subduction induced pore fluid venting and the formation of authigenic carbonates along the cascadia continental margin implications for the global ca cycle abstract pore fluid venting associated with subduction induced sediment deformation causes precipitation of calcium carbonate as prominent carbonate chimneys or cement in the accreted sediments across the active continental margin off oregon and washington a depletion of interstitial ca 2 with a maximum decrease of 50 relative to seawater ca 2 over only 1 5m depth and reduction in porosity in the deformed sediments suggest that interstitial ca 2 is removed to form calcium carbonate cement in contrast the pore waters of the undeformed abyssal plain sediments show no depletion in dissolved ca 2 they are either enriched to a maximum of 5 or show no change in dissolved ca 2 here the background level of caco 3 content in the sediment is only 0 1 to 1 calcium carbonate precipitation in the deformed sediments probably occurs as the result of upward migration and oxidation of biogenic methane and of the increase in carbonate saturation due to release of excess pore pressure during fluid venting upward advection of fluids at rates of 1 28 cm y 1 is predicted from diffusion advection reaction models applied to the downcore concentration profiles of dissolved ca 2 and nh 4 in the tectonically deformed sediments the range of predicted flow rates is related to the type of calcium carbonate lithification i e slow rates generate cement and fast rates generate chimneys carbonate mineral precipitation associated with pore fluid venting requires direct transfer of ca 2 from the oceanic basement to the accretionary complex such a mechanism leads us to propose that the accretionary complexes of the global plate subduction zones are a major sink for crustal ca 2 a global flux of crustal ca 2 that is removed by carbonate mineral precipitation may be as muc3 as the hydrothermal ca input this significant ca flux not previously considered in the global geochemical budget implies that pore fluid venting in subduction zones may also act as a global sink or source for other elements

carbon geochemistry of cold seeps methane fluxes and transformation in sediments from kazan mud volcano eastern mediterranean sea abstract despite growing concerns about potential enhancement of global warming and slope failure by methane produced by gas hydrate dissociation much uncertainty surrounds estimates of gas hydrate reservoir sizes as well as methane fluxes and oxidation rates at the sea floor for cold seep sediments of the eastern mediterranean sea depth dependent methane concentrations and rates of anaerobic oxidation of methane aom are constrained by modeling the measured pore water sulfate profile the calculated dissolved methane distribution and flux are sensitive to the advective flow velocity which is estimated from the depth distributions of conservative pore water constituents na b near complete anaerobic oxidation of the upward methane flux of 6 0 mol m 2 yr 1 is supported by the depth distributions of indicative biomarkers and the carbon isotopic compositions of organic matter and dissolved inorganic carbon pore water and solid phase data are consistent with a narrow depth interval of aom 14 18 cm below the sediment water interface based on an isotopic mass balance the biomass of the microbial population carrying out oxidation of methane coupled to sulfate reduction at the given methane flux represents 20 of the total organic carbon which is a significant pool of in situ formed organic matter model results indicate that the asymptotic methane concentration is reached a few meters below the sediment surface the predicted asymptotic concentration is close to the in situ saturation value with respect to gas hydrate suggesting that the rate of shallow gas hydrate formation is controlled by the ascending methane flux the proposed model approach can be used to predict the formation of gas hydrate and to quantify methane fluxes plus transformation rates in surface sediments where fluid advection is an important transport mechanism

modeling of calcite dissolution by oxic respiration in supralysoclinal deep sea sediments abstract pore water profiles of co2 ph ca2 and o2 in situ concentrations were measured at two stations on the upper continental slope off gabon the present study evaluates these measurements concerning their implications for the calcium carbonate system in deep sea sediments the model cotrem which was used to simulate the dynamics of this complex geochemical system revealed a strong dependence of calcite dissolution on oxic respiration at both sites all simulated calcite dissolution kinetics reached a dynamic equilibrium with almost equal calcite dissolution rates but different sub saturation states and ph values the latter are mainly dependent on boundary conditions and kinetic rate law parameters boundary conditions are of immense importance they define which ph deviations between measured data and the simulated equilibration instantaneous kinetics have still to be fitted by kinetic restrictions per rate law for the equilibration these ph deviations set up the range of possible values for rate constants in a given rate law to yield a well simulated ph a failure in the implementation of these boundary conditions may lead to non linearly flawed rate constants which fit only one usually the maximal ph deviation well the whole depth distribution of ph deviations has to be fitted very well by a kinetic rate law only this procedure secures that the used boundary conditions and rate laws constants are acceptable nevertheless several kinetic rate laws may be used for good ph fits featuring clear differences in parameter values for rate constants and reaction orders the connection between these rate laws with different parameters is examined and the dependence of the rate constant on the given form of the rate law is demonstrated this study achieves rate constants of 0 038 and 18 d for a dissolution rate law of 4 5th reaction order and sub saturation dependence from the term 1 these results are well within the range of rate constants obtained during former field studies for the same form of the dissolution rate law

discovery of an anoxic basin within the strabo trench eastern mediterranean we report here the discovery of a basin which we call the tyro basin in the eastern mediterranean in which anoxic conditions exist and organic rich sediments are accumulating bottom water samples show extremely high salt concentrations a horizontal midwater sound reflector about 70 m above the basin floor was observed in a seismic reflection profile across the basin from shipboard observations we conclude that dissolution of messinian evaporites exposed by faulting in the sides of the basin causes stagnant bottom conditions this basin provides an opportunity to test some of the hypotheses concerning the formation of sapropels present in cores collected from the same area cores taken in an adjacent similar basin for which we propose the name kretheus basin indicate a recent change from anoxic to oxygenated conditions which was probably caused by tectonic activity associated with the strabo trench

thermodynamic and pore water halogen constraints on gas hydrate distribution at odp site 997 blake ridge abstract marine sediment sequences with ch4 hydrate are characterized by an atypical depth profile in dissolved cl squeezed from pore space a shallow subsurface cl maximum overlies a lengthy and pronounced cl minimum this pore water cl profile represents a combination of multiple processes including glacial interglacial variations in ocean salinity advection and diffusion of ions that are excluded during gas hydrate formation at depth and release of fresh water from dissociation of hydrate during core recovery in situ quantities of gas hydrate can be determined from a measured pore water cl profile provided the in situ pore water signature prior to core recovery can be separated ocean drilling program odp site 997 was drilled into a large ch4 hydrate reservoir on the blake ridge in the western atlantic ocean previously we have constructed a high resolution pore water cl profile at this location here we present a coupled chloride hydrate numerical model to explain basic trends in the cl profile and to isolate in situ cl concentrations the model is based on thermodynamic and ecological considerations and uses established equations for describing chemical behavior in marine sediment pore water systems the model incorporates four key concepts 1 most gas hydrate is formed immediately below the so42 reduction zone 2 fluid dissolved ions and gas advect upward through the sediment column 3 ch4 hydrate dissociates at the base of hydrate stability conditions and 4 seawater salinity fluctuates during glacial interglacial cycles of the late pliocene and quaternary rates of upward advection in the model are sufficient to account for measured br and i concentrations as well as ch4 oxidation at the base of the so42 reduction zone in situ pore water cl inferred from the model is similar to that determined by limited direct sampling in situ ch4 hydrate amounts inferred from the model an average of about 4 of porosity are broadly consistent with those determined by direct gas sampling and indirect geophysical techniques the model also predicts production of substantial quantities of free ch4 gas bubbles 2 5 of porosity at a depth immediately below the lowest accumulation of ch4 hydrate in the sediment column our explanation for the pore water cl profile at site 997 is important because it provides a theoretical mechanism for understanding the distribution of interstitial water cl gas hydrate and free gas in a marine sediment column

the use of mixing models and chemical geothermometers for estimating underground temperatures in geothermal systems abstract application of various chemical geothermometers and mixing models indicate underground temperatures of 260 c 280 c and 265 c in the geysir hveravellir and landmannalaugar geothermal fields in iceland respectively mixing of the hot water with cold water occurs in the upflow zones of all these geothermal systems linear relations between chloride boron and 18o constitute the main evidence for mixing which is further substantiated by chloride silica and sulphate relations in the geysir and hveravellir fields a new carbonate silica mixing model is proposed which is useful in distinguishing boiled and non boiled geothermal waters this model can also be used to estimate underground temperatures using data from warm springs this model as well as the chloride enthalpy model and the na li and co2 gas geothermometers invariably yield similar results as the quartz geothermometer sometimes also does by contrast the na k and the na k ca geothermometers yield low values in the case of boiling hot springs largely due to loss of potassium from solution in the upflow the results of these geothermometers are unreliable for mixed waters due to leaching subsequent to mixing

fluid venting activity within the eastern nankai trough accretionary wedge a summary of the 1989 kaiko nankai results fluid flow manifestations within the outer 20 km of the eastern nankai accretionary wedge between the water depths of 4000 and 2000 m are concentrated near the outcrop of a shallow detachment fault immediately behind the frontal thrust near a depth of 3800 m and along a probable strike slip fault on the top of a 2000 m deep pop up structure 20 km inside the wedge using subbottom temperature measurements we estimate darcy upward flow velocities below clams colonies at the 3800 m site and show that one can associate a narrow range of velocities with the different types of colonies then combining a statistical survey of the distribution of colonies with the velocity estimates we compute a yearly outflow budget of 200 m 3 per metre of width of the wedge in the toe area this is forty times larger than the amount expected from steady state compactive dewatering we propose however that 80 90 of this flow is produced by shallow seawater convection because variations in sea bottom temperatures were too large we could not estimate fluid outflow budgets in the 2000 m venting area however 20 000 and 130 000 year old shells fossilized within widespread carbonate concretions indicate that fluid flow has been active in the 2000 m venting area since at least 130 000 years ago probably in a sporadic fashion chemical evidence indicates that a significant part of the fluid is coming from a depth of at least several hundred metres subbottom temperature measurements over a period of two months in the 3800 m venting site show fluctuations of 20 30 in the venting velocity below an active colony that have an apparent period of two weeks although the fluid circulation appears to be controlled by active faults at least in the shallow part of the wedge not every active fault corresponds to an aquifer in the absence of good high resolution seismic data and drill holes we cannot describe this plumbing system in any detail and are not able to show why some active faults correspond to fluid outlets and some do not

fluid flow in and around a mud volcano field seaward of the barbados accretionary wedge results from manon cruise a field of mud diapirs and mud volcanoes situated in the barbados trench at 13 50 n and extending along an old oceanic fracture zone mercurus was investigated during the manon cruise using both surface ship and nautile submersible sampling and measurements the entire zone from 13 50 n up to 14 20 n has an anomalously high heat flow which implies that fluids are drained into it from a segment of the accretionary wedge a few hundred kilometers wide two structures interpreted as diatremes atalante and cyclops expell large amounts of water and methane we propose that they were formed from the release of a light fluid when gas hydrates were dissociated in the sediment as the result of the circulation of warm fluid in the area however they expell only a small fraction of the incoming fluid implying that disperse flow is the dominant mode of expulsion in this area the chemoautotrophic communities on the surface of the structures rely mostly on sulfides submersible observations temperature measurements in the sediment and the chemistry of the pore fluid indicate that convection of seawater occurs within the first few meters of sediment through high permeability channels such as cemented carbonate conduits we propose that this convection is driven by the density difference between the pore fluid and seawater but fresh water released by the dissolution of shallow hydrates may also contribute this shallow convection may be a frequent process in cold seep environments

