sources of magnetic susceptibility in a slate abstract magnetic susceptibility and its anisotropy in the borrowdale volcanic slates at kentmere in the english lake district are attributed largely to preferred orientation of a paramagnetic chlorite of diabantite ripidolite composition in units of 10 6 cgs g the principal susceptibilities for the slates are 9 61 9 42 8 69 and for the chlorite grains the minimum anisotropy is represented by principal susceptibilities of 11 57 11 22 and 9 15 because the magnetic susceptibility is carried by a tightly packed matrix forming mineral that has recrystallised during the deformation it is not possible to imagine simple grain rotation as being responsible for the anisotropy of susceptibility

gps derived velocity and strain fields around dome argus antarctica knowledge of the surface topography velocity field and strain field at an ice core site is critical to the accurate interpretation of ice core records at dome argus dome a where a chinese deep ice core drilling project is being carried out we have produced an accurate surface digital elevation model from gps measurements in january 2013 at 47 sites we identify two peaks at dome a with the northern peak 7 cm higher than the southern peak repeat gps measurements at 12 sites in 2008 and 2013 provide a surface velocity field around the dome the surface velocity ranges from 3 1 2 6 to 29 4 1 2 cm a 1 with a mean of 11 1 2 4 cm a 1 the surface flow directions are near perpendicular to the surface elevation contours velocities from gps are lower than derived from satellite radar interferometry insar from gps velocities the accuracy of velocity from the existing insar velocity field is determined resulting in a standard deviation of 0 570 m a 1 in speed and 117 58 in direction this result is consistent with the reported accuracy of insar showing the value of in situ gps measurements for assessing and correcting remote sensing results a surface strain field for the drilling site over dome a is calculated from 24 strain triangles showing north south extension east west compression and vertical layer thinning

magnetic susceptibility of the rock matrix related to magnetic fabric studies non ferromagnetic minerals constitute what is called the rock matrix whose susceptibility k1 is directly accessible using only high magnetic fields measurements on minerals and a wide range of rock types show that k1 is mainly due to paramagnetism and hardly exceeds 10 3 si with an anisotropy degree p less than 1 35 different methods to estimate the role of the matrix component in low field susceptibility k and its anisotropy include petrological and chemical analysis evolution of p vs k low temperature studies and comparison of k with remanent magnetizations

decadal gps derived ice surface velocity along the transect from zhongshan station to and around dome argus east antarctica 2005 16 using repeat gps measurements during 2005 16 we calculated and updated two dimensional high resolution decadal ice surface velocity estimates along the traverse route from zhongshan station to and around dome argus east antarctica along the 71 sites of the transect the magnitudes of ice velocity increased from near 0 in dome argus to 1 10 and 100 m a 1 at the sites dt416 dt333 and lt980 respectively the comparison between gps and interferometric synthetic aperture radar insar derived results agree well when the magnitude of the ice surface velocities is faster than 5 m a 1 and disagree for slower flow velocities a scale value 1 15 and 0 12 can be applied to insar derived results over this region with ice surface velocity larger and 1 respectively we attributed the cause of the discrepancy to the insensitivity of insar to the magnitude of low ice surface velocities thus confirming the importance of gps fieldwork based ground truth high resolution ice velocity estimates to constrain ice sheet dynamics

paleomagnetism carried by crystal inclusions the effect of preferred crystallographic orientation abstract randomly oriented phlogopite crystals from a pegmatite contain submicroscopic inclusions of magnetite the inclusions have oblate magnetic fabrics subparallel to the ab crystal plane alternating field demagnetization of individual crystals shows that the remanence is influenced by the crystal symmetry of the phlogopite host the magnetizations isolated by alternating field demagnetization either cluster close to the a axis or scatter in the ab plane coarse grained igneous and metamorphic rocks can only record a paleofield direction accurately if there is a suitable orientation distribution of the rock forming minerals that host the ferromagnets an isotropic distribution of rock forming minerals is preferable but it is not obligatory rock forming minerals that have l fabrics or s fabrics with a strong l component are also suitable if they contain oblate inclusion fabrics of ferromagnets

spatial and temporal variability of surface mass balance near talos dome east antarctica 1 predictions concerning antarctica s contribution to sea level change have been hampered by poor knowledge of surface mass balance snow accumulation is the most direct climate indicator and has important implications for paleoclimatic reconstruction from ice cores snow accumulation measurements stake core snow radar taken along a 500 km transect crossing talos dome east antarctica have been used to assess accumulation signals and the representativeness of ice core records stake readings show that accumulation hiatuses can occur at sites with accumulation rates below 120 kg m 2 yr 1 differences between cores and stakes can lead to statistical misidentification of annual layers determined from seasonal signals at sites with accumulation rates below 200 kg m 2 yr 1 because of nondetection of higher and lower values achieving 10 accuracy in the reconstruction of snow accumulation from single cores requires high accumulation 750 kg m 2 yr 1 low accumulation sites are representative if cumulative rates computed over several years are used to reach the 750 kg m 2 yr 1 threshold temporal variability of accumulation over the last two centuries shows no significant increase in accumulation wind driven processes are a fundamental component of surface mass balance spatial variations in accumulation are well correlated with surface slope changes along the wind direction and may exceed 200 kg m 2 yr 1 within 1 km wind driven sublimation rates are less than 50 kg m 2 yr 1 in plateau areas and up to 260 kg m 2 yr 1 in slope areas and account for 20 75 of precipitation whereas depositional features are negligible in surface mass balance

ice discharge of eastern dome c drainage area antarctica determined from airborne radar survey and satellite image analysis eastern dome c southern talos dome and northern taylor dome are drained by the priestley reeves david mawson and mackay outlet glaciers which flow into the scott coast on the west side of the ross sea antarctica airborne radar surveys were conducted on these glaciers to determine ice thickness and bed morphology along transverse and longitudinal profiles of the grounded and floating segments a new analysis of a i andsat thematic mapper satellite image using a tracking technique was used to measure ice velocity at grounding lines and along ice tongues the integration of radar and satellite data helped to locate grounding lines and to calculate the ice discharge changes in ice fluxes of floating glaciers were used to determine basal melting and freezing rates the ice discharge calculated is less than half that required for a zero net surface mass balance according to the inputs given by the accumulation estimates widely adopted at present the basal melting rates of meteoric ice represent 50 of the net ablation rate

a 220 year continuous record of volcanic h2so4 in the antarctic ice sheet continuous h2so4 profiles observed in snow from several antarctic locations reveal four major volcanic events of the past two centuries agung krakatoa tambora and another large scale event not recorded historically acid deposition and interhemispheric distribution mechanisms are quantified and then used to obtain an order of magnitude estimate for the h2so4 emissions from these eruptions

