quantification of the microstructural evolution of polycrystalline fabrics using fame application to in situ deformation of ice abstract in geology glaciology and material science new technological advances result in an ever increasing amount of data and datasets in particular when in situ experiments are conducted rapid rigorous and reliable statistical treatment is needed to allow researchers to access these large datasets for further analysis here we present fame fabric analyser based microstructure evaluation a suite of matlab scripts that utilize the matlab open source toolboxes mtex and polylx optional for rapid quantification of thin section data the data has been collected using an automated fabric analyser at a spatial resolution of 5 m pixel from the dataset grain maps are reconstructed and grain and grain boundary statistics are determined the same scripts calculate orientation density distribution diagrams and eigenvalues of the orientation tensor in the case of 2d in situ plane strain deformation experiments on polycrystalline heavy water d2o a matlab script based batch analysis for each deformation step was performed fame offers the possibility to generate movie files that combine optical data with c axes orientation data and grain statistics application of the presented scripts to analyse in situ deformation experiments of polycrystalline ice shows the value of rigorous quantification of the microstructural evolution data for process oriented research

an assessment of dynamically recrystallized grainsize as a palaeopiezometer in quartz bearing mylonite zones abstract recrystallized grainsize has been measured in quartz and in some cases feldspar in about 200 samples from 22 mylonite zones from 3 discrete tectonic settings 1 1 supracrustal low temperature shallow dipping thrusts 2 2 deeper level major 100 km thrusts in high grade metamorphic rocks and 3 3 steeply dipping fault zones in granite within a low grade palaeozoic fold belt the concept of a steady state dynamically recrystallized grainsize largely unaffected by post creep processes e g static grain growth receives strong support especially from the microstructures and the independence of finite strain and grainsize in most mylonite zones however the usefulness of this grainsize for predicting stress magnitudes is limited by the apparently independent influence of metamorphic environment on grainsize the available theoretical and empirical stress grainsize relationships do not account for these effects the concept of a steady state grainsize and the ease of accurate measurement offer a potentially powerful method for predicting stress intensity during deformation predicted deviatoric stresses have been computed using twiss theoretical model for comparison with other crustal stress estimates and most samples fall in the range from 20 to 150 mpa in a few cases where discrete high strain mylonite zones occur within contemporaneously regionally deformed rocks the recrystallized grainsize indicates that stresses were 1 5 to 2 times higher within the zones there is a clear need for improved theoretical and or empirical stress grainsize relationships for quartz and other minerals before extensive further application of this technique

rock magnetic proxies of wind intensity and dust since 51 200 cal bp from lacustrine sediments of laguna potrok aike southeastern patagonia the sedimentary archive from laguna potrok aike is the only continuous record reaching back to the last glacial period in continental southeastern patagonia located in the path of the southern hemisphere westerly winds and in the source region of dust deposited in antarctica during glacial periods southern patagonia is a vantage point to reconstruct past changes in aeolian activity here we use high resolution rock magnetic and physical grain size data from site 2 of the international continental scientific drilling program icdp potrok aike maar lake sediment archive drilling project pasado in order to develop magnetic proxies of dust and wind intensity at 52 s since 51 200 cal bp rock magnetic analysis indicates the magnetic mineral assemblage is dominated by detrital magnetite based on the estimated flux of magnetite to the lake and comparison with distal dust records from the southern ocean and antarctica klf is interpreted as a dust indicator in the dust source of southern patagonia at the millennial time scale when ferrimagnetic grain size and coercivity influence are minimal comparison to physical grain size data indicates that the median destructive field of isothermal remanent magnetization mdfirm mostly reflects medium to coarse magnetite bearing silts typically transported by winds for short term suspension comparison with wind intensity proxies from the southern hemisphere during the last glacial period and with regional records from patagonia since the last deglaciation including marine lacustrine and peat bog sediments as well as speleothems reveals similar variability with mdfirm up to the centennial time scale mdfirm is interpreted as a wind intensity proxy independent of moisture changes for southeastern patagonia with stronger winds capable of transporting coarser magnetite bearing silts to the lake

holocene dust in east antarctica provenance and variability in time and space in this paper we provide a comprehensive overview of the state of knowledge of dust flux and variability in time and space in different sectors of east antarctica during the holocene by integrati

tracing dust sources and transport patterns using sr nd and pb isotopes continental dust transported through the atmosphere can be a tracer of atmospheric circulation and transport as well as being a source of information about climate in the dust s source area this information about the provenance of dust transported from desert areas and deposited elsewhere on the oceans and continents can be evaluated using several observational techniques satellite imagery has been used to this end in recent decades and air mass back trajectories have been calculated to trace dust deposits back to their source area another method consists of analysis of the concentration and composition of certain tracers in the dust itself and comparing them to soils and sediments from possible source areas this method has the advantage of being useable for paleo atmospheric circulation and paleo dust transport studies whereas satellite imagery and air mass back trajectories are restricted to relatively recent times we review here different kinds of isotopic tracers that have been used to trace dust provenance but special attention is focused on the use of sr nd and pb isotopes we evaluate their use in studies of both spatially as well as temporally varying continental dust source and transport

dust transport from patagonia to antarctica a new stratigraphic approach from the scotia sea and its implications for the last glacial cycle abstract we studied two deep sea cores from the scotia sea to reconstruct past atmospheric circulation in the southern hemisphere and to resolve a long standing debate on the interpretation of magnetic susceptibility ms records in southern ocean so sediment high sedimentation sites md07 3134 0 2 1 2 m kyr and md07 3133 0 3 2 1 m kyr cover the last 92 5 kyr and 36 kyr respectively both exhibit a one to one coupling of the ms and ca2 signal to the non sea salt nss ca2 signal of the edml ice core clearly identifying atmospheric circulation as means of distribution comparison of additional proxies also excludes major influence by volcanic sources sea ice icebergs or oceanic current transport the close resemblance of the dust proxies over the last glacial cycle in turn allows for the establishment of an age model of unprecedented resolution and precision for so deep sea sediment because atmospheric transport involves no major leads or lags this is of particular importance because ms is routinely measured on deep sea cores in the so but the sediments usually lack biogenic carbonate and therefore had only limited stratigraphic control so far southern south america ssa is the likely source of eolian material because site md07 3133 located closer to the continent has slightly higher ms values than site md07 3134 and also the ms record of patagonian site salsa shows comparable variability patagonia was the dust source for both the scotia sea and east antarctica dust fluxes were several times higher during glacial times when atmospheric circulation was either stronger or shifted in latitude sea level was lowered shelf surfaces were exposed and environmental conditions in ssa were dominated by glaciers and extended outwash plains hence ms records of so deep sea sediment are reliable tracers of atmospheric circulation allowing for chronologically constrained reconstructions of the circum antarctic paleoclimate history

the influence of foliation on the fragility of granitic rocks image analysis and quantitative microscopy fabric dependent anisotropy is important in understanding the mechanical behaviour of foliated rocks because the foliation creates mechanically weak discontinuities using optical microscopy a foliation index fix was calculated for a group of granitic rocks in southern sweden that displays a range of textures from foliated to nonfoliated image analysis from scanning electron microscope with backscattered detector sem bse images was used in order to measure the rock texture of these samples the analyses were compared with the los angeles la test which measures resistance of rock aggregate to fragmentation the results demonstrate that the measured grain size shape and spatial arrangement are important parameters controlling the fragility of the rock both the texture and foliation must be taken into account to obtain a significant relationship with the mechanical analyses we suggest that this alternative method could be a helpful tool for predicting a rock s suitability as an aggregate as it gives a better understanding of the material properties compared to mechanical testing

ice magnetization in the epica dome c ice core implication for dust sources during glacial and interglacial periods 1 isothermal remanent magnetization and insoluble dust content of ice samples from epica dome c ice core were measured to characterize the magnetic properties of atmospheric dust despite the larger concentration of dust aerosol during glacial stages the magnetization of the dust fraction was found to be higher during interglacials and exhibits a larger variability changes in magnetic mineralogy of aerosol dust in ice from different climatic stages were also characterized using coercivity of remanence variations of magnetic properties of dust from glacial to interglacial stages indicate changes in dust provenance in agreement with previous results based on geochemical analysis however the extremely large magnetizations of some interglacial samples also suggest that episodical eolian deposition from highly magnetic deposits occurred during interglacial periods

