ambient noise tomography of the pyrenees and the surrounding regions inversion for a 3 d vs model in the presence of a very heterogeneous crust we thank all participants in the fieldwork and the municipalities and landlords that hosted a pyrope temporary station we also acknowledge sismob the french seismic mobile pool a com ponent of the resif research facility for providing us with the seismological instrumentation for the temporary deployments we used data from the fr and rd resif g geoscope and ca institut cartogr afic i geol ogic de catalunya permanent net works resif http portal resif fr is a national research infras tructure recognized as such by the french ministry of higher education and research resif is managed by the resif con sortium composed of 18 research institutions and universities in france resif additionally supported by a public grant overseen by the french national research agency anr as part of the investissements d avenir program reference anr 11 eqpx 0040 andthefrenchministryofecology sustainabledevelopment and energy the pyrope experiment was supported by the french research agency anr blanc program project pyrope anr 09 blan 0229 this is a contribution of the team consolider ingenio 2010 topo iberia csd2006 00041 c

reassessment of net surface mass balance in antarctica abstract recent in situ measurements of surface mass balance and improved calculation techniques are used to produce an updated assessment of net surface mass balance over antarctica a new elevation model of antarctica derived from ers 1 satellite altimetry supplemented with conventional data was used to delineate the ice flow drainage basins across antarctica the areas of these basins were calculated using the recent digital descriptions of coastlines and grounding lines the delineation of drainage basins was achieved using an automatic procedure which gave similar results to earlier hand drawn catchment basins more than 1800 published and unpublished in situ measurements of net surface mass balance from antarctica were collated and then interpolated a net surface mass balance map was derived from passive microwave satellite data being employed as a forcing field to control the interpolation of the sparse in situ observations basinwide integrals of net surface mass balance were calculated using t

influence of antarctic ice sheet lowering on the southern hemisphere climate modeling experiments mimicking the mid miocene a coupled global atmosphere ocean model is used to study the influence of the antarctica ice sheet in a configuration that mimics that of the early miocene on the atmospheric and oceanic circulations based on different climate simulations of the present day ctr and conducted with distinct antarctic ice sheet topography ais exp it is found that the reduction of the antarctic ice sheet topography ais induces warming of the southern hemisphere and reduces the meridional thermal gradient consequently the atmospheric transient low level eddy heat flux overline v prime t prime and the eddy momentum flux overline u prime v prime are reduced causing the reduced transport of heat from the mid latitudes to the pole the stationary flow and transient wave anomalies generate changes in the ssts which modify the rate of deep water formation strengthening the formation of the antarctic bottom water substantial changes are predicted to occur in the atmospheric and oceanic heat transport and a comparison between the total heat transport of the atmosphere ocean system as simulated by the ais exp and the ctr runs shows that the reduction of the ais height leads to reduced southern hemisphere poleward and increased equatorward heat transport these results are in agreement with reduced storm track activities and baroclinicity

the speciation of carbon dioxide in silicate melts the speciation of co2 in dacite phonolite basaltic andesite and alkali silicate melt was studied by synchrotron infrared spectroscopy in diamond anvil cells to 1 000 c and more than 200 kbar upon compression to 110 kbar at room temperature a conversion of molecular co2 into a metastable carbonate species was observed for dacite and phonolite glass upon heating under high pressure molecular co2 re appeared infrared extinction coefficients of both carbonate and molecular co2 decrease with temperature this effect can be quantitatively modeled as the result of a reduced occupancy of the vibrational ground state in alkali silicate nbo t 0 98 and basaltic andesite nbo t 0 42 melt only carbonate was detected up to the highest temperatures studied for dacite nbo t 0 09 and phonolite melts nbo t 0 14 the equilibrium co2 o2 co3 2 in the melt shifts toward co2 with increasing temperature with ln k 4 57 1 68 5 05 1 44 103 t 1 for dacite melt h 42 kj mol 1 and ln k 6 13 2 41 7 82 2 41 103 t 1 for phonolite melt h 65 kj mol 1 where k is the molar ratio of carbonate over molecular co2 and t is temperature in kelvin together with published data from annealing experiments these results suggest that s and h are linear functions of nbo t based on this relationship a general model for co2 speciation in silicate melts is developed with ln k a b t where t is temperature in kelvin and a 2 69 21 38 nbo t b 1 480 38 810 nbo t the model shows that at temperatures around 1 500 c even depolymerized melts such as basalt contain appreciable amounts of molecular co2 and therefore the diffusion coefficient of co2 is only slightly dependent on composition at such high temperatures however at temperatures close to 1 000 c the model predicts a much stronger dependence of co2 solubility and speciation on melt composition in accordance with available solubility data

significance of geological units of the bohemian massif czech republic as seen by ambient noise interferometry broadband recordings of 88 seismic stations distributed in the bohemian massif czech republic and covering the time period of up to 12 years were processed by a cross correlation technique all correlograms were analyzed by a novel approach to get both group and phase dispersion of rayleigh and love waves individual dispersion curves were averaged in five distinct geological units which constitute the bohemian massif saxothuringian tepla barrandean sudetes moravo silesian and moldanubian estimated error of the averaged dispersion curves are by an order smaller than the inherent variability due to the 3d distribution of seismic velocities within the units the averaged dispersion data were inverted for 1d layered velocity models including their uncertainty which are characteristic for each of the geological unit we found that overall the differences between the inverted velocity models are of similar order as the variability inside the geological units suggesting that the geological specification of the units is not fully reflected into the s wave propagation velocities on a regional scale nevertheless careful treatment of the dispersion data allowed us to identify some robust characteristics of the area the vp to vs ratio is anomalously low 1 6 for all the units the moldanubian is the most rigid and most homogeneous part of the bohemian massif middle crust in the depth range of 3 15 km is relatively homogeneous across the investigated region while both uppermost horizon 0 3 km and lower crust 15 km exhibit lower degree of homogeneity

spatial patterns of variability in antarctic surface temperature connections to the southern hemisphere annular mode and the southern oscillation 1 the 17 year 1982 1998 trend in surface temperature shows a general cooling over the antarctic continent warming of the sea ice zone with moderate changes over the oceans warming of the peripheral seas is associated with negative trends in the regional sea ice extent effects of the southern hemisphere annular mode sam and the extrapolar southern oscillation so on surface temperature are quantified through regression analysis positive polarities of the sam are associated with cold anomalies over most of antarctica with the most notable exception of the antarctic peninsula positive temperature anomalies and ice edge retreat in the pacific sector are associated with el nino episodes over the past two decades the drift towards high polarity in the sam and negative polarity in the so indices couple to produce a spatial pattern with warmer temperatures in the antarctic peninsula and peripheral seas and cooler temperatures over much of east antarctica

