CLUES TO MODERN AND ANCIENT METHANE RELEASE: LIVING BENTHIC FORAMINIFERA ASSOCIATED WITH COLD METHANE SEEPS OF MONTEREY BAY, CALIFORNIA

Climatic changes in the Late Paleocene and the Quaternary have been associated with changes in marine methane flux. Although ancient release of marine methane has been inferred from the stable isotopic compositions of fossil benthic foraminifera, few modern analog data exist to assess the characteristics of foraminifera associated with methane seepage. Using the MBARI submersible Ventana,we collected cores from two methane seepage areas (960 m) in Monterey Bay, California.  We examined the distribution, pore water chemistry and stable isotopic composition of living (Rose Bengal stained) benthic foraminifera (>150µm) taken from bacterial mats, clam beds, and a few meters away from the clam beds. Pore water chemistry results suggest that strong advection of sulfide-containing fluids occurred in the bacterial mat compared to the other habitats examined. Benthic foraminifera living in non-seep habitats typically have very low carbon isotopic variability (0.2 per mil or less). Foraminifera living at the same depths within seep sediments, however, had highly variable carbon isotopic values (range over 1.0 per mil for Uvigerina peregrinaand range about 2.6 per mil for Gobobulimina barbata).All of the calcareous species identified from these seeps have been previously found in non-seep environments. Foraminiferal distribution patterns within clam bed sediments have high subsurface variability and are different than distribution patterns in adjacent habitats outside of the clam beds. Results from this study will yield better understanding of the timing and extent of methane release inferred from fossil foraminifera.