stable isotope compositions of serpentinite seamounts in the mariana forearc serpentinization processes fluid sources and sulfur metasomatism the mariana and izu bonin arcs in the western pacific are characterized by serpentinite seamounts in the forearc that provide unique windows into the mantle wedge we present stable isotope o h s and c data for serpentinites from conical seamount in the mariana forearc and s isotope data for torishima seamount in the izu bonin forearc in order to understand the compositions of fluids and temperatures of serpentinization in the mantle wedge and to investigate the transport of sulfur from the slab to the mantle wedge six serpentine mineral separates have a restricted range of 18o 6 5 8 5 antigorite separates have d values of 29 5 to 45 5 that reflect serpentinization within the mantle wedge whereas chrysotile has low d values 51 8 to 84 0 as the result of re equilibration with fluids at low temperatures fractionation of oxygen isotopes between serpentine and magnetite indicate serpentinization temperatures of 300 375 c two late cross fiber chrysotile veins have higher 18o values of 8 9 to 10 8 and formed at lower temperatures as low as 100 c aqueous fluids in equilibrium with serpentine at 300 375 c had 18o 6 5 9 and d 4 to 26 consistent with sediment dehydration reactions at temperatures 200 c in the subducting slab rather than a basaltic slab source three aragonite veins in metabasalt and siltstone clasts within the serpentinite flows have 18o 16 7 24 5 consistent with the serpentinizing fluids at temperatures 250 c 13c values of 0 1 2 5 suggest a source in subducting carbonate sediments the 34s values of sulfide in serpentinites on conical seamount 6 7 to 9 8 result from metasomatism through variable reduction of aqueous sulfate 34s 14 derived from slab sediments despite sulfur metasomatism serpentinites have low sulfur contents generally 164 ppm that reflect the highly depleted nature of the mantle wedge the serpentinites are mostly enriched in 34s median 34ssulfide 4 5 consistent with a 34s enriched mantle wedge as inferred from arc lavas

planetary scale variability in the low latitude e region field aligned irregularities first results from gadanki observations 1 in this paper we present for the first time planetary scale wave signatures in the low latitude e region field aligned irregularities fai observed during june 2004 to may 2005 using the gadanki mesosphere stratosphere troposphere radar we have observed a clear signature of 5 8 day variability in echo occurrence in snr and also in doppler velocity observed above 100 km concurrent temperature observations made using the sounding of the atmosphere using broadband emission radiometry saber on board the thermosphere ionosphere mesosphere energetic and dynamics timed satellite have also clearly shown the presence of 5 8 day variability similar to that of fai the temperature variations have been characterized with zonal wave numbers of 3 and 4 and vertical wavelength of 15 20 km these waves are found to have increasing amplitude with increasing height and phase progressing downward suggesting that they were of lower atmospheric origin it is emphasized that the planetary scale characteristics of neutral atmosphere in the fai observations are important in understanding the vertical coupling of the low latitude ionosphere atmosphere system these observations and the pertinent issues are discussed in the light of current understanding of the planetary scale role on the fai variability

a review and synthesis of glendonites pseudomorphs after ikaite with new data assessing applicability as recorders of ancient coldwater conditions abstract calcite pseudomorphs after ikaite glendonite are associated with coldwater depositional systems including glaciomarine and deepwater settings as dictated by the limited stability field of ikaite ikaite precipitation is favored by elevated alkalinity and dissolved phosphate conditions encountered commonly in association with organic rich marine sediments where methane oxidation is occurring the rapid recrystallization of ikaite to calcite during slight warming or pressure release results in considerable solid volume loss producing a highly porous crystal mesh preservation of the original ikaite crystal form requires precipitation of diagenetic calcite cement during early burial to prevent compaction and collapse of pseudomorph structures during later burial diagenesis remaining pore space may be filled with deeper burial calcite cement glendonites from the permian of the sydney basin occur in subtidal shelf facies containing glacial dropstones and a normal marine fauna stable oxygen isotope signatures of modern ikaite suggest carbonate precipitation in equilibrium with ambient seawater carbon signatures are usually strongly negative relative to normal marine carbonate consistent with derivation of carbonate from methane oxidation review of published data suggests that while holocene glendonite may provide reliable isotopic records of the conditions of ikaite precipitation precipitation of later calcite cement within the glendonite structure reduces the significance of the isotopic signature as an indicator of primary depositional conditions bulk glendonite samples from the permian sydney basin australia have a broad range of 18 o and 13c 18opdb 5 to 15 13c 8 to 16 in contrast to the narrow range for brachiopod carbonate 18opdb 1 to 5 13c 5 to 7 from the same strata handpicked separates of primary glendonite and secondary calcite also have a wide range of stable isotope values the data from sydney basin glendonites indicate that diagenetic precipitation of calcite has blurred the isotopic signature of primary ikaite replacement calcite at the scale of micosampling done in this study

initial indications of abiotic formation of hydrocarbons in the rainbow ultramafic hydrothermal system mid atlantic ridge in the presence of water olivine of ultramafic rock is oxidized during the process referred to as serpentinization water in contact with the olivine is reduced to molecular hydrogen h2 with the concomitant oxidation of fe ii the molecular hydrogen formed may be used as an energy source by lithotrophic bacteria but may at high temperature also be combined with co2 for the abiotic formation of organic compounds such as hydrocarbons and fatty acids through fischer tropsch type ftt synthesis our analyses of fluids from the peridotite hosted rainbow hydrothermal field on the mid atlantic ridge indicate de novo synthesis of linear saturated hydrocarbons the chain length of the hydrocarbons is between 16 and 29 carbon atoms the discovery of ftt reactions in ultramafic hydrothermal systems on earth provides an alternative pathway for the formation of early membranes and the origin of life

