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

decrease in natural marine hydrocarbon seepage near coal oil point california associated with offshore oil production prolific natural hydrocarbon seepage occurs offshore of coal oil point in the santa barbara channel california within the water column above submarine vents plumes of hydrocarbon gas bubbles act as acoustic scattering targets using 3 5 khz sonar data seep distribution offshore of coal oil point was mapped for august 1996 july 1995 and july 1973 comparison of the seep distributions over time reveals more than 50 decrease in the areal extent of seepage accompanied by declines in seep emission volume in a 13 km 2 area above a producing oil reservoir declines in reservoir pressure and depletion of seep hydrocarbon sources associated with oil production are the mechanisms inferred to explain the declines in seep area and emission volume

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

bubble growth and rise in soft sediments the mechanics of uncemented soft sediments during bubble growth are not widely understood and no rheological model has found wide acceptance we offer definitive evidence on the mode of bubble formation in the form of x ray computed tomographic images and comparison with theory natural and injected bubbles in muddy cohesive sediments are shown to be highly eccentric oblate spheroids disks that grow either by fracturing the sediment or by reopening preexisting fractures in contrast bubbles in soft sandy sediment tend to be spherical suggesting that sand acts fluidly or plastically in response to growth stresses we also present bubble rise results from gelatin a mechanically similar but transparent medium that suggest that initial rise is also accomplished by fracture given that muddy sediments are elastic and yield by fracture it becomes much easier to explain physically related phenomena such as seafloor pockmark formation animal burrowing and gas buildup during methane hydrate melting

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

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

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

time series video analysis of bubble release processes at natural hydrocarbon seeps in the northern gulf of mexico abstract this research quantifies the rate and volume of oil and gas released from two natural seep sites in the gulf of mexico lease blocks gc600 1200 m depth and mc118 850 m depth our objectives were to determine variability in release rates and bubble size at five individual vents and to investigate the effects of tidal fluctuations on bubble release observations with autonomous video cameras captured the formation of individual bubbles as they were released through partially exposed deposits of gas hydrate image processing techniques determined bubble type oily gaseous and mixed oily and gaseous size distribution release rate and temporal variations observation intervals ranged from 3 h to 26 d a semi automatic bubble counting algorithm was developed to analyze bubble count and release rates from video data this method is suitable for discrete vents with small bubble streams commonly seen at seeps and is adaptable to multiple in situ set ups two vents at gc600 birthday candles 1 and birthday candles 2 were analyzed they released oily bubbles with an average diameter of 5 0 mm at a rate of 4 7 bubbles s 1 and 1 3 bubbles s 1 respectively approximately 1 km away within the gc600 seep site two more vents mega plume 1 and mega plume 2 were analyzed these vents released a mixture of oily and gaseous bubbles with an average diameter of 3 9 mm at a rate of 49 bubbles s 1 and 81 bubbles s 1 respectively the fifth vent at mc118 rudyville released gaseous bubbles with an average diameter of 3 0 mm at a rate of 127 bubbles s 1 pressure records at mega plume and rudyville showed a diurnal tidal cycle 24 5 h rudyville was the only vent that demonstrated any positive correlation 0 60 to the 24 5 h diurnal tidal cycle however these observations were not conclusive regarding tidal effects on bubble release

the spatial scales distribution and intensity of natural marine hydrocarbon seeps near coal oil point california natural hydrocarbon seepage from marine environments is an important source of methane and other gases to the atmosphere quantifying this flux is necessary for constraining global budgets and understanding local air pollution sources a field of strong hydrocarbon seepage offshore of coal oil point near santa barbara california produces extensive areas of bursting bubbles at the sea surface an instrumented buoy was deployed in the coal oil point field to measure directly the atmospheric gas flux from three seeps of varying size and intensity spatial scales of continuity of the seeps quantified by semivariograms are small ranging from 1 to about 9 m such that flux values on larger scales are uncorrelated these de correlation scales are comparable to the horizontal extents of individual bubble plumes estimated visually at the sea surface semivariograms for each seep are used in an ordinary kriging procedure to interpolate flux measurements onto a regular grid and produce objective maps of the spatial distribution of flux spatial integrals yield total flux estimates from the three seeps of 7400 m 3 day 1 which amount to 4 13 of the total flux from the coal oil point field based on estimates from previous studies

