reconstructability of three dimensional upper ocean circulation from swot sea surface height measurements abstractutilizing the framework of effective surface quasigeostrophic esqg theory this study explores the potential of reconstructing the 3d upper ocean circulation structures including the balanced vertical velocity w field from high resolution sea surface height ssh data of the planned surface water and ocean topography swot satellite mission specifically the authors utilize the 1 30 submesoscale resolving ofes model output and subject it to the swot simulator that generates the along swath ssh data with expected measurement errors focusing on the kuroshio extension region in the north pacific where regional rossby numbers range from 0 22 to 0 32 this study finds that the esqg dynamics constitute an effective framework for reconstructing the 3d upper ocean circulation field using the modeled ssh data as input the esqg reconstructed relative vorticity and w fields are found to reach a correlation of 0 7 0 9 and 0 6 0 7 respectively in the 1000 m upper ocean when compared to the orig

late variscan tectonic evolution by thinning of earlier thickened crust an 40ar39ar study of the montagne noire southern massif central france abstract 40ar 39ar age determinations on samples selected on deformational criteria form the basis of a proposal of a new detailed tectonometamorphic history of the montagne noire the southern part of the massif central france this range is classically divided into a cover and an axial gneissic and migmatitic core which was metamorphosed under high t medium p conditions the basement is structurally overlain by epimetamorphic paleozoic sediments in the north in the south equivalent rocks form a well known pile of recumbent nappes the variscan history of this area comprises early shortening and thickening of the continental crust the climax of this event took place around 320 ma ago as is shown by previous rb sr data and by 40ar 39ar measurements new developments in structural analyses have led to a better understanding of the late evolution of the area in terms of diapiric uplift of the core south southwestwards verging recumbent nappes have been emplaced and were weakly metamorphosed in their lower parts this movement was accompanied and followed by dextral extensional wrenching of the paleozoic cover along the northern and southern margins of the axial zone attendantly ductile shear zones were formed in order to decipher the complex history three structural levels have been dated with the 40ar 39ar method these levels are 1 the migmatitic and gneissic series in the axial core where micas yield ages of c 315 ma 2 mylonites from the northern and southern shear zones where biotites and muscovites yield ages of c 310 ma 3 muscovites and biotites from the epimetamorphic nappe structures yielding ages of c 297 ma the later ages may represent a younger thermal pulse these data are compared and discussed in the light of previous radiometric studies of the area and precise biostratigraphic constraints a detailed geodynamic evolution of the studied segment is proposed

direct observations of microscale turbulence and thermohaline structure in the kuroshio front 1 direct observations of microstructure near the kuroshio front were conducted in august 2008 and october 2009 these show negative potential vorticity pv in the mixed layer south of the front where directly measured turbulent kinetic energy dissipation rates are an order magnitude larger than predicted by wind scaling these elevated dissipation rates scale better with an empirical scaling which considers local wind and ekman buoyancy flux driven by downfront wind near zero pv in the thermocline under the kuroshio mainstream is observed at 200 300 m depth with dissipation exceeding open ocean thermocline values by factors of 10 100 overall the large turbulent dissipation rates measured in the kuroshio can be categorized into two groups one characterized by low richardson number along the kuroshio front thermocline and the other characterized by high stratification away from the kuroshio mainstream the former is attributed to mixing by unbalanced frontal ageostrophic flows and the latter is attributed to internal wave breaking on average both groups appear in regions of large horizontal density gradients observed thermohaline structure shows low salinity tongues from the surface to over 300 m depth and deep cold tongues extending upward from 500 to 100 m depth in a narrow 20 km zone suggesting down and upwelling driven by geostrophic straining which is confirmed by quasigeostrophic omega equation solutions this implies that adiabatic along isopycnal subduction and diabatic diapycnal turbulent mixing acting in tandem at the kuroshio front likely contribute to npiw formation

on sampling the ocean using underwater gliders surface to 1000 m and back took 5 6 h and covered 5 3 km resulting in a horizontal speed of 0 26 m s 1 seasoar undulated between the surface and 400 m completing a cycle in 11 min while covering 2 6 km for a speed of 3 9 m s 1 adjacent profiles of temperature and salinity are compared between the two platforms to prove that each is accurate spray and seasoar data are compared through sections isopycnal spatial series and wave number spectra the relative slowness of the glider results in the projection of high frequency oceanic variability such as internal waves onto spatial structure the projection is caused by doppler smearing because of finite speed and aliasing due to discrete sampling the projected variability is apparent in properties measured on depth surfaces or in isopycnal depth no projected variability is seen in observations of properties on constant density surfaces because internal waves are intrinsically filtered wave number spectra suggest that projected variability affects properties at constant depth at wavelengths shorter than 30 km these results imply that isobaric quantities like geostrophic shear are valid at wavelengths longer than 30 km while isopycnal quantities like spice may be analyzed for scales as small as a glider measures

three dimensional structure of frontal waves and associated salinity minimum formation along the kuroshio extension abstract high resolution hydrographic observations were conducted in september 2002 to describe the detailed structure of frontal waves along the kuroshio extension frontal waves were observed both in the upper and intermediate layers which corresponded to the depths of north pacific subtropical mode water and north pacific intermediate water respectively the frontal wave in the upper layer preceded the intermediate depth frontal wave by about 1 4 wavelength the vertical phase lag created situations in which the low salinity oyashio water in the intermediate layer was superimposed below the upper layer high salinity kuroshio water thus forming a vertical salinity minimum the frontal waves with a wavelength of about 200 km and a phase speed of 0 2 0 3 m s 1 propagating in the downstream direction were consistent with those from satellite images vertical velocity fields were estimated with the quasigeostrophic omega equation downwelling around the trough from the crest to trough of the intermedia

