distribution and circulation of water masses in the gulf of cadiz from in situ observations from data collected during golfo 2001 survey a study was conducted on the circulation and distribution of water masses in the gulf of cadiz in the spring of 2001 the general surface circulation in the gulf of cadiz is anticyclonic with

surface circulation in the gulf of cadiz 2 inflow outflow coupling and the gulf of cadiz slope current 1 a study of the upper slope circulation in the gulf of cadiz is presented observations both original and revisited and realistic numerical modeling are used together to describe the structure and variability of the slope current system above the mediterranean outflow it is shown that the mediterranean inflow outflow coupling plays a stronger role than that of the atmospheric forcing in driving the upper slope currents the mediteranean outflow forces a surface open ocean current toward the strait of gibraltar part of it is entrained into the outflow and the remaining flows into the mediterranean this latter component does not suffice for the observed transport of the atlantic inflow into the mediterranean a secondary contribution to the inflow is therefore needed to complement the transport this contribution comes from a persistent equatorward current along the upper slope between cape st vincent and the strait of gibraltar the jet is 20 30 km wide and significant in the upper 200 m attaining subinertial maxima as much as 0 3 0 4 m s and monthly means in the order of 0 1 0 15 m s this current shows a strong variability at time scales in the order of 2 8 days and displays a significant vertical shear the response of the upper slope current to synoptic and seasonal atmospheric variability is analyzed very low correlation was detected at synoptic scales and the response of the system to seasonal forcing is unclear a cycle of intensification in june july and a decrease in winter is apparent in the measurements but is weak in the model results it is speculated that the cycle in the observed currents is associated with variability in the inflow outflow coupling system rather than driven by seasonally changing wind forcing

bombardment history of asteroid 4 vesta recorded by brecciated eucrites large impact event clusters at 4 50 ga and discreet bombardment until 3 47 ga abstract the thermal impact histories of sixteen eucrite meteorites were investigated three monomict eucrites nwa 999 a 87272 87 and stannern five polymict eucrites nwa 1000 nwa 1666 nwa 5601 y 980066 100 and y 980255 100 three quench textured eucrite melt rocks y 981646 21 y 981651 105 and mil 0766214 one eucrite dominantly comprised of quench textured clasts que 99005 11 three unclassified eucrite breccias lap 031316 9 lar 06870 5 que 99799 4 and one unbrecciated eucrite eet 92004 17 included here due to its shock features we have measured fifteen high precision new 40 ar 39 ar plateau ages on plagioclase and matrix for ten of these meteorites with a tight cluster of nine ages obtained from three different polymict breccias these ages range from 4534 56 ma to 4491 16 ma resulting in a concordant age population p 0 16 the fact that such a cluster of ages is recorded in unrelated breccias which are made of a priori unrelated components leads us to propose that those ages recorded a single heating event on a large scale and is interpreted here as a high energy impact event early in the history of vesta at 4500 4 ma we propose that the debris was ejected and isolated from subsequent large impacts in a secondary rubble pile asteroid where the energy of the outgoing shock wave from an impact is significantly reduced as it compacts the target material holsapple et al 2002 and references therein the other analyses define a spread of five plateau ages ranging from 3851 21 ma to 3469 35 ma over 380 ma an additional apparent plateau age of 4288 38 ma but with a diffusion profile of cumulative 39 ar release along with published u pb apatite age of 4 14 ga suggests that the data might either define a true continuum normal background bombardment from 4 5 ga to 3 47 ga or cluster between 3 85 ga and 3 47 ga excavation of a fresh surface at 3 85 ga continuously bombarded until 3 47 ga both scenarios are compatible with a final ejection age of 3 47 ga when a major impact liberates the bulk of the brecciated meteorites into another secondary rubble pile asteroid where the brecciated eucrites stayed relatively well protected from subsequent major impacts based on these results and recent crater counting measurements we propose that the excavation and bulk ejection were caused by the rheasilvia ca 3 47 ga basin forming impact diffusion models on plagioclase crystals with different ar age spectrum signatures from a single breccia nwa1666 4501 7 ma suggest that either 1 the formation of the breccia is very young or 2 different plagioclase crystals have different diffusion characteristics and or 3 the porosity caused heterogeneous temperatures during an impact heating event particularly likely if the 4 5 ga brecciated eucrites were stored in a rubble pile asteroid many or possibly most large asteroids being re accumulated rubble piles with potential large porosity holsapple et al 2002 scenarios 2 and 3 preclude the usage of multi grain aliquots to decipher the time temperature history of most impact breccia using 40 ar 39 ar thermochronology

marginal sea overflows and the upper ocean interaction abstract marginal sea overflows and the overlying upper ocean are coupled in the vertical by two distinct mechanisms by an interfacial mass flux from the upper ocean to the overflow layer that accompanies entrainment and by a divergent eddy flux associated with baroclinic instability because both mechanisms tend to be localized in space the resulting upper ocean circulation can be characterized as a plume for which the relevant background potential vorticity is set by the slope of the topography that is a topographic plume the entrainment driven topographic plume consists of a single gyre that is aligned along isobaths the circulation is cyclonic within the upper ocean water columns are stretched the transport within one branch of the topographic plume may exceed the entrainment flux by a factor of 2 or more overflows are likely to be baroclinically unstable especially near the strait this creates eddy variability in both the upper ocean and overflow layers and a flux of momentum and e

crystallization recrystallization and impact metamorphic ages of eucrites y792510 and y791186 abstract monomict eucrites y792510 and y791186 of pyroxene metamorphic type 6 contain areas of recrystallized mesostasis and granoblastic pyroxene textural comparisons suggest that the mesostasis areas in these eucrites originally resembled analogous areas in the pristine basaltic eucrite clast y75011 84 39ar 40ar ages were determined for microbreccias y791186 87 and y792510 62 and crystalline clast y792510 65 the 39ar 40ar ages for y791186 87 and y792510 62 are identical within error limits at 3 46 0 18 ga and 3 40 0 16 ga 2 respectively both these samples were involved in an impact event in which ar was quantitatively degassed 3 43 0 10 ga ago y792510 65 has an apparently older 39ar 40ar age of 3 60 0 04 ga 2 suggesting that it was degassed in a separate event or to a lesser degree rb sr and sm nd ages were determined for both y792510 clasts the rb sr age of 3 26 0 24 ga 2 for y792510 65 was totally reset by the impact event s whereas the rb sr age of 4 26 0 62 ga 2 for y792510 62 either was partially reset by the same event s or by earlier recrystallization of mesostasis the 147sm 143nd age calculated for y792510 65 including all data is 4 67 0 22 ga 2 but is likely to have been affected by weathering in the antarctic it becomes 4 57 0 09 ga if only data for the major minerals plagioclase and pyroxene are included in the isochron the 147sm 143nd age of y792510 62 is 4 34 0 06 ga 2 for the same mineral phases but may be biased by the presence of weathered ca phosphates in the pyroxene separate the 146sm 142nd age of y792510 65 is 4 42 0 06 0 04 ga corresponding to initial 146sm 144sm 0 0030 0 0010 relative to 146sm 144sm lew 0 0076 0 0009 for the lew86010 angrite at 4 558 ga ago the y792510 65 ages from the two sm nd chronometers are concordant at 4 48 ga which may be the crystallization age of this eucritic basalt late crystallization alternatively these sm nd ages may have been affected by the event in which ca phosphate and augite in mesostasis were recrystallized and augite and chromite in granoblastic areas were derived from cloudy pyroxenes late recrystallization the subsolidus recrystallization may be a consequence of a thermal spike in the midst of an otherwise monotonically cooling environment resulting from impact cratering of the hot crust of the newly formed eucrite parent body pyroxene homogenization probably occurred prior to formation of granoblastic pyroxene and close to the time of initial crystallization mn cr data provide only a hint of live 53mn t1 2 3 7ma and imply either chromium isotopic equilibration after decay of 53mn or late crystallization impact brecciation and lithification probably accompanied thermal annealing 3 4 3 6 ga ago as given by the 39ar 40ar ages the rb sr age of y792510 65 is consistent with this interpretation the 39ar 40ar and rb sr systematics of minute k rich inclusions in plagioclase and pyroxene formed by previous impact and thermal annealing events probably were reset then these young impact metamorphic ages demonstrate that impact resetting of radiometric ages on the hed parent body asteroid 4 vesta occurred over an interval of at least 0 7 ga

