numerical simulations of rotating bubble plumes in stratified environments the effects of system rotation on the turbulent dynamics of bubble plumes evolving in stratified environments are numerically investigated by considering variations in both the system rotation rate and the gas phase slip velocity the turbulent dispersion of a passive scalar injected at the source of a buoyant plume is strongly altered by the rotation of the system and the nature of the buoyancy at the source when the plume is driven by the density defect associated with the presence of slipping gas bubbles the location of the main lateral intrusion decreases with respect to the single phase case with identical inlet volume momentum and buoyancy fluxes enhanced downdrafts of carrier phase fluid result in increased turbulent mixing and short circuiting of detraining plume water that elevate near field effluent concentrations similarly rotation fundamentally alters dynamic balances within the plume leading to the encroachment of the trapping height on the source and an increase in turbulent dispersion in the near field system rotation even at modest rossby numbers produces a sustained robust anticyclonic precession of the plume core the effects of rotation and the presence of bubbles are cumulative the vertical encroachment of the primary intrusion and the overall dispersion of effluent are greatest at smallest rossby numbers and largest slip velocities the main characteristic feature in rotating single phase plumes namely the robust anticyclonic precession persists in bubble plumes analysis of the momentum budgets reveal that the mechanism responsible for the organized precession i e the establishment of an unstable vertical hydrostatic equilibrium related to radial cyclostrophic balance does not differ from the single phase case

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

seabed bubble flux estimation by calibrated video survey for a large blowout seep in the north sea abstract a new approach to estimating seabed bubble emissions was applied to a rov video survey of the 22 4b blowout crater in the uk north sea video was analyzed to identify and classify bubble plumes and other seabed features plume occurrence then was gridded into quadrats and the total number of plumes in the crater s active portion estimated almost all of the seepage in the 40 45 m crater was localized within a 20 by 18 m ellipse all five major plumes in this ellipse were measured by direct capture with mean emission of 1 34 l s 1 at 12 bar range 0 54 3 5 l s 1 the primary source of variability 71 was temporal demonstrated by repeat measurements of a single vent overall temporal variability was consistent with highly fluid migration through a thick near seabed coarse grained sediment bed underlying the 22 4b crater seabed occurrence data were converted to flux based on direct capture measurements survey video and laboratory experiments where video was collected of bubble plumes of known flow for comparison with field video the derived best estimate total seabed emission flux was 90 l s 1 with an estimated uncertainty of 50 within a scenario uncertainty range of 50 142 l s 1 this is equivalent to 100 million l dy 1 at standard temperature and pressure or an annualized 25 kton however long term monitoring data showing large temporal variability suggests extrapolation to an annual basis is inappropriate

measurement of marine hydrocarbon seep flow through fractured rock and unconsolidated sediment abstract three turbine seep tents measured gas flux variations including an ejection at one tent several conceptual models of hydrocarbon migration were developed from the relationship between fluxes at the tents 1 a resistor capacitor network to model oil and gas flux in the seep system including an oil regulator model 2 a fracture oil deposition model where oil deposited on fracture walls progressively clogs and then blocks fractures also measured were bubble size distributions for minor and major vents that were narrow and broad respectively and varied with time due to oil flux very oily bubbles with different trajectories were observed

long term acoustic monitoring at north sea well site 22 4b highlights first study using long term passive acoustic monitoring of methane seeps at well blowout site 22 4b seep acoustic temporal variations correlated with ocean tides major acoustic transient event recorded on 8 december 2011 with high temporal resolution abstract marine seeps produce underwater sounds as a result of bubble formation and fragmentation upon emission from the seabed the frequency content and sound levels of these emissions are related to bubble size distribution and emission flux providing important information on methane release from the seafloor long term passive acoustic monitoring was used to continuously record seep sounds over a 7 month period within the blowout crater at the abandoned well site 22 4b in the central north sea also recorded were water column fluid velocities and near seafloor water conductivity temperature and pressure acoustic signatures were primarily from 1 to 10 khz key features were relatively broad spectral peaks at about 1 0 1 5 2 2 3 1 3 6 and 5 1 khz temporal variations in spectral levels were apparently associated with tides the recordings also documented a series of major episodic events including a large and persistent increase 10 db in overall sound levels and spectral broadening on 8 december 2011 the acoustic temporal pattern of this event was consistent with other recorded large transient events in the literature and the major event was correlated with dramatic changes in other measurements including increased water column fluid velocities increased pressure and decreased salinity indicating real changes in emission flux observed seabed morphology changes reported elsewhere in this special issue also likely were related to this event these data demonstrate the dynamic nature of marine seepage systems show the value of monitoring systems and provide direct supporting evidence for a violent formation mechanism of many widespread seep associated seabed features like pockmarks

contrasting evolution of fluorine and boron rich tin systems individual sn provinces or regions within provinces are sometimes enriched in fluorine or boron giving rise to fluorine rich and boron rich environments the structural styles of mineralisation within these environments are similar except that hydrothermal intrusive breccia pipes are more common in boron rich environments and apogranite massive greisen systems are more common in fluorine rich environments the increased solubility of h2o in b bearing magmas compared to f bearing magmas may play a role in the structural evolution of the mineralising systems the greater mechanical energy produced during crystallisation of b rich magmas provides a mechanism for breccia pipe and stockwork formation while the more passive crystallisation of f rich magmas often results in the formation of disseminated mineralisation the partitioning of boron toward the aqueous fluid phase and the enhanced solubility of silica in the fluid phase frequently results in tourmalinisation and silicification of the wall rocks in b rich environments in contrast feldspathic and sericitic alterations usually predominate in f rich environments

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

an integrated study of the eolian dust in pelagic sediments from the north pacific ocean based on environmental magnetism transmission electron microscopy and diffuse reflectance spectroscopy

