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

antarctic ice sheet melting in the southeast pacific the first oceanographic measurements across a deep channel beneath the calving front of pine island glacier reveal a sub ice circulation driven by basal melting of 10 12 m yr 1 a salt box model described here gives a melt rate similar to that of ice balance and numerical models 5 50 times higher than averages for the george vi and ross ice shelves melting is fueled by relatively warm circumpolar deep water that floods the deep floor of the amundsen and bellingshausen sea continental shelves reaching the deep draft of this floating glacier a revised melt rate for ice shelves in the southeast pacific sector raises circumpolar ice shelf melting to 756 gt yr 1 given prior estimates of surface accumulation and iceberg calving this suggests that the antarctic ice sheet is currently losing mass to the ocean

ediacaran cambrian far field hydrothermal event in the southeast of the sao francisco craton brazil evidence from zircon u pb shrimp trace elements lu hf and oxygen isotopes abstract iron formation bearing sequences from the guanhaes tectonic block and southern espinhaco belt of the southeastern sao francisco craton were affected by the ediacaran cambrian brasilian orogeny when the guanhaes block was upthrusted onto statherian metasedimentary units of the lower espinhaco supergroup the iron formation contain a number of hydrothermal high grade iron ore bodies e g horto baratinha cuite morro escuro and morro do pilar deposits three different types of zircons were studied in order to characterize the temporal and geochemical evolution of the late orogenic hydrothermal event detrital zircons lower espinhaco supergroup orosirian statherian maximum depositional age zircons from the gneissic basement archean guanhaes complex and zircons from metagranitoid statherian borrachudos suite all populations include zircons with

depositional age and sediment source of the auriferous moeda formation quadrilatero ferrifero of minas gerais brazil new constraints from u pb hf isotopes in zircon and xenotime abstract the moeda formation is a metasedimentary clastic sequence of witwatersrand like metaconglomerate and quartzite at the base of the minas supergroup quadrilatero ferrifero of minas gerais brazil which is also known for its world class iron ore deposits the moeda formation can be subdivided into three units units i to iii from bottom to top with each unit consisting of metaconglomerates at their base mostly auriferous grading into quartzite and locally into phyllite this study presents the first combined u pb and lu hf isotope data from detrital zircons and xenotimes of auriferous metaconglomerates and quartzites from units ii and iii these data indicate that deposition of sediments occurred 2 68 ga for unit ii and 2 62 ga for unit iii as supported by the youngest magmatic zircon grains the data further provide evidence that the source area of sediments was affected by crust re working during two major magmatic metamorphic events at 2 89 2 87 and 2 72 2 69 ga and minor events between 3 3 and 3 0 and at 2 80 and 2 65 ga this interpretation is supported by mainly subchondritic hf t between 10 and 1 4 and large hf t variations including all magmatic events a few superchondritic hf t obtained for the magmatic events at 3 3 2 9 and 2 7 ga point to limited juvenile crust addition the new dataset indicates that the clastic sediments of the auriferous moeda formation were mainly derived from an evolved continental crust in contrast to primitive magmatic arc sources which are suggested for the mesoarchaean auriferous sediments of the witwatersrand basin of south africa and those of the eastern goldfield province of australia

upb geochronology of the central ribeira belt brazil and implications for the evolution of the brazilian orogeny abstract the ribeira belt in southeastern brazil was generated during the brazilian orogeny the south american equivalent of the pan african orogeny 700 450 ma the central sector of the belt is characterised by a series of northwest vergent crustal scale thrust stacks emplaced under amphibolite grade conditions major shear zones separate four lithotectonic domains andrel ndia to the northwest juiz de fora paraiba and coastal domains analyses of zircon monazite and titanite from a variety of rock types from the four domains lead to the following conclusions all domains record an important tectono thermal event at 590 565 ma represented by partial melting granitoid intrusion and remobilisation of older basement gneisses and corresponding to thrusting and development of dextral shear zones also recorded are older metamorphic ages 611 604 ma of unknown significance only the paraiba and coastal domains in the south record a younger metamorphic event m2 at 535 520 ma most likely associated with another episode of thrusting and shear zone development the absence of m2 metamorphism in the andrel ndia and juiz de fora domains can be explained by post 535 520 ma emplacement of the paraiba domain late to post tectonic activity is represented by 503 492 ma metamorphism precursors of the basement gneisses are 2185 2134 ma old rocks generated during the transamazonian orogeny some of which contain a significant archean component with minimum ages of 2981 2846 ma the ages presented above define specific metamorphic events for the brazilian orogeny for the first time in southeastern brazil in addition together with previously published data they indicate that the basement rocks found in the allochthonous domains of the central ribeira belt represent an extension of the units present in the southern sao francisco craton and indicate that the foreland was more extensive than the presently defined craton

on the role of coastal troughs in the circulation of warm circumpolar deep water on antarctic shelves abstractoceanic exchanges across the continental shelves of antarctica play an important role in biological systems and the mass balance of ice sheets the focus of this study is on the mechanisms responsible for the circulation of warm circumpolar deep water cdw within troughs running perpendicular to the continental shelf this is examined using process oriented numerical experiments with an eddy resolving 1 km 3d ocean model that includes a static and thermodynamically active ice shelf three mechanisms that create a significant onshore flow within the trough are identified 1 a deep onshore flow driven by the melt of the ice shelf 2 interaction between the longshore mean flow and the trough and 3 interaction between a rossby wave along the shelf break and the trough in each case the onshore flow is sufficient to maintain the warm temperatures underneath the ice shelf and basal melt rates of o 1 m yr 1 the third mechanism in particular reproduces several features revealed by moorings from m

the role of mesoscale eddies in the rectification of the southern ocean response to climate change abstract simulations from a fine resolution global coupled model the geophysical fluid dynamics laboratory climate model version 2 4 cm2 4 are presented and the results are compared with a coarse version of the same coupled model cm2 1 under idealized climate change scenarios a particular focus is given to the dynamical response of the southern ocean and the role played by the eddies parameterized or permitted in setting the residual circulation and meridional density structure compared to the case in which eddies are parameterized and consistent with recent observational and idealized modeling studies the eddy permitting integrations of cm2 4 show that eddy activity is greatly energized with increasing mechanical and buoyancy forcings buffering the ocean to atmospheric changes and the magnitude of the residual oceanic circulation response is thus greatly reduced although compensation is far from being perfect changes in poleward eddy fluxes partially compensate for the enhanced equatorward

ice shelf melt response to changing winds and glacier dynamics in the amundsen sea sector antarctica it has been suggested that the coastal southern ocean subsurface may warm over the 21st century in response to strengthening and poleward shifting winds with potential adverse effects on west antarctic glaciers however using a 1 128 ocean regional model that includes ice shelf cavities we find a more complex response to changing winds in the amundsen sea simulated offshore subsurface waters get colder under strengthened and poleward shifted winds representative of the sam projected trend the buoyancy driven circulation induced by ice shelf melt transports this cold offshore anomaly onto the continental shelf leading to cooling and decreased melt below 450 m in the vicinity of ice shelf fronts ekman pumping contributes to raise the isotherms in response to changing winds this effect overwhelms the horizontal transport of colder offshore waters at intermediate depths between 200 and 450 m and therefore increases melt rates in the upper part of the ice shelf cavities which reinforces the buoyancydriven circulation and further contributes to raise the isotherms then prescribing an extreme grounding line retreat projected for 2100 the total melt rates simulated underneath thwaites and pine island are multiplied by 2 5 such increase is explained by a larger ocean ice interface exposed to cdw which is then amplified by a stronger melt induced circulation along the ice draft our main conclusions are that 1 outputs from ocean models that do not represent ice shelf cavities e g cmip5 models should not be directly used to predict the thermal forcing of future ice shelf cavities 2 coupled ocean ice sheet models with a velocity dependent melt formulation are needed for future projections of glaciers experiencing a significant grounding line retreat

