Extreme Climate Survey
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“The good news is that the AMOC is slowing down less than we thought, and that means that there’s still time to avert a more serious slowdown,” says oceanographer Hali Kilbourne of the University of Maryland Center for Environmental Science in Solomons, who was not involved in the new study.
But because the reassessed data span only a few decades, she says, “there’s still an outstanding question about whether or not the AMOC has slowed since preindustrial times,” around the mid-1800s.
The AMOC acts like a two-level conveyor belt, circulating heat, salt and nutrients through the Atlantic Ocean (SN: 1/4/17). The belt’s upper level carries warm, near-surface waters from the tropics to the North Atlantic. There, the water cools and sinks to the bottom of the ocean. It then returns south along the belt’s lower level, eventually warming, rising and repeating the cycle.
In the subtropical North Atlantic, most of the water carried by the AMOC’s upper level comes from the Florida Current, which whisks water from the Gulf of Mexico into the Gulf Stream. Since 1982, a seafloor telecommunications cable spanning the Florida Strait has been used to monitor the powerful current, providing the longest observational record of any AMOC component.
Seawater contains charged atoms called ions, which flow across the cable and generate a measurable voltage. By calibrating voltage measurements with direct observations from periodic research cruise surveys, scientists can calculate how much water the current is carrying across the cable on any given day.
But this process isn’t perfect, says oceanographer Denis Volkov of the University of Miami. It’s been managed by several generations of scientists, resulting in some…
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