evidence for reflectors in the lower continental crust before rifting in the valencia trough the past decade has seen a rapid advance in our understanding of the deep structure of the continental crust especially in europe1 3 australia4 and north america5 where seismic profiling has revealed a highly reflective layer in the lower crust on many profiles the reflective layer is associated with regions of extension6 7 suggesting that the reflectors originate by some form of ductile flow or magmatic intrusion during rifting8 9 to test this hypothesis we have examined geophysical and geological data from the valencia trough a rift basin10 12 of late oligocene early miocene age from a comparison of profiles in different parts of the trough and independent constraints on the initial crustal thickness we argue that the reflective layer in this basin was probably already in the crust before rifting and that a mid tertiary extensional event is not required to explain it

an anticyclonic circulation above the northwest georgia rise southern ocean data from a variety of sources reveal a warm core anticyclonic circulation above the northwest georgia rise nwgr an similar to2000 m high bathymetric feature north of south georgia the sense of the circulation is opposite to the general cyclonic flow in the georgia basin the circulation shows the characteristics of a stratified taylor column dimensional analysis shows that the local bathymetry and hydrography are conducive to the formation of such ers2 altimeter data show that the column whilst not fully permanent is nonetheless a recurring feature high concentrations of chlorophyll a are observed at the centre of the circulation indicating that the modulation of the physical environment has significant consequences for the local biogeochemical system via enhanced primary production enhanced chlorophyll a extends in a long plume from the nwgr along pathways indicated by drifters this passive redistribution may have consequences for the larger basin scale ecosystem

abyssal ocean warming around antarctica strengthens the atlantic overturning circulation the abyssal warming around antarctica is one of the most prominent multidecadal signals of change in the global ocean here we investigate its dynamical impacts on the atlantic meridional overturning circulation amoc by performing a set of experiments with the ocean sea ice model nemo lim2 at 1 2 degrees horizontal resolution the simulations suggest that the ongoing warming of antarctic bottom water aabw already affecting much of the southern hemisphere with a rate of up to 0 05 degrees c decade 1 has important implications for the large scale meridional overturning circulation in the atlantic ocean while the abyssal northward flow of aabw is weakening we find the upper amoc cell to progressively strengthen by 5 10 in response to deep density changes in the south atlantic the simulations suggest that the aabw induced strengthening of the amoc is already extending into the subtropical north atlantic implying that the process may counteract the projected decrease of the amoc in the next decades

contribution of deep seismic profiling to the knowledge of the lower crust in france and neighbouring areas abstract in france and neighbouring areas the crust is essentially formed of segments of the variscan orogen 380 300 ma and older formations cratonic basins began to form in the permian but extensive subsidence only occurred from the lias in basins such as the paris and aquitaine basins and also along the margin of the alpine tethys ocean the pyrenees and alps range eventually formed during the tertiary as a result of the collision between the european and african continental plates large grabens were also rifted in the rhine and rhone valleys deep seismic profiles show remarkable features common to the crust of the whole area although it underwent such a complicated geological history the most striking feature is the occurrence of conspicuous flat reflections densely distributed in the lower part of the crust below a comparatively transparent upper crust these reflections hereafter called laminations have been found to occur on most profiles within a large area covering western europe although they vary in depth thickness and energy dipping reflections have frequently been observed in the upper crust some of them extend across the lower crust and even penetrate into the upper mantle they may be reasonably interpreted as variscan compressional features by correlation with surface geology and comparison with similar features found in deep seismic profiles from other regions the origin of the flat laminations which generally lie in the lower part of the crust is more controversial this paper attempts to use the well known geological history of the region to place some constraints on the hypotheses which may be advanced to explain the formation of these laminations these features may be explained by the following tectonothermal events 1 1 compression which prevailed during the variscan orogeny may have formed the laminations as a result of delamination and shearing near the bottom of the crust associated with melting intrusion and metamorphism during the different stages of the crustal evolution 2 2 the thermal equilibration of the upper mantle which occurred in the permian at the end of the variscan orogeny may have caused metamorphism and magmatism in the overlying crust 3 3 a regional thermal event which might be associated with subordinate extension occurred during the rifting of the alpine tethys and the initiation of mesozoic cratonic basins in late triassic middle jurassic times it may also have caused metamorphism and magmatism in the lower crust while the first model implies conservation of the crust material the other two suggest that the crust mantle transition has been somewhat uplifted since the end of the variscan orogeny the latter hypothesis is one way to explain the undeniable occurrence of seismic events below the present moho reflection the above three models are not mutually exclusive and all these phenomena may well have affected the crust to some extent however the data at hand are still insufficient to determine what parts tectonic and nontectonic processes have played in the creation of the laminations in the lower crust and the moho further experiments are needed to check these hypotheses

surface circulation at the tip of the antarctic peninsula from drifters an array of 40 surface drifters drogued at 15 m depth was deployed in february 2007 to the east of the tip of the antarctic peninsula as part of the antarctic drifter experiment links to isobaths and ecosystems adelie project data obtained from these drifters and from a select number of local historical drifters provide the most detailed observations to date of the surface circulation in the northwestern weddell sea the antarctic slope front asf characterized by a 20 cm s 1 current following the 1000 m isobath is the dominant feature east of the peninsula the slope front bifurcates when it encounters the south scotia ridge with the drifters following one of three paths drifters i are carried westward into bransfield strait ii follow the 1000 m isobath to the east along the southern edge of the south scotia ridge or iii become entrained in a large standing eddy over the south scotia ridge drifters are strongly steered by contours of f h coriolis frequency depth as shown by calculations of the first two moments of displacement in both geographic coordinates and coordinates locally aligned with contours of f h an eddy mean decomposition of the drifter velocities indicates that shear in the mean flow makes the dominant contribution to dispersion in the along f h direction but eddy processes are more important in dispersing particles across contours of f h the results of the adelie study suggest that the circulation near the tip of the antarctic peninsula may influence ecosystem dynamics in the southern ocean through antarctic krill transport and the export of nutrients

