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

faunal and stable isotopic analyses of benthic foraminifera from the southeast seep on kimki ridge offshore southern california usa abstract we investigated the benthic foraminiferal faunal and stable carbon and oxygen isotopic composition of a 15 cm push core na075 092b obtained on a telepresence enabled cruise to the southeast seep on kimki ridge offshore southern california the seep core was taken at a depth of 973 m in the vicinity of a beggiatoa bacterial mat and vesicomyid clams calyptogena and compared to previously published data of living assemblages from 714 m four reference cores obtained at 1030 m and another one at 739 m all of the reference sites are also from the inner continental borderland but with no evidence of methane seepage no endemic species were found at the seep site and most of the taxa recovered there have been reported previously from other seep or low oxygen environments q and r mode cluster analyses clearly illustrated differences in the faunal assemblages of the seep and non seep sites the living assemblage at southeast seep was characterized by abundant takayanagia delicata cassidulina translucens and spiroplectammina biformis whereas the non seep san pedro basin reference assemblage was comprised primarily of chilostomella oolina and globobulimina pacifica density and species richness were lower at the seep site compared to the non seep site reflecting the harsher living conditions there the dead assemblage at the seep site was dominated by gyroidina turgida compared to cassidulina translucens at the 1030 m non seep site and cassidulina translucens pseudoparrella pacifica and takayanagia delicata at the 739 m non seep site density was three times lower at southeast seep than at the non seep sites of comparable water depth but species richness was 30 higher stable carbon isotopic values were considerably depleted in the seep samples compared to the non seep samples with a progression from lightest to heaviest average 13c values evident at the seep site reflecting microhabitat preference and vital effect the deep infaunal species of globobulimina the shallow infaunal species uvigerina peregrina the epifaunal species cibicidoides wuellerstorfi and the shallow infaunal but aragonite shelled species hoeglundina elegans the 13c values downcore among each benthic species indicates ongoing fluid seepage through at least the last 3800 cal yr b p at southeast seep besides the continual local seepage evidence from 13c values of planktic foraminifera in the seep core suggest two pulses of methane at 3000 and 3700 cal yr b p were released that were large enough to influence much of the water column paired benthic and planktic foraminiferal stable oxygen isotope records provide evidence that there were no paleoenvironmental changes such as increased bottom water temperature or changes in oxygen isotopic composition of bottom and pore waters during this 3800 year record to induce the methane releases instead southeast seep appears to be the result of local faulting providing pathways for fluid to flow to the seafloor at a fault stepover or transpressional bend in the regional strike slip system

how are benthic foraminiferal faunas influenced by cold seeps evidence from the miocene of italy abstract the miocene termina formation of the northern apennines italy hosts small marl bodies containing a fossil megafauna that is not seen elsewhere in the formation this fauna consists of concentrations of large lucinid clams having living representatives that occur in cold seep settings where they house chemosymbiotic bacteria together with the megafauna a 13 c depletion of their carbonate contents suggests a cold seep derived origin for these bodies they belong to the cluster of mostly carbonate oligo miocene bodies outcropping in the apennine range from piedmont to southern italy where they are included in deep marine units at different geological settings the relatively soft lithology of the bodies from the termina formation permitted the extraction of the microfossil component so that a taxonomically detailed investigation of benthic foraminifera was performed moreover a comparison with assemblages from nearby non seep deposits has allowed an evaluation of their use for recognizing fossil seeps a total of more than 200 species and subspecies of benthic foraminifera has been identified in seep bodies and surrounding non seep deposits and allowed paleodepth estimates within the middle bathyal zone 600 1000 m similarly to present day isobathyal settings the foraminiferal diversity is high with a major contribution by the accessory taxa that account for up to nearly 50 of the total assemblage based upon the microhabitat categories the epifaunal assemblages are largely outnumbered by the infaunal ones our results show that significant differences do not exist between the foraminiferal assemblages recovered from seep influenced bodies and the ones from the enclosing deposits these results agree with the findings from present day seep environments for which however a still limited and insufficient data set is at the moment available a further complication that should be considered is the effect of time averaging on fossil assemblages which would be responsible for some homogenization between foraminiferal stocks of normal marine non seep settings and adjacent assemblages controlled by short term events such as the ones produced by cold seepage

