a numerical study of the mediterranean sea circulation abstract a primitive equation ocean model that makes use of a curvilinear orthogonal grid and a sigma coordinate system was used to simulate the mediterranean sea the model was forced with monthly climatological values of wind stress heat and salinity flux with the help of the curvilinear horizontal grid the larger scales of the entire mediterranean sea are modeled and the topography around the narrow and shallow straits of gibraltar is also reasonably well represented the resulting model inflow and outflow seems to mimic the real mediterranean often in considerable detail levantine intermediate water is formed in the levantine basin and exits through the strait of sicily and the strait of gibraltar deep water formation processes are clearly represented by the model the model results indicate that in the western mediterranean the wind stress is very important in establishing the summer northward shift of the atlantic inflow lateral boundary runoff surface salinity and heat fluxes are necessar

hydrographic structure of the convection regime in the gulf of lions winter 1987 abstract deep winter convection in the northwestern mediterranean gulf of lions and the subsequent formation of mediterranean deep water were observed using advanced oceanographic instrumentation during a six week long experiment in 1987 the severe 1987 european winter forced an intense outbreak of the mistral a cold dry wind blowing down the rhone valley in mid january surface cooling and evaporation were of sufficient intensity to cause an initial episode of deep convection shortly before the experiment described here began however several more mistral events took place during the experiment during several cruises into the area ctd and absolute horizontal velocity profiles were measured in the mixed area over the rhone fan as well as across the southern front of this region in addition continuous records of shipboard meteorological and oceanographic parameters air temperature surface salinity etc were made an early february mistral apparently did not produce enough surface cooling to

residual mean solutions for the antarctic circumpolar current and its associated overturning circulation abstract residual mean theory is applied to the streamwise averaged antarctic circumpolar current to arrive at a concise description of the processes that set up its stratification and meridional overturning circulation on an f plane simple solutions are found in which transfer by geostrophic eddies colludes with applied winds and buoyancy fluxes to determine the depth and stratification of the thermocline and the pattern of associated residual meridional overturning circulation

sea surface circulation variability in the ionian adriatic seas abstract the surface circulation of the ionian and adriatic seas is explored by the re analysis of available datasets that estimate the mean monthly ocean state for the 60 years long time period 1955 2015 emphasis is given to the major recurrent and transitional events in the area two circulation indices are utilized for the quantification of the cyclonic or anticyclonic circulation modes and intensity one based on the vorticity flux of the reconstructed mean monthly surface velocity field and another based on an appropriately modified version of the velocity field such quantification consequently allows for a detailed analysis of the surface circulation variability for the entire ionian and adriatic basins as well as for sub regions of particular interest discontinuities associated with possible regime shifts of the examined flow field were identified by time series analysis of the circulation indices and compared to well documented events in the hydrography of the studied area subsequently the statistically significant components of the surface circulation variability were resolved out of a red noise background in the time frequency domain and their evolution was studied the results highlight the presence of various circulation modes and reversals in different temporal scales mainly seasonal and decadal to inter decadal which are discussed in reference to the dynamics of both the sub regional western northern eastern and southern ionian as well as northern and southern adriatic and of the basin wide ionian or adriatic spatial scales the relationships of the surface circulation variability between the ionian and the adriatic basins are also assessed through wavelet coherence

the mediterranean sea a miniature ocean for climatic and environmental studies and a key for the climatic functioning of the north atlantic the mediterranean sea provides a case study not only for dense water formation and climatic functioning at a basin scale but also as a body of water evolving in response to the effects of environmental changes through marine circulation marine signatures of changes may be used to provide estimates of the evolution of the external driving forces of climate and environment that is to say to provide a coupling between marine sciences and climatic and socio economic studies different examples may be given i nutrients and trace metal changes in the western mediterranean permit quantification of external changes at a basin scale ii sapropels organic rich layers sedimented in anoxic conditions provide records for the last 2 million years of interactions between marine circulation climate and biology iii temperature and salinity changes that have taken place since the 1960s in response to changes in heat and water budgets across the sea surface sapropel studies and ongoing changes in temperature and salinity also require that the mediterranean functioning be considered in relation to global climate and to the atlantic ocean as well as taking into account the changing role of salty mediterranean waters in the atlantic ocean these factors highlight a dual role for the mediterranean sea which acts as a miniature ocean for physical chemical or climatic and environmental studies and also as a key factor in understanding global ocean circulation in which past changes have taken place

seismic structure of the lithosphere from teleseismic converted arrivals observed at small arrays in the southern sierra nevada and vicinity california 21 well distributed teleseisms 30 to 100 distance were recorded by mixed broad band bb and short period sp seismic arrays at mineral king mk and horseshoe meadow hm in the southern sierra nevada and at darwin plateau dp between the inyo and argus ranges these arrays permit identification and separation of direct p and s arrivals reflections from topography scattered energy and arrivals from different back azimuths multipath arrivals p to s conversions can be identified from beamed bb or sp seismograms least squares time domain processing recovered single event receiver functions from these beamed seismograms converted phases attributable to the moho are clear and uncomplicated at dp ps p times of 3 9 4 2 s correspond to crustal thicknesses of 31 33 km assuming a mean p crustal velocity of 6 2 km s and a poisson s ratio of 0 255 ps p times at hm eastern sierra are 3 9 4 6 s 32 37 km excepting some unusual seismograms from events at back azimuths of 225 239 mk western sierra times for ps p show a strong e w asymmetry 3 9 4 1 s 31 33 km from the east and 4 8 5 3 s 39 42 km from the west the mk arrivals from the east are multiple and substantially weaker by comparison with hm and dp these results confirm the absence of a thick crust under the southern high sierra inferred from both a refraction experiment coincident with this experiment and some earlier studies at dp the moho event follows an intracrustal negative polarity event defining the top of an s wave low velocity zone this feature dips west under the sierran crest at hm but is absent farther west at mk this feature appears to be a manifestation of extensional strain and thus indicates that the surficially undeformed sierra overlies a tectonized lower crust sub moho energy is absent under the basin and range dp but is conspicuous under the high sierra at positive arrivals 7 3 s mk and 9 s hm after the p these arrivals might be from the base of a low velocity low density upper mantle body supporting the sierra

