barred olivine chondrules in ordinary chondrites barred olivine chondrules were studied in h l ll3 6 chondrites no important differences were found between barred olivine chondrules in h3 l3 and ll3 chondrites however comparison of type 3 barred olivine chondrules with all chondrule types in h l ll3 ordinary chondrites show that barred olivine chondrules are enriched in feo al2o3 na2o and k2o and are depleted in sio2 and mgo mineral abundances of barred olivine chondrules show that they are enriched in the feldspathic component compared to most chondrules pyroxene is rarely absent and is sometimes a major component pyroxene rich barred olivine chondrules in type 3 chondrites correlate negatively with feldspathic glass rich barred olivine chondrules indicating that pyroxene formed at the expense of olivine bars barred olivine chondrules in ordinary chondrites decrease systematically in cr2o3 and tio2 with increasing petrologic type feo however shows a systematic decrease with petrologic type in h chondrites no change in l chondrites and a systematic increase in ll chondrites the conclusions of this study are 1 barred olivine chondrules are mainly intermediate in major element composition between the abundant fe mg chondrules and the rare al rich chondrules 2 systematic compositional changes in barred olivine chondrules from type 3 6 in h l ll chondrites may be the result of primary differences 3 precursor components that melted to form barred olivine chondrules were enriched in olivine rich and volatile feldspar and feldspathoid rich components the alkalies may have been condensed where alumina was already available

the cr renazzo type carbonaceous chondrite group and its implications abstract a petrologic geochemical and oxygen isotopic study of eight meteorites identified as cr renazzo type chondrites reveals that they have a set of similar properties that distinguishes them from other chondrite groups and confirms cr as a carbonaceous chondrite group characteristics of the cr group include 1 1 abundant large multilayered fe ni metal rich type i chondrules 2 2 abundant matrix and dark inclusions di that contain microchondrules microfragments and magnetite framboids and platelets 3 3 unique assemblages of serpentine and chlorite rich phyllosilicates and ca carbonates 4 4 ca carbonate rims on chondrules 5 5 abundant fe ni metal with a positive ni vs co trend and a solar ni co ratio 6 6 low abundance of refractory rich inclusions 7 7 amoeboid olivine aggregates aoa with mn rich and mn poor forsterite and 8 8 oxygen isotopic compositions that form a unique mixing line the cr chondrites are breccias consisting of two major components the large layered chondrules and the matrix dark inclusions al rais is an anomalous member in having a higher abundance of the dark inclusion component 70 vol and this accounts for its having a higher volatile content than other members of the group the conditions that prevailed during aqueous alteration of the cr chondrites differed from those of other hydrated chondrite groups and may be the result of a higher temperature environment than that for the ci and cm chondrites the cr chondrite components chondrules matrix dark inclusions etc experienced aqueous alteration to differing degrees prior to assembly of the host chondrites and dark inclusions represent a lithology that was altered by water to a greater degree than the rest of the meteorite the overall degree of hydration in cr chondrites varies among meteorites with al rais being the most hydrated the oxygen isotopic variation of the whole rocks chondrules and matrices may be related to degree of hydration indicating that cr chondrites interacted with a water rich component having heavy oxygen and that was the same as ci and cm water

origin of zoned metal grains in the que94411 chondrite laser ablation inductively coupled plasma mass spectrometry la icp ms was used to measure distributions of the siderophile elements p v cr fe co ni mo ru rh pd w re os ir and pt in metal grains in the metal rich chondrite que94411 with a spatial resolution of similar to 30 mum the platinum group elements pges except pd exhibit radial zoning in these grains that mimics that previously observed in ni and co the concentrations of these elements decreases from the cores to the rims of the grains the pge distributions support a condensation origin for the enhanced refractory element abundances in the zoned grains the lack of zoning in pd refutes an origin by a redox controlled process and none of the pge ni relationships support an origin by fractional crystallization from a metallic melt several models of grain formation were explored including equilibrium fractional condensation which failed to yield the correct radial zoning the zoning may be the product of a nonequilibrium fractional condensation process in which the refractory siderophiles remained supersaturated in the cooling solar nebula or of diffusion between refractory enhanced fe ni cores and other fe ni metal that may have been deposited later from the solar nebula copyright c 2001 elsevier science ltd

how does subantarctic mode water ventilate the southern hemisphere subtropics in several regions north of the antarctic circumpolar current acc deep wintertime convection refreshes pools of weakly stratified subsurface water collectively referred to as subantarctic mode water samw samw ventilates the subtropical thermocline on decadal timescales providing nutrients for low latitude productivity and potentially trapping anthropogenic carbon in the deep ocean interior for centuries in this work we investigate the spatial structure and timescales of mode water export and associated thermocline ventilation we use passive tracers in an eddy permitting observationally informed southern ocean model to identify the pathways followed by mode waters between their formation regions and the areas where they first enter the subtropics we find that the pathways followed by the mode water tracers are largely set by the mean geostrophic circulation export from the indian and central pacific mode water pools is primarily driven by large scale gyre circulation whereas export from the australian and atlantic pools is heavily influenced by the acc export from the eastern pacific mode water pool is driven by a combination of deep boundary currents and subtropical gyre circulation more than 50 of each mode water tracer reaches the subtropical thermocline within 50 years with significant variability between pools the eastern pacific pathway is especially efficient with roughly 80 entering the subtropical thermocline within 50 years the time required for 50 of the mode water tracers to leave the southern ocean domain varies significantly between mode water pools from 9 years for the indian mode water pool to roughly 40 years for the central pacific mode water pool

the seasonal cycle of carbonate system processes in ryder bay west antarctic peninsula the carbon cycle in seasonally sea ice covered waters remains poorly understood due to both a lack of observational data and the complexity of the system here we present three consecutive seasonal cycles of upper ocean dissolved inorganic carbon dic and total alkalinity measurements from ryder bay on the west antarctic peninsula we attribute the observed changes in dic to four processes mixing of water masses air sea co2 flux calcium carbonate precipitation dissolution and photosynthesis respiration this approach enables us to resolve the main drivers of the seasonal dic cycle and also investigate the mechanisms behind interannual variability in the carbonate system we observe a strong asymmetric seasonal cycle in the carbonate system driven by physical processes and primary production in summer melting glacial ice and sea ice and a reduction in mixing with deeper water reduce the concentration of dic in surface waters the dominant process affecting the carbonate system is net photosynthesis which reduces dic and the fugacity of co2 making the ocean a net sink of atmospheric co2 in winter mixing with deeper carbon rich water and net heterotrophy increase surface dic concentrations resulting in ph as low as 7 95 and aragonite saturation states close to 1 we observe no clear seasonal cycle of calcium carbonate precipitation dissolution but some short lived features of the carbonate time series strongly suggest that significant precipitation of calcium carbonate does occur in the bay the variability observed in this study demonstrates that changes in mixing and sea ice cover significantly affect carbon cycling in this dynamic environment maintaining this unique time series will allow the carbonate system in seasonally sea ice covered waters to be better understood

