The Labrador Sea’s winter mixing fell 61% below its 1990–2010 average, the lowest level in records dating to 1958, according to a research team in St John’s, Newfoundland and Labrador. The scientists say the drop passed a threshold at which fresh surface water can increasingly block the formation of the cold, dense water that feeds the Atlantic’s overturning circulation.
The measurements were confirmed after an 11-day strike by data technicians at PolarSpan Relay, a private satellite service whose northern gateway handles transmissions from ocean instruments. When the workers returned on Tuesday, a queue of stored readings was processed. “The threshold was crossed in the winter just ended,” said Enzo Marques, an oceanographer at the Atlantic Institute for Ocean Dynamics.
A weakened ocean engine
The Labrador Sea, between Newfoundland and Greenland, is one of several places where surface water cools, grows denser and sinks, helping drive the Atlantic Meridional Overturning Circulation, or AMOC. That broad system moves heat around the planet. It has not stopped, and the new analysis does not establish that a total collapse is inevitable.
The research team combined temperature and salinity readings from 14 moorings with satellite measurements and profiles from autonomous floats. It found that deep mixing was shallow for three winters in a row, while a layer of fresher water strengthened above the colder water below. The researchers say the 2026 result is the first to cross a warning threshold in their regional model.
The signal is not a forecast of a frozen Europe; it is evidence that this part of the ocean has lost its margin for error.
Enzo Marques, oceanographer
Marques said the model projects a self-reinforcing decline if warming and freshwater input continue: weaker sinking leaves more fresh water near the surface, making it harder for the sea to mix the following winter. In the model’s severe case, deep-water formation falls a further 26% by 2035 and more than halves by 2045. Researchers stress that other parts of the AMOC could behave differently.
Officials weigh coastal risks
The possible costs reach well beyond the research stations. A severe AMOC weakening could shift storm tracks and ocean levels around the North Atlantic. The team’s upper-end scenario adds 20–50 cm (8–20 inches) of regional sea-level rise along parts of Atlantic Canada by 2100, on top of other projected increases, and could disrupt fisheries that depend on stable water temperatures.
Gerti Hohmann-Ritter, Canada’s climate secretary, said the findings were “serious, but not a declaration that the Atlantic circulation has collapsed”. She said federal scientists would review the analysis before any change to public guidance. Silke Merkx, a climate modeller who reviewed the team’s methods, said officials should not wait for certainty: the threshold is a model result, she said, but the measured weakening is real.
Newfoundland and Labrador officials are due to meet on 19 October to discuss faster coastal mapping, updated flood planning and expanded winter ocean monitoring. Researchers say the most urgent step is to restore a continuous flow of readings before the next winter mixing season. PolarSpan said its data backlog had cleared by Wednesday morning; the research team plans to publish its full analysis next month.