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

direct observations reveal the deep circulation of the western mediterranean sea direct observations of the deep water circulation in the western mediterranean sea are presented based on the analysis of autonomous profiling floats drifting at 1200m and 1900m depth during the 1997 2002 period the amount of water circulating in the basin is quantified revealing several distinct gyres and boundary currents it was also possible to follow the spreading of the newly formed western mediterranean deep water nwmdw and tyrrhenian deep water tdw two main components of the deep water in the western mediterranean from their origin based on their temperature and salinity signature both boundary currents and isolated eddies carrying the water into the interior are important for this

what sets the strength of the middepth stratification and overturning circulation in eddying ocean models abstract the processes maintaining stratification in the oceanic middepth between approximately 1000 and 3000 m are explored using an eddy resolving general circulation model composed of a two hemisphere semienclosed basin with a zonal reentrant channel in the southernmost eighth of the domain the middepth region lies below the wind driven main thermocline but above the diffusively driven abyssal ocean here it is argued that middepth stratification is determined primarily in the model s antarctic circumpolar current competition between mean and eddy overturning in the channel leads to steeper isotherms and thus deeper stratification throughout the basin than would exist without the channel isotherms that outcrop only in the channel are nearly horizontal in the semienclosed portion of the domain whereas isotherms that also outcrop in the northern hemisphere deviate from horizontal and are accompanied by geostrophically balanced meridional transport a northern source of deep water water with temp

sensitivity of mediterranean thermohaline circulation to gateway depth a model investigation 1 the neogene sedimentary record of the mediterranean sea holds evidence for changes in water properties and circulation these paleoceanographic changes have been attributed to changes in the flow through the ocean gateway between the mediterranean sea and the atlantic ocean we use an oceanic general circulation model to achieve quantitative physics based understanding of the effect of changes in the depth of the gateway such as may result from tectonic activity or variation in sea level to isolate these effects we use idealized basin geometry and impose simplified atmospheric forcing a reference experiment with present day sill depth demonstrates that the model simulates reasonably well the main features of the present day mediterranean thermohaline circulation as inferred from observations and previous numerical studies subsequently a series of sensitivity simulations is performed with different sill depths the model results show that mediterranean temperature salinity and thermohaline circulation depend strongly on sill depth as the sill depth decreases the upper overturning cell is quasi linearly reduced in strength while contrary to what one would expect the deep cell intensifies and does so in a nonlinear way we find that a shoaling of the sill depth induces a blocking effect on the outflow waters which creates a strong recirculation in the deep layers strengthening the deep cell nevertheless deep water formation is reduced and as a consequence the ventilation of the deep layers diminishes we identify three different circulation modes of the mediterranean thermohaline circulation depending on the sill depth shallow sill moderate sill and deep sill modes coupled with strong weak and negligible blocking effects respectively our results are consistent with the pre messinian paleoceanographic record of the mediterranean sea and may be useful to understanding the behavior of other land locked basins both extant and from the geological past

on the relationship between the water mass pathways and eddy variability in the western mediterranean sea the role of eddies on the formation and spreading of water masses in the western mediterranean sea is studied with an ocean general circulation model the model is forced with interannually variable surface forcing for the years from 1979 to 1999 it is found that the model reproduces the major features of the observed mesoscale variability in the gulf of lions and the large eddies evolution in the algerian basin the seasonal evolution of circulation in the gulf of lions and processes of spreading of newly formed intermediate deep waters in the postconvection period is studied for years 1987 and 1992 the model results are compared with data from observations it is shown that the instability of the transition zone between old and newly formed deep waters which takes place after the violent mixing stages of the deep convection leads to collapse of the mixed patch and formation of mesoscale eddies some of these eddies propagate out of the gulf of lions transporting deep waters into the algerian basin the rest of the mesoscale eddies filled with newly formed deep waters remain in the gulf of lions and tend to merge and enlarge after the cyclonic eddies reach the algerian basin they interact with the intense mesoscale field existing there the energy analysis shows that the winter and spring are seasons of intensified baroclinic instability of the mean flow in the two regions of interest the gulf of lions and algerian basin the kinetic energy is released by baroclinic instability in spring and summer the spring spectra in the two regions have maximums at horizontal scales of about 80 100 km which is the typical scale of the eddies in the model these eddies propagate a cyclonic circuit the resulting eddy induced mass transport in deep and intermediate layers is directed out of the gulf of lions and toward the gibraltar strait equivalently we can argue the intermediate and deep waters conveyor belt of the western mediterranean sea is eddy drive

observations with moored acoustic doppler current profilers in the convection regime in the golfe du lion abstract in the golfe du lion south of france favorable conditions for deep winter convection exist and were documented by the medoc experiments during 1969 75 a renewed investigation of that regime with upward looking moored acoustic doppler current profilers adcps was carried out during 24 january 5 march 1987 to record the three dimensional currents associated with the deep mixing while in the earlier studies initial deep convection did not begin until fairly late in the winter season a very strong mistral around 10 january 1987 had already generated a 1arge deep mixed patch homogeneous down to around 2000 m at deployment time three adcps two working at 150 khz and one at 75 khz were moored in a triangle of 15 km sidelength at 550 780 m depth full records at 1 hour ensemble time intervals 400 pings per ensemble 8 m bin lengths were obtained by the 75 khz and one of the 150 khz adcps in mid february a second mistral hit the region with the onset of strong winds and surface cooling the

