Mattia Pecci

and 11 more

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 datasets on air-sea CO2 exchange are available. This study presents the first direct measurements of air-sea CO2 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, CO2 partial pressure in the ocean and in the atmosphere, and wind, using a wind-dependent parameterization for gas transfer velocity. The data show that the Central Mediterranean currently acts as a CO2 sink, with both absorption and emission phases over the course of a year. However, large differences exist between the two autumn-winter seasons comprised in the dataset, with a 30% lower air-sea flux during early 2023 than in early 2022. The possible impact on the CO2 flux of the intense and long-lasting marine heatwave which took place in the period from May 2022 to April 2023 has been investigated by analyzing the dependency of the calculated air-sea CO2 flux on SST and temperature. The reduced incidence of intense wind episodes during the heatwave period appears to be the main driver for the reduced air-sea CO2 exchange taking place during winter 2023, while the higher temperatures appear to produce a small effect on the calculated flux.