A new gas-tight isobaric sampler for hydrothermal fluids

Proc. Natl. Acad. Sci. U.S.A.

German

et al. 2015

Self Cite

288

303

Arguments for an abiotic origin of low-molecular weight organic compounds in deep-sea hot springs are compelling owing to implications for the sustenance of deep biosphere microbial communities and their potential role in the origin of life. Theory predicts that warm H 2 -rich fluids, like those emanating from serpentinizing hydrothermal systems, create a favorable thermodynamic drive for the abiotic generation of organic compounds from inorganic precursors. Here, we constrain two distinct reaction pathways for abiotic organic synthesis in the natural environment at the Von Damm hydrothermal field and delineate spatially where inorganic carbon is converted into bioavailable reduced carbon. We reveal that carbon transformation reactions in a single system can progress over hours, days, and up to thousands of years. Previous studies have suggested that CH 4 and higher hydrocarbons in ultramafic hydrothermal systems were dependent on H 2 generation during active serpentinization. Rather, our results indicate that CH 4 found in vent fluids is formed in H 2 -rich fluid inclusions, and higher n-alkanes may likely be derived from the same source. This finding implies that, in contrast with current paradigms, these compounds may form independently of actively circulating serpentinizing fluids in ultramafic-influenced systems. Conversely, widespread production of formate by ΣCO 2 reduction at Von Damm occurs rapidly during shallow subsurface mixing of the same fluids, which may support anaerobic methanogenesis. Our finding of abiogenic formate in deep-sea hot springs has significant implications for microbial life strategies in the present-day deep biosphere as well as early life on Earth and beyond.abiotic organic synthesis | hydrothermal systems | methane | formate | fluid-vapor inclusions S eawater-derived hydrothermal fluids venting at oceanic spreading centers are a net source for dissolved carbon to the deep sea, with vent fluid carbon contents directly tied to the sustenance of the subseafloor biosphere (1). Highly reducing fluids rich in dissolved H 2 , such as those discharging from serpentinizing hydrothermal systems, are of particular interest because of the potential for abiotic reduction of dissolved inorganic carbon ðΣCO 2 = CO 2 + HCO − 3 + CO 2− 3 Þ to organic compounds (2-6) and their potential role as precursor compounds for prebiotic chemistry associated with the origin of life (7). Although there is increasing evidence that supports an abiotic origin for CH 4 and other low-molecular weight organic compounds in ultramafic-hosted hydrothermal systems (8-10), the physical conditions, reaction pathways, and timescales that control abiotic organic synthesis at oceanic spreading centers remain elusive. Working models for the formation of abiotic CH 4 and other hydrocarbons observed in vent fluids involve reduction of ΣCO 2 and/or CO through Fischer-Tropsch-type processes during active circulation of seawater-derived hydrothermal fluids that are highly enriched in dissolved H 2 because of serpentinization of...

Section: Methodsmentioning

confidence: 99%

Pathways for abiotic organic synthesis at submarine hydrothermal fields

McDermott

Proc. Natl. Acad. Sci. U.S.A.

German

et al. 2015

Self Cite

288

303

“…81 spring water samples were collected by the ROV Jason in two types of bottles: 13 in conventional 750-mL Ti-syringe samplers (Edmond et al, 1992) and 68 in 90-mL isobaric gastight samplers (Seewald et al, 2002). For the gas-tight samplers, temperature was measured continuously over the 1-2 minutes during which the sampler filled.…”

Section: Methodsmentioning

confidence: 99%

Chemistry of hot springs along the Eastern Lau Spreading Center

Mottl

Geochimica et Cosmochimica Acta

Wheat

et al. 2011

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125

The Eastern Lau Spreading Center (ELSC) is the southernmost part of the back-arc spreading axis in the Lau Basin, west of the Tonga trench and the active Tofua volcanic arc.Over its 397-km length it exhibits large and systematic changes in spreading rate, magmatic/tectonic processes, and proximity to the volcanic arc. In 2005 we collected 81 samples of vent water from six hydrothermal fields along the ELSC. The chemistry of these waters varies both within and between vent fields, in response to changes in substrate composition, temperature and pressure, pH, water/rock ratio, and input from magmatic gases and subducted sediment. Hot-spring temperatures range from 229º to 363ºC at the five northernmost fields, with a general decrease to the south that is reversed at the Mariner field. The southernmost field, Vai Lili, emitted water at up to 334C in 1989 but had a maximum venting temperature of only

“…Vent fluid samples were collected using isobaric gas-tight fluid samplers (SEEWALD et al, 2002) deployed from the submersible Alvin. These samplers prevent degassing during ascent to the surface and shipboard processing by maintaining the fluid at seafloor pressures as subsamples are withdrawn through a micrometering valve.…”

Section: Sample Collection and Analysismentioning

confidence: 99%

Geochemistry of low-molecular weight hydrocarbons in hydrothermal fluids from Middle Valley, northern Juan de Fuca Ridge

Cruse

Geochimica et Cosmochimica Acta

2006

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108

Hydrothermal vent fluids from Middle Valley, a sediment-covered mid-ocean ridge on the northern Juan de Fuca Ridge, were sampled in July, 2000. Eight different vents with exit temperatures of 186 to 281°C were sampled from two areas of venting: the Dead Dog and ODP Mound fields. Fluids from the Dead Dog field are characterized by higher concentrations of ΣNH 3 and organic compounds (C 1 -C 4 alkanes, ethene, propene, benzene and toluene) compared with fluids from the ODP Mound field. The ODP Mound fluids, however, are characterized by higher C 1 /(C 2 +C 3 ) and benzene:toluene ratios than those from the Dead Dog field. The aqueous organic compounds in these fluids have been derived from both bacterial processes (methanogenesis in low-temperature regions during recharge) as well as from thermogenic processes in higher-temperature portions of the subsurface reaction zone. As the sediments undergo hydrothermal alteration, carbon dioxide and hydrocarbons are released to solution as organic matter degrades via a stepwise oxidation process. Compositional and isotopic differences in the aqueous hydrocarbons indicate that maximum subsurface temperatures at the ODP Mound are greater than those at the Dead Dog field. Maximum subsurface temperatures were calculated assuming that thermodynamic equilibrium is attained between alkenes and alkanes, benzene and toluene, and carbon dioxide and methane. The calculated temperatures for alkene-alkane equilibrium are consistent with differences in the dissolved Cl concentrations in fluids from the two fields, and indicate that subsurface temperatures at the ODP Mound are hotter than those at the Dead Dog field. Temperatures calculated assuming benzene-toluene equilibrium and carbon dioxide-methane equilibrium are similar to observed exit temperatures, and do not record the hottest subsurface conditions. The difference in subsurface temperatures estimated using organic geochemical thermometers reflects subsurface cooling processes via mixing of a hot, low-salinity vapor with a cooler, seawater salinity fluid. Because of the disparate temperature dependence of alkene-alkane and benzene-toluene equilibria, the mixed fluid records both the high and low temperature equilibrium conditions. These calculations indicate that vapor-rich fluids are presently being formed in the crust beneath the ODP Mound, yet do not reach the surface due to mixing with the lower-temperature fluids.2