Stable isotopic evidence in support of active microbial methane cycling in low-temperature diffuse flow vents at 9°50’N East Pacific Rise

Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 72 (2008): 2005-2023, doi:10.1016/j.gca.2008.01.025.A unique dataset from paired low- and high-temperature vents at 9°50’N East Pacific Rise provides insight into the microbiological activity in low-temperature diffuse fluids. The stable carbon isotopic composition of CH4 and CO2 in 9°50’N hydrothermal fluids indicates microbial methane production, perhaps coupled with microbial methane consumption. Diffuse fluids are depleted in 13C by ~10‰ in values of δ13C of CH4, and by ~0.55‰ in values of δ13C of CO2, relative to the values of the high-temperature source fluid (δ13C of CH4 = -20.1 ± 1.2‰, δ13C of CO2 = -4.08 ± 0.15‰). Mixing of seawater or thermogenic sources cannot account for the depletions in 13C of both CH4 and CO2 at diffuse vents relative to adjacent high-temperature vents. The substrate utilization and 13C fractionation associated with the microbiological processes of methanogenesis and methane oxidation can explain observed steady-state CH4 and CO2 concentrations and carbon isotopic compositions. A mass-isotope numerical box-model of these paired vent systems is consistent with the hypothesis that microbial methane cycling is active at diffuse vents at 9°50’N. The detectable 13C modification of fluid geochemistry by microbial metabolisms may provide a useful tool for detecting active methanogenesis.This work was supported by NSF grants from the division of Ocean Science’s MG&G and RIDGE programs

A preliminary 1-D model investigation of tidal variations of temperature and chlorinity at the Grotto mound, Endeavour Segment, Juan de Fuca Ridge

Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 18 (2017): 75–92, doi:10.1002/2016GC006537.Tidal oscillations of venting temperature and chlorinity have been observed in the long-term time series data recorded by the Benthic and Resistivity Sensors (BARS) at the Grotto mound on the Juan de Fuca Ridge. In this study, we use a one-dimensional two-layer poroelastic model to conduct a preliminary investigation of three hypothetical scenarios in which seafloor tidal loading can modulate the venting temperature and chlorinity at Grotto through the mechanisms of subsurface tidal mixing and/or subsurface tidal pumping. For the first scenario, our results demonstrate that it is unlikely for subsurface tidal mixing to cause coupled tidal oscillations in venting temperature and chlorinity of the observed amplitudes. For the second scenario, the model results suggest that it is plausible that the tidal oscillations in venting temperature and chlorinity are decoupled with the former caused by subsurface tidal pumping and the latter caused by subsurface tidal mixing, although the mixing depth is not well constrained. For the third scenario, our results suggest that it is plausible for subsurface tidal pumping to cause coupled tidal oscillations in venting temperature and chlorinity. In this case, the observed tidal phase lag between venting temperature and chlorinity is close to the poroelastic model prediction if brine storage occurs throughout the upflow zone under the premise that layers 2A and 2B have similar crustal permeabilities. However, the predicted phase lag is poorly constrained if brine storage is limited to layer 2B as would be expected when its crustal permeability is much smaller than that of layer 2A.Woods Hole Oceanographic Institution; NOAA; National Science Foundation Grant Numbers: 9820105 , 0120392 , 0701196 , 0751868 , 08190042017-07-1

Hydrographic and chemical data from the eastern tropical North Pacific Ocean - January 1977

This report presents hydrographic and chemical data from the eastern tropical North Pacific Ocean collected in January 1977 aboard Oregon State University's (OSU) R/V WECOMA during Leg I of Cruise WELOC 77. The purpose of the cruise, WELOC-77-I, was to investigate the distributions of dissolved nitrous oxide and molecular hydrogen' in an oceanic environment characterized by an extensive oxygen minimum layer which is thought to be the major denitrification site in the world ocean (e.g. Codispoti and Richards, 1976; Cline and Kaplan, 1975). Accordingly, the research effort was concentrated on studying the distributions of variables at stations located around the core of the oxygen minimum

