In situ cosmogenic 10Be production-rate calibration from the Southern Alps,New Zealand |
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| Authors: | AE Putnam JM Schaefer DJA Barrell M Vandergoes GH Denton MR Kaplan RC Finkel R Schwartz BM Goehring SE Kelley |
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| Institution: | 1. Department of Earth Sciences and Climate Change Institute, University of Maine, Orono, ME 04469, USA;2. Lamont-Doherty Earth Observatory, Palisades, NY 10964, USA;3. GNS Science, Dunedin, New Zealand;4. GNS Science, Lower Hutt, New Zealand;5. Earth and Planetary Science Dept, University of California, Berkeley, CA 94720, USA;6. ASTER, Centre Européen de Recherche et Enseignement des Géosciences de l''Environnement, Aix-en-Provence 13100, France |
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| Abstract: | We present a 10Be production-rate calibration derived from an early Holocene debris-flow deposit at about 1000 m above sea level in the central Southern Alps, New Zealand, in the mid-latitude Southern Hemisphere. Ten radiocarbon ages on macrofossils from a soil horizon buried by the deposit date the deposit to 9690 ± 50 calendar years before AD2008. Surface 10Be concentrations of seven large boulders partially embedded in the stable surface of the deposit are tightly distributed, yielding a standard deviation of ～2%. Conversion of the 10Be measurements to sea level/high-latitude values using each of five standard scaling methods indicates 10Be production rates of 3.84 ± 0.08, 3.87 ± 0.08, 3.83 ± 0.08, 4.15 ± 0.09, and 3.74 ± 0.08 atoms g?1 a?1, relative to the ‘07KNSTD’ 10Be AMS standard, and including only the local time-integrated production-rate uncertainties. When including a sea level high-latitude scaling uncertainty the overall error is ～2.5% (1σ) for each rate. To test the regional applicability of this production-rate calibration, we measured 10Be concentrations in a set of nearby moraines deposited before 18 060 ± 200 years before AD2008. The 10Be ages are only consistent with minimum-limiting 14C age data when calculated using the new production rates. This also suggests that terrestrial in situ cosmogenic-nuclide production did not change significantly from Last Glacial Maximum to Holocene time in New Zealand. Our production rates agree well with those of a recent calibration study from northeastern North America, but are 12–14% lower than other commonly adopted values. The production-rate values presented here can be used elsewhere in New Zealand for rock surfaces exposed during or since the last glacial period. |
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