hydrogen isotope composition of early proterozoic seawater the hydrogen isotope composition of early proterozoic seawater has been indirectly determined on the basis of d values measured in mafic ultramafic samples from a hydrothermally altered layered flow from the chukotat group of the lower proterozoic 2 0 1 9 ga cape smith fold belt northern quebec this flow and other mafic ultramafic units of the fold belt represent some of the oldest relict oceanic crust identified on earth measured d values of whole rock samples range from 53 to 40 matching closely values found in modern metavolcanic rocks and phanerozoic ophiolites a model of water rock interaction for conditions of metamorphism deduced from mineral parageneses and sr and o isotope data t 200 250 c water rock ratio close to 1 0 indicates that the d values of chukotat flow samples reflect interaction with seawater that had a d 0 20 this result implies that the hydrogen isotope composition of early proterozoic seawater was certainly similar to the modern value and that subduction and ridge processes that control the global water cycle have not changed significantly since the early proterozoic

the relative timing of serpentinisation and mantle exhumation at the ocean continent transition iberia constraints from oxygen isotopes legs 173 and 149 of the ocean drilling program profiled a zone of exhumed mantle peridotite at the ocean continent transition oct beneath the iberia abyssal plain the zone of exhumed peridotite appears to be tens of kilometers wide and is situated betw

a vestige of earth s oldest ophiolite a sheeted dike complex within the 3 8 billion year old isua supracrustal belt isb in southwest greenland provides the oldest evidence of oceanic crustal accretion by spreading the geochemistry of the dikes and associated pillow lavas demonstrates an intraoceanic island arc and mid ocean ridge like setting and their oxygen isotopes suggest a hydrothermal ocean floor type metamorphism the pillows and dikes are associated with gabbroic and ultramafic rocks that together make up an ophiolitic association the paleoarchean isua ophiolite complex these sheeted dikes offer evidence for remnants of oceanic crust formed by sea floor spreading of the earliest intact rocks on earth

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

δ2h of water from fluid inclusions in proterozoic halite evidence for a deuterium depleted hydrosphere abstract 2h were measured in water present in tiny primary fluid inclusions trapped in mesoproterozoic 1 4 ga and neoproterozoic 0 8 ga halite crystals while the hydrogen concentrations range from 300 to 1500 ppm for the whole sample collection 2h values range from 74 to 54 vsmow for the mesoproterozoic halite sampled from the sibley group ontario canada and from 89 to 38 for the neoproterozoic halite from the browne formation officer basin australia the amount of evaporation required to precipitate halite is accompanied by a deuterium enrichment of 30 to 90 it means that the original aqueous solutions had 2h values comprised between 140 and 90 considering the estimated tropical paleolatitudes for both depositional environments surface waters were most likely significantly deuterium depleted relative to modern ones if such interpretation is partly at variance with the geological record it could be reconciliated with some modelling outputs of the long term water cycle indeed several mechanisms produce a progressive deuterium enrichment of the oceans those identified so far are the addition of deuterium rich extraterrestrial water cometary dust the loss of h during water photodissociation by ultraviolet radiation in the upper atmosphere and the isotopic fractionation that takes place during the hydroxylation of nominally anhydrous mantle rock forming minerals we also propose that the major process able to shift through time the 2 of the hydrosphere is the reduction of h2o into h2 during the serpentinization of mantle rocks at mid ocean ridges

halogen chemistry and hydrogen isotopes of apatite from the 3 7 ga isua supracrustal belt sw greenland abstract the origin and evolution of volatiles particularly water in the abiotic early earth environment have been intensively studied and this is a topic of high relevance when considering the timing and conditions of life s emergence investigation of hydrogen isotopes in the oldest crystals of minerals from the apatite group ca10 po4 6 f cl oh 2 should bring new insight to this topic as the d h ratio of apatite has proved useful for establishing the evolution of volatiles in other solar system bodies apatite crystals from metasedimentary and metavolcanic rocks collected from a low strain domain of the eoarchean isua supracrustal belt have been investigated for their d h signatures using secondary ion mass spectrometry and for major and trace element abundances using epma and laser ablation icp ms apatite crystals from isua have a broad range in volatile compositions both within samples from the same lithology e g banded iron formation bif and between different lithologies bif metacarbonate mafic dyke most of the crystals are chlorine rich which is in contrast to typical modern sedimentary apatite that is predominantly carbonate fluorapatite we have used the ree distribution patterns from isua apatite to distinguish those crystals having sedimentary metasomatic and magmatic origins the d h ratios for all samples were determined to be very low with dvsmow values falling within the range from 93 to 56 d values of isua apatite do not correlate with ree signatures of crystals nor could we relate d to the host lithologies we conclude that this geochemical system has been reset during long and multi phase geologic history making it difficult if not impossible to use hydrogen isotopes for assessment of the primary signatures of the archean hydrosphere

high archean climatic temperature inferred from oxygen isotope geochemistry of cherts in the 3 5 ga swaziland supergroup south africa new and compiled oxygen isotope data combined with the results of geological and sedimentological studies demonstrate that enclaves of synsedimentary to very early diagenetic cherts are widely preserved in the 3 5 3 2 ga swaziland supergroup barberton greenstone belt south africa the low 1 8 o values of these cherts indicate extremely high ocean temperatures of 55 85 c previously the large depletion in 1 8 o shown by all barberton cherts relative to their phanerozoic counterparts has been attributed to low 1 8 o in archean oceans chert formation during late diagenesis wholesale loss of 1 8 o during alteration and or regional silicification of sediments around hot springs these alternative explanations are not compatible with the new results cherts in the onverwacht group display an isotopic stratigraphy that is inversely repeated in conglomerates in the overlying fig tree and moodies groups demonstrating that the chert 8 0 o values were fixed prior to archean uplift and erosion which started at 3 26 ga the maximum 1 8 o value in barberton cherts 22 is lower than the minimum values 23 in phanerozoic bedded cherts precluding late diagenesis as the explanation of the overall low 1 8 o values regional metamorphic hydrothermal or long term resetting of original 1 8 o values is also precluded by preservation of 1 8 o values across different metamorphic grades and by systematic 1 8 o differences among interbedded chert types stratigraphic units and conglomerate clasts the 7 1 8 o variation of these archean cherts is similar to that of phanerozoic deep sea cherts formed when opal converted to microquartz during burial but the actual archean values are 10 lower marine opal was apparently converted to microquartz during burial to depths of 1 km cherts with 1 8 o 15 reflect conversion during deepest burial or in local areas of enhanced geothermal gradient and or hydrothermal activity cherts with higher 1 8 o values formed during early diagenesis and indicate an extremely hot archean ocean and surface environment

oxygen isotope study of mid ocean ridge hydrothermal fluids implication for the oxygen 18 budget of the oceans new data are reported for the 18o composition of hot hydrothermal fluids from various sites with different tectonic settings the measured 18o in the range 0 53 2 3 confirm earlier data suggesting that mid ocean ridge hydrothermal vents are a major source of 18o to the ocean in light of this new data we attempt to re evaluate the marine 18o budget from direct quantification of the main sources and sinks of oceanic oxygen 18 within the uncertainty of the flux estimates 18o inputs and outputs are found to balance each other showing that oceanic 18o is presently at a steady state using these present fluxes we examine the past evolution of the 18o composition of the ocean and speculate that the initial 18o oceanic content may have evolved rapidly towards its present value this suggests as already pointed out in previous studies that ocean water may have had a rather constant 18o composition over most of the earth s history and that 18o measurements in ancient cherts and carbonates may primarily record the evolution of the ocean temperature

an integrated chemical and stable isotope model of the origin of midocean ridge hot spring systems chemical and isotopic changes accompanying seawater basalt interaction in axial midocean ridge hydrothermal systems are modeled with the aid of chemical equilibria and mass transfer computer programs incorporating provision for addition and subtraction of a wide range of reactant and product minerals as well as cation and oxygen and hydrogen isotopic exchange equilibria the models involve stepwise introduction of fresh basalt into progressively modified seawater at discrete temperature intervals from 100 to 350 c with an overall water rock ratio of about 0 5 being constrained by an assumed 18 o h 2o at 350 c of 2 0 per mil h craig personal communication 1984 this is a realistic model because 1 the grade of hydrothermal metamorphism increases sharply downward in the oceanic crust 2 the water rock ratio is high 50 at low temperatures and low 0 5 at high temperatures and 3 it allows for back reaction of earlier formed minerals during the course of reaction progress the results closely match the major element chemistry von damm et al 1985 and isotopic compositions craig et al 1980 of the hydrothermal solutions presently emanating from vents at 21 n on the east pacific rise the calculated solution chemistry for example correctly predicts complete loss of mg and so 4 and substantial increases in si and fe however discrepancies exist in the predicted ph 5 5 versus 3 5 measured and state of saturation of the solution with respect to greenschist facies minerals the calculated d h 2o is 2 6 per mil in excellent agreement with analytical determinations the calculated chemical mineralogic and isotopic changes in the rocks are also in good accord with observations on altered basalts dredged from midocean ridges humphris and thompson 1978 stakes and o neil 1982 as well as with data from ophiolites gregory and taylor 1981 predicted alteration products include anhydrite and clay minerals at low temperatures and a typical albite epidote chlorite tremolite greenschist assemblage at 350 c the models demand that the major portion of the water rock interaction occur at temperatures of 300 350 c interaction at temperatures below approximately 250 c results in negative 18 o h 2o shifts contrary to the observed positive 18 o values of the fluids exiting at midocean ridge vents hydrogen isotope fractionation curves by suzuoki and epstein 1976 lambert and epstein 1980 and liu and epstein 1984 among others are compatible with the model and require d h 2o to increase at all temperatures as a result of seawater basalt interaction

