spreading of the western mediterranean deep water after winter 2005 time scales and deep cyclone transport this work is dedicated to the study of the propagation of the western mediterranean deep water wmdw formed in the gulf of lions during the exceptional winter 2005 a simulation of the 1998 2008 period has been carried out with an eddy resolving ocean general circulation model of the mediterranean sea driven by interannual high resolution air sea fluxes this study first presents a validation of the recently improved model configuration against satellite observations then we assess the ability of the model to reproduce the particularly intense deep convection event of winter 2005 in the gulf of lions a huge volume of very dense water is formed in the simulations at that time annual formation rate of about 3 sv the thermohaline characteristics of the new wmdw allow a monitoring of its deep propagation we identify several deep cyclones as mainly responsible of the fast spreading of the wmdw southwards in the western mediterranean by comparing eulerian and lagrangian approaches we estimate different transport times of the wmdw by these cyclonic eddies and compare them to those deduced from several observations finally we argue that these cyclones favour the propagation of the wmdw thermohaline characteristics towards the channel of sardinia and decrease the volume of wmdw which can reach the strait of gibraltar

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

low frequency currents from deep moorings in the southern bay of bengal abstracthigh resolution currents and hydrographic fields were measured at six deep water moorings in the southern bay of bengal bob by the naval research laboratory as part of an international effort focused on the dynamics of the indian ocean currents temperature and salinity were sampled over the upper 500 m for 20 months between december 2013 and august 2015 one of the major goals is to understand the space time scales of the currents and physical processes that contribute to the exchange of water between the bob and the arabian sea the observations captured southwest and northeast monsoon currents seasonally varying large eddies including a cyclonic eddy the sri lanka dome sld and an anticyclonic eddy southeast of the sld the observations further showed intraseasonal oscillations with periods of 30 70 days near inertial currents and tides monthly averaged velocities commonly exceeded 50 cm s 1 near the surface and extreme velocities exceeded 150 cm s 1 during the southwest monsoon ti

dynamical response of equatorial indian ocean to intraseasonal winds zonal flow nonlinear and linear 4 layer ocean models are used to explore the dynamics of intraseasonal 20 90 day periods zonal flow in the equatorial indian ocean the model simulations suggest that the observed 40 60 day zonal surface current is forced primarily by wind associated with the madden julian oscillation mjo which peaks at 40 60 days the strongest spectral peak of zonal flow however occurs at 90 day period in the model and a corresponding 90 day peak appears in the observed sea level data the 90 day current results from the preferential excitation of kelvin and rossby waves by the lower frequency component of intraseasonal wind and from the enhancement by rossby waves reflected from the eastern ocean boundary

sea level budget in the bay of bengal 2002 2014 from grace and altimetry sea level rise is perceived as a major threat to the densely populated coast of the bay of bengal addressing future rise requires understanding the present day sea level budget using a novel method and data from the gravity recovery and climate experiment grace satellite we partition altimetric sea level rise 6 1 mm a over 2002 2014 into mass and steric components we find that current mass trends in the bay of bengal are slightly above global mean while steric trends appear much larger 2 2 3 1 mm a if we disregard a residual required to close the budget and 4 3 4 6 mm a if as an upper bound we attribute this residual entirely to steric expansion our method differs from published approaches in that it explains altimetry and grace data in a least squares inversion while mass anomalies are parameterized through gravitationally self consistent fingerprints and steric expansion through eofs we validate our estimates by comparing to argo and modeling for the indian ocean and by comparing total water storage change twsc for the ganges and brahmaputra basins to the conventional grace approach we find good agreement for twsc and reasonable agreement for steric heights depending on the ocean region and argo product we ascribe differences to weaknesses of the argo data but we also find the inversion to be to some extent sensitive with respect to the eofs finally combining our estimates with cmip5 simulations we estimate that bay of bengal absolute sea level may rise for additional 37 cm under the rcp4 5 scenario and 40 cm under rcp8 5 until 2050 with respect to 2005

mesoscale eddies in the south china sea observed with altimeter data 1 a composite time series 1993 2000 of sea surface height anomaly from several satellites is used to identify eddies in the south china sea scs the eddy lifetime radius strength and straight line travel distance are estimated altogether 58 anticyclonic eddies and 28 cyclonic eddies are identified for this period they are grouped into four geographical zones according to known eddy generation mechanisms and their statistics are discussed accordingly our geographical classification is a useful first step in gaining an overview of their generation

origins and dynamics of the 90 day and 30 60 day variations in the equatorial indian ocean abstract sea level observations in the equatorial indian ocean show a dominant spectral peak at 90 days and secondary peaks at 30 60 days over an intraseasonal period 20 90 days a detailed investigation of the origins and dynamics of these variations is carried out using an ocean general circulation model namely the hybrid coordinate ocean model hycom two parallel experiments are performed in the tropical indian ocean basin for the period 1988 2001 one is forced by ncep 3 day mean forcing fields together with the climate prediction center cpc merged analysis of precipitation cmap pentad precipitation and the other is forced by monthly mean fields to help to understand the role played by the wind driven equatorial wave dynamics a linear continuously stratified ocean model is also used both the observed and modeled 90 day sea level anomaly fields and hycom surface current clearly show equatorial kelvin and first meridional mode rossby wave structures that are forced by the 90 day winds the

seasonal and inter annual variability of surface circulation in the bay of bengal from topex poseidon altimetry abstract sea surface height anomalies ssha from topex poseidon altimeter from january 1993 to december 1997 have been analyzed to document the seasonal intra seasonal and inter annual variability of surface circulation in the bay of bengal the western bay between 12 and 16 n exhibited large variability on all time scales a strong cyclonic gyre prevailed in this region from autumn through winter season and was replaced by an anticyclonic gyre in spring in 1993 and 1997 the intense winter cyclonic gyre was embedded as cyclonic eddy between two anticyclonic cells in the following spring during summer southwest monsoon period alternate cyclonic and anticyclonic circulation cells prevailed in the western bay on inter annual time scales the surface circulation of the bay was closely linked to the el nino southern oscillation enso and the bay circulation responded to all the phases of enso events the ssha and the sea surface temperature anomaly ssta off sumatra and in the bay were negatively correlated to the ssta in the western equatorial pacific both during el nino and la nina the coastal trapped kelvin waves and radiated rossby waves provide the oceanic link between the equatorial region and the bay for the observed variability in ssha

origins of wind driven intraseasonal sea level variations in the north indian ocean coastal waveguide 1 in this paper we show that a linear continuously stratified ocean model reproduces observed wind driven intraseasonal sea level variability in the coastal waveguide of the northern indian ocean nio sensitivity experiments with intraseasonal wind forcing selectively applied in the equatorial region bay of bengal and arabian sea show that a large part of the basin scale sea level variations are driven by zonal wind fluctuations along the equator within the nio coastal waveguide the contribution of remote equatorial forcing decreases from 80 90 in the andaman sea to 50 northeast of sri lanka and then increases to 60 70 along the west coast of india during the southwest monsoon intraseasonal wind variations become stronger over the nio resulting in a larger contribution of local wind forcing to sea level variability along the west up to 60 and east up to 40 coasts of india

mixing at camarinal sill in the strait of gibraltar during the gibraltar experiment in 1985 1986 observations of shear stratification microstructure and acoustic backscatter revealed a complex mixing regime at camarinal sill in the strait of gibraltar the mixing is forced by strong semidiurnal tidal currents and weaker but more steady baroclinic flows flows are characterized as outflow or inflow nearly equivalent to westward or eastward rising water at gibraltar coincides with outflow at all depths we observed two modes of outflow at the sill in may 1986 the transition layer separating atlantic and mediterranean water was between 0 75 mpa and 1 mpa when we sampled east of the sill near neap tide the transition turned down just before reaching the sill crest where the flow became critical increasing shear soon destabilized the transition producing billows which grew to 30 75 m on the west flank of the sill the overturning generated intense turbulence with peak dissipation rates e exceeding 10 2 w kg 1 this turbulence rapidly thickened the transition from z 30 50 m east of the sill to z 130 150 m within 1 2 km west of the sill from the rate of thickening we estimate the rate of formation of new transitional water during neap tide as 0 8 1 2 105 m3 s 1 this outflow mode did not release eastward propagating internal bores when outflow turned to inflow but the inflow did appear to arrest the deep outflow in may the largest average dissipation rate over and just west of the sill had the same magnitude as estimates of the net energy lost by adjustment of velocity and mass across the sill during outflow other averages are smaller than the energy loss presumably because the limited sampling severely underestimates the average dissipation rate during outflow strong shears were observed to rise to 100 times those in the background internal wave field however probably owing to spatial offsets between the ship s acoustic doppler current profiler and our tethered free fall profiler the only statistically significant correlations were found between overturning scales measured directly and those estimated from e in the same profile we observed the other outflow mode in october 1985 when we profiled over the sill near spring tide and the transition was east of the sill centered near 1 5 mpa after encountering the sill the transition rose sharply and remained within 10 20 m of the surface across the sill plunging steeply downward just past the west edge of the sill this was accompanied by intense turbulence and at least one rebound of the transition we did not observe release of eastward propagating bores when inflow turned to outflow but observations by armi and farmer 1988 in april 1986 found bores released at spring tide in regimes similar to the one we observed in october 1985