on the linkage of mesospheric planetary waves with those of the lower atmosphere and ionosphere a case study from indian low latitudes 1 in this paper we study the planetary scale wave features using concurrent observations of mesospheric wind and temperature ionospherich f and tropospheric wind from tirunelveli gadanki and kolhapur all located in the indian low latitudes made during february 2009 our investigations reveal that 3 to 5 day periodicity characterized as ultrafast kelvin ufk waves was persistent throughout the atmosphere during this period these waves show clear signatures of upward wave propagation from troposphere to the upper mesosphere linking the ionosphere through a clear correlation between mesospheric winds and h f variations we also note that the amplitude of this wave decreased as we moved away from the equator these results are the first of their kind from indian sector portraying the vertical as well as latitudinal characteristics of the 3 to 5 day ufk waves simultaneously from the troposphere to the ionosphere

serpentinization and heat generation constraints from lost city and rainbow hydrothermal systems abstract the discovery of ultramafic hosted hydrothermal systems at rainbow 36 n mar and lost city a vent site approximately 15 km west of the mar at 30 n provides unique perspectives on chemical and heat generating processes associated with serpentinization at a range of chemical and physical conditions heat balance calculations together with constraints imposed by geochemical modeling indicate that significant changes in temperature are not likely to occur at either vent system as a result of the exothermic nature of olivine hydrolysis at rainbow the relatively high temperatures in subseafloor reaction zones in excess of 400 c which must be linked to magmatic processes inhibit olivine hydrolysis effectively precluding mineralization induced heating effects geochemical modeling of the lost city vent fluids indicates temperatures in excess of those measured 40 75 c the relatively high subseafloor temperatures 200 50 c requires conductive cooling of the fluids on ascent to the seafloor a scenario in keeping with the mineralization of chimney structures actually observed although the intermediate temperatures predicted for subseafloor reaction zones at lost city could be expected to enhance olivine to serpentine conversion dissolved cl k cl and na cl ratios of the lost city vent fluids are virtually unchanged from seawater values and indicate little hydration of olivine which is a necessary condition for exothermic heat generation by serpentinization apparently the fluid rock mass ratio is too high or fluid residence times too low for this to occur to any significant extent thus in spite of the off axis location of the lost city vents and apparent lack of a localized heat source mineralization reactions likely play an insignificant role in accounting for hydrothermal circulation it is more likely that tectonic processes associated with the slow spreading mar permit access of seawater to relatively deep and still hot lithospheric units and or near axis magmatic heat sources before venting additional chemical and physical temperature flow rate data for lost city and similar hydrothermal systems are needed to test key elements of the proposed model

u th stratigraphy of a cold seep carbonate crust on continental margins oxidation of methane rich fluids from the sediment often leads to formation of authigenic carbonate pavements on the seafloor the biogeochemical processes involved during this carbonate precipitation are increasingly understood but little is known about the duration or mode of carbonate crust formation here we report uranium and thorium concentrations and isotope compositions for a set of 14 samples drilled across an authigenic carbonate pavement which provide the first stratigraphy for a cold seep carbonate crust the 5 5 cm thick crust nl7 cc2 was collected by submersible on the nile deep sea fan in an area of active fluid venting u th analyses must be corrected for initial th and measurement of co existing sediments indicates the presence of both scavenged and detrital initial 230th which must be considered during this correction the calculated 230th u age depth profile for nl7 cc2 provides evidence for continuous downward carbonate precipitation at the studied location over the last 5000 years three distinct phases can be distinguished from top to bottom with average growth rates of 0 4 5 and 0 8 cm kyr respectively corresponding to carbonate precipitation rates ranging from 7 to 92 mol m2 h 1 rates consistent with previous estimates high resolution 13c profiles gontharet s pierre c blanc valleron m m rouchy j m fouquet y bayon g foucher j p woodside j mascle j the nautinil scientific party 2007 nature and origin of diagenetic carbonate crusts and concretions from mud volcanoes and pockmarks of the nile deep sea fan eastern mediterranean sea deep sea res ii 54 1292 1311 and major elements across nl7 cc2 show that the variations in carbonate precipitation rates were also accompanied by changes in carbonate mineralogy and fluid composition we suggest that these changes primarily reflect modification of the diagenetic environment i e a progressive depletion of dissolved sulphate through anaerobic oxidation of methane caused by the initial carbonate crust formation and the resulting reduction in bioirrigation overall u th dating of cold seep carbonates offers a promising tool to bring new insights into biogeochemical processes at cold seeps and to assess the timing and duration of fluid venting on continental margins

one to two month oscillations observed high latitude tropospheric and stratospheric response to tropical forcing abstract careful spectral correlation and coherence analyses of low frequency fluctuations in global geopotential height data are presented attention is paid to proper statistical assessments the main points are 1 one to two month oscillating quasi stationary wavetrains have recently been reported in the extratropical southern hemisphere troposphere as far south as the edge of antarctica however only weak correlations were observed with the supposed tropical forcing region leading to the question of whether the wavetrain is a response to tropical forcing or possibly due to in situ instabilities on 1 2 month time scales the present paper clears up this enigma with analyses of other tropical datasets which reveal clear correlation between low latitude source regions and the sh extratropical troposphere 2 an earlier investigation found strong correlations between 1 2 month oscillations in the upper stratosphere and tropical troposphere yet no vertical propagation was found directly above the tro

