natural gas hydrates on the southeast u s margin constraints from full waveform and travel time inversions of wide angle seismic data strong bottom simulating reflectors bsr have been mapped over a region of approximately 50 000 km2 on the southeastern u s margin and have been associated with possible abundance of natural gas hydrates in june 1992 coincident single channel seismic and wide angle ocean bottom seismic data were acquired in the region focusing on the blake ridge and the carolina rise wide angle reflections from the bsrs were clearly observed at offsets up to 6 km joint travel time inversion was conducted with wide angle and vertical incidence data in order to explore possible regional variation and the resultant two dimensional average velocity models imply higher background velocities on the carolina rise full waveform inversion was then performed to determine the seismic origin of the bsrs the best fit model shows a similar low velocity 1 4 km s beneath the bsr at both sites indicating trapped free gas with low saturation 10 the inversion results also indicate that a thin high velocity wedge with a maximum velocity of 2 3 km s is present just above the blake ridge bsr sediment reflectivities were also calculated and higher reflectivities are observed on the carolina rise an increase in reflectivity below the bsr seems to correspond to the gas bearing zone at both sites concentration of hydrates were estimated based on these velocity models whereas average hydrate concentration of 3 of the total sediment volume is suggested for the lower half of the hydrate stability zone at the blake ridge only a very low average concentration of hydrate can be expected at the carolina rise the hydrates seem to be concentrated near the base of the hydrate stability zone and the maximum hydrate concentration is estimated as 20 at the blake ridge and 7 at the carolina rise both of which are too high to be explained by in situ biogenic activity only and require some secondary accumulation mechanism it is suggested that hydrate recycling caused by the stability field migration may have effectively condensed hydrates at both sites additional enhancement by upward fluid expulsion may also be viable for the blake ridge

effects of bottom water warming and sea level rise on holocene hydrate dissociation and mass wasting along the norwegian barents continental margin 1 gas hydrate gh stability modeling results explain why some major holocene submarine landslides along the norwegian barents margin could have been triggered by gh dissociation during the early to middle holocene not during the lowest sea levels of the last glacial maximum lgm our model results show that subbottom depths of 170 260 m below the pre slide continental slope ca 350 475 m present water depth must have passed out of gas hydrate stability zone ghsz by 8 15 ka as the effect of warm bottom water inflow at 11 ka penetrated into the subbottom overcoming the effects of pressure increase due to sea level rise slr the component of local slr due to the isostatic response to fennoscandian deglaciation is shown to be relatively insignificant particularly for the part of the upper continental slope where the slide probably began the stability relations show that gh could have formed under the ice sheet before deglaciation and below deeper shelf areas after sea levels began to rise but before significant warming near the ghsz base to the extent water deeper than 800 m has remained cold 1 to 0 c since lgm times the ghsz continued to thicken in deep water and gh dissociation could not have triggered holocene failure in that regime the present distribution of gh stability is limited to water depths greater than about 400 m in the storegga slide area and the thickness of the ghsz increases with water depth

kick starting ancient warming rapid global warming marked the boundary between the palaeocene and eocene periods 55 6 million years ago but how the temperature rise was initiated remains elusive a catastrophic release of greenhouse gases from the kilda basin could have served as a trigger

dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the paleocene isotopic records across the latest paleocene thermal maximum lptm indicate that bottom water temperature increased by more than 4 c during a brief time interval 104 years of the latest paleocene 55 6 ma there also was a coeval 2 to 3 excursion in the 13c of the ocean atmosphere inorganic carbon reservoir given the large mass of this reservoir a rapid 13c shift of this magnitude is difficult to explain within the context of conventional hypotheses for changing the mean carbon isotope composition of the ocean and atmosphere however a direct consequence of warming bottom water temperature from 11 to 15 c over 104 years would be a significant change in sediment thermal gradients and dissociation of oceanic ch4 hydrate at locations with intermediate water depths in terms of the present day oceanic ch4 hydrate reservoir thermal dissociation of oceanic ch4 hydrate during the lptm could have released greater than 1 1 to 2 1 1018 g of carbon with a 13c of approximately 60 the release and subsequent oxidation of this amount of carbon is sufficient to explain a 2 to 3 excursion in 13c across the lptm fate of ch4 in oceanic hydrates must be considered in developing models of the climatic and paleoceanographic regimes that operated during the lptm

thermodynamic and pore water halogen constraints on gas hydrate distribution at odp site 997 blake ridge abstract marine sediment sequences with ch4 hydrate are characterized by an atypical depth profile in dissolved cl squeezed from pore space a shallow subsurface cl maximum overlies a lengthy and pronounced cl minimum this pore water cl profile represents a combination of multiple processes including glacial interglacial variations in ocean salinity advection and diffusion of ions that are excluded during gas hydrate formation at depth and release of fresh water from dissociation of hydrate during core recovery in situ quantities of gas hydrate can be determined from a measured pore water cl profile provided the in situ pore water signature prior to core recovery can be separated ocean drilling program odp site 997 was drilled into a large ch4 hydrate reservoir on the blake ridge in the western atlantic ocean previously we have constructed a high resolution pore water cl profile at this location here we present a coupled chloride hydrate numerical model to explain basic trends in the cl profile and to isolate in situ cl concentrations the model is based on thermodynamic and ecological considerations and uses established equations for describing chemical behavior in marine sediment pore water systems the model incorporates four key concepts 1 most gas hydrate is formed immediately below the so42 reduction zone 2 fluid dissolved ions and gas advect upward through the sediment column 3 ch4 hydrate dissociates at the base of hydrate stability conditions and 4 seawater salinity fluctuates during glacial interglacial cycles of the late pliocene and quaternary rates of upward advection in the model are sufficient to account for measured br and i concentrations as well as ch4 oxidation at the base of the so42 reduction zone in situ pore water cl inferred from the model is similar to that determined by limited direct sampling in situ ch4 hydrate amounts inferred from the model an average of about 4 of porosity are broadly consistent with those determined by direct gas sampling and indirect geophysical techniques the model also predicts production of substantial quantities of free ch4 gas bubbles 2 5 of porosity at a depth immediately below the lowest accumulation of ch4 hydrate in the sediment column our explanation for the pore water cl profile at site 997 is important because it provides a theoretical mechanism for understanding the distribution of interstitial water cl gas hydrate and free gas in a marine sediment column

methane hydrate in the global organic carbon cycle the global occurrence of methane hydrate in outer continental margins and in polar regions and the magnitude of the amount of methane sequestered in methane hydrate suggest that methane hydrate is an important component in the global organic carbon cycle various versions of this cycle have emphasized the importance of methane hydrate and in the latest version the role of methane hydrate is considered to be analogous to the workings of an electrical circuit in this circuit the methane hydrate is a condenser and the consequences of methane hydrate dissociation are depicted as a resistor and inductor reflecting temperature change and changes in earth surface history these consequences may have implications for global change including global climate change

