circulation mixing and production of antarctic bottom water abstract the antarctic source of bottom water to the abyssal layer of the world ocean is examined as well as its large scale flow pattern and ultimate entrainment rate into the deep water above we make use of the available high quality station data in the southern ocean to construct bottom maps of neutral density and mean property maps including chlorofluorocarbon cfc for the abyssal layer underneath a selected neutral density surface the maximum density at the sill depth of drake passage is used to distinguish between the voluminous deep water mass that is a continuous component of the antarctic circumpolar current from the relatively denser bottom water originated along the antarctic continental margins based on water density antarctic bottom water aabw is defined here generically to include all volumes of non circumpolar water of antarctic origin over the shelf regime multiple localized sources of specific aabw types contribute to the abyssal layer of the adjacent antarctic basins characteristics of these dense bottom waters reflect closely those observed on the parent shelf water mass spreading paths of newly formed deep and bottom waters over the slope regime and their subsequent oceanic circulation patterns are analyzed on the basis of global property maps for the aabw layer interior mixing and interbasin exchanges of aabw are deduced from mean characteristic curves following the southern streamline of the antarctic circumpolar current outflow and mixing of aabw from the weddell sea to the argentine basin is depicted using density and cfc distributions of two zonal hydrographic lines recirculation and mixing of deep and bottom waters within the weddell gyre are also detailed using a meridional section along the greenwich meridian the strength of all localized sources of aabw combined is estimated by two independent approaches an estimate of the total production rate of aabw is calculated based on the oceanic cfc budget for the aabw layer offshore of the 2500 m isobath the sum of all downslope inputs of well ventilated bottom water types underneath the top isopycnal must account for the measured cfc content in the bottom layer the resulting total aabw production rate is about 8 sv which is a conservative figure that neglects the loss of cfc bearing waters across the top isopycnal in recent years whereas about 9 5 sv is calculated assuming a well mixed bottom layer making use of their transient nature cfc distributions at the top of the aabw layer indicate that more direct and rapid entrainment of cfc rich bottom waters below occurs over localized areas with relatively strong upwelling rates and enhanced vertical mixing a second more ad hoc but independent oceanic mass budget of the bottom layer is also constructed a typical basin wide rate of deep upwelling of 3 10 7 m s 1 requires 10 sv 1 sv 106 m3 s 1 of newly formed aabw to sink down the slope around antarctica we have also formulated a spatial distribution of deep upwelling on the isopycnal at the top of the aabw it is expressed as a combination of wind topographic and turbulent components which in turn are functions of the isopycnal depth bottom depth and bottom layer thickness this non uniform upwelling field yields about 12 sv of aabw exported across the top isopycnal fortuitously the overall average of upward speed at the top isopycnal 3 7 10 7 m s 1 compares well with previous estimates of deep upwelling in the northern basins a series of likely sites for strong vertical entrainment of aabw are clearly identified in the modeled distribution of deep upwelling consonant with the observed cfc distributions on the top isopycnal altogether regions with relatively high upwelling rates 5 10 7 m s 1 occupy only a quarter of the total areal extent of the top isopycnal but they account for as much as 45 of the total vertical transport

assessment of shock effects on amphibole water contents and hydrogen isotope compositions 2 kaersutitic amphibole experiments to constrain the influence of impact shock on water and hydrogen isotope signatures of martian meteorite kaersutites we conducted shock recovery experiments on three terrestrial kaersutite crystals homogeneous impact shock to 32 gpa commensurate with shock levels experienced by martian meteorite kaersutites led to increases in kaersutite water contents h 2o 0 25 0 89 wt decreases in fe 3 fe 4 20 and enrichments in hydrogen isotope composition d 66 to 87 relative to pre shock values the latter values represent the largest shock induced hydrogen isotope fractionations measured to date these observations are explained most completely by a two step shock process first shock induced devolatilization led to hydrogen isotope enrichment through preferential loss of h relative to d second reaction of the kaersutite with the ambient atmosphere led to increased water contents and reduced fe fe reduction and water addition via the reaction fe 2 oh fe 3 o 2 h 2 explain the fe 3 fe data and some of the water data further water addition mechanisms irreversible adsorption shock implantation are necessary to fully explain the increased water contents addition of water from the terrestrial atmosphere which is isotopically light relative to the experimental kaersutite compositions means the measured hydrogen isotope enrichments are likely minima the measured minimum levels of hydrogen isotope enrichment are relevant to the hydrogen isotope variability within and among martian kaersutites but are minor relative to their absolute d values alternatively addition of water from the enriched martian atmosphere could explain both martian kaersutite hydrogen isotope variability and absolute d values however the low martian kaersutite water contents leave little room for significant water addition the importance of the ambient atmosphere to the outcome of the shock experiments makes it difficult to translate our results to mars given the unknown influence of its more tenuous atmosphere on the processes observed in the experiments our results suggest that shock is a feasible mechanism for influencing martian kaersutite water contents and hydrogen isotope compositions but that its complex signature precludes precise determination of that influence

direct observations of the antarctic circumpolar current transport on the northern flank of the kerguelen plateau 1 the standing meander in the antarctic circumpolar current acc found on the northern flank of the kerguelen plateau was investigated during the southern ocean finestructure cruise in november december 2008 an 18 year time series of surface geostrophic currents from satellite altimetry shows that the meander as observed during this survey is typical of the region hydrographic stations were occupied between 65 75 e and 43 48 s on the shelf 200 m depth and slope into the deep ocean to the north of kerguelen 4700 m providing the most detailed survey of this region to date geostrophic shears are referenced to lowered acoustic doppler current profiler velocities to give the first estimate of the total volume transport in this region and the transport budget is closed around the survey box the subtropical front subantarctic front and a northern branch of the polar front together have an associated transport of 174 22 sv eastward while 174 sv is large compared with typical drake passage transports it is reconciled with other estimates of the total transport with the additional 15 sv of the indonesian throughflow baroclinic transport referenced to the deepest common level between station pairs is 119 sv consistent with other estimates of the baroclinic transport in this area at this longitude the fronts of the acc are exceptionally close together we discuss the exchange of properties across the fronts

the antarctic slope current near 30 e the antarctic slope current flows westward above the continental slope of antarctica entering the weddell sea near 30 e and supplying dense water to the deep overturning cell there and contributing to global antarctic bottom water formation observations from the 2008 i6s hydrographic section are used to investigate the strength of the slope current near 30 e a prominent topographic feature the gunnerus bank diverts the slope current upstream of this longitude and has a large effect on the current s structure splitting it into a coastal and offshore component the bank also enhances water mass mixing and lateral exchange across the slope as part of the 2008 occupation an additional line was made along the crest of the bank forming a closed volume over the western side by combining hydrographic and lowered acoustic doppler current profiler measurements in this box using an inverse method the slope current transport is estimated to be 9 6 2 3 sv the transport associated with the antarctic slope front is 4 0 0 3 sv of which 1 8 0 3 sv enters the weddell gyre as recently formed dense water

on the structure and the transport of the eastern weddell gyre abstract the circulation pattern and volume transports in the eastern weddell gyre are estimated on the basis of hydrographic data collected by r v polarstern between 1989 and 1996 in the northeastern edge of the weddell gyre eastward flowing water masses from the antarctic circumpolar current and the weddell sea converge due to the strong effect of topographic constraints on ocean currents in the weakly stratified waters of high latitudes the wedge like structure of the southwest indian ridge can cause the convergence the increased shear leads to instabilities of the current at the eastern end of the ridge which produce an intense mesoscale eddy field between 15 and 30 e in the eddies water from the weddell cold regime and the antarctic circumpolar current waters mix and form the water masses of the weddell warm regime these waters are advected southward and flow towards the westward southern rim current which is driven by the antarctic eastwind band hence there is not a continous flow from the northern to the southern rim but a decay of the mean flow in the northeast and a reformation in the south volume transports across the greenwich meridian estimated on the basis of a combined ctd adcp data set result in an eastward flow of 61 sv in the northern rim current and a westward return flow of 66 sv in the southern part of the gyre the transport is about twice as high as previous estimates between kapp norvegia and the northern tip of the antarctic pensinsula indicating a significant gyre circulation north of 70 s

shock induced devolatilization of calcite the amounts of co 2 and co evolved upon shock compression and decompression of calcite to 18 gpa 180 kbar have been determined using a new gas phase shock recovery technique and gas source mass spectrometry the data demonstrate that from 0 03 to 0 3 mole percent of calcite is devolatilized at shock pressures significantly lower than those predicted 30 gpa for the onset of volatilization by continuum thermodynamic theory and are in qualitative agreement with release adiabat data for calcite and aragonite carbon and oxygen isotope ratios in the shock released co 2 are the same as those in the unshocked hydrothermal calcite demonstrating that the co 2 comes from the calcite rather than other potential sources

a closer look at remanence dominated aeromagnetic anomalies rock magnetic properties and magnetic mineralogy of the russell belt microcline sillimanite gneiss northwest adirondack mountains new york a large distinct negative aeromagnetic anomaly of over 2000 nt associated with microcline sillimanite quartz gneisses in the russell area northwest adirondack mountains was previously shown to be remanence dominated although the carriers of remanence were not well documented russell belt gneisses have a strong natural remanent magnetization with steep remanence directions d 263 i 58 an average intensity of 3 6 a m and typical susceptibilities of 10 4 si the remanence is thermochemical in origin acquired during cooling from peak metamorphic conditions of 650 750 c during the ottawan orogen 1050 1080 ma the reversed polarity of remanence reflects a reversed paleofield rather than self reversed contrary to earlier suggestions the gneisses contain up to 3 oxide predominantly metamorphic titanohematite which accounts for the low susceptibility values and highly stable remanence optical observations show titanohematite grains with multiple generations of ilmenite pyrophanite rutile and spinel exsolution lamellae microprobe analyses confirm titanohematite compositions ranging from 72 to 97 fe2o3 with hematite83 being most typical in rare samples inclusions of magnetite were identified the ubiquitous presence of titanohematite and the rare occurrence of magnetite is supported by thermal and alternating field demagnetization studies saturation magnetization measurements hysteresis properties temperature hysteresis studies and low temperature remanence measurements numerous crustal granulites have titanohematite as part of the oxide assemblage and this may contribute a strong remanent component to what have previously been considered to be solely induced anomalies

