foraminiferal response to an active methane seep environment a case study from the adriatic sea abstractit has been analysed the taxonomic structure and isotopic composition of the cytoplasm and tests of living rose bengal stained protoplasm full and dead empty tests benthic foraminifera 63 m in surface sediments from sites with and without methaneseepage at water depths of about 25 m water in the northern adriatic sea and compared these data to isotope analyses of carbonaterocks at the same locations foraminiferal density is higher in seep samples than in control ones despite the low oxygen and highsulphide contents in sediments the 13 c values in foraminiferal cytoplasm at the seep sites are lower than those in cytoplasm ofthe same species in control samples suggesting that beggiatoa may be a food source for the foraminifera and explaining thehigher foraminiferal density at the seep site in contrast the 13 c values of tests of living and dead benthic foraminifera at seep siteswere not significantly different from those in tests of the same species collected at the control sites therefore the carbon isotopevalues of foraminiferal tests in this area do not reflect the ones of the methane seepage although the authigenic carbonate incalcareous sandstones of the methane seepage area is significantly negative and indicates the contribution of methane seepage thesimilar carbon isotope values measured in the foraminiferal tests from shallow settings of the north eastern adriatic sea seemtherefore to be independent of methane seepages 2006 elsevier b v all rights reserved

an enigmatic kilometer scale concentration of small mytilids late miocene guadalquivir basin s spain abstract upper miocene heterozoan carbonates crop out extensively in a ne sw trending belt 42 km long and 1 5 8 km wide along the so called el alcor topographic high from carmona to dos hermanas seville s spain these carbonates formed at the southern active margin of the guadalquivir basin the foreland basin of the betic cordillera they change to marls basinward ne and to sands landward se and sw therefore carbonate production was constrained to a limited area in an otherwise siliciclastic shelf the carbonates up to 40 m thick overlie a gradually coarsening upward succession of marls followed by silts and sandstones the carbonate sequence can be divided into three subunits corresponding from bottom to top to lowstand transgressive and highstand system tract deposits the lower subunit exhibiting extensive trough cross bedding is interpreted as a shallow water bar deposit the intermediate subunit onlaps underlying sediments and was deposited in deeper low turbulence conditions the upper subunit deposits accumulated in a well oxygenated outer platform based on benthic foraminiferal assemblages the presence of hummocky and swaley cross stratification in these latter deposits suggests that they were affected by storms pervasive fluid escape structures are also observed throughout the carbonates the three subunits consist of bioclastic packstones to rudstones made up of abundant fragments of small mytilids isotopic data from serpulid polychaete ditrupa tubes show 13c depleted values up to 16 1 whereas 18o yields normal marine values additional isotopic data on shells of scallops oysters and small mussels as well as bulk sediment show diagenetic alterations based on actualistic examples of massive concentrations of mussels the nearly monospecific composition of the el alcor deposits together with negative 13c values of ditrupa tubes indicates that cold seeps presumably promoted carbonate formation however the absence of typical features of cold seep deposits such as authigenic carbonates mediated by anaerobic bacterial activity and the typical chemosynthetic shelly organisms makes the large carbonate body of el alcor an unusual cold seep deposit

methane rich plumes on the carolina continental rise associations with gas hydrates seafloor venting of microbial gases occurs at 2167 m water depth over the blake ridge diapir gas rich plumes were identified acoustically in the water column up to 320 m above a pockmarked sea floor associated with active chemosynthetic biological communities plumes and venting fluids emanate from near a small fault that extends downward toward a dome in the bottom simulating reflector indicating that fluid and or gas migration is associated with gas hydrate bearing sediment below these plumes might be caused by gas bubbles or buoyant dumps of gas hydrate that float upward from the seafloor 18 refs 3 figs

