surface eddy momentum flux and velocity variances in the southern ocean from geosat altimetry abstract satellite altimetry has previously been used to map the magnitude of the surface eddy variability of the global oceans but the direction of the time variable velocities have been more difficult to determine here a technique is presented for resolving both magnitude and direction of residual surface geostrophic velocities at geosat altimeter crossover points providing a two year time series with a temporal resolution of 17 days and horizontal resolution of around 100 km the time series of residual velocity components are then used to determine surface eddy statistics in the southern ocean and to investigate the role of transient eddies in the southern ocean momentum balance the surface eddy statistics from geosat crossover points show a complex spatial distribution in the surface reynolds stresses u 2 v 2 u v in contrast to the assumptions of isotropic variability in previous analyses of altimeter data velocity variance ellipses are found to be distinctly anisotropic in many regions

partitioning of kinetic energy in the arctic ocean s beaufort gyre kinetic energy ke in the arctic ocean s beaufort gyre is dominated by the mesoscale eddy field that plays a central role in the transport of freshwater heat and biogeochemical tracers understanding beaufort gyre ke variability sheds light on how this freshwater reservoir responds to wind forcing and sea ice and ocean changes the evolution and fate of mesoscale eddies relate to energy pathways in the ocean e g the exchange of energy between barotropic and baroclinic modes mooring measurements of horizontal velocities in the beaufort gyre are analyzed to partition ke into barotropic and baroclinic modes and explore their evolution we find that a significant fraction of water column ke is in the barotropic and the first two baroclinic modes we explain this energy partitioning by quantifying the energy transfer coefficients between the vertical modes using the quasi geostrophic potential vorticity conservation equations with a specific background stratification observed in the beaufort gyre we find that the quasi geostrophic vertical mode interactions uphold the persistence of ke in the first two baroclinic modes consistent with observations our results explain the specific role of halocline structure on ke evolution in the gyre and suggest depressed transfer to the barotropic mode this limits the capacity for frictional dissipation at the sea floor and suggests that energy dissipation via sea ice ocean drag may be prominent

deep mesoscale eddies in the canada basin arctic ocean 1 numerous eddies have been identified in a seven year time series of mooring observations in the canada basin arctic ocean we focus on a series of deep eddies centered at 1200 m depth and occupying up to 1500 m of the water column the deep eddies are found to be spatially localized only ever being observed at one of four mooring sites of the beaufort gyre observing system in the canada basin however despite only a few previously reported observations of deep eddies in the arctic ocean we find that they are the most prevalent eddy type at this location based on this observation together with an analysis of the temperature salinity structure and the exclusively anticyclonic rotation of the deep eddies we hypothesize that they are formed by a density driven outflow from the chukchi borderland region we also describe a simple analytical model to explain the observed vertical scales of the eddies

significant sink of ocean eddy energy near western boundaries ocean eddies generated through instability of the mean flow are a vital component of the energy budget of the global ocean modelling combined with satellite altimetry data suggests that the energy from westward propagating eddies is scattered and eventually dispersed when they reach the western boundary of an ocean basin

jet structure and scaling in southern ocean models abstract the jet structure of the antarctic circumpolar current acc simulated by two general circulation models gcms fram fine resolution antarctic model and pop parallel ocean program is examined in relation to the bottom topography field despite differences in configuration both gcms display similar behavior the model acc consists of a number of distinct current cores superimposed on broader scale flow the jets display temporal and spatial including vertical coherence with maximum velocities occurring at the surface it is shown that multiple jets can arise in wind forced baroclinic quasigeostrophic flow the main factors influencing the number and spacing of jets are found to be the bottom topography and the proximity of lateral boundaries the meridional spacing of jets on a flat bottomed plane is consistent with the rhines scaling criterion for barotropic plane turbulence with a small modification due to baroclinicity and the presence of meridional boundaries when a zonally orient

estimating eddy stresses by fitting dynamics to observations using a residual mean ocean circulation model and its adjoint a global ocean circulation model is formulated in terms of the residual mean and used to study eddy mean flow interaction adjoint techniques are used to compute the three dimensional eddy stress field that minimizes the departure of the coarse resolution model from climatological observations of temperature the resulting 3d maps of eddy stress and residual mean circulation yield a wealth of information about the role of eddies in large scale ocean circulation in eddy rich regions such as the southern ocean the kuroshio and the gulf stream eddy stresses have an amplitude comparable to the wind stress of order 0 2 n m 2 and carry momentum from the surface down to the bottom where they are balanced

the relationship between u s east coast sea level and the atlantic meridional overturning circulation a review scientific and societal interest in the relationship between the atlantic meridional overturning circulation amoc and u s east coast sea level has intensified over the past decade largely due to 1 projected and potentially ongoing enhancement of sea level rise associated with amoc weakening and 2 the potential for observations of u s east coast sea level to inform reconstructions of north atlantic circulation and climate these implications have inspired a wealth of model and observation based analyses here we review this research finding consistent support in numerical models for an antiphase relationship between amoc strength and dynamic sea level however simulations exhibit substantial along coast and intermodel differences in the amplitude of amoc associated dynamic sea level variability observational analyses focusing on shorter generally less than decadal timescales show robust relationships between some components of the north atlantic large scale circulation and coastal sea level variability but the causal relationships between different observational metrics amoc and sea level are often unclear we highlight the importance of existing and future research seeking to understand relationships between amoc and its component currents the role of ageostrophic processes near the coast and the interplay of local and remote forcing such research will help reconcile the results of different numerical simulations with each other and with observations inform the physical origins of covariability and reveal the sensitivity of scaling relationships to forcing timescale and model representation this information will in turn provide a more complete characterization of uncertainty in relevant relationships leading to more robust reconstructions and projections

a wind driven isopycnic coordinate model of the north and equatorial atlantic ocean 1 model development and supporting experiments numerical approximations to the dynamic equations are given which allow basin size ocean circulation models formulated in isopycnic coordinates to accommodate variable bottom topography and irregular coastlines emphasis is placed on computational economy through the use of a split explicit time integration scheme on the proper formulation of the advection and coriolis terms in the momentum equation in case of strongly varying layer thickness and on the correct estimation of the horizontal pressure gradient force in grid boxes truncated by steep bottom slopes the algorithms are tested in a series of two and three layer double gyre experiments in cases of steady forcing leading to a steady circulation we are able to reproduce the expected motionless final state in coordinate layers that are below the direct influence of the wind forcing this includes layers intersecting topographic obstacles a long term 25 30 year vacillation tentatively associated with the outcropping of isopycnals along the edge of the cyclonic gyre in a steadily forced model is documented the paper forms the basis for a subsequent study in which circulation features obtained in a realistic north atlantic setting will be discussed

the vertical partition of oceanic horizontal kinetic energy to produce an interpretation of the surface kinetic energy as measured by altimeters a survey is made of the vertical structure of kinetic energy profiles in a large number of globally distributed long current meter records although the data are geographically confined primarily to a latitude band in the north pacific to the north atlantic and to a few moorings in the south atlantic the results show generally speaking that most regions are dominated by the barotropic and first baroclinic modes because of the near surface intensification of baroclinic modes altimeters primarily reflect the first baroclinic mode and thus the motion of the main thermocline there is good quantitative agreement with a few exceptions with estimates of the surface kinetic energy obtained from the topex poseidon altimeter and from vertical extrapolations to the surface of the mooring profiles these results are consistent with previous suggestions that barotropic models have little skill in depicting variability as seen in the altimeter data an eof analysis is shown to produce fictitious mode coupling unless the dynamical modes have very different energy levels

on the vorticity balance over steep slopes kuroshio intrusions northeast of taiwan abstractthe circulation of the kuroshio northeast of taiwan is characterized by a large anticyclonic loop of surface intrusion and strong upwelling at the shelfbreak to study the mechanisms of kur

