Possible impacts of volcanic ash emissions of Mount Etna on the primary productivity in the oligotrophic Mediterranean Sea: Results from nutrient-release experiments in seawater

Atmospheric deposition of volcanic ash has recently been recognized as an important nutrient source into the surface ocean. Mount Etna (Italy), one of the worldʹs most active volcanoes, is located in the oligotrophic Mediterranean Sea (MedSea). Despite the active volcanism on Mount Etna, the biogeochemical impacts of volcanic ash fallouts on the marine primary productivity (MPP) remain largely unknown. Here we present the results of seawater nutrient release experiments with volcanic ash samples from Mount Etna that have been collected during different eruptive episodes between 2001 and 2007. Our results show that volcanic ash from Mount Etna releases significant amounts of fixed-N (35–855 nmol/g), P (7–970 nmol/g), Si (3–2060 nmol/g), Fe (10–130 nmol/g) and Zn (< 21 nmol/g). We further estimated an example representative of ash-fall from Etna based on the case-study focusing on 4–5 November 2002 activity, by using the general relation between the thicknesses of the ash deposits and the ash depositional areas. Etna explosive eruptions can transport volcanic ash as far as 800 km, with ash emissions exceeding the particle flux during dust storm events (of 10 g/m2 input) as far as 400 km downwind from the volcano. Our results emphasize that Etna ash can provide a significant supply of nutrients, which can favor the MPP in the central MedSea.