dense water formation beneath a time dependent coastal polynya abstract recent modeling studies of dense water formation beneath an idealized steady coastal polynya have provided simple analytical expressions for the maximum density anomaly achievable as a function of the polynya geometry and the imposed surface buoyancy flux these studies have assumed that the buoyancy flux and polynya geometry are both constant and independent parameters to relax these assumptions dense water formation is examined beneath a coastal polynya whose size and surface buoyancy flux are computed from atmospheric temperature and wind velocity according to a polynya model developed by pease though highly idealized the pease model produces polynyas that open and close on reasonably realistic timescales and it thermodynamically couples the polynya size and buoyancy flux results reveal several interesting and potentially useful features of the ocean response to time dependent polynya forcing first under reasonable atmospheric conditions both the maximum density anomaly achievable and

numerical simulations of marine hydrothermal plumes for europa and other icy worlds abstract the liquid water interiors of europa and other icy moons of the outer solar system are likely to be driven by geothermal heating from the sea floor leading to the development of buoyant hydrothermal plumes these plumes potentially control icy surface geomorphology and are of interest to astrobiologists we have performed a series of simulations of these plumes using the mit gcm ocean circulation model we assume here that europa s ocean is deep of order 100 km and unstratified and that plume buoyancy is controlled by temperature not composition our experiments explore a limited region of parameter space with ocean depth h ranging from 50 to 100 km deep source heat flux q between 0 1 and 10 gw and coriolis parameter f corresponding to europa latitudes between 9 and 47 as predicted by earlier work the plumes in our simulations form narrow cylindrical chimneys a few km across under the influence of the coriolis effect these plumes broaden over time until they become baroclinically unstable breaking up into cone shaped eddies when they become 10 35 km in diameter the shed eddies are of a similar size large scale currents in the region of the plume range between 1 and 5 cm s temperature anomalies in the plume far from the seafloor are tiny varying between 10 and 180 k variations in plume size shape speed and temperature are in excellent agreement with previous laboratory tank experiments and in rough agreement with theoretical predictions plume dynamics and geometry are controlled by a natural rossby number which depends strongly on depth h and coriolis parameter f but only weakly on source heat flux q however some specific theoretical predictions are not borne out by these simulations this may occur because the plumes are reingesting their own emissions a process not considered in our earlier theory

large scale spreading of deep waters in the western mediterranean sea by submesoscale coherent eddies abstract two large scale free drifting isobaric floats experiments sofargos marine science and technology programme phase 2 mast2 and mass transfer and ecosystem response mater mast3 undertaken in 1994 95 in the northwestern mediterranean sea and in 1997 98 in the algerian basin respectively have revealed for the first time that western mediterranean deep water newly formed by deep convection in the gulf of lion the so called medoc site can be advected several hundreds of kilometers away from the formation area by anticyclonic submesoscale coherent vortices scvs this behavior implies that scvs participate actively in the large scale thermohaline circulation and deep ventilation of the western mediterranean sea these scvs are characterized by small radius 5 km very low potential vorticity high aspect ratio 0 1 and extended lifetime 0 5 yr

evolution of the large scale temperature field in the greenland sea during 1988 89 from tomographic measurements the greenland sea ocean acoustic tomography experiment was conducted during 1988 89 as one component of the international greenland sea project to study deep water formation and the response of the gyre to variations in wind stress and ice cover six acoustic transceivers moored in an array 200 km across transmitted to one another at four hour intervals near the end of february 1989 a sub surface temperature maximum at several hundred meters depth disappeared over a surprisingly large area of the central greenland sea while the water column was modified to about 1000 m depth over much of the gyre the surface remained colder than the deeper water contrary to what might be expected from simple models of convective renewal

eddies in the labrador sea as observed by profiling rafos floats and remote sensing abstract data from profiling rafos floats topex poseidon altimetry and the alongtrack scanning radiometer atsr aboard ers 1 have been used to describe the spatial and seasonal patterns of eddy variability in the labrador sea peaks in sea surface height ssh variability appear in two regions off the west greenland shelf near 61 5 n 52 w where the 3000 m isobath separates from the shelf and in the center of the basin at 58 n 52 w both locations show seasonal ranges in ssh variability of up to 40 mm with the greenland site having largest variability in january march leading the central site by 50 days a sea surface temperature image from the atsr at the greenland site shows numerous eddies both cyclonic and anticyclonic being formed by injection of west greenland current water into the labrador sea interior data from profiling rafos floats launched in 1997 as part of the labrador sea deep convection experiment are used to describe three of the west greenland current eddies in detail one of

scales and dynamics of submesoscale coherent vortices formed by deep convection in the northwestern mediterranean sea since 2010 an intense effort in the collection of in situ observations has been carried out in the northwestern mediterranean sea thanks to gliders profiling floats regular cruises and mooring lines this integrated observing system enabled a year to year monitoring of the deep waters formation that occurred in the gulf of lions area during four consecutive winters 2010 2013 vortical structures remnant of wintertime deep vertical mixing events were regularly sampled by the different observing platforms these are submesoscale coherent vortices scvs characterized by a small radius 5 8 km strong depth intensified orbital velocities 10 20 cm s 1 with often a weak surface signature high rossby 0 5 and burger numbers o 0 5 1 anticyclones transport convected waters resulting from intermediate 300 m to deep 2000 m vertical mixing cyclones are characterized by a 500 1000 m thick layer of weakly stratified deep waters or bottom waters that cascaded from the shelf of the gulf of lions in 2012 extending down to the bottom of the ocean at 2500 m the formation of cyclonic eddies seems to be favored by bottom reaching convection occurring during the study period or cascading events reaching the abyssal plain we confirm the prominent role of anticyclonic scvs and shed light on the important role of cyclonic scvs in the spreading of a significant amount 30 of the newly formed deep waters away from the winter mixing areas since they can survive until the following winter they can potentially have a great impact on the mixed layer deepening through a local preconditioning effect

active surface deformation and sub lithospheric processes in the western mediterranean constrained by numerical models we present the results of dynamic modeling of the western mediterranean that accounts for observed global positioning system gps surface deformation of the alboran sea and surrounding rif and betic mountains as the result of the combined effects of relative motion of the eurasian and nubian plates low strength in the alboran sea region and sub lithospheric processes occurring beneath the external rif domain assuming that the lithosphere behaves elastically over the short time period of the gps observations an elastic plate model is considered in our study including an area of weak lithosphere factor of 10 centered on the alboran sea and in which lateral boundary conditions consist of the nubia eurasia oblique convergence sub crustal processes are modeled by application of a horizontal traction on a small area patch at the base of the elastic plate our modeling studies demonstrate the need for sub crustal or sub lithospheric southwestward directed forcing to account for observed southwestward motion of the rif and betic domains based on the location orientation and small area of the traction patch we hypothesize that forcing is associated with delamination and rollback of the subducted african continental lithospheric mantle beneath the external rif zone due to the pull of the oceanic part of the western mediterranean slab a dynamic process that may be similar to that where the over riding plate is driven toward the subduction zone during slab rollback