late cretaceous restructuring of terrestrial communities facilitated the end cretaceous mass extinction in north america the sudden environmental catastrophe in the wake of the end cretaceous asteroid impact had drastic effects that rippled through animal communities to explore how these effects may have been exacerbated by prior ecological changes we used a food web model to simulate the effects of primary productivity disruptions such as those predicted to result from an asteroid impact on ten campanian and seven maastrichtian terrestrial localities in north america our analysis documents that a shift in trophic structure between campanian and maastrichtian communities in north america led maastrichtian communities to experience more secondary extinction at lower levels of primary production shutdown and possess a lower collapse threshold than campanian communities of particular note is the fact that changes in dinosaur richness had a negative impact on the robustness of maastrichtian ecosystems against environmental perturbations therefore earlier ecological restructuring may have exacerbated the impact and severity of the end cretaceous extinction at least in north america

thick bottom nepheloid layers in the western mediterranean generated by deep dense shelf water cascading the analysis of a compilation of deep ctd casts conducted in the western mediterranean from 1998 to 2011 has documented the role that dense water formation and particularly deep dense shelf water cascading off the gulf of lions plays in transporting suspended particulate matter from the coastal regions down to the basin deep ctd casts reveal that after the 1999 and 2005 2006 deep cascading events the western mediterranean deep water wmdw was characterized by the presence of a thick bottom nepheloid layer bnl that corresponded in thickness with a thermohaline anomaly generated by the mixture of dense waters formed by deep convection in the open sea and by deep cascading this bnl can be hundreds of meters thick and in the central part of the basin usually exhibits suspended sediment concentrations of 1 mg l after winter 1999 the bnl spread from the gulf of lions and the catalan margin over the northwestern mediterranean basin reaching west of the balearic islands and the ligurian sea while after winters 2005 2006 the bnl covered the entire western mediterranean basin thickness and concentration of the bnl tend to diminish with time but this trend is highly dependent on the volume of dense water generated both by convection and cascading after winter 1999 the bnl signal vanished in one year but after winters 2005 2006 it lasted for longer and the turbidity signal can still be distinguished at present 2011 particle size distribution in the bnl reveals the presence of large aggregates up to 1 mm in size formed by a mixture of single particles with the same bimodal grain size distribution as the surface sediments found in the northwestern mediterranean slope and basin results presented in this paper highlight the fact that the wmdw can be periodically affected by the arrival of new dense waters loaded with suspended particles mainly introduced by resuspension processes during major cascading events being a key process that could ultimately affect deep sea biogeochemical cycles in the western mediterranean

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

the equatorial undercurrent and its origin in the region between mindanao and new guinea herein the spatial characteristics of the equatorial undercurrent euc in the region between mindanao and new guinea and the origins of the euc and the north equatorial countercurrent necc were investigated using a combination of high resolution argo hydrographic data and numerical modeling the mindanao current mc results in the formation of a strong euc depth eastward current that splits into two branches near the halmahera eddy west of 132 degrees e with one branch directly flowing eastward without experiencing the halmahera eddy rotation effect and the other branch flowing southwestward and then turning northeastward the euc and necc were difficult to distinguish between 132 degrees e and 136 degrees e since the former combined with the latter to form a continuous equator tilted current at similar to 137 degrees e the euc axis started turning toward the equator and an isolated euc core was observed at 143 degrees e and similar to 200 m depth the pacific euc was shown to originate at similar to 130 degrees e where it featured an isolated current core with a maximum velocity of 5 10cm s at similar to 1 degrees n and 200 to 400 m depth the euc and necc in the western tropical pacific were found to have the same water sources namely the mc and the new guinea coastal undercurrent with the shallow parts centered at similar to 100 m depth of mc and new guinea coastal undercurrent finally reaching the necc and their deeper parts centered at similar to 200 m depth finally reaching the euc

a new paradigm for the north pacific subthermocline low latitude western boundary current system abstractsubthermocline western boundary circulation along the low latitude north pacific ocean 2 25 n is investigated by using profiling float and historical ctd expendable ctd xctd data and by analyzing an eddy resolving global ogcm output in contrast to the existing paradigm depicting it as a reversed pattern of the wind driven circulation above the ventilated thermocline i e depth 26 8 the subthermocline western boundary circulation is found to comprise two components governed by distinct dynamical processes for meridional scales shorter than 400 km the boundary flows along the philippine coast exhibit convergent patterns near 7 10 13 and 18 n respectively these short scale boundary flows are driven by the subthermocline eastward zonal jets that exist coherently across the interior north pacific basin and are generated by the triad instability of wind forced annual baroclinic rossby waves for meridional scales longer than 400 km a time mean mindanao undercurrent muc is obs

intraseasonal to semiannual variability of sea surface height in the astern equatorial indian ocean and southern bay of bengal intraseasonal to semiannual variability of sea surface height ssh in the eastern equatorial indian ocean eeio and southern bay of bengal bob is investigated using altimetric data and solutions to 1 layer first baroclinic mode and linear continuously stratified lcs multi baroclinic mode models the amplitude and dominant period of ssh variability differ regionally large amplitude variability is found along the west coast of sumatra in a zonal band across the bob centered along 5 n east of sri lanka and in the northwestern bob respectively along the sumatran west coast ssh variability peaks at 30 60 days 90 days and 180 days along 5 n and east of sri lanka the 30 60 day variability is dominant sensitivity experiments using a nonlinear version of the 1 layer model forced by realistic winds reproduce the observed patterns of intraseasonal variability in the southern bob at 30 60 days the solutions show that eddies nonlinear rossby waves propagating from the east rather than local wind forcing account for most of the variance east of sri lanka furthermore they demonstrate that the variance is significantly enhanced by the nonlinear transfer of 90 120 day energy into the intraseasonal band of 30 60 days the lcs solutions show that the first two baroclinic modes explain most of the ssh variance at 90 180 days the second baroclinic mode dominates the ssh variance at 180 days a consequence of basin resonance and strong wind forcing

seasonal eddy kinetic energy modulations along the north equatorial countercurrent in the western pacific seasonal eddy kinetic energy eke variability and its associated eddy energy conversion processes in the western tropical pacific are investigated using satellite altimeter observations and a global eddy resolving ocean general circulation model ogcm both the altimeter observed sea surface height anomalies and the ogcm simulation show an area with enhanced eke east of the mindanao island centered around 133 e and 5 n this enhanced eke area corresponds to the location of the quasi stationary meander of the north equatorial countercurrent necc and is bordered to the south by the halmahera eddy the mesoscale eke in this area exhibits a clear seasonality strong in summer july august and weak in winter november january and much of this seasonality is confined to the upper 200 m layer an investigation into the upper ocean eddy energetics based on the ogcm simulation reveals that the areal barotropic eddy energy conversion rate has an annual cycle similar to the eke variations while the areal baroclinic eddy energy conversion is found to be much smaller that the barotropic conversion rate and exhibits no clear seasonal changes this indicates that the eke variations are largely controlled by barotropic conversion of the seasonally varying regional circulation by examining the seasonal background circulation changes we find that the amplification of the barotropic eddy energy conversion rate in july august is related to the seasonal evolution of the mindanao current and the new guinea coastal current that amplifies the curvature and amplitude of the quasi stationary meander of the necc and results in an elevated eke level through increased regional barotropic conversion

impact of remote equatorial winds and local mesoscale eddies on the existence of river in the sea along the east coast of india inferred from satellite smap

deep water formation in the western mediterranean wintertime deep convection was studied in the gulf of lions northwestern mediterranean using the chlorofiuoromethane cfm distributions components f11 and f12 from december 1991 and february march 1992 convection occurred on small spatial and temporal scales and it was not complete only convection to 1900 m depth was observed the vertical mixing of the water column above the convection depth turned out to be of major influence regarding the characteristic of newly formed deep water and regarding the boundary conditions for cfms in modeling deep water formation air sea gas exchange and entrainment were found to be negligible these findings are important in estimating deep water formation rates for all water masses renewed by convection e g greenland sea deep water labrador sea water and in evaluating the spreading of deep water masses along the western boundary current a box model is presented which uses cfm and tritium distributions to estimate formation of western mediterranean deep water below 1000 m the model starts with zero tracer concentrations in 1945 the integration step is 1 year and the deep water formation rate is assumed to be constant from 1945 to 1992 the best fit between cfm model concentrations and measurements were obtained at a mean deep water renewal time of 5 7 years equivalent to a conversion of 0 46 sv modified atlantic water 0 to 150 m depth and 0 76 sv levantine intermediate water 150 to 400 m depth into deep water however the tritium measurements are only partly matched by the model by assuming that convection stopped in the years 1964 1968