magnetization of lower crust and interpretation of regional magnetic anomalies example from lofoten and vesteralen norway the interpretation of regional magnetic anomalies commonly observed over continental crust in both satellite and near surface magnetic data has remained enigmatic in its requirement for laterally extensive thick highly magnetic and deep seated sources presented here are the results of a detailed field analytical and experimental study of the magnetic mineralogy and magnetic properties of rocks from lofoten and vesteralen norway a province of deep seated origin with associated regional magnetic and gravity anomalies these rocks have a bulk magnetic character of surprising uniformity with susceptibilities hysteresis and curie temperatures defined solely by coarse grained magnetite stable remanence is observed in samples from sw lofoten but is not of significant magnitude the thermal enhancement of magnetic susceptibility the hopkinson effect is not important rocks from the deepest part of the section have the largest average susceptibilities 6 10 2 si and magnitudes of natural remanent magnetization nrm 5 10 4 a m2 kg these values of susceptibility together with the oft observed viscous character of the nrm suggest that these granulite facies lithologies particularly those of sw lofoten are perfect examples of lower crustal sources of typical regional magnetic anomalies furthermore these intermediate pressure granulites define a unique magnetic petrology especially for mafic compositions at higher grades of metamorphism high pressure granulites and eclogites or lower grades greenschist and amphibolite facies such magnetite bearing assemblages will be unstable and their high or low grade equivalents will be only weakly magnetic this evidence and these conclusions may be used to constrain models of lower crustal sources of regional magnetic anomalies over stable cratons it portrays the lower crust as a highly magnetic unit defined by metamorphic grade with a curie isotherm of 575 c magnetite and magnetization parallel to the ambient geomagnetic field induced and viscous components

observations of the antarctic circumpolar current over the udintsev fracture zone the narrowest choke point in the southern ocean an up to date map of the antarctic circumpolar current acc fronts is constructed from the latest version of mean dynamic topography mdt from satellite altimetry and reveals the narrowest acc width in the udintsev fracture zone ufz with the strongest concentration of the three major acc fronts within a limited distance as short as 170 km about 40 narrower than that at drake passage at 144 w at the entrance of the ufz which lies between the pacific antarctic ridge par and its eastwardly offset segment offset par segment there is a triple confluence of the subantarctic front polar front and southern acc front downstream of this longitude the subantarctic front progressively meanders northward over the relatively shallow offset par segment before channeling through the eltanin fracture zone thus diverging from the polar front which proceeds through the ufz in situ observations from two recent cruises at 144 w confirm the satellite altimetry derived frontal circulation in the ufz region and yield a baroclinic transport relative to the bottom of 113 10 6 m 3 s comparable to that through drake passage the hydrographic sections show no antarctic bottom water colder than 0 2 c characteristics of major water masses are described and the implications for their potential downstream modifications at drake passage are discussed in terms of the meridional overturning circulation across the acc mesoscale eddy activity with periods shorter than 90 days is predominantly concentrated in the immediate downstream area of the offset par segment suggesting a substantial poleward eddy heat flux there

is there a continuous subtropical front south of africa a 14 3 year series of weekly absolute sea surface height ssh and associated geostrophic velocities is used for a study of the subtropical to subantarctic frontal system in the region south of africa detecting the fronts from surface velocity maxima confirms a two stepped transition in both the southeastern atlantic ocean the northern and southern subtropical fronts nstf sstf and southwestern indian ocean the agulhas front and sstf as proposed previously from hydrographic data an additional front associated with westward flow north of the nstf is indicative of a partial eastern closure of the south atlantic subtropical gyre between 11 e and 17 5 e the role of northwestward propagating agulhas rings in connecting the two fronts explains the varying location the sstf which marks the southern limit of subtropical waters is found continuous from the atlantic to the indian ocean in the time averaged ssh field in the weekly fields however the velocity maximum criterion defining the front is often met at the southern flanks of agulhas rings or agulhas eddies at 12 e 23 e indicating front disruptions such discontinuities suggest that no south atlantic central water is directly advected into the indian ocean instead the eastward limb of the indo atlantic super gyre encompassing the subtropical gyres of both oceans would rest at these longitudes on diffusive processes at the upper levels and possibly be enhanced at depth a schematic diagram of the fronts and their relations to agulhas rings and eddies is proposed

shock induced isotope evolution of hydrogen and carbon in meteorites 1 single and multiple shock recovery experiments on murchison meteorite samples were performed to examine the shock induced isotope behavior of their hydrogen and carbon contents d values of the shocked murchison showed an initial increase from 10 6 to 59 1 before declining to 87 6 o as the dehydrogenation progressed isotope behavior of d can be controlled by dehydrogenation involving extremely large isotope fractionation and is attributed to the composition of organic matter in the murchison on the other hand the behavior of 13 c simply decreased from 5 15 o to 17 65 o and is explainable by decarbonization only the plot of those isotope data collected along devolatilization shows a variation curve that suggests the evolution of those isotopes in the meteorites shock is one of the processes effectively controlling the isotope features of the solar system

shock induced devolatilization and isotopic fractionation of h and c from murchison meteorite some implications for planetary accretion incipient shock induced devolatilization of murchison meteorite occurs upon subjecting samples to a minimum shock stress or pressure of about 5 gpa this pressure is similar to that required to initiate devolatilization of 20 porous serpentine upon low velocity impact 61 5 km s the solid shocked products were combusted and isotopic analysis of the resulting h 2o and co 2 was performed h and 13 c are partitioned preferentially over d and 12 c respectively into the released gas suggesting that the inorganic mineral portion of murchison is devolatilized preferentially over the organic kerogen fraction which is relatively enriched in d and 12 c at the shock pressures studied these results are combined with previous results on serpentine devolatilization to derive an empirical h fractionation versus devolatilization relation that is used to evaluate the extent of impact induced isotopic fractionation during planetary accretion during accretion of the earth impact induced devolatilization and formation of the early primitive atmosphere would have begun at a point where the growing earth achieved a radius in the 480 800 km range the present experimental results suggest that the earth s early atmosphere would have been enriched in hydrogen relative to d compared to the residual solid with a fractionation factor of 18 to 23 assuming that current planetary atmospheres have resulted from degassing of planetary interiors after loss of the earliest h enriched atmosphere the above degree of isotopic fractionation is not sufficient by itself to explain the large positive d values of the present martian and venusian atmospheres however this mechanism in conjunction with tectonic recycling over geologic time could contribute to preferential h loss for earth and mars

coherent seasonal acceleration of the weddell sea boundary current system driven by upstream winds abstract the weddell sea is of global importance in the formation of dense bottom waters associated with sea ice formation and ocean ice sheet interaction occurring on the shelf areas in this context the weddell sea boundary current system bcs presents a major conduit for transporting relatively warm water to the weddell sea ice shelves and for exporting some modified form of wedell sea deep and bottom waters into the open ocean this study investigates the downstream evolution of the structure and the seasonality of the bcs along the weddell sea continental slope combining ocean data collected for the past two decades at three study locations the interannual mean geostrophic flow which follows planetary potential vorticity contours shifts from being surface intensified to bottom intensified along stream the shift occurs due to the densification of water masses and the decreasing surface stress that occurs westward towards the antarctic peninsula a coherent along slope seasonal acceleration of the barotropic flow exists with maximum speed in austral autumn and minimum speed in austral summer the barotropic flow significantly contributes to the seasonal variability in bottom velocity along the tip of the antarctic peninsula our analysis suggests that the winds on the eastern north eastern side of the gyre determines the seasonal acceleration of the barotropic flow in turn they might control the export of weddell sea bottom water on seasonal time scales the processes controlling the baroclinic seasonality of the flow need further investigation

the sources of water in martian meteorites clues from hydrogen isotopes abstract h isotope measurements of carbonate phosphate feldspathic and mafic glasses and post stishovite silica phase in the shergottites zagami shergotty sau 005 dag 476 alha 77005 and eeta 79001 as well as in chassigny and alh 84001 show that all these phases contain deuterium enriched water of extraterrestrial origin the minerals and glasses analyzed may contain an initial primary hydrogen component but their isotopic composition was modified to varying degrees by three different processes interaction with a fractionated exchangeable water reservoir on mars hydrogen devolatilization by impact melting and terrestrial contamination positive correlations between d and water abundance in feldspathic glass and post stishovite silica in zagami shergotty and sau 005 is indicative of mixing of a high d component 3000 4000 and a less abundant low d component 0 the high d component is primarily derived from the martian exchangable reservoir but may also have been influenced by isotopic fractionation associated with shock induced hydrogen loss the low d component is either a terrestrial contaminant or a primary magmatic component the negative correlation between d and water abundances in mafic and feldspathic glasses in alh 84001 alha 77005 and eeta 79001 is consistent with the addition of a low d terrestrial contaminant to a less abundant high deuterium martian component the low d of magmatic glass in melt inclusions suggests that the d of martian parent magma was low and that the initial h isotope signature of mars may be similar to that of earth

a new interpretation of decomposition products of serpentine under shock compression dense hydrous magnesium silicates dhmss may play an important role in water transport during planetary accretion and as water reservoirs in the earth s deep mantle we show that the dynamic decomposition products of antigorite mg3si2o5 oh 4 can be interpreted as containing the newly discovered dense hydrous silicate phase h mgsio4h2 the hugoniot for phase h was calculated based on the hugoniots for its constituent oxides and equation of state data derived from first principles calculations the measured antigorite hugoniot previously suggested to decompose into high pressure phases without generating fluid h 2o was compared with those derived from calculations involving phase h sound velocity data were also compared to confirm that the dynamic breakdown product of antigorite at pressures above 40 gpa is most likely phase h plus mgo without formation of fluid h 2o

