agulhas current influence on the shelf dynamics of the kwazulu natal bight abstractthe agulhas current is a fast western boundary current flowing along the south african east coast strongly influencing oceanographic variability on the adjacent kwazulu natal shelf hydrographic observations in january 2010 july 2010 and july 1989 have been used to describe variations in geostrophic currents and water masses and to elucidate mechanisms of change in circulation and thermohaline structure differences in wind forcing precipitation and solar insolation caused modifications in stratification and mixing that resulted in seasonal changes in surface temperature salinity and mixed layer depth zmld between the austral summer and winter surveys during january 2010 surface temperatures were elevated and there was a large range in salinity as the upper 10 m was influenced by river outflow and rainfall in july 2010 and 1989 surface temperatures were lower and the salinity range was significantly less the zmld in january 2010 was much shallower varying between 5 and 40 m while dee

aquifer recharge depletion and connectivity inferences from grace land surface models and geochemical and geophysical data data from the gravity recovery and climate experiment grace and outputs of the clm4 5 model were used to estimate recharge and depletion rates for large aquifers investigate the connectivity of an aquifer s subbasins and identify barriers and preferred pathways for groundwater flow within an aquifer system the nubian sandstone aquifer system and its subbasins dakhla northern sudan platform and kufra in northeast africa were used for demonstration purposes and findings were tested and verified against geological geophysical remote sensing geochronologic and geochemical data there are four major findings 1 the average annual precipitation data over recharge areas in the southern kufra section and the northern sudan platform subbasin were estimated at 54 8 km 3 and 32 8 km 3 respectively and knowing the annual extraction rates over these two areas 0 40 0 20 km 3 recharge rates were estimated at 0 78 0 49 km 3 yr and 1 44 0 42 km 3 yr respectively 2 grace derived groundwater depletion rates over the dakhla subbasin and the northern kufra section were estimated at 4 44 0 42 km 3 yr and 0 48 0 32 km 3 yr respectively 3 the observed depletion in the southern parts of the dakhla subbasin is apparently caused by the presence of the east west trending uweinat aswan basement uplift which impedes the south to north groundwater flow and hence reduces replenishment from recharge areas in the south 4 a major northeast southwest trending shear zone pelusium shear system is apparently providing a preferred groundwater flow pathway from the kufra to the dakhla subbasin our integrated approach provides a replicable and cost effective model for better understanding of the hydrogeologic setting of large aquifers worldwide and for optimum management of these groundwater resources

slow spreading ridge axis tectonics evidence from the lizard complex uk abstract the east coast section of the lizard ophiolite complex cornwall u k preserves a series of interrelated extensional faults and dyke sets which indicate that the formation of this section of obducted oceanic lithosphere resulted from a combination of contemporaneous structural and magmatic events three dolerite dyke sets are evident the first two sets 1 and 2 are cut by and rotated on a series of ridge parallel extensional faults and shear zones later dykes set 3 cross cut the extensional faults these data indicate that both rotation and significant thinning in the region of 40 of this part of the oceanic lithosphere occurred prior to the final period of dyke injection the thinning of the lithosphere was the result of extension along the normal faults all of the dolerite dykes show morb characteristics although the late dykes set 3 are more primitive tending to be aphyric to sparse olivine phyric and show higher cr ni and lower zr values than the typically plagioclase phyric dolerite dykes sets 1 and 2 intruded prior to the ductile shearing event the more primitive dolerites post date the tectonism and indicate the lack of a significant magma chamber following a period of amagmatic extension the data are consistent with observations at present day slow spreading ridge axes and some mafic ultramafic ophiolite sequences and provide insight into the nature of ridge related structures and the interrelationships between tectonism and geochemical evolution of the dykes and record a mechanism listric faulting to account for the presence of peridotites and gabbros commonly dredged at slow spreading centres

the effect of north pacific sea surface temperature anomalies on the january climate of a general circulation model abstract four perpetual january integrations of an atmospheric general circulation model have been performed in each of which a different sea surface temperature sst anomaly was specified in the north pacific the observed sst anomaly for the 1976 77 winter was chosen as the basic anomaly and 1200 day runs were carded out in which this anomaly was multiplied by 1 and 2 a fifth run was performed which combined the basic midlatitude sst anomaly from 1976 77 with a tropical pacific sst anomaly representative of the mature phase of a warm el nino southern oscillation enso episode an ensemble of eight independent 90 day averaged realizations was extracted from each simulation maps of ensemble mean differences from the model climatology are presented in this paper together with estimates of the statistical significance of some of the features which appear on these maps the model response to the basic sst anomaly and to twice the basic sst anomaly is a midiatitude teleconnection pattern the pacifi

discussion on shrimp u pb zircon dating of the exhumation of the lizard peridotite and its emplacement over crustal rocks constraints for tectonic models in this recent contribution nutman et al 2001 provide the first shrimp u pb zircon age data for the lizard peridotite and its immediate envelope and demonstrate the usefulness of ion microprobe geochronology in the unravelling of the complex thermo tectonic history inherent in the emplacement of such assemblages of plausibly oceanic rocks onto continental strata building on the research of cook et al 2000 the authors distinguish clearly between the lizard peridotite proper a mass of c 15 kbar mantle tectonite and the contiguous crousa downs complex of gabbro troctolite and sheeted mafic dykes emplaced into the peridotite following its exhumation and cooling thus although exhibiting many lithologies and structures characteristic of ophiolites the oceanic part of the lizard complex is clearly at least bipartite the studies of cook et al 2000 and nutman et al 2001 rationalize and clarify several problematic relationships in this extensively studied but still ambiguous suite we understand that the editorial handling of nutman et al s paper overlapped with the publication in this journal of our detailed account of the petrogenesis of the kennack gneiss which incorporates an evaluation of the tectonic context of this controversial unit on the basis of an idtims single zircon date sandeman et al 2000 we consider none the less that several aspects of the new contribution require comment these include nutman et al s interpretations of our earlier documentation of the petrology and age relationships of the kennack gneiss sandeman et al 1995 the man of war gneiss sandeman et al 1997 and the porthkerris plagiogranite clark et al 1998 b as well as our overview of the emplacement history of the lizard complex clark et al 1998 a an extended abstract cited but not referenced by nutman et al we employ herein the revised palaeozoic time scale of mckerrow

evidence for the influence of the agulhas current on regional atmospheric circulation patterns abstract the agulhas current is much the strongest western boundary current in the southern hemisphere transporting about 65 sv of warm water along the southeast coast of africa south of africa it retroflects back into the south indian ocean and flows east as the agulhas return current large amounts of heat are lost to the atmosphere from the warm waters of the southern agulhas current its retroflection and the return current particularly during winter and the transition seasons it is thought that this large exchange of heat may have a significant influence on the regional atmospheric circulation the tracks and intensity of transient weather disturbances such as extratropical cyclones and on rainfall received over large parts of neighboring southern africa in an attempt to investigate the potential influence of the agulhas current on the regional atmosphere two ensembles of year long integrations of an atmospheric general circulation model are analyzed in the first ensemble the sea surface tem

the palaeozoic variscan oceans revisited abstract geological evidence supported by biogeographical data and in accord with palaeomagnetic constraints indicates that one ocean models for the variscides should be discarded and confirms instead the existence of three gondwana derived microcontinents which were involved in the variscan collision avalonia north armorica franconia and thuringia subdivided by a failed vesser rift and south armorica central iberia armorica bohemia all divided by small oceans in addition parts of south eastern europe including adria and apulia are combined here under the new name of palaeo adria which was also peri gondwanan in the early palaeozoic oceanic separations were formed by the break up of the northern gondwana margin from the late cambrian onwards most of the oceans or seaways remained narrow but much like the alpine cenozoic oceans gave birth to orogenic belts with hp uhp metamorphism and extensive allochthons the saxo thuringian ocean between north and south armorica and the galicia moldanubian ocean between south armorica and palaeo adria only the rheic ocean between avalonia and peri gondwana was wide enough to be unambiguously recorded by biogeography and palaeomagnetism and its north western arm closed before or during the emsian in europe ridge subduction under the northernmost part of armorica in the emsian created the narrow and short lived rheno hercynian ocean it is that ocean and not the rheic whose opening and closure controlled the evolution of the rheno hercynian foldbelt in south west iberia south west england germany and moravia czech republic devonian magmatism and sedimentation set within belts of early variscan deformation and metamorphism are probably strike slip related the first arrival of flysch on the forelands and or the age of deformation of foreland sequences constrains the sequential closure of the variscan seaways galicia moldanubian in the givetian saxo thuringian in the early famennian rheno hercynian in the tournaisian additional mid to late devonian and partly early carboniferous magmatism and extension in the rheno hercynian saxo thuringian and galicia moldanubian basins overlapped with variscan geodynamics as strictly defined the early carboniferous episode was the start of episodic anorogenic heating which lasted until the permian and probably relates to tethys rifting

