rutile u pb age depth profiling a continuous record of lithospheric thermal evolution abstract understanding of the thermal and geophysical evolution of the lower continental crust is limited by the resolution of conventional thermochronology intracrystalline daughter nuclide distribution profiles preserve a rich and underutilized record of thermal history using laser ablation inductively coupled plasma mass spectrometry we outline here a method to simultaneously acquire 206 pb 238 u age and trace element profiles from u bearing accessory phases inversion of 206 pb 238 u age depth profiles yields thermal history information from an extended temperature range compared to inversion of age versus grain size relationships thermally activated volume diffusion of pb and zr in rutile is sensitive to the thermal evolution of the mid to lower lithosphere we document the ability of laser ablation depth profiling to simultaneously resolve 206 pb 238 u age and zr diffusion profiles in the outer 35 m of lower crustal rutile euhedra from the ivrea zone southern alps with 1 2 m depth resolution inversion of the age profiles reveals a continuous cooling history characterized by initially rapid cooling from 600 c at 180 ma followed by a period of slower cooling from 525 c to 450 c combined with the topology of zr diffusion profiles these data indicate that the ivrea zone underwent a brief thermal pulse in the early jurassic plausibly associated with hyperextension of the adriatic margin inversion of near surface 206 pb 238 u age distributions can be employed to resolve otherwise inaccessible thermal history information from the lower lithosphere

tectonic and metasomatic mixing in a high t subduction zone melange insights into the geochemical evolution of the slab mantle interface abstract the catalina schist california contains an amphibolite grade 0 8 1 1 gpa 640 750 c melange unit consisting of mafic and ultramafic blocks in high mg schistose melange matrix with varying modal proportions of talc chlorite anthophyllite calcic amphibole enstatite and minor phases including zircon rutile apatite spinel and fe ni sulfides this melange unit is interpreted as a kilometer scale zone of tectonic and metasomatic mixing formed within a juvenile subduction zone the study of which may yield insight into chemical mixing processes at greater depths in subduction zones relationships among the major and trace element compositions of the mafic and ultramafic blocks in the melange the rinds developed at the margins of these blocks and the surrounding melange matrix are compatible with the evolution of the melange matrix through a complex combination of infiltrative and diffusional metasomatism and a process resembling mechanical mixing simple linear mixing models are compatible with the development of the melange matrix primarily through simple mixture of the ultramafic and mafic rocks with cr al ratios serving as indicators of the approximate proportions of the two lithologies this conclusion regarding mafic ultramafic mixing is consistent with the field observations and chemical trends indicating strong resemblance of large parts of the melange matrix with rinds developed at the margins of mafic and ultramafic blocks the overall process involved development of metasomatic assemblages through complex fluid mediated mixing of the blocks and matrix concurrent with deformation of these relatively weak rind materials which are rich in layer silicates and amphibole this deformation was sufficiently intense to transpose fabrics progressively disaggregate more rigid block derived materials in weaker chorite and talc rich melange and in some particularly weak lithologies e g chlorite talc and amphibole rich materials intimately juxtapose adjacent lithologies at the sub cm scale approaching grain scale sampled by the whole rock geochemical analyses chemical systematics of various elements in the melange matrix can be delineated based on the cr al based mixing model simple mixing relationships exhibited by al cr mg ni fe and zr provide a geochemical reference frame for considerations of mass and volume loss and gain within the melange matrix the compositional patterns of many other elements are explained by either redistribution local stripping or enrichment at varying scales within the melange ca na k ba and sr or massive addition from external sources si and h2o the latter probably in infiltrating h2o rich fluids that produced the dramatic o and h isotopic shifts in the melange melange formation resulting in the production of high variance ultramafic assemblages with high volatile contents may aid retention of volatiles in this case h2o to greater depths in subduction zones than in original subducted mafic and sedimentary materials the presence of such assemblages i e containing minerals such as talc chlorite and mg rich amphiboles would impact the rheology of the slab mantle interface and perhaps contribute to the low velocity seismic structure observed at near the slab mantle interface in some subduction zones if operative along the slab mantle interface complex mixing processes such as these involving the interplay between fluid mediated metasomatism and deformation also could impact slab incompatible trace element and isotopic signatures ultimately observed in arc magmas producing fluids with geochemical signatures inherited from interactions with hybridized rock compositions

environmental signals in a highly resolved ice core from james ross island antarctica 1 the accumulation isotopic and chemical signals of an ice core from james ross island antarctica are investigated for the interval from 1967 to 2008 over this interval comparison with station satellite and reanalysis data allows for a detailed assessment of the environmental information preserved in the ice accumulation at james ross island is enhanced during years when the circumpolar westerlies are weak allowing more precipitation events to reach the northeastern antarctic peninsula the stable water isotope composition of the ice core has an interannual temperature dependence consistent with the spatial isotope temperature gradient across antarctica and preserves information about both summer and winter temperature variability in the region sea salts in the ice core are derived from open water sources in the marginal sea ice zone to the north of james ross island and transported to the site by strengthened northerly and westerly winds in the winter a strong covariance with temperature means that the sea salt record may be able to be utilized in conjunction with the isotope signal as an indicator of winter temperature marine biogenic compounds in the ice core are derived from summer productivity within the sea ice zone to the south of james ross island this source region may have become significant only in recent decades when the collapse of nearby ice shelves established new sites of open water with high summer productivity these findings provide a foundation for interpreting the environmental signals in the james ross island ice core which extends though the whole holocene and represents the oldest ice core that has been recovered from the antarctic peninsula region

petrology of amphibolite facies mafic and ultramafic rocks from the catalina schist southern california metasomatism and migmatization in a subduction zone metamorphic setting the catalina schist of southern california is a subduction zone metamorphic terrane it consists of three tectonic units of amphibolite high p greenschist and blueschist facies rocks that are structurally juxtaposed across faults forming an apparent inverted metamorphic gradient migmatitic and non migmatitic metabasite blocks surrounded by a meta ultramafic matrix comprise the upper part of the catalina amphibolite unit fluid rock interaction at high p high t conditions caused partial melting of migmatitic blocks metasomatic exchange between metabasite blocks and ultramafic rocks infiltration of silica into ultramafic rocks and loss of an albitic component from nonmigmatitic clinopyroxene bearing metabasite blocks partial melting took place at an estimated p 8 11 kbar and t 640 750 c at high h2o activity the melting reaction probably involved plagioclase quartz trondhjemitic melts were produced and are preserved as leucocratic regions in migmatitic blocks and as pegmatitic dikes that cut ultramafic rocks the metasomatic and melting processes reflected in these rocks could be analogous to those proposed for fluid and melt transfer of components from a subducting slab to the mantle wedge aqueous fluids rather than melts seem to have accomplished the bulk of mass transfer within the mafic and ultramafic complex

hemispheric atmospheric variations and oceanographic impacts associated with katabatic surges across the ross ice shelf antarctica numerical simulations and surface based observations show that katabatic winds persistently converge toward and blow across the siple coast part of west antarctica onto the ross ice shelf about 14 of the time during winter april to august 1988 thermal infrared satellite images reveal the horizontal propagation of this negatively buoyant katabatic airstream for about 1000 km across the ice shelf to its northwestern edge a trajectory that nearly parallels the transantarctic mountains this takes place when the pressure field supports such airflow and is caused by synoptic scale cyclones that decay near and or over marie byrd land the northwestward propagation of the katabatic winds is accompanied by other changes in the hemispheric long wave pattern an upper level ridge develops over wilkes land resulting in an enhancement of the split jet in the pacific ocean then more frequent and or intensified synoptic scale cyclones are steered toward marie byrd land where they become nearly stationary to the northeast of the climatological location the resulting isobaric configuration accelerates the katabatic winds crossing siple coast and supports their horizontal propagation across the ross ice shelf an immediate impact of this katabatic airflow that crosses from the ice shelf to the ross sea is expansion of the persistent polynya that is present just to the east of ross island this polynya is a conspicuous feature on passive microwave images of antarctic sea ice and plays a central role in the salt budget of water masses over the ross sea continental shelf the impact of this katabatic airflow upon mesoscale cyclogenesis over the south pacific ocean is also discussed

