hydrogen sulphide and methane emissions on the central namibian shelf abstract hydrogen sulphide occurs frequently in the waters of the inner shelf coastal upwelling area off central namibia the area affected coincides with hatching grounds of commercially important pelagic fish whose recruitment may be severely affected by recurring toxic sulphidic episodes both episodic biogenic methane gas driven advective and molecular diffusive flux of hydrogen sulphide have been implicated as transport mechanisms from the underlying organic matter rich diatomaceous mud to test hypotheses on the controls of hydrogen sulphide transport from the sediments on the inner namibian shelf water column and sediment data were acquired from four stations between 27 and 72 m water depth over a 3 year long period on 14 cruises temperature salinity dissolved oxygen nitrate methane and total dissolved sulphide were determined from water column samples and pore water dissolved methane total dissolved sulphide biomass of benthic sulphide oxidising bacteria beggiatoa and thiomargarita and bacterial sulphate reduction rates were determined from sediment cores superimposed on a trend of synchronous changes in water column oxygen and nutrient concentrations controlled by regional hydrographic conditions were asynchronous small scale variations at the in shore stations that attest to localized controls on water column chemistry small temporal variations in sulphate reduction rates determined with 35 s labeled sulphate do not support the interpretation that variable emissions of sulphide and methane from sediments are driven by temporal changes in the degradation rates of freshly deposited organic matter the large temporal changes in the concentrations of hydrogen sulphide and the co occurrence of pore water sulphate and methane support an interpretation of episodic advection of methane and hydrogen sulphide from deeper sediment depths possibly due to gas bubble transport effective fluxes of hydrogen sulphide and methane to the water column and methane and sulphide concentrations in the bottom waters were decoupled likely due to the activity of sulphide oxidising bacteria while the causal mechanism for the episodic fluctuations in methane and dissolved sulphide concentrations remains unclear this data set points to the importance of alternating advective and diffusive transport of methane and hydrogen sulphide to the water column

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

frontal surveys with a towed profiling conductivity temperature depth measurement package seasoar in april 1986 rv oceanus participated in the frontal air sea interaction experiment fasinex1 in the region 27 29 n 68 71 w the objective was to survey a pronounced oceanic front2 4 and its effect on the oceanic and atmospheric boundary layers although moorings have yet to be recovered and much of the data analysis is as yet only preliminary it is possible to report here the typical density structure of a front as derived from seasoar5 6 fig 1a observations which were analysed within a few hours of collection previously unreported detail is revealed including subducted pycnostads areas of weak vertical density gradient with anomalous temperature salinity signature splitting of the frontal jet and three dimensional structure not apparent in the surface temperature field

enhanced marine ch4 emissions to the atmosphere off oregon caused by coastal upwelling methane in surface waters and marine air off oregon 44 24 n 44 54 n 124 36 w 125 24 w was continuously surveyed in july 1999 during a high resolution survey after a period of steady winds from the north ch4 concentrations were high in the northeastern region near the shelf edge the highest ch4 concentrations were 2 5 times higher than equilibrium with the atmospheric partial pressure in contrast concentrations were near equilibrium in the western part of the survey area the hydrate ridge the increase in ch4 from southwest to northeast correlates with a drop in sea surface temperature sst from 16 5 c to 13 5 c toward the shelf edge the observed sst pattern was caused by summer upwelling off oregon the results suggest that ch4 derived from bottom sources near the shelf slope break and methane found in connection with shallow 100 300 m turbidity layers is transported to the surface by coastal upwelling which causes an enhanced net flux of ch4 to the atmosphere vertical profiles of the methane distribution on the shelf in october demonstrate the accumulation of methane introduced by shelf sources surface concentrations at these stations in october during nonupwelling conditions were lower than in july during upwelling and were only slightly oversaturated with respect to the atmosphere an acoustic doppler current profiler survey indicates that the observed trend cannot be attributed to a surface flow reversal in the area the low salinity waters in the core of the columbia river plume s 31 showed no enhanced ch4 concentrations the trend of higher ch4 concentrations at lower temperatures existed over the whole 17 day survey but large spatial and temporal variations existed the presence of methane sources in regions of coastal upwelling worldwide such as shallow seeps gas hydrates and intermediate nepheloid layers suggests that the enhancement of ch4 fluxes to the atmosphere by coastal upwelling occurs on a global scale