crystal size distribution csd in rocks and the kinetics and dynamics of crystallization crystal size distributions csds measured in metamorphic rocks yield quantitative information about crystal nucleation and growth rates growth times and the degree of overstepping t of reactions during metamorphism csds are described through use of a population density function n dn dl where n is the cumulative number of crystals per unit volume and l is a linear crystal size plots of ln n vs l for olivine pyroxene and magnetite in high temperature 1000 c basalt hornfelses from the isle of skye define linear arrays indicating continuous nucleation and growth of crystals during metamorphism using the slope and intercept of these linear plots in conjunction with growth rate estimates we infer minimum mineral growth times of less than 100 years at t 10 c and nucleation rates between 10 4 and 10 1 cm3 s garnet and magnetite in regionally metamorphosed pelitic schists from south central maine have csds which are bell shaped we interpret this form to be the result of two processes 1 initial continuous nucleation and growth of crystals and 2 later loss of small crystals due to annealing the large crystals in regional metamorphic rocks retain the original size frequency distribution and may be used to obtain quantitative information on the original conditions of crystal nucleation and growth the extent of annealing increases with increasing metamorphic grade and could be used to estimate the duration of annealing conditions if the value of a rate constant were known finally the different forms of crystal size distributions directly reflect differences in the thermal histories of regional vs contact metamorphosed rocks because contact metamorphism involves high temperatures for short durations resulting csds are linear and unaffected by annealing similar to those produced by crystallization from a melt because regional metamorphism involves prolonged cooling from high temperatures primary linear csds are later modified by annealing to bell shapes

the role of seasonality of mineral dust concentration and size on glacial interglacial dust changes in the epica dronning maud land ice core we present a record of particulate dust concentration and size distribution in subannual resolution measured on the european project for ice coring in antarctica epica dronning maud land edml ice core drilled in the atlantic sector of the east antarctic plateau the record reaches from present day back to the penultimate glacial until 145 000 years b p with subannual resolution from 60 000 years b p to the present mean dust concentrations are a factor of 46 higher during the glacial 850 4600 ng ml compared to the holocene 16 112 ng ml with slightly smaller dust particles during the glacial compared to the holocene and with an absolute minimum in the dust size at 16 000 years b p the changes in dust concentration are mainly attributed to changes in source conditions in southern south america an increase in the modal value of the dust size suggests that at 16 000 years b p a major change in atmospheric circulation apparently allowed more direct transport of dust particles to the edml drill site we find a clear in phase relation of the seasonal variation in dust mass concentration and dust size during the glacial r conc size 0 8 but no clear phase relationship during the holocene 0 r conc size 0 4 with a simple conceptual 1 d model describing the transport of the dust to the ice sheet using the size as an indicator for transport intensity we find that the effect of the changes in the seasonality of the source emission strength and the transport intensity on the dust decrease over transition 1 can significantly contribute to the large decrease of dust concentration from the glacial to the holocene

eight glacial cycles from an antarctic ice core the antarctic vostok ice core provided compelling evidence of the nature of climate and of climate feedbacks over the past 420 000 years marine records suggest that the amplitude of climate variability was smaller before that time but such records are often poorly resolved moreover it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records here we report the recovery of a deep ice core from dome c antarctica that provides a climate record for the past 740 000 years for the four most recent glacial cycles the data agree well with the record from vostok the earlier period between 740 000 and 430 000 years ago was characterized by less pronounced warmth in interglacial periods in antarctica but a higher proportion of each cycle was spent in the warm mode the transition from glacial to interglacial conditions about 430 000 years ago termination v resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases but there are significant differences in the patterns of change the interglacial stage following termination v was exceptionally long 28 000 years compared to for example the 12 000 years recorded so far in the present interglacial period given the similarities between this earlier warm period and today our results may imply that without human intervention a climate similar to the present one would extend well into the future

automatic grain boundary detection and grain size analysis using polarization micrographs or orientation images abstract a simple procedure for creating grain boundary maps from petrographic thin sections termed the lazy grain boundary lgb method has been devised it is based on a set of macro commands programmed for nih image a public domain image processing software the grain boundary detection is based on gradient filtering the procedure makes use of multiple input images sets of regular polarized micrographs or where possible orientation misorientation images on each image of a given input set only the most significant grain boundaries are detected and by combining those a single grain boundary map is obtained image models and criteria for grain boundary identification are discussed briefly the principal aim of the lgb method is to facilitate the production of large grain boundary maps containing several thousand cross sectional areas to provide statistically valid samples for grain size analysis a section of black hills quartzite was used to test the lgb method five different input sets were prepared and used for automatic lgb analysis one set was additionally used for an interactive analysis and for a manual tracing from all seven grain boundary maps the 2 and 3 d grain size distributions were calculated the results are compared and the different image sets and procedures are rated for precision over and undersegmentation and speed of preparation

origin of calcareous dust in argentinean pleistocene periglacial deposits traced by sr c and o isotopic compositions and ree distribution abstract calcareous dust is often closely associated with periglacial features in the pleistocene deposits of extra andean argentina conventionally interpreted as resulting from continental pedogenic weathering and precipitation during interglacial episodes little has yet been demonstrated about its origin strontium oxygen and carbon isotopic compositions and ree distributions were determined for such calcareous dust from a wide geographic area including sites in patagonia the southern pampa and the mendoza pre cordillera the 13 c values between 1 9 and 7 2 v pdb and 18 o values between 2 6 and 6 0 v smow confirm a glaciogenic origin and not the generally advocated pedogenic genesis the narrow 87 sr 86 sr ratio from 0 706463 0 000008 to 0 707477 0 000006 2 and the constant ree distribution with a specific negative ce anomaly both require crystallization in a large and homogeneous reservoir with some seawater supply during successive glacial episodes the homogeneous sr isotopic and ree data suggest that the ca sr and rees released from andean basement rocks during glacial episodes 1 were transported by rivers to the eastern continental shelf of which up to 1 million of km 2 was probably emerged during the successive glacial episodes 2 were mixed there in a semi marine lacustrian meander rich environment with seawater supply where they dissolved and re precipitated before 3 being eroded and dispersed by southeasterly winds over most of argentina

petroleum generation an easy and widespread process in hydrothermal systems an overview abstract the conversion of organic matter to petroleum products by hydrothermal activity is an easy process occurring in nature in many types of environments geologically immature organic matter of marine sediments has been shown to be altered to petroleum products by this process in the guaymas basin escanaba trough bransfield strait and atlantis ii deep and this process probably occurs elsewhere in active sedimented rift systems contemporary organic detritus and or viable microorganisms are also converted in part to petroleum like products when they become entrained by turbulent mixing into hydrothermal vent waters resulting in their instantaneous hydrous pyrolysis this latter case occurs in hydrothermal vent fields without a sedimentary cover emanating directly from oceanic ridges as for example on the east pacific rise at 13 n and 21 n and on the mid atlantic ridge at 26 n this process is probably also ubiquitous for all actively venting sediment starved oceanic ridges the hydrocarbon products generated in these areas have been compared in terms of composition organic matter sources and analogy to reservoir petroleum they represent a major carbon source for chemosynthetic assimilation by vent biota and are compositionally similar to normal petroleum

plastic anisotropy and fabric evolution in sheared and recrystallized quartz single crystals 1 the effect of a lattice preferred orientation on the flow strength of quartz aggregates dynamically recrystallized from single crystals of synthetic quartz was investigated using general shear experiments in a griggs apparatus experiments were conducted at shear strains up to 5 at a temperature of 900 c confining pressure of 1 5 gpa and shear strain rate of 10 5 s 1 three starting orientations of crystal were used to activate three slip systems basal a prism c and prism a although slip induced rotation of the crystal axes in the first two orientations led to the activation of additional slip systems for crystals with higher water contents basal a and prism a orientations are relatively weak and prism c orientations are stronger all three initial crystal orientations undergo dynamic recrystallization with increasing shear strain although the strain required for 100 recrystallization varies 2 for prism c slip 3 8 for basal a slip and 5 for prism a slip for all three starting orientations distinct domains of recrystallized grains develop with c axes parallel to y of the strain ellipsoid ymax replacing recrystallized grains of other orientations the ymax domains increase in size with increasing strain in addition strain markers show that strain is highly localized within the ymax domains indicating geometrical softening of up to an order of magnitude in effective viscosity