field impressed anisotropies of magnetic susceptibility and remanence in minerals the application of alternating af or direct df magnetic fields to samples containing dispersed particles of magnetite titanomagnetite or maghemite has been found to alter significantly the measured low field susceptibility anisotropy even though the particle orientation is unchanged the acquisition of isothermal remanent magnetization irm is also strongly dependent on the previous af treatment given to the samples a method of quantifying the changes brought about by application of the fields is described the samples studied were intrinsically isotropic or only weakly anisotropic and the computed impressed susceptibility or irm ellipsoids produced by the applied fields were ellipsoids of revolution with the unique axis aligned with the applied field axis the size and shape of the field impressed ellipsoids were strongly dependent upon particle size these effects might thus form the basis of a rapid nondestructive means of estimating particle size in rocks the results also have important implications for magnetic fabric analysis and the static af demagnetization of rocks in particular to ensure that the intrinsic magnetic fabric is measured without any field impressed component of anisotropy samples should not be subjected to static af demagnetization prior to the determination of either low field susceptibility anisotropy or irm anisotropy samples should also not carry a significant remanence such as an irm acquired in a field greater than about 5 mt prior to low field susceptibility anisotropy analysis

tributaries of west antarctic ice streams revealed by radarsat interferometry interferometric radarsat data are used to map ice motion in the source areas of four west antarctic ice streams the data reveal that tributaries coincident with subglacial valleys provide a spatially extensive transition between slow inland flow and rapid ice stream flow and that adjacent ice streams draw from shared source regions two tributaries flow into the stagnant ice stream c creating an extensive region that is thickening at an average rate of 0 49 meters per year this is one of the largest rates of thickening ever reported in antarctica

res signatures of ice bottom near to dome c antarctica geophysical surveys have played a fundamental role in glaciology climatology and geology studies conducted at and around the site of the epica dome c ice core antarctica analysis of radio echo sounding res data collected during the 2009 and 2011 italian antarctic expeditions in the immediate vicinity 2 km of the core site reveals the presence of small scale bedrock structures data acquired during the 2011 campaign which applied the latest updates of our instrument show double echoes from the ice bottom separated by very small time intervals these reflections are distributed close to the topographic dome and do not always correspond to particular features of the bedrock structure but instead may correspond to small scale subglacial water storage the unprecedented spatial resolution of the basal environment for dome c from these recent surveys allows us to identify this and other features that have been missed by previous larger scale res surveys of this area

marine cold seeps and their manifestations geological control biogeochemical criteria and environmental conditions characteristics of cold seeps at different geologic settings are the subject of this review primarily based on results of the research consortium sfb 574 criteria are drawn from examples on the erosive convergent margin off costa rica the accretionary margin off chile supplemented by examples from the transform margin of the golf of cadiz and the convergent hikurangi margin off new zealand others are from well studied passive margins of the black sea the golf of mexico the eastern mediterranean sea and the south china sea seeps at all settings transport water and dissolved compounds to the ocean through the seafloor by different forcing mechanism and from different depths of the submerged geosphere 10s of meters to 10s of km the compounds sustain oasis type ecosystems by providing bioactive reductants sulfide methane and hydrogen hereby the interaction between fluid composition flux rates and biota results in a diagnostic hydrocarbon metazoan microbe carbonate association currently well over 100 active sites are known the single most important reaction is microbially mediated anaerobic oxidation of methane with secondary reactions involving s biogeochemistry and carbonate mineral precipitation seep fluids and their seafloor manifestations provide clues as to source depth fluid sediment rock interaction during ascent lifetime and cyclicity of seepage events but less so on the magnitude of return flow at erosive margins cl depleted and b enriched fluids from clay dehydration provide criteria for source depth and temperature the upward material flow generates mud volcanoes at the seafloor above the projected location of dehydration at depth at accretionary margins fluids are derived from more shallow depths by compaction of sediments as they ride on the incoming oceanic plate they are emitted through thrust faults at highly sedimented margins organic rich and evaporite containing strata when present determine the final fluid composition by emitting characteristically gas hydrate derived methane brine associated non methane hydrocarbons or leached elements and their isotopes li 7li b ba from host sediments smectite illite transformation and associated cl depletion from release of interlayer water is a pervasive process at these margins rare earth element pattern in conjunction with redox sensitive metals retained in seep carbonates indicate whether or not they precipitated in contact with oxic bottom water or suboxic fluids clear environmental characterization though currently remains inconclusive more deeply sourced fluids as in transform margins may be characterized by their 87sr 86sr ratios from interaction with oceanic crustal rocks below quantification of flow and reliable estimates of total volatile output from fore arcs remain a challenge to seep research as does understanding the role of geologically derived methane in the global methane cycle

ice and bedrock characteristics underneath dome c antarctica from radio echo sounding data analysis the radio echo sounding res system is one of the most widely used active remote sensing techniques for polar ice sheet exploration including bedrock morphology studies and subglacial lake investigations recently bedrock characterization has been improved through the analysis of radar echo strength in this paper the analysis of the res signal amplitude has been used to collect information about the controversial problem of electromagnetic ice absorption to highlight areas of high reflectivity variation ascribable to wet ice bedrock interfaces a method to distinguish a wet or dry bedrock ice interface using a model to describe the internal ice absorption is proposed and discussed moreover the comparison between the ice absorption rates from res measurements and from european project for ice coring in antarctica dome c antarctica ice core conductivity data the signal amplitude contributions of internal ice layers and different kinds of rock interface is evaluated encouraged by the results the data analysis led to obtaining a bedrock reflectivity variation map of the dome c area this map outlined a wide dispersion of wet dry rock interfaces in the studied area indicating the possibility of flowing water along both sides of the concordia trench

the magnetic fabric of metasediments in a detachment shear zone the example of tinos island greece abstract we present a magnetic fabric study 12 sites in strongly deformed metasediments micaschists and calcschists from a well exposed detachment shear zone at tinos island cyclades greece a gradient of deformation is observed from the southwest side to the northeast side of tinos the detachment shear zone is contemporaneous with a greenschist retrogression episode ca 25 20 ma high pressure hp 45 ma metasediments are preserved in the southwest side of tinos we compared the anisotropy of magnetic susceptibility ams 158 samples to the anisotropy of isothermal remanent magnetization airm 40 samples ams is primarily dominated by phyllosilicates whilst airm reflects the contribution of mixture of ferromagnetic grains magnetite hematite goethite and pyrrhotite interestingly we observe the appearance of goethite feo oh is observed when approaching the detachment area the orientation of the ams and airm axes shows a general consistency on the other hand airm is more prolate and anisotropic than ams we document a close agreement between the ams magnetic foliation and the structural cleavage that has been measured from the core sample the magnetic lineation is generally parallel to the stretching lineation observed on the field however composite magnetic lineations suggest well preserved petrofabrics contemporaneous to the 45 ma hp episode an increase in the ams foliation anisotropy parameter is observed in micaschists when deformation increases unfortunately no quantitative estimate of finite deformation is possible using ams due to the dominant role of phyllosilicates and the complex ferromagnetic mineralogy

