HIGH-RESOLUTION RECONSTRUCTIONS OF LITTLE ICE AGE CLIMATE, GLACIAL RESPONSE, AND PARAGLACIAL SEDIMENTATION FROM GLACIER-DAMMED ICEBERG LAKE, SOUTHCENTRAL ALASKA
The longest stratigraphic section has at least 1760 laminations, and independent dating from both cesium-137 spikes and AMS carbon-14 ages confirms the interpretation of these laminations as annual varves. Importantly, the record begins several centuries before commencement of Little Ice Age cooling, and we found no sedimentary evidence of prehistoric outburst floods. From well before the Little Ice Age until only 4 years ago, then, the large glacier that impounds Iceberg Lake must have been sufficiently advanced to continuously dam the lake. Modern breaches of the ice dam are unprecedented in neoglacial time.
This varve thickness chronology promises a regionally unique record of interannual variability in spring/summer temperatures. The preliminary record correlates most strongly with a published 400 year southcentral Alaskan tree-ring record when lagged behind by several decades, suggesting that the sediment yield reflected in our varve chronology is also a function of glacial processes that respond to climate forcing with a characteristic low frequency lag. We are using a new lichenometry technique to date moraines in the lake's watershed to account explicitly for these processes as we reconstruct the original climate forcing.