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。在连续的深海沉积档案中，代用物记录了在新生代的大部分时间里缓慢的冷却，直到一个阈值被跨越，导致大约2.8 Ma以前北半球大陆冰川的开始。冰期旋回遵循~41 ka的倾斜轨道频率，直至更新世中期，过渡到~100 ka的高振幅周期。这种从~41ka到~ 100ka的气候变率的神秘变化，被称为中更新世转变（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约束，这些约束表明，尽管冰量较小，但最早的劳伦泰德冰盖（LIS）冰推进的空中范围与MPT之后一样大或更大。一个很有希望的假设是，易变形的前冰期风化层被LIS侵蚀逐渐移除。在MPT之前，可变形沉积物降低了基底剪切应力，使LIS流动更快，产生了更薄的冰盖，对轨道强迫作出线性反应。随着风化层的移除，基底剪应力和冰层厚度增加，导致对轨道强迫的非线性响应。该项目利用了两个特殊的沉积档案，保存了过去2.5 Ma在加拿大东部北极沿海低地沉积的叠加冰川和海洋沉积物，以测试MPT的变形床假说。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，可以从沉积物中提取关键的代用物。这些工具可以对沉积物进行可靠的测年，评估上新世晚期以来从冰盖内部输送沉积物的流线的变化，评估海洋表面温度的变化，并对冰盖随时间推移所携带的风化产物进行量化，从而可以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.