Geological, geochemical and cosmogenic nuclides constraints from the NEEM core basal sediments, Greenland

Abstract

<p>As the melting of the Greenland Ice Sheet (GrIS) accelerates, it is critical to improve our knowledge of its Pleistocene history in order to better understand its sensitivity to different climate states. The study of sediment from the base of the ice sheet offers valuable insights, since this material holds useful information about its history and origin. Here, we present various mineralogical and geochemical analysis from basal sediments of the NEEM ice core from northwestern Greenland (NEEM community, 2013), a complement to the first analysis of the basal ice made by Goossens et al. (2016).</p><p>In an effort to specify the provenance and characterize the sediments in the basal ice of the NEEM ice core, strontium and neodymium isotopic ratios were measured in 7 bulk till samples located into the deepest part of the core. Laser granulometry and shape characterization by SEB images of the grains suggest a mixed origin of this material. The deepest sample yield in situ cosmogenic <sup>10</sup>Be and <sup>26</sup>Al concentrations lower than 10<sup>4</sup> at.g<sup>-1</sup> and <sup>21</sup>Ne concentration in the 10<sup>7</sup>-10<sup>8</sup> at.g<sup>-1</sup> range. These preliminary cosmogenic nuclides data suggest that several cycles of waning and waxing of the GrIS had occurred over the last 10 million years. Additional sample material is being processed to reduce the uncertainty of <sup>26</sup>Al and <sup>10</sup>Be measurements and refine this chronology.</p><p>To better characterize the origin of the basal sediment and the duration of pre-burial exposure, measurements of meteoric cosmogenic <sup>10</sup>Be in 7 samples distributed along the basal part of the core are currently in progress. These data will be combined with the measurement of total organic carbon and nitrogen in the same samples. C and N concentrations and isotopes bring useful information about the type of soil and till material in these basal sediments (Bierman et al., 2016).</p><p> </p><p>Bierman, P.R., Shakun, J.D., Corbett, L.B., Zimmerman, S.R., Rood, D.H., 2016. A persistent and dynamic East Greenland Ice Sheet over the past 7.5 million years. Nature 540, 256–260. https://doi.org/10.1038/nature20147</p><p>Goossens, T., Sapart, C.J., Dahl-Jensen, D., Popp, T., El Amri, S., Tison, J.-L., 2016. A comprehensive interpretation of the NEEM basal ice build-up using a multi-parametric approach. The Cryosphere 10, 553–567. https://doi.org/10.5194/tc-10-553-2016</p><p>NEEM community, 2013. Eemian interglacial reconstructed from a Greenland folded ice core. Nature, 493. doi:10.1038/nature11789</p>