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Global niche of marine anaerobic metabolisms expanded by particle microenvironments


In ocean waters, anaerobic microbial respiration should be confined to the anoxic waters found in coastal regions and tropical oxygen minimum zones, where it is energetically favourable. However, recent molecular and geochemical evidence has pointed to a much broader distribution of denitrifying and sulfate-reducing microbes. Anaerobic metabolisms are thought to thrive in microenvironments that develop inside sinking organic aggregates, but the global distribution and geochemical significance of these microenvironments is poorly understood. Here, we develop a new size-resolved particle model to predict anaerobic respiration from aggregate properties and seawater chemistry. Constrained by observations of the size spectrum of sinking particles, the model predicts that denitrification and sulfate reduction can be sustained throughout vast, hypoxic expanses of the ocean, and could explain the trace metal enrichment observed in particles due to sulfide precipitation. Globally, the expansion of the anaerobic niche due to particle microenvironments doubles the rate of water column denitrification compared with estimates based on anoxic zones alone, and changes the sensitivity of the marine nitrogen cycle to deoxygenation in a warming climate.

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Fig. 1: Particle size spectrum and microenvironment model schematic.
Fig. 2: Predicted microenvironment distributions at two sites in the tropical ocean.
Fig. 3: Microenvironment-driven accumulation of trace metals in the tropical North Atlantic.
Fig. 4: Expanded niche of anaerobic metabolism in the ocean.
Fig. 5: Sensitivity of particle denitrification to climate-forced oxygen trends.


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D.B. was supported by NSF grant OCE-1635632; T.S.W. was supported by NSF grant OCE-1635414; C.D. was supported by the Gordon and Betty Moore Foundation (GBMF 3775); and R.K. was supported by the German Science Foundation through the Collaborative Research Center 754 ‘Climate-Biogeochemistry Interactions in the Tropical Ocean’. We thank D. Janssen and S. John for providing trace metal data from the Mauritanian region. We further acknowledge J. Coindat and S. Fevre of Hydroptic, and L. Stemman and M. Picheral for support during work with the UVP5.

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D.B. and T.S.W. conceived the project, developed the microenvironment and particle models, conducted the simulations and analysed output, with contributions from C.D. R.K. provided UVP5 particle observations and suggested their use for model validation. D.B. and T.S.W. wrote the paper, with contributions from C.D. and R.K.

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Correspondence to Daniele Bianchi.

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Code for the particle microenvironment model, in Matlab

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Bianchi, D., Weber, T.S., Kiko, R. et al. Global niche of marine anaerobic metabolisms expanded by particle microenvironments. Nature Geosci 11, 263–268 (2018).

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