Scientists warn about a noticeable shift in the world’s great deep ocean currents, a movement toward subsidence that could slow the circulation patterns in the Atlantic and Southern Oceans. The warming of seawater driven by human-caused climate change is believed to dampen these deep-sea flows. If this trend persists, the ocean may lose a significant capacity to remove carbon dioxide from the atmosphere, a change that would intensify global warming according to Earth system researchers at the University of California, Irvine.
In a recent Nature Climate Change study, investigators examined projections from thirty-six climate models and found that the Atlantic Meridional Circulation and the Southern Meridional Circulation are likely to slow markedly by the year 2100, potentially reaching a 42 percent reduction under certain scenarios. Simulations even suggest a worst case in which this current system could vanish entirely by 2300. The analysis emphasizes that rapid, sustained warming could drive disruptions in deep ocean circulation, with profound climate consequences. These findings are reported by J. Keith Moore, a professor of Earth Systems Sciences at UCI and a co-author of the study, who describes the potential climate outcomes as among the most dramatic since large-scale ice sheets began to melt.
Big currents seem to be on their way to collapse — a caption associated with the study’s imagery helps illustrate the overarching concern about ocean dynamics and climate feedbacks.
In the Atlantic region, warm surface waters move northward, then cool and evaporate, increasing salinity and density. This dense water sinks and travels southward, a circulation pattern that also helps transport nutrients essential for marine ecosystems. If these processes slow or change direction, the downstream effects could ripple through global ocean systems and affect coastal and open-water habitats alike.
Moreover, the planet-wide circulation acts as a large engine for processing atmospheric carbon dioxide. The solubility pump describes the physical and chemical interactions between seawater and the air; CO2 is drawn into the ocean as these exchanges occur. While some carbon returns to the atmosphere through various pathways, a substantial portion remains stored in the ocean’s depths, contributing to long-term carbon sequestration.
Formation of carbonate crusts
A second mechanism helps lock away carbon: biological processes driven by phytoplankton use CO2 during photosynthesis and contribute to carbonate crust formation. When plankton and other marine organisms die, their remains sink, breaking down gradually and releasing carbon and nutrients deep below. Some of these nutrients return to surface layers through circulation and upwelling, but a portion remains buried beneath the waves for extended periods.
The impairment of deep-water circulation could reduce the ocean’s capacity to absorb atmospheric CO2, potentially intensifying hot, dry spells and extending heat waves. This concern is echoed by Moore, who emphasizes that changes in circulation could alter climate patterns and the distribution of heat across the globe.
The study’s results imply that reducing greenhouse gas emissions now may help prevent the complete shutdown of deep ocean circulation in the future and maintain the ocean’s role in climate regulation. The implications extend to marine life and global biodiversity, as shifts in nutrient transport and productivity could reshape food webs and ecosystem services that humans rely on for food, fisheries, and climate resilience.
The research team notes that ongoing modeling efforts will be essential for refining projections and guiding policy decisions. A robust understanding of how deep-ocean currents respond to warming will inform climate risk assessments and help communities prepare for potential changes in weather patterns, sea level behavior, and marine resources.
References: Nature Climate Change study detailing the modeled trajectories of Atlantic and Southern Meridional Circulation under century-scale warming.
This article summarizes the observed and modeled dynamics of deep-ocean circulation and its climate implications, drawing on peer-reviewed research and expert interpretation to present a clear view of potential future outcomes for North American and global audiences. The goal is to convey how long-term changes in the deep ocean could influence climate, ecosystems, and the availability of carbon sinks in the years ahead.