a numerical study of the mediterranean sea circulation abstract a primitive equation ocean model that makes use of a curvilinear orthogonal grid and a sigma coordinate system was used to simulate the mediterranean sea the model was forced with monthly climatological values of wind stress heat and salinity flux with the help of the curvilinear horizontal grid the larger scales of the entire mediterranean sea are modeled and the topography around the narrow and shallow straits of gibraltar is also reasonably well represented the resulting model inflow and outflow seems to mimic the real mediterranean often in considerable detail levantine intermediate water is formed in the levantine basin and exits through the strait of sicily and the strait of gibraltar deep water formation processes are clearly represented by the model the model results indicate that in the western mediterranean the wind stress is very important in establishing the summer northward shift of the atlantic inflow lateral boundary runoff surface salinity and heat fluxes are necessar

a gulf stream model and an altimetry assimilation scheme a continuous data assimilation scheme and a multilayer primitive equation numerical model are described the model is an eddy resolving coastal ocean model that has been extended to include the gulf stream region it has complete thermohaline dynamics a bottom following sigma vertical coordinate system and a coastal following curvilinear orthogonal horizontal coordinate system calculated model fields are used to provide a model climatology and correlations between subsurface temperature and salinity anomalies and surface elevation anomalies an optimal interpolation method the surface to subsurface correlations and estimated model and data errors are the basis of the assimilation technique altimetry anomaly data extracted from the model calculations according to the geosat orbital schedule are used to test the assimilation scheme and to provide nowcasts and forecasts sensitivity studies are performed to test the effects of various parameters of the scheme it is found that the scheme is less efficient in the shallow continental shelf area than in the deeper regions of the model the results show significant nowcast skill with area averaged rms error for surface elevation and subsurface properties of about 40 50 of the corresponding error of the unassimilated case good forecast skill better than persistence is demonstrated for 10 20 days there is little skill after 30 40 days increasing the density of the satellite altimetry data especially by decreasing the separation distance between tracks should decrease the nowcast rms error to about 15 and improve the forecast

hydraulic adjustments of the bosphorus exchange flow 1 a three dimensional model elucidates connection between observed internal hydraulic characteristics of the bosphorus flow and channel configuration a typical two layer quasi steady exchange flow system is shown to be hydraulically adjusted within the strait by a series of morphological features three successive hydraulic controls occur within the southern 10 km zone first near the southern exit due to convex bending of the channel then at the southern sill and at the constriction finally the exchange flow system experiences another hydraulic control at the northern sill near the black sea entrance of the strait the upper and lower layer flows exiting from the strait at both ends with currents of 1 0 m s 1 layer depths of 10 m and g 0 1 ms 2 thus impose maximal exchange conditions

consistent relationship between global climate and surface nitrate utilization in the western subarctic pacific throughout the last 500 ka 1 the open subarctic pacific is at present a high nitrate low chlorophyll hnlc region where nitrate is perennially abundant at the surface theoretically the hnlc status of this region is subject to modification by ocean circulation and or micronutrient supply with implications for the effectiveness of the biological pump and hence carbon sequestration in the ocean interior records of biogenic detritus in sediments from throughout the subarctic pacific indicate that export production was generally lower during glacial maxima while nitrogen isotope measurements from the bering sea have shown that nitrate consumption there was more complete during the last glacial period than it is today here nitrogen isotopic analyses of bulk sediments 15nbulk from three deep water sites in the open subarctic pacific are evaluated in terms of regional nitrate isotopic composition and local relative nitrate utilization the eastern subarctic pacific 15nbulk record bears great similarity to 15nbulk records from the western margin of north america over the last glacial cycle suggesting that variability in the isotopic composition of subeuphotic zone nitrate the growth substrate is reasonably coherent throughout the northeast pacific and dominates at these sites however the two western subarctic pacific records which lie at the heart of the hnlc region display a different pattern implying that significant changes in local relative nitrate utilization overlie the regional background variability after a novel correction intended to remove the background signal associated with denitrification in the eastern tropical north pacific these nitrate utilization records are correlated with a benthic oxygen isotope stack reflecting global deep ocean temperature and ice volume r2 0 65 the correlation implies a strong link between global climate and subarctic pacific nitrate utilization with nearly complete nitrate consumption during glacial periods when export production was low

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

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

numerical modeling of the mean exchange through the strait of gibraltar 1 the three dimensional princeton ocean model is used to investigate the mean flow and the hydraulics regime in the strait of gibraltar the model makes use of a coast following curvilinear orthogonal grid that includes the gulf of cadiz and the alboran sea with very high resolution in the strait 500 m a lock exchange initial condition is used the western part of the model domain is filled with atlantic water whereas the eastern part is filled with mediterranean water a conservative nondiffusive and nondispersive numerical scheme for the horizontal tracers advection has been implemented to simulate the free flow adjustment for the lock exchange initial condition predicted velocities interface depth water and salinity transports are comparable with observed data model results describe circulation of the mediterranean outflow in detail and demonstrate the presence of a mixing layer between the atlantic and mediterranean water the hydraulic regime is analyzed calculating the composite froude number for three layers within the strait results indicate the presence of a hydraulic control at camarinal sill and in the northern part of tarifa narrows in order to understand if the strait of gibraltar is in the submaximal or maximal regime we have formulated a cross strait mean composite froude number this formulation allowed us to limit the values of the composite froude number in the range of 1 2 1 5 at camarinal sill and between 0 4 and 0 8 at tarifa narrows we have concluded that the mean exchange simulated by the model is in submaximal regime

