Hydrothermal recycling of sedimentary ammonium into oceanic crust and the Archean ocean at 3.24 Ga
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The Archean ocean supported a diverse microbial ecosystem, yet studies suggest that seawater was largely depleted in many essential nutrients, including fixed nitrogen. This depletion was in part a consequence of inefficient nutrient recycling under anoxic conditions. Here, we show how hydrothermal fluids acted as a recycling mechanism for ammonium (NH4+) in the Archean ocean. We present elemental and stable isotope data for carbon, nitrogen, and sulfur from shales and hydrothermally altered volcanic rocks from the 3.24 Ga Panorama district in Western Australia. This suite documents the transfer of NH4+ from organic-rich sedimentary rocks into underlying sericitized dacite, similar to what is seen in hydrothermal systems today. On modern Earth, hydrothermal fluids that circulate through sediment packages are enriched in NH4+ to millimolar concentrations because they efficiently recycle organic-bound N. Our data show that a similar hydrothermal recycling process dates back to at least 3.24 Ga, and it may have resulted in localized centers of enhanced biological productivity around hydrothermal vents. Last, our data provide evidence that altered oceanic crust at 3.24 Ga was enriched in nitrogen, and, when subducted, it satisfies the elemental and isotopic source requirements for a low-N, but 15N-enriched, deep mantle nitrogen reservoir as sampled by mantle plumes.
Stueeken , E E , Boocock , T J , Robinson , A , Mikhail , S & Johnson , B 2021 , ' Hydrothermal recycling of sedimentary ammonium into oceanic crust and the Archean ocean at 3.24 Ga ' , Geology , vol. 49 , no. 7 , pp. 822-826 . https://doi.org/10.1130/G48844.1
Copyright © 2021 Geological Society of America. This work has been made available online in accordance with publisher policies or with permission. Permission for further reuse of this content should be sought from the publisher or the rights holder. This is the author created accepted manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.1130/G48844.1
DescriptionFunding was provided by a Natural Environment Research Council studentship (grant NE/R012253/1) to T.J. Boocock, and a National Science Foundation grant (grant EARPF 1725784) and an American Philosophical Society Lewis and Clark Grant, both to B.W. Johnson.
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