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

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

contributions to atmospheric methane by natural seepages on the uk continental shelf natural gas seepages occur on the united kingdom s continental shelf and although published reports suggest that they are very rare the petroleum industry has identified but not publicly reported many more there is also very little data on the flux of gas from seabed seepages and even less on the contribution of seepages to atmospheric concentrations of gases such as methane potential gas source rocks include quaternary peats as well as petroliferous source rocks such as the carboniferous coal measures and the upper jurassic kimmeridge clays there are also other organic rich sediments which are potential source rocks together these cover a considerable part of the u k continental shelf analogue seismic reflection pinger profiles acquired during the british geological survey s regional mapping programme have been reviewed to identify water column targets including fish and plumes of gas bubbles the ability to distinguish targets is critical to an assessment of the distribution of gas seepages both theoretical predictions of target identity and the habits of shoaling fish have been investigated in order to identify a method of distinction data from seabed seepages and measurements of seepage rates have been used to establish likely ranges of gas flux rates and the sizes of gas bubbles the likelihood that a rising bubble will survive and escape into the atmosphere is determined primarily by bubble size and water depth methane the principal constituent of seepage gas is relatively unreactive and sparingly soluble the studies have enabled a new estimate of the distribution of gas seepages on the u k continental shelf and of the contribution to atmospheric methane levels the results suggest that natural gas seepages are significantly more important as a source of methane than had hitherto been established it is estimated that between 120 000 and 3 5 mtonnes of methane per year come from a continental shelf area of about 600 000 km2 this represents between 2 and 40 of the total united kingdom methane emission it is suggested that similar contributions arise from other continental shelf areas worldwide and that geological sources of atmospheric methane are more significant than is generally acknowledged

response of anaerobic methanotrophs and benthic foraminifera to 20 years of methane emission from a gas blowout in the north sea highlights high abundance of active anaerobic methanotrophs in sediments of the blowout crater suggests adaptation to methane seepage within at most two decades fast exchange processes in permeable surface sediments prevent sulfate depletion and probably methane derived carbonate precipitation methane seepage impacts isotopic and assemblage composition of benthic foraminifera abstract methane emissions from marine sediments are partly controlled by microbial anaerobic oxidation of methane aom aom provides a long term sink for carbon through precipitation of methane derived authigenic carbonates mdac estimates on the adaptation time of this benthic methane filter as well as on the establishment of related processes and communities after an onset of methane seepage are rare in the north sea considerable amounts of methane have been released since 20 years from a man made gas blowout offering an ideal natural laboratory to study the effects of methane seepage on initially pristine sediment sediment cores were taken from the blowout crater and a reference site 50 m distance in 2011 and 2012 respectively to investigate porewater chemistry the aom community and activity the presence of authigenic carbonates and benthic foraminiferal assemblages potential aom activity up to 3060 nmol cm 3 sediment d 1 or 375 mmol m 2 d 1 was detected only in the blowout crater up to the maximum sampling depth of 18 cm card fish analyzes suggest that monospecific anme 2 aggregates were the only type of aom organisms present showing densities up to 2 2 107 aggregates cm 3 similar to established methane seeps no evidence for recent mdac formation was found using stable isotope analyzes 13c and 18o in contrast the carbon isotopic signature of methane was recorded by the epibenthic foraminifer cibicides lobatulus 13c 0 66 surprisingly the foraminiferal assemblage in the blowout crater was dominated by cibicides and other species commonly found in the norwegian channel and fjords indicating that these organisms have responded sensitively to the specific environmental conditions at the blowout the high activity and abundance of aom organisms only at the blowout site suggests adaptation to a strong increase in methane flux in the order of at most two decades high gas discharge dynamics in permeable surface sediments facilitate fast sulfate replenishing and stimulation of aom the accompanied prevention of total alkalinity build up in the porewater thereby appears to inhibit the formation of substantial methane derived authigenic carbonate at least within the given time window

u th pb ree systematics of organic rich shales from the ca 2 15 ga sengoma argillite formation botswana evidence for oxidative continental weathering during the great oxidation event article i nfo article history accepted 23 october 2008 theredox sensitive geochemicalbehaviorof uraniumpermits the useof th uratiosasa geochemicalproxy for the oxidation state of the atmosphere during deposition due to the effects of post depositional uranium mobilityonth uratiosduringeventsinvolvingoxygenated fluids directmeasurementsofth uratiosareoften misleading even for drill core samples because both of these elements radioactively decay and produce lead isotopes the pb isotope composition may reflect the depositional th u ratio although the th u ratios induced bychangesshortlyafterdeposition maynotbe distinguished fromthe true depositional th uratios in order to effectively evaluate the time integrated th u ratio a values for the initial depositional pb isotope composition must be determined or accepted from the models for the whole earth while the timing for the rise of atmospheric oxygen is reasonably well constrained now its effect on continental weathering and ocean redox state remains poorly constrained and debated the ca 2 15 ga sengoma argillite formation of botswana contains organic rich shales deposited during the great oxidation event the slope of the

the northeast kingdom batholith vermont magmatic evolution and geochemical constraints on the origin of acadian granitic rocks five devonian plutons west charleston echo pond nulhegan derby and willoughby that constitute the northeast kingdom batholith in vermont show wide ranges in elemental abundances and ratios consistent with major crustal contributions during their evolution the batholith consists of metaluminous quartz gabbro diorite and quartz monzodiorite peraluminous granodiorite and granite and strongly peraluminous leucogranite contents of major elements vary systematically with increasingsio 40 and have small negative eu anomalies the strongly peraluminous willoughby leucogranite has unique trace element abundances and ratios relative to the rest of the batholith including low contents of hf zr sr and ba low values of k rb 80 164 th ta 9 rb cs 7 40 k cs 0 1 0 5 ce pb 0 5 4 high values of rb sr 1 18 low to moderate ree contents and light ree enriched patterns with small negative eu anomalies flat ree patterns with large negative eu anomalies are found in a small hydrothermally altered area characterized by high abundances of sn up to 26 ppm rb up to 670 ppm li up to 310 ppm ta up to 13 1 ppm and u up to 10 ppm there is no single mixing trend fractional crystallization assemblage or assimilationscheme that accounts for all trace elementvariations from quartz gabbro to granite in the northeast kingdom batholith the plutons originated by mixing mantle derived components and crustal melts generated at different levels in the heterogeneous lithosphere in a continental collisional environment hybrid rocks in the batholith evolved by fractional crystallization and assimilation of country rocks 50 by mass and some of the leucogranitic rocks were subsequently disturbed by a mild hydrothermal event that resulted in the deposition of small amounts of sulfide minerals

