application of an inverse method to interpret 231pa 230th observations from marine sediments constraints then sediment 231 pa 230 th data for each time interval are combined with an advection scavenging model in order to determine their in consistency with the modern circulation estimate we find that the majority of sediment 231 pa 230 th data for the holocene lgm or h1 can be brought into consistency with the modern circulation if plausible assumptions are made about the large scale distribution of 231 pa and about model uncertainties moreover the adjustments in the data needed to reach compatibility with a hypothetical state of no flow no advection are positively biased for each time interval suggesting that the 231 pa 230 th data including that for h1 are more consistent with a persistence of some circulation than with no circulation our study does not imply that earlier claims of a circulation change during the lgm or h1 are inaccurate but that these claims cannot be given a rigorous basis given the current uncertainties involved in the analysis of the 231 pa 230 th data

mixing and entrainment in the red sea outflow plume part i plume structure when the salty and heavy water of the red sea exits from the strait of bab el mandeb it continues downslope into the gulf of aden mainly along two channels the 130 km long northern channel nc is topographically confined and is typically only 5 km wide in it the red sea plume shows unanticipated patterns of vertical structure turbulent mixing and entrainment above the seafloor a 25 120 m thick weakly stratified layer shows little dilution along the channel hence this bottom layer undergoes only weak entrainment in contrast a 35 285 m thick interfacial layer shows stronger entrainment and is shown in a companion paper to undergo vigorous turbulent mixing it is thus the interface that exhibits the bulk of entrainment of the red sea plume in the nc the interfacial layer also carries most of the overall plume transport increasingly so with downstream distance the southern channel sc is wider than the nc and is accessed from the latter by a sill about 33 m above the floor of the nc entrainment into the bottom layer of the sc is diagnosed to be strong near the entry into the sc such that the near bottom density and salinity are smaller in the sc than in the nc at the same distance from bab el mandeb in comparison with winter conditions the authors encountered weaker outflow with shallower equilibration depths during the summer cruise bulk froude numbers computed for the whole plume varied within the range 0 2 1 local maxima occurred in relatively steep channel sections and coincided with locations of significant entrainment

structure of unsteady overflow in the slupsk furrow of the baltic sea 1 a data set of closely spaced ctd profiling performed aboard russian and polish research vessels during 1993 2009 and numerical modeling are applied to study the variability in the asymmetric transverse structure of salinity density in the slupsk furrow sf overflow of the baltic sea the numerical simulations show that on the one hand the overflow may be dynamically treated within the sf as a subcritical eddy producing gravity current in a wide channel and on the other at the sill displays some features peculiar to frictionally controlled rotating flows comparison between the field measurements and the simulation results indicates that the variability of the cross channel density structure is caused mainly by meandering of the gravity current and mesoscale eddies mostly above halocline cyclones and intrahalocline anticyclones the meanders and eddies are found to be strongly affected by the bottom topography and wind forcing

a regional modeling study of the entraining mediterranean outflow 1 we have evaluated a regional scale simulation of the mediterranean outflow by comparison with field data obtained in the 1988 gulf of cadiz expedition our ocean model is based upon the hybrid coordinate ocean model hycom and includes the richardson number dependent entrainment parameterization of xu et al 2006 given realistic topography and sufficient resolution the model reproduces naturally the major observed features of the mediterranean outflow in the gulf of cadiz the downstream evolution of temperature salinity and velocity profiles the mean path and the spreading of the outflow plume and most importantly the localized strong entrainment that has been observed to occur just west of the strait of gibraltar as in all numerical solutions there is some sensitivity to horizontal and vertical resolution when the resolution is made coarser the simulated currents are less vigorous and there is consequently less entrainment our richardson number dependent entrainment parameterization is therefore not recommended for direct application in coarse resolution climate models we have used the high resolution regional model to investigate the response of the mediterranean outflow to a change in the freshwater balance over the mediterranean basin the results are found in close agreement with the marginal sea boundary condition msbc a more saline and dense mediterranean deep water generates a significantly greater volume transport of the mediterranean product water having only very slightly greater salinity

transport estimates at the western section of the strait of gibraltar a combined experimental and numerical modeling study 1 three yearlong time series of acoustic doppler current profiler adcp observations at a single station in espartel sill strait of gibraltar were used to compute an outflow of q2 0 82 sv through the main channel the cross strait structure of the velocity field or the outflow through a secondary channel north of the submarine ridge of majuan in espartel section is not captured by observations so that an improved version of a numerical model cepom has been used to fill the observational gap previously the model performance has been checked against historical data sets by comparing harmonic constants of the main diurnal and semidiurnal constituents from observed and modeled data at different sites of the strait considering the great complexity of tidal dynamics in the area the comparison is quite satisfactory and validates the model to infer the exchange at longer timescales using a climatological april in the simulation extracting a single station from the model at the same position as the monitoring station and processing the data similarly the model gives an outflow through the southern channel 13 higher than observations the inclusion of the cross strait structure of velocity reduces the computed outflow through the southern channel whereas the contribution of the northern channel brings the total outflow close to that computed using a single station 5 smaller if the same correction is applied to observations the total outflow would reduce to q2 0 78 sv the paper also assesses the importance of eddy fluxes to the total outflow their contribution being negligible 5

structure of the mediterranean undercurrent and mediterranean water spreading around the southwestern iberian peninsula 1 rafos float and hydrographic data are analyzed to investigate the pathways rates and mechanisms of mediterranean water mw spreading into the north atlantic from the gulf of cadiz with an emphasis on processes other than meddies we find that the transition of the mediterranean outflow from a density current to an intermediate depth jet occurs as it enters portimao canyon south of portugal due to rapidly steepening topography and associated turbulent entrainment this feature was not seen in recent plume model simulations due to their use of smoothed topography in addition to the traditional lower salinity maximum or core a denser deeper continuous vein of mw was also traceable from portimao canyon to cape st vincent the mean velocity structure of the mediterranean undercurrent changes from a 30 km wide jet with peak mean westward speed of 0 2 m s 1 along the southern iberian slope to a broader much weaker northward flow with maximum mean speed of only 0 06 m s 1 along the western iberian slope due in part to changes in the bottom slope lower core mw spread mainly 1 southward into the interior gulf of cadiz 2 northward along the western iberian slope and 3 westward into the deep tagus abyssal plain the average spreading rate was 0 01 0 02 m s 1 toward the west northwest direction meddies forming near the slope were found to have an indirect but profound impact on mw spreading often diverting mw approaching from upstream into the interior the results are compared to recent hydrography based studies of mw spreading pathways

comparative studies of the spreading of mediterranean water through the gulf of cadiz abstract a comparative study is made of observations and model results of the spreading of mediterranean water mw from the strait of gibraltar through the gulf of cadiz past cape st vincent into the eastern north atlantic the observations include a set of hydrographic sections from west of gibraltar to offshore of lisbon the tracking of rafos floats and current meter data the model is a very fine resolution limited area model of the region around cape st vincent and includes model floats both the observational data and the model results show the mw descending into two distinct layers around 800 and 1200 m depth in the gulf of cadiz as the mw leaves the slope meddies are generated and have been tracked by the rafos floats and can be seen in the paths of the model floats

global ocean meridional overturning abstract a decade mean global ocean circulation is estimated using inverse techniques incorporating air sea fluxes of heat and freshwater recent hydrographic sections and direct current measurements this information is used to determine mass heat freshwater and other chemical transports and to constrain boundary currents and dense overflows the 18 boxes defined by these sections are divided into 45 isopycnal neutral density layers diapycnal transfers within the boxes are allowed representing advective fluxes and mixing processes air sea fluxes at the surface produce transfers between outcropping layers the model obtains a global overturning circulation consistent with the various observations revealing two global scale meridional circulation cells an upper cell with sinking in the arctic and subarctic regions and upwelling in the southern ocean and a lower cell with sinking around the antarctic continent and abyssal upwelling mainly below the crests of the major bathymetric ridges

