Determining how climate fluctuations affect ocean ecosystems requires an understanding of how biologicaland physical processes interact across a wide range of scales. Here we examine the role of physical andbiological processes in generating fluctuations in the ecosystem around South Georgia in the SouthAtlantic sector of the Southern Ocean. Anomalies in sea surface temperature (SST) in the South Pacificsector of the Southern Ocean have previously been shown to be generated through atmosphericteleconnections with El Nin˜o Southern Oscillation (ENSO)-related processes. These SST anomalies arepropagated via the Antarctic Circumpolar Current into the South Atlantic (on time scales of more than1 year), where ENSO and Southern Annular Mode-related atmospheric processes have a direct influenceon short (less than six months) time scales.We find that across the South Atlantic sector, these changes inSST, and related fluctuations in winter sea ice extent, affect the recruitment and dispersal of Antarctic krill.This oceanographically driven variation in krill population dynamics and abundance in turn affects thebreeding success of seabird and marine mammal predators that depend on krill as food. Such propagatinganomalies, mediated through physical and trophic interactions, are likely to be an important component ofvariation in ocean ecosystems and affect responses to longer term change. Population models derived onthe basis of these oceanic fluctuations indicate that plausible rates of regional warming of 1oC over the next100 years could lead to more than a 95% reduction in the biomass and abundance of krill across the ScotiaSea by the end of the century.