C052-12
A multi-million-year record of vegetation and ice-cover in the basal sediment from the Camp Century ice core, northwestern Greenland
Monday, 14 December 2020: 18:03
Virtual
Andrew James Christ1, Paul R Bierman2, Joerg M Schaefer3, Dorthe Dahl-Jensen4, Jorgen Peder Steffensen5, Eric J. Steig6, Elizabeth K Thomas7, Tammy M Rittenour8, Dorothy M Peteet9,10, Lee B Corbett2, Jean-Louis Tison11, Pierre-Henri Blard12, Nicolas Perdrial2, David P Dethier13, Andrea Lini2, Alan Hidy14, Marc Caffee15 and John Richard Southon16, (1)University of Vermont, Department of Geology, Burlington, VT, United States, (2)University of Vermont, Burlington, VT, United States, (3)Lamont-Doherty Earth Observ, Palisades, NY, United States, (4)Niels Bohr Institute, Centre for Ice and Climate, Copenhagen, Denmark, (5)Centre for Ice and Climate, Copenhagen, Denmark, (6)University of Washington, Earth and Space Sciences, Seattle, WA, United States, (7)University at Buffalo, Department of Geology, Buffalo, NY, United States, (8)Utah State Univ, Department of Geosciences, Logan, UT, United States, (9)Columbia University of New York, Palisades, NY, United States, (10)NASA Goddard Institute for Space Studies, New York, NY, United States, (11)Université Libre de Bruxelles, Bruxelles, Belgium, (12)CRPG, UMR 7358 CNRS-UL, Nancy, France, (13)Williams College, Williamstown, MA, United States, (14)Lawrence Livermore National Laboratory, Livermore, CA, United States, (15)Purdue University, Purdue Rare Isotope Measurement Laboratory, West Lafayette, IN, United States, (16)Univ California, Irvine, CA, United States
Abstract:
The response of the Greenland Ice Sheet (GrIS) to future warming and its subsequent contribution to sea-level rise remain uncertain. Terrestrial records of a GrIS smaller than today are critical to understanding ice-sheet sensitivity to future warming, yet inaccessible due to present ice cover. Ice-core basal sediments provide an important archive of past ice-free periods. Collected in 1966 from northwestern Greenland, the Camp Century ice core recovered 3.5 m of sub-glacial sediment that was incompletely studied and then forgotten for decades, until it was re-discovered in 2017.
Here, we show that the Camp Century upper- and lower-most sub-glacial sediment documents a multi-million-year record of vegetation and ice cover in northwestern Greenland. The sediment contains abundant macrofossil vegetation, including twigs, moss leaves and stems, and fungal spores, 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. 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. Cosmogenic 26Al/10Be ratios require exposure of the upper sediment within the last 0.6-0.9 Myr. Infrared stimulated luminescence ages from the lower sediment indicates exposure more than 0.7-1.3 Myr ago, but 26Al/10Be ratios require burial no more than 2.6-3.3 Myr.
The Camp Century sub-glacial sediment is unique among Greenland ice cores because it contains a stratigraphic record of ice cover spanning the entire Pleistocene and the paleo-ecosystems that occupied northwestern Greenland during ice-free periods. The lower sediment may derive from a pre-glacial landscape (>2.6 Ma) that was then ice-covered for much of the Pleistocene. Exposure of the upper sediment, and thus ice absence in northwestern Greenland, within the last 0.6-0.9 Myr adds to growing evidence that the GrIS was largely absent at least once during the last 1 Myr. During this timeframe, the most likely times for widespread GrIS absence are Marine Isotope Stages 31 and 11, which were prolonged interglacials with higher global sea level. This implies GrIS sensitivity to sustained warmth, which is concerning given future climate projections.
