preliminary interpretation of tracer experiments conducted in a discrete rock fracture under conditions of natural flow the authors present a preliminary analysis of tracer experiments conducted on a natural horizontal fracture system in shale and limestone at a depth of roughly 10 m an array of 27 boreholes on 5 m spacings was placed into this fracture system and apertures of the fractures were determined hydraulically at each hole a conservative tracer was injected into one borehole and monitored in the array the tracer transport process was modeled by a one dimensional model and indicates that transverse dispersion and diffusion in the matrix are the predominant processes which inhibit tracer migration and result in spreading

variability of marine 14c reservoir ages in the southern ocean highlighting circulation changes between 1910 and 1950 abstract recent changes in the southern ocean overturning circulation have been attributed either to natural variability or to anthropogenic forcing the 14c analyses of mollusk shells from kerguelen islands evidence a high decadal variability of the sea surface radiocarbon reservoir ages in the southern south indian ranging from 832 to 1005 30 years between 1910 and 1930 such high variability is common to the different sectors of the southern ocean southern south pacific and atlantic at inter annual and decadal timescales between 1901 and 1950 notably a decrease of 14 c of 40 increased r of 290 years occurred between 1901 and 1940 followed by an increase of 30 between 1940 and 1958 using a simple box model of ocean atmosphere 14co2 exchange this aging is attributed to increased upwelling of cold and 14c depleted subsurface seawaters due to intensified poleward southern westerlies the sea surface 14c aging is indeed well correlated to a positive phase of the southern hemisphere annular mode and to a cooling of the sea surface temperatures in the southern ocean between 1901 and 1940 these pre 1950 sea surface 14c changes highlight the importance of natural changes in wind intensities and ocean dynamics

development of bedding normal boudins in the pilot mountains nevada boudins with long axes ba oriented subnormal to bedding and to associated fold axes are observed in folded rocks in a thrust sheet exposed near the base of a regionally extensive allochthon in west central nevada usa formation of the boudins is related to development of a regional fold set coeval with major thrusting the axes of boudins lie at a high angle to bedding and in some instances boudins define tight to isoclinal folds which are geometrically associated with the regional deformation quartz c axis fabrics from oriented thin sections of the boudins indicate extension parallel to the boudin axes ba these relations and other mesoscopic structural data indicate a complex deformational history for boudin development the history involves thin layers to become boudins deformed in folds disharmonic to major structures within the thrust sheet followed by flattening and associated extension parallel to fold axes during flattening arcuation occurred within the deforming mass resulting in rotation of fold axes and boudin axes ba toward the axis of finite extension x extension parallel to ba recorded in the petrofabrics of boudins records incremental strain axes oriented at a high angle 50 to the finite x and is probably related to an early plane strain state associated with disharmonic folding the finite extension x is down dip in axial planes of major folds formed during thrusting and indicates a northwest to southeast transport for the thrusts

intermediate water in the brazil malvinas confluence zone a lagrangian view the subsurface flow within the subantarctic and subtropical regions around the brazil malvinas falkland confluence zone is studied using daily hydrographic and kinematic data from four subsurface floats and a hydrographic section parallel to the south american shelf the float trajectories are mapped against sea surface flow patterns as visible in concurrent satellite sea surface temperature sst images with focus on the november 1994 and october november 1995 periods the unprecedented employment of lagrangian s diagrams enables us to trace the advection of patches of fresh antarctic intermediate water aaiw from the confluence zone into the subtropical region the fresh aaiw consists of a mixture of subtropical aaiw and malvinas current core water within the subtropical gyre these patches are discernible for extended periods and drift over long distances reaching north to 34 s and east to 40 w the cross frontal migration of quasi isobaric floats across the confluence zone from the subtropical to the subantarctic environment is observed on three occasions the reverse process float migration from a subpolar to a subtropical environment was observed once these events were located near 40 s 50 w the site of a reoccurring cold core feature subsurface float and sst data comparison reveals similarities with analogous observations made in the gulf stream rossby 1996 where cross frontal processes were observed close to meander crests the limited number of floats of this study and the complex structure of the brazil malvinas confluence zone however restricts the analysis to a description of two events

the antarctic slope current near 30 e the antarctic slope current flows westward above the continental slope of antarctica entering the weddell sea near 30 e and supplying dense water to the deep overturning cell there and contributing to global antarctic bottom water formation observations from the 2008 i6s hydrographic section are used to investigate the strength of the slope current near 30 e a prominent topographic feature the gunnerus bank diverts the slope current upstream of this longitude and has a large effect on the current s structure splitting it into a coastal and offshore component the bank also enhances water mass mixing and lateral exchange across the slope as part of the 2008 occupation an additional line was made along the crest of the bank forming a closed volume over the western side by combining hydrographic and lowered acoustic doppler current profiler measurements in this box using an inverse method the slope current transport is estimated to be 9 6 2 3 sv the transport associated with the antarctic slope front is 4 0 0 3 sv of which 1 8 0 3 sv enters the weddell gyre as recently formed dense water

southern ocean jets and how to find them improving and comparing common jet detection methods this study undertakes a detailed comparison of different methods used for detecting and tracking oceanic jets in the southern ocean the methods under consideration are the gradient thresholding method the probability density function pdf method and the contour method some weaknesses of the gradient thresholding method are discussed and an enhancement the whose method based on techniques from signal processing is proposed the whose method is then compared to the other three methods quantitative comparison is undertaken using synthetic sea surface height fields the whose method and the contour method are found to perform well even in the presence of a strong eddy field in contrast the standard gradient thresholding and pdf methods only perform well in high signal to noise ratio situations the whose pdf and the contour methods are then applied to data from the eddy resolving ocean general circulation model for the earth simulator while the three methods are in broad agreement on the location of the main acc jets the nature of the jet fields they produce differ in particular the whose method reveals a fine scale jet field with complex braiding behavior it is argued that this fine scale jet field may affect the calculation of eddy diffusivities finally recommendations based on this study are made the whose and gradient thresholding methods are more suitable for the study of jets as localized strong currents useful for studies of tracer fluxes the contour and pdf methods are recommended for studies linking jets to hydrographic fronts

tail shortening with developing eddies in a rough walled rock fracture understanding fluid flow and solute transport in rough walled fractures is important in many problems such as geological storage of co2 and siting of radioactive waste repositories the first microscopic observation of fluid flow and solute transport through a rough walled fracture was made to assess the evolution of eddies and their effect on non fickian tailing a noteworthy phenomenon was observed that as the eddy grew the particles were initially caught in and swirled around within eddies and then cast back into main flow channel which reduced tailing this differs from the conventional conceptual model which presumes a distinct separation between mobile and immobile zones fluid flow and solute transport modeling within the 3 d fracture confirmed tail shortening due to mass transfer by advective paths between the eddies and the main flow channel as opposed to previous 2 d numerical studies that showed increased tailing with growing eddies

mesoscale subduction at the antarctic polar front driven by baroclinic instability abstract a study of mesoscale subduction at the antarctic polar front pf is conducted by use of hydrographic data from a high resolution quasi synoptic survey of the front the geostrophic velocity and isopycnal potential vorticity pv fields are computed and the ageostrophic flow diagnosed from the semigeostrophic omega equation it is found that the ageostrophic circulation induced by baroclinic instability counteracts the frontogenesis and frontolysis effected by the confluence and difluence respectively of the geostrophic velocity field though the sense of the ageostrophic circulation is reversed repeatedly along the front the existence of pv gradients along isopycnals leads to a net cross front bolus transport in response to a reversal of this gradient with depth a necessary condition for the onset of baroclinic instability the bolus transport is northward at the protruding temperature minimum layer that characterizes the pf and southward above this net cross front overturning circul

radium isotopes to investigate the water mass pathways on the kerguelen plateau southern ocean abstract natural iron fertilization promotes the phytoplankton bloom that takes place on the kerguelen plateau in the indian sector of the southern ocean we measured 228 ra t 1 2 5 75 yr and 226 ra t 1 2 1602 yr in waters above the kerguelen plateau in order to provide information on the water mass pathways which in turn could help elucidate the mechanisms controlling iron fertilization in that area 228 ra activities are extremely low in this region being in most cases 18 g kg station a3 520 m depth located on the plateau in the middle of the bloom area also displays such low values but with higher 228 ra activities and higher 228 ra 226 ra ratios in the upper 150 m such a pattern suggests the presence of a water mass that recently interacted with sediments and therefore has been advected onto the kerguelen plateau elevated 228 ra activities were found in shallow waters in the vicinity of heard island south of the kerguelen plateau contact of the water masses with the shallow lithogenic sediments likely explains these high 228 ra activities when combined with physical observations these results suggest that the water mass advected onto the plateau originates from the south of the kerguelen plateau this northward advection might represent a supply of dissolved and or particulate fe for the observed phytoplankton bloom using the 228 ra profile obtained at station a3 we could estimate the vertical eddy diffusivity k z on the kerguelen plateau our k z estimate 1 5 10 4 1 3 10 4 m 2 s compares well with that reported by park et al 2008a internal tides and vertical mixing over the kerguelen plateau deep sea research ii doi 10 1016 j dsr2 2007 12 027 based on ctd ladcp data by combining this k z estimate with the gradient of dissolved fe observed at a3 blain s sarthou g laan p 2008 distribution of dissolved iron during the natural iron fertilization experiment keops kerguelen plateau southern ocean deep sea research ii doi 10 1016 j dsr2 2007 12 028 we calculate a vertical fe flux of 1 0 14 3 nmol m 2 d

kinematics of late mesozoic thrusting pilot mountains west central nevada u s a abstract the northern pilot mountains of west central nevada consist of a complexly deformed terrane of imbricate thrust nappes composed of rocks of permian triassic through jurassic and possible cretaceous ages three episodes of fold and thrust generation are recognized on the basis of folded thrusts and thrusted folds and deformation and emplacement of the nappes is constrained as having occurred during the late mesozoic folds are apparently coeval with thrust faults and fold geometry is used in determining approximate directions of thrust displacement the history of thrust displacement is complex and involves three directions of motion on a regionally extensive detachment surface the luning thrust the first motion from nw to se results in displacements of the order of several tens of kilometres and is the probable result of nw se regional compression the final two episodes of motion are ne sw followed by e w they result in small displacements and are possibly the product of gravity sliding of the thrust sheet into depressions in the autochthon sites of downwarp in the autochthon may have been formed either by load induced subsidence or regional compression

glacial and hydrothermal sources of dissolved iron ii in southern ocean waters surrounding heard and mcdonald islands the southern ocean is the largest region in which iron limits the growth of phytoplankton however a phytoplankton bloom thousands of square kilometres in area forms each spring summer in the indian sector of the southern ocean both above and to the east of the kerguelen plateau the central region of the kerguelen plateau hosts the volcanically active islands heard and mcdonald himi the former of which is largely covered by glaciers the sources and processes governing supply of iron from himi to the region are relatively unknown in the austral summer of 2016 the first voyage to focus on biogeochemical cycling in the himi region was undertaken geotraces process study gipr05 using dissolved iron ii dfe ii and hydrogen peroxide h2o2 measurements we are able to resolve iron sources and show that each of the adjacent islands are strong sources of reduced iron though controlled by different supply mechanisms at heard island the greatest dfe ii concentrations 0 57 nmol l 1 were detected north of the island an inverse correlation of dfe ii concentrations with salinity suggests the origin is from a sea terminating glacier on the island at mcdonald islands the greatest dfe ii concentrations 1 01 nmol l 1 were detected east of the islands which based on dfe ii profiles from five targeted stations appears likely to originate from shallow diffuse hydrothermalism elevated dfe ii around himi may increase fe availability for biota and has implications for transport of fe away from the islands to the broader northern kerguelen plateau where the annual plankton bloom is strongest

