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Northeastern Section - 48th Annual Meeting (18–20 March 2013)

Paper No. 5
Presentation Time: 9:10 AM

10BE CONCENTRATION IN GREENLAND SEDIMENT INDICATES SOURCE AND EXPOSURE HISTORY


NELSON, Alice, Geology, University of Vermont, Delehanty Hall, Burlington, VT 05405, BIERMAN, Paul, Geology and School of Natural Resources, University of Vermont, Delehanty Hall, 180 Colchester Ave, Burlington, VT 05405, SHAKUN, Jeremy D., Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138 and ROOD, Dylan H., AMS Laboratory, Scottish Universities Environmental Research Centre (SUERC), East Kilbride, G75 0QF, United Kingdom, ahnelson@uvm.edu

Greenland Ice Sheet extent is dynamic and when ice margins retreat, the exposed landscape accumulates 10Be. Our objective is to understand the in situ 10Be concentration in sediment as it is eroded by the ice sheet and moves across the landscape to the fjords. Greenland sediment is sourced both sub-glacially and sub-aerially and is mixed and stored within lakes and fjords until a period of glacial advance, when the ice sheet erodes and transports surficial materials off shore. Understanding the 10Be concentration in sediment entering the marine realm will help us decipher sediment records from the deep ocean, potentially providing a 5–6 million year history of ice sheet dynamics.

We measured the concentration of in situ 10Be in fluvial quartz sand collected in 2011 and 2012 from Kangerlussuaq (n=14), Narsarsuaq (n=12), and Tasiilaq (n=7) on the west, south, and east coasts of Greenland, respectively. We collected sand sourced from the ice, from tributaries draining exposed hill slopes, and from intermediate locations along ice marginal drainages.

Spatial patterns in data are similar between regions studied, indicating broad consistency in processes controlling in situ 10Be accumulation on the landscape and subsequent erosion and transportation of sediment. 10Be concentration in ice marginal sediment is relatively low (~2–5 x 103 atoms/g), because the landscape from which the sediment is sourced is shielded from cosmic rays by ice. At least some of the 10Be in sub-glacially sourced samples likely accumulated during mid-Holocene exposure when climate was warmer and the ice sheet smaller.

10Be concentration in sub-aerially sourced sediment is much higher (~10–35 x 103 atoms/g) because of exposure to cosmic rays. The highest 10Be concentrations are in sediment sourced from terrain that has been accumulating 10Be since the Last Glacial Maximum.

10Be concentration in drainages spanning the ice margin to the fjord mouth reflects the combined contribution of sediment sourced sub-glacially and sub-aerially. In drainages with little sub-aerial input, 10Be concentrations are low and consistent whereas in drainages receiving sediment from exposed hill slopes, concentrations are higher, and may show a downstream trend towards higher 10Be as sediment is sourced from an increasing area of exposed terrain.

Handouts
  • NEGSA_ANelson.pdf (8.9 MB)

    • Session No. 33

    T11. Dates and Rates: Two Decades of Cosmogenic Studies in Eastern North America, the Canadian Arctic, and Greenland
    Tuesday, 19 March 2013: 8:00 AM-12:00 PM
    Dartmouth Room (Omni Mount Washington Resort)
    Geological Society of America Abstracts with Programs. Vol. 45, No. 1, p.85
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