anaerobic oxidation of methane in hypersaline messinian environments revealed by 13c depleted molecular fossils abstract the messinian sequence of evaporitic deposits in italy includes authigenic carbonates that have been suggested to derive from the microbial degradation of organic compounds but the biogeochemical mechanisms that led to their formation remained unknown to unravel these mechanisms 13 c depleted carbonate rocks including native sulphur bearing limestone calcare solfifero from two locations in sicily and bedded limestone from the northern apennines have been studied their 13 c values as low as 49 reflect incorporation of carbon derived from the oxidation of methane which was previously suggested to have been linked to bacterial sulphate reduction molecular fossils extracted from the limestones reveal that methane was indeed oxidized in an anaerobic process by archaea and sulphate reducing bacteria the observed biomarker patterns resemble those of methane seep carbonates which form as a consequence of the anaerobic oxidation of methane aom aom specific 13 c depleted archaeal biomarkers such as pmi 13 c 101 to 75 as well as compounds derived from sulphate reducing bacteria iso and anteiso fatty acids 13 c as low as 85 were identified in the messinian carbonates although the biomarker results clearly point to aom the compound inventory also revealed distinct differences to patterns found at marine methane seeps for example sn 3 hydroxyarchaeol is in some samples the only hydroxyarchaeol present something usually not found at seeps archaeol is less depleted in 13 c than pmi at most sites 13 c 55 to 30 pointing to the co occurrence of methanogenic or halophilic archaea with archaea involved in aom 1 the presence of calcite pseudomorphs after lenticular gypsum 2 18 o enrichment in carbonates and 3 the biomarkers o phytanyl o sesterterpanyl glycerolether extended archaeol tetrahymanol and possibly phytanylglycerol monoethers as well as non isoprenoidal macrocyclic glycerol diethers confirm that carbonate formation took place under evaporitic conditions aom has previously been shown to be inhibited in some brine pools on the modern seafloor our observations however demonstrate that aom functions in hypersaline environments as well

3d analytic model for testing numerical tidal models a 3d analytic solution is presented for tides in channels with arbitrary lateral depth variation the solution is valid for narrow channels in which the lateral variation of the amplitude of tidal elevation is small the error introduced by the solution is on the order of a few percent in a tidal channel of a few kilometers in width the solution allows an arbitrary lateral depth variation and thus provides a wide choice of depth functions especially those with large bottom slopes the largest amplitude of the along estuary velocity appears on the surface in the deepest water the depth averaged velocity is the largest in the deepest water the time of flood ebb in deep water lags that in shallow water the time of flood ebb on the surface lags that at the bottom since this solution is simple and allows arbitrary lateral depth variations it can be used to demonstrate the first order tidal flow in narrow tidal channels of variable depth and to test high resolution numerical models with large depth gradients

application of a frictional channel flow theory to flow in the prince of wales channel torres strait abstract turbulent flow is considered in a narrow constant depth channel connecting two basins having a time dependent sea level difference the bosom stress is taken to be linear rather than quadratic in velocity even when flows are quite strong this approximation is justified theoretically by comparing appropriate linear and nonlinear solutions simple formulae are available for the depth averaged current speed along the channel axis in terms of the sea level gradient along that axis application of suitable mixing length theory shows that the stress should vary linearly with depth even for time dependent flows the mixing length theory predicts the current profile to be logarithmic near the bottom and slightly greater than logarithmic near the surface the theory was applied to sea level tidal constants and some acoustic doppler and ship drift measurements recently made in the prince of wales channel torres strait sea level gradients and tidal flows in the channel are large because the channel j

vent type taxa in a hydrocarbon seep region on the louisiana slope recent discoveries on the northern gulf of mexico continental slope have altered our understanding of biological and chemical processes occurring in the deep ocean a biological community of hydrothermal vent type organisms was recently discovered at the base of the florida escarpment1 where the fauna are apparently nourished by hydrogen sulphide rich hypersaline water seeping out onto the sea floor dense colonies of deep living chemosynthetic benthic organisms were first discovered during investigations of warm water anomalies along the axis of the galapagos rift in the pacific ocean in 19772 4 and this first discovery of clusters of clams tube worms and other filter feeders in the immediate proximity of warm water vents has been followed by the discovery of a number of other hydrothermal vent sites for example guaymas basin east pacific rise at 21 n the dense population assemblages at these sites are apparently restricted to small areas of the ocean floor where hydrogen sulphide rich water is escaping from spreading centres but the florida escarpment discovery indicates that these communities can also exist on passive margins here we report the discovery of dense biological communities associated with regions of oil and gas seepage on the louisiana continental slope these communities of large epi and infaunal organisms are similar to those associated with the vents of the pacific and the hypersaline brine seeps of the florida escarpment carbon isotope analyses suggest that these communities are chemosynthetic and derive their energy from hydrogen sulphide and or hydrocarbons similar communities may be widely distributed on the sea floor in other oil producing regions of the ocean

highly isotopically depleted isoprenoids molecular markers for ancient methane venting abstract we propose that organic compounds found in a miocene limestone from marmorito northern italy are source markers for organic matter present in ancient methane vent systems cold seeps the limestone contains high concentrations of the tail to tail linked acyclic c20 isoprenoid 2 6 11 15 tetramethylhexadecane crocetane a c25 homolog 2 6 10 15 19 pentamethylicosane pme and a distinctive glycerol ether lipid containing 3 7 11 15 tetramethylhexadecyl phytanyl moieties the chemical structures of these biomarkers indicate a common origin from archaea their extremely 13c depleted isotope compositions 13c 108 to 115 6 pdb suggest that the respective archaea have directly or indirectly introduced isotopically depleted methane derived carbon into their biomass we postulate that a second major cluster of biomarkers showing heavier isotope values 13c 88 is derived from sulfate reducing bacteria srb the observed biomarkers sustain the idea that methanogenic bacteria in a syntrophic community with srb are responsible for the anaerobic oxidation of methane in marine sediments marmorito may thus represent a conceivable ancient scenario for methane consumption performed by a defined two membered bacterial consortium 1 archaea that perform reversed methanogenesis by oxidizing methane and producing co2 and h2 and 2 srb that consume the resulting h2 furthermore the respective organic molecules are unlike other compounds tightly bound to the crystalline carbonate phase the marmorito carbonates can thus be regarded as cold seep microbialites rather than mere authigenic carbonates

methane derived authigenic carbonates formed by subduction induced pore water expulsion along the oregon washington margin authigenic magnesian calcite dolomite and aragonite are precipitated in the uppermost terrigenous sediments of the washington oregon accretionary prism by subduction induced dewatering these distinctive carbonates are methane derived and occur at sites of concentrated pore water expulsion unique biologic communities that subsist at least indirectly on methane suess et al 1985 are also found at some of these sites the methane which is dominantly biogenic is carried to the uppermost sediments of the prism by fluids and is oxidized by sulfate reducers before being incorporated into a carbonate cement carbonate precipitation occurs below the oxic layer probably no deeper than several centimetres to a few metres below the seabed cementation may be induced by three factors 1 increased carbonate alkalinity resulting from microbial sulfate reduction 2 decreased co 2 solubility resulting from a pressure decrease when the pore water escapes the prism and or 3 the addition of ca 2 and mg 2 ions from sea water near the sediment water interface the convergent margin setting engenders precipitation of authigenic carbonates in several ways compressive stresses induce anomalously rapid compaction and dewatering rates and they may cause overpressuring in migrating pore water thereby delaying precipitation of carbonates until pressure is released near the sediment water interface structural deformation of the accretionary prism creates pathways such as fault zones secondary fracture porosity and dipping permeable layers often exposed by mass movement for efficient advection and expulsion of methane enriched pore water these characteristic conditions which lead to the precipitation of methane derived carbonates may be found at other convergent margins

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

predominance of archaea derived hydrocarbons in an early triassic microbialite abstract we investigated the distribution of lipids in lower triassic sedimentary rocks 252 247 myr from south china including a shallow water microbialite in the uppermost section of the outcrop archaeal derived hydrocarbons were the major constituents of the microbialite from the latest early triassic among these we detected i abundant c 40 acyclic and monocyclic biphytanes possibly derived from glycerol dialkyl glycerol tetraether lipids and their degradation products c 30 39 pseudohomologues and ii a c 25 head to tail linked regular isoprenoid hydrocarbon possibly derived from dialkyl glycerol diether lipids dgds and its degradation products c 21 24 pseudohomologues and abundant pristane and phytane through combination of compound specific stable carbon isotope analysis of isoprenoid hydrocarbons which had average 13 c values of 35 to 30 and their molecular distribution it was not possible to unambiguously define the archaeal source for the biphytanes in the microbialite the 13 c values for pristane and phytane were similar to those for head to tail linked c 21 25 isoprenoids potential source organisms for these compounds were halophilic archaea except for methane seep microbialites no other ancient or recent phototrophic microbialites have been reported to contain predominantly archaeal isoprenoid hydrocarbons our findings suggest the presence of a new type of microbialite

bacterial and algal hydrocarbons in sediments from a saline antarctic lake ace lake capillary gas chromatography mass spectrometry c gc ms and iatroscan thin layer chromatography flame ionisation detection tlc fid were used to study hydrocarbon distributions in a sediment core from ace lake a saline meromictic lake in the vestfold hills of antarctica hydrocarbons were abundant in most core sections up to 125 g g dry wt particularly in near surface samples and the distributions were very complex major constituents were identified as phytane 2 6 10 15 19 pentamethyleicosane tetrahydrosqualene a mixture of phytenes cholesta 3 5 diene and fern 7 ene smaller amounts of sterenes and hopenes were also present the predominance of the first 3 acyclic isoprenoids in sediments buried less than 30 cm is consistent with high populations of methanogenic bacteria known to be present phytenes were abundant in all core sections and there was no relationship between their abundance and that of phytane which suggests that they were not derived from methanogenic bacteria phytadienes were minor constituents at all depths studied an unusual feature of some distributions was the high concentrations of fern 7 ene which was the major hydrocarbon in the 20 25 cm core section this alkene was only abundant in sediments which contained high concentrations of methanogen markers suggesting that it may also be indicative of anoxic depositional environments a possible source might be from purple non sulphur bacteria high concentrations of straight chain c29 and c34 alkenes were also found in these sediments but their origin has not been determined major changes in the hydrocarbon distributions with depth indicate that the depositional environment in the lake has altered dramatically since the lake was formed less than 8000 years ago the present condition of permanent anoxic bottom waters probably developed only in the last 1000 years

