antarctic bottom and lower circumpolar deep water circulation in the eastern indian ocean 1 net northward transport below n 28 1 kg m 3 3200 m into the perth basin of between 4 4 and 5 8 sv is estimated from a year long current meter mooring array between the broken and naturaliste plateaus northward transport of between 2 0 and 2 5 sv of antarctic bottom water n 28 2 kg m 3 that must upwell within the southern region of the perth basin results in an area averaged diapycnal velocity and diffusivity of w 2 5 3 1 10 6 m s 1 and 13 15 10 4 m2 s 1 respectively diffusivity estimates for the perth basin are several times larger than area averaged mixing estimates for the abyssal subtropical south atlantic and pacific oceans however the dissipation of turbulent kinetic energy required to maintain the abyssal mixing in the perth basin e o 10 9 w kg 1 is similar to that required in the south atlantic ocean the area averaged diffusivity in the perth basin does not require unreasonable energy dissipation rates as this ocean basin is only weakly stratified the abyssal diffusivity of the perth basin results from intense mixing at the basin boundary and in the basin interior over rough topography the complex bathymetry and low abyssal stratification suggests that the indian ocean for a given energy dissipation may support a larger meridional overturning circulation than other subtropical basins

variability in the location of the antarctic polar front 90 20 w from satellite sea surface temperature data the path of the antarctic polar front pf is mapped using satellite sea surface temperature data from the noaa nasa pathfinder program the mean path and variability of the pf are strongly influenced by bathymetry meandering intensity is weaker where the bathymetry is steeply sloped and increases in areas where the bottom is relatively flat there is an inverse relationship between meandering intensity and both the width of the front and the change in temperature across it there is a persistent large separation between the surface and subsurface expressions of the pf at ewing bank on the falkland plateau

temporal variability of diapycnal mixing in shag rocks passage diapycnal mixing rates in the oceans have been shown to have a great deal of spatial variability but the temporal variability has been little studied here results are presented from a method developed to calculate diapycnal diffusivity from moored acoustic doppler current profiler adcp velocity shear profiles an 18 month time series of diffusivity is presented from data taken by a longranger adcp moored at 2400 m depth 600 m above the seafloor in shag rocks passage a deep passage in the north scotia ridge southern ocean the polar front is constrained to pass through this passage and the strong currents and complex topography are expected to result in enhanced mixing the spatial distribution of diffusivity in shag rocks passage deduced from lowered adcp shear is consistent with published values for similar regions with diffusivity possibly as large as 90 3 10 24 m 2 s 21 near the seafloor decreasing to the expected background level of 0 1 3 10 24 m 2 s 21 in areas away from topography the moored adcp profiles spanned a depth range of 2400 1800 m thus the moored time series was obtained from a region of moderately enhanced diffusivity the diffusivity time series has a median of 3 3 3 10 24 m 2 s 21 and a range from 0 5 3 10 24 to 57 3 10 24 m 2 s 21 there is no significant signal at annual or semiannual periods but there is evidence of signals at periods of approximately 14 days likely due to the spring neap tidal cycle and at periods of 3 8 and 2 6 days most likely due to topographically trappedwaves propagating around the local seamount using the observed stratification and an axisymmetric seamount of similar dimensions to the one west of the mooring in a model of baroclinic topographically trapped waves produces periods of 3 8 and 2 6 days in agreement with the signals observed the diffusivity is anticorrelated with the rotary coefficient indicating that stronger mixing occurs during times of upward energy propagation which suggests that mixing occurs due to the breaking of internal waves generated at topography

a geomorphological investigation of the formation and evolution of the kaiafas sand dune field kyparissiakos gulf ionian sea eastern mediterranean in the late holocene the present investigation concerns the formation and evolution of the dune field of the central part of the kyparissiakos gulf western coast of peloponnesos greece this dune field is associated with the kaiafas lagoon and consists of four dune lines that lie at distances of 600 200 100 and 70 m from the coastline the dune field has developed on top of a barrier beach that formed subsequently to the completion of the last phase of rapid sea level rise i e after 6 000 bp consisting mostly of medium sand with good sorting due to its aeolian formation assuming a steady wind regime and adequate sediment availability during the late holocene a period of approximately 1 350 years has been estimated to be the minimum time required for the formation of the dune field this formation period may also include intervals when the development processes were more or less intensive on the basis of radio carbon dating secondary fluctuations of air temperature and published information it is proposed that the 4th oldest dune line started forming between the years 400 ad and 1 000 ad whilst the 1st youngest dune line started forming after 1 520 ad the dune field especially its youngest line seems to be in equilibrium with its adjacent beach zone and the nearshore hydrodynamics being beyond the reach of wave run up on the other hand the dune field over the past decades has been subjected to intense human intervention agriculture construction forest fires etc that has locally destroyed and or destabilised part of the dunes finally the expected sea level rise due to global warming is undoubtedly a threat to the existence of the dune field

redistribution of energy available for ocean mixing by long range propagation of internal waves ocean mixing which affects pollutant dispersal marine productivity and global climate1 largely results from the breaking of internal gravity waves disturbances propagating along the ocean s internal stratification a global map of internal wave dissipation would be useful in improving climate models but would require knowledge of the sources of internal gravity waves and their propagation towards this goal i present here computations of horizontal internal wave propagation from 60 historical moorings and relate them to the source terms of internal waves as computed previously2 3 analysis of the two most energetic frequency ranges near inertial frequencies and semidiurnal tidal frequencies reveals that the fluxes in both frequency bands are of the order of 1 kw m 1 that is 15 50 of the energy input and are directed away from their respective source regions however the energy flux due to near inertial waves is stronger in winter whereas the tidal fluxes are uniform throughout the year both varieties of internal waves can thus significantly affect the space time distribution of energy available for global mixing

tidal oscillations in the aegean and ionian seas abstract harmonic constants are estimated by analysing tidal observations from 20 ports in the aegean and the ionian seas areas where no similar data were available so far the analysis is based on tidal records 7 years long the resulting values for the m 2 constituent are compared with the results of a hydrodynamic numerical model of the m 2 tide for the mediterranean sea the qualitative agreement between the observations and the model indicates that in spite of the complex topography of the aegean sea the major features of the tidal propagation could be retrieved through the model if better tuned

internal swell generation the spatial distribution of energy flux from the wind to mixed layer near inertial motions the energy flux from the wind to inertial mixed layer motions is computed for all oceans from 50 8 st o 508n for the years 1996 99 the wind stress t is computed from 6 h 2 58 resolution ncep ncar global reanalysis surface winds the inertial mixed layer response ui and the energy flux p5 t ui are computed using a slab model the validity of the reanalysis winds and the slab model is demonstrated by direct comparison with wind and adcp velocity records from ndbc buoys at latitudes 508 the inertial response is too fast to be resolved by the reanalysis wind 6 h output interval midlatitude storms produce the greatest fluxes resulting in broad maxima near 40 8 latitude during each hemisphere s winter concentrated in the western portion of each basin northern hemisphere fluxes exceed those in the southern hemisphere by about 50 the global mean energy flux from 1996 to 1999 and 508 st o 508n is 0 98 6 0 08 3 1023 wm 22 for a total power of 0 29 tw 1 tw 5 1012 w this total is the same order of magnitude as recent estimates of the global power input to baroclinic m2 tidal motions suggesting that windgenerated near inertial waves may play an important role in the global energy balance

kinematic constraints on glacier contributions to 21st century sea level rise on the basis of climate modeling and analogies with past conditions the potential for multimeter increases in sea level by the end of the 21st century has been proposed we consider glaciological conditions required for large sea level rise to occur by 2100 and conclude that increases in excess of 2 meters are physically untenable we find that a total sea level rise of about 2 meters by 2100 could occur under physically possible glaciological conditions but only if all variables are quickly accelerated to extremely high limits more plausible but still accelerated conditions lead to total sea level rise by 2100 of about 0 8 meter these roughly constrained scenarios provide a most likely starting point for refinements in sea level forecasts that include ice flow dynamics