foraminifera from gas hydrate bearing sediments of the northeastern south china sea proxy evaluation and application for methane release activity abstract anomalously low 13c values of foraminifera in the stratigraphy are usually interpreted to reflect activities of paleo methane seepage the application of this proxy however requires to understand the cause of anomalously low 13c signals in foraminifera here we present stable carbon and oxygen isotopes 13c and 18o mg ca ratios and accelerator mass spectrometry ams radiocarbon data from cores gmgs2 08b 0 5 5 m below the seafloor mbsf and 08c 2 23 mbsf at 798 m water depth recovered from the gas hydrate bearing sediments in the northeastern south china sea scs the main objectives are to investigate the primary versus secondary signals of extremely negative 13c values of foraminifera and further recognize the methane emission events mees the 13c values of benthic uvigerina peregrina and cibicidoides spp and planktonic globigerinoides ruber and pulleniatina obliquiloculata foraminifera in these two cores show distinct intervals with negative values as low as 15 85 that indicate the shift of the sulfate methane transition zone smtz and the change in methane release flux in the past the 13c records of u peregrina by a more exhaustive cleaning procedure designed to remove authigenic carbonate coatings show that most 13c values are still lower relative to those in the normal marine environment the mg ca ratios of uvigerina spp by this exhaustive cleaning procedure display higher values and more variable for anomalous tests as high as 13 40 mmol mol than normal ones these observations indicate the 13c depleted signals of foraminifera are mainly originated from diagenetic alteration of authigenic carbonate precipitates with extremely negative 13c values furthermore the mass balance approach is adopted to assess the relative contribution of methane derived authigenic carbonate in the low 13c signals in foraminifera and reveals the maximum contribution can be as high as 30 among the 13c anomalies additionally several major mees with distinct characteristics can be recognized according to remarkable 13c excursions of foraminifera in these two cores

foraminifera as indicators of methane rich environments a study of modern methane seeps in santa barbara channel california methane hydrates have been implicated as a possible forcing mechanism for rapid climate change during the late quaternary via the release of methane from marine reservoirs carbon isotopic excursions of foraminifera observed in high resolution sediment records from santa barbara basin odp site 893 have been interpreted as evidence of episodes of methane release during the late quaternary however the potential relationship between methane in the modern environment and its effect on the stable isotopic composition of benthic and planktonic foraminifera is not well understood short cores taken inside a 500 m diameter pockmark with active methane seeps in santa barbara channel ca usa yield information on the effect of high concentrations of environmental methane on foraminiferal assemblages and their stable isotopic composition these seeps reside at 120 m water depth in the eastern portion of the channel associated with faults and fractures in the miocene monterey formation planktonic foraminiferal assemblages and radiocarbon ages show that surface sediments are of late glacial age 25 300 calendar years this finding suggests an absence of holocene and deglacial sedimentation in the seep area likely due the formation of the pockmarks and subsequent winnowing or lack of sedimentation benthic foraminiferal assemblages are marked by high abundance of bolivina tumida a species previously observed during interstadial episodes and the early holocene in santa barbara basin interpreted to include episodes of high methane flux from the basin while oxygen isotopic values of both benthic and planktonic foraminifera appear normal for cool glacial conditions negative carbon isotopic values are seen in benthic foraminifera primarily in the near surface intervals in one interval 1 2 cm below surface both benthic and planktonic species record highly negative carbon isotopic values implying that isotopically light methane influenced the entire water column this spike is of similar or larger magnitude than several earlier observed spikes in the late quaternary record from odp site 893 single specimen isotopic analyses give an indication of the total range of carbon isotopic values recorded 0 01 to 25 23 for benthics 0 07 to 22 22 for planktonics in the spike interval since modern methane seeps are commonly associated with authigenic carbonate precipitation scanning electron microscopy was used to assess the possibility that post depositional alteration may have affected the isotopic composition of the test these experiments indicate that authigenic carbonate is absent and therefore unable to account for the highly negative carbon isotopic signatures these data improve our understanding of methane associated environments by showing that foraminiferal isotopic composition and assemblages may be used to discern the flux of methane from the oceanic reservoir in the geologic record