isotope geochemistry and revised geochronology of the purrido ophiolite cabo ortegal complex nw iberian massif devonian magmatism with mixed sources and involved mesoproterozoic basement abstract in the purrido ophiolite cabo ortegal complex new u pb zircon dating of the amphibolite g03 8 by laser ablation inductively coupled plasma mass spectrometry confirms the existence of a dominant mesoproterozoic zircon population with a refined age of 1155 14 ma however the u pb zircon dating of two more amphibolite samples by sensitive high resolution ion microprobe has provided new ages of 395 3 ma and 395 2 ma respectively interpreted as the crystallization age hf isotope data for zircon show that most of the devonian zircons crystallized from a juvenile depleted mantle source the mesoproterozoic zircons have relatively juvenile hf isotopic composition reflecting some influence of an older component a few devonian zircon crystals show evidence of mixing with an older component represented by the mesoproterozoic zircons the whole rock sm nd isotope data indicate an important heterogeneity in the composition of the purrido amphibolites only compatible with the generation of their protoliths from two sources we interpret these puzzling data as resulting from the mixing of a devonian mantle derived magma with a mesoproterozoic basement these new data provide new perspectives in the interpretation of the most common ophiolites across the variscan suture in europe supplementary material analytical methods zircon u th pb shrimp analytical data zircon u th pb la icp ms analytical data zircon lu hf la mc icpms analytical data and whole rock sm nd isotope data are available at http www geolsoc org uk sup18449

the missing rheic ocean magmatic arcs provenance analysis of late paleozoic sedimentary clastic rocks of sw iberia abstract early carboniferous turbiditic sedimentary rocks in synorogenic basins located on both sides of the rheic suture in sw iberia were studied for provenance analysis an enigmatic feature of this suture which resulted from closure of the rheic ocean with the amalgamation of pangea in the late carboniferous is that there are no recognizable mid to late devonian subduction related magmatic rocks which should have been generated during the process of subduction on either side of it u pb la icp ms geochronology of detrital zircons from early carboniferous turbidites in the vicinity of the rheic suture in sw iberia where it separates the ossa morena zone with gondwana continental basement to the north from the south portuguese zone with unknown meguma continental basement to the south reveals the abundance of mid to late devonian 51 81 and early carboniferous 13 25 ages the cabrela and mertola turbidites of the ossa morena and south portuguese zones respectively are largely devoid of older zircons differing from the age spectra of detrital zircons in the oldest late devonian strata in the underlying south portuguese zone which contain abundant cambrian and neoproterozoic ages mid to late devonian zircons in the cabrela formation age cluster at c 391 ma eifelian givetian transition and mertola formation age clusters at c 369 ma and at c 387 ma famennian and givetian respectively are attributable to a source terrane made up of magmatic rocks with a simple geological history lacking both multiple tectonic events and older continental basement the terrane capable of sourcing sediments dispersed on both sides of the suture is interpreted to have been completely removed by erosion in sw iberia given that closure of the rheic ocean required subduction of its oceanic lithosphere and the absence of significant arc magmatism on either side of the rheic suture we suggest 1 the source of the zircons in the sw iberia basins was a short lived rheic ocean magmatic arc and 2 given the lack of older zircons in the sw iberia basins this short lived arc was probably developed in an intra oceanic environment

holocene climate change in southernmost south africa rock hyrax middens record shifts in the southern westerlies abstract south africa s southern coastal margin is recognised as being a highly dynamic climatic region that plays a critical role in both regional and global atmospheric and oceanic circulation dynamics our understanding of the past dynamics of this system however has been limited by the number and nature of datasets available that can be used to infer changes in key climatic parameters in the region in this paper we present new high resolution 13c and 15n data from two independently dated rock hyrax procavia capensis middens from seweweekspoort in south africa s groot swartberg mountains these data provide information regarding both past vegetation and hydroclimatic change and allow a regional integration of available data that explore the long term dynamics of mid latitude circulation systems in the african sector of the southern hemisphere combined a negative relationship is apparent between temperature and humidity in this area of the southern cape and these changes can for the first time be clearly linked to variations in antarctic sea ice extent and shifts in the southern westerly storm track this dynamic is particularly evident between 5 and 7 cal kbp when a reduction in sea ice extent and a southward shift of the westerlies are manifested regionally by increased temperatures and a phase of marked aridity

storm tracks in the southern hemisphere abstract from 1979 to 1989 global european centre for medium range weather forecasts ecmwf analyses of many meteorological variables important in baroclinic storms have been bandpass filtered to highlight fluctuations on 2 to 8 day time scales in order to illuminate the relationships among the variables in baroclinic storm track regions because of the greater zonal symmetry in the southern hemisphere sh versus the northern hemisphere nh it is possible to examine these relationships over a zonal sector without being dominated by local effects associated with jet stream entrance and exit regions of the storm tracks the bandpassed variance of geopotential height is used to define the storm track and its meridional profile has a pronounced midlatitude maximum in the sh the locations of the jet stream and the variance maxima of meridional and zonal velocity components vorticity vertical motion specific humidity and temperature all bear a distinctive relationship to the storm track but the lat

potential field imaging of palaeozoic orogenic structure in northern and central europe abstract the trans european suture zone tesz is the most fundamental lithospheric boundary in europe separating the ancient crust of the fennoscandian shield east european craton from the younger crust of central europe and extending deep into the mantle geophysical potential field images provide an overview of the entire palaeozoic orogenic system of northern and central europe for the first time the tesz is largely concealed by sedimentary basins of permian cenozoic age geological observations are largely restricted to local basement highs and deep boreholes and the coverage of deep seismic surveys is widely spaced despite experiments recently acquired within the europrobe programme by contrast the potential field data offer a relatively detailed coverage of standardised observations throughout the tesz while some features of the images may be sourced in the near surface particularly in the gravity image much of their content reflects the structure of the underlying palaeozoic basement at the scale presented the images highlight the most fundamental features of the crustal structure of the tesz these include the strong contrast between the highly magnetic crust of the east european craton and the less magnetic palaeozoic accreted terranes of central europe the lateral continuity of terranes and their internal structure particularly where arc magmatic complexes are involved and the location and geometry of the terrane boundaries oceanic sutures and strike slip zones that separate them

teleconnections in the southern hemisphere abstract teleconnections are calculated from monthly mean anomalies of sea level pressure and 500 mb geopotential height for the southern hemisphere 10 90 s for five month winter and summer seasons the monthly means were calculated from australian analyses for the period from june 1972 to november 1980 zonally averaged anomalies at both sea level and 500 mb display an out of phase relation between low and high latitudes and in midlatitudes are negatively correlated with anomalies in the subtropics and polar regions in winter a striking zonal wavenumber 3 pattern is found over the southern ocean anomalies in 500 mb geopotential heights at 50 s 95 e 58 s 150 w and 38 s 15 w exhibit strong positive correlations while showing weaker negative correlations with heights over antarctica and in low latitudes a similar pattern appears in sea level pressure in summer anomalies in 500 mb geopotential height over the three subtropical continents appear to occur out of phase with anomalies over the su

upper palaeozoic ophiolite generation and obduction in south cornwall the gramscatho flysch sequence of south cornwall including the melanges of the meneage formation and the lizard ophiolite are described in relation to the development of the gramscatho basin the timing and geotectonic evolution of this feature are considered in its regional context within the rhenohercynian zone of northwest europe this zone is interpreted as an intracontinental dextral transform system that developed during the devonian closure of the so called massif central ocean a basin and rise topography is attributed to extension and compression at offsets on major faults e w extension of the gramscatho pull apart basin in middle and upper devonian times is believed to have caused rifting and the development of ocean crust from which the lizard ophiolite was assembled in an oceanic setting at a ridge transform junction the meneage formation was generated as a result of intrabasinal uplift on transcurrent faults a major change of plate motions took place when the massif central ocean finally closed at the end of the devonian and the weak rhenohercynian zone became a site of crustal convergence from which thrust nappes were transported northwards foreland basins were sequentially developed and deformed by thin skinned tectonics as the system advanced northwards during the carboniferous

