carbon geochemistry of cold seeps methane fluxes and transformation in sediments from kazan mud volcano eastern mediterranean sea abstract despite growing concerns about potential enhancement of global warming and slope failure by methane produced by gas hydrate dissociation much uncertainty surrounds estimates of gas hydrate reservoir sizes as well as methane fluxes and oxidation rates at the sea floor for cold seep sediments of the eastern mediterranean sea depth dependent methane concentrations and rates of anaerobic oxidation of methane aom are constrained by modeling the measured pore water sulfate profile the calculated dissolved methane distribution and flux are sensitive to the advective flow velocity which is estimated from the depth distributions of conservative pore water constituents na b near complete anaerobic oxidation of the upward methane flux of 6 0 mol m 2 yr 1 is supported by the depth distributions of indicative biomarkers and the carbon isotopic compositions of organic matter and dissolved inorganic carbon pore water and solid phase data are consistent with a narrow depth interval of aom 14 18 cm below the sediment water interface based on an isotopic mass balance the biomass of the microbial population carrying out oxidation of methane coupled to sulfate reduction at the given methane flux represents 20 of the total organic carbon which is a significant pool of in situ formed organic matter model results indicate that the asymptotic methane concentration is reached a few meters below the sediment surface the predicted asymptotic concentration is close to the in situ saturation value with respect to gas hydrate suggesting that the rate of shallow gas hydrate formation is controlled by the ascending methane flux the proposed model approach can be used to predict the formation of gas hydrate and to quantify methane fluxes plus transformation rates in surface sediments where fluid advection is an important transport mechanism

gas hydrate systems in petroleum provinces of the sw barents sea abstract 3d seismic data of the sw barents sea provided information about the existence of structure ii gas hydrates and shallow gas in marine sediments gas hydrates and shallow gas exist in the sw barents sea in conjunction with deep hydrocarbon reservoir leakage available conventional 3d seismic data show acoustic chimneys that extend to depths 1700 ms two way travel time below the seafloor the location of the chimneys coincides with structural boundaries and fault complexes cutting through mostly jurassic and triassic strata vertical fluid flow through these chimneys transports thermogenic gas to the gas hydrate stability zone causing the formation of a bottom simulating reflector bsr in addition variations of fluid flux across deep seated fault complexes cause changes in heat flow which explains the shoaling of the bsr and the formation of a tilted bsr tbsr at the border between the ringvassoya fault complex and the loppa high the stability model using thermogenic gas composition type i and ii shows gas hydrates are stable at 225 m 345 m depth corresponding to variation in the geothermal gradient for upper bsr 28 7 c km and 37 c km and lower bsr levels 23 4 c km and 28 3 c km these lateral changes in the temperature gradient can be reconciled with changes in upward fluid flow rates of 1 8 2 2 mm yr 1 such gas hydrate and fluid flow systems on arctic continental margins especially in shallow water depths are potential gas emitters due to their sensitivity to warming ocean temperatures

deep water formation and meridional overturning in a high resolution model of the north atlantic the authors use different versions of the model of the wind and thermohaline driven circulation in the north and equatorial atlantic developed under the woce community modeling effort to investigate the mean flow pattern and deep water formation in the subpolar region and the corresponding structure of the basin scale meridional overturning circulation transport a suite of model experiments has been carded out in recent years differing in horizontal resolution 1 1 2 1 3 0 4 1 6 0 2 thermohaline boundary conditions and parameterization of small scale mixing the mass transport in the subpolar gyre and the production of north atlantic deep water nadw appears to be essentially controlled by the outflow of dense water from the greenland and norwegian seas in the present model simulated by restoring conditions in a buffer zone adjacent to the boundary near the greenland scotland ridge deep winter convection homogenizes the water column in the center of the labrador sea to about 2000 m the water mass properties potential temperature about 3 c salinity about 34 9 psu and the volume 1 1 1053 km3 of the homogenized water are in fair agreement with observations the convective mixing has only little effect on the net sinking of upper layer water in the subpolar gyre sensitivity experiments show that the export of nadw from the subpolar north atlantic is more strongly affected by changes in the overflow conditions than by changes in the surface buoyancy fluxes over the labrador and irminger seas even if these suppress the deep convection completely the host of sensitivity experiments demonstrates that realistic meridional overturning and heat transport distributions for the north atlantic with a maximum of 1 pw can be obtained with nadw production rates of 15 16 sv provided the spurious upwelling of deep water that characterizes many model solutions in the gulf stream regime is avoided by adequate horizontal resolution add mixing parameterization

extracting mg isotope signatures of ancient seawater from marine halite a reconnaissance abstract the mg ca ratio of seawater fluctuated remarkably over the phanerozoic the processes that controlled the temporal variation in seawater mg ca ratio may also have caused the secular changes in mg isotope ratios of seawater therefore the mg isotope composition of seawater may be useful to understand the long term variation in seawater chemistry different sedimentary carbonates have been proposed as archives of ancient seawater mg isotope signatures but each type of carbonate has its limitations halite is a common mineral in evaporite deposits and their fluid inclusions may be used to infer the mg isotope composition of contemporary seawater in this study we developed a method to measure the isotope composition of mg in halite with an accuracy of better than 0 1 in 26mg the accuracy of the method was verified systematically using synthetic nacl solutions as well as holocene lacustrine halite samples from the dead sea the 26mg values of marine halite samples show a large variation ranging from 0 1 to 1 6 relative to the dsm3 international mg isotope standard the 26mg values of some ancient salt samples are lower than a published model curve for 26mg of seawater and such inconsistency could be explained by 1 isotopic evolution of brines due to mineral precipitation 2 entrapment of evaporite minerals into halite during halite precipitation or post depositional deformation 3 recrystallization and dissolution of pre existing mg minerals and 4 limitations of the model curve of seawater 26mg values collectively we suggest that mg isotopes in halite are a new geochemical proxy to study the secular variations in seawater chemistry syndepositional and post depositional processes of evaporite deposits our data highlight the importance of understanding the sedimentary background and textural details of evaporites for appropriate interpretations of mg isotope data from halite

novel high pressure culture experiments on deep sea benthic foraminifera evidence for methane seepage related δ13c of cibicides wuellerstorfi in field studies of active hydrocarbon seeps the carbon isotopic composition of rose bengal stained benthic foraminiferal tests 13ctest and bottom water dic 13cdic deviates from their normal marine ratios this circumstance led to ongoing discussions on whether aerobic foraminifers like cibicides wuellerstorfi are capable of living at seepage sites and more importantly if their tests reflect the low 13c values of emanating methane to evaluate the discrepancy between 13cdic and 13ctest we conducted methane seepage emulating culture experiments on undepressurized sediments from the hakon mosby mud volcano a modern methane seepage structure that hosts living c wuellerstorfi with distinct negative 13c values the collected sediments were cultured at a site alike pressure and mean bottom water methane concentration using newly developed high pressure aquaria over an experimental period of 5 months our novel technology enabled a successful reproduction of all calcareous deep sea benthic foraminiferal species living at that site notably the first c wuellerstorfi cultured in the laboratory to show the influence of methane on 13ctest we ran parallel experiments with 99 12c and 99 13c methane in the experimental bottom water during the experimental running time methanotrophs in the water column obviously converted the experimentally added methane source to 13c enriched and depleted dic respectively since whole sediment cores were cultured it was impossible to keep 13cdic constant over the 5 month duration which is reflected in a variability of 13ctest in foraminiferal shells irrespective of that the methane source is reflected in 13ctest of foraminiferal shells and for the natural seep conditions simulating 12c experiment the mean 13cdic and 13ctest in c wuellerstorfi were equal although for future culturing experiments improvements of the experimental conditions are advisable our first results are evidence that persistent methane emanation impacts the carbon isotopic composition of deep sea benthic foraminifera

the hakon mosby mud volcano 330 000 years of focused fluid flow activity at the sw barents sea slope studying the morphology and subsurface geometry of mud volcanoes provides insights into their activity this paper describes the internal structure of the hakon mosby mud volcano hmmv in the southwestern barents sea and presents a conceptual model of its evolution the lack of a mud edifice and the profuse gas flares suggest that in the recent past the mud volcano evolution was predominantly controlled by venting of gas rich fluids and free gas however the analysis of high resolution single channel seismic scs data reveals for the first time the existence of a pseudo mud chamber at the top of the 3 km deep central conduit it was once created at the seabed and is now a buried expression that acts as mud chamber the pseudo mud chamber is situated approximately 300 m below the seafloor directly above the 330 ka bear island slide bis scar reflection and below glacigenic debris flow deposits that constitute the sediment on top the sediment profiler data indicates a younger mud deposit above the debris flows which points to a reactivation of the mud volcano the reactivation was most likely triggered by the contrast in density between the gas rich mud chamber and the high density debris flow deposits three stages i e initiation sealing and reactivation and a second active period define the evolution of this young mud volcano both the morphology and size of the conduit as well as in situ temperature gradients point towards a focused and rapid fluid flow

the role of the kupferschiefer in the formation of hydrothermal base metal mineralization in the spessart ore district germany insight from detailed sulfur isotope studies the spessart district sw germany located at the southwestern margin of the permian kupferschiefer basin in central europe hosts abundant stratabound and structurally controlled base metal mineralization the mineralization styles identified are 1 stratabound cu pb zn ag ores in zechstein sedimentary rocks 2 structurally controlled cu as ag ores in zechstein sedimentary rocks 3 crosscutting co ni bi as and cu fe as veins 4 stratabound metasomatic fe mn carbonate ores in zechstein dolomite 5 barren barite veins and 6 fe mn as veins in permian rhyolites building on previous work that involved mineralogical textural and chemical characterization of the major mineralization types we have performed a comprehensive sulfur isotope study that applied both conventional and novel laser ablation multi collector inductively coupled plasma mass spectrometry techniques the 34s values of sulfide minerals from the different ore types are consistently negative and highly variable in the range between 44 5 and 3 9 whereas the 34s values of barite are all positive in the range between 4 7 and 18 9 remarkably stratabound and structurally controlled mineralization in zechstein sedimentary rocks has the least negative 34s values whereas vein type deposits have consistently more negative 34s values the observed pattern of sulfide 34s values can be best interpreted in terms of fluid mixing at the basement cover interface hydrothermal fluids originating from the crystalline basement migrated upward along subvertical fault zones and were periodically injected into groundwaters that were flowing in the post variscan sedimentary cover these groundwaters had interacted with the zechstein sedimentary rocks resulting in fluids characterized by elevated concentrations of reduced sulfur with negative 34s values and alkaline ph repeated mixing between both chemically contrasting fluids caused rapid and efficient precipitation of sulfide ore minerals in hydrothermal veins with highly variable but distinctly negative 34s values

in situ fluxes and zonation of microbial activity in surface sediments of the hakon mosby mud volcano from the hakon mosby mud volcano hmmv on the southwest barents sea shelf gas and fluids are expelled by active mud volcanism we studied the mass transfer phenomena and microbial conversions in the surface layers using in situ microsensor measurements and on retrieved cores the hmmv consists of three concentric habitats a central area with gray mud a surrounding area covered by white mats of big sulfide oxidizing filamentous bacteria beggiatoa and a peripheral area colonized by symbiontic tube worms pogonophora a fourth habitat comprised gray microbial mats near gas seeps the differences between these four methane fueled habitats are best explained by different transport rates of sulfate into the sediments and pore water upflow rates the upflow velocities were estimated by two independent methods at 3 6 m yr21 in the central area and 0 3 1 m yr21 in beggiatoa mats in the central area no sulfide was found indicating that the rapidly rising sulfate free fluids caused sulfate limitation that inhibited anaerobic oxidation of methane aom under beggiatoa mats a steep sulfide peak was found at 2 to 3 cm below the seafloor bsf most likely due to aom all sulfide was oxidized anaerobically possibly through nitrate reduction by beggiatoa the beggiatoa mats were dominated by a single filamentous morphotype with a diameter of 10 mm and abundant sulfur inclusions a high diversity of sulfide oxidizer morphotypes was observed in a grayish microbial mat near gas vents where aerobic sulfide oxidation was important the sediments colonized by pogonophora were influenced by bioventilation allowing sulfate penetration and aom to 70 cm bsf the hmmv is a unique and diverse ecosystem the structure and functioning of which is mainly controlled by pore water flow

