a basin redox transect at the dawn of animal life multiple eukaryotic clades make their first appearance in the fossil record between 810 and 715 ma molecular clock studies suggest that the origin of animal multicellularity may have been part of this broader eukaryotic radiation animals require oxygen to fuel their metabolism and low oxygen levels have been hypothesized to account for the temporal lag between metazoan origins and the cambrian radiation of large ecologically diverse animals here paleoredox conditions were investigated in the fifteenmile group ogilvie mountains yukon canada which hosts an 811 ma ash horizon and spans the temporal window that captures the inferred origin and early evolution of animals iron based redox proxies redox sensitive trace elements organic carbon percentages and pyrite sulfur isotopes were analyzed in seven stratigraphic sections along two parallel basin transects these data suggest that for this basin oxygenated shelf waters overlay generally anoxic deeper waters the anoxic water column was dominantly ferruginous but brief periods of euxinia likely occurred these oscillations coincide with changes in total organic carbon suggesting euxinia was primarily driven by increased organic carbon loading overall these data are consistent with proposed quantitative constraints on proterozoic atmospheric oxygen being greater than 1 of modern levels but less than present levels comparing these oxygen levels against the likely oxygen requirements of the earliest animals both theoretical considerations and the ecology of modern oxygen deficient settings suggest that the inferred oxygen levels in the mixed layer would not have been prohibitive to the presence of sponges eumetazoans or bilaterians thus the evolution of the earliest animals was probably not limited by the low absolute oxygen levels that may have characterized neoproterozoic oceans although these inferred levels would constrain animals to very small sizes and low metabolic rates

early diagenesis in differing depositional environments the response of transition metals in pore water the cycling of fe mn ni co cu cr v and mo during early diagenesis was investigated in sediments from five different depositional environments in the california borderland dissolved o2 no3 no2 and so4 were also measured at each site to establish the position of redox boundaries pertinent to this study sites were chosen to allow the comparison of several parameters of potential importance to the cycling of these metals bottom water o2 concentration sediment redox conditions cycling of metal oxide carrier phases and the relative contribution of biogenic and terrigenous material to the detrital metal flux at 10 m oxygen and above the sequence of terminal electron acceptor utilization was typical of pelagic sediments differing only in scale under these conditions the recycling of mn oxides resulted in an enriched layer near the interface at bottom water 02 concentrations 5 m mn oxides are not recycled under these conditions fe oxides and so42 are important oxidants the depth of the zone of manganese oxidation with respect to the interface affects the efficiency of metal scavenging by manganese oxides trapping and recycling of ni and co with mn oxides results in remobilization from reducing sediments and enrichment in oxic sediments scavenging of these metals is favored by a deep oxic zone in the sediments in contrast cr v and mo appear to be transported to the sediments as reduced species and are released from the sediments by oxidation the source of the reduced species is assumed to be biogenic material the accumulation of these metals is favored by reducing conditions in the sediments cu is enriched in the sediments by transport with detrital biogenic material followed by adsorption onto sediment solids cu is released at the interface and rapidly removed onto the solids at all sites except the one pelagic site at the base of the slope the magnitude of cu released in the slowly accumulating pelagic sediment exceeds the cu binding capacity of the solids resulting in pore water cu concentrations in excess of 100 nm in general metal cycling associated with the early diagenesis of sediments was observed to decouple transport processes from burial processes for the transition metals measured in this study

redox state of seafloor hydrothermal fluids and its effect on sulfide mineralization abstract the redox conditions f o 2 f s 2 of seafloor hydrothermal fluids were calculated from dissolved h 2 and h 2 s concentrations at conditions of 300 and 350 c 71 409 bars and seawater salinity the results were compared with f o 2 f s 2 conditions estimated from black smoker mineralogy as reported by previous studies and our own investigations for various geological settings including the okinawa trough sediment rich hakurei and sediment poor jade fields the manus back arc basin felsic hosted pacmanus and basalt hosted vienna woods fields and the central indian ridge mafic ultramafic hosted kairei and basalt hosted edmond fields in most cases the calculated fluid f o 2 f s 2 conditions agree well with estimates from primary mineral assemblages and fes contents in sphalerite wurtzite this correlation suggests that the redox states of sulfide mineralization in chimneys typically reflect dissolved h 2 and h 2 s concentrations in vent fluids it should be noted that variable h 2 concentrations in vent fluids 0 01 19 mmol kg dominantly control not only fluid f o 2 but also f s 2 whereas the more uniform h 2 s concentrations 1 20 mmol kg have less of an influence on fluid f s 2 fluid sediment interaction elevates h 2 concentrations to over 1 mmol kg which sufficiently lowers f o 2 f s 2 to the pyrrhotite stability field however low h 2 s concentrations do not necessarily account for low f s 2 calculations for the h 2 poor 0 1 mmol kg and h 2 s rich 10 mmol kg fluids in some felsic hosted arc backarc systems indicate relatively high f o 2 f s 2 states consistent with the bornite pyrite chalcopyrite assemblages these redox conditions result from a combination of fluid mineral equilibria at relatively oxidizing conditions elevated h 2 s concentrations from magmatic degassing redox calculations at 350 c indicate that neither pyrite nor pyrrhotite is stable in the initial hot fluids of the tag and ultramafic hosted mid atlantic ridge systems due to the low h 2 s concentrations with cooling of these fluids either conductively or by interacting with seawater higher f s 2 and f o 2 result and fe sulfides are stable in agreement with the higher f o 2 f s 2 mineral assemblages observed

water column hydrothermal plumes on the juan de fuca ridge hydrographic surveys on the juan de fuca ridge jdfr carried out from 1980 to 1987 show a complex pattern of sup 3 he and mn rich water column plumes produced by venting from several submarine hot spring areas in the vicinity of axial volcano at latitude 46 degree n distinct plumes were detected in 1980 1982 and 1983 with sup 3 he signatures up to delta sup 3 he 64 at approximately 1 500 m depth at distances of approximately 10 km from the seamount summit however the same plumes had no detectable thermal signature a paradox which is attributed to the high sup 3 he heat ratios and low salinities of the fluids venting within the caldera of axial volcano profiles directly over the seamount show hydrothermal sup 3 he in the water column up to 300 m above the caldera floor with the sup 3 he signal increasing with depth to very high and uniform ratios of delta sup 3 he 108 150 below the approximately 1 500 m caldera sill depth another apparent locus of hydrothermal input is helium basin a depression on the northeast flank of axial volcano which had delta sup 3 he 51 when first sampled in 1980 however subsequent hydrocasts into helium basin in 1982 and 1983 yielded lowermore helium enrichments suggesting either a decrease in hydrothermal input or flushing of the basin via a mixing event to the south of axial volcano high delta sup 3 he values of approximately 40 observed over the ridge axis at 45 degree 18 prime n and 45 degree 39 prime n indicate venting on this previously unexplored section of the ridge the water column plumes over the us geological survey vent site at approximately 44 degree 40 prime n on the southern jdfr have very high mn sup 3 he ratios of 4 600 mol cm sup 3 an apparently unique characteristic which can be used to distinguish these plumes from those originating at other jdfr vent fields less

magnetotelluric monitoring of a fluid injection example from an enhanced geothermal system 1 enhanced geothermal systems egs are on the verge of becoming commercially viable for power production where advancements in subsurface characterization are imperative to develop egs into a competitive industry theory of an egs is simple pump fluids into thermally enhanced lithology and extract the hot fluids to produce energy one significant complication in egs development is estimating where injected fluids flow in the subsurface micro seismic surveys can provide information about where fractures opened but not fracture connectivity nor fluid inclusion electromagnetic methods are sensitive to conductivity contrasts and can be used as a supplementary tool to delineate reservoir boundaries in july 2011 an injection test for a 3 6 km deep egs at paralana south australia was continuously monitored by both micro seismic and magnetotellurics mt presented are the first results from continuous mt measurements suggesting transient variations in subsurface conductivity structure generated from the introduction of fluids at depth can be measured furthermore phase tensor representation of the time dependent mt response suggests fluids migrated in a ne direction from the injection well results from this experiment supports the extension of mt to a monitoring tool for not only egs but other hydraulic stimulations

geochemistry of some gases in hydrothermal fluids from the southern juan de fuca ridge five samples of hydrothermal fluids from two vent areas on the southern juan de fuca ridge were analyzed for dissolved gases concentrations in the end member hydrothermal fluid of h2 270 527 mol kg ch4 82 118 mol kg and co2 3920 4460 mol kg are well above values in ambient seawater and are similar to concentrations reported for other ridge crest hydrothermal systems the carbon isotopic ratios of the ch4 13c 17 8 to 20 8 and co2 13c 3 6 to 4 7 suggest that at least some of the ch4 and co2 in the fluids is basalt derived the range of 13c values for the basalt derived co2 is 6 8 to 9 7 calculated by assuming conservation of recharge co2 during hydrothermal circulation apparent temperatures of equilibration between the ch4 and the basalt derived co2 range from 640 c to 750 c small amounts of ethane c2h6 ch4 0 9 10 3 2 2 10 3 propane and butane detected in the samples may also have formed in the basalt one sample of almost pure 95 5 hydrothermal fluid contained a significant fraction up to 63 and 74 respectively of the recharge ar and n2 this suggests that the fluid has not undergone extensive vapor liquid phase separation

noble gas evidence for two fluids in the baca valles caldera geothermal reservoir noble gas elemental and isotopic abundances were measured in steam from four wells in the baca geothermal reservoir located in the valles caldera new mexico the 40ar36ar ratio and noble gas elemental abundances relative to 36ar are all strongly correlated with 1 36ar the inverse of the argon content ratios of n produced 21ne and radiogenic 40ar to total 4he dominantly radiogenic are nearly constant at 2 1 10 8 and 0 20 respectively the 3he4he ratio covers a restricted range of 3 9 to 4 8 times atmospheric the high 3he content of the gas indicates the presence of a helium component ultimately derived from the mantle kr and xe isotopic compositions are close to atmospheric excess 129xe is 0 25 of the total 129xe the high degree of linear correlation among the various noble gas results strongly suggests that the baca reservoir contains two distinct fluids that are produced in varying proportions from individual wells the noble gases in fluid a 2900 mg 1 c1 are air like but with lighter gases and isotopes preferentially enriched the fluid a 36ar content is low only 13 that of 10 c air saturated water asw the second fluid b 1700 mg 1 c1 is the dominant carrier of the radiogenic and mantle derived gases the heavier non radiogenic gases are preferentially enriched in fluid b and its 36ar content is very low only 5 7 asw the source of the noble gases in fluid a is tentatively ascribed to leaching of the relatively young 1 4 m y volcanic bandelier tuff the radiogenic gases and mantle derived helium in fluid b suggest a deeper source possibly including gases escaping from a magma

