on the relationship between southern ocean overturning and acc transport the eddy field in the southern ocean offsets the impact of strengthening winds on the meridional overturning circulation and antarctic circumpolar current acc transport there is widespread belief that the sensitivities of the overturning and acc transport are dynamically linked with limitation of the acc transport response implying limitation of the overturning response here an idealized numerical model is employed to investigate the response of the large scale circulation in the southern ocean to wind stress perturbations at eddy permitting to eddy resolving scales significant differences are observed between the sensitivities and the resolution dependence of the overturning and acc transport indicating that they are controlled by distinct dynamical mechanisms the modeled overturning is significantly more sensitive to change than the acc transport with the possible implication that the southern ocean overturning may increase in response to future wind stress changes without measurable changes in the acc transport it is hypothesized that the dynamical distinction between the zonal and meridional transport sensitivities is derived from the depth dependence of the extent of cancellation between the ekman and eddy induced transports

variability in southern hemisphere ocean circulation from the 1980s to the 2000s abstractinterannual to decadal variability of ocean circulation in the southern hemisphere was examined using data from the 1980s to the 2000s in a box inverse model to estimate transport across hydrographic sections and three ocean general circulation models ogcms the westerly wind stress over the ogcm southern ocean showed a steady increase of 5 8 decade 1 the meridional overturning circulation was quantified by the transport across 30 s the ogcms suggested a slight strengthening from 0 2 1 0 to 0 8 1 3 sv decade 1 1 sv 106 m3 s 1 of the upper meridional cell deacon cell and two ogcms showed a weakening 0 8 0 6 and 1 0 0 3 sv decade 1 of the lower meridional antarctic bottom water aabw cell partly explained by contraction of the aabw volume the box inverse estimates did not contradict these two findings for antarctic circumpolar current transport quantified by zonal transport across four key sections the box inverse model estimated a decrease of 5 21 sv decomposition

residual mean solutions for the antarctic circumpolar current and its associated overturning circulation abstract residual mean theory is applied to the streamwise averaged antarctic circumpolar current to arrive at a concise description of the processes that set up its stratification and meridional overturning circulation on an f plane simple solutions are found in which transfer by geostrophic eddies colludes with applied winds and buoyancy fluxes to determine the depth and stratification of the thermocline and the pattern of associated residual meridional overturning circulation

topographic enhancement of eddy efficiency in baroclinic equilibration abstractthe processes that determine the depth of the southern ocean thermocline are considered in existing conceptual frameworks the thermocline depth is determined by competition between the mean and eddy heat transport with a contribution from the interaction with the stratification in the enclosed portion of the ocean using numerical simulations this study examines the equilibration of an idealized circumpolar current with and without topography the authors find that eddies are much more efficient when topography is present leading to a shallower thermocline than in the flat case a simple quasigeostrophic analytical model shows that the topographically induced standing wave increases the effective eddy diffusivity by increasing the local buoyancy gradients and lengthening the buoyancy contours across which the eddies transport heat in addition to this local heat flux intensification transient eddy heat fluxes are suppressed away from the topography especially upstream indicating that local

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

a barotropic model of eddy saturation abstracteddy saturation refers to a regime in which the total volume transport of an oceanic current is insensitive to the wind stress strength baroclinicity is currently believed to be the key to

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

minimal change in antarctic circumpolar current flow speed between the last glacial and holocene relatively little is known about the dynamics of the antarctic circumpolar current during the last glacial period estimates of current speeds over the past 20 000 years based on sediment grain size suggest that average flow speeds during the last glacial were comparable to modern speeds but not in the areas with overlying winter sea ice

on the transport and angular momentum balance of channel models of the antarctic circumpolar current abstract angular momentum balances are discussed both in general as well as in the context of simple channel models of the antarctic circumpolar current acc particular emphasis is placed on the close relationship between the angular momentum balance and the meridional circulation it is found that topographic form drag is established very early in the integration whereas interfacial form drag can take much longer to develop restrictions on the geostrophic portion of the meridional circulation imposed by zonally reconnecting potential vorticity contours in the upper ocean allow derivation of an estimate for the steady state transport the estimate assumes there to be little or no circumpolar flow at great depth an assumption that stems from the belief that the band of zonally reconnecting geostrophic contours in the southern ocean does not extend to the ocean floor the predicted transport is proportional to the strength of the stratification and compares favorably with numerical results in the lite

the dependence of southern ocean meridional overturning on wind stress an eddy resolving numerical model of a zonal flow meant to resemble the antarctic circumpolar current is described andanalyzedusing the framework of j marshallandt radko in additionto windand buoyancy forcing at the surface the model contains a sponge layer at the northern boundary that permits a residual meridional overturning circulation moc to exist at depth the strength of the residual moc is diagnosed for different strengths of surface wind stress it is found that the eddy circulation largely compensates for the changes in ekman circulation the extent of the compensation and thus the sensitivity of the moc to the winds depend on the surface boundary condition a fixed heat flux surface boundary severely limits the ability of the moc to change an interactive heat flux leads to greater sensitivity to explain the moc sensitivity to the wind strength under the interactive heat flux transformed eulerian mean theory is applied in which the eddy diffusivity plays a central role in determining the eddy response a scaling theory for the eddy diffusivity based on the mechanical energy balance is developed and tested the average magnitude of the diffusivity is found to be proportional to the square root of the wind stress the moc sensitivity to the winds based on this scaling is compared with the true sensitivity diagnosed from the experiments