seasonal variability of water transport through the straits of gibraltar sicily and corsica derived from a high resolution model of the mediterranean circulation abstract the variability of the water transport through three major straits of the mediterranean sea gibraltar sicily and corsica was investigated using a high resolution model this model of the mediterranean circulation was developed in the context of the mercator project the region of interest is the western mediterranean between the strait of gibraltar and the strait of sicily the major water masses and the winter convection in the gulf of lions were simulated the model reproduced the meso scale and large scale patterns of the circulation in very good agreement with recent observations the western and the eastern gyres of the alboran sea were observed but high interannual variability was noticed the algerian current splits into several branches at the longitude of the strait of sicily level forming the tyrrhenian branch and the atlantic ionian stream and the atlantic tunisian current in the eastern mediterranean the north current retroflexed north of the balearic islands and a dome structure was observed in the gulf of lions the cyclonic barotropic algerian gyre which was recently observed during the mater and elisa experiment was evidenced in the simulation from time series of 10 day mean transport the three straits presented a high variability at short time scales the transport was generally maximum in april for the strait of gibraltar in november for the strait of sicily and in january for the strait of corsica the amplitudes of the transport through the straits of gibraltar 0 11 sv and sicily 0 30 sv presented a weaker seasonal variability than that of the strait of corsica 0 70 sv the study of the relation between transport and wind forcing showed that the transport through the strait of gibraltar is dependent on local zonal wind over short time scales 70 which was not the case for the other straits less than 30 the maximum minimum of the transport occurred for an eastward westward wind stress in the strait an interannual event was noticed in november december 2001 which corresponded to a very low transport 0 3 sv which was characterised by a cyclonic circulation in the western alboran sea that circulation was also reproduced by the model for other periods than winter during the interannual simulation the transport through the strait of sicily is not influenced by local wind the wind stress curl of the northwestern mediterranean influenced the transport through the strait of corsica

three layer view of transports and hydraulics in the strait of gibraltar a three dimensional model study 1 the ability of a three dimensional sigma coordinate free surface model to reproduce the interfacial layer between the atlantic and mediterranean waters in the strait of gibraltar is verified the model uses a coastal following curvilinear orthogonal grid that includes the gulf of cadiz and the alboran sea with very high resolution in the strait less than 500 m it is forced by imposing the two major semidiurnal tidal components m2 and s2 along the atlantic and the mediterranean open boundaries the main experiment covers an entire spring neap cycle fortnight period results show that the model is able to reproduce a thick interfacial layer that carries a substantial fraction of the total transport the interfacial thickness is strongly modulated by tidal forcing that enhances the vertical exchanges between layers in order to take into account the thick interfacial layer a three layer approximation is used to study the hydraulics results show that the exchange regime is intermittently maximal due to cyclically controlled regions over camarinal sill and within tarifa narrows the analysis has been repeated in a two layer framework to evaluate the impact of the introduction of an interfacial layer on the calculation of hydraulics in the two layer approximation there is not any controlled region extending on the whole cross section so the exchange is always submaximal concluding the two layer approximation underestimates hydraulic controls in the strait respect to the three layer approach

glacial flour dust storms in the gulf of alaska hydrologic and meteorological controls and their importance as a source of bioavailable iron 1 iron is an essential micronutrient that limits primary productivity in much of the ocean including the gulf of alaska goa however the processes that transport iron to the ocean surface are poorly quantified we combine satellite and meteorological data to provide the first description of widespread dust transport from coastal alaska into the goa dust is frequently transported from glacially derived sediment at the mouths of several rivers the most prominent of which is the copper river these dust events occur most frequently in autumn when coastal river levels are low and riverbed sediments are exposed the dust plumes are transported several hundred kilometers beyond the continental shelf into iron limited waters we estimate the mass of dust transported from the copper river valley during one 2006 dust event to be between 25 80 ktons based on conservative estimates this equates to a soluble iron loading of 30 200 tons we suggest the soluble fe flux from dust originating in glaciofluvial sediment deposits from the entire goa coastline is two to three times larger and is comparable to the annual fe flux to goa surface waters from eddies of coastal origin given that glaciers are retreating in the coastal goa region and in other locations it is important to examine whether fluxes of dust are increasing from glacierized landscapes to the ocean and to assess the impact of associated fe on marine ecosystems

