A New View of Pliocene Glaciations

Brown University, Providence RI

Investigators

Abstract

The Earth's climate system has gone through major changes over time that serve as natural experiments to test our understanding of linkages and feedbacks that may come into play if the Earth continues to warm. This project investigates patterns of climate change between the northern and southern hemispheres during the mid-Pliocene epoch (~3 to 4 million years ago) when the overall climate state was warmer than today. Critically, evidence suggests that the amount of ice on Antarctica was similar to today, but that there was little or no permanent ice on land in the northern hemisphere. Most climate scientists have therefore supposed that climate change would focus on the region around the Antarctic. Recent results by this research team suggest that instead, change initiated in the northern hemisphere propagated all the way southward, and actually determined the timing and amount of temperature change globally. This project will use marine sediment cores widely distributed in the ocean to generate reconstructions of mid-Pliocene climate. A major emphasis is to link data and concepts of orbital-scale variability into international efforts to synthesize Pliocene data and modeling through the international PRISM (Pliocene Research, Interpretation and Synoptic Mapping ) program. Funding also supports research and mentoring of a postdoctoral researcher from a demographic underrepresented in geosciences. The chief intellectual merit of this research is to assemble for the first time an array of data sampled at adequate resolution and geographic range to test a new model of northern hemispheric pacing for dynamics of the period, and to cover the transition from this regime to the later "41 kyr world" of cyclic large-scale glaciation of the northern hemisphere. The research team will constrain the phasing of isotopic and temperature changes recorded in marine sediment cores by synchronizing paleoclimate proxy records to African and Asian monsoonal climate signals with a unique northern hemisphere precessional dependence, following the approach used successfully by Hilgen and colleagues to improve the Neogene time scale. The results are expected lead to advances in the geochronology of late Pliocene time period, a fundamental aspect of paleoclimatic and paleobiological studies of the period. Proxy data that constrain past ocean surface temperatures and global ice volume will be analyzed at roughly 3,000-year resolution in laboratories at Brown University. The hypotheses to be tested in this proposal, especially a revised correlation of orbital forcing to Pliocene climatic features, are central to the PlioMIP (Pliocene Model Intercomparison Project) community, now focused on a time slice at 3.205 Ma and transient simulations between 3.3 and 2.8 Ma.