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

work done by atmospheric winds on mesoscale ocean eddies mesoscale eddies are ubiquitous in the ocean and dominate the ocean s kinetic energy however physical processes influencing ocean eddy energy remains poorly understood mesoscale ocean eddy wind interaction potentially provides an energy flux into or out of the eddy field but its effect on ocean eddies has not yet been determined here we examine work done by atmospheric winds on more than 1 200 000 mesoscale eddies identified from satellite altimetry data and show that atmospheric winds significantly damp mesoscale ocean eddies particularly in the energetic western boundary current regions and the southern ocean furthermore the large scale wind stress curl is found to on average systematically inject kinetic energy into anticyclonic cyclonic eddies in the subtropical subpolar gyres while mechanically damps anticyclonic cyclonic eddies in the subpolar subtropical gyres

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

meridional transport across a zonal channel topographic localization experiments are performed using a two layer isopycnic numerical model in a zonal channel with a large meridional topographic ridge in the lower layer the model is forced only by a steady meridional volume transport in the upper layer and develops a current structure similar to the antarctic circumpolar current meridional volume flux across time mean geostrophic streamlines is found to be due to a combination of the geostrophic eddy bolus flux and the lateral reynolds stress the proportion of each depends on the strength of the forcing the reynolds stress increases with the forcing while the bolus flux is relatively constant topography localizes the eddy fluxes at and downstream of the topography where eddy energies are greatest the strength of the zonal transport is governed by the onset of baroclinic instability and so is relatively insensitive to the strength of the meridional transport

where do winds drive the antarctic circumpolar current the strength of the antarctic circumpolar current acc is believed to depend on the westerly wind stress blowing over the southern ocean although the exact relationship between winds and circumpolar transport is yet to be determined here we show based on theoretical arguments and a hierarchy of numerical modeling experiments that the global pycnocline depth and the baroclinic acc transport are set by an integral measure of the wind stress over the path of the acc taking into account its northward deflection our results assume that the mesoscale eddy diffusivity is independent of the mean flow while the relationship between wind stress and acc transport will be more complicated in an eddy saturated regime our conclusion that the acc is driven by winds over the circumpolar streamlines is likely to be robust

does the sensitivity of southern ocean circulation depend upon bathymetric details the response of the major ocean currents to changes in wind stress forcing is investigated with a series of idealized but eddy permitting model simulations previously ostensibly similar models have shown considerable variation in the oceanic response to changing wind stress forcing here it is shown that a major reason for these differences in model sensitivity is subtle modification of the idealized bathymetry the key bathymetric parameter is the extent to which the strong eddy field generated in the circumpolar current can interact with the bottom water formation process the addition of an embayment which insulates bottom water formation from meridional eddy fluxes acts to stabilize the deep ocean density and enhances the sensitivity of the circumpolar current the degree of interaction between southern ocean eddies and antarctic shelf processes may thereby control the sensitivity of the southern ocean to change

faceted crystal formation in the northeast greenland low accumulation region snow pit analysis in the low accumulation region in northeast greenland indicated a mean annual accumulation of 12 1 6 cm it also revealed numerous faceted layers that were not related to the summer horizon of previous years in general the faceted crystals were found under a wind crust these crusts appear to originate during the winter snow and air temperature data from automatic weather stations suggest that the katabatic storms are responsible for the formation of the wind crusts and the faceted layers frequent abrupt temperature changes up to 30 c were observed within two days due to turbulent mixing of cold air inversions the near surface air temperature variations are correlated with wind speed the latter leading the former by 6 9 hours for increasing wind and 1 4 hours for decreasing wind because of low accumulation katabatic storms affect the same snow surface for several months causing repeated air temperature fluctuations this leads to strong vapor pressure gradients and faceted crystal growth in the top snow layer on average we found two faceted layers in addition to the summer layer per year for a 4 year record in addition to its climatological significance in the snow record the formation of these layers is especially important to understand for the interpretation of microwave satellite observations of the firn

model of wind pumping for layered snow layering affects the air flow through snow caused by surface pressure variations the horizontal and total fluxes are high in hoar layers but the pressure perturbations and vertical components of the flow do not penetrate as deeply as in homogeneous snow that is because the layers pipe the flow horizontally toward the area of low pressure an ice layer at the surface reduces the total flow everywhere the flow decreases as ice layer thickness increases and in general flow changes with permeability however the magnitude of the effect is proportionately weaker when the ice layers are further from the surface the residence time is reduced when hoar layers are present due to shorter flow paths reduced penetration into the deeper snow and higher speeds

