warming of global abyssal and deep southern ocean waters between the 1990s and 2000s contributions to global heat and sea level rise budgets abyssalglobalanddeepsouthern oceantemperature trendsarequantifiedbetweenthe1990sand2000sto assesstheroleofrecentwarmingoftheseregionsin globalheatandsealevelbudgets theauthors1 compute warming rates with uncertainties along 28 full depth high quality hydrographic sections that have been occupied two or more times between 1980 and 2010 2 divide the global ocean into 32 basins defined by the topography and climatological ocean bottom temperatures and then 3 estimate temperature trends in the 24 sampled basins the three southernmost basins show a strong statistically significant abyssal warming trend with that warming signal weakening to the north in the central pacific western atlantic and eastern indian oceans eastern atlantic and western indian ocean basins show statistically insignificant abyssal cooling trends excepting the arctic ocean and nordic seas the rate of abyssal below 4000 m global ocean heat content change in the 1990s and 2000s is equivalent to a heat flux of 0 027 60 009 w m 22 applied over the entire surface of the earth deep 1000 4000 m warming south of the subantarctic front of the antarctic circumpolar current adds 0 068 60 062 w m 22 the abyssal warming produces a 0 053 60 017 mm yr 21 increase in global average sea level and the deep warming south of the subantarctic front adds another 0 093 60 081 mm yr 21 thus warmingin theseregions ventilatedprimarilyby antarcticbottomwater accounts for a statistically significant fraction of the present global energy and sea level budgets

twenty first century warming of a large antarctic ice shelf cavity by a redirected coastal current the redirection of warm water under the filchner ronne ice shelf during the second half of this century could cause the ice shelf base to melt at a rate 20 times higher than at present warm ocean currents are known to erode ice shelves from below but changes in currents can be forced by many different mechanisms leading to uncertain outcomes this study highlights the vulnerability to climate change of a small antarctic coastal region which has potentially severe consequences for the mass balance of a large antarctic ice shelf hellmer et al use climate modelling to show that the projected loss of sea ice in the weddell sea east of the antarctic peninsula leads to an increase in wind stress which in turn accelerates a warm ocean current far underneath the vast filchner ronne ice shelf the authors predict that the increased warmth could increase melt by a factor of 20 with possible consequences for ice stream dynamics in the east antarctic ice sheet the antarctic ice sheet loses mass at its fringes bordering the southern ocean at this boundary warm circumpolar water can override the continental slope front reaching the grounding line1 2 through submarine glacial troughs and causing high rates of melting at the deep ice shelf bases3 4 the interplay between ocean currents and continental bathymetry is therefore likely to influence future rates of ice mass loss here we show that a redirection of the coastal current into the filchner trough and underneath the filchner ronne ice shelf during the second half of the twenty first century would lead to increased movement of warm waters into the deep southern ice shelf cavity water temperatures in the cavity would increase by more than 2 degrees celsius and boost average basal melting from 0 2 metres or 82 billion tonnes per year to almost 4 metres or 1 600 billion tonnes per year our results which are based on the output of a coupled ice ocean model forced by a range of atmospheric outputs from the hadcm35 climate model suggest that the changes would be caused primarily by an increase in ocean surface stress in the southeastern weddell sea due to thinning of the formerly consolidated sea ice cover the projected ice loss at the base of the filchner ronne ice shelf represents 80 per cent of the present antarctic surface mass balance6 thus the quantification of basal mass loss under changing climate conditions is important for projections regarding the dynamics of antarctic ice streams and ice shelves and global sea level rise

impact of atmospheric forcing on antarctic continental shelf water masses the antarctic continental shelf seas feature a bimodal distribution of water mass temperature with the amundsen and bellingshausen seas flooded by circumpolar deep water that is several degrees celsius warmer than the cold shelf waters prevalent in the weddell and ross seas this bimodal distribution could be caused by differences in atmospheric forcing ocean dynamics ocean and ice feedbacks or some combination of these factors in this study a highly simplified coupled sea ice mixed layer model is developed to investigate the physical processes controlling this situation under regional atmospheric forcings and parameter choices the 10 yr simulations demonstrate a complete destratification of the weddell sea water column in winter forming cold relatively saline shelf waters while the amundsen sea winter mixed layer remains shallower allowing a layer of deep warm water to persist applying the weddell atmospheric forcing to the amundsen sea model destratifies the water column after two years and applying the amundsen forcing to the weddell sea model results in a shallower steady state winter mixed layer that no longer destratifies the water column this suggests that the regional difference in atmospheric forcings alone is sufficient to account for the bimodal distribution in antarctic shelf sea temperatures the model prediction of mixed layer depth is most sensitive to the air temperature forcing but a switch in all forcings is required to prevent destratification of the weddell sea water column

decadal warming of the coldest antarctic bottom water flow through the vema channel a decadal warming trend of antarctic bottom water flowing through the vema channel is reanalyzed our data base consists of 94 high precision full depth stations from 19 visits to the vema sill plus twelve stopovers at two additional key locations originally a long term temperature increase in the near bottom jet was noted from 1992 onward after a period of rather constant abyssal temperatures since 1972 from today s perspective the apparent stagnant temperature level until 1991 can be interpreted as a period of feeble rising in comparison with a perspicuous warming trend of 2 8 mk yr 1 in the following 15 years however the clearly manifested temperature rise is superimposed with fluctuations for the first time the available time series appears long enough to indicate an associated slight freshening of the bottom water an attempt is made to trace the observed variability back to its source region in the weddell sea

