Supercomputer simulations of Earth 19,000 years ago found North Pacific iceberg meltwater could independently weaken the Atlantic Meridional Overturning Circulation, challenging the long-held view that North Atlantic iceberg discharge started the slowdown.
Freshwater released in the northeastern Pacific was shown traveling to North Atlantic deepwater formation zones, where it diluted salty water, blocked sinking and stalled the current system.
The study says North Atlantic iceberg melt came after the AMOC had already begun weakening, with later subsurface Atlantic warming then melting northern ice sheets and amplifying the decline.
That shift matters now because scientists already see the AMOC weakening under human-driven climate change, while modern Alaskan and Canadian Pacific glaciers are melting at historic rates.
Published in Nature Communications, the research suggests climate monitoring and collapse forecasts should look beyond Greenland and the North Atlantic to freshwater inputs across the global ocean.