Seafloor deformation and forecasts of the April 2011 eruption at Axial Seamount

Axial Seamount is an active submarine volcano located at the intersection between the Cobb hotspot and the Juan de Fuca spreading centre in the northeast Pacific Ocean1, 2. The volcano has been closely monitored since it erupted in 1998 (refs 3, 4). Since then, Axial Seamount seemed to exhibit a similar inflation–deflation cycle to basaltic volcanoes on land and, on that basis, was expected to erupt again sometime before 2014 or 2020 (refs 5, 6). In April 2011 Axial Seamount erupted. Here we report continuous measurements of ocean bottom pressure that document the deflation–inflation cycle of Axial Seamount between 1998 and 2011. We find that the volcano inflation rate, caused by the intrusion of magma, gradually increased in the months leading up to the 2011 eruption. Sudden uplift occurred 40–55 min before the eruption onset, which we interpret as a precursor event. Based on our measurements of ground deformation through the entire eruption cycle at Axial Seamount, we suggest that another eruption could occur as early as 2018. We propose that the long-term eruptive cycle of Axial Seamount could be more predictable compared with its subaerial counterparts because the volcano receives a relatively steady supply of magma through the Cobb hotspot and because it is located on thin oceanic crust at a spreading plate boundary

Contamination tracer testing with seabed drills: IODP Expedition 357

IODP Expedition 357 utilized seabed drills for the first time in the history of the ocean drilling program, with the aim of collecting intact sequences of shallow mantle core from the Atlantis Massif to examine serpentinization processes and the deep biosphere. This novel drilling approach required the development of a new remote seafloor system for delivering synthetic tracers during drilling to assess for possible sample contamination. Here, we describe this new tracer delivery system, assess the performance of the system during the expedition, provide an overview of the quality of the core samples collected for deep biosphere investigations based on tracer concentrations, and make recommendations for future applications of the system

Eruptive modes and hiatus of volcanism at West Mata seamount, NE Lau basin : 1996–2012

Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 15 (2014): 4093–4115, doi:10.1002/2014GC005387.We present multiple lines of evidence for years to decade-long changes in the location and character of volcanic activity at West Mata seamount in the NE Lau basin over a 16 year period, and a hiatus in summit eruptions from early 2011 to at least September 2012. Boninite lava and pyroclasts were observed erupting from its summit in 2009, and hydroacoustic data from a succession of hydrophones moored nearby show near-continuous eruptive activity from January 2009 to early 2011. Successive differencing of seven multibeam bathymetric surveys of the volcano made in the 1996–2012 period reveals a pattern of extended constructional volcanism on the summit and northwest flank punctuated by eruptions along the volcano's WSW rift zone (WSWRZ). Away from the summit, the volumetrically largest eruption during the observational period occurred between May 2010 and November 2011 at ∼2920 m depth near the base of the WSWRZ. The (nearly) equally long ENE rift zone did not experience any volcanic activity during the 1996–2012 period. The cessation of summit volcanism recorded on the moored hydrophone was accompanied or followed by the formation of a small summit crater and a landslide on the eastern flank. Water column sensors, analysis of gas samples in the overlying hydrothermal plume and dives with a remotely operated vehicle in September 2012 confirmed that the summit eruption had ceased. Based on the historical eruption rates calculated using the bathymetric differencing technique, the volcano could be as young as several thousand years.Support for R.W.E. during this study was by internal NOAA funding to the NOAA Vents Program (now Earth-Ocean Interactions Program). The NSF Ridge 2000 and MARGINS programs played a major role in the planning and justification for the 2009 rapid response proposal that funded the May 2009 expedition. MBARI provided support and outstanding postprocessing of the multibeam bathymetry from the D. Allan B. AUV multibeam sonar used in this study. NSF also provided major funding for the 2009 expedition (OCE930025 and OCE-0934660 to JAR) and for the 210Po-210Pb radiometric dating (OCE-0929881 and for the 210Po-210Pb radiometric dating (OCE-0929881 to KHR)). The NOAA Office of Exploration and Research provided major funding for the 2009 and 2012 field programs.2015-04-3

Metagenomic Identification of Active Methanogens and Methanotrophs in Serpentinite Springs of the Voltri Massif, Italy

The production of hydrogen and methane by geochemical reactions associated with the serpentinization of ultramafic rocks can potentially support subsurface microbial ecosystems independent of the photosynthetic biosphere. Methanogenic and methanotrophic microorganisms are abundant in marine hydrothermal systems heavily influenced by serpentinization, but evidence for methane-cycling archaea and bacteria in continental serpentinite springs has been limited. This report provides metagenomic and experimental evidence for active methanogenesis and methanotrophy by microbial communities in serpentinite springs of the Voltri Massif, Italy. Methanogens belonging to family Methanobacteriaceae and methanotrophic bacteria belonging to family Methylococcaceae were heavily enriched in three ultrabasic springs (pH 12). Metagenomic data also suggest the potential for hydrogen oxidation, hydrogen production, carbon fixation, fermentation, and organic acid metabolism in the ultrabasic springs. The predicted metabolic capabilities are consistent with an active subsurface ecosystem supported by energy and carbon liberated by geochemical reactions within the serpentinite rocks of the Voltri Massif

