displacement pile behaviour in glacial clay the paper describes a programme of field experiments with heavily instrumented displacement piles installed in a stiff lodgement till measurements of the effective stresses recorded at various le

chemical weathering rates and atmospheric soil co2 consumption of igneous and metamorphic rocks under tropical climate in southeastern brazil abstract chemical weathering rates and atmosphere soil co 2 consumption of igneous and metamorphic rocks under tropical climate in southeastern brazil were evaluated using the chemical composition of surface waters and fresh rocks and soil horizon c in the upper sorocaba river basin surface water samples were collected between june 2009 and june 2010 and analyses were performed to assess ph electrical conductivity ec temperature and total dissolved solids tds including na k ca 2 mg 2 cl so 4 2 po 4 3 no 3 and sio 2 fresh rocks and c horizon samples were also collected taking into account their geological context abundance and spatial density to analyze major elements and mineralogy the concentration of tds and dissolved cations anions and silica increased during the dry period in relation to the wet period and the same behavior was observed for ph ec and temperature after corrections of anthropogenic contributions ca 21 t km 2 yr and atmospheric inputs ca 19 t km 2 yr the annual flux due to chemical weathering involving the igneous and metamorphic rocks was ca 29 t km 2 yr the co 2 atmospheric soil consumption in the upper sorocaba river basin was ca 0 2 10 6 mol km 2 yr and when extrapolated to the entire mantiqueira orogenic belt accounted an estimated consumption of 0 07 10 12 mol yr representing 0 6 of the total co 2 consumption flux derived from global average silicate weathering the chemical weathering rates of igneous and metamorphic rocks in the upper sorocaba river basin were estimated at 15 m my respectively the main weathering process in this watershed was the monossialitization with partial hydrolyses of bedrock minerals except quartz which was not weathered and remained in the soil profile the annual specific flux derived from igneous and metamorphic rocks at upper sorocaba river basin could be compared with watersheds in tropical climates however this value is higher than in other north american european asian and african granitoid watersheds and lower than in montane watersheds

the geochemical signatures of variable gas venting at gas hydrate sites diverse evidence suggests that gas venting rates at sites of hydrate crystallization are variable in space and time but the magnitude of these variations has been difficult to quantify the hydrate crystallization model of chen and cathles j geophys res solid earth 108 2003 is used here to analyze 10 years of vent gas chemistry measurements at the bush hill hydrate mound and gas venting site green canyon 185 offshore louisiana gulf of mexico the analysis suggests that at any instant of time gas vents at variable rates in different gas channels at the same site and that the compositional differences in these vent gases are nearly as large as can be produced by hydrate crystallization almost two orders of magnitude differences in venting rate between individual gas channelways are suggested changes in the average vent gas composition over the last 10 years suggest the average venting rate varied by a factor of similar to2 or more over a few years the average c 3 c 4 composition of bush hill hydrates are leaner than could be crystallized from vent gases sampled over the last decade indicating that the venting gas flux was slower in the past by a factor of similar to2 this is compatible with geologic generalizations that venting evolves from fast mud volcano to intermediate hydrate crystallization to slow carbonate precipitation if venting organized into more discrete vents with time c 2004 elsevier ltd all rights reserved

preliminary assessment of resources and economic potential of individual gas hydrate accumulations in the gulf of mexico continental slope abstract some global estimates suggest that gas hydrates represent the largest reservoir of fossil fuel however only a few studies of the resource and economic potential of individual gas hydrate accumulations exist here we estimate the volume of hydrate bound gas at gc green canyon blocks 184 185 gc 234 235 gb garden banks 388 mc mississippi canyon 798 842 gc 204 mc 852 853 and at atwater valley 425 426 sites in the gulf of mexico at water depths 500 2000 m the structural accumulations may contain from 4 7 10 8 to 1 3 10 11 m 3 of gas at standard temperature and pressure the resources in individual gas hydrate accumulations are comparable by volume with the reserves in very small to major conventional gas fields various geologic technologic and economic factors affect the economic potential of studied accumulations the mc 852 853 appears to be characterized by the most favorable combination of these factors and thus is suggested to have the highest economic potential the economic potential of gas hydrate accumulations at gc 204 gb 388 and at 425 426 sites is ranked as average gas hydrate accumulations at gc 234 235 gc 184 185 and mc 798 842 sites contain only small volumes of hydrate bound gas and likely have no economic potential future gas hydrate research should focus on the detailed study of large structural gas hydrate accumulations from which gas may be profitably recovered e g the mc 852 853 site

analysis of the black sea sediments by evaluating dsdp leg 42b drilling data for gas hydrate potential abstract many gas seepages temperature pressure salinity anoxic environment and high source gas potential of the black sea indicates that the black sea might have huge potentials for biogenic and thermogenic gas hydrates however the last important parameter to consider gas hydrate as an energy source is the type of sediments coarse marine sands are considered as good hydrate reservoirs because of high porosity and high permeability only very limited data is available related to the types of lithology of the black sea sediments hence in this study the literature data especially the drilling and coring data of dsdp leg 42b program about gas seepages temperature gradient pressure gradient salinity anoxic environment and high source gas potential and the types of the sediments in the black sea were investigated and analyzed although gas seepages temperature gradient pressure gradient salinity anoxic environment and high source gas potential of the black sea are appropriate for producible gas hydrate reservoirs the sediments of the black sea appear to be generally fine grained with high clay content sandy silt and silty sand layers in turbidites of the black sea might be potential producible hydrate reservoirs but these sediments are fine as well as turbidites separate thin sand layers might be potential gas hydrate reservoirs as an energy source in the black sea

free hydrocarbon gas gas hydrate and authigenic minerals in chemosynthetic communities of the northern gulf of mexico continental slope relation to microbial processes research submersibles and piston cores were used to sample two chemosynthetic communities in the gulf of mexico continental slope at 540 m water depth vent gas from the deep subsurface is the starting material from which other carbon pools are derived including gas hydrate free hydrocarbon gas in sediment and authigenic carbonate rock gas crystallizes as exposed mounds of structure ii gas hydrate and as massive vein fillings in hemipelagic mud venting rates from gas hydrate mounds periodically increase after the temperature of the bottom water increases gas hydrate decomposition is largely restricted to exposed hydrate and at shallow depth in sediment overall gas hydrate is accumulating not decomposing at study sites most free gas in sediment appears to be destroyed in situ by anaerobic microbial oxidation in chemosynthetic communities leading to sequestration of carbon as abundant authigenic carbonate rock depleted in 13c free methane is rapidly oxidized leaving residual methane enriched in 13c some in situ microbial co2 reduction occurs and methane depleted in 13c mixes with vent methane enriched in 13c the c2 c5 hydrocarbons of vent gas initially most depleted in 13c ethane isobutane isopentane are least affected by microbial oxidation whereas hydrocarbons initially enriched in 13c propane normal butane normal pentane are most affected anaerobic microbial oxidation of all c1 c5 hydrocarbon gases not only methane may be significant in chemosynthetic communities microbial processes contribute to the development and stability of chemosynthetic communities by providing required h2s anaerobic microbial processes lead to deposition of diagnostic authigenic minerals related to the carbon carbonate minerals and sulfur cycles pyrite elemental sulfur altering the seafloor seafloor cementation favors fauna such as chemosynthetic tubeworms and seep mussels by forming carbonate hardgrounds on an otherwise unfavorable mud dominated seafloor

complex gas hydrate system in a gas chimney south china sea abstract gas hydrates and deep sea cold seeps are of interest to industry and academia for several reasons including their implications for offshore geohazards and unconventional resources and for global climate change and carbon cycling guangzhou marine geological survey gmgs implemented its fifth gas hydrate drilling expedition in the qiongdongnan sea area qdn sa of the northern south china sea scs from june to september 2018 multidisciplinary investigations including logging while drilling lwd pressure and non pressure coring gas composition analyses in situ temperature and permeability measurements pore water geochemical analyses and a regional seismic survey reveal a complex distribution of gas hydrate within a vertical chimney structure lwd profiles record high resistivity anomalies and high p wave velocity variations at 9 174 mbsf suggesting the coexistence of free gas and gas hydrate in the sediment column throughout the investigated gas chimney hydrate bound and void gas is an admixture of methane 70 1 98 3 and heavier hydrocarbons c2h6 0 16 17 59 c3h8 0 05 9 88 i c4h10