what is magnetic in the lower crust long wavelength and satellite magnetic anomalies require that some regions of the earth s crust contain minerals that are magnetic at lower crustal conditions studies of high grade metamorphic rocks emphased multi domain magnetite as a likely source members of the hematite ilmenite series were not considered because hematite commonly has a relatively weak magnetization and though ilmenite compositions in the range ilm 50 70 can be strong ferrimagnets their low curie t 260 c makes them an unlikely source however recent investigations have described hematite ilmenite magnetism and coercivity in terms of a new ferrimagnetic substructure related to interfaces between ilmenite and hematite in exsolution lamellae down to unit cell thickness in this lamellar magnetism ferrimagnetism is coupled to principal af moments of hematite and retains many properties of titanohematite including high coercivity and thermal stability if exsolution lamellae are the source of the magnetism a temperature above that predicted for lamellar resorption should destroy it to look at behaviour of lamellae at mid to lower crustal conditions we selected a hemo ilmenite sample ilm 84 on which detailed studies of microstructures mineral chemistry and magnetic properties had been made we designed experiments at 10 kbar as an analog for lower crustal conditions after initial 5 day runs at 540 685 and 950 c a temperature of 580 c was chosen for 8 and 21 day runs at one atmosphere this t for ilm 84 is above that predicted for complete resorption of all lamellae to produce a homogeneous paramagnetic r3 ilmenite in these experiments exsolution lamellae coarsened if these features were reproduced in the lower crust hemo ilmenite or ilmeno hematite would retain a magnetic moment and higher than expected coercivity due to the microstructures emp and tem analyses were used to understand the compositional differences between the natural sample products of the experiments and one atmosphere phase diagrams if the experimental changes are interpreted as moving the compositions closer to equilibrium at 580 c 10 kbar then a considerable widening of miscibility gaps as a function of pressure and the 20 geikielite component in the ilmenite as well as an increase in neel temperature of hematite is predicted an alternate is to consider the response as ostwald steps short of equilibrium experimental results indicate that exsolution microstructures play a key role in mineral magnetism and that such microstructures as well as coarse hematite may be preserved at pressures and temperatures of the lower crust

solution and shock induced exsolution of argon in vitreous carbon carbon has been shown by several researchers to be the main noble gas carrier in chondritic meteorites to add to our knowledge of noble gas solution and exsolution in carbonaceous material experiments were performed on vitreous carbon a type of amorphous carbon ar rich vitreous carbon samples were prepared under vapor saturated conditions using argon as the pressurizing medium solubility data were obtained for temperatures of 773 to 973k and pressures of 250 to 1500 bars up to 7 wt ar was dissolved in the carbon the solubility data were compared to a thermodynamic model of argon atoms dissolving into a fixed population of holes in the carbon two variations of the model yielded estimates of the enthalpy of solution of ar in vitreous carbon h ar of 4700 cal mole preliminary shock experiments showed that 28 of the total argon was released by driving 4 gpa shocks into the argon rich carbon it was demonstrated that shock induced argon loss is not simply caused by the impact induced diminution of grain size the present value of shock pressure required for partial impact devolatilization of ar from carbon is below the range 5 30 gpa that h 2o is released from phyllosilicates

bottom currents derived from a shipborne adcp on woce cruise a11 in the south atlantic abstract this paper is divided into two parts the first describing an enhancement of the shipborne adcp system and the second describing information about bottom currents that have been obtained therefrom on woce cruise a11 in the south atlantic punta arenas to cape town rrs discovery has been fitted with a gps3df receiver and an array of antennas about its bridge which determine the instantaneous attitude of the ship the heading record from this instrument has been compared with the ship s gyrocompass throughout the 40 day cruise differences have been calculated and examined according to heading speed and movements underway differences are found insensitive to heading except in a southerly sector but on station differences exhibit a sinusoidal dependence on heading with range 3 steaming from a station led to transient behavior with recognizable effects for 1 hour the results are generally consistent with earlier reports and are attributed to gyro error an improved heading measurement has a

nd isotopic constraints on the origin of suspended particles in the atlantic sector of the southern ocean 1 in the nutrient rich southern ocean fe is a vital constituent controlling the growth of phytoplankton despite much effort the origin and transport of fe to the oceans are not well understood in this study we address the issue with geochemical data and nd isotopic compositions of suspended particle samples collected from 1997 to 1999 in the south atlantic sector of the southern ocean al th and rare earth element ree concentrations as well as 143nd 144nd isotopic ratios in acetic acid leached particle samples representing the lithogenic fraction delineate three major sources 1 patagonia and the antarctic peninsula provide material with nd 4 that is transported toward the east with the polar and subpolar front jets 2 the south african shelf although its influence is limited by the circumpolar circulation and wind direction can account for material with nd of 12 to 14 adjacent to south africa and 3 east antarctica provides material with nd of 10 to 15 to the eastern weddell sea and adjacent antarctic circumpolar current for this region we interpret the nd isotopic evidence in combination with oceanographic atmospheric constraints as evidence for supply of significant amounts of terrigenous detritus by icebergs

shock metamorphic features in amphiboles from the xiuyan crater of china amphibole bearing gneiss fragments are common in the impact breccias of the xiuyan crater china three kinds of amphibole bearing gneiss fragments with different shock metamorphic levels have been identified shock metamorphic features of amphiboles in these gneisses were investigated in situ by optical microscope electron microprobe raman spectroscopy and x ray diffraction amphiboles in the weakly shocked gneiss shock pressure less than 10 gpa basically remain intact amphiboles in the moderately shocked gneiss shock pressure range between 35 and 45 gpa show strong deformation reduced optical interference color and partial loss of oh in the strongly shocked gneiss shock pressure above 50 gpa amphiboles are completely melted and dendritic pyroxenes crystallize from the melt the formation of dendritic pyroxenes shows nearly complete loss of water in the amphibole melt at shock induced high temperature above 1 500 c the occurrence of both diopside and pigeonite dendrites crystallized in the same amphibole melt shows inhomogenous melt composition and rapid cooling of the melt

frontal structure water masses and circulation in the crozet basin due to topographic steering by the crozet and kerguelen plateaus the antarctic circumpolar current acc core in the crozet basin area is shifted to its northernmost position in the southern ocean along the southern limb of the south indian subtropical gyre here the jet like current is embedded within a narrow band 26 5 kg m3 in the western half of the basin and heavier mode 26 7 kg m3 in its eastern half these different varieties of crozet basin mode water are closely correlated with the degree of exchange and mixing between subtropical and subantarctic waters along the dynamically active frontal zone the area north of the kerguelen plateau appears to be an important source of water mass modification antarctic intermediate water advected from the west also undergoes there significant modification by intrusions across the frontal zone of fresher oxygen richer colder subantarctic water energetic eddy activities observed along the frontal zone likely enhance such cross frontal exchange of water masses equatorward spreading of the modified thermocline water masses mode water antarctic intermediate water occurs as part of the anticyclonic circulation in the south indian subtropical gyre which is centered within the basin strong injection of north indian deep water into the acc south of amsterdam island is clearly evidenced for the first time this deep oxygen minimum water centered at about 3000 m can be traced to the east of madagascar from where it spreads southward through the eastern part of the crozet basin due to the influence of this water mass north atlantic deep water characteristics of the circumpolar deep water are significantly altered in kerguelen amsterdam passage our results indicate a cyclonic deep level circulation pattern in the crozet basin with a northward flow 9 sv of circumpolar deep water antarctic bottom water as a deep western boundary current and a partially compensating southward flow 3 sv of north indian deep water through the eastern part of the basin it is concluded that the crozet basin constitutes an important passage for the exchange of water masses between the southern ocean and the indian ocean

winter mixed layer entrainment of weddell deep water observations from the somov during the us ussr weddell polynya expedition show that the mixed layer below the sea ice just prior to the austral spring retreat in the 60 s greenwich meridian region has an oxygen content of 7 4 ml 1 this is 86 of full oxygen saturation representing an oxygen deficit relative to full saturation of 1 1 ml 1 the source of this deficit is believed to be a consequence of oxygen poor 4 5 ml 1 weddell deep water wdw entrainment by the winter mixed layer assuming effective cutoff of ocean atmosphere oxygen exchange by the nearly complete snow and sea ice cover with no net impact of oxygen content as a result of biological factors a mixing ratio of 1 3 for wdw to beginning of winter surface water is required to explain the end of winter mixed layer oxygen content accompanying the wdw transfer into the mixed layer is heat transfer of approximately 7 103 cal cm2 2 9 108 j m2 during the five winter months of sea ice coverage as well as salt transfer which requires 34 cm of fresh water to produce typical mixed layer salinity during the seven ice free months when entrainment is expected to be minor diffusive heat and salt flux continues a mean annual heat flux of 12 w m2 is suggested with an annual demand for freshwater of 46 cm yr consideration of the winter period salinity budget indicates net sea ice melting of 20 cm which can be attributed to regional convergence of sea ice the remaining freshwater is derived from excess precipitation and possibly iceberg melt oxygen undersaturation of the winter surface water suggests slightly less potential for abyssal water ventilation than might be expected from a fully saturated condition

impact induced devolatilization and hydrogen isotopic fractionation of serpentine implications for planetary accretion the degree of impact induced devolatilization of nonporous serpentine porous serpentine and deuterium enriched serpentine was investigated using two independent experimental methods the gas recovery method and the solid recovery method yielding consistent results the gas recovery method enables determination of the chemical and hydrogen isotopic composition of the recovered gases experiments on deuterium enriched serpentine unambiguously identify the samples as the source of the recovered gases as opposed to other possible contaminants for shock pressures near incipient devolatilization p initial 5 0 gpa the hydrogen isotopic composition of the evolved gas is similar to that of the starting material for higher shock pressures the bulk evolved gas is significantly lower in deuterium than the starting material there is also significant reduction of h 2o to h 2 in gases recovered at higher shock pressures probably caused by reaction of evolved h 2o with the metal gas recovery fixture the hydrogen isotopic fractionation between the evolved gas and the residual solid indicates nonequilibrium kinetic control of gas solid isotopic ratios in contrast gaseous h 2o h 2 isotopic fractionation suggests high temperature 800 1300 k isotopic equilibrium between the gaseous species indicating initiation of devolatilization at sites of greater than average energy deposition i e shear bands impact induced hydrogen isotopic fractionation of hydrous silicates during accretion can affect the distribution of hydrogen isotopes of planetary bodies during accretion leaving the interiors enriched in deuterium the significance of this process for planetary development depends on the models used for extrapolation of the observed isotopic fractionation to devolatilizations greater than those investigated experimentally and assumptions about timing and rates of protoatmosphere loss frequency of multiple impacts and rates of gas solid or gas melt isotopic re equilibration a simple model indicates that substantial planetary interior enrichments of d h relative to that of the incident material can result from impact induced hydrogen fractionation during accretion