the effect of the kerguelen plateau on the ocean circulation abstractthe kerguelen plateau is a major topographic feature in the southern ocean located in the indian sector and spanning nearly 2000 km in the meridional direction from the polar to the subantarctic region it deflects the eastward flowing antarctic circumpolar current and influences the physical circulation and biogeochemistry of the southern ocean the kerguelen plateau is known to govern the local dynamics but its impact on the large scale ocean circulation has not been explored by comparing global ocean numerical simulations with and without the kerguelen plateau this study identifies two major kerguelen plateau effects 1 the plateau supports a local pressure field that pushes the antarctic circumpolar current northward this process reduces the warm water transport from the indian to the atlantic ocean 2 the plateau generated pressure field shields the weddell gyre from the influence of the warmer subantarctic and subtropical waters the first effect influences the strength of the antarct

wind energy input to the ekman layer wind stress energy input through the surface ageostrophic currents is studied the surface ageostrophic velocity is calculated using the classical formula of the ekman spiral with the ekman depth determined from an empirical formula the total amount of energy input over the global oceans for subinertial frequency is estimated as 2 4 tw averaged over a period from 1997 to 2002 or 2 3 tw averaged over a period from 1948 to 2002 based on daily wind stress data from ncep ncar thus in addition to the energy input to the near inertial waves of 0 5 0 7 tw reported by alford and by watanabe and hibiya the total energy input to the ekman layer is estimated as 3 tw this input is concentrated primarily over the southern ocean and the storm track in both the north pacific and north atlantic oceans

acceleration of the antarctic circumpolar current by wind stress along the coast of antarctica the influence of wind forcing on variability of the antarctic circumpolar current acc is investigated using a series of eddy permitting ocean sea ice models at interannual and decadal time scales the acc transport is sensitive to both the mean strength of westerly winds along the acc circumpolar path consistent with zonal momentum balance theories and sensitive to the wind stresses along the coast of antarctica consistent with the free mode theory of hughes et al a linear combination of the two factors explains differences in acc transport across 11 regional quasi equilibrium experiments repeated single year global experiments show that the acc can be robustly accelerated by both processes across an ensemble of simulations with realistic forcing over the second half of the twentieth century interannual acc transport variability owing to the free mode mechanism exceeds that due to the zonal momentum balance mechanism by a factor of between 3 5 and 5 to one while the acc transport may not accelerate significantly owing to projected increases in along acc winds in future decades significant changes in transport could still occur because of changes in the stress along the coast of antarctica

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

delta15n measurements as a calibration tool for the paleothermometer and gas ice age differences a case study for the 8200 b p event on grip ice isotopic composition measurement on atmospheric nitrogen 15n trapped in ice cores is established as a gravitational enrichment indicator recently it was discovered that thermal diffusion has a significant influence on this parameter during periods of large temperature fluctuations severinghaus et al 1998 here we present results for the 8200 b p event the largest temperature excursion during the holocene which underpin this view and extend it to medium range temperature changes the thermal diffusion component is about one third of the gravitational enrichment for this event the shortness of this cooling event does not significantly affect the gravitational enrichment as documented by rather constant close off depths therefore the 15n residuals can be directly used to estimate temperature changes hence calibrating the paleothermometer since our 15n record can resolve temperature variations as short as a few decades it complements the calibration technique of borehole temperature measurements for which the resolution decreases rapidly with increasing age we obtained a relation 18oice temperature of 0 30 0 11 k which agrees nicely with the temporal dependence for cold periods about 0 30 k and is significantly lower than today s greenland spatial relation 0 67 k this corresponds to a range of the surface temperature shift for the 8200 b p event in central greenland between 5 4 and 11 7 k with a best estimate of 7 4 k by matching the 15n variations with 18oice variations we estimate the mean gas ice age difference to be 209 15 years which is in good agreement with model estimates

the injection of zonal momentum by buoyancy forcing in a southern ocean model abstractan overturning circulation driven by prescribed buoyancy forcing is used to set a zonal volume transport in a reentrant channel ocean model with three isopycnal layers the channel is designed to represent the southern ocean such that the forced overturning resembles the lower limb of the meridional overturning circulation moc the relative contributions of wind and buoyancy forcing to the zonal circulation are examined it is found that the zonal volume transport is strongly dependent on the buoyancy forcing and that the eddy kinetic energy is primarily set by wind stress forcing the zonal momentum budget integrated over each layer is considered in the buoyancy forced wind forced and combined forcing case at equilibrium sources and sinks of momentum are balanced but the transient spinup reveals the source of momentum for the current in the buoyancy forced case the forcing creates a baroclinic shear with westward flow in the lower layer allowing topographic form stress and bottom fric

the effect of northern hemisphere winds on the meridional overturning circulation and stratification abstractthe current paradigm for the meridional overturning cell and the associated middepth stratification is that the wind stress in the subpolar region of the southern ocean drives a northward e

