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

low frequency variability of the exchanged flows through the strait of gibraltar during canigo time series of the exchanged flows through the strait of gibraltar at the eastern section have been estimated from current meter observations taken between october 1995 and may 1998 within the canary islands azores gibraltar observations canigo project the inflow exhibits a clear annual signal that peaks in late summer simultaneously with a deepening of the interface the cycle seems to be driven by the seasonal signal of the density contrast between the surface atlantic water that forms the inflow and the deep mediterranean water of the outflow the outflow and the depth of the interface have predominant semiannual signals and a smaller annual one whose phase agrees with that of the density contrast as well local wind stress and atmospheric pressure difference between the atlantic and the western mediterranean to less extent have clear semiannual signal so that the possibility that the semiannual cycle of the outflow and of the depth of the interface are forced by them was analyzed the composite froude number in this section is well below the critical value suggesting submaximal exchange therefore the conditions in the alboran basin influence the exchange and some evidence that the size and location of the western alboran gyre contribute to the observed signals both annual and semiannual is provided r 2002 elsevier science ltd all rights reserved

exchange through the bab el mandab during the last 10 years there have been a number of important developments in the understanding of the exchange flow in the bab el mandab new and improved estimates of the fluxes of mass heat and salt through the strait have been made directly from oceanographic measurements and indirectly from air sea flux data hydraulic theory has been applied to explain the seasonal variations in the exchange flow and in particular the three layer summer circulation the effects of wind stress friction and seasonal sea level variability on hydraulic control are addressed in this paper analyses of oceanographic data have failed to provide direct evidence of hydraulic control but they have highlighted the importance of tidal scale variability and differences between real continuously stratified fluids and idealised layer flows often used in hydraulic theory other studies have investigated the coupling between the flow in the strait and the circulation within the red sea

tides in the strait of gibraltar the strait of gibraltar is where the transition occurs between two distinct tidal regimes the north atlantic where tidal ranges are in excess of 2 m and the western mediterranean where tidal ranges are less than 1 m within the strait the tide is principally semidiurnal observations indicate that on average 96 of the bottom pressure and 74 of the current variability are contained in the semidiurnal band 2 cpd the structure of the local cotidal chart of the m2 tidal constituent is complicated but can be explained in terms of the along and across strait momentum balances along the strait the pressure gradient is mainly balanced by the acceleration of the flow although friction can be of appreciable magnitude corresponding to a decay time scale of 3 16 hours across the strait the momentum balance appears mostly geostrophic but better observations would be required to explain residual terms available observations indicate that the m2 tide has no net energy flux through the strait at the sill the tidal transport in the upper layer exceeds that in the lower layer by nearly a factor of 2 at the eastern end of the strait between algeciras and ceuta the tidal transport is larger in the lower layer this apparent shift in the location of maximum tidal transport is explained in terms of the kinematics of the interface between atlantic and mediterranean waters a mean transport of 0 21 sv due to subinertial and tidal flows carries atlantic water through the strait compensated by an approximately equal return in the lower layer

upstream control of the frontal jet regulating plankton production in the alboran sea western mediterranean using a coupled physical biological model we document that a 30 km wide meandering jet constitutes a major source of biological enrichment in the alboran sea western mediterranean even in the absence of wind forcing and tidal dynamics the level of enrichment is shown to vary markedly during the year depending on the upstream characteristics of the jet as it exits from the gibraltar strait when its intensity is sufficiently low and characterized by weaker cross frontal density gradients during winter spring the jet is weakly nonlinear and may not fulfill the necessary conditions for frontogenesis it then remains weakly productive in the case of stronger jet intensity 1 1 sv accompanied by stronger cross frontal density and velocity gradients within the alboran sea during summer autumn the frontal jet becomes strongly nonlinear and ageostrophic with large cross frontal vorticity changes on the order of planetary vorticity under these conditions upward vertical velocities in the range 10 50 m d 1 supply nutrients into the euphotic layer more effectively and support high level frontogenesis induced phytoplankton production on the anticyclonic side of the main jet axis the strong eddy pumping mechanism also provides a comparable level of plankton production within strongly nonlinear elongated cyclonic eddies along the outer periphery of the frontal jet the plankton biomass is advected partially by the jet along its trajectory and dispersed within the basin by mesoscale eddies and meanders

