the contribution of the precambrian continental lithosphere to global h 2 production the production of hydrogen gas from the precambrian continental lithosphere has been underestimated taking into account hydrogen from serpentinization and radiolysis may double estimates previously based on marine systems alone molecular hydrogen produced by interactions between water and rocks in the earth s subsurface and at deep ocean vents can sustain microbial ecosystems it was thought that global h2 production originates mainly from the marine lithosphere with a negligible contribution from precambrian rocks but here the authors present a global compilation of h2 concentration data that identifies the fracture waters in the precambrian continental subsurface as a domain of the terrestrial hydrosphere that produces h2 at a rate comparable to estimates from marine systems this finding revises our understanding of the production of reduced gases in the earth s subsurface and may aid in the exploration of life in deep habitat locations microbial ecosystems can be sustained by hydrogen gas h2 producing water rock interactions in the earth s subsurface and at deep ocean vents1 2 3 4 current estimates of global h2 production from the marine lithosphere by water rock reactions hydration are in the range of 1011 moles per year5 6 7 8 9 recent explorations of saline fracture waters in the precambrian continental subsurface have identified environments as rich in h2 as hydrothermal vents and seafloor spreading centres1 2 and have suggested a link between dissolved h2 and the radiolytic dissociation of water10 11 however extrapolation of a regional h2 flux based on the deep gold mines of the witwatersrand basin in south africa11 yields a contribution of the precambrian lithosphere to global h2 production that was thought to be negligible 0 009 1011 moles per year 6 here we present a global compilation of published and new h2 concentration data obtained from precambrian rocks and find that the h2 production potential of the precambrian continental lithosphere has been underestimated we suggest that this can be explained by a lack of consideration of additional h2 producing reactions such as serpentinization and the absence of appropriate scaling of h2 measurements from these environments to account for the fact that precambrian crust represents over 70 per cent of global continental crust surface area12 if h2 production via both radiolysis and hydration reactions is taken into account our estimate of h2 production rates from the precambrian continental lithosphere of 0 36 2 27 1011 moles per year is comparable to estimates from marine systems

geochemical constraints on chemolithoautotrophic metabolism by microorganisms in seafloor hydrothermal systems mixing of hydrothermal fluids and seawater at the ocean floor combined with slow reaction kinetics for oxidation reduction reactions provides a source of metabolic energy for chemolithotrophic microorganisms which are the primary biomass producers for an extensive submarine ecosystem that is essentially independent of photosynthesis thermodynamic models are used to explore geochemical constraints on the amount of metabolic energy potentially available from chemosynthetic reactions involving s c fe and mn compounds during mixing of hydrothermal fluids with seawater for the vent fluid used in the calculations epr 21 n obs the model indicates that mixing environments are favorable for oxidation of h2s ch4 fe2 and mn2 only below 38 c with methanogenesis and reduction of sulfate or s favored at higher temperatures suggesting that environments dominated by mixing provide habitats for mesophilic but not thermophilic aerobes and thermophilic but not mesophilic anaerobes a maximum of 760 cal per kilogram vent fluid is available from sulfide oxidation while between 8 and 35 cal kg vent fluid is available from methanotrophy methanogenesis oxidation of fe or mn or sulfate reduction the total potential for chemosynthetic primary production at deep sea hydrothermal vents globally is estimated to be about 1013 g biomass per year which represents 0 02 of the global primary production by photosynthesis in the oceans thermophilic methanogens and sulfate and s reducers are likely to be the predominant organisms in the walls of vent chimneys and in the diffuse mixing zones beneath warm vents where biological processes may contribute to the high methane concentrations of vent fluids and heavy 34s32s s ratios of vent sulfide minerals the metabolic processes taking place in these systems may be analogs of the first living systems to evolve on the earth

the abundance of seafloor massive sulfide deposits the possibility of mining seafl oor massive sulfide deposits has stirred debate about the sustainable use of this new resource and whether commercial development is worth the risk among the outstanding questions is how many deposits might be accessible to deep sea mining more than 300 sites of high temperature hydrothermal venting have been identifi ed since the discovery of black smokers but signifi cant massive sulfide accumulation has been found at only 165 of these sites estimates of the total number of vent fields and associated mineral deposits based on plume studies and deposit occurrence models range from 500 to 5000 we have used new deposit occurrence data from 10 000 km of ridge arc and backarc spreading centers to estimate the amount of massive sulfide in the easily accessible neovolcanic zones of the global oceans the total accumulation in these areas is estimated to be on the order of 6 108 tonnes containing 3 107 tonnes of copper and zinc this is similar to the total discovered copper and zinc in cenozoic massive sulfi de deposits mined on land but is insuffi cient to satisfy a growing global demand for these metals

prediction of the occurrence of related strong earthquakes in italy in the seismic flow it is often observed that a strong earthquake se is followed by related strong earthquakes rses which occur near the epicenter of the se with origin time rather close to the origin time of the se the algorithm for the prediction of the occurrence of a rse has been developed and applied for the first time to the seismicity data of the california nevada region and has been successfully tested in several regions of the world the statistical significance of the result being 97 to date it has been possible to make five successful forward predictions with no false alarms or failures to predict

