Effect of Plankton Composition Shifts in the North Atlantic on Atmospheric pCO2

Marine carbon cycle processes are important for taking up atmospheric CO₂ thereby reducing climate change. Net primary and export production are important pathways of carbon from the surface to the deep ocean where it is stored for millennia. Climate change can interact with marine ecosystems via changes in the ocean stratification and ocean circulation. In this study we use results from the Community Earth System Model version 2 (CESM2) to assess the effect of a changing climate on biological production and phytoplankton composition in the high latitude North Atlantic Ocean. We find a shift in phytoplankton type dominance from diatoms to small phytoplankton which reduces net primary and export productivity. Using a conceptual carbon-cycle model forced with CESM2 results, we give a rough estimate of a positive phytoplankton composition-atmospheric CO₂ feedback of approximately 60 GtCO₂/°C warming in the North Atlantic which lowers the 1.5° and 2.0°C warming safe carbon budgets.