This blog post and the “Deep Dive” podcast, created by NotebookLM, are based on “State of the Science Fact Sheet: Atlantic Meridional Overturning Circulation (AMOC)” by NOAA Science Council. This NOAA fact sheet briefly explains the Atlantic Meridional Overturning Circulation (AMOC), defining it as a critical ocean current that transports heat, salt, and carbon by moving warm surface water to the North Atlantic and colder water back south. While the agency uses international partnerships and trans-basin moored arrays to monitor its flow, current observational records are insufficient to establish a statistically significant long-term weakening trend across the entire Atlantic. Nevertheless, climate models consistently project that increasing greenhouse gases will cause warming and greater freshwater input, gradually slowing the AMOC throughout the 21st century by reducing the density of the surface water. This weakening would have significant negative impacts, including a slowdown of the Gulf Stream leading to regional sea level rise and coastal inundation along the U.S. East Coast, as well as reduced nutrient upwelling for marine ecosystems. Ultimately, a slowdown would also decrease the rate at which carbon dioxide is absorbed into the deep ocean, underscoring the necessity for continued monitoring and improved predictive modeling.
Deep Dive Podcast “Atlantic Ocean Conveyor Belt Slowdown Threats”:
Introduction: The Planet’s Hidden Engine
Our planet is governed by immense, hidden forces that shape our weather, climate, and even the food on our plates. Much like a biological circulatory system, these natural engines work constantly in the background, transporting heat and nutrients on a global scale. They are so vast that their day-to-day function goes unnoticed, yet a change in their rhythm could have profound consequences for our daily lives.
One of the most critical of these is the Atlantic Meridional Overturning Circulation (AMOC), often called the “global ocean conveyor belt.” This massive system is showing signs of change, and understanding its potential impacts is crucial for our future. A slowdown in this current isn’t a distant, abstract concept; it has direct and sometimes surprising effects on everything from global temperatures to the height of the tides on our coasts.
It’s a River in the Ocean, and It’s Gigantic
To understand the AMOC’s impact, it’s essential to grasp its basic function and sheer scale. The system acts as a colossal conveyor belt: it carries warm and salty water from the tropics northward into the high-latitude North Atlantic. Along the way, this water releases immense amounts of heat into the atmosphere. As it cools, the water becomes denser and sinks deep into the ocean, beginning a slow return journey southward as a cold, deep current.
The scale of this circulation is difficult to comprehend. On average, the AMOC moves roughly 16-18 million tons of water per second. This powerful current doesn’t just transport water; it carries essential properties like heat, salt, carbon, and nutrients across the entire Atlantic basin. In doing so, it directly influences weather patterns, sea levels, and the health of marine ecosystems.
A Slowdown Could Paradoxically Accelerate Global Warming
It might seem counter-intuitive, but a weakening of this massive North Atlantic circulation could actually speed up the rate of global warming. The reason lies in the ocean’s role as a critical carbon sink. The AMOC contributes to this process by taking carbon dioxide (CO2) that has been absorbed by surface waters and transporting it into the deep ocean as the water sinks.
This mechanism transitions CO2 from the surface into the deep ocean, effectively sequestering it from the atmosphere on timescales of hundreds to thousands of years. If the AMOC weakens, this sinking process slows down. Consequently, the rate at which the deep ocean absorbs CO2 would decrease, leaving more of it in the atmosphere to accelerate global warming.
It Directly Impacts Sea Level on the U.S. East Coast
For millions of people living along the Atlantic seaboard, a change in the AMOC has tangible consequences. A weaker AMOC leads to a slowdown of the Gulf Stream, its most well-known component. This has a direct effect on sea level due to a phenomenon known as the “cross-shore sea level gradient.” A strong Gulf Stream maintains a slope on the ocean’s surface, but as it weakens, this gradient decreases, causing sea level to rise along the U.S. East Coast. It’s important to note that even if the AMOC were to collapse, the Gulf Stream would weaken but not cease to flow, as it is also driven by large-scale wind fields.
This potential sea level rise can lead to increased coastal inundation, and it is an effect that occurs in addition to the global average sea level rise caused by melting ice and the thermal expansion of seawater. A weaker AMOC also has a secondary impact by reducing the upwelling of deep, nutrient-rich water. This suppression of nutrients can harm the vital functions of marine ecosystems, including the fisheries and coastal economies that depend on them.
The Future is a Concern, Even if the Present is Unclear
Scientists are working to understand the AMOC’s long-term behavior, but direct observation is a relatively new field of study. Because most direct measurements have not been collected for a long enough period, observational evidence for a long-term trend across the entire Atlantic is yet to be established. For instance, longer-term observations of the Florida Current, which carries the bulk of the AMOC’s northward flow in the subtropics, suggest that it has remained remarkably steady over the last four decades, highlighting the complexity of detecting a clear trend.
However, climate models offer a clear projection. The models assessed by the Intergovernmental Panel on Climate Change (IPCC) consistently project a gradual weakening of the AMOC throughout the 21st century as greenhouse gas concentrations increase. While a slow decline is expected, the IPCC has also assessed the risk of a more dramatic event.
The IPCC concludes, with “medium confidence”, that an abrupt collapse of the AMOC before 2100 is “very unlikely”.
Conclusion: A Current Worth Watching
The Atlantic Meridional Overturning Circulation is a complex and powerful system with far-reaching impacts on our climate, sea levels, and ecosystems. While the exact pace of its future changes remains an active area of research, its fundamental importance to the stability of the Earth’s systems is undisputed.
For this reason, scientists emphasize the critical need for continued monitoring. They are calling not just to maintain existing observational arrays, but to enhance them with technologies that improve our understanding of ocean physics, biogeochemistry, and the critical interactions between ice sheets and the ocean. These observations are crucial for refining climate models, particularly by increasing their resolution to better simulate the small-scale ocean features that drive this vast system, and to serve as a vital early warning system for significant changes. As this vital ocean current continues to evolve, the key question remains: how will we adapt to the ripples it sends across our planet?
The infographic was generated by Notebook LM.
Sabatello, R. (2024). State of the science fact sheet: Atlantic meridional overturning circulation (AMOC). National Oceanic and Atmospheric Administration. https://doi.org/10.25923/pav0-be22
Ocean to Climate 
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