contribution of topographically generated submesoscale turbulence to southern ocean overturning the ocean s global overturning circulation regulates the transport and storage of heat carbon and nutrients upwelling across the southern ocean s antarctic circumpolar current and into the mixed layer coupled to water mass modification by surface buoyancy forcing has been highlighted as a key process in the closure of the overturning circulation here using twelve high resolution hydrographic sections in southern drake passage collected with autonomous ocean gliders we show that circumpolar deep water originating from the north atlantic known as lower circumpolar deep water intersects sloping topography in narrow and strong boundary currents observations of strong lateral buoyancy gradients enhanced bottom turbulence thick bottom mixed layers and modified water masses are consistent with growing evidence that topographically generated submesoscale flows over continental slopes enhance near bottom mixing and that cross density upwelling occurs preferentially over sloping topography interactions between narrow frontal currents and topography occur elsewhere along the path of the antarctic circumpolar current which leads us to propose that such interactions contribute significantly to the closure of the overturning in the southern ocean

late palaeozoic to neogene geodynamic evolution of the northeastern oman margin when the highlands of arabia were still covered with an ice shield in the latest carboniferous early permian period separation of gondwana started this led to the creation of the batain basin part of the early indian ocean off the northeastern margin of oman the rifting reactivated an infra cambrian rift shoulder along the northeastern oman margin and detritus from this high was shed into the interior oman basin whereas carbonate platform deposits became widespread along the margin of the neo tethys northern rim of oman drifting and oceanization of the batain basin started only in late jurassic early cretaceous time extensional tectonics was followed in the late cretaceous by contraction caused by the northward drift of greater india and afro arabia this resulted in the collision of afro arabia with an intra oceanic trench and obduction of the semail ophiolite and the hawasina nappes south to southwestward onto the northern oman margin 80 m y ago during the middle cretaceous the oceanic lithosphere including the future eastern ophiolites of oman drifted northwards as part of the indian plate at the cretaceous palaeogene transition 65 ma oblique convergence between greater india and afro arabia caused fragments of the early indian ocean to be thrust onto the batain basin subsequently the lower permian to uppermost maastrichtian sediments and volcanic rocks of the batain basin along with fragments of indian ocean floor eastern ophiolites were obducted northwestward onto the northeastern margin of oman palaeogene neo autochtonous sedimentary rocks subsequently covered the nappe pile tertiary extensional tectonics related to red sea rifting in the late eocene was followed by miocene shortening associated with the collision of arabia and eurasia and the formation of the oman mountains

on the skewness of vorticity in the upper ocean conservation of potential vorticity suggests that when the magnitude of relative vorticity approaches the planetary vorticity cyclonic vorticity should be preferred small scale 3 km relative vorticity is examined using shipboard acoustic doppler current profiler adcp velocity measurements and p code global positioning system gps navigation from a cruise in the north pacific the skewness of relative vorticity in the mixed layer is positive consistent with theory the probability density function of vorticity reveals that positive skewness occurs because large vorticities are more likely to be cyclonic than anticyclonic the skewness is shown to be significant relative to measurement and random errors in contrast skewness in the thermocline has no preferred sign the skewness peaks at the surface and decays to zero at the base of the mixed layer

abyssal circulation driven by near boundary mixing water mass transformations and interior stratification the emerging view of the abyssal circulation is that it is associated with bottom enhanced mixing which results in downwelling in the stratified ocean interior and upwelling in a bottom boundary layer along the insulating and sloping seafloor in the limit of slowly varying vertical stratification and topography however boundary layer theory predicts that these upslope and downslope flows largely compensate such that net water mass transformations along the slope are vanishingly small using a planetary geostrophic circulation model that resolves both the boundary layer dynamics and the large scale overturning in an idealized basin with bottom enhanced mixing along a midocean ridge we show that vertical variations in stratification become sufficiently large at equilibrium to reduce the degree of compensation along the midocean ridge flanks the resulting large net transformations are similar to estimates for the abyssal ocean and span the vertical extent of the ridge these results suggest that boundary flows generated by mixing play a crucial role in setting the global ocean stratification and overturning circulation requiring a revision of abyssal ocean theories

