The Atlantic Meridional Overturning Circulation (AMOC) is a major ocean current system in the Atlantic Ocean, classified as a concept in physical geography and oceanography. It is a component of the larger thermohaline circulation, often described as a "global conveyor belt" that moves water, heat, and nutrients around the world's oceans.
The concept's modern understanding arguably originates in 1957, when the Discovery cruises provided data for reliable estimates of the AMOC's size and structure, building on earlier qualitative pictures that can be traced back to 1798. The problem it addresses is the distribution of heat and its profound role in regulating Earth's climate.
The AMOC works through a density-driven mechanism. It is composed of a northward flow of warm, more saline water in the Atlantic's upper layers and a southward, return flow of cold, deep water. Warm, salty water from the tropics flows north, primarily via the Gulf Stream and the North Atlantic Current. As this water reaches the North Atlantic, it cools and, due to its high salinity, becomes dense enough to sink into the deep ocean, a process known as overturning. This cold, dense water then flows southward along the ocean floor, completing the loop. This process is vital because the AMOC carries up to 25% of the total heat toward the Northern Hemisphere, significantly influencing the mild climate of Western Europe.
The AMOC connects directly to the Gulf Stream, which is the largest current in the North Atlantic and is considered a component of the AMOC's warm surface flow. It is also intrinsically linked to climate change and the global carbon cycle, as it moves carbon and dissolved oxygen into the deep ocean.
The AMOC has been changing recently, with studies suggesting it was weaker in 2015 than before the Industrial Revolution. More recent research, published in Science Advances in April 2026, provides direct observational evidence of a consistent decline in a key part of the AMOC along its western boundary over nearly two decades. This weakening is attributed to climate change, which adds freshwater from melting ice sheets, especially in Greenland, making the surface water less dense and inhibiting the sinking process that drives the circulation. Climate models predict the AMOC will further weaken during the 21st century.