freshening of the ross sea during the late 20th century ocean measurements in the ross sea over the past four decades one of the longest records near antarctica reveal marked decreases in shelf water salinity and the surface salinity within the ross gyre these changes have been accompanied by atmospheric warming on ross island ocean warming at depths of 300 meters north of the continental shelf a more negative southern oscillation index and thinning of southeast pacific ice shelves the freshening appears to have resulted from a combination of factors including increased precipitation reduced sea ice production and increased melting of the west antarctic ice sheet

ice ocean processes over the continental shelf of the southern weddell sea antarctica a review 1 interactions between the southern ocean and the weddell sea ice shelves are important both to the antarctic ice sheet and to the production of globally significant water masses here we review the interaction between the filchner ronne ice shelf and the shelf sea in which it floats the continental shelf processes leading to the production of weddell sea deep and bottom waters from the original off shelf source waters are discussed and a new view is offered of the initial production of high salinity shelf water data from ship based measurements at the ice front from glaciological methods and from measurements made within the sub ice shelf cavity itself are used to describe the pattern of flows beneath the ice shelf we also consider the variability observed within the cavity from tidal to interannual time scales and finish with a discussion of future research priorities in the region

late neoproterozoic cambrian granitic magmatism in the aracuai orogen brazil the eastern brazilian pegmatite province and related mineral resources

a suture related accretionary wedge formed in the neoproterozoic aracuai orogen se brazil during western gondwanaland assembly abstract the aracuai orogen represents a branch of the brasiliano orogenic system developed between the sao francisco and congo cratons in neoproterozoic time we conducted detailed studies on a complex schist belt located to the west of the rio doce magmatic arc along the assumed suture zone of the aracuai orogen this 30 km wide and 100 km long ns trending belt includes pelitic schists with intercalations of quartzites metaultramafic schists and diopsidites intruded by collisional granites u pb ages from detrital zircon grains point to distinct provenances for different portions of the schist belt the lower succession shows an age spectra and maximum depositional age 819 ma similar to passive margin deposits of the precursor basin the upper succession yielded a maximum deposition age around 600 ma pointing toward the rio doce arc as the main sediment source thrust to the west onto the guanhaes basement and separated on the east from the ediacaran rio doce magmatic arc by reverse dextral faults the schist belt exhibits the architecture of an asymmetric flower structure developed in transpressional regime the distribution of metamorphic assemblages across the schist belt characterizes a collisional barrovian type metamorphic zoning in which the sillimanite kyanite staurolite and garnet zones are locally duplicated by thrusts p t conditions range from 700 c at 7 5 kbar at the western base of the pile to 550 c at 5 5 kbar at the eastern top of the package zircon u pb ages record metamorphic overprinting on the sheared top of the basement at 560 20 ma and crystallization of collisional granites at 544 10 ma our results allow us to interpret the schist belt as a suture related accretionary wedge and suggest that basin closure during the assembly of west gondwanaland lasted to the ediacaran cambrian boundary in the aracuai orogen

changes in global ocean bottom properties and volume transports in cmip5 models under climate change scenarios abstractchanges in bottom temperature salinity and density in the global ocean by 2100 for cmip5 climate models are investigated for the climate change scenarios rcp4 5 and rcp8 5 the mean of 24 models shows a decrease in density in all deep basins except the north atlantic which becomes denser the individual model responses to climate change forcing are more complex regarding temperature the 24 models predict a warming of the bottom layer of the global ocean in salinity there is less agreement regarding the sign of the change especially in the southern ocean the magnitude and equatorward extent of these changes also vary strongly among models the changes in properties can be linked with changes in the mean transport of key water masses the atlantic meridional overturning circulation weakens in most models and is directly linked to changes in bottom density in the north atlantic these changes are the result of the intrusion of modified antarctic bottom water made possible by the decrease i

rifting events in the southern sector of the paramirim aulacogen ne brazil new geochronological data and correlations for the sao francisco congo paleocontinent abstract the evolutionary history of the paramirim aulacogen is characterized by the superposition of rifts that developed from 1770 to 675 ma in the northern serra do espinhaco fold thrust belt two units of this aulacogen were analyzed in the present study the algodao formation espinhaco supergroup and the santo onofre group sao francisco supergroup in the study area the algodao formation consists of alternating of quartzose to feldspathic metasandstones sericitic metasandstones oligomictic metaconglomerates metasandstones and quartzites laminated metapelites metarhythmites and metasiltites and quartzites in turn the santo onofre group the serra da garapa formation was subdivided into two lithofacies associations the first is composed predominantly by quartzites and hematite rich graphite rich and or manganese rich metapelites and phyllites the second lithofacies association comprises staurolite garnet quartz biotite aluminous schist and quartzites in the boqueirao formation predominates metasubarkoses and lithic metasandstones and metasiltites besides oligomictic metamicroconglomerates u pb geochronological studies la icpms were performed on detrital zircons from these units ages ranging were 2870 17 1958 18 ma and 3177 42 894 38 ma respectively the main primary sources were related to rocks from the basement of the western bahia orogeny of siderian orosirian age as well as volcanites and plutonites both mafic and felsic with ages between ca 1 7 and 0 8 ga related to the evolution of the precursor basins of the aracuai west congo orogen as secondary sources results suggest metavolcanosedimentary sequences and greenstone belts of archean and paleoproterozoic ages as well as rocks from the espinhaco supergroup and macaubas group the lithofacies of serra da garapa formation as well as the ages found in detrital zircons suggest that this formation is chronocorrelate with rio peixe bravo formation of the macaubas group together these formations and matao and duas barras formation represent the pre glacial unit of the santo onofre macaubas basin initiated in tonian some characteristics suggest that the boqueirao formation may be correlated to some of the glacial units of this basin this work suggests that the formations fazendinha and serra da vereda are excluded from the santo onofre group