evolution of dynamics in the eastern mediterranean affecting water mass structures and properties in the ionian and adriatic seas 1 basin wide hydrographic observations performed in the eastern mediterranean during the past 2 decades attest changes in the thermohaline circulation as well as new aspects concerning the onset and the follow up of the major transient event that occurred at the beginning of the 1990s i e the change of the dense water formation site from the adriatic to the aegean sea since 1999 the upper thermohaline circulation has indicated the restoring of the opposite flows of the atlantic water and the levantine intermediate water which were greatly reduced in the period 1987 1995 in the deep layer the comparison between water mass structures observed in 1995 during the mature status of the transient and those observed in 1999 shows a damping of the event and a regained role of the adriatic sea as a primary source of dense waters separate calculations of the salt content in the ionian and in the levantine seas show an overall salt redistribution during 1987 1995 a salt loss of about 25 1012 kg was computed for the upper 800 m constituting only 27 of the salt gain in the deep layer over most of the eastern mediterranean on the contrary during 1995 1999 the restored upper thermohaline circulation caused a salt redistribution between the two basins of about the same amount but in the opposite sense while an extra quantity of 12 1012 kg was deposited in the deep layer in addition calculations of the salt concentration in the convection region of the southern adriatic reveal a remarkable amount of the salt not yet totally transferred into the deep layers by its interior dynamics because of mild winters

array measurements of phases used in receiver function calculations importance of scattering receiver function methods utilize three component teleseismic p coda to determine structure beneath seismographs most methods treat coda complexity as mode conversions and reflections off subhorizontal interfaces beneath the station such as the moho this assumption is evaluated beneath a broadband array in the kopet dagh foothills at geyokcha turkmenistan by applying array processing techniques to p coda waves at frequencies near 1 hz beneath the geyokcha array horizontal components show signals that deviate significantly in slowness and bearing from predictions of a plane layered earth large phases arrive at the same time as the predicted ps conversion from the moho yet systematically come from a single azimuth from nne and travel at phase velocities of 3 to 5 km sec the coda waves appear to be p to s converted waves from a near surface scatterer an inversion for scatterer location is developed and applied to 29 events most coda energy comes from a scatterer 16 km nne of the array this location is coincident with the range bounding faults that separate kopet dagh mountains from adjacent basins thus array analysis shows that signals potentially interpreted as moho conversions are instead scattered from a near surface structure although these results suggest caution is necessary in interpreting single station receiver functions particularly at high frequencies they also demonstrate the power of array sampling in resolving lateral structure variations

internal tides in the strait of gibraltar abstract analysis of moored current measurements in the strait of gibraltar is provided here the vertical internal displacements double amplitudes with a semidiurnal frequency are extremely large and sometimes exceed 200 m it is found that these displacements are associated with forced tidal internal waves over camarinal sill which crosses the strait the separation of tidal components showed that the amplitude of internal tide with m2 frequency is 69 m while the amplitudes of other components of the internal tide s2 k1 o1 are 3 5 times smaller the amplitudes of the waves decrease with the distance from the sill and at a distance of 50 km from the sill the amplitudes are 3 times smaller than over the sill the energy of internal tides is transferred to internal bore and turbulent mixing the wavelength of the internal tide was estimated on the basis of moored measurements the wavelength of the east propagated wave is 90 km while the west propagated wave is 60 km numerical modeling demonstr

mediterranean sea large scale low frequency ocean variability and water mass formation rates from 1987 to 2007 a retrospective analysis abstract we describe a synthesis of the mediterranean sea circulation structure and dynamics from a 23 year long reanalysis of the ocean circulation carried out by adani et al 2011 this mesoscale permitting dynamical reconstruction of past ocean variability in the mediterranean sea allows the study of the time mean circulation and its low frequency decadal components it is found that the time mean circulation is composed of boundary and open ocean intensified jets at the border of cyclonic and anticyclonic gyres the large scale basin circulation is generally characterized in the northern regions by cyclonic gyres and in its southern parts by anticyclonic gyres and eddy dominated flow fields with the exception of the tyrrhenian and the northern ionian sea the time mean tyrrhenian sea circulation is dominated by cyclonic gyres of different intensity and intermittency the northern ionian sea circulation however reverses in sign in two ten year periods the first in 1987 1996 and the second in 1997 2006 which is here called the northern ionian reversal phenomenon this reversal is provoked by the excursion of the atlantic ionian stream from the middle to the northern parts of the basin the decadal variability of other parts of the basin is characterized by changes in strength of the basin scale structures the water mass formation rates and variability are dominated by event like periods where the intermediate and deep waters are formed for 2 3 years at higher rates the largest deep water formation events of the past 23 years occurred separately in the western and eastern mediterranean basin the first coincided with the eastern mediterranean transient roether et al 1996 and the second with the western mediterranean deep water formation event in 2005 2006 smith et al 2008 a new schematic of the basin scale circulation is formulated and commented