seafloor facies related to upward methane flux within a giant pockmark of the lower congo basin the origin of the cold fluid venting from a giant pockmark within the lower congo basin has been elucidated based upon results of precise mapping submersible dives gravity coring and isotopic analyses realized under a total ifremer cooperative project zaiango and biozaire projects during four dives of the ifremer rov victor 6000 the bottom was filmed hard and soft samples were lifted from the sediment and water samples were collected with a ctd rosette system the detailed dip map shows that the 800 m wide giant pockmark is a composite feature due to the coalescence of multiple 100 m wide depressions that displays a broad range of biological mineralogical and chemical features on the seafloor leading to a seafloor anomaly recorded on the multibeam imagery methane rich fluids migrating through the sedimentary column from a buried palaeochannel clearly react with the sulphate rich circulating sea water to produce hydrogen sulphide and bicarbonate ions this situation leads to a concentrical arrangement of the sedimentary facies with methane related features in the centre and sulphide related features at the periphery this organization is correlated with high levels of methane up to 20 mol l measured in the centre of the giant pockmark responsible for the crystallization of gas hydrates at the bottom in this model the concentrical organization of mineralogical and biological features reflects a geochemical partitioning related to the peripheral progressive mixing of the methane flux

surface topography and ice flow in the vicinity of the edml deep drilling site antarctica interpretation of ice core records requires accurate knowledge of the past and present surface topography and stress strain fields the european project for ice coring in antarctica epica drilling site 75 00258 s 0 06848 e 2891 7 m in dronning maud land antarctica is located in the immediate vicinity of a transient and forking ice divide a digital elevation model is determined from the combination of kinematic gps measurements with the glas12 datasets from the icesat based on a network of stakes surveyed with static gps the velocity field around the drilling site is calculated the annual mean velocity magnitude of 12 survey points amounts to 0 74ma 1 flow directions mainly vary according to their distance from the ice divide surface strain rates are determined from a pentagonshaped stake network with one center point close to the drilling site the strain field is characterized by along flow compression lateral dilatation and vertical layer thinning

ice flow physical processes derived from the ers 1 high resolution map of the antarctica and greenland ice sheets accepted 1999 july 7 received 1999 june 7 in original form 1998 june 24 summary the ers 1 satellite launched in 1991 has provided altimetric observations of the greenland ice sheet and 80 per cent of the antarctica ice sheet north of 82 s it was placed in a geodetic 168 day repeat orbit between april 1994 and march 1995 yielding a 1 5 km across track spacing at latitude 70 with a higher along track sampling of 350 m we have analysed the waveform altimetric data from this period to compute maps with a 1 30 grid size data processing consists of correcting for environmental factors and editing and retracking the waveforms a further step consists of reducing the radial orbit error through crossover analysis and correcting the slope error to second order the high resolution topography of both ice sheets reveals numerous details a kilometre scale surface roughness running at 45 from the flow direction is the dominant topographic characteristic of both continents antarctica also exhibits many scars due to local flow anomalies several physical processes can be identified abrupt transitions from deformation to sliding and vice versa and impressive strike slip phenomena inducing en echelon folds

using radar sounding data to identify the distribution and sources of subglacial water application to dome c east antarctica basal radar reflectivity is the most important measurement for the detection of subglacial water however dielectric loss in the overlying ice column complicates the determination of basal reflectivity dielectric attenuation is a function of ice temperature and impurity concentration temperature distribution is a function of climate history basal heat flow and vertical strain rate all of which can be partially inferred from the structure of dated internal layers using 11 dated layers isotope records from dome c east antarctica and a model of the spatial variation of geothermal flux we calculate the vertical strain rate and accumulation rate history allowing identification of areas where the basal melt rate exceeds 1 5 mm a 1 the accumulation rate history and vertical strain rates are then used as inputs for a transient temperature model the model outputs for the present day temperature distribution are then combined with depth dependent ionic concentrations to model dielectric loss and infer basal reflectivity the resulting reflection coefficients are consistent 5 db across a variety of subglacial water bodies we also identify a high reflectivity 15 db in concordia trench and along suspected subglacial water flow routes in vincennes basin highland areas tend to have highly variable reflection coefficients near 30 db consistent with an ice bedrock interface this combined model also identifies three areas of enhanced basal melting along concordia ridge concordia subglacial lake and vincennes basin melt at concordia subglacial lake exceeds 5 mm a 1 the inferred basal melt at these locations is not possible without enhanced geothermal flux we demonstrate how radar sounding data can provide both input and verification for a self consistent model of vertical strain vertical temperature distribution and meltwater distribution

cold seep like macrofaunal communities in organic and sulfide rich sediments of the congo deep sea fan methane rich fluids arising from organic matter diagenesis in deep sediment layers sustain chemosynthesis based ecosystems along continental margins this type of cold seep develops on pockmarks along the congo margin where fluids migrate from deep buried paleo channels of the congo river acting as reservoirs similar ecosystems based on shallow methane production occur in the terminal lobes of the present day congo deep sea fan which is supplied by huge quantities of primarily terrestrial material carried by turbiditic currents along the 800 km channel and deposited at depths of up to nearly 5000 m in this paper we explore the effect of this carbon enrichment of deep sea sediments on benthic macrofauna along the prograding lobes fed by the current active channel and on older lobes receiving less turbiditic inputs macrofaunal communities were sampled using either usnel cores on the channel levees or rov blade cores in the chemosynthesis based habitats patchily distributed in the active lobe complex the exceptionally high organic content of the surface sediment in the active lobe complex was correlated with unusual densitiesof macrofauna for this depth enhanced by a factor 7 to 8 compared with those of the older abandoned lobe whose sediment carbon content is still higher than in angola basin at same depth macrofaunal communities dominated by cossurid polychaetes and tanaids were also more closely related to those colonizing low flow cold seeps than those of typical deep sea sediment in reduced sediments microbial mats and vesicomyid bivalve beds displayed macrofaunal community patterns that were similar to their cold seep counterparts with high densities low diversity and dominance of sulfide tolerant polychaetes and gastropods in the most sulfidic habitats in addition diversity was higher in vesicomyid bivalve beds which appeared to bio irrigate the upper sediment layers high beta diversity is underscored by the variability of geochemical gradients in vesicomyid assemblages and by the vesicomyid population characteristics that vary in density size and composition by modifying the sediment geochemistry differently according to their morphology and physiology the different vesicomyid species play an important role structuring macrofauna composition and vertical distribution dynamics of turbiditic deposits at a longer temporal scale thousands of years and their spatial distribution in the lobe area also resulted in high heterogeneity of the cold seep like communities dynamics of chemosynthetic habitats and associated macrofauna in the active lobe area 2 please note that this is an author produced pdf of an article accepted for publication following peer review the definitive publisher authenticated version is available on the publisher web site resembled those previously observed at the regab pockmark along the congo margin and rapid succession is expected to cope with high physical disturbance by frequent turbiditic events and huge sedimentation rates finally we propose a model of the temporal evolution of these peculiar habitats and communities on longer timescales in response to changes in distributary channels within the lobe complex