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

sea level variations in the western mediterranean studied by a numerical tidal model of the strait of gibraltar aspects of the sea level changes in the western mediterranean sea are investigated using a numerical tidal model of the strait of gibraltar as a prerequisite the performance of this model that is a two dimensional nonlinear two layer boundary fitted coordinate numerical model based on the hydrostatic approximation on an f plane is assessed in the simulation of mean and tidal circulation of the strait of gibraltar the model is forced by imposing mean interface and surface displacements as well as m2 s2 o1 and k1 tidal components along the atlantic and mediterranean model open boundaries model results are compared with observations and with results obtained from a tidal inverse model for the eastern entrance of the strait of gibraltar in general good agreement is found a sensitivity study performed by varying different model parameters shows that the model behaves reasonably well in the simulation of the averaged circulation the model is then used to investigate the climatological sensitivity of the simulated dynamics in the strait of gibraltar to changes in the density difference between atlantic and mediterranean waters for this purpose given a certain density difference between atlantic and mediterranean waters the authors iteratively searched for that sea level drop between the atlantic and the mediterranean that fulfills the mass balance of the mediterranean it is found that an increase of the density difference leads to an increase of the exchange flow and to an increase of the sea level drop between the two basins a trend in the sea level drop of o 1 cm yr21 such as the one observed between 1994 and 1997 is explained by the model as the result of a trend of o 10 24 yr21 in the relative density difference between the mediterranean and atlantic waters the observed north south asymmetry in this trend is also captured by the model and it is found to arise from changes in the along strait velocity results suggest that the dynamics within the strait of gibraltar cannot be neglected when sea level changes in the western mediterranean basin are investigated

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

a general method for determining upstream effects in stratified flow of finite depth over long two dimensional obstacles l ecoulement est suppose hydrostatique avec melange negligeable et ecoulement stratifie represente par un nombre arbitraire de couches discretes on calcule les modifications de l ecoulement resultant d accroissements successifs de hauteur de la topographie a partir de zero determination d une hauteur critique d obstacle perturbant l ecoulement

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

on the pressure gradient force over steep topography in sigma coordinate ocean models abstract the error in computing the pressure gradient force near steep topography using terms following coordinates is investigated in an ocean model using the family of vertical differencing schemes proposed by arakawa and suarez the truncation error is estimated by substituting known buoyancy profiles into the finite difference hydrostatic and pressure gradient terms the error due to hydrostatic inconsistency which is not simply a space truncation error is also documented the results show that the pressure gradient error is spread throughout the water column and it is sensitive to the vertical resolution and to the placement of the grid points relative to the vertical structure of the buoyancy field being modeled removing a reference state as suggested for the atmosphere by gary reduces the truncation error associated with the two lowest vertical modes by a factor of 2 to 3 as an example the error in computing the pressure gradient using a standard 10 level primitive equation model appl

230th normalization an essential tool for interpreting sedimentary fluxes during the late quaternary there is increasing evidence indicating that syndepositional redistribution of sediment on the seafloor by bottom currents is common and can significantly affect sediment mass accumulation rates notwithstanding its common incidence this process generally referred to as sediment focusing is often difficult to recognize if redistribution is near synchronous to deposition the stratigraphy of the sediment is not disturbed and sediment focusing can easily be overlooked ignoring it however can lead to serious misinterpretations of sedimentary fluxes particularly when past changes in export flux from the overlying water are inferred in many instances this problem can be resolved at least for sediments deposited during the late quaternary by normalizing to the flux of 230th scavenged from seawater which is nearly constant and equivalent to the known rate of production of 230th from the decay of dissolved 234u we review the principle advantages and limitations of this method notwithstanding its limitations it is clear that 230th normalization does provide a means of achieving more accurate interpretations of sedimentary fluxes and eliminates the risk of serious misinterpretations of sediment mass accumulation rates

numerical modeling of the semidiurnal tidal exchange through the strait of gibraltar 1 a three dimensional sigma coordinate free surface model is used to investigate the semidiurnal tidal exchange through the strait of gibraltar the model makes use of a coastal following curvilinear orthogonal grid that includes the gulf of cadiz and the alboran sea with very high resolution in the strait 500 m a lock exchange initial condition is used the western part of the model domain is filled with atlantic water whereas the eastern part is filled with mediterranean water the model is forced at the open boundaries through the specification of the semidiurnal m2 and s2 tidal surface elevation the model is run over a spring neap cycle fortnightly period and the results are compared with available observed data simulated cotidal maps of the m2 and s2 tidal elevation components are in quantitative and qualitative good agreement with observed data as well as with the simulated major and minor axis of tidal ellipse the model reproduces the generation and the subsequent propagation of internal bores both eastward and westward showing that they are always generated during the fortnightly period however the principal aim of this work is to quantify the effects of tidal forcing on mean quantities entrainment and transport of atlantic and mediterranean water along the strait model results reveal that the contribution of the semidiurnal tidal component m2 to the transport is relevant over camarinal sill whereas it is negligible at the eastern end of the strait model results indicate also that the effect of the semidiurnal tide is to increment the mean transport by about 30 both for the inflow and the outflow

