Calibrated Seismic Imaging of Eddy-Dominated Warm-Water Transport Across the Bellingshausen Sea, Southern Ocean

Abstract

Seismic reflection images of thermohaline circulation from the Bellingshausen Sea, adjacent to the West Antarctica Peninsula, were acquired during February 2015. This survey shows that bright reflectivity occurs throughout the upper 300 m. By calibrating these seismic images with coeval hydrographic measurements, intrusion of warm water features onto the continental shelf at Marguerite and Belgica Troughs is identified and characterized. These features have distinctive lens-shaped patterns of reflectivity with lengths of 0.75-11.00 km and thicknesses of 100-150 m, suggesting that they are small mesoscale to submesoscale eddies. Abundant eddies are observed along a transect that crosses Belgica Trough. Near Alexander Island Drift, a large, of order (O)102 km 3 , bowl-like feature, that may represent an anticyclonic Taylor column, is imaged on a pair of orthogonal images. A modified iterative procedure is used to convert seismic imagery into maps of temperature that enable the number and size of eddies being transported onto the shelf to be quantified. Finally, analysis of prestack shot records suggests that these eddies are advecting southward at speeds of O(0.1) m s -1 , consistent with limited legacy hydrographic measurements. Concentration of observed eddies south of the Southern Antarctic Circumpolar Current Front implies they represent both a dominant, and a long-lived, mechanism of warm-water transport, especially across Belgica Trough. Our observations suggest that previous estimates of eddy frequency may have been underestimated by up to 1 order of magnitude, which has significant implications for calculations of ice mass loss on the shelf of the West Antarctic Peninsula.