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SUMMARY:Southern Ocean thermocline ventilation - Jean-Baptiste Sallee \, C
 SIRO in Hobart\, Tasmania\, Australia
DTSTART:20100305T110000Z
DTEND:20100305T120000Z
UID:TALK23308@talks.cam.ac.uk
CONTACT:Zhaomin Wang
DESCRIPTION:Interactions between the atmosphere and ocean are mediated by 
 the mixed layer at the ocean surface through the ventilation process. We e
 xplore an approximate mass (volume) budget in the surface layer to reveal 
 the intensity and regional variability of the ventilation process\, and qu
 antify the role of eddies. Ventilation resulting from Ekman pumping is est
 imated from satellite winds\, the geostrophic mean component is assessed f
 rom a climatology strengthened with Argo data and the eddy-induced advecti
 on is included via the parameterization of Gent and McWilliam (1990) toget
 her with eddy mixing estimates. All three components contribute significan
 tly to ventilation. While the circumpolar-average upper cell structure is 
 consistent with the average surface fluxes\, it hides strong longitudinal 
 regional variations and does not represent any local regime. \n\nThe eddy-
 induced contribution is important for the water-mass subduction in the vic
 inity of the Antarctic Circumpolar Current. It balances the horizontal nor
 thward Ekman transport as well as the vertical Ekman pumping. We investiga
 te the pattern of eddy mixing and its control by the mean flow using virtu
 al particle advected by altimetry. While\, the mean flow tends to reduce e
 ddy mixing and therefore eddy-induced transport in the vicinity of the ACC
 \, it increases mixing on its equatorward flank. Eddy-mixing has a large i
 nterannual variability.\n\nSubduction shows strong regional variability wi
 th bathymetrically constrained hotspots of large subduction. This constrai
 nt is mainly driven by lateral induction across large mixed-layer gradient
 s. Therefore variations in mixed-layer depth affect the rate of exchange b
 etween the atmosphere and deeper ocean. We analyse temperature and salinit
 y data from Argo profiling floats to show that the Southern Annular Mode\,
  the dominant mode of atmospheric variability in the southern hemisphere\,
  leads to large-scale anomalies in mixed-layer depth that are zonally asym
 metric. Our result suggest that changes in the Southern Annular Mode\, inc
 luding recent and projected trends attributed to human activity\, drive va
 riations in Southern Ocean mixed-layer depth\, with consequences for air-s
 ea exchange\, ocean sequestration of heat and carbon\, and biological prod
 uctivity.\n
LOCATION:British Antarctic Survey\, Room 307
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