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Geochemistry of Fluids and Gases in the Deep Continental Subsurface and Deep-Sea Hydrothermal Vents: Abiotic and Biotic Interactions in Extreme Environments /

Record Type:	Electronic resources : Monograph/item
Title/Author:	Geochemistry of Fluids and Gases in the Deep Continental Subsurface and Deep-Sea Hydrothermal Vents: Abiotic and Biotic Interactions in Extreme Environments // William Dowd.
Author:	Dowd, William,
Description:	1 electronic resource (186 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 84-07, Section: B.
Contained By:	Dissertations Abstracts International84-07B.
Subject:	Geochemistry. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=29998354
ISBN:	9798368458342

Geochemistry of Fluids and Gases in the Deep Continental Subsurface and Deep-Sea Hydrothermal Vents: Abiotic and Biotic Interactions in Extreme Environments /
Dowd, William,

Geochemistry of Fluids and Gases in the Deep Continental Subsurface and Deep-Sea Hydrothermal Vents: Abiotic and Biotic Interactions in Extreme Environments /William Dowd. - 1 electronic resource (186 pages)

Source: Dissertations Abstracts International, Volume: 84-07, Section: B.

The work presented in this dissertation provides insights into the geochemical landscapes of novel environments in the continental and oceanic subsurface. The physical and chemical properties of fluids in deep crustal reservoirs and deep-sea hydrothermal vents directly influence the habitability of these environments. Thus, this work could have implications for the origin and evolution of life on ancient Earth and elsewhere in our solar system. High-density brines and alkane-rich gases are sourced from deep crustal reservoirs that are hosted in Neoarchean bedrock in the Soudan Underground Mine State Park, Minnesota, USA. Methane (CH4) and C2+ alkanes and alternative electron acceptors (e.g., sulfate (SO4 2-)) are viable energy sources for microorganisms in the fluids, which flow freely from boreholes at a depth of 713.5 m below the surface. Reactions involving the oxidation of alkanes by SO4 2- and NO3-, the reduction of SO4 2- and NO3- by H2, and methanogenesis from CO2 and dimethylamine (DMA) are exergonic. This study presents the first quantification of DMA abundance in a Precambrian shield brine. Dimethylamine may be actively cycled to produce biological CH4 in Soudan's fluids, based on favorable free energy for DMA-based methanogenesis (-ΔG) in kJ/mole, and little available energy per mass fluid (J/kgfluid). The observed low abundance of H2, coupled to C1-C4 abundance ratios and measured stable isotope values (e.g., ?13C, Δ13CH3D) of CH4 and C2+ alkanes allude to a thermogenic origin for C1-C4 n-alkanes, with a minor addition of biologically produced CH4, perhaps from DMA-based methanogenesis.The high volumes of reduced ∑H2S-rich hydrothermal fluid and oxidized SO4 2--rich seawater in hydrothermal systems generate oxidation-reduction (redox) boundaries that can produce intermediate redox-state sulfur species. These species may then be utilized by benthic biological communities. Thiosulfate (S2O32-) and bisulfite (HSO3- ) are present in mixed fluids collected from eight high-temperature (>250 ℃) black smoker vents and two low-temperature (<10 ℃) diffuse vents at 9°46-52'N on the East Pacific Rise. Equilibrium mixing models predict theoretical concentrations of S2O3 2- and HSO3- that compare well to measured compositions, for fluids that have experienced little seawater entrainment. The lack of dissolved oxygen (O2), relatively low abundance of Fe-minerals in samplers, and the thermodynamics of aqueous Fe speciation in fluids with little seawater entrainment suggest that S2O3 2- and HSO3- are likely not produced by ∑H2S oxidation by O2 or Fe3+, nor by SO4 2- reduction by Fe2+. Rather, dissolved S2O3 2- and HSO3- in these fluids are more likely formed through the abiotic reduction of entrained seawater SO4 2- by H2 and/or ∑H2S. If H2 is at sufficient concentrations in the hydrothermal source fluid, mixing models predict that O2 is exhausted and H2 controls redox chemistry in fluids that contain little admixed seawater, complementing these assertions. In fluids that have experienced a higher degree of seawater dilution, several processes may result in the production of S2O3 2- and HSO3- in measured fluids.In submarine back-arc basins and arc volcanos, acid-sulfate, black smoker, and hybrid hydrothermal vents emit magmatic volatiles that can affect habitability of the seafloor. Abundances of anions fluoride (F-) and bromide (Br-) and the stable isotope values (?37Cl) of chloride (Cl-) are used to determine the degree of magmatic volatile input in hydrothermal vents in the Eastern Manus Basin and Brothers arc volcano in the southwest Pacific Ocean. Several fluids measured in this study have Br/Cl ratios similar to that of seawater, while most F/Cl ratios are greater than seawater values, due to input of magmatically sourced HF or leaching of F-enriched bedrock. Acid-sulfate fluids contain Cl with the highest ?37ClCl- values, compared with hybrid and black smoker fluids. Enriched 37Cl is indicative of either a fractionation process, or an additional Cl source beyond the simple entrainment of seawater. Several studies report estimates of mantle ?37Cl and experimentally determined temperature-dependent fractionation factors for magmatic ?37ClHCl(g) and ?37ClCl(aq). Theoretical fractionation factors for magmatic HCl are too small to encompass all endmember ?37ClCl- values in acid-sulfate fluids observed in this study. Rather, elevated ?37Cl values in the acid-sulfate fluids may also reflect 37-enriched Cl supplied from the subducting slab.