recent benthic foraminifera from the continental margin of northwest africa community structure and distribution abstract sediment grab samples were collected at 107 locations along the continental margin of northwest africa these samples form a series of depth transects between the straits of gibraltar and dakar senegal the greater than 250 m size fraction was retained for a census of both the live and dead foraminifera after deleting trace occurrences jaccard and correlation coefficient based cluster analyses were performed to decipher the community structure for this margin the geographic distribution of the four major faunal provinces recognized is conventional in that for both the live and dead assemblages three are related to depth upper slope and shelf middle slope and lower slope and continental rise the biotopes and thanatotopes within these provinces are strongly restricted along vertical or latitudinal boundaries when the data are analysed using jaccard coefficients dendrograms constructed from correlation coefficients emphasize depth related faunal communities dominant species such as cibicides lobatulus trifarina fornasinii planulina ariminensis uvigerina finisterrensis and c wuellerstorfi are generally distributed within a definite depth range along this margin and strongly influence the correlation coefficient based dendrograms other distributions are clearly not depth related but correspond to various environmental variables for example cancris auriculus coarse substrate bolivina subaenariensis oxygen minimum cibicidoides kullenbergi and hoeglundina elegans low organic carbon uvigerina peregrina is also a notable exception to depth dependence in that this dominant species and the province it represents are generally confined to the continental slope south of cape blanc its preference for that region may arise from the high organic carbon and fine grain size of the sediment there from low salinity of the bottom water or from other unknown variables the most important vertical faunal boundary occurs between cape barbas and cape blanc between 22 and 21 n latitude in contrast the canary island ridge intersects the continental margin at a saddle depth of about 1500 m but that physiographic barrier has little effect on provincialism of the deep water benthic foraminifera

relationships between the distribution and stable isotopic composition of living benthic foraminifera and cold methane seep biogeochemistry in monterey bay california 1 as part of an ongoing effort to explore the use of foraminifera as a means to assess modern and ancient methane release we compared ambient pore water chemistry with the distribution and stable isotopic composition of living rose bengal stained foraminifera in mbari rov ventana tube cores taken from modern seepage areas about 1000 m water depth in monterey bay california benthic foraminiferal isotopic differences between sites clearly indicate that methane influenced pore waters affect foraminiferal distributions and carbonate isotope geochemistry carbon isotope signatures of living benthic foraminifera did not conform to the very negative 30 to 48 methane influenced carbon isotope values of the pore waters they live in instead the influence of methane seep pore waters was reflected in the greater range and carbon isotopic variability of living seep foraminifera compared with published 13c values of foraminifera living in nonseep habitats it is not clear what relative influences biological ecological and physical factors have on the carbon isotopic signatures observed in seep foraminifera substantial carbon isotope differences can exist between individuals of the same seep species for instance 13c values of living globobulimina pacifica varied by as much as 2 9 between seeps within 8 km of each other whereas 13c values of living uvigerina peregrina varied by as much as 1 95 within the same seep provided there is no diagenetic alteration of the test carbonate isotopic results of individual seep foraminifera support the hypothesis that foraminifera can be used to assess past and present methane seepage

benthic foraminifera associated with cold methane seeps on the northern california margin ecology and stable isotopic composition release of methane from large marine reservoirs has been linked to climate change as a causal mechanism and a consequence of temperature changes during the quaternary and the paleocene these inferred linkages are based primarily on variations in benthic foraminiferal stable isotope signatures few modern analog data exist however to assess the influence of methane flux on the geochemistry or faunal characteristics of benthic foraminiferal assemblages here we present analyses of the ecology and stable isotopic compositions of living rose bengal stained and dead fossil foraminifera 150 mm from cold methane seeps on the slope off of the eel river northern california 500 525 m and discuss potential applications for reconstructions of methane release in the past and present calcareous foraminiferal assemblages associated with calyptogena clam bed seeps were comprised of species that are also found in organic rich environments cosmopolitan paleoceanographically important taxa were abundant these included uvigerina bolivina chilostomella globobulimina a ndnonionella we speculate that seep foraminifera are attracted to the availability of food at cold seeps and require no adaptations beyond those needed for life in organic rich reducing environments oxygen isotopic values of the tests of living foraminiferal assemblages from seeps had a high range up to 0 69 as did carbon isotopic values up to 1 02 many living foraminiferal isotope values were within the range exhibited by the same or similar species in non seep environments carbon isotopic values of fossil foraminifera found deeper in the sediments 18 20 cm however were 4 10 u peregrina and 3 60 b subargentea more negative than living d 13 c values these results suggest that d 13 c values of foraminiferal tests reflect methane seepage and species specific differences in isotopic composition and can indicate temporal variations in seep activity a better understanding of foraminiferal ecology and stable isotopic composition will enhance paleo seep recognition and improve interpretations of climatic and paleoceanographic change 2000 elsevier science b v all rights reserved

