circulation mixing and production of antarctic bottom water abstract the antarctic source of bottom water to the abyssal layer of the world ocean is examined as well as its large scale flow pattern and ultimate entrainment rate into the deep water above we make use of the available high quality station data in the southern ocean to construct bottom maps of neutral density and mean property maps including chlorofluorocarbon cfc for the abyssal layer underneath a selected neutral density surface the maximum density at the sill depth of drake passage is used to distinguish between the voluminous deep water mass that is a continuous component of the antarctic circumpolar current from the relatively denser bottom water originated along the antarctic continental margins based on water density antarctic bottom water aabw is defined here generically to include all volumes of non circumpolar water of antarctic origin over the shelf regime multiple localized sources of specific aabw types contribute to the abyssal layer of the adjacent antarctic basins characteristics of these dense bottom waters reflect closely those observed on the parent shelf water mass spreading paths of newly formed deep and bottom waters over the slope regime and their subsequent oceanic circulation patterns are analyzed on the basis of global property maps for the aabw layer interior mixing and interbasin exchanges of aabw are deduced from mean characteristic curves following the southern streamline of the antarctic circumpolar current outflow and mixing of aabw from the weddell sea to the argentine basin is depicted using density and cfc distributions of two zonal hydrographic lines recirculation and mixing of deep and bottom waters within the weddell gyre are also detailed using a meridional section along the greenwich meridian the strength of all localized sources of aabw combined is estimated by two independent approaches an estimate of the total production rate of aabw is calculated based on the oceanic cfc budget for the aabw layer offshore of the 2500 m isobath the sum of all downslope inputs of well ventilated bottom water types underneath the top isopycnal must account for the measured cfc content in the bottom layer the resulting total aabw production rate is about 8 sv which is a conservative figure that neglects the loss of cfc bearing waters across the top isopycnal in recent years whereas about 9 5 sv is calculated assuming a well mixed bottom layer making use of their transient nature cfc distributions at the top of the aabw layer indicate that more direct and rapid entrainment of cfc rich bottom waters below occurs over localized areas with relatively strong upwelling rates and enhanced vertical mixing a second more ad hoc but independent oceanic mass budget of the bottom layer is also constructed a typical basin wide rate of deep upwelling of 3 10 7 m s 1 requires 10 sv 1 sv 106 m3 s 1 of newly formed aabw to sink down the slope around antarctica we have also formulated a spatial distribution of deep upwelling on the isopycnal at the top of the aabw it is expressed as a combination of wind topographic and turbulent components which in turn are functions of the isopycnal depth bottom depth and bottom layer thickness this non uniform upwelling field yields about 12 sv of aabw exported across the top isopycnal fortuitously the overall average of upward speed at the top isopycnal 3 7 10 7 m s 1 compares well with previous estimates of deep upwelling in the northern basins a series of likely sites for strong vertical entrainment of aabw are clearly identified in the modeled distribution of deep upwelling consonant with the observed cfc distributions on the top isopycnal altogether regions with relatively high upwelling rates 5 10 7 m s 1 occupy only a quarter of the total areal extent of the top isopycnal but they account for as much as 45 of the total vertical transport

isotope data from ice station weddell implications for deep water formation in the weddell sea helium isotope data 3he 4he ratios and 4he concentrations and h218o h216o ratios obtained from stations occupied during the drift of ice station weddell february to june 1992 are used together with hydrographic data to study formation of deep and bottom water in the western weddell sea the data indicate deep and bottom water formation along the entire track of the ice station 71 4 to 65 8 s 53 w ice shelf water isw seems to contribute significantly to the formation of weddell sea deep water wsdw and weddell sea bottom water wsbw in the southern part of the drift track toward the north the fraction of isw contained in wsdw wsbw decreases this trend is overlaid by high isw fractions in the deep and bottom waters found in the vicinity of the larsen ice shelf the fraction of western shelf water wsw in wsbw shows the opposite trend increasing from south to north the combined fraction of isw and wsw in waters with potential temperatures below 0 c is about 20 corresponding to a roughly 200 m thick layer overall wsw seems to contribute approximately 2 to 3 times more water than isw to the water column below the 0 c isotherm using the estimated flow of isw over the sill north of the filchner depression of 1 sv foldvik et al 1985a together with the ratio of wsw plus winter water ww to isw we calculate a value of about 5 sv for the formation rate of wsbw with a potential temperature of 0 7 c about one third of this flux represents near surface waters wsw ww which have recently been equilibrated with the atmosphere whereas pure isw contributes about 10