surface melting derived from microwave radiometers a climatic indicator in antarctica this paper aims at presenting a new dataset including the melt events derived from microwave remote sensing occurring in antarctica from summer 1979 80 to 2005 06 the method for detecting melt events and sources of error is presented and then trends in melt duration for every pixel are extracted from the dataset mapped and analyzed the analysis focuses on two particular cases and the main results show that 1 the trends over the period 1980 2006 in the antarctic peninsula match with lengthening of the melt season on the ice shelves and surprisingly shortening of the melt season in the mountainous area of the peninsula and 2 the trends over the period 1996 2006 on the entire continent show a dipolar pattern with the western regions experiencing decreasing melt duration whereas east antarctica and the ross ice shelf experience increasing melt duration this pattern closely mirrors the temperature pattern expected when the southern annular mode is in a decreasing trend as it is over the period 1996 2006 for further analysis and validation the dataset has been made available at http www lgge obs ujf grenoble fr picard melting

the evolving instability of the remnant larsen b ice shelf and its tributary glaciers 2015 elsevier b v following the 2002 disintegration of the northern and central parts of the larsen b ice shelf the tributary glaciers of the southern surviving part initially appeared relatively unchanged and hence assumed to be buttressed sufficiently by the remnant ice shelf here we modify this perception with observations from icebridge altimetry and insar inferred ice flow speeds our analyses show that the surfaces of leppard and flask glaciers directly upstream from their grounding lines lowered by 15 to 20 m in the period 2002 2011 the thinning appears to be dynamic as the flow of both glaciers and the remnant ice shelf accelerated in the same period flask glacier started accelerating even before the 2002 disintegration increasing its flow speed by 55 between 1997 and 2012 starbuck glacier meanwhile did not change much we hypothesize that the different evolutions of the three glaciers are related to their dissimilar bed topographies and degrees of grounding we apply numerical modeling and data assimilation that show these changes to be accompanied by a reduction in the buttressing afforded by the remnant ice shelf a weakening of the shear zones between its flow units and an increase in its fracture the fast flowing northwestern part of the remnant ice shelf exhibits increasing fragmentation while the stagnant southeastern part seems to be prone to the formation of large rifts some of which we show have delimited successive calving events a large rift only 12 km downstream from the grounding line is currently traversing the stagnant part of the ice shelf defining the likely front of the next large calving event we propose that the flow acceleration ice front retreat and enhanced fracture of the remnant larsen b ice shelf presage its approaching demise

a doubling in snow accumulation in the western antarctic peninsula since 1850 1 we present results from a new medium depth 136 metres ice core drilled in a high accumulation site 73 59 s 70 36 w on the south western antarctic peninsula during 2007 the gomez record reveals a doubling of accumulation since the 1850s from a decadal average of 0 49 mweq y 1 in 1855 1864 to 1 10 mweq y 1 in 1997 2006 with acceleration in recent decades comparison with published accumulation records indicates that this rapid increase is the largest observed across the region evaluation of the relationships between gomez accumulation and the primary modes of atmospheric circulation variability reveals a strong temporally stable and positive relationship with the southern annular mode sam furthermore the sam is demonstrated to be a primary factor in governing decadal variability of accumulation at the core site r 0 66 the association between gomez accumulation and enso is complex while sometimes statistically significant the relationship is not temporally stable thus at decadal scales we can utilise the gomez accumulation as a suitable proxy for sam variability but not for enso

crustal and uppermost mantle structure of the bohemian massif based on celebration 2000 data 1 the deep structure of the bohemian massif bm the largest stable outcrop of variscan rocks in central europe was studied using the data of the international seismic refraction experiment central european lithospheric experiment based on refraction celebration 2000 the data were interpreted by seismic tomographic inversion and by two dimensional 2 d trial and error forward modeling of p and s waves additional constraint on crustal structure was given by amplitude modeling using the reflectivity method and gravity modeling though consolidated the bm can be subdivided into several tectonic units separated by faults shear zones or thrusts reflecting varying influence of the cadomian and variscan orogeneses the saxothuringian barrandian moldanubian and moravian velocity models determine three types of crust mantle transition in the bm reflecting variable crustal thickness and delimiting contacts of tectonic units in depth the nw area the saxothuringian has a highly reflective lower crustal layer above moho with a strong velocity contrast at the top of this layer this reflective laminated lower crust reaches depths of 26 35 km and is characteristic for the saxothuringian unit which was subject to eastward subduction the moldanubian in the central part is characterized by the deepest 39 km and the most pronounced moho within the whole bm with a strong velocity contrast 6 9 8 1 km s 1 a thick crust mantle transition zone in the se with velocity increase from 6 8 to 7 8 km s 1 over the depth range of 23 40 km seems to be the characteristic feature of the moravian overthrusted by the moldanubian during variscan collision

climate variables along a traverse line in dronning maud land east antarctica temperature density and accumulation data were obtained from shallow firn cores drilled during an overland traverse through a previously unknown part of dronning maud land east antarctica the traverse area is characterised by high mountains that obstruct the ice flow resulting in a sudden transition from the polar plateau to the coastal region the spatial variations of potential temperature near surface firn density and accumulation suggest that katabatic winds are active in this region proxy wind data derived from firn density profiles confirm that annual mean wind speed is strongly related to the magnitude of the surface slope the high elevation of the ice sheet south of the mountains makes for a dry cold climate in which mass loss owing to sublimation is small and erosion of snow by the wind has a potentially large impact on the surface mass balance a simple katabatic wind model is used to explain the variations of accumulation along the traverse line in terms of divergence convergence of the local transport of drifting snow the resulting wind and snowdrift patterns are closely connected to the topography of the ice sheet ridges are especially sensitive to erosion while ice streams and other depressions act as collectors of drifting snow

antarctic temperatures over the past two centuries from ice cores 1 we present a reconstruction of antarctic mean surface temperatures over the past two centuries based on water stable isotope records from high resolution precisely dated ice cores both instrumental and reconstructed temperatures indicate large interannual to decadal scale variability with the dominant pattern being anti phase anomalies between the main antarctic continent and the antarctic peninsula region comparative analysis of the instrumental southern hemisphere sh mean temperature record and the reconstruction suggests that at longer timescales temperatures over the antarctic continent vary in phase with the sh mean our reconstruction suggests that antarctic temperatures have increased by about 0 2 c since the late nineteenth century the variability and the long term trends are strongly modulated by the sh annular mode in the atmospheric circulation

factors controlling the near surface wind field in antarctica abstract using data from the regional atmospheric climate model racmo ant1 the momentum budget of the antarctic atmospheric surface layer sl taken as the lowest model layer located at 6 7 m above the surface is presented in july winter the katabatic pressure gradient force pgf dominates the sl momentum budget over the steep coastal slopes which results in strong 10 15 m s 1 and directionally constant katabatic winds farther inland where surface slopes are more gentle the large scale pgf may become equally important with the circumpolar pressure trough north of the antarctic coastline the large scale pgf acts along with the katabatic pgf in the downslope direction in wilkes land dronning maud land and on the western ross ice shelf the large scale pgf causes equivalent geostrophic winds in excess of 10 m s 1 thermal wind effects that oppose the downslope acceleration are especially strong in areas where large scale forcing is weak which allows cold air to pile up over the flat ice she

