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

bipolar seesaw control on last interglacial sea level our current understanding of ocean atmosphere cryosphere interactions at ice age terminations relies largely on assessments of the most recent last glacial interglacial transition1 2 3 termination i t i but the extent to which t i is representative of previous terminations remains unclear testing the consistency of termination processes requires comparison of time series of critical climate parameters with detailed absolute and relative age control however such age control has been lacking for even the penultimate glacial termination t ii which culminated in a sea level highstand during the last interglacial period that was several metres above present4 here we show that heinrich stadial 11 hs11 a prominent north atlantic cold episode5 6 occurred between 135 1 and 130 2 thousand years ago and was linked with rapid sea level rise during t ii our conclusions are based on new and existing6 7 8 9 data for t ii and the last interglacial that we collate onto a single radiometrically constrained chronology the hs11 cold episode5 6 punctuated t ii and coincided directly with a major deglacial meltwater pulse which predominantly entered the north atlantic ocean and accounted for about 70 per cent of the glacial interglacial sea level rise8 9 we conclude that possibly in response to stronger insolation and co2 forcing earlier in t ii the relationship between climate and ice volume changes differed fundamentally from that of t i in t i the major sea level rise clearly post dates3 10 11 heinrich stadial 1 we also find that hs11 coincided with sustained antarctic warming probably through a bipolar seesaw temperature response12 and propose that this heat gain at high southern latitudes promoted antarctic ice sheet melting that fuelled the last interglacial sea level peak

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

eastern mediterranean transient and reversal of the ionian sea circulation 1 maps of the remotely sensed absolute dynamic topography adt and sea surface temperature sst over the eastern mediterranean in the period june 1993 to june 2001 show a dramatic and sudden change in the sea surface structure this change which is presumably associated with the relaxation of the eastern mediterranean transient emt had taken place by the middle of 1997 and consisted of a complete reversal of the ionian upper layer circulation from anticyclonic to cyclonic in the emt phase sst and adt maps suggest enhanced communication between the ionian and the aegean basins as well as aegean waters spreading northward along the eastern ionian flank negative wind vorticity in the ionian suggests that the switch of the upper layer circulation from anticyclonic to cyclonic cannot be explained in terms of the wind forcing therefore we suggest the predominance of the baroclinic vorticity production term in determining the upper layer circulation inversion

the effect of wind stress over the eastern mediterranean on deep water formation in the adriatic sea abstract we investigate the effect of interannual variability of the wind stress over the eastern mediterranean on adriatic deep water adw formation using an oceanic general circulation model of the mediterranean sea driven by monthly era interim wind stress of the years 1979 2014 this is done by using climatological annual cycle of the surface temperature and freshwater flux but interannually varying wind stress a connection between the wind stress magnitude over the rhodes gyre region and adw outflow is found in association with the formation of levantine intermediate water liw 720 years artificially generated wind stress fields were constructed based on the first 50 empirical orthogonal functions eofs of the wind stress monthly anomalies this simulation strengthen the connection that was found and also reveal a centennial internal variability of both the liw and the adw outflow it is also found that the intensity of the rhodes gyre is almost linearly related to the wind stress amplitude however the adw outflow is non monotonically related to the wind stress amplitude there is an optimal wind stress amplitude for which the adw formation is maximal when the wind stress amplitude is more than 50 the climatological mean wind stress amplitude the adw outflow is weakened this implies a different balance between the saline liw and the fresh atlantic water entering the eastern mediterranean from sicily strait under stronger than present wind stress amplitude

clarifying ambiguity in intraseasonal southern hemisphere climate modes during austral winter the relative importance of annular and nonannular characteristics in the wintertime southern hemisphere circulation is investigated using reanalysis data between 1978 and 2010 weekly averaged data are chosen to capture the typically short time scale of intraseasonal atmospheric variability in existing studies the southern annular mode sam has been shown to exhibit significant nonannular behavior in the western southern hemisphere during austral winter variability in this region is also characterized by wave like disturbances and this overlap in nonannular behavior between different climate modes has led to a lack of consensus when defining and measuring impact from these wave like disturbances a number of approaches are adopted including empirical orthogonal function analysis teleconnection correlation analysis and the application of a vector autoregression model to isolate directions of causality and wave propagation austral winter variability is shown to be dominated by nonannular wavelike disturbances rather than a seesaw pattern between high and middle latitudes the wavelike disturbances have the largest amplitude in the western southern hemisphere are quasistationary and exhibit eastward propagation of information this suggests that the dominant pattern of western southern hemisphere intraseasonal variability during austral winter which is commonly associated with the sam is in fact a wave like mode of variability supporting material

the levantine intermediate water experiment liwex group levantine basin a laboratory for multiple water mass formation processes 1 in winter 1995 the last major field work of the physical oceanography of the eastern mediterranean poem program was carried out the levantine intermediate water experiment liwex in this study a thorough analysis is presented of the data set collected during three successive surveys in january february and march april 1995 the major overall result is that the levantine basin is shown to be the site for multiple and different water mass formation processes levantine deep water ldw was formed in the rhodes gyre with the preconditioning phase starting in december 1994 in late january the chimney was ventilating to the atmosphere in february the strong mixing phase is documented by the convective cell vertically homogeneous to 900 m depth in march april recapping has occurred in the upper 200 m ldw remained confined inside the rhodes gyre cyclonic circulation levantine intermediate water liw is instead deeply affected by the upper thermocline circulation shallow ventilating chimneys with the liw thermostads were found in the january survey inside the cyclonic region of the northern levantine the formation process of liw does not involve deep penetrative convection winter surface cooling and evaporation are sufficient to produce a surface mixed layer 100 m deep with liw characteristics at the mixed layer basis liw subducts and spreads along isopycnal surfaces along pathways determined by the cyclonic anticyclonic structures of the upper thermocline circulation

what induced the exceptional 2005 convection event in the northwestern mediterranean basin answers from a modeling study 1 open sea convection occurring in the northwestern mediterranean basin nwmed is at the origin of the formation of western mediterranean deep water wmdw one of the main mediterranean water masses during winter 2004 2005 a spectacular convection event occurred observed by several experimental oceanographers it was associated with an exceptionally large convection area and unusually warm and salty wmdw explanations were proposed tentatively relating the unusual characteristics of this event to the eastern mediterranean transient emt or to the atmospheric conditions during winter 2004 2005 in the nwmed they could however not be supported until now here we used numerical modeling to understand what drove this convection event the control simulation performed for the period 1961 2006 reproduces correctly the long term evolution of the mediterranean sea circulation the emt and the nwmed convection event of 2004 2005 sensitivity simulations are then performed to assess the respective contributions of atmospheric and oceanic conditions to this event the weakness of the winter buoyancy loss since 1988 in the nwmed prevented strong convection to occur during the 1990s enabling heat and salt contents to increase in this region this resulted in the change of wmdw characteristics observed in 2005 the strong buoyancy loss of winter 2004 2005 was responsible for the intensity of the convection observed this winter in terms of depth and volume of newly formed wmdw the emt did not fundamentally modify the convection process but potentially doubled this volume by inducing a deepening of the heat and salt maximum that weakened the preconvection stratification

a synthesis of the levantine basin circulation and hydrography 1985 1990 abstract the levantine basin circulation derived from recent data consists of a series of sub basin scale to mesoscale eddies interconnected by jets the basin scale circulation is masked by eddy variability that modulates and modifies it on seasonal and interannual time scales long term qualitative changes in the circulation are reflected in the bifurcation pattterns of ther mid basin jets relative strengths of eddies and the hydrographic properties at the core of these eddies confinement within the basin geometry strongly influences the co evolution of the circulation features surface measurements satellite images and the mass field indicate an entire range of scales of dynamical features in the region the complexity of the circulation is consistent with the basin wide and mesoscale heterogeneity of the hydrographic properties the interannual variability of liw levantine intermediate water formation in the region appears correlated with the changes in the circulation wintertime convective overturning of water masses reach intermediate depths and constitute a dominant mechanism of liw formation especially in anticyclonic eddies and along the coasts of the northern levantine basin

seasonal variability of gyre scale circulation in the northern tyrrhenian sea the principal hydrographic structures and dynamic conditions of the northern tyrrhenian sea are studied through the comparison of in situ field data and a modeling simulation the field observations are long term eulerian and lagrangian current measurements associated with two hydrographic campaigns conducted in late summer and in winter the data indicate that a well marked cyclonic gyre affecting the water column from the surface to the bottom is present in the northern tyrrhenian sea in both periods the gyre undergoes significant seasonal changes in both shape and size following the indications of past studies a numerical quasi geostrophic model driven by the wind jet blowing from the strait of bonifacio was able to reproduce the principal gyre characteristics however the wind jet alone does not explain all the gyre features especially its seasonal variation a study of the model results and field data indicates that these variations are linked to the seasonal variability of the northward surface current flowing along the eastern boundary of the tyrrhenian sea