evidence in hydrography and density fine structure for enhanced vertical mixing over the mid atlantic ridge in the western atlantic received 24 august 2001 revised 22 february 2002 accepted 25 march 2002 published 15 october 2002 1 anomalous conditions exist in the salinity oxygen and nutrient fields over the western flank of the northern hemisphere mid atlantic ridge we examine possible advective sources for this anomaly but determine that vertical mixing is the most likely cause we proceed to use knowledge gained from the brazil basin tracer release experiment in the south atlantic where microstructure and fine structure were obtained to explore the intensity spatial distribution and mechanisms of mixing in the deep ocean to interpret density fine structure from common conductivity temperature depth data in the north atlantic these data support the hypothesis that the anomalous hydrographic conditions are associated with enhanced levels of vertical mixing the inferred levels of vertical diffusivity over the northern hemisphere mid atlantic ridge are as high as in the south atlantic 1 10 10 4 m 2 s index terms 4532 oceanography physical general circulation 4536 oceanography physical hydrography 4568 oceanography physical turbulence diffusion and mixing processes keywords diapycnal mixing fine structure recirculation mid atlantic ridge mar hydrography silicate

parameterizing tidal dissipation over rough topography the traditional model of tidal dissipation is based on a frictional bottom boundary layer in which the work done by bottom drag is proportional to a drag coefficient and the velocity cubed however away from shallow coastal regions the tidal velocities are small and the work done by the bottom boundary layer can account for only weak levels of dissipation in the deep ocean the energy flux carried by internal waves generated over rough topography dominates the energy transfer away from barotropic flow a parameterization for the internal wave drag over rough topography is included as a dissipative mechanism in a model for the barotropic tides model results suggest that the inclusion of this dissipation mechanism improves hydro dynamical models of the ocean tide it also substantially increases the amount of modeled tidal dissipation in the deep ocean bringing dissipation levels there into agreement with recent estimates from topex poseidon altimetry data

spatial analysis of gypsiferous soils in the zaragoza province spain using gis as an aid to conservation within the ebro valley the zaragoza province contains the largest area of gypsiferous soils in spain previous mapping of the gypsum outcrops has been the starting point for this study of the soils developed on them in this paper gypsiferous soils are differentiated according to geological age lithological facies and other depositional features the most abundant gypsiferous soils correspond to tertiary outcrops where a typical catena includes leptosols on the crest of the hillslopes regosols on the talus and gypsisols on the valley bottom gypsiferous soils developed on the triassic keuper facies and quaternary materials occupy a relatively small area the gypsiferous soils have been mapped at a scale of 1 200 000 a cad software package has been used for digitizing the soil units a digital elevation model of the zaragoza province has been created from the digitized topography the geographical information system idrisi has been used to integrate all the spatial information generated and to produce maps of the soil types classified according to slope and precipitation in the zaragoza province the gypsiferous soils lithic and eutric leptosols petric calcic and haplic gypsisols gypsic regosols gypsic solonchaks occupy a total area of 229 619 ha 13 of the area of the province 25 of the gypsiferous soils occur within the semiarid area annual rainfall 400 mm indicating that climate is the main limiting factor for soil conservation because of the fragility of gypsiferous soils special care must be taken with land use operations on the 18 137 ha with slopes above 10 the knowledge of the distribution of gypsiferous soils in relation to topographic and climatic factors provides an important basis for soil conservation and management

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

comparison of shear measurements and mixing predictions with a direct observation of diapycnal mixing in the atlantic thermocline four sets of velocity and density profiles have been measured with an autonomous profiler during an upper ocean intentional tracer sf6 diapycnal diffusivity measurement the north atlantic tracer release experiment natre the tracer was injected near 310 m depth in the canary basin two profile sets were collected 6 months after tracer release and two were collected i year after release all within the horizontal boundaries of the sf6 patch shear and strain can be combined with turbulent kinetic energy dissipation and diffusivity measurements published elsewhere to test existing expressions for dissipation and diffusivity due to shear induced turbulence these expressions arise from internal wave decay modeling one expression of dissipation parameterized in terms of shear based on stochastic nonlinear internal wave interaction has fared well empirically its extension to estimate diffusivity is evaluated shear variance of the first two data sets was about 1 6 times gm76 and 2 5 to 3 0 times gm76 in the later sets the average parameterized mixing estimate computed using all of the temporally limited shear measurements overestimates annual mean natre diffusivity 1 5 x 10 m 2 s by a factor of 1 2 a modified parameterization gives an underestimate to first order this supports the present understanding of open ocean diffusivity in terms of fine scale shear and internal wave decay that is the slow diapycnal mixing was not a consequence of unusually low shear adjustment of the shear induced mixing models to better fit the data is not warranted because of the lack of direct comparability between the various measurements the expected natural variability of the shear and sampling errors

abyssal mixing where it is not abstract a parameterization based on internal wave wave interaction theory which infers turbulence production from finescale internal wave shear is applied to 114 full water depth velocity profiles in the sargasso sea an average eddy diffusivity of 0 1 10 4 m2 s 1 independent of depth is inferred this value is consistent with full water depth microstructure measurements from abyssal basins in the eastern north atlantic and eastern north pacific it is an order of magnitude smaller than the values inferred from a simple vertical advection diffusion balance or bulk budgets thus the mixing needed to close deep global water mass budgets does not appear to occur over midlatitude abyssal plains this suggests that ocean mixing is either i confined to boundary layers as in ideal thermocline theory or ii localized to hotspots such as over rough topography or restrictive passages abyssal diffusivities do not display any dependence on bottom slope for slopes less than 7 10 2 based on 5 10 km bathy

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

estimates of the vertical wavenumber frequency spectra of vertical shear and strain abstract measurements of vertical shear and strain were acquired from the research platform flip during the patchex experiment in october 1986 34 n 127 w vertical sheer was shear from two separate doppler sonar systems a long range sonar with independent estimates every 18 m sampled from 150 1200 m in depth a short range sonar measured fine scale shear over 150 180 m depth with 1 5 m vertical resolution vertical strain z was estimated from two repeatedly profiling ctds these sampled to 560 m once every three minutes the time variation of the strain field is monitored in both eulerian fixed depth and semi lagrangian isopycnal following reference frames from 150 406 m depth eulerian vertical wavenumber frequency m spectra of vertical shear and strain exhibit a frequency dependency which is a strong function of wavenumber 2 0 for m 0 01 0 3 cpm in contrast the semi lagrangian strain spectrum is more nearly separable in frequency and wavenumber in closer agreement with t

antarctic circumpolar current transport and barotropic transition at macquarie ridge theory and numerical simulations suggest that topographic interactions are central to the dynamics of the antarctic circumpolar current acc but few observations are available to test these ideas we use direct velocity measurements satellite altimetry and an ocean state estimate to investigate the interaction of the acc with the macquarie ridge satellite altimeter data show that the subantarctic front crosses the ridge through a gap immediately north of macquarie island yearlong current meter records reveal strong deep mean flow 0 2 m s 1 at 3000 m and substantial transport 52 8 106 m3 s 1 in the 50 km wide gap the acc becomes much more barotropic at the ridge acceleration of the deep jet is balanced by the ageostrophic along gap pressure gradient convergence of zonal momentum by the mean vertical velocity and dissipation the study helps explain how the acc negotiates large topographic obstacles and highlights the role of local nonlinear processes in the dynamical balance of the acc

an intermediate complexity model for simulating marine biogeochemistry in deep time validation against the modern global ocean we present a new high resolution 1 d intermediate complexity box model icbm of ocean biogeochemical processes for paleoceanographic applications the model contains 79 reservoirs in three regions that should be generally applicable throughout much of earth history 1 a stratified gyre region 2 a high latitude convective region and 3 an upwelling region analogous to those found associated with eastern boundary currents transport processes are modeled as exchange fluxes between boxes and by eddy diffusion terms significant improvement in the representation of middepth oxygen budgets was achieved by implementing nonlocal mixing between the high latitude surface and gyre thermocline reservoirs the biogeochemical submodel simulates coupled c n p o and s systematics with explicit representation of microbial populations using a process based approach primary production follows redfield stoichiometry while water column remineralization is depth and redox couple dependent settling particulate organic matter is incorporated into a benthic submodel that accounts for burial and remineralization the c p ratio of burial depends on bottom water oxygen denitrification takes place both by classical and anammox pathways the icbm was tested against modern oceanographic observations from the global ocean data analysis project joint global ocean flux study and other databases comparisons of model output with circulation tracers including salinity cfc 12 and radiocarbon permit a test of the physical exchange scheme vertical profiles of biogeochemically reactive components in each of the three regions are in good agreement with observations under modern conditions the upwelling zone displays a pronounced oxygen minimum zone and water column denitrification while these are not present in the high latitude or gyre regions model generated global fluxes also compare well to independent estimates of primary production burial and phosphorous and nitrogen cycling the icbm appears to adequately simulate the long term kyr evolution of several biogeochemical cycles and improves on previous box models in several important ways in a companion paper the model s performance under euxinic conditions is tested against modern black sea data the simple and adaptable structure of the model should make it applicable to a wide range of paleoceanographic problems the model source code is available in matlabtm 7 m files provided as auxiliary material

influence of the enhanced mixing within the southern ocean fronts on the overturning circulation 1 observations indicate that turbulent mixing is enhanced in the major fronts of the antarctic circumpolar current acc penetrating through much of the water column here we employ a simple representation of this process in a global climate model to evaluate its potential impact on the ocean s overturning circulation two effects are obtained first the frontally intensified mixing in the southern ocean increases the transformation of nadw to ucdw second by intensifying the dense water upwelling in the south the vertical mixing in the acc fronts returns a fraction of the northward flowing aabw lcdw as ucdw consistent with recent observational results the corresponding abyssal overturning weakens the results are interpreted using a single basin model

assessment of finescale parameterizations of deep ocean mixing in the presence of geostrophic current shear results of microstructure measurements in the antarctic circumpolar current region