time mean flow as the prevailing contribution to the poleward heat flux across the southern flank of the antarctic circumpolar current a case study in the fawn trough kerguelen plateau the major mechanisms of the oceanic poleward heat flux in the southern ocean are still in debate the long standing belief stipulates that the poleward heat flux across the antarctic circumpolar current acc is mainly due to mesoscale transient eddies and the cross stream heat flux by time mean flow is insignificant this belief has recently been challenged by several numerical modeling studies which stress the importance of mean flow for the meridional heat flux in the southern ocean here this study analyzes moored current meter data obtained recently in the fawn trough kerguelen plateau to estimate the cross stream heat flux caused by the time mean flow and transient eddies it is shown that the poleward eddy heat flux in this southern part of the acc is negligible while that from the mean flow is overwhelming by two orders of magnitude this is due to the unusual anticlockwise turning of currents with decreasing depth which is associated with significant bottom upwelling engendered by strong bottom currents flowing over the sloping topography of the trough the circumpolar implications of these local observations are discussed in terms of the depth integrated linear vorticity budget which suggests that the six topographic features along the southern flank of the acc equivalent to the fawn trough case would yield sufficient poleward heat flux to balance the oceanic heat loss in the subpolar region as eddy activity on the southern flank of the acc is too weak to transport sufficient heat poleward the nonequivalent barotropic structure of the mean flow in several topographically constricted passages should accomplish the required task

cross frontal exchange of antarctic intermediate water and antarctic bottom water in the crozet basin abstract the hydrographic survey made across the antarctic circumpolar current acc in the southwestern crozet basin during the april may 1993 antares 1 cruise revealed unprecedented strong cross frontal injections of newly formed antarctic intermediate water aaiw into the subtropical zone north of the acc the acc in this area is mostly associated with the subantarctic front saf and subtropical front stf which are tightly merged into one structure bordered to the north with the eastward extension of the agulhas return current the oxygen and salinity extrema of the newly injected aaiw at a depth of 1200 m well north of the stf reach as high as 6 17 ml l 1 and 34 15 these values coincide almost exactly with those in the aaiw source found at a depth of 500 m just south of the saf but surpass considerably oxygen by 1 35 ml l 1 and salinity by 0 23 psu those values corresponding to the old aaiw at the nearby subtropical stations such spectacular cross frontal injections of new aaiw were not continuous in space and time but were found to be rather local intermittent and impulsive this was closely correlated with the highly perturbed meandering frontal zone due to the frequent passages of strong atmospheric depressions during the cruise there is also clear evidence of the northward penetration of antarctic bottom water aabw through the crozet kerguelen gap and its northward flow along the deep western boundary of the crozet basin supporting previous observations moreover our observations indicate more precisely the bottom water pathway which is concentrated against the continental rise west of 56 e following roughly the 4000 m isobath it is concluded that the crozet basin frontal zone acts as a barrier only for the upper layer water masses and that it is dynamically transparent for the cross frontal exchange of intermediate and deeper layer water masses of potential density anomalies greater than 27 1 including aaiw and aabw

implications of the deep circulation and ventilation of the indian ocean on the renewal mechanism of north atlantic deep water in the indian ocean sector of the great ocean conveyor scheme the north atlantic deep water nadw replacement is realized by the transformation of the sinking circumpolar deep water cdw from the southern ocean to a prevailingly upward flow in the northern indian ocean this water mass transformation scenario has been studied by using hydrographie data including potential temperature salinity dissolved oxygen and nutrients in a water mass mixing model and by calculation of dianeutral velocity the model comprises a mixing system of three major deep water masses nadw cdw and north indian deep water this third water mass is introduced as a virtual water mass to represent the aged cdw the assumption is feasible as the artificial water mass can be eliminated on the deepest n 28 12 neutral surface characterized by isopycnal mixing the experiment is fulfilled when a conservative variable initial phosphate po40 is introduced and all conservative parameters are used in the mixing scheme the n 28 12 surface provides a major isopycnal transition path of cdw to the northern indian ocean and thus cdw is transformed to an upward flow dominant dianeutral up welling is detected on all four neutral surfaces north of 30 s showing increasingly strong dianeutral velocity toward shallower surfaces with the water mass mixing pattern and spreading path dianeutral circulation and dynamical information of the acceleration potential 10 m2 s 2 mapped on neutral surfaces a schematic of deep water circulation and ventilation of the indian ocean emerges from this study the contribution of nadw is largely limited to the southwest indian ocean the northward cdw is found mainly in two paths one in the western indian ocean apparent between 2000 and 3000 m through the western crozet and madagascar basins and farther north into the somali basin and arabian basin and another in the central indian basin apparent below 3000 m where ridge blocking becomes effective in the west and nadw salinity reaches a maximum while the major path switches from west to the central basin in the deeper layer 3000 3500 m the flow in the western indian ocean reverses southward north of the southeast indian ridge the deep path bifurcates from which point the eastern branch feeds the deep western boundary flow in the west australian basin except for part of the transformed cdw which is contributed to the upward flow in the north the return flow of cdw is found on the eastern side of these basins

slope currents around the kerguelen islands from demersal longline fishing records 1 the kerguelen plateau constitutes a natural obstacle for the eastward progress of the antarctic circumpolar current especially around the kerguelen islands however there is little quantitative knowledge of the current field around the islands due to lack of long term current measurements we performed a systematic analysis of a total of 28917 points of fishing gear drifts from setting and recovery positions of demersal longlines deployed between 2002 and 2007 for patagonian toothfish dissostichus eleginoides fisheries in kerguelen waters this enabled the construction of a realistic field of depth averaged time mean slope currents along the 1000 m isobath all around the kerguelen islands the strongest depth mean velocities of 25 cm s 1 are associated with the polar front which rounds the islands from the south and flows northward along the inner continental slope immediately east of the islands strongly supporting previous hydrographic evidence these results demonstrate the potential for hitherto unexploited historic longline drift data from demersal fishing grounds to provide valuable quantitative information on the regional circulation

the velocity and vorticity structure of the agulhas current at 32 s the full depth velocity field of the agulhas current the western boundary current of the southwest indian ocean has been directly measured using a lowered acoustic doppler current profiler ladcp fifteen combined conductivity temperature depth ctd and ladcp stations were occupied across the current at 32 s off the east coast of south africa in february march 1995 as part of the world ocean circulation experiment indian ocean program the deep velocity structure of the agulhas current was found to be very different than previously described using geostrophic estimates in particular ladcp results reveal a v shaped pattern for the level of no motion across the agulhas current and an agulhas undercurrent is observed flowing equatorward below 800 m depth directly beneath the surface core of the poleward flowing agulhas current comparisons of direct and geostrophic velocities suggest that the velocity structure of the agulhas current is essentially geostrophic below about 200 m depth where differences are generally less than estimated errors above these depths the ladcp measured shears and geostrophic shears exhibit differences and velocities can diverge shipboard adcp data support ladcp results near the surface indicating that both instruments are measuring real signals the geostrophic and ladcp measured shears are well matched away from the surface and a depth averaged fit below 200 m between them exhibits small standard deviations the geostrophic volume transport of the agulhas current as referenced to ladcp is 73 sv and is just 3 different from the direct ladcp transport estimate the most recent full depth estimate of agulhas current transport in the literature is given by toole and warren 1993 who estimate a geostrophic volume transport of 85 sv the baroclinic velocity structures from their section and from this work are similar indicating that the difference in the transport estimates is due to the choice of geostrophic reference level and ultimately to the presence of the previously unobserved agulhas undercurrent combined ctd ladcp data are very useful for potential vorticity analysis since velocity and density measurements are simultaneous and coincident the vorticity structure of the agulhas current suggests the presence of a mixing boundary at middepths similar to features observed in the gulf stream the feature appears to be associated with a sharp upturn in isopycnals coincident with the foot of the continental slope the boundary inhibits cross stream mixing of intermediate water masses and may help explain the appearance of a discrete filament of red sea water inshore of antarctic intermediate waters in the same density layer despite intense cross stream shears

linking foraging behaviour to physical oceanographic structures southern elephant seals and mesoscale eddies east of kerguelen islands in the southern ocean mesoscale features such as fronts and eddies have been shown to have a significant impact in structuring and enhancing primary productivity they are therefore likely to influence the spatial structure of prey fields and play a key role in the creation of preferred foraging regions for oceanic top predators optimal foraging theory predicts that predators should adjust their movement behaviour in relation to prey density while crossing areas with sufficient prey density we expect predators would change their behaviour by for instance decreasing their speed and increasing their turning frequency diving predators would as well increase the useful part of their dive i e increase bottom time thereby increasing the fraction of time spent capturing prey southern elephant seals from the kerguelen population have several foraging areas in antarctic waters on the kerguelen plateau and in the interfrontal zone between the subtropical and polar fronts this study investigated how the movement and diving behaviour of 22 seals equipped with satellite relayed data loggers changed in relation to mesoscale structures typical of the interfrontal zone we studied the links between oceanographic variables including temperature and sea level anomalies and diving and movement behaviour such as displacement speed diving duration and bottom time correlation coefficients between each of the time series were calculated and their significance tested with a parametric bootstrap we focused on oceanographic changes both temporal and spatial occurring during behavioural transitions in order to clarify the connections between the behaviour and the marine environment of the animals we showed that a majority of seals displayed a specific foraging behaviour related to the presence of both cyclonic and anticyclonic eddies we characterized mesoscale oceanographic zones as either favourable or unfavourable based on the intensity of foraging activity as identified by the behavioural variables our findings highlight the importance of mesoscale features for top predators behaviour and introduce a new approach for evaluating the importance to the seals of the origin and intensity of these features

changes in sources and storage in a karst aquifer during a transition from drought to wet conditions summary understanding the sources and processes that control groundwater compositions and the timing and magnitude of groundwater vulnerability to potential surface water contamination under varying meteorologic conditions is critical to informing groundwater protection policies and practices this is especially true in karst terrains where infiltrating surface water can rapidly affect groundwater quality we analyzed the evolution of groundwater compositions major ions and sr isotopes during the transition from extreme drought to wet conditions and used inverse geochemical modeling phreeqc to constrain controls on groundwater compositions during this evolution spring water and groundwater from two wells dominantly receiving diffuse and conduit flow termed diffuse site and conduit site respectively in the barton springs segment of the edwards aquifer central texas usa and surface water from losing streams that recharge the aquifer were sampled every 3 4 weeks during november 2008 march 2010 during this period water compositions at the spring and conduit sites changed rapidly but there was no change at the diffuse site illustrating the dual nature i e diffuse vs conduit of flow in this karst system geochemical modeling demonstrated that within a month of the onset of wet conditions the majority of spring water and groundwater at the conduit site was composed of surface water providing quantitative information on the timing and magnitude of the vulnerability of groundwater to potential surface water contamination the temporal pattern of increasing spring discharge and changing pattern of covariation between spring discharge and surface water steam recharge indicates that that there were two modes of aquifer response one with a small amount of storage and a second that accommodates more storage

contribution of resuspended sedimentary particles to dissolved iron and manganese in the ocean an experimental study abstract a number of trace metals play essential roles in marine ecosystem structure and biological productivity until recently it has been argued that phytoplankton access primarily dissolved iron while particulate iron was considered a refractory material with little use biologically and limited interaction with the dissolved pool in order to assess the transfer mechanisms between sediment sourced particulate trace metals and the dissolved pool we conducted a 14 month incubation that reacted resuspended sediments with natural seawater both originating from the kerguelen area keops cruises southern ocean in the dark and at concentrations replicating natural conditions three types of sediments were investigated named biosi biosi ca and basalt mostly composed of i biogenic silica bsio2 ii bsio2 and calcite and iii basaltic fragments respectively the release of dissolved silicon dsi iron dfe and manganese dmn was monitored regularly throughout the incubation as well as living bacteria density and fe organic ligands depending on the origin and composition of the sediment unique dfe and dmn fluxes were observed including a strong decoupling between dfe and dmn the basaltic sediment released up to 1 09 0 04 nmol l 1 of dfe and 0 28 0 09 nmol l 1 of dmn while the biogenic sediments released a higher 3 91 0 04 nmol l 1 and 8 03 0 42 nmol l 1 of dfe and dmn respectively several factors influencing the release and removal of dfe and dmn were discernable at the temporal sampling resolution of the incubation including the structural composition of the sediment bacterial abundance and the formation of manganese oxides the regular sampling over short timescales and the extended sampling over one year proved to be critical to constrain the processes and exchanges that govern the contribution of the particulate to the dissolved pools overall this incubation provides a strong basis for reassessing the role of resuspended sedimentary particles in the marine biogeochemical cycles of fe and mn indeed we show that biogenic silica calcite rich and basaltic particles can contribute substantial dissolved fe and mn to the overlying water column in the future the global extent of this previously overlooked external metal source should be quantified through further process studies and biogeochemical models this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