annually resolved southern hemisphere volcanic history from two antarctic ice cores the continuous sulfate analysis of two antarctic ice cores one from the antarctic peninsula region and one from west antarctica provides an annually resolved proxy history of southern semisphere volcanism since early in the 15th century the dating is accurate within 3 years due to the high rate of snow accumulation at both core sites and the small sample sizes used for analysis the two sulfate records are consistent with each other a systematic and objective method of separating outstanding sulfate events from the background sulfate flux is proposed and used to identify all volcanic signals the resulting volcanic chronology covering 1417 1989 a d resolves temporal ambiguities about several recently discovered events a number of previously unknown moderate eruptions during late 1600s are uncovered in this chronology the eruption of tambora 1815 and the recently discovered eruption of kuwae 1453 in the tropical south pacific injected the greatest amount of sulfur dioxide into the southern hemisphere stratosphere during the last half millennium a technique for comparing the magnitude of volcanic events preserved within different ice cores is developed using normalized sulfate flux for the same eruptions the variability of the volcanic sulfate flux between the cores is within 20 of the sulfate flux from the tambora eruption

recent increase in south pole snow accumulation this paper summarizes the 37 year history of net accumulation measurements at the geographic south pole obtained by numerous investigators using a variety of techniques these data lead to the conclusion that annual net snow accumulation has increased in the vicinity of south pole station sps since 1955 the records were examined for evidence of a station effect and it is concluded that not all of the observed increase can be attributed to snow drift associated with the presence of the station furthermore the accumulation increase at the south pole appears consistent with increases observed at other locations on the east antarctic plateau and in the peninsula region as well these data suggest that the recent accumulation increase at sps may be regionally extensive over the east antarctic plateau

spatial and temporal variability of snow accumulation in east antarctica from traverse data recent snow accumulation rate is a key quantity for ice core and mass balance studies several accumulation measurement methods stake farm fin core snow radar profiling surface morphology remote sensing were used compared and integrated at eight sites along a transect from terra nova bay to dome c east antarctica to provide information about the spatial and temporal variability of snow accumulation thirty nine cores were dated by identifying tritium b marker levels 1965 66 and non sea salt nss so4 2 spikes of the tambora indonesia volcanic event 1816 in order to provide information on temporal variability cores were linked by snow radar and global positioning system surveys to provide detailed information on spatial variability in snow accumulation stake farm and ice core accumulation rates are observed to differ significantly but isochrones snow radar correlate well with ice core derived accumulation the accumulation ablation pattern from stake measurements suggests that the annual local noise metre scale in snow accumulation can approach 2 years of ablation and more than four times the average annual accumulation with no accumulation or ablation for a 5 year period in up to 40 of cases the spatial variability of snow accumulation at the kilometre scale is one order of magnitude higher than temporal variability at the multi decadal secular scale stake measurements and firn cores at dome c confirm an approximate 30 increase in accumulation over the last two centuries with respect to the average over the last 5000 years

snow megadunes in antarctica sedimentary structure and genesis 1 megadune fields occupy large areas in the interior of the east antarctic ice sheet and are the result of unusual snow accumulation and redistribution processes they therefore are important to surface mass balance and ice core interpretation field observations gps gpr and surface measurements have provided a detailed description of megadune sedimentation and morphology over a 70 km2 area located 200 km east of dome c a combination of remote sensing analysis using landsat and satellite radar altimetry and field measurements indicate that slope in the prevailing wind direction spwd and climatic conditions play a crucial role in megadune genesis the megadune areas tend to be characterized by slightly steeper regional slope and the presence of highly persistent katabatic winds the megadunes represent 2 to 4 m amplitude waves of 2 to 5 km wavelength formed by variable net accumulation ranging between 25 leeward faces to 120 windward faces of the accumulation in adjacent nonmegadune areas leeward faces are characterized by glazed sastrugi free surfaces and extensive depth hoar formation windward faces are covered by large rough sastrugi up to 1 5 m in height

the international trans antarctic scientific expedition itase an overview from its original formulation in 1990 the international trans antarctic scientific expedition itase has had as its primary aim the collection and interpretation of a continent wide array of environmental parameters assembled through the coordinated efforts of scientists from several nations itase offers the ground based opportunities of traditional style traverse travel coupled with the modern technology of gps crevasse detecting radar satellite communications and multidisciplinary research by operating predominantly in the mode of an oversnow traverse itase offers scientists the opportunity to experience the dynamic range of the antarctic environment itase also offers an important interactive venue for research similar to that afforded by oceanographic research vessels and large polar field camps without the cost of the former or the lack of mobility of the latter more importantly the combination of disciplines represented by itase provides a unique multidimensional space and time view of the ice sheet and its history itase has now collected 20 000 km of snow radar recovered more than 240 firn ice cores total length 7000 m remotely penetrated to 4000 m into the ice sheet and sampled the atmosphere to heights of 20 km

matrix deformation in a basement involved fold and thrust belt a case study in the central andes malargue argentina abstract an analysis of the anisotropy of magnetic susceptibility ams is used to investigate the matrix strain record of weakly deformed clastic rocks including sandstones and shales along a cross section of the malargue fold and thrust belt mftb argentina we collected 339 oriented cores from the tres esquinas sandstones the red beds of the tordillo and neuquen formations as well as from shales silts of the mendoza group overall 90 of the magnetic fabrics are well defined and are related to the strain imprint of the layer parallel shortening among the tectonic related fabrics 40 show the development of a magnetic lineation at right angle of the shortening type ii 38 display an apparent loss of magnetic foliation type iii and 21 develops a magnetic foliation at right angle of the shortening type iv there is no lithological control on magnetic fabric typology despite contrasting ferromagnetic mineralogy between the red sandstones and dark shales thin section observations highlight the good match between the orientation of both the susceptibility ellipsoid and microstructure orientation which enables us to infer the preferred orientations of the petrofabric i e finite strain directions in this way two trends can be recognized in the study area shortening directions trending n110 in the north and trending n80 in the south in addition the spatial distribution of magnetic fabric typology and burial data suggests an atypical pattern of deformation from the foreland to hinterland such a pattern contrasts with previous studies in fold thrust belt settings suggesting that at the matrix scale the deformation even in a pre folding setting is compartmentalized and controlled by the occurrence of deep seated thrusts localized along inherited structures from the analysis of cross sections we can distinguish several domains each of them reflecting distinct states of matrix deformation

new gastropods from deep sea hydrocarbon seeps off west africa thirteen new species of gastropods are described from the zairov 1 2 and biozaire 1 3 cruises to the methane seeps off the congo river patellogastropoda paralepetopsis sasakii sp nov neolepetopsidae cocculiniformia pyropelta oluae sp nov and p sibuetae sp nov pyropeltidae tentaoculus granulatus sp nov pseudococculinidae neomphalina leptogyra costellata sp nov family uncertain vetigastropoda puncturella similis sp nov fissurellidae lepetodrilus shannonae sp nov lepetodrilidae caenogastropoda provanna reticulata sp nov and p chevalieri sp nov cordesia provannoides gen et sp nov provannidae phymorhynchus coseli sp nov and p cingulata sp nov conidae heterobranchia hyalogyrina rissoella sp nov hyalogyrinidae all species except t granulatus from a settlement trap belong to groups known from cold seeps and the entire seep fauna here is new to science biogeographical affinity of this gastropod fauna is to the west atlantic seeps not to the mediterranean seeps or mid atlantic vents fragments of the autecology of the species are presented the evolution of the seep gastropod fauna is briefly discussed and a continuous immigration of taxa is supported the oldest verified occurrences of modern taxa in the seeps date back to cenomanian cretaceous time while some taxa seem not to appear until very late tertiary