methane and sulfide fluxes in permanent anoxia in situ studies at the dvurechenskii mud volcano sorokin trough black sea the dvurechenskii mud volcano dmv is located in permanently anoxic waters at 2060 m depth sorokin trough black sea the dmv was studied during the rv meteor expedition m72 2 as an example of an active mud volcano system to investigate the significance of submarine mud volcanism for the methane and sulfide budget of the anoxic black sea hydrosphere our studies included benthic fluxes of methane and sulfide as well as the factors controlling transport consumption and production of both compounds within the sediment the pie shaped mud volcano showed temperature anomalies as well as solute and gas fluxes indicating high fluid flow at its summit north of the geographical center the anaerobic oxidation of methane aom coupled to sulfate reduction sr was repressed in this zone due to the upward flow of sulfate depleted fluids through recently deposited subsurface muds apparently limiting microbial methanotrophic activity consequently the emission of dissolved methane into the water column was high with an estimated rate of 0 46 mol m 2 d 1 on the wide plateau and edge of the mud volcano surrounding the summit fluid flow and total methane flux were lower allowing higher sr and aom rates correlated with an increase in sulfate penetration into the sediment here between 50 and 70 of the methane flux 0 07 0 1 mol m 2 d 1 was consumed within the upper 10 cm of the sediment the overall amount of dissolved methane released from the entire mud volcano structure into the water column was significant with a discharge of 1 3 107 mol yr 1 the dmv maintains also high areal rates of methane fueled sulfide production and emission of on average 0 05 mol m 2 d 1 this is a difference to mud volcanoes in oxic waters which emit similar amounts of methane but not sulfide however based on a comparison of this and other mud volcanoes of the black sea we conclude that sulfide and methane emission into the hydrosphere from deep water mud volcanoes does not significantly contribute to the sulfide and methane inventory of the black sea

sulfur and oxygen isotope fractionation during sulfate reduction coupled to anaerobic oxidation of methane is dependent on methane concentration highlights naturally enriched aom biomass was studied in high pressure continuous incubation we report the first s and o isotope fractionation values by sulfate reduction coupled to aom from culture studies there is a tight link between methane concentration and s and o isotope fractionation s and o isotope fractionation values indicate reversibility of energy limited microbial processes the wide range of environmental s and o isotope signatures can be explained abstract isotope signatures of sulfur compounds are key tools for studying sulfur cycling in the modern environment and throughout earth s history however for meaningful interpretations the isotope effects of the processes involved must be known sulfate reduction coupled to the anaerobic oxidation of methane aom sr plays a pivotal role in sedimentary sulfur cycling and is the main process responsible for the consumption of methane in marine sediments thereby efficiently limiting the escape of this potent greenhouse gas from the seabed to the overlying water column and atmosphere in contrast to classical dissimilatory sulfate reduction dsr where sulfur and oxygen isotope effects have been measured in culture studies and a wide range of isotope effects has been observed the sulfur and oxygen isotope effects by aom sr are unknown this gap in knowledge severely hampers the interpretation of sulfur cycling in methane bearing sediments especially because unlike dsr which is carried out by a single organism aom sr is presumably catalyzed by consortia of archaea and bacteria that both contribute to the reduction of sulfate to sulfide we studied sulfur and oxygen isotope effects by aom sr at various aqueous methane concentrations from 1 4 0 6 mm1 4 0 6 mm up to 58 8 10 5 mm58 8 10 5 mm in continuous incubation at steady state changes in the concentration of methane induced strong changes in sulfur isotope enrichment view the mathml sourcees34 and oxygen isotope exchange between water and sulfate relative to sulfate reduction o o as well as sulfate reduction rates srr smallest view the mathml sourcees34 21 9 1 9 21 9 1 9 and o o 0 5 0 20 5 0 2 as well as highest srr were observed for the highest methane concentration whereas highest view the mathml sourcees34 67 3 26 1 67 3 26 1 and o o 2 5 1 52 5 1 5 and lowest srr were reached at low methane concentration our results show that view the mathml sourcees34 o o and srr during aom sr are very sensitive to methane concentration and thus also correlate with energy yield in sulfate methane transition zones aom sr is likely to induce very large sulfur isotope fractionation between sulfate and sulfide i e 60 60 and will drive the oxygen isotope composition of sulfate towards the sulfate water oxygen isotope equilibrium value sulfur isotope fractionation by aom sr at gas seeps where methane fluxes are high will be much smaller i e 20 to 40

the age of the permian triassic boundary abstract the 5 cm boundary clay bed in the chinese stratotype section through the permian triassic boundary has been recognised as a bentonite shrimp ion microprobe dating of zircons in the bentonite indicates a magmatic age of 251 2 3 4 ma 2 this is the first direct constraint on the numerical age of the permian triassic boundary future refinements of ages at this important but poorly constrained level of the phanerozoic timescale may depend on re analysis of this uniquely placed volcanic horizon and other bentonites in the fossiliferous chinese upper permian and lower triassic the utility of defining the permian triassic boundary in the chinese stratotype section in the vicinity of known dateable horizons should be considered

tip jets and barrier winds a quikscat climatology of high wind speed events around greenland the high topography of greenland results in a number of orographically induced high wind speed flows along its coast that are of interest from both a severe weather and climate perspective here the surface wind field dataset from the nasa jpl seawinds scatterometer on board the quick scatterometer quikscat satellite is used to develop a wintertime climatology of these flows the high spatial resolution and the twice daily sampling of the seawinds instrument allows for a much more detailed view of the surface winds around greenland than has been previously possible three phenomena stand out as the most distinctive features of the surface wind field during the winter months the previously identified tip jets and reverse tip jets as well as the hitherto unrecognized barrier flows along its southeast coast in the vicinity of the denmark strait peak surface wind speeds associated with these phenomena can be as large as 50 m s 1 with winds over 25 m s 1 occurring approximately 10 15 of the time at each location a compositing technique is used to show that each type of flow is the result of an interaction between a synoptic scale parent cyclone and the high topography of greenland in keeping with previous work it is argued that tip jets are caused by a combination of conservation of the bernoulli function during orographic descent and acceleration due to flow splitting as stable air passes around cape farewell while barrier winds are a geostrophic response to stable air being forced against high topography it is proposed that reverse tip jets occur when barrier winds reach the end of the topographic barrier and move from a geostrophic to a gradient wind balance becoming supergeostrophic as a result of their anticyclonic curvature

patterns and variability in geochemical signatures and microbial activity within and between diverse cold seep habitats along the lower continental slope northern gulf of mexico abstract we collected 69 sediment cores from distinct ecological and geological settings along the deep slope in the northern gulf of mexico to evaluate whether specific geochemical or habitat related factors correlated with rates of microbial processes and geochemical signatures by collecting replicate cores from distinct habitats across multiple sites we illustrate and quantify the heterogeneity of cold seep geochemistry and microbial activity these data also document the factors driving unique aspects of the geochemistry of deep slope gas oil and brine seeps surprisingly little variation was observed between replicate n 2 5 cores within sites for most analytes except methane implying that the common practice of collecting one core for geochemical analysis can capture the signature of a habitat in most cases depth integrated concentrations of methane dissolved inorganic carbon dic and calcium were the predominant geochemical factors that correlated with a site s ecological or geological settings pore fluid methane concentration was related to the phosphate and dic concentration as well as to rates of sulfate reduction while distinctions between seep habitats were identified from geochemical signatures habitat specific geochemistry varied little across sites the relative concentration of dissolved inorganic nitrogen versus phosphorus suggests that phosphorus availability limits biomass production at cold seeps correlations between calcium chloride and phosphate concentrations were indicative of brine associated phosphate transport suggesting that in addition to the co migration of methane dissolved organic carbon and ammonium with brine phosphate delivery is also associated with brine advection

strontium isotope stratigraphy potential resolution and event correlation abstract a new generation 87sr 86sr isotope curve for the phanerozoic seawater based on a compilation of 3635 stratigraphically well defined and well preserved skeletal components results in a substantially narrower band with some discrepancies if compared to the curve of burke et al 1982 which is based mostly on whole rock samples the results obtained from low mg calcite shells foraminifers belemnites brachiopods and oysters are mostly superior to those from phosphatic skeletal components such as conodonts even if the latter are exceptionally well preserved cai 1 5 at this stage the phanerozoic data set based on fossils is patchy for the cambrian upper ordovician lower devonian and upper carboniferous triassic intervals the major practical constraint that precludes delineation of an unequivocal sr isotope curve for the phanerozoic seawater is the uncertainty in the assignment of absolute ages to the samples as a result the curve is in reality a band this is a reflection of the limitations of biostratigraphy and geochronology that are inherited by any derivative correlation and dating technique including isotope stratigraphy it is therefore unlikely that in the near future the sr isotope stratigraphy will surpass the resolution capability of biostratigraphy as a global correlation tool on the other hand if complemented by lithostratigraphy it is potentially a valuable tool for correlation of sequences on intrabasinal and regional scales taking into account the above limitations careful consideration must be given to assignment of higher order isotope peaks to specific events within a biozone and to the use of such events as a global correlation tool

microbial activity in surficial sediments overlying acoustic wipeout zones at a gulf of mexico cold seep 1 down core concentration gradients of dissolved methane and sulfate isotope gradients of methane dissolved inorganic carbon and authigenic carbonate and organic matter elemental ratios are incorporated into a vent evolution model to describe spatial and temporal variability of sedimentary microbial activity overlying acoustic wipeout zones at mississippi canyon mc 118 gulf of mexico we tested the hypothesis that these zones indicate areas where sediments are exposed to elevated fluid flux and therefore should contain saturated methane concentrations and enhanced microbial activity from sulfate reduction sr anaerobic oxidation of methane aom and methanogenesis mp thirty surficial cores between 22 and 460 cm deep were collected from sediments overlying and outside the wipeout zones and analyzed for pore water and solid phase constituents outside the wipeout zones sulfate and methane concentrations were similar to overlying water values and did not vary with depth indicating low microbial activity above the wipeouts nine cores showed moderate activity with gently sloping sulfate and methane concentration gradients methane concentrations 20 m and isotope depth gradients indicative of organic matter oxidation in stark contrast to this moderate activity four cores showed high microbial activity where sulfate concentrations were depleted by 50 cm below seafloor maximum methane concentrations in the decompressed cores were above 4 mm and down core profiles of 13c ch4 and 13c dissolved inorganic carbon dic indicated distinct depth zones of sr aom and mp bulk organic matter analysis suggested that the high activity was supported by an organic source that was enriched in carbon c n 15 and depleted in 15n and 13c compared to other activity groups possibly due to the influx of petroleum or chemosynthetically fixed carbon within high activity cores the 13c dic values were similar to the 13c caco3 values a result expected for authigenic carbonate recently precipitated however these values were dissimilar in moderate activity cores suggesting that microbial activity was higher in the past this study provides evidence that the fluid flux at mc 118 varies over time and that the microbial activity responds to such variability it also suggests that sediments overlying wipeout zones are not always saturated with respect to methane which has implications for the formation and detection of gas hydrate

boundary currents and watermass transformation in marginal seas the properties of watermass transformation and the thermohaline circulation in marginal seas with topography and subject to a spatially uniform net surface cooling are discussed the net heat loss within the marginal sea is ultimately balanced by lateral advection from the open ocean in a narrow boundary current that flows cyclonically around the basin heat loss in the interior is offset by lateral eddy fluxes originating in the boundary current the objectives of this study are to understand better what controls the density of waters formed within the marginal sea the temperature of the outflowing waters the amount of downwelling and the mechanisms of heat transport within the marginal sea the approach combines heat budgets with linear stability theory for a baroclinic flow over a sloping bottom to provide simple theoretical estimates of each of these quantities in terms of the basic parameters of the system the theory compares well to a series of eddy resolving primitive equation model calculations the downwelling is concentrated within the boundary current in both a diffusive boundary layer near topography and an eddy driven region on the offshore edge of the boundary current for most high latitude regions the horizontal gyre is expected to transport more heat than does the overturning gyre

using strontium isotopes to determine the age and origin of gypsum and anhydrite beds the variation of 87sr 86sr in seawater with time can be used to determine the age of calcium sulfate beds precipitated from brine derived from seawater the determination of a marine origin can be established by the consistency of strontium isotope results from samples at different stratigraphic levels in a single gypsum anhydrite bed collected at separated sites the scatter of strontium isotope results in the gypsum anhydrite samples examined here is interpreted to result from the contribution of meteoric strontium to the salina strontium isotope results from three evaporite settings the jurassic todilto formation from new mexico the permian blaine formation from blaine county oklahoma and the permian salado formation from new mexico are used to determine the age and origin of the parent brine for these gypsum anhydrite beds the calcium sulfate beds from each of these formations precipitated from salinas that originated with a marine flooding but show at different times and localities volume do

