a tracer migration experiment in a small fracture zone in granite the water flow rate and tracer distribution has been studied in a fracture zone and averagely fractured rock in the stripa underground research laboratory the experimental site is located in granitic rock at a depth of 385 m below the ground surface a 50 m long drift with a diameter of 3 m was excavated the drift was intersected by a 6 m wide fracture zone the upper part of the drift was covered by 150 plastic sheets in which water was collected the water in the lower part of the drift was collected in sump holes different tracers were injected in seven locations at distances between 9 5 and 25 m from the drift more than 50 of the water was found in one sampling area in the drift and more than 90 in only eight sampling areas the recovery of the tracers was also concentrated in a few sheets most of the flow preferentially takes place in a few paths two sets of tracers were used in tandem one set of dyes which had previously been used in stripa and one set of lanthanide dtpa complexes although shown to be nonsorbing in long time high sensitivity laboratory tests the dyes were found to have a somewhat smaller recovery than the metal tracers this observation was used in an attempt to estimate the flow wetted surface into which the dyes can diffuse and sorb the flow porosity was estimated from the tracer residence times for all injection points the flow in the intersected fracture zone is not like that in a porous medium it is highly channeled

palaeogeographical controls on the cambrian trilobite immigration and evolutionary patterns reported in the western gondwana margin abstract southward drifting of the western gondwanan margin during the cambrian has been demonstrated by means of both palaeomagnetic methods and lithological indicators of climate such as carbonates and evaporites recent improvements in biostratigraphical correlations permit an enhanced understanding of the climatic and palaeobiogeographical constraints that controlled the distribution of cambrian benthic communities palaeogeographical and biogeographical reconstructions based on trilobites are reported in this paper in order to test interaction between migration speciation and extinction rates the variability of the documented biogeographical patterns is directly related to species diversity in which wider distribution coincides with transgressive trends and subsequent connection of neighbouring platforms early cambrian trilobite faunas show a high degree of both substrate control and endemicity although transgressions led to parallel shifts in faunal compositions by contrast mid cambrian trilobite faunas are relatively uniform across western gondwana and latest mid and late cambrian associations document influence of an increased similarity with asian trilobite faunas

two regimes of the equatorial warm pool part i a simple tropical climate model abstract atmosphere ocean coupled processes responsible for generating and maintaining the equatorial warm pool were investigated using models of different complexities the primary focus was to answer the following question why is the observed warm pool concentrated around the maritime continent in this first of a two part series the solutions of a simple conceptual model that represents the tropical pacific and indian oceans interacting via the walker circulation are examined when the interbasin coupling is sufficiently strong surface wind convergence over the maritime continent associated with easterly trades over the pacific acts to generate the equatorial westerly over the indian ocean leading to a warm pool spontaneously emerging between the two ocean basins the conceptual model shows that tropical climate has two equilibria depending upon the ocean basin widths a single warm pool regime corresponding to the current climate and a split warm pool regime that accompanies warm pools created in

connectivity permeability and channeling in randomly distributed and kinematically defined discrete fracture network models a major use of dfn models for industrial applications is to evaluate permeability and flow structure in hardrock aquifers from geological observations of fracture networks the relationship between the statistical fracture density distributions and permeability has been extensively studied but there has been little interest in the spatial structure of dfn models which is generally assumed to be spatially random i e poisson in this paper we compare the predictions of poisson dfns to new dfn models where fractures result from a growth process defined by simplified kinematic rules for nucleation growth and fracture arrest davy et al 2010 2013 this so called kinematic fracture model is characterized by a large proportion of t intersections and a smaller number of intersections per fracture several kinematic models were tested and compared with poisson dfn models with the same density length and orientation distributions connectivity permeability and flow distribution were calculated for 3d networks with a self similar power law fracture length distribution for the same statistical properties in orientation and density the permeability is systematically and significantly smaller by a factor of 1 5 to 10 for kinematic than for poisson models in both cases the permeability is well described by a linear relationship with the areal density p32 but the threshold of kinematic models is 50 larger than of poisson models flow channeling is also enhanced in kinematic dfn models this analysis demonstrates the importance of choosing an appropriate dfn organization for predicting flow properties from fracture network parameters

contribution to the circulation climatology of the eastern equatorial pacific lower atmospheric jets novel data sets have been evaluated to reappraise the annual cycle of atmospheric circulation over the pacific in the eastern pacific cross equatorial surface winds from the southern hemisphere generate an oceanic cold tongue immediately to the south of the equator the associated lower tropospheric thickness pattern entails a minimum of absolute topography in the midtroposphere near the equator and together with the small coriolis parameter this causes a jet stream of up to 10 ms 1 at 700 600 mbar centered at 0 2 n the jet is most intense in late boreal winter because then the near equatorial surface low pressure trough is flat the jet is fed by lower tropospheric convergence over equatorial south america and by upper tropospheric convergence and subsidence over a narrow equatorial zone of the eastern pacific over the central pacific a jet of up to 10 ms 1 is found at 10 12 n and 925 850 mbar while friction brakes the flow in the layer of steepest meridional pressure gradient near the surface this lower tropospheric jet as the surface pressure gradient is also strongest in late boreal winter overall the ncep analyses resolve the near surface circulation less well than the long term ship observations however the midtropospheric equatorial jet over the eastern pacific is also borne out by the 1967 1971 radiosoundings over galapagos and the lower tropospheric trade wind jet over the central pacific was also identified from the intense radiosonde program of the march april 1967 line islands experiment

deep structure of the vale of glamorgan south wales uk the deep structure of the vale of glamorgan is investigated using recently acquired seismic data reflection sections from a commercial seismic survey in the vale enable the carboniferous limestone old red sandstone and silurian sequences to be mapped in the subsurface the old red sandstone sequence thins westwards under the southern part of the vale and in the southwest corner of the vale the base of the old red sandstone is interpreted to overstep across the underlying silurian sequence in an analogous manner to its regional overstep in west wales the precambrian basement surface is not clearly represented on the sections but may coincide with the base of a reflective sequence observed in places along one of the reflection lines basement depth estimates from the reflection sections are compared with estimates derived from a new time term analysis of data from long seismic refraction lines basement depths remain uncertain to 1 2 km but appear to be greater under the central part of the vale than under the western part and along the south coastal zone a linked system of variscan forethrusts is traced to outcrop in the core of the cowbridge anticline but none involves major displacement the ty9n y nant moel gilau fault system of the south wales coalfield is shown to be a component of the linked fault system and its current net extension is attributed to mesozoic reactivation of a variscan thrust involving only limited displacement the individual thrusts appear to connect to a basal thrust that may extend northwards into or under the south wales coalfield the amount of displacement along the basal thrust cannot be determined reliably but it may exceed 10 km and involve large scale repetition of palaeozoic sequences under the vale

ocean atmosphere interaction in the making of the walker circulation and equatorial cold tongue abstract the climate over the equatorial pacific displays a pronounced asymmetry in the zonal direction that is characterized by the walker circulation in the atmosphere and the cold tongue in the ocean an intermediate coupled ocean atmosphere model is used to investigate the driving force and the ocean atmosphere interaction mechanism for the generation of the zonal asymmetry in the far eastern pacific the upwelling at the equator is weak because zonal winds are blocked by the andes the off equatorial upwelling induced by southerly cross equatorial winds is thus crucial for cooling the eastern pacific a realistic cold tongue appears in the coupled model only when this southerly wind forcing is included the southerly winds cause the sea surface temperature to fall in the east enhancing the zonal heat contrast and hence intensifying easterly winds across the basin these anomalous easterlies induce more equatorial upwelling and raise the thermocline in the east amplifying the initial cooling by th

processes controlling the mean tropical pacific precipitation pattern part ii the spcz and the southeast pacific dry zone the nature of the south pacific convergence zone spcz is addressed by focusing on the dry and cool zone bounded by it and the coast of south america through numerical experiments as shown in a companion paper this dry zone is due to a large extent to orographically forced subsidence here it is shown that the northwestward expansion of this dry zone can be explained by advection of low moist static energy by the trade winds these results provide an explanation of the geometry of the western edge of the dry zone and therefore of the eastern edge of the adjacent spcz sea surface temperature underneath the spcz is enhanced by relatively high near surface humidity through evaporative processes which feeds back into its organization however in this model this feedback is not critical for the existence of the spcz the subsidence associated with the itcz in the north hemisphere negatively affects the precipitation rate in the spcz it was also found that the sensitivity of the forced response is largest for peak orographic heights below 3000 m which indicates that the exact representation of the andes in numerical models might not be as critical as that of lower orography such as that in southern africa

