shear induced convective mixing in bottom boundary layers on slopes field data from a stratified lake demonstrate that buoyancy driven convective mixing can be an important mechanism for the formation of well mixed bottom boundary layers bbls on slopes convective turbulence is caused by differential transport of stratified water masses along the slope of a basin because the current velocity usually decreases toward the sediment water at some distance from the bottom is transported faster than is water below during upslope flow this process leads to transport of heavier water on top of lighter water and hence to unstable stratification within the bbls analogously strong bbl stratification occurs during downslope flow high frequency acoustic doppler current profiler adcp and temperature measurements in the bbls of a lake revealed the cyclic occurrence of convective turbulence driven by periodic across slope currents of internal seiching the estimated maximum buoyancy flux within the bbls was in good agreement with the highest observed dissipation rates of turbulent kinetic energy this suggests that in our specific case classical bottom shear production and the mentioned buoyancy driven convective production contributed by similar amounts to the turbulent kinetic energy

dispersion of a tracer in the deep gulf of mexico a 25 km streak of cf3sf5 was released on an isopycnal surface approximately 1100 m deep and 150 m above the bottom along the continental slope of the northern gulf of mexico to study stirring and mixing of a passive tracer the location and depth of the release were near those of the deep hydrocarbon plume resulting from the 2010 deepwater horizon oil well rupture the tracer was sampled between 5 and 12 days after release and again 4 and 12 months after release the tracer moved along the slope at first but gradually moved into the interior of the gulf diapycnal spreading of the patch during the first 4 months was much faster than it was between 4 and 12 months indicating that mixing was greatly enhanced over the slope the rate of lateral homogenization of the tracer was much greater than observed in similar experiments in the open ocean again possibly enhanced near the slope maximum concentrations found in the surveys had fallen by factors of 104 107 and 108 at 1 week 4 months and 12 months respectively compared with those estimated for the initial tracer streak a regional ocean model was used to simulate the tracer field and help interpret its dispersion and temporal evolution model data comparisons show that the model simulation was able to replicate statistics of the observed tracer distribution that would be important in assessing the impact of oil releases in the middepth gulf

modeling semidiurnal internal tide variability in the southern california bight abstractthe regional oceanic modeling system roms is applied in a nested configuration with realistic forcing to the southern california bight scb to analyze the variability in semidiurnal internal wave generation and propagation the scb has a complex topography with supercritical slopes that generate linear internal waves at the forcing frequency the model predicts the observed barotropic and baroclinic tides reasonably well although the observed baroclinic tides feature slightly larger amplitudes the strongest semidiurnal barotropic to baroclinic energy conversion occurs on a steep sill slope of the 1900 m deep santa cruz basin this causes a forced near resonant semidiurnal poincare wave that rotates clockwise in the basin and is of the first mode along the radial azimuthal and vertical directions the associated tidal mean depth integrated energy fluxes and isotherm oscillation amplitudes in the basin reach maximum values of about 5 kw m 1 and 100 m and are strongly modulated by the sprin

high temperature chromium isotope fractionation and its implications constraints from the kizildag ophiolite se turkey abstract chromium isotope data were obtained from olivine orthopyroxene and chromite separates of the kizildag ophiolite se turkey to investigate the effects of high temperature magma processes on cr isotope fractionation harzburgite in the kizildag ophiolite has the 53cr values of 0 14 to 0 12 in chromite and 0 08 to 0 01 in bulk rocks these cr isotope fractionations could be driven by partial melting and metasomatism the dunite and chromitite samples from the mantle crust transition zone of the kizildag ophiolite are cumulates and their chromite and olivine have 53cr values of 0 29 to 0 06 and 0 11 to 0 41 respectively the 53cr values of chromite are negatively correlated with the chemical indices of fractional crystallization e g fe of chromite suggesting that cr isotopes were fractionated during fractional crystallization in the chromitite the degree of cr isotope fractionation increases with fractional crystallization with 0 23 cr isotope fractionation occurring at mineral scale during fractional crystallization solid phases preferentially incorporate cr particularly heavy cr isotopes driving the depletion of cr and enrichment of light cr isotopes in the evolved melts the 53cr values of olivine are higher than the coexisting chromite which could be explained by the fact that the olivine grains were probably formed earlier than the chromite the cr isotopic features of chromite in the podiform chromitite 0 22 to 0 04 from the mantle sequence are consistent with the modelled fractional crystallization trend confirming the magmatic origin of the podiform chromitite therefore a significant cr isotope fractionation at chromite from the kizildag ophiolite could be induced by the high temperature fractional crystallization

tracing metal silicate segregation and late veneer in the earth and the ureilite parent body with palladium stable isotopes abstract stable isotope studies of highly siderophile elements hse have the potential to yield valuable insights into a range of geological processes in particular the strong partitioning of these elements into metal over silicates may lead to stable isotope fractionation during metal silicate segregation making them sensitive tracers of planetary differentiation processes we present the first techniques for the precise determination of palladium stable isotopes by mc icpms using a 106pd 110pd double spike to correct for instrumental mass fractionation results are expressed as the per mil difference in the 106pd 105pd ratio 106pd relative to an in house solution standard pd ipgp in the absence of a certified pd isotopic standard repeated analyses of the pd isotopic composition of the chondrite allende demonstrate the external reproducibility of the technique of 0 032 on 106pd using these techniques we have analysed pd stable isotopes from a range of terrestrial and extraterrestrial samples we find that chondrites define a mean 106pdchondrite 0 19 0 05 ureilites reveal a weak trend towards heavier 106pd with decreasing pd content similar to recent findings based on pt stable isotopes creech et al 2017 although fractionation of pd isotopes is significantly less than for pt possibly related to its weaker metal silicate partitioning behaviour and the limited field shift effect terrestrial mantle samples have a mean 106pdmantle 0 182 0 130 which is consistent with a late veneer of chondritic material after core formation

hydraulic control of flow over the sill in observatory inlet observations of density velocity and acoustic backscatter obtained over the sill in observatory inlet british columbia during the ebb tide illustrate several features of internal hydraulic control in a tidally forced stratified flow following high water slack the flow field was initially determined by critical control of the second internal mode at the sill crest as the flow speed increased a transition occurred and control changed to an approach control of the second internal mode located upstream of the sill crest whereas the critical control represents a minimum energy condition at the crest the approach control corresponds to a maximum energy condition upstream of the sill crest later when the ebb currents were just past their maximum values the control condition changed to critical control of the first internal mode the concept of approach control of flow over topography has not previously been discussed in the literature the data described here are believed to represent the first field observations of this phenomenon the changing hydraulic conditions are analyzed in terms of two and three layer hydraulic models model results are consistent with the evolution of the flow patterns although the model cannot reproduce the apparent hysteresis in the response after maximum ebb the concept of an approach control is demonstrated with a simple two layer laboratory model

anatomy of turbulence in thermally stratified lakes turbulence within the thermocline of two thermally stratified lakes lake biwa japan and lake kinneret israel was investigated using a portable flux profiler this instrument provided high resolution profiles of temperature conductivity and two components of velocity within a measuring volume of approximately 8 mm 3 each data profile was segmented into statistically stationary segments a range of properties of the turbulence including direct estimates of the vertical mass flux were then calculated for each segment it was found that turbulence in the thermocline was generally patchy but within a patch dissipation levels were relatively high the turbulent motions were found to be fine grained with small thorpe scales and a large skewness of the distribution of the displacement scale this is distinct to that found in the ocean where shear instability produces large overturns the measurement showed that the net vertical mass flux in the thermocline was negligible and less than that predicted by osborn 1980 this is explained by noting that the net buoyancy flux consisted of two opposing parts a down gradient irreversible flux due to turbulent mixing and an up gradient reversible flux due to restratification that often cancel each other within a segment the low measured net buoyancy flux within the interior of the lakes suggested that other processes such as gravitational adjustments and benthic boundary layer processes should be responsible for the basin averaged vertical transport in these lakes

near coastal satellite altimetry sea surface height variability in the north sea baltic sea area 1 the radiometer wet tropospheric correction is a limiting factor of the application of near coastal altimetry observations in the north sea baltic sea area using an ecmwf model based correction instead we increase the return rate from 70 to 95 with observations as close as 10 km from the coast the altimetry and 39 coastal tide gauges are referenced to the same state of the art regional geoid the two data sets are highly correlated and reveal a consistent mean dynamic topography and two distinct correlation regimes separated by the danish islands the combination of the two data sets in a simple statistical model is shown to estimate the sea surface height with the same error level as state of the art operational models indicating the potential for near coastal applications of satellite altimetry observations

occurrence of hexavalent chromium in ground water in the western mojave desert california abstract about 200 samples from selected public supply domestic and observation wells completed in alluvial aquifers underlying the western mojave desert were analyzed for total dissolved cr and cr vi because cr vi is difficult to preserve samples were analyzed by 3 methods chromium vi was determined in the field using both a direct colorimetric method and epa method 218 6 and samples were speciated in the field for later analysis in the laboratory using a cation exchange method developed for the study described in this paper comparison of the direct colorimetric method and epa method 218 6 with the new cation exchange method yielded r 2 values of 0 9991 and 0 9992 respectively total dissolved cr concentrations ranged from less than the 0 1 g l detection limit to 60 g l and almost all the cr present was cr vi near recharge areas along the mountain front ph values were near neutral dissolved o 2 concentrations were near saturation and cr vi concentrations were less than the 0 1 g l detection limit chromium vi concentrations and ph values increased downgradient as long as dissolved o 2 was present however low cr vi concentrations were associated with low dissolved o 2 concentrations near ground water discharge areas along dry lakes chromium vi concentrations as high as 60 g l occurred in ground water from the sheep creek fan alluvial deposits weathered from mafic rock derived from the san gabriel mountains and cr vi concentrations as high as about 36 g l were present in ground water from alluvial deposits weathered from less mafic granitic metamorphic and volcanic rocks chromium iii was the predominant form of cr only in areas where dissolved o 2 concentrations were less than 1 mg l and was detected at a median concentration of 0 1 g l owing to its low solubility in water of near neutral ph depending on local hydrogeologic conditions and the distribution of dissolved o 2 cr vi concentrations may vary considerably with depth samples collected under pumping conditions from different depths within wells show that cr vi concentrations can range from less than the 0 1 g l detection limit to 36 g l in a single well and that dissolved o 2 concentrations likely control the concentration and redox speciation of cr in ground water

the baltic sea tracer release experiment 1 mixing rates in this study results from the baltic sea tracer release experiment batre are described in which deep water mixing rates and mixing processes in the central baltic sea were investigated in september 2007 an inert tracer gas cf3sf5 was injected at approximately 200 m depth in the gotland basin and the subsequent spreading of the tracer was observed during six surveys until february 2009 these data describe the diapycnal and lateral mixing during a stagnation period without any significant deep water renewal due to inflow events as one of the main results vertical mixing rates were found to dramatically increase after the tracer had reached the lateral boundaries of the basin suggesting boundary mixing as the key process for basin scale vertical mixing basin scale vertical diffusivities were of the order of 10 5 m2 s 1 about 1 order of magnitude larger than interior diffusivities with evidence for a seasonal and vertical variability in contrast to tracer experiments in the open ocean the basin geometry hypsography was found to have a crucial impact on the vertical tracer spreading the e folding time scale for deep water renewal due to mixing was slightly less than 2 years the time scale for the lateral homogenization of the tracer patch was of the order of a few months key points mixing rates in the gotland basin are dominated by boundary mixing processes the time scale for gotland basin deep water renewal is approximately 2 years mixing rates determined from the tracer cf3sf5

