Monday, 15 December 2014
Emily A Walsh1, John B Kirkpatrick1, Robert A Pockalny1, Justine Sauvage1, Mitchell L Sogin2 and Steven D'Hondt1, (1)University of Rhode Island, Narragansett, RI, United States, (2)Marine Biological Laboratory, Woods Hole, MA, United States
Subseafloor sediment hosts to a large1, taxonomically rich2 and metabolically diverse3 microbial ecosystem. However, the factors that control microbial diversity in subseafloor sediment have rarely been explored. Here we show that subseafloor bacterial richness varies directly with sediment age and net rate of organic-fueled respiration. We examined three open-ocean sites (in the Bering Sea and equatorial Pacific) and one continental margin site (Indian Ocean), with sediment depths to 404 meters below seafloor. At all locations, taxonomic richness decreases exponentially with increasing sediment age. Richness declines most rapidly for a few hundred thousand years after sediment deposition. This profile generally matches the canonical relationship between rates of organic oxidation and sediment age 4. To examine the potential link between organic oxidation and taxonomic richness we used pore-water chemical profiles to quantify net rates of organic respiration at the three open-ocean sites (the chemical profiles of the ocean-margin site are not in diffusive steady state). Taxonomic richness and total rate of organic-fueled respiration are highest at the high productivity Bering Sea site and lower at the moderate productivity equatorial Pacific sites. At each of these sites, organic-fueled respiration rate and taxonomic richness are highest at the surface and decline together as sediment depth and age increase. To our knowledge, this is the first evidence that taxonomic richness is closely linked to organic-fueled respiration rate and sediment age in subseafloor sediment.


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2. Inagaki, F. et al. Proceedings of the National Academy of Sciences 103, 2815-2820 (2006).

3. D'Hondt, S. et al. Science 306, 2216-2221, doi:10.1126/science.1101155 (2004).

4. Middelburg, J. J. Geochimica et Cosmochimica Acta 53, 1577-1581, doi:http://dx.doi.org/10.1016/0016-7037(89)90239-1 (1989).