the nature and hydrogeologic significance of mud diapirs and diatremes for accretionary systems in accretionary wedges often morphologically similar sedimentary intrusions when observed by remote geophysical means may have one of two quite different driving mechanisms and a highly variable significance for the regional hydrogeologic picture for example mud diapirs are driven by buoyancy forces that arise from bulk density contrasts in them mud and pore fluid upwell en masse and fluid migration is a related sometimes important but generally subsidiary process in contrast diatremes contain sediments fluidized during rapid fluid advection and are forcibly and directly driven by the hydrogeologic system the nature of fluid input from local and exotic source regions can therefore strongly affect sedimentary intrusive processes and vice versa this complicates the process of defining the main features of the hydrogeological systems operating in accretionary wedges focused vertical advection through steep sided piercement mud diapirs requires conduit systems otherwise flow will be diffuse and directed more horizontally out of the low permeability mud mass however where the permeability of the overburden is less than that of the diapir the whole diapir may act as a conduit apart from this special case conduits will be associated with highly anisotropic scaly fabrics that can sometimes develop in the marginal shear zone of diapirs scaly fabrics form during deformation and compaction of a mud matrix under conditions of constant or increasing effective stress however the effective stress path can be complex as it is both controlled by the relative rates of upward intrusion and burial by sedimentation and or structural thickening and the hydrogeologic system due to this it appears likely that even in a geographically related group of diapirs effective stress histories will vary widely between intrusions so that some can form advective pathways for fluids and some cannot mixed systems of behavior may also be present with local diatremes developing within diapirs above the terminations of conduit systems and rapidly expanding methane gas pockets the potentially heterogeneous near surface behavior may be why the surface manifestations of sedimentary intrusions are so variable when observed in the field diatremes can also form separately as large primary features above any structural or stratigraphic conduit that rapidly expels water or gas into the base of an unlithified sediment column when active large diatremes require enormous quantities of fluid water or gas to drive them particularly if they are long lived features and hence are a direct indication of at least an episodically vigorous hydrogeologic system

deformational styles of the eastern mediterranean ridge and surroundings from combined swath mapping and seismic reflection profiling abstract recent swath mapping and seismic reflection profiling across the eastern levantine branch of the mediterranean ridge mr in the eastern mediterranean sea illustrate a strong variability of the deformational styles that characterize this precollisional accretionary prism along a north south cross section of the mr a structural analysis based on surface mapping combined with vertical seismic reflection data reveals two main structural domains a southern outer domain consists of a series of three disconnected distinct fold belts folding affects a sedimentary cover which includes an approximately 2 km thick pliocene and quaternary wedge in this domain resting on fairly thick messinian evaporitic sequences that act as probable decollement layers the mr inner domain includes three regions showing evidences of strong internal deformations and of numerous probable mud cones and mud flows but no seismic evidence of significant underlying messinian evaporites can be detected the inner sub regions are thrusting northwards over an area made of faulted and locally uplifted acoustic basement blocks that constitute the southernmost extension of the crete continental margin acting as a continental buttress for the mr this innermost domain is itself structurally disconnected from the crete continental margin by the en echelon pliny troughs system that shows evidence of left lateral displacement altogether the different structural and sedimentary cover patterns reveal a strong contrast between both mr inner and outer domains and important lateral variations within the inner mr itself strike slip faulting seams to characterizes both areas and large scale mud accumulations potentially exist in the northern one our results support a model of imbricated accretionary prisms including at least two stages 1 a pre messinian stage during which the inner mr probably developed in response to northward subduction of the african lithosphere beneath southern europe and 2 a messinian to post messinian period during which the kinematics of the aegean anatolian microplates and the presence of thick messinian deposits became prevalent and which led to the creation of the outer mr folded wedge piling against the previous one in our interpretation the occurrence of thick messinian evaporites in this area induces important local and regional modifications of the structural pattern strike slip activities reflect partitioning related to oblique subduction and likely lateral escape of the sedimentary cover in the whole studied area

the accretionary complex of the mediterranean ridge tectonics fluid flow and the formation of brine lakes an introduction to the special issue of marine geology the mediterranean ridge is an accretionary complex that is largely composed of sediments that have been accreted from the african plate which is subducted northeastwards beneath the aegean at about 37 mm yr le pichon et al 1995 the trend of the western part of the ridge is nearly orthogonal to the direction of convergence whereas the eastern branch of the ridge is subject to very oblique convergence fig 1 beneath most of the accretionary complex the subducting crust of the african plate is oceanic in nature but along its southern margin in its central sector the accretionary complex is colliding with the continental margin of africa oi libya chaumillon and mascle 1997 in the 1970s the linear deeps of the hellenic trench south of the cretan arc were interpreted as a trench system similar to trenches at other subduction zones but with the realisation that the mediterranean ridge is an accretionary complex biju duval et al 1978 kastens et al 1992 le pichon et al 1982 ryan et al 1982 it became apparent that the hellenic trench represents a forearc basin with little sediment ll the former bathymetric trench of the subduction zone has been lled by the accretionary complex of the mediterranean ridge which is very wide over 200 km across its western branch comparable to alaska 220 km southern barbados 270 km and the makran 230 km all of which have very thick sequences of sediment on the subducting plate the deformation front of the accretionary complex along its southern margin now lies beyond the crest of the exural bulge in the subducting plate fig 2 shown by a positive gravity anomaly see gs 4 and 5 of le pichon et al 2002 that lies seaward of the trench at most subduction zones the slope of the surface of the southern ank of the mediterranean ridge is low about 1 which from the dynamics of accretionary wedges chapple 1978 davis et al 1983 is indicative of very low shear stress on the decollement at the base of the wedge one feature of the mediterranean ridge that distinguishes it from other accretionary complexes is the presence of a sequence of evaporites of messinian age ryan et al 1973 hsu et al 1978 which lie within the sediments at a depth of a few hundred metres beneath the sea bed these evaporites have the potential to in uence the deformational behaviour of the accretionary complex as their mechanical properties are intrinsically diierent from those of siliciclastic sediments and because of their eiect upon uid ow and uid pressure which control eiective stress the discovery of a lake of concentrated brine in the bannock basin a small basin in the

methane related carbonate cements in pockmarks of the north sea abstract some pockmarks on the norwegian continental shelf contain patches of cemented sediment that can provide hardgrounds attractive to a variety of benthonic organisms detailed examination of a sandstone sample from a pockmark in norwegian block 25 7 in the north sea has revealed the presence of mg calcite and aragonite cements some of the latter forming botryoids all cement types are characterized by extremely light carbon isotopic compositions with a mean 13c value of 56 1 pdb which shows that the cements contain carbonate produced by oxidation of biogenic methane oxidation occurred in both the oxic and anoxic diagenetic zones trace amounts of interstitial methane mean 13c 40 8 and higher hydrocarbon gases up to c5 with a c1 cn ratio of 0 855 0 874 in the pockmark sediments indicate that some thermogenic methane may be mixed with the biogenic gas

control of sulfate pore water profiles by sedimentary events and the significance of anaerobic oxidation of methane for the burial of sulfur in marine sediments abstract gravity driven mass flow deposits proven by sedimentary and digital echosounder data are indicative for prevailing dynamic sedimentary conditions along the continental margin of the western argentine basin in this study we present geochemical data from a total of 23 gravity cores pore water so 4 is generally depleted within a few meters below the sediment surface by anaerobic oxidation of methane aom the different shapes of so 4 profiles concave kink and s type can be consistently explained by sedimentary slides possibly in combination with changes in the ch 4 flux from below thus mostly representing transient pore water conditions since slides may keep their original sedimentary signature a combined analysis and numerical modeling of geochemical physical properties and hydro acoustic data could be applied in order to reconstruct the sedimentary history we present first order estimates of the dating of sedimentary events for an area where conventional stratigraphic methods failed to this day the results of the investigated sites suggest that present day conditions are the result of events that occurred decades to thousands of years ago and promote a persisting mass transport from the shelf into the deep sea depositing high amounts of reactive compounds the high abundance of reactive iron phases in this region maintains low hydrogen sulfide levels in the sediments by a nearly quantitative precipitation of all reduced sulfate by aom for the total region we estimate a so 4 or ch 4 flux of 6 6 10 10 moles per year into the zone of aom projected to the global continental slope and rise area this may sum up to about 2 6 10 12 moles per year provided that the sulfur is completely fixed in the sediments it is about twice the global value of the recent global sulfur burial in marine sediments of 1 2 10 12 moles per year as previously estimated thus aom obviously contributes very significantly to the regulation of global sulfur reservoirs which is hitherto not sufficiently recognized this finding may have implications for global geochemical models as sulfur burial is an important control factor in the development of atmospheric oxygen levels over time

interstitial water chemistry of sediments of the costa rica accretionary complex off the nicoya peninsula interstitial water analyses from numerous piston gravity and alvin push cores show that fluid flow at the costa rica accretionary prism is spatially limited and can only be detected by visually directed cores in zones of biogenic activity most of the sites cored show evidence for normal diagenetic processes in rapidly deposited organic carbon rich sediments with little evidence for fluid advection however in visually directed alvin push cores obtained from black sulfidic sediments characterized by the presence of calyptogena clams or tubeworms evidence for fluids advected upward from greater depth horizons is shown these zones are associated with a large mudvolcano on the prism and with the zoes of out of sequence thrusts as changes from sea water concentrations are still relatively small substantial mixing with sea water must have occurred during this upward fluid movement

structure of the mediterranean ridge accretionary complex from seismic velocity information seismic velocities obtained from ocean bottom hydrophone expanding spread profile and multi channel seismic data were used to compile a velocity model for the mediterranean ridge along a 220 km long transect extending from the sirte abyssal plain to the cleft region near the hellenic trough a 200 300 m thin layer of plio quaternary sediments with velocities of 1800 2200 m s 1 covers the whole ridge the messinian evaporites 4000 4500 m s 1 occur in the southwest as a tectonically thickened layer and in a basin just northeast of the crest of the ridge in the intervening region however the evaporites appear absent and the seismic velocities are generally lower arched reflectors imaged in the depth migrated section suggest that the sediments beneath the ridge crest belong to a pre messinian accretionary wedge beneath the messinian evaporites a northeastward thinning layer of probable tertiary sediments shows laterally increasing velocities from 3300 m s 1 to 4600 m s 1 assuming that the layer thinning is caused by compaction due to increased overburden alone we have calculated a porosity reduction from 15 to 4 and an associated fluid expulsion of 10 km3 km 1 along the trench axis this corresponds to c 60 of the initial fluid volume of an undeformed sediment column from the abyssal plain the almost impermeable evaporitic cap over these sediments leads to high fluid pressures at the base of the evaporites likely to make this horizon the basal decollement of the modern accretionary system a 2 5 km thick unit of probable mesozoic carbonates with velocities of 4500 4600 m s 1 is inferred at c 8 km depth the top of the oceanic crust occurs at a depth of about 10 km the results from this study have widespread implications for the understanding of the regional geological history