geochemistry of reduced gas related to serpentinization of the zambales ophiolite philippines abstract methane hydrogen gas seeps with mantle like c and noble gas isotopic characteristics issue from partially serpentinized ultramafic rocks in the zambales ophiolite philippines new measurements of noble gas and 14c isotope abundances rock mixed volatile equilibrium calculations and previous chemical and isotopic data suggest that these reduced gases are products of periodotite hydration the gas seeps are produced in rock dominated zones of serpentinization and similar gases may be ubiquitous in ultramafic terranes undergoing serpentinization

a serpentinite hosted ecosystem in the southern mariana forearc several varieties of seafloor hydrothermal vents with widely varying fluid compositions and temperatures and vent communities occur in different tectonic settings the discovery of the lost city hydrothermal field in the mid atlantic ridge has stimulated interest in the role of serpentinization of peridotite in generating h2 and ch4 rich fluids and associated carbonate chimneys as well as in the biological communities supported in highly reduced alkaline environments abundant vesicomyid clam communities associated with a serpentinite hosted hydrothermal vent system in the southern mariana forearc were discovered during a dsv shinkai 6500 dive in september 2010 we named this system the shinkai seep field ssf the ssf appears to be a serpentinite hosted ecosystem within a forearc convergent margin setting that is supported by fault controlled fluid pathways connected to the decollement of the subducting slab the discovery of the ssf supports the prediction that serpentinite hosted vents may be widespread on the ocean floor the discovery further indicates that these serpentinite hosted low temperature fluid vents can sustain high biomass communities and has implications for the chemical budget of the oceans and the distribution of abyssal chemosynthetic life

signatures of the 3 day wave in the low latitude and midlatitude ionosphere during the january 2010 ursi world day campaign 1 recent studies of the equatorial ionosphere have found evidence of forcing by atmospheric ultra fast kelvin ufk waves this study investigates the quasi 3 day ufk wave and its effects on the variations of the ionosphere at low latitudes and midlatitudes using coordinated observations of both the atmosphere and ionosphere during the january 2010 ursi world day campaign the global maps of tec from the igs ground based gps product demonstrate a 3 day periodic variation during january 15 25 this variation has the largest amplitude at 15 magnetic latitude and extends into lower latitudes simultaneously a 3 day wave is observed in the mesosphere in the zonal wind measurements by a meteor radar at the magnetic equator the latitudinal range of the tec variation 20 s 20 n is also consistent with that of the 3 day wave the incoherent scatter radar isr observations show a 3 day signature in vertical ion drifts over jicamarca 11 9 s 76 w and in the electron densities in the top side of ionosphere measured from millstone hill 42 6 n 71 5 w this signature is consistent with the fountain effect in the equatorial region and shows the impact on the topside ionosphere at midlatitudes the ufk wave is trapped within 30 geographic latitude but this study shows that the effects of the wave could reach the ionosphere at the higher latitude even as high as 40 n 50 n magnetic latitude

30 000 years of hydrothermal activity at the lost city vent field strontium carbon and oxygen isotope data and radiocarbon ages document at least 30 000 years of hydrothermal activity driven by serpentinization reactions at lost city serpentinization beneath this off axis field is estimated to occur at a minimum rate of 1 2 10 4 cubic kilometers per year the access of seawater to relatively cool fresh peridotite coupled with faulting volumetric expansion and mass wasting processes are crucial to sustain such systems the amount of heat produced by serpentinization of peridotite massifs typical of slow and ultraslow spreading environments has the potential to drive lost city type systems for hundreds of thousands possibly millions of years

evidence from fluid seeps atop serpentine seamounts in the mariana forearc clues for emplacement of the seamounts and their relationship to forearc tectonics abstract the mariana forearc is a non accretionary forearc with numerous seamounts dredge hauls from these seamounts are composed primarily of serpentinite indicating a non volcanic origin in addition dredged carbonate samples reveal 1 the presence of aragonite in water depths greater than the aragonite compensation depth 2 unusual porosity and cement types 3 light carbon and heavy oxygen isotopic compositions and 4 an unusual trace element geochemistry of aragonite and calcite these mineralogic petrologic and geochemical characteristics formed the basis of a prediction that methane bearing fluids are venting from these seamounts subsequent to this prediction submersible dives on a mariana forearc seamount found and sampled chimneys seeping cool water that contains dissolved methane the serpentine substrate beneath the chimneys appears to form from cold gravitational flows of serpentine material fluid inclusion contents of chimney samples also show an earlier history of methane as well as longer chain hydrocarbons aromatics and acetate ions drilling into the flank and the summit of this seamount by the ocean drilling program during leg 125 confirmed the presence of methane other light alkanes and organic acids in the present day interstitial pore fluid of the cores the presence of aromatic compounds and organic acids if derived from the maturation of organic compounds indicates a thermogenic origin for these volatiles strontium isotopic ratios of the aragonitic chimney samples and of the present day interstitial waters range from present day seawater values to significantly lower values the strontium isotopic ratios of the pore waters within the seamount trend toward a relatively less radiogenic composition with increasing depth below the seafloor this strontium isotopic signature is probably not the consequence of near surface processes but more likely a contribution from an igneous source deeper in the lithosphere the lack of a large accretionary prism in the mariana forearc removes the complication of fluid contribution from dewatering of the prism by compression during convergence as in the oregon washington or barbados margins the organic compounds in the fluid inclusions and interstitial pore fluids as well as the isotopic and the geochemical composition of the carbonates and the dissolved constituents suggest that fluids are derived from dewatering compression and dehydration of subducted sediments and the subducting plate furthermore the composition of the fluid is influenced by thermal maturation of organics in subducted sediments as well as by a contribution from a deep igneous source