eddy forcing of the mean flow in the southern ocean we examine the force or acceleration exerted by eddies on the mean flow of the southern ocean using mapped sea surface height anomalies derived from satellite altimeter measurements we compare this with the position of jets in the mean flow indicated by regions of increased gradient in the mean sea surface temperature the eddy force itself is not of primary importance rather the curl of that force affects the mean flow so the irrotational force due to the gradient of eddy kinetic energy can be ignored leaving a remainder that can be interpreted in terms of the eddy vorticity flux unlike previous modeling and altimetric studies we find that the eddies act to decelerate some of the strongest jets and act as vorticity sources for others the strongest jets are clearly not accelerated by eddies a problem of interpretation does remain however since it is not clear how sea surface temperatures are related to the mean flow this ambiguity can only be completely resolved by measurement of the mean flow requiring a geoid that is accurate at length scales of order 100 km

flow of winter transformed pacific water into the western arctic abstract the dynamics of the flow of dense water through barrow canyon is investigated using data from a hydrographic survey in summer 2002 the focus is on the winter transformed bering water the highest volumetric mode of winter water in the chukchi sea which drains northward through the canyon in spring and summer the transport of this water mass during the time of the survey was 0 2 0 3 sv as the layer flowed from the head of the canyon to the mouth it sank decelerated and stretched strong cyclonic relative vorticity was generated on the seaward side of the jet which compensated for the stretching this adjustment was incomplete however in that it did not extend across the entire current possibly because of internal mixing due to shear instabilities the resulting vorticity structure of the flow at the canyon mouth was conducive for baroclinic instability and eddy formation multiple eddies of winter transformed bering water were observed along the chukchi beaufort shelfbreak those to the west of barrow canyon were in the process of being spawned by the eastward flowing shelfbreak current emanating from herald canyon while the single eddy observed to the east originated from the barrow canyon outflow it is argued that such an eddy formation is a major source of the ubiquitous cold core anti cyclones observed historically throughout the canada basin implications for the ventilation of the upper halocline of the western arctic are discussed

eddy saturation of equilibrated circumpolar currents abstractthis study uses a sector configuration of an ocean general circulation model to examine the sensitivity of circumpolar transport and meridional overturning to changes in southern ocean wind stress and global diapycnal mixing at eddy permitting and finer resolution the sensitivity of circumpolar transport to forcing magnitude is drastically reduced at sufficiently high resolution there is little or no sensitivity of circumpolar transport to wind stress even in the limit of no wind in contrast the meridional overturning circulation continues to vary with southern ocean wind stress but with reduced sensitivity in the limit of high wind stress both the circumpolar transport and meridional overturning continue to vary with diapycnal diffusivity at all model resolutions the circumpolar transport becomes less sensitive to changes in diapycnal diffusivity at higher resolution although sensitivity always remains in contrast the overturning circulation is more sensitive to change in diapycnal

southern ocean overturning compensation in an eddy resolving climate simulation the southern ocean s antarctic circumpolar current acc and meridional overturning circulation moc response to increasing zonal wind stress is for the first time analyzed in a high resolution 0 1 ocean and 0 25 atmosphere fully coupled global climate simulation using the community earth system model results from a 20 yr wind perturbation experiment where the southern hemisphere zonal wind stress is increased by 50 south of 30 s show only marginal changes in the mean acc transport through drake passage an increase of 6 136 144 sverdrups sv 1 sv 10 6 m 3 s 1 in the perturbation experiment compared with the control however the upper and lower circulation cells of the moc do change the lower cell is more affected than the upper cell with a maximum increase of 64 versus 39 respectively changes in the moc are directly linked to changes in water mass transformation from shifting surface isopycnals and sea ice melt giving rise to changes in surface buoyancy forcing the increase in transport of the lower cell leads to upwelling of warm and salty circumpolar deep water and subsequent melting of sea ice surrounding antarctica the moc is commonly supposed to be the sum of two opposing components a wind and transient eddy overturning cell here the transient eddy overturning is virtually unchanged and consistent with a large scale cancellation of localized regions of both enhancement and suppression of eddy kinetic energy along the mean path of the acc however decomposing the time mean overturning into a time and zonal mean component and a standing eddy component reveals partial compensation between wind driven and standing eddy components of the circulation

on the dynamics of wind driven circumpolar currents the factors controlling the transport of the antarctic circumpolar current acc have recently been a topic of heated debate at the latitudes of drake passage potential vorticity contours are uninterrupted by coastlines and large amplitude flows are possible even with weak forcing and dissipation the relationship between the dynamics of circumpolar currents and inertial recirculations in closed basins is discussed in previous studies sverdrup balance and baroclinic adjustment theories have both been proposed as theories of the acc transport these theories predict the circumpolar transport as various simple functions of the surface wind stress a series of experiments is performed with a simple channel model with different wind strengths and different idealized basin geometries to investigate the relationship between wind strength and circumpolar transport the results show that baroclinic adjustment theories do predict transport in the special case of a periodic channel with no topographic variations or when the wind forcing is very weak more generally the transport is determined by a complex interplay between wind forcing eddy fluxes and topographic effects there is no support for the idea that sverdrup balance determines the transport through drake passage

homogenization of potential vorticity in planetary gyres the mean circulation of planetary fluids tends to develop uniform potential vorticity q in regions where closed time mean streamlines or closed isolines of mean potential vorticity exist this state is established in statistically steady flows by geostrophic turbulence or by wave induced potential vorticity flux at the outer edge of the closed contours the expelled gradients of q are concentrated beyond this transition lies motionless fluid or a different flow regime in which the planetary gradient of q may be dominant the homogenized regions occur where direct forcing by external stress or heating within the closed isoline is negligible upon the potential density surface under consideration in the stably stratified ocean such regions are found at depths greater than those of direct wind induced stress or penetrative cooling in channel models of the atmosphere we again find constant q when mesoscale eddies cause the dominant potential vorticity flux in the real atmosphere the results here can apply only where internal heating is negligible the derivations given here build upon the prandtl batchelor theorem which applies to non rotating steady two dimensional flow supporting evidence is found in numerical circulation models and oceanic observations

small scale topographic form stress and local dynamics of the southern ocean the contribution of small scale abyssal hill topography to the topographic form stress and local dynamics of the southern ocean is investigated using a high resolution model of the sector of the southern ocean south of tasmania and new zealand the results of two simulations with and without small o 1 100 km scale topography confirm that the effects of small scale topography are exerted through the generation of strong topographic form stress leading to transient eddy dissipation and changes in flow meanders small scale topographic form stress is comparable in magnitude to that generated by large scale topography but with a pairwise distribution of positive and negative stress values upstream and downstream of the macquarie ridge consistent with the meandering of the flow in the experiment without small scale topography the bottom mean flow speed increases while the surface mean speed slightly decreases making the mean flow more barotropic eddy kinetic energy also greatly enhances throughout the water column after removing small scale topography our results suggest that small scale topography has strong impact on transient eddies and plays an important role for setting the vertical structure of the flow and the equilibration and position of flow meanders

