asphalt volcanoes as a potential source of methane to late pleistocene coastal waters natural petroleum seepage emits large volumes of oil and methane to the oceans every year accompanied by the formation of asphalt volcanoes on the sea floor the discovery of seven asphalt volcanoes off the coast of southern california may help to explain high methane emissions recorded during the late pleistocene

methane fluxes and carbonate deposits at a cold seep area of the central nile deep sea fan eastern mediterranean sea abstract high acoustic seafloor backscatter signals characterize hundreds of patches of methane derived authigenic carbonates and chemosynthetic communities associated with hydrocarbon seepage on the nile deep sea fan ndsf in the eastern mediterranean sea during a high resolution ship based multibeam survey covering a 225 km2 large seafloor area in the central province of the ndsf we identified 163 high backscatter patches at water depths between 1500 and 1800 m and investigated the source composition turnover flux and fate of emitted hydrocarbons systematic parasound single beam echosounder surveys of the water column showed hydroacoustic anomalies flares indicative of gas bubble streams above 8 of the high backscatter patches in echosounder records flares disappeared in the water column close to the upper limit of the gas hydrate stability zone located at about 1350 m water depth due to decomposition of gas hydrate skins and subsequent gas dissolution visual inspection of three high backscatter patches demonstrated that sediment cementation has led to the formation of continuous flat pavements of authigenic carbonates typically 100 to 300 m in diameter volume estimates considering results from high resolution autonomous underwater vehicle auv based multibeam mapping were used to calculate the amount of carbonate bound carbon stored in these slabs additionally the flux of methane bubbles emitted at one high backscatter patch was estimated 0 23 to 2 3 106 mol a 1 by combined auv flare mapping with visual observations by remotely operated vehicle rov another high backscatter patch characterized by single carbonate pieces which were widely distributed and interspaced with sediments inhabited by thiotrophic chemosynthetic organisms was investigated using in situ measurements with a benthic chamber and ex situ sediment core incubation and allowed for estimates of the methane consumption 0 1 to 1 106 mol a 1 and dissolved methane flux 2 to 48 106 mol a 1 our comparison of dissolved and gaseous methane fluxes as well as methane derived carbonate reservoirs demonstrates the need for quantitative assessment of these different methane escape routes and their interaction with the geo bio and hydrosphere at cold seeps

determination of sea floor seepage locations in the mississippi canyon abstract the ephemeral nature of marine oil and gas seepages and their complex trajectories in the water column make seep sampling difficult and costly here we report on how active natural seepage can be detected and located in the water column and at the sea bed in real time through the integration of marine x band radar synthetic aperture radar field observations high resolution single beam acoustic methods and meta ocean data from the marine environment with a simple bubble rise model the extent of predictions made using a bubble rise model narrow down the likely seafloor origin point of an observed surface feature to within a radius of 630 m within which clusters of acoustic contacts were detected use of averaged deep current velocities and directions narrows the radius to 130 m and use of a smaller established range of bubble rise speeds from the gulf of mexico can narrow the predicted seafloor origin radius further to 16 5 m these results are useful for focussing detailed sea bed search patterns for natural seepage and are also suggestive of a seep system with complex water column trajectories associated with biloxi dome in the gulf of mexico

petroleum degradation and associated microbial signatures at the chapopote asphalt volcano southern gulf of mexico abstract at the chapopote knoll in the southern gulf of mexico deposits of asphalt provide the substrate for a prolific cold seep ecosystem extensively colonized by chemosynthetic communities this study investigates microbial life and associated biological processes within the asphalts and surrounding oil impregnated sediments by analysis of intact polar membrane lipids ipls petroleum hydrocarbons and stable carbon isotopic compositions 13c of hydrocarbon gases asphalt samples are lightly to heavily biodegraded suggesting that petroleum derived hydrocarbons serve as substrates for the chemosynthetic communities accordingly detection of bacterial diester and diether phospholipids in asphalt samples containing finely dispersed gas hydrate suggests the presence of hydrocarbon degrading bacteria biological methanogenesis contributes a substantial fraction to the methane captured as hydrate in the shallow asphalt deposits evidenced by significant depletion in 13c relative to background thermogenic methane in sediments petroleum migrating from the subsurface stimulates both methanogenesis and methanotrophy at a sulfate methane transition zone 6 7 m below the seafloor in this zone microbial ipls are dominated by archaeal phosphohydroxyarchaeols and archaeal diglycosidic diethers and tetraethers bacterial ipls dominate surface sediments that are impregnated by severely biodegraded oil in the sulfate reduction zone diagnostic ipls indicate that sulfate reducing bacteria srb play an important role in petroleum degradation a diverse mixture of phosphohydroxyarchaeols and mixed phospho and diglycosidic archaeal tetraethers in shallow oil impregnated sediments point to the presence of anaerobic methane oxidizing anme 2 and anme 1 archaea respectively or methanogens archaeal ipls increase in relative abundance with increasing sediment depth and decreasing sulfate concentrations accompanied by a shift of archaeol based to tetraether based archaeal ipls the latter shift is suggested to be indicative of a community shift from anme 2 and or methanogenic archaea in shallower sediments to anme 1 methanogenic archaea and possibly benthic archaea in deeper sediments

ebullition and storm induced methane release from the east siberian arctic shelf vast quantities of carbon are stored in shallow arctic reservoirs such as submarine and terrestrial permafrost submarine permafrost on the east siberian arctic shelf started warming in the early holocene several thousand years ago however the present state of the permafrost in this region is uncertain here we present data on the temperature of submarine permafrost on the east siberian arctic shelf using measurements collected from a sediment core together with sonar derived observations of bubble flux and measurements of seawater methane levels taken from the same region the temperature of the sediment core ranged from 1 8 to 0 degrees c although the surface layer exhibited the lowest temperatures it was entirely unfrozen owing to significant concentrations of salt on the basis of the sonar data we estimate that bubbles escaping the partially thawed permafrost inject 100 630 mg methane m 2 d 1 into the overlying water column we further show that water column methane levels had dropped significantly following the passage of two storms we suggest that significant quantities of methane are escaping the east siberian shelf as a result of the degradation of submarine permafrost over thousands of years we suggest that bubbles and storms facilitate the flux of this methane to the overlying ocean and atmosphere respectively

repeated pulses of vertical methane flux recorded in glacial sediments from the southeast bering sea 1 there is controversy over the role of marine methane hydrates in atmospheric methane concentrations and climate change during the last glacial period in this study of two sediment cores from the southeast bering sea 700 m and 1467 m water depth we identify multiple episodes during the last glacial period of intense methane flux reaching the seafloor within the uncertainty of the radiocarbon age model the episodes are contemporaneous in the two cores and have similar timing and duration as dansgaard oeschger events the episodes are marked by horizons of sediment containing 13c depleted authigenic carbonate minerals 13c depleted archaeal and bacterial lipids which resemble those found in anme 1 type anaerobic methane oxidizing microbial consortia and changes in the abundance and species distribution of benthic foraminifera the similar timing and isotopic composition of the authigenic carbonates in the two cores is consistent with a region wide increase in the upward flux of methane bearing fluids this study is the first observation outside santa barbara basin of pervasive repeated methane flux in glacial sediments however contrary to the clathrate gun hypothesis kennett et al 2003 these coring sites are too deep for methane hydrate destabilization to be the cause implying that a much larger part of the ocean s sedimentary methane may participate in climate or carbon cycle feedback at millennial timescales we speculate that pulses of methane in these opal rich sediments could be caused by the sudden release of overpressure in pore fluids that builds up gradually with silica diagenesis the release could be triggered by seismic shaking on the aleutian subduction zone caused by hydrostatic pressure increase associated with sea level rise at the start of interstadials

characteristics and scaling of bubble plumes from marine hydrocarbon seepage in the coal oil point seep field 1 the fate of marine seep gases in the ocean and atmosphere is intimately connected with bubble and bubble plume processes which are strongly size and depth dependent size dependent flux distributions and vertical velocity functions vz r were measured with a video bubble measurement system in the santa barbara channel california several distinct plume types were identified for which size distributions were measured major minor intermediate and obstructed a further vent class is elastic which was observed but not quantified in addition any plume class could be oily minor plumes generally produced a lower emission flux q and showed narrow peaked that were well described as gaussian the radius of the dominant peak rp of minor plumes varied as q0 40 with correlation coefficient r2 0 84 in agreement with theoretical relationship of rp q0 4 for q above a critical flow rate oil contamination was found to affect rp and was not used in the fit a probability distribution rp for all gaussian bubble plumes was itself well described by a combination of gaussian functions which were different for different seep areas major plumes showed a broad distribution including very small and very large bubbles and were well described by a power law with exponent a which varied with q according to a 0 43 0 55 log q with r2 0 77 one obstructed vent was analyzed and shared characteristics with the minor bubble plumes mixed bubble plume size distributions showed characteristics of both major and minor plume classes i e were described by a combination of gaussian functions and power laws and were steeper higher a than major plumes for the same q oily plumes produced complex confused bubble size distributions upwelling velocities vup r were derived from vz r and increased as vup q0 66 r2 0 64 however consideration of the more intense plumes q 2 cm s 1 showed vup q0 35 in agreement with other published field measurements thus the weaker bubble plumes were observed during the acceleration phase