crustal structure beneath the rif cordillera north morocco from the rifsis wide angle reflection seismic experiment the different geodynamic models proposed since the late 1990s to account for the complex evolution of the gibraltar arc system lack definite constraints on the crustal structure of the rif orogen here we present the first well resolved p wave velocity crustal models of the rif cordillera and its southern continuation toward the atlas made using controlled source seismic data two 300 km long wide angle reflection profiles crossed the rif along ns and ew trends the profiles recorded simultaneously five land explosions of 1tn each using 850 high frequency seismometers the crustal structure revealed from 2 d forward modeling delineates a complex laterally varying crustal structure below the rif domains the most surprising feature seen on both profiles is a 50 km deep crustal root localized beneath the external rif to the east the crust thins rapidly by 20 km across the nekkor fault indicating that the fault is a crustal scale feature on the ns profile the crust thins more gradually to 40 km thickness beneath middle atlas and 42 km beneath the betics these new seismic results are in overall agreement with regional trends of bouguer gravity and are consistent with recent receiver function estimates of crustal thickness the complex crustal structure of the rif orogen in the gibraltar arc is a consequence of the miocene collision between the iberian and african plates both the abrupt change in crustal thickness at the nekkor fault and the unexpectedly deep rif crustal root can be attributed to interaction of the subducting alboran slab with the north african passive margin at late oligocene early miocene times

localized convection in rotating stratified fluid we study the convective overturning of a rotating stratified fluid in the laboratory convection is induced from the surface of a salt stratified fluid by the introduction of salty fluid over a circular area the external parameters are buoyancy forcing of strength b0 applied over a circular area of radius r the rotation rate as measured by f ambient stratification n and the depth h the experiments are motivated by physical scaling arguments which attempt to predict the length and velocity scales of the convective chimney as it adjusts under gravity and rotation and breaks up through baroclinic instability the scales of interest include the number size and typical speeds of the fragments of the broken chimney the final depth of penetration of the convective mixed layer and the total volume of convectively produced water these scales are tested against the laboratory experiments and found to be appropriate in this idealized problem we have found the depth of penetration depends only on the size and strength of the forcing and the ambient stratification encountered by the convection event it does not depend explicitly on rotation the implications of the work to deep water formation in the labrador sea and elsewhere are discussed finally the study has relevance to the role and representation of baroclinic eddies in large scale circulation of the ocean

topographic advection of dense bottom water the time development of a dense eddy placed on a varying topography in a rotating system is the subject of this paper it is shown that if the bathymetric variations are comparable with the thickness of the eddy these will induce a first order time development in the water mass large amplitude geostrophic theory shows that the water is advected along the depth contours with a speed that is proportional to the slope of the bottom the results are applied to a laboratory experiment with a rotating parabolic channel according to theory an initially circular eddy placed in the centre of the channel becomes elliptical while shifting its axis along the channel the outcome of the experiment is in accordance with theory and the importance of topographic advection in the ocean is discussed it is suggested that the mechanism may be important for moving water from deep water formation sites and into the global deep water circulation

a heton model of the spreading phase of open ocean deep convection abstract a point vortex heton model of the lateral dispersion of cold water formed in open ocean deep convection is developed and studied as an idealized representation of the sinking and spreading phase of open ocean deep convection the overturning and geostrophic adjustment of dense fluid on and below the radius of deformation scale formed by cooling on the large scale are parameterized in the model by introducing paired discrete point vortices hetons of cyclonic sense in the surface layer anticyclonic below driving a cold baroclinic vortex the convection site is imagined to be made up of many such baroclinic vortices each with a vertically homogeneous core carrying cold convectively tainted waters the point vortices are introduced at a rate that depends on the large scale cooling and the intensity assumed for each vortex the interaction of many cold baroclinic vortices making up a cloud is studied using point vortex green s function techniques the current solenoids of the individual ele

evolution of retreating subduction boundaries formed during continental collision retreating subduction boundaries formed where the rate of subduction exceeds the rate of overall plate convergence appear to be commonly developed features within regions of early or incomplete continent continent collision they are characterized by regional extension within the overriding plate and at their leading edge by thin skinned arcuate thrust belts that are concave towards the overriding plate as is illustrated by examples from the mediterranean region the formation of retreating subduction boundaries is intimately related to the process of continental collision during the early stages of collision retreating subduction boundaries are commonly formed by lateral ejection from zones of crustal shortening along the main collision boundary retreating plate boundaries can also form before the main collision and the associated thrust belts emplaced as precollisional accretionary assemblages because the driving mechanism for retreating subduction boundaries appears to be gravity acting on a dense subducted slab slab pull subduction usually ceases when and only when thick buoyant continental crust enters the subduction zone thus differences in the evolution and duration of retreating subduction systems can be largely attributed to the size and configuration of the deep water regions available to be subducted in some cases retreating subduction boundaries may escape into the open ocean where they form nearly isolated local tectonic systems in these systems the rate of subduction is approximately compensated by the rate of upper plate extension and migration of the system across the oceanic region may be very rapid for example the horseshoe seamounts located about 800 km offshore in the eastern north atlantic may be the active expression of an east dipping westwardly migrating retreating subduction boundary that has evolved from the betic cordillera rif system active in miocene time and may now be progressing across the atlantic at approximately 50 mm yr an analogous situation may be represented by the scotia arc system a westward dipping retreating subduction system located between the south american and antarctic plates which may have escaped into the south atlantic ocean from a zone of crustal shortening in the andes and is now progressing across the atlantic at a rate of about 80 mm yr

restratification after deep convection abstract an important yet poorly understood aspect of the water mass transformation process in the ocean is the manner in which the convected fluid once formed is accommodated and drawn into the general circulation following violent mixing in the open ocean that creates a deep homogenous body of fluid restratification of the surface 500 m layer is observed to occur rapidly sealing over the convection patch recent hydrographic casts and tomography inversions in the gulf of lions by send et al for example show that very quickly within a week or so of the cessation of cooling a stratified near surface layer develops on top of the mixed patch this restratification occurs much more rapidly than can be accounted for by air sea fluxes by analytical and numerical study the authors argue that advection by geostrophic eddies spawned by the baroclinic instability of the mixed patch is likely to be a principal mechanism by which restratification occurs a restratification timescale restrat 56r

are some of the deep crustal conductive features found in sw iberia caused by graphite abstract recent results obtained from two dimensional inversion of magnetotelluric mt data acquired in sw iberia reveal high conductive features at the middle lower levels of the crust the top of these anomalous structures correlates very well with the depth 10 13 km of an important seismic interface that has been interpreted as a regional detachment horizon very shallow and relatively narrow conductors in the ossa morena zone appear to correspond to small scale fluid deposited graphite systems in the preorogenic metasedimentary sequences some of the midcrustal conductors can be ascribed to graphite bearing thrust zones the formation of graphite with variable crystallinity being a consequence of variscan shearing processes deep seated conductors are tentatively interpreted as a result of relatively continuous highly crystalline grain boundary graphite films presumably preserved in basement granulite rocks assuming that graphite occurs as interconnected films calculations indicate that a fraction of 0 006 0 02 of this accessory mineral is enough to explain the range of the electrical resistivity estimated on the basis of mt models the role of graphite on the thermal behaviour of the crust is also discussed the results show that low contents of graphite do not significantly change the thermal behaviour of earth materials