localization of the gravity field and the signature of glacial rebound the negative free air gravity anomaly centred on hudson bay canada shows a remarkable correlation with the location of the laurentide ice sheet suggesting that this gravity anomaly is the result of incomplete post glacial rebound this region however is also underlain by higher than average mantle seismic velocities suggesting that the gravity low might result instead from dynamic topography associated with convective downwellings here we analyse the global gravity field as a simultaneous function of geographic location and spectral content we find that the hudson bay gravity low is unique with anomalously high amplitude in the spectral band where the power from the laurentide ice load is greatest and the relaxation times predicted for viable models of viscous relaxation are longest we estimate that about half of the hudson bay gravity anomaly is the result of incomplete post glacial rebound and derive a mantle viscosity model that explains both this gravity signature and the characteristic uplift rates for the central laurentide and fennoscandian regions this model has a jump in viscosity at 670 km depth comparable to that in dynamic models of the geoid highs over subducted slabs but lacks a low viscosity asthenosphere consistent with a higher viscosity in the upper mantle beneath shields than in oceanic regions

potential vorticity dynamics of tropical instability vortices abstracttropical instability vortices tivs in the equatorial pacific exhibit energetic horizontal and vertical circulation characterized by regions of high rossby number and low richardson number their strong anticyclonic vorticity and vertical shear can influence the broader scale circulation by driving lateral mixing and vertical exchange between the ocean surface and interior the authors use a set of nested high resolution simulations of the equatorial pacific with a finest grid size of 3 km to examine the vortex dynamics associated with tiv core water formation tiv cores are characterized by low values of the ertel potential vorticity pv as the relative vorticity is anticyclonic with magnitude comparable to the local coriolis parameter a study of the variation of pv and other scalars along lagrangian fluid parcel tracks entering the tivs shows that the low pv water in their cores is a mix of equatorial undercurrent euc water and north equatorial counter current necc water the euc water

gravitational symmetric and baroclinic instability of the ocean mixed layer abstract a hierarchy of hydrodynamical instabilities controlling the transfer of buoyancy through the oceanic mixed layer is reviewed if a resting ocean of horizontally uniform stratification is subject to spatially uniform buoyancy loss at the sea surface then gravitational instability ensues in which buoyancy is drawn from depth by upright convection but if spatial inhomogeneities in the ambient stratification or the forcing are present as always exist in nature then horizontal density gradients will be induced and within a rotation period horizontal currents in thermal wind balance with those gradients will be set up within the mixed layer there are two important consequences on the convective process upright convection will become modified by the presence of the thermal wind shear fluid parcels are exchanged not along vertical paths but rather along slanting paths in symmetric instability theoretical considerations suggest that this slantwise convection sets the potential vorticity of th

global ocean meridional overturning abstract a decade mean global ocean circulation is estimated using inverse techniques incorporating air sea fluxes of heat and freshwater recent hydrographic sections and direct current measurements this information is used to determine mass heat freshwater and other chemical transports and to constrain boundary currents and dense overflows the 18 boxes defined by these sections are divided into 45 isopycnal neutral density layers diapycnal transfers within the boxes are allowed representing advective fluxes and mixing processes air sea fluxes at the surface produce transfers between outcropping layers the model obtains a global overturning circulation consistent with the various observations revealing two global scale meridional circulation cells an upper cell with sinking in the arctic and subarctic regions and upwelling in the southern ocean and a lower cell with sinking around the antarctic continent and abyssal upwelling mainly below the crests of the major bathymetric ridges

