BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:Flow of the Antarctic Circumpolar Current: Origins and glacial-int
 erglacial shifts - Nick McCave (Dept. of Earth Sciences)
DTSTART:20151116T130000Z
DTEND:20151116T140000Z
UID:TALK61540@talks.cam.ac.uk
CONTACT:Doris Allen
DESCRIPTION:The dispute as to whether the ACC was established around 23 Ma
  ago or at approx 30 Ma is now homing in on the earlier date when the Tasm
 an gap (between Tasmania and Antarctica)\, which opened at 33 Ma\, moved i
 nto a position when the westerly winds could drive a flow to the east\, re
 versing the previous flow to the west. This is based on geochemical tracer
 s of water masses. My view (and several others’) had favoured a 23 Ma on
 set based on a step change in deep flow speed at that location\, but that 
 may now be associated with a glacial event.\nDuring the last glacial maxim
 um (LGM) ACC flow speed may have been faster\, unchanged or slower than pr
 esent under either stronger or weaker winds and may have shifted to the no
 rth (or not). As this is the largest current on the planet (transporting a
 pprox. 134 x 106 m3/s)\, it deserves to be better understood.  I have prov
 ided data on the flow of the ACC through the Scotia Sea flow constriction 
 at a past climatic extreme. These data\,  based on sediment grainsize from
  12 cores across the area south of the Subantarctic Front (SAF)\, indicate
  essentially no change in the average flow of the ACC through the Drake Pa
 ssage/Scotia Sea between the LGM and Holocene climatic extremes.  However\
 , ACC flow at the LGM was slower in the southern ice-covered portion of th
 e area\, and faster in the north\, implicating wind stress in spatial curr
 ent variability. This boundary coincides with the northern limit of winter
  (i.e. year-round) sea-ice. However two recent works north of the SAF\, a 
 region through which approx. 30% of the present ACC flows\, suggest signif
 icantly reduced glacial flow relative to present\, and this may mean reduc
 ed flow overall. Slower flow over rough topography and under the ice in th
 e Scotia Sea implies reduced diapycnal mixing in this key region\, consist
 ent with a reduced overturning circulation. Added to the constraints that 
 LGM winter sea-ice extent was approx.5° further north and the frontal sys
 tem was also most likely 5°-7° further north\, some areas of speculation
  are now being restricted by data. However as the recently departed and la
 mented Yogi Berra said “It ain’t over till it’s over”\, and the AC
 C palaeo-flow disputes ain’t over yet.
LOCATION:MR5\, Centre for Mathematical Sciences
END:VEVENT
END:VCALENDAR