preconditioning and formation of maud rise polynyas in a high resolution earth system model abstractopen ocean polynyas oops in the southern ocean are ice free areas within the winter ice pack that are associated with deep convection potentially contributing to the formation of antarct

a seismic refraction study of the quilpie trough and adjacent basement highs eromanga basin eastern australia abstract the jurassic cretaceous eromanga basin in eastern australia is a relatively undisturbed sedimentary sequence covering the devonian quilpie trough and the early palaeozoic canaway ridge and cheepie shelf seismic refraction recording across these three features with additional reflection gravity and well information has been used to determine the velocity structure to a depth of 10 km the thickness of the eromanga basin sequence along the traverse varies between 1 1 and 1 4 km with p wave velocities ranging from 2 0 to 3 8 km s the maximum thickness of the underlying quilpie trough is about 3 8 km but the base of the trough is hard to define the velocities in this devonian sequence range from 4 0 to 5 0 5 5 km s two small bodies with a velocity of 4 0 4 5 km s occur immediately below the eromanga basin sediments on the canaway ridge and the cheepie shelf they may be remnants of devonian sediments on an erosion surface the velocities within the ordovician basement are less below the canaway ridge than under the cheepie shelf and quilpie trough they reach 6 0 km s at 7 km depth below the ridge at 4 km depth under the shelf and at an intermediate depth under the trough from gravity modelling the density of the basement to the quilpie trough increases at a depth of about 7 km this may be related to volcanics found in the basement further north the canaway ridge has a lower density than the cheepie shelf or the basement of the quilpie trough relative vertical movement between these three features may in part be related to these density differences

observations of large scale ocean atmosphere interaction in the southern hemisphere abstract the authors provide a detailed examination of observed ocean atmosphere interaction in the southern hemisphere sh focus is placed on the observed relationships between variability in sh extratropical sea surface temperature sst anomalies the southern annular mode sam and the el nino southern oscillation enso results are examined separately for the warm november april and cold may october seasons and for monthly and weekly time scales it is shown that the signatures of the sam and enso in the sh sst field vary as a function of season both in terms of their amplitudes and structures the role of surface turbulent and ekman heat fluxes in driving seasonal variations in the sam and enso related sst anomalies is investigated analyses of weekly data reveal that variability in the sam tends to precede anomalies in the sst field by 1 week and that the e folding time scale of the sam related sst field anomalies is at least 4 months the persistence of the sam related sst anomalies is

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

p wave velocity features of the lithosphere under the eromanga basin eastern australia including a prominent mid crustal conrad discontinuity abstract the crustal structure of the central eromanga basin in the northern part of the australian tasman geosyncline revealed by coincident seismic reflection and refraction shooting contrasts with some neighbouring regions of the continent the depth to the crust mantle boundary moho of 36 41 km is much less than that under the north australian craton to the northwest 50 55 km and the lachlan fold belt to the southeast 43 51 km but is similar to that under the drummond and bowen basins to the east the seismic velocity boundaries within the crust are sharp compared with the transitional nature of the boundaries under the north australian and lachlan provinces in particular there is a sharp velocity increase at mid crustal depths 21 24 km which has not been observed with such clarity elsewhere in australia the conrad discontinuity in the lower crust the many discontinuous sub horizontal reflections are in marked contrast to lack of reflecting horizons in the upper crust further emphasising the differences between the upper and lower crust the crust mantle boundary moho is characterised by an increase in velocity from 7 1 7 7 km s to a value of 8 15 0 04 km s the depth to the moho under the canaway ridge a prominent basement high is shallower by about 5 km than the regional moho depth there is also no mid crustal horizon under the canaway ridge but there is a very sharp velocity increase at the moho depth of 34 km the ridge could be interpreted as a horst structure extending to at least moho depths but it could also have a different intra crustal structure from the surrounding area the sub crustal lithosphere has features which have been interpreted from limited data as being caused by a velocity gradient at 56 57 km depth with a low velocity zone above it because of the contrasting crustal thicknesses and velocity gradients the lithosphere of the central eromanga basin cannot be considered as an extension of the exposed lachlan fold belt or the north australian craton the lack of seismic reflections from the upper crust indicates no coherent accoustic impedance pattern at wavelengths greater than 100 m consistent with an upper crustal basement of tightly folded meta sedimentary and meta volcanic rocks the crustal structure is consistent with a pericratonic or arc back arc basin being cratonised in an episode of convergent tectonics in the early palaeozoic the seismic reflections from the lower crust indicate that it could have developed in a different tectonic environment