redox and ph constraints in the subseafloor root zone of the tag hydrothermal system 26 n mid atlantic ridge abstract experiments were conducted at 375 400 c 500 bars to assess the role of redox and ph on fe cu and h 2 s concentrations at temperatures pressures and total dissolved chloride concentrations applicable to the trans atlantic geo traverse tag hydrothermal system at 26 n mid atlantic ridge the magnetite bornite anhydrite mineral assemblage imposed redox constraints while ph was buffered with a 0 65 molal na k cl bearing aqueous fluid coexisting with k feldspar muscovite and quartz results indicate a strong inverse correlation between dissolved cu and h 2 s aq whereas dissolved fe is more sensitive to ph magnetite bornite anhydrite fluid equilibria is characterized by unusually low mfe mcu molar ratio and low h 2 aq h 2 s aq activities to form this mineral assemblage during subseafloor hydrothermal alteration however requires elevated fluid rock mass ratios such that the ferrous iron and sulfur in the rock become sufficiently depleted to render pyrite and chalcopyrite unstable the relatively high cu concentrations the low h 2 s aq and mfe mcu ratios observed at tag vent fluids are consistent with constraints imposed by magnetite bornite anhydrite fluid equilibria at ph of approximately 4 9 available chemical data confirm that the tag hydrothermal system has experienced elevated fluid rock mass ratios in keeping with the extent of mass transfer needed to generate oxidizing low h 2 s aq conditions

widespread distribution of ascending fluids transporting mantle helium in the fore arc region and their upwelling processes noble gas and major element composition of deep groundwater in the kii peninsula southwest japan abstract chemical and isotopic studies including analyses of noble gases were comprehensively conducted on the groundwater of the entire kii peninsula which is located in the fore arc region of southwest japan groundwater of na cl hco3 na hco3 cl and na cl types was shown to be distributed across the whole area groundwater in the inland central part of the peninsula shows relatively low salinity whereas groundwater from the area along the ene trending median tectonic line mtl on the north side of the peninsula shows high salinity up to 18 800 mg l of cl and the presence of unusual heavy oxygen isotopes this trend is similar to that documented in saline waters from the arima region the so called arima type thermal water high 3he 4he ratios relative to the atmospheric value up to 6 7 ra were recorded throughout the kii peninsula covering a wider area than documented previously the saline groundwater is also strongly depleted in 20ne and heavy noble gases from the wide distribution of high 3he 4he values and the associated 20ne and cl concentrations we infer that aqueous fluids derived from dehydration of the subducting slab are present at depth beneath almost the entire kii peninsula these aqueous fluids may ascend along the major north dipping boundary faults the isotopic composition of groundwater from the southern part of the peninsula suggests that the contribution from these dehydration derived fluids is relatively small in this region however volatile components e g noble gases and co2 in the groundwater of this area may originate from the dehydration derived fluids upwelling of arima type thermal water of the na cl hco3 type is expected to undergo a phase separation of volatile species due to decompression as the fluid ascends the variety of water types documented may be due to this water gas separation and the subsequent incorporation of gaseous species into shallow meteoric groundwater the observed high 3he 4he ratios in the absence of a mantle wedge below the southern part of the kii peninsula may reflect the oblique ascent of these fluids along north dipping boundary faults

seasonality in the hydrography and biogeochemistry across the pakistan margin of the ne arabian sea abstract a series of cruises were conducted across the pakistan continental shelf edge and upper slope in the ne arabian sea between march and october 2003 coinciding with spring inter monsoon and late to post sw monsoon conditions water column hydrographic profiling together with nutrient chemistry show the upper boundary of the oxygen minimum zone omz rose during the sw monsoon by approximately 80 m leading to an inundation of a substantial area of the continental shelf with low oxygen water while the lower boundary showed only slight movement the core of the omz identified by the presence of a secondary nitrite maximum and high nitrate deficits rose by approximately 200 m nitrite concentrations within the secondary nitrite maximum approximately doubled over the period of study but this was not matched with an increase in the nitrate deficit dissolved oxygen concentrations in the core of the omz showed little or no substantial change during the course of the study hydrographic profiling showed greatest change in water masses around the 200 600 m depth range probably resulting from the northward movement of the west india undercurrent

noble gases in vent water from the juan de fuca ridge abstract hydrothermal vent fluids collected with the dsrv alvin from the southern limb of the juan de fuca ridge are chemically unique having chloride concentrations 2 times ambient seawater the same fluids contain noble gases in relative abundances like 2 c air saturated seawater the expected recharge composition however the absolute noble gas abundances are depleted by 30 relative to seawater the combination of very high chloride and moderately depleted noble gases appears to require the formation of a cl rich gas free brine by phase separation this brine is mixed with recharge seawater at temperatures in excess of 340 c and therefore deep in the hydrothermal system

chloride depletions and enrichments in seafloor hydrothermal fluids constraints from experimental basalt alteration studies na k ca cl fluid was reacted with diabase at 400 and 425 c 400 bars and fluidrock mass ratio of 0 5 to assess the relative mobility of dissolved cl fluids from the present experiments reveal relatively large time and temperature dependent decreases in cl temperature increase enhances cl removal whereas reaction progress has the opposite effect these changes are not due to boiling and or phase separation at 400 and 425 c 400 bars cl removal from solution is accompanied by ca and na fixation respectively both experiments produced mixed layer chlorite smectite clinozoisite and albite olivine was not detected by x ray diffraction or petrographic analysis of run products from either experiment however we propose that the time dependent changes in dissolved cl result from olivine replacement by an fe hydroxy chloride phase followed by hydration effects quenched and washed alteration products however did not reveal anomalous cl which suggests that the cl bearing phase is characterized by retrograde solubility this is consistent with the relative magnitude of cl fixation observed for experiments at both temperatures and from results of an isobaric cooling experiment the experiments provide evidence for the non conservative behavior of cl during hydrothermal alteration of basalt the data are particularly important in light of the cl depleted nature of some ridge crest hot spring fluids and suggest temperatures of formation for these fluids of approximately 410 c assuming sub seafloor pressure of 400 bars in addition the retrograde solubility of the cl bearing phase responsible for cl fixation during high temperature basalt alteration may help to explain cl enrichment in hot spring fluids which have conductively cooled below 350 c

formation of volcanogenic massive sulfide deposits the kuroko perspective abstract the main objective of this paper is to identify the geochemical hydrological igneous and tectonic processes that led to the variations in the physical size geometry and chemical mineralogy metal ratios and zoning characteristics of volcanogenic massive sulfide deposits with respect to space from a scale of mining district size area to a global scale and time from a all volcanogenic massive sulfide deposits vmsds appear to have formed in extensional tectonic settings such as at mid ocean spreading centers backarc spreading centers and intracontinental rifts and failed rifts all vmsds appear to have formed in submarine depressions by seawater that became ore forming fluids through interactions with the heated upper crustal rocks submarine depressions especially those created by submarine caldera formation and or by large scale tectonic activities e g rifting become most favorable sites for the formation of large vmsds because of hydrological physical and chemical reasons the fundamental processes leading to the formation of vmsds include the following six processes 1 1 intrusion of a heat source typically a 10 3 km size pluton into an oceanic crust or a submarine continental crust causes deep convective circulation of seawater around the pluton the radius of a circulation cell is typically 5 km the temperature of fluids that discharge on the seafloor increases with time from the ambient temperature to a typical maximum of 350 c and then decreases gradually to the ambient temperatures in a time scale of 100 to 10 000 years the majority of sulfide and sulfate mineralization occurs during the waxing stage of hydrothermal activity 2 2 reactions between low temperature t 2 4 as disseminated gypsum and anhydrite in the country rocks 3 3 reactions of the modified seawater with higher temperature rocks at depths during the waxing stage cause the transformation of the seawater to metal and h 2 s rich ore forming fluids the metals and sulfide sulfur are leached from the county rocks the previously formed gypsum and anhydrite are reduced by fe 2 bearing minerals and organic matter providing additional h 2 s the mass of high temperature rocks that provide the metals and reduced sulfur is typically 10 11 tons 40 km 3 in volume the roles of magmatic fluids or gases are minor in most massive sulfide systems except for so 2 to produce acid type alteration in some systems 4 4 reactions between the ore forming fluids and cooler rocks in the discharge zone cause alteration of rocks and precipitation of some ore minerals in the stockwork ores 5 5 mixing of the ore forming fluids with local seawater within unconsolidated sediments and or on the seafloor causes precipitation of primitive ores with the black ore mineralogy sphalerite galena pyrite barite anhydrite 6 6 reactions between the primitive ores with later and hotter hydrothermal fluids cause transformation of primitive ores to matured ores that are enriched in chalcopyrite and pyrite variations in the mineralogical and elemental characteristics the geometry and the size of submarine hydrothermal deposits are controlled by the following four parameters 1 a the chemical and physical characteristics of seawater composition temperature density which depend largely on the geographical settings e g equatorial evaporating basins 2 b the chemical and physical characteristics of the plumbing system lithology fractures 3 c the thermal structure of the plumbing system which is determined largely by the ambient geothermal gradient and the size and temperature of the intrusive and 4 d the physical characteristics of the seafloor depth basin topography for example the submarine hydrothermal deposits developed in basaltic plumbing systems are generally poor in pb and ba compared to those developed in felsic plumbing systems the lower temperature systems are generally poorer in sulfides but richer in iron oxides and sulfates the higher temperature and larger hydrothermal systems tend to produce chalcopyrite and pyrite rich ores contrasts in the metal ratios between the noranda type archean vmsds and the younger vmsds reflect the differences in the geothermal gradient of the plumbing systems the submarine hydrothermal deposits developed in the near equatorial regions tend to form large continuous bedded type ores because of the likeliness of creating large stratified basins the basic processes of submarine hydrothermal mineralization have remained essentially the same throughout the geologic history from at least 3 5 billion year ago to the present

atmospheric noble gases in volcanic glasses from the southern lau basin origin from the subducting slab abstract noble gas concentrations and isotopic compositions have been determined for four submarine volcanic glasses from the valu fa ridge vfr in the southern lau basin the samples are the least differentiated ones from this area and they display enrichments in fluid mobile elements similar to the nearby island arc 3he 4he ratios are slightly below average morb 6 8 7 8 times atmospheric whereas ne ar kr and xe have isotopic compositions very similar to air together with previously published data from the valu fa ridge and other spreading segments in the lau basin our data show a systematic latitudinal variation of increasing ne ar kr and xe abundances from north to south as well as ne and ar isotopic compositions changing from morb like to atmosphere like in the same direction moreover isotopic compositions and noble gas abundances of the lavas correlate strongly with ba nb ratios and h2o concentrations based on these observations and mass balance arguments we propose that the atmospheric noble gases come from the subducting oceanic crust and are not due to shallow contamination with air dissolved in seawater or assimilation of old crust our data suggest that the noble gases released from the subducting slab are atmospheric and thus contain little or no solar he and ne in addition to the fact that ratios of he to heavy noble gases are small in aged ocean crust he has possibly fractionated from the other noble gases due to its higher diffusivity and thus he transport from the subducting slab into the mantle wedge is probably insignificant we propose that the 3he 4he ratios lower than morb observed in the vfr lavas result from radiogenic ingrowth of he in a highly depleted and hence degassed mantle wedge after the enrichment of u and th released from the downgoing slab

