Climate interconnections of the Pliocene greenhouse

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Global warming has already reached 1C above the pre-industrial level because of ongoing greenhouse gas emissions. The polar regions are losing ice mass and the ocean is warming, reducing oceanic mixing and ventilation of deep waters, limiting oxygen supply to marine ecosystems. These interconnecting changes are relevant globally but most acute and urgent to study where regional factors predispose the system towards anoxia. A key objective is to extend palaeoclimate records back in time far enough to learn the lessons of the last great interval of sustained CO2-induced global warmth and Antarctic ice sheet retreat: the Pliocene (~3 to 5 million years ago). We will study the Arabian Sea which features the thickest oxygen minimum zone in the global ocean because (i) its cul-de-sac location in the northern Indian Ocean means that cold oxygen-rich water masses can only be supplied from the south (Antarctic-sourced) and (ii) strong southwest Indian summer monsoon winds drive an extremely productive upwelling-fed ecosystem, with intense rain out of organic matter through the water column and oxygen consumption at depth. We will investigate the relationships between past changes in global warmth, Antarctic ice volume, monsoon circulation strength and oxygenation (ventilation) of the ocean.