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SUMMARY:The central-west sector of the Greenland Ice Sheet since the LGM -
  the story from offshore evidence - Dr Kelly Hogan\, Scott Polar Research 
 Institute
DTSTART:20120208T163000Z
DTEND:20120208T173000Z
UID:TALK33999@talks.cam.ac.uk
CONTACT:Steven Palmer
DESCRIPTION:Recent reconstructions of the Greenland Ice Sheet (GrIS) durin
 g the LGM still have large uncertainties along much of the ice sheet's\nma
 rgin\, particularly for the NW\, NE and central-W sectors of the ice sheet
 . This is partly due to the scarcity of information from the offshore reco
 rd that could confirm maximum ice-sheet extent and date the start of degla
 ciation in these areas. Here we present recent work that uses a\nvariety o
 f seismic data to investigate sediments deposited by ice masses retreating
  in to Disko Bay and\, ultimately\, the Jakobshavn and Torssukatak fjord s
 ystems. The sub-bottom profiles show rapid ice-margin retreat through bath
 ymetric troughs and embayments until topographic pinning points close to t
 he present coastline. Once the ice margins were pinned at fjord mouths lar
 ge volumes of sediment were deposited via rainout from turbid meltwater pl
 umes and calculated subglacial sediment fluxes are relatively high when co
 mpared with existing estimates from West Antarctic ice streams. Using exis
 ting marine and terrestrial dates we place these standstills in a chronolo
 gic framework that support an earlier ice-margin retreat in northern Disko
  Bay (Torssukatak) than in southern Disko Bay (Jakobshavn). Using the newe
 st radiocarbon dates available from the offshore record we can now present
  a deglacial chronology for the GrIS from the shelf break several hundred 
 kilometres west of Disko Bay\, through the bay to the fjord mouth\, and th
 en into the fjord itself at c. 7.8-7.6 cal ka BP. We will also present dat
 es from Umanak Trough to the north for which there is an emerging picture 
 of retreat from the shelf edge followed by a significant stillstand or rea
 dvance before c. 10 cal ka BP.
LOCATION:Scott Polar Research Institute\, main lecture theatre
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