T18 Sea Level and Ice-Sheet Changes, Glacial Isostatic Adjustment, and Landscape Evolution I

Monday, 26 October 2020
1:30 PM - 5:30 PM
Meeting Rooms

CAMP CENTURY ICE CORE BASAL SEDIMENTS CONTAIN A MULTI-MILLION-YEAR RECORD OF ICE-COVER AND VEGETATION IN NORTHWESTERN GREENLAND

Paper number: T18-4
Program: Technical Sessions
Time: 2:05 PM – 2:20 PM

Authors

Abstract

Terrestrial paleoclimate records of a Greenland Ice Sheet (GrIS) smaller than present are critical to understanding ice-sheet sensitivity to warming and improving estimates of contributions to sea-level rise. However, due to present ice cover, such archives are rare; thus, basal materials from ice cores are an important archive of past ice-free periods. The Camp Century ice core, collected in 1966 from northwestern Greenland, recovered 3.5 m of subglacial sediment that was incompletely studied and forgotten for decades. Following its rediscovery in 2017, we analyzed the upper- and lower- most sections of the subglacial sediment.

Here we demonstrate that the Camp Century subglacial sediment documents a multi-million-year record of vegetation and ice cover in northwestern Greenland. Enriched δ18O values from sediment pore ice require precipitation at lower elevations consistent with ice-sheet removal and isostatic adjustment of the underlying land surface. The sediment contains abundant macrofossil vegetation, including twigs, moss leaves and stems, and fungal sclerotia, consistent with a tundra ecosystem. Leaf wax chain length distributions and δ13C, δ15N and C/N of woody tissue resemble vegetation from modern ice-free areas of Greenland. Cosmogenic 26Al/10Be ratios require exposure of the upper sediment within the last 0.6-1.1 Myr. Infrared stimulated luminescence ages from the lower sediment indicates exposure prior to 0.7-1.3 Ma, but 26Al/10Be ratios require burial for 2.6-3.3 Myr or less.

The Camp Century sub-glacial sediment contains a stratigraphic record of Pleistocene ice cover and the paleo-ecosystems that occupied northwestern Greenland during ice-free periods, making it unique among Greenland ice cores. The lower sediment may derive from an early advance of the GrIS (>2.6 Ma) that was covered by ice for much of the Pleistocene. Exposure of the upper sediment, and thus ice absence in northwestern Greenland, within the last 0.6-1.1 Ma adds to growing evidence that Greenland was ice-free at least once in the last 1 Myr. During this time frame, prolonged interglacials with higher global sea level, Marine Isotope Stages 31 and 11, are the most likely times for a much smaller GrIS. Our conclusions imply GrIS sensitivity to sustained warmth, which is concerning given future climate projections.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-357268

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