topographic form stress in the southern ocean state estimate we diagnose the southern ocean momentum balance in a six year eddy permitting state estimate of the southern ocean we find that 95 of the zonal momentum input via wind stress at the surface is balanced by topographic form stress across ocean ridges while the remaining 5 is balanced via bottom friction and momentum flux divergences at the northern and southern boundaries of the analysis domain while the time mean zonal wind stress field exhibits a relatively uniform spatial distribution time mean topographic form stress concentrates at shallow ridges and across the continents that lie within the antarctic circumpolar current acc latitudes nearly 40 of topographic form stress occurs across south america while the remaining 60 occurs across the major submerged ridges that underlie the acc topographic form stress can be divided into shallow and deep regimes the shallow regime contributes most of the westward form stress that serves as a momentum sink for the acc system while the deep regime consists of strong eastward and westward form stresses that largely cancel in the zonal integral the time varying form stress signal integrated longitudinally and over the acc latitudes tracks closely with the wind stress signal integrated over the same domain at zero lag 88 of the variance in the six year form stress time series can be explained by the wind stress signal suggesting that changes in the integrated wind stress signal are communicated via rapid barotropic response down to the level of bottom topography this article is protected by copyright all rights reserved

atmosphere ocean momentum exchange in general circulation models a series of two layer quasigeostrophic solutions for the ocean circulation driven by a steady wind in a channel with topography and in a flat bottom rectangular basin are presented in which the atmosphere and ocean are inertially coupled through the surface stress relation the only other frictional processes are biharmonic lateral friction under free slip boundary conditions and topographic form stress there is no bottom friction involved the results indicate that realistic momentum balances can be obtained on this physical basis two types of solutions are obtained which are called i the i series in which the inertial coupling relation is applied directly in the earth reference frame with no current averaging and almost steady stream fields occur and ii the s series in which the inertial coupling relation is applied for long current averaging periods of the order 100 days rather than instantaneously the solutions for the longer current averaging periods produce vigorous eddy fields but their time mean is very similar to the corresponding solution with no current averaging surface stokes drift streamfields are also generated by the inertial coupling mechanism some implications of the results for general circulation modeling are discussed

global observations of submesoscale coherent vortices in the ocean abstract subsurface intensified anticyclones are ubiquitous in the ocean yet their impact on the large scale transport of heat salt and chemical tracers is poorly understood these submesoscale coherent vortices scvs can trap and advect waters thousands of kilometers away from the formation region providing a transport pathway that is unresolved by low resolution earth system models however knowledge of the importance of these eddies for the large scale circulation is hindered by the lack of systematic observations here we take advantage of the global network of argo floats to identify occurrences of these eddies which appear as weakly stratified anomalous water masses with gaussian shaped vertical structures we develop a general algorithm to detect subsurface eddies that have propagated away from their source region and apply it to the database of argo float profiles resulting in roughly 4000 detections from more than 20 years of observations we further group detections into regional populations to identify hot spots of generation and mechanisms of formation analysis of regional scv statistics reveals important sites of scv generation in eastern boundary upwelling systems marginal sea overflows and mode water formation regions along major open ocean fronts because of the heat and salt anomaly contained within their cores scv could leave a significant imprint on the hydrographic properties of water masses in regions of high scv density

mesoscale eddies of the arctic ocean subsurface baroclinic eddies in the arctic ocean have a diameter of 10 20 km and are confined in depth between 50 and 300m during the arctic ice dynamics joint experiment aidjex in the central beaufort sea between march 1975 and may 1976 extensive information on eddy characteristics statistics and behavior was collected from four manned drifting ice camps during this 14 month period 146 eddies were encountered of which 19 were found to be repeated crossings making a total of 127 separate eddies observed during this period on the basis of the 1975 1976 aidjex data set it is concluded that eddies are 1 prevalent in the amerasia basin of the arctic ocean and in particular the beaufort sea where they may occupy up to a quarter of the available surface area 2 located in the depth range of 50 300 m although a few deeper eddies are also present 3 the second largest producers 32 of kinetic energy found within the upper 200 m of the beaufort sea and 4 predominantly anticyclonic in rotational tendency these eddies apparently originate north of point barrow alaska as a result of instability in the eastward flowing alaskan coastal current and transfer seasonally varying water properties from the chukchi sea and alaskan shelf into the arctic ocean they appear to translate in response to barotropic forcing over short time scales and over longer time periods move with the mean geostrophic field the season of formation for an eddy may be identified by the anomalous thermal properties still residing in its core

north atlantic barotropic vorticity balances in numerical models abstractnumerical simulations are conducted across model platforms and resolutions with a focus on the north atlantic barotropic vorticity diagnostics confirm that the subtropical gyre is characterized by an inviscid balance primarily between the applied wind stress curl and bottom pressure torque in an area integrated budget over the gulf stream the northward return flow is balanced by bottom pressure torque these integrated budgets are shown to be consistent across model platforms and resolution suggesting that these balances are robust two of the simulations at 100 and 10 km resolutions produce a more northerly separating gulf stream but obtain the correct integrated vorticity balances in these simulations viscous torque is nonnegligible on smaller scales indicating that the separation is linked to the details of the local dynamics these results are shown to be consistent with a scale analysis argument that suggests that the biharmonic viscous torque in particular is upsetting the inviscid

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

eddy variability and energetics from direct current measurements in the antarctic circumpolar current south of australia two year time series measurements of current velocity and temperature in the subantarctic front saf south of australia from 1993 to 1995 provide estimates of eddy fluxes of heat and momentum across the antarctic circumpolar current acc and further insight into the variability of the acc the saf was found to be an energetic meandering jet with vertically coherent fluctuations varying on a timescale of 20 days with typical amplitude 30 cm s21 at 1150 dbar a daily varying coordinate frame that follows the direction of flow allowed mesoscale variability of the saf to be isolated from variability due to meandering of the front and proved very successful for examining eddy fluxes vertically averaged cross stream eddy heat flux was 11 3 kw m 22 poleward and significantly different from zero at 95 for fluctuations in the 2 90 day band zonally integrated this eddy heat flux 50 9 pw is more than large enough to balance heat lost south of the polar front and is as large as cross saf fluxes found in drake passage cross stream eddy momentum fluxes were small not significantly different from zero and of indeterminate sign but tending to decelerate the mean flow a relationship between vertical motion and meander phase identified in the gulf stream was found to hold for the acc eddy kinetic energy levels were similar to those in drake passage and southeast of new zealand eddy potential energy was up to an order of magnitude larger than at other acc sites most likely because meandering of the front is more common here baroclinic conversion was found to be the dominant mechanism by which eddies grow south of australia typical eddy growth time is estimated to be 30 days approximately twice as fast as in drake passage consistent with eddy energy growing rapidly downstream

topographic coupling of the atlantic overturning and gyre circulations abstractthe vorticity dynamics associated with the mean and time varying gyre and overturning circulations of the atlantic ocean are examined in a realistic ocean model hindcast simulation of the late twentieth century abyssal flow interaction with sloping bottom bathymetry gives rise to the bottom pressure torque bpt term of the vertically integrated vorticity equation the dominance of this term in the closure of the barotropic gyre circulation noted in previous studies is corroborated here for both non eddy resolving and eddy resolving versions of the parallel ocean program pop model this study shows that bpt is also a dominant term in the vorticity balance of the atlantic meridional overturning circulation amoc and therefore represents a key dynamical link between the overturning and gyre streamfunctions the interannual variability of the atlantic circulation over the last several decades viewed in terms of time varying integral vorticity balances demonstrates the fundamental role played by

wind driven freshwater buildup and release in the beaufort gyre constrained by mesoscale eddies recently the beaufort gyre has accumulated over 20 km3 of freshwater in response to strong anticyclonic atmospheric winds that have prevailed over the gyre for almost two decades here we explore key physical processes affecting the accumulation and release of freshwater within an idealized eddy resolving model of the beaufort gyre we demonstrate that a realistic halocline can be achieved when its deepening tendency due to ekman pumping is counteracted by the cumulative action of mesoscale eddies based on this balance we derive analytical scalings for the depth of the halocline and its spin up time scale and emphasize their explicit dependence on eddy dynamics our study further suggests that the beaufort gyre is currently in a state of high sensitivity to atmospheric winds however an intensification of surface stress would inevitably lead to a saturation of the freshwater content a constraint inherently set by the intricacies of the mesoscale eddy dynamics