storm tracks in the southern hemisphere abstract from 1979 to 1989 global european centre for medium range weather forecasts ecmwf analyses of many meteorological variables important in baroclinic storms have been bandpass filtered to highlight fluctuations on 2 to 8 day time scales in order to illuminate the relationships among the variables in baroclinic storm track regions because of the greater zonal symmetry in the southern hemisphere sh versus the northern hemisphere nh it is possible to examine these relationships over a zonal sector without being dominated by local effects associated with jet stream entrance and exit regions of the storm tracks the bandpassed variance of geopotential height is used to define the storm track and its meridional profile has a pronounced midlatitude maximum in the sh the locations of the jet stream and the variance maxima of meridional and zonal velocity components vorticity vertical motion specific humidity and temperature all bear a distinctive relationship to the storm track but the lat

numerical simulation of the interannual variability of the mediterranean sea upper ocean circulation numerical simulations reveal that variations in wind stress and heat fluxes can induce significant interannual fluctuations in the circulation of the upper layers of the mediterranean from january 1980 to november 1988 the atmosphere shows changes in the structure and magnitude of the surface winds and in the air temperatures which induce modifications in the upper ocean structure and currents the model prediction of the interannual fluctuations of the sicily strait baroclinic westward volume transport is in agreement with observations and the variability is explained as a function of the wind curl forcing in the region the current anomalies persist for many months after a winter atmospheric anomalous disturbance has occurred over the basin the eastern mediterranean basin is the area where the interannual ocean response is most pronounced

a mixed layer study of the formation of levantine intermediate water a mixed layer model is used to investigate the formation of levantine intermediate water liw over the eastern mediterranean the one dimensional model is initialized with climatological hydrography and integrated over the levantine basin with forcing by climatological surface fluxes realistic and repeated seasonal mixed layer cycles are obtained if the annual surface heat input and water loss are offset by a parameterized horizontal advection the model integrations show that liw is formed during winter in the mixed layer of the northwestern levantine the preferred formation region for liw is found through idealized experiments to be controlled by the preconditioning of the hydrography especially that of the cold cyclonic rhodes gyre rather than by the pattern of the climatological fluxes the annual mean formation rate of liw is estimated to be 1 0 sv using the climatological surface fluxes the magnitude of the annual surface fluxes alters the formation rate and modifies the formation region an additional annual heat flux reduces the formation rate of liw whereas an extra cooling enhances it as well as forming waters denser than liw in the center of the rhodes gyre

southern hemisphere circulation features associated with el nino southern oscillation events abstract composite seasonal mean and anomaly fields prepared from operational numerical analyses have been used to describe the southern hemisphere sh circulation features associated with el nino southern oscillation enso events the period of analyses available 1972 83 has limited the composites to include only three enso events the reliability and stability of the composites has been tested using multiple permutation methods and by comparison with the results obtained using a longer period 1950 79 of sh rawinsonde station data in the sh winter a weak equivalent barotropic wavetrain pattern of anomalies extends over australia and the south pacific ocean to south america this wavetrain pattern is quite variable in amplitude and location between enso events although it is more stable over the subtropical pacific in the sh summer the circulation anomalies are more zonally symmetric with increased height at low and high latitudes and decreased height in middle latitudes the circulation anoma

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

the association of australian winter climate with ocean temperatures to the west abstract two general circulation model experiments have been conducted with a view toward determining the sensitivity of australian winter circulation and precipitation to the imposition of idealized sea surface temperature anomalies around the western half of australia in the first a positive anomaly was imposed to the northwest of the continent and a negative anomaly to the southwest while in the second this pattern was reversed in the former major changes were simulated in the circulation over the australian sector and significant precipitation increases were induced over more than half of the continent by contrast the responses to the forcing in the latter experiment were considerably less particularly for precipitation over the continent which showed virtually no change of significance the results taken in concert with those of simmonds suggest the important role played by warm ocean temperatures to the northwest of australia in influencing winter rainfall the results suggest that the a

surface geostrophic circulation of the mediterranean sea derived from drifter and satellite altimeter data abstractdrifter observations and satellite derived sea surface height data are used to quantitatively study the surface geostrophic circulation of the entire mediterranean sea for the period spanning 1992 2010 after removal of the wind driven components from the drifter velocities and low pass filtering in bins of 1 1 1 week maps of surface geostrophic circulation mean flow and kinetic energy levels are produced using the drifter and or satellite data the mean currents and kinetic energy levels derived from the drifter data appear stronger higher with respect to those obtained from satellite altimeter data the maps of mean circulation estimated from the drifter data and from a combination of drifter and altimeter data are however qualitatively similar in the western basin they show the main pathways of the surface waters flowing eastward from the strait of gibraltar to the sicily channel and the current transporting waters back westward along the italian french and spanish coasts intermi

u th dating records of cold water coral colonization in submarine canyons and adjacent sectors of the southern adriatic sea since the last glacial maximum abstract the deep southern adriatic sea is home of widespread cold water coral colonization madrepora oculata lophelia pertusa desmophyllum dianthus which is at present limited by large to its western apulian margin and central part including the bari canyon system on the contrary the eastern side is today almost deprived of significant coral growth and this asymmetrical distribution has been ascribed primarily to the action of the north adriatic dense water naddw that impinges more efficiently on the apulian margin the collection of subfossil specimens of m oculata l pertusa and d dianthus provided the very first dates for cold water coral colonization along the eastern margin once combined with known distribution of live cold water corals and fossil occurrences in the southern adriatic sea uranium series dating provides evidence of i coral presence in the southeastern adriatic during the last glacial maximum lgm followed by ii a time of basin wide colonization after the post last glacial maximum and encompassing the younger dryas iii another time of undocumented coral presence with the onset of sapropel s1 perturbations of the thermohaline circulation in this sector of the mediterranean basin might have governed the presence and demise of the resident cold water coral populations interfering with strength and trajectories of main water masses it is hypothesized that the achievement of the current asymmetrical distribution did occur since the end of s1 protracting to present time the post s1 reorganization likely brought to the current hydrological situation where the influence of naddw prevails in the western side and corals are doing at best on its trajectory the scarcity of datable material makes the proposed scenario open to debate and in need of further supporting evidence

relationships between low frequency variability in the southern hemisphere and sea surface temperature anomalies abstract long term trends and interannual variations of circulation anomalies in the southern hemisphere are examined using the national centers for environmental prediction national center for atmospheric research reanalysis from 1949 to 1998 the changes in planetary circulation regimes are linked to global sea surface temperature anomalies sstas empirical orthogonal function eof analysis was performed on 500 hpa height anomalies the leading mode eof1 shows a strong zonal symmetry with a phase reversal between height anomalies in high and midlatitudes apart from zonal symmetry a zonal wavenumber 3 is evident with three centers located in three southern oceans in the low frequency band with fluctuations longer than 60 months eof1 is associated with the second rotated eof mode of sstas with positive loadings over three southern oceans and negative loadings in the north pacific and the north atlantic the next two modes are the pacific south american psa patterns they depict wave 3 patterns in

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

austral summer teleconnections of indo pacific variability their nonlinearity and impacts on australian climate abstractin austral summer el nino southern oscillation enso covaries with the indian ocean basin mode iobm and with the southern annular mode sam the present study addresses how the iobm and the sam modulate the impact of enso on australia the authors show that the modulating effect of the sam is limited in particular the sam does not modify the enso teleconnection pattern however the iobm extends enso induced convection anomalies westward over northern australia and over the eastern indian ocean whereby extending the enso tropical teleconnection to the northwest of australia the iobm also generates an equivalent barotropic rossby wave train through convection anomalies over northern australia the wave train shares an anomaly center over the tasman sea latitudes with the pacific south american psa pattern shifting the anomaly center of the psa pattern to within a closer proximity to australia there is a strong asymmetry in the iobm modulating effect during an iobm negative phase whic