influence of continental growth on mid ocean ridge depth the interconnectedness of life water and plate tectonics is strikingly apparent along mid ocean ridges mor where communities of organisms flourish off the disequilibrium of chemical potentials created by circulation of hydrothermal fluids driven by earth s heat nisbet and sleep 2001 staudigel et al 2004 moreover submarine hydrothermal environments may be critical for the emergence of life on earth nisbet and sleep 2001 oceans were likely present in the hadean valley et al 2002 harrison 2009 but questions remain about early earth s global tectonics van hunen and moyen 2012 including when seafloor spreading began and whether mid oceanic ridges were deep enough for maximum hydrothermal activities kasting et al 2006 for example plate tectonics influences global sea level by driving secular variations in the volume of ocean basins due to continental growth flament et al 2008 similarly variations in the distribution of seafloor age and associated subsidence flament et al 2008 due to assembly and dispersal of supercontinents coltice et al 2012 explains the largest sea level variation over the past 140 myr muller et al 2008 using synthetic plate configurations derived from numerical models of mantle convection coltice et al 2012 2014 appropriate for early earth we show that mor has remained submerged and its depths potentially constant over geologic time thus conditions in the early earth existed for hydrothermal vents at similar depths as today providing environments conducive for the development of life and allowing for processes such as hydrothermal alteration of oceanic crust to influence the mantle s geochemical evolution this article is protected by copyright all rights reserved

triple oxygen and hydrogen isotopic study of hydrothermally altered rocks from the 2 43 2 41 ga vetreny belt russia an insight into the early paleoproterozoic seawater abstract the early paleoproterozoic represents a period of rapid changes in earth systems that could have affected the stable isotopic composition of seawater the well preserved pillow structures hyaloclastites and komatiitic basalts of the 2 43 2 41 ga vetreny belt baltic shield provide a record of high temperature water rock interaction induced by contemporaneous seawater here we present results of mineralogical fluid inclusion hydrogen and triple oxygen isotopic analysis of hydrothermal alteration products emphasis is given to vein filling quartz and epidote as they likely formed at high water rock ratios ten minerals pairs quartz epidote and quartz calcite returned temperatures of isotopic equilibrium between 286 and 387 c which compares well to the homogenization temperatures measured for saline fluid inclusions hosted in vein quartz the computed d and 18o values of equilibrium fluids range between 31 and 12 and 1 36 and 3 20 respectively which overlap with the isotopic composition of ice free world seawater and fluids generated at submarine hydrothermal systems this is the earliest piece of evidence suggesting that early paleoproterozoic seawater had a d value close to 0 we also present triple oxygen isotopic composition of quartz and epidote that formed in similar facies of hydrothermal alteration from the relatively young 6 7 ma oceanic crust as sampled by the odp hole 504b in the eastern pacific ocean these data show similarity to the triple oxygen isotope analyses of the vetreny belt rocks indicating that the 2 43 2 41 ga seawater had the 17o value close to that of modern day seawater due to small fractionation at 300 390 c epidote water 1 epidotes present a strong evidence that equilibrium fluids had 17o values close to 0 based on the previously published quartz water calibration the computed 17o values of equilibrium fluids range between 0 11 and 0 03 significantly lower than that of seawater or inferred seawater derived fluids at low water rock ratios this can be explained by multiple factors including phase separation of fluids or and presence of low temperature quartz overgrowths both are reflected in the fluid inclusion data and in situ 18o measurements by ion microprobe sims presented here overall our study suggests that the 18o 17o and d values of the 2 43 2 41 ga seawater were 1 7 1 1 0 001 0 011 and 0 20 respectively similar to the modern values which reflects the dominant role of submarine hydrothermal alteration in the stable isotopic budget of seawater throughout earth s history

a synvolcanic origin for magnetite rich orebodies hosted by bif in the weld range district western australia abstract iron ore deposits hosted by archean banded iron formation bif in the weld range greenstone belt are representative of most of the documented iron ore deposits in the yilgarn craton they include near surface supergene goethite hematite orebodies that overlie and partly modify deeper occurrences of hypogene magnetite and specular hematite ores the cenozoic goethite hematite rich orebodies in these deposits are unequivocally the product of meteoric fluid alteration affecting bif in the near surface supergene environment however the deeper and likely older magnetite and specular hematite rich orebodies have a more contentious origin this study is the first to present a fluid alteration model for hypogene iron mineralization in the yilgarn craton that uses fluid inclusion and mineral chemistry data to constrain the physical chemical characteristics and source of hypogene fluids responsible for mineralization high grade 57 wt fe magnetite rich iron ore at the beebyn deposit defines a discontinuous series of 440 c and co2 rich paired o and c stable isotope data for stage 1 ferroan dolomite suggest that these fluids had a magmatic source while stage 1 magnetite chemistry e g enrichments in mg mn ca and na indicates chemical exchange took place between the fluids and mafic igneous rocks prior to crystallization of magnetite the presence of monophase carbonic fluid inclusions in stage 1 ferroan dolomite suggest that phase separation of a bicarbonate rich aqueous fluid took place in deeper parts of the hydrothermal system which led to the separation of the resultant volatile rich and brine phases during transport of the stage 1 fluid to shallower crustal levels cooling of the hydrothermal system during the stage 2 fluid event involved i an early brine 275 327 c 36 40 equiv wt nacl with cl br and c and o isotopes values that overlap the ranges for magmatic fluids with minor involvement of archean seawater and extensive chemical exchange with country rocks followed by ii pulses of moderate and lower temperature stage 2 brines 125 260 c 2 24 equiv wt cacl2 with cl br o and c isotope na br and ca ca na signatures that suggest cooling of magmatic derived fluids that mixed with archean seawater and reacted with mafic igneous country rocks in areas more distal to fluid pathways the last stage of formation of magnetite rich ore at the beebyn deposit involved the flow of stage 3 fluids through the existing fault network that controlled earlier fluids stage 3 fluids are lower temperature 98 175 c low to high salinity brines with cl br values that overlap reported ranges for 3 2 ga vent fluids and seawater thus they are likely the product of heated archean seawater that was chemically modified through interaction with mafic country rocks magnetite talc veins at the madoonga deposit have fluid halogen ratios for fluid inclusions hosted by magnetite that are compatible with a range of possible sources including low grade metamorphic fluids geothermal brines or oil field formation waters although their common spatial association with semi massive sulfides suggests their likely precipitation from brines derived from heated archean seawater more locally developed specular hematite quartz veins that cut folded magnetite rich ores at the beebyn and madoonga deposits are the product of iron redistribution in bif by heated meteoric fluids or seawater with precipitation of specular hematite as a consequence of oxidation and cooling of the fluid

early archean serpentine mud volcanoes at isua greenland as a niche for early life the isua supracrustal belt greenland of early archean age 3 81 3 70 ga represents the oldest crustal segment on earth its complex lithology comprises an ophiolite like unit and volcanic rocks reminiscent of boninites which tie isua supracrustals to an island arc environment we here present zinc zn isotope compositions measured on serpentinites and other rocks from the isua supracrustal sequence and on serpentinites from modern ophiolites midocean ridges and the mariana forearc in stark contrast to modern midocean ridge and ophiolite serpentinites zn in isua and mariana serpentinites is markedly depleted in heavy isotopes with respect to the igneous average based on recent results of zn isotope fractionation between coexisting species in solution the isua serpentinites were permeated by carbonate rich high ph hydrothermal solutions at medium temperature 100 300 c zinc isotopes therefore stand out as a ph meter for fossil hydrothermal solutions the geochemical features of the isua fluids resemble the interstitial fluids sampled in the mud volcano serpentinites of the mariana forearc the reduced character and the high ph inferred for these fluids make archean serpentine mud volcanoes a particularly favorable setting for the early stabilization of amino acids

stable isotope δ18o δd δ37cl evidence for multiple fluid histories in mid atlantic abyssal peridotites odp leg 209 abstract serpentinized abyssal peridotites sampled by the ocean drilling program leg 209 along the mid atlantic ridge near the 15 20 n fracture zone have been analyzed for oxygen hydrogen and chlorine isotope compositions in order to determine isotopic behavior under a wide range of serpentinization conditions and place constraints on fluid history oxygen and hydrogen thermometry suggests peak serpentinization temperatures of 300 500 c serpentine separates have low d values possibly due to a magmatic fluid component or low temperature exchange during seafloor weathering chlorine geochemistry focused on three holes 1274a and 1272a serpentinized peridotites and 1268a serpentinite locally altered to talc concentrations of both water soluble chloride wsc and structurally bound chloride sbc are significantly lower at hole 1268a compared to holes 1274a and 1272a the 37cl values for wsc and sbc of serpentinites in holes 1274a and 1272a are slightly positive avg wsc 0 20 n 22 and avg sbc 0 35 n 22 representing typical seawater hydration conditions commonly determined for abyssal peridotite the sbc of serpentinites from hole 1268a are also positive avg 0 63 whereas the sbc in talc dominated samples is negative avg 1 22 the wsc of both talc and serpentine dominated samples are also negative avg 0 15 we interpret the chlorine isotope data to preserve a record of multiple fluid events as seawater hydrated the peridotite 37cl was preferentially incorporated into the forming serpentine and water soluble salts yielding similar 37cl values on a regional scale as sampled by holes 1268a 1274a and 1272a the resultant pore fluid was left depleted in 37cl locally hole 1268a this evolved fluid was remobilized possibly due to the initiation of hydrothermal circulation in response to emplacement of a mafic magma body the low 37cl pore fluids attained elevated sio2 and sulfur concentrations due to interaction with the gabbroic intrusion and when ascending through the surrounding serpentinite caused formation of isotopically negative talc this secondary fluid also flushed the preserved serpentinite of its previously formed salts resulting in negative 37clwsc values the 37clsbc values of the serpentinite samples remained unmodified by reaction with the secondary fluid