magnetic fabric and structural setting of plio pleistocene clayey units in an extensional regime the tyrrhenian margin of central italy abstract results are presented of structural analysis and anisotropy of magnetic susceptibility ams analysis of plio pleistocene clayey units from the extensional tyrrhenian margin of central italy data have been collected in different tectonic settings mainly strike slip and transverse extensional structures at the sites with major evidence of plio pleistocene tectonics there appears a close relationship between magnetic lineations and stretching directions stretching processes that were able to modify the original magnetic fabric pre dated significant normal fault related tilting and therefore were active at the very first stage of extensional deformation the relationships between ams and structural trends in an extensional regime seem distinctively different from those reported in compressional regimes this kind of analysis may be useful in the geodynamic interpretation of ambiguous structures

development of planar and linear fabrics in dauphinois shales and slates french alps studied by magnetic anisotropy and its mineralogical control the progressive development of planar and linear fabrics due to alpine deformation in dogger calcareous shales has been studied in the dauphinois zone of the french alps using measurements of the anisotropy of magnetic susceptibility the axes and shapes of magnetic ellipsoids and petrofabrics show good qualitative correlation through a series of different fabric types from a sedimentary to a highly deformed one together with various petrological techniques magnetization measurements in a variable field up to 5 t and under variable temperature with a cryogenic magnetometer were used to achieve a complete analysis of the magnetic mineralogy with its dia para and ferromagnetic s l contributions the effects on the anisotropy of the complex mineralogy and various geological processes including pressure solution metamorphism and weathering are discussed

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

three dimensional strength reduction finite element analysis of slopes geometric effects the vast majority of slopes both natural and constructed exhibit a complex geometric configuration and three di mensional 3d state whereas slopes satisfying the assumption of plane strain infinite length are seldom encountered ex isting research mainly emphasizes the 3d dimensions and boundary effect in slope stability analysis however the effect of complex geometric ground configuration on 3d slope stability is rarely reported in this paper an elastoplastic finite element method using strength reduction techniques is used to analyze the stability of special 3d geometric slopes a typical 3d slope underlain by a weak layer with groundwater is described to validate the numerical modeling safety factor values and critical slip surface for the 3d slope furthermore a series of special 3d slopes with various geometric configurations are analyzed numerically and the effects of turning corners slope gradient turning arcs and convex and concave shaped sur face geometry on the stability and failure characteristics of slopes under various boundary conditions are discussed in detail

subtle stretching lineation revealed by magnetic fabric of callovian oxfordian black shales french alps abstract the anisotropy of magnetic susceptibility ams of callovian oxfordian black shales from the subalpine massifs of the french alps has been measured the magnetic susceptibility of these formations originates from ferromagnetic titanomagnetite and paramagnetic phyllosilicates illite and chlorite although the magnetic fabric is complicated by the interaction of planar and linear structural elements and the presence of variable amounts of minerals two types of lineation are preserved a stretching lineation which exhibits counterclockwise rotation as a result of deformation from south to north and an intersection lineation parallel to the fold axis this set of new structural data together with semiquantitative analysis of ams is in agreement with the geodynamic evolution of the western alps

antarctic bottom water warming and freshening contributions to sea level rise ocean freshwater budgets and global heat gain abstractfreshening and warming of antarctic bottom water aabw between the 1980s and 2000s are quantified assessing the relative contributions of water mass changes and isotherm heave the analysis uses highly accurate full depth ship based conductivity temperature depth measurements taken along repeated oceanographic sections around the southern ocean fresher varieties of aabw are present within the south pacific and south indian oceans in the 2000s compared to the 1990s with the strongest freshening in the newest waters adjacent to the antarctic continental slope and rise indicating a recent shift in the salinity of aabw produced in this region bottom waters in the weddell sea exhibit significantly less water mass freshening than those in the other two southern basins however a decrease in the volume of the coldest deepest waters is observed throughout the entire southern ocean this isotherm heave causes a salinification and warming on isobaths from the bottom up to the shallow potential tem

large multidecadal salinity trends near the pacific antarctic continental margin abstract ocean temperature and salinity measurements on and near the antarctic continental shelf in the southwest pacific sector are evaluated for evidence of temporal change shelf water in the southwest ross sea has declined in salinity by 0 03 decade 1 from 1958 to 2008 while its temperatures have increased in proportion to the influence of salinity on the sea surface freezing point modified deep water intrusions that reach the central ross ice shelf have freshened at a similar rate and cooled by 0 5 c since the late 1970s salinity has decreased by 0 08 decade 1 in the westward coastal and slope front currents consistent with increased melting of continental ice upstream in the amundsen sea overturning of those near surface waters during winter sea ice formation and mixing across the slope front is sufficient to account for the 5 decade shelf water salinity change a strong correlation between the freshening and change in the southern annular mode index suggests a link with the large scale atmosp

a reconciled estimate of ice sheet mass balance we combined an ensemble of satellite altimetry interferometry and gravimetry data sets using common geographical regions time intervals and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of earth s polar ice sheets we find that there is good agreement between different satellite methods especially in greenland and west antarctica and that combining satellite data sets leads to greater certainty between 1992 and 2011 the ice sheets of greenland east antarctica west antarctica and the antarctic peninsula changed in mass by 142 49 14 43 65 26 and 20 14 gigatonnes year 1 respectively since 1992 the polar ice sheets have contributed on average 0 59 0 20 millimeter year 1 to the rate of global sea level rise

