Just a year ago, scientists suggested a collapse of the Atlantic’s circulation system was unlikely this century. Today, that confidence is beginning to unravel. New evidence points to a far more uncertain future - one that raises serious questions for the whales and dolphins that depend on a stable ocean.
The Atlantic Meridional Overturning Circulation (AMOC) often described as a conveyor belt of ocean currents that redistributes heat, nutrients and oxygen around the planet is showing signs of greater instability than previously thought. New research suggests collapse is significantly more likely than earlier assessments indicated, marking a sharp shift from conclusions reached as recently as last year.
This reflects a growing consensus: the AMOC is not just a theoretical risk, it is already weakening. Accelerating ice melt from Greenland, rising global temperatures, and increasing volumes of freshwater entering the North Atlantic are all disrupting one of the ocean’s most important regulating systems.
At its core, the AMOC relies on differences in temperature and salinity to keep water circulating. Cold, salty water sinks in the North Atlantic, drawing warmer water northwards in a continuous loop. Climate change is now interfering with both elements. Meltwater dilutes salinity, making surface waters less dense and less likely to sink, while warming oceans further reduce density and slow circulation. Together, these processes act like a brake on the system.
For marine life, the consequences are profound. The AMOC helps structure the distribution of plankton—the foundation of the marine food web. As plankton shifts, so too do fish populations and the whales and dolphins that rely on them. Feeding grounds may move, fragment or disappear altogether, forcing species to adapt quickly or face decline.
There are also implications for breeding success. Many cetaceans depend on stable environmental conditions to rear their young. Changes in prey availability and ocean temperature could reduce calf survival or increase the energetic cost of reproduction, placing additional pressure on already vulnerable populations.
Sally Hamilton, CEO of ORCA, explains:
“Whales and dolphins are highly adapted to the rhythms of the ocean. When those rhythms begin to shift, and the signs are there now, the consequences ripple through every aspect of their lives. This is not just a climate issue, but an ecological one, with real implications for species survival.”
Beyond these direct impacts, a weakening AMOC could trigger wider and less predictable changes. Reduced heat transport towards the UK and northwest Europe may lead to cooler, more volatile weather, even as global temperatures rise. Altered ocean circulation can also drive regional sea level rise, disrupt fisheries, and influence major weather systems, including the jet stream and tropical rainfall patterns. The AMOC also plays a role in regulating oxygen and carbon in the ocean, meaning its decline could reduce the ocean’s ability to absorb CO₂ while expanding low-oxygen zones.
While the prospect of collapse is alarming, it is not inevitable. The primary driver remains climate change, and the solution is clear: rapid and sustained reductions in greenhouse gas emissions. Strengthening marine protection and restoring ecosystems can also help build resilience.
For ORCA, this underlines the importance of continued monitoring. Through our work with trained volunteers and seafarers, we are gathering vital data on whale and dolphin distribution across the world’s oceans. As conditions change, this information will be essential in understanding impacts and informing conservation action.