14C-Dead Living Biomass: Evidence for Microbial Assimilation of Ancient Organic Carbon During Shale Weathering
S. T. Petsch,*
T. I. Eglinton,
K. J. Edwards
Prokaryotes have been cultured from a modern weathering profile
developed on a ~365-million-year-old black shale that use macromolecular shale organic matter as their sole organic carbon source. Using natural-abundance carbon-14 analysis of membrane lipids,
we show that 74 to 94% of lipid carbon in these cultures derives from
assimilation of carbon-14-free organic carbon from the shale. These
results reveal that microorganisms enriched from shale weathering
profiles are able to use a macromolecular and putatively refractory
pool of ancient organic matter. This activity may facilitate the
oxidation of sedimentary organic matter to inorganic carbon when
sedimentary rocks are exposed by erosion. Thus, microorganisms may play
a more active role in the geochemical carbon cycle than previously
recognized, with profound implications for controls on the abundance of
oxygen and carbon dioxide in Earth's atmosphere over geologic time.
Department of Marine Chemistry and Geochemistry, Woods Hole
Oceanographic Institution, Woods Hole, MA 02543, USA.
*
To whom correspondence should be addressed. E-mail:
spetsch{at}whoi.edu
