ABSTRACT: Using 10Be dating to pace Laurentide Ice Sheet retreat in polar landscapes: Rapid fiord deglaciation on Baffin Island, Arctic Canada.

CGRG Bibliography of Canadian Geomorphology
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Abstract

The retreat of the last great ice sheets during latest Pleistocene/Holocene warming serves as an analog for contemporary ice sheet response to climate change. Although cosmogenic exposure dating has recently led to improvements in ice sheet retreat chronologies, isotope inheritance has complicated its use in polar landscapes. The application of cosmogenic isotopes to the history and behavior of the northeastern Laurentide Ice Sheet on Baffin Island, Arctic Canada, over the last decade has led to four key insights. First, differential erosion by polythermal ice sheet conditions has led to a complicated pattern of cosmogenic isotope concentration in eastern Baffin Island landscapes. Second, cosmogenic isotopes inherited in locations not significantly eroded provide more information about ice sheet erosion (and burial) than chronology. Third, bedrock suitable for exposure dating commonly only occurs in valley bottoms that experienced significant erosion. Four, erratics in landscapes of insignificant erosion can sometimes be suitable samples for exposure dating. Building on these lessons, we highlight recent efforts to constrain retreat chronology in fiords of eastern Baffin Island. 10Be dating of glacially-polished low-elevation bedrock spanning 120 km of Sam Ford Fiord reveals 80 km of retreat in <1000 years at ~9.5 ka. Deglaciation began prior to 15 ka from a glacial maximum margin on the continental shelf, and the modern Barnes Ice Cap margin, 30 km inland from the head of Sam Ford Fiord, was attained in the late Holocene. Thus, over half of overall ice margin retreat since the last glacial maximum occurred in less than 10% of the deglacial interval. This rapid deglaciation was likely caused by a combination of climate-forced retreat and increased calving rates in up to 900-m-deep water. Although adjacent fiord mouths deglaciated earlier than at Sam Ford Fiord, the middle reaches of all fiords that we have studied along northeastern Baffin Island experienced rapid deglaciation between 10 and 9 ka. Constraining more precise rates of such rapid deglaciation is difficult with 10Be dating, but a similar magnitude of retreat of present ice streams like Greenland's Jakobshavn Isbrae, which occupies a long and deep fiord similar in geometry to those on Baffin Island, is likely if the Arctic continues to warm.

Bibliography of Canadian Geomorphology