anomalous xenon in archean cherts from pilbara craton western australia abstract we report the discovery of anomalies in the xenon isotopic composition of archean cherts belonging to the metasedimentary sequences of pilbara craton western australia the cherts show contemporary excesses of 129 xe and 131 136 xe compared to atmospheric xe the 129 xe excesses are comparable to those observed in mantle derived samples such as morbs xenoliths diamonds and co 2 rich well gases and correlate with excesses of 238 u fissiogenic produced 136 xe close to the mantle ratio however isotope 131 xe is in excess of 238 u fissiogenic xe production the 129 xe 131 xe ratio ranges from 0 7 to 3 2 and it is consistent with production of these two isotopes by neutron capture reactions with tellurium these anomalies are analogous to those measured in metamorphic rocks gneisses and amphibolites in the ktb borehole in germany and probably were produced by reactions with te

sub sea floor boiling of red sea brines new indication from noble gas data hydrothermal brines from the atlantis ii deep red sea have been sampled in situ and analyzed for noble gases the atmospheric noble gas concentrations ne aratm kr xe in the deepest layer lcl are depleted by 20 to 30 relative to the initial concentrations in ambient red sea deep water without a systematic mass fractionation between the different noble gases sub surface boiling during the hydrothermal circulation and subsequent phase separation is shown to be a consistent explanation for the observed depletion pattern using a conceptual model of phase separation under sub critical conditions in which gases are partitioned according to henry s law we reconstruct the fluid history before injection into the atlantis ii deep after having circulated through evaporites and young oceanic crust where it becomes enriched in hemorb and armorb the ascending fluid boils and the residual liquid becomes depleted in noble gas concentrations the depleted fluid rises to the sediment surface and feeds the atlantis ii basin the relatively low boiling degree of about 3 i e the percentage of fluid removed as vapor derived from the model indicates that the atlantis ii system represents an early stage of boiling with relatively small gas loss in contrast to hydrothermal systems at sediment free mid ocean ridges

seismic response of the fractured and faulted granite of soultz sous forets france to 5 km deep massive water injections summary the european enhanced geothermal system egs formerly hot dry rock hdr programme of soultz sous foris organized around three wells drilled to a depth of about 5000 m hydraulic stimulations were performed in the wells in 2000 gpk2 well 2003 gpk3 well and 2004 and 2005 gpk4 well the stimulation of gpk2 induced more than 700 seismic events with a magnitude greater than 1 0 the seismicity depicts a dense homogeneous cloud without any apparent structure medium size earthquakes represent more than 80 per cent of the cumulative seismic moment the b value of the gutenberg and richter law is larger than 1 2 the injectivity has been increased by a factor 20 these characteristics indicate that the stimulation reactivated a 3 d dense network of fractures the stimulation of gpk3 induced only about 250 events with a magnitude greater than 1 0 but with a greater proportion of large events up to 2 9 the hypocentres form clear structures identified as large faults the b value is about 0 9 and the large events m 2 0 account for the greater part of the cumulative seismic moment the injectivity of the well which was already high before the stimulation remained unchanged the stimulation of gpk4 was achieved in two stages this stimulation produced even less induced events making the interpretation difficult the differences between the seismic response of gpk2 and gpk3 are due to the presence of large faults cut by gpk3 or in its close vicinity and reached by the injected water once a seismic event occurs on a fault a sequence of earthquakes is triggered and the seismicity behaves for a large part independent of the injected flow rate the stimulations also show some evidence that creeping could be a major source of deformation if not the main one the future egs programme will have to drill wells in zones free of large faults to avoid poor hydraulic performance and inconvenience to the population

amino acid biogeochemistry and organic matter degradation state across the pakistan margin oxygen minimum zone to assess whether the oxygen minimum zone omz across the pakistan margin causes differences in the lability of sedimentary organic matter sediments were collected in the core of the omz in the upper and lower transition zones and below the omz sediment samples were analysed for total nitrogen tn and organic carbon oc contents mineral surface area sa and total hydrolysable amino acids thaa and enzymatically hydrolysable amino acids ehaa oc contents and organic carbon per unit of mineral surface area oc sa values were clearly elevated in the core and lower omz transition zone these sediments also contained more labile sedimentary organic matter as discerned by higher concentrations of thaa and the contribution of n in thaa to tn a protein amino acid based degradation index revealed that all sedimentary organic matter has undergone significant degradation but sediments in the upper omz transition zone and below the omz are more degraded than inside the omz changes in amino acid composition during diagenesis are attributed to a combination of factors 1 selective preservation in which amino acids in cell walls are better preserved than amino acids in cell plasma 2 formation and accumulation of bacterially derived organic matter there were relatively more living bacteria in the core of the omz and an accumulation of peptidoglycan derived amino acids in degraded sediments in the upper omz transition zone and below the omz and 3 bacterial transformation as the molar percentages of bacterial transformation products alanine bala amino butyric acid gaba and ornithine orn increased with increasing degradation

gradients in the composition of hydrothermal fluids from the endeavour segment vent field phase separation and brine loss hydrothermal fluid samples collected in 1984 1987 and 1988 from a large vent field near 47 57 n on the endeavour segment of the juan de fuca ridge jfr have been analyzed for major and minor elements and gases there are of the order of 100 individual smoker vents on 10 large sulfide structures which are localized along faults and fault intersections across the vent field each sulfide structure has a characteristic fluid composition which varies very little from one vent orifice to the next or from year to year on a given structure however there are large gradients in fluid composition across the vent field with endmember chlorinity increasing from 255 mmol kg in the sw to 505 mmol kg in the ne end member concentrations of major elements are well correlated with chlorinity and endmember volatile concentrations in the lowest chlorinity fluids are approximately twice as high as in the highest chlorinity fluids the gradients in composition across the vent field and measured vent fluid temperatures 400 c are consistent with supercritical phase separation and loss of brine phase below the seafloor the factor of 2 variation in co2 and h2s is larger than expected for loss of a very high chlorinity brine concentrations of iron and manganese are not positively correlated with chlorinity suggesting that temperature and ph are more important in controlling metal solubility elevated ammonia and bromide chloride ratios indicate that there has been subseafloor interaction between the hydrothermal fluids and organic matter and high boron concentrations point to a sedimentary source

salinity variations in submarine hydrothermal systems by layered double diffusive convection various mechanisms have been proposed to explain the salinity variations in vent fluids of seafloor geothermal systems new experiments reacting diabase and evolved seawater were carried out to reproduce earlier published observations of cl depletions attributed to formation of an ephemeral cl bearing mineral the absence of any cl depletions in the present study suggests that the formation of cl bearing minerals is not sufficiently widespread to account for the observed salinity variations in the vent fluids a re evaluation of both field and laboratory evidence has led to a new model for subseafloor circulation that accounts for salinity variations as well as other chemical and mineralogic observations in place of a simple single pass convection system we propose that the seafloor systems consist of two vertically nested convection cells in which a brine layer at depth heats and drives an overlying seawater cell such layering of salinities a process known in fluid mechanics as double diffusive conve

constraints on deformation conditions and the origin of oceanic detachments the mid atlantic ridge core complex at 15 45 n 1 deformed rocks sampled from a corrugated detachment fault surface near the mid atlantic ridge 15 45 n constrain the conditions of deformation and strain localization samples recovered in situ record deformation restricted to the cold shallow lithosphere greenschist facies with no evidence for significant high temperature deformation either at the fault zone or in the footwall near it high temperature deformation 720 750 c is observed only at two sites and cannot be directly linked to the detachment detachment faulting was coeval with dyke intrusions that cross cut it as demonstrated by the presence of undeformed and highly deformed diabase found in shear zones and by the presence of chill margins in diabase against fault rock basalts are very scarce and restricted to clasts in breccias with no evidence of pillows or extrusive structures gabbros crop out along mass wasted and fault scarps structurally below the detachment footwall rocks show little or no deformation due to strain localization along a narrow shear zone 200 m with fluid flow as required to form talc and amphibole schists after an ultramafic protolith we speculate that the alteration front in a heterogeneous lithosphere may be a rheological boundary that may localize deformation during long periods of time our observations and other geological evidence elsewhere suggest that this detachment model limited to the cold shallow lithosphere is applicable to other corrugated surfaces along slow and intermediate spreading ridges these observations preclude detachment models rooting in melt rich zones i e atlantis bank southwest indian ridge or recording high temperature deformation we infer that oceanic detachment faults 1 localize strain at t 500 300 c 2 persist during active magmatism and 3 root at shallow rheological boundaries such as a melt rich zone or magma chamber hot detachments or an alteration front cold detachments

sedimentary pigments on the pakistan margin controlling factors and organic matter dynamics abstract sedimentary pigments can provide information on various aspects of benthic processes and biogeochemistry in this study sediments from sites at depths of 140 to 1850 m spanning the pakistan margin oxygen minimum zone omz and representing dramatic contrasts in depositional conditions and benthic communities were analysed for pigment yields and compositions this has allowed a rare consideration of how different factors including oxygen concentration organic matter om supply and biological activity e g degree of bioturbation may influence sedimentary pigment distribution in a continental margin environment it has also allowed one of the first efforts to study the impact of biological activity on pigment concentrations in the natural environment rather than in a microcosm setting total extractable surface sediment pigment concentrations showed a range of 1 5 49 g g 1 of dry sediment the pigment suite was dominated by pheophytin and pheophorbide which together constituted 75 of total pigments with minor amounts of chlorophyll a alloxanthin diatoxanthin zeaxanthin and carotene low oxygen concentration appeared to influence pigment abundance by increasing the concentration of refractory pigments ultimately buried in addition maximal pigment abundances were associated with minimal amounts of sediment mixing by macrofauna and at one site macrofaunal digestion may have altered the relative dominance of the different pheopigments in contrast the lack of a marked increase in pigment concentrations after the summer monsoon plus the lack of a correlation between pigment concentration and water depth suggest that om supply plays a relatively small role in controlling sedimentary pigments pigment concentrations and suites together with modelled decay half lives 0 8 15 years suggest that in general om on the pakistan margin despite the low oxygen concentrations and monsoon driven productivity is surprisingly degraded compared to that on other continental margins with om rich sediments as an exception to this general situation pigment suites appeared to be relatively fresh i e contained more labile components compared to those found on the oman margin of the arabian sea but overall concentrations were lower this is consistent with the higher oxygen concentrations productivity and macrofaunal abundances found on the western margin of the arabian sea principle component analysis of pigment suites showed that they correlated with an amino acid based degradation index di thus the pigment composition of marine sediments is related to and may serve as an indicator of the state of decay of sedimentary om

