

First Advisor

Kathleen Donohue

Abstract

The Antarctic Circumpolar Current (ACC), the predominant current in the Southern Ocean, flows around the Antarctic continent. It is unique in that it encounters no horizontal boundaries, and instead flows through and connects the Atlantic, Indian, and Pacific basins. The ACC presents a barrier to heat transport due to its strength, vertical structure, and circumpolar path. At a finite number of locations the ACC must negotiate topographic ridge systems and in lee of these ridges, the ACC becomes unstable. In these locations, termed 'hot spots', large eddy heat fluxes occur. In situ deep observations within the ACC are difficult to come by. Even more sparse are observations of deep currents and temperature in the southernmost front of the ACC - the Southern ACC Front (SACCF). Recently acquired observations from 10 months of in situ measurements within the SACCF quantify eddy heat fluxes in the South East Indian Ridge (SEIR) hot spot. Mean eddy heat fluxes are directed poleward across the ACC and arise from a handful of events where abyssal eddies are strengthened under developing ACC meanders. Events are short-lived, typically lasting less than 15 days.

Observed eddy heat flux is nearly depth-independent with slight enhancement above 200 m depth, in agreement with observations in Drake Passage. A general circulation model, 5 years of the free-running global HYCOM at 1/12 of a degree horizontal resolution, reproduces the spatial pattern of mean cross-frontal eddy heat flux. HYCOM slightly overestimates the intensity of these cross-frontal events compared to the observations and similar to observations, yet reproduces the event-like nature of the fluxes with 5-10 events each year. It also provides a broader window in which to examine eddy heat flux, both spatially and temporally. The SEIR complex stands out as a ridge system where all ACC fronts converge as they negotiate the ridge. In the lee of the ridge, the standing meander comprises all three ACC fronts. A HYCOM-based Lagrangian pilot study shows that the SEIR complex is capable to transporting water parcels across all fronts of the ACC.

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