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

on the mechanical role of smectite in subduction zones smectites a group of hydrated phyllosilicate minerals are often a main component of sediments entering a subduction zone they are common in hemipelagic sediments and consist of an authigenetic component that arises from the alteration of volcanic ash intercalated in the sediment and a detrital component smectite rich strata are structurally weak retain water and are highly porous a review of sediment lithology in subduction zones around the world suggests that decollement zones may preferentially form in smectite rich horizons one consequence of this observation is that the assignment of high frictional resistance to materials in a decollement may be unwarranted at deeper structural levels smectite is transformed to illite a mechanically stronger mineral estimates of the depth of this transition coincide with the depth at which earthquakes are first detected along plate interfaces i speculate that the smectite illite transition in subduction zones may be an important component of sediment consolidation processes that trigger interplate seismicity

a geochemical characterisation of deep sea floor sediments of the northern lord howe rise abstract this study presents new information on the regional geochemical characteristics of deep sea floor sediments 1300 2423 m water depth on the lord howe rise deep sea plateau and gifford guyot seamount tablemount remote areas off eastern australia the aim was to provide a coherent synthesis for a suite of geochemical data that can be used to make habitat inferences and to develop surrogates of biodiversity sediment characteristics analysed were mineralogy organic carbon and nitrogen concentrations and isotopic compositions and concentrations of major and trace elements we also measured parameters that convey information about the reactivity of organic matter and on the bio availability of bioactive trace elements e g chlorin indices and acid extractable elements surface sediments from the region were calcareous oozes that were carbon lean 0 26 0 1 and had moderate to high chlorin indices 0 62 0 97 with the exception of arsenic inorganic element concentrations were generally low by global standards statistical and geochemical analyses identified two major dimensions of variation in the elemental composition i the degree of mixing between the detrital sediment and carbonate end members and ii the concentrations of bio available bioactive elements the causes of compositional variation are discussed and include i a strong latitudinal gradient in detrital atmospheric dust deposition ii size fractionation and cation exchange of dust components during transit for non carbonates iii water depth controls on carbonate dissolution and iv topographic hydrodynamic focussing of reactive organic matter reactive organic matter indicators were not well correlated with water depth and did not reflect the regional ocean productivity pattern basalt source signatures were not evident in the mineralogy or geochemistry of sediments overlying the seamount or in the vicinity of volcanoes

the paleomagnetism and u th dating of three canadian speleothems evidence for the westward drift 5 4 2 1 ka bp three speleothems from western canada have been analyzed for their paleomagnetism and u th activity ratios these cave deposits do not appear to show the kind of depositional effects on the recorded magnetic signal as is often the case with sediments in addition the signal may be referred directly to geographic coordinates so that virtual geomagnetic pole plots may be constructed this in turn has allowed assessment of any possible bias of the paleofield the u th activity ratios of two flowstones from the crowsnest pass area of british columbia indicated ages greater than the 350 ka dating limit of the dating method one of the samples was reversely magnetized besides their use in the study of the ancient field these samples have useful geomorphic applications a stalagmite from vancouver island was shown to have recorded clockwise loops of the field vector in the period 5 4 2 1 ka bp this implies a mainly westward drift of the paleofield for this period the corresponding vgp s were mostly far sided

role of spherical particles on magnetic field recording in sediments experimental and numerical results abstract we report deposition experiments using spherical glass beads that possess remanent magnetizations stemming from iron impurities 15 g of glass beads with a well characterized size distribution were loaded in two different sets of tubes with diameters of 2 0 and 3 6 cm each tube contains identical column heights of de ionized water thereby allowing us to assess the effect of sediment concentration on the results 352 versus 90 kg m3 g l respectively the tubes were placed in magnetic fields of variable inclination and intensity in a temperature controlled environment the full vector magnetization and sediment accumulation rates were measured upon deposition times ranging from 10 min to 10 days experiments were run in triplicate to evaluate data reproducibility together with the lack of magnetic interaction and the absence of clumping the experiments elucidate an end member scenario of how sediments acquire remanent magnetizations in the absence of flocculation our results show that inclination shallowing in the range of 7 20 for field inclinations of 30 and 60 is indeed possible with solely spherical particles more importantly we observe a field dependence on the inclination error field dependence on the moment acquisition and inclination error both exhibit non linearity which may complicate interpretations of relative paleointensity data in paleomagnetic records a newly developed numerical model whereby particle collision during settling combined with both rolling and slipping translation on the substrate is consistent with the experimental results

magnetic fingerprint of southern portuguese speleothems and implications for paleomagnetism and environmental magnetism environmental magnetism of speleothems is still in its early stage of development here we report on our investigation of the environmental and paleomagnetic information that has been recorded in speleothems and what are the factors that control its preservation and reliability to address these issues we used a multidisciplinary approach including rock magnetism petrography scanning electron microscopy stable carbon and oxygen isotope compositions and major and trace element concentrations we applied this to a set of samples from different stages of speleothem evolution present day dripwater glass plates a weathered stalactite a fresh stalagmite cave sediments and terra rossa soils these samples come from the penico and excentricas caves located in two distinct aquifers of the algarve region south portugal our results show that the main magnetic carriers of the speleothems under study are primary detrital and consist of maghemite and magnetite similarities in coercivity and temperature dependence of the studied set of samples suggest that iron oxides are inherited from the terra rossa soils that cap the cave and were transported to the speleothems by dripwater hence they represent a regional environmental signature interestingly a stable and probably detrital remanent magnetization could be isolated in the fresh stalagmite whereas the weathered stalactite yielded chaotic magnetic directions and very low remanent intensities we propose that these low intensities can be the result from i different remanence acquisition mechanisms between stalagmite and stalactite and or ii iron dissolution by fungal activity we also suggest that magnetic properties and color and the content in detrital elements in the fresh speleothem inform about environmental processes acting on the interface of rock soil atmosphere while oxygen isotope composition and alkaline earth element concentrations inform about calcite water interaction processes these results provide a better understanding of how environmental information is recorded in speleothems and what the factors are that control the reliability of the paleomagnetic and paleo environmental signal

methane and sulfide fluxes in permanent anoxia in situ studies at the dvurechenskii mud volcano sorokin trough black sea the dvurechenskii mud volcano dmv is located in permanently anoxic waters at 2060 m depth sorokin trough black sea the dmv was studied during the rv meteor expedition m72 2 as an example of an active mud volcano system to investigate the significance of submarine mud volcanism for the methane and sulfide budget of the anoxic black sea hydrosphere our studies included benthic fluxes of methane and sulfide as well as the factors controlling transport consumption and production of both compounds within the sediment the pie shaped mud volcano showed temperature anomalies as well as solute and gas fluxes indicating high fluid flow at its summit north of the geographical center the anaerobic oxidation of methane aom coupled to sulfate reduction sr was repressed in this zone due to the upward flow of sulfate depleted fluids through recently deposited subsurface muds apparently limiting microbial methanotrophic activity consequently the emission of dissolved methane into the water column was high with an estimated rate of 0 46 mol m 2 d 1 on the wide plateau and edge of the mud volcano surrounding the summit fluid flow and total methane flux were lower allowing higher sr and aom rates correlated with an increase in sulfate penetration into the sediment here between 50 and 70 of the methane flux 0 07 0 1 mol m 2 d 1 was consumed within the upper 10 cm of the sediment the overall amount of dissolved methane released from the entire mud volcano structure into the water column was significant with a discharge of 1 3 107 mol yr 1 the dmv maintains also high areal rates of methane fueled sulfide production and emission of on average 0 05 mol m 2 d 1 this is a difference to mud volcanoes in oxic waters which emit similar amounts of methane but not sulfide however based on a comparison of this and other mud volcanoes of the black sea we conclude that sulfide and methane emission into the hydrosphere from deep water mud volcanoes does not significantly contribute to the sulfide and methane inventory of the black sea

microbial methane oxidation and sulfate reduction at cold seeps of the deep eastern mediterranean sea abstract the eastern mediterranean hosts a variety of active cold seep systems such as gas chimneys mud volcanoes and pockmarks in water depths of 500 to 3200 m as part of the nautinil expedition in 2003 the sediments of cold seeps on the nile deep sea fan ndsf were sampled for the first time for biogeochemical and microbiological analyses here we compare rates of the anaerobic oxidation of methane aom and sulfate reduction sr as well as the microbial community structure of a variety of cold seep systems including mud volcanoes pockmarks and brine seeps our results revealed strong differences in microbial activity among the different seep systems of the eastern central and western provinces of the ndsf as well as the olimpi field central mediterranean ridge integrated over a sediment depth of 10 cm below the seafloor sr rates ranged from 0 1 66 mmol m 2 d 1 and aom rates from 0 1 3 6 mmol m 2 d 1 sr was often considerably higher than methane oxidation indicating that electron donors other than methane were utilized in general the lowest rates were associated with pockmarks and carbonate pavements and highest rates with bacterial mats above the gassy sediments of mud volcano centers 16s rrna gene analysis and fluorescence in situ hybridization fish revealed the presence of all known groups of marine methane oxidizing archaea i e anme 1 2 3 and also of methane oxidizing bacteria i e methylobacter sp and relatives in some seep sediments presumably syntrophic sulfate reducing bacterial partners of anmes were also detected in association with the anmes several anmes formed consortia with unknown bacterial partners the microbial community structure reflected the presence of typical seep microorganisms at all sites investigated but differed to varying extents between the different types of seeps despite the high availability of methane and sulfate methanotrophic microbial activity and biomass were lower at the seeps of the eastern mediterranean compared to those of other continental margins for unknown reasons

fluid sediment interactions at eastern mediterranean mud volcanoes a stable isotope study from odp leg 160 abstract pore fluids from two odp sites at eastern mediterranean mud volcanoes have been analyzed for their cl concentration and their 18o and d isotopic composition the cl data span a wide range of concentrations from extremely depleted with respect to seawater as low as 60 mm at the crest of milano dome site 970 to strongly enriched up to 5 4 m at napoli dome site 971 chloride enrichment is known to be due to dissolving messinian evaporites whereas the source of the low cl fluid is deduced from stable isotope data presented here the isotopic composition of the endmember fluid is found to be 10 for 18o and 32 for d for low as well as for high cl waters from this signature it can be concluded that neither gas hydrates nor meteoric water play a significant role in the freshening of the pore water several other processes altering the 18o d composition of pore waters are discussed and considered to be of only negligible influence the process characterizing the isotopic composition of the fluid is found to be clay mineral dehydration mainly smectite illite transformation corresponding to a depth range of 3 5 7 km and an elevated temperature of about 120 165 c a quantitative estimate shows that this reaction is capable of producing the observed extreme cl depletion

