Clams reveal the North Atlantic subpolar gyre has destabilised over recent decades

Amidst the ongoing climate crisis, there is a pressing need to assess the resilience of different components of the climate system. Two candidate tipping elements involve changes in circulation in the Atlantic Ocean, raising alarms about the potential consequences for the climate system and human societies. An approach to measure changes in resilience consists of assessing signs of critical slowing down by measuring changes in lag-1 autocorrelation and variance. However, this approach requires long-term, regularly spaced time-series, characteristics that are rare among observational records, especially in the ocean. The recent development of annually-resolved proxy records based on information encoded in bivalve shells provides a unique opportunity for assessing resilience in the marine environment. Here, we assess changes in resilience in the northern North Atlantic by measuring changes in lag-1 autocorrelation in a compilation of 29 bivalve-derived records. Our findings indicate that the marine environment has lost stability over the last decades over much of the North Atlantic sea shelves. Records that exhibit significant increasing trends in autocorrelation are highly sensitive to temperature variability over the subpolar gyre region, suggesting that the observed slowing down in variability may be associated with this system. Furthermore, bivalves reveal a basin-scale destabilisation episode preceding a documented regime shift in the northern North Atlantic circulation system around 1920, demonstrating their sensitivity to changes in resilience in circulation elements. Both findings suggest that the subpolar North Atlantic circulation system has lost resilience over recent decades and is potentially approaching a tipping point.