NORTHWEST GREENLAND HOLOCENE TEMPERATURES INFERRED FROM ORGANIC ARCHIVES OF LAKEWATER OXYGEN ISOTOPES

The timing and magnitude of temperature fluctuations has varied greatly across the Northern Hemisphere high latitudes through the Holocene, including Greenland where the response of the ice sheet to future warming is the focus of great scientific interest. Two Holocene lake sediment records were recovered during 2012 and 2014 from the Thule region of NW Greenland to provide new constraints on temperature histories at the margin of the ice sheet. In concert with ongoing glacial geologic investigations in the region these lake core records aim to clarify how the Greenland Ice Sheet (GrIS) responded to warming and cooling during the Holocene. Here we utilize aquatic organisms preserved in the sediment record, whose δ¹⁸O compositions record that of growth water, and in appropriate hydrologic settings, the δ¹⁸O of precipitation. Secret Lake, located ~5 km NW of Thule Air Base, is a small lake presumed to be predominantly precipitation-fed based upon its landscape position and similarity between lake water and meteoric δ¹⁸O. A 1.5 meter core recovered from the deepest part of the lake (3.4 m) appears to contain a continuous sedimentary record from at least 7725 ± 65 cal yr BP to present. Wax Lips Lake (informal name) is located 53 km NE of Secret Lake and 1.5 km from the present-day GrIS margin. Similar to Secret Lake, the primary input to the lake appears to be precipitation. No surface outlets were active when the lake was visited in August of 2014 and lake water δ¹⁸O is slightly enriched (1-2 ‰) relative to the local meteoric water line, suggesting possible evaporative influences near the end of the summer season. The basal age of Wax Lips Lake sediments is 10440 ± 140 cal yr BP. We subsampled and analyzed δ¹⁸O of organic material from both cores, including the chitinous remains of chironomid larvae, cladocera ephippia, adult insect parts, and aquatic macrophytes. δ¹⁸O of modern water and subfossil material from a suite of mid to high latitude lakes are used to calibrate modern temperature-δ¹⁸O relationships in order to interpret downcore δ¹⁸O measurements. We present preliminary Holocene temperatures reconstructed from the δ¹⁸O of preserved subfossils at these two lakes.