on the instability and evolutionary age of deep sea chemosynthetic communities abstract though not directly dependent on photosynthesis deep sea chemosynthetic communities have not been sheltered from catastrophic changes affecting earth s photic zone instead the constituent animals may be particularly vulnerable to large climatic changes that have historically affected ocean temperatures and circulation patterns chemosynthetic animals occupy narrow redox zones mostly at hydrothermal vents hydrocarbon seeps or sites of organic deposition where subsurface fluids laden with reduced gases e g sulfides methane hydrogen meet oxygenated seawater dependence on chemolithoautotrophic bacteria as primary producers may render these deep sea communities particularly susceptible to climatic changes that alter the breadth of the oxic anoxic interface the fossil record clearly reveals major transitions of chemosynthetic faunas during the middle to late mesozoic failing to support prior hypotheses that these environments harbor an extraordinary number of ancient relics and living fossils the molecular phylogenetic analyses summarized herein support cenozoic

constraining ice dynamics at dome c antarctica using remotely sensed measurements a first time description is given of the ice flow at dome c antarctica around the epica drilling site we used satellite radar altimetry to obtain the precise ice surface topography airborne radio echo sounding to obtain the ice thickness and satellite sar interferometry to derive one component of the surface velocity field the balance flux around the dome c area is then accurately mapped and comparisons made between driving stress surface and balance velocity to help us describe the ice flow in the region as a by product of the study we also recover anomalies in the ice flow conditions in sub glacial lake locations these effects result from localy invalid shallow ice approximation the results of this study form the basis for future investigations of the ice flow conditions at dome c in relation to ice core interpretation

bedrock features and ice flow near the epica ice core site dome c antarctica the precise bedrock topography near the epica ice core site at dome c in antarctica exhibits impressive bedrock mountains bowls and a clear network of elongated valleys some of these features are probably tectonic and are likely to be buried pre ice sheet landforms the elongated bedrock valleys are clearly detectable in the surface topography suggesting a large scale network the analysis of the relationship between basal and surface elongated structures indicates a damping factor decreasing from 120 near the dome to 80 at few tens of kilometer there is evidence of presence of subglacial water and of erosed bed that can play a role of the ice flow a complete flow modeling taking into account longitudinal stresses should be performed around epica site in order to improve dating of the ice

is this magnetic fabric normal a review and case studies in volcanic formations abstract when studying weakly anisotropic rocks non standard relationships between magnetic and expected petrofabric axes are sometimes observed in particular the so called inverse or intermediate fabrics a review of possible explanations for these effects is presented and leads to the conclusion that a majority of abnormal magnetic fabrics often encountered in magnetite rich volcanic rocks are due to abnormal preferred orientations or distributions of magnetite grains through case studies in dikes from skye island yemen and the iberian peninsula and magma and ash flows from the ethiopian traps and southern corsica the various possible origins of such fabrics are examined it is possible to retrieve reliable magma flow directions from these sites provided proper data selection is performed leading to non unique interpretations

the magnetic fabric of weakly deformed late jurassic shales from the southern subalpines chains french alps evidence for sw directed tectonic transport direction abstract extensive magnetic fabric investigations have been conducted on the late jurassic sedimentary black shales 37 sites 362 samples the so called terres noires formation from the southern subalpine chains western alps this study completes a previous study done in the northern subalpine chains which demonstrated that the terres noires formation preserves a subtle magnetic lineation related to tectonic transport direction in the southern subalpine chains diois devoluy embrunais digne nappe similar magnetic fabrics have been found the shape of the magnetic fabric is oblate and locally mirrors the gradient of deformation in the embrunais footwall the magnetic foliation is parallel to the bedding or to the slaty cleavage about 50 of the magnetic lineations have down dip magnetic directions while the other magnetic lineations are sub horizontal or parallel to the intersection bedding cleavage the tectonic magnetic fabrics recorded in the embrunais confirm the ability of the terres noires to record tectonic transport direction the magnetic fabric geometry suggests sw directed tectonic transport in the southern subalpine chains the diois appears as a tip zone where transport directions are abruptly clockwise rotated from nw directed in the northern subsalpine chains to sw directed the magnetic fabric from the digne nappe exhibits a fan pattern of transport directions in close agreement with the arcuate shape of the thrust

electromagnetic ice absorption rate at dome c antarctica radio echo sounding res is a radar technique widely employed in antarctica and greenland to define bedrock topography but over the last decade it has also played an important role in subglacial lake exploration and hydrogeological studies at the bedrock ice interface in recent studies bedrock characterization has been improved through analysis of radar power echoes to evaluate the electromagnetic em properties of the interface and allow the distinction between wet and dry interfaces the res received signal power depends on ice absorption and bedrock reflectivity which is closely linked to the specific physical condition of the bedrock in this paper an evaluation of em ice absorption was conducted starting from res measurements collected over subglacial lakes in antarctica the idea was to calculate ice absorption starting from the radar equation in the case of subglacial lakes where the em reflectivity value is considered a known constant these values were compared with those obtained from analysis of ice core dielectric profiles from epica ice core drilling data our analysis reveals that the ice absorption rate calculated from res measurements has an average value of 7 2dbkm 1 and it appears constant independent of the subglacial lake depth in different zones of the dome c area

methane seepage effects on biodiversity and biological traits of macrofauna inhabiting authigenic carbonates abstract authigenic carbonate rocks at methane seeps are recognized as hosting diverse and abundant invertebrate assemblages with potential forcing from fluid seepage and hydrography mensurative studies of carbonate macrofauna 0 3 mm at hydrate ridge or revealed little effect of water depth and overlying oxygenation at 600 m and 800 m but a large influence of seepage activity on density taxonomic composition diversity and biological traits feeding lifestyle motility size and calcification rocks exposed to active seepage had 3 4 higher total macrofaunal densities than under inactive conditions assemblages exhibited higher species richness and reduced evenness greater dominance under active seepage than inactive conditions but no difference in h or rarefaction diversity actively seeping sites were characterized by errant motile bacterial grazing small and medium sized heavily calcified species whereas inactive sites exhibited a greater diversity of feeding modes and more burrowers sessile large and lightly calcified species active rocks supported more exogonid syllidae ampharetid and cirratulid polychaetes provannid snails pyropeltid limpets nemerteans and sponges whereas inactive rocks supported higher densities of ophiuroids isopods gammarid amphipods hydroids typosyllis syllidae and tanaids transplant experiments in which rocks were transferred between active and inactive sites at hydrate ridge north 600 m revealed that assemblages respond within 13 months to increase or cessation of seepage taking on the feeding size and calcification characteristics of the background fauna at the new site lifestyles and motility patterns shifted more slowly as the sessile attached species did not track seepage as quickly provannid snails and pyropeltid limpets rapidly colonized rocks transplanted to active sites and disappeared when transplanted to inactive sites given the known variability of fluid fluxes and rapid community response a mosaic of communities changing in space and time is hypothesized to generate the relatively high species diversity at methane seeps

