18O
of the interstitial waters of the Blake Ridge sediments tends to decrease with
depth from +0.5
SMOW of the bottom seawater value to about -0.5
at around 300 mbsf, then recover to +0.2
at ~700 mbsf.1. The 18O
of the interstitial waters of the Blake Ridge sediments tends to decrease with
depth from +0.5
SMOW of the bottom seawater value to about -0.5
at around 300 mbsf, then recover to +0.2
at ~700 mbsf.
2. Interstitial waters squeezed from gas hydrate-bearing sediments are significantly and variably enriched in 18O, reflecting the donation of 18O-enriched water derived from dissociated gas hydrate to pore waters.
3. The 18O
anomalies within the gas hydrate zone correlate with chloride anomalies.
4. Calculated equilibrium
fractionation factors (
)
between natural gas hydrates and interstitial waters are 1.0034 at Site 994 and
1.0037-1.0040 at Site 997.
5. The 18O
anomalies within the gas hydrate zone indicate mean values of about 6% (pore
saturation) at Site 994 and 12% at Site 997, which are about twice as much as
those estimated from chloride anomalies.
6. Uncertainty in the in
situ chloride concentration and in situ 18O
value is thought to be the major factor for the discrepancy in gas hydrate
estimates. Development of new coring/sampling technology to recover in situ pore
waters is crucial to improve volume estimates of marine gas hydrates.
