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SUMMARY:Ocean mixing and the Meridional Overturning Circulation: the South
 ern Ocean crossroads - Dr Alberto Naveira Garabato (National Oceanography 
 Centre\, Southampton)
DTSTART:20070627T150000Z
DTEND:20070627T160000Z
UID:TALK7607@talks.cam.ac.uk
CONTACT:Deb Shoosmith
DESCRIPTION:Today\, we tend to think of the Meridional Overturning Circula
 tion (MOC) of the ocean as a layered circulation with multiple surface sou
 rces of dense water that sinks and flows along density surfaces (isopycnal
 s) until it approaches a boundary\, where it is mixed vertically and trans
 its to a different level of the overturning. In this context\, oceanograph
 ers like to talk about the existence of an "ocean mixing problem"\, in whi
 ch two different schools of thought propose the dominance of either mixing
  along isopycnals by mesoscale eddies or mixing across isopycnals by break
 ing internal gravity waves in closing the MOC by returning deep water to t
 he upper ocean. These two models result in similar-looking oceans (in term
 s of their temperature and salinity distributions) but exhibit very differ
 ent energetics and sensitivities to changing climatic forcing. Further\, e
 ither of the two generally implies that water parcels have long journeys a
 nd residence times in the deep ocean\, a result that shapes our view of ho
 w the ocean regulates the Earth's climate and biogeochemical cycles over c
 limatic time scales.\n \nIn this talk\, I will discuss a collection of cir
 cumstantial evidence from the Southern Ocean to argue for an alternative z
 eroth-order description of the MOC. This new model proposes that the two c
 lassical paradigms of ocean mixing are strongly coupled and cannot be cons
 idered in isolation. It suggests that regions where mesoscale eddies are d
 issipated (in particular\, the Antarctic Circumpolar Current) may host MOC
  short circuits\, or 'hot spots' of rapid flow along and across density su
 rfaces where water parcels can short-circuit their circulation through the
  deep global ocean. Motivated by this and other uncomfortable evidence\, I
  will conclude by outlining a BAS-partnered NERC consortium project that s
 eeks to test and redefine the present paradigm of Southern Ocean mixing. 
LOCATION:British Antarctic Survey
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