Climatically driven fluctuations in Southern Ocean ecosystems

Determining how climate fluctuations affect ocean ecosystems requires an understanding of how biological
and physical processes interact across a wide range of scales. Here we examine the role of physical and
biological processes in generating fluctuations in the ecosystem around South Georgia in the South
Atlantic sector of the Southern Ocean. Anomalies in sea surface temperature (SST) in the South Pacific
sector of the Southern Ocean have previously been shown to be generated through atmospheric
teleconnections with El Nin˜o Southern Oscillation (ENSO)-related processes. These SST anomalies are
propagated via the Antarctic Circumpolar Current into the South Atlantic (on time scales of more than
1 year), where ENSO and Southern Annular Mode-related atmospheric processes have a direct influence
on short (less than six months) time scales.We find that across the South Atlantic sector, these changes in
SST, 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 the
breeding success of seabird and marine mammal predators that depend on krill as food. Such propagating
anomalies, mediated through physical and trophic interactions, are likely to be an important component of
variation in ocean ecosystems and affect responses to longer term change. Population models derived on
the basis of these oceanic fluctuations indicate that plausible rates of regional warming of 1oC over the next
100 years could lead to more than a 95% reduction in the biomass and abundance of krill across the Scotia
Sea by the end of the century.