radiocarbon based carbon source quantification of anomalous isotopic foraminifera in last glacial sediments in the western north pacific a previous study interpreted extremely 13c depleted excursions of planktonic and benthic foraminifera in last glacial sediments 17 500 to 25 400 cal years b p of the core retrieved from off shimokita peninsula and off hokkaido japan as evidence for periodic releases of methane arising from the dissociation of methane hydrate to better understand the formation process of the 13c depleted excursions we conducted high resolution natural radiocarbon measurements and biogeochemical analyses we found highly depleted 13c excursions ranging from 10 2 to 1 6 and 6 8 to 1 6 in planktonic and benthic foraminifera respectively most of the foraminiferal tests in these horizons were brown most likely as a result of postdepositional alteration reflecting the formation of authigenic carbonate on the surface of tests these alterations were also supported by high levels of mg calcite and the acid leaching test for anomalous foraminifera to evaluate the carbon sources in the altered foraminifera tests we quantified the relative contributions of 14c free methane derived carbon sources to the formation of authigenic carbonates in foraminifera with depleted 13c excursions using a coupled mass balance isotopic model 14c c and 13c 12c the radiocarbon ages of both planktonic and benthic 13c depleted foraminifera were approximately 600 to 2000 years older than those of normal tests from nearby horizons the relative contributions of authigenic carbonates derived from the methane oxidizing process reached to 22 wt for planktonic foraminifera and 15 wt for benthic foraminifera the 13c values of methane calculated from the mass balance model were between 29 and 68 for planktonic foraminifera and between 40 and 108 for benthic foraminifera consistent with 13c values reported for thermogenic and abiogenic methane in global methane hydrate reservoirs these data consistently suggest that methane related drastic environmental change occurred in the horizons that included 13c anomalies this study provides important information for interpreting geological records of the methane hydrate instability associated with climate

modeling co2 chemistry δ13c and oxidation of organic carbon and methane in sediment porewater implications for paleo proxies in benthic foraminifera i present a numerical diffusion advection reaction model to simulate co2 chemistry 13c and oxidation of organic carbon and methane in sediment porewater the model takes into account detailed reaction kinetics of dissolved co2 compounds h2o h oh boron and sulfide compounds these reactions are usually assumed to be in local equilibrium which is shown to be a good approximation in most cases the model also includes a diffusive boundary layer across which chemical species are transported between bottom water and the sediment water interface while chemical concentrations and 13ctco2 13ctco2 at these locations are frequently assumed equal i demonstrate that they can be quite different in this case shells of benthic foraminifera do not reflect the desired properties of bottom water even for species living at the sediment water interface z 0 cm environmental conditions recorded in their shells are strongly influenced by processes occurring within the sediment the model is then applied to settings in the santa barbara basin and at hydrate ridge cascadia margin locations of strong organic carbon and methane oxidation in contrast to earlier studies i show that a limited contribution of methane derived carbon to porewater tco2 in the santa barbara basin cannot be ruled out simulation of methane venting shows that at oxidation rates greater than fch4 50 molcm 2y 1 the 13c of porewater tco2 at z 1 cm is depleted by more than 15 relative to bottom water depletions of this magnitude have not been observed in living benthic foraminifera even at methane vents with much higher oxidation rates this suggests that foraminifera at these sites either calcify at very shallow sediment depth or during times when oxidation rates are much lower than 50 mol cm 2 y 1

asphalt volcanoes as a potential source of methane to late pleistocene coastal waters natural petroleum seepage emits large volumes of oil and methane to the oceans every year accompanied by the formation of asphalt volcanoes on the sea floor the discovery of seven asphalt volcanoes off the coast of southern california may help to explain high methane emissions recorded during the late pleistocene

seeping hydrocarbons and related carbonate mineralisations in sediments south of lihir island new ireland fore arc basin papua new guinea hydrocarbon gases have been sampled from both cold seeping and heat venting areas in the new ireland fore arc basin in the vicinity of lihir island highest concentrations of up to 10 l l ch4 with a 13cch4 value of 54 9 pdb have been measured in the deep ocean water within a long and narrow deep sea basin located between edison seamount and an uplifted structure named mussel cliff surface sediments of the seep area were covered with chemoautotrophic deep sea fauna such as calyptogena species and tube worms large authigenic calcite concretions occur in the sediments between 50 and 200 cm sediment depth the carbon isotopes of the carbonates in the concretions range from 15 to 40 pdb indicating a mixture of two co2 sources normal marine inorganic carbon fixed in biogenic shells and co2 from anaerobe bacterial oxidation processes of methane accordingly 14c ams dating suggests that authigenic calcite mineralisation incorporated relatively young carbon from methane oxidation in contrast the c1 c2 ratio of 234 and the 13cch4 value of 24 1 pdb in the hot hydrothermal vent of lihir harbour indicates a mixture of a major abiogenic carbon source for methane formation related to magmatism associated with lihir volcano the observed variable fluid characteristics within only 20 km distance between hot hydrothermal venting and the methane seeping deep sea area indicates highly variable heat flow situations and or sediment distributions which control the gas geochemical characteristics in the new ireland fore arc basin

resonant slow fault slip in subduction zones forced by climatic load stress global positioning system gps measurements at subduction plate boundaries often record fault movements similar to earthquakes but much slower occurring over timescales of 1 week to 1 year these slow slip events have been observed in japan1 2 cascadia3 4 5 6 7 mexico8 9 alaska10 and new zealand11 the phenomenon is poorly understood but several observations hint at the processes underlying slow slip although slip itself is silent seismic instruments often record coincident low amplitude tremor in a narrow 1 5 cycles per second frequency range12 also modelling of gps data3 7 9 and estimates of tremor location13 indicate that slip focuses near the transition from unstable stick slip to stable friction at the deep limit of the earthquake producing seismogenic zone perhaps most intriguingly slow slip is periodic at several locations with recurrence varying from 6 to 18 months depending on which subduction zone or even segment is examined4 5 6 9 here i show that such periodic slow fault slip may be a resonant response to climate driven stress perturbations fault slip resonance helps to explain why slip events are periodic why periods differ from place to place and why slip focuses near the base of the seismogenic zone resonant slip should initiate within the rupture zone of future great earthquakes suggesting that slow slip may illuminate fault properties that control earthquake slip

ch 4 consuming microorganisms and the formation of carbonate crusts at cold seeps to understand the role played by microorganisms in the formation of cold seep carbonates we conducted an integrated microbial mineralogical and organic geochemical study of methane related authigenic carbonate crusts formed on eastern mediterranean mud volcanoes we show that supersaturation with respect to carbonate minerals is induced by microbial anaerobic oxidation of methane combined lipid biomarker analysis and 16s rrna gene surveys identified a highly diversified methane consuming archaeal community possibly comprising novel species implying that the anaerobic oxidation of methane is phylogenetically widespread and directly implicating these organisms in the process of crust precipitation moreover pore water sulphate gradients produced by co occurring methane based sulphate reduction exert the main control on aragonite versus magnesian calcite precipitation we propose that this may be the dominant mode of carbonate crust formation at cold seeps world wide in agreement with aquatic chemistry predictions and explaining carbonate mineralogy

dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the paleocene isotopic records across the latest paleocene thermal maximum lptm indicate that bottom water temperature increased by more than 4 c during a brief time interval 104 years of the latest paleocene 55 6 ma there also was a coeval 2 to 3 excursion in the 13c of the ocean atmosphere inorganic carbon reservoir given the large mass of this reservoir a rapid 13c shift of this magnitude is difficult to explain within the context of conventional hypotheses for changing the mean carbon isotope composition of the ocean and atmosphere however a direct consequence of warming bottom water temperature from 11 to 15 c over 104 years would be a significant change in sediment thermal gradients and dissociation of oceanic ch4 hydrate at locations with intermediate water depths in terms of the present day oceanic ch4 hydrate reservoir thermal dissociation of oceanic ch4 hydrate during the lptm could have released greater than 1 1 to 2 1 1018 g of carbon with a 13c of approximately 60 the release and subsequent oxidation of this amount of carbon is sufficient to explain a 2 to 3 excursion in 13c across the lptm fate of ch4 in oceanic hydrates must be considered in developing models of the climatic and paleoceanographic regimes that operated during the lptm