geochemical and physical constraints for the occurrence of living cold water corals cold water coral communities cover a wide range of possible habitats in terms of latitude ocean basins and depth with ongoing studies continually expanding occurrences in various regions of the global ocean a range of factors determines the formation of cold water coral reefs such as physical hydrochemical and biological e g food supply factors recently more and more modeling studies have emerged using a variety of mathematical approaches have emerged including environmental niche factor analysis enfa and predictive habitat suitability models however only few studies have attempted to characterize the underlying suite of hydro biogeochemical and physical constraints of cold water coral reefs and to differentiate between pristine reef growth vs sites with reduced or no coral occurrences this study concentrates on new data and a compilation of existing data sets on the physical and chemical properties in the ne atlantic and the mediterranean it explores the influence of ambient bottom waters and its characteristics on living cold water reefs and mounds formed by lophelia pertusa several questions are addressed 1 what are the physical and geochemical boundary conditions of living cold water corals 2 do these geochemical parameters correlate with proposed physical prerequisites 3 is there a general difference in the signature of living and dead coral sites

on the abyssal circulation in the glacial atlantic an inverse method is used to evaluate the information contained in sediment data for the atlantic basin during the last glacial maximum defined here as the time interval 18 21 kyr before present the data being considered are an updated compilation of the isotopic ratios 18 o 16 o 18 o and 13 c 12 c 13 c of fossil shells of benthic foraminifera bottom dwelling organisms first an estimate of the abyssal circulation in the modern atlantic is obtained which is consistent with i climatologies of temperature and salinity of the world ocean circulation experiment ii observational estimates of volume transport at specific locations and iii the statements of a finite difference geostrophic model second estimates of water properties 18 o of equilibrium calcite or 18 oc and 13 c of dissolved inorganic carbon or 13 cdic derived from sediment data are combined with this circulation estimate to test their consistency with the modern flow it is found that more than approximately 80 of water property estimates 18 oc or 13 cdic are compatible with the modern flow given their uncertainties the consistency of glacial 13 cdic estimates with the modern flow could be rejected after two assumptions are made i the uncertainty in these estimates is 0 1 this uncertainty includes errors in sediment core chronology and oceanic representativity of benthic 13 c which alone appears better than this value on average and ii 13 cdic in the glacial deep atlantic was dominated by a balance between water advection and organic c remineralization measurements of 13 c on benthic foraminifera are clearly useful but the current uncertainties in the distribution and budget of 13 cdic in the glacial atlantic must be reduced to increase the power of the test

tracking the mediterranean outflow in the gulf of cadiz abstract the mediterranean water leaves the western end of the strait of gibraltar as a bottom wedge of salty and warm waters flowing down the continental slope the salinity of the onset mediterranean outflow water mow is so high that leads to water much denser initially in excess of 1 5 kg m 3 than the overlying central waters during much of its initial descent the mow retains large salinity anomalies causing density anomalies that induce its gravity current character and relatively high westward speeds causing a substantial coriolis force over long portions of its course we use hydrographic data from six cruises a total of 1176 stations plus velocity data from two cruises together with high resolution bathymetric data to track the preferential mow pathways from the strait of gibraltar into the western gulf of cadiz and to examine the relation of these pathways to the bottom topography a methodology for tributary systems in drainage basins modified to account for the coriolis force emphasizes the good agreement between the observed trajectories and those expected from a topographically constrained flow both contour avenues and cross slope channels are important and have complementary roles steering the mow along the upper and middle continental slope before discharging as a neutrally buoyant flow into the western gulf of cadiz our results show that the interaction between bottom flow and topography sets the path and final equilibrium depths of the modern mow furthermore they support the hypothesis that as a result of the high erosive power of the bottom flow and changes in bottom water speed the mow pathways and mixing rates have changed in the geological past

qualitative and quantitative approaches in palaeohydrography a case study from core top parameters in the gulf of cadiz palaeoceanography relies on the assumption that parameters measureable in sediment cores correlate reliably to hydrographic parameters areas of dynamic watermass mixing which generally have steep hydrographic gradients therefore provide both a tempting target large spatial and temporal differences in temperature and salinity and a significant challenge high flow velocities and high noise for palaeoceanographers here we investigate the ability of parameters measured on core tops to be used as the basis for simulating regional hydrography within one globally important area of watermass mixing the gulf of cadiz using grainsize sediment composition benthic foraminiferal assemblage and benthic foraminiferal stable isotope analysis it is possible to build an effective framework for qualitative constraint of the position of the modern mediterranean outflow water mw plume we propose that the gulf of cadiz slope can be sub divided into 8 hydrographic zones reflecting these parameters proximal mw core mw1 steep slopes core mw1 gentle slopes distal mw1 distal mw2 lower limit of mw plume north atlantic deep water and ambient atlantic water we anticipate that compilation of time slice data will reveal hydrographic sub divisions of the slope for the past in a similar manner improving our understanding of past changes in the size and position of the mw plume but more work needs to be done before a secure protocol for quantitative reconstruction can be created stable isotope analysis alone is insufficient for the task with 13c behaving in a non conservative manner and 18ocalcite acting in an ambiguous way due to the competing influences of 18owater and temperature it is likely that if a single parameter that unambiguously determines the difference between mediterranean water and atlantic water can be identified combination with 18ocalcite will allow extension of our qualitative analysis into a quantitative means of palaeohydrographic reconstruction for this region similar complexity to that found in this study would be expected in any mixing region and in particular on the majority of sediment drifts we recommend that core top surveys similar to this study are performed on these sediment drift systems before any form of quantitative palaeohydrology is attempted

sensitivity of mediterranean thermohaline circulation to gateway depth a model investigation 1 the neogene sedimentary record of the mediterranean sea holds evidence for changes in water properties and circulation these paleoceanographic changes have been attributed to changes in the flow through the ocean gateway between the mediterranean sea and the atlantic ocean we use an oceanic general circulation model to achieve quantitative physics based understanding of the effect of changes in the depth of the gateway such as may result from tectonic activity or variation in sea level to isolate these effects we use idealized basin geometry and impose simplified atmospheric forcing a reference experiment with present day sill depth demonstrates that the model simulates reasonably well the main features of the present day mediterranean thermohaline circulation as inferred from observations and previous numerical studies subsequently a series of sensitivity simulations is performed with different sill depths the model results show that mediterranean temperature salinity and thermohaline circulation depend strongly on sill depth as the sill depth decreases the upper overturning cell is quasi linearly reduced in strength while contrary to what one would expect the deep cell intensifies and does so in a nonlinear way we find that a shoaling of the sill depth induces a blocking effect on the outflow waters which creates a strong recirculation in the deep layers strengthening the deep cell nevertheless deep water formation is reduced and as a consequence the ventilation of the deep layers diminishes we identify three different circulation modes of the mediterranean thermohaline circulation depending on the sill depth shallow sill moderate sill and deep sill modes coupled with strong weak and negligible blocking effects respectively our results are consistent with the pre messinian paleoceanographic record of the mediterranean sea and may be useful to understanding the behavior of other land locked basins both extant and from the geological past

new insights into upper mow variability over the last 150kyr from iodp 339 site u1386 in the gulf of cadiz the upper mediterranean outflow water mow paleo oceanographic history in the gulf of cadiz is poorly constrained due to the lack of high resolution records that pre date the last glaciation existing proxy records concentrate on mow variability along the middle slope of the gulf of cadiz here we present a continuous high resolution benthic foraminifera 18o record from the upper mow core at iodp expedition 339 site u1386 in the gulf of cadiz of the past 150 000 years based on 18o grain size and zr al variability comparison of our results with existing mediterranean sea md01 2472 md95 2043 open ocean lr04 and gulf of cadiz md99 2339 records we have gathered new insights into the evolution of the upper mow core on glacial interglacial timescales the influence of the upper mow at site u1386 was strongest during mis 5 and mis 1 similar 18o variability can be seen in the levantine intermediate water liw originating from the levantine basin of the eastern mediterranean sea we found clear indication for a vertical shift of the mow from the upper to the middle slope of the gulf of cadiz during sea level lowstands coinciding with mis 4 and mis 2 but also during mis 3 additionally our results indicate an increased upper mow flow correlated with heinrich events 7 to 10 and the younger dryas and also inversely relate to precession forced monsoonal freshwater inputs into the eastern mediterranean in the context of sapropel formation we could not find conclusive evidence of the proposed mow shutdown in our data