the santa monica basin tracer experiment a study of diapycnal and isopycnal mixing we have studied cross isopycnal diapycnal and lateral mixing and stirring below the sill of santa monica basin by releasing two tracers sulfur hexafluoride and perfluorodecalin as close as possible to an isopycnal surface and measuring their subsequent dispersion the target for the release was a potential temperature surface at about 790 m depth roughly 100 m above the bottom and 50 m below the sill three surveys performed immediately after about 7 weeks after and about 6 months after the release showed that the time scales for lateral stirring and mixing in the basin were between 2 and 5 months the diapycnal diffusivity for the whole period was found to be 0 29 0 06cm2 s near the injection surface where the buoyancy frequency was about 1 1 cph this estimate may include some mixing in the turbulent boundary layer near the walls of the basin our best estimate for the diapycnal diffusivity in the basin interior is 0 25 0 08 cm2 s

small scale turbulence and vertical mixing in lake baikal the water column of lake baikal is extremely weakly but permanently stratified below 250 m despite the thickness of this relatively stagnant water mass of more than 1000 m the water age time since last contact with the atmosphere is only slightly more than a decade indicating large scale advective exchange in the stratified deep water the fate of water constituents is determined by the combined action of advective processes deep water intrusions and small scale turbulent vertical diffusion here vertical diffusivity is addressed through the analysis of 25 temperature microstructure profiles collected in the three major basins of lake baikal to a depth of 600 m in addition in the 1 432 m deep south basin monthly ctd profiles and a two year record of near bottom currents were analyzed balancing turbulent kinetic energy and small scale temperature variance leads to the conclusions that 1 vertical diffusivity in the stratified deep water ranges from 10 90 3 10 24 m 2 s 21 between 600 and 250 m which is three orders of magnitude more than estimated by killworth et al 1996 2 the mixing efficiency is 0 16 comparable to that found in stronger stratification e g the ocean interior 3 turbulence under ice decays with a time scale of 40 6 2 d and 4 the interior of the permanently stratified deep water below 250 m and the bottom boundary layer contribute roughly equally to the tke production the latter implies that mixing in the deep water of lake baikal s three sub basins is dominated by bottom boundary mixing as found in smaller lakes and ocean basins

a model for the exchange of water and salt between the baltic and the skagerrak abstract a model for the exchange of salt and water between the baltic and the sea the skagerrak is presented because of strong inter basin interactions in the baltic entrance area the model must include the kattegat and the belt sea these are modeled by horizontally homogeneous two layer sub models the most prominent dynamical properties of the sub models are wind driven entrainment flows and rotational baroclinic hydraulic controls the model is driven by a meteorologically forced barotropic transport qh calculated from the freshwater supply to the baltic qf and the sea level fluctuations in the kattegat and turbulent entrainment flows coupled to the wind speed w and in the belt sea also to the barotropic transport the most important bathymetric features of the basins are included the model equations are integrated numerically for a test period of 1 years the stratification in the kattegat as well as in the belt sea is quite well predicted it is found that approximately one half of

oxygen isotope evidence for rapid mixing of the hed meteorite parent body abstract the 16 o 17 o and 18 o abundances of howardites eucrites and diogenites have been used to assign them to a single hed parent body thought to be asteroid 4 vesta we report the first evidence of oxygen isotopic heterogeneity among hed meteorites indicating incompletely mixed sources new high precision oxygen isotope measurements of 34 hed meteorites reveal that most have the same 17 o consistent with a very rapid early history of large scale mixing on vesta however howardites are on average very slightly enriched in 16 o whereas ibitira caldera pasamonte and alha78132 are 16 o depleted compared to other investigated eucrites the 17 o of ibitira is completely different from all other heds measured some of the results for eucrites and diogenites can be explained by partial melting and rapid mixing of the interior of vesta others require a separate parent body or indicate that parts of the outer layer of vesta retained some primary isotopic heterogeneity the oxygen isotopic composition of howardites provides an upper limit for the amount of admixed carbonaceous chondritic material into the hed parent body regolith

trapped diurnal internal tides propagating semidiurnal internal tides and mixing estimates in the california current system from sustained glider observations 2006 2012 abstract from 2006 2012 along 3 repeated cross shore transects california cooperative oceanic fisheries investigations lines 66 7 80 and 90 in the california current system 33 609 shear and 39 737 strain profiles from 66 glider missions are used to estimate mixing via finescale parameterizations from a dataset containing over 52 000 profiles elevated diffusivity estimates and energetic diurnal d1 and semidiurnal d2 internal tides are found a within 100 km of the coast on lines 66 7 and 80 and b over the santa rosa cortes ridge srcr in the southern california bight scb on line 90 while finding elevated mixing near topography and associated with internal tides is not novel the combination of resolution and extent in this ongoing data collection is unmatched in the coastal ocean to our knowledge both d1 and d2 internal tides are energy sources for mixing at these latitudes the d1 internal tide is subinertial on line 90 d1 and d2 tides are equally energetic over the srcr the main site of elevated mixing within the scb numerous sources of internal tides at the rough topography in the scb produce standing and or partially standing waves on lines 66 7 and 80 the dominant energy source below about 100 m for mixing is the d1 internal tide which has an energy density of the d2 internal tide on line 80 estimated diffusivity estimated dissipation and d1 energy density peak in summer the d1 energy density shows an increasing trend from 2006 to 2012 its amplitude and phase are mostly consistent with topographically trapped d1 internal tides traveling with the topography on their right the observed offshore decay of the diffusivity estimates is consistent with the exponential decay of a trapped wave with a mode 1 rossby radius of 20 30 km despite the variable mesoscale it is remarkable that coherent internal tidal phase is found

investigation of magnesium isotope fractionation during basalt differentiation implications for a chondritic composition of the terrestrial mantle to investigate whether magnesium isotopes are fractionated during basalt differentiation we have performed high precision mg isotopic analyses by multi collector inductively coupled plasma mass spectrometry mc icp ms on a set of well characterized samples from kilauea iki lava lake hawaii usa samples from the kilauea iki lava lake produced by closed system crystal melt fractionation range from olivine rich cumulates to highly differentiated basalts with mgo content ranging from 2 37 to 26 87 wt our results demonstrate that although these basalts have diverse chemical compositions mineralogies crystallization temperatures and degrees of differentiation their mg isotopic compositions display no measurable variation within the limits of our external precision average 26 mg 0 36 0 10 and 25 mg 0 20 0 07 uncertainties are 2sd this indicates that mg isotopic fractionation during crystal melt fractionation at temperatures of 1055 c is undetectable at the level of precision of the current investigation calculations based on our data suggest that at near magmatic temperatures the maximum fractionation in the 26 mg 24 mg ratio between olivine and melt is 0 07 two additional oceanic basalts two continental basalts bcr 1 and bcr 2 and two primitive carbonaceous chondrites allende and murchison analyzed in this study have mg isotopic compositions similar to the kilauea iki lava lake samples in contrast to a recent report u wiechert a n halliday non chondritic magnesium and the origins of the inner terrestrial planets earth and planetary science letters 256 2007 360 371 the results presented here suggest that the bulk silicate earth has a chondritic mg isotopic composition 2007 published by elsevier b v

a strait outflow circulation process study the case of the alboran sea abstract a three dimensional primitive equation model is used to investigate the physical processes governing the exchanges of water between the mediterranean sea and the atlantic ocean at the level of the strait of gibraltar the circulation is driven by connecting two reservoirs filled with waters of different densities the motion starts from rest and is initiated by removing the dam separating them at the initial time the results are in agreement with observations in the strait the light atlantic water flows into the mediterranean basin in the surface layer while the denser mediterranean water moves toward the ocean as a deep current after a spinup time interval of three days the flow transport in the strait reaches a quasi stationary value of 0 9 sv sv 106 m3 s 1 as it enters the alboran sea the flow of atlantic water experiences a transition regime where the surface current is transformed into a shallow buoyant jet after several days of integration this flow intrudes into the alboran bas

contributors to chromium isotope variation of meteorites we report the results of a comprehensive high precision survey of the cr isotopic compositions of primitive chondrites along with some differentiated meteorites to ensure complete dissolution of our samples they were first fused with lithium borate tetraborate at 1050 1000 c relative to the nist cr standard srm 3112a carbonaceous chondrites exhibit excesses in 54cr 52cr from 0 4 to 1 6e 1e 1 part in 10 000 and ordinary chondrites display a common 54cr 52cr deficit of 0 4e analyses of acid digestion residues of chondrites show that carbonaceous and ordinary chondrites share a common 54cr enriched carrier which is characterized by a large excess in 54cr 52cr up to 200e associated with a very small deficit in 53cr 52cr 2e we did not find 54cr anomalies in either bulk enstatite chondrites or in leachates of their acid digestion residues this either requires that the enstatite chondrite parent bodies did not incorporate the 54cr anomaly carrier phase during their accretion or the phase was destroyed by parent body metamorphism chromium in the terrestrial rocks and lunar samples analyzed here show no deviation from the nist srm 3112a cr standard the eucrite and martian meteorites studied exhibit small deficits in 54cr 52cr the 54cr 52cr variations among different meteorite classes suggest that there was a spatial and or temporal heterogeneity in the distribution of a 54cr rich component in the inner solar system we confirm the correlated excesses in 54cr 52cr and 53cr 52cr for bulk carbonaceous chondrites but the new data yield a steeper slope 6 6 than that reported in shukolyukov and lugmair 2006 the correlated excesses may affect the use of the mn cr chronometer in carbonaceous chondrites we could not confirm the bulk carbonaceous chondrite mn cr isochron reported by shukolyukov and lugmair 2006 and moynier et al 2007 mostly because we find much smaller total variations in e53cr 0 2 all bulk chondrites have small e53cr excesses up to 0 3 relative to the earth most likely reflecting the sub chondritic mn cr ratio of the earth the e53cr variations in chondrites do seem to grossly correlate with mn cr and yield an initial solar system 53mn 55mn value of 5 4 2 4 10 6 corresponding to an absolute age of 4566 4 2 2 ma nuclear interactions with cosmic rays result in coupled excesses in e54cr and e53cr with a 4 1 ratio in phases with high fe cr these are most dramatically demonstrated in the iron meteorite carbo showing excesses in e54cr of up to 140e these new results show that the mn cr chronometer should be used with caution in samples minerals with high fe cr and long cosmic ray exposure ages

stable calcium isotopic composition of meteorites and rocky planets abstract new measurements of mass dependent calcium isotope effects in meteorites lunar and terrestrial samples show that earth moon mars and differentiated asteroids e g 4 vesta and the angrite and aubrite parent bodies are indistinguishable from primitive ordinary chondritic meteorites at our current analytical resolution 0 07 sd for the 44 ca 40 ca ratio in contrast enstatite chondritic meteorites are slightly enriched in heavier calcium isotopes ca 0 5 and primitive carbonaceous chondritic meteorites are depleted in heavier calcium isotopes ca 0 5 the calcium isotope effects cannot be easily ascribed to evaporation or intraplanetary differentiation processes the isotopic variations probably survive from the earliest stages of nebular condensation and indicate that condensation occurred under non equilibrium undercooled nebular gas conditions some of this early high temperature calcium isotope heterogeneity is recorded by refractory inclusions niederer and papanastassiou 1984 and survived in planetesimals but virtually none of it survived through terrestrial planet accretion the new calcium isotope data suggest that ordinary chondrites are representative of the bulk of the refractory materials that formed the terrestrial planets enstatite and carbonaceous chondrites are not the enrichment of light calcium isotopes in bulk carbonaceous chondrites implies that their compositions are not fully representative of the solar nebula condensable fraction

