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A multi-nuclide approach to constrain landscape evolution and past erosion rates in previously glaciated terrains

机译：一种多核方法，可限制先前冰川化地形中的景观演变和过去的侵蚀速率

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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.
机译：宇宙核素通常用于限制暴露年龄，埋葬年龄或侵蚀速率。然而，限制以前的冰川地区的景观历史和过去的侵蚀速度是非常困难的，因为它涉及许多未知因素。因此，在具有复杂的暴露和侵蚀历史的景观中，潜在的宇宙成因核素的使用往往受到很大限制。在这里，我们提出了一种新颖的多核素方法，以研究具有复杂暴露历史的地形中的景观演变和过去的侵蚀速率，特别是在第四纪时期反复被冰川或冰盖覆盖的区域。该方法基于马尔可夫链蒙特卡洛（MCMC）技术，着重于绘制与给定的一组测量的成宇宙核素浓度一致的景观历史范围。该模型方法的基本假设是，场地/位置的暴露历史可以分为两种不同的模式：i）冰川期，其特征是由于覆冰和统一的冰川间侵蚀速率而产生的零屏蔽，以及ii） 100％的屏蔽和均匀的冰川侵蚀速率。通过将阈值应用于全球海洋底栖三角洲O-18记录，我们将暴露历史纳入模型框架中，并将阈值作为免费模型参数包括在内，从而考虑了全球气候变化。但是，有关采样位置冰河间历史的任何可用信息，特别是最后一次冰消事件的发生时间，都可以轻松地纳入模型中，以约束反问题。该模型基于MCMC技术，描绘了最可能的暴露历史，包括冰川和冰川间的侵蚀速率，从而可以在该地点重建掘尸历史。我们将该模型应用于基于合成数据的两个景观方案和基于西格陵兰的Be-10 / Al-26配对数据的两个景观方案，这使得可以量化这些位置的剥蚀率。该模型框架目前结合了以下核素Be-10，Al-26，C-14和Ne-21的任意组合，具有很高的灵活性，可以适应多种不同的景观环境。该模型框架还可与基于物理学的景观演化模型结合使用，以预测景观中不同位置的核素浓度。通过与测得的核素浓度进行比较或设计新的有效采样策略，这可能有助于验证景观模型。 （C）2015作者。由Elsevier B.V.发布

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