megaplume bubble process visualization by 3d multibeam sonar mapping abstract multibeam echosounder data were collected during a surface ship survey of the 22 4b well site in the north sea in september 2011 using a teledyne reson 7125 modern multibeam echosounders are instrumental in providing detection and accurate localization of weak to strong bubble plumes two survey profiles effectively insonified the bubble plumes rising from the main crater at the well site providing snapshot data of bubble plume processes additionally three profiles insonified bubble plumes rising from in and to the south of a secondary crater 1 2 km southeast of the main crater data processing included a simple algorithm that muted mislocated echoes from incomplete sidelobe suppression the data processing produced a cartesian volume of echo intensity from the water column and seabed plume geometry was analyzed to investigate a number of important large scale plume processes including plume bubble detrainment due to currents and stratification downwelling flows sea surface interaction plume heterogeneity and other fluid transport processes the data showed strong upwelling flows with bubble vertical motions generally much faster than currents one important finding was that megaplumes create intrusions above the general thermocline in part because their extensive upwelling flow lifts the thermocline locally as a result the intrusion layer deposits dissolved gases in the upper wave mixed layer of the water column where it is not isolated from the atmosphere unlike dissolved gases in the lower water column the analysis shows that high fidelity multibeam echosounder data can provide a wealth of remote sensing information on bubble plume characteristics and processes with important applications including blowout monitoring and response better understanding of megaplumes such as used in lake destratification and improved characterization of natural seep emission processes

assessing marine gas emission activity and contribution to the atmospheric methane inventory a multidisciplinary approach from the dutch dogger bank seep area north sea abstract we present a comprehensive study showing new results from a shallow gas seep area in 40 m water depth located in the north sea netherlands sector b13 that we call dutch dogger bank seep area it has been postulated that methane presumably originating from a gas reservoir in 600 m depth below the seafloor is naturally leaking to the seafloor our ship based subbottom echosounder data indicate that the migrating gas is trapped in numerous gas pockets in the shallow sediments the gas pockets are located at the boundary between the top of the late pliocene section and overlying fine grained sediments which were deposited during the early holocene marine transgression after the last glaciation we mapped gas emissions during three r v heincke cruises in 2014 2015 and 2016 and repeatedly observed up to 850 flares in the study area most of them 80 were concentrated at five flare clusters our repeated analysis revealed spatial similarities of seep clusters but also heterogeneities in emission intensities a first calculation of the methane released from these clusters into the water column revealed a flow rate of 277 l min sd5140 with two clusters emitting 132 and 142 l min representing the most significant seepage sites above these two flare clusters elevated methane concentrations were recorded in atmospheric measurements our results illustrate the effective transport of methane via gas bubbles through a 40 m water column and furthermore provide an estimate of the emission rate needed to allow for a contribution to the atmospheric methane concentration

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

a new perspective for the sediment provenance evolution of the middle okinawa trough since the last deglaciation based on integrated methods abstract the sediment in the okinawa trough ot preserves considerable information regarding land ocean interactions and palaeoenvironmental evolution in the east asian marginal seas more specifically the sediment provenance in the ot must be studied to recover this information however arguments about this remain especially regarding the contribution of yellow river yr derived materials to middle ot depositions to resolve this problem we systematically investigated a gravity core m063 05 3 87 m in length since the last deglaciation collected from the middle ot by integrating environmental magnetism diffuse reflectance spectroscopy and transmission electron microscopy as well as analyses of sediment grain size clay mineralogy and major elements our results indicated that sediment from the yr has contributed dominantly to this core since the last deglaciation limited contributions were also made from the yangtze river and taiwan rivers during the holocene terrigenous inputs derived from the yr could be well characterized by the ratio of hematite hematite goethite additionally the kuroshio current kc activity since the last deglaciation which is an important influencing factor for sediment provenance changes was well deciphered using a new proxy reldm relative contribution of detrital ferrimagnetic minerals to bulk magnetic properties based on comprehensive analyses of our results and previously published studies we hypothesised that during the last deglaciation abundant resuspended sediment from the palaeo yr mouth was transported to the east china sea ecs continental shelf edge and the northern ot through seaward bottom flow and further spread into the middle ot since the middle to late holocene the central mud area of the south yellow sea and the mud area southwest off cheju island may have become the main sources to provide yr derived materials to the middle ot however the mud area derived sediment could only be restricted to a small range owing to the hindrance of the strengthened kc this study provides a new perspective for sediment provenance evolution of the middle ot since the last deglaciation and proposes new methods and parameters for future research on palaeoenvironmental evolution in the ecs

quantification of methane emissions at abandoned gas wells in the central north sea as a result of extensive hydrocarbon exploration the north sea hosts several thousand abandoned wells many believed to be leaking methane however how much of this greenhouse gas is emitted into the water column and ultimately reaches the atmosphere is not known here we investigate three abandoned wells at 81 93m water depth in the norwegian sector of the north sea all of which show gas seepage into the bottom water the isotopic signature of the emanating gas points towards a biogenic origin and hence to gas pockets in the sedimentary overburden above the gas reservoirs that the wells were drilled into video analysis of the seeping gas bubbles and direct gas flow measurements resolved initial bubble sizes ranging between 3 2 and 7 4mm in diameter with a total seabed gas flow between 1 and 19 tons of ch4 per year per well estimated total annual seabed emissions from all three wells of 24 tons are similar to the natural seepage rates at tommeliten suggesting that leaky abandoned wells represent a significant source of methane into north sea bottom waters however the bubble driven direct methane transport into the atmosphere was found to be negligible 2 due to the small bubble sizes and the water depth at which they are released

role of slip velocity in the behavior of stratified multiphase plumes this paper presents direct measurements of multiphase plumes in stratification and correlates characteristic plume properties with the nondimensional slip velocity un un is defined as the ratio of the bubble slip velocity us to a characteristic plume fluid rise velocity bn 1 4 b is the total kinematic buoyancy flux and n is the buoyancy frequency un is derived by dimensional analysis and is compared to other nondimensional parameters for multiphase plumes in the literature to investigate correlations of the nondimensional numbers with plume properties laboratory experiments were conducted in linear stratification using dispersed phases of air oil and glass beads creating an inverted plume a new type of plume behavior is identified called type 1 in which the horizontal motion in the first detrainment event disperses the relatively weak bubbles creating a diffuse bubble plume that forms out of the intrusion measurements from these and previous experiments for type behavior trap height

