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

rapid injection of near inertial shear into the stratified upper ocean at an antarctic circumpolar current front the impact on the upper ocean of the passage of a short intense storm over a southern ocean site in proximity to an antarctic circumpolar current front is characterized the storm causes a wind induced deepening of the mixed layer and generates an inertial current immediate post storm observations indicate a mixed layer extending to approximately 50 m depth subsequent measurements show the upper ocean to have re stratified injecting near inertial shear in stratified waters within 1 day of the storm s passage this time scale for the development of near inertial shear is one order of magnitude shorter than that predicted by the dispersion paradigm the observed rapid changes in upper ocean stratification point to the existence of an as yet undocumented efficient mechanism for injection of near inertial shear into the stratified ocean that is in turn associated with enhanced turbulence and mixing

internal waves and turbulence in the antarctic circumpolar current abstractthis study reports on observations of turbulent dissipation and internal wave scale flow properties in a standing meander of the antarctic circumpolar current acc north of the kerguelen plateau the authors characterize the intensity and spatial distribution of the observed turbulent dissipation and the derived turbulent mixing and consider underpinning mechanisms in the context of the internal wave field and the processes governing the waves generation and evolution the turbulent dissipation rate and the derived diapycnal diffusivity are highly variable with systematic depth dependence the dissipation rate is generally enhanced in the upper 1000 1500 m of the water column and both the dissipation rate and diapycnal diffusivity are enhanced in some places near the seafloor commonly in regions of rough topography and in the vicinity of strong bottom flows associated with the acc jets turbulent dissipation is high in regions where internal wave energy is high consistent with the idea that i

eddy induced variability in southern ocean abyssal mixing on climatic timescales the southern ocean plays a pivotal role in the global ocean circulation and climate1 2 3 there the deep water masses of the world ocean upwell to the surface and subsequently sink to intermediate and abyssal depths forming two overturning cells that exchange substantial quantities of heat and carbon with the atmosphere4 5 the sensitivity of the upper cell to climatic changes in forcing is relatively well established6 however little is known about how the lower cell responds and in particular whether small scale mixing in the abyssal southern ocean an important controlling process of the lower cell7 8 is influenced by atmospheric forcing here we present observational evidence that relates changes in abyssal mixing to oceanic eddy variability on timescales of months to decades observational estimates of mixing rates obtained along a repeat hydrographic transect across drake passage are shown to be dependent on local oceanic eddy energy derived from moored current meter and altimetric measurements as the intensity of the regional eddy field is regulated by the southern hemisphere westerly winds9 10 our findings suggest that southern ocean abyssal mixing and overturning are sensitive to climatic perturbations in wind forcing

transformation of deep water masses along lagrangian upwelling pathways in the southern ocean upwelling of northern deep waters in the southern ocean is fundamentally important for the closure of the global meridional overturning circulation and delivers carbon and nutrient rich deep waters to the sea surface we quantify water mass transformation along upwelling pathways originating in the atlantic indian and pacific and ending at the surface of the southern ocean using lagrangian trajectories in an eddy permitting ocean state estimate recent related work shows that upwelling in the interior below about 400 m depth is localized at hot spots associated with major topographic features in the path of the antarctic circumpolar current while upwelling through the surface layer is more broadly distributed in the ocean interior upwelling is largely isopycnal atlantic and to a lesser extent indian deep waters cool and freshen while pacific deep waters are more stable leading to a homogenization of water mass properties as upwelling water approaches the mixed layer there is net strong transformation toward lighter densities due to mixing of freshwater but there is a divergence in the density distribution as upper circumpolar deep water tends become lighter and dense lower circumpolar deep water tends to become denser the spatial distribution of transformation shows more rapid transformation at eddy hot spots associated with major topography where density gradients are enhanced however the majority of cumulative density change along trajectories is achieved by background mixing we compare the lagrangian analysis to diagnosed eulerian water mass transformation to attribute the mechanisms leading to the observed transformation

