Microbes control the decomposition of organic matter inmarine sediments. Decomposition, in turn, contributes to oceanic nutrient regeneration and influences the preservation of organic carbon1. Generally, rates of benthic decomposition decline with increasing water depth, although given the vast extent of the abyss, deep-sea sediments are quantitatively important for the global carbon cycle2,3. However, the deepest regions of the ocean have remained virtually unexplored4. Here, we present observations of microbial activity in sediments at Challenger Deep in the Mariana Trench in the central west Pacific, which at almost 11,000 m depth represents the deepest oceanic site on Earth. We used an autonomous micro-profiling system to assess benthic oxygen consumption rates. We show that although the presence of macrofauna is restricted at Challenger Deep, rates of biological consumption of oxygen are high, exceeding rates at a nearby 6,000-m-deep site by a factor of two. Consistently, analyses of sediments collected from the two sites reveal higher concentrations of microbial cells at Challenger Deep. Furthermore, analyses of sediment 210Pb profiles reveal relatively high sediment deposition in the trench. We conclude that the elevated deposition of organic matter at Challenger Deep maintains intensified microbial activity at the extreme pressures that characterize this environment.
We thank A. Glud, R. Abell, T. Brand, B. Christensen, J. P. Meyer, J. Hansen, M. Alisch and T. Sakamoto for excellent technical assistance as well as T. Toyofuku for administrative organization. Further, we wish to thank the Captain and crew of R/V Yokosuka (YK10-16). The study was financially supported by JAMSTEC, the Natural Environment Research Council (NERC, NE/F018612/1; NE/F0122991/1, NE/G006415/1), the commission for Scientific Research in Greenland (KVUG; GCRC6507), ERC through an Advanced Grant (ERC-2010-AdG20100224), the Danish National Research Foundation (DNRF53), The Max Planck Society, The Danish Council for Independent Research (FNU-09-072829), The DFG Research Center MARUM, and Grants-in-Aid for Scientific Research (21244079) from the Ministry of Education, Culture, Sports, Science and Technology of Japan. E. Epping and J. Kallmeyer provided constructive comments that helped improve the manuscript.