a turbulent bottom boundary layer code for use in numerical ocean models abstract a model for a turbulent bottom boundary slab layer is described the model is designed to fit under a standard depth coordinate ocean general circulation model with a view to improving its response both for local and climate problems the depth of the layer varies temporally and spatially both analytical and numerical versions of the model conserve energy the model is tested using a source of dense water on a slope and performs satisfactorily with the plume spreading far more than the equivalent case without a bottom layer

large scale vertical and horizontal circulation in the north atlantic ocean abstract observations of large scale hydrography air sea forcing and regional circulation from numerous studies are combined by inverse methods to determine the basin scale circulation average diapycnal mixing and adjustments to air sea forcing of the north atlantic ocean dense overflows through the denmark strait and faroe bank channels are explicitly included and are associated with strong vertical and lateral circulation and mixing these processes in the far northern atlantic play a fundamental role in the meridional overturning circulation for the entire ocean accompanied by an upper cell of mode water and intermediate water circulation the two cells converge roughly at the mean depth of the midocean ridge crest the labrador sea water layer lies within this convergence south of the overflow region model derived mean diapycnal diffusivities are o 10 5 m2 s 1 or smaller at the base of the thermocline and diapycnal advection is driven primarily by air sea transformation on outcropping layers

dynamics of the mediterranean salinity tongue abstract a reduced gravity planetary geostrophic model of the north atlantic consisting of two active layers overlying a motionless abyss is developed to investigate the effect of the wind field in shaping the dynamics of the mediterranean salinity tongue the model is driven by climatological winds and eastern boundary ventilation in a basin of realistic geometry and includes a parameterization of meddies the upper layer depth from the model shows a clear similarity to observations both in terms of the location and intensity of the subtropical gyre and also the position of the outcropping line in the northern basin potential vorticity in layer two reproduces the sweep of potential vorticity contours southwestward from the eastern boundary and extending westward into the interior and provides the pathways along which mediterranean water spreads into the model interior the authors solve for the steady salinity field in the second layer including sources of upper labrador sea water and antarctic inter

a hydraulic box model study of the mediterranean response to postglacial sea level rise 1 this paper quantifies the role of changing sea level in affecting mediterranean stratification using a new model of the strait basin system which allows for explicit time dependence during the last deglaciation fairbank s meltwater peak 1b leads to rapidly rising global sea levels and a freshening of the oceans and hence increasing influx of ever freshening atlantic water into the mediterranean basin owing to long residence times the salinity of the deep and intermediate water reservoirs would have decreased more slowly so that the basin was more stably stratified for a period with possible implications for sapropel formation our model is used to estimate the size of this reservoir effect in comparison to the freshwater influx from the opening of the black sea at the bosphorus it is found that this mechanism affects the stratification to a similar degree as the black sea opening other climatic mechanisms have also affected the freshwater budget of the mediterranean at this time but their sizes are more difficult to quantify

signatures of the mediterranean outflow from a north atlantic climatology 2 diagnostic velocity fields part 1 of this study is a descriptive analysis of the spreading of mediterranean water based on high resolution maps of salinity and density in the eastern basin in this second part of our study velocity fields for two representative isopycnal surfaces of the mediterranean outflow o 0 s 29 70 and o 0 s 29 90 are estimated from a diagnostic model that combines climatological hydrographic data from the national oceanic data center with long term direct measurements of water exchange through the strait of gibraltar the model is constrained by geostrophic dynamics conservation of mass no flux conditions at the continental shelf and specified flow through the strait of gibraltar our principal data source is a recently assembled database of the north atlantic that consists of climatological mean property fields averaged on isopycnal surfaces the mean fields are based on more than 80 years 1909 1990 of data and have a nominal horizontal resolution of 0 5 o to provide boundary conditions at the strait of gibraltar we use the results of a model developed from data collected during the gibraltar experiment in 1985 the estimated velocity fields show mediterranean water exiting the strait of gibraltar following the southern iberian coast and then entering the tagus basin where it turns anticyclonically to create a reservoir of this water mass the flow continues northward along the eastern boundary penetrating into the rockall channel finally the model flow fields do not show a significant westward advection of mediterranean waters into the subtropical gyre

observations and numerical modelling of the mediterranean outflow splitting and eddy generation during the canigo project the generation of dipolar eddies in the mediterranean water mw layers off south portugal was recorded by subsurface floats from february to november 1998 the role of the bottom topography on the spreading of the mw in the gulf of cadiz and on the generation of these mw eddies was studied in the framework of the medtop project some of the hydrological and velocity observations collected during medtop in 2001 and 2002 also revealed the association of anticyclones meddies and cyclones in the region just south of the portimao canyon the evolution of these structures is studied with subsurface floats deployed in the vortices the splitting of the mw plume in the gulf of cadiz and the generation mechanisms of the mw vortices in the region from portimao canyon to the estremadura promontory are investigated using a bottom following numerical primitive equations model in a regional ocean configuration incorporating the realistic topography of the iberian continental slope the model reproduces the mw division into different cores in the gulf of cadiz as well as the generation of baroclinic dipoles downstream of portimao canyon the role of the bottom topography in the eddy generation process is discussed

a numerical study on the successive formation of meddy like lenses 1 we present a process study on the sustaining mechanism of lens formation using a series of numerical experiments of a density current over a sloping bottom with a cape along the coastline water parcels in the bottom density current are shed into the offshore region leading to periodic formation of anticyclonic lenses as part of baroclinic dipolar vortices the cyclonic partner is more prominent at the surface and the coupled vortices are carried by the mean current established in the offshore region parameter dependence of dipole generation is examined which suggests that the background current is necessary for the detached eddies to be coherent in the downstream direction and for shedding events to repeat nof and pichevin 1996 it is also shown that the density mixing of the bottom current provides criteria for cyclogenesis at the sea surface a detailed analysis is given by a five layer model forced by a water mass source sink which reproduces the baroclinic dipolar vortices similar to those observed in the preceding z coordinate model we find that the dipole generation is due to the finite amplitude divergence convergence of the baroclinic current passing the cape stern and chassignet 2000 the overall analyses suggest three necessary conditions for successive eddy formation 1 a localized variation in the coastline causing the finite amplitude disturbance 2 mixing of mediterranean water with the surrounding fluids leading to anticyclonic rotation of meddies as well as cyclogenesis at the surface and 3 background currents that advect the detached vortices out of the source region index terms 4255 oceanography general numerical modeling 4219 oceanography general continental shelf processes 4520 oceanography physical eddies and mesoscale processes 4528 oceanography physical fronts and jets keywords eddy shedding dense water plume numerical simulation

entrainment in shallow rotating gravity currents a modeling study abstract the physics of shallow gravity currents passing through a rotating channel at subcritical froude number is investigated here with a series of idealized numerical experiments it is found that the combined effects of friction and rotation set up a complex transverse circulation that has some crucial implications for the entrainment process a key component of this secondary circulation is a geostrophically balanced transverse jet in the interface that laterally drains fluid from the interface this effect is shown to result in a strong cross channel asymmetry and a spatial separation of the entrainment process drained interfacial fluid is partly replaced by entrained ambient fluid on the deep side of the gravity current whereas the downward mixing of buoyant fluid occurs on the shallow side these results closely corresponding to recent measurements in a shallow channelized gravity current in the western baltic sea illustrate that the description of entrainment as a strictly vertical mixing p