composition of shelf methane seeps on the cascadia continental margin 1 methane reservoirs and seeps are an active component of the continental margin carbon budget and represent a poorly characterized pathway for reduced carbon cycling and methane input to the atmosphere active gas seeps from three shelf settings on the cascadia continental margin off oregon and northern california contain nearly pure methane with a heavy carbon isotope composition 29 to 35 an extensive study of the gas seep at coquille bank oregon revealed a warm buoyant pore fluid associated with the pockmark as methane enters the water column above these seeps in a steady gas stream a fraction escapes directly to the atmosphere while the balance dissolves into local seawater measured oxidation rates are too slow for significant local oxidation within the water column near the seep large mats of pink and white bacteria including beggiatoa spp are found around the vent demonstrating the activity of sulfide oxidizers in this ecosystem

further observations of a decreasing atmospheric co2 uptake capacity in the canada basin arctic ocean due to sea ice loss 1 using data collected in 2009 we evaluated the potential for the southeastern canada basin arctic ocean to act as an atmospheric co2 sink under the summertime ice free conditions expected in the near future beneath a heavily decayed ice cover we found surprisingly high pco2sw 290 320 atm considering that surface water temperatures were low and the influence of ice melt was strong a simple model simulating melt of the remaining ice and exposure of the surface water for 100 days revealed a weak capacity for atmospheric co2 uptake mean flux 2 4 mmol m 2 d 1 due largely to warming of the shallow mixed layer our results confirm a previous finding that the canada basin is not a significant sink of atmospheric co2 under summertime ice free conditions and that increased ventilation of the surface mixed layer due to sea ice loss is weakening the sink even further

a blast of gas in the latest paleocene simulating first order effects of massive dissociation of oceanic methane hydrate carbonate and organic matter deposited during the latest paleocene thermal maximum is characterized by a remarkable 2 5 excursion in delta 13c that occurred over approximately 10 4 yr and returned to near initial values in an exponential pattern over approximately 2 x 10 5 yr it has been hypothesized that this excursion signifies transfer of 1 4 to 2 8 x 10 18 g of ch4 from oceanic hydrates to the combined ocean atmosphere inorganic carbon reservoir a scenario with 1 12 x 10 18 g of ch4 is numerically simulated here within the framework of the present day global carbon cycle to test the plausibility of the hypothesis we find that 1 the delta 13c of the deep ocean shallow ocean and atmosphere decreases by 2 3 over 10 4 yr and returns to initial values in an exponential pattern over approximately 2 x 10 5 yr 2 the depth of the lysocline shoals by up to 400 m over 10 4 yr and this rise is most pronounced in one ocean region and 3 global surface temperature increases by approximately 2 degrees c over 10 4 yr and returns to initial values over approximately 2 x 10 6 yr the first effect is quantitatively consistent with the geologic record the latter two effects are qualitatively consistent with observations thus significant ch4 release from oceanic hydrates is a plausible explanation for observed carbon cycle perturbations during the thermal maximum this conclusion is of broad interest because the flux of ch4 invoked during the maximum is of similar magnitude to that released to the atmosphere from present day anthropogenic ch4 sources

fluid flow and mass flux determinations at vent sites on the cascadia margin accretionary prism fluid venting from the toe of the accretionary prism off oregon was measured in situ during a series of dives with dsrv alvin in 1987 and 1988 a benthic chamber was placed over active vent sites to sequentially collect samples of venting fluids and to make direct measurements of discharge rates calibrated flow meter measurements and flow rates determined from dissolved methane transfer indicate that discharge from two vent sites alvin 1428 and alvin 1900 ranges roughly between 100 and 500 l m 2 d 1 with the most reliable estimates falling in the range of 125 150 l m 2d 1 these rates imply subsurface advective flow on the order of 100 m yr 1 comparison of observed discharge rates with rates calculated for steady state expulsion supported by accretion related compaction indicates that the observed flow is greater than predicted flow by several orders of magnitude the disparity dictates that fluids are not derived locally but are transported laterally within the prism or that flow is not steady state and that individual vents are short lived features in the ongoing accretion process