seismic and aseismic deformations and impact on reservoir permeability the case of egs stimulation at the geysers california usa author s jeanne p rutqvist j rinaldi ap dobson pf walters m hartline c garcia j abstract 2015 american geophysical union all rights reserved in this paper we use the seismicity based reservoir characterization approach to study the spatiotemporal dynamics of an injection induced microseismic cloud monitored during the stimulation of an enhanced geothermal system and associated with the northwest geysers enhanced geothermal system egs demonstration project california we identified the development of a seismically quiet domain around the injection well surrounded by a seismically active domain then we compare these observations with the results of 3 d thermo hydro mechanical simulations of the egs which accounts for changes in permeability as a function of the effective normal stress and the plastic strain the results of our modeling show that 1 the aseismic domain is caused by both the presence of the injected cold water and by thermal processes these thermal processes cause a cooling stress reduction which prevent shear reactivation and favors fracture opening by reducing effective normal stress and locally increasing the permeability this process is accompanied by aseismic plastic shear strain 2 in the seismic domain microseismicity is caused by the reactivation of the preexisting fractures resulting from an increase in injection induced pore pressure our modeling indicates that in this domain permeability evolves according to the effective normal stress acting on the shear zones whereas shearing of preexisting fractures may have a low impact on permeability we attribute this lack of permeability gain to the fact that the initial permeabilities of these preexisting fractures are already high up to 2 orders of magnitude higher than the host rock and may already be fully dilated by past tectonic straining

oxygen and organic matter thresholds for benthic faunal activity on the pakistan margin oxygen minimum zone 700 1100 m abstract a transition from fully laminated to highly bioturbated sediments on continental margins is thought to derive from increased animal activity associated with increasing bottom water oxygen concentration we examined faunal community responses to oxygen and organic matter gradients across the lower oxygen minimum zone omz on the bathyal pakistan margin where sediments grade from fully laminated sediment at 700 m 0 12 ml l 1 o 2 5 m to highly bioturbated sediment at 1100 m 0 23 ml l 1 o 2 10 m high resolution sampling of the seafloor every 50 m water depth was conducted along a single transect during inter and post monsoon periods in 2003 to address a the existence of oxygen thresholds regulating macrofaunal abundance composition diversity and lifestyles b the interactive effects of organic matter quantity and quality c associated community effects on sediment structure and d potential seasonality in these processes macrofaunal biomass and bioturbation depth were positively correlated with organic matter availability which peaked at 850 950 m 3 39 3 53 org c in contrast macrofaunal diversity h dominance r1d and burrow number exhibited threshold responses at oxygen concentrations of 0 12 0 20 ml l 1 5 9 m with few animals and highly laminated sediments present below this concentration and most taxa present in fully bioturbated sediments above it the highly mobile burrowing amphinomid polychaete linopherus sp exhibited almost complete dominance and high density at 750 850 m 0 12 0 14 ml l 1 o 2 5 6 m but despite its activity sediment laminae remained faintly visible formation of permanent burrows and detritivory were dominant macrofaunal lifestyles within the omz allowing laminae to persist at surprisingly high animal density and biomass results reflect a shift from organic matter to oxygen regulation of body size and biogenic structures following the monsoon this study suggests that for assemblages evolving under permanent severe hypoxia food availability remains a significant determinant of animal abundance and biogenic structure depth oxygen influences patterns of diversity and dominance and interacts with organic matter to generate abrupt faunal transitions on the pakistan margin

apparent apertures from ground penetrating radar data and their relation to heterogeneous aperture fields considering fractures with heterogeneous aperture distributions we explore the reliability of constant aperture estimates derived from ground penetrating radar gpr reflection data we generate geostatistical fracture aperture realizations that are characterized by the same mean aperture and variance but different hurst exponents and cut off lengths for each of the 16 classes of heterogeneity considered we generate 1000 fracture realizations from which we compute gpr reflection data using our recent effective dipole forward model we then use each noise contaminated data set individually to invert for a single apparent aperture that is we assume that the fracture aperture is homogeneous we find that the inferred apparent apertures are only reliable when fracture heterogeneity is non fractal the hurst exponent is close to 1 and the scale of the dominant aperture heterogeneities is larger than the first fresnel zone these results are a direct consequence of the nonlinear character of the thin bed reflection coefficients as fracture heterogeneity is ubiquitous and often fractal our results suggest that robust field based inference of fracture aperture can only be achieved by accounting for the nonlinear response of fracture heterogeneity on gpr data

fugacity concentration relationship of dilute hydrogen in water at elevated temperature and pressure abstract the fugacity vs concentration ratio y of dilute hydrogen dissolved in water was determined at temperatures below 500 c and pressures below 1000 bar by measuring h 2 concentrations in magnetite hematite water and palladium hydride water systems combining these results with reported solubility data of h 2 in water and with the shaw s expression for the activity composition relationship of h 2 h 2 o mixture at higher temperatures the p t y diagram was constructed over the p t range below 900 c and 1000 bar

degradation of the mechanical properties imaged by seismic tomography during an egs creation at the geysers california and geomechanical modeling abstract using coupled thermal hydro mechanical thm modeling we evaluated new seismic tomography results associated with stimulation injection at an egs demonstration project at the northwest geysers geothermal steam field california we studied high resolution seismic tomography images built from data recorded during three time periods a period of two months prior to injection and during two consecutive one month periods after injection started in october 2011 our analysis shows that seismic velocity decreases in areas of most intense induced microseismicity and this is also correlated with the spatial distribution of calculated steam pressure changes a detailed analysis showed that shear wave velocity decreases with pressure in areas where pressure is sufficiently high to cause shear reactivation of pre existing fractures the analysis also indicates that cooling in a liquid zone around the injection well contributes to reduced shear wave velocity a trend of reducing compressional wave velocity with fluid pressure was also found but at pressures much above the pressure required for shear reactivation we attribute the reduction in shear wave velocity to softening in the rock mass shear modulus associated with shear dislocations and associated changes in fracture surface properties also as the rock mass become more fractured and more deformable this favors reservoir expansion caused by the pressure increase and so the fracture porosity increases leading to a decrease in bulk density a decrease in young modulus and finally a decrease in vp

abundance and isotopic composition of helium in hydrothermal sulfides from the east pacific rise at 13 n abstract the helium isotopes composition of fluids trapped in hydrothermal sulfides from the east pacific rise 13 n were measured two extraction techniques i e crushing and heating were tested and sulfldes of different mineralogical types were studied the comparison between the two extraction methods suggests that both should give similar results provided the crushing efficiency is sufficiently high sulfides 3 he 4 he ratio for crushed samples are in the range 6 85 8 10 times the atmospheric ratio r a 1 38 10 6 and the measured helium concentration is of the order of 5 5 10 5 cm 3 stp per gram of trapped fluid comparison with the helium isotope composition of the hydrothermal vent fluids themselves shows that the mineral phases formed at the highest temperature i e with less dilution by the ambient seawater retain the helium information most effectively with values almost indistinguishable from the endmember vent fluid

borehole radar applied to the characterization of hydraulically conductive fracture zones in crystalline rock1 this paper discusses the borehole radar system ramac developed within the framework of the international stripa project which can be used in three different measuring modes single hole reflection cross hole reflection and cross hole tomography the reflection modes basically provide geometrical data on features located at some distance from the borehole in addition the strength of the reflections indicate the contrast in electrical properties single hole reflection data are cylindrically symmetrical with respect to the borehole which means that a unique fracture orientation cannot be obtained a method has been devised where absolute orientation of fracture zones is obtained by combining single hole reflection data from adjacent holes similar methods for the analysis of cross hole reflection data have also been developed and found to be efficient the radar operates in the frequency range 20 60 mhz which gives a resolution of 1 3 m in crystalline rock the investigation range obtained in the stripa granite is approximately 100 m in the single hole mode and 200 300 m in the cross hole model variations in the arrival time and amplitude of the direct wave between transmitter and receiver have been used for cross hole tomographic imaging to yield maps of radar velocity and attenuation the cross hole measurement configuration coupled withmore tomographic inversion has less resolution than the reflection methods but provides better quantitative estimates of the values of measured properties the analysis of the radar data has provided a consistent description of the fracture zones at the stripa cross hole site in agreement with both geological and geophysical observations less

chemistry of hydrothermal solutions from the southern juan de fuca ridge fluids from three vent fields on the southern juan de fuca ridge were sampled in september 1984 using the dsrv alvin the fluids are uniquely high in both chloride which ranges up to twice the seawater value and in metal content simple vapor liquid phase separation could not have produced both the high chlorinity and gas concentrations observed in these fluids the cause of the elevated chlorinity can not be uniquely identified but may be the result of either or a combination of two processes 1 subsurface formation of a degassed brine and subsequent mixing of a small amount of this brine with a hydrothermal seawater which has not undergone a phase separation and 2 dissolution of a chloride rich phase combined with a possible small loss of gas during sampling procedures although measured temperatures were all less than 300 sup 0 c quartz geothermometry suggests that the fluids have equilibrated at greater than 340 sup 0 c quartz geobarometry is also in agreement with geophysical estimates of depth to the local magma chamber copyright american geophysical union 1987

organic content and preservational controls in surficial shelf and slope sediments from the arabian sea pakistan margin abstract in the arabian sea organic rich deposits occur on the continental slope at depths roughly coincident with the impingement of an intense water column oxygen minimum zone omz this relationship has often been taken as causal and such deposits are often proposed as modern analogues of organic rich facies from the palaeorecord however there are numerous other potential preservational controls on continental margins and their relative importance remains unclear and much debated we report the results of organic inorganic and stable c isotope analyses on surficial sediments from three transects of the pakistan margin ranging in depth from well above to well below the omz organic carbon c org and total nitrogen n total contents show expected mid slope maxima although these do not mirror bottom water dissolved o 2 profiles maximal values are observed near the lower boundary of the omz or even in homogenous sediments below it together lignin yields and 13 c org values indicate a general paucity of terrigenous organic matter om this information combined with c org n total relationships suggests that the om contents of all sediments are dictated by differing accumulation of a predominant marine fraction while there are no obvious redox related differences in c org n total or om hydrogen richness across the margin there are clear minima in 13 c org within the omz in apparent contradiction with maximal accumulation of marine om the latter phenomenon is ascribed either to local source effects such as variable algal isotopic signatures or to differences in om preservation state possibly linked to bottom water redox conditions this remains to be clarified but along with the rough correspondence between mid slope sedimentary c org maxima and bottom water o 2 minima may indicate that o 2 availability is an important factor in determining sedimentary om content on this margin however evidence from redox sensitive indicators i c org mn al for persistent accumulation of om rich deposits under oxidizing conditions in homogeneous sediments below the omz clearly indicates that o 2 availability is not the sole or over riding control on om distributions