bacterial proteolytic activity in sediments of the subantarctic indian ocean sector abstract organic material entering the oceanic benthic zone can be permanently buried or recycled to co2 in the sediment therefore it is important to know the carbon flux across the sediment water interface to determine the initial and rate limiting step in carbon oxidation a bacterial enzymatic activity bacterial density and ectoproteolytic activity determined using a fluorogenic substrate analog l leucine 7 amino 4 methyl coumarin leu mca were investigated in the water column and in sediments during the antares 1 jgofs cruise in the indian sector of the southern ocean a strong decrease in ectoproteolytic activity was observed with increasing water depth peak activity in surface water was three orders of magnitude less than in surface sediment analysis of experimental data revealed for most sediment bacterial communities the existence of a biphasic mechanism with different velocities for organic matter degradation and different affinities of enzymatic systems for substrates to explain this we hypothesize a strategy of bacterial communities that use the episodic supplies of organic matter reaching the sediment microbial ectoproteolytic activities were highest in surface sediment horizons and decreased progressively with depth as benthic microbial activities reflect the quantity and quality of organic matter reaching the sea floor high potential ectoproteolytic activities pea measured in the sediment of the polar front zone could indicate a direct and rapid coupling of relatively high surface productivity and deep ocean water by sinking particle fluxes lower values of pea were found in sediment in the northern study area where lateral processes associated with ocean circulation antarctic circumpolar current have an important influence on settling particles the lowest sediment pea values were measured at 52 s a region in which low primary production provides a poor supply of organic matter for the sea floor

dynamically balanced absolute sea level of the global ocean derived from near surface velocity observations 1 the 1992 2002 time mean absolute sea level distribution of the global ocean is computed for the first time from observations of near surface velocity for this computation we use the near surface horizontal momentum balance the velocity observed by drifters is used to compute the coriolis force and the force due to acceleration of water parcels the anomaly of horizontal pressure gradient is derived from satellite altimetry and corrects the temporal bias in drifter data distribution ncep reanalysis winds are used to compute the force due to ekman currents the mean sea level gradient force which closes the momentum balance is integrated for mean sea level we find that our computation agrees within uncertainties with the sea level computed from the geostrophic hydrostatic momentum balance using historical mean density except in the antarctic circumpolar current a consistent horizontally and vertically dynamically balanced near surface global pressure field has now been derived from observations

trace element composition of suspended particulate matter along three meridional clivar sections in the indian and southern oceans impact of scavenging on al distributions abstract we present the trace element composition al si p ca fe and zn of suspended particulate matter spm samples collected in the upper 1000 m along u s clivar co2 repeat hydrography meridional section i09n i08s from the southern ocean to the bay of bengal at 95 e and in surface waters along meridional section i06s from the south african margin to the antarctic shelf edge at 30 e a band of elevated surface ocean pca 0 5 0 3 m over 30 60 s is consistent with the global pattern of high coccolithophore production encircling the southern ocean suggested by remote sensing over 50 60 s both sections exhibit a sharp transition from ca rich to si rich particulate matter up to 2 8 6 5 m indicating a change from coccolithophore to diatom communities in waters with low residual nitrate along i08s diatom blooms display elevated pzn concentrations and zn p ratios 14 9 5 7 mmol mol 1 reflecting cellular zn stoichiometry of southern ocean diatoms regions of high primary productivity in the southern ocean are coincident with unexpectedly high surface ocean pal concentrations max 12 6 26 5 nm compared to background concentrations typically 50 of surface ocean pal in these regions originates from adsorptive scavenging of dissolved al onto biogenic particles along i08s dissolved al reservoirs likely originate from transport of al enriched waters by the agulhas return current local dust deposition and seasonal ice melt along i06s pal distributions suggest larger inputs of dust to the surface mixed layer than have previously been described by contrast pfe concentrations remain low in both surface this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond

ocean circulation and frontal structure near the southern kerguelen plateau the physical context for the kerguelen axis ecosystem study oceanographic observations from ships floats and remote sensing are used to describe the ocean circulation and frontal structure from the southern kerguelen plateau to the antarctic margin the flow of the antarctic circumpolar current acc is largely zonal upstream of the kerguelen plateau the southern branch of the polar front and the northern branch of the southern acc front saccf are deflected to the north by the topography and cross the plateau through the fawn trough the southern branch of the saccf and the southern boundary of the acc pass to the south of banzare bank through the princess elizabeth trough these fronts turn sharply to the north on the eastern flank of the plateau then retroflect to the south before continuing eastward satellite altimetry and float trajectories suggest the acc regime to the east of the plateau is eddy rich and characterised by extensive meandering of the acc fronts in contrast to the low eddy energy and zonal flow observed west of the plateau the antarctic slope current flows west along the upper continental slope with hydrographic data indicating some of the flow turns offshore and feeds the southern boundary flow in the western boundary current flow over the plateau itself is relatively quiescent and floats in this region have a long residence time 1 year the regional circulation is closely associated with the distribution of biological productivity in surface waters as revealed in satellite measurements of ocean colour including high productivity in subpolar waters along the eastern edge of the plateau and over the antarctic continental shelf moderate productivity over the plateau and low productivity in acc waters in the fawn trough and north of the saccf

diatoms preserved in surface sediments of the northeastern kerguelen plateau abstract an island mass effect was observed from the sedimentary distribution of diatoms on the northeastern kerguelen plateau five new samples placed in context to species distributions previously reported from the permanently open ocean zone pooz revealed a plateau community dominated by three species taxa fragilariopsis kerguelensis thalassionema nitzschioides f nitzschioides and chaetoceros hyalochaete resting spores intermediate abundances of thalassiosira antarctica were unique to the plateau sediment signature as were increased abundances of eucampia antarctica v antarctica the off plateau sediment sample contained typical pooz sediment distributions dominated by f kerguelensis thalassiosira lentiginosa and thalassiothrix antarctica the role of deposition from the surface waters to the sediments was investigated by comparison to the diatom thanatocoenose observed in surface waters these results suggest that the use of sediment abundances of c hyalochaete resting spores and f kerguelensis to determine past productivity events such as wind sourced iron enrichment of the southern ocean at the last glacial maximum is not straightforward the elevated abundance of t nitzschioides f nitzschioides on the plateau did not indicate an iron deplete regime but the converse for the evaluation of paleo productivity hypotheses for the open southern ocean we suggest caution in the use of subantarctic and kerguelen plateau sediment signatures and emphasize that there is a need to also study antarctic coastal and especially sea ice melt water stimulated blooms

interannual changes of austral summer coccolithophore assemblages and southward expanse in the southern indian ocean abstract coccolithophore ecology and biogeography in the southern indian ocean was studied during the austral summer of 2009 soe09 late austral summer 2010 soe10 mid austral summer and 2012 isea12 early austral summer during the soe09 and soe10 surface water samples 55 and 54 water samples respectively were collected from two different transects between mauritius and antarctica 48 e 57 3 e whereas during the isea12 22 sea surface water samples were collected between cape town and prydz bay highest coccolithophore diversity was during soe10 36 taxa followed by soe09 and isea12 12 and 7 taxa respectively whereas highest coccolithophore abundance was reported during the isea12 up to 2203 103 coccospheres l followed by soe10 up to 742 103 coccospheres l and soe09 up to 217 103 coccospheres l during each expedition elevated coccolithophore diversity was documented at the subtropical zone whereas the highest abundance was recorded at the subantarctic zone which was dominated by emiliania huxleyi differences in the occurrence and southward expanse of coccolithophores were documented during each expedition i e maximum southward expanse during the soe10 and lowest during the isea12 we show that biogeographic boundaries of coccolithophores are highly variable in the southern indian ocean which is controlled by environmental factors in the early and mid austral summer and grazing pressure in the late austral summer in addition the physical forcing also may play a key role in transport of coccoliths and coccospheres in the high latitudes we indicate that southward expanse of coccolithophores is significant and may occur for short periods during austral summer

kinematics of plate convergence deduced from mesozoic structures in the western cordillera mesozoic structures in the western cordillera of the united states yield important constraints for kinematic reconstruction of plate motions relative to north america structures in the mesozoic arc s of the northern sierra nevada and of northeastern oregon are remarkably uniform in timing style and with late cretaceous and or cenozoic rotations removed orientation rocks of both regions experienced three major episodes of contraction occurring in the triassic early jurassic the late jurassic and the early cretaceous cross folds were developed after the first two deformations but were not associated with significant shortening the three major deformations are nearly homoaxial and have shortening axes oriented subperpendicular ne sw to the regional trend of the arc system in the back arc region of the northwestern great basin deposition was continuous during the triassic and early jurassic and the region was shielded from tectonism in the arc to the west development of a regional fold thrust belt associated with major nw se shortening was initiated in the back arc region during the middle or late jurassic and continued through the early cretaceous corresponding deformation did not occur in the arc and the arc and back arc were decoupled by a major left lateral fault system that subparallelled the arc axis in the mid cretaceous approximately 100 m y b p regional compression in the back arc abruptly changed to ne sw and both the arc and back arc experienced major shortening development of homoaxial structures in the sierran arc is probably analogous to shortening in present day arc systems undergoing oblique subduction in which the shortening axis is parallel to the normal component of convergence thus the dominant structures in the sierran arc simply may be a reflection of the orientation of the trench and may not constrain the sense of obliquity of convergence strike slip faults and related compressional structures such as the back arc left lateral fault and associated fold thrust belt are probably the response to the strike slip component of convergence and indicate a period of left oblique subduction relative plate motions constrained by paleomagnetic data are in agreement with regional structures and indicate strong right lateral components of motion for the last 100 m y before 100 m y b p relative plate motions are inadequately constrained by paleomagnetic data and regional structures indicate a period of left oblique convergence from the middle or late jurassic to approximately 100 m y b p during the triassic and early jurassic the relative sense of convergence is equivocal and the possibility exists that continuous left oblique convergence occurred throughout the late paleozoic and early mesozoic until 100 m y b p based on the available data we cannot discount the possibility that a complex convergence history existed however with changes from right to left convergence in the middle or late jurassic and from left to right convergence in the mid cretaceous

navier stokes flow and transport simulations using real fractures shows heavy tailing due to eddies 1 two dimensional navier stokes flow and transport simulations are conducted for a 15 cm long fracture mapped via x ray computed tomography 1 the actual fracture with irregular aperture 2 a truncated fracture where the largest aperture area is excluded from the domain 3 the truncated fracture with further thinning of other large aperture areas and 4 a fracture with uniform vertical aperture equal to the actual fracture s mean aperture are subjected to the same pressure gradient slight variations in fracture characteristics result in significantly different flow and transport behavior flux is much larger for the uniform aperture fracture compared to the actual fracture a pronounced eddy is present at the largest aperture zone of the actual fracture resulting in a power law tail absent in other cases the uniform aperture fracture has the largest effective dispersion coefficient estimated via inversion of a 1d analytical model the analytical model fit to the other cases is not as robust as in the uniform aperture case

