organic geochemistry and origin of late glacial holocene sapropelic layers and associated sediments in marmara sea abstract organic geochemistry of two sapropel sapropelic sediment units dated 10 6 6 4 and 3 8 3 2 kyr bp and associated sediments in two gravity cores from the marmara sea were studied to characterize the organic matter and discuss its paleoceanographic implications vertical trends of c n ratio 13c and hydrogen indices show that the flooding of the marmara sea by the mediterranean waters at 12 kyr bp and onset of deposition of the lower sapropelic layer at 10 6 yr bp are characterized with a high input of terrestrial organic matter this terrestrial input decreased and marine organic matter contribution increased in time towards the top of the upper sapropelic layer at 3 2 kyr bp the lower sapropelic layer is broadly the same age and has a similar distribution of organic matter type as the s1 sapropel of the aegean sea suggesting their depositions may have been controlled by the same events both the lower marmara sapropelic layer and the aegean s1 sapropel were probably deposited during a time of high influx of organic rich river waters from the black sea this influx of black sea water could have induced water stratification in the marmara sea and aegean sea and lead to the deposition of the sapropels

late pleistocene holocene evolution of the northern shelf of the sea of marmara abstract chirp sub bottom profiling multibeam bathymetric mapping and a combination of faunal and isotopic analysis of molluscs and foraminifera in sediment cores on the northern shelf of the sea of marmara som provide evidence of sea level excursions water exchanges between the adjacent mediterranean and black seas and oscillating salinity over the last 160 ka bp during the marine isotope stages mis 2 mis 3 mis 4 and mis 6 the som disconnected from the mediterranean sea and evolved into a lake during mis 1 mis 5 and mis 7 the som reconnected and became salty once again sapropels formed shortly after each invasion of mediterranean saltwater observed in our cores concurrent suboxic dysoxic conditions prevailed over quite shallow substrates on the shelf ancient shorelines are pervasive at 85 m on the northern shelf and in the region of prince islands coincident with the elevation of the modern bedrock sill in the canakkale dardanelles strait at times when global eustatic sea level dropped below this sill the surface of the som stabilized at its outlet and freshened thus this particular shoreline is interpreted as the edge of the most recent som lake that existed from about 75 ka bp to 12 ka bp the freshening is observed in very light 6 values of 18 o measured on freshwater molluscs and the complete absence of foraminifera two brief lacustrine episodes during mis 5 suggest that the level of the canakkale outlet might have been as shallow as 50 m in the past a likelihood supported by submerged terraces along its margins bounding the modern central channel and the presence of an euryhaline biofacies in unit l4 1 corresponding to mis 5b 18 o profiles and carbon 14 dating show that salinification of the som and the blossoming of bioherms evolved rapidly after the latest connection with the mediterranean at 12 ka bp however freshening proceeded more slowly once the connection was severed

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

the geometry of the north anatolian transform fault in the sea of marmara and its temporal evolution implications for the development of intracontinental transform faults the north anatolian fault is a 1200 km long strike slip fault system connecting the east anatolian convergent area with the hellenic subduction zone and as such represents an intracontinental transform fault it began forming some 13 11 ma ago within a keirogen called the north anatolian shear zone which becomes wider from east to west its width is maximum at the latitude of the sea of marmara where it is 100 km the marmara basin is unique in containing part of an active strike slip fault system in a submarine environment in which there has been active sedimentation in a paratethyan context where stratigraphic resolution is higher than elsewhere in the mediterranean it is also surrounded by a long civilised rim where historical records reach well into the second half of the first millennium bce before common era in this study we have used 210 multichannel seismic reflexion profiles adding up to 6210 km profile length and high resolution bathymetry and chirp profiles reported in the literature