on the fate of the antarctic slope front and the origin of the weddell front 1 data from the deep ocean ventilation through antarctic intermediate layers dovetail and antarctic large scale box analysis and the role of the scotia sea albatross projects are combined in the region of the antarctic peninsula and the south scotia ridge to determine the paths and transports associated with the antarctic coastal current the antarctic slope front and the weddell front the antarctic coastal current flows over the antarctic continental shelf and is not tied to a particular isobath it transports 1 sv westward to the bransfield strait its subsequent course is uncertain but we speculate that it may continue southwest along the western side of the antarctic peninsula close to the coast the antarctic slope front present almost all the way around antarctica tied to the continental slope has not previously been mapped after it reaches the tip of the antarctic peninsula we show that the frontal jet splits into two branches in the northwest powell basin where the isobaths diverge the shoreward portion of the water associated with the front lying above isobaths shallower than 1500 m is able to cross the south scotia ridge and head northwestward and retains many of the properties of the antarctic slope front it is associated with a transport of 7 sv the portion of the front constrained to lie above isobaths deeper than 1500 m becomes the weddell front this takes a path around the northern powell basin and south of the south orkney islands of the 13 sv that circulates around the southern flank of the south orkney plateau 8 sv of weddell sea deep water and warm deep water leaves the front to continue west the remaining shallow and intermediate water retroflects and returns south associated with the weddell front through the orkney passage approximately 5 7 sv is transported eastward associated with the weddell front tied closely to the southern flanks of the bruce and discovery banks above the 2000 2500 m isobaths and forming the southern boundary of the weddell scotia confluence

surface exchange between the weddell and scotia seas within drake passage the southern flank of the antarctic circumpolar current acc hosts the ventilation of deep water the injection of antarctic shelf waters and interactions between westward and eastward boundary currents this exchange is explored through the trajectories of forty surface drifters released in january 2012 in the northwestern weddell sea the drifters detail lagrangian transport pathways between the eastern antarctic peninsula and sites of elevated chlorophyll in the scotia sea acc frontal currents in particular the southern acc front act as dynamical transport barriers to the drifters and influence surface chlorophyll distributions indicating that acc fronts partition weddell source waters in the scotia sea interannual fluctuations in surface chlorophyll in the south scotia sea and the northern weddell sea covary this suggests that scotia sea ecosystem dynamics are linked to water properties injected from the tip of the antarctic peninsula and respond to weddell gyre circulation changes

seismic crustal structure of the proterozoic north australian craton between tennant creek and mount isa seismic recording along a 600 km traverse across the southern part of the north australian craton indicates that lateral velocity variations exist in the middle lower crust taken together with other data from the craton there is evidence for midcrustal velocities increasing from east to west and from south to north these trends could result from a greater proportion of high velocity granulites being emplaced at higher levels in the crust between tennant creek and mount isa the velocity structures near the surface are compatible with an assemblage of younger and older metamorphic rocks intruded by granites near surface 0 5 km p wave velocities on the tennant creek inlier increase from 5 47 km s at the surface to about 6 2 km s at 6 km depth and correspond with low grade metamorphics of the warramunga group interspersed with weathered granites overlying amphibolite facies rocks of older metamorphic domains in the mount isa geosyncline velocities of 6 03 6 15 km s correspond to the leichhart metamorphics interspersed with granites in the middle crust p wave velocities of 6 85 km s occur at a depth of 26 km near tennant creek whereas such velocities are not evident until depths of about 37 km near mount isa there is therefore a trend for midcrust velocities to increase from east to west the lower crust is characterized by velocities of 7 3 7 5 km s and the upper mantle velocities of 8 16 8 20 km s are reached at depths of 51 54 km exposed granulite facies rocks in central australia are low in heat producing elements and are compatible with the low surface heat flow generally measured in precambrian australia these data taken together with laboratory velocity measurements on worldwide samples reported elsewhere indicate that middle to lower crustal rocks could be an assemblage of granulite facies rocks varying from pyroxene granulite in the middle crust through hornblende granulite to garnet granulite in the lower crust

renewal and circulation of intermediate waters in the canadian basin observed on the scicex 96 cruise during the summer of 1996 the nuclear submarine uss pogy occupied a line of stations extending through the middle of the canadian basin between about 88 n 44 w lomonosov ridge and about 78 n 144 w center of the canada basin ctd niskin bottle casts extending to 1600 m were carried out at eight stations providing the first high quality temperature salinity cfc tritium and 3he data obtained from this region although xctd data had previously been collected in this region these data along with data from stations at the basin boundary to the south and west reveal the presence of well ventilated intermediate water beneath the halocline in the center of the canada basin indicating renewal times of the order of 1 2 decades the least ventilated intermediate water was observed at the northern end of the canada basin along the southern flank of the alpha ridge intermediate water is derived from the atlantic ocean and enters the arctic ocean through fram strait and the barents sea it flows around the arctic basins in boundary currents and splits in the eastern amundsen basin with one branch crossing the lomonosov ridge and flowing along the east siberian continental slope and the other flowing along the eurasian flank of the lomonosov ridge from the 1996 scientific ice expedition scicex 96 observations we conclude that the branch that flows along the east siberian continental slope transports this water to the chukchi rise where it apparently enters the central canada basin with some flow continuing along the boundary to the southern canada basin the fram strait branch water mixes extensively with waters from the canadian basin during its transit along the east siberian continental slope being diluted by a factor of about 5 by the time it reaches the central canada basin the barents sea branch water does not undergo such extensive mixing and is diluted by a factor of only about 2 when it reaches the central canada basin

