interaction between a bubble plume and the near field in a stratified lake a steady state bubble plume model is evaluated using full scale temperature salinity and dissolved oxygen data collected in a swiss lake the data revealed a plume generated near field environment that differed significantly from the ambient far field water column properties a near field torus of reduced stratification developed around the plume the extent of which is on the same lateral scale as the horizontal dislocations generated by persistent first mode seiching the plume fallback water was found to penetrate much deeper than expected thereby maintaining reduced vertical gradients in the near field torus the plume entrains a portion of the fallback water leading to short circuiting which generates a complex plume lake interaction and reduces far field downwelling relative to the upward plume flow as the integral plume model incorporates the entrainment hypothesis it is highly sensitive to the near field environmental conditions after identifying appropriate near field boundary conditions the plume model predictions agree well with the field observations

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

a methane bubble curtain in meromictic sakinaw lake british columbia hydroacoustic surveys in meromictic sakinaw lake found an approximate 20 m wide dual column bubble curtain originating from a depth of 42 60 m all around the main basin at the interface between the chemocline and the sediments with the exception of the small upper basin sakinaw lake is oligotrophic and permanently salt stratified with a 30 m mixolimnion overlying an anoxic monimolimnion containing high concentrations of sodium chloride and dissolved sulfide nitrogen is the major factor limiting the lake s phytoplankton productivity the mainly methane bubbles in the curtain have a fairly narrow range of sizes with most of the bubbles 75 having radii between 600 and 850 mm with a peak at 735 mm which is close to a third of the size of bubbles reported for kinneret lake in israel we hypothesize that different bubble generation mechanisms cause this difference a simple bubble evolution model that includes gas dissolution and buoyancy is in good agreement with the acoustically observed bubble characteristics and is used to infer bubble densities and gas flux rates few of the bubbles reach the surface with any methane left in them the bubble flux of methane into the upper part of the lake is 3 mg m22 yr21 the dual column nature of the bubble plume and the extensive and persistent nature of the bubble curtain around the lake suggest that there may be unique physical and biological conditions in sakinaw lake affecting methane generation and bubble ebullition

anomalous seismic velocity drop in iron and biotite rich amphibolite to granulite facies transitional rocks from deccan volcanic covered 1993 killari earthquake region maharashtra india a case study 65 ma deccan volcanic province of western india forms one of the largest flood basaltic eruptions on the surface of the earth the nature of the concealed crust below this earthquake prone region which is marked by several low velocity zones at different depths has hardly been understood these low velocity zones have been invariably interpreted as fluid filled zones genetically connected to earthquake nucleation while carrying out detailed geological and petrophysical studies on the late archean basement cores obtained from a 617 m deep klr 1 borehole drilled in the epicentral zone of 1993 killari earthquake region of the southern deccan volcanic province we came across several instances where we observed remarkable drop in measured p wave velocity in a number of high density cores we provide detailed petrographic and geological data on 11 such anomalous samples which belong to mid crustal amphibolite to granulite facies transitional rocks they are associated with a mean p wave velocity of 6 02 km s range 5 82 6 22 km s conforming to granitic upper crust but in contrast have a high mean density of 2 91 g cm3 range 2 75 3 08 g cm3 which characterise mid to lower crust this velocity drop which is as much as 15 in some cores is primarily attributed to feot enrichment up to about 23 wt during the course of mantle fluid driven retrogressive metasomatic reactions caused by exhumation of deep seated mafic rocks presence of iron content mainly magnetite widely seen as opaques in thin sections of the rocks seems to have resulted into sharp increase in density as well as mean atomic weight our study indicates that the measured vp is inversely related to feot content as well as mean atomic weight of the rock

discovery of a natural co2 seep in the german north sea implications for shallow dissolved gas and seep detection a natural carbon dioxide co2 seep was discovered during an expedition to the southern german north sea october 2008 elevated co2 levels of 10 20 times above background were detected in seawater above a natural salt dome 30 km north of the east frisian island juist a single elevated value 53 times higher than background was measured indicating a possible co2 point source from the seafloor measured ph values of around 6 8 support modeled ph values for the observed high co2 concentration these results are presented in the context of co2 seepage detection in light of proposed subsurface co2 sequestering and growing concern of ocean acidification we explore the boundary conditions of co2 bubble and plume seepage and potential flux paths to the atmosphere shallow bubble release experiments conducted in a lake combined with discrete bubble modeling suggest that shallow co2 outgassing will be difficult to detect as bubbles dissolve very rapidly within meters bubble plume modeling further shows that a co2 plume will lose buoyancy quickly because of rapid bubble dissolution while the newly co2 enriched water tends to sink toward the seabed results suggest that released co2 will tend to stay near the bottom in shallow systems 200 m and will vent to the atmosphere only during deep water convection water column turnover while isotope signatures point to a biogenic source the exact origin is inconclusive because of dilution this site could serve as a natural laboratory to further study the effects of carbon sequestration below the seafloor

distribution and height of methane bubble plumes on the cascadia margin characterized by acoustic imaging submersible investigations of the cascadia accretionary complex have identified localized venting of methane gas bubbles in association with gas hydrate occurrence acoustic profiles of these bubble plumes in the water column in the vicinity of hydrate ridge offshore oregon provide new constraints on the spatial distribution of these gas vents and the fate of the gas in the water column the gas vent sites remained active over the span of two years but varied dramatically on time scales of a few hours all plumes emanated from local topographic highs near the summit of ridge structures the acoustic images of the bubble plumes in the water column disappear at water depths between 500 to 460 m independent of the seafloor depth this coincides with the predicted depth of the gas hydrate stability boundary of 510 to 490 m suggesting that the presence of a hydrate skin on the bubble surface prevents them from rapid dissolution the upper limit of the acoustic bubble plumes at 460 m suggests that dissolution of the residual bubbles is relatively rapid above the hydrate stability zone

geological and morphological setting of 2778 methane seeps in the dnepr paleo delta northwestern black sea abstract the dnepr paleo delta area in the nw black sea is characterized by an abundant presence of methane seeps during the expeditions of may june 2003 and 2004 within the eu funded crimea project detailed multibeam seismic and hydro acoustic water column investigations were carried out to study the relation between the spatial distribution of methane seeps sea floor morphology and sub surface structures 2778 new methane seeps were detected on echosounding records in an area of 1540 km 2 all seeps are located in the transition zone between the continental shelf and slope in water depths of 66 to 825 m the integration of the different geophysical datasets clearly indicates that methane seeps are not randomly distributed in this area but are concentrated in specific locations the depth limit for the majority of the detected seeps is 725 m water depth which corresponds more or less with the stability limit for pure methane hydrate at the ambient bottom temperature 8 9 c in this part of the black sea this suggests that where gas hydrates are stable they play the role of buffer for the upward migration of methane gas and thus prevent seepage of methane bubbles into the water column higher up on the margin gas seeps are widespread but accurate mapping illustrates that seeps occur preferentially in association with particular morphological and sub surface features on the shelf the highest concentration of seeps is found in elongated depressions pockmarks above the margins of filled channels on the continental slope where no pockmarks have been observed seepage occurs along crests of sedimentary ridges there seepage is focussed by a parallel stratified sediment cover that thins out towards the ridge crests on the slope seepage also appears in the vicinity of canyons bottom flanks and margins or near the scarps of submarine landslides where mass wasting breaches the fine grained sediment cover that acts as a stratigraphic seal the seismic data show the presence of a distinct gas front which has been used to map the depth of the free gas within the sea floor sediments the depth of this gas front is variable and locally domes up to the sea floor where the gas front approaches the seafloor gas bubbles were detected in the water column a regional map of the sub surface depth of the gas front emphasises this gas front versus seep relationship the integration of all data sets indicates that the spatial distribution of methane seeps in the dnepr paleo delta is mainly controlled by the gas hydrate stability zone as well as by stratigraphic and sedimentary factors

gas venting that bypasses the feather edge of marine hydrate offshore mauritania methane can be released from the vast marine hydrate reservoirs that surround continents into oceans and perhaps the atmosphere but how these pathways work within the global carbon cycle now and during a warmer world is only partially understood here we use 3 d seismic data to identify what we interpret to be a gas venting system that bypasses the hydrate stability zone hsz offshore of mauritania this venting is manifested by the presence of the acoustic wipe out awo across a densely faulted succession above a salt diapir and a set of morphological features including a substantial 260 m wide and 32 m deep pockmark at the seabed the base of the hsz is marked by a bottom simulating reflector bsr which deflects upwards above the diapir rather than mimicking the seabed we use a numerical modelling to show that this deflection is caused by the underlying salt diapir it creates a trapping geometry for gas sealed by hydrate clogged sediment after entering the hsz some methane accumulated as hydrate in the levees of a buried canyon venting in this locality probably reduces the flux of gas to the landward limit of feather edge of hydrate reducing the volume of gas that would be susceptible for release during a warmer world

