agulhas eddy fluxes in a 1 6 atlantic model a 1 6 resolution primitive equation model of the atlantic circulation is analyzed in the agulhas region the model has a realistic level of eddy kinetic energy and produces anticyclonic agulhas rings as well as cyclonic structures in the model as well as in the data ring trajectories undergo a transition between a turbulent character in the cape basin and a steady propagation in the rest of the south atlantic the topography of the walvis ridge does not seem to play a part in generating this contrast in the model the model shows that cyclones are primarily generated from the negative shear vorticity side of the agulhas current as it leaves the coast and they are most of the time paired with anticyclones in dipolar or tripolar structures contribution of agulhas rings to the transports has been estimated by two methods either focussing on the amount of water trapped inside the eddies and carried with them or as a perturbation to the time mean flow the second estimate always produces smaller mass fluxes than the first even so the transient eddy flux 2 sv of warm water over the agulhas ridge is very large when compared to parameterizations of eddy fluxes used in low resolution climate models

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

deglaciation of a marine based ice sheet late weichselian palaeo ice dynamics and retreat in the southern barents sea reconstructed from onshore and offshore glacial geomorphology abstract marine and terrestrial datasets swath bathymetry 2d and 3d seismic and remote sensing data are used to map the megascale glacial geomorphology of the southern barents sea seafloor northern fennoscandia and the kola peninsula giving new insights into the dynamics and behaviour of the barents sea ice sheet during retreat the glacial geomorphology indicates clear spatial and temporal variations in ice dynamics with evidence for both active ice streaming and frozen bed conditions at the maximum and during deglaciation a five stage reconstruction of the late weichselian deglaciation is proposed at the late weichselian maximum ice covered the whole of the barents sea shelf and the configuration and dynamics of the ice sheet were controlled by the bjornoyrenna bear island trough ice stream this was fed by source areas in the central and north eastern barents sea and in the fennoscandian mainland deglaciation was initiated along the western continental margin available dating results show that this occurred after 19 cal ka bp the bjornoyrenna ice stream retreated rapidly ice margin retreat rates of 275 m a 1 but was periodically grounded as evidenced by a well developed series of grounding zone wedges this was followed by an advance of two short lived ice streams from the eastern sector of the ice sheet into the south western barents sea these ice streams advanced and retreated very rapidly with no evidence for ice margin standstills correlation to dated cores suggests an age of around 16 000 cal ka bp for this readvance the period of operation of these two ice streams was coincident with maximum ice extent along the eastern margin in russia the western barents sea ice margin then retreated onshore with deglaciation continuing at a reduced rate the initiation of deglaciation coincided with rising global eustatic sea level acceleration of calving due to grounding line floatation rapidly opened up a major calving bay in bjornoyrenna encouraging rapid loss of the marine based ice the retreat rate stabilised only once the ice sheet retreated onshore and calving ceased we note that the observed pattern of rapid retreat with high variability in ice streaming for the marine based barents sea ice sheet is similar to that of the marine based sectors of the late weichselian british laurentide and west antarctic ice sheets

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

southern ocean thermocline ventilation abstract an approximate mass volume budget in the surface layer of the southern ocean is used to investigate the intensity and regional variability of the ventilation process discussed here in terms of subduction and upwelling ventilation resulting from ekman pumping is estimated from satellite winds the geostrophic mean component is assessed from a climatology strengthened with argo data and the eddy induced advection is included via the parameterization of gent and mcwilliams together with eddy mixing estimates all three components contribute significantly to ventilation finally the seasonal cycle of the upper ocean is resolved using argo data the circumpolar averaged circulation shows an upwelling in the antarctic intermediate water aaiw density classes which is carried north into a zone of dense subantarctic mode water samw subduction although no consistent net production is found in the light samw density classes a large subduction of subtropical mode water stmw is observed the s

mesoscale eddies in the northeastern pacific tropical subtropical transition zone statistical characterization from satellite altimetry 1 mesoscale eddies in the northeastern pacific tropical subtropical transition zone 16 n 30 n 130 w 102 w are analyzed using nearly 18 years of satellite altimetry and an automated eddy identification algorithm eddies that lasted more than 10 weeks are described based on the analysis of 465 anticyclonic and 529 cyclonic eddy trajectories we found three near coastal eddy prolific areas 1 punta eugenia 2 cabo san lucas and 3 cabo corrientes these three areas are located in places where the coastal morphology changes abruptly and strong surface current intensification occurs at some phase of the seasonal cycle although mesoscale eddies in these areas have been previously reported this study provides their first statistically supported characterization punta eugenia showed the highest eddy production with more cyclones generated followed by cabo corrientes also with more cyclones and cabo san lucas with more anticyclones cabo corrientes eddies showed the highest mean values in propagation speed swirling speed and eddy kinetic energy whereas punta eugenia eddies showed the lowest values cyclonic eddies increased their distance traveled and duration from south to north in contrast anticyclonic eddies increased from north to south in average anticyclones tend to travel faster than cyclones in all the subregions these long lived eddies were mainly nonlinear and therefore can redistribute coastal waters relatively far into the open ocean the peaks in the seasonal signal of eddy generation can be associated with the peaks in the strength of the offshore currents and or in the coastal upwelling index no clear relationship could be established between el nino events and eddy generation

