N transformations in hydrothermal systems are considered to be an important potential source of pre-biotic compounds on early Earth, and may be similarly significant on other planets. We provided the first constraints on the processes that remove reactive N from hydrothermal vent plumes, which ultimately impact chemosynthetic primary productivity and carbon fluxes in hydrothermal vent fluids. Increases in the isotopic composition of NH4  and NO3 , concomitant with decreased concentrations signaled biological consumption in the subsurface at some diffuse (<50°C) vent sites from the Juan de Fuca Ridge in the Northeast Pacific. Furthermore, dual (δ  N and δ  O) NO3  isotope signatures confirmed NO3  regeneration from NH4  oxidation and/or N2 fixation in vent fluids (Bourbonnais et al., 2012a). Rate measurements from   N-labeled incubations clearly showed that denitrification was by far the dominant N-loss pathway in terms of both activity and bacterial gene abundance in sulfidic diffuse hydrothermal vent waters. With quantitative polymerase chain reaction, we further identified an NO3  -reducing, sulfur-oxidizing gammaproteobacteria dominating total bacterial abundance. From our results, we estimated that up to ~10 Tg N yr   (up to 7% of the global marine N-loss estimates) could be removed globally in the subsurface biosphere (Bourbonnais et al., 2012b, Bourbonnais et al., 2013).

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Relevant publications:

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Wankel, S. D., A. Bourbonnais, and C. N. Charoenpong (2017), Microbial nitrogen cycling processes at submarine hydrothermal vents, In Kallmeyer, Jens and Wagner, Dirk (Ed.), Life in Extreme Environments, Life at Vents and Seeps, Volume 5, Berlin, Boston: De Gruyter, pp. 179-221.

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Bourbonnais, A., S. K. Juniper, D. A. Butterfield, R. E. Anderson, M. F. Lehmann (2014), Diversity and abundance of Bacteria and nirS-encoding denitrifiers associated with the Juan de Fuca Ridge hydrothermal system, Annals of Microbiology, 64, 1691–1705.

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Bourbonnais, A., S. K. Juniper, D. A. Butterfield, A. H. Devol, M. M. M. Kuypers, G. Lavik, S. J. Hallam, C. B. Wenk, B. X. Chang, S. A. Murdock, and M. F. Lehmann (2012b), Activity and abundance of denitrifying bacteria in the subsurface biosphere of diffuse hydrothermal vents of the Juan de Fuca Ridge, Biogeosciences, 9, 4661–4678.

 

Bourbonnais, A., M. F. Lehmann, D. A. Butterfield, and S. K. Juniper (2012a), Subseafloor nitrogen transformations in diffuse hydrothermal vent fluids of the Juan de Fuca Ridge evidenced by the isotopic composition of nitrate and ammonium, Geochemistry Geophysics Geosystems, 13, Q02T01, doi:10.1029/2011GC003863.