rhyacian orosirian isotopic records from the basement of the aracuai ribeira orogenic system se brazil links in the congo sao francisco palaeocontinent abstract assembled during the rhyacian orosirian boundary the congo sao francisco palaeocontinent remained linked by a continental bridge from ca 2 ga to the atlantic ocean opening in the cretaceous to the south of that bridge precursor basins and orogenic outcomes encompassed by the neoproterozoic cambrian aracuai ribeira orogenic system aros and its african counterparts developed the aros discloses reworked basement units like the juiz de fora pocrane and quirino complexes which are key units to retrieve the palaeoproterozoic history of the congo sao francisco palaeocontinent this paper presents new u pb ages and the first lu hf in zircon signatures from those complexes all magmatic zircon grains show rhyacian and orosirian ages ranging from c 2250 ma to c 1850 ma the best concordia ages range from 2184 9 ma to 2080 19 ma hf in zircon and whole rock sm nd data disclose mantle related signatures for both the pocrane and juiz de fora complexes suggesting igneous protoliths with no or very few involvement of continental crust similarly to juvenile magmatic arcs conversely hf in zircon data for the quirino complex show an evolved signature compatible with a magmatic arc developed on a continental older crust with archaean components together with a thorough compilation on rhyacian orosirian orogenic systems roos our data allow us to envisage links within the congo sao francisco palaeocontinent comprising orogens characterised by mostly evolved isotopic signatures and zircon inheritance they are grouped into the i w roos including the mantiqueira complex the west segment of the eastern bahia belt intrusions in the south gaviao and porteirinha blocks and parts of the mineiro belt and ii e roos comprising the quirino complex basement rocks of the cabo frio tectonic domain the coastal eastern bahia belt and in africa eburnean and kimezian complexes as well as the western angola shield assembled between the w roos and e roos an orogenic system with prominent juvenile to moderately juvenile isotopic signature ju roos includes the juiz de fora and pocrane complexes and the buerarema complex at the central segment of the eastern bahia belt

cmip5 temperature biases and 21st century warming around the antarctic coast projections of ice sheet mass balance require regional ocean warming projections derived from atmosphere ocean general circulation models aogcms however the coarse resolution of aogcms 1 may lead to systematic or aogcm specific biases and 2 makes it difficult to identify relevant water masses here we employ a large scale metric of antarctic shelf bottom water asbw to investigate circum antarctic temperature biases and warming projections in 19 different coupled model intercomparison project phase 5 cmip5 aogcms forced with two different representative concentration pathways rcps for high emissions rcp 8 5 the ensemble mean 21st century asbw warming is 0 66 0 74 and 0 58 c for the amundsen ross and weddell seas as rs and ws respectively rcp 2 6 ensemble mean projections are substantially lower 0 21 0 26 and 0 19 c all distributions of regional asbw warming are positively skewed for rcp 8 5 four aogcms project warming of greater than 1 8 c in the rs across the ensemble there is a strong rcp independent correlation between ws and rs warming as warming is more closely linked to warming in the southern ocean we discuss possible physical mechanisms underlying the spatial patterns of warming and highlight implications of these results on strategies for forcing ice sheet mass balance projections

an optimized estimate of glacial melt from the ross ice shelf using noble gases stable isotopes and cfc transient tracers 1 isotopes of helium and neon and the h218o h216o ratio of water are proven proxies for melt from glacial ice beneath floating ice shelves and at ice shelf fronts their high concentrations in glacial meltwater compared to other environmental sources make them ideal tracers for studies of the pathways of glacial meltwater from its origins into the ocean interior we combine noble gas and stable isotopes with temperature salinity and dissolved oxygen measurements from three cruises along the ross ice shelf during the austral summers of 1993 1994 and 1999 2000 and to the ross sea in 2000 2001 and use optimal multiparameter analysis to compute the water mass concentration including glacial meltwater the distribution of meltwater at the front of the ross ice shelf extended east from 180 w with the highest concentrations found near 165 w in both 1994 and 2000 the mean meltwater concentration at the ice shelf front was 2 0 0 33 in 1994 2 2 0 36 in 2000 and 0 25 0 1 in the western ross sea in 2001 water mass concentrations are used to correct for bias in the cfc age introduced by mixing with cfc free waters an effect revealed by comparing cfc age with transit time distribution curves the water residence time within the ice shelf cavity using cfcs and the mean meltwater concentration implies a basal melt rate of 33 50 km3 a 1

hydrothermal alteration and mineralization in the faina greenstone belt evidence from the cascavel and sertao orogenic gold deposits abstract the faina greenstone belt is located in central brazil and contains the cascavel and sertao gold deposits 500 000 oz au total resource and past production the bulk of the gold is hosted in quartzite and biotite schist at cascavel and carbonaceous schist and banded iron formation at sertao the metamorphic grade of the host rocks is greenschist facies cascavel is a vein hosted gold deposit with orebodies mainly controlled by f2 fold hinges with minor mineralization in d3 shear zones hydrothermal alteration in quartzite is characterized by distal quartz k feldspar muscovite intermediate quartz fuchsitic mica biotite pyrite and proximal quartz white mica pyrite chalcopyrite the biotite schist is characterized by distal quartz chlorite calcite and proximal white mica biotite tourmaline siderite pyrite native gold is located within intensely deformed quartz veins and locally as free gold disseminated in proximal alteration zones sertao is a shear zone hosted gold deposit with orebodies controlled by d3 shear zones including gold bearing shear veins and surrounding hydrothermally altered wallrocks hydrothermal alteration is characterized by distal quartz ankerite chlorite pyrite chalcopyrite and proximal quartz white mica siderite pyrite arsenopyrite chalcopyrite gold is in equilibrium with arsenopyrite and within arsenopyrite disseminated in the proximal alteration zone chlorite geothermometry suggests temperatures of 335 407 c and 328 397 c for the gold bearing hydrothermal fluids in the sertao and cascavel deposits respectively arsenopyrite geothermometry on arsenopyrite within gold bearing veins in the sertao deposit yields temperatures between 310 and 480 c structures controlling hydrothermal alteration and gold mineralization in both deposits are developed during a regional d2 event and subsequently deformed during a d3 event hydrothermal alteration minerals are consistently replacing metamorphic minerals the alteration assemblages in both deposits are similar albeit their modal mineralogy is controlled by the host rock composition therefore both the cascavel and sertao deposits are interpreted as orogenic mesozonal gold systems comparable with other orogenic gold systems in brazil and worldwide

different magnitudes of projected subsurface ocean warming around greenland and antarctica accurate projections of global sea level rise require information of future ocean warming in the vicinity of the large ice sheets an analysis of 19 climate model projections suggests that subsurface ocean warming near both polar ice sheets will be substantial with the potential to lead to significant increases in ice mass loss

limited retreat of the wilkes basin ice sheet during the last interglacial the response of the east antarctic ice sheet to global warming represents a major source of uncertainty in sea level projections thinning of the east antarctic george v and sabrina coast ice cover is currently taking place and regional ice sheet instability episodes might have been triggered in past warm climates however the magnitude of ice retreat in the past can not yet be quantitatively derived from paleo proxy records alone we propose that a runaway retreat of the george v coast grounding line and subsequent instability of the wilkes basin ice sheet would either leave a clear imprint on the water isotope composition in the talos dome region or prohibit a talos dome ice core record from the last interglacial altogether testing this hypothesis our ice sheet model simulations suggest that wilkes basin ice sheet retreat remained relatively limited during the last interglacial and provide a constraint on last interglacial east antarctic grounding line stability

