Cenozoic High Latitude Paleoceanography: New Perspectives from the Arctic and Subantarctic.

Abstract

The polar oceans are closely linked to climate through their role in the formation and ventilation of the world’s deep water masses, but the feedbacks between climate and deep convection during the Cenozoic remain poorly understood. In this thesis, stable carbon and oxygen isotopes are used to investigate circulation changes in the polar oceans during two intervals of significant climatic interest. First, this thesis examines the paleoceanography of the abyssal subantarctic Pacific during the cooling and ice sheet expansion of the late Neogene, and second, a novel stable isotope technique is used to reconstruct the hydrography of the Arctic Ocean during the exceptionally warm, ice-free conditions of the early Eocene.

This thesis presents a new stable isotope record from the subantarctic Pacific (50˚20’S, 148˚08’W, 4286m). This record was found to contain three major hiatuses spanning the early Pliocene-early Late Pliocene, ~1.57-0.68 Ma, and ~0.53-0.19 Ma. The timing of these hiatuses suggests enhanced vigor of the Antarctic Circumpolar Current (ACC) during three periods: the middle Pliocene and the Mid-Pleistocene and Mid-Brunhes climatic transitions. Correlation with other globally-distributed deep-sea records supports the hypothesis that these periods were associated with intensified global deep water circulation. In contrast, benthic δ18O and δ13C suggest the development of a large pool of cold, CO2-rich deep water in the abyssal Southern Ocean during the late Pliocene expansion of the Northern Hemisphere ice sheets.

Stable isotopic data was obtained from the structural carbonate component of fish apatite found in the carbonate-poor Eocene Arctic sediments recovered during IODP Expedition 302. Although stable isotope analysis of deep-sea apatite carbonate has rarely been undertaken, an assessment of the isotopic integrity of bioapatite shows its potential to record large-scale paleoceanographic trends in carbonate-poor samples. The δ18O values obtained from Eocene Arctic fish debris averaged -4.89‰ compared to 2.77‰ for a Miocene sample from the same site. Thus the Arctic Ocean had an average salinity of 21-25‰ during the Eocene, with the lowest salinities occurring during the Paleocene Eocene Thermal Maximum and two freshwater events at ~48.7 Ma (the Azolla event) and ~47.6 Ma