a three component mixing model for ridge crest hydrothermal fluids the hydrothermal fluid chemistry data set for sediment starved ridge axes is used to estimate endmember compositions and to constrain a three component mixing model based on that of von damm using numerical methods to estimate the endmember compositions the data set includes fe cl h2s na k ca and sr at 11 13 n and 21 n east pacific rise north and south cleft segment southern juan de fuca ridge tag and mark q mode factor analysis shows that the data can be explained 99 9 by 3 factors a constrained optimization of a weighted least squares algorithm assuming conservative mixing and with the constraints that all endmember concentrations and contributions are non negative and that fractional contributions sum to one is used to partition the data set into endmembers mixing of the calculated endmembers consistently found to be phase separated brine vapor and hydrothermally altered seawater reproduces the composition of the vent fluids the model is consistent with the presence of a convecting brine layer in the primary reaction zone at depth as suggested by bischoff and rosenbauer that transfers properties to the overlying circulating seawater by release of a vapor and by diffusion we suggest that future experimental work examine solubility controls in conjunction with and subsequent to phase separation and work with a wider range of fluid salinities

fe ni co o s phase relations in peridotite seawater interactions serpentinization of abyssal peridotites is known to produce extremely reducing conditions as a result of dihydrogen h2 aq release upon oxidation of ferrous iron in primary phases to ferric iron in secondary minerals by h2o we have compiled and evaluated thermodynamic data for fe ni co o s phases and computed phase relations in fo2 g fs2 g and ah2 aq ah2s aq diagrams for temperatures between 150 and 4008c at 50 mpa we use the relations and compositions of fe ni co o s phases to trace changes in oxygen and sulfur fugacities during progressive serpentinization and steatitization of peridotites from the mid atlantic ridge in the 15820 0 n fracture zone area ocean drilling program leg 209 petrographic observations suggest a systematic change from awaruite magnetite pentlandite and heazlewoodite magnetite pentlandite assemblages forming in the early stages of serpentinization to millerite pyrite polydymite dominated assemblages in steatized rocks awaruite is observed in all brucite bearing partly serpentinized rocks apparently buffering of silica activities to low values by the presence of brucite facilitates the formation of large amounts of hydrogen which leads to the formation of awaruite associated with the prominent desulfurization of pentlandite sulfide is removed from the rock during the initial stage of serpentinization in contrast steatitization indicates increased silica activities and that highsulfur fugacity sulfides such as polydymite and pyrite vaesite solid solution form as the reducing capacity of the peridotite is exhausted and h2 activities drop under these conditions sulfides will not desulfurize but precipitate and the sulfur content of the rock increases the co evolution of fo2 g fs2 g in the system follows an isopotential of h2s aq indicating that h2s in vent fluids is buffered in contrast h2 in vent fluids is not buffered by fe ni co o s phases which merely monitor the evolution of h2 activities in the fluids in the course of progressive rock alteration the co occurrence of pentlandite awaruite magnetite indicates h2 aq activities in the interacting fluids near the stability limit of water the presence of a hydrogen gas phase would add to the catalyzing capacity of awaruite and would facilitate the abiotic formation of organic compounds

on the use of dispersive apvo gpr curves for thin bed properties estimation theory and application to fracture characterization the presence of a thin layer embedded in any formation creates complex reflection patterns caused by interferences within the thin bed the generated reflectivity amplitude variations with offset have been increasingly used in seismic interpretation and more recently tested on ground penetrating radar gpr data to characterize nonaqueous phase liquid contaminants phase and frequency sensitivities of the reflected signals are generally not used although they contain useful information the present study aims to evaluate the potential of these combined properties to characterize a thin bed using gpr data acquired along a common midpoint cmp survey carried out to assess velocity variations in the ground it has been restricted to the simple case of a thin bed embedded within a homogeneous formation a situation often encountered in fractured media dispersive properties ofthe dielectric permittivity of investigated materials homogeneous formation thin bed are described using a jonscher parameterization which permitted study of the dependency of amplitude and phase variation with offset apvo curves on frequency and thin bed properties filling nature aperture in the second part we discuss and illustrate the validity of the thin bed approximation as well as simplify assumptions and make necessary careful corrections to convert raw cmp data into dispersive apvo curves two different strategies are discussed to correct the data from propagation effects a classical normal moveout approach and an inverse method finally the proposed methodology is applied to a cmp gpr data set acquired along a vertical cliff it allowed us to extract the characteristics of a subvertical fracture with satisfying resolution and confidence the study motivates interest to use dispersion dependency of the reflection coefficient variations for thin bed characterization

unique event plumes from a 2008 eruption on the northeast lau spreading center the creation of ocean crust by lava eruptions is a fundamental earth process involving immediate and immense transfers of heat and chemicals from crust to ocean this transfer creates event plumes megaplumes massive ellipsoidal eddies with distinctive and consistent chemical signatures here we report the discovery of unique event plumes associated with a 2008 eruption on the northeast lau spreading center instead of a large plume hundreds of meters thick we detected at least eight individual plumes each 50 m thick and apparently only 1 3 km in diameter yet still rising 200 1000 m above the eruption site low and uniform 3he heat 0 041 10 17 mol j and dissolved mn heat 0 04 nmol j ratios in water samples were diagnostic of event plumes high h2 concentrations up to 9123 nm and basalt shards confirmed extensive interactions between molten lava and event plume source fluids remote vehicle observations in 2009 mapped a new small 1 5 5 8 106 m3 lava flow our results suggest that event plumes are more variable and thus perhaps more common than previously recognized small event plumes may be preferentially associated with small or sheet flow eruptions and massive event plumes with slowly extruding pillow mounds 25 75 m thick despite this correlation and high h2 concentrations existing theory and seafloor observations argue that cooling lava cannot transfer heat fast enough to create the buoyancy flux required for event plumes the creation of event plumes under a broad range of eruption conditions provides new constraints for any theory of their formation

characterisation of induced fracture networks within an enhanced geothermal system using anisotropic electromagnetic modelling abstract as opinions regarding the future of energy production shift towards renewable sources enhanced geothermal systems egs are becoming an attractive prospect the characterisation of fracture permeability at depth is central to the success of egs recent magnetotelluric mt studies of the paralana geothermal system pgs an egs in south australia have measured changes in mt responses which were attributed to fracture networks generated during fluid injection experiments however extracting permeabilities from these measurements remains problematic as conventional isotropic mt modelling is unable to accommodate for the complexities present within an egs to circumvent this problem we introduce an electrical anisotropy representation to allow better characterisation of volumes at depth forward modelling shows that mt measurements are sensitive to subtle variations in anisotropy subsequent two dimensional anisotropic forward modelling shows that electrical anisotropy is able to reproduce the directional response associated with fractures generated by fluid injection experiments at the pgs as such we conclude that mt monitoring combined with anisotropic modelling is a promising alternative to the micro seismic method when characterising fluid reservoirs within geothermal and coal seam gas reservoirs

the critical point and two phase boundary of seawater 200 500 c abstract the two phase boundary of seawater was determined by isothermal decompression of fully condensed seawater in the range of 200 500 c the pressure at which phase separation occurred for each isotherm was determined by a comparison of the refractive index of fluid removed from the top and bottom of the reaction vessel the critical point was determined to be in the range of 403 406 c 285 302 bar and was located by the inflection in the two phase boundary and by the relative volume of fluid and vapor as a function of temperature the two phase boundary of 3 2 nacl solution was found to coincide exactly with that of seawater over the range tested in the present study the boundary for both is described by a single seventh order polynomial equation the two phase boundary defines the maximum temperature of seawater circulating at depth in the oceanic crust thus the boundary puts a limit of about 390 c for seawater circulating near the seafloor at active ocean ridges 2 5 km water depth and about 465 c at the top of a magma chamber occurring at 2 km below the seafloor

large organic walled protista gromia in the arabian sea density diversity distribution and ecology abstract the genus gromia includes large marine protists gromiids with filose pseudopodia and sack like organic tests the first deep water species were discovered in the 1990s on the oman margin of the arabian sea and subsequently found on the pakistan margin we present a survey of gromiids in samples collected off oman in 2002 and off pakistan in 2003 in addition to the two species gromia sphaerica and gromia pyriformis already described from this area at least eight undescribed gromiid species were present sausage shaped grape shaped and spherical morphotypes were represented among this material on the oman margin gromiids occurred in densities up to several thousand individuals m 2 at 1400 and 1700 m but were much less common at 1100 and 2000 m apart from g pyriformis which was fairly common several hundred individuals m 2 at 1000 m gromiids were uncommon in core samples taken off pakistan with 11 indiv m 2 at 1200 m and 19 indiv m 2 at 1850 m on both margins these protists occurred at depths 1000 m where bottom water oxygen concentrations exceeded 0 2 ml l 1 8 92 m l 1 land sediments were fully bioturbated and oxidised however they were not observed at similar oxygen levels above the omz most gromiids lived on the sediment surface with their apertures facing down and their pseudopodia presumably deployed into the sediment to feed on surficial material and associated bacteria we conclude that these large protists may play an important ecological role in the bathyal arabian sea particularly in carbon cycling but also in structuring the surficial sediments in addition their tests particularly those of g sphaerica provide substrates for attached foraminifera

estimating the permeability distribution and its uncertainty at the egs demonstration reservoir soultz sous forets using the ensemble kalman filter 1 we present an estimation of the permeability fields of the reservoir at the enhanced geothermal system egs at soultz sous forets france based on the data assimilation technique ensemble kalman filter enkf to this end we assimilate data from a tracer circulation experiment performed in 2005 using a 3 d numerical simulation of fluid transport and chemical tracer dispersion we advance the tracer in time and control the concentration with the enkf we obtain reliable fits for concentration data recorded in both existing production boreholes gpk2 and gpk4 as an alternative to discrete fracture networks our heterogeneous equivalent porous medium approach thus can also characterize the hydraulically fractured zone of the engineered geothermal system we present best estimates for permeabilities 10 14 m2 10 12 m2for the fracture zone and the corresponding uncertainty which is about one order of magnitude after comparing our results to results from a massive monte carlo and from a gradient based bayesian approach it becomes clear that only the enkf of this three approaches is able to fit concentrations at gpk2 and gpk4 simultaneously based on the enkf estimates obtained a long term performance prediction including an uncertainty analysis for the reservoir as it was in 2005 yields no thermal breakthrough in the system within at least 50 years of operation our study demonstrates the efficiency of the enkf when estimating the permeability distribution in an egs reservoir even with sparse data available