the effect of methane seepage on the spatial distribution of oxygen and dissolved sulphide within a muddy sediment the effect of methane gas seepage on the small scale distribution of oxygen and sulphide within muddy seep sediments was studied at a site 310 340 m deep in the central skagerrak the concentrations of oxygen and sulphide were measured in cores 0 5 0 5 m using needle electrodes at 2 cm intervals horizontally along a transect across small seeps and vertically at 1 10 mm intervals to a depth of 10 cm the seep sediments which were densely colonised by the pogonophoran siboglinum poseidoni and the bivalve mollusc thyasira sarsi had high methane concentrations of up to 2567 8 mol dm 3 sed in the upper 13 cm of the sediment in sediments within 10 cm of the seep outlet relatively high concentrations of oxygen up to 48 mol o2 1 1 porewater at 10 cm depth were found while in adjacent non seep sediments similar concentrations of oxygen were found only in the top 1 cm this distribution of oxygen indicates that deep penetration of overlaying sea water into the sediment occurs probably induced by the ebulition of methane gas as has been described from sandy sediments elevated dissolved sulphide concentrations were detected around the periphery of the oxygen penetration zones and may be attributed to locally increased sulphate reduction fuelled by the sulphate and organic substrates drawn down into the sediment

five decades of triggered earthquakes in koyna warna region western india a review abstract we review reservoir triggered seismicity rts in the koyna warna region of india since the impoundment of the koyna reservoir in 1962 until the year 2015 we include seismicity that occurred farther south in response to the impoundment of warna reservoir in 1993 about 35 km to the south of koyna reservoir the on going earthquake activity for more than five decades in a small seismic volume of about 30 20 10 km3 has characterized the koyna warna region as globally unique and significant to date 22 earthquakes of m 5 about 200 earthquakes of m 4 and several thousand smaller earthquakes have been recorded by a dense network of stations in the region various seismological geophysical and hydrological studies have been carried out to understand the phenomenon of triggered seismicity including source mechanism fault geometry crustal structure earthquake processes causal relationship with reservoir water level changes and anomalous water level fluctuations in cased bore wells the present review takes stock of all such studies undertaken so far to summarise the understanding on various geo scientific issues and milestone achievements with regard to mechanism of triggered seismicity and source processes fault plane solutions commensurate with geometry of faulting source parameters seismogenic depth crustal structure and the role of reservoir water level two stage increase in seismic energy release coinciding with peaks of annual filling and draining cycle of reservoir with one month delay vis a vis spurt of moderate earthquakes m 5 due to i rapid rise in reservoir level 12 m week ii reservoir water level exceeding the previous maxima and iii duration for which high reservoir level is retained are characteristic features numerical models simulating diffusion of pore fluid pressure fronts during the filling stage of reservoir suggest stress perturbations of the order of 0 75 2 25 bar at hypocentral depth triggering earthquakes on critically stressed pre existing faults in the year 2005 a 13 station digital seismometers network became functional that characterized the distribution of epicentres in the area with increased accuracy and suggested four major seismic zones with well defined clusters scientific drilling carried out recently provide several new information regarding the subsurface geology and structure in the koyna region such as i thickness of deccan traps 933 in the koyna area and 1185 m in the warna area ii presence of granite gneiss basement directly underlying the deccan traps iii absence of infratrappean sediments and iv temperature not exceeding 150 c at hypocentral depth it is planned to establish a deep borehole observatory close to the seismic source zone for direct measurements of physical and mechanical properties of rocks pore fluid pressure hydrology thermal condition and other parameters of an intra plate active fault zone in the near field of earthquakes before during and after their occurrence results from such experiment and long term in situ monitoring of critical parameters would enhance our understanding on the mechanism of triggered earthquakes and the role of reservoir water level fluctuations

methane rich plumes on the carolina continental rise associations with gas hydrates seafloor venting of microbial gases occurs at 2167 m water depth over the blake ridge diapir gas rich plumes were identified acoustically in the water column up to 320 m above a pockmarked sea floor associated with active chemosynthetic biological communities plumes and venting fluids emanate from near a small fault that extends downward toward a dome in the bottom simulating reflector indicating that fluid and or gas migration is associated with gas hydrate bearing sediment below these plumes might be caused by gas bubbles or buoyant dumps of gas hydrate that float upward from the seafloor 18 refs 3 figs

invsp gathers of local earthquake seismograms an approach for modelling the upper crustal p and s velocity structure summary a new approach is presented here for obtaining invsp gathers of local earthquake seismograms in regions with adequate seismogenic depth range the inverse vertical seismic profiling invsp geometry is in principle quite similar to the up hole surveys of shallow seismic exploration in which shots fired at various depths in boreholes are recorded on the surface at a fixed offset similarly local earthquake seismograms of selected events at different hypocentral depths can be gathered into constant offset invsp sections for various stations of a mobile seismograph network they can be modelled for p and s velocity structure to upper crustal depths at each of the stations in the network with the aid of synthetic seismogram computations using appropriate source mechanisms of the earthquakes used an invsp gather obtained to a depth range of about 10 km at a station with 28 km constant offset is modelled for the upper crustal p and s velocity structure in the koyna warna seismic region in the western indian shield to demonstrate this approach

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

acoustically detected hydrocarbon plumes rising from 2 km depths in guaymas basin gulf of california plumes extending nearly 1000 m from the 1500 2000 m deep seafloor of guaymas basin were detected from below the 23 5 khz inverted echo sounder of the scripps deep two vehicle individual sound reflectors bubbles or drops rise at approximately 17 cm s in one plume the deep tow side scan records provide more information on the plumes structure at the altitude of the vehicle 75 m where some form multiple side scan targets one 20 m across near bottom 4 khz profiles show that plumes overlie young fault traces associated with extensional faulting at the basin s spreading centers of outcrops of tilted beds beside strike slip faults we infer from analysis of the deep tow observations field relationships and knowledge of the geology of this basin that the plumes are made of light hydrocarbons perhaps mainly methane that emanate from seabed seeps one of the acoustically detected plumes was at a spreading axis hydrothermal field which has many buoyant acoustically transparent thermal plumes some of which are rich in dissolved hydrocarbons

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

rising arctic ocean temperatures cause gas hydrate destabilization and ocean acidification vast amounts of methane hydrates are potentially stored in sediments along the continental margins owing their stability to low temperature high pressure conditions global warming could destabilize these hydrates and cause a release of methane ch 4 into the water column and possibly the atmosphere since the arctic has and will be warmed considerably arctic bottom water temperatures and their future evolution projected by a climate model were analyzed the resulting warming is spatially inhomogeneous with the strongest impact on shallow regions affected by atlantic inflow within the next 100 years the warming affects 25 of shallow and mid depth regions containing methane hydrates release of methane from melting hydrates in these areas could enhance ocean acidification and oxygen depletion in the water column the impact of methane release on global warming however would not be significant within the considered time span

methane bubble growth in fine grained muddy aquatic sediment insight from modeling abstract methane ch 4 is the most abundant hydrocarbon and one of the most important greenhouse gases in the atmosphere ch 4 bubble growth and migration within muddy aquatic sediments are closely associated with sediment fracturing in this paper we present the modeling of buoyancy driven ch 4 bubble growth in fine grained muddy aquatic sediment prior to the beginning of its rise we designed a coupled mechanical reaction transport numerical model that enables a differential fracturing over the bubble front as it occurs in nature when the fracturing increment stays constant at the bubble head and subsides towards bubble tail during bubble growth we show that this differential fracturing over the bubble front controls the bubble shape and size temporal evolution and is significantly affected by the critical stress intensity factor of the muddy sediment the intercalated stages of elastic expansion and fracturing during the bubble growth shorten with time as the bubble approaches its terminal size prior to its ascent our simulations reveal a high asymmetry in the bubble shape growing with time with respect to its initial symmetric penny shaped configuration it was found that the bubble grows allometrically while the importance of the bubble surface area growth with time we also confirmed the earlier predictions about the inverted tear drop bubble cross section just prior to the beginning of its rise modeling of the terminal bubble characteristics will permit prediction of the delivery of gaseous methane from the sediment to the atmosphere via the water column

linear bubble plume model for hypolimnetic oxygenation full scale validation and sensitivity analysis 1 an existing linear bubble plume model was improved and data collected from a full scale diffuser installed in spring hollow reservoir virginia were used to validate the model the depth of maximum plume rise was simulated well for two of the three diffuser tests temperature predictions deviated from measured profiles near the maximum plume rise height but predicted dissolved oxygen profiles compared very well with observations a sensitivity analysis was performed the gas flow rate had the greatest effect on predicted plume rise height and induced water flow rate both of which were directly proportional to gas flow rate oxygen transfer within the hypolimnion was independent of all parameters except initial bubble radius and was inversely proportional for radii greater than approximately 1 mm the results of this work suggest that plume dynamics and oxygen transfer can successfully be predicted for linear bubble plumes using the discrete bubble approach