indications of a link between seismotectonics and ch4 release from seeps off costa rica measurements of ch4 concentrations in the bottom water during two discrete sampling periods in subsequent years above different cold seeps at the pacific margin off costa rica indicate large scale variations of ch4 release ch4 is emitted from mud extrusions and a slide scar at 1000 2300 m water depth maximum ch4 concentrations were found to be lower above all investigated sites in autumn 2003 than in autumn 2002 although seep sites are up to 300 km apart tidal and current changes were observed but found to apply only to individual seep sites increased seismic activity connected to the moment magnitude m w 6 4 earthquake offshore costa rica in june 2002 could have had an impact on all seep sites and thereby caused an increase in ch4 emission this is supported by the largest variations of ch4 concentration found above mud extrusions located above faults likely more strongly affected by tectonic movements even though our data indicate a relation between seismicity and ch4 seepage the relation is not proven and future work is needed to comprehensively test this hypothesis

rupture characteristics of the a d 1912 murefte ganos earthquake segment of the north anatolian fault western turkey abstract the ganos fault is the westernmost segment of the north anatolian fault naf that generated the 9 august 1912 murefte ganos earthquake mw 7 4 we study the 1912 earthquake characteristics using co seismic fault slip and fault segmentation coupled with an analysis of historical seismic records surface ruptures with small releasing and restraining structures and 1 5 to 5 5 m right lateral offsets have been measured at 45 sites of the onland 45 km long fault section similar structures are delineated by fresh fault scarps and prominent pull apart basins in the sea of marmara and saros bay a second shock with mw 6 8 occurred on 13 september 1912 implying 20 to 40 km long rupture the damage distribution and analysis of seismic records suggest an epicenter located further west near saros bay which indicates the location of western termination of the 9 august rupture our modeling of historical seismic records reveals a relative source time function between the two events and indicates a 40 second rupture duration in agreement for a 120 30 km long fault rupture for the 9 august shock an estimated total rupture length of 150 30 km for the two earthquakes combined with onshore and offshore fault segmentation allow us to better constrain the western limit of the marmara sea seismic gap and related potential for producing a large earthquake that was sharply increased by the devastating 1999 izmit earthquake in the east

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

seafloor gas seeps and sediment failures triggered by the august 17 1999 earthquake in the eastern part of the gulf of izmit sea of marmara nw turkey abstract on august 17 1999 a major earthquake mw 7 4 occurred affecting a large area in northwestern turkey a 150 km long section of the north anatolian fault ruptured from the entrance of the gulf of izmit to golyaka in the east during the earthquake we utilized high resolution shallow seismic data acquired during a post earthquake cruise to find evidence of gas seeps gas charged sediments and sediment failure in the eastern izmit basin of the gulf of izmit the data showed anomalies that suggest the presence of increased gas in the gulf after the earthquake five major zones of offshore mass movement were found in the study area comparison of data collected before and after the earthquake indicates that the apparent amount of gas increased after the earthquake and the mass movement has a causative relationship to the august 17 1999 earthquake therefore we conclude that the seismic event presence of increased gas and the offshore mass movements in the study area are interrelated

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

the active main marmara fault abstract this paper presents selections from and a synthesis of a high resolution bathymetric sparker and deep towed seismic reflection data set recently acquired by the french ifremer r v le suroit in an e w deep trough that forms the northern half of the sea of marmara in nw turkey it includes the first high resolution complete bathymetric map of this area a single throughgoing dextral strike slip fault system which is the western continuation of the northern branch of the north anatolian fault cuts this trough lengthwise and joins the 1999 8 17 kocaeli earthquake fault with the 1912 8 09 arkoy murefte earthquake fault both of which display strike slip offset in its eastern one fourth the structure follows closely the northern margin of the deep trough whereas in the west it hugs its southern margin the eastern one fourth of the structure has a minor component of its displacement distributed across the deep trough owing to a possible original bend in the course of the dextral structure the present course of the north anatolian fault in the sea of marmara originated some 2 105 a ago by cutting across the older basin fabric generated by a dominant nne ssw extension before it began taking up major motion in the pliocene

