Distribution of Ammonium-Bearing Clay Minerals and their δ 15 N values Occurred in Shallow-Seafloor Hydrothermal System in Kagoshima bay, Southern Kyushu, Japan.
Jaeguk JoToshiro YamanakaYouko MiyoshiJun‐ichiro IshibashiYoshihiro KuwaharaHitoshi ChibaTomoki Kashimura
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Seafloor Spreading
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The concentration of total metal sulfide throughout a water column over a submarine hydrothermal vent in Kikai Caldera south of Kyushu Island, Japan, at ~350 pmol/kg, was higher than that reported in previous studies, at <50 pmol/kg below the halocline. Seawater filtered at 0.2 μm pore size and unfiltered seawater exhibited almost identical metal sulfide concentrations throughout the water column, indicating that most metal sulfide existed in dissolved and particulate forms with diameters <0.2 μm. By using a mass balance calculation with the observed sulfide species of free and metal sulfides and carbonyl sulfide, we showed that ~70% of the metal sulfide supplied from hydrothermal vents were contained in the water column beyond the halocline without undergoing oxidative loss even after mixing into overlying oxic seawater. Our findings clearly indicate that sulfide and trace metals emitted from hydrothermal vents form a stable metal-sulfide complex with diameters <0.2 μm. These results also strongly support the recently proposed theory such that metal-sulfide complexation/nanoparticles play an important role in the long-distance transportation of trace metals in the ocean.
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--Eighteen samples of hydrothermal sediments from the Jade hydrotherrnal field in the central Okinawa Trough have been analyzed. Sulfur isotopic values for 10 sulfide samples vary from 5.2 ×10-3to 7.2× 10-3, δ34S valUes for 7 sulfate samples vary from 16.3 × 10-3 to 22.3 × 10-3, and 1 native sulphur sample has a δ34S value of 8.2 × 10-3. The major sources of sulfur for hydrothermal sediment are intermediate to acid volcanic rocks and sea water sulfate, and it is possible that the partial sulfur of hydrothermal sediment is from the pelagic sediment by the interaction between hydrothermal fluid and sediment. The reasons of causing the distinct differences in sulfur isotopic values for sulfide samples from hydrothermal sediment ( compared with other hydrothermal fields), are the differences in the sources of sulfur, the magmatic activity and the tectonic evolution in different hydrothermal fields. The sulfur evolution is a long and complex process in the seafloor hydrothermal system, involving the ascending of heating sea water, the interaction between fluid and volcanic rocks, the mixing of sea water sulfate and sulfur from intermediate to acid volcanic rocks, and the fluid/pelagic-sediment interaction. And the interaction between sea water and intermediate to acid volcanic rocks is an important mechanism for the sulfur evolution in the Jade hydrothermal field.
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The distribution and concentration of hydrolyzable amino acids and acid-extractable free amino acids in seafloor sediments collected from the Izena and Yoron Cauldrons hydrothermal systems, Okinawa Trough, were determined. The total hydrolyzable amino acid (THAA) concentrations were between 2.95 and 20.58 μmol/g, and Gly was the most abundant amino acid, followed by Asp, Ser, Ala, Val, and Phe. The high concentration of Gly suggests that the samples were hydrothermally altered. Small amounts of D-Asp, D-Glu and D-Ala were observed in the hydrolyzable fraction of sediments. The D/L ratios were <0.15, indicating that the amino acids were biogenic. Thus, it was inferred that the source of the amino acids in the Okinawa Trough hydrothermal field is mainly bio-debris of marine planktons, such as radiolarians and foraminifera, which were observed using a scanning electron microscope with energy-dispersive spectroscopy. The acid-extractable free amino acid concentrations were between 8.56 and 104.33 nmol/g and accounted for 0.1–1.1% of the THAA. The content of free basic amino acids was much less than that of acidic and neutral amino acids, indicating that the amino acids were adsorbed on organic functional groups coating the mineral surfaces via chemical bonds. Amino acids are unstable and they rapidly decompose under hydrothermal conditions. However, the stability and survival of amino acids is enhanced via adsorption on minerals and sediment particles. Adsorption plays a role in controlling the distribution and concentration of amino acids in hydrothermal sediments.
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Abstract. The Onsen site is an active submarine hydrothermal system hosted by the Desmos caldera in the Eastern Manus Basin, Papua New Guinea. The hydrothermal fluid is very acidic (pH=1.5) and abundant native sulfur is deposited around the vent. The δ 34 S values of native sulfur range from ‐6.5 to ‐9.3 %o. δ 34 S values of H 2 S and SO 4 in the hydrothermal fluid are ‐4.3 to ‐9.9 %o and +18.6 to +20.0 %o, respectively. These δ 34 S values are significantly lower than those of the other hydrothermal systems so far reported. These low δ 34 S values and the acidic nature of the vent fluids suggest that volcanic SO 2 gas plays an important role on the sulfur isotope systematic of the Onsen hydrothermal system. Relationship among the δ 34 S values of S‐bearing species can be successively explained by the model based on the disproportionation reaction starting from the volcanic SO 2 gas. The predicted δ 34 S values of SO 2 agree with the measured whole rock δ 34 S values. δD and δ 18 O values of clay minerals separated from the altered rock samples also suggest the contribution of the magmatic fluid to the hydrothermal system. Present stable isotopic study strongly suggests that the Onsen hydrothermal site in the Desmos caldera is a magmatic submarine hydrothermal system.
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