surface circulation in the gulf of cadiz 2 inflow outflow coupling and the gulf of cadiz slope current 1 a study of the upper slope circulation in the gulf of cadiz is presented observations both original and revisited and realistic numerical modeling are used together to describe the structure and variability of the slope current system above the mediterranean outflow it is shown that the mediterranean inflow outflow coupling plays a stronger role than that of the atmospheric forcing in driving the upper slope currents the mediteranean outflow forces a surface open ocean current toward the strait of gibraltar part of it is entrained into the outflow and the remaining flows into the mediterranean this latter component does not suffice for the observed transport of the atlantic inflow into the mediterranean a secondary contribution to the inflow is therefore needed to complement the transport this contribution comes from a persistent equatorward current along the upper slope between cape st vincent and the strait of gibraltar the jet is 20 30 km wide and significant in the upper 200 m attaining subinertial maxima as much as 0 3 0 4 m s and monthly means in the order of 0 1 0 15 m s this current shows a strong variability at time scales in the order of 2 8 days and displays a significant vertical shear the response of the upper slope current to synoptic and seasonal atmospheric variability is analyzed very low correlation was detected at synoptic scales and the response of the system to seasonal forcing is unclear a cycle of intensification in june july and a decrease in winter is apparent in the measurements but is weak in the model results it is speculated that the cycle in the observed currents is associated with variability in the inflow outflow coupling system rather than driven by seasonally changing wind forcing

velocity distribution of turbulent open channel flow with bed suction this study investigates theoretically and experimentally the velocity distributions of turbulent open channel flow with bed suction a velocity profile with a slip velocity at the bed surface and an origin displacement under the bed surface is proposed and discussed based on this assumption a modified logarithmic law is derived the measured experimental velocity distribution verifies the accuracy of the theoretically derived profile the data show a significant increase in the near bed velocity and a velocity reduction near the water surface resulting in the formation of a more uniform velocity distribution the values of the origin displacement slip velocity and shear velocity are found to increase with increasing relative suction the measured data show the occurrence of two flow regions in the suction zone a transitional region in which the velocity readjusts rapidly and an equilibrium region

spatially averaged open channel flow over rough bed in this paper it is suggested that the double averaged in temporal and in spatial domains momentum equations should be used as a natural basis for the hydraulics of rough bed open channel flows especially with small relative submergence the relationships for the vertical distribution of the total stress for the simplest case of 2d steady uniform spatially averaged flow over a rough bed with flat free surface are derived these relationships explicitly include the form induced stresses and form drag as components of the total stress using this approach we define three types of rough bed flows 1 flow with high relative submergence 2 flow with small relative submergence and 3 flow over a partially inundated rough bed the relationships for the double averaged velocity distribution and hydraulic resistance for all three flow types are derived and compared with measurements where possible the double averaged turbulent and form induced intensities and stresses for the case of regular spherical segment type roughness show the dominant role of the double averaged turbulence stresses and form drag in momentum transfer in the near bed region

bed suction effects on structure of turbulent open channel flow the effects of bed suction on the structure of turbulent open channel flow are studied numerically by solving the reynolds averaged navier stokes equations two low r turbulence models of the k e type are used for closing the system of equations the models of nagano and hishida and of launder and sharma give similar predictions for suction rates up to 9 against experimental measurements performed by maclean the bed suction effects on the mean flow characteristics are found to be significant within the suction region the near bed velocities are increased with increasing suction rate as well as the bed shear stress the law of the wall with suction developed by stevenson is found to be applicable for low rates of bed suction up to o 3ty the excess bed shear stress resulting from suction is calculated in the order of three to eight times the respective one with no suction the turbulence levels are greatly reduced with increasing suction rate and a new normalization of the turbulence characteristics is satisfactory for suction rates up to 0 3

direct measurements of bed stress under swash in the field 1 utilizing flush mounted hot film anemometry the bed stress under swash was measured directly in a field experiment conducted on barret beach fire island new york the theory development and calibration of the instrument package are discussed and results from the field experiment are presented examples of bed stress time series throughout a swash cycle are presented and an ensemble averaged swash bed stress cycle is calculated strong asymmetry is observed between the uprush and backwash phases of the swash flow the maximum bed shear stress exerted by the uprush is approximately double that of the backwash while the duration of the backwash is 135 greater than that of the uprush friction coefficients in the swash zone are observed to be similar in magnitude to those from steady flow with the mean observed friction coefficient equal to 0 0037 swash friction coefficients derived from the current measurements exhibit a reynolds number dependence similar to that observed for other flows a systematic difference between coefficients for uprush and backwash is suggested

discussion of effect of seepage induced nonhydrostatic pressure distribution on bed load transport and bed morphodynamics by simona francalanci gary parker and luca solari

plankton blooms ocean circulation and the european slope current response to weather and climate in the bay of biscay and w english channel ne atlantic abstract the flow of upper layer surface water and circulation for the bay of biscay continental slope and in the wider region of the ne atlantic is presented as well as the seasonality of flow and internal tides the marine plankton environments of biscay ocean biscay eddies biscay slope and biscay shelf are defined the shelf region armorican and celtic is further divided into stratified shelf frontal and tidally mixed seasonal distributions of chlorophyll a are given for all environment from in situ measurements and remote sensing data mixing and stabilisation of surface water in the euphotic layer for the start of the spring bloom using in situ profiling measurements is examined some regional responses for the slope current dinoflagellate blooms and interannual variations in spring diatom numbers with respect to weather and climate in the bay of biscay and around the british isles are suggested and discussed an example of the eastern european ocean margin continental slope response to winter weather sea level atmospheric pressure forcing resulting in warm winter water in the southern bay of biscay navidad with eddy production and off the shetland continental slopes the warm water supply route to the arctic is given from the slope climate observation series

direct bed shear measurements under loose bed swash flows shear plate measurements of bed shear stress under fixed and loose bed swash uprush flows are presented and contrasted a shear plate previously developed for fixed bed flows was modified and tested for coarse and fine grain loose beds transient flows were generated by a dam break flow over initially dry horizontal and sloping beds with flows upslope analogous to swash uprush flows on beaches performance of the shear plate varied with grain size for the coarse grained loose beds only the peak shear stress at the leading edge of the swash flow was consistently obtained for fine grained loose beds the shear stress was reliably obtained over the whole uprush swash cycle data were obtained for varying thickness of loose bed material commencing with a single grain layer which correspond to partially starved bed conditions the direct measurements clearly indicate that the bed shear stress comprises of a fluid shear stress component and a grain shear stress component the grain shear stress increases linearly with sediment load and is significantly larger for the coarse loose grain bed tests due to the much larger normal stress compared to that for fine grain loose bed tests with the same number of grain layers the data show a high degree of consistency with the classical theory of bagnold 1956 and the derived coefficient of dynamic internal friction is similar to that observed by hanes and inman 1985

advances in swash zone research small scale hydrodynamic and sediment transport processes abstract extensive research efforts in the last decade have improved knowledge of swash zone processes this paper reviews and synthesizes from 2004 onward the research advances of small scale hydrodynamics and sediment transport processes considering field laboratory and numerical modeling efforts swash zone hydrodynamics are examined by means of shoreline motions fluid velocities pressure gradients flow structure bed shear stress friction coefficients and turbulence subsequently advances related to sediment transport mechanisms and morphological changes are described detailed descriptions of measuring techniques novel findings and the strengths and weaknesses of the different approaches are discussed the review also acknowledges the major advances in the development of instrumentation to collect highly resolved flow and sediment concentration measurements in direct proximity of the bed and the experimental framework for analyzing local dynamics on a wave by wave time scale e g dam break

effect of seepage induced nonhydrostatic pressure distribution on bed load transport and bed morphodynamics bed load transport is commonly evaluated in the condition of a hydrostatic pressure distribution of the flow field while this condition is reasonable for quasi steady quasi uniform rectilinear flows it cannot be satisfied in a large variety of flow conditions i e near an obstacle as in the case of a bridge pier the dimensionless shields number which contains the assumption of a hydrostatic pressure distribution in its denominator therefore cannot be strictly applied to evaluate bed load transport in all the configurations where nonhydrostatic pressure distributions are observed in the present work a generalization of the shields number is proposed for the case of nonhydrostatic pressure distribution produced by groundwater flow experiments showing the effects of vertical groundwater flow on the bed morphodynamics are presented the comparison between the experimental observations and numerical results obtained by means of a morphodynamic model which employs the new formulation of the shields number suggests that the proposed generalization of the shields number is able to account the effect of the nonhydrostatic pressure distribution on the bed load transport

