suppression of eddy diffusivity across jets in the southern ocean abstract geostrophic eddies control the meridional mixing of heat carbon and other climatically important tracers in the southern ocean the rate of eddy mixing is typically quantified through an eddy diffusivity there is an ongoing debate as to whether eddy mixing in enhanced in the core of the antarctic circumpolar current or on its flanks a simple expression is derived that predicts the rate of eddy mixing that is the eddy diffusivity as a function of eddy and mean current statistics this novel expression predicts suppression of the cross jet eddy diffusivity in the core of the antarctic circumpolar current despite enhanced values of eddy kinetic energy the expression is qualitatively and quantitatively validated by independent estimates of eddy mixing from altimetry observations this work suggests that the meridional eddy diffusivity across the antarctic circumpolar current is weaker than presently assumed because of the suppression of eddy mixing by the strong zonal current

microbial sulfate reduction within the iheya north subseafloor hydrothermal system constrained by quadruple sulfur isotopes abstract subseafloor hydrothermal systems may host spatially extended and numerically abundant microbial communities sustained by sulfate reduction as one of the important terminal electron accepting metabolisms in order to estimate microbial sulfate reduction in a subseafloor hydrothermal regime we analyzed sulfur isotopes s 32 s 33 s 34 s 36 of pore water sulfate and mineralized sulfide in the upper 100 m of sedimentary sequences at the iheya north hydrothermal field in the okinawa trough recovered in integrated ocean drilling program expedition 331 iodp exp 331 on the basis of the pore water chemistry and temperature profiles the subseafloor environment is divided into three hydrogeologic units in the topmost unit 1 relatively fresh seawater is recharged and the bottommost unit 3 is characterized by predominance of endmember like high temperature hydrothermal fluid 300 c underlying the impermeable cap rock layers intermediate unit 2 is subject to mixing between the hydrothermal fluid and seawater the 34 s values of sulfate in the unit 2 mixing zone were found to be more 34s enriched than the values expected from simple mixing model of seawater sulfate in the unit 1 with the hydrothermal fluid in the unit 3 the observed s so 4 34 enrichment and sulfate concentration so2 4 depletion suggest sulfate reduction is taking place below the seafloor based on our model calculation the isotope discrimination e 34 is estimated to be 21 this large isotope discrimination together with slight 33 s enrichment and 36 s depletion reveals that sulfate reduction is caused by microbial processes but not by thermochemical processes in addition our numerical simulation points out that sulfate may be reduced prior to presently undergoing mixing with high temperature fluid probably within the seawater recharge zone despite the abundant input of hydrothermal h2s mineralized sulfide below 10 m seafloor mbsf shows characteristic sulfur isotopic signatures that support the significant contribution of subseafloor microbial sulfate reduction potentially corresponding to approximately 20 of the total sulfide mineral formation active microbial sulfate reduction below the seafloor may be promoted by significant input of seawater to the habitats through the vigorous hydrothermal circulation in vicinity of iheya north field

internal waves and turbulence in the antarctic circumpolar current abstractthis study reports on observations of turbulent dissipation and internal wave scale flow properties in a standing meander of the antarctic circumpolar current acc north of the kerguelen plateau the authors characterize the intensity and spatial distribution of the observed turbulent dissipation and the derived turbulent mixing and consider underpinning mechanisms in the context of the internal wave field and the processes governing the waves generation and evolution the turbulent dissipation rate and the derived diapycnal diffusivity are highly variable with systematic depth dependence the dissipation rate is generally enhanced in the upper 1000 1500 m of the water column and both the dissipation rate and diapycnal diffusivity are enhanced in some places near the seafloor commonly in regions of rough topography and in the vicinity of strong bottom flows associated with the acc jets turbulent dissipation is high in regions where internal wave energy is high consistent with the idea that i

a bistable organic rich atmosphere on the neoarchaean earth it has been hypothesized that before widespread oxygenation about 2 45 billion years ago the earth s atmosphere contained an organic haze similar to that on titan however these theoretical predictions have not been substantiated by geological evidence here we use multiproxy geochemical analyses of sediments from the 2 65 2 5 billion year old ghaap group in south africa to reconstruct ocean and atmospheric chemistry during this time we find evidence for oxygen production in microbial mats and localized oxygenation of surface waters carbon and sulphur isotopes indicate that this oxygen production occurred under a reduced atmosphere that was periodically rich in methane consistent with the prediction of a hydrocarbon haze we use a photochemical model to corroborate our geochemical data our simulations predict transitions between two stable atmospheric states one with organic haze and the other haze free the transitions are presumably governed by variations in the amount of biological methane production during the archaean eon we find that the isotopic signatures we observe are evident in other data sets from this period and conclude that methane was an important component of the atmosphere throughout the archaean before the rise of oxygen the atmosphere of the early earth may have consisted of an organic haze geochemical data and modelling suggest that from 2 65 to 2 5 gyr ago several transitions between hazy and haze free atmospheric conditions occurred potentially linked to variations in biogenic methane production

rapid injection of near inertial shear into the stratified upper ocean at an antarctic circumpolar current front the impact on the upper ocean of the passage of a short intense storm over a southern ocean site in proximity to an antarctic circumpolar current front is characterized the storm causes a wind induced deepening of the mixed layer and generates an inertial current immediate post storm observations indicate a mixed layer extending to approximately 50 m depth subsequent measurements show the upper ocean to have re stratified injecting near inertial shear in stratified waters within 1 day of the storm s passage this time scale for the development of near inertial shear is one order of magnitude shorter than that predicted by the dispersion paradigm the observed rapid changes in upper ocean stratification point to the existence of an as yet undocumented efficient mechanism for injection of near inertial shear into the stratified ocean that is in turn associated with enhanced turbulence and mixing

eddy induced variability in southern ocean abyssal mixing on climatic timescales the southern ocean plays a pivotal role in the global ocean circulation and climate1 2 3 there the deep water masses of the world ocean upwell to the surface and subsequently sink to intermediate and abyssal depths forming two overturning cells that exchange substantial quantities of heat and carbon with the atmosphere4 5 the sensitivity of the upper cell to climatic changes in forcing is relatively well established6 however little is known about how the lower cell responds and in particular whether small scale mixing in the abyssal southern ocean an important controlling process of the lower cell7 8 is influenced by atmospheric forcing here we present observational evidence that relates changes in abyssal mixing to oceanic eddy variability on timescales of months to decades observational estimates of mixing rates obtained along a repeat hydrographic transect across drake passage are shown to be dependent on local oceanic eddy energy derived from moored current meter and altimetric measurements as the intensity of the regional eddy field is regulated by the southern hemisphere westerly winds9 10 our findings suggest that southern ocean abyssal mixing and overturning are sensitive to climatic perturbations in wind forcing