the habberley formation youngest tremadoc in the welsh borderlands the habberley formation overlies the shineton shale formation in the shelve inlier shropshire and includes the youngest tremadoc strata known from the welsh basin it probably represents deposition during the interval cut out by the sub arenig unconformity in north wales and removed by the sub caradoc unconformity in the wrekin district there is no angular unconformity between tremadoc and arenig in the shelve inlier the habberley formation is likely to correlate in part with the hunnebergian stage of scandinavia it was deposited probably in a largely stagnant basin and records a shallowing upwards sequence prior to the arenig transgression of the stiperstones quartzite a sparse trilobite fauna proves the presence of the angelina sedg vickii biozone and a succeeding interval is characterized by asaphellus cf graffi the trilobites are briefly described they include the first undistorted material of angelina sedgwvickii the brachiopod lingulella bella walcott hitherto known only from eastern newfoundland is described by a w a rushton

the pacific cold tongue and the enso mode a unified theory within the zebiak cane model abstract the equatorial tropical pacific climate system is a delicate coupled system in which winds driven by gradients of sea surface temperature sst within the basin interact with the ocean circulation to maintain sst gradients this results in a time mean state having a strong zonal temperature contrast along the equator with an eastern cold tongue and a western warm pool by the same coupled processes interannual variability known as the el nino southern oscillation enso is present in the pacific this variability can be attributed to an oscillatory coupled mode the enso mode in the equatorial ocean atmosphere system using a zebiak cane type intermediate coupled model the coexistence of an eastern cold tongue in the annual mean state and enso in the pacific climate system is investigated the enso mode arises as a robust oscillatory mode on a coupled mean state and becomes unstable if the cold tongue of the mean state is sufficiently strong the origin of this mode its propagation mechanis

formation and variability of a northerly itcz in a hybrid coupled agcm continental forcing and oceanic atmospheric feedback abstract despite the equatorial symmetry of the annual mean insolation the intertropical convergence zone itcz and the collocated band of high sea surface temperature sst assume perennial northern latitudes over the eastern pacific and atlantic an atmospheric general circulation model is coupled with an intermediate ocean model to study continental forcing and oceanic atmospheric interaction that act to break the equatorial symmetry the model reaches a statistically symmetric mean state under perfectly symmetric conditions with the continental coasts running along meridians when a bulge of landmass is added to the eastern continent north of the equator it initiates a coupled ocean atmosphere wave front that propagates westward across the ocean basin cooling the ocean surface and suppressing deep convection on and south of the equator as a result the itcz shifts into the northern hemisphere in contrast to this basinwide response little latitudinal asymmetry develops in the coupled model when

a new modular palaeopascichnid fossil curviacus ediacaranus new genus and species from the ediacaran dengying formation in the yangtze gorges area of south china non biomineralizing ediacaran macrofossils are rare in carbonate facies but they offer valuable information about their three dimensional internal anatomy and can broaden our view about their taphonomy and palaeoecology in this study we report a new ediacaran fossil curviacus ediacaranus new genus and species from bituminous limestone of the shibantan member of the dengying formation in the yangtze gorges area of south china curviacus is reconstructed as a benthic modular organism consisting of serially arranged and crescent shaped chambers the chambers are confined by chamber walls that are replicated by calcispars and are filled by micritic sediments such modular body construction is broadly similar to the co occurring yangtziramulus zhangii and other ediacaran modular fossils such as palaeopascichnus the preservation style of curviacus is similar to yangtziramulus although the phylogenetic affinities of both genera remain unresolved the new fossil adds to the diversity of ediacaran modular organisms

lower cambrian halkieriids from oxfordshire uk lower cambrian sediments from the withycombe farm borehole oxfordshire yield isolated halkieriid sclerites all bear prominent ridges and most appear to be either cultrates or palmates although distinction between the two in the available material is generally difficult two other sclerites are more elongate one may represent a spinose sclerite while the other is possibly derived from the siculate zone of the original scleritome adjacent horizons of the withycombe formation yield disc like fossils superficially similar to hyolith opercula or monoplacophorans these are tentatively identified as deriving from the same halkieriid scleritome two main types are identified and these may correspond to the anterior and posterior shells of halkieria evangelista from the lower cambrian sirius passet fauna of north greenland the age of the withycombe formation within the cambrian is not entirely resolved but faunal evidence suggests an equivalence to the cuslett formation of southeast newfoundland which corresponds to either the upper tommotian or lower atdabanian of the standard siberian section

early cambrian palaeogeography and the probable iberia siberia connection abstract the end of the proterozoic beginning of the cambrian is marked by some of the most dramatic events in the history of earth the fall of the ediacaran biota followed by the cambrian explosion of skeletonised bilaterians a pronounced shift in oceanic and atmospheric chemistry and rapid climatic change from snowball earth to greenhouse conditions all happened within a rather geologically short period of time these events took place against a background of the rearrangement of the prevailing supercontinent some authors view this as a sequence of individual supercontinents such as mesoproterozoic midgardia neoproterozoic rodinia and early cambrian pannotia assembled in the mesoproterozoic this supercontinent appears to have existed through the neoproterozoic into the early cambrian with periodic changes in configuration the final rearrangement took place during the precambrian cambrian transition with the cadomian and related phases of the pan african orogeny the distribution of early cambrian molluscs and other small shelly fossils ssf across all continents indicates a close geographic proximity of all major cratonic basins that is consistent with the continued existence of the supercontinent at that time subsequently rodinia experienced breakup that led to the amalgamation of gondwana separation of laurentia baltica siberia and some small terranes and the emergence of oceanic basins between them spreading oceanic basins caused a gradual geographic isolation of the faunal assemblages that were united during the vendian early cambrian

the oldest evidence of bioturbation on earth detailed study of the khatyspyt formation in arctic siberia has shown that contrary to common expectations the earliest ichnofabric is of late ediacaran age records a food seeking behavior and is found in a distal carbonate ramp setting where it co occurs with fossils of avalon type ediacaran soft bodied organisms preserved depth of bioturbation reaches 5 cm the ichnofabric solely comprises nenoxites the oldest known meniscate trace fossil which is interpreted as burrows with terminal backfill structure formed as a result of active displacement of sediment to form a tunnel within the substrate followed by emplacement of the material behind the animal as it progressed through the sediment in addition to being the most reliable paleontological evidence for the existence of bilaterians at ca 555 ma the late ediacaran bioturbation is regarded as a key step in the escalatory engineering of phanerozoic ecospace leading to sudden diversification of macroscopic organisms and macrocommunities

hydrologic issues associated with nuclear waste repositories significant progress in hydrology especially in subsurface flow and solute transport has been made over the last 35 years because of sustained interest in underground nuclear waste repositories the present paper provides an overview of the key hydrologic issues involved and to highlight advances in their understanding and treatment because of these efforts the focus is not on the development of radioactive waste repositories and their safety assessment but instead on the advances in hydrologic science that have emerged from such studies work and results associated with three rock types which are being considered to host the repositories are reviewed with a different emphasis for each rock type the first rock type is fractured crystalline rock for which the discussion will be mainly on flow and transport in saturated fractured rock the second rock type is unsaturated tuff for which the emphasis will be on flow from the shallow subsurface through the unsaturated zone to the repository the third rock type is clay rich formations whose permeability is very low in an undisturbed state in this case the emphasis will be on hydrologic issues that arise from mechanical and thermal disturbances i e on the relevant coupled thermo hydro mechanical processes the extensive research results especially those from multiyear large scale underground research laboratory investigations represent a rich body of information and data that can form the basis for further development in the related areas of hydrologic research

on the occurrence of foraminiferans in the lower cambrian of the llangynog inlier south wales microfossils obtained from dissolution of a limestone horizon from the lower cambrian allt y shed sandstone of the llangynog inlier carmarthenshire south wales are identified as agglutinated foraminiferans two genera and three species are represented and are figured these microfossils add further to the scanty record of cambrian foraminiferans but do not resolve the problem of the precise age of the allt y shed sandstone