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

southern hemisphere circulation anomalies associated with extreme antarctic peninsula winter temperatures the southern hemisphere reveals markedly different circulation patterns associated with extreme warm and cold antarctic peninsula ap winter temperatures warm winters are associated with negative 500 hpa height anomalies in the amundsen sea bellingshausen sea as bs and positive anomalies in the south pacific sp and scotia sea with opposing anomalies existent in cold winters furthermore a switch in the relative strength of the two arms of the new zealand split jet the subtropical jet stj and polar front jet pfj occurs with the pfj stj strengthened and the stj pfj weakened in warm cold years leading to increased cyclonic activity in the as bs sp and a corresponding decrease in the sp as bs these hemispheric anomaly patterns bear a strong resemblance to those associated with el nino southern oscillation enso events and their origins can be ascribed to tropical sea surface temperatures sst changes however the correspondence between warm cold enso events and cold warm winters is not perfect potential contributors to this non linearity include intraseasonal tropical sst variations not necessarily represented in the usual filtered enso indices and the persistence of local sea ice anomalies west of the peninsula

small scale spatio temporal characteristics of accumulation rates in western dronning maud land antarctica spatio temporal variations of the recently determined accumulation rate are investigated using ground penetrating radar gpr measurements and firn core studies the study area is located on ritscherflya in western dronning maud land antarctica at an elevation range 1400 1560 m accumu lation rates are derived from internal reflection horizons irhs tracked with gpr which are connected to a dated firn core gpr derived internal layer depths show small relief along a 22 km profile on an ice flowline average accumulation rates are about 190 kg m 2 a 1 1980 2005 with spatial variability 1 of 5 along the gpr profile the interannual variability obtained from four dated firn cores is one order of magnitude higher showing 1 standard deviations around 30 mean temporal variations of gpr derived accumulation rates are of the same magnitude or even higher than spatial variations temporal differences between 1980 90 and 1990 2005 obtained from two dated irhs along the gpr profile indicate temporally non stationary processes linked to spatial variations comparison with similarly obtained accumulation data from another coastal area in central dronning maud land confirms this observation our results contribute to understanding spatio temporal variations of the accumulation processes necessary for the validation of satellite data e g altimetry studies and gravity missions such as gravity recovery and climate experiment grace

ice core evidence for significant 100 year regional warming on the antarctic peninsula we present a new 150 year high resolution stable isotope record delta o 18 from the gomez ice core drilled on the data sparse south western antarctic peninsula revealing a similar to 2 7 degrees c rise in surface temperatures since the 1950s the record is highly correlated with satellite derived temperature reconstructions and instrumental records from faraday station on the north west coast thus making it a robust proxy for local and regional temperatures since the 1850s we conclude that the exceptional 50 year warming previously only observed in the northern peninsula is not just a local phenomena but part of a statistically significant 100 year regional warming trend that began around 1900 a suite of coupled climate models are employed to demonstrate that the 50 and 100 year temperature trends are outside of the expected range of variability from pre industrial control runs indicating that the warming is likely the result of external climate forcing citation thomas e r p f dennis t j bracegirdle and c franzke 2009 ice core evidence for significant 100 year regional warming on the antarctic peninsula geophys res lett 36 l20704 doi 10 1029 2009gl040104

variability of subantarctic mode water and antarctic intermediate water in the drake passage during the late twentieth and early twenty first centuries a time series of the physical and biogeochemical properties of subantarctic mode water samw and antarctic intermediate water aaiw in the drake passage between 1969 and 2005 is constructed using 24 transects of measurements across the passage both water masses have experienced substantial variability on interannual to interdecadal time scales samw is formed by winter overturning on the equatorward flank of the antarctic circumpolar current acc in and to the west of the drake passage its interannual variability is primarily driven by variations in wintertime air sea turbulent heat fluxes and net evaporation modulated by the el nino southern oscillation enso despite their spatial proximity the aaiw in the drake passage has a very different source than that of the samw because it is ventilated by the northward subduction of winter water originating in the bellingshausen sea changes in aaiw are mainly forced by variability in winter water properties resulting from fluctuations in wintertime air sea turbulent heat fluxes and spring sea ice melting both of which are linked to predominantly enso driven variations in the intensity of meridional winds to the west of the antarctic peninsula a prominent exception to the prevalent modes of samw and aaiw formation occurred in 1998 when strong wind forcing associated with constructive interference between enso and the southern annular mode sam triggered a transitory shift to an ekman dominated mode of samw ventilation and a 1 2 yr shutdown of aaiw production the interdecadal evolutions of samw and aaiw in the drake passage are distinct and driven by different processes samw warmed by 0 3 c and salinified by 0 04 during the 1970s and experienced the reverse trends between 1990 and 2005 when the coldest and freshest samw on record was observed in contrast aaiw underwent a net freshening by 0 05 between the 1970s and the twenty first century although the reversing changes in samw were chiefly forced by a 30 yr oscillation in regional air sea turbulent heat fluxes and precipitation associated with the interdecadal pacific oscillation with a sam driven intensification of the ekman supply of antarctic surface waters from the south contributing significantly too the freshening of aaiw was linked to the extreme climate change that occurred to the west of the antarctic peninsula in recent decades there a freshening of the winter water ventilating aaiw was brought about by increased precipitation and a retreat of the winter sea ice edge which were seemingly forced by an interdecadal trend in the sam and regional positive feedbacks in the air sea ice coupled climate system all in all these findings highlight the role of the major modes of southern hemisphere climate variability in driving the evolution of samw and aaiw in the drake passage region and the wider south atlantic and suggest that these modes may have contributed significantly to the hemispheric scale changes undergone by those waters in recent decades