the role of vertical eddy flux in southern ocean heat uptake 1 the role of changing vertical eddy heat flux on southern ocean heat uptake is investigated in an idealized eddy permitting ocean model enhanced air sea heat flux drives deep reaching southern warming due to a reduction in the isopycnal meridional temperature gradient and therefore decreased upward eddy heat flux this mechanism is qualitatively similar in models with either permitted or parameterized eddies due to its dependence on the isopycnal temperature gradient rather than the dynamical response of the eddy field in contrast increased wind stress drives mid depth southern ocean cooling through an enhancement of the eddy field and resultant eddy heat divergence the transient cooling extends over multiple decades while the mean flow adjusts to balance the faster eddy response this wind driven cooling mechanism has not been captured by coarse resolution models with fixed eddy parameterizations and is a possible candidate for the recent cooling observed in the southern ocean

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

southern ocean eddy phenomenology mesoscale eddies are ubiquitous features in the southern ocean yet their phenomenology is not well quantified to tackle this task we use satellite observations of sea level anomalies and sea surface temperature sst as well as in situ temperature and salinity measurements from profiling floats over the period 1997 2010 we identified over a million mesoscale eddy instances and were able to track about 105 of them over 1 month or more the antarctic circumpolar current acc the boundary current systems and the regions where they interact are hot spots of eddy presence representing also the birth places and graveyards of most eddies these hot spots contrast strongly to areas shallower than about 2000 m where mesoscale eddies are essentially absent likely due to topographical steering anticyclones tend to dominate the southern subtropical gyres and cyclones the northern flank of the acc major causes of regional polarity dominance are larger formation numbers and lifespans with a contribution of differential propagation pathways of long lived eddies areas of dominance of one polarity are generally congruent with the same polarity being longer lived bigger of larger amplitude and more intense eddies extend down to at least 2000 m in the acc eddies show near surface temperature and salinity maxima whereas eddies in the subtropical areas generally have deeper anomaly maxima presumably inherited from their origin in the boundary currents the temperature and salinity signatures of the average eddy suggest that their tracer anomalies are a result of both trapping in the eddy core and stirring

the influence of nonlinear mesoscale eddies on near surface oceanic chlorophyll oceanic rossby waves have been widely invoked as a mechanism for large scale variability of chlorophyll chl observed from satellites high resolution satellite altimeter measurements have recently revealed that sea surface height ssh features previously interpreted as linear rossby waves are nonlinear mesoscale coherent structures referred to here as eddies we analyze 10 years of measurements of these ssh fields and concurrent satellite measurements of upper ocean chl to show that these eddies exert a strong influence on the chl field thus requiring reassessment of the mechanism for the observed covariability of ssh and chl on time scales longer than 2 to 3 weeks the dominant mechanism is shown to be eddy induced horizontal advection of chl by the rotational velocities of the eddies

tracer transport in cold core rings pinched off from the kuroshio extension in an eddy resolving ocean general circulation model 1 using an eddy resolving ocean general circulation model we examine the cold core rings pinched off from the kuroshio extension ke focusing on their tracer transport the origin of the tracers in the rings and how they are trapped are directly investigated by releasing two passive tracers corresponding to the ke water and the water in the mixed water region mwr to the north of the ke the cold core rings carry the tracer in the mwr wrapped by the ke water from the surface to the bottom at the pinch off in and above the upper thermocline 26 4 these tracers are trapped in the ring and move along the ring until the rings rejoin the kuroshio even in the lower thermocline 26 4 27 2 a substantial part of the tracers moves along the ring while gradual leakage occurs vorticity balance in the rings is consistent with the passive tracer experiment indicating that water in the upper thermocline moves along the rings while the synchronous movement in and below the lower thermocline is severely contaminated by baroclinic rossby waves these direct estimations are compared with the indirect diagnoses using pv the ratio of drift velocity of ring to its tangential velocity nonlinear parameter and the largest closed contour of stream function in the comoving frame of the ring these indirect diagnoses are consistent with the direct estimation in the upper thermocline but are not good indicators below the lower thermocline the cause of their insufficient performance is discussed