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

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

energetic bubble plumes in arbitrary stratification field and laboratory experiments were performed to investigate the mixing induced by energetic point source bubble plumes in water columns of arbitrary stable stratification published data from various sources were also used in the present study to increase the parameter range it was found that the bubble plume surface signatures were marked by a central unsteady core consisting of an air water mixture surrounded by an annular up thrusting flow consisting of water only outside this the rising plume water spread radially plunged below the surface and then flowed outward as an intrusive gravity current at a level of neutral buoyancy by equating the observed arbitrary stratification to a linear profile of equal potential energy the radial extent of the plunge point and the net detrainment rate could be parameterized using natural scales of the problem these formulas were verified using field and laboratory data and may thus be used in air diffuser design procedures

oceanic methane layers the hydrocarbon seep bubble deposition hypothesis bubble plumes from hydrocarbon seeps drive upwelling flows in the water column that can disappear if the bubbles dissolve this may lead to formation of a layer enriched in gases and substances transported by the bubbles a process we term bubble deposition a review of observed dissolved methane layers in the north sea showed their existence in an area of active seeping pockmarks at a height of 20 30 m above the sea bed well below the thermocline to test the bubble deposition hypothesis rising seep bubbles were simulated numerically the model predicted a dissolution depth consistent with the observed methane layer for 2700 m radius bubbles the model also predicted that bubbles smaller than 3400 m dissolved subsurface decreasing to 2000 m for a 10 cm s 1 upwelling flow we speculate that this layer may be attractive to marine organisms although north sea seeps are not oily this mechanism also applies to oily bubbles from hydrocarbon seeps or a leaking undersea gas oil pipeline thus bubble deposition can create a subsurface oil layer which rises far slower than either the bubble stream or droplets entrained in the stream

terrestrial methane seeps and mud volcanoes a global perspective of gas origin abstract a global database of gas composition and methane stable isotopes of 143 terrestrial mud volcanoes from 12 countries and 60 seeps independent from mud volcanism from eight countries was compiled and examined in order to provide the first worldwide statistics on the origin of methane seeping at the earth s surface sixteen seep data were coupled with their associated subsurface reservoirs the surface seepage data indicate that at least 76 of the mud volcanoes release thermogenic gas with only 4 biogenic and 20 with mixed character the average 201 data of methane concentration and methane carbon isotope ratios 13 c 1 of mud volcanoes are 90 v v and 46 4 respectively the other types of seeps which are independent from mud volcanism have an average 13 c 1 value that is slightly higher 42 9 gases from mud volcanoes are generally lighter more methane less ethane and propane than their associated reservoir gases suggesting a molecular fractionation during advective fluid migration other types of seeps especially dry seeps maintain the reservoir c 1 c 2 c 3 bernard ratio mud volcanoes behave like a natural refinery and the origin of gas more isotopically enriched than 50 and with c 1 c 2 c 3 500 should be attributed to a thermogenic source rather than partial oxidation of biogenic gas some data that appear biogenic in the bernard diagram can be explained by molecular fractionation of mixed gas consequently the bernard parameter may be misleading when applied to mud volcanoes since it does not always reflect the original gas composition the mechanisms of the molecular advective segregation should be studied quantitatively by specific models and experiments

quantitative estimates of the effect of climate change on dust storm activity in australia during the last glacial maximum quantitative estimates are made of the effect of climate change upon dust activity during the last glacial maximum lgm which peaked 18 000 years ago using present day measurements of the occurrence of dust storms recalculated in the light of information on lgm climatic change dust activity was increased by 57 in northeast australia and by 52 in the southeast in relation to present day dust storm seasons were lengthened and dust paths were modified estimates based upon climate alone without considering the increased supplies of sediment to dust source areas during the lgm however probably underestimate lgm dust activity

