A SYNTHESIS RECORD OF HOLOCENE GLACIER FLUCTUATIONS IN WESTERN NORTH AMERICA AND ITS RELATION TO CLIMATE CHANGE

Most alpine glaciers are nourished by winter snowfall and melt during summer, and so changes in their length and thickness provide information about long-term changes in climate. Yet despite the rich terrestrial record of glacier fluctuations that exists in western North America, few have attempted to reconstruct Holocene climate variability from these records. Here we use an integrated approach to investigate Holocene climate variability in the mountains of western Canada and southern Alaska. We first assemble direct evidence of glacier activity such as radiocarbon-dated stumps in growth position and terminal moraines with minimum-limiting ages for dozens of glaciers in the Coast, Cascade and Rocky Mountains. Dimensionless time-distance and time-thickness curves for the study area are derived from these. We next employ an ice dynamics model, forced by mass balance fields derived from downscaled meteorological data, to simulate length, thickness and extents of contemporary glaciers. The temperature and precipitation fields are subsequently perturbed to allow glaciers to grow to match extents observed in the geological record. Our presentation will discuss the merits and pitfalls of our approach; we will also summarize estimates of past temperature and precipitation change that drove Holocene glacier advances in the study area.