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

formation of parabolic dunes from barchan and transverse dunes along israel s mediterranean coast the mediterranean coastal dunes of israel underwent a land use change during the second half of the 20th century due to intense agricultural and pastoral activity the coastal dunes were stripped of natural vegetation until the end of the first half of the 20th century the barchan and transverse dunes were shaped by strong southwesterly winter winds a decrease in human activity during the second half of the 20th century brought about a renewal of natural vegetation on the dune crest the only area with neither erosion nor deposition the establishment of vegetation on the crest changes the dynamics of these barchan and transverse dunes so that not all of the sand eroded from the windward side is carried to the lee slip face some is trapped by plants consequently there is a change in the shape of the windward slope from convex to concave and the dune gradually becomes parabolic in this study we trace the morphodynamics of the dunes by analysing 12 sets of aerial photographs which were taken from 1944 to 1995 the average rate of advance of 15 dunes has decreased from 3 4 m a 1 to 1 9 m a 1 while the vegetation cover has increased from 4 3 to 17 per cent during this period copyright 2002 john wiley sons ltd

weak mixing in the eastern north atlantic an application of the tracer contour inverse method abstract the tracer contour inverse method is used to infer mixing and circulation in the eastern north atlantic solutions for the vertical mixing coefficient d the along isopycnal mixing coefficient k and a geostrophic streamfunction are all direct outputs of the method the method predicts a vertical mixing coefficient o 10 5 m2 s 1 in the upper 1000 m of the water column consistent with in situ observations the method predicts a depth dependent along isopycnal mixing coefficient that decreases from o 1000 m2 s 1 close to the mixed layer to o 100 m2 s 1 in the interior which is also consistent with observations and previous hypotheses the robustness of the result is tested with a rigorous sensitivity analysis including the use of two independently constructed datasets this study confirms the utility of the tracer contour inverse method the results presented support the hypothesis that vertical mixing is small in the thermocline of the subtropical atlantic ocean a strong depth dependence o

improved global maps and 54 year history of wind work on ocean inertial motions 1 the global distribution and 54 year time dependence of the energy flux from the wind to near inertial motions is computed by driving a slab mixed layer model with ncep ncar reanalysis winds improving upon previous estimates alford 2001 watanabe and hibiya 2002 the slab model is solved spectrally with frequency dependent damping the resulting solutions are more physically sensible than the previous and more skillful at high latitudes where the inertial frequency approaches the 4 daily sampling of the reanalysis winds this enables alford s calculation whose domain was limited to 50 to be extended to the poles the high latitude reliability is demonstrated by direct comparison with a high resolution regional model remo in the ne atlantic the total power input 0 47 tw has increased by 25 since 1948 paralleling observed increases in extratropical cyclone frequency and intensity if believable the trend may have important consequences for modulation of the meridional overturning circulation

spatial variability of turbulent mixing in the abyssal ocean ocean microstructure data show that turbulent mixing in the deep brazil basin of the south atlantic ocean is weak at all depths above smooth abyssal plains and the south american continental rise the diapycnal diffusivity there was estimated to be less than or approximately equal to 0 1 x 10 4 meters squared per second in contrast mixing rates are large throughout the water column above the rough mid atlantic ridge and the diffusivity deduced for the bottom most 150 meters exceeds 5 x 10 4 meters squared per second such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry

on a simple empirical parameterization of topography catalyzed diapycnal mixing in the abyssal ocean abstract the global spatial distribution of the turbulent diapycnal diffusivity in the abyssal ocean is reexamined in light of the growing body of microstructure data revealing bottom intensified turbulent mixing in regions of rough topography a direct and nontrivial implication of the observed intensification is that the diapycnal diffusivity k is depth dependent and patchily distributed horizontally across the world s oceans theoretical and observational studies show that bottom intensified mixing is dependent upon a variety of energy sources and processes whose contributions to mixing are sufficiently complex that their physical parameterization is premature only rudimentary parameterizations of tidally induced mixing have been attempted although the tides likely provide no more than half of the mechanical energy available for diapycnal mixing in the abyssal ocean here an empirical and still rudimentary parameterization of the spatially variable mean diffusivity k based on a large collection

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

reduced mixing from the breaking of internal waves in equatorial waters in the oceans heat salt and nutrients are redistributed much more easily within water masses of uniform density than across surfaces separating waters of different densities but the magnitude and distribution of mixing across density surfaces are also important for the earth s climate as well as the concentrations of organisms most of this mixing occurs where internal waves break overturning the density stratification of the ocean and creating patches of turbulence predictions of the rate at which internal waves dissipate were confirmed earlier at mid latitudes here we present observations of temperature and velocity fluctuations in the pacific and atlantic oceans between 42 degrees n and 2 degrees s to extend that result to equatorial regions we find a strong latitude dependence of dissipation in accordance with the predictions in our observations dissipation rates and accompanying mixing across density surfaces near the equator are less than 10 of those at mid latitudes for a similar background of internal waves reduced mixing close to the equator will have to be taken into account in numerical simulations of ocean dynamics for example in climate change experiments

wind forced internal waves in the north pacific and sargasso sea abstract the three dimensional structure of the near inertial frequency internal wave field was measured at two open ocean sites using expendable velocity profilers both wave fields appear to be dominantly wind forced although their vertical structure and horizontal scales are quite different the hydro 79 data were taken in the sargasso sea in september 1979 the internal wave field is predominantly downward propagating and vertically uniform when wkb scaled in the upper 800 m of the ocean the energy density is roughly equal to munk s 1981 universal value the stkex data were taken during a period of strong storms in the northeastern pacific ocean in november 1980 in the upper few hundred meters the wave field is five times larger horizontally and five times more energetic when wkb scaled than the hydro 79 wave field measurements made after the passage of a strong cold front show an even more energetic and larger scale wave field extending to 500 m comparison with the simulations of price 198

diapycnal mixing in the southern ocean diagnosed using the dimes tracer and realistic velocity fields in this work we use realistic isopycnal velocities with a 3 d eddy diffusivity to advect and diffuse a tracer in the antarctic circumpolar current beginning in the southeast pacific and progressing through drake passage we prescribe a diapycnal diffusivity which takes one value in the se pacific west of 67 w and another value in drake passage east of that longitude and optimize the diffusivities using a cost function to give a best fit to experimental data from the dimes diapycnal and isopycnal mixing experiment in the southern ocean tracer released near the boundary between the upper and lower circumpolar deep water we find that diapycnal diffusivity is enhanced 20 fold in drake passage compared with the se pacific consistent with previous estimates obtained using a simpler advection diffusion model with constant but different zonal velocities east and west of 67 w our result shows that diapycnal mixing in the acc plays a significant role in transferring buoyancy within the meridional overturning circulation