melting of ice shelves and the mass balance of antarctica we calculate the present ice budget for antarctica from measurements of accumulation minus iceberg calving run off and in situ melting beneath the floating ice shelves the resulting negative mass balance of 469 gt year 1 differs substantially from other recent estimates but some components are subject to high temporal variability and budget uncertainties of 20 50 annual accumulation from an earlier review is adjusted to include the antarctic peninsula for a total of 2144 gt year 1 an iceberg production rate of 2016 gt year 1 is obtained from the volume of large icebergs calculated from satellite images since 1978 and from the results of an international iceberg census project ice shelf melting of 544 gt year 1 is derived from physical and geochemical observations of meltwater outflow glaciological field studies and modeling of the sub ice ocean circulation the highest melt rates occur near ice fronts and deep within sub ice cavities run off from the ice sheet surface and from beneath the grounded ice is taken to be 53 gt year 1 less than half of the negative mass balance need come from the grounded ice to account for the unattributed 0 45 mm year 1 in the ipcc best estimate of the recent global sea level rise

crustal growth through successive arc magmatism reconnaissance u pb shrimp data from the northeastern superior province canada abstract north of the la grande subprovince in northern quebec the superior province is dominated by plutonic rocks of the bienville subprovince and minto block which have been further subdivided into domains on the basis of reconnaissance geological mapping and geochronology and projected along strike using aeromagnetic anomalies to test the validity of the extrapolations u pb ages were obtained through shrimp analyses of zircon from 18 small archival samples selected from a suite of 2000 specimens collected during a helicopter reconnaissance survey conducted in the 1960s the results reveal a history of successive arc magmatism between 3 07 and 2 70 ga followed by metamorphism emplacement of crustally derived granites 2 702 2 685 ga and late hydrothermal events ca 2 65 ga in the northeastern minto block the douglas harbour domain previously extrapolated from dated localities to the northeast is substantiated through an age of 2 87 ga the older tonalitic crust is punctured by 2 734 2 725 ga granodioritic plutons of the leaf river suite that locally carry 3 01 ga inherited zircon the northern utsalik domain is made up of pyroxene and hornblende bearing leaf river plutons with consistent 2 725 2 723 ga ages and local inheritance of 2 82 and 2 77 ga however the southern extension of utsalik domain contains pyroxene bearing granodiorites both older 2 762 ga and younger 2 692 ga than the leaf river suite a tonalitic rock from the southern goudalie domain with an age of 2 833 ga supports a linkage to 2 84 2 83 ga units of the qalluviartuuq domain along strike to the north tikkerutuk domain represents a north trending 50 km wide calc alkaline magmatic arc with ages between 2 71 and 2 70 ga that extends southward into the bienville subprovince on the basis of aeromagnetic anomalies and geochronology zircon inheritance ages indicate that the tikkerutuk arc was built upon antecedent arcs of 2 84 2 77 and 2 725 ga the inukjuak domain in the west consists mainly of granite dated in one locality at 2 72 ga

transamazonian orogeny in the southern sao francisco craton region minas gerais brazil evidence for paleoproterozoic collision and collapse in the quadrilatero ferrifero abstract the paleoproterozoic transamazonian orogeny yielded a series of discrete orogens in brazil the present field study in the quadrilatero ferrifero qf indicates that the southern sao francisco craton region of the brazilian highlands preserves a portion of one of these orogens two sets of transamazonian structures occur in this region the first consists of northwest verging folds and thrusts affecting supracrustal sequences it is suggested that this set formed in a fold thrust belt setting shortly after 2 125 ga during the closure of a passive margin basin that had initiated along the margins of a preexisting continental mass at ca 2 5 ga the second set consists of structures defining the prominent dome and keel architecture of the qf this set a consequence of the emplacement of basement domes against supracrustal rocks at 2 095 ga may reflect the consequences of orogenic collapse narrow conglomerate filled intermontane basins may have formed coevally with dome emplacement formation of an ocean basin east of the present day sao francisco craton eventually occurred in late mesoproterozoic in effect the transamazonian orogen of the qf represents the collision and collapse stages of a paleoproterozoic wilson cycle the contractional phase of the transamazonian orogeny probably represents accretion of an offshore arc to the eastern and southeastern margin of the present day sao francisco craton region the arc and an associated suture may be traced in the brasiliano pan african orogen east of the sao francisco craton northwards into the northeastern lobe of the sao francisco craton clearly initial assembly of crustal blocks to form a larger continent involving south america occurred during the paleoproterozoic 2 1 ga post transamazonian rifting of this continent created the basins which were later inverted during the brasiliano assembly of gondwana

decadal freshening of the antarctic bottom water exported from the weddell sea recent decadal changes in southern hemisphere climate have driven strong responses from the cryosphere concurrently there has been a marked freshening of the shelf and bottom waters across a wide sector of the southern ocean hypothesised to be caused by accelerated glacial melt in response to a greater flux of warm waters from the antarctic circumpolar current onto the shelves of west antarctica however the circumpolar pattern of changes has been incomplete no decadal freshening in the deep layers of the atlantic sector had been observed in this study we document a significant freshening of the antarctic bottom water exported from the weddell sea which is the source for the abyssal layer of the atlantic overturning circulation and we trace its possible origin to atmospheric forced changes in the ice shelves and sea ice on the eastern flank of the antarctic peninsula that include an anthropogenic component these findings suggest that the expansive and relatively cool weddell gyre does not insulate the bottom water formation regions in the atlantic sector from the ongoing changes in climatic forcing over the antarctic region

the araa uaa west congo orogen in brazil an overview of a confined orogen formed during gondwanaland assembly abstract the neoproterozoic adamastor brazilide ocean was generated during the breakup of the rodinia supercontinent and remnants of its oceanic lithosphere have been found in the brasiliano pan african orogenic system that includes the aracuai west congo brasilia ribeira kaoko dom feliciano damara and gariep belts the aracuai and the west congo belts are counterparts of the same neoproterozoic orogen the first belt comprises two thirds of the aracuai west congo orogen this orogen is rather unique owing to its confined nature within the embayment outlined by the sao francisco and congo cratons in spite of this the presence of ophiolitic remnants and a calc alkaline magmatic arc indicate that the basin orogen evolution comprise both oceanic spreading and consumption it is assumed that coeval paramirim and sangha aulacogens played a key role by making room for the aracuai west congo basin sedimentary successions record all major stages of a basin that evolved from continental rift when glaciation related sedimentation was very significant to passive margin rifting started around 1 0 0 9 ga the oceanic stage is constrained by an ophiolitic remnant dated at 0 8 ga if the cratonic bridge that once linked the sao francisco and congo palaeocontinental regions did not hinder the opening of an ocean basin it certainly limited its width as a consequence only a narrow oceanic lithosphere was generated and it was subducted afterwards this is also suggested by orogenic calc alkaline granitoids occuping a small area of the orogen geochronological data for pre syn and late collisional granitoids indicate that the orogenic stage lasted from 625 ma to 570 ma a period of magmatic quiescence was followed by intrusion of postcollisional plutons at 535 500 ma the features of the aracuai west congo orogen suggest the development of a complete wilson cycle in a branch of the adamastor ocean which can be interpreted as a gulf with limited generation of oceanic lithosphere

u pb la icp ms detrital zircon ages of the sao joao del rei and carandai basins new evidence of intermittent proterozoic rifting in the sao francisco paleocontinent abstract the tiradentes formation sao joao del rei basin is a shallow marine quartzite succession resting on the paleoproterozoic crust of the southern part of the sao francisco craton a regional angular unconformity separates the tiradentes strata from the younger carandai barroso and prados formations carandai basin the carandai formation is constituted of fault bounded diamictites containing lithoclasts derived from basement rocks and the tiradentes formation the barroso formation is a sag basin limestone succession whereas the prados formation is a pelitic succession that fills a ne sw trending aulacogen weak deformation and metamorphism 600 590 ma overprinted the sao joao del rei and carandai sequences due to the brasiliano orogen and likewise the overlying andrel ndia megasequence

