Abundance, distribution and δ13C analysis of microbial phospholipid-derived fatty acids in a black shale weathering profile

Abstract

Phospholipid ester-linked fatty acids [PFLA] were isolated from a weathering profile developed on Ohio Shale. PLFA distributions were used to describe the microbial communities living in this weathering profile. PLFA are interpreted as mixed aerobic (eukaryote+prokaryote) and anaerobic communities, with a very distinct PLFA distribution at 40–50 cm depth in the core. This depth in the weathering profile corresponds to the onset of shale OM loss and the accumulation of Fe3+ and soil OM. Stable carbon isotopic analysis of PFLA reveals complex patterns of isotopic enrichment and depletion for individual PFLA relative to bulk soil and shale OM. PLFA δ13C values suggest at least some assimilation of shale OM by anaerobic microorganisms. This phospholipids study reveals that weathering profiles developed on black shales are environments of degradation of ancient OM and both accumulation and degradation of more modern soil OM, highlighting the complexity of near-surface microbial processes in sedimentary rocks.