hydrothermal element fluxes from copahue argentina a beehive volcano in turmoil copahue volcano erupted altered rock debris siliceous dust pyroclastic sulfur and rare juvenile fragments between 1992 and 1995 and magmatic eruptions occurred in july october 2000 prior to 2000 the copahue crater lake acid hot springs and rivers carried acid brines with compositions that reflected close to congruent rock dissolution the ratio between rock forming elements and chloride in the central zone of the volcano hydrothermal system has diminished over the past few years reflecting increased water rock ratios as a result of progressive rock dissolution magmatic activity in 2000 provided fresh rocks for the acid fluids resulting in higher ratios between rock forming elements and chloride in the fluids and enhanced mg fluxes the higher mg fluxes started several weeks prior to the eruption model data on the crater lake and river element flux determinations indicate that copahue volcano was hollowed out at a rate of about 20 000 25 000 m 3 yr but that void space was filled with about equal amounts of silica and liquid elemental sulfur the extensive rock dissolution has weakened the internal volcanic structure making flank collapse a volcanic hazard at copahue

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

the bimodal ph distribution of volcanic lake waters abstract volcanic lake waters have a bimodal ph distribution with an acidic mode at ph 0 5 1 5 and a near neutral mode at ph 6 6 5 with relatively few samples having ph 3 5 5 to investigate the reasons for this distribution the irreversible water rock mass exchanges during the neutralization of acid so4 cl waters with andesite under both low and high temperature conditions were simulated by means of the eq3 6 software package version 7 2 reaction path modeling under low temperature and atmospheric pco2 and fo2 suggests that several homogeneous and or heterogeneous ph buffers exist both in the acidic and neutral regions but no buffer is active in the intermediate central ph region again the same titration under high temperature hydrothermal magmatic conditions is expected to produce comparatively infrequent aqueous solutions with ph values in the 3 5 5 range upon their cooling below 100 c substantially different ph values are obtained depending on the cooling paths either through boiling or conductive heat losses these distinct ph values are governed by either hso4 and hcl aq in poorly neutralized aqueous solutions or the co2 aq hco3 couple and the pco2 value as well in neutralized aqueous solutions finally mixing of the acid lake water with the aqueous solutions produced through high temperature titration and cooled below 100 c is unlikely to generate mixtures with ph values higher than 3 unless the fraction of the acidic water originally present in the lake becomes very small which means its virtually complete substitution summing up the evidence gathered through reaction path modeling of the neutralization of acid lake waters with andesite both at low and high temperatures explains the scarcity of volcanic lake waters with measured ph values of 3 5 5

geochemical and isotopic evidences of magmatic inputs in the hydrothermal reservoir feeding the fumarolic discharges of tacora volcano northern chile abstract tacora volcano is a nearly unknown and understudied 5980 m high volcano located on the northernmost border between chile and peru tacora is characterized by intense fumarolic activity with extensive white colored hydrothermal areas along the nw and w flanks of the volcanic structure the chemical and isotopic features of gas emissions indicate that the hydrothermal reservoir is significantly affected by contributions from magmatic degassing despite relatively low outlet temperatures 82 93 c water and gas isotopic signatures stem from degassing of andesitic magmas produced from the sediment poor subducting slab isotopic data suggests ch 4 co 2 isotopic equilibration occurs at 400 c likely in the deepest portion of the hydrothermal magmatic fluid reservoir the h 2 h 2 o co co 2 h 2 ar ch 4 co 2 and c 2 c 3 alkenes alkanes pairs tend to approach a chemical equilibrium at temperatures between 200 and 320 c when redox conditions are more oxidizing than those determined by the typical feo feo 1 5 rock buffer system boiling occurs at shallow depth at 85 c within a discontinuous thin aquifer enough as thermal buffer but not able to scrub the uprising magmatic related acidic gases