on the principal building blocks of mars and earth abstract the terrestrial planets are believed to have been formed from primitive material sampling a broad region of the inner solar system several meteoritic mixing models attempting to reconcile isotopic characteristics of mars and earth have been proposed but because of the inherent non uniqueness of these solutions additional independent observations are required to resolve the question of the primary building blocks of the terrestrial planets here we consider existing isotopic measurements of 17 o 48ca 50ti 54cr 62ni and 84sr for primitive chondrites and differentiated achondrites and mix these stochastically to reproduce the isotopic signatures of mars and earth for both planets we observe 105 unique mixing solutions out of 108 random meteoritic mixtures which are categorised into distinct clusters of mixtures using principal component analysis the large number of solutions implies that isotopic data alone are insufficient to resolve the building blocks of the terrestrial planets to further discriminate between isotopically valid mixtures each mixture is converted into a core and mantle component via mass balance for which geophysical properties are computed and compared to observations for mars the geophysical parameters include mean density mean moment of inertia and tidal response whereas for earth upper mantle mg mg fe ratio and core size are employed the results show that mars requires an oxidised feo rich differentiated object next to chondritic material as main building blocks in contrast earth s origin remains enigmatic from a redox perspective it appears inescapable that enstatite chondrite like matter constitutes a dominant proportion of the building blocks from which earth is made the apparent need for compositionally distinct building blocks for mars and earth suggests that dissimilar planetesimal reservoirs were maintained in the inner solar system during accretion

stable chromium isotopic composition of meteorites and metal silicate experiments implications for fractionation during core formation we present new mass independent and mass dependent cr isotope compositions for meteorites measured by double spike thermal ionisation mass spectrometry small differences in both mass independent 53cr and 54cr relative to the bulk silicate earth are reported and are very similar to previously published values carbonaceous chondrites are characterised by an excess in 54cr compared to ordinary and enstatite chondrites which make mass independent cr isotopes a useful tool for distinguishing between meteoritic groups mass dependent stable cr isotope compositions for the same samples are also reported carbonaceous and ordinary chondrites are identical within uncertainty with average 53cr values of 0 118 0 040 and 0 143 0 074 respectively the heaviest isotope compositions are recorded by an enstatite chondrite and a co carbonaceous chondrite both of which have relatively reduced chemical compositions implying some stable cr isotope fractionation related to redox processes in the circumstellar disk the average 53cr values for chondrites are within error of the estimate for the bulk silicate earth bse also determined by double spiking the lack of isotopic difference between chondritic material and the bse provides evidence that cr isotopes were not fractionated during core formation on earth a series of high pressure experiments was also carried out to investigate stable cr isotope fractionation between metal and silicate and no demonstrable fractionation was observed consistent with our meteorites data mass dependent cr isotope data for achondrites suggest that cr isotopes are fractionated during magmatic differentiation and therefore further work is required to constrain the cr isotopic compositions of the mantles of vesta and mars

recent developments in the study of ocean turbulence abstract this review describes the changes in the understanding of turbulence and mixing in the upper layers of the ocean the abyssal ocean and in continental shelf seas that have come in the past 25 years largely through advances in instruments and methodology

si isotope systematics of meteorites and terrestrial peridotites implications for mg si fractionation in the solar nebula and for si in the earth s core abstract high precision si isotope ratios have been measured for a series of meteorites and terrestrial samples using high resolution multi collector icp ms our results differ from those reported in an earlier study georg et al 2007 si in the earth s core nature 447 1102 1106 in two important aspects first our data set reveals systematic differences in 30 si between different chondrite groups that are correlated with their mg si elemental ratio second in agreement with the previous study 30 si for the terrestrial samples are higher than values for chondrites but the difference between the bulk silicate earth bse and the carbonaceous chondrites 30 si bse c arbonaceous chondrites 0 08 0 04 1 standard deviation is about a factor of 2 smaller than previously reported the 30 si versus mg si trend defined by the chondrite groups can be explained by reaction of olivine with a sio rich vapor to form enstatite starting from a carbonaceous chondrite composition in contrast the difference between the bse and carbonaceous chondrites must reflect a different process and can be explained by incorporation of si into the earth s core during metal silicate equilibration in a deep magma ocean the observed si isotope fractionation is consistent with the temperatures and pressures of metal silicate equilibration derived from siderophile element abundances in the earth s mantle

the recent salt inflow into the baltic sea abstract major inflows of highly saline and oxygenated water into the baltic sea are rare events and many of the basic processes underlying them are unknown in january 1993 strong gales led to an intensive inflow that interrupted the 16 year stagnation of the central baltic deep water the different stages of the overflow across the sill area between the north sea and the baltic are discussed in connection with the forcing conditions and the propagation of the water that flowed into the central baltic is briefly described moreover the potential effects of the recent inflow are estimated

mineralogy of meteorite groups approximately 275 mineral species have been identified in meteorites reflecting diverse redox environments and in some cases unusual nebular formation conditions anhydrous ordinary carbonaceous and r chondrites contain major olivine pyroxene and plagioclase major opaque phases include metallic fe ni troilite and chromite primitive achondrites are mineralogically similar the highly reduced enstatite chondrites and achondrites contain major enstatite plagioclase free silica and kamacite as well as nitrides a silicide and ca mg mn na cr k and ti rich sulfides aqueously altered carbonaceous chondrites contain major amounts of hydrous phyllosilicates complex organic compounds magnetite various sulfates and sulfides and carbonates in addition to kamacite and taenite iron meteorites contain carbides elemental c nitrides phosphates phosphides chromite and sulfides silicate inclusions in iab iiicd and iie iron meteorites consist of mafic silicates plagioclase and various sulfides oxides and phosphates eucrites howardites and diogenites have basaltic to orthopyroxenitic compositions and consist of major pyroxene and calcic plagioclase and several accessory oxides ureilites are made up mainly of calcic chromian olivine and low ca clinopyroxene embedded in a carbonaceous matrix accessory phases include the c polymorphs graphite diamond lonsdaleite and chaoite as well as metallic fe ni troilite and halides angrites are achondrites rich in fassaitic pyroxene i e al ti diopside minor olivine with included magnesian kirschsteinite is also present martian meteorites comprise basalts lherzolites a dunite and an orthopyroxenite major phases include various pyroxenes and olivine minor to accessory phases include various sulfides magnetite chromite and ca phosphates lunar meteorites comprise mare basalts with major augite and calcic plagioclase and anorthositic breccias with major calcic plagioclase several meteoritic phases were formed by shock metamorphism martensite 2 fe ni has a distorted body centered cubic structure and formed by a shear transformation from taenite during shock reheating and rapid cooling the c polymorphs diamond lonsdaleite and chaoite formed by shock from graphite suessite formed in the north haig ureilite by reduction of fe and si possibly from olivine via reaction with carbonaceous matrix material ringwoodite the spinel form of mg fe 2sio4 and majorite a polymorph of mg fe sio3 with the garnet structure formed inside shock veins in highly shocked ordinary chondrites secondary minerals in meteorite finds that formed during terrestrial weathering include oxides and hydroxides formed directly from metallic fe ni by oxidation phosphates formed by the alteration of schreibersite and sulfates formed by alteration of troilite

evidence for enhanced boundary mixing in the santa monica basin transients in the heat content in santa monica and san pedro basins imply a basin wide diapycnal eddy diffusivity greater than 1 cm sup 2 s this is significantly larger than the value for sf sub 6 of 0 25 0 08 cm sup 2 s determined for the interior of santa monica basin for september 1985 to february 1986 by ledwell and watson however the exodus of sf sub 6 from santa monica basin after february 1986 by which time the tracer had mixed to the boundaries of the basin was fast enough to be consistent with a greatly enhanced vertical flux since the kinetic energy in the basin had not changed significantly it is unlikely that a temporal increase in forcing resulted in enhanced fluxes in the interior of the basin the most likely interpretation is that diapycnal fluxes in the basin are dominated by processes in the boundary regions temperature and sf sub 6 profiles from near the edges of the basin do not give conclusive evidence either for or against such enhanced mixing 20 refs 19 figs 5 tabs

the flushing of two deep sea basins southern california borderland a time series of water temperature salinity and nutrient measurements has been made in san pedro and san nicolas basins of the southern california borderland between i977 and 1988 these basins exhibit temporally coincident changes in temperature and nutrient content defining a period of basin flushing 1982 1984 and a period of stagnation 1984 1987 during the flushing period cooler oxygenand no rich water replaces warmer oxygenand no depleted bottom water flushing produces a decrease of 0 2 c in the average temperature of san pedro basin bottom water 790 900 m and an increase in the average oxygen content by 12 pm these values are 0 i and 3 for san nicolas basin 1 400 l 800 m the residence time of water in san pedro basin during the flushing period is 12 6 months and j t2 months in san nicolas basin a box model approach constrained by the time series data for the stagnation period was used to determine values of the effective vertical eddy diffusivities for the 790 m horizon in san pedro basin and 1 400 m horizon in san nicolas basin 1 3 0 4 and 9 9k3 4 cm sk respectively

hydraulic control of sill flow with bottom friction abstract the hydraulics of strait and sill flow with friction is examined using a reduced gravity model it is shown that friction moves the critical or control point from the sill to a location downstream if the strait has constant width the control point lies where the bottom slope is the negative of the drag coefficient cd if cd exceeds the bottom slope everywhere the flow cannot be controlled in the classical sense that energy and flow force are minimized friction also decreases the minimum obstacle height required to establish hydraulically controlled flow in the classical laboratory towing experiment also friction greatly encourages the establishment of stationary hydraulic jumps in the lee of the sill and under certain conditions gives rise to stationary jumps on the upstream face of the obstacle some consequences of these results for deep ocean overflows are given using the iceland faroe overflow as an example

the chromium isotopic composition of seawater and marine carbonates article history chromium isotopes are fractionated during redox reactions and have the potential to provide a record of changes in the oxygenation levels of the oceans in the geological past however cr is a trace metal in seawater and its low concentrations make isotopic measurements challenging here we report the first determinations of 53 cr for seawater from open ocean argentine basin and coastal southampton water settings using a double spike technique the total chromium concentration in seawater from southampton water is 1 85 nm whereas the cr content of argentine basin samples is 5 8 6 6 nm the 53cr value of seawater from the argentine basin is 0 491 0 556 in intermediate and deep waters and varies between 0 412 and 0 664 in surface waters 150 m the 53

