Late Holocene climate change and calving glacier fluctuations along the southwestern margin of the Stikine Icefield, Alaska

Abstract

The retreat of large tidewater- and lake-calving glaciers, as well as nearby land-based glaciers, in southeastern Alaska during the middle to late Holocene was primarily triggered by increases in summer temperature. Shakes, LeConte, Patterson, and Baird glaciers, located along the southwestern margin of the Stikine Icefield in southeastern Alaska, experienced two or three major periods of advance and retreat during this period. Historical, stratigraphic, and dendrochronological evidence suggests that these periods of advance culminated approximately 3,500--3,300, 2,700--2,200, 1,100--900, and 220--110 years ago in the study area. Comparison with previously published regional records from glaciers located along the coast of northwestern North America suggests a general synchrony in the timing of ice advance across the region. Regional intervals of ice maxima date approximately 3,000--1,900, 1,500--900 and 250--100 years ago, and encompass three of the main periods of advance represented in the study area.To determine a regional cause of glacier synchrony, glacier chronologies were compared to local and regional climate and climate proxies. Summer temperature fluctuations in the study area for the past four centuries were derived from trey-ring-width time-series from Crystal Mountain near Petersburg. Previously published precipitation and summer temperature values, inferred from palynological studies, provide a record of climate change for the last 10,000 years. Throughout southeastern Alaska, periods of glacier retreat for both calving glaciers and land-based glaciers tend to correlate with periods of warming summer temperature.The collective data imply that the geologic record left by calving glaciers, like that left by land-based glaciers, has the potential to serve as an important climate-proxy record in a region where few such records have been studied. Furthermore, such a relationship helps further to quantify calving glacier dynamics and improve prediction of calving-glacier response to human-induced global warming.