high resolution records of the late paleocene thermal maximum and circum caribbean volcanism is there a causal link two recently drilled caribbean sites contain expanded sedimentary records of the late paleocene thermal maximum a dramatic global warming event that occurred at ca 55 ma the records document significant environmental changes including deep water oxygen deficiency and a mass extinction of deep sea fauna intertwined with evidence for a major episode of explosive volcanism we postulate that this volcanism initiated a reordering of ocean circulation that resulted in rapid global warming and dramatic changes in the earth s environment

formation processes of framboidal pyrite abstract pyrite framboid formation may be the result of four consecutive processes 1 nucleation and growth of initial iron monosulfide microcrystals 2 reaction of the microcrystals to greigite fe 3 s 4 3 aggregation of uniformly sized greigite microcrystals i e framboid growth and 4 replacement of greigite framboids by pyrite the uniform morphology uniform size range and ordering of the microcrystals in individual framboids as well as the range of observed framboid structures from irregular aggregates to densely packed spherical aggregates and polyframboids are consequences of these processes using dlvo theory derjaguin landau verwey and overbeek we have evaluated the stability of colloidal iron monosulfide suspensions with ionic strengths typical of marine and lacustrine waters in addition to van der waals attractive and double layer repulsive forces a term is included to account for the ferrimagnetic properties of greigite numerical models predict that magnetically saturated greigite particles 0 1 m in diameter will rapidly aggregate in either marine or fresh water the aggregation model is in agreement with the sequence of greigite formation followed by pyrite framboid formation established in a previous experimental study sweeney and kaplan 1973 and is consistent with the occurrence of framboids composed of other magnetic minerals e g greigite magnetite and magnesioferrite based on the temperature dependent magnetic properties of greigite and aging experiments in hydrothermal solutions this mechanism for framboid formation via precursor greigite could operate to temperatures of 200 c consistent with the occasional occurrence of pyrite framboids in the paragenesis of metalliferous ore deposits

a mineralogical and geochemical study of three brazilian coal cleaning rejects demonstration of electron beam applications abstract the background and anthropogenic levels of hazardous elements in the surface soil of a coal mining area depend on the geological setting of the region and the underlying soil material but may also be influenced by water borne or aeolian transport of sediment from adjacent coal related waste piles very few studies have focused on the chemical and mineralogical composition of brazilian coal cleaning rejects ccrs which may represent significant sources of soil or water contamination in this study we have investigated the quantitative distribution of minerals and potentially hazardous elements in ccrs and a run of mine coal from the brazilian states of rio grande do sul and santa catarina the major minerals identified by x ray diffraction xrd high resolution transmission electron microscopy hr tem and field emission scanning electron microscopy energy dispersive x ray analysis techniques fe sem eds are kaolinite quartz mixed layer illite smectite pyrite jarosite melanterite gypsum rutile and calcite while minor minerals include barite hematite siderite sphalerite and goethite galena magnetite zircon and many other species may also occur as accessory trace minerals pyrite and jarosite are relatively abundant in some cases making up to around 4 or 5 of the mineral matter with jarosite melanterite and gypsum probably formed by complex interaction of oxidation products from fe sulfides and clay or carbonate components initiated by exposure and storage of the host material such atmospheric exposure promotes sulfide oxidation that releases substantial sulfate loads as well as ca 2 k mg 2 cl and al 3 metals with the most severe discharges were zn cu mn co ni and cd most of the trace pollutants in the ccrs displayed a ph dependent solubility being immobile in near neutral samples but mobile under the low ph conditions associated with oxidized material the results highlight the complex interactions among mineral matter components of the ccrs during storage and the potential for release of potentially hazardous elements in association with longer term exposure and storage

variable methane fluxes in shallow marine systems over geologic time abstract carbon cycling is an important but poorly understood process on passive continental margins in this study we use the ionic and stable isotopic composition of interstitial waters and the petrology mineralogy and stable isotopic composition of authigenic carbonates collected from ocean drilling program odp leg 174a sites 1071 and 1072 to constrain the origin of the carbonates and the evolution of methane on the outer new jersey shelf the pore fluids of the new jersey continental shelf are characterized by 1 a fresh brackish water plume and 2 organic matter degradation reactions which proceed through sulfate reduction however only minor methanogenesis occurs the oxygen isotopic composition of the pore fluids supports a meteoric origin of the low salinity fluids authigenic carbonates are found in nodules thin 1 cm layers and carbonate cemented pavements siderite is the most common authigenic carbonate followed by dolomite and calcite the oxygen isotopic composition of the authigenic carbonates i e 1 3 6 5 peedee belemnite pdb indicates an origin in marine pore fluids the carbon isotopic composition of dolomite cements range from 16 4 to 8 8 pdb consistent with formation within the zone of sulfate reduction siderite 13c values show a greater range 17 67 16 4 but are largely positive mean 2 8 and are interpreted to have formed throughout the zone of methanogenesis in contrast calcite 13c values are highly negative as low as 41 7 and must have formed from waters with a large component of dissolved inorganic carbon derived from methane oxidation pore water data show that despite complete sulfate reduction methanogenesis appears not to be an important process presently occurring in the upper 400 m of the outer new jersey shelf in contrast the carbon isotopic composition of the siderites and calcites document an active methanogenic zone during their formation the methane may have been either oxidized or vented from shelf sediments perhaps during sea level fluctuations if this unaccounted and variable methane flux is an areally important process during neogene sea level fluctuations then it likely plays an important role in long term carbon cycling on passive continental margins

subglacial methanogenesis a potential climatic amplifier 1 subglacial environments are a previously neglected component of the earth s global carbon cycle a reflection of the view held until recently that they are dominated by abiotic and oxic conditions here we provide a realistic assessment of the theory that the basal regions of the ice sheets that formed over north america and europe during glaciations were host to significant populations of anaerobic microorganisms including methanogens able to metabolize organic carbon sequestered during interglacials and overridden during quaternary glacials in doing so we review the current evidence for subglacial methane release during deglaciation estimate the size of the subglacial reservoir of organic carbon soc and assess the amount of soc available to subglacial microbes and the likely pathways and rates of carbon turnover we then discuss the fate of subglacial methane and the potential impact of its release on atmospheric methane concentrations we calculate that the soc equates to 418 610 pg c and includes carbon from terrestrial soils vegetation peatlands lake and marine sediments the soc that is potentially available for microbial conversion to methane is smaller than this estimate due to 1 glacial erosion 2 accumulation of recalcitrant organic carbon compounds over time 3 conversion to carbon dioxide by aerobic anaerobic respiration and 4 incomplete conversion of labile organic matter to methane we estimate that the total soc available for conversion to methane is 63 pg c our estimates of methane production potentials span a wide range because of the current uncertainty surrounding subglacial metabolic rates we believe however that there is a strong likelihood that subglacial microbes could convert 63 pg of soc to methane during a glacial cycle if this were the case release of this methane from the ice sheet margins during retreat would need to be episodic in order to significantly impact atmospheric methane concentrations our findings suggest that it may well be important to consider subglacial environments as active components of the earth s carbon cycle conclusive determination of the potential impact of subglacial methane production on atmospheric methane concentrations during deglaciation however awaits more precise determination of the ability of subglacial microbes to degrade organic carbon components and their associated rates of metabolism under in situ conditions