sedimentary geology and stromatolites of the middle proterozoic belt supergroup glacier national park montana abstract the belt supergroup is a thick dominantly fine grained sequence of middle proterozoic strata occurring in western montana northern idaho and parts of washington state alberta and british columbia the sequence in glacier national park is located along the northeastern part of present exposures of the belt supergroup it is 2 9 km thick extremely well exposed and for the most part structurally simple although it was subjected to lowermost greenschist facies metamorphism primary sedimentary structures are exceptionally well preserved subtidal intertidal alluvial and possibly deltaic depositional environments appear to be represented in the belt sequence in glacier national park the lowermost unit the altyn limestone is not entirely exposed in the park a partial section 150 m thick consists of impure dolostones deposited largely in shallow subtidal and intertidal settings this carbonate unit is overlain by terrigenous strata of the appekunny and grinnell argillites the appekunny argillite is 700 m thick consists largely of green colored fine grained terrigenous material and appears to have been deposited predominantly in offshore and or deltaic settings the overlying grinnell argillite is 605 m thick and consists of red colored terrigenous material deposited largely on an alluvial plain the overlying siyeh limestone is 780 m thick and consists largely of impure dolostones and dolomitic limestones deposited in shallow subtidal and intertidal settings overlying the siyeh limestone is the 385 m thick snowslip formation which consists of slightly dolomitic predominantly fine grained terrigenous strata deposited largely in intertidal settings the overlying shepard formation is not exposed in its entirety in the central part of glacier national park a 270 m thick section which excludes the uppermost part of the formation consists of impure dolostones and argillites and appears to have been deposited in subtidal and intertidal settings stromatolites are abundant diverse and well preserved in glacier national park with mound shaped forms and columnar forms of the group baicalia occurring in the altyn limestone and siyeh limestone and mound shaped stromatolite like structures occurring in the snowslip and shepard formations particularly prominent is a 24 32 m thick stromatolite unit in the upper siyeh limestone which contains baicalia and conophyton and appears to represent a prograding stromatolite reef with baicalia originating in a moderate energy reef front setting and conophyton originating in a lower energy back reef setting individual units in these cycles can be correlated for 90 km many of the conophyton in these cycles are inclined probably as a result of gentle wave action and the direction of inclination is relatively constant for 90 km with the axes trending sw ssw and plunging 30 60 sw

processes leading to double intertropical convergence zone bias in cesm1 cam5 abstractthe double intertropical convergence zone itcz bias in the eastern pacific in the community earth system model version 1 with community atmosphere model version 5 cesm1 cam5 is diagnosed in cam5 standalone the northern itcz is associated with inertial instability and the southern itcz is thermally forced after air sea coupling the processes on both hemispheres are switched because the spatial pattern of sea surface temperature sst is changed biases occur during boreal spring in both cam5 and the ocean model in cam5 alone weaker than observed equatorial easterly in the tropical eastern south pacific leads to weaker evaporation and an increase in local sst the shallow meridional circulation overly converges in the same region in the cam5 standalone simulation the planetary boundary layer and middle troposphere are too humid and the large scale subsidence is too weak at the middle levels these biases may result from excessive shallow convection behavior in cam5 the extra moisture wou

el nino s tropical climate and teleconnections as a blueprint for pre ice age climates 1 at 2 7 million years ago the warm equable climates of early and middle pliocene time used here to mean from 5 to 2 7 ma were replaced by recurring ice ages most attempts to explain the change appeal either to changes in co2 in the atmosphere or reduced heat transport by the atlantic ocean the sources of the strongest teleconnections in the current climate however lie in the tropics and such connections occur by transport of heat and moisture by the atmosphere the most prominent of these teleconnections link aberrations in sea surface temperatures in the equatorial pacific el nino southern oscillation enso variations with warm and dry or cool and wet anomalies in extratropical climates we show that in most cases early and middle pliocene climate both in equatorial regions and in the extratropics differ from present day climates with the same spatial pattern as that associated with enso for instance not only was canada warmer during early pliocene time than at present as it is during el nino but the region surrounding the gulf of mexico appears to have been cooler and a bit wetter as it commonly is during el nino a virtually permanent el nino like state appears to have characterized pre ice age climates suggesting that transport of heat by the atmosphere was the principal mechanism that maintained extratropical warmth accordingly cooling and the growth of recurring ice sheets in the northern hemisphere resulted from the development of a strong walker circulation and a weakening of the hadley circulation

quantifying diffusive mass transfer in fractured shale bedrock a significant limitation in defining remediation needs at contaminated sites often results from an insufficient understanding of the transport processes that control contaminant migration the objectives of this research were to help resolve this dilemma by providing an improved understanding of contaminant transport processes in highly structured heterogeneous subsurface environments that are complicated by fracture flow and matrix diffusion our approach involved a unique long term steady state natural gradient injection of multiple tracers with different diffusion coefficients br he ne into a fracture zone of a contaminated shale bedrock the spatial and temporal distribution of the tracers was monitored for 550 days using an array of groundwater sampling wells instrumented within a fast flowing fracture regime and a slow flowing matrix regime the tracers were transported preferentially along strike parallel fractures with a significant portion of the tracer plumes migrating slowly into the bedrock matrix movement into the matrix was controlled by concentration gradients established between preferential flow paths and the adjacent rock matrix observed differences in tracer mobility into the matrix were found to be a function of their free water molecular diffusion coefficients the multiple tracer technique confirmed that matrix diffusion was a significant process that contributed to the overall physical nonequilibrium that controlled contaminant transport in the shale bedrock the experimental observations were consistent with numerical simulations of the multitracer breakthrough curves using a simple fracture flow model the simulated results also demonstrated the significance of contaminant diffusion into the bedrock matrix the multiple tracer technique and ability to monitor the fracture and matrix regimes provided the necessary experimental constraints for the accurate numerical quantification of the diffusive mass transfer process the experimental and numerical results of the tracer study were also consistent with indigenous contaminant discharge concentrations within the fracture and matrix regimes of the field site these findings suggest that the secondary source contribution of the bedrock matrix to the total off site transport of contaminants is relatively large and potentially long lived

integrated geophysical geological modelling of the caledonian and precambrian basement of southern britian quantitative modelling of potential field data has been used to test and extend geological sections constructed for the new british geological survey tectonic map of britain and ireland three of the profiles cross part of the anglo brabant massif and provide new information on the nature of the pre mesozoic basement a profile across southern england passing just to the west of london suggests that a significant contribution to observed gravity variations in the region results from changes in the thickness of relatively low density lower palaeozoic rocks it also identifies a major deep seated body with relatively high magnetic susceptibility and low density which is interpreted as a precambrian cratonic core underlying the southeastern part of the midlands microcraton profiles across central and eastern england reveal major boundaries within the precambrian basement some of which coincide with structures mapped at surface a number of intrusions of probable caledonian age have been recognized including bodies beneath the widmerpool gulf and the wash those beneath the wash appear to lie in a discrete basement region which separates belts of more magnetic basement lying to the northwest and southeast

the climate response of the indo pacific warm pool to glacial sea level growing climate proxy evidence suggests that changes in sea level are important drivers of tropical climate change on glacial interglacial time scales these paleodata suggest that rainfall patterns over the indo pacific warm pool ipwp are highly sensitive to the landmass configuration of the maritime continent and that lowered sea level contributed to large scale drying during the last glacial maximum lgm ca 21 000 years before present using the community earth system model version 1 2 cesm1 we investigate in detail the mechanisms by which lowered sea level influenced the climate of the ipwp during the lgm the cesm1 simulations show that in agreement with previous hypotheses changes in atmospheric circulation are initiated by the exposure of the sunda and sahul shelves ocean dynamical processes amplify the changes in atmospheric circulation by increasing the east west sea surface temperature sst gradient along the equatorial indian ocean the coupled mechanism driving this response is akin to the bjerknes feedback and results in a large scale climatic reorganization over the indian ocean with impacts extending from east africa to the western tropical pacific exposure of sahul shelf and the associated changes in surface albedo play a key role because it is more effective at exciting the positive feedback than exposure of the sunda shelf this mechanism could explain the pattern of dry wet eastern western indian ocean identified in climate proxies and lgm simulations however this response also requires a strengthened sst gradient along the equatorial indian ocean and it is currently unclear whether this is detectable in marine paleoreconstructions strategies to resolve this issue are discussed

orbital controls on the el nino southern oscillation and the tropical climate the global synchroneity of glacial interglacial events is one of the major problems in understanding the link between milankovitch forcing and the climate of the late quaternary in this study we isolate a part of the climate system the tropical pacific and test its sensitivity to changes in solar forcing associated with changes in the earth s orbital parameters we use a simplified coupled ocean atmosphere model that is run for the past 150 000 years and forced with milankovitch changes in the solar insolation this system responds primarily to the precessional cycle in solar forcing and is capable of generating a mean response to the changes in the seasonal distribution of solar radiation even while the annual mean insolation is roughly constant the mean response to the precessional forcing is due to an interaction between an altered seasonal cycle and the el nifio southern oscillation enso changes in the enso behavior result in a mean tropical climate change the hypothesis is advanced that such a change in the tropical climate can generate a globally synchronous climate response to milankovitch forcing

