topographic and boundary effects on steady and unsteady flow through straits an overview of topographic and boundary effects in flows through straits is presented the emphasis is on the various types of interaction of uniform and stratified flow with the topography of straits especially the interaction with sills the interaction of a single layer flow in a channel with a sill obstacle depends on the froude number of the flow and the relative height of the sill two classification schemes one steady and one pseudo steady are given for single layer flow in straits where the effects of rotation are important a further parameter the ratio of the channel width to a rossby radius is needed and a similar classification scheme as for the non rotating flows can be obtained unsteady flows often result in bores for single layer flows and internal bores in stratified flows and the behaviour of these is discussed the flow of stratified flow past sills may generate lee waves while the increased flow speeds at the sill may allow deep water to be drawn up and over the sill aspiration features of the strait topography away from the sill including slopes at the side of the channel and also downstream of the sill channel curvature and channel widening have important effects on the character of the flow and on mixing

airborne synthetic aperture radar tracking of internal waves in the strait of gibraltar abstract as part of the international gibraltar experiment we realized on june 22 and 24 1986 two surveys of the strait of gibraltar on board an aircraft equipped with a synthetic aperture radar our objective was to observe at spring tides and during two twelve hour tidal cycles at 24 h interval the generation of internal wave trains linked to the hydraulic jump formed west of the sill during the westward phase of the tidal current and their eastward propagation in the strait the speed of propagation of these waves and the effect of the diurnal component of the tide on their generation and propagation could then be determined our results suggest that two solitary waves of equal amplitude propagated eastwards in the strait on june 22 the tidal coefficient being equal to 92 with a speed relative to the ground of 2 1 to 2 6 m s 1 24 h later during the second survey on june 24 tidal coefficient 90 we observed the propagation of a train of non linear waves the speed of the leading wave of which being about 1 9 ms 1 our data show that other waves pass over the camarinal sill after the release of the bore and secondary internal wave trains are shown to propagate eastwards from there although our sar data show the appearance of waves west of the northern sill at about 4 h after high water hw the mechanism leading to their generation is not clear these waves could propagate eastwards all along the strait and or northwestwards along the western spanish coast they could be responsible for the solitary type events observed at the eastern entrance of the strait at about 7 h after hw by ziegenbein 1969 1970 these events are noticeable in the hydrological parameters time series of armi and farmer 1988 and in the high rate current data 2 min apart from their april 1986 cruise besides these alongstrait waves our sar data show the existence of cross strait waves and give an idea of their wavelength and speed of propagation their presence leads to perturbations in the current revealed by simultaneous current data at the camarinal sill and north of cape cires

fortnightly and monthly variability of the exchange through the strait of gibraltar the fortnightly and monthly variability of the exchange through the strait of gibraltar has been studied from two simultaneous five month long moored datasets at camarinal sill and the east section the study focuses on the msf and mm tidal components and their role for the subinertial exchange a significant monthly signal is observed in the upper layer transport also a significant fortnightly signal is observed in the lower layer transport which minimum maximum flow toward the atlantic takes place approximately on spring tides in consequence the net transport has both signals with maximum taking place during neap tides and a small monthly inequality fortnightly and monthly variability in the interface depth is also observed at camarinal sill the interface being deeper on neap and shallower on spring tides at the east section the interface depth signals are not significant the subinertial variability of the transports is separated in two contributions the first one is called quasistatic transport and arises from the subinertial fluctuations of currents the second contribution called tidally rectified transports arise from the non linear correlation of currents and interface depth at tidal frequencies the tidally rectified transports are important at camarinal but not at the east section an apparent contradiction between the fortnightly signals of the subinertial currents and subinertial transports is resolved when the fortnightly signal of the tidally rectified transports are considered the fortnightly signal of the quasistatic and tidally rectified transports mutually cancel in the upper layer but not in the lower layer where the rectified transports dominate a simple model for the spring tide mixing forcing accounts for the fortnightly variability of the lower layer quasistatic transports but underestimates it for the upper layer finally the observed lower layer transport is compatible with the hydraulic control condition at camarinal sill except for certain periods during intense spring tides 2006 elsevier ltd all rights reserved

evidence of multimodal structure of the baroclinic tide in the strait of gibraltar 1 the multimodal structure of the baroclinic tides in the strait of gibraltar is studied using observations and numerical simulations observational data and model results revealed the presence of two types of tidal internal waves generated over camarinal sill cs one propagates toward the mediterranean and disintegrates into series of nonlinear short internal waves with amplitudes of 50 m and more the second type behind the first propagates slower and has a longer wavelength the vertical structure with both upward and downward displacements of isopycnals can be identified as a manifestation of higher baroclinic modes analysis of the empirical orthogonal functions of the adcp measurements performed over cs and model time series has shown that the second baroclinic mode predominates in the second type of internal waves its amplitude can reach one third that of the first baroclinic mode of the leading waves of depression

water exchange between algeciras bay and the strait of gibraltar a study based on hf coastal radar abstract this study analyses the water mass exchanges at subinertial scale between algeciras bay and the adjacent strait of gibraltar the mechanisms triggering this exchange process is investigated with the aid of recently acquired data on surface currents obtained using a system of hf coastal radars deployed on the eastern side of the strait and remotely sensed images of sea surface temperature sst and chlorophyll from the modis sensor of the aqua satellite hf radar data on surface currents are analyzed by the application of real empirical orthogonal function eof decomposition which produces three eof modes explaining more than 70 of the variance of the surface currents at the mouth of the bay modes 2 3 and 6 mode 2 is related to the fluctuations of the atlantic jet in the central zone of the strait mainly due to a combined effect of the atmospheric pressure fluctuations in the western mediterranean sea and local wind in the eastern side of the strait mode 3 is related to the coastal currents induced by zonal wind forcing on the north western coast of the strait and alboran sea and mode 6 seems to be related to water transport induced by winds blowing with a significant north component into and out of the bay

microstructures textures and deformation mechanisms in hematite abstract deformation and recrystallization of hematite in iron formations and high grade ore bodies of the caue formation from the quadrilatero ferrifero district minas gerais brazil resulted in several types of fabrics depending on the tectonic and metamorphic imprint the fabrics vary from randomly oriented granoblastic to strongly oriented lepidoblastic mylonitic with local development of cataclastic features complete pole figures of the crystallographic planes 003 basal plane 110 prism and 104 rhombohedron were measured on several samples from different areas by means of neutron diffraction revealing a typical crystallographic preferred orientation for the different fabric types the configuration and intensity of the maxima are directly related to the magnitude of the deformation and the type of response of the ore the analysis of the textures and microstructures of the iron ores and comparison with experimental deformation data lead us to the conclusion that three main mechanisms are active basal slip diffusion processes and anisotropic grain growth post tectonic recrystallization and secondary grain growth did not affect the textures developed during deformation

tracking mammoths and mastodons reconstruction of migratory behavior using strontium isotope ratios variations in the strontium isotope ratio 87 sr 86 sr of tooth enamel are used to examine the migration patterns of late pleistocene mammoths and mastodons from florida an animal s 87 sr 86 sr ratio tracks the ratios of its environment which vary with differences in bedrock and soil consequently the environmentally controlled differences in 87 sr 86 sr ratio recorded in mineralized tissue such as tooth enamel may be used to reconstruct the movement patterns of an individual we map variations in local 87 sr 86 sr ratios across modern florida and georgia through analysis of rodent teeth plants and surface water then use this map to interpret the movement patterns of extinct mammals mastodons from northern and central florida have higher 87 sr 86 sr ratios than both modern environmental samples from florida and fossils from nonmigratory species suggesting that mastodons migrated north into georgia mammoths display ratios similar to those of environmental samples and resident species suggesting that they did not migrate outside florida