interpreting zirconium in rutile thermometric results at first sight experimental results and observations on rocks suggest that the zr content in rutile where equilibrated with quartz and zircon should be a useful thermometer for metamorphic rocks however diffusion data for zr in rutile imply that thermometry should not for plausible rates of cooling give the high temperatures commonly observed in high grade metamorphic rocks it is suggested here that such observations can be accounted for by high t diffusive closure of si in rutile causing the interior of rutile grains to become insensitive to the thermometer equilibrium well above the temperature of zr diffusive closure paired with comparatively slow grain boundary diffusion and problematic zircon nucleation this allows for cases of zr retention in rutile through temperatures where zr is still diffusively mobile within rutile grains other observations that may be accounted for in this context are large inter grain ranges of rutile zr contents uncorrelated with rutile grain size and flat zr profiles across individual rutile grains counter to what would be expected from diffusive closure a consequence is that it is unlikely that zr in rutile thermometry will be useful for estimating rock cooling rates

metasomatism and partial melting in a subduction complex catalina schist southern california partial melting accompanied high pressure amphibolitization of eclogitic blocks and metasomatism of blocks and their peridotite matrix in a unit of the catalina schist a subduction zone metamorphic terrane migmatitic blocks contain leucocratic zones veins and pods with albitic plagioclase quartz muscovite mineralogically similar dikes and veins cut the ultra mafic matrix a few veins can be traced back into migmatitic blocks uniform phase proportions and igneous textures indicate that the dikes and veins crystallized from silicate melts field relations mineral and bulk compositions and comparisons with experimental data suggest that the migmatites and dikes are partial melts of variably metasomatized amphibolites element partitioning phase equilibrium and fluid inclusion data are compatible with partial melting of the amphibolites at p 8 11 kbar and t 640 750 c in the presence of a low salinity aqueous fluid although the catalina metamorphism occurred at much shallower levels than those inferred for subduction related magmatism the process envisioned is one of multistage slab derived metasomatic contamination of the mantle in the hanging wall of a subduction zone

petrology and geochronology of rutile rutile tio2 is an important accessory mineral that when present offers a rich source of information about the rock units in which it is incorporated it occurs in a variety of specific microstructural settings contains significant amounts of several trace elements and is one of the classical minerals used for u pb age determination here we focus on information obtainable from rutile in its original textural context we do not present an exhaustive review on detrital rutile in clastic sediments but note that an understanding of the petrochronology of rutile in its source rocks will aid interpretation of data obtained from detrital rutile for further information on the important role of rutile in provenance studies the reader is referred to previous reviews e g zack et al 2004b meinhold 2010 triebold et al 2012 coarse rutile is the only stable tio2 polymorph under all crustal and upper mantle conditions with the exception of certain hydrothermal environments smith et al 2009 as such we will focus on rutile rather than the polymorphs brookite anatase and ultrahigh pressure modifications in this chapter we first review rutile occurrences trace element geochemistry and u pb geochronology individually to illustrate the insights that can be gained from microstructures chemistry and ages then in the spirit of petrochronology we show the interpretational power of combining these approaches using the ivrea zone italy as a case study finally we suggest some areas of future research that would improve petrochronologic research using rutile rutile is a characteristic mineral in moderate to high pressure metapelitic rocks in high pressure metamorphosed mafic rocks and in sedimentary rocks e g force 1980 frost 1991 zack et al 2004b triebold et al 2012 rutile also occurs rarely in magmatic rocks e g anorthosites as well as in some hydrothermal systems coarse grained

concordant pulse in mn y and hrees concentrations during uhp eclogitic garnet growth transient rock dynamics along a cold subduction plate interface abstract we herein report strikingly concordant mn y and hree garnet zoning in ultrahigh pressure low temperature oceanic eclogites found in the fossil devonian carboniferous subduction plate interface in sw tianshan zr in rutile thermometry thermodynamic modeling and diffusion controlled garnet growth modeling show that this type of zoning can be explained by a short lived transient most likely a 80 c thermal pulse from 490 to 570 c this event could be as transient as 300 ka assuming a prograde to peak burial duration of 5 ma such garnet zoning is observed for grains sampled meters apart fig 1d and was detected in other eclogites in the region this transient event could reflect the short lived movement of uhp oceanic slices once detached towards the hotter mantle wedge and or deformation induced remobilization of fluids enhancing diffusion controlled garnet growth

zr and hf diffusion in rutile abstract chemical diffusion of zr and hf under anhydrous conditions has been measured in synthetic and natural rutile the sources of diffusant used were hafnon or zircon powders or a hafnon rutile mixture experiments were run in crimped pt capsules in air or in sealed silica glass capsules with solid buffers to buffer at nno or qfm rutherford backscattering spectrometry rbs was used to measure zr and hf diffusion profiles from these measurements the following arrhenius relations were obtained for zr diffusion parallel to c over the temperature range 750 1100 c d zr c 9 8 10 15 exp 170 30 kj mol 1 rt m 2 s 1 for hf diffusion parallel to c over the temperature range 800 1000 c d hf c 9 1 10 15 exp 169 36 kj mol 1 rt m 2 s 1 for hf diffusion normal to c over the temperature range 750 1050 c d hf c 2 5 10 12 exp 227 62 kj mol 1 rt m 2 s 1 diffusivities for experiments buffered at qfm and nno are similar to those run in air diffusivities in synthetic and natural rutile are likewise similar indicating that these findings can be applied directly in determining zr diffusivities in rutile in natural systems these data indicate that rutile should be moderately retentive of zr chemical signatures with zr diffusivities within an order of magnitude of those for pb in rutile over most geologic conditions when applied in evaluation of the relative robustness of the recently developed zr in rutile geothermometer t zack r moraes a kronz temperature dependence of zr in rutile empirical calibration of a rutile thermometer contributions to mineralogy and petrology 148 2004 471 488 e b watson d a wark j b thomas crystallization thermometers for zircon and rutile contributions to mineralogy and petrology 151 2006 413 433 these findings suggest that zr concentrations in rutile will be somewhat more likely to be affected by later thermal disturbance than the geothermometer based on zr concentrations in titanite l hayden e b watson d a wark a thermobarometer for sphene abstract 16th v m goldschmidt conference 2006 and much less resistant to diffusional alteration subsequent to crystallization than the ti in zircon geothermometer e b watson d a wark j b thomas crystallization thermometers for zircon and rutile contributions to mineralogy and petrology 151 2006 413 433 e b watson t m harrison zircon thermometer reveals minimum melting conditions on earliest earth science 308 2005 841 844

applications and limitations of u pb thermochronology to middle and lower crustal thermal histories abstract volume diffusion of pb occurs over micron length scales in apatite and rutile at temperatures relevant to the evolution of the middle and lower crust continuous thermal history information can be resolved from inversion of intracrystalline u pb date profiles preserved within individual grains recent developments in microbeam analysis permit rapid measurement of these age profiles at sub micron spatial resolution thus heralding a new era for u pb thermochronology here we review the theoretical experimental and empirical basis for u pb thermochronology and show that rutile in particular presents an exceptional opportunity to obtain high resolution thermal history information from the deep crust we present a bayesian procedure that is well suited to the inversion of u pb date profile datasets and balances computational efficiency with a full search of thermal history coordinate space complications relevant to accurate application of u pb thermochronology are discussed i theoretically and ii empirically using a rutile u pb dataset from the lower crust of the grenville orogeny purely diffusive date profiles are shown to be the exception to uniform or step like young profiles suggesting that processes other than thermally activated volume diffusion may control u pb systematics in rutile residing in the lower crust however the data obtained from apparent diffusive profiles systematically match cooling histories inferred from other thermochronometers this result emphasises the importance of integrating microtextural observations and trace element concentrations with u pb age data in order to discriminate between diffusive and non diffusive pb transport mechanisms in accessory phases and thus minimize the risk of generating spurious thermal histories

