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

Area of Science:

• Earth System Science
• Oceanography
• Atmospheric Science

Background:

• Ocean carbon cycle is influenced by atmospheric storms, particularly tropical cyclones (TCs).
• Current Earth system models (ESMs) lack the spatial resolution to accurately represent TCs and their effects.
• TCs are known to drive significant air-sea CO2 fluxes and phytoplankton blooms.

Purpose of the Study:

• To develop and utilize a km-scale coupled ESM to realistically simulate TCs.
• To investigate the physical-biogeochemical mechanisms triggered by TCs in the ocean.
• To understand the impact of TCs on the ocean carbon cycle and phytoplankton dynamics.

Main Methods:

• Employed a km-scale (5 km ocean, 5 km atmosphere) coupled global ESM with ocean biogeochemistry.
• Simulated TCs at a resolution fine enough to capture their dynamics and impacts.
• Analyzed the resulting changes in air-sea CO2 fluxes, ocean temperature, and phytoplankton blooms.

Main Results:

• Simulated TCs enhanced CO2 fluxes by 20-40 times and cooled the surface ocean by 2-3°C.
• TCs inverted CO2 flux direction from outgassing to uptake.
• A significant autumn phytoplankton bloom was triggered by TCs in the western North Atlantic, a phenomenon missed by coarser models.
• TCs caused subsurface ocean warming, counteracting surface cooling effects on organic matter remineralization.

Conclusions:

• The km-scale ESM accurately reproduces previously unresolved ocean carbon cycle variability driven by TCs.
• Fine-scale atmosphere-ocean biogeochemistry interactions are crucial for understanding the ocean carbon cycle.
• This modeling approach provides a foundation for future research on the global and climatic role of km-scale events.