anthropogenic impacts on mineral weathering a statistical perspective abstract correspondence analysis was adopted as tool for investigating the statistical structure of hydrochemical and weathering datasets of groundwater samples with the main purpose of identifying impacts on mineral weathering caused by anthropogenic activities namely fertilizing of farmlands the hydrochemical dataset comprised measured concentrations of major inorganic compounds dissolved in groundwater namely bicarbonate silica usually by products of chemical weathering chloride sulphate and nitrate typically atmospheric plus anthropogenic inputs the weathering dataset consisted of calculated mass transfers of minerals being dissolved in loess sediments of a region located in sw hungary szigetvar area namely na plagioclase calcite and dolomite and of pollution related concentrations of sodium magnesium and calcium a first run of correspondence analysis described groundwater composition in the study area as a system of triple influence where spots of domestic effluents dominated chemistries are surrounded by areas with agriculture dominated chemistries both imprinted over large regions of weathering dominated chemistries a second run revealed that nitrification of n fertilizers is promoting mineral weathering by the nitric acid reaction anthropogenic pathway in concurrence with the retreating of weathering by carbonic acid natural pathway it also indicated that dolomite and calcite are being players in a dedolomitization process driven by dissolution of gypsum fertilizers and nitrification of n fertilizers

evidence of structure h hydrate gulf of mexico continental slope abstract a research submarine was used to sample an amber colored gas hydrate exposed on the sea floor at 540 m water depth in the gulf of mexico continental slope offshore louisiana the hydrate composition is novel for a natural occurrence because i c 5 comprises 41 1 of the total c 1 c 5 hydrocarbon distribution the relative abundance of i c 5 is consistent with an hexagonal h lattice structure that is capable of enclosing larger hydrocarbon molecules than either structure i or ii hydrates structure h hydrate which has not been identified previously in nature coexists with structure ii hydrate on the gulf slope

role of hydraulic diffusivity in the decrease of weathering rates over time summary springs emerging within massifs of crystalline rocks were monitored for discharge rate q and the q values combined with geomorphic and hydrographic parameters in a hydrologic model to calculate hydraulic conductivity k and effective porosity n e of the spring watersheds the spring waters several borehole waters and rain water were analyzed for major dissolved compounds strontium and isotopes 18 o 2 h 13 c and 87 sr 86 sr with a shift to less negative values 18 o and 2 h were fitted by a line approximately parallel to the gmwl but no significant dependence on altitude was found the 18 o and 2h values correlate better with those of precipitation amount the 87 sr 86 sr ratios in drilled well waters correlate positively with the depth of water circulation reported in the borehole logs the corresponding regression equations were used to extrapolate the depth of hydraulic circuits within the spring watersheds the previous data together with groundwater travel times calculated by a water balance model and with reactions of granite metassediment plagioclase and biotite precipitating halloysite gibbsite and vermiculite were assembled in a mass balance model to calculate solute flux weathering rates of plagioclase w pl the w pl s were described as a function of d k n e where d is the hydraulic diffusivity the discrepancies between the w pl values and solid state rates based on the differences between elemental isotopic and mineral compositions measured in present day regoliths and in the assumed protolith were assigned to a decrease in d over time from values in the protolith to values in the weathered aquifer

evolution of the groundwater chemical composition in the poyang lake catchment china in this paper the water rock interactions and anthropogenic effects in the poyang lake catchment china were distinguished using the chemical composition of the shallow groundwater the analysis focuses on those changes which result from water rock interactions it is found that the shallow groundwater in the poyang lake catchment is hco3 ca na or hco3 na ca with an average tds value of 183 mg l the ph value increases with groundwater salinity and changes from acidic to neutral and rarely to slightly alkaline the content of 18o and d suggests that the shallow groundwater is of meteoric origin a detailed analysis reveals that the groundwater can be confined to two different landscapes 1 to red earth soils natural landscapes and 2 to paddy soils landscapes influenced by intensive agricultural activities the main distinction between two types of the groundwater is that the groundwater confined to red earth soils is in equilibrium with kaolinite and hydroxides while the groundwater confined to agricultural landscapes is in equilibrium with montmorillonites and less often with illite and kaolinite the differences between mineral equilibrium character of two main groundwater types result from changing in water exchange rate due to long term agricultural activity with regular flooding and slope terracing it is found that in some areas the shallow groundwater is rich in no3 cl so42 k nh4 no2 po43 f due to overuse of fertilizers sewage water leakage and other pollutants

hydrochemistry weathering and weathering rates on madeira island madeira island consists of miocene to pleistocene lavas and pyroclasts major rock types are alkali basalts basanites and hawaiites principal soil types are leptosols andosols and cambisols our main objective was to link the chemistry of ground waters to weathering reactions and rates we collected 40 shallow groundwater samples remote from human activities with a few exceptions the ranges of electrical conductivities were 29 176 ms cm and of ph 5 8 8 5 the calculated pco2 was generally higher than the atmospheric value the contribution of sea salt to the water chemistry was 30 9 corrected for sea salt the cation concentrations in meq l decrease in the order ca 2 mg 2 na k the concentrations of so42 and no3 are very low we calculated that the total annual chemical denudation rate in the studied area amounts to 37 12 g m 2 consuming 0 86 0 38 mol co2 m 2 to achieve our main objective a set of mole balance equations ax b was used where a is a composite matrix of coefficients including ratios between stoichiometric coefficients as determined by the weathering reactions and coefficients accounting for unconstrained contributions b is the vector with a water composition and x is the set of mole fractions of dissolved primary minerals plus the residual concentrations of the unconstrained contributions olivine ol pyroxene py and plagioclase pl were considered to be the major primary minerals and smectite vermiculite halloysite allophane gibbsite and hematite the secondary minerals in the weathering reactions using iterative procedures whereby mixtures of secondary products as well as the composition of plagioclase are allowed to change we selected one best fit set of weathering reactions for each spring by checking all possible solutions of the mole balances against predefined boundary conditions at odds with goldich 1938 sequence our model results indicate for most best fit sets a weathering rate sequence of pl ol py but such reverse order is not unique on average the annual weathering rates in mol ha y vol mineral are 44 19 pl 29 14 ol and 22 13 py q 2003 elsevier b v all rights reserved

massive vein filling gas hydrate relation to ongoing gas migration from the deep subsurface in the gulf of mexico abstract a gas hydrate mound that contains massive vein filling structure ii gas hydrate occurs on the upper continental slope 540 m water depth of the gulf of mexico southwest of the mississippi delta the mound is located in the green canyon gc block 185 adjacent to jolliet field in gc 184 jolliet field contains oil and gas that filled fault traps caused by salt deformation during late pleistocene holocene time in contrast to reservoir oil in jolliet field which shows bacterial oxidation effects the c 1 c 5 reservoir gas is unaltered by bacterial oxidation disassociated gas is assumed to have recently entered from the subsurface hydrocarbon system vertical migration of gas along faults is ongoing manifested on the sea floor by gas vents gas hydrate complex chemosynthetic communities and by a large gas plume that extends from the vents to the sea surface the isotopic properties of c 1 c 5 hydrocarbons from reservoirs gas vents and gas hydrate correlate closely although outcropping gas hydrate is transiently stable because of variations in seawater temperature the bulk of buried gas hydrate at gc 185 is stable and perhaps increasing in volume because of the copious gas flux the massive accumulation of gas hydrate at the gc 185 site is attributed to the gas that has recently entered the vents largely from jolliet field and to the synchronous activation of fault conduits allowing gas migration to the sea floor synchronous late gas charge and faulting could also explain the wide distribution of gas hydrate across the upper gulf slope