spectral wave dissipation over a barrier reef 1 a 2 week field experiment was conducted to measure surface wave dissipation on a barrier reef at kaneohe bay oahu hawaii wave heights and velocities were measured at several locations on the fore reef and the reef flat which were used to estimate rates of dissipation by wave breaking and bottom friction dissipation on the reef flat was found to be dominated by friction at rates that are significantly larger than those typically observed at sandy beach sites this is attributed to the rough surface generated by the reef organisms which makes the reef highly efficient at dissipating energy by bottom friction results were compared to a spectral wave friction model which showed that the variation in frictional dissipation among the different frequency components could be described using a single hydraulic roughness length scale surveys of the bottom roughness conducted on the reef flat showed that this hydraulic roughness length was comparable to the physical roughness measured at this site on the fore reef dissipation was due to the combined effect of frictional dissipation and wave breaking however in this region the magnitude of dissipation by bottom friction was comparable to wave breaking despite the existence of a well defined surf zone there under typical wave conditions the bulk of the total wave energy incident on kaneohe bay is dissipated by bottom friction not wave breaking as is often assumed for sandy beach sites and other coral reefs

a thermogenic hydrocarbon seep in shallow adriatic sea italy gas origin sediment contamination and benthic foraminifera abstract gaseous and liquid hydrocarbons are seeping from sandy sea bottom 10 m deep about 2 4 km nne of civitanova marche harbour in central adriatic sea italy we investigated the origin of the gas the presence of a wide range of aromatic and aliphatic hydrocarbons and trace metals in shallow sediments as well as the stable carbon and oxygen isotope composition of benthic foraminifera in absence of detailed seismic images and subsurface geochemical data we tried to estimate the source rock type and maturity based only on seep gas geochemistry molecular and isotopic composition of gas bubbles showed that the ch4 rich gas is thermogenic 13 c ch 4 55 2 h ch 4 280 c1 c2 c3 13 c co 2 12 fluid seepage might be due to a local fracture zone corresponding to the intersection of nnw sse thrust faults with a ne sw regional transversal deformation belt compared to other shallow marine seeps in europe the amount of methane released into the atmosphere is negligible 102 103 kg of ch4 per year but the seep also releases ethane and propane 103 104 l per year which are photochemical pollutants and are not emitted by microbial gas seeps compared to a reference site one nautical mile far from the seep the seabed sediments show higher concentrations of various classes of chemicals such as benzene toluene and ethylbenzene semivolatile and non volatile aliphatic hydrocarbons c10 c40 and phenols 2 methylphenol and 2 4 dichlorophenol these compounds likely derive from the oil seepage the sediments at the seepage site and those at the reference site have similar concentrations of trace metals arsenic barium cadmium chromium copper iron manganese nickel lead vanadium zinc mercury typical of uncontaminated and shallow coastal areas finally we provided the first data on foraminifera associated to thermogenic hydrocarbons no endemic foraminifera species or authigenic carbonates occur in the sediments carbon isotopic composition of quinqueloculina padana where oil slick prevails is less variable than in the gas bubbling site however thermogenic methane and oil do not apparently decrease the 13c value of foraminifera carbonate shell