assessment of southern ocean water mass circulation and characteristics in cmip5 models historical bias and forcing response 1 the ability of the models contributing to the fifth coupled models intercomparison project cmip5 to represent the southern ocean hydrological properties and its overturning is investigated in a water mass framework models have a consistent warm and light bias spread over the entire water column the greatest bias occurs in the ventilated layers which are volumetrically dominated by mode and intermediate layers the ventilated layers have been observed to have a strong fingerprint of climate change and to impact climate by sequestrating a significant amount of heat and carbon dioxide the mode water layer is poorly represented in the models and both mode and intermediate water have a significant fresh bias under increased radiative forcing models simulate a warming and lightening of the entire water column which is again greatest in the ventilated layers highlighting the importance of these layers for propagating the climate signal into the deep ocean while the intensity of the water mass overturning is relatively consistent between models when compared to observation based reconstructions they exhibit a slightly larger rate of overturning at shallow to intermediate depths and a slower rate of overturning deeper in the water column under increased radiative forcing atmospheric fluxes increase the rate of simulated upper cell overturning but this increase is counterbalanced by diapycnal fluxes including mixed layer horizontal mixing and mostly vanishes

pan african rifting and orogenesis in southern to equatorial africa and eastern brazil abstract the upper proterozoic pan african belts of africa and brasiliano belts of south america are assumed to have evolved from an elaborate system of continental rifts which formed on the west gondwana continent 1100 1000 ma ago reviews of the damara belt kaoko belt gariep belt saldania belt west congolian belt lufilian arc and zambezi belt of southern and equatorial africa and the ribeira mantiqueira belt of brazil show the applicability of the continental rifting model to all these belts strict application of the rifting model describing the formation and further evolution of rift structures in the continental crust leads to the conclusion that the west congolian belt as traditionally described is incomplete and has to be supplemented by the mayumbian belt and a rift structure situated farther to the west the lufilian arc is assumed to have evolved from two rift structures separated from each other by the later domes region the golfe du katanga which branches off northeastwards from the lufilian arc is interpreted as an aulacogen shaba aulacogen the pan african brasiliano rift system is comparable to the mesozoic arctic north atlantic rift system with regard to size and distribution of rifts ocean floor spreading and opening of a proto south atlantic ocean most probably occurred along a main line of rifting situated between the west coast of africa and eastern brazil the wedge like ocean may have terminated at the sao francisco congo cratonic bridge between northeastern brazil and gabon cameroon there is no evidence of ocean floor spreading in the zambezi belt the lufilian arc and the traditional west congolian belt which are arranged along another major line of rifting closure of the pan african brasiliano rift system took place during two successive orogenic episodes the zambezi belt lufilian arc and west congolian belt underwent their main orogenic deformation with prevailing ene and wsw oriented tectonic transportation directions during the katangan episode at 900 750 ma the transcontinental sinistral mwembeshi shear zone adjusted opposite movement directions in the zambezi belt and lufilian arc and at its western prolongation concurrently supported opening of the khomas trough in the southern damara belt the proto south atlantic ocean still opening during the katangan episode was gradually closed during the damaran episode at 750 500 ma closure proceeded from north to south and was accompanied by northwest directed subduction underneath the brazilian plate and southeast directed tectonic transportation in the kaoko damara and gariep belts in the previously formed west congolian belt lufilian arc and zambezi belt a second deformation phase characterized by strike slip faulting and local emplacement of nappes occurred during this episode

neoproterozoic granulite facies metamorphism and coeval granitic magmatism in the brasilia belt central brazil regional implications of new shrimp u pb and sm nd data abstract new shrimp u pb zircon ages combined with sm nd isotopic characteristics of granulites and associated granitic rocks of the anapolis itaucu complex in the central southern part of the brasilia belt are presented and discussed in this study igneous crystallization ages obtained in zircon grains of orthogranulite and granites vary between 760 and 650 ma growth of new zircon at ca 650 640 ma dates the high grade metamorphism zircon cores from paragranulites and granites give u pb ages between 2 0 and 0 8 ga tdm model ages of the granulitic rocks fall into two age intervals 2 3 1 9 and 1 7 1 4 ga end t values are negative varying between 9 29 and 1 42 shrimp u pb ages of zircon cores indicate that the granulite sedimentary protoliths were deposited after 800 ma ago contradicting previous models which assigned paleoproterozoic or archean ages for these rocks their nd isotopic signature indicate that paleoproterozoic sources within the sao francisco craton as well as younger sources such as the goias magmatic arc contributed to the sediment infilling of the former basin the intrusive granites display nd model age pattern similar to that of the granulitic rocks with most tdm model ages ranging between 1 45 and 1 2 ga end t values are between 2 61 and 7 96 indicative of assimilation of older material by the original magma shrimp u pb data for the granite intrusions indicate that granitoids metamorphosed under amphibolite facies show strong inheritance between 2 1 and 0 8 ga and magmatic metamorphic age at ca 660 650 ma the syn granulite facies granitoid ana 1 gave magmatic and metamorphic ages of ca 650 ma without any discernible inheritance the growth of new zircon occurred at the same time of the high grade metamorphism probably related with the collision event between the goias magmatic arc to the west southwest and the sao francisco craton to the east the data suggest that the anapolis itaucu complex instead of representing the ancient sialic basement of the supracrustal rock units of the brasilia belt constitutes a neoproterozoic high grade metamorphic complex related with the evolution of the brasiliano orogen

interactions between the landers and hector mine california earthquakes from space geodesy boundary element modeling and time dependent friction the m w 7 1 hector mine earthquake happened 7 years after the 1992 m w 7 3 landers earthquake within a system of right lateral strike slip faults comprising the eastern california shear zone because estimates of recurrence intervals of m 7 earthquakes on these faults range anywhere from 1500 to 50 000 years the close temporal spacing of these two earthquakes suggests that there is some interaction between the two current models of simple coulomb static stress interactions between the earthquake ruptures do not predict an obvious cause and effect relationship the interaction between the computed normal and right lateral shear stress reductions induced by the landers earthquake at the hector mine hypocenter is unclear we use a combination of space geodesy boundary element modeling and computer modeling of time dependent fault friction to investigate the interaction between the two earthquakes we compare stress changes on the hector mine rupture plane induced by the landers earthquake with the detailed slip distribution inferred using a combination of gps and insar data the slip distributions of both earthquakes are also used to infer the magnitude of the shear stress drop on each earthquake rupture and the orientation of the remote background stress consistent with these two recent events for each earthquake the azimuth of the remote maximum compressive stress was approximately 17 6 and the magnitude of the shear stress drop was 8 1 mpa on the landers rupture and 10 2 mpa on the hector mine rupture using a simple spring and slider model as a proxy for the rate and state frictional response of the hector mine faults to landers earthquake imposed stress steps we find that while a decrease in normal stress at the hector mine hypocenter would by itself have caused the hector mine earthquake to nucleate immediately the simultaneous decrease in shear stress may have caused a delay in the peak shear loading consideration of an acceptable range of rate and state friction parameters secular strain rates and crustal stiffnesses leads us to conclude that this delay could have been 0 to 40 years

