Atlantic meridional overturning circulation

The Atlantic meridional overturning circulation, or AMOC, is the main ocean current system of the Atlantic Ocean and a major part of how the planet moves heat around. Warm, salty water flows north near the surface, and as it travels it loses heat and becomes dense enough to sink in the Nordic Seas, after which cold, less salty water returns south at depth, a process driven by differences in temperature and salinity known as thermohaline circulation. The AMOC makes up roughly half of the global thermohaline circulation, with the Southern Ocean supplying the other half, and its sinking regions mix heat, oxygen, carbon, and nutrients through the ocean. It carries as much as a quarter of the total heat transported toward the Northern Hemisphere, which is why it keeps northwest Europe markedly milder than it would otherwise be, and current research indicates the circulation has weakened compared to pre-industrial times as the ocean warms and more fresh water enters from melting ice, although how much of that change is natural variability versus human-caused warming is still debated.