Cascading impacts of Atlantic meridional overturning circulation weakening and collapse on marine biogeochemistry

Abstract As anthropogenic emissions continue to increase Earth’s surface temperature, the Atlantic Meridional Overturning Circulation (AMOC) is at risk of weakening substantially and crossing a tipping point. Then, multiple Earth system components may be significantly and irreversibly altered. Here we investigate the responses of ocean carbon uptake, net primary productivity (NPP), oxygen concentration, and carbon storage to an AMOC collapse induced by extremes in the internal variability in the subpolar gyre under a moderate forcing scenario. While similar ensemble splitting has been found in other models, the NASA Goddard Institute for Space Studies (GISS) Earth system model (ESM) was the first to report an AMOC bifurcation due to internal variability, without the need to prescribe freshwater hosing. We find severe regional impacts, including collapsed NPP and deoxygenation in the subpolar North Atlantic, and reduced carbon uptake in the Arctic and subtropical North Atlantic. We identify the physical drivers of these ocean biogeochemical impacts and, for the first time, provide estimates of their lag and latency, i.e. the timescales over which these impacts begin to occur and are fully realized, respectively. Timescales are generally found to increase southward from the deep convection sites, but are remarkably similar between basins at similar latitudes.