a deep seismic profile of 800 km length recorded in southern queensland australia summary in 1984 the australian bureau of mineral resources and the geological survey of queensland recorded a regional seismic reflection profile of over 800 km length from the eastern part of the eromanga basin to the beenleigh block east of the clarence moreton basin a relatively transparent upper crustal basement with an underlying more reflective lower crust is characteristic of much of the region prominent westerly dipping reflectors occur well below the sediments of the eastern margin of the clarence moreton basin and the adjacent beenleigh block and provide some of the most interesting features of the entire survey a wide angle reflection refraction survey of 192 km length and an expanding reflection spread of 25 km length were recorded across the nebine ridge the only clear deep reflectors are interpreted as p to sv or sv to p converted reflections from a mid crustal boundary at a depth of about 17 km the combined nebine ridge data provide well constrained p and s wave velocity models of the upper crust and suggest a crustal structure quite different from that beneath the adjacent mesozoic basins

the australian central eromanga basin project an introduction abstract the australian bureau of mineral resources is carrying out a major multidisciplinary program of geological and geophysical studies in southwestern queensland in cooperation with the geological survey of queensland the project is aimed at providing information on the regional structure and depositional history of the central eromanga basin and the underlying adavale cooper and galilee basins the information being obtained is particularly relevant to a better understanding of the petroleum prospectivity of the area the program includes geophysical surveys involving 1400 km of new six fold cdp seismic reflection coverage on regional traverses up to 400 km long crossing the main structural elements of the area gravity measurements along all new seismic reflection traverses refraction surveys along two major east west and north south traverses and magnetotelluric soundings along the same major east west traverse landsat imagery studies are providing new perspective on many regional structures when used in conjunction with seismic and gravity information wireline logs and synthetic seismograms are being used with the new seismic data to re examine stratigraphic correlations palynologic and lithologic studies are underway to assist in determining depositional environments source rock maturation hydrological and geochemical studies are providing information on the generation and migration of hydrocarbons a significant feature of the program is the extension of the recording time of all new reflection data to 20 s to obtain good quality deep crustal reflection information comparable to that obtained on cocorp programs in the united states the reflection data is being interpreted with the refraction gravity and magnetotelluric data to investigate the relationship of deep crustal and upper mantle features to the sedimentary basins in the central eromanga basin area

the seismic reflection character of the continental mohorovicic discontinuity the continental mohorovicic discontinuity is most often interpreted as a step function velocity boundary however on deep crustal seismic reflection profiles reflections at depths where refraction data places the moho have laminated character and are laterally discontinuous these observations on continental reflection data point to a model of the moho that has thin layered rather than block structure previous workers who have synthetically generated seismic responses from various crust mantle boundary models have shown that thin layered models of alternating high and low velocity generate responses that best emulate observed moho arrivals geologic interpretations of the thin layering include relatively undeformed metasediments cumulate layering tectonic banding and lenses of partial melt to obtain more direct geologic evidence a synthetic seismogram is generated from geologic cross sections of the ivrea verbano zone an exposed section through the lower crust and upper mantle the synthetic shows laminations similar to those observed on reflection data without more direct evidence no single geologic interpretation of the moho is reasonable indeed the moho may be a laterally variable boundary its composition and structure dependent upon the geologic history of the overlying crust

antarctic offshore polynyas linked to southern hemisphere climate anomalies offshore antarctic polynyas large openings in the winter sea ice cover are thought to be maintained by a rapid ventilation of deep ocean heat through convective mixing these rare phenomena may alter abyssal properties and circulation yet their formation mechanisms are not well understood here we demonstrate that concurrent upper ocean preconditioning and meteorological perturbations are responsible for the appearance of polynyas in the weddell sea region of the southern ocean autonomous profiling float observations collected in 2016 and 2017 during the largest polynyas to form near the maud rise seamount since 1976 reveal that the polynyas were initiated and modulated by the passage of severe storms and that intense heat loss drove deep overturning within them wind driven upwelling of record strength weakened haline stratification in the upper ocean thus favouring destabilization in 2016 and 2017 we show that previous weddell polynyas probably developed under similarly anomalous conditions which are associated with a mode of southern hemisphere climate variability that is predicted to strengthen as a result of anthropogenic climate change measurements collected during recent polynya events in the southern ocean reveal that these sea ice openings formed as a result of weakened stratification and severe storms and were sustained by deep overturning

a new tide model for the antarctic ice shelves and seas we describe a new tide model for the seas surrounding antarctica including the ocean cavities under the floating ice shelves the model uses data assimilation to improve its fit to available data typical peak to peak tide ranges on ice shelves are 1 2 m but can exceed 3 m for the filchner ronne and larsen ice shelves in the weddell sea spring tidal ranges are about twice these values model performance is judged relative to the 5 10 cm accuracy that is needed to fully utilize ice shelf height data that will be collected with the geoscience laser altimeter system scheduled to be launched on the ice cloud and land elevation satellite in late 2002 the model does not yet achieve this level of accuracy except very near the few high quality tidal records that have been assimilated into the model some improvement in predictive skill is expected from increased sophistication of model physics but we also require better definition of ice shelf grounding lines and more accurate water column thickness data in shelf seas and under the ice shelves long duration tide measurements bottom pressure gauge or gps in critical data sparse areas particularly near and on the filchner ronne and ross ice shelves and pine island bay are required to improve the performance of the data assimilation model

