Testing the deformable-bed hypothesis for the Mid-Pleistocene Transition with Plio-Pleistocene tills exposed in the Eastern Canadian Arctic.

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。米勒0903024科罗拉多大学在连续的深海沉积档案中记录了新生代大部分时间的缓慢冷却，直到越过一个阈值，导致北方大陆冰川的开始。2.8妈妈以前。冰川周期性遵循倾斜（倾斜）轨道频率，~41 ka，直到中更新世，当它过渡到一个更高的振幅，~100 ka期间。这种从~ 41 ka到~100 ka的神秘变化，被称为中更新世过渡（MPT），特别令人感兴趣，因为它反映了气候系统的基本重组，独立于轨道/辐射强迫。解释MPT的假设必须满足地质条件的限制，表明最早期劳伦泰德冰盖（LIS）冰前进的空中范围与MPT后一样大或更大，尽管冰量较小。一个有希望的假设是逐渐删除的变形，冰前风化层LIS侵蚀。在MPT之前，可变形的沉积物减少了基底剪切应力，使LIS流动得更快，产生了一个更薄的冰盖，线性响应轨道强迫。由于风化层被删除，基底剪切应力和冰的厚度增加，从而在一个非线性的响应轨道forcing.This项目利用两个特殊的沉积档案，保存叠加的冰川和海洋沉积物沉积在过去的2.5马加拿大东部北极地区的沿海低地，以测试变形床的MPT假设。仪器和技术的最新进展提供了一系列新的测年和地球化学工具，使人们能够从沉积物中提取关键的替代物。这些工具允许可靠的冰碛物的年代测定，评估自上新世晚期以来从冰盖内部输送冰碛物的流线变化，评估海面温度的变化，以及量化冰盖随时间推移所携带的风化产物，这将允许对变形床假说进行严格的测试。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Miller 0903024University of ColoradoProxies in continuous deep-sea sedimentary archives document slow cooling through much of the Cenozoic until a threshold was crossed leading to the onset of Northern Hemisphere continental glaciation ca. 2.8 Ma ago. Glacial cyclicity followed the obliquity (tilt) orbital frequency, ~41 ka, until the mid-Pleistocene, when it transitioned to a higher-amplitude, ~100-ka period. This enigmatic change from ~41ka to ~100-ka climate variability, known as the mid-Pleistocene transition (MPT), is of particular interest because it reflects a fundamental reorganization of the climate system, independent of orbital/radiative forcing. Hypotheses to explain the MPT must meet geological constraints showing that the aerial extent of the earliest Laurentide Ice Sheet (LIS) ice advances were as large or larger than after the MPT, despite smaller ice volumes. A promising hypothesis is the gradual removal of deformable, pre-glacial regolith by LIS erosion. Prior to the MPT, deformable sediment reduced basal shear stresses, allowing the LIS to flow more rapidly, producing a thinner ice sheet that responded linearly to orbital forcing. As regolith was removed, basal shear stresses and ice thickness increased, resulting in a non-linear response to orbital forcing.This project exploits two exceptional sedimentary archives that preserve superposed glacial and marine sediment deposited over the past 2.5 Ma on coastal lowlands of the Eastern Canadian Arctic to test the deformable-bed hypothesis for the MPT. Recent advances in instrumentation and techniques provide a battery of new dating and geochemical tools that allow key proxies to be extracted from the sediment. These tools allow reliable dating of the tills, assessment of changes in flow lines delivering till from the interior of the ice sheet since the late Pliocene, assessment of changes in sea surface temperatures, and quantification of weathering products carried by the ice sheet over time that will allow rigorous testing of the deformable-bed hypothesis.