enhancement of mesoscale eddy stirring at steering levels in the southern ocean abstract meridional cross sections of effective diffusivity in the southern ocean are presented and discussed the effective diffusivity keff characterizes the rate at which mesoscale eddies stir properties on interior isopycnal surfaces and laterally at the sea surface the distributions are obtained by monitoring the rate at which eddies stir an idealized tracer whose initial distribution varies monotonically across the antarctic circumpolar current acc in the absence of observed maps of eddying currents in the interior ocean the advecting velocity field is taken from an eddy permitting state estimate of the southern ocean sose a three dimensional advection diffusion equation is solved and the diffusivity diagnosed by applying the nakamura technique on both horizontal and isopycnal surfaces the resulting meridional sections of keff reveal intensified isopycnal eddy stirring reaching values of 2000 m2 s 1 in a layer deep beneath the acc but rising toward the surface on the equatorward flank

turbulence and diapycnal mixing in drake passage abstractdirect measurements of turbulence levels in the drake passage region of the southern ocean show a marked enhancement over the phoenix ridge at this site the antarctic circumpolar current acc is constricted in its flow between the southern tip of south america and the northern tip of the antarctic peninsula observed turbulent kinetic energy dissipation rates are enhanced in the regions corresponding to the acc frontal zones where strong flow reaches the bottom in these areas turbulent dissipation levels reach 10 8 w kg 1 at abyssal and middepths the mixing enhancement in the frontal regions is sufficient to elevate the diapycnal turbulent diffusivity acting in the deep water above the axis of the ridge to 1 10 4 m2 s 1 this level is an order of magnitude larger than the mixing levels observed upstream in the acc above smoother bathymetry outside of the frontal regions dissipation rates are o 10 10 w kg 1 comparable to the background levels of turbulence found throughout most mid and

overturning circulation driven by breaking internal waves in the deep ocean a global estimate of the water mass transformation by internal wave driven mixing in the deep ocean is presented the estimate is based on the energy conversion from tidal and geostrophic motions into internal waves combined with a turbulent mixing parameterization we show that internal wave driven mixing in the deep ocean can sustain 20 30 sv of water mass transformation one third or more of this transformation is attributed to lee waves generated by geostrophic motions flowing over rough topography primarily in the southern ocean while these results are uncertain due to many assumptions poorly constrained parameters and data noise that enter in the calculation the result that lee wave driven mixing plays an important role in the abyssal ocean circulation is likely robust the implication is that lee wave driven mixing should be represented in ocean and climate models but currently it is not citation nikurashin m and r ferrari 2013 overturning circulation driven by breaking internal waves in the deep ocean geophys res lett 40 doi 10 1002 grl 50542

quantifying high frequency wind energy flux into near inertial motions in the southeast pacific abstractwind forced internal waves close to the inertial frequency are ubiquitous throughout the world s oceans but observational constraints on their global energetics and impact on subsurface mixing remain scarce this study reports on velocity measurements from three electromagnetic autonomous profiling explorers em apex deployed in february 2009 these floats observed downward propagating near inertial internal waves near the subantarctic and polar fronts of the antarctic circumpolar current these waves were episodic and enhanced at middepth between 500 and 1000 m depth integrated kinetic energy varied between 1 and 7 kj m 2 and averaged 1 6 kj m 2 with typical group velocities of 40 m day 1 implying an average energy flux of 3 mw m 2 at the mixed layer base decreasing to approximately 25 of that value at 1500 m modeled currents forced by reanalysis winds along each float track agree with observed surface currents from em apex provided that mixed layer depth is restricted to the layer of weak

the global influence of localized dynamics in the southern ocean the circulation of the southern ocean connects ocean basins links the deep and shallow layers of the ocean and has a strong influence on global ocean circulation climate biogeochemical cycles and the antarctic ice sheet processes that act on local and regional scales which are often mediated by the interaction of the flow with topography are fundamental in shaping the large scale three dimensional circulation of the southern ocean recent advances provide insight into the response of the southern ocean to future change and the implications for climate the carbon cycle and sea level rise