lagrangian circulation of antarctic intermediate water in the subtropical south atlantic this study combines float data from different projects collected between 1991 and 2003 in the south atlantic to describe the flow of antarctic intermediate water aaiw velocity space time averages are calculated for various grid resolutions and with cells deformed to match the bathymetry f h or f h with h being the water depth and h being the thickness of the aaiw layer when judged by the degree of alignment between respective isolines and the resulting average velocity fields the best grid is based on a nominal cell size of 3o latitude by 4o longitude with cell shapes deformed according to f h using this grid objectively estimated mean currents and their associated errors as well as meridional and zonal volume transports are estimated results show an anticyclonic subtropical gyre centred near 36os and spanning from 23o 1 s to 46 1os the south atlantic current meanders from 33os to 46os and shows a mean speed of 9 6 7 8 cm s 1 8 5 sv 3 5 sv 1 sv 1 106 m3 s 1 the northern branch of the subtropical gyre is located between 22os and 32os and flows westward with a mean speed of 4 7 3 3 cm s 1 9 3 sv 3 4 sv evidence of a cyclonic tropical gyre divided in two sub cells is visible on the stream function

repeated cfc sections at the greenwich meridian in the weddell sea 1 repeated observations of the tracer chlorofluorocarbon 11 cfc 11 for a section along the greenwich meridian from antarctica 70 s to about 50 s are presented for the period 1984 1998 the cfc sections display a highly persistent pattern a middepth cfc minimum in the central weddell sea is bounded laterally by elevated levels of dissolved cfcs at the southern margin of the weddell basin and by a column of elevated cfc concentrations around 55 s near to the northern margin part of the latter column covers waters of the antarctic circumpolar current which indicates that a moderate portion of these waters was ventilated in the weddell sea deep cfc maxima adjoining the southern and northern margins of the weddell basin indicate advective cores of recently ventilated waters the southern core supports previous notions of deep water import into the weddell sea from the east for all deep and bottom waters the portions ventilated on the cfc timescale 50 years are small effective initial cfc saturations for these portions are estimated to be between 60 and 70 using in part new data from off the filchner ronne ice shelf for various cfc features along the section mostly advective cores ventilated fractions and mean ages of these fractions were obtained with error limits the procedure was to fit an age distribution of a prescribed form to cfc 11 time series for these features constructed from the various realizations of the cfc section the ages are between 3 and 19 years and the ventilated fractions range between 6 and 23 indicating a rather limited ventilation of the interior weddell sea subsurface layer waters on the cfc timescale it is shown that the concurrent cfc 12 data provide little additional information the work demonstrates a high information content of repeated tracer observations and encourages similar approaches also in other ocean regions

on the structure and the transport of the eastern weddell gyre abstract the circulation pattern and volume transports in the eastern weddell gyre are estimated on the basis of hydrographic data collected by r v polarstern between 1989 and 1996 in the northeastern edge of the weddell gyre eastward flowing water masses from the antarctic circumpolar current and the weddell sea converge due to the strong effect of topographic constraints on ocean currents in the weakly stratified waters of high latitudes the wedge like structure of the southwest indian ridge can cause the convergence the increased shear leads to instabilities of the current at the eastern end of the ridge which produce an intense mesoscale eddy field between 15 and 30 e in the eddies water from the weddell cold regime and the antarctic circumpolar current waters mix and form the water masses of the weddell warm regime these waters are advected southward and flow towards the westward southern rim current which is driven by the antarctic eastwind band hence there is not a continous flow from the northern to the southern rim but a decay of the mean flow in the northeast and a reformation in the south volume transports across the greenwich meridian estimated on the basis of a combined ctd adcp data set result in an eastward flow of 61 sv in the northern rim current and a westward return flow of 66 sv in the southern part of the gyre the transport is about twice as high as previous estimates between kapp norvegia and the northern tip of the antarctic pensinsula indicating a significant gyre circulation north of 70 s