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

hydraulic criticality of the exchange flow through the strait of gibraltar abstract the hydraulic state of the exchange circulation through the strait of gibraltar is defined using a recently developed critical condition that accounts for cross channel variations in layer thickness and velocity applied to the output of a high resolution three dimensional numerical model simulating the tidal exchange the numerical model uses a coastal following curvilinear orthogonal grid which includes in addition to the strait of gibraltar the gulf of cadiz and the alboran sea the model is forced at the open boundaries through the specification of the surface tidal elevation that is characterized by the two principal semidiurnal and two diurnal harmonics m2 s2 o1 and k1 the simulation covers an entire tropical month the hydraulic analysis is carried out approximating the continuous vertical stratification first as a two layer system and then as a three layer system in the latter the transition zone generated by entrainment and mixing between the atlantic and mediterranean flows

the medieval climate anomaly in antarctica abstract the medieval climate anomaly mca is a well recognized climate perturbation in many parts of the world with a core period of 1000 1200 ce here we are mapping the mca across the antarctic region based on the analysis of published palaeotemperature proxy data from 60 sites in addition to the conventionally used ice core data we are integrating temperature proxy records from marine and terrestrial sediment cores as well as radiocarbon ages of glacier moraines and elephant seal colonies a generally warm mca compared to the subsequent little ice age lia was found for the subantarctic islands south of the antarctic convergence the antarctic peninsula victoria land and central west antarctica a somewhat less clear mca warm signal was detected for the majority of east antarctica mca cooling occurred in the ross ice shelf region and probably in the weddell sea and on filchner ronne ice shelf spatial distribution of mca cooling and warming follows modern dipole patterns as reflected by areas of opposing temperature trends main drivers of the multi centennial scale climate variability appear to be the southern annular mode sam and el nino southern oscillation enso which are linked to solar activity changes by nonlinear dynamics

seasonal and interannual variability of the surface circulation in the eastern gulf of cadiz sw iberia 1 an 11 year 1996 2007 time series of current meter observations representative of the open sea circulation a 4 year 2001 2005 time series of current meter records over the continental shelf and in situ data during different seasons have been compared in order to study the seasonal and interannual variability of the surface circulation in the eastern gulf of cadiz the open sea velocity observations indicate southeastward flow along the northern continental slope of the gulf of cadiz compatible with anticyclonic circulation during most of the year and more intense during summer months flow reversals northwestward circulation at seasonal time scales in late autumn and early winter preferably december and january are a rather recurrent feature with variable intensity depending on the year anticyclonic circulation is associated with westerlies whereas flow reversals usually take place under easterly episodes suggesting wind driven circulation negative north atlantic oscillation indices indicative of southward displacement of the azores high are also linked to the reversals changes in this mainly wind driven large scale surface circulation are echoed by the shelf circulation the coastal countercurrent that closes the mesoscale cyclonic cell over the eastern shelf in spring summer upwelling season is replaced by and eastward current in autumn and winter

propagation pathways of classical labrador sea water from its source region to 26 n 1 more than two decades of hydrography on the abaco line east of the bahamas at 26 n reveals decadal variability in the salinity of classical labrador sea water clsw despite the long distance from its source region in the north atlantic ocean hydrographic time series from the labrador sea and from the abaco line show a pronounced step like decrease in salinity between 1985 and 1995 in the labrador sea and between 1995 and 2010 at the abaco line suggesting a time lag between the two locations of approximately 9 years the amplitude of the anomaly at the abaco line is 50 of the amplitude in the labrador sea a similar time lag and reduction of amplitude is found in the high resolution ofes model in which salinity anomalies can be observed propagating through the deep western boundary current as well as through a broad interior pathway on its way south to the abaco line the clsw becomes 8 standard deviations saltier due to isopycnal mixing with mediterranean outflow water mow climatological data in the north atlantic suggests that the mixing ratio of mow to clsw at the abaco line is 1 4 and that no variability in mow is required to explain the observed variability at the abaco line the data studied here suggest that decadal clsw anomalies stay relatively coherent while getting advected despite the important role of interior pathways

a model analysis of the behavior of the mediterranean water in the north atlantic abstract the behavior of the mediterranean water in the north atlantic ocean sector of a global ocean general circulation model is explored starting from its entry point at the strait of gibraltar the analysis focuses primarily on one experiment in which explicit watermass exchange between the mediterranean sea and the atlantic at the strait of gibraltar is permitted the model produces an exchange rate of approximately 1 sv sv 106 m3 s 1 this is comparable to estimates derived from field measurements the density of the mediterranean outflow however is lower than observed mainly because of its high temperature more than 2 c higher than in reality the lower density of the outflow and the model s inadequate representation of the entrainment mixing in the outflow region cause the mediterranean water to settle in a depth range 800 1000 m in the north atlantic about 200 m shallower than observed here an interesting current system forms in response to the intrusion of the mediterranean water i

oceanographic processes and morphosedimentary products along the iberian margins a new multidisciplinary approach abstract our understanding of bottom currents and associated oceanographic processes e g overflows barotropic tidal currents including intermittent processes e g vertical eddies deep sea storms horizontal vortices internal waves and tsunamis is rapidly evolving many deep water processes remain poorly understood due to limited direct observations but can generate significant depositional and erosional features on both short and long term time scales this paper represents a review work which describes for the first time these oceanographic processes and examines their potential role in the sedimentary features along the iberian continental margins this review explores the implications of the studied processes given their secondary role relative to other factors such as mass transport and turbiditic processes and highlights three major results a contourite depositional and erosional features are ubiquitous along the margins indicating that bottom currents and associated oceanographic processes control the physiography and sedimentation b the position of interfaces between major water masses and their vertical and spatial variation in time specifically appears to exert primary control in determining major morphologic changes along the slope gradient including the contourite terraces development and c contourites deposits exhibit greater variation than the established facies model suggests therefore a consistent facies model however faces substantial challenges in terms of the wide range of oceanographic processes that can influence in their development an integrated interpretation of these oceanographic processes requires an understanding of contourites seafloor features their spatial and temporal evolution and the near bottom flows that form them this approach will synthesize oceanographic data seafloor morphology sediments and seismic images to improve our knowledge of permanent and intermittent processes around iberia and evaluate their conceptual and regional role in the margin s sedimentary evolution given their complexes three dimensional and temporally variable nature integration of these processes into sedimentary oceanographic and climatological frameworks will require a multidisciplinary approach that includes geology physical oceanography paleoceanography and benthic biology

signatures of the mediterranean outflow from a north atlantic climatology 1 salinity and density fields using historical data from the national oceanic data center the climatology of the eastern north atlantic basin has been investigated for the purpose of detailing the mediterranean outflow water in terms of its salinity density and flow patterns part 1 of this work is a descriptive analysis of the fate of the mediterranean water once it flows out of the strait of gibraltar tracing the salinity and density signatures high resolution maps of the climatological outflow are presented with an emphasis on the continuity of the water from its source from the climatological fields a continuous signal of mediterranean water is tracked northward to 50 20 n yet its westward advection is limited to the tagus basin recirculations of mediterranean water in the gulf of cadiz and in the bay of biscay deduced from property signals are also detailed iorga and lozier this issue present absolute velocity fields from a diagnostic model constrained by geostrophic dynamics conservation of mass and no flux boundary conditions

structure transports and transformations of the water masses in the atlantic subpolar gyre we discuss the distributions and transports of the main water masses in the north atlantic subpolar gyre naspg for the mean of the period 2002 2010 ovide sections 2002 2010 every other year as well as the inter annual variability of the water mass structure from 1997 4x and meteor sections to 2010 the water mass structure of the naspg quantitatively assessed by means of an optimum multiparameter analysis with 14 water masses was combined with the velocity fields resulting from previous studies using inverse models to obtain the water mass volume transports we also evaluate the relative contribution to the atlantic meridional overturning circulation amoc of the main water masses characterizing the naspg identifying the water masses that contribute to the amoc variability the reduction of the magnitude of the upper limb of the amoc between 1997 and the 2000s is associated with the reduction in the northward transport of the central waters this reduction of the northward flow of the amoc is partially compensated by the reduction of the southward flow of the lower limb of the amoc associated with the decrease in the transports of polar intermediate water and subpolar mode water spmw in the irminger basin we also decompose the flow over the reykjanes ridge from the east north atlantic basin to the irminger basin 9 4 4 7 sv into the contributions of the central waters 2 1 1 8 sv labrador sea water lsw 2 4 2 0 sv subarctic intermediate water saiw 4 0 0 5 sv and iceland scotland overflow water isow 0 9 0 9 sv once lsw and isow cross over the reykjanes ridge favoured by the strong mixing around it they leave the irminger basin through the deep to bottom levels the results also give insights into the water mass transformations within the naspg such as the contribution of the central waters and saiw to the formation of the different varieties of spmw due to air sea interaction

