Future Strengthening of North Atlantic Anthropogenic Carbon Transport Despite AMOC Weakening

Ce Bian , Galen A McKinley, Peter Brown, Elaine McDonagh

The North Atlantic is a major hotspot for the uptake, accumulation, and storage of anthropogenic carbon (Canth), processes that are closely linked to the Atlantic Meridional Overturning Circulation (AMOC). However, the role of ocean transport in driving this accumulation remains poorly constrained, leading to uncertainty in future carbon uptake and circulation changes under climate forcing. CMIP6 models reasonably reproduce observed Canth transport at RAPID-MOCHA (26.5°N in the North Atlantic). Our results show that northward Canth transport increases under SSP1-2.6, SSP2-4.5, and SSP5-8.5, despite a concomitant weakening of AMOC-related volume transport. This strengthening occurs because increases in Canth concentration outweigh reductions in circulation strength. The western boundary current serves as the primary pathway for northward Canth transport and is particularly sensitive to future change. A time-of-emergence analysis indicates that trends in Canth transport become detectable within approximately 25–35 years, with earlier emergence under higher-emission scenarios. The RAPID observational record, that began in 2004, is approaching the detectability threshold for Canth transport trends, but it remains too short to robustly resolve long-term changes in AMOC strength, whose emergence timescale is substantially longer.