the presence of polynyas in the weddell sea during the last glacial period with implications for the reconstruction of sea ice limits and ice sheet history cores from a contourite drift on the continental slope in the nw weddell sea antarctica contain up to four sandy foraminifer rich layers wa1 4 with dispersed ice rafted debris ird interbedded with silty clayey sands and sandy muds accelerator mass spectrometry ams 14c dating on neogloboquadrina pachyderma from the foraminifer rich layers wa2 and wa3 yielded ages spanning the last glacial maximum lgm and marine isotope stage mis 2 20 319 28 543 cal yr bp and the middle part of mis 3 41 349 43 242 cal yr bp respectively we attribute the high abundances of planktonic and benthic foraminifera to deposition in a seasonally open marine environment given that the nw weddell sea shelf was covered by grounded ice at the lgm and probably during mis 2 and mis 3 and that diatom based reconstructions place the northern limit of winter and summer sea ice coverage to the north of the core sites during the last glacial period our results document the presence of a seasonal or perennial polynya in the nw weddell sea the polynya may have been formed by katabatic winds blowing off the antarctic peninsula ice sheet apis when it was grounded at the continental shelf break although polynya formation through upwelling of deep water cannot be ruled out in addition we argue that previously published data from the southern southeastern and southwestern weddell sea as well as the ross sea may indicate the widespread occurrence of polynyas along the antarctic continental margin during the last glacial period the widespread occurrence of polynyas could help explain how i aabw formation through brine rejection continued throughout the lgm and ii antarctic shelf benthos survived glacial periods the presence of polynyas through glacial periods also has implications for sea ice reconstructions from ice core records possibly biasing the signal towards a reduced sea ice cover finally we propose that the fringes of the apis which probably influence the presence or absence of polynyas in the nw weddell sea are sensitive to changes in antarctic temperature that may be related to a reduction in oceanic heat transport from the north atlantic

west antarctica s sensitivity to natural and human forced climate change over the holocene the location and intensity of the austral westerlies strongly influence southern hemisphere precipitation and heat transport with consequences for human society and ecosystems with future warming global climate models project increased aridity in southern mid latitudes related to continued poleward contraction of the austral westerlies we utilize antarctic ice cores to investigate past and to set the stage for the prediction of future behaviour of the westerlies we show that holocene west antarctic ice core reconstructions of atmospheric circulation sensitively record naturally forced progressive as well as abrupt changes we also show that recent poleward migration of the westerlies coincident with increased emission of greenhouse gases and the antarctic ozone hole has led to unprecedented penetration compared with 100 000 years ago of air masses bringing warmth extra antarctic source dust and anthropogenic pollutants into west antarctica copyright 2012 john wiley sons ltd

effect of cooling on the water content and mechanical behavior of metamorphosed rocks calculations of the decline in f h2o in equilibrium with typical metamorphic assemblages during cooling indicate that there will be a large drop in pore water pressure within 100 of the metamorphic maximum the loss of pore fluid and the generation of large effective pressures across grain boundaries will inhibit rock deformation by those mechanisms that depend on the presence of an aqueous fluid phase in many metamorphic belts extensive deformation occurs below the metamorphic maximum during heating that is while fluid is being generated whereas rocks do not deform in the same ductile manner on cooling even while temperature is high this may reflect changing mechanical properties of the rocks rather than merely changes in regional stresses mobile belts could be made rigid in this way in about 20 m y

evaluating southern ocean sea ice for the last glacial maximum and pre industrial climates pmip 2 models and data evidence sea ice is recognized as an important factor controlling climate conditions at high latitudes it has a major impact in controlling the ocean to atmosphere exchanges e g for co2 as well as surface oceanic conditions and deep water formation in the high latitude oceans being at the interface of two major components of the climate system sea ice is useful to evaluate and intercompare different climate models we here analyze the results of eight coupled climate models from which seven are from the pmip 2 database against available reconstructions for winter and summer sea ice extent around antarctica to evaluate the ability of models in representing different climate states we compare their results for both the pre industrial and the last glacial maximum lgm we find that models generally have identical seasonal ranges for the two climate states analyzed which is not supported by data inferences indeed data indicate that the lgm seasonality was enhanced compared to the pre industrial the shape of the sea ice distribution is also different in models circular around the antarctic continent and in reconstructions oval shaped distribution similar to modern sea ice distribution we show that models underestimating the sea ice extent for the pre industrial are also underestimating the last glacial maximum extent our results thus point to difficulties for climate models in representing the sea ice dynamics in the southern ocean

implications of near rim compositional zoning in rutile for geothermometry geospeedometry and trace element equilibration in principle compositional profiling of the near rim region of minerals can provide insight into cooling rates but presumes that loss or gain of material from the crystal rim is not kinetically restricted trace element depth profiles collected for zr hf ta nb and u in amphibolite facies rutile grains of the catalina schist southern california show significant variability within a single rock profiles of the same element among different grains can have significantly different slopes grains with indistinguishable zr profiles show vastly different nb profiles and grains with indistinguishable nb profiles show different zr profiles textural and kinetic idiosyncrasies within the matrix apparently affect the ability of specific crystals to accept or release trace elements and impugn the common assumption that mineral surfaces maintain equilibrium at amphibolite facies conditions a new model that limits the flux of zr from rutile grains helps explain commonly observed compositional profiles and implies that inversion of compositional profiles assuming equilibrium among grain surfaces will invariably overestimate cooling rates few grains may record the low closure temperatures that experimentally determined diffusivities imply rather higher temperatures will be retained depending on the proximity of reactants and products in the matrix silicon diffusion does not control zr reequilibration in rutile and relative diffusion coefficients d s of trace elements in rutile are dzr dhf 10dnb 20dta 40du

diffusion induced fractionation of niobium and tantalum during continental crust formation differentiation of the earth into its major spheres crust mantle and core has proceeded dominantly through magmatic processes involving melting and melt separation models that describe these differentiation processes are guided by elemental abundances in the different reservoirs elements are fractionated between coexisting phases during partial melting and geochemical models are generally based on the fundamental assumption that trace element equilibrium is established between the partial melts and the restitic minerals the element pair niobium and tantalum is key to the distinction of different melting regimes involved in crustal differentiation but equilibrium partition models have largely failed to reproduce the nb ta patterns observed in nature posing a long standing geochemical conundrum here we demonstrate that kinetic fractionation of nb and ta by diffusion may have produced the low nb ta observed in the continental crust on the basis of the diffusivities of nb and ta in rutile tio2 determined experimentally in this study we conclude that equilibrium cannot be expected for the natural range of grain sizes temperatures and time scales involved in partial melting of crustal rocks instead the observed fractionation of the geochemical twins nb and ta in the silicate earth most likely proceeds by partial as opposed to complete equilibration of rutile and melt hence the assumption of bulk equilibrium during partial melting for the processes of crustal differentiation may not be justified as is demonstrated here for nb ta the concept presented here is based on kinetic fractionation melting and explains the observed low nb ta ratio of the continental crust

carbon isotope constraints on the deglacial co2 rise from ice cores the stable carbon isotope ratio of atmospheric co2 13catm is a key parameter in deciphering past carbon cycle changes here we present 13catm data for the past 24 000 years derived from three independent records from two antarctic ice cores we conclude that a pronounced 0 3 per mil decrease in 13catm during the early deglaciation can be best explained by upwelling of old carbon enriched waters in the southern ocean later in the deglaciation regrowth of the terrestrial biosphere changes in sea surface temperature and ocean circulation governed the 13catm evolution during the last glacial maximum 13catm and atmospheric co2 concentration were essentially constant which suggests that the carbon cycle was in dynamic equilibrium and that the net transfer of carbon to the deep ocean had occurred before then