the influence of deformation mechanisms on magnetic fabrics in weakly deformed rocks abstract magnetic fabrics of weakly deformed rocks are not simply correlated with the principal finite strain directions depositional magnetic fabrics persist at 30 shortening where the rocks are deformed by particulate flow grain boundary sliding rocks with a spaced stylolitic cleavage believed to be formed by pressure solution and shortened by 20 50 have maximum susceptibility parallel to the intersection of cleavage and bedding this type of magnetic fabric is attributed to the interference of a depositional magnetic fabric between cleavage surfaces with a tectonic magnetic fabric in the cleavage surfaces

the magnetic fabric relationship between sedimentary and basement nappes in the high tatra mountains n slovakia abstract in the high tatra mountains n slovakia the magnetic fabrics are deformational in origin in sedimentary rocks of the kri na nappe in sedimentary rocks covering the underlying crystalline complex and in granitoids and metamorphic rocks of this complex the patterns of the principal susceptibilities are similar in all these units their most important feature is a girdle in magnetic foliation poles oriented nnw sse to n s in sedimentary formations the magnetic fabric pattern is compatible with that predicted by mathematical modelling to develop during a complex deformation comprising lateral shortening and simple shear which is characteristic of nappe deformation consequently the magnetic fabric in the high tatra mountains probably resulted from deformation associated with the formation and movement of the nappes during which not only the sedimentary strata but also the crystalline complex were thrust over the north european platform

slaty cleavage development and magnetic anisotropy fabrics the shale to slate transition preserved in the ordovician martinsburg formation at the lehigh water gap pennsylvania provides an opportunity to study the relationship between magnetic anisotropy fabrics and the development of slaty cleavage our previous work has indicated that anisotropy of magnetic susceptibility ams does not record changes in finite strain associated with cleavage development in these rocks but instead measures the degree of dissolution and new growth of ehlorite additional ams data presented in this paper lend further support to this conclusion conversely anhysteretie remanent magnetization anisotropy arma which is not affected by paramagnetie ehlorite accurately reflects the strain induced rock fabrics associated with cleavage formation arma results show that magnetite dimensional orientations vary from bedding parallel in shale samples to cleavage parallel in samples with well developed slaty cleavage samples with weak and pencil cleavage display scattered arma orientations which lie in between bedding and cleavage these intermediate orientations may be due to either passive rotation of magnetite from bedding parallel to cleavage parallel or re crystallization of magnetite if rotation occurred grain rotation was highly heterogeneous in the samples with incipient cleavage the intermediate arma orientations may also reflect the varying contribution of two magnetite preferred orientations a depositional orientation parallel to bedding and a new growth orientation parallel to cleavage

sensitivity of the ocean s deep overturning circulation to easterly antarctic winds we investigate the sensitivity of the deep meridional overturning circulation moc in the southern ocean to changes in the easterly wind stress over the antarctic continental slope the deep moc is driven by export of dense antarctic bottom water from the antarctic continental shelf and exerts a strong influence on climate by ventilating the deep ocean with oxygen and storing carbon dioxide the possibility that inter climatic modifications of the deep overturning may have been driven by changes in the atmospheric circulation has motivated the recent interest in evaluating the sensitivity of the southern ocean moc to modifications of the mid latitude westerlies using a high resolution eddy resolving model of a sector of the southern ocean we show that the deep cell of the moc is highly sensitive to the strength of the polar easterlies and relatively insensitive to the strength of the mid latitude westerlies our results highlight that determining the deep ocean ventilation in past and future climates demands an accurate evaluation of the concurrent surface wind stress throughout the southern ocean

stability analysis of earthquake induced rock slope based on back analysis of shear strength parameters of rock mass abstract high steep rock slopes are much more likely to collapse and form weir body due to earthquake converting the weir body to hydraulic engineering is a good way to deal with natural disasters however it is difficult to evaluate the stability of earthquake induced rock slope due to the lack of shear strength parameters of rock mass based on three dimension nonlinear finite elements deformation reinforcement theory was adopted in which plastic complementary is used to measure the global stability of slope and unbalanced forces is utilized to identify the damage region the shear strength parameters has been determined through back analysis based on stability and failure status before and after earthquake and monitoring data after earthquake then the stability evaluation under static conditions dynamic conditions and rainfall conditions has been carried out respectively the results show that failure mode of the slope under seismic load is consistent with the actual situation when the lowest material parameters are used the major failure mode of the slope is sliding along the fault f5 and local collapse of the hanging body at the top of the slope under dynamic or rainfall load the local stability can be improved effectively by excavating and taking bolt anchorages on the top of the slope

fluid control of localized mineral domains in limestone pressure solution structures grain to grain and stylolitic solution structures in two central appalachian siluro devonian limestone macroscale folds contain one of four distinct mineral assemblages that are characterized by the dominant iron phase mineral present 1 chloritegillitegpyritegcalciteg quartzgtio2ggoethite 2 chloritegillitegpyrite altered to iron oxide hydroxidegcalcite gquartzgtio2 3 chloritegilliteg magnetitegcalcitegquartz and 4 chloritegilliteggoethitegcalcitegquartzgtio2 optical reflectance microscopy and sem eds was used to characterize the mineralogy and mineral morphology of these structures geochemical modeling was used to constrain the conditions of formation and preservation the primary control on solution structure mineral assemblage was the redox conditions present in the solution structures during burial and deformation the redox conditions on the microscale may have been controlled by the local fluid chemistry and the presence absence of hydrocarbons and organic acids within the formation fluids and the influx of externally derived fluids by fracture formation during the folding process the wide variation in mineralogy of the solution structures shows that they were chemical factories where a variety of chemical reactions took place during rock dissolution in particular the formation of authigenic magnetite in solution structures has significant implications for paleomagnetic applications and use of anisotropy of anhysteretic remanent magnetization and anisotropy of magnetic susceptibility fabrics q 2005 elsevier ltd all rights reserved