impact of weddell sea deep convection on natural and anthropogenic carbon in a climate model a climate model is used to investigate the influence of weddell sea open ocean deep convection on anthropogenic and natural carbon uptake for the period 1860 2100 in a three member ensemble climate change simulation convection ceases on average by year 1981 weakening the net oceanic cumulative uptake of atmospheric co2 by year 2100 4 3 pg c relative to an ocean that has continued convection this net weakening results from a decrease in anthropogenic carbon uptake 10 1 pg c partly offset by an increase in natural carbon storage 5 8 pg c despite representing only 4 of its area the weddell sea is responsible for 22 of the southern ocean decrease in total climate driven carbon uptake and 52 of the decrease in the anthropogenic component of oceanic uptake although this is a model specific result it illustrates the potential of deep convection to produce an intermodel spread in future projections of ocean carbon uptake

large reemergence of anthropogenic carbon into the ocean s surface mixed layer sustained by the ocean s overturning circulation abstractwe evaluate the output from a widely used ocean carbon cycle model to identify the subduction and obduction reemergence rates of anthropogenic carbon cant for climatological conditions during the world ocean circulation experiment woce era in 1995 using a new set of lagrangian diagnostic tools the principal scientific value of the lagrangian diagnostics is in providing a new means to connect cant reemergence pathways to the relatively rapid renewal time scales of mode waters through the overturning circulation our main finding is that for this model with 2 04 pgc yr 1 of uptake of cant via gas exchange the subduction and obduction rates across the base of the mixed layer mlbase are 4 96 and 4 50 pgc yr 1 respectively which are twice as large as the gas exchange at the surface given that there is net accumulation of 0 17 pgc yr 1 in the mixed layer itself this implies the residual downward cant transport of 1 40 pgc yr 1 across the mlbase is associated with diffusion importantly th

simulation of time dependent movements in syncrude tailings dyke foundation foundation movements at the syncrude tailings dyke continued over several years in response to the construction of the dyke major movements have been observed in a relatively narrow layer of previ

the north pacific oxygen uptake rates over the past half century the transport of dissolved oxygen o2 from the surface ocean into the interior is a critical process sustaining aerobic life in mesopelagic ecosystems but its rates and sensitivity to climate variations are poorly understood using a circulation model constrained to historical variability by assimilation of observations we show that the north pacific thermocline effectively takes up o2 primarily by expanding the area through which o2 rich mixed layer water is detrained into the thermocline the outcrop area during the critical winter season varies in concert with the pacific decadal oscillation pdo when the central north pacific ocean is in a cold phase the winter outcrop window for the central mode water class cmw a neutral density range of 25 6 26 6 expands southward allowing more o2 rich surface water to enter the ocean s interior an increase in volume flux of water to the cmw density class is partly compensated by a reduced supply to the shallower densities of subtropical mode water 24 0 25 5 the thermocline has become better oxygenated since the 1980s due partly to strong o2 uptake positive o2 anomalies appear first near the outcrop and subsequently downstream in the subtropical gyre in contrast to the o2 variations within the ventilated thermocline observed o2 in intermediate water density range of 26 7 27 2 shows a declining trend over the past half century a trend not explained by the open ocean water mass formation rate

regional impacts of the westerly winds on southern ocean mode and intermediate water subduction subduction processes in the southern ocean transfer oxygen heat and anthropogenic carbon into the ocean interior the future response of upper ocean subduction in the subantarctic mode water samw and antarctic intermediate water aaiw classes is dependent on the evolution of the combined surface buoyancy forcing and overlying westerly wind stress here the recently observed pattern of a poleward intensification of the westerly winds is divided into its shift and increase components samw and aaiw formation occurs in regional hot spots in deep mixed layer zones primarily in the southeast indian and pacific it is found that the mixed layer depth responds differently to wind stress perturbations across these regional formation zones an increase only in the westerly winds in the indian sector steepens isopycnals and increases the local circulation driving deeper mixed layers and increased subduction conversely in the same region a poleward shift and poleward intensification of the westerly winds reduces heat loss and increases freshwater input thus decreasing the mixed layer depth and consequently the associated samw and aaiw subduction in the pacific sector all wind stress perturbations lead to increases in heat loss and decreases in freshwater input resulting in a net increase in samw and aaiw subduction overall the poleward shift in the westerly wind stress dominates the samwsubduction changes rather than the increase in wind stress the net decrease in samw subduction across all basins would likely decrease anthropogenic carbon sequestration however the net aaiwsubduction changes across the southern ocean are overall minor

southern ocean thermocline ventilation abstract an approximate mass volume budget in the surface layer of the southern ocean is used to investigate the intensity and regional variability of the ventilation process discussed here in terms of subduction and upwelling ventilation resulting from ekman pumping is estimated from satellite winds the geostrophic mean component is assessed from a climatology strengthened with argo data and the eddy induced advection is included via the parameterization of gent and mcwilliams together with eddy mixing estimates all three components contribute significantly to ventilation finally the seasonal cycle of the upper ocean is resolved using argo data the circumpolar averaged circulation shows an upwelling in the antarctic intermediate water aaiw density classes which is carried north into a zone of dense subantarctic mode water samw subduction although no consistent net production is found in the light samw density classes a large subduction of subtropical mode water stmw is observed the s

the interdisciplinary marine system of the amundsen sea southern ocean recent advances and the need for sustained observations the southern ocean exerts a profound influence on the functioning of the earth system in part because its location and unique bathymetric configuration enable direct linkages to the other major ocean basins ganachaud and wunsch 2000 and lumpkin and speer 2007 it is the site of the world s largest current system the antarctic circumpolar current acc which transfers waters and climatically ecologically important tracers between the atlantic indian and pacific oceans rintoul et al 2001 in addition to the strong horizontal connectivity the acc is also characterized by a vigorous overturning circulation which upwells warm nutrient rich waters from intermediate depth to the surface where they are modified by interactions with the atmosphere and cryosphere to form new water masses some of which are lighter and others more dense marshall and speer 2012 this overturning circulation structures the southern ocean both horizontally and vertically dictates the levels of its communication with the rest of the global ocean and is a fundamental control on the sequestration of carbon from the atmosphere into the ocean interior sallee et al 2012 in some locations the upwelled waters can intrude onto the antarctic shelves supplying heat and nutrients to the shallower regions this is believed to be especially effective in west antarctica where the southern edge of the acc moves close to the shelf break martinson 2011 orsi et al 1995 and thoma et al 2008