archaea mediate anaerobic oxidation of methane in deep euxinic waters of the black sea we evaluate anaerobic oxidation of methane aom in the black sea water column by determining distributions of archaea specific glyceryl dialkyl glyceryl tetraethers gdgts and 13c isotopic compositions of their constituent biphytanes in suspended particulate matter spm sinking particulate matter collected in sediment traps and surface sediments we also determined isotopic compositions of fatty acids specific to sulfate reducing bacteria to test for biomarker and isotopic evidence of a syntrophic relationship between archaea and sulfate reducing bacteria in carrying out aom bicyclic and tricyclic gdgts and their constituent 13c depleted monocyclic and bicyclic biphytanes down to 67 indicative of archaea involved in aom were present in spm in the anoxic zone below 700 m depth in contrast gdgt 0 and crenarchaeol derived from planktonic crenarchaeota dominated the gdgt distributions in the oxic surface and shallow anoxic waters fatty acids indicative of sulfate reducing bacteria i e iso and anteiso c15 were not strongly isotopically depleted e g 32 to 25 although anteiso c15 was 5 more depleted in 13c than iso c15 our results suggest that either aom is carried out by archaea independent of sulfate reducing bacteria or those sulfate reducing bacteria involved in a syntrophy with methane oxidizing archaea constitute a small enough fraction of the total sulfate reducing bacterial community that an isotope depletion in their fatty acids is not readily detected sinking particulate material collected in sediment traps and the underlying sediments in the anoxic zone contained the biomarker and isotope signature of upper water column archaea aom specific gdgts and 13c depleted biphytanes characteristic of the spm in the deep anoxic zone are not incorporated into sinking particles and are not efficiently transported to the sediments this observation suggests that sediments may not always record aom in overlying euxinic water columns and helps explain the absence of aom derived biomarkers in sediments deposited during past periods of elevated levels of methane in the ocean

evidence from diatom bound nitrogen isotopes for subarctic pacific stratification during the last ice age and a link to north pacific denitrification changes higher diatom bound d 15 n 70 wt lower opal content and 1200 ppm lower biogenic barium taken together and with constraints on sediment accumulation rate these results suggest a reduced supply of nitrate to the surface due to stronger stratification of the upper water column of the bering sea during glacial times with more complete nitrate consumption resulting from continued iron supply through atmospheric deposition this finding extends the body of evidence for a pervasive link between cold climates and polar ocean stratification in addition we hypothesize that more complete nutrient consumption in the glacial age subarctic pacific contributed to the previously observed ice age reduction in suboxia and denitrification in the eastern tropical north pacific by lowering the nutrient content of the intermediate depth water formed in the subpolar north pacific in the deglacial interval of the bering sea record two apparent peaks in export productivity are associated with maxima in diatom bound and bulk sediment d 15 n the high d 15 n in these intervals may have resulted from greater surface nutrient consumption during this period however the synchroneity of the deglacial peaks in the bering sea with similar bulk sediment d 15 n changes in the eastern pacific margin and the presence of sediment lamination within the bering sea during the deposition of the productivity peaks raise the possibility that both regional and local denitrification worked to raise the d 15 n of the nitrate feeding bering sea surface waters at these times

archaeological sedimentology of overbank silt deposits on the floodplain of the ohio river near louisville kentucky abstract the surface of the floodplain of the ohio river about 20km southwest of louisville kentucky is a series of linear ridges and swales that are subparallel to the channel of the river which here is relatively straight and flows southward numerous prehistoric occupational sites are located on these ridges the sediments that underlie the ridges which were examined in four archaeological excavations as deep as 8 m are predominantly sandy silt and silty fine to very fine sand and appear to be mainly the product of overbank deposition from suspended load abundant cultural material and occupational sites dating as early as 10 000 years bp are found in the sediments at depths as great as 6 5 m the fine sediments of the floodplain are underlain by sand and gravel the context of the cultural materials and the stratigraphy and morphology of the deposits indicate that the ridged deposits began as linear riverside sand and gravel bars these were succeeded upward by fine grained overbank deposits in which the ridged morphology was maintained because the overbank silt and fine sand were deposited as prograding elongate bars at high water as the floodplain ridge built upward the sedimentation rate decreased and the sand content of the sediments diminished and as the river channel occasionally shifted the ridged deposits were built in successive subparallel sequences two archaeological consequences are implicit in this depositional model of orderly growth of the floodplain first available archaeological data from floodplain segments along other parts of the river should confirm the model and second the model should make it possible to search the floodplains of the ohio river for stratified sites of any desired age

distribution and height of methane bubble plumes on the cascadia margin characterized by acoustic imaging submersible investigations of the cascadia accretionary complex have identified localized venting of methane gas bubbles in association with gas hydrate occurrence acoustic profiles of these bubble plumes in the water column in the vicinity of hydrate ridge offshore oregon provide new constraints on the spatial distribution of these gas vents and the fate of the gas in the water column the gas vent sites remained active over the span of two years but varied dramatically on time scales of a few hours all plumes emanated from local topographic highs near the summit of ridge structures the acoustic images of the bubble plumes in the water column disappear at water depths between 500 to 460 m independent of the seafloor depth this coincides with the predicted depth of the gas hydrate stability boundary of 510 to 490 m suggesting that the presence of a hydrate skin on the bubble surface prevents them from rapid dissolution the upper limit of the acoustic bubble plumes at 460 m suggests that dissolution of the residual bubbles is relatively rapid above the hydrate stability zone

repeated pulses of vertical methane flux recorded in glacial sediments from the southeast bering sea 1 there is controversy over the role of marine methane hydrates in atmospheric methane concentrations and climate change during the last glacial period in this study of two sediment cores from the southeast bering sea 700 m and 1467 m water depth we identify multiple episodes during the last glacial period of intense methane flux reaching the seafloor within the uncertainty of the radiocarbon age model the episodes are contemporaneous in the two cores and have similar timing and duration as dansgaard oeschger events the episodes are marked by horizons of sediment containing 13c depleted authigenic carbonate minerals 13c depleted archaeal and bacterial lipids which resemble those found in anme 1 type anaerobic methane oxidizing microbial consortia and changes in the abundance and species distribution of benthic foraminifera the similar timing and isotopic composition of the authigenic carbonates in the two cores is consistent with a region wide increase in the upward flux of methane bearing fluids this study is the first observation outside santa barbara basin of pervasive repeated methane flux in glacial sediments however contrary to the clathrate gun hypothesis kennett et al 2003 these coring sites are too deep for methane hydrate destabilization to be the cause implying that a much larger part of the ocean s sedimentary methane may participate in climate or carbon cycle feedback at millennial timescales we speculate that pulses of methane in these opal rich sediments could be caused by the sudden release of overpressure in pore fluids that builds up gradually with silica diagenesis the release could be triggered by seismic shaking on the aleutian subduction zone caused by hydrostatic pressure increase associated with sea level rise at the start of interstadials

light δ13c events during deglaciation of the east greenland continental shelf attributed to methane release from gas hydrates we have documented high resolution stable isotope records from three marine cores on the east greenland shelf these records exhibit three rapid light 13c events 3 to 7 in benthic and planktic foraminifera during deglaciation that are spatially and temporally transgressive the light 13c events are associated with light planktic 18o indicative of meltwater in kangerlussuaq trough the first 13c event occurs at initial deglaciation 13 94 14 0 cal ka and the second occurs at 12 85 12 9 cal ka a younger event at 10 3 9 3 cal ka is recorded near the mouth of nansen fjord during final deglaciation the hypothesized mechanism for the light 13c is expulsion of methane from gas hydrates in the seafloor from pressure release during ice sheet retreat

orbital scale benthic foraminiferal oxygen isotope stratigraphy at the northern bering sea slope site u1343 iodp expedition 323 and its pleistocene paleoceanographic significance abstract a continuous composite oxygen isotope 18o stratigraphy from benthic foraminifera in the bering sea was reconstructed in order to provide insight into understanding sea ice evolution in response to northern hemisphere glaciation oxygen isotope records from multiple species of benthic foraminifera at integrated ocean drilling program iodp expedition 323 site u1343 54 33 4 n 176 49 0 e water depth 1950 m yield a highly refined orbital scale age model spanning the last 1 2 ma and a refined age model between 1 2 and 2 4 ma an inter species calibration was used to define species offsets and to successfully obtain a continuous composite benthic 18o record correlated with the global composite benthic 18o stack curve lr04 to construct an orbital scale age model the consistency of the benthic 18o stratigraphy with biostratigraphy and magnetostratigraphy confirms the reliability of both methods for constraining age the time difference between cyclic changes in sedimentary physical properties and glacial interglacial cycles since 0 8 ma is notable and suggests that physical properties alone cannot be used to construct an orbital scale age model amplitude changes in physical properties and a significant drop in the linear sedimentation rate during glacials after 0 9 ma indicate that the glacial sea ice edge extended beyond the bering sea slope site u1343 at this time