polar front around the kerguelen islands an up to date determination and associated circulation of surface subsurface waters the circulation of iron rich shelf waters around the kerguelen islands plays a crucial role for a climatically important annually recurrent phytoplankton spring bloom over the sluggish shelf region and its downstream plume area along the antarctic circumpolar flow however there is a long standing confusion about the polar front pf in the kerguelen region due to diverse suggestions in the literature for its geographical location with an extreme difference over 10 of latitude based on abundant historical hydrographic data the in situ hydrographic and current measurements during the 2011 keops2 cruise satellite chlorophyll images and altimetry derived surface velocity fields we determine and validate an up to date location of the pf around the kerguelen islands artificial lagrangian particle trajectories computed from altimetric velocity time series are analyzed for the possible pathways and sources of different surface subsurface waters advected into the chlorophyll bloom area east off the islands studied during the keops2 cruise the pf location determined as the northernmost boundary of the winter water colder than 2 c which is also associated with a band of strong currents appears to be primarily controlled by topography the pf rounds the kerguelen islands from the south to deflect northward along the eastern escarpment up to the northeastern corner of the kerguelen plateau before making its southward retroflection it is shown that the major surface subsurface waters found within the deep basin east of the kerguelen islands originate from the shelf around the heard island rather than from the shallow shelf north of the kerguelen islands

topographic influence on submesoscale dynamics in the southern ocean topography influences the circulation in the southern ocean generating stationary meanders in the lee of topographic features triggering hot spots of mesoscale eddy kinetic energy and modifying jets and fronts however the relationship between topography and submesoscale flows with length scales of order 1 10 km has not yet been explored the first submesoscale resolving 1 80 resolution ocean model with realistic topography of the indian sector of the southern ocean is used to investigate this interaction the results show spatial inhomogeneity in submesoscale activity that is correlated with topography topographic influence is primarily indirect topography controls mesoscale flows which in turn generate submesoscale activity mesoscale eddy kinetic energy and strain rate can be used to first order to infer submesoscale vertical velocity implying a possible route to parameterise submesoscale activity in coarser resolution models

actinium 227 as a deep sea tracer sources distribution and applications abstractactinium is one of the rarest naturally occurring elements on earth we measured its longest lived isotope 227ac half life 21 77 years for the first time in the water column of the southeast pacific the central arctic the antarctic circumpolar current acc and the weddell gyre besides the profile in the southeast pacific which confirms earlier findings about the role of diapycnal mixing for 227ac distribution we found three other different types of vertical profiles these profiles point to a prominent role of advection for 227ac distribution especially in the southern ocean depending on the type of profile found 227ac is proposed as a tracer for different oceanographic questions in the southern ocean up to 4 93 0 32 dpm m 3 227acex 227ac in excess of its progenitor 231pa are found close to the sea floor which are the highest concentrations ever observed in the ocean close to the sea surface in the weddell gyre wg 0 46 0 05 dpm m 3 227acex are detected we use 227acex there to determine the upwelling velocity in the eastern weddell gyre to be about 55 m y 1 in the acc upper and lower circumpolar deep water ucdw and lcdw are found to differ clearly in their 227acex activity high 227acex activities are therefore a promising tracer for recent inputs of lcdw to the sea surface which may help to understand the role of deep upwelling for iron inputs into antarctic surface waters the expected release of 227ac is compared with 228ra to make sure that the large near surface excess in the water column of the southern ocean is not due to lateral inputs by isopycnal mixing results of a model indicate that the 227ac 228ra flux ratio is about 50 times lower on shelves than in the deep sea data from the central arctic and from a transect across the acc confirm that 228ra and 227acex differ strongly in their sources the first measurements of 227ac on suspended matter less than 1 7 of total 227ac close to the sea floor indicate that the particle reactivity of 227ac is negligible in the open ocean in agreement with earlier findings nozaki 1984 despite the extremely low concentrations of 227ac new measurement techniques moore and arnold 1996 point to a comfortable and comparably simple determination of 227ac in the future finally 227acex may become a widely used deep sea specific tracer

the role of eddies in solute transport and recovery in rock fractures implication for groundwater remediation a better understanding of solute transport and retention mechanism in rock fractures has been challenging due to difficulty in their direct observations in microscale rough walled fractures six representative troughs in a rough walled fracture were selected for microscale observations of eddy formation with increasing flow velocity and its effect on spatiotemporal changes of solute concentration this experimental study was enabled by a microscale visualization technique of micro particle image velocimetry with increasing flow velocity re 2 86 no eddies were generated and solutes along the main streamlines transported rapidly whereas those near the wall moved slowly a larger amount of solutes remained trapped at all troughs at re 2 86 than re 10 and this flow range could be favourable for efficient remediation

direct observations of the antarctic circumpolar current transport on the northern flank of the kerguelen plateau 1 the standing meander in the antarctic circumpolar current acc found on the northern flank of the kerguelen plateau was investigated during the southern ocean finestructure cruise in november december 2008 an 18 year time series of surface geostrophic currents from satellite altimetry shows that the meander as observed during this survey is typical of the region hydrographic stations were occupied between 65 75 e and 43 48 s on the shelf 200 m depth and slope into the deep ocean to the north of kerguelen 4700 m providing the most detailed survey of this region to date geostrophic shears are referenced to lowered acoustic doppler current profiler velocities to give the first estimate of the total volume transport in this region and the transport budget is closed around the survey box the subtropical front subantarctic front and a northern branch of the polar front together have an associated transport of 174 22 sv eastward while 174 sv is large compared with typical drake passage transports it is reconciled with other estimates of the total transport with the additional 15 sv of the indonesian throughflow baroclinic transport referenced to the deepest common level between station pairs is 119 sv consistent with other estimates of the baroclinic transport in this area at this longitude the fronts of the acc are exceptionally close together we discuss the exchange of properties across the fronts

subantarctic mode water in the southeast pacific effect of exchange across the subantarctic front 1 this study considered cross frontal exchange as a possible mechanism for the observed along front freshening and cooling between the 27 0 and 27 3 kg m 3 isopycnals north of the subantarctic front saf in the southeast pacific ocean this isopycnal range which includes the densest subantarctic mode water samw formed in this region is mostly below the mixed layer and so experiences little direct air sea forcing data from two cruises in the southeast pacific were examined for evidence of cross frontal exchange numerous eddies and intrusions containing polar frontal zone pfz water were observed north of the saf as well as a fresh surface layer during the summer cruise that was likely due to ekman transport these features penetrated north of the saf even though the potential vorticity structure of the saf should have acted as a barrier to exchange an optimum multiparameter omp analysis incorporating a range of observed properties was used to estimate the cumulative cross frontal exchange the omp analysis revealed an along front increase in pfz water fractional content in the region north of the saf between the 27 1 and 27 3 kg m 3 isopycnals the increase was approximately 0 13 for every 15 of longitude between the 27 0 and 27 1 kg m 3 isopycnals the increase was approximately 0 15 for every 15 of longitude a simple bulk calculation revealed that this magnitude of cross frontal exchange could have caused the downstream evolution of samw temperature and salinity properties observed by argo profiling floats

sources and transport of the deep western boundary current east of the kerguelen plateau east of the kerguelen plateau a deep western boundary current in the australian antarctic basin brings cold dense waters north from the margins of antarctica geostrophic velocities referenced to acoustic doppler cur rent proler data both shipboard and lowered suggest the flow is unidirectional throughout the water column with es timated northwestward transport below potential temper ature 1 co f 28 7x1 0 6 m 3 s 1 and 49 9x1 0 6 m 3 s 1 respectively hydrographic and acoustic doppler current proler data show that the deep boundary current is sup plied by northward flow emerging from the confluence of westward flow along the antarctic continental slope and eastward flow of weddell basin waters through the princess elizabeth trough to the south of the kerguelen plateau 1 0 to 0 5 0 2 1 1 3 1 4 61 7 8 42 5 0 5 to 0 0 2 0 0 3 3 2 8 41 9 14 52 3 0 0 to 0 5 8 1 3 6 1 4 15 03 2 26 04 4 1 0 to 0 5 10 3 2 2 7 7 28 06 7 48 99 4

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

surficial deep sea sediments across the polar frontal system southern ocean indian sector particulate carbon content and microphyte signatures abstract two main subjects are addressed in this study concerning a complex sub antarctic hydrological system during the antares i md75 cruise southern ocean indian sector 1 the 13 c org signature in waters fluffs and sediments and their relationships with anthropogenic effects and 2 the degree of preservation of the deep sea phytodetritus a north to south gradient was observed for the deep sea microphytes signatures with the higher concentrations in the higher latitude chaetoceros spores dominant species chaetoceros cf neglectus were abundant in the fluffy layers from the permanent open ocean zone pooz and associated with the highest chl a concentration the diatom spores were absent in the northern part of that transect the coccolith repartition and preservation also showed a latitudinal gradient the presence of coccoliths more or less intact below the lysocline may result from different sedimentation rates along this gradient undisturbed and thick fluffs in the pooz and southern polar frontal zone stations were enriched with coccoliths and chaetoceros resting spores even at 4700 m and the revival experiments demonstrated their recent origin via a possible in mass or in pulse sedimentation a latitudinal gradient clearly appeared for 13 c org poc and chloropigments with a relationship between 13 c org and chl a direct positive for the phytoplankton and indirect negative for the fluffs and sediments these observed gradients are in part attributed to the latitudinal effects and to the physical characteristic of the water bodies differences between plankton and sediment 13 c org signatures are attributed to an anthropogenic influence however diagenetic processes leading to slight 13 c org enrichment in sediments cannot be absolutely rejected at this stage a stronger deep northward advection to the north of the polar front may also in part explain these north to south bio geochemical deep sea gradients

variability of the antarctic circumpolar current transport through the fawn trough kerguelen plateau abstract the kerguelen plateau is a major topographic obstacle to the eastward flowing antarctic circumpolar current acc while approximately two third of the acc transport is diverted to the north most of the remaining flow engulfs in the fawn trough the only deep passage across the plateau as part of the track transport across the kerguelen plateau project three mooring lines of current meters were deployed in the fawn trough for one year in february 2009 underneath ground track 94 of the jason 2 satellite altimeter full depth ctd ladcp casts carried out during the deployment cruise were previously analyzed to provide a comprehensive description of the regional circulation featuring in particular a volume transport of 43 sv across the fawn trough park et al 2009 here we present a time series of the transport in the fawn trough estimated from current meter observations featuring a mean eastward transport of 34 sv possibly biased low by at most 5 sv and a root mean squared variability of 6 sv consistent with ladcp estimates 43 sv in february 2009 and 38 sv in january 2010 in addition we analyze to what extent the transport can be directly monitored from along track satellite altimeter data which would enable study of the variability of the fawn trough current from a now 20 year long archive the ability to reconstruct the flow from a limited set of moored instruments as well as from altimeter derived surface geostrophic velocity is further assessed from synthetic data extracted from a high resolution peri antarctic simulation while a canonical method to derive transport from altimetry previously applied to the malvinas current gives here unsatisfactory comparisons with in situ estimates an ad hoc approach using only the two northernmost mooring lines yields an estimate well correlated 0 8 with in situ transport at subseasonal time scales during the one year period of observations at interannual time scales however both methods provide significantly correlated 0 7 transport estimates suggesting that long term transport fluctuations across the kerguelen plateau can be confidently estimated from altimetry these consistently indicate a measurable impact of the outstanding 1997 1998 el nino southern oscillation enso event yielding an increase of the annual mean transport of 3 sv possibly with a one year lag the transport estimate based on the ad hoc approach is significantly correlated 0 6 with the southern annular mode sam index at interannual time scales suggesting that an intensification of the circumpolar winds drives an increase in the transport across the kerguelen plateau

observations of the antarctic circumpolar current over the udintsev fracture zone the narrowest choke point in the southern ocean an up to date map of the antarctic circumpolar current acc fronts is constructed from the latest version of mean dynamic topography mdt from satellite altimetry and reveals the narrowest acc width in the udintsev fracture zone ufz with the strongest concentration of the three major acc fronts within a limited distance as short as 170 km about 40 narrower than that at drake passage at 144 w at the entrance of the ufz which lies between the pacific antarctic ridge par and its eastwardly offset segment offset par segment there is a triple confluence of the subantarctic front polar front and southern acc front downstream of this longitude the subantarctic front progressively meanders northward over the relatively shallow offset par segment before channeling through the eltanin fracture zone thus diverging from the polar front which proceeds through the ufz in situ observations from two recent cruises at 144 w confirm the satellite altimetry derived frontal circulation in the ufz region and yield a baroclinic transport relative to the bottom of 113 10 6 m 3 s comparable to that through drake passage the hydrographic sections show no antarctic bottom water colder than 0 2 c characteristics of major water masses are described and the implications for their potential downstream modifications at drake passage are discussed in terms of the meridional overturning circulation across the acc mesoscale eddy activity with periods shorter than 90 days is predominantly concentrated in the immediate downstream area of the offset par segment suggesting a substantial poleward eddy heat flux there