on the sources of weddell gyre antarctic bottom water in march april 1995 as part of the world ocean circulation experiment section a23 we completed 49 hydrographic stations across the weddell gyre and southern antarctic circumpolar current from the antarctic continental shelf 72 5 s 16 5 w to south georgia 55 s 34 5 w chlorofluorocarbon cfc 11 cfc 12 and cfc 113 data collected at these stations reveal that distinct sources renew the antarctic bottom water defined as waters with potential temperatures less than 0 c of the weddell gyre weddell sea bottom water defined as waters with potential temperatures less than 0 7 c formed in the western weddell sea has cfc concentrations about 5 to 6 times higher in the eastward flowing northern weddell gyre than in the westward flowing southern limb our cfc measurements suggest that distinct sources of weddell sea bottom water exist in the western weddell sea in agreement with previous descriptions based on potential temperature and salinity signals in the northern weddell gyre high cfc concentrations in weddell sea deep water potential temperatures between 0 c and 0 7 c confirm the long recognized sources for this water mass in the western and southwestern weddell sea in the southern weddell gyre at about 20 w and along the antarctic continental slope weddell sea deep water with potential temperatures around 0 45 c shows a deep cfc maximum about 1000 m above the seafloor cfc concentrations in this deep southern core are about 80 of those of new weddell sea deep water in the northern weddell gyre near 30 w the a23 cfc and hydrographic data are not consistent with the hypothesis that weddell sea deep waters are derived from a single source in the western weddell sea instead these tracers suggest that an important portion of the weddell sea deep water in the southern weddell gyre originates outside the western weddell sea probably near the amery basin and environs around 75 e these features of the circulation and renewal of the deep weddell gyre should be carefully considered in simulations dealing with fluxes pathways and formation rates of antarctic bottom water

weddell gyre temperature maximum stratum at depths below 200 m relatively warm salty water spreads poleward from the antarctic circumpolar current acc this deep water mass is cooled through interaction with the atmosphere feeding the formation of dense bottom water which in turn influences much of the world ocean significant poleward spreading is accomplished within the weddell gyre of the atlantic sector of the southern ocean an extensive data set obtained in the 1980s within the weddell gyre provides a detailed view of the subsurface temperature maximum t max stratum defining the top of the deep water mass the seasonal sea ice growth and retreat pattern reflects the t max distribution there is evidence for subdivision of the t max into two cold centers which may reflect secondary circulation features within the gyre the primary inflow of warm deep water is derived from the southern edge of the acc near 20 30 e the inflow spreads to the west along 65 s and is divided into smaller pools of relatively warm water west of maud rise with a cold feature directly over the rise in a manner shown by models of topographically generated eddies variability of the t max stratum in the vicinity of maud rise arising from changes in the vigor of the large scale circulation may influence the regional vertical heat fluxes and be related to interannual variability of the sea ice cover and to the recurring polynya feature typical of the region

flow of bottom water in the northwestern weddell sea the weddell sea is known to feed recently formed deep and bottom water into the antarctic circumpolar water belt from whence it spreads into the basins of the world ocean the rates are still a matter of debate to quantify the flow of bottom water in the northwestern weddell sea data obtained during five cruises with r v polarstern between october 1989 and may 1998 were used during the cruises in the weddell sea five hydrographic surveys were carried out to measure water mass properties and moored instruments were deployed over a time period of 8 5 years to obtain quasi continuous time series the average flow in the bottom water plume in the northwestern weddell sea deduced from the combined conductivity temperature depth and moored observations is 1 3 0 4 sv intensive fluctuations of a wide range of timescales including annual and interannual variations are superimposed the variations are partly induced by fluctuations in the formation rates and partly by current velocity fluctuations related to the large scale circulation taking into account entrainment of modified warm deep water and weddell sea deep water during the descent of the plume along the slope between 0 5 sv and 1 3 sv of surface ventilated water is supplied to the deep sea this is significantly less than the widely accepted ventilation rates of the deep sea if there are no other significant sources of newly ventilated water in the weddell sea either the dominant role of weddell sea bottom water in the southern ocean or the global ventilation rates have to be reconsidered