the role of closed gyres in setting the zonal transport of the antarctic circumpolar current abstracteddy permitting simulations are used to show that basinlike gyres can be observed in the large scale barotropic flow of a wind driven channel with a meridional topographic ridge this is confirmed using both two layer quasigeostrophic and 25 level primitive equation models at high horizontal resolution comparing results from simulations with and without the topographic ridge it is shown that the zonal baroclinic transport in the channel increases with increasing wind stress when the bottom topography is flat but not when there is a meridional ridge the saturation of transport for increasing wind occurs in conjunction with the development of recirculating gyres in the large scale barotropic streamfunction this suggests that the total circulation can be thought of as a superposition of a gyre mode which has zero circumpolar transport and a free circumpolar mode which contains all of the transport basinlike gyres arise in the channel because the topography steers the barotropic streamlines a

the transient response of the southern ocean pycnocline to changing atmospheric winds 1 the vertical density structure of the southern ocean is dynamically linked to wind stress at the surface but the nature of this coupling is not fully understood observations from the last several decades show a significant increase in the strength of westerly winds over the southern ocean but an appreciable change in the tilt of constant density surfaces isopycnals has not yet been detected there using a combination of theory and idealized numerical simulations we show that the response of the density structure occurs on centennial timescales making it difficult to detect significant changes with a few decades of hydrographic observations dynamic coupling between the circumpolar current and northern basins regulates the slow adjustment of the density structure our results provide a new interpretation for recent observations and highlight the importance of the interaction between regional southern ocean dynamics and global ocean circulation citation jones d c t ito andn s lovenduski 2011 thetransientresponseofthe southern ocean pycnocline to changing atmospheric winds geophys res lett 38 l15604 doi 10 1029 2011gl048145

the role of mesoscale eddies in the remote oceanic response to altered southern hemisphere winds abstract it has been suggested that a strengthening of the southern hemisphere winds would induce a more vigorous overturning through an increased northward ekman flux bringing more light waters into the oceanic basins and enhancing the upwelling of north atlantic deep water in the southern ocean thereby increasing ocean ventilation simulations from a coarse and a fine resolution version of a coupled model subject to idealized wind stress changes in the southern ocean are presented in the fine resolution eddy permitting model changes in poleward eddy fluxes largely compensate for the enhanced equatorward ekman transport in the southern ocean as a consequence northward transport of light waters pycnocline depth northern hemisphere overturning and southern ocean upwelling anomalies are much reduced compared with simulations in the coarse resolution model with parameterized eddies these results suggest a relatively weak sensitivity of present day global ocean overturning circulation to the proj

eddy saturation of the southern ocean a baroclinic versus barotropic perspective eddy saturation is the regime in which the total time mean volume transport of an oceanic current is relatively insensitive to the wind stress forcing and is often invoked as a dynamical descript

a model of the upper branch of the meridional overturning of the southern ocean a zonal average model of the upper branch of the meridional overturning circulation of the southern ocean is constructed and used to discuss the processes wind buoyancy eddy forcing and boundary conditions that control its strength and sense of circulation the geometry of the thermocline wedge set by the mapping between the vertical spacing of buoyancy surfaces the stratification on the equatorial flank of the antarctic circumpolar current and their outcrop at the sea surface is seen to play a central role by setting the interior large scale potential vorticity distribution it is shown that the action of eddies mixing this potential vorticity field induces a residual flow in the meridional plane much as is observed with upwelling of fluid around antarctica northward surface flow and subduction to form intermediate water

open ocean convection observations theory and models we review what is known about the convective process in the open ocean in which the properties of large volumes of water are changed by intermittent deep reaching convection triggered by winter storms observational laboratory and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales the large scale circulation of the ocean and the prevailing meteorology two aspects make ocean convection interesting from a theoretical point of view first the timescales of the convective process in the ocean are sufficiently long that it may be modified by the earth s rotation second the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability moreover the convective and geostrophic scales are not very disparate from one another detailed observations of the process in the labrador greenland and mediterranean seas are described which were made possible by new observing technology when interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection great progress in our description and understanding of the processes at work is being made

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

sensitivity of antarctic circumpolar current transport and eddy activity to wind patterns in the southern ocean abstractthe southern hemisphere westerly winds have intensified in recent decades associated with a positive trend in the southern annular mode sam however the response of the antarctic circumpolar current acc transport and eddy field to wind forcing remains a topic of debate this study uses global eddy permitting ocean circulation models driven with both idealized and realistic wind forcing to explore the response to interannual wind strengthening the response of the barotropic and baroclinic transports and eddy field of the acc is found to depend on the spatial pattern of the changes in wind forcing in isolation an enhancement of the westerlies over the acc belt leads to an increase of both barotropic and baroclinic transport within the acc envelope with lagged enhancement of the eddy kinetic energy eke in contrast an increase in wind forcing near antarctica drives a largely barotropic change in transport along closed f h contours free mode with little change in eddy activity under

a simple model of the response of the atlantic to the north atlantic oscillation the response of an idealized atlantic ocean to wind and thermohaline forcing associated with the north atlantic oscillation nao is investigated both analytically and numerically in the framework of a reducedgravity model the nao related wind forcing is found to drive a time dependent leaky gyre circulation that integrates basinwide stochastic wind ekman pumping and initiates low frequency variability along the western boundary thisissubsequentlycommunicated togetherwith the stochasticvariability induced bythermohaline forcing at high latitudes to the remainder of the atlantic via boundary and rossby waves at low frequencies the basinwide ocean heat content changes owing to nao wind forcing and thermohaline forcing are found to oppose each other the model further suggests that the recently reported opposing changes of the meridional overturning circulation in the atlantic subtropical and subpolar gyres between 1950 70 and 1980 2000 may be a generic feature caused by interplay between the nao wind and thermohaline forcing

