the anaerobic oxidation of methane and sulfate reduction in sediments from gulf of mexico cold seeps we determined the geochemical characteristics of sediments and measured rates of the anaerobic oxidation of methane aom and sulfate reduction sr in samples collected near thermogenic structure ii gas hydrate mounds and in areas lacking hydrates along the continental slope in the gulf of mexico we used radiotracer c 14 and s 35 techniques to determine rates of aom and sr over depth in sediment cores abundant mats of white and orange beggiatoa spp were common in areas of active seepage and these sediments were enriched in hydrogen sulfide and methane in cores collected from areas without beggiatoa or hydrate concentrations of redox metabolites showed little variation over depth and these sites were inferred to be areas of low seepage integrated aom rates were low in beggiatoa free cores 0 05 mmol m 2 day 1 and averaged 2 8 4 6 mmol m 2 day 1 in seep cores that contained beggiatoa or gas hydrate integrated sr rates were also low in beggiatoa free cores 1 mmol m 2 day 1 and averaged 54 94 mmol m 2 day 1 in cores with beggiatoa or hydrate rates of sr generally exceeded rates of aom and the two processes were loosely coupled suggesting that the majority of sr at gulf of mexico hydrocarbon seep sites is likely fueled by the oxidation of other organic matter possibly other hydrocarbons and oil rather than by aom

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

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

impact of natural oil and higher hydrocarbons on microbial diversity distribution and activity in gulf of mexico cold seep sediments gulf of mexico cold seeps characterized by variable compositions and magnitudes of hydrocarbon seepage were sampled in order to investigate the effects of natural oils methane and non methane hydrocarbons on microbial activity diversity and distribution in seafloor sediments though some sediments were characterized by relatively high quantities of oil which may be toxic to some microorganisms high rates of sulfate reduction sr 27 9714 7 mmol m

anaerobic oxidation of methane and sulfate reduction along the chilean continental margin anaerobic oxidation of methane aom and sulfate reduction sr were investigated in sediments of the chilean upwelling region at three stations between 800 and 3000 m water depth major goals of this study were to quantify and evaluate rates of aom and sr in a coastal marine upwelling system with high organic input to analyze the impact of aom on the methane budget and to determine the contribution of aom to sr within the sulfate methane transition zone smt furthermore we investigated the formation of authigenic carbonates correlated with aom we determined the vertical distribution of aom and sr activity methane sulfate sulfide ph total chlorins and a variety of other geochemical parameters depth integrated rates of aom within the smt were between 7 and 1124 mmol m 2 a 1 effectively removing methane below the sediment water interface single measurements revealed aom peaks of 2 to 51 nmol cm 3 d 1 with highest rates at the shallowest station 800 m the methane turnover was higher than in other diffusive systems of similar ocean depth this higher turnover was most likely due to elevated organic matter input in this upwelling region offering significant amounts of substrates for methanogenesis sr within the smt was mostly fuelled by methane aom led to the formation of isotopically light dic 13c 24 6 vpdb and of distinct layers of authigenic carbonates 13c 14 6 vpdb

sulfur biogeochemistry of cold seeps in the green canyon region of the gulf of mexico abstract cold seeps in the gulf of mexico provide a natural laboratory to study biogeochemical cycling of sulfur carbon and oxygen at hydrate and hydrocarbon rich deep marine settings with obvious additional relevance to studies of diverse modern and ancient seeps of particular interest are the sulfur isotope signatures of microbial sulfate reduction coupled to anaerobic oxidation of methane and other non methane liquid and gaseous hydrocarbons whereas most of the published sulfur isotope data from cold seep systems pertain to pore water species our study integrates both solid and dissolved sulfur acid volatile sulfides savs pyrite spy elemental sulfur s dissolved sulfate and h2s modeled and 35so42 reduction rates and 13c and 18o data for authigenic carbonates are integrated within this sulfur framework our results indicate extreme variability over narrow spatial and temporal scales within short distances meters from active seeps high rates of microbial sulfate reduction can lead to complete consumption of the sulfate within the upper few centimeters of burial while meters away the sulfate profile shows little depletion such small scale variability must reflect the structure and temporal dynamics of hydrocarbon migration in the presence of low amounts of background organic matter our past work demonstrated that electron donors other than methane drive significant levels of microbial activity at these seeps and very recent work has demonstrated that oxidation of higher chain volatile hydrocarbons can contribute to the high levels of microbial activity these findings are consistent with our new results elevated concentrations of pyrite and diagenetic carbonate relative to background sediments are diagnostic of active seepage yet the s isotopes tell more complex stories low levels of the transient instantaneous products of s cycling avs and s show high 34s values that increase with depth most of the pyrite formation however seems to be very early as limited by the availability of reactive fe phases as such 34s values for pyrite at ancient seeps can show consistently low 34s values that undersell the full intensity of microbial sulfate reduction low sedimentation rates and the resulting low detrital iron fluxes may in fact limit our ability to recognize seeps in the geologic record using only 34s compositions for pyrite