submarine landslide identified in md179 cores off joetsu area eastern margin of the sea of japan abstract gas hydrate is exposed on the sea floor and is buried in shallow sediments in the off joetsu area at the eastern margin of the sea of japan sediment cores recovered from topographic highs of the joetsu knoll and umitaka spur show pockmarks and mounds formed by gas hydrate dissociation but those from the un named ridge have no such topographic features all topographic highs and pockmarks mainly comprise bioturbated layers interbedded with thinly laminated tl layers which are common sea of japan sediments recovered sediments are however mostly disturbed by submarine landslides showing tilted horizons faults slump folds and breccia except that from the un named ridge the timing of events is well constrained by identification of the number of tl layers in some sediment cores landslides occurred both during the cold glacial period of the late mis3 to the last glacial maximum lgm and during the warm interglacial period of the post lgm all were caused by the explosive rise of gas hydrate formed at very shallow depths of the sea bottom by the supply of gas from the depth of the gas hydrate stability zone through gas chimney passages developed under the pockmarks seismic activity demands consideration as a factor because the off joetsu area is tectonically active

leaching of elements from bottom ash economizer fly ash and fly ash from two coal fired power plants abstract to assess how elements leach from several types of coal combustion products ccps and to better understand possible risks from ccp use or disposal coal ashes were sampled from two bituminous coal fired power plants one plant located in ohio burns high sulfur about 3 9 upper pennsylvanian pittsburgh coal from the monongahela group of the central appalachian basin the other in new mexico burns low sulfur about 0 76 upper cretaceous fruitland formation coal from the san juan basin colorado plateau the sampled ccps from the ohio plant were bottom ash ba economizer fly ash efa and fly ash fa the sampled ccps from the new mexico plant were ba mixed fa efa fa and cyclone separated coarse and fine fractions of a fa efa and fa blend subsamples of each ash were leached using the long term leaching 60 day duration component of the synthetic groundwater leaching procedure sglp or the toxicity characteristic leaching procedure tclp 18 hour duration these ashes were all alkaline leachate concentrations and leachabilities of the elements from the ccps were similar between corresponding ccp types ba efa and fa from each plant the leachabilities of most elements were lowest in ba least leachable and increased from efa to fa most leachable ca and sr were leached more from efa than from either ba or fa leachability of most elements also increased as fa particle size decreased possibly due in part to increasing specific surface areas several oxyanion forming elements as mo se u and v leached more under sglp than under tclp the opposite was true for most other elements analyzed

metastability of gas hydrate marine occurrences of gas hydrate are normally confined to the top few hundred meters of sediments along deep continental margins the zone of stability for gas hydrate is limited in depth by increases in temperature below the seafloor we use thermodynamic calculations to show that gas hydrate can exist in a metastable state below the usual base of the stability zone we estimate that gas hydrate can be overheated by several degrees and that it may persist in this metastable state in the seafloor for as long as 106 years sudden decomposition of metastable hydrate should produce substantial pore pressure in the sediments contributing to slope failure in locations where gas hydrate is found such a mechanism might help to explain why slumping appears to be more frequent than average during the interval around the last glacial maximum

a model for late quaternary methane ice core signals wetlands versus a shallow marine source 1 a three reservoir model with first order kinetics for methane records in the vostok antarctica and gisp2 greenland ice cores reproduces the sawtooth pattern and the maximum and minimum concentrations the model also returns an atmospheric methane relaxation time of 10 years for both cores which is the same as current estimates the characteristics of the source reservoirs are long relaxation times 33 3 and 100 ky and high initial methane concentrations 2500 and 7000 ppm for gisp2 and vostok respectively these characteristics are consistent with gas hydrate sources in shallow marine sediments but not with wetland sources which have insufficient storage capacity and low source strength

mobility of trace and potentially harmful elements in the environment from high sulfur indian coal mines abstract coal mine rejects and sulfide bearing coals are prone to acid mine drainage amd formation due to aqueous weathering these acidic effluents contain dissolved trace and potentially harmful elements phes that have considerable impact on the environment the behavior of these elements in amd is mainly controlled by ph the focus of the present study is to investigate aqueous leaching of mine rejects for prediction of acid producing potential rates of weathering and release of phes in mine drainage mine reject mr and coal samples from the active mine sites of meghalaya india typically have high s contents 1 8 5 7 in mr and 1 7 4 7 in coals with 75 90 of the s in organic form and enrichment of most of the phes in rejects aqueous kinetic leaching experiments on mine rejects showed high acid producing potential and release of trace and potentially harmful elements the elements sb as cd cr co cu pb mn ni v and zn in mine sample leachates are compared with those in mine waters the concentrations of al si p k ti mn fe co ni cu zn and pb are found to increase with leaching time and are negatively correlated with ph of the solution the processes controlling the release of these elements are acid leaching precipitation and adsorption the critical loads of phes in water affected by amd are calculated by comparing their concentrations with those of regulatory levels the enrichment factors efs and soil pollution indices spis for the elements have shown that phes from coal and mine reject samples are mobilized into the nearby environment and are enriched in the associated soil and sediment

elastic wave velocity characterization of gas hydrate bearing fractured reservoirs in a permafrost area of the qilian mountain northwest china abstract there are two types of gas hydrate bearing reservoirs in the permafrost area of qilian mountain most of the gas hydrates occur mainly in the fractured mudstone reservoirs and rarely in the pores of the sandstone reservoirs in this study for the acoustic velocity characterization of the fractured gas hydrate reservoirs of the qilian mountain permafrost area some mudstone core samples were collected for physical rock experiments such as the acoustic experiment and the porosity and permeability experiment an acoustic velocity numerical simulation of gas hydrate reservoirs was performed according to the biot theory and the differential effective medium theory with the conditions of multiple gas hydrate occurrence models including the suspension model the semi cementation model and the cementation model and considering both infinite and penny shaped cracks fracture porosity was added to the core samples that only contain matrix porosity with fracture porosity ranging from 0 01 to 5 the variation laws between acoustic velocity with fractured porosity and hydrate saturation are obtained 1 in the case of an infinite crack if the fractured porosity is 0 01 1 the p wave velocity decreases rapidly in the case of the three occurrence models if the fractured porosity is higher than 1 the acoustic velocity decreases gradually if the crack shape is a penny shaped crack the p wave velocity decreases almost linearly with increasing fracture porosity 2 if the hydrate occurrence model is the suspension model the p wave velocity increases slightly with increasing hydrate saturation if the occurrence model is the semi cementation model or the cementation model when the gas hydrate saturation of the infinite crack ranges from 0 to 80 the acoustic velocity increases approximately linearly whereas when the gas hydrate saturation ranges from 80 to 100 the velocity increases rapidly if the crack is a penny shaped crack the velocity increases almost linearly with increasing gas hydrate saturation from 0 to 100 3 it is found that the fractured gas hydrate reservoirs of the qilian mountain permafrost area contain both penny shaped and infinite cracks of which the infinite crack is the main crack shape the gas hydrate occurrence in the qilian mountain permafrost area mainly follows the suspension model this has significance for the seismic exploration and log evaluation of gas hydrate bearing fractured reservoirs in the permafrost area of the qilian mountain in studying the acoustic velocity characterization the crack shapes and occurrence models of gas hydrate reservoirs in the study area

