rationalizing the spatial distribution of mesoscale eddy diffusivity in terms of mixing length theory observations and theory suggest that lateral mixing by mesoscale ocean eddies only reaches its maximum potential at steering levels surfaces at which the propagation speed of eddies approaches that of the mean flow away from steering levels mixing is strongly suppressed because the mixing length is smaller than the eddy scale thus reducing the mixing rates the suppression is particularly pronounced in strong currents where mesoscale eddies are most energetic here a framework for parameterizing eddy mixing is explored that attempts to capture this suppression an expression of the surface eddy diffusivity proposed by ferrari and nikurashin is evaluated using observations of eddy kinetic energy eddy scale and eddy propagation speed the resulting global maps of eddy diffusivity have a broad correspondence with recent estimates of diffusivity based on the rate at which tracer contours are stretched by altimetric derived surface currents finally the expression for the eddy diffusivity is extrapolated in the vertical to infer the eddy induced meridional heat transport and the overturning streamfunction

suppression of eddy diffusivity across jets in the southern ocean abstract geostrophic eddies control the meridional mixing of heat carbon and other climatically important tracers in the southern ocean the rate of eddy mixing is typically quantified through an eddy diffusivity there is an ongoing debate as to whether eddy mixing in enhanced in the core of the antarctic circumpolar current or on its flanks a simple expression is derived that predicts the rate of eddy mixing that is the eddy diffusivity as a function of eddy and mean current statistics this novel expression predicts suppression of the cross jet eddy diffusivity in the core of the antarctic circumpolar current despite enhanced values of eddy kinetic energy the expression is qualitatively and quantitatively validated by independent estimates of eddy mixing from altimetry observations this work suggests that the meridional eddy diffusivity across the antarctic circumpolar current is weaker than presently assumed because of the suppression of eddy mixing by the strong zonal current

gravitational symmetric and baroclinic instability of the ocean mixed layer abstract a hierarchy of hydrodynamical instabilities controlling the transfer of buoyancy through the oceanic mixed layer is reviewed if a resting ocean of horizontally uniform stratification is subject to spatially uniform buoyancy loss at the sea surface then gravitational instability ensues in which buoyancy is drawn from depth by upright convection but if spatial inhomogeneities in the ambient stratification or the forcing are present as always exist in nature then horizontal density gradients will be induced and within a rotation period horizontal currents in thermal wind balance with those gradients will be set up within the mixed layer there are two important consequences on the convective process upright convection will become modified by the presence of the thermal wind shear fluid parcels are exchanged not along vertical paths but rather along slanting paths in symmetric instability theoretical considerations suggest that this slantwise convection sets the potential vorticity of th

isopycnal eddy diffusivities and critical layers in the kuroshio extension from an eddying ocean model abstracthigh spatial resolution isopycnal diffusivities are estimated in the kuroshio extension ke region 28 40 n 120 190 e from a global parallel ocean program pop simulation the numerical float tracks are binned using a clustering approach the number of tracks in each bin is thus roughly the same leading to diffusivity estimates that converge better than those in bins defined by a regular geographic grid cross stream diffusivities are elevated in the southern recirculation gyre region near topographic obstacles and downstream in the ke jet where the flow has weakened along stream diffusivities which are much larger than cross stream diffusivities correlate well with the magnitudes of eddy velocity the ke jet suppresses cross stream mixing only in some longitude ranges this study estimates the critical layer depth both from linear local baroclinic instability analysis and from eddy phase speeds in the pop model using the radon transform the latter is a better predictor of large mixi

circulation and stirring in the southeast pacific ocean and the scotia sea sectors of the antarctic circumpolar currenta abstractthe large scale middepth circulation and eddy diffusivities in the southeast pacific ocean and scotia sea sectors between 110 and 45 w of the antarctic circumpolar current acc are described based on a subsurface quasi isobaric rafos float based lagrangian dataset these rafos float data were collected during the diapycnal and isopycnal mixing experiment in the southern ocean dimes the mean flow adjusted to a common 1400 m depth shows the presence of jets in the time averaged sense with speeds of 6 cm s 1 in the southeast pacific ocean and upward of 13 cm s 1 in the scotia sea these jets appear to be locked to topography in the scotia sea but aside from negotiating a seamount chain are mostly free of local topographic constraints in the southeast pacific ocean the eddy kinetic energy eke is higher than the mean kinetic energy everywhere in the sampled domain by about 50 the magnitude of the eke increases drastically by a factor of 2 or more as the current crosses over the hero and