small mesoscale features at a meandering upper ocean front in the western ionian sea mediterranean sea vertical motion and potential vorticity analysis abstract transient mesoscale and submesoscale processes such as small eddies and filaments could play a fundamental role in the marine ecosystem especially in oligotrophic seas like the mediterranean however very little is known about the biological and physical dynamics characterizing such structures in this work the 8 km horizontal resolution data collected during the symplex 1998 survey are analyzed to describe the physical dynamics of small mesoscale features along the atlantic ionian stream western ionian sea the data were optimally interpolated over a regular grid and used to compute the 3d ageostrophic circulation by solution of the q vector formulation of the omega equation the relative importance of stratification relative vorticity and twisting terms in the rossby ertel potential vorticity is thus examined along selected isopycnals together with the associated vertical motions and vortex stretching a surface cyclonic eddy 15 km of radius was observed near a meander of the atlanti

a field study of the behaviour of an anticyclonic eddy on the catalan continental shelf nw mediterranean abstract through the analysis of satellite thermal images mesoscale anticyclonic eddies have been observed to recurrently drift along the nw mediterranean coasts the presence of these eddies is known to cause transient inversions of the shelf slope current by means of an exhaustive analysis of sea surface temperature images a group of anticyclonic structures were monitored in september 2001 one of these eddy like features was tracked and intensely surveyed by means of conductivity temperature depth ctd casts and repeated fast surveys with n shuttle oscillating ctd and acoustic doppler current profiler adcp measurements during the et2001 oceanographic cruise a well developed anticyclonic eddy was surveyed over the catalan continental shelf 60 km north of barcelona in situ velocity data revealed that the anticyclonic motion was characterized by surface velocities of 50 cm s and a diameter of about 45 km the signal of the eddy was found down to 100 m depth well below the seasonal thermocline the passage of the eddy modified the local flow involving advection and subduction of surrounding waters

intensive surveys of the azores front 2 inferring the geostrophic and vertical velocity fields the geostrophic and vertical velocity fields are inferred using density and horizontal velocity data from three seasoar acoustic doppler current profiler surveys of the azores front the analysis is a two step procedure consisting of 1 objective analyses to reflect the observed length scales and 2 dynamical adjustments so that the density field is statically stable and the velocity field is in geostrophic balance the vertical velocity is inferred using a version of the quasi geostrophic omega equation in which the stratification is allowed to vary in the horizontal the resulting vertical velocity peaks at 2 10 4 m s 1 at 200 300 m there is a tendency for the denser water to the north of the front to be downwelled while the warmer water to the south is upwelled the implied heat flux exceeds 10 w m 2 near 100 m depth so the upper 100 m is warmed while the lower water column is cooled tending to stratify the upper ocean ageostrophic horizontal flow is toward the dense side of the front at the surface the dominant terms in the density balance are time rate of change and horizontal advection the inferred circulation cells may be an important mechanism of subduction in the upper ocean

measurements of tidal flow around a headland with a shipboard acoustic doppler current profiler a shipboard acoustic doppler current profiler adcp and moored current meters were used to obtain detailed measurements of the spatial structure of the tidal flow around a headland in vineyard sound massachusetts where tidal currents typically range from 50 to 70 cm s 1 eight shipboard surveys were conducted each of which followed one of five trapezoidal tracks in the vicinity of the headland completing 11 12 circuits in the course of the tidal cycle 12 4 hours the measurements from the adcp compare favorably with moored velocity measurements at two locations rms deviations of 3 cm s 1 but the comparison showed more scatter at two other sites rms deviations of 7 cm s 1 the adcp measurements from separate cruises were merged to form a composite spatial representation of the tidal and residual currents providing resolution of the spatial structure of the flow around the headland at scales from several hundred meters to 10 km the semidiurnal tidal flow is relatively uniform in space roughly following the bathymetry around the headland while a residual current field consists of counterrotating eddies on either side of the headland with spatial scales of 5 8 km and velocities as high as 25 cm s 1 the instantaneous current field indicates the formation of transient eddies on the downstream side of the headland during flood and ebb with clear evidence of flow separation near the tip of the headland

intensive surveys of the azores front 1 tracers and dynamics the hypothesis that fronts are sites of active subduction is examined using density temperature salinity and horizontal velocity data from a trio of surveys of the azores front done in may 1991 and march 1992 these surveys were made using a seasoar equipped with a conductivity temperature depth profiler and a shipboard acoustic doppler current profiler the potential density and potential vorticity indicate that dense water from the north side of the front may be sliding down beneath the surface outcrop this apparently subducting isopycnal has a great deal of temperature and salinity variability horizontal velocity is nearly parallel to isopycnals indicating that the time rate of change and vertical advection must be small the thermal wind balance is observed to be valid especially in the region of the largest horizontal density gradients shear at the base of the mixed layer is likely due to near inertial motions the potential vorticity is dominated by the planetary vorticity except at the front where vertical shears the tilting term become large the tilting term acts to reduce the magnitude of the potential vorticity at the front in agreement with simple theoretical models the magnitude of the tilting term is similar to the total vorticity in the seasonal thermocline

inferring the subduction rate and period over the north atlantic abstract the annual rate at which mixed layer fluid is transferred into the permanent thermocline that is the annual subduction rate sann and the effective subduction period x1d4af eff is inferred from climatological data in the north atlantic from its kinematic definition sann is obtained by summing the vertical velocity at the base of the winter mixed layer with the lateral induction of fluid through the sloping base of the winter mixed layer geostrophic velocity fields computed from the levitus climatology assuming a level of no motion at 2 5 km are used the vertical velocity at the base of the mixed layer is deduced from observed surface ekman pumping velocities and linear vorticity balance a plausible pattern of sann is obtained with subduction rates over the subtropical gyre approaching 100 m yr twice the maximum rate of ekman pumping the subduction period x1d4af eff is found by viewing subduction as a transformation process converting mixed layer fluid into stratified thermocline fluid the effective

reconstructing upper ocean vertical velocity field from sea surface height in the presence of unbalanced motion abstractreconstructability of upper ocean vertical velocity w and vorticity fields from high resolution sea surface height ssh data is explored using the global 1 48 horizontal resolution mitg

the three dimensional circulation near the eastern north pacific subtropical front abstract the purpose of our study is to describe and compute the large scale three dimensional circulation near the subtropical front in the eastern north pacific along 31 n this was accomplished through the use of four extensive hydrographic surveys historical wind stress data and also the movement of surface drifters our results indicate that in wintertime surface water sinks on the north side of the front and rises on its south side during the summer however the subtropical salty surface water overflows the frontal area to the north potential vorticity and heat are best conserved in a vertical flow pattern where the annual mean ekman convergence sinks to a depth of 300 m and water upwells throughout the main thermocline the computed horizontal flow below 700 m amounts to less than 0 6 cm s 1 both strength and direction depend greatly on the treatment of noise within the data set and also on the conservation statement that is specified in addition to geostrophic and hydrostatic dynamics a q