methane and hydrogen in mid ocean ridge basalt glasses analysis by vacuum crushing a comparative study of vacuum crushing methods for analyzing reactive gases in basaltic glasses shows that ball milling is an efficient means of releasing occluded gases but that blank production represents a potentially serious problem that must be accounted for when determining reactive gas compositions production of h2 and ch4 in a stainless steel ball mill in the absence of rock material increases with length of crushing time however test results presented here indicate that blank levels are reduced during the actual crushing process by the presence of rock powder which may act as a cushion to reduce metal metal contact crushing in copper tubes under a hydraulic press produces no blanks for these gases but crushing efficiency and gas release are very low and gas adsorption on rock powder becomes a significant problem experiments with methane adsorption on crushed basalt suggest that the loss of methane is a chemisorption process that is for the most part irreversible applying corrections for

mechanoradical h2 generation during simulated faulting implications for an earthquake driven subsurface biosphere 1 molecular hydrogen h2 is the key component to link the inorganic lithosphere with the subsurface biosphere geochemical and microbiological characterizations of natural hydrothermal fields strongly suggested that h2 is an important energy source in subsurface microbial ecosystems because of its metabolic versatility one of the possible sources of h2 has been considered as earthquakes mechanoradical reactions on fault surfaces generate h2 during earthquake faulting however it is unclear whether faulting can generate abundant h2 to sustain subsurface chemolithoautotrophic microorganisms such as methanogens here we present the result of high velocity friction experiments aimed to estimate the amount of h2 generated during earthquakes our results show that h2 generation increases with frictional work i e earthquake magnitude and that a h2 concentration of more than 1 1 mol kg of fluid can be achieved in a fault zone after earthquakes of even small magnitudes the estimated earthquake derived h2 concentration is sufficiently high to sustain a h2 based subsurface lithoautotrophic microbial ecosystem furthermore earthquakes have initiated on the earth at least since tectonic plate movement began 3 8 ga implying the possible existence of ancient earthquake driven ecosystems seismic h2 based subsurface ecosystems might exist not only over the earth but also other planets

enriched h2 ch4 and 3he concentrations in hydrothermal plumes associated with the 1996 gorda ridge eruptive event abstract the rapid field response in march and april 1996 to diking eruptive events on the northern gorda ridge allowed the first detailed co measurement of 3 he h 2 and ch 4 in plumes associated with a submarine eruption and examination of the chemical transformation of these volatile species during aging of the plumes the diking eruptive event generated extensive event plumes with a low 3 he heat ratio of 0 4 10 12 cm 3 stp gm 1 c 1 while chronic plumes had 3 he heat ratios of 2 1 6 2 10 12 cm 3 stp gm 1 c 1 hydrogen concentrations in the initial event plume ep96a reached a maximum value of 47 nm 235 times that of ocean background concentration 0 2 nm in contrast roughly one month later h 2 concentrations although still elevated had drastically dropped to 40 times background values methane concentrations in both event and chronic plume fluids were also elevated and similar to stable hydrothermal systems in unsedimented ridge environments reaching a maximum value of 7 nm the intense rapid interaction at very high temperatures of hydrothermal fluids with the host rock during dike intrusion or with seawater during extrusion of the basalt likely generated high localized concentrations of h 2 the data indicate however that maximum rates of h 2 production during event plume formation could have lasted a few days at most

archaean plate tectonics revisited 1 heat flow spreading rate and the age of subducting oceanic lithosphere and their effects on the origin and evolution of continents a simple model which relates the rate of seafloor creation and the age of the oceanic lithosphere at subduction to the rate of continental accretion can successfully explain the apparent differences between archaean and phanerozoic terrains in terms of plate tectonics the model has been derived using the following parameters 1 the spreading rate at mid ocean ridges 2 the age of the oceanic lithosphere at the time of subduction 3 the area age distribution of the seafloor 4 the continental surface area as a fraction of the total surface area of the earth and 5 the erosion rate of continents as a function of continental surface area and the total number of continental masses observations in phanerozoic terranes suggest that there are profound differences in the nature and volume of subduction zone igneous activity depending upon the age of the oceanic lithosphere being subducted and the nature of the overriding plate that is either continental or oceanic the subduction of young oceanic lithosphere less than 50 m y old which is thermally buoyant appears to result in a reduced volume of igneous activity most of the igneous activity caused by subduction of young oceanic lithosphere is either siliceous plutonism or bimodal tholeiitic rhyolitic volcanism when very young lithosphere is being subducted 50 m y old appears to result in greater volumes of igneous activity including the eruption of andesitic magmas thus andesites could only begin to be abundant in the rock record when older oceanic lithosphere began to be subducted our model predicts that as the earth aged and as heat flow from the interior of the earth diminished the proportion of old oceanic lithosphere being subducted increased fundamentally changing the nature of subduction zone igneous activity and the rate of continental accretion if the subduction of old oceanic lithosphere results in an 8 10 times greater volume of subduction zone magmatism our model predicts or explains all of the following observed features of earth history 1 archaean terranes appear to record two periods of rapid continental accretion between 3 8 and 3 5 b y ago and between 3 1 and 2 6 b y ago 2 there are very few differences and many marked similarities between rocks from archaean terranes and equivalent rocks from phanerozoic terranes 3 the total continental area appears to have remained essentially constant for the past 2 b y 4 archaean andesites are comparatively rare and the relative abundances of mafic and siliceous rocks appear to change during the archaean and the proterozoic with siliceous volcanics becoming proportionately more abundant in the geologic record with time 5 plutonic tonalites and trondhjemites appear to have been relatively much more abundant during the archaean plate tectonics is thus shown to have evolved over time due to a gradually decreasing rate of creation of oceanic lithosphere meaning that archaean tectonics and phanerozoic tectonics are but two points on an evolutionary continuum