rapid freshening of antarctic bottom water formed in the indian and pacific oceans 1 repeat hydrographic sections occupied in 1995 and 2005 reveal a rapid decline in the salinity and density of antarctic bottom water throughout the australian antarctic basin the basin wide shift of the deep potential temperature salinity s relationship reflects freshening of both the indian and pacific sources of antarctic bottom water the s curves diverge for waters cooler than 0 1 c corresponding to a layer up to 1000 m thick over the antarctic continental slope and rise changes over the last decade are in the same direction but more rapid than those observed between the late 1960s and the 1990s when combined with recent observations of similar freshening of north atlantic deep water these results demonstrate that dense water formed in both hemispheres is freshening in response to changes in the high latitude freshwater balance and rapidly transmitting the signature of changes in surface climate into the deep ocean

a statistics based discrete element modeling method coupled with the strength reduction method for the stability analysis of jointed rock slopes abstract the stability of jointed rock slopes can be effectively analyzed using the discrete element method dem however the criteria for terminating the dem iterative calculation process and determining the factor of safety fos are not well defined in this paper a displacement statistics based discrete element modeling method dsdm is proposed to analyze the stability of jointed rock slopes by coupling with the shear strength reduction method srm in the presented dsdm two important criteria are defined 1 a statistics based criterion for terminating the iterative calculation process of the dem modeling in the stability analysis of jointed rock slopes and 2 a statistics based criterion for determining the fos of a jointed rock slope when coupling dem and srm the novelty of the proposed dsdm is that statistical information of the global displacements around the potential slip surface of the jointed slope rather than the local displacements of several characteristic points are utilized to define the criteria for terminating the dem iterative calculation process and determining the fos to verify the effectiveness of the proposed dsdm the fos of a simplified jointed rock slope is first calculated using the proposed dsdm and then compared with the fos obtained using the finite difference method fdm moreover the proposed dsdm is applied to analyze the stability of a real high steep bedding rock slope the numerical simulation results for the real rock slope are consistent with the in situ observations the proposed dsdm is thus capable of effectively analyzing the stability of jointed slopes with potential slip surfaces

tertiary compressional overprint on aptian albian extensional magnetic fabrics north pyrenean zone abstract the mauleon basin constitutes part of the north pyrenean mesozoic extensional basins inverted during pyrenean late cretaceous tertiary orogeny a structural and magnetic fabric study of the aptian albian black marls of the mauleon basin north pyrenean zone provides new data indicating that when there is an intense deformation associated with the compressional stage formation of a pervasive foliation the magnetic lineation is strongly controlled by the latter tectonic deformation recorded in the basin however some areas of the sedimentary basin can still preserve the primary extensional event depending on its position with respect to basin margin faults and heterogeneous deformation areas structural and ams data define a fabric transition from extensional fabrics indicating an approximate n s extension in the central inner domain of the basin where compressional deformation was moderate to ne sw compressional fabrics in boundary domains close to the inverted faults where compressional deformation was more important k max becomes nearly parallel to the main pyrenean direction nw se consequently fabrics in the mauleon basin can be interpreted as the result of the overprint of compressional deformation onto a primary extensional fabric which in turn endures in the central domain of the basin in spite of its complicated pattern ams is revealed useful when considering the long term history of sedimentary basins undergoing several deformation events

inversion tectonics and magnetic fabrics in mesozoic basins of the western tethys a review abstract positive tectonic inversion of sedimentary basins has been recognized as one of the primary mechanisms of mountain building and intraplate deformation reconstructing the tectonic history of basins is relatively easy for the inversion stage but becomes more difficult for the basinal stage especially when strong deformation involving cleavage development is associated with the subsequent compressional tectonics since tectonic markers for the extensional episodes are not commonly well developed anisotropy of magnetic susceptibility ams has provided recently a tool for analyzing early stages in the evolution of sedimentary basins even in the absence of other outcrop scale mesostructures here we expose and discuss the applicability of magnetic fabrics by means of ams to different types of intra plate sedimentary basins in the western tethys region formed under extensional or transtensional regimes and which underwent different inversion styles total or partial inversion with or without cleavage development forming part of compressional thrust sheets etc owing to specific particular p t conditions and structural controls factors such as lithology magnetic mineralogy position within the sedimentary pile and deformation intensity are key to interpret the obtained magnetic fabrics in terms of tectonic evolution a basin classification is proposed according to inversion styles and magnetic fabrics where inversion did not involve cleavage development magnetic lineation is parallel to the stretching direction corresponding to the extensional stage the transition between non cleaved to inversion related cleaved units is marked by the switch of magnetic lineations from parallel to extension to parallel to the intersection lineation between cleavage and bedding these relationships are enhanced when extension and compression are roughly coaxial then favoring the clustering of axes of the magnetic ellipsoid even when extreme inversion occurs and the early extensional fabric is obliterated magnetic fabrics provide information about the interaction between preferred deformation directions associated with the main stages in basin evolution

