Cosmogenic Nuclide-Based Boundary Conditions for Numerical Ice Sheet Models: A Simulation of the Fennoscandian Ice Sheet through A Glacial Cycle

0138486Harbor0138486Harbor0138486Harbor0138486Harbor0138486Harbor0138486Harbor0138486Harbor0138486Harbor0138486Harbor0138486Harbor0138486Harbor013848486Harbor0138486Harbor0138486Harbor01384848484848484848484848484848484848484848484848484848484848484848484848484848484848484848484848484848484848484848484848这可能会导致不切实际的模拟冰盖的开始，增长和衰减，并在重建冰盖基底边界条件和表面轮廓的不确定性。 例如，在某些地方，纵倾线和风化差异被解释为前冰盖高度的指标，而斯堪的纳维亚半岛冰川侵蚀模式的测绘和宇宙成因核素评估表明，在某些情况下，这些特征代表湿（暖）基侵蚀性冰和干（冷）基非侵蚀性冰之间的内部热边界。 这种根本性的差异解释重建冰盖厚度，动力学和范围，以及来自冰盖重建的古气候解释产生了深远的影响。在斯堪的纳维亚半岛，在多个冰盖覆盖事件的已知范围内，未被侵蚀的地区已经被确定，这一事实表明，这些未被侵蚀的地区必须在整个冰盖的形成、生长和衰减过程中作为非侵蚀（可能是冻床）斑块而生存下来。这一观察代表了一个重要的新的约束冰盖模型的基础热条件，并表示基于实地的地貌和冰川地质学可以提供的约束类型，以提高冰盖建模工作。 在过去的三年里，主要研究员Arjen Stroeven，斯德哥尔摩大学和Derek Fabel，澳大利亚国立大学，在美国国家科学基金会（NSF）和瑞典NSF的支持下合作研究了北方瑞典山区的冰川消融年表和侵蚀模式以及景观保护，芬诺斯堪的纳维亚冰盖（FIS）的核心区域。 结果为提出这项工作的下一阶段提供了基础，在这一阶段，他们将重建FIS厚度，范围和动态（包括总冰量引起的海平面变化）在末次冰期循环的关键时期（海洋同位素阶段[MIS] 5d或5 b，初始阶段; MIS 2，末次冰期最大期（LGM）阶段; MIS 1，冰川消退阶段）。通过一个冰川周期的FIS的古地形（高度）将使用一个国家的最先进的热力学数值冰盖模型进行模拟，与关键的边界条件约束的宇宙成因核素为基础的冰下条件的重建，并通过均衡模型。这项工作的团队已经扩大，包括爱丁堡大学的Alun Hubbard，澳大利亚国立大学的Kurt Lambeck和斯德哥尔摩大学的Jens-Ove Naslund，在冰川学和均衡建模领域。 新的重建将可能具有广泛的意义，无论是欧洲冰盖和古气候重建和评估的证据，海平面低站（代理地球上的总陆基冰），并鼓励重新评估的动态的开始，增长，和全球其他主要冰盖的衰减。

0138486HarborMajor limitations in the successful use of ice sheet models for climate research arise from limited field data for model calibration. This may result in unrealistic simulations of ice sheet inception, growth, and decay, and uncertainties in reconstructing ice sheet basal boundary conditions and surface profiles. For example, trimlines and weathering differences have been interpreted as indicators of former ice sheet height in some locations, while mapping and cosmogenic nuclide-based assessment of glacial erosion patterns in Scandinavia suggest that such features in some cases represent internal thermal boundaries between wet-(warm) based erosive ice and dry-(cold) based non-erosive ice. Such radical differences in interpretation have profound impacts on reconstructed ice sheet thickness, dynamics, and extent, and paleoclimates interpretations derived from ice sheet reconstructions. The fact that uneroded areas have been identified in Scandinavia within the known limits of multiple ice sheet overriding events indicates that these uneroded areas must have survived as non-eroding (presumably frozen-bed) patches throughout ice sheet inception, growth, and decay. This observation represents a significant new constraint on basal thermal conditions for ice sheet models and is indicative of the types of constraints that field-based geomorphology and glacial geology can provide to enhance ice sheet modeling efforts. Over the past three years the Principal Investigator Arjen Stroeven, Stockholm University, and Derek Fabel, Australian National University, have worked collaboratively with support from National Science Foundation (NSF) and Swedish NSF to examine deglaciation chronology and patterns of erosion and landscape preservation in the northern Swedish mountains, the core area of the Fennoscandian Ice Sheet (FIS). The results provide the groundwork for proposing the next phase of this work, in which they will reconstruct FIS thickness, extent, and dynamics (including total ice volume-induced sea level change) over critical periods of the last glacial cycle (Marine Isotope Stage [MIS] 5d or 5b, inception phase; MIS 2, Last Glacial Maximum (LGM) phase, and; MIS 1, deglaciation phase). The paleotopography (height) of the FIS through a glacial cycle will be simulated using a state-of-the-art thermomechanical numerical ice sheet model, with key boundary conditions constrained both by cosmogenic nuclide-based reconstructions of subglacial conditions, and by an isostatic model. The team for this work has been expanded to include Alun Hubbard, University of Edinburgh, Kurt Lambeck, Australian National University, and Jens-Ove Naslund, Stockholm University, in the areas of glaciological and isostatic modeling. New reconstructions will likely have wide significance, both to European ice sheet and paleoclimate reconstructions and evaluations of evidence of sea level low-stands (proxy for total land-based ice on earth) and also in encouraging re-evaluation of the dynamics of inception, growth, and decay of other major ice sheets worldwide.