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

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

nearly contemporaneous evolution of the a and s type fractionated granites in the krusne hory erzgebirge mts central europe abstract the krusne hory erzgebirge mountains is one of the best known provinces of granite magmatism and associated metallogenesis in europe variscan magmatic activity in the krusne hory erzgebirge area spanned the period from 330 to 295 ma for much of this time two types of magma were generated and emplaced in close proximity in this province strongly peraluminous p rich s type melts were formed alongside slightly peraluminous p poor melts a type two suites of strongly peraluminous p f li rb cs u sn rich and zr th y hree poor magmas were intruded in rapid succession over a period of about 10 ma about 330 320 ma over the entire region of the krusne hory several peraluminous rhyolitic dykes near gottesberg mark an isolated event at about 295 ma slightly peraluminous f li rb cs sn zr y hree rich and p poor magmas were intruded in several events separated in space and time 325 295 ma both magmatic episodes culminated with strongly fractionated subvolcanic granite intrusions accompanied by explosive brecciation and followed by sn w mineralization of greisen type successive volcanic eruption of rhyolites and dacites of s type and rhyolites of a type form the fill of the altenberg teplice caldera atc thus demonstrating the close temporal and spatial relationship between these two types of magma when these two geochemically distinct types of rock are in direct contact then the rocks of a type are always younger the absolute time difference between the two types can range from less than 1 ma the first eruption of the teplice rhyolite versus the schonfeld dacite in the atc to about 15 ma eruption of rhyolites at gottesberg versus emplacement of the eibenstock granite the assumed protolith of all late variscan granites in the area of krusne hory erzgebirge is a mixture of fertile quartzo feldspathic rocks with micaceous metapelites enriched in lile and sn w the differences in chemical composition of s and a type melts originated from local changes in the proportion of quartzo feldspathic and pelitic lithologies different pt conditions of melting the degree of melting and the degree of metamorphic dehydratation of the protolith prior to the melting

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

continuous inline mapping of a dissolved methane plume at a blowout site in the central north sea uk using a membrane inlet mass spectrometer water column stratification impedes immediate methane release into the atmosphere highlights mims used to quantify the dissolved ch4 inventory around a bubble emission site conservative estimate of well 22 4b seabed ch4 emission was 1 8 ktons yr 1 stratification impedes immediate ch4 release into the atmosphere the dissolved methane ch4 plume rising from the crater of the blowout well 22 4b in the central north sea was mapped during stratified water column conditions geochemical surveys were conducted close to the seafloor at 80 3 m water depth below the thermocline 61 1 m and in the mixed surface layer 13 2 m using membrane inlet mass spectrometry mims in combination with a towed ctd seawater was continuously transferred from the respective depth levels of the ctd to the mims by using an inline submersible pump close to the seafloor a well defined ch4 plume extended from the bubble release site 460 m towards the southwest along this distance ch4 concentrations decreased from a maximum of 7872 nmol l 1 to less than 250 nmol l 1 below the thermocline the well defined ch4 plume shape encountered at the seafloor was distorted and filaments were observed that extended towards the west and southwest in relation to current direction where the core of the bubble plume intersected this depth layer footprints of high ch4 concentrations of up to 17 900 nmol l 1 were observed in the mixed surface layer the ch4 distribution with a maximum of up to 3654 nmol l 1 was confined to a small patch of 60 m in diameter the determination of the water column ch4 inventories revealed that ch4 transfer across the thermocline was strongly impeded as only 3 of the total water column inventory was located in the mixed surface layer best estimate of the ch4 seabed release from the blowout was 1751 tons yr 1 the fate of the trapped ch4 97 that does not immediately reach the atmosphere remains speculative in wintertime when the water column becomes well mixed as well as during storm events newly released ch4 and the trapped ch4 pool can be transported rapidly to the sea surface and emitted into the atmosphere

tin granites of seward peninsula alaska seven granite plutons spatially and genetically related to tin metalization are exposed in a 170 km long belt across northwestern seward peninsula alaska these plutons are cupolas and epizonal composite stocks that consist of several textural varieties of biotite granite including medium to coarse grained seriate biotite granite porphyritic biotite granite with an aplitic groundmass and fine to medium grained equigranular biotite granite the common accessory minerals are fluorite allanite apatite and zircon other accessory minerals that are locally present include tourmaline sphene opaque oxide minerals and late forming deuteric muscovite and chlorite the granites range in major element contents as follows sio 2 72 5 to 76 6 a1 2 o 3 12 7 to 14 3 na 2 o 2 9 to 4 0 k 2 o 3 9 to 5 6 and cao 0 6 to 1 2 the sum of feo fe 2 o 3 mgo ranges from 0 3 to 2 4 and the k 2 o to na 2 o ratio from 1 1 to 1 8 the 0 1 to 0 9 f and 0 01 to 0 2 cl reflect the over all volatile rich nature of the granites the granites contain average or below average concentrations of co sc cr and zn and generally above average to distinctly high concentrations of th u hf and ta the large cations emphasize the evolved nature of the granites the rb sr ratio is as high as 90 in some samples initial 87 sr 86 sr ratios range from 0 708 to as high as 0 720 the three rb sr isochrons defined by the data agree with k ar age determinations and show that the stocks were emplaced during the late cretaceous between about 70 and 80 m y ago the field petrologic and geochemical data indicate that the plutons had a multistage origin that involved large scale melting of sialic crust emplacement of magmas derived from batholithic fractionation at depth and subsequent evolution of these magmas to generate small volumes of more highly evolved residual magmas although evolution of the granite complexes was largely governed by crystal melt fractionation some minor element variations in the highly evolved granites cannot be explained by this process for example the distribution of rubidium and the light rare earths appears to have been influenced by volatile depletion at the final stages of crystallization the field data petrologic data and variation trends such as distinct shifts toward higher albite contents in the residual granites suggest that the coexistence of a volatile phase was important in their evolution these results require that models seeking to explain compositional gradients in high level granite rhyolite systems fully consider the role of a coexisting volatile phase