magnetic anisotropy of some phyllosilicates magnetic susceptibility anisotropy of susceptibility and hysteresis of single microcrystals of chlorite biotite phlogopite muscovite zinnwaldite and fuchsite were measured in low and high magnetic fields with an alternating gradient force magnetometer micromag their properties are sufficient to account for the low field susceptibility ams of most micaceous rocks nearly all samples show some ferromagnetic contribution at low fields due to inclusions of pseudosingle domain and multidomain magnetite the paramagnetic contribution isolated at high fields usually exceeds the ferromagnetic contribution the paramagnetic susceptibility is intrinsic to the silicate lattice and agrees with values predicted from chemical composition within the limits of error the minimum susceptibility is nearly parallel to c another axis is parallel to b and the third susceptibility usually the maximum is close to a the paramagnetic susceptibility has a disk shaped magnitude ellipsoid with strong anisotropy p 2 the ferromagnetic contributions at low fields have more variably shaped ellipsoids with greater eccentricity p 5 the silicate lattice does not constrain their orientation our technique cannot determine the principal axes of the ferromagnetic component however its principal values usually correspond with the paramagnetic principal susceptibilities in order of magnitude thus the combined paramagnetic ferromagnetic anisotropy recognised in routine studies of ams should faithfully represent the petrofabric of most micaceous rocks nevertheless nearly 10 of our samples have incompatible anisotropy ellipsoids for the silicate host and magnetite inclusions these yield a net inverse ams that does not correctly represent the orientation of the silicate lattice therefore some caution is necessary in petrofabric ams studies of micaceous rocks

trends in the deep southern ocean 1958 2010 implications for antarctic bottom water properties and volume export 1 regional formation of deep and bottom water masses around the antarctic continental shelf is one of the most important processes contributing to variability of the global meridional overturning circulation deep cell southern ocean hydrographic data collected during the years 1958 2010 indicate that dense shelf waters cooled and freshened during that period in the surrounding open ocean antarctic bottom water aabw warmed with no evidence of salinity change as a result of source water property changes aabw exported from the southern ocean to the deep world ocean became lighter over the period analyzed the average rate of density change within the areas that experienced statistically significant change was 0 0019 kg m 3 yr 1 for the last 20 years of the analysis a negative aabw volume anomaly relative to the half century average 1958 2010 was indicated possibly due to production of a lighter aabw variety or to changes in formation rates over the entire five decades the upper isopycnal of the aabw layer deepened at a rate of 8 1 m yr 1 changes in fundamental hydrographic properties such as these can have important implications for long term global ocean circulation and climate

mimoc a global monthly isopycnal upper ocean climatology with mixed layers a monthly isopycnal mixed layer ocean climatology mimoc global from 0 to 1950 dbar is compared with other monthly ocean climatologies all available quality controlled profiles of temperature t and salinity s versus pressure p collected by conductivity temperature depth ctd instruments from the argo program ice tethered profilers and archived in the world ocean database are used mimoc provides maps of mixed layer properties conservative temperature absolute salinity sa and maximum p as well as maps of interior ocean properties sa and p to 1950 dbar on isopycnal surfaces a third product merges the two onto a pressure grid spanning the upper 1950 dbar adding more familiar potential temperature and practical salinity s maps all maps are at monthly 0 5 0 5 resolution spanning from 80 s to 90 n objective mapping routines used and described here incorporate an isobath following component using a fast marching algorithm as well as front sharpening components in both the mixed layer and on interior isopycnals recent data are emphasized in the mapping the goal is to compute a climatology that looks as much as possible like synoptic surveys sampled circa 2007 2011 during all phases of the seasonal cycle minimizing transient eddy and wave signatures mimoc preserves a surface mixed layer minimizes both diapycnal and isopycnal smoothing of s as well as preserves density structure in the vertical pycnoclines and pycnostads and the horizontal fronts and their associated currents it is statically stable and resolves water mass features fronts and currents with a high level of detail and fidelity

exhumation of the sierra de cameros iberian range spain constraints from low temperature thermochronology we present new fission track and u th he data from apatite and zircon in order to reconstruct the exhumation of the sierra de cameros in the northwestern part of iberian range spain zircon fission track ages from samples from the depocentre of the basin were reset during the metamorphic peak at approximately 100 ma detrital apatites from the uppermost sediments retain fission track age information that is older than the sediment deposition age indicating that these rocks have not exceeded 110 c apatites from deeper in the stratigraphic sequence of the central part of the basin have fission track ages of around 40 ma significantly younger than the stratigraphic age recording the time of cooling after peak metamorphic conditions apatite u th he ages in samples from these sediments are 31 40 ma and record the last period of cooling during alpine compression the modelled thermal history derived from the uppermost sediments indicates that the thermal pulse associated with peak metamorphism was rapid and that the region has cooled continuously to the present the estimated palaeogeothermal gradient is around 86 c km 1 and supports a tectonic model with a thick sedimentary fill c 8 km and explains the origin of the low grade metamorphism observed in the oldest sediments

the anisotropy of magnetic susceptibility ams in low grade cleaved pelitic rocks influence of cleavage bedding angle and type and relative orientation of magnetic carriers

rapid bottom melting widespread near antarctic ice sheet grounding lines as continental ice from antarctica reaches the grounding line and begins to float its underside melts into the ocean results obtained with satellite radar interferometry reveal that bottom melt rates experienced by large outlet glaciers near their grounding lines are far higher than generally assumed the melting rate is positively correlated with thermal forcing increasing by 1 meter per year for each 0 1 c rise in ocean temperature where deep water has direct access to grounding lines glaciers and ice shelves are vulnerable to ongoing increases in ocean temperature