control of quaternary sea level changes on gas seeps gas seeping to the seafloor through structures such as pockmarks may contribute significantly to the enrichment of atmospheric greenhouse gases and global warming gas seeps in the gulf of lions western mediterranean are cyclical and pockmark life is governed both by sediment accumulation on the continental margin and quaternary climate changes three dimensional seismic data correlated to multi proxy analysis of a deep borehole have shown that these pockmarks are associated with oblique chimneys the prograding chimney geometry demonstrates the syn sedimentary and long lasting functioning of the gas seeps gas chimneys have reworked chronologically constrained stratigraphic units and have functioned episodically with maximum activity around sea level lowstands therefore we argue that one of the main driving mechanisms responsible for their formation is the variation in hydrostatic pressure driven by relative sea level changes

the fate of bubbles in a large intense bubble megaplume for stratified and unstratified water numerical simulations of 22 4b expedition field data extremely intense bubble plumes like the north sea 22 4b blowout megaplume defined as more than 10 6 l day 1 create very strong upwelling flows 1 m s 1 which lead to detrainment of methane enriched water but leave direct bubble mediated transport unaffected dissolved ch4 depth profiles and atmospheric measurements during a fall 2011 survey of the 22 4b site suggest strong constraint of seabed ch4 below the thermocline seabed bubbles were nearly pure ch4 the effect of the upwelling flow on the fate of bubble plume ch4 was investigated with a numerical bubble propagation model the model considered different representative bubble plume size distributions phi and a global total megaplume bubble size distribution phi synthesized from video survey data and phi from the literature simulations showed that none of the literature plumes or variations in the upwelling flow could constrain ch4 sufficiently below the thermocline two new bubble megaplume processes were simulated vortical bubble trapping slow rise and a hypothesized enhanced bubble gas exchange k be an enhancement factor applied to the normal bubble gas exchange rate k b the latter could arise from plume turbulence increasing bubble boundary layer turbulence and thus its gas exchange observations could not be reproduced solely by slow rise however simulations with k be similar to 6 reproduced observational constraints as could weaker k be in conjunction with slow rise field validation of k be is needed given its implications for the fate of megaplume ch4 emissions anthropogenic or natural for stratified and unstratified conditions kbe suggests marine ch4 geologic contributions to the atmosphere from all but shallow waters primarily arises from bubble plumes that are less than megaplume size

reflection waveform inversion using local descent methods estimating attenuation and velocity over a gas sand deposit prestack seismic reflection data contain amplitudes traveltimes and moveout information waveform inversion of such data has the potential to estimate attenuation levels reflector depths and geometry and background velocities however when inverting reflection data strong nonlinearities can cause reflectors to be incorrectly imaged and can prevent background velocities from being updated to successfully recover background velocities previous authors have resorted to nonlinear global search inversion techniques we propose a two step inversion procedure using local descent methods in which we perform alternate inversions for the reflectors and the background velocities for our reflector inversion we exploit the efficiency of the back propagation method when inverting for a large parameter set for our background velocity inversion we use newton inverse methods during the background velocity inversions it is crucial to adaptively depth stretch the model to preserve the vertical traveltimes this reduces nonlinearity by largely decoupling the effects of the background velocities and reflectors on the data nonlinearity is further reduced by choosing to invert for slownesses and by inverting for a sparse parameter set which is partially defined using geological reflector picks applying our approach to shallow seismic data from the north sea collected over a gas sand deposit we demonstrate that the proposed method is able to estimate both the geometry and internal velocity of a significant velocity structure not present in the initial model over successive iterations the use of adaptive depth stretching corrects the pull down of the base of the gas sand vertical background velocity gradients are also resolved for an insignificant extra cost the acoustic attenuation parameter q is included in the inversion scheme the final attenuation tomogram contains realistic values of q for the expected lithologies and for the effect of partial fluid saturation associated with a shallow bright spot the attenuation image may also indicate the presence of fracturing

reappraisal of the fossil methane budget and related emission from geologic sources converging evidence from new top down and bottom up estimates of fossil radiocarbon free methane emissions indicates that natural geologic sources account for a substantial component of the atmospheric methane budget comparing emission estimates based on atmospheric 14 ch 4 radiomethane with geologic emissions from seepage including terrestrial macroseeps microseepage marine seeps and geothermal volcanic emissions from the earth s crust shows that such geo ch 4 sources can be conservatively estimated at 53 11 tg yr 1 globally this makes geo ch 4 second in importance to wetlands as a natural methane source such a new appraisal can easily be accommodated within the uncertainty of the global methane budget as recently compiled and recognizes the importance of geophysical out gassing of methane generated within the lithosphere we propose a new coherent contemporary budget in which 30 5 based on atmospheric radiomethane measurements of the global source of 582 87 tg yr 1 has fossil origin both natural and anthropogenic

considerable methane fluxes to the atmosphere from hydrocarbon seeps in the gulf of mexico the flux of methane a greenhouse gas from submarine hydrocarbon seeps to the atmosphere is not well quantified direct measurements of methane concentrations and isotopic depth profiles in deepwater hydrocarbon plumes indicate that a significant amount of methane from deep ocean sources could reach the surface ocean the fluxes of the greenhouse gas methane from many individual sources to the atmosphere are not well constrained1 marine geological sources may be significant2 but they are poorly quantified and are not included in the intergovernmental panel on climate change budget1 previous results based on traditional indirect sampling techniques and modelling suggested bubble plumes emitted from marine seeps at depths greater than 200 m do not reach the surface mixed layer because of bubble dissolution and methane oxidation3 4 5 here we report methane concentration and isotope depth profiles from direct submersible sampling of deepwater 550 600 m hydrocarbon plumes in the gulf of mexico we show that bubble size upwelling flows and the presence of surfactants inhibit bubble dissolution and that methane oxidation is negligible consequently methane concentrations in surface waters are up to 1 000 times saturation with respect to atmospheric equilibrium we estimate that diffusive atmospheric methane fluxes from individual plumes are one to three orders of magnitude greater than estimates from shallow water seeps6 7 8 greatly expanding the depth range from which methane seep emissions should be considered significant given the widespread occurrence of deepwater seeps we suggest that current estimates of the global oceanic methane flux to the atmosphere1 may be too low

acoustic estimates of methane gas flux from the seabed in a 6000 km2 region in the northern gulf of mexico seeps of free methane gas escaping the seabed can be found throughout the ocean basins to understand the role of methane gas seeps in the global carbon cycle including both gas added to the atmosphere and that which is dissolved and potentially oxidized in the ocean volume it is important to quantify the amount of methane escaping the seabed few large scale mapping projects of natural methane seeps have been undertaken however and even among these quantitative estimates of flux are rare here we use acoustic mapping techniques to survey 357 natural methane seeps in a large region 6000 km2 of the northern gulf of mexico and outline a general approach for methane seep mapping using a combination of multibeam and split beam echo sounders using additional measurements collected with a remotely operated vehicle rov together with the acoustic mapping results we estimate the total gas flux within the 6000 km2 region to be between 0 0013 and 0 16 tg yr or between 0 003 and 0 3 of the current estimates for global seabed methane seepage rates

velocity model building from seismic reflection data by full waveform inversion full waveform inversion is re emerging as a powerful data fitting procedure for quantitative seismic imaging of the subsurface from wide azimuth seismic data this method is suitable to build high resolution velocity models provided that the targeted area is sampled by both diving waves and reflected waves however the conventional formulation of full waveform inversion prevents the reconstruction of the small wavenumber components of the velocity model when the subsurface is sampled by reflected waves only this typically occurs as the depth becomes significant with respect to the length of the receiver array this study first aims to highlight the limits of the conventional form of full waveform inversion when applied to seismic reflection data through a simple canonical example of seismic imaging and to propose a new inversion workflow that overcomes these limitations the governing idea is to decompose the subsurface model as a background part which we seek to update and a singular part that corresponds to some prior knowledge of the reflectivity forcing this scale uncoupling in the full waveform inversion formalism brings out the transmitted wavepaths that connect the sources and receivers to the reflectors in the sensitivity kernel of the full waveform inversion which is otherwise dominated by the migration impulse responses formed by the correlation of the downgoing direct wavefields coming from the shot and receiver positions this transmission regime makes full waveform inversion amenable to the update of the long to intermediate wavelengths of the background model from the wide scattering angle information however we show that this prior knowledge of the reflectivity does not prevent the use of a suitable misfit measurement based on cross correlation to avoid cycleskipping issues as well as a suitable inversion domain as the pseudo depth domain that allows us to preserve the invariant property of the zero offset time this latter feature is useful to avoid updating the reflectivity information at each non linear iteration of the full waveform inversion hence considerably reducing the computational cost of the entire workflow prior information of the reflectivity in the full waveform inversion formalism a robust misfit function that prevents cycle skipping issues and a suitable inversion domain that preserves the seismic invariant are the three key ingredients that should ensure well posedness and computational efficiency of fullwaveform inversion algorithms for seismic reflection data