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

carbon isotopic distribution of methane in deep sea hydrothermal plume myojin knoll caldera izu bonin arc implications for microbial methane oxidation in the oceans and applications to heat flux estimation the concentration and stable carbon isotopic composition 13c of methane have been measured for both seafloor hydrothermal venting fluids and effluent plume waters supplied from the vents at the myojin knoll caldera izu bonin arc in the western north pacific the hydrothermal end member concentrations and 13c of methane show near homogeneity among vents 41 2 mol kg and 16 3 0 8 pdb respectively while those in the effluent plume are stratified in the caldera and vertically exhibit a large variation 2 1 11 nmol kg and 29 0 to 11 3 pdb respectively comparison of concentration and 13c data between vent fluids and plume waters suggest that the methane is not conserved but microbially oxidized along with the plume gradual decrease of diffusive methane flux in proportion to distance from the vent fields supports the occurrence of significant microbial oxidation within the plume assuming steady state emission of methane from the vents 1 kinetic isotope effect due to the microbial oxidation k12 k13 2 methane flux from the vents fvents 3 heat flux from the vents q and 4 average turnover time of hydrothermal methane tall are estimated to be k12 k13 1 005 0 001 fvents 90 340 mol d q 30 110 mw and tall 60 240 d respectively the estimated turnover times however are not uniform within the water column around the vents a turnover time of less than 50 d for methane is one of the shortest values in the pelagic ocean while those at the distant points correspond to values more typical for deep ocean water

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

the vesicular layer and carbonate collars of desert soils and pavements formation age and relation to climate change abstract the vesicular fine grained a horizon av is the widespread ubiquitous surficial horizon of desert soils in diverse landforms and parent materials of varying ages now known to form mostly through accumulation of eolian dust recent studies show that dust accumulation and concomitant soil development are genetically linked to stone pavement formation changes in the magnitude of eolian activity and effective leaching related to quaternary climatic changes are also hypothesized to have influenced the evolution of the av horizon numerical modeling geochronologic and field laboratory studies elucidate the nature of pedogenic processes controlling compositional evolution of av how the changing av horizon increasingly influences soil infiltration and carbonate translocation and accumulation and the control that clasts of the evolving pavement exert on pedogenic processes results of a model that determines soil bulk chemical composition based on mixing of estimated proportions of externally derived eolian material and parent materials imply that the evolution of the soil bulk composition is strongly influenced by av horizon formation the early development of a weakly to moderately developed av horizon directly over gravelly parent material in late and middle holocene soils moderately influences soil infiltration but significant leaching of very soluble materials and some carbonate in dust are permitted in older pleistocene soils however the texturally more mature av and underlying cumulic nongravelly horizons more strongly limit the rate and depth of leaching and soil bulk composition therefore more closely approximates a simple mixture of dust and parent material other aspects of av horizon development and its relations to the pavement are evaluated through studies of pavement clasts with coatings of soil carbonate referred to as carbonate collars development of a numerical model that integrates soil hydrology a co2 production diffusion model calcite kinetics and thermodynamic considerations composition and thermal characteristics of pavement clasts and the textural and structural properties of the surface horizon provides the basis for testing a hypothesis of collar formation model results combined with results of 13c and 18o analyses of collar carbonate demonstrate how precipitation of calcite on pavement clasts and within the av is favored at a depth much shallower than that indicated by the classic carbonate depth climate relationship of jenny and leonard jenny h j leonard c d 1935 functional relationships between soil properties and rainfall soil science 38 363 381 and arkley arkley r j 1963 calculations of carbonate and water movement in soil from climatic data soil science 96 239 248 or simulated by numerical models of carbonate accumulation simultaneous development of thick carbonate collars and the av horizon requires the sustained pavement clast av horizon coupling for at least centuries to possibly millennia new thermoluminescence ages also indicate that much of the av horizon formed in the holocene and that it is certainly much younger than the older pleistocene pavements this supports the previously proposed hypothesis that increased dust flux during the pleistocene to holocene transition triggered and or greatly accelerated av horizon development an understanding of the genesis of collars provides not just an understanding of how carbonate can accumulate in surface environments but it also provides important clues into processes of pavement evolution and preservation of av horizons during long glacial periods the av horizon is not merely an insignificant surficial zone of recent dust accretion instead its development profoundly influences the genesis of desert soils and pavements