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

holocene coastal dune development and environmental changes in apulia southern italy abstract the coastal area of southern apulia is characterised by marine deposits of pleistocene and holocene ages it shows the effects of different phases of coastal morphology evolution during the middle and upper pleistocene a number of marine terraces were shaped in some places they are characterised by thin beach deposits along with a dune belt and relative back dune deposits two important morphogenetic phases occurred during the holocene the former was characterised by deposition of beach deposits placed slightly above present mean sea level and by formation of dune belts which were radiometrically aged about 6000 years bp this event marks the end of the rapid postglacial transgression that occurred during the holocene climatic optimum during the younger phase dated at about 2500 years bp deposition of aeolian sands occurred archaeological and morphological evidences suggest that this phase should be related to a low sea level stand followed by a slow sea level rise up to the present position and by humid temperate climatic conditions the collected data about the holocene dune belts occurring along the apulian coastline suggest that main phases of dune development could be related to the effects of sea level changes climatic conditions and in a subordinate way to human activity

the role of internal tides in mixing the deep ocean abstract internal wave theory is used to examine the generation radiation and energy dissipation of internal tides in the deep ocean estimates of vertical energy flux based on a previously developed model are adjusted to account for the influence of finite depth varying stratification and two dimensional topography specific estimates of energy flux are made for midocean ridge topography weakly nonlinear theory is applied to the wave generation at idealized topography to examine finite amplitude corrections to the linear theory most internal tide energy is generated at low modes associated with spatial scales from roughly 20 to 100 km the richardson number of the radiated internal tide typically exceeds unity for these motions and so direct shear instability of the generated waves is not the dominant energy transfer mechanism it also seems that wave wave interactions are ineffective at transferring energy from the large wavelengths that dominate the energy flux instead it appears that most of

mixing on the continental slope of the southern weddell sea shipboard hydrography and current profiles collected in 2003 and time series from moored current meters deployed in late 1990s are analyzed to study the variability of mixing in the southeastern weddell sea profiles of eddy diffusivity k are inferred from finescale shear vertical derivative of horizontal velocity and strain vertical derivative of isopycnal displacement variance using parameterizations which relate the internal wave energy to the dissipation rate at small scales the highest mixing rates are seen near the bottom where the eddy diffusivities are elevated by one order of magnitude from those in the interior and exceed 10 4 m 2 s 1 the observations show latitudinal variability in k particularly near the bottom where k significantly increases near 74 28 s the critical latitude for lunar semi diurnal m2 tides in this region the critical latitude coincides with near critical topography on the upper continental slope a situation which favors generation of m2 internal waves consistent with the results from finescale shear and strain parameterizations which indicate highest bottom diffusivities near the critical latitude independent analysis of current time series from moored instruments shows a thickening of the frictional bottom boundary layer near the critical latitude semidiurnal tidal dynamics at the upper continental slope together with the critical latitude effects lead to mixing that might significantly affect the regional heat budget and the circulation in the study area

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

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

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

water mass conversion fluxes and mixing in the scotia sea diagnosed by an inverse model abstract an inverse box model of the scotia sea is constructed using hydrographic tracer and velocity data collected along the rim of the basin during the antarctic large scale box analysis and the role of the scotia sea albatross cruise the model provides an estimate of the time mean three dimensional circulation as the antarctic circumpolar current acc crosses the region it concurrently solves for geostrophic and wind driven ekman transports across the boundaries of the basin air sea driven diapycnal fluxes and interior diapycnal fluxes below the ocean surface an increase is diagnosed in the acc volume transport from 143 13 sv sv 106 m3 s 1 at drake passage to 149 16 sv on leaving the scotia sea supplied by the import of 5 9 1 7 sv of weddell sea deep water wsdw over the south scotia ridge there is a lateral redistribution of the transport primarily in response to a topographically induced branching of the 70 80 sv polar front pf jet and an increase in the transport associa

global rate and spectral characteristics of internal gravity wave generation by geostrophic flow over topography the rate of generation of internal gravity waves in the lee of small length scale topography by geostrophic flow in the world ocean was estimated using linear theory with corrections for finite amplitude topography several global data sets were combined for the calculation including an ocean circulation model for the near bottom geostrophic flow statistics over 500 abyssal current meter records historical climatological data for the buoyancy frequency and two independent estimates of the small scale topographic statistical properties the first topography estimate was based on an empirically derived relationship between paleo spreading rates and abyssal hill roughness with corrections for sedimentation the second estimate was based on small scale 100 km roughness of satellite altimetry derived gravity field using upward continuation relationships to derive estimates of abyssal hill roughness at the seafloor at scales less than approximately 20 km the lee wave generation rate was found to be between 0 34 to 0 49 tw the southern hemisphere produced 92 of the lee wave energy with the southern ocean dominating strength of the bottom flow was the most important factor in producing the global pattern of generation rate except in the indian ocean where extremely rough topography produced strong lee wave generation despite only moderate bottom flows the results imply about one half of the mechanical power input to the ocean general circulation from the extra equatorial wind stress of the world ocean results from abyssal lee wave generation topographic length scales between 176 m and 2 5 km horizontal wavelengths between 1 and 16 km accounted for 90 of the globally integrated generation

energy loss from transient eddies due to lee wave generation in the southern ocean observations suggest that enhanced turbulent dissipation and mixing over rough topography are modulated by the transient eddy field through the generation and breaking of lee waves in the southern ocean idealized simulations also suggest that lee waves are important in the energy pathway from eddies to turbulence however the energy loss from eddies due to lee wave generation remains poorly estimated this study quantifies the relative energy loss from the time mean and transient eddy flow in the southern ocean due to lee wave generation using an eddy resolving global ocean model and three independent topographic datasets the authors find that the energy loss from the transient eddy flow 0 12 tw 1 tw 1012 w is larger than that from the time mean flow 0 04 tw due to lee wave generation lee wave generation makes a larger contribution 0 12 tw to the energy loss from the transient eddy flow than the dissipation in turbulent bottom boundary layer 0 05 tw this study also shows that the energy loss from the time mean flow is regulated by the transient eddy flow and energy loss from the transient eddy flow is sensitive to the representation of anisotropy in small scale topography it is implied that lee waves should be parameterized in eddy resolving global ocean models to improve the energetics of resolved flow

the role of turbulent mixing in the modified shelf water overflows that produce cape darnley bottom water the mixing process associated with modified shelf water msw overflows that eventually mix to form cape darnley bottom water cdbw was investigated by hydrographic and microstructure observations off the cape darnley polynya cdp east antarctica in january 2009 closely spaced microstructure observations revealed that msw properties varied considerably within a distance of 4 km across the shelf edge near the bottom the rate of turbulent kinetic energy dissipation was enhanced to values greater than 10 7 w kg 1 and the vertical scale of the bottom boundary layer bbl was on the order of 10 m the observed bbl around the shelf edge was characterized by strong vertical mixing with turbulent eddy diffusivities of o 10 3 10 2 m2 s 1 a geostrophically balanced density current which resulted from the presence of msw over the continental shelf is considered the primary energy source for the turbulent mixing in the bbl this turbulent mixing transforms the overflowing msw through mixing with ambient water masses specifically with the overlying modified circumpolar deep water the bbl is also thought to partly contribute to the gradual descent of msw down the continental slope through bottom ekman transport we conclude that turbulent mixing primarily caused by a density current plays an important role in cdbw formation by modifying the msw overflowing from the cdp

analysis of horizontal and vertical processes contributing to natural iron supply in the mixed layer in southern drake passage abstract horizontal advection vertical mixing and mixed layer entrainment all affect iron concentrations and biological productivity in the ona basin near the shackleton transverse ridge str in southern drake passage trace metal sampling in the region indicates that dissolved iron concentrations are significantly higher on the continental shelf near the antarctic peninsula and the south shetland islands than they are in the deep waters away from the shelf comparisons between satellite derived sea surface height ssh and chlorophyll a chl a levels in the ona basin show 95 correlation between chl a concentrations and horizontal advection of these iron rich shelf waters during the months of november and december for the years 1997 2010 however no significant correlations are found for january april while high chl a concentrations in the ona basin persist through march enhanced vertical diapycnal mixing and mixed layer entrainment are considered as alternative mechanisms for delivering iron into the ona basin mixed layer and sustaining the high chl a concentrations estimates of iron flux based on in situ measurements of dissolved iron concentrations suggest that diapycnal mixing alone can supply iron to the base of the mixed layer at a rate of 64 2 nmol m 2 day 1 during the summer in addition the summer mixed layer in the ona basin deepens from january to april allowing for iron rich water to be steadily entrained from below estimates based on monthly mixed layer climatologies produce average daily entrainment rates ranging from 5 to 25 nmol m 2 day 1 while neither diapycnal mixing nor entrainment alone is always sufficient to meet the estimated iron demand for the ona basin bloom numerical simulation suggests that the combined effect of the two processes can consistently supply sufficient iron to sustain the bloom

shear and strain in santa monica basin by injecting a cloud of sf6 into santa monica basin at a depth of 790 m and observing its vertical spread ledwell and watson 1991 estimate the average diapycnal diffusivity between 750 and 850 m as kp 2 5 10 5 m2 m 1 this diffusivity is higher than inferred from microstructure measurements in the open ocean thermocline for typical internal wave levels gregg and sanford 1988 to examine shear and strain in the basin we dropped expendable current profilers xcps and calculated strain from conductivity temperature and depth ctd casts shear and strain are above the gm76 model spectrum garrett and munk 1975 cairns and williams 1976 and comparisons with published parameterizations indicate more than enough shear variance to account for the high diffusivity reported by ledwell and watson thus the eddy diffusivity in santa monica basin is not at odds with lower values estimated from microstructure measurements in the open ocean but is due to an elevated internal wave field the spectral shapes however differ from typical open ocean spectra