mineralogical records of early planetary processes on the howardite eucrite diogenite parent body with reference to vesta abstract mineralogical information recovered from the howardite eucrite diogenite hed meteorites was employed to reconstruct the history of the parent body and relate it to 4 vesta these interpreted crustal evolution processes were then compared to the expected geological features on the surface of a likely proto planet 4 vesta the original crustal materials of the hed parent body were preserved as mineral grains and lithic clasts but in many eucrites fe mg ratios in pyroxenes were homogenized by diffusion after crystallization the crystallization trend of the protocrust has been deciphered by 1 examining monomict and crystalline samples and using their mineralogical and chemical information to formulate a sequence of crystallization and cooling trends and by 2 reconstructing the original crust prior to cratering events from lithic clasts and mineral fragments in polymict breccias such as howardites and polymict eucrites mineral components are identical both in the individual hed and in polymict breccias and no remnants of primitive materials were preserved in the polymict breccias a layered crust model reconstructed from such breccias consists of an upper crust with extrusive lava like eucrites that have been brecciated and metamorphosed diogenite mantle and cumulate eucrites of varying thickness between them this model can be used to explain the surface geological features of vesta observed from the hubble space telescope a large crater with diogenitic orthopyroxene at the crater floor is consistent with the deepest diogenitic layer of the layered crust model and an underlying olivine layer is expected from early crystallized olivine in the crystal fractionation model the old terrain of eucritic surface materials of vesta can be howardites polymict eucrites or regolith like eucrites produced from eucrites extruded and impacted on the surface partial melting models of eucrites seem to be favored by the rare earth element ree chemistry and experimental studies unfortunately partial melting models have not demonstrated how the hed parent body is converted to a layered crust without producing any metamorphosed primitive material in the layered crust the origin of cumulate eucrites with systematic variation of textures and chemistries of pyroxene can be explained by the layered crust model with excavation and mixing of trapped liquid discovery of basaltic materials with na rich plagioclase and augite in iron meteorites which are the products of partial melting suggests that eucrites may be unique to a body that underwent large scale differentiation and metamorphism

validation of sentinel 3a sral coastal sea level data at high posting rate 80 hz altimetry data of two and a half years june 2016 november 2018 of sentinel 3a sral s3a sral were validated at the sampling frequency of 80 hz the data were obtained from the european space agency esa grid processing on demand gpod service over three coastal sites in spain huelva hu gulf of cadiz barcelona ba western mediterranean sea and bilbao bi bay of biscay two tracks were selected in each site one ascending and one descending data were validated using in situ tide gauge tg data provided by the spanish puertos del estado the altimetry sea level anomaly time series were obtained using the corrections available in gpod with the exception of the sea state bias ssb correction not available at 80 hz hence the ssb was approximated to 5 of the significant wave height swh the validation was performed using two statistical parameters the pearson correlation coefficient r and the root mean square error rmse in the 5 20 km segment with respect to the coastline the results were 6 8 cm rmse and 0 7 0 8 r for all the tracks the 0 5 km segment was also analyzed in detail to study the land effect on the altimetry data quality the results showed that the track orientation the angle of intersection with the coast and the land topography concur to determine the nearest distance to the coast at which the data retain a similar level of accuracy than in the 5 20 km segment this distance of good quality to shore reaches a minimum of 3 km for the tracks at hu and the descending track at ba

intensive shipboard observations of the flow through the strait of gibraltar during the european project canary island azores gibraltar experiment canigo intensive shipboard observations were carried out in april 1996 and october 1997 in order to observe the spatial and temporal variability of the flow and of the water mass structure in the strait of gibraltar at the sill and the eastern and western entrances to the strait repeated cross strait sections and station time series of the flow and of t s profiles were measured using vessel mounted and lowered acoustic doppler current profilers adcp and conductivity temperature depth probes ctd expendable bathythermographs xbt yielding new views of the rapid changes over tidal cycles and of approximate tidal means it is argued that transport observations might be easier to carry out away from the sill in the eastern part of the strait even though maximum resolved shears were comparable in both places 0 03 0 04 s 1 in the vertical and 0 001 0 016 s 1 in the horizontal in the east coordinated changes in the stratification and the flow field are documented via four time series over m 2 tidal cycles showing a sharpening diffusing of the vertical gradients in the water masses and the flow maximum shear and maximum water mass gradients do not always coincide there and both are much shallower 50 80 m than the delimiter between inflow and outflow 120 150 m the mean salinity of the outflow core decreases from 38 43 in the east to 38 17 west of the sills as a result of the mixing processes the internal bore was followed and directly observed with rapid ctd yoyo stations and with xbt vessel mounted adcp measurements it generates extreme changes in currents and shears on timescales of minutes with directly measured vertical velocities reaching 50 cm s 1 patches of density inversions were observed as the bore passed by consistent with active turbulent mixing along the interface the time series of flow and ctd measurements allow the direct calculation of froude numbers at various locations and over tidal cycles these and along strait sections suggest that the exchange through the strait is maximal in april 1996 and submaximal in october 1997 supporting the expectations of garrett et al 1990

surface lithologic heterogeneity of asteroid 4 vesta abstract high precision spectrophotometry of 4 vesta the third largest asteroid was used to establish the surface composition of this body and to investigate mineralogical variations across its surface the average surface of vesta is analogous to howardite and or polymict eucrite assemblages regolith derived members of the hed meteorite suite which consist of a eucrite matrix containing differing amounts of a diogenite component color and or spectral changes which exhibit a consistent relationship to rotational phasing are evident in 16 of 18 studies of vesta dating back to 1929 including the present work after elimination of possible sources of spurious spectral or color changes it is concluded that these variations arise from hemispheric variations in surface materials and hence provide a means of spatially resolving subhemispheric compositional units on the surface of vesta the background surface of vesta is a relatively dark howardite or polymict eucrite pyroxene plagioclase assemblage with several compositionally distinct bright regions clustered in one hemisphere viewed around the maximum in vesta s lightcurve these include what appears to be an olivine bearing unit suggested name leslie formation located near vesta s equator which probably represents an impact basin and or its associated ejecta that penetrated through the basaltic crust other high albedo compositional units including an apparently low calcium eucrite region and several diogenite pyroxenite regions at least one located near the southern pole may be smaller shallower impact basins by analogy to the eucrite meteorites which represent surface flows or shallow intrusions and which constitute the major component of the regolith derived howardites and polymict eucrites we conclude that the howardite polymict eucrite units represent a regolith gardened original surface of vesta it is probable that the low albedo of the background surface on vesta is due to an age related darkening effect similar to that inferred from the galileo images of gaspra and ida this mechanism is consistent with the correlation of absorption feature intensity with the lightcurve vesta appears to have an old eucritic surface darkened with age and represented among the meteorites by the regolith derived howardites and polymict eucrites on which several impacts on one hemisphere have exposed fresher brighter diogenite and olivine bearing material based on qualitative analysis of the mineralogical variations as a function of rotation a generalized lithologic map of vesta was produced there is reasonable control on the longitude of lithologic features but little control on their latitudes except where specifically noted in producing this map discrete circular features were used on the plausible assumption that impacts have been the most important geologic process on this surface for most of the age of the solar system the shape of the features has thus been assumed rather than derived and is subject to future revision as data improve