geochemical evidence for a large methane release during the last deglaciation from marmara sea sediments abstract recent methane inventories have revealed the potential impact of gas hydrates on the global carbon cycle and hence in climate change milkov 2004 however only a few studies have traced methane release in the geologic record here we show geochemical evidence for a large scale methane release at mid latitudes during the last deglaciation the sea of marmara an enclosed sea between the mediterranean and black seas is located in a tectonically active basin with gas hydrate expulsion and the formation of shallow gas hydrates since depths in the basin are shallower than 1100 m future global temperatures are expected to have a great influence in destabilizing methane clathrates among the suite of biomarkers we have focused on diplopterol and diploptene profiles in core md012430 retrieved from the central basin in the marmara sea our results indicate that during the last 15 000 years hopanoids showed important concentration variations with a pronounced peak during the deglaciation the lack of a relationship between diplopterol diploptene and phytoplanktonic biomarker concentrations as well as a depleted isotopic composition have linked the hopanoid maxima to methanotrophic activity suggesting that an intense methane release occurred at the onset of deglaciation in the marmara sea the vulnerability of the hydrate stability zone to changes in temperature and pressure under this range of shallow water depths as well as the relative timing of the hopanoid maxima and sea surface temperature rise points to thermal destabilization of hydrates as a trigger for methane release in the water column

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

considerable methane fluxes to the atmosphere from hydrocarbon seeps in the gulf of mexico the flux of methane a greenhouse gas from submarine hydrocarbon seeps to the atmosphere is not well quantified direct measurements of methane concentrations and isotopic depth profiles in deepwater hydrocarbon plumes indicate that a significant amount of methane from deep ocean sources could reach the surface ocean the fluxes of the greenhouse gas methane from many individual sources to the atmosphere are not well constrained1 marine geological sources may be significant2 but they are poorly quantified and are not included in the intergovernmental panel on climate change budget1 previous results based on traditional indirect sampling techniques and modelling suggested bubble plumes emitted from marine seeps at depths greater than 200 m do not reach the surface mixed layer because of bubble dissolution and methane oxidation3 4 5 here we report methane concentration and isotope depth profiles from direct submersible sampling of deepwater 550 600 m hydrocarbon plumes in the gulf of mexico we show that bubble size upwelling flows and the presence of surfactants inhibit bubble dissolution and that methane oxidation is negligible consequently methane concentrations in surface waters are up to 1 000 times saturation with respect to atmospheric equilibrium we estimate that diffusive atmospheric methane fluxes from individual plumes are one to three orders of magnitude greater than estimates from shallow water seeps6 7 8 greatly expanding the depth range from which methane seep emissions should be considered significant given the widespread occurrence of deepwater seeps we suggest that current estimates of the global oceanic methane flux to the atmosphere1 may be too low

the double silica maximum in the north pacific the north pacific has two vertical silica maxima the well known intermediate maximum occurs between 2000 and 2500 m with a potential density relative to 2000 dbar of 36 90 in the northeastern pacific the deep maximum which has not been observed extensively before is found at or near the ocean bottom in the northern north pacific in a narrow latitude range maps of silica on isopycnals which intersect the intermediate and bottom maxima show that the lowest silica is found in the western tropical north pacific suggesting a route for the spread of south pacific water into the deep north pacific low silica water is found along the western boundary of the north pacific with a separate broad tongue south of hawaii the highest silica on both isopycnals is in the northeast pacific a bottom maximum in the cascadia basin in the northeastern pacific can be differentiated from both open ocean maxima four sources for the vertical maxima are considered in situ dissolution of sinking particles bottom sediment dissolution hydrothermal venting and upslope advection in the northeastern pacific because not enough is known about any of these sources only rough estimates of their contributions can be made the bottom maximum is most likely to result from bottom sediment dissolution but requires a flux larger than some current direct estimates the cascadia basin bottom maximum may result from both bottom sediment dissolution and hydrothermal venting the intermediate maximum is likely to result primarily from dissolution of sinking particles there is no quantitative estimate of the effect of possible upslope advection or enhancement of bottom fluxes due to the columbia river outflow

marine pore water sulfate profiles indicate in situ methane flux from underlying gas hydrate marine pore water sulfate profiles measured in piston cores are used to estimate methane flux toward the sea floor and to detect anomalous methane gradients within sediments overlying a major gas hydrate deposit at the carolina rise and blake ridge u s atlantic continental margin here sulfate gradients are linear implying that sulfate depletion is driven by methane flux from below rather than by the flux of sedimentary organic matter from above thus these linear sulfate gradients can be used to quantify and assess in situ methane flux which is a function of the methane inventory below

tracing subarctic pacific water masses with benthic foraminiferal stable isotopes during the lgm and late pleistocene abstract as the largest ocean basin the pacific helps to set the global climate state since its circulation affects mean ocean properties air sea partitioning of carbon dioxide and the distribution of global oceanic poleward heat transport there is evidence that during the last glacial maximum lgm the subarctic pacific contained a better ventilated relatively fresh intermediate water mass above 2000 m that may have formed locally the source and spatial extent of this water mass is not known nor do we know how formation of this water mass varied during pleistocene glaciations with different orbital and ice sheet boundary conditions here we present a 0 5 my multi species benthic stable isotope record from site u1345 1008 m on the northern bering slope and a 1 0 my record from u1339 1868 m from the umnak plateau in the southeastern basin we find that the relatively well ventilated low 18o intermediate water reaches 1000 m in the bering sea during mis2 but that the hydrographic divide between this water mass and poorly ventilated deep water was shallower than 1000 m for earlier glaciations we also compare bering sea piston core and iodp expedition 323 uvigerina data from the holocene and lgm with the modern hydrography and to previously published profiles from the okhotsk sea and emperor seamounts we find that the carbon and oxygen stable isotope signatures of well ventilated water in the bering and okhotsk seas are distinct suggesting that there may have been intermediate water formation in both basins during the lgm

multi elemental composition of authigenic carbonates in benthic foraminifera from the eastern bering sea continental margin international ocean discovery program site u1343 abstract bering sea sediments represent exceptional archives offering the potential to study past climates and biogeochemistry at a high resolution however abundant hydrocarbons of microbial origin especially along the eastern bering sea continental margin can hinder the applicability of palaeoceanographic proxies based on calcareous foraminifera due to the formation of authigenic carbonates nonetheless authigenic carbonates may also bear unique opportunities to reconstruct changes in the sedimentary redox environment here we use a suite of visual and geochemical evidence from single specimens of the shallow infaunal benthic foraminiferal species elphidium batialis saidova 1961 recovered from international ocean discovery program iodp site u1343 in the eastern bering sea to investigate the influence of authigenic carbonates on the foraminiferal trace metal composition our results demonstrate that foraminiferal calcite tests act as a nucleation template for secondary carbonate precipitation altering their geochemistry where organoclastic sulphate reduction and anaerobic oxidation of methane cause the formation of low and high mg calcite respectively the authigenic carbonates can occur as encrusting on the outside and or inside of foraminiferal tests in the form of recrystallization of the test wall or as banding along natural laminations within the foraminiferal test walls in addition to mg authigenic carbonates are enriched in u ca mn ca fe ca and sr ca depending on the redox environment that they were formed in our results demonstrate that site specific u ca thresholds are a promising tool to distinguish between diagenetically altered and pristine foraminiferal samples important for palaeoceanographic reconstructions utilising the primary foraminiferal geochemistry consistent with previous studies u mn ratios of foraminifera at iodp site u1343 increase according to their degree of diagenetic alteration suggesting a potential response of authigenic u mn to the microbial activity in turn linked to the sedimentary redox environment

