Collaborative Research: The NE Sector of the Laurentide Ice Sheet: Dating Outlet and Local Glacier Moraines at Clyde with Cosmogenic Isotopes

这是一项与佛蒙特大学、科罗拉多大学和宾利学院的合作提案。我们对劳伦泰德冰盖的看法已经从一个具有相对稳定的中心核心的厚单块圆顶转变为一个更薄、多圆顶和更动态的冰系统，具有固有的不稳定性。冰盖在气候系统中的作用包括随着其高度的增加对大气流动的扰动，以及由于反照率的变化而改变行星能量平衡。此外，通过大量的冰山和融水的排放，冰盖是北大西洋热盐环流的决定因素。关于大陆冰川作用的时间和类型的初步资料在这一概念演变中起了关键作用。沿着劳伦泰德冰原的东北边缘，一系列广泛的冰碛提供了过去冰原行为的直接记录。由于无法直接确定这些沉积物的年代，早期的研究受到了限制。因此，人们提出的论点是，沿冰盖所有边缘的冰川推进的时间和幅度相似，并且在原冰盖的不同部分之间基本上是不同步的响应。随着宇宙成因暴露年代测定法的发展，现在可以直接测定冰碛的年代，并解决了许多争论。首席调查员最近的研究已经通过确定巴芬岛南部冰川特征的年代确定了该方法的实用性，并证明该地区在最后一次冰川极大期完全被冰川覆盖。然而，他们也有证据表明，东北海岸的冰川覆盖程度较低，保存了更长的冰川历史。首席调查员将在克莱德地区进行为期一年的研究，克莱德地区是东北劳伦泰德冰盖的典型地点。基于米勒和戴维斯在巴芬岛广泛的实地经验，以及比尔曼和斯泰格的宇宙成因专业知识，他们将绘制冰川沉积物、冰流特征和冰川地貌的系统变化，并收集样本进行宇宙成因和放射性碳定年。他们的结果将确定该地区宇宙成因暴露测年的适用性，最佳样品类型，并解决第一级问题：广泛的冰碛是保存在末次冰期最大年龄的前陆上，还是代表更古老的冰期？宇宙成因和放射性碳数据与实地冰川沉积物的直接测绘和航空照片相联系，将使他们能够更好地确定冰川作用的类型和时间，以及冰川循环开始阶段的性质。

AbstractMillerOPP- 0004466This is a collaborative proposal with the Universities of Vermont and Colorado and Bentley College. Our view of the Laurentide Ice Sheet has changed from a thick monolithic dome with a relatively stable central core to a thinner, multi-domed and more dynamic ice system with inherent instabilities. The role of the ice sheet in the climate system includes perturbations to atmospheric flow as its height increased, and altering the planetary energy balance due to albedo changes. In addition, through massive ice-berg and meltwater discharges, the ice sheet was a determinant on North Atlantic thermo-haline circulation.Primary information on the timing and style of continental glaciation has played a key role in this conceptual evolution. Along the northeastern margin of the Laurentide Ice Sheet, extensive series of moraines provide a direct record of past ice-sheet behavior. Early studies were limited by an inability to date these deposits directly. Consequently, arguments were advanced for both a similar timing and magnitude of glacial advances along all margins of the ice sheet, and for fundamentally asynchronous responses between different sectors of the former ice sheet. With the development of cosmogenic exposure dating, it is now possible to date the moraines directly and resolve much of this debate. Recent studies by the Principal Investigators have established the utility of the method by dating glacial features on southern Baffin Island and demonstrated that this region was completely glaciated at the last glacial maximum. However, they also have evidence that the northeastern coast was less intensively glaciated and preserves a much longer glacial history.The Principal Investigators will conduct a one-year study in the Clyde region which is the type site for the NE Laurentide Ice Sheet. Building on the extensive Baffin Island field experience of Miller and Davis, and the cosmogenic expertise of Bierman and Steig, they will map glacial deposits, ice-flow characteristics, and systematic changes in the glacial geomorphology, and collect samples for cosmogenic and radiocarbon dating. Their results will establish the suitability of cosmogenic exposure dating in this region, the optimum sample type, and address the first-order question: are the extensive moraines preserved on the forelands of last glacial maximum age or do they represent much older glaciations? The cosmogenic and radiocarbon data, linked to direct mapping of glacial deposits in the field and on aerial photographs, will allow them to better define the style and timing of glaciation, and the nature of the inception phase of a glacial cycle.