methane sources distributions and fluxes from cold vent sites at hydrate ridge cascadia margin to constrain the fluxes of methane ch4 in the water column above the accretionary wedge along the cascadia continental margin we measured methane and its stable carbon isotope signature 13c ch4 the studies focused on hydrate ridge hr where venting occurs in the presence of gas hydrate bearing sediments the vent ch4 has a light 13c ch4 biogenic signature 63 to 66 pdb and forms thin zones of elevated methane concentrations several tens of meters above the ocean floor in the overlying water column these concentrations ranging up to 4400 nmol l 1 vary by 3 orders of magnitude over periods of only a few hours the poleward undercurrent of the california current system rapidly dilutes the vent methane and distributes it widely within the gas hydrate stability zone ghsz above 480 m water depth the methane budget is dominated by isotopically heavier ch4 from the shelf and upper slope where mixtures of various local biogenic and thermogenic methane sources were detected 56 to 28 pdb the distribution of dissolved methane in the working area can be represented by mixtures of methane from the two primary source regions with an isotopically heavy background component 25 to 6 pdb methane oxidation rates of 0 09 to 4 1 per day are small in comparison to the timescales of advection this highly variable physical regime precludes a simple characterization and tracing of downcurrent plumes however methane inventories and current measurements suggest a methane flux of approximately 3 104 mol h 1 for the working area 1230 km2 and this is dominated by the shallower sources we estimate that the combined vent sites on hr produce 0 6 104 mol h 1 and this is primarily released in the gas phase rather than dissolved within fluid seeps there is no evidence that significant amounts of this methane are released to the atmosphere locally

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

methane along the western mexican margin we investigated the processes controlling the water column and sediment methane distributions at 14 stations along the western mexican margin in and around the gulf of california stations were grouped into two categories coastal basins and open margins diffusive methane fluxes from the sediment at all sites as estimated from sediment methane gradients were 0 24 5 5 mmol m 22 d 21 with the highest fluxes observed on the pacific margin of baja california at both basin and open margin sites these high rates occur despite the lack of significant terrestrial input to these sediments reflecting the importance of upwelling induced productivity methane concentrations in the upper water column were supersaturated with respect to the present atmosphere at all sites with sea air fluxes of methane of 0 5 5 9 mmol m 22 d 21 four of the open margin sites had seafloor depths extending below the oxygen minimum zone 400 800 m and contained low methane concentrations below the subsurface methane maximum the remaining margin site was shallow 593 m with a seafloor that intersected the oxygen minimum zone and had elevated methane concentrations throughout the water column this indicates that such sediments may be a significant source of methane to the eastern tropical north pacific etnp the seawater within silled basin sites also had supersaturated methane concentrations reflecting the anoxic conditions within the basins however methane levels were low at the sill depth indicating that the silled basins were unlikely to be significant sources of methane to the etnp we observed an inverse relationship between methane concentration and d 13 c ch4 value in the basin waters consistent with biological aerobic oxidation of methane being released from the sediment an apparent kinetic isotopic fractionation factor of 1 0100 0 0038 was calculated for this process isotopically heavy methane resulting from similar oxidation of seafloor derived methane may be the source of large pools of heavy methane previously

upper ocean water mass characteristics of the california current summer 1993 abstract two large high resolution upper ocean surveys of the california current region were conducted in the summer of 1993 temperature and salinity were measured from a seasoar vehicle and velocity was measured by a ship borne acoustic doppler current profiler both surveys extended from the continental margin to 128 w and consisted of zonal sections 28 km apart the first survey 7 28 june extended from 39 5 n to 36 25 n and the second 16 august to 1 september extended from 39 0 n to 37 0 n the current field was fairly simple in june showing an equatorward surface jet with only one gentle meander a nearly continuous poleward california undercurrent near the continental margin and two anticyclonic subsurface eddies offshore of the jet by august meanders in the surface jet had strengthened and eddies dominated the flow field large scale trends in the water mass characteristics spiciness along three isopycnal surfaces 26 4 26 0 and 25 6 kg m 3 show that temperature and salinity tend to increase towards the equator and towards shore consistent with poleward advection along the continental margin local minima in spiciness tend to coincide with the equatorward surface jet local maxima in spiciness are associated with subsurface anticyclonic eddies which have a core depth of about 150 m and seem to originate in the california undercurrent over the continental slope at local latitudes we identified several different anticyclonic eddies each with different water mass characteristics all of the eddies we observed had diameters larger than the baroclinic radius of deformation water mass characteristics and migration rates are consistent with formation over the continental margin within the preceding 6 8 months

a poleward jet and an equatorward undercurrent observed off oregon and northern california during the 1997 98 el nino abstract the timing and intensity of the effects of the 1997 98 el nino on sea surface temperature sst and coastal sea level along the us west coast are examined using in situ time series measurements and the effects on upper ocean currents on the continental shelf and slope off oregon and northern california are examined using repeated shipborne adcp transects a mid shelf mooring off newport oregon and an hf surface current radar an initial transient positive anomaly was observed in both adjusted sea level and sst during may june 1997 followed by anomalously high coastal sea levels generally strongest during september 1997 through february 1998 and abruptly returned to normal in late february 1998 and by positive temperatures anomalies over the mid shelf that persisted longer into april 1998 low frequency coastal sea level anomalies propagated poleward at 2 1 m s poleward flow over the shelf and slope was enhanced at most depths during the el nino compared with following years northward currents in the upper 12 m over the continental shelf off newport oregon averaged 13 7 cm s stronger during august 1997 through february 1998 than during the same period the following year enhanced poleward flow was present at all latitudes sampled during november 1997 and february 1998 particularly over the continental slope these transects also provided clear views of a fall winter equatorward undercurrent which was both strongest and had the most alongshore similarity of form during the enso finally subsurface intensified anticyclonic eddies originating in the poleward undercurrent appear to be a recurrent feature of the circulation off newport late in the upwelling season