matrix micrite δ13c and δ18o reveals synsedimentary marine lithification in upper jurassic ammonitico rosso limestones betic cordillera se spain abstract matrix micrites are a commonly used carbonate archive for the reconstruction of past environmental parameters but one that is submitted to known limitations main reasons for the often ambiguous value of many micrite based isotope data sets are the unknown origin of the micrite components and their poorly resolved diagenetic history here we present carbon and oxygen isotope data retrieved from oxfordian to tithonian ammonitico rosso nodular micrites sampled from three sections in the betic cordillera southern spain all three sections were correlated and sampled using a rigorous biostratigraphic framework a noteworthy feature is that analyzed matrix micrites are more conservative in terms of their isotopic composition than other carbonate materials commonly considered to resist diagenetic alteration under favourable circumstances remarkably this refers not only to 13 c ratios which reflect the typical late jurassic global trend but also to 18 o ratios that range around 0 3 the 18 o enriched oxygen isotope ratios are considered to represent diagenetic stabilization of carbonate ooze under the influence of marine porewaters within the sediment water interphase i e the immature sedimentary section usually submitted to biogenic activity this interpretation agrees with the very early lithification of micrite nodules with cements precipitated from marine porewaters enriched by the dissolution of aragonite skeletals i e ammonite shells according to the model proposed low sedimentation rates as well as rapid early marine differential cementation under the influence of currents and seawater pumping affected the sediment water interphase of epioceanic swells where deposition resulted in early lithified ammonitico rosso facies the data obtained show that special care must be taken to prevent oversimplified interpretations of carbonate archives particularly in the context of epioceanic settings

manganiferous cherts of the franciscan assemblage i general geology ancient and modern analogues and implications for hydrothermal convection at oceanic spreading centers there are several hundred ophiolitic manganiferous chert deposits primarily of late jurassic to early cretaceous age known within the franciscan assemblage of california the sequences typically consist of one to three massive manganiferous chert lenses containing 30 to 50 percent mn and averaging 1 m in thickness by 15 m subcircular diameter these are separated by an average 2 to 10 m of thin bedded radiolarian cherts and overlie basalts or greenstones both their geology and chemistry indicate that the ore lenses are hydrothermal and may have formed on the flanks of a mid ocean ridge or within a back arc basin it is proposed that the sequences developed as a result of sea floor spreading over a series of deep hydrothermal seawater convection cells paralleling a spreading center and spaced roughly 5 to 10 km apart chemical profiles of mn fe si al cu ni zn co ba ti the rare earth elements and 87 sr 86 sr have been determined through two complete sections these profiles indicate hydrothermal input of mn si cu ni zn and ba and detrital or hydrogenous input of al and co they illustrate the use of ti as a measure of relative detrital sedimentation rates fe is strongly fractionated from mn within the ores fe mn 0 1 and fe mn ratios decrease upward throughout each section suggesting preferential deposition of fe within the sediment and of mn at the seawater interface rare earth element distributions reflect the interaction of sea water and underlying basalts sr isotopic ratios of the ores and basalts demonstrate both strong and moderate seawater influences respectively fluid inclusion analyses on veins of undetermined age show seawater salinity temperatures of roughly 200 degrees c and tentative entrapment pressures corresponding to 1 700 m water depth early and intermediate veins were injected into unconsolidated siliceous sediment producing a characteristic bleached and pseudobrecciated texture an analogy is drawn with the present day field of hydrothermal mounds near the galapagos rift and with ophiolitic complexes of the northern apennines and other localities

spatial geochemistry of upper jurassic marine carbonates iberian subplate abstract chemostratigraphy applied to ancient marine carbonates is commonly based on one dimensional stratigraphic sections or core data as demonstrated from modern oceans this approach underestimates the spatial complexity of physico chemical seawater properties here a several hundred kilometer long transect consisting of seven upper jurassic sections from settings ranging from proximal neritic middle shelf to the epioceanic distal fringe across the southern and eastern palaeomargins of the iberian sub plate reveals variability in sedimentologic stratigraphic and geochemical records the comparison of isotopic and elemental data from different carbonate materials matrix micrite carbonate cements in veinlets belemnite rostra and ammonite shells reveals differential diagenetic pathways microfacies cathodoluminescence and geochemical data retrieved from biostratigraphically well constrained sections reveal that epioceanic matrix micrite geochemical data provide valuable proxies for palaeo seawater properties our data are reviewed in the context of published late jurassic records the outcome shows a higher level of complexity including the potential admixture of marine continental and diagenetic geochemical signals in the epicontinental record the stratigraphic trend in carbon isotopes of epioceanic sections agrees upon that of upper jurassic reference sections from the northern tethyan margins while oxygen isotope ratios are relatively 18o enriched palaeo seawater temperatures across the transect investigated were estimated using 18o as tentative proxy for interpreting distance from shore differences in water masses relative depth variations and potential local forcing factors palaeoenvironmental conditions evaluated through the combined record of isotope 18o elemental mn and skeletal content contrast with relative fluctuations in sea level site specific changes in palaeoceanographic parameters such as water depth seawater temperature salinity and upwelling are considered in comparison to examples from ancient and modern oceans