an upper jurassic methane seep limestone from the fossil bluff group forearc basin of alexander island antarctica an anomalous upper jurassic limestone bed 3 m thick is present within the volcaniclastic infill of a forearc basin exposed on alexander island antarctica the limestone formally designated the gateway pass limestone bed contains laminated crusts and blocks including hardgrounds showing radial fibrous and botryoidal calcite cements carbon isotope values are very negative delta 13 c of 33 5 per thousand to 44 6 per thousand pdb indicating a methane oxidation origin for the carbonate the limestone bed formed around a submarine cold seep in the antarctic peninsula forearc basin adjacent to the accretionary prism in contrast to adjacent nearly barren sea floor the limestone also yields a benthic island assemblage containing abundant gastropods and bivalves the seep is directly comparable to certain jurassic seeps at the convergent margin of the northeast pacific and both are related to subduction at the eastern proto pacific margin

authigenic carbonate formation revealed by lipid biomarker inventory at hydrocarbon seeps a case study from the okinawa trough abstract authigenic carbonates were recovered from the northern okinawa trough at 540 700 m water depth development of microbial communities and seepage dynamics driving the precipitation of authigenic carbonates remains poorly constrained even though the source of methane rich fluids formation of fe rich carbonates and the potential driving forces were previously reported here petrologic observations stable carbon and oxygen isotopic compositions mineralogy and lipid inventories of authigenic carbonates from the northern okinawa trough were analyzed the carbonate minerals were comprised predominantly of aragonite high magnesium calcite and siderite the presence of molecular fossils diagnostic for anaerobic methane oxidizing archaea anme and sulfate reducing bacteria srb with pronounced 13c depletions as low as 134 together with highly negative 13ccarb values as low as 55 8 suggest that the carbonates precipitated from anaerobic oxidation of methane aom with microbial methane as the predominant carbon source the difference between measured and calculated 18ocarb values based on 0 of sea water 18o vs v smow was higher than 3 in one of the carbonates ggd16 reflecting an origin from gas hydrate dissociation most of the carbonates revealed 18o offsets between measured and calculated values within 3 or a lower measured 18o than calculated value suggesting a mixture of methane derived carbonates low 13c high 18o and detrital origin carbonates high 13c low 18o biomarker patterns varied significantly among samples a suite of 13c depleted biomarkers indicated the predominance of an anme 1 assemblage for all samples suggesting carbonates formed at low to medium methane flux the predominance of anme 1 abundant detrital minerals and allochthonous biomarkers as well as low carbonate contents indicate that most samples formed at greater depth within the sediment column only one carbonate sample in this study is interpreted to have precipitated at relatively shallower depth as indicated by the occurrence of crocetane dominance of aragonite and higher overall carbonate content

changing redox conditions at cold seeps as revealed by authigenic carbonates from alaminos canyon northern gulf of mexico anaerobic oxidation of methane in anoxic sediments at cold seeps often leads to formation of authigenic carbonates close to the seafloor along continental margins recent work however indicated that the redox conditions in sediments may vary to some degree during seepage activity in order to shed new light on the extent of this variability authigenic carbonates from alaminos canyon lease block 645 of the northern gulf of mexico have been characterized by means of inorganic and organic geochemistry the carbonates were collected from seep deposits representing various seafloor morphologies including extensive pavements mounds fractured carbonate slabs surrounded by dense bivalve shells and vestimentiferan tubeworm colonies the deposits almost entirely consist of aragonite the 18o values of aragonite vary from 2 6 to 5 8 v pdb suggesting precipitation in slight disequilibrium with the surrounding pore fluids the 13c values of aragonite between 33 9 and 20 4 v pdb agree with variable amounts of carbonate derived from oxidation of thermogenic methane and crude oil methane was primarily oxidized in an anaerobic process as revealed by the presence of 13c depleted molecular fossils of methane oxidizing archaea 13c values as negative as 118 and sulfate reducing bacteria 13c values as negative as 97 the syntrophic partners in the anaerobic oxidation of methane the observed inventories of molecular fossils in the authigenic carbonates mirror those of known consortia of anaerobic methane oxidizing archaea anme and sulfate reducing bacteria namely the anme 2 desulfosarcina desulfococcus dss and anme 3 desulfobulbus dbb consortia in contrast the same carbonates exhibit shale normalized rare earth elements patterns that all display real negative ce anomalies ce ce 0 78 suggesting that at least temporarily oxic conditions prevailed the episodic occurrence of oxic conditions is confirmed by the presence of molecular fossils of aerobic methanotrophic bacteria including 4 methylcholesta 8 14 24 dien 3 ol and two bacteriohopanepolyols aminotetrol and aminotriol the 13c values of the biomarkers of aerobic methanotrophs are as negative as 58 and are consequently less 13c depleted than the molecular fossils of the prokaryotes performing anaerobic oxidation of methane a pattern in accord with culture experiments overall our results suggest that redox conditions at cold seeps are variable this variability probably reflects changes in seepage flux the combination of an inorganic and an organic geochemical approach used here is promising to better assess the variability and diversity of past fluid and gas expulsion at seeps

lipid biomarkers and their specific carbon isotopic compositions of cold seep carbonates from the south china sea abstract cold seep carbonates were studied from two locations dongsha and chiasian in the northern south china sea and on taiwan island lipid biomarkers and their stable carbon isotopic compositions extracted from these seep carbonate samples were analyzed in this study and the results pointed at the anaerobic oxidation of methane aom as responsible for carbonate formation distinct aom communities were indicated by isotopically highly depleted archaeal biomarkers with 13c values as low as 140 8 vpdb and bacterial biomarkers with 13c values as low as 128 6 vpdb which confirmed that biogenic methane was the dominant carbon source lipid biomarker distributions indicated that anme 2 archaea were prevalent in sample tvg3 c2g from dongsha and sample jx8 from chiasian in addition differences of the aom communities between the carbonates appeared to be caused by the respective biogeochemical environments anme 1 archaea tended to be abundant in high mg calcite carbonates and their formation might be linked to low methane fluxes in contrast anme 2 consortia were prevalent in aragonite carbonates and appeared to have prospered at sites with high methane supply our data imply that the mineralogy of the seep carbonates precipitated in the northern south china sea appears to be influenced by the distinct anme consortia which are induced by methane flux

methane derived carbonate conduits from the late aptian of salinac marne bleues vocontian basin france petrology and biosignatures abstract peculiar carbonate bodies occur in distinct marl layers of the marnes bleues formation aptian albian vocontian basin southern france the carbonate conduits exhibit pipe or sausage like forms and a central channel their sizes range between 30 and 60 cm in length and 5 10 cm in diameter the conduit carbonates consist of automicrite authigenically formed within the sediment millimeter sized aggregates of framboidal pyrite are abundant within the conduit automicrites probably representing former colonies of sulfate reducing bacteria the central channel reflects former pathways of reduced fluids in the carbonate conduit ni enrichments at the margins of the central cavity are may be due to the activity of methane related metabolism as ni is an important bio element for respective microbes light stable carbon isotope ratios of the conduit automicrites 25 86 to 23 10 vpdb point to carbonate precipitation linked to anaerobic oxidation of methane aom while less depleted stable carbon isotope ratios of microspar in marginal zones of the central opening 8 96 vpdb are in line with microbial sulfate reduction a methane related origin of the conduit carbonates is confirmed by the presence of authigenic lipid biomarkers tentatively sourced by archaea most of which are characterized by strong 13 c depletions 13 c values down to 104 the presence of organically bound sulfur is well in line with microbial sulfate reduction isorenieratane potentially point to the presence of brown pigmented green sulfur bacteria the methane was probably sourced by older oae black shales which are known to contain isotopically 13 c heavy biomarkers of archaea as reported elsewhere

some exact solutions to the nonlinear shallow water wave equations these exact solutions correspond to time dependent motions in parabolic basins a characteristic feature is that the shoreline is not fixed it is free to move and must be determined as part of the solution in general the motion is oscillatory and has the appropriate small amplitude limit for the case in which the parabolic basin reduces to a flat plane there is a solution for a flood wave these solutions provide a valuable test for numerical models of inundating storm tides

algal and bacterial hydrocarbons in particulate matter and interfacial sediment of the cariaco trench particulate matter samples 53 m size fractions and sediment from the sediment water interface were collected in the cariaco trench an anoxic marine basin on the continental shelf of venezuela and analyzed for hydrocarbons concentrations of hydrocarbons were highest 10 20 ng 1 in oxic surface waters 0 150 m and at the top of the anoxic zone 350 600 m and were low 3 4 ng l in the low oxygen zone above the oxic anoxic interface 150 250 m and anoxic bottom waters 600 1150 m branched c25 trienes and tetraenes dominated the hydrocarbon distributions in 53 m particles particle size and depth distributions of the hydrocarbons demonstrate the importance of algal hydrocarbons in surface waters coupled with increased abundances of bacterial hydrocarbons especially in the 53 m particles in the anoxic zone these observations illustrate the importance of oxic anoxic interfaces even in the oceanic water column as zones of intense microbial alteration of organic matter and as sources of some of the organic compounds found in sediments

authigenic carbonate formation and its impact on the biomarker inventory at hydrocarbon seeps a case study from the holocene black sea and the plio pleistocene northern apennines italy carbonates are widespread at methane and petroleum seeps and are often precipitated as consequence of an alkalinity increase due to the anaerobic oxidation of methane aom or less often reported of higher hydrocarbons these carbonates are taphonomic windows into earth s history because they excellently protect the in situ formed microbial signatures e g lipid biomarkers from diagenetic destruction a complication for paleoreconstructions however is that seep carbonates also encapsulate variable amounts of allochthonous organic matter sometimes even completely obscuring authigenic microbial signatures seep carbonates from the holocene black sea the pleistocene enza river and the pliocene san lorenzo both northern apennines italy provide hints to better understand i the importance of processes other than aom for the formation of seep carbonates and ii the controls of allochthonous and autochthonous contribution of biomarkers to organic matter in seep carbonates biomarker distributions in different parts of a black sea carbonate clearly demonstrate that high allochthonous organic matter is entrapped if aom carbonates are formed intrasedimentary particularly if methane supply is relatively low and external organic matter input high high allochthonous contributions were also found in the biomarker inventory of ancient seep carbonates from the italian northern apennines enza river and san lorenzo pointing at their precipitation within the sediment specific and complex conditions were indicated from our data for the enza river location carbonate facies and particularly biomarker compositions with abundant signatures of sulfate reducing bacteria suggest that sulfate reduction using alkaline and eventually sulfate and higher hydrocarbon enriched fluids triggered the growth of these seep carbonates our and other data suggest that this process has to be more considered if interpreting seep settings particularly where microbial processes rely on rising fluids from deep petroleum reservoirs