methane rich fluids in the oceanic crust analyses of fluid inclusions in plutonic rocks recovered from the slow spreading southwest indian ridge swir record ch4 concentrations of 15 40 times those of hydrothermal vent fluids and of basalt hosted volcanic gases and provide the first direct sampling of co2 ch4 h2o h2 c bearing fluids in the oceanic crust compositional thermal and spatial analyses of these fluids are used to model the evolution of volatiles during the crystallization and cooling of mid ocean ridge magma chambers and to assess the potential importance of carbon bearing fluids in geochemical processes in the lower crustal component of hydrothermal systems results from these analyses show that the earliest fluids to be exsolved from the melts are dominated by co2 rich vapors which with progressive fractionation evolved to more h2o rich compositions these later fluids were most likely exsolved under immiscible conditions and involved the development of co2 h2o rich vapors and co2 h2o nacl brines that were trapped during mineral growth as well as during later high temperature fracturing events co2 ch4 h2o rich fluids in olivine and plagioclase minerals that contain up to 30 50 mol co2 and 33 mol ch4 may reflect respeciation of magmatic co2 during cooling and attendant graphite precipitation phase equilibria suggest that these fluids reequilibrated at 500 600 c and at fo2 s 3 log units below to close to qfm conditions alternatively the inclusions may record respeciation of magmatic fluids attendant with the inward diffusion of h2 into the inclusions and reduction of entrapped co2 during degassing and cooling of the gabbros throughout the subsolidus regime subsequent seawater reaction at minimum temperatures of 400 c with mafic rich layers within the gabbroic rocks or with ultramafic material that underlies the plutonic sequence resulted in the formation of ch4 h2o fluids that contain up to 40 mol ch4 molecular h2 and graphite daughter minerals these data provide strong evidence that the ch4 h2o rich fluids produced during serpentinization reactions were trapped under equilibrium conditions in the presence of graphite at very near to qfm conditions the ubiquitous occurrence of ch4 rich fluids in oceanic crustal layer 3 rocks from the swir indicates that these fluids may be a significant and previously unrecognized source for these volatile species in some hydrothermal systems venting on the seafloor and that the deep seated fluids most likely play an important role in the transfer of carbon from the lithosphere to the hydrosphere

the effects of serpentinization on density and magnetic susceptibility a petrophysical model abstract new measurements are presented of initial magnetic susceptibility and density for serpentinized harzburgites from the josephine peridotite oregon an inverse correlation between density and susceptibility which is typical of these rocks and similar rocks from other localities is not explained by simple serpentinization reactions calculations of density and susceptibility as a function of reaction progress for reactions that produce magnetite show susceptibilities that are larger than those observed at low degrees of serpentinization susceptibilities of fe bearing serpentine and brucite are calculated from a molecular field model initially developed for the olivine and orthopyroxene solid solutions at high degrees of serpentinization susceptibilities that are lower than those observed are predicted by reactions where iron is sequestered by serpentine and brucite observed density susceptibility trends of serpentinized harzburgites fall between the values predicted by these limiting reactions the observed properties may be modelled by multiple reactions involved in multi stage serpentinization processes such that the production of magnetite increases with the degree of serpentinization the empirical and calculated properties provide a complementary characterization of density and susceptibility values of serpentinites

the 1942 southwest indian ocean ridge earthquake largest ever recorded on an oceanic transform the 1942 southwest indian ocean earthquake is the largest ever recorded on an oceanic transform its mechanism has essentially the expected pure strike slip geometry using long period surface wave techniques the seismic moment is found to be 1 3 1028 dyn cm directivity suggests southwestward rupture propagation over approximately 130 km this shock is then much smaller than previously reported on the basis of its high unified richter magnitude m 8 3 it does not show the slow energy release occasionally found in large transform fault events scaling laws and thermal modeling suggest that seismic slip extended at least to the 600 c isotherm

extent of the microbial biosphere in the oceanic crust we estimate the depth of the 120 c isotherm by constructing crustal thermal gradients based on theoretical and observed conductive heat flux as a function of lithospheric age we chose the 120 c isotherm because it is close to the upper limit for prokaryotic life and therefore the isotherm approximates the maximum depth at which life can persist in the ocean crust the depth of the potential microbial biosphere increases with lithospheric age from approximately 0 5 to 1 km for 1 ma lithosphere to as much as 5 km at a subduction age of 180 ma we use global models of oceanic plate creation to estimate the volume of crust occupied by the biosphere today and throughout geologic time presently the volume of the ocean crust that is capable of containing life is similar to the volume of the oceans 1018 m3 depending on the model used for the growth of continental crust the volume of rock available to house the subsurface biosphere may have remained constant or doubled since the archean although the thermal models presented here provide estimates for the potential depth and volume of rock in which microbes may live the biomass in this volume is not well constrained using a previously published model the prokaryotic biomass in the igneous ocean crust is estimated to exceed that in all aquatic and soil environments and is similar to that in the continental subsurface and in marine sediment most of the crustal biomass beneath the sediments is likely contained within the extrusive layer and this has probably been the case since microbes first colonized the oceanic crust in the archean