jets and topography jet transitions and the impact on transport in the antarctic circumpolar current the southern ocean s antarctic circumpolar current acc naturally lends itself to interpretations using a zonally averaged framework yet navigation around steep and complicated bathymetric obstacles suggests that local dynamics may be far removed from those described by zonally symmetric models in this study both observational and numerical results indicate that zonal asymmetries in the form of topography impact global flow structure and transport properties the conclusions are based on a suite of more than 1 5 million virtual drifter trajectories advected using a satellite altimetry derived surface velocity field spanning 17 years the focus is on sites of cross front transport as defined by movement across selected sea surface height contours that correspond to jets along most of the acc cross front exchange is localized in the lee of bathymetric features with more than 75 of crossing events occurring in regions corresponding to only 20 of the acc s zonal extent these observations motivate a series of numerical experiments using a two layer quasigeostrophic model with simple zonally asymmetric topography which often produces transitions in the front structure along the channel significantly regimes occur where the equilibrated number of coherent jets is a function of longitude and transport barriers are not periodic jet reorganization is carried out by eddy flux divergences acting to both accelerate and decelerate the mean flow of the jets eddy kinetic energy is amplified downstream of topography due to increased baroclinicity related to topographic steering the combination of high eddy kinetic energy and recirculation features enhances particle exchange these results stress the complications in developing consistent circumpolar definitions of the acc fronts

displacement and strain patterns from naturally occurring shear zone terminations abstract strain distribution patterns are described from several naturally occurring ductile shear zone terminations and a two fold classification is suggested type i termination patterns show a symmetrical decrease in strain area and intensity and are associated with very low shear strain values in the main shear zone the more common type ii termination patterns show a symmetrical increase in strain area with decrease in strain intensity some brittle ductile examples of type ii terminations contain secondary shears that resemble splay faults all the available evidence suggests that the deformation near the terminations of these shear zones is not plane strain nor do the observed strain patterns readily fit the existing theoretical models

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

diagnosing the southern ocean overturning from tracer fields abstract the strength and structure of the southern hemisphere meridional overturning circulation smoc is related to the along isopycnal and vertical mixing coefficients by analyzing tracer and density fields from a hydrographic climatology the meridional transport of upper circumpolar deep water ucdw across the antarctic circumpolar current acc is expressed in terms of the along isopycnal k and diapycnal d tracer diffusivities and in terms of the along isopycnal potential vorticity mixing coefficient kpv uniform along isopycnal 600 m2 s 1 and low vertical mixing 10 5 m2 s 1 can maintain a southward transport of less than 60 sv sv 106 m2 s 1 of ucdw across the acc which is distributed largely across the south pacific and east indian ocean basins for vertical mixing rates of o 10 4 m2 s 1 or greater the inferred transport is significantly enhanced the transports inferred from both tracer and density distributions suggest a ratio k to d of o 2 106 particularly on deeper layers

control of lower limb overturning circulation in the southern ocean by diapycnal mixing and mesoscale eddy transfer a simple model is developed of the lower limb of the meridional overturning circulation in the southern ocean based on residual mean theory it is hypothesized that the strength of the lower limb overturning is strongly controlled by the magnitude of abyssal diapycnal mixing and that of mesoscale eddy transfer k in particular it is argued that k the scaling and associated theory find support in a suite of sensitivity experiments with an idealized ocean general circulation model this study shows that intense diapycnal mixing is required to close the buoyancy budget of the lower limb overturning circulation in contrast to the upper limb where air sea buoyancy fluxes can provide the required diabatic forcing

palynology and chronostratigraphy of the upper cretaceous in the subsurface of the barinas area western venezuela palynological and well log analyses of cretaceous strata from southeastern venezuela allow the recognition of third order eustatic cycles and are the basis for a chronostratigraphic framework with a datum approximately every 0 8 m y this definition permits the correlation of events in the local geologic evolution with regionally important sedimentological and tectonic events an early cretaceous marine transgression reached areas north of the andes before 113 ma however according to our framework the transgression extended into the barinas area shortly after 98 ma an interval of relatively low sea level from 95 5 ma to 91 5 ma is represented by oil bearing sandstones and dolomitic limestones a second marine transgression reached the area at approximately 91 5 ma and resulted in the deposition of organic rich clastics that are correlatable with source rocks from areas to the north a major hiatus santonian campanian encompasses approximately 11 m y and probably is related to the emplacement of oceanic rocks in western colombia a younger major hiatus maastrichtian eocene encompasses approximately 26 m y and probably is related to the emplacement of the lara nappes in northern venezuela two other minor intra turonian and intra maastrichtian hiatuses are recognized and encompass approximately 1 5 m y each