three dimensional circulation in the nw africa coastal transition zone abstract high resolution data collected southeast of the canary islands during late winter 2006 are analyzed to describe the hydrography and three dimensional circulation in the coastal transition zone off nw africa the data are optimally interpolated over a regular grid the geostrophic velocity field is calculated and the q vector formulation of the omega equation is used to compute the quasi geostrophic qg mesoscale vertical velocity the coastal transition zone is divided into upwelling frontal and offshore regions with distinct physical and dynamic characteristics the upwelling region is characterized by cold and weakly stratified waters flowing towards the equator with a poleward undercurrent of approximately 0 05 m s 1 over the continental slope the frontal region exhibits a southwestward baroclinic jet associated with cross shore raising isopycnals the jet transport is close to 1 sv with maximum velocities of 0 18 m s 1 at surface decreasing to 0 05 m s 1 at 300 db vertical sections across the frontal region show the presence of deep eddies probably generated by the topographic blocking of the islands to the southward current as well as much shallower eddies that likely have arisen as instabilities of the baroclinic upwelling jet the qg mesoscale vertical velocity field is patchy estimated to range from 18 to 12 m day 1 with the largest absolute values corresponding to an anticyclonic eddy located south of fuerteventura island these values are significantly larger than estimates for other vertical velocities diapycnal vertical velocities associated with mixing in the frontal region a few meters per day and wind induced vertical velocities non linear ekman pumping arising from the interaction between the wind stress and the background vorticity maximum values of a few meters per day linear ekman pumping due to the divergence of ekman transport a fraction of a meter per day or the coastal constraint in the upwelling region about 0 7 m day 1 however the patchiness in both the qg mesoscale vertical velocity and the non linear ekman pumping velocity cause their integrated vertical transports to be one order of magnitude smaller than either coastal ekman transport 0 08 sv integrated linear ekman pumping 0 05 sv or diapycnal transfer about 0 1 0 2 sv the pattern of the near surface fluorescence field is a good indicator of these different contributions with large homogeneous values in the coastal upwelling region and a patchy structure associated with the offshore mesoscale structures

a diagnostic analysis of the presidents day storm of february 1979 abstract a diagnostic analysis of the presidents day storm of february 1979 is used to extend and quantify earlier findings of bosart the initial growth of cyclonic vorticity in the lower troposphere is driven primarily by convergence along the carolina coastal front rapid cyclone spinup accompanies the approach of a potent midtropospheric short wave trough from the ohio valley an analysis of the vorticity structure discloses that cyclone spinup is enhanced by the vertical advection of vorticity in the strongly cyclonic in situ vorticity environment along the coast as the upper level trough overspreads the region similarly a downward extension of high semige strophic potential vorticity air accompanies a tropopause fold to the west of thecyclone and prior to the rapid cyclogenesis stage confirming a result of uccellini and others semigeostrophic potential vorticity is poorly conserved however and there is evidence for a separate region of semigeostrophic potential vorticity growth below 800 mb n

restratification at a california current upwelling front part i observations abstracta coordinated survey between a subsurface lagrangian float and a ship towed triaxus profiler obtained detailed measurements of a restratifying surface intensified front above 30 m within

the subpolar front of the japan east sea part ii inverse method for determining the frontal vertical circulation abstract an inverse method for inferring vertical velocities from high resolution hydrographic velocity surveys is formulated and applied to observations collected at the subpolar front of the japan east sea jes taken during several cold air outbreaks the method is distinct from vertical velocity inferences based on the omega equation in that the driving mechanism for the ageostrophic flow is inferred rather than assumed and hence is particularly appropriate for application to wind or buoyancy forced upper ocean currents where friction mixing inertial superinertial motions or higher order effects can contribute along with shear strain of the geostrophic flow to force vertical motions the inferred vertical circulation at the subpolar front of the jes has amplitudes o 100 m day 1 compared to the 20 m day 1 vertical velocities predicted by the omega equation time dependent near inertial motions driven by the winds and modified by the vertical vorticity of the frontal jet appear to be the primary

mesoscale subduction at the antarctic polar front driven by baroclinic instability abstract a study of mesoscale subduction at the antarctic polar front pf is conducted by use of hydrographic data from a high resolution quasi synoptic survey of the front the geostrophic velocity and isopycnal potential vorticity pv fields are computed and the ageostrophic flow diagnosed from the semigeostrophic omega equation it is found that the ageostrophic circulation induced by baroclinic instability counteracts the frontogenesis and frontolysis effected by the confluence and difluence respectively of the geostrophic velocity field though the sense of the ageostrophic circulation is reversed repeatedly along the front the existence of pv gradients along isopycnals leads to a net cross front bolus transport in response to a reversal of this gradient with depth a necessary condition for the onset of baroclinic instability the bolus transport is northward at the protruding temperature minimum layer that characterizes the pf and southward above this net cross front overturning circul

the azores front since the last glacial maximum the spatial distribution of warm surface water in the atlantic ocean reflects the state of the thermohaline circulation the azores current front which is a recirculation of the gulf stream marks the northeastern boundary of the north atlantic subtropical gyre its position is therefore diagnostic of the width of the atlantic warm water sphere here we report high resolution stable isotope and faunal abundance records of planktonic foraminifera in a sediment core from the gulf of cadiz southwest spain which reflects shifting of the azores front since the last glacial maximum lgm today the azores front does not penetrate into the gulf of cadiz even though the front resides at the same latitude as the gulf of cadiz in the atlantic our results indicate that the azores front is a robust feature of the atlantic surface circulation and that is present both in interglacial times and during the lgm at roughly the same latitude however during the lgm prior to 16 ka bp and during the younger dryas the azores front did penetrate eastward into the gulf of cadiz

