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How can melting ice reduce the sinking of water in the North Atlantic?

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World map showing major ocean current systems, with arrows indicating the direction and speed of warm and cold currents in the Atlantic, Pacific, Indian, Southern, and Arctic Oceans. Warm currents are marked in red and cold currents in blue, with currents labeled by name and symbols denoting those that reverse direction seasonally. A legend explains current speed categories and color codes. — ocean current Major ocean current systems of the world.

Melting ice reduces the sinking of water in the North Atlantic by lowering the density of surface waters.12

The thermohaline circulation—specifically the Atlantic Meridional Overturning Circulation (AMOC)—relies on the formation of cold, salty, and dense water in polar regions that sinks to the seafloor. As glaciers and ice sheets, particularly those in Greenland, melt due to global warming, they release large volumes of freshwater into the subpolar North Atlantic.123

Because freshwater is less dense than saline water, this influx dilutes the surface layer, preventing it from becoming dense enough to sink. By inhibiting this sinking motion, the freshwater intrusion weakens the mechanism that drives the large-scale circulation of the ocean. This process has historical precedent; for example, the sudden release of meltwater from a glacial lake during the last glacial period is believed to have shut down North Atlantic convection, leading to the Younger Dryas cooling event.124