effect of lithostatic pressure and tectonic deformation on the magnetic fabric anisotropy of magnetic susceptibility in low grade metamorphic rocks the role of lithostatic pressure and strain in low grade metamorphic cover rocks is analyzed through the anisotropy of magnetic susceptibility ams of jurassic and cretaceous siltstones and limestones from the cameros basin north spain for rocks initially characterized by precleavage magnetic fabric the main change in the magnetic fabric produced by the increase of lithostatic pressure is the increment in the degree of anisotropy pj in rocks affected by syncleavage deformation the magnetic fabric depends on the mechanism of internal deformation involved in fabric development in siltstones where cleavage is correlated with synkinematic recrystallization of phyllosilicates and rigid body rotation of grains the magnetic fabric is coherent with the internal deformation determined by strain analysis on deformed nodules on the contrary in limestones we observe a complete reorganization of the magnetic fabric probably due to the discontinuous character of the cleavage formation mechanism detailed analysis of the parameter angle between the bedding pole and the minimum susceptibility axis parallel to the cleavage pole indicates that for rocks characterized by syncleavage magnetic fabric the different variation pattern of tj and pj parameters is closely related to the deformation mechanisms responsible for the fabric development

widespread rapid grounding line retreat of pine island thwaites smith and kohler glaciers west antarctica from 1992 to 2011 we measure the grounding line retreat of glaciers draining the amundsen sea sector of west antarctica using earth remote sensing ers 1 2 satellite radar interferometry from 1992 to 2011 pine island glacier retreated 31 km at its center with most retreat in 2005 2009 when the glacier ungrounded from its ice plain thwaites glacier retreated 14 km along its fast flow core and 1 to 9 km along the sides haynes glacier retreated 10 km along its flanks smith kohler glaciers retreated the most 35 km along its ice plain and its ice shelf pinning points are vanishing these rapid retreats proceed along regions of retrograde bed elevation mapped at a high spatial resolution using a mass conservation technique that removes residual ambiguities from prior mappings upstream of the 2011 grounding line positions we find no major bed obstacle that would prevent the glaciers from further retreat and draw down the entire basin 2014 american geophysical union all rights reserved

glacier surge after ice shelf collapse the possibility that the west antarctic ice sheet will collapse as a consequence of ice shelf disintegration has been debated for many years this matter is of concern because such an event would imply a sudden increase in sea level evidence is presented here showing drastic dynamic perturbations on former tributary glaciers that fed sections of the larsen ice shelf on the antarctic peninsula before its collapse in 1995 satellite images and airborne surveys allowed unambiguous identification of active surging phases of boydell sjogren edgeworth bombardier and drygalski glaciers this discovery calls for a reconsideration of former hypotheses about the stabilizing role of ice shelves

southern ocean bottom water characteristics in cmip5 models 1 southern ocean deep water properties and formation processes in climate models are indicative of their capability to simulate future climate heat and carbon uptake and sea level rise southern ocean temperature and density averaged over 1986 2005 from 15 cmip5 coupled model intercomparison project phase 5 climate models are compared with an observed climatology focusing on bottom water bottom properties are reasonably accurate for half the models ten models create dense water on the antarctic shelf but it mixes with lighter water and is not exported as bottom water as in reality instead most models create deep water by open ocean deep convection a process occurring rarely in reality models with extensive deep convection are those with strong seasonality in sea ice optimum bottom properties occur in models with deep convection in the weddell and ross gyres bottom water formation processes are poorly represented in ocean models and are a key challenge for improving climate predictions

strain partitioning of deformation mechanisms in limestones examining the relationship of strain and anisotropy of magnetic susceptibility ams abstract in order to investigate the relationship between rock strain and anisotropy of magnetic susceptibility ams strain partitioning and ams analysis was conducted at 35 sites from two stratigraphically adjacent paleozoic limestone units in the patterson creek and wills mountain anticlines in the central appalachian orogen of west virginia in addition anisotropy of anhysteretic remanent magnetization aarm was conducted on selected samples to examine the role of preferentially oriented magnetite on the ams fabric strain is partitioned into bed normal shortening due to compaction solution strain 35 0 shortening bed parallel shortening due to tectonic solution strain 13 3 shortening calcite twinning strain 5 8 shortening and grain boundary sliding 26 7 shortening the ams fabrics in the rocks were found to be a result of a complex interaction between rock lithology deformation mechanisms and strain magnitude although all the rocks have experienced the same deformation conditions six different ams fabrics are exhibited each of the different ams fabrics is a composite fabric resulting from the overprinting of three components 1 an inherent primary depositional ams fabric that is attributed to preferentially oriented phyllosilicates in the rock matrix 2 a diagenetic and or compaction ams fabric formed during burial that is due to preferentially oriented phyllosilicates in solution structures and in the rock matrix and 3 a tectonic ams fabric that was imparted on the rocks by layer parallel shortening deformation prior to folding and is also attributed to preferentially oriented phyllosilicates in solution structures and in the rock matrix as well as twinning of ferroan calcite

