Geochemical observations within the water column at the CO2‐rich hydrothermal systems Hatoma Knoll and Yonaguni Knoll IV, in the southern Okinawa Trough. Issue 9 (9th September 2016)

• Record Type: Journal Article
• Authors: Kedzior, Stine; Buß, Antje; Schneider, Bernd; Schneider von Deimling, Jens; Sültenfuß, Jürgen; Walter, Maren; Mertens, Christian; Rehder, Gregor
• Is Part Of: Journal of geophysical research. Volume 121:Issue 9(2016:Sep.)
• Page Start: 6618
• Page End: 6634
• Publication Date: 2016-09-09
• Subjects: BAB -- Ph -- CO2 -- 3He -- hydrothermal; Oceanography -- Periodicals; 551.4605
• DOI: 10.1002/2016JC012003
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: The Okinawa Trough is one of three known hydrothermal sites worldwide where liquid carbon dioxide is emitted from the seafloor into the water column. In March 2008, investigations were performed at two active areas, Yonaguni Knoll IV and Hatoma Knoll, in order to identify impacts of hydrothermal venting on the water column chemistry. Vertical profiles of pH and redox potential (Eh) were recorded and discrete water samples were taken for the analysis of total carbon dioxide (CT ) and helium ( 3 He, 4 He). Anomalies with respect to reference stations (ΔCT, ΔpH) and 3 He with respect to saturation with the atmosphere ( 3 He excess ) were used to characterize the impact of hydrothermal vents. These data indicate that the flux of CO2 into the water column is dominated by hot hydrothermal CO2 ‐rich vents located in close proximity to the liquid CO2 emission sites. Bubbles and droplets sampled at the cold gas outlets at Hatoma Knoll differed considerably from the water column regarding CO2 / 3 He ratios, and thus, provide additional evidence that cold liquid phase CO2 is of minor importance for the total CO2 flux at both hydrothermal systems. Although hydrothermal vents at back‐arc basins are known to emit large amounts of acids other than CO2, the correlation between ΔpH and ΔCT at both research areas clearly suggests that the observed pH reduction is mainly caused by the addition of CO2 . Deviating ΔCT / 3 He and ΔCT /ΔpH ratios and the prevailing water currents indicate a yet undiscovered vent site at the flank of a seamount in the northeast. Key Points: Hot hydrothermal fluids dominate geochemical anomalies in the water column Second highest CO2 / 3 He ratio measured so far Acidification of the water column mainly caused by CO2 addition