impact excavation on asteroid 4 vesta hubble space telescope results hubble space telescope images of asteroid 4 vesta obtained during the favorable 1996 apparition show an impact crater 460 kilometers in diameter near the south pole color measurements within the 13 kilometer deep crater are consistent with excavation deep into a high calcium pyroxene rich crust or olivine upper mantle about 1 percent of vesta was excavated by the crater formation event a volume sufficient to account for the family of small vesta like asteroids that extends to dynamical source regions for meteorites this crater may be the site of origin for the howardite eucrite and diogenite classes of basaltic achondrite meteorites

instability dynamics of a subtropical jet and applications to the azores front current system eddy driven mean flow abstract the azores front is associated with an eastward flowing subtropical jet which coincides with the northern edge of the north atlantic subtropical gyre and forms a southern branch of the gulf stream an intensive study of the eddy driven mean flow induced by the nonlinear instability of the jet has been conducted using a primitive equation numerical model initialized with the summer hydrological fields typical of the azores front the authors show that the mesoscale patterns that appear after a few months are largely determined by baroclinic instability processes the jet and its associated mesoscale turbulence have a strong meridional asymmetry due to the strongly sloping thermocline in general an anticyclonic meander which grows and deforms northwestward generates a pinched off anticyclone while a cyclonic meander which grows and deforms southwestward degenerates in a thin filamental structure that will dissipate before any cyclone can be pinched off the authors propose a mechanism that

oxygen and asteroids hundreds of thousands of asteroids have been discovered in the asteroid belt and in near earth space oxygen is an abundant element in meteorites and presumably in most asteroids spectral reflectance measurements of asteroids in the visible and near infrared can identify oxygen bearing minerals such as those found in the olivine pyroxene and serpentine groups due to their distinctive absorption features interpretation of the mineralogy of asteroids is complicated by the effects of space weathering which tends to redden and darken the surfaces of asteroids asteroids are primarily classified into a number of taxonomic classes and subclasses according to their spectral properties in the visible wavelength region however asteroids with similar spectral properties in the visible may have different spectral properties in the near infrared and therefore different interpreted mineralogies definite trends in the abundances of different taxonomic classes versus heliocentric distance are apparent these trends appear to be a function of both composition differences and degree of heating however dynamical processes have significantly affected these trends close observation of asteroids by spacecraft such as near shoemaker to 433 eros and hayabusa to 25143 itokawa are currently the best way to discern the mineralogies of individual asteroids

three basaltic earth approaching asteroids and the source of the basaltic meteorites we report five color photometry near infrared spectra 0 8 2 5 m and thermal observations of the earth approaching asteroids 3551 1983 rd 3908 1980 pa and 4055 1985 do2 we derive their diameters as 1 2 1 0 and 3 4 km respectively apart from greater absorption band depths the spectra of these three small asteroids are nearly identical to that of vesta which is known to have a differentiated basaltic surface the deeper pyroxene bands 0 9 and 1 9 m relative to vesta are consistent with more pyroxene rich surfaces larger mineral grain sizes in their optically immature regoliths more bare rock surfaces or all of these factors these small earth approaching asteroids have similar orbits with perihelia near earth s orbit in july august they are probably not fragments of vesta but may be fragments of one or more vesta like parent bodies the spectra of vesta and the three earth approachers resemble those of the basaltic meteorites i e eucrites howardites and diogenites hed meteorites we find that hed fall times show a weak peak in july august suggesting that 3551 3908 and 4055 may be fragments of the source bodies of the hed meteorites or perhaps of a single common hed parent body the kilometer size asteroids have regoliths with significant insulating properties but these regoliths differ from that of the moon in that the particle sizes are larger than on the moon and lunar like glasses and agglutinates are largely absent the causes of these differences are related to impact velocities impact shaking and debris retention on small bodies differentiated basalt or mantle like asteroids may have impacted earth and left discontinuities in the geologic climatic record without leaving the chemical signatures associated with the k t boundary event

vesta and the vestoids a new rock group abstract moderate spectral resolution observations of the 505 nm fe2 pyroxene absorption feature were obtained for 13 asteroids dynamically linked to 4 vesta or located between vesta and the 3 1 resonance gap eleven showed spectra with deep 0 9 m mafic silicate absorptions suggesting a pyroxene composition binzel and xu 1993 spectra of only six of these asteroids show the absorption feature centered at 506 5 nm suggestive of an augite high calcium component to the surface pyroxenes consistent with previous spectral observations across the surface of vesta cochran and vilas 1998 five of the six asteroids include all objects observed at heliocentric distances between vesta and the 3 1 resonance gap the spectrum of only one asteroid interior to vesta s orbit showed this feature no correlation between the presence or absence of this feature and the strength of the 1 m mafic silicate feature was found

remotely sensed sea surface thermal patterns in the gulf of cadiz and the strait of gibraltar variability correlations and relationships with the surface wind field satellite image sequences covering periods of a few days throughout the annual cycle of the waters off southern iberia have been analyzed in conjunction with concurrent surface wind speed data from coastal stations qualitative analysis reveals a large degree of temporal and spatial variability in the thermal signature of the sea surface over periods of both a few days and several months during the summer a cool seasurface temperature signature extends from the western iberian coast around cape st vincent and eastward as far as faro at the same time a warm signature originating on the iberian coast between faro and cadiz extends into the strait of gibraltar these two features are shown to sometimes adopt more westerly positions and the strait experiences regions of cool thermal signature originating at its southern side during winter the surface flow into the mediterranean through the strait of gibraltar is anomalously warm and appears to come from the interior of the gulf of cadiz quantitative measurements show that temporal variability over timescales of a few days at individual sites is maximum in midsummer spatial thermal variability over the whole region is found to peak toward the end of the summer statistical analyses of the data reveal the coupling between the surface wind field in the gulf of cadiz and the surface thermal pattern especially during the summer wind induced across stream upwelling in the strait of gibraltar although dynamically subordinate to tidal and density driven processes is shown to occasionally dominate the surface thermal signature

the source of the canary current in fall 2009 1 the source of the canary current has been inferred from an inverse box model applied to the hydrographic data of a survey carried out in 2009 in the northeast subtropical gyre 29 37 n 9 24 w the portugal current is observed between 13 5 and 14 8 w at 37 n carrying 1 8 0 4 sv southward this current presumably merges with the eastward transport of the azores current system and partly contributes to the mediterranean inflow and partly to the northward recirculation of the azores current through the gulf of cadiz the azores current system is located in the meridional range 33 50 36 25 n at 24 50 w this system transports eastward 7 2 0 5 sv in the thermocline layers and 1 1 0 8 sv at intermediate layers the azores current intermediate water mass has the highest portion of sub arctic intermediate water saiw in the region while the azores countercurrent intermediate waters mass is mainly mediterranean water the canary current extends from 22 25 to 18 50 w at 29 n the westernmost position ever observed this current transports southward 6 2 0 6 sv in the thermocline layers and 2 0 0 8 sv in the intermediate layers this intermediate flow shows a relative maximum of oxygen and a relative minimum in nutrient concentration indicating the presence of saiw the study concludes that at least in fall 2009 the canary current extends to the intermediate waters n 27 9220 approximately 1600 dbar and that azores current feeds the canary current at surface and intermediate layers

