The influence of Antarctica and the Southern Ocean on Late Pliocene global climate reconstructions has remained ambiguous due to a lack of well-dated Antarctic-proximal, paleoenvironmental records. Here we present ice sheet, sea-surface temperature, and sea ice reconstructions from the ANDRILL AND-1B sediment core recovered from beneath the Ross Ice Shelf. We provide evidence for a major expansion of an ice sheet in the Ross Sea that began at ~3.3 Ma, followed by a coastal sea surface temperature cooling of ~2.5°C, a stepwise expansion of sea ice, and polynya-style deep mixing in the Ross Sea between 3.3 and 2.5 Ma. The intensification of Antarctic cooling resulted in strengthened westerly winds and invigorated ocean circulation. The associated northward migration of Southern Ocean fronts has been linked with reduced Atlantic Meridional Overturning Circulation by restricting surface water connectivity between the ocean basins, with implications for heat transport to the high latitudes of the North Atlantic. While our results do not exclude low-latitude mechanisms as drivers for Pliocene cooling, they indicate an additional role played by southern high-latitude cooling during development of the bipolar world.

A minimum of 300 valves were counted in each sample at a magnification of 600×. A magnification of 1,000× was used to confirm species identifications. For centric diatoms, a specimen was counted as 'one' if the central area and a portion of the margin could be identified, or if at least one-half of the valve was preserved. For pennate diatoms, each identifiable apex was counted as 'one-half', and the total count for each species was divided by two before relative abundance percentages were calculated. Data extracted in the frame of a joint ICSTI/PANGAEA IPY effort, see http://doi.pangaea.de/10.1594/PANGAEA.150150

Supplement to: McKay, Robert M; Naish, Tim R; Carter, Lionel; Riesselman, Christina R; Dunbar, Robert G; Winter, Diane M; Sjunneskog, Charlotte; Sangiorgi, Francesca; Warren, Courtney E; Pagani, Mark; Schouten, Stefan; Willmott, Verónica; Levy, Richard H; DeConto, Robert M; Powell, Ross (2012): Antarctic and Southern Ocean influences on Late Pliocene global cooling. Proceedings of the National Academy of Sciences of the United States of America, 109(17), 6423-6428