the influence of ocean surface temperature gradient and continentality on the walker circulation part i prescribed tropical changes abstract a coarse mesh global climate model developed at the goddard institute for space studies giss has been used to assess the influence of ocean surface temperature ost gradient and continentality on the walker circulation the basic model climate was established by a five year integration in which the prescribed seasonal cycle in ost distribution was identical for each year in the model climate the walker circulation is characterized in the zonal plane by three pairs of clockwise and counterclockwise cells to the troposphere three separate winter experiments were performed in which the normal west to east ost gradients in the tropical pacific were replaced by a uniform distribution in the band from 8 n to 16 s each experiment was characterized by osts set at the warmest coldest or mean temperatures in the band the model response features statistically significant changes in the intensity of the various cells and branches with small shifts in the east west extent the overall structure in

what controls the mean east west sea surface temperature gradient in the equatorial pacific the role of cloud albedo abstractthe mean east west sea surface temperature gradient along the equator is a key feature of tropical climate tightly coupled to the atmospheric walker circulation and the oceanic east west thermocline tilt it effectively defines tropical climate conditions in the pacific its presence permits the el nino southern oscillation phenomenon what determines this temperature gradient within the fully coupled ocean atmosphere system is therefore a central question in climate dynamics critical for understanding past and future climates using a comprehensive coupled model community earth system model cesm the authors demonstrate how the meridional gradient in cloud albedo between the tropics and midlatitudes sets the mean east west sea surface temperature gradient in the equatorial pacific to change in the numerical experiments the authors change the optical properties of clouds by modifying the atmospheric water path but only in the shortwave radiation scheme of the model when is va

the problems and potential of using animal fossils and trace fossils in terminal proterozoic biostratigraphy abstract despite the discovery of soft bodied megascopic fossils of late neoproterozoic age at numerous localities world wide there has been slow acceptance of their potential for intercontinental correlation the stratigraphic thickness of sediments separating individual occurrences of such fossils from the base of the cambrian is very varied basic questions have also been posed as to the classification of the organisms represented and hence their likely time significance recent geochronological studies support notions of a narrow time distribution well studied neoproterozoic sequences in eurasia eastern and western north america and southern australia show strikingly similar patterns of increase in the numbers and diversity of trace fossils and soft bodied megascopic remains up section though strata immediately preceding the cambrian are relatively barren other than for a sparse palynoflora and compressions of primitive plants trace fossils from australian sections relating to an early part of the ediacaran apparently overlap a time of abundance of large process bearing acritarchs and big leiosphaerids this overlap of early animal traces and distinctive acritarchs may prove to be of significant biostratigraphic importance rare discoveries of forms resembling rangea gurich in the flinders ranges of south australia precede the classical ediacara assemblage and may provide a possible correlation with occurrences of this genus in namibia the distinctive remains and trace fossils at this level constituting the rangeid hiemalora assemblage zone resemble a biota from the podolia region of the ukraine and show a similarity to finds in parts of the windermere supergroup of the northwest territories canada similarly the offshore frondose assemblage of newfoundland is comparable with the biota of charnwood forest england the type ediacara assemblage of the flinders ranges characterizing the dickinsonia costata assemblage zone is a climax biota with diverse taxa and large individual species as well as some 20 ichnogenera it closely correlates with a late redkinian or early kotlinian assemblage in the upper part of the section on the zimny gory coast of the white sea northern russia the trace fossils of these levels show that significant diversification began before the cambrian

a coupled theory of tropical climatology warm pool cold tongue and walker circulation abstract based on results from analytic and general circulation models the authors propose a theory for the coupled warm pool cold tongue and walker circulation system the intensity of the coupled system is determined by the coupling strength the local equilibrium time and latitudinal differential heating most importantly this intensity is strongly regulated in the coupled system with a saturation level that can be reached at a modest coupling strength the saturation west east sea surface temperature difference and the associated walker circulation corresponds to about one quarter of the latitudinal differential equilibrium temperature this regulation is caused primarily by the decoupling of the sst gradient from a strong ocean current the author s estimate suggests that the present pacific is near the saturation state furthermore the much weaker walker circulation system in the atlantic ocean is interpreted as being the result of the influence of the adjacent land which is able to extend

trace fossils in the ediacaran cambrian transition behavioral diversification ecological turnover and environmental shift abstract after taxonomic revision trace fossils show a similarly explosive diversification in the ediacaran cambrian transition as metazoan body fossils in shallow marine deposits of ediacaran age trace fossils are horizontal simple and rare and display feeding strategies related to exploitation of microbial matgrounds equally notable is the absence of arthropod tracks and sinusoidal nematode trails this situation changed in the early cambrian when a dramatic increase in the diversity of distinct ichnotaxa is associated was followed by the onset of vertical bioturbation and the disappearance of a matground based ecology agronomic revolution on deep sea bottoms animals have been present already in the ediacaran but ichnofaunas were poorly diverse and dominated by the horizontal burrows of undermat miners as shown by the ichnogenus oldhamia this life style continued to be predominant into the early and to a lesser extent middle cambrian nevertheless there was an explosive radiation of behavioral programs during the early cambrian when exactly the bioturbational revolution arrived in the deep sea is uncertain in any case the nereites ichnofacies was firmly established in the early ordovician the rich ichnofauna in the early cambrian guachos formation of northwest argentina probably marks a first step in this ecological onshore offshore shift

pelletal structures in peruvian upwelling sediments late quaternary sediments from the peru upwelling zone have been investigated using backscattered electron imagery the dysaerobic to anaerobic conditions which persist within the strong oxygen minimum zone intersecting the shelf and upper slope sediments have resulted in the preservation of a wide range of microscopic fine structure relating to biological activity two forms of pelletal structures are present pellets and aggregate structures 1 pellets are oval in cross section with a mean diameter of 610 m and sharp boundaries three common pellet types have been identified a crushed diatom and clay pellets b intact diatom pellets and c silt pellets 2 aggregate structures are smaller than pellets with a mean diameter of 360 m they have indistinct boundaries and may be composed either of pure diatom ooze or a mix of clay silt and diatoms the size shape and mode of occurrence of aggregate structures suggest that they are the product of a meiofauna redistributing the topmost sediment during periods of very slight increases in oxygen most of the crushed diatom clay pellets and intact diatom pellets are probably also the product of a surficial deposit feeding fauna tolerant of low dissolved oxygen levels such as polychaete worms silt pellets may record the chamber building activities of agglutinating foraminifera

ocean atmosphere interaction and the tropical climatology part i the dangers of flux correction abstract this sequence of papers examines the role of dynamical feedbacks between the ocean and the atmosphere in determining features of the tropical climatology a stripped down intermediate coupled ocean atmosphere model is used to provide a prototype problem for the pacific basin here the authors contrast the fully coupled case with the case where flux correction is used to construct the climatology in the fully coupled case the climatology is determined largely by feedback mechanisms within the ocean basin winds driven by gradients of sea surface temperature sst within the basin interact with the ocean circulation to maintain sst gradients for all realistic cases these lead to a unique steady solution for the tropical climatology in the flux corrected case the artificially constructed climatology becomes unstable at sufficiently large coupling leading to multiple steady states as found in a number of coupled models using continuation methods we show that there is a topological change i

carbonate carbon isotope chemostratigraphy and u pb zircon geochronology of the liuchapo formation in south china constraints on the ediacaran cambrian boundary in deep water sequences abstract the ediacaran cambrian transition was one of the most significant intervals in geological history witnessing the origin of the metazoans and major environmental changes establishing a precise chronostratigraphic framework for the ediacaran cambrian transition has great significance for understanding the geological and evolutionary processes during this transition an integrated study on carbonate carbon isotopes and u pb zircon dating was conducted within the liuchapo formation in the sifangjing section in northeastern guizhou province south china to recognize the ediacaran cambrian boundary in slope facies of the yangtze block a substantial negative carbonate carbon isotope excursion was recognized within the lower part of the liuchapo formation moreover a weighted mean u pb zircon age of 540 7 3 8 6 6 ma was obtained from a tuffaceous interlayer approximately 2 m above the interval of the negative carbon isotope excursion the carbon isotope and age dating results indicate that the ediacaran cambrian boundary within the sifangjing section should be placed in the lower part of the liuchapo formation additionally in the sifangjing section a distribution of horodyskia minor extends up to the basal cambrian while the last appearance datum lad of palaeopascichnus jiumenensis correlates to the large negative carbon isotope excursion within the liuchapo formation this relationship indicates that the lad of the palaeopascichnus jiumenensis is a potential tool for the stratigraphic correlation of the ediacaran cambrian boundary successions in slope and deep water basin settings of the yangtze block