gas hydrate formation and its accumulation potential in mohe permafrost china abstract the mohe region is an area of continuous permafrost in northernmost china with strong similarities to other known gas hydrate bearing regions permafrost thickness is typically 20 80 m average surface temperature ranges from 0 5 c to 3 0 c and the geothermal gradient is roughly 1 6 c 100 m we estimate that 204 66 1012 m3 of hydrocarbon gases have been generated in the mohe basin from nearly 1000 m middle jurassic dark mudstones providing ample gas source for gas hydrate formation numerous folds in the shallow section provide opportunities to trap gas within sandstones and siltstones reservoirs bounded by competent mudstone seals gas migration to the shallow section is enabled via fault fracture zones and fracture systems based on core description and observations of gas releases from drilled wells we infer that the mohe region could hold large quantities of natural gas in the form of gas hydrate

benthic foraminifera associated with cold methane seeps on the northern california margin ecology and stable isotopic composition release of methane from large marine reservoirs has been linked to climate change as a causal mechanism and a consequence of temperature changes during the quaternary and the paleocene these inferred linkages are based primarily on variations in benthic foraminiferal stable isotope signatures few modern analog data exist however to assess the influence of methane flux on the geochemistry or faunal characteristics of benthic foraminiferal assemblages here we present analyses of the ecology and stable isotopic compositions of living rose bengal stained and dead fossil foraminifera 150 mm from cold methane seeps on the slope off of the eel river northern california 500 525 m and discuss potential applications for reconstructions of methane release in the past and present calcareous foraminiferal assemblages associated with calyptogena clam bed seeps were comprised of species that are also found in organic rich environments cosmopolitan paleoceanographically important taxa were abundant these included uvigerina bolivina chilostomella globobulimina a ndnonionella we speculate that seep foraminifera are attracted to the availability of food at cold seeps and require no adaptations beyond those needed for life in organic rich reducing environments oxygen isotopic values of the tests of living foraminiferal assemblages from seeps had a high range up to 0 69 as did carbon isotopic values up to 1 02 many living foraminiferal isotope values were within the range exhibited by the same or similar species in non seep environments carbon isotopic values of fossil foraminifera found deeper in the sediments 18 20 cm however were 4 10 u peregrina and 3 60 b subargentea more negative than living d 13 c values these results suggest that d 13 c values of foraminiferal tests reflect methane seepage and species specific differences in isotopic composition and can indicate temporal variations in seep activity a better understanding of foraminiferal ecology and stable isotopic composition will enhance paleo seep recognition and improve interpretations of climatic and paleoceanographic change 2000 elsevier science b v all rights reserved

timing of the late quaternary amazon fan complex masstransport deposits this paper is included in the special publication entitled geological evolution of ocean basins results from the ocean drilling program edited by a cramp c j macleod s v lee and e j w jones the amazon fan at the mouth of the amazon river is a large highly structured muddy deep sea fan sediment recovered by ocean drilling program leg 155 has allowed us to reconstruct the structure of the late quaternary amazon fan complex a significant sedimentary component of the complex are the mass transport deposits mtds formed by catastrophic failure of the continental slope there are two sets of mtds the near surface mtds and the deep mtds the near surface mtds are divided into the eastern and western debris flows which are capped by holocene sediments the deep debris flows are divided into the unit r mtd in the western amazon fan complex and the deep eastern mtd in the eastern amazon fan complex the mtds each cover an area of up to 25 000 km2 reach a maximum thickness of 200 m and consist of approximately 50 000 gigatonnes of sediment a characteristic of the mtds is the inclusion of reworked glacial and interglacial material from both the continental slope and the surrounding fan the relatively thin interglacial deposits below the mtds are from the nanofossil zones cn14b and cn15a and thus younger than 460 ka bio seismic and magnetostratigraphy and sedimentation rate constraints have been used to date the top of both the near surface and the deep mtds it seems that the near surface western and eastern debris flows were last active during termination i the deep eastern mtd was last active at about 33 ka while the unit r mtd was last active at about 45 ka it is inferred that the interglacial deposits beneath these mtds were formed during oxygen isotope stages 7 9 and 11 we speculate that the mtds were triggered by climatically induced changes in sea level and that the interglacal deposits may have acted as slip planes for the mtds

leaching of trace elements from pittsburgh coal mill rejects compared with coal combustion products from a coal fired power plant in ohio usa abstract we investigated the leachability of elements from mill rejects from the high sulfur bituminous upper pennsylvanian pittsburgh coal using the synthetic groundwater leaching procedure sglp long term leaching ltl and the u s environmental protection agency s epa s toxicity characteristic leaching procedure tclp and compared their leaching behavior with that of three coal combustion products ccps bottom ash economizer fly ash and fly ash from the same coal none of the environmentally hazardous resource conservation and recovery act of 1976 rcra metals analyzed in the leachates from the mill rejects or the ccps exceeded u s epa toxicity characteristics as ba cd cr hg pb and se most trace elements leached the least from mill rejects and bottom ash and leached the most from fly ash the elements ca co mg mn and sr however were more concentrated in mill reject leachates than ccp leachates most trace elements increased in concentration with increasing sglp and ltl leaching duration but as and v decreased in concentration with time in mill reject leachates suggesting sorption or precipitation of these elements was occurring

sources of atmospheric ch4 in early postglacial time at the terminations that marked the ends of the oldest and younger dryas at the close of the last major glaciation atmospheric methane levels rose sharply biological sources may have played a part in this increase but it is unlikely that they could have accounted for the suddenness of the rise in methane production some fossil methane stores such as marine and continental hydrates may have become unstable at the time of the terminations and there is much geological evidence that many catastrophic releases of methane occurred it is possible that part of the increase in global atmospheric methane may have been the result of these releases which may also have played a partial role in recharging the inventory of carbon in the atmosphere biosphere system the younger dryas cooling may represent a transient response to a later reduction in greenhouse forcing when the ch4 mixing ratio in the atmosphere dropped this transient response would have been more marked in the northern hemisphere than in the southern the termination of the younger dryas may have occurred after a further catastrophic release of fossil methane

