Tropical Instability Vortices reduce Pacific Ocean ENSO-Driven CO 2 outgassing

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Abstract. The relationship between the intensity of Pacific Ocean Tropical Instability Vortices (TIVs), ENSO variability, and dissolved inorganic carbon (DIC) remains poorly constrained. Here, we use a 30-year-long eddy-resolving ocean biogeochemistry simulation to quantify the effects of TIVs on DIC budget components at both synoptic and interannual timescales. At synoptic scales, TIVs primarily influence DIC through advection, especially along the leading edge of the wave fronts, while vertical diffusion and biological processes play secondary roles. To investigate interannual variability, we develop a TIV index to classify strong and weak TIV phases within each ENSO state. In the upper 50 meters, TIV-driven advection shapes large-scale DIC transport pathways while enhancing, yet spatially confining, primary production. Consequently, during El Niño, TIVs tend to amplify oceanic CO2 uptake, associated with a 57 % decrease in CO2 partial pressure (pCO2). During La Niña, they suppress CO2 outgassing, even reversing the ocean's role from a source to a sink. TIVs also affect the upper thermocline carbon inventory by modulating both biological activity and lateral transport. Strong TIVs during El Niño reduce DIC inventories in the upper thermocline by 8.5 GtC due to increased vertical mixing and enhanced transport, while during La Niña, strong TIVs lead to a 77 % higher DIC accumulation compared to weak TIVs. These findings underscore the critical role of TIVs in regulating the equatorial Pacific carbon budget and highlight the need to accurately represent them in Earth system models.

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