observations of the labrador sea eddy field this paper is an observational study of small scale coherent eddies in the labrador sea a region of dense water formation thought to be of considerable importance to the north atlantic overturning circulation numerical studies of deep convection emphasize coherent eddies as a mechanism for the lateral transport of heat yet their small size has hindered observational progress a large part of this paper is therefore devoted to developing new methods for identifying and describing coherent eddies in two observational platforms current meter moorings and satellite altimetry details of the current and water mass structure of individual eddy events as they are swept past by an advecting flow can then be extracted from the mooring data a transition is seen during mid 1997 with long lived boundary current eddies dominating the central labrador sea year round after this time and convectively formed eddies similar to those seen in deep convection modeling studies apparent prior to this time the topex poseidon altimeter covers the labrador sea with a loose net of observations through which coherent eddies can seem to appear and disappear by concentrating on locating and describing anomalous events in individual altimeter tracks a portrait of the spatial and temporal variability of the underlying eddy field can be constructed the altimeter results reveal an annual pulsation of energy and of coherent eddies originating during the late fall at a particular location in the boundary current pinpointing the time and place of the boundary current type eddy formation the interannual variability seen at the mooring is reproduced but the mooring site is found to be within a localized region of greatly enhanced eddy activity notably lacking in both the annual cycle and interannual variability is a clear relationship between the eddies or eddy energy and the intensity of wintertime cooling these eddy observations as well as hydrographic evidence suggest an active role for boundary current dynamics in shaping the energetics and water mass properties of the interior region

clausthalite pbse and tiemannite hgse from the type locality new observations and implications for metallogenesis in the harz mountains germany abstract clausthalite and tiemannite from the type locality clausthal in the harz mountains germany have virtually gone undocumented since their discovery in the nineteenth century the minerals and their selenide assemblages are here documented in historical samples from the konigin charlotte mine in the former clausthal pb zn ag mining district clausthalite and tiemannite are the main selenide components naumannite is generally subordinate whereas klockmannite and eskebornite are accessory minerals the absence of inversion lamellae in naumannite constrains the formation temperature to 87 sr 86 sr values of 0 70914 and 0 71133 for two samples of tiemannite aggregates containing celestine anhydrite inclusions the clausthal selenide assemblages postdated the main sulfide bearing polymetallic vein style mineralisation of the harz mountains

labrador sea boundary currents and the fate of the irminger sea water abstract the general circulation of the labrador sea is studied with a dataset of 53 surface drifters drogued at 15 m and several hydrographic sections done in may 1997 surface drifters indicate three distinct speed regimes fast boundary currents a slower crossover from greenland to labrador and a slow eddy dominated flow in the basin interior mean eulerian velocity maps show several recirculation cells located offshore of the main currents in addition to the cyclonic circulation of the labrador sea above the northern slope of the basin the surface drifters have two preferential paths one between the 1000 m and 2000 m isobaths and the other close to the 3000 m isobath the vertical shear estimated from ctd data supports the presence of two distinct currents around the basin one current more baroclinic flows between the 1000 m and 2000 m isobaths the other one more barotropic flows above the lower continental slope the irminger sea water carried by the boundary currents is altered as it tr

numerical modeling of carbonate crust formation at cold vent sites significance for fluid and methane budgets and chemosynthetic biological communities at many cold vent sites authigenic carbonates precipitate due to the release of carbonate alkalinity during the anaerobic oxidation of methane carbonate precipitation often induces the formation of massive crusts at the sediment surface or within surface sediments the range of physical and biogeochemical conditions allowing for the formation of carbonate crusts is largely unknown so that the significance of these widespread manifestations of fluid flow is unclear here we use numerical modeling to investigate the conditions that induce carbonate crust formation in the sediment and the effect of crust formation on sediment porosity and fluid flow rate starting with the conditions prevailing at a previously investigated reference site located on hydrate ridge off oregon several parameters are systematically varied in a number of numerical experiments these parameters include coefficients of bioturbation and bioirrigation sedimentation rate fluid flow velocity methane concentration in the ascending vent fluids and ph and saturation state at the sediment water interface the simulations show that carbonate crusts in the sediments only form if the fluids contain sufficient dissolved methane 50 mm and if bioturbation coefficients are low 50 cm ka 1 inhibit crust formation bioirrigation induces a downward displacement of the precipitation zone and accelerates the formation of a solid crust crusts only form over a rather narrow range of upward fluid flow velocities 20 60 cm a 1 which is somewhat enlarged up to 90 cm a 1 if the overlying bottom waters are supersaturated with respect to calcite at higher flow rates methane is rapidly exported into the water column so that methane oxidation and carbonate precipitation cannot proceed within the surface sediment the formation of a several centimeters thick carbonate crust in surface sediments is typically completed after a few hundred years 100 500 a crust formation reduces the supply of methane to surface sediments which imposes a strong resistance against diffusive and advective methane transport therefore rates of anaerobic methane oxidation and sulfide production are diminished and thus the density and metabolism of chemosynthetic biological communities is limited by crust formation due to the moderate flow rates and the slow diffusive transport only very little methane escapes into the bottom water overlying carbonate encrusted vent areas

open ocean convection in the irminger sea open ocean deep convection is known to occur in a very few locations in the present climate convection is important for the ventilation of the oceans and for the operation of the meridional overturning circulation using data from ships and profiling floats we present evidence for the occurrence of convection in the irminger sea of the north atlantic south east of greenland confirmation of this convective site in the north atlantic will influence our understanding of the connection of the atmosphere to the ocean depths and of the mechanisms of climate variability

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

the sulfur and strontium isotopic compositions of permian evaporites from the zechstein basin northern germany the sulfur isotopic composition of stratigraphically well constrained samples from five evaporitic cycles of the german zechstein upper permian displays no systematic lateral variation and no significant temporal trend with an average 34s value close to 11 results confirm the previously determined sulfur isotope minimum for phanerozoic seawater least radiogenic 87sr 86sr ratios for these sulfates define a clear temporal variation with a minimum value at 0 707008 a conclusive assessment of this temporal trend in comparison with other data sets for upper permian seawater is not possible due to substantial differences in bio stratigraphic assignments

interdecadal variations of the thermohaline circulation in a coupled ocean atmosphere model abstract a fully coupled ocean atmosphere model is shown to have irregular oscillations of the thermohaline circulation in the north atlantic ocean with a time scale of approximately 50 years the irregular oscillation appears to be driven by density anomalies in the sinking region of the thermohaline circulation approximately 52 n to 72 n combined with much smaller density anomalies of opposite sign in the broad rising region the spatial pattern of see surface temperature anomalies associated with this irregular oscillation bears an encouraging resemblance to a pattern of observed interdecadal variability in the north atlantic the anomalies of sea surface temperature induce model surface air temperature anomalies over the northern north atlantic arctic and northwestern europe

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

intraformational fluid flow in the thuringian syncline germany evidence from stable isotope data in vein mineralization of upper permian and mesozoic sediments abstract vein mineralization observed in boreholes quarries and outcrops of upper permian and mesozoic sediments in the thuringian syncline germany was investigated for the first time by petrography electron microprobe analysis and stable isotope analysis the objective was a characterization of paleo fluid systems within this basin veins are mostly restricted to nw se trending fault systems and comprise carbonates calcite dolomite minor sulfates gypsum anhydrite celestite barite and rarely sulfides they are variably distributed within the late paleozoic to mesozoic succession calcite vein mineralization occurs in almost all triassic strata though dominating in the lower muschelkalk subgroup mu gypsum anhydrite veins occur in the middle keuper subgroup km middle muschelkalk subgroup mm middle and upper buntsandstein subgroup sm so as well as in the upper permian zechstein sulfate and carbonate isotope analyses indicate that most vein mineralization dominantly crystallized from intraformational fluids within the upper permian and triassic sediments crystallization from descending meteoric waters was observed especially for calcite veins in the lower muschelkalk but also for gypsum anhydrite veins in the upper buntsandstein mineralization from ascending carbonate ph buffered warm waters was restricted to individual parts of the southern deep reaching main border fault zone of the thuringian syncline mixing and fault crossing fluid movements are subordinate within the thuringian syncline we conclude that no large scale cross formational fluid flow occurred in thuringian syncline over the last millions of years

correlation and comparison of seawater δ34ssulfate records at the permian triassic transition abstract correlation of carbonate associated sulfate cas 34 s analysed permian triassic p tr sections via conodont biostratigraphy and sequence stratigraphy shows distinct phases in the oceanic 34 s sulfate evolution during the period 1 million years m y either side of the p tr boundary a 34 s sulfate rise in the changhsingian prior to the end permian mass extinction is followed by a period of about 350 000 years of erratic and substantial 34 s sulfate movements range 1 to 28 the mass extinction occurring in the middle of this period the sharp swings in this phase indicate severe changes in the oceanic sulfur geochemistry and perhaps stages of ocean inhomogeneity low 34 s sulfate values coincide with the mass extinction horizon suggesting the extinction is related to an input of relatively 32 s enriched sulfur into the oceanic sulfate reservoir the source of this sulfur most likely being h 2 s from euxinic waters after the erratic 34 s sulfate phase there is a stabilisation of 34 s sulfate values 17 until the later griesbachian however there is a possibility of discrepant panthalassan and tethyan data sets during the early to mid griesbachian but this requires further work for confirmation 34 s sulfate values are erratic in the late griesbachian to early dienerian suggesting further perturbation of the sulfur cycle the poorly age constrained smithian record shows a wide range of 34 s sulfate values probably indicating swings during that time also the 34 s sulfate movements from the changhsingian to smithian indicate the permian triassic transition is a time of intense changes in the sulfur fluxes to and from the oceans and perhaps stages of ocean inhomogeneity

hydrate ridge a natural laboratory for the study of microbial life fueled by methane from near surface gas hydrates hydrate ridge cascadia convergent margin is characterized by abundant methane hydrates at and below the seafloor active venting of fluids and gases chemosynthetic communities composed of giant sulfide oxidizing bacteria and clams authigenic carbonates and some of the highest methane oxidation rates ever found in the marine environment fluid flow rates vary over six orders of magnitude among closely spaced settings at the crest of hydrate ridge the distribution of benthic communities is mainly related to the sulfide flux from the subsurface sediments produced by anaerobic oxidation of methane aom even at high flux rates aom removes most of the methane seeping from the subsurface less than 50 of the methane escapes from bacterial mats from calyptogena fields 15 and from acharax beds no methane is emitted to the water column the precipitation of carbonate derived from aom is a significant and permanent carbon sink hence compared to the amount of gas hydrates and methane derived carbonates stored at the summit of hydrate ridge the emission of methane is relatively low due to the efficient filtering capacity of methanotrophic microbial communities this present review updates current knowledge of the geology of hydrate ridge summarizes recently published data on geomicrobiology and biogeochemistry and derives a local methane budget

benthic respiration in a seep habitat dominated by dense beds of ampharetid polychaetes at the hikurangi margin new zealand many biological seep studies focused on the distribution structure nutrition and food web architecture of seep communities as well as on their interaction with the seep geochemistry however overall respiration at cold seeps received only little attention we conducted in situ oxygen flux measurements in combination with ex situ oxygen micro profiles respiration measurements as well as rate determinations of microbial methane and sulfate turnover to assess respiration pathways as well as carbon turnover at a seep habitat that was recently discovered alongside the hikurangi margin offshore northern new zealand this habitat is dominated by dense beds of tube building heterotrophic ampharetid polychaetes average total oxygen uptake tou from this habitat was very high 83 7 mmol m 2 day 1 tou at a non seep reference site ranged between 2 7 and 5 8 mmol m 2 day 1 about 37 30 8 mmol m 2 day 1 of the average tou was consumed by ampharetids considering mean diffusive oxygen uptake 8 5 mmol m 2 day 1 the remaining fraction of 53 of the tou 44 4 mmol m 2 day 1 might be explained by respiration of epibenthic organisms as well as aerobic methane and sulfide oxidation at the sediment water interface the strongly negative carbon isotopic signatures 52 9 5 vpdb of the ampharetid tissues indicate a methane derived diet however carbon production via anaerobic oxidation of methane aom was too low 0 1 mmol c m 2 day 1 to cover the mean carbon demand of the ampharetid communities 21 mmol c m 2 day 1 likely organic carbon generated via aerobic methane oxidation represents their major carbon source this is in contrast to other seep habitats where energy bound in methane is partly transferred to sulfide via aom and finally consumed by sulfide oxidizing chemoautotrophs providing carbon that subsequently enters the benthic food web

biogeochemical signatures and microbial activity of different cold seep habitats along the gulf of mexico deep slope abstract microorganisms and the processes they mediate serve as the metabolic foundation of cold seeps we characterized a suite of biogeochemical constituents and quantified rates of two key microbial processes sulfate reduction sr and anaerobic oxidation of methane aom to assess variability between habitats at water depths exceeding 1000 m in the northern gulf of mexico rates of sr were highest in sediments beneath microbial mats lower in brine influenced and oil influenced sediments and lowest in animal habitats sediments collected near tubeworms had the highest sr rates for animal habitats rates of aom generally were low but higher rates were associated with brine influenced oil influenced tubeworm and urchin inhabited sediments rates of both sr and aom were orders of magnitude lower at deep slope sites compared to upper slope sites examined previously as observed at upper slope sites sr and aom rates were often loosely coupled at one site aom rates exceeded sr rates suggesting that an alternate electron acceptor for aom is possible extremely depleted 13c values in methane illustrated the broad significance of biogenic methane production at deep slope sites brine influenced habitats were characterized by extremely high concentrations of ammonium and dissolved organic carbon serving as important focused sources of these chemicals to adjacent environments

numerical modeling of gas hydrate emplacements in oceanic sediments we have implemented a 2 dimensional numerical model for simulating gas hydrate and free gas accumulation in marine sediments the starting equations are those of the conservation of the transport of momentum energy and mass as well as those of the thermodynamics of methane hydrate stability and methane solubility in the pore fluid these constitutive equations are then integrated into a finite element in space finite difference in time scheme we are then able to examine the formation and distribution of methane hydrate and free gas in a simple geologic framework with respect to the geothermal heat flow fluid flow the methane in situ production and basal flux three simulations are performed leading to the build up of hydrate emplacements largely linear through time models act primarily as free gas accumulators and are relatively inefficient with respect to hydrate emplacements 26 33 of formed methane are converted to hydrate seepage of methane across the sea floor is negligible for fluid flow below 2 10 11 kg m2 s at 5 625 10 11 kg m2 s however 9 7 of the formed methane seeps out of the model moreover along strike variation arising in the 2 dimensional model are outlined in the absence of focused flow the thermodynamics of hydrate accumulation are primarily one dimensional however changes in free methane compressibility density and methane solubility the intrinsic dissolved methane flux subtlety impact on the formation of a free gas zone and the distribution of the hydrate emplacements in our 2 dimensional simulations