circumpolar structure and distribution of the antarctic circumpolar current fronts 2 variability and relationship to sea surface height 1 in part 1 of this study we showed that the antarctic circumpolar current acc consisted of multiple fronts each of which was consistently associated with a particular contour of sea surface height ssh or approximate streamline in part 2 we have used maps of ssh to examine the variability of the acc fronts between 1992 and 2007 the ssh label associated with each frontal branch is nearly constant around the circumpolar belt the front labels are also nearly constant in time the bands of enhanced ssh gradient i e fronts occur along the same streamlines throughout the 15 year period of observations both short and long period changes of the ssh frontal labels of the acc are small based on a tight relationship between dynamic height and cumulative baroclinic transport of the acc the baroclinic transport variability of the individual branches of the acc is also expected to be small the major change in the total acc baroclinic transport occurs in the drake passage the streamline associated with the northern branch of the saf saf n does not pass through drake passage and the waters carried by this branch are not observed there instead the transport of the saf n turns north in the pacific to supply the export of water to the indian ocean north and south of australia strong eddy activity in the southeast pacific acts to dissipate the hydrographic signature of the saf n there in the atlantic the saf n reappears as the same streamline is again associated with enhanced ssh gradients to the east of the brazil malvinas confluence zone while the large changes in ssh have occurred in the southern ocean between 1992 and 2007 there are strong regional differences because the acc fronts are robustly associated with particular ssh contours the changes in ssh reflect shifts in the position of the acc fronts in the circumpolar average each of the acc fronts has shifted to the south by about 60 km the changes in ssh in the southern ocean are largely due to changes in ocean circulation rather than warming and freshening by atmospheric fluxes much larger changes in ssh are observed in some locations of the southern ocean particularly where the fronts interact with large scale topography the northern branch of the pf pf n near the kerguelen plateau is an extreme example where the pf n followed a path around the northern end of kerguelen plateau between 1992 and 1997 passed through the fawn trough after 2003 and oscillated between the two paths between 1997 and 2003

bio optical footprints created by mesoscale eddies in the sargasso sea 1 we investigate the bio optical footprints made by mesoscale eddies in the sargasso sea and the processes that create them through an eddy centric approach many 10 000 eddies are identified and followed in time using satellite altimetry observations and the spatial ocean color patterns surrounding each eddy are assessed we find through a sequence of statistical hypothesis tests that not one but several mechanisms i e eddy pumping eddy advection and eddy ekman pumping are responsible for the spatial temporal ocean color patterns following individual eddies both eddy pumping and the eddy ekman pumping mechanisms alter subsurface nutrient distributions thereby driving biogeochemical cycles while the eddy advection mechanism to first order stirs existing horizontal gradients in bio optical properties this work illustrates both the promise and some of the limitations of satellite observations for assessing the biogeochemical impacts of mesoscale eddies

an avenue of eddies quantifying the biophysical properties of mesoscale eddies in the tasman sea 1 the tasman sea is unique characterised by a strong seasonal western boundary current that breaks down into a complicated field of mesoscale eddies almost immediately after separating from the coast through a 16 year analysis of tasman sea eddies we identify a region along the southeast australian coast which we name eddy avenue where eddies have higher sea level anomalies faster rotation and greater sea surface temperature and chlorophyll a anomalies the density of cyclonic and anticyclonic eddies within eddy avenue is 23 and 16 higher respectively than the broader tasman sea we find that eddy avenue cyclonic and anticyclonic eddies have more strongly differentiated biological properties than those of the broader tasmansea as a result of larger anticyclonic eddies formed from coral sea water depressing chl a concentrations and for coastal cyclonic eddies due to the entrainment of nutrient rich shelf waters cyclonic eddies within eddy avenue have almost double the chlorophyll a 0 35 mg m 3 of anticyclonic eddies 0 18 mg m 3 the average chlorophyll a concentration for cyclonic eddies is 16 higher in eddy avenue and 28 lower for anticyclonic eddies when compared to the tasman sea with a strengthening east australian current the propagation of these eddies will have significant implications for heat transport and the entrainment and connectivity of plankton and larval fish populations citation everett j d m e baird p r oke and i m suthers 2012 an avenue of eddies quantifying the biophysical properties of mesoscale eddies in the tasman sea geophys res lett 39 l16608 doi 10 1029 2012gl053091

