THE LAST THOUSAND YEARS OF GLACIATION IN ALASKA: A TEMPERATURE RECORD

Comparison of composite chronologies from land-terminating glaciers in three key climate regions of Alaska offers a significant record of century to decadal-scale change. The three regions include: Arctic Alaska, with a set of 179 lichen-dated moraines at 94 glaciers in the Brooks Range; the southern interior, based on nine tree-ring and radiocarbon-dated glacial histories from the Wrangell and northern St. Elias mountains; and, the Gulf of Alaska coast, with tree-ring-dated histories of 12 glaciers in the St. Elias, Chugach, and Kenai mountains.

Chronologies show that across Alaska, glaciers recovered from a period of contracted glacier margins about AD 1000 (Medieval Optimum) to reach extended Little Ice Age (LIA) positions during the 13th century AD. Following an interval of retraction and forest growth displayed in the southern regions, a strong readvance occurred in all regions centered on AD1650. An interval of retreated ice margins followed until about the mid- to late-1800s when many glaciers reached their Holocene maxima. Since the LIA, general ice retreat has dominated at most land-terminating glaciers across Alaska in response to increased temperatures. Retreat is accelerating as atmospheric temperatures continue to rise.

This Alaska-wide transect is an integrated record of snowline fluctuations acting over many decades to centuries and is primarily a record of temperature change. The low frequency temperature signal extracted from glacial histories together with higher resolution proxy records sensitive to annual and decadal changes, provide a rather complete characterization of the climate system over the past thousand years.