the record of continental dust from australia in tasman sea sediments abstract the flux of aeolian dust from australia to sediments of the tasman sea has increased during glacial stages of the last four glacial cycles low fluxes of dust from australia before 350 ka were followed by an increase in stage 10 and high fluxes in peak glacial periods thereafter the initiation of higher dust fluxes in stage 10 is consisten with previous estimates of the age of onset of aridity in the source area dust flux to the tasman sea is thought to record the intensity of deflation from the source area in interior southeastern australia which was marked by arid conditions and possibly greater windiness during the last glacial a transect of five cores from the central tasman sea revealed consistently low dust fluxes north of 33 s increasing southward to approximately 40 s glacial to interglacial movement of the northern boundary of the dust plume governed by the position of the subtropical ridge was less than 6 latitude probably closer to 3 350 km the position of the dust plume determined in this study and its response to climate change are significantly different from a previous reconstruction based on the measurement of quartz content of the non biogenic sediment fraction

hydroacoustic methodology for detection localization and quantification of gas bubbles rising from the seafloor at gas seeps from the eastern black sea 1 detailed acoustic investigation of bubble streams rising from the seafloor were conducted during r v meteor cruise m72 3a at a deep submarine hydrocarbon seep environment the area is located offshore georgia eastern part of the black sea at a water depth between 840 m and 870 m the sediment echosounder parasound ds 3 p70 was used for detecting bubbles in the water column that causes strong backscatter in the echographs flares employing the swath echsounder kongsberg em710 flares in the water column were mapped along the entire swath width of approximately 1000 m at high spatial resolution the exact location of the flares could be extracted manually subsequently the horizontally looking sonar kongsberg digital telemetry ms1000 mounted on a remotely operated vehicle rov was utilized to quantify the flux of bubbles a model was developed that is based on the principle of finding the acoustic mass in order to quantify the bubble flux at various seeps the acoustic approach from the backscatter data of the rov sonar resulted in bubble fluxes in the range of 0 01 to 5 5 l min corresponding to 0 037 to 20 5 mol ch4 min at in situ conditions 850 m water depth 9 c independent flux estimations using a funnel shaped device showed that the acoustic model consistently produced lower values but the offset is less than 12 furthermore the deviation decreased with increasing flux rates a field of bubble streams was scanned three times from different directions in order to reveal the reproducibility of the method flux estimations yielded consistent fluxes of about 2 l min 7 4 mol ch4 min with variations of less than 10 although gas emissions have been found at many sites at the seafloor in a range of geological settings the amount of escaping gas is still largely unknown with this study presenting a novel method of quantifying bubble fluxes employing a horizontally looking sonar system it is intended to contribute to the global effort of better constraining bubble fluxes at deep sea settings

passive acoustic records of seafloor methane bubble streams on the oregon continental margin abstract we present acoustic records of methane bubble streams recorded 10 km southwest of heceta bank on the oregon continental margin using an autonomous hydrophone the hydrophone was deployed at 1228 m water depth via a remotely operated vehicle rov during the e v nautilus expedition na072 in june 2016 bubble sound is produced by detachment of the gas bubble from the end of a tube or conduit which causes the bubble to oscillate producing a sound signal despite persistent ship propeller and rov noise the acoustic signature of the overall bubble seep site can be seen in the hydrophone record as a broadband 1 0 45 khz series of short duration 10 20 ms oscillatory signals that occur in clusters lasting 2 3 s the frequency of an individual bubble s oscillation is proportional to the bubble s radius estimates here of bubble radii are consistent with bubble sizes observed in rov still images acoustic signal loss models imply bubble sounds might be recorded over an area of seafloor from 300 3 2 104 m2 this study represents a first step in attempting to identify and quantify deep ocean bubble stream sounds using passive acoustic techniques

the acoustic signature of marine seep bubbles observations of seabed bubbles 62m depth at a natural marine hydrocarbon seep by passive acoustic and optical approaches are compared the acoustic and optical methods observed a bimodal distribution with peaks at 1500 and 1750hz and 2200 and 2800 m radius respectively radii were 20 lower than predicted by the minnaert formula frequency shifts were observed for bubbles emitted within a few milliseconds and were attributed to coupling between nearby bubbles surfactants also may have played a role