submesoscale processes in the coastal margins of the strait of gibraltar the trafalgar alboran connection abstract the present manuscript analyses the role of the submesoscale hydrodynamic patterns close to the coastal margin of the strait of gibraltar in the exchange of properties between the western side of the strait and the western alboran sea to achieve this goal a multi approach analysis was performed using several datasets obtained during an oceanographic survey drifters satellite data and numerical simulation experiments three areas were identified trafalgar camarinal and the north western corner of the alboran sea in which the water exhibits a high residence time and relatively high phytoplankton concentrations in addition evidence of transport processes that take place along the coastal margin is shown between trafalgar and the alboran sea these transport processes seem to connect the phytoplankton that grows in the gulf of cadiz strip in response to the nutrients supplied by the guadalquivir river to the phytoplankton populations in the western alboran sea furthermore the transport of properties along this margin is clearly disrupted by strong and persistent easterly winds

the importance of sub mesoscale processes for the exchange of properties through the strait of gibraltar abstract this article presents a detailed analysis of the sub mesoscale transport processes in the strait of gibraltar the interest is focussed on the camarinal sill region and special attention is paid to the across strait transport processes the divergences and convergences in the central zone and the small scale circulation patterns along the northern coastal margin the analysis is based on high resolution 7 m sst images acquired by an air borne hyper spectral scanner and has been complemented with a rhodamine release experiment continuous thermo salinograph records acoustic doppler current adcp profiles from both moorings and vessel mounted experiments and numerical modelling it is deduced from the analysis that the coupling between the upwelling processes induced by the internal tide and the generation of large amplitude internal waves and the cyclonic eddies formed on the coastal margin seems to be the mechanism that explains the chlorophyll maxima frequently found on the coastal margin of the studied area further as a consequence of the small scale patterns of circulation induced by the internal waves the suspended substances are displaced from the coastal margins toward the central zones and later are carried by the westward current toward the convergence zones created by the internal waves where they may be retained and accumulate then in the eastward phase of the tidal current over the camarinal sill these nuclei of concentrated substances nutrients chlorophyll and plankton are transported toward the alboran sea where they must contribute in part to the primary productivity there

paleoproterozoic basin development and sedimentation in the lake superior region north america abstract the peneplaned archean craton in the lake superior region was the platform upon which a continental margin assemblage was deposited extension resulted in localized rifts that received thicker accumulations of sediments and volcanic rocks than did adjacent parts of the platform seas transgressed onto the continent several times and an ocean basin opened south of the present day lake superior island arcs that formed during subduction collided with the craton margin as the ocean basin closed oceanic crust is poorly preserved as a dismembered ophiolite sequence the arc volcanics are preserved as the wisconsin magmatic terranes the collision resulted in a fold and thrust belt known as the penokean orogen to the north of the fold and thrust belt a northward migrating foreland basin the animikie basin developed thick turbidite successions were deposited along the basin axis and terrigenous clastics and lake superior type iron formation were deposited on the shelf along the northern margin of the basin the primary paleoclimatic indicators are 1 glaciogenic rocks at the base of the paleoproterozoic succession in michigan indicating ice house conditions 2 remnants of a paleosol on the glaciogenic rocks indicative of deep weathering probably under subtropical conditions and therefore of greenhouse conditions and 3 carbonate minerals after gypsum halite and anhydrite in stromatolitic dolomite indicative of aridity three second order depositional sequences are bounded by major unconformities and can be correlated throughout the lake superior region

development and evaluation of geochemical methods for the sourcing of archaeological maize abstract strontium sr isotope values on bone from deer mice pairs from 12 field sites in the chaco canyon area new mexico were compared with isotope values of synthetic soil waters from the same fields the data indicate that mice obtain sr from near surface sources and that soil samples collected at depths ranging from 25 to 95 cm contain sr that is more accessible to the deep roots of maize thus synthetic soil solutions provide better data for the sourcing of archaeological maize however the sr isotope composition of mice may be more valuable in sourcing archaeological remains of animals such as rabbit turkey and deer in a separate study five native american maize zea mays l ssp mays accessions grown out at new mexico state university agricultural science center farmington new mexico were used to determine if soil water metal pairs partition systematically into cobs and kernels the sampled maize included landraces from three native american groups acoma hopi zuni that still occupy the four corners area two cobs each were picked from 10 plants of each landrace partitioning of the ba mn ba sr ca sr and k rb metal pairs from the soil water to the cob appears to behave in a systematic fashion in addition 51 rare earth element ree pairs also appear to systematically partition from the soil water into cobs however the ratios of the ree dissolved in the soil waters are relatively invariant therefore the distribution coefficients that describe the partitioning of ree from the soil water to the cob may not apply to archeological cobs grown under chemically heterogeneous conditions partitioning of ba rb ba sr mg p and mn p metal pairs from the soil water to kernels also behaves in a systematic fashion given that modern native american landraces were grown under optimal environmental conditions that may not have been duplicated by prehistoric native americans the distribution coefficients obtained in this study should be used with caution

a numerical model of internal wave refraction in the strait of gibraltar abstract the relative importance of depth cross strait interface till and horizontal current shear upon the wave front shapes of internal waves in the strait of gibraltar are examined by means of a numerical refraction model results from the model are also compared with observations of wave front shape made in the eastern strait using a shore based marine radar which imaged the surface effects of the waves the model is linear and assumes a time independent two layer fluid in which the depth of each layer may be any function of position the effect of current on the propagation is modeled by the addition of a term in the dispersion relation that increments the phase speed by an amount equal to the current component in the propagation direction at the depth of maximum internal wave displacement this current may also be any function of position the results suggest that in the strait of gibraltar interface tilt and horizontal shear both have a strong influence on the refraction whereas total depth is

development and application of methods used to source prehistoric southwestern maize a review archaeological cobs free of mineral contaminants should be used to source the soils in which they were grown mineral contaminants often contain much higher concentrations of metals than vegetal materials and can alter a cob s apparent metal and heavy isotope content cleaning a cob via immersion in an acid solution for more than a few minutes will result in the incongruent and sometimes complete leaching of metals including strontium sr from the cob when using 87sr 86sr to determine the location of potential agriculture fields it is best to either integrate several depth integrated soil samples or to integrate several vegetation samples from individual fields biologically labile sr in semi arid southwestern soils largely originates from eolian source or sources and usually is not derived from underlying bedrock existing sr isotope data indicate that archaeological cobs from aztec ruins came from either the mesa verde mcelmo dome or totah areas that pueblo bonito and chetro ketl cobs from chaco canyon that predate a d 1130 probably came from the rio chaco corridor and that cobs from chaco canyon that postdate a d 1130 probably came from either the totah or zuni areas