glacial interglacial changes of southern hemisphere wind circulation from the geochemistry of south american dust abstract the latitudinal displacement of the southern westerlies and associated climate systems is a key parameter for understanding the variations of southern hemisphere atmospheric circulation during the late quaternary period to increase understanding of past atmospheric circulation and of the paleo environmental conditions associated with continental dust sources we dig deeper into dust provenance in paleo archives of the southern hemisphere we present here a sr nd isotopic and rare earth element study of surface sediments collected along a 4000 km latitudinal band from arid and semi arid terrains in southern south america findings from terrains that served as paleo dust suppliers are compared with modern dust collected from monitoring stations along the same latitudinal band which affords a test on how actual present day aeolian compositions compare to those of the past potential source areas moreover the comparison between past and present day datasets is useful for understanding present day atmospheric circulation armed with a new comprehensive dataset we revise previous interpretations of the provenance of dust trapped in the antarctic ice and sediments deposited in the south atlantic sector of the southern ocean these comparisons support multiple source regions in southern south america that changed with climates the findings reveal that although patagonia plays an important role in contributing dust to the higher latitudes central western argentina and to a lesser extent the southern puna region also emerge as potentially important dust sources during glacial times the southern altiplano appears to be a major contributor during interglacial periods as well we rely in part on an understanding of modern wind dust activities to conclude that the possible presence of southern south america source regions other than patagonia in east antarctic ice is consistent with an overall equatorward displacement during glacial times of both the mid latitude westerlies and the subtropical jet stream

links between patagonian ice sheet fluctuations and antarctic dust variability during the last glacial period mis 4 2 abstract antarctic and greenland ice core records reveal large fluctuations of dust input on both orbital and millennial time scales with potential global climate implications at least during glacial periods the antarctic dust fluctuations appear to be largely controlled by environmental changes in southern south america we compare dust flux records from two antarctic ice cores to variations in the composition of the terrigenous supply at odp site 1233 located off southern chile and known to record fluctuations in the extent of the northern part of the patagonian ice sheet npis during the last glacial period marine isotope stage mis 4 to 2 within age uncertainties millennial scale glacial advances retreats of the npis correlate to antarctic dust maxima minima in turn npis fluctuations were closely related to offshore sea surface temperature sst changes this pattern suggests a causal link involving changes in temperature in rock flour availability in latitudinal extensions of the westerly winds and in foehn winds in the southern pampas and patagonia we further suggest that the long term trend of dust accumulation is partly linked to the sea level related changes in the size if the patagonian source area due to the particular morphology of the argentine shelf we suggest that sea level drops at the beginning of mis 4 and mis 2 were important for long term dust increases while changes in the patagonian dust source regions primarily control the early dust decrease during the mis 4 3 transition and termination 1

modern and holocene aeolian dust variability from talos dome northern victoria land to the interior of the antarctic ice sheet abstract high elevation sites from the inner part of the east antarctic plateau sample windborne dust representative of large portions of the southern hemisphere and are sensitive to long range atmospheric transport conditions to polar areas on the periphery of the ice sheet conversely the aeolian transport of particles from high elevation ice free areas can locally represent a relatively important additional input of dust to the atmosphere and the interplay of atmospheric dynamics dust transport and deposition is strictly related to the regional atmospheric circulation behaviour both at present day and in the past the understanding of the spatial extent where local sources can influence the mineral dust budget on the ice sheet is fundamental for understanding the atmospheric dust cycle in antarctica and for the interpretation of the dust history in marginal glaciological settings in this work we investigate the spatial variability of dust flux and provenance during modern pre industrial and holocene times along a transect connecting talos dome to the internal sites of the antarctic plateau and we extend the existing documentation of the isotopic sr nd fingerprint of dust sized sediments from victoria land source areas dust flux grain size and isotopic composition show a marked variability between talos dome mid point d4 and dome c vostok suggesting that local sources play an important role on the periphery of the ice sheet microscope observations reveal that background mineral aerosol in the taldice core is composed by a mixture of dust volcanic particles and micrometric sized fragments of diatoms these latter representing a small but pervasive component of antarctic sediments a set of samples from victoria land mostly consisting of regolith and glacial deposits from high elevation areas was collected specially for this work and the isotopic composition of the dust sized fraction of samples was analyzed results reveal a close relationship with the parent lithologies but direct comparison between source samples and firn ice core dust is problematical because of the ubiquitous volcanic contribution to the environmental particulate input in the talos dome area the frequency of events potentially suitable for peripheral dust transport to talos dome appears relatively high for present day conditions according to back trajectories calculations and the related air flow pattern well defined from a seasonal and spatial perspective also as expected from palaeo data these events appear extremely uncommon for internal sites

a new andean deep ice core from nevado illimani 6350 m bolivia abstract a new ice core record from the nevado illimani 16 s bolivia covers approximately the last 18 000 years bp a comparison with two published ice records from sajama 18 s bolivia thompson et al science 282 1998 1858 1864 and huascaran 9 s peru thompson et al science 269 1996 46 50 documents a regionally coherent transition from glacial to modern climate conditions in south america north of 20 s the strong resemblance between the illimani and huascaran water isotope records and their differences from the sajama record in particular during the period from 9000 years bp to 14 000 years bp suggest that local water recycling or local circulation changes played a major role for sajama we interpret the common illimani huascaran water isotope history in terms of a common change from wetter cooler conditions during glacial times to drier warmer conditions in the early holocene

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

magnetization of polar ice a measurement of terrestrial dust and extraterrestrial fallout abstract laboratory induced remanent magnetization of polar ice constitutes a measurement of the magnetization carried by the ferromagnetic dust particles in the ice this non destructive technique provides a novel kind of information on the dust deposited on the surface of polar ice sheets measurements made on ice samples from greenland north grip ice core and antarctica vostok and epica dome c ice cores allowed the recognition of a fraction of magnetic minerals in ice whose concentration and magnetic properties are directly related to that of insoluble dust the source of this fraction of magnetic minerals thus appears closely related to terrestrial dust transport and deposition and its magnetic properties are informative of the dust provenance areas the rock magnetic properties of the dust may reflect distinct changes of dust source areas from glacial to interglacial periods in agreement with and adding further information to the isotopic 87 sr 86 sr and 143 nd 144 nd analyses a second magnetic fraction consists of particles of nanometric size which are superparamagnetic at freezer temperature and whose concentration is independent of the mass of aerosol dust found in the ice the source of these nanometric sized magnetic particles is ascribed to fallout of meteoric smoke and their concentration in ice was found to be compatible with the extraterrestrial fallout inferred from ir concentrations the diameter of the smoke particles as inferred from magnetic measurements is in the range of about 7 20 nm

computational study of deformation mechanisms and grain size evolution in granulites implications for the rheology of the lower crust abstract most of granulite terrains worldwide are characterized by large mean grain sizes of 1 mm or more an important exception are the high pressure felsic granulites in the bohemian massif the european variscan belt there recrystallization of original coarse grained ternary feldspar led to formation of a fine grained 100 m mixed matrix dominated by plagioclase and k feldspar this change occurred at temperatures of 850 c and was probably caused by chemically induced decomposition related to slight cooling and enhanced by deformation during continental collision the resulting microstructure shows indications of diffusion creep assisted by melt enhanced grain boundary sliding further on minor coarsening occurred associated with deformation by dislocation creep and aggregation of mineral phases using a thermodynamics based model of grain size evolution we show that stability of the fine grained microstructure crucially depends on zener pinning in the two phase mineral matrix pinning efficiently hinders grain growth and the small grain size that resulted from the ternary feldspar decomposition can be stable even at high temperatures the late switch from the grain size sensitive creep to dislocation creep is rather difficult to explain by temperature and strain rate or stress changes only however a simple incorporation of melt solidification can successfully simulate this behavior alternatively the switch and the associated grain size growth can be related to mineral phase aggregation at lower pressure temperature conditions resulting into a decrease of pinning efficiency this study suggests that the fine grain size of the bohemian granulites in contrast to the common coarse grained type stems from abrupt recrystallization during the high pressure high temperature conditions and pinning in the fine grained matrix such a process may in some cases significantly and suddenly reduce the strength of the lower continental crust and allow for its efficient redistribution