surface circulation in the gulf of cadiz model and mean flow structure 1 the mean flow structure of the gulf of cadiz is studied using a numerical model the model consists of a set of one way nested configurations attaining resolutions on the order of 2 6 km in the region of the gulf of cadiz in the large scale configuration the entrainment of the mediterranean water is parameterized implicitly through a nudging term in medium and small scale nested configurations the mediterranean outflow is introduced explicitly the model reproduces all the known features of the azores current and of the circulation inside the gulf of cadiz a realistic mediterranean undercurrent is generated and meddies develop at proper depths on the southwest tip of the iberian slope the hypothesis that the azores current may generate in association with the mediterranean outflow plume theories is confirmed by the model results the time mean flow is dominated by a cyclonic cell generated in the gulf which expands westward and has transports ranging from 4 to 5 sv the connection between the cell and the azores current is analyzed at the scale of the gulf the time mean flow cell is composed by the westward mediterranean undercurrent and by a counterflow running eastward over the outer edge of the mediterranean undercurrent deeper vein as the latter is forced downslope this counterflow feeds the entrainment at the depths of the mediterranean undercurrent and the atlantic inflow at shallower levels coastward and upslope of this recirculation cell a second current running equatorward all the way along the northern part of the gulf is revealed this current is a very robust model result that promotes continuity between the southwestern iberian coast and the strait of gibraltar and helps explain many observations and recurrent sst features of the gulf of cadiz

a census of meddies in a long term high resolution simulation the output from a high resolution two decade long mediterranean outflow simulation is analysed here to provide a census of mediterranean water eddies aka meddies both anticyclones and cyclones the formation rate of meddies that survive for at least 90 days is of 12 meddies yr 1 of which 12 are cyclones the rate of formation reaches 40 meddies yr 1 30 cyclones when considering all the meddies living over 15 days about 70 of the population is born along the southwestern iberian slope but several robust meddies also originate in points of convergence of the main pathways into the open ocean the longest lived meddies propagate northwestwards but most of the anticyclones veer southwestwards after a while as the meddies drift away from their birthplace their radius tends to increase gradually from 15 to 30 km the thickness depth difference between isopycnals 27 2 and 27 5 of anticyclones born near cape st vincent contracts by approximately 100 m after travelling 1000 km from their source their mean swirl velocities range from about 21 cm s 1 at z 1000 m up to 27 cm s 1 at z 600 m mean salinity and temperature anomalies are significantly lower for cyclones which in general are also more slowly rotating shallower and thinner than anticyclones cyclones are more easily tracked at 600 m depth where longer trajectories are recorded in the vicinity of portimao canyon cyclones outnumber anticyclones while the reverse happens downstream of cape st vincent

common asteroid break up events of eucrites diogenites and howardites and cosmic ray production rates for noble gases in achondrites we determined the cosmic ray produced noble gas abundances in eight diogenites four eucrites and four howardites using these and additional noble gas and chemical data from the literature composition and shielding dependent production rates of achondrites for 3he 21ne 38ar 78kr 83kr and126xe were derived based on 81krkr exposure ages the cosmogenic ratio 22ne 21ne is found to be a valid shielding indicator for all howardites eucrites and diogenites heds this ratio correlates with other shielding dependent ratios such as 78kr 83kr 80kr 83kr 124xe 131xe 126xe 131xe and 128xe 131xe we show that strong correlations for these ratios also exist for basaltic lunar rocks the new production rates were used for the calculation of exposure ages for all heds with known noble gas abundances two major exposure age clusters at 21 ma and 38 ma are observed in all three classes we find that five asteroid break up events characterized by exposure ages 6 1 ma 12 2 ma 21 4 ma 38 8 ma and 73 3 ma produced all diogenites fifteen out of seventeen howardites and twenty eight out of thirty nine eucrites we conclude that asteroidal or cometary impact events at such times on one or several parent bodies are responsible for the ejection of eucrites howardites and diogenites probable parent bodies are multiple 4 vesta derived kilometer sized objects of basaltic achondritic composition reaching the 3 1 resonance region a proposed source area for meteorites the direct ejection from vesta and capture by earth of basaltic meteorites has been shown to be dynamically difficult in such a scenario large events 38 ma and 21 ma ago are required liberating simultaneously material representing vesta s surface eucrites howardites and interior regions diogenites

on the inner shelf circulation in the northern gulf of cadiz southern portuguese shelf abstract a new look at the inner shelf circulation in the northern gulf of cadiz sw iberian peninsula is taken results reveal the introduction of a sharp spatial heterogeneity in the wind field by the coastal geometry around cape st vincent and nearby mountain chains direct observations taken in november december 2001 reveal the alternating nature of the coastal flow along the sw iberian peninsula featuring a sharp current inversion on time scales of less than 2 days along shore gradients of the oceanic wind stress were detected which may contribute to the coastal circulation patterns in the region over the observational period the sea level variability in the gulf of cadiz is better explained by the action of along shore winds outside the gulf than by local winds this is confirmed by a scale analysis done on the vertically integrated momentum equation it is shown that to a first approximation the expected behaviour of the inner shelf flow responds to linear dynamics in this approximation the along shore sea level slope 5 cm over 100 km is the dominant term overriding the linear bottom and surface stress terms this suggests control by large scale atmospheric pressure systems and negligible dynamical influence from local wind stress

observations and numerical modelling of the mediterranean outflow splitting and eddy generation during the canigo project the generation of dipolar eddies in the mediterranean water mw layers off south portugal was recorded by subsurface floats from february to november 1998 the role of the bottom topography on the spreading of the mw in the gulf of cadiz and on the generation of these mw eddies was studied in the framework of the medtop project some of the hydrological and velocity observations collected during medtop in 2001 and 2002 also revealed the association of anticyclones meddies and cyclones in the region just south of the portimao canyon the evolution of these structures is studied with subsurface floats deployed in the vortices the splitting of the mw plume in the gulf of cadiz and the generation mechanisms of the mw vortices in the region from portimao canyon to the estremadura promontory are investigated using a bottom following numerical primitive equations model in a regional ocean configuration incorporating the realistic topography of the iberian continental slope the model reproduces the mw division into different cores in the gulf of cadiz as well as the generation of baroclinic dipoles downstream of portimao canyon the role of the bottom topography in the eddy generation process is discussed

zonal structure of the mean flow and eddies in the azores current system 1 the surface circulation and eddy field from the azores current system are studied here by analyzing surface drifters records and altimetry maps collected over more than 16 years clear differences in mean flow and eddy characteristics allow for a classification of the azores current in three zonal sectors west of 30 w between the mid atlantic ridge and the hyeres atlantis seamount system between 30 w and the longitude of madeira and east of madeira a detailed and quantitative characterization of each sector is given the transition between the western and central parts is controlled by the hyeres atlantis ridge in the transition to the eastern sector there is a change in the dynamics and the flow is forced by the cyclonic recirculation driven by the mediterranean outflow there is no clear expression of a continuous surface northern counterflow but three distinct westward flows are seen one along the southeastern border of the azores plateau another one southwest of madeira and a third one along 31 n west of the hyeres seamount no clear tilt in the axis of the azores current is found in the calculated mean surface flow from surface drifters observations from both drifters and altimetry data show that anticyclonic features dominate in the northern region whereas cyclonic ones dominate in the southern region overall cyclones are more numerous constituting 60 of large eddies the eddy features detected in the west tend to be larger than those in the east both in size and sea level anomaly there is indication of different mean propagation speeds east and west of 25 w 30 w with the mean speeds consistently increasing by 25 45 in the west estimates for the rate of formation of strong eddies range from 1 4 to 2 4 year 1 for cyclones and 1 2 to 1 7 year 1 for anticyclones

the distribution of basaltic asteroids in the main belt abstract we present the observational results of a survey designed to target and detect asteroids whose photometric colors are similar to those of vesta family members and thus may be considered as candidates for having a basaltic composition fifty basaltic candidates were selected with orbital elements that lie outside of the vesta dynamical family optical and near infrared spectra were used to assign a taxonomic type to 11 of the 50 candidates ten of these were spectroscopically confirmed as v type asteroids suggesting that most of the candidates are basaltic and can be used to constrain the distribution of basaltic material in the main belt using our catalog of v type candidates and the success rate of the survey we calculate unbiased size frequency and semi major axis distributions of v type asteroids these distributions in addition to an estimate for the total mass of basaltic material suggest that vesta was the predominant contributor to the basaltic asteroid inventory of the main belt however scattered planetesimals from the inner solar system a 2 0 au and other partially fully differentiated bodies likely contributed to this inventory in particular we infer the presence of basaltic fragments in the vicinity of asteroid 15 eunomia which may be derived from a differentiated parent body in the middle main belt 2 5 a 2 8 we find no asteroidal evidence for a large number of previously undiscovered basaltic asteroids which agrees with previous theories suggesting that basaltic fragments from the 100 differentiated parent bodies represented in meteorite collections have been battered to bits burbine t h meibom a binzel r p 1996 meteorit planet sci 31 607 620