the role of eddies in the southern ocean temperature response to the southern annular mode the role of eddies in modulating the southern ocean response to the southern annular mode sam is examined usinganoceanmodelrunatmultipleresolutionsfromcoarsetoeddyresolving thehigh resolution versionsof the model showan increase in eddy kinetic energy that peaks 2 3 yr after a positive anomalyin the sam index previous work has shown that the instantaneous temperature response to the sam is characterized by predominant cooling south of 458s and warming to the north at all resolutions the model captures this temperatureresponse this responseis also evidentin the coarse resolution implementation of the model with no eddy mixing parameterization showing that eddiesdo not play an important role in the instantaneous response on the longer time scales an intensification of the mesoscale eddy field occurs which causes enhanced poleward heat flux and drives warming south of the oceanic polar front this warming is of greater magnitude and occurs for a longer period than the initial cooling response the results demonstrate that this warming is surface intensified and strongest in the mixed layer non eddy resolving models are unable to capturethedelayededdy driventemperatureresponsetothesam theauthorsthereforequestiontheability

eddy driven exchange between the open ocean and a sub ice shelf cavity the exchange between the open ocean and sub ice shelf cavities is important to both water mass transformations and ice shelf melting here we use a high resolution 500 m numerical model to investigate to which degree eddies produced by frontal instability at the edge of a polynya are capable of transporting dense high salinity shelf water hssw underneath an ice shelf the applied surface buoyancy flux and ice shelf geometry is based on ronne ice shelf in the southern weddell sea an area of intense wintertime sea ice production where a flow of hssw into the cavity has been observed results show that eddies are able to enter the cavity at the southwestern corner of the polynya where an anticyclonic rim current intersects the ice shelf front the size and time scale of simulated eddies are in agreement with observations close to the ronne ice front the properties and strength of the inflow are sensitive to the prescribed total ice production flushing the ice shelf cavity at a rate of 0 2 0 4 106 m3 s 1 depending on polynya size and magnitude of surface buoyancy flux eddy driven hssw transport into the cavity is reduced by about 50 if the model grid resolution is decreased to 2 5 km and eddies are not properly resolved

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

ice sheet model sensitivities to environmental forcing and their use in projecting future sea level the searise project ten ice sheet models are used to study sensitivity of the greenland and antarctic ice sheets to prescribed changes of surface mass balance sub ice shelf melting and basal sliding results exhibit a large range in projected contributions to sea level change in most cases the ice volume above flotation lost is linearly dependent on the strength of the forcing combinations of forcings can be closely approximated by linearly summing the contributions from single forcing experiments suggesting that nonlinear feedbacks are modest our models indicate that greenland is more sensitive than antarctica to likely atmospheric changes in temperature and precipitation while antarctica is more sensitive to increased ice shelf basal melting an experiment approximating the intergovernmental panel on climate change s rcp8 5 scenario produces additional first century contributions to sea level of 22 3 and 8 1 cm from greenland and antarctica respectively with a range among models of 62 and 14 cm respectively by 200 years projections increase to 53 2 and 26 7 cm respectively with ranges of 79 and 43 cm linear interpolation of the sensitivity results closely approximates these projections revealing the relative contributions of the individual forcings on the combined volume change and suggesting that total ice sheet response to complicated forcings over 200 years can be linearized

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

evolution of polycyclic basement complexes in the aracuai orogen based on u pb shrimp data implications for brazil africa links in paleoproterozoic time paleoproterozoic basement of the aracuaorogen is composed of amphibolite and granulite facies orthogneiss units known as mantiqueira and juiz de fora complexes six u pb shrimp crystallization ages for the mantiqueira complex range from 2137 19 to 2041 7 ma studied samples are characterized by the abundance of inherited archean zircon grains tdm model ages ranging from 2 9 to 3 2 ga and strongly negative end t 9t o 13 gneiss protholits were mainly generated by partial melting of older continental material and the mantiqueira complex is related to active margin and syn collisional magmatism high grade gneiss samples of the juiz de fora complex yields crystallization ages of 2119 16 and 2084 13 and inherited zircon grains are absent this plutonic unit much probably evolved within an oceanic magmatic arc setting or on a very stretched continental crust the mantiqueira and juiz de fora complexes together with the kimezian basement of the west congo belt were parts of a paleoproterozoic orogenic system disrupted and deeply reworked during the evolution of the aracuacongo orogen neoproterozoic metamorphic overprint is dated at ca 590 574 ma 2007 elsevier b v all rights reserved

kinematic evolution of the aracuai west congo orogen in brazil and africa nutcracker tectonics during the neoproterozoic assembly of gondwana abstract the neoproterozoic aracuai west congo a wc orogen is one of many brasiliano pan african orogens that developed during the assembly of west gondwana this orogen was split apart in mesozoic time due to opening of the south atlantic the aracuai orogen now underlies eastern brazil whereas the west congo belt fringes central africa s atlantic coast significantly at the time it formed the a wc orogen was bounded on the west north and east by the sao francisco congo craton a crustal block that had the shape of a lopsided upside down u thus the orogen was partially confined during tectonism in that it occupied an enclave surrounded on three sides by cratonic crust formation of the a wc orogen resulted in kinematically complex deformation substantial crustal shortening and production of a large volume of magma how such features could develop in this particular setting has long been a mystery our field studies in the aracuai orogen together with published data on the west congo belt characterize the kinematic picture of the a wc orogen and lead to a tectonic model that addresses its evolution in our model the a wc orogen formed in response to closure of the macaubas basin this basin was underlain by oceanic crust in the south but tapered northward into a continental rift which terminated against the cratonic bridge linking the eastern and western arms of the sao francisco congo craton closure occurred when the western arm now the sao francisco craton rotated counterclockwise towards the eastern arm now the congo craton this closure may have been driven by collision of the paranapanema amazonian and kalahari cratons against the external margins of the sao francisco congo craton rather than by slab pull associated with subduction of the macaubas basin s floor thus the process of forming the a wc orogen resembled the process of crushing of a nut between two arms of a nutcracker such nutcracker tectonics led to a series of kinematically distinct deformation stages initially internal portions of the orogen flowed northwards then substantial crustal thickening occurred in the orogen s interior and the deformation front migrated outwards producing thrust belts that overlapped the internal margins of the craton with continued closure space in the enclave became restricted and the orogen s interior underwent lateral escape to the south late stage extensional collapse triggered both production of late to post collisional granites and exhumation of high grade rocks from mid crustal levels

the granulite facies rocks of the northern segment of the ribeira belt eastern minas gerais se brazil abstract granulite rocks are exposed in eastern minas gerais brazil its early neoproterozoic evolution is characterised by a history of an active continental margin including the accretion of suspect terranes the manhuacu terrane is one of those which is represented by a granitic continental plutonic arc and terrigeneous metasediments reflecting a continental margin a metasedimentary gneiss belt at this margin with shallow to deep marine clastic lithologies as well as metavolcanic and metaplutonic mafic rocks was interpreted as an extensive tectonic segment with suspect development in a back arc setting fragments of a volcanic arc are identified and interpreted as an evidence for a probable island arc domain the granulites occur as massive rocks as well as high grade gneisses and show lithological structural and metamorphic attributes consistent with their host belt type in the western portion granulites derived from sedimentary protoliths have been deposited deformed and metamorphosed together with the mafic intrusions and as well as with their crystallization regional uplift exposed these rocks probably immediately after the metamorphism in these belts the metamorphic grade is not uniform especially where uplifting has exposed oblique cross sections over the granulitic rocks geothermobarometric calculations indicate that the granulites has been generated under t conditions between 800 and 990 50 c and from medium 4 8 kb to relatively high 10 0 kb pressures