nature and extent of the deep biosphere in the last three decades we have learned a great deal about microbes in subsurface environments once these habitats were rarely examined perhaps because so much of the life that we are concerned with exists at the surface and seems to pace its metabolic and evolutionary rhythms with the overt planetary solar and lunar cycles that dictate our own lives and it certainly remains easier to identify with living beings that are in our midst most obviously struggling with us or against us for survival over time scales that are easiest to track using diurnal monthly or annual periods yet research efforts are drawn again and again to the subsurface to consider life there no doubt this has been due to our parochial interests in the resources that exist there the water minerals and energy that our society continues to require and that in some cases are created or modified by microbes however we also continue to be intrigued by the scientific curiosities that might only be solved by going underground and examining life where it does and does not exist but really is life underground just a peculiarity of most life on the planet and only a recently discovered figment of life or is it actually a more prominent and fundamental if unseen theme for life on our planet our primary purpose in this chapter is to provide an incremental assembly of knowledge of subsurface life with the aim of moving us towards a more complete conceptual model of deep life on the planet we aim to merge the consideration of the subsea floor and the continental subsurface because it is only through such a unified treatment that we can reach a comprehensive view of this underground life we also provide some thoughts on a way forward with what we

bubble momentum plume as a possible mechanism for an early breakdown of the seasonal stratification in the northern north sea the presence of a seasonal thermocline likely plays a key role in restraining methane released from a seabed source in the deeper water column thereby inhibiting exchange to the atmosphere the bubble plume itself however generates an upward motion of fluid e g upwelling and may thereby be partially responsible for an early breakdown of the seasonal thermocline measurements at site 22 4b located at 57 550n 1 380e in the uk central north sea 200 km east of the scottish mainland where gas is still being released since a blow out in 1990 have been used to identify the generation of the seasonal thermocline and thus the depth of the upper mixed layer and its breakdown in autumn data derived from two landers containing an acoustic doppler current profiler and a conductivity temperature depth recorder were used to determine the mixed layer depth and the breakdown of the thermocline mixing of upper layer fluid into the lower layer has been inferred from large amplitude variations in the nearbottom temperature the adcps estimate velocity profiles in four beam directions using doppler shifted frequency from acoustic pings sent out and received by four different transducers in a specific configuration besides that the intensity of the backscattered sound per transducer is also recorded bubbles from the nearby plume contaminate the signal during part of the tidal cycle but in bubble free periods the mixed layer depth can be estimated using the acoustic backscatter signal as local maxima results show that the thermocline broke down between mid october and early november several weeks earlier than the breakdown of the thermocline in nearby comparable areas likely caused by bubble induced downwelling at the site the early breakdown of the thermocline was accompanied by multiple occurrence of a strong jet like structure associated with the seasonal tidal mixing front

impact of hot fluid advection on hydrocarbon gas production and seepage in mud volcano sediments of thick cenozoic deltas hydrocarbon seeps are ubiquitous at gas prone cenozoic deltas such as the nile deep sea fan ndsf2 where seepage into the bottom water has been observed at several mud volcanoes mvs3 including north alex mv namv4 here we investigated the sources of hydrocarbon gases and sedimentary organic matter together with biomarkers of microbial activity at four locations of namv to constrain how venting at the seafloor relates to the generation of hydrocarbon gases in deeper sediments at the centre high upward flux of hot 70 c hydrocarbon rich fluids is indicated by an absence of biomarkers of anaerobic oxidation of methane aom and nearly constant methane ch4 concentration depth profile the presence of lipids of incompatible thermal maturities points to mixing between early mature petroleum and immature organic matter indicating that shallow mud has been mobilized by the influx of deep sourced hydrocarbon rich fluids methane is enriched in the heavier isotopes with values of 13c 46 6 vpdb and d 228 vsmow and is associated with high amounts of heavier homologues c2 suggesting a co genetic origin with the petroleum on the contrary at the periphery a lower but sustained ch4 flux is indicated by deeper sulphate methane transition zones and the presence of 13c depleted biomarkers of aom consistent with predominantly immature organic matter values of 13c ch4 60 vpdb and decreased concentrations of 13c enriched c2 are typical of mixed microbial ch4 and biodegraded thermogenic gas from plio pleistocene reservoirs of the region the maturity of gas condensate migrated from pre miocene sources into miocene reservoirs of the western ndsf is higher than that of the gas vented at the centre of namv supporting the hypothesis that it is rather released from the degradation of oil in neogene reservoirs combined with the finding of hot pore water and petroleum at the centre our results suggest that clay mineral dehydration of neogene sediments which takes place posterior to reservoir filling may contribute to intense gas generation at high sedimentation rate deltas

impact of early diagenesis and bulk particle grain size distribution on estimates of relative geomagnetic palaeointensity variations in sediments from lama lake northern central siberia summary high resolution analyses of rock magnetic and sedimentological parameters were conducted on an 11 m long sediment core from lama lake northern siberia which encompasses the late pleistocene and the holocene epochs the results reveal a strong link between the median grain size of the magnetic particles identified as magnetite and the oxidation state of the sediment reducing conditions associated with a relative high total organic carbon toc content of the sediment characterize the upper 7 m of the core holocene and these have led to a partial dissolution of detrital magnetite grains and a homogenization of grain size related rock magnetic parameters the anoxic sediments are characterized by significantly larger median magnetic grain sizes as indicated for example by lower median destructive fields of the natural remanent magnetization mdfnrm and lower ratios of saturation remanence to saturation magnetization msr ms consequently estimates of relative geomagnetic palaeointensity variations yielded large amplitude shifts associated with anoxic oxic boundaries despite the partial reductive dissolution of magnetic particles within the anoxic section and consequent minimal variations in magnetic concentration and grain size palaeointensity estimates for this part of the core were still lithologically distorted by the effects of particle size and subsidiary toc variations anomalously high values coincide with an interval of significantly more fine grained sediment which is also associated with a decrease in toc content which may thus imply a decreased level of magnetite dissolution in this interval calculation of relative palaeointensity estimates therefore seems to be compromised by a combined effect of shifts in the particle size distribution of the bulk sediment and by partial magnetite dissolution varying in association with the toc content of the sediment

methane in the western part of the sea of okhotsk in 1998 2000 1 we measured oceanic methane in the western part of the sea of okhotsk in 1998 1999 and 2000 an anomalously high methane concentration was found in near bottom water above the shelfbreak 200 m off northeast sakhalin every year up to 488 nmol kg 1 in 1998 981 nmol kg 1 in 1999 and 556 nmol kg 1 in 2000 this anomalously high concentration can be used to trace the water with density range 26 6 to 26 8 in the upper dense shelf water in the shelf off east sakhalin a strong stratification caused by freshwater from amur river controlled the upward transport of methane through the suppression of vertical convection the calculated methane flux was largest in the northeastern shelf region of sakhalin 88 mol ch4 km 2 d 1 in the western part of the sea of okhotsk 0 73 106 km2 51 of total sea of okhotsk area the emission rate of methane was 11 gg ch4 yr 1

a quantitative assessment of methane cycling in hikurangi margin sediments new zealand using geophysical imaging and biogeochemical modeling takahe seep located on the opouawe bank hikurangi margin is characterized by a well defined subsurface seismic chimney structure ca 80 500 m2 in area sub seafloor geophysical data based on acoustic anomaly layers indicated the presence of gas hydrate and free gas layers within the chimney structure reaction transport modeling was applied to porewater data from 11 gravity cores to constrain methane turnover rates and benthic methane fluxes in the upper 10 m model results show that methane dynamics were highly variable due to transport and dissolution of ascending gas the dissolution of gas up to 3761 mmol m 2 yr 1 dwarfed the rate of methanogenesis within the simulated sediment column 2 6 mmol m 2 yr 1 dissolved methane is mainly consumed by anaerobic oxidation of methane aom at the base of the sulfate reduction zone and trapped by methane hydrate formation below it with maximum rates in the central part of the chimney 946 and 2420 mmol m 2 yr 1 respectively a seep wide methane budget was constrained by combining the biogeochemical model results with geophysical data and led to estimates of aom rates gas hydrate formation and benthic dissolved methane fluxes of 3 68 104 mol yr 1 73 85 104 mol yr 1and 1 19 104 mol yr 1 respectively a much larger flux of methane probably escapes in gaseous form through focused bubble vents the approach of linking geochemical model results with spatial geophysical data put forward here can be applied elsewhere to improve benthic methane turnover rates from limited single spot measurements to larger spatial scales