spatial variation in fluid flow and geochemical fluxes across the sediment seawater interface at the carlos ribeiro mud volcano gulf of cadiz submarine mud volcanism is an important pathway for transfer of deep sourced fluids enriched in hydrocarbons and other elements into the ocean numerous mud volcanoes mvs have been discovered along oceanic plate margins and integrated elemental fluxes are potentially significant for oceanic chemical budgets here we present the first detailed study of the spatial variation in fluid and chemical fluxes at the carlos ribeiro mv in the gulf of cadiz to this end we combine analyses of the chemical composition of pore fluids with a 1 d transport reaction model to quantify fluid fluxes and fluxes of boron lithium and methane across the sediment seawater interface the pore fluids are significantly depleted in chloride but enriched in lithium boron and hydrocarbons relative to seawater pore water profiles of sulphate hydrogen sulphide and total alkalinity indicate that anaerobic oxidation of methane occurs at 34 180 cm depth below seafloor clay mineral dehydration and in particular the transformation of smectite to illite produces pore fluids that are depleted in chloride and potassium profiles of boron lithium and potassium are closely related which suggests that lithium and boron are released from the sediments during this transformation pore fluids are expelled into the water column by advection fluid flow velocities are 4 cm yr 1 at the apex of the mv but they rapidly decrease to 0 4 cm yr 1 at the periphery the associated fluxes of boron lithium and methane vary between 7 301 0 5 6 and 0 806 mmol m 2 yr 1 respectively we demonstrate that fluxes of li and b due to mud volcanism may be important on a global scale however release of methane into the overlying water column is suppressed by microbial methanotrophy

fluid sources and pathways of the costa rica erosional convergent margin 1 the margins community has only relatively recently begun to examine the tectonics and associated hydrologic systems of erosive convergent margins which are substantially different as compared with accretionary margins in this respect the type example erosive margin is the costa rica system which has been the subject of numerous recent large scale investigations here pore fluids expelled at the wedge toe and at midslope mounds and mud volcanoes have been interpreted to have a common deep source of dehydrating clays analogous to that at accretionary margins however we report unusually high b li molar ratios in pore fluids from a recent mudflow on mound 11 offshore costa rica which together with unusually low b li ratios previously reported at the wedge toe reveal that alternative fluid sources and or processes must be operating at the costa rica margin as serpentine formation is the only subduction zone process that significantly fractionates b and li we propose that the difference in fluid chemical composition is the result of erosion of upper plate serpentinites ongoing serpentinization and serpentine mineral phase transitions in the subduction channel these processes provide both a source of fluids and fluid pathways that lead to the unique geochemical signature observed at this erosional margin this conclusion is compatible with and supported by the current view of the tectonics geology and hydrogeology of the costa rica margin and the similarity of the pore fluid to that of two other convergent margins both with known fluid serpentinite interactions

trinidad mud volcanoes where do the expelled fluids come from abstract in order to establish the origin of fluids expelled from mud volcanoes in trinidad we analyzed their major element trace element and isotopic h o sr compositions the mineralogical chemical and sr isotope compositions of associated expelled muds were also determined on the basis of their chemical and sr isotope compositions the fluids were divided into two groups those southwest and northeast of a major right lateral wrench fault the los bajos fault that both controls the chemical quality of the fluids and acts as a drain strontium isotopes were derived via mixing between a radiogenic source 0 71135 and a nonradiogenic source 0 70671 for both southwest and northeast groups however the nonradiogenic source possibly feeding the northeast group showed a lower sr concentration than that of the southwest group h and o isotope data show that the fluids became enriched in 18 o through interaction with wall rocks the fluids were originally oceanic but their properties were subsequently modified by diagenesis as evidenced by chemical data and mixing between fluids issued from two deep seated reservoirs and surface aquifer end members the gas phase expelled with the mud and the fluid through the mud volcanoes is composed mainly of methane with minor carbon dioxide the amount of expelled gas seems the same in samples from both sides of the los bajos fault the almost unique methane content of the gas phase and the large positive 18 o shifts of the reservoir end member as well as b li and ba contents reveal that the fluids from the deep seated reservoirs inherited their chemical compositions at high temperature fluid rock interactions estimates of equilibrium temperatures of the two deep seated reservoirs suggest that to acquire the estimated higher temperature 150 c the mud volcanoes must have been fed partly by a reservoir located at a depth of more than 3 km this depth corresponds to previous geologic information which located the deep seated reservoir in miocene sediments at such a comparable depth the mixing of the original fluids with a less deep seated reservoir and meteoric waters on the ascending path suggests the presence of a recharge mechanism and contributes to the dynamics of the expulsion itself

inverse magnetic fabric in carbonate bearing rocks abstract the observation of a magnetic susceptibility ellipsoid whose maximum axis corresponds to the minimum axis of petrofabric pole of bedding or schistosity is referred to as an inverse magnetic fabric the investigation of the magnetic properties of some ferroan carbonate monocrystals and paramagnetic limestones demonstrates that c axis preferred orientation of paramagnetic carbonates results in a maximum susceptibility parallel to the flattening direction inverse magnetic fabrics due to magnetite are also encountered in weakly deformed limestones a mineralogical model based on the property of single domain grains to have a zero susceptibility parallel to their long axis is proposed however more complex cases are also encountered

origin of gases and water in mud volcanoes of andaman accretionary prism implications for fluid migration in forearcs abstract extensive mud volcanism on the andaman accretionary prism occurs above a complex network of faults and is caused by the convergence of the indian plate and the burmese microplate mud volcanoes of the andaman forearc have received little attention in spite of the fact that they are one of the important features of this tectonic setting located within an ocean basin that has one of the highest sedimentation rates in the world and that the materials emitted by them present a unique opportunity to study the chemistry of the detachable parts of the subducting slab in this study we present mineralogical chemical and isotopic data for argillaceous matter mud matrix gases and water emitted by these mud volcanoes and attempt to understand the variations in terms of their sources and processes within the forearc the mud matrix is composed of smectite illite kaolinite chlorite plagioclase quartz calcite assemblage derived both from sediments and altered oceanic crust and originates from a deep burial diagenetic environment the modes of 13 c distributions for methane 42 ethane 27 and co 2 45 to 135 mm than seawater and its 18 o 0 2 to 2 6 and d 24 to 14 isotopic compositions fall well below the global meteoric water line from their trace element contents and stable isotopic compositions we infer that the mud water is a mixture of sediment pore water ancient seawater and water released from dehydration of clay minerals the 87 sr 86 sr of mud water 0 7071 confirms the above inference and points out that altered oceanic crust plays a significant role in controlling the chemistry of water the formation temperatures of mud ejecta derived from mineralogical smectite illite chemical k na and isotopic d 18 o geothermometers lie in the range of 50 c 120 c which corresponds to a depth zone of 2 to 6 km within the andaman forearc based on all the evidences we conclude that the sampled mud volcano ejecta originate at the plate boundary decollement zone from the sediments and altered oceanic crust of the subducting indian plate

boron isotopic composition of mud volcano fluids implications for fluid migration in shallow subduction zones abstract mud volcanoes are important conduits for deep fluids to migrate upward providing an important window to study fluid sediment interactions at depth in accretionary prisms fluids emitting from mud volcanoes in southern and eastern taiwan were analyzed for dissolved chemical composition and b isotopes to delineate the sources and chemical alteration occurring during fluid migration concentrations of dissolved major elements cl na k ca mg and so4 in most of the mud volcano fluids were lower than seawater concentrations except for the high ca samples in eastern taiwan which were probably affected by fluids igneous rock interactions the high concentrations of b ba and li in the mud volcano fluids are consistent with a scenario that involves intense sediment alteration and clay dehydration at depth the reaction temperatures estimated using chemical thermometers fall within the range of 70 170 c with some variation by location in nearby mud volcano sites the concentration of dissolved major elements varied little but the b stable isotope compositions varied by as much as 20 supporting the argument that dissolved b concentrations were over printed with effects of sediment adsorption this explains the occurrence of b enriched and heavy 11b fluids at moderate depths in subduction zones it is probable that the fluids in mud volcanoes in taiwan originated from 2 to 5 km depth and are influenced by processes involving tectonic shortening sediment alteration and clay dehydration and subsequent retrograde adsorption during fluid migration

organic carbon provenance and maturity in the mud breccia from the napoli mud volcano indicators of origin and burial depth abstract mud volcanism on the mediterranean ridge is caused by extrusion of overpressured sediments with consequent formation of spectacular dome shaped features composed of mud breccias at the seafloor the organic material in the mud breccia of the napoli mud volcano is a mixture of different facies stratigraphic origin and thermal maturities one portion is synsedimentary organic material with only minor diagenetic alterations and represents sedimenting material that was embedded into the mud volcano during its extrusion the mud breccia also contains thermally mature organic material of mainly terrestrial provenance with algae of fresh and brackish water origin vitrinite reflectance data of this maturity generation range from 0 65 to 0 90 roil and thus characterize thermally mature source rocks a rank which is corroborated by fluorescence and molecular characteristics the predominance of vitrinite in the maceral assemblages and the occurrence of biomarkers of terrigenous origin suggest that the major part of the mud matrix derives from a lacustrine or riverine sedimentary unit in the subsurface possibly from the messinian stage a third generation of organic material includes inertinites and vitrinites of high reflectance which represent recycled organic matter present in any marine sediment by use of the lopatin method for modelling the thermal maturation of hydrocarbon source rocks from the vitrinite reflectance data we calculated that the depth of mobilization ranges from 4900 m to 7500 m depending upon the temperature gradient used

the paleomagnetism and u th dating of mexican stalagmite das2 a 72 cm high stalagmite from mexico das2 has been analyzed for its paleomagnetism and has provided a record of secular variation beginning about 1200 years ago to present the stalagmite did not grow uniformly and a low content of magnetic material has rendered the record less precise in some parts a topographic test involving the magnetic measurement of coeval specimens from the sides of the stalagmite has shown that the record is detectably free from depositional errors age data were provided by the u th method and concordancy checked by14c and226ra methods shallow inclinations at the base of the record are followed by a partial anticlockwise loop in the declination inclination plot there is good agreement between the das2 data and the southwest u s a archeomagnetic record and with a lacustrine record from oregon from 750 to 1400 ad comparison of the record with the present field at the site latitude shows that westward drift of the field has persisted for at least 1200 years at a drift rate of about 0 30 yr 1 a close match in declinations with the present field at the site latitude suggests that the stalagmite may have recorded the passing of the northern edge of the gulf of guinea negative anomaly about 1000 years ago though the corresponding inclination feature is not present in the record an archeomagnetic synthesis by merrill and mcelhinny of worldwide data to estimate positions of the main dipole shows that it was tilted away from mexico from 500 to 1250 ad and this may account for the shallow inclinations seen at the start of the record