the role of mesoscale eddies in the rectification of the southern ocean response to climate change abstract simulations from a fine resolution global coupled model the geophysical fluid dynamics laboratory climate model version 2 4 cm2 4 are presented and the results are compared with a coarse version of the same coupled model cm2 1 under idealized climate change scenarios a particular focus is given to the dynamical response of the southern ocean and the role played by the eddies parameterized or permitted in setting the residual circulation and meridional density structure compared to the case in which eddies are parameterized and consistent with recent observational and idealized modeling studies the eddy permitting integrations of cm2 4 show that eddy activity is greatly energized with increasing mechanical and buoyancy forcings buffering the ocean to atmospheric changes and the magnitude of the residual oceanic circulation response is thus greatly reduced although compensation is far from being perfect changes in poleward eddy fluxes partially compensate for the enhanced equatorward

estimating suppression of eddy mixing by mean flows particle and tracer based estimates of lateral diffusivities are used to estimate the suppression of eddy mixingacrossstrongcurrents particlesandtracersare advectedusingavelocityfieldderivedfromseasurface height measurements from the south pacific in a region west of drake passage this velocity field has been used in a companion paper to show that both particle and tracer based estimates of eddy diffusivities are equivalent despite recent claims to the contrary these estimates of eddy diffusivities are here analyzed to show 1 that the degree of suppression of mixing across the strong antarctic circumpolar current is correctly predicted by mixing length theory modified to include eddy propagation along the mean flow and 2 that the suppressioncan beinferredfromparticletrajectoriesby studyingthestructureofthe autocorrelationfunction of the particle velocities beyond the first zero crossing these results are then used to discuss how to compute lateral and vertical variations in eddy diffusivities using floats and drifters in the real ocean

resedimentation of basin centre sulphate deposits middle miocene badenian of carpathian foredeep southern poland abstract the middle badenian anhydrite sections in the central part of the carpathian foredeep consist mainly of interbedded laminated anhydrite and anhydrite breccia these facies display features characteristic of redeposited sediments such as distortions due to slumping erosional boundaries and graded bedded laminae lamination in laminated anhydrite is rarely regular and often accompanied by disruptions the predominance of clasts of laminated anhydrite combined with the observed brecciation of laminated anhydrite indicates that a short distance for transport and even in situ reworking were common a high degree of convolution indicates that some reworked sediments were unconsolidated when they moved but in many cases they were probably at least partly lithified this is evidenced by the anhydrite breccia consisting of clasts of laminated anhydrite as well as the brecciation in situ the resedimentation processes have not been related to regional bathymetrical differences as indicated by minor differences along seismic profiles a great deal of redeposition within the basin centre of the middle badenian evaporite basin combined with the in situ brecciation suggests that the triggering mechanism for redeposition could be earthquakes they generated mass flows and eventually turbidites so that earlier deposited grains could be redeposited this implies that in other evaporite basins the laminar facies might be at least partly related to redeposition and not necessarily to changes of surface brine concentration as usually supposed

distribution of reynolds stress carried by mesoscale variability in the antarctic circumpolar current satellite altimeter data collected by the u s navy s geosat exact repeat mission were used to investigate turbulent stress resulting from the variability of surface geostrophic currents in the antarctic circumpolar current the altimeter measured sea level along the subsatellite track the variability of the along track slope of sea level is directly proportional to the variability of surface geostrophic currents in the cross track direction we used the two components of the slope at points where the satellite ground tracks cross to calculate orthogonal components of the current s variability because the grid of crossover points is dense at high latitudes the satellite data could be used for mapping the temporal and spatial variability of the current two and a half years of data were used to compute the statistical structure of the variability leading to a better understanding of the role of variability in the dynamics of the current the statistics included the probability distribution functions for each component of the current the time lagged auto correlation functions of the variability and the reynolds stress produced by the variability the results demonstrate that stress is correlated with bathymetry in some areas the distribution of negative stress indicate that eddies contribute to an acceleration of the mean flow strengthening the hypothesis that baroclinic instability makes important contributions to strong oceanic currents