microbial methane oxidation and sulfate reduction at cold seeps of the deep eastern mediterranean sea abstract the eastern mediterranean hosts a variety of active cold seep systems such as gas chimneys mud volcanoes and pockmarks in water depths of 500 to 3200 m as part of the nautinil expedition in 2003 the sediments of cold seeps on the nile deep sea fan ndsf were sampled for the first time for biogeochemical and microbiological analyses here we compare rates of the anaerobic oxidation of methane aom and sulfate reduction sr as well as the microbial community structure of a variety of cold seep systems including mud volcanoes pockmarks and brine seeps our results revealed strong differences in microbial activity among the different seep systems of the eastern central and western provinces of the ndsf as well as the olimpi field central mediterranean ridge integrated over a sediment depth of 10 cm below the seafloor sr rates ranged from 0 1 66 mmol m 2 d 1 and aom rates from 0 1 3 6 mmol m 2 d 1 sr was often considerably higher than methane oxidation indicating that electron donors other than methane were utilized in general the lowest rates were associated with pockmarks and carbonate pavements and highest rates with bacterial mats above the gassy sediments of mud volcano centers 16s rrna gene analysis and fluorescence in situ hybridization fish revealed the presence of all known groups of marine methane oxidizing archaea i e anme 1 2 3 and also of methane oxidizing bacteria i e methylobacter sp and relatives in some seep sediments presumably syntrophic sulfate reducing bacterial partners of anmes were also detected in association with the anmes several anmes formed consortia with unknown bacterial partners the microbial community structure reflected the presence of typical seep microorganisms at all sites investigated but differed to varying extents between the different types of seeps despite the high availability of methane and sulfate methanotrophic microbial activity and biomass were lower at the seeps of the eastern mediterranean compared to those of other continental margins for unknown reasons