pockmarks in the witch ground basin central north sea marine sediments host large amounts of methane ch4 which is a potent greenhouse gas quantitative estimates for methane release from marine sediments are scarce and a poorly constrained temporal variability leads to large uncertainties in methane emission scenarios here we use 2d and 3d seismic reflection multibeam bathymetric geochemical and sedimentological data to i map and describe pockmarks in the witch ground basin central north sea ii characterize associated sedimentological and fluid migration structures and iii analyze the related methane release more than 1500 pockmarks of two distinct morphological classes spread over an area of 225 km2 the two classes form independently from another and are corresponding to at least two different sources of fluids class 1 pockmarks are large in size 6 m deep 250 m long and 75 m wide show active venting and are located above vertical fluid conduits that hydraulically connect the seafloor with deep methane sources class 2 pockmarks which comprise 99 5 of all pockmarks are smaller 0 9 3 1 m deep 26 140 m long and 14 57 m wide and are limited to the soft fine grained sediments of the witch ground formation and possibly sourced by compaction related dewatering buried pockmarks within the witch ground formation document distinct phases of pockmark formation likely triggered by external forces related to environmental changes after deglaciation thus greenhouse gas emissions from pockmark fields cannot be based on pockmark numbers and present day fluxes but require an analysis of the pockmark forming processes through geological time

surface and subsurface expressions of gas seepage to the seabed examples from the southern north sea expressions of gas seepage observable within north sea seismic and acoustic data include seabed pockmarks seepage plumes in the water column acoustic blanking shallow enhanced reflectors and shallow seismic chimneys three areas were selected for a marine survey in

atmospheric remote sensing constraints on direct sea air methane flux from the 22 4b north sea massive blowout bubble plume abstract a new airborne remote sensing approach to estimate an upper limit of the direct sea air methane emission flux was applied over the 22 4b blowout site located at n57 92 e1 63 in the north sea passive remote sensing data using sunglint sunglitter geometry were collected during instrumental tests with the methane airborne mapper mamap instrument installed aboard the alfred wegener institute awi polar 5 aircraft on 3 june 2011 mamap is a passive short wave infrared swir remote sensing spectrometer for airborne measurements and retrieval of the atmospheric column averaged dry air mole fractions of methane xch 4 and carbon dioxide xco 2 in addition to mamap a fast ch 4 in situ analyzer los gatos research inc rmt 200 two 5 hole turbulence probes and the polar 5 basic sensor suite comprising different temperature pressure humidity and camera sensors were installed aboard the aircraft the collected mamap remote sensing data acquired in the vicinity of the 22 4b blowout site showed no detectable increase in the derived xch 4 with respect to the atmospheric background based on the absence of a detectable xch 4 column increase an approximate top down upper limit for the direct atmospheric 22 4b blowout ch 4 emissions from the main bubble plume of less than 10 ktch 4 yr has been derived the constraint has been determined by comparing xch 4 information derived by the remote sensing measurements with results obtained from a gaussian plume forward model simulation taking into account the actual flight track the instrument sensitivity and measurement geometry as well as the prevailing atmospheric conditions

the uk22 4b blowout 20 years on investigations of continuing methane emissions from sub seabed to the atmosphere in a north sea context abstract the 22 4b blowout occurred in the uk sector of the north sea in november 1990 but during a survey in september 2011 strong gas emissions still were occurring this manuscript summarizes the findings of the 2011 survey and subsequent studies considering them in the context of previous investigations and the regional geologic and oceanographic environments the seabed crater formed during the initial event is still there as is a previously undiscovered secondary crater seabed bubble flux estimates indicate methane emission rates of 90 l s 1 at the time however this methane s fate s remains unclear the very strong thermocline that persists for more than half the year acts as an effective barrier to upward migration despite the presence of strong upwelling flows around the bubble plume clearly a large proportion of the methane is advected away from the site to be either oxidized microbially in the water column or released to the atmosphere as a result of normal sea air gas exchange processes nevertheless a significant atmospheric methane anomaly persists in the vicinity of the blowout site this has been constrained to likely less than 0 72 mscfd 5 kton yr 1 and possibly less than 0 36 mscfd 2 5 kton yr 1 during the late fall to early spring months when there is no thermocline direct methane emissions to the atmosphere are expected to increase significantly also long term monitoring has shown that periodic eruptive events occur which likely expel great quantities of methane these demonstrate the dynamic nature of the system and suggest that migration pathways in and between the deep sub seabed and seabed remain active the 22 4b study resulted in the development and adaptation of novel techniques that are applicable to other studies of seabed seepage and the development of a number of critical hypotheses with application to megaplume seepage by natural migration pathways or from the result of anthropogenic intervention

fluorine as an indicator of mineralization hydrogeochemistry of a precambrian mineralized belt in sri lanka abstract a hydrogeochemical survey carried out on the highland eastern vijayan boundary of sri lanka known to be a mineralized belt revealed anomalous concentrations of fluoride in the groundwater of the region a sharp increase of the fluoride concentrations across the mineralized belt particularly in the northeastern and eastern sectors was observed base metals such as cu zn v and co also showed relative enrichments at the mineralized belt the sharp increase of fluorine along the belt appears to have been associated with granite magmatism and exhalations of volatiles through the highland eastern vijayan rift zone the presence of uraniferous granites hot springs serpentinites massive sulphide deposits with cu ag b be pb v co and zn at the mineralized belt along with high f concentrations indicate a deep seated fracture in a marine based environment where f could well have acted as a mineralizer the results of this study indicate that fluorine could be used as a promising indicator of mineralization particularly in areas of deepseated fractures and granitic magmatism