episodic methane release events from last glacial marginal sediments in the western north pacific 1 according to recent observations of anomalous bottom simulating reflections bsr the northwest pacific marginal sediments around japan main islands bear large abundances of methane hydrate satoh 2002 during the last glacial direct and indirect evidence accumulated from geochemical data suggests that methane episodically released from hydrate trapped in the seafloor sediments dickens et al 1995 hinrichs et al 2003 kennett et al 2000 here we show that marginal sediments from the western north pacific contain a hopanoid 17 h 21 h hop 22 29 ene diploptene derived from the activity of methanotrophic bacteria in water column and or surface sediment during a warming period interstadial 3 in the last glacial the carbon isotopic compositions of diploptene range between 41 0 and 27 9 relative to pdb in the horizon indicative of a contribution of methanotrophic bacteria foraminiferal isotope signals were also found with highly depleted 13c compositions of planktonic foraminifera 1 9 pdb and benthic foraminifera 0 8 pdb suggesting indirect records of enhanced incorporation of 13c depleted co2 formed by methanotrophic process that use 12c enriched methane as their main source of carbon from combined isotopic data of molecular diploptene and foraminifera the most prominent signal of methane release was detected in the sediments deposited around 25 4 cal kyr bp 100 year time span corresponding to the interstadial 3 this is the first evidence of methane hydrate instability in the open western north pacific during the last glacial considering the glacial interglacial hydrographic conditions in this region the instability of methane hydrate may be modulated by intermediate water warming and or the lowering of sea level our results suggest that the western north pacific marginal regions may be a profound effect on rapid global warming climate changes during the last glacial

the deglacial history of surface and intermediate water of the bering sea the lithology of deglacial sediments from the bering sea includes intervals of laminated or dysaerobic sediments these intervals are contemporaneous with the occurrence of laminated sediments from the california margin and gulf of california which suggests widespread low oxygen conditions at intermediate depths in the north pacific ocean the cause could be reduced intermediate water ventilation increased organic carbon flux or a combination of the two we infer abrupt decreases of planktonic foraminifer d 18 o at 14 400 and 11 650 yr bp which may be a combination of both freshening and warming on the shirshov ridge the abundance of sea ice diatoms of the genus nitzschia reach local maxima twice during the deglaciation the latter of which may be an expression of the younger dryas these findings expand the extent of the expression of deglacial millennial scale climate events to include the northernmost pacific r 2005 elsevier ltd all rights reserved

is methane venting at the seafloor recorded by δ13c of benthic foraminifera shells the research was supported by wcnurp grant pf806880 and by nsf grants oce 9731157 oce 9815186 and oce 9906944 curation of sediment cores at the osu norcor repository is supported by nsf

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

natural marine seepage blowout contribution to atmospheric methane the release of methane sequestered within deep sea methane hydrates is postulated as a mechanism for abrupt climate change however whether emitted seabed methane reaches the atmosphere is debatable we observed methane emissions for a blowout from a shallow 22 m hydrocarbon seep the emission from the blowout was determined from atmospheric plume measurements simulations suggest a 1 1 gas loss to dissolution compared to 10 loss for a typical low flux bubble plume transfer to the atmosphere primarily was enhanced by the rapid upwelling flows induced by the massive discharge this mechanism could allow methane suddenly released from deeper 250 m waters to contribute significantly to atmospheric methane budgets copyright 2006 by the american geophysical union

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

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

correlated transient fluid pulsing and seismic tremor in the costa rica subduction zone continuous measurements of fluid flow were made over a six month period across the nicoya peninsula costa rica pacific convergent margin utilizing osmotically driven fluid flow meters designed to quantify both inflow and outflow rates on the order of 10 5 to 3 cm d significant transience in flow was observed through the surface of the forearc three periods of correlated flow signals were seen on the subduction forearc among three instruments located in the out of sequence thrust oost zone over along margin strike distances of 30 km amplitudes of ground velocity recorded on collocated ocean bottom seismometers obs increase during the three correlated flow events the seismic signal has frequency characteristics that resemble volcanic and non volcanic tremor we hypothesize that repeated plate boundary slow slip events potentially originating at the up dip limit of the seismogenic zone generate the observed signals within the toe of the forearc we propose a model in which the poro elastic stress strain field around a series of creep dislocations simultaneously forces flow through fracture networks in the forearc and oceanic basement rocks and induces diffuse flow through the shallow sediments the former generates the seismic tremor like noise recorded by the obss and the latter generates the flow transients recorded by the fluid flow meters we suggest that high sensitivity fluid flow meters can be utilized to detect transient tectonic strain events in offshore environments where traditional geodetic techniques lack resolution or are not possible d 2005 elsevier b v all rights reserved

significance of mud volcanism 1 mud volcanism and diapirism have puzzled geoscientists for 2 centuries they have been described onshore and offshore in many places on earth and although they occur in various tectonic settings the majority of the features known to date are located in compressional tectonic scenarios this paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described mud volcanoes show variable geometry up to tens of kilometers in diameter and several hundred meters in height and a great diversity regarding the origin of the fluid and solid phases gas predominantly methane water and mud may be mobilized at subbottom depth of only a few meters but in places can originate from several kilometers depth with minor crustal or mantle input the possible contribution of mud extrusion to global budgets both from quiescent fluid emission and from the extrusive processes themselves is important in regions where mud volcanoes are abundant such as the collision zones between africa and eurasia fluid flux through mud extrusion exceeds the compaction driven pore fluid expulsion of the accretionary wedge also quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and hence to greenhouse climate

a molecular recorder of methane hydrate destabilization 1 the magnitude and timing of temporal variation of 13c recorded in benthic and planktic foraminifera from the santa barbara basin strongly suggest episodic events of methane hydrate destabilization during the late quaternary kennett et al 2000 however this and similar evidence from earlier in the geologic past are indirect and therefore not unambiguous here i report a direct geochemical response to elevated levels of methane in the late quaternary santa barbara basin molecular paleontological data provide clear cut evidence for strongly elevated concentrations of methane in bottom waters at times coinciding with diagnostic foraminiferal assemblages and carbon isotopic compositions

structural diversity and fate of intact polar lipids in marine sediments abstract marine sediments harbor an enormous quantity of microorganisms including a multitude of novel species the habitable zone of the marine sediment column begins at the sediment water interface and probably extends to depths of several thousands of meters studies of the microbial diversity in this ecosystem have mostly relied on molecular biological techniques we used a complementary method analysis of intact polar membrane lipids to characterize the in situ microbial community in sediments covering a wide range of environmental conditions from peru margin equatorial pacific hydrate ridge and juan de fuca ridge bacterial and eukaryotic phospholipids were only detected in surface sediments from the peru margin in contrast deeply buried sediments independent of their geographic location were dominated by archaeal diether and tetraether lipids with various polar head groups and core lipids we compared ring distributions of archaeal tetraether lipids derived from polar glycosidic precursors with those that are present as core lipids the distributions of these related compound pools were distinct suggestive of different archaeal sources i e the polar compounds derive from sedimentary communities and the core lipids are fossil remnants from planktonic communities with possible admixtures of decayed sedimentary archaea this in situ production of distinct archaeal lipid populations potentially affects applications of the tex86 paleotemperature proxy as demonstrated by offsets in reconstructed temperatures between both pools we evaluated how varying cell and lipid stabilities will influence the sedimentary pool by using a box model the results are consistent with i a requirement of continuous inputs of freshly synthesized lipids in subsurface sediments for explaining the observed distribution of intact polar lipids and ii decreasing lipid inputs with increasing burial depth

oceanic gas hydrate instability and dissociation under climate change scenarios 1 global oceanic deposits of methane gas hydrate clathrate have been implicated as the main culprit for a repeated remarkably rapid sequence of global warming effects that occurred during the late quaternary period however the behavior of contemporary oceanic methane hydrate deposits subjected to rapid temperature changes like those predicted under future climate change scenarios is poorly understood and existing studies focus on deep hydrate deposits under equilibrium conditions in this study we simulate the dynamic response of several types of oceanic gas hydrate accumulations to temperature changes at the seafloor and assess the potential for methane release into the ecosystem the results suggest that while many deep hydrate deposits are indeed stable under the influence of rapid seafloor temperature variations shallow deposits such as those found in arctic regions or in the gulf of mexico can undergo rapid dissociation and produce significant carbon fluxes over a period of decades

