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

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Miller 0903024 University of Colorado Proxies 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.