transformation of deep water masses along lagrangian upwelling pathways in the southern ocean upwelling of northern deep waters in the southern ocean is fundamentally important for the closure of the global meridional overturning circulation and delivers carbon and nutrient rich deep waters to the sea surface we quantify water mass transformation along upwelling pathways originating in the atlantic indian and pacific and ending at the surface of the southern ocean using lagrangian trajectories in an eddy permitting ocean state estimate recent related work shows that upwelling in the interior below about 400 m depth is localized at hot spots associated with major topographic features in the path of the antarctic circumpolar current while upwelling through the surface layer is more broadly distributed in the ocean interior upwelling is largely isopycnal atlantic and to a lesser extent indian deep waters cool and freshen while pacific deep waters are more stable leading to a homogenization of water mass properties as upwelling water approaches the mixed layer there is net strong transformation toward lighter densities due to mixing of freshwater but there is a divergence in the density distribution as upper circumpolar deep water tends become lighter and dense lower circumpolar deep water tends to become denser the spatial distribution of transformation shows more rapid transformation at eddy hot spots associated with major topography where density gradients are enhanced however the majority of cumulative density change along trajectories is achieved by background mixing we compare the lagrangian analysis to diagnosed eulerian water mass transformation to attribute the mechanisms leading to the observed transformation

uv induced mass independent sulfur isotope fractionation in stratospheric volcanic sulfate 1 sulfuric acid aerosols produced in the stratosphere following massive volcanic eruptions possess a mass independent sulfur isotopic signature acquired when volcanic so2 experiences uv photooxidation the volcanic data are consistent with laboratory so2 photooxidation experiments using uv light at 248 nm maximum absorption of ozone whereas sulfur isotopic anomalies previously observed in archean samples are consistent with photodissociation at 190 220 nm a mechanism of so2 photooxidation occurring in the early stage of a stratospheric volcanic plume in the range of 220 320 nm weak band absorption of so2 is also proposed since mass independent sulfur isotope anomalies in stratospheric volcanic sulfate appear to depend on the exposure of so2 to uv radiation their measurements might therefore offer the possibility to determine the degree of uv penetration in the ozone absorption window for the present and past atmospheres they can also be used to determine the stratospheric or tropospheric nature of volcanic eruptions preserved in glaciological records offering the possibility to reassess the climatic impact of past volcanic eruptions

multiple sulfur isotope geochemistry of dharwar supergroup southern india late archean record of changing atmospheric chemistry abstract earth s tectonic and climatic systems may have changed fundamentally before the great oxidation event goe at about 2 3 ga sulfur mass independent fractionation s mif has demonstrated that earth s atmosphere was virtually oxygen free before the goe during 3 0 to 2 4 ga the change in 33s and 36s signals may reflect the perturbation of atmospheric chemistry though the mechanisms of the change are uncertain here we reported multiple sulfur isotopic studies of archean volcano sedimentary sequences of the dharwar supergroup distributed in the chitradurga schist belt csb southern india new field mapping and zircon u pb dating allows us to reconstruct detailed lithostratigraphy of the dharwar supergroup the lower unit consists of post 3 0 ga conglomerate stromatolitic carbonate siliciclastics with diamictite chert bif and pillowed basalt in ascending order all of which are older than the 2676 ma dacite dyke that had intruded into the lower unit the upper unit unconformably overlies the pillow basalts at the top of the lower unit and consists of conglomerate sandstone with 2600 ma detrital zircons komatiitic basalt bif and siliciclastic sequence with mafic volcanics sulfur isotope analysis of extracted sulfides shows mif signals s 33 1 with clear s 33 s 36 correlations the lower group of the dharwar supergroup shows a s 36 s 33 slope of 1 48 the middle group shows 1 16 and 1 07 and the upper group shows 0 94 reassessment of all the archean s mif records from sedimentary rocks indicates that the s 36 s 33 slope systematically changed during the archean period the observed trend in the indian section is similar to those of its pilbara kaapvaal equivalents thus it could reflect a global atmospheric signature moreover the isotopic trend seems to correlate with mid archean glaciation thus the s 36 s 33 slope could be a useful tracer for atmospheric chemistry and its link with climate change before the goe

enhancement of mesoscale eddy stirring at steering levels in the southern ocean abstract meridional cross sections of effective diffusivity in the southern ocean are presented and discussed the effective diffusivity keff characterizes the rate at which mesoscale eddies stir properties on interior isopycnal surfaces and laterally at the sea surface the distributions are obtained by monitoring the rate at which eddies stir an idealized tracer whose initial distribution varies monotonically across the antarctic circumpolar current acc in the absence of observed maps of eddying currents in the interior ocean the advecting velocity field is taken from an eddy permitting state estimate of the southern ocean sose a three dimensional advection diffusion equation is solved and the diffusivity diagnosed by applying the nakamura technique on both horizontal and isopycnal surfaces the resulting meridional sections of keff reveal intensified isopycnal eddy stirring reaching values of 2000 m2 s 1 in a layer deep beneath the acc but rising toward the surface on the equatorward flank

microchemical and sulfur isotope constraints on the magmatic and hydrothermal evolution of the black swan succession western australia the black swan succession consists of an archean bimodal dacite komatiite association largely dominated by ultramafic cumulates hosting a number of massive and disseminated magmatic sulfide orebodies although it was affected by multiple alteration events the low degree of penetrative deformation allowed the preservation of magmatic textures and stratigraphic relationships in this context we apply a combined multiple sulfur isotope and microchemical approach to unravel the potential of sulfides to simultaneously retain information about their magmatic and hydrothermal history negative 33s signatures in both massive 0 56 and disseminated 0 66 sulfide orebodies reflect the assimilation of photochemically derived sulfur into the komatiite magma which attained sulfide liquid supersaturation through the assimilation of crustal material analogous to the intercalated breccia dacite hosting colloform sulfides 33s 0 91 the slightly different 33s signatures between disseminated and massive orebodies reflect the assimilation of different proportions of crustally derived sulfur and imply that the respective sulfide liquids segregated from distinct komatiite magma pulses subsequent alteration episodes imparted to the black swan succession a concentric zonation consisting of a serpentinite core and talc carbonate margins the black swan disseminated orebody extends through both alteration styles without major variations in the dominant millerite pyrite sulfide assemblage pyrite in both serpentinite and talc carbonate samples exhibits a consistent trace element signature suggesting a relative immobile behavior of ni and co during the percolation of the talc carbonate fluids conversely variable 34s signatures between the two alteration styles reflect mobilization of sulfur during talc carbonate alteration whereas the 2 range of 34s values in serpentinites can be attributed to moderate equilibrium fractionation processes the 10 range of 34s values in talc carbonate rocks suggests that highly oxidizing fluids promoted the mobilization of sulfur as so42 which decreased the 34s of the disseminated sulfides furthermore sulfur isotope and microchemical signatures of euhedral pyrite from intercalated dacitic breccia indicate that this pyrite generation was deposited from a late hydrothermal event which is characterized by variable and least negative 33s signatures between 0 20 and 0 48 relative to all sulfide orebodies these features suggest that the late fluids developed in a heterogeneous hydrothermal system with a minor component of sulfur recycled from the sulfide orebodies

turbulence and diapycnal mixing in drake passage abstractdirect measurements of turbulence levels in the drake passage region of the southern ocean show a marked enhancement over the phoenix ridge at this site the antarctic circumpolar current acc is constricted in its flow between the southern tip of south america and the northern tip of the antarctic peninsula observed turbulent kinetic energy dissipation rates are enhanced in the regions corresponding to the acc frontal zones where strong flow reaches the bottom in these areas turbulent dissipation levels reach 10 8 w kg 1 at abyssal and middepths the mixing enhancement in the frontal regions is sufficient to elevate the diapycnal turbulent diffusivity acting in the deep water above the axis of the ridge to 1 10 4 m2 s 1 this level is an order of magnitude larger than the mixing levels observed upstream in the acc above smoother bathymetry outside of the frontal regions dissipation rates are o 10 10 w kg 1 comparable to the background levels of turbulence found throughout most mid and

