Dataset Information

Abiotic hydrogen (H₂) sources and sinks near the Mid-Ocean Ridge (MOR) with implications for the subseafloor biosphere.

ABSTRACT: Free hydrogen (H₂) is a basal energy source underlying chemosynthetic activity within igneous ocean crust. In an attempt to systematically account for all H₂ within young oceanic lithosphere (<10 Ma) near the Mid-Ocean Ridge (MOR), we construct a box model of this environment. Within this control volume, we assess abiotic H₂ sources (?6 × 10¹² mol H₂/y) and sinks (?4 × 10¹² mol H₂/y) and then attribute the net difference (?2 × 10¹² mol H₂/y) to microbial consumption in order to balance the H₂ budget. Despite poorly constrained details and large uncertainties, our analytical framework allows us to synthesize a vast body of pertinent but currently disparate information in order to propose an initial global estimate for microbial H₂ consumption within young ocean crust that is tractable and can be iteratively improved upon as new data and studies become available. Our preliminary investigation suggests that microbes beneath the MOR may be consuming a sizeable portion (at least ?30%) of all produced H₂, supporting the widely held notion that subseafloor microbes voraciously consume H₂ and play a fundamental role in the geochemistry of Earth's ocean-atmosphere system.

SUBMITTER: Worman SL

PROVIDER: S-EPMC7306814 | biostudies-literature | 2020 Jun

REPOSITORIES: biostudies-literature

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Publications

Abiotic hydrogen (H2) sources and sinks near the Mid-Ocean Ridge (MOR) with implications for the subseafloor biosphere.

Worman Stacey L SL Pratson Lincoln F LF Karson Jeffrey A JA Schlesinger William H WH

Proceedings of the National Academy of Sciences of the United States of America 20200601 24

Free hydrogen (H2) is a basal energy source underlying chemosynthetic activity within igneous ocean crust. In an attempt to systematically account for all H2 within young oceanic lithosphere (<10 Ma) near the Mid-Ocean Ridge (MOR), we construct a box model of this environment. Within this control volume, we assess abiotic H2 sources (∼6 × 1012 mol H2/y) and sinks (∼4 × 1012 mol H2/y) and then attribute the net differenc ...[more]

PMID: 32482880

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Project description:Textures and compositions of minerals can be used to infer the physiochemical conditions present within magmatic systems. Given that plagioclase is an abundant phase in many magmatic systems, understanding the link between texture and process is vital. Here, we present a database of textural and compositional data for?>?1800 plagioclase crystals in mid-ocean ridge basalt from the Gakkel Ridge (Arctic Ocean) to investigate the physiochemical conditions and processes that govern the formation of plagioclase textures and compositions. The Gakkel basalts have high modal crystal contents (up to 50%). The crystal cargo is complex, with both individual plagioclase and glomerocrysts showing large variations in crystal habit, zoning and resorption. The most common types of zoning are reverse and patchy; we attribute patchy zoning to infilling following either skeletal growth or resorption. Resorption is abundant, with multiple resorption events commonly present in a single crystal, and results from both magmatic recharge and decompression. Periods of strong undercooling, distinct to quench crystallisation, are indicated by matured skeletal crystals and thin normally zoned melt inclusion-rich bands following resorption. Individual samples often contain diverse textural and compositional plagioclase groups. Furthermore, most plagioclase is not in equilibrium with its host melt. Finally, the porous open structures of some glomerocrysts suggest that they represent pieces of entrained disaggregated mush. We interpret this to indicate that the crystal cargo is not generally phenocrystic in origin. Instead, plagioclase crystals that formed in different parts of a mush-dominated plumbing system were entrained into ascending melts. The textures of individual crystals are a function of their respective histories of (under)cooling, magma mixing and decompression. The morphologies of melt inclusion trapped in the plagioclase crystals are associated with specific host crystal textures, suggesting a link between plagioclase crystallisation processes and melt inclusion entrapment. The database of plagioclase presented herein may serve as a template for the interpretation of plagioclase textures in magmatic systems elsewhere.

Dataset Information

Abiotic hydrogen (H₂) sources and sinks near the Mid-Ocean Ridge (MOR) with implications for the subseafloor biosphere.

Publications

Abiotic hydrogen (H<sub>2</sub>) sources and sinks near the Mid-Ocean Ridge (MOR) with implications for the subseafloor biosphere.

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