A BERYLLIUM-10 RECORD OF THE GLACIAL GEOLOGIC HISTORY OF MOUNT KATAHDIN, MAINE, USA

The transition out of the last ice age and into warmer interglacial conditions included abrupt climate fluctuations, such as Heinrich Stadial 1 (HS1: 17.8 – 14.7 ka). While HS1 has traditionally been interpreted as a period of cooler temperatures, emerging evidence from the North Atlantic region supports rapid ice melt during this time. To test the seasonality hypothesis, we aim to develop a record of summer temperature fluctuations using the glacial-geologic history of the Laurentide Ice Sheet, from which Katahdin emerged during deglaciation. Here, we present the results of glacial-geomorphic mapping and ¹⁰Be exposure ages of glacially transported boulders. We investigated the Basin Ponds moraine, which flanks the eastern face of the mountain at an elevation of ~750 m, and the Abol moraines, which wrap around the southern face of the mountain and often occur as kame terraces. We also collected samples at higher elevations on the tablelands and summit. While the high elevation samples frequently exhibit nuclide inheritance, indicating a complicated exposure history, we interpret the youngest ages at high elevation as the start of the thinning record. Our preliminary ¹⁰Be ages suggest significant ice-surface lowering from the summit (1606 m) to the Basin Ponds moraine (750 m) between ~18 and ~16 ka. After a stillstand or readvance at ~16 ka which allowed the deposition of the Basin Ponds moraine, ice retreated down into the lowlands to an elevation of ~300 m by 14.5 ka. While the Basin Ponds moraine represents a short-lived time of climatic cooling at 16 ka, overall, the ice thinned by more than a kilometer during HS1. This may indicate warmer than average summer temperatures during much of HS1, in contrast to cooler than average temperatures recorded in other proxy records.