CAN BENTHIC FORAMINIFERA BE USED AS INDICATORS OF CLATHRATE DISSOCIATION?

Frozen methane hydrates (clathrates), represent a tremendous store of methane beneath the ocean floor. Workers have recently suggested that clathrates and their subsequent emissions play significant roles in the global climate system. The geochemistry of fossil benthic foraminifera have been used as indicators of ancient methane release. Examination of modern and fossil assemblages of benthic foraminifera from Pacific margin seeps indicates that the stable isotopic geochemistry of benthic foraminifera may be useful as an indicator of methane dissociation. Carbon isotope values of living (rose Bengal stained) benthic foraminifera from the California Margin off Eel River and in Monterey Bay do not reflect the negative (up to -48 per mil) values of the pore waters they inhabit. However, the range of delta 13C values of some species (2.6 per mil for Globobulimina barbata and over 1.0 per mil for Uvigerina peregrina) far exceed the non-seep variation of about 0.2-0.4 per mil. Fossil specimens have a far greater range in delta 13C values. The vertical distribution of living specimens within seep sediments may also be affected by methane-influenced pore waters. Results from this study indicate that high variability of delta 13C values within benthic foraminiferal species can indicate methane seepage.