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SUMMARY:Polar Oceans PhD Student talks - David Bett and Rachael Sanders\, 
 BAS
DTSTART:20180618T130000Z
DTEND:20180618T140000Z
UID:TALK106984@talks.cam.ac.uk
CONTACT:Dr Emma Boland
DESCRIPTION:Speakers:\n\n*David Bett* - *The effect of the Amundsen Sea fr
 eshwater balance on ocean melting of the West Antarctic Ice Sheet.*\n\n*Ra
 chael Sanders* - *Drivers of Subantarctic Mode Water variability.*\n\nAbst
 racts:\n\n*The effect of the Amundsen Sea freshwater balance on ocean melt
 ing of the West Antarctic Ice Sheet*: The Amundsen Sea has some of the hig
 hest thinning rates of ice shelves in Antarctica\, due to increased ocean 
 melting. This increased input of freshwater into the region could affect t
 he currents and mixing\, due to density being strongly dictated by salinit
 y in the polar regions. However first a clear understanding of the sources
  and sinks of freshwater in the region is lacking\, which is needed before
  the effect of this excess freshwater can be understood. Therefore here we
  present the preliminary results and methods of investigating the distribu
 tion and effect of freshwater from different sources in the Amundsen Sea\,
  using passive tracers in both idealised and realistic regional MITgcm mod
 els. The vertical distribution of ice shelf meltwater is investigated in a
 n idealised model and is found to be dependent on the Circumpolar Deep Wat
 er layer thickness. Meanwhile the local freshwater feedback of ice shelf m
 eltwater on melt rates is found to be small for the oceanographic ranges s
 een in the Amundsen Sea. Climatological freshwater distributions are also 
 investigated in the realistic model\, where we found that ice shelf and se
 a ice freshwater tracers climatologically dominate close to the coast\, in
  the shelf sea regions of the model.\n\n*Drivers of Subantarctic Mode Wate
 r variability*: Subantarctic Mode Water (SAMW) forms on the northern edge 
 of the Antarctic Circumpolar Current in the Southern Ocean. The formation 
 is critical to the subducting portion of the Southern Ocean overturning ci
 rculation\, which is vital to the transfer of carbon and heat from the atm
 osphere into the deep ocean. A number of processes are involved in the for
 mation\, and freshwater fluxes due to sea ice have been shown to make a si
 gnificant contribution. In recent decades\, there has been an observed fre
 shening of SAMW\, linked to changes in the concentration and northward tra
 nsport of sea ice\, but variability in these mechanisms is not well unders
 tood. Here we present the methods and preliminary results of a study inves
 tigating the drivers of recent variability in SAMW properties. Using the o
 utput from the Southern Ocean State Estimate (SOSE)\, a data assimilating 
 Southern Ocean model\, we compute the mixed layer budgets in the SAMW form
 ation region of the southeast Pacific to determine the processes responsib
 le for changes in mixed layer temperature and salinity\, which subsequentl
 y drive changes in the subducted SAMW. We find that calculating these budg
 ets using the methods of Dong et al. (2007) leaves a significant residual 
 between the rate of change of salinity/temperature and the sum of the proc
 esses driving these changes.  We therefore focus on adjusting the calculat
 ion of each individual term to obtain budgets that are as near to closure 
 as possible.
LOCATION:British Antarctic Survey\, Seminar Room 330b
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