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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.

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(a) Tectonic setting and location map of the Tokara Islands; bathymetric maps and water column images of Daiichi-Amami Knoll (b,c) and Kotakara Shima (d,e); rhyolite lava and cold seep mussels (f) at Daiichi-Amami Knoll. Stars on the bathymetric maps (b and d) represent the CTD operated sites during this cruise, and the yellow stars are the stations shown in Fig. 2; ST. refers to the water column sample station. The yellow circles in both (c,e) indicate eruptive centers; BSR means the bottom-simulating reflector. (a) was prepared using the Ocean Data View software50 and both (b,d) were produced with GMT version 5.3.0 (http://gmt.soest.hawaii.edu).
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f1: (a) Tectonic setting and location map of the Tokara Islands; bathymetric maps and water column images of Daiichi-Amami Knoll (b,c) and Kotakara Shima (d,e); rhyolite lava and cold seep mussels (f) at Daiichi-Amami Knoll. Stars on the bathymetric maps (b and d) represent the CTD operated sites during this cruise, and the yellow stars are the stations shown in Fig. 2; ST. refers to the water column sample station. The yellow circles in both (c,e) indicate eruptive centers; BSR means the bottom-simulating reflector. (a) was prepared using the Ocean Data View software50 and both (b,d) were produced with GMT version 5.3.0 (http://gmt.soest.hawaii.edu).

Mentions: The Ryukyu Arc, a typical trench-arc system, is formed by the Philippine Sea plate subducting northwestward beneath the Eurasian plate, with variable convergent rates in the range of 4 to 7 cm/yr14. The Ryukyu Arc extends approximately 1,200 km from Kyushu Island (Japan) to Taiwan and can be classified into three segments, namely north, central and south Ryukyu Arc. The separations between these segments are marked by the Tokara Strait and the Kerama Gap. A new chain of submarine volcanoes has been identified by the detailed topography and petrology survey conducted during the cruise KS-14-10 of the R/V Shinsei Maru. This chain of submarine volcanoes has been classified as part of the Tokara Islands and as a part of the volcanic front of the Ryukyu Arc15 (Fig. 1a). To elucidate the regional tectonic setting and the formation of submarine volcanoes, we integrate geomorphological, geophysical and geochemical proxies from a field cruise survey during which we collected water samples from various hydrothermal plumes. We also report the first water column images acquired using multi-beam echo sounder techniques in the region of the Tokara Islands (Daiichi-Amami Knoll and Kotakara Shima; see Fig. 1 and Supplementary Video). These images suggest that degassing in form of bubbles occurs from the investigated shallow hydrothermal systems. Furthermore, we estimate the helium and methane fluxes and the origins of the respective gas species based on the elemental and isotopic analyses of the acquired samples. Our results may be useful for future research related to the carbon cycle and for the risk management of submarine volcanic eruptions in the investigated areas.


Helium and methane sources and fluxes of shallow submarine hydrothermal plumes near the Tokara Islands, Southern Japan
(a) Tectonic setting and location map of the Tokara Islands; bathymetric maps and water column images of Daiichi-Amami Knoll (b,c) and Kotakara Shima (d,e); rhyolite lava and cold seep mussels (f) at Daiichi-Amami Knoll. Stars on the bathymetric maps (b and d) represent the CTD operated sites during this cruise, and the yellow stars are the stations shown in Fig. 2; ST. refers to the water column sample station. The yellow circles in both (c,e) indicate eruptive centers; BSR means the bottom-simulating reflector. (a) was prepared using the Ocean Data View software50 and both (b,d) were produced with GMT version 5.3.0 (http://gmt.soest.hawaii.edu).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: (a) Tectonic setting and location map of the Tokara Islands; bathymetric maps and water column images of Daiichi-Amami Knoll (b,c) and Kotakara Shima (d,e); rhyolite lava and cold seep mussels (f) at Daiichi-Amami Knoll. Stars on the bathymetric maps (b and d) represent the CTD operated sites during this cruise, and the yellow stars are the stations shown in Fig. 2; ST. refers to the water column sample station. The yellow circles in both (c,e) indicate eruptive centers; BSR means the bottom-simulating reflector. (a) was prepared using the Ocean Data View software50 and both (b,d) were produced with GMT version 5.3.0 (http://gmt.soest.hawaii.edu).
Mentions: The Ryukyu Arc, a typical trench-arc system, is formed by the Philippine Sea plate subducting northwestward beneath the Eurasian plate, with variable convergent rates in the range of 4 to 7 cm/yr14. The Ryukyu Arc extends approximately 1,200 km from Kyushu Island (Japan) to Taiwan and can be classified into three segments, namely north, central and south Ryukyu Arc. The separations between these segments are marked by the Tokara Strait and the Kerama Gap. A new chain of submarine volcanoes has been identified by the detailed topography and petrology survey conducted during the cruise KS-14-10 of the R/V Shinsei Maru. This chain of submarine volcanoes has been classified as part of the Tokara Islands and as a part of the volcanic front of the Ryukyu Arc15 (Fig. 1a). To elucidate the regional tectonic setting and the formation of submarine volcanoes, we integrate geomorphological, geophysical and geochemical proxies from a field cruise survey during which we collected water samples from various hydrothermal plumes. We also report the first water column images acquired using multi-beam echo sounder techniques in the region of the Tokara Islands (Daiichi-Amami Knoll and Kotakara Shima; see Fig. 1 and Supplementary Video). These images suggest that degassing in form of bubbles occurs from the investigated shallow hydrothermal systems. Furthermore, we estimate the helium and methane fluxes and the origins of the respective gas species based on the elemental and isotopic analyses of the acquired samples. Our results may be useful for future research related to the carbon cycle and for the risk management of submarine volcanic eruptions in the investigated areas.

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.


Related in: MedlinePlus