P06h  IAPSO (Physical Oceanography)
P06 The Southern Ocean: where Ocean, Ice and Atmosphere Meet

01-Jul-2015 10:30 12:00
Abstract: IUGG-5320
Influence of the northern Deep Waters on Southern Ocean water properties and cryosphere

The Deep Waters originating in the Atlantic, Indian and Pacific upwell in the Southern Ocean, with the warmest waters reaching the Antarctic shelves in the eastern South Pacific sector (Bellingshausen Sea). Hydrographic data and circulation analysis, including that from the Southern Ocean State Estimate, shows that the water that warms the west Antarctic Peninsula (WAP) shelves, hence is implicated in ocean-ice shelf interaction where the ice shelf is melting fastest, is Upper Circumpolar Deep Water (UCDW), which derives from Indian and Pacific Deep Waters, rather than North Atlantic Deep Water, which lies deeper in the Southern Ocean. 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 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 WAP and changes in sea ice extent. The observed changes are suggestive of a strengthening of the ACC, although not necessarily its location. Within the Ross Sea, the nearly adiabatic bottom 1000 m layer continues to warm, based on 1992, 2005, 2011, 2014 hydrographic surveys.

L. Talley1, R. Abernathey2, M. Mazloff3, A. Orsi4, J. Swift3, B. Sloyan5.
1UCSD, Scripps Institution of Oceanography, La Jolla, USA.
2Columbia University, Lamont-Doherty Earth Observatory, New York- NY, USA.
3UCSD, Scripps Institution of Oceanography, La Jolla- CA, USA.
4Texas A&M, College of Geosciences, College Station- TX, USA.
5CSIRO, CMAR, Hobart- Tasmania, Australia.


Keywords: ocean circulation     overturning circulation     MOC     southern ocean changes