three dimensional model results for an electrical hole to surface method application to the interpretation of a field survey an important objective of borehole geophysics is to maximize information about inhomogeneities in the vicinity of existing boreholes three dimensional models parallelepipedic inhomogeneities in a homogeneous half space are used here to characterize the responses of an electrical hole to surface method elecent electrode enterree where conductive or resistive inhomogeneities orebodies occur in the vicinity of a borehole two types of surface measurements are carried out simultaneously at each station electrical potential v as in mise a la masse and associated electrical field e these two measured parameters give rise to three other parameters two apparent resistivities one for each v and e case and another parameter quantifying the orientation of the e field the influence of various geometrical and electrical parameters such as the horizontal and vertical distances between the current source the stations and the inhomogeneity and the size and resistivity of the inhomogeneity on the five

a multiwavenumber theory for eddy diffusivities and its application to the southeast pacific dimes region abstracta multiwavenumber theory is formulated to represent eddy diffusivities it expands on earlier single wavenumber theories and includes the wide range of wavenumbers encompassed in eddy motions in the limiting case in which ocean eddies are only composed of a single wavenumber the multiwavenumber theory is equivalent to the single wavenumber theory and both show mixing suppression by the eddy propagation relative to the mean flow the multiwavenumber theory was tested in a region of the southern ocean 70 45 s 110 20 w that covers the drake passage and includes the tracer float release locations during the diapycnal and isopycnal mixing experiment in the southern ocean dimes cross stream eddy diffusivities and mixing lengths were estimated in this region from the single wavenumber theory from the multiwavenumber theory and from floats deployed in a global parallel ocean program pop simulation compared to the single wavenumber theory the horizontal structures of cross stream mixing l

initiation and growth of gypsum piercement structures in the zechstein basin abstract the importance of tectonic processes in initiating halite diapirs has become much better understood in recent years less well understood is the development of diapiric structures involving rocks composed predominantly of gypsum below about 1000 m gypsum dehydrates to anhydrite which often obscures primary sedimentary textures if the strain associated with diapiric rise in the rock induces the transition to anhydrite obliteration of primary features in the gypsum can be expected in our study we infer that the diapiric movement in the werra anhydrite member of cycle 1 of the zechstein formation of europe occurred before the initial transition of gypsum to anhydrite based on the presence of pseudomorphs of bedded primary gypsum crystals the overburden lithologies and depositional environment and the mechanical properties of gypsum anhydrite and carbonate rocks faulting and differential loading of a shallow overburden were the key components in initiating the gypsum diapirism the transition to anhydrite occurred after burial and after cessation of diapirism in comparison the diapirism of calcium sulfate of the leine anhydrite into the leine halite members of cycle 3 of the zechstein formation probably occurred much later after burial and appears to have been triggered by halite diapirism which in turn triggered the dehydration reaction causing the calcium sulfate to become the incompetent phase relative to the halite

global surface eddy diffusivities derived from satellite altimetry 1 velocities derived from aviso sea surface height observations adjusted to be nondivergent are used to simulate the evolution of passive tracers at the ocean surface eddy mixing rates are derived from the tracer fields in two ways first the method of nakamura is applied to a sector in the east pacific second the osborn cox diffusivity is calculated globally to yield estimates of diffusivity in two dimensions the results from the east pacific show weak meridional mixing at the surface in the southern ocean 1000 m2 s 1 consistent with previous results but higher mixing rates 3000 5000 m2 s 1 in the tropical ocean the osborn cox diagnostic provides a global picture of mixing rates and agrees reasonably well with the results from the east pacific it also shows extremely high mixing rates 104 m2 s 1 in western boundary current regions the osborn cox diffusivity is sensitive to the tracer initialization which we attribute to the presence of anisotropic mixing processes the mixing rates are strongly influenced by the presence of a mean flow nearly everywhere as shown by comparison with an eddy only calculation with the mean flow absent finally results are compared with other recent estimates of mixing rates using lagrangian and inverse methods

float derived isopycnal diffusivities in the dimes experiment as part of the diapycnal and isopycnal mixing experiment in the southern ocean dimes 210 subsurface floats were deployed west of the drake passage on two targeted density surfaces absolute single particle diffusivities are calculated for the floats the focus is on the meridional component which is less affectedby the meanshear the diffusivitiesare estimatedin severalways including a novelmethodbased on the probability density function of the meridional displacements this allows the determination of the range of possible lateral diffusivities as well as the period over which the spreading can be said to be diffusive the method is applied to the float data and to synthetic trajectories generated with the massachusetts institute of technologygeneral circulationmodel mitgcm becauseof ballastingproblems manyofthefloatsdid not remain on their targeted density surface however the float temperature records suggest that most occupied asmallrangeofdensities sothefloatsweregroupedtogetherfortheanalysis thelatterfocuseson asubsetof 109 of the floats launched near 1058w the different methods yield a consistent estimate for the diffusivity of 800 6 200m 2 s 21 the same calculations were made with model particles deployed on 20 different density surfaces and the result for the particles deployed on the neutral density surface g 5 27 7 surface was the same within the errors the model was then used to map the variation of the diffusivity in the vertical near the core of the antarctic circumpolar current acc the results suggest mixing is intensified at middepths between 1500 and 2000m consistent with several previous studies