the role of deformation in the formation of banded iron formation hosted high grade iron ore deposits hamersley province australia abstract the hamersley province western australia hosts some of the world s largest iron ore deposits but despite decades of research their genesis is still extensively debated many iron ore deposits are hosted in complexly deformed archean to paleoproterozoic banded iron formations comprising thin chert and iron oxide bands interlayered with silicate rich shales and carbonates current iron ore genesis models have identified a strong structural control on ore formation linked to extensive hypogene and supergene fluid circulation along fault structures these fluid pathways facilitate the removal of vast amounts of gangue minerals leading to enrichment of the iron oxide residue to iron ore however the evolution of the associated structures has not yet been considered as a key element in ore genesis here we show through multiscale structural analyses that deformation not only forms suitable fluid channels but that folding and shearing also result in significant synkinematic removal of gangue minerals our multidisciplinary investigation of the structural evolution of the mount tom price deposit combines microtectonic field geology and 3d implicit modelling techniques to establish a link between deformation structures at various scales microscale shear bands and outcrop scale asymmetric parasitic folds share striking similarities in their evolution and their controlling mechanisms both features record substantial non coaxial deformation accompanied by volume changes due to stress induced silica remobilisation the closely spaced layering of rheologically different lithologies within hamersley province strata plays a crucial role in complex multilayer deformation which resulted in extensive strain partitioning our study suggests that deformation was of major significance in the upgrading of banded iron formation to iron ore and was active from the early stages of banded iron formation during diagenesis deformation structures also established a micro to deposit scale lateral and vertical fluid network which enabled infiltration by hypogene and supergene fluids during or after deformation these new insights have important implications for iron ore genesis models structural applications in the mine environment and for understanding complex multilayer deformation with volume loss

isotope domain mapping of 87sr 86sr biosphere variation on the isle of skye scotland abstract the potential of 87 sr 86 sr isotope composition for tracking and determining the origin of material whether it is humans animals water or wine can be fully realized only if high quality reference datasets are available against which to compare the unknowns this is currently not the case despite the rapid increase in 87 sr 86 sr based provenance studies of biosphere materials there are no well documented maps available most researchers resort to generating reference maps from a variety of geological datasets plus the analysis of sparse environmental9 samples a major reason for this lack of reference material is the investment needed to undertake systematic sampling and analysis over large areas a further problem is associated with the choice of proxy material as organisms differ in their habitat and exploitation of resources in this paper various approaches to isotope biosphere sampling are considered some of the problems are assessed the precision required for the study of human populations is discussed and a first attempt is made to condense all of the available information into an isotope package9 map the work is based on a study undertaken on the isle of skye in the inner hebrides and reduces the complexity of geological and isotope data into five main 87 sr 86 sr packages package 1 northern area 0 705 0 7092 package 2 ne coast 0 7082 0 7102 package 3 granitic rocks 0 716 0 720 package 4 metamorphic rocks 0 7092 0 7188 package 5 seawater 0 7092 0 005 2 the approach of trying to constrain the isotope composition of certain areas and or lithologies offers the possibility of extrapolating to other similar areas without having to sample at the original density

effects of tidal amplitude on intertidal resource availability and dispersal pressure in prehistoric human coastal populations the mediterranean atlantic transition abstract in this paper i argue that there is a growing body of evidence supporting an increasingly central position of coastal environments in human evolution and dispersals rather than as merely peripheral habitats eustatic fluctuations during glacial cycles have meant that most prehistoric coastlines are now underwater and lack of evidence to date of a close relationship between people and the coast can be most plausibly ascribed to the limited studies so far on submerged sites coastal environments provide high diversity in food resources consisting of multiple ecotones in close proximity which reduces the need to forage widely one of the richest and most easily exploited coastal resources by human populations living on the coast are molluscs from marine rocky intertidal communities which recent evidence has highlighted as important as far back as the middle palaeolithic however the density of these resources is limited by a number of factors and this varies geographically one of the main large scale factors limiting rocky intertidal mollusc densities is tidal amplitude beyond which smaller scale local factors such as exposure to wave action and shore aspect further affect species distributions the area around the strait of gibraltar is used as a case study of an area which is affected by large variations in tidal amplitudes thus allowing for quantitative comparisons between taxonomically and climatically similar regions shorelines along the mediterranean coast with reduced tidal amplitudes exhibit compressed zonations and harbour fewer macro mollusc individuals with the reverse being the case along the atlantic coast which has significantly larger tides data from middle and upper palaeolithic sites along the strait are used to establish harvested species and present day data are used to model the potential distributions and associated variables such as calorific returns of key food species an optimal foraging model is used to explore the effects of differential levels of resource availability along these coastlines results suggest that the nature and variability of the coastline has a direct influence on the tempo and mode of subsistence strategy followed and whether certain strategies can be adopted at all the possible implications of these biogeographical distributions for foraging economics dispersals and social structures in homo are discussed

significance of bottom currents in deep sea morphodynamics an example from the alboran sea we present an interdisciplinary study of the geomorphology sedimentology and physical oceanography of the alboran sea south western mediterranean sea to evaluate the potential role of bottom currents in shaping the spanish and moroccan continental margins and adjacent basins bathymetric and seismic data have allowed the recognition of the contourite deposits including depositional plastered sheeted channel related mounded confined elongated and separated drifts erosive moats channels and furrows and mixed terraces and scarps features hydrographic data offer new insights into the distribution of the mediterranean water masses and reveal that bottom circulation of the western intermediate water wiw and the levantine intermediate water liw interact with the spanish slope and the western mediterranean deep water wmdw on the moroccan slope spanish base of slope and deep basins the integration of distinct datasets and approaches allows a proposal of a new sedimentary model for the alboran sea that details the significance of bottom current processes in shaping deep sea morphology this model considers the bottom circulation of water masses governs physiography that interface positions of water masses with contrasting densities sculpt terraces on a regional scale and that the morphologic obstacles play an essential role in the local control of processes and water mass distributions our findings demonstrate the pivotal role of bottom water circulation in seafloor shaping and sedimentary stacking patterns for continental margins establishing a new outlook for future studies of deep marine sedimentation

remotely sensed sea surface thermal patterns in the gulf of cadiz and the strait of gibraltar variability correlations and relationships with the surface wind field satellite image sequences covering periods of a few days throughout the annual cycle of the waters off southern iberia have been analyzed in conjunction with concurrent surface wind speed data from coastal stations qualitative analysis reveals a large degree of temporal and spatial variability in the thermal signature of the sea surface over periods of both a few days and several months during the summer a cool seasurface temperature signature extends from the western iberian coast around cape st vincent and eastward as far as faro at the same time a warm signature originating on the iberian coast between faro and cadiz extends into the strait of gibraltar these two features are shown to sometimes adopt more westerly positions and the strait experiences regions of cool thermal signature originating at its southern side during winter the surface flow into the mediterranean through the strait of gibraltar is anomalously warm and appears to come from the interior of the gulf of cadiz quantitative measurements show that temporal variability over timescales of a few days at individual sites is maximum in midsummer spatial thermal variability over the whole region is found to peak toward the end of the summer statistical analyses of the data reveal the coupling between the surface wind field in the gulf of cadiz and the surface thermal pattern especially during the summer wind induced across stream upwelling in the strait of gibraltar although dynamically subordinate to tidal and density driven processes is shown to occasionally dominate the surface thermal signature