fluid venting in the eastern aleutian subduction zone fluid venting has been observed along 800 km of the alaska convergent margin the fluid venting sites are located near the deformation front are controlled by subsurface structures and exhibit the characteristics of cold seeps seen in other convergent margins the more important characteristics include 1 methane plumes in the lower water column with maxima above the seafloor which are traceable to the initial deformation ridges 2 prolific colonies of vent biota aligned and distributed in patches controlled by fault scarps over steepened folds or outcrops of bedding planes 3 calcium carbonate and barite precipitates at the surface and subsurface of vents and 4 carbon isotope evidence from tissue and skeletal hard parts of biota as well as from carbonate precipitates that vents expel either methane or sulfide dominated fluids a biogeochemical approach toward estimating fluid flow rates from individual vents based on oxygen flux measurements and vent fluid analysis indicates a mean value of 5 5 0 7 l m 2 d 1 for tectonics induced water flow wallmann et al 1997b a geophysical estimate of dewatering from the same area von huene et al 1997 based on sediment porosity reduction shows a fluid loss of 0 02 l m 2 d 1 for a 5 5 km wide converged segment near the deformation front our video guided surveys have documented vent biota across a minimum of 0 1 of the area of the convergent segment off kodiak island hence an average rate of 0 006 l m 2 d 1 is estimated from the biogeochemical approach the two estimates for tectonics induced water flow from the accretionary prism are in surprisingly good agreement

a time dependent model of the earth s magnetic field and its secular variation for the period 1980 2000 1 this study presents an investigation and description of the secular variation of the earth s magnetic field between 1980 and 2000 a time dependent model c3fm continuous covariant constrained endpoints field model of the main field and its secular variation between 1980 and 2000 is developed with gauss coefficients expanded in time on a basis of cubic b splines this model is constrained to fit field models from high quality vector measurements of magsat in 1980 and orsted in 2000 and to fit both magnetic observatory and repeat station secular variation estimates for the period in between these secular variation estimates first time derivatives are derived from observatories monthly or annual means and repeat station data in order to reduce the contributions of crustal noise annual and semiannual variation on average the model input consists secular variation estimates of the x y and z components at 130 locations per month treatment of covariance between the different components allows a higher temporal sensitivity of the model due to the exclusion of some external field variation the model is computed up to degree and order 15 the model is a useful extension of the hitherto existing time dependent description of the secular variation gufm which describes the secular variation until 1990 it reveals a short term secular variation on subdecadal timescale and has a higher spatial resolution than previously resolved the model is also valuable to test the frozen flux hypothesis and to link features of the radial field at the core mantle boundary to the geodynamo

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

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

methane sources and sinks in the subtropical south pacific along 17 s as traced by stable isotope ratios abstract we analyzed the concentration and stable carbon isotopic ratio 13 c ch 4 of methane in the atmosphere and in dissolved methane in water column along 17 s in the subtropical south pacific additionally the hydrogen isotopic ratios d ch 4 of some water samples were analyzed the sea air ch 4 flux is high in the eastern region and off the west coast of australia which is related to the high concentrations of dissolved ch 4 and high wind speeds moreover there is a positive correlation between the ch 4 and chlorophyll a concentrations at the surface this consistency suggested that active ch 4 productions related to the primary production cause surface ch 4 accumulation ch 4 shows a decrease in concentration and an increase in 13 c ch 4 and d ch 4 values from the surface to the depth of about 1000 m the relationship between 13 c ch 4 values and ch 4 concentration indicates that the isotopic enrichment of ch 4 reflects microbial oxidation of ch 4 with isotopic fractionation during vertical transport via vertical sinking and or zooplankton migration east of 120 w 13 c ch 4 values at around 1000 m exceed 30 0 the relationships among the 13 c ch 4 values ch 4 concentrations and oxygen concentrations indicate that the 13 c enriched ch 4 originates not only from in situ ch 4 production and oxidation but also from ch 4 transported from the eastern margin off peru furthermore at a site near the central lau spreading centers in the lau basin high 13 c ch 4 values up to 21 4 are observed in the benthic water suggesting a hydrothermal field source