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

soil genesis on beach ridges of pluvial lake mojave implications for holocene lacustrine and eolian events in the mojave desert southern california summary silver lake and soda lake playas mojave desert california are bounded by locally well preserved shoreline features that reflect the presence of pluvial lake mojave a well preserved sequence of five beach ridges is present in the northernmost part of silver lake playa radiocarbon dating show that the topographically highest three beach ridges range from

mechanical response of sediments to bubble growth modeling the process of bubble growth in sediments requires an understanding of the physics that controls bubble shape and the interaction of the growing bubble with the sediment to acquire this understanding we have conducted experiments in which we have injected gas through a fine capillary into natural and surrogate sediment samples and have monitored pressure during bubble growth to provide information about stress and strain in gas injection studies with natural sediment samples we have observed two modes of bubble growth behavior one of these modes characterized by a saw tooth record of pressure as the bubble grows is consistent with fracture of the medium observations indicate that bubble growth by fracture should correspond to bubbles that are coin or disk shaped this shape is confirmed in observations of bubbles in natural sediments and in our studies of bubble injection into gelatin a surrogate sediment material interpretation of the stress strain results for bubble growth also required that we measure young s modulus e the measurements show e to be near 0 14 mn m2 which differs by more than 4 orders of magnitude from values that have been reported in the literature our measurements of e give substantially better estimates of bubble shape than are predicted using the literature values our data are interpreted with linear elastic fracture mechanics lefm which predicts that the critical pressure for bubble growth will depend on the bubble volume v raised to the 1 5 power while evidence of substantial heterogeneity in sediment properties is apparent in our results this v 1 5 dependence is confirmed through application of lefm theory we have determined the critical stress intensity factor k1c a material property and the principal determinant of bubble shape and growth by fracture our values of k1c range from 2 8 10 4 mn m 3 2 to 4 9 10 4 mn m 3 2 for our natural sediment samples from cole harbor nova scotia we have also estimated the critical stress intensity factor for eckernforde bay samples by analyzing published images of natural bubbles the k1c obtained in this way is similar to our cole harbor results and is 5 5 10 4 mn m 3 2

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

a soil chronosequence on lake mega frome beach ridges and its implications for late quaternary pedogenesis and paleoenvironmental conditions in the drylands of southern australia abstract the terminal lake systems of central australia are key sites for the reconstruction of late quaternary paleoenvironments paleoshoreline deposits around these lakes reflect repeated lake filling episodes and such landforms have enabled the establishment of a luminescence based chronology for filling events in previous studies here we present a detailed documentation of the morphology and chemistry of soils developed in four well preserved beach ridges of late pleistocene and mid to late holocene age at lake callabonna to assess changes in dominant pedogenic processes all soil profiles contain evidence for the incorporation of eolian derived material likely via the formation of desert pavements and vesicular horizons and limited illuviation due to generally shallow wetting fronts even though soil properties in the four studied profiles also provide examples of parent material influence or site specific processes related to the geomorphic setting there is an overall trend of increasing enrichment of eolian derived material since at least 33 ka compared to the holocene profiles the derived average accumulation rates for the late pleistocene profiles are significantly lower and may suggest that soils record important regional changes in paleoenvironments and dust dynamics related to shifts in the southern hemisphere westerlies

quaternary aeolian dust processes and sediments in the australian region abstract aeolian dust processes have played an important role in the evolution of the australian landscape yet little is known of the processes and their sediments two major dust transport pathways are described based upon paleo dune patterns and present day dust storms and related processes these dust pathways have been fed by alluvium deposited in internally draining river basins during the period leading up to and including the late pleistocene aridity rates of dust entrainment transport and deposition were significantly higher than at present the ocean sediments of the tasman sea the pacific and indian oceans received massive amounts of aeolian sediment dust contributions to some australian soils have also been considerable

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

an improved bathymetric model for the modern and palaeo lake eyre abstract here we demonstrate the applicability of using altimetry data and landsat imagery to provide the most accurate digital elevation model dem of australia s largest playa lake lake eyre we demonstrate through the use of geospatial techniques a robust assessment of lake area and volume of recent lake filling episodes whilst also providing the most accurate estimates of area and volume for larger lake filling episodes that occurred throughout the last glacial cycle we highlight that at a depth of 25 m lake mega eyre would merge with the adjacent lake mega frome to form an immense waterbody with a combined area of almost 35 000 km2 and a combined volume of 520 km3 this would represent a vast water body in what is now the arid interior of the australian continent the improved dem is more reliable from a geomorphological and hydrological perspective and allows a more accurate assessment of water balance under the modern hydrological regime the results presented using glas icesat data suggest that earlier historical soundings were correct and the actual lowest topographic point in australia is 15 6 m below sea level the results also contrast nicely the different basin characteristics of two adjacent lake systems lake eyre and lake frome