natural marine seepage blowout contribution to atmospheric methane the release of methane sequestered within deep sea methane hydrates is postulated as a mechanism for abrupt climate change however whether emitted seabed methane reaches the atmosphere is debatable we observed methane emissions for a blowout from a shallow 22 m hydrocarbon seep the emission from the blowout was determined from atmospheric plume measurements simulations suggest a 1 1 gas loss to dissolution compared to 10 loss for a typical low flux bubble plume transfer to the atmosphere primarily was enhanced by the rapid upwelling flows induced by the massive discharge this mechanism could allow methane suddenly released from deeper 250 m waters to contribute significantly to atmospheric methane budgets copyright 2006 by the american geophysical union

natural flux of greenhouse methane from the timor sea to the atmosphere 1 methane gas bubbles from the cornea seep were sampled at the sea surface in the timor sea continental shelf area in june 2005 total bubble gas flux was 0 076 to 0 76 l m 2 h 1 during the 6 h d 1 periods of low neap tides in june 2005 this bubble gas contained an average of 26 mmol ch4 l 1 and about 0 16 and 0 006 mmol l 1 of ethane and propane we estimate the daily flux from the sea surface to the atmosphere to be 0 012 to 0 12 mol ch4 m 2 d 1 or 0 13 to 1 3 t ch4 d 1 from an area of about 0 7 km2 this methane flux came from a 500 1400 m carbonate pavement dome on the seafloor at 84 m water depth the seep hard ground was swath mapped and 3 5 khz subbottom profile data indicate that the seep dome was strongly reflective with poor penetration into the subsurface consistent with the presence of a carbonate hard ground carbon and deuterium isotope ratios 13c 41 to 42 d 157 to 158 of the seep bubble gas indicate that this methane had a thermogenic origin and was in the same isotopic range as gas within the late cretaceous cornea oil and gas field we could not detect inputs of fluids containing nutrients or short lived radium isotopes at this site commonly associated with other cold seeps tens to a hundred of kilometers seaward from the cornea seep site water column dissolved methane concentrations in this sector of the timor sea shelf and slope were 100 500 times supersaturated with respect to the atmosphere and thus the water column is expected to be degassing additional methane to the atmosphere perhaps there are thousands of other methane seeps of similar magnitude to the cornea seep on this shelf and slope to account for all the excess dissolved methane 86 000 t measured in the water column these measured and calculated fluxes provide evidence for the hypothesis that shallow sea seeps may be a significant source of atmospheric methane in contrast to deep sea vents where most of the methane is dissolved and oxidized in seawater and does not reach the atmosphere

high intensity gas seepage causes rafting of shallow gas hydrates in the southeastern black sea abstract submarine gas hydrates are a major global reservoir of the potent greenhouse gas methane since current assessments of worldwide hydrate bound carbon vary by one order of magnitude new technical efforts are required for improved and accurate hydrate quantifications here we present hydrate abundances determined for surface sediments at the high flux batumi seep area in the southeastern black sea at 840 m water depth using state of the art autoclave technology pressure sediment cores of up to 2 65 m in length were recovered with an autoclave piston corer backed by conventional gravity cores quantitative core degassing yielded volumetric gas bulk sediment ratios of up to 20 3 proving hydrate presence the cores represented late glacial to holocene hemipelagic sediments with the shallowest hydrates found at 90 cmbsf calculated methane concentrations in the different cores surpassed methane equilibrium concentrations in the two lowermost lithological black sea units sampled the results indicated hydrate fractions of 5 2 of pore volume in the sapropelic unit 2 and mean values of 21 pore volume in the lacustrine unit 3 we calculate that the studied area of 0 5 km2 currently contains about 11 3 kt of methane bound in shallow hydrates episodic detachment and rafting of such hydrates is suggested by a rugged seafloor topography along with variable thicknesses in lithologies we propose that sealing by hydrate precipitation in coarse grained deposits and gas accumulation beneath induces detachment of hydrate sediment chunks floating hydrates will rapidly transport methane into shallower waters and potentially to the sea atmosphere boundary in contrast persistent in situ dissociation of shallow hydrates appears unlikely in the near future as deep water warming by about 1 6 c and or decrease in hydrostatic pressure corresponding to a sea level drop of about 130 m would be required because hydrate detachment should be primarily controlled by internal factors in this area and in similar hydrated settings it serves as source of methane in shallow waters and the atmosphere which is mainly decoupled from external forcing

monitoring of natural oil seepage in the lower congo basin using sar observations abstract synthetic aperture radar sar is a spaceborne tool allowing near real time imagery over large ground footprints of areas hundreds of kilometres wide sar also allows persistent observations of the process of oil discharges benefiting from 1 day and night observations 2 independence of cloud cover and 3 high revisiting frequencies the interpretation of 82 sar scenes over the lower congo basin for the 1994 2012 period allowed the recognition of 1400 natural seepage slicks associated with 102 individual seep sites we acquired an additional sar data set with a short revisit time over a selected prolific area the data set consisted of 22 sar scenes acquired over a 10 day period meaning a maximum revisiting period of 12 h between subsequent sar acquisitions the short term approach shows that seepage slicks were detected with wind speeds between 1 5 and 6 5 m s 2 91 to 12 63 knots both long term and short term monitoring evidences that seepage events are intermittent with the occurrence rate of oil release ranging from 5 to 80 short term monitoring shows that the seepage pace is independent between seep sites suggesting contrasted controlling factors it also shows that the residence time of seepage slicks is systematically shorter than 12 h which is far below reported values understanding the seepage slick residence time is essential to provide an accurate estimation of the fluid flow and to compute the volumetric outflow the integration of in situ mooring points measuring the current velocity 10 m below the sea surface in addition to local wind field and slick length allowed us to more accurately estimate the residence time of oil slicks at the sea surface before vanishing the results show that the sea surface residence time of oil slicks is limited to a few hours with a median value of 3 h 15 min these new residence time estimations allowed us to propose a quantification of the regional oil output in the lower congo basin estimated at 4380 m3 year this area may therefore be considered as the world s third biggest oil supplying province from natural leakages

stable isotope trophic patterns in echinoderm megafauna in close proximity to and remote from gulf of mexico lower slope hydrocarbon seeps abstract hydrocarbon seep communities in the gulf of mexico have a high biomass that is exploited as a food source to varying degrees by the photosynthesis dependent fauna inhabiting the surrounding mud bottom a decline concurrent with ocean depth in detritus influx to that background habitat results in a much lower background biomass the biomass contrast between population rich seeps and depauperate mud bottom leads to the prediction that seep utilization by the background fauna should be extensive at all depths and should increase with depth species depth zonation makes like species comparisons over the full depth of the gulf of mexico impossible seeps and normal bottom above 1000 m have different fauna from those below 1000 m lower slope seeps are surrounded by a fauna rich in echinoderm species especially asteroids ophiuroids and holothuroids all three taxa have species that are abundant within seeps and are probably endemic to them they also contain species found only in mud background or within mud and seeps backgrounds tissue analyses of 13 c and 15 n of echinoderms collected by rov within seeps and trawling away from seeps indicate a pattern of utilization similar to that found in upper slope seeps exploited by different taxa seastar and ophiuroid species abundant in or endemic to seeps have tissue isotope values reflecting seep chemosynthetic input via a free living microbial detritus or predation a single seep endemic deposit feeding holothuroid showed distinct seep tissue values background deposit feeding holothuroids collected within seeps showed either no or only minor incorporation of seep carbon indicating either a lack of access to seep detritus or short feeding times within the seep a predicted extensive utilization of seep productivity at the deeper seeps was not found seeps may be relatively closed systems that require special adaptations of species in order for them to enter exploit and survive alternately the surrounding deep benthos may not be as food poor as assumed from biomass measurements and flux estimates