ocean convergence and the dispersion of flotsam floating oil plastics and marine organisms are continually redistributed by ocean surface currents prediction of their resulting distribution on the surface is a fundamental long standing and practically important problem the dominant paradigm is dispersion within the dynamical context of a nondivergent flow objects initially close together will on average spread apart but the area of surface patches of material does not change although this paradigm is likely valid at mesoscales larger than 100 km in horizontal scale recent theoretical studies of submesoscales less than 10 km predict strong surface convergences and downwelling associated with horizontal density fronts and cyclonic vortices here we show that such structures can dramatically concentrate floating material more than half of an array of 200 surface drifters covering 20 20 km2 converged into a 60 60 m region within a week a factor of more than 105 decrease in area before slowly dispersing as predicted the convergence occurred at density fronts and with cyclonic vorticity a zipperlike structure may play an important role cyclonic vorticity and vertical velocity reached 0 001 s 1 and 0 01 ms 1 respectively which is much larger than usually inferred this suggests a paradigm in which nearby objects form submesoscale clusters and these clusters then spread apart together these effects set both the overall extent and the finescale texture of a patch of floating material material concentrated at submesoscale convergences can create unique communities of organisms amplify impacts of toxic material and create opportunities to more efficiently recover such material

ekman layers and two dimensional frontogenesis in the upper ocean a two dimensional modified semi geostrophic model is used to study the evolution of oceanic fronts in the presence of vertical mixing the parameterization used for mixing is an elevated constant value of vertical viscosity and friction hence the ekman layer acts as a surrogate mixed layer with however vertical shear allowed everywhere an initial condition representative of the observed fields in frontal air sea interaction experiment fasinex is used and its modification in the presence of vertical mixing alone is investigated without external forcing an ekman layer results because of the presence of vertical geostrophic shear at the surface the maximum density gradient moves toward the dense side of the front driven by this flow convergence of ekman flow results in downward bowing of the isopycnals beneath the surface expression of the front a feature reminiscent of density sections taken during fasinex this feature is not evident when a barotropic convergence field is applied in the absence of mixing or in fully nonlinear simulations of the evolution of fronts with baroclinic instability an analytic theory suggests that the maximum density gradient will increase over time when vertical mixing alone is present in the presence of negative uniform wind stress in the direction opposite to the surface geostrophic flow the front moves toward the denser water and the jet uniformly decreases in strength in the presence of a positive uniform wind in the direction of the surface geostrophic flow the surface jet initially weakens but then strengthens again as the wind driven ekman flow opposes the frictionally driven ekman flow and the cross front density gradient increases

restratification of the surface mixed layer with submesoscale lateral density gradients diagnosing the importance of the horizontal dimension abstract a depth cycling towed conductivity temperature depth ctd and vessel mounted acoustic doppler current profiler adcp were used to obtain four dimensional measurements of the restratification of the surface mixed layer sml at a submesoscale lateral density gradient near the subtropical front with the objective of studying the role of horizontal processes in restratification the thermohaline and velocity fields were monitored for 33 h by 16 small scale 15 km2 surveys centered on a drogued float daytime warming by insolation caused a unidirectional displacement of the initially vertical isopycnals toward increasing density across the entire sml 50 m vertical scale solar insolation accounted for 60 of observed restratification but over 10 m scales the percentage decreased with depth from 80 at 25 35 m to 25 at 55 65 m below 35 m stratification was enhanced by the vertically sheared horizontal advection of the lateral density gradient due to a near inertial wave of 100 m vertica

separation of tidal and subtidal currents in ship mounted acoustic doppler current profiler observations a simple method is developed to analyze current measurements obtained from a moving platform the need for this is motivated by the now common use of the ship mounted acoustic doppler current profiler adcp to acquire absolute velocity data during an oceanographic survey of a given region the full potential of this new measurement technique is severely hindered when the presence of high frequency phenomena e g tidal or inertial motions prevents a clear visualization of the lower frequency current structure of interest our analysis method is based on a spatial interpolation scheme using arbitrary functions that allows for the tidal current time variability which then permits the tide induced motions to be subtracted from the adcp data to yield the subtidal current field the method also allows nearby moored and drifter current measurements if available to be combined with the shipboard adcp observations in a single analysis to obtain the best description of the tidal and subtidal currents to illustrate this method we present results from the analysis of adcp data taken during oceanographic surveys in two different continental shelf regions the east china sea and the amazon shelf a 5 day conductivity temperature depth ctd and adcp survey was made in the east china sea near the mouth of the yellow sea during january 1986 there the currents were essentially barotropic and dominated by the semidiurnal tide the adcp derived cotidal chart for the m2 12 42 hours component agrees well with existing charts derived empirically from sea level observations or from regional numerical models the adcp derived steady flow is also consistent with the observed density field and indicates little flow in or out of the yellow sea and a transport of about 1 sv toward the tsushima strait two ctd adcp surveys lasting 21 and 23 days were conducted over the amazon shelf during march and may 1990 simultaneously moored current observations were also obtained at three locations along a cross shelf array 200 km north of the amazon river mouth for a common period of at least 2 months february 12 to april 13 over the shelf tidal and subtidal currents were comparable in magnitude our analysis indicates that the tidal currents were essentially barotropic semidiurnal and polarized in the cross shelf direction increasing in magnitude toward the inner shelf where current values of more than 2 m s are common the adcp derived steady currents were aligned in the along shelf direction and strongly influenced by the north brazil current nbc during both adcp surveys the northwestward flowing nbc was transporting more than 2 sv over the shelf at depths shallower than 100 m

vertical vorticity balance in meanders downstream the agulhas retroflection abstract the agulhas current flows poleward along the western boundary of the southeastern indian ocean where at the southernmost latitude of the african continent it executes a dramatic anticyclonic turn or retroflection to the east since 1978 a large number of drifting buoys have passed through this eastward flowing agulhas return current arc or the zonal frontal boundary between subtropical and subpolar waters of the south indian ocean the spatial distribution of the ensemble averaged near surface velocity along the arc axis reveals a series of steady state meanders of 700 km wavelength and amplitudes that decrease from 170 km in the first meander to 50 km in the following four meanders here an analysis of vorticity balance of the meandering arc speed axis is presented that demonstrates a balance between the term and advection of curvature vorticity this balance implies that the arc axis or frontal region is horizontally nondivergent in agreement with the other observations of flow in t