evidence of time mean cyclonic cell southwest of iberian peninsula the mediterranean outflow driven β plume 1 first observational evidence of time mean cyclonic recirculation southwest of iberia is presented data sets of hydrography satellite altimetry and surface drifters velocities are analyzed jointly in order to obtain an accurate time averaged circulation in the mid latitude northeast atlantic off the gulf of cadiz a cyclonic recirculation cell with characteristics similar to those predicted by theoretical and modeling studies is detected in all computed velocity fields the cell in the upper 1000 m layer exhibits transports of 3 to 4 sv that are only slightly smaller than the model transports the cell is centered at approximately 36 n 10 w is elongated zonally and extends to 15 w westwards wind driven sverdrup transport and plume dynamics are both suggested to play a role in the generation of the cyclonic cell but the relative contribution of these effects is yet to be clarified the core of the recirculation appears compact and the magnitude of the cell fades westwards much faster than predicted by the theoretical and modeling studies considered

seasonal and interannual variability of the surface circulation in the eastern gulf of cadiz sw iberia 1 an 11 year 1996 2007 time series of current meter observations representative of the open sea circulation a 4 year 2001 2005 time series of current meter records over the continental shelf and in situ data during different seasons have been compared in order to study the seasonal and interannual variability of the surface circulation in the eastern gulf of cadiz the open sea velocity observations indicate southeastward flow along the northern continental slope of the gulf of cadiz compatible with anticyclonic circulation during most of the year and more intense during summer months flow reversals northwestward circulation at seasonal time scales in late autumn and early winter preferably december and january are a rather recurrent feature with variable intensity depending on the year anticyclonic circulation is associated with westerlies whereas flow reversals usually take place under easterly episodes suggesting wind driven circulation negative north atlantic oscillation indices indicative of southward displacement of the azores high are also linked to the reversals changes in this mainly wind driven large scale surface circulation are echoed by the shelf circulation the coastal countercurrent that closes the mesoscale cyclonic cell over the eastern shelf in spring summer upwelling season is replaced by and eastward current in autumn and winter

equilibrium structure and dynamics of the california current system this paper addresses the structure and dynamical mechanisms of regional and mesoscale physical variability in the subtropical northeast pacific ocean using the regional oceanic modeling system roms the model is configured with a u s west coast domain that spans the california current system ccs with a mesoscale horizontal resolution up to as fine as 3 5 km its mean seasonal forcing is by momentum heat and water fluxes at the surface and adaptive nudging to gyre scale fields at the open water boundaries its equilibrium solutions show realistic mean and seasonal states and vigorous mesoscale eddies fronts and filaments the level of eddy kinetic energy eke in the model is comparable to drifter and altimeter estimates in the solutions with sufficiently fine resolution because the model lacks nonseasonal transient forcing the authors conclude that the dominant mesoscale variability in the ccs is intrinsic rather than transiently forced the primary eddy generation mechanism is the baroclinic instability of upwelling alongshore currents there is progressive movement of meanseasonal currents and eddy energy offshore and downward into the oceanic interior in an annually recurrent cycle the associated offshore eddy heat fluxes provide the principal balance against nearshore cooling by mean ekman transport and upwelling the currents are highly nonuniform along the coast with important influences by capes and ridges in both maintaining mean standing eddies and launching transient filaments and fronts

meddy dynamics and interaction with neighboring eddies southwest of portugal observations and modeling 1 during the semane 2000 experiment southwest of portugal two meddies were found in near contact these meddies had hydrological radii of about 20 and 30 km thickness of 900 m maximum temperatures of 12 45 c and 13 45 c and maximum salinities of 36 52 and 36 78 the smaller meddy with more pronounced thermohaline anomalies was clearly double cored at 750 and 1300 m depths while the wider one was more diffuse and more homogeneous the associated geostrophic velocities referenced at 2000 m locally reached 0 5 m s in the smaller meddy and 0 2 m s in the wider one three rafos floats and two deep drogued surface drifters seeded in the two meddies rapidly gathered in the more intense meddy this meddy trajectory revealed by the float motion was first eastward then southward maps of sea level anomaly indicate that this motion did not correspond to the long term evolution of the initial positive sea level anomaly signature of the meddies and that neighboring cyclones must have played a role in the meddy evolution to determine the role of each eddy in the observed evolution several scenarios were studied with a three layer quasi geostrophic numerical model the interaction of two meddies in isolation did not result in the observed meddy trajectories on the long term the interaction of these two meddies with successive neighboring cyclones provided a more realistic trajectory of the meddy containing the floats

momentum and energy balance of the mediterranean outflow field data taken in the gulf of cadiz have been analyzed to describe some aspects of the momentum and energy balance of the mediterranean outflow a crucial component of the momentum balance is the total stress entrainment stress and bottom drag which has been estimated from a form of the bernoulli function evaluated from density and current observations for the first 60 km west of the camarinal sill the outflow was confined within a narrow channel on the continental shelf at about 70 km downstream the outflow crossed over the shelf slope break and began to descend the continental slope the buoyancy force increased substantially and the outflow underwent a geostrophic adjustment albeit one heavily influenced by mixing and dissipation the current direction turned 90 degrees to the right at a near inertial rate in this region the estimated geostrophic velocity greatly underestimated the actual current and the estimated curvature rossby number was about 0 5 current speeds were in excess of 1ms 2 1 and the total stress was as large as 5 pa the entrainment stress estimated independently from property fluxes reached a maximum of about 1 pa or considerably smaller than the inferred bottom stress by about 130 km downstream the current was aligned approximately along the local topography the current amplitude and the estimated stress were then much less about 0 3 m s21 and 0 3 pa the entrainment stress was also very small in this region well downstream of the strait this slightly damped geostrophic flow continued on to cape st vincent where the outflow began to separate from the bottom bottom stress thus appears to be a crucial element in the dynamics of the mediterranean outflow allowing or causing the outflow to descend more than a kilometer into the north atlantic in the regions of strongest bottom stress the inferred drag coefficient was about 2 2 12 3 10 23 depending upon which outflow speed is used in the usual quadratic form entrainment stress was small by comparison to the bottom stress but the entrainment effect upon the density anomaly was crucial in eroding the density anomaly of the outflow the observed entrainment rate appears to follow roughly a critical internal froude number function

the azores current system from a meridional section at 24 5 w 1 high spatial resolution hydrographic data including lowered acoustic doppler current profiler ladcp measurements were acquired along a meridional section at 24 5 w in october 2009 the data are analyzed in detail with the purpose of definitively defining and quantifying the zonal azores current system the azores current and azores countercurrent are delimited each extending meridionally for 110 km the azores current is located between 33 5 n and 34 5 n flanked to the north by the azores countercurrent 35 25 36 25 n vertically both currents reach the n 27 975 kg m 3 level 2000 m depth their mass transports ranging across thermocline as well as intermediate layers the azores current transports 13 9 sv 1 sv 106 m3 s 1 109 kg s 1 eastward with its maximum associated with the azores front 33 75 n the azores countercurrent flows below the surface transporting 5 5 sv westward this contributes to a net eastward flow of 8 4 sv across the section at intermediate layers the azores countercurrent transports mixed mediterranean water to the west and the azores current transports mixed sub arctic intermediate water to the east shipboard adcp and satellite derived geostrophic velocity are used to confirm the transports revealed by the hydrographic data