influence of landscape position and vegetation on long term weathering rates at the hubbard brook experimental forest new hampshire usa the spatial variability of long term chemical weathering in a small watershed was examined to determine the effect of landscape position and vegetation we sampled soils from forty five soil pits within an 11 8 hectare watershed at the hubbard brook experimental forest new hampshire the soil parent material is a relatively homogeneous glacial till deposited 14 000 years ago and is derived predominantly from granodiorite and pelitic schist conifers are abundant in the upper third of the watershed while the remaining portion is dominated by hardwoods the average long term chemical weathering rate in the watershed calculated by the loss of base cations integrated over the soil profile is 35 meq m 2 yr 1 similar to rates in other 10 to 15 ka old soils developed on granitic till in temperate climates the present day loss of base cations from the watershed calculated by watershed mass balance exceeds the long term weathering rate suggesting that the pool of exchangeable base cations in the soil is being diminished despite the homogeneity of the soil parent material in the watershed long term weathering rates decrease by a factor of two over a 260 m decrease in elevation estimated weathering rates of plagioclase potassium feldspar and apatite are greater in the upper part of the watershed where conifers are abundant and glacial till is thin the intra watershed variability across this small area demonstrates the need for extensive sampling to obtain accurate watershed wide estimates of long term weathering rates

a kinetic model for the pattern and amounts of hydrate precipitated from a gas steam application to the bush hill vent site green canyon block 185 gulf of mexico 1 we construct a linear kinetic model of hydrate crystallization from a gas stream we use this model to predict the fraction of gas that crystallizes as hydrate in the subsurface of bush hill and the depth profile of subsurface hydrate accumulation this is possible because the bush hill vent is fed by reservoir gas from the nearby jolliet field whose composition is known on the average 9 of the vent gas is precipitated as hydrate in the subsurface although other explanations are possible the observed vent gas compositions and the greater range of hydrate gas compositions are consistent with a single source gas whose venting rate varies by a factor of at least 3 over periods of a few years or less the predicted depth profile of hydrate accumulation and the hydrate content of the bush hill mound suggest that between 1 1 109 and 2 8 109 m3 stp of gas may have accumulated as hydrate between the seafloor and 614 m depth for the radiometrically and geologically suggested system age of 10 000 years the time average venting rate is 106 m3 yr 0 7 106 kg yr if distributed evenly across the 600 m diameter mound as suggested by echo sounder images the methane flux is 3 2 kg m2 yr this is 103 times that inferred for hydrates associated with bottom simulating seismic reflectors the subsurface hydrate accumulation and the cumulative methane venting are related we show how both may be estimated from measurements of vent gas composition bottom water temperature and geothermal gradient

gas hydrate and crude oil from the mississippi fan foldbelt downdip gulf of mexico salt basin significance to petroleum system abstract structure ii gas hydrate methane ethane hydrate and crude oil occur on the sea floor at 1920 1930 m water depth in atwater valley at block 425 near the juncture of the lower slope of the gulf of mexico salt basin and the abyssal plain the site is in the eastern mississippi fan foldbelt mff a distinct structural province at the downdip limit of the gulf of mexico salt basin the presence of thermogenic hydrocarbons confirms an active petroleum system in the deep eastern mff the hydrate bound c 2 c 5 hydrocarbon gases of the mff are isotopically distinct when compared to other gases from the upper and middle slope being strongly depleted in 13 c the biomarkers m z 191 and 217 of oil inclusions from at 425 gas hydrate are also distinct when compared to oils of the upper gulf slope and the smackover trend biomarkers of at 425 oil are consistent with a marine source rock deposited in an area of strong siliciclastic influx with possible higher plant organic matter the presence of a shale or mudstone source rock at the downdip limit of the gulf raises new questions as to paleogeography during source rock deposition emergent highlands immediately to the south and east of the downdip limit of the gulf of mexico salt basin during the mesozoic may explain the occurrence of the shale or mudstone source rock that gave rise to the gas and oil at at 425

hydrocarbons of experimental and natural gas hydrates gulf of mexico continental slope abstract gas hydrate was experimentally precipitated for the first time in the deep sea using natural starting materials the experiments were performed using a research submarine on the gulf of mexico continental slope at a water depth of 540 m at 9 0 9 2 c starting materials were thermogenic hydrocarbon gases similar in composition to gases in underlying subsurface reservoirs these gases vented to the water column in association with sea floor mounds of natural yellow orange gas hydrate structure ii the vent gases were captured in transparent lexan tubes at ambient conditions and precipitation of white to yellow gas hydrate dendrites and coatings was seen to occur within minutes experimental hydrates show 13c of methane and c1 c5 hydrocarbon compositions that are similar to the vent gases from which they precipitated

chemical weathering in granitic environments abstract factors controlling chemical weathering in granitic environments are deduced using an extensive database from the literature based on a transition state theory model we evaluated the effects on chemical weathering of runoff temperature and ph the dependence between temperature and runoff and chemical weathering is complicated by other factors such as the presence depth of soil cover soil cover favors chemical weathering when it is thin and rich in weatherable minerals in contrast it reduces chemical weathering when is thick and poor in primary minerals processes that increase the contact time and the surface of the water rock interactions such as physical denudation increase chemical weathering rates in granitic environments the effect of temperature can be quantified assuming an apparent activation energy value of 48 7 kj mol to describe chemical weathering of silica in granitic crystalline environment under high runoff conditions

mineralogic controls on the composition of natural waters dominated by silicate hydrolysis a detailed mineral solute mass balance spreadsheet model has been developed to improve understanding of mineralogic controls on water composition in surface waters and groundwater systems dominated by silicate lithologies the spreadsheet based approach is used to investigate mass balance solutions over a range of mineral compositions for predominant multi element phases such as plagioclase biotite chlorite amphibole and dioctahedral smectite the mass balance technique has been applied to a variety of hydrogeologic environments including calibrated watersheds springs and groundwater systems lithologic settings include plutonic metamorphic minor volcanic and sedimentary alluvial and glacial deposits materials sites investigated most of which allowed comparison with earlier work include ephemeral and perennial springs of the central sierra nevada mountains california the loch vale colorado high altitude watershed four catchments in the inyo mountains california and nevada watersheds in the catoctin mountain maryland area and ground water flow systems in vekol valley arizona and in the trout lake area wisconsin analytical mass balances were derived with a novel approach that permits graphic analysis of the functional dependency of mineral mass transfer coefficients on variations in major silicate composition a 10 x 10 matrix of mineral solute reaction equations was used to solve for the best mass balances alternative methods were developed to investigate cases where the number of mineral phases exceeds the number of solute constraints 10 that are commonly found in clastic silicate dominated systems with diverse sources and or phase mixtures of variable chemistry such as an assortment of plagioclase compositions techniques were also developed to allow for important structurally controlled compositional variation in clay minerals final mass balance choices were tempered by thermodynamic stability calculations for various minerals under near surface weathering conditions mineral mass transfer ratios were also found to be useful in restricting mass balances additional constraints were provided by establishing consistent sets of similar mineral assemblages and mineral compositions for a series of wells along a ground water flow path or through comparison of multiple nearby watersheds subject to similar climatic and vegetative conditions whereas unique analytical solutions from spreadsheet mass balances were not always possible a surprisingly limited range was obtained for mineral assemblages and compositions satisfying observed mineral occurrences and thermodynamic stability conditions our results demonstrate the importance of having well characterized mineral compositions for both reactant and product phases the mass balance results are particularly sensitive to the compositions of plagioclase dioctahedral smectite and a few primary mafic mineral groups trioctahedral mica amphibole and pyroxene in addition to mineral controls the specific examples studied demonstrate effects of dolomite and calcite overprints on silicate weathering biomass fluctuations road salt contamination and on buried evaporite salts a comparison of the mass balance results from surface and groundwater systems indicates strong similarities suggesting that similar processes dominate the mineral controls in both settings and that under soil weathering conditions ion exchange might have been overemphasized except under conditions where pre existing waters are displaced by solutions of significantly different composition

