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1550406 
Journal Article 
Gas geochemical characteristics of hydrothermal plumes at the HAKUREI and JADE vent sites, the Izena Cauldron, Okinawa Trough 
Kawagucci, S; Shirai, K; Lan, TF; Takahata, N; Tsunogai, U; Sano, Y; Gamo, T 
2010 
1 
Geochemical Journal
ISSN: 0016-7002
EISSN: 1880-5973 
44 
6 
507-518 
WOS:000285804400006 
Hydrothermal plumes above the HAKUREI and JADE sites two
high-temperature hydrothermal vent sites in the Izena Cauldron at the mid-Okinawa Trough were
investigated in order to gain a preliminary understanding of gas geochemical characteristics at
underlying hydrothermal vent sites Three geochemical tracers, H-2, CH4 and delta He-3 covary with
each other above the HAKUREI site but only CH4 and delta He-3 are correlated above the JADE site
The carbon isotope ratio of methane within the Izena Cauldron can be accounted by a combination
of the fluid dilution by ambient seawater and microbial consumption with the kinetic carbon
isotope effect (KIE) of 1 007 An estimated endmember delta C-13 value of -32 parts per thousand
in the HAKUREI fluid was obtained Both the plumes above the HAKUREI and JADE sites showed C-1/C-2
ratios between 10(3)similar to 10(4) Only the bottom water around the HAKUREI site showed
significant N2O excess with isotopically light delta N-15 and delta O-18, suggesting N2O input
from microbial activity in the sediment A linear con elation between H-2 and CH4 in the HAKUREI
plume gives a H-2/CH4 ratio of the HAKUREI fluid of more than 0 022 The estimated H-2/CH4 ratio
in the HAKUREI fluid is significantly higher than that of the JADE fluid comparable with those of
fluids venting at other sediment related hydrothermal systems, and also comparable with those of
thermogenic gases produced by hydrothermal sediment experiments These facts suggest that fluid
sediment interaction during fluid upwelling appears to modify gas geochemical characteristics at
the HAKUREI site but have little influence at the JADE site This study demonstrates the
availability of the Izena Cauldron hydrothermal field and the HAKUREI and JADE sites as a natural
laboratory for investigating the fluid-sediment interaction during fluid upwelling 
hydrothermal plume; gas geochemical characteristics; Okinawa; Trough; H-2/CH4 ratio fluid sediment interaction