from gullies to mountain belts a review of sediment budgets at various scales this paper reviews the state of the art in the concept as well as in the application of sediment budgets in sedimentary research sediments are a product of mass dispersal at the earth surface and take part in global cycles sediment budgets aim at quantifying this mass transfer based on the principle of mass conservation and are the key to determine ancient fluxes of solid matter at the earth surface this involves fundamental questions about the interplay of uplift climate and denudation in mountain belts and transfer of sediments from the continents to the oceans as well as applied issues such as soil and gully erosion reservoir siltation and coastal protection first after introducing basic concepts relevant scales and methodologies the different components of quaternary routing systems from erosion in headwaters river systems glacial and paraglacial systems lakes deltas estuaries coasts shelves epicontinental seas and deep sea fans are discussed in terms of their sediment budget most suitable are sedimentologically closed or semi closed depositional environments e g alluvial fans lakes deltas and deep sea fans in a second step the dynamics of passive active and collisional tectonic settings and sediment budgets in related sedimentary basins are explored and new concepts of sediment portioning at large geodynamic scales are introduced ancient routing systems are more or less incomplete and may be intensively fragmented or destroyed in active tectonic settings in terms of sedimentary basin types rifts intracontinental and epicontinental settings are preferred objects of sediment budgets because of their persistence and relatively simple overall sedimentary architecture however closing basins such as foreland forearc retroarc piggy back and wedge top basins may provide excellent snapshots of orogenic sediment fluxes in a third step the large long lived routing systems of the amazon the ganges brahmaputra and the rhine are reviewed for each system estimates of either sediment volumes mass or sediment fluxes of continental and marine subsystems have been compiled in order to receive a complete routing in terms of mass conservation for specific time periods since the late glacial maximum as well as the cenozoic following lessons can be taken from these case studies i depositional centers and fluxes show strong shifts in space and time and call for caution when simply looking at subsystems ii the response times of these large systems are within the milankovich time interval thus lower than predicted from diffusion models iii cyclic routing of sediments in continental basins is much more dominated by climate human control than by eustacy and iv at long time scales ultimate sinks win over intermittent storage it is concluded from this review that the quantitative understanding of global sediment cycling over historic and geologic time and its response to allogenic forcing is still in its infancy and further research is needed towards a holistic view of sediment routing systems at various temporal and spatial scales and their coupling with global biogeochemical cycles this includes i to better determine response times of large routing systems by linking quaternary with cenozoic sediment budgets and continental with marine sub systems ii to combine advanced provenance techniques with sediment budgets in order to reconstruct ancient systems iii to study sediment partitioning at the basin scale iv to reconcile continental supply dominated sequence stratigraphy with the eustatic dominated marine concept and iv to account for non actualism of ancient systems with respect to their erosion and transport mode in particular during glaciations and pronounced arid intervals glacial and eolian sediment routing may cross over hydrologic boundaries of drainage basins thus challenging the principle of mass conservation

slope transport of suspended particulate matter on the aquitanian margin of the bay of biscay abstract spatial and temporal characteristics of the water masses and the dispersion of the suspended particulate matter were investigated using current meter hydrographic and nephelometric observations gathered during the ecofer experiment 1989 1991 in the cap ferret canyon on the aquitanian margin of the bay of biscay while characteristics of the deep water masses were stable from one year to another large hydrographic change in the upper 500 m related to winter renewal induced by poleward advection of warm and saline water along the continental slope the slope circulation and seasonal eddy activity appear as important dynamical mechanisms that control the entrainment and the dispersion of the suspended particulate matter from the neritic domain to the deep ocean a predominantly northward along slope current with occasional reversal characterizes this circulation the nephelometric structures also showed seasonal changes in the overall suspended particulate matter content but recurrent features such as the presence of intermediate nepheloid layers at the shelf break depth and various depths along the slope 500 1000 and 2000 m were observed these nepheloid layers extended off the slope to about 10 30 km but especially laterally along the slope their presence indicated that suspended particulate matter exchanges between the shelf and the slope occurred mainly in the head of the canyon and along the southern open slope the intermediate nepheloid layers around 500 m depth detached from the slope particularly in regions where the bottom slope is close to critical for the m2 internal tide

biogeochemical processes controlling authigenic carbonate formation within the sediment column from the okinawa trough abstract authigenic carbonates are one type of conspicuous manifestation in seep environments that can provide long term archives of past seepage activity and methane cycling in the oceans comprehensive investigations of the microbial community functional structure and their roles in the process of carbonate formation are however lacking in this study the mineralogical geochemical and microbial functional composition were examined in seep carbonate deposits collected from the west slope of the northern section of the okinawa trough ot the aim of this work was to explore the correspondence between the mineralogical phases and microbial metabolism during carbonate deposit formation the mineralogical analyses indicated that authigenic carbonate minerals aragonite magnesium rich calcite dolomite ankerite and siderite and iron bearing minerals limonite chlorite and biotite were present in these carbonate samples the carbon and oxygen isotopic values of the carbonate samples varied between 51 1 to 4 7 and 4 8 to 3 7 respectively a negative linear correlation between carbon and oxygen isotopic compositions was found indicating a mixture of methane derived diagenetic low 13c high 18o carbonates and detrital origin high 13c low 18o carbonates at the ot geochip analyses suggested that various metabolic activities of microorganisms including methanogenesis methane oxidation sulfite oxidation sulfate reduction and metal biotransformations all occurred during the formation process on the basis of these findings the following model for the methane cycle and seep carbonate deposit formation in the sediment column at the ot is proposed 1 in the upper oxidizing zone aerobic methane oxidation was the main way of methane consumption 2 in the sulfate methane transition zone sulfate dependent aom anaerobic oxidation of methane consumes methane and authigenic minerals such as aragonite magnesium calcite and sulfide minerals precipitate 3 in the underlying sulfate depleted zone the presence of iron oxides supplied by hydrothermal fluids and terrestrial inputs created thermodynamically favorable conditions for fe dependent aom to consume methane and dolomite and siderite ankerite precipitate in this zone

