ABSTRACT: Ice cap retreat in northern Baffin Island: providing a context for current Arctic warming.

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Abstract

Evidence of current warming of the Earth’s climate can be found from widespread regions around the globe. However, the magnitude of this warming varies geographically. Nowhere is warming felt more strongly than in the Arctic, where average temperatures have increased between 2-4ºC since 1970, due to positive feedbacks such as earlier snow melt and reduced sea ice extent (Serreze et al., 2000). One of the biggest questions posed to climate scientists today is: is this warming within the realm of natural variability or is its rate and magnitude beyond that which can be explained by natural phenomena? The aim of this project is to provide a Holocene context for 20th century Arctic warming. How unusual is the magnitude of this warming? When was the Arctic last as warm as it is now? Is this degree of warmth within the range of natural variability or is it unprecedented? The rapid melting of ice caps within the interior of Baffin Island, arctic Canada, has been documented over the last 50 years by aerial photography, satellite imagery and ground observations. Ice extent on the plateau is known to be far greater during the Little Ice Age (LIA) based on the pattern of lichen-free rocks, known as the lichen-kill zone (Locke and Locke, 1977). LIA ice coverage can be estimated from the pattern of lichen-kill derived from satellite imagery and from this, we find that these ice caps have diminished by 97% in area from their extent during the Little Ice Age. Many have already melted away completely, while those that exist today are projected to disappear before 2050 based on their current retreat rates. This project is designed to answer three questions: (1) When was the last time this area was warm enough to be ice-free? (2) For how much of the Holocene has this area of the Arctic been this warm? And (3) for how many distinct intervals was the climate comparable to today and for how long did those intervals last? To answer question (1), moss that has been preserved beneath the ice caps was dated using 14C. These dates indicate the last time that that particular place was free of ice. Results from these dates reveal that the last time the ice caps melted to their current extent was between 400-1000 calendar years before present (BP). Two locations along the ice cap margin reported dates just over 1000 years BP, signifying that this area has not experienced warming comparable to that of today for the last 1000 years (Figures 1 and 2). To answer question (2), we use cosmogenic 14C, produced in quartz to determine for how long rocks along the ice cap margins have been exposed to cosmogenic radiation. Because of its short half-life, cosmogenic 14C concentration is only comprised of atoms that have accumulated during periods of exposure in the Holocene, as any accumulation from prior periods of exposure will have decayed away while this area was covered by the Laurentide Ice Sheet. These exposure histories will reveal the total time the area has been without ice during the Holocene, which must have occurred before 400-1000 years BP. To answer question (3), we cored three lakes adjacent to the ice caps. Variations in sediment and organic content in the sediment cores are a result of variations in ice cover and should reveal discreet periods of ice cover or lack of ice cover. We will also date organic material within the cores to determine when these intervals occurred. Used together, these three techniques can provide a picture of ice cap extent throughout the Holocene and help to place their current retreat in a larger time frame.

Bibliography of Canadian Geomorphology