mesoscale and submesoscale processes in the southeast atlantic and their impact on the regional thermohaline structure the turbulent processes in the cape basin the southeasternmost gate of the atlantic ocean play a key role in the transport and mixing of upper to intermediate water masses entering the area from the indian ocean making them especially relevant for the indo atlantic transfer of heat and salt in this paper two numerical simulations at different horizontal resolutions are used to study meso and submesoscale dynamics their phenomenology their evolution and their impact on the local water masses submesoscale processes seasonally affect both the upper and intermediate layers but there are clear dynamical differences between the two layers several types of instabilities underline this spatial and temporal variability near the surface mixed layer instabilities occur during winter while mesoscale driven instabilities as the symmetric type prevail in summer the connection between these two seasonal regimes is ensured in anticyclonic eddies and within the mixed layers by charney baroclinic instabilities involved in the local formation and subduction of mode water that we have dubbed as agulhas rings mode water intermediate depths are instead characterized by mesoscale mechanisms of density compensation and lateral stirring of the tracer variance triggering a significant filamentogenesis whose vertical scales are comparable to those mentioned in previous studies this leads to a particularly efficient mixing of antarctic intermediate waters of indian and atlantic origins lagrangian estimates highlight the new and significant role of fine scale structures in setting the water masses properties of upper and lower thermocline waters materializing the indo atlantic exchange and therefore potentially affecting the global ocean circulation

ophiolitic mylonites in the lizard complex ductile extension in the lower oceanic crust ophiolitic rocks in the lizard complex southwestern england preserve fine examples of mylonitic schists within low angle amphibolite facies shear zones two prominent shear zones with type localities at carrick luz and porthoustock both have a footwall in the mafic ultramafic interface at the base of the oceanic crust the carrick luz shear zone shows mylonitized gabbro above peridotite mafic dikes both predate and postdate the shearing the porthoustock shear zone brings down higher oceanic crustal levels gabbro sheeted dike complex against ultramafic rocks and has an extensional geometry shear sense indicators show hanging wall movement directions different from those predicted by previous northward obduction models generation of these ophiolitic mylonites is interpreted instead as due to ductile extension at an oceanic spreading center

geochemistry and u pb and 40ar 39ar geochronology of the man of war gneiss lizard complex sw england pre hercynian arc type crust with a sudeten iberian connection the man of war gneiss is a variably deformed meta igneous body that ranges in composition from gabbro to tonalite and comprises part of the basal structural slice of the lizard ophiolite complex sw england u pb dating of zircon demonstrates that the parental magmas crystallized in the earliest ordovician 499t s 3 ma but 40 ar 39 ar step heating analysis of amphiboles suggests that at least the northernmost zone of the gneiss was subjected to an amphibolite grade metamorphic event at c 374 ma probably associated with thrust emplacement of the ophiolite the gneiss exhibits major trace and rare earth element variations in conformity with an origin through partial melting of an amphibolitic source containing hornblende and plagioclase probably with minor garnet and zircon the elemental abundances and variations are characteristic of granitoids formed in supra subduction zone environments a granitoid sill within the adjacent old lizard head series schists previously inferred to be related to the man of war gneiss is trondhjemitic and exhibits higher sio 2 tio 2 and mgo but lower zr v ba and sr contents and therefore is probably not genetically related to the latter the sill may record local melting during ophiolite emplacement the man of war gneiss probably represents a structural inlier of pre hercynian basement incorporated in the hercynian nappes of sw england during nnw directed thrusting we emphasize the geological and geochronological similarities between variably deformed granitoid units of the lizard complex the sudeten massif of southern poland and the allochthonous complexes of northern portugal and nw spain these granitoid rocks may represent dispersed remnants of tremadoc arcs that formed oceanward from the northern margin of gondwana this is further convincing evidence that at this time eastern avalonia was separated from northern gondwana by an ocean basin that may have been connected with the tornquist sea

mesoscale convective complexes over southern africa abstractthe maximum spatial correlation technique mascotte is an objective and automated method developed to simultaneously determine both the structural properties and evolution tracking of cloud shields of convective systems originally designed to monitor systems over the amazon region this method has now been adapted for subtropical southern africa in this paper a detailed climatology of 70 mesoscale convective complexes mccs that occurred during the austral summer months over southern africa during the 1998 2006 period are presented most mccs are clustered along the eastern regions of southern africa adjacent to the warm waters of the mozambique channel and agulhas current a few infrequent systems are found to be developing in namibia and botswana the systems are found to predominantly occur during the months of november february with maximum activity occurring in november and december the transition from a more midlatitude dominated circulation to a tropical circulation over the regio

siegenian generation of the lizard ophiolite u pb zircon age data for plagiogranite porthkerris cornwall the long controversial age of the lizard ophiolite is resolved by u pb dating of three single magmatic zircons from a plagiogranite dyke near porthkerris point this demonstrates that the axial oceanic crust was undergoing extensional ductile shearing mylonitization amphibolite facies metamorphism and probably anatexis at 397 2 2 ma in conjunction with published k ar 40 ar 39 ar and rb sr data for the complex this early devonian age predicates a protracted interval between intra oceanic magmatism and deformation on the one hand and obduction during late devonian northwestward displacement of the normannian high on the other

a model for the tectonic evolution of south cornwall a stratigraphy for south cornwall is combined with an analysis of the chronology of thrust nappe emplacement the resulting model suggests that northward overthrusting of nappes of flysch and olistostrome ophiolite and continental basement is related to the closure of an oceanic basin in south cornwall involving southward subduction throughout the devonian the subsequent continental collision between the normannian high and part of laurentia occurred in the upper devonian with deformatian continuing until late carboniferous times

constraints on the p t conditions and age of emplacement of the lizard ophiolite cornwall amphibole plagioclase thermobarometry and 40ar 39ar geochronology of basal amphibolites the basal slice of the lizard complex incorporates strongly foliated amphibolitic metabasites lower landewednack schists interpreted as the remnants of a dynamothermal aureole formed beneath the ophiolite during intraoceanic thrusting structurally overlying the basal slice and occurring predominantly within the overlying lizard peridotite is the kennack gneiss a controversial banded and gneissose unit comprising intimately mixed amphibolitic and granitic components interpreted to represent commingled melts thermobarometry of hornblende plagioclase pairs indicates that both the landewednack schists and the mafic component of the kennack gneiss recrystallized synkinematically at ca 600 c and 300 400 mpa three amphiboles two from the kennack gneiss and one from the landewednack schists yield disturbed 40ar 39ar age spectra characterized by low temperature overprinting but with good high temperature plateaux with ages of 366 1 4 2 364 2 4 8 and 359 8 7 4 ma respectively theoretical dif

utilizing the geophysical and hydrogeological data for the assessment of the groundwater occurrences in gallaba plain western desert egypt the investigated region is located in the western desert fringes of the nile valley which requires studies of groundwater related to the many projects of land reclamation the key objective of this paper is to estimate the qualitative and geometrical features of the investigated aquifer using 60 vertical electrical sounding and time domain electromagnetic soundings allows us to suggest one possible model of the geometrical features of the local aquifer a hydrogeological monitoring has been undertaken to investigate the current groundwater situation at the gallaba plain such hydrological monitoring has not been undertaken before in detail the results show that the investigated region has high groundwater potentialities in two main aquifers which belong to pleistocene shallow fresh water and deep brackish water the lithological and structural elements contribute mainly to recharge and store the groundwater in the western part of the river nile in kom ombo graben the geochemical properties of the groundwater of the studied aquifers reflect meteoric water which is a fresh to slightly brackish water the small amount of groundwater salinity arises from silicate weathering and evaporation processes occurring in the aquifer matrix moreover most of the studied groundwater samples are unfit for human consumption such samples are very satisfactory for livestock and poultry purposes and they can be used for irrigation using modern and improved irrigation methods e g sprinkler and drip methods furthermore the hydrogeological monitoring of the concerned area indicates that it has high groundwater potentialities which will support its sustainable development