u and th concentrations and isotope ratios in modern carbonates and waters from the bahamas the short residence times of th and pa in seawater make them very responsive to changes in the ocean environment we use a new multi ion counting technique to make th and pa isotope measurements in seawaters from a near shore environment in which oceanic chemical tracers are not overwhelmed by terrestrial inputs the bahamas an unusual feature of the bahamas setting is the shallow depth of water residing on the bank tops these waters have significantly lower 232th 230th 10 000 than those immediately adjacent to the banks 24 000 31 000 and a 231pa 230th near the production ratio 0 1 the change in 232th 230th and 231pa 230th on the bank tops is explained by almost quantitative removal of th and pa by scavenging and their replacement with a mixture of 230th and 231pa alpha recoiled from the underlying carbonates together with th from dust dissolution analysis of a water profile in the tongue of the ocean which separates the great and little bahama banks allows us to trace the movement of bank top water to depth a distinct minimum in both 232th 230th 13 000 and 231pa 230th 0 5 is observed at 430 m and is interpreted to reflect density cascading of bank top water with entrained carbonate sediment these results suggest that th and pa can be used as water mass tracers in near shore environments uranium concentration measurements on the same waters demonstrate that u is conservative across a range in salinity of 2 psu with a concentration of 3 33 ppb at a salinity of 35 the incorporation of u and th isotopes into marine carbonates has also been assessed by analyzing carbonate samples from the same location as these bahamas waters such incorporation is critical for u th geochronology u isotope analyses demonstrate that seawater 234u averages 146 6 and does not vary by more than 2 5 o and that carbonates capture this value additional high precision measurements 1 o on modern carbonates confirm that all oceans have identical 234u modern marine carbonates are shown to have 232th 230th ratios that reflect the local seawater in which they formed

u th systematics and 230th ages of carbonate chimneys at the lost city hydrothermal field the lost city hydrothermal field lchf is a serpentinite hosted vent field located 15 km west of the spreading axis of the mid atlantic ridge in this study uranium thorium u th geochronological techniques have been used to examine the u th systematics of hydrothermal fluids and the 230th ages of hydrothermally precipitated carbonate chimneys at the lchf fluid sample analyses indicate that endmember fluids likely contain only 0 0073 ng g u or less compared to 3 28 0 03 ng g of u in ambient seawater for fluid samples containing only 2 21 ambient seawater 1 1 11 mmol kg mg th concentration is 0 11 0 13 pg g and surrounding seawater concentrations average 0 133 0 016 pg g the 230th 232th atomic ratios of the vent fluids range from 1 10 10 6 to 11 5 10 6 are less than those of seawater and indicate that the vent fluids may contribute a minor amount of non radiogenic 230th to the lchf carbonate chimney deposits chimney 238u concentrations range from 1 to 10 g g and the average chimney corrected initial 234u is 147 2 0 8 which is not significantly different from the ambient seawater value of 146 5 0 6 carbonate 232th concentrations range broadly from 0 0038 0 0003 to 125 16 ng g and 230th 232th atomic ratios vary from near seawater values of 43 8 10 6 up to 530 25 10 3 chimney ages corrected for initial 230th range from 17 6 yrs to 120 13 kyrs the youngest chimneys are at the intersection of two active steeply dipping normal faults that cut the atlantis massif the oldest chimneys are located in the southwest portion of the field vent deposits on a steep fault bounded wall on the east side of the field are all 4 kyrs old indicating that mass wasting in this region is relatively recent comparison of results to prior age dating investigations of submarine hydrothermal systems shows that the lchf is the most long lived hydrothermal system known to date it is likely that seismic activity and active faulting within the atlantis massif and the atlantis fracture zone coupled with volumetric expansion of the underlying serpentinized host rocks play major roles in sustaining hydrothermal activity at this site the longevity of venting at the lchf may have implications for ecological succession of microorganisms within serpentinite hosted vent environments

compressibility of sorptive porous media part 1 background and theory this paper the first of a two part series provides a sound background of the volumetric response of sorptive porous media to gas depletion under in situ boundary conditions in producing reservoirs as a first step the overall rock matrix deformation is split into two separate components elastic deformation caused by mechanical decompression and the nonelastic swelling or shrinkage strain induced by adsorption or desorption of gas the shrinkage or swelling compressibility is estimated by the first derivative of pure adsorption or desorption strain with variations of gas pressure the pore volume or fracture compressibility is then estimated by application of a semi empirical model under uniaxial strain conditions based on the proposed model both shrinkage or swelling and pore volume compressibilities show strong pressure dependence for sorbing gases and are thus variables for which gas production is controlled by desorption of gas in part 2 the experimental work under best replicated in situ conditions is described in detail along with the results obtained and application of the theory presented in this paper

