Can Saharan Dust Intrusions Alter the Isotopic Composition of Atmospheric Methane and Carbon Dioxide?

This study investigates the potential influence of Saharan dust intrusions on the stable carbon isotopes of methane (CH4) and carbon dioxide (CO2), using continuous in situ measurements from the ICOS (Integrated Carbon Observation System) atmospheric station at the CNR-IMAA Atmospheric Observatory (CIAO) in Tito, Basilicata, southern Italy. The analysis builds upon the recent investigation of a two-month isotopic dataset (20 February–20 April 2025), which identified anomalous isotopic behavior in March, coinciding with three distinct dust events. The observations reveal shifts in δ13C–CH4 values that align temporally with the dust intrusions, accompanied by a decrease in CH4 mole fractions. Such patterns could suggest fractionation processes affecting CH4, potentially driven by enhanced oxidation promoted by mineral aerosols. At the same time, δ13C–CO2 shows a gradual decline, deviating from the typical springtime enrichment associated with intensified photosynthetic uptake of 12CO2. This unexpected decrease suggests that dust-related radiative effects, particularly the attenuation of incoming solar radiation, may inhibit photosynthesis, thereby altering the isotopic composition of atmospheric CO2. Consistently, CO2 mole fractions exhibit a modest increase during periods of declining δ13C–CO2, reinforcing the interpretation of reduced photosynthetic activity. These findings provide new observational data beyond existing studies from Atlantic regions and highlight the need for further research on the role of mineral dust in shaping greenhouse gas isotopic variability in the Mediterranean, where such events are frequent and climatically relevant.