Ancient Ocean Currents Manipulated Intensity of Ice Ages

Ancient ocean currents, it turns out, manipulated the intensity and duration of ice ages, according to a new study published in the journal Science, solving a mystery that had long puzzled scientists.

About 900,000 years ago, ice-age cycles all of a sudden became longer and more intense, switching from 1,000-year cycles to 100,000-year cycles. Until now, no one knew what was the driving force behind this dramatic shift.

Researchers from the Earth Institute at Columbia University found that during this time, the deep ocean currents that move heat around the globe stalled or even stopped, possibly due to expanding ice cover in the north. The slowing currents increased carbon dioxide storage in the ocean, leaving less in the atmosphere, which kept temperatures cold and kicked the climate system into a new phase of colder but less frequent ice ages, according to their new theory.

"The oceans started storing more carbon dioxide for a longer period of time," lead author Leopoldo Pena said in a statement. "Our evidence shows that the oceans played a major role in slowing the pace of ice ages and making them more severe."

Ice ages ebb and flow in a predictable pattern based on changes in the Earth's orbit around the Sun, and how much sunlight falls on the planet. However, this mechanism alone isn't enough to explain such a climactic shift as the one that occurred 950,000 years ago.

Researchers confirmed that over the last 1.2 million years, ocean currents strengthened during warm periods and weakened during ice ages, as previously thought. But, they also found that 950,000 years ago ocean circulation weakened and stayed that way for another 100,000 years. Also, the planet skipped the usual interglacial period - the warm interval between ice-ages. This turning point supposedly kept ocean period weak during ice ages, and the ice ages themselves became colder.

"Our discovery of such a major breakdown in the ocean circulation system was a big surprise," said study co-author Steven Goldstein, a geochemist at Columbia University's Lamont-Doherty Earth Observatory. "It allowed the ice sheets to grow when they should have melted, triggering the first 100,000-year cycle."

The researchers hypothesize that the subsequent advancing ice might have triggered the a slowdown in deep ocean currents, leading the oceans to vent less carbon dioxide, which suppressed the interglacial that should have followed.