comparing idealized and complex topographies in quasigeostrophic simulations of an antarctic circumpolar current abstractthe circumpolar transport of a wind driven quasigeostrophic antarctic circumpolar current is considered simple theory suggests transport in a strongly forced regime the focus of this study is largely determined by a partitioning of the southward sverdrup flux into drake passage latitudes some streamlines feed a basin contribution to the circumpolar transport and others feed a large scale recirculation gyre simulations assuming an idealized scotia ridge topography are considered to test for sensitivity to resolution considerable sensitivity to both vertical and horizontal resolution is found and associated with this is a tight stationary eddy trapped on the western flank of the ridge that is this eddy is sensitive to resolution and exerts an influence that acts to reduce the circumpolar transport simulations using the scotia ridge like topography are also compared to others using more realistic topography in the idealized ridge topography experiments there is only a single ridge again

decadal mean impact of including ocean surface currents in bulk formulas on surface air sea fluxes and ocean general circulation abstractthe decadal mean impact of including ocean surface currents in the bulk formulas on surface air sea fluxes and the ocean general circulation is investigated for the first time using a global eddy permitting coupled ocean sea ice model although including ocean surface currents in air sea flux calculations only weakens the surface wind stress by a few percent it significantly reduces wind power input to both geostrophic and ageostrophic motions and damps the eddy and mean kinetic energy throughout the water column furthermore the strength of the horizontal gyre circulations and the atlantic meridional overturning circulation are found to decrease considerably by 10 15 and 13 respectively as a result of the weakened ocean general circulation the maximum northward global ocean heat transport decreases by about 0 2 pw resulting in a lower sea surface temperature and reduced surface heat loss in the northern north atlantic additional sensitivity model experiments further demonstrate that

implementation of a geometrically informed and energetically constrained mesoscale eddy parameterization in an ocean circulation model abstractthe global stratification and circulation as well as their sensitivities to changes in forcing depend crucially on the representation of the mesoscale eddy field in a numerical ocean circ

bathymetric effects on estuarine plume dynamics 1 the influence of bathymetry on an estuary plume at an estuary shelf transition is studied with a three dimensional ocean circulation model to understand the response of the plume to bathymetry several types of estuarine shapes and shelf geometries were adopted in this numerical study the channel s shape and its width to depth aspect ratio affected the fate of the plume by determining flow characteristics inside the estuary moreover the bathymetry of the shelf such as the shelf slope and the direction of a submarine channel defined the plume characteristics on the shelf an estuarine channel with a triangular cross section generated relatively stronger exchange flows at midestuary than a rectangular cross section which resulted in a larger surface plume over the shelf the extension of the submarine channel onto the shelf favored increased plume water transport out to the shelf a result of reduced frictional effects on the shelf the orientation of the submarine channel changed the direction of the plume over the shelf with no additional external forces two fronts developed at the edges of the submarine channel because of enhanced lateral shears in the flow when the estuary was relatively wide compared to the internal rossby radius kelvin number ke 5 or when the relative strength of the freshwater discharge compared to the estuary width was weak rossby number ro 0 05 the coastal plume did not expand up shelf in fact results indicated that freshwater up shelf transport in a coastal current moving against coriolis accelerations was proportional to ro

the response of southern ocean eddies to increased midlatitude westerlies a non eddy resolving model study 1 the midlatitude westerlies of the southern hemisphere have intensified since the 1970s non eddy resolving general circulation models respond to such wind intensification with steeper isopycnals a faster antarctic circumpolar current acc and a stronger atlantic meridional overturning circulation amoc however hydrographic observations show little change in the slope of the southern ocean isopycnals over the past 40 years this insensitivity seems to result from a compensating mechanism whereby an initial increase in the slope of the isopycnals causes eddy activity to intensify and forces the isopycnal slopes down climate models do not yet resolve ocean eddies and the eddy parameterizations included in them do not capture well the compensation mechanism mentioned above we present simulations with a non eddy resolving model incorporating an eddy parameterization in which eddy compensation is greatly enhanced by the use of a non constant spatially varying thickness diffusivity the sensitivity of the simulated acc and amoc to increased southern hemisphere westerlies is greatly reduced compared to simulations using constant and uniform diffusivities