direct bed shear stress measurements in bore driven swash direct measurements of bed shear in the swash zone are presented the data were obtained using a shear plate in medium and large scale laboratory bore driven swash and cover a wide range of bed roughness data were obtained across the full width of the swash zone and are contrasted with data from the inner surf zone estimates of the flow velocities through the full swash cycle were obtained through numerical modelling and calibrated against measured velocity data the measured stresses and calculated flow velocities were subsequently used to back calculate instantaneous local skin friction coefficients using the quadratic drag law the data show rapid temporal variation of the bed shear stress through the leading edge of the uprush which is typically two four times greater than the backwash shear stresses at corresponding flow velocity the measurements indicate strong temporal variation in the skin friction coefficient particularly in the backwash the general behaviour of the skin friction coefficient with reynolds number is consistent with classical theory for certain stages of the swash cycle a spatial variation in skin friction coefficient is also identified which is greatest across the surf swash boundary and likely related to variations in local turbulent intensities skin friction coefficients during the uprush are approximately twice those in the backwash at corresponding reynolds number and cross shore location it is suggested that this is a result of the no slip condition at the tip leading to a continually developing leading edge and boundary layer into which high velocity fluid and momentum are constantly injected from the flow behind and above the tip region finally the measured stress data are used to determine the asymmetry and cross shore variation in potential sediment transport predicted by three forms of sediment transport formulae crown copyright c 2009 published by elsevier b v all rights reserved

physical oceanography of the western iberia ecosystem latest views and challenges the present review is focused on the mesoscale physical processes recognized in the western iberia ecosystem complementing earlier reviews dedicated to larger scales recent studies support the idea that the mesoscale processes superimposed on the larger scale variability are the major factor controlling the ecosystem functioning in the region a complex structure of interleaved alongshore slope shelf and coastal currents that interact with eddies buoyant plumes upwelling filaments and fronts surface layer expressions of the subsurface circulation and internal waves is revealed by the latest research all of these contribute in different ways to have an effect on the ecosystem the supposedly less variable winter circulation also exhibits significant mesoscale activity in the form of eddy shedding from the poleward slope current intermittent upwelling events and transient nearshore poleward flows the present incomplete knowledge of this complex system presents a number of challenges and questions that must be addressed if we are to arrive at a satisfactory understanding and predictive capability for the system as a whole 2007 elsevier ltd all rights reserved

monitoring of a quasi stationary eddy in the bay of biscay by means of satellite in situ and model results the presence of a quasi stationary anticyclonic eddy within the southeastern bay of biscay centred around 44 30 n 4 w has been reported on various occasions in the bibliography the analysis made in this study for the period 2003 2010 by using in situ and remote sensing measurements and model results shows that this mesoscale coherent structure is present almost every year from the end of winter beginning of spring to the beginning of fall during this period it remains in an area limited to the east by the landes plateau to the west by le danois bank and torrelavega canyon and to the northwest by the jovellanos seamount all the observations and analysis made in this contribution suggest that this structure is generated between capbreton and torrelavega canyons detailed monitoring from in situ and remote sensing data of an anticyclonic quasi stationary eddy in 2008 shows the origin of this structure from a warm water current located around 43 42 n 3 30 w in mid january this coherent structure is monitored until august around the same area where it has a marked influence on the sea level anomaly sea surface temperature and surface chlorophyll a concentration an eddy tracking method applied to the outputs of a numerical model shows that the model is able to reproduce this type of eddy with similar 2d characteristics and lifetimes to that suggested by the observations and previous works this is the case for instance of the simulated may04 eddy which was generated in may 2004 around torrelavega canyon and remained quasi stationary in the area for 4 months the diameter of this eddy ranged from 40 to 60 km its azimuthal velocity was less than 20 cm s 1 its vertical extension reached 3000 3500 m depth during april and may and it was observed to interact with other coherent structures

dam break flows acquisition of experimental data through an imaging technique and 2d numerical modeling this paper presents experimental and two dimensional 2d numerical results of four tests concerning rapidly varying flows induced by the sudden removal of a sluice gate for the acquisition of the experimental data an imaging technique capable of providing spatially distributed information was adopted a coloring agent was added to the water the opalescent bottom of the facility was backlighted and photographs of the area of interest were taken the gray tones of the acquired images were converted into water depths by means of transfer functions derived from a static calibration the potential sources of error of the proposed procedure are discussed a local comparison with an ultrasonic device showed a 20 maximum deviation in 95 of the observations the tests were simulated through a 2d muscl hancock finite volume numerical model based on the classical shallow water approximations in which the intercell water depths are estimated according to the surface gradient method a global analysis of the relative frequency distributions of the deviation between numerical and experimental results is performed despite some evident differences at a local scale the adopted 2d numerical model is capable of reproducing the main features of the flow fields under investigation

observations of morphological change and sediment transport on a steep gravel beach abstract observations of morphological change and swash sediment loads concurrent with measurements of water level waves and currents were obtained during a spring to spring tidal cycle on a steep macrotidal gravel beach in southwest england the wave conditions experienced during the field experiment were relatively calm and the significant inshore wave height and period averaged 0 4 m and 6 s respectively incident frequency water motions dominated the hydrodynamics and the phasing between water surface elevation and cross shore and alongshore currents was inconsistent with standing edge wave motion morphological change was directly related to maxima in shoreline elevation and four modes of berm adjustment identified regression and rollover in response to falling and rising water levels respectively and removal and reformation during and after storms respectively swash processes transported substantial amounts of sediment at rates comparable to sand beaches and the net transport under modal wave conditions was estimated to be 1 kg per swash onshore per unit metre beach width steep hydrodynamic gradients induced by the abrupt slope breaks of the step and berm are one of the main causes of the large morphological variability characteristic of gravel beaches

modes of mesoscale sea surface height and temperature variability in the east australian current 1 mesoscale variability where the east australian current eac separates from the coast is studied using sea surface temperature and surface velocity streamfunction observed by satellite and a regional numerical model the mean circulation simulated by the model the regional ocean modeling system roms is compared to a high resolution regional climatology and the realism of the simulated mesoscale variability is tested by comparison to statistical analyses of the satellite data both roms and data show spectral peaks in the mesoscale energy band at periods between 90 and 180 days complex empirical orthogonal function eof analysis identifies two significant modes of mesoscale variability in the data an eddy mode for which the variability propagates southwestward along the coast and a wave mode for which phase propagation is predominantly onshore the regional model open boundary conditions include only annual and semiannual harmonics of variability so remote mesoscale forcing is absent the eddy mode is represented well in the model indicating this aspect of the circulation results from local instabilities of the flow and that its underlying dynamical process is simulated well while the observed and modeled wave modes have some similarities their differences suggest the model is deficient in representing westward propagation of mesoscale period variability in the region whatever the source of this energy the orthogonality property of the eof analysis indicates the wave mode does not interact significantly with eddy processes in the eac separation

characteristics of two counter rotating eddies in the leeuwin current system off the western australian coast abstract a multi disciplinary r v southern surveyor cruise was conducted in october 2003 to quantify upper ocean productivity within two adjacent counter rotating mesoscale eddies an eddy pair off the coast of western australia wa in the southeast indian ocean in this study a combination of satellite data altimeter sea surface temperature and chlorophyll a and shipboard measurements acoustic doppler current profiler adcp and conductivity temperature depth ctd were used to characterize the temporal evolution and spatial structures of the eddy pair satellite data show that the eddy pair evolved from meander structures of the poleward flowing leeuwin current lc in may 2003 and fully detached from the current in late august early september gaussian fits to the adcp velocities show that the anticyclonic eddy had a maximum azimuthal velocity of 65 cm s 1 at 63 km from the eddy centre the apparent radius and the cyclonic eddy had a maximum azimuthal velocity of 60 cm s 1 at the apparent radius of 49 km the mixed layer temperature and salinity properties in the cores of the eddy pair were quite stable over the period of the cruise temperature salinity diagrams indicate that the mixed layer water in the core of the anticyclonic eddy was composed mainly of lc water while in the core of the cyclonic eddy the mixed layer water was similar to surrounding open ocean water the total volume of the lc water retained in the anticyclonic eddy was 5 6 1012 m3 equivalent to 19 days annual mean transport of the lc the chlorophyll a concentration in the surface layer of the anticyclonic eddy lc water was higher than in the cyclonic eddy open ocean water which was likely a result of the entrainment of the productive water from the continental shelf during the eddy formation stage the offshore transport of the chlorophyll a biomass may be important for the pelagic ecosystem off the coast of wa

hydrodynamics and sediment transport in the swash zone a review and perspectives the dominant hydrodynamic forcing and resulting sediment transport mechanisms in the swash zone are reviewed combined with a discussion of future measurement and modelling requirements the importance of swash zone processes in the overall behaviour of the nearshore littoral zone are identified with the paper subsequently focusing on aspects that directly relate to sediment transport on beaches the review considers analytical and numerical modelling work and both field and laboratory data the hydrodynamics of the swash zone are first discussed with reference to the surf zone boundary swash characteristics forcing mechanisms and shoreline oscillations subsequent sections consider more micro scale processes such as the internal flow kinematics turbulence the bed boundary layer and infiltration exfiltration through permeable beds the second part of the paper outlines the fundamental mechanics of sediment transport in the swash zone followed by a more detailed discussion of sediment transport modes induced by the dominant hydrodynamic conditions modelling concepts are reviewed and the strengths and weaknesses of different approaches identified a final summary and future modelling perspectives conclude the paper