isopycnal eddy mixing across the kuroshio extension stable versus unstable states in an eddying model the kuroshio extension ke jet transitions between stable and unstable states on interannual time scales cross jet eddy mixing in the two states is contrasted in the ke region 28 40 n 125 165 e using a global eddying 0 1 configuration of the parallel ocean program with online numerical particles the four year period chosen june 1994 to may 1998 covers a full cycle of the stable state unstable state and the transition period large values of cross jet eddy diffusivities within the ke jet are concentrated in the upper 1000m in the upper ocean elevated cross jet mixing within the ke jet is mainly concentrated in the downstream part of the ke jet where the jet is weak but eddy activity is strong the simulated time mean ke jet is more intense and extends further east in the stable state than in the unstable state consequently strong cross jet mixing within the ke jet is located west of 150oe during june 1996 may 1997 a typical unstable state but east of 150oe during june 1995 may 1996 a typical stable state however average mixing within the ke jet is indistinguishable in the typical stable and unstable states in the deep ocean mixing is strongly influenced by topography and thus their horizontal structures have less inter annual variability than in the upper ocean one caveat is that results here cover one representative cycle of the two states to obtain the climate mean mixing structures for the stable or unstable state one would need numerical output covering a period much longer than four years

phase speed spectra of transient eddy fluxes and critical layer absorption abstract tropospheric zonal mean eddy fluxes of heat and momentum and the divergence of the eliassen palm flux are decomposed into contributions from different zonal phase speeds data analyzed are ecmwf operational global analyses covering 1980 87 eastward moving medium scale waves zonal waves 4 7 dominate the spectra of lower tropospheric heat fluxes in both hemispheres and all seasons upper tropospheric wave flux spectra are similar to the low level spectra in midlatitudes but shift to slower zonal phase speeds as low latitudes are approached the cause of this shift is the selective absorption of faster moving components in midlatitudes as the waves propagate meridionally latitude phase speed distributions of eddy fluxes are constructed and compared to the zonal mean wind structure these results demonstrate that upper tropospheric eddies break and decelerate the zonal mean flow approximately 10 20 in latitude away from their critical line where phase speed equals zonal wind speed compari

eddy momentum flux and its contribution to the southern ocean momentum balance a large amount of momentum is transferred to the southern ocean by strong westerly winds analytical and numerical models have suggested that transient eddies may be important in transporting this momentum away from the region of wind forcing either horizontally1or vertically downwards where it is balanced by bottom topographic drag2 5 there are however few long term in situ observations of horizontal eddy momentum flux6 8 and no large scale measurements of vertical eddy fluxes to test these models as a result the momentum balance of the antarctic circumpolar current acc remains uncertain and the role of eddies controversial here we use geosat satellite altimeter data to resolve directional eddy kinetic energy and horizontal eddy momentum flux in the acc on fine spatial and temporal scales the complex spatial distribution of surface eddy momentum flux is strongly influenced by bottom topography the horizontal eddy momentum flux tends generally to concentrate the mean flow although some regions of divergence are observed our results show that the zonally averaged horizontal eddy momentum flux from transient eddies is an order of magnitude too small and in the wrong direction to directly balance the eastward momentum input from wind1