origin of waters responsible for serpentinization of the izu ogasawara mariana forearc seamounts in view of hydrogen and oxygen isotope ratios many serpentinite seamounts occur over a region 20 120 km west of the trench axis in the izu ogasawara mariana forearc regions the hydrogen and oxygen isotopic compositions of serpentine from these regions indicate that there are at least two kinds of waters responsible for serpentinization seawater and water derived from dehydration of the descending slab serpentine from two mariana and two torishima samples with microscopically ductile and sheared texture sheared type have lower d 63to 52 and slightly higher 18o values 6 1 to 8 2 than that of other nine ogasawara samples with mesh texture mesh type d 43to 49 and 18o 5 8to 6 7 this suggests that the sheared type serpentine with lower d and slightly higher 18o values was formed within the wedge mantle by interaction with water derived from a descending slab the sheared texture is likely to have been produced during diapiric uplift the unaltered portion of the ultramafic bodies later interacted with seawater after emplacement at or near the seafloor resulting in formation of the mesh type serpentine with higher d values

isotope composition and volume of earth s early oceans oxygen and hydrogen isotope compositions of earth s seawater are controlled by volatile fluxes among mantle lithospheric oceanic and continental crust and atmospheric reservoirs throughout geologic time the oxygen mass budget was likely conserved within these earth system reservoirs but hydrogen s was not as it can escape to space isotopic properties of serpentine from the approximately 3 8 ga isua supracrustal belt in west greenland are used to characterize hydrogen and oxygen isotope compositions of ancient seawater archaean oceans were depleted in deuterium expressed as d relative to vienna standard mean ocean water vsmow by at most 25 5 but oxygen isotope ratios were comparable to modern oceans mass balance of the global hydrogen budget constrains the contribution of continental growth and planetary hydrogen loss to the secular evolution of hydrogen isotope ratios in earth s oceans our calculations predict that the oceans of early earth were up to 26 more voluminous and atmospheric ch4 and co2 concentrations determined from limits on hydrogen escape to space are consistent with clement conditions on archaean earth

archaean plate tectonics revisited 1 heat flow spreading rate and the age of subducting oceanic lithosphere and their effects on the origin and evolution of continents a simple model which relates the rate of seafloor creation and the age of the oceanic lithosphere at subduction to the rate of continental accretion can successfully explain the apparent differences between archaean and phanerozoic terrains in terms of plate tectonics the model has been derived using the following parameters 1 the spreading rate at mid ocean ridges 2 the age of the oceanic lithosphere at the time of subduction 3 the area age distribution of the seafloor 4 the continental surface area as a fraction of the total surface area of the earth and 5 the erosion rate of continents as a function of continental surface area and the total number of continental masses observations in phanerozoic terranes suggest that there are profound differences in the nature and volume of subduction zone igneous activity depending upon the age of the oceanic lithosphere being subducted and the nature of the overriding plate that is either continental or oceanic the subduction of young oceanic lithosphere less than 50 m y old which is thermally buoyant appears to result in a reduced volume of igneous activity most of the igneous activity caused by subduction of young oceanic lithosphere is either siliceous plutonism or bimodal tholeiitic rhyolitic volcanism when very young lithosphere is being subducted 50 m y old appears to result in greater volumes of igneous activity including the eruption of andesitic magmas thus andesites could only begin to be abundant in the rock record when older oceanic lithosphere began to be subducted our model predicts that as the earth aged and as heat flow from the interior of the earth diminished the proportion of old oceanic lithosphere being subducted increased fundamentally changing the nature of subduction zone igneous activity and the rate of continental accretion if the subduction of old oceanic lithosphere results in an 8 10 times greater volume of subduction zone magmatism our model predicts or explains all of the following observed features of earth history 1 archaean terranes appear to record two periods of rapid continental accretion between 3 8 and 3 5 b y ago and between 3 1 and 2 6 b y ago 2 there are very few differences and many marked similarities between rocks from archaean terranes and equivalent rocks from phanerozoic terranes 3 the total continental area appears to have remained essentially constant for the past 2 b y 4 archaean andesites are comparatively rare and the relative abundances of mafic and siliceous rocks appear to change during the archaean and the proterozoic with siliceous volcanics becoming proportionately more abundant in the geologic record with time 5 plutonic tonalites and trondhjemites appear to have been relatively much more abundant during the archaean plate tectonics is thus shown to have evolved over time due to a gradually decreasing rate of creation of oceanic lithosphere meaning that archaean tectonics and phanerozoic tectonics are but two points on an evolutionary continuum

what caused the rise of atmospheric o2 abstract oxygenic photosynthesis appears to have evolved well before o 2 levels increased in the atmosphere at around 2 4 ga this has led to numerous suggestions as to what may have kept o 2 suppressed and then eventually allowed it to rise these suggestions include changes in the recycling of carbon and sulfur relative to water or hydrogen a switch from dominantly submarine to dominantly subaerial volcanism gradual oxidation of the continents and a concomitant decrease in reduced metamorphic gases a decline in deposition of banded iron formations a decline in nickel availability and various proposals to increase the efficiency of photosynthesis several of these different mechanisms could have contributed to the rise of o 2 although not all of them are equally effective to be considered successful any proposed mechanism must make predictions that are consistent with the carbon isotope record in marine carbonates which shows relatively little change with time apart from transient but occasionally spectacular excursions the reasons for this constancy are explored here but are not fully resolved in the process of making these comparisons a self consistent redox balance framework is developed which will hopefully prove useful to others who may work on this problem and to astronomers who may one day try to decipher spectral signatures of oxygen on earth like exoplanets

factors influencing physical structure and lower trophic levels of the eastern bering sea shelf in 2005 sea ice tides and winds abstract in spring and fall 2005 cross and along shelf transects were sampled to evaluate the influence of physical forcing including sea ice tides and winds on the lower trophic levels of the bering sea ecosystem the hydrography nutrients chlorophyll and zooplankton abundance and species composition were all affected by the presence or absence of sea ice on a north south transect along the 70 m isobath in may shelf waters between 59 n and 62 n were cold and relatively fresh and benthic invertebrate larvae and chaetognaths were a significant fraction of the zooplankton community while to the south the water was warmer saltier and the zooplankton community was dominated by copepods the position of the transition between ice affected and ice free portions of the shelf was consistent among temperature salinity nutrients and oxygen this transition in the hydrographic variables persisted through the summer but it shifted 150 km northward as the season progressed while a transition also occurred in zooplankton species composition it was farther north than the physical chemical transition and did not persist through the summer mooring data demonstrated that the change in the position of the transition in physical and chemical properties was due to northward or eastward advection of water onto and across the shelf from south to north along the 70 m isobath tidal energy decreased resulting in a less sharply stratified water column on the northern portion of the middle shelf as opposed to a well defined two layered system in the southern portion this more gradual stratification in the north permitted a greater response to mixing from winds which were homogeneous from north to south thus the physical and biological structure at any one location over the middle shelf is dynamic over the course of a year and results from a combination of in situ processes and climate mediated regional forcing which is dominated in most years by sea ice

oceanography of the eastern bering sea ice edge zone in spring1 the ice edge region of the southeast bering sea was studied in terms of the hydrographic regime phytoplankton biomass and primary productivity during the springs of 1975 through 1977 the results showed that a phytoplankton bloom occurs at the ice edge just as the spring ice decay period begins and that this accounts for a significant proportion of the annual carbon input over the shallow shelf the bloom is intensified in time and space by the influence of the ice edge on the physical structure of the water column specifically melting ice seems to increase the stability of the water column near and under the ice by lowering the salinity frontal structure in salinity and temperature are apparent at the ice edge and are attributed to the melting ice but also at times to wind driven ekman type upwelling these data are also related to recent short term ca months year climatic fluctuations that seem to control the seasonal position of the ice edge zone relative to the shelf break in cold years the ice edge comes southward to the shelf break and overlies the more nutrientrich alaska stream bering sea source water in warm years the ice edge zone does not reach this nutrient rich water this may be important to the biology of the ice edge ecosystem the edge zones of seasonal sea ice are biologically productive serving as focal points for the congregation of large numbers of marine birds and mammals and thus represent ecologically critical habitats in subpolar regions the presence of a cold and solid boundary influences the biological regime in several ways including effects on the physical and chemical regimes in the adjacent seawater at least three structural features of the water column often associated with high oceanic primary production can occur in such an area simultaneously water column stability frontal structures and under certain conditions ice edge upwelling we show here that there is enhanced primary production due to water column stability and frontal structure at the edge of the seasonal sea ice in spring our data also suggest that ice edge upwelling occurs we show further that the intense