fossil clams from a serpentinite hosted sedimented vent field near the active smoker complex rainbow mar 36 13 n insight into the biogeography of vent fauna hydrothermal circulation at ultramafic hosted sites supports a large variety of high and low temperature hydrothermal vents and associated ecosystems the discovery of abundant fossil vesicomyid and thyasirid shell accumulations at the ridge crest approximately 2 5 km east of the active rainbow vent field on the mid atlantic ridge mar 36 degrees 13 n increased our knowledge regarding the diversity of vent communities at slow spreading ridges bivalve molluscs of the family vesicomyidae were represented by the genus phreagena here we present the first record of this genus in the atlantic ocean this second vesicomyid species known from the mar phreagena sp was found to be associated with a thyasira species that is affiliated with t southwardae at the logatchev vent field on the mar and with t vulcolutre in the gulf of cadiz these two clams have close relationships with seep taxa along the continental margin and were likely associated with sedimented vent fields delta o 18 and delta c 13 analyses of the shells suggested that the burrowing bivalve thyasira could incorporate isotopically light carbon derived from the oxidation of methane in the sediment while the signature of phreagena sp shells denoted a different carbonate source c 14 dating of the shells denoted that the hydrothermal activity in the rainbow area began at least similar to 25 5 kyr bp which is similar to the model of the hydrothermal vent field distribution that was proposed for the logatchev hydrothermal site the results provide new insight regarding the diversity of chemosynthetic fauna on the mar over geologic time ultramafic hosted on axis sedimented vent fields extend the range of habitats for chemosynthetic communities underlying the need to further explore the geology of these types of environments on slow spreading ridges and to determine their role in the ecology of deep sea vent communities

large scale waves in the mesosphere and lower thermosphere observed by saber observations made by the sounding of the atmosphere using broadband emission radiometry saber instrument on board nasa s thermosphere ionosphere mesosphere energetics and dynamics timed satellite have been processed using salby s fast fourier synoptic mapping ffsm algorithm the mapped data provide a first synoptic look at the mean structure and traveling waves of the mesosphere and lower thermosphere mlt since the launch of the timed satellite in december 2001 the results show the presence of various wave modes in the mlt which reach largest amplitude above the mesopause and include kelvin and rossby gravity waves eastward propagating diurnal oscillations non sunsynchronous tides and a set of quasi normal modes associated with the so called 2 day wave the latter exhibits marked seasonal variability attaining large amplitudes during the solstices and all but disappearing at the equinoxes saber data also show a strong quasi stationary rossby wave signal throughout the middle atmosphere of the winter hemisphere the signal extends into the tropics and even into the summer hemisphere in the mlt suggesting ducting by westerly background zonal winds at certain times of the year the 5 day rossby normal mode and the 4 day wave associated with instability of the polar night jet are also prominent in saber data

seismic imaging of magma sills beneath an ultramafic hosted hydrothermal system hydrothermal circulation at mid ocean ridge volcanic segments extracts heat from crustal magma bodies however the heat source driving hydrothermal circulation in ultramafic outcrops where mantle rocks are exhumed in low magma supply environments has remained enigmatic here we use a three dimensional p wave velocity model derived from active source wide angle refraction reflection ocean bottom seismometer data and pre stack depth migrated images derived from multichannel seismic reflection data to investigate the internal structure of the rainbow ultramafic massif which is located in a non transform discontinuity of the mid atlantic ridge seismic imaging reveals that the ultramafic rocks composing the rainbow massif have been intruded by a large number of magmatic sills distributed throughout the massif at depths of 2 10 km these sills which appear to be at varying stages of crystallization can supply the heat needed to drive high temperature hydrothermal circulation and thus provide an explanation for the hydrothermal discharge observed in this ultramafic setting our results demonstrate that high temperature hydrothermal systems can be driven by heat from deep sourced magma even in exhumed ultramafic lithosphere with very low magma supply

sources and cycling of carbon in continental serpentinite hosted alkaline springs in the voltri massif italy abstract active serpentinization systems are abundant on present day earth and are of increasing interest because water rock reactions lead to alkaline ca oh fluids that have the potential to sequester co 2 and form reduced chemical species e g ch 4 and h 2 that can support chemolithoautotrophy we present a study of alkaline ph 10 12 springs in the voltri massif italy that focuses on the sources and cycling of inorganic carbon in the basement rocks the interacting fluids and the resulting surface carbonate deposits most springs are located in mantle rocks that underwent varying degrees of ocean floor serpentinization and incorporation of carbon as carbonate and organic carbon in the jurassic which is preserved during subsequent subduction and uplift onto the continent the springs are fed by meteoric water that evolves into alkaline ca rich spring waters that have 2 3 times higher ca concentrations than the adjacent rivers our study is consistent with previous reaction path modeling and identifies the formation of clay minerals in serpentinites that have been altered by alkaline fluids these strongly altered basement rocks contain up to 2 wt c in the shallow subsurface also documented by the presence of late calcite veins concentrations of dissolved inorganic carbon dic of the alkaline fluids are generally low 13 c dic is between 24 2 and 1 3 we argue that the concentrations and isotopic composition of the dic in the alkaline waters provide evidence for 1 the precipitation of calcium carbonate under closed system conditions with respect to atmospheric co 2 and 2 removal of dic by microbial activity in the subsurface late stage uptake of atmospheric co 2 in the shallow subsurface or at the exit sites subsequent to water rock microbe interactions in the basement result in fluids with lower ph and ca and enrichment in dic and 13 c at the surface interaction of the high ph ca oh fluids with atmospheric co 2 causes precipitation of carbonates as travertines or crusts on the basement rocks storing co 2 as calcium carbonate carbonate precipitation at the exit sites is strongly dominated by kinetic processes leading to carbon and oxygen isotope compositions as low as 27 2 and 18 7 respectively with increasing distance from the springs the 13 c and 18 o content of the carbonate increases and the fluid ph changes towards neutral our study shows that surficial carbonate precipitation plays a subordinate role in carbon sequestration but that the evolution from mg hco 3 spring waters to ca oh waters removes significant amounts of carbon presumably in the subsurface we calculate that the serpentinites have the capacity to sequester up to 0 50 to 2 05 10 9 mol carbon per year and conclude that they can take up significantly more co 2 than they currently contain