flare imaging with multibeam systems data processing for bubble detection at seeps multibeam sonar surveys have been conducted since their invention in the 1970s however mainly reflections from the seafloor were considered so far more recently water column imaging with multibeam is becoming of increasing interest for fisheries buoy mooring or gas detection in the water column using elac seabeam 1000 data we propose a technique to detect gas bubbles flares although this system is originally not designed to record water column data the described data processing represents a case study and can be easily adapted to other multibeam systems multibeam data sets from the black sea and the north sea show reflections of gas bubbles that form flares in the water column at least for reasonably intense gas escape the detection of bubbles is feasible the multibeam technique yields exact determination of the source position and information about the dimension of the gas cloud in the water compared to conventional flare imaging by single beam echo sounders the wide swath angle of multibeam systems allows the mapping of large areas in much shorter time

a review of oceanographic and meteorological controls on the north sea circulation and hydrodynamics with a view to the fate of north sea methane from well site 22 4b and other seabed sources abstract the north sea hydrodynamics are key to the redistribution of methane released at the 22 4b site located at 57 55 n 1 38 e in the uk central north sea 200 km east of the scottish mainland this review summarizes the current state of knowledge on the north sea circulation stratification and variability therein and briefly discusses the potential consequences for the distribution and fate of methane released from site 22 4b or other seabed sources astronomical tidal waves follow a counter clockwise path and tide topography interaction generates a residual circulation in the same direction wind stress forcing can enhance reduce or even reverse this circulation variations in the strength of the fair isle current fic are important the fic enters the north sea between the orkneys and shetland follows approximately the 100 m isobath passes along site 22 4b and ends up in the norwegian trench the north atlantic oscillation nao also causes variability a positive negative nao index is associated with stronger weaker than normal westerly winds nao situations strengthen the circulation in the north sea whereas it weakens during nao conditions and is directed northeastward high positive correlations exist between the sst at site 22 4b and the nao index climate change can have a long term effect on the hydrodynamics of the north sea seasonal stratification has potentially the most important imprint on methane derived from the well 22 4b site summertime heating stratifies the northern part of the north sea in autumn loss of heat to the atmosphere causes the stratification to breakdown until tides and storms mix the entire water column during the period of stratification the bulk of dissolved methane released from site 22 4b gets trapped below the thermocline the loss of methane to the atmosphere thus becomes a function of the relative time scales of transport and horizontal and vertical mixing processes versus the time scale of microbial degradation oxidation in the water column

the mckinley sequence of granitic rocks a key element in the accretionary history of southern alaska the mckinley sequence of granitic rocks consists of several discrete plutons in the central alaska range most of these plutons crop out south of the denali fault system dfs in the talkeetna quadrangle plutons of the mckinley sequence largely intrude deformed upper meszoic flysch between the dfs and the northern edges of wrangellia and the peninsular terrane which jointly make up the talkeetna superterrane the average k ar age of biotite from nine granites of the mckinley sequence is 57 3 ma rb sr data for whole rock samples indicate that the mckinley sequence cannot be older than 60 ma a selected suite of 20 samples of granite and granodiorite range in sio2 from 65 9 to 77 6 all 20 samples are corundum normative and 18 are moderately peraluminous initial 87sr 86sr ratios range from 0 7054 to 0 7085 the 18o values range from 11 2 to 14 6 these high and variable sr isotopic ratios peraluminous nature rare earth element patterns and high 18o values suggest that granitic rocks of the mckinley sequence crystallized from hybrid magmas produced by assimilation of sedimentary rocks by a mantle derived melt mesozoic flysch is the likely source of the crustal component of the hybrid magmas geologic evidence suggests that the talkeetna superterrane collided with stable alaska after early cretaceous time the flysch basin lying south of stable alaska was closed by northward movement of the talkeetna superterrane maximum age for basin closure and terrane accretion is middle cretaceous cenomanian paleomagnetic evidence indicates that all terranes north of the dfs have been part of stable alaska since the paleocene and that northward movement of wrangellia was completed by 50 ma granitic rocks of the mckinley sequence may be products of terrane accretion the granitic rocks crystallized from hybrid magmas produced during terrane collision and deformation of the flysch basin isotopic ages of the mckinley sequence establish the time of final accretion of the talkeetna superterrane as paleocene

isotope fractionation and mixing in methane plumes from the logatchev hydrothermal field as methane is consumed in the deep sea its 13c 12c ratio progressively increases because of kinetic isotope fractionation many submarine hydrothermal vents emit methane with carbon isotope ratios that are higher than those of background methane in the surrounding ocean since the latter exists at low concentrations mixing of background methane with vent fluid tends to decrease the 13c 12c ratio as concentration decreases opposite to the trend produced by consumption we investigated ch4 concentration and 13c together with 3he in plumes from the logatchev hydrothermal field lhf located at 14 45 n 45 w which generates relatively heavy methane 13c 13 by serpentinization of ultramafic rock the measured methane and 3he were well correlated at high concentrations indicating a ch4 3he ratio of 1 108 in the vent fluids these tracer distributions were also simulated with an advection diffusion model in which methane consumption only occurs above a certain threshold concentration we utilized 3he to calculate the methane remaining in solution after oxidation f and the deviation of 13c from the value expected from mixing alone 13c both in the model and in the data the entire set of 13c values are not correlated with log f which is due to continuous oxidation within the plume while mixing with background seawater a linear relationship however is found in the model for methane at concentrations sufficiently above background and many of the samples with elevated ch4 north of lhf exhibit a linear trend of 13c versus log f as well from this trend the kinetic isotope fractionation factor in the lhf plumes appears to be about 1 015 this value is somewhat higher than found in some other deep sea studies but it is lower than found in laboratory incubation experiments

