Subsurface viruses and bacteria in Holocene/Late Pleistocene sediments of Saanich Inlet, BC: ODP Holes 1033B and 1034B, Leg 169S

Abstract

Little is known of long-term processes affecting microbial abundance in buried marine sediments. In collaboration with geochemists and sedimentologists involved in ODP Leg169S, we undertook a study of bacterial and viral abundance throughout the entire Holocene sediment section in Saanich Inlet, British Columbia, Canada. Sediments were sampled at 1.5-m intervals from the sediment surface down into Pleistocene sequences at depths of >100 m. Preparations of formalin-fixed sediment were stained with the nucleic acid stain Yo-Pro and bacteria and viruses were enumerated using epifluorescence microscopy. Viral presence was confirmed by electron microscopy. More widely spaced measurements of adenosine triphosphate (ATP) and the biogenic pore water gases H2, CH4 and CO were used as indices of microbial metabolic activity. Bacterial and viral abundances were high (>109 gdw−1) in these organic-rich sediments relative to oceanic areas, and were highly correlated, indicating a probable close functional dependence characteristic of predator–prey relations. The upper Holocene section showed a significant subsurface peak in microbial abundance that was correlated negatively with sediment organic matter content, but corresponded with biogenic gas accumulation. The interpretation of these and other significant trends is discussed in relation to the Holocene/late Pleistocene history of organic matter sedimentation and diagenetic processes.