the relationship between the southern hemisphere annular mode and antarctic peninsula summer temperatures analysis of a high resolution model climatology abstract the large regional summer warming on the east coast of the northern antarctic peninsula ap which has taken place since the mid 1960s has previously been proposed to be caused by a trend in the southern hemisphere annular mode sam the authors utilize a high resolution regional atmospheric model climatology 14 km grid spacing to study the mechanisms that determine the response of the near surface temperature to an increase in the sam t sam month to month variations in near surface temperature and surface pressure are well represented by the model it is found that north of 68 s t sam is much larger on the eastern lee side than on the western windward side of the barrier this is because of the enhanced westerly flow of relatively warm air over the barrier which warms and dries further as it descends down the lee slope the downward motion on the eastern side of the barrier causes a decrease in surface mass balance and cloud cover south of 68 s vertical deflection across

carbon dioxide speciation in silicate melts a restart abstract using infrared spectroscopy we investigated the speciation of carbon dioxide in albitic and synthetic iron free dacitic glasses after annealing the glasses below the glass transition temperature in the temperature range 673 973 k at 0 5 gpa samples were rapidly quenched under constant pressure the experiments show that the ratio of the integrated intensities of the 2350 cm 1 band due to molecular co 2 to that of the band doublet at 1700 1375 cm 1 due to co 3 2 increases with higher annealing temperatures for both glass compositions our study demonstrates that in contrast to recent suggestions the equilibrium of the co 2 species reaction co 2 o 2 co 3 2 in silicate glasses melts shifts towards molecular co 2 with increasing temperature the co 2 species concentrations and an ideal solution model were used to determine equilibrium constants for the homogeneous species reaction we derived preliminary values for the enthalpy h 0 and entropy s 0 of this reaction assuming that the species concentrations reflect those at experimental temperatures h 0 12 2 kj mol 1 and s 0 23 3 j mol 1 k 1 for albitic composition h 0 29 2 kj mol 1 and s 0 32 3 j mol 1 k 1 for dacitic composition

downward particle fluxes wind and a phytoplankton bloom over a polar continental shelf a stormy impulse for the biological pump abstract downward particle fluxes were collected on two sites on the antarctic continental shelf 407 m to 491 m depth during 30 days in the austral spring and summer 2003 2004 the sampling period included the onset and demise of a phytoplankton bloom and the occurrence of a storm the calm period previous to the storm enabled the phytoplankton to flourish and set conditions for a bloom the storm enhanced mixing production and particle aggregation that increased the transport of organic matter to the seabed the wind induced particle pulse represented 53 306 mg oc m 2 and 826 mg bsi m 2 of the total mass flux collected during the study period at midwater column 179 m depth close to the seabed 28 m above the seafloor the sample corresponding to the period of the highest flux in the upper trap was lost however high oc and bsi fluxes 279 mg oc m 2 and 901 mg bsi m 2 were still collected three days after these fluxes were 42 and 30 of the respective fluxes collected at this depth throughout the study diatom aggregates and faecal pellets were the main vehicles for the transport of organic matter faecal pellets and foraminifera tests were ubiquitous in the traps however ellipsoidal faecal pellets were only present in the deeper traps where in some periods were more abundant than the faecal strings comparatively smaller particle fluxes than in other antarctic settings during the same season were found and the differences attributed to the denser sea ice coverage 60 observed during the present study the chemical quality and the magnitude of the particle fluxes suggest that the phytoplankton bloom and the storm developed at least over a 75 km long area the coincidence of these events produced in three days organic carbon and biogenic silica pulses over an area of at least 805 km2 of the continental shelf that may have amounted 85 to 225 tons and 308 to 725 tons respectively the occurrence of storms 15 m s 1 during the spring summer season in the last 20 years averaged 12 events per season suggesting that the action of the wind could be very important in the development of organic matter rich green mats on the sea floor

temporal and spatial variation of stable isotope ratios and accumulation rates in the hinterland of neumayer station east antarctica four firn cores were retrieved in 2007 at two ridges in the area of the ekstrom ice shelf dronning maud land coastal east antarctica in order to investigate the recent regional climate variability and the potential for future extraction of an intermediate depth core stable water isotope analysis tritium content and electrical conductivity were used to date the cores for the period 1981 2006 a strong and significant correlation between the stable isotope composition of firn cores in the hinterland and mean monthly air temperatures at neumayer station was r 0 54 0 71 no atmospheric warming or cooling trend is inferred from our stable isotope data for the period 1962 2006 the stable isotope record of the ice firn cores could expand well beyond the meteoro logical record of the region no significant temporal variation of accumulation rates was detected however decreasing accumulation rates were found from coast to hinterland as well as from east halvfarryggen to west sorasen the deuterium excess d exhibits similar differences higher d at sorasen lower d at halvfarryggen with a weak negative temporal trend on halvfarryggen 0 04 a 1 probably implying increasing oceanic input we conclude that halvfarryggen acts as a natural barrier for moisture carrying air masses circulating in the region from east to west

changes in antarctic temperature wind and precipitation in response to the antarctic oscillation output of a 14 year integration with a high resolution 55 km 55 km regional atmospheric climate model is used to study the response of antarctic near surface climate to the antarctic oscillation aao the periodical strengthening and weakening of the circumpolar vortex in the southern hemisphere in spite of the relatively short record wind temperature and precipitation show widespread and significant aao related signals when the vortex is strong high aao index northwesterly flow anomalies cause warming over the antarctic peninsula ap and adjacent regions in west antarctica and the weddell sea in contrast cooling occurs in east antarctica the eastern ross ice shelf and parts of marie byrd land most of the annual temperature signal stems from the months march august the spatial distribution of the precipitation response to changes in the aao does not mirror temperature changes but is in first order determined by the direction of flow anomalies with respect to the antarctic topography when the vortex is strong high aao index the western ap becomes wetter while the ross ice shelf parts of west antarctica and the lambert glacier basin east antarctica become drier

