endolithic biodegradation of cool water skeletal carbonates on scott shelf northwestern vancouver island canada abstract biodegradation of shell material is widespread in the cool water skeletal carbonate deposits on scott shelf northwestern vancouver island and is especially evident in the large aragonitic bivalves glycymeris and humilaria major primary sediment contributors ten types of endolithic microborings have been identified in the shells including representatives of green algae e g ostreobium quekettii blue green algae e g plectonema terebrans scytonema sp fungi bacteria and clionid sponges as well as macroborings of phoronids polychaetes and naticid gatropods microcrystalline carbonate is not precipitated in vacated bores boring physically weakens the shells rendering them more prone to mechanical abrasion during sediment transport and bioturbation and to biological abrasion by grazing benthos tumbling experiments demonstrate that the rate of carbonate mud production is much greater for bored as compared to fresh bivalve shells and that mud production rates decrease with tumbling time because most endolithic microborings are confined to the periphery of grains boring also increases significantly the porosity and surface area of skeletal grains and destroys their organic matrix making them susceptible to maceration and dissolution on cool water shelves fostered by the generally low rates of carbonate production and accumulation many aragonitic bivalve shells on scott shelf have become thoroughly degraded through a combination of endolithic microboring maceration and dissolution within about 1000 years in ambient sea water in geologic terms such selective taphonomic loss of skeletal material may be considerable in ancient temperate shelf limestones and should be evaluated when interpreting their paleoecology and paleoenvironments

tropical sea surface temperatures for the past four centuries reconstructed from coral archives most annually resolved climate reconstructions of the common era are based on terrestrial data making it a challenge to independently assess how recent climate changes have affected the oceans here as part of the past global changes ocean2k project we present four regionally calibrated and validated reconstructions of sea surface temperatures in the tropics based on 57 published and publicly archived marine paleoclimate data sets derived exclusively from tropical coral archives validation exercises suggest that our reconstructions are interpretable for much of the past 400 years depending on the availability of paleoclimate data within and the reconstruction validation statistics for each target region analysis of the trends in the data suggests that the indian western pacific and western atlantic ocean regions were cooling until modern warming began around the 1830s the early 1800s were an exceptionally cool period in the indo pacific region likely due to multiple large tropical volcanic eruptions occurring in the early nineteenth century decadal scale variability is a quasi persistent feature of all basins twentieth century warming associated with greenhouse gas emissions is apparent in the indian west pacific and western atlantic oceans but we find no evidence that either natural or anthropogenic forcings have altered el nino southern oscillation related variance in tropical sea surface temperatures our marine based regional paleoclimate reconstructions serve as benchmarks against which terrestrial reconstructions as well as climate model simulations can be compared and as a basis for studying the processes by which the tropical oceans mediate climate variability and change

effects of rheology and mantle temperature structure on edge driven convection implications for partial melting and dynamic topography abstract edge driven convection which affects partial melting intraplate volcanism and dynamic topography is small scale convection that occurs along a lithospheric keel with a sharp contrast in lithospheric thickness various factors including rayleigh number lateral mantle temperature heterogeneity and geometry of the keel influence the edge driven convection and the correlation between edge driven convection and surface expressions dynamic topography and volcanism is complicated we performed a finite element study to quantify the effects of these factors on dynamic topography and partial melting we found that the dynamic topography is more prominent when a strong edge driven convection cell develops which corresponds to homogeneous mantle temperatures and the absence of mantle wind in contrast the development of edge driven convection cells and dynamic topography near the lithospheric keel are hindered when the mantle temperature is strongly heterogeneous laterally varying 280 k this indicates that a large lateral contrast in mantle temperature results in a strong mantle wind that may prevent the development of edge driven convection cells an increase in the rayleigh number results in more vigorous convection and enhances partial melting our study shows that the location of volcanic activity at craton edges and passive margins can be reproduced in models with weakly heterogeneous mantle temperature for given mantle viscosity the existence of a strong mantle wind e g related to subducting slabs or mantle plumes may inhibit the formation of an edge driven convection cell and its related partial melt near a lithospheric keel however mantle conditions with weak temperature heterogeneity 17 1019 pa s which corresponds to the rayleigh number of 1 8 106 do not induce partial melts despite the development of edge driven convection cells our model parametrized the condition and location of edge driven convection cells and partial melts which can contribute to understanding anomalous intraplate volcanisms such as in jeju island south of the korean peninsula and the tanzania craton near the east african rift

interannual modulation of east african early short rains by the winter arctic oscillation in the present study we analyzed the interannual linkage between the boreal winter arctic oscillation ao and east african early short rains when the indian ocean dipole and el nino southern oscillation variance are excluded by linear regression the boreal winter ao index is significantly correlated with the october east african precipitation over the domain of 5 n 5 s and 35 45 e for the period 1979 2014 r 0 46 the upper ocean heat content likely acts as a medium that links the ao and east african precipitation significant subsurface warming and positive upper ocean heat content anomalies occur over the western indian ocean during the autumn following positive ao winters which enriches the atmospheric moisture intensifies convection and enhances precipitation oceanic dynamics play a key role in causing this subsurface warming winter ao related atmospheric circulation creates anomalous wind stress which forces a downwelling oceanic rossby wave between 60 75 e and 5 10 s where the thermocline significantly deepens this rossby wave propagates westward and accompanies significant subsurface warming along the thermocline the rossby wave arrives at the western indian ocean in the late summer significantly warming the region to the west of 55 e at a depth of 60 100 m this warming remains significant through october correspondingly the upper ocean heat content significantly increases by approximately 2 3 108 j m 2 in the region west of 60 e between 5 and 10 s the role of these oceanic dynamics in linking the winter ao and anomalous subsurface warming was tested by numerical experiments with an oceanic general circulation model the experiments were performed with the forcing of ao related wind stress anomalies over the indian ocean in the winter the oceanic rossby wave generated in the central indian ocean during boreal winter the consequent subsurface warming and the anomalous upper ocean heat content in october over the western indian ocean were all adequately reproduced the winter ao can serve as a precursor of east african short rain anomalies

hercynian structure of the axial zone of the pyrenees the aran valley cross section spain france abstract in the axial zone of the pyrenees palaeozoic rocks crop out with superimposed hercynian and alpine deformation the hercynian structures present two domains infrastructure and suprastructure a complete crosssection of the central part of the axial zone of the pyrenees is presented in which hercynian structures of both domains can be observed in the aran valley cross section the infrastucture corresponds to the garona dome domain where the main hercynian structures are north vergent recumbent folds with an associated mainly flatlying foliation s 2 in the garona dome domain the peak of the medium to high grade metamorphism is simultaneous with the main hercynian structures the aran valley and noguera ribagorca areas correspond to the suprastructure in these domains the main hercynian structures are upright folds with an associated mainly steep lying foliation s 3 in these suprastructural domains low grade syn s 3 metamorphism is present this crosssection relates the structures of the infra and the suprastructure suggesting a deformational sequence for the axial zone of the pyrenees this sequence is deduced from the fact that the north vergent folds observed in the garona dome are earlier than the main structures of the suprastructure the boundary of the garona dome and the suprastructure is a decollement level observed at the base of the silurian the deformational sequence proposed here provides some constraints for models of hercynian evolution and the emplacement of the alpine structures of the pyrenees

reconstructing east african rainfall and indian ocean sea surface temperatures over the last centuries using data assimilation the relationship between the east african rainfall and indian ocean sea surface temperatures ssts is well established the potential interest of this covariance to improve reconstructions of both variables over the last centuries is examined here this is achieved through an off line method of data assimilation based on a particle filter using hydroclimate related records at four east african sites lake naivasha lake challa lake malawi and lake masoko and ssts related records at six oceanic sites spread over the indian ocean to constrain the last millennium ensemble of simulations performed by cesm1 skillful reconstructions of the indian ssts and east african rainfall can be obtained based on the assimilation of only one of these variables when assimilating pseudo proxy data deduced from the model cesm1 the skill of these reconstructions increases with the number of particles selected in the particle filter although the improvement becomes modest beyond 99 particles when considering a more realistic framework the skill of the reconstructions is strongly deteriorated because of the model biases and the uncertainties of the real proxy based reconstructions however it is still possible to obtain a skillful reconstruction of ssts over most of the indian ocean only based on the assimilation of the six sst related proxy records selected as far as a local calibration is applied at all individual sites this underlines once more the critical role of an adequate integration of the signal inferred from proxy records into the climate models for reconstructions based on data assimilation

the stress field in europe optimal orientations with confidence limits this article has been accepted for publication in geophysical journal international the authors 2003 published by oxford university press on behalf of the royal astronomical society all rights reserved