titaniq a titanium in quartz geothermometer titanium is one of many trace elements to substitute for silicon in the mineral quartz here we describe the temperature dependence of that substitution in the form of a new geothermometer to calibrate the titaniq thermometer we synthesized quartz in the presence of rutile and either aqueous fluid or hydrous silicate melt at temperatures ranging from 600 to 1 000 c at 1 0 gpa the ti contents of quartz in ppm by weight from 13 experiments increase exponentially with reciprocal t as described by text log left x text qtz text ti right 5 69 pm 0 02 frac 3765 pm 24 t k application of this thermometer is straightforward typically requiring analysis of only one phase quartz this can be accomplished either by epma for crystallization temperatures above 600 c or by sims for temperatures down to at least 400 resulting temperature estimates are very precise usually better than 5 c potentially allowing detailed characterization of thermal histories within individual quartz grains although calibrated for quartz crystallized in the presence of rutile the thermometer can also be applied to rutile absent systems if tio2 activity is constrained

lithium and its isotopes as tracers of subduction zone fluids and metasomatic processes evidence from the catalina schist california usa abstract the catalina schist well studied for its tectonometamorphic history and geochemical evolution provides a field area in which to evaluate the extent of li mobility in subduction zone fluids and the degree to which li isotopes can trace metamorphic fluid rock interactions a suite of 63 samples of the catalina schist that represent a range of metamorphic grades and diverse lithologies was analyzed for li concentration and isotope composition metasedimentary rocks show no evidence for significant loss of li with increasing metamorphic grade despite the wide range of prograde p t histories represented by the five tectonometamorphic units with the highest grade rocks having experienced peak temperatures near 750 c metamafic rocks similarly show no change in li concentration as a function of grade that can be directly related to varying degrees of devolatilization the li concentrations and 7 li of metasedimentary rocks appear to best correlate with a chemical alteration index that likely reflects differential extents of weathering in the sediment sources the 7 li of most metamafic rocks including gabbroic metaconglomerate cobbles veins and melange matrix reflects overprinting of the li isotope compositions derived through transfer of li in fluids from sedimentary lithologies in the same tectonometamorphic units thus it appears that li was mobilized in fluids released from metasedimentary rocks but that the loss was insufficient to affect the bulk 7 li and li content of the metasedimentary rocks veins and melange matrix have the highest li concentrations of all samples analyzed ranging up to 70 ppm some veins and amphibolite grade mafic rocks have low 7 li suggestive of li diffusion through an intergranular fluid taken together these observations suggest mobilization of li during high pressure temperature p t fluid rock interactions that also resulted in enrichments in b n and some large ion lithophile elements k rb cs ba in the veins melange matrix and cobbles this study demonstrates that although li is mobile in high p t metamorphic fluids it does not partition into fluids to the extent demonstrated for n b and cs the latter elements showing large depletions in the higher grade catalina schist metasedimentary rocks thus even in relatively warm subduction zones deeply subducted metasedimentary rocks are expected to largely retain their li inventory to depths of at least 40 km the maximum depth at which units of the catalina schist experienced peak metamorphism

the record of continental dust from australia in tasman sea sediments abstract the flux of aeolian dust from australia to sediments of the tasman sea has increased during glacial stages of the last four glacial cycles low fluxes of dust from australia before 350 ka were followed by an increase in stage 10 and high fluxes in peak glacial periods thereafter the initiation of higher dust fluxes in stage 10 is consisten with previous estimates of the age of onset of aridity in the source area dust flux to the tasman sea is thought to record the intensity of deflation from the source area in interior southeastern australia which was marked by arid conditions and possibly greater windiness during the last glacial a transect of five cores from the central tasman sea revealed consistently low dust fluxes north of 33 s increasing southward to approximately 40 s glacial to interglacial movement of the northern boundary of the dust plume governed by the position of the subtropical ridge was less than 6 latitude probably closer to 3 350 km the position of the dust plume determined in this study and its response to climate change are significantly different from a previous reconstruction based on the measurement of quartz content of the non biogenic sediment fraction

a melange of subduction temperatures evidence from zr in rutile thermometry for strengthening of the subduction interface abstract the catalina schist contains a spectacular km scale amphibolite facies melange zone thought to be part of a cretaceous convergent margin plate interface in this setting blocks ranging from centimeters up to 100 m in diameter are surrounded by finer grained matrix that is derived from the blocks blocks throughout the melange represent a diversity of protoliths derived from basalts cherts and other sediments and hydrated mantle but all contain assemblages consistent with upper amphibolite facies conditions suggesting a relatively restricted range of depths and temperatures over which material within the melange was metamorphosed this apparent uniformity of metamorphic grade contrasts with other melanges such as the franciscan complex where coexisting rocks with highly variable peak metamorphic grade suggest extensive mixing of materials along the subduction interface this mixing has been ascribed to flow of material within relatively low viscosity matrix the zr content of rutile in samples from across the amphibolite facies melange of the catalina schist was measured to determine peak metamorphic temperatures identify whether these temperatures were different among blocks and whether the spatial distribution of temperatures throughout the melange was systematic or random resolvably different zr contents between 290 and 720 10 40 ppm are found among the blocks corresponding to different peak metamorphic temperatures of 650 to 730 2 16 c at an assumed pressure of 1 gpa these results are broadly consistent with previous thermobarometric estimates no systematic distribution of temperatures was found however like other melange zones material flow within the catalina schist melange was likely chaotic but appears to have occurred on a more restricted scale compared to some other localities progressive metamorphism of melange matrix is expected to produce rheologically stiffer matrix minerals such as amphiboles and pyroxenes at the expense of weaker matrix minerals sheet silicates affecting the overall rheological behavior of the melange and dictating the scale of flow the catalina schist amphibolite facies melange matrix appears to provide a snapshot of hotter stiffer portions of a subduction interface perhaps more representative of rheological behavior at depths approaching the subarc than is found in some other exhumed melange zones

the last interglacial as represented in the glaciochemical record from mount moulton blue ice area west antarctica abstract understanding climate during the last interglacial is critical for understanding how modern climate change differs from purely naturally forced climate change here we present the first high resolution ice core record of the last interglacial and transition to the subsequent glacial period from antarctica and the first glaciochemical record for this period from west antarctica samples were collected from a horizontal ice trench in the mt moulton blue ice area bia in west antarctica and analyzed for their soluble major anions cl no 3 so 4 2 major and trace elements na mg ca sr cd cs ba la ce pr pb bi u as al s ti v cr mn fe co cu zn and water hydrogen isotopes d the last interglacial is characterized by warmer temperatures d weakened atmospheric circulation dust elements seasalts aerosols decreased sea ice extent na nssso 4 2 and decreased oceanic productivity nssso 4 2 a combined examination of mt moulton seasalts dust nssso 4 2 and d records indicates that the last interglacial was extremely stable compared to glacial age climate events and it ended through a long period of gradual cooling unlike that projected for future holocene climate

catch a falling star meteorites and old ice a model for the process of meteorite concentration in blue ice regions of the antarctic ice sheet is proposed based on data from near the allan hills and the assumptions that both meteorite influx and glacial flow have been constant the meteorite influx is calculated to be 60 x 10 6 kilogram per square kilometer per year and the age of the exposed ice to be 0 to 600 000 years varying with distance from the allan hills these results are in line with other estimates of influx rate and with measurements of the terrestrial ages of the meteorites providing support for the assumption of steady flow and meteorite influx this may be the oldest sequence of ice in stratigraphic order yet discovered and the results imply that this part of the east antarctic ice sheet has been approximately steady during this time interval