natural oil slicks in the gulf of mexico visible from space natural oil seepage in the gulf of mexico causes persistent surface slicks that are visible from space in predictable locations a photograph of the sun glint pattern offshore from louisiana taken from the space shuttle atlantis on may 5 1989 shows at least 124 slicks in an area of about 15 000 km2 a thematic mapper tm image collected by the landsat orbiter on july 31 1991 shows at least 66 slicks in a cloud free area of 8200 km2 that overlaps the area of the photograph samples and descriptions made from a surface ship from aircraft and from a submarine confirmed the presence of crude oil in floating slicks the imagery data show surface slicks near eight locations where chemosynthetic communities dependent upon seeping hydrocarbons are known to occur on the seafloor additionally a large surface slick above the location of an active mud volcano was evident in the tm image in one location the combined set of observations confirmed the presence of a flourishing chemosynthetic community active seafloor oil and gas seepage crude oil on the sea surface and slick features that were visible in both images we derived an analytical expression for the formation of floating slicks based on a parameterization of seafloor flow rate downstream movement on the surface half life of floating oil and threshold thickness for detection applying this equation to the lengths of observed slicks suggested that the slicks in the atlantis photograph and in the tm image represent seepage rates of 2 2 30 m3 1000 km 2 d 1 and 1 4 18 m3 1000 km 2 d 1 respectively generalizing to an annual rate suggests that total natural seepage in this region is of the order of at least 20 000 m3 yr 1 120 000 barrels yr 1

geochemical studies in the drainage basin of the rio vouga portugal abstract the hydrothermal waters in the vouzela region portugal have a temperature of 68 c and are characterized by a high content of f li b bicarbonate sulphate and silica ninety three water samples including two hydrothermal waters were analyzed for major and trace elements in order to investigate the genesis of the hydrothermal water in the vouzela region two older hercynian granites are exposed the abas granite and the sao pedro do sul granite the abas granite is intersected by the ribama fault albitization is ubiquitous other alteration effects are tourmalinization k feldspathization and muscovitization these processes and the associated sn w deposits were induced by the intrusion of the younger viseu granite in the present situation rainwater penetrates into the abas granite especially via the ribama fault and the greisenization zone it becomes part of a hydrothermal system leaches li f b and silica and rises via the termas fault in the hydrothermal springs of termas de sao pedro do sul geothermal equilibrium calculations yield a temperature of 205 10 c for the thermal reservoir the percentage of mixing with cold groundwater near the surface in the circulation system is estimated at 73 the circulation system is possibly maintained by the heat generated by the decay of u th k and their daughter products elements which are encountered in extremely high concentrations in the sao pedro do sul granite

hydrate occurrence in europe a review of available evidence abstract large national programs in the united states and several asian countries have defined and characterised their marine methane hydrate occurrences in some detail but european hydrate occurrence has received less attention the european union funded project marine gas hydrate an indigenous resource of natural gas for europe migrate aimed to determine the european potential inventory of exploitable gas hydrate to assess current technologies for their production and to evaluate the associated risks we present a synthesis of results from a migrate working group that focused on the definition and assessment of hydrate in europe our review includes the western and eastern margins of greenland the barents sea and onshore and offshore svalbard the atlantic margin of europe extending south to the northwestern margin of morocco the mediterranean sea the sea of marmara and the western and southern margins of the black sea we have not attempted to cover the high arctic the russian ukrainian and georgian sectors of the black sea or overseas territories of european nations following a formalised process we defined a range of indicators of hydrate presence based on geophysical geochemical and geological data our study was framed by the constraint of the hydrate stability field in european seas direct hydrate indicators included sampling of hydrate the presence of bottom simulating reflectors in seismic reflection profiles gas seepage into the ocean and chlorinity anomalies in sediment cores indirect indicators included geophysical survey evidence for seismic velocity and or resistivity anomalies seismic reflectivity anomalies or subsurface gas escape structures various seabed features associated with gas escape and the presence of an underlying conventional petroleum system we used these indicators to develop a database of hydrate occurrence across europe we identified a series of regions where there is substantial evidence for hydrate occurrence some areas offshore greenland offshore west svalbard the barents sea the mid norwegian margin the gulf of cadiz parts of the eastern mediterranean the sea of marmara and the black sea and regions where the evidence is more tenuous other areas offshore greenland and of the eastern mediterranean onshore svalbard offshore ireland and offshore northwest iberia we provide an overview of the evidence for hydrate occurrence in each of these regions we conclude that around europe areas with strong evidence for the presence of hydrate commonly coincide with conventional thermogenic hydrocarbon provinces

gas hydrate systems at hydrate ridge offshore oregon inferred from molecular and isotopic properties of hydrate bound and void gases abstract we report and discuss molecular and isotopic properties of hydrate bound gases from 55 samples and void gases from 494 samples collected during ocean drilling program odp leg 204 at hydrate ridge offshore oregon gas hydrates appear to crystallize in sediments from two end member gas sources deep allochthonous and in situ as mixtures of different proportions in an area of high gas flux at the southern summit of the ridge sites 1248 1250 shallow 0 40 m below the seafloor mbsf gas hydrates are composed of mainly allochthonous mixed microbial and thermogenic methane and a small portion of thermogenic c2 gases which migrated vertically and laterally from as deep as 2 to 2 5 km depths in contrast deep 50 105 mbsf gas hydrates at the southern summit sites 1248 and 1250 and on the flanks of the ridge sites 1244 1247 crystallize mainly from microbial methane and ethane generated dominantly in situ a small contribution of allochthonous gas may also be present at sites where geologic and tectonic settings favor focused vertical gas migration from greater depth e g sites 1244 and 1245 non hydrocarbon gases such as co2 and h2s are not abundant in sampled hydrates the new gas geochemical data are inconsistent with earlier models suggesting that seafloor gas hydrates at hydrate ridge formed from gas derived from decomposition of deeper and older gas hydrates gas hydrate formation at the southern summit is explained by a model in which gas migrated from deep sediments and perhaps was trapped by a gas hydrate seal at the base of the gas hydrate stability zone ghsz free gas migrated into the ghsz when the overpressure in gas column exceeded sealing capacity of overlaying sediments and precipitated as gas hydrate mainly within shallow sediments the mushroom like 3d shape of gas hydrate accumulation at the summit is possibly defined by the gas diffusion aureole surrounding the main migration conduit the decrease of gas solubility in shallow sediment and refocusing of gas by carbonate and gas hydrate seals near the seafloor to the crest of the local anticline structure

rate effects from pile shaft resistance measurements to be able to properly analyse rapid load pile tests in clay soils e g statnamic an understanding of the material s behaviour at elevated shearing rates is required as clays demonstrate nonlinear shearing resistance as the rate of shearing increases to determine the relationship between pile resistance under static and elevated rates of loading rate effect parameters for viscous damping have historically been derived from pile head measurements on full scale pile tests these parameters are then attributed to a soil type with little recognition of what aspects of a soil may give further variation to them to study this variation a test pile was installed in glacial till and instrumented with strain gauged sister bars at various levels down the pile shaft direct measurements of pile shaft resistance in both rapid load and static pile tests show that derivation of average parameters from pile head readings masks the variation in rate effect along a pile shaft the variation of rate effects along the

modeling rock weathering in small watersheds summary many mountainous watersheds are conceived as aquifer media where multiple groundwater flow systems have developed toth 1963 and as bimodal landscapes where differential weathering of bare and soil mantled rock has occurred wahrhaftig 1965 the results of a weathering algorithm pacheco and van der weijden 2012a 2014 which integrates topographic hydrologic rock structure and chemical data to calculate weathering rates at the watershed scale validated the conceptual models in the river sordo basin a small watershed located in the marao cordillera north of portugal the coupling of weathering groundwater flow and landscape evolution analyses as accomplished in this study is innovative and represents a remarkable achievement towards regionalization of rock weathering at the watershed scale the river sordo basin occupies an area of approximately 51 2 km 2 and was shaped on granite and metassediment terrains between the altitudes 185 1300 m the groundwater flow system is composed of recharge areas located at elevations 700 m identified on the basis of 18 o data discharge cells comprehend terminations of local intermediate and regional flow systems identified on the basis of spring density patterns infiltration depth estimates based on 87 sr 86 sr data and spatial distributions of groundwater ph and natural mineralization intermediate and regional flow systems defined where infiltration depths 125 m develop solely along the contact zone between granites and metassediments because fractures in this region are profound and their density is very large weathering is accelerated where rocks are covered by thick soils being five times faster relative to sectors of the basin where rocks are covered by thin soils differential weathering of bare and soil mantled rock is also revealed by the spatial distribution of calculated aquifer hydraulic diffusivities and groundwater travel times