combined carbonate carbon isotopic and cellular ultrastructural studies of individual benthic foraminifera 2 toward an understanding of apparent disequilibrium in hydrocarbon seeps 1 numerous previous studies show disequilibrium between stable carbon isotope ratios of foraminiferal calcite and pore water dissolved inorganic carbon in hydrocarbon seeps calling into question the utility of this widely used paleoceanographic tracer as a proxy we use a recently developed method to compare stable carbon isotope ratios of foraminiferal carbonate with cell ultrastructural observations from individual benthic foraminifera from seep under chemosynthetic bivalves and nonseep habitats in monterey bay california to better understand control s of benthic foraminiferal carbon isotope ratios two attributes previously proposed to cause the isotopic offsets are diet and symbionts ultrastructural analysis shows that positive staining with rose bengal indicates presence of foraminiferal cytoplasm bacterial biomass or a combination of both and thus is not an unequivocal indicator of viability we also show for the first time that some living seep foraminifera have endobionts results from our unique yet limited data set are consistent with suggestions that in our sites several foraminiferal species collected from seep clam beds may not survive there diet and symbiont presence do not appear to be major contributors to disequilibrium little calcification of seep tolerant foraminiferal species occurs while seep conditions prevail and microscale variability in habitats could influence 13c of benthic foraminiferal carbonate results further suggest that our knowledge of benthic foraminiferal ecology and biomineralization especially in extreme habitats such as seeps must be bolstered before we fully understand the fidelity of paleoenvironmental records derived from benthic foraminiferal test 13c data

ongoing methane discharge at well site 22 4b north sea and discovery of a spiral vortex bubble plume motion highlights mega ebullition of biogenic methane from an abandoned offshore gas well north sea evidence for midwater bubble plume intrusion fallback and short circuiting of the plume effective trapping of seabed released methane underneath the thermocline first observation of a spiral vortex methane plume and marginal turbulences megaplumes appear less efficient in terms of vertical methane transport than previously thought abstract first direct evidence for ongoing gas seepage activity on the abandoned well site 22 4b northern north sea 57 55 n 01 38 e and discovery of neighboring seepage activity is provided from observations since 2005 a manned submersible dive in 2006 discovered several extraordinary intense seepage sites within a 60 m wide and 20 m deep crater cut into the flat 96 m deep seafloor capture and isotope chemical analyses of the gas bubbles near the seafloor revealed in situ concentrations of methane between 88 and 90 vol with 13c ch4 values around 74 vpdb indicating a biogenic origin bulk methane concentrations throughout the water column were assessed by 120 niskin water samples showing up to 400 000 nm ch4 in the crater at depth in contrast concentrations above the thermocline were orders of magnitude lower with a median value of 20 nm a dye tracer injection into the gas seeps revealed upwelling bubble and water motion with gas plume rise velocities up to 1 ms 1 determined near the seabed however the dissolved dye did not pass the thermocline but returned down to the seabed measurements of direct bubble mediated atmospheric flux revealed low values of 0 7 0 3 kty 1 much less than current state of the art bubble dissolution models would predict for such a strong and upwelling in situ gas bubble flux at shallow water depths i e 100 m acoustic multibeam water column imaging data indicate a pronounced 200 m lateral intrusion at the thermocline together with high methane concentration at this layer a partly downward orientated bubble plume motion is also visible in the acoustic data with potential short circuiting in accordance to the dye experiment this observation could partly explain the observed trapping of most of the released gas below the well established thermocline in the north sea moreover 3d analyses of the multibeam water column data reveal that the upwelling plume transforms into a spiral expanding vortex while rising through the water column such a spiral vortex motion has never been reported before for marine gas seepage and might represent an important process with strong implication on plume dynamics dissolution behavior gas escape to the atmosphere and is considered very important for respective modeling approaches

quantification of gas bubble emissions from submarine hydrocarbon seeps at the makran continental margin offshore pakistan 1 evidence for twelve sites with gas bubble emissions causing hydroacoustic anomalies in 18 khz echosounder records flares was obtained at the convergent makran continental margin the hydroacoustic anomalies originating from hydrocarbon seeps at water depths between 575 and 2870 m disappeared after rising up to 2000 m in the water column dives with the remotely operated vehicle quest 4000 m revealed that several individual bubble vents contributed to one hydroacoustic anomaly analyzed gas samples suggest that bubbles were mainly composed of methane of microbial origin bubble size distributions and rise velocities were determined and the volume flux was estimated by counting the emitted bubbles and using their average volume we found that a low volume flux flare 1 at 575 mbsl 90 ml min caused a weak hydroacoustic signal in echograms whereas high volume fluxes flare 2 at 1027 mbsl 1590 ml min flare 5 c at 2870 mbsl 760 ml min caused strong anomalies the total methane bubble flux in the study area was estimated by multiplying the average methane flux causing a strong hydroacoustic anomaly in the echosounder record with the total number of equivalent anomalies an order of magnitude estimate further considers the temporal variability of some of the flares assuming a constant flux over time and allows a large range of uncertainty inherent to the method our results on the fate of bubbles and the order of magnitude estimate suggest that all of the 40 32 106 mol methane emitted per year within the gas hydrate stability zone remain in the deep ocean

fate of rising methane bubbles in stratified waters how much methane reaches the atmosphere there is growing concern about the transfer of methane originating from water bodies to the atmosphere methane from sediments can reach the atmosphere directly via bubbles or indirectly via vertical turbulent transport this work quantifies methane gas bubble dissolution using a combination of bubble modeling and acoustic observations of rising bubbles to determine what fraction of the methane transported by bubbles will reach the atmosphere the bubble model predicts the evolving bubble size gas composition and rise distance and is suitable for almost all aquatic environments the model was validated using methane and argon bubble dissolution measurements obtained from the literature for deep oxic saline water with excellent results methane bubbles from within the hydrate stability zone typically below 500 m water depth in the ocean are believed to form an outer hydrate rim to explain the subsequent slow dissolution a model calibration was performed using bubble dissolution data from the literature measured within the hydrate stability zone the calibrated model explains the impressively tall flares 1300 m observed in the hydrate stability zone of the black sea this study suggests that only a small amount of methane reaches the surface at active seep sites in the black sea and this only from very shallow water areas 100 m clearly the black sea and the ocean are rather effective barriers against the transfer of bubble methane to the atmosphere although substantial amounts of methane may reach the surface in shallow lakes and reservoirs

sulfate dependent anaerobic oxidation of methane at a highly dynamic bubbling site in the eastern sea of marmara cinarcik basin abstract during the marsitecruise expedition in november 2014 on board the rv pourquoi pas multidisciplinary sampling was carried out with the rov victor 6000 in order to investigate biogeochemical processes taking place at cold seep environments in the sea of marmara pore water bottom water sediment and authigenic carbonate samples were collected from two short push cores mrs dv5 pc04 8 cm mrs dv5 pc01 12 5 cm at an active methane bubbling site in the southeastern part of the cinarcik basin sulfate sulfur and oxygen isotope data as well as sulfide isotope data indicate that sulfate dependent anaerobic oxidation of methane is the dominant process in the sediments this is confirmed by archaeal lipids diagnostic for anaerobic methane oxidizers detected with strong 13c depletions the available data even allows to distinguish the dominant aom assemblages specific lipid patterns are consistent with a dominance of anme 2 archaea within the microbial community abundant authigenic carbonates mostly aragonite found at all depths show a narrow range in 13c values between 27 69 and 33 40 the carbon isotopic composition of the dissolved inorganic carbon as well as strontium and calcium isotopes confirm that the current reaction zone sulfate methane transition zone starts at the bottom of the core all shallower carbonates are witnesses of paleo seepage activity u th dating of four pure aragonite samples show the short time span that is preserved in core mrs dv5 pc01 235 60 yr b p two major earthquakes of 1766 ce and 1754 ce in the cinarcik basin might potentially have triggered the increased seepage of methane at this location

formation of carbonate chimneys in the mediterranean sea linked to deep water oxygen depletion marine sediments at ocean margins vent substantial amounts of methane1 2 microbial oxidation of the methane released can trigger the precipitation of carbonate within sediments and support a broad diversity of seafloor ecosystems3 4 the factors controlling microbial activity and carbonate precipitation associated with the seepage of submarine fluid over geological time remain poorly constrained here we characterize the petrology and geochemistry of rocks sampled from metre size build ups of methane derived carbonate chimneys located at the amon mud volcano on the nile deep sea fan we find that these carbonates comprise porous structures composed of aggregated spherules of aragonite and closely resemble microbial carbonate reefs forming at present in the anoxic bottom waters of the black sea5 using u series dating we show that the amon carbonate build ups formed between 12 and 7 thousand years ago contemporaneous with the deposition of organic rich sediments in the eastern mediterranean the so called sapropel layer s1 we propose that the onset of deep water suboxic or anoxic conditions associated with sapropel formation resulted in the development of intense anaerobic microbial activity at the sea floor and thus the formation of carbonate chimneys