flux forced simulations of the paleocirculation of the mediterranean 1 a series of experiments with an ocean general circulation model of the mediterranean forced by artificial but realistic surface fluxes of heat and freshwater are performed the model has a stable thermohaline circulation under the baseline fluxes small decreases in excess evaporation 8 produce a linear weakening of the thermohaline circulation with less water formation and smaller strait transports levantine intermediate water production is shown to be very sensitive to additional freshwater input the dominant circulation mode in wetter climates is one with adriatic intermediate water formation and dispersal leading to ventilation of intermediate depths of the basin although the deep layers are not ventilated stratification is generally weak as the excess evaporation decreases stratification increases a 60 80 decrease leads to conditions closest to those suggested for sapropel s1 with a west east salinity gradient of half of today

the mediterranean sea overturning circulation abstractthe time mean zonal and meridional overturning circulations of the entire mediterranean sea are studied in both the eulerian and residual frameworks the overturning is characterized by cel

inversion of p coda for isotropic scatterers at the yucca flat test site although many studies have addressed the statistical properties of p coda there have been few attempts to analyze coda in a deterministic framework in this analysis 1050 teleseismic p wave seismograms from 32 yucca flat explosions are inverted for the locations of any isotropic point scatterers in the source region that contribute coherent arrivals to the coda a rectangular grid of potential scattering locations is constructed around the source array and the semiblance a measure of waveform ensemble coherence for each point is computed by slant stacking the full set of seismograms at various move out velocities the potential resolution or sensitivity of the method for this data set is tested by constructing a corresponding suite of synthetic seismograms with direct arrivals plus arrivals from various point scatters and calculating the semiblance at each point on the grid the particular source station geometry produces better sensitivity near the array sensitivity is enhanced parallel to the trend of the elongated source array and diminished in the orthogonal direction stacking the data for a velocity of 2 5 km sec yields relatively high semiblance values in the central portion of the test site as well as about 10 km to the ene and moderately high semiblance valuesmore about 10 km to the wnw less

a scattered wave image of subduction beneath the transverse ranges over 5600 short period recordings of teleseismic events were used to create deterministic maps of p wave scatterers in the upper mantle beneath southern california between depths of 50 and 200 kilometers the southern flank of the slab subducting beneath the transverse ranges is marked by strong scattering the marked scattering indicates that the edge of the slab is a sharp thermal boundary such a boundary could be produced by slab shearing or small scale convection in the surrounding mantle the northern limb of the slab is not a strong scatterer consistent with thicker lithosphere north of the transverse ranges

velocity shift in heterogeneous media with anisotropic spatial correlation summary converted waves analysis is used to map the anisotropy as a function of depth in the upper mantle stacking of sv a ndt component records of several seismic events well distributed in azimuth helps to detect these converted waves weighting coe cients are used to extract the anisotropic signal in the records synthetic examples show that a harmonic analysis helps to separate azimuthal anisotropy eiects from the eiects of lateral heterogeneity such as those resultingfrom dipping structures a good azimuthal coverage of the data set is important in order to separate the diierent eiects in the stack sections obtained for diierent azimuthal orders the procedure is applied to data observed at geoscope station can and gives a model with two anisotropic layers in the upper mantle the upper layer located between the crust and a depth of140 km has its fast axis in an east west direction the lower layer 40 km thick has its fast axis in a north south direction the fast axis directions are in agreement with results obtained from surface wave analysis and tectonic information

seismic waves converted from velocity gradient anomalies in the earth s upper mantle summary modelling of elastic wave propagation in 1 d structures is frequently performed using reflectivity techniques in which the earth s velocity profile is approximated by stacks of homogeneous layers the complete reflection transmission r t response of a zone with arbitrary 1 d depth variation including both gradients and discontinuities in material properties can however be calculated using invariant embedding techniques results from earlier studies are here extended to derive exact expressions for r t matrices in arbitrary 1 d anisotropic media using a form of born approxi mation valid for thin scatterers and which does not assume small perturbations in material properties the r t matrices are solutions to a system of non linear ordinary differential equations of ricatti type and may be manipulated using standard r t matrix algebra in an equivalent description the wavefield within the heterogeneous zone is considered in terms of depth dependent contributions from up and downgoing waves propagating within the embedding reference medium this leads to efficient calculation of the internal wavefield using r t matrices of the heterogeneous stratification and portions thereof at minor additional expense mode conversion of teleseismic p and s phases from velocity gradients is examined by way of examples and comparison with three component data from broad band stations of the yellowknife seismic array the frequency dependence of such wave interactions depends on the differences in vertical slowness between incident and scattered modes it is shown that significant energy is converted from transition zones with extent l p 2 a broader interval than will generally produce intramode reflections a layer structure identified from ps conversions near 75 km depth below the slave craton is shown to be compatible with a 10 km thick gradient zone in which anisotropy increases from ambient levels to vp 5 per cent vs 2 5 per cent at a discontinuous upper boundary this characterization supports a previous interpretation as the upper strata of a former oceanic plate juxtaposed against overriding lithosphere during an ancient episode of shallow subduction

a closing ligurian sea two earthquakes occurred in the ligurian sea in december 1989 and april 1990 both were widely felt along the french and italian rivieras thus reminding us of the seismic risk in this region the significant increase in the number of seismic stations in the area facilitated the study of these two shocks and their related aftershocks using different techniques absolute and relative hypocentral locations doublet analysis and waveform modeling we computed accurate hypocentral locations and estimated the location error range for earthquakes in this area we also computed the focal mechanisms for both mainshocks and we present here a synthesis that integrates previous data the reactivation in compression of the ligurian sea sphenochasm is confirmed which would eventually result in the closing of an aborted oceanic domain as the seismic activity is clearly restricted to the northern margin we suggest it locally results from the lateral expulsion of the south western alps along the apulian indenter