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

frontal structure water masses and circulation in the crozet basin due to topographic steering by the crozet and kerguelen plateaus the antarctic circumpolar current acc core in the crozet basin area is shifted to its northernmost position in the southern ocean along the southern limb of the south indian subtropical gyre here the jet like current is embedded within a narrow band 26 5 kg m3 in the western half of the basin and heavier mode 26 7 kg m3 in its eastern half these different varieties of crozet basin mode water are closely correlated with the degree of exchange and mixing between subtropical and subantarctic waters along the dynamically active frontal zone the area north of the kerguelen plateau appears to be an important source of water mass modification antarctic intermediate water advected from the west also undergoes there significant modification by intrusions across the frontal zone of fresher oxygen richer colder subantarctic water energetic eddy activities observed along the frontal zone likely enhance such cross frontal exchange of water masses equatorward spreading of the modified thermocline water masses mode water antarctic intermediate water occurs as part of the anticyclonic circulation in the south indian subtropical gyre which is centered within the basin strong injection of north indian deep water into the acc south of amsterdam island is clearly evidenced for the first time this deep oxygen minimum water centered at about 3000 m can be traced to the east of madagascar from where it spreads southward through the eastern part of the crozet basin due to the influence of this water mass north atlantic deep water characteristics of the circumpolar deep water are significantly altered in kerguelen amsterdam passage our results indicate a cyclonic deep level circulation pattern in the crozet basin with a northward flow 9 sv of circumpolar deep water antarctic bottom water as a deep western boundary current and a partially compensating southward flow 3 sv of north indian deep water through the eastern part of the basin it is concluded that the crozet basin constitutes an important passage for the exchange of water masses between the southern ocean and the indian ocean

winter mixed layer entrainment of weddell deep water observations from the somov during the us ussr weddell polynya expedition show that the mixed layer below the sea ice just prior to the austral spring retreat in the 60 s greenwich meridian region has an oxygen content of 7 4 ml 1 this is 86 of full oxygen saturation representing an oxygen deficit relative to full saturation of 1 1 ml 1 the source of this deficit is believed to be a consequence of oxygen poor 4 5 ml 1 weddell deep water wdw entrainment by the winter mixed layer assuming effective cutoff of ocean atmosphere oxygen exchange by the nearly complete snow and sea ice cover with no net impact of oxygen content as a result of biological factors a mixing ratio of 1 3 for wdw to beginning of winter surface water is required to explain the end of winter mixed layer oxygen content accompanying the wdw transfer into the mixed layer is heat transfer of approximately 7 103 cal cm2 2 9 108 j m2 during the five winter months of sea ice coverage as well as salt transfer which requires 34 cm of fresh water to produce typical mixed layer salinity during the seven ice free months when entrainment is expected to be minor diffusive heat and salt flux continues a mean annual heat flux of 12 w m2 is suggested with an annual demand for freshwater of 46 cm yr consideration of the winter period salinity budget indicates net sea ice melting of 20 cm which can be attributed to regional convergence of sea ice the remaining freshwater is derived from excess precipitation and possibly iceberg melt oxygen undersaturation of the winter surface water suggests slightly less potential for abyssal water ventilation than might be expected from a fully saturated condition

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

intermediate depth circulation of the indian and south pacific oceans measured by autonomous floats as part of the world ocean circulation experiment 306 autonomous floats were deployed in the tropical and south pacific ocean and 228 were deployed in the indian ocean to observe the basinwide circulation near 900 m depth mean velocities seasonal variability and lateral eddy diffusivity from the resultant 2583 float years of data are presented area averages local function fits and a novel application of objective mapping are used to estimate the mean circulation patterns of mean circulation resemble those at the surface in both basins well developed subtropical gyres twice as strong in the indian ocean as in the pacific feed western boundary currents tropical gyres are separated by eastward flow along the equator in both hemispheres of both basins although the indian subcontinent splits the north indian tropical gyre the antarctic circumpolar current acc and west wind drifts are prominent in both basins generally tending slightly southward but deviating to the north behind the del cano kerguelen and campbell plateaus and of course south america remarkably the eastern boundaries of the southern subtropical gyres in all three basins apparently occur in the ocean interior away from land the indian ocean s subtropical gyre and perhaps part of the south atlantic s reaches east to a retroflection just upstream of the campbell plateau south of new zealand seasonal variability at 900 m is focused around the equator with weaker variability found near certain bathymetric features there is a remarkable agreement between the observed seasonable variability and that predicted by the jet propulsion laboratory jpl estimating the circulation and climate of the ocean ecco data assimilating numerical model aside from seasonal effects eddy variability is greatest along the equator in tropical and subtropical western basins and along the acc integrals of velocity across regional passages tasman sea mozambique channel provide useful reference for hydrographic analyses of transport across whole ocean basins however the uncertainty associated with the appropriate continuity relation for horizontal flow e g geostrophy vs nondivergence is comparable to the mean flow

circumpolar structure and distribution of the antarctic circumpolar current fronts 1 mean circumpolar paths 1 high resolution hydrographic sections and maps of the gradient of sea surface height ssh reveal that the antarctic circumpolar current acc consists of multiple jets or frontal filaments here we use a 15 year time series of ssh observations to determine the circumpolar structure and distribution of the acc fronts the jets are consistently aligned with particular streamlines along the entire circumpolar path confirming and extending the results of an earlier study restricted to the region south of australia the intensity of the fronts as measured by the cross front gradient of ssh varies along the fronts and the individual branches merge and diverge often in response to interactions with bathymetry maps of absolute velocity at 1000 m depth derived from argo trajectories confirm the existence of multiple current cores throughout the southern ocean high resolution hydrographic sections and profiles of temperature and salinity from argo floats are used to show that the front locations derived from fitting ssh contours to maps of ssh gradient are consistent with locations inferred from the traditional criteria based on water mass properties suitably modified to account for multiple frontal branches three regions are examined in detail the crozet plateau the kerguelen plateau and the scotia sea these examples show how recognition of the multiple jets of the acc can help resolve discrepancies between previous studies of acc fronts

structure and transport of the antarctic circumpolar current and agulhas return current at 40 e hydrographic data are presented from a near meridional section across the agulhas return current the subtropical front and the antarctic circumpolar current acc in the southwest indian sector of the southern ocean the location and characteristics of the fronts are examined and the water masses are defined the agulhas return current emerges as a strong current as far east as 40 e which forms a marked front that is separate from the subtropical front and can be distinguished by a separate water mass comparisons are made with a similar hydrographic section at the greenwich meridian and several notable differences are found the subantarctic front at the greenwich meridian is a pronounced feature carrying a large proportion of the geostrophic transport of the acc on the southwest indian section however the subantarctic front is merged with the polar front at 48 s where the flow associated with the acc is concentrated geostrophic calculations show a large volume transport 84 to 103 sverdrup 1 sv 106 m3 s 1 associated with the agulhas return current at 40 s this is quite separate from the transport of the acc which totals 138 sv south of the subantarctic zone and the crozet plateau or 150 sv including flow in the subantarctic zone the transport of the acc out of the south atlantic sector appears to be higher than the transport into the south atlantic sector at drake passage with the extra transport most probably carried by upper layer and intermediate waters eddies are seen to be an important feature of the subantarctic zone where they help to modify the water masses antarctic intermediate water appears in two forms a saline 34 4 indian ocean variety and a fresh 34 2 atlantic ocean variety the atlantic variety is freshest at the polar front and occupies the southern half of the subantarctic zone within the eddies in the central subantarctic zone there is interleaving between these two forms of antarctic intermediate water north atlantic deep water is unable to cross the southwest indian ridge but can pass south of the crozet plateau in the form of circumpolar deep water which is slightly more saline 34 75 than at drake passage 34 73

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

water mass and biogeochemical variability in the kerguelen sector of the southern ocean a machine learning approach for a mixing hot spot author s rosso isabella mazloff matthew r talley lynne d purkey sarah g freeman natalie m maze guillaume

antares i a biogeochemical study of the indian sector of the southern ocean abstract the first expedition of the antares program the french contribution to southern jgofs investigated the biology and the chemistry of the benthic environment and the water column in a region located between 60 s 72 e and 39 s 55 e in this special issue we present a detailed description of the transports of water masses across the polar front zone which are corroborated by chemical and microbial tracer studies a description of the sediment water interface bridging biological chemical and microbial studies and new insights into the diagenesis of biogenic silica

the south indian ocean current in this paper the historical hydrographic database for the south indian ocean is used to investigate i the hydrographic boundary between the subtropical gyre and the antarctic circumpolar current acc the subtropical front stf and especially ii the southern current band of the gyre a current band of increased zonal speeds in the upper 1000 m is found just north of the stf in the west near south africa and at the surface stf in the open indian ocean until the waters off the coast of australia are reached as neither any other investigation of this current nor a name for it are known the flow has been called the south indian ocean current sioc this name is anologous to the same current band in the south atlantic ocean the south atlantic current the stf is located in the entire south indian ocean near 40 degrees s the associated current band of increased zonal speeds is the sioc which is found at or north of the stf east of 100 degrees e the sioc separates from the stf and continues to the northeast the zonal flow south of the stf is normally weak and serves to separate the south indian ocean and circumpolar currents near africa the sioc has a typical volume transport of 60 sv 1 sv 10 6 m3 s 1 in the upper 1000 m relative to deep potential density surfaces of sigma 4 45 87 kg m 3 2800 3500 m or sigma 2 36 94 kg m 3 1500 2500 m near western australia the sioc is reduced to about 10 sv as it turns to the northeast

a linear decomposition of the southern ocean thermohaline structure the thermohaline structure of the southern ocean is deeply influenced by the presence of the antarctic circumpolar current acc where water masses of the world ocean are advected transformed and redistributed to the other basins it remains a challenge to describe and visualize the complex 3d pattern of this circulation and its associated tracer distribution here a simple framework is presented to analyze the southern ocean thermohaline structure a functional principal component analysis pca is applied to temperature and salinity s profiles to determine the main spatial patterns of their variations using the southern ocean state estimate sose this study determines the vertical modes describing the southern ocean thermohaline structure between 5 and 2000 m the first two modes explain 92 of the combined s variance thus providing a surprisingly good approximation of the thermohaline properties in the southern ocean the first mode 72 of total variance accurately describes the north south property gradients the second mode 20 mostly describes salinity at 500 m in the region of antarctic intermediate water formation these two modes present circumpolar patterns that can be closely related with standard frontal definitions by projecting any given hydrographic profile onto the sose based modes it is possible to determine its position relative to the fronts the projection is successfully applied on the hydrographic profiles of the woce sr3 section the southern ocean thermohaline decomposition provides an objective way to define water mass boundaries and their spatial variability and has useful application for comparing model output with observations

