Description: Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America 111 (2014): 5474-5479, doi:10.1073/pnas.1400643111.

Description: Simple alkyl thiols such as methanethiol (CH3SH) are widely speculated to form in seafloor hot spring fluids. Putative CH3SH synthesis by abiotic (non-biological) reduction of inorganic carbon (CO2 or CO) has been invoked as an initiation reaction for the emergence of proto-metabolism and microbial life in primordial hydrothermal settings. Thiols are also presumptive ligands for hydrothermal trace metals and potential fuels for associated microbial communities. In an effort to constrain sources and sinks of CH3SH in seafloor hydrothermal systems, we determined for the first time its abundance in diverse hydrothermal fluids emanating from ultramafic, mafic and sediment-covered mid-ocean ridge settings. Our data demonstrate that the distribution of CH3SH is inconsistent with metastable equilibrium with inorganic carbon, indicating production by abiotic carbon reduction is more limited than previously proposed. CH3SH concentrations are uniformly low (~10-8 M) in high-temperature fluids (〉200°C) from all unsedimented systems, and in many cases suggestive of metastable equilibrium with CH4 instead. Associated low-temperature fluids (〈200°C) formed by admixing of seawater, however, are invariably enriched in CH3SH (up to ~10-6 M) along with NH4+ and low molecular weight hydrocarbons relative to high-temperature source fluids, resembling our observations from a sedimented system. This strongly implicates thermogenic interactions between upwelling fluids and microbial biomass or associated dissolved organic matter during subsurface mixing in crustal aquifers. Widespread thermal degradation of subsurface organic matter may be an important source of organic production in unsedimented hydrothermal systems, and may influence microbial metabolic strategies in cooler near-seafloor and plume habitats.

Description: 2014-09-27

Description: © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 8 (2017): 1114, doi:10.1038/s41467-017-01228-6.

Description: Little is known about evolutionary drivers of microbial populations in the warm subseafloor of deep-sea hydrothermal vents. Here we reconstruct 73 metagenome-assembled genomes (MAGs) from two geochemically distinct vent fields in the Mid-Cayman Rise to investigate patterns of genomic variation within subseafloor populations. Low-abundance populations with high intra-population diversity coexist alongside high-abundance populations with low genomic diversity, with taxonomic differences in patterns of genomic variation between the mafic Piccard and ultramafic Von Damm vent fields. Populations from Piccard are significantly enriched in nonsynonymous mutations, suggesting stronger purifying selection in Von Damm relative to Piccard. Comparison of nine Sulfurovum MAGs reveals two high-coverage, low-diversity MAGs from Piccard enriched in unique genes related to the cellular membrane, suggesting these populations were subject to distinct evolutionary pressures that may correlate with genes related to nutrient uptake, biofilm formation, or viral invasion. These results are consistent with distinct evolutionary histories between geochemically different vent fields, with implications for understanding evolutionary processes in subseafloor microbial populations.

Description: R.E.A. was supported by a NASA Postdoctoral Fellowship with the NASA Astrobiology Institute. This work was supported by a NASA Astrobiology Science and Technology for Exploring Planets (ASTEP) grant NNX-327 09AB75G and a grant from Deep Carbon Observatory's Deep Life Initiative to J.A.H. and J.S.S., and the NSF Science and Technology Center for Dark Energy Biosphere Investigations (C-DEBI). Ship and vehicle time in 2012 was supported by the NSF-OCE grant OCE-1061863 to J.S.S.

Description: Author Posting. © The Authors, 2010. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America 107 (2010): 14020-14025, doi:10.1073/pnas.1009205107.

Description: Thirty years after the first discovery of high-temperature submarine venting, the vast majority of the global Mid Ocean Ridge remains unexplored for hydrothermal activity. Of particular interest are the world’s ultra-slow spreading ridges which were the last to be demonstrated to host high-temperature venting, but may host systems particularly relevant to pre-biotic chemistry and the origins of life. Here we report first evidence for diverse and very deep hydrothermal vents along the ~110 km long, ultra-slow spreading Mid-Cayman Rise. Our data indicate that the Mid- Cayman Rise hosts at least three discrete hydrothermal sites, each representing a different type of water-rock interaction, including both mafic and ultra-mafic systems and, at ~5000 m, the deepest known hydrothermal vent. Although submarine hydrothermal circulation, in which seawater percolates through and reacts with host lithologies, occurs on all mid-ocean ridges, the diversity of vent-types identified here and their relative geographic isolation make the Mid-Cayman Rise unique in the oceans. These new sites offer prospects for: an expanded range of vent-fluid compositions; varieties of abiotic organic chemical synthesis and extremophile microorganisms; and unparalleled faunal biodiversity - all in close proximity.