3d structure of the earth s crust beneath the northern part of the bohemian massif abstract the sudetes 2003 wide angle refraction reflection experiment covered the area of the south western poland and the northern bohemian massif the good quality data that were gathered combined with the data from previous experiments polonaise 97 celebration 2000 allowed us to prepare a 3d seismic model of the crust and uppermost mantle for this area we inverted travel times of both refracted and reflected p waves using the jive3d package this allowed us to obtain a model of p wave velocity distribution as well as the shape of major boundaries in the crust we also present a detailed uncertainty analysis for both the boundary depths and the velocity field in doing the uncertainty analysis we found an interesting strong dependence between uncertainty and inversion scheme order of used phases we also compared the model with surface geology and found good correlation between velocity inhomogeneities in the uppermost crust down to 2 km and major geological units the higher velocity lower crust 6 9 7 2 km s could result from remelting of the lower crust or magmatic underplating

peculiarities of surface wave propagation across central eurasia abstract the recent installation of six broadband digital iris ida seismic stations in the ussr has provided new opportunities for studying surface wave propagation across eurasia group velocities of fundamental rayleigh and love modes between epicenters and these stations were determined for 35 events that occurred since april 1989 to the middle of july 1990 near eurasia differential phase velocities were found for the same arrivals along paths between several pairs of stations group and phase velocities were obtained in the period range from 15 to 300 sec frequency time polarization analysis was used for studying polarization properties of surface waves in some cases significant anomalies in the particle motion for periods up to 100 sec were observed they are attributed to surface wave refraction and scattering due to lateral inhomogeneities at the boundaries and inside the eurasia continent

momentum budget of the east antarctic atmospheric boundary layer results of a regional climate model output of a regional atmospheric climate model is used to quantify the average january and july momentum budget of the atmospheric boundary layer abl over the east antarctic ice sheet and the surrounding oceans results are binned in nine elevation intervals over the ice sheet and six distance intervals over the ocean in january when surface cooling is weak the large scale pressure gradient force dominates the abl momentum budget in july under conditions of strong surface cooling a shallow katabatic jet develops over the gentle slopes of the interior ice sheet and a strong deep jet over the steep coastal slopes in the coastal regions the abl thickens considerably caused by the piling up of cold air over the adjacent sea ice and ice shelves this represents the main opposing force for the katabatic winds horizontal and vertical advection are generally small in the cross slope direction the momentum budget represents a simple balance between surface drag and coriolis turning intraseasonal variability of the large scale wind field in the abl can be explained in terms of the strength of the polar vortex the background baroclinicity and the topography of the ice sheet subsidence is found over the interior ice sheet and rising motion in the coastal zone reflecting the acceleration and deceleration of the katabatic circulation however vertical velocities are generally small because the downslope mass flux in the abl is confined to a shallow layer below the wind speed maximum

holocene accumulation and ice sheet dynamics in central west antarctica 1 we derive depth age relationships across the ice divide between the ross and amundsen seas by tracking radar detected layers from the byrd ice core and a dated 105 m core near the divide the depth age relationships and an ice flow model are used to establish histories of accumulation and ice sheet dynamics over the past 8000 years results show that accumulation was approximately 30 higher than today from 5000 to 3000 years ago antarctic climate variability today is dominated by periodic fluctuations in strength of the circumpolar vortex which raises the possibility that the vortex was systematically weaker during the period of high accumulation accumulation today decreases almost linearly across the divide it is unlikely that this pattern has changed through the holocene the radar detected stratigraphy shows no evidence of the arched layers that are expected beneath a stable divide that is frozen to its bed implying that the divide has also been migrating and or the basal ice has been sliding through the holocene we cannot rule out the possibility of sliding because the basal ice is near its pressure melting point other evidence indicates that divide migration is likely the ross sea sector is now near steady state but it had a strong negative imbalance 200 years ago when kamb ice stream was active in contrast recent speedups of pine island and thwaites glaciers have likely caused the mass balance of the amundsen sea sector to become negative the divide is likely migrating toward the ross sea today

a century of climate variability in central dronning maud land east antarctica and its relation to southern annular mode and el nino southern oscillation stable isotope records of oxygen and hydrogen were studied from a 65 m long ice core retrieved from the central dronning maud land east antarctica in order to reconstruct the coastal antarctic climate variability during the last century and its relation to the southern annular mode sam and el nino southern oscillation enso the 18 o records showed a significant relation to the sam with a dominant 4 years variability except during specific periods 1918 1927 19381947 1989 2005 when enso teleconnection was established through the in phase relation between sam and southern oscillation index soi the combined influence of enso and sam was seen on surface air temperatures in this region mainly during the austral summer season from 1989 to 2005 further a significant relationship between 18 o and sam was observed on a decadal scale which overrides the intermittent influence of enso major shifts in the deuterium excess record were observed during periods of enso teleconnections which support a shift in moisture source regions during the periods of stronger enso teleconnections surface air temperatures estimated using the 18 o t spatial slope for this region depicted a significant warming of 1 c for the past century the study reveals that throughout the last century sam was the dominant mode of climatic variability in the coastal region of central dronning maud land on a decadal scale

central west antarctica among the most rapidly warming regions on earth the west antarctic ice sheet is contributing to sea level rise but temperature trends in the region have remained uncertain a complete temperature record for byrd station in central west antarctica spanning from 1958 to 2010 establishes west antarctica as one of the fastest warming regions globally

spatial and temporal variability in snow accumulation at the west antarctic ice sheet divide over recent centuries mean annual accumulation rates of 0 200 0 204 and 0 221 mweq a 1 respectively small scale spatial variability ssv was determined using an analysis of variance of accumulation in the ice core array thereby quantifying the uncertainty in individual accumulation records results indicate that the spatial variability was 0 030 mweq a 1 o r approximately 15 of the average annual accumulation an accumulation record representative of the wais divide local area over recent centuries was developed using a principal component analysis to identify the coherent accumulation signal the wais divide local record exhibited 14 interannual variability 1 standard deviation of the mean with the ssv reduced to 0 017 mweq a 1 correlations of the wais divide local accumulation record with atmospheric indices e g antarctic oscillation exhibited periods when the records oscillate in and out of phase thus reconstructing local and global atmospheric indices from wais divide accumulation records over recent centuries may prove problematic

the influence of the fluid phase composition on the solidus temperatures in the haplogranite system naalsi3o8 kalsi3o8 sio2 h2o co2 the solidus temperatures in the haplogranite system naalsi3o8 kalsi3o8 sio2 h2o co2 have been determined up to 15 kbar for a constant molar ratio of sodium to potassium of 1 1 and for fluid compositions ranging from pure water to pure carbon dioxide the data for the water saturated solidus are virtually identical with those of previous studies at constant pressure the solidus curve as a function of the fluid phase composition exhibits a point of inflection in the range of the water rich compositions this phenomenon is attributed to chemical interactions between the co2 and the h2o in the silicate melt the point of inflection disappears if the co2 in the gas phase is replaced by molecular nitrogen the co2 saturated solidi have been measured at 2 and 5 kbars the data at 5 kbar indicate a melting point depression in the order of 40 c compared to the dry solidus of huang and wyllie 1975 the experimental data can be used to estimate the melting temperatures of common quartz and feldspar bearing crustal rocks under the conditions of granulite facies metamorphism since for most fluid phase compositions the solidus curves are very steep in the p t diagram the beginning of melting is nearly exclusively determined by the fluid composition and almost independent of pressure between about 2 and more than 10 kbar therefore the onset of partial melting in quartz and feldspar containing rocks under granulite facies conditions can be used to estimate the composition of a coexisting h2o co2 fluid phase if geothermometric data are available the temperature range between the beginning of granulite facies metamorphism and the initiation of melting expands with increasing carbon dioxide content in the h2o co2 fluid phase at a co2 molar fraction of 0 9 this range extends from about 600 c to 900 c and is almost independent of pressure

