Spatio-temporal anthropogenic footprints on ecosystem drivers of the interior North Atlantic

Jerry Tjiputra, NORCE Norwegian Research Centre and Bjerknes Centre for Climate Research, Bergen, Norway and Leonardo Bertini, NORCE Norwegian Research Centre, Climate, Norway
The North Atlantic is a key region for buffering climate change through its uptake of carbon and heat from the atmosphere. Future large scale changes in circulation patterns, e.g. the Atlantic Meridional Overturning Circulation, are projected to affect the upper ocean biogeochemistry. In addition, as the main gateway for the global thermohaline circulation, the interior North Atlantic will experience these anthropogenically-induced changes very early on. Similarly, any effects due to future mitigation efforts, such as a reduction of anthropogenic carbon emissions, will eventually propagate into the interior ocean. Nevertheless, the time scale and regional extent at which the climate change signal reaches the interior North Atlantic are still poorly understood. We use an IPCC-class Earth system model (NorESM) to simulate an idealized scenario of rapid climate change (warming) followed by rapid mitigation (cooling) through increasing and reducing the atmospheric CO2 concentrations. We investigate the propagation of the anthropogenic footprint, the recovery dynamics and timescales of key marine ecosystem drivers (temperature, oxygen, and pH) projected by the model. Our results reveal complex and spatially heterogeneous responses of these drivers with distinct contrasts between the upper ocean, the interior and the deep North Atlantic, as a result of the interplay between changing ocean biogeochemistry, ventilation and circulation. Due to the delayed changes in the interior ocean circulation, climate change and recovery signals could take hundreds of years to reach parts of the North Atlantic deep ocean. Sensitive areas (or climate change hotspots) and key mechanistic drivers associated with climate change onset and recovery will be highlighted.