boundary current eddies and their role in the restratification of the labrador sea an idealized model is used to study the restratification of the labrador sea after deep convection with emphasis on the role of boundary current eddies shed near the west coast of greenland the boundary current eddies carry warm buoyant irminger current water into the labrador sea interior for a realistic end of winter state it is shown that these irminger current eddies are efficient in restratifying the convected water mass in the interior of the labrador sea in addition it is demonstrated that irminger current eddies can balance a significant portion of the atmospheric heat loss and thus play an important role for the watermass transformation in the labrador sea

exhumation of high pressure rocks driven by slab rollback rocks metamorphosed under high pressure hp and ultra high pressure uhp conditions in subduction zones come back to the surface relatively soon after their burial and at rates comparable to plate boundary velocities in the mediterranean realm their occurrence in several belts related to a single subduction event shows that the burial exhumation cycle is a recurrent transient process using the calabria apennine and aegean belts as examples we show that the exhumation of hp rocks is associated in time and space with the subduction of small continental lithosphere blocks that triggers slab rollback creating the necessary space for the exhumation of the buoyant continental crust that was deeply buried just before the buoyancy force of the subducted crust increases until this crust detaches from the downgoing slab it then exhumes at a rate that depends directly on the velocity of trench retreat to become part of the overriding plate heated from below by the asthenosphere that flows into the opening mantle wedge the exhumed crust weakens and undergoes core complex type extension responsible for a second stage of exhumation at a lower rate the full sequence of events that characterizes this model crust mantle delamination slab rollback and trench retreat hp rock exhumation asthenosphere heating and core complex formation arises entirely from the initial condition imposed by the subduction of a small continental block no specific condition is required regarding the rheology and erosion rate of hp rocks the burial exhumation cycle is transient and can recur every time a small continental block is subducted

geodynamic evolution of the lithosphere and upper mantle beneath the alboran region of the western mediterranean constraints from travel time tomography an edited version of this paper was published by the american geophysical union copyright 2000 agu see also http www agu org pubs crossref 2000 2000jb900024 shtml http atlas geo cornell edu morocco publications calvert2000 htm

on the connection between dense water formation overturning and poleward heat transport in a convective basin an isopycnal two layer idealized model for a convective basin is proposed consisting of a convecting interior region and a surrounding boundary current buoyancy and wind driven parameterized eddy fluxes govern the exchange between the two to balance the interior buoyancy loss the boundary current becomes denser as it flows around the basin geostrophy imposes that this densification be accompanied by sinking in the boundary current and hence by an overturning circulation the poleward heat transport associated with convection in the basin can thus be viewed as a result of both an overturning and a horizontal circulation when adapted to the labrador sea the model is able to reproduce the bulk features of the mean state the seasonal cycle and even the shutdown of convection from 1969 to 1972 according to the model only 40 of the poleward heat buoyancy transport of the labrador sea is associated with the overturning circulation an exact solution is presented for the linearized equations when changes in the boundary current are small numerical solutions are calculated for variations in the amount of convection and for changes in the remotely forced circulation around the basin these results highlight how the overturning circulation is not simply related to the amount of dense water formed a speeding up of the circulation around the basin due to wind forcing for example will decrease the intensity of the overturning circulation while the dense water formation remains unvaried in general it is shown that the fraction of poleward buoyancy or heat transport carried by the overturning circulation is not an intrinsic property of the basin but can vary as a result of a number of factors

mantle structure under gibraltar constrained by dispersion of body waves 1 westudytheafrica iberiaplateboundaryinthevicinity of gibraltar numerous models have been proposed for that region throughout the last decades proposing mechanisms that range widely from continental delamination convective removal to subduction of oceanic lithosphere to better constrain upper mantle structure under the region we study waveforms of p waves that traverse the alboran sea region between spain and morocco these show dispersive behavior which together with early arrival times confirms the presence of an anomalous upper mantle structure under the alboran sea the dispersion is consistent with that expected from subducted lithosphere waveforms of body waves therefore provide a way to better constrain the elusive mantle structure and dynamics of the alboran sea region citation bokelmann g and e maufroy 2007 mantle structure under gibraltar constrained by dispersion of body waves geophys res lett 34 l22305 doi 10 1029 2007gl030964

lateral heat exchange after the labrador sea deep convection in 2008 abstractthe mechanisms through which convected water restratifies in the labrador sea are still under debate the labrador sea restratification after deep convection in the 2007 08 winter is studied with an eddy resolving numerical model the modeled mixed layer depth during wintertime resembles the argo observed mixed layer very well and the lateral heat flux during the subsequent restratification is in line with observations the irminger rings irs are reproduced with fresher caps above the 300 m depths and they are identified and tracked automatically the model underestimates both the number of irs in the convection area and the heat they carry the underestimation is most likely caused by the errors in the direction of the west greenland currents in the model which causes more irs propagating westward and only the irs originating south of 61 5 n are able to propagate southward yet with speed much slower than observed speed the model still observed three eddies propagating into the convection

crustal structure of the central sector of the betic cordillera se spain deep seismic reflection gravimetric and magnetometric data allow the main features of the deep structure of the central sector of the betic cordillera to be established the moho is horizontal or dips slightly toward the s below the mountain chain and its morphology has no direct relationship with the region s topography the deep reflectors are not deformed by the neogene kilometric scale folds that produced the main topographic features probably due to the existence of detachment levels in the crust the crust is slightly thickened in the betic cordillera almost 35 km and has an abrupt transition to the thin crust of the alboran sea 15 km in the central alboran sea along an e w oriented narrow band subparallel to the coast line where the moho dips more than 60 n the neogene evolution of the mountain chain caused compressive deformation in the external zones in the internal zones pre tortonian low angle normal faults developed after the alpine metamorphism and later high and low angle normal faults and strike slip faults occurred up to the quaternary geophysical and field geology data can be used to establish a geological model for the recent evolution of the crustal deformation in this model the recent evolution of the region is probably determined by thrusting of the thin continental crust of the alboran sea toward the nw over the southern margin of the iberian massif this deformation could be a consequence of the oblique convergent movement between the african and eurasian plates which may have uplifted the entire region causing regressions in the sedimentary basins and the formation of folds and extensional structures in the upper part of the thickened crust