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

dense bottom layers in the scotia sea southern ocean creation lifespan and destruction the lower limb of the atlantic overturning circulation is renewed by dense waters from the southern ocean a substantial portion of which flow through the scotia sea we report dense bottom layers here with gradients in temperature and salinity comparable to those seen near the surface of the southern ocean these are overlain by layers with much weaker stratification and are caused by episodic overflows of dense waters across the south scotia ridge and topographic trapping within deep trenches one such layer was found to be at least 3 4 years older than the water immediately above the estimated vertical diffusivity to which this layer was subject is substantially less than the strong basin average deep mixing reported previously we conjecture that a vertical mixing in the scotia sea is strongly spatially inhomogeneous and b the flushing of these layers like their formation is related to overflow events and hence also strongly episodic

direct estimate of lateral eddy diffusivity upstream of drake passage abstractthe first direct estimate of the rate at which geostrophic turbulence mixes tracers across the antarctic circumpolar current is presented the estimate is computed from the spreading of a tracer released upstream of drake passage as part of the diapycnal and isopycnal mixing experiment in the southern ocean dimes the meridional eddy diffusivity a measure of the rate at which the area of the tracer spreads along an isopycnal across the antarctic circumpolar current is 710 260 m2 s 1 at 1500 m depth the estimate is based on an extrapolation of the tracer based diffusivity using output from numerical tracers released in a one twentieth of a degree model simulation of the circulation and turbulence in the drake passage region the model is shown to reproduce the observed spreading rate of the dimes tracer and suggests that the meridional eddy diffusivity is weak in the upper kilometer of the water column with values below 500 m2 s 1 and peaks at the steering level near 2 km where the eddy ph

moho geometry gravity inversion experiment moggie a refined model of the australian moho and its tectonic and isostatic implications abstract at the continent scale models of moho depth based on seismic estimates alone can be inadequate due to irregular or sparse data gravity based moho modelling provides better coverage however the methods used are typically hampered by an inability to explicitly honour seismic constraints and are also limited by over simplistic model conditions e g laterally homogenous layering i present a new method to generate a continent scale moho model based on the constrained inversion of free air gravity data this method explicitly honours seismic moho estimates and accounts for a laterally heterogeneous crust and mantle resolution and sensitivity testing shows that for wavelengths greater than 200 km crustal density and moho depth are recovered with reasonable accuracy 30 kg m 3 and 3 km respectively moggie uses a six layer model incorporating ocean sedimentary basin upper crust lower oceanic crust eclogitised crust and mantle inversion variables were the density of the crustal layers constrained by a standard density model and the depths to intra crustal boundaries and the moho constrained by 230 seismic depth estimates the results demonstrate that a balanced approach to seismically constrained gravity inversion has the capability to generate detailed and well constrained models of the moho and crustal density at the continent scale for australia this is a clear improvement on the sparse and irregular resolution of the moho provided by seismic estimates of crustal thickness which fail to resolve short wavelength features newly defined tectonic features include extensive magmatic underplates crustal scale shear zones and the boundaries between tectonic blocks isostatic analysis reveals that little of the continent is close to isostatic equilibrium with isostatic disequilibria preserved at multiple scales from hundreds of kilometres to the entire continent these disequilibria are interpreted to indicate long wavelength flexure of highly competent continental lithosphere

deep crustal reflection results from the central eromanga basin australia abstract from 1980 to 1982 deep seismic reflection profiles were recorded across the central eromanga basin in eastern australia to study the regional structure stratigraphy and geological history of the eromanga basin and infra basins the reflection data were recorded to 20 s to obtain additional information on the nature and structure of the crust below the sediments and their relationship to the development of the basins the seismic sections show good quality reflections from the deep crust as well as from the sedimentary layers based on the character strength coherence continuity and spatial distribution of the reflections the sections can be divided into four zones the tope zone between 0 and 2 5 s shows fairly uniform coherent and continuous events which correlate with the mesozoic and late palaeozoic sediments the zone from 2 5 to 8 s 4 to 22 km does not show any primary reflections and is interpreted as the highly deformed metasedimentary and metavolcanic rocks of the early palaeozoic thomson orogen underlying the sediments without any recognisable reflection or diffraction patterns in this zone it is difficult to say whether the faulting and folding observed in the sediments extend into the upper crustal basement the deeper zone of numerous reflection segments between 8 and 12 5 s 22 to 36 km is interpreted as thin laminae of alternating low and high velocity intermediate and basic rocks and correlates with the lower crust bounded by refraction velocity discontinuities the lowest zone of no reflections below 12 5 s corresponds with the upper mantle the reflection character and thickness as well as the refraction velocity structure of the crust under the central eromanga basin area are significantly different from those of the precambrian crust under the georgina basin to the northwest it is proposed that the crust under the eromanga basin is extensionally attenuated crust which had been intruded by sills of basaltic melt from the underlying asthenosphere

mid crustal detachments controlling basin deformation ramp synforms in southwestern queensland abstract deep seismic data from the adavale basin region of southwestern queensland suggest that westward carboniferous movement of the upper crust over mid crustal ramps was responsible for the present day geometry of two synforms containing devonian sediments we interpret the troughs as hanging wall synforms formed by sub vertical simple shear within the upper crust during down dip movement over the ramp one of these structures the quilpie trough in the southern adavale basin is an asymmetric trough interpreted to be an extensional ramp syncline it overlies a west dipping ramp in the boundary between the seismically non reflective upper crust and the seismically reflective lower crust formation of this basin by the relative movement of the upper crustal thomson fold belt over the mid crustal ramp is postulated the significant asymmetry of the trough suggests that lower crustal extension by pure shear may have occurred during upper crustal translation the other structure the westgate trough contains two palaeozoic sequences we propose that the devonian lower sequence is in a ramp syncline formed by folding of the sediments in a conveyor belt style mechanism during a translation of the upper crust the upper sequence is interpreted as a ramp basin in which sediments were deposited in the synform as it developed deep seismic reflection data from the central eromanga basin region indicate that relative horizontal translation can occur between the upper and lower crust on mid crustal detachments the geometry of the synforms suggests that above these detachments crustal deformation has a sub vertical simple shear style whereas the lower crust below the detachments seems to deform in a pure shear style recognition of relative movement of tens of kilometres on mid crustal detachments is important for our understanding of basin geometry and development in the central eromanga basin