Description: This research was funded through NASA (ASTEP) and WHOI (Ocean Ridge Initiative).

Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2015

Description: This thesis examines the controls on organic, inorganic, and volatile species distributions in hydrothermal fluids venting at Von Damm and Piccard, two vent fields at the ultraslow spreading Mid-Cayman Rise, Earth’s deepest mid-ocean ridge. In Chapter 2, abiotic organic synthesis is shown to occur via two distinct mechanisms in the serpentinizing Von Damm system. Chapters 3 and 4 present in-depth studies of the chemical and isotopic compositions of aqueous species in vent fluids at Von Damm and Piccard to elucidate the role of reaction temperature, pressure, substrate composition, and water/rock mass ratios during the chemical evolution of hydrothermal fluids. At Von Damm, sequential reaction of gabbroic and peridotite substrates at intermediate temperatures can explain generation of the observed fluids. At Piccard, extremely high temperature subsurface water/rock reaction results in fluids that are richer in dissolved H2 than any previously observed fluids worldwide. In Chapter 5, multiple sulfur isotopes were measured on metal sulfide deposits, S0, and fluid H2S to constrain sulfur sources and the isotopic systematics of precipitation in a wide variety of seafloor hydrothermal vents. Areas studied include the eastern Manus Basin and Lau Basin back-arc spreading centers, the unsedimented basalt-hosted Southern East Pacific Rise, and the sediment-hosted Guaymas Basin mid-ocean ridge spreading centers.

Description: This thesis research was funded by the National Aeronautics and Space Administration through grant NNX09AB75G and by the National Science Foundation grant OCE-1061863.

Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geochimica et Cosmochimica Acta 228 (2018): 95-118, doi:10.1016/j.gca.2018.01.021.

Description: Hosted in basaltic substrate on the ultra-slow spreading Mid-Cayman Rise, the Piccard hydrothermal field is the deepest currently known seafloor hot-spring (4957–4987 m). Due to its great depth, the Piccard site is an excellent natural system for investigating the influence of extreme pressure on the formation of submarine vent fluids. To investigate the role of rock composition and deep circulation conditions on fluid chemistry, the abundance and isotopic composition of organic, inorganic, and dissolved volatile species in high temperature vent fluids at Piccard were examined in samples collected in 2012 and 2013. Fluids from the Beebe Vents and Beebe Woods black smokers vent at a maximum temperature of 398 °C at the seafloor, however several lines of evidence derived from inorganic chemistry (Cl, SiO2, Ca, Br, Fe, Cu, Mn) support fluid formation at much higher temperatures in the subsurface. These high temperatures, potentially in excess of 500 °C, are attainable due to the great depth of the system. Our data indicate that a single deep-rooted source fluid feeds high temperature vents across the entire Piccard field. High temperature Piccard fluid H2 abundances (19.9 mM) are even higher than those observed in many ultramafic-influenced systems, such as the Rainbow (16 mM) and the Von Damm hydrothermal fields (18.2 mM). In the case of Piccard, however, these extremely high H2 abundances can be generated from fluid-basalt reaction occurring at very high temperatures. Magmatic and thermogenic sources of carbon in the high temperature black smoker vents are described. Dissolved ΣCO2 is likely of magmatic origin, CH4 may originate from a combination of thermogenic sources and leaching of abiotic CH4 from mineral-hosted fluid inclusions, and CO abundances are at equilibrium with the water–gas shift reaction. Longer-chained n-alkanes (C2H6, C3H8, n-C4H10, i-C4H10) may derive from thermal alteration of dissolved and particulate organic carbon sourced from the original seawater source, entrainment of microbial ecosystems peripheral to high temperature venting, and/or abiotic mantle sources. Dissolved ΣHCOOH in the Beebe Woods fluid is consistent with thermodynamic equilibrium for abiotic production via ΣCO2 reduction with H2 at 354 °C measured temperature. A lack of ΣHCOOH in the relatively higher temperature 398 °C Beebe Vent fluids demonstrates the temperature sensitivity of this equilibrium. Abundant basaltic seafloor outcrops and the axial location of the vent field, along with multiple lines of geochemical evidence, support extremely high temperature fluid-rock reaction with mafic substrate as the dominant control on Piccard fluid chemistry. These results expand the known diversity of vent fluid composition, with implications for supporting microbiological life in both the modern and ancient ocean.

