Ocean Acidification

Coastal waters contribute significantly to the total oceanic carbon uptake. In this context, the cumulative influence exerted by marginal seas may be conspicuous. However sparse and unevenly distributed observations in such regions pose a serious limit to an accurate, experimentally based quantification of carbon dynamics. The Southern Adriatic (SAd) is one of the key sites of the Mediterranean Sea where open-ocean deep water formation occurs, a process recognized as a major driver of carbon sequestration. However, observations in this region remained sparse, thus quantitative assessment of surface carbon dynamics and air-sea carbon flux are still limited. In this study, a recently validated, decade-long (2015–2024) high-resolution time series of surface partial pressure of CO₂ (pCO_2 sw) and hydrographic measurements collected at the EMSO-E2M3A South Adriatic observatory, located at the centre of the Southern Adriatic Pit, has been analysed. The results showed that seasonal temperature variability and winter vertical mixing were the dominant drivers of pCO_2 sw variability, with biological processes likely contributing during the post-convective period. Air–sea CO₂ flux (FCO₂), derived from in situ observations, indicated a clear seasonal pattern, with the SAd acting as a CO₂ sink during winter and as a source during summer. Importantly, the results revealed that the SAd acted as a weak-to-moderate annual carbon sink over the last decade. However, the magnitude of FCO₂ was strongly influenced by the selected gas transfer velocity parametrization. Similarly, the use of a different wind speed input, for instance ERA5 reanalysis, also altered the estimated CO₂ flux, highlighting the importance of carefully selecting wind products for regional air-sea FCO₂ calculations. Finally, the results presented here showed how time series such as the SAd dataset can serve as critical assets for validating operational ocean models, such as the European Copernicus Marine Service for the Mediterranean, by helping to identify discrepancies in the simulation of key processes.

Dentico C., Cossarini G., Civitarese G., Giani M., Rubino A. & Cardin V., 2026. Air–sea CO₂ exchange in the Southern Adriatic Sea: assessing its role as a moderate carbon sink over the last decade (2015–2024). Biogeosciences 23: 5399–5418. Article.