evolution of fluid geochemistry at the turrialba volcano costa rica from 1998 to 2008 turrialba 10 02 n 83 45 w is a 3 349 m high stratovolcano belonging to the holocene cordillera central volcanic belt of costa rica the summit consists of three ew oriented craters east central and west since its last eruptive phase 1864 1866 the central and west craters have displayed modest fumarolic activity with outlet temperatures clustering around 90 c in 2001 seismic swarms ground deformation and increasing fumarolic activity occurred from 2005 to 2008 new fumarolic vents opened between and within the central and west craters and along the western and southwestern outer flanks of the volcanic edifice these physical changes were accompanied by a drastic modification in the gas chemistry that can be divided in three stages 1 hydrothermal from 1998 to autumn 2001 characterized by the presence of h2o co2 h2s and to a very minor extent hcl and hf 2 hydrothermal magmatic autumn 2001 2007 with the appearance of so2 and a significant increase of hcl and hf and 3 magmatic dominated 2007 2008 characterized by increased so2 content so2 h2s 100 and temperatures up to 282 c accordingly gas equilibrium in the co2 ch4 h2 system suggests a progressive evolution of the deep fluid reservoir toward higher temperatures and more oxidizing conditions the chemical physical modifications of turrialba in the last decade can be interpreted as part of a cyclic mechanism controlling the balance between the hydrothermal and the magmatic systems nevertheless the risk of rejuvenation of the volcanic activity cannot be excluded and an appropriate seismic ground deformation and geochemical monitoring program is highly recommended turrialba lies at a distance of 35 and 15 km from san jose and cartago respectively the two largest cities in costa rica

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 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

influences of thermal and fluid characteristics of methane and hydrothermal seeps on the stable oxygen isotopes of living benthic foraminifera abstract the serendipitous discovery of methane seep fluids with elevated temperatures 3 6 5 2 c described as a hydrothermal seepage by levin et al 2012 has led to questions about the prevalence of this previously overlooked habitat stable oxygen isotopic analysis of cibicidoides wuellerstorfi schwager 1866 attached to tubeworms near the hydrothermal seep described by levin et al 2012 reflect 18o values consistent with elevated seepage temperatures temperature reconstructions based on c wuellerstorfi 18o from additional seeps in the pacific mounds 11 12 offshore costa rica and hydrate ridge produced variability that is likely a result of influences of seep source temperature and salinity larger ranges in 18o 0 10 paired with traditional isotopic seep indicators e g 13c 0 15 have the potential to geochemically discern whether foraminifera were calcifying in areas of active methane seepage or nearby surrounding off seep environments elevated temperatures derived from foraminiferal reconstructions at jaco scar indicate that it is possible to use foraminiferal 18o to identify the presence and extent of these recently discovered environments seep fluids with elevated temperatures may be common seafloor features and benthic foraminiferal 18o may be an effective means to detect and determine the spatial and temporal extent and possible origin of hydrothermal seepage

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

isotopic evidence for the incorporation of methane derived carbon into foraminifera from modern methane seeps hydrate ridge northeast pacific the presence of modern methane seeps at hydrate ridge offshore oregon provide an opportunity to study the influence of methane seeps on the ecology and geochemistry of living foraminifera a series of cores were collected from the southern summit of hydrate ridge in 2002 samples were preserved and stained to determine the 13c composition of three species of live stained and dead benthic foraminifera uvigerina peregrina cibicidoides mckannai and globobulimina auriculata specimens were examined under light and scanning electron microscopy sem and exhibit no evidence of diagenesis or authigenic carbonate precipitation individual living foraminifera from seep sites recorded 13c values from 0 4 to 21 2 indicating the isotopic influence of high methane concentrations average 13c values calculated from single specimens range from 1 28 to 5 64 at seep sites and 0 81 to 0 85 at a control off seep site two distinct seep environments distinguished by the presence of microbial mats or clam fields were studied to determine environmental influences on 13c values individual foraminifera from microbial mat sites exhibited more depleted 13c values than those from clam field sites we interpret these differences as an effect of food source and or symbiotic microbes on foraminiferal carbon isotopic values acting to magnify the negative 13c values recorded via the dic pool no statistical difference was found between 13c values of live vs dead specimens this suggests that authigenic carbonate precipitation did not play a dominant role in the observed isotopic compositions however a few dead specimens with extremely negative 13c composition 12 do indicate potential evidence for an authigenic influence on the recorded 13c composition