interpretation of recent southern hemisphere climate change climate variability in the high latitude southern hemisphere sh is dominated by the sh annular mode a large scale pattern of variability characterized by fluctuations in the strength of the circumpolar vortex we present evidence that recent trends in the sh tropospheric circulation can be interpreted as a bias toward the high index polarity of this pattern with stronger westerly flow encircling the polar cap it is argued that the largest and most significant tropospheric trends can be traced to recent trends in the lower stratospheric polar vortex which are due largely to photochemical ozone losses during the summer fall season the trend toward stronger circumpolar flow has contributed substantially to the observed warming over the antarctic peninsula and patagonia and to the cooling over eastern antarctica and the antarctic plateau

a damage mechanics assessment of the larsen b ice shelf prior to collapse toward a physically based calving law calving is a primary process of mass ablation for glaciers and ice sheets though it still eludes a general physical law here we propose a calving framework based on continuum damage mechanics coupled with the equations of viscous deformation of glacier ice we introduce a scalar damage variable that quantifies the loss of load bearing surface area due to fractures and that feeds back with ice viscosity to represent fracture induced softening the calving law is a standard failure criterion for viscous damaging materials and represents a macroscopic brittle instability quantified by a critical or threshold damage we constrain this threshold using the ice sheet system model issm by inverting for damage on the larsen b ice shelf prior to its 2002 collapse by analyzing the damage distribution in areas that subsequently calved we conclude that calving occurs after fractures have reduced the load bearing capacity of the ice by 60 10 2012 american geophysical union all rights reserved

an antarctic circumpolar wave in surface pressure wind temperature and sea ice extent the southern ocean is the only oceanic domain encircling the globe it contains the strong eastward flow of the antarctic circumpolar current and is the unifying link for exchanges of water masses at all depths between the world s major ocean basins1 as these exchanges are an important control on mean global climate the southern ocean is expected to play an important role in transmitting climate anomalies around the globe interannual variability has been often observed at high southern latitudes and observations of sea ice extent suggest that such features propagate eastwards around the southern ocean2 3 here we use data from a variety of observational techniques to identify significant interannual variations in the atmospheric pressure at sea level wind stress sea surface temperature and sea ice extent over the southern ocean these anomalies propagate eastward with the circumpolar flow with a period of 4 5 years and taking 8 10 years to encircle the pole this system of coupled anomalies which we call the antarctic circumpolar wave is likely to play an important role in climate regulation and dynamics both within and beyond the southern ocean

spatial and temporal variability of antarctic ice sheet microwave brightness temperatures 1 annual and interannual variability of 21 years of passive microwave brightness temperatures on the antarctic ice sheet is documented through principal component analysis the leading modes show that brightness temperatures are dominantly forced by the annual temperature cycle with surface melting signals explaining about 5 of the total variance of the data analysis of the data with the annual cycle and melting signals removed results in two significant interannual modes the first is consistent with the antarctic oscillation and its influence on antarctic surface temperatures while the second reflects regional scale variability that appears to be linked to sea ice anomalies and the el nino southern oscillation the expression of these characteristic patterns of southern hemisphere climate variability on the antarctic continent provides a framework for interpreting modern climate records as well as a basis for reconstructing past climate variability with ice cores

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

differing source water inputs moderated by evaporative enrichment determine the contrasting δ18ocellulose signals in maritime antarctic moss peat banks 1 oxygen isotope palaeoclimate records preserved in moss tissue cellulose are complicated by environmental influences on the relationships between source water inputs and evaporative conditions we carried out stable isotope analyses of precipitation collected from the maritime antarctic and cellulose extracted from co located chorisodontium aciphyllum dominated moss peat bank deposits accumulated since 1870 a d analyses of stable oxygen and hydrogen isotope composition of summer precipitation on signy island 60 7 s 45 6 w established a local meteoric water line lmwl similar to both the global mwl and other lmwls and almost identical to the hadam3 isotope enabled global circulation model output the oxygen isotopic composition of cellulose 18oc revealed little temporal variation between four moss peat banks on signy island since 1870 however 18oc followed two patterns with sites a and d consistently 3 enriched relative to 18oc values from sites b and c the growing moss surfaces at sites a and d are likely to have been hydrated by isotopically heavier summer precipitation whilst at sites b and c the moss banks are regularly saturated by the isotopically depleted snow melt streams laboratory experiments revealed that evaporative enrichment of c aciphyllum moss leaf water by 5 occurred rapidly following saturation ecologically equivalent to post rainfall or snow melt periods in addition to the recognized source water cellulose fractionation extent of 27 3 such a shift would account for the 32 difference measured between 18o of signy island precipitation and cellulose

structural controls of co 2 on y la and sr incorporation in sodium rich silicate carbonate melts by in situ high p t exafs abstract carbonate rich silicate and carbonate melts play a crucial role in deep earth magmatic processes and their melt structure is a key parameter as it controls physical and transport properties carbon rich melts can be strongly enriched in trace elements but the structural incorporation mechanisms of these elements are difficult to study because such melts generally cannot be quenched to glasses in this contribution we investigate the influence of co 2 on the local environments of trace elements contained in silicate glasses with variable co 2 concentrations and in silicate and carbonate melts the melts were studied in situ at high pressure and temperature conditions using the paris edinburgh press 2 2 to 2 6 gpa and 1200 to 1500 c the compositions studied include sodium rich peralkaline silicate melts and glasses and carbonate melts similar to those occurring naturally at oldoinyo lengai volcano the local environments of yttrium y lanthanum la and strontium sr were investigated using extended x ray absorption fine structure exafs spectroscopy main findings of the study suggest 1 in peralkaline silicate glasses the local structure of y is unaffected by the co 2 content contrary a slight increase of oxygen bond lengths of sr and la is inferred with increasing co 2 content in peralkaline glasses while they remain constant in glasses of even higher peralkalinity independent of the co 2 content 2 in silicate melts of different co 2 contents y o bond lengths are constant while a slight increase within carbonate melt compositions is deduced on the other hand a steady bond lengths increase over the whole compositional range is inferred for la o and sr o this may well be explained by distinct preferences of these elements for specific local environments based on these new data we suggest potential mechanisms for the structural incorporation of these elements a key step towards understanding their partitioning behavior in natural magmatic systems