diagnosis of 3d vertical circulation in the upwelling and frontal zones east of hainan island china abstractusing the generalized omega equation and cruise observations in july 2012 this study analyzes the 3d vertical circulation in the upwelling region and frontal zone east of hainan island china the results show that there is a strong frontal zone in subsurface layer along the 100 m isobath which is characterized by density gradient of o 10 4 kg m 4 and vertical eddy diffusivity of o 10 5 10 4 m2 s 1 the kinematic deformation term sdef ageostrophic advection term sadv and vertical mixing forcing term smix are calculated from the observations their distribution patterns are featured by banded structure that is alternating positive negative alongshore bands distributed in the cross shelf direction correspondingly alternating upwelling and downwelling bands appear from the coast to the deep waters the maximum downward velocity reaches 5 10 5 m s 1 within the frontal zone accompanied by the maximum upward velocity of 7 10 5 m s 1 on two sides the dynamic diagnosis indicates that sadv

two dimensional ageostrophic secondary circulation at ocean fronts due to vertical mixing and large scale deformation 1 ageostrophic secondary circulation asc in frontal data sets have been previously diagnosed using only adiabatic versions of omega equations this study includes the effect of vertical mixing on such diagnostics modified quasi geostrophic and semigeostrophic balance equations are examined for the existing azores front data sets and idealized fronts in the presence of diabatic vertical mixing as well as a large scale deformation field the relevant dimensionless parameter representing the relative importance of large scale deformation and vertical mixing is the inverse of the ekman number based on the deformation rate h2 ao where is large scale deformation rate h is vertical scale of the front and ao is the maximum vertical eddy viscosity when this parameter is smaller than o 102 the influence of vertical mixing may be important other relevant parameters include burger number bu and prandtl number pr the vertical velocity in ascs caused by diabatic mixing in all diagnostics solutions except for large bu cases shows good agreement with the garrett loder scaling the structure of ascs is found to be sensitive to pr the diagnostics of ascs for the azores front data set indicates that the vertical mixing intensifies the asc in the upper ocean 100 m and should not be neglected when the large scale deformation rate is o 10 6 s 1 or smaller the magnitude of vertical velocity in ascs due to mixing contributions reaches o 10 m d 1 with downwelling on the dense side and upwelling on the less dense side of azores front

finescale vertical structure of the upwelling system off southern peru as observed from glider data abstractthe upwelling system off southern peru has been observed using an autonomous underwater vehicle a slocum glider during october november 2008 nine cross front sections have been carried out across an intense upwelling cell near 14 s during almost two months profiles of temperature salinity and fluorescence were collected at less than 1 km resolution between the surface and 200 m depth estimates of alongshore absolute geostrophic velocities were inferred from the density field and the glider drift between two surfacings in the frontal region salinity and biogeochemical fields displayed cross shore submesoscale filamentary structures throughout the mission those features presented a width of 10 20 km a vertical extent of 150 m and appeared to propagate toward the shore they were steeper than isopycnals and kept an aspect ratio close to f n the inverse of the prandtl ratio these filamentary structures may be interpreted mainly as a manifestation of submesoscale turbulence through sti

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

the relationship between water mass formation and the surface buoyancy flux with application to phillips red sea model abstract a buoyancy flux across the sea surface between the outcropping of isopycnals must be balanced by a subsurface diapycnal buoyancy flux if this flux were only advective its derivative with respect to buoyancy would provide a direct estimate of the buildup of volume between isopycnals or rate of water mass formation a diapycnal velocity however requires diapycnal mixing which also causes a diapycnal buoyancy flux and it is shown that there is no reason to expect a simple relationship between the advective and diffusive fluxes for a surface layer with vigorous vertical mixing and weak horizontal mixing however the diapycnal diffusive flux of buoyancy is small and the flow through the base of the mixed layer can be derived from the derivative of the surface buoyancy flux with respect to buoyancy these points are illustrated by examination of the phillips similarity solution for the convective circulation driven in a channel by a uniform surface buoyancy loss

diagnosis of the three dimensional circulation in mesoscale features with large rossby number several diagnoses of three dimensional circulation using density and velocity data from a high resolution upper ocean seasoar and acoustic doppler current profiler adcp survey of a cyclonic jet meander and adjacent cyclonic eddy containing high rossby number flow are compared the q vector form of the quasigeostrophic omega equation two omega equations derived from iterated geostrophic intermediate models an omega equation derived from the balance equations and a vertical velocity diagnostic using a primitive equation model in conjunction with digital filtering are used to diagnose vertical and horizontal velocity fields the results demonstrate the importance of the gradient wind balance in flow with strong curvature high rossby number horizontal velocities diagnosed from the intermediate models the iterated geostrophic models and the balance equations which include dynamics between those of quasigeostrophy and the primitive equations are significantly reduced enhanced in comparison with the geostrophic velocities in regions of strong cyclonic anticyclonic curvature consistent with gradient wind balance the intermediate model relative vorticity fields are functionally related to the geostrophic relative vorticity field anticyclonic vorticity is enhanced and cyclonic vorticity is reduced the iterated geostrophic balance equation and quasigeostrophic vertical velocity fields are similar in spatial pattern and scale but the iterated geostrophic and to a lesser degree the balance equation vertical velocity is reduced in amplitude compared with the quasigeostrophic vertical velocity this reduction is consistent with gradient wind balance and is due to a reduction in the forcing of the omega equation through the geostrophic advection of ageostrophic relative vorticity the vertical velocity diagnosed using a primitive equation model and a digital filtering technique also exhibits reduced magnitude in comparison with the quasigeostrophic field a method to diagnose the gradient wind from a given dynamic height field has been developed this technique is useful for the analysis of horizontal velocity in the presence of strong flow curvature observations of the nondivergent ageostrophic velocity field measured by the adcp compare closely with the diagnosed gradient wind ageostrophic velocity