benthic foraminifera of the blake ridge hydrate mound western north atlantic ocean abstract in a 240 m 70 m area at the top of the blake ridge diapir water depth 2150 m the benthic foraminiferal assemblage in surface sediment 0 1 cm consists of about 130 species hydrocarbon seepage is indicated here by the presence of methanotrophic bivalves and white bacterial mats and by present day formation of gas hydrate the foraminiferal assemblage density is generally high indicating an abundance of food bolivina lowmani and globocassidulina subglobosa dominate the assemblage in the silt clay substrate whether at the edge of bathymodiolid mussel beds or under bacterial mats the only notable difference between these two sample groups is in the higher variation of foraminiferal density in the mussel bed samples a control sample at 32 29 654 n and 76 11 324 w taken from bioturbated sediment light grey silt and clay with no visible bacterial or molluscan colonization is comparable to the seep samples in the distribution of calcareous species but shows a much higher diversity and abundance of agglutinated species no segregation of foraminiferal species by substrate geochemistry can be inferred for the seep samples and the possible effect of variable sulfide or methane fluxes on the community cannot be demonstrated by our data

wave set up on coral reefs 2 set up on reefs with various profiles abstract all available laboratory data for wave set up on two dimensional reef profiles of various shapes have been compared with data from an idealised horizontal reef with a steep reef face gourlay 1996 the data is generally well represented by a relationship between the relative set up parameter gh r t o and the submergence parameter g h r h r h o and the relative set up on reef profiles of natural form is found to be less than that observed on the idealised horizontal reef the important influences of reef rim slope and variable water depths on the reef top have been investigated and some methods for allowing for them are suggested comparison of data for irregular waves with that for regular waves has led to the development of a simple method for estimating the effects of wave groups upon the magnitude of the steady state mean wave set up gh r the results of the analyses are applied to the determination of wave set up and its effects at three specific coral reef sites

methane seepages recorded in benthic foraminifera from miocene seep carbonates northern apennines italy abstract benthic foraminifera from seep carbonates and from enclosing non seep marls present within miocene formations in the northern apennines italy were investigated as proxies of methane seepage in the marine environment negative 13c values of benthic foraminifera from these seeps indicate unambiguously the local influence of co2 produced by microbial anaerobic methane oxidation on the benthic ecosystem calcareous species living within methane seeps display 13c values ranging from 9 04 to 25 74 pdb whereas in the coeval surrounding marls the same species display 13c values from 1 54 to 0 62 pdb different species cibicidoides kullenbergi c pachyderma siphonina rethiculata planulina wuellestorfi bolivina miocenica brizalina dilatata vulvulina pennatula and cibicides praecinctus in different seep carbonates indicate that benthic foraminifera independently of the taxa and of microhabitat preferences have more negative 13c values than those found in the enclosing marls therefore each species represents a potential proxy for past seafloor methane emissions in addition to the calcareous species the agglutinated species vulvulina pennatula displays 27 5 pdb in seep carbonates against 2 69 pdb in the enclosing marls this suggests that the species utilized strongly 13c depleted carbonate particles from authigenic carbonate precipitation during the mineralization of their tests

trophic control of benthic foraminiferal abundance and microhabitat in the bathyal gulf of lions western mediterranean sea surface sediment was sampled at two bathyal sites in the southwestern gulf of lions in the western mediterranean sea in february and august 1997 to study the distribution and microhabitat of living rose bengal stained deep sea benthic foraminifera both standing stock and diversity of the faunas and the microhabitat of distinct species mirror the trophic situation and the depth of the oxidised layer at the different sites our results suggest that the faunas do not comprise highly opportunistic species and are adapted to rather stable environments in the axial channel of the lacaze duthiers canyon organic matter fluxes are enhanced due to advective transport of organic matter resulting in elevated oxygen consumption rates in the surface sediment and a rather thin oxidised layer the corresponding benthic foraminiferal fauna is characterised by rather high standing stock and diversity and a well developed deep infauna in addition to freshly deposited phytodetritus more degraded organic matter seems to be an important food source in contrast at the open slope organic matter fluxes and oxygen consumption rates in the surface sediment are lower and the oxidised layer is much thicker than inside the canyon the corresponding benthic foraminiferal fauna comprises mainly epifaunal and shallow infaunal species with much lower standing stocks and clear differences between february and august in august standing stocks are higher and the average living depths of most species shift towards the sediment surface these differences can be attributed to patchiness or represent a seasonal trophic signal