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

decadal variations of circulation in the central mediterranean and its interactions with mesoscale gyres abstract the most prominent oceanographic features in the central mediterranean are decadal reversals of the northern ionian gyre nig interpreted in terms of internal processes altimetry data drifter data and model surface salinity products are used in this paper to define some specific features of the circulation related to the anticyclonic or cyclonic nig modes results not only highlight different shapes and intensities of the mid ionian jet and northern ionian meander among the two circulation mode but emphasize distinct behaviour within the same mode imputable to the variability of the mesoscale quasi permanent features the wind driven messina rise vortex on the western side of the northern ionian and the pelops gyre on the eastern side of the northern ionian show different behaviour during the first 1993 1996 and the second 2006 2010 anticyclonic periods related to the cyclonic activity along the dense water pathway when the dense water was of aegean origin 1993 1996 aegean anticyclone the cyclonic mesoscale activity on the eastern flank of the ionian overwhelmed the anticyclonic wind forcing and led to the disappearance of the pelops gyre when the dense water was of adriatic origin 2006 2010 adriatic anticyclone the strengthening of cyclonic mesoscale activity on the western flank of the ionian caused the shape change of the messina rise vortex favouring its longitudinal extension the zonally elongated messina rise vortex reduced the inflow of atlantic water in the northern ionian and induced a strengthening of the eastward flowing mid ionian jet in the southern ionian and cretan passage from these results it emerges that the interannual variability of the wind driven quasi permanent mesoscale gyres in the ionian is influenced by internal forcing location of the deep water formation site aegean or adriatic sea in turn related to the major local climatic shift occurred in the last decades the eastern mediterranean transient we show that the interplay between decadal and interannual variability or rather between basin wide and mesoscale circulation affected the intrinsic characteristics of the nig reversals

observed relationships between the el nino southern oscillation and the extratropical zonal mean circulation abstract there is increasing evidence indicating that the climate response to variations in the el nino southern oscillation enso includes not only thermally forced zonal wind anomalies in the subtropics but also eddy driven zonal wind anomalies that extend into the mid high latitudes of both hemispheres in this study new insights into the observed seasonally varying signature of enso in the extratropical zonal mean circulation are provided and the associated linkages with the dominant patterns of extratropical variability are examined the zonal mean extratropical atmospheric response to enso is characterized by two principal features an equivalent barotropic dipole in the southern hemisphere sh zonal mean zonal flow with centers of action located near 40 and 60 during austral summer and a weaker but analogous dipole in the northern hemisphere nh with centers of action located near 25 and 45 during early and late boreal winter both structures are accompanied by eddy momentum flux ano

mediterranean climate and oceanography and the periodic development of anoxic events sapropels mediterranean sapropels are layers with elevated organic carbon concentrations that contrast with surrounding sediments which are organic poor sapropels occur quasi periodically in sedimentary sequences of the last 13 5 million years and exist both in the eastern and western mediterranean sub basins they have been the subject of extensive study based on records from both short conventional and long ocean drilling program sediment cores and from a wide variety of uplifted marine sediment sequences on the basin margins and islands previous syntheses in the 1990s and 2000s have discussed how the formation of sapropels is commonly ascribed to deep sea anoxia enhanced export productivity or a combination of these effects however a wealth of new evidence and insights has emerged during the past 1 2 decades based on traditional and novel proxy data as well as modelling which has revealed intriguing new aspects and nuances to the reconstructed conditions hence it is timely to present a new synthesis of current understanding of the processes behind the formation of sapropels which have over the past decade also become a matter of commercial interest in sub salt hydrocarbon exploration in this review we present a context of modern mediterranean climate and oceanography followed by an integrated assessment of the growing understanding of climatological and ocean circulation changes that were associated with sapropel deposition we find that sapropels predominantly formed during astronomically timed episodes when climatic and oceanographic conditions and ecological responses broadly preconditioned the basin for sapropel deposition there is strong correspondence with times of monsoon intensification fuelling runoff from north africa into the mediterranean sea while preconditioning due to sea level rise and regional precipitation and runoff may have contributed as well within these broad episodes of surface buoyancy gain and resultant decline in deep water ventilation specific deposition under dysoxic anoxic or even euxinic conditions occurred within a clearly dynamic system that was characterised by complex spatial and depth dependent patterns gradients with distinct temporal variability on at least decadal to centennial millennial timescales in the final section we evaluate the implications of different modes of deep water removal from silled basins to investigate why sapropels are more frequently and often more intensely developed in the eastern mediterranean than in the western mediterranean

cretan deep water outflow into the eastern mediterranean abstract a simple hydraulic model is used to estimate the deep water fluxes of cretan deep water cdw through the cretan arc straits and into the eastern mediterranean basins the input to the model consists of the height of the deep water reservoir above sill depth and its density difference from the overlying water masses data from four hydrographic cruises which took place in 1995 1991 and 1987 are used to estimate the depth of the reservoir above the sill and the density difference the results show a significant cdw outflow of 0 75 106 m3 s 1 in early 1995 the outflow of cdw through kassos strait in the east is 0 53 106 m3 s 1 while 0 22 106 m3 s 1 outflows through the antikithira strait in the west the model results agree with fluxes estimated from current meter observations the cdw outflow has been neither steady nor uniform during the period 1987 95 in the kassos strait the outflow commenced in 1987 and increased rapidly until 1991 since then it appears to have stabilised in the antikithira strait in contrast the outflow has increased steadily since 1987 such modifications in the cdw outflow are associated with changes in its hydrographic characteristics the salinity of cdw increased constantly by approximately 0 1 between 1987 and 1995 while its temperature warmed between 1987 and 1991 and then cooled

different modes of variability over the tasman sea implications for regional climate abstracta new approach is used to detect atmospheric teleconnections without being bound by orthogonality such as empirical orthogonal functions this method employs negative correlations in a global dataset to detect potential teleconnections one teleconnection occurs between the tasman sea and the southern ocean it is related to el nino southern oscillation enso the indian ocean dipole iod and the southern annular mode sam this teleconnection is significantly correlated with sam during austral summer fall and winter with iod during spring and with enso in summer it can thus be described as a hybrid between these modes given previously found relationships between iod and enso and iod s proximity to the teleconnection centers correlations to iod are generally stronger than to enso increasing pressure over the tasman sea leads to higher lower surface temperature over eastern australia the southwestern pacific in all seasons and is related to reduced surface temperature over wilkes

comparing and contrasting the behaviour of arctic and antarctic sea ice over the 35 year period 1979 2013 we examine the evolution of sea ice extent sie over both polar regions for 35 years from november 1978 to december 2013 as well as for the global total ice arctic plus antarctic our examination confirms the ongoing loss of arctic sea ice and we find significant p 0 001 negative trends in all months seasons and in the annual mean the greatest rate of decrease occurs in september and corresponds to a loss of 3 x 10 6 km 2 over 35 years the antarctic shows positive trends in all seasons and for the annual mean p 0 01 with summer attaining a reduced significance p 0 10 based on our longer record which includes the remarkable year 2013 the positive antarctic ice trends can no longer be considered small and the positive trend in the annual mean of 15 29 3 85 x 10 3 km 2 a 1 is almost one third of the magnitude of the arctic annual mean decrease the global annual mean sie series exhibits a trend of 35 29 5 75 x 10 3 km 2 a 1 p

severe heat waves in southern australia synoptic climatology and large scale connections this paper brings a new perspective on the large scale dynamics of severe heat wave hw events that commonly affect southern australia through an automatic tracking scheme the cyclones and anticyclones associated with hws affecting melbourne adelaide and perth are tracked at both the surface and upper levels producing for the first time a synoptic climatology that reveals the broader connections associated with these extreme phenomena the results show that a couplet or pressure dipole formed by transient cyclones and anticyclones can reinforce the hw similarly to what is observed in cold surges cs with an obvious opposite polarity our results show that there is a large degree of mobility in the synoptic signature associated with the passage of the upper level ridges before they reach australia and the blocking is established with hw associated surface anticyclones often initiating over the west indian ocean and decaying in the eastern pacific in contrast to this result the 500 hpa anticyclone tracks show a very small degree of mobility responding to the dominance of the upper level blocking ridge an important feature of hws is that most of the cyclones are formed inland in association with heat troughs while in cs the cyclones are typically maritime often explosive associated with a strong cold front hence the influence of the cyclone is indirect contributing to reinforce the blocking ridge through hot and dry advection on the ridge s western flank additional insights are drawn for the record adelaide case of march 2008 with fifteen consecutive days above 35 c breaking the previous record by 7 days sea surface temperatures suggest a significant air sea interaction mechanism with a broad increase in the meridional temperature gradient over the indian ocean amplifying the upstream rossby waves that can trigger hw events a robust cooling of the waters close to the australian coast also contributes to the maintenance of the blocking highs locally which is a fundamental ingredient to sustain the hws

unexpected covariant behavior of the aegean and ionian seas in the period 1987 2008 by means of a nondimensional sea surface height index