the molecular structure of melts along the carbonatite kimberlite basalt compositional joint co2and polymerisation transitional melts intermediate in composition between silicate and carbonate melts form by low degree partial melting of mantle peridotite and might be the most abundant type of melt in the asthenosphere their role in the transport of volatile elements and in metasomatic processes at the planetary scale might be significant yet they have remained largely unstudied their molecular structure has remained elusive in part because these melts are difficult to quench to glass here we use ftir raman 13c and 29si nmr spectroscopy together with first principle molecular dynamic fpmd simulations to investigate the molecular structure of transitional melts and in particular to assess the effect of co2on their structure we found that carbon in these glasses forms free ionic carbonate groups attracting cations away from their usual depolymerising role in breaking up the covalent silicate network solution of co2in these melts strongly modifies their structure resulting in a significant polymerisation of the aluminosilicate network with a decrease in nbo si of about 0 2 for every 5 mol co2dissolved this polymerisation effect is expected to influence the physical and transport properties of transitional melts an increase in viscosity is expected with increasing co2content potentially leading to melt ponding at certain levels in the mantle such as at the lithosphere asthenosphere boundary conversely an ascending and degassing transitional melt such as a kimberlite would become increasingly fluid during ascent hence potentially accelerate carbon rich transitional melts are effectively composed of two sub networks a carbonate and a silicate one leading to peculiar physical and transport properties

synchronous variability in the southern hemisphere atmosphere sea ice and ocean resulting from the annular mode zonally symmetric fluctuations of the midlatitude westerly winds characterize the primary mode of atmospheric variability in the southern hemisphere during all seasons this is true not only in observations but also in an unforced 15 000 yr integration of a coarse resolution r15 coupled ocean atmosphere model here it is documented how this mode of atmospheric variability known as the southern annular mode sam generates ocean circulation and sea ice variations in the model integration on interannual to centennial timescales that are tightly in phase with the sam the positive phase of the sam is associated with an intensification of the surface westerlies over the circumpolar ocean around 608s and a weakening of the surface westerlies farther north this induces ekman drift to the north at all longitudes of the circumpolar ocean and ekman drift to the south at around 308s through mass continuity the ekman drift generates anomalous upwelling along the margins of the antarctic continent and downwelling around 458s the anomalous flow diverging from the antarctic continent also increases the vertical tilt of the isopycnals in the southern ocean so that a more intense circumpolar current is also closely associated with positive sam in addition the anomalous divergent flow advects sea ice farther north resulting in an increase in sea ice coverage finally positive sam drives increases in poleward heat transport at about 308s while decreases occur in the circumpolar region ocean and sea ice anomalies of the opposite sign occur when the sam is negative the ocean and sea ice fluctuations associated with the sam constitute a significant fraction of simulated ocean variability poleward of 308s year round the robustness of the mechanisms relating the sam to oceanic variability suggests that the sam is likely an important source of large scale variability in the real southern hemisphere ocean

crustal structure at the easternmost termination of the variscan belt based on celebration 2000 and alp 2002 data abstract the eastern margin of the variscan belt in europe comprises plate boundaries between continental blocks and terranes formed during different tectonic events the crustal structure of that complicated area was studied using the data of the international refraction experiments celebration 2000 and alp 2002 the seismic data were acquired along sw ne oriented refraction and wide angle reflection profiles cel10 and alp04 starting in the eastern alps passing through the moravo silesian zone of the bohemian massif and the fore sudetic monocline and terminating in the tesz in poland the data were interpreted by seismic tomographic inversion and by 2 d trial and error forward modelling of the p waves velocity models determine different types of the crust mantle transition reflecting variable crustal thickness and delimiting contacts of tectonic units in depth in the alpine area few km thick lvz with the vp of 5 1 km s 1 dipping to the sw and outcropping at the surface represents the molasse and helvetic flysch sediments overthrust by the northern calcareous alps with higher velocities in the bohemian massif lower velocities in the range of 5 0 5 6 km s 1 down to a depth of 5 km might represent the se termination of the elbe fault zone the fore sudetic monocline and the tesz are covered by sediments with the velocities in the range of 3 6 5 5 km s 1 to the maximum depth of 15 km beneath the mid polish trough the moho in the eastern alps is dipping to the sw reaching the depth of 43 45 km the lower crust at the eastern margin of the bohemian massif is characterized by elevated velocities and high vp gradient which seems to be a characteristic feature of the moravo silesian slightly different properties in the moravian and silesian units might be attributed to varying distances of the profile from the moldanubian thrust front as well as a different type of contact of the brunia with the moldanubian and its northern root sector the moho beneath the fore sudetic monocline is the most pronounced and is interpreted as the first order discontinuity at a depth of 30 km

tropical pacific high latitude south atlantic teleconnections as seen in δ18o variability in antarctic coastal ice cores 1 we use a network of eight ice cores from coastal dronning maud land dml antarctica to examine the role of the tropical enso el nino southern oscillation in the temporal variability of 18o in annual accumulation the longest record from the s100 ice core covering the period 1737 1999 is used to analyze the teleconnections between the tropical pacific and coastal dml on decadal scales and longer a shorter stacked coastal dml 18o series spanning 1955 1999 is constructed to assess the variability of enso teleconnection on interannual scales results suggest that on typical enso timescales of 2 6 years the strength of the teleconnection varies in time being stronger for years with generally negative phase of the southern annular mode sam on the timescales of approximately two decades bidecadal positive isotope anomalies are associated with oceanic warming and a westward sea surface temperature sst gradient in the equatorial pacific bidecadal variability in sam forced by the tropical pacific is proposed as a critical element in the teleconnection our analysis suggests that a multidecadal positive trend in the annual mean 18o values from the analyzed cores can be indicative of the atmospheric warming that begun in this part of the dml already in the 1910s the trend in 18o quantified in terms of long term surface air temperature sat changes is consistent with the instrumental data yet we speculate that the accurate estimation of sat trends requires an assessment of the potential role of secular sam and sea ice extent changes in shaping the isotopic signal