quartz microstructures and crystallographic preferred orientation which shear sense do they indicate abstract crystallographic preferred orientation cpo and shape fabrics of dynamically recrystallized quartz are currently used as shear sense indicators we show that the cpo and shape fabric in a polyphase rock do not necessarily indicate the shear sense at the global scale of the shear zone but rather at the local scale of the deforming and recrystallizing quartz aggregates in lower amphibolite facies shear zones in the gran paradiso metagranodiorite magmatic quartz grains have recrystallized dynamically by subgrain rotation and grain boundary migration and deform inside a very fine grained feldspar mica matrix the quartz cpo has a peripheral c axis maximum inclined synthetically with the local shear sense the orientation of the surface fabric is related to the orientation of the c axis maximum and the microscopic shear sense in the quartz aggregate the geometry of the surface fabric ranges from monoclinic to symmetric depending on the relative contribution of grain boundary migration it is inferred that flow partitioning between the quartz aggregates and the matrix controls the local kinematics cpos are only reliable shear sense indicators in polyphase rocks if the most highly strained parts are analyzed where spin of the aggregates with respect to the shear zone boundary has ceased

multiple sources supply eolian mineral dust to the atlantic sector of coastal antarctica evidence from recent snow layers at the top of berkner island ice sheet the sr and nd isotopic composition of dust extracted from recent snow layers at the top of berkner island ice sheet located within the filchner ronne ice shelf at the southern end of the weddell sea enables us for the first time to document dust provenance in antarctica outside the east antarctic plateau eap where all previous studies based on isotopic fingerprinting were carried out berkner dust displays an overall crust like isotopic signature characterized by more radiogenic 87sr 86sr and much less radiogenic 143nd 144nd compared to dust deposited on the eap during glacial periods differences with eap interglacial dust are not as marked but still significant indicating that present day berkner dust provenance is distinct at least to some extent from that of the dust reaching the eap the fourteen snow pit sub seasonal samples that were obtained span a two year period 2002 2003 and their dust sr and nd isotopic composition reveals that multiple sources are at play over a yearly time period southern south america patagonia in particular likely accounts for part of the observed spring summer dust deposition maxima when isotopic composition is shifted towards younger isotopic signatures in the spring possible additional inputs from australian sources would also be supported by the data most of the year however the measured isotopic signatures would be best explained by a sustained background supply from putative local sources in east antarctica which carry old crust like isotopic fingerprints whether the restricted east antarctic ice free areas produce sufficient eolian material has yet to be substantiated however the fact that large 5 mu m particles represent a significant fraction of the samples throughout the entire time series supports scenarios that involve contributions from proximal sources either in patagonia and or antarctica possibly including snow free areas in the antarctic peninsula and other areas as well this also indicates that additional dust transport which does not reach the eap must occur at low tropospheric levels to this coastal sector of antarctica

the fry method applied to an augen orthogneiss problems and results the application of the fry method to measure strain in deformed porphyritic granites is discussed this method requires that the distribution of markers has to satisfy at least two conditions it has to be homogeneous and isotropic statistics on point distribution with the help of a morishita diagram can easily test homogeneity isotropy can be checked with a cumulative histogram of angles between points application of these tests to undeformed mte capanne granite elba and to deformed randa orthogneiss alps of switzerland porphyritic granite reveals that their k feldspars phenocrysts both satisfy these conditions and can be used as strain markers with the fry method other problems are also examined one is the possible distribution of deformation on discrete shear bands providing several tests are met we conclude that the fry method can be used to estimate strain in deformed porphyritic granites

grain boundary hierarchy development in a quartz mylonite abstract orientation contrast imaging using forescatter detectors and backscattered electron diffraction techniques in the scanning electron microscope have been used to investigate the boundary hierarchy characteristics of a quartz mylonite shear zone from torridon nw scotland the boundary hierarchy is defined as the relationship between the boundary misorientations their enclosed domain size and their frequency distribution by measuring the misorientation across every grain and subgrain boundary the characteristics of the boundary hierarchy can be found two microstructural domains were studied one partially recrystallized low strain domain with large relict grains and one fully recrystallized high strain mylonitic domain our results indicate that the processes of recovery subgrain rotation and grain boundary migration recrystallization each produce identifiable boundary hierarchy signatures in the relict quartz grains we have identified the processes of recovery and subgrain rotation in the recrystallized quartz a cyclic steady state exists between these and other processes coupling these data with traditional microstructural observations allows a more rigorous investigation into the development of a high strain fine grained mylonite from a coarse grained undeformed protolith we suggest that this type of detailed crystallographic microstructural analysis can greatly further our understanding of microstructural development in shear zones and may have implications for the effective use of sub grain size palaeopiezometers

defining the geochemical composition of the epica dome c ice core dust during the last glacial interglacial cycle the major element composition of the insoluble windborne long range dust archived in the european project for ice coring in antarctica dome c ice core has been determined by particle induced x ray emission analyses the geochemistry of dust from the last glacial maximum lgm and from the holocene is discussed in terms of past environmental changes throughout the last climatic cycle antarctic dust from glacial and interglacial climate clearly reveals different geochemical compositions the weathered crustal like signature of lgm dust is characterized by a low compositional variability suggesting a dominant source under the glacial regime the close correspondence between the major element composition of antarctic glacial dust and the composition of southern south american sediments supports the hypothesis of a dominant role of this area as major dust supplier during cold conditions conversely the major element composition of holocene dust displays high variability and high al content on average this implies that an additional source could also play some role comparison with size selected sediments suggests that a contribution from australia is likely during warm times when a reduced glacial erosion decreases the primary dust production and a more intense hydrological cycle and larger vegetation cover inactivates dust mobility in a large part of southern south america weakening its contribution as a massive dust supplier to antarctica

dust provenance in antarctic ice during glacial periods from where in southern south america 1 the origin of dust deposited in east antarctica is not fully understood yet this study demonstrates that contrary to nd sr isotopes are strongly fractionated in the finest sized material representing potential dust sources in south america analysis of nd isotopes suggests that argentine loess southern ocean sediments and antarctic dust may all have a related origin or can represent comparable mechanisms of eolian sediment transport and deposition this analysis also concludes that the patagonian signature can explain a high proportion of the isotopic composition of dust trapped in antarctic ice during glacial periods the puna altiplano plateau emerges as the second possible important sediment contributor explaining the crustal like signature found in east antarctic dust and should be considered as a potential source area when quaternary paleoclimate is reconstructed from argentine loess antarctic dust and south atlantic sediment records

homogeneous climate variability across east antarctica over the past three glacial cycles recent ice core studies have raised the disturbing possibility that glacial interglacial climate changes may be non uniform across antarctica1 2 these findings have been confined to records from the ross sea sector of the continent but significant deviations in other areas would call into question the widely assumed validity of the climate record obtained from vostok east antarctica on large spatial scales3 here we present an isotopic profile from a core drilled at dome fuji4 5 situated 1 500 km from vostok in a different sector of east antarctica the two records show remarkable similarities over the past three glacial cycles the extent of the dome fuji record in both large amplitude changes such as terminations interglacials and interstadials and more subtle glacial events even when the origin of precipitation is accounted for our results indicate that antarctic climate is essentially homogeneous at the scale of the east antarctic plateau possibly as a consequence of the symmetry of the plateau and the adjacent ocean