the pattern and variability of winter kuroshio intrusion northeast of taiwan the variations of the kuroshio path and velocity northeast of taiwan are analyzed based on along track satellite altimeter data as well as high resolution model experiments observations reveal that in winter the kuroshio intrusion into the east china sea ecs at this location is manifested by a secondary maximum current core smcc shoreward of the kuroshio s main path the smcc varies significantly on interannual time scale and its variability is strikingly out of phase with that of the kuroshio entering the ecs meaning that the stronger the kuroshio the weaker the smcc and vice versa model experiments corroborate the observational results and more importantly indicate that the kuroshio intrusion here follows two primary routes a large anticyclonic loop that separates from the kuroshio at the northern end of taiwan and moves forward to form the smcc and a straight northward path onto the shelf when the kuroshio turns sharply eastward along the continental slope of the ecs the intrusion is controlled by both local forcing and remote effect with its pattern and variability depending mostly on the local heat flux and the inertia of the kuroshio current

estimating swash zone friction coefficients on a sandy beach abstract video based swash motions from three studies on two separate beaches were analyzed with respect to theoretical swash trajectories assuming plane beach ballistic motions under quadratic friction friction coefficient values for both the uprush and backwash were estimated by comparing measured swash space time trajectories to these theoretical expectations given an initial velocity and beach slope observations were made spanning high tides and in one case during a light rain analysis of over 4500 individual swash events showed that the uprush friction coefficient was nearly constant during all three studies with a mean value of roughly 0 007 and showed no trends over a tidal cycle in contrast backwash friction coefficient values varied over the tidal cycles ranging between 0 01 and 0 07 with minimum values corresponding to the highest tides although these values are close to the theoretical estimates based on a law of the wall formulation and values commonly referenced in the literature these observations show a consistent tendency for backwash friction estimates to greatly exceed uprush friction estimates the disparity between uprush and backwash friction coefficients can be partially attributed to the exclusion of a pressure gradient term in the ballistic model however results indicate that backwash friction coefficients adjusted to account for this effect may be three times larger than the uprush friction values during lower tides this tidal dependence for backwash friction coefficients is attributed to a complex interaction between swash infiltration and entrained sediment loads these findings imply that friction estimates necessary for sediment transport calculations and hydrodynamic predictions based solely on grain roughness may not be correct for backwash flows

seasonal dynamics in the azores gibraltar strait region a climatologically based study abstract annual and seasonal mean circulations in the azores gibraltar strait region north eastern atlantic are described based on climatological data an inverse box model is applied to obtain absolute water mass transports consistent with the conservation of volume salt and heat and the equations of the thermal wind the large scale gyre circulation azores current azores counter current canary current and portugal current is well represented in climatological data the azores current annual mean transport was estimated to be 6 5 0 8 sv 1 sv 106 m3 s eastward exhibiting a seasonal signal with minimum transport in the spring 5 3 0 8 sv and maximum transport in autumn 7 3 0 8 sv the azores current transport is twice that of the azores counter current in spring and autumn and is four times higher in summer and winter the southward portugal and canary currents show similar seasonal cycles with maximum transports in spring 3 5 0 6 and 6 6 0 4 sv respectively the overturning circulation within the area has an annual mean magnitude of 2 2 0 1 sv and two seasonal extremes the highest in summer 2 6 0 1 sv and the lowest in winter 1 7 0 1 sv of the annual mean about two thirds 1 4 sv of the overturning circulation results from water mass transformation west of the strait of gibraltar the downwelling and recirculation of upper central water 0 6 sv in the intermediate layer the entrainment of central water 0 6 sv into the mediterranean outflow and the contribution of antarctic intermediate water 0 2 sv to the mediterranean outflow the remaining 0 8 sv relates to the overturning in the mediterranean sea through the two layer exchange at the gibraltar strait accordingly the density level dividing the upper inflowing and lower outflowing limbs of the overturning circulation was found to be 1 31 65 kg m 3 1 potential density referred to 1000 db which is above the isopycnal that typically separates central and mediterranean water 1 31 8 kg m 3 in terms of water masses we describe quantitatively the water mass composition of the main currents focusing on the spread of mediterranean water we found that when the northward mediterranean water branch weakens in spring and autumn the westward mediterranean water vein strengthens and vice versa the maximum net transports of mediterranean water across the northern and western sections of the box were estimated at 1 9 0 6 sv summer and 0 8 0 2 sv spring respectively within the error bar 0 2 sv we found no significant net volume transport of mediterranean water across the southern section

observations and predictions of fluid velocities in the surf and swash zones 1 surfzone and swashzone water level fluctuations and cross shore fluid velocities observed at seven cross shore locations for 139 51 min periods on a low sloped fine grained sandy beach are shown to be modeled well by the depth averaged nonlinear shallow water equations the model initialized with observations about 150 m from the shoreline in 300 cm water depth accurately predicts the observed decrease in sea swell wave heights and orbital velocities with decreasing water depth across the surf zone and the observed maxima in infragravity orbital velocities and offshore directed mean flows near the outer edge of the swash zone in the surf zone both the observed and predicted velocity fluctuations are dominated by sawtoothed shaped pitched forward asymmetrical sea swell waves in the swash zone infragravity waves contribute substantially to the total velocity variance and asymmetry shoreward of the outer swash zone observed and predicted total and infragravity velocity asymmetry decrease onshore changing sign from positive to negative in the upper swash

experimental study of flash flood surges down a rough sloping channel flood waves resulting from flash floods and natural dam overtopping have been responsible for numerous losses in the present study surging waters down a flat stepped waterway slope 3 4 degrees were investigated in a 24 m long chute wave front propagation data were successfully compared with hunt s 1982 1984 theory visual observations highlighted strong aeration of the leading edge instantaneous distributions of void fractions showed a marked change in shape for t ts g do 1 3 which may be caused by some major differences between the wave leading edge and the flow behind including non hydrostatic pressure distributions plug slug flow regime and different boundary friction regime practically the results quantified the large amount of entrained air i e white waters at the wave front which in turn reduces buoyancy and could affect sediment motion at the leading edge because the sediment relative density is inversely proportional to the entrained air content

swash zone sediment fluxes field observations abstract this paper describes newly obtained high frequency observations of beach face morphological change over numerous tidal cycles on a macrotidal sandy beach made using a large array of ultrasonic altimeters these measurements enable the net cross shore sediment fluxes associated with many thousands of individual swash events to be quantified it is revealed that regardless of the direction of net morphological change on a tidal time scale measured net fluxes per event are essentially normally distributed with nearly equal numbers of onshore and offshore directed events the majority of swash events cause net cross shore sediment fluxes smaller than 50 kg m 1 and the mean sediment flux per swash event is only o 1 kg m 1 leading to limited overall morphological change however much larger events which deposit or remove hundreds of kilograms of sand per meter width of beach occur at irregular intervals throughout the course of a tide it was found that swash swash interactions tend to increase the transport potential of a swash event and the majority of the swash events that cause these larger values of sediment flux include one or more interactions the majority of the larger sediment fluxes were therefore measured in the lower swash zone close to the surf swash boundary where swash swash interactions are most common despite the existence of individual swash events that can cause fluxes of sediment that are comparable to those observed on a tidal time scale frequent reversals in transport direction act to limit net transport such that the beach face volume remains in a state of dynamic equilibrium and does not rapidly erode or accrete

intensification of upwelling along oman coast in a warming scenario the oceanic impact of poleward shift in monsoon low level jet mllj is examined using a regional ocean modeling system roms two sets of downscaling experiments were conducted using roms with boundary and initial conditions from six cmip5 models while outputs from the historical run 1981 2000 acts as forcing for the first the second uses rcp8 5 2080 2099 by comparing the outputs it is found that oman coast will experience an increase in upwelling in tune with mllj shift consistent with the changes in upwelling and zonal ekman transport temperature salinity and productivity show significant changes near the oman coast the changes in mllj causes the coastal wind to angle against the oman coast in such a fashion that the net upwelling increases in the next century and so does the marine productivity this study contrasts the general view of weakening of upwelling along the arabian coasts due to the weakening of monsoon winds

structure and circulation of the upper atlantic ocean northeast of the azores historical data primarily from the igy but spanning the years 1914 1983 have been re examined in an attempt to define the structure and circulation of the upper ocean 0 800 m in the eastern north atlantic 30 50 n 10 40 w the saline greater than 35 7 anticyclonic surface gyre shallows to the north like a wedge being 300 500 m deep at 36 n east of 30 w and outcropping at about 45 n it lies above the mediterranean water separated from it by a salinity minimum and by a pycnostad of subpolar mode water mccartney and talley 1982 eastward flow between 36 n and 46 n is primarily confined to the saline wedge with speeds of 2 4 cm s 1 the flow converges gradually towards the east resulting in fronts and strong meridional property gradients e g mixed layer depth robinson bauer and schroeder 1979 east of 15 w the majority of the supolar mode water is formed by deep winter convection north of the saline wedge and subducts to the south under it southward advection and ventilation rates in the northeast atlantic the main ventilation region for the north atlantic sarmiento rooth and roether 1982 are similar estimated to be 0 2 cm s 1 the freshening of the surface layer between 1967 and 1976 that has been found in widely separated regions of the north atlantic rockall trough sargasso sea labrador sea is also present northeast of the azores salinities down to 500 m have decreased by 0 1 equivalent to an addition of a 1 4 m column of fresh water at the surface the freshening on t 27 1 decreases to negligible values southwards of 40 n it is suggested that changes in the balance of evaporation and precipitation must have occured