trace element systematics in granulite facies rutile implications for zr geothermometry and provenance studies metamorphic rutile from granulite facies metapelitic rocks of the archean pikwitonei granulite domain pgd manitoba canada provides constraints on the systematics of trace elements in rutile during high temperature conditions and subsequent slow cooling compositional profiles and maps of the zr concentrations in rutile grains 120 600 m from three metapelitic gneisses were acquired by electron probe micro analysis using a spatial resolution of down to 2 m simultaneously profiles were analysed for nb cr and v which have significantly different diffusion characteristics in rutile the profiles of all elements show relatively homogeneous concentrations within most grains but significant inter grain differences even within a single thin section some rutile grains display a slight concentration decrease from a neighbouring garnet towards the matrix for all measured elements the lack of diffusion profiles for all analysed elements shows that these are highly immobile in rutile and that distributions of these elements are primary and preserve prograde information the nb and cr concentrations overlap with ranges that are ascribed to different provenances indicating that source discrimination based on these elements is not possible in all cases high retentiveness for zr implies that the zr in rutile geothermometer is highly robust to diffusive re equilibration even during very slow cooling 2 c ma 1 from granulite facies conditions most grains have high zr contents 3000 4600 ppm differences between high zr contents suggest that during growth under vapour absent conditions there may not be saturation of zr in rutile even if zircon is present therefore several rutile grains need to be analysed in a sample to obtain a useful minimum peak temperature the highest zr concentrations correspond to 900 c this is significantly higher than previous peak temperature estimates of 820 c based on two feldspar thermometry on a regional scale this implies that part of the pgd was affected by ultra high temperature uht metamorphism it also implies that rutile is able to preserve primary compositions even to uht conditions this study shows that if combined with textural information zr in rutile has the potential to be a very useful tool for estimating rutile crystallization temperatures and peak metamorphic conditions for granulite facies rocks zr in rutile yields more reliable peak metamorphic temperatures than most other exchange geothermometers which tend to partially re equilibrate by diffusion during cooling

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

preserved zr temperatures and u pb ages in high grade metamorphic titanite evidence for a static hot channel in the himalayan orogen abstract titanite grains from 800 c gneisses of the c 6 km thick greater himalayan sequence of central nepal were analyzed for zr in titanite temperatures and u pb ages to investigate the formation and evolution of a former weak mid crustal channel in the himalaya laser ablation icp ms depth profiles and spot analyses of titanite zr and u pb isotopic compositions are inconsistent with diffusional reequilibration on scales greater than 1 2 m and instead data appear to faithfully record both temperature and age titanite records protracted heating from 700 750 c at 37 ma to 775 c at 24 ma and possibly slight cooling to 765 c at 20 ma such temperatures exceed partial melting reactions in associated metapelites and imply profoundly weak rheologies i e a hot channel yet predate initiation of the bounding main central thrust and south tibetan detachment systems by as much as 15 myr evidently thick but weak crustal channels may remain stationary with respect to the convergence direction for 10 myr even during one of earth s biggest continent continent collisions

the 18o isotope exchange rate between firn air co2 and the firn matrix at three antarctic sites 1 having measured 18o of firn air co2 for three antarctic sites dronning maud land dome concordia and berkner island we established that at depth the 18o co2 values are systematically shifted away from atmospheric values toward isotope equilibrium with h2o from precipitation firn matrix the 18o co2 shifts increase with depth and thus with co2 age the equation of a first order reaction is used to describe and calculate co2 oxygen isotope exchange rates the calculated exchange rates clearly show a correlation with firn temperatures assuming that the same mechanism operates at different sites and at different temperatures a pseudoactivation energy of 7 8 0 8 kcal mol is estimated the occurrence of exchange means that firn is not chemically inert in that sense that some form of co2 hydration takes place possible mechanisms of co2 oxygen isotope exchange are discussed and liquid like layers on firn grains are the most likely interface where this exchange takes place other gases e g cos may likewise be sensitive to hydration or related reactions and this may reduce their integrity in firn a formal translation of the reaction rates of co2 oxygen isotope exchange in firn to a cos hydration rate appears to indicate cos preservation on the scale of tens of thousands of years we suggest that the value of co2 oxygen exchange rate in firn expressed as half reaction time t may be used as a new firn characteristic giving a measure of hydration activity in firn an indirect measure of firn metamorphism and be correlated with other firn processes near a pore close off depth t values may possibly correlate with the process of he and ne diffusion expulsion during the close off of pores in firn as well as the release of 14co produced in situ in the firn matrix

reconstruction of changes in the weddell sea sector of the antarctic ice sheet since the last glacial maximum the weddell sea sector is one of the main formation sites for antarctic bottom water and an outlet for about one fifth of antarctica s continental ice volume over the last few decades studies on glacial geological records in this sector have provided conflicting reconstructions of changes in ice sheet extent and ice sheet thickness since the last glacial maximum lgm at ca 23 19 calibrated kiloyears before present cal ka bp terrestrial geomorphological records and exposure ages obtained from rocks in the hinterland of the weddell sea ice sheet thickness constraints from ice cores and some radiocarbon dates on offshore sediments were interpreted to indicate no significant ice thickening and locally restricted grounding line advance at the lgm other marine geological and geophysical studies concluded that subglacial bedforms mapped on the weddell sea continental shelf subglacial deposits and sediments over compacted by overriding ice recovered in cores and the few available radiocarbon ages from marine sediments are consistent with major ice sheet advance at the lgm reflecting the geological interpretations different ice sheet models have reconstructed conflicting lgm ice sheet configurations for the weddell sea sector consequently the estimated contributions of ice sheet build up in the weddell sea sector to the lgm sea level low stand of 130 m vary considerably in this paper we summarise and review the geological records of past ice sheet margins and past ice sheet elevations in the weddell sea sector we compile marine and terrestrial chronological data constraining former ice sheet size thereby highlighting different levels of certainty and present two alternative scenarios of the lgm ice sheet configuration including time slice reconstructions for post lgm grounding line retreat moreover we discuss consistencies and possible reasons for inconsistencies between the various reconstructions and propose objectives for future research the aim of our study is to provide two alternative interpretations of glacial geological datasets on antarctic ice sheet history for the weddell sea sector which can be utilised to test and improve numerical ice sheet models

comparison of ice rafted debris and physical properties in odp site 1094 south atlantic with the vostok ice core over the last four climatic cycles abstract visual counts of ice rafted debris ird foraminifera and radiolaria were made for 1500 samples in site 1094 spanning the last four climatic cycles marine isotope stages 1 11 most but not all of the ird variability is captured by whole core physical properties including magnetic susceptibility and ray attenuation bulk density glacial periods are marked by high ird abundance and millennial scale variability which may reflect instability of ice shelves in the weddell sea region each interglacial period exhibits low ird and high foraminiferal abundance during the early part of the interglacial indicating relatively warm sea surface temperatures and reduced influence of sea ice ird increases and foraminiferal abundances decrease during the latter part of each interglacial indicating a return to more glacial like conditions glacial terminations i and v are each characterized by a step wise reduction in ice rafting punctuated by a brief pulse in ird delivery and reversal in 18o the coarse fraction of the sediment is dominated by ash and radiolaria and the relative abundance of these components is remarkably similar to the concentration of na in vostok each of these variables is believed to be controlled mainly by sea ice cover thereby providing a means for sediment ice core correlation

the berkner island antarctica ice core drilling project we describe a project to retrieve a 948 m deep ice core from berkner island antarctica using relatively lightweight logistics and a small team the drilling operation over three austral summer seasons used electromechanical drilling technology described in detail from a covered shallow pit and a fluid filled borehole a basal temperature well below pressure melting point meant that no drilling problems were encountered when approaching the bed and the borehole penetrated through to the base of the ice sheet and sediment was retrieved from beneath the ice

