ECOLOGICAL IMPORTANCE OF THE SOUTHERN BOUNDARY OF THE ANTARCTIC CIRCUMPOLAR CURRENT

The Southern Ocean surrounds the Antarctic continent and supports one of the most productive marine ecosystems. Migratory and endemic specie s of whales, seals and birds benefit from the high biomass of their pr incipal prey, krill (Euphausia superba) and cephalopods, in this area. Most species of baleen whales and male sperm whales in the Southern H emisphere migrate between low-latitude breeding grounds in winter and highly productive Antarctic feeding grounds in summer. Here I show the importance of the southernmost reaches of the strongest ocean current , the Antarctic Circumpolar Current (ACC), to a complex and predictabl e food web of the Southern Ocean, The circumpolar distributions of blu e, fin and humpback whales from spring to midsummer trace the non-unif orm high-latitude penetration of shoaled, nutrient-rich Upper Circumpo lar Deep Water, which is carried eastward by the ACC, The poleward ext ent of this water mass delineates the Southern Boundary(1) of the ACC and corresponds not only to the circumpolar distributions of baleen wh ales, but also to distributions of krill and to regions of high, seaso nally averaged, phytoplankton biomass, Sperm whales, which feed on cep halopods(2), also congregate in highest densities near the Southern Bo undary. The association of primary production, Krill, and whales with the Southern Boundary, suggests that it provides predictably productiv e foraging for many species, and is of critical importance to the func tion of the Southern Ocean ecosystem.