The cooling of a patch of the North Atlantic known as the "cold blob" is being driven by a weakening of a major ocean current system that may be approaching a tipping point, according to a study published in the journal Geophysical Research Letters and reported by Phys.org on June 8.

The findings add observational weight to a long-running scientific debate over the region south of Greenland and Iceland, which has cooled even as global temperatures have risen.

The study attributes the trend to the Atlantic Meridional Overturning Circulation (AMOC), a system of currents that transports warm surface water north from the tropics and cold, dense water south, regulating the redistribution of heat across the planet. A slowing of this circulation appears to be delivering less warm water to the area.

The research team used observation-based reanalysis data for ocean heat content and surface fluxes, drawing on satellite and temperature measurements from 1955 and 1993, combined with climate models and a heat budget analysis.

The results indicated that the cooling is a deep-ocean phenomenon driven by changes in ocean heat transport rather than surface temperature changes.

The data showed that surface heat loss in the cold blob region has decreased, contradicting the competing theory that increased surface cooling is responsible.

"A further weakening of the AMOC could have major repercussions for future climate for millennia, given that the AMOC is known to have a tipping point beyond which it is likely to shut down," the study authors wrote.

The researchers said further weakening could affect weather, sea level and ecosystems, and urged policymakers to develop risk management strategies.

"While large uncertainty remains over how close Earth is to this tipping point, standard CMIP6 simulations of future global warming scenarios suggest it is crossed in a substantial subset of these model simulations around the middle of this century," the authors wrote.