the distribution of methane in the upper waters of the southern california bight profiles of dissolved methane in the upper 300 m of a 190 000 km2 area of southern californian waters were determined during november 1989 and march 1990 methane in near surface waters ranged from 1 to 1416 nmol l 1 the lowest concentrations were at depths 200 m the highest levels were found along the coast especially in the region extending from point conception to santa barbara vertical profiles of methane are characterized by maxima in supersaturation within a narrow density band located within the pycnocline this layer is continuous over a large geographic area offshore stations exhibiting elevated levels of methane are spatially coincident with mesoscale eddies of the california current system interpretation of hydrographic and chemical data suggests that ch4 rich waters are upwelled from relatively shallow areas that are characterized by numerous hydrocarbon seeps the data are consistent with a nearshore source of methane presumably submarine seeps subsurface maxima in offshore waters are likely maintained by lateral transport of allochthonous ch4 along density surfaces from coastal waters and autochthonous microbial production

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

upper water column methane geochemistry in the eastern tropical north pacific1 upper water column 400 m profiles of methane suspended matter biological indicators and hydrographic parameters were obtained from nine stations in the eastern tropical north pacific ocean methane was consistently supersaturated with respect to atmospheric eguilibrium and displayed a subsurface maximum containing about 2 3 times near surface conccntrations associated with the upper part of the pycnocline correlations between methane and the particulate and biological parameters at all nine stations taken together were low although several stations individually exhibited significant correspondences the methane distribution was largely controlled by physical oceanographic processes microbial activity associated with suspended particles possibly recycled by repetitive zooplankton grazing is believed most likely responsible for the excess methane

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

marine methane cycle simulations for the period of early global warming geochemical environments fates and effects are modeled for methane released into seawater by the decomposition of climate sensitive clathrates a contemporary global background cycle is first constructed within the framework of the parallel ocean program input from organics in the upper thermocline is related to oxygen levels and microbial consumption is parameterized from available rate measurements seepage into bottom layers is then superimposed representing typical seabed fluid flow the resulting ch sub 4 distribution is validated against surface saturation ratios vertical sections and slope plume studies injections of clathrate derived methane are explored by distributing a small number of point sources around the arctic continental shelf where stocks are extensive and susceptible to instability during the first few decades of global warming isolated bottom cells are assigned dissolved gas fluxes from porous media simulation given the present bulk removal pattern methane does not penetrate far from emission sites accumulated effects however spread to the regional scale following the modeled current system both hypoxification and acidification are documented sensitivity studies illustrate a potential for material restrictions to broaden the perturbations since methanotrophic consumers require nutrients and trace metals when such factors are considered methane buildup within the arctic basin is enhanced however freshened polar surface waters act as a barrier to atmospheric transfer diverting products into the deep return flow uncertainties in the logic and calculations are enumerated including those inherent in high latitude clathrate abundance buoyant effluent rise through the column representation of the general circulation and bacterial growth kinetics

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

a separating coastal upwelling jet at cape blanco oregon and its connection to the california current system the coastal upwelling region near cape blanco oregon 433n o the west coast of the united states was studied using a towed ctd on seasoar a shipboard acoustic doppler current pro ler adcp satellite sea surface temperature maps and surface drifters during august 1995 the equatorward upwelling jet was inshore of the shelfbreak north of cape blanco meandered gently o shore around the cape and then veered sharply o shore just to the south of the cape analysis of vertical sections of density velocity and spicinessa con rmed the separation of an upwelling jet and front the jet was followed from over the shelfbreak north of the cape to 100 km o shore downstream of the cape the separating jet originates from the coastal upwelling jet leaving the shelf but is augmented by an o shore branching of the poleward undercurrent by combining information from adcp streamfunction maps with analysis of hydrographic data including distributions of the tracer like quantity spicinessa a conceptual model of the three dimensional circulation near the cape emerges a mid shelf upwelling jet encounters a coastal promontory then turns o shore stretching and deepening as it crosses the continental margin the jet then turns back shoreward cyclonically where the deepened equatorward ow encounters the top of the poleward undercurrent owing along the continental slope this causes a portion of the undercurrent to turn o shore to join and strengthen the equatorward transport in the separated jet throughout the separation process the coastal upwelling front and jet are continuous robust features separation of a coastal upwelling jet is an important mechanism for cross shelf transport from the coast to the deep ocean cape blanco appears to be the northernmost point where an equatorward jet regularly separates from the coast to become an oceanic jet and thus serves as the northern boundary of the region where an intense meandering current characteristic of the california current system