Methane-Based Life in a Deep-Sea Concrete Jungle

Presenter: Victoria Orphan, California Institute of Technology
When: April 21, 2014 11AM PDT

Deep-sea authigenic carbonates are a common byproduct of sulfate-coupled methane oxidation, frequently paving extensive areas of the seafloor within and surrounding areas of active methane seepage. These carbonates record the diagnostically light carbon isotopic signature of methane within the inorganic and organic fractions and serve as a longstanding record of past methane seepage. Substantial research has been conducted on the geochemical, mineralogical, isotopic and organic signatures of authigenic carbonates in both modern and paleo-seep settings.

However, the extent to which seep carbonates represent a viable habitat for anaerobic methanotrophs and how these microbial assemblages may respond to changing environmental conditions is poorly understood. Integrating FISH microscopy and secondary ion mass spectrometry (SIMS-based) stable isotope analysis of carbonate-associated cells with conventional radioisotope rate assays and molecular microbiological approaches, we demonstrate these lithified systems support active and abundant endolithic microorganisms capable of net anaerobic methane-oxidation. Year-long ecological colonization and transplant experiments at the seabed, between areas of active seepage and locations of low methane flux, further enabled the examination of short term shifts in the carbonate-associated archaeal and bacterial community in response to seepage activity. Together, this work highlights the importance of authigenic carbonates as an additional sink for methane and as a dynamic endolithic niche for anaerobic methane oxidizing microorganisms.

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