GLACIAL VOLUME CHANGE ON THE JUNEAU ICEFIELD: PAST AND PRESENT

Continuing measurements of glacial advance and retreat as well as paleoclimatic reconstruction of major magnitude regime changes on the Taku and Llewellyn Glacier System of the Juneau Icefield, Alaska, document exceptionally large ice volume increases since the height of the Thermal Maximum some 5000 years B.P. Combined geomorphic, paleontologic, geobotanic, climatologic and geophysical evidence support the interpretation that all sea-level glaciers in this sector of the Alaska panhandle completely wasted away during the Thermal Maximum, leaving only local cirque ice centers at the highest elevation of the Alaska/Canada Boundary Range. Recent dramatic changes in ice extent document ongoing changes in the region's climate. This presentation is the result of an interdisciplinary team effort extending over eight field seasons of the Juneau Icefield Research Program since 1994. A series of seismic ice depths across the icefield show that below sea-level fiord topography formerly characterized branches of today's glacier system. Ice depths today range from 1200 to 1500 meters deep. These former fiords extended as far as 55 kilometers up-valley from the present Taku Glacier terminus. This indicates that the icefield literally did not exist during Thermal Maximum time. The chronology of post-Thermal Maximum glacial extent has been further documented by radiocarbon. lichenometric, soils analysis as well as ongoing GPS measurements of glacial advance and retreat in the region.