40ar 39ar dating of late permian evaporites southeastern new mexico usa 40ar 39ar dating of the potassium magnesium sulfate mineral langbeinite from permian evaporites of the salado formation near carlsbad new mexico provides quantitative evidence that some salts in these deposits have not recrystallized for 251 myr since deposition survival of permian salts supports the possibility that bacillus bacteria recovered from nearby halite was isolated in a closed system and represents a sample of uncontaminated permian life local recrystallization of langbeinite and other nearby minerals is also indicated by the dating suggesting both the need and the opportunity to document closed system behavior more rigorously the shoaling and desiccation event recorded by the salado formation began at least 1 myr before the permian triassic boundary temporal correlation of the salado with the zechstein evaporites of north central europe supports previously inferred regression models for the origin of these deposits significant paleoenvironmental change at the permian triassic boundary thus occurred on a time scale more protracted than that implied by geologically instantaneous events such as bolide impacts

the thermal structure of the dvurechenskii mud volcano and its implications for gas hydrate stability and eruption dynamics the sediment temperature distribution at mud volcanoes provides insights into their activity and into the occurrence of gas hydrates if ambient pressure and temperature conditions are close to the limits of the gas hydrate stability field the sediment temperature distribution not only limits the occurrence of gas hydrates but is itself influenced by heat production and consumption related to the formation and dissociation of gas hydrates located in the sorokin trough in the northern black sea the dvurechenskii mud volcano dmv was in the focus of detailed investigations during the m72 2 and m73 3a cruises of the german r v meteor and the rov quest 4000 m in february and march 2007 a large number of in situ sediment temperature measurements were conducted from the rov and with a sensor equipped gravity corer gas hydrates were sampled in pressurized cores using a dynamic autoclave piston corer dapc the thermal structure of the dmv suggests a regime of fluid flow at rates decreasing from the summit towards the edges of the mud volcano accompanied by intermittent mud expulsion at the summit modeled gas hydrate dissociation temperatures reveal that the gas hydrates at the dmv are very close to the stability limits changes in heat flow due to variable seepage rates probably do not result in changes in sediment temperature but are compensated by gas hydrate dissociation and formation c 2009 elsevier ltd all rights reserved

tide driven deep pore water flow in intertidal sand flats sulfidic seeps with methane ebullition were observed at the low water line of intertidal sand flats at a number of locations in the wadden sea bioturbating fauna was absent in the seep areas but abundant in the more central areas of the tidal flat at one site the vertical methane and sulfate distribution in pore water was determined along transects from the low water line toward the interior of the sand flat the resulting two dimensional distributions showed a plume of methane rich and sulfate depleted pore water reaching from a depth below 1 2 m beneath the sand surface up to the sediment surface at the low water line the 13c of methane released at the seeps was 68 6 indicating a biological origin the 14c signature of methane was clearly elevated by anthropogenic radiocarbon which shows that the methane was formed less than 50 yr ago the observations indicate an internal circulation where water enters the sand flats in the central area and exits at the low water line pore water flow patterns in the sand flat during the tidal cycle were calculated from the surface topography and from the pressure distribution at the flat surface across the tidal cycle the calculated flow patterns explain the measured methane and sulfate distributions and predict a residence time of the seepage water of about 30 yr intertidal sand flats act as one way valves passing water from the central surface through the interior of the flat to an outflow zone at and below the low water line with a velocity of millimeters to centimeters per day the flow causes permeable tidal flats to emit methane to the surface water and atmosphere in substantial amounts 2008 by the american society of limnology and oceanography inc

in situ sediment temperature measurements and geochemical porewater data suggest highly dynamic fluid flow at isis mud volcano eastern mediterranean sea isis mud volcano is located on the upper slope of the nile deep sea fan and has been described as the surface expression of a deep seated gas chimney loncke l gaullier v mascle j vendeville b 2002 shallow structure of the nile deep sea fan interactions between structural heritage and salt tectonics consequences on sedimentary dispersal in ciesm ed turbidite systems and deep sea fans of the mediterranean and the black seas ciesm workshop series vol 17 monaco detailed geothermal and geochemical investigations of isis mv have been carried out during the nautinil 2003 and mimes 2004 cruises within the framework of the euro margins mediflux project sediment temperatures of more than 40 c at 10 m below the seafloor at the center of the mud volcano indicate an exceptionally high level of activity rapidly decreasing temperature gradients away from the center support the hypothesis of a dominantly axisymmetric functioning of isis mv the microbathymetry along dive tracks of the submersible nautile reveals the presence of terraces and shows that the temperature gradients at shallow sediment depth follow the morphology at the center porewater profiles are characterized by a rapid decrease of chlorinity within the uppermost meter of the sediments whereas the chlorinity of cores taken at short distances away is equal to bottom water values applying simple analytical models to the data provides evidence of recent mud volcano activity but no straightforward explanation of the observed anomalies which points to a transient regime of variable fluid flow possibly accompanied by episodic mud eruptions numerical modeling suggests that rapid cooling of the sediment column and downward progression of the sharp decrease in porewater chlorinity observed between the two cruises is related to episodic infiltration of bottom seawater into the mud

fluid flow or mud eruptions sediment temperature distributions on hakon mosby mud volcano sw barents sea slope hakon mosby mud volcano is located on the sw barents sea slope at a water depth of approximately 1250 m in situ temperature measurements using gravity corers equipped with autonomous temperature loggers and a short temperature lance operated by an rov were collected during three cruises between 2003 and 2006 revealing an exceptionally high level of activity and a complex thermal structure of the mud volcano simple analytical models were applied to the measured data to estimate rates of specific discharge and to test the hypothesis of episodic mud eruptions strongly curved profiles from 4 to 16 m below the seafloor suggest fluid flow at rates from 1 m year close to the limits of the central area to more than 4 m year approaching the geometrical center at the limits of the central area the profiles show distinct maxima at sediment depths of about 10 to 15 m which are interpreted as the result of lateral flow repeated measurements at shallow depths along a transect crossing the central area revealed a persistent pattern of temperature gradients while changes in the absolute values point to temporal variability temperatures gradients of more than 40 c m within the upper half meter of the sediments close to the geometrical center suggest even higher rates of specific discharge than estimated from the deeper profiles these high rates of fluid flow are most likely accompanied by frequent mud eruptions of small volume and limited local extent

the production of north atlantic deep water sources rates and pathways updating an earlier account by dickson et al 1990 this paper reviews the initial development phase of north atlantic deep water nadw production from the points where the dense inflows from nordic seas cross the greenland scotland ridge to the point off south greenland where the buildup of new production appears almost complete in particular three long term current meter arrays totaling 91 instruments and set at 160 km intervals south from the denmark strait sill are used to validate earlier short term arrays by others and in combination with these earlier arrays to describe the downstream evolution of mean speed depth and entrainment the variability of the overflow current in space and time and the likely contribution of the other three main constituents of nadw production at densities greater than 27 8 from the points of overflow 5 6 sv the transport within this range increases by entrainment and confluence with other contributory streams to around 13 3 sv at cape farewell while recirculating elements prevent us from determining the net southgoing transport a nadw transport of this order appears consistent with recent estimates of net abyssal flow passing south through the north and south atlantic

variation in 87 sr 86 sr of permian seawater an overview the strontium isotope ratio 87sr s6sr of seawater has changed significantly through time in response to variations in the input of sr to the oceans from various crust and upper mantle sources with differing 87sr 86sr values an important aspect of this temporal variation is the empirical finding that while the 87sr 86sr of seawater may vary through time at any given time the sr isotope ratio of the oceans is everywhere the same isotopic uniformity is achieved because the marine residence time of sr 4 x 106 yr is long e g veizer 1989 compared to the oceanic circulation time 103 yr the oceans therefore are well mixed with respect to both sr and sr isotope ratio and all coeval marine derived carbonates sulfates and phosphates will possess the same initial 87sr s6sr value consequently the temporal changes in the 87sr s6sr of seawater can be used to correlate and date marine strata and can provide insight into the global processes that have shaped our world

quantification of methane emission from bacterial mat sites at quepos slide offshore costa rica seafloor methane emission from the quepos slide on the submarine segment of the costa rica fore arc margin was estimated by extrapolating flux measurements from individual seeps to the total area covered by bacterial mats this approach is based on the combination of detailed mapping to determine the abundance of seeps and the application of a numerical model to estimate the amount of benthic methane fluxes model results suggest that the majority of the studied seeps transport rather limited amount of methane on average 177 mol cm 2 a 1 into the water column due to moderate upward advection allowing for intense anaerobic oxidation of methane aom on average 53 of the methane flux is consumed depth integrated aom rates 56 1 538 mol ch4 cm 2 a 1 are comparable with values reported from other active seep sites the overall amount of dissolved methane released into the water column from the entire area covered by bacterial mats on the quepos slide is estimated to be about 0 28 106 mol a 1 this conservative estimate which relies on rather accurate determinations of seafloor methane fluxes emphasizes the potential importance of submarine slides as sites of natural methane seepage however at present the global extent of methane seepage from submarine slides is largely unknown

spatial distribution of mud flows chemoautotrophic communities and biogeochemical habitats at hakon mosby mud volcano marine mud volcanoes are significant source locations contributing to the marine methane cycle enhanced heat flow unique chemoautotrophic communities occurrence of massive gas hydrates and large gas plumes are direct evidences of elevated methane concentrations and the dynamic environment of mud volcanoes related to the high concentrations and large inventories of ch4 in surface sediments only a fraction of the methane is exported to the bottom water this is mainly due to chemoautotrophic communities oxidizing methane and proving a microbial filter reducing ch4 fluxes although these processes were studied for several mud volcanoes still little is known about the spatial pattern and the areas covered by chemoautotrophic communities or by present mud flows for this purposes the hakon mosby mud volcano hmmv which is located at the continental slope of the barents sea was studied by several dives with the remotely operated vehicle victor6000 during these dives a high resolution microbathymetric map with a footprint of 25 25 cm and a vertical resolution of better than 10 cm was derived furthermore video streams of the bottom camera were converted into georeferenced mosaics providing a detailed image about the spatial distribution of seafloor features as bacterial mats pogonophorans both indicating methane oxidation or mud flows based on visual inspection of 2310 georeferenced mosaics covering an area of 46 160 m 2 different biogeochemical habitats were identified and quantified on a m 2 basis by application of geostatistic techniques as indicator kriging the distribution of different biogeochemical habitats was quantified and mapped for the entire hmmv considering the flat and hummocky area of hmmv approximately 16 115 165 m 2 of the flat centre is nearly void of any benthic communities this area is considered as a region of high methane discharge into bottom water an area of 5 38 244 m 2 located in the south eastern part is densely inhabited by beggiatoa the hummocky outer part is colonised dominantly by pogonophoran tube worms 37 3 276 121 m 2 and only occasional by beggiatoa source locations and drainage directions for current mud flows were identified by computation of trend surfaces and consideration of temperature data this suggests that present mud flow ascend close to the northern edge of the flat unit of hmmv and that the drainage pattern of mud flows shifted from a westward to a south south eastern direction 2007 elsevier b v all rights reserved