methane driven late pleistocene δ13c minima and overflow reversals in the southwestern greenland sea a core transect across the southwestern greenland sea reveals coeval events of extremely negative planktic and benthic 1 3 c excursions between 40 and 87 ka the most pronounced event event 1 began at peak dansgaard oeschger stadial 22 85 ka with a duration of 18 k y during this episode incursions of atlantic intermediate water caused a bottom water warming of up to 8 c the amplitude timing and geographic pattern of the 1 3 c events suggest that this bottom water warming triggered clathrate instability along the east greenland slope and a methane induced depletion of 1 3 c d i c dic dissolved inorganic carbon since 1 3 c event 1 matches a major peak in atmospheric ch 4 concentration this clathrate destabilization may have contributed to the rise in atmospheric ch 4 and thus to climate warming over marine isotope stage 5 1

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

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

chemical and isotopic composition of fumarolic gases and the so2 flux from volcan de colima mexico between the 1994 and 1998 eruptions volcan de colima is the most active volcano in mexico including a significant effusive eruption in 1991 and a weak explosive event in 1994 geochemical monitoring of the volcano started in january 1996 with collection of fumarolic gases approximately every 3 months from two sites in the summit crater z3 800 c and z2 400 c chemical compositions of volcanic gases from the z2 fumarole showed a peak in s cl in the middle of 1997 14 15 months before the start of the 1998 lava eruption high temperature volcanic vapors from z3 changed progressively in water isotopic composition and showed a weak trend of increasing hcl hf and a peak in s cl at the same time starting from the summer of 1997 the volcanic water became gradually enriched in deuterium which probably indicated an increasing contribution from deep less degassed magma a negative correlation between d and cl content for the z3 fumarolic gases is explained by shallow degassing of the colima hot lava plug this hypothesis is consistent with published data on cl contents and solubilities in magmas and supported by the observed positive trends of s cl and hcl hf with d for the z3 fumarole until september 1998 the so2 flux from the volcano was at a low level 100 tons day and often below the detection limit of the instrument 30 tons day a sharp increase in the so2 flux was recorded 1 month before the eruption started it jumped from 400 50 tons day to 1600 tons day 2 days before new lava emerged on 20 november 1998 the so2 flux correlated well with seismicity

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

dynamic fluid recycling at laguna caliente poas costa rica before and during the 2006 ongoing phreatic eruption cycle 2005 10

tracing seafloor methane emissions with benthic foraminifera results from the ana submarine landslide eivissa channel western mediterranean sea article the hypothesis that benthic foraminifera are useful proxies of local methane emissions from the seafloor has been verified on sediment core ks16 from the headwall of the ana submarine landslide in the eivissa channel western mediterranean sea the core ms312 from a nearby location with no known methane emis sions is utilised as control the core was analysed for biostratigraphy benthic foraminiferal assemblages hyalinea balthica and uvigerina peregrina carbon and oxygen stable isotope composition and sedimentary structures the upper part of the core records post landslide deglacial and holocene normal marine hemipe lagic sediments with highly abundant benthic foraminifera species that are typical of outer neritic to upper bathyal environment in this interval the 13 c composition of benthic foraminifera indicates normal marine environment analogous to those found in the control core below the sedimentary hiatus caused by the em placement of the slide the foraminiferal assemblages are characterised by lower density and higher shannon index markedly negative 13 c shifts in benthic foraminifera are attributed to the release of methane through the seabed the mean values of the 13 c anomaly in u peregrina are 0 951 0 208 in the pre landslide sediments and 0 269 0 152 in post slide reworked sediments deposited immediately above the hiatus the 13