sulfate platform basin transition of the lower werra anhydrite zechstein upper permian western poland facies and petrography abstract the peripheral evaporite platform of the zechstein upper permian werra anhydrite of western poland comprises a series of shoals with thick sulfate deposits and lows with thin sulfate and thick halite deposits three cores were selected to examine facies variations from a sulfate platform slope and basin the basal unit of the lower werra anhydrite is represented by different varieties of nodular bedded nodular fluidal nodular and brecciated facies some nodular fabrics probably originated within sabkha and or gypsumpond environments and the deposit was then mechanically redistributed the absence of nodular structures in units other than the lower one in two of the wells suggests that the origin of these structures cannot be related to deep burial other units of the lower werra anhydrite represent subaqueous deposits the facies in the middle and upper units have no recent analog in coastal salina environments turbidity currents displaced sulfates from the platform to the adjacent basin the origin of lenticular bedded anhydrite may be related to deformation by compaction or by ravitational instability and slumping which may have initiated crystallization or recrystallization of anhydrite the vertical sequence of facies shows a distinct deepening upward trend starting from the top of the basal nodular units deposition in shallow salina environments dominated the early history of the lower werra anhydrite basin although it was probably preceded by transgressive sabkha deposits relatively thick nodular anhydrites probably formed by syndepositional diagenesis of probable salina deposits and minor sabkha sediments gypsum was the original sedimentary mineral it was later transformed into anhydrite during either early or late burial diagenesis we show that in deeply buried evaporites not only some macroscopic primary textures remain but also even microscopic details which allow reconstruction of depositional environments and primary mineralogy of ancient anhydrites

rapid cross density ocean mixing at mid depths in the drake passage measured by tracer release diapycnal mixing across density surfaces is an important process in the global ocean overturning circulation1 2 3 mixing in the interior of most of the ocean however is thought to have a magnitude just one tenth of that required to close the global circulation by the downward mixing of less dense waters4 some of this deficit is made up by intense near bottom mixing occurring in restricted hot spots associated with rough ocean floor topography5 6 but it is not clear whether the waters at mid depth 1 000 to 3 000 metres are returned to the surface by cross density mixing or by along density flows7 here we show that diapycnal mixing of mid depth 1 500 metres waters undergoes a sustained 20 fold increase as the antarctic circumpolar current flows through the drake passage between the southern tip of south america and antarctica our results are based on an open ocean tracer release of trifluoromethyl sulphur pentafluoride we ascribe the increased mixing to turbulence generated by the deep reaching antarctic circumpolar current as it flows over rough bottom topography in the drake passage scaled to the entire circumpolar current the mixing we observe is compatible with there being a southern component to the global overturning in which about 20 sverdrups 1 sv 106 m3 s 1 upwell in the southern ocean with cross density mixing contributing a significant fraction 20 to 30 per cent of this total and the remainder upwelling along constant density surfaces the great majority of the diapycnal flux is the result of interaction with restricted regions of rough ocean floor topography

lateral diffusivity from tracer release experiments in the tropical north atlantic thermocline lateral diffusivity is computed from a tracer release experiment in the northeastern tropical atlantic thermocline the uncertainties of the estimates are inferred from a synthetic particle release using a high resolution ocean circulation model the main method employed to compute zonal and meridional components of lateral diffusivity is the growth of the second moment of a cloud of tracer the application of an areal comparison method for estimating tracer based diffusivity in the field experiments is also discussed the best estimate of meridional eddy diffusivity in the guinea upwelling region at about 300 m depth is estimated to be inline image m2 s 1 the zonal component of lateral diffusivity is estimated to be inline image m2 s 1 while areal comparison method yields areal equivalent zonal diffusivity component of inline image m2 s 1 in comparison to ky kx is about twice larger resulting from the tracer patch stretching by zonal jets employed conceptual jet model indicates that zonal jet velocities of about inline image m s 1 are required to explain the enhancement of the zonal eddy diffusivity component finally different sampling strategies are tested on synthetic tracer release experiments they indicate that the best sampling strategy is a sparse regular sampling grid covering most of the tracer patch

direct estimate of lateral eddy diffusivity upstream of drake passage abstractthe first direct estimate of the rate at which geostrophic turbulence mixes tracers across the antarctic circumpolar current is presented the estimate is computed from the spreading of a tracer released upstream of drake passage as part of the diapycnal and isopycnal mixing experiment in the southern ocean dimes the meridional eddy diffusivity a measure of the rate at which the area of the tracer spreads along an isopycnal across the antarctic circumpolar current is 710 260 m2 s 1 at 1500 m depth the estimate is based on an extrapolation of the tracer based diffusivity using output from numerical tracers released in a one twentieth of a degree model simulation of the circulation and turbulence in the drake passage region the model is shown to reproduce the observed spreading rate of the dimes tracer and suggests that the meridional eddy diffusivity is weak in the upper kilometer of the water column with values below 500 m2 s 1 and peaks at the steering level near 2 km where the eddy ph

