Using in situ cosmogenic 10 Be to identify the source of sediment leaving Greenland

• Published in: Earth Surface Processes and Landforms
• Main Authors: Nelson, Alice H., Bierman, Paul R., Shakun, Jeremy D., Rood, Dylan H.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: John Wiley and Sons 2014
• Subjects: Greenland; Ice Sheet; Narsarsuaq
• Online Access: http://eprints.gla.ac.uk/95176/

We use the concentration of in situ 10 Be in quartz isolated from fluvial and morainal sand to trace sediment sources and to determine the relative contribution of glacerized and deglaciated terrain to Greenland’s sediment budget. We sampled along the western, eastern, and southern margins of the Greenland Ice Sheet, and collected sediment sourced from glacerized (n = 19) and non-glacerized terrain (n = 10), from channels where sediment from glacerized and non-glacerized terrain is mixed (n = 28), from Holocene glacial-fluvial terraces (n = 4), and from one sand dune. In situ 10 Be concentrations in sediment range from 1600 to 34 000 atoms g-1. The concentration of in situ 10 Be in sediment sourced from non-glacerized terrain is significantly higher than in sediment sourced from glacerized areas, in mixed channel sediment, and in terrace sediment that was deposited during the Holocene. To constrain the timing of landscape exposure for the deglaciated portion of the Narsarsuaq field area in southern Greenland, we measured in situ 10 Be concentration in bedrock (n = 5) and boulder (n = 6) samples. Paired bedrock and boulder ages are indistinguishable at 1σ uncertainty and indicate rapid exposure of the upland slopes at ~10.5 ka. The isotope concentration in sediment sourced from non-glacerized terrain is higher than in sediment sourced from glacerized terrain because the non-glacerized landscape has been exposed to cosmic radiation since early Holocene deglaciation. Sediment from glacerized areas contains a low, but measurable concentration of 10 Be that probably accumulated at depth during a prolonged period of exposure, probably before the establishment of the Greenland Ice Sheet. The concentration of 10 Be in mixed fluvial sediment and in terrace sediment is low, and similar to the concentration in sediment from glacerized areas, which indicates that the Greenland Ice Sheet is the dominant source of sediment moving through the landscape outside the glacial margin in the areas we sampled.