observed features of the halmahera and mindanao eddies 1 the structure and variability of the halmahera and mindanao eddies he and me which are thought to be quasi stationary eddies are described based on onboard and time series observations in the gateway region of the indonesian throughflow itf the he was found to have a clear anticyclonic eddy structure during all cruises it tilted northward and or westward with increasing depth the he mixes waters from the northern and southern hemispheres and transfers this mixed water to the eastern route of the itf the he shifted northwestward in the boreal summer and the cold phase of enso el nino and southern oscillation and southeastward in the boreal winter and the warm phase of enso in contrast the me with its cyclonic eddy structure was observed only once and seems not to be a quasi stationary eddy it appears in the mean field and is confined above the thermocline the stationary northward undercurrent the mindanao undercurrent was also not found at 7 n east of mindanao but the northern tip of the he was found at this latitude

dynamical ocean forcing of the madden julian oscillation at lead times of up to five months abstractthe authors show that a simple three dimensional ocean model linearized about a resting basic state can accurately simulate the dynamical ocean response to wind forcing by the madden julian oscillation mjo this includes the propagation of equatorial waves in the indian ocean from the generation of oceanic equatorial kelvin waves to the arrival of downwelling oceanic equatorial rossby waves in the western indian ocean where they have been shown to trigger mjo convective activity simulations with idealized wind forcing suggest that the latitudinal width of this forcing plays a crucial role in determining the potential for such feedbacks forcing the model with composite mjo winds accurately captures the global ocean response demonstrating that the observed ocean dynamical response to the mjo can be interpreted as a linear response to surface wind forcing the model is then applied to study primary madden julian events which are not immediately preceded by any mjo activity or by any apparen

subthermocline and intermediate zonal currents in the tropical pacific ocean paths and vertical structure abstractthe mean subthermocline and intermediate zonal circulation in the tropical pacific is investigated using a compilation of shipboard adcp measurements and absolute geostrophic velocities constructed from a high resolution 0 2000 m argo climatology referenced to a 1000 m velocity field derived from argo float drifts this reference field is dominated by basinwide alternating zonal jets with a meridional wavelength of about 3 in regions where the sampling of sadcp data is sufficient the consistency between the two independent datasets is striking using the argo drift reference is crucial to capture the current structures two apparently distinct systems of alternating westward and eastward zonal jets are seen in both datasets equatorward of 10 a series of low latitude subthermocline currents llscs below the thermocline extending from about 200 to 800 m including the eastward tsuchiya jets and a series of low latitude intermediate currents llics extending from about 700 to at least 2000

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

monitoring open ocean deep convection from space deep convection dc is a key process of the oceanic circulation costly to monitor in situ and under the influence of climate change our study is a first step toward monitoring dc from space we investigate the feasibility of observing its variability using improved satellite altimetry an oceanic simulation of the mediterranean circulation was performed for the 1999 2007 period dc interannual variability is realistically modelled and the sea surface elevation sse is in agreement with altimetry data numerical results show a strong correlation between the annual dc characteristics and the winter sse from that we propose a method to monitor dc interannual variability and long term evolution using altimetry data our method applied to the longest available altimetry series represents correctly the interannual variability of dc in the northwestern mediterranean between 1994 and 2007 citation herrmann m j bouffard and k beranger 2009 monitoring open ocean deep convection from space geophys res lett 36 l03606 doi 10 1029 2008gl036422

the fraser gyre a cyclonic eddy off the coast of eastern australia this paper examines the on shelf circulation of the eastern australian continental shelf for a region off southeast queensland we identify a characteristic seasonally reoccurring wind driven cyclonic flow it influences the cross shelf exchange with the east australian current eac which is the western boundary current of the south pacific ocean we refer to this cyclonic circulation as the fraser gyre it is located south of fraser island between about 25 s and 27 s the region is adjacent to the intensification zone of the eac where the current accelerates and establishes a swift albeit seasonally variable southward boundary flow through the analysis of several data sets including remotely sensed sea surface temperature and sea surface height anomaly satellite tracked surface drifters ocean and atmospheric reanalysis data as well as geostrophic currents from altimetry we find that the on shelf fraser gyre develops during the southern hemisphere autumn and winter months the gyre is associated with a longshore near coast northward flow maximum northward on shelf depth averaged velocities are estimated with about 0 15 0 26 ms 1 the flow turns eastward just to the south of fraser island and joins the persistent southward eac flow along the shelf break the annual mean net cross shelf outward and inward flow associated with the gyre is about 1 17 0 23 sv in the north and 0 23 0 13 sv 1 sv 106 m3s 1 in the south mean seasonal water renewal time scales of the continental shelf are longest during austral winter with an average of about 3 3 days due to the fraser gyre retaining water over the shelf however monthly estimates range from 2 to 8 days with the longer timescale during the austral autumn and winter the southerly wind during austral autumn and winter is identified as controlling the on shelf circulation and is the principal driver of the seasonally appearing fraser gyre the conceptual model of the fraser gyre is consistent with general physical principals of the coastal shelf circulation a southerly wind is associated with surface layer flow toward the coast a near coast positive ssha with a current in the direction of the wind down welling and export of shelf water the fraser gyre influenced cross shelf exchanges are possibly facilitating the offshore transport of fish larvae sediments nutrients river discharges and other properties across the shelf break and into the southward flowing eac during the austral autumn and winter

observation of an abrupt disruption of the long term warming trend at the balearic sea western mediterranean sea in summer 2005 1 the properties of the western mediterranean deep water in a wide area located at the western boundary of the mediterranean sea including the balearic sea have revealed intense changes when observed in summer 2005 between february and june 2005 a temperature drop of 0 14 c reverted dramatically the progressive warming trend of 0 011 c yr 1 that had been observed since 1996 in the waters below 600 dbar north of the balearic channels a similar temperature drop has been observed east of the minorca island below the levantine intermediate water and down to 1500 dbar in the deepest levels a complex thermohaline structure which implies different waters masses as sources was tracked more than 400 km along the western boundary of the mediterranean sea from barcelona to the algerian basin it is suggested that the changes may be linked to the severe 2004 2005 winter occurred at the northwestern mediterranean sea

basin resonances in the equatorial indian ocean abstractprevious studies have investigated how second baroclinic mode n 2 kelvin and rossby waves in the equatorial indian ocean io interact to form basin resonances at the semiannual 180 day and 90 day periods this paper examines unresolved issues about these resonances including the reason the 90 day resonance is concentrated in the eastern ocean the time scale for their establishment and the impact of complex basin geometry a hierarchy of ocean models is used an idealized one dimensional 1d model a linear continuously stratified ocean model lcsm and an ocean general circulation model ogcm forced by quick scatterometer quikscat wind during 2000 08 results indicate that the eastern basin concentration of the 90 day resonance happens because the westward propagating rossby wave is slower and thus is damped more than the eastward propagating kelvin wave results also indicate that superposition with other baroclinic modes further enhances the eastern maximum and weakens sea level

the diversity of sauropod dinosaurs and their first taxonomic succession from the latest cretaceous of southwestern europe clues to demise and extinction article i nfo southwestern europe is a key setting to evaluate the diversity of non avian dinosaurs before the end of the cretaceous below the k pg boundary the ancient ibero armorican island encompassing the current regions of north east iberia and south france provides a substantial record of sauropod fossils the study of multiple sauropod femora from localities where upper campanian to uppermost maastrichtian successions are both exposed together with the integration of the information gathered from previously known localities has allowed the biodiversity of sauropods to be reassessed within a precise and clear chronostratigraphic framework from the studied sample several titanosaur forms have been distin guished including a gracile and small sized titanosaur lirainosaurus astibiae a robust medium sized titanosaur ampelosaurus atacis a gracile medium sized titanosaur atsinganosaurus velauciensis and five other indeterminate but distinct titanosaurs which span the late campanian through the entire maastrichtian the youngest of these occurs in the uppermost part of palaeomagnetic chron c30n in the latest maastrichtian 0 4 1m a before the k pg boundary representing the youngest sauropod yet doc umented in eurasia the pattern of diversity on the ibero armorican island rules out a decline in sauropod diversity at the very end of the cretaceous as with other regions during the late cretaceous the abundance and quality of the sauropod fossil record is probably influenced by multiple biases sampling ecological and environmental