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

the antarctic circumpolar current between the falkland islands and south georgia abstract hydrographic and lowered acoustic doppler current profiler data along a line from the falkland islands to south georgia via the maurice ewing bank are used to estimate the flow of circumpolar water into the argentine basin and to study the interaction of the antarctic circumpolar current with the falkland plateau the estimated net transport of 129 21 sv sv 106 m3 s 1 across the section is shared between three major current bands one is associated with the subantarctic front saf 52 6 sv and the other two with branches of the polar front pf over the sill of the falkland plateau 44 9 sv and in the northwestern georgia basin 45 9 sv the latter includes a local reinforcement 20 sv by a deep anticyclonic recirculation around the maurice ewing bank while the classical hydrographic signature of the pf stands out in this eastbound branch it is less distinguishable in the northbound branch over the plateau other circulation features are a southward entrainment of diluted nor

sea level rise trends in the attico cycladic region aegean sea during the last 5000 years abstract sea level change during the last 18 000 years is a combination of eustatic isostatic and tectonic contributions in an effort to minimize the tectonic contributions our study of sea level changes in the aegean sea within historical times is focused on the aseismic attico cycladic geotectonic zone on the basis of archaeological information and radiocarbon dating of coastal sedimentological formations a sea level curve for the attico cycladic massif has been constructed for the past 5000 years and compared with existing curves according to this curve the rapid increase of sea level concluded prior to 5 5 ka and was followed by a slow steady rise at a rate of 0 9 mm a up to its present stage the latter is attributed primarily to the process of thermal expansion and secondarily to the residual melting of the glaciers and existing ice caps by extrapolation of the curve the sea level at the end of the 20th century is predicted to be about 9 cm higher than the present level this value is much lower than the prediction of the last ipcc report 49 cm if higher slr rates are realised in the next few decades then the excess 40 cm of the ipcc prediction can be attributed to human induced global climatic change

seasonal and spatial variations of southern ocean diapycnal mixing from argo profiling floats in the large scale ocean circulation and climate 4 6 here we use high resolution hydrographic profiles from argo floats in combination with the iridium communications system to investigate diapycnal mixing in the southern ocean we find that the spatial distribution of turbulent diapycnal mixing in the southern ocean at depths between 300 and 1 800 m is controlled by the topography by means of its interaction with the antarctic circumpolar current the seasonal variation of this mixing can largely be attributed to the seasonal cycle of surface wind stress and is more pronounced in the upper ocean over flat topography we suggest that additional highresolution profiles from argo floats will serve to advance our understanding of mixing processes in the global ocean interior the southern ocean is an important source of bottom water in the world s oceans and is a key upwelling site of deep water pointing to diapycnal mixing that is mixing across surfaces of equal density in the region as an important controlling factor of the global meridional overturning circulation moc refs 7 8 modelling studies have demonstrated that the global strength of the moc depends critically on the details of the representation of mixing processes in the southern ocean interior 9 a few existing observations 1014 in this region have revealed dramatic spatial heterogeneity in diapycnal mixing with values of diffusivity over smooth topography comparable to those in the mid latitude ocean interior of the order of 10 5 m 2 s 1 and enhanced mixing of the order of 10 4 m 2 s 1 or larger extending far from rough topography however discerning the nature of diapycnal mixing over the entire southern ocean is still a formidable challenge because of the very limited sampling of the necessary parameters in the region furthermore in general the temporal variability of diapycnal mixing remains poorly assessed and understood throughout most of the world s oceans but in some cases the causes of such variability might be reasonably straightforward to document asanexample recentanalysisofhistoricalhydrographic data reveals that the subsurface turbulent diapycnal mixing in the northwestern pacific displays a pronounced seasonal variability stirred by surface wind stress 15 the international argo program has created the first global array for observing the subsurface ocean a subset of argo floats deployed are designed to use the iridium communications system henceforth referred to as argo iridium floats and are able to provide high resolution 2m profiles that are able to resolve fine scale tens to hundreds of meters strain these floats

mixing in the romanche fracture zone the romanche fracture zone is a major gap in the mid atlantic ridge at the equator which is deep enough to allow significant eastward flows of antarctic bottom water from the brazil basin to the sierra leone and guinea abyssal plains while flowing through the romanche fracture zone bottom water properties are strongly modified due to intense vertical mixing the diapycnal mixing coefficient in the bottom water of the romanche fracture zone is estimated by using the finestructure of ctd profiles the microstructure of high resolution profiler data and by constructing a heat budget from current meter data the finestructure of density profiles is described using the thorpe scaleslt it is shown from microstructure data taken in the bottom water that the ozmidov scale lo is related to lt by the linear relationship lo 5 0 95lt similar to other studies which allows an estimate of the diapycnal mixing coefficient using the osborn relation the thorpe scale and the diapycnal mixing coefficient estimates show enhanced mixing downstream eastward of the main sill of the romanche fracture zone in this region a mean diapycnal mixing coefficient of about 1000 3 1024 m2 s21 is found for the bottom water estimates of cross isothermal mixing coefficient derived from the heat budgets constructed downstream of the current meter arrays deployed in the romanche fracture zone and the nearby chain fracture zone are in agreement with the finestructure estimates of the diapycnal mixing coefficient within the romanche fracture zone although the two fracture zones occupy only 0 4 of the area covered by the sierra leone and guinea abyssal plains the diffusive heat fluxes across the 1 4 8c isotherm in the romanche and chain fracture zones are half that found over the abyssal plains across the 1 88c isotherm emphasizing the role of these passages for bottom water property modifications

global abyssal mixing inferred from lowered adcp shear and ctd strain profiles abstract internal wave wave interaction theories and observations support a parameterization for the turbulent dissipation rate e and eddy diffusivity k that depends on internal wave shear vz2 and strain z2 variances its latest incarnation is applied to about 3500 lowered adcp ctd profiles from the indian pacific north atlantic and southern oceans inferred diffusivities k are functions of latitude and depth ranging from 0 03 10 4 m2 s 1 within 2 of the equator to 0 4 0 5 10 4 m2 s 1 at 50 70 diffusivities k also increase with depth in tropical and subtropical waters diffusivities below 4500 m depth exhibit a peak of 0 7 10 4 m2 s 1 between 20 and 30 latitudes where semidiurnal parametric subharmonic instability is expected to be active turbulence is highly heterogeneous though the bulk of the vertically integrated dissipation e is contributed from the main pycnocline hotspots in e show some correlation with small scale bottom roughness and near bottom flow at sites where st

the pattern of gypsum transport in the ebro river network summary a study of gypsum transport in the ebro river basin during the hydrological period 1970 1985 was carried out gypsum load increases throughout the network and reaches 2 95 million tons per year 43 of total salinity at tortosa the mouth of the basin as a whole the ebro basin annually supplies 35 tons of gypsum per square kilometer of surface area to the sea non point sources are identified as the major contributors to gypsum supplies the tributaries on the ebro s left bank supply the highest load but those on the right bank exhibit the highest concentrations of gypsum

