Physical forcing in the southwest Atlantic: ecosystem control

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Abstract
In the southwest Atlantic sector of the Southern Ocean, temporal variability in the physical environment has been recorded since the early part of the last century. For example, sea-surface temperature at South Georgia shows periodicity of approximately 3 to 4 years. Variability at South Georgia also reflects temperature fluctuations in the Pacific, with the Pacific leading South Georgia by approximately 3 years. Increased krill biomass at South Georgia coincides with cold periods. In contrast, periods of reduced predator breeding performance are strongly correlated with warm anomaly periods, but these lag behind by a number of months. For some predators the most critical periods appear to be prior to the breeding season during the summer and early autumn of the preceding year. Such relationships between predator breeding performance and the physical environment most probably reflect prey (krill) availability. PHYSICAL VARIABILITY IN THE SOUTHERN OCEAN In the Southern Ocean, phase relationships in physical anomalies (e.g. Lemke et al. 1980, Zwally et al. 1983) and the movement of such anomalies have been identified and linked with transport by ocean currents (e.g. Lemke et al. 1980, Jacka & Budd 1991), principally the Antarctic Circumpolar Current (ACC) which connects the major ocean basins in an unbroken flow. Indeed, it is now thought that the ACC plays an important role in the transfer of climatic variability between the Pacific, Atlantic and Indian oceans (Murphy et al. 1995, White & Peterson 1996, Connolley 2002, Trathan & Murphy 2002).