radiometric dating of submarine hydrocarbon seeps in the gulf of mexico massive abiotic carbonates and calcareous shells of the chemosynthetic mytilid bathymodiolus sp containing a detailed history of hydrocarbon seepage were investigated using radiocarbon and u series isotopes stable carbon isotopes and 87 sr 86 sr ratios were also determined in order to provide insights on the carbon source and the nature of the hydrocarbon rich fluids samples from five seepage sites on the northern gulf of mexico sea floor overlying subsurface salt diapirs and encompassing depths from 125 to 2000 m were selected as representative of the spectrum of active and extinct seeps examined from submersible dives in general paired 14 c and 230 th dates of carbonate buildups consisting of aragonite high mg calcite and dolomite mineralogies are highly discordant the cause of the discordance established on the basis of paired 14 c and 13 c values 14 c 898 to 992 13 c 9 5 to 53 3 for n 27 lies with the impairment of the radiocarbon dates resulting from dilution of the 14 c pool with fossil hydrocarbon derived carbon the validity of the ionium dates based on u rich 2 4 7 6 ppm samples is demonstrated by the concordance between 234 u 238 u and 230 th 234 u evolution in time and by the 234 u 238 u o activity ratios that are generally within the range of sea water value of 1 14 0 04 2 sigma some dolomite rich samples are exceptional because their 234 u 238 u o ratios are significantly higher 1 22 1 38 than sea water suggesting deposition from anoxic pore waters where the soluble u reached anomalous 234 u 238 u ratios the formation of the carbonates from sea water derived fluids rather than from formation fluids advecting from deep aquifers is supported by the 87 sr 86 sr composition of the samples mean 0 709145 19 10 6 n 14 that compares well with modern nonseep marine carbonates and the ambient gulf of mexico sea water 0 709171 8 10 6 calcareous shells the 13 c values of which indicate a carbon source in sea water 13 c 4 3 to 1 1 yield valid radiocarbon ages and show fair concordancy between their radiocarbon and ionium dates isotope migration attested by the observed u uptake in the fossil shells is likely to affect the accuracy of their ionium dates radiometric ages from extinct and senescent seep sites at upper bathyal depths indicate that hydrocarbon seepage occurred there during late pleistocene time 195 13 ka ages derived from nascent seep sites at mid bathyal and abyssal depths 12 3 0 0 ka indicate that currently vigorous seepage was initiated at the end of the last deglaciation these radiometric ages most likely reflect the time of sedimentary loading and associated salt diapirism that activated the fault conduits to the sea floor

fluid flow due to the advance of basin scale silica reaction zones the conversion of biogenic silica opal a to opal ct cristobalite and tridymite in biosiliceous sediment causes increased rates of water expulsion because of the reduction in sediment porosity and dehydration of the amorphous opal a phase this release of water occurs over large tracts of sedimentary basins during sediment burial within discrete diagenetic reaction zones analysis of two dimensional and three dimensional seismic data sets from basins in the northern hemisphere provides geophysical evidence for a variety of fluid conduits and roughly circular erosional depressions at the contemporaneous seabed we interpret these features as indicative of water expulsion and focused fluid flow emanating from opal a to opal ct reaction zones at burial depths within the range 200 800 m the rate at which water is expelled depends upon the degree of porosity reduction and the weight fraction of bound water at the reaction zone as well as the rate of advance of the reaction zone where the reaction is actively taking place within homogeneous biosiliceous sediment the rate of water expulsion is independent of the reaction rate this is because water is released across the entire reaction zone therefore slow reaction rates are compensated for by expulsion of water across wider reaction zones we calculate the rate and volume of water expulsion for the faeroe shetland basin where the sediment immediately below the reaction zone contains on average 30 opal ct by weight the estimated volumetric rate of water expulsion per unit surface area at the present day is 6 m3 my 1 per square meter which is greater than the vertical flux of water at the same depth from compaction of the deeper basin fill the average volumetric rate of water expulsion is 120 km3 my 1 across the whole basin biogenic silica is particularly rich in neogene successions in high latitude and equatorial regions and where silica reaction zones are identified they should be factored into sediment compaction and fluid flow histories

fate of rising methane bubbles in stratified waters how much methane reaches the atmosphere there is growing concern about the transfer of methane originating from water bodies to the atmosphere methane from sediments can reach the atmosphere directly via bubbles or indirectly via vertical turbulent transport this work quantifies methane gas bubble dissolution using a combination of bubble modeling and acoustic observations of rising bubbles to determine what fraction of the methane transported by bubbles will reach the atmosphere the bubble model predicts the evolving bubble size gas composition and rise distance and is suitable for almost all aquatic environments the model was validated using methane and argon bubble dissolution measurements obtained from the literature for deep oxic saline water with excellent results methane bubbles from within the hydrate stability zone typically below 500 m water depth in the ocean are believed to form an outer hydrate rim to explain the subsequent slow dissolution a model calibration was performed using bubble dissolution data from the literature measured within the hydrate stability zone the calibrated model explains the impressively tall flares 1300 m observed in the hydrate stability zone of the black sea this study suggests that only a small amount of methane reaches the surface at active seep sites in the black sea and this only from very shallow water areas 100 m clearly the black sea and the ocean are rather effective barriers against the transfer of bubble methane to the atmosphere although substantial amounts of methane may reach the surface in shallow lakes and reservoirs

massive dissociation of gas hydrate during a jurassic oceanic anoxic event in the jurassic period the early toarcian oceanic anoxic event about 183 million years ago is associated with exceptionally high rates of organic carbon burial high palaeotemperatures and significant mass extinction heavy carbon isotope compositions in rocks and fossils of this age have been linked to the global burial of organic carbon which is isotopically light in contrast examples of light carbon isotope values from marine organic matter of early toarcian age have been explained principally in terms of localized upwelling of bottom water enriched in 12c versus 13c refs 1 2 5 6 here however we report carbon isotope analyses of fossil wood which demonstrate that isotopically light carbon dominated all the upper oceanic biospheric and atmospheric carbon reservoirs and that this occurred despite the enhanced burial of organic carbon we propose that as has been suggested for the late palaeocene thermal maximum some 55 million years ago the observed patterns were produced by voluminous and extremely rapid release of methane from gas hydrate contained in marine continental margin sediments

fluid venting in the eastern aleutian subduction zone fluid venting has been observed along 800 km of the alaska convergent margin the fluid venting sites are located near the deformation front are controlled by subsurface structures and exhibit the characteristics of cold seeps seen in other convergent margins the more important characteristics include 1 methane plumes in the lower water column with maxima above the seafloor which are traceable to the initial deformation ridges 2 prolific colonies of vent biota aligned and distributed in patches controlled by fault scarps over steepened folds or outcrops of bedding planes 3 calcium carbonate and barite precipitates at the surface and subsurface of vents and 4 carbon isotope evidence from tissue and skeletal hard parts of biota as well as from carbonate precipitates that vents expel either methane or sulfide dominated fluids a biogeochemical approach toward estimating fluid flow rates from individual vents based on oxygen flux measurements and vent fluid analysis indicates a mean value of 5 5 0 7 l m 2 d 1 for tectonics induced water flow wallmann et al 1997b a geophysical estimate of dewatering from the same area von huene et al 1997 based on sediment porosity reduction shows a fluid loss of 0 02 l m 2 d 1 for a 5 5 km wide converged segment near the deformation front our video guided surveys have documented vent biota across a minimum of 0 1 of the area of the convergent segment off kodiak island hence an average rate of 0 006 l m 2 d 1 is estimated from the biogeochemical approach the two estimates for tectonics induced water flow from the accretionary prism are in surprisingly good agreement

holocene mississippi river floods and geoarchaeological site formation processes in the sny bottom western illinois usa abstract holocene alluvial deposits are well represented in the sny bottom a reach of the mississippi river in western illinois characterized by the presence of a long anabranch channel the sny prior to its engineered confinement the flood stage mississippi functioned as an anastomosed system comprised of many secondary landscape elements hierarchically arranged to distribute water out across a broad floodplain radiocarbon dated stratigraphic sequences are used to reconstruct the geological history of this river reach as it metamorphosed from a sandy late pleistocene braided floodplain into a system dominated by mud by 7400 cal bp the mississippi migrated to its present position and began to build the natural levee it would use for the remainder of the holocene major subsequent geomorphological adjustments to the system resulted from large floods at ca 6900 4900 3300 and 2000 cal bp valley fill is a complex arrangement of individual sedimentary bodies that accumulated at highly variable rates vertical accretion by sedimentation and soil upbuilding acted together to preserve numerous buried archaeological sites of all ages