biogeochemical and 16s rrna gene sequence evidence supports a novel mode of anaerobic methanotrophy in permanently ice covered lake fryxell antarctica lake fryxell mcmurdo dry valleys antarctica contains a constantly cold water column and perennial ice cover although carbon and sulfur cycling in this amictic lake have been studied previously a paired investigation of 16s rrna gene based microbial diversity and geochemistry of lake fryxell is lacking here we used a combination of radiotracer based rate measurements geochemical measurements and molecular microbial community analysis to investigate the anaerobic oxidation of methane aom and associated processes in lake fryxell the results show that while aom and sulfate reduction appear coupled in the upper regions of the anoxic water column in deep anoxic waters where aom rates are highest sulfate is unlikely to be the electron acceptor for aom despite significant rates of aom in these waters no putative aom associated archaea or bacteria were observed due to a lack of documented aom electron acceptors and putative anmes we suggest novel modes of aom dominate in this extreme environment first the notable abundance of the bacterial genus dehalococcoides suggests that reductive dehalogenation could fuel aom further taxa of the candidate phylum op9 the atribacteria and the bathyarchaeota formerly known as the miscellaneous crenarchaeotal group both commonly observed at cold methane seeps globally may mediate aom possibly using humic acids as electron shuttles in lake fryxell

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

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

particulate size spectra behavior and origin of nepheloid layers over the nova scotian continental rise 1 26 32 m measured by coulter counter on 10 cm 3 samples correlate linearly with light beam attenuation coefficient correlation between particle volume and weight concentration indicates lower apparent particle density for low concentration suspensions a feature that is attributed to aggregation during aging of the suspension particle size distributions show unimodal form with a peak at 4 m in high concentrations near the bed changing to a bimodal form with an additional mode at 16 m in low concentrations high above the bed 500 and 1000 m a b meters above bottom the presence of the coarse mode at 1000 m a b coupled with its increase in the lower 250 m of the water column suggests that it both settles from the surface and is resuspended from the bed ultrasonic disaggregation experiments show that much of the fine mode is of aggregates but the coarse mode is single solid particles distributions with a low volume concentration increase in volume when disaggregated and are interpreted as having a relatively large part of their total distribution in unmeasured sizes 32 m distributions with a high concentration decrease in counted volume on disaggregation inversions in the light attenuation profiles are taken to indicate the presence of former bottom mixed layers and their occurrence suggests thickening of the nepheloid layer by detachment and lateral injection of these turbid mixed layers they occur at levels sufficiently high as to provide a nepheloid layer over 1500 m thick over the adjacent sohm abyssal plain the coarse mode probably comprises solid particles with a calculated settling velocity of 12 m day its absolute concentration increases toward the bed but as a proportion of the distribution it increases upward it is thus thought to be particles of surface origin both settling to the bottom and in the lower 250 m of the water column resuspended from the bed the fine mode at 4 m has a spatially constant form thought to be controlled by physical coagulation mechanisms rates of coagulation estimated from shear mechanisms suggest that the postulated change of peaked into flat size distribution by particle aggregation and settling has a time scale of a few years rather than months which is probably long when compared with the lateral injection process lower in the nepheloid layer for that reason distribution with a fine mode peak are found well above the bottom mixed layer