improvements in seismic reflection techniques for studying the lithosphere in australia abstract over the last 25 years the australian bureau of mineral resources bmr has attempted to record seismic reflection data in several parts of australia to determine if good quality near vertical reflections could be obtained from the deep crust and upper mantle data recorded prior to 1976 using analogue instruments and large shots did obtain good to fair quality deep events but the short lengths of the traverses recorded did not allow discrimination between primary reflections and the coherent noise the high cost of the special effort prevented recording of long traverses and hence the study of the true nature of the deep reflections from 1976 onwards with the advent of digital recording and processing equipment and techniques it became possible to obtain good quality deep reflection data on long traverses with the parameters such as small charges short spreads etc which are normally used for recording good sedimentary reflections the recent data allow better identification of reflections and study of their character and provide a higher resolution picture of the nature and structure of the deep crust and upper mantle than had been possible before bmr is therefore now recording good deep reflection data on all traverses during normal sedimentary basin surveys and accumulating the information necessary for studying the evolution of lithosphere in australia

the contribution of the weddell gyre to the lower limb of the global overturning circulation the horizontal and vertical circulation of the weddell gyre is diagnosed using a box inverse model constructed with recent hydrographic sections and including mobile sea ice and eddy transports the gyre is found to convey 42 8 sv 1 sv 106 m3 s 1 across the central weddell sea and to intensify to 54 15 sv further offshore this circulation injects 36 13 tw of heat from the antarctic circumpolar current to the gyre and exports 51 23 msv of freshwater including 13 1 msv as sea ice to the mid latitude southern ocean the gyre s overturning circulation has an asymmetric double cell structure in which 13 4 sv of circumpolar deep water cdw and relatively light antarctic bottom water aabw are transformed into upper ocean water masses by mid gyre upwelling at a rate of 2 2 sv and into denser aabw by downwelling focussed at the western boundary 8 2 sv the gyre circulation exhibits a substantial throughflow component by which cdw and aabw enter the gyre from the indian sector undergo ventilation and densification within the gyre and are exported to the south atlantic across the gyre s northern rim the relatively modest net production of aabw in the weddell gyre 6 2 sv suggests that the gyre s prominence in the closure of the lower limb of global oceanic overturning stems largely from the recycling and equatorward export of indian sourced aabw

circulation retention and mixing of waters within the weddell scotia confluence southern ocean the role of stratified taylor columns the waters of the weddell scotia confluence wsc lie above the rugged topography of the south scotia ridge in the southern ocean meridional exchanges across the wsc transfer water and tracers between the antarctic circumpolar current acc to the north and the subpolar weddell gyre to the south here we examine the role of topographic interactions in mediating these exchanges and in modifying the waters transferred a case study is presented using data from a free drifting intermediate depth float which circulated anticyclonically over discovery bank on the south scotia ridge for close to 4 years dimensional analysis indicates that the local conditions are conducive to the formation of taylor columns contemporaneous ship derived transient tracer data enable estimation of the rate of isopycnal mixing associated with this column with values of o 1000 m2 s obtained although necessarily coarse this is of the same order as the rate of isopycnal mixing induced by transient mesoscale eddies within the acc a picture emerges of the taylor column acting as a slow steady blender retaining the waters in the vicinity of the wsc for lengthy periods during which they can be subject to significant modification a full regional float data set bathymetric data and a southern ocean state estimate are used to identify other potential sites for taylor column formation we find that they are likely to be sufficiently widespread to exert a significant influence on water mass modification and meridional fluxes across the southern edge of the acc in this sector of the southern ocean

deep seismic reflection data suggest major compressional deformation of the crust in the central eromanga basin area during the mid carboniferous abstract scismic reflection data recorded to 20 s in the central eromanga basin area show good quality reflections from the deep crust as well as the shallow sedimentary layers the data along a 270 km long east west traverse indicate warping and low angle faulting in the lower crust which is compatible with asymmetric folding in the devonian sediments this interpretation is consistent with a major compressional deformation of the crust in this area during the mid carboniferous kanimblan orogeny