isotopic constraints on the source of argentinian loess with implications for atmospheric circulation and the provenance of antarctic dust during recent glacial maxima we present rare earth element ree and sr nd isotopic data for argentinian loess 28 38 s with two aims 1 to examine the source regions of argentinian loess and the constraints that these put on palaeo wind directions 2 to further investigate the source of antarctic ice core dust and to test the hypothesis that some of it could be derived from a region to the north of patagonia into which the dry dusty westerly dominated patagonian climate expanded during quaternary glacial maxima sr nd isotopic data for argentinian loess from north of 37 s are distinct from patagonian loess compositions in that they have more radiogenic sr 87sr 86sr 0 7059 0 7123 and less radiogenic nd nd 0 8 to 6 4 ree patterns and sr nd isotopic values are relatively homogeneous for multiple samples taken from single loess sections but show significant differences between sections in general there is a northward change from patagonia like ree patterns and isotopic values away from volcanogenic signatures and towards those that are more like the continental crust the latitudinal nd isotopic pattern is remarkably similar to that for andean volcanic rocks and suggests derivation of loess from the andes by more or less direct westerly transport for loess sections in the north the data imply a contribution from palaeozoic gneisses to the northwest in the chilean altiplano sr nd data for extra patagonian argentinian loess north of 37 s do not support a significant role for this source region in supplying dust to antarctica at the last glacial maximum this conclusion contrasts with previous studies that suggest a significant northward shift in the climatic belts and in particular the westerlies and the antarctic polar front during quaternary glacial maxima very systematic relations between the sr nd isotopic composition of loess and their andean source highlights shifts in the sr isotopic composition of loess to more radiogenic values and strongly suggests that the slight offset between patagonian loess and ice core dust identified by previous workers is due to grain size differentiation effects

a uniform isotopic and chemical signature of dust exported from patagonia rock sources and occurrence in southern environments patagonia is considered to be the most important source of dust from south america that is deposited in surrounding areas and we present here a systematic sr and nd isotopic study of sediment currently being exported eolian and suspended riverine sediments from patagonia have a homogeneous chemical and isotopic composition that results from the mixing of by products from explosive andean volcanism derived from the extensive jurassic silicic province of chon aike and pyroclastic materials from the basic to intermediate southern andean quaternary arc which are easily denudated and dispersed the main andean uplift and the glaciations that began in the late tertiary account for the extensive distribution of these sediments in the extra andean region the present geochemical signature of patagonian sediments was produced during the pleistocene along with the onset of the southern andean explosive arc volcanism previously published compositions of sediments from other southern south american source regions assumed to be representative of patagonia are distinct from our data considering the alleged importance of patagonia as a dust source for different depositional environments in southern latitudes it is surprising to verify that the chemical and isotopic signatures of patagonian sourced sediments are different from those of sediments from the southern ocean the pampean region or the antarctic ice sediments from these areas have a crustal like geochemical signature reflecting a mixed origin with sediment from other southern south american sources whereas patagonian sediments likely represent the basic to intermediate end member composition

healing microstructures of experimental and natural fault gouge 1 the healing of fault gouge was studied by examining microstructures of naturally and experimentally produced granitoid fault rock we performed deformation experiments on intact granitoid rock samples at t 300 500 c pc 500 mpa and 1 2 10 4 1 3 10 7 s 1 with 0 2 wt h2o added healing experiments were carried out on deformed samples at t 200 500 c pc 500 mpa for 4 h to 14 days under hydrostatic and nonhydrostatic conditions the grain size distributions gsd of the deformed samples were quantified using the d value slope of log frequency log radius of the gsd for quartz and feldspar fault gouge healing causes a decrease in the d value from 2 0 to 1 5 the time dependence of the d decrease is described by a hydrostatic healing law of the form d d t df a e t the results of the laboratory experiments were compared to three natural fault systems 1 nojima fault zone japan 2 fault zones in the black forest germany and 3 orobic thrust italian alps natural and experimental gouges have similar d values healing is only observed in monomineralic aggregates polymineralic i e mixed fault gouges retain their high d value after extended healing times because grain growth is inhibited healing under nonhydrostatic conditions is more rapid than hydrostatic healing the low strain rates which were measured during nonhydrostatic healing are temperature dependent and suggest that diffusive mass transfer processes take place during deformation thus fault rocks at upper to midcrustal depth may deform by combined cataclasis and diffusive mass transfer

antarctic dome c ice core dust at 18 k y b p isotopic constraints on origins we have determined the source area from which dusts from the last glacial maximum lgm section of the dome c ice core were derived by comparing their strontium and neodymium isotopic ratios with those of samples from potential source areas the87sr 86sr and143nd 144nd isotope ratios of the dusts deposited 18 k y b p at the east antarctic dome c site were compared with potential antarctic australian southern african and south american sources the isotope ratios clearly define the patagonian provenance of the dust with the other potential source areas being at most minor contributors contributions by volcanic ash and tephra to the dust sample were also determined to be minimal based on the patterns of rare earth elements knowing the source of the dusts places constraints on the aeolian trajectory by which it was transported to antarctica and this serves as a test of the simulation of southern hemispheric circulation by atmospheric global circulation models during the lgm

the nature distribution and formation of pans in arid zones abstract pans closed depressions are a widespread feature of many of the world s drylands by using literature survey air photographs topographic maps orbital photographs and imagery combined with field work it is possible to describe the major areas where these features occur their distribution is controlled to a great extent by the availability of susceptible surfaces they also develop in certain particular environmental settings palaeolacustrine basins palaeodrainages interdunes and on coastal plains many of the pans have a distinctive morphology while on their lee sides they may have lunette dunes many processes combine to create and maintain pans and these can be considered in a general model which has certain key elements the first of these is that the area should not be one where fluvial processes are fully integrated it should also not be one where aeolian accumulation is such as to infill any irregularities in the land s surface if these two predisposing conditions are fulfilled then under dryland conditions if susceptible surfaces are present there are various circumstances that may lead to hollow development and enlargement although in some cases such processes as solution suffosion and animal activities may play a role we believe that the predominant reason why pans have the characteristics that they do including their shapes lunettes alignments etc is that they result from the operation of the twin processes of salt weathering and aeolian deflation

generation of a crust mantle magma mixture magma sources and contamination at cerro panizos central andes cerro panizos a large caldera in the central andes mountains produced two large dacitic ignimbrites at 7 9 ma and 6 7 ma and many andesitic and dacitic lava flows and domes the older rhyodacitic cienago ignimbrite represents the most silicic magma erupted by the system the younger much larger volume dacitic cerro panizos ignimbrite is very crystal rich containing up to 50 biotite plagioclase and quartz crystals in the pumice it is weakly zoned with most of the zoning apparent between two main cooling units major and most trace elements show little variation through the cerro panizos ignimbrite but the small range of composition is consistent with typical fractionation trends sr nd and pb isotopic ratios are very crustal with initial 87sr 86sr values of 0 711 to 0 715 nd values of 7 5 to 10 2 and nearly invariant pb isotopic ratios 206pb 204pb 18 85 207pb 204pb 15 67 and 208pb 204pb 38 80 the limited zonation observed in the cerro panizos ignimbrite is explained by impeded crystal settling due to high crystal content the magma body was a crystal liquid mush before ascent to the pre eruption crustal levels crystals formed but did not separate easily from the magma limited fractionation of plagioclase and biotite may have occurred but the composition was largely controlled by lower crustal mash processes afc modeling shows that the cerro panizos magmas resulted from a mixture of roughly equal proportions of late miocene mantle derived basalts and melts from 1 0 ga grenville age lower crust this occurred in a mash zone in the lower crust and set the crustal isotopic ratios observed in the cerro panizos magmas the great thickening of the crust beneath the central andes mountains sent upper and middle crustal rock types to lower crustal and deeper depths and this explains the upper crustal isotopic signatures of the cerro panizos rocks minor upper crustal assimilation of early miocene volcanic or subvolcanic rocks produced much of the isotopic variation seen in the system the nearly invariant high pb isotopic values and high pb concentrations indicate that pb came almost entirely from the crustal source and was little altered by any subsequent upper crustal assimilation this pb signature is isotopically similar to that of the southern bolivian tin belt suggesting a widely distributed pb source the great difference between compositions of miocene and quaternary central andean volcanic rocks is explained by crustal thickening in early miocene time leading to abundant lower crustal water and associated fluxed melting during the time of the earlier eruptions the lower crust dried out considerably by quaternary time so less crustal component is present