stratification at the earth s largest hyperacidic lake and its consequences volcanic lakes provide windows into the interior of volcanoes as they integrate the heat flux discharged by a magma body and condense volcanic gases volcanic lake temperatures and geochemical compositions therefore typically serve as warnings for resumed unrest or prior to eruptions if acidic and hot these lakes are usually considered to be too convective to allow any stratification within their waters kawah ijen volcano featuring the largest hyperacidic lake on earth volume of 27 million m3 is less homogeneous than previously thought hourly temperature measurements reveal the development of a stagnant layer of cold waters 30 c overlying warmer and denser water generally above 30 c and density 1 083 kg m3 examination of 20 yrs of historical records and temporary measurements show a systematic thermal stratification during rainy seasons the yearly rupture of stratification at the end of the rainy season causes a sudden release of dissolved gases below the cold water layer which appears to generate a lake overturn i e limnic eruption and a resonance of the lake i e a seiche highlighting a new hazard for these extreme reservoirs a minor non volcanic event such as a heavy rainfall or an earthquake may act as a trigger the density driven overturn requires specific salinity temperature conditions for the colder and less saline top water layer to sink into the hot saline water spectacular degassing occurs when the dissolved gases progressively stored during the rainy season due to a weakened diffusion of carbon dioxide in the top layer are suddenly released these findings challenge the homogenization assumption at acidic lakes and stress the need to develop appropriate monitoring setups

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

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

volcanic lake systematics ii chemical constraints abstract a database of 373 lake water analyses from the published literature was compiled and used to explore the geochemical systematics of volcanic lakes binary correlations and principal component analysis indicate strong internal coherence among most chemical parameters compositional variations are influenced by the flux of magmatic volatiles and or deep hydrothermal fluids the chemistry of the fluid entering a lake may be dominated by a high temperature volcanic gas component or by a lower temperature fluid that has interacted extensively with volcanic rocks precipitation of minerals like gypsum and silica can strongly affect the concentrations of ca and si in some lakes a much less concentrated geothermal input fluid provides the mineralized components of some more dilute lakes temporal variations in dilution and evaporation rates ultimately control absolute concentrations of dissolved constituents but not conservative element ratios most volcanic lake waters and presumably their deep hydrothermal fluid inputs classify as immature acid fluids that have not equilibrated with common secondary silicates such as clays or zeolites many such fluids may have equilibrated with secondary minerals earlier in their history but were re acidified by mixing with fresh volcanic fluids we use the concept of degree of neutralization as a new parameter to characterize these acid fluids this leads to a classification of gas dominated versus rock dominated lake waters a further classification is based on a cluster analysis and a hydrothermal speedometer concept which uses the degree of silica equilibration of a fluid during cooling and dilution to evaluate the rate of fluid equilibration in volcano hydrothermal systems

intense magmatic degassing through the lake of copahue volcano 2013 2014 here we report on the first assessment of volatile fluxes from the hyperacid crater lake hosted within the summit crater of copahue a very active volcano on the argentina chile border our observations were performed using a variety of in situ and remote sensing techniques during field campaigns in march 2013 when the crater hosted an active fumarole field and in march 2014 when an acidic volcanic lake covered the fumarole field in the latter campaign we found that 566 to 1373 t d 1 of so2 were being emitted from the lake in a plume that appeared largely invisible this combined with our derived bulk plume composition was converted into flux of other volcanic species h2o 10989 t d 1 co2 638 t d 1 hcl 66 t d 1 h2 3 3 t d 1 and hbr 0 05 t d 1 these levels of degassing comparable to those seen at many open vent degassing arc volcanoes were surprisingly high for a volcano hosting a crater lake copahue s unusual degassing regime was also confirmed by the chemical composition of the plume that although issuing from a hot 65 c lake preserves a close to magmatic signature eq3 6 models of gas water rock interaction in the lake were able to match observed compositions and demonstrated that magmatic gases emitted to the atmosphere were virtually unaffected by scrubbing of soluble s and cl species finally the derived large h2o flux 10 988 t d 1 suggested a mechanism in which magmatic gas stripping drove enhanced lake water evaporation a process likely common to many degassing volcanic lakes worldwide