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

short period sea level oscillations at strait of gibraltar observations versus model results abstract tide gauge records from different ports of the strait of gibraltar area show events of short period oscillations minutes to tens of minutes that persist for several days although its charactestic duration is of the order of a day these events are observed throughout the year although when characterized by variables that account for their amplitude and duration simultaneously they are biased toward summer months the frequencies of these oscillations which accumulate energy within bands centered at 7 5 12 19 25 min 1 are characteristic of each port with tarifa showing a more selective tuning than ceuta or algeciras the numerical model developed to investigate these oscillations confirms that they correspond to harbor resonance excited at the mouth of the port by oscillations in the strait

the effects of nonrectangular cross section friction and barotropic fluctuations on the exchange through the strait of gibraltar abstract the inviscid two layer hydraulic model of farmer and armi has two types of solution in the eastern end of the strait of gibraltar for flow that is critical at camarinal sill the solution corresponding to maximal exchange has a fast supercritical flow with a shallow interface whereas the solutions corresponding to submaximal exchange show a much slower subcritical flow with a rather deep interface we extend their model to include physically important effects such as nonrectangular cross section friction and barotropic fluctuations allowing for realistic cross sections reduces the exchange and raises the interface everywhere along the strait realistic interfacial friction has little influence on the exchange but lateral friction at the sloping sides of the cross sections has a significant effect on the flow and brings the two solutions supercritical and subcritical closer together the effect of the earth s rotation is also summarized but dealt with in more detail in a companion paper by bor

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

meteorologically forced subinertial flows through the strait of gibraltar the observed transport due to subinertial flows with periods ranging from days to a few months through the strait of gibraltar reaches values up to 106 m3 s 1 and is well correlated with atmospheric pressure fluctuations over the mediterranean sea this transport is barotropic and accounts for 84 of the variance observed at these frequencies a second mode accounts for 12 of the variance and is characterized by a node zero amplitude located at the mean depth of the interface between atlantic and mediterranean waters this baroclinic mode is modulated by the spring neap tidal cycle corresponding to an increased exchange of waters between atlantic and mediterranean at neap tides a simple model of the mediterranean which includes two basins and two straits indicates that the system has two resonant frequencies at periods of 1 2 and 5 6 days the 1 2 day resonance corresponds to the eastern and western basins oscillating through the strait of sicily while that at 5 6 days is the resonance of the mediterranean sea with the north atlantic ocean a good approximation to the observed flows is obtained when this model is forced with the most energetic mode of the atmospheric pressure over the eastern and the western mediterranean and a friction term is included to limit the flow through the strait of gibraltar restricting the flow through the strait of sicily does not improve the agreement between the model and the observations for the flows at gibraltar

contrasting sea surface responses between the western mediterranean sea and eastern subtropical latitudes of the north atlantic during abrupt climatic events of mis 3 abstract dinoflagellate cyst dinocyst analysis was conducted on two cores from the sw iberian margin and central alboran sea from which high quality records of marine isotope stage 3 have been previously derived our aim in this study is to compare the dinocyst signature between 50 and 25 ka bp with existing datasets of foraminiferal and geochemical proxies related to hydrological parameters quantitative reconstructions of sea surface temperatures ssts and salinities sss based on dinocysts are performed for the first time in this area the results are compared to ssts derived from planktonic foraminifera and alkenone measurements and to sss calculated from planktonic 18 o and foraminiferal sst significant oscillations related to dansgaard oeschger cycles are recorded in both cores dinocyst derived hydrological parameters exhibit synchronous fluctuations and similar values to those derived from the other methods in particular when considering quantitative reconstructions for february based on foraminifera and dinocysts our study shows that the influence of subpolar waters was felt during each greenland stadial gs off portugal and that the amplification of the heinrich stadial cooling in the alboran sea was related to the penetration of subpolar waters through the strait of gibraltar during greenland interstadials gi we provide evidence for the occurrence of warm and nutrient rich sea surface waters in the alboran sea probably due to gyre induced upwelling finally the difference between august and february dinocyst sst estimates suggests higher seasonal contrasts during gs compared to gi at the two core sites additionally precession appears to have an imprint on dinocyst derived long term seasonality record however this observation needs to be confirmed by longer records