nb and zr behavior in rutile during high grade metamorphism and retrogression an example from the ivrea verbano zone abstract detailed textural observations and in situ analyses emp sims and la icp ms are used to characterize trace element behavior during prograde and retrograde metamorphic reactions involving rutile the ivrea verbano zone is a classic granulite area and rocks from the strona and d ossola valleys are an example of the amphibolite to granulite facies transition although different rock types occur in the area detailed sampling and petrographic work show that rutile only occurs in granulite facies paragneisses these rocks show a rich inventory of textures that allow not only for the investigation of trace element behavior in response to prograde rutile growth but also for the effect of post peak processes on rutile chemistry nb concentrations in rutile from lower grade samples show a larger spread from 500 to 5000 ppm within one sample when compared to those from higher grades this pattern can be modeled using prograde rutile growth formed from biotite breakdown zr concentrations in rutile are characterized by an anomalously large spread and a bimodal distribution maximum zr concentrations increase according to the general metamorphic gradient known for this area temperatures from zr in rutile thermometry although feasible are considerably higher than previous calculations increasing from ca 850 to 930 c a second cluster of zr concentrations in rutile occurs at rather constant concentrations ca 1000 ppm for all localities and is interpreted to be related to intense fluid influx at high temperature and or to post peak diffusional resetting favored by slow cooling rates alteration textures characterized by a complex network of micro veins are evidence for the late fluid influx the fluid strongly affected the rutiles which is evidenced by corrosion of older rutile grains and formation of rutile veinlets

a minimum thermodynamic model for the bipolar seesaw 1 the simplest possible model is proposed to explain a large fraction of the millennial climate variability measured in the isotopic composition of antarctic ice cores the model results from the classic bipolar seesaw by coupling it to a heat reservoir in this thermal bipolar seesaw the heat reservoir convolves northern time signals with a characteristic timescale applying the model to the data of grip and byrd we demonstrate that maximum correlation can be obtained using a timescale of about 1000 1500 years higher correlations are obtained by first filtering out the long term variability which is due to astronomical and greenhouse gas forcing and not part of the thermal bipolar seesaw the model resolves the apparent confusion whether northern and southern climate records are in or out of phase synchronous or time lagged

state of the antarctic and southern ocean climate system this paper reviews developments in our understanding of the state of the antarctic and southern ocean climate and its relation to the global climate system over the last few millennia climate over this and earlier periods has not been stable as evidenced by the occurrence of abrupt changes in atmospheric circulation and temperature recorded in antarctic ice core proxies for past climate two of the most prominent abrupt climate change events are characterized by intensification of the circumpolar westerlies also known as the southern annular mode between 6000 and 5000 years ago and since 1200 1000 years ago following the last of these is a period of major trans antarctic reorganization of atmospheric circulation and temperature between ad1700 and 1850 the two earlier antarctic abrupt climate change events appear linked to but predate by several centuries even more abrupt climate change in the north atlantic and the end of the more recent event is coincident with reorganization of atmospheric circulation in the north pacific improved understanding of such events and of the associations between abrupt climate change events recorded in both hemispheres is critical to predicting the impact and timing of future abrupt climate change events potentially forced by anthropogenic changes in greenhouse gases and aerosols special attention is given to the climate of the past 200 years which was recorded by a network of recently available shallow firn cores and to that of the past 50 years which was monitored by the continuous instrumental record significant regional climate changes have taken place in the antarctic during the past 50 years atmospheric temperatures have increased markedly over the antarctic peninsula linked to nearby ocean warming and intensification of the circumpolar westerlies glaciers are retreating on the peninsula in patagonia on the sub antarctic islands and in west antarctica adjacent to the peninsula the penetration of marine air masses has become more pronounced over parts of west antarctica above the surface the antarctic troposphere has warmed during winter while the stratosphere has cooled year round the upper kilometer of the circumpolar southern ocean has warmed antarctic bottom water across a wide sector off east antarctica has freshened and the densest bottom water in the weddell sea has warmed in contrast to these regional climate changes over most of antarctica near surface temperature and snowfall have not increased significantly during at least the past 50 years and proxy data suggest that the atmospheric circulation over the interior has remained in a similar state for at least the past 200 years furthermore the total sea ice cover around antarctica has exhibited no significant overall change since reliable satellite monitoring began in the late 1970s despite large but compensating regional changes the inhomogeneity of antarctic climate in space and time implies that recent antarctic climate changes are due on the one hand to a combination of strong multi decadal variability and anthropogenic effects and as demonstrated by the paleoclimate record on the other hand to multi decadal to millennial scale and longer natural variability forced through changes in orbital insolation greenhouse gases solar variability ice dynamics and aerosols model projections suggest that over the 21st century the antarctic interior will warm by 3 4 1oc and sea ice extent will decrease by 30 ice sheet models are not yet adequate enough to answer pressing questions about the effect of projected warming on mass balance and sea level considering the potentially major impacts of a warming climate on antarctica vigorous efforts are needed to better understand all aspects of the highly coupled antarctic climate system as well as its influence on the earth s climate and oceans

on the glaciological meteorological and climatological significance of antarctic blue ice areas this paper presents the current state of our knowledge about antarctic blue ice areas scattered widely over the antarctic continent yet covering only approximately 1 of its surface area blue ice areas have some peculiar characteristics that make them of particular interest for planetary geologists glaciologists meteorologists and climatologists for instance blue ice areas are subject to net ablation mainly by sublimation since any accumulation is easily swept off their smooth surfaces by winds moreover they are significantly warmer than their surroundings and the wind over them is generally more gusty an important feature of blue ice is its relatively low albedo 0 56 compared with that of snow 0 80 blue ice is probably considerably smoother than snow in the aerodynamic sense with roughness lengths as low as 3 10 6 m which indicates that blue ice is probably the only permanent natural surface over which the air flow is mainly in the aerodynamic smooth regime further since it is likely that very old ice is exposed at the surface of some blue ice areas this ice would be of great interest for paleoclimatic studies it has also been suggested that blue ice areas are sensitive to climate change this would make them useful as antarctic climate indicators because they can easily be monitored by satellite finally this paper addresses several gaps in our knowledge about blue ice areas and gives suggestions for future blue ice area research

ice core records as sea ice proxies an evaluation from the weddell sea region of antarctica 1 ice core records of methanesulfonic acid msa from three sites around the weddell sea are investigated for their potential as sea ice proxies it is found that the amount of msa reaching the ice core sites decreases following years of increased winter sea ice in the weddell sea opposite to the expected relationship if msa is to be used as a sea ice proxy it is also shown that this negative msa sea ice relationship cannot be explained by the influence that the extensive summer ice pack in the weddell sea has on msa production area and transport distance a historical record of sea ice from the northern weddell sea shows that the negative relationship between msa and winter sea ice exists over interannual 7 year period and multidecadal 20 year period timescales national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data suggest that this negative relationship is most likely due to variations in the strength of cold offshore wind anomalies traveling across the weddell sea which act to synergistically increase sea ice extent sie while decreasing msa delivery to the ice core sites hence our findings show that in some locations atmospheric transport strength rather than sea ice conditions is the dominant factor that determines the msa signal preserved in near coastal ice cores a cautious approach is thus required in using ice core msa for reconstructing past sea ice conditions including the need for networks of ice core records and multiproxy studies to assess the significance of past msa changes at different locations around antarctica

interpreting titanite u pb dates and zr thermobarometry in high grade rocks empirical constraints on elemental diffusivities of pb al fe zr nb and ce length scales of compositional heterogeneity in titanite from 750 to 1000 c metamorphic rocks from southern madagascar were measured to provide empirical constraints on elemental diffusivities the calculated pb diffusivity is comparable to experimental estimates of sr diffusivity because of this u pb dates from rocks that reached peak temperatures 900 c thus zr in titanite thermobarometry should not be reset by diffusion in all but the smallest grains in the hottest rocks al and nb diffuse at similar rates to zr ce and fe diffuse slower than pb but faster than zr differences in empirical and experimental estimates of elemental diffusivities might be related to the complexity of most natural titanite solid solutions compared to the near end member titanite used in experiments