the 2 7 2 0 ga volcano sedimentary record of africa india and australia evidence for global and local changes in sea level and continental freeboard abstract the 2 7 2 0 ga volcano sedimentary records of the african indian and australian cratons indicate two broadly defined periods of extensive drowning of the emergent continental areas concomitant with lowered freeboard carbonate banded iron formation bif platforms characterised the first such event at ca 2 6 2 4 ga africa and australia to 2 7 ga india these earlier globally enhanced sea levels are ascribed to increased mid ocean ridge activity possibly related to breakup of a postulated late archaean southern supercontinent alternatively a transition from global scale catastrophic mantle overturn events to the onset of plate tectonics may have occurred in the late archaean nelson 1998 earth planet sci lett 158 109 119 both explanations of increased mid ocean ridge activity are compatible with significant early to middle archaean crustal growth armstrong 1981 phil trans r soc london a 301 443 472 with the emergent high freeboard cratons being subjected to aggressive weathering and erosion enhanced continental crustal growth near the archaean proterozoic boundary mclennan and taylor 1982 j geol 90 347 361 related to the development of significant island arc complexes would have resulted in common lowered freeboard enhanced sea level conditions at the passive margins of the southern cratons the diachronous nature of these earlier transgressions in the various cratons may reflect the effect of local tectonic movements and or the thermal state of the cratons from ca 2 4 2 2 ga cratons that make up the present day continents of india africa and australia had relatively high continental freeboard and lowered sea levels glacigenic deposits are preserved on the kaapvaal africa singhbhum india and pilbara australia cratons the second broadly defined drowning event at ca 2 15 ga was probably due to post glacial climatic amelioration freeboard was reduced by the combination of eustatic rise and the reestablishment of aggressive weathering as warmer palaeoclimates returned in india carbonates were more prominent than the siliciclastic sediments including prominent black shales seen in africa and australia

isotope sourcing of prehistoric willow and tule textiles recovered from western great basin rock shelters and caves proof of concept isotope and trace metal analyses were used to determine the origin of plants used to manufacture prehistoric textiles basketry and matting from archaeological sites in the western great basin research focused on strontium 87 sr 86 sr and oxygen 18 o 16 o isotope ratios of willow salix sp and tule schoenoplectus sp the dominant raw materials in great basin textiles the oxygen isotope data indicated that the willow and tule used to produce the textiles were harvested from the banks of rivers or in marshes characterized by flowing water and not from lakes or sinks the strontium isotope data were useful in showing which plants came from the humboldt river and which came from rivers headed in the sierra nevada published by elsevier ltd

spatial variations in biosphere 87sr 86sr in britain abstract strontium isotopes are a powerful tool for investigating the geographical origins of people and animals but assignment of provenance requires reference maps and databases this paper presents a map of strontium isotope variations across britain for use in archaeological and other studies and is produced by direct measurement of strontium isotope compositions of biosphere components predominantly plants the map characterizes the biosphere signature of specific lithologies a technique that is applicable worldwide marine derived strontium from both rainwater and coastal sea splash and spray is an important contribution to the british biosphere particularly on the western seaboard which is subject to high rainfall and prevailing westerly winds supplementary material methods full data table and full size version of figure 1b are available at http www geolsoc org uk sup18388

control variability and internal bore evolution in the strait of gibraltar a 2 d two layer model study a two dimensional high resolution non linear two layer free surface boundary fitted co ordinate hydrostatic model was applied to study the time space variability of hydraulic controls and the development of internal bores in the strait of gibraltar the model predicts the occurrence of four averaged over a tropical month controls located to the west of the spartel sill at the spartel and camarinal sills and in the tarifa narrows the last of these controls is apparent in the sense that it consists of discrete fragments alternating with subcritical flow regions the only control which extends over the whole width of the strait is the control at the camarinal sill but it breaks down during neap tide too this control exists concurrently with the control in the tarifa narrows for short periods while for much of the tropical month there is either just one or neither of the controls the model predicts the development of a hydraulic jump and a jump drop pair near the camarinal sill the appearance of bulges of mediterranean water to the east and west of the sill the large amplitude and small amplitude internal bores released from the camarinal sill which travel respectively eastward and westward and their transformation due to radial spreading and dissipative effects also presented here are the results illustrating the effects of earth s rotation on the internal bores in the strait of gibraltar

the gulf of cadiz pelagic ecosystem a review abstract the gulf of cadiz strategically situated between the north atlantic ocean and the mediterranean sea has been the focus of attention of a few oceanographic studies dealing with the deep circulation in order to understand the dynamics of the dense plume of mediterranean water much less attention has been paid to the surface pelagic layer which holds important living resources of commercial and ecological interest this overview summarizes the recent advances that have been made concerning the regional oceanography of the northern half of this important basin from an interdisciplinary point of view probably the most relevant oceanographic feature of the basin is its strong seasonality which is linked to the meteorologically induced seasonality of the eastern boundary current system of the north atlantic the prominent cape santa maria divides the continental shelf off the southern iberian peninsula in two shelves of different shape that hold different oceanographic processes which in turn determine the characteristics of the pelagic ecosystem mass and energy inputs from land as well as tidally driven processes makes the wider eastern shelf be more productive while the narrower western shelf cut by a sharp submarine canyon is under the influence of the almost permanent upwelling spot off cape san vicente under easterlies the west going warm coastal countercurrent that is observed in the eastern shelf may invade the western shelf thus connecting biologically both shelves in an east to west direction westerlies induce generalised upwelling off the southern iberia peninsula which adds to the almost permanent one off cape san vicente and generates an upwelling jet that moves eastwards cape santa maria may deflect this flow by generating a cold filament that extends southward and diverts water from the western shelf to the open ocean this pattern of circulation hampers the biological connection between shelves in the west to east direction which is therefore less effective the eastern shelf is prone to hold a cyclonic circulation cell during summer this cell seems to be part of the reproductive strategy of fish species like anchovy with significant commercial interest in the region the coupling between spawning and circulation is particularly beneficial under westerlies when productivity in the eastern shelf is enhanced and the plankton is confined within the cyclonic cell easterlies favour oligotrophy and the westward export of plankton which has an adverse effect on the recruitment and correlates low anchovy catches with periods of noticeable easterly intensity

the generation and trapping of solitary waves over topography observations of tidal flow over a sill show that upstream solitary wave generation occurred in conjunction with the downstream movement of a streamline bifurcation over the obstacle crest solitary waves appeared upstream of the bifurcation riding on the surface stratification shear flow instabilities on the plunging interface were also evident and may contribute to wave generation through subharmonic interaction nonlinear waves generated downstream of an internal control became trapped in the supercritical flow

improving the analysis of biogeochemical patterns associated with internal waves in the strait of gibraltar using remote sensing images abstract high amplitude internal waves haiws are physical processes observed in the strait of gibraltar the narrow channel between the atlantic ocean and the mediterranean sea these internal waves are generated over the camarinal sill western side of the strait during the tidal outflow toward the atlantic ocean when critical hydraulic conditions are established haiws remain over the sill for up to 4 h until the outflow slackens being then released mostly towards the mediterranean sea these have been previously observed using synthetic aperture radar sar which captures variations in surface water roughness however in this work we use high resolution optical remote sensing with the aim of examining the influence of haiws on biogeochemical processes we used hyperspectral images from the hyperspectral imager for the coastal ocean hico and high spatial resolution 10 m images from the multispectral instrument msi onboard the sentinel 2a satellite this work represents the first attempt to examine the relation between internal wave generation and the water constituents of the camarinal sill using hyperspectral and high spatial resolution remote sensing images this enhanced spatial and spectral resolution revealed the detailed biogeochemical patterns associated with the internal waves and suggests local enhancements of productivity associated with internal waves trains

