biological production
; concentration (composition)
; iron
; lacustrine environment
; nitrogen cycle
; nutrient dynamics
; phosphorus
; Proterozoic
; upwelling
; water column
; water retention
; East Africa
英文摘要:
Nitrogen limitation during the Proterozoic has been inferred from the great expanse of ocean anoxia under low-O 2 atmospheres, which could have promoted NO 3 â ' reduction to N 2 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 NO 3 â ' reduction. Although 60% of this NO 3 â ' is reduced to N 2 through canonical denitrification, a large fraction (40%) is reduced to NH 4 +, leading to N retention rather than loss. We also find that NO 3 â ' 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 NO 3 â ' reduction to NH 4 + could have enhanced biological production, fuelling sulfate reduction and the development of mid-water euxinia overlying ferruginous deep oceans. This NO 3 â ' reduction to NH 4 + could also have partly offset 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 μM) 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.
Microbiology and Immunology and Earth, Ocean, and Atmospheric Sciences Departments, University of British Columbia, Vancouver, BC, Canada; Chemical Oceanography Unit, Université de Liège, Liège, Belgium; Department of Earth AndEnvironmental Sciences, KU Leuven, Leuven, Belgium; Microbiology AndImmunology Department, Universitat Autònoma de Barcelona, Barcelona, Spain; Institute of Life Sciences (ISV), Université Catholique de Louvain, Louvain-la-Neuve, Belgium; Ecologie des Systèmes Aquatiques, Université Libre de Bruxelles, Bruxelles, Belgium; Institute of Biology, Nordic Center for Earth Evolution, University of Southern Denmark, Odense, Denmark; Research Unit in Environmental and Evolutionary Biology (URBE), University of Namur, Namur, Belgium
Recommended Citation:
Michiels C.C.,Darchambeau F.,Roland F.A.E.,et al. Iron-dependent nitrogen cycling in a ferruginous lake and the nutrient status of Proterozoic oceans[J]. Nature Geoscience,2017-01-01,10(3)