High rates of microbial carbon turnover in sediments in the deepest oceanic trench on Earth

Journal name:
Nature Geoscience
Volume:
6,
Pages:
284–288
Year published:
DOI:
doi:10.1038/ngeo1773
Received
Accepted
Published online

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 11,000m 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.

At a glance

Figures

  1. Photos of the sediment surface at the two sites.
    Figure 1: Photos of the sediment surface at the two sites.

    a,b, The sea floor at the reference site (6,037m water depth; a) and at Challenger Deep (10,900m water depth; b). Photos were grabbed from high-definition video recordings. In both photos, the sediment surfaces show micro-topographic variations, mounds, depressions and tracks as formed by fauna activity. Scavenging amphipods (seen in b) were moving in and out of the sediment at both sites, but most intensively at the reference station.

  2. Benthic O2 distribution measured in situ at the two sites.
    Figure 2: Benthic O2 distribution measured in situ at the two sites.

    a,b, O2 micro-profiles at the reference site (6,018m water depth; a) and at Challenger Deep (10,817m water depth; b). Altogether, 36 and 51 micro-profiles were measured at the two sites, respectively. The horizontal dashed line indicates the estimated position of the sediment surface. The faster attenuation in O2 concentration at the trench site reflects intensified O2 consumption within the sediment.

  3. Sediment characteristics at the two sites.
    Figure 3: Sediment characteristics at the two sites.

    af, Organic carbon content, phytopigment concentration and prokaryotic abundances of sediment from the reference site (Ref; a,c,e) and Challenger Deep (CD; b,d,f). Error bars on the respective depth profiles reflect ±1s.d. on triplicate analysis of sediment samples from given sediment cores (core names are indicated). Depth profiles in b,f reflect parallel measurements in two separate sediment cores recovered during the same instrument deployment.

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Affiliations

  1. University of Southern Denmark, Nordic Centre for Earth Evolution, 5230 Odense M, Denmark

    • Ronnie N. Glud &
    • Donald E. Canfield
  2. Scottish Association for Marine Science, Scottish Marine Institute, Oban PA37 1QA, UK

    • Ronnie N. Glud &
    • Robert Turnewitsch
  3. Greenland Climate Research Centre, 3900 Nuuk, Greenland

    • Ronnie N. Glud
  4. Max Planck Institute for Marine Microbiology, 28359 Bremen, Germany

    • Frank Wenzhöfer
  5. Alfred-Wegener-Institute for Polar and Marine Research, 27570 Bremerhaven, Germany

    • Frank Wenzhöfer
  6. University of Copenhagen, Marine Biological Section, 3000 Helsingør, Denmark

    • Mathias Middelboe
  7. Japan Agency for Marine-Earth Science and Technology, Institute of Biogeosciences, Yokosuka, Kanagawa 237-0061, Japan

    • Kazumasa Oguri &
    • Hiroshi Kitazato
  8. Japan Agency for Marine-Earth Science and Technology, Marine Technology and Engineering Center, Yokosuka, Kanagawa 237-0061, Japan

    • Kazumasa Oguri

Contributions

R.N.G. and D.E.C. wrote the manuscript. R.N.G., F.W., M.M., K.O. and R.T. carried out the measurements, and performed the analytical work and the theoretical analyses. H.K., K.O., R.N.G., F.W. and M.M. helped organize and realize the expedition. All authors discussed the results and their implications and commented on the manuscript as it progressed.

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The authors declare no competing financial interests.

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