mesoscale dynamics and vertical motion in the alboran sea abstract the inflow of atlantic water through the strait of gilbraltar usually exhibits a stationary wavelike pattern in the alboran sea we use an objective analysis technique for quantitative scale separation to investigate the interaction of scales in the region the large scale is clearly dominated by an anticyclonic gyre smaller scale analysis shows the existence of several mesoscale cyclonic eddies along the northern boundary of the western alboran sea anticyclonic gyre the relationship between the large scale mesoscale variability and the induced ageostrophic vertical motion is established using the q vector formulation we find that on the macroscale upward motion occurs upstream of the anticyclonic gyre upstream of a wave crest while downward motion takes place downstream upstream of a trough we also show that the vertical motion associated with the mesoscale eddies is an order of magnitude higher than the large scale vertical motion these patterns of large scale and mesoscale vertical m

possible sources of archaeological maize found in chaco canyon and aztec ruin new mexico abstract maize played a major role in chaco s interaction with outlying communities in the southern colorado plateau this paper seeks to determine where archaeological corn cobs brought to chaco canyon were grown strontium isotope and trace metal ratios of 180 soil water and 18 surface water sites in the southern colorado plateau have revealed possible source areas for some of 37 archaeological corn cobs from chaco canyon and 10 archaeological corn cobs from aztec ruin new mexico the most probable source areas for cobs that predate the middle 12th century drought include several upper rio chaco sites not including chaco canyon there are many potential source areas for cobs that date to the late a d 1100s and early 1200s all of which lie in the eastern part of the study area some athapascan age cobs have potential source areas in the totah lobo mesa and dinetah regions one gallo cliff dwelling cob has a strontium isotope ratio that exceeds all measured soil water values field sites for this cob may exist in association with paleozoic and precambrian rocks found 80 90 km from chaco canyon potential source areas for most aztec ruin cobs many of which were found in rooms dating to the first half of the 13th century appear to be associated with a loess deposit that blankets the mesa verde and mcelmo dome regions

the boiling water phenomena at camarinal sill the strait of gibraltar abstract a detailed description of high amplitude steady topographic internal waves recorded at camarinal sill during a survey on the r v investigador is presented these internal waves are generated during the maximum outflow westward stage of the tidal current and remain over the sill for more than 4 h until the outflow slackens then being released towards the mediterranean their amplitudes are comparable to the well known internal bore of camarinal sill occurring during maximum outflow during spring tides however they respond to a different physical origin and their spatial features are also quite different in fact the favourable hydraulic conditions for the generation of steady waves over the sill inhibit the internal bore generation and vice versa analysis of the observations suggests that steady internal waves are the result of a resonant response of the stratified fluid over the sill to the forcing of the flow on the across sill topography an important consequence of the steady internal waves with clear biological implications is the significant mixing phenomena that are induced mixing is enabled by an enhancement of the shear at the trough together with a significant induced vertical advection

wind driven upwelling along the african coast of the strait of gibraltar 1 regular remote sensing data from various sensors are used here for the study of the wind driven upwelling phenomenon along the african coast of the strait of gibraltar it is shown for an extended summer period may 15 till september 15 2003 that sea surface temperature sst data in the strait are correlated with ncep winds each westward wind increase being followed by a clear surface temperature decrease local surface temperature of about 22 c at that time drops down to 15 c value corresponding to the 80 120 m depth conditions the analysis of subsequent images indicates that the cold upwelling plume typically moves first to the atlantic during wind forcing and then to the mediterranean after the wind event the presence of the northern coast of the strait is taken as responsible for a rise of a cross strait sea level gradient and the enhancement of the associated westward geostrophic current that explains the first stage of the plume deployment sea level difference measured between tarifa european coast and ceuta african coast well described by a linear equation in term of the westward wind component supports this idea as well as the subsequent remotely sensed sst distributions

submesoscale tidally induced biogeochemical patterns in the strait of gibraltar abstract tidal forcing and its fortnightly variation are known to be one of the main regulating agents of physical and biogeochemical signatures in the strait of gibraltar and surrounding areas samples obtained during spring and neap tides in the region were analyzed to determine the influence of this tidal variation on the submesoscale distribution of water masses and biological elements during spring tides strong and intermittent mixing processes between mediterranean and atlantic waters occur in the vicinity of the camarinal sill together with an eastward advection of those mixed waters into the alboran sea furthermore the intense suction of surface coastal waters into the main channel of the strait was detected as chlorophyll patches in the alboran sea during spring tides in contrast the most characteristic phenomenon during neap tides was the arrival of pulses of relatively nutrient rich north atlantic central waters to the surface regions of the alboran sea in addition traces of the suction of coastal waters were observed for the first time during neap tides therefore our results show that submesoscale processes are crucial in the dynamics of the strait of gibraltar and they must be considered for the correct description of the biogeochemical features of alboran sea especially during an inactive period of the coastal upwelling

a study of internal wave propagation in the strait of gibraltar using shore based marine radar images abstract an x band marine radar on windmill hill gibraltar was used to monitor the propagation of internal waves in the strait of gibraltar during march april and june 1986 surface roughness features of the waves were observed out to a range of 15 km from photographic images of the radar screen the positions of image features were measured manually using a digitizing table and these data were then computer processed to give wave arrival times and phase speeds during most tidal cycles an internal undular bore generated at camarinal sill was observed to pass eastward a waves these occurred throughout the experiments although less frequently near neap tides the time of travel to gibraltar varied significantly so that the bore arrived between four and nine hours after high water arrival times were found to be closely related to the amplitude of the upper layer tidal current this current had a strong diurnal component which was manifested as an inequality between the arrival times of success

sr isotope evidence for population movement within the hebridean norse community of nw scotland the excavation at cnip isle of lewis scotland of the largest and only known family cemetery from the early norse period in the hebrides provided a unique opportunity to use sr isotope analysis to examine the origins of people who may have been norwegian vikings sr isotope analysis permits direct investigation of a person s place of origin rather than indirectly through acquired cultural and artefactual affiliations sr isotope data suggest that the norse group at cnip was of mixed origins the majority were consistent with indigenous origins but two individuals of middle age and different sex were immigrants they were however not from norway but were raised separately most probably on tertiary volcanic rocks e g the inner hebrides or ne ireland or for the female on marine carbonate rocks

carbonate mounds in a mud volcano province off north west morocco key to processes and controls abstract this paper presents a new cluster of carbonate mounds discovered in 2002 in the gulf of cadiz off morocco r v belgica 2002 in water depths of 500 to 600 m amidst a field of giant mud volcanoes multibeam bathymetry side scan sonar imagery and 2d seismics are analyzed to present four mound provinces 1 the pen duick mound province on the pen duick escarpment 2 the renard mound province on the renard ridge 3 the vernadsky mound province on the vernadsky ridge and the al idrisi mound province on the gas blanked sediments above the buried al idrisi ridge video imagery and surface samples are described to ground truth the different mound areas the paradox is that nearly no live corals are presently being observed at the surface of the mounds while the mound cores display throughout a high number of reef forming cold water coral fragments scleractinians in association with numerous associated fauna formerly inhabiting the econiches provided by the coral framework environmental and oceanographic conditions during the recent past glacials stadials were probably more favourable for cold water coral growth pore water analyses in on mound cores at the south eastern edge of pen duick escarpment give evidence of focused higher methane fluxes and sulphate reduction rates on mounds than in the surrounding sediments cores from several mounds display horizons of strong corrosion and dissolution of the coral fragments a three phase model for carbonate mound evolution in these settings is proposed 1 in a first stage external controls positive oceanographic and environmental conditions the presence of an active planktonic food chain based on a high primary production and a suitable substrate are responsible for the initiation of cold water coral growth 2 once the cold water corals established an initial framework sedimentation becomes an important factor controlling mound growth the cold water corals baffle the sediments 3 throughout mound growth the mound may episodically be affected by diagenetic processes responsible for aragonite dissolution and probably carbonate precipitation