hydraulic fracturing controlled dynamics of microseismic clouds 1 several dynamic processes related to propagation of hydraulic fracture modify the stress state in rocks and therefore they are relevant for triggering of microseismicity for instance these are the creation of a new fracture volume fracturing fluid loss and its infiltration into reservoir rocks as well as diffusion of the injection pressure into the pore space of surrounding rocks and inside the fracture using real data we show that some of these processes can be seen from features of spatio temporal distributions of the induced microseismicity especially the initial stage of fracture volume opening as well as the back front of the induced seismicity starting to propagate after termination of the fluid injection can be well identified and used for reservoir engineering

single hole gpr reflection imaging of solute transport in a granitic aquifer 1 identifying transport pathways in fractured rock is extremely challenging as flow is often organized in a few fractures that occupy a very small portion of the rock volume we demonstrate that saline tracer experiments combined with single hole ground penetrating radar gpr reflection imaging can be used to monitor saline tracer movement within mm aperture fractures a dipole tracer test was performed in a granitic aquifer by injecting a saline solution in a known fracture while repeatedly acquiring single hole gpr sections in the pumping borehole located 6 m away the final depth migrated difference sections make it possible to identify consistent temporal changes over a 30 m depth interval at locations corresponding to fractures previously imaged in gpr sections acquired under natural flow and tracer free conditions the experiment allows determining the dominant flow paths of the injected tracer and the velocity 0 4 0 7 m min of the tracer front

suboxic trace metal geochemistry in the eastern tropical north pacific abstract we analyzed al ti fe mn cu ba cd u mo v and re in water column settling particulate and sediment 0 to 22 cm samples from the intense oxygen minimum zone omz of the eastern tropical north pacific near mazatlan mexico the goal was to determine how the geochemistry of these elements was influenced by suboxic water column conditions and whether the sediments have a unique suboxic geochemical signature the water column was characterized by a mn maximum reaching 8 nmol kg 1 at 400 m concentrations of cu ba cd mo re u and v were unaffected by the low o2 conditions and were comparable to those of the open ocean sinking particles were composed of lithogenic particles of detrital origin and nonlithogenic particles of biogenic origin al ti and fe were mostly at least 79 lithogenic about 75 of the mn was nonlithogenic significant amounts at least 58 of cu ba cd and mo were nonlithogenic sediment geochemistry varied across the continental shelf and slope cadmium u and re have prominent maxima centered at 310 m with 12 3 ppm 10 9 ppm and 68 3 ppb respectively at the core top high values of mo averaging 6 8 ppm and v averaging 90 ppm are seen in omz surface sediment additional down core enrichment occurs for all redox sensitive elements in the top 10 cm for u mo v and re surface sediments are a poor indicator of metal enrichment comparison of the nonlithogenic composition of sediments with sinking particles suggests that direct input of plankton material enriched in metals makes a significant contribution to the total composition especially for cd u and mo we evaluated re mo and cd u ratios as tracers for redox environments rhenium and mo concentrations and re mo ratios do not lead to consistent conclusions concurrent enrichments of re and mo are an indicator of an anoxic depositional environment in contrast high re mo ratios are an indicator of suboxic conditions cadmium is enriched in surface sediments while u has considerable down core enrichment the concentrations of cd and u and the cd u ratio do not follow patterns predicted from thermodynamics though the water column is suboxic these four redox sensitive elements indicate that the sediments are anoxic the implication for paleostudies is that a trace metal sediment signature that indicates anoxic conditions is not necessarily attributable to an anoxic water column

macrofaunal communities and sediment structure across the pakistan margin oxygen minimum zone north east arabian sea abstract benthic macrofauna and sediment column features were sampled at five stations along a bathymetric transect depths 140 300 940 1200 1850 m through the pakistan margin oxygen minimum zone omz during the 2003 intermonsoon march may and late post monsoon august october periods objectives were to compare patterns with those described from other omzs particularly the oman margin of the arabian sea in order to assess the relative influence of bottom water oxygenation and sediment organic content on macrofaunal standing stock and community structure macrofaunal density was highest at the 140 m station subject to monsoon driven shoaling of the omz but there was no elevation of density at the lower omz boundary 1200 m numbers was extremely low in the omz core 300 m and were not readily explicable from the environmental data there was no consistent depth related trend in macrofaunal biomass macrofaunal densities were consistently lower than found off oman but there was less contrast in biomass a significant post monsoon decline in macrofaunal density at 140 m was driven by selective loss of polychaete taxa polychaeta was the most abundant major taxon at all stations but did not dominate the macrofaunal community to the extent reported from oman cirratulidae and spionidae were major components of the polychaete fauna at most stations but acrocirridae ampharetidae amphinomidae and cossuridae were more important at 940 m polychaete assemblages at each station were almost completely distinct at the species level polychaete species richness was positively correlated with bottom water dissolved oxygen and negatively correlated with sediment toc c n ratio and total phytopigments community dominance showed the opposite pattern the strongly inverse correlation between oxygen and measures of sediment organic content made it difficult to distinguish their relative effects the strongly laminated sediments in the omz core contrasted with the homogeneous heavily bioturbated sediments above and below this zone but were associated with minimal macrofaunal biomass rather than distinctive functional group composition in general data from the oman margin were weak predictors of patterns seen off pakistan and results suggest the importance of local factors superimposed on the broader trends of macrofaunal community composition in omzs

helium heat and the generation of hydrothermal event plumes at mid ocean ridges hydrothermal event plumes are unique water column features observed over mid ocean ridges presumably generated by the sudden release of large volumes of hot buoyant fluid although the specifics of event plume generation are unknown event plumes have been attributed to the rapid emptying of a hydrothermal reservoir or to rapid heat extraction from a recently emplaced dike or seafloor lava flows the chemical and thermal signatures of event plumes as compared to the underlying steady state plumes offer important clues to the generation of event plumes event plumes have low 3he heat ratios of 0 4 10 17 mol j 1 similar to vent fluids from mature hydrothermal systems in contrast the steady state plumes found beneath the event plumes have elevated and variable 3he heat ratios of 2 to 5 10 17 mol j 1 fluids collected directly over fresh lava flows have even higher 3he heat ratios of 2 to 8 10 17 mol j 1 up to 30 times the event plume values these disparate 3he heat ratios place strong constraints on models of event plume generation especially models which rely on heat extraction from seafloor eruptions published by elsevier science b v

sedimentary denitrification rates across the arabian sea oxygen minimum zone abstract sedimentary denitrification was measured at sites across the pakistan margin oxygen minimum zone omz during cruises before and after the 2003 southwest sw monsoon denitrification rates were calculated using nitrate fluxes and n 2 production rates in shipboard whole core incubations and benthic lander deployments we observed generally good agreement between the sedimentary denitrification rates obtained from nitrate consumption and n 2 production results of these investigations indicate that sedimentary denitrification is a persistent process within the arabian sea omz and the regions proximal to the permanent omz e g 140 and 1200 m sedimentary denitrification in the region intensified during the sw monsoon as noted by the increase in associated rates between the inter monsoon april may 2003 and post monsoon september october 2003 assessments sedimentary denitrification was observed at all stations during the inter monsoon period nitrate consumption rates ranged from 0 40 to 3 17 mmol n m 2 d 1 during the post monsoon assessment apparent sedimentary denitrification rates increased in the shallow sites 140 and 300 m likely in response to a shoaling of the omz but were not definitively observed at the deepest site 1850 m where observed post monsoon sedimentary denitrification rates increased to 0 66 3 78 mmol n m 2 d 1 these rates compare favorably to sedimentary denitrification rates obtained in other shelf environments and are higher than abyssal sedimentary denitrification rates by extrapolating these rates to the entire pakistan margin omz we estimate a net annual sedimentary denitrification flux of 1 1 10 5 tg n yr 1 moderately higher than current estimates of sedimentary denitrification in this region and in line with estimates of regional sedimentary denitrification in other sites

selenium isotopes record extensive marine suboxia during the great oxidation event abstract it has been proposed that an oxygen overshoot occurred during the early paleoproterozoic great oxidation event goe in association with the extreme positive carbon isotopic excursion known as the lomagundi event moreover it has also been suggested that environmental oxygen levels then crashed to very low levels during the subsequent extremely negative shunga francevillian carbon isotopic anomaly these redox fluctuations could have profoundly influenced the course of eukaryotic evolution as eukaryotes have several metabolic processes that are obligately aerobic here we investigate the magnitude of these proposed oxygen perturbations using selenium se geochemistry which is sensitive to redox transitions across suboxic conditions we find that 82 78se values in offshore shales show a positive excursion from 2 32 ga until 2 1 ga mean 1 03 0 67 selenium abundances and se toc total organic carbon ratios similarly show a peak during this interval together these data suggest that during the goe there was pervasive suboxia in near shore environments allowing nonquantitative se reduction to drive the residual se oxyanions isotopically heavy this implies o2 levels of 0 4 m in these settings unlike in the late neoproterozoic and phanerozoic when negative 82 78se values are observed in offshore environments only a single formation evidently the shallowest shows evidence of negative 82 78se this suggests that there was no upwelling of se oxyanions from an oxic deep ocean reservoir which is consistent with previous estimates that the deep ocean remained anoxic throughout the goe the abrupt decline in 82 78se and se toc values during the subsequent shunga francevillian anomaly indicates a widespread decrease in surface oxygenation

the short term fate of organic carbon in marine sediments comparing the pakistan margin to other regions abstract pulse chase experiments with isotopically labelled phytodetritus conducted across the pakistan margin reveal that the impact of biological activities on benthic c cycling varies markedly among sites exhibiting different seafloor conditions in this study patterns of biological c processing across the pakistan margin oxygen minimum zone omz are compared with those observed in previous tracer studies variations in site environmental conditions are proposed to explain the considerable variations in c processing patterns among this and previous studies three categories of c processing pattern are identified 1 respiration dominated where respiration accounts for 75 of biological c processing and uptake by metazoan macrofauna foraminifera and bacteria are relatively minor processes these sites tend to show several although not necessarily all of the properties of being cold and deep and having low inputs of organic carbon to the sediment and relatively low biomass metazoan macrofaunal communities 2 active faunal uptake where respiration accounts for 2 h 1 and seem to be dominantly controlled by seafloor temperature rates of metazoan macrofaunal uptake of organic matter om on the pakistan margin are larger than those in most other studies and this is attributed to the large and active metazoan macrofaunal communities in the lower omz characteristic of omz boundaries finally biological mixing of pakistan margin sediments was reduced compared to that observed in comparable tracer studies on other margins this probably reflects faunal feeding and burrowing strategies consistent with low oxygen concentrations and a relatively abundant supply of sedimentary om