sulfate reduction using methane in sediments beneath a bathyal cold seep giant clam community off hatsushima island sagami bay japan two sandy sediment cores cores d227 120 and d380 were collected from inside a deep sea giant clam calyptogena soyoae community off hatsushima island western sagami bay central japan 35 59 9 n 139 13 6 e 1160 m deep and a muddy sediment core core d227 202 was obtained from outside the community by the submersibleshinkai 2000 the chloride concentration of the pore waters is constant vertically and sulfate reduction using sedimentary organic matter occurs in core d227 202 21 cm long the chloride concentrations are lower by 7 at the 7 5 9 cm depth in core d227 120 9 cm long and by 3 at the 11 12 cm depth in core d380 16 cm long than those of the overlying bottom waters in the cores from inside of the community sulfate concentration decreases remarkably and dissolved inorganic carbon alkalinity ammonium n and hydrogen sulfide concentrations increase significantly with increasing depth in core d380 34s values of sulfate ions increase from 20 5 to 35 3 and 13c values of dissolved inorganic carbon decrease drastically from 7 0 to 45 with increasing depth from the top to the bottom of the core although the 13c values of the organic carbon of the sediments are 23 7 0 9 in core d380 these results indicate that sulfate reduction using methane is active within the sediments just beneath the living clams and that the hydrogen sulfide produced can be used by endosymbiotic sulfur oxidizing bacteria living in the gills ofc soyoae in the community

recent sapropel formation in the eastern mediterranean during the 1983 expedition of the rv tyro in the eastern mediterranean a combined programme of seismological micropalaeontological and geochemical research was performed the geochemical research focused mainly on the interstitial water and the chemical composition and origin of sapropels for this purpose box cores piston cores and bottom water samples were collected we report here that some of these cores showed clear evidence of long term stagnant bottom water conditions in a small basin south of crete for which we propose the name tyro basin 1 the bottom water is strongly anoxic whereas the sediment down to at least 400 cm is sapropel to sapropelic as salt concentrations in the bottom water are eight times higher than in normal seawater the anoxic conditions in this basin are probably due indirectly to dissolution of salt from a nearby diapir

evaluating the source and seasonality of submarine groundwater discharge using a radon 222 pore water transport model article i nfo pore water radon 222 rn distributions from indian river lagoon florida are characterized by three zones a lower zone where pore water 222 rn and sediment bound radium 226 ra are in equilibrium and concentration gradients are vertical a middle zone where 222 rn is in excess of sediment bound 226 ra and concentration gradients are concave downward and an upper zone where 222 rn concentration gradients are

the origin of magnetic remanence in stalagmites observations from electron microscopy and rock magnetism 1 speleothems especially stalagmites hold great potential as recorders of the earth s ancient magnetic field however our understanding of the magnetic mineral assemblages within speleothems is not well developed we present tandem rock magnetic characterization of bulk samples and electron microscopy of magnetic extracts from five north american stalagmites magnetite and goethite are present in all samples albeit in varying abundances and morphologies magnetite grains are likely detrital showing evidence of transport and weathering including plumose markings and etch pits these grains are unlikely to have precipitated abiotically in the cave environment titanomagnetite and exsolved intergrowths of fe ti oxides indicate that a significant portion of the magnetic mineral assemblage is allochthonous and was transported into the caves these ti rich grains display a range of morphologies from euhedral to well rounded indicating that earlier morphological models for speleothem magnetization do not apply in all geologic settings goethite was observed in three morphologies isolated needles needle aggregates and polycrystalline aggregates of randomly oriented nanoscale grains the magnetite and titanomagnetite as well as their partially oxidized equivalents likely hold a depositional remanent magnetization drm whereas if goethite grains were precipitated in situ on the stalagmite drip surface they are more likely to hold a chemical remanent magnetization crm because of their small size and low saturation magnetization until the remanence of goethite can be shown to be paleomagnetically meaningful we propose that paleomagnetic studies of speleothems include a 150 c thermal demagnetization step to remove any goethite remanence

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

geochemical characterization of two distinctive systems with evidence of chemosynthetic activity explored at the se pacific margin off chile 46 s and 33 s this study presents the geochemical composition of superficial sediment under oxic and suboxic bottom water conditions along the chilean continental margin se pacific where evidence for benthic chemosynthetic activity associated with diffuse seeping of chemically reduced fluids has been reported the exploration was carried out at 1 the chilean triple junction ctj at a water depth of 2900 m with the additional indication of hydrothermal activity near a methane rich cold seep area 46 s german et al 2010 and 2 the el quisco methane seep site eqss at 340 m water depth 33 s melo et al 2007 krylova et al 2014 while the deeper ctj is located within an oxic environment dissolved oxygen in the bottom waters 164 m the shallower eqss lies within a suboxic environment dissolved oxygen in bottom water 23 m located within the lower limit of the se pacific oxygen minimum zone omz pore water from short cores was analyzed for dissolved major minor and trace elements cl na mg k ca sr si b p ba pb mn fe cd u and mo 13dic sulfide sulfate and methane the solid sediment fraction was likewise analyzed for total organic carbon toc metals and redox potential elevated sediment temperatures were found in superficial sediments 5 13 c at the ctj site which could be due to warm fluids associated with the proximity of the ridge where hydrothermal vents may occur reduced fluids were also present here indicated by higher mn fluxes toward the water column even in oxidized sediments rpd 8 cm which contrasted with the lower fluxes in reduced sediments of the eqss site rpd 2 cm 13c depleted dic anomalously low pore water cl 15 ppb and low concentrations of other major elements may be the result of dilution by fluid seeping and precipitation of major elements producing authigenic enrichment ca mg sr the fluid could also a be diluted by pure water produced during methane hydrate dissociation as observed in other cold seep areas and b correspond to clay mineral dehydration as reported in plate subduction systems the reducing conditions established at the ctj conduct the cd enrichment at a similar magnitude of that seen at the shallower suboxic site eqss evidence of chimney or vent fauna was not observed at the eqss higher toc and total sulfide contents were consistent with enhanced deposition of organic matter and reducing conditions developed in the omz favoring the authigenic enrichment of cd u and pb the geochemical evidence based only on methane concentrations and 13dic is insufficient to establish the presence of methane seeps as previously reported

the geochemistry and origin of the hydrothermal water erupted at lusi indonesia abstract the spectacular lusi mud eruption started in northeast java the 29th of may 2006 despite extensive research the origin of the erupted water remains elusive and poorly constrained here we present a comprehensive study of the geochemistry of lusi waters compared with those collected from surrounding areas all collected between 2006 and 2013 including data from mud volcanoes and volcano hosted hydrothermal springs within this broad context the geochemical characteristics of the fluids expelled in the lusi region suggest that we can classify the waters in three groups 1 meteoric waters expelled in cold springs and artesian wells 2 hydrothermal waters typically mixed with meteoric waters and 3 formation water from marine sediments altered by diagenetic processes such as clay mineral dehydration samples collected from the lusi crater are cl and na dominated up to 527 mm and 471 7 mm respectively similar to seawater indicating that altered sedimentary formation waters are predominant in this system in addition they are enriched in sr up to 808 4 m and other elements commonly associated with hydrothermal systems such as li up to 877 6 m compared to 26 m in seawater some of these elements are up to ten times enriched compared to seawater values high temperature fluid mineral interactions in the subsurface appear to have facilitated the transfer of li and other mobile elements into the fluids high temperature fluid mineral interaction reactions are also supported by si concentrations significantly higher compared to other sampled mud volcanoes in the island crater samples also show the highest 18o values 5 after correction for evaporation compared to 1 at the mv localities 87sr 86sr ratios vary between of 0 7077 and 0 7083 and seem to reflect a general mixture of fluids from clay mineral dehydration carbonate recrystallization alteration of volcanic rocks and hydrothermal imprint eight years of geochemical monitoring indicate that the composition of the deep sourced lusi fluids remain fairly constant through time thus our findings show that the lusi crater waters represent a regional geochemical anomaly and we suggest that a combination of high temperatures in the source region and fluid rock interactions with silicates and possibly carbonate rich lithologies can explain the data this is consistent with a model where the emitted gases migrate from a deep seated 4 km source region likely associated with the presence of hot igneous intrusions and or high t reactions related to the presence of neighbouring active volcanoes

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

pore water geochemistry of eastern mediterranean mud volcanoes implications for fluid transport and fluid origin abstract the pore water chemistry of mud volcanoes from the olimpi mud volcano field and the anaximander mountains in the eastern mediterranean sea have been studied for three major purposes 1 modes and velocities of fluid transport were derived to assess the role of upward advection and bioirrigation for benthic fluxes 2 differences in the fluid chemistry at sites of milano mud volcano olimpi area were compiled in a map to illustrate the spatial heterogeneity reflecting differences in fluid origin and transport in discrete conduits in near proximity 3 formation water temperatures of seeping fluids were calculated from theoretical geothermometers to predict the depth of fluid origin and geochemical reactions in the deeper subsurface no indications for downward advection as required for convection cells have been found instead measured pore water profiles have been simulated successfully by accounting for upward advection and bioirrigation advective flow velocities are found to be generally moderate 3 50 cm y 1 compared to other cold seep areas depth integrated rates of bioirrigation are 1 2 orders of magnitude higher than advective flow velocities documenting the importance of bioirrigation for flux considerations in surface sediments calculated formation water temperatures from the anaximander mountains are in the range of 80 to 145 c suggesting a fluid origin from a depth zone associated with the seismic decollement it is proposed that at that depth clay mineral dehydration leads to the formation and advection of fluids reduced in salinity relative to sea water this explains the ubiquitous pore water freshening observed in surface sediments of the anaximander mountain area multiple fluid sources and formation water temperatures of 55 to 80 c were derived for expelled fluids of the olimpi area

recent deep sourced methane mud discharge at the most active mud volcano in the western mediterranean abstract active mud volcanism in the west alboran basin wab is closely associated with tectonically mobilized overpressurized shales and shale diapirism this appears to control mud expulsion at carmen mud volcano a cone shaped structure 65 m high and 1 km in basal diameter the presence of gas rich mud breccia living chemosynthetic fauna the absence of hemipelagic draping and the abrupt transition that occurs between high dissolved sulfate in the uppermost interval and low sulfate together with high methane concentrations in the lowermost sediment interval all point to a recent expulsion of mud breccia at the summit of carmen mv for the lowermost interval the depletion of major elements i e ca2 and mg2 and the enrichment of trace species i e li and b in the pore water all indicate a deep fluid source the 18opw 5 7 vsmow and dpw 10 vsmow of pore water in the lowermost interval correspond with smectite dehydration as the main pore water freshening mechanism water formation temperatures calculated with empirical geo thermometers k na k mg 18opw dpw and dissolved b reveal that fluids were generated at temperatures of 140 20 c taking a regional geothermal gradient for the wab of 25 27 c km this points to a fluid source from 5 1 km sediment depth this is not only consistent with the depth of overpressurized shales and megabreccia of lower to middle miocene age but it also fits nicely with the upper middle miocene seawater value for the porewater 87sr 86sr derived from dissolving carbonates the stable carbon and hydrogen isotopic composition of methane 13cmethane 59 4 vpdb and dmethane 184 vsmow for the deepest samples of summit core gp05pc is consistent with the mentioned deep origin mud breccia expulsion of overpressurized deep sedimentary units would be accompanied by rigorous degassing leading to rapid instantaneous replacement of pore fluid by bottom water in the upper sediments the absence of oxidized sediment draping the seawater like pore water composition in the uppermost part of the mud breccia interval and the abrupt methane to sulfate transition all provide evidence for a very recent mud expulsion the distinctively kink shaped pore water cl profile in core gp05pc has been used in a numerical transport reaction model to derive the timing for this event this eruptive event appears to have taken place very recently namely 12 5 yrs prior to the 2012 coring thus in the year 2000 ce

