Variability of the southern Antarctic Circumpolar Current front north of South Georgia

Abstract

South Georgia (∼54°S, 37°W) is an island in the eastern Scotia Sea, South Atlantic that lies in the path of the Antarctic Circumpolar Current (ACC). The southern ACC front (SACCF), one of three major fronts associated with the ACC, wraps anticyclonically around South Georgia and then retroflects north of the island. This paper investigates temporal variability in the position of the SACCF north of South Georgia that is likely to have an effect on the South Georgia ecosystem by contributing to the variability in local krill abundance. A meridional hydrographic section that crossed the SACCF three times demonstrates that the SACCF is associated with a geopotential anomaly of 4.5 J kg −1 in the eastern Scotia Sea. A high resolution (1/4°×1/4°) map of historical geopotential anomaly shows the mean position of the SACCF retroflection north of South Georgia to be at 36°W, 400 km further east than in previous work. It also reveals temporal variability associated with the SACCF in the South Georgia region. A near-surface drifter provides evidence for variability in the western extent of the SACCF north of South Georgia and for the presence of eddies in the region. Output from a 3-year (1993–1995) high frequency wind forced run of the eddy-permitting Ocean Circulation and Climate Advanced Modelling project (OCCAM) model, used to investigate the frontal variability, shows two periods of anomalous westward extent of the SACCF north of South Georgia and associated eddy-shedding. The SACCF variability affects the near-surface transport of passive drifters into the region with implications for the South Georgia ecosystem.