relative timing of deglacial climate events in antarctica and greenland the last deglaciation was marked by large hemispheric millennial scale climate variations the bolling allerod and younger dryas periods in the north and the antarctic cold reversal in the south a chronology from the high accumulation law dome east antarctic ice core constrains the relative timing of these two events and provides strong evidence that the cooling at the start of the antarctic cold reversal did not follow the abrupt warming during the northern bolling transition around 14 500 years ago this result suggests that southern changes are not a direct response to abrupt changes in north atlantic thermohaline circulation as is assumed in the conventional picture of a hemispheric temperature seesaw

equilibrium and disequilibrium trace element partitioning in hydrous eclogites trescolmen central alps elements pb th and u whereas phengite hosts ba and is along despite the widespread presence of hydrous phases in subductionwith clinopyroxene and paragonite an important phase for b related systems experimental d trace element values for many however because of their low modal abundance in eclogite facies hydrous phases are lacking to fill this gap we present a set of rocks phengite and paragonite do not control the b whole rock budget d values where min indicates amphibole zoisite we infer that estimated d values from equilibrium phengite paragonite or apatite derived from equilibrium parageneses assemblages can be used as a good approximation for partition of eclogites from trescolmen central alps switzerland these coefficients under the given pt conditions 650 c and 2 0 data can be combined with experimental data for d gpa deformation induced dynamic recrystallization seems to be to estimate d values for the hydrous phases thus circumventing the driving process necessary for a close approach towards trace experimental problems with the direct determination of such values element equilibrium this process should work efficiently during we analysed li be b sr y zr nb ba ce nd sm pb th subduction close to the slab mantle interface affecting sediments and u in coexisting phases by laser ablation microprobe inductively and low t altered mid ocean ridge basalt but is of less importance coupled plasma mass spectrometry many of the values are extremely inside the slab knowledge of d values from equilibrium assemblages low for example nb ba ce th and u are in the lower ppb determined in this study is useful not only for large scale subductionrange in clinopyroxene attainment of equilibrium was evaluated zone modelling but also as an aid in the selection of equilibrium by textural and major and trace element characteristics nonsubassemblages in imperfectly equilibrated samples so that a equilibrated assemblages are common in most eclogite localities crystallization sequence can be derived including trescolmen and using such samples would lead to the derivation of erroneous values for equilibrium partitioning however four of the 10 studied eclogites from trescolmen having homogeneous

do blue ice moraines in the heritage range show the west antarctic ice sheet survived the last interglacial abstract we present a hypothesis that best explains cosmogenic isotope data on blue ice moraines in the heritage range west antarctica the age of the moraines implies that they and the related ice sheet surface with which they are associated have persisted on the flanks of nunataks throughout at least the last interglacial glacial cycle the implication is that although the west antarctic ice sheet wais may have fluctuated in thickness during glacial cycles the central dome has remained intact for at least 200 kyr and possibly even for 400 kyr such a finding if substantiated would contribute to our understanding of the sensitivity of the wais to climate change further it would be a powerful geomorphic constraint on models of the past behaviour of the ice sheet during glacial cycles and thus those predicting the future of the ice sheet in a warming world

elevation change and ice flow at horseshoe valley patriot hills west antarctica patriot hills is located at 80 18 s 81 22 w at the southernmost end of the heritage range ellsworth mountains west antarctica a comparison of glacier elevation data and ice velocities obtained by the differential global positioning system in the period 1996 97 is presented ablation accumulation rates measured at a network of stakes in horseshoe valley show average accumulation of 70 kg m 2 a 1 in the central part of the valley and a maximum ablation of 170 kg m 2 a 1 at the edge of the blue ice area close to patriot hills changes in the surface elevation of the glacier measured at 81 stakes in the period 1995 97 show a mean thickening of 0 43 0 42 m a 1 which considering the uncertainties indicates that the ice sheet around patriot hills is in near steady state surface velocities in combination with ice thicknesses obtained by ground based radio echo sounding are used to compute the ice flux across the horseshoe valley transect a total outflow of 0 44 0 08 km 3 a 1 is obtained considering a catchment area for horseshoe valley of 1087 km 2 upstream from the flow transect and a net accumulation rate of 100 kg m 2 a 1 a total input of 0 11 0 04 km 3 a 1 by snow accumulation is obtained accepting a near equilibrium condition for the ice sheet the flux difference i e 0 33 km 3 a 1 must be supplied by flow from the inland ice sheet through ice cliffs located in mountain gaps in the heritage range if horseshoe valley is not in steady state but is thickening the positive mass balance could be due to increased snow accumulation or enhanced ice flow from the interior of the ice sheet new data are needed to elucidate this

late pleistocene and early holocene change in the weddell sea a new climate record from the patriot hills ellsworth mountains west antarctica the transition from the late pleistocene to the holocene 30 000 5000 years ago was a period of considerable climate variability which has been associated with changes in deep water formation and the intensity of the meridional overturning circulation although numerous records exist across the north atlantic region few antarctic ice core records have been obtained from the south here we exploit the potential of upwelling ancient ice so called blue ice areas bias from the patriot hills in the ellsworth mountains to derive the first deuterium isotope record d from continental antarctica south of the weddell sea gas analysis and glaciological considerations provide a first relative chronology inferred temperature trends from the patriot hills bia and snow pit suggest changing climate influences during the transition between the last glacial period and holocene under modern conditions the interplay between the antarctic high pressure system and the southern annular mode appears to play a significant role in controlling katabatic wind flow over the site while the bia record suggests that greater sea ice extent during the last glacial period was a major control our results demonstrate the considerable potential of the patriot hills site for reconstructing past climate change in the south atlantic region

sulfur partitioning between apatite and melt and effect of sulfur on apatite solubility at oxidizing conditions the effect of sulfur on phosphorus solubility in rhyolitic melt and the sulfur distribution between apatite anhydrite melt and fluid have been determined at 200 mpa and 800 1 100 c via apatite crystallization and dissolution experiments the presence of a small amount of sulfur in the system 0 5 wt s under oxidizing conditions increases the solubility of phosphorus in the melt probably due to changing calcium activity in the melt as a result of the formation of ca s complexing cations apatite solubility geothermometers tend to overestimate temperature in ca poor s bearing system at oxidizing conditions in crystallization experiments the sulfur content in apatite decreases with decreasing temperature and also with decreasing sulfur content of the melt the sulfur partition coefficient between apatite and rhyolitic melt increases with decreasing temperature kdsapatite melt 4 5 14 2 at t 1 100 900 c under sulfur undersaturated conditions no anhydrite the sulfur partition coefficient is lower in anhydrite saturated melt 8 at 800 c than in anhydrite undersaturated melt suggesting that kdsapatite melt depends not only on the temperature but also on the sulfur content of the melt these first results indicate that the sulfur content in apatite can be used to track the evolution of sulfur content in a magmatic system at oxidizing conditions

exhumation history of a section of the sikkim himalayas india records in the metamorphic mineral equilibria and compositional zoning of garnet the exhumation history of pelitic migmatite samples from the high himalayan crystalline complex hhc near the south tibetian detachment system in the sikkim darjeeling section has been determined on the basis of thermo barometric analyses retrograde breakdown reactions and compositional zoning of garnet the peak metamorphic condition is estimated to be 10 4 kbar 800 c from thermo barometric and phase equilibrium constraints the observed retrograde breakdown of garnet to spinel and cordierite requires near isothermal and hence extremely rapid 15 mm yr exhumation up to the depth of 15 km numerical modeling suggests that the initial rapid exhumation must have been followed by a much slower process 2 mm yr up to at least 5 km depth to lead to the development of the observed compositional zoning of garnet the dramatic change of the exhumation velocity vz might reflect a process of tectonic thinning followed by erosion and or horizontal flow at shallow depth assuming that the vz did not change significantly below 5 km depth these results suggest that the hhc samples studied in this work exhumed from a depth of 34 km within 8 ma