flow variability at the tip of the antarctic peninsula recently ventilated water leaves the landlocked northwestern weddell sea near the antarctic peninsula and possibly spreads out into the basins of the world oceans at shallow to intermediate depths to determine the pathways of the water through the complex topography and the flow variability water mass circulation and properties are described in the northwestern weddell sea and along the boundary of the powell basin by means of data from current meter moorings and hydrographic sections the mean flow is strongly controlled by the topography meso scale seasonal and interannual fluctuations are superimposed the mean northward volume transport of shelf water which represents the potential source water for intermediate layer ventilation is estimated for the time interval between may 1996 and march 1998 to be 2 4 1 0 sv water mass properties suggest that much of this water leaves the weddell sea to bransfield strait and therefore does not reach the weddell scotia confluence the water masses are able to serve as the only source of bransfield strait deep water since the shelf water properties in the northwestern weddell sea vary over time within a range that corresponds to the required source waters the scotia sea is supplied by water from the powell basin which has varied significantly over the past two decades

relict sea floor ploughmarks record deep keeled antarctic icebergs to 45 s on the argentine margin abstract this paper reports ploughmarks on the argentine continental margin up to 44 50 s the most northerly morphological evidence of giant icebergs in the southern atlantic more than 2500 ploughmarks up to 32 km long 685 m wide and more than 20 m deep have been observed at modern water depths up to 646 m taking into account these iceberg sizes and ocean current directions which appear to have remained similar from the last full glacial to the present interglacial the icebergs that produced the ploughmarks are interpreted to be calved from fast flowing ice streams draining huge basins of the west antarctic ice sheet and the western antarctic peninsula during the last glacial maximum lgm about 20 000 years ago ploughmarks at the deepest water depths correspond to icebergs more than 500 m thick and at least 2 km wide given a sea level rise of 120 m since the lgm the icebergs after having drifted northeast in the antarctic circumpolar current were transported northward by the falklands malvinas current a total distance of 2000 to 4000 km the waters north of the falkland islands in particular were probably several degrees colder than today to prevent rapid iceberg melting and deterioration

seismic reflection imaging of a pull apart sag within tan lu strike slip fault zone cenozoic structure and evolution of the weibei sag southeastern bohai bay basin china abstractthe weibei sag is a cenozoic sag located within the tan lu strike slip fault zone southeast of the bohai bay basin china the sag is controlled by two branches of the tan lu right lateral strike slip fault zone strike n30 e and the gucheng weihekou normal fault strike e w this sag was thought to be a promising exploration area after several oil fields were found there however the most highly productive oil and gas wells are located on traps far from the source rocks a situation thought to be related to the tectonic evolution of this sag thus a regional study of the weibei sag involving three dimensional seismic data sets and drilling cores has been undertaken to document the sag s evolution five groups of secondary faults are distinguished within the weibei sag wnw e w and ene striking normal faults and nnw and nne striking strike slip faults except for the preexisting wnw striking faults the other four groups of faults developed under cenozoic tectonic movement the combined

a numerical model of the weddell sea large scale circulation and water mass distribution a circumpolar model for regional studies of the wind driven and thermohaline circulation of the southern ocean including the major sub ice shelf areas is described a first series of numerical experiments focusing on the weddell sea reveals a pronounced and persistent double cell structure of the weddell gyre with a maximum transport of 60 sv in agreement with observations experiments with artificial passive tracers point to the shallow shelf areas off the filchner ronne ice shelf as main locations for bottom water production the trajectories of lagrangian floats are used to determine the pathways and timescales of water mass spreading in the model in addition the effect of sub ice shelf forcing on the water mass characteristics is evaluated it is shown that water modified in the sub ice cavities contributes significantly to the deep and bottom water formation along the continental slope and affects the water mass characteristics throughout the weddell sea by increasing the stability of the near surface stratification and preventing deep convection