earth model building from shallow to deep with full waveform inversion full waveform inversion fwi is a high resolution model building technique that uses the entire recorded seismic data content to build the earth model conventional fwi usually utilizes diving and refracted waves to update the low wavenumber background components of the model however the update is often depth limited due to the limited offset range acquired to extend conventional fwi beyond the limits of the transmitted energy we must use reflection data synthetic and field data examples demonstrate that even in a complex subsalt gulf of mexico setting the background velocity model can be updated from shallow to deep water using conventional fwi followed by reflection based fwi a future refinement of the technique shows that after updating the sediment model the salt boundaries can be further updated by level set technology

asphalt volcanism and chemosynthetic life in the campeche knolls gulf of mexico in the campeche knolls in the southern gulf of mexico lava like flows of solidified asphalt cover more than 1 square kilometer of the rim of a dissected salt dome at a depth of 3000 meters below sea level chemosynthetic tubeworms and bivalves colonize the sea floor near the asphalt which chilled and contracted after discharge the site also includes oil seeps gas hydrate deposits locally anoxic sediments and slabs of authigenic carbonate asphalt volcanism creates a habitat for chemosynthetic life that may be widespread at great depth in the gulf of mexico

basin wide estimates of the input of methane from seeps and clathrates to the black sea numerous methane emitting bottom features such as seeps methane clathrate hydrates clathrates and mud volcanoes have been identified recently in the black sea the fluxes of methane from these sources averaged over large spatial scales are unknown here we take advantage of the fact that the black sea is a semi enclosed basin with restricted deep water circulation to establish first order estimates of basin wide fluxes of methane from these sources to the water column and atmosphere first we measured the natural radiocarbon content of methane 14c ch4 dissolved in the water column and emitted from seeps the 14c ch4 results showed that the dominant source of methane to the water column is emitted from seeps and a smaller source is diagenetically produced in relatively modern sediments the 14c ch4 results were then used to partition a basin wide total methane budget this analysis estimated the basin wide flux of methane from seeps and clathrates to the water column to be 3 60 to 4 28 tg yr 1 second a geochemical box model was used to calculate possible distributions of methane inputs from seeps and clathrates as well as provide additional estimates of the basin wide flux of methane from seeps and clathrates to the water column 4 95 to 5 65 tg yr 1 2006 elsevier b v all rights reserved

using carbon isotope fractionation to constrain the extent of methane dissolution into the water column surrounding a natural hydrocarbon gas seep in the northern gulf of mexico

trace element behaviour at cold seeps and the potential export of dissolved iron to the ocean seawater samples were collected by submersible above methane seeps in the gulf of guinea regab and baboon pockmarks in order to investigate the behaviour of iron fe manganese mn and rare earth elements ree during fluid seepage our aim was to determine whether cold seeps may represent potential sources of dissolved chemical species to the ocean dissolved 0 45 m filtered samples and total dissolvable unfiltered samples concentrations were determined over 50 m long vertical transects above the seafloor and at various discrete locations within the pockmarks we show that substantial amounts of fe and mn are released into seawater during seepage of methane rich fluids mn is exported almost quantitatively in the dissolved form more than 90 of total mn mean mndiss 12 11 nmol kg 12 11 nmol kg although a significant fraction of fe is bound to particulate phases the dissolved iron pool still accounts on average for approximately 20 percent of total iron flux at vent sites mean fediss 22 11 nmol kg 22 11 nmol kg this dissolved fe fraction also appears to remain stable in the water column in contrast there was no evidence for any significant benthic fluxes of pore water ree associated with fluid seepage at the studied sites overall our results point towards distinct trace element behaviour during fluid seepage with potential implications for the marine geochemical budget the absence of any dissolved ree enrichments in bottom waters clearly indicates effective removal in sub surface sediments most likely precipitation of authigenic mineral phases at cold seeps i e carbonates represents a net sink for these elements while mn appears to behave near conservatively during fluid seepage the observed relative stability of dissolved fe in the water column above seepage sites could be explained by complexation with strong organic ligands and or the presence of fe bearing sulfide nanoparticles as reported previously for submarine hydrothermal systems considering the ubiquitous occurrence of methane vents at ocean margins cold seeps could represent a previously unsuspected source of dissolved fe to the deep ocean

initiation of gas hydrate pockmark in deep water nigeria geo mechanical analysis and modelling abstract a review of recent literature shows that two geomorphologically different types of pockmarks contribute to gas seepage at the seafloor type 1 pockmarks are defined as seafloor craters associated to fluid seepage and are the most classical type referred to as pockmarks in the literature in contrast type 2 pockmarks reveal a complex seafloor morphology that may result from the formation decomposition of gas hydrates in underlying sedimentary layers interpretation of very high resolution seismic data sedimentological analyses and geotechnical measurements acquired from the eastern niger submarine delta reveal that type 2 pockmarks are associated to the presence at depth of a conical body of massive gas hydrates based on acquired data theoretical analysis and numerical modelling it was possible to propose a novel geo mechanical mechanism controlling the irregular seafloor deformations associated to type 2 pockmark and to show that pockmark shapes and sizes are directly linked to the initial growth and distribution of sub seafloor gas hydrates the study illustrates the role of gas hydrates formation in the fracturation deformation of the subsurface sediment and the formation of type 2 pockmarks

theoretical simulation of the evolution of methane hydrates in the case of northern south china sea since the last glacial maximum the distribution and inventory of gas hydrates in a region is determined by the sediment characteristics methane supply and evolution of the reservoir in recent decades the geo environmental constraints and sources of methane have been intensively investigated and numerous experimental and numerical simulation tools have been developed to evaluate the inventory of hydrates however information regarding the evolution of hydrate reservoirs remains limited this study developed a simulator to theoretically model the evolution of specific reservoirs since the last glacial maximum lgm the lgm was a recent cold epoch that occurred approximately 18 000 years ago since the lgm the earth s climate system has experienced a continuous increase of surface temperature and rising sea level given a sufficient supply of methane and a transport system hydrates may form in marine sediments if sea level rises or melt if the temperature increases a one dimensional simulator that represents the sediment was developed and uses the current hydrate profiles as the initial conditions and reliable paleoenvironmental data obtained in sites located in the northern shelf of the south china sea scs as boundary conditions two types of hydrate profiles were reversely simulated till the lgm 1 a gaussian profile which was observed in the shenhu area and 2 a trapezoidal profile which was observed in the dongsha area scs the evolution and past quantities of local hydrate reservoirs were estimated the model results demonstrated that shallow 500 700 m below the seafloor or mbsf moderate saturation 50 pore volume or v v hydrate deposits will form if they are subjected to recent climate changes the inventory of hydrates in the nscs increased by only 0 7 over the past 18 000 years under various scenarios a sensitivity analysis was performed to identify the most pertinent parameters that control the formation and dissociation of hydrates including the grain size temperature gradient and deposition depth the distribution and depth of the reservoir were determined to be the most critical factors in the evolution of the studied hydrates

hydrothermal metal supplies enhance the benthic methane filter in oceans an example from the okinawa trough abstract anaerobic oxidation of methane aom is an important process that regulates methane budget in the global carbon cycle sulfate is traditionally regarded as the most important electron acceptor for aom however recent studies reveal that reactive metal reduction driven aom metal aom may also present on natural environments partitioning the methane c sink from anaerobic oxidation between sulfate reduction driven aom sulfate aom and metal aom is thus becoming a scientific challenge to be addressed this study aimed to show that metal aom has a potential to complement sulfate aom especially when methane seeps met sediments enriched in iron and manganese oxides supplied by hydrothermal plumes samples of authigenic carbonate were collected from the cold seeps on the western slope of the okinawa trough ot a semi enclosed back arc basin with cold seeps and hydrothermal activities coexist spatially petrologic and mineralogical observations provided faithful evidence of a close genetic relationship between goethite and authigenic carbonates likely indicating the presence of metal aom although some contributions of organoclastic fe reduction cannot be ruled out the most possible place of metal aom was between the lower part of the sulfate methane transition zone smtz and the immediate upper part of the methanogenic zone the characteristics of 13ccarb 53 7 to 3 3 vienna peedee belemnite vpdb also point to our carbonate samples as the products of aom these authigenic carbonates was further identified as three possible types of carbonate of different sources sulfate aom metal aom and hydrothermal carbonates depending on the correlations among concentrations of carbonate associated sulfate cas 13ccarb and 18ocarb based on these findings we tentatively suggested that the reduction of reactive metals carried by hydrothermal plumes might drive the methane oxidation in the adjacent cold seep areas resulting in the precipitation of unique carbonates and enhancement the efficiency of the benthic methane filter this study reported the coupling or interaction between the two extreme submarine environments by metal aom for the first time which might help in understanding and improving the global carbon and metal cycles now and in the past