can friction coefficient be estimated from cross stream flow structure in tidal channels 1 bottom drag coefficient is usually estimated from vertical structures of horizontal flows analytic models have demonstrated that bottom friction causes cross channel variations of velocity such that the amplitude of the along channel velocity increases with depth and the velocity in shallow water has a phase lead i e flood and ebb occur earlier in shallow water along the same cross channel transect based on these facts we have developed a simple method to estimate the drag coefficient using lateral flow structure the method is verified by data from a vessel towed acoustic doppler current profiler adcp in unstratified tidal channels of georgia us the cross channel average of the drag coefficient is 4 55 x 10 3 1 18 6 a reasonable value compared to previous results

satellite synthetic aperture radar detection of delaware bay plumes jet like feature analysis current structure sech 2 h constitutes a determining factor for the radar image the modeled image intensity depends on the axial velocity decreasing as x 1 along the jet axis and is sensitive to the wind direction with respect to the jet axis the model was used to interpret synthetic aperture radar sar images of delaware bay plumes taken by the radarsat 1 canadian radar satellite and ers 2 european remote sensing satellite satellites during a period from summer 1996 to spring 1997 in all seasons the low salinity plumes appear as relatively bright jet like patterns on sar images from a morphological interpretation of the image features both summer and winter plumes can be divided into three sections along the axis source jet and dispersion region along the transverse direction sar image interpretations indicate that the plumes have a twin jet structure which conforms to decomposition of field measurements in summer the typical axial velocity is estimated at 6 10 1 ms 1 with a reynolds number of 18 at about 5 km downstream from the source the plume behaves like a turbulent jet and beyond that range down to about 10 km downstream it behaves like a laminar jet in winter the plumes become weaker than in summer the typical axial velocity is estimated at 4 10 1 ms 1 with a reynolds number of 3 the jet behaves like the laminar jet off the source down to about 4 km downstream in both summer and winter cases the sar images were taken at maximum flood tide and the plumes appeared as jets in the spring case the sar image was taken at early flood tide the plume appeared as an integrated body with relatively uniform bright tunes in all cases the plume disperses within about 25 km downstream index terms 4235 oceanography general estuarine processes 4528 oceanography physical fronts and jets 4546 oceanography physical nearshore processes 4568 oceanography physical turbulence diffusion and mixing processes keywords delaware bay estuarine plume radar image

stereochemical studies of acyclic isoprenoids xii lipids of methanogenic bacteria and possible contributions to sediments abstract abundant volatile lipids of methanobacterium thermoautotrophicum and methanosarcina barkeri include isoprenoid hydrocarbons c30 and c15 c20 and c25 isoprenoid alcohols m barkeri contains 2 6 10 15 19 pentamethyleicosane whose relative stereochemistry is the same as found in marine sediments indicating that it is a marker of methanogenic activity the c20 c30 and c25 alkenes in m thermoautotrophicum also have a preferred sterochemistry the latter have the 2 6 10 14 18 pentamethyleicosanyl skeleton suggesting that the alkane in marine sediments may derive from methanogens the stereochemistry of squalane in a marine sediment is also compatible with an origin in methanogens in contrast the stereochemistry of pristane in m thermoautotrophicum indicates a fossil fuel contaminant origin suggesting that this and certain other alkanes reported in archaebacteria might also be of contaminant origin there is therefore little evidence at present that the pristane in immature marine sediments originates in methanogens the c15 and c20 saturated alcohols in m thermoautotrophicum have mainly the all r configuration if this is generally true for methanogens the c20 alcohol in the messel shale may originate mainly from methanogens whereas that in the green river shale may originate mainly from photosynthetic organisms

a two dimensional analytic tidal model for a narrow estuary of arbitrary lateral depth variation the intratidal motion an innovative method is introduced to solve a two dimensional depth averaged analytic model for narrow estuaries or tidal channels with arbitrary lateral depth variations the solution is valid if the lateral variation of the amplitude of tidal elevation a is small i e a a where a is the amplitude of the tidal elevation this assumption is supported by a 60 day observation of elevation in the james river estuary using pressure sensors at both sides of a cross section of the estuary the error introduced by the solution is of the order of a a which has a maximum of 5 in the james river estuary the propagation of the tidal wave elevation is therefore essentially one dimensional along the estuary regardless of the depth distribution whereas tidal velocity has a strong transverse shear and is three dimensional in general dozens of depth functions in six groups of various forms are used to calculate the solution the tidal velocity is highly correlated with the bathymetry the largest amplitude of the along channel velocity is in the deepest water the phase of the along channel velocity in the shallow water leads that in deep water causing a delay in time of flood or ebb in the deep water the transverse velocity is generally small in the middle of a channel but reaches its maximum over the edges of bottom slopes the depth function has a significant effect on the ellipticity and the sense of rotation of the tidal ellipses by fitting the observed phase of semidiurnal tide in the james river estuary to the phase of the momentum equation we have obtained optimal values of the drag coefficient 1 5 10 3 and 1 8 10 3 for the spring and neap tides respectively then we apply these values of the drag coefficient and the model to the james river estuary using the real bathymetry results show remarkable agreement between the observations and the model along the transects for both spring and neap tides the cross channel phase difference of the along channel velocity between the channel and the shoal is found to be 1 hour a value consistent with that from the model the model estimated lateral variation of elevation is 2 5 of the tidal amplitude which is slightly smaller than the observed value

buoyancy driven lacustrine calving glaciar nef chilean patagonia glaciar nef a 164 km 2 eastern outlet of hielo patagonico norte the northern patagonia icefield terminates in a proglacial lake that has formed in conjunction with 20th century glacier retreat the terminus is inferred to be transiently afloat a hinge calving mechanism is proposed in which buoyant forces impose a torque on the glacier tongue resulting in the release of coherent sections of the glacier tongue as tabular icebergs a simple model shows how torque and tensile stress reach a maximum at the up glacier limit of the buoyant zone and that glacier thinning causes this point to migrate up glacier empirical evidence supporting this model includes elevated thermo erosional notches 6 5 m above lake level and the ubiquitous presence since 1975 of tabular icebergs with surface areas 0 3 km 2 flow speeds of 1 2 1 3 m d 1 were measured near the terminus in february 1998 extrapolations from these short term data yield a calving rate of 785 835 m a 1 and a calving flux of 232 10 6 m 3 a 1 or 0 2 km 3 a 1 the calculated mean water depth at the terminus is 190 m this calving rate is higher than at grounded temperate glaciers calving in fresh water but is nevertheless almost an order of magnitude less than calving rates at both grounded and floating tidewater glaciers

gc ms detection and significance of crocetane and pentamethylicosane in sediments and crude oils abstract the occurrence of the archaeal biomarkers crocetane and pentamethylicosane pmi in sediments and crude oils was investigated using gc ms and gc ms ms selected ion monitoring sim and multiple reaction monitoring mrm protocols designed to detect the c 20 and c 25 irregular isoprenoids were evaluated a method for the preferential detection of crocetane over phytane its more abundant isomer was refined using authentic compounds crocetane was found to be present in modern sediments from both aerobic and anaerobic water columns and in sediment from the 1640 ma barney creek formation providing evidence for the antiquity of its biosynthesis crocetane was also detected in several perth basin crude oils and in the kockatea shale their putative source rock and in canning basin oils although mrm analysis could only verify its occurrence in canning oils of devonian age equivocal data from ordovician and carboniferous canning basin oils highlight the need for extreme caution when attempting to distinguish between acyclic isoprenoid isomers pmi was identified by mrm in a miocene monterey sediment and in a modern antarctica sediment on the other hand the c 25 isoprenoid hydrocarbon peak detected in triassic and older sediments was consistently identified as the regular isomer i 25 reg whenever it was sufficiently abundant for mrm to be applied

three series of rearranged hopanes in toarcian sediments northern italy abstract a suite of 36 shales and marls from the toarcian oceanic anoxic event section at three localities in northern italy was found to contain variable contents of three series of rearranged hopanes 17 diahopanes c 27 and c 29 34 and trace c 35 18 neohopanes c 27 and c 29 30 and an unidentified early eluting series c 27 and c 29 35 principal component analysis pca shows the 17 diahopanes and the early eluting rearranged hopanes to closely covary suggesting a related diagenetic mechanism for the formation of their rearranged skeletons a general covariance with diasteranes is also noted the 18 neohopanes show no covariance with diasteranes or the other two series of rearranged hopanes we also report 2 methyl analogues of the 17 diahopanes and early eluting rearranged hopanes we propose that the neohopanes may be at least partly derived from different biohopanoid precursors than the other two series of rearranged hopanes and that the diagenetic origin of the neohopane structure differs from that of the 17 diahopanes and the unidentified early eluting series

anaerobic methane oxidation on the amazon shelf anaerobic methane oxidation on the amazon shelf is strongly controlled by dynamic physical sedimentation processes rapidly accumulating physically reworked deltaic sediments characteristic of much of the shelf typically support what appear to be low rates of steady state anaerobic methane oxidation at depths of 5 8 m below the sediment water interface methane oxidation in these cases is responsible for 10 m methane charged sediment directly to seawater in this nonsteady state situation methane is a major source of recently produced co2 and an important reductant for sulfate these observations suggest that authigenic sedimentary carbonates derived from anaerobic methane oxidation may sometimes reflect physically enhanced nonsteady state exposure of methane to sulfate in otherwise biogeochemically unreactive deposits the concentration profiles of ch4 so 4 and co2 in the eroded deposit were reproduced by a coupled reaction transport model this area of the shelf was reexposed to seawater approximately 5 10 years ago based on the model results and the assumption that the erosion of the deposit occurred as a single event that has now ceased the necessary second order rate constant for anaerobic methane oxidation was 0 1 mm 1 d 1