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

influence of diagenesis on the stable isotopic composition of biogenic carbonates from the gulf of tehuantepec oxygen minimum zone in order to evaluate the influence of diagenetic and post sampling processes on the stable oxygen and carbon isotope compositions of biogenic carbonates we conducted a multiproxy study of organic rich sediments from the eastern pacific oxygen minimum zone core md02 2520 which was retrieved from the gulf of tehuantepec mexico has seasonal laminations and covers the last 40 kyr together with the presence of gypsum crystals and inorganic calcite aggregates the occurrence of large excursions in the stable oxygen and carbon isotope records of both planktonic and benthic foraminifera as large as 3 in d18o and 5 in d13c point to significant secondary transformations storage related gypsum precipitation was ruled out since it implies sulfide reoxidation by oxygen that triggers biogenic calcite dissolution which proved to be of minor importance here instead precipitation of authigenic calcite during early diagenesis appears to be the most likely process responsible for the observed isotopic excursions the d13c composition for inorganic calcite aggregates 5 to 7 suggests a major contribution from anaerobic oxidation of organic matter the d34s composition for gypsum crystals 10 to 15 suggests a major contribution from anaerobic reoxidation of authigenic sulfides potentially involving reactions with metal oxides and sulfur disproportionation a minor part of the gypsum might possibly have formed as a result of local pore water salinity increases induced by gas hydrate formation

biogeochemical controls on authigenic carbonate formation at the chapopote asphalt volcano bay of campeche abstract the campeche knolls in the bay of campeche southern gulf of mexico were investigated through detailed seafloor mapping rov surveys and sediment and pore water sampling the knolls are elongated submarine hills created by salt tectonics with a positive relief of up to 800 m above the surrounding seafloor several of the knolls are associated with sea surface oil slicks identified from satellite data indicating the presence of hydrocarbon seeps on the seafloor one of the knolls named chapopote was studied in detail during two international research expeditions so174 2 and m67 2 and is characterized by extensive hydrocarbon seepage including large asphalt flows oil and gas seeps and seafloor gas hydrate deposits chemosymbiotic biological communities and authigenic carbonate deposits are associated with the seeps and are the result of both biogeochemical turnover and the interaction between downward diffusing seawater and hydrocarbon rich pore fluids at shallow sediment depth authigenic carbonates are characterized by aragonite exhibit a porous texture and are cemented by a matrix of microsparitic to sparitic aragonite macropores of the carbonates were completely filled with liquid oil carbonate microfabrics include peloidal or clotted fabrics that may indicate the existence of microenvironments resulting from microbial metabolism banded botryoidal aragonite cements line the intra and bioclasts and incompletely fill the pore spaces the stable carbon isotopic composition of authigenic aragonite varies between 28 6 and 17 9 pdb identifying oil oxidation as the primary source of carbon to the dic pool while lipid biomarker data demonstrate the concurrent existence of microbial communities responsible for anaerobic oxidation of methane aom these observations indicate the presence of additional aom independent reactions responsible for carbon sequestration at hydrocarbon seeps and demonstrate the complexity of biogeochemical processes at seep sites in the gulf of mexico basin oxygen isotope data of authigenic aragonite vary from 2 5 to 3 8 pdb indicating carbonate precipitation in slight disequilibrium with the surrounding pore fluids

short term occupation surfaces in the lower ohio river valley exposing more of the late holocene hidden record as in other larger river valleys holocene alluvial deposition in the lower ohio river valley created a sampling bias towards certain prehistoric archaeological sites by burying them too deep to be accessed by conventional archaeological methods alternatively archaeological site types that do not leave a large signature i e a large sample of artifacts may also be obscured since they are not associated with recognizable geomorphic or soil development features such as a buried a horizon this obscuration has led to an incomplete record of the region s prehistory to better understand the age and type of prehistoric sites that may be buried within this alluvial landscape it is necessary to understand the structure and history of the alluvium in the valley this can be done by reconstructing the chronological development of alluvial deposits and the soils that formed in them regional models for the age and development of ohio river valley alluvium and the cultural deposits they may contain have been previously developed but must be continuously reviewed and revised as to their applicability to all and any alluvial packages found within the lower ohio river valley this study tests and expands some of these models through the investigation of an alluvial landscape near the confluence of the ohio and great miami rivers in indiana an age based landscape reconstruction which focuses on late holocene alluvium is presented cultural deposits can be linked to brief stability periods within alluvial packages stability periods that were too brief to have formed an a horizon this study shows that short term or ephemeral prehistoric occupations may co occur with periods where the surface of an alluvial landscape or landform was geomorphically stable for a brief period identifying these short term stable surfaces could likely lead to the better identification of underrepresented prehistoric cultural components or archaeological site types and help to reduce sampling bias in the regional prehistoric record

modeling soil geomorphic associations and archaic stratigraphic sequences in the lower ohio river valley abstract adequate sampling of buried occupations in large river valleys requires an understanding of both the structure of valley fills at different scales and the properties of the archaeological record broad tracts of holocene alluvium representing compound bank side and point bars are present in the lower ohio river valley a substantial record of archaic sites also exists although certain hunter gatherer sites from the late wisconsin early holocene and middle holocene are poorly represented primarily because of their low archaeological visibility especially in buried contexts this study uses an extensive geological and archaeological base line data set from the caesars archaeological project to model soil geomorphic relationships and archaic stratigraphic sequences in alluvial units to better define the sampling parameters of these poorly known periods soil weathering properties as reflected in soil order are a proposed indicator of alluvium age radiocarbon ages from other sites in the lower ohio river valley which provide a test of this proposition are found to be correlated with the order of soil series alfisol mollisol entisol inceptisol mapped on landforms of different age early and late holocene alluvium are differentially distributed in the region a factor that may account for a better documented early archaic record below the falls of the ohio

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

calibration of stable isotopic data an enriched δ18o standard used for source gas mixing detection and correction we present empirically based calibrations of our measurements made on a finnigan mat252 equipped with a kiel device to vienna pee dee belemnite using an enriched 18o standard calibrations include corrections for biases caused by the differences in isotopic composition of carbonate standards measured on the two parallel extraction lines of the kiel device and for decreases in the isotopic difference between the reference and sample gas caused by mixing in the source after correcting for these biases the precision of 2200 nbs19 analyses 10 300 g is 0 07 for 18o and 0 03 for 13c we have shared our standard enriched in 18o with 18 laboratories engaged in paleoceanographic research producing the first large scale interlaboratory calibrations for this community using correction procedures reported here water mass reconstructions using data produced on multiple mass spectrometers may now be possible with a precision approaching the level necessary to reconstruct temperature salinity and density variability in the deep ocean

stromatolitic fabric of authigenic carbonate crusts result of anaerobic methane oxidation at cold seeps in 4 850 m water depth methane seepage leads to mg calcite and aragonite precipitation at a depth of 4 850 m on the aleutian accretionary margin stromatolitic and oncoid growth structures imply encrustation of microorganisms microbial mats in the host sediment with a unique growth direction downward into the sediment forming crust shaped lithologies biomarker investigations of the residue after carbonate dissolution show strong enrichments in crocetane and archaeol which contain extremely low 13c values this indicates the presence of methane consuming archaea and 13c values of 42 to 51 pdb indicate that methane is the carbon source for the carbonate crusts thus it appears that stromatolitic encrustations of methanotrophic anaerobic archaea probably occurs in a consortium with sulphate reducing bacteria and that carbonate precipitation proceeds downward into the sediment where ascending cold fluids provide a methane source strontium and oxygen isotope analyses as well as 14c ages of the carbonates suggest that the fluids come from deep within the sediment and that carbonate precipitation began about 3 000 years ago