tungsten stable isotope compositions of terrestrial samples and meteorites determined by double spike mc icpms abstract tungsten stable isotopes hold great potential to examine a variety of physical and chemical processes operating during the accretion and differentiation of asteroids and terrestrial planets such as core formation and mantle crust differentiation to assess the magnitude and origin of w isotope fractionations we determined the w stable isotopic compositions of six usgs geological reference materials a nist steel and 24 iron meteorites and chondrites the w isotope data were obtained using multi collector inductively coupled plasma mass spectrometry mc icpms and using a 180 w 183 w double spike chondrites and iron meteorites exhibit a very narrow range in w stable isotope compositions resulting in a mean 184 183 w 0 027 0 007 95 conf relative to the nist 3163 w standard this value represents a good estimate for the w stable isotope composition of bulk planetary bodies from the inner solar system the 184 183 w of some iron meteorites slightly deviates from this value most likely due to w isotope fractionations induced during crystallization of the metal cores of iron meteorite parent bodies the investigated terrestrial silicate rocks exhibit a narrow range in 184 183 w which for most samples is indistinguishable from the mean value of chondrites and iron meteorites however felsic samples tend to be isotopically lighter than mafic samples indicating that magmatic processes on earth induced w isotope fractionations these fractionations are possibly related to the fluid mobility of w in subduction zones but more data are needed to test this hypothesis given that most terrestrial igneous rocks are isotopically indistinguishable from chondrites and iron meteorites core formation on earth does not seem to have induced a measurable isotopic fractionation for w however more data are needed to firmly arrive at this conclusion

oxygen isotopic compositions of enstatite chondrites and aubrites oxygen isotopic compositions have been measured for ten eh chondrites eight el chondrites and nine aubrites the mean 18o and 17o values are 5 31 and 2 74 5 57 and 2 96 5 24 and 2 70 respectively within the eh group more equilibrated meteorites are fractionated toward higher heavy isotope abundances than the less equilibrated meteorites small departures of individual meteorites from a common mass fractionation occur for some of the eh samples the aubrites may be genetically related to either the eh or el group or to both almost all of the measured isotopic compositions are indistinguishable from the terrestrial oxygen isotope fractionation line suggesting a genetic relationship among the earth the moon and the enstatite the meteorites

shear and strain in santa monica basin by injecting a cloud of sf6 into santa monica basin at a depth of 790 m and observing its vertical spread ledwell and watson 1991 estimate the average diapycnal diffusivity between 750 and 850 m as kp 2 5 10 5 m2 m 1 this diffusivity is higher than inferred from microstructure measurements in the open ocean thermocline for typical internal wave levels gregg and sanford 1988 to examine shear and strain in the basin we dropped expendable current profilers xcps and calculated strain from conductivity temperature and depth ctd casts shear and strain are above the gm76 model spectrum garrett and munk 1975 cairns and williams 1976 and comparisons with published parameterizations indicate more than enough shear variance to account for the high diffusivity reported by ledwell and watson thus the eddy diffusivity in santa monica basin is not at odds with lower values estimated from microstructure measurements in the open ocean but is due to an elevated internal wave field the spectral shapes however differ from typical open ocean spectra

sediment resuspension and mixing by resonantly generated internal solitary waves the observation of internal solitary waves isws propagating upstream along a strongly stratified bottom layer on the california shelf is reported an increased concentration of particulates in the water column accompanies the passage of these isw packets the estimated local richardson number in the bottom vicinity is around 1 4 and a vertical coefficient of eddy diffusivity of order 1022 m2 s21 is associated with the upstream propagating leading isw the leading isw gave rise to reversed flow in an 8 m layer above the bottom it is argued that the upstream propagating isws were generated by resonant flow over bottom topography internal waves generated in this way seem to be frequent in the record of a month long experiment model results suggest that the isws can carry up to 73 of such generated long wave energy the ocean conditions at the site are similar to those of other coastal sites which suggests that the phenomenon described here may be common

observations of mixing near the sides of a deep lake in winter the dissipation rate of turbulent kinetic energy per unit mass vertical eddy diffusivity kz and the rate of dissipation of temperature variance x are estimated over the sloping sides of lake geneva both far from and near the bed using temperature data from horizontal tracks of a submarine during periods of winter cooling the estimated values are about one order of magnitude greater near the slope than those distant from it the mean dissipation rate per unit mass averaged over the epilimnion varies between o 10 210 m 2 s 23 in calm weather to o 10 28 m 2 s 23 in winds of 8 m s 21 for surface buoyancy fluxes of 6 3 10

a fluorescein tracer release experiment in the hydrothermally active crater of vailulu u volcano samoa 1 on 3 april 2001 a 20 kg point source of fluorescein dye was released 30 m above the bottom of the active summit caldera of vailulu u submarine volcano samoa vailulu u crater is 2000 m wide and at water depths of 600 1000 m with the bottom 200 m completely enclosed it thus provides an ideal site to study the hydrodynamics of an active hydrothermal system the magmatically driven hydrothermal system in the crater is currently exporting massive amounts of particulates manganese and helium the dispersal of the dye was tracked for 4 days with a fluorimeter in tow yo mode from the u s coast guard icebreaker polar sea lateral dispersion of the dye ranged from 80 to 500 m d 1 vertical dispersion had two components a diapycnal diffusivity component averaging 21 cm2 s 1 and an advective component averaging 0 025 cm s 1 these measurements constrain the mass export of water from the crater during this period to be 8 1 3 4 6 107 m3 d 1 which leads to a turnover time for water in the crater of 3 2 days coupled with temperature data from ctd profiles and mn analyses of water samples the power output from the crater is 610 100 350 mw and the manganese export flux is 240 kg d 1 the mn heat ratio of 4 7 ng j 1 is significantly lower than ratios characteristic of hot smokers and diffuse hydrothermal flows on mid ocean ridges and points to phase separation processes in this relatively shallow hydrothermal system

vertical mixing in the baltic sea and consequences for eutrophication a review abstract in the transition area between the north sea and the baltic sea entrainment processes dominate the vertical mixing in the inflowing saline bottom water the hot spots of these processes are located at the darss sill and the bornholm channel in the western baltic sea in the central baltic sea the horizontal advection of saline water in deep layers below the permanent halocline dominate the temporal changes and associated transports this is accompanied by the turbulent vertical transport through the halocline into the surface layers the related vertical salt transport into the entire surface mixed layer estimated by various methods is slightly above 30 kg m 2 a during stagnation periods the residence time of the deep water in the eastern gotland basin increases roughly by a factor of five vertical mixing through the halocline is drastically reduced when inflows are lacking the potential processes of diapycnal mixing are discussed to the present knowledge the turbulent motion resulting from breaking internal waves is capable of turbulent transports through the halocline corresponding to the estimates of the salt transport into the surface mixed layer the actual knowledge about boundary mixing due to internal waves in the baltic sea is poor mesoscale eddies may contribute to the vertical mixing but it is not known whether they really do and which of the possible direct and indirect mixing mechanisms is most effective near bottom currents induced by inflow events likely enhance vertical mixing coastal upwelling certainly contributes to the vertical transport but the depth of its origin and the volume transport are hard to determine for large scale quantifications the short spatiotemporal scale of turbulent transports through the halocline resulting in a weakening of the halocline during summer together with the mixing of the entire surface layer down to the halocline in winter form a consistent description of the vertical salt transport it is hypothesised that the longer residence time of the deep water during stagnation periods results from the lack of energy imported by the inflows and directly or indirectly feeding the diapycnal mixing processes the vertical transport of nutrients such as the phosphate is quantitatively not sufficiently understood and needs further interdisciplinary research activities

the rotating hydraulics of the open channel flow between two basins the theory of rotating open channel flow between two basins is presented and experimentally verified for three cases the first case considered is the submerged weir flow i e the height of the channel floor is below the free surface height of the fluid in the lower basin flow for this case is found to depend on the fluid level in the downstream basin when the fluid level there is high and is independent of the fluid level downstream as soon as the level falls below a critical height at that point the flow in the channel becomes critical controlled the dependence of the flow on upstream potential vorticity and on rotation rate is also examined it is shown that transport of the flow decreases whenever rotation rate or upstream potential vorticity is increased the second case studied is controlled flow through a channel of irregular cross section the truncated channel transport of this flow is shown to increase at some moderate rotations if the channel floor has a cross channel slope similar to that of the surface of the current otherwise the transport always decreases with rotation rate the final case is concerned with supercritical separation of the current downstream of the control section i e the current separates from the left wall of the channel looking downstream visual evidence and measurements of formation of such a boundary current are obtained comparisons between the theory and the experiment for the three cases are generally reasonable except when flow separates in the control section the theory is found inapplicable to such separation

experimental evidence for mo isotope fractionation between metal and silicate liquids stable isotope fractionation of siderophile elements may inform on the conditions and chemical consequences of core mantle differentiation in planetary objects the extent to which mo isotopes fractionate during such metal silicate segregation however is so far unexplored we have therefore investigated equilibrium fractionation of mo isotopes between liquid metal and liquid silicate to evaluate the potential of mo isotopes as a new tool to study core formation we have performed experiments at 1400 and 1600 c in a centrifuging piston cylinder tin was used to lower the melting temperature of the fe based metal alloys to 1400 c while variable fe oxide contents were used to vary oxygen fugacity in graphite and mgo capsules isotopic analyses were performed using a double spike technique in experiments performed at 1400 c the 98mo 95mo ratio of silicate is 0 19 0 03 0 19 0 03 95 confidence interval heavier than that of metal this fractionation is not significantly affected by the presence or absence of carbon molybdenum isotope fractionation is furthermore independent of oxygen fugacity in the range iw 1 79 to iw 0 47 which are plausible values for core formation experiments at 1600 c show that at equilibrium the 98mo 95mo ratio of silicate is 0 12 0 02 0 12 0 02 heavier than that of metal and that the presence or absence of sn does not affect this fractionation equilibrium mo isotope fractionation between liquid metal and liquid silicate as a function of temperature can therefore be described as mometal silicate98 95 4 70 0 59 105 t2 our experiments show that mo isotope fractionation may be resolvable up to metal silicate equilibration temperatures of about 2500 c rendering mo isotopes a novel tool to investigate the conditions of core formation in objects ranging from planetesimals to earth sized bodies

a tracer study of mixing in the santa cruz basin a tracer release experiment to study diapycnal and isopycnal mixing was performed in santa cruz basin in 1988 1989 approximately 1450 g of sulfur hexafluoride were injected close to an isopycnal surface at 1500 m depth in may 1988 this depth is midway between the bottom of the basin at 1920 m and the sill at 1084 m the diapycnal dispersion measured during the first few months while the tracer was still mixing to the walls of the basin yielded a diapycnal eddy diffusivity of 1 0 cm2 s 1 within a factor of 1 5 this is approximately 4 times larger than the diffusivity found by ledwell and watson 1991 in the interior of santa monica basin where the buoyancy frequency was 5 times greater the tracer was well mixed to the walls 6 months after the injection and at that time the diapycnal spread of the tracer was greater near the walls than in the interior the rate of diapycnal dispersion of the tracer increased dramatically after the tracer had mixed to the walls of the basin indicating enhanced boundary mixing an effective basin wide diapycnal diffusivity of 10 cm2 s 1 would be required to support the fluxes of tracer observed a one dimensional model for tracer and heat diffusion does not simulate the results very well however probably because of the finite mixing time between the boundary region and interior and because of the complexity of the processes in the boundary region