contributions of water rock interactions to the composition of groundwater in areas with a sizeable anthropogenic input a case study of the waters of the fundao area central portugal we used a combination of a grouping algorithm and a weathering algorithm to assess the contributions made by chemical weathering and anthropogenic inputs to the groundwater composition in a granitoid area the first algorithm is based on the mathematical concept of equivalent relations between objects and is used to find groups of water samples using the grouping algorithm we identified groups with similar chemistries in a set of data relating to the water composition in 160 springs and wells in the fundao area portugal the second algorithm is based on stoichiometries mass and charge balances in weathering reactions and is used to relate the water composition of each identified group to water mineral interactions in the area background information on the petrology and mineralogy of the area allowed us to choose the most realistic water mineral interactions we also had information about the use and composition of fertilizers in this agricultural area in applying the weathering algorithm we considered all dissolved silica and bicarbonate to be produced by chemical weathering and all dissolved chloride sulphate and nitrate to be derived from other sources mainly from fertilizers the anthropogenic contributions to the water chemistries in the area are high despite the high background concentrations derived from pollution we were able to assess the contribution of weathering to the water chemistries we obtained realistic results with the two algorithms supported by the fact that the spatial distribution of the samples belonging to the various groups shows a good correlation with the geology and petrology of the area

mimicking natural systems methane hydrate formation decomposition in depleted sediments we have initiated a systematic study of sediment hydrate interaction under subsurface mimic conditions to initially focus on marine hydrates a major obstacle to studying natural hydrate systems has been the absence of a sophisticated mimic apparatus in which the hydrate formation phenomenon can be reproduced with precision we have designed and constructed a bench top unit namely flexible integrated study of hydrates fish for this purpose the unit is fully instrumented to precisely record temperatures pressures and changes in gas volume during absorption evolution the labview software allows rapid and continuous data collection during the hydrate formation dissociation cycle in our integrated approach several host sediments collected from blake ridge a well researched hydrate site were characterized using the computed microtomography technique at beamline x 26a of the national synchrotron light source at brookhaven national laboratory the characterized depleted sediments were then used to study the hydrate formation decomposition kinetics under various pressures in the fish unit we report two hydrate formation methods one under continuous methane gas flow conditions dynamic mode and the other in which hydrates are formed from the dissolved gas phase by diffusion static mode also reported is a depressurization method namely the step down pressure method to yield gas evolution data data from suchmore runs with host sediment from the deepest site 667 metres is presented during hydrate formation the data reveals a temperature signature that is consistent with an exothermic hydrate formation event in the decomposition cycle data at various pressures was analysed to yield curves with similar slopes suggesting a zero order dependence the capabilities of the fish unit and the implications of these runs in establishing a database of sediment hydrate kinetics and pore saturation are discussed less

the ubiquitous nature of accessory calcite in granitoid rocks implications for weathering solute evolution and petrogenesis calcite is frequently cited as a source of excess ca sr and alkalinity in solutes discharging from silicate terrains yet no previous effort has been made to assess systematically the overall abundance composition and petrogenesis of accessory calcite in granitoid rocks this study addresses this issue by analyzing a worldwide distribution of more than 100 granitoid rocks calcite is found to be universally present in a concentration range between 0 028 to 18 8 g kg 1 mean 2 52 g kg 1 calcite occurrences include small to large isolated anhedral grains fracture and cavity infillings and sericitized cores of plagioclase no correlation exists between the amount of calcite present and major rock oxide compositions including cao ion microprobe analyses of in situ calcite grains indicate relatively low sr 120 to 660 ppm negligible rb and 87sr 86sr ratios equal to or higher than those of coexisting plagioclase solutes including ca and alkalinity produced by batch leaching of the granitoid rocks 5 co2 in di water for 75 d at 25 c are dominated by the dissolution of calcite relative to silicate minerals the correlation of these parameters with higher calcite concentrations decreases as leachates approach thermodynamic saturation in longer term column experiments 1 5 yr reactive calcite becomes exhausted solute ca and sr become controlled by feldspar dissolution and 87sr 86sr by biotite oxidation some accessory calcite in granitoid rocks is related to intrusion into carbonate wall rock or produced by later hydrothermal alteration however the ubiquitous occurrence of calcite also suggests formation during late stage subsolidus magmatic processes this conclusion is supported by petrographic observations and 87sr 86sr analyses a review of thermodynamic data indicates that at moderate pressures and reasonable co2 fugacities calcite is a stable phase at temperatures of 400 to 700 c

benthic tars in the gulf of mexico chemistry and sources abstract benthic tars were collected at 14 locations in the northern gulf of mexico by trawling tars were altered to varying degrees by microbial degradation and dissolution most if not all of the benthic tars analyzed were significantly different from known production in the northern gulf of mexico differences in composition include light carbon isotope ratios high contents of sulfur nickel and vanadium an excess of phytane and norhopane over pristane and hopane respectively the presence of oleanane and moretanes in tars and the low levels of diasteranes in tars these benthic tars appear to be derived from oils produced in other areas of the world that have been transported into the gulf of mexico by man or natural agents benthic tars are widespread in the gulf of mexico and represent an important sink for pelagic tars

the role of trace minerals in chemical weathering in a high elevation granitic watershed estibere france chemical and mineralogical evidence we investigated chemical weathering in a high elevation granitic environment in three selected watersheds located in the pyrenees france the sites were located on glacial deposits derived from similar hercynian 300 ma granites characterized by the occurrence of zoned plagioclases and trace calcic phases epidote prehnite sphene apatite the surface waters at those sites show high ca na molar ratios 1 which could not be explained by the dissolution of the major plagioclase oligoclase present in the rocks the coupled approach of investigating stream water chemistry and the mineralogy and chemistry of rocks and soils allowed us to explore the role of the weathering of trace calcic minerals in calcium export at the watershed scale the weathering of the trace calcic minerals which represent 1 of the total rock volume are responsible for more than 90 of the calcium export at the sites annual cationic fluxes 23 104 eq km2 yr calculated for the estibere watershed are among the highest reported for high elevation systems draining granitic rocks and 80 of this annual cationic flux can be attributed to the weathering of trace calcic phases calculations based on isotopic values 87sr 86sr go in the same direction except apatite the trace calcic phases appear to be mainly silicates thus the type of chemical weathering observed in the estibere watershed may have an influence on atmospheric co2 consumption by granite weathering however comparison with other watersheds draining granitic environments worldwide and with the two other sites in the pyrenees indicate that the role of trace calcic phases is important in most young environments exposed to chemical weathering e g high elevation catchments on glacial deposits other factors such as the date of glacial retreat the physical denudation rate the hydrological functioning of the watershed and the nature and structure of the soil cover are also important

a review of the geochemistry of methane in natural gas hydrate the largest accumulations on earth of natural gas are in the form of gas hydrate found mainly offshore in outer continental margin sediment and to a lesser extent in polar regions commonly associated with permafrost measurements of hydrocarbon gas compositions and of carbon isotopic compositions of methane from natural gas hydrate samples collected in subaquatic settings from around the world suggest that methane guest molecules in the water clathrate structures are mainly derived by the microbial reduction of co2 from sedimentary organic matter typically these hydrocarbon gases are composed of 99 methane with carbon isotopic compositions 13cpdb ranging from 57 to 73 in only two regions the gulf of mexico and the caspian sea has mainly thermogenic methane been found in gas hydrate there hydrocarbon gases have methane contents ranging from 21 to 97 with 13c values ranging from 29 to 57 at a few locations where the gas hydrate contains a mixture of microbial and thermal methane microbial methane is always dominant continental gas hydrate identified in alaska and russia also has hydrocarbon gases composed of 99 methane with carbon isotopic compositions ranging from 41 to 49 these gas hydrate deposits also contain a mixture of microbial and thermal methane with thermal methane likely to be dominant published by elsevier science ltd

comparison of rapid load test analysis techniques in clay soils abstractrapid load pile testing rlt techniques such as statnamic were developed as an alternative to more frequently adopted static and dynamic tests the existing unloading point method upm for deriving equivalent static load settlement behavior from rapid load tests seems to be adequate in coarse grained soils but may result in poor prediction in clays and silts to address these shortcomings the upm has been improved to reflect soil type and new analysis techniques have been developed to test the performance of the improved upm and new analysis techniques pile tests from two clay sites were analyzed the first case study site was underlain by very to extremely high plasticity quaternary london clay and the second site was underlain by low to intermediate plasticity matrix dominant glacial till the best predictions of static equivalent load settlement behavior for very high plasticity clay were obtained from a new analysis technique that incorporated a soil specific rate effect parameter sel

