Warming Antarctic deep waters are contributing to sea level rise in the North Atlantic

Analysis of mooring observations and hydrographic data suggests that the deep-water branch of the Atlantic Meridional Overturning Circulation (AMOC) in the North Atlantic has weakened. Two decades of continuous observations allow us to better understand the Earth’s climate control system.

But a study just showed that warming Antarctic deep waters are contributing to sea level rise in the North Atlantic.

Scientists studied data from several observational programs study how a cold, dense and deep body of water, located more than 4,000 meters below the ocean’s surface, moves over time. This body of water, originating in the Southern Ocean, moves north and then rises to shallower depths in other ocean regions such as the North Atlantic.

What happens in Antarctic waters has implications for the North Atlantic.

A new study published in the journal Nature Geoscience, conducted by scientists from the University of Miami’s School of Marine, Atmospheric and Geosciences and the National Oceanic and Atmospheric Administration’s Atlantic Oceanographic and Meteorological Laboratory, found that human-caused environmental changes around Antarctica are contributing to sea level rise in the North Atlantic.

The research team analyzed two decades of deep oceanographic data collected through mooring observation programs. to show that a critical portion of Earth’s global ocean current system in the North Atlantic has weakened by about 12%. over the past two decades.

“Although these regions are tens of thousands of kilometers apart, and the abyssal zones are only a few kilometers from the ocean surface, Our results support the idea that even the most remote areas of the world’s oceans have not remained untouched by human activity.” said lead study author Thiago Bilo, an assistant scientist at NOAA’s Cooperative Institute of Marine and Atmospheric Research at the Rosenstiel School.

As part of the NOAA-funded DeepT (Innovative Deep and Deep Temperature Analysis with Bottom-Moored Instruments) project, Scientists analyzed data from multiple observing programs to study the evolution over time of a cold, dense, deep-sea mass more than 4,000 meters below the ocean surface that flows north from the Southern Ocean and eventually reaches shallower depths in other parts of the world. An ocean, such as the North Atlantic.

AIOC is at stake

This contracting branch of the deep ocean, which scientists call the abyssal branch, is part of the Atlantic Meridional Overturning Circulation (AMOC). a three-dimensional system of ocean currents that acts as a “drive belt” to distribute heat, nutrients and carbon dioxide throughout the world’s oceans.

This benthic branch consists of Antarctic bottom waters resulting from the cooling of seawater in the Southern Ocean around Antarctica during the winter months. Among the various mechanisms of formation of these bottom waters, we can note Perhaps most important is the release of brine, a process that occurs when salt water freezes. When sea ice forms, it releases salt into the surrounding water, increasing its density. This dense water sinks to the ocean floor, creating a layer of dense cold water that spreads north and fills all three ocean basins: the Indian Ocean, the Pacific Ocean and the Atlantic Ocean.

During the 21st century, The researchers noticed that the flow of this Antarctic layer along 16°N latitude in the Atlantic had slowed. reducing the flow of cold water to higher latitudes and causing deep ocean waters to warm.

“The areas affected by this warming extend over thousands of kilometers in north-south and east-west directions, at depths of 4,000 to 6,000 meters,” said co-author William Jones, professor of ocean sciences at the Rosenstiel School. “This results in a significant increase in the heat content of the abyssal ocean, which contributes to local sea level rise due to the thermal expansion of water.

Responsible human activity

“Our observational analysis is consistent with what the numerical models predict: human activity could lead to changes in circulation throughout the ocean.” Mr. Bilo said. “This analysis was only made possible through decades of planning and the collective efforts of many oceanographic institutions around the world.

A study called “Weakening of the abyssal branch of the Atlantic meridional circulation in the North Atlantic”, was published in the April 19, 2024 issue of Nature Geoscience.

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