Study of the Distribution of Inorganic Nutrients in the Natural Fertilization Induced by the Submarine Volcano Tagoro (El Hierro) and the Effect of Sample Freezing.

Since its eruption in 2011, the submarine volcano Tagoro (El Hierro, Canary Islands) has been continuously monitored by the Spanish Institute of Oceanography (IEO-CSIC), as it is one of the few submarine volcanoes studied from the onset of its formation. This study analyzes data from the VULCANA-0421 and VULCANA-0125 cruises, focusing on key inorganic nutrients essential for marine productivity: silicate, phosphate, ammonium, nitrite, and nitrate. The results reveal that, more than a decade after the eruption, intense hydrothermal activity persists, continuing to alter the chemical composition of the water column. Elevated and spatially variable concentrations of all nutrients were observed, with enrichment levels reaching up to 57.00-fold for silicate and 3.96-fold for phosphate in the vicinity of the Tagoro volcano. Nitrogen species exhibited an increasing oxidation gradient with distance, suggesting active nitrification processes. In addition, the effect of sample freezing on silicate measurements was evaluated, showing underestimations at concentrations above 40 μmol/kg. As a methodological improvement, a thermal treatment at 50 °C is proposed to enhance analytical accuracy. This study underscores the importance of long-term monitoring and contributes valuable insights into nutrient dynamics in volcanically disturbed marine environments.