role of tropics in changing the response to milankovich forcing some three million years ago appeared in regions that today have intense oceanic upwelling the eastern equatorial pacific and the coastal zones of southwestern africa and california there was furthermore a significant change in the earth s response to milankovich forcing obliquity signals became large but those associated with precession and eccentricity remained the same the latter change in the earth s response can be explained by hypothesizing that the global cooling during the cenozoic affected the thermal structure of the ocean it caused a gradual shoaling of the thermocline around 3 ma the thermocline was sufficiently shallow for the winds to bring cold water from below the thermocline to the surface in certain upwelling regions this brought into play feedbacks involving

the stratigraphy and setting of the precambrian rocks of the llangynog inlier dyfed south wales detailed mapping of the precambrian rocks of the llangynog inlier made possible by a series of new exposures has allowed the establishment for the first time of the 1100 m thick succession within the precambrian rocks of the area all boundaries of the precambrian rocks with younger strata in the area are either faults or unconformities some 350 400 m of rhyolitic lavas form the oldest rocks seen in the area they are extensively silicified and devitrified and show little of their original texture although flow banding is visible in some outcrops and the presence of perlitic and snowflake textures imply that originally they were glassy in part these lavas are succeeded by a varied succession dominated by volcaniclastic siltstones showing evidence of shallow water deposition and containing medusoids and trace fossils of ediacaran age interbedded in the sediments are basaltic lavas autobreccias and rare hyaloclastites displaying textural features characteristic of submarine eruption and rhyolitic pumiceous and shardic ash flow tuffs the name coomb volcanic formation is proposed for this succession within which are recognized two members a lower castell cogan rhyolite member succeeded by the coed cochion volcaniclastic member in association are varied intrusions comprising both dolerites and dacites a palaeoenvironmental model built on evidence of petrography palaeontology and sedimentology is that of shallow water to emergent volcanic islands

a candidate stratotype for the precambrian cambrian boundary fortune head burin peninsula southeastern newfoundland the burin peninsula exhibits an exceptionally thick and essentially continuous succession of marine strata through the precambrian cambrian transition fossils are abundant and include trace fossils small shelly fossils vendotaenid algae soft bodied megafossils and microfossils the burin peninsula is readily accessible and has long been considered a potential area for a precambrian cambrian boundary stratotype a continuous section through the upper part of member 1 and all of member 2 of the chapel island formation is exposed at fortune head and this section is herein proposed as a global stratotype for the precambrian cambrian boundary the boundary horizon is located 2 4 m above the base of member 2 of the chapel island formation this horizon marks the base of the basal cambrian phycodes pedum ichnofossil zone and immediately overlies the top of the late precambrian harlaniella podolica ichnofossil zone shelly fossils sabelliditids first appear a few metres below the proposed boundary sof

diffusion in the matrix of granitic rock field test in the stripa mine three field experiments in granitic rock were performed at 360 m depth in a mine to investigate diffusion in the undisturbed rock matrix the results from all three experiments showed that tracers had migrated through the disturbed zone close to the injection hole and a distance into the undisturbed rock matrix these results show that it is possible for dissolved compounds to migrate into the rock matrix in its natural stress environment diffusivities and hydraulic conductivities obtained in this in situ experiment compare well with those obtained in laboratory experiments

reappraising the neoproterozoic east avalonian terranes of southern great britain abstract inliers of late neoproterozoic basement rocks exposed in southern great britain described in summary herein have been previously attributed to a series of terranes bounded by major crustal lineaments that form a dissected remnant of a single subduction complex together these terranes have been termed east avalonia and interpreted as correlative with west avalonia of the northern appalachian orogen a review of age and nd and o isotopic data shows an essentially ensialic complex with two broad overlapping divisions 1 the monian composite terrane of nw wales and fenland terrane of eastern england that are characterised by felsic intrusions at around 615 ma and have more evolved end t 7 5 to 2 5 older t dm 1868 ma to 1269 ma and generally more elevated 18 o up to 13 7 and 2 a more diverse assemblage represented by the cymru wrekin and charnwood terranes including more substantive volcano sedimentary successions and intrusions ranging in age between around 710 ma and 566 ma in which 615 ma magmatic rocks are not represented less evolved end t 2 5 to 3 5 younger t dm 1501 994 ma and lower 18 o 6 5 to 10 1 comparison with other neoproterozoic basement units throughout the northern appalachian orogen shows that both divisions from southern great britain have closer isotopic affinity with igneous components of ganderia which generally have evolved compositions interpreted to reflect an ensialic setting and the input of gondwanan cratonic source components they are mostly dissimilar from magmatic rocks of west avalonia which typically have less evolved compositions interpreted to reflect the contribution of juvenile mesoproterozoic source components

a large scale flow and tracer experiment in granite 2 results and interpretation water and tracer flow has been monitored in a specially excavated drift in the stripa mine several new experimental techniques and equipment were developed and used the whole ceiling and the upper part of the walls were covered with 375 individual plastic sheets where the water flow into the drift could be collected eleven different tracers were injected at distances between 11 and 50 m from the ceiling of the drift the flow rate and tracer monitoring was kept up for more than 2 years the tracer breakthrough curves and flow rate distributions were used to study the flow paths velocities hydraulic conductivities dispersivities and channeling effects in the rock in a companion paper the experimental design and performed experiments are described the present paper describes the interpretation of flow and tracer movement in the rock outside the drift the tracer movement was measured by the more than 160 individual tracer curves the tracer experiments have permitted the flow porosity and dispersion to be studied the possible effects of channeling and the diffusion of tracers into stagnant waters in the rock matrix and in stagnant waters in the fractures have also been addressed

estimating central equatorial pacific sst variability over the past millennium part i methodology and validation abstractconstraining the low frequency lf behavior of general circulation models gcms requires reliable observational estimates of lf variability this two part paper presents multiproxy reconstructions of nino 3 4 sea surface temperature over the last millennium applying two techniques composite plus scale cps and hybrid regularized expectation maximization regem truncated total least squares ttls to a network of tropical high resolution proxy records this first part presents the data and methodology before evaluating their predictive skill using frozen network analysis fna and pseudoproxy experiments the fna results suggest that about half of the nino 3 4 variance can be reconstructed back to a d 1000 but they show little lf skill during certain intervals more variance can be reconstructed in the interannual band where climate signals are strongest but this band is affected by dating uncertainties which are not formally addressed here the cps reliably estimates interannual varia

tracer transport in fractured crystalline rock evidence of nondiffusive breakthrough tailing extended tailing of tracer breakthrough is often observed in pulse injection tracer tests conducted in fractured geologic media this behavior has been attributed to diffusive exchange of tracer between mobile fluids traveling through channels in fractures and relatively stagnant fluid between fluid channels along fracture walls or within the bulk matrix we present a field example where tracer breakthrough tailing apparently results from nondiffusive transport tracer tests were conducted in a fractured crystalline rock using both a convergent and weak dipole injection and pumping scheme deuterated water bromide and pentafluorobenzoic acid were selected as tracers for their wide range in molecular diffusivity the late time behavior of the normalized breakthrough curves were consistent for all tracers even when the pumping rate was changed the lack of separation between tracers of varying diffusivity indicates that strong breakthrough tailing in fractured geologic media may be caused by advective transport processes this finding has implications for the interpretation of tracer tests designed to measure matrix diffusion in situ and the prediction of contaminant transport in fractured rock

cambrian burgess shale animals replicated in clay minerals although the evolutionary importance of the burgess shale is universally acknowledged there is disagreement on the mode of preservation of the fossils after burial elemental mapping demonstrates that the relative abundance of elements varies between different anatomical features of the specimens these differences reflect the compositions of the minerals that replicated the decaying organism which were controlled by contrasts in tissue chemistry delicate morphological details are replicated in the elemental maps showing that authigenic mineralization was fundamental to preserving these fossils even though some organic remains are also present

