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Human-induced environmental change around Antarctica is contributing to sea level rise in the North Atlantic, according to a new study by scientists at the University of Miami’s Rosenstiel School.

“Our observational analysis matches what the numerical models have predicted — human activity could potentially impose circulation changes on the entire ocean,” said Tiago Biló, an assistant scientist at the school’s Cooperative Institute for Marine and Atmospheric Studies.

The research team analyzed two decades of deep sea oceanographic data collected by observational mooring programs. It showed that a critical component of ocean currents in the North Atlantic has weakened by about 12% over the past two decades.

The findings were published Friday in Nature Geoscience, co-authored by scientists from  NOAA’s Atlantic Oceanographic and Meteorological Laboratory, and the Alfred-Wegener-Institute Helmholtz Center for Polar and Marine Research in Germany.

The scientists studied changes over time in a mass of cold, dense, and deep water at depths greater than 2.5 miles. The water mass flowed from the Southern Ocean northward and eventually to shallower depths in other parts of the global ocean such as the North Atlantic.

“Although these regions are tens of thousands of miles away from each other, and abyssal areas are a few miles below the ocean surface, our results reinforce the notion that even the most remote areas of the world’s oceans are not untouched by human activity,” Biló said.

This weakened deep-ocean branch — that scientists call the abyssal limb – is part of the Atlantic Meridional Overturning Circulation (AMOC), a three-dimensional system of ocean currents that act as a conveyor belt to distribute heat, nutrients, and carbon dioxide across the world’s oceans. 

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One significant change is the so-called brine rejection, a process when salty water freezes. As ice forms, it releases salt into the surrounding water, increasing its density. The dense water then sinks to the ocean floor, creating a cold, dense water layer that spreads northward to fill all three ocean basins – the Indian, Pacific, and Atlantic.

“The areas affected by this warming spans thousands of miles in the north-south and east-west directions between 4,000- and 6,000-meters of depth,” said William Johns, a co-author and professor of ocean sciences at the Rosenstiel School. “As a result, there is a significant increase in the abyssal ocean heat content, contributing to local sea level rise due to the thermal expansion of the water.”

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