integrating topography hydrology and rock structure in weathering rate models of spring watersheds weathering rate models designed for watersheds combine chemical data of discharging waters with morphologic and hydrologic parameters of the catchments at the spring watershed scale evaluation of morphologic parameters is subjective due to difficulties in conceiving the catchment geometry besides when springs emerge from crystalline massifs rock structure must be accounted in formulas describing the area of minerals exposed to the percolating fluids for a realistic evaluation of the rates these particular features are not included in the available approaches and for that reason a new model was developed coined throw model this is a lumped approach that integrates t opography h ydrology ro ck structure and w eathering in a single algorithm the study area comprises several stream watersheds and spring sites of the vouga river basin northern portugal shaped on granites firstly the throw model couples a terrain modeling analysis with hydrologic models based on discharge rates to determine hydraulic conductivities k effective porosities ne and annual recharges vr at the stream watershed scale subsequently these parameters are used in a water balance model to estimate concomitant groundwater travel times t the mean k 4 7 3 2 10 7 m s 1 and ne 2 0 1 3 10 2 values are adopted as proxies for the spring watersheds and a firm regression equation is defined between time and stream watershed area a secondly two more runs of terrain modeling analysis are executed to extrapolate morphologic parameters for the spring watersheds the first run hinges on scaling properties of the drainage networks known as horton laws and is used to scale watershed areas across stream orders i the scaling function is described by another regression equation the second run evaluates the order of a spring watershed defined as equivalent order ieq and equated to the mean order of the surrounding stream watersheds having calculated the ieq spring watershed areas and travel times were downscaled using the regression equations a 10 km2 and t 1 4 2 8 year standing on the physical and hydrologic parameters of the spring watersheds the throw model finally calculates plagioclase weathering rates in the vicinity of the spring sites the sib model pacheco and van der weijden 1996 was used before to estimate the contribution of plagioclase dissolution to the chemical composition of these springs van der weijden and pacheco 2006 the chemical data were now coupled with k ne and t in a rate equation to estimate chemical weathering rates of plagioclase in the basin in the throw model the rate equation describes the exposed surface area as a function of fracture spacings openings and porosities pacheco and alencoao 2006 the calculated rates wpl 2 5 1 2 10 14 mol m 2 s 1 are consistent with previous reports and with results of experimental kinetic models the sib results predict formation of halloysite and gibbsite along the flow path which were indeed close to equilibrium with the dissolved al and si activities o develop a weathering model that incorporates rock structure in the rate equation o conceive a weathering model especially designed for fracture artesian springs o create a model that integrates topography hydrology rock structure and weathering

thickness of the gas hydrate stability zone gulf of mexico continental slope the maximum thickness of the gas hydrate stability zone ghsz at key gas hydrate study sites was estimated and a generalized ghsz profile across part of the central gulf of mexico slope was constructed maximum thickness of the ghsz increases with water depth at the shallowest site 540 m water depth from about 450 m to about 1150 m at the deepest site 1930 m water depth the occurrence of gas hydrate in the subsurface is largely controlled by structural focussing of hydrocarbons with gas hydrate most abundant at the rims of salt withdrawal basins and less abundant within intrasalt basins the postulated geometry of large subsurface gas hydrate accumulations shows strong structural control bottom simulating reflectors bsrs are absent or infrequently observed in the gulf of mexico because of structural focusing of the free hydrocarbon gases that form gas hydrate new insight to the geometry of the ghsz in the gulf of mexico continental slope will contribute to improved application of geophysics to map the distribution of gas hydrates improved understanding of three dimensional geometry of gas hydrate accumulations will contribute to better assessment of gas hydrate volumes as a future energy resource as a geohazard and will constrain theories relating the role of gas hydrate in past climate change

new insights into cerium anomalies and mechanisms of trace metal enrichment in authigenic carbonate from hydrocarbon seeps authigenic carbonates that form at marine hydrocarbon seeps provide a unique geological archive of past local environmental conditions and pore fluid geochemistry recent work on such carbonates revealed variable cerium ce anomalies and anomalous enrichments of certain trace metals however the mechanisms accounting for such anomalies remain poorly constrained here we characterize the rare earth element ree patterns of carbonate phases and the trace metal patterns of bulk carbonate rocks sampled at three hydrocarbon seeps located at congo fan pockmarks cf and the gulf of mexico sites ac645 and gb425 the analyzed cf gb425 and ac645 carbonates yielded different ree patterns displaying positive no as well as negative ce anomalies the covariation of molybdenum mo with uranium u including authigenic mo moauth and u uauth enrichments as well as mo u auth ratios proved useful to obtain new insight into the applicability of ce anomalies to constrain past redox conditions trace element patterns suggest that 1 cf carbonates formed in a restricted sulfidic environment while 2 the ac645 site experienced intermittent oxygenation causing negative ce anomalies and 3 environmental conditions were variable at the gb425 mud volcano site interestingly gb425 carbonates show significant mo arsenic as and antimony sb enrichments with the enrichment factor of as asef correlating well with the authigenic fe fraction these results suggest that iron oxyhydroxides played an important role in the adsorption of mo as and sb in the water column and their transfer to the sediment the combination of trace metal and ree geochemistry of authigenic carbonates used here is a promising tool to better assess past variability of redox conditions and biogeochemical processes at marine hydrocarbon seeps

hydrogeochemistry in the vouga river basin central portugal pollution and chemical weathering abstract to quantify and explain the contributions by pollution and chemical weathering to their composition we studied the chemistries of springs and surface waters in the mountainous part of the vouga river basin water samples were collected during a number of consecutive summer campaigns recharge rates were derived from monitored discharge rates within the basin very large contributions by meteoric agricultural and domestic sources to the water chemistries were found identified by the chloride sulfate and nitrate concentrations on average only 1 4 to 1 3 of the solutes could be attributed to chemical weathering two petrologic units characterize the river basin granites and metasediments the waters collected within metasediment units are distinct from those in granite terrain by a higher magnesium concentration on that basis it could be estimated that the rio vouga when leaving the mountainous part of the basin has for some 2 5 a signature determined by chemical weathering in the metasediments the dominant primary minerals subject to chemical weathering are plagioclase pl and biotite in granite or pl and chlorite in metasediment kaolinite gibbsite and vermiculite are the major weathering products where annual precipitation p 1000 mm y 1 and kaolinite vermiculite and smectite where p was lower using an algorithm based on the ratio of dissolved silica to bicarbonate the contributions of chemical weathering of primary minerals could be unraveled the results show that in granite the export rate as mol ha 1 y 1 wt mineral 1 of oligoclase pl with an10 30 was 5 0 2 6 and of biotite 3 2 2 6 while in metasediment these rates for albite pl with an0 10 are 16 5 8 9 and for chlorite are 0 5 0 5 the observed decrease of dissolved silica in surface waters relative to springs was ascribed to summer uptake by aquatic biota

the role of disseminated calcite in the chemical weathering of granitoid rocks accessory calcite present at concentrations between 300 and 3000 mg kg 1 occurs in fresh granitoid rocks sampled from the merced watershed in yosemite national park ca usa loch vale in rocky mountain national park co usa the panola watershed ga usa and the rio icacos puerto rico calcite occurs as fillings in microfractures as disseminated grains within the silicate matrix and as replacement of calcic cores in plagioclase flow through column experiments using de ionized water saturated with 0 05 atm co2 produced effluents from the fresh granitoid rocks that were dominated by ca and bicarbonate and thermodynamically saturated with calcite during reactions up to 1 7 yr calcite dissolution progressively decreased and was superceded by steady state dissolution of silicates principally biotite mass balance calculations indicate that most calcite had been removed during this time and accounted for 57 98 of the total ca released from these rocks experimental effluents from surfically weathered granitoids from the same watersheds were consistently dominated by silicate dissolution the lack of excess ca and alkalinity indicated that calcite had been previously removed by natural weathering the extent of ca enrichment in watershed discharge fluxes corresponds to the amounts of calcite exposed in granitoid rocks high ca na ratios relative to plagioclase stoichiometries indicate excess ca in the yosemite loch vale and other alpine watersheds in the sierra nevada and rocky mountains of the western united states this ca enrichment correlates with strong preferential weathering of calcite relative to plagioclase in exfoliated granitoids in glaciated terrains in contrast ca na flux ratios are comparable to or less than the ca na ratios for plagioclase in the subtropical panola and tropical rio icacos watersheds in which deeply weathered regoliths exhibit concurrent losses of calcite and much larger masses of plagioclase during transport limited weathering these results indicate that the weathering of accessory calcite may strongly influence ca and alkalinity fluxes from silicate rocks during and following periods of glaciation and tectonism but is much less important for older stable geomorphic surfaces