a laboratory model of thermocline depth and exchange fluxes across circumpolar fronts a laboratory experiment has been constructed to investigate the possibility that the equilibrium depth of a circumpolar front is set by a balance between the rate at which potential energy is created by mechanical and buoyancy forcing and the rate at which it is released by eddies in a rotating cylindrical tank the combined action of mechanical and buoyancy forcing builds a stratification creating a large scale front at equilibrium the depth of penetration and strength of the current are then determined by the balance between eddy transport and sources and sinks associated with imposed patterns of ekman pumping and buoyancy fluxes it is found that the depth of penetration and transport of the front scale like l and wel2 respectively where fw g9 e we is the ekman pumping g9 is the reduced gravity across the front f is the coriolis parameter and l is the width scale of the front last the implications of this study for understanding those processes that set the stratification and transport of the antarctic circumpolar current acc are discussed if the laboratory results scale up to the acc they suggest a maximum thermocline depth of approximately h 5 2 km a zonal current velocity of 4 6 cm s 21 and a transport t 5 150 sv 1 sv 106 m3 s 21 not dissimilar to what is observed

seismic tomography from local crustal earthquakes beneath eastern rif mountains of morocco we applied a tomographic method to image an aseismic strike slip fault in north morocco and found that the occurrence of earthquakes is not only controlled by the state of tectonic stress but also by material heterogeneity in the crust we have constructed an integrated model of seismic electric magnetic and heat flow properties across northeastern morocco primarily based on a tomography inversion of local earthquake arrival times the seismic images obtained show a pronounced lowvelocity zone at 5 km depth parallels to the nekor fault coinciding with an anomalously high conductive and low gravity structure which is interpreted as a fault gouge zone and or a fluid filled subsurface rock matrix below 10 km depth a weak positive velocity zone indicates that the fault gouge is stable the seismicity and the seismic velocity results for the alhoceimas region show that the concentrations of earthquakes are confined in the high velocity area this anomaly is interpreted to be a brittle and competent layer of the upper crust that sustains seismogenic stress on the eastern coast line of morocco we infer that a high density high velocity body exists in the shallowest layers of the upper crust probably formed by miocene volcanic rocks d 2003 elsevier science b v all rights reserved

a rapid method to map the crustal and lithospheric thickness using elevation geoid anomaly and thermal analysis application to the gibraltar arc system atlas mountains and adjacent zones we present a method based on the combination of elevation and geoid anomaly data together with thermal field to map crustal and lithospheric thickness the main assumptions are local isostasy and a four layered model composed of crust lithospheric mantle sea water and the asthenosphere we consider a linear density gradient for the crust and a temperature dependent density for the lithospheric mantle we perform sensitivity tests to evaluate the effect of the variation of the model parameters and the influence of rms error of elevation and geoid anomaly databases the application of this method to the gibraltar arc system atlas mountains and adjacent zones reveals the presence of a lithospheric thinning zone sw ne oriented this zone affects the high and middle atlas and extends from the canary islands to the eastern alboran basin and is probably linked with a similarly trending zone of thick lithosphere constituting the western betics eastern rif rharb basin and gulf of cadiz a number of different even mutually opposite geodynamic models have been proposed to explain the origin and evolution of the study area our results suggest that a plausible slab retreating model should incorporate tear and asymmetric roll back of the subducting slab to fit the present day observed lithosphere geometry in this context the lithospheric thinning would be caused by lateral asthenospheric flow an alternative mechanism responsible for lithospheric thinning is the presence of a hot magmatic reservoir derived from a deep ancient plume centred in the canary island and extending as far as central europe

a high electrical conductive zone at lower crustal depth beneath the betic chain spain abstract magnetotelluric data with periods of up to 2000 s were collected and the conductivity structure of the crust and upper mantle was imaged in the central betic chain interpretation of the impedance tensor components and the geomagnetic transfer functions was made in terms of a two dimensional resistivity model along a nw se profile from the guadalquivir foreland basin and across the boundary between the external and the internal betics elongated high conductivity zones in the upper and middle crust related to fluid circulation along both sediments and faults were detected the conductors in the upper crust coincide with the areal distribution of the cenozoic and mesozoic sedimentary rocks from the guadalquivir basin and the external betics and the conductors in the middle crust with the major miocene extensional detachments affecting the basement rocks of the internal betic zone a high conductivity zone at lower crustal levels beneath the outer internal betics was also detected next to an area where earlier seismic reflection data had imaged a duplication of the reflective moho this conductor was interpreted as partial melting of a southeast dipping subducted iberian lower crust the geodynamic significance of this subduction depends mainly on whether the overthrusting lower crust belongs to the alboran domain or to the iberian plate in the former case it would correspond to a major plate boundary and in the latter to an intraplate feature

parameterization of mixed layer eddies part i theory and diagnosis ageostrophic baroclinic instabilities develop within the surface mixed layer of the ocean at horizontal fronts and efficiently restratify the upper ocean in this paper a parameterization for the restratification driven by finite amplitude baroclinic instabilities of the mixed layer is proposed in terms of an overturning streamfunction that tilts isopycnals from the vertical to the horizontal the streamfunction is proportional to the product of the horizontal density gradient the mixed layer depth squared and the inertial period hence restratification proceeds faster at strong fronts in deep mixed layers with a weak latitude dependence in this paper the parameterization is theoretically motivated confirmed to perform well for a wide range of mixed layer depths rotation rates and vertical and horizontal stratifications it is shown to be superior to alternative extant parameterizations of baroclinic instability for the problem of mixed layer restratification two companion papers discuss the numerical implementation and the climate impacts of this parameterization

dynamics of downwelling in an eddying marginal sea contrasting the eulerian and the isopycnal perspective abstractin this study we explore the downward branch of the atlantic meridional overturning circulation amoc from a perspective in depth space eulerian downwelling as well as from a perspectiv

rheological and tectonic modeling of salt provinces abstract technological improvements and a more rigorous research approach have led the petroleum industry to renew and expand its interest in physical modeling of faulting associated with halokinesis salt tectonics and the formation of structural hydrocarbon traps can be reproduced in models using viscous polymers for the substratum and frictional plastic granular materials for the overburden the fault patterns simulated in these dynamically scaled models are remarkably similar to those in depth converted seismic sections scale models are therefore useful for generating new concepts and for reconstructing the structural evolution of hydrocarbon traps although even unsealed models may help generating ideas the full transfer of quantitative data requires that models be dynamically scaled to their natural prototypes previously published scaling theory for salt tectonics has erroneously assumed fluid behaviour of the overburden this paper provides a sound scaling approach for geological deformations involving brittle overburdens on ductile substrata rheological data from overburden rocks and salt are compiled and compared to model rheologies using dimensions of laboratory analogs and other intrinsic material properties scaling approaches are compared and rules are formulated for achieving dynamic similarity in models of salt tectonics including those with synkinematic sedimentation

