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Summer temperatures during the Medieval Warm Period and Little Ice Age inferred from varved proglacial lake sediments in southern Alaska
Iceberg Lake is a proglacial, ice-dammed lake located on the northern margin of the Bagley Icefield in southern Alaska’s Wrangell St. Elias National Park and Preserve. The lake was 60 m deep and 4.4 km2 prior to 1999, when the first of several jokulhlaups catastrophically drained the previously stable lake. Lacustrine sediments exposed by these drainage events were examined in the summers of 2001-2003.
Varve thickness at Iceberg Lake is positively correlated with short (<50 yr) instrumental temperature records from nearby stations, and also with a longer (>400 yr) temperature reconstruction based on maximum latewood density of white spruce. The correlations are weak, but trends in the varve-based temperature reconstruction are corroborated by other geological evidence, and suggest that maximum temperatures over the last 1500+ years have occurred in the late 20th century, with a minimum in the late 6th century. Click here to see the temperature reconstruction from Iceberg Lake.