Nutrient Supply To Planetary Biospheres From Anoxic Weathering Of Mafic Oceanic Crust

By Keith Cowing
June 8, 2021
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Nutrient Supply To Planetary Biospheres From Anoxic Weathering Of Mafic Oceanic Crust
(a) Representative electron microscopy maps of Al, Fe, and P from grains derived from ground basalt sampled from the Juan de Fuca Ridge used in the seafloor weathering experiments. Phosphorus is concentrated along areas of altered grains that are concentrated in Fe, attributable to a mixture of secondary Fe3+ -oxide minerals and clays formed upon interaction with seawater at the sampling location. (b) Activity diagram showing the speciation of phosphorus in solution as a function of pH and solution redox state (Eh) at 25ºC. The open circle shows the conditions of our seafloor weathering experiments, while the grey lines show the stability limits of water. Hot colors towards red represent high concentrations of the element of interest.

Phosphorus is an essential element for life, and the phosphorous cycle is widely believed to be a key factor limiting the extent of Earth’s biosphere and its impact on remotely detectable features of Earth’s atmospheric chemistry.

Continental weathering is conventionally considered to be the only source of bioavailable phosphorus to the marine biosphere, with submarine hydrothermal processes acting as a phosphorus sink. Here, we use a novel 29Si tracer technique to demonstrate that alteration of submarine basalt under anoxic conditions leads to significant soluble phosphorus release, with an estimated ratio between phosphorus release and CO2 consumption (P/CO2) of 3.99+/-1.03 umol/mmol. This ratio is comparable to that of modern rivers, suggesting that submarine weathering under anoxic conditions is potentially a significant source of bioavailable phosphorus to planetary oceans and that volatile-rich Earth-like planets lacking exposed continents could develop robust biospheres capable of sustaining remotely detectable atmospheric biosignatures.

Drew D. Syverson, Christopher T. Reinhard, Terry T. Isson, Cerys Holstege, Joachim Katchinoff, Benjamin M. Tutolo, Barbara Etschmann, Joël Brugger, Noah J. Planavsky

Comments: Manuscript under consideration in Geophysical Research Letters
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2002.07667 [astro-ph.EP] (or arXiv:2002.07667v2 [astro-ph.EP] for this version)
Submission history
From: Christopher Reinhard
[v1] Tue, 18 Feb 2020 15:58:11 UTC (6,404 KB)
[v2] Fri, 4 Jun 2021 18:46:14 UTC (546 KB)
Astrobiology, Astrochemistry,

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