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The critical role of Atlantic-Arctic water mixing in global ocean circulation uncovered
by Sophie Jenkins
London, UK (SPX) Sep 01, 2024
A new study has highlighted the significant role that the interaction between Atlantic and Arctic waters plays in sustaining the Atlantic Meridional Overturning Circulation (AMOC), a key process for regulating the Earth’s climate.
Researchers from the University of Southampton, the Indian Institute of Technology Bhubaneswar, the National Oceanography Centre, and Stockholm University analyzed ocean data spanning from 1979 to 2021 to gain a deeper understanding of how the mixing of these waters supports the AMOC.
The AMOC functions as a vast ocean conveyor belt, transporting warm water from tropical regions northward and returning cold water southward, which helps distribute heat across the planet. This circulation is crucial for maintaining relatively mild temperatures in Northern Europe, including the UK, compared to other regions at similar latitudes.
The study, published in ‘Nature Communications’, revealed that the lower limb of the AMOC-comprising deep, cold, dense water flowing southward in the Atlantic Ocean-consists of 72 percent Atlantic waters and 28 percent Arctic waters.
“As the warm water reaches the cooler regions of the North Atlantic, it loses heat to the atmosphere, becomes denser, and sinks to great depths,” explained Dr. Dipanjan Dey, the study’s lead author, who conducted the research as a postdoctoral researcher at the University of Southampton.
“We found that while some of this dense water immediately returns south, much of it travels northward, where it mixes with colder, fresher Arctic waters in regions like the Denmark Strait, between Iceland and Greenland. This mixing process makes the waters even denser before they too flow southward, contributing to the AMOC’s strength.”
The researchers estimated that the mixing of Atlantic and Arctic waters accounts for 33 percent of the transformation of warm, salty water into colder, fresher, and denser water, with the remaining 67 percent attributed to interactions between the ocean and the atmosphere.
This study challenges previous assumptions that mainly focused on heat loss in specific areas, without considering the essential role of Atlantic-Arctic water mixing.
Models predict that the AMOC could slow down as the planet warms due to climate change. A weaker, shallower AMOC, similar to what occurred during the last Ice Age, could have major consequences for global climate patterns.
The new insights into the mixing of Atlantic and Arctic waters provide a better understanding of these processes.
Professor Robert Marsh, a coauthor of the study from the University of Southampton, added: “As the ocean surface warms and becomes fresher, the resulting increase in stratification (layering of water) hinders this crucial mixing between Atlantic and Arctic waters. This reduced mixing weakens the AMOC by decreasing the density and depth of its southward flow, potentially leading to an overall slowdown of the circulation.
“A slowdown in the AMOC would have major consequences, from much colder temperatures in Northern Europe to sea level rises along the eastern coast of the United States. If it weakens significantly, there could be abrupt, dramatic, and potentially irreversible changes to our planet’s climate.”
A weakened AMOC could also reduce the time that carbon dioxide remains in the ocean before being released back into the atmosphere, potentially accelerating climate change and its impacts.
“Climate models need to accurately represent these water mixing processes to better predict future climate scenarios,” emphasized Dr. Dey. “Our study highlights the complex interplay between our climate and global ocean circulation processes. We need to urgently address global warming to avoid crossing potential tipping points where the circulation could slow down significantly, or even collapse.”
Research Report:Formation of the Atlantic Meridional Overturning Circulation lower limb is critically dependent on Atlantic-Arctic mixing
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