interaction between the enso and the asian monsoon in a coral record of tropical climate the oxygen isotopic composition of a banded coral from the western equatorial indian ocean provides a 150 year long history of the relation between the el nino southern oscillation enso phenomenon and the asian monsoon interannual cycles in the coral time series were found to correlate with pacific coral and instrumental climate records suggesting a consistent linkage across ocean basins despite the changing frequency and amplitude of the enso however decadal variability that is characteristic of the monsoon system also dominates the coral record which implies important interactions between tropical and midlatitude climate variability one prominent manifestation of this interaction is the strong amplitude modulation of the quasi biennial cycle

atmospheric hydrospheric mechanisms of climate anomalies in the western equatorial indian ocean atmosphere ocean mechanisms of rainfall anomalies at the coast of eastern africa are studied using long term ship observations in the indian ocean surface current measurements subsurface casts upper air analyses by the european centre for medium range weather forecasts rain gauge series in eastern africa and india and an index of the southern oscillation so the high so phase being defined by anomalously high low pressure at tahiti darwin the causalities of precipitation anomalies at the coast of eastern africa differ for the two rainy seasons centered on april may and october november and only the latter is strongly related to the so in the high so phase april may pressure is low over the entire indian ocean domain whereas in october november pressure is high in the west and low in the east concomitantly surface waters are anomalously cold in the west and strong westerlies sweep the equatorial zone of the indian ocean eastern african rainfall anomalies are related to the so through a combination of cooperative mechanisms that function most effectively in the boreal autumn rainy season of eastern africa 1 equatorial westerly winds are conducive to lower tropospheric divergence over equatorial east africa and in the high so phase these are accelerated especially in october november owing to the anomalous eastward pressure gradient 2 the equatorial westerly winds drive the eastward equatorial jet in the upper hydrosphere which entails cold water upwelling in the western extremity of the basin where sea surface temperature further hydrostatically affects the zonal pressure gradient and thus feeds back into the equatorial westerly winds 3 in addition cold water anomalies in the western indian ocean most pronounced in october november during the high so phase also suppress convection 4 in the high so phase the indian summer monsoon tends to be strong leaving behind an anomalously cold western indian ocean which in turn feeds into mechanisms 1 to 3 the eastward equatorial jet thus has a role to play in feedback mechanisms contributing to the anomalies of the boreal autumn rains at the coast of eastern africa

bathymetric zonation of modern microborers in dead coral substrates from new caledonia implications for paleodepth reconstructions in holocene corals abstract microboring endoliths were studied in dead modern corals collected at various depths and in growth position on la surprise atoll in new caledonia eight taxa of microborers were regularly observed three cyanobacteria hyella caespitosa mastigocoleus testarum and plectonema terebrans two chlorophytes ostreobium quekettii and phaeophila dendroides and three fungal forms dodgella priscus and two unidentified fungi the relative abundance of each taxon was determined in the modern corals throughout the studied sampling interval from 0 down to 40 m water depth this allowed us to propose for the first time a bathymetric model based on microendolith assemblages colonizing in situ hard substrates of corals in this model the occurrence of the cyanobacteria hyella and mastigocoleus indicates a bathymetric range from 0 down to a water depth of 3 and 6 m respectively the chlorophyta o quekettii associated with the cyanobacterium p terebrans and fungi is dominant from 10 to 40 m depth which is the lower limit of our sampling the distribution ranges of individual taxa observed in the dead coral substrates from new caledonia are much narrower than those reported in the literature for other substrates the bathymetric model based on distribution of microborers in modern corals was then applied to interpret the trace assemblages of microborers observed in holocene corals collected by drilling on two reef sites of new caledonia la surprise islet in the vicinity of the sampling sites of the modern corals and the barrier reef of bayes on the ne coast of grande terre the paleodepth interpretations performed at various levels along the cores allow identification of several shallowing upward sequences during the last 7000 years of reef growth in new caledonia differences in the thickness of these sequences between la surprise and bayes sites were interpreted as differences in the space available for accommodation between the two sites in turn related to the differential subsidence that affected new caledonia during holocene times the use of the microendolith trace assemblages in paleodepth reconstructions of holocene reefs from new caledonia allowed detection of relative sea level variations finer than those deduced from changes in coralgal assemblages

paired coral sr ca and δ18o records from the chagos archipelago late twentieth century warming affects rainfall variability in the tropical indian ocean understanding the relationship between sea surface temperature sst and precipitation is a significant challenge for climate models particularly for the tropics here we present a new monthly coral sr ca record from the tropical indian ocean chagos archipelago that extends from 1950 to 1995 the coral sr ca ratio shows a stationary relationship with local sst and documents a warming of 0 3 c since 1950 previous work has shown that the 18 o values measured in the same coral core provide a proxy record of precipitation in the tropical indian ocean the coral 18 o record shows a nonstationary relationship with local sst and a correlation between 18 o and sst only emerges in the 1970s it was proposed that this nonstationary behavior is due to an increase in mean ssts in the tropical indian ocean during the 1970s ssts reached a critical threshold 28 5 c beyond which small sst anomalies can have a significant impact on atmospheric convection as a result the covariance between sst and precipitation in the tropical indian ocean increased our new sr ca data confirm that the warming of the indian ocean during the late twentieth century affects atmospheric convection and rainfall variability moreover our proxy data show that the relationship between sst and precipitation is nonlinear and characterized by threshold behavior

african hydroclimatic variability during the last 2000 years abstract the african continent is characterised by a wide range of hydroclimate regimes ranging from humid equatorial west africa to the arid deserts in the northern and southern subtropics the livelihoods of much of its population are also vulnerable to future climate change mainly through variability in rainfall affecting water resource availability a growing number of data sources indicate that such hydroclimatic variability is an intrinsic component of africa s natural environment this paper co authored by members of the pages africa 2k working group presents an extensive assessment and discussion of proxy historical and instrumental evidence for hydroclimatic variability across the african continent spanning the last two millennia while the african palaeoenvironmental record is characterised by spatially disjunctive datasets with often less than optimal temporal resolution and chronological control the available evidence allows the assessment of prominent spatial patterns of palaeomoisture variability through time in this study we focus sequentially on data for six major time windows the first millennium ce the medieval climate anomaly 900 1250 ce the little ice age 1250 1750 ce the end of the lia 1750 1850 ce the early modern period 1850 1950 and the period of recent warming 1950 onwards this results in a continent wide synthesis of regional moisture balance trends through history allowing consideration of possible driving mechanisms and suggestions for future research

zonal circulations over the equatorial indian ocean abstract the ncep ncar 1958 97 upper air dataset and surface observations have been analyzed for evidence of zonal vertical circulations along the indian ocean equator and their role in climatic variability the long term mean upper tropospheric circulation is dominated in boreal winter by divergent outflow from the southern indian ocean northwestward into southern asia and in summer from southern asia southwestward into the southern hemisphere in boreal autumn only divergent easterlies blow from indonesia along the equator into an upper tropospheric convergence band over east africa and only then a closed zonal vertical circulation cell materializes along the indian ocean equator between the centers of ascending motion over indonesia and of subsidence over equatorial east africa and featuring westerlies in the lower layers the boreal autumn zonal vertical circulation varies interannually a regime of intense circulation features accelerated equatorial surface westerlies enhanced subsidence and d

rapid 20th century warming in the caribbean and impact of remote forcing on climate in the northern tropical atlantic as recorded in a guadeloupe coral we have generated 104 year long 1895 1999 monthly 18o and sr ca time series from a fast growing diploria strigosa coral core drilled off guadeloupe island lesser antilles coral sr ca reliably records interannual to decadal surface air temperature sat variations in the region and shows a pronounced warming of approximately 1 5 c since 1950 with the strongest warming 1 2 c occurring since 1975 this warming is also evident in sat measured at guadeloupe which ends in 1951 thus our sr ca series extends the air temperature record by 56 years we find that the past few decades are the warmest years over the entire period of record the accelerated warming since 1950 is accompanied by a pronounced decrease in regional precipitation this dampens the warming signal indicated by coral 18o which is too low only 0 7 0 8 c since 1951 consistently 18osw estimated from the coral proxies also shows a strong decrease since 1950 our data suggest an inverse relationship between sat and precipitation i e warmer and drier for the latter half of the 20th century with the strongest trends since the mid 1970s this is consistent with recent observational and model data which report that while over the tropical oceans rainfall has increased due to an increase in sea surface temperatures precipitation over land regions is reduced a continuation of this warming and drying trend over caribbean land regions would have severe societal consequences especially in the context of anthropogenic warming the el nino southern oscillation enso and the north atlantic oscillation nao are the two major climate modes affecting large scale sst variability in the northern tropical atlantic both sr ca and 18o show a close relationship to enso and the nao a quantitative comparison between extremes in mean march may coral 18o and the nino3 and nao indices imply that climate variability in the northern tropical atlantic is mainly forced by tropical pacific and north atlantic variability spectral analysis suggests that the relative importance of enso and the nao is frequency dependent with enso dominating at interannual and the nao dominating at interdecadal time scales