variability of marine 14c reservoir ages in the southern ocean highlighting circulation changes between 1910 and 1950 abstract recent changes in the southern ocean overturning circulation have been attributed either to natural variability or to anthropogenic forcing the 14c analyses of mollusk shells from kerguelen islands evidence a high decadal variability of the sea surface radiocarbon reservoir ages in the southern south indian ranging from 832 to 1005 30 years between 1910 and 1930 such high variability is common to the different sectors of the southern ocean southern south pacific and atlantic at inter annual and decadal timescales between 1901 and 1950 notably a decrease of 14 c of 40 increased r of 290 years occurred between 1901 and 1940 followed by an increase of 30 between 1940 and 1958 using a simple box model of ocean atmosphere 14co2 exchange this aging is attributed to increased upwelling of cold and 14c depleted subsurface seawaters due to intensified poleward southern westerlies the sea surface 14c aging is indeed well correlated to a positive phase of the southern hemisphere annular mode and to a cooling of the sea surface temperatures in the southern ocean between 1901 and 1940 these pre 1950 sea surface 14c changes highlight the importance of natural changes in wind intensities and ocean dynamics

southern ocean overturning compensation in an eddy resolving climate simulation the southern ocean s antarctic circumpolar current acc and meridional overturning circulation moc response to increasing zonal wind stress is for the first time analyzed in a high resolution 0 1 ocean and 0 25 atmosphere fully coupled global climate simulation using the community earth system model results from a 20 yr wind perturbation experiment where the southern hemisphere zonal wind stress is increased by 50 south of 30 s show only marginal changes in the mean acc transport through drake passage an increase of 6 136 144 sverdrups sv 1 sv 10 6 m 3 s 1 in the perturbation experiment compared with the control however the upper and lower circulation cells of the moc do change the lower cell is more affected than the upper cell with a maximum increase of 64 versus 39 respectively changes in the moc are directly linked to changes in water mass transformation from shifting surface isopycnals and sea ice melt giving rise to changes in surface buoyancy forcing the increase in transport of the lower cell leads to upwelling of warm and salty circumpolar deep water and subsequent melting of sea ice surrounding antarctica the moc is commonly supposed to be the sum of two opposing components a wind and transient eddy overturning cell here the transient eddy overturning is virtually unchanged and consistent with a large scale cancellation of localized regions of both enhancement and suppression of eddy kinetic energy along the mean path of the acc however decomposing the time mean overturning into a time and zonal mean component and a standing eddy component reveals partial compensation between wind driven and standing eddy components of the circulation

alh85085 a unique volatile poor carbonaceous chondrite with possible implications for nebular fractionation processes abstract allan hills 85085 is a unique chondrite with affinities to the al rais renazzo clan of carbonaceous chondrites its constituents are less than 50 m in mean size chondrules and microchondrules of all textures are present nonporphyritic chondrules are unusually abundant the mean compositions of porphyritic nonporphyritic and barred olivine chondrules resemble those in ordinary chondrites except that they are depleted in volatile elements ca al rich inclusions are abundant and largely free of nebular alteration they comprise types similar to those in cm and co chondrites as well as unique types calcium dialuminate occurs in several inclusions metal silicate and sulfide compositions are close to those in cm co chondrites and al rais and renazzo c1 chondrite clasts and metal rich reduced clasts are present but opaque matrix is absent siderophile abundances in alh85085 are extremely high e g fe si 1 7 solar and volatiles are depleted e g na si 0 25 solar s si 0 03 solar nonvolatile lithophile abundances are similar to those in al rais renazzo and cm and co chondrites alh85085 agglomerated when temperatures in the nebula were near 1000 k in the same region where renazzo al rais and the ci chondrites formed agglomeration of high temperature material may thus be a mechanism by which the fractionation of refractory lithophiles occurred in the nebula chondrule formation must have occurred at high temperatures when clumps of precursors were small after agglomeration alh85085 was annealed and lightly shocked c1 and other clasts were subsequently incorporated during late stage brecciation

subduction of carbon nitrogen and oxygen in the northeast atlantic 1 northeast atlantic mode waters neamw are formed by subduction in a region known to be a strong sink of atmospheric co2 this study investigates the biological and physical carbon pumps involved in this sink for that purpose we estimate the annual transfer of carbon nitrogen and oxygen from the surface into the ocean interior through neamw subduction our estimates are based on a model simulation constrained with data collected during the programme ocean multidisciplinaire meso echelle pomme we found that subduction accounts for a large proportion of carbon export below the mixed layer in the pomme region 38 n 45 n 16 w 22 w fifty percent of labile organic carbon is exported by the biological pump and 50 by subduction 98 of the total carbon flux below the mixed layer is due to carbon subduction essentially in the form of dissolved inorganic carbon and of more refractory dissolved organic matter this is because they are the dominant pools of carbon and are passing through the winter mixed layer depth gradient that characterizes the region our results emphasize that the net export of carbon represents a small fraction of the fluxes of carbon across the mixed layer through the processes of subduction and obduction moreover our results indicate that neamw subduction occurs before the spring bloom this implies that neamw is mostly subducted with end winter characteristics with in particular relatively high nutrient content this reflects a relative inefficiency in nutrient utilization and contrasts with subtropical mode waters which are subducted during the bloom and are thus relatively poor in nutrients when they are subducted

soil mechanics and the observational method challenges at the zelazny most copper tailings disposal facility this paper illustrates the geotechnical aspects of the development of one of the world s largest copper tailings disposal facilities located at zelazny most in south west poland its operation commenced in 1977 and by the end of 2013 527 106 m3 of tailings had already been stored within a confining embankment dam ring dam of about 14 3 km in total length the foundations of the ring dam lie on pleistocene deposits underlain by a thick sequence of pliocene sediments the period of operation of the facility will continue until exhaustion of the ore body which is estimated to occur in 2042 when the total volume of tailings stored will reach 1000 106 m3 the development and the use of the zelazny most facility is affected by a number of significant geotechnical hazards including the phenomenon of flow liquefaction as is often the case for such structures however the most important geotechnical hazard at zelazny most is a consequence of its location in an area that during the pleistocene ex

multi iteration approach to studying tracer spreading using drifter data abstracta novel multi iteration statistical method for studying tracer spreading using drifter data is introduced the approach allows for the best use of the available drifter data by making use of a simple iterative procedure which results in the statistically probable map showing the likelihood that a tracer released at some source location would visit different geographical regions along with the associated arrival travel times the technique is tested using real drifter data in the north atlantic two examples are considered corresponding to sources in the western and eastern north atlantic ocean that is massachusetts bay like and irish sea like sources respectively in both examples the method worked well in estimating the statistics of the tracer transport pathways and travel times throughout the entire north atlantic the role of eddies versus mean flow is quantified using the same technique and eddies are shown to significantly broaden the spread of a tracer the sensitivity of the results

