Christian Zdanowicz, Geological Survey of Canada

Some 18,000 years ago most of Canada was covered by the vast Laurentide ice sheet, which stretched from Newfoundland to the western Cordillera, and from the Arctic shores south to Iowa. When the ice sheet retreated, it left behind a few remnants in the form of small ice caps, some of which continued to exist for thousands of years after the main ice sheet itself had vanished. Relicts of the Laurentide ice sheet can still be found today on Baffin Island, buried in the deepest layers of the Penny and Barnes ice caps. Owing to the slow shrinkage of the Barnes ice cap, ancient layers of Laurentide ice are now exposed along its margins, in the same way that ancient rock strata become exposed on the flanks of eroding mountains or in river canyons. These ancient layers of ice preserve a "memory" of past climates and air composition which we are now attempting to decipher by analyzing chemical impurities and air bubbles trapped within. In this way, we hope to achieve a better understanding of the environmental changes that accompanied that disappearance of the Laurentide ice sheet at the end of the last great ice age.

The Barnes Ice Cap (Baffin Island) is a remnant of the Laurentide Ice Sheet that separated from it about 8500 years ago. Owing to recession of the ice cap during the Holocene, Pleistocene-age ice strata are now exposed along its margin in a distinctive white ice band with low δ¹⁸O values. In summer, 2000, a reconnaissance sampling transect was effected on the southwestern margin of the Barnes Ice Cap. Findings show that the mean ice crystal size and particulate impurity content in the white (Pleistocene) ice are noticeably smaller and greater, respectively, than in younger (Holocene) blue ice strata. The δ¹⁸O profile across the white ice resembles pre-Holocene isotopic records in other Canadian Arctic ice caps, and suggests that the oldest strata in the Barnes Ice Cap is of early to mid-Wisconsin age. An hypothetical model reconstruction of the Laurentide Ice Sheet during the Last Glacial Maximum indicates that late glacial strata in the Barnes Ice Cap may have originated high up (> 2400 m above sea level) and far "inland" on the ice sheet. A follow-up expedition is planned in summer, 2002, to obtain more samples from the Barnes Ice Cap for further paleoenvironmental studies.

• National Glaciology Group

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Ice core sampling	Steady-state reconstruction of the Laurentide ice sheet during the Late Glacial Maximum shows the present position of Barnes(B) and Penny(P) ice caps with respect the the ancestral Foxe dome(F).
The Barnes Ice Cap	Compared crystal size (a) and impurity content (b,c) in blue ice (Holocene) and white ice (Pleistocene) from the margin of the Barnes Ice Cap.