contrast comparison of differential diagenetic pathways of lower tithonian carbonate materials from the betic cordillera s spain evidence for physico chemical paleo seawater properties abstract the reconstruction of paleoenvironmental conditions is based on the study of ancient rock materials for this purpose skeletal materials are often assumed to have higher preservation potential sometimes favored over the use of matrix micrite however factors such as ecology depositional setting mineralogy and diagenetic processes may obscure original geochemical signals and care must be taken when reading such an intricate record this work provides a thorough comparison between geochemical signatures of different carbonate materials interpreted in the light of their paleoenvironmental significance burial and diagenetic processes are taken into account contextualized by ammonite and belemnite ecology two sections deposited in epioceanic tethyan areas and corresponding to the same lower tithonian ammonite biozone are under scope a condensed pelagic and cephalopod rich limestone the alamedilla sector intercalated in thick mafic rocks piles and a typical ammonitico rosso facies the cardador section in contrast to depositional and taphonomic histories typical for a tethyan top swell site i e rather calcareous ammonitico rosso events of carbonate mud deposition rapid burial and early lithification synsedimentary sliding and over imposition of firmground horizons characterize pelagic cephalopod rich limestones differential taphonomy of carbonate skeletals agrees with differential preservation favoring inner cast preservation in ammonitico rosso and shell preservation neomorphic calcite in pelagic cephalopod rich limestones stable carbon and oxygen isotope data together with trace element data sr mg fe mn are presented for a wide range of carbonate materials matrix micrite neomorphic ammonite shells belemnite rostra and carbonate cements optical inspection including cathodoluminescence imaging and geochemical data suggest a fair preservation of the above mentioned materials except for diagenetic marine burial carbonate cements carbon isotope values fall within the typical tethyan late jurassic range ca 2 except data from belemnite rostra which are depleted around 1 which is interpreted as resulting from metabolic fractionation oxygen isotope values are more variable but the clustering of different carbonate materials within a narrow range of values between 1 and 1 is consistent with conservative diagenesis warmer burial fluids explain lower values in later diagenetic carbonate cements no evidence of pervasive diagenetic imprint is revealed by elemental composition the increased abundance of mg fe and especially mn up to 1500 ppm is recognized as hydrothermal contamination proximity to hydrothermal sources the mid subbetic volcanic ridge accords with higher mn concentration at the alamedilla site interestingly the timing of the mineralogical stabilization of each carbonate material reveals a potential record of a post sedimentary geochemical event the obtained information demonstrates the complexity of ancient carbonate records and encourages future research focused on the preservation potential of geochemical proxies throughout time the studied case hopes to be a representative example to approach the interpretation of potential past and present rare analogs

geochemistry of manganese bearing cherts associated with alpine ophiolites and the hawasina formations in oman abstract based on correlation coefficients and analogies with studies on recent mn enrichments the major and trace elements of mn occurrences associated with ophiolites that have been variously affected by regional alpine metamorphism were attributed to different origins mn zn v ce nd and la are hydrothermal al ti k zr rb ga sc and some fe and pb are detrital and si p u y nb and the remainder of the fe are biogenic preliminary studies of mn occurrences in the wahrah formation of oman reveal a very similar geochemistry as the extensive exposure of this formation does not display any evidence of hydrothermal systems only a hydrothermal supply of mn to seawater from a distant source is envisaged for these and other deposits