equilibration of a warm pumped lens on a β plane abstract the dynamics of a warm lens created by a surface buoyancy flux and ekman pumping in an initially homogeneous unbounded fluid on a plane is studied in a set of high resolution numerical experiments a simple analytical model for the equilibrium structure of the lens is developed that assumes that the input of vorticity and buoyancy from the ekman layer is balanced through transfer by baroclinic eddies that carry the warm fluid laterally away from the lens the importance of eddy induced diapycnal flux in the western intensification region is emphasized by developing a boundary layer theory based entirely on the cross frontal mass exchange due to eddies the theory is successfully tested against direct numerical eddy resolving simulations possible oceanographic implications of the study for understanding subtropical gyres and the antarctic circumpolar current are discussed

two receiver measurements of phase velocity cross validation of ambient noise and earthquake based observations phase velocities derived from ambient noise cross correlation are compared with phase velocities calculated from cross correlations of waveform recordings of teleseismic earthquakes whose epicentres are approximately on the station station great circle the comparison is conducted both for rayleigh and love waves using over 1000 station pairs in central europe we describe in detail our signal processing method which allows for automated processing of large amounts of data ambient noise data are collected in the 5 80 s period range whereas teleseismic data are available between about 8 and 250 s resulting in a broad common period range between 8 and 80 s at intermediate periods around 30 s and for shorter interstation distances phase velocities measured from ambient noise are on average between 0 5 per cent and 1 5 per cent lower than those observed via the earthquake based method this discrepancy is small compared to typical phase velocity heterogeneities 10 per cent peak to peak or more observed in this period range we nevertheless conduct a suite of synthetic tests to evaluate whether known biases in ambient noise cross correlation measurements could account for this discrepancy we specifically evaluate the effects of heterogeneities in source distribution of azimuthal anisotropy in surface wave velocity and of the presence of near field rather than far field only sources of seismic noise we find that these effects can be quite important comparing individual station pairs the systematic discrepancy is presumably due to a combination of factors related to differences in sensitivity of earthquake versus noise data to lateral heterogeneity the data sets from both methods are used to create some preliminary tomographic maps that are characterized by velocity heterogeneities of similar amplitude and pattern confirming the overall agreement between the two measurement methods

baroclinic instability and submesoscale eddy formation in weakly stratified oceans under cooling 1 numerical experiments with a three dimensional nonhydrostatic model have been performed to investigate baroclinic instability and submesoscale eddy formation in weakly stratified oceans under cooling two types of baroclinic instability can exist in a two layered ocean where the convectively formed deep mixed layer overlies the weakly stratified lower layer one rapidly develops in the mixed layer with short wavelengths shallow mode and the other occupies the whole ocean depth with long wavelengths deep mode when a background flow is deep the shallow mode develops first but the deep mode replaces it in several days in contrast only the shallow mode is excited in the mixed layer overlying the strongly stratified layer the linear stability analysis explains these results well despite active cooling subsequently formed eddies restratify the mixed layer and modify water density over the whole depth when a background flow is shallow baroclinic instability is confined to the mixed layer and produces a dipole of surface intensified cyclonic eddy and middepth intensified anticyclonic eddy both of which are of submesoscale 10 km the anticyclonic eddy consisting of convectively formed but weakly stratified water moves across the front to ventilate the deep layer where convection does not reach locally in this way density modification extends below the mixed layer surface cooling as well as baroclinicity enhances restratification of the mixed layer and density modification at depths by activating submesoscale eddy formation the results can explain the restratification of the deep mixed layer observed during a cooling season and the origins of submesoscale coherent vortices recently detected in polar oceans

heat flux partitioning in open ocean convection abstract cold air blowing out over a warm ocean leads to convection over an isolated region of the ocean basin this phenomenon known as open ocean convection is often simulated by convective forcing from a circular disk much smaller than the dimension of the domain an important feature of these simulations is the development of eddies at the edge of the disk that serve to transport heat horizontally this has sparked interest in the heat flux characteristics of such a system this paper deals with the thermodynamic properties of this type of convective flow using a rotating tank with bottom mounted hotplate as the experimental apparatus experiments are performed in an initially unstratified fluid for a set of values of the nondimensional forcing parameter rc b1 2 hf3 2 where b is the buoyancy flux h is the fluid depth and f is the coriolis parameter the ratio of the frontal eddy size to the hotplate radius is shown to be an important parameter the experiments reported are for the regi

variability of the large scale general circulation of the mediterranean sea from observations and modelling a review abstract in this paper we present an overview of the most recent findings about the mediterranean sea present day circulation structure both historical observations and numerical model simulations are presented outlining the differences and agreement the model simulations are presented for both an eddy resolving and a coarse resolution numerical model and the results are intercompared the importance of the mesoscales in modifying the large scale flow field is elucidated the critical point is the discovery of the large amplitude interannual variability of the circulation and water mass structure associated with the anomalies of atmospheric forcing over the basin the seasonal variability can be strictly related to changes in heat and momentum fluxes while the interannual variability has a component which is related to the mesoscale field the latter is very intense in the algerian current region and levantine basin but different in structure in the two regions results are shown which confirm the importance of wind driving in establishing the kinetic energy of the flow field by comparing the current transport at the strait of corsica with observations in conclusion the essential characteristics of the present day circulation are associated with the atmospheric forcing and the basin topographic structure results from palaeoceanographic simulations for the last 20 000 years show that changing the atmospheric forcing can cause large changes in the circulation structure which may have affected sapropel formation

open ocean convection observations theory and models we review what is known about the convective process in the open ocean in which the properties of large volumes of water are changed by intermittent deep reaching convection triggered by winter storms observational laboratory and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales the large scale circulation of the ocean and the prevailing meteorology two aspects make ocean convection interesting from a theoretical point of view first the timescales of the convective process in the ocean are sufficiently long that it may be modified by the earth s rotation second the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability moreover the convective and geostrophic scales are not very disparate from one another detailed observations of the process in the labrador greenland and mediterranean seas are described which were made possible by new observing technology when interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection great progress in our description and understanding of the processes at work is being made

modeling the deep convection in the northwestern mediterranean sea using an eddy permitting and an eddy resolving model case study of winter 1986 1987 1 in the northwestern mediterranean sea winter 1986 1987 was particularly cold inducing a strong open ocean convection event in order to investigate the impact of numerical models spatial resolution on the convection representation and the effects of deep convection on the northwestern mediterranean circulation we perform two numerical three dimensional simulations eddy permitting versus eddy resolving models are forced at the surface by the era40 atmospheric fluxes with a simple heat flux correction to better mimic the observed value we examine the characteristics of the deep convection mixed layer water masses characteristics convection zone and mesoscale structures and perform temporal analysis of this event in terms of kinetic energy buoyancy equilibrium and deep water dw evolution the convection characteristics are similarly represented on a global scale by both models and are in good agreement with observations except for the size of the convection region however the eddy resolving model better reproduces the mesoscale structures whose role in the dw formation mixing and transport is shown to be essential the boundary circulation and the overturning are enhanced during the convection event sixty six percent of the dw spreading is due to the bleeding effect into the catalan sea during the convection event whereas 33 is due to the mesoscale structures southwestward advection after the event sixty percent of the restratification with respect of the water column initial structure occurs before july 1987 and is due to light water advection afterward restratification is due to the mixing and is not complete before next year convection