boundary versus internal diapycnal mixing in stratified natural waters using the fluorescent dye uranin tracer release experiments to study the contribution of bottom boundary mixing to diapycnal transport in stratified natural waters were performed in lake alpnach central switzerland during 1992 1995 a first experiment involved injecting the tracer from a point source into the center of the hypolimnion that part of the lake below the surface mixed layer an in situ fluorometer was then employed to detect the horizontal and vertical spreading of the tracer cloud allowing rates of diapycnal diffusivity to be determined as long as the tracer was confined to the interior water region the diapycnal diffusivity was relatively small however after the tracer cloud had reached the lake boundary the diapycnal diffusivity increased by approximately one order of magnitude in a second experiment the tracer was released near the sediment water interface in this case the dynamics of vertical tracer spreading were opposite during the first few hours after tracer release diapycnal diffusivities were large subsequently decreasing as the tracer cloud drifted away from the lake boundary basin wide diapycnal diffusivities calculated from heat flux measurements based on temperature profiles obtained from thermistor chains or conductivity temperature depth casts agreed well with the values obtained from the vertical tracer diffusion after horizontal homogenization the results of the tracer experiments corroborate the hypothesis that diapycnal fluxes are determined predominantly by mixing in the bottom boundary region

the baltic sea tracer release experiment 2 mixing processes 1 deep water mixing processes in the largest basin of the baltic sea gotland basin are investigated here with the help of long term moored instrumentation and turbulence microstructure measurements budgets for heat and salinity reveal a strong temporal variability in the deep water mixing coefficients that is shown to be coupled to the wind forcing down to time scales of individual wind events consistent with the results from a simultaneously conducted tracer release experiment near boundary turbulence was identified as the key processes for basin scale mixing turbulent bottom boundary layers were found to be thick and stable in the flat deep part of the basin where highest dissipation rates were observed and comparatively thin less energetic and highly variable on the slopes due to a permanent tendency for boundary layer restratification in the absence of internal tides strongly damped basin scale topographic waves with periods of a few days a deep rim current and to a smaller extent near inertial waves were identified as the main energy sources for boundary mixing these results are likely to be relevant also for other medium sized stratified basins

comment on influence of sea level rise on the dynamics of salt inflows in the baltic sea by r hordoir l axell u loptien h dietze and i kuznetsov

siderophile elements in martian meteorites and implications for core formation in mars noble metals mo w and 24 other elements were determined in six snc meteorites of presumably martian origin based on element correlations representative siderophile element concentrations for the silicate mantle of mars were inferred from a comparison with experimentally determined metal silicate partition coefficients of the moderately siderophile elements fe ni co w mo and ga it is concluded that equilibrium between core forming metal and silicates in mars has occurred at high temperatures around 2200 c and low pressures 1 gpa this suggests that metal segregation occurred concurrently with rapid accretion of mars which is consistent with the inference from excess 182w in martian meteorites lee and halliday 1997 concentrations of ir os ru pt and au in the analyzed martian meteorites except alh84001 are at a level of approximately 10 2 10 3 ci the comparatively high abundances of noble metals in martian meteorites require the addition of chondritic material after core formation the similarity in au la and pt ca ratios between alh84001 and the other martian meteorites suggests crystallization of alh84001 after complete accretion of mars

deep water dynamics and boundary mixing in a nontidal stratified basin a modeling study of the baltic sea recent results from a tracer release experiment have shown that similar to many lakes and ocean basins deep water mixing in the baltic sea is largely determined by mixing processes occurring in the energetic near bottom region due to the complexity and small vertical extent of this region however previous modeling studies of the baltic sea have so far not been able to provide a numerically and physically sound representation of boundary mixing here we discuss first results from a nested high resolution simulation of the central baltic sea that aims at a realistic description of the turbulent bottom boundary layer with the help of new numerical techniques adaptive coordinates and state of the art turbulence modeling using a comprehensive data set from the baltic sea tracer release experiment we show that the model is able to reproduce the key dynamical processes near inertial waves topographic waves and a rim current with excellent accuracy boundary mixing triggered by these processes was found to result in simulated basin scale mixing rates in close agreement with observations including a seasonal variability that has been emphasized in previous studies these results may be relevant also for the description of mixing in large lakes and other stratified basins

silicon in the earth s core the earth and moon have iron isotopic abundances that are slightly heavy compared with mars the asteroid vesta and primitive meteorites the reason for this has been unclear one suggestion is that there was a large scale isotopic equilibration during the giant impact the collision between the early earth and a mars sized body that created the moon but this has seemed unlikely given that most other elements do not show the effect an analysis of 44 meteorite and terrestrial samples now shows that the silicon isotopic compositions of basaltic rocks from the earth and moon are also distinctly heavy the finding is consistent with the isotopic equilibration model and it suggests that silicon was already partitioned into the earth s core as a light element before the moon formed the silicon isotopic compositions of basaltic rocks from the earth and moon are distinctly heavy the similar isotopic composition of the bulk silicate earth and the moon are consistent with large scale isotopic equilibration during the giant impact indicating that si was already a light element in the earth s core before the moon formed small isotopic differences between the silicate minerals in planets may have developed as a result of processes associated with core formation or from evaporative losses during accretion as the planets were built up basalts from the earth and the moon do indeed appear to have iron isotopic compositions that are slightly heavy relative to those from mars vesta and primitive undifferentiated meteorites1 2 3 4 chondrites explanations for these differences have included evaporation during the giant impact that created the moon when a mars sized body collided with the young earth however lithium5 and magnesium6 lighter elements with comparable volatility7 8 9 reveal no such differences rendering evaporation unlikely as an explanation here we show that the silicon isotopic compositions of basaltic rocks from the earth and the moon are also distinctly heavy a likely cause is that silicon is one of the light elements in the earth s core we show that both the direction and magnitude of the silicon isotopic effect are in accord with current theory10 based on the stiffness of bonding in metal and silicate the similar isotopic composition of the bulk silicate earth and the moon is consistent with the recent proposal11 that there was large scale isotopic equilibration during the giant impact we conclude that si was already incorporated as a light element in the earth s core before the moon formed

silicon isotopes in meteorites and planetary core formation the silicon si isotope compositions of 42 meteorite and terrestrial samples have been determined using mc icpms with the aim of resolving the current debate over their compositions and the implications for core formation no systematic 30si differences are resolved between chondrites 30si 0 49 0 15 2 sd and achondrites 30si 0 47 0 11 2 sd although enstatite chondrites are consistently lighter 30si 0 63 0 07 2 sd in comparison to other meteorite groups the data reported here for meteorites and terrestrial samples display an average difference 30sibse meteorite 0 15 0 10 which is consistent within uncertainty with previous studies no effect from sample heterogeneity preparation chemistry or mass spectrometry can be identified as responsible for the reported differences between current datasets the heavier composition of the bulk silicate earth is consistent with previous conclusions that si partitioned into the metal phase during metal silicate equilibration at the time of core formation fixing the temperature of core formation to the peridotite liquidus and using an appropriate metal silicate fractionation factor e 0 89 the 30sibse meteorite value from this study indicates that the earth core contains at least 2 5 and possibly up to 16 8 wt si

manganese chromium isotope systematics of carbonaceous chondrites abstract in this article we present the results of cr isotope investigations of different types of carbonaceous chondrites and of the pallasite eagle station the 53 cr 52 cr ratios in the bulk samples of carbonaceous chondrites are correlated with 55 mn 52 cr ratios the slope of the correlation line yields a 53 mn 55 mn ratio of 8 5 1 5 10 6 at the time of mn cr fractionation mapping this ratio onto an absolute time scale yields a time for this event of 4568 1 0 8 1 1 ma ago this time is very similar to the formation age of efremovka cais of 4567 2 0 6 ma y amelin a n krot i d hutcheon a a ulyanov lead isotopic ages of chondrules and calcium aluminum rich inclusions science 297 2002 1678 1683 to a time of the chondrule formation of 4568 1 ma ago l e nyquist d lindstrom d mittlefehldt c y shih h wiesmann s wentworth r martinez manganese chromium formation intervals for chondrules from the bishunpur and chainpur meteorites meteorit planet sci 36 2001 911 938 which most likely constrains early global high temperature mn cr fractionation in a nebular setting the bulk samples of carbonaceous chondrites exhibit clear 54 cr excesses 54 cr that are correlated with the 53 cr excesses 53 cr and also with mn cr ratios one possible explanation of this correlation is that 54 cr is also radiogenic like 53 cr and was formed by the decay of the short lived parent radionuclide 54 mn the very short half life of 54 mn of 312 days would require that both short lived radionuclides 53 mn and 54 mn were generated locally in spallation reactions during the early period of an active sun the alternative and possibly more plausible explanation is the heterogeneous addition of presolar material the presolar component enriched in 54 cr is mostly contained in the matrix of carbonaceous chondrites the relative amount of matrix decreases in the sequence ci cm co cv a large proportion of mn is associated with the matrix while cr preferentially resides in the chondrules thus the mn cr ratio also follows the sequence ci cm co cv and is correlated with 54 cr the acid resistant residues of carbonaceous chondrites are characterized by relatively large excesses of 54 cr and moderate deficits of 53 cr the magnitude of these excesses and deficits decreases in the sequence ci cm cv and may imply that cr in the cm and cv residues is increasingly more equilibrated with cr from the rest of the meteorites the 53 cr 52 cr and 54 cr 52 cr ratios in the residues are anti correlated indicating that there are at least two cr components of possibly presolar origin all residues have large excesses of the most neutron rich ti isotope 50 ti the pattern of 50 ti does not exactly follow that observed for 54 cr but it is generally similar the cr isotope systematic of the pallasite eagle station indicates that the precursor of this meteorite was a cv type material the 53 mn 53 cr system indicates that the cr isotopes equilibrated in this meteorite 4557 5 0 6 ma ago

basin wide circulation and ventilation study in the east sea sea of japan using chlorofluorocarbon tracers abstract near synoptic basin wide distributions of the chlorofluorocarbon cfc tracers were observed during the summer of 1999 in the east sea sea of japan to study its circulation and ventilation the cfcs penetrate throughout the water column and the bottom water bw cfc concentrations have increased over measurements made in 1995 and 1996 indicating a continuous weak renewal of deep waters in the east sea during this recent period the cfc 11 water column inventory estimated in 1999 2000 5500 nmol m 2 is substantially higher than that of the adjacent north pacific ocean a striking anticorrelation between the bw dissolved oxygen and cfc concentrations in the japan basin is attributed to more active vertical mixing along the basin boundary a dynamically isolated deep eastern japan basin and recent changes in deep water ventilation the bw of the eastern japan basin with the lowest cfc content is the oldest water parcel in the east sea although it is colder and contains higher oxygen concentration than the surrounding bw active entrainment of overlying deep water is inferred from the unexpectedly higher bw cfc concentrations in the yamato basin this may explain why the yamato basin bw is warmer and less oxygenated than the other basins in the east sea although it is believed to be a terminus of the ventilated dws mesoscale anticyclonic eddies which have been fused with other deeply convected waters in the northwestern east sea seem to play an important role in transferring surface water properties to depths greater than 2500 m the subsurface cfc maximum centered within the typical east sea intermediate water esiw layer is more widely distributed south of the subpolar front than previously reported the esiw consists primarily of the colder and fresher winter surface water in the northern region that has subducted below the subpolar front

