Pathways of the Deep Water Upwelling to the Antarctic Shelves: a Water Mass Perspective

The Deep Waters originating in the Atlantic, Indian and Pacific upwell in the Southern Ocean, with the warmest waters, of Indian and Pacific origin (Upper Circumpolar Deep Water) reaching the Antarctic shelves in the eastern South Pacific sector (Bellingshausen Sea). The pathways of these deep waters to the upper Southern Ocean is strongly mitigated by topography at Drake Passage latitudes, including Kerguelen Plateau, the East Pacific Rise, and the Southwest Indian Ridge. Topographic steering of the southern boundary of the Antarctic Circumpolar Current by the mid-ocean ridges extends the Antarctic winter sea ice edge far to the north, while regions with less steering allow the ice edge to shift back southwards; this pattern is strongly related to the observed pattern of decadal sea ice gain and retreat, respectively. Observed changes in CDW properties in the Ross/Amundsen/Bellingshausen Seas, from 1992 to 2011, suggest increased ventilation by the northern Deep Waters, which increases heat content in the upper ocean, freshens the abyssal layer, and could be associated with increased ocean temperatures along the West Antarctic Peninsula and changes in sea ice extent. The observed heat and sea ice changes are consistent with a strengthening of the southern ACC circulation and adjoining subpolar gyres.