widespread intense turbulent mixing in the southern ocean observations of internal wave velocity fluctuations show that enhanced turbulent mixing over rough topography in the southern ocean is remarkably intense and widespread mixing rates exceeding background values by a factor of 10 to 1000 are common above complex bathymetry over a distance of 2000 to 3000 kilometers at depths greater than 500 to 1000 meters this suggests that turbulent mixing in the southern ocean may contribute crucially to driving the upward transport of water closing the ocean s meridional overturning circulation and thus needs to be represented in numerical simulations of the global ocean circulation and the spreading of biogeochemical tracers

radiation and dissipation of internal waves generated by geostrophic motions impinging on small scale topography application to the southern ocean abstract recent estimates from observations and inverse models indicate that turbulent mixing associated with internal wave breaking is enhanced above rough topography in the southern ocean in most regions of the ocean abyssal mixing has been primarily associated with radiation and breaking of internal tides in this study it is shown that abyssal mixing in the southern ocean can be sustained by internal waves generated by geostrophic motions that dominate abyssal flows in this region theory and fully nonlinear numerical simulations are used to estimate the internal wave radiation and dissipation from lowered acoustic doppler current profiler ladcp ctd and topography data from two regions in the southern ocean drake passage and the southeast pacific the results show that radiation and dissipation of internal waves generated by geostrophic motions reproduce the magnitude and distribution of dissipation previously inferred from finescale measurements in the region suggesting that it is one of the

four views of a portion of the north atlantic subtropical gyre abstract data from four cruises to the triangle centered at 27 n 32 30 w were smoothed by fitting second degree polynomials at each of about 30 different density surfaces the density intervals were p 0 3 corresponding to about 50 db intervals in pressure from the polynomials determination was made of central values horizontal derivatives and laplacians of the fields of pressure salt oxygen and dynamic height in addition maps of the fits and deviations of each nation from the smoothed fits were produced from the steady advective diffusive equation and the smoothed fits to the age oxygen and dynamic height fields the lateral isopycnal diffusivity as estimated to be kh 0 5 103 m2 s 1 although the salt field was reasonably stable from cruise to cruise the variability of the baroclinic velocity shear was found to be as large as the baroclinic shear itself the maps suggest a wobble of the gyre the standard deviation of the fluctuations at each nation from the smoothed fits when norma

lateral extrusion in transpression zones the importance of boundary conditions the homogeneous transpression strain model formulated by sanderson and marchini journal of structural geology 6 449 458 1984 has proved to be a useful tool in the analysis of complex three dimensional deformation patterns however some of the boundary conditions introduced in the mathematical model may be unrealistic and unnecessarily restrictive in this paper a strain matrix for unconfined transpression and transtension is derived in which material is allowed to move not only vertically but also horizontally in and out of the deforming zone parallel to its length lateral extrusion three end member plane strain components are defined wrench simple shear pure shear in xy lateral stretch and pure shear in yz vertical stretch these biaxial strains can be viewed as the apices of a strain triangle for unconfined transpression or transtension the edges of the triangle correspond to triaxial pure shear non coaxial biaxial lateral extrusion and the triaxial confined transpressional or transtensional strain of sanderson and marchini during unconfined transpression the orientation and in particular the geometry k value of the finite strain ellipsoid depends upon not only the amount of shortening across the zone and the amount of strike slip parallel to the zone but also upon the ratio of vertical to lateral stretch this can present serious difficulties when attempting to use finite strains to infer the direction and magnitude of zone boundary displacements examples of transpression zones in which there is evidence of a component of lateral extrusion are described from sw cyprus and central scotland these examples illustrate that antithetic strike slip shearing is a kinematic requirement of laterally unconfined transpression implying that synchronous shear sense indicators may give opposite senses of movement in shear zones specific geometric and mechanical boundary conditions together with internal fault zone rheologies may favour the lateral extrusion of material kinematic partitioning can occur to form fault bounded domains in which end member biaxial and or non coaxial strains are developed analysis of such domains can give a clearer understanding of regional scale triaxial deformations these findings illustrate the importance of establishing displacement boundary conditions when qualitatively or quantitatively analysing crustal deformation zones

strain partitioning in ductile shear zones an example from a lower pennine nappe of switzerland abstract the rocks of the maggia nappe a lower pennine nappe of the swiss alps were deformed in at least three phases during alpine orogeny hercynian granites in the core of the nappe developed ductile shear zones during the early phases of deformation but between shear zones they remained almost undeformed both heterogeneous simple shear and heterogeneous volume change played an important role in the formation of the ductile shear zones partitioning of different strain components indicates a volume loss of nearly 80 90 towards the centres of some of the shear zones such a large amount of volume loss is also corroborated by strain analysis of deformed xenoliths in other shear zones of the same region a comparative study of theoretical strain paths and the natural results indicates constant shear strain rate but changing dilation rate during deformation