coherent eddies in the labrador sea observed from a mooring abstract during june november 1994 a mooring in the central labrador sea near the former ocean weather station bravo recorded a half dozen anomalous events that prove to be two different types of coherent eddies comparisons with simple analytical models are used to classify these events as coherent eddies on the basis of their velocity signatures the first clear examples of long lived convectively generated eddies are reported these four small radius 5 15 km eddies are exclusively anticyclonic with cold fresh middepth potential temperature and salinity s cores surrounded by azimuthal currents of 15 cm s 1 their s properties identify them unambiguously as the products of wintertime deep convection in the interior labrador sea compared with eddies in other regions these anticyclones are unusual for their strong surface expressions and composite s cores two warm cyclones are also seen these are larger radius 15 km than the anticyclones and about as energetic currents 15 cm s 1

discussion of origins of hinterland basins to the rif betic cordillera and carpathians abstract the hinterland basins of the rif betic cordillera western alboran sea and the carpathians pannonian basin are in part composed of a thick in excess of 3 4 km thermal sag basin sequence the underlying crust has been thinned to 25 km in parts of the pannonian basin and to 15 km in parts of the alboran sea modern tectonic models for these areas envision tectonic collision and thickening of the crust followed by crustal thinning either by gravitational collapse back arc extension or a combination of the two contemporaneous with thrusting basin and range type extension has been envisioned for parts of these extensional collapse systems extensional features are common and they interact in a complex way with strike slip systems flexural cantilever modelling agrees with earlier mckenzie type pure shear modelling of the extensional systems in suggesting that extension alone cannot generate sufficient thermal decay to explain the great thickness of the sag basins associated with the alboran sea and pannonian basin consequently it is suggested that uplift of the asthenosphere accompanying subduction roll back is an important factor in the evolution of these basins roll back of the mantle lithosphere permits hot asthenospheric mantle to upwell and lie close to the base of the crust initially uplift and erosion of the crust overlying the asthenosphere occurs as the thermal perturbation cools the crust thermally subsides to produce a large sag basin

the interannual variability of the surface eddy kinetic energy in the labrador sea abstract the variability of the surface eddy kinetic energy eke in the labrador sea is investigated with a suite of numerical integrations using a regional ocean model simulations are performed over the period 1980 2001 and are compared to satellite observations over the last 9 years the surface eke pattern in the basin is dominated by a region along the west coast of greenland where eddies mainly anticyclonic are formed by instability of the main currents flowing over the continental slope consistent with previous idealized results here the interannual changes are linked to the shear of the incoming boundary current system imposed as boundary condition to the model domain the highly variable strength of the east greenland current at the northeast boundary derived from the simple ocean data assimilation soda reanalysis strongly influences the vortex formation in the center of the labrador sea where deep convection occurs a statistically significant portion of the modeled interannual surface eke variability is correlated with the local atmospheric forcing and both heat and wind fluxes play an important role and can be adopted as predictors at a lag of 2 3 months the arctic oscillation index can also be used as a remote indicator of the atmospheric fluxes but with lower skill than local measurements in contrast the north atlantic oscillation index does not correlate significantly with the surface eke at intraseasonal and interannual scales the analysis of altimeter data over the 1993 2001 supports the existence of this asymmetry between the regime locally forced by the atmosphere in the central basin and the regime remotely forced by the incoming boundary current along the west greenland coast those results have important implications for monitoring and predicting the surface eddy kinetic energy variability in the labrador sea

mixed layer instabilities and restratification abstract the restratification of the oceanic surface mixed layer that results from lateral gradients in the surface density field is studied the lateral gradients are shown to be unstable to ageostrophic baroclinic instabilities and slump from the horizontal to the vertical these instabilities which are referred to as mixed layer instabilities mlis differ from instabilities in the ocean interior because of the weak surface stratification spatial scales are o 1 10 km and growth time scales are on the order of a day linear stability analysis and fully nonlinear simulations are used to study mlis and their impact on mixed layer restratification the main result is that mlis are a leading order process in the ml heat budget acting to constantly restratify the surface ocean climate and regional ocean models do not resolve the scales associated with mlis and are likely to underestimate the rate of ml restratification and consequently suffer from a bias in sea surface temperatures and ml depths in a

recent advances in observing the physical oceanography of the western mediterranean sea the mediterranean sea has been investigated intensively since the early nineties using modern techniques and collaborative approaches this overview summarizes some of the resulting advances that were made concerning the physical oceanography of the western mediterranean the water mass formation processes are now much better understood and have been quantified to a large extent the boundary conditions of the system in terms of surface fluxes and strait transports can be determined with improved accuracy thus enabling future investigation of interannual variability the dynamics of the surface and intermediate layers have revealed a variety of eddy and mesoscale processes that are important for the circulation and spreading of water masses the deep circulation is being investigated with lagrangian techniques tracers and floats first results show a large component of the deep water originating from the tyrrhenian sea and intense cyclonic and anticyclonic eddy flows

can eddies set ocean stratification abstract a simple theory is presented for the buoyancy anomaly and depth of penetration of a warm lens created by a surface buoyancy flux and ekman pumping in an initially homogeneous rotating fluid it is assumed that the overturning of isopycnals induced by pumping and differential heating balances the counteroverturning tendency of baroclinic instability baroclinic eddies not only develop on the stratified lens but also play a fundamental role in setting its stratification the theory is successfully tested against numerical and laboratory experiments in which the mechanically induced deepening of a buoyant lens is arrested by its baroclinic instability finally the possibility is discussed that the eddy transfer process studied here might play a role in setting the stratification and depth of the main thermocline in the ocean

observations of the labrador sea eddy field this paper is an observational study of small scale coherent eddies in the labrador sea a region of dense water formation thought to be of considerable importance to the north atlantic overturning circulation numerical studies of deep convection emphasize coherent eddies as a mechanism for the lateral transport of heat yet their small size has hindered observational progress a large part of this paper is therefore devoted to developing new methods for identifying and describing coherent eddies in two observational platforms current meter moorings and satellite altimetry details of the current and water mass structure of individual eddy events as they are swept past by an advecting flow can then be extracted from the mooring data a transition is seen during mid 1997 with long lived boundary current eddies dominating the central labrador sea year round after this time and convectively formed eddies similar to those seen in deep convection modeling studies apparent prior to this time the topex poseidon altimeter covers the labrador sea with a loose net of observations through which coherent eddies can seem to appear and disappear by concentrating on locating and describing anomalous events in individual altimeter tracks a portrait of the spatial and temporal variability of the underlying eddy field can be constructed the altimeter results reveal an annual pulsation of energy and of coherent eddies originating during the late fall at a particular location in the boundary current pinpointing the time and place of the boundary current type eddy formation the interannual variability seen at the mooring is reproduced but the mooring site is found to be within a localized region of greatly enhanced eddy activity notably lacking in both the annual cycle and interannual variability is a clear relationship between the eddies or eddy energy and the intensity of wintertime cooling these eddy observations as well as hydrographic evidence suggest an active role for boundary current dynamics in shaping the energetics and water mass properties of the interior region

