HR: 0830h
AN: OS31C-0217    [PDF]
TI: Helium isotopes and heavier noble gas abundances of water in adjacent sea of Japan
AU: * Sano, Y
EM: ysano@ori.u-tokyo.ac.jp
AF: Ocean Research Institute, The University of Tokyo, 1-15-1 Minamidai, Nakanoku, Tokyo, 164-8639 Japan
AU: Takahata, N
EM: ntaka@ori.u-tokyo.ac.jp
AF: Ocean Research Institute, The University of Tokyo, 1-15-1 Minamidai, Nakanoku, Tokyo, 164-8639 Japan
AU: Watanabe, T
EM: nabe@ori.u-tokyo.ac.jp
AF: Ocean Research Institute, The University of Tokyo, 1-15-1 Minamidai, Nakanoku, Tokyo, 164-8639 Japan
AU: Shirai, K
EM: shirai@ori.u-tokyo.ac.jp
AF: Ocean Research Institute, The University of Tokyo, 1-15-1 Minamidai, Nakanoku, Tokyo, 164-8639 Japan
AU: Nishizawa, M
EM: nishizawa@ori.u-tokyo.ac.jp
AF: Ocean Research Institute, The University of Tokyo, 1-15-1 Minamidai, Nakanoku, Tokyo, 164-8639 Japan
AB: We have measured helium isotopic ratios of water samples collected with various depths in adjacent sea of Japan. The $^{3}$He/$^{4}$He ratios vary significantly from 0.989 Ratm to 1.242 Ratm where Ratm is the atmospheric ratio of 1.39x10$^{-6}$. It is confirmed that all deep sea water (2000 - 2500 m) of western North Pacific is affected by the mantle helium with a high $^{3}$He/$^{4}$He ratio. More precisely mid-depth (750 - 1500 m) profiles of $^{3}$He/$^{4}$He ratios of northwestern Philippine Sea (Nansei Trench) and east of East China Sea (northeast and southwest of Okinawa Trough) are higher than those of western North Pacific (Off Joban) and comparable to those of northern Philippine Sea (Nankai Trough). Excess $^{3}$He of the mid-depth samples may be attributable to the subduction-type mantle helium originated from high-temperature hydrothermal sites in the Okinawa Trough. Noble gas abundances (neon, argon, krypton and xenon) were measured in water samples collected in western North Pacific and northwestern Philippine Sea. Neon abundances show slight excess relative to air saturated sea water at ambient temperature and salinity. This may be due to either air bubble effect or contamination during the sampling. When these effects are corrected using the neon anomaly, heavier noble gas abundances (argon, krypton and xenon) of samples with the temperature higher than $5\deg$C (shallower than 500m) agree well with those of calculated air saturated seawater, while the lower temperature samples (deeper than 500 m) indicate anomaly of -7% to +10%.
DE: 1040 Isotopic composition/chemistry
DE: 1050 Marine geochemistry (4835, 4850)
DE: 4808 Chemical tracers
DE: 4820 Gases
DE: 4894 Instruments and techniques
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting