Fluctuations of the Deming Glacier and theoretical equilibrium line altitudes during the Late Pleistocene and Early Holocene on Mount Baker, Washington, USA

摘要

The Deming Glacier is presently nourished by an ice-cap type accumulation area on Mount Baker (3285 m a.s.l.). The specific meso-scale (> 10 km) form and isolation of the Mount Baker stratovolcano seem to influence temperature and precipitation gradients ( contemporary climate data). These data are used as a reference when calculating paleo-equilibrium-line altitudes (ELAs). Six radiocarbon dates are reported, between 10 680 +/- 70 and 10 500 +/- 70 C-14 yr BP (12 903 - 12 183 cal. yr BP) from detrital logs in drift that were buried during an advance of the Deming Glacier ( altitude 3230 - 1158 m) during possibly the Younger Dryas interval. The calculated range of theoretical ELA depressions (Delta ELA) relative to modern is 400 - 355 m using two different methods. Assuming no change in precipitation, ablation-season temperature would have been 2.5 - 2.2 degrees C cooler, which is consistent with other paleoclimatic reconstructions in this region. Alternatively, assuming that the modern reference climate is appropriate, and based on regressions of modern-day glacial conditions, the predicted mean winter precipitation necessary to support the former Deming Glacier was in the order of 200 - 150% ( mean 175%) or 119 - 86% ( mean 103%). This amount of precipitation could result from reinvigorated moisture transport into the North Cascades and increased seasonality at the end of the last glaciation.