climatic variations of the work done by the wind on the ocean s general circulation 1 the southern hemisphere westerlies exert an important influence on global climate supplying nearly half of the mechanical energy for the deep overturning circulation in a coarse resolution ocean model northward shifted winds increase the work done on surface geostrophic flows due to enhanced velocities associated with the antarctic circumpolar current acc alternatively energy supply is diminished by southward shifted winds primarily through reduced correspondence between wind stress and surface velocity in the southern ocean due to dynamical and topographic constraints on the acc when combined perturbations in latitude and magnitude of the westerlies are applied these results are reconciled with estimates of recent trends in wind work and volume transport in the southern ocean from observations and coupled climate models this indicates that the strength of the winds exerts a dominant effect that masks the opposing consequences of latitudinal migration in particular transport through drake passage shows a clear relationship with wind work and velocity when the winds move poleward leading to a reduction in all three quantities however under equatorward shifted winds stronger polar easterlies adjacent to the antarctic continent establishes a recirculation gyre leading to increased mechanical energy input and swifter currents but reduced transport significant o 25 changes in the mechanical energy supply from the winds may be possible on climatic time scales particularly associated with the spatial correlation between winds and the acc that does not depend critically on unresolved eddy processes in this model leading to a pathway for altering abyssal diapycnal mixing rates and stratification of the ocean interior

vertical structure of eddies and rossby waves and their effect on the atlantic meridional overturning circulation at 26 5 n the meridional overturning circulation moc at inline image in the atlantic has a standard deviation of 4 9 sv and contains large fluctuations at subannual periods the geostrophic component of the moc is believed to be influenced on subannual time scales by eddies and rossby waves to quantify this effect the vertical structure and surface characteristics of westward propagating signals are studied using altimetric data and full depth mooring measurements from the rapid array at inline image westward propagating features are observed in the western north atlantic in both data sets and have periods of 80 250 days in the first baroclinic mode these features are still observed by the rapid moorings 20 km offshore of the western boundary the western boundary also exhibits deep variability characterized by enhanced energy in higher baroclinic modes the effect of eddies and rossby waves on the geostrophic transport is quantified by representing their vertical structure with the first baroclinic mode in total 42 of the variance of the transbasin thermocline transport inferred from geostrophic calculations at inline image can be attributed to first mode variability which is associated with eddies and rossby waves at periods of 80 250 days the standard deviation of the transbasin thermocline transport due to eddies and rossby waves is estimated to be 2 6 sv

generation and separation of mesoscale eddies from surface ocean fronts abstractthis study is motivated by arctic ocean observations of sub mixed layer eddies found at large distances from their assumed formation region of a surface ocean front eddy formation is explored through high resolution numerical simulations of surface fronts separating two mixed layers with a range of configurations similar to those observed in the arctic ocean this study finds that frontal instabilities lead to the development of self propagating dipoles which have the potential to propagate far from the front if interactions with other eddies are avoided however most dipoles are unbalanced consisting of a dominating surface cyclone and a weaker anticyclone below and thus propagate on curved trajectories with eventual recirculation back to the front their maximum separation distance from the front depends on the ratio of self advecting velocities balanced dipoles that have 1 and the ability to propagate far from the front for dipoles generated numerically this study estimates u

an exploration of the role of transient eddies in determining the transport of a zonally reentrant current the meridional ekman transport in a zonally reentrant channel may be balanced by diabatic circulations standing eddies associated with topography or by lagrangian mean eddy mass fluxes a simple model is used to explore the interaction between these mechanisms a key assumption of this study is that diabatic forcing in the poleward edge of the channel acts to create lighter fluid as is the case with net freshwater fluxes into the southern ocean for weak wind forcing or strong diabatic constraint a simple scaling argument accurately predicts the level of baroclinic shear however given our understanding of the relative magnitudes of ekman flux and deep upwelling this is not the appropriate parameter range for the antarctic circumpolar current with stronger wind stresses eddies are prominent with baroclinic instability initially developing in the vicinity of large topography arguments have been advanced by a number of authors that baroclinic instability should limit the velocity shear leading to a stiff upper limit on the transport of the current however in the simulations presented here baroclinic instability is largely confined to the region of topographic highs and the approach to a current that is independent of the wind stress occurs gradually several recent parameterizations of transient eddy fluxes do not reproduce key features of the observed behavior

characterizing the eddy field in the arctic ocean halocline ice tethered profilers itp deployed in the arctic ocean between 2004 and 2013 have provided detailed temperature and salinity measurements of an assortment of halocline eddies a total of 127 mesoscale eddies have been detected 95 of which were anticyclones the majority of which had anomalously cold cores these cold core anticyclonic eddies were observed in the beaufort gyre region canadian water eddies and the vicinity of the transpolar drift stream eurasian water eddies an arctic wide calculation of the first baroclinic rossby deformation radius rd has been made using itp data coupled with climatology rd 13 km in the canadian water and 8 km in the eurasian water the observed eddies are found to have scales comparable to rd halocline eddies are in cyclogeostrophic balance and can be described by a rankine vortex with maximum azimuthal speeds between 0 05 and 0 4 m s the relationship between radius and thickness for the eddies is consistent with adjustment to the ambient stratification eddies may be divided into four groups each characterized by distinct core depths and core temperature and salinity properties suggesting multiple source regions and enabling speculation of varying formation mechanisms

the scales and equilibration of midocean eddies freely evolving flow quasigeostrophic turbulence theory and numerical simulation are used to study the mechanisms determining the scale structure and equilibration of mesoscale ocean eddies the present work concentrates on using freely decaying geostrophic turbulence to understand and explain the vertical and horizontal flow of energy through a stratified horizontally homogeneous geostrophic fluid it is found that the stratification profile in particular the presence of a pycnocline has significant qualitative effects on the efficiency and spectral pathways of energy flow specifically with uniform stratification energy in high baroclinic modes transfers directly quickly within a few eddy turnaround times and almost completely to the barotropic mode by contrast in the presence of oceanlike stratification kinetic energy in high baroclinic modes transfers intermediately to the first baroclinic mode whence it transfers inefficiently and incompletely to the barotropic mode the efficiency of transfer to the barotropic mode is reduced as the pycnocline is made increasingly thin the b effect on the other hand improves the efficiency of barotropization but for oceanically realistic parameters this effect is relatively unimportant compared to the effects of nonuniform stratification finally the nature of turbulent cascade dynamics is such as to lead to a concentration of first baroclinic mode kinetic energy near the first radius of deformation which in the case of a nonuniform and oceanically realistic stratification has a significant projection at the surface this may in part explain recent observations of surface eddy scales by topex poseidon satellite altimetry which indicate a correlation of surface height variance with the scale of the first deformation radius

evolution of the eddy field in the arctic ocean s canada basin 2005 2015 the eddy field across the arctic ocean s canada basin is analyzed using ice tethered profiler itp and moored measurements of temperature salinity and velocity spanning 2005 to 2015 itps encountered 243 eddies 98 of which were anticyclones with approximately 70 of these having anomalously cold cores the spatially and temporally varying eddy field is analyzed accounting for sampling biases in the unevenly distributed itp data and caveats in detection methods the highest concentration of eddies was found in the western and southern portions of the basin close to topographic margins and boundaries of the beaufort gyre the number of lower halocline eddies approximately doubled from 2005 2012 to 2013 2014 the increased eddy density suggests more active baroclinic instability of the beaufort gyre that releases available potential energy to balance the wind energy input this may stabilize the gyre spin up and associated freshwater increase