drilling to gabbro in intact ocean crust sampling an intact sequence of oceanic crust through lavas dikes and gabbros is necessary to advance the understanding of the formation and evolution of crust formed at mid ocean ridges but it has been an elusive goal of scientific ocean drilling for decades recent drilling in the eastern pacific ocean in hole 1256d reached gabbro within seismic layer 2 1157 meters into crust formed at a superfast spreading rate the gabbros are the crystallized melt lenses that formed beneath a mid ocean ridge the depth at which gabbro was reached confirms predictions extrapolated from seismic experiments at modern mid ocean ridges melt lenses occur at shallower depths at faster spreading rates the gabbros intrude metamorphosed sheeted dikes and have compositions similar to the overlying lavas precluding formation of the cumulate lower oceanic crust from melt lenses so far penetrated by hole 1256d

geochemical controls on hydrothermal fluids from the kairei and edmond vent fields 23 25 s central indian ridge prior to 2000 no mid ocean ridge hydrothermal systems were identified and sampled in the indian ocean the kairei field central indian ridge was discovered and sampled in 2000 gamo et al 2001 hashimoto et al 2001 this paper reports the chemical composition of hydrothermal fluids collected in 2001 from both the kairei and newly discovered edmond hydrothermal systems data are used to infer subsurface processes and conditions at the two sites as well as to place them within the global context of known hydrothermal sites on the mid ocean ridge system while both sites are located on the intermediate spreading central indian ridge their hydrologic systems have affinities with those observed on slow spreading ridges although the compositions of fluids from the four individual vents sampled at edmond and the three individual vents sampled at kairei vary respectively our interpretation is that a single source fluid at each site is subsequently modified by processes including phase separation subsurface mixing with seawater and deposition and or remobilization of metal sulfide deposits to generate the observed range of compositions both fields are located 6 km from the neovolcanic zone on steps on the east wall of the axial valley with the edmond field 160 km north of kairei and almost 1000 m deeper 3300 versus 2450 m the edmond fluids are extremely hot with maximum measured temperatures of 382 c compared to 365 c for kairei all of the fluids sampled have chlorinities greater than local ambient seawater due to phase separation of seawater at supercritical conditions visual observations suggest both sites have been active for a substantial period of time again similar to observations of slow spreading ridges our chemical data suggest that the substrate underlying kairei is highly altered while that at edmond is not significant albitization appears to be occurring below the edmond field but not at kairei the edmond fluids are by far the hottest brines yet observed venting from a mid ocean ridge hydrothermal site resulting in unusually high concentrations of several transition metals

neo deterministic and probabilistic seismic hazard assessments a comparison over the italian territory estimates of seismic hazard obtained using the neo deterministic approach ndsha and the probabilistic approach psha are compared for the italian territory the ndsha provides values larger than those given by the psha in areas where large earthquakes are observed and in areas identified as prone to large earthquakes but lower values in low seismicity areas these differences suggest the adoption of the flexible robust and physically sound ndsha approach to overcome the proven shortcomings of psha thus allowing for a reliable seismic hazard estimation especially for those areas characterized by a prolonged quiescence i e in tectonically active sites where events of only moderate size have occurred in historical times

a starving majority deep beneath the seafloor the rocks and sediments beneath the seafloor may harbor most of earth s microorganisms molecular approaches are beginning to provide clues regarding the energy sources fueling their metabolic activity

understanding a submarine eruption through time series hydrothermal plume sampling of dissolved and particulate constituents west mata 2008 2012 four cruises between 2008 and 2012 monitored the continuing eruption of west mata volcano in the ne lau basin as it produced plumes of chemically altered water above its summit although large enrichments in 3he co2 fe and mn were observed in the plumes the most notable enrichment was that of h2 which reached concentrations as high as 14 843 nm strongly enriched h2 concentrations in the water column result from reactions between seawater or magmatic water and extremely hot rocks in 2008 the observation of elevated h2 concentrations in the water column above west mata pointed to vigorous ongoing eruptions at the volcano s summit the eruption was confirmed by visual observations made by the rov jason 2 in 2009 and demonstrated that h2 measurements are a vital instrument to detect ongoing volcanic eruptions at the seafloor elevated h2 in 2010 showed that the eruption was ongoing although at a reduced level given a maximum h2 concentration of 4410 nm in 2012 h2 levels in the water column declined significantly to a maximum of only 7 nm consistent with visual observations from the quest 4000 rov that found no evidence of an ongoing volcanic eruption methane behaved independently of other measured gases and its concentrations in the hydrothermal plume were very low we attribute its minimal enrichments to a mixture of mantle carbon reduced to ch4 and biological ch4 from diffuse flow sites this study demonstrates that ongoing submarine volcanic eruptions are characterized by high dissolved h2 concentrations present in the overlying water column

