Abstract
The residual hydrothermalism associated with submarine volcanoes, following an eruption event, plays an important role in the supply of CO2 to the ocean. The emitted CO2 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 CO2 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 CO2 added to the water column for each surveyed section. The inputs of CO2 along multiple sections combined with measurements of oceanic currents produced an estimated volcanic CO2 flux = 6.0 105 ± 1.1 105 kg d−1 which is ~0.1% of global volcanic CO2 flux. Finally, the CO2 emitted by El Hierro increases the acidity above the volcano by ~20%.
Highlights
Emissions of CO2 gas and carbonate alkalinity from El Hierro accounted for 60% and 40%, respectively, of the pH change in local seawater
When both CO2 and carbonate alkalinity are added, pH decreases, but the decrease is less than when only CO2 is added. These results are in agreement with previous studies in which carbonate alkalinity from diffuse low-temperature venting accounted for 20% to 40% of the changes observed in pH at submarine volcanoes Ruby, Maug, and Esmeralda[19]
CO2 flux data from hydrothermally and volcanically active submarine volcanoes in the ocean are scarce, it is estimated that mid-ocean ridge, arcs and plumes contribute[35] with 2.7 108 kg d−1, 3.0 108 kg d−1 and 3.6 108 kg d−1, respectively
Summary
Emissions of CO2 gas and carbonate alkalinity from El Hierro accounted for 60% and 40%, respectively, of the pH change in local seawater. These results are in agreement with previous studies in which carbonate alkalinity from diffuse low-temperature venting accounted for 20% to 40% of the changes observed in pH at submarine volcanoes Ruby, Maug, and Esmeralda[19]. Sites like these provide an excellent opportunity to study the carbonate system, the volcanic contribution to the global volcanic carbon flux, and the potential environmental impact of these emissions on the surrounding ocean.
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