the three dimensional overturning circulation of the southern ocean during the woce era a box inverse model of the southern ocean during the world ocean circulation experiment is constructed to investigate the three dimensional structure of the regional overturning circulation in that era the model has many features in common with various preceding inverse studies but also contains several novel elements that make it well suited for addressing many of the significant uncertainties that surround the circulation at present the net overturning circulation of the southern ocean is found to consist of two well defined cells of similar strength the upper cell consists of a northward transport of 18 8 5 5 sv of surface mode and intermediate waters lighter than the 27 5 kg m 3 isoneutral and an equivalent southward flow in the approximate 27 5 27 9 kg m 3 neutral density range encompassing the bulk of the upper circumpolar deep water the lower cell involves the northward export of 18 6 0 9 sv of antarctic bottom water and lower circumpolar deep water denser than 28 08 kg m 3 and an opposing transport in the lighter classes of that water mass substantial structural differences between the overturning circulations of the atlantic indian and pacific basins are indicated by the model s solution overall the diagnosed southern ocean circulation shares many qualitative and some quantitative features with previous inverse estimates particularly as regards the large scale depth integrated lateral circulation and associated energy fluxes in the subtropics and in the antarctic circumpolar current and the strength of the upper overturning cell however it also suggests several significant adjustments to current views of the regional circulation most notable amongst these are the subpolar circulation of the southern ocean is more vigorous and zonally interconnected than generally thought the associated lower overturning cell is more intense than indicated by most preceding estimates contrary to common perception sub surface mixing processes play a role of comparable importance to air sea ice exchanges of buoyancy in underpinning the dianeutral closure of the southern ocean overturning even at shallow mode and intermediate water levels and the connection between north atlantic deep water formation and southern ocean upwelling is fundamentally three dimensional such that deep waters from the north atlantic must upwell dianeutrally before being returned to the permanent pycnocline of the northern oceans

spatial and temporal patterns of small scale mixing in drake passage temperature and salinity profiles obtained with expendable ctd probes throughout drake passage between february 2002 and july 2005 are analyzed to estimate turbulent diapycnal eddy diffusivities to a depth of 1000 m diffusivity values are inferred from density temperature inversions and internal wave vertical strain both methods reveal the same pattern of spatial variability across drake passage diffusivity estimates from inversions exceed those from vertical strain by a factor of 3 over most of drake passage the polar front pf separates two dynamically different regions strong thermohaline intrusions characterize profiles obtained north of the pf south of the pf stratification is determined largely by salinity and temperature is typically unstably stratified between 100 and 600 m depth in the upper 400 m turbulent diapycnal diffusivities are o 10 3 m2 s 1 north of the pf but decrease to o 10 4 m2 s 1 or smaller south of the pf below 400 m diffusivities typically exceed 10 4 m 2 s 1 diffusivities decay weakly with depth north of the pf whereas diffusivities increase with depth and peak near the local temperature maximum south of the pf the meridional pattern in near surface mixing corresponds to local maxima and minima of both wind stress and wind stress variance near surface diffusivities are also found to be larger during winter months north of the pf wind driven near inertial waves strong mesoscale eddy activity and double diffusive convection are suggested as possible factors contributing to observed mixing patterns

an investigation of internal mixing in a seasonally stratified shelf sea the shelf sea seasonal thermocline is a critical interface within the marine environment separating the euphotic zone from nutrient rich deep water fluxes across the thermocline therefore represent a key biogeochemical pathway in this paper we quantify the rate of mixing across the seasonal thermocline for a location in the celtic sea and investigate the processes responsible for driving thermocline fluxes profiles of the rate of dissipation of turbulent kinetic energy e show enhanced dissipation within the thermocline region similar to 6 x 10 5 w m 3 the diffusivity implied by these measurements is similar to 0 5 cm 2 s 1 similar to previous shelf sea studies and is sufficient to explain the observed warming of the deep water suggesting that vertical mixing is the dominant control on water column structure two potential sources of mixing energy are identified the internal tide and near inertial waves the mechanism of energy transfer from the candidate mixing mechanisms to turbulence is not clear thermocline dissipation rates were found to have no richardson number dependence but scaled positively with n 2 and s 2 in agreement with a previous turbulence parameterization application of this model to our data does a good job of capturing the mean characteristics of the observed heating flux across the thermocline although none of the short term fluctuations in mixing were reproduced

mixing variability in the southern ocean a key remaining challenge in oceanography is the understanding and parameterization of small scale mixing evidence suggests that topographic features play a significant role in enhancing mixing in the southern ocean this study uses 914 high resolution hydrographic profiles from novel em apex profiling floats to investigate turbulent mixing north of the kerguelen plateau a major topographic feature in the southern ocean a shear strain finescale parameterization is applied to estimate diapycnal diffusivity in the upper 1600m of the ocean the indirectestimates of mixing match direct microstructure profiler observations made simultaneously it is found that mixing intensities have strong spatial and temporal variability ranging from o 10 26 t oo 10 23 m 2 s 21 this study identifies topographic roughness current speed and wind speed as the main factors controlling mixing intensity additionally the authors find strong regional variability in mixing dynamics and enhanced mixing in the antarctic circumpolar current frontal region this enhanced mixing is attributed to dissipating internal waves generated by the interaction of the antarctic circumpolar currentandthetopographyofthekerguelenplateau extendingthemixingobservationsfromthekerguelen region to the entire southern ocean this study infers a large water mass transformation rate of 17 sverdrups sv 1sv 10 6 m 3 s 21 across the boundary of antarctic intermediate water and upper circumpolar deep water in the antarctic circumpolar current this work suggests that the contribution of mixing to the southern ocean overturning circulation budget is particularly significant in fronts

the impact of small scale topography on the dynamical balance of the ocean the impact of small scale topography on the ocean s dynamical balance is investigated by quantifying the rates at which internal wave drag extracts angular momentum and vorticity from the general circulation the calculation exploits the recent advent of two near global descriptions of topographic roughness on horizontal scales on the order of 1 10 km which play a central role in the generation of internal lee waves by geostrophic flows impinging on topography and have been hitherto unresolved by bathymetric datasets and ocean general circulation models alike it is found that while internal wave drag is a minor contributor to the ocean s dynamical balance over much of the globe it is a significant player in the dynamics of extensive areas of the ocean most notably the antarctic circumpolar current and several regions of enhanced small scale topographic variance in the equatorial and southern hemisphere oceans there the contribution of internal wave drag to the ocean s angular momentum and vorticity balances is generally on the order of ten to a few tens of percent of the dominant source and sink terms in each dynamical budget which are respectively associated with wind forcing and form drag by topography with horizontal scales from 500 to 1000 km it is thus suggested that the representation of internal wave drag in general circulation models may lead to significant changes in the deep ocean circulation of those regions a theoretical scaling is derived that captures the basic dependence of internal wave drag on topographic roughness and near bottom flow speed for most oceanographically relevant regimes

hydrogeochemistry of continental brackish waters in the southern coastal plain israel abstract the southern coastal plain in israel incorportates a transitional fringe of the desert in which three different chemical types of groundwater are found 1 near surface waters from springs along the besor river course 2 shallow to moderate depth waters from the slightly westward dipping pleistocene coastal aquifer this aquifer which consists of sandstone layers of the kurkar group is recharged in the coastal plain and 3 deep waters of the westward dipping upper cretaceous judea group carbonates which are recharged in the mountains in the east a thick aquiclude of upper cretaceous tertiary rocks separates the judea group aquifer from the overlying coastal aquifer in the southern coastal plain isotopically light oxygen and depleted deuterium characterize the judea group waters as expected from high altitude recharge the isotopic composition of the coastal plain waters is variable but for the most part enriched in 18o and d within the southern coastal plain aquifer a southern subgroup comprises waters more depleted in heavy isotopes than those of either the northern or eastern subgroups the besor waters are isotopically similar to the judea group waters reflecting their origin in the mountain region and flow through the surficial river gravels and sands it is suggested that leakage of the besor waters into the underlying southern coastal plain aquifer results in mixing of the two water types the most prominent chemical feature characterizing the groundwater of the southern coastal plain is na cl 1 this na cl ratio can be maintained only by a continuous input from a non marine source of na the most plausible source of this na is the dissolution of feldspar derived from the windblown loess deposits which cover the area and or leaching of trona minerals found in the unsaturated zone combined with base exchange processes

