Bewertung von neuen submarinen CO2 Austritten als potenzielle natürliche Laboratorien zur Untersuchung der Akklimatisierung von Korallenriffen an die Versauerung der Ozeane
Mineralogie, Petrologie und Geochemie
Zusammenfassung der Projektergebnisse
Fieldwork was conducted at three marine shallow-water hydrothermal systems (MSWHS) in the coastal ocean along the south side of Luzon, Philippines, in 2022 and 2023. At all three sites, gas venting and hydrothermal fluid emission were known to the local community but had never been studied scientifically. Hydrothermal venting occurs in shallow (5 to 25 m) water along the inner shelf that contains a patchy distribution of coral-algal reefs. Two types of venting were observed. (1) Focused discharge of a clear fluid from discrete orifices, 3 to 5 cm in diameter. Discharge temperatures ranged from 73 and 96 °C. (2) Dispersed or diffuse discharge consists of streams of gas bubbles and seeping of hydrothermal fluid through the seafloor sediment. Fieldwork aimed to establish the variability within a single occurrence of hydrothermal activity and between the three sites. Hydrothermal fluids, gases and precipitates/sediments were collected by Scuba diving for laboratory-based analyses of mineralogical, elemental and isotopic composition. Compared to seawater, the hydrothermal fluids were depleted in Cl, Br, SO4, Na, K, Ca and Mg and enriched in CO2, B, Si, Li, Mn, Fe, Sr and As. The composition of the hydrothermal gases was dominated by CO2 (94 to 99 %) with minor amounts of H2, N2, O2, CH4 and He. The original hypothesis that hydrothermal fluids from those MSWHS could be low in arsenic (As) concentrations and thus be suitable for the study of ocean acidification had to be dismissed since concentrations were up to 3.4 mg/L, more than 2000 times that of seawater. Hence, the study shifted focus to investigate the chemical and isotopic composition of the hydrothermal fluids, gases and precipitates. As a result, one of the three sites was identified as the first submarine “bicarbonate” hydrothermal system.