a quasi synoptic view of the frontal circulation in the crozet basin during the antares 4 cruise abstract with the major objective of estimating the secondary vertical circulation a fine grid survey of hydrographic and current fields across the crozet basin frontal zone was made as a physical component of the multidisciplinary antares 4 cruise this frontal zone forms the boundary of the antarctic circumpolar current and the agulhas return current with the quasi permanent existence of strong eddy activity prior to any quantitative diagnosis of the vertical circulation from the fine grid data it is necessary to place the mesoscale circulation and its time variability of the survey area within the basin wide context we give a quasi synoptic view of the ambient frontal circulation during the cruise period using satellite derived chlorophyll concentrations and sea surface temperature particular emphasis is placed on evaluation of the degree of synopticity of our fine grid measurements by comparing mesoscale features on satellite images the limited survey area 1 5 latitude 2 longitude lies precisely within the southernmost and easternmost convergent zone of the two current systems cutting across mesoscale meanders having typical wavelengths of 400 km and periods of 4 months both these satellite images and topex poseidon sea surface height data indicate little temporal variability of the survey area during the 14 days of measurement although fortuitous this quasi steady state of circulation enables us to use the ensemble of fine grid data as a set of synoptic data for diagnosing the vertical circulation using quasi geostrophic dynamics preliminary analysis of the horizontal and vertical hydrographic structure of the fine grid hints at the existence of wave like cross frontal intrusions having a mean along front wavelength of about 30 km

the circulation and water masses of the antarctic shelf and continental slope between 30 and 80 e abstract the circulation and water masses from the antarctic continental shelf to 62 s between 30 and 80 e are described using hydrographic data collected on seven hydrographic sections during the baseline research on oceanography krill and the environment west broke west experiment the eastern limb of the weddell gyre dominates circulation between 30 and 40 e and is significantly cooler and fresher than the region to the east the antarctic circumpolar current acc extends from the north into the survey region east of 40 e reaching as far south as 65 5 s at 60 e this results in increasing observed maximum temperature and salinities progressively towards the east peaking at 80 e due to the intrusion of the southern acc front saccf to 63 s this southward extension is steered by the southern end of kerguelen plateau causing a horizontal shear of over 0 15 m s 1 between the eastward acc and westward flowing antarctic slope current asc the asc is observed at all six meridional sections immediately north of the shelf break it is strongly barotropic and transports a total of 15 8 7 4 sv westwards while the bottom referenced baroclinic component only contributes 1 3 0 3 sv at each section this current intensifies to a narrow westward jet with absolute velocities up to 0 3 m s 1 over the steepest shelf slope gradients at 70 e a v shape is observed in the asf this and the nearby presence of denser shelf water and ice shelf water is characteristic of antarctic bottom water aabw formation but no new aabw is found on this section instead significantly warmer saltier and less oxygenated aabw to the east and newly formed aabw high on the continental slope immediately to the west suggest a formation region just west of 70 e this newly formed aabw progressively becomes warmer and saltier west of 60 e and is observed extending offshore and moving westward below eastward flowing water masses acc frontal positions are found to be 1 2 farther north in the survey region than suggested by historical climatology

the isotopic composition of diatom bound nitrogen in southern ocean sediments treatment of diatom microfossils from southern ocean sediments with hot perchloric acid leaves a diatom bound n fraction which is 0 4 lower in 15n than the bulk sediment typically 3 lower in recent antarctic diatom ooze results from southern ocean surface sediments indicate that early diagenetic changes in bulk sediment n content and 15n are not reflected in diatom bound n suggesting that diatom bound n is physically protected from early diagenesis by the microfossil matrix a meridional transect of multicores from the indian sector of the southern ocean shows a northward increase in the 15n of diatom bound n suggesting that diatom bound 15n like bulk sedimentary 15n varies with nitrate utilization in the overlying surface waters the 15n of diatom bound n is 3 4 higher in glacial age antarctic sediments than in holocene sediments supporting the hypothesis previously based on bulk sediment 15n that nitrate utilization in the surface antarctic was higher during the last ice age while there are important uncertainties the inferred range of utilization changes could potentially explain the entire 80 ppm amplitude of observed glacial interglacial variations in atmospheric co2

measurement and analysis of dissolution patterns in rock fractures 1 nuclear magnetic resonance imaging nmri is applied to noninvasively measure flow and dissolution patterns in natural rough walled water saturated halite fractures three dimensional images of water density and flow velocity acquired with nmri allow quantification of the developing fracture morphology and flow patterns the flow patterns are correlated strongly to the local apertures and the large scale wall roughness the correlations of the dissolution patterns to the fracture morphology flow patterns and mineralogical composition of the rock matrix are a function of the overall dimensionless damkohler number at high damkohler numbers the dissolution patterns are dominated by the flow structure in addition at high damkohler numbers buoyancy stratified flow becomes important in such cases the dissolution patterns also depend on the orientation and elevation of the fracture walls resulting in preferential upward dissolution at low damkohler numbers the dissolution patterns depend mainly on the mineralogical composition of the rock matrix these findings suggest that coupled flow and dissolution processes are much more complex and unpredictable than commonly assumed even under simplified conditions

a tale of three islands downstream natural iron fertilization in the southern ocean iron limitation of primary productivity prevails across much of the southern ocean but there are exceptions in particular the phytoplankton blooms associated with the kerguelen plateau crozet islands and south georgia these blooms occur annually fertilized by iron and nutrient rich shelf waters that are transported downstream from the islands here we use a highresolution 1 12 ocean general circulation model and lagrangian particle tracking to investigate whether inter annual variability in the potential lateral advection of iron could explain the inter annual variability in the spatial extent of the blooms comparison with ocean color data 1998 to 2007 suggests that iron fertilization via advection can explain the extent of each island s annual bloom but only the inter annual variability of the crozet bloom the area that could potentially be fertilized by iron from kerguelen was much larger than the bloom suggesting that there is another primary limiting factor potentially silicate that controls the inter annual variability of bloom spatial extent for south georgia there are differences in the year to year timing of advection and consequently fertilization but no clear explanation of the inter annual variability observed in the bloom s spatial extent has been identified the model results suggest that the kerguelen and crozet blooms are terminated by nutrient exhaustion probably iron and or silicate whereas the deepening of the mixed layer in winter terminates the south georgia bloom therefore iron fertilization via lateral advection alone can explain the annual variability of the crozet bloom but not fully that of the kerguelen and south georgia blooms this article is protected by copyright all rights reserved

distribution of dissolved iron during the natural iron fertilization experiment keops kerguelen plateau southern ocean abstract the southern ocean is the largest high nutrient low chlorophyll hnlc region of the world ocean it is now well recognized that the low biological productivity in this region is mainly due to the limitation of phytoplankton growth by iron however in the core of the southern ocean a massive bloom occurs annually above the kerguelen plateau in the context of keops kerguelen plateau and ocean compared study we investigated the three dimensional distribution of dissolved iron dfe concentrations southeast of the island we show that in surface waters dfe was low and not significantly different above and outside the plateau 0 090 0 034 and 0 073 0 014 nm respectively by contrast below 150 m major differences in vertical profiles of dfe were observed the deep waters above the plateau were clearly enriched with dfe concentrations up to 0 6 nm near the seafloor the regeneration from sinking biogenic material and the input from the sediments are very likely the major processes delivering dfe to the deep water the deep iron rich reservoir existing above the plateau was responsible for the natural iron fertilization of the surface water by two different mechanisms i winter mixing provided 5 times more dfe to the surface waters above the plateau than outside and ii enhanced vertical gradients of dfe and elevated vertical diffusivity resulted in an 8 fold higher diapycnal diffusive flux the natural iron fertilization presented major differences from artificial iron fertilization experiments carried out in the southern ocean the amount of dfe required to stimulate the biological activity is much less and the mode of addition is clearly different the quantification of the excess of dfe supplied in the naturally fertilized area leads to the conclusion that the natural iron fertilization is 10 150 times more efficient to export carbon below 200 m than in artificial fertilization experiments the bloom above the kerguelen plateau was contingent to iron fertilization but it was also sustained by continuous input of major nutrients thus the natural fertilization described here mimics quite well glacial period scenarios where iron fertilization of the southern ocean might have occurred from below

shear enhanced nonlinear flow in rough walled rock fractures abstract nonlinear flow in 3d rough walled rock fractures is simulated by solving the navier stokes equations the emphasis is on the impact of shear caused aperture changes variable apertures and asperity contacts and flow conditions inertial term upon nonlinear flow behavior in order to compare shear effects two 3d fracture models with and without shear were established with identical initial rough walled surfaces topographies of a realistic rock sample five groups of simulations with different inflow boundary conditions of flowrates reynolds numbers re were conducted to demonstrate shear enhanced nonlinearity of flow fields and limitations of local cubic law lcl approach the flow results clearly show channeling flow along the preferential paths transverse flow around the contact spots and eddy flows behind contact spots with increasing re which cannot be observed in 2d models the effective transmissivity of the 3d fracture model was calculated from the modeling results of velocity and pressure fields the results showed that the effective transmissivity is a function of local apertures with important uncertainties even when re is small i e re 0 4 in this study thus the validity of the transmissivity evaluation using lcl approach for nonlinear flow in 3d rough walled rock fractures is questionable

determination of the surface geostrophic velocity field from satellite altimetry 1 presently available marine geoid models are not accurate enough to extract the mean surface circulation directly from satellite altimetry a novel method for estimating the mean velocity field of major ocean current systems is derived from the free surface boundary condition with a given quasi geostrophic balance for the horizontal surface flow a scaling analysis of this boundary condition indicates that although the vertical velocity w is mostly balanced by the local change of the free surface t useful information on the mean current is contained in a small ageostrophic departure t w our method consists in the development of a simple algebraic equation with two unknowns and an adjustable parameter associated with t assuming that the latter is proportional to t w most interestingly t and all other coefficients of the equation can be determined from altimetry the altimeter data used is combined topex poseidon ers gridded data and the solution is obtained by least squares minimizing the contribution from the time variable part of the parameter and prescribing the zonal direction of the mean current the method which is found to be particularly useful for quasi zonal high energy current systems has been validated against direct observations in the gulf stream and southern ocean comparisons with direct observations and monte carlo experiments suggest an overall solution error of about 10 cm s 1 once calibrated against regional velocity statistics this method will be able to determine from altimetry the mean or instantaneous surface velocity field down to the frontal scale with a realism that has been inaccessible because of the geoid constraint

tracer transport in fractured crystalline rock evidence of nondiffusive breakthrough tailing extended tailing of tracer breakthrough is often observed in pulse injection tracer tests conducted in fractured geologic media this behavior has been attributed to diffusive exchange of tracer between mobile fluids traveling through channels in fractures and relatively stagnant fluid between fluid channels along fracture walls or within the bulk matrix we present a field example where tracer breakthrough tailing apparently results from nondiffusive transport tracer tests were conducted in a fractured crystalline rock using both a convergent and weak dipole injection and pumping scheme deuterated water bromide and pentafluorobenzoic acid were selected as tracers for their wide range in molecular diffusivity the late time behavior of the normalized breakthrough curves were consistent for all tracers even when the pumping rate was changed the lack of separation between tracers of varying diffusivity indicates that strong breakthrough tailing in fractured geologic media may be caused by advective transport processes this finding has implications for the interpretation of tracer tests designed to measure matrix diffusion in situ and the prediction of contaminant transport in fractured rock