origin and stability of a permafrost methane hydrate occurrence in the canadian shield abstract relatively little attention has been given to the stability of methane hydrates formed during periods of past climate change currently in areas of continuous permafrost although a large portion of the canadian arctic is underlain by crystalline rocks the occurrence phase and origin of alkanes in crystalline rocks under thick permafrost conditions 500 m have not been reported for the first time composition and isotopic data for gases from a crystalline shield environment currently under permafrost conditions are presented gas and water samples were collected from exploration boreholes and seeps between 890 and 1130 m depths in the lupin gold mine nunavut canada gases were methane dominate 64 87 with nitrogen 10 37 the next largest component and smaller amounts of ethane propane and carbon dioxide pressure and temperature measurements indicated gas hydrates were stable at the site prior to mining operations a conclusion supported by noble gas and salinity determinations gas hydrate stability over the last 120 kyr glacial cycle was demonstrated by calculating transient subsurface pressure and temperature conditions utilizing the memorial university university of toronto glacial systems model mun uoft gsm and the hydrogeosphere groundwater flow model model results also indicated glacial loading increased subsurface pressures resulting in increased hydrate stability fields during glacial periods subglacial groundwater recharge would be limited by any significant formation of gas hydrates gas composition combined with carbon and hydrogen isotopic determinations on methane 56 to 42 vpdb and 349 to 181 vsmow carbon dioxide 55 to 15 vpdb ethane 37 to 27 vpdb and 330 to 228 vsmow and propane 34 to 27 vpdb and 196 to 172 vsmow indicated formation of natural gases by thermogenic processes mixed with bacteriogenic gas reasonable given site geologic history methane hydrate formation affected gas composition and gas 2 h values complicating the interpretation gas production is not a modern process at this location and the overall contribution to the global carbon budget is small glacial groundwater recharge models need to account for methane hydrate formation and dissipation due to changes in subsurface stability fields during glaciation and the effect of methane hydrate on hydraulic conductivity

snowball earth termination by destabilization of equatorial permafrost methane clathrate the recovery from the marinoan snowball ice age of about 635 million years ago is one of the most severe climate change events known to have occurred on earth hypotheses accounting for the abruptness of deglaciation include ice albedo feedback deep ocean out gassing during post glacial oceanic overturn or methane hydrate destabilization martin kennedy and colleagues now report the broadest range of oxygen isotope values yet measured in marine sediments in methane seeps in marinoan deglacial sediments underlying a thin interval of carbonate these deposits are thought to record widespread oceanic carbonate precipitation during postglacial sea level rise the range of values is likely the result of mixing between ice sheet derived meteoric waters and clathrate derived fluids during the flushing and destabilization of a clathrate field by glacial meltwater their findings suggest that methane released from low latitude permafrost clathrates acted as a trigger and or strong positive feedback for deglaciation and warming this paper reports the broadest range of oxygen isotope values yet measured in marine sediments in methane seeps in marinoan deglacial sediments underlying a thin interval of carbonate these deposits are thought to record widespread oceanic carbonate precipitation during postglacial sea level rise the range of values is likely the result of mixing between ice sheet derived meteoric waters and clathrate derived fluids during the flushing and destabilization of a clathrate field by glacial meltwater the start of the ediacaran period is defined by one of the most severe climate change events recorded in earth history the recovery from the marinoan snowball ice age 635 myr ago ref 1 marinoan glacial marine deposits occur at equatorial palaeolatitudes2 and are sharply overlain by a thin interval of carbonate that preserves marine carbon and sulphur isotopic excursions of about 5 and 15 parts per thousand respectively3 4 5 these deposits are thought to record widespread oceanic carbonate precipitation during postglacial sea level rise1 3 4 this abrupt transition records a climate system in profound disequilibrium3 6 and contrasts sharply with the cyclical stratigraphic signal imparted by the balanced feedbacks modulating phanerozoic deglaciation hypotheses accounting for the abruptness of deglaciation include ice albedo feedback3 deep ocean out gassing during post glacial oceanic overturn7 or methane hydrate destabilization8 9 10 here we report the broadest range of oxygen isotope values yet measured in marine sediments 25 to 12 in methane seeps in marinoan deglacial sediments underlying the cap carbonate this range of values is likely to be the result of mixing between ice sheet derived meteoric waters and clathrate derived fluids during the flushing and destabilization of a clathrate field by glacial meltwater the equatorial palaeolatitude implies a highly volatile shelf permafrost pool that is an order of magnitude larger than that of the present day a pool of this size could have provided a massive biogeochemical feedback capable of triggering deglaciation and accounting for the global postglacial marine carbon and sulphur isotopic excursions abrupt unidirectional warming cap carbonate deposition and a marine oxygen crisis our findings suggest that methane released from low latitude permafrost clathrates therefore acted as a trigger and or strong positive feedback for deglaciation and warming methane hydrate destabilization is increasingly suspected as an important positive feedback to climate change11 12 13 that coincides with critical boundaries in the geological record14 15 and may represent one particularly important mechanism active during conditions of strong climate forcing

methane fluxes from the sea to the atmosphere across the siberian shelf seas the laptev and east siberian seas have been proposed as a substantial source of methane ch4 to the atmosphere during summer 2014 we made unique high resolution simultaneous measurements of ch4

low temperature high stress deformation of olivine under water saturated conditions abstract low temperature high stress rheology of olivine was investigated under water saturated conditions by large strain shear deformation experiments using the griggs type apparatus samples at t 1273 1373 k and p 2 gpa under water saturated conditions deformed under a significantly lower applied stress than expected from the power law relation and the strain rate increases more rapidly with stress these observations suggest that an exponential flow law operates under the present experimental conditions in which the stress dependence of activation enthalpy is characterized by the peierls stress the peierls stress is determined between 1 6 and 2 9 gpa depending on the choice of the form of stress dependence of the activation enthalpy these values are significantly smaller than the peierls stress under dry conditions 9 1 gpa we suggest that water hydrogen incorporated in the olivine lattices decreases the peierls stress and hence the rate of deformation in the exponential creep is significantly enhanced by the presence of water the reduction of the peierls stress by water results in the highly anisotropic weakening effect of water that causes the fabric transitions in olivine the transition between the power law and the exponential creep occurs at relatively low stress 100 mpa at a geologically relevant strain rate of 10 15 s 1 when temperature is lower than 1273 k and under water rich conditions hence the exponential creep might be dominated in olivine rich rocks at low temperature and high stress under water rich conditions and such regions could be widespread in the subduction zone upper mantle where the cold lithospheric plates sink into the mantle