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

heterogeneities in the mantle transition zone from observations of p to sv converted waves abstract the method of detection of p to sv converted waves from distant earthquakes vinnik 1977 was applied to sets of long period records from a few seismograph stations in europe and the west of north america the results obtained suggest that the converted phases related to the major boundaries in the mantle can be reliably detected and the depths of conversion evaluated with an accuracy of a few kilometres the depth of the olivine spinel transition is close to 400 km and no difference between the estimates for the north of europe and the west of north america is found the depth of the boundary separating the upper and lower mantle is close to 640 km which is 30 km less than in the recent earth reference models fine s velocity stratification of this transition changes laterally from a high gradient layer 50 km thick terminated at the bottom by a sharp discontinuity to a gradient layer 100 km or more thick without the discontinuity a striking anomaly of the mantle transition zone is found in the rio grande rift area where a well pronounced boundary is found at 510 km depth

a synthesis of the ionian sea hydrography circulation and water mass pathways during poem phase i abstract in this paper we revisit with a thorough in depth analysis the dataset collected in the hydrographic surveys of the international collaborative programme poem physical oceanography of the eastern mediterranean in the period 1986 1987 the work has two major objectives the first is to refine the dynamic picture of the ionian upper thermocline sub basin scale circulation rather less definitive than the dynamic picture of the levantine sea circulation the second is to identify the pathways of the major water masses of the basin not only in the near surface but also in the intermediate and deep layers to our knowledge this is the first work defining the pathways of the levantine intermediate water liw and of the adriatic deep water adw eastern mediterranean deep water emdw that characterize the intermediate and deep circulations the major novel results can be summarized as follows in the upper thermocline 1 the atlantic ionian stream ais jet entering the sicily straits bifurcates into two main branches at 37 n 17 e it advects the modified atlantic water maw into the ionian sea interior the first branch turning directly southward encloses an overall anticyclonic area comprising multiple centers around which the maw is advected 2 the second ais branch extends further into the northeastern ionian where it too turns southward before crossing the entire ionian sea meridionally advecting maw on its left side and ionian surface water isw on its right this branch of the jet is confined to the ionian margin and does not pass around the pelops gyre 3 a new water mass the lsw is formed in the levantine basin and enters the cretan passage then is first veered cyclonically south of crete by the cretan gyre and successively is entrained anticyclonically around the pelops gyre and then enters the aegean sea 4 a permanent cyclone located in the northeastern ionian determines the pathway of mixed adriatic surface water ionian surface water asw isw 5 a permanent cyclone is found in all the surveys near the tip of the italian boot this novel analysis of the liw pathways shows that 1 the major source of intermediate liw during the period 1986 1987 was actually in the levantine sea liw formed there entered the cretan passage was veered cyclonically by the cretan gyre south of crete and then entered the southern ionian sea the major liw pathway was westward directly to the sicilian straits 2 secondary important liw pathways were determined by the interior structures the strong pelops anticyclone was entraining liw around its periphery and was determining the liw northward pathway that closely followed the eastern greek coastline it was along this pathway that liw entered the otranto strait a further branch of liw was entrained and recirculated around the multiple ionian anticyclones ia of the western ionian sea 3 the cretan cyclone is a feature confined to the upper thermocline intermediate layer it disappears at 400 dbar while the pelops anticyclone is strongly barotropic below the upper 100 dbar and penetrates quite intense down to 800 dbar 4 a further completely novel result concerns the new water mass found in the deep layer that spreads on the 29 15 kg m3 isopycnal surface this water mass characterized by high salinity and high oxygen content is formed inside the aegean sea and is observed to spread out all around the cretan arc straits the final fully novel result is the demonstration of a second pathway for the adw exiting from the otranto strait that is transformed into emdw and occupies the abyssal layers of the ionian sea interior the traditional pathway for emdw is along the isobaths along the western side of italy but adw was observed to be exiting from the otranto strait in the eastern hellenic trench at 39 5 n both during poem on86 and poem as87 this second pathway for emdw follows isobath contours along the western side of greece the two emdw routes converge and merge between 36 n and 35 n so producing a deep layer of emdw that occupies uniformly the abyssal plain of the interior of the ionian sea

evolutionary model for alpine corsica mechanism for ophiolite emplacement and exhumation of high pressure rocks a tectonic model of alpine corsica is proposed based on geological studies its evolution starts after the jurassic with intraoceanic subduction followed by mid cretaceous subduction of the european continental margin under the oceanic segment of the adriatic plate after subduction of the continental crust to a depth of 150 km slices of crustal material are buoyantly uplifted together with high pressure oceanic rocks ophiolites and schistes lustres high pressure low temperature continental gneiss units overthrust the outer segments of the european crust while producing a normal sense motion along the upper surface of the rising crustal body during the eocene the closure of the remnant ligurian oceanic basin separating the proto corsican belt and adria resulted in a second orogenic phase with the emplacement of unmetamorphosed ophiolitic nappes which overthrust the previously exhumed and eroded hp belt this corsican model suggests an original evolutionary path for orogenic belts when continental collision is preceded by intraoceanic subduction