flow and strain patterns at the terminations of tapered shear zones with the help of corner flow theory this paper numerically analyzes the deformation pattern at the terminations of tapered shear zones the walls of which are rigid and move parallel to each other in opposite directions the overall flow pattern is characterized by curvilinear particle paths that show convexity towards and opposite to the tapering direction respectively for low 10 inclinations of the wall verging opposite to the sense of wall movement in tapered shear zones there are two distinct fields of instantaneous shortening and extension parallel to the direction of wall movement numerical models reveal that the finite strain distributions are generally asymmetrical with larger strain concentration occurring near the wall verging opposite to sense of wall movement the s foliation trajectories show a curvilinear pattern convexing against the tapering direction the analysis of rotationality vorticity indicates that the sense of vorticity near the synthetically verging wall is reverse to the sense of wall movement however wk is one everywhere within the shear zone

isopycnal dispersion in natre abstract finescale velocity and density fluctuations consist of both internal waves and vorticity containing perturbations vortical modes a recent decomposition of observations obtained as part of the north atlantic tracer release experiment natre permits one to investigate isopycnal stirring associated with vortical modes this stirring is treated here as a relative dispersion problem in the context of 2d turbulence isopycnal diffusivities attain values on the order of 1 m2 s 1 after an initial transient of 5 10 days after 2 weeks a patch of tracer with initial radius of 25 m is predicted to have evolved into a convoluted web having an rms radius of 2 4 km these estimates agree with observations of the evolution of an anthropogenic tracer in natre

the deformation matrix for simultaneous simple shearing pure shearing and volume change and its application to transpression transtension tectonics simultaneous simple shearing and pure shearing with or without additional volume change can be combined into a single upper triangular deformation matrix the off diagonal term is named the effective shear strain and is a simple function of the pure shearing and simple shearing components a three dimensional deformation matrix for the simultaneous combination of coaxial deformation with or without additional volume change and up to three simple shearing systems with mutually orthogonal shear planes is also presented by using this matrix one can easily extract the various properties of incremental as well as finite strain and the progressive as well as finite rotation of passive markers during deformation the case of transpression transtension is revised using the unified deformation matrix the orientation of the major axis of the strain ellipsoid 1 is always horizontal if the deformation is transtensional switches from horizontal to vertical during transpressional wrenching 1 wk 0 81 for constant vorticity deformations and is always vertical for highly transpressional deformations wk 0 81 for transpression material lines initially rotate towards the horizontal shearing direction but generally turn to rotate towards the vertical axis after a certain strain for transtension all material lines rotate towards a direction in the horizontal plane which is oblique to the shearing direction

eddy induced modulation of turbulent dissipation over rough topography in the southern ocean abstractmesoscale eddies are universal features of the ocean circulation yet the processes by which their energy is dissipated remain poorly understood one hypothesis argues that the interaction of strong geostrophic flows with rough bottom topography effects an energy transfer between eddies and internal waves with the breaking of these waves causing locally elevated dissipation focused near the sea floor this study uses hydrographic and velocity data from a 1 yr mooring cluster deployment in the southern ocean to test this hypothesis the moorings were located over a small 10 km topographic obstacle to the east of drake passage in a region of high eddy kinetic energy and one was equipped with an adcp at 2800 m depth from which internal wave shear variance and dissipation rates were calculated examination of the adcp time series revealed a predominance of upward propagating internal wave energy and a significant correlation r 0 45 between shear variance levels and subinertial near bottom cur