coherent composition of glacial dust on opposite sides of the east antarctic plateau inferred from the deep epica ice cores 1 the dust provenance identification through isotopic and geochemical tracers focused mostly on ice cores drilled in the pacific indian sector of antarctica where a common provenance of dust from southern south america during glacial ages was demonstrated conversely in other areas of the east antarctic plateau as dronning maud land provenance was deduced indirectly from back trajectory analyses and soluble chemistry records in this work we present the first comparison of major elemental composition of dust archived in two ice cores from opposite sides of antarctica in the framework of the epica project mineral particles extracted from the edc and edml cores date back to glacial mis 2 4 and 6 over the last 200 kyr results reveal a coherent geochemical dust composition at both locations providing experimental evidence of a common provenance over the wide area of east antarctica during glacials and key analytical constrains for atmospheric general circulation models

dust size evidence for opposite regional atmospheric circulation changes over east antarctica during the last climatic transition three east antarctic ice cores dome b epica dome c and komsomolskaia give evidence for a uniform dust input to the polar plateau during the last glacial maximum lgm holocene transition 20 to 10 kyr bp and the 87sr 86sr versus 143nd 144nd isotopic signature of the mineral particles highlights a common provenance from southern south america at that time however the size distribution of dust from the three ice cores highlights important differences within the east antarctic during the lgm and shows clearly opposite regional trends during the climatic transition between dome b and dome c the timing of these changes is also different a geographical diversity also arises from the different phasing of the short term multi secular scale dust size oscillations that are superposed at all sites on the main trends of glacial to interglacial changes we hypothesize the dust grading is controlled by size fractionation inresponse to its atmospheric pathway either in terms of horizontal trajectory or in altitude of transport such mechanism is supported also by the dust size changes observed during a volcanic event recorded in vostok ice ice core dust size data suggest preferential upper air subsidence over the edc kms region and easier penetration of relatively lower air masses to the db area during the lgm at the end of the last glacial period and during the climatic transition the region of relatively higher subsidence progressively moved southward the scenario proposed supported also by the lgm holocene regional changes of snow accumulation likely operates even at sub millennial time scale

loess of southern south america abstract loess and loessoid loess like reworked loess sediments extend across the chaco pampean plains and the nw mountain environments of argentina and in neighbouring countries paraguay brazil uruguay bolivia loessoid sediments are much more abundant than primary loess the beginning of the loessoid sedimentation cycle was related to a phase of late miocene orogeny in the andes the plio pleistocene record is mostly composed of loessoid sediments modified by pedogenesis which produced welded palaeosols the late pleistocene holocene loess record reveals a heterogeneous composition across the region coarse textures and an andean derived volcanic composition prevail in the southern pampas finer textures and material coming from the andes and the other two sources sierras pampeanas and the parana basin characterize the loess deposits of the northern pampas and the eastern chaco a southern patagonian source is also suggested for the mountain valley loess of tucuman although a western andean provenance has been proposed it is believed that the material in the western chaco was derived from the bolivian andes loess deposition was related to a multistage transport mechanism involving fluvial and aeolian processes inferred westerly and southwesterly wind directions as dominant carriers of the aeolian deposits are in agreement with westerly palaeowind simulations using climate models however the role played by westerly tropospheric winds and northerly winds remains to be established

patagonian origin of glacial dust deposited in east antarctica vostok and dome c during glacial stages 2 4 and 6 abstract the source area of continental dust deposited at both vostok and dome c sites east antarctica during the glacial stages stage 2 18 ka last glacial maximum stage 4 60 ka and stage 6 160 ka of the last two climatic cycles has remained constant the isotopic composition 87 sr 86 sr and 143 nd 144 nd of the ice core dust has been compared with the isotopic composition of the potential source areas antarctica new zealand southern africa australia and south america this comparison reveals the southern south american provenance of the dust for all three glacial periods as has already been shown for the lgm 1 we show that the patagonian loess and the marine shelf sediments from the argentine continental shelf which was variably emerged during glacial periods display different isotopic compositions and that the composition of the patagonian loess best matches the signature of the ice core dust the identification of the patagonian region as the source of the windblown dust deposited over east antarctica during all the latest glacial periods permits a better understanding of paleo atmospheric circulations of the last climatic cycles and a better constraint on the parametrization of dust sources for paleoatmospheric general circulation models

micro investigation of epica dome c bottom ice evidence of long term in situ processes involving acid salt interactions mineral dust and organic matter abstract the epica dome c ice core edc reached a final depth of 3260 m at a maximum height of about 15 m above the ice bedrock interface in december 2004 we present here data gained from a detailed investigation of selected samples of the deeper part of the core located below 3200 m and referred to as bottom ice this part of the core has been poorly investigated so far mainly because there are significant challenges in interpreting paleo records that were very likely modified by long term in situ processes our study combines high resolution ion chromatography high resolution synchrotron x ray micro fluorescence micro xrf scanning and transmission electron microscopy our aim was to identify the long term physico chemical processes at work close to the bedrock to determine how they have altered the initial registers and ultimately to extract information on the very ancient antarctic environment the ubiquitous presence of nanometer iron oxide crystals at the surface of wind borne dust aggregates containing also large amount of organic matter raises the possibility that the consolidation of windborne dust clusters formed during ice recrystallization could be related to microbial iron reduction and thus to the progressive reactivation of dormant bacterial activity in warming ice inclusions of size and number density increasing with depth observed in the 12 last meters 3248 3260 m contain liquid and solid species among them marine biogenic acids numerous wind borne dust aggregates and clusters of large reversible calcium carbonate particles precipitated once the inclusion was formed and often covered by secondary gypsum the refreezing of slush lenses is discussed as a potential cause of the formation of such heterogeneous and complex mixtures in addition to the very fine micrometer size minerals windborne from extra antarctic continental sources and often accreted in large aggregates single medium size particles a few to ca 20 m and among them organic debris are commonly encountered their size surface shape and mineralogy suggest that aerosol transport from antarctic ice free areas played a significant role at the time edc bottom ice was formed concentrations and concentration ratios of biogenic sulfur species also advocate for the strengthening of peri antarctic meteorological patterns that favor the inland penetration of disturbed flow carrying local material very large well preserved mineral particles several tens of micrometers in diameter and biotope relics in deeper ice close to 3260 m likely come from the sub glacial environment

extended east antarctic ice core tephrostratigraphy three new tephra layers have been identified and analysed in the deeper sections of the epica dome c edc and vostok ice record east antarctic plateau one from edc 358 ka old originated from an antarctic volcano and two from vostok 406 and 414 ka old respectively which are related to antarctic volcanoes and to southern andes and or antarctic peninsula centres respectively these layers represent the oldest tephra bearing events so far detected in deep polar ice cores and extend the regional tephrostratigraphic framework back to the fourth climatic cycle although differences between the drill sites are observed new and previously published tephra data from deep ice cores broadly confirm that the clockwise circum antarctic atmospheric circulation played a major role in the dispersal of volcanic dust onto the plateau while the last 220 ka core sections contain about a dozen visible tephra fall layers the ice representing the time interval from 220 ka back to 800 ka i e the edc core bottom is almost devoid of observed tephras although it is possible that the reduced frequency is an observational artefact the observed pattern could alternatively reflect late quaternary activity fluctuations of sources for tephra in the east antarctic plateau particularly south sandwich islands with enhanced explosive activity in the last two glacial cycles with respect to previous periods

provenance of dust to antarctica a lead isotopic perspective antarctic ice preserves an 800 kyr record of dust activity in the southern hemisphere major efforts have been dedicated to elucidate the origin of this material in order to gain greater insight into the atmospheric dust cycle on the basis of pb isotopes in antarctic dust samples and potential sources this contribution demonstrates for the first time that patagonia is the main contributor of dust to antarctica during interglacial periods as well as glacials although the potential importance of tierra del fuego remains unclear because of its geochemical similarities to patagonia an important new finding is that the puna altiplano sector of the continent is a second important dust source to eastern antarctica during both glacials and interglacials being more prominent during interglacials the data indicate south america is the primary dust source to antarctica during both glacials and interglacials