fluid and chemical cycling at bush hill implications for gas and hydrate rich environments 1 the results of a deployment of aqueous flux meters at the bush hill hydrate mound show that persistent hydrologic instability is a primary feature of the globally abundant gas and hydrate rich cold seep environment seven flux meters were deployed for 14 weeks in the area of the bush hill hydrate mound instruments were deployed on microbial mats bivalves adjacent to the surface hydrate mound and a site without visible fauna flow rates were observed to range from downflow of 0 01 mm day to upflow of 15 mm day temporal variability and a major hydrological event were observed to occur on all instruments there is evidence that this event was related to a gas expulsion episode the two instruments which exhibited downflow during the event were near surface hydrates and bubbling vents nearby instruments recorded a rapid increase in flow rates at the time of the event with a subsequent decrease in rates to the previous background values two instruments showed significant output of seawater like fluids while the others output typical methane seep type pore fluids these results at a passive margin site along with our previously published convergent margin results at gas rich northeast pacific cold seeps hydrate ridge eel river margin illustrate the hydrologic complexity of these environments we now propose that these and our earlier results are characteristic of seafloor environments which have abundant free gas and hydrates these mechanisms have major consequences for the near surface geochemical and microbial environment and for the way we interpret measurements made in these areas

field observations of wave refraction and propagation pathways on coral reef platforms field experiments were conducted to investigate the refraction and propagation of ocean waves across two coral reef platforms in the maldives central indian ocean a total of seven pressure sensors were deployed on each reef to quantify temporal and spatial variations in wave characteristics across the platform surfaces directional wave properties were calculated from high frequency 2 hz wave and current records obtained at two locations on each reef and corroborate theoretically predicted propagation pathways derived from an analytical wave refraction model results demonstrate that reef geometry critically controls the refraction and propagation behaviour of incident swell across the reef structures differences in the magnitude of refraction approximately 57 and 14 observed on each reef can be attributed to variations in platform shape and orientation to incident waves results demonstrate that reef flat wave patterns define the segmentation of platform surfaces into distinctive high and low wave energy zones furthermore wave focussing has been identified as a major mechanism controlling the transformation of wave energy across the reefs results provide the first field based validation of wave refraction and convergence on coral reefs and have significant implications for sedimentation processes and the formation of platform deposits reef configurations which promote marked wave convergence are more likely to retain sediment on the reef surface whereas platforms that induce less refraction and changes in the direction of incident waves have a higher potential for the off reef evacuation of sediment over leeward reef margins results of wave measurements substantiate such projections and provide a first order explanation for the existence and absence of a coral cay on the two study reefs the study presents empirical evidence of wave refraction and convergence on coral reefs and establishes a baseline for future investigations of hydrodynamic process controls on platform sedimentation and island formation copyright 2012 john wiley sons ltd

