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

9405117 Jenson不稳定的冰盖行为现在被认为是最后一次冰期劳伦泰德冰盖（LIS）的一个重要特征，它在迫使环北大西洋地区甚至全球气候突变方面发挥了关键作用。在这项合作工作中，我们建议评估机制不稳定的冰盖行为的基础上晚更新世沉积记录的得梅因和密歇根湖的裂片沿着南部边缘的LIS。这种行为是更好地记录了这些叶比任何其他部门的冰盖，从而提供了最好的机会来探索这种行为的机制，它与气候突变的关系。这项研究的结果将有显着的应用到其他地区的LIS发生不稳定的行为，但较少受到地质记录（例如，哈德逊海峡）。到目前为止，冰盖不稳定性的模型都把不稳定性的来源看作是由内部冰盖动力学引起的，涉及到饱和的、变形的冰下沉积物。得梅因和密歇根湖的裂片穿过细粒沉积物前进，当水饱和时，这些沉积物会在冰施加的剪切应力下变形。然而，更多的研究表明，外部（气候）强迫机制导致了冰盖的不稳定行为.我们将继续我们的合作工作，整合现场，实验和建模研究，以调查潜在的强迫机制。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的冰下过程的最多信息，以及与建模研究的比较。我们的实验工作将涉及使用细粒度diamictons沉积的叶片的岩土工程分析，以确定不同的直到片的流变参数的范围内所需的组成泥沙流动法，我们在建模研究中使用。我们将使用一个一维耦合的冰-沉积物数值模式，该模式整合了实验工作的结果，以研究由于内部冰盖动力学或外部气候强迫而导致的冰盖不稳定行为的机制。最后，我们将着重于冰下水文、冰下沉积过程和沉积物输运通量的实地和模拟研究结果的相互比较。

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.