Ice Stream Dynamics during Deglaciation of the Laurentide Ice Sheet

Thursday, 18 December 2014: 1:40 PM
Chris Stokes1, Martin Margold1 and Chris Clark2, (1)University of Durham, Durham, United Kingdom, (2)Univ Sheffield, Sheffield, United Kingdom
Ice streams can rapidly drain large sectors of ice sheet interiors. At present, they account for approximately 50% and 90% of the mass loss from Greenland and Antarctica, respectively, but there are concerns over recent increases in ice discharge. This has been linked to atmospheric and oceanic warming, but the longer-term implications for ice sheet deglaciation are less clear. A key question is whether the activity of ice streams is predictably linked to climate-driven ice sheet mass balance, or whether their activity might accelerate deglaciation. To explore this, we analyse ice streaming during deglaciation of the Laurentide Ice Sheet (LIS) from ~18 to ~7 ka. Following a recent mapping inventory, we bracket the timing of >100 ice streams using published ice margin chronologies. At the Last Glacial Maximum (LGM), ice streams formed a drainage network similar to modern ice sheets. Numerous ice streams were located in topographic troughs and likely operated for thousands of years from the LGM. These drained the marine-based sectors of the northern and eastern margins of the ice sheet until ~11 ka and show a degree of spatial self-organisation. Other ice streams operated on much shorter time-scales and turned on and off, perhaps in as little as a few hundred years. These include large ice streams that switched positions over sedimentary bedrock at the western and southern terrestrial margins until ~13 ka. As the LIS retreated onto its low-relief and predominantly crystalline bedrock interior (after ~11 ka), a smaller number of large ice streams operated that were very wide (50-100 km), and have no modern analogue. Overall, the number of ice streams decreased during deglaciation and they drained a smaller proportion of the ice sheet margin: 30% at the LGM (similar to present-day Antarctica), 15% at 12 ka, and 12% at 10 ka. We use simple scaling relationships to estimate the mass loss delivered by ice streams and examine their role during deglaciation.