regional progressive high pressure metamorphism seward peninsula alaska blueschist facies rocks on the seward peninsula constitute a structurally coherent terrane measuring at least 100 150 km radiometric age data indicate that high pressure metamorphism probably occurred in jurassic rather than in palaeozoic or precambrian time as previously suggested protolith sediments nome group are of intracontinental basin or continental margin type and of lower palaeozoic and possibly late precambrian age thus predating the high pressure metamorphism by more than 200 m y blueschist facies mineral assemblages were developed in almost all lithologies of the nome group and are best preserved in feti rich metabasites glaucophane almandine epidote and pelites glaucophane chloritoid phengite a lawsonite crossite subfacies was developed in possible nome group rocks on the east flank of the darby mountains albite epidote amphibolite facies assemblages characterize nome group rocks in the southwestern part of the peninsula metamorphism in the central zone of the terrane passed from early lawsonitic to subsequent epidote almandine glaucophane schist subfacies with the local development east of the nome river of eclogitic assemblages the high pressure metamorphic minerals were synkinematic with the development of mesoscopic scale intrafolial isoclinal folds and a flattening foliation of consistent orientation initiation of uplift probably corresponded to the growth of barroisite rims on earlier sodic and actinolitic amphiboles and partial post kinematic greenschist facies replacements record later stages of decompression ophiolites and melange are not associated with the seward peninsula blueschists the high pressure metamorphism was caused by tectonic loading of a continental plate by an allochthon of indeterminate origin the pt conditions of high pressure metamorphism were approximately 9 11 kbar 400 450 c thus falling between the pt paths of the shuksan and franciscan terranes

engineered and natural marine seep bubble driven buoyancy flows abstract bubble plume upwelling flows were studied in the marine environment through dye releases into engineered plumes and a natural hydrocarbon seep plume for engineered plumes these experiments measured the water column averaged upwelling flow vup zo from release depth zo to the sea surface for a wide range of flows q and zo from vup zo the local upwelling flow vup z where z is depth was calculated and found to vary with q as vup z q0 23 for plumes strong enough to penetrate a shallow thermally stratified layer which was in good agreement with published relationships between vup z and q these data were used to interpret data collected at a natural marine seep for the seep the upwelling flow decelerated toward the sea surface in contrast to the engineered plumes which accelerated toward the sea surface data showed the seep bubble plume upwelling flow lifted significantly colder and more saline water the increased density difference between this upwelling fluid and the surrounding

diagenetic reddening of early eocene paleosols on king george island antarctica abstract the objective of this study was to determine if the early eocene paleosols on king george island maritime antarctica have acquired their reddish color during the paleopedogenesis by burial diagenesis and or by heating of a covering lava flow we used micromorphology diffuse reflectance spectroscopy x ray diffraction and mineral magnetic properties to identify the iron oxides in these paleosols these are weakly moderately developed paleosols formed on a basaltic tephra under a cool humid paleoclimate therefore prone to ferrihydrite and goethite rather than hematite formation however the iron oxide assembly was dominated by maghemite and hematite nevertheless the large grain size and high crystallinity of hematites suggested they are rather diagenetic than pedogenic the clustering content and distribution of hematites finely dispersed on the groundmass coating replacing primary minerals and as mottles and or nodules rather than their crystal size were responsible for the color differences these properties were likely the result of past pedogenesis processes forming originally ferrihydrite linked with paleodrainage conditions heating by the covering lava flow affected the magnetic properties of two profiles but without affecting their color taken together all these results suggest that the burial reddening took place by dehydration and transformation of ferrihydrite to hematite our findings highlight the importance of detailed mineralogical analysis to identify iron oxides present in reddish paleosols because identification based solely on morphology e g yellowish color gradual horizon transitions can lead to misinterpretation of paleoenvironmental conditions

estimating the concentration of aluminum substituted hematite and goethite using diffuse reflectance spectrometry and rock magnetism feasibility and limitations this study was supported by the national natural science foundation of china 41374073 and 41430962 the national program on global changes and air sea interaction gasi 04 01 02 and the chinese continental shelf deep drilling program gzh201100202 pengxiang hu was further supported by the china scholarship council 2013 3009 david heslop and andrew roberts were supported by australian research council discovery project dp110105419

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

dike swarms on seward peninsula alaska and their implications for the kinematics of cretaceous extension in the bering strait region late cretaceous dike swarms on seward peninsula northwestern alaska represent the youngest local manifestation of a 115 75 ma magmatic event in the bering strait region magmatism accompanied and followed high grade metamorphism and ductile deformation a late cretaceous extensional tectonic setting for the region is suggested by the thickness and seismic reflection characteristics of the crust regional basin development formation of high strain tectonites with subhorizontal foliations bimodal magmatism and dike swarms the orientation of the dike swarms is used to address the kinematics of extension a diabase dike swarm in the kigluaik mountains consists of dikes that strike northeast 040 and dip steeply phenocrysts include plagioclase clinopyroxene orthopyroxene and hornblende geochemical data indicate that sio2 ranges from 48 to 56 and k2o from 1 2 to 4 0 the dikes are geochemically similar to the mafic to intermediate root of the 90 ma kigluaik pluton sr and nd isotope data show that initial 87 sr 86 sr ranges from 0 7070 to 0 7077 and initial end ranges from 0 85 to 2 90 field relations and 40 ar 39 ar geochronology bracket the dike ages between 90 and 84 ma diabase dikes in the york mountains are associated with normal faults that strike east west to east northeast dikes in the bendeleben mountains are both mafic and felsic but their orientations are unknown alkalic dikes in the darby mountains strike 030 050 similar to those in the kigluaik mountains regional relationships including the orientation of dikes normal faults mineral stretching lineations and other shear sense indicators suggest that between 110 and 90 ma extension on seward peninsula was generally oriented north south to north northwest south southeast

linked sediment and water column methanotrophy at a man made gas blowout in the north sea implications for methane budgeting in seasonally stratified shallow seas large quantities of the greenhouse gas methane ch4 are stored in the seafloor the flux of ch4 from the sediments into the water column and finally to the atmosphere is mitigated by a series of microbial methanotrophic filter systems of unknown efficiency at highly active ch4 release sites in shallow marine settings here we studied ch4 oxidation and the methanotrophic community at a high ch4 flux site in the northern north sea well 22 4b where ch4 is continuously released since a blowout in 1990 vigorous bubble emanation from the seafloor and strongly elevated ch4 concentrations in the water column up to 42 m indicated that a substantial fraction of ch4 bypassed the highly active up to 2920 nmol cm 3 d 1 zone of anaerobic ch4 oxidation in sediments in the water column we measured rates of aerobic ch4 oxidation up to 498 nm d 1 that were among the highest ever measured in a marine environment and under stratified conditions have the potential to remove a significant part of the uprising ch4 prior to evasion to the atmosphere an unusual dominance of the water column methanotrophs by type ii methane oxidizing bacteria mob is partially supported by recruitment of sedimentary mob which are entrained together with sediment particles in the ch4 bubble plume our study thus provides evidence that bubble emission can be an important vector for the transport of sediment borne microbial inocula aiding in the rapid colonization of the water column by methanotrophic communities and promoting their persistence close to highly active ch4 point sources