mesoscale eddy dissipation by a zoo of submesoscale processes at a western boundary mesoscale eddies are ubiquitous dynamical features that tend to propagate westward and disappear along ocean western boundaries using a multiscale observational study we assess the extent to which eddies dissipate via a direct cascade of energy at a western boundary we analyze data from a ship based microstructure and velocity survey and an 18 month mooring deployment to document the dissipation of energy in anticyclonic and cyclonic eddies impinging on the topographic slope east of the bahamas in the north atlantic ocean these observations reveal high levels of turbulence where the steep and rough topographic slope modified the intensified northward flow associated with in particular anticyclonic eddies elevated dissipation was observed both near bottom and at mid depths 200 800 m near bottom turbulence occurred in the lee of a protruding escarpment where elevated froude numbers suggest hydraulic control energy was also radiated in the form of upward propagating internal waves elevated dissipation at mid depths occurred in regions of strong vertical shear where the topographic slope modified the vertical structure of the northward eddy flow here low richardson numbers and a local change in the isopycnal gradient of potential vorticity pv suggest that the elevated dissipation was associated with horizontal shear instability elevated mid depth dissipation was also induced by topographic steering of the flow this led to large anticyclonic vorticity and negative pv adjacent to the topographic slope suggesting that centrifugal instability underpinned the local enhancement in dissipation our results provide a mechanistic benchmark for the realistic representation of eddy dissipation in ocean models

dynamics of the transition zone under europe inferred from wavelet cross spectra of seismic tomography abstract tomographical results are commonly presented in the form of color images and not much statistical quantification has been carried out on the derived models correlation between different depths can shed important light concerning the dynamics we have generalized the application of multidimensional wavelets to investigate the products of two field variables such as the cross spectrum which is of paramount importance for quantifying the correlation between two depth levels of seismic tomography with a multiple scale character for two multidimensional fields a and b we calculate the correlation c by projecting this as an hermitian inner product in physical space with a two dimensional 2d fourth derivative of the gaussian wavelet as the weighting function the correlation function c becomes now a multi scaled function a map cast in terms of both the scale and location of the wavelet transform having calculated c we can delineate the locations and length scales of the prominent features in the landscape of the correlation function this wavelet formulation is very general and can be extended to other types of statistical analysis for example in a kalman filter system we have used a high resolution finer than 1 seismic tomographical model for analyzing the extent of mantle layering under europe by focussing on the different length scales in the correlation function involving the 3d seismic anomalies lying between 400 and 600 km depth between the depths of 500 and 600 km under europe the wavelet correlation analysis shows that an ellipse shaped object exists with an area of 2000 km 4000 km having a strong correlation for length scales of around 400 km and weaker correlation for shorter length scales of around 150 km on the other hand between depths of 400 and 600 km the correlation deteriorates on the long length scales and becomes even worse at the short length scales from the wavelet correlation spectra we can extract an horizontal characteristic length scale of around 100 km which may be related to the boundary interaction between the slab and the ambient mantle the correlation results suggest that the thickness of the recumbent fast cold material in the transition zone is between 100 and 150 km this large elliptical pattern of presumably cold material would act to inhibit the vigor of mantle convection locally beneath europe today

centrifugal instability and mixing in the california undercurrent abstracta regional numerical study of the california current system near monterey bay california is conducted using both hydrostatic and nonhydrostatic models frequent sighting of strong anticyclones cuddies have occurred in the area and previous studies have identified monterey bay as an apparent region of strong unbalanced flow generation here by means of a downscaling exercise a domain just downstream of point sur is analyzed and argued to be a preferred site of diapycnal mixing the scenario suggested by the simulations involves the generation of negative relative vorticity in a bottom boundary layer of the california undercurrent on the continental shelf break at point sur the current separates from the coast and moves into deep waters where it rapidly develops finite amplitude instabilities these manifest as isopycnal overturnings but in contrast to the normal kelvin helmholtz paradigm for mixing this study argues that the instability is primarily centrifugal the evidence for this com