geological constraints on the eruption of the jwaneng centre kimberlite pipe botswana abstract geological mapping has allowed constraints to be placed on the eruption mechanisms involved in the formation of the late permian early triassic jwaneng centre kimberlite pipe botswana twelve lithofacies and three lithofacies associations lfa 1 3 are recognised lfa 1 comprises massive to bedded volcaniclastic kimberlite and marginal shale breccias and outcrops over 65 of the surface area of the pipe it is characterised by a lithic population dominated by transvaal shale clasts lfa 1 grades into lfa 2 which comprises massive and bedded volcaniclastic kimberlite and volcaniclastic breccias and outcrops over 19 of the surface area of the pipe the lithic population of lfa 2 is dominated by contorted and fluidal outlined karoo age mudstones and siltstones lfa 3 comprises a wedge shaped unit in the north of the pipe and consists of a series of allochthonous megablocks of sedimentary and volcaniclastic strata the juvenile clast type and matrix mineral assemblages of the volcaniclastic deposits in the centre pipe differ from those in many other southern african kimberlite pipes various emplacement models for kimberlite pipes are discussed and evaluated in the light of the new geological data both a maar diatreme model and an explosive volatile driven eruption model could account for much of the geology of the centre pipe and distinguishing between the two models based on deposits alone is difficult there is strong circumstantial evidence for ambient conditions favourable to phreatomagmatism at the time of the eruption and the influence of external water may explain the differences between the jwaneng centre pipe and the class 1 kimberlites common across southern africa in terms of both the juvenile clasts and of the inter clast cement however low abundances of some types of lithic inclusions derived from major country rock units pose an unresolved problem for a classic maar diatreme model of pipe formation

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

evaluation of regional ocean circulation models for the mediterranean sea at the strait of gibraltar volume transport and thermohaline properties of the outflow a set of simulations from different configurations of the nemomed8 nemomed12 and nemomed36 ocean regional circulation models for the mediterranean sea has been studied in order to assess the accuracy of their representation of the exchange through the strait of gibraltar the model volume transport and thermohaline properties of the mediterranean outflow have been compared with observational data collected at espartel sill the westernmost sill of the strait by a permanent station moored since october 2004 in the frame of the ingres projects results show that in terms of volume transport nemomed8 simulations perform a better representation of the exchange while nemomed12 36 underestimate both the mean inflow and outflow the reason for this underestimation is a too low velocity of the flow which could be consequence of an enhanced roughness effect due the flow bathymetry interaction an important improvement in the representation of the exchange seasonality is achieved by the simulations including sea surface height variability of the atlantic area of the domain the results for the themohaline characteristics of the mediterranean outflow are better for nemomed12 and nemomed36 as a consequence of their better representation of the local dynamical processes that leads to a more realistic composition of the mediterranean waters comprising the flow

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

calcareous plankton response to orbital and millennial scale climate changes across the middle pleistocene in the western mediterranean abstract the paleoenvironmental conditions through mis 15 9 at the mediterranean ocean drilling program odp site 975 were interpreted by high resolution study of calcareous plankton assemblages compared with available 18o and 13c records and high resolution paleoclimate proxies from the atlantic ocean sea surface temperatures ssts have been estimated from planktonic foraminiferal assemblages using the artificial neural networks method calcareous plankton varied dominantly on a glacial interglacial scale as testified by the sst record foraminiferal diversity total coccolith abundance and changes in warm water calcareous nannofossil taxa a general increase in foraminiferal diversity and of total coccolith abundance is observed during interglacials warmest ssts are reached during mis 11 while mis 12 and mis 10 represent the coldest intervals of the studied record during mis 12 one of the most extreme glacials of the last million years occurrence of globorotalia inflata and of neogloboquadrinids indicates a shoaling of the interface between atlantic inflowing and mediterranean outflowing waters among calcareous nannofossils the distribution of gephyrocapsa margereli gephyrocapsa muellerae 4 m also supports a reduced atlantic mediterranean exchange during mis 12 superimposed on glacial interglacial variability six short term coolings are recognized during mis 12 and 10 which appear comparable in their distribution and amplitude to the heinrich type events documented in the atlantic ocean in the same interval during these h type events neogloboquadrina pachyderma s and g margereli g muellerae 4 m increase as a response to the enhanced inflow of cold atlantic water into the mediterranean via the strait of gibraltar mediterranean surface water hydrography appears to have been most severely affected at termination v during the h type event ht4 possibly as a response to a large volume of atlantic meltwater inflow via the strait of gibraltar and or to freshwater terrigenous input deriving from local mountain glaciers three additional sst coolings are recorded through mis 14 16 but these are not well correlated with heinrich type events documented in the atlantic ocean in the same interval during these cooling episodes only the subpolar turborotalita quinqueloba increases these results highlight the sensitive response of the mediterranean basin to millennial scale climate variations related to northern hemisphere ice sheet instability and support the hypothesis that the tight connection between high latitude climate dynamics and mediterranean sea surface water features can be traced through the middle pleistocene