on the interannual variability of ocean temperatures around south georgia southern ocean forcing by el nino southern oscillation and the southern annular mode abstract the ocean around south georgia in the southwest atlantic sector of the southern ocean is highly productive with large stocks of antarctic krill supporting extensive colonies of marine and land based predators the operation of this ecosystem is strongly influenced by physical forcings and the role of the el nino southern oscillation enso phenomenon has been highlighted previously here we examine in detail the transmission of enso signals to south georgia and investigate other sources of interannual variability enso variability generates anomalies in sea surface temperature sst across the south pacific via atmospheric teleconnections these anomalies are advected toward south georgia within the antarctic circumpolar current acc and previous studies have focussed on long period advection order of 2 3 years from the southwest pacific we observe here however that the region close to the antarctic peninsula in the southeast pacific is especially susceptible to enso forcing via anomalous meridional winds this induces sst anomalies that are advected to south georgia on a much more rapid timescale order 5 6 months the phasing of these teleconnections is such that anomalies that reach the southeast pacific from farther west tend to be reinforced here by air sea ice interaction we also find an important role for the southern annular mode sam in determining sst variability at south georgia this is a circumpolar mode of climate variability and thus can readily influence local sst at south georgia directly the sam is however not perfectly zonally symmetric and like enso has a particular impact on meridional winds in the southeast pacific the average timescale for sam influence on south georgia sst is shorter than that of enso since it includes a stronger component of direct local forcing the south georgia ecosystem is not self sustaining with import of krill from breeding and nursery grounds upstream in the acc being important we speculate here that these varying meridional winds close to the antarctic peninsula play a direct role in promoting restricting the injection of shelf waters and the krill therein into the acc following which anomalies in krill density would be advected toward south georgia this offers a dynamical mechanism that might contribute to interannual changes in biological communities at south georgia in addition to existing theories both sam and enso have shown long period changes in recent decades with enso exhibiting a higher preponderance of el nino events compared with la nina events and the sam showing a marked trend toward a higher index state such long period behaviour is likely to induce changes in the south georgia ecosystem via their impacts on advection and sst for which an understanding of the physical mechanisms elucidated here will be key to unravelling

deep reflection experiments in northeastern australia 1976 1978 between 1976 and 1978 the australian bureau of mineral resources bmr recorded deep crustal reflection data at seven sites in northeastern australia over continuous profiles up to 15 km long by simply extending the recording time to 16 sec during normal sedimentary basin surveys the record sections show many events with variable strength continuity dip and spatial distribution by comparing the sections from the longer and the shorter perpendicular traverses it is possible to discriminate between primary reflections and diffractions multiples and other noise events based on their character the reflections can be grouped into zones which are interpreted in terms of the nature and structure of the crust most of the reflection sections show below the sedimentary reflections a thin 2 3 sec reflection free zone underlain by a thick 9 sec or more zone of numerous reflection segments which varies in thickness and the distribution of reflection segments the data thus suggest that the upper crust

new seismic reflection results in the central eromanga basin queensland australia the key to understanding its tectonic evolution abstract regional seismic traverses were recorded from 1980 to 1982 by the bureau of mineral resources geology and geophysics as part of a major multidisciplinary program aimed at studying the geological evolution of the central eromanga basin area and its petroleum potential six fold cdp reflection data were obtained to 20 s reflection time on 1400 km of traverses up to 400 km long crossing the main structural features of the area additional seismic reflection information to complement the study was obtained from 2300 km of older mainly single coverage analogue data which was transcribed to digital format and reprocessed the central eromanga basin area has a complex history and contains four phanerozoic potentially hydrocarbon bearing basins each separated by unconformities i e the devonian adavale basin the late carboniferous to triassic cooper and galilee basins and the jurassic cretaceous eromanga basin the seismic results are being interpreted with the aid of synthetic seismograms from key wells to provide information on the extent nature and relationship of these basins the quality of the reflection data from the devonian sequence is generally very good and these data are proving to be most useful in the study thick devonian sediments were deposited over a wide area well beyond the present confines of the adavale basin and its associated troughs intensive folding and faulting accompanied by major basement uplift including the canaway ridge in the centre of the area took place during the mid carboniferous kanimblan orogeny this was followed by a period of erosion which truncated the devonian sequence and resulted in separation of the adavale basin from the other devonian troughs in the area the preliminary seismic results give some indication also of the extent and nature of the cooper and galilee basins sediments these are generally thin in the central area and thicken to the west and east respectively where coal measures produce good lithologic and seismic markers gentle folding and minor faulting apparent in the seismic reflection sections from the overlying eromanga basin sequence have resulted mainly from basement uplift and minor movements along pre existing faults continuing into the late mid tertiary and possibly from some compaction of the thick sedimentary section the seismic information is also assisting in studies of the petroleum potential of the area providing information particularly on structuring timing and depth of burial of the prospective sediments

lower crustal involvement in upper crustal thrusting summary basement structures mapped in the devonian adavale basin eastern australia indicate two styles of lower crustal involvement in the formation of upper crustal structures the first style is typified by thrust features in the upper crustal sedimentary section and basement a response to lower crustal shortening over a wide area the second style includes lower crustal thrusting and thickening in a limited region with associated uplift of the upper crust these two styles suggest that the upper and lower crust were mechanically decoupled during palaeozoic compressive episodes 1 tectonic structures in the upper crust basement involved thrust faults have been mapped in the southern adavale basin australia using both bureau of mineral resources and industry seismic data finlayson et al in press these faults were grouped into two sets those striking predominantly north south gumbardo and corona and those striking predominantly east west como paradise and grenfield and form an orthogonal network of faults in this region fig 1 mechanical considerations dictate that these orthogonal thrust sets did not form synchronously relative thinning of stratigraphic units over basement faults has been used to date uplift movement on these faults retrodeformed sections produced by restoring the mid devonian cooladdi dolomite unit or its lateral equivalent were used to date initiation of thrusting the sections show that the east west striking thrusts developed first during the lower devonian in response to north south crustal shortening the thrust faults were separated by tear faults which transferred the relative strain between the fault blocks dalhstrom 1970 the second phase of tectonic activity commenced in the late devonian and continued into the carboniferous this phase is interpreted to be due to east west crustal shortening and reversed the roles of the thrust and tear faults developed during the previous episode leven et al in press the north south striking gumbardo and corona faults were reactivated as thrusts while previous thrusts acted as transfer faults for this deformation during the latter portion of this second tectonic episode sediments of the adavale basin were deformed into large scale predominantly north south trending folds the folding style of this later deformation contrasts with the faulting associated with the earlier episode carboniferous erosion which veevers et al 1984 suggest was caused by an extensive ice sheet effectively removed most of the sediment of the newly formed adavale basin leaving only the remnant synclinal cores these are represented in the southern adavale basin region by the cooladdi quilpie and blackwater troughs the wavelength of this basin wide folding is about 100 km and the amplitude in the case of the cooladdi trough exceeds 8 km but diminishes towards the west the warrabin trough to