synchronisation of palaeoenvironmental records over the last 60 000 years and an extended intimate event stratigraphy to 48 000 b2k the intimate protocol for the correlation of marine ice core and terrestrial records is here updated reflecting recent developments in palaeoclimate research originally focussed on last glacial to interglacial transition lgit 22 000 11 500 years b p the intimate group has now extended its study period back to 60 000 years as a first step the intimate event stratigraphy has now been extended to include 8000 48 000 b2k based on a combined ngrip and grip isotope profile against a gicc05 chronology and key tephra horizons from iceland and continental european volcanic sources in this lead article of this intimate special issue we introduce some of the recent achievements of the intimate community and discuss the challenges associated with extending the intimate approach back in time focussing in particular on the chronological problems inherent in comparing different proxy records the intimate approach has thus far been limited predominantly to the north atlantic and australasian regions and we also discuss the potential to extend the intimate protocol beyond these regions

effects of matrix grain size on the kinetics of intergranular diffusion a linear relationship exists between the mean volume of garnet porphyroblasts and the squared inverse of mean matrix grain diameter for six samples of garnetiferous mica quartzite with identical thermal histories and similar mineralogy and modes this relationship accords with theoretical predictions of the dependence of intergranular diffusive fluxes on the volume fraction of grain edges that function as diffusional pathways during porphyroblast growth the impact of matrix grain size is large compared to a rock with a 1 mm matrix a rock with a 10 m matrix would experience rates of diffusion controlled porphyroblast growth that are 10 000 times faster and characteristic length scales for chemical equilibration that are 100 times larger precursor grain sizes may therefore exert a major influence on crystallization kinetics if matrix coarsening occurs during prograde reaction a decrease in the volume fraction of diffusional pathways will tend to counteract the exponential thermal increase in diffusive fluxes the impact of such matrix grain growth although difficult to assess without firm knowledge of coarsening rates in polymineralic aggregates might be significant for matrices finer than c 100 m at temperatures above c 500 600 c but is likely negligible for coarser grain sizes and lower temperatures

synchronisation of palaeoenvironmental events in the north atlantic region during the last termination a revised protocol recommended by the intimate group abstract the north atlantic intimate group of the inqua palaeoclimate commission has previously recommended an event stratigraphy approach for the synchronisation of records of the last termination using the greenland grip isotopic record as the regional stratotype and intcal98 for the calibration of radiocarbon dates lowe j j hoek w intimate group 2001 inter regional correlation of palaeoclimatic records for the last glacial interglacial transition a protocol for improved precision recommended by the intimate project group quaternary science reviews 20 1175 1187 here we present a revised protocol for time stratigraphic correlation in the north atlantic region over a more extended time period 30 8 ka this employs the new ngrip isotopic record and associated greenland ice core chronology 2005 gicc05 as the regional stratotype intcal04 for the calibration of radiocarbon dates bayesian based statistical procedures for the construction of age models and tephrochronology to validate correlations between regional site records

interhemispheric ice sheet synchronicity during the last glacial maximum the timing of the last maximum extent of the antarctic ice sheets relative to those in the northern hemisphere remains poorly understood we develop a chronology for the weddell sea sector of the east antarctic ice sheet that combined with ages from other antarctic ice sheet sectors indicates that the advance to and retreat from their maximum extent was within dating uncertainties synchronous with most sectors of northern hemisphere ice sheets surface climate forcing of antarctic mass balance would probably cause an opposite response whereby a warming climate would increase accumulation but not surface melting our new data support teleconnections involving sea level forcing from northern hemisphere ice sheets and changes in north atlantic deep water formation and attendant heat flux to antarctic grounding lines to synchronize the hemispheric ice sheets

pb diffusion in rutile diffusion of pb was measured in natural and synthetic rutile under dry 1 atmosphere conditions using mixtures of pb titanate or pb sulfide and tio2 as the sources of diffusant pb depth profiles were then measured with rutherford backscattering spectrometry rbs over the temperature range 700 1100 c the following arrhenius relation was obtained for the synthetic rutile d 3 9 10 10exp 250 12 kj mol 1 rt m2s 1 results for diffusion in natural and synthetic rutile were quite similar despite significant differences in trace element compositions mean closure temperatures calculated from the diffusion parameters are around 600 c for rutile grains of 100 m size this is about 100 c higher than rutile closure temperature determinations from past field based studies suggesting that rutile is more resistant to pb loss through volume diffusion than previously thought

diffusion obstacles and opportunities in petrochronology many of the approaches in petrochronology are rooted in the assumption of equilibrium diffusion is an expression of disequilibrium the movement of mass in response to chemical potential gradients and isotopes in response to isotopic gradients it is extremely important that we be aware of how the effects of diffusion can place obstacles across our path towards petrochronologic enlightenment conversely the effects of diffusion also provide opportunities for understanding rates processes and conditions experienced by rocks the enormity of the field does not permit us to provide a comprehensive review of either the mathematics of diffusion or quantitative data that have been obtained relevant to the interpretation of diffusive processes in rocks and minerals many resources cover these topics including rimg volume 72 diffusion in minerals and melts zhang and cherniak 2010 and several textbooks crank 1975 glicksman 2000 particularly relevant to the discussion of petrochronology are summaries of the theory and controls on diffusion brady and cherniak 2010 zhang 2010 as well as diffusion rates in feldspar cherniak 2010a accessory minerals cherniak 2010b garnet ganguly 2010 mica pyroxene and amphibole cherniak and dimanov 2010 and melts zhang and ni 2010 zhang et al 2010 rather than duplicate that material our goal is to explore the obstacles and opportunities presented by the effects of diffusion as they inform the rates of petrologic processes to achieve this goal we emphasize key principles and illustrative examples quantitative interpretation of the effects of diffusion assumes predictability of numerous factors that may affect chemical or isotopic transport including temperature initial and boundary conditions water and oxygen fugacities activities of other components multiple mechanisms of diffusion and crystal chemistry coupling of the substitution of elements into different crystallographic sites additionally the extraction of meaningful ages durations of events and temperatures requires

the surface windfield over the antarctic ice sheets the intense radiative cooling of air over the ice slopes of antarctica generates a surface wind regime that is strongly controlled by topography and plays a key role in determining the behaviour of the atmosphere and ocean in high southern latitudes1 7 resultant surface winds are intimately linked to the orientation of the ice terrain fig 1 and display the highest degree of persistence found on earth the close coupling between wind and topography allows estimation of the former if the latter is known with some precision here we report on time averaged near surface airflow over the antarctic continent during winter diagnosed from a recent accurate synthesis of terrain slopes and from estimates of the lower atmospheric temperature structure the simulated drainage pat tern exhibits strong spatial variability with the airflow concentrated into several zones near the coastal margin these confluence regions are responsible for strong persistent katabatic winds over downstream coastal stretches and are indicative of zones of greatest katabatic potential

a revised 1000 year atmospheric δ13c co2 record from law dome and south pole antarctica 1 we present new measurements of 13c of co2 extracted from a high resolution ice core from law dome east antarctica together with firn measurements performed at law dome and south pole covering the last 150 years our analysis is motivated by the need to better understand the role and feedback of the carbon c cycle in climate change by advances in measurement methods and by apparent anomalies when comparing ice core and firn air 13c records from law dome and south pole we demonstrate improved consistency between law dome ice south pole firn and the cape grim tasmania atmospheric 13c data providing evidence that our new record reliably extends direct atmospheric measurements back in time we also show a revised version of early 13c measurements covering the last 1000 years with a mean preindustrial level of 6 50 finally we use a kalman filter double deconvolution to infer net natural co2 fluxes between atmosphere ocean and land which cause small 13c deviations from the predominant anthropogenically induced 13c decrease the main features found from the previous 13c record are confirmed including the ocean as the dominant cause for the 1940 a d co2 leveling our new record provides a solid basis for future investigation of the causes of decadal to centennial variations of the preindustrial atmospheric co2 concentration those causes are of potential significance for predicting future co2 levels and when attempting atmospheric verification of recent and future global carbon emission mitigation measures through coupled climate carbon cycle models