aeromagnetic anomalies magnetic petrology and rock magnetism of hemo ilmenite and magnetite rich cumulate rocks from the sokndal region south rogaland norway aeromagnetic maps of the egersund mid proterozoic igneous province show a spectacular range of positive and negative magnetic anomalies with a contrast up to 15 600 nt the positive magnetic anomalies are over magnetite norites and overlying mangerites and quartz mangerites of the bjerkreim sokndal layered intrusion these rocks are dominated by multi domain md magnetite the negative magnetic anomalies are over ilmenite rich norites of the bjerkreim sokndal layered intrusion the tellnes ilmenite norite ore deposit and massif anorthosites these rocks are dominated by hemo ilmenite and or by silicates containing fine grained oxide exsolution lamellae electron microprobe analyzes of coexisting fe ti oxides in the layered intrusion confirm earlier observations that oxides in early magmatic rocks are dominated by hemo ilmenite with minor end member magnetite followed by more reduced oxides dominated by titanomagnetite with minor near end member ilmenite what is not fully understood is the property of ilmenite with hematite exsolution lamellae or even more striking hematite with ilmenite lamellae to produce strong remanent magnetization of high coercivity and with a neel temperature equal to or above the curie temperature of magnetite this property makes the rhombohedral oxides an important candidate to explain some high amplitude deep crustal anomalies on earth or strong remanent magnetization on other planets a remarkable feature in the egersund province is that primitive magmas produced rocks rich in hemo ilmenite causing negative magnetic anomalies related to magnetic remanence and more evolved magmas produced rocks rich in magnetite related to positive induced magnetic anomalies all in the course of crystallization differentiation

the velocity and vorticity structure of the agulhas current at 32 s the full depth velocity field of the agulhas current the western boundary current of the southwest indian ocean has been directly measured using a lowered acoustic doppler current profiler ladcp fifteen combined conductivity temperature depth ctd and ladcp stations were occupied across the current at 32 s off the east coast of south africa in february march 1995 as part of the world ocean circulation experiment indian ocean program the deep velocity structure of the agulhas current was found to be very different than previously described using geostrophic estimates in particular ladcp results reveal a v shaped pattern for the level of no motion across the agulhas current and an agulhas undercurrent is observed flowing equatorward below 800 m depth directly beneath the surface core of the poleward flowing agulhas current comparisons of direct and geostrophic velocities suggest that the velocity structure of the agulhas current is essentially geostrophic below about 200 m depth where differences are generally less than estimated errors above these depths the ladcp measured shears and geostrophic shears exhibit differences and velocities can diverge shipboard adcp data support ladcp results near the surface indicating that both instruments are measuring real signals the geostrophic and ladcp measured shears are well matched away from the surface and a depth averaged fit below 200 m between them exhibits small standard deviations the geostrophic volume transport of the agulhas current as referenced to ladcp is 73 sv and is just 3 different from the direct ladcp transport estimate the most recent full depth estimate of agulhas current transport in the literature is given by toole and warren 1993 who estimate a geostrophic volume transport of 85 sv the baroclinic velocity structures from their section and from this work are similar indicating that the difference in the transport estimates is due to the choice of geostrophic reference level and ultimately to the presence of the previously unobserved agulhas undercurrent combined ctd ladcp data are very useful for potential vorticity analysis since velocity and density measurements are simultaneous and coincident the vorticity structure of the agulhas current suggests the presence of a mixing boundary at middepths similar to features observed in the gulf stream the feature appears to be associated with a sharp upturn in isopycnals coincident with the foot of the continental slope the boundary inhibits cross stream mixing of intermediate water masses and may help explain the appearance of a discrete filament of red sea water inshore of antarctic intermediate waters in the same density layer despite intense cross stream shears

magnetic properties of exposed deep crustal rocks from the superior province of manitoba abstract a traverse across precambrian rocks of the superior province in central manitoba provided 56 samples for magnetic study from the pikwitonei granulite domain and the adjacent cross lake subprovince these rocks represent a cross section of the continental crust presently exposed at the surface thirty one samples are dominantly paramagnetic and three contain pyrrhotite twenty two samples from silicic plutonic rocks which make up about 80 of the section by volume contain nearly pure magnetite and have susceptibilities that are almost constant between room temperature and 540 c averaging about 1 10 2 si units the mafic supracrustal rocks with much higher iron content are about an order of magnitude less magnetic because they contain little or no magnetite susceptibility is generally independent of metamorphic grade or apparent depth in the crust the discrepancy between induced magnetizations of measured lower crustal rocks and the source requirements of long wavelength magnetic anomalies may be due to a high temperature viscous magnetization in the deep crust

the transport of the weddell gyre across the prime meridian abstract current meter observations from instruments moored from 1996 to 2001 are used to determine the structure and the volume transport of the weddell gyre on the greenwich meridian the record length mean volume transport is 45 sv to the east within the northern and 56 sv to the west within the southern limb of the weddell gyre thus 11 sv must leave the gyre circulation west of the greenwich meridian and enter it east of it the deficit occurs with 8 sv mainly in the circumpolar deep water cdw warm deep water wdw layer surface waters and weddell sea deep water wsdw contribute 2 and 3 sv respectively in contrast to this 3 sv more of weddell sea bottom water wsbw flow in the northern limb to the east than in the southern limb to the west which suggests a wsbw formation rate of about 3 sv in the western weddell sea in the southern boundary of the antarctic circumpolar current acc a volume transport of 35 16 sv was found using geostrophic calculations adjusted with two measurements of the absolute velocity the large heat content of the northern limb points to an extensive heat exchange between the weddell sea and the world ocean west of the prime meridian hence the heat transport as well as the volume transport suggest that the water masses of the weddell gyre are not exclusively replaced in its eastern part but that there is a significant exchange of water masses to the west of the prime meridian

diffusion induced li isotopic fractionation during the cooling of magmatic rocks the case of pyroxene phenocrysts from nakhlite meteorites ion microprobe was used to measure li abundances and isotopic compositions in pyroxenes from three martian meteorites belonging to the nakhlite family the profiles performed across augite crystals from northwest africa 817 show a large isotopic zoning from crystal cores 7li not vert similar 0 to rims 7li not vert similar 20 while li abundances are almost constant not vert similar9 2 g g unlike nwa 817 the pyroxene studied in the miller range 03346 nakhlite shows a zoning in li abundance with concentrations increasing from not vert similar2 5 g g in the core to not vert similar9 g g in the rim the augite rim 7li 7 is slightly enriched in 7li with regard to the core 7li 4 but most of the isotopic variations observed occur at an intermediate position along the profile where 7li falls down to not vert similar 11 in the case of nakhla li concentrations in augite increase from cores not vert similar3 5 g g to rims not vert similar6 5 g g while the 7li variation is restricted i e between 7li 6 0 and 12 6 for the three meteorites the li abundances were also measured in the groundmass which was found to be enriched in lithium not vert similar10 g g conventional magmatic and post magmatic processes such as alteration and fractional crystallization fail to explain the dataset obtained on nakhlites degassing processes which were previously proposed to explain the li distribution in shergottite crystals cannot result in the strong decoupling between li abundances and isotopic composition observed in nakhlites we suggest that the original magmatic li distributions concentrations and isotopic compositions in nakhlites have been modified by diffusion of li from the li rich groundmass towards the pyroxene crystals during sub solidus cooling diffusion appears to have been efficient for nwa 817 and mil 03346 but apparently did not produce a significant migration of li in nakhla possibly because of the lower abundance of groundmass in the latter diffusion induced li redistributions may also affect terrestrial porphyric rocks but very specific cooling rates are required to quench the diffusion profiles as observed in two of the present nakhlites

assessment of shock effects on amphibole water contents and hydrogen isotope compositions 1 amphibolite experiments abstract kaersutitic amphiboles found within a subset of the martian meteorites have low water contents and variably heavy hydrogen isotope compositions in order to assess if impact shock induced devolatilization and hydrogen isotope fractionation were determining factors in these water and isotopic characteristics of the martian kaersutites we conducted impact shock experiments on samples of gore mountain amphibolite in the ames vertical gun range avgr a parallel shock experiment conducted on an anorthosite sample indicated that contamination of shocked samples by the avgr hydrogen propellant was unlikely petrographic study of the experimental amphibolite shock products indicates that only 10 of the shock products experienced levels of damage equivalent to those found in the most highly shocked kaersutite bearing martian meteorites 30 35 gpa ion microprobe studies of highly shocked hornblende from the amphibolite exhibited elevated water contents h 2 o 0 1 wt and enriched hydrogen isotope compositions d 10 relative to unshocked hornblende water and hydrogen isotope analyses of tens of milligrams of unshocked moderately shocked and highly shocked hornblende samples by vacuum extraction uranium reduction and isotope ratio mass spectrometry irms respectively are largely consistent with analyses of single grains from the ion microprobe the mechanisms thought to have produced the excess water in most of the shocked hornblendes are shock induced reduction of hornblende fe and or irreversible adsorption of hydrogen addition of the isotopically enriched martian atmosphere to the martian meteorite kaersutites via these mechanisms could explain their enriched and variable isotopic compositions alternatively regrouping the water extraction and irms analyses on the basis of isotopic composition reveals a small but consistent degree of impact induced devolatilization 0 1 wt h 2 o and h isotope enrichment d 10 extrapolating the shock signature of the regrouped data to grains that experienced martian meteorite like shock pressures suggests that shock induced water losses and hydrogen isotope enrichments could approach 1 wt h 2 o and d 100 respectively if these values are valid then impact shock effects could explain a substantial fraction of the low water contents and variable hydrogen isotope compositions of the martian meteorite kaersutites