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

refractory calcium aluminum rich inclusions and aluminum diopside rich chondrules in the metal rich chondrites hammadah al hamra 237 and queen alexandra range 94411 the metal rich chondrites hammadah al hamra hh 237 and queen alexandra range que 94411 paired with que 94627 contain relatively rare 1 vol calcium aluminum rich inclusions cais and al diopside rich chondrules forty cais and cai fragments and seven al diopside rich chondrules were identified in hh 237 and que 94411 94627 the cais 50 400 mum in apparent diameter include a 22 56 pyroxene spinel melilite forsterite rim b 11 28 forsterite bearing pyroxene spinel melilite anorthite forsterite rim c 2 5 grossite rich spinel melilite pyroxene rim d 2 5 hibonite melilite spinel pyroxene forsterite rim e 1 2 hibonite bearing spinel perovskite melilite pyroxene rim f 1 2 spinel melilite pyroxene anorthite and g 1 2 amoeboid olivine aggregate each type of cai is known to exist in other chondrite groups but the high abundance of pyroxene spinel melilite cais with igneous textures and surrounded by a forsterite rim are unique features of hh 237 and que 94411 94627 additionally oxygen isotopes consistently show relatively heavy compositions with delta o 17 ranging from 6 parts per thousand to 10 parts per thousand 1 sigma 1 3 parts per thousand for all analyzed cai minerals grossite hibonite melilite pyroxene spinel this suggests that the cais formed in a reservoir isotopically distinct from the reservoir s where normal o 16 rich delta o 17 20 cais in most other chondritic meteorites formed

heavily hydrated lithic clasts in ch chondrites and the related metal rich chondrites queen alexandra range 94411 and hammadah al hamra 237 fine grained heavily hydrated lithic clasts in the metal rich cb chondrites queen alexandra range que 94411 and hammadah al hamra 237 and ch chondrites such as patuxent range pat 91546 and allan hills alh 85085 are mineralogically similar suggesting genetic relationship between these meteorites these clasts contain no anhydrous silicates and consist of framboidal and platelet magnetite prismatic sulfides pentlandite and pyrrhotite and fe mn mg bearing ca carbonates set in a phyllosilicate rich matrix two types of phyllosilicates were identified serpentine with basal spacing of similar to0 73 nm and saponite with basal spacings of about 1 1 1 2 nm chondrules and feni metal grains in cb and ch chondrites are believed to have formed at high temperature 1300 k by condensation in a solar nebula region that experienced complete vaporization the absence of aqueous alteration of chondrules and metal grains in cb and ch chondrites indicates that the clasts experienced hydration in an asteroidal setting prior to incorporation into the ch and cb parent bodies the hydrated clasts were either incorporated during regolith gardening or accreted together with chondrules and feni metal gains after these high temperature components had been transported from their hot formation region to a much colder region of the solar nebula

oxygen isotopes of chondritic components we review the oxygen isotopic compositions of chondrite components refractory inclusions chondrules and matrix and their inter and intra crystalline oxygen isotopic distributions primary oxygen isotopic compositions acquired before planetesimal accretion are easily disturbed by parent body processes such as aqueous alternation and thermal metamorphism primary or original oxygen isotopic compositions of refractory inclusions ca al rich inclusions and amoeboid olivine aggregates distribute along a slope 1 line on the three oxygen isotope diagram over the range of 60 17 o 18 o 16 o rich and 17 o 18 o rich during refractory inclusion formation on the other hand primary minerals of most chondrules have small isotopic variations and are enriched in 17 o and 18 o relative to refractory inclusions suggesting that chondrule formation occurred in 17 o 18 o rich nebular gas however rare 16 o rich chondrules have been found suggesting some overlap in the timing of formation of chondrules and refractory inclusions in the solar nebula oxygen isotopic compositions of matrix grains distribute along the slope 1 line over the same range as refractory inclusions and chondrules the similarity in oxygen isotopic distributions suggests that matrix was originally a mechanical mixture of nebular dusts co generated with chondrules and refractory inclusions presolar grains with oxygen isotopic compositions that are clearly distinct from those of solar nebular materials are a trace component of chondrite matrices based on these oxygen isotopic characteristics more than 99 5 of the solid materials in the nebula formed locally in the solar nebula and the remainder formed in interstellar space the astrophysical setting of chondrite component formation in the early solar system is also discussed refractory inclusions and 16 o rich matrix dusts formed around the inner edge of the solar nebula on the other hand most chondrules and 17 o 18 o rich matrix dusts seem to have formed elsewhere in the solar nebula efficient large scale radial mixing of the solar nebular materials may have been an essential process in the formation of chondritic planetesimals

shock melts in que 94411 hammadah al hamra 237 and bencubbin remains of the missing matrix we have studied the cb carbonaceous chondrites queen alexandra range que 94411 hammadah al hamra hh 237 and bencubbin with an emphasis on the petrographical and mineralogical effects of the shock processing that these meteorite assemblages have undergone iron nickel metal and chondrule silicates are the main components in these meteorites these high temperature components are held together by shock melts consisting of droplets of dendritically intergrown fe ni metal sulfide embedded in silicate glass which is substantially more feo rich 3040 wt than the chondrule silicates feo 5 wt fine grained matrix material which is a major component in most other chondrite classes is extremely scarce in que 94411 and hh 237 and has not been observed in bencubbin this material occurs as rare hydrated matrix lumps with major and minor element abundances roughly similar to the ferrous silicate shock melts and cl we infer that hydrated fine grained material compositionally similar to these matrix lumps was originally present between the fe ni metal grains and chondrules but was preferentially shock melted other shock related features in que 94411 hh 237 and bencubbin include an alignment and occasionally strong plastic deformation of metal and chondrule fragments

frontal circulation and submesoscale variability during the formation of a southern ocean mesoscale eddy observations made in the scotia sea during the may 2015 surface mixed layer evolution at submesoscales smiles research cruise captured submesoscale o 1 10 km variability along the periphery of a mesoscale o 10 100 km meander precisely as it separated from the antarctic circumpolar current acc and formed a cyclonic eddy 120 km in diameter the meander developed in the scotia sea an eddy rich region east of the drake passage where the subantarctic and polar fronts converge and modifications of subantarctic mode water samw occur in situ measurements reveal a rich submesoscale structure of temperature and salinity and a loss of frontal integrity along the newly formed southern sector of the eddy a mathematical framework is developed to estimate vertical velocity from collocated drifter and horizontal water velocity time series under certain simplifying assumptions appropriate for the current dataset upwelling downwelling rates of o 100 m day 1 are found in the northern southern eddy sector favorable conditions for submesoscale instabilities are found in the mixed layer particularly at the beginning of the survey in the vicinity of density fronts shallower mixed layer depths and increased stratification are observed later in the survey on the inner edge of the front evolution in temperature salinity t s space indicates modification of water mass properties in the upper 200 m over 2 days modifications along 27 27 2 kg m 3 have climate related implications for mode and intermediate water transformation in the scotia sea on finer spatiotemporal scales than observed previously