role of a strong oxygen deficient zone in the preservation and degradation of organic matter a carbon budget for the continental margins of northwest mexico and washington state rates of organic carbon oxidation in marine sediments were determined for the continental margins of northwest mexico and washington state with the goal of assessing the role of oxygen in the preservation of organic matter on a margin with a strong oxygen deficient zone and on a typical western continental margin total carbon oxidation rates including rates for individual electron acceptors o2 no3 and so4 were determined at depths ranging from 100 to 3000 m on both margins carbon oxidation rates were generally higher on the washington margin than on the mexican margin the relative importance of the different electron acceptors varied across the two margins and was related primarily to the availability of o2 and no3 from the overlying water the relative contribution of o2 consumption increased in deeper sediments 2000 m as aerobic processes began to dominate the total carbon oxidation rate denitrification rates were highest in washington sediments however denitrification represented a larger fraction of the total carbon oxidation rate in the mexican sediments 40 for mexico vs 30 for washington sulfate reduction accounted for as much as 79 of the total carbon oxidation rate in shallow sediments and less than 20 in deep sediments on both margins the offshore trends in carbon oxidation rate appeared to be related to the organic carbon input rate pore water o2 and no3 penetration depths were shallowest in nearshore stations and increased offshore regeneration ratios of c n p reveal non redfield behavior on both margins carbon budgets for the two margins demonstrate that off mexico a much greater percentage of the organic matter produced in the surface ocean reached the sediments 15 vs 8 for mexico and washington respectively on the mexican margin 8 of the primary production escaped oxidation in the surface sediments to be permanently buried as compared with only 1 2 of the primary production on the washington margin this suggests that oxygen deficient conditions on mexican margin are linked to enhanced carbon preservation

carbon and nitrogen elemental and stable isotopic compositions of surficial sediments from the pakistan margin of the arabian sea abstract the factors controlling sedimentary organic matter distributions are the subject of ongoing debate we report here the carbon and nitrogen contents and stable isotopic compositions for surface sediments and downcore profiles from sites ranging in water depth from 140 to 3200 m located across the indus margin of the arabian sea the sites spanned the intense midwater oxygen minimum zone omz and showed dramatic differences in bottom water redox conditions benthic communities and degrees of bioturbation five primary stations were studied at 140 300 940 1200 and 1850 m water depth with sampling in march may intermonsoon and august october late to postmonsoon 2003 high resolution sampling was also conducted across the upper 140 275 m and lower omz 600 1200 m boundaries the sampling strategy was selected to help clarify the roles of oxygen availability and other potential environmental factors in determining sediment organic matter content and composition the extent of organic matter cycling within the sediments under contrasting depositional conditions and the fate of organic matter deposited during the southwest monsoon as previously noted on this and other omz margins there was a roughly inverse spatial relationship between bottom water oxygen and sedimentary organic matter concentrations however variability in organic carbon content within the omz that was unrelated to oxygen and the fact that maximal organic carbon contents occurred under relatively oxidizing conditions towards the lower omz boundary rather than at the omz core indicate that factors other than oxygen contribute significantly as controls on carbon distributions despite a 3 fold range in organic carbon content carbon to nitrogen ratios showed no systematic trends across the omz with values reflecting uniform predominantly marine organic matter inputs nitrogen isotopic signatures 15n values in the range of 6 5 8 5 also did not show clear cross omz trends and are attributed to a 14n depleted nitrate pool created by pelagic denitrification there was little downcore change in organic matter content at any site suggesting either that organic matter decay occurs largely in the water column or that decay within the sediments at oxygenated sites is masked by bioturbation seasonal variability in organic matter content and composition was restricted to the most surficial sediments and changes were ephemeral suggesting rapid turnover of organic matter deposited during the southwest monsoon on timescales of weeks stable c isotopic compositions trended towards more negative values in surficial sediments at hypoxic sites within the omz core this is attributed to a chemosynthetic bacterial imprint

hydrothermal alteration and microbial sulfate reduction in peridotite and gabbro exposed by detachment faulting at the mid atlantic ridge 15 20 n odp leg 209 a sulfur and oxygen isotope study whole rock sulfur and oxygen isotope compositions of altered peridotites and gabbros from near the 15 20 n fracture zone on the mid atlantic ridge were analyzed to investigate hydrothermal alteration processes and test for a subsurface biosphere in oceanic basement three processes are identified 1 high temperature hydrothermal alteration 250 350 c at sites 1268 and 1271 is characterized by 18o depletion 2 6 4 4 elevated sulfide s and high 34s up to 2 wt and 4 4 10 8 fluids were derived from high temperature 350 c reaction of seawater with gabbro at depth these cores contain gabbroic rocks suggesting that associated heat may influence serpentinization 2 low temperature 150 c serpentinization at sites 1272 and 1274 is characterized by elevated 18o up to 8 1 high sulfide s up to 3000 ppm and negative 34s to 32 1 that reflect microbial reduction of seawater sulfate these holes penetrate faults at depth suggesting links between faulting and temperatures of serpentinization 3 late low temperature oxidation of sulfide minerals caused loss of sulfur from rocks close to the seafloor sulfate at all sites contains a component of oxidized sulfide minerals low 34s of sulfate may result from kinetic isotope fractionation during oxidation or may indicate readily oxidized low 34s sulfide derived from microbial sulfate reduction results show that peridotite alteration may be commonly affected by fluids heat derived from mafic intrusions and that microbial sulfate reduction is widespread in mantle exposed at the seafloor

organic matter preservation through the oxygen deficient zone of the ne arabian sea as discerned by organic carbon mineral surface area ratios abstract it is debated whether there is a causal or even correlative relationship between the presence of a minimum in bottom water oxygen bwo concentration and the preservation of organic matter in underlying marine sediments one relationship that has not been examined in this regard is the relationship between sedimentary organic carbon content and mineral surface area normalization of organic matter content to mineral surface area eliminates the mass based problems associated with traditional weight percent carbon measurements and thus may allow better evaluation of carbon preservation we measured organic carbon to mineral surface area ratios oc sa on 26 sediment samples from along the ne edge of the arabian sea and on 21 hydrodynamically sorted fractions using split flow lateral transport thin splitt fractionation from three of these stations samples spanned from above to well below the minimum in local bwo concentration sediments deposited under the oxygen minimum had oc sa ratios in excess of 1 1 mg oc m 2 indicative of enhanced preservation a bioturbated sediment at the edge of the oxygen minimum bwo 35 m also had a high oc sa ratio with the exception of the anomalous sample along the slope all samples from shallower and deeper than the oxygen depleted water mass bwo 35 m have oc sa ratios that fall within the typically observed range 0 5 1 1 mg oc m 2 while further work will be necessary to discern what causes this relationship our data indicate that organic matter preservation as estimated by oc sa is enhanced within the general locale of the bwo minimum in ne arabian sea sediments if this relationship proves to be robust repeatable and stable over time in other modern bwo minimum zones surface area normalized organic carbon loadings may be a useful paleoceanographic proxy for past bwo levels

measurements of diffusivity near the sediment water interface with a fine scale resistivity probe fine scale profiles of the sedimentary formation factor f were obtained from measurements of resistivity at millimetre intervals in marine sediments these profiles demonstrated that rapid decreases in diffusivity occurred in the upper few centimeters of both compact intertidal sands and fine silty muds in the compact sands a 70 decrease in the formation factor was observed within 2 cm of the interface close correlations were found between the formation factor and sediment porosity for both sediment types profiles of 1f predicted from these correlations and porosity profiles were very similar to those obtained from measurements of resistivity these correlations also suggested that 3 is a better approximation of the formation factor in fine muds than the archie relation 2 in both sediments the interfacial value of the diffusion coefficient was estimated to be between 74 and 87 of its value in free solution a value much higher than is normally assumed

sedimentary oxygen consumption and microdistribution at sites across the arabian sea oxygen minimum zone pakistan margin abstract biogeochemical processes and fluxes occurring across the sediment water interface on continental margins impacted by oxygen minimum zones omzs are important to bioelement cycles ocean inventories and productivity the nature and magnitude of these processes depend heavily on spatial and temporal variability in dissolved o 2 concentrations in bottom waters and porewaters in 2003 four research cruises to the indus margin of the arabian sea pakistan were undertaken to survey the benthic biogeochemical processes in the resident omz before and after the southwest monsoon sediment o 2 microdistribution and consumption rates were measured at five stations along a depth transect 140 1850 m across the omz during the spring intermonsoon and the late to post southwest monsoon periods using in situ benthic research platforms landers lander o 2 electrode data show that the intermonsoon and late to postmonsoon bottom water o 2 levels had little to no variation 300 m no change 940 m 1 7 2 8 m 1200 m 10 2 12 6 m and 1850 m 82 80 m in contrast at the shallowest station 140 m a large fluctuation occurred between the intermonsoon o 2 44 5 m and the late to postmonsoon o 2 1 m due to monsoon forced shoaling of the upper omz boundary oxygen did not penetrate into the sediments at the 300 m site during either sampling season during the intermonsoon season at the 140 m site o 2 penetrated to a depth of 3 mm but no measurable o 2 penetration occurred after the monsoon at the 940 and 1200 m sites o 2 penetration into the sediments was small ca 1 2 mm at both sites and did not measurably change between the two sampling seasons in contrast at the 1850 m site o 2 penetration decreased after the monsoon 18 12 mm calculated late to postmonsoon o 2 consumption rates were generally similar to or lower than intermonsoon values 0 vs 2 22 mmol m 2 d 1 at 140 m 0 37 vs 0 31 mmol m 2 d 1 at 1200 m and 0 73 vs 1 01 mmol m 2 d 1 at 1850 m the relatively small seasonal signal suggests that organic matter delivered during the monsoon period may have already been largely remineralized by the late to postmonsoon sampling period modelling of porewater o 2 profiles indicates that subsurface o 2 consumption associated oxidation of reduced inorganic species makes a significant contribution to total o 2 consumption at some sites similarly differences in o 2 consumption rates determined by porewater profile modelling and whole core incubations at some sites indicate significant contributions associated with bioturbation and bioirrigation

hydraulic stimulation of natural fractures as revealed by induced microearthquakes carthage cotton valley gas field east texas we produced a high resolution microseismic image of a hydraulic fracture stimulation in the carthage cotton valley gas field of east texas we improved the precision of microseismic event locations four fold over initial locations by manually repicking the traveltimes in a spatial sequence allowing us to visually correlate waveforms of adjacent sources the new locations show vertical containment within individual targeted sands suggesting little or no hydraulic communication between the discrete perforation intervals simultaneously treated within an 80 m section treatment i e fracture zone lengths inferred from event locations are about 200 m greater at the shallow perforation intervals than at the deeper intervals the highest quality locations indicate fracture zone widths as narrow as 6 m similarity of adjacent source waveforms along with systematic changes of phase amplitude ratios and polarities indicate fairly uniform source mechanisms fracture plane orientation and sense of slip over