gravity field and deep structure of the bengal fan and its surrounding continental margins northeast indian ocean abstract a revised gravity anomaly map for the northeast indian ocean shows that the shelf edge underlying the eastern continental margin of india is a rather narrow but extensively linear gravity low minimum free air 149 mgal the bengal fan seaward of the shelf has a depressed gravity field average free air 20 to 30 mgal in spite of the enormous thickness of sediments of as much as 10 15 km the two buried ridges below the bengal fan the 85 east and 90 east ridges have a large negative 75 mgal and a substantial positive 40 mgal free air anomaly respectively the andaman and burmese arcs lying along the east margin of the bengal fan are active subduction areas which have typical bipolar gravity signatures with a maximum amplitude of 300 mgal gravity interpretation for three regional traverses across the central and northern parts of the bengal fan and their surrounding continental margins suggests that a thickened oceanic crustal wedge juxtaposes the transitional crust under the eastern continental slope of india the 85 east ridge that was created when the indian ocean lithosphere was very juvenile appears to underlie a nearly 10 km thick and 120 km wide oceanic crustal block consisting of the ridge material embedded in the upper lithosphere while the 90 east ridge submarine topography buried load below the bengal fan is probably isostatically compensated by a low density mass acting as a cushion at the base of the crust the bengal fan crust with its thick sediment layer is carried down the andaman subduction zone to a depth of about 27 km where possibly phase transition takes place under higher pressure the maximum sediment thickness at the andaman burmese subduction zone is of the order of 10 12 km the gravity model predicts a low density zone about 60 km wide below the andaman burmese volcanic arc penetrating from crustal to subcrustal depths in the overriding burma plate a more complex density distribution is however envisaged for the andaman volcanic arc that is split by the neogene back arc spreading ridge the ocean continent crustal transition possibly occurs farther east of the volcanic arc below the shan plateau margin in burma or below the mergui terrace at the malayan continental margin east of the andaman sea

temporal and spatial evolution of a gas hydrate bearing accretionary ridge on the oregon continental margin a seismic reflection survey on the oregon continental margin conducted in 1989 indicates the widespread presence of gas hydrate beneath the middle and lower slope of this accretionary margin the seismic signature of gas hydrate a bottom simulating reflector bsr with negative polarity that locally cuts across stratigraphic horizons is especially well developed beneath hydrate ridge this anomalously shallow accretionary ridge was drilled during ocean drilling program leg 146 to study fluid venting in this paper we focus on the seismic data from the southern part of hydrate ridge where little evidence of active venting has previously been reported but where the seismic data indicate a complicated subsurface plumbing system apparent disruptions of the bsr beneath the western ridge flank suggest dissociation of gas hydrate in response to slumping a double bsr beneath the southern crest suggests hydrate destabilization in response to tectonic uplift and folding on the basis of these and other observations we propose a qualitative model for the evolution of a hydrate bearing ridge in an active accretionary complex in which gas hydrate initially stabilizes the sea floor permitting construction of large ridges that are then eaten away by slumps along their margins the north to south variation in sea floor venting and subsurface seismic structure along hydrate ridge may reflect different stages in the temporal evolution of one of these ridges

fluid expulsion from the dvurechenskii mud volcano black sea part i fluid sources and relevance to li b sr i and dissolved inorganic nitrogen cycles significant sediment ocean chemical fluxes are produced by the expulsion of sedimentary fluids at continental margins although such fluxes could play a role in global geochemical cycles few quantitative estimates of their global or even regional significance exist we carried out a pore water geochemical study of fluids expelled from the dvurechenskii mud volcano dmv in the black sea with the aim of understanding the role played by mud volcanoes in black sea geochemical cycles the dmv is presently expelling highly saline fluids particularly enriched in geochemically important species such as li 1 5 mm b 2 17 mm ba2 0 57 mm sr2 0 79 mm i 0 4 mm and dissolved inorganic nitrogen din 22 mm a combination of geochemical indicators shows that this geochemical signature was acquired via organic matter and silicate alteration processes in the subsurface down to 3 km depth and near surface gas hydrate formation we used a simple transport model to estimate the benthic fluxes of these solutes at the dmv our results show that the dmv is expelling fluids at a rather low seepage rate 8 25 cm year 1 resulting in a total water flux of 9 4 10 5 km3 year 1 this gentle regime of fluid expulsion results in li b sr2 i and din fluxes between 3 8 104 and 2 1 106 mol year 1 surface biogeochemical processes affect the benthic fluxes of ba2 such that the deep ba2 flux is completely consumed through the precipitation of authigenic barite baso4 in surface sediments the black sea i cycle is likely to be affected by mud volcanism if the 50 known black sea mud volcanoes share the rather sluggish activity of the dmv mud volcano fluxes of li b sr and din instead are too small to affect black sea geochemical cycles on a global scale mud volcanism could play a role in the marine cycles of li b sr i and din if current estimates of mud volcano abundance are correct

periodic variation of stress field in the koyna warna reservoir triggered seismic zone inferred from focal mechanism studies abstract the koyna warna region in western india is globally recognized as the premier site of reservoir triggered seismicity rts associated with the koyna and warna reservoirs the region is characterized by continuous seismic activity observed since several decades including the world s largest triggered earthquake of m6 3 which occurred in koyna in 1967 while the role of reservoirs in triggering earthquakes has been widely discussed the actual tectonic mechanism controlling earthquake genesis in this region is hardly understood the koyna warna region is exclusively governed by earthquakes of strike slip and normal fault mechanism distinct from the thrust faulting seen in other active zones in the indian region in the present study a comprehensive catalog of 50 focal mechanism solutions of earthquakes that occurred during the last 45 years in the koyna warna region is developed both from previous literature and from moment tensor inversion studies by the authors using broadband data from a local seismic network operating since 2005 the seismicity and fault plane data have enabled precise delineation of trends of the major causative faults which are further accentuated using the double difference technique stress inversion of the focal mechanism data has provided the best fitting principal compressive and tensile stress field of the region which in conjunction with the deciphered fault zones provides a feasible model of seismogenesis in this region based on the observed temporal variation of faulting mechanism a model of alternating cycles of predominantly strike slip and normal faulting is proposed which is attributed to a periodic peaking and relaxation respectively of the horizontal compressive stress field in this region due to the indian plate collision with eurasia

dissolved methane concentrations in the water column and surface sediments of hanna shoal and barrow canyon northern chukchi sea abstract current estimates of methane ch 4 flux suggest that arctic shelves may be a significant source of atmospheric ch 4 a potent greenhouse gas however little information is known about the ch 4 flux from most arctic shelves other than the east siberian arctic shelf we report here dissolved ch 4 concentrations in the water column and within surface sediments of the northern chukchi sea we hypothesized that this area contains high concentrations of ch 4 because it receives nutrient rich waters through the bering strait promoting primary production that enhances an organic rich material flux to the seafloor and eventual microbial methanogenesis in the sediments in august 2012 as part of the chukchi sea offshore monitoring in drilling area comida project fourteen stations were sampled on hanna shoal a shallow feature on the shelf and ten stations across the undersea barrow canyon on hanna shoal water column ch 4 concentrations ranged from 14 to 74 nm and surface concentrations were up to 15 times supersaturated in ch 4 compared to equilibrium with the average atmospheric concentrations 3 nm ch 4 concentrations at the sediment water interface were around 1 500 nm and typically increased with depth in the sediment at the head of barrow canyon water column ch 4 concentrations ranged from 5 to 46 nm with the highest concentrations in the deepest waters that were sampled 118 m overall the calculated fluxes to the atmosphere ranged from 1 to 80 mol ch 4 m 2 d 1 for hanna shoal and 4 to 17 mol ch 4 m 2 d 1 across the barrow canyon stations although there was a large range in these fluxes the average atmospheric flux 20 mol ch 4 m 2 d 1 across hanna shoal was 12 times lower than the flux reported from the east siberian arctic shelf in summer we conclude that while there is a positive flux of ch 4 to the atmosphere this part of the chukchi sea is not a significant source of atmospheric ch 4 compared to the east siberian sea shelf

1300 m high rising bubbles from mud volcanoes at 2080m in the black sea hydroacoustic characteristics and temporal variability a mud volcano area in the deep waters 2000 m of the black sea was studied by hydroacoustic measurements during several cruises between january 2002 and june 2004 gas bubbles in the water column give strong backscatter signals and thus can be detected even in great water depths by echosounders as the 38 khz ek500 scientific split beam system that was used during the surveys because of their shape in echograms and to differentiate against geochemical plumes and real upwelling bubble water plumes we call these hydroacoustic manifestations of bubbles in the water column flares digital recording and processing of the data allows a 3d visualization and data comparison over the entire observation period without artefacts caused by changing system settings during our surveys we discovered bubble release from three separate mud volcanoes dvurechenskiy dmv vodianitskiy vmv and the nameless seep site nss in about 2080 m water depth simultaneously bubble release was observed between 9 june 2003 and 5 june 2004 the most frequently surveyed dmv was found to be inactive during very intensive studies in january 2002 the first activity was observed on 27 june 2002 which finally ceased between 5 and 15 june 2004 after a period of continuously decreasing activity this observed 2 yr bubble release period at a mud volcano may give an indication for the duration of active periods the absence of short term variations within days or hours may indicate that the bubble release from the observed mud volcanoes does not undergo rapid changes the recorded echograms show that bubbles rise about 1300 m high through the water column to a final water depth of about 770 m which is 75 m below the phase boundary of pure methane hydrate in the black sea with a release depth from 2068 m and a detected rise height of 1300 m the flare at vmv is among the deepest and highest reported so far and gives evidence of highly extended bubble life times up to 108 min in deep marine environments to better understand how a methane bubble gas analyses of the pore water and gas hydrate gave 99 4 methane can rise so high without dissolving we applied a recently developed bubble dissolution model that takes into account a decreased mass transfer due to an immediately formed gas hydrate rim using the hydroacoustically determined bubble rising speeds 19 22 cm s at the bottom 12 14 cm s at the flare top and the relation between the rising speed of dirty gas hydrate rimmed bubbles and the bubble size we could validate that a gas hydrate rimmed bubble with a diameter of 9 mm could survive the 1300 m rise through the water column before it is finally dissolved a diameter of about 9 mm is reasonable for bubbles released at seep sites and the coincidence between the observed bubble rising speed and the model approach of a 9 mm bubble supports the assumption of gas hydrate rimmed bubbles