inferring precipitation anomaly gradients from tree rings abstract long term information on gradients in precipitation anomaly over tens to hundreds of km is important to hydroclimatology for improved understanding of the spatiotemporal variability of moisture delivery systems and runoff site centered reconstructions of cool season nov apr precipitation at 36 quercus douglasii tree ring sites in the central valley of california usa are generated regionalized and evaluated for ability to track north south gradients in precipitation anomaly event series are constructed for overall wet w overall dry d wetter to north w d and wetter to south d w conditions 1557 2001 interesting features of the event series are clustering of w events in the 1780 1790s and a three year run of d w events in 1816 1818 coincidentally following the eruption of tambora in 1815 the most recent 25 years of the event series stand out for a high frequency of w and d events and low frequency of events associated with strong gradients in precipitation anomaly the five strongest w events in this period and seven of the nine w events since 1934 match el nino years recent changes in the event series may be a central valley footprint of a well documented post 1976 change in the atmosphere ocean climate system over the north pacific similar studies may prove useful in other geographical areas where networks of tree ring data sufficiently sensitive to precipitation are available

freshening of the marmara sea prior to its post glacial reconnection to the mediterranean sea during the last glaciation the marmara sea was isolated from the mediterranean sea because global sea level was below the depth of the dardanelles sill prior to the postglacial reconnection to the mediterranean sea 14 7 cal kyr bp the surface waters of the marmara sea were brackish marmara lake freshening of a previously saline marmara sea could have happened via spill out of brackish to fresh water from the surface water of the black sea through the bosphorus strait this hypothesis has not been tested against alternative possibilities salt flushing by river run off and precipitation here we use the dissolved cl and stable isotope composition o18 and d of marmara sea sediment pore water to estimate the salinity and stable isotope composition of marmara lake bottom water and to evaluate possible freshening scenarios we use a transport model to simulate pore water cl o18 and d in marmara sea sediments in the past 130 kyr which includes the last interglacial 130 75 cal kyr bp the last glacial 75 14 cal kyr bp and the current postglacial period our results show that the bottom waters of the marmara lake were brackish 4 salinity and isotopically depleted o18 10 2 and d 70 respectively compared to modern seawater their salinity and stable isotope ratios show that they are a mixture of mediterranean waters and danube like waters implying that the freshening took place via spill out of freshwater through the bosphorus our modelling approach indicates that the transit of fresh water from glacial eurasia to the mediterranean via the marmara sea started at least 50 cal kyr bp was continuous throughout most of the last glaciation and persisted up to the post glacial reconnection to the mediterranean through the dardanelles sill 14 7 cal kyr bp these results are consistent with previously published micropaleontological and geochemical investigations of sediment cores that indicate lacustrine conditions in the marmara sea from about 75 to 14 7 cal kyr bp

geochemical and isotopic approach to maturity source mixing estimations for natural gas and associated condensates in the thrace basin nw turkey abstract the tertiary thrace basin located in nw turkey comprises 9 km of clastic sedimentary column ranging in age from early eocene to recent in age fifteen natural gas and 10 associated condensate samples collected from the 11 different gas fields along the nw se extending zone of the northern portion of the basin were evaluated on the basis of their chemical and individual c isotopic compositions for the purpose of the study the genesis of ch4 thermogenic c2 gases and associated condensates were evaluated separately methane appears to have 3 origins group 1 ch4 is bacteriogenic calculated 13cc1 c 61 48 silivri field and found in oligocene reservoirs and mixed with the thermogenic group 2 ch4 they probably formed in the upper oligocene coal and shales deposited in a marshy swamp environment of fluvio deltaic settings group 2 13cc1 c 35 80 hamitabat field and group 3 13c1 c 49 10 degirmenkoy field methanes are thermogenic and share the same origin with the group 2 and group 3 c2 gases the group 2 c2 gases include 63 of the gas fields they are produced from both eocene overwhelmingly and oligocene reservoirs these gases were almost certainly generated from isotopically heavy terrestrial kerogen 13c 21 present in the eocene deltaic hamitabat shales the group 3 c2 gases produced from one field were generated from isotopically light marine kerogen 13c 29 lower oligoce ne mezardere shales deposited in pro deltaic settings are believed to be the source of these gases the bulk and individual n alkane isotopic relationships between the rock extracts gases condensates and oils from the basin differentiated two groups of condensates which can be genetically linked to the group 2 and 3 thermogenic c2 gases however it is crucial to note that condensates do not necessarily correlate to their associated gases maturity assessments on the group 1 and 2 thermogenic gases based on their estimated initial kerogen isotope values 13c 21 29 and on the biomarkers present in the associated condensates reveal that all the hydrocarbons including gases condensates and oils are the products of primary cracking at the early mature st age req 0 55 0 81 it is demonstrated that the open system source conditions required for such an early mature hydrocarbon expulsion exist and are supported by fault systems of the basin