sulfur isotope fractionation by broadband uv radiation to optically thin so 2 under reducing atmosphere abstract photochemical mechanisms of sulfur mass independent fractionation s mif are still poorly understood previous laboratory experiments have indicated that the s mif depends largely on the spectrum of the incident light source and the partial pressure of so2 though the basic character of the archean s mif s 36 s 33 1 has never been reproduced we have conducted new photochemical experiments at low pso2 1 10 pa conditions under the presence of co and found a reasonable mechanism to reproduce the 36s 33s slope about 1 as previously suggested ono et al 2013 the low pso2 is key to studying the self shielding effect within a range of realistic atmospheric conditions also reducing conditions are critical for simulating the o2 poor atmosphere whereas photolysis of pure so2 provides excess o atoms that significantly change the overall chemistry our experimental results confirmed that significant s mif s 36 s 33 2 4 can be produced by self shielding in the so2 photolysis band 185 220 nm even if the so2 column density is as low as 1016 molecules cm 2 thus photolysis within a volcanic plume of 0 1 ppm so2 is capable of producing a large s mif signature the isotopic fractionations originating from the different absorption cross sections of so2 isotopologues i e wavelength dependent effect without self shielding are only minor potentially up to 4 for 33s under reducing conditions however another s mif signal with 36s 33s ratio of 0 7 is produced due to collision induced intersystem crossing isc from singlet to triplet states of so2 whitehill et al 2013 and should also be transferred into the final product that is responsible for changing the 36s 33s slope based on a photochemical model of the s o c system with the two s mif yielding reactions the largest s mif observed in the late archean mt mcrae fm s 33 9 4 s 36 7 5 can be reproduced by solar uv irradiation of a so2 column of 6 4 10 16 molecules cm 2 with a sufficiently high concentration of reducing gasses 2 co or ch4 where the isc derived mif contributes 3 through the photoexcitation channel initiated in the 240 340 nm region our work shows that a photochemical model considering the two major s mif yielding reactions so 2 h so o and so 2 1 m so 2 3 m can explain the behavior of the s mif observed in laboratory experiments the combination of the two effects is more important under reducing condition and should be considered to interpret the geological record

overturning circulation driven by breaking internal waves in the deep ocean a global estimate of the water mass transformation by internal wave driven mixing in the deep ocean is presented the estimate is based on the energy conversion from tidal and geostrophic motions into internal waves combined with a turbulent mixing parameterization we show that internal wave driven mixing in the deep ocean can sustain 20 30 sv of water mass transformation one third or more of this transformation is attributed to lee waves generated by geostrophic motions flowing over rough topography primarily in the southern ocean while these results are uncertain due to many assumptions poorly constrained parameters and data noise that enter in the calculation the result that lee wave driven mixing plays an important role in the abyssal ocean circulation is likely robust the implication is that lee wave driven mixing should be represented in ocean and climate models but currently it is not citation nikurashin m and r ferrari 2013 overturning circulation driven by breaking internal waves in the deep ocean geophys res lett 40 doi 10 1002 grl 50542

quantifying high frequency wind energy flux into near inertial motions in the southeast pacific abstractwind forced internal waves close to the inertial frequency are ubiquitous throughout the world s oceans but observational constraints on their global energetics and impact on subsurface mixing remain scarce this study reports on velocity measurements from three electromagnetic autonomous profiling explorers em apex deployed in february 2009 these floats observed downward propagating near inertial internal waves near the subantarctic and polar fronts of the antarctic circumpolar current these waves were episodic and enhanced at middepth between 500 and 1000 m depth integrated kinetic energy varied between 1 and 7 kj m 2 and averaged 1 6 kj m 2 with typical group velocities of 40 m day 1 implying an average energy flux of 3 mw m 2 at the mixed layer base decreasing to approximately 25 of that value at 1500 m modeled currents forced by reanalysis winds along each float track agree with observed surface currents from em apex provided that mixed layer depth is restricted to the layer of weak

the global influence of localized dynamics in the southern ocean the circulation of the southern ocean connects ocean basins links the deep and shallow layers of the ocean and has a strong influence on global ocean circulation climate biogeochemical cycles and the antarctic ice sheet processes that act on local and regional scales which are often mediated by the interaction of the flow with topography are fundamental in shaping the large scale three dimensional circulation of the southern ocean recent advances provide insight into the response of the southern ocean to future change and the implications for climate the carbon cycle and sea level rise

jets and topography jet transitions and the impact on transport in the antarctic circumpolar current the southern ocean s antarctic circumpolar current acc naturally lends itself to interpretations using a zonally averaged framework yet navigation around steep and complicated bathymetric obstacles suggests that local dynamics may be far removed from those described by zonally symmetric models in this study both observational and numerical results indicate that zonal asymmetries in the form of topography impact global flow structure and transport properties the conclusions are based on a suite of more than 1 5 million virtual drifter trajectories advected using a satellite altimetry derived surface velocity field spanning 17 years the focus is on sites of cross front transport as defined by movement across selected sea surface height contours that correspond to jets along most of the acc cross front exchange is localized in the lee of bathymetric features with more than 75 of crossing events occurring in regions corresponding to only 20 of the acc s zonal extent these observations motivate a series of numerical experiments using a two layer quasigeostrophic model with simple zonally asymmetric topography which often produces transitions in the front structure along the channel significantly regimes occur where the equilibrated number of coherent jets is a function of longitude and transport barriers are not periodic jet reorganization is carried out by eddy flux divergences acting to both accelerate and decelerate the mean flow of the jets eddy kinetic energy is amplified downstream of topography due to increased baroclinicity related to topographic steering the combination of high eddy kinetic energy and recirculation features enhances particle exchange these results stress the complications in developing consistent circumpolar definitions of the acc fronts

in situ quadruple sulfur isotopic compositions of pyrites in the ca 3 2 2 72 ga metasedimentary rocks from the pilbara craton western australia abstract the sulfur mass independent fractionation s mif of mesoarchean is distinct from the other archean periods by the dampened magnitudes of 33s and a steeper slope of 36s 33s compared with the archean reference array ara according to previous studies however samples available of this interval are limited owing to poor or no preservation additionally the majority of the data were obtained by analysis of bulk rocks thus are essentially the sulfur isotopic compositions of mixed sulfur components due to multiple stages of post diagenesis overprints and modifications this study systematically measured the multiple sulfur isotopic compositions of pyrites nodular disseminated in ca 3 2 2 72 ga metasedimentary rocks from the pilbara craton western australia where one of the best preserved archean records occur using the upgraded shrimp si after detailed pyrite generation and genesis investigation by bse imaging and naocl etching the results show that 33s values of the diagenetic pyrites in these metasedimentary rocks range from 2 4 to 0 8 such a range is inconsistent with the other archean intervals and any experiment producing s mif so far where the magnitude of the maximum positive 33s value is considerably larger than the corresponding minimum negative 33s value the dampened positive 33s is explained in several ways from the perspective of production and preservation including original photochemical products with larger magnitudes of negative 33s than positive 33s in a different atmospheric composition non zero 33s of initial so2 different mechanism producing s mif chain formation and destruction of positive 33s by subduction the downward 36s 33s deviations from ara in the diagenetic pyrites of 2 72 ga tumbiana formation can be attributed to modifications induced by microbial activities this is based on the negative 0 9 33s 36s values similar to biological products and the large range of negative 34s values the downward 36s 33s offsets in the hydrothermally altered diagenetic pyrites of 2 78 ga mt roe basalt are most likely mixing of primary sulfur on ara with later sulfur disobeying ara the upward 36s 33s deviations in the diagenetic pyrites of 2 93 ga mosquito creek formation likely reflect different atmospheric composition