generation and unstable evolution of a density driven eastern poleward current the iberian poleward current 1 the generation and evolution of a density driven eastern poleward current is investigated using a high resolution primitive equation numerical model the simulations focus on the iberian poleward current ipc as a case study the flow is generated by a meridional upper ocean density gradient balanced by an eastward surface intensified flow that adjusts at the coastal margin the resulting current system has a baroclinic character with poleward flow at the surface layer and equatorward flow underneath a few weeks after initialization the sheared along slope flow generates several vorticity structures downstream of the main topographic features in the lee of the topography persistent anticyclones are observed and deep cyclogenesis is induced in relation to the meandering of the upper layer jet these structures evolve preferentially as cyclone anticyclone eddy pairs and after interaction some dipoles are ejected offslope within a period of a few months the initial meridional gradient evolves into a complex system of fronts eddies and slope flows the dynamics of flow topography interaction is analyzed a comparison with satellite imagery of the ipc is conducted and similarity in scales and patterns is noted

turbulence experiments in the swash zone abstract turbulence and water surface elevation measurements were carried out in the swash zone which was induced by plunging and collapsing breakers in a wave flume three different period regular waves were generated on a 1 10 smooth impermeable concrete beach and the water surface elevations were collected by a number of wave gauges and a run up meter lying on the bottom velocity measurements were carried out by a laser doppler velocimeter system at spatial steps of 1 mm from the bottom along three vertical sections in the swash zone the data have been used to describe the wave front dynamics to derive the length and velocity macro and micro scales and the eulerian frequency spectrum in some points it shows a double structure the results add to and expand on similar results obtained by other researchers in the surf zone

the swash of solitary waves on a plane beach flow evolution bed shear stress and run up the swash of solitary waves on a plane beach is studied using large scale experiments ten wave cases are examined which range from non breaking waves to plunging breakers the focus of this study is on the influence of breaker type on flow evolution spatiotemporal variations of bed shear stresses and run up measurements are made of the local water depths flow velocities and bed shear stresses using a shear plate sensor at various locations in the swash zone the bed shear stress is significant near the tip of the swash during uprush and in the shallow flow during the later stages of downrush in between the flow evolution is dominated by gravity and follows an explicit solution to the nonlinear shallow water equations i e the flow due to a dam break on a slope the controlling scale of the flow evolution is the initial velocity of the shoreline immediately following waveform collapse which can be predicted by measurements of wave height prior to breaking but also shows an additional dependence on breaker type the maximum onshore directed bed shear stress increases significantly onshore of the stillwater shoreline for non breaking waves and onshore of the waveform collapse point for breaking waves a new normalization for the bed shear stress which uses the initial shoreline velocity is presented under this normalization the variation of the maximum magnitudes of the bed shear stress with distance along the beach which is normalized using the run up follows the same trend for different breaker types for the uprush the maximum dimensionless bed shear stress is approximately 0 01 whereas for the downrush it is approximately 0 002

circulation on the northwestern iberian margin swoddies abstract we study the eddies that form by destabilization of the iberian poleward current some anticyclones have been identified in satellite sea surface temperature as they are persistent and remarkably warm and they contain ipc waters in their core the number of observed eddies is small and little is known about their statistics places of formation separation processes and behavior away from the slope in this study the output of a 20 year high resolution numerical simulation is analyzed to study the formation of anticyclonic and cyclonic eddies by destabilization of the iberian poleward current using an automatic eddy detection algorithm the model reproduces the formation of some of the eddies at the same time and place and with similar sizes as observed in satellite sst although it fails to reproduce their observed trajectories as they propagate away from the slope we found distinct layers with different relative vorticity distribution the top 200 m of the water column has an anticyclonic dominance with stronger anticyclones in the layer between 200 and 600 m there are more and stronger cyclones and from 600 to 1000 m there is again an anticyclonic dominance with more and stronger anticyclones than cyclones the results show that the cyclones form mainly where topographic contours veer cyclonically in the poleward direction while the anticyclones tend to form in places where topographic contours veer anticyclonically we found that there is a relationship between the formation of eddies and the wind variability a sudden decrease in southerly winds results in the development of instabilities in the ipc and formation of eddies the shedding of the surface intensified anticyclones is accompanied by the shedding of deeper layer cyclones in general the deep cyclones spin down faster than the surface anticyclones anticyclones are tracked and conserve their maximum relative vorticity for longer periods the vertical structure of these surface intensified anticyclones at the moment of formation extends to deeper than 1200 m and this vertical extent decreases with time they can survive winter deep convection that homogenizes their core

video derived near bed and sheet flow sediment particle velocities in dam break driven swash abstract this short communication considers a video based approach to quantify near bed and sheet flow swash zone sediment particle velocities over a mobile bed in a laboratory setting and relate the profile shape to sheet thickness and a velocity that can be measured outside the sheet layer by for instance a current meter near bed high speed imagery was recorded during a dam break driven swash event in a flume with optically clear walls repeated swash events for two different median sediment sizes were tested optical current meter ocm analysis was applied to bed parallel image time stacks extracted at elevations from below the at rest bed to within the lower water column ocm results were compared to in situ velocity measurements where possible obtained with an acoustic doppler profiling velocimeter adpv ocm results compared well with adpv measurements for moderate suspended sediment concentrations based on visual observation sediment concentrations were not measured too high of a sediment concentration over saturated the image and did not provide distinct sediment particle trajectories in a consistent direction for ocm analysis this saturation occurred during uprush for both sediment sizes too little of a sediment concentration provided an inadequate number of sediment particle trajectories to track such as during flow reversal for the coarser sediment for coarser sediment backwash velocities were well resolved in ocm analysis with velocities comparing well correlation coefficient 0 8 to adpv estimates the dimensionless backwash sheet flow sediment particle velocity profile normalized by the velocity at the top of the sheet scaled with the dimensionless elevation normalized by the sheet layer thickness to the 0 62 power with 95 confidence intervals for the exponent ranging from 0 47 to 0 76

numerical modelling of the flow and bed evolution of a single bore driven swash event on a coarse sand beach abstract this paper examines the numerical prediction of the sediment transport and bed evolution for a single swash event on a coarse sediment beach in these conditions bed load is the dominant mode of sediment transport laboratory experiments of a single bore driven swash event are simulated numerically using a fully coupled model that solves the system of non linear shallow water equations and the exner sediment conservation formula the analysis focuses on two aspects the optimal choice of parameters for the meyer peter and muller sediment transport formula and the model used for computing the shear stress the methods tested for the bed shear stress are the momentum integral method and the chezy formulation in which the friction factor is computed using two different formulae infiltration into the beach and its effects on the shear stress and sediment transport are also modelled results show that the basic meyer peter and muller sediment transport formula provides good results in the run up on the other hand the sediment transport in the early stage of the backwash is overestimated a reduction of the sediment mobility constant in the formula in the backwash marginally improves the results however the causes of the overestimation of the sediment transport at the early stage of the backwash is the overestimation of the shear stress while at later stages there are several contributions that are identified i e modelling of the sediment transport and infiltration it is also suggested that the meyer peter and muller sediment transport formula might not capture the complexity of the processes involved during the backwash the comparison of the methods for the estimate of the bed shear stress show that comparable results can be obtained using the momentum integral method and the chezy formulation with time and space varying friction factor the resulting bed evolution is also described in the predicted final profile deposition is found in the upper part of the beach and erosion in the lower part a bed step is formed just below the position of the initial shoreline this feature is determined by the onset of a hydraulic jump during the backwash

a multiproxy approach of the holocene evolution of shelf slope circulation on the nw iberian continental shelf abstract textural mineralogical geochemical and microfaunal data benthic foraminifera were studied along the omex core ksgx 40 recovered in the galicia mud deposit of the nw iberian outer continental shelf off the ria de vigo north of spain this core included the records of the last ca 4 8 ka cal bp and consists from the base to the top of a sedimentary sequence exhibiting gradual upward decrease in grain size sediments of this core are mainly siliciclastic largely composed of quartz k feldspars plagioclases and phyllosilicates mica illite kaolinite and chlorite showing a great continental influence in this zone two periods of deposition of finer sediments are registered between 2 2 1 2 ka cal bp and 0 5 0 ka cal bp since the last 2 2 ka bp but mainly during both muddy intervals the galicia mud deposit was nourished with a lower and finer supply of detrital minerals compensated by higher amounts of organic matter as it is suggested by a benthic foraminifera high productivity bfhp proxy processes involved in organic matter degradation by aerobic organisms led to depressed levels of oxygen in the sediments as shown by a benthic foraminiferal oxygen index bfoi peaks of redox sensitive elements like mn fe cu ni cr co zn ni and pb as well as the presence of diagenetic minerals such as pyrite suggest the development of anoxic conditions beneath the sedimentary surface and early diagenetic changes due to high organic matter flux in both muddy intervals two different hydrodynamic regimes were inferred through the analysis of the different proxies textural mineralogical geochemical and benthic foraminifera 1 a strong hydrodynamic regime between 4 8 and 2 2 ka cal bp characterized by the prevalence of winter storms which gave rise to a deep mixed layer on the shelf 2 weak hydrodynamic regime between 2 2 1 2 ka cal bp and 0 5 0 ka cal bp with a high predominance of upwelling and an increase in oceanic stratification