dissolved methane and carbon dioxide fluxes in subarctic and arctic regions assessing measurement techniques and spatial gradients abstract here we use a portable method to obtain high spatial resolution measurements of concentrations and calculate diffusive water to air fluxes of ch 4 and co 2 from two subarctic coastal regions kasitsna and jakolof bays and an arctic lake toolik lake the goals of this study are to determine distributions of these concentrations and fluxes to 1 critically evaluate the established protocols of collecting discrete water samples for these determinations and to 2 provide a first order extrapolation of the regional impacts of these diffusive atmospheric fluxes our measurements show that these environments are highly heterogeneous areas with the highest dissolved ch 4 and co 2 concentrations were isolated covering less than 21 of the total lake and bay areas and significant errors can be introduced if the collection of discrete water samples does not adequately characterize these spatial distributions a first order extrapolation of diffusive fluxes to all arctic regions with similar characteristics as toolik lake suggests that these lakes are likely supplying 0 21 and 15 77 tg of ch 4 and co 2 to the atmosphere annually respectively similarly we found that the subarctic coastal ocean is likely supplying 0 027 tg of ch 4 annually and is taking up roughly 524 tg of co 2 per year although diffusive fluxes at toolik lake may not be as substantial when comparing against present seep ebullition and spring ice out values warming in the arctic may result in the increase of methane discharge and methane emissions to the atmosphere thus further work is needed to understand this changing environment this study suggests that high spatial resolution measurement protocols similar to the one used here should be incorporated into field campaigns to reduce regional uncertainty and refine global emission estimates

mixed gas hydrate structures at the chapopote knoll southern gulf of mexico abstract in underwater hydrocarbon seepage environments gas hydrates are considered to play a significant role as shallow gas reservoirs and buffers for light hydrocarbon expulsion here we report on mixed hydrate structures from the chapopote knoll in the southern gulf of mexico and discuss several options on how a mixture of structure i si and structure ii sii gas hydrate may occur in nature locally resolving microscopic methods are needed to characterize the coexistence of different hydrate structures at geological hydrate deposits we used raman spectroscopy x ray diffraction and gas chromatography for our investigations gas hydrates were found within the matrix and pores of the asphalts extruded at the seafloor two of the three hydrate pieces investigated comprised only si formed mostly from methane in contrast one piece comprised an intimate mixture of both si and sii with sii representing ca 25 wt and si ca 75 wt of the hydrate present the two structures were closely associated within individual grain agglomerates the crystallites of sii were significantly larger than of si suggesting differences in the nucleation density or different crystallite ages the structural coexistence may be a result of one or more processes i de mixing into two hydrate structures during the growth from the gas phase which provides an additional degree of freedom for lowering the free energy in the system ii fractionated crystallization with a subsequently changing molecular composition iii crystallization from separated gas bubbles with different hydrocarbon compositions and water and iv partial transformation from sii to si after hydrate nucleation ceasing when a thermodynamically stable state was reached the presented work will affect future assessments of natural hydrate deposits at thermogenic hydrocarbon systems as it shows that both hydrate types i and ii can be present at a certain geological site and may provide a lingering strength to the system if conditions fall below the si stability limit this suggests that present worldwide hydrate occurrences are likely to be underestimated

the link between bottom simulating reflections and methane flux into the gas hydrate stability zone new evidence from lima basin peru margin bottom simulating reflections bsrs are probably the most commonly used indicators for gas hydrates in marine sediments it is now widely accepted that bsrs are primarily caused by free gas beneath gas hydrate bearing sediments however our insight into bsr formation to date is mostly limited to theoretical studies two endmember processes have been suggested to supply free gas for bsr formation i dissociation of gas hydrates and ii migration of methane from below during a recent campaign of the german research vessel sonne off the shore of peru we detected bsrs at locations undergoing both tectonic subsidence and non sedimentation or seafloor erosion tectonic subsidence and additionally perhaps seafloor erosion causes the base of gas hydrate stability to migrate downward with respect to gas hydrate bearing sediments this process rules out dissociation of gas hydrates as a source of free gas for bsrs at these locations instead free gas at bsrs is predicted to be absorbed into the gas hydrate stability zone bsrs appear to be confined to locations where the subsurface structure suggests focusing of fluid flow we investigated the seafloor at one of these locations with a tv sled and observed fields of rounded boulders and slab like rocks which we interpreted as authigenic carbonates authigenic carbonates are precipitations typically found at cold vents with methane expulsion we retrieved a small carbonate cemented sediment sample from the seafloor above a bsr about 20 km away this supported our interpretation that the observed slabs and boulders were carbonates all these observations suggest that bsrs in lima basin are maintained predominantly by gas that is supplied from below demonstrating that this endmember process for bsr formation exists in nature results from ocean drilling program leg 112 showed that methane for gas hydrate formation on the peru lower slope and the methane in hydrocarbon gases on the upper slope is mostly of biogenic origin the 13c composition of the recovered carbonate cement was consistent with biologic methane production below the seafloor although possibly above the bsr we speculate that the gas for bsr formation in lima basin also is mainly biogenic methane this would suggest the biologic productivity beneath the gas hydrate zone in lima basin to be relatively high in order to supply enough methane to maintain bsrs

a magma mass beneath casa diablo further evidence from reflected seismic waves a forty station seismographic network operating in long valley caldera in california during the summer of 1997 recorded a number of earthquakes with unusual secondary phases the phases can be seen on several stations throughout the network allowing the use of particle motions and differential travel times to examine their nature and points of origin based on amplitude frequency and travel time considerations it appears that some of the phases are mode converted s to p reflec tions from a zone below the casa diablo area near mammoth lakes ca the locus of reflection points was imaged using time domain signal migration and stacking under the assumptions of first order scattering theory the results indicate that the reflecting zone is a curved 1 5 km by 2 km surface 7 6 km below and 1 4 km west of the casa diablo geothermal plant previous studies show low p wave velocities and high s wave attenuations in the same location as the reflecting zone an amplitude analysis of the suspected reflec tions suggests they are produced by large contrasts in material properties with the possible range of transitions including solid to partially molten or dry to fluid satu rated rock given these observations plus the volcanic history of the caldera and its recent tectonic activity the most straightforward interpretation of the reflections is that they come from either the top of a sill or intrusion or the overlying hydrothermal system of such structures

methane in the northern atlantic controlled by microbial oxidation and atmospheric history during may august 1997 the distributions of dissolved methane and ccl3f cfc11 were measured in the atlantic between 50 and 60 n in surface waters throughout the region methane was observed to be close to equilibrium with the atmospheric mixing ratio implying that surface ocean methane is tracking its atmospheric history in regions of north atlantic deep water formation despite the different atmospheric history and ocean chemistry of ch4 and cfc11 their spatial distribution patterns in the water column are remarkably similar one dimensional distributions have been simulated with an advection diffusion model forced by the atmospheric histories the results suggest that the similar patterns result from the increasing input of ch4 and cfc11 to newly formed deep waters over time combined with the effect of horizontal mixing and the oxidation of methane on a 50 year time scale

noble gas anomalies related to high intensity methane gas seeps in the black sea dissolved noble gases and tritium were analyzed at a series of high intensity methane gas seeps in the black sea to study the transport and gas exchange induced by bubble streams in the water column these processes affect marine methane emissions to the atmosphere and are therefore relevant to climate warming the seep areas investigated are located in the dnepr paleo delta west of crimea and in the sorokin trough mud volcano area south east of crimea noble gas concentration profiles at active seep sites revealed prominent anomalies compared to reference profiles that are unaffected by outgassing supersaturations of the light noble gases helium and neon observed relatively close to the sea floor are interpreted as effects of gas exchange between the water and the rising bubbles depletions of the heavy noble gases argon krypton and xenon that were detected above an active bubble releasing mud volcano appear to be related to the injection of fluids depleted in noble gases that undergo vertical transport in the water column due to small density differences in both cases the noble gas anomalies clearly document seep specific processes which are difficult to detect by other methods helium is generally enriched in the deep water of the black sea due to terrigenic input although exceptionally high helium concentrations observed in one seep area indicate a locally elevated helium flux most of the seeps studied seem to be negligible sources of terrigenic helium noble gas analyses of sediment pore waters from the vicinity of a mud volcano showed large vertical gradients in helium concentrations the helium isotope signature of the pore waters points to a crustal origin for helium whereas the deep water of the black sea also contains a small mantle type component