a novel hybrid method for gas hydrate filling modes identification via digital rock abstract gas hydrates are one of the most abundant clean energy resources and can effectively solve the energy crisis with a lower carbon footprint gas hydrates typically exhibit complex microscopic filling modes including adhesive mode cemented mode and scattered mode furthermore the scientific understanding of such filling modes and the associated petrophysical parameters is essential for successful exploitation and development of hydrate formations however a precise identification of such filling modes remains a big challenge thus here we proposed a novel hybrid gas hydrate filling mode identification method via digital rock technique the hybrid method uses a combination of multiple methodologies firstly the dry core samples were scanned by the high resolution micro scale 3d x ray computed tomography ct and the digital rock models were built then the resistivity was simulated as a function of gas hydrate saturation with three idealized gas hydrate filling modes the differences between the resistivity of three idealized gas hydrate filling modes were analyzed and based on the correlations obtained the idealized gas hydrate saturation calculation models were formulated we then considered well log data from a real hydrate reservoir in order to evaluate the application of proposed hydrate saturation model and identify the filling mode essentially the gas hydrate saturation results from digital rock models and field well logging data are compared and the filling modes in the research reservoir were successfully identified

sulfur and carbon isotope geochemistry of coal and derived coal combustion by products an example from an eastern kentucky mine and power plant abstract the isotopic compositions of s 34 s and c 13 c were determined for the coal utilized by a power plant and for the fly ash produced as a by product of the coal combustion in a 220 mw utility boiler the coal samples analyzed represent different lithologies within a single mine the coal supplied to the power plant the pulverized feed coal and the coal rejected by the pulverizer the ash was collected at various stages of the ash collection system in the plant there is a notable enrichment in 34 s from the base to the top of the coal seam in the mine with much of the variation due to an upwards enrichment in the 34 s values of the pyrite variations in 34 s and in the amount of pyritic s in the coal delivered to the plant show that there was a change of source of coal supplied to the plant between week one and week two of monitoring supporting a previous study based on metal and sulfide geochemistry for the same plant the fly ash has a more enriched 34 s than the pulverized coal and in general the 34 s is more enriched in fly ashes collected at cooler points in the ash collection system this pattern of 34 s suggests an increased isotopic fractionation due to temperature with the fly ash becoming progressively depleted in 34 s and the flue gas s containing components becoming progressively enriched in 34 s with increasing temperatures substantially less variation is seen in the c isotopes compared to s isotopes there is little vertical variation in 13 c in the coal bed with 13 c becoming slightly heavier towards the top of the coal seam an 83 93 loss of solid phase c occurs during coal combustion in the transition from coal to ash owing to loss of co 2 despite the significant difference in total c content only a small enrichment of 0 44 0 67 in 13 c in the ash relative to the coal is observed demonstrating that redistribution of c isotopes in the boiler and convective passes prior to the arrival of the fly ash in the ash collections system is minor

balancing the deglacial global carbon budget the hydrate factor abstract the discovery that methane from dissociation of gas hydrates could be an important factor in the global carbon cycle resolves the major discrepancy in estimates of the increase of terrestrial biomass from the last glacial period to the present carbon isotope budgeting using the marine carbon isotopic record results in an estimate centered around 500 gtc whereas palaeovegetation reconstruction with biosphere models gives averages around 1000 gtc the discrepancy may be resolved by considering release of isotopically light methane through destabilization of gas hydrates this provides a unique means of estimating the contribution of gas hydrates to the deglacial rise in atmospheric methane a release of 120 gtc methane makes a biospheric carbon transfer of 1000 gtc compatible with the marine carbon isotope data this however represents less than 30 of the enhanced atmospheric methane production between 18 and 8 ka observed in ice cores supporting the theory that glacial interglacial variations in atmospheric methane were driven primarily by changes in the extent of tropical and temperate wetlands and not by methane release from clathrates by balancing the deglacial carbon budget we demonstrate that global carbon models will have to incorporate glacial interglacial vegetation shifts of at least 1000 gtc which many currently find difficult

the end of the ice age methane gas hydrates may have contributed to the rapid rise in atmospheric ch4 co2 and global temperatures at the end of the last major glaciation about 13 500 years ago given suitable orbital conditions and insolation at high latitude a small triggering event such as the release of one or more arctic gas pools may have initiated massive release of methane from hydrate under ice and in permafrost the consequent greenhouse warming would have provided strong positive feedback amplifying emission this warming driven by ch4 may have induced the release of co2 from the oceans to the biosphere stabilizing the interglacial carbon cycle

linking continental slope failures and climate change testing the clathrate gun hypothesis it has been suggested that the release of clathrates rather than expansion of wetlands is the primary cause of the rapid increases observed in the ice core atmospheric methane record during the pleistocene because submarine sediment failures can involve as much as 5000 gt of sediment and have the capacity to release vast quantities of methane hydrates one of the major tests of the clathrate gun hypothesis is determining whether the periods of enhanced continental slope failure and atmospheric methane correlate to test the clathrate gun hypothesis we have collated published dates for submarine sediment failures in the north atlantic sector and correlated them with climatic change for the past 45 k y more than 70 by volume of continental slope failures during the past 45 k y was displaced in two periods between 15 and 13 ka and between 11 and 8 ka both these intervals correlate with rising sea level and peaks in the methane record during the bolling allerod and preboreal periods these data support the clathrate gun hypothesis for glacial interglacial transitions the data do not however support the clathrate gun hypothesis for glacial millennial scale climate cycles because the occurrence of sediment failures correlates with heinrich events i e lows in sea level and atmospheric methane a secondary use of this data set is the insight into the possible cause of continental slope failures glacial period slope failures occur mainly in the low latitudes and are associated with lowering sea level this finding suggests that reduced hydrostatic pressure and the associated destabilization of gas hydrates may be the primary cause the bolling allerod sediment failures were predominantly low latitude suggesting an early tropical response to deglaciation e g enhanced precipitation and sediment load to the continental shelf or warming of intermediate waters in contrast sediment failures during the preboreal period and the majority of the holocene occurred in the high latitudes suggesting either isostatic rebound related earthquake activity or reduced hydrostatic pressure caused by isostatic rebound causing destabilization of gas hydrates