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

a pluvial episode identified in arid australia during the medieval climatic anomaly optically stimulated luminescence osl ages from a relict shoreline on lake callabonna record a major pluvial episode in southern central australia between 1050 70 and 1100 60 common era ce w

ephemerality of discrete methane vents in lake sediments methane is a potent greenhouse gas whose emission from sediments in inland waters and shallow oceans may both contribute to global warming and be exacerbated by it the fraction of methane emitted by sediments that bypasses dissolution in the water column and reaches the atmosphere as bubbles depends on the mode and spatiotemporal characteristics of venting from the sediments earlier studies have concluded that hot spots persistent high flux vents dominate the regional ebullitive flux from submerged sediments here the spatial structure persistence and variability in the intensity of methane venting are analyzed using a high resolution multibeam sonar record acquired at the bottom of a lake during multiple deployments over a 9 month period we confirm that ebullition is strongly episodic with distinct regimes of high flux and low flux largely controlled by changes in hydrostatic pressure our analysis shows that the spatial pattern of ebullition becomes homogeneous at the sonar s resolution over time scales of hours for high flux periods or days for low flux periods demonstrating that vents are ephemeral rather than persistent and suggesting that long term lake wide ebullition dynamics may be modeled without resolving the fine scale spatial structure of venting

tracking an oil slick from multiple natural sources coal oil point california oil slicks on the ocean surface emitted from natural marine hydrocarbon seeps offshore from coal oil point in the santa barbara channel california were tracked and sampled over a 2 h period the objectives were to characterize the seep oil and to track its composition over time using a new sampling device a catamaran drum sampler catdrums the sampler was designed and developed at ucsb chromatograms showed that oil originating from an informally named very active seep area shane seep primarily evolved during the first hour due to mixing with oil originating from a convergence zone slick surrounding shane seep

earthquake related speleothem damages observations from the 2008 mw 7 9 wenchuan china abstract a speleoseismological study has been conducted at over a dozen cave sites along the longmen shan fault zone of the eastern qinghai tibet plateau the aim was to assess the damage inflicted on speleothems by the mw 7 9 wenchuan earthquake results show that the earthquake led to either partial or complete collapse of the caves soda straws are shown to be particularly vulnerable to earthquake damage but statistical analyses indicate that the spindle and slender shapes are also very likely to break cave depth is also shown to play an important role in the fracture development during the earthquake the measured orientations of fallen stalactites are preferentially aligned to the coseismic surface offset peaks and therefore to the direction of earthquake wave propagation several such damaged speleothems resulting from sudden co seismic movements were observed the direction of ceiling hanging wall movement caused by the wenchuan earthquake is nw nnw consistent with block motion on the footwall of the yingxiu beichuan fault we inferred that the faults in the caves were not co seismic structures of the wenchuan earthquake but instead they are likely normal faults as the result of gravity creeping induced by the earthquake

gaia s breath global methane exhalations abstract methane ch 4 is the most abundant organic compound in the earth s atmosphere where it acts as a greenhouse gas and thus has implications for global climate change the current atmospheric ch 4 budget however does not take into account geologically sourced ch 4 seepage geological sources of ch 4 include natural macro and micro seeps mud volcanoes and other miscellaneous sources such as gas hydrates magmatic volcanoes geothermal regions and mid ocean ridges macro seeps contribute 25 tg teragrams ch 4 yr to the atmosphere whereas micro seepage contributes perhaps 7 tg ch 4 yr mud volcanoes emit 5 tg ch 4 yr and miscellaneous sources emit 8 tg ch 4 yr to the atmosphere thus the total contribution to the atmosphere from geological sources is estimated to be 45 tg ch 4 yr which is significant to the atmospheric organic carbon cycle and should be included in any global inventory of atmospheric ch 4 we argue that the atmospheric ch 4 global inventory of the interplanetary panel on climate change must be adjusted in order to incorporate geologically sourced ch 4 from naturally occurring seepage

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