methane and minor oil macro seep systems their complexity and environmental significance abstract the two main observations characterising marine and lacustrine methane macro seeps are ebullition through holes in the sea or lake bed and hydroacoustic flares in the water column this paper reviews multi year multi scale and multi discipline results from three seep locations in the north sea and combines the knowledge with recent seafloor and water column results from seeps in the santa barbara basin california a seep off west africa seeps in the gulf of mexico and in lake baikal russia we have identified a total of 12 characteristics of methane and minor oil macro seeps that are not only geological in nature but also biological and geochemical these are shown to impact the marine environment in different ways not least in benefactory manners as primary producers mainly bacteria and archaea tend to bloom during seepage therefore the seepage is inferred to have a fertilizing effect on both the seafloor and the water column which may be of broad ecological and biological significance the study concludes with a holistic conceptual seep model which is expected to be of interest to a broad range of researchers in the fields of oceanography and limnology

temporal variation of methane flares in the ocean above hydrate ridge oregon abstract while bubble plumes have been acoustically imaged in the water column above marine gas hydrate deposits in many studies little is known about the temporal variation in plume intensity in july 2008 we conducted surveys using 3 5 and 12 khz echosounders and a 75 khz acoustic doppler current profiler adcp over the northern and southern summits of hydrate ridge on the cascadia continental margin our study included multiple surveys at both sites including a survey of the northern summit that was repeated 16 times in 19 h seafloor depth at the northern summit is 600 m well within the hydrate stability zone hsz which was below 510 m during our survey based on ctd data three distinct flares a term used to denote the acoustic signature of bubble plumes were detected at northern hydrate ridge nhr and one was detected at southern hydrate ridge shr coincident with where flares were observed a decade ago indicating that the supply of gas is stable on this time scale high resolution bathymetric surveys of nhr and shr acquired with an autonomous underwater vehicle auv flown 50 m above the seafloor indicate that flare locations are correlated with a distinctive pattern of short wavelength seafloor roughness supporting the inference of long term stability in the location of bubble expulsion sites as in previous studies at hydrate ridge flares were not detected with the 3 5 khz echosounder but were clearly imaged at 12 khz by reprocessing routine shipboard adcp data we show that they are also observed in at 75 khz indicating that a wide range of bubble sizes is present the intensity of the flares varied strongly with time two primary sources for flares were observed one located on the regional topographic high showed continuous activity with two times periods of particularly strong flares that are not correlated with tidal height the other located on a local topographic high shows a pulse of increased backscatter that occurred on a falling tide while the time period of observation is not enough to constrain the effect of tidal changes in seafloor pressure on venting the data suggest that tides are not the dominant factor controlling release of bubbles from the seafloor the data support previously suggested models in which temporary sealing of vents by gas hydrate formation and breaking of these barriers as gas pressure builds up is responsible for burp like pulses of gas expulsion we also report the first observations of flares originating within the hsz that extend well above the hsz with little loss of backscatter intensity these represent a new source of methane injection into the upper ocean and possibly the atmosphere flare extension above the hsz may be due to coating of some bubbles by oil or biofilms or to inclusion of particulate matter possibly including floating pieces of hydrate in the plumes although this study provides tantalizing new information on both short term variability in gas expulsion rate and long term stability of vent sites longer well calibrated observations that integrate bubble flux over entire vent fields as a function of time are needed to develop accurate models for the flux of methane into the ocean and atmosphere from seafloor methane vents

fluxes and fate of dissolved methane released at the seafloor at the landward limit of the gas hydrate stability zone offshore western svalbard widespread seepage of methane from seafloor sediments offshore svalbard close to the landward limit of the gas hydrate stability zone ghsz may in part be driven by hydrate destabilization due to bottom water warming to assess whether this methane reaches the atmosphere where it may contribute to further warming we have undertaken comprehensive surveys of methane in seawater and air on the upper slope and shelf region near the ghsz limit at 400 m water depth methane concentrations are highest close to the seabed reaching 825 nm a simple box model of dissolved methane removal from bottom waters by horizontal and vertical mixing and microbially mediated oxidation indicates that 60 of methane released at the seafloor is oxidized at depth before it mixes with overlying surface waters deep waters are therefore not a significant source of methane to intermediate and surface waters rather relatively high methane concentrations in these waters up to 50 nm are attributed to isopycnal turbulent mixing with shelf waters on the shelf extensive seafloor seepage at 100 m water depth produces methane concentrations of up to 615 nm the diffusive flux of methane from sea to air in the vicinity of the landward limit of the ghsz is 4 20 mol m 2 d 1 which is small relative to other arctic sources in support of this analyses of mole fractions and the carbon isotope signature of atmospheric methane above the seeps do not indicate a significant local contribution from the seafloor source

rock magnetism of late neogene and pleistocene deep sea sediments relationship to sediment source diagenetic processes and sediment lithology we use bivariate scatter plots to illustrate variations in selected rock magnetic properties low field susceptibility anhysteretic and isothermal remanence of late neogene and pleistocene deep sea sediments from 16 sites in the arctic ocean north atlantic equatorial atlantic and north pacific ocean and the arabian sea our intention is to examine the ability of the rock magnetic properties to differentiate the sediments according to factors such as lithology geographical area and the dominant mode of terrigenous sedimentation which at these sites is via ice rafting via bottom currents or via eolian processes overall correlations between sediment magnetic properties and gross lithology is poor and factors such as the source and transport path of terrigenous sediment and detrital magnetic minerals together with the action of reductive diagenetic processes are the major controls on the magnetic properties on the bivariate scatter plots sites with major ice rafted contributions tend to have high sedimentary ferrimagnetic mineral concentrations relatively coarse ferrimagnetic grain sizes and scattered sample point distributions in contrast sites where we infer significant bottom current supply of terrigenous material have tightly grouped sample point distributions carbonate sediments in which the terrigenous component is supplied by eolian processes tend to have a broad range of magnetic mineral concentration caused by glacial interglacial fluctuations in carbonate accumulation and eolian activity sediments containing significant volcanogenic material have high concentrations of relatively coarse grained ferrimagnetic material reductive diagenesis is a significant determinant of sediment magnetic properties in high productivity areas and has the effect of preferentially removing the fine grained ferrimagnetic fraction causing a coarsening of the ferrimagnetic grain size distribution and a rise in the antiferromagnetic ferrimagnetic ratio

dynamics of the gas flux from shallow gas hydrate deposits interaction between oily hydrate bubbles and the oceanic environment decomposition of methane hydrates on the continental margins is a potentially significant source of atmospheric methane but the input depends upon the poorly understood fate of the hydrocarbon bubbles rising from the sea floor during a field trip to the gulf of mexico three different seepages were imaged and analyzed three different imaging techniques were tried side front and back illumination of which back illumination produced the best results the images were analyzed and the size dependent bubble distribution mass flux and rise speeds determined the total observed gas flux was 62 3 10 3 mol s 1 primarily methane of which a single vent produced seven times the next largest vent of this major vent 50 of the bubble mass was contained in the largest bubbles r 5500 m the vertical velocities demonstrated that these bubbles were heavily contaminated with oil which was also corroborated by bubble shape and oscillation observations

the sensitivity of gas hydrate reservoirs to climate change perspectives from a new combined model for permafrost related and marine settings abstract gas hydrate reservoirs store large quantities of gas in sediments on continental margins in deep lakes and in continental and relic sub shelf permafrost the gas hydrate structure is only stable at sufficiently low temperature and high pressure and may therefore collapse under changing climatic conditions if a temperature rise or pressure drop e g through falling sea level is effective enough to dissociate hydrate deposits methane the most common gas component in hydrates and a potent greenhouse gas is released from the hydrate structure and may eventually enter into the atmosphere this may generate a positive feedback effect as resulting enhanced greenhouse gas levels would additionally warm the atmosphere and hence maintain or reinforce hydrate dissociation the significance of this mechanism has been debated over the past decades often within the framework of geologically rapid quaternary climatic oscillations and present day climate warming an extensive set of studies has addressed the climate sensitivity of gas hydrate reservoirs in various study areas and geological settings and by means of various approaches no real consensus has yet been reached on the matter in this study we seek to evaluate the sensitivity of gas hydrate reservoirs to changes in global climate from a more general perspective by firstly reviewing the available literature and secondly developing a new numerical model to quantify gas hydrate destabilization under changing environmental conditions qualities of the model include the wide applicability to both marine and permafrost related hydrate reservoirs and the integrative approach combining existing hydrate formation models with a dissocation model that accounts for the consumption of latent heat during hydrate dissociation to determine which settings are most vulnerable and to acquire insight into the extent fashion and rates of hydrate dissociation we apply the model to four distinct types of hydrate reservoirs across a hypothetic high latitude continental margin under two specific cases of climate change the last deglaciation following the last glacial maximum and present day climate warming the simulations indicate that hydrates on the upper continental slope and in association with thin sub shelf permafrost are most sensitive to the imposed climatic variations whereas deepwater and onshore permafrost related reservoirs react in a more stable way however the deep i e at several tens to hundreds of meters subsurface depth stratigraphic type hydrates considered in this study constitute by far the largest fraction of the global gas hydrate volume but dissociate on slow timescales of thousands to hundreds of thousands of years even in the most sensitive environments in contrast shallow i e at or a few meters below the surface or seafloor structural type hydrates are able to respond to climatic variations on sub millennial timescales but the volumes of gas they may release are probably insignificant to the global carbon cycle and climate quaternary and present day climate change do affect the stability of gas hydrate reservoirs but at long timescales where hydrate volumes are large and on short timescales where hydrate volumes are small consequently gas hydrates dissociate to an extent that is too small or at a pace that is too slow to create a strong positive feedback effect while the release of methane from the disintegration of gas hydrates is observed on different margins today it is not likely to have played a leading role in quaternary climatic variations or to become a significant process in the coming centuries as a result of present day rising temperatures