detailed characterization of a cold antarctic eddy 1 eddy formation in the southern ocean plays a critical role in meridional exchanges of heat and salt it has also been shown to have a significant impact on primary productivity and on the creation of preferred feeding regions for birds and other predators this eddy formation is not geographically uniform but is concentrated in certain specific regions particularly where the antarctic circumpolar current crosses shallow bathymetry one such region is at the south west indian ridge where eddies are formed that subsequently drift past the prince edward islands we have studied such an eddy in detail it was at least 1000 m deep had a radius of 60 90 km a heat content of 5 40 1019 j and rotated at a rate of 1 revolution every 5 days altimetric observations show that it was formed at 51 s 32 e and that its intensity as expressed as its sea level anomaly declined by 40 of the original value within 144 days this relatively rapid dissipation suggests that these eddies do not have a lifetime of more than 14 months during that period they will have carried their anomalous heat and salt content about 1 5 degrees of latitude

oceanic isopycnal mixing by coordinate rotation abstract current numerical models of oceanic circulation differentiate between the eddy diffusion and viscosity transport along the geopotential horizontal and vertical directions only in order to model the effect of anisotropic turbulence as diffusive transport along and across density surfaces the isopycnal mixing tensor has been transformed from a diagonal second rank tensor in the isopycnal coordinate system to a tensor containing off diagonal elements in the geopotential coordinate system

eddy heat fluxes from direct current measurements of the antarctic polar front in shag rocks passage 1 determining meridional heat flux in the southern ocean is critical to the accurate understanding and model simulation of the global ocean mesoscale eddies provide a significant but poorly defined contribution to this transport an eighteen month deep water current meter array deployment in shag rocks passage 53 s 48 w between may 2003 and november 2004 provides estimates of the eddy flux of heat across the polar front we calculate a statistically nonzero 99 level vertically coherent local poleward heat flux of 12 0 5 8 kw m 2 within the eddy frequency band at 2750 m depth exceeding previous deep water estimates by up to an order of magnitude this highlights the large spatial variation in flux estimates and illustrates that constriction of circumpolar fronts facilitates large eddy transfers of heat southwards

thermal recalcitrance of the organic d rich component of ordinary chondrites carbonaceous and ordinary chondrites ccs and ocs contain insoluble organic matter iom with large d excess compared to other objects in the solar system the higher the temperature experienced by ccs the lower the d h ratio of their iom it seems to be the opposite for ocs here we report nanosims h and n isotopic imaging of iom of three ocs that experienced thermal metamorphism in the sequence semarkona bishunpur and gro 95502 in addition we performed flash heating experiments on the iom of gro 95502 at 600 c and characterized the residues using nanosims raman and xanes spectroscopy the present study shows that in contrast to iom of ci cm and cr iom of ocs exhibits very few d rich or 15n rich hotspots furthermore although the evolution of the molecular structure of oc and cc iom is similar upon heating their d h ratios do not follow the same trend the d h of oc iom drastically increases while the d h of cc iom decreases in contrast to cc iom the d rich component of which does not survive at high temperatures the present results highlight the thermal recalcitrance of the d rich component of oc iom this suggests that ccs and ocs did not accrete the same organic material thereby challenging the hypothesis of a common precursor on chondritic parent bodies the present results support the hypothesis that oc iom contains an organic component that could originate from the interstellar medium

eddy activity in the four major upwelling systems from satellite altimetry 1992 2007 eddy activity in the four major eastern boundary upwelling systems ebus is investigated using 15 years of satellite altimetry data based on the analysis of more than 4000 long lived eddy trajectories in every ebus we show that mesoscale structures are mainly generated along the continental coasts and south of the main archipelagos and propagate westward with velocities increasing toward the equator these mesoscale eddies having radii of 70 160 km are then frequently observed along the coastal transition zones and frontal regions and some large oceanic areas are preferentially populated by cyclonic or anticyclonic eddies temporal variations of the number of newly formed eddies and the associated eddy activity index defined as the mean eddy energy density are finally examined at seasonal and interannual scales the strongest seasonal interannual respectively variations are observed in the california benguela upwelling systems the proposed indices also exhibit contrasted long term trends in each ebus which suggests that eddy activity might be sensitive to a warming climate

simulated changes in the extratropical southern hemisphere winds and currents 1 the results from 12 global climate models show a remarkably consistent strengthening and poleward shifting of the zonal wind stress through the 20th and 21st centuries at extratropical southern hemisphere latitudes changes in the zonal circulation of the ocean in the region are broadly consistent with the changes in zonal wind stress in particular the climate models simulate a strengthening and a poleward shift of the antarctic circumpolar current the strengthening of the zonal wind stress also results in intensifying northward ekman transport across the antarctic circumpolar current which in the unblocked latitudes of drake passage implies increasing southward geostrophic transport in the ocean below about 2000 m zonal wind stress changes such as these may be expected to enhance the mesoscale eddy activity in the southern ocean