processes driving thunderstorms over the agulhas current 1 lightning occurs predominantly over land and is not common over the open ocean we study here one oceanic region in which thunderstorms are frequently found namely the warm agulhas current off the southeast coast of south africa the seasonal and interannual lightning variability is derived from satellite and terrestrial data sets favorable climatic conditions for lightning are investigated using both era interim and ncep ncar reanalysis data we find peak lightning in austral autumn over the agulhas current but with low seasonality i e there is considerable lightning throughout the year while the climatological wind direction varies strongly with latitude and season the wind direction is predominantly northerly throughout the region during thunderstorms a composite of sea level pressure during thunderstorm days indicates that thunderstorms are related to eastward propagating synoptic scale wave trains passing through the agulhas current region the strong convective activity during thunderstorms occur in the warm sector of a cyclone and is associated with horizontal convergence and lifting of warm moist surface air originating over the warm agulhas current

numerical modeling of groundwater resource management options in the east oweinat area sw egypt southwest egypt is an arid area with no surface water and limited resources of useable groundwater in the well known nubian sandstone aquifer system these groundwater reserves have been heavily exploited since the 1960s which has led to substantial decline in the potentiometric surface of the aquifer a calibrated regional numerical model with refined grids on the pumping centers has been used to investigate the hydrodynamic impacts of different groundwater management options on the potentiometry of the aquifers the results indicate that there is a real danger of either dewatering the shallow aquifer in some areas e g kharga oasis or increasing the water depth to uneconomic lifting depth they also indicate that although the planned extraction rates in dakhla farafra and bahariya oases are feasible for at least the coming 100 years the present rate for kharga oasis and the planned rate for the east oweinat area have to be reduced substantially

groundwater flow modeling and particle tracking for chemical transport in the southern voltaian aquifers groundwater is the major source of water supply for most uses in the rural settlements in ghana a groundwater flow model was calibrated for some aquifers of the southern voltaian sedimentary system under steady state conditions the objective was to determine estimates of the hydraulic conductivities of the different hydrostratigraphic units of the southern voltaian and the distribution of recharge from precipitation data on the stable isotopes of oxygen and hydrogen from the study area suggest that groundwater recharge in the area is from rainfall the calibrated steady state model suggests that aquifer hydraulic conductivities in the study area range from 1 19 to 6 3 m day hydrostratigraphic unit specific hydraulic conductivities are discussed the calibrated recharge ranges from 3 81e 05 m day to 6 0e 04 m day which represents 0 9 6 of the precipitation in the form of rainfall six distinct flowpaths have been defined using particle tracking the particle tracking simulation suggests travel times in the range of 380 to 5 199 years from recharge areas to discharge areas along the flowpaths identified a contaminant dropped at the recharge areas in the central sections of the model area would travel at these rates along the flowpaths assuming that advection is the dominant transport process inverse geochemical modeling indicates the dissolution of albite k feldspars and anorthite respectively along flowpaths i and iv the inverse modeling along flowpaths i and iv suggest the dissolution of albite k feldspar and anorthite respectively at 1 085e 06 3 16e 08 and 3 168e 07 mmol year

moisture uptake in the boundary layer above the agulhas current a case study shipboard meteorological measurements and radiosonde ascents are used to describe the modification of the marine atmospheric boundary layer as air is advected across the warm agulhas current toward the coast the data were collected on april 28 1995 during the agulhas current air sea exchange experiment south of port alfred south africa in a region characterized by a strong sea surface temperature gradient the surface latent heat flux increased from approximately 160 w m 2 over the seaward border to 270 w m 2 over the current approximately 80 90 km wide and decreased dramatically to approximately 40 w m 2 over the cool shelf this spatial heat flux gradient was reflected in the overlying atmosphere by a transition in atmospheric stability from the warm current to the cool continental shelf a convective boundary layer over the current was replaced by a stable boundary layer over the cool shelf where a deep residual moisture layer indicated the former vertical extent of convective eddies a progressive accumulation of moisture occurred within the boundary layer as the air mass was advected over the current mean specific humidity and precipitable water vapor content in the boundary layer over the shelf were 20 25 higher than over the seaward border of the current the results give credence to the assertion by many investigators that moisture uptake above the agulhas current may contribute significantly to moisture convergence and rainfall over the interior of south africa

the south indian ocean current in this paper the historical hydrographic database for the south indian ocean is used to investigate i the hydrographic boundary between the subtropical gyre and the antarctic circumpolar current acc the subtropical front stf and especially ii the southern current band of the gyre a current band of increased zonal speeds in the upper 1000 m is found just north of the stf in the west near south africa and at the surface stf in the open indian ocean until the waters off the coast of australia are reached as neither any other investigation of this current nor a name for it are known the flow has been called the south indian ocean current sioc this name is anologous to the same current band in the south atlantic ocean the south atlantic current the stf is located in the entire south indian ocean near 40 degrees s the associated current band of increased zonal speeds is the sioc which is found at or north of the stf east of 100 degrees e the sioc separates from the stf and continues to the northeast the zonal flow south of the stf is normally weak and serves to separate the south indian ocean and circumpolar currents near africa the sioc has a typical volume transport of 60 sv 1 sv 10 6 m3 s 1 in the upper 1000 m relative to deep potential density surfaces of sigma 4 45 87 kg m 3 2800 3500 m or sigma 2 36 94 kg m 3 1500 2500 m near western australia the sioc is reduced to about 10 sv as it turns to the northeast

the emplacement of peridotites and associated oceanic rocks from the lizard complex southwest england upper mantle peridotites and associated oceanic rocks from the lizard complex south west england preserve evidence for a multistage geological history steeply dipping pre emplacement fabrics record high temperature 900 1100 c shearing and exhumation of the mantle peridotites apparently formed during localized ne sw rifting in a pull apart basin setting c 400 390 ma associated oceanic rocks landewednack amphibolites preserve a pre emplacement prograde brown amphibole bearing metamorphic assemblage and steeply dipping fabric thought to have formed as the newly formed oceanic crust was juxtaposed with newly exhumed hot mantle peridotite during ne sw rifting in both the peridotites and landewednack amphibolites steep pre emplacement structures are cross cut by low angle mylonitic fabrics thought to have formed during the initial phases of emplacement of mantle over crustal rocks in a partially intra oceanic setting c 390 375 ma the fabrics in peridotites and amphibolites exhibit retrograde mineral assemblages c 500 800 c with the amphibolites preserving two superimposed assemblages green amphibole titanite and colourless magnesio hornblende respectively that are thought to record progressive down temperature deforma tion during thrusting emplacement related structures in both the basal peridotites and amphibolites consistently dip at low to moderate angles nw with down dip lineations and kinematic indicators showing consistent top to the nw senses of shear syn emplacement magmatism is recorded by intrusions of foliated kennack gneiss anastomosing serpentine filled faults mark many existing low angle contacts between the peridotites and landewednack amphibolites and appear to represent the final lowest temperature 250 c stages of emplacement c 370 ma this study shows that dynamothermal aureoles in ophiolites may preserve evidence for tectonothermal events that pre date thrust emplacement

impacts of sst anomalies in the agulhas current system on the regional climate variability abstractthe potential impact of the variability in the agulhas current system on the large scale atmospheric state in the southern hemisphere is examined using the monthly near surface baroclinicity as the key parameter for the period between september 1980 and august 2002 dominant patterns of anomalous near surface baroclinicity found from empirical orthogonal function eof analyses in the region that includes most of the agulhas current system show a wide variety of anomaly patterns some of which indicate spatial shifts in the position of the agulhas retroflection and or agulhas return current composited anomalies in various atmospheric fields sea surface temperature and the net surface heat flux at the air sea boundary based on the signals in the eofs suggest that sea surface temperature anomalies in the agulhas current system thermally force the atmosphere on the synoptic scale via modification of the near surface baroclinicity in march and april and possibly in january and february as well

deformation and emplacement of the lizard ophiolite complex sw england based on evidence from the basal unit the basal unit of the lizard ophiolite complex preserves evidence of a protracted deformation and accretion history the earliest recognizable events record the construction of ocean crust and the generation of the lizard ophiolite complex in a slow spreading ridge axis environment the initial stages of deformation involved the development of a sub horizontal crustal scale shear zone and its progressive deformation by ductile thrusting and folding subsequent deformation progressed with the out of sequence stacking of ocean lithosphere in which detachment initiated at mid crustal levels culminated in mantle decoupling as thrust slices were derived from progressively deeper crustal levels the progressive emplacement of a coherent slice of ocean lithosphere over previously accreted units and the generation of a dynamothermal aureole are consistent with models suggesting rapid overthrusting of young ocean lithosphere evidence from the dynamothermal aureole indicates that syn emplacement extensional collapse of the complex occurred in response to thrust loading foreland directed offsliding and lateral thrusting mark the final stages in the collapse of the complex