free energy distribution and hydrothermal mineral precipitation in hadean submarine alkaline vent systems importance of iron redox reactions under anoxic conditions abstract thermodynamic calculations of mixing between hypothetical seawater and hydrothermal fluid in the hadean deep ocean were carried out to predict saturation states of mineral precipitates and redox reactions that could occur in hadean submarine alkaline hydrothermal systems associated with the serpentinization of ultramafic rocks in the calculations the seawater was assumed to be weakly acidic ph 5 5 and to include carbon dioxide ferrous iron and silica with or without nitrate while the hadean hydrothermal fluid was assumed to be highly alkaline ph 11 and to contain abundant molecular hydrogen methane and bisulfide based on the archean geologic record the modern low temperature alkaline hydrothermal vent fluid lost city field and experimental and theoretical considerations the modeling indicates that potential mineral precipitates in the mixing zone hydrothermal chimney structures could consist mainly of iron sulfides but also of ferrous serpentine and brucite siderite and ferric iron bearing minerals such as goethite hematite and or magnetite as minor phases the precipitation of ferric iron bearing minerals suggests that chemical iron oxidation would be made possible by ph shift even under anoxic condition in the mixing zone comprising an inorganic barrier precipitated at the interface of the two contrasting solutions various redox reactions release free energy with the potential to drive endergonic reactions assuming the involvement of coupling inorganic protoenzymes hydrogenotrophic methanogenesis and acetogenesis long considered the most ancient forms of biological energy metabolisms are able to achieve higher maximum energy yield 0 5 kj kg hydrothermal fluid than those in the modern serpentinization associated seafloor hydrothermal systems e g kairei field furthermore the recently proposed methanotrophic acetogenesis pathway was also thermodynamically investigated it is known that methanotrophic acetogenesis would require additional exergonic reactions to compensate its most endergonic methane to methanol conversion reaction at the oxidative entry to the metabolic pathway our calculations support the view that this thermodynamic barrier could be overcome by the reduction of nitrate in seawater at low temperature as previously suggested however the thermodynamic calculations also revealed that the reduction of ferric iron bearing minerals would occur at the outer margin and within the hydrothermal chimney wall the maximum available energy of iron reducing methanotrophic acetogenesis was calculated to be 0 25 0 35 kj kg hydrothermal fluid although this value is lower than theoretically available through nitrate reduction which approaches 0 45 1 25 kj kg hydrothermal fluid on the outer cool margins of a putative hadean alkaline chimney it is higher than that of sulfate reducing anaerobic oxidation of methane in the lost city field these results suggest that iron reduction had the potential to drive methanotrophy and that the hadean hydrothermal mixing zone was energetically more favorable to methanotrophy than previously thought we conclude that iron oxidation and reduction in oxyhydroxides probably played important roles in the early evolution of energy metabolisms in the hadean alkaline hydrothermal system

a warm or a cold early earth new insights from a 3 d climate carbon model abstract oxygen isotopes in marine cherts have been used to infer hot oceans during the archean with temperatures between 60 c 333 k and 80 c 353 k such climates are challenging for the early earth warmed by the faint young sun the interpretation of the data has therefore been controversial 1d climate modeling inferred that such hot climates would require very high levels of co2 2 6 bars previous carbon cycle modeling concluded that such stable hot climates were impossible and that the carbon cycle should lead to cold climates during the hadean and the archean here we revisit the climate and carbon cycle of the early earth at 3 8 ga using a 3d climate carbon model we find that co2 partial pressures of around 1 bar could have produced hot climates given a low land fraction and cloud feedback effects however such high co2 partial pressures should not have been stable because of the weathering of terrestrial and oceanic basalts producing an efficient stabilizing feedback moreover the weathering of impact ejecta during the late heavy bombardment lhb would have strongly reduced the co2 partial pressure leading to cold climates and potentially snowball earth events after large impacts our results therefore favor cold or temperate climates with global mean temperatures between around 8 c 281 k and 30 c 303 k and with 0 1 0 36 bar of co2 for the late hadean and early archean finally our model suggests that the carbon cycle was efficient for preserving clement conditions on the early earth without necessarily requiring any other greenhouse gas or warming process

2 7 ga metamorphic peridotites from southeast greenland record the oxygen isotope composition of archean seawater abstract the 18 o value of seawater is presently buffered by high temperature hydrothermal alteration and low temperature weathering of lithospheric rocks it is much debated whether the 18 o of seawater has been buffered to this steady state value throughout earth s history or alternatively whether it gradually increased towards the present value since the archean a third possibility is that the 18 o of seawater was buffered at a higher value before continents emerged and has been buffered at its current value 18 o 1 since the emergence of continents in this contribution we reconstruct the 18 o of archean seawater from triple oxygen isotope 17 o 18 o variations in 2 7 ga ultramafic rocks that reacted with fluids that in turn had been derived from seawater in the archean the samples that were studied are peridotites from the ivnartivaq complex an ultramafic lens in the archean kuummiut terrane rae craton southeast greenland that have unusually low 18 o values for peridotites in olivine 1 7 18 o 4 6 relative to vsmow bulk rock trace element concentrations mineral compositions and u pb dating of zircon grains in the peridotites indicate that these samples are metamorphic peridotites that formed by the dehydration of serpentinites 2 7 ga ago the serpentinite protoliths in turn had formed by alteration of ultramafic cumulate rocks at high temperatures 250 450 c by fluids that were derived from seawater triple oxygen isotope variations in olivine from the peridotites indicate that the fluids could not have been derived from seawater with a significantly higher or lower 18 o value than that of seawater in the phanerozoic but could have been derived from seawater with a value of 18 o 1 i e the modern ice free seawater composition we conclude that the 18 o of seawater had reached its current steady state value by 2 7 ga ago

the neoarchaean storo supracrustal belt nuuk region southern west greenland an arc related basin with continent derived sedimentation we present new major and trace element data as well as sm nd isotope compositions for archaean supracrustal rocks and a gabbro anorthosite complex from the island of storo in godthabsfjord southern west greenland we also provide new u pb isotope data for zircon extracted from these rocks the storo rocks have experienced amphibolite facies metamorphism and the entire sequence forms an east dipping frontal thrust ramp in tectonic contact with mesoarchaean nuk gneisses to the west and eoarchaean itsaq gneisses to the east these orthogneisses record a complex regional accretion history as established by previous work the present study aims at explaining the geochemical features of the storo supracrustal belt ssb which comprises metavolcanic and metasedimentary rocks that are situated within this collisional zone the ssb has a maximum age of ca 2800 ma constrained by the youngest detrital zircon population found in a metasedimentary unit the minimum age of the ssb is 2707 8 ma defined by previously published re os isotope data the metavolcanic rocks have a tholeiitic basaltic composition with relatively flat primitive mantle normalised trace element patterns and generally negative nb anomalies nb nb 0 30 0 90 they plot above the mantle array in th yb nb yb space consistent with a subduction zone affinity as also proposed by previous studies a thin fault contact separates the ssb from a gabbro anorthosite complex formally defined here as the storo anorthosite complex which has an age of ca 3050 ma the sm nd isotope data of the ssb suggest that these metavolcanic rocks experienced contamination by a crustal source that was isotopically similar to the storo anorthosite complex sac this in turn suggests that the sac could have formed the basement for the younger volcanic sequence of the ssb or alternatively that the mantle source of the ssb was contaminated by melts derived from sac aged crust or sediments the metasedimentary rocks of ssb show a mixed mafic felsic component with variable degrees of maturity highly mature metasediments of the ssb contain several age populations of regionally well known magmatic events and thus support a significant local crustal provenance furthermore the youngest documented detrital zircon is found in a thin metasedimentary unit within the metavolcanic rocks and thereby shows that the ssb formed in close proximity to subaerially exposed continental crust i e a back arc environment and not a distal island arc setting as previously proposed finally this suggests that relatively cool lower continental crust which was capable of supporting subaerial mountains existed at least locally during the meso neoarchaean

on the recent warming of the southeastern bering sea shelf abstract during the last decade the southeastern bering sea shelf has undergone a warming of 3 c that is closely associated with a marked decrease of sea ice over the area this shift in the physical environment of the shelf can be attributed to a combination of mechanisms including the presence over the eastern bering sea shelf of a relatively mild air mass during the winter especially from 2000 to 2005 a shorter ice season caused by a later fall transition and or an earlier spring transition increased flow through unimak pass during winter which introduces warm gulf of alaska water onto the southeastern shelf and the feedback mechanism whereby warmer ocean temperatures during the summer delay the southward advection of sea ice during winter while the relative importance of these four mechanisms is difficult to quantify it is evident that for sea ice to form cold arctic winds must cool the water column sea ice is then formed in the polynyas during periods of cold north winds and this ice is advected southward over the eastern shelf the other three mechanisms can modify ice formation and melt and hence its extent in combination these four mechanisms have served to temporally and spatially limit ice during the 5 year period 2001 2005 warming of the eastern bering sea shelf could have profound influences on the ecosystem of the bering sea from modification of the timing of the spring phytoplankton bloom to the northward advance of subarctic species and the northward retreat of arctic species

oxygen and hydrogen isotope evidence for a temperate climate 3 42 billion years ago the widely held view that the archaean climate around 3 5 billion years ago was remarkably warm with ocean temperatures perhaps as high as 80 c has been questioned on the grounds that the established method of estimating ancient ocean temperature from the oxygen isotope ratios of sedimentary deposits is subject to significant uncertainty michael hren et al have adopted a different approach to estimating ocean temperature based on an analysis of both oxygen and hydrogen isotopes of 3 4 billion year old buck reef chert sediments from south africa the isotopes sampled are consistent with formation in waters no warmer than about 40 c suggesting that earth s early oceans may have been far cooler than previously thought the study of stable oxygen isotope ratios 18o of precambrian cherts suggests that ocean temperatures during the archaean era about 3 5 billion years ago were between 55 c and 85 c but uncertainty about the 18o of the primitive ocean has led to considerable debate regarding this conclusion here a combined analysis of oxygen and hydrogen istopes sampled from 3 42 billion year old buck reef chert rocks in south africa indicates that the ancient ocean was much cooler than previously thought stable oxygen isotope ratios 18o of precambrian cherts have been used to establish much of our understanding of the early climate history of earth1 2 3 and suggest that ocean temperatures during the archaean era 3 5 billion years ago were between 55 c and 85 c ref 2 but because of uncertainty in the 18o of the primitive ocean there is considerable debate regarding this conclusion examination of modern and ancient cherts indicates that another approach using a combined analysis of 18o and hydrogen isotopes d rather than 18o alone can provide a firmer constraint on formational temperatures without independent knowledge of the isotopic composition of ambient waters4 5 here we show that 18o and d sampled from 3 42 billion year old buck reef chert rocks in south africa are consistent with formation from waters at varied low temperatures the most 18o enriched buck reef chert rocks record the lowest diagenetic temperatures and were formed in equilibrium with waters below 40 c geochemical and sedimentary evidence suggests that the buck reef chert was formed in shallow to deep marine conditions so our results indicate that the palaeoarchaean ocean was isotopically depleted relative to the modern ocean and far cooler 40 c than previously thought2

