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B. H. Jacobsen

A multi-nuclide approach to quantify long-term erosion rates and exposure history through multiple glacial-interglacial cycles

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Cosmogenic nuclides are traditionally used to either determine the glaciation history or the denudation history of the most recent exposure period. A few studies use the cosmogenic nuclides to determine the cumulative exposure and burial durations of a sample. However, until now it has not been possible to resolve the complex pattern of exposure history under a fluctuating ice sheet. In this study, we quantify long-term erosion rates along with durations of multiple exposure periods in West Greenland by applying a novel Markov Chain Monte Carlo (MCMC) inversion approach to existing 10Be and 26Al.

The new MCMC approach allows us to constrain the most likely landscape history based on comparisons between simulated and measured cosmogenic nuclide concentrations. It is a fundamental assumption of the model that the exposure history at the site/location can be divided into two distinct regimes: i) interglacial periods characterized by zero shielding due to overlying ice and a uniform interglacial erosion rate, and ii) glacial periods characterized by 100 % shielding and a uniform glacial erosion rate. We incorporate the exposure/burial history in the model framework by applying a threshold value to the global marine benthic d18O record and include the threshold value as a free model parameter, hereby taking into account global changes in climate. The other free parameters include the glacial and interglacial erosion rates as well as the timing of the Holocene deglaciation. The model essentially simulates numerous different landscape scenarios based on these four parameters and zooms in on the most plausible combination of model parameters.

We apply the MCMC-model to the concentrations of 10Be and 26Al measured in previously published studies from Upernavik, Uummannaq and Sisimiut and quantify the most likely exposure/burial history integrated with erosion rates. Our results show a clear trend of decreasing erosion rate with increasing altitude, with a lowest total denudation rate of 1.7±0.2 m/Ma at 841 m a.s.l. and the highest rate of 25.6 ± 10.4 m/Ma at 150 m a.s.l. We find that the three areas have been exposed during 17 previous interglacials and quantify the most likely temporal extent of each of these, which enables us to reconstruct the ice margin fluctuation across the West Greenland fjord area throughout the last 1 million years. Our results contribute to understanding the landscape evolution under multiple glacial-interglacial cycles and provide a temporal framework for the sparse pre-LGM data that has been found, but have proven difficult to constrain in time.
Original languageEnglish
Publication year2016
Publication statusPublished - 2016
EventThird Nordic Workshop on Cosmogenic Nuclides - Stockholm, Stockholm, Sweden
Duration: 8 Jun 201611 Jun 2016


ConferenceThird Nordic Workshop on Cosmogenic Nuclides

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