barotropic and deep referenced baroclinic ssh variability derived from pressure inverted echo sounders pies south of africa 1 the objective of this paper is to evaluate the baroclinic and barotropic components of sea surface height ssh anomalies in the southern ocean and investigates the causes for the weak correlation between hydrographically derived and satellite measured ssh anomalies to this end data obtained by six pressure inverted echo sounders pies deployed south of africa were used to derive baroclinic and barotropic ssh anomalies our results show that the barotropic component accounts for 30 60 of the variability between the jets of the antarctic circumpolar current acc in contrast the jets associated with the major acc fronts are predominantly baroclinic the deep baroclinic component is important in the acc and accounts for the major part of the baroclinic variability the comparison with along track satellite altimetry jason 1 2 shows correlations coefficients of 0 24 0 92 with low values in regions of high barotropic variability the comparison with gridded aviso satellite altimetry generally shows higher correlation coefficients 0 33 0 92 and lower root mean square rms errors compared to the along track product in conclusion the barotropic ssh anomaly plays a major role in this region and has to be accounted for when assimilating ssh into ocean models due to their high baroclinic component the correct representation of the time and space varying acc fronts seems to be crucial for the right ssh anomaly partitioning used for assimilation purposes gridded products namely aviso seems to be more suitable compared to along track products jason 1 2 in representing the variability of ssh anomalies

the transport of the weddell gyre across the prime meridian abstract current meter observations from instruments moored from 1996 to 2001 are used to determine the structure and the volume transport of the weddell gyre on the greenwich meridian the record length mean volume transport is 45 sv to the east within the northern and 56 sv to the west within the southern limb of the weddell gyre thus 11 sv must leave the gyre circulation west of the greenwich meridian and enter it east of it the deficit occurs with 8 sv mainly in the circumpolar deep water cdw warm deep water wdw layer surface waters and weddell sea deep water wsdw contribute 2 and 3 sv respectively in contrast to this 3 sv more of weddell sea bottom water wsbw flow in the northern limb to the east than in the southern limb to the west which suggests a wsbw formation rate of about 3 sv in the western weddell sea in the southern boundary of the antarctic circumpolar current acc a volume transport of 35 16 sv was found using geostrophic calculations adjusted with two measurements of the absolute velocity the large heat content of the northern limb points to an extensive heat exchange between the weddell sea and the world ocean west of the prime meridian hence the heat transport as well as the volume transport suggest that the water masses of the weddell gyre are not exclusively replaced in its eastern part but that there is a significant exchange of water masses to the west of the prime meridian

multistage processes linked to tectonic transition in the genesis of orogenic gold deposit a case study from the shanggong lode deposit east qinling china abstract the shanggong lode deposit represents one of the largest mesozoic orogenic gold deposits in the east qinling metallogenic belt of central china here we investigate the texture trace element and sulfur isotopic composition of pyrite from this deposit to gain insights in the ore genesis three types of pyrite are recognized by its texture py1 is represented by coarse grained cubic and pentagonal dodecahedron belonging to the stage i quartz pyrite vein py2 comprises fine grained disseminated pentagonal dodecahedron belonging to stage ii quartz sulfides vein py2 can be further divided into core and rim porous cores py2c carrying abundant visible mineral inclusions and significantly higher arsenic concentration and clean rims py2r with low arsenic systematic la icpms trace elements and sims sulfur isotopic analyses reveal two distinct stages of mineralization with diverse source materials 1 the early stage is represented by py1 which contains 0 65 70 ppm au average 11 6 ppm with relatively low and variable concentrations of cu ag te pb zn and bi the 34 s values of py1 range from 2 7 to 7 2 suggesting that the sulfur source for the early stage fluid was mainly derived from the taihua and xiong er groups and that the depleted 34 s values reflect changes of ph f o2 and fluid rock interaction 2 the main stage is represented by py2 which contains au in the range of 0 14 189 ppm average 39 7 ppm the py2 carries significantly higher contents of compatible elements ni co v and cr and ore metals e g au ag pb zn as te than those in py1 with the ore metals occurring as invisible lattice bound or nanosized particles and visible micron sized inclusions the 34 s values of py2 show marked depletion with a range of 16 3 to 11 7 attributing to the fractionation between barite and sulfide minerals together with previous studies and trace element characters in py2 we identify a contribution of au from mantle source into the ore forming fluid system during the main stage we propose that the two stages of gold mineralization in the shanggong deposit in response to the collisional assembly of qinling orogenic belt preserve evidence for diverse metal sources with the early stage derived from partial melting of the lower crust taihua and xiong er groups in the compressional stage and the main stage characterized by mantle contribution in a post collisional extensional setting our findings may have important implications for the exploration of regional triassic gold and molybdenum deposits

