Resolved tropical cyclones trigger CO₂ uptake and phytoplankton bloom in an Earth system model simulation.

Abstract

The ocean carbon cycle is directly impacted by storms in the atmosphere. Tropical cyclones (TCs), particularly, are known to drive intense air-sea CO₂ fluxes and to trigger phytoplankton blooms. However, the current generation of Earth system models (ESM) cannot realistically represent TCs due to their coarse spatial resolution (typically 100 to 200 km grid spacing). Here, we present a km-scale coupled, global, storm- and eddy-resolving (5 km ocean, 5 km atmosphere) ESM simulation including ocean biogeochemistry that is able to resolve TCs, and the cascade of physical-biogeochemical mechanisms that unfold in their response. Our simulated TCs enhance CO₂ fluxes by 20 to 40 times and cool the surface ocean by 2 to 3 ^°C, thus contributing to inverting the CO₂ flux direction from ocean outgassing to uptake. Our TCs furthermore trigger a phytoplankton bloom in autumn in the western North Atlantic, which is missed by coarser ESMs. While TCs cool the ocean surface, they also warm the subsurface, thus causing counteracting impacts on temperature-dependent organic matter remineralization. In summary, our model configuration reproduces mechanisms underlying the ocean carbon cycle variability that remained so far unresolved in ESMs. By representing fine-scale atmosphere-ocean biogeochemistry interactions in our ESM, we pave the way for future work to constrain uncertainties in the role of km-scale events in the ocean carbon cycle at global and climatic scales.