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

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

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

on the relationship between the decadal oscillations of the northern ionian sea and the salinity distributions in the eastern mediterranean 1 we study the impact of decadal inversions of the ionian upper layer circulation denominated as adriatic ionian bimodal oscillation system on thermohaline properties of the levantine and cretan seas lagrangian drifter data and surface geostrophic currents show that the atlantic water aw flow is well organized and most intense when the ionian circulation is cyclonic during the ionian anticyclonic phase the aw spreading pathway is the longest contributing to its prolonged mixing and higher salinity once it reaches the levantine thus the levantine basin is subject to less dilution by aw during the anticyclonic surface circulation phase empirical orthogonal function analysis of the sea level shows a large amplitude circular feature in the northern ionian which matches the cyclonic anticyclonic gyre obtained from lagrangian measurements furthermore it reveals the out of phase variability of the north ionian gyre and the aegean and levantine sea levels we further show that the surface salinity of the levantine basin variation is out of phase with that of the ionian surface layers salinity variations of the deepwater column in the aegean are out of phase with the ionian surface salinity values owing probably to a fast transfer of the surface salinity changes via winter deep convection the changing of the levantine and cretan seas salinity parallel to the ionian circulation inversions suggests that the preconditioning for the eastern mediterranean transient emt is driven by internal processes as the ionian inversions are cyclical events we conclude that the emt is not an isolated episode but potentially a recurrent phenomenon

contourite distribution and bottom currents in the nw mediterranean sea coupling seafloor geomorphology and hydrodynamic modelling abstract contourites are common morphological features along continental margins where currents encounter the seafloor they can provide long term archives of palaeoceanography may be prone to sediment instability and can have a great potential for hydrocarbon exploration despite their importance and increasingly recognised ubiquitous occurrence worldwide the link between oceanographic processes and contourite features is poorly constrained in particular it is unclear under which specific conditions sediments are mobilised modified and deposited by bottom currents here we aim to determine key bottom current characteristics velocity and bottom shear stress affecting contourite deposition by assuming that recent oceanographic regimes may be extended back in time over the past glacial interglacial cycles with strong winter circulation assumed similar to glacial conditions and weak summer circulation to interglacials we present an integrated study from the nw mediterranean sea that couples results of the mars3d hydrodynamic model with high resolution sedimentological and geophysical data piston cores multibeam bathymetry and high resolution seismic data near bottom circulation was modelled during winter and summer 2013 as representative of past periods of high and low current intensity respectively model results match well with the extent of contourite depositional systems and their different localised morphologic elements we deduce that higher intensity events control the formation of erosional features such as moats and abraded surfaces the heterogeneous distribution of bottom current intensity on slopes explains the development of different types of contourite drifts plastered drifts form in zones of low bottom current velocities constrained upslope and downslope by higher current velocities separated elongated mounded drifts develop where fast bottom currents decelerate at foot of the slope in contrast no mounded contourite morphologies develop when the current velocity is homogeneous across the slope especially in margins prone to downslope sediment transport processes in confined basins gyres may transport sediment in suspension from a margin with a high sediment supply to an adjacent starved margin favouring the development of fine grained contourites in the latter our results provide new insights into how detailed bottom circulation modelling and seafloor geomorphological analyses can improve the understanding of palaeoflow regimes at least over time spans when the overall paleogeography and the distribution of contourite drifts is comparable to present day conditions the approach of coupled hydrodynamic models and geomorphological interpretations proposed here for depositional erosional and mixed contourite features may be used to understand other areas affected by bottom currents and for a better conceptual understanding of bottom current processes and their interactions with the seafloor

propagation of the arctic oscillation from the stratosphere to the troposphere geopotential anomalies ranging from the earth s surface to the middle stratosphere in the northern hemisphere are dominated by a mode of variability known as the arctic oscillation ao the ao is represented herein by the leading mode the first empirical orthogonal function of low frequency variability of wintertime geopotential between 1000 and 10 hpa in the middle stratosphere the signature of the ao is a nearly zonally symmetric pattern representing a strong or weak polar vortex at 1000 hpa the ao is similar to the north atlantic oscillation but with more zonal symmetry especially at high latitudes in zonal mean zonal wind the ao is seen as a north south dipole centered on 40 45 n in zonal mean temperature it is seen as a deep warm or cold polar anomaly from the upper troposphere to 10 hpa the association of the ao pattern in the troposphere with modulation of the strength of the stratospheric polar vortex provides perhaps the best measure of coupling between the stratosphere and the troposphere by examining separately time series of ao signatures at tropospheric and stratospheric levels it is shown that ao anomalies typically appear first in the stratosphere and propagate downward the midwinter correlation between the 90 day low pass filtered 10 hpa anomaly and the 1000 hpa anomaly exceeds 0 65 when the surface anomaly time series is lagged by about three weeks the tropospheric signature of the ao anomaly is characterized by substantial changes to the storm tracks and strength of the midtropospheric flow especially over the north atlantic and europe the implications of large stratospheric anomalies as precursors to changes in tropospheric weather patterns are discussed

unraveling north african riverine and eolian contributions to central mediterranean sediments during holocene sapropel s1 formation hydroclimate variability has exerted a fundamental control on the alternating deposition of organic lean marl and organic rich sapropel sediments in the eastern mediterranean sea ems however the exact mechanisms regarding the freshwater sources and related changes are still debated here sr and nd isotopes and high resolution elemental data are used to constrain different riverine and eolian supplies to the central mediterranean over the past 9 8 ka the detrital sediments in core cp10bc taken at the margin of the libyan shelf in the southwestern ionian sea can be described by a three endmember mixing system based on sr and nd isotopic compositions the same systematics can also be deduced from ti and k compositional variability the endmembers comprise saharan dust aegean nile and libyan soil representing the eolian supply from north africa the riverine inputs from the aegean nile areas as well as the riverine and shelf derived fluxes from the libyan tunisian margin respectively for the sapropel s1 period in particular we find important detrital supplies from fossil river wadi systems along the libyan tunisian margin activated by intensified african monsoon precipitation combining the temporal profiles with the consistent variability observed in the 87sr 86sr 1000 sr diagram such libyan contribution has been most prominent during the uppermost period of sapropel s1 in core cp10bc this observation is in agreement with hydroclimate reconstructions of northwestern libya comparison of the sr nd isotope data between core cp10bc and four cores taken along a west east transect throughout the ems shows that this detrital supply originated mainly from western libya tunisia and was transported as far eastward as 25 e while being diluted by an increasing nile contribution

lagrangian and eulerian observations of the surface circulation in the tyrrhenian sea 1 this paper focuses on the study of the tyrrhenian sea a subbasin of the western mediterranean whose surface and near surface dynamics are still relatively poorly known in particular its southern region its circulation is described first by a set of 53 surface drifters deployed in the area between december 2001 and february 2004 in order to supplement the drifter data with continuously and uniformly sampled observations and to characterize the seasonal as well as higher frequency variability of the surface circulation the lagrangian analysis was associated to simultaneous satellite remotely sensed altimeter covering the period 2001 2004 the investigation was based on trajectory analysis and on the computation of the pseudo eulerian statistics using the same binning and space time averaging for drifter and altimeter data the data reveal a complex pattern of the circulation especially in the southern region of the tyrrhenian dominated by semipermanent recirculations and transient features which sometimes makes it difficult to identify a consistent mean flow while the northern subbasin is characterized by a pair composed of cyclonic and anticyclonic circulations known in the literature as the north tyrrhenian cyclone and north tyrrhenian anticyclone the pseudo eulerian statistics computed with the two data sets evidenced the representativeness of a joint analysis of altimeter and drifter data and yielded useful indications about proper preliminary preprocessing and resampling procedures so as to make the comparison statistically sound

late quaternary bottom current activity in the south aegean sea reflecting climate driven dense water production abstract the eastern mediterranean transient emt represents a recent early 1990s to today water circulation phenomenon during which more arid climatic conditions in the mediterranean lead to the production of very dense surface water masses in the north aegean sea the produced north aegean dense water nadw sinks to seafloor flows to the south aegean sea and then spills into the eastern mediterranean sea through the cretan straits contributing to the rejuvenation of the bottom water a large dataset of vintage high resolution seismic reflection profiles indicates that the floors of the basins in the southwest aegean sea are characterised by late quaternary erosional gullies abraded surfaces and channel related sediment drifts such structures provide evidence for the presence of strong bottom currents which originate from the southward propagation of nadw masses the basins have depths of 300 m to 1000 m and are connected to each other by narrow a few km straits and sills the dominance of abraded surfaces and erosional gullies on the northern flank of the basins and in the narrow straits sills between them provides evidence that the southward propagation of the nadw occurs by the filling and flooding of each basin by dense water which then spills and cascades into the next basin southward seismic stratigraphy suggests that the formation of the drifts started at marine isotope stage mis 11 420 ka bp the coincidence of at least three erosional surfaces within the sediment drifts with interglacial mis 11 5 and 1 respectively suggests that bottom currents were mostly active during high sea level stands and sluggish during glacial low sea level stands a 90 100 m drop of the sea level below the current level would have resulted in the emergence of the eastern cyclades plateau and thus in the disconnection of the southwest aegean sea from the north aegean sea several 0 05 0 5 m thick beds of gravelly sand with algal and mollusc debris laminated to mottled sand and mottled mud are observed in the sediment cores analysed in this paper these beds can be confidently correlated from core to core and are interpreted as bottom current deposits the separation of these beds by hemipelagic sediments indicates that bottom current activity in the southwest aegean is not permanently established but episodic six episodes of intense bottom current activity are recorded in the mis 2 4 10 80 ka sediments and they appear to correlate well with the cold and dry younger dryas and heinrich 3 4 5 6 and 7 events in contrast at least three episodes of intense bottom current activity are recorded in the cores during the holocene the higher frequency of strong bottom current episodes in the southwest aegean sea during the holocene is attributed to the higher sea level stand that makes the circulation of water masses in the aegean sea more sensitive to climatic changes