the impact of turbulence and convection on transport in the southern ocean volume transport in the presence of fully resolved convection and turbulence is investigated in a reentrant channel model of the southern ocean the response of the meridional overturning and zonal transport to variations in wind and buoyancy forcing is quantified our simulations show two overturning cells a buoyancy driven lower cell and a wind driven upper cell the lower overturning cell is much larger in meridional extent and magnitude than the upper cell the mean component of the overturning transport is smaller than the fluctuating component in the lower overturning cell indicating that transport is dominated by eddies and or turbulent convective flow in contrast the upper cell can be primarily described as a mean flow indicating minimal eddy compensation both cells strengthen with increasing winds with the upper cell being more sensitive to increasing wind intensity than the lower cell scaling for the mean upper overturning is also derived and matches previous theories which predict a linear sensitivity of the upper cell to wind zonal transport remains insensitive to increasing wind stress suggesting that the system is eddy saturated when turbulence and eddies are resolved these results suggest that fine scale flows control zonal transport and abyssal meridional overturning in the southern ocean while wind stress drives the upper meridional overturning transport highlighting the importance of accurately characterizing turbulence and convection in large scale models

on the loss of wind induced near inertial energy to turbulent mixing in the upper ocean wind induced near inertial energy has been believed to be an important source for generating the ocean mixing required to maintain the global meridional overturning circulation in the present study the near inertial energy budget in a realistic 1 12 degrees model of the north atlantic ocean driven by synoptically varying wind forcing is examined the authors find that nearly 70 of the wind induced near inertial energy at the sea surface is lost to turbulent mixing within the top 200 m and hence is not available to generate diapycnal mixing at greater depth assuming this result can be extended to the global ocean it is estimated that the wind induced near inertial energy available for ocean mixing at depth is at most 0 1 tw this confirms a recent suggestion that the role of wind induced near inertial energy in sustaining the global overturning circulation might have been overemphasized

a simple theory for the fate of buoyant coastal discharges abstract a simple theory that predicts the vertical structure and offshore spreading of a localized buoyant inflow onto a continental shelf is formulated the theory is based on two competing mechanisms that move the buoyant fluid offshore 1 the radial spread of the lighter water over the ambient water being deflected by the coriolis force and producing an anticyclonic cyclostrophic plume and 2 offshore transport of buoyant water in the frictional bottom boundary layer that moves the entire plume offshore while maintaining contact with the bottom the surface expression of the cyclostrophic plume moves offshore a distance ys 2 3g h0 2i 2g h0 2i 1 2f where g is reduced gravity based on the inflow density anomaly h0 is the inflow depth i is the inflow velocity and f is the coriolis parameter the plume remains attached to the bottom to a depth given by hb 2l ih0f g 1 2 where l is the inflow width both scales are based solely on parameters of the buoyant inflow at its source there

decadal variability of wind energy input to the world ocean abstract wind stress energy input to the oceans is the most important source of mechanical energy in maintaining the oceanic general circulation previous studies indicate that wind energy input to the ekman layer and surface waves has varied greatly over the past 50 years in this study wind energy input to surface current and surface geostrophic current was calculated as the scalar product of wind stress and surface current and surface geostrophic current the surface geostrophic current was calculated in two ways the surface geostrophic velocity was diagnosed from the topex poseidon altimeter data between 1993 and 2003 and calculated from the sea surface height of the numerical model the surface velocity was obtained from a numerical model estimate of wind energy input based on altimetric data averaged over 1993 2003 is 0 84 tw 1 tw 1 0 12 w excluding the equatorial band within 3 of the equator estimate of the wind energy input to the surface geostrophic current based on the numerical model is 0 87 tw averaged from 1993 to 2003 and wind energy input to the surface current for the same period is 1 16 tw this input is primarily concentrated over the southern ocean and the equatorial region 2 0 s 2 0 n this energy varied greatly on interannual and decadal time scales and it increased 12 over the past 25 years and the interannual variability mainly occurs in the latitude band of 4 0 s 6 0 s and the equatorial region

influence of wind stress wind stress curl and bottom friction on the transport of a model antarctic circumpolar current abstracteddy permitting simulations of a wind driven quasigeostrophic model in an idealized southern ocean setting are used to attempt to describe what sets the wind driven circumpolar transport of the antarctic circumpolar current acc for weak forcing the transport is well described as a linear sum of channel and basin components the authors main focus is on stronger forcing in this regime an eddy driven recirculation appears in the abyssal layer and all time mean circumpolar streamlines are found to stem from a sverdrup like interior the sverdrup flux into drake passage latitudes can then be thought of as the sum of one part that feeds the circumpolar current and another that is associated with the recirculation the relative fractions of this partitioning depend on the bottom drag the midchannel wind stress and the wind stress curl increasing the strength of the bottom drag reduces the recirculation and increases circumpolar transport increasing a zero curl eastward wind stress reduces th

firn processes and δ15n potential for a gas phase climate proxy abstract in order to quantify the sequence of events between changes in atmospheric composition and climate changes recorded in ice cores we must accurately account for the age difference between ice and gas at a given depth this gas age ice age difference depends on the age of the ice at the bottom of the firn layer where the bubbles are closed off firn densification models are used to calculate how this age difference varied in the past but have an uncertainty on the order of 1000 years for central antarctic sites here we explore the possibility that 15 n of n 2 is a gas phase proxy of climate which can be used to synchronize gas and ice records we present the 15 n record from the epica dome c edc ice core covering the last three glacial terminations and five glacial interglacial cycles between 300 and 800 ka previous studies have shown that gravitational settling enriches 15 n as a function of the diffusive column height in the firn if densification models prediction of deeper firn close off under glacial conditions is correct then we would expect heavier 15 n during glacial periods and a negative correlation with temperature instead edc 15 n is positively correlated with the ice deuterium content a proxy for temperature as previously reported at vostok dome fuji and epica dronning maud land we propose a mechanism that links accumulation rate firn permeability and convective mixing in the top meters of the firn to explain this correlation between 15 n and ice deuterium content the tightest correlation is observed over glacial terminations supporting the idea that 15 n is a property in the gas phase that records changes in surface conditions linked to deglacial warming