iron oxyhydroxide and sulphide mineralization in hydrocarbon seep related carbonate submarine chimneys gulf of cadiz sw iberian peninsula this paper aims to investigate the iron mineralization hosted in the submarine hydrocarbon seep related carbonate chimneys from the gulf of cadiz continental slope sw iberia chimneys are made of a general fine groundmass of major fe rich dolomite ankerite and calcite small grains of quartz and phyllosilicates and some foraminifer tests and ostracod shells primary porosity is frequently generated inside foraminifer chambers and ostracod shells and is filled with closely packed microcrystals of iron oxyhydroxide and sulphide minerals forming framboids some extremely peculiar multiframboidal textures are also detected corresponding to microcrystal groups spherical framboids and euhedral crystals without framboidal texture the mineralogy observed is mainly goethite pyrite pseudomorphs traces of tiny grains of pyrite were also observed cubic octahedral and pyritohedral are the habits observed in both minerals chemical analyses of framboids and euhedral crystals display high often erratic amounts of as co ni and mo in oxyhydroxides and mo pb v and co in sulphides versus almost always negligible concentrations of cu and zn a textural geochemical and mineralogical evolution is proposed to explain the coexistence of different morphologies in the multiframboidal texture a growth and aggregation of microcrystals as typical framboidal type mineralogical associations b development of euhedral habits c coalescence and homogenization of the microcrystal into large size euhedral to anhedral crystals and d formation of euhedral crystals or polycrystalline masses with complete loss of framboidal texture along this process an increase of the concentration of fe s mn and ti linked to a decrease in mg si al as p ca and v was observed the study of the iron mineralization in the gulf of cadiz is a first and can give clues to understand the complex geobiological interactions in this and other similar extreme hydrocarbon bearing submarine ecosystems

holocene methane derived dolomite cemented sandstone pillars from the kattegat denmark abstract dolomite cemented sandstone pillars up to 4 m high and 1 m in diameter are recorded from 10 12 m of water in the kattegat denmark the framework of the sandstone pillars is similar to that of the adjacent sediments i e medium grained well sorted quartz sand the carbonate cement consists of equicrystalline ca rich dolomite mg47 ca53 co3 10 30 m in diameter exhibiting a sucrosic texture the sr content is relatively constant at approximately 1000 ppm whereas the fe and mn contents are highly variable with mean values of 1870 and 320 ppm respectively the carbon isotopic signature of the dolomite cement displays negative 13c values in the range of 44 to 40 the oxygen isotope composition shows 18o values in the range of 3 7 to 3 9 and is enriched in 18o by approximately 3 in comparison with co existing high mg calcite the negative 13c values suggest that the dolomite has derived its carbon via methane oxidation the genetic connection between dolomite cement formation and methane oxidation is visually supported by gas seeps from the seabed and vents in the sandstone pillars themselves it is believed that the methane originates from shallow gas in late quaternary marine deposits which led to a discharge of methane in the diagenetic zones of the topmost sedimentary column the dolomite precipitation most probably took place as a result of anaerobic methane oxidation subsequently the lithified sandstone pillars were exposed on the seafloor by large scale submarine erosion

authigenic carbonates from methane seeps of the northern congo fan microbial formation mechanism abstract authigenic carbonates were collected from methane seeps at hydrate hole at 3113 m water depth and diapir field at 2417 m water depth on the northern congo deep sea fan during rv meteor cruise m56 the carbonate samples analyzed here are nodules mainly composed of aragonite and high mg calcite abundant putative microbial carbonate rods and associated pyrite framboids were recognized within the carbonate matrix the 13c values of the hydrate hole carbonates range from 62 5 to 46 3 pdb while the 13c values of the diapir field carbonate are somewhat higher ranging from 40 7 to 30 7 pdb indicating that methane is the predominant carbon source at both locations relative enrichment of 18o 18o values as high as 5 2 pdb are probably related to localized destabilization of gas hydrate the total content of rare earth elements ree of 5 hno3 treated solutions derived from carbonate samples varies from 1 6 ppm to 42 5 ppm the shale normalized ree patterns all display positive ce anomalies ce ce 1 3 revealing that the carbonates precipitated under anoxic conditions a sample from hydrate hole shows a concentric lamination corresponding to fluctuations in 13c values as well as trace elements contents these fluctuations are presumed to reflect changes of seepage flux

late cretaceous maastrichtian shallow water hydrocarbon seeps from snow hill and seymour islands james ross basin antarctica fossil hydrocarbon seeps are present in latest cretaceous maastrichtian volcaniclastic shallow shelf sediments exposed on snow hill and seymour islands james ross basin antarctica the seeps occur in the snow hill island formation on snow hill island and are manifest as large sized cement rich carbonate bodies containing abundant thyasirid bivalves and rarer ammonites and solemyid bivalves these bodies have typical seep cement phases with 13c values between 20 4 and 10 7 and contain molecular fossils indicative of terrigenous organic material and the micro organisms involved in the anaerobic oxidation of methane including methanotrophic archaea and sulphate reducing bacteria on seymour island the seeps occur as micrite cemented burrow systems in the lopez de bertodano formation and are associated with thyasirid solemyid and lucinid bivalves and background molluscan taxa the cemented burrows also have typical seep cement phases with 13c values between 58 0 and 24 6 there is evidence from other data that hydrocarbon seepage was a common feature in the james ross basin throughout the maastrichtian and into the eocene the snow hill and seymour island examples comprise the third known area of maastrichtian hydrocarbon seepage but compared to most other ancient and modern seep communities the james ross basin seep fauna is of very low diversity being dominated by infaunal bivalves all of which probably had thiotrophic chemosymbionts but which were unlikely to have been seep obligates absent from the james ross basin seep fauna are typical obligate seep taxa from the cretaceous and the cenozoic reasons for this may have been temporal palaeolatitudinal palaeobathymetric or palaeoecological

anaerobic methane oxidation by bacteria employing 14c methane uncontaminated with 14c carbon monoxide 14c labelled methane biologically prepared by methanobacterium thermoautotrophicum is widely used to determine methane oxidation rates however m thermoautotrophicum synthesizes carbon monoxide as a by product during methanogenesis in this study sulfate reducing bacteria utilizing the acetyl coa carbon monoxide dehydrogenase pathway were able to form 14co2 from 14ch4 containing 14co 14c labelled carbon monoxide was removed from 14ch4 by oxidation over hopcalite to carbon dioxide and fixation in sodium hydroxide solution measurable formation of 14co2 from purified 14c labelled methane by sulfate reducing bacteria was not observed therefore reported anaerobic methane oxidation rates in marine habitats measured with 14ch4 from m thermoautotrophicum are inclined to include carbon monoxide oxidation rates anaerobic oxidation of 14ch4 by sulfate reducing and acetogenic bacteria and methanogenic archaebacteria was tested only methanogenic species produced up to 900 ppm 14co2 from 14ch4 applied this observation and the absence of methane oxidation by sulfate reducing bacteria sustain the hypothesis that methanogenic archaebacteria in a syntrophic community might be responsible for the oxidation of methane in anaerobic habitats

experimental fracture and mechanical properties of antarctic ice preliminary results an experimental study of the fracture mechanics and rheology of ice from the ronne ice shelf antarctica is currently being undertaken the apparent critical stress intensity factor or apparent fracture toughness k q for crack propagation has been measured using a three point bend method for inducing crack growth perpendicular to the axis of cylindrical ice core specimens tensile crack nucleation under applied uniaxial compressive stress has also been evaluated both methods have allowed a profile of ice elastic and fracture properties with depth through the ice shelf to be constructed preliminary results indicate that the measured elastic modulus increases with depth through the firn and upper meteoric ice before reaching a constant value in the deeper dense meteoric and basal marine ice the resistance to fracture as measured by changes in apparent fracture toughness and crack nucleation stress increases with depth right through the firn and meteoric ice layers a simple fracture mechanics model applied to the ronne ice shelf indicates that crevasses form from small surface cracks less than 40 cm deep which quickly grow to depths of 40 60m and then remain stable

asymmetric tidal straining across an inlet lateral inversion and variability over a tidal cycle abstract tidal straining is a phenomenon of temporal variations in stratification and mixing resulting from the interaction of a longitudinal salinity gradient with the vertical shear of the horizontal tidal velocity as a result the theory predicts stronger and weaker stratification during ebb low tide and flood high tide respectively in contrast to this well known temporal asymmetry in this study we document in situ measurements demonstrating a lateral asymmetry and lateral inversion of tidal straining at barataria pass a narrow 600 m wide tidal inlet of barataria bay in southeastern louisiana during flood the eastern side of the channel had strong stratification of 4 psu salinity change over a 1 5 m thin layer while the western side had a 2 psu change over a 12 m water column this strong lateral difference decreased as flood continued until near the end of the flood when it reached vertically well mixed condition across the channel during ebb it was just the opposite such that the western side became stratified while the eastern end was well mixed this resulted to a small correlation coefficient of 0 05 for stratification between the west and east sides although the central channel and east side have a high correlation coefficient of 0 88 the tidally averaged salinity was higher on the western end than the eastern end except in a narrow boundary layer close to the eastern shore this is an apparent contradiction to what the coriolis effect would produce in classical estuarine dynamics our hypothesis for the observed difference arises from the influence of the river water coming out of the mississippi river through the southwest pass of the birdfoot delta this water mass may have played a role in the observed complicated lateral inversion of the tidal straining this study underlines the complexity of estuarine dynamics proximal to large deltaic systems and we anticipate that these results will underscore the need for a modeling study to further investigate this dynamic process