u th dating of marine isotope stage 7 in bahamas slope sediments in order to understand the driving forces for pleistocene climate change more fully we need to compare the timing of climate events with their possible forcing in contrast to the last interglacial marine isotope stage mis 5 the timing of the penultimate interglacial mis 7 is poorly constrained this study constrains its timing and structure by precise u th dating of high resolution n 18 o records from aragonite rich bahamian slope sediments of odp leg 166 sites 1008 and 1009 the major glacial interglacial cycles in n 18 o are distinct within these cores and some mis 7 substages can be identified these sediments are well suited for u th dating because they have uranium concentrations of up to 12 ppm and very low initial 230 th contributions with most samples showing 230 th 232 th activity ratio of s 75 u and th concentrations and isotope ratios were measured by thermal ionisation mass spectrometry and multiple collector inductively coupled plasma mass spectrometry with the latter providing dramatically better precision twenty nine of the 41 samples measured have a n 234 u value close to modern seawater suggesting that they have experienced little diagenesis ages from 27 of the 41 samples were deemed reliable on the basis of both their u and their th isotope ratios ages generally increase with depth although we see a repeated section of stratigraphy in one core extrapolation of constant sedimentation rate through each substage suggests that the peak of mis 7e lasted from v237 to 228 ka and that 7c began at 215 ka this timing is consistent with existing low precision radiometric dates from speleothem deposits the beginning of both these substages appears to be slightly later than in orbitally tuned timescales the end of mis 7 is complex but also appears to be somewhat later than is suggested by orbitally tuned timescales although this event is not particularly well defined in these cores fl 2002 elsevier science b v all rights reserved

low temperature volatile production at the lost city hydrothermal field evidence from a hydrogen stable isotope geothermometer although commonly utilized in continental geothermal work the water hydrogen and methane hydrogen isotope geothermometers have been neglected in hydrothermal studies here we report d ch4 and d h2 values from high temperature black smoker type hydrothermal vents and low temperature carbonate hosted samples from the recently discovered lost city hydrothermal field methane deuterium content is uniform across the dataset at 120 12 hydrogen d values vary from 420 to 330 at high temperature vents to 700 to 600 at lost city the application of several geothermometer equations to a suite of hydrothermal vent volatile samples reveals that predicted temperatures are similar to measured vent temperatures at high temperature vents and 20 60 c higher than those measured at the lost city vents we conclude that the overestimation of temperature at lost city reflects 1 that methane and hydrogen are produced by serpentinization at n110 c and 2 that isotopic equilibrium at temperatures b70 c is mediated by microbial sulfate reduction the successful application of hydrogen isotope geothermometers to low temperature lost city hydrothermal samples encourages its employment with lowtemperature diffuse hydrothermal fluids 2005 elsevier b v all rights reserved

microbial utilization of abiogenic carbon and hydrogen in a serpentinite hosted system abstract mantle rocks exposed on the seafloor constitute a highly reactive chemical and thermal system in which interaction with seawater to produce serpentinite has major consequences for lithospheric cooling global geochemical cycles and microbial activity serpentinite hosted hydrothermal activity is exemplified by the lost city hydrothermal field 30 n mid atlantic ridge where fluid rock reactions in the underlying ultramafic rocks result in high concentrations of abiotic hydrogen methane c 2 alkanes and formate such systems have been proposed as possible analogs to the early earth environments that gave rise to the first biochemical pathways thus characterizing the local microbial communities and their potential link with abiogenic compounds is of particular significance here we demonstrate that in active carbonate chimneys where microbial sulfate reduction is important up to 50 of the microbial biomass is synthesized from mantle carbon conversely mantle carbon contributes only 10 of the biomass in areas with minimal sulfate reduction we attribute this difference to greater incorporation of formate or methane by the dominant microbial species the lost city methanosarcinales in locations where sulfate reducers are able to facilitate this assimilation the ability of autotrophic communities at lost city to capitalize on the steady stream of chemical products resulting from serpentinization reactions and to utilize abiogenic mantle carbon lend credence to the hypothesis that early biosynthetic pathways could have developed in similar environments

the hydrothermal plumbing of a serpentinite hosted detachment evidence from the west iberia non volcanic rifted continental margin this study documents the critical role of structurally induced fluid flow during the evolution of the footwall succession to a major low angle normal detachment fault drilled by the ocean drilling program leg 173 site 1068 beneath the southern iberia abyssal plain the fault zone comprises carbonate altered rodingitized and albitized metabasite rich sedimentary breccias and serpentinized mantle peridotites the brittle infrastructure of the detachment consists of mineralized high dilation breccias and meshes of mineralized extensional and shear veins that root into chlorite and serpentine cataclasite and gouge the fault rocks are underlain by cohesive serpentinite that shows kernel textures indicative of volume expansion accompanying serpentinization of peridotite the texture is disrupted and offset by small scale fractures and faults the distribution of serpentine polytypes carbonates fe ni alloys sulfides oxides and other silicate phases varies across the fault zone in patterns consistent with mineralization and replacement from solutions derived from two end member components seawater and ch4 bearing calcium hydroxide enriched hydrothermal solutions the latter form when heated seawater reacts with peridotite to form serpentinite at low water to rock ratios serpentine mineral chemistries indicate that fracture controlled serpentinite recrystallization and replacement occurred at various fo2 asio2 and ca2 conditions in places this also involved mild prograde thermal events the serpentinite also hosts tochilinite valleriite group minerals and aragonite both are interpreted as indicators of sea water incursions into the upper reaches of the detachment to account for the evidence of coeval hydrothermal mineralization and displacements across the detachment we relate hydrothermal discharge to the buffering of high pore fluid pressures by fault slip localized sources of high fluid pressures at depth are attributed to serpentinization of peridotite around the fault that promotes changes to solution mass density exothermic reactions and swelling pressures sealing of the fault between the serpentinization front and the top of the detachment results from hydrothermal mineralization alteration and serpentine gouges hydrothermal discharges from the detachment accompanying shear failure allow for variable mixing between the hydrothermal solutions and seawater and post slip convective draw down of seawater into the detachment it is suggested that the latter may have been limited in duration by ongoing mineralization leading to the restoration of the fault seal concomitant serpentinization around the detachment at depth provides scope for cyclic hydrothermal discharges and fault slip