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

oxygen and carbon stable isotopes of modern land snail shells as environmental indicators from a low latitude oceanic island abstract land snails provide a unique opportunity to study terrestrial paleoenvironments because their shells which are generally highly abundant and well preserved in the fossil record contain a temporal record of environmental change in the form of isotope codes to evaluate the utility of this approach for a low latitude oceanic setting 207 modern shells of 18 species of land snail were analyzed for their oxygen and carbon isotope composition along a north and south facing altitudinal gradient 10 2160 m a s l in tenerife island 28 n of the canary archipelago shells collected at each locality showed a relatively large range in isotope composition which was greater along the south facing transect drier and hotter suggesting that the variance in shell isotope values may be related to water stress although pooled isotope values did not generally show strong relationships with environmental variables i e altitude temperature and precipitation mean isotope values were strongly associated with some climatic factors when grouped by site the mean 18o value of the shell 18oshell by site displayed a negative correlation with elevation which is consistent with the positive relationship observed between temperature and the 18o value of rain 18orain calculated 18o values of the snail body water 18obody derived from observed temperatures and 18oshell values using the equation of grossman and ku grossman e l and ku t l 1986 oxygen and carbon isotope fractionation in biogenic aragonite chem geol isotope geosci sec 59 59 74 displayed a trend with respect to altitude that was similar to measured and hypothetical 18o values for local rain water the calculated 18obody values from the shell declined 0 17 vsmow per 100 m which is consistent with the altitude effect observed for tropical rains in western africa and it correlated negatively with rainfall amount accordingly lower 18oshell values indicate lower temperatures lower 18orain values and possibly higher rainfall totals a positive correlation between the mean 13c values of shells 13cshell and plants by site suggests that shells potentially record information about the surrounding vegetation the 13cshell values varied between 15 7 and 0 6 vpdb indicating that snails consumed c3 and c4 cam plants where more negative 13cshell values probably reflects the preferential consumption of c3 plants which are favored under wetter conditions individuals with more positive 13cshell values consumed a larger percentage of c4 plants other potential factors such as carbonate ingestion or atmospheric co2 contribution were unlikely that were more common at lower elevations of the hotter and drier south facing transect the relatively wide range of shell isotope values within a single site requires the analysis of numerous shells for meaningful paleoclimatic studies although small differences were observed in isotope composition among snail species collected at a single sampling site they were not significant suggesting that isotope signatures extracted from multi taxa snail data sets may be used to infer environmental conditions over a broad range of habitats

a survey of methane isotope abundance 14c 13c 2h from five nearshore marine basins that reveals unusual radiocarbon levels in subsurface waters methane ch4 in the subsurface ocean is often supersaturated compared to equilibrium with the modern atmosphere in order to investigate sources of ch4 to the subsurface ocean isotope surveys 14c ch4 13 c ch4 2 h ch4 were conducted at five locations skan bay sb santa barbara basin sbb santa monica basin smb cariaco basin cb and the guaymas basin gb depth distributions of ch4 concentration and isotopic abundance were determined for both the sediment and water column at the sb sbb smb and cb sites ch4 emitted from seeps on the continental shelf adjacent to the sbb as well as seeps and decomposing clathrate hydrates in the gb was also collected purified and analyzed methane isotope distributions in the sediments were consistent with known methanogenic and methanotrophic activity seep and clathrate hydrate derived ch4 was found to be depleted in radiocarbon however surprising results were obtained in the water column at all sites investigated in sb the radiocarbon content of the subsurface ch4 concentration maximum was on average 41 less than its suspected sediment ch4 source suggesting ch4 seepage in the bay in the sbb smb and cb the 14c ch4 contents in the subsurface ocean were 1 2 to 3 6 times greater than modem carbon quantities suggesting a source of 14c from atmospheric nuclear weapons testing nuclear power plant effluents or cosmogenic isotope production copyright 2008 by the american geophysical union

abrupt changes of intermediate water properties on the northeastern slope of the bering sea during the last glacial and deglacial period 1 millennial scale variability in the behavior of north pacific intermediate water during the last glacial and deglacial period and its association with dansgaard oeschger d o cycles and heinrich events are examined based on benthic foraminiferal oxygen and carbon isotopes 18obf and 13cbf and caco3 using a sediment core recovered from the northeastern slope of the bering sea a suite of positive 18obf excursions at intermediate depths of the bering sea which seem at least in part associated with increases in the 18obf gradients between the bering and okhotsk seas suggest the bering sea as a proximate source of intermediate water during several severe stadial episodes in the last glacial and deglacial period absence of such 18obf gradients during periods of high surface productivity in the bering and okhotsk seas which we correlate to d o interstadials suggests a reduction in intermediate water production in the bering sea and subsequent introduction of nutrient rich deep waters from the north pacific into intermediate depths of the bering sea we argue that a reorganization of atmospheric circulation in the high latitude north pacific during severe cold episodes in the last glacial and deglacial period created favorable conditions for brine rejection in the northeastern bering sea the resulting salinity increase in the cold surface waters could have initiated intermediate and deep water formation that spread out to the north pacific

distributional variations in marine crenarchaeotal membrane lipids a new tool for reconstructing ancient sea water temperatures it has recently been shown that membrane lipids of marine crenarchaeota a ubiquitous and abundant component of plankton occur in relatively high concentrations in recent and ancient sediments in this study we investigated the environmental controls on the relative distribution of these lipids in surface sediments we especially focussed on temperature as it is known from the thermophilic genetic relatives of marine crenarchaetoa that the composition of their membrane strongly depends on growth temperature indeed a significant linear correlation r2 0 92 is found between the number of cyclopentane rings in sedimentary membrane lipids derived from marine crenarchaeota and the annual mean sea surface temperatures this suggests that the mechanism of physical adaptation of their membrane compositions to temperature is identical to that of their thermophilic relatives in turn archaeal lipid distributions in sediments may thus allow the reconstruction of sea water temperatures of ancient marine environments

methane derived carbonates and authigenic pyrite from the northwestern black sea abstract methane seeps in the northwestern black sea are accompanied by carbonate and pyrite precipitates sediments were sampled at locations on the romanian 120 m depth and ukrainian 180 200 m depth shelf and slope layered carbonate crusts are formed of i carbonate cemented siliciclastic sediment containing dreissenoid bivalves ii microcrystalline high mg calcite or aragonite and iii aragonitic cement the dreissena sediment is subrecent and was deposited during the freshwater phase of the black sea it has been affected by seepage of methane rich fluids which induced intergranular precipitation of authigenic carbonates the microcrystalline carbonates exhibit an intense autofluorescence high mg calcite contains 11 14 mol mgco3 the aragonitic cement 8300 9500 ppm sr forms either isopachous layers or botryoids microbial filaments about 10 20 m in diameter and up to 900 m in length are preserved within and on carbonate crusts the carbonates are depleted in 13c microcrystalline carbonate ranges from 27 to 41 pdb and botryoidal aragonite ranges from 26 to 38 pdb the 13c depletion indicates that the carbonates predominantly derive from the microbial oxidation of methane carbonate deposits do not project up into the oxic water column they are restricted to the anoxic water column and to anoxic sediments revealing the crucial role of anaerobic methane oxidation for carbonate precipitation 14c contents give apparent radiocarbon ages of 20 640 180 a bp for a sample of botryoidal aragonite and 19 110 180 a bp for a sample of microcrystalline carbonate compatible with minimum ages of carbon derived from a fossil hydrocarbon source the 18o values of methane derived carbonates show a narrow range from 1 2 to 0 2 pdb 87sr 86sr ratios of microcrystalline carbonate mean 0 70927 and aragonitic cement mean 0 70918 are indistinguishable from ambient seawater mean 0 70917 and thus indicate a shallow sr source higher 87sr 86sr ratios of the dreissena sediment mean 0 71005 are probably caused by sr derived from detrital mica carbonates are accompanied by blocks and crusts composed of pyrite the framboidal sulphide exhibits a palisade like fabric with framboids arranged to parallel pillars sulphur isotopic ratios 34s ranging from 16 8 to 19 7 cdt indicate that the sulphur derives not from the 34s depleted h2s of the water column or the uppermost sediment layers most likely pyrite formed in the lacustrine sediments after the first incursion of mediterranean seawater

gas hydrate destabilization and methane release events in the krishna godavari basin bay of bengal abstract methane release events have been linked to global warming alteration of the carbon cycle and influence on biota however unequivocal evidence of paleomethane release events are limited we report several negative carbon stable isotope excursions in planktic and benthic foraminifera in a core md161 8 from the krishna godavari k g basin bay of bengal the most negative 13 c spikes are recorded during the marine isotope stages mis 4 and at the transition of mis 5 to 4 occurrence of highly 13 c depleted average 13 c 48 2 4 vpdb authigenic high magnesian calcite are also reported within this time window from the core md161 8 in the present work an unequivocal explanation for the observed 13 c depletion in the marine planktic and benthic foraminifera is difficult to achieve solely from the optical electron microscopy or c o stable isotope ratio analyses due to possible influence of diagenetic alteration we attribute the observed episodic methane expulsion events as inferred from the negative 13 c excursions and earlier reports on the occurrence chemosynthetic bivalves and mo concentration anomaly to the destabilization of the base of gas hydrate stability zone bghsz sea level drop and shale tectonics induced focused fluid flow are the two possible causes of hydrate destabilization discussed here shale tectonics were possibly responsible for creating fault systems which acted as the conduit for gas flow through the sediment column and subsequent seepage shale and salt tectonics in the passive continental margins being a globally observed phenomenon its role as an important driving force for enhanced methane emission needs detailed investigation to understand the climatic perturbations through geologic time additional evidence of methane emission from site md161 15 further supports the link between shale tectonics and methane emission

