Mixing of Atlantic and Arctic waters is crucial for climate

Aug. 29 () –

The mixing of Atlantic and Arctic waters plays a role a vital role in maintaining the Atlantic Meridional Overturning Circulation (AMOC in English), crucial to regulating the Earth’s climate.

Researchers from the University of Southampton, the Indian Institute of Technology Bhubaneswar, the National Oceanography Centre and Stockholm University analysed ocean data from 1979 to 2021 to better understand how the mixing of Atlantic and Arctic waters helps maintain AMOC.

The AMOC acts as a giant oceanic conveyor belt, moving warm water from the tropics northwards and cold water southwards, distributing heat across the planet. It helps keep northern Europe, including the UK, relatively temperate compared to other regions at similar latitudes.

72 PERCENT ATLANTIC ORIGIN AND 28 PERCENT ARCTIC

The study published in Nature Communications discovered that the lower branch of the AMOC – the part of this “conveyor belt” consisting of deep, cold, dense water flowing southward into the Atlantic Ocean – is made up of 72 percent Atlantic waters and 28 percent Arctic waters.

“As warm water reaches the colder regions of the North Atlantic, it loses heat to the atmosphere, becomes denser and sinks to great depths“, he explains in a statement Dr Dipanjan Dey, lead author of the paper on the research as a postdoctoral researcher at the University of Southampton.

“We found that while some of this dense water immediately flows back south, much of it travels north, where it mixes with cooler, fresher Arctic waters in regions like the Denmark Strait between Iceland and Greenland. This mixing process makes the waters even denser before they also flow south, contributing to the strength of the AMOC.”

Researchers estimate that the mixing of Atlantic and Arctic waters is responsible for 33 percent of the transformation of warm, salty water into colder, fresher, denser water, and 67 percent is attributed to interactions between the ocean and the atmosphere.

The study challenges previous assumptions that focused primarily on heat loss in specific areas without taking into account the critical role of Atlantic and Arctic water mixing.

Models predict that the AMOC could slow down as the planet warms due to climate change. A weaker, shallower AMOC circulation, as happened during the last Ice Age, has important consequences for global weather patterns.

New insights into the role of mixing of Atlantic and Arctic waters help us better understand these processes.

Professor Robert Marsh, co-author of the paper from the University of Southampton, explains: “As the ocean surface warms and becomes cooler, the resulting increase in stratification (layers of water) hampers 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 a general slowdown in circulation.

COLDER IN EUROPE AND RISING SEA RANGE ON THE US EAST COAST

“A slowdown in the AMOC circulation would have major consequences, from much colder temperatures in northern Europe to rising sea levels along the US East Coast. If it weakens significantly, “There could be abrupt, dramatic and potentially irreversible changes in our planet’s climate.”

A weaker, shallower AMOC could also shorten the time carbon dioxide remains in the ocean before being released back into the atmosphere, potentially accelerating climate change and its impacts.

“Climate models must accurately represent these water mixing processes to better predict future climate scenarios,” says Dr. Dey. “Our study highlights the complex interplay between our climate and global ocean circulation processes. We urgently need to address global warming to avoid crossing potential tipping points where circulation could slow significantly or even collapse.”