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

methane escape from gas hydrate systems in marine environment and methane driven oceanic eruptions 1 huge quantities of ch4 are stored in marine sediment in the form of methane hydrate bubbles and dissolved ch4 in pore water here i discuss the various pathways for methane to enter the ocean and atmosphere including i methane hydrate dissolution or dissociation as it rises through seawater the dissociation rate can be 2 to 3 orders of magnitude greater than the dissolution rate ii the dissolution and expansion of a bubble with or without a hydrate shell as it rises through seawater there is a critical radius which depends on depth above which a bubble would reach the surface or even become larger as it rises i also propose and model the dynamics of a new type of terrestrial gas driven eruptions methane driven oceanic eruptions such eruptions not only represent a yet unrecognized geohazard but also provide a pathway for ch4 to rapidly enter the atmosphere as a greenhouse gas

spatial variation in fluid flow and geochemical fluxes across the sediment seawater interface at the carlos ribeiro mud volcano gulf of cadiz submarine mud volcanism is an important pathway for transfer of deep sourced fluids enriched in hydrocarbons and other elements into the ocean numerous mud volcanoes mvs have been discovered along oceanic plate margins and integrated elemental fluxes are potentially significant for oceanic chemical budgets here we present the first detailed study of the spatial variation in fluid and chemical fluxes at the carlos ribeiro mv in the gulf of cadiz to this end we combine analyses of the chemical composition of pore fluids with a 1 d transport reaction model to quantify fluid fluxes and fluxes of boron lithium and methane across the sediment seawater interface the pore fluids are significantly depleted in chloride but enriched in lithium boron and hydrocarbons relative to seawater pore water profiles of sulphate hydrogen sulphide and total alkalinity indicate that anaerobic oxidation of methane occurs at 34 180 cm depth below seafloor clay mineral dehydration and in particular the transformation of smectite to illite produces pore fluids that are depleted in chloride and potassium profiles of boron lithium and potassium are closely related which suggests that lithium and boron are released from the sediments during this transformation pore fluids are expelled into the water column by advection fluid flow velocities are 4 cm yr 1 at the apex of the mv but they rapidly decrease to 0 4 cm yr 1 at the periphery the associated fluxes of boron lithium and methane vary between 7 301 0 5 6 and 0 806 mmol m 2 yr 1 respectively we demonstrate that fluxes of li and b due to mud volcanism may be important on a global scale however release of methane into the overlying water column is suppressed by microbial methanotrophy

upwarped high velocity mafic crust subsurface tectonics and causes of intraplate latur killari m 6 2 and koyna m 6 3 earthquakes india a comparative study abstract a unique attempt is made to understand the genesis of intraplate seismicity in the latur killari and koyna seismogenic regions of india through derived crustal structure by synthesizing active and passive seismic magnetotelluric gravity and heat flow data it has indicated presence of relatively high velocity density intermediate granulite and amphibolite facies rocks underneath the deccan volcanic cover caused mainly due to a continuous geodynamic process of uplift and erosion since precambrian times these findings have been independently confirmed by detailed borehole geological geochemical and mineralogical investigations the crystalline basement rock is found to contain 2 wt of carbon di oxide fluid components the presence of geodynamic process associated with thermal anomalies at subcrustal depths is supported by a high mantle heat flow 29 36 mw m2 beneath both regions although some structural and compositional variations may exist as evidenced by p and s wave seismic velocities we suggest that the stress caused by ongoing uplift and a high mantle heat flow is continuously accumulating in this denser and rheologically stronger mafic crust within which earthquakes tend to nucleate these stresses appear to dominate over and above those generated by the india eurasia collision the role of fluids in stress generation as advocated through earlier studies appears limited

societal need for improved understanding of climate change anthropogenic impacts and geo hazard warning drive development of ocean observatories in european seas society s needs for a network of in situ ocean observing systems cross many areas of earth and marine science here we review the science themes that benefit from data supplied from ocean observatories understanding from existing studies is fragmented to the extent that it lacks the coherent long term monitoring needed to address questions at the scales essential to understand climate change and improve geo hazard early warning data sets from the deep sea are particularly rare with long term data available from only a few locations worldwide these science areas have impacts on societal health and well being and our awareness of ocean function in a shifting climate substantial efforts are underway to realise a network of open ocean observatories around european seas that will operate over multiple decades some systems are already collecting high resolution data from surface water column seafloor and sub seafloor sensors linked to shore by satellite or cable connection in real or near real time along with samples and other data collected in a delayed mode we expect that such observatories will contribute to answering major ocean science questions including how can monitoring of factors such as seismic activity pore fluid chemistry and pressure and gas hydrate stability improve seismic slope failure and tsunami warning what aspects of physical oceanography biogeochemical cycling and ecosystems will be most sensitive to climatic and anthropogenic change what are natural versus anthropogenic changes most fundamentally how are marine processes that occur at differing scales related the development of ocean observatories provides a substantial opportunity for ocean science to evolve in europe here we also describe some basic attributes of network design observatory networks provide the means to coordinate and integrate the collection of standardised data capable of bridging measurement scales across a dispersed area in european seas adding needed certainty to estimates of future oceanic conditions observatory data can be analysed along with other data such as those from satellites drifting floats autonomous underwater vehicles model analysis and the known distribution and abundances of marine fauna in order to address some of the questions posed above standardised methods for information management are also becoming established to ensure better accessibility and traceability of these data sets and ultimately to increase their use for societal benefit the connection of ocean observatory effort into larger frameworks including the global earth observation system of systems geoss and the global monitoring of environment and security gmes is integral to its success it is in a greater integrated framework that the full potential of the component systems will be realised highlights societies increasingly depend on timely information on ecosystems and natural hazards data is needed to improve climate related uncertainty and geo hazard early warning observatory networks coordinate and integrate the collection of standardised data ocean observatories provide opportunity for ocean science to evolve

the effects of co2 brine rheology on leakage processes in geologic carbon sequestration 1 leakage from geologic carbon sequestration gcs sites is inherently challenging to study because co2 driven by buoyant forces travels over long distances undergoing phase changes and encountering numerous connate brine and formation chemistries as it rises to the surface this work explores the effect that co2has on the rheological properties of brine solutions over a range of gcs relevant temperature pressure ionic strength and shear conditions under the fluid liquid equilibrium conditions that prevail in the deep subsurface viscosity of co2 brine mixtures was found to be a function of temperature and pressure alone once leakage conditions ensue discrete co2bubbles form in brine resulting in the vapor liquid equilibrium vle and these mixtures exhibit complex linear viscoelastic time dependent and thixotropic behavior the presence of co2 g bubbles on the flow of the bulk fluid could have important impacts on impeding via shear drag force leakage depending on the geometrical geochemical and geophysical characteristics of a storage site under vle conditions the effective viscosity of co2 brine mixtures was found to be up to five times higher than brine alone but the microstructure was easily destroyed and not readily regained under high shear conditions at higher temperatures and higher ionic strength the effect is less pronounced these results were considered in the context of flow through porous media and the effect on buoyancy driven flow is significant understanding this effect is important for developing an accurate constitutive relationship for leaking co2 which will lead to better capacity to select and monitor gcs sites

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

localization and characterization of a gas bubble stream at a congo deep water seep site using a 3d gridding approach on single beam echosounder data abstract this study investigates the geometry and temporal variation of a prominent gas bubble stream from a seafloor pockmark in the lower congo basin we present results of a 3d gridding approach of singlebeam echosounder water column data parasound 18 khz that increases the lateral resolution and improves the localization of anomalies beyond the inherent depth dependent footprint size of the sonar system this allows a detailed reconstruction of gas bubble trajectories through the water column revealing a stable gas bubble stream for the deepest 1000 m the bubbles are shifted laterally by 200 m in the transition zone between north atlantic deep water and antarctic intermediate water with a reconstructed current velocity of 4 cm s the direction of lateral shift varies throughout the 15 h survey possibly because of internal waves and small scale eddies at the water mass boundary furthermore a stacking of sbes water column data acquired during sampling stations showed a periodic variation in seepage intensity with periods of 6 and 8 min which are likely related to temporally modulated gas supply to the sea floor singlebeam echosounder are commonly limited by their small coverage of the survey area during individual passes and their footprint size in detailed imaging of individual seep sites especially in the deep sea the presented gridding method for singlebeam echosounder data may facilitate the use of such data in deep water gas bubble stream identification and localization

