TESTING THE REGOLITH HYPOTHESIS: INVESTIGATING SUBSTRATE CHANGE THROUGH THE MID-PLEISTOCENE TRANSITION USING OSMIUM ISOTOPES

The Mid-Pleistocene Transition (MPT) occurred between 1250 and 650 ka and is expressed in the marine oxygen isotope record as a shift from 41-ky to 100-ky cyclicity in glacial-interglacial periodicity. The MPT occurred in the absence of changes to orbital forcing parameters, leaving the trigger of the MPT largely unexplained. Proposed drivers of this transition include intensification of CO₂ storage in the oceans, regolith removal from the North American continent resulting in slower, hard-based ice flowing over bedrock, increases in global ice volume by the buildup of the Laurentide Ice Sheet or a varying combination of internal and external shifts. While robust climate proxies shed light on the nature of the ocean-atmosphere system, few empirical records are able to directly record changes in ice sheet substrate. Here, we aim to elucidate the origin of changes in internal ice sheet dynamics through the osmium (Os) isotope system. This radiogenic isotope system is a powerful tool and well-suited to deconvolving fluctuations in continental weathering as Os has a short residence time in the oceans (~50 kyr) and is highly sensitive to variations in source (e.g., Precambrian crystalline bedrock vs. Mesozoic or Tertiary regolith). In order to assess changes in continental weathering provenance during glacial-interglacial cycles through the MPT we analyzed Os isotopes from deep sea sediment core retrieved from the North Atlantic. This data allows us to evaluate the degree to which sub-ice sheet physical processes influenced the MPT.