tidal dissipation in enceladus uneven fractured ice shell abstract analysis of enceladus gravity topography and libration data suggests that the thickness of the ice crust significantly varies which may have important consequences for the heat transfer across and the tidal dissipation within the ice shell understanding these processes is a critical prerequisite for analyzing enceladus thermal evolution and assessing the long term stability of its subsurface ocean here we investigate the impact of ice shell thickness variations on the tidal deformation of the moon and the associated heat production using a finite element model that includes faults tiger stripes in the south polar region spr since the tidal deformation and the thermal structure of the ice shell are coupled through temperature and deviatoric stress we simultaneously solve the equations governing the anelastic deformation of ice and also equations which model conductive heat transfer in the ice shell we find that tidal heating is concentrated in a narrow low viscosity zone near the base of the ice shell and along faults outside the spr the thickness of this zone is about 1 10 of the local ice thickness and the associated volumetric heating is 1 0 6 w m 3 corresponding to less than 1 gw of dissipated power in the spr the tidal effects are enhanced by the combined action of faults and ice shell thinning although the volumetric heating in this relatively small region may be larger than 10 4 w m 3 the total heat production in this region does not exceed 1 1 gw our computations show that tidal heating in the ice shell can explain only a small fraction of enceladus heat production derived from astrometric observations implying that enceladus heat engine is powered by dissipation in the core or in the ocean

observations of open ocean deep convection in the northwestern mediterranean sea seasonal and interannual variability of mixing and deep water masses for the 2007 2013 period we present here a unique oceanographic and meteorological data set focus on the deep convection processes our results are essentially based on in situ data mooring research vessel glider and profiling float collected from a multiplatform and integrated monitoring system moose mediterranean ocean observing system on environment which monitored continuously the northwestern mediterranean sea since 2007 and in particular high frequency potential temperature salinity and current measurements from the mooring lion located within the convection region from 2009 to 2013 the mixed layer depth reaches the seabed at a depth of 2330m in february then the violent vertical mixing of the whole water column lasts between 9 and 12 days setting up the characteristics of the newly formed deep water each deep convection winter formed a new warmer and saltier vintage of deep water these sudden inputs of salt and heat in the deep ocean are responsible for trends in salinity 3 3 0 2 10 3 yr and potential temperature 3 2 0 5 10 3 c yr observed from 2009 to 2013 for the 600 2300 m layer for the first time the overlapping of the three phases of deep convection can be observed with secondary vertical mixing events 2 4 days after the beginning of the restratification phase and the restratification spreading phase still active at the beginning of the following deep convection event

several location methods for underwater shots in the gulf of genoa western mediterranean structural implications abstract during the egt survey 50 underwater shots were detonated on a n s section through the gulf of genoa running from the northern margin 44 12 n towards corsica 42 90 n along the 9 e meridian the aim of this work is in a first stage to establish the propagation model of regional phases in this region and consequently to improve the location of epicentres and afterwards to refine our structural knowledge of this complex crustal area the relocation of these shots was carried out with arrival times of seismic signals recorded at land stations we have used different location methods all of which led to similar crustal models they reveal a low p n velocity area in the northern ligurian sea and in the gulf of genoa with a 20 km thick crust in the southern part approximately south of latitude 43 7n a 4 km thick oceanic crust covered by 8 km of sediments is clearly confirmed using these models a significant improvement of epicentre locations was obtained these improvements to propagation models lead to the two main structural conclusions 1 1 in the southern part of the investigated area the spread of an oceanic type domain as far as the foot of the continental margin 2 2 a sharp transition between the two domains of different stretching rate the northern one with a moho depth of about 20 km and the southern one with an average moho depth of about 14 km these observations substantiate the presence of a transform margin between the rifted gulf of genoa and the oceanic type ligurian basin

energetics of semienclosed basins with two layer flows at the strait examination of the energy budget for semienclosed seas with two layer exchange flow at the strait shows that the energy flux at the open portion of the boundary the strait is proportional to the surface buoyancy fluxintegratedoverthebasinarea withtheconstantofproportionalitygivenbytheinterfacedepth whenthe surface buoyancy flux is positive the energy flux is negative these types of basins have an estuarine circulation antiestuarine basins have a negative surface buoyancy flux which provides a positive energy flux augmenting the wind work in powering the circulation the energy budget for the semienclosed seas with vertically separated flows at the strait is examined using reanalysis products for four major semienclosed basins the mediterranean and red seas antiestuarine and the black and baltic seas estuarine important differencesintherelativecontributiontotheenergybudgetofthewindworkversusthesurfacebuoyancyflux are found within basins of the same type and these differences help explain some qualitative aspects of the basins flow

transport estimates in the strait of gibraltar with a tidal inverse model to estimate the volume transport through the strait of gibraltar and to study the spatial structure of the time variable flow a varying number of current meter moorings were maintained at the eastern entrance of the strait between october 1994 and april 1998 and was complemented with intensive shipboard measurements during the european union project canary island azores gibraltar experiment canigo a tidal inverse model is used to merge these data sets in order to investigate the flow at the eastern entrance of the strait the two dimensional structure of the tidal flow was described by simple analytical functions harmonics with the seven most important tidal frequencies were used as temporal functions with this model the tidal currents can be predicted for any time and location at the eastern entrance of the strait and more than 92 of the variance of the lower layer flow is explained it was used to remove the tidal currents from the individual measurements and to calculate the mean flow through the strait from the residuals combined with a similar inverse model for determining the depth of the interface between mediterranean and atlantic water the volume transport was estimated to be 0 81 0 07 sv for the upper layer and 0 76 0 07 sv for the lower layer the correlation of the tidal currents and the fluctuations of the interface accounts for 7 of the transport at the eastern entrance