tightly linked zonal and meridional sea surface temperature gradients over the past five million years the climate of the tropics and surrounding regions is defined by pronounced zonal east west and meridional equator to mid latitudes gradients in sea surface temperature these gradients control zonal and meridional atmospheric circulations and thus the earth s climate global cooling over the past five million years since the early pliocene epoch was accompanied by the gradual strengthening of these temperature gradients here we use records from the atlantic and pacific oceans including a new alkenone palaeotemperature record from the south pacific to reconstruct changes in zonal and meridional sea surface temperature gradients since the pliocene and assess their connection using a comprehensive climate model we find that the reconstructed zonal and meridional temperature gradients vary coherently over this time frame showing a one to one relationship between their changes in our model simulations we systematically reduce the meridional sea surface temperature gradient by modifying the latitudinal distribution of cloud albedo or atmospheric co2 concentration the simulated zonal temperature gradient in the equatorial pacific adjusts proportionally these experiments and idealized modelling indicate that the meridional temperature gradient controls upper ocean stratification in the tropics which in turn controls the zonal gradient along the equator as well as heat export from the tropical oceans we conclude that this tight linkage between the two sea surface temperature gradients posits a fundamental constraint on both past and future climates global mean temperatures during the pliocene epoch were warmer than at present with a shallow meridional temperature gradient numerical simulations suggest that since the pliocene the meridional and zonal temperature gradients have varied in tandem

eocene el nino evidence for robust tropical dynamics in the hothouse much uncertainty surrounds the interactions between the el nino southern oscillation enso and long term global change past periods of extreme global warmth exemplified by the eocene 55 to 35 million years ago provide a good testing ground for theories for this interaction here we compare eocene coupled climate model simulations with annually resolved variability records preserved in lake sediments the simulations show pacific deep ocean and high latitude surface warming of approximately 10 degrees c but little change in the tropical thermocline structure atmosphere ocean dynamics and enso in agreement with proxies this result contrasts with theories linking past and future hothouse climates with a shift toward a permanent el nino like state

degassing of deep groundwater in fractured rock around boreholes and drifts deep groundwater contains dissolved gases that may come out of solution if the water pressure is lowered water pressures are often decreased down to atmospheric pressure when water is withdrawn from deep boreholes and drifts in the bedrock for example in investigations regarding nuclear waste disposal groundwater degassing may then contribute to the development of a local unsaturated zone around the borehole or drift which may affect inflow and as a consequence the outcome of hydraulic and tracer tests in fractured rock laboratory experiments with gas saturated water in rock fracture replicas have demonstrated that degassing causes considerable hydraulic conductivity reduction under certain conditions degassing has also been hypothesized to be the cause of observed flow reductions in the field however supporting field experiments have so far been lacking we report results that constitute the first field support of the development of an unsaturated zone and as a consequence hydraulic conductivity reduction due to groundwater degassing around a borehole the borehole tests were conducted approximately 450 m below the groundwater table at the aspo hard rock laboratory in southeastern sweden no hydraulic conductivity reductions were observed at gas contents of about 1 whereas a 50 reduction in hydraulic conductivity was observed at a gas content of 13 formal hypothesis testing based on all available field and laboratory degassing tests supports degassing as the actual cause of the observed hydraulic conductivity reduction at the higher gas content we also show analytically that hydraulic conductivity reductions due to degassing may occur at much lower gas contents around drifts than around boreholes

solute transport through fractured rock radial diffusion into the rock matrix with several geological layers for an arbitrary length decay chain the paper presents a model development to derive a semi analytical solution to describe reactive solute transport through a single channel in a fracture with cylindrical geometry the model account

consequences of shoaling of the central american seaway determined from modeling nd isotopes the central american seaway played a pivotal role in shaping global climate throughout the late cenozoic recent geological surveys have provided new constraints on timing of the seaway shoaling while neodymium isotopic e nd data measured on fossil teeth debris and ferromanganese crusts have helped define the history of water masses in the region here we provide the first 3 d simulations of e nd responses to the shoaling seaway our model suggests that a narrow and shallow seaway is sufficient to affect interoceanic circulation that inflow outflow balance between the caribbean and the antilles responds nonlinearly to sill depth and that a seaway narrower than 400 km is consistent with an active atlantic meridional overturning circulation during the late miocene simulated e nd values in the caribbean confirm that inputs from radiogenic pacific waters in the caribbean decrease as the seaway shoals despite model limitations a comparison between our results and e nd values recorded in the caribbean helps constrain the depth of the central american seaway through time and we infer that a depth between 50 and 200 m could have been reached 10 ma ago

processes controlling the mean tropical pacific precipitation pattern part i the andes and the eastern pacific itcz abstract the question of why the intertropical convergence zone itcz is generally north of the equator in the tropical pacific is addressed experiments with an atmospheric general circulation model coupled to idealized representations of the ocean show that the presence of the andes is enough to lower sea surface temperature sst off the west coast of south america through evaporation thus promoting a north south asymmetry with the itcz north of the equator which is amplified by interactions between the ocean and the atmosphere the evaporative cooling results mainly from the subsidence of low specific humidity air which is due in turn to the mechanical effect of the andes on the zonal mean flow the positive feedback from low level clouds on sst is an important factor for the efficiency of the mechanism described west of 120 w the presence of the rockies and himalayas produces a comparable forcing to that of the andes but this is not enough to reverse or neutralize the north south asymmetry se

simulation of enso with a global atmospheric gcm coupled to a high resolution tropical pacific ocean gcm abstract a global atmospheric general circulation model gcm coupled to an oceanic gcm that is dynamically active only in the tropical pacific simulates variability over a broad spectrum of frequencies even though the forcing the annual mean incoming solar radiation is steady of special interest is the simulation of a realistically irregular southern oscillation between warm el nino and cold la nina states its time scale is on the order of 5 years the spatial structure is strikingly different in the eastern and western halves of the ocean basin sea surface temperature changes have their largest amplitude in the central and eastern tropical pacific but the low frequency zonal wind fluctuations are displaced westward and are large over the western half of the basin these zonal wind anomalies are essentially confined to the band of latitudes 10 to 10 s so that they form a jet and have considerable latitudinal shear during el nino the associated curl contributes to a pair of pronounced minima in th

a simple model for the pacific cold tongue and enso abstract a conceptual model is constructed based upon the bjerknes hypothesis of tropical atmosphere ocean interaction it is shown that strong feedbacks among the trade winds equatorial zonal sea surface temperature contrast and upper ocean heat content occur in the tropical pacific basin coupled atmosphere ocean dynamics produce both the strong pacific cold tongue climate state and the el nino southern oscillation enso phenomenon the cold tongue climate state is unstable and gives rise to the self sustained enso which can be understood as an equatorial ocean recharge oscillator the small basin size and the influence of a wind system resulting from heating sources of its adjacent landmasses are responsible for a weak and stable atlantic cold tongue state that cannot support enso like interannual variability the presence of westerly wind associated with the walker circulation ascending at the western pacific warm pool disables the dynamical coupling processes in the equatorial indian ocean as a

a stability analysis of tropical ocean atmosphere interactions bridging measurements and theory for el nino abstract interactions between the tropical oceans and atmosphere permit a spectrum of natural modes of oscillation whose properties period intensity spatial structure and direction of propagation depend on the background climatic state i e the mean state this mean state can be described by parameters that include the following the time averaged intensity of the pacific trade winds the mean depth h of the thermocline and the temperature difference across the thermocline t a stability analysis by means of a simple coupled ocean atmosphere model indicates two distinct families of unstable modes one has long periods of several years involves sea surface temperature variations determined by vertical movements of the thermocline that are part of the adjustment of the ocean basin to the fluctuating winds requires a relatively deep thermocline and corresponds to the delayed oscillator the other family requires a shallow thermocline has short periods of a year or two has sea surface tempe

the interaction between the western indian ocean and enso in cesm several previous studies have suggested that a cool western indian ocean may induce convection over indonesia leading to surface convergence and easterlies over the western equatorial pacific ocean these easterlies then increase the pacific warm water volume favouring el nino in the next year we investigate this mechanism of indian pacific interaction using output from two simulations at 0 1 circ and 1 circ ocean model resolution with the community earth system model cesm no conclusive evidence for the suggested interaction mechanism is found in cesm like many other coupled models cesm has an overly strong sea surface temperature variability in the eastern indian ocean due to an exaggerated sensitivity of the sea surface temperature to thermocline variations due to this bias the effect of the western indian ocean signals on the pacific as found from observational analysis is hidden our analysis shows that this bias can be traced to errors in the time mean vertical temperature profile in the indian ocean this bias needs to be reduced to allow a better investigation of the subtle interactions between the indian and pacific oceans