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

buoyancy forcing by turbulence above rough topography in the abyssal brazil basin abstract observations of turbulent dissipation above rough bathymetry in the abyssal brazil basin are presented relative to regions with smooth bathymetry dissipation is markedly enhanced above rough topography of the mid atlantic ridge with levels above bathymetric slopes exceeding levels observed over crests and canyon floors furthermore mixing levels in rough areas are modulated by the spring neap tidal cycle internal waves generated by barotropic tidal flow over topography are the likely mechanism for supplying the energy needed to support the observed turbulent dissipation a model of the spatial and temporal patterns in the turbulent dissipation rate is used to constrain the diapycnal advection in an inverse calculation for the circulation in an area of rough bathymetry this inverse model uses both beta spiral and integrated forms of the advective budgets for heat mass and vorticity and contains sufficient information to resolve the full three dimensional flow the inverse model solution re

impact of nonlinear waves on the dissipation of internal tidal energy at a shelf break the vertical and temporal structure of the dissipation of turbulent kinetic energy within the internal tide at a location 5 km shoreward of the shelf break on the malin shelf has been determined using a combination of the free falling light yo yo profiler and acoustic doppler current profilers two distinct internal wave regimes were encountered period i in which large amplitude high frequency nonlinear internal waves niws occurred around neap tides and period ii in which the internal wave spectral continuum was not dominated by any particular frequency band around spring tides empirical orthogonal function analysis shows that for the low frequency waves 76 of the variance was described by mode 1 rising to 95 for the high frequency waves during period i the dissipation and vertical mixing were characterized by the niws and 70 of the dissipation occurred in the bottom boundary layer during period ii the depth integrated dissipation was more evenly distributed throughout the tidal cycle whereas vertical mixing was greatly enhanced during a single hour long episode of elevated thermocline dissipation coincident with weakened stratification during both periods i and ii 30 of the total measured dissipation occurred within the thermocline when averaged over 12 4 hours the remainder occurred within the bottom boundary layer bbl tidal average values for depth integrated dissipation and vertical eddy diffusivity for period i ii were 1 1 10 2 w m 2 4 0 10 2 w m 2 and 5 cm2 s 1 12 cm2 s 1 respectively decay rates and internal damping are discussed and vertical heat fluxes are estimated observed dissipation rates are compared with a simple model for bbl dissipation

observations of shear and vertical stability from a neutrally buoyant float measurements of 1 to 5 m shear and strain from a neutrally buoyant float are used to examine the statistics and causes of shear instability in a 9 day record unstable conditions defined as vz n 2 where vz vz are due to higher than average shear rather than lower than average buoyancy frequency and there are no instances of unstable buoyancy frequency or overturns on the 0 5 m spacing of the thermistors shear is dominated by upward propagating near inertial motions unstable events were more frequent when a near inertial wave packet occupied the water parcel tracked by the float groups of unstable events occur roughly every 5 7 hours at scales 2 5 m and much less often at larger scales events typically last 10 min one buoyancy period or longer these time scales appear to be controlled by vertical advection of 1 m fine structure past the float sensors so do not represent the intrinsic time scales of instability turbulent and mixing quantities are estimated from these fine scale measurements giving a dissipation rate of e 2 3 16 10 10 w kg and an eddy diffusivity of k 3 10 6 m2 s in agreement with direct microstructure estimates therefore the float adequately resolves those quantities needed to estimate turbulent dissipation and could be used to monitor turbulent mixing in the ocean

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

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

on challenges in predicting bottom water transport in the southern ocean abstractchanges in the southern ocean lower limb overturning circulation are analyzed using a set of climate models in agreement with some recently developed theoretical models it is found that the overturning can be strongly affected by winds in particular the simulated strengthening of large scale southward transport in the abyss is explicitly driven by zonal wind stress however there is a considerable range among the climate models in their projected changes of southern ocean wind stress furthermore the strengthening of large scale southward transport tends to be compensated by eddy induced northward flows in the abyss particularly at eddy permitting resolution as a result the net antarctic bottom water aabw export may only be weakly affected however none of the models considered accounts for the possibility that a fraction of the eddy kinetic energy may be converted to diapycnal mixing if this were the case the presented energetic arguments suggest that stronger southern ocean winds w

near boundary mixing above the flanks of a midlatitude seamount fine scale velocity and density profile data with concurrent turbulent velocity and temperature dissipation estimates obtained above the flanks of fieberling guyot a seamount in the eastern north pacific ocean are examined for evidence of near bottom boundary mixing fine scale shear and strain spectral levels were elevated over the flanks of the seamount in a 500 m thick stratified layer above the bottom the velocity shear was horizontally isotropic clockwise and counterclockwise with depth shear spectral levels were comparable and no significant correlation between shear and strain was observed above the steepest bottom slopes near the seamount summit rim excess vertical strain relative to shear was observed as compared to the background internal wave field suggesting the presence of high frequency internal waves these signals may have been the product of wave reflections from the steep flanks of the seamount and or wave generation from tidal currents flowing over the rough bottom associated with the enhanced shears and strains were more frequent occurrences of low 10 m richardson number events increased overturning scales and larger estimated turbulent eddy diffusivity relative to observations 15 km or more from the seamount in particular turbulent diffusivity estimates increased from o 0 1 10 4 m2 s 1 in the ocean interior to 1 5 10 4 m2 s 1 within 500 m vertically 1 3 km horizontally of the seamount flank a simple geometric scaling argument suggests that boundary mixing of this intensity has relevance to the large scale circulation at abyssal depths where a large fraction of the ocean waters is in close proximity to the bottom

radiation and dissipation of internal waves generated by geostrophic motions impinging on small scale topography theory abstract observations and inverse models suggest that small scale turbulent mixing is enhanced in the southern ocean in regions above rough topography the enhancement extends o 1 km above the topography suggesting that mixing is supported by the breaking of gravity waves radiated from the ocean bottom in this study it is shown that the observed mixing rates can be sustained by internal waves generated by geostrophic motions flowing over bottom topography weakly nonlinear theory is used to describe the internal wave generation and the feedback of the waves on the zonally averaged flow vigorous inertial oscillations are driven at the ocean bottom by waves generated at steep topography the wave radiation and dissipation at equilibrium is therefore the result of both geostrophic flow and inertial oscillations differing substantially from the classical lee wave problem the theoretical predictions are tested versus two dimensional high resolution numerical simulations with parameters representative of

spatial variability of mixing in the southern ocean 1 strain variance from standard hydrographic profiles in the southern hemisphere oceans shows that turbulent mixing is vertically and spatially non uniform in the south atlantic indian and south pacific oceans enhanced diffusivities are found over rough topography consistent with internal tide generated mixing the water column diffusivity returns to background levels 500 m to 1000 m off the sea floor in the southern ocean enhanced diffusivities throughout the entire water column below 1500 m are found in the antarctic circumpolar current over complex topography differences in the vertical extent of enhanced diffusivity profiles in the antarctic circumpolar current between the parameterizations based on tidal models and topography and of the present estimate of strain variance imply that elevated vertical diffusivity profiles in the southern ocean are due to the interaction between the mean geostrophic current and bottom topography

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

variability of the turbulent kinetic energy dissipation along the a25 greenland portugal transect repeated from 2002 to 2012 abstractthe variability of the turbulent kinetic energy dissipation due to internal waves is quantified using a finescale parameterization applied to the a25 greenland portugal transect repeated every two years from 2002 to 2012 the internal wave velocity shear and strain are estimated for each cruise at 91 stations from full depth vertical profiles of density and velocity the 2002 12 averaged dissipation rate e2002 2012 in the upper ocean lays in the range 1 10 10 10 w kg 1 at depth e2002 2012 is smaller than 1 10 10 w kg 1 except over rough topography found at the continental slopes the reykjanes ridge and in a region delimited by the azores biscay rise and eriador seamount there the vertical energy flux of internal waves is preferentially oriented toward the surface and e2002 2012 is in the range 1 20 10 10 w kg 1 the interannual variability in the dissipation rates is remarkably small over the whole transect a few strong dissipation rate events exceeding the uncertainty of the fi

idealized solutions for the energy balance of the finescale internal wave field abstract recent fine and microstructure observations indicate enhanced finescale shear and strain in conjunction with bottom intensified turbulent dissipation above rough bathymetry in the brazil basin such observations implicate the bottom boundary as an energy source for the finescale internal wave field simple analytical and numerical solutions to an equation governing the spatial and temporal evolution of the finescale wave field are described here the governing equation implicitly treats the effects of wave breaking on the vertical propagation of internal waves through a flux representation of nonlinear transports associated with internal wave wave interactions these solutions identify the rate of dissipation of turbulent kinetic energy with downscale energy transports at high vertical wavenumber resulting in an estimate of dissipation versus depth the sensitivity of the turbulent dissipation depth profile to various environmental parameters is examined observed dissipation profiles and shear