Description: This work was supported by the National Aeronautics and Space Administration (NASA) Astrobiology Science and Technology for Exploring Planets program [award number NNX09AB75G to CRG and JSS]; and the National Science Foundation [award number OCE-1061863 to CRG and JSS].

Description: © The Author(s), 202. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in McDermott, J. M., Sylva, S. P., Ono, S., German, C. R., & Seewald, J. S. Abiotic redox reactions in hydrothermal mixing zones: decreased energy availability for the subsurface biosphere. Proceedings of the National Academy of Sciences of the United States of America, 117(34), (2020): 20453-20461, doi:10.1073/pnas.2003108117.

Description: Subseafloor mixing of high-temperature hot-spring fluids with cold seawater creates intermediate-temperature diffuse fluids that are replete with potential chemical energy. This energy can be harnessed by a chemosynthetic biosphere that permeates hydrothermal regions on Earth. Shifts in the abundance of redox-reactive species in diffuse fluids are often interpreted to reflect the direct influence of subseafloor microbial activity on fluid geochemical budgets. Here, we examine hydrothermal fluids venting at 44 to 149 °C at the Piccard hydrothermal field that span the canonical 122 °C limit to life, and thus provide a rare opportunity to study the transition between habitable and uninhabitable environments. In contrast with previous studies, we show that hydrocarbons are contributed by biomass pyrolysis, while abiotic sulfate (SO42−) reduction produces large depletions in H2. The latter process consumes energy that could otherwise support key metabolic strategies employed by the subseafloor biosphere. Available Gibbs free energy is reduced by 71 to 86% across the habitable temperature range for both hydrogenotrophic SO42− reduction to hydrogen sulfide (H2S) and carbon dioxide (CO2) reduction to methane (CH4). The abiotic H2 sink we identify has implications for the productivity of subseafloor microbial ecosystems and is an important process to consider within models of H2 production and consumption in young oceanic crust.

Description: Financial support was provided by the National Aeronautics and Space Administration (NASA) Astrobiology program (Awards NNX09AB75G and 80NSSC19K1427 to C.R.G. and J.S.S.) and the NSF (Award OCE-1061863 to C.R.G. and J.S.S.). Ship and vehicle time for cruise FK008 was provided by the Schmidt Ocean Institute. We thank the ROV Jason II and HROV Nereus groups, and the captain, officers, and crew of R/V Atlantis (AT18-16) and R/V Falkor (FK008) for their dedication to skillful operations at sea. We thank our scientific colleagues from both cruises, as well as Meg Tivey, Frieder Klein, and Scott Wankel for insightful discussions. We are grateful to the editor and two anonymous reviewers for providing helpful comments and suggestions.

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Wu, J., Parnell‐Turner, R., Fornari, D., Kurras, G., Berrios‐Rivera, N., Barreyre, T., & McDermott, J. Extent and volume of lava flows erupted at 9°50’N, East Pacific Rise in 2005–2006 from autonomous underwater vehicle surveys. Geochemistry Geophysics Geosystems, 23, (2022): e2021GC010213, https://doi.org/10.1029/2021gc010213.

Description: Seafloor volcanic eruptions are difficult to directly observe due to lengthy eruption cycles and the remote location of mid-ocean ridges. Volcanic eruptions in 2005–2006 at 9°50′N on the East Pacific Rise have been well documented, but the lava volume and flow extent remain uncertain because of the limited near-bottom bathymetric data. We present near-bottom data collected during 19 autonomous underwater vehicle (AUV) Sentry dives at 9°50′N in 2018, 2019, and 2021. The resulting 1 m-resolution bathymetric grid and 20 cm-resolution sidescan sonar images cover 115 km2, and span the entire area of the 2005–2006 eruptions, including an 8 km2 pre-eruption survey collected with AUV ABE in 2001. Pre- and post-eruption surveys, combined with sidescan sonar images and seismo-acoustic impulsive events recorded during the eruptions, are used to quantify the lava flow extent and to estimate changes in seafloor depth caused by lava emplacement. During the 2005–2006 eruptions, lava flowed up to ∼3 km away from the axial summit trough, covering an area of ∼20.8 km2; ∼50% larger than previously thought. Where pre- and post-eruption surveys overlap, individual flow lobes can be resolved, confirming that lava thickness varies from ∼1 to 10 m, and increases with distance from eruptive fissures. The resulting lava volume estimate indicates that ∼57% of the melt extracted from the axial melt lens probably remained in the subsurface as dikes. These observations provide insights into recharge cycles in the subsurface magma system, and are a baseline for studying future eruptions at the 9°50′N area.