active submarine eruption of boninite in the northeastern lau basin subduction of oceanic crust and the formation of volcanic arcs above the subduction zone are important components in earth s geological and geochemical cycles subduction consumes and recycles material from the oceanic plates releasing fluids and gases that enhance magmatic activity feed hydrothermal systems generate ore deposits and nurture chemosynthetic biological communities among the first lavas to erupt at the surface from a nascent subduction zone are a type classified as boninites these lavas contain information about the early stages of subduction yet because most subduction systems on earth are old and well established boninite lavas have previously only been observed in the ancient geological record here we observe and sample an active boninite eruption occurring at 1 200 m depth at the west mata submarine volcano in the northeast lau basin southwest pacific ocean we find that large volumes of h2o co2 and sulphur are emitted which we suggest are derived from the subducting slab these volatiles drive explosive eruptions that fragment rocks and generate abundant incandescent magma skinned bubbles and pillow lavas the eruption has been ongoing for at least 2 5 years and we conclude that this boninite eruption is a multi year low mass transfer rate eruption thus the lau basin may provide an important site for the long term study of submarine volcanic eruptions related to the early stages of subduction boninite lavas are erupted during the early stages of subduction however they have previously been found only in the ancient geological record discovery of an active boninite eruption shows that abundant volatile gases derived from the subducting slab drive this violent eruptive activity even in the deep sea

low temperature volatile production at the lost city hydrothermal field evidence from a hydrogen stable isotope geothermometer although commonly utilized in continental geothermal work the water hydrogen and methane hydrogen isotope geothermometers have been neglected in hydrothermal studies here we report d ch4 and d h2 values from high temperature black smoker type hydrothermal vents and low temperature carbonate hosted samples from the recently discovered lost city hydrothermal field methane deuterium content is uniform across the dataset at 120 12 hydrogen d values vary from 420 to 330 at high temperature vents to 700 to 600 at lost city the application of several geothermometer equations to a suite of hydrothermal vent volatile samples reveals that predicted temperatures are similar to measured vent temperatures at high temperature vents and 20 60 c higher than those measured at the lost city vents we conclude that the overestimation of temperature at lost city reflects 1 that methane and hydrogen are produced by serpentinization at n110 c and 2 that isotopic equilibrium at temperatures b70 c is mediated by microbial sulfate reduction the successful application of hydrogen isotope geothermometers to low temperature lost city hydrothermal samples encourages its employment with lowtemperature diffuse hydrothermal fluids 2005 elsevier b v all rights reserved

unique event plumes from a 2008 eruption on the northeast lau spreading center the creation of ocean crust by lava eruptions is a fundamental earth process involving immediate and immense transfers of heat and chemicals from crust to ocean this transfer creates event plumes megaplumes massive ellipsoidal eddies with distinctive and consistent chemical signatures here we report the discovery of unique event plumes associated with a 2008 eruption on the northeast lau spreading center instead of a large plume hundreds of meters thick we detected at least eight individual plumes each 50 m thick and apparently only 1 3 km in diameter yet still rising 200 1000 m above the eruption site low and uniform 3he heat 0 041 10 17 mol j and dissolved mn heat 0 04 nmol j ratios in water samples were diagnostic of event plumes high h2 concentrations up to 9123 nm and basalt shards confirmed extensive interactions between molten lava and event plume source fluids remote vehicle observations in 2009 mapped a new small 1 5 5 8 106 m3 lava flow our results suggest that event plumes are more variable and thus perhaps more common than previously recognized small event plumes may be preferentially associated with small or sheet flow eruptions and massive event plumes with slowly extruding pillow mounds 25 75 m thick despite this correlation and high h2 concentrations existing theory and seafloor observations argue that cooling lava cannot transfer heat fast enough to create the buoyancy flux required for event plumes the creation of event plumes under a broad range of eruption conditions provides new constraints for any theory of their formation

surface area measurements of marine basalts implications for the subseafloor microbial biomass colonization ssa ranged from 0 3 to 52 m 2 g of basalt with the lowest value coming from pillow basalt and the highest value from breccia the average for massive and pillow basalts combined was 2 3 m 2 g the total specific surface area of the extrusive volcanic rocks of the ocean crust is estimated to be 10 24 m 2 this surface area could provide attachment for up to 10 34 cells if cell density is the same as that of experimentally colonized basalt surfaces independent measures and calculations of biomass in basalts suggest that cell densities on surfaces are only 10 4 times those in laboratory experiments and therefore the surface area of basalt does not limit microbial biomass in the igneous ocean crust citation nielsen m e and m r fisk 2010 surface area measurements of marine basalts implications for the subseafloor microbial biomass geophys res lett 37 l15604 doi 10 1029 2010gl044074

h2 generation by reaction between h2o and crushed rock an experimental study on h2 degassing from the active fault zone granite and quartz were crushed under moist conditions in the temperature range of 25 270 c in order to obtain the information on the mechanism operative for h2 degassing along active faults it was found that the amounts of h2 gas released by crushing granite and quartz increased with temperature up to around 200 c and then decreased suddenly the results indicate that h2 gas is generated by a chemical reaction between water and such radicals as si and si o formed on the fresh surfaces when the si o si bonds are destroyed by crushing and that the existence of a maximum for amount of h2 gas is due to the decrease of the lifetime of si o radical at the temperature higher than about 200 c the results lend credence to the possibility that h2 gas is generated in the temperature range of 25 270 c along the active fault through the reaction between groundwater and the fresh surfaces of underground rocks formed by the fault movements

global rates of mantle serpentinization and h2 production at oceanic transform faults in 3 d geodynamic models previous studies have estimated that mantle serpentinization reactions generate h2 at a rate of 1010 1012mol per year along the global mid ocean ridge mor system here we present results of 3 d geodynamic simulations that predict rates of additional mantleserpentinization and h2 production at oceanic transform faults otf we find that the extent and rate of mantle serpentinization increases with otf length and is maximum at intermediate slip rates of 5 to 10 cm per year the additional global otf relatedproduction of h2 is found to be between 6 1 and 10 7 x 1011mol per year which is comparable to the predicted background mor rateof 4 1 15 0 x 1011mol h2 yr this points tooceanic transform faults as potential sites of intense fluid rock interaction where chemosynthetic life could be sustained by serpentinization reactions