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

tide at the eastern section of the strait of gibraltar from october 1995 to april 1996 three mooring lines were deployed at the eastern entrance of the strait of gibraltar the spatial coverage of the mooring array allows for a good description of the tides they exhibit a dominant semidiurnal nature and a noticeable baroclinic structure that matches the one of the mean exchange tidal currents in the upper layer are irregular and usually too weak to reverse the mean upper layer flow that keeps on flowing east lower layer flow reverses with semidiurnal periodicity because of the smallness of the mean flow and the appreciable amplitude of the regular semidiurnal oscillation of tidal currents in this layer tidal transports can be satisfactorily compared with previous estimates of bryden et al 1994 if we allow for strong internal divergences associated with the internal tide no significant eddy flux of water transport tidal rectification is observed at the eastern section contrary to the almost 50 of the total layer transport found by bryden et al 1994 in camarinal sill section time dependent hydraulic theory provides a good scenario for interpreting these two independent sets of observations despite the fact that the composite froude number does not reach the critical values predicted in the hydraulic models most of the time

exchange through the strait of gibraltar to measure the exchange between the atlantic and mediterranean through the strait of gibraltar an array of current meter moorings was deployed for a year in the strait during 1985 1986 a novel aspect of these measurements is the inclusion of conductivity as well as temperature and pressure sensors on each current meter so that the salinity of the flows could be monitored continuously these salinity measurements determine the water mass characteristics of the flows crossing the sill they allow definition of the 37 psu isohaline as the interface between inflowing fresher atlantic water and outflowing saltier mediterranean water and they enable time series to be developed for the depth of this interface for the upper layer inflow and for the lower layer outflow from these measurements the time averaged outflow of mediterranean water is estimated to be 0 68sv 1sv 1 106m3s 1 and the outflow salinity transport defined to be the outflow times the salinity excess above a basic atlantic water salinity of 36 1 psu is estimated to be 1 50 103m3s 1 1sv 1psu 1 103m3s 1 equivalent to a net evaporation over the mediterranean basin of 52cm y 1 extrapolated measurements of the inflow from current meters generally deployed below 100m depth yield an estimate for the time averaged inflow of 0 93sv which is believed to be unrealistically high in view of the better measured outflow and net evaporation thus a more realistic estimate of the inflow is 0 72sv equal to the sum of the outflow and net evaporation as required by the mass budget for the mediterranean sea such estimates of the exchange are smaller by almost a factor of 2 than previous values for the exchange by lacombe and richez 1982 the exchange across the gibraltar sill is found to be due in nearly equal parts to the mean currents and to the tidal fluctuations the mean currents are smaller than had been expected reaching a peak value of only about 60 cm s 1 in the deep outflow over the sill the tidal exchange is due to a strong correlation over the tidal period between the depth of the interface and the strength of the inflowing currents for the m2 tide at the sill the amplitude of the interface depth is 51 m and the amplitude of the tidal currents is 1 2m s 1 furthermore the inflow and interface depth have similar phases as a consequence the upper layer is deep on the inflowing tide so that a large slug of atlantic water crosses the sill into the mediterranean on the outflowing tide the interface is shallow so that a large slug of mediterranean water crosses the sill into the atlantic similar processes occur for the s2 o1 and k1 tides though the amplitude are smaller in this manner tidal oscillations lead to a time averaged exchange of water masses across the gibraltar sill the inflow and outflow defined to be the instantaneous transports above and below the 37psu isohaline interface exhibit m2 tidal amplitudes of 2 3 sv and 1 3sv respectively thus the tides are large enough to reverse the mean upper layer inflow and lower layer outflow daily averaged inflow and outflow transports exhibit low frequency fluctuations with standard deviations of 0 37sv and 0 22sv respectively such low frequency fluctuations have been shown previously to be associated with barotropic flows through the strait of gibraltar compensating for sea level variations over the mediterranean due to atmospheric pressure fluctuations candela winant and bryden 1989 finally from these measurements there appear to be little fortnightly or annual period fluctuations in the exchange through the strait of gibraltar

