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a
b
c
CH 4 (µmol/kg)
10 - 1
CO 2 (mmol/kg)
H 2 (µmol/kg)
10 1
10 3
10 5
10 2
10 3
0
20
40 0
1
10
0
0
0
1
1
1
2
2
2
3
3
3
4
4
4
d
e
f
δ 13 C CH4 (‰)
- 120
δ 13 C CO2 (‰)
- 60 - 40
δ D H2 (‰)
- 80
- 40
- 20
0
- 760
- 750
- 740
0
0
0
1
1
1
2
2
2
3
3
3
4
4
4
g
( 3 He/ 4 He) corr (R atm )
0.1
0
0.2
0
1
2
3
4
Fig. 4 Chemical and isotopic compositions of dissolved gases in pore water from Oomine Ridge.
Open symbols denote water samples and solid symbols denote gas samples
Fig. 5 Plot of 3 He/ 4 He and
4 He/ 20 Ne ratios of gas
samples from Oomine Ridge
of this study ( dots ) and those
of Nankai Trough ( crosses )
from Sano and Wakita
( 1987 ). Dashed lines are
mixing lines between mantle-
derived He and air-saturated
seawater at 0°C (ASW) and
between crustal radiogenic
He and ASW
10
Mantle
ASW
1
0.1
Crust
0.01
0.1
1
10
100
1000
4 He/ 20 Ne
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