ICE CAP RETREAT IN NORTHERN BAFFIN ISLAND: PROVIDING A CONTEXT FOR CURRENT ARCTIC WARMING

Evidence of modern warming of the Earth's climate can be found from widespread regions around the globe but none so much as in the Arctic, where average temperatures have increased between 2-4ºC since 1970 and are evidenced by decreasing sea ice extent, earlier snow melts, decreasing permafrost coverage and retreating glaciers. Identifying previous variations in Arctic climate is a critical step toward understanding current climate and the direction in which it is headed. To do this beyond the instrumental record, we must rely on proxy records such as ice extent to infer past climate in the Arctic.

Within the interior of northern Baffin Island, arctic Canada, the rapid melting of cold-based ice caps has been documented over the last 50 years. Remote sensing analysis shows that 97% of Little Ice Age ice cover has since disappeared. Many of these ice caps have already melted away completely, while all others are projected to disappear by 2050 based on their current retreat patterns. The demise of these ice caps leads to the questions: has this happened before in the Holocene? If so, when and for how long? Answering these questions will help to put the modern warming trend into the larger picture of the Holocene and to determine whether our current warming has a precedent or is a truly unusual occurrence and possibly of anthropogenic origin. This research focuses on these questions using several techniques. (1) Coring lakes recently exposed by the receding ice caps and 14C-dating plant macrofossils within the sediment cores. Denser layers within the cores indicate the presence of ice cover. Dating fossils within these layers gives the age of onset of ice cover and dating the base of the core gives the age of inception of sedimentation in the lakes, concurrent with deglaciation of the Laurentide Ice Sheet in the early Holocene. (2) 14C-dating preserved vegetation beneath and at the edges of the ice caps indicates the most recent time when the plateau has been ice-free. (3) Using cosmogenic 14C from quartz to calculate the total exposure time of the plateau during the Holocene. Used with the dates from lake cores on the timing of ice-free intervals, this gives an estimate on the duration of prior periods of warmth in the Arctic and places current warming in a broader context.