seismic investigation of magmatic unrest beneath mammoth mountain california usa i present a reinvestigation of the seismic activity during an 11 mo long seismic swarm between 1989 and 1990 beneath mammoth mountain in eastern california united states this swarm believed to be the result of a shallow intrusion of magma beneath mammoth mountain was followed by the emission of magmatic co 2 gas resulting in tree die off in 1990 and posing a signifi cant human health risk around mammoth mountain in this study i apply a state of the art approach to estimate the ratio of compressional to shear wave velocity vp vs within similar event clusters using differential times from waveform crosscorrelation a high resolution three dimensional seismic velocity model and a precise earthquake location catalog are obtained to complement the analysis of the in situ vp vs ratios the majority of the relocated seismicity below sea level is distributed in an anomalous body with low vp and high vp vs consistent with the seismic expression of the magma body that triggered the seismic swarm abrupt changes in vp vs ratios with lower values for the shallow depths are observed near sea level indicating the source of the 1989 co 2 fl ux is a shallow co 2 reservoir instead of the hypothesized basaltic magma at mid crustal depths of 10 25 km from sea level to the surface low vp vs ratios in a near vertical zone suggest involvement of fl uid in the upward migration of the seismicity

climate variability and socio environmental changes in the northern aegean ne mediterranean during the last 1500 years abstract we provide new evidence on sea surface temperature sst variations and paleoceanographic paleoenvironmental changes over the past 1500 years for the north aegean sea ne mediterranean the reconstructions are based on multiproxy analyses obtained from the high resolution decadal to multi decadal marine record m2 retrieved from the athos basin reconstructed ssts show an increase from ca 850 to 950 ad and from ca 1100 to 1300 ad a cooling phase of almost 1 5 c is observed from ca 1600 ad to 1700 ad this seems to have been the starting point of a continuous sst warming trend until the end of the reconstructed period interrupted by two prominent cooling events at 1832 15 ad and 1995 1 ad application of an adaptive kernel smoothing suggests that the current warming in the reconstructed ssts of the north aegean might be unprecedented in the context of the past 1500 years internal variability in atmospheric oceanic circulations systems as well as external forcing as solar radiation and volcanic activity could have affected temperature variations in the north aegean sea over the past 1500 years the marked temperature drop of approximately 2 c at 1832 15 yr ad could be related to the 1809 d unknown and the 1815 ad tambora volcanic eruptions paleoenvironmental proxy indices of the m2 record show enhanced riverine continental inputs in the northern aegean after ca 1450 ad the paleoclimatic evidence derived from the m2 record is combined with a socio environmental study of the history of the north aegean region we show that the cultivation of temperature sensitive crops i e walnut vine and olive co occurred with stable and warmer temperatures while its end coincided with a significant episode of cooler temperatures periods of agricultural growth in macedonia coincide with periods of warmer and more stable ssts but further exploration is required in order to identify the causal links behind the observed phenomena the black death likely caused major changes in agricultural activity in the north aegean region as reflected in the pollen data from land sites of macedonia and the m2 proxy reconstructions finally we conclude that the early modern peaks in mountain vegetation in the rhodope and macedonia highlands visible also in the m2 record were very likely climate driven

some features of the algerian current an analysis of infrared images leads to a new conception of the dynamics of the atlantic water in the algerian basin in situ current measurements are not yet available but coherent hypotheses are presented with the aim to initiate further experimental and theoretical works the algerian current flows steadily along the coast near 0 and becomes unstable near 1 2 e eddies of both signs are generated that are advected by the mean current but only the anticyclonic eddies increase in size diameter about 100 km as they extract more energy from the mean current they are advected more slowly and they may detach from the coast and drift for several weeks in the algerian basin they grow as deep as 1000m at least and they are able to pull lenses of intermediate water seaward from the sardinian continental slope coastal upwelling cells are generated near 1 2 e between the cyclonic and the anticyclonic eddies they are also advected by the mean current and are definitively not wind induced these turbulent structures create intense mixing between the atlantic and mediterranean waters which account for the large eastward gradient of salinity encountered in the surface layer therefore the algerian basin is characterized by a large mesoscale variability mainly due to the instability of the algerian current it appears to be a reservoir in which the water of atlantic origin is amassed and it forms a buffer zone which disconnects the flow of atlantic water coming in at gibraltar from the flow of hygly modified atlantic water exiting the basin through the strait of sardinia and into the ligurian sea

climate variability of the last 2700 years in the southern adriatic sea coccolithophore evidences new information on palaeoenvironmental conditions over the past 2700 years in the central mediterranean sea have been acquired through the high resolution study of calcareous nannofossils preserve

the origin and characteristics of the algerian current satellite and ship data collected between may 1 and 22 1986 show that the algerian current originates in the almeria oran front and remains within 30 km of the algerian coast for over 300 km between oran and algiers the differences between the water masses of the current and the resident regional waters are clearly observed in the chlorophyll concentrations and optical characteristics thus permitting the resulting patterns to be used as tracers of the circulation during this field period the algerian current begins as an extension of the almeria oran front which is found at the western periphery of the eastern alboran gyre this major oceanographic salinity front s 1 km delineates the boundary of the algerian current which has average surface velocities of 40 cm s and maximum speeds reaching 80 cm s the current which has a volume transport between 0 4 and 0 5 sv is confined to the upper 150 m and is in geostrophic balance a sequence of coastal zone color scanner czcs and advanced very high resolution radiometer avhrr satellite imagery showing the rapidly evolving surface circulation features is augmented with in situ ship data of current and water mass characteristics rapid undulations and frontal movements of the current were observed during the study period however the flow remained unbroken between 1 and 3 e current instability increased eastward as the undulations were sharper and the current appeared to depart from the coast near algiers

currents water masses eddies and jets in the mediterranean levantine basin abstract hydrographic measurements in the southeastern levantine basin are analyzed and the climatological water masses of the region and their seasonal variations are identified we observe the formation of the salty and warm levantine surface water layer lsw we characterize the subsurface atlantic water layer aw and we describe the properties of the thermocline waters called levantine intermediate waters liw the baroclinic dynamical modes are computed for the climatological stratification parameters the empirical orthogonal function eof analysis of the vertical shear profiles shows that considerable energy is contained in the second eof at the thermocline and deep levels maps of the baroclinic streamfunction field referred to 700 meters are displayed 16 instantaneous flow field realizations show an intense mesoscale eddy file never revealed before in the region the space scales of the eddies are about 100 km and a smaller scale 60 70 km variability is also evident the eddies are pres

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

observed southern hemisphere eddy statistics at 500 mb frequency and spatial dependence abstract nearly eight years of daily southern hemisphere analyses at 500 mb have been used to define the spatial dependence of the variance fields of geopotential height and the two geostrophic wind components the corresponding covariance fields and the transient kinetic energy the fields are further examined in the frequency domain by using lorenz 1979 poor man s spectral analysis technique in view of the small variation in eddy statistics as a function of the time of the year in the sh this study removes the first four harmonies of the annual cycle and then considers all data together so that contributions from all time scales from 2 to 4096 days 11 years can be resolved the main results are based on analyses from may 1972 january 1978 but are verified with analyses from the relatively data rich fgge period results for the zonal mean statistics are compared with those from previous studies the zonal means of the geopotential height and westerly wind component have spectra which roughly

small synoptic mesoscale eddies and energetic variability of the eastern levantine basin mesoscale eddies are energetically dominant over most of the world s ocean1 the local dynamics of eddies is now a central problem of physical oceanography2 and their statistics control aspects of the general circulation3 the horizontal scale of eddies is generally related to but somewhat larger than the rossby internal deformation radius the depth scale multiplied by the buoyancy frequency divided by the coriolis frequency in the eastern mediterranean which is not well explored or understood the internal radius is known to be 12 km or 4 times smaller than in the north atlantic the study of such eddies requires very fine sampling which hinders their accidental discovery by using a dedicated data set and objective analysis methods we have estab ished the existence of small synoptic mesoscale eddies and jets which constitute a variable and turbulent current regime and dominate the general circulation flow of the levantine basin their existence in the mediterranean has an impact on all aspects of basic and applied marine science there both conceptually and with respect to experimental and monitoring programme designs