comparison of warm and cold years on the southeastern bering sea shelf and some implications for the ecosystem the southeastern middle shelf of the bering sea has exhibited extreme variability in sea ice extent temperature and the distribution and abundance of species at multiple trophic levels over the past four decades from 1972 2000 there was high interannual variability of areal extent of sea ice during spring march april in 2000 this shifted to a 5 year 2001 2005 period of low ice extent during spring which transitioned to a 4 year 2007 2010 period of extensive sea ice high low areal extent of sea ice in spring was associated with cold warm water column temperatures for the following 6 7 months the ocean currents also differed between warm and cold years during cold years the monthly mean currents over the shelf were largely westward while in warm years the direction of currents was more variable with northward flow during december february and relatively weak flow during the remainder of the year the types and abundance of zooplankton differed sharply between warm and cold years this was especially true during the prolonged warm period 2001 2005 and cold period 2007 2010 and was less evident during the years of high interannual variability during the warm period there was a lack of large copepods and euphausiids over the shelf however their populations rebounded during cold period small crustacean zooplankton taxa did not appear to vary between and warm and cold years for both walleye pollock and pacific cod year class strength recruitment was low during the prolonged warm period but improved during the following cold period year class strength did not appear to vary as a function of warm and cold years during the period of high year to year variability also recruitment of arrowtooth flounder a predator of pollock and cod did not appear influenced by the warm or cold years finally the distribution and relative abundance of fin whales appeared to differ in warm and cold years with fewer whales on the southeastern middle shelf during warm years

oxygen isotopes in authigenic quartz from massive salt deposits abstract we describe a new geochemical tool that could provide temperatures of ancient basins in which massive evaporites were deposited the oxygen isotope composition of fine crystalline quartz found in large halite bodies such quartz is well preserved from post depositional alterations and it can be relatively easily separated for the purpose of this study five halite samples were selected from four various evaporite basins spanning in age from the early cambrian to the late jurassic the obtained isotope temperatures refer to locations where evaporites were deposited i e in subtropical zones of the earth as it may be estimated from continental distribution during phanerozoic times reasonable temperatures are obtained with an assumption for the 18o of brines ranging from 1 to 0 during halite deposition the assumption of higher 18o values leads to unrealistic temperatures higher than the homogenization temperatures of fluid inclusions in halite

spring and fall phytoplankton blooms in a productive subarctic ecosystem the eastern bering sea during 1995 2011 abstract the timing and magnitude of phytoplankton blooms in subarctic ecosystems often strongly influence the amount of energy that is transferred through subsequent trophic pathways in the eastern bering sea spring bloom timing has been linked to ice retreat timing and production of zooplankton and fish a large part of the eastern bering sea shelf 500 km wide is ice covered during winter and spring four oceanographic moorings have been deployed along the 70 m depth contour of the eastern bering sea shelf with the southern location occupied annually since 1995 the two northern locations since 2004 and the remaining location since 2001 chlorophyll a fluorescence data from the four moorings provide 37 realizations of a spring bloom and 33 realizations of a fall bloom we found that in the eastern bering sea if ice was present after mid march spring bloom timing was related to ice retreat timing p n 11 a fall bloom also commonly occurred usually in late september average day 274 se 4 2 n 33 and its timing was not significantly related to the timing of storms p 0 88 df 1 27 or fall water column overturn p 0 49 df 1 27 the magnitudes of the spring and fall blooms were correlated p 0 011 df 28 the interval between the spring and fall blooms varied between four to six months depending on year and location we present a hypothesis to explain how the large crustacean zooplankton taxa calanus spp likely respond to variation in the interval between blooms spring to fall and fall to spring

precambrian paleosols and atmospheric co2 levels abstract precambrian atmospheric pco2 levels were previously estimated using a simple thermodynamic model based on the mineral assemblage in paleosols in addition to theoretical flaws with that model recalculation of pco2 levels using more recent thermodynamic data gives significantly lower values a new model based on the mass balance of weathering in paleosols gives consistent results from three separate 2 2 ga old paleosols the calculated pco2 value of 23 3 3 times present atmospheric levels is insufficient to overcome the faint young sun paradox suggesting that another greenhouse gas such as ch4 was present at elevated levels relative to the present atmosphere to account for the discrepancy applying this new approach to other precambrian paleosols a proterozoic pco2 curve is generated which indicates consistently high pco2 from 2 5 to 1 8 ga ago and a substantial drop in atmospheric pco2 at some time between 1 8 and 1 1 ga ago

clumped isotope thermometry of magnesium carbonates in ultramafic rocks abstract magnesium carbonate minerals produced by reaction of h 2 o co 2 with ultramafic rocks occur in a wide range of paragenetic and tectonic settings and can thus provide insights into a variety of geologic processes including 1 deposition of ore grade massive vein cryptocrystalline magnesite 2 formation of hydrous magnesium carbonates in weathering environments and 3 metamorphic carbonate alteration of ultramafic rocks however the application of traditional geochemical and isotopic methods to infer temperatures of mineralization the nature of mineralizing fluids and the mechanisms controlling the transformation of dissolved co 2 into magnesium carbonates in these settings is difficult because the fluids are usually not preserved clumped isotope compositions of magnesium carbonates provide a means to determine primary mineralization or re equilibration temperature which permits the reconstruction of geologic processes that govern magnesium carbonate formation we first provide an evaluation of the acid fractionation correction for magnesium carbonates using synthetic magnesite and hydromagnesite along with natural metamorphic magnesite and low temperature hydromagnesite precipitated within a mine adit we show that the acid fractionation correction for magnesium carbonates is virtually indistinguishable from other carbonate acid fractionation corrections given current mass spectrometer resolution and error in addition we employ carbonate clumped isotope thermometry on natural magnesium carbonates from various geologic environments and tectonic settings cryptocrystalline magnesite vein deposits from california red mountain magnesite mine austria kraubath locality turkey tutluca mine eskisehir district and iran derakht senjed deposit exhibit broadly uniform 47 compositions that yield apparent clumped isotope temperatures that average 23 7 5 0 c based on oxygen isotope thermometry these clumped isotope temperatures suggest mineralization at shallow crustal depths in the presence of meteoric water hydrous magnesium carbonates from a 400 km latitudinal transect along the serpentinized peridotite bodies of the california coast ranges record clumped isotope temperatures between 14 2 and 22 7 2 8 c in agreement with historical maximum temperatures during the rainy season for california talc carbonate alteration of ultramafic rocks in greenland isua supracrustal belt and vermont ludlow yields clumped isotope alteration temperatures of magnesite and dolomite between 326 and 490 c broadly consistent with paragenesis and thermodynamic analysis for co 2 metasomatism of ultramafic rocks these metamorphic carbonates extend the applicability of clumped isotope thermometry to high temperature magnesium carbonate systems and indicate equilibrium blocking temperatures for magnesite of 490 c our study demonstrates the applicability of the clumped isotope approach to provide information on the formation of magnesium carbonates as ore resources surface records of climate and metamorphic assemblages

oxygen isotope analysis of fossil organic matter by secondary ion mass spectrometry we have developed an analytical procedure for the measurement of oxygen isotope composition of fossil organic matter by secondary ion mass spectrometry sims at the sub per mill level with a spatial resolution of 20 30 m the oxygen isotope composition of coal and kerogen samples determined by sims are on average consistent with the bulk oxygen isotope compositions determined by temperature conversion elemental analysis isotope ratio mass spectrometry tc ea irms but display large spreads of 18o of 5 10 attributed to mixing of remnants of organic compounds with distinct 18o signatures most of the 18o values obtained on two kerogen residues extracted from the eocene clarno and early devonian rhynie continental chert samples and on two immature coal samples range between 10 and 25 based on the average 18o values of these samples and on the o isotope composition of water processed by plants that now constitute the eocene clarno kerogen we estimated 18owater values ranging between around 11 and 1 which overall correspond well within the range of o isotope compositions for present day continental waters sims analyses of cyanobacteria derived organic matter from the silurian zdanow chert sample yielded 18o values in the range 12 20 based on the o isotope composition measured on recent cyanobacteria from the hypersaline lake natron tanzania and on the o isotope composition of the lake waters in which they lived we propose that 18o values of cyanobacteria remnants are enriched by about 18 2 to 22 2 relative to coeval waters this relationship suggests that deep ocean waters in which the zdanow cyanobacteria lived during early silurian times were characterised by 18o values of around 5 4 this study establishing the feasibility of micro analysis of phanerozoic fossil organic matter samples by sims opens the way for future investigations of kerogens preserved in archean cherts and of the o isotopic composition of ocean water at that period in time

coupled nitrification denitrification in sediment of the eastern bering sea shelf leads to 15n enrichment of fixed n in shelf waters 1 we studied the nitrogen biogeochemistry of the ice covered eastern bering sea shelf using the isotope ratios 15n 14n and 18o 16o of no3 and other n species the 15n 14n of late winter no3 on the shelf decreases inshore and is inversely correlated with bottom water nh4 consistent with an input of low 15n 14n no3 from partial nitrification of nh4 remineralized from the sediments an inshore 15n 14n increase in total dissolved n tdn suggests that 1 the sediment derived nh4 is elevated in 15n due to the same partial nitrification that yields the low 15n 14n no3 and 2 15n deplete no3 from partial nitrification within the sediments is denitrified to n2 the proportion of newly nitrified no3 on the shelf evidenced by an inshore decrease in no3 18o 16o is correlated with the n deficit further implicating nitrification coupled to denitrification however a simple n isotope budget indicates a comparable rate of denitrification supported by diffusion of no3 into the sediments the isotopic impact of benthic n loss is further demonstrated by a correlation between the 15n 14n of shelf surface sediment and the n deficit of the overlying water column both of which increase inshore and northward as well as by arctic no3 isotope data indicating that the fixed n transported through bering strait has a 15n 14n higher than is found in the open bering sea the significant net isotope effect of benthic n loss on the bering shelf 6 8 is at odds with previous assumptions regarding the global ocean s n isotope budget

