Characterizing the Plio-Pleistocene evolution of sea surface conditions using the alkenone organic proxy

Concern about future changes in Earth's climate has generated intense interest in the past behavior of the climate system. Over the past 5 million years the Earth's climate has transitioned from the warm early Pliocene interval, to the colder, more variable late Pliocene and Pleistocene periods, which were marked by the growth of large ice-sheets in the Northern Hemisphere. This dissertation applies a novel approach to understanding this important climatic transition by using the alkenone organic proxy to characterize past climatic variations in sea surface temperature and productivity. This work reviews the discovery, development, calibration, and potential caveats to the application of the alkenone organic proxy, explicitly examining the use of this method to study climatological problems over long (>1 Myr) timescales and concluding that there is enormous potential to apply this valuable tool to the study of long-term paleoclimate. Additionally, this dissertation documents the application of the alkenone organic proxy to the characterization of long-term climatic change at sites in the Coral Sea, eastern equatorial Pacific (EEP) and North Atlantic. Results from the western Coral Sea indicate that the late Quaternary rise of the Australian Great Barrier Reef was not caused by a warming of regional sea surface temperatures as previously proposed and highlights the ability of the alkenone organic proxy to provide valuable climate information in regions where carbonate diagenesis has rendered other commonly used carbonate-based techniques unreliable. Work from the EEP and North Atlantic provide the first continuous, high-resolution records of variations in sea surface conditions through the Plio-Pleistocene climatic transition. These records indicate marked spatial heterogeneity in the evolution of sea surface temperature and productivity during this time interval. These datasets probe the validity of several existing theories for the Plio-Pleistocene transition and lay the foundation for an array of sites that will provide a spatial fingerprint of Pliocene to modern sea surface conditions.