origin of two distinct multiple sulfur isotope compositions of pyrite in the 2 5ga klein naute formation griqualand west basin south africa abstract quadruple sulfur isotope ratios 32s 33s 34s 36s were measured by a high precision sf6 method for early diagenetic pyrite in the 2 5 ga upper prieska facies of the griqualand west basin from the agouron drill core gkp01 measured 33s 33s 0 515 34s values range between 2 3 and 8 5 with no apparent meter scale stratigraphic trend for 70 m section it was found that early diagenetic pyrites occur in two texturally and isotopically distinct populations such that bulk rock isotope data would reflect mixing of these two sulfur pools nodular and layered pyrite yield mostly negative down to 2 3 and relatively constant 33s values over a few tens of cm scale disseminated pyrites in contrast yield positive 0 0 8 5 33s values that are heterogeneous in sub cm scales the former pyrite sulfur was likely derived from seawater sulfate through microbial sulfate reduction and the latter preferentially sampled aqueous h2s s0 reservoirs in late archean oceans relatively constant 33s values for layered pyrite suggest archean sulfate reservoirs had residence times of a few million years most data yield a well defined 36s 33s ratios of 0 9 suggesting predominance of a single s mif source reaction four analyses of a two cm length sample 306 5 m yield 36s 33s slope of 1 6 this slope is consistent with the relationship expected for a symmetry breaking isotope effect during the s s2 reaction but deviations from the main archean array i e 36s 33s 0 9 may also result from various combinations of so photolysis and so2 oxidation high spatial resolution high precision sf6 measurements of archean pyrite provide significant new insights into the origin of archean sulfur mass independent fractionation s mif and the late archean sulfur cycle

global surface eddy diffusivities derived from satellite altimetry 1 velocities derived from aviso sea surface height observations adjusted to be nondivergent are used to simulate the evolution of passive tracers at the ocean surface eddy mixing rates are derived from the tracer fields in two ways first the method of nakamura is applied to a sector in the east pacific second the osborn cox diffusivity is calculated globally to yield estimates of diffusivity in two dimensions the results from the east pacific show weak meridional mixing at the surface in the southern ocean 1000 m2 s 1 consistent with previous results but higher mixing rates 3000 5000 m2 s 1 in the tropical ocean the osborn cox diagnostic provides a global picture of mixing rates and agrees reasonably well with the results from the east pacific it also shows extremely high mixing rates 104 m2 s 1 in western boundary current regions the osborn cox diffusivity is sensitive to the tracer initialization which we attribute to the presence of anisotropic mixing processes the mixing rates are strongly influenced by the presence of a mean flow nearly everywhere as shown by comparison with an eddy only calculation with the mean flow absent finally results are compared with other recent estimates of mixing rates using lagrangian and inverse methods

reconstructing earth s surface oxidation across the archean proterozoic transition the archean proterozoic transition is characterized by the widespread deposition of organic rich shale sedimentary iron formation glacial diamictite and marine carbonates recording profound carbon isotope anomalies but notably lacks bedded evaporites all deposits refl ect environmental changes in oceanic and atmospheric redox states in part associated with earth s earliest ice ages time series data for multiple sulfur isotopes from carbonateassociated sulfate as well as sulfi des in sediments of the transvaal supergroup south africa capture the concomitant buildup of sulfate in the ocean and the loss of atmospheric massindependent sulfur isotope fractionation in phase with sulfur is the earliest recorded positive carbon isotope anomaly convincingly linking these environmental perturbations to the great oxidation event ca 2 3 ga

diagnosing the southern ocean overturning from tracer fields abstract the strength and structure of the southern hemisphere meridional overturning circulation smoc is related to the along isopycnal and vertical mixing coefficients by analyzing tracer and density fields from a hydrographic climatology the meridional transport of upper circumpolar deep water ucdw across the antarctic circumpolar current acc is expressed in terms of the along isopycnal k and diapycnal d tracer diffusivities and in terms of the along isopycnal potential vorticity mixing coefficient kpv uniform along isopycnal 600 m2 s 1 and low vertical mixing 10 5 m2 s 1 can maintain a southward transport of less than 60 sv sv 106 m2 s 1 of ucdw across the acc which is distributed largely across the south pacific and east indian ocean basins for vertical mixing rates of o 10 4 m2 s 1 or greater the inferred transport is significantly enhanced the transports inferred from both tracer and density distributions suggest a ratio k to d of o 2 106 particularly on deeper layers

control of lower limb overturning circulation in the southern ocean by diapycnal mixing and mesoscale eddy transfer a simple model is developed of the lower limb of the meridional overturning circulation in the southern ocean based on residual mean theory it is hypothesized that the strength of the lower limb overturning is strongly controlled by the magnitude of abyssal diapycnal mixing and that of mesoscale eddy transfer k in particular it is argued that k the scaling and associated theory find support in a suite of sensitivity experiments with an idealized ocean general circulation model this study shows that intense diapycnal mixing is required to close the buoyancy budget of the lower limb overturning circulation in contrast to the upper limb where air sea buoyancy fluxes can provide the required diabatic forcing

widespread intense turbulent mixing in the southern ocean observations of internal wave velocity fluctuations show that enhanced turbulent mixing over rough topography in the southern ocean is remarkably intense and widespread mixing rates exceeding background values by a factor of 10 to 1000 are common above complex bathymetry over a distance of 2000 to 3000 kilometers at depths greater than 500 to 1000 meters this suggests that turbulent mixing in the southern ocean may contribute crucially to driving the upward transport of water closing the ocean s meridional overturning circulation and thus needs to be represented in numerical simulations of the global ocean circulation and the spreading of biogeochemical tracers

radiation and dissipation of internal waves generated by geostrophic motions impinging on small scale topography application to the southern ocean abstract recent estimates from observations and inverse models indicate that turbulent mixing associated with internal wave breaking is enhanced above rough topography in the southern ocean in most regions of the ocean abyssal mixing has been primarily associated with radiation and breaking of internal tides in this study it is shown that abyssal mixing in the southern ocean can be sustained by internal waves generated by geostrophic motions that dominate abyssal flows in this region theory and fully nonlinear numerical simulations are used to estimate the internal wave radiation and dissipation from lowered acoustic doppler current profiler ladcp ctd and topography data from two regions in the southern ocean drake passage and the southeast pacific the results show that radiation and dissipation of internal waves generated by geostrophic motions reproduce the magnitude and distribution of dissipation previously inferred from finescale measurements in the region suggesting that it is one of the