geology and tectonic evolution of palaeoproterozoic basins of the eastern capricorn orogen western australia abstract the palaeoproterozoic yerrida bryah padbury and earaheedy basins extend for about 700 km along the northern margin of the yilgarn craton and are part of the capricorn orogen the basins developed between ca 2 2 and 1 8 ga recording periods of sedimentation volcanism rifting accretion and passive margin tectonism the oldest is the 2 17 ga yerrida basin which began as an intracontinental sag within which siliciclastics and evaporites accumulated at about 2 0 ga convergence of the yilgarn craton and the glenburgh terrane closed an oceanic arm resulting in the accretion of oceanic crust and plateaux onto the yilgarn margin and the western side of the yerrida sag basin this accretion produced the narracoota formation which together with the clastic and chemical banded iron formation sedimentation that followed forms the bryah basin continuing collision resulted in the establishment around 1 96 ga of the padbury foreland basin developed on top of the bryah basin rocks the ca 1 83 ga convergence and collision of the pilbara and yilgarn cratons capricorn orogeny resulted in deformation of the bryah padbury basins and orogenic uplift with coarse clastic sedimentation accompanied by the eruption of flood basalts into the yerrida basin to the east of the collision zone and possibly postdating collision a passive margin was present sedimentation along it consisted of clastic and chemical sediments granular iron formation which form the earaheedy basin during the ca 1 79 ga yapungku orogeny due to the convergence of the north australian and western australian cratons the northern margin of the earaheedy basin was deformed stanley fold belt this last deformation event concludes the palaeoproterozoic history of the eastern capricorn orogen basins

observations of internal waves and associated mixing phenomena in the portimao canyon area internal wave activity and induced mixing phenomena in the portimao canyon area southern portuguese coast are analysed observations of current velocities and ctd measurements were taken during a 24 h period at two fixed stations located along the main axis of the canyon the station nearest shore was located close to the canyon head and the other station was 5 km seaward these basic measurements are complemented with vertical sections of temperature acquired by xbt casts along the main axis of the canyon and also with time series of temperatures recorded by a thermistor chain moored on the continental shelf near the canyon head the time sequences of velocities and density profiles recorded at the fixed stations were analysed using a procedure based on empirical orthogonal function eof analysis and dynamical modes decomposition dmd techniques by this method two different sources for internal wave activity are identified a clear internal tide signal on the one hand and a shorter than tidal period internal waves which exhibit greater current velocities and density oscillation amplitudes than internal tide on the other it is suggested that these shorter period internal waves are responsible for the vertical mixing affecting the water column over the slope and shelf waters in this region finally it is also suggested that the evacuation of these mixed water masses formed around the continental shelf break may be related to a core of relatively cold water flowing over the continental slope toward west

coastal altimetry products in the strait of gibraltar this paper analyzes the availability and accuracy of coastal altimetry sea level products in the strait of gibraltar all possible repeats of two sections of the envisat and altika ground tracks were used in the eastern and western portions of the strait for envisat along track sea level anomalies slas at 18 hz posting rate were computed using ranges from two sources namely the official sensor geophysical data records sgdrs and the outputs of a coastal waveform retracker the adaptive leading edge subwaveform ales retracker in addition slas at 1 hz were obtained from the centre for topographic studies of the ocean and hydrosphere ctoh for altika along track sla at 40 hz was also computed both from sgdr and ales ranges the sea state bias correction was recomputed for the ales retracked envisat sla the quality of these altimeter products was validated using two tide gauges located on the southern coast of spain for envisat the availability of data close to the coast depends crucially on the strategy followed for data screening most of the rejected data were due to the radar instrument operating in a low precision nonocean mode we observed an improvement of about 20 in the accuracy of the envisat slas from ales compared to the standard sgdr and the reprocessed ctoh data sets altika shows higher accuracy with no significant differences between sgdr and ales the use of products from both missions allows longer times series leading to a better understanding of the hydrodynamic processes in the study area

upwelling spots and vertical velocities in the gulf of cadiz an approach for their diagnose by combining temperature and ocean colour remote sensing abstract upward velocities have been diagnosed through the development of an approach based on remotely sensed daily images of both chlorophyll and temperature at the ocean surface in the gulf of cadiz this novel approach allows to the detection of areas with vigorous vertical velocities w through the generation of a calculation algorithm built from the simple lagrangian model of phytoplankton growth that occurs during the shoaling of deep waters to surface the fast initial evolution of chlorophyll and temperature in surface limits the implementation of the algorithm to high upward velocities assuming this limitation the values of w diagnosed have been found to be coherent with independent estimations based on diffusive and advective inputs of nitrogen into the euphotic zone in the area the new production resulting from vertical advection of nitrogen during a regular upwelling event in the basin was more than two orders of magnitude greater than that maintained by vertical diffusion according to our calculations the maintenance of vertical advection for 1 week under upwelling conditions could support new production equivalent to that due to residual vertical mixing during about half a year under conditions of stratification

ageostrophic secondary circulation in a subtropical intrathermocline eddy abstractvertical motions play a key role in the enhancement of primary production within mesoscale eddies through the introduction of nutrients into the euphotic layer however the details of the vertical velocity field w driving these enhancements remain under discussion for the first time the mesoscale w associated with an intrathermocline eddy is computed and analyzed using in situ high resolution three dimensional 3d fields of density and horizontal velocity by resolving a generalized omega equation valid for high rossby numbers in the seasonal pycnocline the diagnosed w reveals a multipolar structure with upwelling and downwelling cells located at the eddy periphery in the main pycnocline w is characterized by a dipolar structure with downwelling velocities upstream of the propagation path and upwelling velocities downstream maximum values of w reach 6 4 m day 1 an observed enhancement of chlorophyll a at the eddy periphery coincides with the location of the upwelling and downwelling cells a

time spatial variability observed in velocity of propagation of the internal bore in the strait of gibraltar 1 some aspects of the time spatial variability of the phase speed of the internal bore generated almost every tidal cycle in camarinal sill are revised using a set of high resolution experimental data collected in two different positions of the strait during may 2003 this variability is mainly driven by the intense tidal currents comparable with the intrinsic propagation velocity of the first mode baroclinic bore it is shown that the importance of the diurnal tide in the strait of gibraltar induces a considerable diurnal inequality on the bore velocity with an observed maximum difference of 0 7 ms 1 between the speed of two consecutives bores propagating along the eastern part of the strait a regularly spatial pattern has been also found the internal bore reaches its maximum velocity in tarifa narrows a theoretical estimation predicts an extreme phase speed of 2 6 ms 1 during our period of study