incorporation of seawater into mid ocean ridge lava flows during emplacement evidence for the interaction between seawater and lava during emplacement on the deep seafloor can be observed in solidified flows at a variety of scales including rapid quenching of their outer crusts and the formation of lava pillars through the body of the flow recently an additional interaction incorporation of heated seawater vapor into the body of a flow has been proposed large voids and vesicles beneath the surface crusts of mid ocean ridge crest lobate and sheet lava flows and lava drips found within those cavities have been cited as evidence for this interaction the voids resulting from this interaction contribute to the high porosity of the shallow ocean crust and play an important role in crustal permeability and hydrothermal circulation at mid ocean ridges and thus it is important to understand their origin we analyze lava samples from the fast spreading east pacific rise and intermediate spreading galapagos spreading center to characterize this process identify the source of the vapor and investigate the implications this would have on submarine lava flow dynamics we find that lava samples that have interacted with a vapor have a zone of increased vesicularity on the underside of the lava crust and a coating of precipitate minerals i e crystal fringe that are distinct in form and composition from those crystallized from the melt we use thermochemical modeling to simulate the reaction between the lava and a vapor and find that only with seawater can we reproduce the phase assemblage we observe within the crystal fringes present in the samples model results suggest that large scale contamination of the lava by mass exchange with the vapor is unlikely but we observe local enrichment of the lava in cl resulting from the incorporation of a brine phase separated from the seawater we suggest that high eruption rates are necessary for seawater incorporation to occur but the mechanism by which seawater enters the flow has yet to be resolved a persistent vapor phase may be important in inhibiting the collapse of lava flow roofs during natural waxing and waning of lava levels during emplacement allowing lava pathways to be maintained during long lived eruptions in addition we illustrate the potential for a persistent vapor layer to increase local flow rates within submarine flows by up to a factor of three thereby influencing how lava is distributed across the ridge crest

chemical reaction rates and entrainment within the endeavour ridge hydrothermal plume the aging of the hydrothermal plume over the endeavour segment of the juan de fuca ridge was estimated by measuring the222rn3he ratio in the plume as it dispersed despite uncertainties in the source function of hydrothermal input it wa determined that the relative sequence of removal from the plume ish2 c 222rn ch4 mn where c is a measure of particle concentration and the mean life of222rn is 5 5 days h2 is removed from the plume within hours of input while mn is not removed within the two week timescale of the radon helium clock entrainment of bottom water within the buoyant plume may introduce additional chemical signatures into the spreading effluent layer over that which would be introduced by hydrothermal discharge alone this is particularly significant for those chemical species which are not greatly enriched in the vent fluids relative to bottom water concentration and which display a nutrient like profile in the deep ocean thus we found that significant fractions of the si and226ra anomalies in the plume were not of hydrothermal origin but were derived from entrained bottom water which has a higher concentration of these elements than ambient water at plume height

influence of subsurface biosphere on geochemical fluxes from diffuse hydrothermal fluids hydrothermal vents along mid ocean systems host unique highly productive biological communities based on microbial chemoautotrophy that thrive on the sulphur metals nitrogen and carbon emitted from the vents into the deep ocean geochemical studies of vents have centred on analyses of high temperature focused hydrothermal vents which exhibit very high flow rates and are generally considered too hot for microbial life geochemical fluxes and metabolic activity associated with habitable lower temperature diffuse fluids remain poorly constrained as a result little is known about the extent to which microbial communities particularly in the subsurface influence geochemical flux from more diffuse flows here we estimate the net flux of methane carbon dioxide and hydrogen from diffuse and focused hydrothermal vents along the juan de fuca ridge using an in situ mass spectrometer and flowmeter we show that geochemical flux from diffuse vents can equal or exceed that emanating from hot focused vents notably hydrogen concentrations in fluids emerging from diffuse vents are 50 to 80 lower than predicted we attribute the loss of hydrogen in diffuse vent fluids to microbial consumption in the subsurface and suggest that subsurface microbial communities can significantly influence hydrothermal geochemical fluxes to the deep ocean

a note on the fluxes of abiogenic methane and hydrogen from mid ocean ridges the concentrations of methane and hydrogen in hydrothermal vent fluids issuing from mid ocean ridges tend to fall into two groups one with high concentrations of these gases in ultramafic hosted vent fields and a second group with relatively lower concentrations in basalt hosted vent fluids ultramafic hosted systems however appear to be restricted to slow spreading ridges and constitute only a fraction of the hydrothermal systems found there in this note the hydrothermal fluxes of methane and hydrogen have been calculated by estimating the percentages of the total subsurface hydrothermal circulation that circulate through each type of host rock even though the percentage of the total subsurface flow that is affected by serpentinization appears to be rather small 8 it still appears that this process produces about 70 of the total mid ocean flux of these gases the total production of methane and hydrogen is calculated to be about 20 x 10 9 mol yr 1 and 190 x 10 9 mol yr 1 respectively the hydrogen flux is comparable to that most recently calculated on the basis of the rate of hydration of mantle rock in newly formed crust and the stoichiometry of the serpentinization reaction this suggests that except for the production of methane a major portion of the hydrogen produced in the subsurface is not consumed before venting

