The Atlantic Ocean contains one of the most powerful influences on our planet’s climate, the Atlantic Meridional Overturning Circulation (AMOC). This system, known as the Atlantic’s “great conveyor belt,” carries warm, salty water from the tropics north into the Arctic, where the water cools, sinks and returns south.
The AMOC’s role in redistributing heat plays a large part in shaping temperatures, weather events, ecosystems and even sea level rise. Northern Europe, for example, could experience higher sea levels and much harsher winters if not for the AMOC bringing warm surface water north and releasing heat into the atmosphere.
But there are scientific reports raising concern that the AMOC may be slowing, which could lead to dramatic shifts in Earth’s climate.
At the University of Georgia’s Skidaway Institute of Oceanography (SkIO), physical oceanographer Nicholas Foukal is looking into this problem and untangling the many questions that surround it. An assistant professor in UGA Franklin College of Arts and Sciences’ Department of Marine Sciences, Foukal has spent the bulk of his professional career studying where, when and how the ocean transports its heat.
“The AMOC is fascinating to me because of its scale,” Foukal said. “It covers the entire North Atlantic basin and has enormous impacts on society, yet still so little is known about it. I am constantly discovering new aspects of the AMOC that we don’t know. This search for knowledge — and especially societally relevant knowledge — motivates me to continue researching the AMOC.”
Foukal’s early work
The AMOC isn’t a single current, but a system of moving water made up of interconnected components, such as surface-intensified gyres and abyssal flows. Off the coast of Georgia, for example, the Gulf Stream current is a key part of the AMOC, bringing warm, salty water north.
Foukal, who came to SkIO after working as an assistant scientist at the Woods Hole Oceanographic Institution (WHOI), has been studying the AMOC since his time at Duke University, where he earned his doctorate in Earth and Ocean Sciences.
In 2017, while at Duke, Foukal authored a paper published in JGR Oceans that assessed the size and strength of the North Atlantic subpolar gyre, which is a counterclockwise circulation of ocean currents off the coast of Greenland that serves as the mixing basin for warm waters brought north by southern currents, cooling them and preparing them to sink and return south. His findings suggested that the gyre was weakening, but at a much smaller rate than previous estimates based on satellite data. The research was funded by a National Science Foundation (NSF) grant to support the Overturning in the Subpolar North Atlantic Program (OSNAP).
Studying the role of freshwater
Freshwater intrusions, such as from melting glaciers, are a big driver of fears related to the AMOC’s slowing. The AMOC’s movement relies on dense, salty water sinking into the North Atlantic. When freshwater, which is less dense than saltwater, melts from glaciers and mixes into the ocean, it reduces the density of surface waters.
Much of Foukal’s recent research has focused on answering questions related to how freshwater from melting ice in the Arctic flows and affects the strength and structure of the AMOC.
In a 2020 paper published in Science Advances, Foukal and his colleagues showed that a substantial portion of Arctic freshwater flows south along the East Greenland shelf in the narrow East Greenland Coastal Current, rather than directly spreading into the open ocean. This finding is significant because it suggests not all freshwater immediately enters deep-water mixing regions. Some of it may stay along the shelf, delaying or dampening its impact on overturning circulation. This research was also funded by the NSF OSNAP award.
A 2024 Science Advances paper co-authored by Foukal showed that extreme wind events, called tip jets, around the southern tip of Greenland can push freshwater from the East Greenland shelf into the nearby Irminger Basin. The study suggests the frequency of the wind events can serve as a good indicator of the amount of Arctic freshwater exported off the shelf. This work was funded by an NSF grant led by Foukal to deploy free-drifting instruments around the southern tip of Greenland.
In a 2025 paper published in Oceanography, Foukal and a group of colleagues synthesized much of the literature on this subject in an article titled, “Is there robust evidence for freshwater-driven AMOC change?” They concluded that while there is evidence leading to a consensus of past AMOC weakening, though still debated, the mechanisms behind those changes are complex. While adding a large amount of freshwater to the North Atlantic is one plausible contributor to AMOC weakening, the authors explained that it doesn’t tell the full story. They also cautioned that existing predictions for an AMOC decline are based on historical observations that are too short to detect trends with high confidence.