diapycnal mixing in the antarctic circumpolar current the vertical dispersion of a tracer released on a density surface near 1500 m depth in the antarctic circumpolar current west of drake passage indicates that the diapycnal diffusivity averaged over 1 yr and over tens of thousands of square kilometers is 1 3 6 0 2 3 10 25 m 2 s 21 diapycnal diffusivity estimated from turbulent kinetic energy dissipation measurements about the area occupied by the tracer in austral summer 2010 was somewhat less but still within a factor of 2 at 0 75 6 0 07 3 10 25 m 2 s 21 turbulent diapycnal mixing of this intensity is characteristic of the midlatitude ocean interior where the energy for mixing is believed to derive from internal wave breaking indeed despite the frequent and intense atmospheric forcing experienced by the southern ocean the amplitude of finescale velocity shear sampled about the tracer was similar to background amplitudes in the midlatitude ocean with levels elevated to only 20 50 above the garrett munk reference spectrum these results add to a long line of evidence that diapycnal mixing in the interior middepth ocean is weak and is likely too small to dictate the middepth meridional overturning circulation of the ocean

eulerian and lagrangian isopycnal eddy diffusivities in the southern ocean of an eddying model abstractlagrangian isopycnal diffusivities quantify the along isopycnal mixing of any tracer with mean gradients along isopycnal surfaces they are studied in the southern ocean of the 1 10 parallel ocean program pop model using more than 50 000 float trajectories concurrent eulerian isopycnal diffusivities are estimated directly from the eddy fluxes and mean tracer gradients consistency spatial variation and relation to mean jets are evaluated the diffusivities are calculated in bins large enough to reduce contributions from the rotational components that do not lead to net tracer mixing because the mean jets are nonzonal and nonparallel meridional dispersion includes standing eddies and is significantly different from cross stream dispersion with the subtraction of the local eulerian mean the full lagrangian diffusivity tensor can be estimated along stream diffusivities are about 6 times larger than cross stream diffusivities along streamline averages of eulerian and lagrangian isopycnal d

mixing of a tracer in the pycnocline a patch of sulfur hexafluoride was released in may 1992 in the eastern north atlantic on an isopycnal surface near 300 m depth and was surveyed over a period of 30 months as it dispersed across and along isopycnal surfaces the diapycnal eddy diffusivity k estimated for the first 6 months was 0 12 0 02 cm2 s while for the subsequent 24 months it was 0 17 0 02 cm2 s the vertical tracer distribution remained very close to gaussian for the full 30 months as the root mean square rms dispersion grew from 5 to 50 m lateral dispersion was measured on several scales the growth of the rms width of the tracer streaks from less than 100 m to approximately 300 m within 2 weeks implies an isopycnal diffusivity of 0 07 m2 s at scales of 0 1 to 1 km larger than expected from the interaction between vertical shear of the internal waves and diapycnal mixing teasing of the overall patch initially about 25 km across into streaks with an overall length of 1800 km within 6 months supports predictions of exponential growth by the mesoscale strain field at a rate of 3 0 5 10 7 s 1 the rms width of these streaks estimated as 3 km and maintained in the face of the streak growth indicates an isopycnal diffusivity of 2 m2 s at scales of 1 to 10 km much greater than expected from internal wave shear dispersion the patch was painted in albeit streakily by 12 months confirming expectations from analytical and numerical models homogenization of the patch continued during the subsequent 18 months while the patch continued to spread with an effective isopycnal eddy diffusivity on the order of 1000 m2 s acting at scales of 30 to 300 km

evidence for enhanced eddy mixing at middepth in the southern ocean abstract satellite altimetric observations of the ocean reveal surface pressure patterns in the core of the antarctic circumpolar current acc that propagate downstream eastward but slower than the mean surface current by about 25 the authors argue that these observations are suggestive of baroclinically unstable waves that have a steering level at a depth of about 1 km detailed linear stability calculations using a hydrographic atlas indeed reveal a steering level in the acc near the depth implied by the altimetric observations calculations using a nonlinear model forced by the mean shear and stratification observed close to the core of the acc coinciding with a position where mooring data and direct eddy flux measurements are available reveal a similar picture albeit with added details when eddy fluxes are allowed to adjust the mean state computed eddy kinetic energy and eddy stress are close to observed magnitudes with steering levels between 1 and 1 5 km broadly consistent with observatio