lagrangian transport pathways in the northeast atlantic and their environmental impact this study focused on mapping the general transport pathways of the northeast atlantic ocean by using the regional oceanic modeling system to calculate ocean current velocity components u v w and ariane an off line fortran code dedicated to the computation of three dimensional streamlines from velocity fields to calculate the transport of particles around the numerical model domain the study was undertaken using a 10 year climatic simulation statistical comparisons with satellite and in situ data showed that the ocean circulation model captured known regional oceanographic features four depth ranges showed different lagrangian transport pathways 0 10 m 20 200 m 300 500 m and 600 2000 m confirming that these routes are consistent with the known ocean circulation patterns our results were supported by multiple sources i connectivity between the african coast and the canary islands for sardine sardina pilchardus anchovy engraulis encrasicolus ii panmixia of lobsters scyllarides latus and palinurus elephas and european conger eel conger conger iii connectivity between azores and canary archipelagos for sponge phorbas fictitius and iv observed drifting of crude oil from the prestige oil tanker spill these results should help guide future observational campaigns as well as the interpretation of open ocean transport patterns and the distribution of marine organisms and chemical tracers in the northeast atlantic region

dense water dynamics along the strait of sicily mediterranean sea abstract hydrographic and current meter data gathered in different periods in the strait of sicily and in the southern tyrrhenian sea allow the outflow characteristics from the eastern toward the western mediterranean basin to be analyzed the evolution through the strait of a deep vein of dense water coming from the eastern mediterranean is described together with the dynamic interaction with overlying layers these data are related to a slightly generalized version of recent density current models such as those of emms and those of baringer and price taking into account the dynamic influence of the overlying currents and in particular their friction and mixing this model explains the path of this deep flow and enables estimates of entrainment and bottom friction to be made with these new data a phenomenon of considerable interest namely the dynamics of density currents crossing and outflowing from a strait is examined and discussed

eddy generation in the mediterranean undercurrent abstract in the framework of the european union mast iii project canary islands gibraltar azores observations 24 rafos floats were deployed in the mediterranean water mw undercurrent off south portugal between september 1997 and september 1998 a preliminary analysis of this lagrangian approach complemented with xbt and current meter data show some of the major aspects of the flow associated with the undercurrent as well as associated eddy activity floats that stayed in the undercurrent featured a downstream deceleration and a steering by bottom topography three meddy formations at cape st vincent could be isolated from the float data the dynamical coupling of meddies and cyclones was observed for a considerable period of time the generation of two dipolar structures in the portimao canyon region also was observed with the float data a major bathymetric relief gorringe bank was not only an important constraint to the eddy trajectories and of the flow at the mw levels but also a site for meddy formation

the mediterranean outflow splitting a comparison between theoretical models and canigo data abstract the mediterranean outflow in the atlantic is vertically subdivided into two main cores that are identified by temperature and salinity maxima hydrological data collected west of the strait of gibraltar and off the south and south west coasts of portugal in september 1997 have been used in two different models to shed some light on the mechanisms that cause a splitting of the mediterranean outflow these models are i a steady one dimensional streamtube model and ii a local time dependent model that includes cross stream variations the streamtube model applied at the northern respectively the southern part of the outflow appears capable of reproducing the observed density difference between the two cores the vertical separation however was underestimated the results from the local model suggest that a bump in the bottom topography may be a determining factor for the splitting tendency of the flow

properties and pathways of mediterranean water eddies in the atlantic abstract data from ship vertical casts nodc data set argo profiling floats coriolis data set and rafos type neutral density floats woce data set are used to study characteristics of meddies in the northeast atlantic in total 241 mediterranean water eddies meddies and 236 parts of float trajectories within meddies are selected for detailed analysis the results suggest that the meddy generation rate at the southern and southwestern iberian peninsula portimao canyon cap st vincent estremadura promontory gorringe bank is 3 times that at the northwestern iberian peninsula porto aveiro canyons cape finisterre and galicia bank meddies generated south of estremadura promontory the southern meddies as compared to those generated north of it the northern meddies have smaller radii smaller vertical extension higher aspect ratio higher rossby number and higher stability stronger potential vorticity anomaly these latter properties result from the southern meddies higher relative vorticity and stronger buoyancy frequency anomaly away from the generation regions meddy drift concentrates along four main paths three quasi zonal paths northern central southern and a path following the african coast coastal the quasi zonal paths are aligned to the isolines of the ambient potential vorticity field several cross path exchanges identified in this work are aligned to topographic rises northward translation of the northern meddies within the north atlantic current to the subpolar gyre is detected within the first 600 km from the coast meddy merger is proved to be a common event this explains the observed difference in radii between the newly generated meddies and those away from the iberian margin the decay of the southern meddies proceeds mainly via the loss of their skirts and does not affect meddy cores until the latest stages the decay of the northern meddies goes in parallel with the decay of their cores in average meddy decay is achieved within 1 2 years although may take over 3 years collisions with the mid atlantic ridge and seamounts sensibly decrease meddy lifetimes meddy decay also speeds up when meddies meet the azores current or the north atlantic current a rapid drop in the number of meddies south of the azores current proves that it represents a dynamic barrier for weak meddies

dynamics of rotating shallow gravity currents passing through a channel part i observation of transverse structure abstract a detailed dataset describing a quasi stationary bottom gravity current approximately 10 m thick and 10 km wide passing through a channel like constriction in the western baltic sea is presented the data include full depth synoptic and highly resolved transects of stratification and turbulence parameters as well as detailed velocity transects across the gravity current at different down channel locations the velocity data reveal a persistent transverse circulation creating a characteristic wedge shaped density structure in the interface a strong asymmetry was also found in the interior of the gravity current where the evolution of a dynamically significant transverse density gradient to the right of the down channel flow was observed spectral analysis of the near bottom velocities showed a surprisingly strong contribution to the bottom stress from low frequency motions with periods up to 30 min that are possibly related to internal wave effects cross channel transects of shear microst

on the mediterranean water composition abstractthe mediterranean outflow water mow spills from the mediterranean sea east north atlantic basin west off the strait of gibraltar as mow outflows it entrains eastern north atlantic central waters enacw and intermediate waters to form the neutrally buoyant mediterranean water mw that can be traced over the entire north atlantic basin its high salinity content influences the thermohaline properties of the intermediate deep water column in the north atlantic and its dynamics here the composition of mw in its source region the gulf of cadiz west off strait of gibraltar is investigated on the basis of an optimum multiparameter analysis the results obtained indicate that mixing of mow 34 1 0 3 occurs mainly with overlying enacw 57 1 0 8 in a process broadly known as central water entrainment a diluted form 80 of dilution of the antarctic intermediate water aaiw reaches the region and also takes part in mw formation 8 3 0 5 finally the underlying labrador sea wat

