The Antarctic krill (Euphausia superba) populations at South Georgia, which is in the eastern Scotia Sea, are hypothesized to be sustained by import of individuals from upstream regions, such as the western Antarctic Peninsula.
To test this hypothesis a modeling framework consisting of the Harvard Ocean Prediction System (HOPS) and a time-dependent, size-structured, physiologically-based krill growth model was developed. The simulated circulation fields obtained from HOPS were used with drifter studies to determine regions and pathways that allow transport of Antarctic krill to South Georgia. Pelagic phytoplankton concentrations along the simulated drifter trajectories were extracted from historical Coastal Zone Color Scanner measurements and sea ice algae concentrations were calculated from sea ice concentration and extent extracted along particle trajectories from Special Sensor Microwave/Imager measurements. As additional food sources, a time series of heterotrophic food was constructed from historical data, and time series of detritus concentrations along simulated drifter trajectories were calculated using phytoplankton concentrations extracted from Coastal Zone Color Scanner measurements together with measured particulate organic carbon to chlorophyll a ratios. These food resources, along specified drifter trajectories were then input to the krill
growth model to determine the size and viability of krill during transport from the source region to South Georgia.

The drifter simulations showed that krill spawned along the mid to northern portion of the west Antarctic Peninsula continental shelf, coinciding with known krill spawning areas, can be entrained into the Southern Antarctic Circumpolar Current Front and be transported across the Scotia Sea to South Georgia in 10 months or less. Drifters originating on the continental shelf of the Weddell Sea can reach South Georgia as well; however, transport from this region averages about 20 months.

The krill growth model simulations showed that no single food source, such as pelagic phytoplankton, detritus, sea ice algae, or zooplankton, can support continuous growth of Antarctic krill during the 168 to 225 days needed for transport from the western Antarctic Peninsula to South Georgia. However, combinations of the food
sources during the transport time enhanced krill survival, with zooplankton (heterotrophic food) and detritus being particularly important during
periods of low pelagic phytoplankton concentrations. The growth model simulations also showed that larval and juvenile krill originating along the western Antarctic Peninsula can grow to the sizes observed at South Georgia during the time needed for transport to this region.

Additional simulations examined the effects of variability in wind stress, the transport through Drake Passage, and changes in the location of the Southern Antarctic Circumpolar Current Front on the transport and growth of Antarctic krill. A 20\% decrease in wind stress or a 12\% decrease in transport of the Antarctic Circumpolar Current decreases the ability of krill to reach South Georgia, potentially endangering the survival of the local population. A 10 km northward shift in the location of the SACCF also reduces the delivery of krill to South Georgia, especially from the main spawning area along the Western Antarctic Peninsula and in the Bransfield Strait, thereby reducing the potential recruits to the krill populations at South Georgia.

The results of this study show that the krill populations along the Antarctic Peninsula and the Weddell Sea are likely the source populations that provide krill to the population in South Georgia. However, the successful transport of krill to South Georgia is shown to depend on a multitude of factors, such as the location of the spawning area and timing of spawning, food concentrations during transport, predation, and variations in the location of the SACCF and in sea ice extent. Therefore, this study provides insight into which biological and environmental factors control the successful transport of krill across the Scotia Sea and their survival during that time, and with it insight into krill distribution and production in the Scotia Sea.