simulation of impact of present and future groundwater extraction from the non replenished nubian sandstone aquifer in southwest egypt a numerical time dependent groundwater model of the nubian sandstone aquifer in egypt is presented a complete database of the hydrogeological and drilling information of 850 water wells drilled in the period 1960 2000 was evaluated and used for the model parameter input as well as for its calibration a steady state condition is rejected even for the pre development time as the subsurface inflow across the egyptian sudanese borders is lower than discharge and the observed hydraulic gradient is residual gradient and not due to steady state flow the results of the long period simulation 10 000 years indicated that the nubian sandstone aquifer is still under the influence of the past humid period and has been in an unsteady deplenishing process therefore groundwater development plans should be based on this concept the calibrated model was used to investigate the hydrodynamic impacts of the present and planned groundwater extraction on the potentiometry of the aquifer the simulation results indicate that there is a real danger of groundwater depletion particularly in the shallow aquifer in some areas in fact if the planned extraction of 1 200 million m3 year in east oweinat area is imposed drawdown after 100 years could be as much as 200 m relative to1960s levels by this time the cone of depression will extend to dakhla and kharga oases

re interpreting the devonian ophiolites involved in the variscan suture u pb and lu hf zircon data of the moeche ophiolite cabo ortegal complex nw iberia new u pb zircon data of a mylonitic greenschist from the moeche ophiolite one of the mafic units involved in the variscan suture in the cabo ortegal complex nw of the iberian massif yielded an age of 400 3 ma consequently this unit can be considered one of the devonian ophiolites the most extended group of oceanic units in the variscan belt the mafic rocks show transitional compositions between n morb and island arc tholeiites although lu hf isotope signatures of its zircons clearly indicate contribution from an old continental source ehf values in the analysed zircons are negative generally below ehf 5 and thence they are not compatible with their generation from a juvenile mantle source accordingly the igneous protoliths were generated in a setting where juvenile mafic magmas interacted with an old continental crust the devonian ophiolites from the variscan suture have been repeatedly interpreted as remnants of the rheic ocean however the presence of a continental source in the origin of the mafic rocks of the moeche ophiolite allows discarding an intraoceanic setting for their generation at least for the nw iberian counterparts the tectonic setting for the devonian ophiolites of nw iberia is very likely represented by an ephemeral oceanic basin opened within a continental realm herein the real rheic ocean suture could only be located west of the terrane represented by the upper units of the allochthonous complexes apparently that suture is not represented in nw iberia

mitigation of groundwater level deterioration of the nubian sandstone aquifer in farafra oasis western desert egypt el farafra oasis is included in the new valley project which started in the 1960s this project is based exclusively on groundwater of the well known nubian sandstone aquifer nsa the hydraulic head drawdown problem in farafra oasis constitutes a big problem because it threatens the availability of the only water source in the oasis hydrogeologically farafra oasis belongs to the huge artesian unrenewable fossil water nubian from sandstone aquifer the problem began to appear at the end of the 1990s instantaneously with increased drilling of deep water wells huge quantities of water 267 million m3 are derived from the aquifer every year hydraulic head depression cones are formed around the main reclamation areas where the groundwater surface lowered by 35 m below the ground surface numerical modeling was used to investigate the hydrodynamic impacts of the present and planned groundwater extraction on the groundwater levels besides the possible means of mitigating the continuous decrease of the groundwater levels the aquifer simulation indicated that there is a significant head decline of the groundwater particularly in the first productive zone four scenarios were applied to signify the present and future development plans for the next 20 years i e year 2033 applying the present conditions reveal that heads are more declined than now another 30 and 17 8 m in the first and second productive zones respectively are expected to be added to the present groundwater drawdowns groundwater is expected to decline significantly if the pumping rates are to be increased by 50 in response to natural development of the agricultural society and continuous need to more cultivation lands groundwater heads are expected to be lower by about 40 m in the first productive zone and 24 m in the second productive zone the third plan examines the impact of reducing the pumping rate by about 25 on groundwater levels by applying recent irrigation techniques as drop and sprinkler irrigation methods instead of the presently used flood irrigation in this case simulated drawdowns are expected to decline and the maximum drawdowns recorded are 19 and 10 m through the next 20 years in the first and second productive zones respectively to mitigate the groundwater level deterioration the study suggests the reduction of pumping rates by about 20 by applying the recent irrigation techniques besides reclamation of about 11 000 feddan 4620 hectare to accommodate the increasing population and need of cultivation lands in the oasis in the next 20 years according to plan the simulated groundwater levels are expected to decrease by about 20 3 and 12 m at the end of the simulation period year 2033 this means that the rate of head decline is lowered to about 1 m year for the first productive zone and 0 6 m year for the second productive zone with the increase in the cultivation area by about 16 therefore the study recommends the fourth plan to manage the groundwater resource in farafra oasis

south african palaeoenvironments during marine oxygen isotope stage 4 a context for the howiesons poort and still bay industries abstract spanning the period from 74 58 ka and being broadly coeval with marine oxygen isotope stage 4 mis 4 the still bay and howiesons poort industries represent important phases in the development of the material culture of early modern humans how and why these industries occurred when they did however remain matters for speculation a key element of this debate has been the question of what role environmental change during the early stages of the last glacial period may have had on influencing human activity unfortunately well dated palaeoenvironmental evidence from this period is limited and the debate has out of necessity been driven by the application of conceptual models of environmental change many of which associate colder and warmer global climates with increased aridity and humidity respectively in this paper the regional marine and terrestrial evidence is synthesised to create an evidence based palaeoenvironmental context based on the information available to date it appears that rather than being characterised by dry conditions mis 4 was a period of relatively cool moist climates the ubiquity of which transcends the modern regional climate boundaries it is suggested that orbital parameters at this time created greater interaction between tropical and temperate circulation systems bringing more moisture to the subcontinent these findings highlight the distinct nature of southern african climate systems and caution against the application extra regional conceptual models or inferring linear relationships with polar records

pathline calibrated groundwater flow models of nile valley aquifers esna upper egypt abstract strongly concentrated agriculture along the river nile in egypt combined with hydrologic changes related to the construction of the aswan high dam in the 1970 s has led to increasing salinization and waterlogging of agricultural areas successful control and remediation of these problems requires accurate understanding of the shallow quaternary aquifers within the nile valley while extensive conceptual models have been developed by the egyptian rigw published numerical models have yet to incorporate all features of the conceptual model in particular marine affinity of some shallow groundwaters within the valley cl as the predominant anion indicates significant leakage from deeper cretaceous aquifers into the shallow quaternary aquifers a feature that is not present in current models in this study groundwater profile modeling incorporating the bedrock leakage demonstrates that its shallow appearance requires hydraulic separation of surficial from deep recharged zones of the quaternary aquifer this separation occurs near the boundary between reclaimed and traditional agricultural lands which is also the primary site of waterlogging apparently excessive recharge presumed to occur beneath the reclaimed lands does not penetrate deeply and therefore might be easily remediated with shallow drains profound similarities exist between the nile valley salinization cases and the occurrence of shallow nuisance water in desert southwestern u s cities e g las vegas the u s experience with this problem may provide useful guidance in addressing nile valley salinization and waterlogging issues in the future in general irrigation related recharge from the reclaimed lands in the nile valley may have a much more localized impact on traditional lands than previously thought

groundwater potential for irrigation in the east oweinat area western desert egypt the nubia sandstone aquifer system is one of the most extensive groundwater systems in north africa covering an area of about 2 000 000 km2 including parts of egypt libya sudan and chad in the western desert of egypt the nubian formation has a thermal gradient of 1 1 5 c 100 m 1 with the exception of the east oweinat area located in the southern part of the western desert this is the only part of this huge system where ground water occurs under unconfmed conditions in an area where the nubian sandstone crops out and is underlain by shallow basement rocks in this area groundwater has no thermal characteristics the aquifer system in the east oweinat area attains a relatively high hydraulic conductivity the direction of groundwater flow is generally northeastwards but is distorted at faults and fracture zones chemical analyses of groundwater in the area indicate a low salt content and suitability for irrigation purposes as the estimated recharge to the area is low compared with the foreseen irrigation water requirement the development of groundwater in the east oweinat should be based on groundwater mining although the evaluation of the groundwater resources in east oweinat has indicated that groundwater can be extracted at a rate of 4 7 106 m3 d 1 the long term economics of extraction that can sustain large scale development projects has to be assessed