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

the formation of nonzonal jets over sloped topography coherentjetsareubiquitousfeaturesoftheocean scirculation andtheircharacteristics suchasorientation and energetics may be influenced by topography in this study the authors introduce a large scale topographic slope with an arbitrary orientation into quasigeostrophic doubly periodic barotropic and baroclinic systems in both systems the flow organizes itself into coherent tilted nonzonal jets that are aligned perpendicular to the barotropic potential vorticity pv gradient in the two layer system the upper layer the lower layer and the barotropic pv gradients all have different orientations and therefore the jets cross the layer wise pv gradients the fact that the jets cross layer wise pv gradients and the requirement of conservation of pv for fluid parcels together results in the drift of the tilted jets across the domain like their zonalcounterparts thetiltedjetsexhibitstrongtransportanisotropy thedynamicalresponsetojetdeflection is very strong in the two layer baroclinic case with eddy energy production increasing by orders of magnitude as the topographic slope becomes more zonal this increase in eddy energy is also reflected in an increase in jet spacing and a reduction in strength of the across jet transport barriers shown using an effective diffusivity diagnostic the dynamics identified here while formally valid within the constraints of quasigeostrophic scalings provide important insight into the sensitive relationship between flow orientation and flow stability in regions with broad topographic slopes

eddies in the canada basin arctic ocean observed from ice tethered profilers five ice tethered profilers itps deployed between 2004 and 2006 have provided detailed potential temperature and salinity s profiles from 21 anticyclonic eddy encounters in the central canada basin of the arctic ocean the 12 35 m thick eddies have center depths between 42 and 69 m in the arctic halocline and are shallower and less dense than the majority of eddies observed previously in the central canada basin they are characterized by anomalously cold and low stratification and have horizontal scales on the order of or less than the rossby radius of deformation about 10 km maximum azimuthal speeds estimated from dynamic heights assuming cyclogeostrophic balance are between 9 and 26 cm s 1 an order of magnitude larger than typical ambient flow speeds in the central basin eddy s and potential vorticity properties as well as horizontal and vertical scales are consistent with their formation by instability of a surface front at about 80 n that appears in historical ctd and expendable ctd xctd measurements this would suggest eddy lifetimes longer than 6 months while the baroclinic instability of boundary currents cannot be ruled out as a generation mechanism it is less likely since deeper eddies that would originate from the deeper reaching boundary flows are not observed in the survey region

multiple jets of the antarctic circumpolar current south of australia abstract maps of the gradient of sea surface height ssh and sea surface temperature sst reveal that the antarctic circumpolar current acc consists of multiple jets or frontal filaments the braided and patchy nature of the gradient fields seems at odds with the traditional view derived from hydrographic sections that the acc is made up of three continuous circumpolar fronts by applying a nonlinear fitting procedure to 638 weekly maps of ssh gradient ssh it is shown that the distribution of maxima in ssh i e fronts is strongly peaked at particular values of absolute ssh i e streamlines the association between the jets and particular streamlines persists despite strong topographic and eddy mean flow interactions which cause the jets to merge diverge and fluctuate in intensity along their path the ssh values corresponding to each frontal branch are nearly constant over the sector of the southern ocean between 100 e and 180 the front positions inferred from ssh agree closely with

rapid formation of rock varnish and other rock coatings on slag deposits near fontana california manganiferous rock varnish silica glaze and iron skins have formed on 20 to 40 year old slag piles near fontana southern california rapid rock varnish formation is associated with an unidentified cocci bacterium that grows rapidly in culturing experiments combined with the likelihood that mn rich solutions flow over slag surfaces a new model is proposed for the formation of silica glaze involving soluble al si complexes and the nature of wetting films iron skins occur where runoff is concentrated and where iron bacteria grow observations indicate i substrate can be important in supplying mn as well as maintaining a stable surface and channelling runoff to microspots where varnish grows ii ignorance of boundary layer ph eh conditions makes chemical physical models of varnish formation speculative iii the balance between cementation of recently nucleated varnishes and erosional shear stresses is poorly understood but is probably an important limiting factor on varnish growth rates and iv there must be at least two steps in biotic varnishing accretion of mn fe in casts followed by cementation of clays by either in situ cast residue or mn fe remobilized from casts varnish accretion may be limited by the rate at which both steps occur rapid development of readily distinguishable manganiferous rock varnishes at this post 1952 site highlights the danger of speculation on the ages of landforms based solely on the appearance of rock varnish coatings

a barotropic vorticity budget for the subtropical north atlantic based on observations abstractto ground truth the large scale dynamical balance of the north atlantic subtropical gyre with observations a barotropic vorticity budget is constructed in the ecco state estimate and compa

deterioration of perennial sea ice in the beaufort gyre from 2003 to 2012 and its impact on the oceanic freshwater cycle time series of ice draft from 2003 to 2012 from moored sonar data are used to investigate variability and describe the reduction of the perennial sea ice cover in the beaufort gyre bg culminating in the extreme minimum in 2012 negative trends in median ice drafts and most ice fractions are observed while open water and thinnest ice fractions 0 3 m have increased attesting to the ablation or removal of the older sea ice from the bg over the 9 year period monthly anomalies indicate a shift occurred toward thinner ice after 2007 in which the thicker ice evident at the northern stations was reduced differences in the ice characteristics between all of the stations also diminished so that the ice cover throughout the region became statistically homogenous the moored data are used in a relationship with satellite radiometer data to estimate ice volume changes throughout the bg summer solid fresh water content decreased drastically in consecutive years from 730 km3 in 2006 to 570 km3 in 2007 and to 240 km3 in 2008 after a short rebound solid fresh water fell below 220 km3 in 2012 meanwhile hydrographic data indicate that liquid fresh water in the bg in summer increased 5410 km3 from 2003 to 2010 and decreased at least 210 km3 by 2012 the reduction of both solid and liquid fresh water components indicates a net export of approximately 320 km3 of fresh water from the region occurred between 2010 and 2012 suggesting that the anticyclonic atmosphere ocean circulation has weakened

wind driven flow over topography in a zonal β plane channel a quasi geostrophic model of the antarctic circumpolar current abstract the paper gives a detailed account of the dynamical balance of a wind driven zonally unbounded flow over topography the problem is investigated with a quasi geostrophic plane channel with two layers and eddy resolution the channel has a width of 1500 km and a zonal periodicity of 4000 km apart from the dimensions the model structure is similar to the one used by mcwilliams et al the experiments with this model address the problem of the relative role of transient and standing eddies as well as bottom friction and topographic form stress in the balance of a current driven by a steady surface windstress the response of the system is investigated for different values of the friction parameter and various locations of topographic obstacles in the bottom layer of the channel the principal momentum balance emerging from these experiments supports the concept of munk and palmen for the dynamics of the antarctic circumpolar current which proposes that the momentum input by windstress is transfe

basin and channel contributions to a model antarctic circumpolar current the idea that basinlike dynamics may play a major role in determining the antarctic circumpolar current acc transport is revisited a simple analytic model is developed to describe the relationship between the wind stress and transport at very low wind stress a nonzero minimum is predicted this is followed by two distinct dynamical regimes for stronger forcing 1 a stommel regime in which transport increases linearly with forcing strength and 2 a saturation regime in which the transport levels off the baroclinic structure of the sverdrup flux into the drake passage latitude band is central to the analytic model and the geometry of characteristics or geostrophic contours is key to predicting the transition between the two regimes a robustness analysis is performed using an eddy permitting quasigeostrophic model in idealized geometries many simulations were carried out in large domains across a range of forcing strengths the simulations agree qualitatively with the analytic model with two main discrepancies being related to zonal jet structures and to a western boundary inertial recirculation eddy fluxes associated with zonal jets modify the baroclinic structure and lower the saturation transport value inertial effects increase the transport although this effect is mainly limited to smaller domains