four views of a portion of the north atlantic subtropical gyre abstract data from four cruises to the triangle centered at 27 n 32 30 w were smoothed by fitting second degree polynomials at each of about 30 different density surfaces the density intervals were p 0 3 corresponding to about 50 db intervals in pressure from the polynomials determination was made of central values horizontal derivatives and laplacians of the fields of pressure salt oxygen and dynamic height in addition maps of the fits and deviations of each nation from the smoothed fits were produced from the steady advective diffusive equation and the smoothed fits to the age oxygen and dynamic height fields the lateral isopycnal diffusivity as estimated to be kh 0 5 103 m2 s 1 although the salt field was reasonably stable from cruise to cruise the variability of the baroclinic velocity shear was found to be as large as the baroclinic shear itself the maps suggest a wobble of the gyre the standard deviation of the fluctuations at each nation from the smoothed fits when norma

increased subaerial volcanism and the rise of atmospheric oxygen 2 5 billion years ago the hypothesis that the establishment of a permanently oxygenated atmosphere at the archaean proterozoic transition approximately 2 5 billion years ago occurred when oxygen producing cyanobacteria evolved is contradicted by biomarker evidence for their presence in rocks 200 million years older to sustain vanishingly low oxygen levels despite near modern rates of oxygen production from approximately 2 7 2 5 billion years ago thus requires that oxygen sinks must have been much larger than they are now here we propose that the rise of atmospheric oxygen occurred because the predominant sink for oxygen in the archaean era enhanced submarine volcanism was abruptly and permanently diminished during the archaean proterozoic transition observations are consistent with the corollary that subaerial volcanism only became widespread after a major tectonic episode of continental stabilization at the beginning of the proterozoic submarine volcanoes are more reducing than subaerial volcanoes so a shift from predominantly submarine to a mix of subaerial and submarine volcanism more similar to that observed today would have reduced the overall sink for oxygen and led to the rise of atmospheric oxygen

exsolution in hornblende and its consequences for 40ar39ar age spectra and closure temperature abstract step heating studies of hornblende and biotite which coexist in an amphibolite near north walpole vermont reveal dramatically different 40 ar 39 ar age spectra the biotite mg 59 is characterized by a plateau over 98 percent 39ar release at 343 5 ma in strong contrast to the amphibole which exhibits both a complex age spectrum and a k ar age significantly younger than the biotite the amphibole release pattern contains three complete age cycles which range between extremes of 199 ma and 408 ma interestingly the k ca ratio calculated from reactor produced isotopes also varies with ar release but follows a trend which is antipathetic to the 40 ar 39 ar age pattern detailed microstructural examination including transmission electron microscopy tem reveals a complex exsolution structure that is consistent with both the complexity of the release pattern as well as the low degree of radiogenic 40ar 40ar retentivity in the amphibole this result underscores the variability of closure temperature tc for 40ar in metamorphic amphiboles and should warn against accepting a single universal value of tc

pathways for neoarchean pyrite formation constrained by mass independent sulfur isotopes it is generally thought that the sulfate reduction metabolism is ancient and would have been established well before the neoarchean it is puzzling therefore that the sulfur isotope record of the neoarchean is characterized by a signal of atmospheric mass independent chemistry rather than a strong overprint by sulfate reducers here we present a study of the four sulfur isotopes obtained using secondary ion ms that seeks to reconcile a number of features seen in the neoarchean sulfur isotope record we suggest that neoarchean ocean basins had two coexisting significantly sized sulfur pools and that the pathways forming pyrite precursors played an important role in establishing how the isotopic characteristics of each of these pools was transferred to the sedimentary rock record one of these pools is suggested to be a soluble sulfate pool and the other pool atmospherically derived elemental sulfur is suggested to be largely insoluble and unreactive until it reacts with hydrogen sulfide we suggest that the relative contributions of these pools to the formation of pyrite depend on both the accumulation of the insoluble pool and the rate of sulfide production in the pyrite forming environments we also suggest that the existence of a significant nonsulfate pool of reactive sulfur has masked isotopic evidence for the widespread activity of sulfate reducers in the rock record

quadruple sulfur isotope analysis of ca 3 5 ga dresser formation new evidence for microbial sulfate reduction in the early archean abstract multiple sulfur isotope system is a powerful new tracer for atmospheric volcanic and biological influences on sulfur cycles in the anoxic early earth here we report high precision quadruple sulfur isotope analyses 32s 33s 34s 36s of barite pyrite in barite and sulfides in related hydrothermal and igneous rocks occurring in the ca 3 5 ga dresser formation western australia our results indicate that observed isotopic variations are mainly controlled by mixing of mass dependently md and non mass dependently fractionated non md sulfur reservoirs based on the quadruple sulfur isotope systematics 34s 33s 36s for these minerals four end member sulfur reservoirs have been recognized 1 non md sulfate 34s 5 2 33s 3 1 2 md sulfate 34s 10 3 3 non md sulfur 34s 6 33s 4 and 4 igneous md sulfur 34s 33s 0 the first and third components show a clear non md signatures thus probably represent sulfate and sulfur aerosol inputs the md sulfate component 2 is enriched in 34s 10 3 and may have originated from microbial and or abiotic disproportionation of volcanic s or so2 our results reconfirm that the dresser barites contain small amounts of pyrite depleted in 34s by 15 22 relative to the host barite these barite pyrite pairs exhibit a mass dependent relationship of 33s 34s with slope less than 0 512 which is consistent with that expected for microbial sulfate reduction and is significantly different from that of equilibrium fractionation 0 515 the barite pyrite pairs also show up to 1 difference in 36s values and steep 36s 33s slopes which deviate from the main archean array 36s 33s 0 9 and are comparable to isotope effects exhibited by sulfate reducing microbes 36s 33s 5 to 11 these new lines of evidence support the existence of sulfate reducers at ca 3 5 ga whereas microbial sulfur disproportionation may have been more limited than recently suggested

isopycnal dispersion in natre abstract finescale velocity and density fluctuations consist of both internal waves and vorticity containing perturbations vortical modes a recent decomposition of observations obtained as part of the north atlantic tracer release experiment natre permits one to investigate isopycnal stirring associated with vortical modes this stirring is treated here as a relative dispersion problem in the context of 2d turbulence isopycnal diffusivities attain values on the order of 1 m2 s 1 after an initial transient of 5 10 days after 2 weeks a patch of tracer with initial radius of 25 m is predicted to have evolved into a convoluted web having an rms radius of 2 4 km these estimates agree with observations of the evolution of an anthropogenic tracer in natre

methanotrophs regulated atmospheric sulfur isotope anomalies during the mesoarchean tumbiana formation western australia abstract the 2 73 billion year old tumbiana formation of the fortescue group in the pilbara craton western australia preserves one of the best records of the fortescue negative carbon isotope excursion with organic 13 c values as low as 60 the prevailing environmental conditions at this biological excursion are not well understood here we present an integrated carbon 12 c 13 c and multiple sulfur 32 s 33 s 34 s 36 s isotopes study of a pristine diamond drill core through the tumbiana formation collected at meentheena by the pilbara drilling project our results show centimeter to meter scale heterogeneities in sulfur and carbon contents and isotope compositions organic 13 c values vary at the meter scale and display a bimodal distribution with peaks at about 44 and 34 this bimodal distribution is interpreted to reflect variations in the contribution of methanotrophic metabolism to the biomass the 34 s v cdt values of sedimentary pyrite vary from 5 73 to 2 75 sulfur isotopes sulfur contents and s c ratios are variable suggesting a complex local biotic sulfur cycling sedimentary pyrite preserves mass independent fractionation of sulfur mif s with 33 s v cdt ranging between 0 25 and 1 64 average 0 47 corresponding to the characteristic dampened mesoarchean anomalies positive correlation between sulfide mif s and a 13 c depletion of organic matter argues for a causal link between methanotrophs activity and the preservation of mif s anomalies in the rock record

eddy induced modulation of turbulent dissipation over rough topography in the southern ocean abstractmesoscale eddies are universal features of the ocean circulation yet the processes by which their energy is dissipated remain poorly understood one hypothesis argues that the interaction of strong geostrophic flows with rough bottom topography effects an energy transfer between eddies and internal waves with the breaking of these waves causing locally elevated dissipation focused near the sea floor this study uses hydrographic and velocity data from a 1 yr mooring cluster deployment in the southern ocean to test this hypothesis the moorings were located over a small 10 km topographic obstacle to the east of drake passage in a region of high eddy kinetic energy and one was equipped with an adcp at 2800 m depth from which internal wave shear variance and dissipation rates were calculated examination of the adcp time series revealed a predominance of upward propagating internal wave energy and a significant correlation r 0 45 between shear variance levels and subinertial near bottom cur