mediterranean sea level and barotropic flow through the strait of gibraltar for the period 1958 2001 and reconstructed since 1659 sea level values from a two dimensional model of the mediterranean sea forced by atmospheric pressure and wind are used to estimate the barotropic flow through the strait of gibraltar for the period 1958 2001 the mediterranean mean sea level derived from the model ranges between 20 cm with a standard deviation of 5 5 cm and is correlated to the north atlantic oscillation nao index thus nao historical data and reconstructions are used to derive the mediterranean sea level variability from 1659 until 2001 the accuracy of the reconstruction is estimated in 2 7 cm for monthly mean values 0 41 cm for annual mean values and 0 22 cm for decadal mean values 0 48 cm for decadal winter mean sea level the barotropic flow through the strait is computed from the model output as the time derivative of the total volume of the basin during the period 1958 2001 the estimated daily flow ranges between 2 7 sv with a standard deviation of 0 56 sv the dominant periodicities are in between 1 and 2 weeks at these scales the model successfully reproduces previously published flow estimates based on current meter observations which confirms that atmospheric pressure and wind dominate the intraseasonal variability of the flow for the annual cycle the variability of the atmospherically induced flow is similar to the variability of the flow induced by the evaporation precipitation e p budget 0 025 sv though absolute values of the first are about a third of the latter at longer timescales the atmospheric contribution is much smaller than the e p induced flow

fluid evolution in the baia mare epithermal gold polymetallic district inner carpathians romania the baia mare district romania represents a complex segment of the neogene quaternary subduction related volcanic chain of the carpathians in this province the calc alkaline volcanism and associated mineralization are closely related to a major strike slip fault and an underlying pluton the ore deposits of the district have many features typical of low sulfidation or adularia sericite epithermal deposits the combination of fluid inclusion microthermometry raman spectroscopy bulk crush leach analysis laser ablation optical emission spectrometry la oes of individual fluid inclusions and stable isotope data has been used to characterize the ore forming solutions involved with gold polymetallic mineralization in three of the largest deposits ore fluids at baia sprie cavnic and sasar deposits had temperatures of 320 to 150 c and salinities in the range 0 21 wt nacl equiv during phreatomagmatic activity fracturing and periods of vein dilation the pressure fluctuations may have caused boiling the hydrothermal fluids were na k li ca chloride solutions with lesser amounts of so4 and f the na k ratios and the stable isotope compositions are consistent with equilibration of the fluids with country rocks at progressively lower temperatures the halogen ratios br cl 103 in the range 0 13 1 21 together with sulfur isotopic systematics 34s 0 3 5 2 per mil are consistent with a dominantly magmatic origin of the solutes and probably of the ore fluids themselves

surface circulation in the alboran sea western mediterranean inferred from remotely sensed data 1 in this study for the first time at regional scale the combined use of remote sensing data altimetry and sea surface temperature records provides a description of the persistent recurrent and transient circulation regimes of the alboran sea circulation the analysis of 936 altimeter derived weekly absolute dynamic topography adt and surface geostrophic current maps for 1993 2010 reveals the presence of a dominant annual signal and of two interannual modes of variability the winter spring phase is characterized by two stable gyral scale features the well known western anticyclonic gyre within the western area and the central cyclonic gyre a new structure not identified in former studies occupying the central and eastern parts of the alboran sea a double anticyclonic gyre regime constitutes the stable circulation system of the summer autumn period when the eastern anticyclonic gyre is formed within the eastern alboran basin in this case the central cyclonic gyre is narrower and located closer to the western anticyclonic gyre they represent two stable states of the system robust at the decadal time scale whereas transient changes reflect perturbations on these stable states and are mainly observed at an interannual scale the circulation variability and the gyral features development may be dynamically linked to the corresponding changes of the gibraltar transport rates citation renault l t oguz a pascual g vizoso and j tintore 2012 surface circulation in the alboran sea western mediterranean inferred from remotely sensed data j geophys res 117 c08009 doi 10 1029 2011jc007659