mantle plume the invisible serial killer application to the permian triassic boundary mass extinction the earth experienced a severe mass extinction at the permian triassic boundary ptb about 252 million years ago this biological catastrophe was accompanied by major changes in geochemical composition of the atmosphere and ocean and the appearance of sedimentary features which had not occurred since the precambrian time the eruption of the largest continental flood basalt the siberian traps overlapped this mass killing many hypotheses have been proposed but no definitive conclusion currently exits here we present characteristics of three sections from iran and china and propose that an active mantle plume initiated a series of processes which led to the mass mortality and produced major sedimentological mineralogical and geochemical changes observed in the transition from the paleozoic to the mesozoic the injection of mantle plume related igneous dike swarms into the continental margin facilitated the release of massive amounts of ch 4 primarily from the dissociation of marine gas hydrates and secondarily from the maturation of organic rich sediments and fracturing of hydrocarbon reservoirs the bulk of the ch 4 was aerobically oxidized in the water column producing dissolved co 2 with low 13 c values this co 2 saturated seawater became acidic to the point of dissolution of shelf carbonates promoting precipitation of siliciclastic rich strata in the transition from the permian to the triassic methane derived co 2 also lowered carbon isotopic composition of seawater leading to the observed decline in 13 c composition of organic and inorganic marine carbon at the ptb gas charged oceans released large volumes of co 2 and ch 4 into the atmosphere which created a severe global warming the end permian inferno causing the release of additional ch 4 from the dissociation of polar gas hydrates these events lowered 13 c compositions of terrestrial carbon simultaneously feeder dikes from the mantle plume formed the siberian traps flood basalt marine mass extinction was the result of a change in seawater composition due to the injection and oxidation of ch 4 in the water column causing low ph high concentrations of co 2 ca 2 and hco 3 and low co 3 2 values combined with a hot seawater temperature these changes made calcification of marine organisms difficult and produced major physiological crisis including reduced metabolic rates high sensitivity to environmental stress and hampered growth and reproduction terrestrial mass extinction can be attributed to severe global warming and soil acidification produced by increased atmospheric co 2 acid rain that was generated by so 2 derived from the siberian trap eruption and loss of habitat cessation of the plume activity during early triassic stopped the release of ch 4 into the ocean and terminated continental flood basalt eruption ending the environment of death on land and in sea the cut off of co 2 production in the ocean instantly increased carbonate saturation of seawater resulting in extensive seafloor cementation it also resulted in the deposition of marine carbonates by microbial activities in the hostile post extinction environment from the trigger to recovery the perturbation which included the end permian mass mortality could have lasted for at least 2 myr several major mass extinctions of the phanerozoic are temporally accompanied by flood basalt eruptions so far these two events have been interpreted in a cause and effect relation flood basalt eruption causes mass extinction this study proposes that flood basalts and their time correlative biological crises are themselves the consequence of a complex perturbation caused by mantle plume activities if so major disturbances in the near surface of the earth are ultimately controlled by changes in the mantle the physical sedimentological observations presented here combined with previous paleontological evidence cast doubt on other interpretations which use geochemical variables numerical modeling biomarkers and ce anomaly to suggest that late permian ocean was anoxic all the way to the photic zone

atmospheric methane from organic carbon mobilization in sedimentary basins the sleeping giant abstract the mass of organic carbon in sedimentary basins amounts to a staggering 1016 t dwarfing the mass contained in coal oil gas and all living systems by ten thousand fold the evolution of this giant mass during subsidence and uplift via chemical physical and biological processes not only controls fossil energy resource occurrence worldwide but also has the capacity for driving global climate only a tiny change in the degree of leakage particularly if focused through the hydrate cycle can result in globally significant greenhouse gas emissions to date neither climate models nor atmospheric co2 budget estimates have quantitatively included methane from thermal or microbial cracking of sedimentary organic matter deep in sedimentary basins recent estimates of average low latitude eocene surface temperatures beyond 30 c require extreme levels of atmospheric co2 methane degassing from sedimentary basins may be a mechanism to explain increases of atmospheric co2 to values as much as 20 times higher than pre industrial values increased natural gas emission could have been set in motion either by global tectonic processes such as pulses of activity in the global alpine fold belt leading to increased basin subsidence and maturation rates in the prolific jurassic and cretaceous organic rich sediments or by increased magmatic activity such as observed in the northern atlantic around the paleocene eocene boundary increased natural gas emission would have led to global warming that was accentuated by long lasting positive feedback effects through temperature transfer from the surface into sedimentary basins massive gas hydrate dissociation may have been an additional positive feedback factor during hyperthermals superimposed on long term warming such as the paleocene eocene thermal maximum petm as geologic sources may have contributed over one third of global atmospheric methane in pre industrial time variability in methane flux from sedimentary basins may have driven global climate not only at time scales of millions of years but also over geologically short periods of time earth system models linking atmospheric ocean and earth surface processes at different timescales with the sedimentary organic carbon cycle are the tools that need to be developed in order to investigate the role of methane from sedimentary basins in earth s climate

excess pore pressure resulting from methane hydrate dissociation in marine sediments a theoretical approach 1 this study quantifies the excess pore pressure resulting from gas hydrate dissociation in marine sediments the excess pore pressure in confined pore spaces can be up to several tens of megapascals due to the tendency for volume expansion associated with gas hydrate dissociation on the other hand the magnitude of excess pore pressure in well connected sediment pores is generally smaller depending primarily on the hydrate dissociation rate and the sediment permeability volume expansion due to gas hydrate dissociation in well connected pore spaces is related via darcy s law to an increase in pore pressure and its gradient in sediment which drives an additional upward fluid flow through the sediment layer overlying the gas hydrate dissociation area the magnitude of this excess pore pressure is found to be proportional to the rate of gas hydrate dissociation and the depth below seafloor and inversely proportional to sediment permeability and the depth below sea level the excess pore pressure is the greatest at low initial pressures and decreases rapidly with increasing initial pressure excess pore pressure may be the result of gas hydrate dissociation due to continuous sedimentation tectonic uplift sea level fall heating or inhibitor injection the excess pore pressure is found to be potentially able 1 to facilitate or trigger submarine landslides in shallow water environments 2 to result in the formation of vertical columns of focused fluid flow and gas migration and 3 to cause the failure of a sediment layer confined by low permeability barriers in relatively deep water environments