tectonic levels in the palaeozoic basement of the pyrenees a review and a new interpretation reply abstract two different structural domains developed during the main hercynian deformation events were recognized by de sitter zwart in the hercynian basement of the central pyrenees a deep seated level infrastructure made of medium to high grade metasediments and orthogneisses with dome shaped gently dipping foliations contrasts with a shallow level suprastructure of low to very low grade metasediments with rather steep foliations since the recognition of this structural zonation different interpretations have been proposed disagreements concern timing of deformation and tectonic regime considered to be prevalent of the structural development of each tectonic level the proposed interpretation regards the progressive development and differentiation of both structural domains and considers the following factors to be significant for the structural arrangement of the pyrenean segment of the hercynian belt an increase with depth of the horizontal shear component of deformation related to tangential and transcurrent tectonics a marked inhomogeneity of deformation and penetrability of related foliations and the gradual evolution from an earlier compressive crustal shortening event to a late transpressive event responsible for crustal shortening and trend parallel stretching

hercynian low pressure high temperature regional metamorphism and subhorizontal foliation development in the canigou massif pyrenees france evidence for crustal extension a detailed study has been made of the structural and metamorphic history of part of the hercynian low pressure high temperature regional metamorphic terrane exposed in the canigou massif france microtextural relations between and compositional zoning within porphyroblast phases in pelitic rocks indicate that the pressure temperature time p t t trajectory followed by the massif during metamorphism involved decompression under prograde and retrograde conditions clockwise p t t trajectory the geometric relations between inclusion trails within these porphyroblasts and the structures in the adjacent matrix indicate that metamorphism was synchronous with the development of the regional subhorizontal foliation s3 the s3 foliation formed in response to noncoaxial bulk strain the absence of a marked hiatus in sedimentation in the pyrenean region during hercynian metamorphism and deformation and the widespread preservation of low grade hercynian metasedimentary rocks suggest that low p high t metamorphism occurred in an extensional tectonic environment and that extension manifested itself in asymmetric top to the northwest shear during d3

foliation development and refraction in metamorphic rocks reactivation of earlier foliations and decrenulation due to shifting patterns of deformation partitioning reactivation of early foliations accounts for much of the progressive strain at more advanced stages of deformation its role has generally been insufficiently emphasized because evidence is best preserved where por phyroblasts which contain inclusion trails are present reactivation occurs when progressive shearing operating in a synthetic anastomosing fashion parallel to the axial planes of folds changes to a combination of coarse and fine scale zones of progressive shearing some of which operate antithetically relative to the bulk shear on a fold limb reactivation of earlier foliations occurs in these latter zones reactivation decrenulates pre existing or just formed crenulations generating shearing along the decrenulated or rotated pre existing foliation planes partitioning of deformation within these foliation planes such that phyl losilicates and or graphite take up progressive shearing strain and other minerals accom modate progressive shortening strain causes dissolution of these other minerals this results in concentration of the phyllosilicates in a simi lar but more penetrative manner to the for mation of a differentiated crenulation cleavage except that the foliation can form or intensify on a fold limb at a considerable angle to the axial plane of synchronous macroscopic folds reactivation can generate bedding parallel schistosity in multideformed and meta morphosed terrains without associated folds heterogeneous reactivation of bedding gen erates rootless intrafolial folds with sigmoidal axial planes from formerly through going struc tures reactivation causes rotation or refrac tion of axial plane foliations forming in the same deformation event causing reactivation in those beds or zones in which an earlier foli ation has been reactivated and results in destruction of the originally axial plane foli ation at high strains reactivation also provides a simple explanation for the apparently wrong sense but normally observed rotation of gar net porphyroblasts whereby the external foli ation has undergone rotation due to antithetic shear on the reactivated foliation alter natively the rotation of the external foliation can be due to its reactivation in a subsequent deformation event porphyroblasts with inclusion trails com monly preserve evidence of reactivation of earl ier foliations and therefore can be used to ident ify the presence of a deformation that has not been recognized by normal geometric methods because of penetrative reactivation reac tivation often reverses the asymmetry between pre existing foliations and bedding on one limb of a later fold leading to problems in the geo metric analysis of an area when the location of early fold hinges is essential the stretching lineation in a reactivated foliation can be rad ically reoriented potentially causing major errors in determining movement directions in mylonitic schistosities in folded thrusts geometric relationships which result from reactivation of foliations around porphyroblasts can be used to aid determination of the timing of the growth of porphyroblasts relative to deformation events other aspects of reac tivation however can lead to complications in timing of porphyroblast growth if the presence of this phenomenon is not recognized for example d grown porphyroblasts may be dis solved against reactivated s and hence appear to have grown syn d

dynamics of the surface wind field over the equatorial indian ocean the annual cycle and interannual variability of the equatorial westerlies over the indian ocean are examined in the context of the equations of motion using long term surface ship observations eastward pressure gradient along the equator may accelerate equatorial westerlies but the process is more intricate the south indian ocean trade winds can recurve in the southern hemisphere only with an eastward pressure gradient this is counteracted by the coriolis acceleration directed at right angles to the left of the motion with weak trades and strong eastward pressure gradient the flow can recurve at relatively high southern latitudes thus allowing a broad equatorial zone in which westerlies can develop in the annual cycle the southern indian ocean high and trade winds are closest to the equator and strongest in austral winter when however the eastward pressure gradient in the equatorial zone is also steepest accordingly the latitude of flow recurvature in the southern trade winds stays farthest away from the equator in boreal spring and autumn consequently the equatorial westerlies peak in these short transition seasons the boreal autumn equatorial westerlies are the surface manifestation of a powerful zonal circulation cell along the indian ocean equator the interannual variability of boreal autumn is characterized by weak westerlies accompanying a slack zonal pressure gradient and strong southern trade winds with recurvature near the equator such an ensemble of circulation departures is characteristic of abundant rainfall in east africa and deficient precipitation in indonesia copyright 2004 royal meteorological society

a model based test of accuracy of seawater oxygen isotope ratio record derived from a coral dual proxy method at southeastern luzon island the philippines 1 the oxygen isotope ratio in seawater 18osw is an important indicator of past hydroclimatic conditions in the tropics in this study we apply a dual proxy approach using 18o and sr ca in coral skeletons to estimate 18osw due to a lack of long term continuous observational data for 18osw a simplified one dimensional box model of the ocean surface associated with historical surface atmospheric data is used for comparison with coral derived 18osw record the atmospheric data consist of the precipitation and evaporation values together with their 18o compositions from the global isotope reanalysis data the model successfully reproduces a multidecadal time series for 18osw at southeastern luzon island the philippines for the period 1979 2001 r 0 57 p 0 01 the result suggests that the coral records are an accurate indicator of hydrological cycle changes at the site a discrepancy between the reproduction and the coral record in the wet season december february may be caused by seasonal variation in the depth of the mixed layer and upwelling since these factors are not accounted for in the model the reproduction is in good agreement with the coral records in the dry season april june implying that 18osw estimated using the coral dual proxy method is more robust at this time of year

hydrogeomorphic processes of thermokarst lakes with grounded ice and floating ice regimes on the arctic coastal plain alaska thermokarst lakes cover 20 of the landscape throughout much of the alaskan arctic coastal plain acp with shallow lakes freezing solid grounded ice and deeper lakes maintaining perennial liquid water floating ice thus lake depth relative to maximum ice thickness 1 5 2 0 m represents an important threshold that impacts permafrost aquatic habitat and potentially geomorphic and hydrologic behaviour we studied coupled hydrogeomorphic processes of 13 lakes representing a depth gradient across this threshold of maximum ice thickness by analysing remotely sensed water quality and climatic data over a 35 year period shoreline erosion rates due to permafrost degradation ranged from 0 2 m year in very shallow lakes 0 4 m up to 1 8 m year in the deepest lakes 2 6 m this pattern of thermokarst expansion masked detection of lake hydrologic change using remotely sensed imagery except for the shallowest lakes with stable shorelines changes in the surface area of these shallow lakes tracked interannual variation in precipitation minus evaporation p el with periods of full and nearly dry basins shorter term 2004 2008 specific conductance data indicated a drying pattern across lakes of all depths consistent with the long term record for only shallow lakes our analysis suggests that grounded ice lakes are ice free on average 37 days longer than floating ice lakes resulting in a longer period of evaporative loss and more frequent negative p el these results suggest divergent hydrogeomorphic responses to a changing arctic climate depending on the threshold created by water depth relative to maximum ice thickness in acp lakes copyright 2011 john wiley sons ltd