sediment dynamics in a submarine canyon a case of river sea interaction this paper presents findings from a 1 month field experiment conducted during the flood season of 2000 on the southern coast of taiwan to examine the delivery of lithogenic siliciclastic sediment to kao ping submarine canyon from the nearby kao ping river and shelf sources and the transport of suspended lithogenic and nonlithogenic particles near the canyon floor collected time series data included simultaneous measurements of coastal winds salinity temperature flow field suspended sediment concentration ssc and size composition of suspended particles at the river mouth and inside the submarine canyon as well as results from seawater and sediment trap data other collected data included river discharge and sediment load and hydrographic measurements along and across the axis of the canyon during the experiment two significant episodic river sediment discharge events occurred relating to a typhoon and extreme precipitation conditions the findings show that theoretically the time difference between sand and clay siliciclastic grains to settle from the sea surface to the canyon floor is on the order of hours to months analogous to a sorting process river plume dynamics and the coastal wind field largely control the delivery of terrigenous fine grained sediment to the canyon inside the canyon the behavior of suspended lithogenic and nonlithogenic particles of different sizes can be differentiated into a coarse grained group sand which forms the drop in population and a fine grained group mud which forms the standing population each group has distinct spectral characteristics the coarse grained group is delivered directly to the canyon by the river effluent and by wave resuspension of the shelf substrate during the study period the net transport of suspended particles near the canyon floor was landward mostly by tidal currents whose direction was also modulated by spring neap tide both lithogenic and nonlithogenic particles contribute to high mass fluxes exceeding 700 g m 2 day 1 in the lower part of the canyon this river sea system represents a type of systems that consist of three geographically separated dynamic entities the river plume the shelf and the canyon under fair weather conditions the river plume and shelf processes are coupled through the tide and wind field the river and canyon form a direct source to sink link via coarse grained siliciclastic sediment during the flood season in both continuous and pulsed fashion in the typhoon season the shelf becomes a pulsed source region for coarse grained sediment

microbial community structure and methane cycling activity of subsurface sediments at mississippi canyon 118 before the deepwater horizon disaster abstract the deepwater horizon disaster caused a shift in microbial communities in gulf of mexico seawater but less is known about the baseline for microbial communities in the underlying sediments we compared 16s rrna and functional gene sequences deriving from dna and rna with geochemical profiles sulfate and methane concentrations 13c of methane and carbon dioxide and chloride concentrations of a sediment gravity core from the upper continental slope of the northwestern gulf of mexico mc118 in 2008 15 km from the spill site the highest number of archaeal sequences were anme 1 and anme 2 archaea in the sulfate reducing upper core segments 12 and 42 cmbsf anme 1 and methanomicrobiales in the middle methanogenic depths 200 and 235 cmbsf and anme 1 at the deepest depths 309 400 and 424 cmbsf the presence of mcra gene transcripts showed that members of the anme 1 group are active throughout the core and transcribe the mcra gene a key gene of methanogenesis and anaerobic methane oxidation the bacterial community consists mostly of members of the deltaproteobacteria chloroflexi cytophaga epsilonproteobacteria and the japan sea group 1 throughout the core the commonly detected genera of gammaproteobacterial hydrocarbon degrading bacteria in the water column are not found in this sediment survey indicating that the benthic sediment is an unlikely reservoir for these aerobes however the sediments contain members of the sulfate reducing families desulfobulbaceae and desulfobacteraceae some members of which degrade and completely oxidize aromatic hydrocarbons and alkanes and the desulfobacterium anilini lineage of obligately aromatics degrading sulfate reducers thus the benthic sediments are the most likely reservoir for the active deltaproteobacterial populations that were observed repeatedly after the deepwater horizon spill in the fall of 2010

sediment budget and transfer of suspended sediment from the gironde estuary to cap ferret canyon abstract a study of the particulate organic carbon content the grain size of suspended sediment and turbidity in a transect between the gironde estuary and cap ferret canyon indicates that particles from the gironde river are transferred to near the bottom of the canyon the separation of turbid estuarine water into bottom and surface nepheloid layers takes place in the gironde itself and in the nearshore zone the development of these two separate turbid layers is due to vertical a turbid surface plume and horizontal bottom layer salinity gradients the bottom nepheloid layer is caused primary by a horizontal supply of suspended sediment from the gironde rather than from resuspension or vertical sedimentation as suggested by other workers on the median and outer shelf the distribution of particles in the water column is influenced by thermal stratification the thickness of the bottom nepheloid layer increases from the estuary towards cap ferret canyon as a function of the thickness of the bottom waters detached nepheloid layers are observed at the shelf break coinciding with isopycnal surfaces due to the presence of cold waters in the cap ferret canyon superimposed advective inputs from the northern part of the shelf and resuspension of particles from mud patches contribute to the supply of particles towards the canyon suspended sediment in transit over the shelf break represents 2 3 of the total discharge from the gironde estuary this is a considerable amount as 50 of the suspended sediment is trapped in the west gironde mud patch and another undefined portion of the gironde sediment load is transported along the coast by tidal currents

