Bhubaneswar: Do you know how mixing of ocean waters plays a crucial role in distribution of heat around Earth and thus help in regulating its climate? A new study, conducted by researchers from IIT Bhubaneswar, the University of Southampton, the National Oceanography Centre and Stockholm University have found out that the mixing of Atlantic and Arctic waters plays an important role in sustaining the Atlantic Meridional Overturning Circulation (AMOC), much needed for regulating Earth’s climate.
AMOC acts like a giant ocean conveyor belt moving warm water from the tropics north and cold water south, helping in heat distribution around the planet, said the researchers, who analyzed the ocean data from 1979 to 2021 to come up with the latest finding.
The findings have been published in Nature Communications. According to the latest study, the lower limb of the AMOC, consisting of deep, cold and dense water flowing southward in the Atlantic Ocean, is composed of 72% Atlantic and 28% Arctic waters.
The IIT Bhubaneswar researcher in the team, Dipanjan Dey, said 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.
“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,” Dey said.
While 33% of the warm and salty water is transformed into colder, fresher and denser water due to the mixing of Atlantic and Arctic waters, 67% happens due to interactions between the ocean and the atmosphere. This challenges the previous assumptions on heat loss in specific areas.
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 major consequences for global climate patterns. The new insights into the role of the mixing of Atlantic and Arctic waters help us to better understand these processes.
How will slower AMOC circulation weaken Indian summer monsoon?
Dey insists that the study is also relevant in the Indian context. For over 300 years, the monsoon was believed to result from large-scale land-sea breezes driven by temperature differences. However, in the1980s, the introduction of satellite imagery revealed that the cloud patterns over India closely resembled the Inter-tropical Convergence Zone (ITCZ), a low-pressure zone near the equator. This discovery led to the monsoon being identified as a seasonal migration of the ITCZ from the ocean toward land.
“The ITCZ generally stays just north of the equator, and research indicates that the northward flow of warm water in the Atlantic Meridional Overturning Circulation (AMOC) plays a critical role in maintaining this position,” Dey adds.
However, due to global warming, the AMOC is predicted to slow down, reducing the northward movement of warm water and energy. This can shift the ITCZ southward, potentially weakening the Indian summer monsoon.