energetics of a global ocean circulation model compared to observations 1 the majority of the eddy kinetic energy eke in the ocean is found on scales of 50 km to 500 km encompassed by mesoscale eddies and the meanders and rings of the boundary currents mesoscale eddies play a critical role in the dynamics of the ocean circulation with instabilities of the strong mean currents generating eddies in the upper ocean interactions between eddies transfer energy from the upper ocean to the deep ocean where eddies interact with bottom topography to generate abyssal mean flows and eddies transfer momentum back to the mean currents the kinetic energy in a global hybrid coordinate ocean circulation model hycom is compared with long term observations from surface drifters geostrophic currents from satellite altimetry subsurface floats and deep current meter moorings hycom configured at 1 12 5 9 km typical of the present generation of high resolution models is deficient in eke in both the upper and abyssal ocean depths greater than 3000 m by 21 and 24 respectively compared to surface drifting buoys and deep current meters increasing the model resolution to 1 25 4 4 km or injecting mesoscale eddies through the assimilation of surface observations in a 1 12 5 model increases the surface and the abyssal eke to levels consistent with the observations in these models the surface abyssal eke is increased by 23 51 and 15 46 for the higher resolution or data assimilative models respectively compared to the 1 12 5 non assimilative model while data assimilation increases the eke in both the upper and abyssal ocean the kinetic energy of the mean flow in the upper ocean is decreased in the data assimilative hindcast

evidence of a southward eddy corridor in the south west indian ocean mesoscale eddies and meanders have been shown to be one of the dominant sources of flow variability in the world s ocean one example of an isolated eddy hotspot is the south west indian ridge swir several investigations have shown that the swir and the corresponding planetary potential vorticity field f h exert a strong influence on the location and dynamics of the antarctic circumpolar current acc resulting in substantial fragmentation of the jets downstream of the ridge the easterly extension of this eddy corridor appears to be restricted to the deep channel separating the conrad rise from the del cano and crozet plateau however while the fate of eddies formed at the swir has been widely investigated and the frontal character of this eastward extension is well known the zone of diminishing variability that extends southwards to approximately 60 s remains poorly sampled using a combination of argo aviso and ncep ncar datasets the character of this eddy corridor as a conduit for warm core eddies to move across the acc into the antarctic zone is investigated in this study we track a single warm core eddy as it moves southwards from an original position of 31 e 50 20 s to where it dissipates 10 months later in the enderby basin at 56 20 s an argo float entrained within the eddy confirms that its water masses are consistent with water found within the antarctic polar frontal zone north of the apf latent and sensible heat fluxes are on average 8w m2 and 10w m2 greater over the eddy than directly east of this feature it is estimated that the eddy lost an average of 5w m2 of latent heat and 5w m2 of sensible heat over a 1 year period an amount capable of melting approximately 0 92m of sea ice in addition using an eddy tracking algorithm a total of 28 eddies are identified propagating southwards 25 of which are anti cyclonic in rotation based on the new argo float data combined with aviso and ncep ncar datasets these results suggest that the southward passage of warm core eddies act as vehicles transporting heat salt and biota southwards across the acc and into the eastern boundary of the weddell gyre

mesoscale variability in the northeastern tropical pacific forcing mechanisms and eddy properties 1 the generation mechanisms and properties of the mesoscale eddies in the northeastern tropical pacific netp are studied using a series of numerical solutions and satellite observations the spatial and temporal resolution of mountain wind jets over the gulfs of tehuantepec and papagayo are essential for an accurate modeling of the regional mesoscale variability three previously proposed eddy generation mechanisms are the local transient wind forcing the combined low frequency wind and boundary forcing and the remote equatorial kelvin wave forcing in our model the transient wind forcing was represented by wind fields with synoptic variability and the remote equatorial kelvin wave forcing by 5 day open boundary conditions with interannual variability solutions with and without high frequency forcings are contrasted to evaluate the contributions of the three mechanisms the combined low frequency wind and boundary forcing is the primary eddy forcing mechanism in the netp in the tehuantepec region the high frequency wind forcing contributes more to the mesoscale variability than the remote equatorial kelvin wave forcing while in the papagayo region their contributions are comparable eddies in the tehuantepec and papagayo regions are larger in both amplitude and size and are more likely to deflect equatorward than eddies in the rest of the netp the maximum temperature anomaly of eddies is at around 50 m depth eddies with lifetimes 6 weeks are more likely anticyclonic while eddies with lifetimes 6 weeks are more likely cyclonic the anticyclone dominance for large amplitude long lived eddies is the combined consequence of wind driven asymmetric dipole spin up and the evolutionary fragility of large amplitude cyclones