dynamic distributed drainage implied by the flow evolution of the 1996 1998 adventure trench subglacial lake discharge abstract the transport of subglacial water beneath the east antarctic ice sheet is an enigmatic and difficult to observe process which may affect the flow of the overlying ice and mixing of the oceans in the sub ice shelf cavities and ultimately global climate periodic outbursts are a critical mechanism in this process recent analysis of satellite data has inferred a subglacial hydraulic discharge totaling 2 km 3 traveling some 260 km along the ice bed interface of the adventure subglacial trench between 1996 and 1998 wingham et al 2006 rapid discharge connects antarctic subglacial lakes nature 440 1033 1036 using radar echo sounding data from the adventure subglacial trench region in conjunction with the previously reported satellite observations along with some basic modeling we calculate a mass budget and infer a flow mechanism for the 1996 1998 event the volume released from the source lake exceeded the volume received by the destination lakes by 1 1 km 3 this discrepancy indicates that some water must have escaped downstream from the lowest destination lake from 1997 onward the downstream release of water from the destination lakes continued until at least 2003 several years after the 1998 cessation of surface subsidence at the source lake by 2003 a total of 1 5 km 3 or nearly 75 of the water released by the source lake had traveled downstream from the destination lakes the temporal evolution of discharge from the outlet can be simulated with the classic ice walled semicircular channel model if and only if the retreat of the source lake shoreline is taken into account further downstream the ice bedrock geometry along the inferred flow path downstream includes many sections where thermal erosion of the overlying ice would not be sustainable along these reaches mechanical lifting of the ice roof and or erosion of a sedimentary substrate by a broad shallow water system would be most effective means of sustaining the discharge a distributed system is also consistent with the 3 month delay between water release at the source lake and water arrival at the destination lake observations of intermittent flat bright bed reflections in radar data acquired along the flow path are consistent with the presence of a broad shallow water system ultimately the presence of large subglacial lakes along the flow path of the 1996 1998 adventure subglacial trench flow path delayed the arrival of water to points downstream by approximately 12 months

a tentative chronology for the epica dome concordia ice core a tentative age scale edc1 for the last 45 kyr is established for the new 788 m epica dome c ice core using a simple ice flow model the age of volcanic eruptions the end of the younger dryas event and the estimated depth and age of elevated 10be about 41 kyr ago were used to calibrate the model parameters the uncertainty of edc1 is estimated to 10 yr for 0 to 700 yr bp up to 200 yr back to 10 kyr bp and up to 2 kyr back to 41 kyr bp the age of the air in the bubbles is calculated with a firn densification model in the holocene the air is about 2000 yr younger than the ice and about 5500 yr during the last glacial maximum

physiography and tectonic setting of the subglacial lake district between vostok and belgica subglacial highlands antarctica summary we present the interpretation of 11 radio echo sounding res missions carried out over the vostok dome concordia region during the italian antarctic expeditions in the period 1995 2001 the extension and the density of the radar data in the surveyed area allowed to reconstruct a reliable subglacial morphology and to identify four relevant morphological structures namely the aurora trench the concordia trench the concordia ridge and the south hills these structures show evidence compatible with the presence of tectonic features morphological considerations indicate their development in cenozoic time hybrid cellular automata hca based numerical modelling allowed to justify a possible role played by the tectonics of the aurora and concordia trench evolution this was accomplished by matching the bed profiles along opportunely projected sections with the modelled surfaces as derived by the activity of normal faults with variable surfaces within the continental crust the vostok dome c region is characterized by a large number of subglacial lakes from the analysis of basal reflected power echo we identified 14 new lakes and obtained information about their physiography as well as their possible relations with tectonics we propose a grouping of subglacial lakes on the base of their physiography and geological setting namely relief lakes basin lakes and trench lakes relief lakes located in the belgica subglacial highlands and are characterized by sharp and steep symmetric edges suggesting a maximum water depth of the order of 100 m their origin may well relate to localized positive geothermal flux anomalies basin lakes located in the vincennes subglacial basin and are characterized by wider dimension that allow the development of well defined flat ice surface anomalies trench lakes characterize the aurora and concordia trenches as the possible effect of normal fault activity

the contribution of discontinuous rock mass failure to glacier erosion geomechanical rock mass properties control the response of bedrock to applied stresses and can be summarized in a linear mohr coulomb equation which defines the principal parameters determining failure nevertheless in studying the erosion of bedrock by glacier ice little attention has been paid to failure criteria though a coincidence of erosion all and forms with fracture systems at regional and local scales has been demonstrated few studies have analysed the precise nature of the fracture geometry or proposed its mechanical impact in association with glacier ice this investigation proposes that since almost all bedrock possesses identifiable fracture systems the properties of discontinuous rock mass drm be regarded as defining primary conditions of stress and stability which are subsequently modified directly and indirectly by glacier ice consequent rock mass failure modes are prescribed by discontinuity geometry and applied stresses and evidence from north wales confirms the validity of the theoretical treatment of rock mass properties and explains the accordance of landforms with structure

snow grain size measurements in antarctica grain size is an important but not well known characteristics of snow at the surface of antarctica in the past grain size has been reported using various methods the reliability reproducibility and inter comparability of which is not warranted in this paper we present and recommend depending on available logistical support 3 techniques of snow grain sampling and or imaging in the field as well as an ariginal digital image processing method which we have proved to provide reproducible and intercomparable measures of a snow grain size parameter the mean convex radius results from more than 500 samples and 3000 images of snow grains presented which yield a still spatially limited yet unprecendtedly wide picture of near surface snow grain size distribution from field work in antarctica in particular except at sites affected by a very particular meteorology surface grains in the interior of the ice sheet are uniformly small o 1 to 0 2 mm the climate related increase of grain size with depth through metamorphism is as expected not spatially uniform our antarctic snow grain size database will continue to grow as field investigators bring new samples images and measures of snow grain size

composite magnetic fabric in weakly deformed black shales abstract the anisotropy of magnetic susceptibility ams of weakly deformed sediments of the subalpine terres noires french alps is due to phyllosilicates matrix contribution and detrital titanomagnetites ferromagnetic contribution of variable grain size various rock magnetic and anisotropy techniques have been carried out to understand the origin of the scattering of maximum and minimum susceptibility axes we demonstrate the major contribution of the matrix both to susceptibility and ams anisotropy even when mean matrix susceptibility is weak this suggests that phyllosilicates are better oriented within the foliation plane and that intrinsic anisotropy of the detrital titanomagnetite grains is probably weaker than expected also the separation of the two magnetic subfabrics of three selected sites by coupling together low field ams hfa high field ams and aas anisotropy of anhysteretic remanence demonstrates the existence of a competition between two magnetic lineations and an interchange of the intermediate and minimum ams axes as a result of fine titanomagnetite this is the first evidence of the so called intermediate fabric as predicted by theory