heat distribution in the southeast pacific is only weakly sensitive to high latitude heat flux and wind stress the southern ocean features regionally varying ventilation pathways that transport heat and carbon from the surface ocean to the interior thermocline on timescales of decades to centuries but the factors that control the distribution of heat along these pathways are not well understood in this study we use a global ocean state estimate eccov4 to 1 define the recently ventilated interior pacific rvp using numerical passive tracer experiments over a 10 year period and 2 use an adjoint approach to calculate the sensitivities of the rvp heat content rvph to changes in net heat flux and wind stress we find that rvph is most sensitive to local heat flux and wind stress anomalies north of the sea surface height contours that delineate the antarctic circumpolar current with especially high sensitivities over the south pacific gyre surprisingly rvph is not especially sensitive to changes at higher latitudes we perform a set of step response experiments over the south pacific gyre the subduction region and the high latitude so in consistency with the adjoint sensitivity fields rvph is most sensitive to wind stress curl over the subtropical gyre which alter isopycnal heave and it is only weakly sensitive to changes at higher latitudes our results suggest that despite the localized nature of mode water subduction hotspots changes in basin scale pressure gradients are an important controlling factor on rvph because basin scale wind stress is expected to change in the coming decades to centuries our results may have implications for climate via the atmosphere ocean partitioning of heat

oceanic isopycnal mixing by coordinate rotation abstract current numerical models of oceanic circulation differentiate between the eddy diffusion and viscosity transport along the geopotential horizontal and vertical directions only in order to model the effect of anisotropic turbulence as diffusive transport along and across density surfaces the isopycnal mixing tensor has been transformed from a diagonal second rank tensor in the isopycnal coordinate system to a tensor containing off diagonal elements in the geopotential coordinate system

probabilistic stability analysis of a tailings dyke on presheared clay shale probabilistic slope stability analysis offers an efficient framework for logical systematic incorporation of un certainty into slope design the slow integration of probabilistic slope analyses into practice is attributed among other factors to the lack of published studies illustrating the implementation and benefits of such techniques a spreadsheet based probabilistic slope analysis methodology is applied to evaluate the stability of a section of the syncrude tailings dyke in fort mcmurray canada the dyke is approximately 44 m high and is founded on presheared clay shale the performance of the dyke is governed by uncertainties about material properties and pore water pressures starting with field and laboratory data this study demonstrates the techniques used in quantifying the various components of param eter uncertainty conducting a probabilistic assessment and estimating the probability of unsatisfactory performance the probability of unsatisfactory performance of the dyke is estimated to be 1 6 10 3 field monitoring data indicate that the dyke performance is adequate the study thus provides a first link between probability figures and perfor mance the analysis also quantifies the relative contributions of the various sources of uncertainty to the overall uncer tainty in the factor of safety

decadal 1994 2008 change in the carbon isotope ratio in the eastern south pacific ocean we determined the 14 year change in the anthropogenic co2 inventory in the eastern south pacific ocean along the 110 w meridian from 67 s to 21 n using seawater 13c data sets collected in 1994 and 2008 the vertical integral of the 14 year 13c change was assessed in five latitude bands and found to be greatest 14 7 m yr 1 in the subpolar band 38 s 55 s and smallest 3 0 m yr 1 in the tropical band 21 n 18 s the 13c change in each of the latitudinal bands was primarily caused by inputs of anthropogenic co2 via air sea exchange and transport more than 50 of the total anthropogenic co2 was added to the subpolar band via the northward movement of antarctic intermediate water aaiw from the south and the remaining 50 was added via air sea exchange we also calculated the ratio of the temporal change in 13c to the change in dissolved inorganic carbon which is a measure of the efficiency of oceanic uptake of anthropogenic co2 the ratio for aaiw in 1994 0 017 mol kg 1 1 was greater than that in 2008 0 010 mol kg 1 1 based on the change in preformed 13c and dissolved inorganic carbon dic indicating reduced efficiency of co2 uptake by the southern ocean in 2008 relative to that in 1994 aaiw remained at the surface for a shorter period in 2008 relative to 1994 and thus would have taken up less atmospheric co2 prior to subduction the projected reduction in this ratio indicates a weakening of co2 uptake by the southern ocean in the future

changes in the advection of antarctic intermediate water to the northern chilean coast during the last 970 kyr 1 the antarctic intermediate water aaiw is a key player in global scale oceanic overturning processes and an important conduit for heat fresh water and carbon transport the aaiw past variability is poorly understood mainly due to the lack of sedimentary archives at intermediate water depths we present records of benthic stable isotopes from sediments retrieved with the seafloor drill rig marum mebo at 956 m water depth off northern chile geob15016 27 29 48 s 71 07 58 w that extend back to 970 ka the sediments at this site are presently deposited at the boundary between aaiw and pacific deep water pdw for previous peak interglacials our results reveal similar benthic 13c values at site geob15016 and of a newly generated stack of benthic 13c from various deep pacific cores representing the average pdw this suggests unlike today the absence of aaiw at the site and the presence of nearly pure pdw in contrast more positive 13c values at site geob15016 compared to the stack imply a considerable aaiw contribution during cold phases of interglacials and especially during glacials besides we used three short sediment cores to reconstruct benthic 13c values from the aaiw core during the last glacial and found a 13c signature similar to today s assuming that this was the case also for the past 970 kyr we demonstrate that sea level changes and latitudinal migrations of the aaiw formation site can only account for about 50 of the full range of past 13c increases at site geob15016 during cold periods other processes that could explain the remaining of the positive 13c anomalies are increases in glacial aaiw production and or deeper convection of the aaiw with respect to preceding interglacials

pathways of anthropogenic carbon subduction in the global ocean the oceanic uptake of anthropogenic carbon is tightly coupled to carbon subduction i e the physical carbon transfer from the well ventilated surface ocean to its interior despite their importance pathways of anthropogenic carbon subduction are poorly understood here we use an ocean carbon cycle model to quantify the mechanisms controlling this subduction over the last decade 90 of the oceanic anthropogenic carbon is subducted at the base of the seasonally varying mixed layer vertical diffusion is the primary mechanism of this subduction contributing 65 of total subduction despite very low local fluxes in contrast advection drives the spatial patterns of subduction with high positive and negative local fluxes our results suggest that vertical diffusion could have a leading role in anthropogenic carbon subduction which highlights the need for an accurate estimate of vertical diffusion intensity in the upper ocean to further constrain estimates of the future evolution of carbon uptake