the three dimensional overturning circulation of the southern ocean during the woce era a box inverse model of the southern ocean during the world ocean circulation experiment is constructed to investigate the three dimensional structure of the regional overturning circulation in that era the model has many features in common with various preceding inverse studies but also contains several novel elements that make it well suited for addressing many of the significant uncertainties that surround the circulation at present the net overturning circulation of the southern ocean is found to consist of two well defined cells of similar strength the upper cell consists of a northward transport of 18 8 5 5 sv of surface mode and intermediate waters lighter than the 27 5 kg m 3 isoneutral and an equivalent southward flow in the approximate 27 5 27 9 kg m 3 neutral density range encompassing the bulk of the upper circumpolar deep water the lower cell involves the northward export of 18 6 0 9 sv of antarctic bottom water and lower circumpolar deep water denser than 28 08 kg m 3 and an opposing transport in the lighter classes of that water mass substantial structural differences between the overturning circulations of the atlantic indian and pacific basins are indicated by the model s solution overall the diagnosed southern ocean circulation shares many qualitative and some quantitative features with previous inverse estimates particularly as regards the large scale depth integrated lateral circulation and associated energy fluxes in the subtropics and in the antarctic circumpolar current and the strength of the upper overturning cell however it also suggests several significant adjustments to current views of the regional circulation most notable amongst these are the subpolar circulation of the southern ocean is more vigorous and zonally interconnected than generally thought the associated lower overturning cell is more intense than indicated by most preceding estimates contrary to common perception sub surface mixing processes play a role of comparable importance to air sea ice exchanges of buoyancy in underpinning the dianeutral closure of the southern ocean overturning even at shallow mode and intermediate water levels and the connection between north atlantic deep water formation and southern ocean upwelling is fundamentally three dimensional such that deep waters from the north atlantic must upwell dianeutrally before being returned to the permanent pycnocline of the northern oceans

deep inflow into the mozambique basin more than 200 conductivity temperature depth ctd stations were worked around the southwest indian ridge and del cano rise as part of the world ocean circulation experiment a selection of these data provides information about the inflow of bottom water into the mozambique basin the basin is closed below 3000 m yet the inflow is significantly large of order 1 sv 1 sv 106 m3 s 1 estimates of the basin scale upwelling at 4000 m suggest that the vertical velocity is also large 10 10 5 cm s 1 or more an order of magnitude greater than global ocean estimates examination of the characteristics of the bottom water in the mozambique and agulhas basins and the prince edward fracture zone shows that bottom water enters the mozambique basin from the agulhas basin and also directly from the enderby basin most of the transport enters the mozambique basin via the agulhas basin where two regions of northward flow below 4000 m are found the major flow on the eastern flank of the mozambique ridge is through and above the deep extending 5900 m trench that connects the agulhas and mozambique basins the second weaker flow enters the transkei basin along the deep eastern flank of the agulhas plateau then turning east into the mozambique basin the only source of bottom water to the agulhas basin is the enderby basin but a more direct route between the enderby and mozambique basins exists via the prince edward fracture which extends deeper than 4000 m throughout its length and links the two basins directly across the southwest indian ridge full depth ctd stations trace the changing characteristics of the deep and bottom water in the fracture and moored current meter data show the strength and persistence of the throughflow strong mixing with the overlying deep water elevates the salt content of the bottom water by comparison with the other water in the mozambique basin thus two distinct bottom waters of the mozambique basin originate in the same place the enderby basin and their different characteristics are solely a function of the routes they have taken and the processes encountered along the different pathways

impact melt hygrometer for mars the case of shergottite elephant moraine eeta 79001 we report volatile concentrations and hydrogen isotope compositions of impact melts and minerals in eeta 79001 we observed chemical changes in pyroxene maskelynite or feldspathic glass and merrillite in contact with or inside impact melts all pyroxene grains analyzed here are inside or close to impact melt pockets and contain 10 41 ppm h 2o and enriched in d d 1729 to 3707 with the highest values found in a grain enclosed in an impact melt pocket maskelynite or feldspathic glass contains 6 3 to 98 ppm h 2o with d values of 1604 to 3938 the high h 2o and d values were obtained in those enclosed inside or in contact with the impact melts whereas low h 2o content 4 ppm and terrestrial like d h value d of 90 82 were found in one maskelynite grain away from impact melts contains rims of 5 m thickness of merrillite grains next to impact melts display na depletion by 0 9 wt and the sides in contact with impact melts show mg enrichment by 0 5 wt however the h 2o and d values of merrillite interiors 39 242 ppm h 2o and d of 1682 to 3884 do not show correlation with their proximity to the impact melts rather d and 1 h 2o of merrillite form a negative trend different from that of impact melt pockets and maskelynite suggesting post crystallization or late crystallization interactions with the crustal fluids the impact melt pockets in eeta 79001 contain 121 646 ppm h 2o 4 3 13 ppm f 13 50 ppm cl 707 2702 ppm s and the d values of 3368 to 4639 the correlations between h 2o f cl p 2o 5 and d values of impact melts and feldspathic glass are consistent with mixing between a volatile rich and high d 3000 to 5000 endmember and a volatile poor and low d endmember the volatile poor and low d endmember is consistent with magmatic volatiles stored in silicates the volatile rich and high d endmember represents pre impact alteration materials by subsurface water alteration from the subsurface water equilibrated with the present day like martian atmosphere occurred after the crystallization of the rock 170 ma and before impact launch 0 7 ma our conclusion is different from the previous suggestion of an isotopically distinct subsurface water reservoir with a d value of 1000 to 2000 in eeta 79001 although heterogeneous subsurface water on mars is possible the previous study was likely biased by a limited number of analyses n 2 and possible terrestrial contamination the d value of the subsurface source in eeta 79001 is 4200 similar to those in the tissint meteorite crystallization at 600 ma impact launch at 0 7 ma and lar 06319 crystallization at 200 ma impact launch at 3 ma suggesting stable water chemistry for the subsurface environment in the last 600 myrs

fronts transport and weddell gyre at 30 e between africa and antarctica a detailed description of the frontal structure of major currents and estimates of transport between africa and antarctica at 30 e were made on the basis of a finely resolved hydrographic section made during the 1996 civa 2 cruise particular emphasis was put on a refinement of the eastern boundary of the weddell gyre by analyzing also supplementary hydrographic data from the 1993 civa 1 cruise and the best available historical hydrographic data in the weddell and enderby basins contrary to the general belief our results show that the weddell gyre extends far beyond 30 e reaching at least as far east as the enderby land promontory 53 e from this point westward currents along the antarctic continental margin constitute the gyre s southern boundary thus closing the cyclonic circulation of the gyre at its easternmost end as the most convincing evidence for this refined circulation scheme significant westward transport south of 65 s has been identified from the civa 1 acoustic doppler current profiler data we have shown also using an inertial jet model that the blocked feature of the weddell cold regime 57 s to the west of 25 e is due to the topographic control of flow by local bathymetry during the civa 2 cruise 70 of the antarctic circumpolar current acc was concentrated near the polar front 51 s with surface speeds reaching up to 70 cm s 1 the baroclinic current field in the subpolar area south of the weddell front 58 s for civa 2 and 57 s for civa 1 is featureless 3 cm s 1 but yielding a nonnegligible eastward transport of 15 sv 1 sv 106 m3 s 1 this bottom referenced baroclinic transport is entirely compensated by a substantial westward barotropic transport south of 65 s the acc transport across the 30 e section during the civa 2 cruise is estimated to be 160 sv

nanoscale haematite ilmenite lamellae in massive ilmenite rock an example of lamellar magnetism with implications for planetary magnetic anomalies summary massive nearly pure haemo ilmenite layers from historic ore deposits in rogaland norway contain very few silicates or other oxides and typically produce remanence dominated magnetic anomalies these rocks are ideal for evaluating the magnetic properties of fine exsolution intergrowths and the larger titanohaematite lamellae in the host ilmenite grains a typical bulk composition ilm 84 exsolved at high temperature to produce host ilmenite ilm 94 and micron sized haematite lamellae ilm 23 as measured by electron microprobe emp subsequent undercooling of the ilmenite and the micron scale haematite lamellae led to metastable nucleation of nanoscale lamellae down to unit cell scale leaving depleted hosts between lamellae with compositions of ilm 98 and ilm 15 13 as measured by tem edx samples have high coercivities and average nrm values of 25 a m 1 which typically show 2 per cent saturation in the nrm state the amount of magnetization in these samples is too high to be solely accounted for by a spin canted af moment in the haematite based on monte carlo simulations of haematite ilmenite interfaces at the atomic scale and on measured rock magnetic properties we predict that the magnetization is carried by a ferrimagnetic substructure produced at the contacts of the very fine scale titanohaematite and ilmenite exsolution lamellae

shock induced dehydrogenation of polycyclic aromatic hydrocarbons with or without serpentine implications for planetary accretion abstract polycyclic aromatic hydrocarbons pahs were shocked across a peak shock pressure range of 5 8 to 36 6 gpa with or without serpentine and were then evaluated with an elemental analyzer an x ray diffractometer a gas chromatograph and a gas chromatograph mass spectrometer on the basis of the results we examined the shock induced dehydrogenation of pahs and the matrix s effects on it moreover we discussed the hydrogen amounts supplied to the earth s atmosphere and interior during its formation as well as the d values of those amounts we did not find any matrix effects on the dehydrogenation of pahs in the pressure range used in this study the incipient dehydrogenation of pahs occurred at 10 gpa and dehydrogenation was almost completed at 36 5 gpa assuming that carbonaceous chondrites such as the murchison meteorite accreted on and formed the earth they should have started and completed dehydrogenation at a point where the growing earth reached a radius of 1020 km and 3060 km respectively by the end of the accretion most of the hydrogen delivered to the earth had been discharged into the atmosphere the cumulative amount of hydrogen in the earth s interior at that point and its d value were calculated to be 3 3 10 21 kg and 47 respectively these calculated data were comparable to those already established for the earth s interior however to explain the isotopically light juvenile hydrogen d 125 in the deep earth reported by hauri chem geol 183 2002 115 141 we should consider materials that have low d values e g 850 of the presolar nebular as sources of the earth s hydrogen