benthic biological and biogeochemical patterns and processes across an oxygen minimum zone pakistan margin ne arabian sea abstract oxygen minimum zones omzs impinging on continental margins present sharp gradients ideal for testing environmental factors thought to influence c cycling and other benthic processes and for identifying the roles that biota play in these processes here we introduce the objectives and initial results of a multinational research program designed to address the influences of water depth the omz 150 1300 m and organic matter om availability on benthic communities and processes across the pakistan margin of the arabian sea hydrologic sediment and faunal characterizations were combined with in situ and shipboard experiments to quantify and compare biogeochemical processes and fluxes om burial efficiency and the contributions of benthic communities across the omz in this introductory paper we briefly review previous related work in the arabian sea building the rationale for integrative biogeochemical and ecological process studies this is followed by a summary of individual volume contributions and a brief synthesis of results five primary stations were studied at 140 300 940 1200 and 1850 m water depth with sampling in march may intermonsoon and august october late to postmonsoon 2003 taken together the contributed papers demonstrate distinct cross margin gradients not only in oxygenation and sediment om content but in benthic community structure and function including microbial processes the extent of bioturbation and faunal roles in c cycling hydrographic studies demonstrated changes in the intensity and extent of the omz during the sw monsoon with a shoaling of the upper omz boundary that engulfed the previously oxygenated 140 m site oxygen profiling and microbial process rate determinations demonstrated dramatic differences in oxygen penetration and consumption across the margin and in the relative importance of anaerobic processes but surprisingly little seasonal change a broad maximum in sediment om content occurred on the upper slope roughly coincident with the omz but the otherwise poor correlation with bottom water oxygen concentrations indicated that other factors are important in determining sediment om distributions downcore profiles generally showed little clear evidence of in situ om alteration and there was little sign of om enrichment resulting from the southwest monsoon in sediments collected in the late to postmonsoon sampling this is interpreted to be due to rapid cycling of labile om organic geochemical studies confirmed that sediment om is overwhelmingly of marine origin across the margin but also that it is heavily altered with only small changes in degradation state across the omz more negative stable c isotopic compositions in surficial sediments at hypoxic sites within the omz core are attributed to a chemosynthetic bacterial imprint dramatic changes in benthic community structure occurred across the lower omz transition apparently related to om availability and quality as well as to do concentrations high resolution sampling biomarkers and isotope tracer studies revealed that oxygen availability appears to exert threshold type controls on benthic community structure and early faunal c processing biomarker studies also provided evidence of faunal influence on sediment om composition together the results offer strong evidence that benthic fauna at sites across the margin play important roles in the early cycling of sediment om through differential feeding and bioturbation activities

manganese iron and sulphur cycling on the pakistan margin abstract benthic biogeochemical processes in the oceans oxygen minimum zones omzs are of global significance yet they remain poorly defined here sedimentary manganese iron and sulphur cycling are studied at sites above within and below the omz on the pakistan margin of the arabian sea before and immediately after the southwest monsoon mechanisms and rates of sedimentary mn fe and s cycling demonstrated down slope variation according to the position of the omz no significant seasonal change was evident except at one station on the upper margin where bottom waters became hypoxic during the late to post monsoon sampling due to the shoaling of the upper omz boundary within the omz mn 4 reduction within the water column limited supply of reactive mn to the underlying sediments the majority of reactive mn reaching the sedimentary environment is reduced abiotically via reaction with fe 2 sediments within the omz act as a source of mn 2 to the overlying water below the omz mn 2 is re oxidised within the water column and is deposited on the surface of the underlying sediments manganese is then reduced microbially and re oxidised within the oxygenated surface sediments uniform surface sediment fe al ratios across the margin suggest that fe 3 reduction is lacking within the water column omz in contrast fe is actively cycled within the sediments with fe 3 reduction occurring via dissimilatory pathways an absence of potential fe 2 oxidants within the omz results in an efflux of fe 2 from the sediments to the water column below the omz greater oxidant availability ensures that fe is retained within the sediments measured sulphate reduction rates at all sites across the margin were surprisingly low 0 0 45 mmol m 2 d 1 relative to rates observed on other omz margins the abundance of fe oxides in the sedimentary environment appears to suppress sulphate reduction

investigating multi polarization gpr wave transmission through thin layers implications for vertical fracture characterization this is the published version copyright 2006 american geophysical union all rights reserved

porewater nutrient concentrations and benthic nutrient fluxes across the pakistan margin omz abstract porewater concentrations and benthic fluxes of phosphate silicate ammonia nitrate and nitrite were measured at five sites spanning the pakistan margin oxygen minimum zone omz in order to characterise the biogeochemical processes occurring and to assess whether oxygen concentration and a seasonal pulse of organic matter are controlling factors typical concentrations of 1 70 m 50 250 m 0 270 m 30 cm in the sediment these processes are all redox sensitive and their intensities varied across the margin suggesting that oxygen concentration exerts a strong influence over nutrient concentrations and cycling variation in nutrient concentrations and fluxes before and after the summer monsoon was limited to an oxygen driven change to the po43 profile at one site indicating that either nutrient profiles do not generally alter on seasonal timescales or that any impact of the monsoon had subsided before the post monsoon sampling period porewater profile modelling tended to underestimate the magnitude of fluxes but was in general agreement with the directions of measured fluxes and in situ and shipboard flux measurements also generally agreed phosphate and h4sio4 concentrations and benthic fluxes on the pakistan margin were similar to those reported at abyssal sites from around the world while nh4 and no3 concentrations and fluxes were comparable to shallower more productive and or hypoxic marine settings

faunal responses to oxygen gradients on the pakistan margin a comparison of foraminiferans macrofauna and megafauna the pakistan margin is characterised by a strong mid water oxygen minimum zone omz that intercepts the seabed at bathyal depths 150 1300 m we investigated whether faunal abundance and diversity trends were similar among protists foraminiferans and gromiids metazoan macrofauna and megafauna along a transect 140 1850 m water depth across the omz during the 2003 intermonsoon march may and late post monsoon august october seasons all groups exhibited some drop in abundance in the omz core 250 500 m water depth o2 0 10 0 13 ml l 1 4 46 5 80 m but to differing degrees densities of foraminiferans 63 m were slightly depressed at 300 m peaked at 738 m and were much lower at deeper stations foraminiferans 300 m were the overwhelmingly dominant macrofaunal organisms in the omz core macrofaunal metazoans reached maximum densities at 140 m depth with additional peaks at 850 940 and 1850 m where foraminiferans were less abundant the polychaete linopherus sp was responsible for a macrofaunal biomass peak at 950 m apart from large swimming animals fish and natant decapods metazoan megafauna were absent between 300 and 900 m o2 0 2 ml l 1 8 92 m the progressively deeper abundance peaks for foraminiferans 63 m linopherus sp and ophiuroids probably represent lower omz boundary edge effects and suggest a link between body size and tolerance of hypoxia macro and megafaunal organisms collected between 800 and 1100 m were dominated by a succession of different taxa indicating that the lower part of the omz is also a region of rapid faunal change species diversity was depressed in all groups in the omz core but this was much more pronounced for macrofauna and megafauna than for foraminiferans oxygen levels strongly influenced the taxonomic composition of all faunal groups calcareous foraminiferans dominated the seasonally and permanently hypoxic sites 136 300 m agglutinated foraminiferans were relatively more abundant at deeper stations where oxygen concentrations were 0 13 ml l 1 5 80 m polychaetes were the main macrofaunal taxon within the omz calcareous macrofauna and megafauna molluscs and echinoderms were rare or absent where oxygen levels were lowest the rarity of larger animals between 300 and 700 m on the pakistan margin compared with the abundant macrofauna in the omz core off oman is the most notable contrast between the two sides of the arabian sea this difference probably reflects the slightly higher oxygen levels and better food quality on the western side

hydrogeophysical characterization of transport processes in fractured rock by combining push pull and single hole ground penetrating radar experiments the in situ characterization of transport processes in fractured media is particularly challenging due to the considerable spatial uncertainty on tracer pathways and dominant controlling processes such as dispersion channeling trapping matrix diffusion ambient and density driven flows we attempted to reduce this uncertainty by coupling push pull tracer experiments with single hole ground penetrating radar gpr time lapse imaging the experiments involved different injection fractures chaser volumes and resting times and were performed at the fractured rock research site of ploemeur in france h network hplus ore fr en for the gpr acquisitions we used both fixed and moving antenna setups in a borehole that was isolated with a flexible liner during the fixedantenna experiment time varying gpr reflections allowed us to track the spatial and temporal dynamics of the tracer during the push pull experiment during the moving antenna experiments we clearly imaged the dominant fractures in which tracer transport took place fractures in which the tracer was trapped for longer time periods and the spatial extent of the tracer distribution up to 8 meters at different times this demonstrated the existence of strongly channelized flow in the first few meters and radial flow at greater distances by varying the resting time of a given experiment we identified regions affected by density driven and ambient flow these experiments open up new perspectives for coupled hydrogeophysical inversion aimed at understanding transport phenomena in fractured rock formations

widespread assimilation of a seawater derived component at loihi seamount hawaii many tholeiitic and transitional pillow rim and fragmental glasses from loihi seamount hawaii have high cl contents and cl k 2o ratios and ratios of cl to other incompatible components such as p 2o 5 h 2o etc relative to other hawaiian subaerial volcanoes e g mauna loa mauna kea and kilauea we suggest that this results from widespread contamination of loihi magmas by a cl rich seawater derived component assimilation of high cl phases such as saline brine or cl rich minerals halite or iron hydroxychlorides with high cl h 2o ratios can explain the range and magnitude of cl contents in loihi glasses as well as the variations in the ratios of cl to other incompatible elements brines and cl rich minerals are thought to form from seawater within the hydrothermal systems associated with submarine volcanoes and loihi magmas could plausibly have assimilated such materials from the hydrothermal envelope adjacent to the magma chamber our model can also explain semiquantitatively the observed contamination of loihi glasses with atmospheric derived noble gases provided the assimilant has concentrations of ne and ar comparable to or slightly less than seawater this is more likely for brines than for cl rich minerals leading us to favor brines as the major assimilant cl br ratios for a limited number of loihi samples are also seawater like and show no indication of the higher values expected to be associated with the assimilation of cl rich hydrothermal minerals although cl enrichment is a common feature of lavas from loihi submarine glasses from other hawaiian volcanoes show little kilauea or no mauna loa mauna kea evidence of this process suggesting that assimilation of seawater derived components is more likely to occur in the early stages of growth of oceanic volcanoes summit collapse events such as the one observed at loihi in october 1996 provide a ready mechanism for depositing brine bearing rocks from the volcanic edifice into the top of a submarine summit magma chamber