recent atmospheric warming and retreat of ice shelves on the antarctic peninsula in 1978 mercer1 discussed the probable effects of climate warming on the antarctic ice sheet predicting that one sign of a warming trend in this region would be the retreat of ice shelves on the antarctic peninsula analyses of 50 year meteorological records have since revealed atmospheric warming on the antarctic peninsula2 3 and a number of ice shelves have retreated4 8 here we present time series of observations of the areal extent of nine ice shelves on the antarctic peninsula showing that five northerly ones have retreated dramatically in the past fifty years while those further south show no clear trend comparison with airtemperature data shows that the pattern and magnitude of ice shelf retreat is consistent with the existence of an abrupt thermal limit on iceshelf viability the isotherm associated with this limit having been driven south by the atmospheric warming ice shelves therefore appear to be sensitive indicators of climate change

winter water variability in the indian ocean sector of southern ocean during austral summer abstract winter water ww is a feature in the upper layers of the southern ocean during austral summer the interaction of this cold water with surface and deeper subsurface layers can alter the heat budget as well as the carbon cycle however the structure and characteristics of the ww in the southern ocean is poorly understood due to the lack of in situ data in this study hydrographic data collected from the indian expeditions during 2010 and 2011 and from other expeditions during 2003 2006 and 2007 in the southern ocean have been utilized to understand the ww variability and its characteristics in the region between 40 e and 90 e the analysis shows large zonal variations in the distribution of ww during austral summer east of 60 e the ww shows warmer temperature with weaker gradients than the western side which is observed to have a larger meridional extension the high frequency of eddies surface warming and upwelling of the upper circumpolar deep water due to shallow bathymetric features of the kerguelen plateau situated in the eastern side of the study region is proposed as the major mechanisms for this variability the direct impact of southern annular mode on ww variability is investigated and a short term response is observed

the future of antarctica s surface winds simulated by a high resolution global climate model 2 drivers of 21st century changes antarctica s katabatic winds are among the strongest near surface winds on earth and among the most consistent ones as these winds are primarily due to the strong surface cooling greenhouse warming of the surface may act to reduce the strength of these winds as well as their consistency here we use the atmospheric component of the global climate model ec earth in prescribed sea surface temperature sst simulations of the present day 2002 2006 and future 2094 2098 climates using two model resolutions 1 t159l62 100 km 62 vertical levels and 2 t799l91 20 km 91 vertical levels to investigate changes in antarctica s surface winds and the reasons thereof circumpolar westerlies over the southern ocean strengthen and shift poleward because of the deepening of the circumpolar trough and the associated increase in southern annular mode sam especially in high resolution causing weaker coastal easterlies generally surface wind speeds over the antarctica mainland exhibit a small decrease according to the simulations the temperature deficit or inversion strength and associated katabatic forcing exhibit only minor changes over the continent changes in the surface winds over antarctica s slopes can thus be attributed mainly to changes in the synoptic forcing large scale pressure gradient hence with modeled 21st century changes in the katabatic forcing being small changes in zonal and meridional surface winds in and around antarctica are largely decoupled from those over the southern ocean and are governed by changes in synoptic forcing and large scale pressure gradients as a result these changes are largely independent on model resolution

three dimensional seismic modelling of the crustal structure between east european craton and the carpathians in se poland based on celebration 2000 data summary in this paper we present results of 3 d first arrival tomography applied to data recorded in se poland during the celebration 2000 seismic experiment the target area covers ca 500 500 km 2 and represents a complex geological setting from old precambrian platform east european craton eec through the crustal blocks terranes that form the transeuropean suture zone tesz to the young alpine orogen the carpathians contrasting velocity distributions in various geological units makes the tomographic inversion challenging for this reason much attention was paid to the inversion methodology we tested multioffset and multiscale approaches by increasing the offset range in the multioffset inversion we have independently constrained different depth ranges of our model we have found that the multiscale method that is the gradual stepping from bigger to smaller model cells produced the preferred solution resolution of the resultant crustal model was determined by performing checkerboard and restoration resolution tests lateral resolution of the order of 25 km is inferred down to 10 km depth and 50 km down to 25 30 km depth we have also applied a quasi monte carlo analysis to determine the absolute errors of model parameters which to our knowledge is the first such attempt in case of a 3 d wide angle data set the mean uncertainties of our tomographic velocities are 0 1 km s 1 but some anomalies are recovered with

new reconstruction of antarctic near surface temperatures multidecadal trends and reliability of global reanalyses a reconstruction of antarctic monthly mean near surface temperatures spanning 1958 2012 is presented itsprimarygoalistotakeadvantageofarecentlyrevisedkeytemperaturerecordfromwestantarctica byrd to shed further light on multidecadal temperature changes in this region the spatial interpolation relies on a kriging technique aided by spatiotemporal temperature covariances derived from three global reanalyses the european centre for medium range weather forecasts ecmwf interim re analysis erainterim modern era retrospective analysis for research and applications merra and climate forecast system reanalysis cfsr for 1958 2012 the reconstruction yields statistically significant annual warming in the antarctic peninsula and virtually all of west antarctica but no significant temperature change in east antarctica importantly the warming is of comparable magnitude both in central west antarctica and in most of the peninsula rather than concentrated either in one or the other region as previousreconstructions have suggested the transantarctic mountains act for the temperature trends as a clear dividing line between east and west antarctica reflecting the topographic constraint on warm air advection from the amundsen sea basin the reconstruction also serves to highlight spurious changes in the 1979 2009 time series of the three reanalyses that reduces the reliability of their trends illustrating a longstanding issue in high southern latitudes the study concludes with an examination of the influence of the southern annular mode sam on antarctic temperature trends the results herein suggest that the trend of the sam toward its positive phase in austral summer and fall since the 1950s has had a statistically significant cooling effect not only in east antarctica as already well documented and but also only in fall in west antarctica

the link between climate warming and break up of ice shelves in the antarctic peninsula a review of in situ and remote sensing data covering the ice shelves of the antarctic peninsula provides a series of characteristics closely associated with rapid shelf retreat deeply embayed ice fronts calving of myriad small elongate bergs in punctuated events increasing flow speed and the presence of melt ponds on the ice shelf surface in the vicinity of the break ups as climate has warmed in the antarctic peninsula region melt season duration and the extent of ponding have increased most break up events have occurred during longer melt seasons suggesting that meltwater itself not just warming is responsible regions that show melting without pond formation are relatively unchanged melt ponds thus appear to be a robust harbinger of ice shelf retreat we use these observations to guide a model of ice shelf flow and the effects of meltwater crevasses present in a region of surface ponding will likely fill to the brim with water we hypothesize building on weertman 1973 hughes 1983 and van der veen 1998 that crevasse propagation by meltwater is the main mechanism by which ice shelves weaken and retreat a thermodynamic finite element model is used to evaluate ice flow and the strain field and simple extensions of this model are used to investigate crack propagation by meltwater the model results support the hypothesis