formation of carbonate pipes in the northern okinawa trough linked to strong sulfate exhaustion and iron supply abstract the microbial anaerobic oxidation of methane aom a key biogeochemical process that consumes substantial amounts of methane produced in seafloor sediments can lead to the formation of carbonate deposits at or beneath the sea floor although fe oxide driven aom has been identified in cold seep sediments the exact mode by which it may influence the formation of carbonate deposits remains poorly understood here we characterize the morphology petrology and geochemistry of a methane derived fe rich carbonate pipe in the northern okinawa trough ot we detect abundant authigenic pyrites as well as widespread trace fe within microbial mat like carbonate veins in the pipe the in situ 34 s values of these pyrites range from 3 9 to 31 6 vcdt suggesting a strong consumption of seawater sulfate by sulfate driven aom at the bottom of sulfate reduction zone the positive 56 fe values of pyrite and notable enrichment of fe in the ot pipe concurrently indicate that the pyrites are primarily derived from fe oxides in deep sediments we propose that the fe rich carbonate pipe formed at the bottom of sulfate reduction zone below which fe driven aom rather than fe oxide reduction coupled to organic matter degradation might be responsible for the abundantly available fe 2 in the fluids from which pyrites precipitated the fe rich carbonate pipe described in this study probably represents the first fossil example of carbonate deposits linked to fe driven aom because fe rich carbonate deposits have also been found at other cold seeps worldwide we infer that similar processes may play an essential role in biogeochemical cycling of sub seafloor methane and fe at continental margins

lipid biomarkers preserved in hydrate associated authigenic carbonate rocks of the gulf of mexico anaerobic oxidation of methane aom is common in ocean margin sediments where it is mediated by consortia of archaea and bacteria and can result in the formation of authigenic carbonate including extensive carbonate crusts previous work indicates that aom is associated with gulf of mexico hydrocarbon seeps and is mediated by similar organisms as identified in other settings however biological investigations have not been done on the associated 13c depleted carbonates here we show that 13c depleted archaeal and bacterial biomarkers are abundant in gulf of mexico authigenic carbonate rocks revealing that aom mediating organisms are closely associated with carbonate authigenesis moreover the rocks share general characteristics of the background soft sedimentary archaeal and bacterial community inferred from biomarker analysis suggesting that the organisms associated with carbonate authigenesis are the same as those that live elsewhere in the hydrocarbon seep environment this provides further evidence that aom by archaea and sulfate reducing bacteria can result in the sequestration of significant quantities of methane derived carbon in carbonate rocks

algal and archaeal polyisoprenoids in a recent marine sediment molecular isotopic evidence for anaerobic oxidation of methane 1 analyses of 13c contents of individual organic molecules in a marine sediment show that crocetane 2 6 11 15 tetramethylhexadecane an isomer of phytane is produced by microorganisms that use methane as their main source of carbon the sediments lie at a water depth of 68 m in the kattegat the strait between denmark and sweden crocetane appears first 185 cm below the sediment water interface in the zone marking the transition from sulfate reduction to methanogenesis its 13c value is 90 10 versus vienna pee dee belemnite vpdb its structure which includes four isoprene units arranged symmetrically around a tail to tail linkage suggests that it is produced by a member of the archaea growing at the intersection of the diffusion gradients for sulfate and methane in sedimentary pore waters the source organism apparently functions as a methane consuming member of the microbial consortium responsible for the anaerobic oxidation of methane hoehler et al 1994 in which as first demonstrated quantitatively in these sediments iversen and jorgensen 1985 electrons are transferred from methane to sulfate the presence of archaeal biomass throughout the sediment section is indicated by significant concentrations of 2 6 10 15 19 pentamethylicosane pmi and of ether bound phytane and biphytane the pmi reaches a minimum value of 47 well below the transition zone its isotopic depletion could reflect either methanogenic or methanotrophic sources the ether bound lipids are isotopically uniform throughout the section and are presumed to derive from archaea that utilize a carbon source unaffected by the oxidation of methane

in situ thermal profiles and laboratory impact experiments on iceberg ice a series of 40 impact tests was conducted on large right circular cylinders 68 5 cm diameter and 25 7 cm thickness of iceberg ice collected from an iceberg in labrador temperature profiles were also obtained for the iceberg and the profiles exhibited differences associated with the probe location temperatures as low as 15 c were measured at penetration depths of about 8 m the impact specimens were confined at the perimeter and base by a rigid metallic ring and plate a spherically terminated impactor with center mounted pressure transducer was dropped on to the flat top surface of specimens from various heights and with various added masses impact velocity varied from 1 8 to 3 9 m s 1 impactor mass varied from 155 to 510 kg and the ice specimen temperature varied from 0 5 to 14 5 c peak center pressures averaged from about 25 mpa at the highest temperature to about 41 mpa at the lowest temperature with the highest recorded pressure being 50 mpa crater volume increased with increasing impact energy as expected however the specific energy of the ejected material was found to decrease as the energy of impact and crater volume increased a mechanism for this observed behaviour is proposed

geochemical signature related to lipid biomarkers of anmes in gas hydrate bearing sediments in the ulleung basin east sea korea abstract the emission of methane as a greenhouse gas is controlled by the anaerobic oxidation of methane aom which plays an important role in the biogeochemical methane cycle during the second ulleung basin gas hydrate drilling expedition ubgh2 the distribution of lipid biomarkers and their compound specific stable carbon isotope ratios related to methane were investigated in venting and non venting sites ubgh2 3 ubgh2 10 of gas hydrate bearing sediments in the ulleung basin the objective of this study was to understand the microbial signatures related to methane cycling in organic rich sediment in a marginal sea east sea japan sea of the western north pacific the concentrations of methane related specific biomarkers archaeol and sn 2 hydroxyarchaeol at the sulphate methane transition zone smtz sediment depth in ubgh2 3 1 2 mbsf in ubgh2 10 6 8 mbsf are typically higher than in other sediment sections and their 13 c valuesare apparently depleted 73 3 to 102 7 in the ubgh2 3 and ubgh2 10 study sites however the 13 c values of archaeol and sn 2 hydroxyarchaeol between 59 6 and 66 5 are not depleted with the increased methane concentration in the sediments below the smtz in ubgh2 3 compared to the 13 c values about 60 of in situ methane this suggests that methane production processes should be dominant in the deeper sediment sections 2 7 3 8 mbsf rather than methane consumption by anaerobic methanotrophs anmes at the corresponding sediment depths there were also higher 13 c values 47 to 32 for archaeol and sn 2 hydroxyarchaeol in the 3 6 mbsf sections at ubgh2 10 suggesting the prevalence of methanogenic activities however the 13 c values 89 0 to 92 2 of archaeol and sn 2 hydroxyarchaeol were unexpectedly depleted in the deeper sediment section 5 2 mbsf of the venting site ubgh2 3 indicating that the past aom occurred under low sulphate concentrations in the corresponding pore water this study used the biomarker ratio sn 2 hydroxyarchaeol archaeol of archaea as a tool to demonstrate the different anme communities which was supported by 16s rrna analysis in the sediments of venting and non venting sites ubgh2 3 ubgh2 10 consequently the biochemical signatures of methanotrophic and methanogenic activity were found at varying sediment depths at both sites

early carboniferous low temperature hydrothermal vent communities from newfoundland living vent communities dependent on microbial chemosynthesis rather than photosynthesis were discovered only in the 1970s1 since then six fossil vent communities have been identified they range in age from early carboniferous to early tertiary2 7 here we describe fossil tubes an abundant low diversity fauna and sulphide mineralization in 340 myr old carboniferous carbonate mounds in newfoundland fig 1a these features together with evidence for microbial activity point to the existence of a seventh chemosynthetic community clustered around low temperature hydrothermal vents the remarkable preservation of this newfoundland community allows a direct comparison to be made with the composition and structure of modern vent communities

characterization and flexural strength of iceberg and glacier ice flexural strength of iceberg and glacier ice was determined from four point beam bending experiments a large quantity of glacial ice was collected from four icebergs and one glacier and a detailed ice characterization program was performed on samples from the five sources beam bending experiments were conducted at four temperatures in the range 1 to 16 c and at strain rates of 10 3 and 10 5 s 1 the flexural strength was found to increase with increasing strain rate based on extreme fibre strain and decreasing temperature the data suggest that air bubble inclusions play an important role in determining the flexural strength of glacial ice and this can explain the significant differences in mean strength of the ice from the five sources at a strain rate of 10 3 s 1 and temperature of 11 c the flexural strength was found to increase as the number of bubbles per unit volume increased reduction of crack initiating stresses at grain boundaries by softening of grains due to intragranular air bubble inclusions is thought to be the mechanism

characterizing lipid biomarkers in methanotrophic communities of gas hydrate bearing sediments in the sea of okhotsk abstract we studied specific lipid biomarkers of archaea and bacteria that are associated with the anaerobic oxidation of methane aom in a cold seep environment as well as the origin of sedimentary organic matter on the continental slope off ne sakhalin in the sea of okhotsk the organic geochemical parameters demonstrated that most of the sedimentary organic matter containing hydrate layers could be derived from marine phytoplankton and bacteria except for a station lv39 29h which was remarkably affected by terrestrial vascular plant specific methanotrophic archaea biomarkers was vertically detected in hydrate bearing cores lv39 40h coinciding with the negative excursion of the 13corg at core depths of 90 100 cm below the seafloor these results suggest that methane provided from gas hydrates are already available substrates for microbes thriving in this sediment depth in addition the stable isotope mass balance method revealed that approximately 2 77 3 41 of the total organic carbon or 0 036 0 044 dry weight sediment was generated by the activity of the aom consortium in the corresponding depth of core lv39 40h on the other hand the heavier 13c values of archaeol in the gas hydrate stability zone may allow ongoing methanogenesis in deeper sediment depth

lipid biomarker patterns of authigenic carbonates reveal fluid composition and seepage intensity at haima cold seeps south china sea abstract authigenic carbonates retrieved from sites rov1 and rov2 of the haima hydrocarbon seeps of the south china sea at approximately 1390 m water depth were studied using lipid biomarker analyses abundant molecular fossils of anaerobic methane oxidizing archaea anme and sulfate reducing bacteria srb with strong 13c depletions 13c values as low as 126 in combination with low 13ccarbonate values 42 7 to 36 8 provide evidence that anaerobic oxidation of methane aom was the major process driving the precipitation of the studied seep carbonates the extremely low 13c values of archaeal biomarkers confirm that biogenic methane was the main carbon source but the seepage of accessory crude oil is also suggested by the presence of unresolved complex mixtures in the hydrocarbon fractions a suite of 13c depleted biomarkers indicate the predominance of anme 1 dss consortia at both sites which indicates that the studied carbonates formed during low to medium methane flux somewhat higher contents of archaeal biomarkers and their stronger 13c depletion at site rov2 probably reflect at least temporarily higher seepage intensities than at site rov1 abundant bacterial dialkyl glycerol diethers dages revealing a large offset of their 13c values compared to srb derived terminally branched fatty acids were possibly produced by distinct srb species other than members of the dss cluster the encountered hopanoids are attributed to aerobic methanotrophic bacteria based on their moderate 13c depletion the application of molecular fossils in combination with their compound specific isotope signatures is an efficient tool to reconstruct the composition of seepage fluids and seepage intensities

