PLIO-PLEISTOCENE CLIMATE CHANGE: INSIGHTS FROM A NEW SEA SURFACE TEMPERATURE RECORD FROM THE SOUTHERN PACIFIC OCEAN

Studying past climates is the key to better understanding the climate system of the present and future; one way to determine dominant trends and cycles in Earth’s recent climate history is by analyzing sea surface temperature (SST) records generated from ocean sediment cores. This research investigates SSTs of the Plio-Pleistocene, a time in Earth’s history when we see a shift from the warm, stable climate of the Pliocene (5.3 to 2.7 million years ago; Ma) to the colder, more variable climate of the Pleistocene (2.7 to 0.01 Ma). While there are many published SST records spanning this interval from the northern hemisphere and equatorial regions, there is a significant gap in our knowledge of southern hemisphere climate behavior over the last 5 million years. We present the first southwest Pacific Plio-Pliocene SST record of its kind, generated using the alkenone paleothermometer at high (~2 kyr) temporal resolution, in order to enhance our understanding of southern hemisphere climatic responses. We analyze our record to determine the southern hemisphere response to orbitally-driven Milankovitch cycles, which drive the climate system through changes in orbital eccentricity, precession, and obliquity. Specifically, we investigate the theory that a globally synchronous climate response to obliquity forcing emerged in conjunction with the intensification of northern hemisphere glaciation at ~2.7 Ma (Herbert et al., 2010), and the hypothesis that the mid-Pleistocene transition from 41-kyr to 100-kyr glacial cycles was caused by a change in the southern hemisphere response to precessional forcing (Raymo et al., 2006). We also document the timing of the emergence of a strong 100 kyr SST response in the southern Pacific and compare this response with other climate records in order to gain insights into the origin of the 100-kyr climate system cycle itself. Our analysis extends our knowledge about how the southern hemisphere responded to orbital forcing during the Plio-Pleistocene and how southern hemisphere climate change is connected to changes in the global climate system.