intermediate sulfur oxidation state compounds in the euxinic surface sediments of the dvurechenskii mud volcano black sea abstract the deep black sea is known to be depleted in electron acceptors for sulfide oxidation this study on depth distributions of sulfur species s ii s 0 s n 2 s 2 o 3 2 so 3 2 so 4 2 in the dvurechenskii mud volcano a cold seep situated in the permanently anoxic eastern black sea basin sorokin trough 2060 m water depth showed remarkable concentrations of sulfide oxidation products sulfite concentrations of up to 11 mol l 1 thiosulfate concentrations of up to 22 mol l 1 zero valent sulfur concentrations of up to 150 mol l 1 and up to five polysulfide species were measured in the upper 20 cm of the sediment electron acceptors found to be available in the dvurechenskii mud volcano dmv for the oxidation of hydrogen sulfide to sulfide oxidation intermediates are iron minerals and probably also reactive manganese phases up to 60 mol g 1 of reactive iron minerals and up to 170 mol l 1 dissolved iron was present in the central summit with the highest fluid upflow and fresh mud outflow thus the source for the oxidative power in the dmv are reactive iron phases extruded with the mud from an ancient source in the deeply buried sediments leading to the formation of various sulfur intermediates in comparably high concentrations another possible source of sulfide oxidation intermediates in dmv sediments could be the formation of zero valent sulfur by sulfate dependent anaerobic microbial oxidation of methane followed by disproportionation of zero valent sulfur sulfide oxidation intermediates which are produced by these processes do not reach thermodynamic equilibrium with rhombic sulfur especially close to the active center of the dmv due to a short equilibration time thus mud volcano sediments such as in the dmv can provide oxidizing niches even in a highly reduced environment like the abyssal part of the black sea

down the thermodynamic ladder a comparative study of marine redox gradients across diverse sedimentary environments the thermodynamic succession of electron acceptors used in microbial oxidation of organic matter and associated redox products lead to the vertical chemical zonation in diffusion controlled marine sediments the structure of this gradient is a key player in the recycling of organic carbon and nutrients in the marine environment however little attention has been given to the advection dominated sedimentary systems where the co existence of different reduced and oxidized chemical species is expected in this study performing multi analyte au hg voltammetric microelectrode profiling on cores from diverse sediment depositional settings in the mediterranean sea lagoon coastal marine submarine canyon and shallow water vent sediments it is shown that there exists an excess of reducing species h2s mn2 fe2 and fesaq in the advective shallow vent sediments compared to similar upper sediment sections of diffusion controlled environments the ex situ upward diffusive flux of reduced species accounted for at least 26 percent of oxygen consumption in the shallow water vent sediments and this figure is likely higher when in situ advective fluxes and the oxidation of other known vent derived reduced components are taken into account in contrast the upward fluxes of reduced species do not significantly contribute to oxygen consumption in the studied lagoon coastal or submarine canyon sediments where organic matter oxidation by oxygen likely dominates a major implication of these findings is that the reduced substrate advection in shallow vents leads to a potential for chemoautotrophy in an otherwise oligotrophic marine system whereas in diffusion controlled sediments the vertical input of organic matter and its heterotrophic use is more important

microbial distributions detected by an oligonucleotide microarray across geochemical zones associated with methane in marine sediments from the ulleung basin abstract the biogeochemical processes that occur in marine sediments on continental margins are complex however from one perspective they can be considered with respect to three geochemical zones based on the presence and form of methane sulfate methane transition smtz gas hydrate stability zone ghsz and free gas zone fgz these geochemical zones may harbor distinct microbial communities that are important in biogeochemical carbon cycles the objective of this study was to describe the microbial communities in sediments from the smtz ghsz and fgz using molecular ecology methods i e phylochip microarray analysis and terminal restriction fragment length polymorphism t rflp and examining the results in the context of non biological parameters in the sediments non metric multidimensional scaling and multi response permutation procedures were used to determine whether microbial community compositions were significantly different in the three geochemical zones and to correlate samples with abiotic characteristics of the sediments this analysis indicated that microbial communities from all three zones were distinct from one another and that variables such as sulfate concentration hydrate saturation of the nearest gas hydrate layer and depth or unmeasured variables associated with depth e g temperature pressure were correlated to differences between the three zones the archaeal anaerobic methanotrophs typically attributed to performing anaerobic oxidation of methane were not detected in the smtz however the marine benthic group b which is often found in smtz was detected within the ghsz samples that were typically closer to layers that contained higher hydrate saturation had indicator sequences related to vibrio type taxa these results suggest that the biogeographic patterns of microbial communities in marine sediments are distinct based on geochemical zones defined by methane

microbial methane turnover at mud volcanoes of the gulf of cadiz the gulf of cadiz is a tectonically active area of the european continental margin and characterised by a high abundance of mud volcanoes diapirs pockmarks and carbonate chimneys during the r v sonne expedition gap gibraltar arc processes so 175 in december 2003 several mud volcanoes were surveyed for gas seepage and associated microbial methane turnover pore water analyses and methane oxidation measurements on sediment cores recovered from the centres of the mud volcanoes captain arutyunov bonjardim ginsburg gemini and a newly discovered mud volcano like structure called no name show that thermogenic methane and associated higher hydrocarbons rising from deeper sediment strata are completely consumed within the seabed the presence of a distinct sulphate methane transition zone smt overlapping with high sulphide concentrations suggests that methane oxidation is mediated under anaerobic conditions with sulphate as the electron acceptor anaerobic oxidation of methane aom and sulphate reduction sr rates show maxima at the smt which was found between 20 and 200 cm below seafloor at the different mud volcanoes in comparison to other methane seeps aom activity 383 mmol m 2 year 1 and diffusive methane fluxes 321 mmol m 2 year 1 in mud volcano sediments of the gulf of cadiz are low to mid range corresponding lipid biomarker and 16s rdna clone library analysis give evidence that aom is mediated by a mixed community of anaerobic methanotrophic archaea and associated sulphate reducing bacteria srb in the studied mud volcanoes little is known about the variability of methane fluxes in this environment carbonate crusts littering the seafloor of mud volcanoes in the northern part of the gulf of cadiz had strongly 13c depleted lipid signatures indicative of higher seepage activities in the past however actual seafloor video observations showed only scarce traces of methane seepage and associated biological processes at the seafloor no active fluid or free gas escape to the hydrosphere was observed visually at any of the surveyed mud volcanoes and biogeochemical measurements indicate a complete methane consumption in the seafloor our observations suggest that the emission of methane to the hydrosphere from the mud volcano structures studied here may be insignificant at present

thermohaline circulation at three key sections in the north atlantic over 1985 2002 efforts are presently underway to monitor the thermohaline circulation thc in the north atlantic a measuring strategy has been designed to monitor both the meridional overturning circulation moc in the subtropics and dense outflows at higher latitudes to provide a historical context for these new observations we diagnose an eddy permitting ocean model simulation of the period 1985 2002 we present time series of the thc moc and heat transport at key hydrographic sections in the subtropics the northeast atlantic and the labrador sea the simulated thc compares well with observations we find considerable variability in the thc on each section most strikingly in the labrador sea during the early 1990 s consistent with observed changes overturning in the northeast atlantic declines by 20 over the 1990 s coincident with an increase in the subtropics we speculate that moc weakening may soon be detected in the subtropics if the decline continues in mid latitudes

impact of labrador sea convection on the north atlantic meridional overturning circulation abstract the overturning and horizontal circulations of the labrador sea are deduced from a composite vertical section across the basin the data come from the late spring early summer occupations of the world ocean circulation experiment woce ar7w line during the years 1990 97 this time period was chosen because it corresponded to intense wintertime convection the deepest and densest in the historical record suggesting that the north atlantic meridional overturning circulation moc would be maximally impacted the composite geostrophic velocity section was referenced using a mean lateral velocity profile from float data and then subsequently adjusted to balance mass the analysis was done in depth space to determine the net sinking that results from convection and in density space to determine the diapycnal mass flux i e the transformation of light water to labrador sea water the mean overturning cell is calculated to be 1 sv 1 sv 106 m3 s 1 as compared with a horizontal gyre of 18 sv the

multifrequency geoacoustic imaging of fluid escape structures offshore costa rica implications for the quantification of seep processes quantification of fluid fluxes from cold seeps depends on accurate estimates of the spatial validity of flux measurements these estimates are strongly influenced by the choice of geoacoustic mapping tools multibeam bathymetry side scan sonar and chirp subbottom profiler data of several mound shaped cold seeps offshore central costa rica show great variety in morphology and structure although the features are only a few kilometers apart mound 11 a 35 m high and 1000 m in diameter structure situated in the se of the study area has an irregular morphology but a smooth surface on side scan sonar data while mound 12 30 m high 600 m across is a cone of more regular outline but with a rough surface and mound grillo 5 m high 500 m across shows the same rough surface as mound 12 but without relief video observations and sediment cores indicate that the structures are formed by the precipitation of authigenic carbonates and indications for extensive mud extrusion are absent except for one possible mudflow at mound 11 different sonar frequencies result in variable estimates of the extent of these mounds with low frequencies suggesting much wider cold seeps consequently overestimating fluid fluxes the absence of mud volcanism compared to accretionary prisms where mud volcanism occurs is related to different tectonic styles strong sediment overpressure and thrust faulting in typical accretionary prisms can generate mud volcanism while subduction erosion and normal faulting extension of the overriding plate at the costa rican margin result in fluid venting driven by only slight fluid overpressures

u pb calcite age of the late permian castile formation delaware basin a constraint on the age of the permian triassic boundary abstract organic rich calcite laminated with gypsum in the evaporitic non fossiliferous castile formation of the delaware basin southwest usa yields a total pb u isochron age of 251 5 2 8 ma mswd 1 3 the castile formation is almost certainly late permian based on its 87 sr 86 sr value of 0 706923 identical to the distinct minimum in the late permian sr curve in this paper we explore the potential for using u pb calcite ages to date traditionally undatable sections and show how this southern midcontinent usa far west texas and southeast new mexico deposit can be correlated to the type section in china we accept that diagenetic alteration can bias u pb results but the data set we present shows no evidence for such alteration clearly with alteration the age we present would represent a minimum age for the castile formation if the age actually dates the castile formation then it requires the permian triassic boundary to be younger than 251 5 2 8 ma

cold seep like macrofaunal communities in organic and sulfide rich sediments of the congo deep sea fan methane rich fluids arising from organic matter diagenesis in deep sediment layers sustain chemosynthesis based ecosystems along continental margins this type of cold seep develops on pockmarks along the congo margin where fluids migrate from deep buried paleo channels of the congo river acting as reservoirs similar ecosystems based on shallow methane production occur in the terminal lobes of the present day congo deep sea fan which is supplied by huge quantities of primarily terrestrial material carried by turbiditic currents along the 800 km channel and deposited at depths of up to nearly 5000 m in this paper we explore the effect of this carbon enrichment of deep sea sediments on benthic macrofauna along the prograding lobes fed by the current active channel and on older lobes receiving less turbiditic inputs macrofaunal communities were sampled using either usnel cores on the channel levees or rov blade cores in the chemosynthesis based habitats patchily distributed in the active lobe complex the exceptionally high organic content of the surface sediment in the active lobe complex was correlated with unusual densitiesof macrofauna for this depth enhanced by a factor 7 to 8 compared with those of the older abandoned lobe whose sediment carbon content is still higher than in angola basin at same depth macrofaunal communities dominated by cossurid polychaetes and tanaids were also more closely related to those colonizing low flow cold seeps than those of typical deep sea sediment in reduced sediments microbial mats and vesicomyid bivalve beds displayed macrofaunal community patterns that were similar to their cold seep counterparts with high densities low diversity and dominance of sulfide tolerant polychaetes and gastropods in the most sulfidic habitats in addition diversity was higher in vesicomyid bivalve beds which appeared to bio irrigate the upper sediment layers high beta diversity is underscored by the variability of geochemical gradients in vesicomyid assemblages and by the vesicomyid population characteristics that vary in density size and composition by modifying the sediment geochemistry differently according to their morphology and physiology the different vesicomyid species play an important role structuring macrofauna composition and vertical distribution dynamics of turbiditic deposits at a longer temporal scale thousands of years and their spatial distribution in the lobe area also resulted in high heterogeneity of the cold seep like communities dynamics of chemosynthetic habitats and associated macrofauna in the active lobe area 2 please note that this is an author produced pdf of an article accepted for publication following peer review the definitive publisher authenticated version is available on the publisher web site resembled those previously observed at the regab pockmark along the congo margin and rapid succession is expected to cope with high physical disturbance by frequent turbiditic events and huge sedimentation rates finally we propose a model of the temporal evolution of these peculiar habitats and communities on longer timescales in response to changes in distributary channels within the lobe complex

