Antarctic Biological Invasions Driven by Stokes Drift and Mesoscale Variability

Antarctica has long been considered biologically isolated, with many Antarctic organisms found nowhere else on the planet. Biologists have presumed that the Southern Ocean fronts and circulation act as a barrier to dispersal, preventing the southward drift of organisms from the subantarctic islands to the north. Genomic analysis of foreign kelp recently found washed up on the Antarctic coast revealed that southward oceanic dispersal is possible. We use Lagrangian particle tracking to investigate the oceanographic processes impacting surface drift in the Southern Ocean. We find that both wave-driven Stokes drift and mesoscale variability are required for surface oceanographic connectivity between the subantarctic islands and Antarctica. When both Stokes drift and mesoscale variability are included in the Lagrangian modelling, Antarctic incursions are remarkably frequent and rapid.

We infer that Antarctica’s long-standing ecological differences are the result of environmental extremes that have prevented colonisations of temperate-adapted organisms, rather than the result of isolation. With global warming, we should expect to see successful establishment of numerous non-Antarctic species. Our modelling highlights that, at least in the Southern Ocean, Stokes drift plays a fundamental role in surface biological dispersal. This is in contrast to the vast majority of previous biological Lagrangian studies that have ignored the effect of Stokes drift.