Abstract:
Between the Pliocene and Pleistocene epochs, Earth's climate transitioned from the warm and mostly stable conditions of the early Pliocene, a time period often used as an analog for future warm climate scenarios, to the much colder and more variable conditions of the Pleistocene. Here, we present new records of sea surface temperature (SST), ocean productivity, and global ice volume for the late Pliocene and Pleistocene, which are based on stable isotope and alkenone analyses performed on marine sediments at Ocean Drilling Program (ODP) Site 1125 in the southwest Pacific (42 degrees S, 178 degrees W). Our data indicate that SSTs cooled approximately 3 degrees C between the late Pliocene and late Pleistocene, a magnitude of cooling comparable to that observed at mid-latitude sites in both the South (Site 1090; 43 degrees S) and North Atlantic (Site 607; 41 degrees N). These observations suggest a hemispherically symmetric contraction of the low latitude warm pool at the end of the early Pliocene warm period. On orbital time scales, oxygen isotope records (a proxy for global ice volume) in both hemispheres are dominated by obliquity beats that are in phase between the hemispheres. However, orbitally-paced variations in sea surface conditions are asymmetric between the Northern and Southern Hemispheres. SST variations at Site 1125 (southwest Pacific) during the Pliocene are characterized by precessional beats, matching the dominant period of variability at Site 1090 in the South Atlantic during this time interval. Precession also plays an important role in ocean productivity variations at Site 1125. In contrast, SST and productivity records from the North Atlantic and from the tropics show strong obliquity power, but weak to negligible precessional power over this time interval. The presence of precessional power in Southern Hemisphere SST and productivity records suggests a strong influence of local insolation changes on sea surface conditions in the Southern Hemisphere.