from bif to red beds sedimentology and sequence stratigraphy of the paleoproterozoic koegas subgroup south africa abstract the 2 4 ga old koegas subgroup of the transvaal supergroup contains siliciclastics and iron formations it occupies a transitional stratigraphic position between the major iron formations on the kaapvaal craton and strata with evidence for oxygenation of the environment koegas siliciclastics reflect a new phase of uplift and erosion on the craton after a period of chemical deposition paleocurrent data indicate transport to the west and northwest away from the craton however no precise source area can as yet be defined rocks were deposited in foreshore to offshore environments of a prograding delta or submarine fan system immature arkosic wackes and subarkoses occur in proximal parts and pass to terrigenous mudstones and chemical iron formations in offshore environments with low detrital input lateral facies transitions and the hierarchical stratigraphic stacking pattern of the koegas subgroup allow a sequence stratigraphic interpretation in which regressive coarse siliciclastics prograded repeatedly over transgressive units of chemical iron formations metals in the transgressive units have an intrabasinal hydrothermal source similar to underlying iron formations localized iron stained detrital units resemble red beds they reflect additional diagenetic fe remobilization from deeper water iron formations or possibly a continental fe source the second possibility would imply the presence of some free oxygen in the environment

near surface circulation in the southern gulf of cadiz abstract we have used several data sets expandable bathythermograph sections buoy trajectories current meter moorings and surface wind stress to investigate the temporal variation of the upper thermocline north atlantic central waters circulation patterns in the southern gulf of cadiz the main data set consists of eight expandable bathythermograph sections two per season running between the strait of gibraltar and cape beddouza just offshore the continental slope and approximately parallel to the morocco coastline a salinity temperature polynomial obtained from historical conductivity temperature depth data is used to infer dynamic properties salinity density dynamic height geostrophic velocity and transport dynamic heights are calculated referred to the 1027 25 kg m 3 neutral density surface which we justify is a good reference level for this section these observations are then combined with a process oriented one layer quasigeostrophic model for the northeastern corner of the north atlantic subtropical gyre with modified eastern boundary conditions the results indicate the existence of about 1 sv onshore transport all year long into a 300 km long coastal transition zone off morocco which must follow south as a narrow current during winter the flow is zonal towards the slope and recirculates south as a very narrow jet of less than 100 km width during summer the flow probably becomes more intense but is deflected southeastward before reaching the slope such that the onshore geostrophic transport into the coastal transition zone decreases and the recirculating band widens

study of the generation and propagation of internal waves in the strait of gibraltar using a numerical model and synthetic aperture radar images of the european ers 1 satellite a weakly nonhydrostatic two layer numerical model based on the boussinesq equations is presented which is capable of describing among others the generation and propagation of nonlinear weakly dispersive internal waves in the strait of gibraltar the model depends on one space coordinate only but it retains several features of a fully three dimensional model by including a realistic bottom profile a variable channel width and a trapezoidal channel cross section the nonlinear primitive boussinesq equations include horizontal diffusion bottom friction and friction between the two water layers the model is driven by a height difference of the mean interface depth between the atlantic and the mediterranean boundaries and by semidiurnal tidal oscillations of the barotropic transport the model presented in this paper describes 1 the mean and tidal flow in the strait of gibraltar 2 the variation of the depth of the interface during a tidal cycle 3 the generation of strong depressions of the interface at the western sides of the spartel sill and the camarinal sill 4 the generation of strong eastward propagating internal bores and 5 their disintegration into trains of internal solitary waves the surface convergence patterns associated with depressions of the interface at the camarinal sill internal bores and internal solitary waves are calculated and compared with roughness patterns visible on synthetic aperture radar sar images of the first european remote sensing satellite ers 1 in total 155 ers 1 sar scenes from 94 satellite overflights over the strait of gibraltar which were acquired in the period from january 1992 to march 1995 have been analyzed it is shown that the proposed model is capable of explaining the observed temporal and spatial evolution of surface roughness patterns associated with eastward propagating internal waves inside the strait of gibraltar as well as the observed east west asymmetry of the internal wave field

physical biological coupling in the strait of gibraltar this study presents a joint analysis of the distributions of some biogeochemical variables and their relation to the hydrodynamics of gibraltar strait it is a synthesis paper that brings together many results obtained during canigo project we show the role of hydrodynamics as a forcing agent for the plankton community structure in the strait with emphasis on the two physical processes that we propose as key factors for the coupling interface position and oscillations and mixing processes along the strait as a general pattern autotrophic plankton biomass increases at the strait from southwest to northeast a tendency that coincides with a gradual elevation of the interface depth in the same direction the different mechanisms of mixing that take place in the strait are briefly reviewed the occurrence of the internal hydraulic jump is an important mechanism of mixing constrained to the spring tide situations but other processes such as the generation of arrested internal waves of wavelength around 1 km are proposed as a complementary mixing mechanism particularly during neap tides situations both mechanisms the elevation of the pycnocline and these mixing events can enhance biological productivity and biomass accumulation on the northeastern sector of the strait since phytoplankton cells are there packaged in a water mass with sufficient light and nutrients and smaller advective velocity there is a clear north south difference in the biological response to these upwelling episodes in the eastern section with high nutrient and low chlorophyll in the south and the opposite in the north the deeper interface and the greater water speed are the proposed reasons for this lower nutrient uptake on the southeastern sector finally the temporal scales of variation of the mixing events the influence of its periodicity on the productivity of the area and the influence of these upwelling episodes in the nearest albor an sea are discussed r 2002 elsevier science

book review iron formation facts and problems developments in precambrian geology 6 edited by a f trendall and r c morris elsevier sciences publishers b v amsterdam oxford new york tokyo 1983 xiv 588 pp price us 106 00 u s a and canada dfl 275 00 rest of world isbn 0 444 42144 0 hardback

baroclinic m2 tidal circulation in algeciras bay and its implications for the water exchange with the strait of gibraltar observational and 3 d model results 1 the m2 tidal circulation in algeciras bay strait of gibraltar is analyzed using a 3 d nonlinear baroclinic hydrodynamic model in conjunction with observed data series results show the influence of the density stratification on the vertical structure of the m2 currents in algeciras bay although its tidal dynamics shows major differences with respect to the strait of gibraltar whereas the m2 currents in the strait present mainly barotropic behavior the baroclinic effects prevail in algeciras bay a notable finding is the presence of a tidal m2 counter current system between the upper atlantic and the lower mediterranean water layers within the bay with amplitudes of up to 25 cm s 1 the interface between the two layers oscillates in antiphase relation with respect to the free surface elevation with amplitudes of almost 20 m the presence of the submarine algeciras canyon was found to be determinant in the three dimensional structure of tidal currents within the bay strengthening the baroclinic tidal regime of currents this situation has quantitative consequences for the flow exchange processes between algeciras bay and the outer strait with rates 20 times higher than those obtained when considering only the barotropic behavior as well as inflow outflow lateral recirculation volumes during half a tidal cycle that account for more than 20 of the net accumulated volume this flow exchange system was found to be affected by the nonlinear interaction processes between the first baroclinic period of resonance of algeciras bay and the m2 tide