the differences between early and midwinter atmospheric responses to sea surface temperature anomalies in the northwest atlantic abstract using an atmospheric global spectral model it is shown that the winter atmosphere in the midlatitudes is capable of reacting to prescribed sea surface temperature sst anomalies in the northwest atlantic with two very different responses the nature of the response is determined by the climatological conditions of the winter regime experiments are performed using either the perpetual november or january conditions with or without the prescribed sst anomalies warm sst anomalies in november result in a highly significant anomalous ridge downstream over the atlantic with a nearly equivalent barotropic structure in january the response is a statistically less significant trough the presence of the sst anomalies also causes a northward southward shift of the atlantic storm track in the november january cases a diagnostic analysis of the anomalous heat advection in the simulations reveals that in the january cases the surface heating is offset primarily by the strong horizontal cold advect

a general circulation model study of the atmospheric response to extratropical sst anomalies observed in 1950 79 abstract a 30 year experiment with an atmospheric general simulation model has been performed the lower boundary condition at all oceanic grid points between 38 s and 60 n has been prescribed to follow the observed month to month variation of the sea surface temperature sst field during the 1950 79 period much of the model diagnosis presented here pertains to the midlatitude atmospheric response to recurrent sst patterns in the north pacific and north atlantic in winter the principal modes of variability of the seasonally averaged 515 mb height and sst fields have been identified using rotated principal component rpc analysis the extrema of the first atmospheric mode reside over the north atlantic and eurasia whereas the second mode is associated with height anomalies in the north pacific north american sector cross correlation analysis reveals that these two atmospheric modes am linked to leading patterns of the sst field in the north atlantic and north pacific respectively it is also demonst

a climatology of southern hemisphere extratropical cyclones a climatology of extratropical cyclones determined by an objective automatic scheme applied to 15 years 1975 89 of once daily australian bureau of meteorology hemispheric analyses is presented contour maps of the positions of formation cyclogenesis dissipation cyclolysis together with other cyclone statistics are presented the distribution of cyclones through the hemisphere was found to be dominated by a permanent high latitude core coincident with the circumpolar trough during the winter and intermediate seasons two mid latitude branches are evident in the cyclone density originating in the tasman sea and south american sectors both spiraling poleward and merging with the circumpolar core in the southern oceans systems were observed to move in an castsouth east direction away from their location of formation exhibiting peak speeds of migration in the mid latitudes little seasonality was evident in the densitiy distribution of cyclones through the southern oceans but a considerable amount was found in their central pressure

space and time in the tectonic evolution of the northwestern iberian massif implications for the variscan belt recent advances in geochemical studies of igneous rocks isotopic age data for magmatism and metamorphism quantitative pressure temperature p t estimates of metamorphic evolution and structural geology in the northwestern iberian massif are integrated into a synthesis of the tectonic evolution that places the autochthonous

a numerical model study of an intense cutoff low pressure system over south africa abstract investigations of extreme rainfall events in the southern african region are limited by the paucity of the observational network furthermore the lack of full radar coverage for south africa makes quantitative precipitation estimation difficult therefore numerical modeling represents the most effective method for improving the understanding of the mechanisms that contribute to extreme rainfall events in this region with the caveat that accurate validation of model simulations is hampered by the limited observations in the region this paper describes an intense cutoff low event over south africa that led to record rainfall and flash flooding along the south coast of the country and adjoining hinterland analyses from the global forecast system model showed that the cutoff aloft was accompanied by a strong low level jet llj impinging onto the south coast where rainfall was heaviest and that lapse rates were steep in the lower troposphere simulations of the event were carried out using a num

moisture transport between the south atlantic ocean and southern africa relationships with summer rainfall and associated dynamics moisture exchange between the south atlantic and southern africa is examined in this study through zonal moisture transport along the west coast of southern africa a multivariate analysis of the zonal flow of moisture computed from ncep doe amip ii re analyses reveals a primary mode of variability typical of variations in intensity and of the latitudinal migration of the circulation associated with the midlatitude westerlies and the south atlantic anticyclone in austral summer january february this mode referred to as the south atlantic midlatitude mode is found to be well correlated with rainfall over southern africa i e to the south of the upper lands surrounding the congo basin its positive negative phases are found to correspond with surface pressures changes over the south atlantic region in austral summer when the south atlantic anticyclone is shifted northward southward respectively such changes are accompanied by dipole like sst anomalies in the midlatitude south atlantic ocean while simultaneous sst anomalies with a similar structure are also found over south indian ocean regions in january february positive negative events linked to the south atlantic midlatitude mode are marked by meridional shifts northward southward and weakening strengthening of the itcz over the southern tropics together with modulations in intensity weakened sustained of the angola low which could act as a tropical source of moisture for tropical temperate troughs ttts in association with a strengthened weakened zonal component of the southern extension of the african easterly jet aej this could modulate the meridional transfer of moisture south of 15 s to the advantage detriment of angolan coastal regions where above below rainfall are expected variations in the latitudinal position northward southward of the south atlantic anticyclone and thus of the midlatitude westerlies are also found to reduce favour moisture advection towards southern africa subtropics allowing the southern indian trades to penetrate less more over the subcontinent south of 25 s this would create a situation where convection processes are inhibited supported within the sicz ttts region resulting in drier wetter conditions locally for positive negative events respectively

the kennack gneiss of the lizard peninsula cornwall sw england commingling and mixing of mafic and felsic magmas accompanying givetian continental incorporation of the lizard ophiolite the kennack gneiss comprises a suite of interlayered mafic and felsic igneous rocks that intruded the 397 ma lizard ophiolite complex cornwall at 376 4 1 7 ma u pb single zircon date and were shortly thereafter c 370 ma metamorphosed to the amphibolite facies weakly deformed examples at the type locality of kennack sands reveal net veining of the mafic by the felsic component dispersed enclaves of the former in the latter and flame like interfingering of the two features indicative of magmatic commingling and mixing the silicic components of the kennack gneiss range from granodiorite to syenogranite and from metaluminous to peraluminous the least silicic rocks being the most peraluminous they were generated through anatexis of a predominantly metasedimentary crustal source having trace element and isotopic compositions comparable to those of the devonian gramscatho group of south cornwall the mafic component of the gneiss includes members group 1 which are weakly enriched in light ree have minor negative ta nb p and ti anomalies in extended trace element plots and display primitive time corrected 143 nd 144 nd and 87 sr 86 sr values and others group 2 which are more strongly enriched in all incompatible trace elements exhibit more prominent negative ta nb p and ti anomalies and have isotopic ratios intermediate between group 1 mafic components and the associated felsic gneiss group 2 represents mixtures of group 1 and granitic melts whereas group 1 rocks are comparable to emorb and were probably generated through partial melting of a weakly enriched mantle source emplacement of two commingled magmas into the base of the lizard ophiolite one representing the products of crustal anatexis implies that the ophiolite was removed from its oceanic setting and was in the process of obduction in the givetian

generation of plagiogranite by amphibolite anatexis in oceanic shear zones field geochronological and rare earth element ree evidence obtained from the fournier oceanic fragment of the canadian appalachians indicates that its plagiogranite component was generated by the anatexis of amphibolite and not by the fractionation of basic magma we propose that the process occurred in two stages first gabbro was plastically deformed at high temperature to form dry low angle shear zones that subsequently evolved to amphibolite via the addition of light ree enriched hydrothermal solutions second the amphibolite underwent partial melting during shear to yield a migmatite comprising bands of plagiogranite alternating with amphibolite restite the plagiogranite locally coalesced to form pods dikes and lenses that injected the surrounding undeformed gabbro we attribute the development of the fournier plagiogranite to dynamothermal processes occurring in proximity to a spreading center due to asthenosphere induced shear within ocean layer 3 this serves as an important illustration of the dynamic nature of metamorphism and melting that can occur in the ocean crust