maximal two layer exchange over a sill and through the combination of a sill and contraction with barotropic flow the analysis of two layer exchange flow through contractions with a barotropic component treated by armi farmer 1986 is extended to include exchange flows over sills and through a combination of a sill and contraction it is shown that exchange over a sill is fundamentally different from exchange through a contraction control at the sill crest acts primarily through the deeper layer into which the sill projects and only indirectly controls the surface layer this asymmetry in the control results in asymmetrical flows the interface depth above the crest is not one half the total depth as assumed in other studies by analogy with flow through contractions but is somewhat deeper the maximal exchange rate is less than for flow through a contraction of equal depth when both a sill and a contraction are present the contraction influences control at the sill crest only if it lies between the sill and the source of denser water the response to barotropic flow is also asymmetrical the transition to single layer flow occurs at much lower speeds for a barotropic component in one direction than the other results of the analysis are applied to exchange flow through the strait of gibraltar which includes both a sill and a contraction it is shown that maximal exchange conditions apply throughout part of the tidal cycle and observations illustrate several of the analytical predictions for barotropic flows including the formation of fronts single layer flow submaximal exchange and reverse flow

mean sea level and surface circulation variability of the mediterranean sea from 2 years of topex poseidon altimetry we describe the circulation and mean sea level variations of the mediterranean sea from 2 years of topex poseidon altimetric data it is first shown that the response of the mediterranean sea to atmospheric pressure forcing is close to an inverse barometer except at high frequencies which means that the adjustment is accompanied by a flow through the straits of sicily and gibraltar we then use topex poseidon to study the mean sea level variations representing steric effects and integrated large scale changes of the mass of the mediterranean sea we observe an annual cycle with a fast drop during winter steric effects account for about half of the observed variations the remaining signal is believed to be driven by evaporation minus precipitation e p forcing and internal hydraulic control in the straits of gibraltar using suboptimal space time objective analysis the classic components of the mediterranean surface circulation are recovered despite low signal to noise ratio the rms of sea level variability is less than 10 cm the variable mediterranean circulation is seen as a complex combination of mesoscale and large scale variations the surface circulation is more complex in the eastern basin than in the western basin in the east it is composed of subbasin scale gyres such as the so called mersa matruh and shikmona gyres which do not have an obvious recurrence period we also observe an intensification of the large scale cyclonic winter circulation in the western and in the ionian basins several mesoscale structures such as the alboran gyres and the ierepetra gyre show a clear seasonal cycle with a maximum in summer the good qualitative and quantitative agreement of the results with previous data from the mediterranean illustrates the improved accurary of topex poseidon over its predecessors

transport estimates in the strait of gibraltar with a tidal inverse model to estimate the volume transport through the strait of gibraltar and to study the spatial structure of the time variable flow a varying number of current meter moorings were maintained at the eastern entrance of the strait between october 1994 and april 1998 and was complemented with intensive shipboard measurements during the european union project canary island azores gibraltar experiment canigo a tidal inverse model is used to merge these data sets in order to investigate the flow at the eastern entrance of the strait the two dimensional structure of the tidal flow was described by simple analytical functions harmonics with the seven most important tidal frequencies were used as temporal functions with this model the tidal currents can be predicted for any time and location at the eastern entrance of the strait and more than 92 of the variance of the lower layer flow is explained it was used to remove the tidal currents from the individual measurements and to calculate the mean flow through the strait from the residuals combined with a similar inverse model for determining the depth of the interface between mediterranean and atlantic water the volume transport was estimated to be 0 81 0 07 sv for the upper layer and 0 76 0 07 sv for the lower layer the correlation of the tidal currents and the fluctuations of the interface accounts for 7 of the transport at the eastern entrance

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

paleoceanography of the atlantic mediterranean exchange overview and first quantitative assessment of climatic forcing 1 the mediterranean sea provides a major route for heat and freshwater loss from the north atlantic and thus is an important cause of the high density of atlantic waters in addition to the traditional view that loss of fresh water via the mediterranean enhances the general salinity of the north atlantic and the interior of the eastern north atlantic in particular it should be noted that mediterranean water outflowing at gibraltar is in fact cooler than compensating inflowing water the consequence is that the mediterranean is also a region of heat loss from the atlantic and contributes to its large scale cooling uniquely this system can be understood physically via the constraints placed on it by a single hydraulic structure the gibraltar exchange here we review the existing knowledge about the physical structure of the gibraltar exchange today and the evidential basis for arguments that it has been different in the past using a series of quantitative experiments we then test prevailing concepts regarding the potential causes of these past changes we find that 1 changes in the vertical position of the plume of mediterranean water in the atlantic are controlled by the vertical density structure of the atlantic 2 a prominent early holocene contourite gap within the gulf of cadiz is a response to reduced buoyancy loss in the eastern mediterranean during the time of sapropel 1 deposition 3 changes in buoyancy loss from the mediterranean during mis3 caused changes in the bottom velocity field in the gulf of cadiz but we note that the likely cause is reduced freshwater loss and not enhanced heat loss and 4 strong exchange at gibraltar during atlantic freshening phases implies that the gibraltar exchange provides a strong negative feedback to reduced atlantic meridional overturning given the very counterintuitive way in which the strait of gibraltar system behaves we recommend that without quantitative supporting work qualitative interpretations of how the system has responded to past external forcing are unlikely to be robust