sources of mud volcano fluids in the gulf of cadiz indications for hydrothermal imprint mud volcanism in the gulf of cadiz occurs over a large area extending from the shelf to more than 3500 m water depth and is triggered by compressional stress along the european african plate boundary affecting a deeply faulted sedimentary sequence of locally more than 5 km thickness the investigation of six active sites shows that mud volcano mv fluids on average are highly enriched in ch4 li b and sr and depleted in mg k and br the purity of the fluids is largely controlled by the intensity of upward directed flow flow rates could be constrained by numerical modelling and vary between 0 05 and 15 cm yr 1 application of d 18o systematics identifies clay mineral dehydration most likely within mesozoic and tertiary shales and marls as the major source of fluids hence cl and na in the pore fluids are mostly depleted below seawater values following a general trend of dilution however deviations from this trend occur and are likely caused by the dissolution of halite in evaporitic deposits other secondary processes overprinting the original fluid composition may occur along the flow path such as dissolution of anhydrite or gypsum and or the formation of calcite and dolomite different sources of fluids are also indicated by variations in 87sr 86sr which range from 0 7086 to 0 7099 at the different sites dehydration may be induced primarily by overburden and tectonic compression however very high concentrations of li and b specifically at captain arutyunov mv camv indicate additional leaching at temperatures above 150 c which could be explained by the injection of hot fluids along deep penetrating major e w strike slip fault systems this hypothesis is supported by the occurrence of generally thermogenic but significantly ch4 enriched light volatile hydrocarbon gases at camv which cannot be explained by shallow microbial methanogenesis li and li b ratios from different types of hot and cold vents are used to infer that high temperature signals seem to be preserved at various cold vent locations and indicate a closer coupling of both systems in continental margin environments than outlined in previous studies

archaea mediating anaerobic methane oxidation in deep sea sediments at cold seeps of the eastern aleutian subduction zone cold seeps in the aleutian deep sea trench support prolific benthic communities and generate carbonate precipitates which are dependent on carbon dioxide delivered from anaerobic methane oxidation this process is active in the anaerobic sediments at the sulfate reduction methane production boundary and is probably performed by archaea working in syntrophic co operation with sulfate reducing bacteria diagnostic lipid biomarkers of archaeal origin include irregular isoprenoids such as 2 6 11 15 tetramethylhexadecane crocetane and 2 6 10 15 19 pentamethylicosane pmi as well as the glycerol ether lipid archaeol 2 3 di o phytanyl sn glycerol these biomarkers are prominent lipid constituents in the anaerobic sediments as well as in the carbonate precipitates carbon isotopic compositions of the biomarkers are strongly depleted in 13c with values of 13c as low as 130 3 pdb the process of anaerobic methane oxidation is also reflected in the carbon isotope composition of organic matter with 13c values of 39 2 and 41 8 and of the carbonate precipitates with values of 45 4 and 48 7 this suggests that methane oxidizing archaea have accumulated within the microbial community which is active at the cold seep sites the dominance of crocetane in sediments at one station indicates that probably due to decreased methane venting archaea might no longer be growing whereas high amounts of crocetenes found at other more active stations may indicate recent fluid venting and active archaea comparison with other biomarker studies suggests that various archaeal assemblages might be involved in the anaerobic consumption of methane the assemblages are apparently dependent on specific conditions found at each cold seep environment selective conditions probably include water depth temperature degree of anoxia and supply of free methane

