The NAtl is essential to the sink of anthropogenic CO2 via deep water formation and subduction, setting the pace for the meridional overturning circulation (AMOC). We used an Earth System Model (NorESM) to unravel biogeochemical responses in the mesopelagic North Atlantic (NAtl) under a scenario of rapid warming followed by rapid cooling, which was achieved by altering atmospheric CO2.
Understanding the impacts of climate change on the mesopelagic is key given that it is the transition between the surface and deep ocean and home to hotspots of life which can enhance export of particulate organic carbon (POC<sub>export</sub>) to the deep ocean, namely reef-forming cold water corals and their associated fauna.
We assessed the extent of change in biogeochemical drivers (T, pH, DO, AOU, Ω<sub>c</sub>) and obtained timescales of climate change onset and recovery via time series analyses which involved prescribed envelopes of Pre-industrial variability. Our results suggest climate change onset <100 years for all the drivers, unlikely recoveries in the subtropics and recoveries within the simulation time span for pH, AOU and Ω<sub>c</sub> at higher latitudes. In the subtropical upper mesopelagic, counterintuitive oxygenation was observed (+20%), indicating that decreased remineralization dominates decreased ventilation, controlling DO variability in such a scenario.