the ph of enceladus ocean abstract saturn s moon enceladus is a geologically active waterworld the prevailing paradigm is that there is a subsurface ocean that erupts to the surface which leads to the formation of a plume of vapor and ice above the south polar region the chemistry of the ocean is just beginning to be understood but is of profound geochemical and astrobiological interest here we determine the ph of the ocean using a thermodynamic model of carbonate speciation observational data from the cassini spacecraft are used to make a chemical model of ocean water on enceladus the model suggests that enceladus ocean is a na cl co3 solution with an alkaline ph of 11 12 the dominance of aqueous nacl is a feature that enceladus ocean shares with terrestrial seawater but the ubiquity of dissolved na2co3 suggests that soda lakes are more analogous to the enceladus ocean the high ph implies that the hydroxide ion should be relatively abundant while divalent metals should be present at low concentrations owing to buffering by carbonates and phyllosilicates on the ocean floor carboxyl groups in dissolved organic species would be negatively charged while amino groups would exist predominately in the neutral form knowledge of the ph improves our understanding of geochemical processes in enceladus ocean the high ph is interpreted to be a key consequence of serpentinization of chondritic rock as predicted by prior geochemical reaction path models although degassing of co2 from the ocean may also play a role depending on the efficiency of mixing processes in the ocean serpentinization leads to the generation of h2 a geochemical fuel that can support both abiotic and biological synthesis of organic molecules such as those that have been detected in enceladus plume serpentinization and h2 generation should have occurred on enceladus like on the parent bodies of aqueously altered meteorites but it is unknown whether these critical processes are still taking place or if enceladus rocky core has been completely altered by past hydrothermal activity the presence of native h2 in the plume would provide strong evidence for contemporary aqueous alteration that replenishes this source of energy for possible life the high ph also suggests that the delivery of strong oxidants from the surface to the ocean has not been significant otherwise sulfuric acid would be produced which would be consistent with geophysical models of episodic resurfacing activity on enceladus this paper represents an expansion of chemical oceanography to an ocean planet beyond earth

iron deposits hosted by banded iron formations in the yilgarn craton products of sequential iron enrichment by magmatic marine and meteoric fluids abstract mesoarchean algoma type bif in the yilgarn craton are locally enriched by secondary processes to iron concentrations approaching 72 wt fe while their near surface goethite hematite ores are unequivocally the product of supergene fluid alteration their deeper magnetite and crystalline hematite martite ores have a contentious origin this study shows that magnetite ores formed after diagenesis and peak greenschist facies metamorphism of bif coinciding with regional deformation events the ores formed by a multi stage process involving initial replacement of primary quartz bands in bif by hypogene carbonate minerals followed by the dissolution of the carbonate and concentration of magnetite at the beebyn deposit the earliest fluids were hot 440 c co2 vapor rich and were likely derived from felsic magmatic fluids in contrast the fluids responsible for carbonate alteration at the matthew ridge koolyanobbing and windarling deposits were cooler 366 to 125 c and aqueous rich with salinities from 0 3 to 43 9 wt nacl equiv their cl br and c o isotopic ratios suggest they are the product of mixing between magmatic fluids and heated seawater in all deposits later cooling 178 to 98 c of these fluids led to dissolution of carbonate minerals and concentration of magnetite dated monazite and xenotime from magnetite ores demonstrates that fluid alteration of bif began in the mesoarchean and continued episodically through to the paleoproterozoic later specular hematite rich veins that cut and modify magnetite ores crystallized from aqueous rich fluids that are more oxidized with salinities from 0 to 28 7 wt nacl equiv and crystallization temperatures of 243 to 85 c their cl br and c o isotopic fluid ratios indicate that they formed from mixing between heated seawater and meteoric waters the bif hosted iron deposits in the yilgarn craton show remarkable similarities with the well studied iron deposits in the carajas mineral province and hamersley basin they all show the same transition through time from magnetite to hematite rich ores subsequent episodic tectonically driven fluid alteration events led to further iron enrichment in these deposits the transition in ore types most likely corresponds to a common guiding process namely the uplift of crustal rocks containing bif resulting in the progressive shallowing of fluid alteration pathways and the greater influence of cooler more oxidized hydrothermal fluids unlike iron deposits hosted by algoma type bif in the yilgarn and carajas iron deposits hosted by superior type bif in the hamersley basin display a greater influence of oxidized marine and meteoric waters without involvement of magmatic fluids

stratification on the eastern bering sea shelf revisited abstract the timing and magnitude of stratification can have profound influences on the marine ecosystem on the eastern bering sea shelf in the absence of strong wind mixing stratification can be initiated by the melting of seasonal sea ice or by springtime warming of the surface temperature and salinity both influence the stratification of the eastern bering sea shelf with their relative importance varying spatially and temporally in the northern middle shelf domain north of 60 n salinity stratification is often as important as temperature stratification on the southern middle shelf while the influence of temperature on stratification dominates during summer the influence of salinity stratification plays a role in the interannual variability mooring 2 m2 56 9 n 164 1 w has been deployed at 70 m depth in the southern middle shelf domain since 1995 data from this mooring show that stratification typically begins to set up in may and to break down in september october but these dates can vary by 30 d while no trend is found in the timing of the spring setup the fall stratification breakdown exhibited a trend toward later breakdown 2 d later per year from 1996 to 2009 results suggest that it may be difficult to forecast stratification on the eastern bering sea shelf from climate models as simple indices of wind mixing or heat fluxes are not correlated with stratification contrary to intuition the strength of summer stratification is not correlated with depth averaged temperature warm years such as 2000 and 2001 can have low stratification and cold years such as 2007 can have very high stratification this decoupling of stratification and temperature has implications for forecasting the ecosystem in the face of climate change as we cannot assume that projections of a warmer climate simply imply higher stratification in the future

limited archaean continental emergence reflected in an early archaean 18 o enriched ocean the origin and evolution of earth s biosphere were shaped by the physical and chemical histories of the oceans marine chemical sediments and altered oceanic crust preserve a geochemical record of these histories marine chemical sediments for example exhibit an increase in their 18o 16o ratio through time the implications of this signal are ambiguous but are typically cast in terms of two endmember but not mutually exclusive scenarios the oceans may have been much warmer in the deep past if they had an oxygen isotope composition similar to that of today alternatively the nature of fluid rock interactions including the weathering processes associated with continental emergence may have been different in the past leading to an evolving oceanic oxygen isotope composition here we examine approximately 3 24 billion year old hydrothermally altered oceanic crust from the panorama district in the pilbara craton of western australia as an alternative oxygen isotope archive to marine chemical sediments we find that at that time seawater at panorama had an oxygen isotope composition enriched in 18o relative to the modern ocean with a 18o of 3 3 0 1 vsmow we suggest that seawater 18o may have decreased through time in contrast to the large increases seen in marine chemical sediments to explain this possibility we construct an oxygen isotope exchange model of the geologic water cycle which suggests that the initiation of continental weathering in the late archaean between 3 and 2 5 billion years ago would have drawn down an 18o enriched early archaean ocean to 18o values similar to those of modern seawater we conclude that earth s water cycle may have gone through two separate phases of steady state behaviour before and after the emergence of the continents the water cycle was in two different steady states before and after continental emergence as recorded in the decreasing oxygen isotope values of seawater since the archaean according to an inverse geochemical model of the oceanic crustal record

recent bering sea warm and cold events in a 95 year context the meteorology and oceanography of the southeastern bering sea shelf was recently dominated by a multi year warm event 2000 2005 followed by a multi year cold event 2007 2010 we put these recent events into the context of the 95 year air temperature record from st paul island and with concurrent spatial meteorological fields for march 2000 2005 the mean air temperature anomaly at st paul was 2 1 1c above the long term mean and for march 2007 2010 the mean temperature anomaly at st paul was 4 7 1c below the long term mean the only multi year temperature deviations comparable to the first decade of the 2000s are a cold event from 1971 to 1976 followed by a warm event from 1978 to 1983 there was also a short warm event 1935 1937 the temperature transition between warm and cold events in the 1970s and 2000s took two years while there are theoretical arguments for some physical memory processes in the north pacific climate system we cannot rule out that the recent warm and cold events are of a random nature they are rare in the st paul temperature record they are dominated by north pacific wide sea level pressure events rather than local bering sea processes and they are consistent with a red noise model of climate variability the 1970s transition

sea ice and water column structure on the eastern bering sea shelf abstract seasonal sea ice is a defining characteristic of the eastern bering sea shelf and plays a critical role in determining the vertical structure of temperature and salinity over this shelf ice movement relative to local winds ice composition and the impact of both arrival and retreat of ice on the water column at four mooring sites over the middle shelf are examined ice forms primarily in coastal regions and is advected over the southern and outer shelves ice drift from satellite data for two representative years 2003 and 2007 was 2 of local ncep wind speed and oriented 44 to the right of the winds r 2 0 25 measurements from 30 ice cores collected in 2006 2009 gave an average salinity of 5 62 0 88 and an average nitrate concentration of 0 99 0 83 m time series data collected at the biophysical moorings in the bering sea 1995 2012 were used to explore the evolution of the water column under ice at the northern mooring m8 the water column had mixed and cooled to 1 c prior to the arrival of ice little melt occurred after ice arrival at the other three moorings the ocean temperature was 2 4 c when ice arrived resulting in extensive melt melting ice freshened and cooled the upper water column resulting in stratification which persisted for 10 25 days wind induced water column mixing occurred more slowly under the ice than in ice free waters an estimated 1 4 m of ice melted with the first arrival of ice at the three southern moorings where the latent heat of fusion accounted for approximately half the observed cooling during ice retreat there appeared to be little ice melt around the southern two moorings but an estimated 0 8 m at m5 and m8 the extent of ice melt sets up the water column for the following summer