deep and high temperature hydrothermal circulation in the oman ophiolite petrological and isotopic evidence a systematic search for evidence of high temperature hydrous alteration within the gabbros of the samail ophiolite oman shows that most of the gabbros have been affected by successive stages of alteration starting above 975 c and ending below 500 c sr and o isotopic analyses provide constraints on the nature and origin of the fluids associated with these alteration events massive gabbros dykes and veins and their associated minerals depart from mid ocean ridge basalt morb source magma signatures 87sr 86sr 0 7032 and depleted 18o 10 a second group of samples including massive gabbros and high temperature dykes and veins is characterized by lower water rock ratios in the range of 3 5 these samples display a high temperature hydrothermal alteration related to seawater ingression the main fluid channels may be sub millimetre sized microcracks with a dominantly vertical attitude which constitute the recharge hydrothermal system whereas the dykes and veins represent the discharge part this model requires that these dykes have been generated by hydration of the crystallizing gabbros via seawater penetration near the internal wall of the magma chamber

iron and sulfide oxidation within the basaltic ocean crust implications for chemolithoautotrophic microbial biomass production microbial processes within the ocean crust are of potential importance in controlling rates of chemical reactions and thereby affecting chemical exchange between the oceans and lithosphere we here assess the oxidation state of altered ocean crust and estimate the magnitude of microbial biomass production that might be supported by oxidative and nonoxidative alteration compilations of fe2o3 feo and s concentrations from dsdp odp drill core samples representing upper basaltic ocean crust suggest that fe3 fe increases from 0 15 0 05 to 0 45 0 15 within the first 10 20 myr of crustal evolution within the same time frame 70 25 of primary sulfides in basalt are oxidized with an annual production of 4 0 1 8 1015 g of upper 500 200 m crust and average initial concentrations of 8 0 1 3 wt fe and 0 125 0 020 wt s we estimate annual oxidation rates of 1 7 1 2 1012 mol fe and 1 1 0 7 1011 mol s we estimate that 50 of fe oxidation may be attributed to hydrolysis producing 4 5 3 0 1011 mol h2 yr thermodynamic and bioenergetic calculations were used to estimate the potential chemolithoautotrophic microbial biomass production within ridge flanks combined aerobic and anaerobic fe and s oxidation may support production of up to 48 21 1010 g cellular carbon c hydrogen consuming reactions may support production of a similar or larger microbial biomass if iron reduction nitrate reduction or hydrogen oxidation by o2 aq are the prevailing metabolic reactions if autotrophic sulfate reduction or methanogenesis prevail the potential biomass production is 9 7 1010 g c yr and 3 2 1010 g c yr respectively combined primary biomass production of up to 1 1012 g c yr may be similar to that fueled by anaerobic oxidation of organic matter in deep seated heterotrophic systems these estimates suggest that water rock reactions may support significant microbial life within ridge flank hydrothermal systems these estimates suggest that water rock reactions may support significant microbial life within ridge flank hydrothermal systems

hydrothermal circulation through mid ocean ridge flanks fluxes of heat and magnesium thermally driven convection of seawater occurs through oceanic crust of all ages at the seafloor spreading axis on mid ocean ridge flanks and in the ocean basins at the ridge axis and on the flanks circulating seawater produces a major chemical exchange between the oceans and the crust based on heat budget constraints and the composition of hot springs between 10 and 40 of the river flux of mg can be taken up during high temperature alteration of the basaltic crust along the ridge axis most of the hydrothermal heat loss however occurs on the mid ocean ridge flanks where the temperatures are lower and the seawater flux correspondingly larger the estimated heat loss on the flanks is so large that upwelling must occur over a large fraction 5 30 of the seafloor less than 65 ma in age if temperatures are 20 c and seepage velocities are on the order of 10 to 100 cm y the circulating seawater needs to lose on average less than 1 2 of its mg content in order to solve the mg mass balance for the oceans chemical fluxes through mid ocean ridge flanks are poorly known because of the wide range of crustal conditions that prevail there and the paucity of study to date the most critical parameter for characterizing crustal conditions is temperature in basement which is a function of crustal age basement topography and sediment thickness and permeability basement temperature which can usually be inferred from heat flow and seismic reflection surveys largely determines the change in the composition of seawater circulating through basement this change can be inferred in turn from profiles of sediment porewater chemistry all sites studied to date with temperatures at the sediment basement interface 25 c have a large component of advective heat loss and show only a small 80 mg loss both types of sites may be important for chemical fluxes whether the cooler sites are important depends on how much the seawater changes in composition as it circulates through the crust only small changes are needed whether the warmer sites are important depends on how much heat is lost by advection in this type of setting the warmer sites could produce significant chemical fluxes even if they are scarce they could account for the entire river input of mg to the oceans even if they represent only 8 20 of the total advective heat loss on ridge flanks

abiotic hydrogen h2 sources and sinks near the mid ocean ridge mor with implications for the subseafloor biosphere 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