intensification of the oxygen minimum zone in the northeast pacific off vancouver island during the last deglaciation ventilation and or export production 1 the oxygen minimum zone omz off vancouver island was more oxygen depleted relative to modern conditions during the allerod 13 5 to 12 6 calendar kyr and again from 11 to 10 kyr the timing of omz intensification is similar to that seen throughout the north pacific although the onset appears to have been delayed by 1500 years off vancouver island radiocarbon dating of coeval benthic and planktonic foraminifera shows that between 16 0 and 12 6 kyr the age contrast between surface and intermediate waters 920 m depth off vancouver island was similar to or slightly less than that today there is no evidence of an increased age difference i e decreased ventilation during the deglaciation particularly during the allerod however sedimentary marine organic carbon concentration and mass accumulation rate increased substantially in the allerod suggesting that increased organic matter export was the principal cause of late pleistocene omz intensification off vancouver island

modelling of seasonal exchange flows through the dardanelles strait abstract the dardanelles strait is a remarkable example of a long narrow shallow and strongly stratified strait with bidirectional exchange that is governed by both baroclinic and barotropic forcing with a wide spectrum of variability a three dimensional free surface primitive equation model is applied to study seasonal hydrodynamics variability in this strait the calculated vertical structure of temperature salinity and velocity fields agrees well with available survey data seasonal monthly values of the volume exchange at the aegean and marmara exits are estimated it is found that the seasonal exchange dynamics is governed by the turbulent friction and entrainment at the nara passage area the mean annual water transport in the upper layer is increased by 80 after the nara passage about 25 of water entering in the dardanelles bottom layer reaches the marmara sea in winter and 50 reaches it in summer the estimate of the dardanelles hydrodynamics according to hydraulic and viscous advective diffusive regime classification shows significant deviation from the two layer hydraulic asymptotic however according to three layer hydraulic theory the flow is found to be critical in the nara passage area

active mud volcanism in the west alboran basin geochemical evidence of hydrocarbon seepage abstract the west alboran basin was previously classified as a mud volcanic province consisting of two mud volcano mv fields that are inactive at the present day the northern spanish and the southern moroccan fields the discovery of the first active mud volcano carmen cruise ttr 17 in 2008 along with several pockmarks at the central part of the basin motivates more careful geological and geochemical analysis of previous data and comparison to new observations gas bubbling from the crater of carmen mv was observed and recorded using an underwater tv system and a large tv grab sample the gas mainly consisted of methane with less than 1 wetness however all sets of homologues up to pentane were detected in the mud breccia of carmen mv both molecular and stable carbon isotopic compositions and their distribution along the core length suggest a deep thermogenic source of hydrocarbons hcs composition of the pore water from carmen mv also points to a deep source of mud volcanic water the isotopic results indicate that the source of mud volcanic water is the dehydration of clay minerals in the thermal zone of the smectite to illite transformation our observations allow us to infer the presence of structure ii gas hydrates in mud breccia on the top of carmen mv high hc gas saturation in sediments in some pockmarks accompanied with live chemosynthetic fauna directly indicates the strong seepage activity of these structures for the first time authigenic carbonate crusts and chimneys with associated living chemosynthetic bivalves and tubeworms were sampled from a seep site in the west alboran sea authigenic carbonates consist of aragonite and calcite and are characterized by a light carbon isotopic signature up to 37 2 pdb which points to their methane derived origin

the role of the interface in exchange through the strait of gibraltar five cross strait hydrographic sections repeated several times during the gibraltar experiment in 1985 1986 are used to examine the structure of the interface layer between the inflowing atlantic waters and outflowing mediterranean waters in the strait of gibraltar the interface is 60 100 m thick with a strong vertical salinity gradient identified by fitting individual salinity profiles to a piecewise linear three layer model the interface is deeper thicker fresher and colder on the west end of the strait than in the narrows where there is a minimum in thickness and a maximum in salinity gradient farther east the interface thickens again and continues to get saltier warmer and shallower property variations in all three layers are also cast in terms of the three principal water types involved in the exchange the traditional knudsen model of exchange is extended to three layers assuming that the interface is a transport carrying third layer with uniform vertical shear as much as half of the inflowing or outflowing transport occurs in the interface layer transport converges in both the upper and lower layers implying over the length of the strait vertical exchange between layers that is comparable to about half the horizontal exchange the richness of structure and complexity of interaction between the interface and the upper and lower layers argues against the use of two layer models to characterize exchange through the strait of gibraltar

the effect of rotation on the surface inflow through the strait of gibraltar abstract gull s theory for rotating hydraulics is applied as a reduced gravity model to the surface inflow through the strait of gibraltar into the mediterranean as it is shown that rotation is mostly important east of tarifa narrows where only the upper layer is active details of the flow depend on the volume flux q and on the potential vorticity of the inflow we examine two extreme cases for this in both examples the model predicts that supercritical inflow separates from the north share about half way between tarifa and gibraltar so that at gibraltar the flow is separated the comparison of i conditions for criticality ii separation widths and iii interface depths and velocities in midstrait between this 2d model and the id models of farmer and armi and of bormans and garrett suggests that the use of a simple 1d model is appropriate for the strait of gibraltar for both subcritical and separated supercritical flows however for the latter the prediction of the point of separation and o