archaeal and bacterial lipids in authigenic carbonate crusts from eastern mediterranean mud volcanoes abstract we investigated the distributions and 13 c values of lipid biomarkers in authigenic methane related carbonate crusts formed on eastern mediterranean mud volcanoes a highly diverse suite of microbial membrane lipids was detected strongly 13 c depleted lipids diagnostic for archaea include isoprenoid glycerol diethers isoprenoid glycerol dialkyl glycerol tetraethers and several c 20 c 35 isoprenoid hydrocarbons bacterial lipids mainly consist of dialkyl glycerol diethers branched fatty acids and hopanoids showing important 13 c depletions albeit less than archaeal lipids the data provide further evidence for the involvement of archaea and bacteria in the anaerobic oxidation of methane aom and in the sequestration of methane derived carbon in authigenic carbonate crusts varying distributions and isotopic compositions of 13 c depleted lipids argue for heterogeneous aom related microbial consortia expanding on existing work at cold seeps distinctive biomarker features and inferred microbial assemblages are observed in these crusts in agreement with available phylogenetic data for the samples our results support the potential of lipids for distinguishing methanotrophic communities despite the observed variances conservative features in the abundances and isotopic offsets of microbial biomarkers occur likely reflecting the overall relationships between archaea and bacteria and the nature of carbon flow between them

lipid geochemistry of methane seep related black sea carbonates abstract carbonates recovered from anoxic waters between 235 and 1555 m depth in the northwestern black sea were analyzed for lipid biomarkers and stable carbon isotopic compositions in addition a methane seep related microbial mat and a sample of surface sediment recovered from a non seep site were studied for comparison high concentrations of strongly 13 c depleted lipids attributed to bacteria and archaea mediating the anaerobic oxidation of methane aom were found in all samples except for the sediment differences of the dominant aom performing communities between the carbonates indicated by specific lipid patterns appear to be caused by the respective biogeochemical settings high proportions of anme 2 consortia are found at sites of assumingly high partial pressures of methane while anme 1 associations dominate at locations of moderate methane supply in the sedimentary concretion a complex mixture of biomarkers for terrestrial and planktonic organisms was found different molecular structures along with strong variations in the stable carbon isotopic compositions 13 c 20 2 to 94 3 allow for an estimation of the proportions of tetraether bound biphytanes derived from planktonic crenarchaeota and methanotrophic euryarchaeota our data imply that the shape of aom derived carbonate precipitates in black sea environments is crucially influenced by the respective methane supply active aom driven chimney like bioherms similar to those previously observed on the ukrainian shelf might also develop in the deep euxinic zone at 1555 m water depths

high resolution observations of a shear front in a tidal channel abstract the characteristics of a shear front system in a tidal channel have been investigated through a field study high resolution sampling including three dimensional measurements of current temperature salinity and turbidity was performed on repeated transects across the frontal zone both with fronts apparent and with fronts absent the density measured using conductivity temperature depth sensors provides a field proof that the shear front is present whether a density gradient exists it is distinguishable from conventional buoyant shear fronts which require a strong along channel density gradient the velocities measured using an acoustic doppler current profiler adcp and trapping global position system gps drifters indicate that shear front evolution has a four stage dynamic process in a tidal cycle 1 a directional shear front of shoal flood and channel ebb during the slack before flood and early flood 2 a speed shear front of shoal quick and channel slow after the early flood 3 a directional shear front of shoal ebb and channel flood during the slack before ebb and early ebb and 4 a speed shear front of shoal slow and channel quick ebb during the late ebb thus the velocity shear a variation in the current speed and direction on either side of the front is the generation mechanism of the observed shear front system it is caused by the unequal tidal durations between deep channels and shallow shoals in the channel discussed herein the coriolis effect is found to be negligible through the momentum balance analysis the unequal tidal durations can be caused by the following alternative mechanisms according to the analysis and model simulation 1 differential friction owing to the steep bathymetry between the shallow shoal and the deep channel and 2 circulation owing to the coastline bend of the shallow shoal

lower eocene carbonate cemented chimneys varna ne bulgaria formation mechanisms and the a biological mediation of chimney growth abstract in the area of pobiti kamani varna northeast bulgaria massive carbonate cemented columns chimneys up to 1 5 m diameter and 8 m high and horizontal interbeds 1 5 m thickness occur in dispersed outcrops over an area of 70 km2 within loose lower eocene sands field observations and petrographical and stable isotope geochemical characterisation of four studied locations reveal a relationship between these structures and processes of ancient hydrocarbon seepage column and interbed structures both consist of similar well sorted silt to sand sized nummulitic host sediments predominantly cemented by early diagenetic low magnesium calcite filamentous textures about 10 m in diameter and 80 650 m long are only locally detected within interparticle calcite cement of columns column samples from two sites reveal a similar linear and inverse covariant trend of 13c 18o values which was interpreted as a mixing trend between two end member fluid precipitation conditions i e 1 a methane and or higher hydrocarbon derived carbon member characterised by 13c values as low as 43 and marine controlled precipitation conditions with 18o of 1 0 5 v pdb and 2 a member with less contribution of methane which was mixed most likely with less depleted carbon sources explaining 13c values ranging up to 8 v pdb the corresponding depleted 18o values with many samples clustering around 8 v pdb are interpreted in terms of precipitation at elevated temperatures this suggests the venting system was not a true cold seep sensu stricto furthermore column cross transects often document an internal pattern consisting of concentric zones with distinct isotopic signatures which vary between the two end members the mixing and internal pattern of column isotopic data together with petrographical observations are qualitatively interpreted as evidence of alternating precipitation conditions controlled by varying seepage rates of a single fluid source at depth during build up of individual chimney pipes near the sediment surface based on several field observations migration of the hydrocarbon charged fluids in lower eocene times was possibly channelled along ne oriented faults isotopic signatures of calcite cemented horizontal interbeds with depleted 18o ratios as low as 8 88 v pdb and variable 13c 1 to 16 mainly around 5 to 7 suggest that ascending fluids contributed to their cementation or resetted the calcite cement isotopic signature predominantly during periods of active seepage of warmer fluids only few petrographical and preliminary lipid biomarker evidence has been found pointing to the presence or possibly former activity of microbiota involved in carbon cycling and calcite precipitation typical of cold seep settings this may result from diagenetic alteration of organic components however considering the processes of chimney formation a cementation process governed by the inorganic oxidation of hydrocarbons in which interstitial oxygen is rapidly consumed without bacterial mediation is considered

life at cold seeps a synthesis of biogeochemical and ecological data from kazan mud volcano eastern mediterranean sea recent field observations have identified the widespread occurrence of fluid seepage through the eastern mediterranean sea floor in association with mud volcanism or along deep faults gas hydrates and methane seeps are frequently found in cold seep areas and were anticipated targets of the medinaut medineth initiatives the study presented herein has utilized a multi disciplinary approach incorporating observations and sampling of visually selected sites by the manned submersible nautile and by ship based sediment coring and geophysical surveys the study focuses on the biogeochemical and ecological processes and conditions related to methane seepage especially the anaerobic oxidation of methane aom associated with ascending fluids on kazan mud volcano in the eastern mediterranean sampling of adjacent box cores for studies on the microbiology biomarkers pore water and solid phase geochemistry allowed us to integrate different biogeochemical data within a spatially highly heterogeneous system geophysical results clearly indicate the spatial heterogeneity of mud volcano environments results from pore water geochemistry and modeling efforts indicate that the rate of aom is similar to 6 mol m 2 year 1 which is lower than at active seep sites associated with conditions of focused flow but greater than diffusion dominated sites furthermore under the non focused flow conditions at kazan mud volcano advective flow velocities are of the order of a few centimeters per year and gas hydrate formation is predicted to occur at a sediment depth of about 2 m and below the methane flux through these sediments supports a large and diverse community of micro and macrobiota as demonstrated by carbon isotopic measurements on bulk organic matter authigenic carbonates specific biomarker compounds and macrofaunal tissues because the aom community appears to be able to completely oxidize methane at the rate it is seeping through the sediments ultimate sinks for methane in this environment are authigenic carbonates and biomass significant differences in organic geochemical data between this site and those of other cold seep environments even within the eastern mediterranean mud volcanoes indicate that the microbiological communities carrying out aom varies depending on specific conditions such as methane flux and salinity c 2004 elsevier b v all rights reserved

stable carbon isotope records of carbonates tracing fossil seep activity off indonesia stable isotope records of carbonates from up to 20 m long sediment cores from the forearc basin of the sunda arc display significant 13c depletion deviating from expected normal marine levels by 5 to 40 peedee belemnite pdb this depletion is interpreted to be caused by methane seepage and associated authigenic carbonate precipitation in sediments near the seafloor about 2 m sized globular carbonate particles found in isotopically depleted samples support this interpretation their shape suggests microbial mediation of the precipitation process investigation of benthic foraminiferal assemblages in cores which record seep influence indicate times of high abundance with an up to twentyfold increase of the population and a dominance of opportunistic infaunal taxa we relate these events to the seepage of methane thus providing an understanding of the duration and age of this postdepositional process postulated seep activity is most intense between 3 7 kyr b p and 27 33 kyr b p as cores with 13c isotope depletion were taken atop active fault zones in the forearc we suggest a tectonic control of the seepage records of seep activity thus may have the potential to archive imprints of tectonic activity