multiple sulfur isotopic evidence for the origin of elemental sulfur in an iron dominated gas hydrate bearing sedimentary environment abstract elemental sulfur is commonly regarded as the product of oxidative sulfur cycling in the sediment however reports on the occurrence of elemental sulfur in seepage areas are few and thus its origin and mechanisms controlling its distribution are insufficiently understood here we analyzed the multiple sulfur isotopic compositions for elemental sulfur and pyrite from an iron dominated gas hydrate bearing sedimentary environment of the south china sea to unravel the impact of sulfate driven anaerobic oxidation of methane so4 aom on the formation of elemental sulfur the multiple sulfur isotopes reveal variable ranges for both elemental sulfur and pyrite 34s between 15 7 and 23 3 for elemental sulfur and between 35 3 and 34 4 for pyrite 33s between 0 08 and 0 06 for elemental sulfur and between 0 03 and 0 15 for pyrite the enrichment of 34s in pyrite throughout the sediment core suggests pronounced so4 aom in paleo sulfate methane transition zones smtz in addition the occurrence of seep carbonates with very negative 13c values as low as 57 v pdb coincides with the inferred paleo smtzs and agrees with formerly locally pronounced so4 aom interestingly the multiple sulfur isotopic composition of elemental sulfur reveals a different pattern from that of pyrite derived from organoclastic sulfate reduction i e with low 34s and high 33s values for the latter in comparison to coexisting pyrite most of the elemental sulfur reveals higher 34s values as much as 28 9 which is best explained by an enrichment of 34s in the residual pool of dissolved sulfide generated by so4 aom as an intermediate sulfur phase elemental sulfur can form via sulfide oxidation coupled to iron reduction but it can only persist in the absence of free sulfide therefore the occurrence of 34s enriched elemental sulfur is likely to represent an oxidative product after hydrogen sulfide had vanished due to vertical displacement of the smtz our observations suggest that elemental sulfur may serve as a useful recorder for reconstructing the dynamics of sulfur cycling in modern and possibly ancient seepage areas

ventilation and transformation of labrador sea water and its rapid export in the deep labrador current a model of the subpolar north atlantic ocean is used to study different aspects of ventilation and water mass transformation during a year with moderate convection intensity in the labrador sea the model realistically describes the salient features of the observed hydrographic structure and current system including boundary currents and recirculations ventilation and transformation rates are defined and compared the transformation rate of labrador sea water lsw defined in analogy to several observational studies is 6 3 sv sv 106 m3 s 1 in the model using an idealized ventilation tracer mimicking analyses based on chlorofluorocarbon inventories an lsw ventilation rate of 10 sv is found differences between both rates are particularly significant for those water masses that are partially transformed into denser water masses during winter the main export route of the ventilated lsw is the deep labrador current lc backward calculation of particle trajectories demonstrates that about one half of the lsw leaving the labrador sea within the deep lc originates in the mixed layer during that same year near the offshore flank of the deep lc at about 55 w the transformation of lsw begins in january and is at a maximum in february march while the export of transformed lsw out of the central labrador sea continues for several months lsw generated near the boundary current is exported more rapidly with maximum transport rates during march april within the deep lc

winter mixed layer development in the central irminger sea the effect of strong intermittent wind events abstract the impact of the greenland tip jet on the wintertime mixed layer of the southwest irminger sea is investigated using in situ moored profiler data and a variety of atmospheric datasets the mixed layer was observed to reach 400 m in the spring of 2003 and 300 m in the spring of 2004 both of these winters were mild and characterized by a low north atlantic oscillation nao index a typical tip jet event is associated with a low pressure system that is advected by upper level steering currents into the region east of cape farewell and interacts with the high topography of southern greenland heat flux time series for the mooring site were constructed that include the enhancing influence of the tip jet events this was used to force a one dimensional mixed layer model which was able to reproduce the observed envelope of mixed layer deepening in both winters the deeper mixed layer of the first winter was largely due to a higher number of robust tip jet events which in turn was caused by the stee

hydrography of the labrador sea during active convection the hydrographic structure of the labrador sea during wintertime convection is described the cruise part of the deep convection experiment took place in february march 1997 amidst an extended period of strong forcing in an otherwise moderate winter because the water column was preconditioned by previous strong winters the limited forcing was enough to cause convection to approximately 1500 m the change in heat storage along a transbasin section relative to an occupation done the previous october gives an average heat loss that is consistent with calibrated national centers for environmental prediction surface heat fluxes over that time period 200 wm 22 deep overturning was observed both seaward of the western continental slope which was expected as well as within the western boundary current itself something that had not been directly observed previously these two geographical regions separated by roughly the 3000 m isobath produce separate water mass products the offshore water mass is the familiar cold fresh dense classical labrador sea water lsw the boundary current water mass is a somewhat warmer saltier lighter vintage of classical lsw though in the far field it would be difficult to distinguish these products the offshore product was formed within the cyclonic recirculating gyre measured by lavender et al in a region that is limited to the north most likely by an eddy flux of buoyant water from the eastern boundary current the velocity measurements taken during the cruise provide a transport estimate of the boundary current throughput and offshore recirculation finally the overall trends in stratification of the observed mixed layers are described

eddy kinetic energy of the north atlantic subpolar gyre from satellite altimetry the surface eddy kinetic energy field of the north atlantic subpolar gyre 40 65 n 5 60 w is studied using the altimetric satellites geosat 1987 1988 and ers 1 1992 1993 this is on the whole an area of low eddy activity previous studies of the north atlantic have usually concentrated on the highly variable gulf stream system we review what is known of the surface circulation of the region we confirm that there is a close relationship between the eddy kinetic energy and the mean currents and that it is strongly constrained by the topography the eddy field occurs in deep water and follows the contours particularly around the flemish cap high eddy kinetic energy is seen on the flanks of topography and is higher where the slope is steeper this is particularly clear on both east and west flanks of the rockall plateau interannual changes in the currents are revealed by the differences between the geosat and ers 1 eddy kinetic energy maps in some years 1988 and 1992 1993 the northern core of the north atlantic current nac usually assumed to be tied to the charlie gibbs fracture zone 52 n is considerably weaker and may not exist at all while in 1987 there is a distinct core here in 1988 and 1992 1993 the main eddy region shifts farther to the south to about 49 n in 1988 and 50 n in 1992 1993 in 1987 there is also a current core even farther south centered at about 47 n implying that in that year the nac is arranged into two distinct branches

permian strontium isotope stratigraphy cvu acknowledges funding from the leopoldina german national academy of sciences grant no lpds 2014 08

early diagenesis in the sediments of the congo deep sea fan dominated by massive terrigenous deposits part iii sulfate and methane based microbial processes abstract geochemical profiles so 4 2 h 2 s ch 4 13 ch 4 and phylogenetic diversity of archaea and bacteria from two oceanographic cruises dedicated to the lobes sediments of the congo deep sea fan are presented in this paper in this area organic rich turbidites reach 5000 m and allow the establishment of patchy cold seep like habitats including microbial mats reduced sediments and vesicomyid bivalves assemblages these bivalves live in endosymbiosis with sulfur oxidizing bacteria and use sulfides to perform chemosynthesis in these habitats unlike classical abyssal sediments anoxic processes are dominant total oxygen uptake fluxes and methane fluxes measured with benthic chambers are in the same range as those of active cold seep environments and oxygen is mainly used for reoxidation of reduced compounds especially in bacterial mats and reduced sediments high concentrations of methane and sulfate co exist in the upper 20 cm of sediments and evidence indicates that sulfate reducing microorganisms and methanogens co occur in the shallow layers of these sediments simultaneously anaerobic oxidation of methane aom with sulfate as the electron acceptor is evidenced by the presence of anmes anaerobic methanotroph dissolved sulfide produced through the reduction of sulfate is reoxidized through several pathways depending on the habitat these pathways include vesicomyid bivalves uptake adults or juveniles in the bacterial mats habitats reoxidation by oxygen or iron phases within the reduced sediment or reoxidation by microbial mats sulfide uptake rates by vesicomyids measured in sulfide rich sea water 90 18 mmol s m 2 d 1 were similar to sulfide production rates obtained by modelling the sulfate profile with different bioirrigation constants highlighting the major control of vesicomyids on sulfur cycle in their habitats

geochemical processes and chemosynthetic primary production in different thiotrophic mats of the hakon mosby mud volcano barents sea we have investigated if in a cold seep methane or sulfide is used for chemosynthetic primary production and if significant amounts of the sulfide produced by anaerobic oxidation of methane are oxidized geochemically and hence are not available for chemosynthetic production geochemically controlled redox reactions and biological turnover were compared in different habitats of the ha kon mosby mud volcano the center of the mud volcano is characterized by the highest fluid flow and most primary production by the microbial community depends on oxidation of methane the small amount of sulfide produced is oxidized geochemically with oxygen or is precipitated with dissolved iron in the medium flow peripheral beggiatoa habitat sulfide is largely oxidized biologically the oxygen and nitrate supply is high enough that beggiatoa can oxidize the sulfide completely and chemical sulfide oxidation or precipitation is not important an internally stored nitrate reservoir with average concentrations of 110 mmol l21 enables the beggiatoa to oxidize sulfide anaerobically the ph profile indicates sequential sulfide oxidation with elemental sulfur as an intermediate gray thiotrophic mats associated with perturbed sediments showed a high heterogeneity in sulfate turnover and high sulfide fluxes balanced by the opposing oxygen and nitrate fluxes so that biological oxidation dominates over geochemical sulfide removal processes the three habitats indicate substantial small scale variability in carbon fixation pathways either through direct biological use of methane or through indirect carbon fixation of methane derived carbon dioxide by chemolithotrophic sulfide oxidation

recirculating components to the deep boundary current of the northern north atlantic abstract the meridional overturning system of the north atlantic is conventionally thought of as transporting warm water 4 c to high latitudes and covd water to low latitudes the northern cold water sources for this system are dense overflow from the nordic seas and less dense water from the labrador sea lsw the overflow components are carried westward by a deep northern boundary current dnbc that is shown here actually to begin southeast of the overflow regions the dnbc lies along the southern side of a system of islands and submarine ridges that divides the nordic seas from the subpolar basins the overflows act to increase the transport of the dnbc and this transport is further increased through the entrainment of warm waters once inside the labrador sea the dnbc is joined by lsw before continuing south to low latitudes as a cold deep western boundary current dwbc however published transport estimates are larger than can be explained by warm water entrainment alone thus indicating entrainment also of recirculating cold components the subject of this paper their sources are shown to be the lsw and cold abyssal waters originating from the southern hemisphere the lsw is entrained downward into the denser part of the dnbc and laterally into the upper part of the dwbc whereas the cold abyssal waters are supplied by an eastern intensified northward flow in the eastern atlantic that serves as the initial source of the dnbc and by a similar northward flow in the western atlantic the meridional overturning system described includes recirculations and poleward transport of cold water in addition tothe components described by the conventional system the cold abyssal waters in both the eastern and western basins have relatively low levels of oxygen and high concentrations of silicate reflecting their southern origin but their influence in the northwestern atlantic is somewhat obscurred by strong recirculating cyclonic gyres in the newfoundland and labrador basins this influence is detected by a deep silicate maximum extending poleward from the mid latitude western atlantic through the two gyres with eastern concentration and recirculating back diluted toward the south in the dwbc within the respective basins such a maximum also extends northward through the irminger basin into the dnbc but there is an ambiguity as to whether this is a direct extension of the signal from the south in the western basin or if it comes from the mid latitude eastern basin by way of westward flow through the charlie gibbs fracture zone it is perhaps consequence of both estimates of the volume transports of the various recirculating cold components indicate that they supply about as much water to the deep boundary currents as do the combined cold water sources in the north

gulf stream generated topographic rossby waves abstract an inverse ray tracing model is applied to observations of 40 day topographic rossby waves on the continental slope off of cape hatteras north carolina to determine their origin the rays are traced seaward and extend into the deep gulf stream where the bottom slope remains strong enough that topographic dominates planetary this enable coupling to occur between eastward propagating gulf stream meanders and topographic waves with eastward phase speed and matching zonal wavelength previous satellite observations indicate that the most frequently occurring gulf stream meanders have a period of 40 days and the model reveals that as these meanders pass a topographic bend near 71 72 w they are able to couple to the observed topographic waves traced back from cape hatteras the 40 day gulf stream meanders occur in bursts which leads to associated bursts of the topographic waves

