Emissions of Fe(II) and its kinetic of oxidation at Tagoro submarine volcano, El Hierro

Abstract

The eruptive process that took place in October 2011 in the submarine\r\nvolcano Tagoro off the Island of El Hierro and the subsequent\r\ndegasification stage, five months later, have increased the\r\nconcentration of TdFe(II) (Total dissolved iron(II)) in the waters\r\nnearest to the volcanic edifice. In order to detect any variation in\r\nconcentrations of TdFe(II) due to hydrothermal emissions, three cruises\r\nwere carried out two years after the eruptive process in October 2013,\r\nMarch 2014 and May 2015. The results from these cruises confirmed\r\nimportant positive anomalies in TdFe(II), which coincided with negatives\r\nanomalies in pH(Fjs) (pH in free scale, at in situ conditions) located\r\nin the proximity of the main cone. Maximum values in TdFe(II) both at\r\nthe surface, associated to chlorophyll a maximum, and at the sea bottom,\r\nwere also observed, showing the important influence of organic\r\ncomplexation and particle re-suspension processes. Temporal variability\r\nstudies were carried out over periods ranging from hours to days in the\r\nstations located over the main and two secondary cones in the volcanic\r\nedifice with positive anomalies in TdFe(II) concentrations and negative\r\nanomalies in pH(Fjs) values. Observations showed an important\r\nvariability in both pH(Fjs) and TdFe(II) concentrations, which indicated\r\nthe volcanic area was affected by a degasification process that remained\r\nin the volcano after the eruptive phase had ceased. Fe(II) oxidation\r\nkinetic studies were also undertaken in order to analyze the effects of\r\nthe seawater properties in the proximities of the volcano on the\r\noxidation rate constants and t(1/2) (half-life time) of ferrous iron.\r\nThe increased TdFe(II) concentrations and the low associated pH(Fjs)\r\nvalues acted as an important fertilization event in the seawater around\r\nthe Tagoro volcano at the Island of El Hierro providing optimal\r\nconditions for the regeneration of the area.