the mediterranean ridge and related mud diapirism a background abstract the mediterranean ridge stretching from the calabrian rise to the florence rise is the largest structural unit of the eastern mediterranean sea it is directly related to ongoing convergence and collision of the african and eurasian plates starting in the oligocene and is considered to be a giant accretionary complex consisting of intensively folded and faulted rocks of the african margin since its origin in the late miocene the ridge continued to grow up and outward experiencing more deformation because of the developing collision the mud diapirism and mud volcanism are usual and wide spread phenomena for the mediterranean ridge that developed as a result of an intensive tectonic overburden due to stacking of rock units by thrusting and strong lateral compressional stress pressing up and squeezing plastic sedimentary series out onto the seafloor

lithium isotope geochemistry of marine pore waters insights from cold seep fluids lithium concentration and isotope data 7li are reported for pore fluids from 18 cold seep locations together with reference fluids from shallow marine environments a sediment hosted hydrothermal system and two mediterranean brine basins the new reference data and literature data of hydrothermal fluids and pore fluids from the ocean drilling program follow an empirical relationship between li concentration and 7li 7li 6 0 0 3 ln li 51 1 2 reflecting li release from sediment or rocks and or uptake of li during mineral authigenesis cold seep fluids display 7li values between 7 5 and 45 7 mostly in agreement with this general relationship ubiquitous diagenetic signals of clay dehydration in all cold seep fluids indicate that authigenic smectite illite is the major sink for light pore water li in deeply buried continental margin sediments deviations from the general relationship are attributed to the varying provenance and composition of sediments or to transport related fractionation trends pore fluids on passive margins receive disproportionally high amounts of li from intensely weathered and transported terrigenous matter by contrast on convergent margins and in other settings with strong volcanogenic input li concentrations in pore water are lower because of intense li uptake by alteration minerals and most notably adsorption of li onto smectite the latter process is not accompanied by isotope fractionation as revealed from a separate study on shallow sediments a numerical transport reaction model was applied to simulate li isotope fractionation during upwelling of pore fluids it is demonstrated that slow pore water advection order of mm a 1 suffices to convey much of the deep seated diagenetic li signal into shallow sediments if carefully applied li isotope systematics may thus provide a valuable record of fluid mineral interaction that has been inherited several hundreds or thousands of meters below the actual seafloor fluid escape structure

isotopic evidence 87sr 86sr δ7li for alteration of the oceanic crust at deep rooted mud volcanoes in the gulf of cadiz ne atlantic ocean the chemical and isotopic composition of pore fluids is presented for five deep rooted mud volcanoes aligned on a transect across the gulf of cadiz continental margin at water depths between 350 and 3860 m generally decreasing interstitial li concentrations and sr 87 sr 86 ratios with increasing distance from shore are attributed to systematically changing fluid sources across the continental margin although highest li concentrations at the near shore mud volcanoes coincide with high salinities derived from dissolution of halite and late stage evaporites clayey terrigenous sediments are identified as the ultimate li source to all pore fluids investigated light delta li 7 values partly close to those of hydrothermal vent fluids delta li 7 11 9 parts per thousand indicate that li has been mobilized during high temperature fluid sediment or fluid rock interactions in the deep sub surface intense leaching of terrigenous clay has led to radiogenic sr 87 sr 86 ratios similar to 0 7106 in pore fluids of the near shore mud volcanoes in contrast non radiogenic sr 87 sr 86 ratios similar to 0 7075 at the distal locations are attributed to admixing of a basement derived fluid component carrying an isotopic signature from interaction with the basaltic crust this inference is substantiated by temperature constraints from li isotope equilibrium calculations suggesting exchange processes at particularly high temperatures 200 degrees c for the least radiogenic pore fluids of the most distal location advective pore fluids in the off shore reaches of the gulf of cadiz are influenced by successive exchange processes with both oceanic crust and terrigenous fine grained sediments resulting in a chemical and isotopic signature similar to that of fluids in near shore ridge flank hydrothermal systems this suggests that deep rooted mud volcanoes in the gulf of cadiz represent a fluid pathway intermediate between mid ocean ridge hydrothermal vent and shallow marginal cold seep due to the thicker sediment coverage and slower fluid advection rates the overall geochemical signature is shifted towards the sediment diagenetic signal compared to ridge flank hydrothermal environments c 2009 elsevier ltd all rights reserved

secular variation from mexican stalagmites their potential and problems abstract as part of a feasibility study to see whether stalagmites could provide useful records of secular variation nine oriented stalagmites were collected from the states of chiapas and san luis potosi mexico of these six have yielded measurable natural remanent magnetizations nrms throughout their length the cleaned magnetizations of one of these samples were shown unequivocally to have recorded the ambient field and there is no reason to believe that this is not true of the primary magnetizations of other samples the sequences of palaeofield directions up the samples length have varying degrees of resolution and serial correlation depending on the rate of field change as averaged by the stalagmite growth rate and the thickness of the measured specimens ages and growth rates were estimated by the u th method the main problem in stalagmite palaeomagnetic analysis is a weak nrm although this may be avoided by judicious choice of the sample samples which possess significant viscous components may be cleaned by alternating field or thermally if there is sufficient magnetic material unlike many sediments stalagmites do not appear to suffer from depositional error problems dating problems may include low initial u content yielding ages with large errors and the presence of allogenic 230 th in detritus which causes older apparent ages the dating limit is 350 ka it is usually not possible to obtain long records comparable with those of most lake sediments and there are aesthetic reasons for not spoiling caves adorned with stalagmites the method is seen to be complementary to the use of sedimentary sequences to study palaeosecular variation studies of the rock magnetism of stalagmites are presented to suggest the mineral carriers of the magnetization and the origins of the natural remanence

magnetic anisotropy in the trenton limestone results of a new technique anisotropy of anhysteretic susceptibility a new method for determining magnetic anisotropy using anhysteric remanence susceptibility is described the magnetic fabric of a collection of trenton limestone specimens has been determined using this method as well as by conventional anisotropy of magnetic susceptibility the results demonstrate the usefulness of the new method for finding the magnetic fabric of rock units such as the trenton in which the bulk magnetic susceptibilities are low a model is proposed to explain the observed foliated and lineated fabric as a consequence of overburden compaction and regional horizontal stresses the original fabric is inferred to have been isotropic the anisotropy resides in secondary magnetite of late paleozoic age it is argued that the observed magnetic fabric must therefore be alleghenian or younger in age our method has the potential to determine paleostress directions in carbonates elsewhere provided our assumptions are correct

neotectonic evolution of the anaximander mountains at the junction of the hellenic and cyprus arcs abstract the anaximander mountains occupying an outer arc position at the junction of the hellenic and cyprus arcs have been studied using a suite of geophysical data including multibeam swath bathymetry backscatter images seismic reflection profiles and gravity and magnetic data which support an improved description of its deformation history lithologically the western mountains can be correlated with the neritic limestones of the bey daglar unit of sw turkey the eastern mountains relate to the ophiolitic antalya nappe complex in addition to this lithological contrast a deep seated crustal difference which is best reflected in gravimetry relates to the mid tortonian aksu thrust phase after the early middle miocene eastward emplacement of the lycian nappes the serravallian tortonian stage was characterized by the development of an array of grabens with n120 e strikes which occupied a vast continental area that extended from southern aegean to southwestern turkey during the mid tortonian the last phase of thrusting marked the onset of a different kinematic regime related to the westward rotation of the anatolian platelet this late miocene change marked the start of differential subsidence that resulted in the formation of the anaximander mountains and which is reflected by an unconformity surface between the lower middle miocene and plio quaternary units the messinian quaternary period in the western part of the anaximander mountains was characterized by distributed sinistral shear parallel to n70 e which was marked by the onset of an extension on n20 e striking normal faults that formed long graben like depressions during the pliocene these basins were transected by n70 e striking sinistral strike slip fault zones although continued crustal extension suggests deformation in transtension the eastern part of the anaximander mountains is instead characterized by n150 e striking normal and or oblique normal fault zones which lack significant evidence of strike slip deformation close examination of newly calculated predicted relative plate motions between africa from nuvel 1a and anatolia from gps measurements indicates that plate motion vectors change rapidly at the junction between the hellenic and cyprus arcs because of the close proximity to the pole of anatolian rotation these calculations indicate that along both the eastern hellenic arc and the western cyprus arcs the florence rise the relative motion between the anatolian and african plates is sinistral on the southern florence rise deformation is characterized by pure left lateral faulting whereas farther northwest in the eastern anaximander mountains the component of strike slip decreases although arc normal convergence predicts the occurrence of thrust faulting southwestward trench retreat also causes an extension internal to this outer arc domain such that the preexisting n120 e striking thrust faults of the aksu phase have been reactivated as normal to oblique normal faults during the pliocene and quaternary the observed sinistral faulting on faults striking n70 e in the western mountains is consistent with the relative plate motion along the eastern hellenic arc and merges with the extensional domain in the eastern mountains

chemical and isotopic evidence for sources of fluids in a mud volcano field seaward of the barbados accretionary wedge chemical isotopic and heat budgets are controlled by fluid flow and venting at convergent margins fluids vent from accretionary complex sediments via numerous pathways including mud volcanoes which are common at the barbados convergent margin chemical and isotopic compositions of fluids collected from four mud volcanoes located east of the barbados deformation front at 13 50 n indicate venting is sufficiently rapid to prevent diffusion from seawater in sediments surrounding the mud volcanoes the rate of nonfocused fluid flow is 0 26 cm yr although this rate is 3 orders of magnitude slower than the flow from the mud volcanoes significantly more fluid vents from the sediments surrounding the mud volcanoes than from the restricted areas of rapid flow from the volcanoes chloride concentrations are depleted to a minimum of 211 mm 45 of seawater value primarily by mixing diagenetically altered pore fluids with an 18o enriched fresh water released from the dissociation of methane hydrate this reaction is accompanied by the release of sufficient methane to form a free gas phase and initiate eruption of the mud volcanoes the geochemical compositions of the diagenetically altered pore fluids reflect the interplay between five major reactions 1 clay mineral dehydration which releases h2o and influences a range of chemical and isotopic compositions 2 organic matter regeneration which increases alkalinity nh4 and br and decreases so42 concentrations 3 cation exchange with clay minerals which increases na and decreases nh4 concentrations 4 carbonate recrystallization and precipitation which decrease ca2 but increase sr2 concentrations and 5 conversion of volcanic ash to clay minerals which utilizes h2o and decreases mg2 concentrations the geochemistry of the pore fluids suggests that these reactions occurred at temperatures ranging from 75 to 115 c thus at the regional geothermal gradients of 27 to 40 c km these temperatures indicate that the source regions are at 2 to 4 5 km depth