lagrangian observations of meddy formation during a mediterranean undercurrent seeding experiment mediterranean eddies meddies play an important role in maintaining the temperature and salinity distributions in the north atlantic but relatively little is known about their early life histories including where how often and by what mechanism they form a major field program called a mediterranean undercurrent seeding experiment has been carried out to directly observe meddy formation and the spreading pathways of mediterranean water into the north atlantic between may 1993 and march 1994 49 rafos floats were deployed sequentially in the mediterranean undercurrent south of portugal and tracked acoustically for up to 11 months the float deployments were accompanied by high resolution xbt sections across the undercurrent nine meddy formation events were observed in the float trajectories six near cape st vincent at the southwestern corner of the iberian peninsula and three near the estremadura promontory along the western portuguese continental slope meddy formation thus occurs where the continental slope turns sharply to the right when facing in the downstream direction of the undercurrent after conditionally sampling the float dataset to identify floats that were well seeded in the undercurrent the authors have estimated a meddy formation rate of 15 20 meddies per year the timescale for meddy formation at cape st vincent was found to be 3 7 days shorter than previous estimates based on the volume of larger meddies meddies were observed to form most frequently when the speed of the mediterranean undercurrent was relatively fast the meddy formation process at cape st vincent resembles the conceptual model of e a d asaro whereby anticyclonically rotating eddies are formed by separation of a frictional boundary layer with negative relative vorticity at a sharp corner comparison of the relative vorticity in the anticyclonic shear zone of the undercurrent and that of the newly formed meddies shows that much of the anticyclonic relative vorticity in meddies can be accounted for by the horizontal shear in the undercurrent this confirms earlier work suggesting that the classical mechanism for the generation of submesoscale coherent vortices by collapse and geostrophic adjustment of a weakly stratified fluid injected into a stratified ocean may not be the principle mechanism at work in the formation of meddies at cape st vincent

water mass circulation on the continental shelf of the gulf of cadiz acoustic doppler current profiler data collected during three successive surveys in the gulf of cadiz in may june 2001 have been used to analyse the surface circulation on the continental shelves of the gulf of cadiz and how this circulation matches the circulation in the ocean side of the gulf the wider and larger eastern continental shelf holds a cyclonic circulation bounded at the south by a shelf break jet that is identified with the huelva front the coastal current that closes the gyre at the north is identified with the warm counterflow mentioned in the literature under westerly winds this counter current recirculates toward the east while recent upwelled water near cape santa maria is advected downstream by the shelf break jet leaving the cold signature at the surface that has been identified historically with the huelva front under easterlies part of the coastal counterflow invades the western continental shelf while the remaining recirculates eastward to close the cyclonic cell the western continental shelf and slope is occupied by a larger scale cyclonic eddy that extends into the deep ocean this eddy has vertical length scale of hundreds of metres and is linked to the general wind forcing in the area both cyclonic structures are bounded at the south by a jet that enters in the gulf of cadiz moving around the second eddy and eastward to feed the atlantic inflow through the strait of gibraltar r 2006 elsevier ltd all rights reserved

eddy generation in the mediterranean undercurrent abstract in the framework of the european union mast iii project canary islands gibraltar azores observations 24 rafos floats were deployed in the mediterranean water mw undercurrent off south portugal between september 1997 and september 1998 a preliminary analysis of this lagrangian approach complemented with xbt and current meter data show some of the major aspects of the flow associated with the undercurrent as well as associated eddy activity floats that stayed in the undercurrent featured a downstream deceleration and a steering by bottom topography three meddy formations at cape st vincent could be isolated from the float data the dynamical coupling of meddies and cyclones was observed for a considerable period of time the generation of two dipolar structures in the portimao canyon region also was observed with the float data a major bathymetric relief gorringe bank was not only an important constraint to the eddy trajectories and of the flow at the mw levels but also a site for meddy formation

seasonal variability of the canary current a numerical study 1 a high resolution numerical model study of the canary basin in the northeast subtropical atlantic ocean is presented a long term climatological solution from the regional oceanic modeling system roms reveals mesoscale variability associated with the azores and canary current systems the northwest african coastal upwelling and the canary island archipelago the primary result concerns the canary current canc which in the solution transports 3 sv southward in line with observations the simulated canc has a well defined path with pronounced seasonal variability this variability is shown to be mediated by the westward passage of two large annually excited counterrotating anomalous structures that originate at the african coast the anomalies have a sea surface expression permitting their validation using altimetry and travel at the phase speed of baroclinic planetary rossby waves the role of nearshore wind stress curl variability as a generating mechanism for the anomalies is confirmed through a sensitivity experiment forced by low resolution winds the resulting circulation is weak in comparison to the base run but the propagating anomalies are still discernible so we cannot discount a further role in their generation being played by annual reversals of the large scale boundary flow that are known to occur along the african margin an additional sensitivity experiment where the azores current is removed by closing the strait of gibraltar presents the same anomalies and canc behavior as the base run suggesting that the canc is rather insensitive to upstream variability from the azores current

the mediterranean outflow splitting a comparison between theoretical models and canigo data abstract the mediterranean outflow in the atlantic is vertically subdivided into two main cores that are identified by temperature and salinity maxima hydrological data collected west of the strait of gibraltar and off the south and south west coasts of portugal in september 1997 have been used in two different models to shed some light on the mechanisms that cause a splitting of the mediterranean outflow these models are i a steady one dimensional streamtube model and ii a local time dependent model that includes cross stream variations the streamtube model applied at the northern respectively the southern part of the outflow appears capable of reproducing the observed density difference between the two cores the vertical separation however was underestimated the results from the local model suggest that a bump in the bottom topography may be a determining factor for the splitting tendency of the flow

impact origin of the vesta family the compelling petrographic link consolmagno and drake 1977 gaffey 1983 between basaltic achondrite meteorites and the 530 km diameter asteroid 4 vesta has been tempered by a perceived difficulty in launching rocks from this asteroid s surface at speeds sufficient to bring them to earth wasson and wetherill 1979 without obliterating vesta s signature crust i address this impasse in response to recent imaging zellner et al 1996 dumas and hainaut 1996 of a 450 km impact basin across vesta s southern hemisphere thomas et al 1997 and model the basin forming collision using a detailed two dimensional hydrocode with brittle fracture including self gravitational compression cf asphaug and melosh 1993 a 42 km diameter asteroid striking vesta s basaltic crust atop a denser mantle and iron core at 5 4 km s launches multikilometer fragments up to 600 m s without inverting distal stratigraphy according to the code this modeling together with collisional dynamical rheological and exposure age timescales marzari et al 1996 welten et al 1996 and observations of v type asteroids binzel and xu 1993 suggests a recent 1 ga impact origin for the vesta family and a possible vesta origin for earth approaching v type asteroids cruik shank et al 1991

geologic mapping of vesta from 1994 hubble space telescope images we utilize the 56 images of asteroid 4 vesta obtained through four mineralogically diagnostic filters by the hubble space telescope zellneret al 1997 icarus to construct a geologic map vesta s surface is found to be geologically diverse and to be dichotomous at a hemispheric scale the eastern hemisphere longitude definition from thomaset al 1997 icarus is dominated by units interpreted to be impact excavated plutonic material composed of magnesium rich and calcium poor pyroxene the mineralogy of this region is most analogous to diogenite meteorites several eastern hemisphere units which have the deepest and broadest 1 m absorption bands may contain a substantial olivine component the locations of these units are consistent with a previous map based on rotationally resolved groundbased spectroscopy gaffey 1997 icarus the western hemisphere is dominated by units interpreted to consist of a single component of iron rich and relatively calcium rich pyroxene analogous to surface basalts such as eucrite meteorites we investigate the spectral properties of 20 representative surface regions and find a correlation between the 1 m absorption band depth and albedo the units with lower albedos have shallower band depths such a relation could arise from differences in lithologies differences in surface particle sizes or from a weathering effect which decreases albedo and band depth over time because of vesta s geologic diversity and hemispheric dichotomy it is apparent that any major impact events such as those possibly related to the formation of the vesta family binzel and xu 1993 science260 186 191 did not globally resurface the planet the spectral evidence for remnants of a basaltic crust implies that the oldest units on the surface date back to the time of their emplacement most likely 4 5 byr ago if a weathering process exists which alters the albedo then the lowest albedo units such as the feature with the proposed name olbers most likely represent remnants of vesta s ancient basaltic crust