structural evolution of the northern end of the oman ophiolite and enclosed granulites abstract a combined structural field mapping microstructural and petrographic study has been undertaken to better understand the origin and evolution of the northernmost part of the oman ophiolite khawr fakkan massif in the framework of an oceanic spreading centre emplacement of a sheet of granulite facies metamorphic rocks into the peridotites occurred at temperatures at which the peridotites deformed ductily the metamorphic rocks define the southern extension of a block boundary which separates an eastern peridotite part displaying high temperature fabrics from a western one with porphyroclastic to mylonitic fabrics granitoid intrusions representing partial melts from the metamorphic rocks occur only in the ophiolitic part overlying the metamorphic rocks thus delineating the same boundary between the two mantle blocks this high temperature boundary is not visible on satellite or aerial photographs the granulite facies foliations and lineations in the metamorphic rocks can be correlated with porphyroclastic textures developed at decreasing temperatures in the associated peridotites and to the obduction of the ophiolite the final emplacement of the metamorphic rocks in their present position was accompanied by retrograde hydration decompression and continuous deformation at temperatures ranging from 800 to 300 c the hydration is extended along the wadi ham fault two models are proposed for the emplacement of the metamorphic rocks in the first model the protolith of the metamorphic rocks was deposited in a pull apart basin along a transform fault and then subducted along the transform fault after reversal from transtension to transpression in this model the ophiolite obduction occurred later along another thrust plane in the second model the protolith material descends along an intraoceanic subduction zone and is emplaced into the ophiolite hanging wall along a secondary thrust caused by transpressive or rotational movements during the ophiolite obduction in this case the ophiolite obduction occurred along the same intraoceanic subduction plane

centrifugal and symmetric instability during ekman adjustment of the bottom boundary layer flow along isobaths of a sloping lower boundary generates an across isobath ekman transport in the bottom boundary layer when this ekman transport is down the slope it causes convective mixing much like a downfront wind in the surface boundary layer destroying stratification and potential vorticity in this manuscript we show how this can lead to the development of a forced centrifugal or symmetric instability regime where the potential vorticity flux generated by friction along the boundary is balanced by submesoscale instabilities that return the boundary layer potential vorticity to zero this balance provides a strong constraint on the boundary layer evolution which we use to develop theory that explains the evolution of the boundary layer thickness the rate at which the instabilities extract energy from the geostrophic flow field and the magnitude and vertical structure of the dissipation finally we show using theory and a high resolution numerical model how the presence of centrifugal or symmetric instabilities alters the time dependent ekman adjustment of the boundary layer delaying ekman buoyancy arrest and enhancing the total energy removed from the balanced flow field submesoscale instabilities of the bottom boundary layer may therefore play an important largely overlooked role in the energetics of flow over topography in the ocean

hydrothermal chert and associated siliceous rocks from the northern pacific their geological significance as indication od ocean ridge activity adachi m yamamoto k and sugisaki r 1986 hydrothermal chert and associated siliceous rocks from the northern pacific their geological significance as indication of ocean ridge activity sediment geol 47 i25 148 analyses of 42 cretaceous rock samples from deep sea drilling project dsdp leg 32 in tile northern pacific show that chert and porcellanite are enriched in fe mn p cu ba mo ni and pb relative to both triassic biogenic cherts of central japan and cretaceous dsdp cherts of leg 62 the iron enrichment up to 6 68ve fe20 as total iron is most prominent in chert immediately overlying basal basah which is the only chert free of radiolarians and veined by megaquartz containing many fluid inclusions chemical features characterized by a low ratio for a1 ai fe mn and ai z tio 2 and a high ratio for total fe2oj tio 2 mno tio 2 and mo tio 2 as well as petrological evidence indicatc that the cherts formed in an intense submarine hydrothermal environment on or near the cretaceous japanese spreading center which separated the kula plate from the pacific plate the spreading rate of the cretaceous japanese spreading center estimated from the chemical composition of the cherts was about 3 7 cm r i the rate is comparable to that inferred from the geomagnetic data

abyssal upwelling and downwelling driven by near boundary mixing abstracta buoyancy and volume budget analysis of bottom intensified mixing in the abyssal ocean reveals simple expressions for the strong upwelling in very thin continental boundary layers and the interior near boundary downwelling in the stratified ocean interior for a given amount of antarctic bottom water that is upwelled through neutral density surfaces in the abyssal ocean between 2000 and 5000 m up to 5 times this volume flux is upwelled in narrow turbulent sloping bottom boundary layers while up to 4 times the net upward volume transport of bottom water flows downward across isopycnals in the near boundary stratified ocean interior these ratios are a direct result of a buoyancy budget with respect to buoyancy surfaces and these ratios are calculated from knowledge of the stratification in the abyss along with the assumed e folding height that characterizes the decrease of the magnitude of the turbulent diapycnal buoyancy flux away from the seafloor these strong diapycnal upward and downwa