thermogenic gas hydrates and hydrocarbon gases in complex chemosynthetic communities gulf of mexico continental slope abstract where abundant at the sea floor thermogenic gas hydrates impact bacterially mediated processes in chemosynthetic communities dependent on methane and h2s our main gas hydrate sites are at 540 m water depth and relatively low temperature 7 c gas hydrates outcrop as vein fillings in hemipelagic muds near gas vents within chemosynthetic communities molecular and isotopic properties of hydrate forming c1 c5 hydrocarbons and co2 provide insight to bacterially mediated processes hydrate bound methane is altered by bacterial oxidation as indicated by enrichment of 13c and deuterium d and by co2 depleted in 13c the degree of gas hydrate alteration appears related to duration of exposure at the sea floor in hydrate associated sediments bacterial oxidation of a mixed pool of hydrocarbons yields a net production of co2 depleted in 13c bacterial oxidation of hydrate bound methane and free hydrocarbon gases in adjacent sediments could contribute to gas hydrate decomposition some thermogenic carbon in sediments could be recycled via methanogenesis to yield a net production of bacterial methane depleted in 13c our results strengthen the hypothesis that gas hydrates could favor life in other extreme environments at low temperatures

climatic and lithologic controls on the temporal and spatial variability of co2 consumption via chemical weathering an example from the australian victorian alps abstract a detailed geochemical study on river waters of the australian victorian alps was carried out to determine i the relative significance of silicate carbonate evaporite and sulfide weathering in controlling the major ion composition and ii the factors regulating seasonal and spatial variations of co2 consumption via silicate weathering in the catchments major ion chemistry implies that solutes are largely derived from evaporation of precipitation and chemical weathering of carbonate and silicate lithologies the input of solutes from rock weathering was determined by calculating the contribution of halite dissolution and atmospheric inputs using local rain and snow samples despite the lack of carbonate outcrops in the study area and waters being undersaturated with respect to calcite the dissolution of vein calcite accounts for up to 67 of the total dissolved cations generating up to 90 of dissolved ca and 97 of mg dissolved sulfate has 34s values of 16 to 20 cdt indicating that it is derived predominantly from atmospheric deposition and minor gypsum weathering and not from bacterial reduction of fes2 this militates against sulphuric acid weathering in victorian rivers ratios of si vs the atmospheric corrected na and k concentrations range from 1 1 to 4 3 suggesting incongruent weathering from plagioclase to smectite kaolinite and gibbsite estimated long term average co2 fluxes from silicate weathering range from 0 012 106 to 0 039 106 mol km2 yr with the highest values in rivers draining the basement outcrops rather than sedimentary rocks this is about one order of magnitude below the global average which is due to low relief and the arid climate in that region time series measurements show that exposure to lithology high physical erosion and long water rock contact times dominate co2 consumption fluxes via silicate weathering while variations in water temperature are not overriding parameters controlling chemical weathering because the atmospheric corrected concentrations of na k and mg act non conservative in victorian rivers the parameterizations of weathering processes and net co2 consumption rates in particular based on major ion abundances should be treated with skepticism

3 d basin scale reconstruction of natural gas hydrate system of the green canyon gulf of mexico our study presents a basin scale 3d modeling solution quantifying and exploring gas hydrate accumulations in the marine environment around the green canyon gc955 area gulf of mexico it is the first modeling study that considers the full complexity of gas hydrate formation in a natural geological system overall it comprises a comprehensive basin re construction accounting for depositional and transient thermal history of the basin source rock maturation petroleum components generation expulsion and migration salt tectonics and associated multi stage fault development the resulting 3d gas hydrate distribution in the green canyon area is consistent with independent borehole observations an important mechanism identified in this study and leading to high gas hydrate saturation 80 vol at the base of the gas hydrate stability zone ghsz is the recycling of gas hydrate and free gas enhanced by high neogene sedimentation rates in the region our model predicts the rapid development of secondary intra salt mini basins situated on top of the allochthonous salt deposits which leads to significant sediment subsidence and an ensuing dislocation of the lower ghsz boundary consequently large amounts of gas hydrates located in the deepest parts of the basin dissociate and the released free methane gas migrates upwards to recharge the ghsz in total we have predicted the gas hydrate budget for the green canyon area that amounts to 3 256 mt of gas hydrate which is equivalent to 340 mt of carbon 7 x 1011 m3 of ch4 at stp conditions and consists mostly of biogenic hydrates

life at the edge of methane ice microbial cycling of carbon and sulfur in gulf of mexico gas hydrates the processes of methane oxidation and sulfate reduction were examined in subsamples of gas hydrate associated materials collected along the gulf of mexico continental slope standard radiotracer techniques were used to determine rates of microbial activity in different layers of the hydrate environment including outer sediment os interface sediment is worm burrow sediment wb interior hydrate in and a mixture of hydrate and sediment mix the anaerobic oxidation of methane aom and sulfate reduction sr were observed in all hydrate samples examined and the rates of these processes showed similar spatial trends between different hydrate layers highest rates of both aom and sr were observed at interface between the sediment and hydrate aom rates were about 3 11 nmol cm 3 day 1 in worm burrow and interface sediments as compared to 1 nmol cm 3 day 1 in other hydrate material types rates of sr ranged from 59 to 490 nmol cm 3 day 1 in worm burrow and interface sediments while rates in interior hydrate samples were an order of magnitude lower these rates observed in hydrate materials are lower than rates from nearby methane rich sediments at ambient temperatures nevertheless our data show that active microbial populations inhabit all layers of the hydrate environment and suggest their activity may impact biogeochemical methane and sulfur cycling in this unique niche d 2004 elsevier b v all rights reserved

the origin of thermogenic gas hydrates on the northern cascadia margin as inferred from isotopic 13c 12c and d h and molecular composition of hydrate and vent gas the isotopic 13c and d and hydrocarbon compositions of hydrate bound and vent gas collected from the seafloor of barkley canyon northern cascadia margin offshore vancouver island canada were evaluated to characterize the gas and infer the type and maturity of the source rock kerogen the hydrate gas contained methane having 13c values from 43 4 to 42 6 d values from 143 to 138 and a large percentage 14 9 to 31 9 of c2 to c5 hydrocarbons these data are consistent with a thermogenic gas source the data from barkley canyon are interpreted within the context of similar data from the gulf of mexico and caspian sea thermogenic hydrates which occur in regions where the petroleum systems supporting gas and oil generation are better understood a stable carbon isotope based natural gas plot model and d h data from the hydrate gas indicate that the source rock for the barkley canyon hydrate and vent gas had primarily type iii kerogen mixed with a small fraction of type ii kerogen oil from a seep having a pristane phytane ratio of 3 2 was identified as a gas condensate which supports the conclusions drawn from the gas data a mechanism for explaining how fluids are conducted from the deep petroleum reservoir to the seafloor of barkley canyon is proposed