sm nd and sr isotope fingerprinting of iron mining tailing deposits spilled from the failed samarco fundao dam 2015 accident at mariana se brazil abstract this work presents the first sm nd and sr isotope tims data on the fine grained fraction 3 of a quartz and iron oxide rich slurry composed of water fine sand and silt that flowed into the gualaxo do norte and carmo rivers and eventually along the whole doce river samples were collected between 5 and 80 km downstream from the fundao dam along the santarem creek and the gualaxo do norte and carmo rivers xrd analyses show that samples are 90 composed of quartz and iron oxides hematite goethite and magnetite with minor phyllosilicates kaolinite and mica owing to sediment transport processes heavy hematite goethite magnetite to light quartz phyllosilicates mineral fractionation is observed as with xrd data major and trace element compositions also closely match those of the original paleoproterozoic caue formation bif iron ore the studied samples yielded nd between 17 0 and 19 7 pptt part per ten thousand with the exception of one sample with nd of 23 2 pptt strontium 87 sr 86 sr ratios show variability between 0 7351 and 0 7729 the t dm ages scatter between 1 94 ga and 2 75 ga with a negative correlation with phyllosilicate contents indicating that the latter has preferential provenance from younger more juvenile sources than the caue fm itabirites this interpretation is corroborated by two component mixing models of nd and sr isotope ratios where the nd sr isotopic signatures of the studied samples are compatible with 98 of the caue fm itabirite component mixed with a neoproterozoic juvenile mafic rocks component such as those from the ophiolitic assemblages of the distal macaubas group or tholeiitic mafic rocks of the pedro lessa suite the reported sm nd and sr isotope compositions closely match those of the original iron ore and contrast with either those of the upriver or downriver precambrian to ordovician bedrock units the firstly defined isotope signature can thus be potentially used as a proxy for ongoing suspended sediment dispersion studies farther downstream along the doce river and in adjacent marine environment

antarctic bottom water production and export by tides in the ross sea 1 current measurements in the western ross sea show that antarctic bottom water is produced at the outer edge of the continental shelf by tidal stirring of antarctic surface water circumpolar deep water and shelf water current amplitudes during spring tides are greater than 1 m s sufficient to carry circumpolar deep water onto the shelf from offshore and stir at least the lower portion of the water column to a nearly homogeneous mixture the antarctic bottom water produced every day during spring tides does not appear to have a seasonal signal its export rate is estimated to be 1 95 1 85 10 6 m 3 s

the effect of atmospheric forcing resolution on delivery of ocean heat to the antarctic floating ice shelves abstractoceanic melting at the base of the floating antarctic ice shelves is now thought to be a more significant cause of mass loss for the antarctic ice sheet than iceberg calving in this study a 10 km horizontal resolution circum antarctic ocean sea ice ice shelf model based on the regional ocean modeling system roms is used to study the delivery of ocean heat to the base of the ice shelves the atmospheric forcing comes from the era interim reanalysis 80 km resolution and from simulations using the polar optimized weather research and forecasting model 30 km resolution where the upper atmosphere was relaxed to the era interim reanalysis the modeled total basal ice shelf melt is low compared to observational estimates but increases by 14 with the higher resolution winds and just 3 with both the higher resolution winds and atmospheric surface temperatures the higher resolution winds lead to more heat being delivered to the ice shelf cavities from the adjacent ocean and an increase in the

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

eddy mediated transport of warm circumpolar deep water across the antarctic shelf break the antarctic slope front asf modulates ventilation of the abyssal ocean via the export of dense antarctic bottom water aabw and constrains shoreward transport of warm circumpolar deep water cdw toward marine terminating glaciers along certain stretches of the continental shelf particularly where aabw is exported density surfaces connect the shelf waters to the middepth circumpolar deep water offshore offering a pathway for mesoscale eddies to transport cdw directly onto the continental shelf using an eddy resolving process model of the asf the authors show that mesoscale eddies can supply a dynamically significant transport of heat and mass across the continental shelf break the shoreward transport of surface waters is purely wind driven while the shoreward cdw transport is entirely due to mesoscale eddy transfer the cdw flux is sensitive to all aspects of the model s surface forcing and geometry suggesting that shoreward eddy heat transport may be localized to favorable sections of the continental slope

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

archean and paleoproterozoic crust of the sao francisco craton bahia brazil geodynamic features abstract recent geological geochronological and isotopic studies allow the identification of four important crustal segments in the basement of the sao francisco craton in bahia the oldest is the gaviao block in the wsw part of the studied area and comprises granitic granodioritic and migmatitic continental crust including remnants of 3 4 ga ttgs which are amongst the oldest rocks in south america and are associated with archean greenstone belts the youngest segment is exposed in the itabuna salvador curaca belt which extends from se bahia along the atlantic coast to salvador then northwards into ne bahia it is mainly composed of a low k calc alkaline plutonic suite and also contains strips of intercalated metasediments and ocean floor back arc basin gabbro and basalt in the ssw part of the area the jequie block comprises granulitic migmatites with inclusions of supracrustal rocks intruded by many charnockite plutons in the ne the serrinha block is composed of orthogneisses and migmatites which form the basement for paleoproterozoic greenstone belts during the paleoproterozoic transamazonian cycle these four crustal segments collided resulting in the formation of an important mountain belt the regional metamorphism resulting from the crustal thickening associated with the collision occurred at around 2 0 ga major mineralizations were formed during the evolution of the four archean blocks and also during and after the paleoproterozoic collision

stronger ocean circulation and increased melting under pine island glacier ice shelf the ice shelf buttressing antarctica s pine island glacier has been melting rapidly observations taken between 1994 and 2009 show that meltwater production has increased by about 50 since 1994 as a result of a stronger circulation below the ice shelf

petrogenesis of the orthogneisses of the mantiqueira complex central ribeira belt se brazil an archaean to palaeoproterozoic basement unit reworked during the pan african orogeny abstract the occidental terrane of the central segment of the brasiliano pan african ribeira belt comprises two crustal scale thrust sheets andrel ndia and juiz de fora domains taken as reworked neoproterozoic products of the sao francisco cratonic margins pre 1 8 ga orthogneisses and associated rocks of the mantiqueira complex comprise the basement for rocks of the andrel ndia depositional cycle within the andrel ndia tectonic domain geochemical data indicate that the mantiqueira complex comprises rocks that can be grouped as follows intermediate to acid calc alkaline rocks and a transitional basaltic series on the basis of quantitative analysis of the lithogeochemical data these lithotypes cannot be related statistical and or petrological criteria made it possible to define suites and or groups within each one of those units and to constrain petrogenetic models based mostly on their ree data simple least square regression analysis indicates that the basic rocks are unlikely to constitute a single suite themselves the results of the geochemical modelling presented in this work suggest that crustal partial melting rather than fractional crystallisation is the most likely petrogenetic process associated with the rocks of the mantiqueira complex the partial melting processes might have taken place under oxidising conditions typical of tectonic settings associated with the generation of calc alkaline rocks