large and mesoscale variability of the water masses and the deep chlorophyll maximum in the azores front 1 coupling between the physical and biological fields in the upper ocean around the azores front af was studied in summer 1998 during an oceanographic cruise to the southern azores islands 30 n 38 n and 20 w 33 w on the basis of conductivity temperature depth ctd acoustic doppler current profiler adcp and fluorescence data several large scale mesoscale and submesoscale physical features are described the adcp data and geostrophic field revealed an eastward transport associated with the azores current ac and weak countercurrents to the south and north of the ac the water mass field shows a strong latitudinal variation in the af with an eastward modification from the surface to 300 dbar the saline distribution strongly defined the af as a very sharp vertical front the horizontal thermohaline gradient increased to the east and reached a maximum at approximately 150 dbar the 16 2 c isotherm and 36 2 isohaline at 150 dbar precisely located the af along the whole area in agreement with the dynamic field to the west of 26 w the azores current was 140 km wide while the af was only 15 25 km wide to the east of 26 w the ac underwent a strong meandering the water mass characteristics in the southern part of the af show an eastward evolution between 18 c seawater and madeira mode water data from a ctd fluorometer mounted on an undulator system allowed the small scale structure of af to be mapped describing several eddies and meanders the deep chlorophyll maximum dcm showed highest values 0 9 to 1 2 mg chl m 3 toward the west 32 w on the southern side of the af chlorophyll concentrations at the dcm 0 4 0 6 mg chl m 3 on the northern side of the study area were moderate and fairly constant whereas low values 0 3 mg chl m 3 were measured at the very deep dcm 120 140 m in the southeast associated with high saline waters examination of a cold eddy showed similar chlorophyll concentrations to those found on the northern side of the af the thermohaline structure of the eddy was similar to the af with northern water enclosed within saline and warm southern water

excess aluminum in deep sea sediments of the central indian basin abstract the aluminum concentration in the marine sediments has long been considered an indicator of terrigenous abundance the al ti values 48 5 of the central indian basin subsurface siliceous sediment are up to three times that of post archean australian shale paas the estimation of structurally unsupported al al ex from six sediment cores suggests that an average of 40 of total al is from noncrustal sources higher al ti or al ex values are often but not exclusively associated with abundant volcanic unaltered glass shards electron microprobe analysis of 60 of these glass shards reveals that they are rhyolitic in composition and of youngest toba 74 ka origin from northern sumatra these glass shards have very high al ti ratio of 175 mean al ti values are also above the paas in sediment where glass shards are absent which could be due to scavenging of dissolved al by biogenic components

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

observations of submesoscale variability and frontal subduction within the mesoscale eddy field of the tasman sea abstractsubmesoscale lenses of water with anomalous hydrographic properties have previously been observed in the east australian current eac system embedded within the thermocline of mesoscale a

vorticity and vertical circulation at an ocean front abstract density and velocity data with 4 km horizontal resolution from a survey of a front during fasinex frontal air sea interaction experiment are combined to describe the structure of the top 300 m of the ocean the geostrophic velocity field is derived and is used to examine the relative importance of stratification relative vorticity and twisting terms in ertel s potential vorticity q tenfold isopycnic changes in q are found across a horizontal scale of only 10 km these changes are confined to isopycnals that outcrop from the seasonal thermocline into the mixed layer the ageostrophic velocity field is quantified by solution of the omega equation and vertical velocities of up to 40 m day 1 are found small 40 km surface trapped top 200 m eddies are found to play a crucial role in the transport and effective diffusion of properties across the thermocline out of the mixed layer

mesoscale to submesoscale transition in the california current system part i flow structure eddy flux and observational tests in computational simulations of an idealized subtropical eastern boundary upwelling current system similar to the california current a submesoscale transition occurs in the eddy variability as the horizontal grid scale is reduced to o 1 km this first paper in a series of three describes the transition in terms of the emergent flow structure and the associated time averaged eddy fluxes in addition to the mesoscale eddies that arise from a primary instability of the alongshore wind driven currents significant energy is transferred into submesoscale fronts and vortices in the upper ocean the submesoscale arises through surface frontogenesis growing off upwelled cold filaments that are pulled offshore and strained in between the mesoscale eddy centers in turn some submesoscale fronts become unstable and develop submesoscale meanders and fragment into roll up vortices associated with this phenomenon are a large vertical vorticity and rossby number a large vertical velocity relatively flat horizontal spectra contrary to the prevailing view of mesoscale dynamics a large vertical buoyancy flux acting to restratify the upper ocean a submesoscale energy conversion from potential to kinetic a significant spatial and temporal intermittency in the upper ocean and material exchanges between the surface boundary layer and pycnocline comparison with available observations indicates that submesoscale fronts and instabilities occur widely in the upper ocean with characteristics similar to the simulations

elevated mixing at a front 1 the mesoscale submesoscale and microscale structure of a front in the california current was observed using a towed vehicle outfitted with microconductivity sensors thirteen 60 km cross front sections from 0 to 350 m in depth were covered in 3 5 days objectively mapped data are fit via the omega equation to obtain vertical velocity a composite cross front section shows elevated mixing on the dense side within 10 20 km of the front water downwells and gradients are elevated there i e rossby number ro horizontal strain spice gradients and microscale thermal dissipation thermal eddy diffusivity kt reaches 10 3 m2 s 1 and increases 3 10 from the anticyclonic to the cyclonic side with a depth mean of 10 4 m2 s 1 the spatial structure of kt ro and are similar on the dense side suggesting an energy cascade from the mesoscale via the submesoscale to the microscale however it is unclear whether frontogenesis internal wave blocking by elevated vorticity or internal wave trapping by large produces the elevated mixing the mean turbulent heat flux opposes the mean restratifying mesoscale heat flux of 10 w m 2 and may allow the front to persist turbulent nitrate fluxes are 0 1 0 3 mmol m 2 s 1 chlorophyll fluorescence and beam transmission reveal a 6 km wide 100 km long alongfront streamer which is a deep biomass maximum time scales for mixing and nutrient fluxes are 0 3 3 days which are similar to phytoplankton growth rates and the time scale for frontal evolution

enhanced radiation of near inertial energy by frontal vertical circulations abstractnear inertial waves niws radiate energy out of the mixed layer when they develop small lateral scales refraction of these waves by gradients in planetary and vertical vorticity has tradi