on the reasons for the formation and variability of the azores current abstract recent studies have shown that the formation of the well defined zonally oriented azores current may be the result of water mass transformation associated with the mediterranean outflow in the gulf of cadiz as the denser mediterranean water descends down the continental slope it entrains overlying north atlantic central water it is believed that the azores current then forms as part of the horizontal recirculating gyre generated through the plume mechanism in this study the authors further explore this hypothesis by performing a series of numerical experiments these experiments are based on a high resolution general circulation model that includes the mediterranean sea and that realistically simulates the water mass exchange through the strait of gibraltar and the transport and variability of the azores current the authors show that the divergence of the relative vorticity flux and the planetary vorticity flux associated with planetary waves are the main factors determining the variab

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

on the connection between the mediterranean outflow and the azores current as the salty and dense mediteranean overflow exits the strait of gibraltar and descends rapidly in the gulf of cadiz it entrains the fresher overlying subtropical atlantic water a minimal model is put forth in this study to show that the entrainment process associated with the mediterranean outflow in the gulf of cadiz can impact the upper ocean circulation in the subtropical north atlantic ocean and can be a fundamental factor in the establishment of the azores current two key simplifications are applied in the interest of producing an economical model that captures the dominant effects the first is to recognize that in a vertically asymmetric twolayer system a relatively shallow upper layer can be dynamically approximated as a single layer reduced gravity controlled barotropic system and the second is to apply quasigeostrophic dynamics such that the volume flux divergence effect associated with the entrainment is represented as a source of potential vorticity two sets of computations are presented within the 1 layer framework a primitive equation based computation which includes the divergent flow effects is first compared with the equivalent quasigeostrophic formulation the upper ocean cyclonic eddy generated by the loss of mass over a localized area elongates westward under the influence of the b effect until the flow encounters the western boundary in the steady state the circulation pattern consists of bidirectional zonal flows with a limited meridional extent eastward to the south of the sink and westward to the north of the sink the localized sink drives a horizontal circulation in the interior ocean whose strength is approximately an order of magnitude greater than the sink s strength it is demonstrated that the induced circulation in the far field from a localized sink is insensitive to the neglect of the divergent flow component a set of parameter sensitivity experiments is then undertaken with the quasigeostrophic model for an idealized midlatitude circulation driven both by wind forcing and thermohaline flow through the open southern and northern boundaries when a sink near the eastern boundary is superimposed on the idealized midlatitude circulation it is shown to alter significantly the upper ocean flow and induce an eastward zonal current which resembles the azores current in location and transport this mechanism also generates a westward current to the north of the sink location which could be associated with the azores countercurrent an extensive series of sensitivity experiments is conducted to determine the response of this current system to changes in the boundary layer processes sink strength sink distribution model resolution and wind forcing the magnitude of the current transports is found to be sensitive to the sink intensity and to its distance from the coastline

mixing and spreading of the mediterranean outflow abstract hydrographic and current profiler data taken during the 1988 gulf of cadiz expedition have been analyzed to diagnose the mixing spreading and descent of the mediterranean outflow the s properties and the thickness and width of the outflow were similar to that seen in earlier surveys the transport of pure mediterranean water i e water with s 38 4 psu was estimated to be about 0 4 106 m3 s 1 which is lower than historical estimates most of which were indirect but comparable to other recent estimates made from direct velocity observations the outflow transport estimated at the west end of the strait of gibraltar was about 0 7 106 m3 s 1 of mixed water and the transport increased to about 1 9 106 m3 s 1 within the eastern gulf of cadiz this increase in transport occurred by entrainment of fresher north atlantic central water and the salinity anomaly of the outflow was consequently reduced the velocity weighted salinity decreased to 36 7 psu within 60 km of the strait and decre

late quaternary multi genetic processes and products on the northern gulf of cadiz upper continental slope sw iberian peninsula abstract on continental margins the upper slope to shelf break environment forms a critical region where sediment supply hydrographic activity and gravitational processes determine how and when sediments are partitioned between the shallow and deep marine realm on the sw iberian margin relatively few studies have addressed the dynamics of this region although it holds key information regarding the link between the sedimentary evolution of the continental shelf and the contourite depositional system on the middle slope this work therefore presents a high resolution analysis of the morphological and stratigraphic expressions of late quaternary dominantly last glacial and present day interglacial sedimentary processes on the upper slope and shelf margin sector between 7 and 7 30 w the integration of seismic bathymetric and hydrographic data reveals the presence of alongslope processes and products a bottom current related plastered drift moat erosional surface and terrace an internal wave tide controlled sediment wave field downslope gravitational processes and products an upper slope shelf margin valley system slumps debrites gullies neotectonic elements diapirs and fluid flow features pockmarks bright spots the spatial distribution of these features indicates that the study area becomes increasingly alongslope dominated towards the w and oppositely more downslope dominated towards the e because sediment supply to the latter area is enhanced under the dominant eastward dispersal of fluvially supplied sediments on the shelf in addition glacial interglacial variations in the amount of sediments supplied to the shelf edge and the intensity of oceanographic processes in the study area also generate a distinct temporal variability with glacial and interglacial intervals respectively recording principally downslope and alongslope controlled morphological elements finally regardless of these overall spatial and temporal patterns diapirism and fluid flow are inferred to locally destabilize sediments and induce small scale mass wasting in the study area these findings are not only relevant to the northern gulf of cadiz but also to the general understanding of sedimentary dynamics and controls in mixed downslope and alongslope controlled upper slope to shelf margin settings worldwide

quasi synoptic transport budgets and water mass transformation in the azores gibraltar strait region during summer 2009 abstract we describe the circulation patterns in the azores gibraltar strait region north eastern atlantic during the 2009 caibox cruise on the basis of hydrographic and direct current velocity measurements this study offers new data for a region where importation of central waters subpolar and subtropical modes of eastern north atlantic central water and exports of mediterranean water are strongly related to large scale dynamics in the north atlantic ocean azores current mediterranean water system the description is backed up quantitatively by the results of a box inverse model which was used to obtain absolute water mass transport values consistent with thermal wind equations and with conservation of volume salt and heat the contributions of water masses were determined in an extended optimum multiparameter analysis from a quasi synoptic point of view providing detail in addition to volume salt and heat transport the surface subsurface large scale current system in the region consists of the azores current 13 1 2 5 sverdrup sv 1 sv 10 6 m 3 s 1 the azores counter current 5 2 2 1 sv the portugal current 4 5 1 4 sv and the canary current 7 1 1 1 sv broadly speaking central waters are imported into the caibox region at a rate of 1 6 0 9 sv and mediterranean water is exported at a rate of 1 5 0 4 sv the downwelling of central waters west of gibraltar strait was quantified at 1 1 sv not all this volume participates in mw formation but 0 8 sv of entrained central waters of which 0 5 sv are from central waters of subpolar origin and 0 3 sv from subtropical central waters of the 4 9 sv of subtropical central waters advected by the azores current about 0 7 sv would reach the gulf of cadiz region either to take part in central water entrainment or to flow across the gibraltar strait as part of the atlantic inflow to the mediterranean sea