sensitivity of circumpolar deep water transport and ice shelf basal melt along the west antarctic peninsula to changes in the winds circumpolardeepwater cdw can be found near the continental shelfbreak around most of antarctica advection of this relatively warm water up to 28c across the continental shelf to the base of floating ice shelves is thought to be a critical source of heat for basal melting in some locations a high resolution 4 km regional ocean sea ice ice shelf model of the west antarctic peninsula wap coastal ocean was used to examine the effects of changes in the winds on across shelf cdw transport and ice shelf basal melt increases and decreases in the strength of the wind fields were simulated by scaling the present day winds by a constant factor additional simulations considered effects of increased antarctic circumpolar current acc transport increased wind strength and acc transport increased the amount of cdw transported onto the wap continental shelf but did not necessarily increase cdw flux underneath the nearby ice shelves the basal melt underneath some of the deeper ice shelves actually decreased with increased wind strength increased mixing over the wap shelf due to stronger winds removed more heat from the deeper shelf waters than the additional heat gained from increased cdw volume transport the simulation results suggest that the effect on the wap ice shelves of the projected strengthening of the polar westerlies is not a simple matter of increased winds causing increased or decreased basal melt a simple budget calculation indicated that iron associated with increased vertical mixing of cdw could significantly affect biological productivity of this region

marine ice sheet collapse potentially under way for the thwaites glacier basin west antarctica resting atop a deep marine basin the west antarctic ice sheet has long been considered prone to instability using a numerical model we investigated the sensitivity of thwaites glacier to ocean melt and whether its unstable retreat is already under way our model reproduces observed losses when forced with ocean melt comparable to estimates simulated losses are moderate 1 mm per year of sea level rise collapse in the different simulations within the range of 200 to 900 years

multidecadal warming of antarctic waters decadal trends in the properties of seawater adjacent to antarctica are poorly known and the mechanisms responsible for such changes are uncertain antarctic ice sheet mass loss is largely driven by ice shelf basal melt which is influenced by ocean ice interactions and has been correlated with antarctic continental shelf bottom water asbw temperature we document the spatial distribution of long term large scale trends in temperature salinity and core depth over the antarctic continental shelf and slope warming at the seabed in the bellingshausen and amundsen seas is linked to increased heat content and to a shoaling of the mid depth temperature maximum over the continental slope allowing warmer saltier water greater access to the shelf in recent years regions of asbw warming are those exhibiting increased ice shelf melt

antarctic ice sheet loss driven by basal melting of ice shelves accurate prediction of global sea level rise requires that we understand the cause of recent widespread and intensifying glacier acceleration along antarctic ice sheet coastal margins atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves potentially limiting their ability to buttress the flow of grounded tributary glaciers indeed recent ice shelf collapse led to retreat and acceleration of several glaciers on the antarctic peninsula but the extent and magnitude of ice shelf thickness change the underlying causes of such change and its link to glacier flow rate are so poorly understood that its future impact on the ice sheets cannot yet be predicted here we use satellite laser altimetry and modelling of the surface firn layer to reveal the circum antarctic pattern of ice shelf thinning through increased basal melt we deduce that this increased melt is the primary control of antarctic ice sheet loss through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow the highest thinning rates occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of antarctic ice shelves through ocean upwelling in the amundsen and bellingshausen seas and atmospheric warming on the antarctic peninsula this implies that climate forcing through changing winds influences antarctic ice sheet mass balance and hence global sea level on annual to decadal timescales

composite magnetic anisotropy fabrics experiments numerical models and implications for the quantification of rock fabrics housen b a richter c and van der pluijm b a 1993 composite magnetic anisotropy fabrics experiments numerical models and implications for the quantification of rock fabrics tectonophysics 220 1 12 magnetic fabrics from rocks with multiple mineral preferred orientations may have anisotropy ellipsoids whose shape and orientation arise from the addition of two or more component fabrics our numerical models and experiments demonstrate that such composite magnetic fabrics do not directly reflect the shapes and or orientations of the individual mineral fabrics and we provide criteria for the recognition and interpretation of composite fabrics in natural rocks these criteria include 1 the orientation of the maximum susceptibility axis is located at the intersection of two planar fabrics and 2 the shape of the susceptibility ellipsoid changes from oblate to prolate and the degree of anisotropy decreases as the relative intensity of two planar component fabrics becomes equal and as the angle between the planar fabrics increases composite magnetic fabrics are observed in the shales and slates of the martinsburg formation lehigh gap pennsylvania modeling of the ams anisotropy of magnetic susceptibility and arma anhysteretic remanent magnetization anisotropy behavior constrains the relative degree of anisotropy of the bedding parallel and cleavage parallel fabrics in particular arma model results allow a good estimate of magnetite fabric strength we conclude that in the presence of composite magnetic fabrics quantitative measures of finite strain in deformed rocks are limited by the ability to accurately determine the degree of anisotropy and relative susceptibility of each component fabric such determinations require knowledge of the mineral s that are responsible for the measured magnetic fabric and their behavior during deformation

rapid subsurface warming and circulation changes of antarctic coastal waters by poleward shifting winds the southern hemisphere westerly winds have been strengthening and shifting poleward since the 1950s this wind trend is projected to persist under continued anthropogenic forcing but the impact of the changing winds on antarctic coastal heat distribution remains poorly understood here we show that a poleward wind shift at the latitudes of the antarctic peninsula can produce an intense warming of subsurface coastal waters that exceeds 2 c at 200 700 m depth the model simulated warming results from a rapid advective heat flux induced by weakened near shore ekman pumping and is associated with weakened coastal currents this analysis shows that anthropogenically induced wind changes can dramatically increase the temperature of ocean water at ice sheet grounding lines and at the base of floating ice shelves around antarctica with potentially significant ramifications for global sea level rise