chromium isotope fractionation between modern seawater and biogenic carbonates from the great barrier reef australia implications for the paleo seawater δ53cr reconstruction abstract this study investigates chromium isotope variations 53 cr and ree patterns in present day biogenic carbonates and ocean waters from lady elliot island lei located in the southern great barrier reef gbr australia which is one of the world s largest carbonate producing shelf ecosystems our results from thoroughly cleaned biogenic carbonates collected at lei with no detectable evidence for lithogenic cr and or mn fe oxide coating contamination revealed a systematic and statistically significant correlation r 2 0 83 p 0 05 between 53 cr and cerium anomaly ce ce data in molluscan shells i e gastropods this in turn implies a redox controlled incorporation of cr from seawater into a shell during mineralization mediated by the organism in particular shells with higher 53 cr values which approach the cr isotope composition of local seawater tend to be associated with more negative ce ce importantly the intercept of the above 53 cr vs ce ce correlation points to the cr isotope composition of local ocean water which has an average 53 cr of 0 82 0 13 2 relative to srm 979 these findings thus indicate that the above multi proxy approach could be used to reconstruct the 53 cr signature of local paleo seawater based on ce ce and 53 cr data in a set of well preserved fossil skeletal carbonates i e molluscan shells collected at a specific site interestingly the only calcifying organism from lei that yielded identical 53 cr vs ce ce values as those in ambient ocean water was a microbial calcitic carbonate produced by red coralline algae lithothamnion sp this organism thus seems to incorporate cr isotopes and ree from seawater without additional biological discrimination and or isotope fractionation effects considering that calcite is a more stable caco3 polymorph during post depositional alternation and diagenetic stabilization of marine carbonates compared to aragonite the fossil counterparts of these algal microbial carbonates microbialites might thus represent ideal natural archives of the paleo seawater 53 cr and ce ce variations over geological time finally our compilation of 53 cr data from recent marine biogenic carbonates originating from the main oceanic provinces south north pacific south north atlantic caribbean mediterranean sea confirms that marine carbonates tend to be systematically enriched in light cr isotopes relative to local ocean waters trace element constraints however indicate that some of these shifts to lower 53 cr values i e approaching 0 1 per mil are related to a presence of lithogenic cr in the shells causing a diagenetic overprint of the primary marine 53 cr signal

mixing of a tracer in the pycnocline a patch of sulfur hexafluoride was released in may 1992 in the eastern north atlantic on an isopycnal surface near 300 m depth and was surveyed over a period of 30 months as it dispersed across and along isopycnal surfaces the diapycnal eddy diffusivity k estimated for the first 6 months was 0 12 0 02 cm2 s while for the subsequent 24 months it was 0 17 0 02 cm2 s the vertical tracer distribution remained very close to gaussian for the full 30 months as the root mean square rms dispersion grew from 5 to 50 m lateral dispersion was measured on several scales the growth of the rms width of the tracer streaks from less than 100 m to approximately 300 m within 2 weeks implies an isopycnal diffusivity of 0 07 m2 s at scales of 0 1 to 1 km larger than expected from the interaction between vertical shear of the internal waves and diapycnal mixing teasing of the overall patch initially about 25 km across into streaks with an overall length of 1800 km within 6 months supports predictions of exponential growth by the mesoscale strain field at a rate of 3 0 5 10 7 s 1 the rms width of these streaks estimated as 3 km and maintained in the face of the streak growth indicates an isopycnal diffusivity of 2 m2 s at scales of 1 to 10 km much greater than expected from internal wave shear dispersion the patch was painted in albeit streakily by 12 months confirming expectations from analytical and numerical models homogenization of the patch continued during the subsequent 18 months while the patch continued to spread with an effective isopycnal eddy diffusivity on the order of 1000 m2 s acting at scales of 30 to 300 km

evidence for internal hydraulic control in the northern oresund new observations of mainly flow velocity salinity and temperature are used to show and discuss some of the physical conditions in oresund the strait between denmark and sweden one of three connections between the brackish baltic sea and the saline north sea the main geometric features are a contraction in the northern oresund and the shallow drogden sill at the entrance to the baltic the observations show that the two layer flows through the contraction are often hydraulically controlled the observations also reveal details of the transition from subcritical to supercritical flow in terms of the composite froude number on the basis of local flow parameters these details are that the flow may be subcritical as well as supercritical in different areas of some cross section existing theories on rotating hydraulics are unable to account for these circumstances which are due to the strong influence of the earth s rotation and the curvature of the streamlines in the present study it is not attempted to explain these conditions but the probable effects of rotation and curvature on the controlled flow rate are discussed briefly also the possible effects of hydraulic control on the exchange of the baltic are discussed it is argued that the stratification in the kattegat the sea to the north is more important than the presence of the drogden sill for the amount of high saline water to enter the baltic through oresund this result is supported by observations of the stratification in oresund and the flow at the sill the observations show that the interface in oresund rises significantly during flow to the baltic and that the transport of saline water into the baltic is closely connected to the shallowness of the interface in oresund

variability in two deep coastal basins santa monica and san pedro off southern california time series of midbasin hydrographic samples and of an array of moored temperature velocity sensors are used to examine subtidal to interannual scale variability in two 900 m deep basins off the southern california coast the deepest sill that allows entry into the basins is at 740 m and the two basins santa monica and san pedro are separated by a sill about 40 m high the mean flow 40 m above and 60 m below the 740 m sill depth is in the counterclockwise direction and the magnitude is 0 5 1 0 cm s 1 the data indicate that the waters at deeper levels of the basins are neither quiescent at one extreme nor are they filled with random noise at the other extreme rather at all scales examined the variability is significant and much of it is spatially coherent the amplitude of the subtidal velocity fluctuations is 4 cm s 1 almost an order of magnitude greater than that of the mean flow the amplitude of the subtidal temperature fluctuations is 0 1 c at 700 m and 0 05 c at 800 m the temperature variance is roughly a factor of 2 smaller at midbasin than on the basin perimeter this is not the case with the velocity variance which is generally greatest at midbasin and on the coastal edges of both basins much of the subtidal variability in both temperature and velocity appears to be associated with topographic waves that travel counterclockwise around the pair of basins the observed period of the waves 10 20 days is roughly consistent with that predicted by a barotropic model of free waves in an elliptical basin mysak 1985 comparison of time series of currents in the upper 200 m water column with those in the lower water column suggests that the waves are forced by the circulation in the upper water column which is directed over rather than around the basins seasonal variability was observed in both temperature and velocity fields as deep as 800 m i e below the depth of the deepest sill along the perimeters of both basins and at midbasin in santa monica but not in san pedro temperature increases and salinity and density decrease from spring to fall consistent with the seasonal development of the poleward flowing california countercurrent in the upper water column the seasonal cycle of water properties has significant spatial variability over the basins the amplitude is a factor of 2 greater on the seaward side of santa monica basin than at midbasin and on its coastal edges and on the edges of san pedro basin the variance of the subtidal velocity and temperature fields also exhibit a seasonal signal maximum variance occurs during fall minimum variance occurs during spring interannual variability dominates the 4 year time series of water properties of the near bottom water in each basin and differs somewhat between the two basins the interannual variability is dominated by events associated with renewal of basin bottom water two such events were identified a minor one in 1987 and a major one in 1988 each beginning in may of that year in both cases the actual renewal occurs in less than a month and the most rapid return to near normal conditions occurs over a period of about 3 5 months

stratification and mixing on sloping boundaries 1 in lakes as well as in the ocean vertical transport is to a large extent controlled by localized mixing along the boundaries of the respective basin direct measurements of turbulent mixing and density stratification in the bottom boundary layer of a large and deep lake reveal the importance of cross slope advection near sloping boundaries for local and basin scale vertical transport the periodic internal wave driven occurrence of up and downslope directed currents results in periodic heating and cooling of the boundary layer cooling of the boundary layer during periods of up slope flow is associated with unstable stratification and turbulent diffusivities exceed those observed during periods of down slope flow by almost one order of magnitude the periodic replacement of water in this layer with water from the interior of the basin maintains vertical density gradients and thus enhances the overall efficiency of the boundary mixing

turbulent mixing and exchange with interior waters on sloping boundaries abstractmicrostructure measurements along the axes of monterey and soquel submarine canyons reveal 200 300 m thick well stratified turbulent near bottom layers with average turbulent kinetic energy dissipation rates e 4 10 8 w kg 1 and eddy diffusivities k 16 10 4 m2 s 1 assuming mixing efficiency 0 2 to at least thalweg depths of 1200 m turbulent dissipation rates are an order of magnitude lower in overlying waters whereas buoyancy frequencies are only 25 higher well mixed bottom boundary layer thicknesses hn are an order of magnitude thinner than the stratified turbulent layer hn he because well stratified turbulent layers are commonly observed above slopes arguments that mixing efficiency should be reduced on sloping boundaries do not hold in cases of energetic internal wave generation or interaction with topography an advective diffusive balance is used to infer velocities and transports predicting horizontal upslope flows of 10 50 m day 1 extrapolating this estimate globa

a laboratory model of vertical ocean circulation driven by mixing a model of deep ocean circulation driven by turbulent mixing is produced in a long rectangular laboratory tank the salinity difference is substituted for the thermal difference between tropical and polar regions freshwater gently flows in at the top of one end dense water enters at the same rate at the top of the other end and an overflow in the middle removes the same amount of surface water as is pumped in mixing is provided by a rod extending from top to bottom of the tank and traveling back and forth at constant speed with reynolds numbers 500 a stratified upper layer thermocline deepens from the mixing and spreads across the entire tank simultaneously a turbulent plume deep ocean overflow from a dense water source descends through the layer and supplies bottom water which spreads over the entire tank floor and rises into the upper layer to arrest the upper layer deepening data are taken over a wide range of parameters and compared to scaling theory energetic considerations and simple models of turbulently mixed fluid there is approximate agreement with a simple theory for reynolds number 1000 in experiments with a tank depth less than the thermocline depth a simple argument shows that mixing and plume potential energy flux rates are equal in magnitude and it is suggested that the same is approximately true for the ocean

modeling of hydraulically controlled exchange flow in the bosphorus strait abstract recent hydrographic observations obtained in the bosphorus strait illustrate several features of the flow that may be related with the internal hydraulics a two layer numerical model indicates that the two way exchange flow may indeed be subject to a series of internal hydraulic adjustments along the strait due to morphological features such as sills a contraction and abrupt expansion of the width of the strait the model identifies three distinct regions of the supercritical flow the lower layer flow of the marmara sea origin is directed to the north towards the black sea in a progressively thinning layer and is controlled by the sill located near the black sea entrance of the strait the upper layer water of the black sea origin flows in the opposite direction and is controlled upon reaching the constricted region located about 10 12 km away from the marmara end of the strait the upper layer flow is then matched to the subsequent subcritical conditions by undergoing an internal hydraulic ju

flow resistance in the great belt the biggest strait between the north sea and the baltic sea abstract the danish straits are part of the transition area between the north sea and the central baltic sea more precisely the danish straits connect kattegat to the arkona basin and includes the relatively narrow and shallow sub areas great belt little belt fehmarn belt and sound the flow resistances in the straits are hydraulically determined by among other factors the contractions sills and stratification found in the straits close to the entrance to the arkona basin the darss and drogden sills are located that trap inflowing dense water partially before it enters the central baltic sea hence the resistances in the danish straits are of crucial importance for the stratification and ecosystems in the central baltic sea the present work comprises calculations of flow resistance in the great belt based on measurements collected as part of the great belt fixed link investigations the specific resistance in the great belt is determined to be an average of 41 2 10 12 s 2 m 5 but it depends heavily on the interface position when calculating long term discharge time series on the basis of the momentum equation it is advised to apply a seasonal varying resistance