quasi biennial modulation of the southern ocean coherent mode empirical orthogonal function eof analysis of two independent southernocean sea level datasets for the period 1992 2002 shows that the coherent oceanicmode a zonally symmetric counterpart to the atmospheric southern annular mode sam consistently emerges as the predominant mode of variability and is revealedto be a reliable proxy for circumpolar transport upon subannual to interannualtime scales cross validation of the coherent mode from each dataset and that ofa global barotropic model demonstrates a high degree of correspondence betweensea level observations and model estimations and also indicates that the coherentoceanic mode is largely barotropically driven upon subannual time scales whilstbaroclinic oceanic effects predominate at longer periods both the coherent modeand transport are shown to be modi ed by the stratospheric quasi biennial oscilla tion qbo and a mechanism is described by which qbo dependent planetary waveactivity may be guided from the stratosphere towards the surface by high latitudeeasterly and westerly jets inducing wind anomalies that force sea level variabilitythrough equatorward ekman transport a longer 18 year tide gauge record fromthe vernadsky faraday station and a 22 year time series of sea level estimationsfrom an ocean general circulation model are used to show that qbo inducedsea level and transport variability may be modulated upon longer time scales by aquasi decadalcycleofsolaractivity copyright c 2010royalmeteorologicalsociety

hyporheic exchange with heterogeneous streambeds laboratory experiments and modeling 1 hyporheic exchange is generally analyzed with the assumption of a homogeneous hyporheic zone in reality streambed sediments have a heterogeneous structure and this natural heterogeneity produces spatially variable interfacial fluxes and complex hyporheic exchange patterns to assess the basic effects of sediment structure on hyporheic exchange we performed salt and dye injection experiments in a recirculating laboratory flume with two heterogeneous sediment beds characterized by negative exponential correlated random hydraulic conductivity fields dye injections showed that the hyporheic flow structure was controlled by the spatial relationship of bed forms to high and low permeability regions of the streambed as no existing model could represent these effects we developed a new finite element model to calculate the pore water flow field resulting from the interaction of the bed form induced boundary head distribution and the heterogeneous sediment structure a numerical particle tracking approach was then used to assess the resulting hyporheic exchange the combined flow transport model did an excellent job of predicting the complex hyporheic flow pathways in the heterogeneous bed and the net hyporheic exchange up to t 30 hours the heterogeneous hydraulic conductivity field caused both greater spatial variability in the water flux through the bed surface and a greater average interfacial flux than would have occurred with a homogeneous bed the layered correlation structure of the streambed produced an effective anisotropy that favored longitudinal pore water flow and caused a relatively rapid decrease of the mean pore water velocity with depth as a result solute penetration into the bed was confined to a more shallow region than would have occurred with a homogeneous bed the combination of faster near surface transport and shallower solute penetration produced a shorter mean hyporheic residence time on the basis of the combination of experimental results and model simulations we conclude that the structural heterogeneity of streambed sediments produces more spatially limited hyporheic exchange that occurs with greater spatial variability and at a higher overall rate

interactions between western boundary currents and shelf waters a mechanism for coastal upwelling a geostrophic adjustment model has been developed to describe interactions between shelf waters and an offshore current such as a western boundary current a simple analysis demonstrates the response of coastal waters to the gradual encroachment of a western boundary current and reveals how this can lead to strong upwelling when bottom friction is taken into account conditions favorable to upwelling actually occur well before the western boundary current comes into direct contact with the bottom some aspects of the theory have been compared with laboratory experiments on interacting currents over sloping topography the comparisons are quite favorable for relatively stable flows however under other conditions baroclinic instabilities grow into large eddies which dramatically enhance exchange between the two currents results from the study are used to interpret documented observations of coastal encroachment by the east australian current and associated phytoplankton blooms

a conceptual model of ocean heat uptake under climate change abstracta conceptual model of ocean heat uptake is developed as a multilayer generalization of gnanadesikan the roles of southern ocean ekman and eddy transports north atlantic deep water nadw formation and diapycnal mixing in controlling ocean stratification and transient heat uptake are investigated under climate change scenarios including imposed surface warming increased southern ocean wind forcing with or without eddy compensation and weakened meridional overturning circulation moc induced by reduced nadw formation with realistic profiles of diapycnal mixing ocean heat uptake is dominated by southern ocean ekman transport and its long term adjustment controlled by the southern ocean eddy transport the time scale of adjustment setting the rate of ocean heat uptake increases with depth for scenarios with increased southern ocean wind forcing or weakened moc deepened stratification results in enhanced ocean heat uptake in each of these experiments the role of diapycnal mixing in settin