Description: This project is supported by National Science Foundation grants OCE-1834797, OCE-1949485, OCE-194893, OCE-1949938, and by Scripps Institution of Oceanography's David DeLaCour Endowment Fund.

Description: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Environmental Microbiology 18 (2016): 1970–1987, doi:10.1111/1462-2920.13173.

Description: Warm fluids emanating from hydrothermal vents can be used as windows into the rocky subseafloor habitat and its resident microbial community. Two new vent systems on the Mid-Cayman Rise each exhibits novel geologic settings and distinctively hydrogen-rich vent fluid compositions. We have determined and compared the chemistry, potential energy yielding reactions, abundance, community composition, diversity, and function of microbes in venting fluids from both sites: Piccard, the world's deepest vent site, hosted in mafic rocks; and Von Damm, an adjacent, ultramafic-influenced system. Von Damm hosted a wider diversity of lineages and metabolisms in comparison to Piccard, consistent with thermodynamic models that predict more numerous energy sources at ultramafic systems. There was little overlap in the phylotypes found at each site, although similar and dominant hydrogen-utilizing genera were present at both. Despite the differences in community structure, depth, geology, and fluid chemistry, energetic modelling and metagenomic analysis indicate near functional equivalence between Von Damm and Piccard, likely driven by the high hydrogen concentrations and elevated temperatures at both sites. Results are compared with hydrothermal sites worldwide to provide a global perspective on the distinctiveness of these newly discovered sites and the interplay among rocks, fluid composition and life in the subseafloor.

Description: National Aeronautics and Space Administration Grant Number: NNX09AB756; Alfred P. Sloan Foundation; NSF Grant Number: OCE106183

Description: Author Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 223 (2018): 141-158, doi:10.1016/j.gca.2017.11.030.

Description: Hot-spring fluids emanating from deep-sea vents hosted in unsedimented ultramafic and mafic rock commonly contain high concentrations of methane. Multiple hypotheses have been proposed for the origin(s) of this methane, ranging from synthesis via reduction of aqueous inorganic carbon (ΣCO2) during active fluid circulation to leaching of methane-rich fluid inclusions from plutonic rocks of the oceanic crust. To further resolve the process(es) responsible for methane generation in these systems, we determined the relative abundances of several methane isotopologues (including 13CH3D, a “clumped” isotopologue containing two rare isotope substitutions) in hot-spring source fluids sampled from four geochemically-distinct hydrothermal vent fields (Rainbow, Von Damm, Lost City, and Lucky Strike). Apparent equilibrium temperatures retrieved from methane clumped isotopologue analyses average 310−42 +53 °C, with no apparent relation to the wide range of fluid temperatures (96 to 370 °C) and chemical compositions (pH, [H2], [ΣCO2], [CH4]) represented. Combined with very similar bulk stable isotope ratios (13C/12C and D/H) of methane across the suite of hydrothermal fluids, all available geochemical and isotopic data suggest a common mechanism of methane generation at depth that is disconnected from active fluid circulation. Attainment of equilibrium amongst methane isotopologues at temperatures of ca. 270 to 360 °C is compatible with the thermodynamically-favorable reduction of CO2 to CH4 at temperatures at or below ca. 400 °C under redox conditions characterizing intrusive rocks derived from sub-ridge melts. Collectively, the observations support a model where methane-rich aqueous fluids, known to be trapped in rocks of the oceanic lithosphere, are liberated from host rocks during hydrothermal circulation and perhaps represent the major source of methane venting with thermal waters at unsedimented hydrothermal fields. The results also provide further evidence that water-rock reactions occurring at temperatures lower than 200 °C do not contribute significantly to the quantities of methane venting at mid-ocean ridge hot springs.

Description: Financial support from the U.S. National Science Foundation (NSF awards EAR-1250394 to S.O., and OCE-1061863 and OCE-0549829 to J.S.S.), the National Aeronautics and Space Administration (NASA) (NNX-327 09AB75G to J.S.S., and the NASA Astrobiology Institute “Rock- Powered Life” project under cooperative agreement NNA15BB02A to S.O.), the Alfred P. Sloan Foundation via the Deep Carbon Observatory (to S.O. and J.S.S.), the U.S. Department of Defense (DoD) through a National Defense Science & Engineering Graduate (NDSEG) Fellowship (to D.T.W.), a Shell-MIT Energy Initiative Fellowship, and the Kerr-McGee Professorship at MIT (to S.O.) is gratefully acknowledged.

Description: Author Posting. © The Oceanography Society, 2018. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 31, no. 1, supplement (2018): 42-43.