diagnoses of simulated water mass subduction formation transformation in the japan east sea jes abstract the impacts of surface atmospheric forcing of different time space scales on the simulation of water mass formation and spreading of formed water are investigated by quantifying water mass subduction formation transformation for the japan east sea jes the princeton ocean model pom was implemented for the jes jes pom to simulate interannual seasonal and mesoscale variations in velocity and mass fields three sets of atmospheric flux data were used 1 6 h fluxes calculated from 6 h atmospheric variables syn 2 monthly means of 6 h fluxes empm and 3 fluxes calculated from monthly averaged atmospheric variables mont the mass exchange between the mixed layer and interior in the jes was diagnosed in terms of annual subduction rate sann three areas of local maximum sann 500 m yr occurred area v 41 43 n west of 137 e k 36 39 n west of 132 e and kb near korea bay area v corresponds to the flux center i e maximum heat and momentum fluxes described by kawamura and wu 1998 formation mechanism of japan sea proper water in the flux center off vladivostok j geophys res 103 c10 21611 21622 the subduction region suggested by senjyu and sudo 1994 the upper portion of the japan sea proper water its source and circulation as deduced from isopycnal analysis j oceanogr 50 663 690 1996 interannual variation of the upper portion of the japan proper water and its probable cause j oceanogr 52 72 42 and yoshikawa et al 1999 formation and circulation processes of intermediate water in the japan sea j phys oceanogr 29 8 1701 1722 and the wintertime convection location identified by seung and yoon 1995 some features of winter convection in the japan sea j oceanogr 51 61 73 with monthly forcing mont there is no localized maximum value off vladivostok while with forcing influenced by synoptic events monthly empm and 6 h syn either one or two localized areas with a high subduction rate occur with year to year variations the presence of simulated dense surface water 26 8 in the northern jes is due to the effects of synoptic events during winter months when large heat loss and strong wind stress associated with cold air outbreaks and extratropical cyclones occur the convection magnitudes as a result of air sea interaction are 3 0 4 0 and 6 0 sv for mont empm and syn respectively a net flux of mass from the interior to the mixed layer entrainment occurs in the density range between 24 0 and 26 2 for both empm 3 5 sv and syn 3 0 sv while it occurs in the density range between 24 0 and 25 8 for mont 2 8 sv the diffusive fluxes across the winter mixed layer base are about 0 8 1 0 and 1 4 sv for mont empm and syn respectively an undiagnosed eddy induced turbulent mixing the residual of the balance after removing discretization error for syn is almost twice that for the other two cases mont and empm these results indicate that without synoptic atmospheric forcing the diagnostics using the numerical circulation model may significantly underestimate buoyancy loss at the surface and hence water mass formation as well as mixing and spreading of the formed water mass

unlocking the zinc isotope systematics of iron meteorites zinc isotope compositions 66zn and concentrations were determined for metal samples of 15 iron meteorites across groups iab iiab and iiiab also analyzed were troilite and other inclusions from the iab iron toluca furthermore the first zn isotope data are presented for metal silicate partitioning experiments that were conducted at 1 5 gpa and 1650 k three partitioning experiments with run durations of between 10 and 60 min provide consistent zn metal silicate partition coefficients of 0 7 and indicate that zn isotope fractionation between molten metal and silicate is either small at less than about 0 2 0 2 or absent metals from the different iron meteorite groups display distinct ranges in zn contents with concentrations of 0 08 0 24 g g for iiabs 0 8 2 5 g g for iiiabs and 12 40 g g for iabs in contrast all three groups show a similar range of 66zn values reported relative to jmc lyon zn from 0 5 0 5 to 3 0 3 0 with no clear systematic differences between groups however distinct linear trends are defined by samples from each group in plots of 66zn vs 1 zn and these correlations are supported by literature data based on the high zn concentration and 66zn 0 determined for a chromite rich inclusion of toluca modeling is employed to demonstrate that the zn trends are best explained by segregation of chromite from the metal phase this process can account for the observed zn 66zn cr systematics of iron meteorite metals if zn is highly compatible in chromite and zn partitioning is accompanied by isotope fractionation with 66znchr met 1 5 1 5 based on these findings it is likely that the parent bodies of the iab complex iiab and iiiab iron meteorites featured 66zn values of about 1 0 to 0 5 0 5 similar to the zn isotope composition inferred for the bulk silicate earth and results obtained for chondritic meteorites together this implies that most solar system bodies formed with similar bulk zn isotope compositions despite large differences in zn contents

chromium isotope variations δ53 52cr in mantle derived sources and their weathering products implications for environmental studies and the evolution of δ53 52cr in the earth s mantle over geologic time here we report chromium isotope compositions expressed as delta cr 53 52 in per mil relative to nist 979 measured in selected cr rich minerals and rocks formed by the primary magmatic as well as the secondary metamorphic and weathering processes the main objectives of this study were i to further constrain the isotope composition of the earth s mantle cr inventory and its possible variation during geological history based on the analysis of globally distributed and stratigraphically constrained mantle derived chromites and ii to investigate the magnitude and systematics of cr isotope fractionation during oxidative weathering and secondary alteration i e hydration serpentinization of the magmatic cr sources specifically we analyzed delta cr 53 52 in a set of globally distributed mantle derived chromites femgcr2o4 n 30 collected from various locations in europe asia africa and south america and our results confirm that a chromite hosted earth s mantle cr inventory is uniform at 0 079 0 129 2sd which we named here as a canonical mantle d 53 52 cr signature furthermore our dataset of stratigraphically constrained chromites whose crystallization ages cover most of the earth s geological history indicate that the bulk cr isotope composition of the chromite hosted mantle inventory has remained uniform within about 0 100 since at least the early archean times similar to 3500 million years ago ma to investigate the systematics of cr isotope fractionation associated with alteration processes we analyzed a number of secondary cr rich minerals and variably altered ultramafic rocks i e serpentinized harzburgites lherzolites that revealed large positive delta cr 53 52 anomalies that are systematically shifted to higher values with an increasing degree of alteration and serpentinization the degree of aqueous alteration and serpentinization was quantified by the abundances of fluid mobile rb k elements and by the loss on ignition loi parameter which determines the amount of structurally bound water oh h2o present in secondary hydrated minerals like serpentine overall we observed that altered ultramafic rocks that yielded the highest loi values and the lowest amounts of fluid mobile elements also yielded the heaviest delta cr 53 52 signatures therefore we conclude that secondary alteration i e hydration serpentinization of ultramafic rocks in near surface oxidative environments tend to shift the bulk cr isotope composition of the weathered products to isotopically heavier values pointing to a dynamic redox cycling of cr in the earth s crustal and near surface environments hence if validated by future

isotopic composition of silicon in meteorites abstract samples of bulk meteorites show only mass dependent fractionation of silicon isotopes no isotopic anomalies were found the variation of the ratios 29 si 28 si and 30 si 28 si over the meteorite classes is small 1 per mass unit difference the average si isotopic composition for each class of meteorites is identical within analytical uncertainties this is quite unlike o whose anomalous isotopic abundances in bulk samples differentiate among the classes of meteorites the overlapping abundance ranges of si isotopes among many classes of meteorites suggest closed system behavior for this element prior to meteorite accretion and allow calculation of an average solar system si isotope composition

a reassessment of the iron isotope composition of the moon and its implications for the accretion and differentiation of terrestrial planets abstract the fe isotope composition of planetary bodies may provide constraints on their accretion modes and or differentiation processes but to do so the fe isotope systematics of key planetary reservoirs needs to be determined to investigate this for the moon we measured the fe isotope compositions for a suite of 33 bulk lunar mare basalts and highland rocks combined with published data a compendium of 73 different lunar bulk rocks reveals a statistically significant fe isotope difference between low ti and high ti mare basalts yielding average 57fe 0 127 0 012 2se n 27 and 57fe 0 274 0 020 2 se n 25 respectively relative to the irmm 14 isotopic reference material as lunar basalts are thought to reflect the fe isotope composition of their respective mantle sources the estimated relative proportion of the low ti and high ti source mantle suggests that the lunar upper mantle 57fe value should be close to 0 142 0 026 whilst the composition of highland rocks ferroan anorthosites and mg suite rocks should provide a more global view of the moon the calculation of the mean 57fe value of 15 available highland rock analyses yields 57fe 0 078 0 124 such a value is not defined precisely enough to be of critical use for comparative planetology ferroan anorthosites and mg suite rocks also give unresolvable means it appears that fe isotope heterogeneity among the lunar highland rocks is caused by non representatively too small sample aliquots of coarse grained rocks it can also be the result of mixed lithologies for some when the kinetic effect of olivine tending towards low 57fe and feldspar with predominantly high 57fe is cancelled a more precise 57fe value of 0 094 0 035 is calculated it is indistinguishable from the mean 57fe of impact melts and is also similar to the upper lunar mantle estimate obtained from mare basalts collectively this newly determined fe isotope composition of the bulk moon is indistinguishable from that of the earth and heavier than those reported for other planetary bodies this planetary isotope relationship is only observed for silicon given the currently available mass dependent stable isotope database because both iron and silicon reside in the earth s metallic core in significant quantities this may point to the involvement of metallic cores of the earth and moon in the interplanetary fe and si isotope fractionation rather than via high pressure metal silicate fractionation at the core mantle boundary this would more likely be achieved by partial vaporization of the liquid outer metallic core in the aftermath of a moon forming giant impact

silicon isotopes in lunar rocks implications for the moon s formation and the early history of the earth silicon isotopic data from a range of lunar samples are presented to assess the degree of heterogeneity of the lunar mantle and its similarity to bulk silicate earth bse multi collector inductively coupled plasma mass spectrometry mc icpms was used to analyse 24 samples including both high and low ti basalts as well as highland anorthosites and picritic glasses covering all the apollo sample return missions no systematic 30si differences are found between any of the bulk sample lithologies 2 sd 30silow ti basalt 0 29 0 06 30sihigh ti basalt 0 32 0 09 30silunar glass 0 29 0 05 and 30sihighland rocks 0 27 0 10 the average of the lunar samples is 30si 0 29 0 08 2 sd which is identical to the composition of bse 30si 0 29 0 08 2 sd from savage et al 2010 the bse si isotope composition is thought to be the result of si partitioning between metal and silicate and consequent isotopic fractionation during core formation the moon forming impactor would not be expected to share that composition because it is thought to have been relatively small 0 1 earth masses like mars and formed under relatively low temperatures and pressures that are insufficient for si to partition into the core therefore the identical lunar and bse si isotope data show that si isotopes like those of oxygen must have homogenised in the aftermath of the moon forming impact if smooth particle hydrodynamic simulations of the giant impact are correct in showing that most lunar material should have originated from the impactor rather than the earth the data presented here are in agreement with other isotope systems and experimental studies that indicate that the majority of core formation happened early and before the giant impact it has been predicted pahlevan et al 2011 that the moon and the bse should show a 0 14 offset in 30si for the moon to have an fe fe mg ratio twice that of bse the current resolution and sample population size of the si data for the moon and earth would allow such an offset to be detected the fact that is it not observed can put constraints on the element ratios and lunar budgets as modelled by pahlevan et al 2011 in particular it constrains the fe fe mg ratio of the moon to be only 1 1 3 bse