characteristics of mesoscale eddies in the kuroshio oyashio extension region detected from the distribution of the sea surface height anomaly abstract this study investigates the distribution of the sea surface height anomaly ssha with the aim of quantifying the characteristics of mesoscale eddies in the kuroshio oyashio extension region koer where intense mesoscale eddies are commonly observed during hydrographic surveys dense distributions of both anticyclonic eddies aes and cyclonic eddies ces are detected for the first time in koer with sufficient temporal and spatial coverage using the okubo weiss parameter without smoothing their contribution to the total ssha variance is estimated to be about 50 the zones of highest amplitudes are located north and south of the axis of the kuroshio extension ke for aes and ces which represent warm core and cold core rings respectively the areas extend poleward along the japan and kuril kamchatka trenches especially for aes eddies of both polarities and with moderate amplitudes are also recognized along the subarctic front saf eddies in areas north and south of the ke generally pro

long range transport of a quasi isolated chlorophyll patch by an agulhas ring 1 using satellite retrievals of sea surface chlorophyll and geostrophic currents we study the evolution of a distinct chlorophyll patch transported by an agulhas ring along a 1 500 km track throughout an 11 months period of the total 2 years eddy lifetime the shape of the chlorophyll patch is consistently delimited by the horizontal transport barriers associated with the eddy analysis of lagrangian time series of sea surface variables in and around the eddy suggests that the evolution of the chlorophyll patch is driven by two processes i slow lateral mixing with ambient waters mediated by horizontal stirring in filaments and ii rapid events of wind induced vertical mixing these results support the idea that mesoscale eddies shape biological production through the combination of horizontal and vertical dynamical processes and emphasize the important role of horizontal eddy transport in sustaining biological production over the otherwise nutrient depleted subtropical gyres

a frontal challenge for climate models the ocean surface is filled with a convoluted web of fronts that separate waters of different temperatures and salinities see the figure just as thin ducts in the lung called alveoli facilitate the rapid exchange of gases when breathing fronts are the ducts through which heat carbon oxygen and other climatically important gases enter into the deep ocean a lack of observations however has hampered progress in understanding the dynamics of fronts which can be as narrow as hundreds of meters and as wide as tens of kilometers global satellite measurements of ocean surface velocities and air sea fluxes for instance are only available at resolutions of a few hundred kilometers although shipboard researchers can sample vertical ocean profiles down to centimeter scales only rarely do they collect profiles that are less than 100 km apart on page 318 of this issue d asaro et al 1 present a breakthrough in observing ocean fronts providing direct observations of the workings of the kuroshio front off japan on scales from kilometers to millimeters this detailed and wide ranging portrait was made possible by the development of towed instruments that continuously sample the waters behind a steaming ship the deployment of freely drifting instruments that follow ocean currents and the exercising of a great deal of ingenuity in keeping all these tools along the front for a few weeks in 2007

observational evidence for a southern hemisphere oceanic supergyre 1 a high resolution hydrographic atlas resolves the narrow boundary flow of the western pacific gyre and its pathway around tasmania southern australia and into the indian ocean basin this confirms recent model descriptions of a southern hemisphere supergyre a nested system of subtropical gyres the observations show that the gyre flow is squeezed into a narrow band between tasmania and the antarctic circumpolar current the residue of east australian current transport turns westward around tasmania and leaks into the indian ocean while there is also a limited form of gyre connection between the indian and atlantic systems south of africa with a mean outflow of agulhas current water into the atlantic basin these gyre circulations remain far more discrete the gyre coupling and the east australian current in particular provide the mechanism by which sub antarctic mode water and antarctic intermediate water are distributed between the ocean basins

the evolution and propagation of quasigeostrophic ocean eddies abstractthe long term evolution of initially gaussian eddies is studied in a reduced gravity shallow water model using both linear and nonlinear quasigeostrophic theory in an attempt to understand westward propagating mesoscale eddies observed and tracked by satellite altimetry by examining both isolated eddies and a large basin seeded with eddies with statistical characteristics consistent with those of observed eddies it is shown that long term eddy coherence and the zonal wavenumber frequency power spectral density are best matched by the nonlinear model individual characteristics of the eddies including amplitude decay horizontal length scale decay and zonal and meridional propagation speed of a previously unrecognized quasi stable state are examined the results show that the meridional deflections from purely westward flow poleward for cyclones and equatorward for anticyclones are consistent with satellite observations examination of the fluid transport properties of the eddies shows that an