climatically driven changes in sediment supply on the sw iberian shelf since the last glacial maximum the assemblages of marine sediments on the sw iberian shelf have been controlled by contributions from distinct sources which have varied in response to environmental changes since the last glacial maximum lgm the rapid decadal scale mediterranean overturning circulation permits mixing of suspended particles from the entire mediterranean sea they are entrained into the suspended particulate matter spm carried by mediterranean outflow water mow which enters the eastern north atlantic through the strait of gibraltar and spreads at intermediate depths in the gulf of cadiz and along the portuguese continental margin other major sediment sources that have contributed to the characteristics and budget of spm along the flow path of mow on the sw iberian shelf are north african dust and river transported particles from the iberian peninsula to reconstruct climate and circulation driven changes in the supply of sediments over the past 23 000 cal yr b p radiogenic nd sr and pb isotope records of the clay size sediment fraction were obtained from one gravity core in the gulf of cadiz 577 m water depth and from two gravity cores on the portuguese shelf 1745 m 1974 m water depth these records are supplemented by time series analyses of clay mineral abundances from the same set of samples contrary to expectations the transition from the lgm to the holocene was not accompanied by strong changes in sediment provenance or transport whereas heinrich event 1 h1 and the african humid period ahp were marked by significantly different isotopic signatures reflecting changes in source contributions caused by supply of ice rafted material originating from the north american craton during h1 and diminished supply of saharan dust during the ahp the data also reveal that the timing of variations in the clay mineral abundances was decoupled from that of the radiogenic isotope signatures

another description of the mediterranean sea outflow abstract papers about the outflow in the strait of gibraltar assume that i it is composed of only two mediterranean waters mws the levantine intermediate water liw and the western mediterranean deep water wmdw from the eastern and western basins respectively ii both mws are mixed near 6 w hence producing a homogeneous outflow that is then split into veins due to its cascading along different paths and to different mixing conditions with the atlantic water aw a re analysis of 1985 1986 ctd profiles gibraltar experiment indicates two other mws the winter intermediate water wiw from the western basin and the tyrrhenian dense water tdw basically originated from the eastern basin in the central alboran subbasin these four mws are clearly differentiated roughly lying one above the other in proportions varying from north to south proportions also vary with time so that the outflow can be mostly of either eastern or western origin while progressing westward the mws can still be differentiated and associated isopycnals tilt up southward as much as being in the sill surroundings roughly parallel to the moroccan continental slope where the densest mws are the mws at the sill are thus juxtaposed and they all mix with aw leading to an outflow that is horizontally heterogeneous just after the sill 5 45 w before progressively becoming vertically heterogeneous as soon as 6 15 w there can be little liw and or no wmdw outflowing for a while an analysis of new 2003 2008 time series from two ctds moored ciesm hydro changes programme at the sill 270 m and on the moroccan shelf 80 m confirms the juxtaposition of the mws their individual and generally intense mixing with aw as well as the large temporal variability of the outflow composition only liw and tdw were indicated at the sill while on the shelf only liw tdw sometimes denser there than 200 m below and wmdw were indicated but none of the mws has been permanently outflowing at one or the other place the available data can be analyzed coherently intermediate and deep mws are formed in both basins in amounts that although variable from year to year allow their tracing up to the strait four major mws circulate alongslope counterclockwise as density currents and as long as they are not trapped within a basin which is necessarily the case for the deep mws in the alboran the intermediate mws wiw liw and upper tdw circulate in the north while the deep mws lower tdw and wmdw are uplifted hence relatively motionless and mainly pushed away in the south since both the intermediate and deep mws outflow at the sill they are considered as light and dense mws the light dense mws interface possibly intersecting the aw mws interface in the sill surroundings considering an outflow east of the sill composed of only two light dense homogeneous layers gives significant results across the whole strait the outflow has spatial and temporal variabilities much larger than previously assumed the mws are superposed in the sea and lead at the sill to juxtaposed and vertically stratified suboutflows that will cascade independently before forming superposed veins in the ocean these veins can have similar densities and hydrographic characteristics even if associated with different mws which accounts for the features permanency assumed up to now the outflow structure downstream of the sill depends on its composition upstream and more importantly on that of aw in the sill surroundings where fortnightly and seasonal signals are imposed on the whole outflow

simulation of the interactions between gravity processes and contour currents on the algarve margin south portugal using the stratigraphic forward model sedsim abstract the margin of the gulf of cadiz is swept by an intermediate current the mediterranean outflow water mow flowing from the mediterranean to the atlantic on the northern margin of the gulf algarve margin south portugal the mow intensity is low and fine grained contourite drifts are built up with an alongslope alignment recent sedimentological studies emphasize the presence of complex process interactions resulting in the formation of a unique depositional architecture alongslope processes related to contour currents generate contourite drift while downslope processes form canyons and channels aligned on deep faults this paper uses a combined oceanographic and geological dataset to simulate the different types of interactions between gravity processes and contour currents which were evidenced on this margin an extrapolation of the contour current intensity has been used based on the present day velocity field and sea level fluctuations over the simulated geological time scale according to our model results the construction of the contourite drift is closely linked to contour current velocities and directions the types of sediments transported and the existing topography using modern sedimentological understanding of the area we have correlated gravity flow s strongest activity to sea level lowstand periods mainly due to a closer connection between canyon s mouth and river or deltaic systems the simulated gravity flows are initialized at different locations and times on the margin depending on the preserved lobes retrieved from seismic analysis their resulting morphological features are identified as perched lobes with volumes and forms close to the ones observed on portimao and lagos drifts this study provides a process based understanding of the construction of contourite system and a physical evaluation of the interactions between gravity flows perpendicular to the slope and alongslope processes in addition it shows the influence of autocyclic factors in the construction of contourite sedimentation which is important to consider in future sedimentary paleo reconstruction interpretations

on the reasons for the formation and variability of the azores current abstract recent studies have shown that the formation of the well defined zonally oriented azores current may be the result of water mass transformation associated with the mediterranean outflow in the gulf of cadiz as the denser mediterranean water descends down the continental slope it entrains overlying north atlantic central water it is believed that the azores current then forms as part of the horizontal recirculating gyre generated through the plume mechanism in this study the authors further explore this hypothesis by performing a series of numerical experiments these experiments are based on a high resolution general circulation model that includes the mediterranean sea and that realistically simulates the water mass exchange through the strait of gibraltar and the transport and variability of the azores current the authors show that the divergence of the relative vorticity flux and the planetary vorticity flux associated with planetary waves are the main factors determining the variab

on the connection between the mediterranean outflow and the azores current as the salty and dense mediteranean overflow exits the strait of gibraltar and descends rapidly in the gulf of cadiz it entrains the fresher overlying subtropical atlantic water a minimal model is put forth in this study to show that the entrainment process associated with the mediterranean outflow in the gulf of cadiz can impact the upper ocean circulation in the subtropical north atlantic ocean and can be a fundamental factor in the establishment of the azores current two key simplifications are applied in the interest of producing an economical model that captures the dominant effects the first is to recognize that in a vertically asymmetric twolayer system a relatively shallow upper layer can be dynamically approximated as a single layer reduced gravity controlled barotropic system and the second is to apply quasigeostrophic dynamics such that the volume flux divergence effect associated with the entrainment is represented as a source of potential vorticity two sets of computations are presented within the 1 layer framework a primitive equation based computation which includes the divergent flow effects is first compared with the equivalent quasigeostrophic formulation the upper ocean cyclonic eddy generated by the loss of mass over a localized area elongates westward under the influence of the b effect until the flow encounters the western boundary in the steady state the circulation pattern consists of bidirectional zonal flows with a limited meridional extent eastward to the south of the sink and westward to the north of the sink the localized sink drives a horizontal circulation in the interior ocean whose strength is approximately an order of magnitude greater than the sink s strength it is demonstrated that the induced circulation in the far field from a localized sink is insensitive to the neglect of the divergent flow component a set of parameter sensitivity experiments is then undertaken with the quasigeostrophic model for an idealized midlatitude circulation driven both by wind forcing and thermohaline flow through the open southern and northern boundaries when a sink near the eastern boundary is superimposed on the idealized midlatitude circulation it is shown to alter significantly the upper ocean flow and induce an eastward zonal current which resembles the azores current in location and transport this mechanism also generates a westward current to the north of the sink location which could be associated with the azores countercurrent an extensive series of sensitivity experiments is conducted to determine the response of this current system to changes in the boundary layer processes sink strength sink distribution model resolution and wind forcing the magnitude of the current transports is found to be sensitive to the sink intensity and to its distance from the coastline

