RETREAT OF THE LAURENTIDE ICE SHEET AND GLOBAL SEA LEVEL RISE

Abrupt rises in sea level (melt water pulses or mwp) at 19 ka (10 to 15 m sea level rise), 14.6 ka (mwp-1a; ~ 20 m sea level rise) 11.6 ka (mwp-1b; ~ 8 m of sea level rise), and 7.6 ka (~ 5 m sea level rise) punctuated the more uniform sea level rise from the Last Glacial Maximum. Although the rates of sea level rise are relatively well constrained, the sources and partitioning of pulses among global ice sheets are poorly known. To better constrain this issue of mwp source, I use Dyke’s (2003) latest compilation of the aerial extent of the Laurentide Ice Sheet (LIS) to calculate its retreat rate during the last deglaciation. Comparison of this time series with global relative sea level data suggests an association between rapid LIS retreat and 3 of the 4 mwp. These interpretations are based only on the area of the LIS and do not include potential changes in ice thickness that may occur independent of aerial changes. During the 19 ka mwp, the LIS lost ~ 9 % of its total extent, with a retreat rate of ~ 14 % lost kyr^-1. This initial retreat occurred primarily along the climatically sensitive southern margin following a period of North Atlantic warming. Its contribution to sea level rise may have destabilized marine-based portions of the LIS and other ice sheets, causing further sea level rise. The LIS again retreated rapidly at ~ 11.6 ka, losing ~ 14 % of its area at a rate of ~ 12 to 23 % lost kyr^-1. This event occurred at the end of the Younger Dryas cold period and may have contributed to mwp-1b. The final period of rapid retreat began ~ 9 ka during which the LIS lost ~ 33 % of its area in ~ 1.4 kyr. The early part of this rapid retreat reflects recession of the LIS and its calving margin associated with the opening of Hudson Bay. However, rapid retreat was maintained once the LIS was land based possibly in response to the ice-albedo feedback, and this ice loss may have contributed to the 7.6 ka mwp. In contrast to these mwp, the LIS lost only 5 % of its aerial extent and maintained a slow and uniform retreat (~ 5 % lost kyr^-1) during mwp-1a, suggesting an alternate source of water for this mwp.