a geologic perspective on the miocene evolution of the antarctic circumpolar current system abstract the dominant geologic feature of pelagic sediment accumulation patterns at intermediate water depths in the southern ocean is the sequential northward migration and replacement of a calcareous ooze sedimentary facies by a siliceous ooze facies following the late oligocene opening of the drake passage and the subsequent initiation of the antarctic circumpolar current closely spaced whole core measurements of bulk density are evaluated for four sites drilled in the southern ocean during ocean drilling program odp legs 113 sites 689 and 690 and 120 sites 747 and 751 these sites are all located on submarine rises in open ocean pelagic depositional environments south of the polar front a major oceanographie and sedimentologic boundary high resolution profiles of bulk density are used to correlate between adjacent drill holes on the maud rise where multiple overlapping sedimentary sequences were recovered using the advanced hydraulic piston core barrel apc stratigraphie age models have been applied to the bulk density data to provide a temporal framework for a discussion of the sedimentologic basis for paleoceanographic interpretations and also to constrain future acoustic research studies the early to middle miocene intervals at sites 689 and 690 are marked by distinct sequences of meter scale alternating carbonate and siliceous units separated by several proposed stratigraphie hiatuses at least six dissolution productivity events are identified in the middle to late miocene on the maud rise and others are noted at the odp sites on the kerguelen plateau the downhole profiles are used to identify the density signature and position of sediment facies changes and proposed stratigraphie hiatuses in sediment cores of late oligocene to late miocene age based on the reversals inflections and discontinuities in the downhole bulk density trends an analysis of the observed bulk density trends at these sites is combined with a review of other tectonic sedimentologic oceanographie and modeling studies to develop a hypothesis for explaining the observed sediment accumulation patterns at intermediate water depths of the southern ocean

vertical scales and dynamics of eddies in the arctic ocean s canada basin a decade of moored measurements from the arctic ocean s northwestern beaufort gyre collected as a component of the beaufort gyre exploration project are analyzed to examine the range of mesoscale eddies over the water column and the dynamical processes that set eddy vertical scales a total of 58 eddies were identified in the moored record all anticyclones with azimuthal velocities ranging from 10 to 43 cm s these are divided into three classes based on core depths shallow eddies core depths around 120 m are shown to be vertically confined by the strong stratification of the halocline typical thicknesses are around 100 m deep eddies core depths around 1200 m are much taller thicknesses around 1300 m owing to the weaker stratification at depth consistent with a previous study eddies centered around mid depths all have two cores vertically aligned and separated in depth characterized by velocity maxima and anomalous temperature and salinity properties one core is located at the base of the halocline around 200 m depth and the other at the depth of the atlantic water layer around 400 m depth these double core eddies have vertical scales between those of the shallow and deep eddies the strongly decreasing stratification in their depth range motivates a derivation for the quasi geostrophic adjustment of a nonuniformly stratified water column to a potential vorticity anomaly the result aids in interpreting the dynamics and origins of the double core eddies providing insight into transport across a major water mass front separating canadian and eurasian water

relative and absolute dating of land surfaces abstract the dating of land surfaces has long posed problems for geomorphologists relative methods stratigraphic geomorphic topographic are sound and convincing exhumed forms may complicate identification and relationships for both epigene and etch forms have been buried and exhumed but in tectonically undisturbed areas the higher surfaces are older than those preserved at lower levels also surfaces have an age range the relationship of surfaces with volcanic deposits old shorelines and genetically related sedimentary sequences provides sound ages and correlation with dated duricrusts and faults is also useful there are no temporal limits to relative dating for the methods are equally applicable to the dating say of proterozoic surfaces as of those of pleistocene age the disadvantage of such methods is that the necessary evidence is frequently either not preserved or not exposed the so called absolute physical numerical methods and especially those based on exposure age dating with in situ cosmogenic radionuclides are appealing because they produce direct numerical ages and appear to be widely applicable but there are severe temporal limitations and sampling problems complicate and may invalidate interpretation absolute age determinations must be consistent with the stratigraphic and geomorphologic settings the best results are obtained when physicists and earth scientists pool their knowledge and experience a background in local and regional geology is especially important

topographic control of basin and channel flows the role of bottom pressure torques and friction the topographical control of western boundary currents within a basin and zonal jets in a channel is investigated in terms of the potential vorticity pv and barotropic vorticity bv the curl of the depth integrated velocity budgets using isopycnic adiabatic wind driven experiments along the western boundary the wind driven transport is returned across latitude lines by the bottom pressure torque while friction is only important in altering the pv within an isopycnic layer and in allowing a closed circulation these contrasting balances constrain the geometry of the flow through integral relationships for the bv and pv for both homogenous and stratified basins with sloping sidewalls the northward subtropical jet separates from the western wall and has opposing frictional torques on either side of the jet which cancel in a zonal integral for bv but alter the pv within a layer streamline in a channel with partial topographic barriers the bottom pressure torque is again important in returning wind driven flows along western boundaries and in transferring bv from neighboring wind driven gyres into a zonal jet the depth integrated flow steered by topography controls where the bottom friction alters the pv which can lead to different pv states being attained for separate subbasins along a channel

the role of ocean gateways in the dynamics and sensitivity to wind stress of the early antarctic circumpolar current the date of inception of the antarctic circumpolar current is debated due to uncertainty in the relative opening times of drake passage and the tasman seaway using an idealized eddy resolving numerical ocean model we investigate whether both ocean gateways have to be open to allow for a substantial circumpolar current we find that overlapping continental barriers do not impede a circumpolar transport in excess of 50sv as long as a circumpolar path can be traced around the barriers however the presence of overlapping barriers does lead to an increased sensitivity of the current s volume transport to changes in wind stress this change in sensitivity is interpreted in terms of the role of pressure drops across continental barriers and submerged bathymetry in balancing the momentum input by the surface wind stress specifically when the pressure drop across continents is the main balancing sink of momentum the zonal volume transport is sensitive to changes in wind stress changes in zonal volume transport take place via altering the depth independent part of the circumpolar transport rather than that arising from thermal wind shear in such a scenario isopycnals continue to slope steeply across the model southern ocean implying a strong connection between the deep and surface oceans this may have consequences for the meridional overturning circulation and its sensitivity to wind stress

the deacon cell and the other meridional cells of the southern ocean abstract the meridional circulation cells of the southern ocean are investigated using the results from a fine resolution primitive equation model zonal integration along depth levels shows the classical series of meridional cells but integration along density layers shows a number of differences including the virtual disappearance of the deacon cell to investigate the differences the meridional transport is calculated as a function of both density and depth the results show that the deacon cell is associated with systematic changes in the depth of density surfaces between the western boundary current region off south america and the return flow in the interior of the ocean water flowing on each density surface produces a meridional cell with a vertical excursion of a few hundred meters thew cells combine without water crossing density surfaces to produce a single integrated deacon cell extending from the surface to below 2000 m the results also show that at each latitude water on each of the

why western boundary currents in realistic oceans are inviscid a link between form stress and bottom pressure torques it is shown that wind stress curl is balanced by bottom pressure torque in a zonal integral over any strip wide enough to smooth out the effect of nonlinear terms typically about 3 of latitude the derivation is completely general as long as the zonal wind stress is balanced by form stress at each latitude as is known to be the case in the ocean this implies that viscous torques are not important in western boundary currents their place being taken by bottom pressure torques the prediction is confirmed in the context of a global eddy permitting numerical ocean model this link between form stress and bottom pressure torques makes it easier to consider southern ocean dynamics and subtropical gyre dynamics in the same conceptual framework with topographic interactions being important in both cases