lizardite versus antigorite serpentinite magnetite hydrogen and life the serpentinization of peridotite operates according to one or the other or a combination of two end member mechanisms in low temperature environments 50 300 c where lizardite is the predominant serpentine mineral olivine is consumed by reaction with h2o but its composition mg remains unchanged mg rich lizardite magnetite and dihydrogen gas brucite are products of the reaction at higher temperatures 400 600 c rates of mgfe diffusion in olivine are orders of magnitude faster with the result that the growth of mg rich antigorite can be accommodated by a compositional adjustment of olivine eliminating the need to precipitate magnetite and evolve hydrogen this latter end member mechanism probably best reflects the situation in the forearc mantle wedge

nutrient and phytoplankton dynamics on the inner shelf of the eastern bering sea the nitrogen cycle on the inner shelf of the southeastern bering sea is complicated due to limited nutrient replenishment across this broad shelf and substantial nitrogen loss through sedimentary processes while diffusion at the inner front may periodically support new production the shelf is generally hypothesized to be a regenerative system this study uses a combination of hydrographic surveys and measurements of nitrogen assimilation and benthic fluxes to examine nitrogen cycling on the inner shelf and connectivity between the middle and inner shelves of the southern and central bering sea results establish the inner shelf as primarily a regenerative system even in spring although new production can occur at the inner front results also identify key processes that influence nutrient supply to the inner shelf and reveal coupling between the middle shelf nutrient pool and production on the inner shelf this article is protected by copyright all rights reserved

lithospheric flexure in the sichuan basin and longmen shan at the eastern edge of tibet 1 the mountain range at the steep eastern edge of the tibetan plateau the longmen shan was deformed by a mw7 9 earthquake with oblique thrust and strike slip motion in 2008 the tectonic processes and structure of the lithosphere beneath this range have been controversial gravity measurements reflect the distribution of mass within the earth including the large load of rock above the geoid in mountain ranges we investigate the response of the lithosphere to the load of the longmen shan and estimate the flexural rigidity or effective elastic thicknessteusing new gravity data acquired by recent satellites and the combined goco2s and eigen 6c datasets the free air gravity anomalies over the longmen shan show that its mass is supported by flexure of the adjacent sichuan basin lithosphere similar to the flexural support of the himalayas analysis of a stacked profile of the free air anomalies shows that the effective elastic thickness of the basin lithosphere is greater than 10 km but has a broad minimum misfit function with no upper limit on the thickness two dimensional admittance analysis shows thete of easternmost tibet is very low approximately 7 km

contrasting serpentinization processes in the eastern central alps stable isotope compositions have been determined for serpentinites from between davos arosa platta nappe switzerland and the valmalenco italy d and 18o values 120 to 60 and 6 10 respectively in the arosa platta nappe indicate that serpentinization took place on the continent at relatively low temperatures in the presence of limited amounts of metamorphic fluids that contained a component of meteoric water one sample of chrysotile has a 18o value of 13 providing evidence of high w r ratios and low formation temperature of lizardite chrysotile in this area in contrast relatively high d values 42 to 34 and low 18o values 4 4 7 4 for serpentine in the eastern part of the valmalenco suggest a serpentinization process that took place at moderate temperatures in fluids that were dominated by ocean water the antigorite in the valmalenco is the first reported example of continental antigorite with an ocean water signature an amphibole sample from a metasomatically overprinted contact zone to metasediments d 36 indicates that the metasomatic event also took place in the presence of ocean water lower d values 93 to 60 of serpentines in the western part of the valmalenco suggest a different alteration history possibly influenced by fluids associated with contact metamorphism low water rock ratios during regional metamorphism and metasomatism have to be assumed for both regions

sulfur and oxygen isotope constraints on the sedimentary history of apparent conglomerates from the nuvvuagittuq greenstone belt nunavik quebec abstract mafic igneous rocks of the nuvvuagittuq greenstone belt ngb crystallized before 3 8 ga and possibly as early as 4 3 ga potentially making the belt the oldest known supracrustal sequence on earth however detrital zircons from a rare quartz biotite schist in the ngb yield significantly younger ages of 3 77 ga or less these appear to be inconsistent with the ages of the mafic igneous rocks as the quartz biotite schist has been interpreted as a metaconglomerate formed by the dismantling of preexisting lithologies in order to assess this genetic interpretation we performed a sulfur and oxygen isotope study of the quartz biotite schist sulfide grains found in quartz clasts and the matrix show significant mass independent fractionation of sulfur isotopes 0 2 33s 1 0 mean 33s 0 5 0 1 secondary sulfides from crosscutting veins do not show mass independent fractionation of sulfur isotopes 0 1 33s 0 3 mean 33s 0 1 0 1 oxygen isotope compositions of quartz from clasts matrix and a fine grained lens are highly enriched in 18o 16 9 18o 26 7 non zero 33s values indicate a surficial origin for sulfur probably the eoarchean atmosphere while high 18o values suggest a low temperature 65 18 c origin for the quartz likely as chemical precipitation of a chert precursor from si saturated seawater therefore the coupled s and o isotope measurements show that primary isotopic signatures characteristic of surficial environments survived the protracted metamorphic history of the ngb and suggest that the quartz biotite schist contains material that originated as chemical metasediments the near mono mineralic compositions of the clasts quartz and their shared 18o enrichment suggest that they had a common protolith which was deposited prior to the formation of the schist and subsequently reworked whether the quartz biotite schist represents a metaconglomerate or a structural melange it preserves remnants of some of the oldest chemical sediments on earth

what processes contribute to the spring and fall bloom co variability on the eastern bering sea shelf abstract observations indicate that spring and fall phytoplankton blooms on the eastern bering sea ebs continental shelf tend to co vary on inter annual scales that is a year with a strong spring bloom also tends to have a strong fall bloom similar co variability of primary production is also seen in the multi year 1987 2007 integration of a coupled physical biological model moreover the modeled seasonal amplitudes of 10 meter chlorophyll a concentrations at the ebs middle shelf mooring locations computed using the canonical redfield ratio and a mean carbon to chlorophyll a ratio are generally consistent with the in situ mooring measurements the coupled physical biological model simulation is used to examine the relative contributions of wind mixing local nutrient recycling regeneration horizontal nutrient advection and water column stability to this co variability there is no significant correlation between the spring and fall surface wind mixing although wind mixing is an important mechanism for bringing nutrients in the lower water column to the surface layers it is not the mechanism tying the two seasons productivity together local regeneration recycling of the nutrients initially fueling spring production is an important mechanism for spring to fall nutrient accumulation in the bottom layers at the middle shelf horizontal advection does not appear to be the dominant factor for supplying nutrients to the middle shelf during the spring to fall period fall primary production in the model is strongly influenced by the lower water column stability stratification taken together these results highlight the importance of local recycling regeneration of nutrients assimilated by spring phytoplankton bloom in linking together the spring and fall primary productions on ebs middle shelf

o and h stable isotope compositions of oceanic crust and upper mantle rocks exposed in the hess deep near the galapagos triple junction abstract a large variety of rocks consisting of basalts dolerites gabbros and ultramafics are exposed on the intra rift ridge in the hess deep representing a section of the oceanic crust formed at the east pacific ridge 1 we conducted a stable isotope study of o and h to assess the nature of the interaction between seawater and the oceanic crust in this region fresh basalt and dolerite samples have magmatic morb values 18o 6 0 105 d 70 and low h2o content 57 and h2o contents 1 3 most gabbros have 18o 5 6 essentially identical to their initial magmatic values their d values are generally higher than 57 suggesting that they have reacted with some seawater derived fluids as is also suggested by their mineralogy in gabbros displaying little or no visual evidence of alteration of their plagioclases and pyroxenes 18oplagioclase pyroxene is small 0 3 and consistent with magmatic values the calcic an 50 plagioclases have magmatic 18o 5 8 albitized prehnitized plagioclases have variable 18o values 4 8 it also appears that the 18o modified gabbros are those in which plagioclases are transformed into albite and or prehnite which are characteristic of greenschist facies conditions the lack of calcic an 50 plagioclases depleted in 18o and hornblende suggests that most of the gabbros did not react extensively under amphibolite facies conditions with seawater derived fluids t 400 c or that they were subsequently altered to greenschist facies gabbros the serpentinized peridotites were depleted in 18o 3 3 4 9 in one sample the 18oserpentine magnetite 5 7 corresponds to a temperature of about 325 50 c these values are compatible with serpentinization by seawater derived fluids at temperatures between 200 and 350 c another sample has a higher 18o value of 10 corresponding to a serpentinization temperature of less than 50 c the 18o mass balance between seawater and the oceanic crust seems to have attained steady state where enrichment in 18o of metabasalts is balanced by the depletion in 18o of metadolerites the contribution of the gabbros is minor the depletion in 18o of the serpentinized peridotites is not taken into account since we believe that the high temperature serpentinization is characteristic of the hess deep and cannot be extrapolated to the normal oceanic crust

sea ice impacts on spring bloom dynamics and net primary production in the eastern bering sea 1 in the eastern bering sea changes in sea ice have been implicated in recent major upper trophic level shifts however the underlying relationships between sea ice and primary producers have not been well tested here we combine data from multiple satellite platforms reanalysis model results and biophysical moorings to explore the dynamics of spring and summer primary production in relation to sea ice conditions in the northern bering sea sea ice consistently retreated in late spring leading to ice edge phytoplankton blooms in cold 0 1 c waters however in the southeastern bering sea sea ice retreat was far more irregular although this did not significantly alter bloom timing late retreat led to blooms at the ice edge while early retreat led to blooms in open waters that were warmer 5 4 c and 70 more productive early sea ice retreat also led to higher productivity in summer likely due to weaker thermal stratification overall annual net primary production during warm years of early sea ice retreat was enhanced by 40 50 compared to years with late sea ice retreat in the southeastern bering sea these findings suggest the potential for future sea ice loss to enhance overall carrying capacity of the southeastern bering sea ecosystem consistently warm blooms in the future may also channel more energy flow toward the pelagic rather than benthic environment to date however neither sea ice extent nor the timing of its retreat have undergone long term changes in the eastern bering sea

