Iron-dependent nitrogen cycling in a ferruginous lake and the nutrient status of Proterozoic oceans

Céline C. Michiels, Francois Darchambeau, Fleur A. E. Roland, Cédric Morana, Marc Llirós, Tamara García-Armisen, Bo Thamdrup, Alberto V. Borges, Donald Eugene Canfield, Pierre Servais, Jean-Pierre Descy, Sean Andrew Crowe

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Nitrogen limitation during the Proterozoic has been inferred from the great expanse of ocean anoxia under low-O2
atmospheres, which could have promoted NO3
􀀀 reduction to N2 and fixed N loss from the ocean. The deep oceans were Fe
rich (ferruginous) during much of this time, yet the dynamics of N cycling under such conditions remain entirely conceptual,
as analogue environments are rare today. Here we use incubation experiments to show that a modern ferruginous basin,
Kabuno Bay in East Africa, supports high rates of NO3
􀀀 reduction. Although 60% of this NO3
􀀀 is reduced to N2 through
canonical denitrification, a large fraction (40%) is reduced to NH4
C, leading to N retention rather than loss.We also find that
􀀀 reduction is Fe dependent, demonstrating that such reactions occur in natural ferruginous water columns. Numerical
modelling of ferruginous upwelling systems, informed by our results from Kabuno Bay, demonstrates that NO3
􀀀 reduction
to NH4
C could have enhanced biological production, fuelling sulfate reduction and the development of mid-water euxinia
overlying ferruginous deep oceans. ThisNO3
􀀀 reduction to NH4
C could also have partly oset a negative feedback on biological
production that accompanies oxygenation of the surface ocean. Our results indicate that N loss in ferruginous upwelling
systems may not have kept pace with global N fixation at marine phosphorous concentrations (0.04–0.13 M) indicated by
the rock record. We therefore suggest that global marine biological production under ferruginous ocean conditions in the
Proterozoic eon may thus have been P not N limited.
TidsskriftNature Geoscience
Sider (fra-til)217-221
StatusUdgivet - mar. 2017



Michiels, C. C., Darchambeau, F., Roland, F. A. E., Morana, C., Llirós, M., García-Armisen, T., Thamdrup, B., Borges, A. V., Canfield, D. E., Servais, P., Descy, J-P., & Crowe, S. A. (2017). Iron-dependent nitrogen cycling in a ferruginous lake and the nutrient status of Proterozoic oceans. Nature Geoscience, 10, 217-221.