sources of eddy kinetic energy in the labrador sea experiments with a suite of north atlantic general circulation models are used to examine the sources of eddy kinetic energy eke in the labrador sea a high resolution model version 112 quantitatively reproduces the observed signature a particular feature of the eke in the labrador sea is its pronounced seasonal cycle with a maximum intensity in early winter as already found in earlier studies based on altimeter data in contrast to a previously advanced hypothesis the seasonally varying eddy field is not related to a forcing by high frequency wind variations but can be explained by a seasonally modulated instability of the west greenland current wgc the main source of eke in the labrador sea is an energy transfer due to reynolds interaction work barotropic instability in a confined region near cape desolation where the wgc adjusts to a change in the topographic slope geostrophic contours tend to converge upstream of cape desolation such that the topographically guided wgc narrows as well and becomes barotropically unstable the eddies spawned from the wgc instability area dominating the eke in the interior labrador sea are predominantly anticyclonic with warm and saline cores in the upper kilometer of the water column while the few cyclones originating as well from the instability area show a more depth independent structure companion experiments with a model exhibit the strength of the wgc influenced by either changes in the wind stress or heat flux forcing as a leading factor determining seasonal to interannual changes of eke in the labrador sea

upper and intermediate circulation in the western equatorial pacific ocean in october 1999 and april 2000 1 the upper and intermediate circulation 0 1200 m in the western equatorial pacific ocean is examined thanks to lowered acoustic doppler current profiler ladcp measurements carried out during two cruises in october 1999 and april 2000 several new features of the equatorial circulation are discussed it is shown that the secondary south subsurface countercurrent ssscc laying at 6 s 400 m depth had a deep extension at 165 e with a maximum core velocity around 5 s 1000 m furthermore the equatorial intermediate current eic and the lower eic leic displayed a strong temporal variability between 165 e and 180 as these two westward currents were replaced by eastward flow along the equator on the second cruise finally during the april 2000 cruise the zonal velocity profile carried out at the equator east of the gilbert island around 175 e broke into small vertical scales possibly reflecting topographic effect and or destabilization mechanism that leads to the formation of long zonal jet like structures

eddy dynamics in a primitive equation model sensitivity to horizontal resolution and friction a primitive equation model of an idealized ocean basin driven by simple study wind and buoyancy forcing at the surface is used to study the dynamics of mesoscale eddies model statistics of a six year integration using a fine grid 1 6 0 2 with reduced coefficients of horizontal friction are compared to those using a coarser grid 1 3 0 4 but otherwise identical configuration eddy generation in both model cases is primarily due to the release of mean potential energy by baroclinic instability horizontal reynolds stresses become significant near the midlatitude jet of the fine grid case with a tendency for preferred energy transfers from the eddies to the mean flow using the finer resolution eddy kinetic energy nearly doubles at the surface of the subtropical gyre and increases by factors of 3 4 over the jet region and in higher latitudes the spatial characteristics of the mesoscale fluctuations are examined by calculating zonal wavenumber spectra and velocity autocorrelation functions with the higher resolution the dominant eddy scale remains approximately the same in the subtropical gyre but decreases by a factor of 2 in the subpolar areas the wavenumber spectra indicate a strong influence of the model friction in the coarse grid case especially in higher latitudes using the coarse grid there is almost no separation between the energetic eddy scale and the scale where friction begins to dominate leading to steep spectra beyond the cutoff wavenumber using the finer resolution an inertial subrange with a k 3 power law begins to emerge in all model regions outside the equatorial belt despite the large increase of eddy intensity in the fine grid model effects on the mean northward transport of heat are negligible strong eddy fluxes of heat across the midlatitude jet are almost exactly compensated by changes of the heat transport due to the mean flow

interactions between mesoscale eddies and synoptic oscillations in the bay of bengal during the strong monsoon of 2019

east pacific ocean eddies and their relationship to subseasonal variability in central american wind jets subseasonal variability in sea surface height ssh over the east pacific warm pool off central america is investigated using satellite observations and an eddy resolving ocean general circulation model ssh variability is organized into two southwest tilted bands on the northwest flank of the tehuantepec and papagayo wind jets and collocated with the thermocline troughs eddy like features of wavelength similar to 600 km propagate southwestward along the high variance bands at a speed of 9 13 cm s wind fluctuations are important for eddy formation in the gulf of tehuantepec with a recurring interval of 40 90 days when forced by satellite wind observations the model reproduces the two high variance bands and the phase propagation of the tehuantepec eddies our observational analysis and model simulation suggest the following evolution of the tehuantepec eddies on the subseasonal timescale in response to the gap wind intensification a coastal anticyclonic eddy forms on the northwest flank of the wind jet and strengthens as it propagates offshore in the following two to three weeks an energetics analysis based on the model simulation indicates that besides wind work barotropic and baroclinic instabilities of the mean flow are important for the eddy growth both observational and model results suggest a re intensification of the anticyclonic eddy in response to the subsequent wind jet event off papagayo ocean eddy formation is not well correlated with local wind jet variability in both the gulfs of tehuantepec and papagayo subseasonal ssh variability is preferentially excited on the northwest flank of the wind jet factors for this asymmetry about the wind jet axis as well as the origins of wind jet variability are discussed

response of a high resolution ocean circulation model to winds from different sources in simulating summer monsoon freshening in the north bay of bengal a case study abstract a very high resolution model for the bay of bengal is configured to simulate submesoscale flow features which are otherwise absent in coarse resolution models in this manuscript we present the response of this model to simulate summer monsoon freshening in the northern bay of bengal when forced with two different winds one based on weather forecast model output from national centre for medium range weather forecast ncmrwf and the other based on satellite derived scatsat ocean surface winds for 2017 as a case study our results reveal that the spatio temporal evolution of lateral freshwater dispersal in the northern bay of bengal is sensitive to wind vorticity and eddy formation evolution a reasonably realistic decrease of 2 3 psu in the sea surface salinity at the mooring location of 18on 90oe towards the end of september 2017 is simulated in the model when forced with the scatsat winds whereas significantly weaker freshening occurs at the mooring location when the model is forced with the ncmrwf winds a filament of strong positive vorticity connecting two cyclonic eddies in the north central bay in the ncmrwf wind forced simulations prevents the direct southward advection of freshwater resulting in higher salinity at the mooring location a similar mechanism that would prevent southward advection of fresh water is absent in the scatsat forced model run westward moving rossby waves in the scatsat forced model run are found to play an important role in the evolution of freshening events at various locations in the northern bay of bengal lagrangian coherent structures lcs derived from the model currents suggest that the background conditions were favourable to advect freshwater from ganges brahmaputra towards the mooring location in the northern bay of bengal in the scatsat forced simulations

subthermocline eddies in the western equatorial pacific as shown by an eddy resolving ogcm abstractsporadic in situ observations have shown evidence that subthermocline eddies exist off the mindanao coast these subthermocline eddies are believed to play an important role in the heat freshwater and other ocean property transports of the region but their characteristics and in particular their pathway and source of energy are poorly explored because of the lack of long term observations analysis of results from an eddy resolving general ocean circulation model has revealed that most subthermocline eddies off the mindanao coast originate from the equatorial south pacific ocean to the west of the ninigo group these eddies propagate northward along the new guinea coast cross the equator in the far western pacific and reach the mindanao coast at a typical propagation speed of 0 12 m s 1 the dominant time scales of these eddies range between 50 and 60 days

interaction of dense shelf water cascading and open sea convection in the northwestern mediterranean during winter 2012 the winter of 2012 experienced peculiar atmospheric conditions that triggered a massive formation of dense water on the continental shelf and in the deep basin of the gulf of lions multiplatforms observations enabled a synoptic view of dense water formation and spreading at basin scale five months after its formation the dense water of coastal origin created a distinct bottom layer up to a few hundreds of meters thick over the central part of the nw mediterranean basin which was overlaid by a layer of newly formed deep water produced by open sea convection these new observations highlight the role of intense episodes of both dense shelf water cascading and open sea convection to the progressive modification of the nw mediterranean deep waters

results from a velocity transect along the equator from 125 to 159 w abstract during march april 1980 a velocity and ctd transect was made in the pacific along the equator from 110 to 180 w the horizontal baroclinic pressure gradient was observed to be primary confined between 160 and 130 w direct velocity profiles between 125 and 159 w showed the equatorial undercurrent to be a continuous feature maximum eastward transport per unit width in the undercurrent was 2 5 108 cm2 s 1 at 150 w and decreased both westward and eastward to about 1 5 108 cm2 s 1 at 159 w and at 125 w despite these variations the maximum speeds along the transect remained 150 cm s 1 beneath the undercurrent the velocities decreased and were of the order of 25 cm s 1 they exhibited small scale variation in the vertical as has recently been observed at other equatorial locations above 1600 m the vertical wavelength of these variations in the zonal component was 300 m small scale features in these zonal velocities were identifiable over 10 of longitude 1000 km the small vertical an

critical frequencies at ocean boundaries past theoretical work has shown that for low frequency flow at a given ocean boundary location a critical frequency c exists such that for c unforced motion is trapped to the coast while for c energy leaves the coast alternatively for motion of a given frequency on the boundary there exists a critical latitude such that the motion is trapped to the coast poleward of that latitude but equatorward it is not this theory is discussed physically for both meridional and nonmeridional boundaries the simple formula for critical frequency along a nonmeridional boundary is used to document critical periods for the eastern and western atlantic pacific and indian ocean boundaries the theory occasionally breaks down when boundary curvature is too large