thermogenic methane injection via bubble transport into the upper arctic ocean from the hydrate charged vestnesa ridge svalbard we use new gas hydrate geochemistry analyses echosounder data and three dimensional p cable seismic data to study a gas hydrate and free gas system in 1200 m water depth at the vestnesa ridge offshore nw svalbard geochemical measurements of gas from hydrates collected at the ridge revealed a thermogenic source the presence of thermogenic gas and temperatures of similar to 3 3 degrees c result in a shallow top of the hydrate stability zone thsz at similar to 340 m below sea level mbsl therefore hydrate skinned gas bubbles which inhibit gas dissolution processes are thermodynamically stable to this shallow water depth this was confirmed by hydroacoustic observations of flares in 2010 and 2012 reaching water depths between 210 and 480 mbsl at the seafloor bubbles are released from acoustically transparent zones in the seismic data which we interpret as regions where free gas is migrating through the hydrate stability zone hsz these intrusions result in vertical variations in the base of the hsz bhsz of up to similar to 150 m possibly making the shallow hydrate reservoir more susceptible to warming such arctic gas hydrate and free gas systems are important because of their potential role in climate change and in fueling marine life but remain largely understudied due to limited data coverage in seasonally ice covered arctic environments

natural oil seepage at kobuleti ridge eastern black sea abstract analysis of advanced synthetic aperture radar satellite images in combination with water column and seafloor investigations documented natural oil seepage from pechori mound and colkheti seep in 1000 1200 m water depth in the eastern black sea offshore georgia hydroacoustic imaging of the water column using multibeam echosounder evidenced numerous gas emissions from both structures gas bubbles rose as high as 45 m below sea surface it is proposed that oil coatings around gas bubbles hamper their dissolution allowing them to reach the sea surface where widespread oil slicks are formed slow rise velocities 14 1 cm s 1 of bubbles with radii of 2 6 0 3 mm n 101 derived from video data obtained with the remotely operated vehicle marum quest4000 corroborate the assumption that bubbles are oil coated high resolution seafloor mapping with the autonomous underwater vehicle marum seal5000 at colkheti seep revealed a crater strewn morphology whose formation is explained by frequent rafting of shallow gas hydrate deposits satellite imaging of oil slicks on the sea surface above both sites indicates that oil seepage is rather persistent since 2003 an order of magnitude estimation of minimum oil seepage rates suggests discharge rates of 40 liters per hour from both sites the data presented are the first comprehensive description of oil seepage in the black sea

stable carbon isotopic evidence for methane oxidation in plumes above hydrate ridge cascadia oregon margin 1 the transport and consumption of methane in the water column in the vicinity of the cold seeps of hydrate ridge on the cascadia oregon margin were characterized using measurements of the stable carbon isotope composition of methane the 13c ch4 values measured in the water column ranged from approximately 65 to 16 pdb the combination of measured methane concentration data and the stable carbon isotope values from the same depths support the hypothesis of biogenically produced methane which enters the water column from dissolving bubbles released from cold seepages likely as a consequence of destabilized methane hydrate 13c ch4 65 pdb kinetic fractionation factors associated with aerobic bacterial methane oxidation in the water column were calculated using a rayleigh distillation equation applied to a subset of the data fractionation factors ranged from 1 002 to 1 013 mean 1 008 and were in the lower end of the range of those reported in the literature a result likely due to the influence of temperature and mixing in plume waters the fraction of methane remaining after oxidation calculated using the same rayleigh model approach suggests that the aerobic oxidation of methane in the water column over hydrate ridge is nearly quantitative

controls on methane concentration and stable isotope δ2h ch4 and δ13c ch4 distributions in the water columns of the black sea and cariaco basin methane ch4 concentration and stable isotope 2h ch4 and 13c ch4 depth distributions show large differences in the water columns of the earth s largest ch4 containing anoxic basins the black sea and cariaco basin in the deep basins the between basin stable isotope differences are large 83 for 2h ch4 and 9 for 13c ch4 and the distributions are mirror images of one another the major sink in both basins anaerobic oxidation of ch4 results in such extensive isotope fractionation that little direct information can be obtained regarding sources recent measurements of natural 14c ch4 show that the ch4 geochemistry in both basins is dominated 64 to 98 by inputs of fossil radiocarbon free ch4 from seafloor seeps we derive open system kinetic isotope effect equations and use a one dimensional vertical stable isotope box model that along with isotope budgets developed using radiocarbon permits a quantitative treatment of the stable isotope differences we show that two main factors control the ch4 concentration and stable isotope differences 1 the depth distributions of the input of ch4 from seafloor seeps and 2 anaerobic oxidation of ch4 under open system steady state conditions in the black sea and open system non steady state conditions in the cariaco basin copyright 2006 by the american geophysical union

dynamic morphology of gas hydrate on a methane bubble in water observations and new insights for hydrate film models predicting the fate of subsea hydrocarbon gases escaping into seawater is complicated by potential formation of hydrate on rising bubbles that can enhance their survival in the water column allowing gas to reach shallower depths and the atmosphere the precise nature and influence of hydrate coatings on bubble hydrodynamics and dissolution is largely unknown here we present high definition experimental observations of complex surficial mechanisms governing methane bubble hydrate formation and dissociation during transit of a simulated oceanic water column that reveal a temporal progression of deep sea controlling mechanisms synergistic feedbacks between bubble hydrodynamics hydrate morphology and coverage characteristics were discovered morphological changes on the bubble surface appear analogous to macroscale sea ice processes presenting new mechanistic insights an inverse linear relationship between hydrate coverage and bubble dissolution rate is indicated understanding and incorporating these phenomena into bubble and bubble plume models will be necessary to accurately predict global greenhouse gas budgets for warming ocean scenarios and hydrocarbon transport from anthropogenic or natural deep sea eruptions

dissolved methane in the beaufort sea and the arctic ocean 1992 2009 sources and atmospheric flux methane concentration and isotopic composition was measured in ice covered and ice free waters of the arctic ocean during 11 surveys spanning the years of 1992 1995 and 2009 during ice free periods methane flux from the beaufort shelf varies from 0 14 mg ch4 m 2 d 1 to 0 43 mg ch4 m 2 d 1 maximum fluxes from localized areas of high methane concentration are up to 1 52 mg ch4 m 2 d 1 seasonal buildup of methane under ice can produce short term fluxes of methane from the beaufort shelf that varies from 0 28 mg ch4 m 2 d 1 to 1 01 mg ch4 m 2 d 1 scaled up estimates of minimum methane flux from the beaufort sea and pan arctic shelf for both ice free and ice covered periods range from 0 02 tg ch4 yr 1 and 0 30 tg ch4 yr 1 respectively to maximum fluxes of 0 18 tg ch4 yr 1 and 2 2 tg ch4 yr 1 respectively a methane flux of 0 36 tg ch4 yr 1 from the deep arctic ocean was estimated using data from 1993 to 1994 the flux can be as much as 2 35 tg ch4 yr 1 estimated from maximum methane concentrations and wind speeds of 12 m s representing only 0 42 of the annual atmospheric methane budget of 560 tg ch4 yr 1 there were no significant changes in methane fluxes during the time period of this study microbial methane sources predominate with minor influxes from thermogenic methane offshore prudhoe bay and the mackenzie river delta and may include methane from gas hydrate methane oxidation is locally important on the shelf and is a methane sink in the deep arctic ocean