effects of shock and martian alteration on tissint hydrogen isotope ratios and water content abstract the tissint meteorite a picritic shergottite fell to earth in morocco on the 18th of july 2011 and is only the fifth martian meteorite witnessed to fall hydrogen isotope ratios and water contents are variable within different minerals in tissint ringwoodite and shock melt pockets contain elevated d h ratios relative to terrestrial values d 761 4224 these high ratios in recrystallized phases indicate significant implantation of hydrogen from the d rich martian atmosphere during shock in contrast although olivine has detectable water abundances 230 485 ppm it exhibits much lower d h ratios d 88 to 150 suggesting this water was not implanted from the martian atmosphere the minimal terrestrial weathering experienced by tissint gives confidence that the olivine hosted water has a martian origin but its high concentration indicates direct inheritance from the parental melt is improbable especially given the low pressure of olivine crystallisation incorporation of a low d crustal fluid or deuteric alteration during crystallisation could explain the relatively high water contents and low d h ratios in tissint olivine

the contribution of the weddell gyre to the lower limb of the global overturning circulation the horizontal and vertical circulation of the weddell gyre is diagnosed using a box inverse model constructed with recent hydrographic sections and including mobile sea ice and eddy transports the gyre is found to convey 42 8 sv 1 sv 106 m3 s 1 across the central weddell sea and to intensify to 54 15 sv further offshore this circulation injects 36 13 tw of heat from the antarctic circumpolar current to the gyre and exports 51 23 msv of freshwater including 13 1 msv as sea ice to the mid latitude southern ocean the gyre s overturning circulation has an asymmetric double cell structure in which 13 4 sv of circumpolar deep water cdw and relatively light antarctic bottom water aabw are transformed into upper ocean water masses by mid gyre upwelling at a rate of 2 2 sv and into denser aabw by downwelling focussed at the western boundary 8 2 sv the gyre circulation exhibits a substantial throughflow component by which cdw and aabw enter the gyre from the indian sector undergo ventilation and densification within the gyre and are exported to the south atlantic across the gyre s northern rim the relatively modest net production of aabw in the weddell gyre 6 2 sv suggests that the gyre s prominence in the closure of the lower limb of global oceanic overturning stems largely from the recycling and equatorward export of indian sourced aabw

pressure dependence of fe ti order in the ilmenite hematite solid solution implications for the origin of lower crustal magnetization the view the mathml source to view the mathml source cation ordering phase transition in the ilmenite fetio3 hematite fe2o3 solid solution has been studied at high temperature and pressure using in situ time of flight powder neutron diffraction experiments were performed on a synthetic sample of fetio3 0 65 fe2o3 0 35 at t 933 c and p 1 1 gpa using an internally heated paris edinburgh cell the degree of cation order is observed to increase significantly with pressure thermodynamic analysis reveals an increase in the transition temperature from 911 c at atmospheric pressure to 1010 c at p 0 64 gpa this increase is much larger than that predicted on the basis of the volume change for the transition indicating that the pressure dependence of cation ordering is dominated by enhanced cation cation interaction and not by volume strain we predict an increase in the eutectoid temperature of up to 150 c at 1 gpa this implies that intergrowths of antiferromagnetic hematite and paramagnetic ilmenite could be stable at temperatures up to 540 c at 1 gpa and cannot be ruled out as a potential source of lower crustal magnetization

interannual changes of austral summer coccolithophore assemblages and southward expanse in the southern indian ocean abstract coccolithophore ecology and biogeography in the southern indian ocean was studied during the austral summer of 2009 soe09 late austral summer 2010 soe10 mid austral summer and 2012 isea12 early austral summer during the soe09 and soe10 surface water samples 55 and 54 water samples respectively were collected from two different transects between mauritius and antarctica 48 e 57 3 e whereas during the isea12 22 sea surface water samples were collected between cape town and prydz bay highest coccolithophore diversity was during soe10 36 taxa followed by soe09 and isea12 12 and 7 taxa respectively whereas highest coccolithophore abundance was reported during the isea12 up to 2203 103 coccospheres l followed by soe10 up to 742 103 coccospheres l and soe09 up to 217 103 coccospheres l during each expedition elevated coccolithophore diversity was documented at the subtropical zone whereas the highest abundance was recorded at the subantarctic zone which was dominated by emiliania huxleyi differences in the occurrence and southward expanse of coccolithophores were documented during each expedition i e maximum southward expanse during the soe10 and lowest during the isea12 we show that biogeographic boundaries of coccolithophores are highly variable in the southern indian ocean which is controlled by environmental factors in the early and mid austral summer and grazing pressure in the late austral summer in addition the physical forcing also may play a key role in transport of coccoliths and coccospheres in the high latitudes we indicate that southward expanse of coccolithophores is significant and may occur for short periods during austral summer

magnetic petrology of deep crustal rocks ivrea zone italy magnetic petrology is an extension of petrology integrating magnetic property studies with conventional petrology for the purpose of understanding the development and modification of the magnetization in rocks the magnetic properties of a suite of samples from the ivrea zone northern italy are described with the aim of developing a magnetic petrology for deep crustal rocks samples studied include a variety of metamorphosed mafic granulites granofelses plagioklasfelse amphibolite pyriclasite and pelitic quartzo feldspathic rocks acid granulites stronalite and kinzigite gneisses schists and representative ultramafic rocks phlogopite peridotite pyroxenite hornblendite ilmenite is the chief oxide mineral in a majority of the samples but in a few mafic rocks magnetite is the principal oxide constituent cr al spinel is common in ultramafic samples and rutile is present in some metapelites sulfides are generally subordinate in abundance to oxide minerals the mafic rocks in the ivrea section have the broadest range of magnetic properties and include the most strongly magnetic samples the ivrea ultramafic rocks are moderately magnetic the magnetite present appears to be secondary and is associated with crustal alterations while pelitic and quartzo feldspathic lithologies are dominantly paramagnetic or only weakly magnetic the main ferromagnetic mineral in all strongly magnetic samples is magnetite that is nearly pure fe3o4 in composition consequently curie temperatures are 565 580 c for these rocks pyrrhotite contributes to the magnetism in several ultramafic and mafic rocks and it is the sole ferromagnetic mineral in the pelitic and quartzo feldspathic samples the results of our study indicate that certain mafic rock types amphibolites mafic granulites pyriclasites are the most likely source of the ivrea zone s regional scale magnetic anomalies if the ivrea zone represents a tectonically exposed cross section of continental crust the geographic distribution of these rock types suggests the presence of multiple and variably thick strongly magnetic layers with magnetite curie temperatures in the deep crust petrographic evidence suggests however that the magnetic mineralogy of the sampled ivrea rocks might have been changed subsequent to peak metamorphic conditions therefore considerable care must be taken in evaluating the magnetic record in these crustal cross sections particularly if they are to be used to model the magnetic characteristics of the lower crust

structure and transport of the antarctic circumpolar current and agulhas return current at 40 e hydrographic data are presented from a near meridional section across the agulhas return current the subtropical front and the antarctic circumpolar current acc in the southwest indian sector of the southern ocean the location and characteristics of the fronts are examined and the water masses are defined the agulhas return current emerges as a strong current as far east as 40 e which forms a marked front that is separate from the subtropical front and can be distinguished by a separate water mass comparisons are made with a similar hydrographic section at the greenwich meridian and several notable differences are found the subantarctic front at the greenwich meridian is a pronounced feature carrying a large proportion of the geostrophic transport of the acc on the southwest indian section however the subantarctic front is merged with the polar front at 48 s where the flow associated with the acc is concentrated geostrophic calculations show a large volume transport 84 to 103 sverdrup 1 sv 106 m3 s 1 associated with the agulhas return current at 40 s this is quite separate from the transport of the acc which totals 138 sv south of the subantarctic zone and the crozet plateau or 150 sv including flow in the subantarctic zone the transport of the acc out of the south atlantic sector appears to be higher than the transport into the south atlantic sector at drake passage with the extra transport most probably carried by upper layer and intermediate waters eddies are seen to be an important feature of the subantarctic zone where they help to modify the water masses antarctic intermediate water appears in two forms a saline 34 4 indian ocean variety and a fresh 34 2 atlantic ocean variety the atlantic variety is freshest at the polar front and occupies the southern half of the subantarctic zone within the eddies in the central subantarctic zone there is interleaving between these two forms of antarctic intermediate water north atlantic deep water is unable to cross the southwest indian ridge but can pass south of the crozet plateau in the form of circumpolar deep water which is slightly more saline 34 75 than at drake passage 34 73

effect of fine scale microstructures in titanohematite on the acquisition and stability of natural remanent magnetization in granulite facies metamorphic rocks southwest sweden implications for crustal magnetism mid proterozoic granulites in sw sweden having opaque minerals hematiteilmenite with minor magnetite and occurring in an area with negative aeromagnetic anomalies have strong and stable reversed natural remanent magnetization 9 2 a m with 100 remaining after demagnetization to 100 mt samples were characterized by optical microscopy electron microprobe emp transmission electron microscopy tem and rock magnetic measurements earliest oxide equilibrium was between grains of titanohematite and ferri ilmenite at 650 600 c initial contacts were modified by many exsolution cycles hematite and ilmenite ilm hosts and lamellae by emp are ilm 24 25 ilm 88 93 like titanohematite and ilmenite above 520 c on burton s diagram 1991 finer hosts and lamellae by tem are ilm16 3 and ilm 88 4 like coexisting antiferromagnetically ordered af hematite and ilmenite below 520 c on burton s diagram this may be the first example of analytical identification in one sample of former hematite now finely exsolved and af hematite tem microstructures consist of gently curving semicoherent ilmenite lamellae within hematite flanked by precipitate free zones and abundant ilmenite disks down to unit cell scale 1 2 nm strain contrast of disks suggests full coherence with the host and probable formation at the reaction titanohematite af hematite ilmenite at 520 c magnetic properties are a consequence of chemical and magnetic evolution of hematite and ilmenite with bulk compositions ilmenite richer than ilm 28 that apparently exsolved without becoming magnetized down to 520 c where hematite broke down to af hematite plus ilmenite producing abundant af hematite below its neel temperature intensity of magnetization is greater than possible with hematite alone and tem work suggests that ultrafine ilmenite disks in af hematite are associated with a ferrimagnetic moment due to local imbalance of up and down spins at coherent interfaces