tracing the origin of arctic driftwood 1 arctic environments where surface temperatures increase and sea ice cover and permafrost depth decrease are very sensitive to even slight climatic variations placing recent environmental change of the high northern latitudes in a long term context is however complicated by too short meteorological observations and too few proxy records driftwood may represent a unique cross disciplinary archive at the interface of marine and terrestrial processes here we introduce 1445 driftwood remains from coastal east greenland and svalbard macroscopy and microscopy were applied for wood anatomical classification a multi species subset was used for detecting fungi and information on boreal vegetation patterns circumpolar river systems and ocean current dynamics was reviewed and evaluated four conifer pinus larix picea and abies and three deciduous populus salix and betula genera were differentiated species specific identification also separated pinus sylvestris and pinus sibirica which account for 40 of all driftwood and predominantly originate from western and central siberia larch and spruce from siberia or north america represents 26 and 18 of all materials respectively fungal colonization caused different levels of driftwood staining and or decay our results demonstrate the importance of combining wood anatomical knowledge with insight on boreal forest composition for successfully tracing the origin of arctic driftwood to ultimately reconstruct spatiotemporal variations in ocean currents and to better quantify postglacial uplift rates we recommend consideration of dendrochronologically dated material from many more circumpolar sites

evolution of the pannonian basin system 1 tectonics the carpathian arc formed during cretaceous to miocene time by continental collision between europe and smaller continental fragments following southward and westward subduction of ocean floor during the last stages of thrusting in the outer carpathians a set of discrete basins formed behind the carpathian loop these basins are regions of middle to late miocene extension and are connected to each other and to areas of coeval shortening in the outer carpathian thrust belt by a system of strike slip faults sinistral northeast trending and dextral northwest trending sets of conjugate shears reflect overall east west extension of the intra carpathian region during middle to late miocene time palinspastic reconstruction of the basins indicates about 100 50 km of east west extension across the intra carpathian region during this time we interpret the vienna basin which is superimposed partly on the flysch nappes of the outer west carpathians as the result of thin skinned extensional tectonics above a shallow detachment surface within the crust extension of upper crustal rocks above this detachment was probably accomodated by thrusting of the outermost nappes of the west carpathians over the european platform extension of basins farther inside the carpathian loop probably involved rocks at deeper crustal levels and within the upper mantle the most internally situated basins formed by extensional processes that involved the entire lithosphere thus the depth to which extension occurred seems to be closely related to the proximity of each basin to the active thrust front in the carpathians this can be related to the geometry of the subduction zone extension within the intra carpathian basins began first in the northernmost basins and migrated southward and eastward over a ten million year period palinspastic reconstruction of the basins at three different times during the miocene 17 5 16 5 and 13 0 ma predicts eastward migration of the zone of thrusting and shortening within the carpathian mountains to accomodate the synchronous eastward and southward migration of areas of extension from these reconstructions about 120 60 km of east west shortening is predicted across the outer east carpathians from about 17 5 ma until present both predictions are in good agreement with the timing and magnitude of shortening in the carpathian thrust belt as determined directly from rocks within the belt from this we infer a close relationship for middle to late miocene extension of the intra carpathian region and middle to late miocene crustal shortening within the outer carpathians during middle and late miocene time deformation of the pannonian fragment was dominated by extensional and wrench tectonics except along a narrow zone in the outer carpathian thrust belt middle and late miocene thrusting in the carpathians is interpreted as the result of simple shear caused by relative motion between europe and the overriding pannonian fragment at the subduction boundary rather than of regional compression of lithospheric rocks at depth the initiation of extensional tectonics within the intra carpathian region in middle miocene time can be related to reorganization of major fragment boundaries of the eastern european alpine system

paleobathymetric implications of microborings in tertiary strata of alaska usa abstract microboring algae bacteria and fungi that lived under non tropical conditions are abundantly present in four richly fossiliferous marine strata of paleocene to miocene age in alaska by comparing their boring trace communities with endolithic guide ichnocoenoses characterizing various photic zones which have been previously defined mainly in tropical and subtropical environments the alaska strata can be placed in bathymetric zones as follows the lower upper paleocene prince creek formation in the dysphotic zone the lower oligocene stepovak formation in the shallow euphotic zone shallow euphotic zone iii and the upper miocene tachilni formation in the deep euphotic zone these interpretations agree very well with bathymetric reconstructions inferred from other criteria a fourth formation the lower middle miocene narrow cape formation contains only heterotrophic microborers as if it had been deposited in the aphotic zone in contrast to previous reconstructions in this formation the periostracum of the mollusc shells is exceptionally well preserved this may explain the absence of boring algae because only heterotrophs can penetrate through organic shell layers the absolute depth ranges of these ichnocoenoses zones are inferred from their ranges in comparable latitudes of the modern north atlantic the most important features of bathymetrically controlled tropical and subtropical guide ichnocoenoses are also present at the non tropical alaskan sites although some boring algae that are widespread in tropical realms are absent

subtropical sst dipole events in the southern indian ocean sea surface temperature sst anomalies in the subtropical southern indian ocean show interannual dipole events that are seasonally phase locked to the austral summer a positive phase of the event is characterized by cold sst anomalies in the eastern part i e off australia and warm sst anomalies in the southwestern part south of madagascar such an event is found to produce above normal rainfall over many regions in south central africa the cooling of sst in the eastern part is mainly caused by the enhanced evaporation this is associated with stronger winds along the eastern edge of the subtropical high which is strengthened and shifted slightly to the south during the event on the other hand relative decrease in the seasonal latent heat loss due to reduced evaporation dominates the warming in the southwestern part evolution of such subtropical dipole events shows quite a contrast to that of the tropical dipole events discovered recently in the indian ocean

ferrous iron diffusion in ferro periclase across the spin transition we present first principle calculations on absolute diffusion rates of high and low spin ferrous iron in ferro periclase the diffusivity of high and low spin iron depends on the physical conditions pressure and temperature iron concentration and the value of the chosen hubbard u we also find that low spin iron swaps back to high spin during migration our results show that throughout the earth s lower mantle iron diffuses at a faster rate than magnesium up to an order of magnitude thus the effect of the spin transition only has a small impact on the rheology of periclase in the earth s mantle using reasonable vacancy concentrations we find that ferro periclase is much weaker than mgsio3 perovskite throughout the mantle we conclude therefore that ferro periclase controls the viscosity of the mantle in regions where it becomes interconnected such as regions of high strain around slabs or near plumes at very high pressures such as in super earths low spin iron diffusion is expected to become much slower than magnesium eventually making ferro periclase more viscous than pure periclase c 2010 elsevier b v all rights reserved

reconstructing seawater δ18o from paired coral δ18o and sr ca ratios methods error analysis and problems with examples from tahiti french polynesia and timor indonesia we compare several statistical routines that may be used to calculate delta o 18 and sss from paired coral sr ca and delta o 18 measurements typically the delta o 18 coral sst relationship is estimated by linear regression of coral delta o 18 vs sst if this method is applied evidence should be given that at a particular site sst and sss do not co vary in the tropical oceans sst and delta o 18 sw sss often co vary and this will bias the estimate of the regression slope of delta o 18 coral sst using a stochastic model we show that covariance leads to a bias in the coefficients of the univariate regression equations as the slope of the delta o 18 coral sst relationship has known we propose to insert this value for gamma 1 in the regression models this requires that the constants of the regression equations are removed to omit the constants we propose to center the regression equations i e to remove the mean values from the variables the statistical error propagation is calculated to assess our ability to resolve past variations in delta o 18 sw sss at tahiti we find that the combined analytical uncertainties of coral delta o 18 and sr ca equal the amplitude of the seasonal cycle of delta o 18 sw sss therefore we cannot resolve the seasonal cycle of sss at tahiti at timor the error of reconstructed delta o 18 sw sss is lower than the magnitude of seasonal variations of delta o 18 sw sss and the seasonal cycle of delta o 18 sw sss can be resolved c 2008 elsevier ltd all rights reserved

