Abrupt Climate Change during the Last Glacial Termination in Maine

October 26, 2022 Expeditions, Expeditions 2022

Expedition Team Members:

Maraina Miles¹ ²

¹Climate Change Institute, University of Maine

²School of Earth and Climate Science, University of Maine

Expedition Dates: May-October 2022

Funding Support: The Robert & Judith Sturgis Family Foundation

Summary: Katahdin, the largest mountain in Maine, offers a unique view into the climate of the past. Draped along the flanks of the mountain are glacial deposits that can reveal how the climate of the North Atlantic region responded to the abrupt warming of the end of the last ice age. In the face of climate change, there is an urgent need to understand how each part of Earth’s climate system reacts to abrupt change. We are currently entering uncharted territory; however, the fast-changing climate of the last glacial termination (11,700-18,000 years ago) can provide an analogue to guide the development of future climate models – the first step in helping society prepare for an uncertain future. Our goal for the 2022 field season was to collect samples from glacially transported boulders for beryllium-10 surface exposure age dating to reveal the thinning history of the Maine Ice Cap, which we plan to use to reconstruct the pattern of climate change during the termination.

Fig. 1. Moraines on the flanks of Katahdin. Basin Ponds moraine are in green, and Abol moraines are in purple, Togue pond moraine in yellow.

Fig. 2. The ice sheet (Maine Ice Cap) wrapping around Katahdin ~16ka, when the Basin Ponds moraine was deposited. One question we seek to answer is if there were cirque glaciers present on the mountain at this time.

Methods: To find out when the ice retreated or readvanced, we began by mapping glacial landforms in ArcGIS Pro using newly released LiDAR imagery of the area. Next, we collected rock samples from boulders on these landforms. The samples were brought back to the UMaine Cosmogenic Isotope Laboratory and are currently being processed for beryllium-10 (10Be) surface exposure dating. This method works like an isotopic ‘clock’ and reveals when the boulders were deposited by a glacier. The boulders were plucked from the underlying bedrock by a flowing glacier and then deposited on a moraine. Once a boulder is released from the glacier and exposed to the atmosphere, it begins accumulating 10Be, a cosmogenic isotope that forms within a rock as is it bombarded with cosmic rays, which are constantly raining down on Earth. Therefore, the amount of 10Be in a boulder can tell us when that boulder was deposited by a glacier, and thus when the glacier was last at that location. To isolate the 10Be, the samples are crushed into a fine sand and etched in acid until only pure quartz remains. The quartz is then dissolved, and the 10Be is extracted in a series of chemical steps.

Project Goals & Initial Results: One of our goals during the summer of 2022 was to collect samples along a newly discovered lower-elevation moraine in the southern section of Baxter State Park, dubbed the
‘Togue Pond moraine.’ This moraine may have been deposited in the Bølling–Allerød (14.7-13.0 ka), a period when the climate changed rapidly but displayed many complexities that we don’t yet understand. Because of the steep slope of the moraine, this may be evidence of a glacial readvance during the Bølling–Allerød. Overall, 10 samples were collected on the moraine. We also collected six samples above the moraine, on smaller recessional ridges, and eight below it to fully constrain the timing of moraine deposition. Along with the lower-elevation work, we collected samples at higher elevations on the tableands to determine if ice was present during the last glacial maximum. We also explored North Basin to assess if cirque glaciers were present during the termination. Many of these samples have been processed (fig.1), however many more are currently in progress and await analysis at Lawrence Livermore National Laboratory in California.