In their study, the researchers say the major cooling of Earth and continental ice build-up in the Northern Hemisphere 2.7 million years ago coincided with a shift in the circulation of the ocean – which pulls in heat and carbon dioxide in the Atlantic and moves them through the deep ocean from north to south until it’s released in the Pacific.
The ocean conveyor system, Rutgers scientists believe, changed at the same time as a major expansion in the volume of the glaciers in the northern hemisphere as well as a substantial fall in sea levels. It was the Antarctic ice, they argue, that cut off heat exchange at the ocean’s surface and forced it into deep water. They believe this caused global climate change at that time, not carbon dioxide in the atmosphere.
The ocean conveyor transports water and heat through the deep ocean basins. Credit: NASA
Scientists believe that the different pattern of deep ocean circulation was responsible for the elevated temperatures 3 million years ago when the carbon dioxide level in the atmosphere was arguably what it is now and the temperature was 4 degree Fahrenheit higher. They say the formation of the ocean conveyor cooled the earth and created the climate we live in now.
“Our study suggests that changes in the storage of heat in the deep ocean could be as important to climate change as other hypotheses – tectonic activity or a drop in the carbon dioxide level – and likely led to one of the major climate transitions of the past 30 million years,” says Yair Rosenthal, co-author and professor of marine and coastal sciences at Rutgers.
Earth’s climate underwent a major transition from the warmth of the late Pliocene, when global surface temperatures were ~2-3°C higher than today, to extensive Northern Hemisphere glaciation (NHG) at ~2.73 Ma. We show that North Pacific deep waters were significantly colder (4°C) and likely fresher than North Atlantic deep water prior to the intensification of NHG. At ~2.73 Ma, the Atlantic-Pacific temperature gradient was reduced to less 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 m sea-level fall from 3.15-2.75 Ma, and the development of a strong polar halocline, fundamentally altered deep ocean circulation, which enhanced inter-hemispheric heat and salt transport thereby contributing to the NHG.
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