formation of the cold tongue and enso in the equatorial pacific basin abstract this paper proposes a mechanism that explains how coupled dynamics alone can spontaneously give rise to a realistic west east asymmetric mean state and an enso like interannual variability without requiring the existence of an external preexisting west east asymmetry in circulation the essence of the newly proposed mechanism is that the basinwide ocean atmosphere coupling acts to reduce the effective restoring force as a result the coupled oceanic waves travel more and more slowly within the equatorial ocean basin as the coupling strength increases when the coupling strength reaches a critical value the zonally leveled thermocline becomes unstable as a result of the weakening of the effective restoring force at which the theoretical limit of the traveling timescale would be infinite without nonlinearity due to nonlinearity in the coupled system this primary air sea interaction instability leads to a west east asymmetric mean state in which the atmosphere has a prevailing easterly and the

channeling with diffusion into stagnant water and into a matrix in series numerous field observations show that most water flow in fractured rocks takes place in only a small part of the fractures we call these channels solutes in the flowing water can diffuse in and out of stagnant water in the porous rock matrix that the flowing water contacts via the so called flow wetted surface fws in addition the solutes can diffuse into stagnant water in the fractures themselves and from this water further into the rock matrix for narrow channels with small fws the transport via the stagnant water in the fracture can considerably add to the exchange of solutes between flowing water and matrix water for sorbing solutes that interact with the micropore surfaces in the matrix the effect can be very strong some models that account for these processes are developed and solved using laplace transforms some examples are presented that show the effects of first diffusion into stagnant waters in fractures with subsequent diffusion into the rock matrix effects of slit like and tube like channels are considered as well as the presence of intersecting fractures the solutions are especially useful to model solute transport in complex three dimensional channels networks where wide and narrow or even tube like channels with widely varying flow rates combine into a multitude of different paths

the maintenance of an equatorially asymmetric state in a hybrid coupled gcm abstract an ocean general circulation model is coupled with a simple atmosphere model to investigate the formation mechanism of the intertropical convergence zone in the eastern pacific which is observed in the northern hemisphere the coupled model develops an asymmetric state under conditions symmetric about the equator the zonal variation in equatorial upwelling leads to pronounced differences between the western and other parts of the ocean in the western warm water pool region where the cooling effect of the equatorial upwelling is suppressed both atmospheric and oceanic surface conditions are symmetric about the equator on the other hand in the central region where the upwelling cools the equatorial ocean a single itcz forms off the equator in the northern or southern hemisphere depending on the initial condition a strong contrast exists in the sea surface temperature sst between the hemispheres sst is much higher at the latitude of the itcz than that on the other side of the equator thi

oxygen and carbon isotope stratigraphy of early cambrian carbonates in southeastern newfoundland and england carbonate rocks have been sampled through predominantly siliciclastic sediments above the precambrian cambrian global stratotype level in southeastern newfoundland to assess their potential for oxygen and carbon isotope stratigraphy comparable successions were sampled at nuneaton and comley in england greatly depleted 18 o signals are attributed to widespread thermal alteration during deep burial and granitic intrusion including within the stratotype region carbon isotope ratios appear to have been less affected and these are described from nine sections a provisional composite 13 c curve is based on non ferroan pink nodular and bedded micrites several 13 c excursions occur in the fossiliferous bonavista group and allow the position of the tommotian atdabanian boundary to be identified chemostratigraphic correlation of the new precambrian cambrian boundary stratotype may however prove difficult because of the lack of suitable well preserved carbonates the search must begin for a comparable reference section allowing global correlation of the boundary level using chemostratigraphy as well as biostratigraphy

petrology and geochemistry of chert on the marginal zone of yangtze platform western hunan south china during the ediacaran cambrian transition the ediacaran cambrian transition was one of the most critical intervals in earth history during this interval widespread chert was precipitated commonly as a stratal wedge in carbonates along the southern margin of the yangtze platform south china the chert wedge passes into a full chert succession further basinward to the south east four lithotypes of chert are identified across the marginal zone in western hunan mounded vein brecciated and bedded chert the mounded chert is characterized by irregular to digitiform internal fabrics generally with abundant original vesicles and or channels that mostly are lined by botryoidal chalcedony cements with minor quartz and barite crystals the host chert or matrix of these mounds is dominated by amorphous cryptocrystalline silica commonly disseminated with pyrite the vein chert with minor quartz locally generally cross cuts the overlying dolostone and chert horizons and terminates under the mounded and or bedded chert bodies the brecciated chert commonly occurs as splayed intrusions or funnel shaped wedges and cross cuts the topmost dolostones the bedded chert the most common type generally is thin to medium bedded and laminated locally it is composed of amorphous silica with minor amounts of black lumps microthermometry of fluid inclusions from vein and void lining minerals mainly quartz and barite revealed homogenization temperatures from 120 to 180 c for the trapped primary fluids compositionally these chert deposits generally are pure with sio2 92 wt and only minor fe2o3 and al2o3 contents most of which show positive europium anomalies in rare earth element patterns especially for the mounded chert all these data suggest that the marginal zone chert deposits resulted from a low temperature silica rich hydrothermal system in which the mounded chert was precipitated around the releasing vents i e as silica chimneys the vein and splayed brecciated chert however was formed along the syndepositional fault fracture conduits that linked downward while the bedded chert was precipitated in the quieter water column from the fallout of hydrothermal plumes onto the sea floor these petrological and geochemical data provide compelling evidence and a new clue to the understanding of the extensive silica precipitation rapid tectonodepositional and oceanic changes during the ediacaran cambrian transition in south china

problematic bedding plane markings from the middle proterozoic manganese subgroup bangemall basin western australia abstract enigmatic bedding plane markings impressions resembling isolated strings of beads occur in sandy and argillaceous strata of the stag arrow formation in the middle proterozoic manganese subgroup bangemall group of the bangemall basin east of newman western australia markings are abundant at two localities and traces are found at a third structures similar in both morphology and dimension have previously been reported from the appekunny formation in the middle proterozoic belt supergroup of u s a the manganese subgroup structures provide further details of morphology enabling comparison with a variety of biogenic and non biogenic structures a source for the markings still cannot be determined with certainty but a biogenic origin is favoured and affinities with the green or brown algae suggested such an origin is consistent with records of megascopic algae from rocks of similar age

ocean atmosphere interaction and the tropical climatology part ii why the pacific cold tongue is in the east abstract the influence of coupled process on the climatology of the tropical pacific is studied in a model for the interaction of equatorial sst the associated component of the walker circulation and upper ocean dynamics in this part the authors show how different physical mechanisms affect the spatial pattern of the pacific warm pool and cold tongue in this coupled climatology when model parameters give a suitable balance between effects of upwelling and thermocline depth on sea surface temperature and for suitable atmospheric parameters a good prototype for the observed cold tongue configuration is produced this is largely determined by coupled ocean atmosphere processes within the basin presence of an easterly wind s component produced by factors external to the pacific basin can be important in setting up a cooling tendency but this is magnified and modified by a chain of nonlinear feedbacks between trade winds and ocean dynamics affecting the sst gradient within the basin these feedbacks d

silicified horodyskia and palaeopascichnus from upper ediacaran cherts in south china tentative phylogenetic interpretation and implications for evolutionary stasis horodyskia is one of the earliest known macroscopic life forms with a fossil record dating from c 1 4 ga palaeopascichnus represents a key ediacaran element with world wide distribution however their body constructions and affinities are poorly understood partly because previously described species are mostly preserved as casts and moulds in siliciclastic rocks silicified specimens from the upper ediacaran liuchapo formation in eastern guizhou south china are described as horodyskia minor sp nov and palaeopascichnus jiumenensis sp nov their taxonomic assignments are based on their uniserial arrangement of spheroidal or discoidal units which are connected by a filament and surrounded by a quartz halo they are unlikely to be brown algae animal traces faecal pellets colonial metazoans or giant sulphide oxidizing bacteria instead we propose that horodyskia and palaeopascichnus may be phylogenetically related and their collective morphologies allow tentative comparison with agglutinated foraminifers the segments can be compared with cytoplasm filled chambers connecting filament with small passage between chambers and quartz haloes with agglutinated tests however their ontogeny appears to be distinct from that of modern foraminifers the occurrences of horodyskia fossils in mesoproterozoic and ediacaran rocks indicate an extremely long range c 900 ma and echoes the proposition of extended evolutionary stasis in the proterozoic