evidence for extensive methane venting on the southeastern u s atlantic margin we present the first evidence for widespread seabed methane venting along the southeastern united states atlantic margin beyond the well known blake ridge diapir seep recent ship and autonomous underwater vehicle auv collected data resolve multiple water column anomalies 1000 m height and extensive new chemosynthetic seep communities at the blake ridge and cape fear diapirs these results indicate that multiple highly localized fluid conduits punctuate the areally extensive blake ridge gas hydrate province and enable the delivery of significant amounts of methane to the water column thus there appears to be an abundance of seabed fluid flux not previously ascribed to the atlantic margin of the united states

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

magma hydrothermal system interaction inferred from volcanic gas measurements obtained during 2003 2008 at meakandake volcano hokkaido japan phreatic eruptions occurred at the meakandake volcano in 1988 1996 1998 2006 and 2008 we conducted geochemical surveillance that included measurements of temperature so2 emission rates and volcanic gas composition from 2003 to 2008 at the nakamachineshiri nm northwest nw and akanuma ak fumarolic areas and the 96 1 vent where historical eruptions had occurred the elemental compositions of the gases discharged from the different areas are similar compared with the large variations observed in volcanic gases discharged from subduction zones all the gases showed high apparent equilibrium temperatures suggesting that all these gases originated from a common magmatic gas the gases discharged from each area also exhibited different characteristics which are probably the results of differences in the conditions of meteoric water mixing quenching of chemical reactions and vapor liquid separation the highest apparent equilibrium temperatures about 500 c were observed in the case of nw fumarolic gases despite the low outlet temperature of about 100 c at these fumaroles since the nw fumaroles were formed as a result of the 2006 phreatic eruption the high temperature gas supply to the nw fumarole suggests that the phreatic eruption was caused by the ascent of high temperature magmatic gases the temperatures compositions and emission rates of the nm and 96 1 gases did not show any appreciable change after the 2006 eruption indicating that each fumarolic system had a separate magmatic hydrothermal system the temperatures compositions and emission rates of the nm fumarolic gases were apparently constant and these fumaroles are inferred to be formed by the evaporation of a hydrothermal system with a constant temperature of about 300 c the 96 1 gas compositions showed large changes during continuous temperature decrease from 390 to 190 c occurred from 2003 to 2008 but the sulfur gas emission rates were almost constant at about four tons day at the 96 1 vent the so2 h2s ratio decreased while the h2 h2o ratio remained almost constant this was probably caused by the rock buffer controlled chemical reaction during the temperature decrease

interactions of phosphorus with sediments in the river swale yorkshire uk the ultimate fate of inorganic phosphorus in natural waters is to a large degree determined by interactions with sediments the interactions in river bed sediments have been investigated by a combination of methods using surface sediments 2 mm in diameter collected from a 55 km stretch of the river swale in yorkshire uk the sediments were analysed by digestion fe ca and p clay mineralogy and their equilibrium phosphate concentration all the equilibrium phosphate concentrations were below 2 mol dm 3 which is much less than the concentration in the overlying water and indicates a net uptake of phosphorus by the sediments experiments in a fluvarium channel with a coarse sediment also showed that the release and uptake of soluble phosphorus was towards a steady state concentration in the overlying solution consistent with measurements of the equilibrium phosphate concentration a kinetic model describing the net uptake of soluble reactive phosphorus by river sediments was applied to chemical data collected during an intensive monitoring exercise in the catchment copyright 1999 john wiley sons ltd

