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Helium and methane sources and fluxes of shallow submarine hydrothermal plumes near the Tokara Islands, Southern Japan

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ABSTRACT

Shallow submarine volcanoes have been newly discovered near the Tokara Islands, which are situated at the volcanic front of the northern Ryukyu Arc in southern Japan. Here, we report for the first time the volatile geochemistry of shallow hydrothermal plumes, which were sampled using a CTD-RMS system after analyzing water column images collected by multi-beam echo sounder surveys. These surveys were performed during the research cruise KS-14-10 of the R/V Shinsei Maru in a region stretching from the Wakamiko Crater to the Tokara Islands. The 3He flux and methane flux in the investigated area are estimated to be (0.99–2.6) × 104 atoms/cm2/sec and 6–60 t/yr, respectively. The methane in the region of the Tokara Islands is a mix between abiotic methane similar to that found in the East Pacific Rise and thermogenic one. Methane at the Wakamiko Crater is of abiotic origin but affected by isotopic fractionation through rapid microbial oxidation. The helium isotopes suggest the presence of subduction-type mantle helium at the Wakamiko Crater, while a larger crustal component is found close to the Tokara Islands. This suggests that the Tokara Islands submarine volcanoes are a key feature of the transition zone between the volcanic front and the spreading back-arc basin.

No MeSH data available.


Origin of helium in a shallow marine hydrothermal system.Error assigned to the symbol is 2σ. ASSW is air-saturated seawater.
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f3: Origin of helium in a shallow marine hydrothermal system.Error assigned to the symbol is 2σ. ASSW is air-saturated seawater.

Mentions: A positive relationship between the δ3He value (where δ3He = (R − 1) × 100, R = 3He/4He) and the excess 4He/20Ne ratio relative to air-saturated seawater values suggests two-component mixing between the atmospheric and volcanic sources (Fig. 3). The end member for the Wakamiko Crater samples exhibits a subduction-type mantle helium signature of approximately 7 Ra, which is consistent gases from volcanoes and hot springs in the Circum-Pacific belt with the high 3He/4He ratios (up to 7.86 Ra)19. The Tokara Islands helium isotopic composition is affected by addition of a larger amount of crustal He (which has R/Ra typical of 0.02–0.03 Ra) lowering the mantle value down to 4 Ra.


Helium and methane sources and fluxes of shallow submarine hydrothermal plumes near the Tokara Islands, Southern Japan
Origin of helium in a shallow marine hydrothermal system.Error assigned to the symbol is 2σ. ASSW is air-saturated seawater.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5037448&req=5

f3: Origin of helium in a shallow marine hydrothermal system.Error assigned to the symbol is 2σ. ASSW is air-saturated seawater.
Mentions: A positive relationship between the δ3He value (where δ3He = (R − 1) × 100, R = 3He/4He) and the excess 4He/20Ne ratio relative to air-saturated seawater values suggests two-component mixing between the atmospheric and volcanic sources (Fig. 3). The end member for the Wakamiko Crater samples exhibits a subduction-type mantle helium signature of approximately 7 Ra, which is consistent gases from volcanoes and hot springs in the Circum-Pacific belt with the high 3He/4He ratios (up to 7.86 Ra)19. The Tokara Islands helium isotopic composition is affected by addition of a larger amount of crustal He (which has R/Ra typical of 0.02–0.03 Ra) lowering the mantle value down to 4 Ra.

View Article: PubMed Central - PubMed

ABSTRACT

Shallow submarine volcanoes have been newly discovered near the Tokara Islands, which are situated at the volcanic front of the northern Ryukyu Arc in southern Japan. Here, we report for the first time the volatile geochemistry of shallow hydrothermal plumes, which were sampled using a CTD-RMS system after analyzing water column images collected by multi-beam echo sounder surveys. These surveys were performed during the research cruise KS-14-10 of the R/V Shinsei Maru in a region stretching from the Wakamiko Crater to the Tokara Islands. The 3He flux and methane flux in the investigated area are estimated to be (0.99–2.6) × 104 atoms/cm2/sec and 6–60 t/yr, respectively. The methane in the region of the Tokara Islands is a mix between abiotic methane similar to that found in the East Pacific Rise and thermogenic one. Methane at the Wakamiko Crater is of abiotic origin but affected by isotopic fractionation through rapid microbial oxidation. The helium isotopes suggest the presence of subduction-type mantle helium at the Wakamiko Crater, while a larger crustal component is found close to the Tokara Islands. This suggests that the Tokara Islands submarine volcanoes are a key feature of the transition zone between the volcanic front and the spreading back-arc basin.

No MeSH data available.