impact of localized tropical and extratropical sst anomalies in ensembles of seasonal gcm integrations a series of 120 day ensemble integrations of a general circulation model designed to assess the impact of geographically localized sea surface temperature sst anomalies in both the tropics and extratropics are described these experiments contribute firstly to an appraisal of the relative roles of tropical and extratropical sst anomalies on interannual variability of the large scale circulation in the northern extratropics and secondly to an assessment of the role of quasi stationary diabatic heating anomalies on model systematic error including blocking activity overall it is found that sst anomalies associated with el nino and la nina have a larger and more reproducible impact on the extratropics than the chosen extratropical sst anomalies these extratropical anomalies were localized to the north west pacific and north west atlantic with realistic amplitude however unlike earlier studies a response to the extratropical north pacific sst anomalies has been obtained over the north pacific which is correlated with the sign of the imposed sst anomaly the response to extratropical sst anomalies in the north west atlantic are similar to the results obtained from an earlier study the downstream responses to the extratropical pacific and atlantic sst anomalies are qualitatively similar to one another overall it is concluded that the northern large scale flow is influenced by such extratropical sst anomalies the response to idealized tropical sst anomalies was also studied in particular a localized anomaly over indonesia had a very substantial impact on the hadley circulation on zonal flow and on blocking frequency over the north pacific and europe this response was such as to reduce model systematic error locally in the vicinity of the sst anomaly remotely around the tropics and remotely in the extratropics a similar though weaker impact on euro atlantic blocking was obtained with an idealized caribbean sst anomaly further statistical and dynamical analyses suggested that the extratropical response to the indonesian sst anomaly occurs through the creation of two distinct planetary scale regimes in one of which the formation of blocks is much favoured by increased ridges on the north eastern side of the oceans

subtropical indian ocean sst dipole events and southern african rainfall an atmospheric general circulation model agcm is used to examine how the regional atmospheric circulation and rainfall over southern africa respond to a recently observed dipole in subtropical sea surface temperature sst over the south indian ocean observations suggest that when sst is warm to the south of madagascar and cool off western australia increased summer rains occur over large areas of southeastern africa the model results suggest that this sst pattern leads to increased rainfall via enhanced convergence of moister than average air over the region increased evaporation occurs over the warm pole in the south west indian ocean and this moist air is advected towards mozambique and eastern south africa as a result of the low pressure anomaly generated over this pole which strengthens the onshore flow

hot or cold emplacement of the lizard complex regional prograde pumpellyite actinolite facies metamorphism ml has affected the gramscatho group sediments and volcanics structurally underlying the lizard complex metamorphism took place synchronously with the main penetrative deformation dl there is no evidence of any increase in the regional gradient towards the lizard complex or of any local thermal overprinting it is concluded that the lizard complex was emplaced in a cooled thrust sheet during dl deformation during a regional heat flow which produced very low grade metamorphism temperatures of 250 350 c and a pressure of several kilobars are estimated

ridge axis deformation and coeval melt migration within layer 3 gabbros evidence from the lizard complex u k ridge parallel extensional shear zones within the layer 3 gabbros of the lizard ophiolite have recorded varied and numerous chemical and mineralogical changes under a variety of p t conditions these changes accompany tectonic exhumation of lower crustal levels by a listric fault mechanism during amagmatic extension at a slow spreading centre deformation within the mid crustal level of layer three resulted in the migration and impregnation of an evolved iron titanium rich silica poor melt along the shear zones this syntectonic infiltration occurred along the lowermost portions of listric faults which rooted in a partially molten zone beneath the ridge axis residual melt was tapped from this underlying zone and tectonically redistributed about deforming gabbros situated immediately above the partially molten zone the occurrence of sub solidus synkinematic assemblages within the shear zones which were generated at various temperatures and water rock ratios is explained in terms of their simultaneous development on listric fault planes in the presence of a hydrothermal fluid phase the sequential overprinting of pre existing assemblages arises from repeated block rotation during amagmatic episodes of extension within an oceanic slow spreading environment

equilibrium atmospheric response to north atlantic sst anomalies abstract the equilibrium general circulation model gcm response to sea surface temperature sst anomalies in the western north atlantic region is studied a coarse resolution gcm with realistic lower boundary conditions including topography and climatological sst distribution is integrated in perpetual january and perpetual october modes distinguished from one another by the strength of the midlatitude westerlies an sst anomaly with a maximum of 4 c is added to the climatological sst distribution of the model with both positive and negative polarity these anomaly runs are compared to one another and to a control integration to determine the atmospheric response in all cases warming cooling of the midlatitude ocean surface yields a warming cooling of the atmosphere over and to the east of the sst anomaly center the atmospheric temperature change is largest near the surface and decreases upward consistent with this simple thermal response the geopotential height field displays a baroclinic

an integrated approach for identification of potential aquifer zones in structurally controlled terrain wadi qena basin egypt abstract wadi qena basin represents one of the most promising regions for future development in egypt fresh water supplies are crucial for such plans we provide an integrated remote sensing landsat aster dem geoeye 1 geophysical aeromagnetic isotopic 18 o 2 h field stratigraphic and structural interpretation and geochemical major dissolved ions approach to delineate zones of potential groundwater resources in wadi qena basin four water bearing horizons were sampled fractured crystalline aquifer nubian aquifer system nas post nubian aquifer system pnas and the quaternary aquifer findings include 1 spatial analysis of remote sensing data in a gis environment indicates extensive structural deformation by dextral faults trending ne sw i e qena safaga shear zone qs and sinistral faults trending nw se i e najd shear zone and sufficient surface water supply from the east through wadi fattera sub basin 2 analysis of geophysical data indicates that these faults control the water bearing horizons in the subsurface 3 isotopic analysis reveals four isotopic groups including two end members one mixed group and one mixed and evaporated group group i highly depleted fossil nubian waters range 18 o from 6 39 to 6 74 and 2 h from 48 21 to 52 46 group ii modern waters in fractured basement range 18 o from 1 41 to 1 51 and 2 h from 5 46 to 6 04 group iii a mixed cluster between nas and modern waters range 18 o from 4 82 to 5 05 and 2 h from 33 28 to 38 54 and group iv samples which have both mixing between the nubian and meteoric waters and also have a considerable deviation from the global meteoric water line gmwl range 18 o from 0 58 to 4 69 and 2 h from 19 59 to 38 68 4 samples with a mixed isotopic signature in group iii which tap the nas and are located along the main channel of wadi fattera area 3600 km 2 provide evidence for modern recharge along surface exposures of the nas and enhanced infiltration along deep seated faults 5 samples with a mixed isotopic signature in group iv which tap the quaternary and pnas aquifers and are located along deep seated faults provide evidence of artesian upward leakage from the deep nas into the shallower quaternary and pnas aquifers the present study improves our understanding of the role of structural control and modern recharge in exploration for aquifer potential in arid environments

conceptualization of the hydrogeological system of some sedimentary aquifers in savelugu nanton and surrounding areas northern ghana groundwater resources play a pivotal role in the rural water delivery system in ghana the hydrogeological system of middle voltaian terrain was simulated using available data on hydraulic heads and boundary conditions the objective was to characterize the general groundwater flow pattern and provide local estimates of the distribution of hydraulic conductivity and recharge fields the results suggest a predominant ne sw flow direction which ties in with the general regional structural trend and indicates that the hydrogeological conditions of the rocks are controlled by structural entities created in the wake of fracturing and or weathering of the rocks whose primary permeabilities are considerably reduced because of high compaction and low grade metamorphism calibrated hydraulic conductivities range between 1 90 and 10 81 m d the spatial distribution appears to reflect the intensity of fracturing and or weathering of the rock and the proportion of the clay fraction of the weathered zone vertical groundwater recharge has been estimated to range between 0 3 and 4 1 of the annual rainfall this recharge rate is quite low and reflects the imperviousness of the thick overburden because of high clay content in some places and high compaction in others despite this apparently low recharge rate groundwater resources potential in the area appear to be high and increased abstraction from existing abstraction wells by up to 50 does not appear to register significant effects on groundwater budgets at the simulated recharge rates this suggests that the well yields are much lower than the potential of the aquifer system the apparently low yields might be associated with poor well development and the choice of inappropriate well completion materials this study recommends a monitoring system to be developed for a much more regional groundwater flow simulation under transient conditions copyright 2012 john wiley sons ltd