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

geophysical studies over the continental margins of the east coast of india abstract results of six profiles of continuous echosounding magnetic and gravity data collected across the continental margin of the east coast of india between 10 and 20 n in the bay of bengal aboard r v chain in 1973 are presented continuity of surface and subsurface features from profile to profile is indicated two major structural elements viz the marginal high situated at the foot of the continental slope and extending along the east coast of india and the marginal basin wide in the south becoming narrower towards the north have been delineated based on the topography and the gravity and the magnetic anomalies the eastern margin of india may be divided into two parts viz the southern and northern margins the southern margin is broader and more stable than the northern margin over which lava flows occur

thermal and visual time series at a seafloor gas hydrate deposit on the gulf of mexico slope ambient temperature is a critical factor determining the stability of gas hydrate deposits on continental margins to study this process directly under varying conditions a monitoring array comprising a time lapse camera and in situ temperature probes was deployed at a hydrocarbon seep known as bush hill where gas hydrates deposits are exposed at the seafloor in a water depth of 570 m for intervals of 91 days and 30 days the digital camera recorded several daily images of a prominent gas hydrate mound consisting of structure ii gas hydrate the temperature probes were constructed with one autonomous thermistor at each end of a 50 cm pvc wand and recorded temperatures with precision of better than 0 1 8c at 30 min intervals over 327 days one probe was implanted with a tight seal into a drill hole about 7 cm deep in the top of the gas hydrate mound the second was inserted about 50 cm deep into the adjacent sediments for each probe the top thermistor recorded the ambient water temperature while the bottom thermistor synoptically recorded the internal temperature of the hydrate or sediment the bottom water temperatures ranged from 6 64 to 9 73 8c with a mean of 7 90 8c and standard deviation of 0 437 photographic results showed no dramatic changes in the size shape or gas venting from the mound by comparing the temperatures recorded at the tips of the probes with the synoptic water temperature we estimate that thermal diffusivity for the gas hydrate deposit was 7 14d 10 8 to 8 33d 10 8 m 2 s 1 and was 1 77d 10 7 to 3 01d 10 7 m 2 s 1 for the sediments at the sites where temperatures were recorded the diffusivity measured in gas hydrate was lower than that measured under laboratory conditions stability of gas hydrate in this setting is not likely to be affected by short term changes in bottom water temperature within the range observed d 2005 elsevier b v all rights reserved

mesoscale biogeophysical characterization of woolsey mound northern gulf of mexico a new attribute of natural marine hydrocarbon seeps architecture abstract located on the continental slope in 900 m of water woolsey mound dominates seafloor morphology at mississippi canyon 118 the carbonate hydrate mound is the site of the gulf of mexico hydrates research consortium s seafloor observatory to investigate and monitor hydrographic geophysical geological geochemical and biological processes of the hydrocarbon system northern gulf of mexico innovative survey and monitoring systems sensors and tools have been developed to extract samples and data to unravel the history character and composition of the site many hours of visual data have been collected to investigate benthic communities thriving at the cold seep site associated with the mound these communities habitats are described here for the first time in terms of faunal assemblage substrate nature and presence absence of chemosynthetic species based on these factors we grouped them into four benthic meso habitats we speculate that the spatial distribution of these meso habitats is large enough to make this characteristic comparable to the geophysical response of the seismo acoustic systems we have tested this hypothesis carefully analyzing the relationship between benthic habitats zonation and the geophysical response of side scan sonar chirp subbottom surface source deep receiver ssdr vertical incidence profiler and 3 d oil industry multichannel data we observe that the geophysical response is not unique a single habitat may correlate with many geophysical attributes or a single geophysical attribute may span many habitats however we find that geophysical data can predict seep locations they can also convey some information concerning community composition and complexity that function as proxies for seep duration age while specific community components are believed to reflect composition of seep fluids although preliminary this approach represents a novel classification characterization for seafloor hydrocarbon seeps one that reflects a historical component

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

gas hydrate destabilization enhanced dewatering benthic material turnover and large methane plumes at the cascadia convergent margin mixed methane sulfide hydrates and carbonates are exposed as a pavement at the seafloor along the crest of one of the accretionary ridges of the cascadia convergent margin vent fields from which methane charged low salinity fluids containing sulfide ammonia 4he and isotopically light co2 escape are associated with these exposures they characterize a newly recognized mechanism of dewatering at convergent margins where freshening of pore waters from hydrate destabilization at depth and free gas drives fluids upward this process augments the convergence generated overpressure and leads to local dewatering rates that are much higher than at other margins in the absence of hydrate discharge of fluids stimulates benthic oxygen consumption which is orders of magnitude higher than is normally found at comparable ocean depths the enhanced turnover results from the oxidation of methane hydrogen sulfide and ammonia by vent biota the injection of hydrate methane from the ridge generates a plume hundreds of meters high and several kilometers wide a large fraction of the methane is oxidized within the water column and generates 13c anomalies of the dissolved inorganic carbon pool

observations of bubbles in natural seep flares at mc 118 and gc 600 using in situ quantitative imaging this paper reports the results of quantitative imaging using a stereoscopic high speed camera system at two natural gas seep sites in the northern gulf of mexico during the gulf integrated spill research g07 cruise in july 2014 the cruise was conducted on the e v nautilus using the rov hercules for in situ observation of the seeps as surrogates for the behavior of hydrocarbon bubbles in subsea blowouts the seeps originated between 890 and 1190 m depth in mississippi canyon block 118 and green canyon block 600 the imaging system provided qualitative assessment of bubble behavior e g breakup and coalescence and verified the formation of clathrate hydrate skins on all bubbles above 1 3 m altitude quantitative image analysis yielded the bubble size distributions rise velocity total gas flux and void fraction with most measurements conducted from the seafloor to an altitude of 200 m bubble size distributions fit well to lognormal distributions with median bubble sizes between 3 and 4 5 mm measurements of rise velocity fluctuated between two ranges fast rising bubbles following helical type trajectories and bubbles rising about 40 slower following a zig zag pattern rise speed was uncorrelated with hydrate formation and bubbles following both speeds were observed at both sites ship mounted multibeam sonar provided the flare rise heights which corresponded closely with the boundary of the hydrate stability zone for the measured gas compositions the evolution of bubble size with height agreed well with mass transfer rates predicted by equations for dirty bubbles

moment and duration of shallow earthquakes from love wave modelling for regional distances abstract love waves from five earthquakes in southwest germany italy yugoslavia greece and algeria as recorded at the broadband grafenberg array in eastern bavaria are modelled in detail using an extended reflectivity method the focal mechanisms are taken from the literature or determined from long period wwnss data the theoretical double couple moment function used for modelling increases smoothly during the risetime t from zero to the seismic moment m0 t and m0 are determined by matching the observed and theoretical love wave seismograms in the long period wwnss frequency band t is approximately equal to the rupture duration values from 1 4 to 20 s are found seismic moments generally agree within a factor of about two with those found by other authors from larger data sets the earthquakes in southwest germany and greece were simple events and can be modelled very well by one double couple in the case of the other earthquakes the theoretical love wave seismograms are too short for these earthquakes there is some independent evidence for a multiple event nature this evidence is condensed into source models consisting of two or three double couples representing separate and complete sub earthquakes which then explain the observations quite well in the case of the algerian earthquake the long love wave duration may also be due to complications in structure along the wavepath across the mediterranean and the alps the present results show that accurate love wave modelling for a single station at regional distance from an epicentre is a reliable method for estimation of seismic moment and rupture duration use of a digitally recording station with large dynamic range allows events over a large magnitude interval to be studied the grafenberg array is well suited for such an investigation of european and north african earthquakes

waveform inversion of broad band data of local earthquakes in the koyna warna region western india summary the koyna warna region in western india is the best example of reservoir triggered seismicity the world s largest triggered earthquake of magnitude 6 3 occurred in koyna in 1967 followed by several moderate to small earthquakes ever since a digital seismograph network deployed for seismic monitoring during 2005 august to 2008 december has indicated a shift in concentration of seismicity towards south in the warna region including a new zone of seismic activity to the southwest during the observation period 13 earthquakes of magnitude 4 and greater have occurred of which 11 occurred near the warna region while only two occurred in koyna in this study we modelled broad band waveform data of six of these earthquakes near warna using waveform inversion approach initially a new velocity model was determined using a joint hypocentral determination approach that simultaneously solves for the velocity structure as well as the hypocentral parameters a trap thickness of 1 2km with a p wave velocity of 4 40kms 1 and an upper crustal layer down to 10km with a velocity of 5 96kms 1 are obtained the new model not only provides the minimum residual error for the traveltimes but consistently provides the least mismatch error in the waveform inversion of all the events performing better than any of the previously determined velocity models in general focal mechanisms of normal type with ns to nnw sse oriented fault planes are obtained for all these events that are correlated with probable faults inferred from satellite images and aeromagnetic anomalies focal depths in the range of 5 6km are obtained for earthquakes in the warna region based on the sensitivity of whole waveform inversion at local distances it is felt that joint inversion of waveform data of several earthquakes with a wider spatial distribution along with the velocity structure would help in precisely characterizing the faulting mechanism and seismogenic depth range for the koyna warna region in future

carbon dioxide dynamics in kelud volcanic lake 1 in november 2007 the extrusion of a new lava dome evaporated kelud volcanic lake in java indonesia four months before a detailed echo sounding survey of the volcanic lake coupled to floating accumulation chamber measurements detected abnormally high carbon dioxide emissions it constituted the earliest sign of the volcanic unrest well before any other monitored parameter co2 flux is quantified using an empirical equation based on the volume of bubbles backscattered in the water column its comparison with the fluxes retrieved from the floating chamber method better constrain carbon dioxide dynamics in the volcanic lake it reveals that 70 of the carbon dioxide enters the lake in a dissolved form while the remaining 30 is supplied to the lake on a gaseous state almost three quarter of the ascending bubbles dissolve in the water column leaving the majority of the 330 tons day 1 of carbon dioxide diffusing at the air water interface

methane hydrate recycling offshore of mauritania probably after the last glacial maximum to what extent methane liberated from marine hydrate will enter the ocean during a warmer world is unknown although methane release due to hydrate dissociation has been modelled it is unclear whether or not methane will reach the seafloor during a warmer world and therefore contribute to oceanic and atmospheric budgets here we show using a new three dimensional 3 d seismic dataset that some hydrate deposits surround the gas chimneys passing through the hsz bottom water warming since the last glacial maximum lgm is interpreted to cause hydrate dissociation but critically some of the released methane was not vented to the ocean the released gas caused seal failure and free gas entered the hydrate stability zone hsz through vertical gas chimneys to where new hydrate accumulations formed this process is a new evidence for methane recycling and could account in part for the lack of methane in ice core records that cover warming events during the late quaternary this research provides new insight into how methane could be recycled rather than vented during a warmer world