zinc and nickel isotopes in seawater from the indian sector of the southern ocean the impact of natural iron fertilization versus southern ocean hydrography and biogeochemistry abstract the southern ocean is the site of 20 of global ocean carbon export and the origin of water masses that significantly impact the chemistry of the global ocean much of the southern ocean is a high nutrient low chlorophyll hnlc region iron is the primary limiting nutrient for phytoplankton growth and may also be an important control on the biogeochemistry of the water masses emanating from the southern ocean here we investigate the response of zn and ni and their isotopes to natural fe fertilization from southern ocean islands using samples collected during the keops 2 oct nov 2011 program in the early austral spring near the kerguelen plateau indian sector of the southern ocean zinc and ni concentrations show depth distributions and relationships to major nutrients that are very similar to published data from the atlantic sector of the southern ocean away from island fertilization as in the atlantic sector and other regions outside the southern ocean there is a slight minimum in 66zn at about 100 150 m depth and a slightly heavier value at the surface at the keops 2 sites the light sub surface zn isotopes occur at the depth level where measured chl a has declined to near zero the heaviest zn isotope values in either the atlantic or indian sectors occur in bottom waters are associated with samples that show high dissolved si relative to zn these latter represent possible evidence for a heavy input directly to deep water or from sediment and the zn si 66zn systematics are consistent with a source in diatom opal nickel concentrations show much less variation than those of zn with the most depleted surface value only 15 20 lower than those in upwelled deep water in the southern ocean these small variations in ni concentration are associated with no significant variability in ni isotopes as also previously observed in the atlantic sector overall the key feature of the dataset is the apparent absence of any significant impact of natural fe fertilization on the distribution of zn and ni with the dominant control being the station location relative to the polar front in both the atlantic and indian sectors zinc and ni isotopes are invariant in surface waters whether inside or outside the fertilized zone and whether south or north of the polar front this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

contrasting structural histories of the salmon river belt and wallowa terrane implications for terrane accretion in northeastern oregon and west central idaho the salmon river belt is composed of metamorphic tectonites with poorly dated mesozoic and paleozoic protoliths that lie between volcanic arc assemblages of northeastern oregon and the western margin of the north american continent in west central idaho to the west the salmon river belt overlies late paleozoic and mesozoic volcanic arc rocks of the wallowa terrane on a shallowly east dipping fault to the east the belt is separated from north american rocks by the western idaho shear zone the salmon river belt is divided into western and eastern assemblages composed of greenschist and amphibolit facies metamorphic tectonites respectively and is deformed in three and locally four generations of penetrative structures first generation structures are synmetamorphic west vergent tight to isoclinal folds with a penetrative axial planar cleavage and downdip stretching lineation second and third phase structures are postmetamorphic and consist of open to close upright to slightly overturned folds with north south and east west trending penetrative axial planar cleavages respectively low angle faults truncate metamorphic structures within the salmon river belt and juxtapose rocks with different metamorphic grades the faults formed together with second generation structures and are deformed by third generation folds the age of metamorphic and postmetamorphic structures is constrained by deformed carbonate rocks of late triassic age and clastic rocks of late early jurassic age and by the ca 145 ma emplacement of an undeformed tonalitic pluton along the eastern margin of the salmon river belt structures are overprinted and transposed by a younger steeply east dipping mylonitic shear zone the mid cretaceous western idaho shear zone synmetamorphic structures within the salmon river belt formed before amalgamation of the wallowa terrane and the north american fringing arc complex and developed as part of a regional belt of intra arc metamorphic tectonites the pr cretaceous docking of the wallowa terrane is recorded within the salmon river belt by development of postmetamorphic structures and predates formation of the western idaho shear zone the western idaho shear zone formed after the amalgamation of the arc terranes and records the intraplate deformation associated with the collapse of the fringing arc and back arc basin system

effect of fracture aperture variations on the dispersion of contaminants dispersion of dissolved contaminants in fractured rocks is strongly dependent on the variability of fracture aperture large fracture aperture regions result in significant channeling of the fluid flow accelerating the movement of solutes in a particular direction which may differ locally with respect to the main flow direction from high to low hydraulic potential this may result in very early breakthrough of the contaminants significantly earlier than in the conventional parallel plate simplification of fluid flow in fractured systems in addition flow and transport in the low aperture regions can be orders of magnitude smaller which has major implications for remediating contaminated fractured media in this study we observed the transport of a nonsorbing solute in a naturally fractured rock which was characterized at very high resolution using computed tomography scanning to determine the fracture aperture distribution we compared the observed breakthrough curve of the solute at various flow rates with the predicted breakthrough curve using the fracture s geostatistics and small perturbation analysis as well as direct numerical simulation of flow through the fracture using the measured fracture aperture distribution the experimentally determined fracture transmissivity and dispersivity are within a factor of 2 of those predicted using either the small perturbation approach using the fracture geostatistics or explicit numerical modeling of breakthrough which differ by around 20 indicating that the geostatistics of the fracture aperture can be used to predict the approximate shape of the breakthrough curve for a fracture

large scale circulation over and around the northern kerguelen plateau abstract the kerguelen plateau is known to constitute a major barrier to the eastward flowing antarctic circumpolar current however there is limited knowledge on the regional circulation due to sparse observations especially in the northern kerguelen plateau between the fawn trough and the kerguelen islands as part of the physical component of the multidisciplinary keops cruise systematic ctd measurements along three sw ne oriented sections were made on the latter plateau cutting through the annual phytoplankton bloom across the eastern flank of the plateau into deep water major hydrographic features and geostrophic velocities perpendicular to the sections were first documented from these in situ observations in order to interpret the results within the general circulation context and to trace the upstream pathways of the observed water masses we established a synthetic picture of the large scale circulation over and around the entire northern kerguelen plateau using the combination of new data from keops with historical hydrographic data together with all available information on mid depth and near surface velocities derived from autonomous floats surface drifting buoys and satellite altimetry this synthesis shows that the time mean geostrophic flow over the shallow platform is sluggish of the order of 3 5 cm s 1 with a general anticyclonic circulation roughly following the local bathymetry this weak flow is bordered to the east by relatively strong up to 18 cm s 1 northwestward flow along the eastern flank of the northern kerguelen plateau due to a northward bifurcation of cold antarctic waters of eastern enderby basin origin carried by the powerful fawn trough current we have shown the utmost importance of the general circulation for the spatial distribution of primary productivity in that the sluggish circulation over the complex shallow topography of the northern kerguelen plateau may precondition the recurrence of annual blooms in contrast to neighboring strong advective regimes without blooming in deep water

flow dependence of matrix diffusion in highly heterogeneous rock fractures diffusive mass transfer in rock fractures is strongly affected by fluid flow in addition to material properties the flow dependence of matrix diffusion is quantified by a random variable transport resistance denoted as t l and computed from the flow field by following advection trajectories the numerical methodology for simulating fluid flow is mesh free using fup basis functions a generic statistical model is used for the transmissivity field featuring three correlation structures i highly connected non multi gaussian ii poorly connected or disconnected non multi gaussian and iii multi gaussian the moments of are shown to be linear with distance irrespective of the structure after approximately 10 integral scales of ln t percentiles of are found to be linear with the mean when considering all three structures taking advantage of this property a potentially useful relationship is presented between percentiles and the fracture mean water residence time that integrates all structures with high variability it can be used in discrete fracture network simulations where t statistical data on individual fractures are not available

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

internal tides and vertical mixing over the kerguelen plateau within the context of the natural iron fertilization study keops time series measurements of ctd and ladcp profiles at a site 50 6 s 72 e 528 m coinciding with an annual phytoplankton bloom over the kerguelen plateau were made during the january february 2005 keops cruise an important activity of highly nonlinear semidiurnal internal tides having peak to peak isopycnal displacements of up to 80 m is identified these internal tides appear to be a principal agent for promoting elevated vertical mixing indispensable for upward transfer of iron within the seasonal thermocline we estimate local vertical eddy diffusivities of the order of 4 10 4 m2 s 1 using a thorpe scale analysis although this estimate is higher by an order of magnitude than the canonical value o 0 1 10 4 m2 s 1 in the open ocean away from boundaries it is consistent with nonlinear internal wave wave interaction theories as verified by independent diffusivity estimates using the vertical wavenumber spectral methods for shear and strain it is also suggested that the general ocean circulation may play an important role in preconditioning the bloom in that the relatively sluggish circulation over the shallow plateau compared to the much more dynamic neighbouring deep ocean may foster the bloom s observed annual recurrence over the plateau

direct observations of the acc transport across the kerguelen plateau 1 major pathways and transport of the antarctic circumpolar current acc crossing the kerguelen plateau were directly observed during the 2009 track cruise the net eastward transport to the south of the heard mcdonald islands is estimated as 56 sv 1 sv 106 m3 s 1 43 sv of which is tightly channelled into the fawn trough that appears as a predominant cross plateau gateway of circumpolar flow associated with the southern acc front saccf there are also two secondary passages with one 6 sv being attached to the nearshore slope just south of the heard mcdonald islands and the other 7 sv passing through the northern princess elizabeth trough with an additional 2 sv inferred just south of the kerguelen islands the transport across the entire plateau amounts to 58 sv accounting for 40 of the total acc transport transiting through the region 147 152 sv quantities consistent with other independent estimates in the indian sector of the southern ocean

fe binding dissolved organic ligands near the kerguelen archipelago in the southern ocean indian sector abstract during the ke rguelen o cean and p lateau compared s tudy keops january february 2005 cruise the area southeast of the kerguelen archipelago in the indian sector of the southern ocean was investigated to identify the mechanisms of natural iron fertilization of the kerguelen plateau in this study the organic speciation of fe is described samples were determined immediately on board using competing ligand adsorptive cathodic stripping voltammetry cl adcsv the dissolved organic ligands were always in excess of the dissolved fe concentration increasing the residence time in the water column and the potential availability for phytoplankton the concentration of the dissolved organic ligands ranged from 0 44 to 1 61 n eq of m fe complexation site for fe with an average concentration of 0 91 n eq of m fe s d 0 28 n 113 and a mean logarithm of conditional stability constant log k of 21 7 s d 0 28 n 113 a second weaker dissolved organic ligand group was detected in 32 of the samples with fe binding characteristics at the edge of the detection window of the applied method the occurrence of the highest concentrations of dissolved organic ligands in the wind mixed surface layer and near the sediment at the bottom of the water column indicated that both phytoplankton and the sediment act as sources both sources are in concert with the general conclusions from the keops research on the sources of fe where fe was regenerated organic fe binding ligands were formed in the upper layers and both fe and ligands were supplied by the sediment

three dimensional flow measurements in rock fractures nuclear magnetic resonance imaging is applied to measure flow patterns in natural water saturated rough walled rock fractures from three dimensional water density and velocity vector images the fracture morphology and flow patterns are determined the parabolic nature and asymmetry of the velocity profiles and thus the accuracy of local cubic law flow rate predictions vary greatly this depends on the degree of wall roughness particularly complex flow patterns are found in one sample which contains a sharp fracture wall discontinuity a power law for the flow rate versus aperture for the low flow region was found without considering the hydraulic gradients

bottom currents derived from a shipborne adcp on woce cruise a11 in the south atlantic abstract this paper is divided into two parts the first describing an enhancement of the shipborne adcp system and the second describing information about bottom currents that have been obtained therefrom on woce cruise a11 in the south atlantic punta arenas to cape town rrs discovery has been fitted with a gps3df receiver and an array of antennas about its bridge which determine the instantaneous attitude of the ship the heading record from this instrument has been compared with the ship s gyrocompass throughout the 40 day cruise differences have been calculated and examined according to heading speed and movements underway differences are found insensitive to heading except in a southerly sector but on station differences exhibit a sinusoidal dependence on heading with range 3 steaming from a station led to transient behavior with recognizable effects for 1 hour the results are generally consistent with earlier reports and are attributed to gyro error an improved heading measurement has a

