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Key Ocean Current Contains a Warning on Climate

Nature – Five million years of Antarctic Circumpolar Current strength variabilityVia Scientific Frontline:”It carries more than 100 times as much water as all the world’s rivers combined. It reaches from the ocean’s surface to its bottom, and measures as much as 2,000 kilometers across. It connects the Indian, Atlantic and Pacific oceans, and plays a key role in regulating global climate. Continuously swirling around the southernmost continent, the Antarctic Circumpolar Current is by far the world’s most powerful and consequential mover of water. In recent decades it has been speeding up, but scientists have been unsure whether that is connected to human-induced global warming, and whether the current might offset or amplify some of warming’s effects. In a new study, an international research team used sediment cores from the planet’s roughest and most remote waters to chart the ACC’s relationship to climate over the last 5.3 million years. Their key discovery: During past natural climate swings, the current has moved in tandem with Earth’s temperature, slowing down during cold times and gaining speed in warm ones―speedups that abetted major losses of Antarctica’s ice. This suggests that today’s speedup will continue as human-induced warming proceeds. That could hasten the wasting of Antarctica’s ice, increase sea levels, and possibly affect the ocean’s ability to absorb carbon from the atmosphere. “This is the mightiest and fastest current on the planet. It is arguably the most important current of the Earth climate system,” said study coauthor Gisela Winckler, a geochemist at Columbia University’s Lamont-Doherty Earth Observatory who co-led the sediment sampling expedition. The study “implies that the retreat or collapse of Antarctic ice is mechanistically linked to enhanced ACC flow, a scenario we are observing today under global warming,” she said.”

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