swash zone sediment transport step dynamics and morphological response on a gravel beach abstract state of the art morphodynamic field data were collected from slapton sands uk a fine gravel beach d50 2 10 mm over a 10 day period under a range of wave tide conditions comprising a mixture of southerly swell and easterly wind waves hs 0 5 1 m ts 4 8 s tide range 3 4 m over the field period the upper beach experienced accretion and berm formation during tides with low steepness swell dominated wave conditions h l 0 01 surprisingly the intertidal beach showed an opposite trend with sediment losses under swell conditions and an increase in sediment volume due to wind waves and suggests that upper beach morphological change can be decoupled from the overall sediment budget a submerged accretionary feature the beach step grew and migrated onshore on the rising tide typically reaching a maximum relief of around 0 5 m then gradually decreased in prominence while migrating offshore as the tide fell resulting in little net morphological change the step was better developed during the falling tide than the rising tide and through its control on the swash hydro and sediment dynamics the step had a significant effect on the development of the berm swash flow velocities under the conditions measured were often in excess of 2 m s 1 for both the uprush and the backwash onshore mean flows occurred in the upper swash region 40 inundation was characterised by offshore mean flows swash infiltration losses in the swash zone increased from 40 in the lower swash region to 100 in the upper swash region the most energetic swash flows and the strongest offshore mean flows occurred at the transition between swash zone and surf zone 90 100 inundation

sea surface temperature reconstructions over the last 70 kyr off portugal biomarker data and regional modeling this study aims at providing robust temperature reconstructions for a key oceanographic setting in the north atlantic and at understanding the nature of the temperature signal recorded by the two biomarkers u 37 k and tex86 considering season and depth of production to do so high resolution signals of u 37 k and tex86 are determined for the last 70kyr for core md95 2042 located off portugal signals of u 37 k and tex86 present a tight correlation demonstrating a dominant temperature effect u 37 k signals correspond well to the annual mean sea surface temperature sst whereas tex86h derived temperatures are 5 6 degrees c higher which is unrealistically warm for this area unsuitable tex86 global linear calibrations on the iberian margin may suggest a possible occurrence of archaeal communities with specific temperature response to assess the impact of different season or depth of production of the biomarkers on the recorded temperature in the sediment modeled temperature proxies tproxies are introduced in a regional oceanic modeling system and tested for different seasons annual summer winter and depths surface and 0 200m of production for three climate modes present day pd last glacial maximum lgm and heinrich stadials hs similar temperature amplitudes between climate modes are found at md95 2042 core site for observations for both biomarkers and for modeled annual surface production tproxy 5 5 7 degrees c for t pd lgm and 3 4 degrees c for t lgm hs therefore we propose a new tex86h regional calibration to reconstruct present and past annual mean ssts on the iberian margin

breaking waves over a mild gravel slope experimental and numerical analysis 1 an experimental and numerical study of the effects of a gravel slope on wave shoaling and breaking is presented herein in the laboratory experiments fluid velocities pressure and water surface elevations were measured experiments were conducted for both spilling and plunging breakers and for gravel slopes with different gravel sizes since gravel slopes caused additional energy dissipation wave heights in the shoaling zone as well as at the breaking point were reduced on the other hand the mean free surface setup inside the surf zone increased it was also observed that the gravel slope had a stronger influence on the vertical profile of undertow under spilling breaker than on that under a plunging breaker moreover the undertow became weaker over a gravel slope with a larger gravel size outside the surf zone turbulent velocities near the gravel slope were relatively high because of the bottom roughness and percolation inside the surf zone turbulence generated by wave breaking dominated over the gravel bed generated turbulence the vertical flow induced by the gravel slope changed the turbulence pattern only at cross sections very close to the shoreline numerical simulations of the wave breaking processes over a gravel slope were performed the numerical model was tested by comparing numerical results with experimental data the model accurately simulated the mean flow quantities the magnitude of turbulence and turbulence characteristics were also simulated reasonably well

subinertial response of a density driven eastern boundary poleward current to wind forcing a high resolution primitive equation numerical model is used to generate a poleward flow along a meridionally oriented eastern boundary slope shelf system by imposing an along coast density gradient as the forcing mechanism wind forcing is applied to the resulting quasi steady current system and the subinertial response is analyzed parallel experiments with no slope poleward flow are conducted for comparison moderately strong upwelling and downwelling favorable week to month scale wind events modify the poleward flow but do not significantly change the density driven current structure at the slope the alongshore transport within the slope region is reduced by 0 2 0 3 sv from 1 2 sv where sv 106 m3 s 21 under the influence of either downwelling or upwelling winds independent of the wind direction the density driven poleward flow always remains surface intensified wind driven shelf currents develop with a considerable degree of independence from the slopepoleward circulation on the shelf the density field is modified by cross shelf buoyancy advection within the boundary layers and by strong vertical mixing the presence of the poleward flow over the slope constitutes an important factor in the behavior of the bottom boundary layer at the shelf break and for the patterns of crossslope circulation

an experimental study of the interaction of two successive solitary waves in the swash a strongly interacting case and a weakly interacting case abstract the interaction of successive solitary waves in the swash zone have been studied using large scale experiments with a simple bathymetry of a constant depth region where the water depth was 1 72 m and a plane beach whose slope was 1 12 two wave cases were considered where two successive solitary waves of the same height were generated one after the other so that the wave crests were separated by the effective wavelength associated with a single solitary wave in the weakly interacting case the swash period associated with a single solitary wave is smaller than the time period separating the successive wave crests which leads to similar run ups for the first and second wave whereas in the strongly interacting case the swash period associated with a single solitary wave is larger than the time period separating the successive wave crests which leads to a significant reduction in the run up of the second wave the degree to which there is an interaction between the swash uprush of the second wave and the downrush of the first wave is found to be related to the solitary wave slope parameter which predicts breaker type of the first wave previous data from literature are found to support this claim measurements of bed shear stress bed pressure and the free surface displacement at a location near the stillwater shoreline are used to describe how the dynamics of the boundary layer differ when the downrush of the first wave meets the incoming second wave in both cases

eulerian flow velocities in the swash zone field data and model predictions measurements of eulerian flow velocity obtained within the swash zone on a relatively steep beach face gradient 1 23 are compared with an extended ballistic swash model the model only requires a friction factor beach slope and terminal bore velocity as input the following model predictions matched well with observations 1 the maximum eulerian flow velocity is the shoreline velocity when it arrives at the fixed point of interest on the beach face 2 at any location the time of flow reversal occurs prior to the shoreline reaching its maximum landward excursion 3 the maximum flow velocity in the backwash is the velocity recorded as the shoreline recedes past the fixed point of interest and this is less than the maximum uprush velocity and 4 the duration of the uprush flow is shorter than the duration of the backwash flow previous studies have already confirmed that the ballistic swash model including friction can accurately predict shoreline motion and maximum run up on steep beaches this study shows that it is similarly successful in predicting eulerian flow velocities during individual swash events the model does not presently account for interacting swash however and so may be less appropriate on gently sloping beaches

a simple criterion for gyre formation by the surface outflow from a strait with application to the alboran sea a survey of relevant numerical laboratory and observational studies combined with our own laboratory experiments suggests that the surface outflow from a strait generally forms a gyre in the adjacent sea if the exit corner is sharp the gyre grows from an initial separation bubble of radius u f where u is the current speed and f the coriolis frequency the criterion for the maintenance of a coastal jet along a curved coast instead of separation and gyre formation seems to be that the rossby number u frw 1 1 with rw the radius of curvature of the exit corner so that the coriolis force can hold the current to the coast this synthesis disregards factors such as the variation of u across the current but applied to the flow through the strait of gibraltar into the alboran sea suggests that a gyre should always form as the exit corner is sharp we suggest though that the relevant curvature is that where the interface between the two layers intersects the seafloor rather than where the sea surface meets the coast if this is the case supercritical flow or some subcritical flows at the eastern end of the strait should still always lead to gyre formation but the observed replacement of the gyre by a coastal jet along the moroccan coast could be related to subcritical flow that is reduced below its normal value by a barotropic fluctuation or by changes in the interface depth in the mediterranean

morphodynamical modelling of field scale swash events in the present work data for three single swash events are selected from those available for an accretive tide that occurred at le truc vert beach france during a measurement field campaign at that location these events are primarily chosen because of the different final bed change they produced namely variable accretion seaward erosion landward deposition and variable erosion along the swash zone these data are compared to results obtained from a state of the art numerical fully coupled 1d morphodynamical shallow water solver driven by measurements made of those events in the lower swash inner surf zone it is found that the hydrodynamics is reasonably well represented although the computed results exhibit reduced maximum inundations in comparison with the observed ones the model reproduces the correct order of magnitude of the morphodynamic change after each event and sometimes the pattern of erosion and deposition but this change is generally underestimated sensitivity analyses are conducted with respect to more uncertain physical parameters and assumed initial conditions they suggest that initial spatial distributions for velocity and pre suspended sediment concentration play a key role in the quantitative and qualitative prediction of the bed change