a geomagnetic field model for the holocene based on archaeomagnetic and lava flow data abstract we propose a new geomagnetic field model for the holocene period based on archaeomagnetic and lava flow data avoiding the use of lake sediment data the source of data comes from the geomagia50v2 database which has been updated with the new archaeomagnetic and volcanic studies published during the last 3 yr the model called sha dif 14k allows us to analyse the behaviour of the geomagnetic field for the last 14 000 yr from 12 000 bc to 1900 ad for the model construction we use the spherical harmonic analysis in space and the penalized cubic b splines in time both spatial and temporal regularization norms are used to constrain the inversion problem and applied at the core mantle boundary cmb to assure the convergence of the model for the last 3 ka the model predictions agree with those given by the global model arch3k 1 and the european model scha dif 3k for older epochs the new model presents a clear improvement in field resolution with respect to other current models of the geomagnetic field for the holocene for the last 9 ka the time evolution of the dipolar moment obtained from the dipole field shows a clear minimum between 5500 bc and 3000 bc and the well known continuous decreasing trend of the geomagnetic field strength for the last millennium and a half a general view of the time average evolution of the geomagnetic field flux lobes at the cmb for the northern hemisphere suggests a marked lobe of positive magnetic flux when the dipole moment was maximum this lobe vanishes when the dipolar field is decreasing the north polar wander paths of both north magnetic dip and geomagnetic poles were obtained showing an average rate of motion of 5 1 km yr and 3 7 km yr respectively the model shows that the geomagnetic field can be averaged as axial dipolar in 2000 yr within an error of 5 the typical uncertainty of the palaeomagnetic studies finally and following the recent definition of archaeomagnetic jerks we found 8 critical events in the time evolution of the geomagnetic field for the last 8 ka characterized by a maximum in the hemispheric asymmetry of the proposed model the model is available in the earth ref digital archive at http earthref org erda 1897

sources of mud volcano fluids in the gulf of cadiz indications for hydrothermal imprint mud volcanism in the gulf of cadiz occurs over a large area extending from the shelf to more than 3500 m water depth and is triggered by compressional stress along the european african plate boundary affecting a deeply faulted sedimentary sequence of locally more than 5 km thickness the investigation of six active sites shows that mud volcano mv fluids on average are highly enriched in ch4 li b and sr and depleted in mg k and br the purity of the fluids is largely controlled by the intensity of upward directed flow flow rates could be constrained by numerical modelling and vary between 0 05 and 15 cm yr 1 application of d 18o systematics identifies clay mineral dehydration most likely within mesozoic and tertiary shales and marls as the major source of fluids hence cl and na in the pore fluids are mostly depleted below seawater values following a general trend of dilution however deviations from this trend occur and are likely caused by the dissolution of halite in evaporitic deposits other secondary processes overprinting the original fluid composition may occur along the flow path such as dissolution of anhydrite or gypsum and or the formation of calcite and dolomite different sources of fluids are also indicated by variations in 87sr 86sr which range from 0 7086 to 0 7099 at the different sites dehydration may be induced primarily by overburden and tectonic compression however very high concentrations of li and b specifically at captain arutyunov mv camv indicate additional leaching at temperatures above 150 c which could be explained by the injection of hot fluids along deep penetrating major e w strike slip fault systems this hypothesis is supported by the occurrence of generally thermogenic but significantly ch4 enriched light volatile hydrocarbon gases at camv which cannot be explained by shallow microbial methanogenesis li and li b ratios from different types of hot and cold vents are used to infer that high temperature signals seem to be preserved at various cold vent locations and indicate a closer coupling of both systems in continental margin environments than outlined in previous studies

detrital remanence inclination errors and anhysteretic remanence anisotropy quantitative model and experimental results summary we suggest that inclination errors in detrital remanent magnetization drm may be recognized and corrected by measurement of the anisotropy of anhysteretic remanent magnetization arm arm anisotropy reflects directional variations in the remanence capacity of relatively fine grained magnetic particles in rocks or sediments generally the same particles that carry the stable component of drm relative vertical and horizontal drm magnitudes are controlled by this directional remanence capacity as well as by the alignment efficiency of the particle magnetic moments which in turn is governed by the relative intensities of the vertical and horizontal components of the ambient magnetic field thus the respective vertical and horizontal components of palaeointensity and therefore palaeofield inclination may be obtained by normalizing the measured drm components by parallel arm intensities synthetic sediments containing silica kaolin and sized magnetite powders have previously been found to acquire experimental drm with an inclination error that is a direct function of kaolin concentration further experiments have now shown that arm anisotropy in the synthetic sediments is also a direct function of kaolin content and thus a correlation exists between drm inclination errors and arm anisotropy multiplying the measured drm vector by the inverse of the arm anisotropy matrix yields an improved estimate of the actual laboratory depositional field in all cases for samples with acicular 0 5 m magnetite this procedure reduces a mean inclination error of over 5 to less than 0 5 samples with subequant magnetite of slightly larger grain size 0 75 m exhibit similar arm anisotropy 10 per cent but somewhat larger inclination errors 10 we interpret this in terms of stronger horizontal alignment but weaker particle anisotropies for the larger more equant magnetites

early diagenesis in the sediments of the congo deep sea fan dominated by massive terrigenous deposits part iii sulfate and methane based microbial processes abstract geochemical profiles so 4 2 h 2 s ch 4 13 ch 4 and phylogenetic diversity of archaea and bacteria from two oceanographic cruises dedicated to the lobes sediments of the congo deep sea fan are presented in this paper in this area organic rich turbidites reach 5000 m and allow the establishment of patchy cold seep like habitats including microbial mats reduced sediments and vesicomyid bivalves assemblages these bivalves live in endosymbiosis with sulfur oxidizing bacteria and use sulfides to perform chemosynthesis in these habitats unlike classical abyssal sediments anoxic processes are dominant total oxygen uptake fluxes and methane fluxes measured with benthic chambers are in the same range as those of active cold seep environments and oxygen is mainly used for reoxidation of reduced compounds especially in bacterial mats and reduced sediments high concentrations of methane and sulfate co exist in the upper 20 cm of sediments and evidence indicates that sulfate reducing microorganisms and methanogens co occur in the shallow layers of these sediments simultaneously anaerobic oxidation of methane aom with sulfate as the electron acceptor is evidenced by the presence of anmes anaerobic methanotroph dissolved sulfide produced through the reduction of sulfate is reoxidized through several pathways depending on the habitat these pathways include vesicomyid bivalves uptake adults or juveniles in the bacterial mats habitats reoxidation by oxygen or iron phases within the reduced sediment or reoxidation by microbial mats sulfide uptake rates by vesicomyids measured in sulfide rich sea water 90 18 mmol s m 2 d 1 were similar to sulfide production rates obtained by modelling the sulfate profile with different bioirrigation constants highlighting the major control of vesicomyids on sulfur cycle in their habitats

stable carbon isotope behaviour of natural seepage of deep underground 13c rich methane detected along a fault zone and adsorbed in mudstone tokyo bay area japan abstract gas was sampled regionally including by drilling into faults in the south kanto gas field around tokyo bay japan gas samples were collected from cores in a gas sampling container immediately after drilling a value of 13c1 44 3 was obtained for gas in the container and 13c1 36 3 for seeping gas in a fault zone however typical ch4 in this dissolved in water gas field is mainly depleted in 13c and 13c1 values range from 66 to 68 owing to microbial degradation of organic material 13c rich ch4 is so far uncommon in the south kanto gas field seepages were observed from the surface along the north south fault zone the natural gas is stored below the sandstone layer by impermeable mudstone underlying the boundary at a depth of 30 m gas seepages were not observed below a depth of 40 m gas rises along the fault zone dissolved in groundwater up to the shallow region and then separates from the groundwater 13c rich ch4 adsorbed ch4 was found to have desorbed from drilled mudstone core samples taken at depths of 1400 1900 m in the main gas production strata similarly 13c rich ch4 was found in black shale overlying the oceanic crust forming part of a sedimentary accretionary prism underling the tokyo region it also appears in the spring water of spa wells originating at a depth of 1200 1500 m along a tectonic line methane generated by microbial degradation of organic material through co2 reduction in the south kanto gas field mainly originates as biogenic gas mixed with a small amount of 13c rich ch4 derived from thermogenic gas without oil components in strata it is assumed that 12c rich ch4 is easily detached from core or pore water through gas production whereas 13c rich ch4 is strongly adsorbed on the surfaces of particles the 13c rich ch4 rises along the major tectonic line or up the 50 m wide normal fault zone from relatively deep sources in the kanto region

shipboard routine and pressure filtration system for pore water extraction from suboxic sediments abstract a shipboard working procedure for the handling and porewater extraction of suboxic sediments is outlined in addition a detailed description is given of the shipboard pressure filtration system that has been used to extract porewater this procedure in combination with the pressure filtration system has been demonstrated to produce reliable porewater from suboxic sediments

boron isotope and geochemical evidence for the origin of urania and bannock brines at the eastern mediterranean effect of water rock interactions the origin of hypersaline brines from urania and bannock deep anoxic basins in the eastern mediterranean sea has been investigated by integrating geochemical data and boron isotopic ratios bottom brines from urania basin have chloride contents up to 4200 mmole kg h2o and a marine na cl ratio 0 87 all the other ionic ratios are different from the marine ratios and show a relative enrichment in ca k br and b and depletion in mg and so4 as normalized to the chloride ion the 11b values of the urania brines 11b 29 8 2 9 n 7 are lower than that of mediterranean seawater 39 the concentrations of cl and na which make up 95 of the total dissolved ions in molal units suggest that the urania brines were derived from eightfold evaporated seawater the relative enrichment of ca and depletion of mg and so4 reflect dolomitization gypsum precipitation and sulfate reduction processes which modified the original evaporated seawater while the brines were entrapped as interstitial waters in the sedimentary section of the mediterranean the relative enrichments of br b and k and the low 11b value of the urania brines suggest high temperatures interactions of the evaporated sea water with sediments mass balance calculations suggest that desorption of exchangeable b from the sediments 11b 20 modified the marine b isotopic composition of the original eightfold evaporated seawater potassium was also leached from clay minerals whereas br was contributed from degradation of organic matter in the sediments this is consistent with a thermal anomaly up to 45 c recorded at depth in the region of urania basin in contrast bottom brines and shallow interstitial fluids from bannock basin with low temperatures 15 c show marine 11b 11b 39 6 2 8 n 5 38 5 2 2 n 5 respectively and b cl ratios 7 10 4 the b isotope data confirm that the bannock brines were derived from twelvefold evaporated seawater we argue that the brines from both basins are relics of fossil evaporated seawater that was entrapped in late miocene sediments and accumulated in the deep basins of the mediterranean seafloor

