The effects of climate change recorded in the waters and ice in the Southern Ocean are contributing to sea level rise in the North Atlantic, a long-range phenomenon that is due to the alteration of currents in very deep waters of the known phenomenon as Atlantic Meridional Overturning Circulation (AMOC), according to a study led by experts from the Rosenstiel School of Marine, Atmospheric and Earth Sciences at the University of Miami (USA) and the Oceanographic Laboratory and Atlantic Meteorological Service of the National Oceanic and Atmospheric Administration (NOAA, USA).
The consequence of global warming on the branch (part or variant) of the deep waters of the AMOC that we are now trying to explain is complex and very little known, and may have cumulative negative effects on the most studied process of weakening the entirety of this marine current of vital importance for the climate of much of Europe. The results of this research have been published in the journal Nature Geosciences (April 19).
The research team analyzed two decades of deep-sea oceanographic data collected by mooring observing programs to show that a critical piece of Earth's global ocean current system in the North Atlantic has weakened by about 12 percent in recent years. last two decades.
"Although these regions are tens of thousands of kilometers away from each other and the abyssal areas are a few kilometers below the ocean surface, our results reinforce the notion that even the most remote areas of the world's oceans are not outside human activity," explained the lead author of the study, Tiago Biló, assistant scientist at NOAA's Cooperative Institute for Marine and Atmospheric Studies at the Rosenstiel School.
As part of the NOAA-funded DeepT (Innovative Analysis of Deep and Abyssal Temperatures from a Deep-Moored Instrument) project, the scientists responsible for the new publication analyzed data from several observing programs to study changes over time in a cold, dense, deep mass of water located at depths of more than 4,000 meters that flows from the Antarctic or Southern Ocean northward and eventually emerges at shallower depths in other parts of the global ocean, such as the North Atlantic.
This shrinking band of water in the deep ocean, which scientists call the abyssal branch, is part of the Atlantic Meridional Overturning Circulation (AMOC), a system of ocean currents that acts as a "conveyor belt" for distribute heat, nutrients and carbon in the world's oceans, recall the authors of the new study.
The deep waters near Antarctica become especially cold in the southern winter months and are in the Southern Ocean around Antarctica during the winter months. Among the different mechanisms for the formation of this strip or branch of water at great depth, perhaps the most important is the so-called brine rejection, a process that occurs when salt water freezes. As 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 toward the Indian, Pacific, and Atlantic ocean basins. For some years now, various teams of researchers have observed that the flow of this Antarctic layer along latitude 16°N in the Atlantic has slowed down, reducing the entry of cold waters to higher latitudes and causing warming of the waters in the depths of the ocean.
"The areas affected by this warming extend for thousands of kilometers in north-south and east-west directions, between 4,000 and 6,000 meters deep," details William Johns, co-author and professor of ocean sciences at the Rosenstiel School. "As a result, there is a significant increase in heat content in the deeper parts of the Atlantic Ocean, contributing to local sea level rise due to thermal expansion of water."
"Our observational analysis coincides with what numerical models have predicted: human activity could impose circulation changes throughout the Atlantic Ocean," concludes Tiago Biló in statements published by Eurekalert.