foraminiferal oxygen and carbon isotopes during the last 34 kyr off northern japan northwestern pacific abstract oxygen and carbon isotopes of foraminifera were analyzed in core pc4 water depth 1366 m off northern japan near the east side of the tsugaru strait 130 m depth between the open northwestern pacific ocean and the japan sea at present the site is at the confluence of the tsugaru warm current which flows eastwards out of the sea of japan through the tsugaru strait the subarctic oyashio current and the subtropic kuroshio current during the last glacial maximum lgm the oyashio current penetrated further to the south and outflow from the japan sea was restricted by glacio eustatic sea level lowering the isotopic values of the planktic foraminifer neogloboquadrina pachyderma sinistral and the benthic foraminifer uvigerina akitaensis reflect rapid millennial scale paleoceanographic changes between 34 and 6 ka hydrographic changes during deglaciation were related to events at high northern latitudes but holocene hydrographic changes were dominated by local effects such as the development of the outflow of the tsugaru warm current high values of planktic 18 o during the lgm reflect the southward advance of the oyashio current these values decreased by 0 3 from 19 4 to 18 9 ka then increased by 0 5 at 18 ka with highest values between 17 5 and 15 ka the 18 o oscillations between 19 4 and 15 ka may reflect millennial scale warm cold oscillations during heinrich event 1 planktic microfossil data indicate that cold oyashio waters flowed from the northwestern pacific into the japan sea via the tsugaru strait between 17 and 16 ka consistent with the occurrence of the highest planktic 18 o values in core pc4 planktic 18 o values rapidly decreased by 0 9 at 15 ka possibly reflecting the effects of both a rapid increase in fresh water flux and rising temperatures in the subarctic north pacific during the younger dryas cold event planktic 18 o values increased by 0 5 followed by a gradual decrease by 1 from the early to middle holocene reflecting a gradual increase in eastward outflow via the tsugaru strait with sea level rise both planktic and benthic foraminiferal 13 c values oscillated between 34 and 10 ka at relatively large amplitudes about 0 5 then remained relatively stable during the last 10 kyr several negative planktic and benthic 0 7 13 c excursions were present in sediment dated between the precipitation of secondary carbonates during episodic methane release possibly associated with methane release from continental margin sediments

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales

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

geological geochemical and microbiological heterogeneity of the seafloor around methane vents in the eel river basin offshore california marine methane vents and cold seeps are common features along continental margins worldwide serving as localized sites for methane release and colonization by microbial and chemosynthetic megafaunal communities the eel river basin erb located on the continental slope off northern california contains active methane vents and seep associated chemosynthetic biological communities cbc on the crests of anticlines in 520 m water depth seep related features on the seafloor have a patchy distribution and include active bubbling vents chemosynthetic clam beds and sulfide oxidizing bacterial mats methane sources supplying local seeps are heterogeneous on all spatial scales and support a large and diverse microbial assemblage involved in the anaerobic oxidation of methane aom to develop a comprehensive understanding of the complex biological geochemical and physical processes associated with and influencing seafloor methane seepage a multidisciplinary approach is required here we present an integrative multidisciplinary study that illustrates the diverse processes associated with seafloor methane seepage within the eel river basin and the complex interactions defining the geochemistry mineralogy and microbiology within this environment

pole tide modulation of slow slip events at circum pacific subduction zones episodic slow slip ess events have been detected at several circum pacific subduction zones such as cascadia japan and mexico notably at least eight ess events along the northern cascadia subduction zone recurred with a period of 13 16 months we study the relationship between pole tide associated with chan dler wobble with a period of 14 months induced stress and the occurrence of the ess events our quantitative analysis shows that 14 of the 20 documented ess events occurred during the ascension phase prior to the maximum of a pole tide induced coulomb failure stress change and three events occurred at the stress change peak the pole tides modulate the stress field at the downdip edge of the transition zone along the plate interface and may trigger ess events when conditions are favorable the phase advance of the triggered events with respect to the induced coulomb failure stress change may reflect that the fault slip is dictated by a rate and state dependent friction law inferred from laboratory experiments

rates of anaerobic oxidation of methane and authigenic carbonate mineralization in methane rich deep sea sediments inferred from models and geochemical profiles abstract pore water chemical data obtained from a 10 5 m long giant gravity core collected in methane rich sediments from 647 m water depth in the northern gulf of mexico n 28 04 00 w 89 43 15 defines sub bottom gradients in unprecedented detail this core penetrated the sulfate methane interface smi at 300 cm below the seafloor cmbsf at the smi dissolved inorganic carbon dic concentrations reach a maximum 13 5 mm and pore water 13 c dic 63 2 pdb and 13 c methane 89 5 pdb values are most negative below the smi pore water sulfate is nearly depleted methane concentrations rise sharply with simultaneous occurrence of a bubble textured sediment and fine grained methane derived authigenic carbonate nodules and cements are common the sharp peaks in dic concentration and isotope values centered at the smi indicate that dic is being produced by anaerobic oxidation of methane aom within a narrow zone centered at the smi the detailed sulfate and dic concentration profiles and dic 13 c values have enabled geochemical models to be constructed that explore the rate of dic formation by aom and its effect on pore water dic 13 c values model results closely match measured dic concentration and 13 c isotope profiles and indicate that microbiological conversion of methane carbon to dic is rapid in geologic terms and that aom is occurring at the present position of the smi isotope values for authigenic carbonate found immediately below the present day smi 13 c 60 2 0 7 pdb at 440 cmbsf are consistent with derivation of the carbonate carbon from methane via aom at the former location of a smi these observations and model results suggest that aom is occurring at rates that would generate the observed profiles and begin the precipitation of methane derived carbonate occur on time scales of centuries model results also show that the time needed to produce the resulting authigenic cements is an order of magnitude greater than that for aom to produce the observed dic profiles the metabolic rates for dic production by aom inferred from modeling the geochemical profiles compare favorably with available rate data obtained from laboratory microbial incubations and radiolabeled tracer experiments

mineralogical geochemical and isotopic characterization of authigenic carbonates from the methane bearing sediments of the bering sea continental margin iodp expedition 323 sites u1343 u1345 abstract during expedition 323 of the integrated ocean drilling program to the bering sea july 5 september 4 2009 three sites were drilled along the bering sea northeastern continental margin u1343 down to 745 meters below sea floor mbsf u1344 745 mbsf u1345 150 mbsf diagenetic carbonates are present at all sites within the clayey diatom rich oozes of the bering sea where pore waters are also characterized by extremely high methane concentrations we here present mineralogical elemental and isotopic data obtained from the authigenic carbonate rich intercalations within the clay rich pleistocene sediments deposited along the bering sea continental margin the mineralogy of the authigenic carbonates is generally represented by composite mixtures of very small crystals of magnesian calcite dolomite and iron rich carbonates with the latter phases occurring below 260 mbsf at site u1343 below 200 mbsf at site u1344 and below 130 mbsf at site u1345 element geochemistry shows that ca mg fe ba mn sr and u are enriched in the carbonate rich intercalations relative to the background sediments due to their incorporation into the carbonates and into other authigenic phases e g barite and pyrite the oxygen and carbon isotopic compositions of the authigenic carbonate minerals show that they were sequentially precipitated from pore waters at different temperatures i e different burial depths and with different isotopic compositions of dissolved inorganic carbon dic the authigenic mg calcite precipitated early during diagenesis and shallow burial from a 13 c depleted dic pool whereas dolomite and fe rich carbonates formed during later diagenesis and deeper burial from a 13 c enriched dic pool these authigenic carbonate occurrences are interpreted as resulting from microbial sulfate reduction combined with anaerobic oxidation of methane and methanogenesis that was intimately linked to the alteration of silicates especially iron rich clay minerals