authigenic barite records of methane seepage at the carlos ribeiro mud volcano gulf of cadiz submarine mud volcanoes mvs are dynamic features that episodically expel gas charged fluids and mud onto the seafloor transferring various chemical constituents into the overlying water column the temporal variability in mv activity is however poorly understood so their importance as a source of methane ch4 and higher hydrocarbons for the oceanic carbon budget although thought to be significant cannot be properly constrained in this study the history of fluid and gas seepage at the carlos ribeiro mv gulf of cadiz is assessed via geochemical analyses and transport reaction modelling of pore fluids and barium ba rich layers ba fronts in sediment cores recovered along a transect from the eye to the periphery of the mv x ray fluorescence data reveal that ba fronts are absent at the eye while a single front with up to 1740 ppm ba is present at the margin of the summit three ba fronts occur at 45 85 and 130 cm depth within a mudflow to the southeast of the crater spectrometric analyses indicate that barite is the ba rich mineral in these layers upward advecting pore fluids are enriched in barium but depleted in calcium ca2 relative to seawater modelling of the ba2 and ca2 pore fluid profiles indicates that the positions of the ba fronts reflect both the present day hydrodynamic conditions as well as higher fluxes of methane in the past fluid advection appears to have decreased since 340 cal yr before present but degassing of the mudflow is ongoing and is potentially an important source of ch4

controls on gas hydrate system evolution in a region of active fluid flow in the sw barents sea abstract the location and stability of gas hydrates in the sw barents sea is poorly constrained due to complex geological geochemical and geophysical conditions including poor controls on regional heat flow and gas chemistry understanding the stability of gas hydrates in this region is important as recent studies suggest destabilizing hydrates may lead to methane discharge into the ocean and possibly in to the atmosphere here we use high resolution 3d p cable seismic data combined with 3d heat flow and fluid flow models to place new constraints on gas hydrate stability in this region the 3d p cable seismic data acquired in 2009 west of loppa high show cross cutting reverse polarity high amplitude reflectors interpreted as the base of gas hydrate stability to constrain heat flow fluid flow and gas hydrate stability within the 3d seismic volume we use a 3d steady state finite difference diffusive thermal model that incorporates regional bottom water temperature from ctd casts expected geothermal gradients and gas composition derived from well data in general modelled bottom simulating reflectors are deeper than observed bsrs our analysis weighs multiple factors that might explain the discrepancy between observed and modelled bottom simulating reflector depths from this analysis we propose that the most significant discrepancies in bsr depth are likely related to changes in regional fluid heat flow and fluid geochemistry the anomalously shallow bottom simulating reflectors can be explained via vertical fluid flow that might include ensuing potential effects on gas composition pore water salinity and temperature our estimate suggest that a maximum vertical fluid flux of approximately 12 mm y is necessary to explain the most significant anomalies our study provides new insight into regional heat flow geochemistry and end member vertical fluid flux rates in the barents sea moreover it documents that the fluid flow system is active and most likely very dynamic

active mud volcanoes on the continental slope of the canadian beaufort sea the major geochemical characteristics of red sea brine are summarized for 11 brine filled deeps located along the central graben axis between 19 n and 27 n the major element composition of the different brine pools is mainly controlled by variable mixing situations of halite saturated solution evaporite dissolution with red sea deep water the brine chemistry is also influenced by hydrothermal water rock interaction whereas magmatic and sedimentary rock reactions can be distinguished by boron lithium and magnesium calcium chemistry moreover hydrocarbon chemistry concentrations and 13 c data of brine indicates variable injection of light hydrocarbons from organic source rocks and strong secondary bacterial or thermogenic degradation processes a simple statistical cluster analysis approach was selected to look for similarities in brine chemistry and to classify the various brine pools as the measured chemical brine compositions show remarkably strong concentration variations for some elements the cluster analysis indicates two main classes of brine type i brine chemistry oceanographer and kebrit deeps is controlled by evaporite dissolution and contributions from sediment alteration the type ii brine suakin port sudan erba albatross discovery atlantis ii nereus shaban and conrad deeps is influenced by variable contributions from volcanic magmatic rock alteration the chemical brine classification can be correlated with the sedimentary and tectonic setting of the related depressions type i brine filled deeps are located slightly off axis from the central red sea graben a typical collapse structure formation which has been defined for the kebrit deep by evaluating seismic and geomorphological data probably corresponds to our type i brine type ii brine located in depressions in the northern red sea i e conrad and shaban deeps could be correlated to volcanic intrusion extrusion related deep formation the chemical indications for hydrothermal influence on conrad and shaban deep brine can be related to brines from the multi deeps region in the central red sea where volcanic magmatic fluid rock interaction is most obvious the strongest hydrothermal influence is observed in atlantis ii brine central multi deeps region which is also the hottest red sea brine body in 2011 68 2 c

fluid flow methane fluxes carbonate precipitation and biogeochemical turnover in gas hydrate bearing sediments at hydrate ridge cascadia margin numerical modeling and mass balances a numerical model was applied to investigate and to quantify biogeochemical processes and methane turnover in gas hydrate bearing surface sediments from a cold vent site situated at hydrate ridge an accretionary structure located in the cascadia margin subduction zone steady state simulations were carried out to obtain a comprehensive overview on the activity in these sediments which are covered with bacterial mats and are affected by strong fluid flow from below the model results underline the dominance of advective fluid flow that forces a large inflow of methane from below 869 mumol cm 2 a 1 inducing high oxidation rates in the surface layers anaerobic methane oxidation is the major process proceeding at a depth integrated rate of 870 mumol cm 2 a 1 a significant fraction 14 of bicarbonate produced by anaerobic methane oxidation is removed from the fluids by precipitation of authigenic aragonite and calcite the total rate of carbonate precipitation 120 mumol cm 2 a 1 allows for the build up of a massive carbonate layer with a thickness of i m over a period of 20 000 years aragonite is the major carbonate mineral formed by anaerobic methane oxidation if the flow velocity of methane charge fluids is high enough greater than or equal to10 cm a 1 to maintain super saturation with respect to this highly soluble carbonate phase it precipitates much faster within the studied surface sediments than previously observed in abiotic laboratory experiments suggesting microbial catalysis the investigated station is characterized by high carbon and oxygen turnover rates approximate to1000 mumol cm 2 a 1 that are well beyond the rates observed at other continental slope sites not affected by fluid venting this underlines the strong impact of fluid venting on the benthic system even though the flow velocity of 10 cm a 1 derived by the model is relative low compared to fluid flow rates found at other cold vent sites non steady state simulations using measured fluid flow velocities as forcing demonstrate a rapid respond of the sediments within a few days to changes in advective flow moreover they reveal that efficient methane oxidation in these sediments prevents methane outflow into the bottom water over a wide range of fluid flow velocities 80 cm a 1 only at flow rates exceeding approximately 100 cm a 1 does dissolved methane break through the sediment surface to induce large fluxes of up to 5000 mumol ch4 cm 2 a 1 into the overlying bottom water

on the connection between dense water formation overturning and poleward heat transport in a convective basin an isopycnal two layer idealized model for a convective basin is proposed consisting of a convecting interior region and a surrounding boundary current buoyancy and wind driven parameterized eddy fluxes govern the exchange between the two to balance the interior buoyancy loss the boundary current becomes denser as it flows around the basin geostrophy imposes that this densification be accompanied by sinking in the boundary current and hence by an overturning circulation the poleward heat transport associated with convection in the basin can thus be viewed as a result of both an overturning and a horizontal circulation when adapted to the labrador sea the model is able to reproduce the bulk features of the mean state the seasonal cycle and even the shutdown of convection from 1969 to 1972 according to the model only 40 of the poleward heat buoyancy transport of the labrador sea is associated with the overturning circulation an exact solution is presented for the linearized equations when changes in the boundary current are small numerical solutions are calculated for variations in the amount of convection and for changes in the remotely forced circulation around the basin these results highlight how the overturning circulation is not simply related to the amount of dense water formed a speeding up of the circulation around the basin due to wind forcing for example will decrease the intensity of the overturning circulation while the dense water formation remains unvaried in general it is shown that the fraction of poleward buoyancy or heat transport carried by the overturning circulation is not an intrinsic property of the basin but can vary as a result of a number of factors

estimating mud expulsion rates from temperature measurements on hakon mosby mud volcano sw barents sea the hakon mosby mud volcano hmmv located on the norwegian barents svalbard continental margin in 1250 m water depth has been identified and described as a structure caused by upward transport of mud pore water and gas e g eldholm o sundvor e vogt p r hjelstuen b o crane k nilsen a k gladczenko t p 1999 sw barents sea continental margin heat flow and hakon mosby volcano geo marine letters 19 29 37 during rv polarstern expedition ark xix 3b in 2003 an integrated study took place to investigate the detailed morphology biology chemistry and geophysical aspects of hmmv klages m thiede j foucher j p 2004 the expeditions ark xix 3a 3b and 3c berichte zur polarforschung 488 in this paper we describe a detailed survey involving more than 100 temperature gradient measurements in order to reveal the temperature structure of hmmv values of apparent heat flow up to 3000 mw m 2

deep convection in the irminger sea forced by the greenland tip jet open ocean deep convection one of the processes by which deep waters of the world s oceans are formed is restricted to a small number of locations for example the mediterranean and labrador seas recently the southwest irminger sea has been suggested as an additional location for open ocean deep convection the deep water formed in the irminger sea has the characteristic temperature and salinity of the water mass that fills the mid depth north atlantic ocean which had been believed to be formed entirely in the labrador basin here we show that the most likely cause of the convection in the irminger sea is a low level atmospheric jet known as the greenland tip jet which forms periodically in the lee of cape farewell greenland and is associated with elevated heat flux and strong wind stress curl using a history of tip jet events derived from meteorological land station data and a regional oceanic numerical model we demonstrate that deep convection can occur in this region when the north atlantic oscillation index is high which is consistent with observations this mechanism of convection in the irminger sea differs significantly from those known to operate in the labrador and mediterranean seas

how does the deep western boundary current cross the gulf stream abstract the manner in which the deep western boundary current dwbc crosses the gulf stream is investigated using data from a hydrographic survey conducted in 1990 absolute geostrophic velocity vectors are computed using in situ float data to obtain the reference level three density layers are considered in detail two mid depth layers which together make up the shallowest water mass component of the dwbc 500 1200 m and a deep layer consisting of the norwegian greenland overflow water 2500 3500 m the shallowest layer does not make it through the crossover and is completely entrained by the gulf stream however the resulting drop in equatorward transport is almost completely replenished by offshore entrainment just south of the crossover in the intermediate layer which is denser than the gulf stream coming off the shelf part of the dwbc recirculates to the northeast while the onshoremost portion continues equatorward in the deep layer only a small amount of recirculation occurs the lateral

zechstein saline brines in poland evidence of overturned anoxic ocean during the late permian mass extinction event abstract bromine concentrations in halite sulfate isotopes 34 s and 18 o and major ion concentrations in primary fluid inclusions from three boreholes in the late permian zechstein evaporites have revealed sharp variations in marine derived brines within the polish sector of the european southern permian basin the base of the older halite na2 during the latest permian registers a change from sulfate rich brines similar in composition to modern evaporated seawater to sulfate depleted brines calcium rich this change coincides with a drop in 34 s to values close to 9 not observed in 18 o counterparts opposite isotope 34 s 18 o trends through the na2 unit cannot be explained by changes in restriction conditions we propose that the change to sulfate depleted calcium rich brines during halite deposition of the pz2 stassfurt cycle is related to the overturn of anoxic sulfidic deep waters from the panthalassa stratified superocean coinciding in time with the permian triassic mass extinction event the reconstruction of chemical changes in brines reveals two major evaporite sequences of increasing concentration that do not match the classic lithostratigraphic cycles the first evaporite sequence pzes 1 contain the evaporite units of the pz1 werra cycle the pz2 stassfurt cycle the main anhydrite a3 and the base of the younger halite na3 of the pz3 leine cycle the second evaporite sequence pzes 2 is represented by almost the entire na3 unit and the pz4 aller cycle

the formation of labrador sea water part i large scale processes abstract data obtained in the western labrador sea during march 1976 by hudson are analysed to show that new labrador sea water was being formed at this time on the basis of hydrographic and moored current meter data it is hypothesized that a 200 km scale cyclonic gyre forms in winter in the western labrador sea and that this gyre retains the developing deep mixed layers in this general area long enough for the transformation to labrador sea water to take place using a model it is demonstrated that water columns found along the western boundary of the labrador sea can be modified by cooling evaporation and mixing to form deep mixed layers with the properties of labrador sea water approximately 105 km3 of new labrador sea water was formed in 1976 an estimate that is consistent with earlier estimates of mean annual production rates this water 2 9 c 34 84 is some 0 6 c cooler and 0 06 fresher than that defined by lazier 1973 from his data collected in 1966 the variation of labrador sea water