eddy induced mixed layer shallowing and mixed layer thermocline exchange the effects of eddies on the mixed layer and on the transfer of properties between the mixed layer and thermocline are studied in a high resolution model of an unstable front a spring scenario is considered with a mixed layer maintained against surface warming by wind mixing tilting of the buoyancy gradients by ageostrophic flow is found to shallow the mixed layer over the front giving a mixed layer as shallow as 10 m in some places compared with the equilibrium monin obukhov depth of 30 m away from the front variations of mixed layer depth with time and lateral advection lead to a subduction field that is substantially different from the vertical velocity field vertical velocities associated with the growing instabilities push tongues of a ventilation tracer initially only present within the surface layer down to depths of up to 100 m after 24 days a quarter of this ventilation tracer has been deposited in the thermocline conversely the vertical motions pull nutrients from the thermocline up into the mixed layer giving enhanced surface values along the front in the basin average the geostrophic eddies give vertical eddy diffusivities for a ventilation tracer of o 3 10 10 4m2s 1

mesoscale and submesoscale effects on mixed layer depth in the southern ocean the authors gratefully acknowledge support from the natural environment research council awards ne j010472 1 and ne j009857 1

frontal dynamics in a california current system shallow front 1 frontal processes and tracer structure 1 the three dimensional dynamics in a shallow front are examined using density and current data from two surveys 100 km offshore of monterey bay california survey 1 is forced by down front winds and both surveys have considerable cross front density gradients and flow curvature the maximum rossby numbers on the dense side reached maxima of 0 60 in survey 1 and 0 45 in survey 2 downwelling occurs in regions of confluence frontogenesis associated with potential vorticity pv change and thermal wind imbalance streamers of particulate matter and pv are advected southeastward by the frontal jet and downward nonlinear ekman currents advect dense water over light water in the presence of down front winds which leads to upwelling along the front and downwelling on the light side of the front at sites of active ageostrophic secondary circulation asc induced by frontogenesis or ekman effects the observed cross front ageostrophic velocity is consistent with the diagnosed vertical velocity furthermore in survey 2 ageostrophic divergence may play an important role at the curved front presumably counteracting quasi geostrophic frontogenesis due to isopycnal confluence downward frictional vertical pv flux below the surface extracts pv from the pycnocline and reinforces the frontogenetic vertical pv flux pv destruction at the surface is inferred from a low pv anomaly below the mixed layer in survey 2 since the magnitude of the frontogenetic asc is only twice the magnitude of ekman suction external forcing may have a considerable impact on the vertical heat and pv fluxes

the heat budget in the north atlantic subtropical frontal zone the heat budget in the north atlantic subtropical frontal zone is examined using moored measurements of horizontal velocity temperature and surface heat flux obtained during the frontal air sea interaction experiment fasinex the three moorings used in this calculation defined a triangle with base of 19 km and height of 28 km and were densely instrumented from the surface to 160 m depth empirical orthogonal functions eofs are employed to identify components of current and temperature variability with scales that are resolved by the observations a least squares fit to the eof filtered data is used to derive maps of velocity and temperature the temperature field is dominated by the passage of fronts with the highest variability at 160 m horizontal temperature gradients at 160 m peak at values approaching 1 10 4 c m 1 and are indicative of a tilting of the seasonal thermocline velocities are directed primarily along isotherms and are swifter at the surface than at depth the heat budget of the upper 160 m for periods longer than 48 hours is essentially a balance between rate of change of heat and horizontal advection the correlation between these terms is 0 7 a simple explanation is the northward advection by a mean current of a series of fronts the effect of surface heating becomes apparent in the upper 40 m notably at the diurnal frequency and its first harmonic an imbalance in the mean 102 days heat budget can be rectified by a mean downwelling velocity of 5 10 5 m s 1 at 160 m

surface currents in the canary basin from drifter observations satellite tracked drifting buoys deployed in the canary basin as part of the subduction experiment between july 1991 and october 1993 and the french semaphore experiment during october 1993 were used to obtain a description of surface currents and temperature in the canary basin the study focuses on surface water convergence eddy energy production and heat transport the azores current associated with the subtropical convergence zone is clearly visible at 34 n and bifurcates around 22 w with the major branch of the current circling the madeira plateau and joining the canary current along the continental slope eddy kinetic energy maxima are found along the azores current the mean current revealed a region of maximum convergence north of the azores current around longitude 29 w occurring with a negative heating anomaly and positive work done by the reynolds stress the southward meridional temperature fluxes in the ekman layer 0 50 m between 37 w and the african and european coast are estimated between 0 076 0 022 l015 w produced by mean southward volume transport in our study area the residual between local surface heat fluxes and horizontal convergence of heat implies a vertical heat convergence process associated with mesoscale temperature and flow fields

circulation and heat fluxes during the austral fall in george vi sound antarctic peninsula abstract a mesoscale survey was conducted in northern george vi sound as part of the united states southern ocean global ocean ecosystems dynamics program in austral fall 2001 to examine the circulation and heat fluxes the absolute dynamic height field is determined from a combination of measured currents detided using model predicted tidal currents streamfunction fitting and the thermal wind equation based on hydrographic measurements the results have revealed surface coastal currents of 0 2 m s 1 intruding into northern george vi sound from marguerite bay mb and mesoscale eddies formed within the deep trough both antarctic surface waters and modified circumpolar deep water were transported into the sound along the eastern side of the sound while ice shelf influenced waters exited to mb along the western side analysis indicates that predominant southward winds during the season were responsible for driving the basin wide circulation in the sound both convergence of horizontal heat transports and vertical upwelling heat fluxes were significant to the contribution or delay of local ice formation in george vi sound which is critical for the austral winter ecosystem

wind waves and fronts frictional effects in a generalized ekman model abstractocean currents in the surface boundary layer are sensitive to a variety of parameters not included in classic ekman theory including the vertical structure of eddy viscosity finite boundary layer depth baroclinic pressure gradients and surface waves these parameters can modify the horizontal and vertical flow in the near surface ocean making them of first order significance to a wide range of phenomena of broad practical and scientific import in this work an approximate green s function solution is found for a model of the frictional ocean surface boundary layer termed the generalized ekman or turbulent thermal wind balance the solution admits consideration of general more physically realistic forms of parameters than previously possible offering improved physical insight into the underlying dynamics closed form solutions are given for the wind driven flow in the presence of coriolis stokes shear a result of the surface wave field and thermal wind shear arising from a baroclinic