rapid emplacement of the oman ophiolite thermal and geochronologic constraints in understanding of ophiolite emplacement requires knowledge of the elapsed time between igneous crystallization and intraoceanic thrusting and the rate and duration of that thrusting hornblende 4oar 39ar ages demonstrate that the igneous oceanic crust in oman crystallized and cooled to 825 k in 1 2 m y hornblende ages from metamorphic rocks and from cross cutting dikes require that the basal metamorphic thrust fault beneath the ophiolite also cooled below 825 k in 1 2 m y motion along the sole thrust accounted for 200 km of displacement at a rate of 100 200 mm yr on the basis of age relationships and thermal considerations we favor a two stage model for the initial stages of samall ophiolite emplacement intraoceanic thrusting over 2 m y old lithosphere at 150 km m y parallel to a spreading ridge for 1 2 m y followed by equally rapid and brief thrusting over cold and old lithosphere preservation of the samail ophiolite is a direct result of its young age and positive buoyancy at the time of ocean closure and we propose that all ophiolites that originated near spreading centers and were emplaced onto continents were young at the time of intraoceanic thrusting

the warm interglacial marine isotope stage 31 evidences from the calcareous nannofossil assemblages at site 1090 southern ocean article i nfo calcareous nannofossil assemblages have been investigated at ocean drilling program odp site 1090 located in the modern subantarctic zone through the pleistocene marine isotope stages mis 34 29 between 1150 and 1000 ka a previously developed age model and new biostratigraphic constraints provide a reliable chronological framework for the studied section and allow correlation with other records two relevant biostratigraphic events have been identified the first common occurrence of reticulofenestra asanoi distinctly correlated to mis 31 32 the re entry of medium gephyrocapsa at mis 29 unexpectedly similar to what was observed at low latitude sites the composition of the calcareous nannofossil assemblage permits identification of three intervals i iii intervals i and iii correlated to mis 34 32 and mis 30 29 respectively are identified as characteristic of water masses located south of the subtropical front and reflecting the southern border of subantarctic zone at the transition with the polar front zone this evidence is consistent with the hypothesis of a northward shift of the frontal system in the early pleistocene with respect to the present position and therefore a northernmost location of the subantarctic front during interval ii which is correlated to mis 31 calcareous nannofossil assemblages display the most significant change characterized by a distinct increase of syra cosphaera spp and helicosphaera carteri lasting about 20 ky an integrated analysis of calcareous nannofossil abundances and few mineralogical proxies suggests that during interval ii site 1090 experienced the influence of subtropical waters possibly related to a southward migration of the subtropical front coupled with an expansion of the warmer agulhas current at the core location this pronounced warming event is associated to a minimum in the austral summer insolation the present results provide a broader framework on the mid pleistocene dynamic of the ocean frontal system in the atlantic sector of the southern ocean as well as additional evidence on the variability of the indian atlantic ocean exchange

highly depleted oceanic lithosphere in the rheic ocean implications for paleozoic plate reconstructions the rheic ocean formed at ca 500 ma when several peri gondwanan terranes e g avalonia and carolinia drifted from the northern margin of gondwana and were consumed during the late carboniferous collision between laurussia and gondwana a key event in the formation of pangea several mafic complexes ranging in age from ca 400 330 ma preserve many of the lithotectonic and or chemical characteristics of ophiolites they are characterized by anomalously high end values that are typically either between or above the widely accepted model depleted mantle curves these data indicate derivation from a highly depleted hd mantle and imply that i the mantle source of these complexes displays time integrated depletion in nd relative to sm and ii depletion is the result of an earlier melting event in the mantle from which basalt was extracted the extent of mantle depletion indicates that this melting event occurred in the neoproterozoic possibly up to 500 million years before the rheic ocean formed if so the mantle lithosphere that gave rise to the rheic ocean mafic complexes must have been captured from an adjacent older oceanic tract the transfer of this captured lithosphere to the upper plate enabled it to become preferentially preserved possible mesozoic cenozoic analogues include the capture of the caribbean plate or the scotia plate from the pacific to the atlantic oceanic realm our model implies that virtually all of the oceanic lithosphere generated during the opening phase of the rheic ocean was consumed by subduction during laurentia gondwana convergence

terminal pleistocene and holocene dynamics of southern africa s winter rainfall zone based on carbon and oxygen isotope analysis of bovid tooth enamel from elands bay cave abstract southern africa s winter rainfall zone wrz is sensitive to changes in the earth s atmospheric and oceanic systems this region has the potential to provide valuable insight into both regional and global paleoenvironmental dynamics 13 c values of herbivore tooth enamel apatite reflect the proportions of c 3 and c 4 plants consumed here we present 13 c and 18 o values for 86 samples of tooth enamel from grazing and browsing bovids from the terminal pleistocene and holocene layers of elands bay cave the assemblage is dominated by steenbok raphicerus campestris and grysbok raphicerus melanotis which are known to feed on browse if available however the assemblage also includes large grazers this study aims to determine whether the grasses they were eating were purely c 3 indicating a winter rainfall regime or included a c 4 component signaling at least some summer rainfall results show that terminal pleistocene and early holocene vegetation communities were overwhelmingly c 3 late holocene animals show slightly more enriched 13 c values indicating that c 4 grasses and perhaps some cam plants utilizing c 4 photosynthesis became more common we infer that late pleistocene including the lgm to early holocene rainfall was largely restricted to the winter months in the late holocene the increased proportion of c 4 cam vegetation may be indicative of changes in the position of storm tracks associated with the westerlies this finding is consistent with other proxy records from southernmost africa that suggest extension of the growing season into warmer months and or relatively warmer temperatures during the late holocene 18 o values from enamel carbonate reflect a complex combination of meteoric drinking water diet and physiological processes and vary quite widely within and between species browsers have more positive 18 o than grazers because a significant proportion of their moisture intake is from leaves enriched in 18 o as a result of evapotranspiration

the rb sr isochron age of the kennack gneiss and its bearing on the age of the lizard complex cornwall an acid vein from a borehole in the kennack gneiss has given a whole rock rb sr isochron age of 369 12 ma this is interpreted as a metamorphic age recording the time of emplacement of the lizard complex this emplacement in late devonian times was part of an early phase of the hercynian orogeny which also affected the gramscatho 9series9 of s cornwall

a modelling and observational study of the relationship between sea surface temperature in the north west atlantic and the atmospheric general circulation results from four pairs of 50 day wintertime integrations of the meteorological office s 5 level general circulation model with warm and cold sea surface temperature s s t anomalies of about 3 k in the northwest atlantic are described difference fields between the warm and cold integrations are statistically significant at the 1 level with positive geopotential height over the central north atlantic and weaker negative height over europe the storm track over the atlantic is displaced from its normal position results from four further pairs of integrations with halved s s t anomalies are also described the response is approximately linear with systematic differences in 500 mb geopotential height over the atlantic parts of which are just significant at the 10 level with half the full s s t anomaly overall however the model s response is weaker than could be obtained with tropical s s t anomalies of the same magnitude results from the model integrations are compared with results from an observational study of the relationship between wintertime s s t in the north west atlantic and mean sea level pressure and 500mb height two independent 30 year periods were chosen for study thus minimizing the influence of long term trends in s s t over the atlantic and europe the model results compared well with the observations with s s t data lagging the atmosphere by one month the observational study appears to show that the s s t anomalies are initially forced by perturbations in the atmospheric circulation with s s t data leading the atmosphere by one month results show that atmospheric and s s t anomalies are most persistent in the period october to december throughout the winter these lagged relationships are much weaker and not statistically significant diagnostics of e vector divergence from the gcm experiments are used to suggest that anomalous baroclinic wave activity over the atlantic is important as a momentum forcing for the anomalous time mean flow pattern on the other hand the role of thermal forcing provided by anomalous diabatic heating and transient eddy heat flux convergence may be important to substantiate this statement a simple linear steadystate two layer model of the response to extratropical thermal forcing is described with a suitable basic state flow and a mid tropospheric heat source given mainly by the transient eddy heat flux convergence the response is shown to be equivalent barotropic with a downstream ridge and ascent over the thermal source conversely results from an ocean mixed layer model are discussed which suggest that warm s s t anomalies could be maintained by a positive surface pressure perturbation positioned downstream of the anomaly through anomalous northward advection of warm ocean water by ekman drift currents this northward advection would balance the sensible and latent heat loss into the atmosphere over the s s t anomaly hence it is possible that some positive ocean atmosphere feedback may account for the persistence of such atmospheric and oceanic anomalies