The AMOC stayed strong even as a major ocean “lifeline” nearly shut down
Ancient seafloor sediments have revealed a surprising twist in how the Atlantic’s massive circulation system works. During a cold period about 3.4 million years ago, the flow of warm, salty water from the Indian Ocean into the Atlantic nearly shut down—but the AMOC did not weaken as expected. Parts of the overturning circulation actually grew stronger.
Scientists have discovered that the Agulhas Leakage, a flow of warm, salty water from the Indian Ocean into the Atlantic, does not always result in the expected response from the Atlantic Meridional Overturning Circulation (AMOC). This contradicts the long-held belief that changes in Agulhas Leakage directly impact the AMOC. Researchers from the Netherlands, USA, China, and the UK analyzed geological evidence from the late Pliocene, a period of significant climate change.
They examined sediments from International Ocean Discovery Program Site U1475 on the Agulhas Plateau and interpreted fossilized microplankton to track changes in ocean temperatures and positions of the subtropical front. Their findings suggest that a weakening Agulhas Leakage did not lead to a weakened AMOC. Instead, during the glacial event, North Atlantic Deep Water formation strengthened and the thermocline, the boundary between surface and deep waters, became shallower across the Atlantic.
This challenges the traditional understanding of how the AMOC works and highlights the complexity of ocean circulation systems.
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