a review of the history of dating rock varnishes the history of rock varnish dating spans almost 20 years from the initial suggestion to use uranium series isotopes through the use of a geochemical ratio cation ratio dating to the current application of accelerator mass spectrometry radiocarbon dating ams 14c uranium isotopes were ignored while other dating methods were tested exhaustively on several continents evidence of the unreliable dating of the formation of varnishes using cation ratios was demonstrated by examples of environmental and textural observations reflecting localised leaching and by chemical analyses that contradicted the fundamental assumptions of the method the radiocarbon dating of substances embedded in varnishes is also problematic where carbon compounds and sources are not identified the incompatible coexistence of different carbonaceous components a recent controversial issue is explained with reference to different environments of formation the future of ams 14c dating of rock varnishes centres around overcoming the practical limitations of sampling and analysing extremely small quantities of carbon bearing substances future directions for dating varnished rock surfaces may include innovative refinements to the u series cosmogenic isotope and luminescence methods

energetic eddies at the northern edge of the antarctic circumpolar current in the southwest pacific abstract two year time series measurements of current and temperature were made at the northern edge of the antarctic circumpolar current in the southwestern pacific from 1978 to 1980 to investigate eddy heat and momentum fluxes in the circumpolar region the measurement site near 49 30 s 170 w is at a transition zone or front between subantarctic and subtropical waters in which meridional temperature and salinity gradients and hence vertical shear in eastward velocity extend down to 2 000 m depth energetic eddies are found to have typical amplitudes of 20 cm s 1 at 1 000 m depth to be vertically coherent over the depth range from 1 000 to 5 000 m to vary over temporal scales of 20 days and horizontal scales of 60 km and to propagate southeastward at about 12 cm s 1 observed eddy kinetic energy of 169 cm2 s at 1 000 m depth is larger than that at comparable depths in the gulf stream and kuroshio extension regions and in central drake passage like drake passage eddies these eddies transport a significant amount of heat poleward in the band of periods between 20 and 50 days but this band does not dominate the spectrum the way it does in drake passage energetic fluctuations with periods longer than 50 days effect an eddy heat flux whose sign is ambiguous so that the net meridional heat flux is not statistically significant eddy momentum fluxes transport eastward momentum northward away from the circumpolar current these fluxes are statistically significant but are only about one fourth of the size required to balance the eastward momentum put into the water column by the wind an estimate of the standing eddy momentum flux due to large spatial scale variations in the circumpolar current is also too small so that pressure forces against bottom topography is likely to be the mechanism by which the wind input is balanced

routes to energy dissipation for geostrophic flows in the southern ocean wind power inputs at the surface ocean are dissipated through smaller scale processes in the ocean interior and turbulent boundary layer simulations suggest that seafloor topography enhances turbulent mixing and energy dissipation in the ocean interior

subantarctic mode water variability influenced by mesoscale eddies south of tasmania 1 subantarctic mode water samw is formed by deep mixing on the equatorward side of the antarctic circumpolar current the subduction and export of samw from the southern ocean play an important role in global heat freshwater carbon and nutrient budgets however the formation process and variability of samw remain poorly understood largely because of a lack of observations to determine the temporal variability of samw in the australian sector of the southern ocean we used a 15 year time series of repeat expendable bathythermograph sections from 1993 to 2007 seven repeat conductivity temperature depth sections from 1991 to 2001 and sea surface height maps the mean temperature of the samw lies between 8 5 c and 9 5 c mean of 8 8 c standard deviation of 0 3 c and there is no evidence of a trend over the 18 year record however the temperature salinity and pycnostad strength of the samw can change abruptly from section to section in addition the samw pool on a single section often consists of two or more modes with distinct temperature salinity and vertical homogeneity characteristics but similar density we show that the multiple types of mode water can be explained by the advection of anomalous water from eddies and meanders of the fronts bounding the subantarctic zone and by recirculation of samw of different ages our results suggest that infrequently repeated sections can potentially produce misleading results because of aliasing of high interannual variability

mechanisms of pacific summer water variability in the arctic s central canada basin pacific water flows northward through bering strait and penetrates the arctic ocean halocline throughout the canadian basin sector of the arctic in summer pacific summer water psw is modified by surface buoyancy fluxes and mixing as it crosses the shallow chukchi sea before entering the deep ocean measurements from ice tethered profilers moorings and hydrographic surveys between 2003 and 2013 reveal spatial and temporal variability in the psw component of the halocline in the central canada basin with increasing trends in integrated heat and freshwater content a consequence of psw layer thickening as well as layer freshening and warming it is shown here how properties in the chukchi sea in summer control the temperature salinity properties of psw in the interior by subduction at isopycnals that outcrop in the chukchi sea results of an ocean model forced by idealized winds provide support to the mechanism of surface ocean ekman transport convergence maintaining psw ventilation of the halocline

eddies in the western arctic ocean from spaceborne sar observations over open ocean and marginal ice zones the western arctic ocean is a host to major ocean circulation systems many of which generate eddies that can transport water masses and corresponding tracers over long distances from their formation sites however comprehensive observations of critical eddy characteristics are currently not available and are limited to spatially and temporally sparse in situ observations here we use high resolution spaceborne synthetic aperture radar measurements to detect eddies from their surface imprints in ice free sea surface roughness and in sea ice patterns throughout marginal ice zones we provide the first estimate of eddy characteristics extending over the seasonally ice free and marginal ice zone regions of the western arctic ocean including their locations diameters and monthly distribution using available synthetic aperture radar data we identified over 4 000 open ocean eddies as well as over 3 500 eddies in marginal ice zones from june to october in 2007 2011 and 2016 eddies range in size between 0 5 and 100 km and are frequently found over the shelf and near continental slopes but also present in the deep canada basin and over the chukchi plateau we find that cyclonic eddies are twice more frequent compared to anticyclonic eddies at the surface distinct from the dominating anticyclonic eddies observed at depth by in situ moorings and ice tethered profilers our study supports the notion that eddies are ubiquitous in the western arctic ocean even in the presence of sea ice and emphasizes the need for improved ocean observations and modeling at eddy scales

circumpolar response of southern ocean eddy activity to a change in the southern annular mode 1 analysis of satellite altimeter data reveals anomalously high eddy kinetic energy eke in the antarctic circumpolar current acc during the period 2000 2002 around 2 3 years earlier 1998 the circumpolar eastward wind stress as quantified by the southern annular mode sam showed a significant positive peak and we have shown previously that the acc peaked around 1998 in response an eddy resolving ocean model is used to investigate the delay between wind forcing and the eddy response and demonstrates that the lag is due to the time taken to influence the deep circulation of the acc winds over the southern ocean have shown a strong climatic increase over the past few decades if this increase in winds is also reflected as an increase in eddy activity as our analysis suggests it might then the increased poleward heat flux may have played a significant role in the observed warming of the southern ocean citation meredith m p and a m hogg 2006 circumpolar response of southern ocean eddy activity to a change in the southern annular mode geophys res lett 33 l16608 doi 10 1029 2006gl026499

spin down of baroclinic eddies under sea ice a linear model is used to examine the spin down of a baroclinic eddy under the sea ice for anti cyclonic eddies the ice stress besides directly spinning down the azimuthal flow within the mixed layer generates an ekman divergence that raises the pycnocline near the eddy axis for eddies of the size of the baroclinic radius of deformation based on the unperturbed mixed layer depth h and the density jump across the pycnocline the doming reaches a quasi stationary state on the frictional time scale t defined as h where is the resistence coefficient at the ice water interface which generally is of the order of days upward entrainment of the fluid across the pycnocline causes a flow convergence below the mixed layer that continues to spin down the deeper flow and flatten the dome the erosion of the dome however occurs over a much longer time scale of n 1t where and n are dimensionless parameters characterizing the entrainment rate and the deep stratification using realistic parameter values for the polar eddies this time scale is of the order of a year or longer the pycnocline dome observed over the antarctic warm cells is thus likely to survive into the following freezing season and provide a preconditioning for the deep convection in the weddell sea