In fall 2024, Foukal was awarded funding from NASA’s Surface Water Ocean Topography (SWOT) program to use NASA SWOT satellite data to map the circulation of the Northwest Atlantic continental shelf, which stretches from the shores of Cape Hatteras, North Carolina, to Baffin Island, Canada, and better understand where, when and why cold, fresh Arctic waters are leaving the shelf in exchange for subtropical Gulf Stream waters.
Freshwater from the Arctic tends to accumulate on the Canadian shelf, Foukal explained. As part of an earlier NSF-funded project he led, moorings were placed on the Labrador shelf to measure, for the first time, how much Arctic freshwater flowed down to eastern Canada. Foukal sees the SWOT project as an extension of this work, using advanced satellite technology to cover an even broader geographic area.
And in September 2025, Foukal and colleagues deployed six moorings on the northeast Greenland shelf to track current and salinity measurements of the East Greenland Coastal Current for a year. In part, the researchers are seeking to understand the origin of freshwater at the various mooring locations. The international research project, funded by the NSF, is the first to measure the strength and variability of the East Greenland Coastal Current continuously over the course of an entire year. The project is part of a larger program, including collaborators from Norway and Iceland and domestically from Johns Hopkins University, to collect measurements across the entire western Nordic Seas and simulate the region with numerical computer models.
Measuring and understanding the AMOC’s stability
In a 2024 paper published in Oceanography, Foukal and Léon Chafik of Stockholm University called for a universal approach to measuring the AMOC. Currently, some scientists measure the AMOC by tracking how much water moves north or south at different depths. The authors argue that the universal approach should instead be to measure the AMOC by density, as density is what causes water to separate and form layers. Adopting a universal approach would make comparisons across models and observations more consistent and lead to a more accurate overall understanding of the AMOC’s strength.
A 2025 Nature Communications paper co-authored by Foukal reconstructed air-sea heat exchange to assess the strength of the AMOC from 1963 to 2017 and found no significant long-term decline during that period. While earlier studies have suggested a weakening of the AMOC based on sea surface temperature measurements, the authors argue air-sea heat fluxes provide a more reliable indicator of the AMOC’s strength. This work was funded by the NSF and WHOI and was shared widely by media outlets, including The Washington Post.
“This study made an impact because it came to two important conclusions,” said Foukal. “First, previous results from sea surface temperatures indicating the AMOC is currently collapsing are not founded, and secondly that a better indicator of AMOC variability developed from air-sea fluxes indicates the AMOC has been stable since the 1960s. Both of these results seem to be good news, but people should know that neither finding comments on the future trajectory of the AMOC. The AMOC remains a potentially unstable tipping point in our climate system and one that we should treat with a lot of caution. Limiting future warming by reducing carbon emissions is our only way to ensure we stay away from these dangerous tipping points including the AMOC.”
Looking forward
With so much uncertainty surrounding the AMOC, including its strength and durability, as well as the environmental, economic and health consequences of its potential weakening, the need to understand the system is significant.
Through international collaboration and the use of advanced scientific technology, Foukal and his colleagues are working to reduce some of that uncertainty.
“I feel that we are experiencing an inflection point in AMOC research,” Foukal said. “A huge amount of progress is being made in the field, and our questions are becoming more focused and coherent. I look forward to the next five to 10 years of progress and hope that we can get to the point where uncertainty in our future projections approach those of other known climate impacts such as global temperature and sea level rise.”
About SkIO
The UGA Skidaway Institute of Oceanography (SkIO) is a multidisciplinary research and education institution located on Skidaway Island near Savannah, Georgia. The Institute was founded in 1967 with a mission to conduct research in all fields of oceanography. In 2013, SkIO was merged with the University of Georgia. The campus serves as a gateway to coastal and marine environments for programs throughout the University System. The Institute’s primary goals are to further the understanding of marine and environmental processes, conduct leading-edge research on coastal and marine systems, and train tomorrow’s scientists.