First Derivations of Air‐Sea CO 2 Fluxes in the Central Mediterranean and Possible Impact of the 2022–2023 Marine Heatwave

Abstract Marginal seas significantly impact the global carbon cycle. However, current knowledge on the role of marginal seas is limited, and only a few in situ data sets on air‐sea CO 2 exchange are available. This study presents the first direct measurements of CO 2 partial pressure (p) and derived air‐sea flux carried out in the central Mediterranean region. Measurements used in this study were made at the Lampedusa Oceanographic Observatory (35.49°N, 12.47°E) and cover the period from December 2021 to June 2023. The daily air‐sea flux is calculated based on high‐resolution measurements of sea temperature, salinity, p in the ocean and in the atmosphere, and wind. The study takes advantage of the presence of two close observation sites contributing to the oceanic and atmospheric domains of the Integrated Carbon Observation (ICOS) network. The data show that the Central Mediterranean on the annual scale currently acts as a CO 2 sink, with an absorption phase in winter and an emission phase during summer. However, large differences exist between the two consecutive absorption periods included in the data set, with a 30% lower absorption rate during early 2023 compared to early 2022. An intense and prolonged marine heatwave occurred from May 2022 to April 2023, and the potential effects of this heatwave on air‐sea fluxes have been investigated. The reduced incidence of intense wind episodes during the heatwave period appears to be the main driver for the reduced air‐sea CO 2 exchange taking place during winter 2023.