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

a three dimensional numerical study of deep water formation in the northwestern mediterranean sea abstract deep water formation dwf in the northwestern mediterranean sea and the subsequent horizontal circulation are investigated in a rectangular basin with a three dimensional primitive equation model the basin is forced by constant climatological heat and salt fluxes convective motion is parameterized by a simple nonpenetrative convective adjustment process plus richardson number dependent vertical eddy viscosity and diffusivity a homogeneous column of dense water is progressively formed in the forcing area meanders of 40 km wavelength develop at the periphery of the column these features agree with observations energy studies show that the meanders are generated mainly through a baroclinic instability process these meanders and the associated cells of vertical motion contribute to the process of dwf they generate vertical advection while the associated horizontal advection tends to restratify the surface water of the column and thus to inhibit very deep convection just before the end o

modeling the mediterranean sea interannual variability during 1961 2000 focus on the eastern mediterranean transient 1 this work is dedicated to the study of the climate variability of the mediterranean sea in particular the study of the eastern mediterranean transient emt which occurred in the early 1990s simulations of the 1961 2000 period have been carried out with an eddy permitting ocean general circulation model of the mediterranean sea driven by realistic interannual high resolution air sea fluxes using different databases for the river runoff black sea inflow and atlantic thermohaline characteristics at climatological or interannual scales we assess the effects of the non atmospheric hydrological forcings on the simulation of the interannual variations of the mediterranean circulation the evolution of the basin scale heat content is in very good agreement with the observations especially in the surface and intermediate layers while the agreement is lower for the evolution of the salt content convection events in the aegean sea are noticed in the simulations between 1972 and 1976 in the late 1980s and around the emt period the formation rates of cretan deep water cdw are different during these periods allowing or preventing the spreading of cdw into the eastern mediterranean the sequence of the emt events is well reproduced the high winter oceanic surface cooling and net evaporation over the aegean sea in the early 1990s the high amount of dense cdw formed during these winters and then the overflow and the spreading of this cdw in the eastern mediterranean among the preconditioning processes suggested in the literature we find that changes in the levantine surface circulation possibly induced by the presence in the cretan passage of anticyclonic eddies and a lasting period with reduced net precipitation over the eastern mediterranean lead to an increase of the salt content of the aegean sea changes in the black sea freshwater inflow or in the characteristic of the atlantic water entering at the gibraltar strait also modify the thermohaline state of the aegean sea before the emt but as none of these preconditioning factors has a lasting impact on lowering the vertical stratification of the aegean sea we conclude that concerning the emt the major triggering elements are the atmospheric fluxes and winds occurring in winters 1991 1992 and 1992 1993

spreading of levantine intermediate waters by submesoscale coherent vortices in the northwestern mediterranean sea as observed with gliders since 2007 gliders have been regularly deployed in the northwestern mediterranean sea a crucial region regarding the thermohaline circulation of the mediterranean sea it revealed for the first time very warm 10 48c and saline 10 1 submesoscale anticyclones at intermediate depth characterized by a small radius 5 km high rossby 0 3 and burger 0 7 numbers they are likely order of 10 to be formed each year have a life time order a year and certainly contribute significantly to the spreading of the levantine intermediate waters liw toward the whole subbasin thus potentially impacting wintertime vertical mixing through hydrographical and dynamical preconditioning they could be mainly formed by the combined action of turbulent mixing and flow detachment of the northward flow of liw at the northwestern headland of sardinia upwelling conditions along the western coast of sardinia associated with a southward geostrophic flow within the upper layers seem to play a key role in their formation process

on the salinity structure in the south adriatic as derived from float and glider observations in 2013 2016 abstract between 2013 and 2016 a drastic change in the vertical salinity structure in the south adriatic pit was recorded by argo floats and ocean gliders the analysis revealed that high salinity waters characterised 2013 at the surface and intermediate layers creating the conditions for dense water formation the year 2014 was instead marked by less saline water dominant in the first 100 m that spread in the entire pit heat gain negative e p anomalies and abundant river runoff during that period maintained this saline stratification for more than a year this water mass contributed to the dilution of the underlying layer during the convection event of 2015 the spring transition period later in 2015 as defined by new saline water placed over the winter formatted water mass and the unperturbed part of the existent salinity profile in the deeper layers resulted in a particular vertical structure characterised by a double salinity maximum high salinity waters continued to be present at the surface and intermediate layers until the end of 2016 when the strong convection led to a deep mixing eliminating that structure the analysis of the available datasets in the south adriatic pit since 1984 linked the presence of these high salinity waters with the cyclonic phase of the north ionian gyre additionally revealing also years of a decreasing trend during the anticyclonic mode of the gyre

basin to mesoscale surface circulation of the western mediterranean manifested by satellite derived data products abstract in this article there is an overview of the potential of different mostly altimetry derived products for manifesting features of basin and mesoscale circulation of the western mediterranean basin in terms of detection of mesoscale eddies and larger gyres the comparison was performed between eddy statistics extracted directly from fields of sea surface temperature sst on the one hand and reconstructed from different scalar and vector altimetry derived fields on the other hand among the products being analysed there are fields of i sea level anomaly sla ii geostrophic currents and iii finite size lyapunov exponents fsle comparison of the eddy statistics provided by such different data sources revealed that altimetry based techniques tended to overestimate the number of big cyclones and thus failed to reproduce cyclonic anticyclonic eddy asymmetry which was shown by fields of sst defining the spatial scale of eddies via altimetry based techniques seemed particularly problematic fsle product analysed in the study showed significant disagreements with vortical structures observed in fields of sst both in terms of the spatial scale and the sign of rotation in order to scrutinize basin scale features of surface circulation in the region of interest fields of i geostrophic currents ii total currents reconstructed by the globcurrent project and iii surface currents provided by the reanalysis technique were analysed as a result of the comparison performed a conclusion was made on the complementarity of the datasets analysed

toward an understanding of deep water renewal in the eastern mediterranean abstract this paper presents a scenario for understanding the unexpectedly large changes of deep waters and thermohaline circulation in the eastern mediterranean during the past decade it is demonstrated as a possible deep water renewal mechanism in the eastern mediterranean in a numerical simulation with a high resolution model which has successfully reproduced the observed 1987 and 1995 regimes as shown by the two meteor cruises a budget study of the model simulation has shown that more than 75 of the salt added to the deep layers of the eastern mediterranean could have come from the top 1000 m by a salinity redistribution process triggered by intensive cooling over the aegean sea a water transformation process analysis is carried out in the model simulation to reveal how colder and fresher dense deep water formed in the aegean is turned into the eastern mediterranean deep water emdw as observed surface heat and freshwater fluxes are diagnosed to show the roles of each component during the trans

contourite identification along italian margins the case of the portofino drift ligurian sea abstract a brief review of the published evidence of current deposits around italy is the occasion to test the robustness of matching bottom current velocity models and seafloor morphologies to identify contourite drifts not yet documented we present the result of the regional hydrodynamic model mars3d in the northern tyrrhenian and ligurian sea with horizontal resolution of 1 2 km and 60 levels with focus on bottom current data are integrated over summer and winter 2013 as representative of low and high intensity current conditions the eastern ligurian margin is impacted by the levantine intermediate water liw with modeled mean velocity of bottom current up to 20 cm s 1 in winter 2013 and calculated bottom shear stress exceeding 0 2 n m 2 in water depth of 400 800 m by crossing this information with seafloor morphology and geometry of seismic reflections we identify a sediment drift formerly overlooked at ca 1000 m water depth the portofino separated mounded drift has a maximum thickness of at least 150 m and occurs in an area of mean current velocity minimum independent evidence to support the interpretation include bottom current modelling seafloor morphology seismic reflection geometry and sediment core facies the adjacent areas impacted by stronger bottom currents present features likely resulted from bottom current erosion such as a marine terrace and elongated pockmarks compared to former interpretation of seafloor morphology in the study area our results have an impact on the assessment of marine geohazards submarine landslides offshore portofino are small in size and coexist with sediment erosion and preferential accumulation features sediment drifts originated by current dominated sedimentary processes furthermore our results propel a more general discussion about contourite identification in the italian seas and possible implications