in situ raman detection of gas hydrates exposed on the seafloor of the south china sea gas hydrates are usually buried in sediments here we report the first discovery of gas hydrates exposed on the seafloor of the south china sea the in situ chemical compositions and cage structures of these hydrates were measured at the depth of 1 130 m below sea level using a raman insertion probe rip gh that was carried and controlled by a remotely operated vehicle rov faxian this in situ analytical technique can avoid the physical and chemical changes associated with the transport of samples from the deep sea to the surface natural gas hydrate samples were analyzed at two sites the in situ spectra suggest that the newly formed hydrate was structure i but contains a small amount of c3h8 and h2s pure gas spectra of ch4 c3h8 and h2s were also observed at the scs sgh02 site these data represent the first in situ proof that free gas can be trapped within the hydrate fabric during rapid hydrate formation we provide the first in situ confirmation of the hydrate growth model for the early stages of formation of crystalline hydrates in a methane rich seafloor environment our work demonstrates that natural hydrate deposits particularly those in the early stages of formation are not monolithic single structures but instead exhibit significant small scale heterogeneities due to inclusions of free gas and the surrounding seawater there inclusions also serve as indicators of the likely hydrate formation mechanism these data also reinforce the importance of correlating visual and in situ measurements when characterizing a sampling site

chemical weathering and associated co2 consumption in the mahanadi river basin india abstract chemical weathering of continents is one of the major geochemical processes which consumes atmospheric co2 and exerts a strong impact on the global climate the major ion chemistry of the mahanadi river basin one of the largest river basins in india is determined to investigate the sources of major ions and their spatio temporal variability chemical weathering rates and associated co2 consumption in the basin the results reveal that the ions in the basin are dominated by ca and hco3 the total dissolved solids 215 mg l 1 in monsoon and 270 mg l 1 in pre monsoon and total cation concentration 2367 eq in monsoon and 3214 eq in pre monsoon in the basin are relatively higher than the global average the dissolved loads in the basin are dominantly controlled by rock weathering particularly chemical weathering of silicates and carbonates the estimated chemical weathering rates based on the forward model are 44 94 t km 2 yr 1 in monsoon and 2 45 t km 2 yr 1 in pre monsoon with annual average chemical weathering rate of 23 7 t km 2 yr 1 the contribution of silicate weathering rates in the basin is 32 and 1 55 t km 2 y 1 during monsoon and pre monsoon period respectively the estimated co2 consumption rate associated with chemical weathering in the basin is 13 3 105 mol km 2 yr 1 during monsoon and 0 66 105 mol km 2 yr 1 during pre monsoon period with an average annual rate of 6 9 105 mol km 2 yr 1 which is higher than the global average the net rate of co2 consumption by silicate weathering is estimated to be approximately 4 78 105 mol km 2 yr 1 it is observed that the runoff and lithology are the major factors influencing chemical weathering in the basin however the basin elevation has a good negative correlation with chemical weathering rate

geochemical and palaeohydrological controls on the composition of shallow groundwater in the netherlands with the exception of the south of the country the netherlands has a strong bipartite hydrogeology the holocene part with a coastal dune belt and confining top layer of clay and peat further inland and the pleistocene where thick phreatic aquifers dominate this research aimed to ascertain the geochemical and palaeohydrological controls on the composition of shallow groundwater in 27 regions close to 6000 groundwater analyses were grouped and interpreted in terms of 1 salinity 2 redox status 3 acid base and carbonate status and 4 natural nutrients nh4 and po4 the a priori classification into geographical regions and geological formations revealed many statistically significant differences in medians even for geologically or geographically related data groups the compound specific interpretation indicates that there are geogenically controlled systematic differences in groundwater composition at the regional scale the imprint of the geological sediments on the groundwater composition decreases in the order marine estuarine via limnological fluvial to aeolian the imprints with respect to ph and carbonate status natural nutrients and redox status are not necessarily interrelated the vertical stratification in groundwater composition turns out to be often limited at the regional scale due to mutual occurrence of infiltrating and exfiltrating groundwater in regions and either the presence of a highly reactive holocene confining top layer or temporal changes in contamination in the holocene part the salinity is controlled by the palaeoenvironmental conditions during the holocene and by the recharge origin the average cl concentration decreases from estuarine via lagoonal to the former zuider sea which was a bay the most reduced states and also the highest nutrient concentrations and highest co2 pressure are related to the presence of holocene marine sediments in the confining top layer degradation of marine derived organic matter as a nutrient source is likely more intense in the holocene deposits than that of peat and sedimentary remnants of terrestrial plants a broad range in ph carbonate status and redox status is encountered in the pleistocene part here the palaeohydrological evolution in terms of carbonate leaching together with the geological controls on the calcareous nature of the shallow sedimentary deposits cause regional differences in ph calcite saturation and silicate weathering one region with late pleistocene limnological deposits has deviating groundwater characteristics and appears more similar to the holocene part of the netherlands furthermore reactive fe is not abundant in all pleistocene fluvial sediments nor is it maximally mobilised as not all anoxic groundwater in these sediments is siderite saturated this leads to considerable intra and inter region variability 2013 elsevier ltd

exclusion of 2 methylbutane isopentane during crystallization of structure ii gas hydrate in sea floor sediment gulf of mexico structure ii gas hydrate is abundant across the central gulf of mexico continental slope sediment that directly overlies nodular gas hydrate was collected with a piston core at1920 m water depth in the atwater valley at 425 area of the lower continental slope the gas hydrate has c1 c5 molecular and isotopic properties consistent with structure ii gas hydrate that crystallized from relatively unaltered thermogenic vent gas the gas hydrate contains mainly methane ethane propane and butanes with 2 methylbutane isopentane as a minor component 0 2 sediment that closely overlies the gas hydrate within 1 m is characterized by an anomalous abundance of 2methylbutane as much as 9 6 because the molecular diameter of 2 methylbutane is too large for structure ii gas hydrate the 2 methylbutane appears to accumulate preferentially in adjacent sediment as a direct consequence of massive gas hydrate crystallization the 2 methylbutane is interpreted to be a molecular marker of recent or ongoing net accumulation of structure ii gas hydrate abundant 2 methylbutane in sediment also could be a precursor to the natural occurrence of structure h gas hydrate and other new gas hydrate structures not yet discovered in the geologic environment 2000 elsevier science ltd all rights reserved

bacterial methane oxidation in sea floor gas hydrate significance to life in extreme environments samples of thermogenic hydrocarbon gases from vents and gas hydrate mounds within a sea floor chemosynthetic community on the gulf of mexico continental slope at about 540 m depth were collected by research submersible the study area is characterized by low water temperature mean 7 c high pressure about 5 400 kpa and abundant structure ii gas hydrate bacterial oxidation of hydrate bound methane ch sub 4 is indicated by three isotopic properties of gas hydrate samples relative to the vent gas from which the gas hydrate formed 1 methane bound methane is enriched in sup 13 c by as much as 3 8 pdb peedee belemnite 2 hydrate bound methane is enriched in deuterium d by as much as 37 smow standard mean ocean water and 3 hydrate bound carbon dioxide co sub 2 is depleted in sup 13 c by as much as 22 4 pdb hydrate associated authigenic carbonate rock is also depleted in sup 13 c bacterial oxidation of methane is a driving force in chemosynthetic communities and in the concomitant precipitation of authigenic carbonate rock that modifies sea floor geology bacterial oxidation of hydrate bound methane expands the potential boundaries of life in extreme environments

seasonal variations of water quality in a highly populated drainage basin se brazil water chemistry assessment and geochemical modeling approaches the sao joao drainage basin is a very important and strategic waterbody located in the lagos region rio de janeiro state one of the most popular tourist regions of brazil however the fast economic and subsequent population growth in that region has created untreated wastes from several anthropogenic activities which include the trace metals disposal into the surface waterbody this study aims to relate the major ions and trace metals behavior during a 1 year sampling campaign and to provide information about the sources of chemical constituents and the factors that control their concentrations in the three main fluvial compartments of the drainage basin including the juturnaiba reservoir which has a crucial role for water supply in the lagos region the chemical data reveal that rainfall is the main factor responsible for the physicochemical parameters and the water dissolved constituent s variations the geological and anthropogenic factors which are the main sources of water constituents were assessed by the inorganic chemical index those data corroborate the great influence of rainfall and reveal the importance of anthropogenic sources of chemical constituents in some parts of the juturnaiba reservoir the geochemical modeling suggests that hydrolysis reactions are primarily responsible for the trace metals availability in the three fluvial compartments in both dry and wet seasons followed by carbonate and sulfate complexation

pile driveability in low to medium density chalk pile driving in low to medium density chalk is subject to significant uncertainty predictions of chalk resistance to driving crd often vary considerably from field driving behaviour with both p