the stable cr isotopic compositions of chondrites and silicate planetary reservoirs abstract the depletion of chromium in earth s mantle 2700 ppm in comparison to chondrites 4400 ppm indicates significant incorporation of chromium into the core during our planet s metal silicate differentiation assuming that there was no significant escape of the moderately volatile element chromium during the accretionary phase of earth stable cr isotope compositions expressed as the difference in 53 cr 52 cr from the terrestrial reference material srm979 53 52 cr srm979 values of planetary silicate reservoirs might thus yield information about the conditions of planetary metal segregation processes when compared to chondrites the stable cr isotopic compositions of 7 carbonaceous chondrites 11 ordinary chondrites 5 hed achondrites and 2 martian meteorites determined by a double spike mc icp ms method are within uncertainties indistinguishable from each other and from the previously determined 53 52 cr srm979 value of 0 124 0 101 for the igneous silicate earth extensive quality tests support the accuracy of the stable cr isotope determinations of various meteorites and terrestrial silicates reported here the uniformity in stable cr isotope compositions of samples from planetary silicate mantles and undifferentiated meteorites indicates that metal silicate differentiation of earth mars and the hed parent body did not cause measurable stable cr isotope fractionation between these two reservoirs our results also imply that the accretionary disc at least in the inner solar system was homogeneous in its stable cr isotopic composition and that potential volatility loss of chromium during accretion of the terrestrial planets was not accompanied by measurable stable isotopic fractionation small but reproducible variations in 53 52 cr srm979 values of terrestrial magmatic rocks point to natural stable cr isotope variations within earth s silicate reservoirs further and more detailed studies are required to investigate whether silicate differentiation processes such as partial mantle melting and crystal fractionation can cause stable cr isotopic fractionation on earth and other planetary bodies

the degeneration of internal waves in lakes with sloping topography in a laboratory study we quantified the temporal energy flux associated with the degeneration of basin scale internal waves in closed basins the system is two layer stratified and subjected to a single forcing event creating available potential energy at time zero a downscale energy transfer was observed from the wind forced basin scale motions to the turbulent motions where energy was lost due to high frequency internal wave breaking along sloping topography under moderate forcing conditions steepening of nonlinear basin scale wave components was found to produce a high frequency solitary wave packet that contained as much as 20 of the available potential energy introduced by the initial condition the characteristic lengthscale of a particular solitary wave was less than the characteristic slope length leading to wave breaking along the sloping boundary the ratio of the steepening timescale required for the evolution of the solitary waves to the travel time until the waves shoaled controlled their development and degeneration within the domain the energy loss along the slope the mixing efficiency and the breaker type were modeled using appropriate forms of an internal iribarren number defined as the ratio of the boundary slope to the wave slope amplitude wavelength this parameter allows generalization to the oceanographic context analysis of field data shows the portion of the internal wave spectrum for lakes between motions at the basin and buoyancy scales to be composed of progressive waves both weakly nonlinear waves sinusoidal profile with frequencies near 10 24 hz and strongly nonlinear waves hyperbolic secant squared profile with frequencies near 10 23 hz the results suggest that a periodically forced system may sustain a quasi steady flux of 20 of the potential energy introduced by the surface wind stress to the benthic boundary layer at the depth of the pycnocline

non chondritic magnesium and the origins of the inner terrestrial planets abstract high precision magnesium mg isotope data obtained using a large geometry high resolution mc icpms are reported for 9 carbonaceous and ordinary chondrites 9 eucrites and diogenites generally considered to originate from asteroid 4 vesta together with 4 martian meteorites and a variety of terrestrial and lunar materials the variation in mg isotopic composition found for mafic and ultramafic rocks mafic minerals and chondrites is smaller than reported previously the range of 26mg and 25mg of 0 6 and 0 3 defines a single mass dependent fractionation line consistent with a homogeneous mix of nucleosynthetic components data for the earth mars and vesta display no systematic mg isotopic differences despite large variations in the level of depletion in moderately volatile elements lunar mare basalts exhibit a significant range in 26mg 0 53 to 0 05 and 25mg 0 27 to 0 02 attributable to magmatic differentiation in the lunar magma ocean lmo lunar basalts derived from early segregated cumulates and thought to be the most primitive are on average slightly 0 17 26mg heavy relative to basalts from the earth mars and vesta however the difference is not well resolved more strikingly all differentiated planets and planetesimals as sampled have mg that is on average isotopically heavy compared with most chondrites analyzed thus far chondrules and cais also are generally heavy in terms of mg so this might reflect sorting of material in the proto planetary disk such an explanation would be similar to one previously proposed hewins r h and herzberg c t 1996 earth planet sci lett 144 1 7 to explain the non chondritic si mg of the earth in this model chondrule like objects separate from volatile rich planetary dust by accumulation in stagnant regions between eddies in the solar nebula small 1 km planetesimals formed by accumulation of such molten material then develop into planetary embryos and thence to larger terrestrial planets by combinations of runaway growth and collisions as such accumulation of molten chondrule like droplets provides an explanation that obviates some of the dynamic difficulties associated with the onset of planetary accretion the non chondritic mg isotopic composition of the earth is consistent with data for li and has important implications for earth s bulk composition and putative hidden reservoirs

the stable cr isotope inventory of solid earth reservoirs determined by double spike mc icp ms abstract we present the first comprehensive set of stable cr isotope data for the major igneous silicate earth reservoirs cr iii rich ores and minerals and hydrothermal chromates these were determined by mc icp ms using a double spike technique mantle xenoliths ultramafic rocks cumulates as well as oceanic and continental basalts share a common cr isotope composition with an average 53 52 cr value of 0 124 0 101 2 sd relative to the isotopically certified chromium standard nist srm 979 an isotopic difference between mantle xenoliths and basalts as was reported for iron was not observed for chromium thus the change in oxidation state that is observed when solid mantle rocks containing only trivalent chromium partially melt to form basaltic melts which predominantly contain bivalent chromium does not cause any measurable cr isotope fractionation chromite separates from major chromitite seams of the bushveld and great dyke layered igneous complexes are invariable in their cr isotope compositions and reproduce within uncertainties the average 53 52 cr srm 979 value of igneous silicate earth reservoirs this is important for environmental stable cr isotope studies because it labels the approximate isotope composition of industrial cr vi pollutants the cr isotope compositions of hydrothermal lead chromates crocoites pbcr vi o 4 from various localities yield 53 52 cr srm 979 values between 0 640 and 1 037 these cr isotope compositions are substantially heavier than those of igneous silicate rocks from which the chromium was leached precipitation experiments revealed an isotope fractionation of 53 52 cr crocoite cr vi aq of only ca 0 10 0 05 at a temperature of 20 c thus the heavy cr isotope signature of crocoites is most likely the result of repeated redox cycling of chromium in hydrothermal processes

nickel isotope heterogeneity in the early solar system article i nfo ni of bulk iron and chondritic meteorites carbonaceous chondrites have variable positive e 62 ni 0 05 to 0 25 whereas ordinary chondrites have negative e 62 ni 0 04 to 0 09 the ni isotope compositions of iron meteorites overlap with those of chondrites and define an array with negative slope in the e 60 ni versus e 62 ni diagram the ni isotope compositions of the volatile depleted group ivb irons are similar to those of the refractory co cv carbonaceous chondrites whereas the other common magmatic iron groups have ni isotope compositions similar to ordinary chondrites only enstatite chondrites have identical ni isotope compositions to earth and so appear to represent the most appropriate terrestrial building material differences in e 62 ni reflect distinct nucleosynthetic components in precursor solids that have been variably mixed but some of the e 60 ni variability could reflect a radiogenic component from the decay of 60 fe comparison of the e 60 ni of iron and chondritic meteorites with the same e 62 ni allows us to place upper limits on the 60 fe 56 fe of planetesimals during core segregation we estimate that carbonaceous

internal wave reflection and mixing at fieberling guyot the structure of internal wave reflection off a sloping bottom on the steep flank of a tall north pacific ocean seamount is observed in year long moored array records to differ substantially from the form predicted by linear theory although linear theory accounts for several qualitative features of the process this study documents new features of wave reflection as described below wave reflection is detectable as far as 750 m above the bottom motions are dominated by a single empirical mode whose phase structure obeys linear internal wave dispersion but whose amplitude decays with a scale comparable to the wavenumber while the dominant mode has scales appropriate to the reflection of a first baroclinic mode wave incident from the open ocean its decay from the bottom is such that current vectors in the vertical plane rotate clockwise in time when viewed with shallow water to the right this flow resembles the lower half of the deepest cell pattern predicted by linear reflection from a uniform slope at the local internal wave critical frequency the dominant mode has nearly a vanishing wavenumber rather than the infinite wavenumber predicted by linear reflection reflected waves are aligned parallel to the bottom slope measured on wave spatial scales rather than shorter ones wave reflection causes large frequent density overturns implying mixing the rate and strength of these overturns imply a local vertical eddy viscosity of 2 6 10 4 m2 s over the bottom few hundred meters the contribution of bottom intensified mixing to the open deep ocean is roughly equivalent to that found in situ although reflection from gentler slopes or at lower latitude may produce greater contribution from internal wave reflection induced mixing

boundary mixing and the dynamics of three dimensional thermohaline circulations boundary mixing is implemented in an ocean general circulation model such that the vertical mixing coefficient ky is nonzero only near side boundaries and in convection regions the model is used in a highly idealized configuration with no wind forcing and very nearly fixed surface density to investigate the three dimensional dynamics of the thermohaline circulation for ky 5 20 3 1024 m2 s21 and lower the meridional overturning strength to great accuracy is proportional to meridional heat transport is proportional to the circulation 2 3 1 2 kk y y patterns resemble those from runs with uniform vertical mixing but vertical motion is entirely confined to the boundary regions near the western boundary there is upwelling everywhere near the eastern boundary there is a consistent pattern of downwelling above upwelling with downwelling reaching deeper at high latitudes this pattern is explained by convection and vertical advective diffusive balance underneath for ky 5 30 3 1024 m2 s21 and higher no steady solutions have been found the meridional overturning oscillates on a timescale of about 25 years a time averaged thermally direct overturning cell is not supported dynamically because convection extends longitudinally across the entire basin and upwelling near the western boundary does not lead to densities higher than at the eastern boundary assuming uniform upwelling in the west level isopycnals near the equator and level isopycnals along the eastern boundary south of the outcropping latitude permits the analytic determination of convection depth at the eastern wall and hence the density difference between the eastern and western walls this difference is at most one quarter the surface density difference between high and low latitudes and agrees in magnitude and latitudinal dependence with the numerical experiments scaling arguments estimate overturning strength as of the order of 10 3 106 m3 s21 and confirm the 2 3 power dependence onky the derivation also gives a dependence of overturning strength with latitude that agrees qualitatively with the numerical results the scaling for the dependence of meridional heat transport on latitude agrees well with the model results scaling for heat transport amplitude agrees less well but correctly predicts a weaker dependence on ky than maximum overturning