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

a device for measuring downwearing rates on cohesive shore platforms the device described in this paper known as the traversing erosion beam is believed to be the first to be designed specifically for measuring rates of downwearing of cohesive foreshores such as clay shore platforms under high energy wave conditions it is primarily constructed of flexlink aluminium structural system components and consists of a horizontal beam with a main leg and two further support legs a sliding dolly module is moved along the beam at precise intervals using a longitudinal scale as a reference the topographic profile of the measurement surface is transferred to the dolly by a vertical sliding steel alloy rod from which the relative height differences are measured by a separate engineer s digital height gauge placed on the dolly the main leg of the device fits into a marine grade stainless steel box which is deeply embedded into the foreshore or shore platform to act a permanent datum the box is robust and can be expected to have a lifetime of at least a year and possibly even five years or more sample data are provided from a clay shore platform at warden point in the isle of sheppey kent uk which demonstrate that the teb can provide information on seasonal as well as annual rates of downwearing the device has also been tested successfully on a peat and clay foreshore at pett level in sussex and on a shore platform cut in glacial till at easington yorkshire

anaerobic methane oxidation in low organic content methane seep sediments abstract sulfate dependent anaerobic oxidation of methane aom is the key sedimentary microbial process limiting methane emissions from marine sediments and methane seeps in this study we investigate how the presence of low organic content sediment influences the capacity and efficiency of aom at bullseye vent a gas hydrate bearing cold seep offshore of vancouver island canada the upper 8 m of sediment contains

subsurface methane sources and migration pathways within a gas hydrate mound system gulf of mexico 1 geochemical profiles were coupled with seismic information to examine subsurface hydrocarbon source migration and fate at a gulf of mexico carbonate gas hydrate mound woolsey mound three seafloor features were investigated in detail 1 major faults resulting from a rising salt body 2 an acoustic backscatter anomaly and 3 a pockmark associated with a major fault we analyzed sulfate chloride dissolved inorganic carbon and hydrocarbon concentrations and carbon isotopes in pore water extracted from 20 m piston cores to characterize gas source and calculate methane flux dissolved biogenic methane dominated the off fault sites while the contribution of thermogenic methane increased near a major fault where thermogenic gas hydrates were recovered within the pockmark methane concentrations were low and isotopes indicated a biogenic source since pockmarks are typically formed from expulsive fluid flow this suggests that either the pockmark is the legacy of a conduit that has become plugged or that the expulsed fluid is confined within the fault walls at the acoustic anomaly nonsteady state sulfate profiles suggested temporal variability in methane flux estimates from 75 gravity cores collected across woolsey mound since 2002 were mapped to display the spatial variability in methane flux relative to the faults methane flux to the seafloor was generally low but increased several fold near the faults suggesting that the faults may provide conduits for hydrocarbons to bypass the microbial biofilter and cross the sediment water interface

weak coupling between sulfate reduction and the anaerobic oxidation of methane in methane rich seafloor sediments during ex situ incubation abstract we investigated coupling between sulfate reduction sr and anaerobic oxidation of methane aom by quantifying pore water geochemical profiles determining rates of microbial processes and examining microbial community structure at two sites within mississippi canyon lease block 118 mc118 in the northern gulf of mexico sediments from the northwest seep contained high concentrations of methane while sediments from the southwest seep contained methane gaseous n alkanes and liquid hydrocarbons and had abundant surficial accumulations of gas hydrate volumetric 21 5 mol cm 3 day 1 and integrated 1429 mmol m 2 day 1 rates of sr at mc118 in ex situ incubations are the highest reported thus far for seafloor environments aom rates were small in comparison with volumetric rates ranging from 0 1 to 12 6 nmol cm 3 day 1 diffusion cannot adequately supply the sulfate required to support these high sr rates so additional mechanisms possibly biological sulfide oxidation and or downward advection play important roles in supplying sulfate at these sites the microbial communities at mc118 included sulfate reducing bacteria phylogenetically associated with desulfobacterium anilini which is capable of complex hydrocarbon degradation despite low aom rates the majority of archaea identified were phylogenetically related to previously described methane oxidizing archaea to evaluate whether weak coupling between sr and aom occurs in habitats lacking the complex hydrocarbon milieu present at mc118 we compiled available sr and aom rates and found that the global median ratio of sr to aom was 10 7 1 rather than the expected 1 1 the global median integrated aom rate was used to refine global estimates for aom rates at cold seeps these new estimates are only 5 of the previous estimate