convection with rotation in a neutral ocean a study of open ocean deep convection abstract the intensity and scale of the geostrophically adjusted end state of the convective overturning of a homogeneous rotating ocean of depth h at a latitude where the coriolis parameter is f induced by surface buoyancy loss of magnitude b0 are studied by numerical experiment the experiments are related to observations and laboratory studies of open ocean deep convection a numerical model based on the nonhydrostatic boussinesq equations is used the grid spacing of the model is small enough that gross aspects of convective plumes themselves can be resolved yet the domain of integration is sufficiently large to permit study of the influence of plumes on the large scale and geostrophic adjustment of the convected water numerical simulations suggest that cooling at the sea surface is offset by buoyancy drawn from depth through the agency of convective plumes these plumes efficiently mix the water column to generate a dense chimney of fluid which subsequently breaks up through the mechanism of bar

an estimate of the eddy induced circulation in the labrador sea regions of oceanic deep convection such as the labrador sea are prone to baroclinic instability the resulting geostrophic eddies play a crucial role in the post convection adjustment process which involves both rearrangement of mass so as to release available potential energy and exchange of heat and salt with the boundaries in this study it is proposed that the slumping of isopycnals associated with baroclinic instability drives an eddy induced overturning circulation consisting of a surface intensified flow transporting low salinity water from the boundary currents into the interior sinking motion in the interior and an outflow at depth transporting newly ventilated labrador sea water towards the boundaries typical eddy induced velocities estimated from hydrographic data are roughly 0 5 cm s for the surface inflow 1 m day for the vertical motion and 0 1 cm s for the deeper outflow in close agreement with those calculated in a numerical model

active tectonics of the western mediterranean geodetic evidence for rollback of a delaminated subcontinental lithospheric slab beneath the rif mountains morocco surface deformation in morocco derived from five years of global positioning system gps survey observations of a 22 station network four continuously recording gps cgps stations and four international gnss service igs stations in iberia indicates roughly southward motion 3 mm yr of the rif mountains morocco relative to stable africa motion of the rif is approximately normal to the direction of africa eurasia relative motion which is predominantly strike slip and results in shortening of the rif and subsequent crustal extension of the adjacent alboran sea region the sense and the n s asymmetry of the observed deformation i e no evidence for north directed shortening in the betic mountains north of the alboran sea cannot be easily explained in terms of crustal plate interactions suggesting that dynamic processes below the crust are driving the recent geologic evolution of the western mediterranean the model that best fits the observations involves delamination and southward rollback of the african lithospheric mantle under the alboran and rif domains

the ghomarides nappes rif coastal range morocco a variscan chip in the alpine belt the ghomarides nappes are the uppermost basement nappes in the rifan alpine belt paleozoic rocks constitute the prominent part of these nappes together with triassic and younger cover sediments four nappes are distinguished each one with a distinct stratigraphical sequence especially for the devonian and carboniferous periods sedimentological and structural arguments plead for an initial location on the northern margin of the african continent the main folding and metamorphic events are shown to be eo variscan late acadian tectonic vergence was to the north present coordinates late variscan hercynian shortening gave upright nw se trending folds alpine ductile overprints are scarce except at the base of the lowest nappe where k ar phengite ages are about 25 ma the ghomarides nappes correlate with the malaguides nappes betic cordilleras southern spain the kabylian northern algeria and calabrian southern italy paleozoic nappes the tuscan south alpine basement and the upper austro alpine nappes the proposed correlations allow us to restaure the southern margin of the hercynian belt along northwestern africa

hydrothermal plume dynamics on europa implications for chaos formation 1 hydrothermal plumes may be responsible for transmitting radiogenic or tidally generated heat from europa s rocky interior through a liquid ocean to the base of its ice shell this process has been implicated in the formation of chaos regions and lenticulae by melting or exciting convection in the ice layer in contrast to earlier work we argue that europa s ocean should be treated as an unstratified fluid we have adapted and expanded upon existing work describing buoyant plumes in a rotating unstratified environment we discuss the scaling laws governing the flow and geometry of plumes on europa and perform a laboratory experiment to obtain scaling constants and to visualize plume behavior in a europa like parameter regime we predict that hydrothermal plumes on europa are of a lateral scale at least 25 50 km comparable to large chaos regions they are too broad to be responsible for the formation of individual lenticulae plume heat fluxes 0 1 10 w m 2 are too weak to allow complete melt through of the ice layer current speeds in the plume 3 8 mm s are much slower than indicated by previous studies the observed movement of ice blocks in the conamara chaos region is unlikely to be driven by such weak flow index terms 6218 planetology solar system objects jovian satellites 5418 planetology solid surface planets heat flow 5430 planetology solid surface planets interiors 8147 4540 oceanography physical ice mechanics and air sea ice exchange processes 4568 oceanography physical turbulence diffusion and mixing processes keywords chaos europa hydrothermal plumes

observation of a deep convection regime with acoustic tomography in the winter of 1991 1992 a convection experiment was conducted in the western mediterranean gulf of lions combining a variety of observational techniques an essential component was an acoustic tomography array consisting of six moorings designed to observe the time evolution of the large scale processes believed to be relevant in a convection regime here two dimensional slice inversions in three directions from the central mooring are used to estimate the volume of convected water and the mean convection depth and to observe the preconditioning and restratification processes before and after the convection the near surface layer is well sampled by the acoustics which show cooling and subsequent entrainment of the warmer levantine intermediate water liw from below in agreement with mixedlayer calculations during the 2 months prior to the main convection event the total heat loss of the large scale field is in approximate agreement with the surface heat fluxes showing that little net warm water advection takes place from outside the convection region the implied confinement of water by the local circulation should be an important factor in setting the location and extent of the deep convection patch the volume of water modified by convection in this winter is estimated to correspond to an area of order 60 km radius and 1500 m depth it is argued that the homogenized area implies an annual mean deep water replenishment of 0 3 sv the restratification by the return of less dense water in the surface and liw layers occurs first by rapid capping in the near surface region thereafter the southern and eastern parts of the region restratify in the deeper layers on a 40 day timescale while a dense core of 50 60 km diameter remains in the northwest until the end of the experiment

horizontal stratification during deep convection in the labrador sea abstractdeep convection the process by which surface waters are mixed down to 1000 m or deeper forms the primary downwelling of the meridional overturning circulation in the northern hemisphere high resolution hydrographic measurements from seagliders indicate that during deep convection though water is well mixed vertically there is substantial horizontal variation in density over short distances tens of kilometers this horizontal density variability present in winter january february contains sufficient buoyancy to restratify the convecting region to observed levels 2 5 months later as estimated from argo floating platforms these results highlight the importance of small scale heterogeneities in the ocean that are typically poorly represented in climate models potentially contributing to the difficulty climate models have in representing deep convection

