Variability in transport pathways on and around the South Georgia shelf, Southern Ocean: Implications for recruitment and retention

Abstract

The waters around South Georgia are among the most productive in the Southern Ocean, with zooplankton populations close to the island, in particular Antarctic krill, supporting vast colonies of higher predators. However, our understanding of the processes governing variability in the supply of these food resources is limited by the poor spatial and temporal resolution of available data. Here, we use a numerical modeling approach to examine the underlying physical processes driving the recruitment and retention of zooplankton to the South Georgia shelf. Variability in the magnitude and spatial distribution of recruitment was dominated by the proximity and orientation of the southern Antarctic Circumpolar Current front to the shelf edge. Shelf retention was highest for source sites on the southwest shelf, with the main transport routes off the shelf to the north and northwest. Retention was lowest in the austral summer and winter; in summer increased glacial melt drives stronger off‐shelf near‐surface currents, while in winter, stronger winds lead to an increase in off‐shelf transport. Of particular note was the prediction of a significant increase in retention for particles released throughout the shelf in April and July 2000. This period coincided with the development of pronounced anticlockwise shelf flows, associated with horizontal density gradients due to reduced wind mixing of shelf waters, and differences between shelf and oceanic waters, which significantly reduced off‐shelf transport rates. Such findings are crucial for understanding the influence of variability in physical processes on the ecosystem at South Georgia.

Predicting krill swarm characteristics important for marine predators foraging off East Antarctica

“…A general retention within this region is consistent with the documented oceanic recirculation: some component of the westward flow along the Antarctic shelf break turns north between 80–90°E along the eastern flank of the Kerguelen Plateau, with an eastward return flow near 63°S forming a regional gyre closed at 115°E (Nicol et al , Rintoul et al ). The extent to which ocean circulation processes, and krill behaviour, may modulate dispersal and maintain regionally distinct krill populations continues to be an active research topic (Hofmann and Murphy , Murphy et al , Nicol , Young et al ). Overall, the ‘Kerguelen Axis’ region, linking the sub‐Antarctic islands in the north (Kerguelen, Heard and McDonald islands) along the submarine Kerguelen Plateau to the Antarctic continent, is a known region of enhanced biological productivity in the South Indian sector of the Southern Ocean (Arrigo et al , Duhamel and Welsford , Patterson et al ).…”

Oceanography and life history predict contrasting genetic population structure in two Antarctic fish species

“…; Young et al. ) and has been adapted for the simulation of C. gunnari and N. rossii eggs and larvae (Young et al. ).…”

Environmental correlates of Antarctic krill distribution in the Scotia Sea and southern Drake Passage

“…At South Georgia, krill density was greatest near the coast and decreased towards the shelf edge, possibly due to local circulation patterns. Results from a high-resolution ocean model of the South Georgia shelf suggest that in addition to flux across the northern shelf of the island, originating from both the southern shelf and offshore, there are several areas of retention on the northern shelf (Young et al, 2014), which may increase krill density closer to shore. In contrast, on the shelves of the Antarctic Peninsula and South Orkney Islands, krill density increased from the inner to outer shelf.…”