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SUMMARY:Ocean water masses reveal the geographic pattern of water cycle ch
 ange - Jan Zika\, UNSW Sydney
DTSTART:20221007T090000Z
DTEND:20221007T100000Z
UID:TALK182738@talks.cam.ac.uk
CONTACT:Dr. Shenjie Zhou
DESCRIPTION:Anthropogenic climate change threatens to disrupt the global w
 ater cycle and consequently the human and ecological systems which rely on
  freshwater. Salinity observations offer a route to quantifying historical
  water cycle change in the face of scarce direct observations of rainfall\
 , runoff and evaporation. Due to the dynamic nature of ocean circulation a
 nd mixing\, however\, robustly relating local (i.e. in a Eulerian referenc
 e frame) surface salinity changes to local fresh water fluxes remains chal
 lenging. In this presentation\, we harness water mass-based methods to def
 ine insightful metrics for water cycle change based on ocean salinity obse
 rvations.\n\nFirst\, we explore whether fresh regions of the ocean are get
 ting fresher and salty regions are getting saltier by analysing the distri
 bution of sea water as a function of salinity. As the contrast between fre
 sh and salty regions intensifies\, the distribution becomes wider. This wi
 dening in the distribution can be expressed as a metric which can be attri
 buted to water cycle change. \n\nSecond\, we investigate the climatologica
 l regions these changes in fresh water transport occur between\, namely\, 
 the hot tropics\, warm sub-tropical regions or cool sub-polar regions. To 
 do this we consider the ‘T-S’ curve of classical oceanography.  From 1
 970 to 2014\, the T-S curve has become ‘curvier’\, indicating a dramat
 ic shift in fresh water from the warm to cold oceans - a trend not capture
 d by climate reconstructions. \n\nFinally\, we present a new method based 
 on optimal transport theory which allows us to attribute air-sea water flu
 x changes to geographically distinct regions. The method optimises the con
 tributions of mixing\, circulation and air-sea heat and fresh water fluxes
  necessary to explain observed changes in the ocean’s water mass distrib
 ution. Based on this approach\, we provide new estimates of the geographic
 al distribution of water flux changes over the ocean surface. 
LOCATION:https://ukri.zoom.us/j/95640767988\; BAS Seminar Room 2
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