hydrothermal heat enhances abyssal mixing in the antarctic circumpolar current upwelling in the world s strongest current the antarctic circumpolar current is thought to be driven by wind stress surface buoyancy flux and mixing generated from the interaction between bottom currents and rough topography however the impact of localized injection of heat by hydrothermal vents where the antarctic circumpolar current interacts with mid ocean ridges remains poorly understood here a circumpolar compilation of helium and physical measurements are used to show that while geothermal heat is transferred to the ocean over a broad area by conduction heat transfer by convection dominates near hydrothermal vents buoyant hydrothermal plumes decrease stratification above the vent source and increase stratification to the south altering the local vertical diffusivity and diapycnal upwelling within 500 m of the sea floor by an order of magnitude both the helium tracer and stratification signals induced by hydrothermal input are advected by the flow and influence properties downstream

wind wave cast in the mediterranean sea an advanced third generation wave model has been repeatedly applied to the mediterranean sea we have studied the accuracy of the results and the factors that control it the grid resolution when less than 0 5 is shown to have in general negligible effect in the open sea the related accuracy of description of the coastal border can have a relevant effect on the wave field on the side and on the wake of the coastal details for a distance of a few grid points the difficulty of correctly evaluating the wind in the mediterranean basin is dramatically shown by comparing the results obtained using wind fields with different resolution the crucial role of the orography in shaping the wind fields and the need for higher resolution models is established it is found that owing to the strong dependence of wave height on wind speed for resolution coarser than 70 km the loss of accuracy of the wind fields even if meteorologically acceptable makes them useless for an efficient evaluation of the wave conditions the exception explained by the local absence of relevant mountain ridges is the case of a southerly wind in the eastern mediterranean the accuracy of wave forecasting is obtained by comparing analysis and forecast fields for a very severe storm in connection with the preferential west to east flow of most of the mediterranean storms and with the scarcity of information on the atlantic ocean the equality of the meteorological forecast rapidly deteriorates beyond 1 or 2 days of forecast this leads to an even faster deterioration of the wave forecast whose practical limits in the western mediterranean can at present be established at 1 day

intense mixing of antarctic bottom water in the equatorial atlantic ocean the spreading of antarctic bottom water the densest global scale water mass is highly constrained by ocean floor topography in the atlantic ocean the mid atlantic ridge confines this water mass mainly to the western basins the bottom waters in the eastern basins being renewed by flows through gaps in the ridge1 one such gap is the romanche fracture zone a large offset of the ridge which straddles the equator it has been observed2 that sills within this fracture zone block the passage of waters colder than 0 9 c warmer less dense waters passing over the sills appear to cascade downslope where they are modified by mixing here we present direct measurements which quantify these processes the flow is vertically sheared and exhibits remarkably intense turbulence comparable to that seen at the ocean surface in the presence of winds of l0ms 1 this turbulence mixes the densest waters passing through the fracture zone with the warmer overlying waters so that the coldest waters exiting this region have been warmed by 0 6 c during transit topographic obstructions and turbulent mixing together thus determine the properties of the flows renewing the deepest waters of the atlantic ocean s eastern basins

upper ocean state estimation in the southern ocean gas exchange experiment region using the four dimensional variational technique 1 a prototypical ocean circulation model and associated 4 d variational data assimilation system is configured in support of the southern ocean gas exchange experiment southern ocean gasex the regional circulation model has 4 km horizontal resolution and 5 m vertical resolution in the upper ocean in situ temperature and salinity observations and remotely sensed gridded sea surface temperature and sea surface height observations are combined with the circulation model between 6 march and 4 april 2008 the benefits of customized data assimilation in support of a single oceanographic cruise are illustrated using southern ocean gasex as a case study the assimilated fields fit the observations within their respective uncertainties and fit 4 6 times better than the initial guess solution before assimilation the fit of the assimilated fields is up to 100 times closer to observations than various global state estimate products using a cost function variance metric the space time variability in mixed layer depth is consistent with the southern ocean gasex observations and shows a deepening through march 2008 this variability is correlated with sea level height anomalies sea surface temperature and air temperature during the assimilation window the mixed layer depth estimate between 21 march and 4 april 2008 at the location of the southern ocean gasex deliberate tracer release is 41 54 6 m the average zonal volume flux estimate is 16 1 9 sv 1 sv is 106 m3 s 1 for latitudes 50 7 s 51 8 s longitude 38 5 w the zonal volume flux approximately halves during 6 16 march temporal changes in volume flux are associated with geostrophic circulation but not with the ekman circulation

high mixing rates in the abyssal southern ocean mixing of water masses from the deep ocean to the layers above can be estimated from considerations of continuity in the global ocean overturning circulation but averaged over ocean basins diffusivity has been observed to be too small to account for the global upward flux of water and high mixing intensities have only been found in the restricted areas close to sills and narrow gaps here we present observations from the scotia sea a deep ocean basin between the antarctic peninsula and the tip of south america showing a high intensity of mixing that is unprecedented over such a large area using a budget calculation over the whole basin we find a diffusivity of 39 plus minus 10 x 104 m2 s 1 averaged over an area of 7 x 105 km2 the scotia sea is a basin with a rough topography situated just east of the drake passage where the strong flow of the antarctic circumpolar current is constricted in width the high basin wide mixing intensity in this area of the southern ocean may help resolve the question of where the abyssal water masses are mixed towards the surface

two repeat crossings of drake passage in austral summer 2006 short term variations and evidence for considerable ventilation of intermediate and deep waters abstract a high resolution full depth hydrographic section across drake passage with tracers and horizontal velocity measurements was repeated within three weeks in austral summer 2006 in situ data temperature salinity dissolved oxygen and horizontal current velocities are used to determine the location of the fronts and eddies of the antarctic circumpolar current acc inferred by barre et al 2011 from 7 day composite dynamic topography maps along the transect frontal displacements are about 40 km 2 stations along the section considerable differences in properties between the two sections are observed throughout the whole water column with values as high as 0 2 c in temperature 0 01 in salinity 0 03 kg m 3 in neutral density and 10 mol kg 1 in dissolved oxygen concentration found below a depth of 3000 m only part of the differences is attributable to frontal or eddy displacements along the section the other part results from the spatial heterogeneity of water properties upstream the section and the funnelling of the flow due to the topographic constraints of the shackleton fracture zone sfz the considerable short term differences in water properties in rather large scale structures that cannot be accounted for by frontal motions along the section call for caution when interpreting differences in hydrographical properties obtained by oceanographic cruises that are years apart in terms of climatic signals the two sections show efficient ventilation of antarctic intermediate water aaiw by winter water ww in the yaghan basin with an estimated eddy enhanced subduction rate of over 170 m year 1 the sfz constitutes a barrier causing the two southern acc fronts saccf branches to separate by about 400 km and creating sheltered conditions in partial isolation from the acc while promoting an active recirculation region in the ona basin this active recirculation marked by cyclonic eddies carrying cold fresh and oxygenated water from south of the southern boundary of the acc causes effective ventilation of the whole circumpolar deep water cdw density range the differences in small scale structures between the two sections deserve further analyses

abyssal mixing in the brazil basin one of the major objectives of the deep basin experiment a component of the world ocean circulation experiment was to quantify the intensity and spatial distribution of deep vertical mixing within the brazil basin in this study basin averaged estimates of deep vertical mixing rates are calculated using two independent methodologies and datasets 1 vertical fluxes are derived from large scale temperature and density budgets using direct measurements of deep flow through passages connecting the brazil basin to surrounding basins and a comprehensive hydrographic dataset within the basin interior and 2 vertical mixing rates are estimated from finescale bathymetry and hydrographic data using a functional relationship between turbulent dissipation and bathymetric roughness deduced from localized measurements of ocean microstructure obtained during the deep basin experiment the space time mean estimates of vertical mixing diffusivities across representative surfaces within the antarctic bottom water layer fell in the range 1 5 3 1024 m2 s 21 and were indistinguishable k from each other within the estimation uncertainties the mixing rates inferred from potential temperature budgets update and are consistent with earlier estimates that were based on less data mixing rates inferred from budgets bounded by neutral surfaces are not significantly different from the former this implies that lateral eddy fluxes along isopycnals are not important in the potential temperature budgets at least within the large estimation uncertainties unresolved processes such as cabbeling and low frequency variability which complicate inference of mixing from large scale budgets have been considered the agreement between diffusivity estimates based on a modeled relationship between bathymetric roughness and turbulent dissipation with those inferred from large scale budgets provides independent confirmation that the mixing rates have been accurately quantified