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 - 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 - 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 - GEN A1 - Egholm, David L. A1 - Andersen, Jane Lund A1 - Faurschou Knudsen, Mads A1 - Jansen, John D. A1 - Nielsen, S. B. T1 - The periglacial engine of mountain erosion BT - Part 2: Modelling large-scale landscape evolution T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - There is growing recognition of strong periglacial control on bedrock erosion in mountain landscapes, including the shaping of low-relief surfaces at high elevations (summit flats). But, as yet, the hypothesis that frost action was crucial to the assumed Late Cenozoic rise in erosion rates remains compelling and untested. Here we present a landscape evolution model incorporating two key periglacial processes - regolith production via frost cracking and sediment transport via frost creep - which together are harnessed to variations in temperature and the evolving thickness of sediment cover. Our computational experiments time-integrate the contribution of frost action to shaping mountain topography over million-year timescales, with the primary and highly reproducible outcome being the development of flattish or gently convex summit flats. A simple scaling of temperature to marine delta O-18 records spanning the past 14 Myr indicates that the highest summit flats in mid-to high-latitude mountains may have formed via frost action prior to the Quaternary. We suggest that deep cooling in the Quaternary accelerated mechanical weathering globally by significantly expanding the area subject to frost. Further, the inclusion of subglacial erosion alongside periglacial processes in our computational experiments points to alpine glaciers increasing the long-term efficiency of frost-driven erosion by steepening hillslopes. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 552 KW - situ produced BE-10 KW - glacial erosion KW - southern Alps KW - New-Zealand KW - rates KW - climate KW - sediment KW - surfaces KW - uplift KW - AL-26 Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-409718 SN - 1866-8372 IS - 552 ER - TY - GEN A1 - Andersen, Jane Lund A1 - Egholm, David L. A1 - Faurschou Knudsen, Mads A1 - Jansen, John D. A1 - Nielsen, S. B. T1 - The periglacial engine of mountain erosion BT - Part 1: Rates of frost cracking and frost creep T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - With accelerating climate cooling in the late Cenozoic, glacial and periglacial erosion became more widespread on the surface of the Earth. The resultant shift in erosion patterns significantly changed the large-scale morphology of many mountain ranges worldwide. Whereas the glacial fingerprint is easily distinguished by its characteristic fjords and U-shaped valleys, the periglacial fingerprint is more subtle but potentially prevails in some mid- to high-latitude landscapes. Previous models have advocated a frost-driven control on debris production at steep headwalls and glacial valley sides. Here we investigate the important role that periglacial processes also play in less steep parts of mountain landscapes. Understanding the influences of frost-driven processes in low-relief areas requires a focus on the consequences of an accreting soil mantle, which characterises such surfaces. We present a new model that quantifies two key physical processes: frost cracking and frost creep, as a function of both temperature and sediment thickness. Our results yield new insights into how climate and sediment transport properties combine to scale the intensity of periglacial processes. The thickness of the soil mantle strongly modulates the relation between climate and the intensity of mechanical weathering and sediment flux. Our results also point to an offset between the conditions that promote frost cracking and those that promote frost creep, indicating that a stable climate can provide optimal conditions for only one of those processes at a time. Finally, quantifying these relations also opens up the possibility of including periglacial processes in large-scale, long-term landscape evolution models, as demonstrated in a companion paper. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 530 KW - soil production function KW - mantled hillslopes KW - sediment transport KW - southern Alps KW - New-Zealand KW - ice-sheet KW - bedrock KW - model KW - rock KW - evolution Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-409656 SN - 1866-8372 IS - 530 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 -