petrography and environmental controls on the formation of phanerozoic marine carbonate hardgrounds early marine seafloor lithification of carbonate sediments leads to the formation of hardgrounds and is known from rocks as old as the proterozoic hardground surfaces however are more commonly recorded in the phanerozoic sedimentological archive while ecological studies of hardground biota abound the environmental and physico chemical parameters leading to the development of seafloor lithification remain in many cases poorly understood and documented this paper reviews published evidence on the petrography mineralogy and geochemistry of phanerozoic carbonate hardgrounds within a process oriented context of their environmental controls hardgrounds typically develop in warm and shallow agitated tropical waters that are saturated with respect to caco3 but are also reported from hemi pelagic to bathyal realms and from cool water temperate settings a range of early marine cement types are documented from present day hardgrounds whereas preserved cement fabrics and related mineralogies are less diverse in early phanerozoic hardgrounds carbonate hardgrounds are widespread during calcite sea periods e g ordovician and cretaceous as opposed to some preservation bias ancient aragonite seas e g permian and triassic obviously the relation between seawater chemistry and hardground abundance and attributes is not an easy one here the concept of aragonite versus calcite seas serves as a first order template for the sake of a structured discussion whereas modern aragonite mode oceans document a significant diversity in spatial and bathymetric seawater properties this spatio temporal complexity is perhaps reflected in the scarce record of calcite sea hardgrounds from the devonian or paleogene rock record contrasted by the abundance in aragonite holocene and recent seas holocene hardgrounds allow for the direct assessment of rates of and reasons for early subaquatic lithification and in most cases escaped subsequent non marine diagenetic overprint conversely studies of ancient hardgrounds are often biased by early biological and mechanical erosion the degree of diagenetic overprint and tectonic to orogenic processes the formation distribution and physical properties of hardgrounds depend on the global climatic context greenhouse icehouse modes on sea level changes on ocean stratification on the spatial extent of epicontinental seas and carbonate depositional environments and on the spatially different mineralogies and rates of carbonate production the fabrics and mineralogies of early hardgrounds cement seem to substantially hinge on variations in atmospheric co2 thus the application of lessons from modern to ancient hardground case examples is not straightforward a holistic model explaining the full variability of controls on submarine hardground formation and their cement petrography throughout the phanerozoic is as yet lacking a more critical view on secular changes in hardground formation patterns is clearly needed future work should rely on the combination of sedimentological stratigraphic palaeoecological petrographic and geochemical approaches specific emphasis should be given to time intervals triassic carboniferous cambrian etc where the bulk of reported case studies is at best scarce

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

diagnostic and prognostic numerical circulation studies of the south atlantic bight some of the results from a series of diagnostic and prognostic numerical simulations of the circulation in the south atlantic bight sab are described the numerical model developed for the study is a three dimensional primitive equation time dependent coordinate model with an imbedded turbulent closure submodel which should yield realistic ekman surface and bottom layers an implicit numerical scheme in the vertical direction and a mode splitting technique in time are adopted for computational efficiency a significant portion of the paper is concerned with realistic specification of initial conditions for temperature and salinity surface forcing and lateral open boundary conditions the latter are determined by a simple diagnostic geostrophic and ekman dynamics model which provides dynamically consistent temperature salinity and velocity boundary conditions it appears from an exaination of the numerical simulations that the full model yields results that share many features in common with our general understanding of the circulation of the south atlantic bight the region includes shallow shelf waters as well as deeper water dominated by the gulf stream data for synoptic skill assessment however are not available

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

environmental change in the sea of okhotsk during the last 1 1 million years on the basis of two sedimentary records from the central sea of okhotsk we reconstruct the closely coupled glacial interglacial changes in terrigenous flux marine productivity and sea ice coverage over the past 1 1 myr the correspondance of our sedimentary records to the china loess grain size record china loess particle timescale chiloparts suggests that environmental changes in both the sea of okhotsk area and in se asia were closely related via the siberian atmospheric high pressure cell during full glacial times our records point to a strong siberian high causing northerly wind directions the extension of the sea ice cover and a reduced amur river discharge deglacial maxima of terrigenous flux were succeeded by or synchronous to high productivity events marine productivity was strengthened during glacial terminations because of an effective nutrient utilization at times of enhanced water column stratification and high nutrient supply from fluvial runoff and sea ice thawing during interglacials se monsoonal winds prevailed analogous to today s summer situation of a pronounced mongolian heat low and a strong hawaiian high strong freshwater discharge induced by high precipitation rates in the amur drainage area and a seasonally reduced and mobile sea ice cover favored marine productivity although being considerably lower than during the terminations and a lowered flux of ice rafted detritus

a sensitivity study of the general circulation of the western mediterranean sea part i the response to density forcing through the straits abstract in this paper the influence of the density gradients at the straits of gibraltar and sicily on the large scale circulation of the western mediterranean sea is investigated through a 3d numerical model the topography constraint is analyzed by comparing an experiment with a flat bottom with an experiment with a realistic bathymetry the results show the ability of the density gradients at the straits to force a cyclonic surface circulation in the whole basin particularly in the northern basin where the transport in the liguro provencal current is about 40 of the observed one these experiments point out the key role played by the strait of sicily and its topography there the eastward surface flow separates into two branches one enters the eastern mediterranean sea while the other flows along the italian coasts to feed the cyclonic circulation of the northern basin in the alboran sea which is a priori the region where the dynamics is the most strongly induced by the transport through the st

