Camp Century ice core basal sediments record the absence of the Greenland Ice Sheet within the last million years

• DOI: 10.5194/egusphere-egu2020-12243
• Publication Date: 2020-03-09T22:43:21Z
• Authors: Andrew Christ; Paul Bierman; Dorthe Dahl-Jensen; Jørgen Steffensen; Dorothy Peteet; Elizabeth Thomas; Owen Cowling; Eric Steig; Lee Corbett; Joerg Schaefer; Alan Hidy; Marc Caffee; Tammy Rittenour; Jean-Louis Tison; Pierre-Henri Blard; Marie Protin; John Southon
• Keywords: Greenland ice sheet; Ice core; Paleoclimatology

<p>The Greenland Ice Sheet (GrIS) is melting in response to a rapidly warming climate.  It imperative understand GrIS sensitivity past climate, especially during periods when the ice sheet was smaller than present or possibly absent. The Camp Century core from NW Greenland, collected 1966 and first be drilled bed of GrIS, revolutionized our understanding global paleoclimate since 125 ka. However, basal sediment not fully explored then sat storage for decades – until it re-discovered two years ago. We are now investigating these unique samples sub-glacial environment using modern analyses. </p><p>Here, we initial results samples, upper lower portions >4 m sediment. applied an array geochemical analyses characterize paleoenvironment (lipid biomarkers, δ<sup>13</sup>C, δ<sup>15</sup>N), infer climatic conditions (δ<sup>18</sup>O, δD) frozen pore water, determine exposure burial history sediments below (optically stimulated luminescence [OSL], cosmogenic <sup>10</sup>Be, <sup>26</sup>Al, <sup>21</sup>Ne). </p><p>The consists poorly sorted, reddish-brown, quartz-rich diamict, with paleo-permafrost features some layers. This material contains woody macrofossils, fungal sclerotia (<em>Cenococcum geophilum</em>), mosses (<em>Tomenthypnum nitens, Polytrichum juniperinum</em>) that yield <sup>14</sup>C age >55 Woody tissue stable δ<sup>13</sup>C ratios -26.7±0.1‰ -29.6±0.1‰ δ<sup>15</sup>N 2.4±0.8‰ -2.3±0.8‰. Leaf wax (n-alkanoic acid) distributions similar Arctic shrubs. Frozen water yielded δ<sup>18</sup>O -23.06±0.08‰ -21.49±0.08‰, enriched relative all overlying (<-27‰). Deuterium-excess values 4.3±0.8 ‰ 13.4±0.4 ‰, respectively.  These isotope measurements suggest snowfall precipitation at temperatures today if site were ice-free. OSL minimum depositional >600 In situ <sup>10</sup>Be concentrations quartz decrease depth 7.7±0.1 x10<sup>4</sup> atoms/g (500-850 µm)  6.6±0.2 (250-500 1.6±0.1 1.8±0.1 <sup>26</sup>Al/<sup>10</sup>Be ratio also decreases depth. sediment, range between 4.2 4.9 indicating > 900 ka burial. 1.4 2.0 >2 Ma Measured <sup>21</sup>Ne/<sup>10</sup>Be exceed 1000, which could indicate long-term and/or presence nucleogenic <sup>21</sup>Ne.</p><p>These demonstrate exposed under ice-free supported vegetation today. Cosmogenic data deeper has been buried most Pleistocene date rules out surface MIS 11. analysis indicates sample experienced less more recent re-exposure. consistent growing body evidence dynamic even pre-industrial climate system atmospheric CO<sub>2</sub> did ~300 ppm.</p>