Pliocene-Pleistocene evolution of sea surface and intermediate water temperatures from the southwest Pacific
Wiley & American Geophysical Union (AGU)
©2016. The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Over the last 5 million years, the global climate system has evolved toward a colder mean state, marked by large-amplitude oscillations in continental ice volume. Equatorward expansion of polar waters and strengthening temperature gradients have been detected. However, the response of the mid latitudes and high latitudes of the Southern Hemisphere is not well documented, despite the potential importance for climate feedbacks including sea ice distribution and low-high latitude heat transport. Here we reconstruct the Pliocene-Pleistocene history of both sea surface and Antarctic Intermediate Water (AAIW) temperatures on orbital time scales from Deep Sea Drilling Project Site 593 in the Tasman Sea, southwest Pacific. We confirm overall Pliocene-Pleistocene cooling trends in both the surface ocean and AAIW, although the patterns are complex. The Pliocene is warmer than modern, but our data suggest an equatorward displacement of the subtropical front relative to present and a poleward displacement of the subantarctic front of the Antarctic Circumpolar Current (ACC). Two main intervals of cooling, from ~3 Ma and ~1.5 Ma, are coeval with cooling and ice sheet expansion noted elsewhere and suggest that equatorward expansion of polar water masses also characterized the southwest Pacific through the Pliocene-Pleistocene. However, the observed trends in sea surface temperature and AAIW temperature are not identical despite an underlying link to the ACC, and intervals of unusual surface ocean warmth (~2 Ma) and large-amplitude variability in AAIW temperatures (from ~1 Ma) highlight complex interactions between equatorward displacements of fronts associated with the ACC and/or varying poleward heat transport from the subtropics.
The new data presented here are stored at the NOAA-National Climatic Data Center (NCDC) paleoclimate repository (available at https://www.ncdc.noaa.gov/ paleo/study/20225). This work was supported by the UK Natural Environment Research Council (awards NE/I027703/1 and IP-1339-1112 to E.L.M. and NE/I024372/1 to S.K.) and a Philip Leverhulme Prize (awarded to E.L.M.). This work was also funded (in part) by The European Research Council (grant 2010-NEWLOG ADG-267931 (awarded to H.E.). We thank Jessica Bownes, Martin West, Benjamin Petrick, Joanne Menegazzo, Hilary Sloane, and James Rolfe for the laboratory support and analytical assistance. We thank David Evans and Stella Woodard for their discussions, and two anonymous reviewers for providing valuable comments to improve the manuscript. This research used samples provided by the Integrated Ocean Drilling Program (IODP), and we would like to thank the Kochi IODP Core Center Repository for the help with core sampling.
This is the final version of the article. Available from the publisher via the DOI in this record.
Vol. 31, pp. 895 - 913