fronts transport and weddell gyre at 30 e between africa and antarctica a detailed description of the frontal structure of major currents and estimates of transport between africa and antarctica at 30 e were made on the basis of a finely resolved hydrographic section made during the 1996 civa 2 cruise particular emphasis was put on a refinement of the eastern boundary of the weddell gyre by analyzing also supplementary hydrographic data from the 1993 civa 1 cruise and the best available historical hydrographic data in the weddell and enderby basins contrary to the general belief our results show that the weddell gyre extends far beyond 30 e reaching at least as far east as the enderby land promontory 53 e from this point westward currents along the antarctic continental margin constitute the gyre s southern boundary thus closing the cyclonic circulation of the gyre at its easternmost end as the most convincing evidence for this refined circulation scheme significant westward transport south of 65 s has been identified from the civa 1 acoustic doppler current profiler data we have shown also using an inertial jet model that the blocked feature of the weddell cold regime 57 s to the west of 25 e is due to the topographic control of flow by local bathymetry during the civa 2 cruise 70 of the antarctic circumpolar current acc was concentrated near the polar front 51 s with surface speeds reaching up to 70 cm s 1 the baroclinic current field in the subpolar area south of the weddell front 58 s for civa 2 and 57 s for civa 1 is featureless 3 cm s 1 but yielding a nonnegligible eastward transport of 15 sv 1 sv 106 m3 s 1 this bottom referenced baroclinic transport is entirely compensated by a substantial westward barotropic transport south of 65 s the acc transport across the 30 e section during the civa 2 cruise is estimated to be 160 sv

modeling ice shelf cavities in a z coordinate ocean general circulation model 1 processes at the ice shelf ocean interface and in particular in ice shelf cavities around antarctica have an observable effect on the solutions of basin scale to global coupled ice ocean models despite this these processes are not routinely represented in global ocean and climate models it is shown that a new ice shelf cavity model for z coordinate models can reproduce results from an intercomparison project of earlier approaches with vertical or isopycnic coordinates as a proof of concept ice shelves are incorporated in a 100 year global integration of a z coordinate model in this simulation glacial meltwater can be traced as far as north as 15 s the observed effects of processes in the ice shelf cavities agree with previous results from a coordinate model notably the increase in sea ice thickness however melt rates are overestimated probably because the parameterization of basal melting does not suit the low resolution of this configuration

impacts of open ocean deep convection in the weddell sea on coastal and bottom water temperature a high resolution global ocean sea ice model is employed to investigate the impacts of open ocean deep convection on coastal and bottom water temperature in the weddell sea the imposed strong and persistent cyclonic wind forcing and the large loss of bottom water weaken the stratification and eventually trigger the occurrence of open ocean deep convection in the southern limb of the weddell gyre in this model the production rate of the bottom water induced by the deep convection is estimated to be about 5 sv 1 sv 106 m3 s for a polynya with a similar size to that of the observed weddell polynya in the mid 1970s the cooling induced by deep convection at mid depth is transported towards the shelf regions by standing meanders or eddies to affect the basal melting of ice shelves and is transported westward by an intensified slope current interior coastal temperature in regions with a broader continental shelf is less affected by the deep convection as the intensified slope current acts to suppress heat exchanges across the shelf break also the deep convection causes warming in the weddell bottom water around the convection site when the simulated polynya size is similar to that of the observed weddell polynya in the mid 1970s this finding sheds light on the observed non monotonic decadal change cooling between 1984 1992 and warming between 1998 2008 in the weddell bottom water temperature when the simulated polynya further develops into a large size across the weddell sea the sustained broad deep convection causes large cooling in the bottom water in the western weddell sea and warming in the eastern weddell sea with the bottom water temperature also being strongly modulated by a greatly intensified weddell gyre