dynamical properties of developing tropical cyclones using lagrangian flow topology the goal of this study is to characterize the dynamics and structure of tropical cyclone formation from global model analyses to determine thresholds marking the various stages of development that can be computed from the analysis data we introduce here a new methodology for identifying disturbances that show high likelihood of becoming a tropical depression or tropical storm we use lagrangian frame independent quantities to define intrinsic coordinates for candidate disturbances prior to and post tropical depression declaration in the best track data hurdat2 we use these lagrangian quantities also as metrics for quantifying the strength of these systems within global model analyses as they are declared depressions storms or hurricanes in hurdat2 the criteria proposed are more precise than similar eulerian criteria since the minimum thresholds for development in the best track data set are very close to the threshold at which no false alarms are produced in the global model analyses since only very loose thermodynamic thresholds are required these criteria can be considered dynamically based and require no statistical analysis to compensate for uncertainties in moisture or convection we describe further the structure of the developing systems using a set of objective profiles where level contours of the lagrangian averaged rotation rate are mapped to an equivalent radius composites of these profiles reveal that the transition to tropical storm strength vortices is marked by the existence of a notable shear sheath outside a region of enhanced solid body rotation

a serpentinite hosted ecosystem the lost city hydrothermal field the serpentinite hosted lost city hydrothermal field is a remarkable submarine ecosystem in which geological chemical and biological processes are intimately interlinked reactions between seawater and upper mantle peridotite produce methane and hydrogen rich fluids with temperatures ranging from 40 to 90 c at ph 9 to 11 and carbonate chimneys 30 to 60 meters tall a low diversity of microorganisms related to methane cycling archaea thrive in the warm porous interiors of the edifices macrofaunal communities show a degree of species diversity at least as high as that of black smoker vent sites along the mid atlantic ridge but they lack the high biomasses of chemosynthetic organisms that are typical of volcanically driven systems

the seismic moment budget of slowly spreading ridges mid ocean ridges with well developed median valleys are commonly the sites of large normal faulting earthquakes1 2 a recent global study3 6 of the centroid depths and source mechanisms of such earthquakes has yielded two important conclusions first that all the largest mid ocean ridge earthquakes occur beneath the inner floor of the median valley and second that the maximum thickness of the seismogenic layer increases with decreasing spreading rate these results lend support to the hypothesis that the median valley arises from the necking of a strong brittle lithosphere under horizontal extension7 9 here we compare the global rate of seismic moment release along slowly spreading mid ocean ridges with the rate predicted if widening of the median valley occurs entirely by seismogenic extension of the brittle lithosphere beneath the inner floor we find that earthquakes account for no more than about 10 20 of the rate of plate separation across the central median valley

implications of present day abiogenic methane fluxes for the early archean atmosphere 1 during earth s early history greenhouse warming by atmospheric methane helped to maintain elevated surface temperatures here we estimate the present day abiogenic ch4 flux generated by mineral alteration serpentinization at mid ocean ridges volcanic emissions and geothermal sources in addition we assess the impact that abiogenic methane may have had on greenhouse warming during the early prebiotic archean based on estimates of the rate of seafloor spreading and the degree of serpentinization within the oceanic crust the flux of methane generated by serpentinized lithosphere is calculated to be 1 35 mt ch4 y 1 while volcanic and geothermal sources are estimated to contribute 0 1 and 0 9 mt ch4 y 1 respectively furthermore it is shown that if atmospheric co2 partial pressures were above 0 01 bar the present day level of abiogenic methane production could have been sufficient to maintain above freezing surface temperatures during the archean the very high temperatures 70 c that have been suggested for the early archean however would have required extremely high methane fluxes or more likely greatly elevated atmospheric co2 levels

dissolved hydrogen and methane in the oceanic basaltic biosphere abstract the oceanic basaltic crust is the largest aquifer on earth and has the potential to harbor substantial subsurface microbial ecosystems which hitherto remains largely uncharacterized and is analogous to extraterrestrial subsurface habitats within the sediment buried 3 5 myr old basaltic crust of the eastern juan de fuca ridge flank the circulating basement fluids have moderate temperature 65 c and low to undetectable dissolved oxygen and nitrate concentrations sulfate present in high concentrations is therefore expected to serve as the major electron acceptor in this subsurface environment this study focused on the availability and potential sources of two important electron donors methane ch4 and hydrogen h2 for the subseafloor biosphere high integrity basement fluids were collected via fluid delivery lines associated with integrated ocean drilling program iodp circulation obviation retrofit kits corks that extend from basement depths to outlet ports at the seafloor two new corks installed during iodp 327 in 2010 1362a and 1362b were sampled in 2011 and 2013 the two corks are superior than earlier style corks in that they are equipped with coated casing and polytetrafluoroethylene fluid delivery lines reducing the interaction between casing materials with the environment additional samples were collected from an earlier style cork at borehole 1301a the basement fluids are enriched in h2 0 05 1 8 mol kg suggesting that the ocean basaltic aquifer can support h2 driven metabolism the basement fluids also contain significant amount of ch4 5 32 mol kg revealing ch4 as an available substrate for subseafloor basaltic habitats the 13c values of ch4 from the three boreholes ranged from 22 5 to 58 while the 2h values ranged from 316 to 57 the isotopic compositions of ch4 and the molecular compositions of hydrocarbons suggest that ch4 in the basement fluids is of both biogenic and abiotic origins varying among sites and sampling times the 2h values of ch4 in cork 1301a fluid samples are much more positive than found in all other marine environments investigated to date and are best explained by the partial microbial oxidation of biogenic ch4 in conclusion our study shows that ch4 and h2 are persistently available to fuel the deep biosphere and that ch4 is both produced and potentially consumed by microorganisms in the oceanic basement