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

direct measurements of upper ocean currents and water properties across the tropical pacific during the 1990s abstract meridional sections of upper ocean zonal currents potential temperature and salinity are estimated at ten longitudes from 143 e to 95 w using conductivity temperature depth and acoustic doppler current profiler data from 172 synoptic sections taken in the tropical pacific between 138 e and 86 w mostly in the 1990s data reduction is carried out in a potential isopycnal and mixed layer framework to preserve a sharp pycnocline a mixed layer water property extrema and velocity extrema mean zonal currents potential temperatures and salinities are produced at each longitude the seasonal cycles of these fields are also estimated as well as a simple el nino southern oscillation enso cycle zonal sections along the equator are also presented properties of the near equatorial zonal currents including transports temperatures and salinities are estimated separately from the synoptic sections the seasonal cycles of these quantities and their correlations with the southern oscillation index are investigated the work is distinguished from most existing literature in that direct estimates of zonal velocity are combined with contemporaneous temperature and salinity data allowing trans pacific estimates of near equatorial current transports and properties including those of the northern branch of the south equatorial current the new guinea coastal undercurrent and the equatorial undercurrent

intraseasonal response of the northern indian ocean coastal waveguide to the madden julian oscillation a new observational record of upper ocean currents at 15 n on the western coast of india is dominated by intraseasonal 55 110 day variations of alongshore currents whereas sea level at the same location has a clear seasonal signal these observations can be interpreted within the framework of linear wave theory at 15 n the minimum period for planetary waves is 90 day meaning that intraseasonal energy is largely trapped at the coast in the form of poleward propagating kelvin waves while lower frequency signals associated with the annual cycle can radiate offshore as planetary waves this dynamical difference results in a steeper offshore slope of sea level at intraseasonal timescale and thus stronger geostrophic alongshore currents a consequence is that the alongshore currents are in phase with intraseasonally filtered sea level near the coast and a gridded satellite product is shown to reproduce the current variations reasonably well the intraseasonal current variations along the west coast of india are part of basin scale sea level fluctuations of the northern indian ocean equatorial and coastal waveguides the wind forcing associated with this basin scale circulation closely matches surface wind signals associated with the madden julian oscillation copyright 2009 by the american geophysical union

enso driven interhemispheric pacific mass transports previous studies have shown that enso s anomalous equatorial winds including the observed southward shift of zonal winds that occurs around the event peak can be reconstructed with the first two empirical orthogonal functions eofs of equatorial region wind stresses using a high resolution ocean general circulation model we investigate the effect of these two eofs on changes in warm water volume wwv interhemispheric mass transports and indonesian throughflow itf wind stress anomalies associated with the first eof produce changes in wwv that are dynamically consistent with the conceptual recharge oscillator paradigm the itf is found to heavily damp these wwv changes reducing their variance by half wind stress anomalies associated with the second eof which depicts the southward wind shift are responsible for wwv changes that are of comparable magnitude to those driven by the first mode the southward wind shift is also responsible for the majority of the observed interhemispheric upper ocean mass exchanges these winds transfer mass between the northern and the southern hemisphere during el nino events whilst water is transferred in the opposite direction during la nina events the magnitude of this exchange is roughly half of that seen during el nino events thus the discharging of wwv during el nino events is meridionally asymmetric while the wwv recharging during a la nina event is largely symmetric the inclusion of the southward wind shift is also shown to allow enso to exchange mass with much higher latitudes than that allowed by the first eof alone

an extensive western mediterranean deep water renewal between 2004 and 2006 1 the deep waters of the western mediterranean are known to have an almost constant trend towards higher salinity and temperature values since the 1950s recent observations have shown an acceleration of this tendency which has been attributed by some authors to the effect of the propagation of the signal of the eastern mediterranean transient from east to west from 2004 to 2006 five basin scale oceanographic cruises evidenced a relevant change in the deep structure of the western mediterranean in less than two years almost the whole deep basin has been filled with highly saline and warm new deep water which substantially renewed the resident deep water the paper shows evidence of the rapid basin wide extension of the event giving insights into the origin and the propagation of the new deep water towards the basin interior and showing the evolution of the deep characteristics

arabian sea and bay of bengal exchange of salt and tracers in an ocean model exchanges of mass and salt between the mixed layers in the arabian sea and the bay of bengal are examined in a model of the indian ocean using passive tracers as a tool to map the pathways inflow of high salinity water from the arabian sea into the bay of bengal is significant and occurs after the mature phase of the southwest monsoon freshwater transport out of the bay of bengal is southward throughout the year along the eastern boundary of the indian ocean low salinity water transport into the arabian sea occurs in the somali current during the southwest monsoon closing a clockwise path of water mass transport only a small fraction of low salinity water is advected into the eastern arabian sea from the bay of bengal

improving the quality of satellite altimetry data over continental shelves 1 satellite altimetry has proven to be a useful tool to study oceanic processes in the deep ocean over continental shelves however the aliasing of unresolved high frequency signals of tidal and wind induced origin is the source of long wavelength errors that corrupt altimetry measurements and limit their use in shallow waters in 2005 ssalto duacs performed a complete reanalysis of altimeter data to accommodate the latest tidal model got2000 and a correction for the aliased high frequency signals using a hydrodynamic model mog2d g this paper examines the quality and the performance of the newly released altimetry data over the northwest european shelf this region is known for complex tides and for frequent storm surges the newly corrected maps of sea level anomalies were compared with a previous altimetry product residual tidal aliasing was analyzed and the impact of mog2d g and got2000 models was assessed altimeter records were compared with tide gauge measurements this research showed a significant reduction in the contamination of data by high frequency aliasing achieved through the use of the aforementioned models however aliased shallow water tidal constituents pose a serious problem and it is obvious that future tidal corrections should feature local tides nonaliased physical sea level variability was also studied focusing on interannual seasonal and intra annual periods from 20 days to 1 year modes the magnitudes and the contributions of each mode to the total variance were estimated it was demonstrated that the newly corrected data can successfully be used to study the variability of sea level over continental shelves

on the circulation in the bay of bengal during northern spring inter monsoon march april 1987 abstract temperature and salinity data collected from the bay of bengal 22 march 28 april 1987 northern spring inter monsoon identified the seasonal anticyclonic gyre acg at 16 n 86 e characterized by warm 24 c and low salinity 34 85 psu at their cores the velocity of wbbc increased from 0 40 ms 1 at 12 n to 0 70 ms 1 at 17 5 n where it left the coast and turned eastward the mean northward transport of the wbbc in the upper 200 m was 12 sv 1 sv 10 6 m 3 s 1 these circulation features the acg wbbc and cyclonic eddies are well depicted in the maps of sea surface height ssh topography derived from the residual sshs of geosat altimeter for the period 12 february 28 april 1987 the results show that the wbbc flowed against the northeasterly winds during february and that the current sets up almost three months ahead of the wind reversal the acg and in turn the wbbc intensified with the wind reversal in april when the wind stress curl attained a negative maximum the ssh maps further indicate that formation of the acg started in february and reached its maximum intensity during april with the coalescence of two anticyclonic cells

how much energy propagates vertically in the equatorial oceans abstract vertically propagating linear wave calculations using realistic equatorial buoyancy profiles are presented which show the percentage of the downward surface energy flux that reaches the deep equatorial oceans the percentages vary widely depending upon the buoyancy profile and the equivalent depth but can be as low as 10 on average for equivalent depths between 1 cm and 1 m if the thermocline is sharp this means that models with constant or weak thermocline buoyancy profiles which allow all or most downward surface energy flux to reach the deep ocean are very unrealistic in this respect another conclusion is that the observed very low frequency small vertical scale deep jets cannot be explained by linear wave theory as caused by surface forcing it is also shown that a wkb analysis of observations can be misleading even if applied to a single vertically propagating wave in a region that excludes the main thermocline implications are that comparing estimates of the equivalent depth from th

