Interannual to decadal variability in the Southern Ocean surface CO2 fluxes in relation with the large-scale atmospheric modes
(English) Abstract The Southern Ocean (<35◦S), which encircles Antarctica, plays a disproportionately large role in the global carbon cycle, accounting for nearly half of the ocean’s uptake of anthropogenic CO₂. This critical function has helped mitigate the pace of atmospheric CO₂ accumulation a...
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| Formato: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2025 |
| País: | España |
| Recursos: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/695422 |
| Acesso em linha: | http://hdl.handle.net/10803/695422 https://dx.doi.org/10.5821/dissertation-2117-443207 |
| Access Level: | acceso abierto |
| Palavra-chave: | Oceanography Southern Ocean Carbon cycle Atmospheric modes Àrees temàtiques de la UPC::Enginyeria civil Àrees temàtiques de la UPC::Desenvolupament humà i sostenible 624 - Enginyeria civil i de la construcció en general 502 - Natura. Estudi conservació i protecció de la natura |
| Resumo: | (English) Abstract The Southern Ocean (<35◦S), which encircles Antarctica, plays a disproportionately large role in the global carbon cycle, accounting for nearly half of the ocean’s uptake of anthropogenic CO₂. This critical function has helped mitigate the pace of atmospheric CO₂ accumulation and climate change. However, observations over recent decades have revealed substantial interannual to decadal variability in the Southern Ocean carbon sink, characterized by alternating periods of weakening and reinvigoration. Understanding the drivers of this variability is crucial for improving predictions of the ocean’s future carbon uptake capacity and its feedbacks on the climate system. This thesis investigates the atmospheric and oceanic processes underlying the variability of Southern Ocean CO₂ fluxes, with a focus on the influence of major climate modes including the Southern Annular Mode (SAM), the Pacific-South American (PSA) pattern, and Zonal Wave 3 (ZW3). Through a combination of reanalysis datasets, empirical orthogonal function and wavelet analyses, observation-based CO₂ flux products, and ocean-only numerical simulations, the thesis systematically diagnoses the mechanisms linking atmospheric variability to ocean carbon dynamics. The results identify SAM as the principal driver of CO₂ flux variability on seasonal to decadal timescales, modulating surface wind patterns, Ekman upwelling, and sea surface temperature (SST) anomalies that affect CO₂ exchange. ENSO and ZW3 are shown to exert important secondary effects, introducing regional asymmetries and modulating the physical and biological drivers of CO₂ fluxes, particularly in the Pacific sector. A novel finding is the detection of a delayed warming mechanism, whereby positive SAM phases enhance eddy kinetic energy, amplifying thermal effects on surface pCO₂ and partially offsetting the expected CO₂ uptake from weakened upwelling. The thesis also conducts a comprehensive evaluation of nine observation-based CO₂ products, highlighting uncertainties, mismatches, and shared patterns that improve our understanding of carbon cycle variability. Importantly, the results underscore the need to improve the representation of mesoscale processes, asymmetric climate modes, and atmosphere-ocean coupling in Earth system models to enhance their predictive capability. Overall, this research provides new insights into the drivers of Southern Ocean CO₂ variability, offering a framework to refine predictions of future carbon-climate feedbacks and to better anticipate the ocean’s role in mitigating anthropogenic climate change. |
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