kinematics of orogenic collapse in the variscan pyrenees deduced from microstructures in porphyroblastic rocks from the lys caillaouas massif in the pyrenees a phase of bulk vertical shortening d3 is indicated by a horizontal crenulation cleavage s3 which is developed in a pre existing schistosity s2 porphyroblasts of the lys caillaouas massif regionally preserve 1 1 the initial pre d3 orientation of s2 in the form of a vertical and e w trending preferred orientation of their inclusion trails 2 2 a vertical l2 stretching lineation defined by the elongation of the inclusions these data are consistent with n s compression and crustal thickening during d2 the angle between the inclusion trails s2 i and the external schistosity s2 e records the subsequent rotation of s2 from vertical to gently dipping orientations at higher crustal levels s2 remained steep suprastructure and little d3 deformation is evidenced with depth d3 deformation progressively intensifies and zones can be distinguished with opposite dip directions of s2 opposite apparent porphyroblast rotation senses and opposite f3 crenulation asymmetries these micro structures on a n s section through the lys caillaouas and the garonne dome massifs record a regional partitioning of bulk coaxial vertical shortening this deformation partitioning was probably controlled by a not exposed gneiss dome which behaved relatively rigid as compared to its metasedimentary cover in zones of non coaxial d3 deformation s2 was extended reactivated and forms the dominant schistosity where d3 was locally more coaxial s2 was shortened isoclinally crenulated and s3 forms the macroscopic cleavage the fact that d3 extension in the lys caillaouas massif immediately followed d2 compression and that similar extension is recorded in large parts of the variscan foldbelt suggests gravitational collapse of a thickened orogen this is consistent with the flattening type of d3 strain recognized in a number of pyrenean variscan massifs peak high t low p metamorphic conditions coincide with the onset of orogenic extension when very little crustal thinning could have been accomplished yet this suggests that heat induced strain softening within the orogen may have triggered its collapse

an investigation of interannual rainfall variability in africa abstract interannual variations in african rainfall are examined using rotated principal component analysis pca applied to anomalies from the annual mean as well as seasonal anomalies the rotated pca loading patterns suggest several preferred continental scale rainfall anomaly patterns the dominant features of year to year variations in african rainfall appear to be the high spatial coherence of rainfall anomalies over large portions of the continent in addition several dipole regions that is adjacent regions which tend to experience rainfall anomalies of opposite sign are found and discussed one dipole region the sub saharan region appears to have a relationship with a characteristic atlantic sea surface temperature anomaly pattern during boreal summer during austral summer the tendency for a large scale dipole pattern in southeast africa is apparent as is an association of this pattern with the warm and cold phases of the el nin southern oscillation enso phenomenon normalized rainfal

anthropogenic ocean warming and acidification recorded by sr ca li mg δ11b and b ca in porites coral from the kimberley region of northwestern australia abstract the impact of climate changes on corals living in naturally extreme environments is poorly understood but crucial to longer term sustainability of coral reefs here we report century long temperature sr ca and li mg and calcifying fluid cf carbonate chemistry 11b and b ca records for a long lived 1919 to 2016 porites coral from the high thermally variable kimberley region of northwestern australia we investigate how increasing temperatures and ocean acidification are manifested in the carbonate chemistry of coral s cf and impacts of climate change on calcification using sr ca and li mg multiproxy we show that annual temperature in the nearshore kimberley exhibited a gradual increase 0 009 0 003 c yr from the 1920s onward however for the most recent years 2000 2015 more rapid summer warming 0 05 0 01 c yr are registered indicative of intensified warming despite that we find no significant trend for calcification rate of this coral over the past century as well as normal seasonal variability in coral s cf carbonate chemistry importantly the coral s ability to concentrate inorganic carbon seems to be affected by recent warming with reduced diccf observed during 2008 to 2015 while the minimally affected phcf acts to compensate the decreases of diccf with the calcification rate showing only slight decrease additionally we also find that ocean acidification has clearly led to the long term reduction in the ph of the cf

porphyroblast non rotation during crustal extension in the variscan lys caillaouas massif pyrenees abstract the dominant foliation s 2 in the variscan lys caillaouas massif central pyrenees france spain formed in a subvertical orientation during crustal thickening d 2 subsequent non coaxial crustal extension produced a subhorizontal crenulation cleavage s 3 whereby s 2 was folded and rotated andalusite staurolite cordierite and biotite porphyroblasts grew very early during this extension d 3 and included s 2 as straight curved and weakly crenulated inclusion trails these inclusion trails exhibit a strong subvertical preferred orientation which is independent of the local magnitude of d 3 strain the dip angle of the external main foliation s 2 or the aspect ratio and shape orientation of porphyroblasts this indicates that porphyroblasts did not rotate in the d 3 deformation field and hence preserve the orientation of s 2 at the time it was trapped in the porphyroblast relative to the bulk d 3 flow plane porphyroblasts could maintain a stable orientation in the d 3 flow due to complete accommodation of the bulk flow vorticity by heterogeneous shear strain the lack of vorticity of local volumes of zero shear strain such as porphyroblasts was balanced by concentration of shear strain in planar zones anastomosing around them it is likely that s 2 maintained a subhorizontal orientation throughout the d 3 crustal extension which would imply that porphyroblasts also remained stationary relative to the earth s surface during d 3 whereas s 2 in the deforming matrix experienced shear induced rotation a late brittle ductile folding event d 4 involving differential rigid block rotations dispersed the orientation of inclusion trails to some degree these late rotations could be corrected for by artificial unfolding of the f 4 folds

application of the ncar regional climate model to eastern africa 2 simulation of interannual variability of short rains we have applied the ncar regcm2 to the simulation of the interannual variability of precipitation over eastern africa for the short rains season by performing a set of experiments for the years 1982 to 1993 the model reproduced the observed interannual variability of precipitation in most of the years the results show that remote factors play a dominant role in determining the precipitation anomalies interannual variability of precipitation over tanzania is closely related to el nino events in their mature phase and sea surface temperature sst anomalies over the indian and atlantic oceans the southward shift of the arabian high results in a southward shift of the zonal component of the intertropical convergence zone itcz which is responsible for early onset of the rainy season e g 1982 and 1986 the enhanced st helena high and weaker mascarene high lead to the eastward shift of the meridional branch of the itcz for the wet years model simulations confirmed a strong positive correlation between precipitation anomalies over lake victoria and the warm el nino southern oscillation events by which enhanced moist westerly flow from the atlantic ocean and the mainly easterly flow from the indian ocean converge over lake victoria during wet years the interannual variability of precipitation over lake victoria and the western kenya highlands wkh are strongly coupled positive precipitation anomalies over the wkh region are usually associated with weaker arabian high and mascarene high which weaken the large scale divergence over the wkh region and favor the development of convection the interannual variability of precipitation over eastern kenya highlands ekh is not directly related to the el nino events but the association with a warm sst anomaly pattern over the western indian ocean is evident during wet years an el nino signal is however evident for wet years over the turkana channel warm sst anomalies over the northern indian ocean contribute enhanced water vapor transport over the region

abrupt rainfall transitions over the greater horn of africa observations and regional model simulations 1 we examine the yearly occurrence of a monsoon jump of approximately 20 latitude during the boreal spring and summer rainy seasons over the greater horn of africa gha this jump is in contrast with a simple model of a smoothly varying itcz over the region the rainfall jump is observed annually during april and may in three precipitation data sets and in regional climate model simulations using the psu ncar mesoscale model mm5 the mm5 simulations show the rainfall jump to be roughly coincident with abrupt circulation changes that occur as the somali jet develops during april may and june in particular the cross equatorial meridional branch of the somali jet forms along the east african coast in april bringing moisture and rainfall northward to the southern slopes of the ethiopian plateau this meridional branch forms well before the northern zonal branch of the jet which diverts moisture eastward from southern ethiopia and feeds the indian monsoon these results establish a framework for understanding the precipitation cycle over the gha and provide a foundation for improving subseasonal forecasts over drought prone regions of eastern africa

relative role of dynamic and thermodynamic processes in the development of the indian ocean dipole an ogcm diagnosis 1 the relative role of oceanic dynamics and surface heat fluxes in the initiation and development of the indian ocean dipole was investigated by analyzing results from an oceanic general circulation model the model was forced by observed surface wind stress and heat flux fields for 1958 1997 the results show that it was capable of reproducing observed dipole events over the tropical indian ocean the diagnosis of the mixed layer heat budget indicates that the sst anomaly ssta in the east pole is primarily induced by anomalous surface latent heat flux and vertical temperature advection whereas in the west pole it is mainly caused by meridional and vertical temperature advection anomalies in both regions shortwave radiation anomalies tend to damp the ssta the ocean rossby waves are essential in linking the anomalous wind and sst off sumatra and subsurface temperature variations in southwest indian ocean

carbon and oxygen isotopic composition of a guam coral and their relationships to environmental variables in the western pacific we examine the high resolution 32 samples year carbon and oxygen isotopic composition 13ccoral and 18ocoral in a coral core porites lobata from double reef guam over the years 1980 2000 the 13ccoral shows clear seasonal variations with mean seasonal amplitude of 1 89 which roughly corresponds with seasonal variations in solar radiation the seasonal amplitude of 18ocoral variations are small 0 23 0 57 but they are significantly correlated with sea surface temperature sst and salinity sss the 18ocoral and sst are more strongly correlated during el nino southern oscillation enso warm phases r 0 81 p 28 c and lower values of 18osw at guam these differences in oceanic parameters result from movements of the western pacific warm pool wpwp during the different phases of enso anomalies in 18osw inferred from the 18ocoral and instrumental sst are consistent with sss anomalies for the years 1980 2000 these 18osw anomalies may reflect changes in sss and evaporation precipitation due to movements of the wpwp this detailed analysis of a coral from guam suggests that it may contain an excellent archive of past enso events