inputs of glacially derived dissolved and colloidal iron to the coastal ocean and implications for primary productivity 1 glacial meltwaters draining shield bedrock under the greenland ice sheet gis contain 0 4 m total dissolved fe tdfe with an average flow weighted concentration of 53 nm the concentrations of 0 03 and 0 03 0 4 m fe vary over the ablation period with weighted means for each of these fractions being respectively 22 4 nm and 30 8 nm these concentrations are lower estimates as an adjacent larger glacier a more representative source of glacial meltwater had higher dissolved fe concentrations and reactions of meltwaters with proglacial sediments could also enhance dissolved fe concentrations this source of tdfe is additional to the reactive oxyhydr oxide phases identified by raiswell et al 2006 that are also introduced to adjacent polar seas from glaciers the fe concentrations in the shield bedrock underlying the gis are lower than those of other crustal rocks 4 0 cf 6 2 but we argue that these fe concentrations are not limiting on the total dissolved fe concentrations we measure the biogeochemical weathering processes operating on the subglacial debris and suspended sediment in our catchment are likely to be similar to those in other glaciated catchments therefore the meltwater fe concentrations reported here can be used to give a first estimate of global fluxes of meltwater dissolved fe to coastal polar waters a lower estimate of the global flux of tdfe from glacial meltwaters is 75 106 moles fe a this glacial meltwater input of fe to adjacent polar waters will be greatest around greenland where there are highest annual meltwater discharges however the greatest impact of this source of glacial meltwater fe is anticipated to be in antarctic high nutrient low chlorophyll hnlc waters where phytoplankton productivity is typically limited by availability of fe for antarctic waters the estimated meltwater fe tdfe input is about 10 of that suggested to come from sea ice melting but glacial inputs continue throughout the austral summer ablation period after sea ice melt is complete

gps studies of active deformation in the pyrenees summary the pyrenees mountain belt which separates the iberian peninsula from the rest of the european continent is part of the alpine himalayan orogenic belt formed as a result of a collision between the african and eurasian plates although the instrumental seismicity in the pyrenees is moderate in the past centuries a number of destructive earthquakes have occurred which could indicate continuing tectonic activity of the area we analyse gps observations spanning 3 5 yr from 35 continuous stations in the pyrenees region and find significant on going extension perpendicular to the range at 2 5 0 5 nstrain yr 1 with the possibility of higher strain rates concentrated in the westernmost part of the range this finding is in agreement with the predominantly normal faulting focal mechanisms of earthquakes that occur in the area and suggests a recurrence time for magnitude 6 5 earthquakes of 2200 2500 yr

mediterranean outflow mixing and dynamics the mediterranean sea produces a salty dense outflow that is strongly modified by entrainment as it first begins to descend the continental slope in the eastern gulf of cadiz the current accelerates to 1 3 meters per second which raises the internal froude number above 1 and is intensely turbulent through its full thickness the outflow loses about half of its density anomaly and roughly doubles its volume transport as it entrains less saline north atlantic central water within 100 kilometers downstream the current is turned by the coriolis force until it flows nearly parallel to topography in a damped geostrophic balance the mixed mediterranean outflow continues westward slowly descending the continental slope until it becomes neutrally buoyant in the thermocline where it becomes an important water mass

observations of a mode 2 nonlinear internal wave on the northern heng chun ridge south of taiwan 1 a research cruise was carried out over the heng chun ridge during june 27 july 1 2010 near 21 34 n 120 54 e about 35 km south of taiwan the goal of the cruise was to determine if the location is an active generation site for internal tides and high frequency nonlinear internal waves nliws in the northeastern south china sea scs the method was to sample a series of across ridge sections using an underway conductivity temperature depth uctd profiler and to conduct a time series at a fixed point atop the ridge using a ctd with lowered acoustic doppler current profiler ladcp instrumentation a hull mounted adcp and acoustic backscatter device were also operated throughout the cruise the site was a very high energy region with the northward kuroshio current exceeding 100 cm s 1 and the primarily zonal barotropic tidal currents exceeding 140 cm s 1 the most remarkable feature observed was a convex type mode 2 nliw with a westward propagating core centered near 100 m depth the wave was clearly visible in the velocity and backscatter data and had surface expressions visible both on radar and with the naked eye the horizontal and vertical velocity structure was a good match for theoretical mode 2 waves in the scs the wave generation was consistent with local lee wave dynamics which favored mode 2 generation over mode 1 at peak ebb tide given the currents stratification and bottom slope at the site the wave could not be tracked farther west and apparently did not escape the opposing kuroshio

