Reconstruction of the Green Bay, Lake Michigan and DesMoines Lobes, 21-11,000 B.P.: Ice Surfaces Profiles, Landform- Sediment Associations & Deglaciation Chronolog

米克尔森9627798只有几项研究考察了大型冰川裂片的动力学，尽管它们控制了劳伦蒂冰盖的质量平衡。通过分析冰面剖面、地貌-沉积物组合和进退年代学，研究了21-11000BP冰川消融期间不同时期洛伦蒂德南部三个冰川瓣的相互关系。这三条独立的证据线：冰川重建、地形沉积物组合和年代学的结合，应该会增加对这些冰盖的动态历史以及它们是否对劳伦蒂冰盖的崩塌有重大贡献的理解。地貌证据表明，这些波瓣有时经历了涌浪或流动状态。也有证据表明，冰川边缘停滞和快速退缩。特定地点或时间的水流状态取决于当前的河床条件和影响质量平衡的气候因素。该项目将记录流态的这些变化，并根据现场证据对河床条件进行估计。最终的结果将是一个改进的概念模型，即大型冰川小叶如何对最后一次冰川消融期间不断变化的条件做出反应。这将导致对气候、冰盖和沉积记录之间关系的更有信心的解释。到目前为止，已经重建了洛伦蒂德南部冰盖在几个早期冰川消融阶段的两个冰叶。重建的冰川剖面表明，在冰川消融过程中，基面切应力在25kpa到5kpa之间变化，常见的是涌浪型流动和稳定的片状流动。关于南洛伦蒂冰冠的一个主要悬而未决的问题是，退缩是以-40到100米/年的速率递进发生，还是以-500到1000米/年的灾难速度发生。这个问题的答案对于理解洛伦蒂冰缘南部的行为以及解释这些冰冠的冰川消融年代学是至关重要的。格陵兰冰芯是否出现了与快速变暖和气候变化相对应的快速崩塌？冰川沉积表明可能存在某种关系，但地表暴露日期(10Be、25Al和36Cl)必须从年代不佳的陆地记录中获得，才能提供对现有年代学的独立测试。将调查地貌-沉积物组合，以确定它们与古冰川条件重建的关系。将描述沉积物组构、沉积结构和底部接触，以确定13,000 BP之前和之后的冰川床输送类型是否存在重大差异。将对低剖面涌浪型波瓣与细粒湖泊沉积物和湖盆的关联进行调查和记录。如果可以记录冰面坡度的明显差异，对相关沉积物的仔细检查应该区分湿变形床和冰床交界处的水集中。因此，三个不同的数据集被用来记录沿劳伦蒂冰盖南缘消退期间的冰川条件：冰面轮廓、地形-沉积物关联和年代学。

Mickelson 9627798 Only a few studies have examined the dynamics of large glacier lobes, even though they controlled the mass balance of the Laurentide ice sheet. By analyzing ice-surface profiles, landform-sediment associations, and advance-retreat chronologies, this research process relationships of three southern Laurentide glacier lobes, at various time during deglaciation 21-11,000 BP. This integration of three separate lines of evidence: glacier reconstructions, landform sediment associations, and chronology should increase understanding of the dynamic history of these lobes and whether or not they contributed significantly to the collapse of the Laurentide ice sheet. Geomorphic evidence suggests that these lobes at times experienced surge type or streaming flow regimes. There is also evidence suggesting ice marginal stagnation and rapid retreat. Flow regime at a specific site or time depended on bed conditions present and climatic factors influencing mass balance. This project will document these changes in flow regime and derive from field evidence estimates of bed conditions. The final result will be an improved conceptual model of how large glacier lobes responded to changing conditions during the last deglaciation. This will lead to more confident interpretations of the relationships between climate, ice sheets, and the sedimentary record. Reconstructions of two lobes of the southern Laurentide ice sheet during several early phases of deglaciation have been produced so far. Reconstructed glacier profiles indicate that basal shear stresses varied from 25 kPa to 5 kPa during deglaciation and that surge-type flow and steady sheet-type flow were common. A major unanswered question about southern Laurentide lobes is whether retreat occurred progressively at rates of -40 to 100 m/y or catastrophically with rates of -500 to 1000 m/y. The answer to this question is fundamental to understanding the behavior of the southern Laurentide ice margin as well as in interpreting the deglaciation chronologies of these lobes. Was there a rapid collapse corresponding to a rapid warming and climate change seen in Greenland ice cores? Glacial deposits suggest there could be a relationship, but surface exposure dates (10be, 25Al, and 36Cl) must be obtained from the poorly dated terrestrial record to provide an independent test of existing chronologies. Landform-sediment associations will be investigated to determine their relationship to reconstructions of paleoglacier conditions. Sediment fabric, sedimentary structures, and basal contacts will be described to determine whether there are major differences in the type of glacier bed transport between pre- and post- 13,000 BP advances. The association of low profile surge-type lobes with fine-grained lake sediments and lake basins will be investigated and documented. Where a clear difference in ice surface slope can be documented, careful examination of the associated sediment should distinguish a wet deforming bed from concentration of water at the ice-bed interface. Thus, three different data sets are used to document glacier conditions during retreat along the southern margin of the Laurentide ice sheet: ice surface profiles, landform-sediment associations, and chronology.