trapping and migration of methane associated with the gas hydrate stability zone at the blake ridge diapir new insights from seismic data abstract the blake ridge diapir is the southernmost of a line of salt diapirs along the carolina trough diapirs cause faulting of the superjacent sediments creating pathways for migration of fluids and gas to the seafloor we analyzed reflection seismic data from the blake ridge diapir which is located in a region with known abundant gas hydrate occurrence a striking feature in these data is a significant shallowing of the base of gas hydrate stability bghs over the center of the diapir the seafloor is warped up by about 100 m above the diapir from about 2300 m to about 2200 m the bghs as indicated by a bottom simulating reflection bsr is about 4 5 s off the flanks of the diapir rising to about 4 15 s at the center above the diapir a fault system appears to rise vertically from the bghs to about 0 05 s below the seafloor 40 50 m it then diverges into several steeply dipping faults that breach the seafloor and cover an area 700 m in diameter other secondary faults diverge from the main fault or emerge directly from the bghs near the crest of the diapir gas and other fluids may migrate upward through the faults we performed complex trace analysis to compare the reflection strength and instantaneous frequency along individual reflections a low frequency anomaly over the center of the diapir indicates high seismic attenuation this is interpreted to be caused by migration of fluids probably methane along fault pathways the migration of gas i e probably mainly methane through the gas hydrate stability zone is not yet understood we speculate that pore fluids in the faults may be too warm and too salty to form gas hydrate even at depths where gas hydrate is stable away from the diapir alternatively gas hydrates may seal the fault walls such that water supply is too low to transform all the gas into gas hydrates the shallowing of the bsr may reflect increased heatflow above the diapir either caused by the high thermal conductivity of the underlying salt or by advective heat transport along with fluids high pore water salinity shifts the gas hydrate stability to lower temperatures and may also play a significant role in bsr shallowing we therefore investigated the possible effect of pore water salinity on shallowing of the bsr we found that bsr shallowing may theoretically be entirely caused by increased salinity over the diapir although geologically this would not be reasonable this observation demonstrates the potential importance of pore water salinity for lateral variations of bsr depths in particular above salt structures

late holocene foraminifera of blake ridge diapir assemblage variation and stable isotope record in gas hydrate bearing sediments abstract the presence of gas hydrates on the blake ridge diapir northeastern atlantic ocean offers an opportunity to study the impact of methane seepage on the ecology and geochemistry of benthic foraminifera in the late holocene three push cores covering a time span of 1000 yrs were retrieved from three distinct microhabitats at the top of the diapir at a water depth of 2150 m i sediments away from seepage control core ii sediments overlain by clusters of methanotrophic and thiotrophic bivalves and iii chemoautotrophic microbial mats the foraminiferal assemblages at the two seep sites are marked by a reduction in benthic foraminiferal species diversity coupled with a near absence of agglutinated species however an opportunistic population rise in ch4 or h2s tolerant calcareous species e g globocassidulina subglobosa and cassidulina laevigata that utilize the abundant trophic resources at the seeps has led to an increase in the overall assemblage density there the 18o and 13c values of three species of benthic foraminifera gyroidinoides laevigatus globocassidulina subglobosa and uvigerina peregrina and the planktonic species globorotalia menardii were acquired from all three cores the benthic species from methane seeps yield 13c values of 0 1 to 4 2 vpdb that are distinctly more 13c depleted relative to the 13c of 0 4 to 1 0 vpdb at the control off seep site the species from a mussel bed site exhibit more negative 13c values than those from microbial mats possibly reflecting different food sources and higher rate of anaerobic oxidation of methane the positive 13c values in the paired planktonic species suggest that authigenic carbonate precipitation did not overprint the observed 13c depletions hence the probable cause of negative 13c of benthic foraminifera is primary calcification from dissolved inorganic carbon dic containing mixed carbon fractions from a highly 13c depleted microbially oxidized methane and b a seawater source

stable isotope tracers natural and anthropogenic recharge orange county california abstract stable isotopic techniques have been utilized to locate occurrences and trace movements of a variety of naturally and anthropogenically recharged waters in aquifers of orange county california this basin is of particular interest not only because it provides the dominant water supply for the two million residents of this well populated county but also because it is representative of a common arid environment where natural recharge is dominated by distant high elevation precipitation transported by a major river such arid basins are particularly sensitive to climatic and anthropogenic disturbance of their recharge and their subsurface hydrology in order to identify distinctive waters oxygen and hydrogen stable isotope ratios from orange county wells have been compared with a regional database including an array of surface water samples representative of watershed runoff four distinctive subsurface water types can be resolved waters of local rainfall and imported colorado river aqueduct origins are easily distinguished from dominant native santa ana river compositions by use of hydrogen and oxygen stable isotope analysis recent human interference with santa ana river flow and recharge is also marginally resolvable by isotopic techniques distinguishable isotopic signatures of recent santa ana recharge appear to be due to evaporative loss perhaps during storage in the prado reservoir or in percolation ponds prior to recharge into orange county aquifers characterization of traceable isotopic signatures of distinct natural and anthropogenic recharge components provides a major advance towards use of such techniques for developing a well constrained three dimensional hydrologic model for this complex basin