thermohaline stratification below the southern ocean sea ice the end of winter stratification within the cold cyclonic trough of the weddell gyre near 60 s between 5 e and the greenwich meridian is resolved with the mikhail somov data set the temperature maximum of the weddell deep water wdw is for the most part less than 0 5 c but warmer cells of wdw are found these warm wdw cells have temperature salinity and oxygen properties similar to the wdw characteristic of the weddell gyre inflow which is situated to the southeast of the mikhail somov study region the warm wdw cells are accompanied by domes in the pycnocline of 40 m amplitude over the surrounding pycnocline while deeper isopycnals are depressed anticyclonic shear below the 27 83 isopycnal within the warm wdw cells is compensated by the cyclonic shear associated with the pycnocline dome the pycnocline domes are exposed to about 50 greater entrainment by the turbulently active winter mixed layer relative to the regional entrainment rate this entrainment can significantly erode the warm cells in a single winter season introducing excess heat and salt into the mixed layer while the heat is lost to the atmosphere the excess salt is not necessarily compensated by increased fresh water introduction it is hypothesized that the warm wdw cells within the weddell gyre trough are derived from instability within the frontal zone which extends from maud rise to the northeast separating the weddell warm regime from the cold regime greater than normal injection of warm wdw cells into the weddell gyre trough would increase the surface salinity which would tend to destabilize the pycnocline increasing the probability of deep convection and polynya events

on the transport variability and origin of dense water masses crossing the south scotia ridge abstract the deep scotia sea is filled with ventilated weddell sea deep water this in turn is an essential contributor to the ventilation of the world ocean abyss depending on the formation process and or its location along the weddell sea periphery deep and bottom water masses follow different routes to cross the south scotia ridge a primitive equation hydrostatic terrain following coordinate ocean general circulation model brios 1 is used to investigate the water mass export from the weddell sea the model is circumpolar focusing on the weddell sea with particularly high resolution 20 km in the dovetail area eastward weddell sea deep water transport of 24 106 m3 s 1 is found in the northern limb of the weddell gyre across 44 w export rates of weddell sea deep water through gaps in the south scotia ridge are estimated to be 6 4 106 m3 s 1 with a semi annual cycle of 0 6 106 m3 s 1 which can be correlated to atmospheric cyclone activity and weddell gyre strength sensitivity studies considering extreme sea ice conditions in the weddell sea show higher lower exports in years of minimum maximum winter sea ice extent lagrangian particle trajectories illustrate the pathways of water masses from the inner weddell sea into the scotia sea through various gaps in the south scotia ridge they highlight the existing flow divergence on the northwestern continental shelf with one branch entering bransfield strait and the other continuing eastwards subsequently filling the deep weddell and scotia seas water masses flowing through the major gaps originate from the southwestern and southeastern weddell sea continental shelves however water masses formed east of the weddell sea e g prydz bay also seem to feed the deep scotia sea since a large portion of floats flowing northward through the gaps of the south scotia ridge have been in contact with the mixed layer processes outside the inner weddell sea

notes on southern ocean hydrography sea ice and bottom water formation abstract the southern ocean circulation and sea ice distribution is briefly described the formation of extremely cold bottom water in the weddell sea and its relation to the floating ronne filchner ice shelves is discussed it is shown that a concentrated swift eroding bottom current with anomalous low 18 o ratio transports the cold and dense ice shelf water from the shelf towards large depths comments are made on possible implications of this process for the large scale deep water circulation and for the interpretation of sediment cores

deep and bottom water of the bransfield strait eastern and central basins temperature salinity oxygen and chlorofluorocarbon cfc data obtained in september 1997 define the water types ventilating the deep eastern and central basins of the bransfield strait these water types are observed adjacent to joinville island and are clearly derived from the weddell sea the eastern basin bottom water characteristics closely match that of the bottom water at 310 dbar depth 50 km east of joinville island the eastern basin bottom water is a simple mixture of low salinity freezing point shelf water 65 and relatively warm saline weddell deep water 35 with a cfc 113 cfc il ratio age of 8 5 years the eastern basin bottom water shares a common origin with a weak salinity minimum observed at 1000 dbar within the central basin though overflow from the central basin to the eastern basin floor may also occur the bottom water within the central basin is colder and saltier with higher concentrations of oxygen and cfc il than that of the eastern basin the central basin bottom water with a cfc ratio age of 7 5 years is composed of same weddell water types that form the eastern basin bottom water plus a large contribution of high salinity freezing point shelf water of the characteristics of water observed 10 km northeast of joinville island and a small amount of pacific pycnocline water the components and their percentage are weddell deep water 11 low salinity shelf 24 high salinity shelf 60 to pacific pycnocline 5