subtidal water flux through a multiple inlet system observations before and during a cold front event and numerical experiments 1 this paper examines the net transport through a multiple inlet bay under a combined force of strong wind and tide with observations and a model experiment the observations were made in central georgia in sapelo and altamaha sounds between 13 and 17 september 2000 wind was weak in the beginning of the survey an air pressure trough as a weak cold front passed the area on 16 september when the wind changed to the northeast and increased in magnitude this front was associated with a midlatitude cyclone in the new england area this weather event with an episode of strong northeasterly winds prompted a numerical model experiment on an idealized three inlet bay with a set of nonlinear 2 d shallow water equations on an f plane which provides some insight to the wind driven circulation under the presence of tidal forcing it is found that tidally induced currents are small compared to wind induced flows when the wind direction is not perpendicular to the alignment of the three inlets the net outward flow tends to occur at the inlet farther away in the downwind direction this is associated with a net inward transport in the inlet opposite of the downwind direction as a result the middle inlet has the minimum of the net flow when the wind is perpendicular to the barrier islands and if the three inlets have different maximum depth values the deeper inlet tends to have a net flow against the wind while the shallower inlet tends to have a net flow in the direction of the wind offshore onshore currents may develop outside of the inlet with outward inward flow as an effect of fluxes through the inlets on the coastal ocean

isotopically heavy carbon in the c21 to c25 regular isoprenoids in halite rich deposits from the sdom formation dead sea basin israel abstract a series of miocene pliocene halite deposits with extremely low organic carbon contents from the sdom formation dead sea basin israel have been studied distributions and 13c contents of biomarkers have been determined using gc ms and irm gcms analyses respectively the hydrocarbon fractions consist mainly of pristane phytane and c21 to c25 regular isoprenoids the predominance of c21 regular isoprenoids in the dead sea halites and other hypersaline deposits indicate that these components could be derived from ether bound membrane lipids of halophilic archaea the lack of intact ether bound lipids in the polar fractions indirectly infers that such components have already been released at early stages of diagenesis their 13c contents are enriched in 13c by up to 7 compared to the biomarkers of presumed phytoplanktonic origin i e steranes and hopanes within the same sediment sample in agreement with a source other than algae and cyanobacteria thus tentatively assigned as halophilic archaea based on biomarker distributions 13c contents and mineral compositions these sediments appear to have been deposited in a salinity stratified water body with a bottom water brine continual evaporation and deposition of the higher salts i e carnallites are favourable conditions for the growth of halophilic archaeal communities

the effect of channel length on the residual circulation in tidally dominated channels with an analytic model this paper describes the subtidal circulation in tidally dominated channels of different lengths with arbitrary lateral depth variations the focus is on an important parameter associated with the reversal of the exchange flows this parameter is defined as the ratio between the channel length and one quarter of the tidal wavelength which is determined by water depth and tidal frequency in this study a standard bottom drag coefficient cd 0 0025 is used for a channel with smaller than 0 6 0 7 short channels the exchange flow at the open end has an inward transport in deep water and an outward transport in shallow water this situation is just the opposite of channels with a value larger than 0 6 0 7 long channels for a channel with a value of about 0 35 0 5 the exchange flow at the open end reaches the maximum of a short channel for a channel with a value of about 0 85 1 0 the exchange flow at the open end reaches the maximum of a long channel with the inward flux of water occurring over the shoal area and the outward flow in the deep water area however near the closed end of a long channel the exchange flow appears as that in a short channel that is the exchange flow changes direction along the channel from the head to the open end of the channel for a channel with a value of about 0 6 0 7 the tidally induced subtidal exchange flow at the open end reaches its minimum when there is little flow across the open end and the water residence time reaches its maximum the mean sea level increases toward the closed end for all values however the spatial gradient of the mean sea level in a short channel is much smaller than that of a long channel the differences between short and long channels are caused by a shift in dynamical balance of momentum or equivalently a change in tidal wave characteristics from a progressive wave to a standing wave

comments on buoyancy driven lacustrine calving glaciar nef chilean patagonia by c warren d benn v winchester and s harrison

biomarker and 16s rdna evidence for anaerobic oxidation of methane and related carbonate precipitation in deep sea mud volcanoes of the sorokin trough black sea many mud volcanoes were recently discovered in the euxinic bottom waters of the sorokin trough ne black sea three of them i e nioz odessa and kazakov were selected for a detailed biogeochemical investigation four methane related carbonate crusts covered with microbial mats and sediments dmud brecciat from these mud volcanoes were collected during the 11th training through research cruise ttr 11 in 2001 the first finding of methanotrophic microbial mats associated with authigenic carbonates in the deep black sea we measured the concentrations and 13c values of methane and specific archaeal and bacterial lipids and determined archaeal and bacterial 16s rrna gene sequences the 13c of the microbial lipids reflected the carbon isotopic values of the methane indicating that methane was the main carbon source for microorganisms inducing carbonate formation anaerobic oxidation of methane aom in these settings was performed by archaea affiliated with the so called anme 1 group none of the identified archaeal sequences were closely related to known methanogens the combined 16s rrna gene sequence and biomarker data revealed a distinct difference in archaeal assemblage between the carbonate crusts and mud breccias besides gene sequences of sulfate reducing bacteria dna analysis of bacterial communities revealed a diversity of bacteria with apparent contrasting metabolic properties the methane utilization via aom processes was detected in the uppermost sediments where it subsequently induces authigenic carbonate precipitation most probably below seafloor the results of integrated biomarker and 16s rrna gene study reveal a crucial role of aom processes in formation of authigenic carbonates in methane seep environments

first biomarker evidence for methane oxidation at cold seeps in the southeast atlantic regab pockmark abstract sediment cores from the regab pockmark an active cold seep area in the southeast atlantic were analysed for their lipid biomarker distribution and associated stable carbon isotopic composition substantial amounts of diagnostic archaeal lipids were found consisting mainly of archaeol sn 2 hydroxyarchaeol and crocetane all archaeal lipids were profoundly depleted in 13c with 13c values as low as 133 concurrently abundant monoalkylglycerolethers mage assigned to sulphate reducing bacteria were identified and showed strong 13c depletions 13c between 86 and 95 the structural and isotopic patterns of these microbial lipids provided compelling evidence for anaerobic oxidation of methane aom occurring in regab sediments mediated by archaea and sulphate reducing bacteria lipid fingerprints indicated that anaerobic methanotrophic archaea anme 2 and sulphate reducing bacteria from the desulfosarcina desulfococcus cluster are the dominant aom assemblages depth profiles implied that highest aom takes place below the upper 2 cm mainly in the 6 12 cm depth interval significant abundances of 13c depleted diploptene and 4 methylsterols were found as well inferring that aerobic methanotrophy occurs in the surface sediment interval this first biomarker study at the recently investigated cold seeps in the se atlantic expand on existing work on aom settings and add new evidence for aerobic and anaerobic methanotrophic communities occurring in close vicinity

tidally driven residual circulation in shallow estuaries with lateral depth variation tidally driven residual circulation in shallow estuaries with lateral depth variation has been studied analytically using a two dimensional depth averaged model the solution is presented for a v shaped channel exchange flow is found to be correlated with the topography the magnitude of this exchange flow depends mainly on four parameters the ratio between the minimum depth on the shoal and the maximum depth in the channel the ratio between the tidal amplitude at the mouth and the mean depth the ratio between the length of the estuary and the tidal wave length and the ratio between the tidal timescale and the decay timescale due to friction generally a net landward flow occurs over the shoals and is balanced by a return flow in the channel the along channel residual velocity changes nearly linearly across the estuary the residual velocity decreases monotonically toward the head of the estuary the transverse residual velocity is convergent in the channel and divergent on the shoals the residual velocity is highly dependent on the length of the estuary when the length of the estuary is much smaller than a quarter of the wave length the residual velocity is relatively small when the length of the estuary is about a quarter of the wave length the magnitude of the residual velocity reaches its maximum when the length of the estuary is much larger than a quarter of the wave length the residual circulation approaches the pattern found in an infinite length estuary on the basis of the analysis of the solution we conclude that exchange flow generated by tides in a shallow estuary is the result of competition among several processes an inward flux is caused by local nonlinearity both in the bottom friction and from propagation of the tidal wave of finite amplitude this inward flux is larger on the shoals and smaller in the channel owing to larger nonlinearity in the shallow water the residual inward flow creates a setup residual surface elevation of water at the head of the estuary that produces a pressure gradient this residual pressure gradient is approximately uniform across the estuary and drives an outward flow that is larger in the channel than on the shoals in all of the parameter space the competition results in a net inflow on the shoals and a net outflow in the channel

triaxial experiments on iceberg and glacier ice triaxial experiments at confining pressures in the range 0 13 79 mpa have been performed on glacial ice collected from four icebergs and one glacier tests were conducted at strain rates in the range of 5 10 5 to 5 10 2 s 1 and at four temperatures in the range of 1 to 16 c depending on test conditions the ice failed by one of four possible modes ductile deformation due to extensive non interacting microcracks fracture along a shear plane followed by continuous or stick slip sliding large scale brittle fracture and combined ductile and shear plane fracture and slip the strength increased with decreasing temperature increasing strain rate up to 5 10 3 s 1 and increasing confining pressure at the lower temperatures the strength at 5 10 2 s 1 was lower than at 5 10 s 1 probably because extension and interaction of microcracks is enhanced at the higher rate for higher confining pressures at 1 c the strength decreased due to freezing point depression the ice from the different sources exhibited different mean uniaxial compressive strengths the mean number of air bubbles per unit volume correlated with the mean uniaxial compressive strengths and this may be the dominant factor distinguishing the strengths of the various ice types

cretaceous cold seep communities and methane derived carbonates in the canadian arctic lower cretaceous cold seep fossil assemblages have been found in the canadian arctic archipelago serpulid worm tubes and bivalves are most abundant in these communities in contrast fossils are scarce in the surrounding strata the fossils are contained in an isotopically light delta 13 c 25 to 50 per mil carbonate rock groundmass that is interpreted to have formed from bacterial oxidation of methane the rocks were deposited at intermediate depth 400 meters in a cold marine environment nearby normal faults may have provided a conduit for seeping methane and hydrogen sulfide needed to fuel chemosynthetic bacteria and in turn the higher life forms