late quaternary multi genetic processes and products on the northern gulf of cadiz upper continental slope sw iberian peninsula abstract on continental margins the upper slope to shelf break environment forms a critical region where sediment supply hydrographic activity and gravitational processes determine how and when sediments are partitioned between the shallow and deep marine realm on the sw iberian margin relatively few studies have addressed the dynamics of this region although it holds key information regarding the link between the sedimentary evolution of the continental shelf and the contourite depositional system on the middle slope this work therefore presents a high resolution analysis of the morphological and stratigraphic expressions of late quaternary dominantly last glacial and present day interglacial sedimentary processes on the upper slope and shelf margin sector between 7 and 7 30 w the integration of seismic bathymetric and hydrographic data reveals the presence of alongslope processes and products a bottom current related plastered drift moat erosional surface and terrace an internal wave tide controlled sediment wave field downslope gravitational processes and products an upper slope shelf margin valley system slumps debrites gullies neotectonic elements diapirs and fluid flow features pockmarks bright spots the spatial distribution of these features indicates that the study area becomes increasingly alongslope dominated towards the w and oppositely more downslope dominated towards the e because sediment supply to the latter area is enhanced under the dominant eastward dispersal of fluvially supplied sediments on the shelf in addition glacial interglacial variations in the amount of sediments supplied to the shelf edge and the intensity of oceanographic processes in the study area also generate a distinct temporal variability with glacial and interglacial intervals respectively recording principally downslope and alongslope controlled morphological elements finally regardless of these overall spatial and temporal patterns diapirism and fluid flow are inferred to locally destabilize sediments and induce small scale mass wasting in the study area these findings are not only relevant to the northern gulf of cadiz but also to the general understanding of sedimentary dynamics and controls in mixed downslope and alongslope controlled upper slope to shelf margin settings worldwide

transient upwelling hot spots in the oligotrophic north pacific 1 vertical exchange between deep nutrient rich and nutrient depleted surface waters controls the physical supply of nutrients into the euphotic zone in the oligotrophic waters of the subtropical north pacific ocean sea surface temperature and ocean color satellite images are used in this study to show that submesoscale chlorophyll patches are locally intensified these patches are associated with surface temperature fronts and regions of strong stretching of the eddying flow the latter are identified by calculating the finite size lyapunov exponents of the geostrophic flow derived from the sea surface height field from altimetry surface frontogenesis and nonlinear ekman pumping nlep arise as natural candidates for the sporadic generation of large vertical velocities that could favor the formation of these features a high resolution regional numerical model simulation confirms that large vertical velocities are indeed associated with strong density fronts and gradients of relative vorticity using the q vector divergence as a proxy for frontogenetically generated vertical velocities yields good agreement with the model vertical velocities particularly in regions where they are large the pattern and magnitude of nlep suggests that it is also contributing to the strong vertical motions although nlep and model vertical velocities are not necessarily in phase surface frontogenesis and nlep provide a possible explanation for the episodic injection of nutrients at the submesoscale which are then horizontally stirred and modulated by the unstable manifolds of the flow field given that these surface intensified processes would be biogeochemically more effective when the pycnocline is shallow they could also serve as one possible explanation for the late summer chlorophyll blooms that are known to occur in the region

internal waves and short scale distribution patterns of chlorophyll in the strait of gibraltar and alboran sea 1 a selection of asar images have been analyzed together with instantaneous images of surface chlorophyll recorded with meris and modis in order to study the relationship between the physical and biological processes associated with internal waves in the strait of gibraltar and alboran sea the images show peak levels of chlorophyll at the coastal edges to the north and south of the camarinal sill cs during the generation of internal waves and peak levels of chlorophyll associated with the wave fronts as they travel into the alboran sea the images have been compared with in situ data the results seem to indicate that during the generation of the internal waves a suction process takes place by which coastal waters rich in chlorophyll are drawn towards the center of the channel and then accompany the internal waves as they move towards the alboran sea

analysis of short period internal waves using wave induced surface displacement a three dimensional model approach in algeciras bay and the strait of gibraltar 1 a three dimensional nonlinear high resolution sigma coordinate hydrodynamic model was applied to study the sea surface manifestation of short period internal waves measured in algeciras bay and the strait of gibraltar model results reproduce the tidally induced generation of the internal bore over the camarinal sill and its disintegration into wave trains as it moves eastward while propagating along the strait of gibraltar toward the mediterranean sea the wave trains partly penetrate into algeciras bay with typical oscillation periods of 20 and 40 min the modeled wave induced surface train structures are compared with satellite images and in situ observational data obtained from two pressure sensors located inside the bay results demonstrate that wave induced sea surface displacements are indicators of the presence of internal waves and may be used in the context of the internal wave analysis when surface oscillations are captured with sufficient precision

pb and sr concentrations and isotopic compositions in prehistoric north american teeth a methodological study abstract we present pb and sr isotopic compositions and elemental concentrations for dentin and enamel from 28 human teeth from 10 locations in the southwestern united states these teeth represent native american communities that were functioning between 300 bce and 1200 ce we wished to assess whether pb isotopic data can extend the interpretations made from sr isotopic data alone and to determine the analytical requirements for doing sr and pb analyses from single samples pb concentrations in our samples are between 0 06 and 48 ppm with sr concentrations between 10 and 3300 ppm 87 sr 86 sr compositions lie between 0 708 and 0 712 pb isotopic compositions are more variable with 206 pb 204 pb ranging between 17 9 and 21 7 isotopic compositions and elemental concentrations for both sr and pb can be determined on samples smaller than 1 mg but there is real heterogeneity between samples of this size neither concentrations nor isotopic compositions are reproducible to within analytical uncertainty in replicate aliquots from individual teeth we cannot determine whether this variability is an in vivo or a diagenetic effect combined pb and sr isotopic data discriminate most locations and the inclusion of pb data provides a stronger basis for archeological interpretations our data suggest that pb is more susceptible to post mortem exchange than sr background isotopic data are needed to characterize pb and sr sources in the study areas pb concentration data for enamel samples indicate a blood pb load of 0 1 0 2 g pb dl for preindustrial native americans

the flow of atlantic water through the strait of gibraltar abstract we describe and analyze observations of the water exchange through the strait of gibraltar the primary observations were taken in april 1986 and included data from moored recording instruments at four locations in the strait together with an intensive survey by ship these measurements included extensive ctd profiling acoustic doppler current profiling numerous profiles from expendable instruments and imaging using a high frequency echo sounder the analysis focuses on the internal hydraulics of the strait and in particular the presence of hydraulic controls and their influence on the exchange our observations during april 1986 show that the maximal exchange condition in which a subcritical flow is bounded by supercritical flow at both ends of the strait did occur although with various subtleties not explicitly incorporated in our previous theoretical developments the atlantic water moving east along the surface encounters a control at tarifa narrows in the eastern part of the strait the mediterranean water passes through controls both at camarinal sill and at spartel sill further west at our westernmost mooring at spartel the outflowing mediterranean water is continuously supercritical with little tidal variability the control at camarinal sill is periodically lost due to tidal action and reappears on a reverse flow during a falling spring tide tangier basin bounded by camarinal and spartel sills acts as an internal reservoir for the outflowing mediterranean water the interface rising and falling through each tidal cycle during spring tides the tangier basin interface rises high enough to flood the control at camarinl sill and produces a reverse flow of the lower layer when control is lost at camarinal sill a travelling bore is released this bore may modify the location of the control acting on the surface layer in tarifa narrows the atlantic water enters the alboran sea as a jet which may have a well defined northern boundary where it separates from the european coast this boundary may be identified by the presence of a slick although the internal jump west of camarinal sill is almost certainly an area of intense mixing frictional effects do not appear to be dominant in the subcritical portion of the flow