recent deep sea benthic foraminiferal distributions in the south china and sulu seas thirty nine surface sediment samples collected from the south china and sulu seas were examined to determine the bathymetric distribution of benthic foraminifera in these two basins and the factors responsible for these distributions the benthic foraminiferal faunas of both basins are highly diverse but have low absolute abundances benthic number and species diversity systematically decrease with increasing water depth four faunal assemblages were identified for each basin byq mode principal component analysis theglobocassidulina subglobosa uvigerina assemblage 1500 m and theuvigerina assemblage 1400 m represent the shallowest assemblages in the south china sea and sulu sea respectively and are found within the oxygen minimum zone of each basin where the sedimentary organic carbon content is highest and the pore water oxygen penetration depth zo is shallowest thebulimina aculeata assemblage occurs at water depths between 1700 and 2000 m in the southeastern south china sea and is also associated with relatively high sedimentary organic carbon content theastrononion pusillum assemblage is found in south china sea at the depths between 1500 and 3200 m below the lysocline 3200 m in the south china sea this assemblage is replaced by the agglutinatedrhabdammina abyssorum assemblage this assemblage reflects the presence of a water mass that is highly undersaturated with respect to calcite in the sulu sea thepyrgo murrhina assemblage occupies water depths from 1400 to 2200 m below 2200 m two deep water assemblages are present that are both dominated byoridorsalis umbonatus a correlation between various environmental and benthic foraminiferal variables indicates that salinity temperature sediment grain size water depth and bottom water oxygen concentration are not key factors controlling the benthic foraminiferal distribution in either the south china sea or the sulu sea rather organic carbon content and oxygen penetration depth in sediments appear to play important roles in determining the distribution of benthic foraminifera in both basins

the effects of anaerobic methane oxidation on benthic foraminiferal assemblages and stable isotopes on the hikurangi margin of eastern new zealand abstract a study of benthic foraminiferal assemblages from cold hydrocarbon seeps of the hikurangi margin new zealand was undertaken during rv sonne cruise so191 3 to establish what effects if any methane influenced pore waters had on the foraminiferal assemblages and the carbon isotopes of their tests the results of this study indicate that hikurangi margin foraminiferal assemblages are consistent with modern and fossil seeps worldwide foraminiferal distribution species richness density and diversity were little different between seep and non seep sites though there were noteworthy exceptions the non seep reference core samples were greatly enriched in agglutinate species which constituted 45 of the total assemblage of that core by contrast seep sites contained a maximum of 11 agglutinate foraminifera seep and non seep sites were not separated by density or diversity except for the single site beneath a bacterial mat that exhibited the lowest density and diversity of all sites assemblages at all sites were dominated by uvigerina peregrina a species known to inhabit fossil and modern seeps elsewhere but that also is well documented from normal marine environments carbon isotope data significantly differentiates seep and non seep sites through the greater 13 c depletion and heterogeneity of 13 c values in seep foraminifera 13 c values for u peregrina were as low as 15 2 pdb in addition specimens of pyrgo depressa and hoeglundina elegans exhibited minimum 13 c values of 29 8 and 35 7 pdb respectively showing the influence of carbon that was derived from sulphate dependent anaerobic oxidation of methane authigenic carbonates and vesicomyid bivalve shells from seep station 198 also recorded depleted 13 c values with the lightest values 55 4 pdb clearly within the range of biogenic methane sources