on the upwelling of downwelling currents abstract the term downwelling currents refers to currents with a downslope mass flux in the bottom boundary layer examples are the malvinas and southland currents in the southern hemisphere and the oyashio in the northern hemisphere although many of these currents generate the same type of highly productive ecosystems that is associated with upwelling regimes the mechanism that may drive such upwelling remains unclear in this article it is postulated that the interaction between a downwelling current and the continental slope generates shelfbreak upwelling the proposed mechanism is relatively simple as a downwelling current flows along the continental slope bottom friction and lateral diffusion spread it onto the neighboring shelf thus generating along shelf pressure gradients and a cross shelf circulation pattern that leads to shelfbreak upwelling at difference with previous studies of shelfbreak dynamics e g gawarkiewicz and chapman chapman and lentz and pickart the shelfbreak upwelli

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

role of residual overturning for the sensitivity of southern ocean isopycnal slopes to changes in wind forcing abstractthe antarctic circumpolar current plays a central role in the ventilation of heat and carbon in the global ocean in particular the isopycnal slopes determine where each water mass outcrop

on the alongshelf evolution of an idealized density front abstract observations reveal a strong tendency for fronts to locate over the outer continental shelf and the upper portions of the continental slope in this paper we consider a model of the alongshelf evolution of a quasi steady density front which separates relatively light nearshore water from the offshore results show how in the absence of any external forcing the frictional stress associated with bottom geostrophic velocities can result in the cross shelf migration of a front as one progresses down the shelf in the direction of long coastal trapped wave propagation the primary results are derived for the hypothetical case of a flat shelf adjoining a very deep offshore region in this case the rate of cross shelf migration of a density front is similar to that of a passive scalar front in a barotropic fluid the offshore displacement of a front separating the lighter inshore from the heavier offshore water increases exponentially in the direction of shelf wave propagation on the frictional dec

location of the antarctic polar front from amsr e satellite sea surface temperature measurements abstract the location of the southern ocean polar front pf is mapped from the first 3 yr of remotely sensed advanced microwave scanning radiometer for the earth observing system amsr e sea surface temperature sst measurements in agreement with previous studies the mean path of the antarctic pf and its standard deviation are strongly influenced by bottom topography however the mean pf path diverges slightly from previous studies in several regions where there is high mesoscale variability although the sst and sst gradient at the pf show spatially coherent seasonal variations with the highest temperature and the lowest temperature gradient during summer the seasonal variations in the location of the pf are not spatially coherent the temporal mean sst at the pf corresponds well to the mean pf path the temperature is high in the atlantic and indian ocean sections and is low in the pacific ocean section where the pf has a more southerly position the relationship of the wind field with the antar

impact of synoptic atmospheric forcing on the mean ocean circulation abstractthe impact of synoptic atmospheric forcing on the mean ocean circulation is investigated by comparing simulations of a global eddy permitting ocean sea ice model forced with and without synoptic atmospheric phenomena consistent with previous studies transient atmospheric motions such as weather systems are found to contribute significantly to the time mean wind stress and surface heat loss at mid and high latitudes owing to the nonlinear nature of air sea turbulent fluxes including synoptic atmospheric forcing in the model has led to a number of significant changes for example wind power input to the ocean increases by about 50 which subsequently leads to a similar percentage increase in global eddy kinetic energy the wind driven subtropical gyre circulations are strengthened by about 10 15 whereas even greater increases in gyre strength are found in the subpolar oceans deep convection in the northern north atlantic becomes significantly more vigorous which in turn leads to an increa

the effects of mesoscale eddies on the stratification and transport of an ocean with a circumpolar channel abstract the effects of eddies in a primitive equation ocean model configured in a single hemisphere domain with circumpolar channels at their poleward ends are investigated in particular two regimes for the mass balance in the channel are investigated with small overlying winds the channel stratification is largely set by diffusion operating in the gyre portion of the domain the depth scale varies with a fractional power of the diffusivity but has little dependence on the wind stress as the winds are increased the depth becomes increasingly controlled by a tendency toward small residual circulation in this limit a scaling theory is derived for the stratification in the channel that predicts the overall depth of the thermocline as a power of the wind stress and that allows the eddy length scale to differ from the channel length scale the predicted depth depends on the details of the closure chosen for the eddy buoyancy flux but in general it varies as some fractional power of the wind stress a

the role of eddy transfer in setting the stratification and transport of a circumpolar current abstract high resolution numerical experiments of a circumpolar current are diagnosed to study how lateral and vertical transfer of buoyancy by geostrophic eddies balances advection by a meridional circulation driven by surface wind stresses and buoyancy fluxes a theory is developed in the framework of the residual circulation to relate the vertical and horizontal stratification set up to the transfer properties of eddies and the patterns of imposed wind and buoyancy forcing simple expressions are found for the depth of penetration stratification baroclinic transport and residual circulation of the current finally the ideas are applied to the antarctic circumpolar current acc and yield predictions for how its properties depend on wind and buoyancy forcing