This image, based on newly obtained core samples from the ocean floor near Australia and Antarctica, shows a revised conception of current flow past those continents around 33 million years ago. At that time, the continents were just beginning to drift apart, and scientists have theorized that a warm-water current flowing southward along the Australian coast reached Antarctica, keeping that continent largely ice-free. But fossil plankton in the core samples indicate that a cold current flowed past Antarctica for about two million years before the continent developed its mile-thick ice cap, suggesting that the ice formed as a result of some other mechanism – possibly a variation in greenhouse gases in the ancient atmosphere. (Purdue University graphic/Huber laboratory)
A longstanding theory that provides much of the basis for our understanding of climate change – that the mile-thick ice sheet covering Antarctica developed because of a shift in ocean currents millions of years ago – has been challenged by Purdue University scientists.
Though climate scientists have theorized for decades that the circulation of warm ocean currents was responsible for keeping Antarctica largely ice-free during the Eocene epoch prior to 35 million years ago, a series of deep-sea core samples taken recently from the ocean floor south of Australia indicates that this theory needs reworking. The sampled sediments, which were deposited during the period when Australia and Antarctica were beginning to drift apart, show that cold-loving plankton, including diatoms and dinoflagellates, were common in the waters then located to the east of the two then-adjacent continents.
"These fossils indicate that a cold current, not the warm one that has been theorized, was flowing past the Antarctic coast for millions of years before the ice sheet developed," said Matthew Huber, lead author and assistant professor in the earth and atmospheric sciences department in Purdue’s College of Science. "Because the ice sheet then appeared very rapidly, over a period of just a few thousand years, some other factor must have caused the rapid cooling that allowed it to form."
Matthew Huber | EurekAlert!
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