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SUMMARY:The Influence of Southern Ocean Winds on the North Atlantic Carbon
  Sink - Ben Bronselaer\, Univ. Oxford
DTSTART:20151028T140000Z
DTEND:20151028T150000Z
UID:TALK60707@talks.cam.ac.uk
CONTACT:Dr Dave Munday
DESCRIPTION:Under climate change\, the increase in Southern Ocean winds is
  thought to upwell deep ocean carbon and increase atmospheric CO2\, result
 ing in a positive atmospheric CO2 feedback due to changes in the local dyn
 amics. Using idealised MITgcm simulations\, we demonstrate that the increa
 se in Southern Ocean winds can increase atmospheric CO2 even further via a
  non-local and novel mechanism by which the chemistry of the North Atlanti
 c sub-polar gyre is altered. The increase in Southern Ocean winds leads to
  a local increase in the upwelling of deep ocean nutrients and an intensif
 ication of the upper ocean meridional transport of nutrient towards low la
 titudes\, resulting in higher biological productivity in the tropical Atla
 ntic. The increase in tropical biological productivity alters the chemistr
 y of sub-thermocline waters in the oxygen minimum zone. These waters are s
 ubsequently advected to the North Atlantic sub-polar gyre through interior
  ocean pathways\, where the gyre’s capacity for absorbing atmospheric ca
 rbon is reduced. We show that the atmospheric CO2 feedback induced by the 
 increase in Southern Ocean winds due to non-local dynamical pathways is of
  the same order of magnitude as the feedback induced by the local Southern
  Ocean dynamics. As a result\, the effect of Southern Ocean winds on atmos
 pheric CO2 is larger than previously thought. The results demonstrate the 
 importance of circulation pathways within the ocean and show that an incre
 ase in biologic productivity in key regions such as the tropics can cause 
 an increase in atmospheric CO2 levels. While the results are presented usi
 ng idealised MITgcm simulations\, we show evidence that the same novel mec
 hanism is present in complex CMIP5 models under 4xCO2 forcing.\n
LOCATION:British Antarctic Survey\, Room 307
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