reduction of co2 during serpentinization of olivine at 300 c and 500 bar co 2 reduction processes occurring during experimental serpentinization of olivine at 300 c and 500 bar confirm that ultramafic rocks can play an important role in the generation of abiogenic hydrocarbon gas data reveal that conversion of fe ii in olivine to fe iii in magnetite during serpentinization leads to production of h 2 and conversion of dissolved co 2 to reduced c species including methane ethane propane and an amorphous carbonaceous phase hydrocarbon gases generated in the process fit a schulz flory distribution consistent with catalysis by mineral reactants or products magnetite is inferred to be the catalyst for methanization during serpentinization because it has been previously shown to accelerate fischer tropsch synthesis of methane in industrial applications involving mixtures of h 2 and co 2 the carbonaceous phase was predominantly aliphatic but had a significant aromatic component although this phase should ultimately be converted to hydrocarbon gases and graphite if full thermodynamic equilibrium were established its formation in these experiments indicates that the pathway for reduction of co 2 during serpentinization processes is complex and involves a series of metastable intermediates

brucite chimney formation and carbonate alteration at the shinkai seep field a serpentinite hosted vent system in the southern mariana forearc brucite carbonate chimneys were discovered from the deepest known 5700 m depth serpentinite hosted ecosystem the shinkai seep field ssf in the southern mariana forearc textural observations and geochemical analysis reveal three types i iii of chimneys formed by the precipitation and dissolution of constitutive minerals type i chimneys are bright white to light yellow have a spiky crystalline and wrinkled surface with microbial mat and contain more brucite these formed as a result of rapid precipitation under high fluid discharge conditions type ii chimneys exhibit white to dull brown coloration tuberous textures like vascular bundles and are covered with grayish microbial mats and dense colonies of phyllochaetopterus this type of chimney is characterized by inner brucite rich and outer carbonate rich zones and is thought to have precipitated from lower fluid discharge conditions than type i chimneys type iii chimneys are ivory colored have surface depressions and lack living microbial mats or animals this type of chimney mainly consists of carbonate and is in a dissolution stage stable carbon isotope compositions of carbonates in the two types i and ii of active chimneys are extremely 13c enriched up to 24 1 which may reflect biological 12c consumption under extremely low dissolved inorganic carbon concentration in alkaline fluid type iii chimneys have 13c compositions indicating re equilibration with seawater our findings demonstrate for the first time that carbonate chimneys can be form below carbonate compensation depth and provide new insights about linked geologic hydrologic and biological processes of the global deep sea serpentinite hosted vent systems this article is protected by copyright all rights reserved

authigenesis of carbonate minerals in modern and devonian ocean floor hard rocks abstract petrographic and stable isotope 13c 18o patterns of carbonates from the logatchev hydrothermal field lhf the gakkel ridge gr and a late devonian outcrop from the frankenwald germany were compared in an attempt to understand the genesis of carbonate minerals in marine volcanic rocks specifically were the carbonate samples from modern sea floor settings and the devonian analog of hydrothermal origin low temperature abiogenic origin as inferred for aragonite in serpentinites from elsewhere on the mid atlantic ridge or biogenic origin aragonite is the most abundant carbonate mineral in serpentinites from the two modern spreading ridges and occurs within massive sulfides of the lhf the precipitation and preservation of aragonite suggests high mg2 and sulfate concentrations in fluids values of 18opdb as high as 5 3 for serpentinite hosted aragonite and as high as 4 2 for sulfide hosted aragonite are consistent with precipitation from cold seawater most of the corresponding

fossil evidence for serpentinization fluids fueling chemosynthetic assemblages among the deep sea hydrothermal vent sites discovered in the past 30 years lost city on the mid atlantic ridge mar is remarkable both for its alkaline fluids derived from mantle rock serpentinization and the spectacular seafloor carbonate chimneys precipitated from these fluids despite high concentrations of reduced chemicals in the fluids this unique example of a serpentinite hosted hydrothermal system currently lacks chemosynthetic assemblages dominated by large animals typical of high temperature vent sites here we report abundant specimens of chemosymbiotic mussels associated with gastropods and chemosymbiotic clams in approximately 100 kyr old lost city like carbonates from the mar close to the rainbow site 36 n our finding shows that serpentinization related fluids unaffected by high temperature hydrothermal circulation can occur on axis and are able to sustain high biomass communities the widespread occurrence of seafloor ultramafic rocks linked to likely long range dispersion of vent species therefore offers considerably more ecospace for chemosynthetic fauna in the oceans than previously supposed