determination of magnetic properties of rocks by analysis of demagnetization curves hematite ilmenite bearing rocks from sw sweden granulites from the high grade sveconorwegian corresponding to grenvillian gneiss terrane of sw sweden were investigated in order to relate magnetic properties to the granulite facies mineralogy and the amphibolite facies retrograde mineralogy we used standard paleomagnetic techniques susceptibility measurements electron and optical microscopy and a new way to analyze demagnetization curves based on vector difference sums the new technique allowed quantitation of the relative contributions of partial natural remanent magnetization nrm components as well as numerical extraction of thermal and coercive force alternating field af unblocking data two major components were identified one stable which is carried by hematite ilmenite and one less stable carried by multidomain md magnetite the age of the hematite ilmenite component is circa 930 ma and it has steep negative inclination coercivities in excess of 150 mt and unblocking temperatures between 540 degrees c and 640 degrees c two corresponding poles are reported 1 paleolatitude paleolongitude plat plong 218 degrees 24 3 with dp dm 9 4 degrees 9 9 degrees paleopole and 2 plat plong 203 degrees 51 degrees with d p d m 4 4 degrees 5 6 degrees vgp the md magnetite component is a recent or cretaceous paleogene steeply positive inclined nrm component associated with strong induced magnetization plat plong 2 degrees 74 degrees and d p d m 11 degrees 14 degrees vgp the md magnetite was unblocked at conditions of 6 40 mt and 60 400 degrees c our new analysis method was successful in showing that retrograde amphibole formation strongly decreases the importance of the hematite ilmenite component on behalf of the md magnetite it has a diminishing effect on a negative aeromagnetic anomaly in the area the 930 ma components constitute 80 0 of the vector difference sums depending on rock composition however as this fraction goes down to 60 the induced magnetization seems to outweigh the hematite ilmenite influence on aeromagnetic anomalies due to its opposite direction these rocks still have a strong and stable hematite ilmenite dominated nrm less

thermohaline stratification below the southern ocean sea ice the end of winter stratification within the cold cyclonic trough of the weddell gyre near 60 s between 5 e and the greenwich meridian is resolved with the mikhail somov data set the temperature maximum of the weddell deep water wdw is for the most part less than 0 5 c but warmer cells of wdw are found these warm wdw cells have temperature salinity and oxygen properties similar to the wdw characteristic of the weddell gyre inflow which is situated to the southeast of the mikhail somov study region the warm wdw cells are accompanied by domes in the pycnocline of 40 m amplitude over the surrounding pycnocline while deeper isopycnals are depressed anticyclonic shear below the 27 83 isopycnal within the warm wdw cells is compensated by the cyclonic shear associated with the pycnocline dome the pycnocline domes are exposed to about 50 greater entrainment by the turbulently active winter mixed layer relative to the regional entrainment rate this entrainment can significantly erode the warm cells in a single winter season introducing excess heat and salt into the mixed layer while the heat is lost to the atmosphere the excess salt is not necessarily compensated by increased fresh water introduction it is hypothesized that the warm wdw cells within the weddell gyre trough are derived from instability within the frontal zone which extends from maud rise to the northeast separating the weddell warm regime from the cold regime greater than normal injection of warm wdw cells into the weddell gyre trough would increase the surface salinity which would tend to destabilize the pycnocline increasing the probability of deep convection and polynya events

magnetism at depth a view from an ancient continental subduction and collision zone recent sophisticated global data compilations and magnetic surveys have been used to investigate the nature of magnetization in the lower crust and upper mantle two approaches to constraining magnetizations are developed providing minimum 0 01 si and maximum 0 04 si susceptibility estimates given some assumed thickness 15 km here these values are higher than are found in many continental rocks are there rocks deeper in the crust or upper mantle that are more magnetic than expected or are the model assumptions incomplete what is the magnetic behavior of deep crustal and upper mantle rocks when slightly cooler than the curie or neel temperatures of their magnetic minerals after being exhumed from locations of high grade metamorphism at greater depth different sets of equilibrium metamorphic minerals can be considered that would form under different conditions results on 1501 samples from the western gneiss region wgr norway mainly from mafic and ultramafic bodies subducted to depths of 60 200 km and temperatures of 750 up to 950 c at the very highest pressures show that rocks did not fully equilibrate to the dominant metamorphic facies conditions there is a large variation in petrophysical properties oxide minerals and mineral assemblages in wgr samples though they cannot explain the broad high amplitude deep seated anomalies measured in this region the presence of magnetite and exsolved titanohematite and hemo ilmenite in samples shows those magnetic phases are preserved even at eclogite facies conditions in part because complete eclogite facies equilibrium was rarely achieved

shock induced volatile loss from a carbonaceous chondrite implications for planetary accretion solid recovery impact induced volatile loss experiments on the murchison c2m meteorite indicate that for an impact of a given velocity h 2o and total volatiles are driven from the sample in the same proportion as present initially we infer that the volatiles other than h 2o driven from the meteorite also have the same bulk composition as those of the starting material thus the early bulk composition of an impact induced atmosphere of a planet growing by accretion from material like murchison would be the same as the volatile composition of the incident planetesimals incipient devolatilization of murchison occurs at an initial shock pressure of about 11 gpa and complete devolatilization occurs at a pressure of about 30 gpa if an earth sized planet were formed from the infall of planetesimals of murchison composition incipient and complete devolatilization of accreting planetesimals would occur when the planet reached approximately 12 and 27 respectively of its final radius thus impact induced devolatilization of accreting planetesimals and of the hydrated surface would profoundly affect the distribution of volatiles within the accreting planet for example for a cold homogeneous accretion of a planet prior to metallic core formation and internal differentiation the growing planet would have a very small core with the same volatile content as the incident material a volatile depleted mantle and an extremely volatile rich surface

magnetization of exsolution intergrowths of hematite and ilmenite mineral chemistry phase relations and magnetic properties of hemo ilmenite ores with micron to nanometer scale lamellae from allard lake quebec hemo ilmenite ores from allard lake quebec were first studied over 50 years ago interest was renewed in these coarsely exsolved oxides based on the theory of lamellar magnetism as an explanation for the high and stable natural remanent magnetizations nrms 32 to 120 a m reported here to understand the magnetism and evolution of the exsolution lamellae the microstructures and nanostructures were studied using scanning electron microscopy and transmission electron microscopy tem phase chemistry and relations between mineral chemistry and the hematite ilmenite phase diagram cycles of exsolution during slow cooling resulted in lamellae down to 1 2 nm thick combined electron microprobe tem and x ray diffraction xrd results indicate that hematite hosts reached a composition approximately ilmenite ilm 14 4 and ilmenite hosts ilm 98 the bulk of the very stable nrm which shows thermal unblocking 595 620 c was acquired during final exsolution in the two phase region canted antiferromagnetic r3c hematite r3 ilmenite hysteresis measurements show a very strong anisotropy with a stronger coercivity normal to than parallel to the basal plane orientation of the lamellae magnetic saturation m s values are up to 914 a m compared to 564 a m predicted for a modally equivalent spin canted hematite corrected for 15 r 2 tio 3 substitution low temperature hysteresis ac susceptibility measurements and mossbauer results indicate a neel temperature t n of the geikielite substituted ilmenite at 43 k the low temperature hysteresis and ac susceptibility measurements also show a cluster spin glass like transition near 20 k below t n of ilmenite an exchange bias occurs with a 40 mt shift at 10 k

shock wave equation of state of serpentine to 150 gpa implications for the occurrence of water in the earth s lower mantle the shock equation of state of serpentine has been determined to 150 gpa four distinct regions occur along the hugoniot a low pressure phase a mixed phase region a high pressure phase and a very high pressure phase the low pressure phase lpp exists under shock pressures to about 40 gpa this material exhibits shock properties that are partially consistent with those of low pressure serpentine but steep release paths and a low value of k 2 77 suggest transformation to another possibly amorphous assemblage thermodynamic calculations indicate that under equilibrium conditions serpentine would decompose to oxides plus water at conditions below 10 gpa along the hugoniot a mixed phase region begins at 40 gpa with complete transition to a high pressure phase occurring by about 55 gpa the high pressure phase hpp occurs at shock pressures between 55 gpa and 125 gpa model hugoniots based on perovskite plus periclase plus water and brucite plus periclase plus stishovite reproduce the serpentine hpp hugoniot within experimental error so definitive identification of the hpp as a distinct hydrous mineral phase or as a free water containing mixture is not possible above 125 gpa a transition to a very compressible phase possibly a hydrous partial melt occurs the serpentine hpp hugoniot is about 15 20 less dense than the earth s lower mantle models of the lower mantle based on shock equations of state for olivine pyroxene and serpentine indicate that for an atomic mg mg fe ratio of 0 80 the presence of 2 wt h 2o is consistent with seismically determined lower mantle density estimates greater amounts of h 2o can be accommodated if accompanied by an increase in fe content calculated hugoniot sound speeds of the serpentine hpp although poorly constrained are broadly consistent with lower mantle sound speeds thus the high pressure density and sound speed of an h 2o rich magnesium silicate determined from shock equation of state experiments indicate that the observed seismic properties of the lower mantle allow the existence of several weight percent of water in the lower mantle

