ADVANCES IN UNDERSTANDING HOLOCENE ALPINE GLACIATION, SOUTHERN COASTAL ALASKA

The extensively glaciated coastal ranges of Alaska continue to be a significant source of global sea-level rise. High-resolution glacial chronologies assembled from calendar – dated forests along with new records of winter climate variability, have allowed comparisons that have generated fresh questions regarding the forcings of Holocene glacier variability. New proxies from tree rings include traumatic resin duct chronologies that are sensitive to winter precipitation, and blue intensity measurements that are tuned to summer temperature. The relative roles of summer temperature and winter precipitation driving ice fluctuations can now be examined in more detail than before. Early results suggest that at times with depressed summer temperatures during the Little Ice Age (LIA), a strengthened Aleutian Low (AL) may have provided the snowfall needed to drive ice expansions. Furthermore, over the past two millennia ice cores and other Pacific climate proxy records suggest that a strengthening AL may have had a role in driving ice margins to be ever-larger through the late Holocene, with the latest LIA maxima often being the most extensive. Conventional ideas link the ever-expanding ice extent to decreased summer insolation over the past several millennia driven by Milankovitch forcing, however, some of the expansion may be driven by increased winter precipitation. Another aspect of the glacial system that can benefit from these new records is a better understanding of tidewater glacier behavior. Well-dated tidewater glacier chronologies can be used to calibrate numerical flow models, which, in turn, can be forced by tree-ring based mass balance reconstructions to explore the past and anticipate the future behavior of these complex systems.