geochemistry of high h2 and ch4 vent fluids issuing from ultramafic rocks at the rainbow hydrothermal field 36 14 n mar the flores diving cruise was part of the mast iii amores 1995 1998 program funded by the european union one of the major achievements of the flores cruise was the discovery of the rainbow hydrothermal field hosted in ultramafic rocks south of the amar segment on the mid atlantic ridge mar the rainbow hydrothermal fluids exhibit temperatures of 365 c ph of 2 8 high chlorinity 750 mmol kg and low silica 6 9 mmol kg the uniformity in endmember major minor trace element concentrations and gas contents suggests that all rainbow fluids originate from the same deep source although h2s content is relatively low 1 20 mmol kg all vent fluids show extraordinary high h2 16 mmol kg ch4 2 5 mmol kg and co 5 mol kg endmember concentrations compared to fluids collected from other vent sites along the mar hydrogen represents more than 40 of the total gas volume extracted from the fluids at rainbow h2 production is likely associated with alteration of olivine and orthopyroxene minerals during serpentinization given that exposures of ultramafic rock may be common particularly along slow spreading ridges the production of h2 may have important implications for microbial activity at and beneath the seafloor

non equilibrium fractionation of stable carbon isotopes in chemosynthetic mussels abstract chemosynthetic bivalves from deep sea hydrothermal vents exploit the energy derived from chemical compounds such as methane sulfide or hydrogen using symbiotic bacteria that are able to fix inorganic carbon available chemical resources in their habitat vary widely at various scales from the vent field scale to the micro habitat scale parallel to this environmental heterogeneity bathymodiolus species are considered to be flexible in their energy acquisition pathways the goal of this study was to determine whether the isotopic compositions archived in the shells of hydrothermal vent mussels could trace chemical energy sources and their variability over spatial and temporal scales two different species bathymodiolus azoricus and bathymodiolus thermophilus inhabiting three vent fields with contrasted geochemical features on the mid atlantic ridge mar rainbow and menez gwen and the east pacific rise epr 9 47 n were considered for carbon isotopes and growth rate variation along the shell length the study revealed that 13c fractionation between shells and seawater is higher than expected from calcite bicarbonate equilibrium fractionation suggesting a significant influence of the chemosynthetic pathway on the shell composition furthermore significant differences in 13cshell fractionation with respect to seawater are observed between sites and habitats of the two mar vent fields suggesting that different chemosynthetic pathway e g methanotrophic and thiotrophic could lead to variable enrichments of the shell in 13c mussels supposed to rely more largely on methanotrophy at rainbow where free sulfide is unavailable display a lower 13cshell values than mussels relying also on sulfide oxidizing symbiosis at menez gwen variability in 13cshell between habitats or between individuals within the same assemblage could thus reflect differences in the symbiosis activity at a micro habitat scale these isotopic signatures could provide useful information on the relationships between micro habitat properties symbiont activity and shell mineralization

submarine columns of ikaite tufa in the small ikka fjord in southwestern greenland we have studied remarkable submarine tufa columns forming over alkaline springs by abiotic precipitationof the metastable cold water mineral ikaite caco3 6h2o 1 3 the columns which support a rich marine life are up to 20 m high with annual growth of more than 50 cm we wish to nominate the locality which seems to be unique for classification as a geological world heritage site

fluid mixing and the deep biosphere of a fossil lost city type hydrothermal system at the iberia margin subseafloor mixing of reduced hydrothermal fluids with seawater is believed to provide the energy and substrates needed to support deep chemolithoautotrophic life in the hydrated oceanic mantle i e serpentinite however geosphere biosphere interactions in serpentinite hosted subseafloor mixing zones remain poorly constrained here we examine fossil microbial communities and fluid mixing processes in the subseafloor of a cretaceous lost city type hydrothermal system at the magma poor passive iberia margin ocean drilling program leg 149 hole 897d brucite calcite mineral assemblages precipitated from mixed fluids ca 65 m below the cretaceous paleo seafloor at temperatures of 31 7 4 3 c within steep chemical gradients between weathered carbonate rich serpentinite breccia and serpentinite mixing of oxidized seawater and strongly reducing hydrothermal fluid at moderate temperatures created conditions capable of supporting microbial activity dense microbial colonies are fossilized in brucite calcite veins that are strongly enriched in organic carbon up to 0 5 wt of the total carbon but depleted in 13c 13ctoc 19 4 we detected a combination of bacterial diether lipid biomarkers archaeol and archaeal tetraethers analogous to those found in carbonate chimneys at the active lost city hydrothermal field the exposure of mantle rocks to seawater during the breakup of pangaea fueled chemolithoautotrophic microbial communities at the iberia margin possibly before the onset of seafloor spreading lost city type serpentinization systems have been discovered at midocean ridges in forearc settings of subduction zones and at continental margins it appears that wherever they occur they can support microbial life even in deep subseafloor environments

a serpentinite hosted ecosystem the lost city hydrothermal field the serpentinite hosted lost city hydrothermal field is a remarkable submarine ecosystem in which geological chemical and biological processes are intimately interlinked reactions between seawater and upper mantle peridotite produce methane and hydrogen rich fluids with temperatures ranging from 40 to 90 c at ph 9 to 11 and carbonate chimneys 30 to 60 meters tall a low diversity of microorganisms related to methane cycling archaea thrive in the warm porous interiors of the edifices macrofaunal communities show a degree of species diversity at least as high as that of black smoker vent sites along the mid atlantic ridge but they lack the high biomasses of chemosynthetic organisms that are typical of volcanically driven systems