assessment of southern ocean water mass circulation and characteristics in cmip5 models historical bias and forcing response 1 the ability of the models contributing to the fifth coupled models intercomparison project cmip5 to represent the southern ocean hydrological properties and its overturning is investigated in a water mass framework models have a consistent warm and light bias spread over the entire water column the greatest bias occurs in the ventilated layers which are volumetrically dominated by mode and intermediate layers the ventilated layers have been observed to have a strong fingerprint of climate change and to impact climate by sequestrating a significant amount of heat and carbon dioxide the mode water layer is poorly represented in the models and both mode and intermediate water have a significant fresh bias under increased radiative forcing models simulate a warming and lightening of the entire water column which is again greatest in the ventilated layers highlighting the importance of these layers for propagating the climate signal into the deep ocean while the intensity of the water mass overturning is relatively consistent between models when compared to observation based reconstructions they exhibit a slightly larger rate of overturning at shallow to intermediate depths and a slower rate of overturning deeper in the water column under increased radiative forcing atmospheric fluxes increase the rate of simulated upper cell overturning but this increase is counterbalanced by diapycnal fluxes including mixed layer horizontal mixing and mostly vanishes

petrographic and oxygen isotopic study of refractory forsterites from r chondrite dar al gani 013 r3 5 6 unequilibrated ordinary and carbonaceous chondrites we have conducted petrographic chemical and in situ oxygen isotopic studies of refractory forsterites from unequilibrated ordinary and carbonaceous chondrites as well as an unequilibrated r chondrite refractory forsterites occur in all types of unequilibrated chondrites and all have very similar chemical composition with low feo and high refractory lithophile element rle contents refractory forsterites are typically enriched in 16o relative to normal olivine independent of the bulk o isotope ratios of the parent meteorites analyses of refractory forsterites spread along a 17o mixing line with 17o ranging from 2 to 10 due to similarities in oxygen isotopes and chemical compositions we conclude that refractory forsterites of various types of chondrites come from a single common reservoir implications of this hypothesis for the chemical and o isotope evolution of silicates in the early solar nebular are discussed

impacts of climate change on the subduction of mode and intermediate water masses in the southern ocean abstract changes in the temperature salinity and subduction of subantarctic mode water samw and antarctic intermediate water aaiw between the 1950s and 2090s are diagnosed using the csiro mark version 3 5 mk3 5 climate system model caps under a co2 forcing that reaches 860 ppm by the year 2100 these southern ocean upper limb water masses ventilate the ocean interior and changes in their properties have been related to climate change in numerous studies over time the authors follow the low potential vorticity and salinity minimum layers describing samw and aaiw and find that the water column in the 2090s shifts to lighter densities by approximately 0 2 kg m 3 the model projects a reduction in the samw and aaiw annual mean subduction rates as a result of a combination of a shallower mixed layer increased potential vorticity at the base of the mixed layer and a net buoyancy gain there is little change in the projected total volume of samw transported into the ocean interior via the subduction

physical pathways for carbon transfers between the surface mixed layer and the ocean interior 1 although they are key components of the surface ocean carbon budget physical processes inducing carbon fluxes across the mixed layer base i e subduction and obduction have received much less attention than biological processes using a global model analysis of the preindustrial ocean physical carbon fluxes are quantified and compared to the other carbon fluxes in and out of the surface mixed layer i e air sea co2gas exchange and sedimentation of biogenic material model based carbon obduction and subduction are evaluated against independent data based estimates to the extent that was possible we find that climatological physical fluxes of dissolved inorganic carbon dic are two orders of magnitude larger than the other carbon fluxes and vary over the globe at smaller spatial scale at temperate latitudes the subduction of dic and to a much lesser extent 10 the sinking of particles maintain co2undersaturation whereas dic is obducted back to the surface in the tropical band 75 and southern ocean 25 at the global scale these two large counter balancing fluxes of dic amount to 275 5 pgc yr 1 for the supply by obduction and 264 5 pgc yr 1 for the removal by subduction which is 3 to 5 times larger than previous estimates moreover we find that subduction of organic carbon dissolved and particulate represents 20 of the total export of organic carbon at the global scale we evaluate that of the 11 pgc yr 1 of organic material lost from the surface every year 2 1 pgc yr 1 is lost through subduction of organic carbon our results emphasize the strong sensitivity of the oceanic carbon cycle to changes in mixed layer depth ocean currents and wind

oxygen isotopic compositions of chondrules from the metal rich chondrites isheyevo ch cbb mac 02675 cbb and que 94627 cbb abstract it has been recently suggested that 1 ch chondrites and the cbb ch like chondrite isheyevo contain two populations of chondrules formed by different processes i magnesian non porphyritic cryptocrystalline and barred chondrules which are similar to those in the cb chondrites and formed in an impact generated plume of melt and gas resulted from large scale asteroidal collision and ii porphyritic chondrules formed by melting of solid precursors in the solar nebula 2 porphyritic chondrules in isheyevo and ch chondrites are different from porphyritic chondrules in other carbonaceous chondrites krot et al 2005 krot et al 2008a krot et al 2008b in order to test these hypotheses we measured in situ oxygen isotopic compositions of porphyritic magnesian type i and ferroan type ii and non porphyritic magnesian and ferroan cryptocrystalline chondrules from isheyevo and cbb chondrites mac 02675 and que 94627 paired with que 94611 using a cameca ims 1280 ion microprobe on a three isotope oxygen diagram 17o vs 18o compositions of chondrules measured follow approximately slope 1 line data for 19 magnesian cryptocrystalline chondrules from isheyevo 24 magnesian cryptocrystalline chondrules and 6 magnesian cryptocrystalline silicate inclusions inside chemically zoned fe ni metal condensates from cbb chondrites have nearly identical compositions 17o 2 2 0 9 2 3 0 6 and 2 2 1 0 2 respectively these observations and isotopically light magnesium compositions of cryptocrystalline magnesian chondrules in cbb chondrites gounelle et al 2007 are consistent with their single stage origin possibly as gas melt condensates in an impact generated plume in contrast 17o values for 11 type i and 9 type ii chondrules from isheyevo range from 5 to 4 and from 17 to 3 respectively in contrast to typical chondrules from carbonaceous chondrites seven out of 11 type i chondrules from isheyevo plot above the terrestrial fractionation line we conclude that i porphyritic chondrules in isheyevo belong to a unique population of objects suggesting formation either in a different nebular region or at a different time than chondrules from other carbonaceous chondrites ii isheyevo cb and ch chondrites are genetically related meteorites they contain non porphyritic chondrules produced during the same highly energetic event probably large scale asteroidal collision iii the differences in mineralogy petrography chemical and whole rock oxygen isotopic compositions between ch and cb chondrites are due to various proportions of the nebular and the impact produced materials