are the north atlantic oscillation and the northern annular mode distinguishable this study addresses the question of whether persistent events of the north atlantic oscillation nao and the northern annular mode nam teleconnection patterns are distinguishable from each other standard daily index time series are used to specify the amplitude of the nao and nam patterns the above question is examined with composites of sea level pressure and 300 and 40 hpa streamfunction along with tests of field significance a null hypothesis is specified that the nao and nam persistent events are indistinguishable this null hypothesis is evaluated by calculating the difference between time averaged nao and nam composites it is found that the null hypothesis cannot be rejected even at the 80 confidence level the wave breaking characteristics during the nam life cycle are also examined both the positive and negative nam phases yield the same wave breaking properties as those for the nao the results suggest that not only are the nao and nam persistent events indistinguishable but that the nao nam events are neither confined to the north atlantic nor are they annular

a new collective view of oceanography of the arctic and north atlantic basins abstract we review some historical aspects of the major observational programs in the north atlantic and adjacent regions that contributed to establishing and maintaining the global ocean climate monitoring network the paper also presents the oceanic perspectives of climate change and touches the important issues of ocean climate variability on time scales from years to decades some elements of the improved understanding of the causes and mechanisms of variability in the subpolar north atlantic and adjacent seas are discussed in detail the sophistication of current oceanographic analysis especially in connection with the most recent technological breakthroughs notably the launch of the global array of profiling argo floats allows us to approach new challenges in ocean research we demonstrate how the ocean climate changes in the subpolar basins and polar seas correlate with variations in the major climate indices such as the north atlantic oscillation and atlantic multidecadal oscillation and discuss possible connections between the unprecedented changes in the arctic and greenland ice melt rates observed over the past decade and variability of hydrographic conditions in the labrador sea furthermore a synthesis of shipboard and argo measurements in the labrador sea reveals the effects of the regional climate trends such as freshening of the upper layer possible causes of which are also discussed on the winter convection in the labrador sea including its strength duration and spatial extent these changes could have a profound impact on the regional and planetary climates a section with the highlights of all papers comprising the special issue concludes the preface

the north pacific oscillation west pacific teleconnection pattern mature phase structure and winter impacts abstract the north pacific oscillation npo in sea level pressure and its upper air geopotential height signature the west pacific wp teleconnection pattern constitute a prominent mode of winter midlatitude variability the npo wp its mature phase expression is identified from principal component analysis of monthly sea level pressure variability as the second leading mode just behind the pacific north american variability pattern npo wp variability primarily on subseasonal time scales is characterized by a large scale meridional dipole in slp and geopotential height over the pacific and is linked to meridional movements of the asian pacific jet and pacific storm track modulation the hemispheric height anomalies at upper levels resemble the climatological stationary wave pattern attributed to transient eddy forcing the npo wp divergent circulation is thermal wind restoring pointing to independent forcing of jet fluctuations intercomparison of sea level pressure geopotential height and zonal

variability of the cyprus warm core eddy during the cyclops project the circulation of the southeastern levantine basin eastern mediterranean as determined from several oceanographic cruises carried out in april may and august 2001 and in march may and august 2002 was investigated within the framework of the cyclops experiment the may cruises were part of cyclops while the others which provide supporting data were part of the ongoing cybo project the may 2002 data provided the location of the eddy and physical description of the circulation which were crucial for the in situ phosphate sf6 addition experiment of cyclops the major flow features observed in the region south of cyprus displayed strong variability within the period of the observations throughout the entire study period the warm core anticyclonic eddy known as the cyprus eddy was a dominant component of the circulation during the 18 months covered by the cruises the eddy drifted slowly to the southwest at the end of the cyclops cruises the center of this persistent recurrent eddy was found approximately 100 150 km west of its previously observed location since the 1980s the mid mediterranean jet mmj associated with the rim of this eddy followed a complex path south of cyprus depending upon the eddy s shape and location during most of the study period the mmj surface currents near the northern periphery of the rim of the eddy were as high as 35 45 cm s in may 2002 during the in situ experiment the near surface seasonal thermocline inhibited downward mixing of the added tracers while the strong horizontal current around the rim of the clearly defined eddy core limited the lateral spreading and dilution of the patch finally the westward shift of the cyprus eddy allowed space for the generation of a secondary anticyclonic eddy in the eastern part of the domain the co existence of the two anticyclonic eddies during 2002 along with the development of a third anticyclonic eddy closer to the coast of egypt provides strong evidence for the re establishment of the previously observed multi pole sub basin scale shikmona gyre r 2005 elsevier ltd all rights reserved

climate forcing of terrigenous sediment input to the central mediterranean sea since the early pleistocene clay mineralogy of odp site 964 in the ionian sea was investigated in order to reconstruct variations in detrital sediment input to the central mediterranean sea and to reconstruct the corresponding climatic processes over the last 1500 kyr the clay mineralogy of odp site 964 indicates a major shift in sedimentary sources from the saharan desert which is characterized by a clay mineral assemblage of palygorskite illite kaolinite to the apennine peninsula characterized by an illite smectite clay assemblage at 700 kyr prior to 700 kyr the low smectite content 10 20 and the strong precessional cycles in the variations of kaolinite illite and palygorskite indicate that terrigenous sediment to the central mediterranean sea mainly originated from saharan dust and was strongly affected by the african monsoon with a minor contribution of sediment deriving from the apennine peninsula an increase in the illite kaolinite ratio in the maxima of boreal summer insolation indicates a decreased dust input from the southern sahara as a result of the northward displacement of the african monsoon itcz system a gradual increase in smectite content has been identified between 1050 and 500 kyr probably associated with environmental vegetation and or hydrological changes in southern europe linked to the occurrence of the mpt and partly to tectonic uplift in the apennine peninsula a marked increase in terrigenous flux is observed at around 350 kyr coeval with a major phase of uplift in the calabrian arc

the shape propagation and mean flow interaction of large scale weather systems abstract for a zonal average operator the eliassen palm flux provides a diagnostic of both eddy behavior and the feedback of the eddies onto the mean flow this paper addresses the diagnosis problem for other averaging operators and in particular for time averaging which has proved in recent years such a powerful means of viewing the three dimensional tropospheric flow the horizontal velocity correlation tensor gives a measure of the characteristic horizontal eddy shape at a point it also implies the direction of the group velocity relative to the mean flow in cases where such a concept is valid however the major emphasis here is on the mean flow feedback of eddies in this respect the eddy vorticity flux is determined by derivatives of the components of the anisotropic part of the tensor making a reasonable approximation allows the eddy vorticity flux convergence to be written in terms of e v 2 u 2 u v a simple interpretation of the mean flow feedback of eddies is then possible a sligh

understanding the sam influence on the south pacific enso teleconnection the relationship between the el nino southern oscillation enso and the southern hemisphere annular mode sam is examined with the goal of understanding how various strong sam events modulate the enso teleconnection to the south pacific 45 70 s 150 70 w the focus is on multi month multi event variations during the last 50 years a significant p 0 10 relationship is observed most marked during the austral summer and in the 1970s and 1990s in most cases the significant relationship is brought about by la nina el nino events occurring with positive negative phases of the sam more often than expected by chance the south pacific teleconnection magnitude is found to be strongly dependent on the sam phase only when enso events occur with a weak sam or when a la nina el nino occurs with a positive negative sam phase are significant south pacific teleconnections found this modulation in the south pacific enso teleconnection is directly tied to the interaction of the anomalous enso and sam transient eddy momentum fluxes during la nina sam and el nino sam combinations the anomalous transient momentum fluxes in the pacific act to reinforce the circulation anomalies in the midlatitudes altering the circulation in such a way to maintain the enso teleconnections in la nina sam and el nino sam cases the anomalous transient eddies oppose each other in the midlatitudes overall acting to reduce the magnitude of the high latitude enso teleconnection

on the midlatitude thermal response to tropical warmth 1 observations reveal a global scale thermal response to el nino and la nina featuring a band of tropospheric anomalies opposite in sign to those in the tropics when an idealized dynamical model is forced by increased tropical heating a similar response with an enhanced subtropical thermal gradient results in the idealized model this response is produced by changes in transient eddy fluxes of heat and momentum and consequent changes in the mean meridional circulation the similarity between the two level model results and those from observations as well as the zonally averaged behavior of a gcm suggests that the same dynamics operate in nature this represents a tropical midlatitude teleconnection distinct from and in addition to that mediated by stationary rossby wave trains