stationary atmospheric responses to an idealized sea surface temperature anomaly in the southern ocean abstractthe stationary atmospheric response to an idealized sea surface temperature anomaly ssta is studied with a quasigeostrophic atmospheric model of the southern hemisphere sensitivity of the stationary response to the midlatitude ssta location is determined and responses are decomposed on vertical modes the ssta almost directly forces baroclinic responses inducing warm air anomalies 40 50 downstream eastward to the ssta these baroclinic responses arise from an equilibrium between the ssta induced anomalous vortex stretching and i advection by the quasi stationary flow and ii dissipation by high frequency eddies the barotropic response consists of a midlatitude ridge trough and a south pole trough ridge for sstas localized from the drake passage to the western indian ocean from south of australia to the center of the pacific ocean this response can be further decomposed into i a zonally asymmetric component a quasi stationary wave train forced by a barotropic ridge downstream of

calibrated seismic imaging of eddy dominated warm water transport across the bellingshausen sea southern ocean seismic reflection images of thermohaline circulation from the bellingshausen sea adjacent to the west antarctica peninsula were acquired during february 2015 this survey shows that bright reflectivity occurs throughout the upper 300 m by calibrating these seismic images with coeval hydrographic measurements intrusion of warm water features onto the continental shelf at marguerite and belgica troughs is identified and characterized these features have distinctive lens shaped patterns of reflectivity with lengths of 0 75 11 00 km and thicknesses of 100 150 m suggesting that they are small mesoscale to submesoscale eddies abundant eddies are observed along a transect that crosses belgica trough near alexander island drift a large of order urn x wiley 21699275 media jgrc22803 jgrc22803 math 0001 km3 bowl like feature that may represent an anticyclonic taylor column is imaged on a pair of orthogonal images a modified iterative procedure is used to convert seismic imagery into maps of temperature that enable the number and size of eddies being transported onto the shelf to be quantified finally analysis of prestack shot records suggests that these eddies are advecting southward at speeds of urn x wiley 21699275 media jgrc22803 jgrc22803 math 0002 m s 1 consistent with limited legacy hydrographic measurements concentration of observed eddies south of the southern antarctic circumpolar current front implies they represent both a dominant and a long lived mechanism of warm water transport especially across belgica trough our observations suggest that previous estimates of eddy frequency may have been underestimated by up to 1 order of magnitude which has significant implications for calculations of ice mass loss on the shelf of the west antarctic peninsula

investigating the stratigraphy and palaeoenvironments for a suite of newly discovered mid cretaceous vertebrate fossil localities in the winton formation queensland australia the winton formation of central queensland is recognized as a quintessential source of mid cretaceous terrestrial faunas and floras in australia however sedimentological investigations linking fossil assemblages and palaeoenvironments across this unit remain limited the intent of this study was to interpret depositional environments and improve stratigraphic correlations between multiple fossil localities within the preserved winton formation in the eromanga basin including isisford lark quarry and bladensburg national park twenty three facies and six repeated facies associations were documented indicating a mosaic of marginal marine to inland alluvial depositional environments these developed synchronously with the final regression of the eromanga seaway from central australia during the late albian early turonian investigations of regional and local scale structural features and outcrop core and well analysis were combined with detrital zircon provenance signatures to help correlate stratigraphy and vertebrate faunas across the basin significant palaeoenvironmental differences exist between the lower and upper portions of the preserved winton formation warranting informal subdivisions a lower tidally influenced fluvial deltaic member and an upper inland alluvial member this work further demonstrates that the isisford fauna is part of the lower member of the preserved winton formation whereas fossil localities around winton including lark quarry and bladensburg national park are part of the upper member of the winton formation these results permit a more meaningful framework for both regional and global comparisons of the winton flora and fauna

an eddy permitting southern ocean state estimate abstract an eddy permitting general circulation model of the southern ocean is fit by constrained least squares to a large observational dataset during 2005 06 data used include argo float profiles ctd synoptic sections southern elephant seals as oceanographic samplers seaos instrument mounted seal profiles xbts altimetric observations envisat geosat jason 1 and ocean topography experiment topex poseidon and infrared and microwave radiometer observed sea surface temperature an adjoint model is used to determine descent directions in minimizing a misfit function each of whose elements has been weighted by an estimate of the observational plus model error the model is brought into near agreement with the data by adjusting its control vector here consisting of initial and meteorological boundary conditions although total consistency has not yet been achieved the existing solution is in good agreement with the great majority of the 2005 and 2006 southern ocean observations and better repr