Paired bedrock and boulder 10Be concentrations resulting from early Holocene ice retreat near Jakobshavn Isfjord,western Greenland |
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| Authors: | Lee B. Corbett Nicolás E. Young Paul R. Bierman Jason P. Briner Thomas A. Neumann Dylan H. Rood Joseph A. Graly |
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| Affiliation: | 1. Department of Geology, University of Vermont, Burlington, VT 05405, USA;2. Department of Geology, State University of New York at Buffalo, Buffalo, NY 14260, USA;3. NASA Goddard Space Flight Center, Greenbelt, MD 20770, USA;4. Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA;5. Earth Research Institute, University of California, Santa Barbara, CA 93106, USA;1. Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN 47907, USA;2. Department of Physics and Astronomy and Purdue Rare Isotope Measurement Laboratory (PRIME Lab), Purdue University, 525 Northwestern Avenue, West Lafayette, IN 47907, USA;3. Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, P.O. Box 808, L-397, Livermore, CA 94550, USA;4. Space Sciences Laboratory #7450, University of California, 7 Gauss Way, Berkeley, CA 94720, USA;5. Department of Earth & Environmental Science, New Mexico Tech, 801 Leroy Place, Socorro, NM 87801, USA;6. Department of Earth and Environmental Sciences, Tulane University, 6823 St Charles Avenue, New Orleans, LA 70118, USA;7. Department of Earth Sciences, Dalhousie University, PO Box 15000, Halifax, NS B3H 4R2, Canada;8. Department of Earth and Space Sciences, University of Washington, 4000 15th Avenue NE, Seattle, WA 98195, USA;9. Lamont-Doherty Earth Observatory, The Earth Institute at Columbia University, Route 9W, Palisades, NY 10964, USA;10. Golder Associates, 18300 NE Union Hill Road, Suite 200, Redmond, WA 98052, USA;11. Geosciences Department and Arizona Accelerator Mass Spectrometry Laboratory, University of Arizona, 1040 East 4th St, Tucson, AZ 85721, USA;12. Department of Nuclear Physics, Research School of Physical Sciences and Engineering, The Australian National University, Canberra, ACT 0200, Australia;1. Department of Earth Sciences, University of Gothenburg, Sweden;2. Earth and Environmental Sciences Institute, Pennsylvania State University, USA;3. Geomorphology and Glaciology, Department of Physical Geography and Bolin Centre for Climate Research, Stockholm University, Sweden;4. Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, USA;1. Department of Earth Sciences, Dartmouth College, Hanover, NH 03755, USA;2. Department of Geology, University of Cincinnati, Cincinnati, OH 45221, USA;3. Earth and Environmental Systems Institute, Pennsylvania State University, University Park, PA 16802, USA;4. Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA;5. Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USA;6. Ecole Polytechnique Federale de Lausanne, Station 2, CH-1015 Lausanne, Switzerland;7. Cooperative Institute for Research in Environmental Sciences, University of Colorado, 216 UCB, Boulder, CO 80309, USA;8. Department of Geosciences, University of Arizona, Tucson, AZ 85721, USA;1. Indiana University Purdue University Indianapolis, Dept. of Earth Sciences, Indianapolis, IN, USA;2. University of Vermont, Dept. of Geology, Burlington, VT, USA;3. NASA Goddard Space Flight Center, Greenbelt, MD, USA;1. Department of Geoscience, University of Wisconsin-Madison, WI, Madison 53706, USA;2. College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA;3. Scottish Universities Environmental Research Centre (SUERC), University of Glasgow, East Kilbride G75 0QF, UK;4. Earth Research Institute, University of California-Santa Barbara, Santa Barbara, CA 93106, USA |
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| Abstract: | We measured in situ cosmogenic 10Be in 16 bedrock and 14 boulder samples collected along a 40-km transect outside of and normal to the modern ice margin near Sikuijuitsoq Fjord in central-west Greenland (69°N). We use these data to understand better the efficiency of glacial erosion and to infer the timing, pattern, and rate of ice loss after the last glaciation. In general, the ages of paired bedrock and boulder samples are in close agreement (r2 = 0.72). Eleven of the fourteen paired bedrock and boulder samples are indistinguishable at 1σ; this concordance indicates that subglacial erosion rates are sufficient to remove most or all 10Be accumulated during previous periods of exposure, and that few, if any, nuclides are inherited from pre-Holocene interglaciations. The new data agree well with previously-published landscape chronologies from this area, and suggest that two chronologically-distinct land surfaces exist: one outside the Fjord Stade moraine complex (～10.3 ± 0.4 ka; n = 7) and another inside (～8.0 ± 0.7 ka; n = 21). Six 10Be ages from directly outside the historic (Little Ice Age) moraine show that the ice margin first reached its present-day position ～7.6 ± 0.4 ka. Early Holocene ice margin retreat rates after the deposition of the Fjord Stade moraine complex were ～100–110 m yr?1. Sikuijuitsoq Fjord is a tributary to the much larger Jakobshavn Isfjord and the deglaciation chronologies of these two fjords are similar. This synchronicity suggests that the ice stream in Jakobshavn Isfjord set the timing and pace of early Holocene deglaciation of the surrounding ice margin. |
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