equilibration of the antarctic circumpolar current by standing meanders the insensitivity of the antarctic circumpolar current acc s prominent isopycnal slope to changes in wind stress is thought to stem from the action of mesoscale eddies that counterbalance the wind driven ekman overturning a framework verified in zonally symmetric circumpolar flows substantial zonal variations in eddy characteristics suggest that local dynamics may modify this balance along the path of the acc analysis of an eddy resolving ocean gcm shows that the acc can be broken into broad regions of weak eddy activity where surface winds steepen isopycnals and a small number of standing meanders across which the isopycnals relax meanders are coincident with sites of i strong eddy induced modification of the mean flow and its vertical structure as measured by the divergence of the eliassen palm flux and ii enhancement of deep eddy kinetic energy by up to two orders of magnitude over surrounding regions within meanders the vorticity budget shows a balance between the advection of relative vorticity and horizontal divergence providing a mechanism for the generation of strong vertical velocities and rapid changes in stratification temporal fluctuations in these diagnostics are correlated with variability in both the eliassen palm flux and bottom speed implying a link to dissipative processes at the ocean floor at larger scales bottom pressure torque is spatially correlated with the barotropic advection of planetary vorticity which links to variations in meander structure from these results it is proposed that the flexing of standing meanders provides an alternative mechanism for reducing the sensitivity of the acc s baroclinicity to changes in forcing separate from an acc wide change in transient eddy characteristics

lagrangian pathways of upwelling in the southern ocean the spatial and temporal variability of upwelling into the mixed layer in the southern ocean is studied using a 1 10 ocean general circulation model virtual drifters are released in a regularly spaced pattern across the southern ocean at depths of 250 500 and 1000 m during both summer and winter months the drifters are advected along isopycnals for a period of four years unless they outcrop into the mixed layer where lateral advection and a parameterization of vertical mixing is applied the focus of this study is on the discrete exchange between the model mixed layer and the interior localization of interior mixed layer exchange occurs downstream of major topographic features across the indian and pacific basins creating hotspots of outcropping minimal outcropping occurs in the atlantic basin while 59 of drifters outcrop in the pacific sector and in drake passage the region from 140 w to 40 w a disproportionately large amount even when considering the relative basin sizes due to spatial and temporal variations in mixed layer depth the lagrangian trajectories provide a statistical measure of mixed layer residence times for each exchange into the mixed layer the residence time has a rayleigh distribution with a mean of 30 days the cumulative residence time of the drifters is 261 194 days over a period of four years these results suggest that certain oceanic gas concentrations such as co 2 and 14 c will likely not reach equilibrium with the atmosphere before being re subducted

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

antarctic intermediate water and subantarctic mode water formation in the southeast pacific the role of turbulent mixing abstract during the 2005 austral winter late august early october and 2006 austral summer february mid march two intensive hydrographic surveys of the southeast pacific sector of the southern ocean were completed in this study the turbulent kinetic energy dissipation rate diapycnal diffusivity and buoyancy flux jb are estimated from the ctd o2 and xctd profiles for each survey enhanced of o 10 3 to 10 4 m2 s 1 is found near the subantarctic front saf during both surveys during the winter survey enhanced was also observed north of the subduction front the northern boundary of the winter deep mixed layer north of the saf in contrast the summer survey found enhanced across the entire region north of the saf below the shallow seasonal mixed layer the enhanced below the mixed layer decays rapidly with depth a number of ocean processes are considered that may provide the energy flux necessary to support the observed diffusivity the observed buoyancy flux 4 0 10 8 m2 s 3 surr

terminations of ductile shear zones abstract we propose a plane strain model for ductile shear zone terminations in rocks that otherwise record no visible shear strain this model may explain the strain distribution patterns in naturally occurring terminations of shear zone which show in the xz plane of finite strain 1 a decrease in the area of finite strain and in strain intensity ellipsoidal or lens like feature and 2 an increase in the strained area as strain intensity decreases splay like or horse tail feature

a microscale view of mixing and overturning across the antarctic circumpolar current abstractthe relative roles of isoneutral stirring by mesoscale eddies and dianeutral stirring by small scale turbulence in setting the large scale temperature salinity relation of the southern ocean against the action of the overturning circulation are assessed by analyzing a set of shear and temperature microstructure measurements across drake passage in a triple decomposition framework it is shown that a picture of mixing and overturning across a region of the antarctic circumpolar current acc may be constructed from a relatively modest number of microstructure profiles the rates of isoneutral and dianeutral stirring are found to exhibit distinct characteristic and abrupt variations most notably a one to two orders of magnitude suppression of isoneutral stirring in the upper kilometer of the acc frontal jets and an order of magnitude intensification of dianeutral stirring in the subpycnocline and deepest layers of the acc these variations balance an overturning circulation with meridional flo