submarine fault scarps in the sea of marmara pull apart north anatolian fault implications for seismic hazard in istanbul earthquake scarps associated with recent historical events have been found on the floor of the sea of marmara along the north anatolian fault naf the marmarascarps cruise using an unmanned submersible rov provides direct observations to study the fine scale morphology and geology of those scarps their distribution and geometry the observations are consistent with the diversity of fault mechanisms and the fault segmentation within the north marmara extensional step over between the strike slip ganos and izmit faults smaller strike slip segments and pull apart basins alternate within the main step over commonly combining strike slip and extension rapid sedimentation rates of 1 3 mm yr appear to compete with normal faulting components of up to 6 mm yr at the pull apart margins in spite of the fast sedimentation rates the submarine scarps are preserved and accumulate relief sets of youthful earthquake scarps extend offshore from the ganos and izmit faults on land into the sea of marmara our observations suggest that they correspond to the submarine ruptures of the 1999 izmit mw 7 4 and the 1912 ganos ms 7 4 earthquakes while the 1999 rupture ends at the immediate eastern entrance of the extensional cinarcik basin the 1912 rupture appears to have crossed the ganos restraining bend into the sea of marmara floor for 60 km with a right lateral slip of 5 m ending in the central basin step over from the gulf of saros to marmara the total 1912 rupture length is probably about 140 km not 50 km as previously thought the direct observations of submarine scarps in marmara are critical to defining barriers that have arrested past earthquakes as well as defining a possible segmentation of the contemporary state of loading incorporating the submarine scarp evidence modifies substantially our understanding of the current state of loading along the naf next to istanbul coulomb stress modeling shows a zone of maximum loading with at least 4 5 m of slip deficit encompassing the strike slip segment 70 km long between the cinarcik and central basins that segment alone would be capable of generating a large magnitude earthquake mw 7 2 other segments in marmara appear less loaded

a fore arc origin for the thrace basin nw turkey hydrocarbon bearing thrace basin occupies much of the european part of turkey the middle eocene to oligocene sequence in the centre of the basin exceeds 9 km in thickness based on the stratigraphy structure and the regional context of this basin we propose that it developed as a fore arc basin between the medial eocene and the oligocene above the northward subducting intra pontide ocean its post miocene history has been dominated mainly by wrench tectonics resulting from the activity of the now deactivated northwestern strand of the present day north anatolian fault zone

a possible connection of caspian sea level fluctuations with meteorological factors and seismicity abstract the caspian sea has exhibited significant wide range fluctuations that have been traditionally attributed to variations in climatic agents the objective of this research is to estimate the hydrologic budget and sea surface heights of the caspian sea from 1998 to 2005 to assess the contribution of meteorological and geological process to the caspian sea level variations the water budget of the caspian sea from 1998 to 2005 was calculated using the state of the art remote sensing techniques and ground truth data the sea surface heights of the caspian sea were constructed from the refined topex poseidon altimetry data the national centers for environmental prediction department of energy reanalysis 2 meteorological data provided all the variables necessary for the penman method to estimate evaporation over the caspian sea the data of the tropical rainfall measuring mission were utilized to estimate precipitation onto the caspian sea a strong agreement between the water budget residuals and caspian sea level variations signifies that caspian sea level oscillations for this time window are essentially controlled by climate related factors on the other hand the relatively larger gaps between the water balance residuals and caspian sea level heights during 2000 and 2001 may indicate an impact of seismicity on caspian sea level oscillations as a result of two major earthquakes on november 25 2000