mechanisms for anomalous warming in the western indian ocean during dipole mode events 1 during a typical indian ocean dipole mode iod event the weakening and reversal of winds in the central equatorial indian ocean lead to the development of unusually warm sea surface temperatures ssts in the western indian ocean here we report an analysis of model results and observations for the 1990 1999 period showing the anomalous warming that occurred during 1997 1998 and 1994 1995 iod events in the western indian ocean it was primarily the result of the internal oceanic processes within the arabian sea rather than a direct response to external forcing from the eastern indian ocean as previously suggested we compare the evolution of subsurface temperatures in the arabian sea just prior to 1996 1997 representative of a normal year and during the iod event 1997 1998 to infer the physical processes responsible for the anomalous warming during the iod events in a normal year such as 1996 the existence of a unique open ocean upwelling feature the arabian sea dome asd raises the thermocline in the southern arabian sea a result of the positive wind stress curl of the winter monsoon during an iod year 1997 with the collapse of the monsoon wind system in the arabian sea the cold tongue the strip of cool water indicative of asd that normally occupies the southern arabian sea fails to develop as a result the thermocline remains deep which in turn enhances the heat content of the upper ocean leading to warm ssts volume integrated heat budget terms in the asd region illustrate the role of horizontal and vertical advection in the upper ocean warming an implication is that ssts remain higher than 28 c in the southern arabian sea thereby supporting large scale deep convection in the atmosphere during the winter monsoon a band of deep convective cloud forms directly over the warm asd region during the iod events which bring greater than average rainfall over the southern arabian sea and east africa whereas convection is suppressed over the cold asd region during the normal years resulting in less than average rainfall

tibetan uplift intensified the 400 k y signal in paleoclimate records at 4 ma knowledge of when and how a specific climatic threshold is crossed is one key to an understanding of the evolution of earth s climate system we have observed a simultaneous intensification of the similar to 400 k y cycle in both proxy records for global ice volume and for east asian monsoon precipitation on the chinese loess plateau at ca 4 ma indicating that important climatic thresholds were crossed the 400 k y climatic cycles can be substantially intensified by clipped responses to insolation we argue that tibetan uplift accelerated at ca 4 ma and triggered such responses the weaker orbital band climatic signal during the interval 4 3 6 ma indicates that the thresholds were only crossed slightly

sea surface temperature and salinity reconstruction from coral geochemical tracers massive scleractinian corals secrete an aragonitic skeleton which incorporates a large array of chemical tracers corals present several advantages for palaeoclimate research they grow continuously and can live up to 1000 years they are easy to date and they can be sampled at high resolution weekly to monthly resolution both live and fossil corals can be collected in the field in the past two decades significant efforts have been made to identify robust tracers of sea surface temperature sst and salinity sss in corals to date sr ca and 18o are considered to be the most reliable sst tracers although changes in seawater 18o can significantly alter sst reconstructed from coralline 18o because these variations in seawater 18o can be linked to sss changes this initial problem can in fact be turned into an advantage and provide us with an sss tracer the sst component in the coral 18o signal can either be evaluated through sr ca measurements or in some case simply filtered out however there is still much uncertainty concerning the exact mode of incorporation of trace elements and stable isotopes into the coral skeleton the effects of growth rate light intensity feeding habits ph and water chemistry are still poorly documented a review of the strength and weaknesses of sr ca and 18o is presented together with some examples of sst and sss reconstructions other potential sst tracers are also reviewed it is expected that the ability to grow corals in aquarium under controlled conditions and that the development of sophisticated analytical techniques at the micrometric level should help us understand better the robustness of each tracers and the factors controlling their incorporation in coral aragonite

modification of the southern african rainfall variability enso relationship since the late 1960s analysis of 149 raingauge series 1946 1988 shows a weak positive correlation between late summer rainfalls january march in tropical southern africa and the southern oscillation index soi the correlation coefficients have been unstable since world war ii they were close to zero before 1970 and significant thereafter before 1970 southern african late summer rainfalls were more specifically correlated with regional patterns of sea surface temperature sst mainly over the southwestern indian ocean after 1970 teleconnections with near global sst anomaly patterns i e over the central pacific and indian oceans dominate the regional connections the increase in the sensitivity of the southern african rainfall to the global so related circulation anomalies is simultaneous with the correlation between soi and more extensive sst anomalies particularly over the southern indian ocean this feature is part of longer term decadal global sst variability as inferred from statistical analyses numerical experiments using the meteo france general circulation model arpege climat are performed to test the impact of the observed sst warming in the southern indian and extratropical oceans during el nino southern oscillation enso events on southern african rainfall simulated results show that enso events which occurred in the relatively cold background of the pre 1970 period in the southern oceans had a little effect on southern africa climatic conditions and atmospheric circulation by contrast more recent enso events with warmer sst over the southern oceans lead to a climatic bipolar pattern between continental southern african and the western indian ocean which is characterized by reduced enhanced deep convection and rainfall over the subcontinent the western indian ocean a weaker subtropical high pressure belt in the southwestern indian ocean is also simulated along with a reduced penetration of the moist southern indian ocean trade winds over the southern african plateau these results are consistent with the strong droughts observed over all southern africa during enso events since 1970

a calibration of the oxygen isotope paleothermometer of coral aragonite from porites the oxygen isotopic composition 18oaragonite of coral aragonite is dependent upon two parameters temperature and water oxygen isotopic composition this tracer allows temperature reconstruction in tropical zones different published 18o temperature relationships show a slope derived from the regression 18o against t c which varies between 0 16 and 0 23 for porites genus this implies greater uncertainty for paleoclimatic reconstruction the calibrations were generated differently they were obtained from several colonies collected in different locations or the formula was derived from the same coral head following seasonal variations of temperature the relationships took into account of 18osw fluctuation or 18osw were estimated from salinity or were not considered we show by using isotopic data from weber and woodhead 1972 and assessing the 18osw value by two different methods that a thermodynamically significant formula is generated

enhanced multidecadal climate variability in the seventeenth century from coral isotope records in the western indian ocean 1 the slowly growing coral diploastreaheliopora affords a novel opportunity to obtain multicentury records of paleoclimate including details of the interannual rhythms associated with the el nino southern oscillation enso system we examine climate variability in an enso teleconnected region using new oxygen isotope records from d heliopora spanning most of the twentieth 1896 1998 and seventeenth 1622 1722 centuries from the mafia archipelago tanzania the modern record demonstrates coherency with relevant instrumental and proxy time series documents twentieth century warming and displays significant power at enso periodicities the seventeenth century record lacks any trend exhibits interannual variance comparable to the modern record and displays a pronounced interdecadal signal not evident in the twentieth century that correlates with other tropical and hemispheric climate records we find no clear evidence of solar irradiance influence on interannual variability in the western indian ocean during these intervals although the mean sea surface temperature appears to vary inversely with insolation

calcite and quartz microstructural geothermometry of low grade metasedimentary rocks northern range trinidad abstract the northern range of trinidad is a mountainous exposure of deformed metasedimentary rocks with mesozoic depositional ages and tertiary metamorphic ages located in the caribbean south american plate boundary zone these rocks lack precise mineralogical indicators of metamorphic grade using temperature sensitive quartz and calcite microstructures and fission track data we identify describe quantify and map a nearly continuous spectrum of relatively low l50 c to relatively high 250 400 c deformation temperatures from east to west across the range average estimated rock exhumation rates also increase systematically along this trend the analysis illuminates a sharp east west trending major thermal discontinuity i e a fault along the southern boundary of the range kinematic analysis of faults and shear bands adjacent to this boundary and modeling indicate that the fault probably dips southward at 80 85 and accommodated normal dip slip at rates that decreased from west to east earlier experimental studies at high strain rates illustrated a strong strain rate dependency for quartz microstructural transitions our work indicates a possible strong temperature control for quartz microstructural transitions at natural strain rates

nonstationary enso precipitation teleconnection over the equatorial indian ocean documented in a coral from the chagos archipelago d 18 oc o f aporites coral from the chagos archipelago 71 e 5 s only after the mid 1970s a strong enso signal emerges in the d 18 oc during the analyzed period 1950 1994 in the 1970s the increasing sea surface temperature sst shifted the mean sst closer to the deep convection threshold at about 28 5 c enso related sst variability largely controls the deep convection and precipitation in the central equatorial indian ocean ceio when the sst is at this critical level the anomalies in the precipitation induce changes in the isotopic composition of the surface ocean waters the precipitation signal amplifies the sst signal in the coral d 18 oc and raises the correlation to enso the presented results have important implications for the reconstruction of enso indices from corals within the indian ocean citation timm o m pfeiffer and w c dullo 2005 nonstationary ensoprecipitation teleconnection over the equatorial indian ocean documented in a coral from the chagos archipelago geophys res lett 32 l02701 doi 10 1029 2004gl021738