deev jahi model of the permian triassic boundary mass extinction a case for gas hydrates as the main cause of biological crisis on earth the smoking gun revealing the secrets of the end permian mass mortality is a unique 1 2 m thick layer consisting of 5 20 cm long crystals of calcite that occurs precisely at the permian triassic boundary ptb in iran armenia turkey and china this layer is interpreted as synsedimentary abiotic seafloor cement indicative of precipitation from a highly carbonate supersaturated seawater its 13 c composition 13 c 0 pdb is 4 to 5 pdb lower than the typical upper permian values 4 to 5 pdb suggesting the involvement of massive amounts of gas hydrate ch 4 13 c 60 pdb the temporal coincidence of the cement layer with the ptb suggests that the process that promoted seafloor cementation was also responsible for the biological crisis a cementation model is developed based on accumulation dissociation cycle of gas hydrates which also explains the mass extinction at the ptb the upper permian accumulation period of gas hydrates ended abruptly adjacent to the ptb and the dissociation event began releasing 3 2 to 4 7 10 18 g ch 4 into the ocean oxidation of ch 4 in the water column created a seawater that was charged with co 2 an oceanic acid bath and had lower than normal o 2 content but not anoxic this oceanic acid bath first dissolved suspended fine grained carbonate particles and small calcareous organisms followed by extensive dissolution of platform carbonates raising ca 2 and hco 3 concentrations of seawater when the release of ch 4 declined the acid bath ocean became a soda ocean precipitating massive amount of seafloor cements observed globally at the ptb the study suggests that prior to cement precipitation the ptb ocean was charged with co 2 warm had low oxygen high ca 2 and high hco 3 concentrations these conditions collectively created stressful conditions causing the marine mass mortality the leakage of ch 4 to the atmosphere produced a super hot climate resulting in the biological devastation on land the proposed kill mechanism is developed on the basis of the physical clue the cement layer left behind by the killing process the change in ocean chemistry the accumulation dissociation cycles of gas hydrates also explain the 13 c pattern of marine carbonates and the periodicity of mass extinction events during the phanerozoic accumulation periods were long 5 to 20 my providing favorable conditions for ecosystem development pardeess phase the dissociation events were short and catastrophic 10 to 500 ky causing low oxygenation super hot climate and biological devastation doozakh phase it appears that most mass extinctions of the phanerozoic have been related to the internal working of the earth system during the phanerozoic methane has played the role of the deev jahi a female demon in persian mythology whose task is to attack the earth every so often to kill life on land and in sea

a review of methane and gas hydrates in the dynamic stratified system of the blake ridge region offshore southeastern north america abstract the blake ridge region lies on the passive margin of southeastern north america and contains a large amount of methane gas hydrate the methane and methane gas hydrate are predominantly biogenic apparently produced by co2 reduction reflection seismics indicate that bottom simulating reflectors bsrs enclose 55 000 km2 with high amplitude bsrs covering 26 000 km2 ocean drilling program odp leg 164 drilled three deep holes on a 10 km long transect sites 994 995 and 997 water depth 2770 2798 m based on sampling and geochemical thermal seismic and borehole geophysical measurements gas hydrates are most likely present between 190 and 450 m in sediment column gas hydrate is most often disseminated throughout the sediment column although concentrations occur within specific sedimentary horizons within supposed fault zones and at the base of gas hydrate stability bghs where methane recycling produces more pervasive concentrations of gas hydrate estimates of gas hydrate inventory are based on a variety of methods including geochemical proxies vertical seismic profiling electric logging and measurements of in situ methane over the entire sediment column at least 2 4 of pore space volume 1 2 sediment volume is occupied by methane gas hydrates but average and maximum estimates are 5 4 and 12 respectively extrapolation of vertical gas hydrate and methane inventory over the area containing high amplitude bsrs yields estimates of 67 406 gt gigatons 1015 g of methane gas hydrate or 9 52 gt of methane and 2 6 27 gt of methane occurring as gas bubbles below the bghs average values are 185 gt of gas hydrate and 24 gt of methane as gas hydrate any gas hydrate occurring outside the area underlain by bsrs as suggested by geochemical evidence or that associated with low amplitude bsrs may increase these estimates by an unknown factor various data give conflicting pictures of mass transport with blake ridge sediments the data can be reconciled by viewing the upper sedimentary section accumulation of gas hydrate in the blake ridge sediments depends on the amount of methane leaving the system versus the amount of methane entering the gas hydrate stability zone ghsz over geologic time although there are some point sources of methane loss from the sediments e g seafloor seeps odp site 996 of unknown magnitude most of the documented methane loss occurs through diffusion and consumption at the sulfate methane interface smi by anaerobic methane oxidation amo 2 108 mol year 1 methane entering the ghsz at a rate of 1 3 109 mol year 1 indicates a methane trapping efficiency of 85 129i measurements suggest that the blake ridge system has accumulated gas hydrate over as much as 55 million years

a first estimation of gas hydrates offshore patagonia chile abstract in many places along the central and southern chilean active continental margin sedimentary successions covering the forearc contain methane hydrate resulting from a mixture of biogenic and thermogenic processes here we report the spatial distribution of gas hydrate in the accretionary prism and forearc sediments offshore western patagonia 50 s and 57 s landward of the antarctica south america plate boundary knowledge of the forearc structure here is limited owing to the small number of reflection seismic profiles available lack of high resolution bathymetry data and the absence of scientific drillholes however bottom simulating reflectors bsr indicative of gas hydrate occur regionally extensive below about one third of the forearc slope between about 280 and 630 m below sea floor bsr derived heat flow was calculated at about 30 and 70 mwm 2 these are typical values above subduction zones of oceanic crust older than 10 ma where vigorous fluid flow above young and hot subducting oceanic crust has leveled off to move towards an estimate of gas hydrate present in the sediments the velocity model was converted into a gas phase concentration model using data from one of the seismic sections average thickness of gas hydrate is about 290 m and average concentrations estimated are in a range of 3 4 10 if we use the minimum value of 3 4 the amount of methane present in the region is about 3 0 10 13 m 3 at standard pressure temperature conditions we conclude that the pacific forearc of patagonia area is an important reservoir of methane hydrates and we propose this area be considered as a potential methane hydrate concentrated zone and a key area to be investigated in the future

holocene mass wasting on upper non polar continental slopes due to post glacial ocean warming and hydrate dissociation 1 incorporating both late post glacial bottom water warming and eustatic sealevel rise into a mh methane hydrate stability model explains why at least some major submarine landslides e g the storegga slide norwegian margin may have been triggered by mh dissociation during the early holocene rising sealevels not during the lowest sealevels of the lgm last glacial maximum 18 20 ka in the case of storegga failure may have been initiated either below the upper slope or under the shelf for fresh pore water especially with admixed ethane at water depths below ca 800m persistent low bottom water temperatures allowed the sealevel rise to thicken the mh stability zone over time ruling out holocene initiation of failure mh release by holocene mass wasting cannot have initiated deglaciation

formation of gas hydrate from dissolved gas in natural porous media abstract migration of methane bearing fluids from the depth is commonly proposed to explain the formation of marine gas hydrate this formation mechanism is viable only if the gas hydrate can nucleate and grow directly from an aqueous solution while phase equilibrium calculations suggest that the gas hydrate should crystallize from the dissolved gas barriers associated with nucleation may impede or even prevent hydrate formation at present experimental support for the phase equilibrium calculations is insufficient to confirm whether the hydrate can form in the sea floor from the dissolved gas here we report on a set of experiments in which the hydrate is crystallized from dissolved co 2 in natural porous media the experiments demonstrate that the hydrate crystals can nucleate in the absence of free gas providing important experimental justification for models of hydrate formation that depend on fluid migration our results are also relevant for other formation models that depend on in situ methane generation from biogenic sources experimental evidence for hydrate formation at low gas concentrations implies less stringent requirements on the biogenic sources of methane compared with some previous estimates