symmetric instability in the gulf stream abstract analyses of wintertime surveys of the gulf stream gs conducted as part of the clivar mode water dynamic experiment climode reveal that water with negative potential vorticity pv is commonly found within the surface boundary layer sbl of the current the lowest values of pv are found within the north wall of the gs on the isopycnal layer occupied by eighteen degree water suggesting that processes within the gs may contribute to the formation of this low pv water mass in spite of large heat loss the generation of negative pv was primarily attributable to cross front advection of dense water over light by ekman flow driven by winds with a down front component beneath a critical depth the sbl was stably stratified yet the pv remained negative due to the strong baroclinicity of the current suggesting that the flow was symmetrically unstable a large eddy simulation configured with forcing and flow parameters based on the observations confirms that the observed structure of the sbl is consistent with the dynamics of symmetric instability si forced by wind and surface cooling the simulation shows that both strong turbulence and vertical gradients in density momentum and tracers coexist in the sbl of symmetrically unstable fronts si is a shear instability that draws its energy from geostrophic flows a parameterization for the rate of kinetic energy ke extraction by si applied to the observations suggests that si could result in a net dissipation of 33 mw m 2 and 1 mw m 2 for surveys with strong and weak fronts respectively the surveys also showed signs of baroclinic instability bci in the sbl namely thermally direct vertical circulations that advect biomass and pv the vertical circulation was inferred using the omega equation and used to estimate the rate of release of available potential energy ape by bci the rate of ape release was found to be comparable in magnitude to the net dissipation associated with si this result points to an energy pathway where the gs s reservoir of ape is drained by bci converted to ke and then dissipated by si and its secondary instabilities similar dynamics are likely to be found at other strong fronts forced by winds and or cooling and could play an important role in the energy balance of the ocean circulation

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

aster capability in mapping of mineral resources of arid region a review on mapping of mineral resources of the sultanate of oman abstract advanced space borne thermal emission and reflection radiometer aster has exclusive capability to map minerals and ore deposits and able to discriminate rock types useful for geological applications especially the improved spectral and spatial resolutions of spectral bands of the sensor are well utilized by the exploration geologists working on arid region where the surface deposits are directly exposed to the sensor without disturbances of the vegetation several fruitful research studies have been carried out to map mineral resources in arid region with inaccessible rugged mountains and deserts area where it is difficult to do conventional geological mapping these were demonstrated and documented in the scientific publications using the aster spectral bands and image processing methods this study reviews scientific literatures published on mapping of the economic mineral resources of the sultanate of oman using aster and simples image processing methods

turbulent mixing and exchange with interior waters on sloping boundaries abstractmicrostructure measurements along the axes of monterey and soquel submarine canyons reveal 200 300 m thick well stratified turbulent near bottom layers with average turbulent kinetic energy dissipation rates e 4 10 8 w kg 1 and eddy diffusivities k 16 10 4 m2 s 1 assuming mixing efficiency 0 2 to at least thalweg depths of 1200 m turbulent dissipation rates are an order of magnitude lower in overlying waters whereas buoyancy frequencies are only 25 higher well mixed bottom boundary layer thicknesses hn are an order of magnitude thinner than the stratified turbulent layer hn he because well stratified turbulent layers are commonly observed above slopes arguments that mixing efficiency should be reduced on sloping boundaries do not hold in cases of energetic internal wave generation or interaction with topography an advective diffusive balance is used to infer velocities and transports predicting horizontal upslope flows of 10 50 m day 1 extrapolating this estimate globa