a 70 ka record of explosive eruptions from the taldice ice core talos dome east antarctic plateau the new antarctic taldice ice core 72 49 s 159 11 e 1620 m depth containing abundant primary tephras provides the opportunity to elucidate the late quaternary volcanic history of the south polar region as well as to broaden the east antarctic tephrostratigraphic framework here grain size and glass compositional data for representative tephra layers from the last 70 ka core section are used for source identification results point to origin of layers from centres of the melbourne volcanic province mcmurdo volcanic group located 250 km from the coring site occurrence of tephra layers within the ice core record suggests that explosive activity in the identified source was not constant over the considered period with a minimum of activity between 20 and 35 ka and increased activity back to 65 ka in addition to palaeovolcanic implications the taldice tephra layers offer prospects for firm correlations between diverse widely separated palaeoarchives and for accurate dating of the antarctic climatic record

quantitative analysis of crystal grain sizes and their distributions in 2d and 3d abstract we review methods to estimate the average crystal grain size and the crystal grain size distribution in solid rocks average grain sizes often provide the base for stress estimates or rheological calculations requiring the quantification of grain sizes in a rock s microstructure the primary data for grain size data are either 1d i e line intercept methods 2d area analysis or 3d e g computed tomography serial sectioning these data have been used for different data treatments over the years whereas several studies assume a certain probability function e g logarithm square root to calculate statistical parameters as the mean median mode or the skewness of a crystal size distribution the finally calculated average grain sizes have to be compatible between the different grain size estimation approaches in order to be properly applied for example in paleo piezometers or grain size sensitive flow laws such compatibility is tested for different data treatments using one and two dimensional measurements we propose an empirical conversion matrix for different datasets these conversion factors provide the option to make different datasets compatible with each other although the primary calculations were obtained in different ways in order to present an average grain size we propose to use the area weighted and volume weighted mean in the case of unimodal grain size distributions respectively for 2d and 3d measurements the shape of the crystal size distribution is important for studies of nucleation and growth of minerals the shape of the crystal size distribution of garnet populations is compared between different 2d and 3d measurements which are serial sectioning and computed tomography the comparison of different direct measured 3d data stereological data and direct presented 2d data show the problems of the quality of the smallest grain sizes and the overestimation of small grain sizes in stereological tools depending on the type of csd

comparing the epica and vostok dust records during the last 220 000 years stratigraphical correlation and provenance in glacial periods a new aeolian dust record from the first 2200 m of the epica dome c ice core 75 06 s 123 21 e covering about 220 000 years of climatic history is compared to the vostok 78 28 s 106 48 e ice core nature 399 1999 429 the two dust profiles are very similar and several common dust events allow to establish stratigraphical links the late quaternary period is characterized at both sites and likely overall east antarctic plateau by high dust input during glacial periods in the epica dome c ice core the dust flux rises by a factor of 25 20 and 12 in glacial stages 2 4 and 6 with respect to interglacial periods holocene and stage 5 5 the magnitude and pattern of changes are comparable in the vostok ice core in this study the geographical origin of ice core dust icd in cold periods has been investigated at both sites through 87sr 86sr versus 143nd 144nd isotopic tracers following the previous studies of grousset et al earth planet sci lett 111 1992 175 and basile et al earth planet sci lett 146 1997 573 the new data and the existing ones allow to define the isotopic fields for dust at the two antarctic sites that are almost identical and restricted into the 0 708 87sr 86sr 0 711 and 5 end 0 5 ranges this suggests a common geographical provenance for dust at vostok and dome c and for all the glacial periods of the late pleistocene to decipher the icd provenance more than 50 samples of loess and aeolian deposits sands and fluvioglacial sediments from the potential source areas psas of the southern hemisphere have been collected however the methodology has been refined with respect to former studies first the isotopic fractionation that can occur in function of grain size has been taken into account and the psa s signature has been defined in the 5 m size range within which fine grained dust reaching antarctica is found moreover a possible contribution from carbonates on the samples from psas has also been also considered south africa and australia can be excluded as dominant sources but a partial overlap arises among southern south america new zealand and the antarctic dry valleys isotopic fields these latter two documented for the first time a possible contribution from all these three sources cannot be excluded but complementary arguments suggest the dominant contribution to east antarctic dust in glacial times deriving from the southern south american region of patagonia and the pampas this study shows a first order uniformity in the dust flux and geographical provenance to the east antarctica plateau during glacial periods

a new technique to automatically quantify microstructures of fine grained carbonate mylonites two step etching combined with sem imaging and image analysis a two step etching technique for fine grained calcite mylonites using 0 37 hydrochloric and 0 1 acetic acid produces a topographic relief which reflects the grain boundary geometry with this technique calcite grain boundaries become more intensely dissolved than their grain interiors but second phase minerals like dolomite quartz feldspars apatite hematite and pyrite are not affected by the acid and therefore form topographic peaks based on digital backscatter electron images and element distribution maps acquired on a scanning electron microscope the geometry of calcite and the second phase minerals can be automatically quantified using image analysis software for research on fine grained carbonate rocks e g dolomite calcite mixtures this low cost approach is an attractive alternative to the generation of manual grain boundary maps based on photographs from ultra thin sections or orientation contrast images

identification of multiple natural and anthropogenic sources of dust in snow from zhongshan station to dome a east antarctica the stable oxygen isotope composition major ions and isotopic compositions of strontium sr neodymium nd and lead pb in insoluble dust from recent surface snow samples along the transect from the zhongshan and progress stations located on the amery ice shelf east antarctica to dome a summit antarctica were analysed no previous isotopic fingerprinting studies have been conducted for this transect these data were used to document the dust provenances in antarctica along the transect up to the highest site dome a for the first time the insoluble dust in snow samples along the coast displays an overall crust line isotopic signature that is characterised by highly radiogenic 87 sr 86 sr values and less radiogenic 143 nd 144 nd values these signatures are comparable with those of samples collected near the ice free areas of the zhongshan and progress stations spatial differences are statistically significant along the transect and the sr nd and pb isotope components in insoluble dust from two continuous snow samples at dome a exhibit marked differences indicating that additional dust reaches the east antarctic plateau the isotopic characteristics of insoluble dust from this transect indicate that the long distance natural dust and anthropogenic pollutants in these samples primarily originate from australia

the influence of three dimensional grain size distributions on the rheology of polyphase rocks abstract in this study the relation between the deformational behaviour of two phase rocks and the grain size distributions of the constituent phases is investigated samples of hot isostatically pressed 50 50 volume percent mixtures of calcite and anhydrite were experimentally deformed in a triaxial apparatus at a temperature of 500 c a confining pressure of 300 mpa and a strain rate of 2 10 5 s 1 for calcite and anhydrite these are the deformational conditions for dislocation and diffusion creep respectively and for a grain size of 8 m these are the conditions of the equiviscous point it was found that samples from different batches of the synthetic material while having an identical average two dimensional grain size displayed significantly different rheological behaviour the ensuing full analysis revealed that the volumetric three dimensional grain size distributions of the different phases and the different batches varied significantly since the anhydrite is in the transition between the dislocation and the grain size sensitive diffusion creep regime the deformational behaviour of the bulk depends critically on the grain size distribution of the anhydrite phase the usefulness of the concept of an average grain size is discussed

continuous record of microparticle concentration and size distribution in the central greenland ngrip ice core during the last glacial period 1 a novel laser microparticle detector used in conjunction with continuous sample melting has provided a more than 1500 m long record of particle concentration and size distribution of the ngrip ice core covering continuously the period approximately from 9 5 100 kyr before present measurements were at 1 65 m depth resolution corresponding to approximately 35 200 yr particle concentration increased by a factor of 100 in the last glacial maximum lgm compared to the preboreal and sharp variations of concentration occurred synchronously with rapid changes in the 18o temperature proxy the lognormal mode of the volume distribution shows clear systematic variations with smaller modes during warmer climates and coarser modes during colder periods we find 1 7 m diameter during lgm and 1 3 m during the preboreal on timescales below several 100 years and the particle concentration exhibit a certain degree of independence present especially during warm periods when generally is more variable using highly simplifying considerations for atmospheric transport and deposition of particles we infer that 1 the observed changes of in the ice largely reflect changes in the size of airborne particles above the ice sheet and 2 changes of are indicative of changes in long range atmospheric transport time from the observed size changes we estimate shorter transit times by roughly 25 during lgm compared to the preboreal the associated particle concentration increase from more efficient long range transport is estimated to less than one order of magnitude