sedimentology and paleoenvironmental evolution of messinian evaporites in the iskenderun hatay basin complex southern turkey abstract messinian evaporites which resulted from the salinity crisis during the final closure of the mediterranean sea are exposed in se turkey these evaporites formed in two isolated sub basins iskenderun arsuz ia and hatay samandag hs which belong to different depositional configurations and tectonic structures the neogene fill of these sub basins consists of a thick sedimentary succession that started with early miocene terrestrial clastics followed by reefs middle miocene and shallow water siliciclastics tortonian early to late miocene and finally messinian evaporates these sub basins accumulated in a diverse range of depositional environments from very shallow to deeper water evaporite facies in the ia sub basin consist of sabkhas saline lagoons and ponds they are mainly represented by chemical deposits such as scattered gypsum nodules and balls nodular bedded gypsum laminated gypsum type a and selenites type s1 evaporites in the hs sub basin mainly consist of detrital gypsum composed of gypsum laminae type b c gypsum arenite rudites and deeper water selenites 20 m and resedimented selenites type s2 which were deposited on a sulfate platform with a slope basin transitional zone secondary gypsum with alabastrine and porphyroblastic textures as well as satin spar veins is commonly associated with the sabkha type evaporites of the ia sub basin deeper water clastic evaporites of the hs sub basin have generally remained as primary gypsum or have only been slightly affected by diagenetic alterations the isotope values 87 86 sr 18 o smow and 34 s cdt from the different kinds of gypsum lithofacies of the sub basin are similar to those of the messinian evaporites in other peri mediterranean basins indicating an origin from marine water without external or basinal contributions the messinian evaporites examined in this paper are overlain by early pliocene zanclean deposits composed of shallow and deep water siliciclastics and carbonates with local intercalations of lago mare type strata throughout the messinian evaporitic stage the ia sub basin was mainly comprised of shallow water evaporites while the hs sub basin underwent deepening related to regional tectonics induced by the dead sea fault during the construction of the hatay graben

global variability of the wavenumber spectrum of oceanic mesoscale turbulence abstractthe wavenumber spectra of sea surface height from satellite altimeter observations have revealed complex spatial variability that cannot be explained by a universal theory of mesoscale turbulence near the edge of the core regions of high eddy energy agreement is observed with the prediction of the surface quasigeostrophic sqg turbulence theory which has fundamental differences from that of the traditional quasigeostrophic qg turbulence theory in the core regions of high eddy energy the spectra are consistent with frontogenesis that is not fully accounted for by the sqg theory however the observations in the vast ocean interior of low eddy energy exhibit substantial differences from the predictions of existing theories of oceanic mesoscale turbulence the spectra in these regions may reflect the ocean s response to short scale atmospheric forcing and air sea interaction the observations presented in this paper serve as a test bed for new theories and ocean general circulation models

quantifying and interpreting striations in a subtropical gyre a spectral perspective abstractthe amplitude origin and direction of striations in the subtropical gyre are investigated using simulated and analytical multidimensional spectra striations defined as banded structures in the low frequency motions account for a noticeable percentage of zonal velocity variability in the east north pacific enp 25 42 n 150 130 w and central north pacific cnp 10 22 n 132 e 162 w regions in an eddying global ocean model thus they likely are nonnegligible in mixing and transport processes striations in the enp region are nonzonal and are embedded in the nonzonal gyre flow whereas striations in the cnp region are more zonal as are the mean gyre flows an idealized 1 5 layer model shows the gyre flow partially determines their directions which qualitatively resemble those in the global eddying model in the linear limit structures are quasi stationary frequency 0 linear rossby waves and the gyre flow influences the direction by influencing the nature of the zero rossby wave f

a multidimensional spectral description of ocean variability abstractan updated empirical analytical model for the frequency and wavenumber distribution of balanced motion in the ocean is presented the spectrum model spans periods longer than the inertial but shorter than a decade and wavelengths between 100 and 10 000 km assuming geostrophic dynamics a spectrum model for the streamfunction is constructed to be consistent with a range of observations including sea surface height from satellite altimetry velocity from moored and shipboard instruments and temperature from moorings first order characteristics of the observed spectra including amplitude and spectral moments vary slowly geographically the spectrum model is horizontally anisotropic accommodating observations that zonal wavenumber frequency spectra are dominated by a nondispersive line qualitative and quantitative agreement is found with one dimensional frequency and wavenumber spectra and observed vertical profiles of variance illustrative application is made of the model spectrum to obse