nature and origin of lamellar magnetism in the hematite ilmenite series grains consisting of finely exsolved members of the hematite ilmenite solid solution series such as are present in some slowly cooled middle proterozoic igneous and metamorphic rocks impart unusually strong and stable remanent magnetization tem analysis shows multiple generations of ilmenite and hematite exsolution lamellae with lamellar widths ranging from millimeters to nanometers rock magnetic experiments suggest remanence is thermally locked to the antiferromagnetism of the hematite component of the intergrowths yet is stronger than can be explained by canted antiferromagnetic caf hematite or coexisting paramagnetic pm fe ti ordered r 3 ilmenite alone in alternating field demagnetization to 100 mt many samples lose little remanence indicating that the nrm is stable over billions of years this feature has implications for understanding magnetism of deep rocks on earth or on planets like mars that no longer have a magnetic field atomic scale simulations of an r 3 ilmenite lamella in a caf hematite host based on empirical cation cation and spin spin pair interaction parameters show that contacts of the lamella are occupied by contact layers with a hybrid composition of fe ions intermediate between fe2 rich layers in ilmenite and fe3 rich layers in hematite structural configurations dictate that each lamella has two contact layers magnetically in phase with each other and out of phase with the magnetic moment of an odd non self canceling fe3 rich layer in the hematite host the two contact layers and the odd hematite layer form a magnetic substructure with opposite but unequal magnetic moments a lamellar ferrimagnetism made possible by the exsolution because it is confined to magnetic interaction involving the moments of just three ionic layers associated with each individual exsolution lamella lamellar magnetism is unique and quite distinct from conventional ferrimagnetism simulation cells indicate that the magnetic moments of contact layers are locked to the magnetic moments of adjacent af hematite layers and are parallel to the basal plane 001 thus lamellar magnetism is created at the temperature of chemical exsolution and is a chemical remanent rather than thermal remanent magnetization however in thermal demagnetization experiments too short for lamellar resorption demagnetization temperatures are those of the caf hematite considerably higher than temperatures of original lamellae formation internal crystal structure cannot dictate that the contact layers of different lamellae will form magnetically in phase with each other to give the highest net magnetic moment but magnetic moments of lamellae can be made to form in phase by the external force of the magnetizing field at the time of exsolution a thesis of this paper is that an external magnetic field can dictate the magnetic moments and hence the chemical location of ilmenite lamellae in a hematite host and that once in place neither the location nor the magnetic moment will be easily disturbed in an ilmenite host the external magnetic field cannot control the chemical location of a hematite lamella which is dictated by the enclosing ilmenite but once lamellae have formed the field can dictate their magnetic moments these moments however are not locked chemically to the host resulting in lower coercivity the effectiveness of the external force in single crystals is dictated by their orientation with respect to the magnetizing field in grains with 001 oriented parallel to the field it would be effective in producing in phase magnetic moments and very strong remanence in grains with 001 normal to the field the field would be less effective in producing in phase magnetic moments hence producing weak remanence the most intense lamellar magnetism per formula unit occurs with in phase magnetization high lamellar yields and the largest number of lamellae per unit volume i e smallest lamellar size compared to the magnetic moment per formula unit m pfu and magnetic moment per unit volume m v of end member magnetite m pfu 4 b m v 480 ka m and hematite m pfu 0 0115 b m v 2 1 ka m results for some atomic models reasonably tied to natural conditions are m pfu 0 46 1 36 b and m v 84 250 ka m

the circulation and water masses of the antarctic shelf and continental slope between 30 and 80 e abstract the circulation and water masses from the antarctic continental shelf to 62 s between 30 and 80 e are described using hydrographic data collected on seven hydrographic sections during the baseline research on oceanography krill and the environment west broke west experiment the eastern limb of the weddell gyre dominates circulation between 30 and 40 e and is significantly cooler and fresher than the region to the east the antarctic circumpolar current acc extends from the north into the survey region east of 40 e reaching as far south as 65 5 s at 60 e this results in increasing observed maximum temperature and salinities progressively towards the east peaking at 80 e due to the intrusion of the southern acc front saccf to 63 s this southward extension is steered by the southern end of kerguelen plateau causing a horizontal shear of over 0 15 m s 1 between the eastward acc and westward flowing antarctic slope current asc the asc is observed at all six meridional sections immediately north of the shelf break it is strongly barotropic and transports a total of 15 8 7 4 sv westwards while the bottom referenced baroclinic component only contributes 1 3 0 3 sv at each section this current intensifies to a narrow westward jet with absolute velocities up to 0 3 m s 1 over the steepest shelf slope gradients at 70 e a v shape is observed in the asf this and the nearby presence of denser shelf water and ice shelf water is characteristic of antarctic bottom water aabw formation but no new aabw is found on this section instead significantly warmer saltier and less oxygenated aabw to the east and newly formed aabw high on the continental slope immediately to the west suggest a formation region just west of 70 e this newly formed aabw progressively becomes warmer and saltier west of 60 e and is observed extending offshore and moving westward below eastward flowing water masses acc frontal positions are found to be 1 2 farther north in the survey region than suggested by historical climatology

on the origins of deep and bottom waters of the indian ocean the characteristics of the deep and bottom waters of the indian ocean when illustrated on potential density anomaly surfaces indicate that the waters enter from both the atlantic and pacific oceans the paths of spreading are constrained by the complex topography and characteristics are seen to be altered by exchange with the overlying and underlying water and with the sediments especially in the northern indian ocean the weddell sea contributes to the densest waters found in the western basins and the ross sea and adelie coast to the densest waters found in the eastern basins both dense water varieties are altered by and incorporated in the less dense water above initially water carried by the circumpolar current then water from the north atlantic and finally by deep water whose characteristics are derived in the northern indian ocean contact with the sediments increases the silica content of the bottom water in the southern ocean in the northern indian ocean the sediments alter the silica of the water at the bottom and together with enhanced salinity from diffusion of saline overflows from the marginal seas above imprint unique markers to the deep water that flows back to the south at middepths the series of ridges between madagascar and australia confine the flow to a series of gyres that carry characteristics from the circumpolar current equatorward and the northern indian ocean characteristics southward within the circumpolar current low oxygen deep water from the pacific is carried across the atlantic and into the indian ocean south of africa part flows around the cyclonic weddell sea gyre and part extends across the southern ocean water from another pacific source can be seen near 2000 m extending westward from the tasman sea south of aus tralia and across the indian ocean and perhaps to the aghulas current region southeast of africa in this study we show some maps of deep and bottom water characteristics of the indian ocean which may be used in a qualitative sense to infer pathways of spreading of water below a depth of about 2000 m the indian ocean has numerous ridges and basins figure 1 that severely restrict possible pathways of deep and bottom wa ter flow in the following we will begin by looking at char acteristics at the bottom of the ocean to reveal the path ways of spreading of the densest bottom waters from basin to basin then a series of six potential density anomaly surfaces at progressively shallower depths from about 4000 m up to about 2000 m will be shown to see what character istics influence the deep waters and how pathways of flow are constrained by the bathymetry of the indian ocean the choice of the specific density levels table 1 was based primarily on various property extrema shown by the 18os atlantis ii cruise 93 colored sections that accompany warren s 1981 detailed discussion of the major features of the central indian ocean between madagascar and aus tralia the sections approximately midway between antarctica and the northern indian ocean boundaries are well positioned to show features originating from both the north and the south as well as some brought into the indi an ocean by the antarctic circumpolar current the full ocean area isopycnal maps provide essential evidence on the origins and fates of features seen in the sections and

actinium 227 as a deep sea tracer sources distribution and applications abstractactinium is one of the rarest naturally occurring elements on earth we measured its longest lived isotope 227ac half life 21 77 years for the first time in the water column of the southeast pacific the central arctic the antarctic circumpolar current acc and the weddell gyre besides the profile in the southeast pacific which confirms earlier findings about the role of diapycnal mixing for 227ac distribution we found three other different types of vertical profiles these profiles point to a prominent role of advection for 227ac distribution especially in the southern ocean depending on the type of profile found 227ac is proposed as a tracer for different oceanographic questions in the southern ocean up to 4 93 0 32 dpm m 3 227acex 227ac in excess of its progenitor 231pa are found close to the sea floor which are the highest concentrations ever observed in the ocean close to the sea surface in the weddell gyre wg 0 46 0 05 dpm m 3 227acex are detected we use 227acex there to determine the upwelling velocity in the eastern weddell gyre to be about 55 m y 1 in the acc upper and lower circumpolar deep water ucdw and lcdw are found to differ clearly in their 227acex activity high 227acex activities are therefore a promising tracer for recent inputs of lcdw to the sea surface which may help to understand the role of deep upwelling for iron inputs into antarctic surface waters the expected release of 227ac is compared with 228ra to make sure that the large near surface excess in the water column of the southern ocean is not due to lateral inputs by isopycnal mixing results of a model indicate that the 227ac 228ra flux ratio is about 50 times lower on shelves than in the deep sea data from the central arctic and from a transect across the acc confirm that 228ra and 227acex differ strongly in their sources the first measurements of 227ac on suspended matter less than 1 7 of total 227ac close to the sea floor indicate that the particle reactivity of 227ac is negligible in the open ocean in agreement with earlier findings nozaki 1984 despite the extremely low concentrations of 227ac new measurement techniques moore and arnold 1996 point to a comfortable and comparably simple determination of 227ac in the future finally 227acex may become a widely used deep sea specific tracer

dynamic compression and volatile release of carbonates particle velocity profiles upon shock compression and adiabatic release were measured for polycrystalline calcite solenhofen limestone to 12 24 gpa and for porous calcite dover chalk o 1 40 g cm 3 49 porosity to between 5 and 11 gpa the electromagnetic particle velocity gauge method was used upon shock compression of solenhofen limestone the hugoniot elastic limit was determined to vary from 0 36 to 0 45 gpa transition shocks at between 2 5 and 3 7 gpa possibly arising from the calcite ii iii transition were observed for the solenhofen limestone the release paths lie relatively close to the hugoniot evidence for the occurrence of the calcite iii ii transition upon release was observed but no rarefaction shocks were detected initial release wave speeds suggest retention of shear strength up to at least 20 gpa with a possible loss of shear strength at higher pressures the measured equation of state is used to predict the fraction of material devolatilized upon adiabatic release as a function of shock pressure the effect of ambient partial pressure of co 2 on the calculations is demonstrated p co 2 should be taken into account in models of atmospheric evolution by means of impact induced mineral devolatilization mass fractions of co 2 released expected on the basis of a continuum model are much lower than determined experimentally this discrepancy and radiative characteristics of shocked calcite indicate that localization of thermal energy shear banding occurs under shock compression even though no solid solid transitions occur in this pressure range release adiabatic data indicate that dover chalk loses its shear strength when shocked to 10 gpa pressure at 5 gpa the present data are ambiguous regarding shear strength for dover chalk continuum shock entropy calculations result in a minimum estimate of 90 devolatilization upon complete release from 10 gpa for calcite isentropic release paths from calculated continuum hugoniot temperatures cross into the cao solid co 2 vapor field at improbably low pressures for example 10 gpa for a shock pressure of 25 gpa however calculated isentropic release paths originating from pt points corresponding to previous color temperature under shock measurements cross into the melt plus vapor field at pressures greater than 0 5 gpa suggesting that devolatilization is initiated at the shear banding sites