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

0138486港口成功使用冰盖模型进行气候研究的主要限制来自于用于模型校准的现场数据有限。这可能导致对冰盖开始、生长和衰退的不切实际的模拟，以及重建冰盖基本边界条件和表面轮廓的不确定性。例如，一些地方的切线和风化差异被解释为以前冰盖高度的指标，而对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，这种特征代表了湿(暖)侵蚀冰和干(冷)非侵蚀冰之间的内部热边界。这种根本性的解释差异对重建的冰盖厚度、动力学和范围以及由冰盖重建得出的古气候解释产生了深远的影响。在斯堪的纳维亚半岛，在多次冰盖盖过事件的已知界限内发现了未被侵蚀的区域，这一事实表明，这些未被侵蚀的区域在整个冰盖的形成、生长和衰退过程中肯定是以非侵蚀(假设为冰床)的形式存活下来的。这一观察结果对冰盖模型的基本热条件提出了新的重大限制，并表明了实地地貌和冰川地质学可为加强冰盖建模工作提供的约束类型。在过去的三年里，斯德哥尔摩大学的首席研究员Arjen Stroven和澳大利亚国立大学的Derek Fabel在国家科学基金会(NSF)和瑞典NSF的支持下合作，研究了瑞典北部山区的冰川消融年表和侵蚀模式以及景观保护，瑞典北部山区是芬诺斯坎迪亚冰盖的核心区域。这些结果为提出这项工作的下一阶段提供了基础，他们将在最后一次冰川周期的关键时期(海洋同位素阶段5d或5b，初始阶段；MIS2，最后一次冰川最大(LGM)阶段，和MIS1，去冰期)重建FIS的厚度、范围和动力学(包括总冰量引起的海平面变化)。将使用最先进的热机械数值冰盖模型来模拟冰川周期中FIS的古地形(高度)，关键边界条件既受基于宇宙成因核素的冰下条件重建的约束，也受均衡模型的约束。这项工作的团队已经扩大到包括爱丁堡大学的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，在冰川学和均衡模拟领域。新的重建可能对欧洲冰盖和古气候的重建和海平面低水位证据的评估(地球上总的陆基冰)具有广泛的意义，也在鼓励重新评估世界其他主要冰盖的形成、增长和衰退的动力学方面。

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.