Bacterial abundances and pore water acetate concentrations in sediments of the Southern Ocean (Sites 1088 and 1093)

• Main Authors: Wellsbury, Peter, Mather, I. D., Parkes, Ronald John
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Ocean Drilling Program 2001
• Subjects: QE Geology; QR Microbiology; Southern Ocean
• Online Access: https://orca.cardiff.ac.uk/id/eprint/8677/; http://www-odp.tamu.edu/publications/177_SR/chap_03/chap_03.htm; https://doi.org/10.2973/odp.proc.sr.177.109.2001

Bacterial populations and pore water acetate concentrations were quantified at two sites in the southeast Atlantic sector of the Southern Ocean during Ocean Drilling Program (ODP) Leg 177. Bacterial abundances in the carbonate-rich, low organic carbon Sites 1088 and 1093 were lower than the general trend for bacteria in deep marine sediments. Site 1088, which is ~10° closer to the equator and only approximately half the water depth of Site 1093, had the lowest bacterial populations. Calcium carbonate was ~10 times more abundant in Site 1088 sediments (average = 88.2 wt%) compared to Site 1093 (average = 9.2 wt%). Thus, neither latitude nor water depth is as significant as organic carbon in controlling bacterial distributions. Including data for carbonate-rich sediments to a previous model, the global bacterial biomass in marine sediments extrapolates to ~10.2% of living carbon in the surface biosphere. Pore water acetate concentrations at both sites were generally low (0-15 µM). At Site 1093 many acetate peaks (to 110 µM) were present, probably because of the presence of localized diatom-rich laminae in the sediments. The low acetate concentrations are in marked contrast with data from gas hydrate sediments at Blake Ridge (ODP Leg 164), where concentrations exceeded 15,000 µM by ~700 m below seafloor, suggesting that high acetate concentrations may be a characteristic of gas hydrate sediments and not the general situation in deep marine sediments.