Ice Stream Dynamics during Deglaciation of the Laurentide Ice Sheet

Abstract:

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.