contribution of oceanic gas hydrate dissociation to the formation of arctic ocean methane plumes contribution of oceanic gas hydrate dissociation to the formation of arctic ocean methane plumes matthew t reagan 1 george j moridis 1 scott m elliott 2 mathew maltrud 2 lawrence berkeley national laboratory 1 cyclotron rd berkeley ca 94720 usa los alamos national laboratory p o box 1663 los alamos nm 87545 usa e mail mtreagan lbl gov

influences of temperature and mg ca ratio on caco3 precipitates from seawater the mg ca ratio at which the calcium carbonate mineral that has pseudohomogeneously precipitated from seawater changes from calcite to aragonite was experimentally determined as a function of temperature results indicate a dramatic change in the critical mg ca ratio over a relatively small temperature range for example in normal seawater with a mg ca of 5 1 the critical temperature is 6 3 c at a temperature of 25 c however mg ca must be less than 1 4 0 1 for calcite to form these data indicate that paleoclimatic conditions at the time of carbonate deposition must be considered when attempting to make inferences about variation in other factors such as paleo p co 2 p pressure and paleo mg ca ratios that may control carbonate mineral formation by abiotic processes however the inverse relation between inferred global paleoclimatic conditions and the dominant type of caco 3 polymorph being abiotically deposited i e warm conditions and low mg calcite versus cool conditions and aragonite suggest that substantial changes must have taken place in ocean chemistry over phanerozoic time

the circulation and hydrography of the marmara sea abstract a comprehensive set of data collected during 1986 1992 reveal seasonal and interannual variability in the circulation and hydrography of the marmara sea waters which have contrasting properties and originate from the adjacent basins supply the two layer stratified flows in the sea of marmara turbulent entrainment into the upper layer in the exit region of the bosphorus jet and wind stirring in winter both contribute equally to the basin vertical mixing the upper layer circulation of the marmara sea is determined from adcp measurements and from dynamical calculations based on hydrographic data the mean upper layer circulation is anti cyclonic mainly driven by the southward flowing bosphorus jet in the enclosed domain the bosphorus inflow is well defined except during the periods of low discharge in autumn and winter when the jet becomes weaker and tends to become attached to the west coast near the exit mediterranean water entering from the dardanelles supply the suhalocline layer the negatively buoyant plume of well oxygenated water is the only means of renewal of the deep waters partially compensating for the oxygen consumed by the degradation of organic matter sinking from the upper layer into the lower layer yet the subhalocline waters remain permanently deficient in oxygen as a result of the internal balances of diffusion advection and consumption the depth to which the plume penetrates is a function of the seasonal characteristics of the inflow density modified in the strait and the weak interior stratification

stable isotope evidence for chemosynthesis in an abyssal seep community communities of abundant organisms similar to those which surround the hydrothermal vents of the east pacific rise epr occur in 3 266 m of water in the gulf of mexico they were discovered with the alvin at 26 02 n 84 55 w in an area where pore waters seep from the cretaceous limestones of the adjacent platform at the contact between the florida escarpment and the holocene hemipelagic sediments of the abyssal gulf because of the unusual abundance of organisms in this deep sea environment and the taxonomic similarities to the chemosynthetically based communities which surround the hydrothermal vents on the epr the seep communities are suspected to exist on a local non photosynthetic food source1 we have now measured isotope ratios in tissues of organisms which surround these saline seeps to determine the origin of the local food chain the tissues have extremely negative 13c 42 to 77 pdb and 15n 2 72 to 9 34 air values such highly fractionated carbon and nitrogen isotopes are unknown in food chains based on photosynthesis suggesting that these communities are chemosynthetic the cause of this extreme fractionation is attributed either to assimilation from local supplies of isotopically depleted methane and ammonium or to biochemical fractionation the tissues of these animals contain significant amounts of 14c 60 modern so the source of this fractionated carbon is not predominantly fossil methane

