GSA 2020 Connects Online

Paper No. 18-3
Presentation Time: 2:05 PM


CHRIST, Andrew J.1, BIERMAN, Paul R.2, SCHAEFER, Joerg M.3, DAHL-JENSEN, Dorthe4, STEFFENSEN, Jorgen Peter4, STEIG, Eric J.5, THOMAS, Elizabeth K.6, PETEET, Dorothy M.7, RITTENOUR, Tammy M.8, CORBETT, Lee B.2, TISON, Jean-Louis9, BLARD, Pierre-Henri10, PERDRIAL, Nicolas2, DETHIER, David P.11, LINI, Andrea12, HIDY, Alan J.13, CAFFEE, Marc W.14 and SOUTHON, John15, (1)Department of Geology, University of Vermont, Delehanty Hall, 180 Colchester Ave., Burlington, VT 05405, (2)Department of Geology, University of Vermont, Delehanty Hall, 180 Colchester Ave, Burlington, VT 05405, (3)Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, (4)Neils Bohr Institute, University of Copenhagen, Tagensvej 16, Copenhagen, 2200, Denmark, (5)Earth and Space Sciences, University of Washington, Box 351310, 70 Johnson Hall, Seattle, WA 98195, (6)Department of Geology, University at Buffalo, The State University of New York, 126 Cooke Hall, University at Buffalo, North Campus, Buffalo, NY 14260, (7)Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964; NASA, Goddard Institute for Space Studies, 2880 Broadway, NY, NY 10025, (8)Dept. of Geosciences, Utah State University, 4505 Old Main Hill, Logan, UT 84322-4505, (9)Laboratoire de Glaciologie, DGES-IGEOS, Université Libre de Bruxelles, Brussels, 1050, Belgium, (10)Centre de Recherches Pétrographiques et Géochimiques, CNRS - Université de Lorraine, Vandoeuvre-lès-Nancy, 54500, France, (11)Department of Geosciences, Williams College, Williamstown, MA 01267, (12)Department of Geology, University of Vermont, Burlington, VT 05405, (13)Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, (14)Department of Physics and Astronomy and Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN 47907, (15)Earth System Science, University of California, B321 Croul Hall, Irvine, CA 92697

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.