diagnosis of the three dimensional circulation associated with mesoscale motion in the california current a high resolution upper ocean survey of a cyclonic jet meander and an adjacent cyclonic eddy in the california current region near 388n 1268w was conducted as part of the summer of 1993 eastern boundary currents program temperature and salinity were measured from a seasoar vehicle and velocity was measured by shipboard acoustic doppler current profiler adcp seasoar data show a density front at a depth of 70 100 m with strong cyclonic curvature the geostrophic velocity fields referenced to the adcp data at 200 m show a strong surface intensified jet maximum speed of 0 9 m s 21 that follows the density front along a cyclonic meander relative vorticities within the jet are large ranging from 20 8 f to 11 2 f where f is the local coriolis parameter the seasoar density and adcp velocity data are used to diagnose the vertical velocity via the q vector form of the quasigeostrophic omega equation the diagnosed vertical velocity field shows a maximum speed of 40 45 m d21 the lateral distribution of vertical velocity is characterized by two length scales a large 75 km pattern where there is downwelling upstream and upwelling downstream of the cyclonic bend and smaller patches arrayed along the jet core with diameters of 20 30 km geostrophic streamline analysis of vertical velocity indicates that water parcels make net vertical excursions of 20 30 m over 2 3 days resulting in net vertical velocities of 7 15 m d21 water parcels moving along geostrophic streamlines experience maximum vertical velocities in the regions of maximum alongstream change in relative vorticity an indication of potential vorticity conservation

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

a comparison of techniques for tide removal from ship mounted acoustic doppler measurements along the southwest coast of vancouver island two approaches are examined for the removal of tidal currents from acoustic doppler current profiler henceforth adcp measurements the first uses predictions from a numerical model foreman and walters 1990 whose domain includes the measurement region although the numerical model is barotropic adjustments are made to correct for baroclinicity in accordance with historical observations from stationary current meters in the region the second approach originally proposed by candela et al 1990 performs a least squares polynomial or biharmonic spline fit to the adcp data in order to determine the spatially varying amplitudes and phases of major tidal constituents and the magnitude of the residual flow both tide removal techniques are applied to adcp data taken during a 3 day cruise off the southwest coast of vancouver island and their relative effectiveness is compared some of the detided currents are seen to compare well with geopotential surfaces and clearly show the juan de fuca eddy freeland and denman 1982 a discussion of the results and limitations of each technique is also presented

meddies and decadal changes at the azores front from 1980 to 2000 twenty years of time series observations from the deep sea mooring kiel276 are used to obtain information on the frequency and propagation of meddies mediterranean water eddies on long term changes in flow properties and on a possible relation to the north atlantic oscillation the mooring was set at the nominal position 33 n 22 w at a water depth of more than 5200 m in the northern canary basin it is located near the southern boundary of the azores current ac which is part of the north atlantic subtropical gyre and also in the large scale mediterranean water mw tongue originating from the strait of gibraltar the amplitudes of time varying vertical quasi geostrophic modes and the correlation of current and temperature changes at levels in the mw and the north atlantic central water above are used to identify meddies a total of 10 meddies passed the mooring during the period 1980 2000 half of the events can be related to earlier observations directional changes in meddy related velocities are used to estimate speeds and directions of meddy propagation directions of propagation are very homogeneous with all the 10 meddies observed propagating with a southward velocity component within a sector of 90 and typical speeds are 2 3 cm s meddy occurrence was uneven in time with six meddies found during the first four years and only four meddies during the remaining 16 years decadal changes show the annual mean and the fluctuating kinetic energy levels at the site changing from lower values in the 1980s to high values in the 1990s this change appears to be correlated with variations in the north atlantic oscillation nao index with a delay in oceanic response of about 3 years a conceptual model of ac meanders is used to identify meander signals in the upper layer time series the ac axis appears to be closer to the site during the 1990s than during the preceding decade and indicates a southward or southwestward displacement of the ac with increasingly positive values of the nao index meddy frequency is lower when the ac gets closer from the north a reduction in meddy occurrence in the region just south of the ac is possibly caused by the shear induced blocking of some meddies crossing the front from the north

subduction on the northern and southern flanks of the gulf stream abstract sections of temperature salinity dissolved oxygen and velocity were made crossing the gulf stream in late january 2006 to investigate the role of frontal processes in the formation of eighteen degree water edw the subtropical mode water of the north atlantic the sections were nominally perpendicular to the stream and measured in a lagrangian frame by following a floating spar buoy drifting in the gulf stream s warm core during the survey edw was isolated from the mixed layer by the stratified seasonal pycnocline suggesting that edw was not yet actively being formed at this time in the season and at the longitudes over which the survey was conducted 64 70 w however in two of the sections the seasonal pycnocline in the core of the gulf stream was broken by an intrusion of cold fresh weakly stratified water nearly saturated in oxygen that appears to have been subducted from the surface mixed layer north of the stream the intrusion was identified in three of the sections in profi

diagnosing surface mixed layer dynamics from high resolution satellite observations numerical insights high resolution numerical experiments of ocean mesoscale eddy turbulence show that the wind driven mixed layer ml dynamics affects mesoscale motions in the surface layers at scales lower than o 60 km at these scales surface horizontal currents are still coherent to but weaker than those derived from sea surface height using geostrophy vertical motions on the other hand are stronger than those diagnosed using the adiabatic quasigeotrophic qg framework an analytical model based on a scaling analysis and on simple dynamical arguments provides a physical understanding and leads to a parameterization of these features in terms of vertical mixing these results are valid when the wind driven velocity scale is much smaller than that associated with eddies and the ekman number related to the ratio between the ekman and ml depth is not small this suggests that in these specific situations three dimensional ml motions including the vertical velocity can be diagnosed from high resolution satellite observations combined with a climatological knowledge of ml conditions and interior stratification