TY - JOUR A1 - Knudsen, Mads Faurschou A1 - Egholm, David L. A1 - Jacobsen, Bo Holm A1 - Larsen, Nicolaj Krog A1 - Jansen, John D. A1 - Andersen, Jane Lund A1 - Linge, Henriette C. T1 - A multi-nuclide approach to constrain landscape evolution and past erosion rates in previously glaciated terrains JF - Quaternary geochronology : the international research and review journal on advances in quaternary dating techniques N2 - Cosmogenic nuclides are typically used to either constrain an exposure age, a burial age, or an erosion rate. Constraining the landscape history and past erosion rates in previously glaciated terrains is, however, notoriously difficult because it involves a large number of unknowns. The potential use of cosmogenic nuclides in landscapes with a complex history of exposure and erosion is therefore often quite limited. Here, we present a novel multi-nuclide approach to study the landscape evolution and past erosion rates in terrains with a complex exposure history, particularly focusing on regions that were repeatedly covered by glaciers or ice sheets during the Quaternary. The approach, based on the Markov Chain Monte Carlo (MCMC) technique, focuses on mapping the range of landscape histories that are consistent with a given set of measured cosmogenic nuclide concentrations. A fundamental assumption of the model approach is 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 history in the model framework by applying a threshold value to the global marine benthic delta O-18 record and include the threshold value as a free model parameter, hereby taking into account global changes in climate. However, any available information on the glacial-interglacial history at the sampling location, in particular the timing of the last deglaciation event, is readily incorporated in the model to constrain the inverse problem. Based on the MCMC technique, the model delineates the most likely exposure history, including the glacial and interglacial erosion rates, which, in turn, makes it possible to reconstruct an exhumation history at the site. We apply the model to two landscape scenarios based on synthetic data and two landscape scenarios based on paired Be-10/Al-26 data from West Greenland, which makes it possible to quantify the denudation rate at these locations. The model framework, which currently incorporates any combination of the following nuclides Be-10, Al-26, C-14, and Ne-21, is highly flexible and can be adapted to many different landscape settings. The model framework may also be used in combination with physics-based landscape evolution models to predict nuclide concentrations at different locations in the landscape. This may help validate the landscape models via comparison to measured nuclide concentrations or to devise new effective sampling strategies. (C) 2015 The Authors. Published by Elsevier B.V. KW - Cosmogenic-nuclide geochronology KW - Markov Chain Monte Carlo inversion KW - Glacial landscape history KW - Erosion rate reconstructions KW - Quaternary climate Y1 - 2015 U6 - https://doi.org/10.1016/j.quageo.2015.08.004 SN - 1871-1014 SN - 1878-0350 VL - 30 SP - 100 EP - 113 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Egholm, David L. A1 - Jansen, John D. A1 - Braedstrup, Christian F. A1 - Pedersen, Vivi K. A1 - Andersen, Jane Lund A1 - Ugelvig, Sofie V. A1 - Larsen, Nicolaj K. A1 - Knudsen, Mads F. T1 - Formation of plateau landscapes on glaciated continental margins JF - Nature geoscience N2 - Low-relief plateaus separated by deeply incised fjords are hallmarks of glaciated, passive continental margins. Spectacular examples fringe the once ice-covered North Atlantic coasts of Greenland, Norway and Canada, but low-relief plateau landscapes also underlie present-day ice sheets in Antarctica and Greenland. Dissected plateaus have long been viewed as the outcome of selective linear erosion by ice sheets that focus incision in glacial troughs, leaving the intervening landscapes essentially unaffected. According to this hypothesis, the plateaus are remnants of preglacial low-relief topography. However, here we use computational experiments to show that, like fjords, plateaus are emergent properties of long-term ice-sheet erosion. Ice sheets can either increase or decrease subglacial relief depending on the wavelength of the underlying topography, and plateau topography arises dynamically from evolving feedbacks between topography, ice dynamics and erosion over million-year timescales. This new mechanistic explanation for plateau formation opens the possibility of plateaus contributing significantly to accelerated sediment flux at the onset of the late Cenozoic glaciations, before becoming stable later in the Quaternary. Y1 - 2017 U6 - https://doi.org/10.1038/NGEO2980 SN - 1752-0894 SN - 1752-0908 VL - 10 SP - 592 EP - + PB - Nature Publ. Group CY - New York ER - TY - JOUR A1 - Mey, Jürgen A1 - Scherler, Dirk A1 - Wickert, Andrew D. A1 - Egholm, David L. A1 - Tesauro, Magdala A1 - Schildgen, Taylor F. A1 - Strecker, Manfred T1 - Glacial isostatic uplift of the European Alps JF - Nature Communications Y1 - 2016 U6 - https://doi.org/10.1038/ncomms13382 SN - 2041-1723 VL - 7 SP - 2357 EP - 2371 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Strunk, Astrid A1 - Knudsen, Mads Faurschou A1 - Egholm, David L. A1 - Jansen, John D. A1 - Levy, Laura B. A1 - Jacobsen, Bo H. A1 - Larsen, Nicolaj K. T1 - One million years of glaciation and denudation history in west Greenland JF - Nature Communications N2 - The influence of major Quaternary climatic changes on growth and decay of the Greenland Ice Sheet, and associated erosional impact on the landscapes, is virtually unknown beyond the last deglaciation. Here we quantify exposure and denudation histories in west Greenland by applying a novel Markov-Chain Monte Carlo modelling approach to all available paired cosmogenic Be-10-Al-26 bedrock data from Greenland. We find that long-term denudation rates in west Greenland range from >50 m Myr(-1) in low-lying areas to similar to 2 m Myr(-1) at high elevations, hereby quantifying systematic variations in denudation rate among different glacial landforms caused by variations in ice thickness across the landscape. We furthermore show that the present day ice-free areas only were ice covered ca. 45% of the past 1 million years, and even less at high-elevation sites, implying that the Greenland Ice Sheet for much of the time was of similar size or even smaller than today. Y1 - 2017 U6 - https://doi.org/10.1038/ncomms14199 SN - 2041-1723 VL - 8 PB - Nature Publishing Group UK CY - London ER -