experimental study of bore driven swash hydrodynamics on impermeable rough slopes abstract a detailed experimental investigation of the hydrodynamics of large scale bore driven swash on impermeable rough beach slopes is described the experiments were carried out on 1 10 impermeable rough slopes with three different surface roughnesses based on 1 3 mm sand 5 4 mm gravel and 8 4 mm gravel the large scale discrete swash event was produced by the collapse of a dambreak generated bore on the beach simultaneous depths and velocities were measured using lif laser induced fluorescence and piv particle image velocimetry respectively yielding better resolution of the hydrodynamics than previous studies depth time series instantaneous velocity profiles depth averaged velocities instantaneous turbulent kinetic energy profiles depth averaged turbulent kinetic energy reynolds stress profiles and bed shear stresses are presented for five cross shore measurement locations in the swash the measurements resolve the backwash shoreline position and the late backwash period when depths are shallow and velocities are high the detailed data can be used to test and develop advanced numerical models for bore driven waves on rough slopes

subsurface processes generated by bore driven swash on coarse grained beaches 1 large scale laboratory experiments presented in this paper involved bore driven swash on permeable immobile coarse grained beaches two different sediments were used d50 1 5 and 8 5 mm resulting in different beach permeability and surface roughness the experiments yielded detailed measurements of swash depth and velocities wetting front pressure and groundwater levels across the swash zone this paper is focused on the processes occurring within the beach the measurements provide the shape of the wetting front and the groundwater table and reveal the behavior of air in the unsaturated region of the beach air is initially at atmospheric pressure but the pressure builds up when air becomes encapsulated between the saturated region formed below the swash and the groundwater table for the 1 5 mm beach entrapped air significantly affected the water exchange between the swash and the subsurface the considerable buildup of interstitial air pressure reduced vertical hydraulic gradients and thus infiltration rates at the lower end of the beach the hydraulic gradients even became negative indicating flow reversal and exfiltration in contrast for the 8 5 mm beach the rate of infiltration was only slightly affected by the buildup of pore air pressure the vertical hydraulic gradients were more than twice the magnitude of those within the 1 5 mm beach the results presented in the paper clarify the mechanisms that drive and impede the water exchange between the surface and subsurface flow in particular infiltration into the initially unsaturated part of the beach and the resulting air entrapment play a significant role in swash and similar flows

surface circulation in the eastern north atlantic from drifters and altimetry a description of the near surface circulation and its properties is the result of the analysis of a drifting buoy data set in the eastern north atlantic between the iberian peninsula the azores and the canary islands world ocean circulation experiment tropical ocean global atmosphere experiment drifters equipped with holey sock drogues centered at 15 m depth collected a total of 14 4 years of data the drifters sampled a rather inhomogeneous velocity field with a weak mean flow regime and eddies of different scales they meandered southward everywhere in the study region except in the iberian coastal transition zone north of 41degreesn where they headed northward the near surface mean velocity field obtained from the drifter data set shows all important mean currents including the poleward portugal coastal countercurrent during the fall winter and early spring off western and northern iberia the southward portugal coastal current the slow offshore southward flow of the portugal current during the whole year the southwestward canary current and the eastward azores current which extends to the vicinity of the african coast near the gulf of cadiz maps of the eddy kinetic energy field were obtained from the drifters and from satellite altimetry it provides the largest part of the total kinetic energy the rate of dispersion is estimated from the lagrangian statistics of the drifting buoys the dispersion of the drifters in the study region is well modeled by a simple description of eddy diffusion assuming homogeneous turbulence ensemble mean diffusivities k and the langrangian integral length scales and timescales l and t were obtained for the zonal and meridional directions the sea surface temperature measured along the drifter trajectories is used to produce estimates of the eddy diffusivity which is compared with the diffusivity estimates obtained from the theory of taylor the eddy diffusivity is found to be approximately proportional to the eddy kinetic energy discrete eddies and meanders were observed using drifters and altimetry in order to map and describe their geographical distribution and characteristics in the eastern north atlantic

extreme cross shelf transport induced by eddy interactions southwest of iberia in winter 2001 1 unusually high for winter time satellite derived chlorophyll a concentrations southwest of iberia were detected in february 2001 analysis of satellite data seawifs avhrr sea level anomaly from topex poseidon and ers revealed that the phytoplankton rich waters were associated with an extremely long filament up to 400 km induced by eddy eddy interactions occurring in the vicinity of the continental margin the eddy interaction occurred simultaneously with an accumulation of coastal fresh water over the shelf the event promoted an export of biogenic material offshore along with an estimated shelf flushing in a 5 to 6 day period that resulted in a dramatic offshore growth of phytoplankton a description of the event is given and preliminary estimates of the cross shelf transport are presented and discussed

glider observations of the northwestern iberian margin during an exceptional summer upwelling season glider observations from the northwestern iberian margin during the exceptionally strong 2010 summer upwelling season resolved the evolution of physical and biogeochemical variables during two upwelling events upwelling brought low oxygen eastern north atlantic central water from 190 m depth onto the shelf up to a depth of 50 m during the two observed periods of upwelling a poleward jet developed over the shelf break the persistent upwelling favourable winds maintained equatorward flow on the outer shelf for two months with no reversals during relaxation periods a phenomenon not previously observed during upwelling near surface chlorophyll a concentration increased by more than 6 mg m 3 oxygen supersaturation in the near surface increased by more than 20 6 days after the chlorophyll a maximum

flow velocities sediment transport and morphological change in the swash zone of two contrasting beaches abstract as part of a large uk research project focussing on the role of swash on shoreline change two field experiments were conducted on contrasting sandy beaches a flatter dissipative beach and a steeper intermediate beach this paper describes almost 300 h of nearshore velocity data collected during this project supplemented by suspended sediment transport sediment tracer and beach profile data during both field experiments the upper part of the beach experienced progressive accretion indicating that onshore sediment transport prevailed in the swash and inner surf zones suspended sediment transport and tracer dispersal were also onshore the associated cross shore flow field was however dominated by offshore directed mean flows especially on the steeper beach velocity skewness defined as u 3 u 2 1 5 where u is the cross shore velocity and kurtosis defined as u 3 u u 2 2 were mainly directed offshore implying that energetics based sediment transport models are unable to predict the direction of sediment transport in the swash zone possible explanations for the observed accretion include enhanced bed shear stress on the uprush due to in exfiltration effects flow acceleration and or bore turbulence and advection of bore entrained sediment into the swash zone

rans v2 f simulation of a swash event detailed flow structure the flow structure of a swash event over a uniform slope is studied using a rans vof numerical model coupled with a v2 f turbulence closure the model is compared with experimental data of recent laboratory experiments the ability of the turbulence modelling for simulating swash flow and the evolution of the computed bed shear stress during run up and run down are investigated the agreement between numerical results and measured data such as water depth depth averaged velocity and bed shear stress is very good during run up main discrepancies are found during run down the paper also examines the aeration of the water layer in the swash flow taking advantage of the plic method for computing the air water interfaces air is continuously entrapped in the swash front and released at its rear during run up a detailed analysis indicates that the flow reversal is initiated near the bottom at the outer boundary of the swash zone and progresses landward the study highlights the asymmetry between run up and run down during run up the swash front propagation determines the turbulence properties and the bed shear stress profile on the beach whereas the flow properties are more homogeneously distributed in the swash area during run down

palaeoproductivity changes and upwelling variability in the galicia mud patch during the last 5000 years geochemical and microfloral evidence theholocenepalaeoclimatichistoryofthegaliciancontinentalshelfhasbeeninvestigatedthrough theanalysesofdiatomremains othersiliceouscompounds biogenicsilica bsi andmetalscontentinamul tiproxyapproachtoagravitycorerecoveredfromthegaliciamudpatch nwiberianpeninsula coveringthe last 5000 years downcore changes in diatom assemblages composition and abundance reflect changes in diatomproductionrelatedtolong short termvariationsinclimate regionaloceanography upwellingstrength and river influx off the coast of nw spain and portugal palaeoclimatic variability was related to the relative strengths and position of the azores high and iceland low pressure cells metals and microflora fluctuations are interpreted as changes in the riverine influence and upwelling intensity paced by oceanographic atmos pheric and climatic changes lack of diatoms between 4700 3300 and 1800 1200 cal yr bp could be linked to early diagenetic processes taking place in the sediment after burial biogenic barium baexcess metals and diatomassemblages showageneralincreaseofmarineproductivityforthelast1200cal yrbp between800 and500cal yrbphighproductionofthemicrofloraistriggeredbyinfluxofriver derivednutrientsundercon ditionsofswwindsandstormsresultingfromanaonegative likephase thebiosiliceousandgeochemical signatures of sediments from the last 500 cal yr bp indicate conditions of enhanced upwelling and increased