a dynamical ocean feedback mechanism for the madden julian oscillation composite analysis is applied to study the dynamical ocean response to madden julian mj events measured by anomalies in sea surface height from the merged topex poseidon european remote sensing satellite altimetry dataset in each of the tropical ocean basins significant equatorial waves are forced which are shown to modulate the sea surface temperature sst by 0 2 0 3 degc in the absence of strong surface heat fluxes in the indian ocean there is a clear dynamical response which may play a significant role in generating later mj events surface westerly winds associated with the active phase of the madden julian oscillation mjo force an eastward propagating oceanic downwelling equatorial kelvin wave which on reaching the eastern boundary at sumatra forces reflected downwelling equatorial rossby waves and coastal kelvin waves the coastal kelvin waves propagate southwards towards northern australia and northwards into the bay of bengal and will be important for local physical chemical and biological processes the equatorial rossby waves propagate westward across the indian ocean arriving in the western indian ocean approximately 80 100 days after the initial kelvin wave was generated the arrival of these waves generates positive sst anomalies which leads to convection and may trigger the next but one mj event or amplify the low frequency tail of the mjo this constitutes a coupled feedback mechanism from the ocean dynamics onto the mjo somewhat similar to the delayed oscillator mechanism for the el nino southern oscillation

recent changes 2004 2016 of temperature and salinity in the mediterranean outflow temperature and salinity series near the seafloor at espartel sill strait of gibraltar have been used to analyze the thermohaline variability of the mediterranean outflow the series shows temperature drops by the end of most winters early springs which are the remote response to western mediterranean deep water wmdw formation events in the gulf of lion that uplift old wmdw nearby the strait this process distorts the seasonal cycle of colder warmer water flowing out in summer winter likely linked to the seasonality of the western alboran gyre the series show positive trends in agreement with previous values which are largely increased after 2013 it is tentatively interpreted as the western mediterranean transition wmt signature that started with the very cold winters of 2005 and 2006 it was only after the large new wmdw production of 2012 and 2013 harsh winters that wmt waters were made available to flow out of the mediterranean sea

intraseasonal vertical velocity variation caused by the equatorial wave in the central equatorial indian ocean intraseasonal vertical velocity variation in the central equatorial indian ocean was investigated using observations from the field experiment mirai indian ocean cruise for the study of the mjo convection onset mismo and from the research moored array for african asian australian monsoon analysis and prediction rama in october november 2006 using an array of four subsurface moored acoustic doppler current profilers adcps we estimated vertical velocity by applying the continuity equation results indicated alternating downwelling and upwelling episodes at around thermocline depth with maximum amplitudes larger than 8 0 10 5 m s 1 or about 7 m per day the vertical velocity variation was mainly produced by the divergence convergence of meridional currents with a quasi biweekly period of 11 16 days the temporal changes in temperature around thermocline depth were consistent with variations in vertical velocity whereas upwelling had less impact on the surface layer temperature intraseasonal variations in the ocean may be a part of biweekly fluctuations by remotely forced mixed rossby gravity waves which have a meridional current maximum at the equator accompanied by divergence convergence in the surface layer a few degrees from the equator

intraseasonal variability of sea surface height in the bay of bengal intraseasonal variability isv of sea surface height ssh over the bay of bengal bob is studied using altimetry data and an eddy resolving ocean model in both the model hindcast and satellite observations large ssh isv is found along the eastern and northern coasts of the bob in the western bob and in a zonal band across the bay centered near 5 degrees n the isv displays a clear seasonality in the western bob it reaches its annual maximum in spring whereas it does so in summer and autumn southeast of sri lanka driven by equatorial intraseasonal winds equatorial kelvin waves propagate eastward reach the western coast of sumatra and reflect there to propagate around the perimeter of the bob as coastally trapped waves two distinct bands of high eddy activity are detected in the western and central bob respectively in both bands isolated eddies propagate southwestward eddy formation in the eddy train in the central bay is linked to the coastal wave as it bends around the corner of the irrawaddy delta off myanmar eddy activity contributes to the high isv in the central bay to some extent an energetics analysis indicates that high total eddy energy in the western bob is due to barotropic baroclinic instability of the mean current citation cheng x s p xie j p mccreary y qi and y du 2013 intraseasonal variability of sea surface height in the bay of bengal j geophys res oceans 118 816 830 doi 10 1002 jgrc 20075

role of mesoscale eddies on the variability of biogenic flux in the northern and central bay of bengal 1 mesoscale cyclonic eddies cold core are though known to enhance the phytoplankton biomass in the bay of bengal their contribution to the carbon export to the deep ocean are yet to be quantified using biogenic flux data obtained from the sediment traps located at 17 27 n 89 13 e northern bay of bengal trap nbbt and 13 07 n 84 24 e central bay of bengal trap cbbt we explored the variability of biogenic flux in response to cyclonic eddies temporal variation of the biogenic flux at nbbt 1994 1998 and cbbt 1993 1996 showed four distinct peaks with no well defined seasonal pattern the inverse relationship between the high flux events and sea surface height anomaly ssha along with the dominant periodicity of 10 15 weeks from the chi square analysis of ssha confirmed the role of eddies in the observed higher biogenic fluxes during the eddy events enhanced opal flux suggested eddy driven new production while lower carbonate to opal ratio along with high organic carbon indicated large export via diatoms finally we show that 42 of the total organic carbon collected at mid depth 1000 m in the bay of bengal is contributed by eddy driven processes via diatom bloom making it a regional sink for co2

annual reversal of the equatorial intermediate current in the pacific observations and model diagnostics abstract a large reversal of zonal transport below the thermocline was observed over a period of 6 months in the western pacific ocean between 2 s and the equator from 26 2 sv 1 sv 106 m3 s 1 eastward in october 1999 to 28 6 sv westward in april 2000 to document this reversal and assess its origin an unprecedented collection of adcp observations of zonal currents 2004 06 together with a realistic ogcm simulation of the tropical pacific was analyzed the results of this study indicate that this reversal is the signature of intense annual variability in the subsurface zonal circulation at the equator at the level of the equatorial intermediate current eic and the lower equatorial intermediate current l eic in this study the eic and the l eic are both shown to reverse seasonally to eastward currents in boreal spring and winter for the l eic over a large depth range extending from 300 m to at least 1200 m the peak to peak amplitude of the annual cycle of subthermocline zonal currents at

dynamics of andaman sea circulation and its role in connecting the equatorial indian ocean to the bay of bengal circulation in the bay of bengal bob is driven not only by local winds but are also strongly forced by the reflection of equatorial kelvin waves ekws from the eastern boundary of the indian ocean the equatorial influence attains its peak during the monsoon transition period when strong eastward currents force the strong ekws along the equator the andaman sea lying between the andaman and nicobar island chains to its west and indonesia thailand and myanmar to the south east and north is connected to the equatorial ocean and the bob by three primary passages the southern 6 n middle 10 n and northern 15 n channels we use ocean circulation models together with satellite altimeter data to study the pathways by which equatorial signals pass through the andaman sea to the bob and associated dynamical interactions in the process the mean coastal circulation within the andaman sea and around the islands is primarily driven by equatorial forcing with the local winds forcing a weak sea level signal on the other hand the current forced by local winds is comparable to that forced remotely from the equator our results suggest that the andaman and nicobar islands not only influence the circulation within the andaman sea but also significantly alter the circulation in the interior bay and along the east coast of india implying that they need to be represented accurately in numerical models of the indian ocean

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

shape of mesozoic dinosaur richness the richness of mesozoic dinosauria is examined through the use of a new global database mesozoic dinosaurs show a steadily increasing rate of diversification in part attributable to the development of new innovations driving an increasing variety of behavioral strategies the data do not suggest that dinosaurs were decreasing in richness leading to extinction during the last 10 m y of the cretaceous refinement of the dating of dinosaur fossils rather than the collection of more dinosaurs is the best way to resolve globally the rate of the cretaceous tertiary dinosaur extinction

characteristics of the near surface currents in the indian ocean as deduced from satellite tracked surface drifters part i pseudo eulerian statistics using the 1985 2013 record of near surface currents from satellite tracked drifters the pseudo eulerian statistics of the near surface circulation in the indian ocean io are analyzed it is found that the distributions of the current velocities and mean kinetic energy mke in the io are extremely inhomogeneous in space and nonstationary in time the most energetic regions with climatologic mean velocity over 50cms 21 and mke over 500cm 2 s 22 are found off the eastern coast of somalia with maxima of over 100cms 21 and 1500cm 2 s 22 and the equatorial io associated with the strong annually reversing somalia current and the twice a year eastward equatorial jets high eddy kinetic energy eke is found in regions of the equatorial io western boundary currents and agulhas return current with a maximum of over 3000cm 2 s 22 off the eastern coast of somalia the lowest eke 500cm 2 s 22 occurs in the south subtropical gyre between 308 and 408s and the central eastern arabian sea annual and semiannual variability is a significant fraction of the total eke off the eastern coast of somalia and in the central eastern equatorial io in general both the mke and eke estimated in the present study are qualitatively in agreement with but quantitatively larger than estimates from previous studies these pseudo eulerian mke and eke fields based on the most extensivedrifterdatasettodate arethemostpreciseinsituestimatestodateandcanbeusedtovalidatesatellite and numerical results