turning ocean mixing upside down abstractit is generally understood that small scale mixing such as is caused by breaking internal waves drives upwelling of the densest ocean waters that sink to the ocean bottom at high latitudes however the observational evidence that the strong turbulent fluxes generated by small scale mixing in the stratified ocean interior are more vigorous close to the ocean bottom boundary than above implies that small scale mixing converts light waters into denser ones thus driving a net sinking of abyssal waters using a combination of theoretical ideas and numerical models it is argued that abyssal waters upwell along weakly stratified boundary layers where small scale mixing of density decreases to zero to satisfy the no density flux condition at the ocean bottom the abyssal ocean meridional overturning circulation is the small residual of a large net sinking of waters driven by small scale mixing in the stratified interior above the bottom boundary layers and a slightly larger net upwelling driven b

deep bottom mixed layer drives intrinsic variability of the antarctic slope front the antarctic slope front asf is located along much of the antarctic continental shelf break and helps to maintain a barrier to the movement of circumpolar deep water cdw onto the continental shelf the stability of the asf has a major control on cross shelf heat transport and ocean driven basal melting of antarctic ice shelves here the asf dynamics are investigated for continental shelves with weak dense shelf water dsw formation which are thought to have a stable asf common for regions in east antarctica using an ocean process model this study demonstrates how offshore bottom ekman transport of shelf waters leads to the development of a deep bottom mixed layer at the lower continental slope and subsequently determines an intrinsic variability of the asf the asf variability is characterized by instability events that affect the entire water column and occur every 5 10 years and last for approximately half a year during these instability events the cross shelf density gradient weakens and cdw moves closer to the continent stronger winds increase the formation rate of the bottom mixed layer which causes a subsequent increase of instability events if the observed freshening trend of continental shelf waters leads to weaker dsw formation more regions might be vulnerable for the asf variability to develop in the future

submesoscale baroclinic instability in the bottom boundary layer abstractweakly stratified layers over sloping topography can support a submesoscale baroclinic instability mode a bottom boundary layer counterpart to surface mixed layer instabilities the instab

generation of submesoscale vortices a new mechanism small scale intense vortices composed of water with anomalous values of quasi conservative tracers have been observed in many oceans they are particularly numerous in the beaufort gyre of the arctic ocean possible mechanisms responsible for the generation of these features are examined conservation of temperature salinity and nutrients requires that beaufort sea vortices be created from water that flows into the arctic ocean from the pacific ocean across the broad shallow chukchi sea much of this water passes through barrow canyon near point barrow alaska observations in the canyon show the generation of vortices of approximately the same size as those observed in the beaufort sea barrow canyon is therefore a likely site for the generation of beaufort sea vortices most observed beaufort sea vortices have a central potential vorticity near zero because of a relative vorticity close to their chukchi sea source water is typically stratified with little relative vorticity so that its potential vorticity is nonzero a key step in the generation of the vortices is therefore the reduction of the potential vorticity of chukchi sea water to nearly zero it is proposed that this occurs through the action of frictional torques occurring as the chukchi sea water flows through barrow canyon rather than througji the action of vertical mixing because this flow is driven by a downstream pressure gradient it is concentrated on the right hand wall of the canyon by the coriolis force the frictional torques thus preferentially reduce the potential vorticity of the fluid anticyclonic vortices are therefore preferentially generated it is suggested that a similar scenario may play a role in the generation of submesoscale vortices containing water from the mediterranean and labrador seas

rapid mixing and exchange of deep ocean waters in an abyssal boundary current the overturning circulation of the global ocean is critically shaped by deep ocean mixing which transforms cold waters sinking at high latitudes into warmer shallower waters the effectiveness of mixing in driving this transformation is jointly set by two factors the intensity of turbulence near topography and the rate at which well mixed boundary waters are exchanged with the stratified ocean interior here we use innovative observations of a major branch of the overturning circulation an abyssal boundary current in the southern ocean to identify a previously undocumented mixing mechanism by which deep ocean waters are efficiently laundered through intensified near boundary turbulence and boundary interior exchange the linchpin of the mechanism is the generation of submesoscale dynamical instabilities by the flow of deep ocean waters along a steep topographic boundary as the conditions conducive to this mode of mixing are common to many abyssal boundary currents our findings highlight an imperative for its representation in models of oceanic overturning