one dimensional velocity model station correction and earthquake relocation of local earthquakes in the koyna warna region india in this paper we investigated the feasibility of using the higher frequency waveforms to characterize the seismicity in the koyna warna region globally well known for its reservoir triggered earthquakes the local seismicity and source parameters have been extensively explored by many researchers using various types of data e g analog data broadband seismological data and deep seismic sounding data however here we have utilized the seismological data recorded by 97 temporary 4 5 hz geophones to locate the local seismicity in the region we first investigated an appropriate 1 d p wave velocity model through the inversion of p and s times in order to compensate for the thick and laterally heterogeneous basalt we incorporated the station corrections in the 1 d velocity inversion process the station correction varies from 0 09 to 0 20 s for the p waves with clear demarcations of positive and negative station corrections corresponding to the northern and southern regions respectively the patterns of positive and negative station corrections suggested that the northern part is characterized by lower velocity while slighter higher velocities present in the southern part of the study area are relative to the estimated 1 d velocity model the earthquake locations are further improved by using the double difference hypodd approach which enabled us to accurately map shallow subsurface seismogenic faults in the region the data comprises 10 062 p wave and 9049 s wave catalog differential times from 348 earthquakes 1 0 ml 4 5 the precisely relocated earthquakes erh 0 05 km erz 0 5 km and rms 0 02 s form the three clusters of earthquakes in the nw se direction along the lineaments close to warna reservoir the observed seismicity trends on the surface could be due to the vertical manifestations of faults or fractures their alignments are confirmed by the analysis of focal mechanism which exhibits a predominant normal type of faults with one nodal plane consistent with the main alignment of the seismic events

evidence for extensive methane venting on the southeastern u s atlantic margin we present the first evidence for widespread seabed methane venting along the southeastern united states atlantic margin beyond the well known blake ridge diapir seep recent ship and autonomous underwater vehicle auv collected data resolve multiple water column anomalies 1000 m height and extensive new chemosynthetic seep communities at the blake ridge and cape fear diapirs these results indicate that multiple highly localized fluid conduits punctuate the areally extensive blake ridge gas hydrate province and enable the delivery of significant amounts of methane to the water column thus there appears to be an abundance of seabed fluid flux not previously ascribed to the atlantic margin of the united states

anomalous sea floor backscatter patterns in methane venting areas dnepr paleo delta nw black sea the relation between acoustic sea floor backscatter and seep distribution is examined by integrating multibeam backscatter data and seep locations detected by single beam echosounder this study is further supported by side scan sonar recordings high resolution 5 khz seismic data pore water analysis grain size analysis and visual sea floor observations the datasets were acquired during the 2003 and 2004 expeditions of the ec funded crimea project in the dnepr paleo delta area northwestern black sea more than 600 active methane seeps were hydroacoustically detected within a small 3 96 km by 3 72 km area on the continental shelf of the dnepr paleo delta in water depths ranging from 72 m to 156 m multibeam and side scan sonar recordings show backscatter patterns that are clearly associated with seepage or with a present dune area seeps generally occur within medium to high backscatter areas which often coincide with pockmarks high resolution seismic data reveals the presence of an undulating gas front i e the top of the free gas in the subsurface which domes up towards and intersects the sea floor at locations where gas seeps and medium to high backscatter values are detected pore water analysis of 4 multi cores taken at different backscatter intensity sites shows a clear correlation between backscatter intensity and dissolved methane fluxes all analyzed chemical species indicate increasing anaerobic oxidation of methane aom from medium to high backscatter locations this is confirmed by visual sea floor observations showing bacterial mats and authigenic carbonates formed by aom grain size analysis of the 4 multi cores only reveals negligible variations between the different backscatter sites integration of all datasets leads to the conclusion that the observed backscatter patterns are the result of ongoing methane seepage and the precipitation of methane derived authigenic carbonates mdacs caused by aom the carbonate formation also appears to lead to a gradual self sealing of the seeps by cementing fluid pathways horizons followed by a relocation of the bubble releasing locations

sublacustrine mud volcanoes and methane seeps caused by dissociation of gas hydrates in lake baikal four lake floor seeps have been studied in the gas hydrate area in lake baikal s south basin by using side scan sonar detailed bathymetry measurements of near bottom water properties heat flow measurements and selected seismic profiles in relation to results from geochemical pore water analysis the seeps at the lake floor are identified as methane seeps and occur in an area of high heat flow where the base of the gas hydrate layer shallows rapidly toward the vent sites from 400 m to 150 m below the lake floor at the site of the seep a vertical fluid conduit disrupts the sedimentary stratification from the base of the hydrate layer to the lake floor the seeps are interpreted to result from local destabilization of gas hydrate caused by a pulse of hydrothermal fluid flow along an active fault segment this is the first time that methane seeps and or mud volcanoes as sociated with gas hydrate destabilization have been observed in a sublacustrine setting the finding demonstrates the potential of tectonically controlled gas hydrate destabiliza tion to cause extreme pore fluid overpressure and short lived mud volcanism

morpho acoustic characterization of a shallow water mud volcano offshore scoglio d affrica northern tyrrhenian sea responsible for a violent gas outburst in 2017 abstract a violent gas outburst occurred offshore the scoglio d affrica islet tuscan archipelago northern tyrrhenian sea on march 16th 2017 with local fishermen observing columns of dirty water rising up to 10 m above the sea surface the integration of video footage and dissolved ch4 measurements collected 5 days after the event with high resolution multibeam data collected 4 months later allowed us to characterize the source area of the outburst corresponding to a shallow water mud volcano the mud volcano covers an area of ca 170 000 m2 has a vertical relief of ca 30 m with respect to the surrounding seafloor and an estimated volume of ca 1 106 m3 based on bathymetric reconstruction the elongated nnw sse shape of the mud volcano is compatible with local structural trends indicating a tectonic control for its development the mud volcano is made up of two mounds whose tops are located at a depth of ca 10 m the southern mound was responsible for the 2017 outburst as testified by a 15 20 m wide circular crater on its summit where a large amount of mud breccia and diffuse seepage from small pockmarks were observed in video footage the flanks of the mud volcano are steep and characterized in the upper part by a hummocky morphology and multiple sediment flows on the western flank the characterization of the mud volcano and the deposits associated with the 2017 gas outburst provides insight into seafloor shaping processes linked to fluid seepage in shallow water sectors this is a particularly relevant issue considering both the paucity of studies on shallow water mud volcanoes as well as the hazard associated with violent gas outbursts in such settings as witnessed by the march 16th 2017 event

structural controls on seepage of thermogenic and microbial methane since the last glacial maximum in the harstad basin southwest barents sea the harstad basin is a structural block on the continental shelf of sw barents sea where gas hydrates likely occurred below the grounded ice sheet during the last glaciation and it hosts active gas seepage at numerous seafloor sites we present an integrated study of fluid flow systems in the harstad basin by combining seismic profile interpretations and gas flare mapping data with the geochemical results obtained on seafloor seeping gas and methane derived carbonate crusts more than 190 acoustic gas flares were registered in water column many of them in association with pockmarks and carbonate crust fields however weak or absent seepage observed during remotely operated underwater vehicle transects across many pockmarks and crust fields suggests that seepage activity may have decreased since the last deglaciation in the western harstad basin seeps of microbial methane occur mainly above tertiary formations that are pinching out below the glacial sediments high amplitude seismic anomalies suggest the presence of gas pockets at the base of the glacial sediments and within tertiary deposits in contrast gas seeping in the eastern harstad basin originates from a biodegraded thermogenic source tentatively connected to the deeply faulted mesozoic rocks occurring below glacial sediments this spatial variability in fluid sources is also recorded in the carbon isotope data of seafloor carbonate crusts with 13 c values typically between 55 and 42 and 40 and 20 vpdb for carbonate crusts associated with microbial and thermogenic fluids respectively u th chronology combined with the stable isotope data suggests that this discrepancy in fluid sources over a distance of about 20 km has been stable since the last glaciation and highlights the significance of regional underlying geology in mediating fluid supply to the seafloor

increased fluid flow activity in shallow sediments at the 3 km long hugin fracture in the central north sea the north sea hosts a wide variety of seafloor seeps that may be important for transfer of chemical species such as methane from the earth s interior to its exterior here we provide geochemical and geophysical evidence for fluid flow within shallow sediments at the recently discovered 3 km long hugin fracture in the central north sea although venting of gas bubbles was not observed concentrations of dissolved methane were significantly elevated up to six times background values in the water column at various locations above the fracture and microbial mats that form in the presence of methane were observed at the seafloor seismic amplitude anomalies revealed a bright spot at a fault bend that may be the source of the water column methane sediment porewaters recovered in close proximity to the hugin fracture indicate the presence of fluids from two different shallow 500m sources i a reduced fluid characterized by elevated methane concentrations and or high levels of dissolved sulfide up to 6 mmol l 1 and ii a low chlorinity fluid cl 305 mmol l 1 that has low levels of dissolved methane and or sulfide the area of the seafloor affected by the presence of methane enriched fluids is similar to the footprint of seepage from other morphological features in the north sea

