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SUMMARY:How ice sheets collapse: a lesson from the Laurentide Ice Sheet - 
 Chris Stokes\, Durham University
DTSTART:20170504T163000Z
DTEND:20170504T173000Z
UID:TALK71078@talks.cam.ac.uk
CONTACT:Della Murton
DESCRIPTION:The contribution of the Greenland and West Antarctic ice sheet
 s to sea level has increased in recent decades\, largely due to the thinni
 ng and retreat of rapidly-flowing outlet glaciers and ice streams. This 
 ‘dynamic’ loss is a serious concern\, with some modelling studies sugg
 esting that the collapse of a major ice sheet could be imminent or potenti
 ally underway in West Antarctica\, but others predicting a more limited re
 sponse. A major problem is that observations used to initialize and calibr
 ate models typically span only a few decades and\, at the ice-sheet scale\
 , it is unclear how the entire drainage network of ice streams evolves ove
 r longer timescales. This represents one of the largest sources of uncerta
 inty when predicting the contributions of ice sheets to sea-level rise. A 
 key question is whether ice streams might increase and sustain rates of ma
 ss loss over centuries or millennia\, beyond those expected for a given oc
 ean–climate forcing. In this paper\, we utilise a unique Quaternary reco
 rd of 117 ice streams that operated at various times during deglaciation o
 f the Laurentide Ice Sheet from about 22\,000 to 7\,000 years ago). We sho
 w that as they activated and deactivated in different locations\, their ov
 erall number decreased\, they occupied a progressively smaller percentage 
 of the ice sheet perimeter and their total discharge decreased. The underl
 ying geology and topography clearly influenced ice stream activity\, but
 — at the ice-sheet scale—their drainage network adjusted and was stron
 gly linked to changes in ice sheet volume. It is unclear whether these fin
 dings can be directly translated to modern ice sheets. However\, contrary 
 to the view that sees ice streams as unstable entities that can accelerate
  ice-sheet deglaciation\, we conclude that ice streams exerted progressive
 ly less influence on ice sheet mass balance during the retreat of the Laur
 entide Ice Sheet.
LOCATION:Cripps Auditorium\, Cripps Court\, Magdalene College
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