Modelling dispersal of juvenile krill released from the Antarctic ice edge: ecosystem implications of ocean movement

Sea ice retreat is a key event affecting Southern Ocean ecosystems during spring and summer. The impacts of this change can be seen in these ecosystems from primary producers to top predators, through biological, chemical and physical systems. We apply a Lagrangian particle tracking method to investigate transport processes from the retreating sea ice edge in the Southern Ocean during spring and summer. The resulting distribution of surface krill patches is used as an case study for our modelling approach. Antarctic krill (Euphausia superba), a secondary producer, plays a key role in the Southern Ocean ecosystems. Antarctic krill are highly abundant in the Southern Ocean with a complex distribution pattern both in the horizontal and vertical dimensions. Observations dating back to the 1930s show that juvenile krill often form surface patches – high density clusters of krill at the ocean surface – throughout the Southern Ocean during the spring and summer seasons.

We develop a hypothesis, based on historical observations, that surface krill patches composed of juvenile krill move passively with ocean currents after their release from the sea ice edge zone in spring. Applying this hypothesis and method to the Southern Hemisphere spring/summer, leads to results that indicate that the observed changes in distribution of krill patches from historical to contemporary records could be related to the southward shift of the sea ice edge over the last century.