a review of the tagus river tufa deposits central spain age and palaeoenvironmental record here we determined the aminostratigraphy and aminochronology of tufa deposits located in central spain associated w i t h the tagus river and some o f its tributaries the henares dulce cifuentes ruguilla trabaque escabas and guadiela rivers w e used aspartic acid and glutamic acid racemization ratios obtained from the ostracod herpetocypris reptans tufa accumulations were found to be of different origins those in t h e henares cifuentes and ruguilla rivers are of paludal origin w h i l e those in t h e dulce and tagus rivers are o f fluvial origin a generally g o o d correspondence was found b e t w e e n the age o f the deposits and the position of the terraces above the current thalweg however the geomorphological evolution of the henares cifuentes and ruguilla rivers infilling of pre existing valleys has produced deposits of distinct ages at the same elevation above the current river thalweg and sometimes older tufas are located b e l ow younger ones we distinguished eight main tufa deposition episodes these occurred predominantly during even marine isotopic stages mis at 4 0 6 90 mis 11 2 6 4 68 mis 7e 189 4 0 mis 7a 130 27 mis 6 5e 101 2 5 mis 5c 3 2 10 mis 3 1 4 4 mis 1 a n d 6 2 mis l k a these results are in agreement w i t h the dating of similar deposits from nearby areas and other zones of s p a i n a n d europe the tufa stable isotope compositions were similar to other examples in central and southern spain a n d their plot falls in the same field as other lowland european stream tufas o x y g e n stable isotopes were influenced mainly b y temperature a n d rainfall the 51 3c values indicated a major effect o f soil derived carbon rather t h a n carbon from the catchment area but moderated in each tributary b y evaporation flow regime and biological effects photosynthesis

origin and morphosedimentary evolution of fine grained modern continental shelf deposits the gironde mud fields bay of biscay france the gironde mud fields are thin blankets 4 m that extend from the inner to mid shelf over a restricted area 600 km 2 and overlie palimpsest sands and gravels seaward of the modern gironde estuary south western france the bulk of the mud has accumulated over the last two millennia and reflects the complex interactions of 1 an increasing estuarine supply of suspended particulate matter 2 resuspension of substrate material by storm events and 3 biological mixing the combination of these processes has produced various features within the deposits related to 1 the water depth and distance from source of the fine grained material which are manifested as a proximal distal cross shelf trend from an area of alternating mud sedimentation temporary after large river flows with resuspension by storm events to an area of mud accumulation in deeper water where bioturbation predominates 2 expansions of the mud depocentres over time such that they become more remote from sources of coarser shelf sediment resulting in an upward fining trend the lithofacies of the gironde shelf mud fields exhibit a number of similarities to those of larger scale modern muddy shelves and ancient shallow water mudrocks this work provides a detailed description of a facies model for fine grained shelf sediments deposited under relatively constant sea level

grain size relationship between suspended matter originating in the gironde estuary and shelf mud patch deposits abstract the grain size variations of the elementary fraction without aggregates of gironde suspended matter during its transfer to the shelf were analyzed and compared with those of the surficial sediment of the west gironde mud patch located between water depths of 30 and 70 m which is considered as a preferential deposition area for estuarine suspended matter sm the results made it possible to show that two processes complicate the relationships between the estuary and the shelf a biogenic contribution identified as early as at the gironde outlet corresponding to a mode at 15 20 m in the sm of the turbid plume and an inorganic contribution of a fine grained fraction coming from sandy shelf deposits corresponding to micas with a mode at 50 60 m and settling on the inner part of the mud patch the nourishment of the western and deeper part of this mud patch by estuarine suspended matter is derived from the benthic nepheloid layer in terms of grain size distribution this supply is characterized by the 7 5 m mode which is typical of particulate matter originating in the gironde estuary