Significant discharge of CO 2 from hydrothermalism associated with the submarine volcano of El Hierro Island

Abstract

The residual hydrothermalism associated with submarine volcanoes, following an eruption event, plays an important role in the supply of CO 2 to the ocean. The emitted CO 2 increases the acidity of seawater. The submarine volcano of El Hierro, in its degasification stage, provided an excellent opportunity to study the effect of volcanic CO 2 on the seawater carbonate system, the global carbon flux, and local ocean acidification. A detailed survey of the volcanic edifice was carried out using seven CTD-pH-ORP tow-yo studies, localizing the redox and acidic changes, which were used to obtain surface maps of anomalies. In order to investigate the temporal variability of the system, two CTD-pH-ORP yo-yo studies were conducted that included discrete sampling for carbonate system parameters. Meridional tow-yos were used to calculate the amount of volcanic CO 2 added to the water column for each surveyed section. The inputs of CO 2 along multiple sections combined with measurements of oceanic currents produced an estimated volcanic CO 2 flux = 6.0 10 5 ± 1.1 10 5 kg d '1 which is ∼0.1% of global volcanic CO 2 flux. Finally, the CO 2 emitted by El Hierro increases the acidity above the volcano by ∼20%.