geochemistry mineralogy and chemical modeling of the acid crater lake of kawah ijen volcano indonesia the kawah ijen volcano with a record of phreatic eruptions has its 1000 m wide crater filled with a lake that has existed for at least one century at present the lake waters are hot t 37 c strongly mineralized tds 105 g l and extremely acidic ph 0 4 by its volume the javanese lake is probably the largest accumulation in the world of such acidic waters mineralogy of the suspended solids within the lake waters suggests that concentrations of si ca ti and ba are controlled by precipitation of silica gypsum anatase and barite lake sediment is composed of chemical precipitates with composition similar to the suspended solids thermodynamic calculations predict that the lake waters have reached equilibrium with respect to cristobalite barite gypsum anglesite celestite and amorphous silica in agreement with the analytical observations significant concentrations of ferric iron suggest that the current lake waters are fairly oxidized sulfides are absent in the water column but are always present in the native s spherules that form porous aggregates which float on the lake the presence of native s provides direct evidence of more reduced conditions at the lake floor where h 2 s is probably being injected into the lake with progressive addition of h 2 s to the acid waters native s pyrite and enargite are theoretically predicted to be saturated reactions between upward streaming h 2 s bearing gases discharged by subaqueous fumaroles and metals dissolved in the acidic waters could initiate precipitation of these sulfides a model of direct absorption of hot magmatic gases into cool water accounts for the extreme acidity of the crater lake results show that strongly acidic sulfate rich solutions are formed under oxidizing conditions at high gas water ratios reactions between the acidic fluids and the ijen andesite were modeled to account for elevated cation concentrations in lake water current concentrations of conservative rockforming elements are produced by dissolution of approximately 60 g of andesite per kg of acid solution complete neutralization of the acid lake waters by reaction with the wallrock produces a theoretical alteration assemblage equivalent to that observed in volcano hosted acid sulfate epithermal ore deposits

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

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

carbon stable isotopic composition of benthic foraminifera from pliocene cold methane seeps cascadia accretionary margin abstract cold methane seep carbonates preserve the distinctive carbon stable isotope signatures of their ambient porewaters thus facilitating the identification of methane sources and fluid migration pathways this study employs an isotopic indicator from microfossils in a diffuse fossil seep for the recognition and characterization of methane seepage in the rock record benthic foraminifera from the pliocene quinault formation western washington state are plentiful and provide a temporal link between modern and more ancient seeps stable carbon isotope analyses of individual foraminiferal tests revealed a clear distinction between seep and non seep foraminifera infaunal species globobulimina pacifica and nonion basispinatum collected from seep samples exhibited 13 c values that were highly variable and often strongly depleted values ranged from 33 1 to 55 3 pdb in g pacifica and from 2 1 to 42 9 pdb in n basispinatum the epifaunal species cibicidoides mckannai though less depleted also showed considerable variability with 13 c values ranging from 1 7 to 3 1 pdb in contrast non seep specimens were much more enriched and less variable non seep specimens of n basispinatum displayed 13 c values clustering between 0 5 and 1 5 pdb while non seep specimens of c mckannai yielded a range of 1 1 to 1 8 pdb sem analyses and oxygen isotope values of foraminiferal tests indicated minimal diagenetic alteration 13 c values from authigenic blebs small nodules with wispy indistinct boundaries ranged from 8 7 to 38 4 pdb by combining these inorganic carbonate data with the foraminiferal values the association of seep specific bivalves and the present day leakage of thermogenic methane from the nearby garfield gas mound we conclude that these foraminifera precipitated their tests in the presence of methane derived carbon thus they record pore water 13 c depletion and syn depositional fluid flow pathways near the sediment water interface in a seep system active 3 4 mya and continuing onshore and offshore today the range and degree of 13 c depletion in the pliocene microfossils is due to the heterogeneity of seepage caused by different methane sources i e thermogenic and biogenic the tortuosity of fluid migration pathways reaching the seafloor sediments and mixing of seep fluids with dissolved inorganic carbon dic and marine organic carbon