40ar 39ar incremental heating study of mineral separates from the early archean east indian craton implications for the thermal history of a section of the singbhum granite batholithic complex 40ar 39ar incremental heating studies on mineral separates from three sets of rocks in the singbhum craton in eastern india have helped unravel the thermochronometric history of the terrane and explain an earlier discrepancy between sm nd 3800 ma and rb sr 3100 ma whole rock ages for the older metamorphic tonalitic gneiss omtg high precision plateau ages for hornblende separates from the older metamorphic group of rocks omg suggest that this unit is older than 3300 ma and that enclaves of both the omtg and omg within the batholithic complex cooled to 500 c at 3300 15 ma following engulfment in magma forming the singbhum granite sg results from a biotite separate from the omtg imply that slow cooling continued to a temperature of 300 c at 3160 ma study of a feldspar separate from the singbhum granite suggests final cooling uplift through the 150 c isotherm 660 ma ago we suggest that an earlier rb sr whole rock age of 3130 85 ma on the omtg did not yield the crystallisation a

equilibration of the antarctic circumpolar current by standing meanders the insensitivity of the antarctic circumpolar current acc s prominent isopycnal slope to changes in wind stress is thought to stem from the action of mesoscale eddies that counterbalance the wind driven ekman overturning a framework verified in zonally symmetric circumpolar flows substantial zonal variations in eddy characteristics suggest that local dynamics may modify this balance along the path of the acc analysis of an eddy resolving ocean gcm shows that the acc can be broken into broad regions of weak eddy activity where surface winds steepen isopycnals and a small number of standing meanders across which the isopycnals relax meanders are coincident with sites of i strong eddy induced modification of the mean flow and its vertical structure as measured by the divergence of the eliassen palm flux and ii enhancement of deep eddy kinetic energy by up to two orders of magnitude over surrounding regions within meanders the vorticity budget shows a balance between the advection of relative vorticity and horizontal divergence providing a mechanism for the generation of strong vertical velocities and rapid changes in stratification temporal fluctuations in these diagnostics are correlated with variability in both the eliassen palm flux and bottom speed implying a link to dissipative processes at the ocean floor at larger scales bottom pressure torque is spatially correlated with the barotropic advection of planetary vorticity which links to variations in meander structure from these results it is proposed that the flexing of standing meanders provides an alternative mechanism for reducing the sensitivity of the acc s baroclinicity to changes in forcing separate from an acc wide change in transient eddy characteristics

lagrangian pathways of upwelling in the southern ocean the spatial and temporal variability of upwelling into the mixed layer in the southern ocean is studied using a 1 10 ocean general circulation model virtual drifters are released in a regularly spaced pattern across the southern ocean at depths of 250 500 and 1000 m during both summer and winter months the drifters are advected along isopycnals for a period of four years unless they outcrop into the mixed layer where lateral advection and a parameterization of vertical mixing is applied the focus of this study is on the discrete exchange between the model mixed layer and the interior localization of interior mixed layer exchange occurs downstream of major topographic features across the indian and pacific basins creating hotspots of outcropping minimal outcropping occurs in the atlantic basin while 59 of drifters outcrop in the pacific sector and in drake passage the region from 140 w to 40 w a disproportionately large amount even when considering the relative basin sizes due to spatial and temporal variations in mixed layer depth the lagrangian trajectories provide a statistical measure of mixed layer residence times for each exchange into the mixed layer the residence time has a rayleigh distribution with a mean of 30 days the cumulative residence time of the drifters is 261 194 days over a period of four years these results suggest that certain oceanic gas concentrations such as co 2 and 14 c will likely not reach equilibrium with the atmosphere before being re subducted

atmospheric sulfur rearrangement 2 7 billion years ago evidence for oxygenic photosynthesis mass independently fractionated sulfur isotopes mif s provide strong evidence for an anoxic atmosphere during the archean moreover the temporal evolution of mif s shows increasing magnitudes between 2 7 and 2 5 ga until the start of the great oxidation event g o e at around 2 4 ga the conclusion of a completely anoxic atmosphere up to the g o e is in contrast to recent studies on redox sensitive elements which suggest slightly oxidizing conditions during continental weathering already several hundred million years prior to the g o e in order to investigate this apparent inconsistency we present multiple sulfur isotopes for 2 71 ga pyritic black shales derived from the kidd creek area ontario canada these samples display high positive 33s values up to 3 8 and the typical late archean slope in 36s 33s of 0 9 in contrast the time period before 3 2 2 73 ga is characterized by greatly attenuated mif s magnitudes and a slope in 36s 33s of 1 5 we attribute the increase in 33s magnitude as well as the contemporaneous change in the slope of 36s 33s to changes in the relative reaction rate of different mif s source reactions and changes in atmospheric sulfur exit channels both of these are dependent on atmospheric ch4 co2 and o2 mixing ratios we propose a distinct change in atmospheric composition at 2 7 ga resulting from increased fluxes of oxygen and methane as the best explanation for the observed neoarchean mif s record our data and modeling results suggest that oxygenic photosynthesis was a major contributor to primary productivity 2 7 billion years ago

evidence for enhanced eddy mixing at middepth in the southern ocean abstract satellite altimetric observations of the ocean reveal surface pressure patterns in the core of the antarctic circumpolar current acc that propagate downstream eastward but slower than the mean surface current by about 25 the authors argue that these observations are suggestive of baroclinically unstable waves that have a steering level at a depth of about 1 km detailed linear stability calculations using a hydrographic atlas indeed reveal a steering level in the acc near the depth implied by the altimetric observations calculations using a nonlinear model forced by the mean shear and stratification observed close to the core of the acc coinciding with a position where mooring data and direct eddy flux measurements are available reveal a similar picture albeit with added details when eddy fluxes are allowed to adjust the mean state computed eddy kinetic energy and eddy stress are close to observed magnitudes with steering levels between 1 and 1 5 km broadly consistent with observatio