response of the antarctic circumpolar current to atmospheric variability abstract historical hydrographic profiles combined with recent argo profiles are used to obtain an estimate of the mean geostrophic circulation in the southern ocean thirteen years of altimetric sea level anomaly data are then added to reconstruct the time variable sea level and this new dataset is analyzed to identify and monitor the position of the two main fronts of the antarctic circumpolar current acc during the period 1993 2005 the authors relate their movements to the two main atmospheric climate modes of the southern hemisphere the southern annular mode sam and the el nino southern oscillation enso the study finds that although the fronts are steered by the bathymetry which sets their mean pathway on first order in flat bottom areas the fronts are subject to large meandering because of mesoscale activity and atmospheric forcing while the dominant mode of atmospheric variability in the southern hemisphere sam is relatively symmetric the oceanic response of the fronts is not show

pattern and velocity of propagation of the global ocean eddy variability 1 satellite altimeter data are used to study the characteristics of the horizontal propagation of eddy variability of the global oceans decade long time series of sea surface height is analyzed for finding the maximum cross correlation with neighboring time series within a window of space and time lags the space and time lags corresponding to the maximum correlation allow an estimate of the propagation velocity of the eddy variability that dominates the variance of sea surface height anomalies the method cannot distinguish the various forms of eddy variability isolated eddies and fronts the meandering of ocean currents or planetary waves however the results provide at a given location of the global oceans a uniquely determined propagation velocity that represents a time averaged description of the tendency of the movement of the local eddy variability the propagation velocity is highly inhomogeneous in space outside the equatorial zone the zonal propagation is intrinsically westward modified by ocean currents which could reverse the zonal propagation to eastward in regions like the gulf stream and the antarctic circumpolar current at midlatitudes and high latitudes the propagation pattern is highly affected by the path of ocean currents and the shape of bottom topography at tropical latitudes the meridional propagation is convergent toward the equator in the western basins and divergent away from the equator in the eastern basins comparison with the simulations of an eddy permitting ocean general circulation model shows overall agreement especially in the latitudinal variation of the zonal propagation velocity the result suggests that the model has captured the essence of the dynamics governing the propagation of ocean eddy variability

spatial and temporal variability of global ocean mixing inferred from argo profiles 1 the influence of turbulent ocean mixing transcends its inherently small scales to affect large scale ocean processes including water mass transformation stratification maintenance and the overturning circulation however the distribution of ocean mixing is not well described by sparse ship based observations since this mixing is both spatially patchy and temporally intermittent we use strain information from argo float profiles in the upper 2 000 m of the ocean to generate over 400 000 estimates of the energy dissipation rate indicative of ocean mixing these estimates rely on numerous assumptions and do not take the place of direct measurement methods temporally averaged estimates reveal clear spatial patterns in the parameterized dissipation rate and diffusivity distribution across all the oceans they corroborate previous observations linking elevated dissipation rates to regions of rough topography we also observe heightened estimated dissipation rates in areas of high eddy kinetic energy as well as heightened diffusivity in high latitudes where stratification is weak the seasonal dependence of mixing is observed in the northwest pacific suggesting a wind forced response in the upper ocean

a three dimensional eddy census of a high resolution global ocean simulation 1 a three dimensional eddy census data set was obtained from a global ocean simulation with one tenth degree resolution and a duration of 7 years the census includes 6 7 million eddies in daily data which comprise 152 000 eddies tracked over their lifetimes using a minimum lifetime cutoff of 28 days variables of interest include eddy diameter thickness vertical extent minimum and maximum depth location rotational direction lifetime and translational speed distributions of these traits show a predominance of small thin short lived and slow eddies still a significant number of eddies possess traits at the opposite extreme thousands of eddies larger than 200 km in diameter appeared in daily data each year a tracking algorithm found hundreds of eddies with lifetimes longer than 200 days a third of the eddies are at least 1000 m tall and many penetrate the full depth of the water column the antarctic circumpolar current contains the thickest and highest density of eddies thick eddies are also common in the gulf stream kuroshio current and agulhas ring pathway the great majority of eddies extend all the way to the surface confirming that eddy censuses from surface observations are a good proxy for the full depth ocean correlations between variables show that larger diameter eddies tend to be thicker and longer lived than small eddies