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

the deglacial transition on the southeastern alaska margin meltwater input sea level rise marine productivity and sedimentary anoxia 1 oxygen isotope data from planktonic and benthic foraminifera on a high resolution age model 44 14c dates spanning 17 400 years document deglacial environmental change on the southeast alaska margin 59 33 32 n 144 9 21 w 682 m water depth surface freshening i e 18o reduction of 0 8 began at 16 650 170 cal years b p during an interval of ice proximal sedimentation likely due to freshwater input from melting glaciers a sharp transition to laminated hemipelagic sediments constrains retreat of regional outlet glaciers onto land circa 14 790 380 cal years b p abrupt warming and or freshening of the surface ocean i e additional 18o reduction of 0 9 coincides with the bolling interstade of northern europe and greenland cooling and or higher salinities returned during the allerod interval coincident with the antarctic cold reversal and continue until 11 740 200 cal years b p when onset of warming coincides with the end of the younger dryas an abrupt 1 reduction in benthic 18o at 14 250 290 cal years b p likely reflects a decrease in bottom water salinity driven by deep mixing of glacial meltwater a regional megaflood event or brine formation associated with sea ice two laminated opal rich intervals record discrete episodes of high productivity during the last deglaciation these events precisely dated here at 14 790 380 to 12 990 190 cal years b p and 11 160 130 to 10 750 220 cal years b p likely correlate to similar features observed elsewhere on the margins of the north pacific and are coeval with episodes of rapid sea level rise remobilization of iron from newly inundated continental shelves may have helped to fuel these episodes of elevated primary productivity and sedimentary anoxia

hydraulic interpretation of direct velocity measurements in the bab al mandab abstract acoustic doppler current profiler velocity measurements in the bab al mandab during the period june 1995 march 1996 are used to assess the hydraulic character of the exchange flow the strait is 150 km long and contains two distinct geometrical choke points the hanish sill and perim narrows the authors use a three layer approximation of the monthly mean velocity and density structure at the sill and narrows to calculate the phase speeds of the first and second internal long gravity waves the first second mode is generally characterized by in phase out of phase motions of the two interfaces the calculations take cross strait topographic variations into consideration by using a piecewise linear representation of the actual bottom the resulting phase speeds are used to determine whether the flow is subcritical supercritical or critical with respect to the first and second modes subcritical supercritical means that the two wave pairs corresponding to a given mode propagate in opposite

modeling the baroclinic circulation in the area of the sicily channel the role of stratification and energy diagnostics 1 aspects of the circulation of the sicily channel region are studied with a high resolution primitive equation sigma coordinate model this work is an attempt to study the process governing the purely baroclinic dynamics and its sensitivity to seasonal stratification thus no atmospheric forcing is used two numerical experiments are analyzed using as initial conditions diagnostic velocity fields derived from the winter and summer climatological hydrologies the quasi steady state is characterized by circulation patterns in the depth range of the modified atlantic water maw and the levantine intermediate water liw strongly controlled by mesoscale eddies and topography seasonal difference is found in the surface current which exhibits the major variability on the african side downstream of adventure bank and the ionian slope where the absolute maximum occurs the intermediate circulation instead does not show relevant seasonal differences liw enters through the two passages south of malta plateau and preferentially flows along the sicilian shelf edge exiting over the northern sill its pathway is strongly controlled by subsurface cyclonic and anticyclonic cells the results are in good agreement with observations an energy diagnostics is applied to model results and sheds important light on dynamical characteristics of the mesoscale eddy field and indicates seasonal differences in the energetic exchange with the mean flow the analysis of the mean mke and eddy eke kinetic energy the transfer terms between energy compartments and the eddy momentum flux divergence indicates how eddies are strongly energetic in summer and exchange energy more efficiently with the mean flow in the quasi steady state maw volume transport and mke and eke fluctuations are strongly correlated this result suggests that mesoscale motions can control up to 40 of volume transport variability

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

energetics of semienclosed basins with two layer flows at the strait examination of the energy budget for semienclosed seas with two layer exchange flow at the strait shows that the energy flux at the open portion of the boundary the strait is proportional to the surface buoyancy fluxintegratedoverthebasinarea withtheconstantofproportionalitygivenbytheinterfacedepth whenthe surface buoyancy flux is positive the energy flux is negative these types of basins have an estuarine circulation antiestuarine basins have a negative surface buoyancy flux which provides a positive energy flux augmenting the wind work in powering the circulation the energy budget for the semienclosed seas with vertically separated flows at the strait is examined using reanalysis products for four major semienclosed basins the mediterranean and red seas antiestuarine and the black and baltic seas estuarine important differencesintherelativecontributiontotheenergybudgetofthewindworkversusthesurfacebuoyancyflux are found within basins of the same type and these differences help explain some qualitative aspects of the basins flow

