Oral

IAMAS

M01 - Atmospheric Chemistry in the Anthropocene: From the Urban to Global Scales

A 25-year record of atmospheric deposition in the East Mediterranean: pH change and impact on iron speciation

A 25-year record of wet deposition has been obtained at Finokalia station on Crete island in the East Mediterranean from 1997 to 2022. Rain water samples were analysed for pH, main anions and cations. In addition Fe(II), soluble iron (DSRFe) and total Iron (Fe) were determined since 2004. A significant temporal increase in rain pH values is observed, mainly due to the reduction in sulfur concentrations. Regardless of the pH value of the rain, the Fe(II)/DSRFe ratio appeared to remain always above 50%, indicating that a significant amount of Fe(II), hence bioavailable iron, enters the sea surface via rain. However, Fe(II)/DSRFe ratio gradually decreases from 0.70 to 0.52 with increasing pH until pH 7.0, while from pH 7.0 and above it increases again, reaching an average value of about 0.67 at very basic pH levels. This is related to the general decrease in Fe solubility with increasing pH and the respective association of the forms in which Fe(II) and Fe(III) exist. It is therefore evident that the observed increase in pH in wet deposition affects the amount of dissolved iron deposited in the oceans, particularly Fe(II), that is directly bioavailable to the marine ecosystem, with consequent impacts on marine productivity. This research was funded by the project ��Support for Enhancing the Operation of the National Network for Climate Change (CLIMPACT)��, National Development Program, General Secretariat of Research and Innovation, Greece (2023��A11900001 - ��. 5201588).