variations in the structure of the anticyclonic gyres found in the alboran sea historical satellite aircraft and in situ data have shown that two anticyclonic gyres the western and eastern alboran gyres are major ocean features of the alboran sea an examination of several years of satellite imagery indicates that large variations in the surface expression of these two gyres occur and that on occasion one or the other gyre disappears the disappearance of both gyres at the same time was not seen the initial disappearance of either gyre occurs on a time scale of a week to 2 weeks whereas the return may take from 3 weeks to 2 months various forcing mechanisms i e winds mass flux inflow through the straits of gibraltar and sicily and or density have been used in numerical ocean circulation models to study the dynamics of the western mediterranean sea various model results show relationships similar to those shown by the satellite imagery however no single forcing mechanism has been positively identified as the source of the disappearances and the events may be a result of a combination of forcing mechanisms

seasonal evolutions of atmospheric response to decadal sst anomalies in the north pacific subarctic frontal zone observations and a coupled model simulation abstractpotential impacts of pronounced decadal scale variations in the north pacific sea surface temperature sst that tend to be confined to the subarctic frontal zone safz upon seasonally varying atmospheric states are investigated by using 48 yr observational data and a 120 yr simulation with an ocean atmosphere coupled general circulation model cgcm sst fields based on in situ observations and the ocean component of the cgcm have horizontal resolutions of 2 0 and 0 5 respectively which can reasonably resolve frontal sst gradient across the safz both the observations and cgcm simulation provide a consistent picture between sst anomalies in the safz yielded by its decadal scale meridional displacement and their association with atmospheric anomalies correlated with sst anomalies persistent in the safz from fall to winter a coherent decadal scale signal in the wintertime atmospheric circulation over the north pacific starts emerging in november and develops into an equivalent barotropic an

structure and dynamics of the rhodes gyre system and dynamical interpolation for estimates of the mesoscale variability abstract a coastal quasigeostrophic qg methodology is extended in an exploration of the mesoscale variability of the rhodes gyre region of the eastern mediterranean sea given multiscale data taken as part of the poem program standard objective analysis procedures are modified to include a coastal constraint that prohibits geostrophic flow normal to the coastline and imposes a characteristic nearshore variability in the coastal portion of the domain objectively analyzed fields are dynamically adjusted in short qg model integrations and then interpreted for the structure and characteristics of the subbasin scale flow system and the mesoscale two week simulations are then performed to explore the stability of the subbasin scale flow the dynamical balances and the variabilities and interactions of the mesoscale a matrix of simulation experiments is described to test the sensitivities to two variations in initial conditions and three parameterizations of the bottom topography an energy and vorticity

deep water circulation within the eastern mediterranean sea over the last 95 kyr new insights from stable isotopes and benthic foraminiferal assemblages the response of eastern mediterranean sea ems circulation to climate forcings over the last 95 kyr bp was studied using core md04 2722 collected at 1780 m water depth within the levantine sea foraminiferal stable isotopes and benthic assemblages were combined in order to reconstruct deep water ventilation and oxygenation in relation to surface water freshening over the last deglaciation benthic foraminiferal 13c values and oxygen index decreased while the 18o gradient between benthic and planktonic foraminifera increased the results respectively indicate slower ventilation bottom water oxygen depletion and stronger stratification prior to s1 sapropel deposition a combination of deglacial sea level rise and fresher north atlantic surface water contributions were determined to be a precondition for s1 formation within the levantine sea local nile river freshwater supplied during the african humid period further strengthened water column stratification as for s3 deposit the central role of monsoonal precipitation was estimated for the last glacial period three events at around 53 46 and 37 ka bp were marked by a deep water circulation reduction at the core location considering the influence of north atlantic surface water salinity on mediterranean sea circulation we propose that the 46 and 37 ka bp events are responses to heinrich events 4 and 5 that supplied fresher surface water to the mediterranean sea since the 53 ka event was also characterized by the appearance of low oxygen benthic indicators as observed within the s1 and s3 layers we tentatively attributed it to missing sapropel s2 our results indicate that intense stagnation within the ems could occur when both the local freshwater supply and fresher north atlantic surface water are contributors the influence of north atlantic conditions was significant to ems circulation under warm and cold climate conditions

the adriatic sea general circulation part ii baroclinic circulation structure abstract in the second part of the paper dedicated to the adriatic sea general circulation the horizontal structure of the hydrographic parameters and dissolved oxygen fields is described on a seasonal timescale maps of temperature and salinity climatological fields reveal the enhanced seasonal variability of the adriatic sea which at the surface is associated with the major dilution effects of river runoff the density and derived dynamic height fields show for the first time the baroclinic geostrophic structure of the general circulation winter is dominated by compensation effects between temperature and salinity fronts along the western coastline the resulting baroclinic circulation is weak and suggests the presence of barotropic current components not accessible by the dataset spring and summer seasons have the smallest spatial scales in the temperature and salinity fields and stronger subbasin scale gyres and current systems which have been classified in a schematic representation of the circu

the dynamics of the sicily strait a comprehensive study from observations and models abstract the dynamics of the sicily strait are investigated in a comprehensive study using recent in situ observations ocean general circulation model ogcm simulations and process model results in particular results of a very high resolution mediterranean model med16 developed in the context of the mercator project are described the circulation in the sicily strait can be described as a two layer exchange of atlantic water aw and eastern mediterranean outflow water eow the algerian current brings aw the upper layer eastwards and splits into two branches at the entrance to the sicily strait one flowing to the tyrrhenian sea the other into the sicily strait the later is composed of two streams referred to as the atlantic ionian stream ais and the atlantic tunisian current atc in winter the atc signature is more pronounced in summer the ais is associated with a number of well known semi permanent features including the intermittent northward extension of the ais called nais at the ionian shelf break which seems to be driven by the surface density contrast between waters of the sicilian and the ionian basins new intermittent patterns are shown by the med16 simulations for example an anticyclonic eddy called mca south of the malta channel and an anticyclonic gyre associated to the nais called naisa upwelling is well developed in august with temperature lower than 24 c along the western and southern coasts of sicily the seasonal transport of the aw through the strait has a maximum value 1 4 sv in winter and a minimum value at the end of summer 0 8 sv in the lower layer at the exit of the sicily strait the eow mainly composed of levantine intermediate water liw outflows into the tyrrhenian sea and veers to the right then as well known the liw flows along the northern coast of sicily before reaching the sardinia channel a new liw path from the sicily strait towards the sardinia channel is shown by the med16 model and is due to intermediate eddy shedding at the exit of the sicily strait the topography of the sill in the sicily strait plays a major role in the circulation a combination of barotropic baroclinic double kelvin waves on both side of the sill provides a mechanism for splitting the algerian current

mapping of decadal middle adriatic oceanographic variability and its relation to the bios regime we analyzed long term time series of temperature salinity and dissolved oxygen do concentrations collected along the palagru a sill transect middle adriatic between 1952 and 2010 the data have been mostly collected on seasonal basis allowing for extraction of seasonal signal from the series by applying self organizing maps som method a kind of unsupervised neural network method the processes on a decadal time scale emerged as the most relevant for changes of oceanographic properties in the middle adriatic area sensitivity studies revealed that oceanographic patterns obtained by som were not sensitive to shortening of time series to removal of data from one station or to removal of do from the analysis simultaneous som based mapping of sea surface heights in the northern ionian sea with these heights serving as a proxy for the adriatic ionian bimodal oscillating system bios revealed asymmetry between anticyclonic and cyclonic bios patterns and correlated the decadal oscillations in the middle adriatic with the reversals in the bios circulation regimes these reversals are found to either rapidly change oceanographic properties in the middle adriatic e g during the eastern mediterranean transient or to change them with a time lag of 2 3 years the mapped connections may be used for a short time a few years forecasting of the adriatic oceanographic properties or for mapping future climate decadal oscillations as seen by ocean climate models

observation of a western alboran gyre migration event abstract in the western alboran sea light atlantic water and dense mediterranean waters meet this gives rise to intense density fronts and energetic mesoscale features such as two semi permanent anticyclonic vortices the western and eastern alboran gyres however the circulation in the alboran sea is strongly varying in time with episodes where neither the western alboran gyre nor the eastern alboran gyre are present in october 1996 four consecutive high resolution surveys of the western alboran gyre wag were carried out and lagrangian floats were released during the first survey the western alboran sea was occupied by the wag surrounded by the atlantic jet the following surveys showed the wag drifting eastward beginning a wag migration event as confirmed 15 days later by the lagrangian float tracks and the sst images to replace the old gyre one month later a new gyre was formed analysis of adcp velocities sst images and ts properties show a change between the first and the second survey in the atlantic inflow through the strait of gibraltar the relationships between this change in the atlantic inflow a drop in the atmospheric pressure at ceuta the tidal regime and the wag migration are discussed the existence of a high resolution sampling in space together with the possibility of addressing the temporal variability has allowed us to describe in detail and for the first time the time evolution of the western alboran sea during a wag migration event relating the migration to changes in the inflow through the strait of gibraltar