tidally controlled gas bubble emissions a comprehensive study using long term monitoring data from the neptune cabled observatory offshore vancouver island long term monitoring over one year revealed high temporal variability of gas emissions at a cold seep in 1250 m water depth offshore vancouver island british columbia data from the north east pacific time series underwater networked experiment observatory operated by ocean networks canada were used the site is equipped with a 260 khz imagenex sonar collecting hourly data conductivity temperature depth sensors bottom pressure recorders current meter and an ocean bottom seismograph this enables correlation of the data and analyzing trigger mechanisms and regulating criteria of gas discharge activity three periods of gas emission activity were observed a short activity phases of few hours lasting several months b alternating activity and inactivity of up to several day long phases each and c a period of several weeks of permanent activity these periods can neither be explained by oceanographic conditions nor initiated by earthquakes however we found a clear correlation of gas emission with bottom pressure changes controlled by tides gas bubbles start emanating during decreasing tidal pressure tidally induced pressure changes also influence the subbottom fluid system by shifting the methane solubility resulting in exsolution of gas during falling tides these pressure changes affect the equilibrium of forces allowing free gas in sediments to emanate into the water column at decreased hydrostatic load we propose a model for the fluid system at the seep fueled by a constant sub surface methane flux and a frequent tidally controlled discharge of gas bubbles into the ocean transferable to other gas emission sites in the world s oceans

measurements of the fate of gas hydrates during transit through the ocean water column 1 we report on controlled experiments to document the fate of naturally occurring methane hydrate released from the sea floor 780 m 4 3 c by remotely operated vehicle rov disturbance images of buoyant sediment coated solids rising 0 24 m s from the debris cloud soon revealed clear crystals of methane hydrate as surficial material sloughed off decomposition and visible degassing began close to the predicted phase boundary yet pieces initially of 0 10 m size easily survived transit to the surface ocean smaller pieces dissolved or dissociated before reaching the surface ocean yet effectively transferred gas to depths where atmospheric ventilation times are short relative to methane oxidation rates

split beam echo sounder observations of natural methane seep variability in the northern gulf of mexico a method for positioning and characterizing plumes of bubbles from marine gas seeps using an 18 khz scientific split beam echo sounder sbes was developed and applied to acoustic observations of plumes of presumed methane gas bubbles originating at approximately 1400 m depth in the northern gulf of mexico a total of 161 plume observations from 27 repeat surveys were grouped by proximity into 35 clusters of gas vent positions on the seafloor profiles of acoustic target strength per vertical meter of plume height were calculated with compensation for both the sbes beam pattern and the geometry of plume ensonification these profiles were used as indicators of the relative fluxes and fates of gas bubbles acoustically observable at 18 khz and showed significant variability between repeat observations at time intervals of 1 h 7 5 months active gas venting was observed during approximately one third of the survey passes at each cluster while gas flux is not estimated directly in this study owing to lack of bubble size distribution data repeat surveys at active seep sites showed variations in acoustic response that suggest relative changes in gas flux of up to 1 order of magnitude over time scales of hours the minimum depths of acoustic plume observations at 18 khz averaged 875 m and frequently coincided with increased amplitudes of acoustic returns in layers of biological scatterers suggesting acoustic masking of the gas bubble plumes in these layers minimum plume depth estimates were limited by the sbes field of view in only five instances

understanding conspicuous gravity low over the koyna warna seismogenic region maharashtra india and earthquake nucleation a paradigm shift the continued seismicity in koyna warna region of the western part of maharastra india and its relationship with subsurface structures concealed below thick volcanic sequences are studied in detail using gravity field along with newly available deep scientific drilling results this seismically active zone is marked by a large conspicuous negative gravity anomaly the causes of which are yet to be fully understood recent findings from the boreholes drilled in the koyna gupta et al in int j earth sci 104 1511 1522 2015 and killari seismic zones both of which penetrated the thick deccan volcanic cover and the underlying archean crystalline basement have motivated us to revisit the bouguer gravity field over this region using a newly developed finite element method of regional residual separation our study reveals the presence of two thick low density low velocity crustal zones below the koyna warna region the shallower one between 5 and 13 km depth and the deeper one between 35 and 43 km depth just above the moho both of these zones appear to contain mantle metasomatised and fractionated magmatic material respectively interestingly the hypocenters of all m 5 koyna earthquakes occur within the upper low velocity low density zone we also suggest high order crustal exhumation below this region which led to the removal of the entire sedimentary and granitic upper crustal column this process has brought denser mid crustal lithological facies close to the surface quaternary uplifting and movement of fault blocks along the old as well as newly created fault planes seem to be still continuing a paleo rift may have existed beneath this region below which moho temperatures 600 c and mantle heat flow 31 mw m2 are still high

structural lineaments from the magnetic anomaly maps of the eastern continental margin of india ecmi and nw bengal fan abstract three major structural lineaments are inferred from the magnetic and bathymetry data collected over the eastern continental margin of india ecmi and nw bengal fan covering the area between 10 55 n to 20 15 n and 80 e to 88 e analysis of magnetic data associated with these trends suggests that 1 trend i located at the foot of the continental slope around 3000 m water depth represents the ocean continent boundary ocb of ecmi 2 trend ii represents the northern extension of 85 e ridge abutting the continental shelf off chilka lake and 3 trend iii located over the continental shelf slope between visakhapatnam and paradip represents a folded ridges and depressions nature of the continental basement the study also reveals the occurrence of dyke intrusions within the continental crust landward of ocb which might be related to the rift phase volcanism along the ecmi

crustal seismic velocity structure in the epicentral region of the latur earthquake september 29 1993 southern india inferences from modelling of the aftershock seismograms abstract we present 1 d models of crustal p and s wave velocity structure in the epicentral region of the devastating 1993 latur earthquake in southern india travel time and relative amplitude modelling of a seismogram section of well located aftershocks out to 80 km offset by reflectivity synthetic seismograms reveal alternating low velocity layers lvls for p and s waves in the upper crust at depths of 6 5 9 0 km and 12 3 14 5 km with about 7 velocity reduction a lower crustal lvl at 24 26 km depth is also inferred by modelling the seismic activity in the latur region is essentially confined to shallow upper crustal depths of less than 6 km above the lvls the upper crustal velocity models further reveal a relatively low vp vs ratio of 1 65 while synthetic seismogram models consistent with the upper crustal p wave reflection phases reveal a qp qs ratio certainly less than 1 a high conductivity zone at a shallow depth of 6 10 km brought out by broad band mt soundings in this region is found to be coincident with the upper crustal lvls these coincident anomalous properties of the upper crust suggest the presence of fluids probably in a partially or slightly under saturated state below the hypocentral region of the latur earthquake and its aftershocks

modeling of methane bubbles released from large sea floor area condition required for methane emission to the atmosphere article i nfo massive methane release from sea floor sediments due to decomposition of methane hydrate and thermal decomposition of organic matter by volcanic outgassing is a potential contributor to global warming however the degree of global warming has not been estimated due to uncertainty over the proportion of methane flux from the sea floor to reach the atmosphere massive methane release from a large sea floor area would result in methane saturated seawater thus some methane would reach the atmosphere in this study we discussed the possibility of the methane release from a large sea floor area to the atmosphere focusing on methane saturation in the water column necessary for a methane bubble to reach the atmosphere using a one dimensional numerical model integrated over time we predict methane bubbles and methane concentration in the water column under the condition of continuous methane input from the sea floor to the water column we found that some methane bubbles reach the atmosphere even when the methane saturation fraction in the water column is much lower than 100 we compared the methane input from the sea floor required for a methane bubble to reach the atmosphere to the amount of methane in the sediment in the form of methane hydrate and free gas in most cases our results suggest that the typical amount of methane in the sediment i e typical hydrate fraction of 2 and free gas of two thirds of the amount of hydrate is significantly lower than the required minimum methane input it is therefore suggestedthat exceptinthecaseofanextraordinarymethane flux themassivequantityof methanebubbles released from sea floor gas hydrate would not reach the atmosphere directly but would be dissolved in the seawater with regard to global warming due to human activities the release of methane bubbles due to methane hydrate decomposition may not be enough to significantly accelerate total global warming in the case of metamorphic methane release during petm there is the possibility that the released methane resulted in methane saturated seawater allowing some methane to reach the atmosphere

active hydrate destabilization in lake baikal siberia abstract in this paper we present new seismic and heat flow data that show the base of the hydrate stability zone bhsz in lake baikal to be locally characterized by abnormal variations in depth with distinct regions of deeper than normal and regions of shallower than normal bhsz these variations are related to strong lateral variations in heat flow and occur in close association with important rift basin faults areas of shallow bhsz are also characterized by the presence of several methane seeps and mud volcanoes at the lake floor we infer that the seeps are the surface expression of escape pathways for overpressured fluids generated by the dissociation of pre existing hydrates in response to a thermal pulse caused by an upward flow of hydrothermal fluids towards the bhsz it thus seems that present day hydrate dissociation in lake baikal is modulated by the tectonic activity in the rift rather than by climatically controlled changes in lake level or water temperature

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