radar based subglacial lake classification in antarctica 1 subglacial lakes in east antarctica can be separated into four categories specified by radar reflection properties definite lakes are brighter than their surroundings by at least 2 db relatively bright and both are consistently reflective specular and have a reflection coefficient greater than 10 db absolutely bright dim lakes are relatively bright and specular but not absolutely bright indicating nonsteady ice dynamics fuzzy lakes are both relatively and absolutely bright but not specular and may indicate saturated sediments or swamps indistinct lakes are absolutely bright and specular but no brighter than their surroundings lakes themselves and the different classes of lakes are not arranged randomly throughout antarctica but are clustered around ice divides ice stream onsets and prominent bedrock troughs with each cluster demonstrating a different characteristic lake classification distribution the lake classification algorithm expands on previous studies and demonstrates a novel way to characterize ice water interactions in east antarctica

ice velocity from static gps observations along the transect from zhongshan station to dome a east antarctica dome a the highest point on the antarctic ice sheet at just over 4000 m a s l is located near the centre of east antarctica chinese national antarctic research expeditions have studied ice sheet dynamics and mass balance along a traverse route from zhongshan station to dome a during the austral summers from 1996 97 to 2004 05 nineteen gps sites were occupied on at least two occasions at approximately 50 km intervals the purpose of the surveys was to provide accurate ice dynamics data a dual frequency gps receiver was used and each site was occupied for 1 12 hours gps data were processed using gamit globk software and horizontal accuracies were within 0 1 m repeat gps measurements provided ice velocities the horizontal surface ice velocities increase from the summit of the ice sheet to the coast in the dome a area the velocities are 10m a 1 in the plateau area velocities range from 8 to 24 m a 1 and reach about 98 2 m a 1 at a site lt980 near the coast the flow directions are roughly perpendicular to the ice sheet surface elevation contours primarily toward the lambert glacier basin

snow dunes and glazed surfaces in antarctica new field and remote sensing data as part of the international trans antarctic scientific expedition project the italian antarctic programme undertook two traverses from the terra nova station to talos dome and to dome c along the traverses the party carried out several tasks drilling glaciological and geophysical exploration the difference in spectral response between glazed surfaces and snow makes it simple to identify these areas on visible near infrared satellite images integration of field observation and remotely sensed data allows the description of different mega morphologic features wide glazed surfaces sastrugi glazed surface fields transverse dunes and megadunes topography global positioning system ground penetrating radar and detailed snow surface surveys have been carried out providing new information about the formation and evolution of mega morphologic features the extensive presence up to 30 of glazed surface caused by a long hiatus in accumulation with an accumulation rate of nil or slightly negative has a significant impact on the surface mass balance of a wide area of the interior part of east antarctica the aeolian processes creating these features have important implications for the selection of optimum sites for ice coring because orographic variations of even a few metres per kilometre have a significant impact on the snow accumulation process remote sensing surveys of aeolian macro morphology provide a proven high quality method for detailed mapping of the interior of the ice sheet s prevalent wind direction and could provide a relative indication of wind intensity

the deuterium excess records of epica dome c and dronning maud land ice cores east antarctica new high resolution deuterium excess d data from the two epica ice cores drilled in dronning maud land edml and dome c edc are presented here the main moisture sources for precipitation at edc and edml are located in the indian ocean and atlantic ocean respectively the more southward moisture origin for edml is reflected in a lower present day d value compared to edc the edml and edc isotopic records 18o and d show the main climate features common to the east antarctic plateau and similar millennial scale climate variability during the last glacial period however quite large 18o and d differences are observed during mis5 5 and the glacial inception with a long term behaviour a possibility for this long term difference could be related to uncertainties in past accumulation rate which are used in the glaciological models regional climate anomalies between the two sites during mis5 5 could also be consistent with the observed edml edc 18o and d gradient anomalies simulations performed with the general circulation model echam4 for different time slices provide a temporal temperature isotope slope for the edml region in fair agreement to the modern spatial slope tsite and tsource records are extracted from both ice cores using a modelling approach after corrections for past 18o seawater and elevation changes a limited impact of d on antarctic temperature reconstruction at both edml and edc has been found with a higher impact only at glacial inception the aim antarctic isotope maximum events in both ice cores are visible also after the source correction suggesting that these are real climate features of the glacial period the different shape of the aim events between edc and edml as well as some climate features in the early holocene points to a slightly different climate evolution at regional scale a comparison of our temperature reconstruction profiles with the aerosol fluxes show a strong coupling of the nssca fluxes with antarctic temperatures during glacial period and a tighter coupling of 18o and tsite with ssna flux at edml compared to edc during the glacial period and mis5 5

widespread complex flow in the interior of the antarctic ice sheet it has been suggested that as much as 90 of the discharge from the antarctic ice sheet is drained through a small number of fast moving ice streams and outlet glaciers fed by relatively stable and inactive catchment areas here evidence obtained from balance velocity estimates suggests that each major drainage basin is fed by complex systems of tributaries that penetrate up to 1000 kilometers from the grounding line into the interior of the ice sheet this finding has important consequences for the modeled or estimated dynamic response time of past and present ice sheets to climate forcing

the microstructure of polar ice part i highlights from ice core research polar ice sheets play a fundamental role in earth s climate system by interacting actively and passively with the environment active interactions include the creeping flow of ice and its effects on polar geomorphology global sea level ocean and atmospheric circulation and so on passive interactions are mainly established by the formation of climate records within the ice in form of air bubbles dust particles salt microinclusions and other derivatives of airborne impurities buried by recurrent snowfalls for a half century scientists have been drilling deep ice cores in antarctica and greenland for studying such records which can go back to around a million years experience shows however that the ice sheet flow generally disrupts the stratigraphy of the bottom part of deep ice cores destroying the integrity of the oldest records for all these reasons glaciologists have been studying the microstructure of polar ice cores for decades in order to understand the genesis and fate of ice core climate records as well as to learn more about the physical properties of polar ice aiming at better climate record interpretations and ever more precise models of ice sheet dynamics in this part i we review the main difficulties and advances in deep ice core drilling in antarctica and greenland together with the major contributions of deep ice coring to the research on natural ice microstructures in particular we discuss in detail the microstructural findings from camp century byrd dye 3 grip gisp2 northgrip vostok dome c edml and dome fuji besides commenting also on the earlier results of some pioneering ventures like the jungfraujoch expedition and the norwegian british swedish antarctic expedition among others in the companion part ii of this work faria et al 2014 the review proceeds with a survey of the state of the art understanding of natural ice microstructures and some exciting prospects in this field of research