overturning the mediterranean thermohaline circulation for more than five decades the mediterranean sea has been identified as a region of so called thermohaline circulation namely of basin scale overturning driven by surface heat and freshwater exchanges the commonly accepted view is that of an interaction of zonal and meridional conveyor belts that sink at intermediate or deep convection sites however the connection between convection and sinking in the overturning circulation remains unclear here we use a multidecadal eddy permitting numerical simulation and glider transport measurements to diagnose the location and physical drivers of this sinking we find that most of the net sinking occurs within 50 km of the boundary away from open sea convection sites vorticity dynamics provides the physical rationale for this sinking near topography only dissipation at the boundary is able to balance the vortex stretching induced by any net sinking which is hence prevented in the open ocean these findings corroborate previous idealized studies and conceptually replace the historical offshore conveyor belts by boundary sinking rings they challenge the respective roles of convection and sinking in shaping the oceanic overturning circulation and confirm the key role of boundary currents in ventilating the interior ocean

modeling the dispersal of levantine intermediate water and its role in mediterranean deep water formation this paper demonstrates the importance of levantine intermediate water liw in the deep water formation process in the mediterranean using the modular ocean general circulation model at 0 25 resolution 19 vertical levels over the entire mediterranean with an open gibraltar strait liw formation is strongly prescribed in the rhodes gyre region by haney 1971 relaxation while in other regions surface salinity relaxation is much reduced by applying the mixed thermohaline surface boundary conditions isopycnal diagnostics are used to trace water mass movements and volume fluxes are monitored at straits low viscosity and diffusion are used to permit baroclinic eddies to play a role in water mass dispersal the overall water budget is measured by an average flux at gibraltar of 0 8 sv of which 0 7 sv is exchanged with the eastern basin at sicily liw density around 28 95 spreads rapidly after formation throughout the entire levantine due to baroclinic eddies toward the west liw accumulates in the northern and central ionian with some entering the adriatic through otranto and some mixing southward in eddies and exiting to the western mediterranean through sicily liw is converted to deep water in the south adriatic at an average rate of 0 4 sv water exchange through the otranto strait appears to be buoyancy driven with a strong bias to the end of winter march april while at sicily the exchange has a strong symmetric seasonal cycle with maximum transport of 1 1 sv in december indicating the effects of wind driving liw pathways in the west are complex and variable in the tyrrhenian intermediate water becomes uniform on isopycnal surfaces due to eddy stirring west of sardinia two liw boundary currents are formed in the balearic basin one flows northward up the west coast of sardinia and corsica and one westward along the northern african coast the northward current is consistent with observations while the westward current is intermittent for the first 10 years often breaking up into eddies which enter the basin interior some observations of high salinity waters near the african coast may support this interpretation liw retains a subsurface salinity maximum of 38 4 38 5 practical salinity units psu when reaching the northwestern mediterranean contrasting with surface waters fresher than 38 0 psu west mediterranean deep water is formed below 1500 m depth with climatological characteristics when it is mixed and cooled during winter convection in lions gyre

crustal structure deduced from receiver functions via single scattering migration an investigation of the teleseismic p wave coda is performed using the single scattering approximation the method allows one to image short wavelength scale 2 km velocity and density heterogeneities and structures that are barely detected by traveltime tomography source effects are removed by using receiver functions for data interpretation but the amplitude especially the sign of the signal is synthesized both broad band seismological stations in the southwestern alps france and campanian plain italy are used for the illustration of the proposed method because of the large aperture of our arrays laterally small scale heterogeneities are difficult to image and we must assume lateral continuity of the detectable structure if so we show that this depth migration based on a single scattering approach can recover both the depth and the geometry of the main discontinuities below the studied areas in the southwestern alps we underline a complex crustal structure and moho dipping topography the moho depth increases from 20 to 30 km between the coastline and the mercantour range in the campanian plain surrounding mount vesuvius we also find a southeastwards dipping moho furthermore the three main discontinuities are imaged showing a relatively shallow mantle crust discontinuity and a deeper one near the coastline

crustal structure below the valley of mexico estimated from receiver functions abstract receiver functions rfs from two permanent stations cuig and zaig of the mexican broadband network were calculated to infer the crustal structure at both sites the data were stacked to allow uncertainty estimations and inverted using two global optimization algorithms simulated annealing and genetic algorithms strong and systematic azimuthal dependence was observed in the stacked functions at cuig site which is located in the mexican volcanic belt mvb assuming a one dimensional five layer model per azimuthal stack these variations were explained with the same upper crustal structure including a superficial 2 km thick low velocity layer associated with the mvb and a well defined conrad interface around 15 km depth different depths for the moho discontinuity and variations in both the s wave velocity and poisson s ratio for the upper mantle our inversion of observed rfs at cuig and theoretical considerations suggest an eastward crustal thickening of at least 5 km below the valley of mexico we tested the sensitivity of the modeling procedure by applying it to the recordings at zaig station in this case no azimuthal dependence was noticed in the stacked functions after a simultaneous inversion of three different azimuthal stacks a single four layer model satisfactorily explained all data thus revealing a flat one dimensional crustal model below the mexican mesa central where zaig station is located these results support the resolution and robustness of the applied method at both sites

lithospheric structure of the southern french alps inferred from broadband analysis abstract broadband receiver functions analysis is commonly used to evaluate the fine scale s velocity structure of the lithosphere we analyse teleseismic p waves and their coda from 30 selected teleseismic events recorded at three seismological stations of to the french tgrs network in the alpes maritimes receiver functions are computed in the time domain using an svd matrix inversion method dipping moho and lateral heterogeneities beneath the array are inferred from the amplitude arrival time and polarity of locally generated ps phases we propose that the moho dips 11 towards 25 10 n below station calf in the outer part of the alpine belt at this station we determine a moho depth of about 20 2 km the same depth is suggested below saof station also located in the fold trust belt beneath station stet located in the inner part of the alpine belt the moho depth increases to 30 km and dips towards the n nw moreover 1d modelling of summed receiver function from stet station constrains a crustal structure significantly different from that observed at stations located in the outer part of the alps indeed beneath calf and saof stations we need a 2 km thick shallow low velocity layer to fit best the observed receiver functions whereas this layer seems not to be present beneath stet station because recent p coda studies have shown that near receiver scattering can dominate teleseismic p wave recordings in tectonically complicated areas we account for effect of scattering energy in our records from array measurements as the array aperture is wide relative to the heterogeneity scale length in the area the array analysis produces only smooth imaging of scatterers beneath the stations