variscan extension in the pyrenees evidence for variscan extension in the pyrenees is summarized and used with other geological and geochronological data to reconstruct the variscan extensional geometry and kinematics at a crustal scale a regionally consistent pattern of ese wnw trending synmetamorphic stretching directions indicates variscan extension roughly parallel to the present alpine trend of the belt the spatial distribution of variscan low pressure high temperature metamorphic domes is interpreted as being possibly due to the activity of few moderately dipping crustal scale shear zones allowing heterogeneous ductile extension of the variscan middle and lower crust extension occurred synchronous with uplift and emergence of large parts of the crust and deposition during the upper carboniferous and permian of up to 2500 m of continental sediments and intercalated basaltic andesitic volcanics in fault bounded extensional halfgrabens the extensional structures and related metamorphism postdate a namurian to early westphalian stage of crustal thickening characterized by thrusting and steep folding it is suggested that variscan extension in the pyrenees was driven by the gravitational potential energy of an initially thickened lithosphere enhanced by detachment of a cold and gravitationally unstable lithospheric root which caused progressive uplift tectonic denudation and a highly anomalous thermal structure of the variscan crust leading to extensive lower crustal melting and granodioritic intrusion during the early permian

mild and arid climate in the eastern sahara arabian desert during the late little ice age the climate of the sahara and arabian deserts during the little ice age is not well known due to a lack of annually resolved natural and documentary archives we present an annual reconstruction of temperature and aridity derived from sr ca and oxygen isotopes in a coral of the desert surrounded northern red sea our data indicate that the eastern sahara and arabian deserts did not experience pronounced cooling during the late little ice age 1750 1850 but suggest an even more arid mean climate than in the following 150 years the mild temperatures are broadly in line with predominantly negative phases of the north atlantic oscillation during the little ice age the more arid climate is best explained by meridional advection of dry continental air from eurasia we find evidence for an abrupt termination of the more arid climate after 1850 coincident with a reorganization of the atmospheric circulation over europe

mid brunhes strengthening of the indian ocean dipole caused increased equatorial east african and decreased australasian rainfall 1 the tropical indian ocean is an important component of the largest warm pool marked by changes in sea surface temperatures and depths of thermocline and mixed layer in its western and eastern extremities leading to the development of a dipole mode the indian ocean dipole iod a narrow band of westerlies 7 n to 7 s sweep the equatorial indian ocean during the april may and october november transitions between the summer and winter monsoon seasons these indian ocean equatorial westerlies iew are closely related to the iod intensifying the upper ocean eastward equatorial current also known as wyrtki jets the strength of the iod iew determines the moisture content in east africa a major decrease in the strength of the iew strengthening or positive mode of the iod during the mid brunhes epoch 300 250 kyr bp coincides with a wetter equatorial east africa a drier australasia and a stronger indian summer monsoon indicating that the iod iew play a significant role in driving climate change in east africa australasia and south asia

mayotte coral reveals hydrological changes in the western indian ocean between 1881 and 1994 we reconstruct the hydrologic history of the tropical western indian ocean by calculating the 18oseawater from coupled coral sr ca and 18o measurements in a massive porites coral from mayotte comoros between 1881 and 1994 we found that the precipitation evaporation balance varies naturally on time scales of 5 6 years and 18 25 years high low ssts are associated with positive negative 18oseawater implying that atmospheric variability is linked with remote climate modes in the indian ocean and the tropical extratropical pacific ocean warm el nino southern oscillation events are associated with a negative freshwater balance at mayotte this case study demonstrates that a much denser network of 18oseawater reconstructions is crucial for understanding the spatial patterns of hydrological conditions

multidecadal and interannual changes of stationary rossby waves changes in stationary rossby waves srw are connected to regional climate change and the propagation of these waves has a large influence on the evolution and development of the general circulation since the late 1970s and early 1980s many studies have noted a major shift in the structure of large scale circulation occurring in both hemispheres this paper explores the changes in the srw pattern and their propagation associated with these climate shifts first multidecadal changes in srw activity are examined using ncep ncar reanalysis data for two periods 1948 1978 and 1979 2000 for comparison of these two periods the zonal wind srw kinetic energy pattern along the waveguide and stationary wavenumber ks are analysed the results showed that in the northern hemisphere nh the srw propagation is favoured in the asian jet stream ajs waveguide ks 7 in the period 1979 2000 mainly in the east asia region there are indications that this could be associated with the pacific decadal oscillation warm phase a favoured srw propagation also occurs in the north atlantic subtropical jet nasj waveguide ks 5 region in the latter period and could be linked with positive north atlantic oscillation in the southern hemisphere sh a favoured srw propagation in the polar jet waveguide ks 4 region is observed in the latter period and this could be associated indirectly with tropical sea surface temperature fluctuations the interannual changes in the srw propagation during stronger el nino and la nina events which occurred from 1948 to 2000 are then examined the results showed that during stronger el nino events in nh the srw propagation in the ajs mainly in the east asia region and in the nasj waveguides ks 7 5 respectively is reduced on the other hand in sh the srw propagation in australian and polar waveguides ks 7 4 respectively is favoured copyright 2011 royal meteorological society

orbital scale variation of primary productivity in the central equatorial indian ocean maldives during the early pliocene abstract we investigate the response of the central equatorial indian ocean odp site 716 maldives upwelling system to orbital forcing between 3 64 and 4 19 ma this time interval in the early pliocene was characterized by global average temperatures considerably warmer than present and reduced zonal and meridional sea surface temperature gradients across the major oceans chlorin a degradation product of chlorophyll and a potential indicator of primary productivity was previously shown to record orbital scale variations at this site to confirm that chlorin records primary productivity and to understand the mechanism controlling the orbital variations we compare changes in the planktic foraminiferal assemblages with the chlorin content of the sediment cross wavelet analysis demonstrates the in phase relationship between the abundance of thermocline species and chlorin content indicating that upwelling and a shallower thermocline drive the productivity changes the aragonite content in periplatform carbonates is known to reflect variations in sea level and or climate with high values generally indicating sea level highstands the aragonite content in the studied interval shows precession and eccentricity astronomical cycles whereas the primary productivity proxies show only precessional cycles the negative correlation between aragonite content and the relative abundance of thermocline species on the precessional band implies that the primary productivity increased during sea level lowstands this phase coupling is consistent with quaternary productivity records from the central indian ocean that were proposed to be controlled by orbital induced variations of the el nino southern oscillation enso we therefore propose that a similar mechanism was active in the early pliocene despite major changes in the global boundary conditions

a recipe for simulating the interannual variability of the asian summer monsoon and its relation with enso this study investigates how accurately the interannual variability over the indian ocean basin and the relationship between the indian summer monsoon and the el nino southern oscillation enso can be simulated by different modelling strategies with a hierarchy of models from an atmospherical general circulation model agcm forced by observed sst to a coupled model with the ocean component limited to the tropical pacific and indian oceans the role of heat fluxes and of interactive coupling is analyzed whenever sea surface temperature anomalies in the indian basin are created by the coupled model the inverse relationship between the enso index and the indian summer monsoon rainfall is recovered and it is preserved if the atmospherical model is forced by the ssts created by the coupled model if the ocean model domain is limited to the indian ocean changes in the walker circulation over the pacific during el nino years induce a decrease of rainfall over the indian subcontinent however the observed correlation between enso and the indian ocean zonal mode iozm is not properly modelled and the two indices are not significantly correlated independently on season whenever the ocean domain extends to the pacific and enso can impact both the atmospheric circulation and the ocean subsurface in the equatorial eastern indian ocean modelled precipitation patterns associated both to enso and to the iozm closely resemble the observations

interannual displacements of convection and surface circulation over the equatorial indian ocean the interannual variability of surface observations in the equatorial indian ocean is investigated from 23 years of ship reports 1954 1976 in october and november during certain years the monthly analyses show strong wind anomalies in the eastern and central equatorial indian ocean simultaneously cloud cover anomalies of opposite signs are observed in the eastern indian ocean and in the central indian ocean a linear analysis of heat induced circulation suggests that the surface wind anomalies are forced by anomalies of rainfall this circulation is probably dissipative with time scales in the range two to five days the reasons for the maintenance of anomalous circulations are not well known it is noted that during most el nino events in the pacific ocean anomalies are observed in the indian ocean however there are other years with the same anomalous pattern 1961 for example during the years with anomalously little cloudiness in the eastern indian ocean sea surface temperatures lower than normal are found in the eastern indian ocean this suggests that coupled air sea dynamics must be taken into account to understand the interannual variability