English

ISBN: 9798368458342Subjects--Topical Terms:

539092
Geochemistry.
Subjects--Index Terms:

Fluids

Geochemistry of Fluids and Gases in the Deep Continental Subsurface and Deep-Sea Hydrothermal Vents: Abiotic and Biotic Interactions in Extreme Environments /
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520 $a The work presented in this dissertation provides insights into the geochemical landscapes of novel environments in the continental and oceanic subsurface. The physical and chemical properties of fluids in deep crustal reservoirs and deep-sea hydrothermal vents directly influence the habitability of these environments. Thus, this work could have implications for the origin and evolution of life on ancient Earth and elsewhere in our solar system. High-density brines and alkane-rich gases are sourced from deep crustal reservoirs that are hosted in Neoarchean bedrock in the Soudan Underground Mine State Park, Minnesota, USA. Methane (CH4) and C2+ alkanes and alternative electron acceptors (e.g., sulfate (SO4 2-)) are viable energy sources for microorganisms in the fluids, which flow freely from boreholes at a depth of 713.5 m below the surface. Reactions involving the oxidation of alkanes by SO4 2- and NO3-, the reduction of SO4 2- and NO3- by H2, and methanogenesis from CO2 and dimethylamine (DMA) are exergonic. This study presents the first quantification of DMA abundance in a Precambrian shield brine. Dimethylamine may be actively cycled to produce biological CH4 in Soudan's fluids, based on favorable free energy for DMA-based methanogenesis (-ΔG) in kJ/mole, and little available energy per mass fluid (J/kgfluid). The observed low abundance of H2, coupled to C1-C4 abundance ratios and measured stable isotope values (e.g., ?13C, Δ13CH3D) of CH4 and C2+ alkanes allude to a thermogenic origin for C1-C4 n-alkanes, with a minor addition of biologically produced CH4, perhaps from DMA-based methanogenesis.The high volumes of reduced ∑H2S-rich hydrothermal fluid and oxidized SO4 2--rich seawater in hydrothermal systems generate oxidation-reduction (redox) boundaries that can produce intermediate redox-state sulfur species. These species may then be utilized by benthic biological communities. Thiosulfate (S2O32-) and bisulfite (HSO3- ) are present in mixed fluids collected from eight high-temperature (>250 ℃) black smoker vents and two low-temperature (<10 ℃) diffuse vents at 9°46-52'N on the East Pacific Rise. Equilibrium mixing models predict theoretical concentrations of S2O3 2- and HSO3- that compare well to measured compositions, for fluids that have experienced little seawater entrainment. The lack of dissolved oxygen (O2), relatively low abundance of Fe-minerals in samplers, and the thermodynamics of aqueous Fe speciation in fluids with little seawater entrainment suggest that S2O3 2- and HSO3- are likely not produced by ∑H2S oxidation by O2 or Fe3+, nor by SO4 2- reduction by Fe2+. Rather, dissolved S2O3 2- and HSO3- in these fluids are more likely formed through the abiotic reduction of entrained seawater SO4 2- by H2 and/or ∑H2S. If H2 is at sufficient concentrations in the hydrothermal source fluid, mixing models predict that O2 is exhausted and H2 controls redox chemistry in fluids that contain little admixed seawater, complementing these assertions. In fluids that have experienced a higher degree of seawater dilution, several processes may result in the production of S2O3 2- and HSO3- in measured fluids.In submarine back-arc basins and arc volcanos, acid-sulfate, black smoker, and hybrid hydrothermal vents emit magmatic volatiles that can affect habitability of the seafloor. Abundances of anions fluoride (F-) and bromide (Br-) and the stable isotope values (?37Cl) of chloride (Cl-) are used to determine the degree of magmatic volatile input in hydrothermal vents in the Eastern Manus Basin and Brothers arc volcano in the southwest Pacific Ocean. Several fluids measured in this study have Br/Cl ratios similar to that of seawater, while most F/Cl ratios are greater than seawater values, due to input of magmatically sourced HF or leaching of F-enriched bedrock. Acid-sulfate fluids contain Cl with the highest ?37ClCl- values, compared with hybrid and black smoker fluids. Enriched 37Cl is indicative of either a fractionation process, or an additional Cl source beyond the simple entrainment of seawater. Several studies report estimates of mantle ?37Cl and experimentally determined temperature-dependent fractionation factors for magmatic ?37ClHCl(g) and ?37ClCl(aq). Theoretical fractionation factors for magmatic HCl are too small to encompass all endmember ?37ClCl- values in acid-sulfate fluids observed in this study. Rather, elevated ?37Cl values in the acid-sulfate fluids may also reflect 37-enriched Cl supplied from the subducting slab.
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653 $a Fluids
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653 $a Oxidation
653 $a Geochemical landscapes
653 $a Oceanic subsurface
690 $a 0996
710 2 $a Lehigh University. $b Earth and Environmental Sciences. $e degree granting institution. $3 3814466
720 1 $a McDermott, Jill $e degree supervisor.
773 0 $t Dissertations Abstracts International $g 84-07B.
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791 $a Ph.D.
792 $a 2023
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