Holocene glaciation of Perfection Valley, Baffin Island, Arctic Canada
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Imminent changes in the Arctic's cyrosphere are expected to occur over the next century as a result of global warming. The Intergovernmental Panel on Climate Change (IPCC, 2007) has announced that under all modeled conditions global sea-ice is projected to shrink up to 17 x 10 6 km 2 during the 21 st century. Therefore, it has become essential to examine climate variability on a longer time-scale than what exists in our brief observational records. Can the climate conditions of the early Holocene, a time when Arctic temperatures were higher-than-present, be used as an analog for near-future warmth? To help answer this question, lake sediments have been examined from well-dated lake sediment cores from proglacial Lake Longspur (N 69° 24", W 69° 13"), northeastern Baffin Island, Arctic Canada. The objectives of this research are to determine the existence of glaciers during the warmer-than-present early Holocene, determine the timing of glacier re-growth during Neoglaciation, and assess how 20 th century warmth has impacted glaciers in this basin. The entire record for this study area spans from 8,600 years BP to ∼1973 A.D. based on 10 radiocarbon dates and one 137 Cs profile. Fluctuations in magnetic susceptibility, percent loss-on-ignition, and grain size suggest that glaciers persisted in the Lake Longspur basin during the early Holocene despite higher-than-present temperatures. Based on dramatic changes in silt and a radical change in the depositional environment, glaciers in this basin appear to have readvanced around 3,700 years BP. Moraine ages derived through lichenometry indicate that peak glacier extent during the LIA occurred at ∼1200 and ∼1800 cal yr AD. The glaciers responsible for creating these moraines have retreated 10's of meters just in the past ∼35 years. This retreat is strikingly obvious when seen in a time series of remote imagery taken between 1957 and 2006. The influence of 20 th century warmth affecting these glaciers is apparent in the lacustrine environment as well. Distinct laminated couplets, interpreted to be varves based on 137 Cs analysis, appear to record regional summer temperature fluctuations; in an overlaping period from 1945 to 1973, varve thickness and summer temperature from nearby Clyde River weather station are significantly correlated (r 2 =0.37). The increase in varve thickness in the 20 th century corresponds with, and is remarkably similar to, the melt-layer record from the Agassiz and Devon ice caps located several hundred km to the north. Combined with existing records, these data improve our understanding of the timing and spatial pattern of Neoglaciation, as well as help identify a warming trend that ensued during the later part of the 20 th century on Baffin Island.