using crater lake chemistry to predict volcanic activity at poas volcano costa rica monitoring of crater lake chemistry during the recent decline and disappearance of the crater lake of poas volcano revealed that large variations in so4 cl f cl and mg cl ratios were caused by the enhanced release of hcl vapor from the lake surface due to increasing lake temperature and solution acidity variation in the concentration of polythionic acids h2sxo6 x 4 6 was the most reliable predictor of renewed phreatic eruptive activity at the volcano exhibiting sharp decreases three months prior to the initiation of phreatic eruptions in june 1987 polythionic acids may offer a direct indicator of changing subsurface magmatic activity whereas chloride based element ratios may be influenced by surface volatilization of hcl and subsequent recycling of acidic fluids in crater lake volcanoes

the 2012 2016 eruptive cycle at copahue volcano argentina versus the peripheral gas manifestations hints from the chemical and isotopic features of fumarolic fluids this study presents the chemical and isotopic compositions of hydrothermal gases from fumaroles discharging around copahue volcano argentina gas samples including those from two fumaroles at the active summit crater were collected during 13 surveys carried out by different research teams from 1976 to february 2016 the time series of h2 co and light hydrocarbons showed episodic increases related to the main events of the last eruptive cycle that started on 19 july 2012 concentration peaks were likely caused by enhanced input of hot magmatic fluids affecting the hydrothermal reservoir these data contrast with the temporal variations shown by rc ra and 13c co2 values in 2012 2014 which indicated an increasing input from a crustal fluid source in 2015 2016 however these isotopic parameters showed opposite trends their composition became closer to that of the two summit fumaroles which possibly corresponds to that of the deep magmatic related end member the delayed and reduced compositional changes in the peripheral hydrothermal fluid discharge in response to the 2012 2016 eruptive events suggest that geochemical surveys of these emissions are unlikely to provide premonitory signals of volcanic unrest if the volcanic activity remains centered in the main crater instead an instrument which is able to provide measurements of volcanic gases in the air e g multigas may be used to detect changes at the summit crater otherwise monitoring of seismic activity and ground deformation as well as the periodic measurement of the chemistry of the water in the rio agrio which is fed by thermal discharge from the summit crater seem to represent the most reliable means of monitoring at copahue however the relative compositional stability of the hydrothermal reservoir is a great advantage in terms of geothermal resource exploitation and could encourage new investments in the copahue geothermal project which was abandoned in the 1990s

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

distribution and isotopic composition of foraminifera at cold seep site 973 4 in the dongsha area northeastern south china sea abstract a 1375 cm long gravity core site 973 4 was acquired from the dongsha cold seep area of the northeastern south china sea scs we measured its stable isotopes of planktonic foraminifera and investigated benthic foraminiferal assemblage compositions accelerator mass spectrometry 14c analysis of planktonic foraminifera shows that some intervals are dated to marine isotope stage mis 3 pulleniatina obliquiloculata has positive 13c 0 25 1 25 except for a negative carbon isotopic excursion up to 13c 1 15 but its light carbon sources remain elusive the benthic 13c values uvigerina of non seep and cold seep boreholes from the scs have no systematic difference therefore the benthic 13c at site 973 4 did not record the enhanced seepage activities if occurred during the last sea level lowstand in the dongsha area in the pre holocene sediments the foraminiferal assemblages have lower diversities shannon wiener indices evenness indices simpson indices and higher calcareous proportions like typical cold seep settings the changes in oxygen levels lower in the glacial period than those in the holocene indicated by foraminiferal indices reflect either bottom water oxygen variations on the glacial interglacial scale or enhanced seepage activities during the last glacial period