Weak winds and heat waves reduce the absorption of CO₂ in the Mediterranean

Weak winds reduce the absorption of CO₂ in the Mediterranean. Specifically, this year the central Mediterranean absorbed 30% less carbon dioxide at the beginning of 2023 compared to the same period the previous year, coinciding with light winds and an intense marine heat wave. It is one of the main results of the study conducted by Enea researchers and published in the Journal of Geophysical Research: Oceans, which collects for the first time continuous data on the exchange of carbon dioxide between the atmosphere and the sea in this area of ​​the Mediterranean.

For Alcide di Sarra, researcher at the Laboratory of Models and Measurements for Air Quality and Climatic Observations of Enea, the exceptional heat wave that occurred also "probably also had an important impact on the exchange of CO2 between the atmosphere and the ocean, with a significant release from the ocean into the atmosphere".

«The data collected at the Lampedusa Oceanographic Observatory during the exceptional marine heat wave of summer 2026 - adds di Sarra, responsible, together with Damiano Sferlazzo, of the Lampedusa Oceanographic Observatory - show temperature values ​​that exceeded 31°C at 1 meter, 30°C at 5 and 18 meters depth. Such high values ​​and for such an extended period have never been observed since records began."

At the center of the study, measurements between 2021 and 2023 in the central Mediterranean which, underlines di Sarra, «functions as a large carbon dioxide reservoir, absorbing CO₂ from the atmosphere in winter and releasing it during the summer». Hence the role of the sea in removing carbon dioxide.

«The data collected is the first to show that, on an annual basis, this Mediterranean region contributes to removing CO₂ from the atmosphere - he adds -. Between May 2022 and April 2023, however, we observed a clear reduction in CO₂ exchanges between the atmosphere and the sea, coinciding with an intense and prolonged marine heat wave."

Reading the study, it emerges that already in 2022 the surface temperature of the Mediterranean Sea was "significantly higher than the average values ​​of the period 1991-2020, due to an intense and persistent marine heat wave, which lasted from May 2022 to April 2023".

On average, over the entire basin, the increase reached around 1.5-2 °C, while in the central Mediterranean even higher peaks were recorded, up to 4 °C above the seasonal average.

In the same period, the researchers detected "a marked reduction in the frequency of intense winds, with 42 average daily wind speed values ​​above 8 m/s, compared to the 71 recorded in the previous year". On the contrary, "the number of days characterized by weak winds increased, with 47 days in which the average daily speed was lower than 5 m/s, compared to only 26 days the previous year". Conditions which, the researchers underline, "favored the maintenance of the marine heat wave in the study area, the central Mediterranean".

Not a final result but the starting point for new studies.

«Thanks to over a year and a half of continuous surveys we were able to measure the impact of this extreme climate event on the marine carbon cycle - concludes di Sarra -. These data form the basis for building a set of long-term observations, useful for better understanding the evolution of these phenomena in a climate hotspot such as the Mediterranean, particularly sensitive to climate change and increasingly characterized by extreme events such as Mediterranean hurricanes, the so-called medicana, and marine heat waves".