formation of carbonate chimneys in the mediterranean sea linked to deep water oxygen depletion marine sediments at ocean margins vent substantial amounts of methane1 2 microbial oxidation of the methane released can trigger the precipitation of carbonate within sediments and support a broad diversity of seafloor ecosystems3 4 the factors controlling microbial activity and carbonate precipitation associated with the seepage of submarine fluid over geological time remain poorly constrained here we characterize the petrology and geochemistry of rocks sampled from metre size build ups of methane derived carbonate chimneys located at the amon mud volcano on the nile deep sea fan we find that these carbonates comprise porous structures composed of aggregated spherules of aragonite and closely resemble microbial carbonate reefs forming at present in the anoxic bottom waters of the black sea5 using u series dating we show that the amon carbonate build ups formed between 12 and 7 thousand years ago contemporaneous with the deposition of organic rich sediments in the eastern mediterranean the so called sapropel layer s1 we propose that the onset of deep water suboxic or anoxic conditions associated with sapropel formation resulted in the development of intense anaerobic microbial activity at the sea floor and thus the formation of carbonate chimneys

seafloor authigenic carbonate crusts along the submerged part of the north anatolian fault in the sea of marmara mineralogy geochemistry textures and genesis abstract extensive seafloor authigenic carbonate crusts occur as pavements mounds and chimneys along the north anatolian fault system nafs in the sea of marmara they are often covered or surrounded by patches of black fe sulphide rich sediments and associated with hydrocarbon rich gas and brackish water emissions in the 1250 m deep deep basins and with deep saline formation waters and hydrocarbons emissions from mud volcanoes and anticlines on the 350 650 m deep compressional highs the authigenic carbonate crusts are commonly porous with sinter like botryoidal and sugary granular textures and constructed from cementation of framework elements consisting mainly of bivalve shells and shell fragments serpulid tubes fibrous microbial organic matter and rarely pebbles the authigenic cements consist mainly of aragonite in most sites but high mg calcite occurs as a major carbonate cement at some basinal sites where the brackish former marmara lake waters emerge the buoyant emission of brackish waters in the deep marmara basins and deeply sourced fluids from the tertiary thrace basin at the compressional highs are supported by relatively low 18o values 0 5 to 3 8 v pdb average 2 1 v pdb n 24 of carbonates in the former and high values 2 6 to 3 4 v pdb average 3 0 n 9 in the latter areas low 13c values 47 6 to 13 7 v pdb average 34 9 v pdb n 33 and close association with black reduced sediments indicate that the seafloor authigenic carbonates are formed by the anaerobic oxidation of methane aom at or near the seafloor as result of high methane flux possibly during periods of high seismic activity authigenic carbonates from the western and central highs are relatively less depleted in 13c than those of the deep basin sites suggesting both microbial and thermogenic methane source for the deep basins carbonates and mainly thermogenic hydrocarbon with some contribution from the biodegradation of heavy hydrocarbons and gas hydrate dissociation for carbonates from the compressional highs u th ages of the authigenic carbonates range from less than 1 ka bp to 9 6 ka bp the age distribution together with the geochemical and mineralogical data suggests that different processes such as seismo tectonics and gas hydrates destabilization might have played important role in the authigenic carbonate formation in the sea of marmara over the last 10 ka

corrosion patterns of seep carbonates from the eastern mediterranean sea terra nova 23 206 212 2011 abstract porous seep carbonates are exposed at mud volcanoes in the eastern mediterranean sea the 13c depleted aragonitic carbonates formed as a consequence of the anaerobic oxidation of methane in a shallow sub surface environment besides the macroscopically visible cavernous fabric extensive carbonate corrosion was revealed by detailed analysis after erosion of the background sediments the carbonates became exposed to oxygenated bottom waters that are periodically influenced by the release of methane and upward diffusion of hydrogen sulphide we suggest that carbonate corrosion resulted from acidity locally produced by aerobic oxidation of methane and hydrogen sulphide in the otherwise with respect to aragonite oversaturated bottom waters although it remains to be tested whether the mechanisms of carbonate dissolution suggested herein are valid this study reveals that a better estimate of the significance of corrosion is required to assess the amount of methane derived carbon that is permanently fixed in seep carbonates