mesoscale eddies in the labrador sea and their contribution to convection and restratification abstract the cycle of open ocean deep convection in the labrador sea is studied in a realistic high resolution 4 km regional model embedded in a coarser north atlantic setup this configuration allows the simultaneous generation and evolution of three different eddy types that are distinguished by their source region generation mechanism and dynamics very energetic irminger rings irs are generated by barotropic instability of the west greenland and irminger currents wgc ic off cape desolation and are characterized by a warm salty subsurface core they densely populate the basin north of 58 n where their eddy kinetic energy eke matches the signal observed by satellite altimetry significant levels of eke are also found offshore of the west greenland and labrador coasts where boundary current eddies bces are spawned by weakly energetic instabilities all along the boundary current system bcs baroclinic instability of the steep isopycnal slopes that result from a deep convective over

crustal resistivity structure of the southwestern transect of the rif cordillera morocco a ne sw magnetotelluric 110 km long profile including 18 sites was acquired across the western rifcordillera along the eurasian african plate boundary allowing to constrain its poorly known deepstructure it extends from the internal zones close to the alboran coast crossing the external zones andup to the gharb foreland basin the periods recorded range from 0 001 s to 1000 s the combination ofmagnetotelluric data with available geological data provides new insight regarding the relationship

dynamics of isolated convective regions in the ocean abstract an initially resting ocean of stratification n is considered subject to buoyancy loss at its surface of magnitude b0 over a circular region of radius r at a latitude where the coriolis parameter is f initially the buoyancy loss gives rise to upright convection as an ensemble of plumes penetrates the stratified ocean creating a vertically mixed layer however as deepening proceeds horizontal density gradients at the edge of the forcing region support a geostrophic rim current which develops growing meanders through baroclinic instability eventually finite amplitude baroclinic eddies sweep stratified water into the convective region at the surface and transport convected water outward and away below setting up a steady state in which lateral buoyancy flux offsets buoyancy loss at the surface in this final state quasi horizontal baroclinic eddy transfer dominates upright plume convection by using parcel theory to consider the energy transformations taking place it is shown that the de

the dynamics of mixed layer deepening during open ocean convection abstractopen ocean convection is a common phenomenon that regulates mixed layer depth and ocean ventilation in the high latitude oceans however many climate model simulations overestimate mixed l

on mapping the diapycnal water mass transformation of the upper north atlantic ocean abstractdiapycnal water mass transformation is the essence behind the atlantic meridional overturning circulation amoc and the associated heat freshwater transports existing studies have mostly

evidence of a large deep conductive body within the basement of the guadalquivir foreland basin betic cordillera s spain from tipper vector modelling tectonic implications abstract the betic cordillera is an alpine belt formed by the interaction of the eurasian and african plates and the westward motion of the alboran domain long period magnetotelluric observations at 26 sites in its westernmost part provide induction arrows that have been compared with 3d forward models including bathymetry and major geological bodies the results highlight the presence of a major conductive body 0 05 m unknown to date and located within the basement of the guadalquivir foreland basin aeromagnetic and field magnetic measurements further support the occurrence of magnetic anomalies related to the top of this anomalous body this major structure is interpreted as an intermediate or basic igneous rock with a high proportion of metallic mineralization its origin is discussed in the framework of the regional geological setting possibly produced in the southern iberian variscan massif by a huge concentration of volcanogenic massive sulphide vms in the prolongation of the iberian pyrite belt during devonian early carboniferous times another possibility is that the conductive anomaly is due to magmatic intrusions associated with the mesozoic fragmentation of southern iberia and the opening of the tethys

isolating the role of mesoscale eddies in mixing of a passive tracer in an eddy resolving model 1 this study examines the role of mesoscale eddies in distribution of chlorofluorocarbon cfc in a numerical model of the north atlantic our main conclusions are based on a comparison of two eddy resolving experiments one with and one without eddy advection of cfc the cfc distributions in these two experiments exhibit substantial differences within the subpolar gyre in particular in the presence of eddies the horizontal distribution of cfc in the upper 1000 m is more uniform and the cfc concentration is lower in the lower 1500 m our analysis demonstrates that these basin wide differences are caused by the interactions of eddy advection with convection and mean advection in several isolated locations the corresponding eddy flux divergence terms are spatially non uniform in magnitude their effects are often nonlocal and sometimes work against the spreading of cfc being carried out by the mean advection these conclusions are further confirmed by a third experiment in which the eddy advection was replaced by a down gradient diffusive parameterization our results demonstrate that advection by mesoscale eddies is crucial to the mixing of atmospheric gasses into the ocean and outline difficulties in representing eddies by the down gradient diffusion

multiscale observations of deep convection in the northwestern mediterranean sea during winter 2012 2013 using multiple platforms during winter 2012 2013 open ocean deep convection which is a major driver for the thermohaline circulation and ventilation of the ocean occurred in the gulf of lions northwestern mediterranean sea and has been thoroughly documented thanks in particular to the deployment of several gliders argo profiling floats several dedicated ship cruises and a mooring array during a period of about a year thanks to these intense observational efforts we show that deep convection reached the bottom in winter early in february 2013 in a area of maximum 28 3 109 m2 we present new quantitative results with estimates of heat and salt content at the subbasin scale at different time scales on the seasonal scale to a 10 days basis through optimal interpolation techniques and robust estimates of the deep water formation rate of 2 0 0 2 sv we provide an overview of the spatiotemporal coverage that has been reached throughout the seasons this year and we highlight some results based on data analysis and numerical modeling that are presented in this special issue they concern key circulation features for the deep convection and the subsequent bloom such as submesoscale coherent vortices scvs the plumes and symmetric instability at the edge of the deep convection area

mechanisms of buoyancy transport through mixed layers and statistical signatures from isobaric floats idealized nonhydrostatic numerical calculations that resolve both plumes and geostrophic eddies are used to mimic isobaric float observations taken in the labrador sea deep convection experiment and study mechanisms of buoyancy transport through mixed layers the plumes and eddies are generated in a periodic channel initialized with a vertical profile of temperature and cooled by surface heat loss varying across the channel probability density functions and time series of vertical velocity and temperature computed from the floats are interpreted in terms of the kinematics of plumes and geostrophic eddies and their role in buoyancy transport estimates from eulerian time series from the numerical model suggest that geostrophic eddies and plumes have a comparable contribution to vertical heat flux

the role of eddy transfer in setting the stratification and transport of a circumpolar current abstract high resolution numerical experiments of a circumpolar current are diagnosed to study how lateral and vertical transfer of buoyancy by geostrophic eddies balances advection by a meridional circulation driven by surface wind stresses and buoyancy fluxes a theory is developed in the framework of the residual circulation to relate the vertical and horizontal stratification set up to the transfer properties of eddies and the patterns of imposed wind and buoyancy forcing simple expressions are found for the depth of penetration stratification baroclinic transport and residual circulation of the current finally the ideas are applied to the antarctic circumpolar current acc and yield predictions for how its properties depend on wind and buoyancy forcing