numerical model of swash motion and air entrapment within coarse grained beaches abstract the paper presents a numerical model for bore driven swash on permeable coarse grained beaches the surface flow module is modelled using the non linear shallow water equations nlswes solved using the godunov based finite volume ader scheme which is suitable for handling steep bores as well as large source terms in the nlswes the subsurface flow comprises i infiltration and exfiltration modelled as vertical piston like flow ii horizontal pore air movement within the unsaturated region of the beach iii the horizontal groundwater flow model predictions of the surface and subsurface flow are in good agreement with measurements from large scale laboratory experiments for swash on permeable immobile beaches in these simulations air velocity was sufficiently small to justify using darcy s resistance law for the air flow whereas the quadratic forchheimer law had to be used for the infiltration and groundwater flow the validated numerical model provides insight into the surface subsurface water exchange for bore driven swash on coarse grained beaches the impact of air entrapped between the wetting front and the groundwater level on the water exchange is examined in particular

on the cross shore profile change of gravel beaches abstract this paper investigates cross shore profile changes of gravel beaches with particular regard to discussing the tendency for onshore transport and profile steepening in the swash zone the discussion includes observed morphological changes on a gravel beach from experimental investigations at the large wave flume gwk in hanover germany during the tests all the profile changes occurred in the swash zone resulting in erosion below the still water line swl and formation of a berm above the swl we investigate the profile evolution evaluating the transport rates from a bed load sediment transport formulation coupled with velocities calculated from a set of boussinesq equations that have been validated for its use in the surf and swash zones lynett p j wu t r and liu l f p 2002 modelling wave runup with depth integrated equations coastal engineering 46 89 107 otta a k and pedrozo acuna a 2004 swash boundary and cross shore variation of horizontal velocity on a slope in j m smith editor proceedings 29th international conference on coastal engineering world scientific lisbon portugal pp 1616 1628 we discuss the influence of bottom friction on the predicted profiles using reported friction factors from experimental studies it is shown that the use of a different friction factor within a realistic range in each phase of the swash uprush and backwash improves prediction of the beach profiles although quantitative agreement between the measured and computed profile evolutions is not satisfactory furthermore if the friction factor and the transport efficiency c of the sediment transport formulation are kept the same in the uprush and backwash accurate representation of profile evolution is not possible indeed the features of the predicted profiles are reversed however when the c parameter is set larger during the uprush than during the backwash the predicted profiles are closer to the observations differences between the predicted profiles from setting non identical c values and friction factors for the swash phase are believed to be linked to both the infiltration effects on the flow above the beachface and the more accelerated flow in the uprush

airglow imaging of gravity waves 2 critical layer filtering images of the variations of oh intensities have been recorded by a three station network of scanning radiometers in southwestern ontario during the period from may until september 1998 the ensemble of gravity waves seen in all three instruments is analyzed and observed to have a strong dependence in their propagation direction with the majority of waves seen at each of the three sites having a horizontal wave vector in the northeast direction in order to understand these results a model of the transmission of gravity waves through the atmosphere was employed the gravity waves observed by the oh scanning radiometers ohscrs are assumed to originate in the troposphere with an isotropic spectrum meaning that the average wave amplitudes are equal in all directions the gravity waves propagate upward where they will undergo a selection process owing to the effect of the background winds using the horizontal winds from the horizontal wind model hwm 93 the transmission of gravity waves from a tropospheric source is modeled and shown to be consistent with the observations the strong zonal winds account for the summer eastward and winter westward propagation but it is the tidal components of the meridional wind that account for the northward tendency of wave propagation and the corresponding relative absence of southward propagating waves in order to further validate the transmission model winter measurements from the ohscr data set are examined and shown to be consistent

laboratory and numerical study of dambreak generated swash on impermeable slopes new laboratory experiments have produced detailed measurements of hydrodynamics within swash generated by bore collapse on a steep beach the experiments are based on a dambreak rig producing a highly repeatable large scale swash event enabling detailed measurements of depths and velocities at a number of locations across the swash zone experiments were conducted on two beaches differentiated by roughness results are presented for uprush shoreline motion flow depths depth averaged velocity velocity profiles and turbulence intensity estimates of the time and spatially varying bed shear stress are obtained via log law fitting to the velocity profiles and are compared with the shear plate measurements of barnes et al 2009 for similar experimental conditions experimental results are compared with model predictions based on a nlswe model with momentum loss parameterised using the simple quadratic stress law in terms of the depth averaged velocity predicted and measured flow depths and depth averaged velocities agree reasonably well for much of the swash period but agreement is not good at the time of bore arrival and towards the end of the backwash the parameterisation of total momentum loss via the quadratic stress law cannot adequately model the swash bed shear stress at these critical times

flow velocity and sediment transport in the swash zone of a steep beach detailed measurements of flow velocity and total sediment load were obtained in the swash zone on a steep beach swash motion was measured using ducted impeller flow meters and capacitance water level probes during wave uprush the onshore flow increased almost instantaneously from zero to its maximum velocity after the arrival of the leading edge of the swash lens and subsequently decreased gradually to zero for the remainder of the uprush during backwash the offshore flow increased steadily from zero to its maximum towards the end of the backwash and dropped rapidly to zero as the beach fell dry the duration of backwash was typically longer than that of uprush and maximum water depth on the beach was attained just prior to the end of the uprush the total sediment load was measured for 35 individual wave uprush events using a sediment trap the amount of sediment transported by a single uprush was typically two to three orders of magnitude greater than the net transport per swash cycle difference between uprush and backwash inferred from surveys of beach profile change the measured immersed weight total load transport rate displayed a strong relationship with the time averaged velocity cubed which is consistent with equations for both bedload transport and total load transport under sheet flow conditions the bagnold 1963 1966 bedload transport model was tested against our field data and yielded ib ku3tu tan tan where ib is the immersed weight of bedload transported during the entire uprush kg m 1 k is a coefficient kg m 4 s2 u is the time averaged flow velocity for the uprush m s 1 tu is the uprush duration s is the friction angle of the sediment and is the beach slope the empirically determined value for the coefficient k was 1 37 0 17

large eddy simulation of dam break driven swash on a rough planar beach turbulence characteristics in the swash zone are investigated using a 3d large eddy simulation model the numerical model is implemented based on openfoam which solves the filtered navier stokes equations for two immiscible fluids with a standard smagorinsky sub grid scale closure the numerical model is validated with laboratory data for swash flow driven by a dam break apparatus the model results demonstrate that the main characteristics of turbulence in the swash zone are different from those in the surf zone which are mainly induced by surface wave breaking during uprush phase bore generated turbulence has 2d turbulence characteristics because of limited water depth near bed generated turbulence is mainly observed during backwash turbulence production and turbulent dissipation rate estimated from the model results indicate an imbalance possibly due to advection at swash front and large roughness used touching down of turbulent coherent structure tcs is observed during uprush which drives intense bed shear stress during the backwash interaction between tcs and bed is less clear however finger like patterns in the spatial extent of bed shear stress and vertical components of vorticity are predicted during the backwash the location of the strongest finger patterns in the vertical direction is collocated with that of maximum turbulence production these finger patterns are likely caused by boundary layer instabilities injected vertically from the bed this article is protected by copyright all rights reserved

quasi synoptic transport budgets and water mass transformation in the azores gibraltar strait region during summer 2009 abstract we describe the circulation patterns in the azores gibraltar strait region north eastern atlantic during the 2009 caibox cruise on the basis of hydrographic and direct current velocity measurements this study offers new data for a region where importation of central waters subpolar and subtropical modes of eastern north atlantic central water and exports of mediterranean water are strongly related to large scale dynamics in the north atlantic ocean azores current mediterranean water system the description is backed up quantitatively by the results of a box inverse model which was used to obtain absolute water mass transport values consistent with thermal wind equations and with conservation of volume salt and heat the contributions of water masses were determined in an extended optimum multiparameter analysis from a quasi synoptic point of view providing detail in addition to volume salt and heat transport the surface subsurface large scale current system in the region consists of the azores current 13 1 2 5 sverdrup sv 1 sv 10 6 m 3 s 1 the azores counter current 5 2 2 1 sv the portugal current 4 5 1 4 sv and the canary current 7 1 1 1 sv broadly speaking central waters are imported into the caibox region at a rate of 1 6 0 9 sv and mediterranean water is exported at a rate of 1 5 0 4 sv the downwelling of central waters west of gibraltar strait was quantified at 1 1 sv not all this volume participates in mw formation but 0 8 sv of entrained central waters of which 0 5 sv are from central waters of subpolar origin and 0 3 sv from subtropical central waters of the 4 9 sv of subtropical central waters advected by the azores current about 0 7 sv would reach the gulf of cadiz region either to take part in central water entrainment or to flow across the gibraltar strait as part of the atlantic inflow to the mediterranean sea