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

paleomagnetism of 1 79 ga para de minas mafic dykes testing a sao francisco congo north china rio de la plata connection in columbia abstract paleogeographic connections between sao francisco congo north china and rio de la plata cratons through the paleoproterozoic have been proposed on the basis of geological and paleomagnetic data we conducted new paleomagnetic analyses for mafic dykes of the 1790 ma para de minas swarm occurring in the southern sao francisco craton the data revealed south southwestern low inclination magnetic directions after alternating field af and thermal demagnetization providing a paleomagnetic pole at 39 8 s 196 8 e a95 17 0 the characteristic remanent magnetization is interpreted as a thermo remanent magnetization carried by stable pseudo single domain magnetite grains being acquired during the cooling of the dykes at 1790 ma as attested by a positive baked contact test performed on one of the dykes the new pole in conjunction with 1790 1750 ma paleomagnetic poles available for other blocks allowed an improved reconstruction of columbia nuna supercontinent at this time frame laurentia baltica siberia proto amazonia west africa and proto australia were positioned as in previously proposed models the main difference from our reconstruction concerns the link of the sao francisco congo north china and rio de la plata cratons implying that much of the columbia supercontinent had already agglutinated around 1850 1800 ma ago this configuration is consistent with the onset of eventual taphrogenic episodes over most blocks accompanied by the emplacement of mafic dyke swarms and granitic intrusions at 1790 1750 ma

insights into spatial sensitivities of ice mass response to environmental change from the searise ice sheet modeling project i antarctica atmospheric oceanic and subglacial forcing scenarios from the sea level response to ice sheet evolution searise project are applied to six three dimensional thermomechanical ice sheet models to assess antarctic ice sheet sensitivity over a 500 year timescale and to inform future modeling and field studies results indicate i growth with warming except within low latitude basins where inland thickening is outpaced by marginal thinning ii mass loss with enhanced sliding with basins dominated by high driving stresses affected more than basins with low surface slope streaming ice and iii mass loss with enhanced ice shelf melting with changes in west antarctica dominating the signal due to its marine setting and extensive ice shelves cf minimal impact in the terre adelie george v oates and victoria land region of east antarctica ice loss due to dynamic changes associated with enhanced sliding and or sub shelf melting exceeds the gain due to increased precipitation furthermore differences in results between and within basins as well as the controlling impact of sub shelf melting on ice dynamics highlight the need for improved understanding of basal conditions grounding zone processes ocean ice interactions and the numerical representation of all three key points sensitivity study of antarctica to atmospheric oceanic and subglacial forcings different sectors of antarctica are vulnerable to the forcings atmospheric forcing lead to a growth but dynamic forcing lead to a mass loss 2013 american geophysical union all rights reserved

the complex tale of mantiqueira and juiz de fora a comment on eoarchean to neoproterozoic crustal evolution of the mantiqueira and the juiz de fora complexes se brazil petrology geochemistry zircon u pb geochronology and lu hf isotopes abstract in a recent volume of precambrian research vol 323 pp 82 101 kuribara et al 2019 published a paper on the eoarchean to neoproterozoic evolution of the mantiqueira and juiz de fora complexes of se brazil in this work kuribara et al 2019 suggest that the complexes were previously indicated to be part of the neoproterozoic to cambrian brasiliano orogeny and that the results of their work instead show that these complexes are fragments of archaean crust that accreted during the 590 560 ma brasiliano orogeny kuribara et al 2019 also present conventional thermobarometry for both complexes that they interpret represents the single metamorphic event that they obtain zircon u pb age data for from the juiz de fora complex no metamorphic ages were obtained from the mantiqueira complex instead they have used the metamorphic ages that many workers have obtained from the mantiqueira province in this comment we show that the archaean crustal input in the mantiqueira complex has long been known and the juiz de fora complex has long been considered a palaeoproterozoic ocean arc the mantiqueira complex records a polymetamorphic history with high grade metamorphism occurring at ca 2020 1940 ma and a later amphibolite facies brasiliano overprint at 580 540 ma the mantiqueira province and mantiqueira complex are different geological entities and while the mantiqueira complex is affected by the brasiliano event and occurs within the mantiqueira province the use of metamorphic ages from the mantiqueira province is not appropriate for the mantiqueira complex finally we show that the data presented by kuribara et al 2019 actually fits in with the most recent version of the model for the formation of the two complexes

stabilization of the southern portion of the sao francisco craton se brazil through a long lived period of potassic magmatism abstract although the southern portion of the sao francisco craton in southeast brazil encompasses one of the largest segments of meso to neoarchaean crust in the south american plate there is little understanding of the processes leading to cratonization of this region our combined field and u pb age data show that the crust experienced massive intrusions of potassic k rich granitoids between 2750 and 2600 ma and that this magmatic event marked the beginning of a fundamental change in the tectonics of the terrain with the ensuing billion years being dominated by the deposition of a series of thick clastic and chemical sedimentary successions thus deep crustal partial melting and subsequent transport and intrusion of these granites in the upper crust is a likely mechanism by which this segment of the sao francisco crust attained buoyancy to survive recycling regional mapping indicates that the potassic granitoids are distributed over an area of 25 000 km 2 and are related to one of the most prolific periods of potassic magmatism in the craton la icp ms and shrimp u pb data from 16 samples of potassic granitoids together with published tims ages suggest a long lived period of magmatism from 2750 to 2700 ma and a small pulse of granite crystallisation at ca 2612 ma the u pb shrimp and la icp ms data also indicate that the archaean granitoids do not record evidence of u pb zircon resetting our interpretation is that partial melting and transport of granitoid melts rich in heat producing elements to the upper crust gave rise to a thermally stable lower crust and that this lower crustal segment in the craton area became sufficiently refractory and resistant to further partial melting

zircon inheritance in diatexite granodiorites and its consequence on geochronology a case study in lusatia and the erzgebirge saxo thuringia eastern germany abstract we used detailed investigations of zircon morphology and internal structures for the interpretation of zircon age data of diatexite migmatites the fine and medium grained varieties of cadomian granodiorites from lusatia and the erzgebirge are interpreted on the base of their geological geochemical and isotope characteristics as well as zircon populations as migmatites where no segregation of melt from residuum occurred whereas coarse grained varieties contain a large proportion of new formed zircons with a limited age range 540 530 ma most zircons in medium and especially fine grained granodiorites seem to be inherited from their source rock with only a small proportion of new zircon material in form of rare single grains or overgrowths therefore we consider mean evaporation zircon ages from these rocks as mixed ages consequently the formerly inferred age span of magmatic activity from 587 17 to 542 9 ma and the interpretation of three successive magmatic episodes kroner et al geol rundsch 83 1994 357 reported values of 585 563 and 542 ma have to be reconsidered as a mixture of two successive magmatic events i the late cadomian event about 540 530 ma that formed the granodiorites and ii a former magmatic event about 580 570 ma in the source indicated by inherited zircons