interrelationship of fluid venting and structural evolution alvin observations from the frontal accretionary prism oregon seismic reflection and sea beam bathymetric data plus submarine geological measurements define a ramp anticline at the deformatoin front of the central oregon subduction zone at its northern termination the ramp anticline is deeply incised by a large 500 m deep submarine canyon and cut by a probable backthrust to the south along the strike of the fold a smaller submarine canyon shallowly erodes the anticline and backthrusting is not apparent in the submersible observations two alvin dives along a transect through the southern canyon show active fluid vents demarked by biological communities at the frontal thrust and at the breached crest of the anticline along a northern transect encompassing the large submarine canyon 10 alvin dives indicated no venting on the formal thrust limited venting in the canyon but numerous biological communities along a scarp interpreted as the surface trace of the backthrust these observations suggest a scenario of vent and structural geomorphic development consisting of 1 frontal thrust faulting and associated venting facilitated by high fluid pressure 2 erosion of the oversteepened seaward flank of the ramp anticline assisted by seepage forces and leading to fluid flow out of stratigraphically controlled conduits in the limbs of the overthrust deposits 3 lockingmore of the frontal thrust due to dewatering or a local decrease in wedge taper associated with development of the large canyon leading to failure along the backthrust and 4 redirection of fluid flow by the backthrust thus within le 0 3 m y deformation of the relatively permeable sediments of the oregon margin results in stratigraphically controlled flow being partially captured by faults less

quantifying submarine fluid seep activity along the north anatolian fault zone in the sea of marmara abstract the sea of marmara presents the rare case where active seafloor venting sites are found on the surface trace of a major plate boundary fault the north anatolian fault zone the objective of the 2007 marnaut project was to quantify the level of activity of these venting sites and the source of the fluids emitted with the goal of understanding the processes involved and setting a baseline for long term studies of the relationship between seismic activity and fluid migration expulsion processes sites for flow meter and fluid sampler deployment and coring included basin bounding transtensional faults and strike slip faults cutting through the topographic highs significant fluid flow appears to be primarily an episodic phenomenon at all sites with background rates on the order of mm yr to cm yr except at or very near rare focused vents basin bounding faults expel primarily shallow sourced fluid with a strong influence of brackish pleistocene lake marmara water with the notable exception of the main active fault along the northern edge of the cinarcik basin expulsion sites where the main fault crosses topographic highs are more complex with evidence for deep sourced fluids including thermogenic gas one site on the western high displayed two mound structures that appear to be chemoherms atop a deep seated fluid conduit the fluids being expelled are brines with an exotic fluid chemistry along with thermogenic gas and oil our work shows that submerged continental transform plate boundaries can be hydrologically active and exhibit a diversity of sources and processes

hydrology in the sea of marmara during the last 23 ka implications for timing of black sea connections and sapropel deposition 1 sediments deposited under lacustrine and marine conditions in the sea of marmara hold a late quaternary record for water exchange between the black sea and the mediterranean sea here we report a multiproxy data set based on oxygen and strontium isotope results obtained from carbonate shells major and trace elements and specific organic biomarker measurements as well as a micropaleontological study from a 14c dated sediment core retrieved from the sea of marmara pronounced changes occurred in 18o and 87sr 86sr values at the fresh and marine water transition providing additional information in relation to micropaleontological data organic biomarker concentrations documented the marine origin of the sapropelic layer while changes in n alkane concentrations clearly indicated an enhanced contribution for organic matter of terrestrial origin before and after the event when compared with the black sea record the results suggest that the black sea was outflowing to the sea of marmara from the last glacial maximum until the warmer bolling allerod the first marine incursion in the sea of marmara occurred at 14 7 cal ka b p however salinification of the basin was gradual indicating that black sea freshwaters were still contributing to the marmara seawater budget after the younger dryas which is associated with a high input of organic matter of terrestrial origin both basins were disconnected resulting in a salinity increase in the sea of marmara the deposition of organic rich sapropel that followed was mainly related to enhanced primary productivity characterized by a reorganization of the phytoplankton population