determining basal ice sheet conditions in the dome c region of east antarctica using satellite radar altimetry and airborne radio echo sounding large subglacial lakes manifest themselves as flat regions on the ice surface ers 1 satellite radar altimetry of the dome c region of east antarctica was analyzed to correlate unusually flat areas on the ice surface with known locations of subglacial lakes identified from airborne radio echo sounding res data the mean length of subglacial lakes which have an expression in the ice sheet surface was 8 3 km whilst those that did not exhibit a surface morphological manifestation had a mean length of 3 3 km thus lakes up to about 4 km in length are unlikely to be detected from satellite radar altimetry of the ice surface given that the spacing of radio echo flight tracks within the spri nsf tud antarctic database is 50 100 km in many areas a number ofsubglacial lakes probably lie undetected beneath the ice sheet res information from two large flat surface regions within dome c and a further flat area located at 80 s 127 e indicates the absence ofsubglacial lakes beneath the ice surface features however these areas are characterised by relatively strong radio echo returns which may indicate the presence of water saturated basal sediments we suggest that 1 blankets of water saturated basal sediments may cause similar surface morphological features to those produced by subglacial lakes and 2 misidentification ofsubglacial lakes from satellite altimeter observations of the ice sheet surface is possible without the support of res information relating to the ice sheet base furthermore our study indicates a lack of sub glacial lake signals from res data over relatively thick regions of east antarctica such as the adventure subglacial trough we conclude that subglacial water produced in such regions may be transported by a basal hydrological system driven by overburden pressure to less thick regions of the ice sheet where subglacial lakes have been identified

anisotropy of magnetic susceptibility of magnetically oriented rock powders to estimate the maximum magnetic anisotropy of the ensemble of magnetic carriers present in a rock we measured the anisotropy of magnetic low field susceptibility ams of magnetically oriented rock powder we studied basaltic rock chaine des puys massif central france and metasediments coffs harbour australia in the basaltic powder psd titanomagnetites show maximum anisotropy of l 1 16 in the metasediments the foliation anisotropy is constant f 1 3 controlled by iron bearing phyllosilicates the linear anisotropy goes up to l 2 in pyrrhotite bearing rocks in contrast magnetite bearing samples show low linear anisotropy l 1 1

random fluctuations of snow accumulation over antarctica and their relation to sea level change short term changes in the volume of ice sheets as analyzed by radar altimetry may not be related to long term climatic change indeed the large relaxation time of an ice sheet induces a low frequency response to random fluctuations of snow accumulation however the time scale of the response is big compared to the average human lifetime and the effect of these random fluctuations on sea level change may be important even if they are not linked to climatic change in this study the relaxation time of an ice sheet is expressed with respect to the ice thickness surface slope and ice velocity these parameters are deduced from the precise topography derived from the geodetic cycle of the ers1 radar altimeter the variance of the induced effect on ice elevation is found to be around 3 m over a 30 year scale and with a maximum of 10 m in wilkes land and in the western part of the west antarctic ice sheet near the coast this effect can mask a climatic signal and thus be critical for altimetric mass balance surveys the estimated changes in antarctica s elevation between the seasat 1978 and ers 1993 epochs could be explained at least partially by such processes in terms of sea level change over the 30 year scale the standard deviation of the induced effect is 8 2 8 cm finally we show that the probability of a present day induced sea level rise of between 0 5 and 1 mm year over a 30 year time scale is estimated at 10 10 with coastal areas accounting for half of this signal

re establishment of ice surface velocity field and snow surface elevation change around dome argus east antarctica in january 2016 static gps measurements were carried out in a 30 30 km2 area centered around kunlun station at dome argus dome a east antarctica to acquire high precision 3 d geodetic coordinates at 49 sites by comparing the coordinates with previous gps measurements in 2008 and 2013 at the same sites we constructed a detailed and long term record of the ice surface velocity field 2008 2016 around dome a during this time span the estimated ice surface velocity ranges from 0 8 0 3 to 28 7 1 6 cm a 1 with a mean of 10 4 0 3 cm a 1 from 2013 to 2016 the surface elevation of most dome a areas exhibits a rising trend and the maximum increase of snow surface elevation is 84 8 cm the mean snow surface elevation change rate at dome a is estimated to be 6 6 0 7 cm a 1 the difference of 1 0 cm a 1 between the snow surface change rate derived from gps and pole height change rate from surface mass balance is suspected to be a result of a combination of firn densification and basal melt under dome a

influence of seep emission on the non symbiont bearing fauna and vagrant species at an active giant pockmark in the gulf of guinea congo angola margin detailed surveying with an rov found that a dense and diverse cold seep community colonises a giant pockmark located at 3200 m depth 8 km north from the deep congo channel several types of assemblages either dominated by mytilidae and vesicomyidae bivalves or siboglinidae polychaetes are distributed on the 800 m diameter active area the site is characterised by a most active central zone in a depression with abundant carbonate concretions and high methane fluxes where high density clusters of mussels and siboglinids dominate in contrast the peripheral zones display large fields of dead and live vesicomyids on soft sediment with a lower mean density and lower methane concentration in seawater the associated megafauna includes alvinocarididae shrimps echinoids holothurians of the family synaptidae several species of gastropods two species of galatheids and zoarcidae and ophidiidae fishes multivariate analyses of video transect data show that the distribution of these major megafauna species at the pockmark scale is influenced by the habitat heterogeneity due to fluid or gas emission occurrence of hydrates substratum variability and by the presence of large symbiont bearing species several assemblages dominated either by mytilids vesicomyids or siboglinids have been sampled for megafauna densities and biomass estimations and stable isotope measurements 13c and 15n of dominant species and food sources the highest estimates of megafauna densities have been obtained in mytilid beds according to their stable isotopes values non symbiont bearing species mainly rely on chemosynthesis originated carbon either as primary consumers of chemoautotrophic microorganisms or at higher trophic level recycling organic matter or relying on bivalve and tubeworm production most of them likely feed on different sources like shrimps but differences according to habitat have been evidenced carbon and nitrogen isotope ratios of galatheids and benthic or benthopelagic fishes captured by trawls at increasing distances from the pockmark provide evidence of the high variability in the proportion of chemosynthesis originated carbon in their diet from 15 to 38 according to the species captured as far as 4 km to the site

assessment of electromagnetic absorption of ice from ice core measurements ice core drillings have been performed in various zones in antarctica and greenland to obtain climatological information study ice properties or analyze air and dust encapsulated in the ice during the quaternary period during these procedures a set of measurements to characterize the ice and to evaluate its physical and chemical properties are usually performed in situ in particular using known temperature and dielectric profiles dep measurements it is possible to evaluate the ice electromagnetic power absorption profile valid at the drilling site in the last decades bedrock characterization through radio echo sounding surveys has been improved by the analysis of the power of radar echoes this way analysis of the electromagnetic properties of bedrock interfaces makes it possible to assess the physical characteristics and to distinguish between wet and dry conditions power variation of the received echoes also depends on ice absorption and on bedrock reflectivity due to specific physical conditions of the ice in this paper the propagation of electromagnetic waves through the ice sheet is examined and in particular a new method for establishing the electromagnetic absorption profile for ice from core drilling measurements is proposed and discussed variation in the ice absorption is deduced starting from the analysis of ice core data from the european project for ice coring in antarctica epica at the concordia station antarctica and from the greenland ice core project grip site greenland this direct method of measurement is proposed with the aim of defining common characteristics of the ice absorption rate that are valid both in antarctica and in greenland