origins of eddy kinetic energy in the bay of bengal by analyzing satellite observational data and ocean general circulation model experiments this study investigates the key processes that determine the spatial distribution and seasonality of intraseasonal eddy kinetic energy eke within the bay of bengal bob it is revealed that a complicated mechanism involving both local and remote wind forcing and ocean internal instability is responsible for the generation and modulation of eke in this region high level eke mainly resides in four regions east of sri lanka region 1 the western bob region 2 northwest of sumatra region 3 and the coastal rim of the bob region 4 the high eke levels in regions 1 and 2 are predominantly produced by ocean internal instability which contributes 90 and 79 respectively prominent seasonality is also observed in these two regions with higher eke levels in boreal spring and fall due to enhanced instability of the east indian coast current and the southwest monsoon current respectively in contrast ocean internal instability contributes 49 and 52 of the total eke in regions 3 and 4 respectively whereas the atmospheric forcing of intraseasonal oscillations isos also plays an important role isos produce eke mainly through wind stress involving both the remote effect of equatorial winds and the local effect of monsoonal winds equatorial origin wave signals significantly enhance the eke levels in regions 3 and 4 in the form of reflected rossby waves and coastal kelvin waves respectively the local wind forcing effect through ekman pumping also has a significant contribution in regions 3 and 4 24 and 22 respectively

deep and intermediate water in the western mediterranean under the influence of the eastern mediterranean transient 1 the well known changes in the deep thermohaline circulation of the eastern mediterranean sea the so called eastern mediterranean transient emt which modified the outflow characteristics through the sicily strait led to significant changes in the western mediterranean sea since the early 90 s in spring 2005 an oceanographic survey carried out in the central part of the western basin showed the presence of a recently formed layer of western mediterranean deep water spreading at the bottom of the whole algero provencal basin it was characterized by unusual 0 s shapes as its temperature salinity and density were higher with respect both to the resident deep waters and to the climatological values the possible influence of the emt on the deep water formation processes occurred in the gulf of lions in the previous winter is here evidenced even taking into account other data sets previously collected in the western mediterranean

numerical simulation of the observed near surface east india coastal current on the continental slope we simulate the east india coastal current eicc using two numerical models resolution 0 1 circ times 0 1 circ an oceanic general circulation model ogcm called modular ocean model and a simpler linear continuously stratified lcs model and compare the simulated current with observations from moorings equipped with acoustic doppler current profilers deployed on the continental slope in the western bay of bengal bob we also carry out numerical experiments to analyse the processes both models simulate well the annual cycle of the eicc but the performance degrades for the intra annual and intraseasonal components in a model resolution experiment both models run at a coarser resolution of 0 25 circ times 0 25 circ simulate well the currents in the equatorial indian ocean eio but the performance of the high resolution lcs model as well as the coarse resolution ogcm which is good in the eicc regime degrades in the eastern and northern bob an experiment on forcing mechanisms shows that the annual eicc is largely forced by the local alongshore winds in the western bob and remote forcing due to ekman pumping over the bob but forcing from the eio has a strong impact on the intra annual eicc at intraseasonal periods local equatorial forcing dominates in the south north because the kelvin wave propagates equatorward in the western bob a stratification experiment with the lcs model shows that changing the background stratification from eio to bob leads to a stronger surface eicc owing to strong coupling of higher order vertical modes with wind forcing for the bob profiles these high order modes which lead to energy propagating down into the ocean in the form of beams are important only for the current and do not contribute significantly to the sea level

interannual variability of tehuantepec eddies 1 topex poseidon satellite altimeter observations and the naval research laboratory layered ocean model simulations show interannual variability in the number and intensity of tehuantepec eddies off the mexican southwest coast analysis of the results illustrates that downwelling coastally trapped waves which are generated in the equatorial pacific play a crucial role in the modulation and generation of tehuantepec eddies and a dominant role in tehuantepec eddy interannual variability this introduces a new paradigm in which the generation and modulation of tehuantepec eddies is not exclusively explained in terms of the strong and intermittent tehuantepec wind events in fact the results show anticyclonic eddy formation during periods of calm tehuantepec winds that is specifically exemplified by the formation of two anticyclonic tehuantepec eddies during a 5 month period of weak gulf of tehuantepec winds during summer of 1997 furthermore the satellite observed and nlom simulated proliferation of tehuantepec eddies during el nino years is explained by the corresponding increase in downwelling coastally trapped waves and a lack of increase in the number and strength of tehuantepec wind events during el nino years

kinematics of the pacific equatorial undercurrent an eulerian and lagrangian approach from gcm results abstract three dimensional monthly velocity fields from an ocean general circulation model are used to study the annual mean mass balance of the pacific equatorial undercurrent euc eulerian diagnostics are used to evaluate the various meridional vertical and zonal mass fluxes related to the euc there are several distinct regimes along the equator showing clear asymmetries between the western and eastern parts of the basin and between the northern and southern edges of the euc meridional fluxes are decomposed into pure ekman divergence and geostrophic convergence and it is shown that the asymmetries are mainly related to the spatial structure of the ekman divergence and thus to that of the trade winds lagrangian calculations are used to evaluate accurately the mass transfers between various sections of the euc and between the euc domain and the tropics the authors show that geostrophic convergence only ventilates the upper layers of the euc and that the euc really is a tongue of water flowing

monitoring the 1979 1985 equatorial pacific current transports with expendable bathythermograph data geostrophic transports of the major equatorial currents including the equatorial undercurrent and the south equatorial current have been estimated on a bimonthly basis in the central and western pacific over the 1979 1985 period this was made possible by a collection of carefully checked expendable bathythermograph xbt data and a few hydrocast and conductivity temperature depth data this collection considerably improved the number and quality of temperature profiles of the original institut francais de recherche scientifique pour le developpement en cooperation orstom scripps institute of oceanography tropical pacific xbt ship of opportunity program the temperature profiles were first grouped independently of longitude in regions around mean xbt tracks dynamic heights were then calculated relative to 400 db through a t s relationship deduced from the climatological levitus file geostrophic currents were calculated along the roughly south north oriented fiji hawaii and new caledonia japan mean xbt tracks using a specific technique this technique which combines fourier filtering in the meridional direction and in time also ensures the continuity across the equator between geostrophic currents deduced from the first and second derivatives of the meridional pressure field the filter coefficients in the meridional direction were determined through an adjustment of geostrophic currents to directly measured currents using the mean of data collected along 165 e during six tropical ocean and global atmosphere toga orstom cruises finally transports of the main equatorial currents were computed in a subjective way between 20 n and 20 s 0 400 m using monthly charts of geostrophic currents along the two mean xbt tracks the transports in the central pacific were compared to the transports derived from the semicontinuous direct current measurements taken during the hawaii tahiti shuttle experiment in 1979 1980 and during the line island profiling project pacific equatorial ocean dynamics experiment in 1982 1983 reasonable agreement demonstrates that it is possible to use xbt data for transport indexes of the major equatorial currents in the central and western pacific

deep and intermediate layer warming in the western mediterranean water mass changes and heaving 1 temperature and salinity have increased in the western mediterranean deep water during the second half of the 20th century but surprisingly the two water masses contributing to its formation atlantic water and levantine intermediate water show no clear warming trends at least for the same period of time previous studies concerned with long term ts property changes in the western mediterranean had dealt with changes on isobaric surfaces in this study we decompose these changes into their two natural contributions changes on isopycnal surfaces and changes induced by heaving vertical displacements of density surfaces this decomposition shows that liw temperature and salinity have increased when changes on density surfaces are analyzed the upward movement of deep layers has induced cooling on isobaric levels masking liw temperature trends and underestimating deep layers temperature trends

seasonality of surface stirring by geostrophic flows in the bay of bengal abstract stirring of passive tracers in the bay of bengal driven by altimetry derived daily geostrophic surface currents is studied on subseasonal timescales to begin with hovmoller plots wavenumber frequency diagrams and power spectra confirm the multiscale nature of the flow advection of latitudinal and longitudinal bands highlights the chaotic nature of stirring in the bay via repeated straining and filamentation of the tracer field an immediate finding is that stirring is local i e of the scale of the eddies and does not span the entire basin further stirring rates are enhanced along the coast of the bay and are relatively higher in the pre and post monsoonal seasons indeed finite time lyapunov exponent ftle and finite size lyapunov exponent fsle maps in all the seasons are patchy with minima scattered through the interior of the bay further these maps bring out a seasonal cycle wherein rapid stirring progressively moves from the northern to southern bay during pre and post monsoonal periods respectively the non uniform stirring of the bay is reflected in long tailed probability density functions of ftles that become more stretched for longer time intervals quantitatively advection for a week shows the mean ftle lies between 0 13 0 07 day 1 while extremes reach almost 0 6 day 1 averaged over the bay relative dispersion initially grows exponentially followed by a power law at scales between approximately 100 and 250 km which finally transitions to an eddy diffusive regime quantitatively below 250 km a scale dependent diffusion coefficient is extracted that behaves as a power law with cluster size while above 250 km eddy diffusivities range from 6 10 3 1 6 10 4 m2s 1 in different regions of the bay these estimates provide a useful guide for resolution dependent diffusivities in numerical models that hope to properly represent surface stirring in the bay

