SPECTRAL EVOLUTION OF SEA SURFACE TEMPERATURE CHANGE IN THE SOUTHWEST PACIFIC FROM 3 MILLION YEARS AGO TO THE PRESENT

Though it is fundamentally understood that orbital cycles exert a strong influence on the climate system, major unknowns remain about how different parts of the system respond to orbital forcing and why the overall response of the climate system to orbital forcing has evolved from the 41 kyr world of the early Pleistocene (0.8 to 2.7 million years ago, Ma) to the 100 kyr world of the late Pleistocene (0-0.8 Ma). Many of the climate records that we use to better understand these questions are from sites in the tropics and the northern hemisphere (NH), whereas few records exist from the southern hemisphere (SH), particularly from the extra-tropical Pacific Ocean. Here we present an alkenone-based sea surface temperature (SST) record and accompanying oxygen isotope stratigraphy from ODP Site 1125 in the southwest Pacific from 3.0 Ma to the present, which we use in order to both document SH temperature patterns and to compare the SH response to orbital forcing to that of the tropics and NH. We assess the phasing of the SH SST response in the 23 kyr band in order to address the Raymo et al. (2006) hypothesis that during the 41 kyr world, precessional climate responses in the NH and SH were out of phase with one another. Secondly, we assess whether SH changes in the 41 kyr band are synchronous with those found in the tropics in order to test the hypothesis that greenhouse gas feedbacks strengthened in conjunction with the intensification of NH glaciation and helped amplify and synchronize the climate system response to obliquity forcing (Herbert et al., 2010). Thirdly we look at Site 1125 SST variability in the 100 kyr band to determine whether strong 100 kyr variability emerged in the SH prior to the transition to the 100 kyr world. Our orbital analysis of Site 1125 SST change provides valuable insight into the response of the SH to orbital forcing throughout the Pleistocene.