atmospheric response to mesoscale sea surface temperature anomalies assessment of mechanisms and coupling strength in a high resolution coupled model over the south atlantic many aspects of the coupling between the ocean and atmosphere at the mesoscale on the order of 20 100 km remain unknown while recent observations from the southern ocean revealed that circular fronts associated with oceanic mesoscale eddies leave a distinct imprint on the overlying wind cloud coverage and rain the mechanisms responsible for explaining these atmospheric changes are not well established here the atmospheric response above mesoscale ocean eddies is investigated utilizing a newly developed coupled atmosphere ocean regional model consortium for small scale modeling regional ocean modelling system cosmo roms configured at a horizontal resolution of 10 km for the south atlantic and run for a 3 month period during austral winter of 2004 the model simulated changes in surface wind cloud fraction and rain above the oceanic eddies are very consistent with the relationships inferred from satellite observations for the same region and time from diagnosing the model s momentum balance it is shown that the atmospheric imprint of the oceanic eddies are driven by the modification of vertical mixing in the atmospheric boundary layer rather than secondary flows driven by horizontal pressure gradients this is largely due to the very limited ability of the atmosphere to adjust its temperature over the time scale it takes for an air parcel to pass over these mesoscale oceanic features this results in locally enhanced vertical gradients between the ocean surface and the overlying air and thus a rapid change in turbulent mixing in the atmospheric boundary layer and an associated change in the vertical momentum flux

variability of the near surface eddy kinetic energy in the california current based on altimetric drifter and moored current data low pass filtered velocities obtained from world ocean circulation experiment woce surface drifters deployed in the california current off northern california during 1993 1995 have been compared with surface geostrophic velocity estimates made along subtracks of the topex poseidon altimeter and with moored acoustic doppler current profiler adcp data to obtain absolute geostrophic velocities a mean sea surface height ssh field was estimated using the mean drifter velocities and historical hydrographic data and was added to the altimetric ssh anomalies the correlation between collocated drifter and altimetric velocities is 0 73 significant at the 95 level the component of the drifter velocity which was uncorrelated with the altimetric velocity was correlated with the wind in the ekman transport sense monthly averages of eddy kinetic energy eke estimated using all drifter and altimeter data within the domain 124 132 w 33 40 5 n show energy levels for the drifters that are about 13 greater than those for the altimeter drifter altimeter and adcp measurements all exhibit similar seasonal cycles in eke with the altimeter data reaching maximum values of about 0 03 m 2 s 2 in late summer fall wavenumber spectra of the altimeter velocity indicate that the velocity fluctuations were dominated by features with wavelengths of 240 370 km while the adcp data suggest that the temporal scales of these fluctuations are at least several months between 36 and 40 5 n the region of monthly maximum eke migrates westward to about 128 w on a seasonal timescale this region of maximum eke coincides with the maximum zonal ssh gradient with increased eke associated with increased southward flow a simple model shows that much of the seasonal cycle of the ssh anomalies can be produced by linear processes forced by the curl of the wind stress although the model cannot explain the offshore movement of the front

rapid southern ocean front transitions in an eddy resolving ocean gcm the formation of persistent multiple fronts is an established feature of the antarctic circumpolar current acc front strength and location are closely linked to eddy properties and therefore have important implications for the eddy driven closure of the southern ocean meridional overturning circulation acc front structure is analyzed here by calculating regional probability density functions pdfs of potential vorticity diagnosed in an eddy resolving ocean general circulation model rapid spatial transitions in the number of fronts and in the density classes over which they occur are found front transitions are associated with the major topographic obstacles kerguelen island campbell plateau and drake passage multiple fronts are preferentially found downstream of these features these findings highlight the significant departure from zonal symmetry of the acc front structure and emphasize the importance of local dynamics on large scale southern ocean properties

average circulation seasonal cycle and mesoscale dynamics of the peru current system a modeling approach h isolines the pccc appears to be directly forced by the cyclonic wind stress curl the model is able to produce the upwelling front the cold water tongue which extends toward the equator and the equatorial front as described in the literature model seasonal changes in sst and ssh are compared to measurements for the central pcs model eke is 10 to 30 lower than the observations the model eddy diameters follow a strong equatorward increase the injection length scales derived from the energy spectra strongly correlate to the rossby radius of deformation confirming the predominant role of baroclinic instability at 3 s the model solution appears to switch from a turbulent oceanic regime to an equatorial regime dominated by zonal currents

divergent pathways of cyclonic and anti cyclonic ocean eddies satellite altimetry is used to study the propagation pathways of warm and cold ocean eddies in different ocean basins we consider eddies that have a life span longer than 3 months and we present three regional studies in the southeast indian the southeast atlantic and the northeast pacific oceans the case studies show that simple theories for vortex propagation on a plane work in regions where energetic eddies propagate though a weak background flow under these conditions anticyclonic cyclonic eddies propagate westward and equatorward poleward this divergence in the eddy pathways implies a net equatorward eddy heat flux and has implications for the meridional transport of freshwater carbon nutrients etc