modulation of frontogenetic plankton production along a meandering jet by zonal wind forcing an application to the alboran sea we present a coupled physical biological modeling study to elucidate the changes in ageostrophic frontal dynamics and the frontogenetic plankton production characteristics of a meandering jet under the impacts of successive westerly easterly wind events combined with seasonal variations in the upstream transport and buoyancy flux characteristics of the jet using a case study for the alboran sea western mediterranean their nonlinear coupling is shown to result in different forms of physical and biological characteristics of the background jet structure that follows a meandering path around two anticyclonic gyres in the western and eastern basins and a cyclonic eddy in between the westerly downfront wind events broaden the jet and result in stronger cross frontal density contrast and intensify ageostrophic cross frontal secondary circulation thus they improve the frontogenetic plankton production with respect to the no wind case they also support higher production along the northern coast in response to wind induced coastal upwelling and spreading of resulting nutrient rich productive water by mesoscale stirring these features weaken gradually as the jet transport reduces in contrast stronger and longer lasting easterlies during the reduced jet transport phase weaken the currents and frontal density structure change the circular western alboran gyre to an elongated form and shift the main axis of the jet towards the southern basin then frontogenesis fails to contribute to phytoplankton production that becomes limited to the eddy pumping within cyclones apart from the frontogenetic production eddy pumping mesoscale stirring and diapycnal mixing of nutrients support intermittent and localized phytoplankton patches over the basin

variations in the structure of the anticyclonic gyres found in the alboran sea historical satellite aircraft and in situ data have shown that two anticyclonic gyres the western and eastern alboran gyres are major ocean features of the alboran sea an examination of several years of satellite imagery indicates that large variations in the surface expression of these two gyres occur and that on occasion one or the other gyre disappears the disappearance of both gyres at the same time was not seen the initial disappearance of either gyre occurs on a time scale of a week to 2 weeks whereas the return may take from 3 weeks to 2 months various forcing mechanisms i e winds mass flux inflow through the straits of gibraltar and sicily and or density have been used in numerical ocean circulation models to study the dynamics of the western mediterranean sea various model results show relationships similar to those shown by the satellite imagery however no single forcing mechanism has been positively identified as the source of the disappearances and the events may be a result of a combination of forcing mechanisms

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

detrital input productivity fluctuations and water mass circulation in the westernmost mediterranean sea since the last glacial maximum 1 by presenting sea surface temperatures planktonic oxygen isotope profiles and bulk geochemical composition of core sediments we offer a multiparameter reconstruction of western mediterranean oceanography from the last glacial maximum until the middle holocene 20 000 5000 cal years b p sediments from ocean drilling program site 975 in the algero balearic basin have been compared with three alboran basin cores ttr 300g ttr 302g and ttr 304g all of them investigated at high resolution this multiproxy approach has allowed two different modes of circulation to be recognized 1 during the lgm and from 8 0 cal ka b p onward no surface gradient in 18og bulloides is found associated with low productivity in close analogy to modern conditions 2 during the bolling allerod and early holocene significant surface isotopic gradients are found with periods probably indicating an unstable water column associated with enhanced productivity and low bottom oxygen conditions the close synchrony between the occurrence of the surface isotopic offset and organic rich layer formation implicates that the origin of these features is linked probably via shoaling of the regional thermohaline circulation paleo ssts derived from planktonic foraminifer assemblages indicate abrupt changes in surface conditions during the analyzed time interval fluctuations in marine productivity based on ba and total organic carbon are related to water column stability and atmospheric conditions a sharp warming and 18og bulloides excursion at the end of the younger dryas is probably linked to glacial meltwater influence the riverine input has been reconstructed using the mg al ratio and mg al peaks during arid periods greenland stadial 2a and younger dryas related to bypass margin processes