carbonate chemistry in the mertz polynya east antarctica biological and physical modification of dense water outflows and the export of anthropogenic co2 1 dense shelf water dsw is formed in east antarctica from enhanced sea ice production driven by air sea interaction in coastal polynyas cross shelf export and downslope mixing of this dsw produces antarctic bottom water contributing to the lower limb of the global overturning circulation we present biogeochemical observations from the mertz polynya region in summer 2007 2008 with additional observations from spring 2001 and winter 1996 the seasonal changes in mixed layer carbonate chemistry are driven by a combination of air sea co2 exchange biological activity and the formation and melt of sea ice the air sea fluxes in 2008 were 15 mmol c m 2 d 1 and net community production estimated from the summertime surface dissolved inorganic carbon dic deficit ranged from 0 9 to 1 2 mol c m 2 yr 1 we show that biological modification of carbonate chemistry over the shelf in summer preconditions the dsw outflows from the adelie depression this process appears to supply both organic material and water depleted in co2 and with enhanced carbonate saturation state relative to inflowing water to coral communities on the slope we combined model based transports of exported dsw with the natural and anthropogenic cant carbon concentrations and estimate that the annual outflows of dic and cant from the mertz polynya range from 320 to 560 tg c yr 1 and from 3 to 6 tg cant yr 1 respectively the formation and export of dense water from this region and by extension all similar polynyas around antarctica is an effective mechanism for the transfer of anthropogenic carbon into the deep ocean

impacts of ice shelf melting on water mass transformation in the southern ocean from e3sm simulations abstractthe southern ocean overturning circulation is driven by winds heat fluxes and freshwater sources among these sources of freshwater antarctic sea ice formation and melting play the domin

primitive feni metal grains in ch carbonaceous chondrites formed by condensation from a gas of solar composition some feni metal grains similar to 150 mu m in apparent diameter in ch carbonaceous chondrites are concentrically zoned in ni similar to 5 10 wt co 0 2 0 4 wt and cr 0 3 0 8 wt silicon is present at the similar to 0 1 wt level these observations are consistent with predicted gas solid condensation from a gas of solar composition at temperatures of similar to 1370 1270 k and total pressure of similar to 10 4 bar estimates of feni metal grain growth and cooling rates in this temperature range are consistent with brief and localized thermal episodes in the solar nebula compositionally similar feni metal grains have also been reported in cr and bencubbin like chondrites because feni metal is highly susceptible to secondary alteration i e metamorphism melting oxidation the observed feni metal condensates in ch bencubbin like and cr chondrites indicate that these meteorites experienced no thermal processing after their lithification and thus are among the most primitive meteorites in our collections

carbon dynamics of the weddell gyre southern ocean the accumulation of carbon within the weddell gyre and its exchanges across the gyre boundaries are investigated with three recent full depth oceanographic sections enclosing this climatically important region the combination of carbon measurements with ocean circulation transport estimates from a box inverse analysis reveal that deep water transports associated with warm deep water wdw and weddell sea deep water dominate the gyre s carbon budget while a dual cell vertical overturning circulation leads to both upwelling and the delivery of large quantities of carbon to the deep ocean historical sea surface pco2 observations interpolated using a neural network technique confirm the net summertime sink of 0 044 to 0 058 0 010 pg c yr 1 derived from the inversion however a wintertime outgassing signal similar in size results in a statistically insignificant annual air to sea co2 flux of 0 002 0 007 pg c yr 1 mean 1998 2011 to 0 012 0 024 pg c yr 1 mean 2008 2010 to be diagnosed for the weddell gyre a surface layer carbon balance independently derived from in situ biogeochemical measurements reveals that freshwater inputs and biological drawdown decrease surface ocean inorganic carbon levels more than they are increased by wdw entrainment resulting in an estimated annual carbon sink of 0 033 0 021 pg c yr 1 although relatively less efficient for carbon uptake than the global oceans the summertime weddell gyre suppresses the winter outgassing signal while its biological pump and deep water formation act as key conduits for transporting natural and anthropogenic carbon to the deep ocean where they can reside for long timescales

a mechanism of mixed layer formation in the indo western pacific southern ocean preconditioning by an eddy driven jet scale overturning circulation abstractthe formation of a narrow band of the deep winter mixed layer hereinafter mixed layer wedge in the indo western pacific southern ocean is examined using an eddy resolving parallel ocean program pop model simulation the mixed layer wedge starts to deepen in june centered at 47 5 s with a meridional scale of only 2 latitude its center is located 1 north of the model s subantarctic front saf the argo based observed mixed layer is similarly narrow and occurs adjacent to the observed saf in the small sector of 130 142 e where the saf is persistent and the mixed layer is deepest the formation of the narrow mixed layer wedge coincides with destratification underneath the mixed layer this destratification can be attributed primarily to the downwelling branch of a jet scale overturning circulation jsoc the jsoc which was reported in an earlier study by the authors is driven by eddy momentum flux convergence and is therefore thermally indirect its descending branch occurs on the

mesoscale and submesoscale effects on mixed layer depth in the southern ocean the authors gratefully acknowledge support from the natural environment research council awards ne j010472 1 and ne j009857 1

three compartment structure of subsurface intensified mesoscale eddies in the ocean mesoscale eddies are energetically dominant and pervasive over most of the world s oceans among them many are subsurface intensified with strongest signals in the ocean interior such as mode water eddies which trap water masses with distinctive properties and carry them over long distances with both argo profiling floats and atmospheric reanalysis data we showed that the structure of these eddies obeys a universal rule hence their three dimensional hydrographic fields can be readily reconstructed from very limited information more interestingly the volume of water trapped and moved by a mode water eddy is much greater than previously thought it has a three compartment structure in the vertical with the mode water being sandwiched between two layers of notably different properties and accounting for only a portion of the total trapped volume this article is protected by copyright all rights reserved

response of the antarctic circumpolar current to atmospheric variability abstract historical hydrographic profiles combined with recent argo profiles are used to obtain an estimate of the mean geostrophic circulation in the southern ocean thirteen years of altimetric sea level anomaly data are then added to reconstruct the time variable sea level and this new dataset is analyzed to identify and monitor the position of the two main fronts of the antarctic circumpolar current acc during the period 1993 2005 the authors relate their movements to the two main atmospheric climate modes of the southern hemisphere the southern annular mode sam and the el nino southern oscillation enso the study finds that although the fronts are steered by the bathymetry which sets their mean pathway on first order in flat bottom areas the fronts are subject to large meandering because of mesoscale activity and atmospheric forcing while the dominant mode of atmospheric variability in the southern hemisphere sam is relatively symmetric the oceanic response of the fronts is not show