deciphering bottom current velocity and paleoclimate signals from contourite deposits in the gulf of cadiz during the last 140 kyr an inorganic geochemical approach contourites in the gulf of cadiz gc preserve a unique archive of mediterranean outflow water mow variability over the past 5 3 ma in our study we investigate the potential of geochemical data obtained by xrf scanning to decipher bottom current processes and paleoclimatic evolution at two different sites drilled during iodp expedition 339 through contourites in the northern gc site u1387 which is bathed by the upper mow core and site u1389 located more proximal to the strait of gibraltar the lack of major downslope transport during the pleistocene makes both locations ideally suited for our study the results indicate that the zr al ratio representing the relative enrichment of heavy minerals zircon over less dense alumnosilicates under fast bottom current flow is the most useful indicator for a semiquantitative assessment of current velocity although most elements are biased by current related processes the bromine br record representing organic content preserves the most pristine climate signal rather independent of grain size changes hence br can be used for chronostratigraphy and site to site correlation in addition to stable isotope stratigraphy based on these findings we reconstructed mow variability for marine isotope stages mis 1 5 using the zr al ratio from site u1387 the results reveal abrupt millennial scale variations of mow strength during greenland stadials gs and interstadials gi with strong mow during gs and glacial terminations and a complex behavior during heinrich stadials millennial scale variability persisting during periods of poorly expressed gs gi cyclicities implies a strong internal oscillation of the mediterranean north atlantic climate system

mixing and spreading of the mediterranean outflow abstract hydrographic and current profiler data taken during the 1988 gulf of cadiz expedition have been analyzed to diagnose the mixing spreading and descent of the mediterranean outflow the s properties and the thickness and width of the outflow were similar to that seen in earlier surveys the transport of pure mediterranean water i e water with s 38 4 psu was estimated to be about 0 4 106 m3 s 1 which is lower than historical estimates most of which were indirect but comparable to other recent estimates made from direct velocity observations the outflow transport estimated at the west end of the strait of gibraltar was about 0 7 106 m3 s 1 of mixed water and the transport increased to about 1 9 106 m3 s 1 within the eastern gulf of cadiz this increase in transport occurred by entrainment of fresher north atlantic central water and the salinity anomaly of the outflow was consequently reduced the velocity weighted salinity decreased to 36 7 psu within 60 km of the strait and decre

rupture complexity of a moderate intraplate earthquake in the alps the 1996 m5 epagny annecy earthquake summary the magnitude 5 epagny annecy earthquake of 1996 july 15 is the largest seismic event to have occurred in the alps since the introduction of modern digital instrumentation this strike slip event was located on the vuache fault near the town of annecy in the northern french alps the aim of our work was to retrieve the main parameters of the rupture process of this earthquake from seismograms recorded at local and regional distances 20 300 km to eliminate path and site evects from the seismograms we compared the main shock recordings at each station with those of the largest aftershocks nearby we used a combination of techniques including pulse width measurements and cross correlation of velocity traces comparison of p wave displacement pulses and empirical green s function deconvolution to retrieve the apparent duration of the rupture process as seen at each station our results demonstrate that in the absence of on scale data p wave pulse width measurements on clipped signals can be misleading if the rupture process is complex in the case of the annecy earthquake comparisons of on scale p wave displacement seismograms and the empirical green s function deconvolutions show that the rupture process consisted of at least two subevents separated by 0 2 0 3 s and with a total duration of about 0 5 s the systematic azimuthal dependence of both the shape and duration of the apparent source time function is consistent with a nearly unilateral propagation of the main rupture phase in a southeast direction along the fault plane and parallel to the direction of slip an isochron analysis reveals that the first subevent occurred slightly to the northwest of the nucleation point but that the second subevent was located further to the southeast thus confirming the overall rupture directivity towards the southeast an interpretation of our results in light of the previously documented aftershock distribution and of observations of ground cracks in the epicentral area suggests that the main shock occurred on the vuache fault and that rupture in a northwest direction was inhibited by a right lateral stepover in the fault accordingly the vast majority of the subsequent aftershocks which include several magnitude 3 4 events occurred on a fault segment that is slightly ovset from the inferred surface trace of the vuache fault and that was activated by the main shock

the sines contourite depositional system along the sw portuguese margin onset evolution and conceptual implications abstract the sines contourite depositional system located in the southwest portuguese margin is a central segment of the iberian contourite depositional complex built under the influence of the mediterranean outflow water mow this work presents the onset and evolution of this system using multibeam bathymetry multichannel seismic reflection lines sediment cores and well data six seismic units of late miocene through holocene age have been identified which defined three evolutionary stages for drift construction a an onset and initial stage from the latest miocene to the late pliocene 5 33 2 5 ma where a sheeted drift was built under a weak flowing mow b a growing stage from the early to middle quaternary 2 5 0 7 ma characterized by the deposition of a mounded drift in the south and a sheeted drift in the north which is correlated with a strengthening of the mow and c a maintenance stage between the middle pleistocene and holocene 0 7 ma present where the modern depositional and erosional contourite features developed associated with three intensification periods of the mow at 0 7 ma 0 4 ma and 20 ka the development of the sines contourite depositional system was constrained in the long term by seafloor paleomorphologies inherited from the mesozoic rifting phases of the southwest portuguese margin the nnw sse horsts and grabens built during the mesozoic rifting provided accommodation for drift growth with limited lateral migration and locally enhanced the alongslope bottom current in short term environmental climate and sea level fluctuations modulated changes in bottom current density and intensity determining sedimentary cycles in the depositional record especially during the quaternary our findings emphasize the occurrence of three main plastered morphologies throughout the seismic record which were compared with other plastered drifts in different continental margins to establish a conceptual model

atlantic forcing of the mediterranean oligotrophy 1 the mediterranean sea shows a peculiar anomaly in its nutrient pattern compared to the global ocean as there is decrease in nutrient concentration from west to east this feature has been attributed to the antiestuarine circulation at the strait of gibraltar where an eastward flow of atlantic nutrient poor surface waters is compensated by a westward countercurrent of mediterranean nutrient rich deep waters this water exchange has been suggested as the ultimate cause for the oligotrophy of the mediterranean basin even though only a few studies have accurately examined the magnitude of the nutrient flux through the strait of gibraltar in this work data from the gibraltar fixed time series gift between 2005 and 2008 were used to assess nutrient distributions applying a two layer model of water mass exchange and using the mediterranean outflow recorded in situ the net export of nutrients from the mediterranean to the atlantic was calculated as 139 and 4 8 gmol yr 1 of nitrate and phosphate respectively the results also demonstrated that the atlantic inflow is not nutrient depleted and in particular contains significant levels of phosphate which is the limiting factor for biological productivity in the eastern mediterranean the distribution of the quasi conservative parameter n in the western and eastern basins indicated that nitrate deficient surface waters are transformed into phosphate deficient bottom waters by internal cycling processes therefore phosphate depletion in the mediterranean does not have its origin in the entry of a phosphorus impoverished atlantic inflow through the strait of gibraltar

mesoscale variability in denmark strait the pv outflow hypothesis abstract the outflow through denmark strait shows remarkable mesoscale variability characterized by the continuous formation of intense mesoscale cyclones just south of the sill these cyclones have a diameter of about 30 km and clear signatures at the sea surface and in currents measured near the bottom they have a remnant of arctic intermediate water aiw in their core the authors hypothesis is that these cyclones are formed by stretching of the high potential vorticity pv water column that outflows through denmark strait the light upper layer of the outflow the east greenland current remains on the surface in the irminger sea while the dense overflow water descends the east greenland continental slope the midlevel waters mostly aiw could thus be stretched by more than 100 which would induce very strong cyclonic relative vorticity the main test of this new hypothesis is by way of numerical experiments carried out with an isopycnal coordinate ocean model configured to have a marginal sea