authigenic carbonates from the eastern black sea as an archive for shallow gas hydrate dynamics results from the combination of ct imaging with mineralogical and stable isotope analyses authigenic carbonates associated with cold seeps provide valuable archives of changes in the long term seepage activity to investigate the role of shallow buried hydrates on the seepage strength and fluid composition we analysed methane derived carbonate precipitates from a high flux hydrocarbon seepage area batumi seep area located on the south eastern black sea slope in ca 850 m in a novel approach we combined computerized x ray tomography ct with mineralogical and isotope geochemical methods to get additional insights into the three dimensional internal structure of the carbonate build ups x ray diffractometry revealed the presence of two different authigenic carbonate phases i e pure aragonitic rims associated with vital microbial mats and high mg calcite cementing the hemipelagic sediment as indicated by the ct images the initial sediment has been strongly deformed first plastic then brittle leading to brecciation of the progressively cemented sediment the aragonitic rims on the other hand represent a presumably recent carbonate growth phase since they cover the already deformed sediment the stable oxygen isotope signature indicates that the high mg calcite cement incorporated pore water mixed with substantial hydrate water amounts this points at a dominant role of high gas fluid flux from decomposing gas hydrates leading to the deformation and cementation of the overlying sediment in contrast the aragonitic rims do not show an influence of 18o enriched hydrate water the differences in 18o between the presumably recent aragonite precipitates and the older high mg cements suggest that periods of hydrate dissociation and vigorous fluid discharge alternated with times of hydrate stability and moderate fluid flow these results indicate that shallow buried gas hydrates are prone to episodic decomposition with associated vigorous fluid flow this might have a profound impact on the seafloor morphology resulting e g in the formation of carbonate pavements and pockmark like structures but might also affect the local carbon cycle

seafloor gas seeps triggered by a northern california earthquake abstract a series of marine surveys using high resolution seismic reflection and side scan sonar profiling was conducted on the klamath river delta from 1977 to 1985 in november 1980 near the middle of this 8 year time period a major earthquake magnitude 7 occurred in the area the earthquake caused liquefaction of shelf deposits off the klamath river and while mapping the sediment failures we observed an inordinate number of gas vents and acoustic anomalies in the sediment gas charging and water column gas clouds our analyses indicate that a change in gas seepage occurred after the earthquake there was a marked increase in gas abundance immediately after the earthquake a gradual decrease over the next year and stabilization at pre earthquake gas levels within five years or less the acoustic anomalies were observed in pre quaternary rocks as well as in surficial holocene deposits and gas seeps overlay truncated anticlines faults and syncline exposures thus the gas released may have been in part thermogenic in origin a large area 20 km 2 on the delta failed during the earthquake and the abundance of gas seeps and craters in the area suggests that sediment degassing may have been an important process contributing to failure

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

subduction zone earthquake as potential trigger of submarine hydrocarbon seepage methane is abundant in marine sediments analysis of sediment cores and seismic images of marine sediments obtained off the coast of pakistan show fracturing of gas hydrates and an increase in upward methane flux in the decades following a large earthquake in the arabian sea in 1945 suggesting that quakes can trigger hydrocarbon seepage

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

tracing the paleo sulfate methane transition zones and h2s seepage events in marine sediments an application of c s mo systematics 1 microbially mediated anaebic oxidation of methane aom coupled with sulfate consumption within the sulfate methane transition zone smtz in marine sediments is a widely recorded biogeochemical reaction and has profound influence on the atmospheric ch4budget marine carbon cycle and composition of sediment pore fluids recognizing the paleo smtzs in the marine sediments rock records can throw light on the variation of paleo methane fluxes and occurrences of cold seep h2s ch4 events through geologic time here we present results from carbonate carbon pyrite sulfur and molybdenum analyses for two sediment cores overlying the methane hydrate deposits in the bay of bengal the results show intimate association of isotopically depleted carbonate carbon and enriched pyrite sulfur constraining the paleo smtz within the sediment column in addition anomalous enrichments of mo concentrations indicate hydrogen sulfide seepage events here we propose a geochemical tool using c s mo sytematics to decipher the paleo smtzs in marine sediments and rocks