baroclinic eddy generation at a sharp corner in a rotating system laboratory experiments were conducted to investigate the generation of anticyclonic gyres by separation of a surface current from a coast in a rotating two layer system the experiments were motivated by the hypothesis that the flow of coastal currents around capes can generate oceanic eddies as well as by the observation of gyres at the mouths of various straits in the experiments the gyre is formed when the current which flows with the coast to its right if one is oriented in the downstream direction encounters a sharp convex corner the current overshoots the corner loops to the right and reattaches to the coast downstream of the corner between the current loop and the coast is an anticyclone whose width grows with time if a countercurrent flows under the surface current a similar separation in the lower layer results in the generation of a cyclone as well under some circumstances the cyclone and anticyclone advect each other away from the coast as a heton previous studies on related systems found that the corner must be sufficiently sharp for a gyre to form i show that for a very sharp corner the angle made by the corner must be above a critical value of between 40 and 45 for a gyre to form this is in contrast to nonrotating flows of comparable rayleigh number which will separate from a sharp corner at virtually any angle for angles below the critical value the current profile downstream of the corner changes as a function of corner angle indicating that it is the stagnation of the flow nearest the wall which causes the anticyclone to form this stagnation is reminiscent of the two dimensional nonrotating picture of viscous boundary layer dynamics forcing separation of a boundary current however the gyre grows more slowly when the lower layer is much thicker than the upper layer indicating that baroclinic processes are at least quantitatively important in the generation of the gyre by varying the initial condition of the current it is shown that the gyre formation is not a product of the interaction of the nose of the current with the corner in conclusion the experiments indicate that the basic mechanism of gyre formation may be viscous boundary effects as in nonrotating systems but that rotation tends to inhibit eddy generation while baroclinic effects tend to enhance it

swash zone sediment transport modes abstract the result of field experiments designed to investigate the relative proportions of bedload and suspended load are described the ratio of bedload to suspended sediment load in the swash zone is examined in both swash and backwash on four beaches by measuring the amounts collected in a sediment trap bedload transport is found to dominate the backwash the relative proportions of bedload and suspended load change over the tidal cycle with increasing bedload dominance at low tide the total amount of sediment transported as swash and backwash is noticeably greater at high tide than at low tide more sediment is transported on the flood tide than on the ebb

circulation on the northwestern iberian margin vertical structure and seasonality of the alongshore flows abstract we describe the seasonal cycle of the alongshore flows on the northwestern iberian margin and explain what are the important mechanisms forcing the system we used a 20 year model simulation at 2 3 km horizontal resolution with realistic atmospheric forcing and covering the whole western iberian margin the model results are compared with satellite data with data measured at two moored buoys and with a compilation of current meter data available for the study region we show that currents over the slope are divided in three different cores the iberian poleward current ipc occupying the top 350 m a deeper core at mediterranean water levels 600 1200 m and in between the two an equatorward core centered just beneath the ipc core the upper slope countercurrent uscc the ipc is present almost yearlong including in summer months when it is close to the shelf break and topped by the equatorward upwelling jet after september the ipc intensifies and its core surfaces heat and salinity budgets on the shelf and slope are dominated by advection confirming the important role of the ipc in driving the temperature and salinity seasonal cycles analysis of the seasonal cycle of the barotropic vorticity equation on the slope shows that the main forcing mechanism of northward flows is the joint effect of baroclinicity and relief jebar whose contribution is higher in summer than in winter in december and january when the ipc is stronger and surface intensified the main contribution is from southerly winds the cross shore analysis of these terms shows that jebar decreases substantially at the core of the ipc because as advection terms become important the northward density flux diminishes the local meridional density gradients resulting in the decrease of jebar in the months of strong ipc

sediment transport partitioning in the swash zone of a large scale laboratory beach abstract swash zone sheet flow and suspended sediment transport rates are estimated on a coarse sand beach constructed in a large scale laboratory wave flume three test cases under monochromatic waves with wave heights of 0 74 m and wave periods of 8 and 12 2 s were analyzed sediment flux in the sheet flow layer exceeds several hundred kg m 2 s 1 during both uprush and backwash suspended sediment flux is large during uprush and can exceed 200 kg m 2 s 1 instantaneous sediment flux magnitudes in the sheet layer are nearly always larger than those for suspended sediment flux however sediment transport rates those integrated over depth indicate that suspended load transport is dominant during uprush for all cases and during the early stages of backwash except in the case for the 12 2 s wave case when the foreshore was steeper results could not be obtained for an entire swash event and were particularly truncated during backwash when water depths fell below the elevation of the lowest current meter

swash zone sediment suspension and transport and the importance of bore generated turbulence a study of swash zone sediment transport was conducted at gleneden beach oregon during february 25 28 1994 the data collected included suspended sediment concentration ssc sea surface elevation and velocity initially 4 and 8 cm above the bed at three cross shore locations within the swash zone spanning high tides ensemble averages of 6 9 and 12 s duration swash events showed that the uprush suspension was high concentrated in the leading edge and nearly vertically uniform above the lower 1 2 cm of the water column shortly after the sensors were inundated by run up the sediment rapidly settled out of the water during flow reversal the ssc was small but increased again in the backwash backwash vertical profiles were markedly different from uprush profiles with much of the suspension being confined to very near the bed where strong vertical gradients in ssc existed these marked differences show that the backwash is not simply the reverse of the uprush implying significant differences in the underlying fluid dynamics and sediment transport mechanisms backwash sediment suspension increased with flow duration however ensemble averaged ssc profiles of varying duration showed that the backwash concentrations were not consistent at the same temporal phases which suggests that water depth in addition to flow duration may be a controlling factor strong cross shore gradients in ssc suggest that bore derived turbulence may affect local sediment transport specifically our data show this bore generated turbulence turbulent kinetic energy directly influences local sediment suspension hence standard bed shear bagnold type sediment transport models may no longer be valid in the vicinity of the bore in the vicinity of the bore a higher correlation between bore generated turbulence and suspended sediment transport was found than between a bagnold type formulation and suspended sediment transport

evolution of the turbulence structure in the surf and swash zones the velocity field and turbulence structure within the surf and swash zones forced by a laboratory generated plunging breaking wave were investigated using a particle image velocimetry measurement technique two dimensional velocity fields in the vertical plane from 200 consecutive monochromatic waves were measured at four cross shore locations shoreward of the breaker line the phase averaged mean flow fields indicate that a shear layer occurs when the uprush of the bore front interacts with the downwash flow the turbulence characteristics were examined via spectral analysis the larger scale turbulence structure is closely associated with the breaking wave and the bore generated turbulence in the surf zone then the large scale turbulence energy cascades to smaller scales as the turbulent kinetic energy tke evolves from the outer surf zone to the swash zone smaller scale energy injection during the latter stage of the downwash phase is associated with the bed generated turbulence yielding a 1 slope in the upper inertial range in the spatial spectra depth integrated tke budget components indicate that a local tke equilibrium exists during the bore front phases and the latter stage of the downwash phases in the outer surf zone the tke decay resembles the decay of grid turbulence during the latter stage of the uprush and the early stage of the downwash as the production rate is small because of the absence of strong mean shear during this stage of the wave cycle as well as the relatively short time available for the growth of the bed boundary layer

eddy formation through the interaction between the leeuwin current leeuwin undercurrent and topography abstract the surface and subsurface circulation off south west australia was simulated using the regional ocean modelling system roms a primitive equation ocean model with terrain following s coordinates the major currents in this region the leeuwin current and leeuwin undercurrent were reproduced by specifying only temperature and salinity distributions from climatology the application of wind stress subsequent to the model reaching a quasi steady state resulted in the generation of the seasonal capes current a northward flowing current on the continental shelf associated with coastal upwelling the simulated currents compared well with the observed current patterns including the location and maximum current speeds shelf topography variations and bottom shear which generated vorticity influenced eddy formation eddies separated from the leeuwin current and the leeuwin undercurrent migrated westward and exited the model domain through merging dissipating or through an open boundary in the model simulations the undercurrent produced mostly cyclonic eddies due to strong negative vorticity where the current flowed against the continental slope the leeuwin current produced anticyclonic warm core eddies initiated from the formation of meanders which were strongest at the surface the eddy field was dominated by anticyclonic eddies at the surface and cyclonic eddies at 500 m the interaction between the leeuwin current and leeuwin undercurrent led to the formation of eddy pairs

boundary layer dynamics in the swash zone under large scale laboratory conditions this paper presents the results of a laboratory experiment of swash hydrodynamics on a coarse sand barrier beach backed by a lagoon boundary layer dynamics have been analyzed using the high resolution near bed velocities measured by acoustic doppler velocity profilers deployed in the swash zone swash events have been ensemble averaged in order to study mean hydrodynamic patterns a proposed velocity gradient criterion allowed identification of the boundary layer growth during the backwash phase but it was unable to characterize boundary layer variability during uprush cross shore velocity profiles were well represented by the logarithmic model for a large portion of the ensemble averaged swash duration uprush and backwash logarithmic estimated friction factors were of the same order of magnitude with a strong variability related to the boundary layer growth during the backwash the momentum integral method provided smaller bed shear stresses than the logarithmic model a result possibly related to either the assumptions involved in the momentum integral method or to an underestimation of the boundary layer thickness during uprush a decrease of friction coefficients for increasing reynolds numbers at the early backwash was observed this behavior is consistent with traditional results for steady and uniform flows in a transitional regime