Atmospheric Synoptic Variability and Pacific Ocean Biogeochemistry in the Current and Future Climate (SyVarBio)

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Projections based on Earth system models (ESMs) suggest that the ocean environment will dramatically change in the next 100 years should global surface warming continue at the present rate. A future expansion of the tropical “Oxygen Minimum Zones” (OMZs) associated with changes of the functioning of the Eastern Boundary Upwelling Systems (EBUSs) will have major regional and global consequences for the marine ecosystems and the climate. One of the main mechanisms controlling the oxygen levels and the upwelling productivity is the wind-driven ocean circulation. The water transport and the surface buoyancy fluxes depend not only on the intensity of the time-averaged winds but also on the magnitude of the high-frequency Atmospheric Synoptic Variability (ASV), in particular related to extreme events such as tropical cyclones, storms, strong convective patterns. While both time-averaged and high-frequency components will change in a future climate, the specific impacts of a change in ASV are currently overlooked. The objectives of SyVarBio are to: i) understand the relative roles of changes in ASV and time-averaged winds in impacting marine biogeochemical cycles and OMZs by performing dedicated sensitivity experiments with a state-of-art coupled atmosphere – ocean – biogeochemical modeling framework. Large-scale and mesoscale experiments will be performed using the Nucleus for European Modeling of the Ocean (NEMO) framework and will make use of previously simulated fields by the Kiel Climate Model System. A regional focus will be given to the Costa Rica thermal dome in the Eastern Tropical North Pacific, a biodiversity hotspot located close to the Intertropical Convergence Zone and in the most extended OMZ of the world; ii) investigate whether the ASV is realistically represented in a suite of ESMs and to which extent future changes in oxygen levels and productivity are related to changes in ASV. A subsample of simulations performed in the context of the Coupled Model Intercomparison Project phase 6 (CMIP6) will be analyzed using statistical tools and machine learning techniques. By combining these two objectives, involving a process study complemented by an intercomparison analysis of an existing model database, the project SyVarBio will help filing in a knowledge gap regarding the importance of the ASV in the modulation of the Pacific Ocean tropical and subtropical circulation and biogeochemical cycles in the current and future climate.