Extending the Chatham Rise (ODP Site 1123) Deep Ocean Temperature Record into the Plio-Pleistocene: Inception of Northern Hemisphere Glaciation

The Plio-Pleistocene was a time of global climate cooling: a transition from a state of significant and prolonged climate warmth (Mid Pliocene) to a state of bi-polar glacials (Pleistocene), marked by the onset and intensification of continental ice sheets in the Northern hemisphere (Late Pliocene) and the reorganization of glacial cycle amplitude and frequencies (Mid Pleistocene Transition). This is an interesting and important chapter of climate history for understanding the sensitivity of large ice sheets to perturbations in the climate system on glacial-interglacial and much longer timescales. Of possible priming mechanisms (incl. closure of Panama seaway, orographic uplift), the decline of atmospheric carbon dioxide is considered to have a strong connection with the late Pliocene cooling and ice sheet inception, although the causal mechanism for its decline remains relatively unknown. High-resolution, long term climate records are necessary to further constrain the timings of ice volume evolution and the associated driving factors during the Plio-Pleistocene, however such records are presently limited.

ODP Site 1123 (Chatham Rise, southwest Pacific, 3290m) records the evolution of the deep western boundary current of the southwest Pacific, a primary feeder of Antarctic Bottom Water to the global deep ocean. By calculating the oxygen stable isotope composition of past seawater, a proxy calculation combining Mg/Ca-palaeothermometry and δ¹⁸O from benthic foraminifera, we present a high-resolution record of global ice volume as a measure of climate change, extending the existing 0-1.5 Ma record (Elderfield et al., 2012) at ODP 1123 to the Plio-Pleistocene (1.5-3.0 Ma). We use this measure of global ice volume evolution to assess the relative timing and magnitude of northern hemisphere glaciation and concomitant deep ocean temperature decline, which aids to infer temperatures around Antarctica during this time. Deep ocean temperature results show high frequency glacial-cycles, approaching near-freezing temperatures at peak glacials.

Reference

Elderfield, H., Ferretti, P., Greaves, M., Crowhurst, S., McCave, I.N., Hodell, D., Piotrowski, A.M. (2012), Science, 337, 704-709.