so2 photoexcitation mechanism links mass independent sulfur isotopic fractionation in cryospheric sulfate to climate impacting volcanism natural climate variation such as that caused by volcanoes is the basis for identifying anthropogenic climate change however knowledge of the history of volcanic activity is inadequate particularly concerning the explosivity of specific events some material is deposited in ice cores but the concentration of glacial sulfate does not distinguish between tropospheric and stratospheric eruptions stable sulfur isotope abundances contain additional information and recent studies show a correlation between volcanic plumes that reach the stratosphere and mass independent anomalies in sulfur isotopes in glacial sulfate we describe a mechanism photoexcitation of so2 that links the two yielding a useful metric of the explosivity of historic volcanic events a plume model of s iv to s vi conversion was constructed including photochemistry entrainment of background air and sulfate deposition isotopologue specific photoexcitation rates were calculated based on the uv absorption cross sections of 32so2 33so2 34so2 and 36so2 from 250 to 320 nm the model shows that uv photoexcitation is enhanced with altitude whereas mass dependent oxidation such as so2 oh is suppressed by in situ plume chemistry allowing the production and preservation of a mass independent sulfur isotope anomaly in the sulfate product the model accounts for the amplitude phases and time development of 33s 34s and 36s 33s found in glacial samples we are able to identify the process controlling mass independent sulfur isotope anomalies in the modern atmosphere this mechanism is the basis of identifying the magnitude of historic volcanic events

recognition of extraneous argon components through incremental release 40ar39ar analysis of biotite and hornblende across the grenvillian metamorphic gradient in southwestern labrador 40ar39ar incremental release ages have been determined for 15 hornblende and 20 biotite concentrates separated from rocks collected across the garnet and kyanite zones of grenvillian metamorphism in southwestern labrador most hornblende spectra from the kyanite zone are slightly discordant with low temperature increments yielding ages older than the ca 1000 ma date suggested for culmination of grenvillian metamorphism in the area however all the hornblende concentrates record well defined plateau ages these range from 968 to 905 ma across the kyanite zone and date times of diachronous post metamorphic cooling the discordant spectra are interpreted to result from low temperature liberation of excess 40ar components from grain margins two hornblende concentrates from the garnet zone display very discordant spectra total gas ages of 2100 and 3017 ma in which incremental dates systematically decrease during analysis this pattern of discordance suggests that excess argon components are inhomogeneously distributed throughout these hornblende grains most biotites from the garnet and kyanite zones record total gas or plateau ages in excess of 1000 ma 2066 857 ma reflecting the widespread presence of excess argon components because most of the 40ar39ar age spectra are internally concordant the ratios of excess 40ar relative to radiogenic 40ar must have been uniform in the various gas fractions liberated from each sample this is also reflected in the inability of isotope correlation diagrams to differentiate between excess radiogenic and atmospheric argon components the biotite total gas or plateau dates show marked local variation this is interpreted to indicate that the biotite grains were in contact with a post metamorphic intergranular vapor phase that was characterized by large and variable 40ar36ar ratios such ratios most likely resulted from widespread diffusion of the argon liberated from adjacent archean basement gneisses during the grenvillian metamorphic overprint

antarctic intermediate water and subantarctic mode water formation in the southeast pacific the role of turbulent mixing abstract during the 2005 austral winter late august early october and 2006 austral summer february mid march two intensive hydrographic surveys of the southeast pacific sector of the southern ocean were completed in this study the turbulent kinetic energy dissipation rate diapycnal diffusivity and buoyancy flux jb are estimated from the ctd o2 and xctd profiles for each survey enhanced of o 10 3 to 10 4 m2 s 1 is found near the subantarctic front saf during both surveys during the winter survey enhanced was also observed north of the subduction front the northern boundary of the winter deep mixed layer north of the saf in contrast the summer survey found enhanced across the entire region north of the saf below the shallow seasonal mixed layer the enhanced below the mixed layer decays rapidly with depth a number of ocean processes are considered that may provide the energy flux necessary to support the observed diffusivity the observed buoyancy flux 4 0 10 8 m2 s 3 surr

can organic haze and o2 plumes explain patterns of sulfur mass independent fractionation during the archean abstract the existence of mass independently fractionated sulfur in archean rocks is almost universally accepted as evidence for low atmospheric o2 and o3 concentrations at that time but the detailed patterns of the 33 s values and of the ratios 33 s 34 s and 36 s 33 s remain to be explained and the mechanism for producing the mass independent fractionation remains controversial here we explore the hypothesis that the relatively low 33 s values seen during the mid archean 2 7 3 5 ga were caused by the presence of organic haze produced from photolysis of methane this haze helped shield so2 from photolysis while at the same time providing surfaces on which unfractionated short chain sulfur species could condense the evolution of oxygenic photosynthesis and the concomitant disappearance of organic haze towards the end of the archean allowed more negatively fractionated s4 and s8 to form thereby generating large positive fractionations in other sulfur species including sulfate and h2s reduction of this sulfate to h2s by bacteria followed by incorporation of h2s into pyrite produced the large positive 33 s values observed in the neoarchean rock record 2 5 2 7 ga

a small s mif signal in martian regolith pyrite implications for the atmosphere abstract the past martian atmosphere is often compared to the archean earth s as both were dominated by co2 rich and o2 poor chemistries archean earth rocks preserve mass independently fractionated sulfur isotopes s mif non zero 33s and 36s originating from photochemistry in an anoxic atmosphere thus martian crustal rocks might also be expected to preserve a s mif signature providing insights into past atmospheric chemistry we have used secondary ion mass spectrometry sims to investigate in situ the sulfur isotope systematics of nwa 8171 paired to nwa 7034 a martian polymict breccia containing pyrite that formed through hydrothermal sulfur addition in a near surface regolith setting in this meteorite pyrite grains have a weighted mean of 33s of 0 14 0 08 and 36s 0 70 0 40 2 s e m so the s mif signature is subtle sulfur isotope data for four additional shergottites yield 33s values that are not resolvable from zero as in previous studies of shergottites at first glance the result for the polymict breccia might seem surprising but no martian meteorite yet has yielded a s mif signature akin to the large deviations seen on earth we suggest that s mif bearing aerosols h2so4 and s8 were produced when volcanic activity pushed a typically oxidising martian atmosphere into a reduced state after rain out of these aerosols s8 would tend to be oxidised by chlorate dampening the s mif signal which might be somewhat retained in the more abundant photolytic sulfate then in the regolith mixing of aqueous surface derived sulfate with igneous sulfide the latter with zero mif to form the abundant pyrite seen in nwa 8171 would further dampen the s mif signal nonetheless the small negative 33s anomalies seen in martian meteorites imply that volcanic activity was sufficient to produce a reducing atmosphere at times this volcanically driven atmospheric evolution would tend to produce high levels of carbonyl sulfide ocs given that ocs is a relatively long lived strong greenhouse gas the s mif signal implies that volcanism periodically generated warmer conditions perhaps offering an evidence based solution to the young wet mars paradox

multiple sulfur isotopes and the evolution of the atmosphere interest in multiple sulfur isotope analyses has been fueled by recent reports of mass independent sulfur isotope signatures in the geologic record a non zero multiple isotopic signature of sulfur 33s and 36s is produced primarily through photochemical reactions and it is an almost perfect tracer of the source of sulfur once the signature is passed on to a given sulfur reservoir it will be preserved unless there is addition of sulfur with a different 33s or 36s in the geological record this signature has been used to study the evolution of the earth s atmosphere and to trace movement of sulfur through geological systems early in earth s history recently small but significant mass independent signatures have been reported for some younger samples raising the possibility of additional applications of multiple isotope studies the purpose of this review is to introduce and discuss the implications of multiple isotope studies and to focus attention on these anomalous but not uncommon isotopic signatures

