Antarctic role in Northern Hemisphere glaciation

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Science  14 Nov 2014:
Vol. 346, Issue 6211, pp. 847-851
DOI: 10.1126/science.1255586

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Earth’s climate underwent a major transition from the warmth of the late Pliocene, when global surface temperatures were ~2° to 3°C higher than today, to extensive Northern Hemisphere glaciation (NHG) ~2.73 million years ago (Ma). We show that North Pacific deep waters were substantially colder (4°C) and probably fresher than the North Atlantic Deep Water before the intensification of NHG. At ~2.73 Ma, the Atlantic-Pacific temperature gradient was reduced to <1°C, suggesting the initiation of stronger heat transfer from the North Atlantic to the deep Pacific. We posit that increased glaciation of Antarctica, deduced from the 21 ± 10–meter sea-level fall from 3.15 to 2.75 Ma, and the development of a strong polar halocline fundamentally altered deep ocean circulation, which enhanced interhemispheric heat and salt transport, thereby contributing to NHG.

Leading a wintry march from a distance

When the Antarctic ice sheet began to expand around 3 million years ago, it caused changes in deep ocean circulation, hastening the pace of glaciation in the Northern Hemisphere. Woodard et al. analyzed marine sediments from the northwest Pacific Ocean. A substantial fraction of the sea level fall actually occurred before the Northern Hemispheric ice sheets began to grow rapidly, probably because of continental ice growth in Antarctica. Thus, Antarctic glaciers appear to be more dynamic than anticipated, which has implications for the stability of the Antarctic ice sheet in a warming world.

Science, this issue p. 847

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