tracing organic compounds in aerobically altered methane derived carbonate pipes gulf of cadiz sw iberia abstract the primary geochemical process at methane seeps is anaerobic oxidation of methane aom performed by methanotrophic archaea and sulfate reducing bacteria srb the molecular fingerprints biomarkers of these chemosynthetic microorganisms can be preserved in carbonates formed through aom however thermal maturity and aerobic degradation can change the original preserved compounds making it difficult to establish the relation between aom and carbonate precipitation here we report a study of amino acid and lipid abundances in carbonate matrices of aerobically altered pipes recovered from the seafloor of the gulf of cadiz sw iberian peninsula this area is characterized by a complex tectonic regime that supports numerous cold seeps studies so far have not determined whether the precipitation of carbonate pipes in the gulf of cadiz is a purely chemical process or whether microbial communities are involved samples from this site show signs of exposure to oxygenated waters and of aerobic alteration such as oxidation of authigenic iron sulfides in addition the degradation index calculated from the relative abundance of preserved amino acids indicates aerobic degradation of organic matter although crocetane was the only lipid identified from methanotrophic archaea the organic compounds detected n alkanes regular isoprenoids and alcohols are compatible with an origin from aom coupled with bacterial sulfate reduction bsr and subsequent aerobic degradation we establish a relation among aom bsr and pipe formation in the gulf of cadiz through three types of analysis 1 stable carbon and oxygen isotopic composition of carbonate minerals 2 carbonate microfabrics and 3 mineralogical composition our results suggest that carbonate pipes may form through a process similar to the precipitation of vast amounts of carbonate pavements often found at cold seeps our approach suggests that some organic compound patterns in combination with additional evidence of aom and bsr may help indicate the source of altered methane derived carbonates commonly occurring in ancient and modern deposits

molecular indicators of methane metabolisms at cold seeps along the united states atlantic margin abstract anaerobic oxidation of methane aom and the environmental conditions supporting aom on continental margins is an essential component to global methane budgets diagnostic lipid biomarkers and their compound specific isotope analysis preserved in authigenic carbonates at cold seeps can serve as fingerprints to archaeal bacterial consortia involved in aom however despite the discovery of several hundreds of seeps along the united states atlantic margin usam there are relatively few biomarker investigations of cold seep carbonates along this passive margin a lipid biomarker carbon isotope and dna marker gene study was therefore undertaken to determine the microbial origins of authigenic carbonates from two usam seeps norfolk and the baltimore canyon seep fields results from this study capture a distinct archaeal lipid signature from putative methanotrophic archaea including archaeol i sn 2 hydroxyarchaeol 2 6 10 15 19 pentamethylicosane pmi and crocetane the 13c depleted aom related archaeal lipid samples i e archaeol 91 6 sn 2 hydroxyarchaeol 129 2 pmi 92 8 and crocetane 70 9 confirm the dominance of methane assimilation and isotope fractionation during aom these results are consistent with the detection of archaeal anaerobic methanotrophs anmes based on 16s rrna gene sequencing the norfolk authigenic carbonate contained anme 1a 1b 2a 2b and 2c whereas only the anme 2 clade was detected at baltimore and present as the subclusters 2a 2b and 2b the anme 2d clade may also be present particularly at the baltimore seep site given the high abundance of candidatus methanoperedens nitroreducens detected in the mcra gene sequencing the presence of terminally branched fatty acids antesio and iso c15 0 components as well as c16 1 7 with 13c values as low as 107 6 are indicative of sulfate reducing bacteria srb at the norfolk seep site and supports syntrophy of srb with methane oxidizing archaea in contrast nitrate driven aom in syntrophy m nitroreducens at the baltimore seep site is consistent with elevated fatty acid 13c values and lack of deltaproteobacteria at the baltimore seep site taken together the range in lipid composition distribution and carbon isotopic composition observed at the norfolk and baltimore seep sites suggests aom is performed by multiple archaea instead of a single species and may be paired with either or both nitrate and sulfate reduction given the heterogeneous nature of cold seep ecosystems this study fills a critical spatial gap in our knowledge of aom activity at two seep sites along a passive margin

summertime tidal flushing of barataria bay transports of water and suspended sediments the edges of the inlet the net flux of total suspended sediment out of the bay was determined to be 8800 t of which 20 was organic matter demonstrating a significant source of organic matter to the base of the coastal ocean detrital food chain the time evolution and net fluxes of water and suspended sediments showed that the net flow resembles conventional estuarine circulation patterns with net outward flow on the surface and shallow ends of the inlet and with net inward flow in the center and at the bottom of the center of the inlet the west side has a much larger outward flow than the east side while the east side is fresher these differences suggest that the louisiana coastal current from around the bird s foot delta derived from the mixing of shelf water with the mississippi river freshwater may have entered the bay this must have been mostly from the east side during the survey which resulted in a smaller outward flow on the eastern side a numerical experiment further confirmed this assumption and the model was verified by field observations on 5 may 2010

molecular and isotopic analysis of anaerobic methane oxidizing communities in marine sediments convergent lines of molecular carbon isotopic and phylogenetic evidence have previously indicated hinrichs k u hayes j m sylva s p brewer p g delong e f 1999 methane consuming archaebacteria in marine sediments nature 398 802 805 that archaea are involved in the anaerobic oxidation of methane in sediments from the eel river basin offshore northern california now further studies of those same sediments and of sediments from a methane seep in the santa barbara basin have confirmed and extended those results mass spectrometric and chromatographic analyses of an authentic standard of sn 2 hydroxyarchaeol hydroxylated at c 3 in the sn 2 phytanyl moiety have confirmed our previous tentative identification of this compound but shown that the previously examined product was the mono tms rather than di tms derivative further analyses of 13 c depleted lipids appreciably more abundant in samples from the santa barbara basin have shown that the archaeal lipids are accompanied by two sets of products that are only slightly less depleted in 13 c these are additional glycerol ethers and fatty acids the alkyl substituents in the ethers mostly monoethers with some diethers are non isoprenoidal the carbon number distributions and isotopic compositions of the alkyl substituents and of the fatty acids are similar suggesting strongly that they are produced by the same organisms their structures n alkyl and methyl branched n alkyl require a bacterial rather than archaeal source the non isoprenoidal glycerol ethers are novel constituents in marine sediments but have been previously reported in thermophilic sulfate and nitrate reducing organisms which lie near the base of the rrna based phylogenetic tree based on previous observations that the anaerobic oxidation of methane involves a net transfer of electrons from methane to sulfate it appears likely that the non archaeal 13 c depleted lipids are products of one or more previously unknown sulfate reducing bacteria which grow syntrophically with the methane utilizing archaea their products account for 50 of the fatty acids in the sample from the santa barbara basin at all methane seep sites examined the preservation of aquatic products is apparently enhanced because the methane oxidizing consortium utilizes much of the sulfate that would otherwise be available for remineralization of materials from the water column

estimation of drag coefficient in james river estuary using tidal velocity data from a vessel towed adcp 1 a phase matching method is introduced to calculate the bottom drag coefficient in tidal channels with significant lateral variation of depth the method is based on the fact that the bottom friction in a tidal channel causes tidal velocity to have a phase difference across the channel the calculation involves a few steps first the observed horizontal velocity components are analyzed to obtain the amplitude and phase of the velocity at the major tidal frequency the phase of the longitudinal velocity is then fitted to a relationship derived from the linearized momentum balance the drag coefficient is then calculated this method is applicable to narrow approximately a few kilometers wide tidal channels without strong stratification and where the cross channel variation of surface elevation is negligible compared to tidal amplitude this analytic approach is easy to implement when appropriate observational data are available it allows a spatial variation of the drag coefficient and the resolution is only limited by that of the observations the method is validated by identical twin experiments and applied to tidal velocity data obtained in the james river estuary using an acoustic doppler current profiler during spring tides and neap tides in october november 1996 the obtained bottom drag coefficient ranged from 1 2 10 3 to 6 9 10 3 at different positions along two cross channel transects each 4 km long and 2 to 14 m deep the maximum drag coefficient is found in the shallowest water near the banks of the estuary while the minimum values occur between 9 and 12 m in the center of the channel the friction of the lateral boundary may have contributed to the apparent increase of the bottom friction on the banks the transverse mean values of the drag coefficient ranges between 2 2 and 2 3 10 3 for the spring and neap tides respectively index terms 4594 oceanography physical instruments and techniques 4203 oceanography general analytical modeling 4560 oceanography physical surface waves and tides 1255 4568 oceanography physical turbulence diffusion and mixing processes keywords drag coefficient tides analytic model

mapping of tide and tidal flow fields along a tidal channel with vessel based observations 1 we present the results of a study focused on the tidal regime of a shallow channel with a large intertidal area data from a vessel towed acoustic doppler current profiler adcp were used to infer tidal constituents for both tidal elevation and tidal current along an upstream portion of the okatee river south carolina the tidal elevation is estimated from the depth recorded by the moving adcp this tidal elevation is then used to correct the vertical coordinates of each depth bin below the adcp for the velocity profiles the ability to resolve both tidal elevation and velocity allows us to determine that the tide is a standing wave a statistical analysis demonstrates that the along channel velocity has a stronger tidal signal larger r2 values than the across channel velocity when only the m2 and mean components are included in the harmonic analysis about 75 of the covered area along the ship track has a good fit where at least 70 of the variability can be explained by the tidal and mean components by adding the m4 component to the harmonic analysis an additional 2 of the covered area has good fit for the elevation depth averaged velocity and mid depth velocity but 12 for the near surface velocity the observed spatial distribution of the residual flow is in reasonable agreement with that predicted by an unstructured grid finite volume coastal ocean model fvcom

seismic multiplet response triggered by melt at blood falls taylor glacier antarctica 1 meltwater input often triggers a seismic response from glaciers and ice sheets it is difficult however to measure melt production on glaciers directly while subglacial water storage is not directly observable therefore we document temporal changes in seismicity from a dry based polar glacier taylor glacier antarctica during a melt season using a synthesis of seismic observation and melt modeling we record icequakes using a dense six receiver network of three component geophones and compare this with melt input generated from a calibrated surface energy balance model in the absence of modeled surface melt we find that seismicity is well described by a diurnal signal composed of microseismic events in lake and glacial ice during melt events the diurnal signal is suppressed and seismicity is instead characterized by large glacial icequakes we perform network based correlation and clustering analyses of seismic record sections and determine that 18 of melt season icequakes are repetitive multiplets the epicentral locations for these multiplets suggest that they are triggered by meltwater produced near a brine seep known as blood falls our observations of the correspondingp wave first motions are consistent with volumetric source mechanisms we suggest that surface melt enables a persistent pathway through this cold ice to an englacial fracture system that is responsible for brine release episodes from the blood falls seep the scalar moments for these events suggest that the volumetric increase at the source region can be explained by melt input