recombination reactions as a possible mechanism of mass independent fractionation of sulfur isotopes in the archean atmosphere of earth a hierarchy of isotopically substituted recombination reactions is formulated for production of sulfur allotropes in the anoxic atmosphere of archean earth the corresponding system of kinetics equations is solved analytically to obtain concise expressions for isotopic enrichments with focus on mass independent isotope effects due to symmetry ignoring smaller mass dependent effects proper inclusion of atom exchange processes is shown to be important this model predicts significant and equal depletions driven by reaction stoichiometry for all rare isotopes 33s 34s and 36s interestingly the ratio of capital formula see text values obtained within this model for 33s and 36s is 1 16 very close to the mass independent fractionation line of the archean rock record this model may finally offer a mechanistic explanation for the striking mass independent fractionation of sulfur isotopes that took place in the archean atmosphere of earth

redox states of archean surficial environments the importance of h2 g instead of o2 g for weathering reactions abstract redox states of the archean eon have been constrained by various lines of evidence including atmospheric photochemical and ecological models mass independent fractionations of sulfur isotopes fe depletion of paleosols and preservation of diagnostic detrital minerals although these lines of evidence present seemingly consistent upper limits on po2 g they are conceptually contradictory about the redox state of archean surficial environments atmospheric photochemical and ecological modeling studies suggest weakly reducing environments under redox states represented by moderate h2 g levels however current interpretations of fe depletion in paleosols and the preservation of detrital minerals are based on low o2 g levels at which the reducing detrital minerals are thermodynamically unstable and survive because of slow kinetics of oxidative weathering in this study we show that under the redox state indicated by the archean ph2 g range fe2 and reducing fe ii minerals are actually thermodynamically stable and have no tendency to be oxidized we emphasize that ph2 g values are orders of magnitude higher than po2 g in the archean atmosphere and that h2 g and o2 g are not in equilibrium the redox states of archean surface environments behave as though they were controlled by the more abundant h2 instead of the very low o2 as in modern anoxic basins weathering in this case should have involved non redox acidic dissolution of fe ii species or reductive reaction of fe iii species fe ii depleted paleosols and the preservation of relatively reduced detrital minerals are natural consequences of their thermodynamic stabilities in the archean eon s reducing environments rather than slow kinetics of oxidizing reactions after the appearance of oxygenic photosynthesis probably in the middle late archean locally oxygenated environments could have existed while the atmosphere as a whole remained anoxic the profile of redox states on the archean surface seems to be a reverse analogue to the modern earth although oxidizing dissolution of transition metals could happen in o2 oases quick reduction of oxyanions by abundant reductants such as aqueous fe2 fe ii minerals and h2 might have restricted riverine transport of oxyanions and potentially complicate the interpretation of signals of o2 whiffs in marine sediments

a microscale view of mixing and overturning across the antarctic circumpolar current abstractthe relative roles of isoneutral stirring by mesoscale eddies and dianeutral stirring by small scale turbulence in setting the large scale temperature salinity relation of the southern ocean against the action of the overturning circulation are assessed by analyzing a set of shear and temperature microstructure measurements across drake passage in a triple decomposition framework it is shown that a picture of mixing and overturning across a region of the antarctic circumpolar current acc may be constructed from a relatively modest number of microstructure profiles the rates of isoneutral and dianeutral stirring are found to exhibit distinct characteristic and abrupt variations most notably a one to two orders of magnitude suppression of isoneutral stirring in the upper kilometer of the acc frontal jets and an order of magnitude intensification of dianeutral stirring in the subpycnocline and deepest layers of the acc these variations balance an overturning circulation with meridional flo

new insights into archean sulfur cycle from mass independent sulfur isotope records from the hamersley basin australia we have measured multiple sulfur isotope ratios 34 s 33 s 32 s for sulfide sulfur in shale and carbonate lithofacies from the hamersley basin western australia the v 33 s values v 33 swn 33 s30 515un 34 s shift from 31 9 to 6 9x over a 22 m core section of the lower mount mcrae shale v2 5 ga likewise sulfide sulfur analyses of the jeerinah formation v2 7 ga yield v 33 s values of 30 1 to 8 1x over a 50 m section of core despite wide variations in v 33 s and n 34 s these two shale units yield a similar positive correlation between v 33 s and n 34 s in contrast pyrite sulfur analyses of the carawine dolomite v2 6 ga yield a broad range in n 34 s 3 2 to 16 2x but a relatively small variation and negative values in v 33 s 32 5 to 31 1x the stratigraphic distribution of n 33 s n 34 s and v 33 s in western australia allows us to speculate on the sulfur isotopic composition of archean sulfur reservoirs and to trace pathways in the archean sulfur cycle our data are explained by a combination of massindependent fractionation mif in the atmosphere and biological mass dependent fractionation in the ocean in the archean volcanic sulfur bearing gas species were photolysed by solar ultraviolet uv radiation in an oxygen free atmosphere resulting in mif of sulfur isotopes aerosols of s8 with v 33 ss 0 and sulfuric acid with v 33 s6 0 formed from the products of uv photolysis and carried mass independently fractionated sulfur into the hydrosphere the signatures of atmospheric photolysis were preserved by precipitation of pyrite in sediments pyrite precipitation was mediated by microbial enzymatic catalysis that superimposed mass dependent fractionation on mass independent atmospheric effects multiple sulfur isotope analyses provide new insights into the early evolution of the atmosphere and the evolution and distribution of early sulfur metabolizing organisms a 2003 elsevier science b v all rights reserved

re evaluation of so2 release of the 15 june 1991 pinatubo eruption using ultraviolet and infrared satellite sensors 1 in this study ultraviolet toms total ozone mapping spectrometer satellite data for so2 are re evaluated for the first 15 days following the 15 june 1991 pinatubo eruption to reflect new data retrieval and reduction methods infrared satellite so2 data from the tovs hirs 2 tiros television infrared observation satellite optical vertical sounder high resolution infrared radiation sounder 2 sensor whose data sets have a higher temporal resolution are also analyzed for the first time for pinatubo extrapolation of so2 masses calculated from toms and tovs satellite measurements 19 118 hours after the eruption suggest initial so2 releases of 15 3 mt for toms and 19 4 mt for tovs including so2 sequestered by ice in the early pinatubo cloud tovs estimates are higher in part because of the effects of early formed sulfate the toms so2 method is not sensitive to sulfate but can be corrected for the existence of this additional emitted sulfur the mass of early formed sulfate in the pinatubo cloud can be estimated with infrared remote sensing at about 4 mt equivalent to 3 mt so2 thus the total s release by pinatubo calculated as so2 is 18 4 mt based on toms and 19 4 mt based on tovs the so2 removal from the volcanic cloud during 19 374 hours of atmospheric residence describes overall e folding times of 25 5 days for toms and 23 5 days for tovs these removal rates are faster in the first 118 hours after eruption when ice and ash catalyze the reaction and then slow after heavy ash and ice fallout so2 mass increases in the volcanic cloud are observed by both toms and tovs during the first 70 hours after eruption most probably caused by the gas phase so2 release from sublimating stratospheric ice ash gas mixtures this result suggests that ice sequestered so2 exists in all tropical volcanic clouds and at least partially explains so2 mass increases observed in other volcanic clouds in the first day or two after eruption