deformation in rocks from itajai basin southern brazil revealed by magnetic fabrics magnetic measurements were performed on sedimentary and volcanic rocks from the itajai basin rock magnetism analyses reveal that magnetite and hematite and paramagnetic minerals show different contributions to magnetic susceptibility magnetic fabrics were determined in 19 sites by applying both anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanence magnetization aarm the analysis at the individual site scale defines three ams fabric types the first type shows kmin perpendicular to the bedding plane while kmax and kint are scattered within the bedding plane itself this fabric is usually interpreted as primary the second type 77 of the sites shows the three well clustered ams axes with kmin still perpendicular to the bedding plane the third type is characterized by well clustered kmax in the bedding plane while kmin and kint are distributed along a girdle perpendicular to kmax the second and third fabric types are interpreted as combinations of sedimentary compactional and tectonic contributions at the earliest and at a slightly later stage of deformation respectively ams represents the contribution of all the rock forming minerals while aarm isolates the contribution of remanence bearing minerals with coercivity 100 mt for some sites the ams and aarm fabrics are non coaxial mainly with respect to the lineation orientations the comparison of magnetic lineations and the regional structural data indicates that the rocks with no mesoscopic or macroscopic deformation were affected by the two deformation phases that occurred in the region one of them results from compressional tectonics related to the collisional orogen d1 and the other is extensional related to post collisional orogen d2 after the former tectonic event the volcanic rocks were emplaced at the top of the stratigraphic sequence and after that the itajai basin as a whole was deformed by the extensional tectonic d2 that occurred after 560 ma which is the age of the intrusion

important role for ocean warming and increased ice shelf melt in antarctic sea ice expansion changes in sea ice significantly modulate climate change because of its high reflective and strong insulating nature in contrast to arctic sea ice sea ice surrounding antarctica has expanded1 with record extent2 in 2010 this ice expansion has previously been attributed to dynamical atmospheric changes that induce atmospheric cooling3 here we show that accelerated basal melting of antarctic ice shelves is likely to have contributed significantly to sea ice expansion specifically we present observations indicating that melt water from antarctica s ice shelves accumulates in a cool and fresh surface layer that shields the surface ocean from the warmer deeper waters that are melting the ice shelves simulating these processes in a coupled climate model we find that cool and fresh surface water from ice shelf melt indeed leads to expanding sea ice in austral autumn and winter this powerful negative feedback counteracts southern hemispheric atmospheric warming although changes in atmospheric dynamics most likely govern regional sea ice trends4 our analyses indicate that the overall sea ice trend is dominated by increased ice shelf melt we suggest that cool sea surface temperatures around antarctica could offset projected snowfall increases in antarctica with implications for estimates of future sea level rise

extensional subsidence contractional folding and thrust inversion of the eastern cameros basin northern spain tectonic analysis of the cameros massif northern spain demonstrates the need to integrate detailed structural analysis with stratigraphic studies in order to understand the development of inverted basins the cameros massif underwent three major tectonic events each characterized by different mechanisms of deformation the first event tithonian early albian manifested as continental rifting and formation of the cameros basin and was attended by normal faulting and related folding of pre and syn rift sedimentary sequences up to 9 km thick it corresponded to the beginning of rifting and opening of the bay of biscay to the north of the massif the second event occurred at the end of the early cretaceous the basin underwent contraction manifested as gentle folds containing axial plane cleavage this contraction was due to the migration of the center of rifting away from the basin and toward the northeast and correlates with the onset of oceanic spreading in the bay of biscay deformation happened during a low grade metamorphism period that reached its thermal peak after folding and cleavage formation 90 100 ma the final stage of deformation eocene miocene following a structurally quiescent period of approximately 40 ma occurred during the convergence collision between iberia and europe it formed contractional folds related to large e w striking overthrusts the mesozoic basin was inverted and transported 25 km toward the north during this stage both unfolding and tightening of the former folds occurred as determined from analysis of cleavage orientation associated with the previous shortening

platelet ice the southern ocean s hidden ice a review basal melt of ice shelves is not only an important part of antarctica s ice sheet mass budget but it is also the origin of one of the most peculiar types of sea ice found in the polar oceans platelet ice in many regions around coastal antarctica tiny ice crystals form and grow in supercooled plumes of ice shelf water releasing heat into the surrounding ocean they usually rise towards the surface eventually becoming trapped under an ice shelf as marine ice frequently masses of those crystals are advected out of the ice shelf cavity and accumulate below a solid sea ice cover to form a semiconsolidated layer when the overlying sea ice grows into this so called sub ice platelet layer the loose crystals are consolidated adding additional thickness to the sea ice these phenomena are generally referred to as platelet ice although confusion about the terminology is widespread in the literature the presence of platelet ice has a profound impact on sea ice properties and processes in several regions of antarctica with numerous implications for the local polar marine biosphere most notably sub ice platelet layers provide a stable sheltered nutrient and food rich habitat which usually results in a highly productive and uniquely adapted ecosystem it has also been hypothesised that platelet ice may be an indicator of the state of an ice shelf although comprehensive time series are limited to the ross sea this paper clears up the terminology by providing exact definitions of the relevant terms we review platelet ice formation observational methods as well as geographical and seasonal occurrence the physical properties and ecological implications are merged in a way understandable for physicists and biologists alike to lay the foundation for the interdisciplinary research that is necessary to tackle the current knowledge gaps