evolution of a late mesozoic back arc fold and thrust belt northwestern great basin u s a abstract the luning fencemaker fold and thrust belt was active from the middle or late jurassic through the early cretaceous and involves rocks of the mesozoic marine province of the northwestern great basin rocks of the marine province were deposited in a back arc basin bound on the west by the sierran arc they are underlain by simatic crust formed either in a paleozoic marginal basin formed on the west coast of north america or in an exotic oceanic arc accreted to north america in the permo triassic deposition in the marine province was localized by the underlying simatic crust which later controlled the locus of back arc thrusting to the south in areas of the back arc region overlying continental crust mesozoic rocks are terrestrial volcanic and volcanogenic deposits rocks of this area are not disrupted by thrusts of significant magnitude until the southwestern end of the sevier thrust belt is encountered during contraction the luning fencemaker thrust belt underwent several hundred kilometers of nw se shortening which was not developed in the sierra nevada to the west the arc and back arc regions were separated by a regionally extensive left lateral fault system that was active during back arc thrusting the marine province was partially coupled with the sierra nevada during transpressional motion on the left lateral fault resulting in imbrication and emplacement of the luning fencemaker thrust belt in the continental region to the south decoupling was more complete and only minor thrusting was associated with the southerly displacement of the sierran arc farther south where the paleozoic miogeoclinal hingeline was encountered conditions apparently changed and the sevier thrust belt developed timing relations suggests that the andean type margin of the western united states had paired back arc thrust belts luning fencemaker and sevier for much of the late mesozoic the belts were separated by a region that underwent relatively minor internal shortening the intervening region probably was decoupled at depth and the thrust belts may have shared a decollement development of the luning fencemaker thrust belt and the associated left lateral fault system extended over a period of 40 50 m y and is best explained as a product of plate convergence the nw se shortening axis for the thrust belt and the inferred left slip on the strike slip fault are not compatible with the generally accepted right oblique subduction proposed for the sierran arc since the early triassic they suggest an interval of left oblique convergence for the middle to late jurassic and early cretaceous regionally developed structures indicate a return to right oblique convergence in the late early cretaceous

correlation between groundwater flow and deformation in the fractured carbonate gran sasso aquifer infn underground laboratories central italy the gran sasso massif is a carbonate fractured aquifer with a spring discharge of more than 18 m3 s 1 the water table has been partially drained by two motorway tunnels and an underground laboratory ul located into the core aquifer karst features have limited role below the water table where groundwater flow is mainly regulated by the fracture network two paired laser extensometers ba and bc recorded ground deformation in the ul changes in deformation correlate with the seasonal recharge discharge cycle of groundwater flow and its long term changes hydrostatic conditions prevail during the recharge phases because of the low permeability of local fractures favoring compression and hydraulic gradient increase above the ul fast groundwater flow through the high permeability fault outcropping in the ul can enhance local dilatation for short periods spring discharge during exhaustion periods is fed by the low permeability fracture network fostering hydrodynamic conditions by hydraulic gradient decrease diminishing compression and consequently favoring dilatation independent support to this conceptual model comes from local tests and a numerical model which highlights the hydromechanical strain effects induced by the hydrological cycle on the jointed rock mass along ba and the role of the hydraulic gradient on the rock mass deformation

deep inflow into the mozambique basin more than 200 conductivity temperature depth ctd stations were worked around the southwest indian ridge and del cano rise as part of the world ocean circulation experiment a selection of these data provides information about the inflow of bottom water into the mozambique basin the basin is closed below 3000 m yet the inflow is significantly large of order 1 sv 1 sv 106 m3 s 1 estimates of the basin scale upwelling at 4000 m suggest that the vertical velocity is also large 10 10 5 cm s 1 or more an order of magnitude greater than global ocean estimates examination of the characteristics of the bottom water in the mozambique and agulhas basins and the prince edward fracture zone shows that bottom water enters the mozambique basin from the agulhas basin and also directly from the enderby basin most of the transport enters the mozambique basin via the agulhas basin where two regions of northward flow below 4000 m are found the major flow on the eastern flank of the mozambique ridge is through and above the deep extending 5900 m trench that connects the agulhas and mozambique basins the second weaker flow enters the transkei basin along the deep eastern flank of the agulhas plateau then turning east into the mozambique basin the only source of bottom water to the agulhas basin is the enderby basin but a more direct route between the enderby and mozambique basins exists via the prince edward fracture which extends deeper than 4000 m throughout its length and links the two basins directly across the southwest indian ridge full depth ctd stations trace the changing characteristics of the deep and bottom water in the fracture and moored current meter data show the strength and persistence of the throughflow strong mixing with the overlying deep water elevates the salt content of the bottom water by comparison with the other water in the mozambique basin thus two distinct bottom waters of the mozambique basin originate in the same place the enderby basin and their different characteristics are solely a function of the routes they have taken and the processes encountered along the different pathways

investigation of flow in water saturated rock fractures using nuclear magnetic resonance imaging nmri the application of nuclear magnetic resonance imaging nmri to the direct three dimensional measurement of flow in rough walled water saturated rock fractures is presented for the first time the study demonstrates the abilities of nmri to noninvasively measure rock water interfaces and water flow velocities in these fractures and investigates the effects of wall morphology on flow patterns inside a typical rock fracture two and three dimensional flow encoded spin echo pulse sequences were applied the stability and reproducibility of the water flow patterns were confirmed by analyzing two dimensional velocity images a variety of geometrical and hydraulic features were determined from three dimensional velocity images including the rock water interfaces the fracture aperture distribution and the critical aperture path velocity profiles and volumetric flow rates flow and stagnant regions and the critical velocity path in particular the effects of a sharp step discontinuity of the fracture walls and the applicability of the cubic law were examined as a result of the complex three dimensional geometry velocity profiles are generally parabolic but often highly asymmetric with respect to the fracture walls these asymmetric velocity profiles are clustered together with significant correlations they are not just local random phenomena however theoretical considerations indicate that the effects of the measured asymmetry on volumetric flow rates and hydraulic conductivities are insignificant in that the overall flow inside rough fractures still obeys the cubic law the features discussed in this study emphasize the strong heterogeneity and the highly three dimensional nature of the flow patterns in natural rock fractures and consequently the need for three dimensional flow analysis

roughness decomposition and nonlinear fluid flow in a single rock fracture abstract the objective of this paper is to investigate the effects of wall surface roughness on fluid flow through rock fractures a wavelet analysis technique was developed to define a mathematical criterion for decomposing the original wall surface roughness profiles of a fracture into a high frequency secondary roughness profile and a low frequency primary roughness profile in order to examine their impacts on fluid flow by solving the navier stokes equations nse without linearization using a self developed 2d finite volume method fvm code the results indicate that the high frequency secondary roughness is the main cause for dynamic evolution of eddy flow regions in the fracture flow field besides the reynolds number re in the original fracture model with the high frequency secondary roughness our results show that fluid flow fields are not only generally non linear but also with non stop generation and motions of eddies in the boundary layer regions of rough fractures when the re 1000 in this study which will affect the solute transport processes in fractured rock masses the complete nse were solved without removing acceleration and inertial terms so that the impacts of surface roughness on the nonlinear and dynamic flow behavior of rock fractures were calculated and visualized more accurately which is important for modeling mass and energy transport processes in fractures and fractured rock masses

dissolved rare earth elements tracing lithogenic inputs over the kerguelen plateau southern ocean abstract dissolved rare earth elements rees were measured in the water masses upstream from and over the kerguelen plateau indian sector of the southern ocean upstream from the plateau the ree profiles were consistent with published data from the southern and indian oceans over the plateau a one box model yields a lithogenic nd flux from the dissolution of lithogenic material of 89 20 t nd y 1 and a corresponding dissolved iron input larger than 100 000 t fe y 1 however despite evidence of this significant lithogenic input dissolved fe is strongly depleted in the upper layers contrasting with the enriched ree concentrations this contrast stresses the different behaviours of ree and iron in the surface waters and the fact that strong fertilization does not imply dissolved fe replete waters

on the origins of deep and bottom waters of the indian ocean the characteristics of the deep and bottom waters of the indian ocean when illustrated on potential density anomaly surfaces indicate that the waters enter from both the atlantic and pacific oceans the paths of spreading are constrained by the complex topography and characteristics are seen to be altered by exchange with the overlying and underlying water and with the sediments especially in the northern indian ocean the weddell sea contributes to the densest waters found in the western basins and the ross sea and adelie coast to the densest waters found in the eastern basins both dense water varieties are altered by and incorporated in the less dense water above initially water carried by the circumpolar current then water from the north atlantic and finally by deep water whose characteristics are derived in the northern indian ocean contact with the sediments increases the silica content of the bottom water in the southern ocean in the northern indian ocean the sediments alter the silica of the water at the bottom and together with enhanced salinity from diffusion of saline overflows from the marginal seas above imprint unique markers to the deep water that flows back to the south at middepths the series of ridges between madagascar and australia confine the flow to a series of gyres that carry characteristics from the circumpolar current equatorward and the northern indian ocean characteristics southward within the circumpolar current low oxygen deep water from the pacific is carried across the atlantic and into the indian ocean south of africa part flows around the cyclonic weddell sea gyre and part extends across the southern ocean water from another pacific source can be seen near 2000 m extending westward from the tasman sea south of aus tralia and across the indian ocean and perhaps to the aghulas current region southeast of africa in this study we show some maps of deep and bottom water characteristics of the indian ocean which may be used in a qualitative sense to infer pathways of spreading of water below a depth of about 2000 m the indian ocean has numerous ridges and basins figure 1 that severely restrict possible pathways of deep and bottom wa ter flow in the following we will begin by looking at char acteristics at the bottom of the ocean to reveal the path ways of spreading of the densest bottom waters from basin to basin then a series of six potential density anomaly surfaces at progressively shallower depths from about 4000 m up to about 2000 m will be shown to see what character istics influence the deep waters and how pathways of flow are constrained by the bathymetry of the indian ocean the choice of the specific density levels table 1 was based primarily on various property extrema shown by the 18os atlantis ii cruise 93 colored sections that accompany warren s 1981 detailed discussion of the major features of the central indian ocean between madagascar and aus tralia the sections approximately midway between antarctica and the northern indian ocean boundaries are well positioned to show features originating from both the north and the south as well as some brought into the indi an ocean by the antarctic circumpolar current the full ocean area isopycnal maps provide essential evidence on the origins and fates of features seen in the sections and

paleomagnetic assessment of oroflexural deformation in west central nevada and significance for emplacement of allochthonous assemblages abrupt westerly deflections of north south trending facies boundaries the isopleth of 87sr 86sr 0 076 and arcuate structural trends of paleozoic mesozoic and cenozoic age in the west central basin and range province have been explained by 1 post early jurassic oroflexural folding and shear 2 the existence of a pre late jurassic resistant block along the western continental margin possibly representing late precambrian breakup and 3 regional flexure mina deflection prior to intrusion of late cretaceous plutons which crosscut flexure related structural trends paleomagnetic data gathered from late cretaceous plutons and remagnetized metasedimentary rocks along and north of the northern margin of the zone of east west structural trends are not in support of significant oroflexural folding and attending major clockwise rotation since late cretaceous time the data water canyon pluton d 1 i 57 95 4 k 9 n 132 gunmetal pluton d 354 i 60 95 6 k 21 n 29 east garfield hills pluton d 349 i 74 95 11 k 14 n 12 la panta pluton d 22 i 66 95 10 k 16 n 13 gillis canyon pluton d 354 i 50 95 4 k 20 n 50 and folded units of the excelsior mountains d 309 i 79 95 7 k 12 n 37 are dispersed from expected cretaceous directions for the mina deflection region but they do not conform to a model of major systematic regional clockwise rotation the generally small deflections of unit means from expected directions could be explained by irregular components of late cenozoic tilting and or rotation the paleomagnetic data do not deny the possibility of pre late cretaceous oroclinal bending nevertheless regional structural analysis complimented by the paleomagnetic results indicate that the mina deflection is in all likelihood a primary feature whose geometry reflects the late precambrian fragmentation of western north america structures related to the accretion of allochthonous assemblages between middle devonian and cretaceous time in this part of the cordillera also reflect the primary nature of this feature