Tropical cyclone simulations. © DKRZ/MPI-M/UHH
Resolved tropical cyclones increase CO₂ uptake and trigger phytoplankton blooms in an Earth system model.
Atmospheric storms strongly affect the ocean carbon cycle. Tropical cyclones (TCs) in particular can cause large exchanges of CO₂ between the ocean and the atmosphere and can stimulate phytoplankton growth. However, most current Earth system models (ESMs) are too coarse to represent TCs realistically, as they typically use grid sizes of 100–200 km.
In this study, we use a global, fully coupled Earth system model with kilometer-scale resolution (5 km in both the ocean and atmosphere) that includes ocean biogeochemistry. This model can explicitly resolve tropical cyclones and the chain of physical and biogeochemical processes they generate.
The simulated TCs increase air–sea CO₂ fluxes by 20 to 40 times and cool the ocean surface by 2–3 °C. This cooling can reverse the usual direction of CO₂ exchange, turning the ocean from a source of CO₂ into a sink. In addition, TCs trigger an autumn phytoplankton bloom in the western North Atlantic, a feature that is not captured by coarser models. While TCs cool the surface ocean, they also warm deeper layers, leading to opposing effects on temperature-dependent organic matter breakdown.
Overall, this high-resolution model captures key processes that control ocean carbon cycle variability and that have so far been missing in Earth system models. By resolving small-scale atmosphere–ocean and biogeochemical interactions, this approach helps reduce uncertainties in the role of intense, kilometer-scale events in the global ocean carbon cycle and climate system.
source the journal PNAS
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