cambrian successions of the meguma terrane nova scotia and harlech dome north wales dispersed fragments of a peri gondwanan basin abstract the meguma terrane of nova scotia and the harlech dome of north wales preserve similar sedimentary successions of cambrian age both successions comprise a thick succession of early cambrian sandstone turbidites overlain by early to middle cambrian alternating mud rich and sand rich units in which manganese is concentrated in two stratigraphic intervals above these both successions comprise anoxic organic rich turbidites shallowing upward into paler more bioturbated tremadocian mudstone with rhabdinopora within the limited constraints of the available biostratigraphic and geochronological data major changes in environment occurred synchronously in the two successions both successions show much greater similarity to each other than to adjacent successions on avalonia9 a detrital zircon analysis from the rhinog formation low in the harlech dome succession reveals distinct clusters of ages around 537 ma and 2 0 2 1 ga a close similarity to analyses from the meguma terrane suggests proximity between the two terranes on the margin of gondwana during the cambrian period we suggest the term megumia for the palaeogeographical domain that included the two successions which was dispersed during subsequent appalachian and caledonian movements these observations suggest that megumia may have separated terranes previously regarded as parts of avalonia supplementary material u pb detrital zircon analytical data are available at http www geolsoc org uk sup18431

equatorial mid tropospheric easterly jet over the eastern pacific comparison from the ecmwf and ncep ncar reanalyses 1 the upper air data set of the european centre for medium range weather forecasts ecm 1979 93 reanalysis is evaluated in comparison to the national centers for environmental prediction national center for atmospheric research ncp reanalysis for the same period attention is focused on the equatorial mid tropospheric easterly jet emtej over the eastern pacific first noted from a short series of rawin soundings at galapagos and then corroborated in its broad spatial context from the ncp 40 year reanalysis the present follow up study contributes a comparison of evidence from the two sources with different model assimilations the major characteristics of the emtej are confirmed although the winds from ecm are overall slower and those from ncp faster than the measurements over galapagos in both ecm and ncp the easterly speed maximum along the equator is over the eastern pacific located around 600 700 mb and further westward at progressively lower elevations divergence prevails in the realm of the speed maximum and is primarily fed by subsidence from aloft the ecm evidence differs from ncp by a more westward location of the easterly speed maximum and overall weaker flow

the asian australian monsoon and el nino southern oscillation in the ncar climate system model features associated with the asian australian monsoon system and el nino southern oscillation enso are described in the national center for atmospheric research ncar global coupled climate system model csm simulation characteristics are compared with a version of the atmospheric component of the csm the ncar ccm3 run with time evolving ssts from 1950 to 1994 and with observations the csm is shown to represent most major features of the monsoon system in terms of mean climatology interannual variability and connections to the tropical pacific this includes a representation of the southern oscillation links between strong asian australian monsoons and associated negative sst anomalies in the eastern equatorial pacific the equatorial sst gradient across the pacific in the csm is shown to be similar to the observed with somewhat cooler mean ssts across the entire pacific by about 18 28c the seasonal cycle of ssts in the eastern equatorial pacific has the characteristic signature seen in the observations of relatively warmer ssts propagating westward in the first half of the year followed by the reestablishment of the cold tongue with relatively colder ssts propagating westward in the second half of the year like other global coupled models the propagation is similar to the observed but with the establishment of the relatively warmer water in the first half of the year occurring about 1 2 months later than observed the seasonal cycle of precipitation in the tropical eastern pacific is also similar to other global coupled models in that there is a tendency for a stronger than observed double itcz year round particularly in northern spring but with a well reproduced annual maximum of itcz strength north of the equator in the second half of the year time series of area averaged ssts for the nino3 region in the eastern equatorial pacific show that the csm is producing about 60 of the amplitude of the observed variability in that region consistent with most other global coupled models global correlations between nino3 time series global surface temperatures and sea level pressure slp show that the csm qualitatively reproduces the major spatial patterns associated with the southern oscillation lower slp in the central and eastern tropical pacific when nino3 ssts are relatively warmer and higher slp over the far western pacific and indian oceans with colder water in the northwest and southwest pacific indices of asian australian monsoon strength are negatively correlated with nino3 ssts as in the observations spectra of time series of indian monsoon australian monsoon and nino3 sst indices from the csm show amplitude peaks in the southern oscillation and tropospheric biennial oscillation frequencies 3 6 yr and about 2 3 yr respectively as observed lag correlations between the nino3 sst index and upper ocean heat content along the equator show eastward propagation of heat content anomalies with a phase speed of about 0 3 m s21 compared to observed values of roughly 0 2 m s21 composites of el nino la nina events in the csm show similar seasonal evolution to composites of observed events with warming cooling of greater than several tenths of a degree beginning early in northern spring of year 0 and diminishing around northern spring of year 11 but with a secondary resurgence in the csm events later in northern spring of year 11 the csm also shows the largest amplitude enso sst and low level wind anomalies in the western tropical pacific with enhanced interannual variability of ssts extending northeastward and southeastward toward the subtropics compared to largest interannual sst variability in the central and eastern tropical pacific in the observations

problematic fossils in the late neoproterozoic wonoka formation south australia abstract complex biogenic structures are described from the upper wonoka formation late neoproterozoic of the adelaide geosyncline south australia the structures are preserved within silty limestones and calcareous siltstones as dark bedding plane markings defining branching arrays of parallel elongate curved elements the fossils bear at least a superficial resemblance to the putative trace fossil palaeopascichnus normally preserved in siliciclastic sediments and reported from a number of late neoproterozoic sections worldwide the material from the wonoka formation is not a trace fossil and seems most likely to represent a surface encrusting alga the nature of palaeopascichnus needs to be carefully reassessed in the light of the possibility that the wonoka fossils represent a different preservational window into the same phenomenon the thin ca 2 m but widespread nature of the fossil horizon makes it a useful stratigraphic marker within the wonoka formation with the potential to aid in regional correlation within the adelaide geosyncline

palaeozoic palaeomagnetic studies in the welsh basin recent advances in the last two years new palaeomagnetic data fro m wale s have resulted i n radical revision of the ordovician palaeogeography of eastern avalonia part of the southern margin of the iapetus ocean combined with palaeozoic palaeomagnetic data from laurentia and gondwana these data suggest that eastern avalonia was a peri gondwanide high latitude continental fragment during at least part of ordovician time with a palaeolatitude of about 62 s and 51 s in arenig and llanvirn time respectively this implies a latitudinal width of the early ordovician iapetus ocean between eastern avalonia and laurentia of at least 30 geological evidence for the proximity of eastern avalonia and laurentia suggests that the intervening iapetus ocean closed during silurian time from late llandovery to early ludlow recent palaeolatitude data from the iapetus bordering continents are consistent wit h closure b y middle to late silurian time new pre acadian early devonian palaeomagnetic data from the old red sandstone places the welsh basin at about 17 s consistent with a palaeogeography in which laurentia baltica avalonia armorica and possibly gondwana wer e part o f a singl e supercontinent pervasiv e lat e carboniferous early permia n remagnetization affect s the welsh basin the remagnetization i s probably associated with fluids emanating from th e variscan thrust front w e do not observe remagnetization associate d with acadian orogen y and the remagnetizations which have been studied in more detail in north america appear to be a unique feature of the variscan hercynian alleghenian orogeny

a large scale flow and tracer experiment in granite 1 experimental design and flow distribution this paper describes the stripa three dimensional experiment where water and tracer flow has been monitored in a specially excavated drift in the stripa mine several new experimental techniques and equipment were developed and used the experiment was performed in a specially excavated drift 100 m long at the 360 m level in granite the whole ceiling and the upper part of the walls were covered with 375 individual plastic sheets where the water flow into the drift could be collected eleven different tracers were injected at distances between 11 and 50 m from the ceiling of the drift the flow rate and tracer monitoring was kept up for more than 2 years the tracer breakthrough curves and flow rate distributions were used to study the flow paths velocities hydraulic conductivities dispersivities and channeling effects in the rock this paper describes the experimental techniques the fracture mapping the tracer and flow rate measurements and the results of the flow rate measurements the detailed observations made possible by the plastic sheeting technique have given some qualitative as well as quantitative information on flow rate distribution in fractured rock which previously has not been available these observations may be of importance for assessing the transport of dissolved species such as radionuclides through fractured rock

the eastern subtropical pacific origin of the equatorial cold bias in climate models a lagrangian perspective abstractglobal climate models frequently exhibit cold biases in tropical sea surface temperature sst in the central and eastern equatorial pacific here lagrangian particle back trajectories are used to investigate the source regions of the water that upwells along the equator in the ipsl climate model to test and confirm the hypothesis that the sst biases are caused by remote biases advected in from the extratropics and to identify the dominant source regions water in the model is found to be sourced primarily from localized regions along the western and eastern flanks of the subtropical gyres however while the model sst bias is especially large in the northwestern subtropical pacific about 5 c it is found that the eastern subtropics contribute to the equatorial bias the most this is due to two distinct subsurface pathways connecting these regions to the equator the first pathway originating in the northwestern subtropical pacific has relatively long advection time scales close to or exceed