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

the geology and coal petrology of a pleistocene lignite profile at horemi mine megalopolis basin peloponnese southern greece abstract the present study describes the geology coal petrology and geochemistry of a pleistocene coal bearing succession at horemi mine megalopolis basin southern greece within a 45 m interval 9 coal seams are exposed ranging in thickness from 20 cm to 10 m reflectances measured on the maceral type eu ulminite b range between 0 24 and 0 31 mean r random this indicates a coalification stage in the transition zone between peat and lignite rank of the a s t m classification for the horemi coals petrographic studies demonstrated the immature nature of these coals and the low degree of compaction during diagenesis compositionally the horemi coals are characterized by low amounts 5 3 vol of the inertinite group macerals moderate amounts 11 9 vol of liptinite group macerals and very high amounts 82 8 vol of the huminite group macerals on average and mineral matter free basis within the latter group densinite attrinite and ulminite make up the bulk of the samples results from proximate and ultimate analysis gave on average 53 7 bed moisture and 37 3 ash 45 8 volatiles and 18 1 fixed carbon d b calorific value determinations vary between 1805 and 5470 kcal kg mineral matter is high varying within the range 20 8 51 9 vol identifiable mineral constituents include quartz anhydrite illite feldspars calcite gypsum and chlorite and minor amounts of barite and pyrite reflectances obtained from ulminite were found to be negatively correlated with volatile matter whereas there is a trend for a positive correlation of them with calorific values

short term variability of the mediterranean in and out flows 1 a re analysis of ctd profiles collected in the strait of gibraltar during the 1985 1986 gibraltar experiment shows that a large variability can occur within a 10 day interval in the nature of the atlantic water found in the sill surroundings and expected to flow into the mediterranean sea and in the set of mediterranean waters outflowing from the sea since both strongly mix together within the strait the outflow in the atlantic ocean can display a tremendous short term variability mainly due to the variability of the inflow specifying any nominal characteristic for the outflow all its way downstream a fortiori any nominal characteristic for the various veins into which it is split thus needs monitoring the whole water column within the strait

a three dimensional simulation of the hudson raritan estuary part i description of the model and model simulations abstract a time dependent three dimensional finite difference simulation of the hudson raritan estuary is presented the calculation covers july september 1980 the model estuary is forced by time dependent observed winds tidal elevation at open boundaries and river and sewage discharges turbulence mixing coefficients in the estuary are calculated according to a second moment turbulence closure submodel horizontal diffusivities are zero in the simulation and small scale eddies produced by the interaction of unsteady three dimensional velocity and salinity fields with coastline and bottom bathymetry were resolved by the model these eddies are important physical elements in shear dispersion processes in an estuary model results show unstably stratified water columns produced by advection of waters of different densities these instabilities produce intense mixing with vertical eddy diffusivities reaching 2 3 times their neutral values they occur most frequently at slack currents during initial s

british columbian continental shelf as a source of dissolved iron to the subarctic northeast pacific ocean 1 the distribution of dissolved 0 4 m iron fe across the continental shelf and slope of queen charlotte sound on the west coast of canada was examined to estimate the potential of these waters as a source of fe to the fe limited waters of the subarctic northeast pacific iron profiles obtained in shelf slope and offshore waters demonstrate decreasing concentrations of fe with distance from the continent within 50 m of the shelf sediments dissolved fe concentrations were 5 3 0 3 nm this signal was detected although attenuated by 80 along the isopycnal surface at offshore stations 40 50 km seaward of the shelf break strongly suggesting cross shelf transport of an fe rich plume originating in low dissolved oxygen 3 ml l 1 130 mol kg 1 waters in subsurface water over the continental shelf several physical mechanisms that may cause these fe enriched waters to advect offshore in this region i e tidal currents and ekman transport in the bottom boundary layer coastal downwelling relaxation from upwelling and the formation of anticyclonic westward propagating coastal eddies are discussed we suggest that strong tidal currents over broad continental shelves may play a key role in fe supply to ocean basins

controls on deglacial changes in biogenic fluxes in the north pacific ocean the subarctic north pacific ocean holds a large co2 reservoir that is currently isolated from the atmosphere by a low salinity layer it has recently been hypothesized that the reorganization of these high co2 waters may have played a crucial role in the degassing of carbon dioxide to the atmosphere during the last deglaciation this reorganization would leave some imprint on paleo productivity records here we present 230th normalized biogenic fluxes from an intermediate depth sediment core in the northwest pacific rc10 196 54 7 n 177 1 e 1007 m and place them within the context of a synthesis of previously published biogenic flux data from 49 deep sea cores north of 20 n ranging from 420 to 3968 m water depth the 230th normalized opal carbonate and organic carbon fluxes from rc10 196 peak approximately 13 000 calendar years bp during the bolling allerod b a period our data synthesis suggests that biogenic fluxes were in general lowest during the last glacial period increased somewhat in the northwest pacific during heinrich event 1 and reached a maximum across the entire north pacific during the b a period we evaluate several mechanisms as possible drivers of deglacial change in biogenic fluxes in the north pacific including changes in preservation sediment focusing sea ice extent iron inputs stratification and circulation shifts initiated in the north atlantic and north pacific our analysis suggests that while micronutrient sources likely contributed to some of the observed changes the heterogeneity in timing of glaciogenic retreat and sea level make these mechanisms unlikely causes of region wide contemporaneous peaks in export production we argue that paleoobservations are most consistent with ventilation increases in both the north pacific during h1 and north atlantic during b a being the primary drivers of increases in biogenic flux during the deglaciation as respectively they were likely to bring nutrients to the surface via increased vertical mixing and shoaling of the global thermocline

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