new cnes cls09 global mean dynamic topography computed from the combination of grace data altimetry and in situ measurements 1 an accurate knowledge of the ocean mean dynamic topography mdt is mandatory for the optimal use of altimetric data including their assimilation into operational ocean forecasting systems a new global 1 4 resolution mdt was computed for the 1993 1999 time period with improved data and methodology compared to the previous rio05 mdt field first a large scale mdt is obtained from the cls01 altimetric mean sea surface and a recent geoid model computed from 4 5 years of grace gravity recovery and climate experiment data altimetric sea level anomalies and in situ measurements are then combined to compute synthetic estimates of the mdt and the corresponding mean currents while the rio05 mdt was based on 10 years of in situ dynamic heights and drifting buoy velocities the new field benefits from an enlarged data set of in situ measurements ranging from 1993 to 2008 and includes all hydrological profiles from the argo array moreover the processing of the in situ data has been updated a new ekman model was developed to extract the geostrophic velocity component from the drifting buoy measurements the handling of hydrologic measurements has also been revisited compared to the previous rio05 solution the new global mdt resolves much stronger gradients in western boundary currents with mean velocities being doubled in some places moreover in comparison to several other recent mdt estimates we find that the new cnes cls09 mdt is in better agreement with independent in situ observations

shape of mesozoic dinosaur richness comment and reply comment the recent article by fastovsky et al 2004 1 examines the mesozoic record of dinosaur diversity for this study they utilized recently published dinosaur distribution data complied by weishampel et al 2004 2 a major concern of fastovsky et al 2004 1 was the dinosaur record during

the very first transformation of the mediterranean outflow in the strait of gibraltar 1 time series collected in the camarinal and espartel sills the two main sills of the strait of gibraltar have been analyzed to assess the first transformation of the mediterranean outflow in espartel west of camarinal sill the outflow has been estimated from a 6 year long time series of acoustic doppler current profiler observations the near bottom water flowing out at espartel is around 0 1 units saltier and 0 1 c warmer than at camarinal which is explained by entrainment and mixing of atlantic water by the outflow inside the basin bounded by both sills the constancy of heat and salinity transport implies an atlantic water entrainment of 0 03 sv which is about 4 of the outflow observed at espartel 0 77 sv and a flow of 0 74 sv at camarinal 96 of the flow at espartel it is also shown that the high energy dissipation rate associated with internal tides is enough to sustain the entrainment and a thorough mixing of the entrained water

variable bottom water in the western mediterranean basin the deep water of the western mediterranean has long been considered to have practically constant values of s and between 1909 1910 the thor expedition and the 1970 cruise of the jean charcot the deep water at more than 1800 m depth showed very little variation the small changes which appeared through the years could be due in part to changes in instrumentation analysis and methods of sampling in 1972 and 1973 during the medoc cruises a bottom layer of 200 300 m thickness was found its temperature and salinity showed a small gradient producing at the bottom an increase of potential temperature of about 0 01 to 0 02 c and an increase in salinities of about 0 010 00 relative to a minimum of and s in the deep water at 1800 2000 m these minima of and s were found to be homogeneous horizontally at all stations occupied in the medoc area and in the ligurian sea in 1973 interestingly the bottom layer was not present in 1974 however in november 1981 during the cruise mediprod iv the variable bottom water was again present extending from the ligurian sea and medoc areas along the western coasts of corsica and sardinia to the eastern alboran sea in most cases the maximum values of and s were recorded at the bottom and were higher than the 1973 values by about 0 03 c and up to 0 0150 00 but with a rather high spatial variability by february 1982 cruise dyome ii the situation had become more complicated not only was a layer of minimum and s present but it was underlain by a layer of maximum and s below which a decrease appeared producing a new minimum at the very bottom in addition a number of stations displayed higher values of by about 0 05 c and of s by about 0 0150 00 in the layers of minimum and maximum characteristics as well as on the bottom in contrast to the situation in 1973 high spatial variability was found in the deep layering the variability may have been due to patchy deep convention activity possibly in the ligurian sea the phenomenon of variable bottom water and the processes which produce it may be relevant to our understanding of water mass formation

interannual variability of the mediterranean outflow observed in espartel sill western strait of gibraltar 1 four year time series of observations in espartel sill at the western part of the strait of gibraltar have been analyzed in order to investigate the variability of the mediterranean outflow it is assumed that the observed variability comes from the changing properties of the dense waters that are located at the maximum depth from where they can be uplifted in the upstream basin alboran sea inside the mediterranean sea and evacuated through the strait from this perspective the following three mechanisms are investigated 1 the replenishment of the deep basin by newly formed western mediterranean deep water that depending on its density can either uplift old resident waters or lay above them leaving in any case a cold signature in the temperature series 2 the presence absence of the energetic anticyclonic gyres in the alboran sea particularly the western one which can transfer momentum to the underlying mediterranean vein and provide it with additional energy to ascend over the sills of the strait and 3 the meteorologically enhanced flows that follow the rapid changes of atmospheric pressure over the western mediterranean basin which would be able to aspire deeper waters residing in the upstream basin the three mechanisms act on different timescales from annual in case 1 to monthly in case 2 to weekly in case 3 although these two latter are modulated annually by the seasonal prevalence of the western alboran gyre in summer and of the strong meteorologically driven fluctuations in winter the mechanisms overlap at annual timescales making it difficult to separate out the different contributions

signature of la nina in interannual variations of the east india coastal current during spring we have investigated interannual variations of the spring february april average east india coastal current eicc magnitude between 2000 and 2018 using oscar ocean surface current analysis real time current and a linear continuously stratified lcs model interannual variability of the eicc shows significant decrease in magnitude during spring of 2000 2008 and 2011 the years when high negative oni oceanic nino index for sea surface temperature value has been observed due to dominance of strong la nina events our lcs model also successfully simulates these interannual variability of the spring average eicc between 2000 and 2018 we carried out numerical experiments using lcs model related to local and remote forcing response on eicc dynamics of the eicc during spring are dominated by four different forcing processes local wind along east coast of india remote forcing response from the eastern and northern boundary of the bob including islands interior bob and the equatorial indian ocean eio during el nino and normal spring years strong poleward interannual eicc are due to very weak negligible order of 0 5 cm s 1 eicc from eio remote response and in phase poleward eicc formation using other three forcings however during la nina spring years weak order of 0 10 cm s 1 poleward interannual eicc are formed due to destructive interference between equatorward current order of 10 25 cm s 1 from eio forcing and in phase poleward current from other three forcings we have also found propagation of interannual upwelling downwelling favorable kelvin wave from eio via eastern and western boundary of the bob during spring in the el nino la nina years the interannual variations in the propagation of eio kelvin wave are associated with the changes in the eio zonal wind direction by climate mode like enso el nino southern oscillation

strong intraseasonal variability of meridional currents near 5 n in the eastern indian ocean characteristics and causes abstractthis paper reports on strong intraseasonal upper ocean meridional currents observed in the indian ocean between the bay of bengal bob and the equator and elucidates the underlying physical processes responsible for them in situ measurements from a subsurface mooring at 5 n 90 5 e reveal strong intraseasonal variability of the meridional current with an amplitude of 0 4 m s 1 and a typical period of 30 50 days in the upper 150 m which by far exceeds the magnitudes of the mean flow and seasonal cycle such prominent intraseasonal variability is however not seen in zonal current at the same location further analysis suggests that the observed intraseasonal flows are closely associated with westward propagating eddylike sea surface height anomalies sshas along 5 n the eddylike sshas are largely manifestations of symmetric rossby waves which result primarily from intraseasonal wind stress forcing in the equatorial waveguide and reflection of the equatorial kelvin waves at the eastern bou

annual and interannual variability of the tropical instability vortices in the equatorial eastern pacific observed from lagrangian surface drifters abstractthis study documents the spatial distributions and temporal variations of anticyclonic eddies with identified radii 100 km in the equatorial eastern tropical pacific ocean viz tropical instability vortices tivs using lagrangian surface drifters the tivs identified from lagrangian surface drifters are distributed in a band along 5 n and are closely associated with latitudinal barotropically unstable shear between the westward south equatorial current sec and the eastward north equatorial countercurrent necc fewer tivs are identified from february to june when the shear between the sec and necc is weak whereas more tivs are found from july to january when the shear is enhanced the number of identified tivs also exhibits substantial interannual variability with fewer tivs identified during el nino events and more tivs found during la nina events this relationship is likely associated with the interannual variations of the zonal circulation in the equatorial pacific modulated by el ni