hydrothermal metasomatic and tectono metamorphic processes in the isua supracrustal belt west greenland a multi isotopic investigation of their effects on the earth s oldest oceanic crustal sequence abstract despite superimposed metamorphic overprinting and metasomatic alterations primary volcanic features remain preserved in low strain domains of mafic volcanic sequences in the western isua supracrustal belt isb west greenland these basaltic successions represent the hitherto oldest known fragments of oceanic crust on earth early archean metasomatic fluids rich in light rare earth elements lree th u pb ba and alkalies invaded the supracrustal package and distinctively altered the basaltic sequences field relationships source characteristics traced by pb isotopes and geochronological results provide indications that these fluids were genetically related to the emplacement of tonalite sheets into the isb between 3 81 and 3 74 ga ago subsequent early archean metamorphism homogenized the mixed primary and metasomatic mineral parageneses of these metavolcanic rocks allanite occurs as the most characteristic and critical secondary metasomatic metamorphic phase and is developed in macroscopically discernible zones of increased metsomatic alteration even in domains of low strain because of its high concentration of lree th and u this secondary mineral accounts for much of the disturbances recorded by the sm nd and th u pb isotope systematics of the pillowed metabasalts the supracrustal sequences were tectono metamorphically affected to varying degrees during a late archean 2 6 to 2 8 ga old event also recognized in the adjacent gneiss terranes of the isuakasia area the degree to which bulk rocks were isotopically reequilibrated is directly dependent on the different relative contributions of allanite hosted parent daughter elements to the overall whole rock mass budget of the respective isotope systems although low strained initially only weakly metasomatized pillow basalts remained more or less closed with respect to the u pb and rb sr systems since 3 74 ga the sm nd system appears to have been partially opened on a whole rock scale during the late archean event this diversified behavior of the whole rock isotope systems with respect to late archean overprinting is explained by the combination of mass budget contributions of the respective elements added during metasomatism and the partial opening of metasomatic macroenvironments during late archean recrystallization processes with associated renewed fluid flow in reactivated zones of high strain where primary metasomatic alteration is most prominently developed late archean partial resetting also of the u pb isotope system on a whole rock scale occurred this is consistent with an apparent late archean age of kyanite which initially crystallized during the early archean metamorphism its age is controlled by the u pb systematics of allanite inclusions which have exchanged their isotopic properties during the tectono metamorphic event that overprinted the oceanic crustal sequence at isua more than 1000 myr later these results underline the need for care in the interpretation of whole rock geochemical data from polymetamorphic rocks in general and from the isua oceanic crustal sequences in particular to constrain isotopic models of early earth s evolution likewise this study cautions against the indiscriminate use of geochemical data of metavolcanic rocks from isua to infer models for geotectonic settings relevant for their formation

subduction and atmospheric escape of earth s seawater constrained by hydrogen isotopes abstract the hydrogen isotopic d h ratio reflects the global cycling and evolution of water on earth as it fractionates through planetary processes we model the water cycle taking seafloor hydrothermal alteration chemical alteration of continental crust slab subduction hydrogen escape from the early earth and degassing at mid ocean ridges hot spots and arcs into account the differences in d h ratios between present day oceans oceanic and continental crust and mantle are thought to reflect isotopic fractionation through seafloor alteration chemical alteration and slab dehydration however if the speed of plate tectonics has been nearly constant throughout earth s history the degassing and regassing rates are too small to reach the present day d h ratios we show that a hydrogen escape from reduced early atmosphere b secular net regassing or c faster plate tectonics on early earth is needed to reproduce the present day d h ratios of the water reservoirs the low d h ratio of archean seawater at 3 8 ga has previously been interpreted as a signature of a hydrogen escape but we find it can also be explained either by b secular net degassing or by c faster plate tectonics on early earth the rates of hydrogen escape from early earth and secular regassing on present day earth are constrained to be lower than 2 1 10 11 kg yr and 3 9 10 11 kg yr consequently the volume of water in the present day mantle could result entirely from the regassing through earth s history in that case the volume of initial oceans could be 2 to 3 times larger than that of current earth we suggest that in addition to the d h ratio of archean seawater identifying the d h ratios of both seawater and mantle throughout earth s history would allow to distinguish these evolutionary scenarios

from evaporated seawater to uranium mineralizing brines isotopic and trace element study of quartz dolomite veins in the athabasca system abstract stable isotope o h c radiogenic isotope sr nd and trace element analyses have been applied to quartz dolomite veins and their uranium u bearing fluid inclusions associated with proterozoic unconformity related uo 2 uraninite ores in the athabasca basin canada in order to trace the evolution of pristine evaporated seawater towards u mineralizing brines during their migration through sediments and basement rocks fluid inclusion data show that quartz and dolomite have precipitated from brines of comparable chemistry excepted for relatively small amounts of co 2 found in dolomite hosted fluid inclusions however 18 o values of quartz veins 18 o 11 to 18 and dolomite veins 18 o 13 to 24 clearly indicate isotopic disequilibrium between quartz and dolomite hence it is inferred that this isotopic disequilibrium primarily reflects a decrease in temperature between the quartz stage 180 c and the dolomite stage 120 c the 13 c values of co 2 dissolved in dolomite hosted fluid inclusions 13 c 30 to 4 and the 13 c values of dolomite 13 c 23 5 to 3 5 indicate that the co 2 dissolved in the mineralizing brines originated from brine graphite interactions in the basement the resulting slight increase in the fluid partial pressure of co 2 p co 2 may have triggered dolomite precipitation instead of quartz 18 o values of quartz veins and previously published 18 o values of the main alteration minerals around the u ores illite chlorite and tourmaline show that quartz and alteration minerals were isotopically equilibrated with the same fluid at 180 c the ree concentrations in dolomite produce paas normalized patterns that show some similarities with that of uo 2 and are clearly distinct from that of the other main ree bearing minerals in these environments monazite zircon and aluminum phosphate sulfate aps minerals the radiogenic isotope compositions of dolomite 87 sr 86 sr i 0 7053 to 0 7161 and e nd t 8 8 to 20 3 differ from one deposit to another reflecting both heterogeneity in the basement geology and variable preservation of the original composition of brines the previously published 87 sr 86 sr i and e nd t values of uo 2 compare with the most evolved dolomites i e dolomites precipitated from brines that exchanged the most with the basement this reinforces a close genetic link between dolomites and uo 2 deposition and implies that uo 2 deposition occurred in a cooling system during the transition from quartz to dolomite formation the 18 o and d values of the mineralizing brines 18 o 1 to 8 and d 150 to 50 are considerably shifted from that of their theoretical original values acquired during evaporation of seawater 18 o 3 and d 40 the positive 18 o shift is explained by protracted fluid rock interaction within the basin and basement rocks the negative d shift is attributed to incomplete mixing between the u mineralizing brines and low d water this low d water was likely produced during the abiogenic synthesis of bitumen by fisher tropsch like reactions involving co 2 derived from brine graphite interaction in the basement and radiolytic h 2 the resulting low d brines have been equilibrated with alteration minerals this may explain why some alteration minerals yield anomalously low d values whose significance has long been debated

serpentinization of oceanic peridotites temperature dependence of mineralogy and boron content serpentine mineralogy 18o 16o ratios and boron content were determined in equatorial atlantic serpentinized ultramafic rocks of mantle derivation the oxygen isotope data were used to estimate the temperatures of serpentinization a relationship appears to exist between temperature of serpentinization mineralogy of the serpentinites and their boron content orthochrysotile is the dominant serpentine phase in the 200 120 c range of serpentinization temperatures lizardite and polygonal serpentine are dominant in the 120 80 c range and clinochrysotile and lizardite in the 80 30 c temperature range these results are interpreted in terms of p t stability of serpentine phases and of changes in chemistry of circulating seawater during ascent of the ultramafic bodies in the oceanic crust an inverse relationship was found between temperature of serpentinization and boron content of the serpentinites suggesting that boron is acquired by the serpentinites from seawater at low temperature

evidence of prolonged aragonite undersaturations in the bottom waters of the southern bering sea shelf from autonomous sensors abstract the southeastern shelf of the bering sea is a dynamic area that experiences seasonal variability in primary production and remineralization of organic matter both of which control the carbon biogeochemistry of the water column surface water partial pressure of carbon dioxide p co 2 is greatly reduced in summer by biological production which increases carbonate mineral saturation states in contrast the export of large quantities of organic matter from surface blooms drives an active remineralization loop that sharply increases p co 2 near the bottom lowering ph and suppressing new observations from moored biogeochemical sensors in 2011 showed that seasonal net community production lowers surface water p co 2 causing large gradients between the ocean and atmosphere that are sustained throughout the summer confirming that these waters likely remain supersaturated with respect to aragonite throughout the open water season on the other hand moored sensors deployed near the bottom showed that p co 2 levels exceed 500 atm by early june and remain at these high levels well into the autumn months indicating that the bottom waters are likely continuously undersaturated in aragonite for at least several months during each year only a small fraction of the increased p co 2 can currently be attributed to the intrusion of anthropogenic co 2 from the atmosphere while the majority is due to natural respiration processes the biological impacts along with the timing and duration of these undersaturation events could play a role in the development of larval and juvenile calcifiers in the region and will change as anthropogenic co 2 concentrations continue to rise