1. Palaeoecology, Institute of Environmental Biology, Faculty of Science, Laboratory of Palaeobotany and Palynology,
2. Department of Geochemistry, Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, The Netherlands
3. Department of Marine Organic Biogeochemistry, NIOZ Royal Netherlands Institute of Sea Research, PO Box 59, 1790 AB Den Burg, Texel, The Netherlands
4. Earth and Planetary Sciences Department and Institute of Marine Sciences, University of California, Santa Cruz, 1156 High St, Santa Cruz, California 95064, USA

Correspondence to: Peter K. Bijl¹ Correspondence and requests for materials should be addressed to P.K.B. (Email: p.k.bijl@uu.nl).

Abstract

Relative to the present day, meridional temperature gradients in the Early Eocene age (56–53 Myr ago) were unusually low, with slightly warmer equatorial regions¹ but with much warmer subtropical Arctic² and mid-latitude³ climates. By the end of the Eocene epoch (34 Myr ago), the first major Antarctic ice sheets had appeared^{4, 5}, suggesting that major cooling had taken place. Yet the global transition into this icehouse climate remains poorly constrained, as only a few temperature records are available portraying the Cenozoic climatic evolution of the high southern latitudes. Here we present a uniquely continuous and chronostratigraphically well-calibrated TEX₈₆ record of sea surface temperature (SST) from an ocean sediment core in the East Tasman Plateau (palaeolatitude 65° S). We show that southwest Pacific SSTs rose above present-day tropical values (to 34 °C) during the Early Eocene age (53 Myr ago) and had gradually decreased to about 21 °C by the early Late Eocene age (36 Myr ago). Our results imply that there was almost no latitudinal SST gradient between subequatorial and subpolar regions during the Early Eocene age (55–50 Myr ago). Thereafter, the latitudinal gradient markedly increased. In theory, if Eocene cooling was largely driven by a decrease in atmospheric greenhouse gas concentration⁶, additional processes are required to explain the relative stability of tropical SSTs given that there was more significant cooling at higher latitudes.

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