molecular and isotopic partitioning of low molecular weight hydrocarbons during migration and gas hydrate precipitation in deposits of a high flux seepage site detailed knowledge of the extent of post genetic modifications affecting shallow submarine hydrocarbons fueled from the deep subsurface is fundamental for evaluating source and reservoir properties we investigated gases from a submarine high flux seepage site in the anoxic eastern black sea in order to elucidate molecular and isotopic alterations of low molecular weight hydrocarbons lmwhc associated with upward migration through the sediment and precipitation of shallow gas hydrates for this near surface sediment pressure cores and free gas venting from the seafloor were collected using autoclave technology at the batumi seep area at 845 m water depth within the gas hydrate stability zone vent gas gas from pressure core degassing and from hydrate dissociation were strongly dominated by methane 99 85 mol of c1 c4 co2 molecular ratios of lmwhc c1 c2 c3 1000 and stable isotopic compositions of methane 13c 53 5 v pdb d h around 175 smow indicated predominant microbial methane formation c1 c2 ratios and stable isotopic compositions of lmwhc distinguished three gas types prevailing in the seepage area vent gas discharged into bottom waters was depleted in methane by 0 03 mol c1 c4 co2 relative to the other gas types and the virtual lack of 14c ch4 indicated a negligible input of methane from degradation of fresh organic matter of all gas types analyzed vent gas was least affected by molecular fractionation thus its origin from the deep subsurface rather than from decomposing hydrates in near surface sediments is likely as a result of the anaerobic oxidation of methane lmwhc in pressure cores in top sediments included smaller methane fractions 0 03 mol c1 c4 co2 than gas released from pressure cores of more deeply buried sediments where the fraction of methane was maximal due to its preferential incorporation in hydrate lattices no indications for stable carbon isotopic fractionations of methane during hydrate crystallization from vent gas were found enrichments of 14c ch4 1 4 pmc in short cores relative to lower abundances max 0 6 pmc in gas from long cores and gas hydrates substantiates recent methanogenesis utilizing modern organic matter deposited in top sediments of this high flux hydrocarbon seep area

the geochemical characteristics of granitoids in contrasting arcs and comments on magma sources geochemical variations in modern subduction related igneous suites with respect to arc maturity in time and space are illustrated using data for both volcanic suites basalt andesite and dacite and intrusive granitoid suites diorite tonalite granodiorite and granite from circum pacific arcs using trace element data we suggest that two groups of processes control the natural variation in the parental magmas of both suites a subduction zone enrichment of lithospheric mantle locally coupled with crustal assimilation allied with fractional crystallization afc in zones of thickened crust all of which yield magmas with enhanced concentrations of the large ion lithophile lil elements k rb th u lrees etc b with increasing distance from the active trench contributions from within plate sub continental lithosphere producing mantle derived magmas with enhanced levels of high field strength hfs elements among which nb ta hf and y are particularly distinctive thus even for the evolved granitoids of intrusive arc series ratios of hfs lil elements not significantly affected by crystal fractionation such as ta nb k rb la may throw some light on the origin of mafic intermediate precursor magmas in terms of these elements we suggest the following groupings for interpreting the tectonic associations of granitoid suites 1 primitive calcic arc granitoids with low lil and hfs element abundances 2 normal calc alkaline continental arc granitoids with enhanced lil element abundances and low hfs lil ratios 3 mature alkali calcic arc granitoids with high levels of lil and hfs elements and higher hfs lil ratios 4 back arc anorogenic alkaline granitoids with the highest levels of hfs elements

authigenic minerals from the paola ridge southern tyrrhenian sea evidences of episodic methane seepage abstract paola ridge along the nw calabrian margin southern tyrrhenian sea is one of the few reported deep sea sites of precipitation of authigenic carbonates in the tyrrhenian sea here the changing composition of the seeping fluids and the dynamic nature of the seepage induced the precipitation of pyrite siderite and other carbonate phases the occurrence of this array of authigenic precipitates is thought to be related to fluctuation of the sulfate methane transition zone smtz concretions of authigenic minerals formed in the near sub bottom sediments of the paola ridge were investigated for their geochemical and isotopic composition these concretions were collected in an area characterized by the presence of two alleged mud volcanoes and three mud diapirs the mud diapirs are dotted by pockmarks and dissected by normal faults and are known for having been a site of fluid seepage for at least the past 40 kyrs present day venting activity occurs alongside the two alleged mud volcanoes and is dominated by co2 rich discharging fluids this discover led us to question the hypothesis of the mud volcanoes and investigate the origin of the fluids in each different domed structure of the study area in this study we used stable isotopes carbon and oxygen of carbonates coupled with rare earth element ree composition of different carbonate and non carbonate phases for tracing fluid composition and early diagenesis of authigenic precipitates the analyses on authigenic precipitates were coupled with chemical investigation of venting gas and sea water authigenic calcite aragonite concretions from surficial sediments on diapiric structures have depleted 13c isotopic composition and slightly positive 18o values by contrast siderite concretions generally found within the first 6 m of sediments on the alleged mud volcanoes yielded positive 13c and 18o values the siderite ree pattern shows consistent lree light ree fractionation mree medium ree enrichment and positive gd and la anomalies as shown by the ree distribution the 13c depleted composition and their association with chemosymbiotic fauna calcite aragonite precipitated at time of moderate to high methane flux close to the seafloor under the influence of bottom seawater authigenic siderite on the other hand formed in the subseafloor during periods of lower gas discharges under prolonged anoxic conditions within sediments in equilibrium with 13c rich dissolved inorganic carbon dic and 18o rich water likely related to methanogenesis and intermittent venting of deep sourced co2