a pliocene mixed contourite turbidite system offshore the algarve margin gulf of cadiz seismic response margin evolution and reservoir implications abstract a buried mixed contourite turbidite system has been identified in the pliocene succession of the algarve basin in the northern gulf of cadiz this margin is currently dominated by the mediterranean outflow water and associated contourite deposition analysis of seismic data along with careful geographical and oceanographic reconstructions of the margin show the gradual move from a turbidite dominated towards a contourite dominated margin and the subsequent birth of an impressive elongate mounded contourite drift system the faro albufeira drifts the contourite drift can be distinguished from down slope turbiditic and mass transport deposits based on the acoustic character distribution analysis and through careful margin reconstruction in the earliest pliocene seismic unit p1 has been interpreted as a dominant down slope most likely turbidite system sourced mainly from the northeast there is clear evidence of contourite reworking at seismic unit p2 where upslope progradation and a sheeted morphology are observed high amplitude reflections are thought to be a result of more vigorous bottom currents in the early upper pliocene that were capable to redistributing coarser sediments however in the northeast of the study area a thick sequence of chaotic seismic facies has been interpreted as mass transport deposits sourced from the north indicate that the bottom currents were unable to dominate over the entire margin due to high down slope clastic influx semi transparent seismic unit p3 indicates that the upper pliocene initially experienced a reduction in bottom current intensity however upslope progradation shows that a mixed system was maintained above the base quaternary discontinuity ca 2 6 ma highly erosive discontinuities and high amplitude seismic reflections are evidence of pronounced intensification of the mediterranean outflow water and a move to a fully contourite dominated slope mixed turbidite contourite systems such as the one identified in the algarve basin could provide impressive petroleum potential where downslope clastics are winnowed and reworked by bottom water currents to leave good reservoir properties here we present a conceptual model for sheeted drifts as hydrocarbon reservoirs in the subsurface

the very first transformation of the mediterranean outflow in the strait of gibraltar 1 time series collected in the camarinal and espartel sills the two main sills of the strait of gibraltar have been analyzed to assess the first transformation of the mediterranean outflow in espartel west of camarinal sill the outflow has been estimated from a 6 year long time series of acoustic doppler current profiler observations the near bottom water flowing out at espartel is around 0 1 units saltier and 0 1 c warmer than at camarinal which is explained by entrainment and mixing of atlantic water by the outflow inside the basin bounded by both sills the constancy of heat and salinity transport implies an atlantic water entrainment of 0 03 sv which is about 4 of the outflow observed at espartel 0 77 sv and a flow of 0 74 sv at camarinal 96 of the flow at espartel it is also shown that the high energy dissipation rate associated with internal tides is enough to sustain the entrainment and a thorough mixing of the entrained water

numerical simulation of the red sea outflow using hycom and comparison with redsox observations abstract the outflow of warm salty and dense water from the red sea into the western gulf of aden is numerically simulated using the hybrid coordinate ocean model hycom the pathways of the modeled overflow temperature salinity velocity profiles from stations and across sections and transport estimates are compared to those observed during the 2001 red sea outflow experiment as in nature the simulated outflow is funneled into two narrow channels along the seafloor the results from the three dimensional simulations show a favorable agreement with the observed temperature and salinity profiles along the channels the volume transport of the modeled overflow increases with the increasing distance from the southern exit of the bab el mandeb strait due to entrainment of ambient fluid such that the modeled transport shows a reasonable agreement with that estimated from the observations the initial propagation speed of the outflow is found to be smaller than the estimated interfacial wave speed the

vertical and lateral mixing processes deduced from the mediterranean water signature in the north atlantic the conservation equations of heat salt and mass are combined in such a way that a simple relation is found between the known volume flux of mediterranean water entering the north atlantic ocean and the effects of lateral and vertical mixing processes the method is a form of inverse method in which the only unknowns are the vertical and lateral diffusivities for each isohaline contour on each neutral density surface the authors develop one equation in two unknowns arguing that other terms that cannot be evaluated are small by considering several such isohaline contours the method becomes overdetermined for each density layer and results are found for both the vertical and lateral diffusivity that vary smoothly in the vertical direction giving some confidence in the method

lagrangian observations of meddy formation during a mediterranean undercurrent seeding experiment mediterranean eddies meddies play an important role in maintaining the temperature and salinity distributions in the north atlantic but relatively little is known about their early life histories including where how often and by what mechanism they form a major field program called a mediterranean undercurrent seeding experiment has been carried out to directly observe meddy formation and the spreading pathways of mediterranean water into the north atlantic between may 1993 and march 1994 49 rafos floats were deployed sequentially in the mediterranean undercurrent south of portugal and tracked acoustically for up to 11 months the float deployments were accompanied by high resolution xbt sections across the undercurrent nine meddy formation events were observed in the float trajectories six near cape st vincent at the southwestern corner of the iberian peninsula and three near the estremadura promontory along the western portuguese continental slope meddy formation thus occurs where the continental slope turns sharply to the right when facing in the downstream direction of the undercurrent after conditionally sampling the float dataset to identify floats that were well seeded in the undercurrent the authors have estimated a meddy formation rate of 15 20 meddies per year the timescale for meddy formation at cape st vincent was found to be 3 7 days shorter than previous estimates based on the volume of larger meddies meddies were observed to form most frequently when the speed of the mediterranean undercurrent was relatively fast the meddy formation process at cape st vincent resembles the conceptual model of e a d asaro whereby anticyclonically rotating eddies are formed by separation of a frictional boundary layer with negative relative vorticity at a sharp corner comparison of the relative vorticity in the anticyclonic shear zone of the undercurrent and that of the newly formed meddies shows that much of the anticyclonic relative vorticity in meddies can be accounted for by the horizontal shear in the undercurrent this confirms earlier work suggesting that the classical mechanism for the generation of submesoscale coherent vortices by collapse and geostrophic adjustment of a weakly stratified fluid injected into a stratified ocean may not be the principle mechanism at work in the formation of meddies at cape st vincent

a review of the physical oceanography of the mediterranean outflow abstract the physical oceanography of the mediterranean sea is reviewed with particular emphasis on the mediterranean outflow in the gulf of cadiz in this region the dense mediterranean water forms a high velocity bottom current that interacts strongly with the sea floor the major energy source for the plume comes from the release of potential energy as the plume descends the continental slope and the major energy sink is work against bottom stress which is as large as 4 pa where the plume begins to descend the continental slope in this region the current makes a nearly inertial turn that would otherwise appear to be steered by the underlying topography the mediterranean plume entrains the overlying north atlantic central water and thereby loses much of its density anomaly the mixed mediterranean water becomes neutrally buoyant in the lower portion of the north atlantic thermocline near cape st vincent there are then two preferred transport modes having somewhat different temperature and salinity whose distinct characteristics can be found far into the open north atlantic the temperature salinity and volume of the mediterranean water in the strait of gibraltar and in the gulf of cadiz appear to be roughly constant since modern measurements have been made the estimated westward transport of mediterranean water has gone down considerably as direct measurement techniques have been applied a recent estimate is that the westward transport of pure mediterranean water is only about a half a sv 1 sv 106 m3 s 1 the transport of mixed mediterranean water in the western gulf of cadiz is larger by about a factor of three or four because of the entrainment of north atlantic water

the upper oceanic response to overflows a mechanism for the azores current abstract the oceanic response to overflows is explored using a two layer isopycnal model overflows enter the open ocean as dense gravity currents that flow along and down the continental slope while descending the slope overflows typically double their volume transport by entraining upper oceanic water the upper oceanic layer must balance this loss of mass and the resulting convergent flow produces significant vortex stretching overflows thus represent an intense and localized mass and vorticity forcing for the upper ocean in this study simulations show that the upper ocean responds to the overflow induced forcing by establishing topographic plumes that are aligned more or less along isobaths and that have a transport that is typically a few times larger than that of the overflows for the topographic plume driven by the mediterranean overflow the occurrence of eddies near cape st vincent portugal allows the topographic plume to flow across isobaths the modeled topographic plume circu