water masses and circulation in the central region of the eastern mediterranean eastern ionian south aegean and northwest levantine 1986 1987 in the framework of the major multinational coordinated poem ii 86 march april 1986 and poem v 87 september october 1987 cruises in the eastern mediterranean high resolution hydrographic ctd data were collected by r v aegaio in the eastern ionian sea south aegean sea and northwest levantine basin the intercalibrated data sets were analyzed objectively for an optimal estimation of the basin s circulation in two different seasons the analysis reveals a rather complex general circulation pattern consisting of basin sub basin and mesoscale features during both study periods the major results concern the advection of the modified atlantic water maw along its eastward route the spreading of the levantine intermediate water liw and its trapping by the eddy fields the interaction between the south aegean sea and the eastern mediterranean and the reverse circulation in the cretan sea during winter and summer from the hydrography and the dynamic height maps synthetic schemes show the main circulation features in the two seasons

a process study of the adriatic ionian system baroclinic dynamics the driving mechanisms behind the decadal reversal of the ionian sea upper layer circulation recently sparked a considerable discussion in the mediterranean scientific community it has been suggested that the reversal can be driven by variations in wind stress curl over the basin baroclinic dynamics acting within the adriatic ionian system aisys or baroclinic dynamics driven by thermohaline properties at the aisys eastern boundary here we perform numerical simulations in order to assess the relative importance of remote forcings wind stress thermohaline fluxes thermohaline open boundary conditions on the vorticity and energy budget of the ionian sea a mechanistic understanding of the aisys dynamics is achieved with an approach based on an increasing complexity in the model forcings and domain our experiments suggest that wind stress does not play a leading role in the vorticity and energy budgets of the ionian sea wind stress can reinforce or weaken the circulation but it is not able to reverse its sign its role becomes dominant only in the absence of inflows through the antikythira strait and cretan passage instead reversals in the upper layer circulation of the ionian sea take place only in the presence of an active boundary on the aegean sea levantine basin side and appear to be correlated with substantial exchanges of availalble potential energy between the two basins as observed at the end of the eastern mediterranean transient from an energetic point of view aisys can be explained therefore only if the role of the aegean sea is explicitly condidered this article is protected by copyright all rights reserved

aegean sea water masses during the early stages of the eastern mediterranean climatic transient 1988 90 abstract the aegean water masses and circulation structure are studied via two large scale surveys performed during the late winters of 1988 and 1990 by the r v yakov gakkel of the former soviet union the analysis of these data sheds light on the mechanisms of water mass formation in the aegean sea that triggered the outflow of cretan deep water cdw from the cretan sea into the abyssal basins of the eastern mediterranean sea the so called eastern mediterranean transient it is found that the central aegean basin is the site of the formation of aegean intermediate water which slides southward and depending on their density renews either the intermediate or the deep water of the cretan sea during the winter of 1988 the cretan sea waters were renewed mainly at intermediate levels while during the winter of 1990 it was mainly the volume of cdw that increased this aegean water mass redistribution and formation process in 1990 differed from that in 1988 in two major aspects i during the winter of

dense intermediate water outflow from the cretan sea a salinity driven recurrent phenomenon connected to thermohaline circulation changes data collected from different platforms in the cretan sea during the 2000s decade present evidence of gradually increasing salinity in the intermediate and deep intermediate layers after the middle of the decade the observed gradual salt transport toward the deeper layers indicates contributions of dense water masses formed in various aegean sea subbasins the accumulation of these saline and dense water masses in the cretan sea finally led to outflow from both cretan straits with density greater than typical levantine cretan intermediate water but not dense enough to penetrate into the deep layers of the eastern mediterranean we name this outflowing water mass as dense cretan intermediate water dciw a retrospective analysis of in situ data and literature references during the last four decades shows that similar events have occurred in the past in two occasions a in the 1970s and b during the eastern mediterranean transient emt onset 1987 1991 we argue that these salinity driven aegean outflows are mostly attributed to recurrent changes of the eastern mediterranean upper thermohaline circulation that create favorable dense water formation conditions in the aegean sea through salinity preconditioning we identify these phenomena as emt like events and argue that in these cases internal thermohaline mechanisms dominate over atmospheric forcing in dense water production however intense atmospheric forcing over an already salinity preconditioned basin is indispensable for creating massive deep water outflow from the cretan sea such as the emt event

a theory of deep stratification and overturning circulation in the ocean abstract a simple theoretical model of the deep stratification and meridional overturning circulation in an idealized single basin ocean with a circumpolar channel is presented the theory includes the effects of wind eddies and diapycnal mixing predicts the deep stratification in terms of the surface forcing and other problem parameters makes no assumption of zero residual circulation and consistently accounts for the interaction between the circumpolar channel and the rest of the ocean the theory shows that dynamics of the overturning circulation can be characterized by two limiting regimes corresponding to weak and strong diapycnal mixing the transition between the two regimes is described by a nondimensional number characterizing the strength of the diffusion driven compared to the wind driven overturning circulation in the limit of weak diapycnal mixing deep stratification throughout the ocean is produced by the effects of wind and eddies in a circumpolar channel and maintained even in the