in situ sediment temperature measurements and geochemical porewater data suggest highly dynamic fluid flow at isis mud volcano eastern mediterranean sea isis mud volcano is located on the upper slope of the nile deep sea fan and has been described as the surface expression of a deep seated gas chimney loncke l gaullier v mascle j vendeville b 2002 shallow structure of the nile deep sea fan interactions between structural heritage and salt tectonics consequences on sedimentary dispersal in ciesm ed turbidite systems and deep sea fans of the mediterranean and the black seas ciesm workshop series vol 17 monaco detailed geothermal and geochemical investigations of isis mv have been carried out during the nautinil 2003 and mimes 2004 cruises within the framework of the euro margins mediflux project sediment temperatures of more than 40 c at 10 m below the seafloor at the center of the mud volcano indicate an exceptionally high level of activity rapidly decreasing temperature gradients away from the center support the hypothesis of a dominantly axisymmetric functioning of isis mv the microbathymetry along dive tracks of the submersible nautile reveals the presence of terraces and shows that the temperature gradients at shallow sediment depth follow the morphology at the center porewater profiles are characterized by a rapid decrease of chlorinity within the uppermost meter of the sediments whereas the chlorinity of cores taken at short distances away is equal to bottom water values applying simple analytical models to the data provides evidence of recent mud volcano activity but no straightforward explanation of the observed anomalies which points to a transient regime of variable fluid flow possibly accompanied by episodic mud eruptions numerical modeling suggests that rapid cooling of the sediment column and downward progression of the sharp decrease in porewater chlorinity observed between the two cruises is related to episodic infiltration of bottom seawater into the mud

interpretation of temperature measurements from the kaiko nankai cruise modeling of fluid flow in clam colonies during the kaiko nankai detailed submersible survey numerous measurements of the temperature gradient inside the sediment were performed on the deepest active zone of fluid venting which is situated on the anticline related to the frontal thrust using the ifremer t naut temperature probe operated from the submersiblenautile we thus obtained the temperature structure below different types of clam colonies associated with fluid venting we used the finite element method to model the thermal structure and fluid flow pattern of these vents and to determine the velocity of upward fluid flow through the colonies on a biological basis four types of clam colonies are defined each biological type has distinctive thermal characteristics and corresponds to a particular fluid flow pattern darcian flow velocity in the most active type of colony type a is of the order of 100 m a the total amount of fluid flowing through colonies in the studied area is estimated to be 200 m3 a 1 per metre width of subduction zone most of the flow is vented through type a colonies this value is more than one order of magnitude too high to be compatible with the amount of water available from steady state compaction of sediments in the whole wedge thermal arguments suggest that downwelling of seawater occurs around type a colonies and that seawater is then mixed with upcoming fluids at a depth of 1 or 2 metres furthermore finite element modeling shows that a salinity difference of a few parts per mil between the upcoming fluids and seawater is sufficient to drive convection around the colonies as water samples from a few vents indicate that the fluid source should actually be significantly less saline than seawater we propose that the very high fluid flows measured are a consequence of the dilution of the fluid of deep origin with seawater by a factor of 5 to 10

palaeomagnetism of stalagmites speleothems in sw japan summary a palaeomagnetic study has been carried out on three stalagmites from two limestone caves in sw japan remanent magnetizations of the stalagmite samples are weak but stable enough to record the geomagnetic field the results indicate an internal consistency between several time equivalent samples drilled from the same stalagmite a tentative correlation is suggested between palaeomagnetic data from two stalagmites collected from the same cave and data from two different limestone caves combined curves of declination and inclination variations are constructed on the basis of this tentative correlation between the alternatingfield cleaned results from the three stalagmites these variation curves can also be tentatively correlated with those deduced from archaeomagnetic studies in sw japan in consequence the curves are believed to represent records of past geomagnetic secular variation the tentative age of the oldest end of this secular variation curve can be estimated at about 15 ooo yr bp based on the correlation with the archaeomagnetic results a possible long period of westerly declination and steep inclination is recognized in the older part of the variation

modeling of subsurface calcite dissolution including the respiration and reoxidation processes of marine sediments in the region of equatorial upwelling off gabon abstract mineralization of organic matter and the subsequent dissolution of calcite were simulated for surface sediments of the upper continental slope off gabon by using microsensors to measure o2 ph pco2 and ca2 in situ pore water concentration profiles of no3 nh4 fe2 and mn2 and so42 ex situ as well as sulfate reduction rates derived from incubation experiments the transport and reaction model cotrem was used to simulate the degradation of organic matter by o2 no3 fe oh 3 and so42 reoxidation reactions involving fe2 and mn2 and precipitation of fes model application revealed an overall rate of organic matter mineralization amounting to 50 mol c cm 2 yr 1 of which 77 were due to o2 17 to no3 and 3 to fe oh 3 and 3 to so42 the best fit for the ph profile was achieved by adapting three different dissolution rate constants of calcite ranging between 0 01 and 0 5 d 1 and accounting for different calcite phases in the sediment a reaction order of 4 5 was assumed in the kinetic rate law a caco3 flux to the sediment was estimated to occur at a rate of 42 g m 2 yr 1 in the area of equatorial upwelling the model predicts a redissolution flux of calcite amounting to 36 g m 2 yr 1 thus indicating that 90 of the calcite flux to the sediment is redissolved

long term changes in precipitation recorded by magnetic minerals in speleothems speleothems are important paleoclimate archives researchers typically compile measurements of stable isotopic ratios dated using high precision u th radiometric techniques to reconstruct regional and global climate magnetic material incorporated within speleothems can provide an independent means of connecting large scale climatic changes with their impact on more localized processes in soils overlying cave systems under certain environmental conditions pedogenic processes can produce magnetite nanoparticles enhancement of pedogenic magnetite in soil profiles depends strongly on local precipitation pedogenic magnetite can be subsequently transferred via drip waters into underlying cave systems and incorporated into speleothems as they grow here we employ high resolution magnetic methods to analyze a well dated stalagmite from buckeye creek cave west virginia usa and find that changes in magnetite concentration follow both changes in stable isotopes measured in the same stalagmite and global climate proxies we interpret the changes in magnetite concentration as reflecting variations in local pedogenic processes controlled by changes in regional precipitation this record demonstrates how magnetic measurements on speleothems can constrain interpretations of speleothem climate proxies

magnetic fabric of stalagmites and its formation mechanism 1 speleothems have been regarded as ideal archives for recording variations of the earth s magnetic field because they crystallize rapidly and are seldom modified by post depositional processes and because they can be precisely dated magnetic fabric research on speleothems has potential to reveal details of their interior structure and the distribution of ferrimagnetic minerals which would benefit investigations of geomagnetic field behavior two stalagmites hs4 and wd1 from caves in the middle reaches of the yangtze river were collected for magnetic fabric study the anisotropy of magnetic susceptibility ams of the stalagmites is mainly controlled by calcite crystals and the directions of the minimum axes of ams ellipsoids indicate that their crystallographic orientations are roughly perpendicular to the growth laminae anisotropy of the isothermal remanent magnetization airm indicates that the distributions of ferrimagnetic minerals in the stalagmites are not correlated with stalagmite growth laminae mean directions of the maximum principal axes of airm r1 axes for wd1 are close to that of the natural remanent magnetization which suggests that the orientation of ferrimagnetic minerals in this stalagmite are likely to have been controlled by the geomagnetic field

quantifying fluid flow solute mixing and biogeochemical turnover at cold vents of the eastern aleutian subduction zone in situ oxygen fluxes were measured at vent sites in the aleutian trench at a water depth of almost 5000 m using a tv guided benthic flux chamber the flux was 2 orders of magnitude greater than benthic oxygen fluxes in areas unaffected by venting on the continental margin off alaska porewater profiles taken from the surface sediment below a vent site showed high concentrations of sulfide methane and ammonia the reduced carbon and nitrogen compounds are transported to the vent site by fluids expelled from deeper anoxic sediment layers by the forces of plate convergence the tectonically driven fluid flow was determined from the biochemical turnover in vent communities and was found to be 3 4 0 5 m yr 1 a model was used to quantify the transport of silica ca2 and sulfate via diffusion advection and bioirrigation through the surface sediments of a vent site a nonlocal mixing coefficient of 20 30 yr 1 was determined by fitting the model curves to the measured porewater profiles showing that the transport of solutes within the near surface sediments and across the sediment water interface is dominated by the activity of the vent fauna sulfate containing oceanic bottom water and methane rich vent fluids were mixed below the clam colony to produce sulfide and a caco3 precipitate the vent biota shape their immediate environment and control the sediment water exchange and the benthic fluxes at vent sites the oxygen consumption at vent sites is a major sink for oxygen at the study area

the effect of speleothem surface slope on the remanent magnetic inclination speleothems are of interest for high resolution reconstruction of the earth s magnetic field however little is known about the influence of speleothem morphologies on their natural remanent magnetization nrm record here we report on a high resolution paleomagnetic study of a dome shaped speleothem of middle holocene age from southern portugal with special attention to the anisotropy of magnetic susceptibility ams and anisotropy of anhysteretic remanent magnetization aarm to assess the potential influence of the slope of the speleothem surface on the recorded remanent magnetization we compare magnetic directions and ams and aarm fabrics from sub horizontal to gradually sub vertical calcite growth layers collected in a transversal cross section of the speleothem a linear correlation is observed between magnetic inclinations calcite laminae slope and aarm k1 inclination the ams fabric is mostly controlled by calcite crystals with direction of the minimum axes k3 perpendicular to laminae growth magnetic inclinations recorded in inclined and vertical calcite growth layers are underestimated when compared to a global paleosecular variation psv model after extrapolating magnetic inclinations to the horizontal the corrected data better fit the psv model but are still lower than the predicted magnetic inclinations suggesting that inclination shallowing affects the entire speleothem we suggest that speleothem morphology exerts a critical role on the magnetic inclination recording which is controlled by the earth s magnetic field but also influenced by particle rolling along the sloping surfaces these observations open new avenues for reconstructing high resolution paleomagnetic secular variations records from speleothems and provide new insights into their nrm acquisition mechanisms

quantification of methane emission from bacterial mat sites at quepos slide offshore costa rica seafloor methane emission from the quepos slide on the submarine segment of the costa rica fore arc margin was estimated by extrapolating flux measurements from individual seeps to the total area covered by bacterial mats this approach is based on the combination of detailed mapping to determine the abundance of seeps and the application of a numerical model to estimate the amount of benthic methane fluxes model results suggest that the majority of the studied seeps transport rather limited amount of methane on average 177 mol cm 2 a 1 into the water column due to moderate upward advection allowing for intense anaerobic oxidation of methane aom on average 53 of the methane flux is consumed depth integrated aom rates 56 1 538 mol ch4 cm 2 a 1 are comparable with values reported from other active seep sites the overall amount of dissolved methane released into the water column from the entire area covered by bacterial mats on the quepos slide is estimated to be about 0 28 106 mol a 1 this conservative estimate which relies on rather accurate determinations of seafloor methane fluxes emphasizes the potential importance of submarine slides as sites of natural methane seepage however at present the global extent of methane seepage from submarine slides is largely unknown

freshwater discharges in a simulation of the last glacial maximum climate using improved river routing 1 the large ice sheets over north america and europe at the last glacial maximum lgm strongly disturbed river pathways this has never been taken into account in simulations of the lgm climate even if it could have an impact on the freshwater input to the ocean here we have introduced a more realistic river routing in lgm atmospheric general circulation model simulations a comparison with classical lgm simulations shows that the discharge into the arctic ocean is not drastically different even if the ob and yenisei rivers could not reach the arctic ocean because of the fennoscandian ice sheet which results in a lake south of this ice sheet the discharge of other rivers nearby is increased due to the influence of this lake the maximum monthly discharge into the north atlantic ocean decreases by 34000 m3 s between 54 and 66 n while it is stronger by 35000 m3 s between 28 and 54 n