MULTI-MILLENNIAL-SCALE TREE RING RECORDS FROM GLACIER BAY NATIONAL PARK AND PRESERVE: PALEOENVIRONMENTAL RECONSTRUCTION AND PLACING ONGOING CRYOSPHERE/ECOSPHERE CHANGES INTO A LONG-TERM CONTEXT

Ongoing tree-ring work from living forests and a collection of subfossil logs from Glacier Bay National Park and Preserve are providing new insights into the past behavior of tidewater glaciers, and of present and past ecosystems. Tree-rings offer an exactly-dated chronology of changes in climate, ice volume and forest response, which is vital to understanding global change and placing contemporary changes into a long-term context. Collaborative research in this sector of southern Alaska has focused on developing tree-ring series from an archive of subfossil wood preserved in glacier sediments that potentially spans the Holocene. The dynamic icescape, the large amplitude warming over the last several decades, and the rich human history of the region offers a large range of research projects and outreach efforts. Glacier Bay has a rich history of glacial studies and a set of over 400 radiocarbon ages is available to guide assembling the long tree ring record. A continuous ring-width record for the past almost 2000 years is in place, and further work adding floating ring-width series is ongoing.

Student projects in collaboration with park historians, community members and educators are examining the response of hemlock, spruce, pine and cedar forests to modern and past changes in climate. Assessing the relative health of these forests is key to managing and evaluating changes in these these carbon reservoirs. Other research focusing on the glacial history seeks to place contemporary retreat of the spectacular glaciers in Glacier Bay into a long-term context. This is accomplished by exactly dating times of advance, and determining intervals of past forest growth when portions of the fjord system were ice free. Some past ice losses within the fjord may have taken place over intervals comparable to the present catastrophic ice retreat. Reconstructed intervals of ice advance using calendar-dated trees killed by ice expansion record some of the fastest rates of tidewater flow. The glacier history also has its impact on resources and is linked with native communities; our new dates on physical changes in the region adds detail to these well-documented legends.