Biochemical Characterization of a Structure-Specific Resolving Enzyme from Sulfolobus islandicus Rod-Shaped Virus 2

Sulfolobus islandicus rod shaped virus 2 (SIRV2) infects the archaeon Sulfolobus islandicus at extreme temperature (70°C–80°C) and acidity (pH 3). SIRV2 encodes a Holliday junction resolving enzyme (SIRV2 Hjr) that has been proposed as a key enzyme in SIRV2 genome replication. The molecular mechanism for SIRV2 Hjr four-way junction cleavage bias, minimal requirements for four-way junction cleavage, and substrate specificity were determined. SIRV2 Hjr cleaves four-way DNA junctions with a preference for cleavage of exchange strand pairs, in contrast to host-derived resolving enzymes, suggesting fundamental differences in substrate recognition and cleavage among closely related Sulfolobus resolving enzymes. Unlike other viral resolving enzymes, such as T4 endonuclease VII or T7 endonuclease I, that cleave branched DNA replication intermediates, SIRV2 Hjr cleavage is specific to four-way DNA junctions and inactive on other branched DNA molecules. In addition, a specific interaction was detected between SIRV2 Hjr and the SIRV2 virion body coat protein (SIRV2gp26). Based on this observation, a model is proposed linking SIRV2 Hjr genome resolution to viral particle assembly

Magmatism, serpentinization and life: Insights through drilling the Atlantis Massif (IODP Expedition 357)

IODP Expedition 357 used two seabed drills to core 17 shallow holes at 9 sites across Atlantis Massif ocean core complex (Mid-Atlantic Ridge 30°N). The goals of this expedition were to investigate serpentinization processes and microbial activity in the shallow subsurface of highly altered ultramafic and mafic sequences that have been uplifted to the seafloor along a major detachment fault zone. More than 57 m of core were recovered, with borehole penetration ranging from 1.3 to 16.4 meters below seafloor, and core recovery as high as 75% of total penetration in one borehole. The cores show highly heterogeneous rock types and alteration associated with changes in bulk rock chemistry that reflect multiple phases of magmatism, fluid-rock interaction and mass transfer within the detachment fault zone. Recovered ultramafic rocks are dominated by pervasively serpentinized harzburgite with intervals of serpentinized dunite and minor pyroxenite veins; gabbroic rocks occur as melt impregnations and veins. Dolerite intrusions and basaltic rocks represent the latest magmatic activity. The proportion of mafic rocks is volumetrically less than the amount of mafic rocks recovered previously by drilling the central dome of Atlantis Massif at IODP Site U1309. This suggests a different mode of melt accumulation in the mantle peridotites at the ridge-transform intersection and/or a tectonic transposition of rock types within a complex detachment fault zone. The cores revealed a high degree of serpentinization and metasomatic alteration dominated by talc-amphibole-chlorite overprinting. Metasomatism is most prevalent at contacts between ultramafic and mafic domains (gabbroic and/or doleritic intrusions) and points to channeled fluid flow and silica mobility during exhumation along the detachment fault. The presence of the mafic lenses within the serpentinites and their alteration to mechanically weak talc, serpentine and chlorite may also be critical in the development of the detachment fault zone and may aid in continued unroofing of the upper mantle peridotite/gabbro sequences. New technologies were also developed for the seabed drills to enable biogeochemical and microbiological characterization of the environment. An in situ sensor package and water sampling system recorded real-time variations in dissolved methane, oxygen, pH, oxidation reduction potential (Eh), and temperature and during drilling and sampled bottom water after drilling. Systematic excursions in these parameters together with elevated hydrogen and methane concentrations in post-drilling fluids provide evidence for active serpentinization at all sites. In addition, chemical tracers were delivered into the drilling fluids for contamination testing, and a borehole plug system was successfully deployed at some sites for future fluid sampling. A major achievement of IODP Expedition 357 was to obtain microbiological samples along a west–east profile, which will provide a better understanding of how microbial communities evolve as ultramafic and mafic rocks are altered and emplaced on the seafloor. Strict sampling handling protocols allowed for very low limits of microbial cell detection, and our results show that the Atlantis Massif subsurface contains a relatively low density of microbial life