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

the dynamics of mixed layer deepening during open ocean convection abstractopen ocean convection is a common phenomenon that regulates mixed layer depth and ocean ventilation in the high latitude oceans however many climate model simulations overestimate mixed l

localized subduction of anthropogenic carbon dioxide in the southern hemisphere oceans the southern ocean makes a substantial contribution to the oceanic carbon sink observationally based estimates of carbon subduction suggest that carbon sequestration depends on physical properties such as mixed layer depth ocean currents wind and eddies that are potentially sensitive to climate variability and change

a multibasin residual mean model for the global overturning circulation the ocean s overturning circulation is inherently three dimensional yet modern quantitative estimates of the overturning typically represent the subsurface circulation as a two dimensional two cell streamfunction that varies with latitude and depth only this approach suppresses information about zonal mass and tracer transport in this article the authors extend earlier zonally averaged overturning theory to explore the dynamics of a figure eight circulation that cycles through multiple basins a three dimensional residual mean model of the overturning circulation is derived and then simplified to a multibasin isopycnal box model to explore how stratification and diabatic water mass transformations in each basin depend on the basin widths and on deep and bottom water formation in both hemispheres the idealization to multiple two dimensional basins permits zonal mass transport along isopycnals in a southern ocean like channel while retaining the dynamical framework of residual mean theory the model qualitatively reproduces the deeper isopycnal surfaces in the pacific basin relative to the atlantic this supports a transfer of antarctic bottom water from the atlantic sector to the pacific sector via the southern ocean which subsequently upwells in the northern pacific basin a solution for the full isopycnal structure in the southern ocean reproduces observed stratification differences between atlantic and pacific basins and provides a scaling for the diffusive boundary layer in which the zonal mass transport occurs these results are consistent with observational indications that north atlantic deep water is preferentially transformed into antarctic bottom water which undermines the importance of an adiabatic upper overturning cell in the modern ocean

subantarctic and polar fronts of the antarctic circumpolar current and southern ocean heat and freshwater content variability a view from argo abstractargo profiling floats initiated a revolution in observational physical oceanography by providing numerous high quality global year round in situ 0 2000 dbar temperature and salinity observations this study uses argo s unprecedented sampling of the southern ocean during 2006 13 to describe the position of the antarctic circumpolar current s subantarctic and polar fronts comparing and contrasting two different methods for locating fronts using the same dataset the first method locates three fronts along dynamic height contours each corresponding to a local maximum in vertically integrated shear the second approach locates the fronts using specific features in the potential temperature field following orsi et al results from the analysis of argo data are compared to those from orsi et al and other more recent studies argo spatial resolution is not adequate to resolve annual and interannual movements of the fronts on a circumpolar scale since they are on the order of 1 latitude kim an

evaluating southern ocean carbon eddy pump from biogeochemical argo floats the vertical transport of surface water and carbon into ocean s interior known as subduction is one of the main mechanisms through which the ocean influences earth s climate new instrumental approaches have shown the occurrence of localized and intermittent subduction episodes associated with small scale ocean circulation features these studies also revealed the importance of such events for the export of organic matter the so called eddy pump however the transient and localized nature of episodic subduction hindered its large scale evaluation to date in this work we present an approach to detect subduction events at the scale of the southern ocean using measurements collected by biogeochemical autonomous floats bgcargo we show how subduction events can be automatically identified as anomalies of spiciness and apparent oxygen utilization aou below the mixed layer using this methodology over more than 4 000 profiles we detected 40 subduction events unevenly distributed across the sothern ocean events were more likely found in hot spots of eddy kinetic energy eke downstream major bathymetric features moreover the bio optical measurements provided by bgcargo allowed measuring the amount of particulate organic carbon poc being subducted and assessing the contribution of these events to the total downward carbon flux at 100 m ep100 we estimated that the eddy pump represents less than 19 to the ep100 in the southern ocean although we observed particularly strong events able to locally duplicate the ep100 this approach provides a novel perspective on where episodic subduction occurs that will be naturally improved as bgcargo observations continue to increase

importance of mesoscale eddies and mean circulation in ventilation of the southern ocean this study examines the relative importance of the mean advection and mesoscale currents in the property exchange between the southern ocean mixed layer and downstream in the upper 2000 meters this exchange is referred to as ventilation a new highly efficient offline tracer model employed here uses pre calculated velocities to advect dynamically passive tracers two idealized tracers are considered the boundary impulse response bir tracer which helps to determine the ventilation pathways and time scales and the transient surface tracer tst which is relevant to transient atmospheric tracers the importance of eddies is isolated by contrasting the control simulation with a simulation without mesoscale currents the analysis reveals complex three dimensional ventilation pathways controlled by the interplay between the mean advection and eddy induced spreading the mean currents carry the tracers eastward within acc and contribute to the formation of the antarctic intermediate water aaiw in the south pacific and south atlantic the main effect of eddies is to disperse tracers away from the mean pathways and this dispersion acts to retain the bir tracer in the atlantic and indian sectors and reduce the upstream influence of these regions on the south pacific in addition the eddy induced along isopycnal spreading within acc increases the ventilated depth and the inventory of tst the results can be used to interpret distribution of tracers in the ocean in numerical simulations and observations this article is protected by copyright all rights reserved

formation of metal and silicate globules in gujba a new bencubbin like meteorite fall gujba is a coarse grained meteorite fall composed of 41 vol large kamacite globules 20 vol large light colored silicate globules with cryptocrystalline barred pyroxene and barred olivine textures 39 vol dark colored silicate rich matrix and rare refractory inclusions gujba resembles bencubbin and weatherford in texture oxygen isotopic composition and in having high bulk 15n values 685 the 3he cosmic ray exposure age of gujba 26 7 ma is essentially identical to that of bencubbin suggesting that they were both reduced to meter size fragments in the same parent body collision the gujba metal globules exhibit metal troilite quench textures and vary in their abundances of troilite and volatile siderophile elements we suggest that the metal globules formed as liquid droplets either via condensation in an impact generated vapor plume or by evaporation of preexisting metal particles in a plume the lower the abundance of volatile elements in the metal globules the higher the globule quench temperature we infer that the large silicate globules also formed from completely molten droplets their low volatile element abundances indicate that they also formed at high temperatures probably by processes analogous to those that formed the metal globules the coarse grained bencubbin weatherford gujba meteorites may represent a depositional component from the vapor cloud enriched in coarse and dense particles a second class of bencubbin like meteorites represented by hammadah al hamra 237 and que 94411 may be a finer fraction derived from the same vapor cloud

analysis of foundation deformations beneath the syncrude tailings dyke the paper presents the results obtained in the finite element simulation of 8 years of construction of a section of syncrude s tailings dyke which is located in northern alberta and has been used to store oil sand mining waste the site investigation for the construction of this dyke indicated that a region of the foundation contained a presheared overconsolidated clay shale lying practically horizontal at about 20 m depth significant horizontal displacements have occurred along this layer the section analyzed in this work is the one which showed the largest horizontal movements in the foundation high pore pressures have been measured along this section and the lateral displacements measured in the foundation have reached values over 25 cm the major purposes of the finite element analyses were to identify the factors that have significantly influenced the deformation mechanisms and to determine a combination of parameters within the acceptable range of values for each material that would reproduc