Collaborative Research: Unstable Behavior of the Southern Margin of the Laurentide Ice Sheet & Implications for Ice Sheet Dynamics & Climate Change

9405117詹森不稳定冰盖行为现在被认为是劳伦蒂冰盖(LIS)在最后一次冰川期间的一个重要特征，它在迫使环北大西洋地区乃至全球气候突变方面发挥了关键作用。在这项合作工作中，我们建议根据LIS南缘得梅因和密歇根湖冰盖晚更新世的沉积记录来评估不稳定冰盖行为的机制。与冰盖的任何其他部分相比，这些冰叶的准确记录更好地记录了这种行为，从而为探索这种行为的机制及其与气候突变的关系提供了最好的机会。这项研究的结果将对LIS发生不稳定行为但受地质记录约束较少的其他地区(例如哈德逊海峡)具有重要的应用价值。到目前为止，冰盖不稳定的模型认为不稳定的来源是由内部冰盖动力学引起的，涉及饱和的、变形的冰下沉积物。得梅因和密歇根湖带穿过细粒沉积物，当水饱和时，这些沉积物会在冰施加的剪应力下变形。然而，更多的研究表明，外部(气候)强迫机制导致了不稳定的冰盖行为。我们将继续合作，整合实地研究、实验研究和模型研究，以研究潜在的强迫机制。我们的实地研究将集中在沉积物记录的那些方面，这些方面提供了关于冰盖行为机制方面的冰下过程的最多信息，并与模型研究进行了比较。我们的实验工作将涉及使用岩土技术分析由波瓣沉积的细粒直径，以确定我们在模拟研究中使用的本构泥沙流动规律中所需的不同冰片的流变参数的范围。我们将使用一个整合了实验结果的一维冰沙耦合数值模式来研究由于内部冰盖动力学或外部气候强迫而导致的不稳定冰盖行为的机制。最后，我们将着重于冰下水文、冰下沉积过程和沉积物输送通量的现场研究和模拟研究的结果的相互比较。

9405117 Jenson Unstable ice-sheet behavior is now recognized as an important characteristic of the Laurentide Ice Sheet (LIS) during the last glaciation, and it played a crucial role in forcing abrupt climate change in the circum-North Atlantic region and perhaps globally. In this collaborative work, we propose to evaluate mechanisms of unstable ice-sheet behavior based on the late-Pleistocene sedimentary record of the Des Moines and Lake Michigan lobes along the southern margin of the LIS. This behavior is far better documented by well-dated records of these lobes than for any other sector of the ice sheet, thus providing the best opportunity to explore mechanisms of such behavior and it relationship to abrupt climate change. Results from this research will have significant application to other areas where unstable behavior of the LIS occurred, but which are less well-constrained by the geologic record (for example, Hudson Strait). Models of ice-sheet instability thus far have treated the sources of the instability as arising from internal ice-sheet dynamics involving saturated, deforming subglacial sediment. The Des Moines and Lake Michigan lobes advanced across fine-grained sediments that, when water saturated, would have deformed under the shear stress applied by the ice. Additional studies, however, suggest external (climate) forcing mechanisms for unstable ice- sheet behavior. We will continue our collaborative work of integrating field, experimental, and modeling studies to investigate potential forcing mechanisms. Our field studies will center on those aspects of the sediment record that offer the most information on subglacial processes with respect to mechanisms of ice-sheet behavior as well as for comparison to modeling studies. Our experimental work will involve using geotechnical analyses of fine-grained diamictons deposited by the lobes to define the range in rheological parameters of different till sheets that are needed in the co nstitutive sediment flow law we use in modeling studies. We will use a one-dimensional coupled ice-sediment numerical model that integrates results of experimental work to investigate mechanisms of unstable ice-sheet behavior due to internal ice-sheet dynamics or external climate forcing. Finally, we will focus on intercomparison of results from field and modeling studies of subglacial hydrology, subglacial sediment processes, and sediment transport fluxes.