terrestrial mud volcanoes of the salse di nirano italy as a window into deeply buried organic rich shales of plio pleistocene age abstract the terrestrial mud volcanoes of the salse di nirano are situated in the northern apennines italy and were formed by the expulsion of mud water liquid hydrocarbons and gases predominantly methane ch 4 previous studies revealed that methane is consumed by microbial associations using the anaerobic oxidation of methane aom a process also occurring in marine settings this was supported by the presence of 13 c depleted biomarkers specific to sulfate reducing bacteria and archaea however the vast majority of biomarkers appeared to have other so far unexplained sources than microorganisms that in situ feed on hydrocarbon gases therefore lipid biomarker distributions of fluid samples from the salse di nirano mud volcanoes were revisited and compared to those extracted from organic rich shales from the underlying geological formations the organic chemical analyses of the mud volcano fluids revealed signals of various eukaryotic bacterial and archaeal organisms in addition to signals from higher plants specific bacterial dialkyl glycerol diethers dage in particular ai 15 ai 15 and 16 16 were found which putatively originate from sulfate reducing bacteria srb the presence of archaea is evidenced by archaeol and trace amounts of sn2 hydroxyarchaeol most biomarkers were not depleted in 13 c suggesting mainly non methane consuming source organisms organic chemical analyses of the plio pleistocene shales from the underlying geological formation revealed the same pattern for most of the bacterial and archaeal components the strong similarities between both samples suggest that the majority of the biomarkers in the emitted fluids in nirano originate from these marine organic rich deposits through which the fluids passed these biomarkers clearly obscure signals from microorganisms growing in situ in the mud volcanoes but the extent of this process is spatially and temporarily highly variable

seafloor oxygen consumption fuelled by methane from cold seeps the leakage of cold methane rich fluids from subsurface reservoirs to the sea floor sustains some of the richest ecosystems on the sea bed these cold seep communities consume around two orders of magnitude more oxygen than the surrounding sea floor as a result of the microbial consumption of seep methane

an evaporite based high resolution sulfur isotope record of late permian and triassic seawater sulfate abstract variations in the sulfur isotope composition of dissolved marine sulfate through time reflect changes in the global sulfur cycle and are intimately related to changes in the carbon and oxygen cycles a large shift in the sulfur isotope composition of sulfate at the permian triassic boundary has been recognized for long time and a number of studies were carried out to understand the causes and significance of this shift however data for the middle and late triassic are very sparse and the stratigraphic evolution of the sulfur isotope composition of seawater is poorly constrained due to the small number of samples analyzed and or due to the limited stratigraphic intervals studied moreover in the last few years the triassic timescale has significantly changed due to a wealth of new radiometric and stratigraphic data in this study we show that for the late permian and the triassic it is possible to obtain a precise reconstruction of the evolution of the sulfur cycle for parts of it at sub million year resolution by analyzing exclusively gypsum and anhydrite deposits we base our reconstruction on new data from the middle and late triassic evaporites of northern switzerland and literature data from evaporites from germany austria italy and the middle east we propose a revised correlation between the well dated marine tethyan sections in northern italy and the evaporites from northern switzerland and from the germanic basin calibrated to the newest radiometric absolute age scale this new correlation allows for a precise dating of the evaporites and constructing a composite sulfur isotope evolution of seawater sulfate from the latest permian lopingian epoch to the norian we show that a rapid positive shift of approximately 24 at the permian triassic boundary can be used to constrain seawater sulfate concentrations in the range of 2 6 mm thus higher than previous estimates but with less rapid changes finally we discuss two possible evolution scenarios for the middle triassic negative shift to values of 15 that subsequently remain constant during the late triassic

in situ measurements of hydrogen sulfide oxygen and temperature in diffuse fluids of an ultramafic hosted hydrothermal vent field logatchev 14 45 n mid atlantic ridge implications for chemosymbiotic bathymodiolin mussels the logatchev hydrothermal vent field 14 45 n mid atlantic ridge is located in a ridge segment characterized by mantle derived ultramafic outcrops compared to basalt hosted vents logatchev high temperature fluids are relatively low in sulfide indicating that the diffuse low temperature fluids of this vent field may not contain sufficient sulfide concentrations to support a chemosymbiotic invertebrate community however the high abundances of bathymodiolin mussels with bacterial symbionts related to free living sulfur oxidizing bacteria suggested that bioavailable sulfide is present at logatchev to clarify if diffuse fluids above mussel beds of bathymodiolus puteoserpentis provide the reductants and oxidants needed by their symbionts for aerobic sulfide oxidation in situ microsensor measurements of dissolved hydrogen sulfide and oxygen were combined with simultaneous temperature measurements high temporal fluctuations of all three parameters were measured above the mussel beds h2s and o2 coexisted with mean concentrations between 9 and 31 m h2s and 216 and 228 m o2 temperature maxima 7 4 c were generally concurrent with h2s maxima 156 m and o2 minima 142 m long term measurements for 250 days using temperature as a proxy for oxygen and sulfide concentrations indicated that the mussels were neither oxygen limited nor sulfide limited our in situ measurements at logatchev indicate that sulfide may also be bioavailable in diffuse fluids from other ultramafic hosted vents along slow and ultraslow spreading ridges

active pockmarks in a large lake lake constance germany effects on methane distribution and turnover in the sediment in the eastern part of lake constance the second largest prealpine lake in europe about 500 pockmarks morphological depressions on the lake floor were recently discovered the diameters of these pockmarks are as large as 16 m and about 24 of them continuously release methane in the form of visible bubbles the isotopic composition of the escaping gas indicated that the methane was of biogenic origin and was predominantly produced by the co2 reduction pathway in shallow water pockmarks 9 m and 12 m pore water analysis revealed increased methane concentrations of 1100 mol l 1 in the sediment diffusive methane fluxes and oxidation rates within these shallow pockmarks were much higher than in sediments outside pockmarks an estimated methane ebullition into the water column of about 40 l h 1 per pockmark showed that methane ebullition is by far the dominant pathway of methane release from these shallow pockmarks meiofauna abundance and organic carbon contents of the sediment were also higher in the shallow pockmarks but there were no differences in macrofauna in a deep pockmark 80 m even though bubble release was observed the sediment inside the pockmark had almost the same methane concentrations and isotopic compositions as a site outside of the pockmark at both sites the shallow and deep pockmark act mainly as sedimentation traps the emanating gas has only minor influence on the methane inventory of the sediments and therefore gas bubbles enter the water column essentially unaffected

paleo environmental controls on cold seep carbonate authigenesis in the sea of marmara abstract the factors controlling fluid emission dynamics at ocean margins are poorly understood in particular there are significant uncertainties on how fluid seepage at cold seeps may have responded to abrupt environmental changes in the geological past this study reports on a detailed geochemical investigation of seafloor carbonate crusts sampled at cold seeps along the submerged part of the north anatolian fault system in the sea of marmara an inland sea which has experienced major paleo environmental changes over the last deglaciation period we also analyzed a series of authigenic carbonate concretions recovered from two sediment cores at the western high ridge an active fluid venting area the ages of seafloor carbonate crusts derived from isochron u th dating cover the last 7 kyr suggesting that fluid activity along the fault system remained continuous over that time interval in the sediment cores carbonate concretions are concentrated at the lacustrine to marine transition which corresponds to the period when mediterranean waters flowed into the marmara basin about 12 14 kyr ago u th isotopic data indicate that most of these concretions formed later during the holocene around 9 10 kyr ago a period coinciding with an important anoxic event that led to the deposition of a sapropel layer in the sea of marmara based upon these results we suggest that the absence of carbonate concretions in the lacustrine sediment unit indicates that dissolved sulfate concentrations in the marmara lake pore waters during glacial time were too low to promote significant anaerobic methane oxidation thereby preventing sedimentary carbonate authigenesis in contrast the progressive inflow of mediterranean waters into the glacial marmara lake after 15 ka provided a source of dissolved sulfate that allowed anaerobic oxidation of methane to proceed within the anoxic sediment importantly the synchronism between the main phase of authigenic carbonate precipitation at the studied sites average 9 4 1 8 ka n 16 and the regional anoxic sapropel event support the idea that the drop in bottom water dissolved oxygen content was probably a key factor to enhance microbial activity and associated carbonate precipitation at that time overall these results provide straightforward evidence that fluid emission dynamics and hydrocarbon oxidation at cold seeps can be directly related to changing environmental conditions through time

long term coordinated changes in the convective activity of the north atlantic the north atlantic is a peculiarly convective ocean the convective renewal of intermediate and deep waters in the labrador sea and greenland iceland sea both contribute significantly to the production and export of north atlantic deep water thus helping to drive the global thermohaline circulation while the formation and spreading of 18 degree water at shallow to intermediate depths off the us eastern seaboard is a major element in the circulation and hydrographic character of the west atlantic for as long as time series of adequate precision have been available to us it has been apparent that the intensity of convection at each of these sites and the hydrographic character of their products have been subject to major interannual change as shown by aagaard 1968 clarke et al 1990 and meincke et al 1992 for the greenland sea in the ows bravo record from the labrador sea eg lazier 1980 et seq and at the panulirus hydrostation s site in the northern sargasso off bermuda eg jenkins 1982 talley and raymer 1982 this paper reviews the recent history of these changes showing that the major convective centres of the greenland and labrador seas are currently at opposite convective extrema in our postwar record with vertical exchange at the former site limited to 1000 m or so but with labrador sea convection reaching deeper than previously observed to over 2300 m as a result greenland sea deep water has become progressively warmer and more saline since the early 70 s due to increased horizontal exchange with the arctic ocean through fram strait while the labrador sea water has become progressively colder and fresher over the same period through increased vertical exchange most recently convection has become deep enough there to reach into the more saline nadw which underlies it so that cooler but now saltier and denser lsw has resulted

metabolic variability in seafloor brines revealed by carbon and sulphur dynamics brine fluids supply the sea floor with energy rich substrates geochemical and genetic analyses indicate that the associated microbial communities and their dominant metabolisms vary between seep sites with different supplies of sulphate and organic matter brine fluids that upwell from deep hot reservoirs below the sea bed supply the sea floor with energy rich substrates and nutrients that are used by diverse microbial ecosystems contemporary hypersaline environments formed by brine seeps may provide insights into the metabolism and distribution of microorganisms on the early earth1 or on extraterrestrial bodies2 here we use geochemical and genetic analyses to characterize microbial community composition and metabolism in two seafloor brines in the gulf of mexico an active mud volcano and a quiescent brine pool both brine environments are anoxic and hypersaline however rates of sulphate reduction and acetate production are much higher in the brine pool whereas the mud volcano supports much higher rates of methane production we find no evidence of anaerobic oxidation of methane despite high methane fluxes at both sites we conclude that the contrasting microbial community compositions and metabolisms are linked to differences in dissolved organic matter input from the deep subsurface and different fluid advection rates between the two sites

fate of sulfide in the frasassi cave system and implications for sulfuric acid speleogenesis abstract the oxidation of hydrogen sulfide h 2 s has led to the formation of some of the world s largest caves through a process known as sulfuric acid speleogenesis sas here we present a multi year study of the large sulfidic and actively forming frasassi cave system italy we show that despite the presence of abundant sulfide oxidizing biofilms in frasassi streams h 2 s g degassing to the cave atmosphere was the major sink for dissolved sulfide degassing rates ranged from 0 9 to 80 mol m 2 s 1 whereas microbial oxidation rates were between 0 15 and 2 0 mol m 2 s 1 furthermore microsensor measurements showed that sulfuric acid is not a major end product of microbial sulfide oxidation in the streams our results suggest that subaerial sas will be important for karstification and more important than subaqueous sas wherever ground waters with high sulfide concentrations emerge as flowing streams in contact with cave air

quantifying fluid flow solute mixing and biogeochemical turnover at cold vents of the eastern aleutian subduction zone in situ oxygen fluxes were measured at vent sites in the aleutian trench at a water depth of almost 5000 m using a tv guided benthic flux chamber the flux was 2 orders of magnitude greater than benthic oxygen fluxes in areas unaffected by venting on the continental margin off alaska porewater profiles taken from the surface sediment below a vent site showed high concentrations of sulfide methane and ammonia the reduced carbon and nitrogen compounds are transported to the vent site by fluids expelled from deeper anoxic sediment layers by the forces of plate convergence the tectonically driven fluid flow was determined from the biochemical turnover in vent communities and was found to be 3 4 0 5 m yr 1 a model was used to quantify the transport of silica ca2 and sulfate via diffusion advection and bioirrigation through the surface sediments of a vent site a nonlocal mixing coefficient of 20 30 yr 1 was determined by fitting the model curves to the measured porewater profiles showing that the transport of solutes within the near surface sediments and across the sediment water interface is dominated by the activity of the vent fauna sulfate containing oceanic bottom water and methane rich vent fluids were mixed below the clam colony to produce sulfide and a caco3 precipitate the vent biota shape their immediate environment and control the sediment water exchange and the benthic fluxes at vent sites the oxygen consumption at vent sites is a major sink for oxygen at the study area