topographic control of southern ocean gyres and the antarctic circumpolar current a barotropic perspective abstractin the southern ocean the antarctic circumpolar current is significantly steered by large topographic features and subpolar gyres form in their lee the geometry of topographic features in

the beaufort gyre intensification and stabilization a model observation synthesis a model observation synthesis is conducted to investigate changes in the upper ocean circulation and stratification in the canada basin cb of the arctic ocean results show that the beaufort gyre bg has been generally intensifying during 1992 2015 in conjunction with changes in sea ice and the upper ocean including increasing sea surface height ssh sea ice and ocean speed ekman transport convergence and downwelling and freshwater content decreasing ice thickness and upper ocean salinity shoaling summer halocline and mixed layer and deepening winter halocline and mixed layer increasing ekman transport convergence draws more water from surrounding areas into the cb thus lowering ssh in those areas and raising ssh in the cb the rate of change in the cb began to decrease in 2008 and the bg circulation appears to be stabilizing if not relaxing slightly this is reflected in the general plateauing of ssh the intensity of the sea ice and ocean circulation and various measures of the cb thermohaline stratification the bg intensification and subsequent stabilization appear to have been strongly controlled by atmospheric changes in the cb characterized by generally increasing anticyclonic wind circulation and sea level pressure slp before 2008 and falling wind strength and slp to below average levels in some years after 2008 changes in slp are highly correlated with changes in ocean surface stress curl and downwelling since 2008 the magnitude of the stress curl and downwelling in much of the cb has declined contributing to bg stabilization the general leveling off of sea ice thickness also contributes to the stabilization by limiting melt water input to the cb that increases freshwater content temperatures in the near surface temperature maximum layer trended upward slightly over 1992 2015 which is closely correlated with decreasing sea ice thickness upper ocean heat content increased over the study period mainly due to strong temperature increases in the summer pacific water layer

gulf stream dynamics along the southeastern u s seaboard abstractthe gulf stream strongly interacts with the topography along the southeastern u s seaboard between the straits of florida and cape hatteras the dynamics of the gulf stream in this region is investigated with a set of realistic very high resolution simulations using the regional ocean modeling system roms the mean path is strongly influenced by the topography and in particular the charleston bump there are significant local pressure anomalies and topographic form stresses exerted by the bump that retard the mean flow and steer the mean current pathway seaward the topography provides through bottom pressure torque the positive input of barotropic vorticity necessary to balance the meridional transport of fluid and close the gyre scale vorticity balance the effect of the topography on the development of meanders and eddies is studied by computing energy budgets of the eddies and the mean flow the baroclinic instability is stabilized by the slope everywhere except past the bump the flow

influence of topography on the large scale ocean circulation abstract the influence of the bottom topography on the large scale ocean circulation is discussed and illustrated with a simple model based on the ideal fluid thermocline equations the requirement that fluid remains in linear vorticity balance while conserving its density leads to a coupled problem but one that can be reduced to a single characteristic equation under an assumption of uniform potential vorticity on density surfaces the characteristics are intermediate between the f h contours found in a homogeneous ocean and the f contours found in an ocean with a motionless abyss the extent to which topography influences the circulation in upper layers is quantified and is shown to depend on both the strength of the bottom currents and on the vertical profile of stratification in a realistic limit in which the abyssal waters are sluggish and weakly stratified the circulation in surface layers is relatively indifferent to the topography beneath the direction in which a current deflects around a top

progress on the formation dynamics of the layered circulation in the south china sea abstract in the south china sea scs an alternating cyclonic anticyclonic cyclonic cac circulation is recognized in the upper middle deep layers based on the principle of stokes theorem the cac circulation is driven extrinsically by the east asia monsoonal winds a vertical sandwich like inflow outflow inflow through luzon strait ls and intrinsically by the slope current topography interaction the understandings on the formation mechanisms of cac circulation have been achieved based on different principles and the physically solid interpretation on the cac circulation need to be further clarified in this paper we review different dynamic perspectives from recent researches that describe the combined effects of surface wind forcing lateral external forcing and the intrinsic coupling among different layers our aim is to obtain a consistent understanding of the dynamics of the circulation in the scs the cac circulation forms largely from the planetary vorticity flux that is extrinsically induced by the inflow outflow inflow through ls which is predominantly balanced by the interaction between the cac flow and bottom topography inside basin the vertical motion dynamically links the circulation in three layers and its spatial pattern has a strong impact on the basin circulation particularly in the middle and deep layers vertical coupling of the layers occurs mainly over the slope because of the cross slope motion due to interaction between strong slope current and topography the internal layered circulation and intensified mixing in turn affect and maintain the layered current structure in ls based on the review of the forcing mechanisms we offer perspectives for further investigations

beaufort gyre freshwater reservoir state and variability from observations 1 we investigate basin scale mechanisms regulating anomalies in freshwater content fwc in the beaufort gyre bg of the arctic ocean using historical observations and data collected in 2003 2007 specifically the mean annual cycle and interannual and decadal fwc variability are explored the major cause of the large fwc in the bg is the process of ekman pumping ep due to the arctic high anticyclonic circulation centered in the bg the mean seasonal cycle of liquid fwc is a result of interplay between the mechanical ep and thermal ice transformations factors and has two peaks one peak occurs around june july when the sea ice thickness reaches its minimum maximum ice melt the second maximum is observed in november january when wind curl is strongest maximum ep and the salt input from the growing ice has not yet reached its maximum interannual changes in fwc during 2003 2007 are characterized by a strong positive trend in the region varying by location with a maximum of approximately 170 cm a 1 in the center of ep influenced region decadal fwc variability in the period 1950 2000 is dominated by a significant change in the 1990s forced by an atmospheric circulation regime change the center of maximum fwc shifted to the southeast and appeared to contract in area relative to the pre 1990s climatology in spite of the areal reduction the spatially integrated fwc increased by over 1000 km 3 relative to climatology

the prevalence of oceanic surface modes satellite observations have revolutionized oceanography capturing diverse phenomena over much of the globe however it remains to understand how surface fields like sea surface height reflect the motion occurring at depth the vertical structure of ocean eddies is often expressed in terms of baroclinic modes which are basis functions derived assuming a flat ocean bottom bathymetry alters the modes though weakening the bottom velocities using analytical solutions we demonstrate that with realistic bathymetry and or bottom friction the bottom velocities are nearly zero the resulting surface modes should be ubiquitous in the ocean this would explain the dominant mode of variability obtained from globally distributed current meter data and is consistent with energy spectra derived from sea surface height data the results yield a simple way to infer subsurface velocities from satellite data and suggest that ocean analyses should be made in terms of surface modes and topographic waves

the role of sloping sidewalls in forming potential vorticity contrasts in the ocean interior the role of sidewalls in determining the interior distribution of potential vorticity pv is investigated using eddy resolving isopycnic experiments the layer model is integrated at 1 8 resolution for a wind driven double gyre with either vertical or sloping sidewalls if there are vertical sidewalls eddy stirring leads to pv homogenization within unforced interior density layers if there are sloping sidewalls frictional torques lead to bands of low and high pv being formed along the western boundary of the subpolar and subtropical gyres respectively these regions of low and high pv are transferred into the interior by a separated jet at the intergyre boundary over a limited domain this injection of the pv contrast can prevent eddy homogenization from occurring however over a larger scale domain eddies provide a downgradient transfer of pv reducing the pv contrast downstream along the jet and enabling homogenization to occur for intermediate layers within the basin interior diabatic mixing along the slope can introduce low pv for intermediate layers and even mask the frictional contributions