atmospheric decadal variability from high resolution dome c ice core records of aerosol constituents beyond the last interglacial along the epica dome c ice core we measured concentrations of different water soluble aerosol constituents and deduced total depositional flux records here we present high resolution sodium calcium ammonium and nitrate data covering the last 173 000 years the first three of these species are passive tracers and reveal source and long range transport changes whereas nitrate is deposited reversibly however it can be used to check isotope derived accumulation rate estimates a prerequisite to calculate total depositional fluxes during the last two transitions from glacial to interglacial periods changes in the total depositional flux differ strongly for different aerosol species the largest changes are observed in the terrestrial aerosol proxy non sea salt calcium only moderate changes occur in the marine sea salt indicator sodium while ammonium a proxy for marine bioproductivity remains rather constant in agreement with previous studies we find that only considerable glacial interglacial changes at both the terrestrial and the marine sea salt aerosol source can explain the observed pronounced changes the unprecedented high resolution of our data allows for the first time the examination of decadal variability back to the penultimate glacial period on the one hand we find occasional fast shifts occurring within a few years here we present such an event in the calcium record from the penultimate glacial period on the other hand we examine variation coefficients and pairwise correlation coefficients both determined in 200 year windows they generally reveal only moderate changes during glacial periods slightly lower variation coefficients are found concurrent with slightly higher correlation coefficients which points to a more uniform and stronger coupled atmospheric long range transport of the different aerosol species to the east antarctic plateau and less influence of cyclonic activities during cold periods the opposite is observed for interglacial periods with probably even reinforced importance of cyclonic influences during the last interglacial period the marine isotope stage 5 5 this period reveals no evidence for abrupt climatic changes in any of the species however the marine sea salt aerosol indicator sodium shows a distinct minimum followed by a pronounced increase this pattern is explained by significantly reduced sea ice production in the indian southern ocean sector which is believed to be the dominant source of sodium deposited in dome c during warm periods

aeolian dust in the talos dome ice core east antarctica pacific ross sea sector victoria land versus remote sources over the last two climate cycles a new ice core taldice drilled at talos dome east antarctica ross sea sector preserves a ca 250 ka long record of palaeoclimate and atmospheric history we investigate dust variability and provenance at the site during glacial periods and the holocene through the sr nd isotopic composition of ice core dust and potential source areas psa we provide new isotopic data on dust sources from victoria land such as regoliths glacial drifts aeolian sands and beach deposits some of these sources are located at high altitude and are known to have been ice free throughout the pleistocene the major features of the taldice dust record are very similar to those from central east antarctica during glacial times south america was the dominant dust supplier for talos dome as well as for the entire east antarctic plateau conversely during the holocene the principal input of mineral dust at talos dome probably derives from proximal sources which are the ice free areas of northern victoria land located at similar altitude with respect to the drilling site atmospheric mobilisation of dust from these neighbouring areas and transport inland to talos dome can be ultimately associated with advection of maritime air masses from the pacific ross sea region copyright 2010 john wiley sons ltd supporting information can be found in the online version of this article

ground satellite observations and atmospheric modeling of dust storms originating in the high puna altiplano deserts south america implications for the interpretation of paleo climatic archives 1 this study provides a detailed description of the sources transport dispersion and deposition of two major dust events originating from the high altitude subtropical puna altiplano plateau 15 26 s 65 69 w in south america a long and severe drought provided the right conditions for the onset of both events in july 2009 and 2010 dust was transported se and deposited over the pampas region and was observed to continue to the atlantic ocean dust monitoring stations located downwind recorded both events and samples were characterized through chemical and textural analysis through a combination of meteorological data and satellite observations calipso and modis detectors we estimate the emission flux for the 2010 event this estimate was used to constrain the hybrid single particle lagrangian integrated trajectory hysplit transport model and simulate the dust event both satellite imagery and model results agree in the location and extension of the dust cloud calipso detected dust between 6000 and 8500 m a s l which remained at this height during most of its trajectory the dust cloud mixed with a strong convective system in the region and the associated precipitation brought down significant amounts of dust to the ground dust particle size analysis for both events indicates that near the sources dust samples show median modes of 12 4 14 1 m similar to modes observed 1300 km away chemical composition of sediments from potential dust sources shows distinct signatures within the puna altiplano plateau the puna sector being clearly different from the altiplano area in addition both sources are markedly different from the patagonian chemical fingerprint these results have important implications to improve the interpretation of paleo environmental archives preserved on the argentine loess antarctic ice cores and southern ocean marine sediments

influence of patagonian glaciers on antarctic dust deposition during the last glacial period dust deposition over antarctica was much higher during the last glacial period but the causes of this flux remain unclear an analysis of the composition and age of glacial outwash sediments indicates that growth and decay of glaciers in patagonia may have influenced dust transport to antarctica at that time

geographic provenance of aeolian dust in east antarctica during pleistocene glaciations preliminary results from talos dome and comparison with east antarctic and new andean ice core data abstract the strontium and neodymium isotopic signature of aeolian mineral particles archived in polar ice cores provides constraints on the geographic provenance of dust and paleo atmospheric circulation patterns data from different ice cores drilled in the centre of the east antarctic plateau such as epica dome c edc 75 06 s 123 21 e and vostok 78 28 s 106 48 e suggested a uniform geographic provenance for dust during pleistocene glacial ages likely from southern south america ssa in this work the existing dust isotopic data from edc have been integrated with new data from marine isotopic stage mis 14 about 536 ka before 1950ad and in parallel some first results are shown for the new taldice ice core which was drilled on the edge of the east antarctic plateau talos dome 72 48 s 159 06 e on the opposite side with respect to ssa interestingly the isotopic composition of taldice glacial dust is remarkably similar to that obtained from glacial dust from sites located in the east antarctic interior overall the glacial dust isotopic field obtained from six east antarctic ice cores matches well south american data obtained from target areas in this respect it was recently suggested that dust exported long range from south america originates from patagonia and from the puna altiplano plateau to test this hypothesis we analysed the isotopic composition of dust from an ice core drilled on the illimani glacier bolivia 16 37 s 67 46 w 6350 m a s l in order to obtain information on the isotopic composition of regional mineral aerosol uplifted from the altiplano area and likely transported over a long distance altogether ice core and source data strongly suggest that the westerly circulation pattern allowed efficient transfer of dust from south america to the east antarctic plateau under cold quaternary climates isotopic data support the hypothesis of a possible mixing of dust from patagonia and from the puna altiplano plateau interestingly high glacial dust inputs to antarctica are characterized by less radiogenic nd values an issue suggesting that enhanced dust production in patagonia was associated with the activation of a secondary source still patagonia was the most important supplier for dust to central east antarctica during quaternary glaciations

the glaciogenic origin of the pleistocene calcareous dust in argentina on the basis of field mineralogical textural and geochemical analyses calcareous dust occurs in argentina as layers and pockets closely associated with pleistocene deposits and periglacial features from southernmost patagonia to at least the mendoza precordillera and has been traditionally interpreted as a soil horizon resulting from postdepositional pedogenesis during interglacials detailed field and microscopic observations and sedimentological and geochemical analyses of more than 100 samples collected from lower to upper pleistocene deposits between 51 s and 33 s and from near sea level to 2800 m asl allow us to interpret the dust as synchronous with the host sediment all observations and analyses lead us to conclude that 1 the cryogenic morphology and the chemical signatures of the calcite component show that the dust is glaciogenic 2 the dust was carried by southeasterly antarctic winds and 3 it was deposited over most of southern and central argentina field observations geomorphic evidence and radiocarbon dates suggest that the dust was deposited during several pleistocene glacial episodes