regional slaty cleavage formation and fold axis rotation by re use and reactivation of pre existing foliations the fiery creek slate belt north queensland abstract a deformation history comprised of six separate deformation events of differing intensity has affected the rocks of the south palmer river region of the the hodgkinson province north queensland within this region a zone of pervasive slaty cleavage herein termed the fiery creek slate belt has developed as a result of the superposition of fabrics formed during several of these events the most important processes in the formation of this composite cleavage were the re use and reactivation of the favourably oriented steep n s trending s2 foliation by the intense fourth deformation event d4 this produced micro meso and macroscopic folds in an originally shallow s3 foliation produced during the intervening d3 deformation with an axial planar s2 s4 foliation the d4 stretching lineation l44 plunges subvertically to steeply north and indicates that shear during d4 was oriented steeply north south in the fiery creek slate belt d2 fold axes are interpreted to have formed in much shallower orientations than their present moderately n s plunging to subvertical orientations we consider this to be a result of d4 shear which caused variable degrees of rotation of d2 fold axes toward the d4 stretching lineation due to subparallelism of the bulk shortening directions of the d2 and d4 events near total destruction of the pre d4 foliations during slaty cleavage formation has produced a misleading impression of a simple deformation history there is no relationship between metamorphic grade and intensity of slaty cleavage development

detecting and characterising an englacial conduit network within a temperate swiss glacier using active seismic ground penetrating radar and borehole analysis englacial hydrology plays an important role in routing surface water to the glacier s bed and it consequently affects the glacier s dynamics however it is often difficult to observe englacial conduit conditions on temperate glaciers because of their short lived nature we acquired repeated active surface seismic data over the rhone glacier switzerland to monitor and characterise englacial conduit conditions amplitude versus angle analysis suggested that the englacial conduit is water filled and between 0 5 and 4 m thick a grid of gpr profiles acquired during the 2018 melt season showed the englacial conduit network persisting and covering 14 000 m 2 in late summer 2018 several boreholes were drilled into the conduit network we observed generally stable water pressure but there were also short sudden increases a borehole camera provided images of a fast flowing englacial stream transporting sediment through the conduit from these observations we infer that the englacial conduit network is fed by surface meltwater and morainal streams the surface and morainal streams merge together enter the glacier subglacially and flow through subglacial channels along the flank these subglacial channels flow into highly efficient englacial conduits traversing the up glacier section of the overdeepening before connecting with the subglacial drainage system

evaluation of sampling methods for fracture network characterization using outcrops outcrops provide valuable information for the characterization of fracture networks sampling methods such as scanline sampling window sampling and circular scanline and window methods are available to measure fracture network characteristics in outcrops and from well cores these methods vary in their application the parameters they provide and therefore have advantages and limitations we provide a critical review on the application of these sampling methods and apply them to evaluate two typical natural examples 1 a large scale satellite image from the oman mountains oman 120 000 m2 1 291 669 ft2 and 2 a small scale outcrop at craghouse park united kingdom 19 m2 205 ft2 the differences in the results emphasize the importance to 1 systematically investigate the required minimum number of measurements for each sampling method and 2 quantify the influence of censored fractures on the estimation of fracture network parameters hence a program was developed to analyze 1300 sampling areas from 9 artificial fracture networks with power law length distributions for the given settings the lowest minimum number of measurements to adequately capture the statistical properties of fracture networks was found to be approximately 110 for the window sampling method followed by the scanline sampling method with approximately 225 these numbers may serve as a guideline for the analyses of fracture populations with similar distributions furthermore the window sampling method proved to be the method that is least sensitive to censoring bias reevaluating our natural examples with the window sampling method showed that the existing percentage of censored fractures significantly influences the accuracy of inferred fracture network parameters

assessing the impact of diagenesis on foraminiferal geochemistry from a low latitude shallow water drift deposit abstract due to their large heat and moisture storage capabilities the tropics are fundamental in modulating both regional and global climate furthermore their thermal response during past extreme warming periods such as super interglacials is not fully resolved in this regard we present high resolution analytical foraminiferal geochemical 18 o and mg ca records for the last 1800 kyr from the shallow 487 m inner sea drift deposits of the maldives archipelago in the equatorial indian ocean considering the diagenetic susceptibility of these proxies in carbonate rich environments we assess the integrity of a suite of commonly used planktonic and benthic foraminifera geochemical datasets globigerinoides ruber white globigerinita glutinata with bulla pulleniatina obliquiloculata with cortex and cibicides mabahethi and their use for future paleoceanographic reconstructions using a combination of spot secondary ion mass spectrometer electron probe micro analyzer and scanning electron microscope image data it is evident that authigenic overgrowths are present on both the external and internal test shell surfaces yet the degree down core as well as the associated bias is shown to be variable across the investigated species and proxies given the elevated authigenic overgrowth mg ca 12 22 mmol mol and 18 o values closer to the benthic isotopic compositions the whole test planktonic g ruber w geochemical records are notably impacted beyond 627 4 ka 24 7 mcd yet considering the setting i e bottom water location for overgrowth formation the benthic foraminifera 18 o record is markedly less impacted with only minor diagenetic bias beyond 790 0 ka 28 7 mcd even though only the top of the g ruber w and c mabahethi records whole test data would be suitable for paleo reconstructions of absolute values i e sea surface temperature salinity seawater 18 o the long term cycles while dampened appear to be preserved furthermore planktonic species with thicker tests i e p obliquiloculata w c might be better suited in comparison to thinner test counter parts i e g glutinata w b g ruber w for traditional whole test geochemical studies in shallow carbonate rich environments a thicker test equates to a smaller overall bias from the authigenic overgrowth overall if the diagenetic impact is constrained as done in this study these types of diagenetically altered geochemical records can still significantly contribute to studies relating to past tropical seawater temperatures latitudinal scale ocean current shifts and south asian monsoon dynamics

circulation mechanisms of kenya rainfall anomalies abstract expanding earlier studies on the boreal spring and autumn rainy seasons in equatorial east africa pending challenges on the mechanisms of rainfall variability are investigated eastward pressure gradient and slack south indian ocean trade winds allow surface equatorial westerlies in spring and autumn complementing that upper tropospheric easterlies are required for the development of a zonal vertical circulation cell along the indian ocean equator because of the summer warming and high stand of upper tropospheric topography over south asia strong upper tropospheric easterlies over the tropical northern and equatorial indian ocean persist from summer into autumn thus allowing the development of a zonal vertical circulation cell by contrast the winter cooling entails low stand of upper tropospheric topography in the north thus hindering easterlies over the equator consequently an equatorial zonal circulation cell does not develop in boreal spring the equatorial zonal circulation cell

hercynian crustal scale extensional shear zone in the pyrenees detailed structural analysis of metasedimentary rocks and gneisses in the hospitalet massif pyrenees has revealed that upright structures in low grade rocks are in a structurally higher position and older than gently inclined to flat lying structures in higher grade rocks the steep structures were sub vertically flattened during formation of the flat lying structures indicating that the higher grade rocks formed as part of a shear zone system a similar conclusion can be drawn from the relation between deformation and metamorphism in the higher grade rocks we suggest that the shear zone may have accommodated crustal extension

decadal rainfall dipole oscillation over southern africa modulated by variation of austral summer land sea contrast along the east coast of africa abstracta rainfall dipole mode characterized by negative correlation between subtropical southern africa and equatorial eastern africa is identified in instrumental observation data in the recent 100 years the dipole mode shows a pronounced oscillation signal at a time scale of about 18 years this study investigates the underlying dynamical mechanisms responsible for this dipole pattern it is found that the southern african rainfall dipole index is highly correlated to the land sea contrast along the east coast of africa when the land sea thermal contrast strengthens the easterly flow toward the continent becomes stronger the stronger easterly flow via its response to east coast topography and surface heating leads to a low pressure circulation anomaly over land south of the maximum easterly flow anomalies and thus causes more rainfall in the south on a decadal time scale an enso like sst pattern acts to modulate this land sea contrast and the consequent rainfall dipole during a wet in the south

step wise growth of biotite porphyroblasts in pelitic schists of the western lys caillaouas massif pyrenees abstract detailed optical and electron microscope sem and tem examination of biotite blasts from pelitic schists of the western lys caillaouas massif in the pyrenees reveals a variety of microstructures suggesting growth of the blasts before and after a thermal peak during the d2 deformation in the early stages of growth the biotites had 001 at high angles to s1 and they appear to have existed as thin 001 parallel plates in many cases blastesis is suggested to have involved growth of the biotites into their own continuously dilating pressure shadows inclusions with dentate grain boundaries banded structures and radiator fin intergrowths suggest a mechanism analogous to the ramsay crack seal model for vein formation but here involving step wise dilation of a pressure shadow cavity into which the adjacent blast itself was growing