is the south pacific helium 3 plume dynamically active it is suggested that the hydrothermal vents of the south pacific rise produce a beta governed circulation at mid depth and that perhaps the associated plume of excess3he lupton and craig 1 points westward because of the dynamics of this circulation rather than as a passive tracer

paleoceanography of the atlantic mediterranean exchange overview and first quantitative assessment of climatic forcing 1 the mediterranean sea provides a major route for heat and freshwater loss from the north atlantic and thus is an important cause of the high density of atlantic waters in addition to the traditional view that loss of fresh water via the mediterranean enhances the general salinity of the north atlantic and the interior of the eastern north atlantic in particular it should be noted that mediterranean water outflowing at gibraltar is in fact cooler than compensating inflowing water the consequence is that the mediterranean is also a region of heat loss from the atlantic and contributes to its large scale cooling uniquely this system can be understood physically via the constraints placed on it by a single hydraulic structure the gibraltar exchange here we review the existing knowledge about the physical structure of the gibraltar exchange today and the evidential basis for arguments that it has been different in the past using a series of quantitative experiments we then test prevailing concepts regarding the potential causes of these past changes we find that 1 changes in the vertical position of the plume of mediterranean water in the atlantic are controlled by the vertical density structure of the atlantic 2 a prominent early holocene contourite gap within the gulf of cadiz is a response to reduced buoyancy loss in the eastern mediterranean during the time of sapropel 1 deposition 3 changes in buoyancy loss from the mediterranean during mis3 caused changes in the bottom velocity field in the gulf of cadiz but we note that the likely cause is reduced freshwater loss and not enhanced heat loss and 4 strong exchange at gibraltar during atlantic freshening phases implies that the gibraltar exchange provides a strong negative feedback to reduced atlantic meridional overturning given the very counterintuitive way in which the strait of gibraltar system behaves we recommend that without quantitative supporting work qualitative interpretations of how the system has responded to past external forcing are unlikely to be robust

circulation on the northwestern iberian margin vertical structure and seasonality of the alongshore flows abstract we describe the seasonal cycle of the alongshore flows on the northwestern iberian margin and explain what are the important mechanisms forcing the system we used a 20 year model simulation at 2 3 km horizontal resolution with realistic atmospheric forcing and covering the whole western iberian margin the model results are compared with satellite data with data measured at two moored buoys and with a compilation of current meter data available for the study region we show that currents over the slope are divided in three different cores the iberian poleward current ipc occupying the top 350 m a deeper core at mediterranean water levels 600 1200 m and in between the two an equatorward core centered just beneath the ipc core the upper slope countercurrent uscc the ipc is present almost yearlong including in summer months when it is close to the shelf break and topped by the equatorward upwelling jet after september the ipc intensifies and its core surfaces heat and salinity budgets on the shelf and slope are dominated by advection confirming the important role of the ipc in driving the temperature and salinity seasonal cycles analysis of the seasonal cycle of the barotropic vorticity equation on the slope shows that the main forcing mechanism of northward flows is the joint effect of baroclinicity and relief jebar whose contribution is higher in summer than in winter in december and january when the ipc is stronger and surface intensified the main contribution is from southerly winds the cross shore analysis of these terms shows that jebar decreases substantially at the core of the ipc because as advection terms become important the northward density flux diminishes the local meridional density gradients resulting in the decrease of jebar in the months of strong ipc

mesoscale patterns in the cape sao vicente iberian peninsula upwelling region 1 the coastal upwelling region near cape sao vicente the southwestern tip of the iberian peninsula where the southern zonal coast meets the meridional western coast was studied using over 1200 advanced very high resolution radiometer avhrr satellite images of sea surface temperature and time series of sea level height wind velocities and nearshore sea surface temperature recorded at coastal sites within 200 km of the cape summer upwelling is more intense and persistent off the western coast than off the southern coast where a recurrent warm coastal countercurrent flows westward and at times turns northward along the western coast after reaching the cape in this region the equatorward current jet of cold water upwelled off the western coast is no longer bounded by a coast three preferred directions for the spreading of this water are identified the most persistent is eastward along the southern shelf break and slope possibly merging with waters previously upwelled locally which becomes separated from shore by the coastal progression of the warmer counterflow the second preferred direction results in the southward development of a cold filament feature fed by cold waters upwelled farther north and represents the southernmost extent of the intense coastal upwelling jet which overshoots the cape the least frequent feature to develop is a cold filament that grows westward at the latitude of the cape appearing to result from the meandering of the equatorward jet the coastal countercurrent is seen to interact with the equatorward jet at times of relaxation not only by separating the cold upwelled water from the coast but when it is energetic enough breaking westward offshore through the equatorward cold flow and separating the eastward and southward cold features from the upcoast cold waters empirical evidence shows the presence of an alongshore pressure gradient stronger in summer driving the coastal progression of the warm counterflow wind forcing plays an important role in the circulation by augmenting or diminishing the effect of the preexisting alongshore pressure gradients the extent of the progression of the warm coastal countercurrent along the southern and western coast is dictated by the the strength of the upwelling favorable wind stress which is able to balance and reverse the alongshore flow at least in the upper layers

tracking the mediterranean outflow in the gulf of cadiz abstract the mediterranean water leaves the western end of the strait of gibraltar as a bottom wedge of salty and warm waters flowing down the continental slope the salinity of the onset mediterranean outflow water mow is so high that leads to water much denser initially in excess of 1 5 kg m 3 than the overlying central waters during much of its initial descent the mow retains large salinity anomalies causing density anomalies that induce its gravity current character and relatively high westward speeds causing a substantial coriolis force over long portions of its course we use hydrographic data from six cruises a total of 1176 stations plus velocity data from two cruises together with high resolution bathymetric data to track the preferential mow pathways from the strait of gibraltar into the western gulf of cadiz and to examine the relation of these pathways to the bottom topography a methodology for tributary systems in drainage basins modified to account for the coriolis force emphasizes the good agreement between the observed trajectories and those expected from a topographically constrained flow both contour avenues and cross slope channels are important and have complementary roles steering the mow along the upper and middle continental slope before discharging as a neutrally buoyant flow into the western gulf of cadiz our results show that the interaction between bottom flow and topography sets the path and final equilibrium depths of the modern mow furthermore they support the hypothesis that as a result of the high erosive power of the bottom flow and changes in bottom water speed the mow pathways and mixing rates have changed in the geological past

average circulation seasonal cycle and mesoscale dynamics of the peru current system a modeling approach h isolines the pccc appears to be directly forced by the cyclonic wind stress curl the model is able to produce the upwelling front the cold water tongue which extends toward the equator and the equatorial front as described in the literature model seasonal changes in sst and ssh are compared to measurements for the central pcs model eke is 10 to 30 lower than the observations the model eddy diameters follow a strong equatorward increase the injection length scales derived from the energy spectra strongly correlate to the rossby radius of deformation confirming the predominant role of baroclinic instability at 3 s the model solution appears to switch from a turbulent oceanic regime to an equatorial regime dominated by zonal currents

the upper oceanic response to overflows a mechanism for the azores current abstract the oceanic response to overflows is explored using a two layer isopycnal model overflows enter the open ocean as dense gravity currents that flow along and down the continental slope while descending the slope overflows typically double their volume transport by entraining upper oceanic water the upper oceanic layer must balance this loss of mass and the resulting convergent flow produces significant vortex stretching overflows thus represent an intense and localized mass and vorticity forcing for the upper ocean in this study simulations show that the upper ocean responds to the overflow induced forcing by establishing topographic plumes that are aligned more or less along isobaths and that have a transport that is typically a few times larger than that of the overflows for the topographic plume driven by the mediterranean overflow the occurrence of eddies near cape st vincent portugal allows the topographic plume to flow across isobaths the modeled topographic plume circu

the near neutral marine atmospheric boundary layer with no surface shearing stress a case study abstract data from a marine coastal experiment over the baltic sea comprising airborne measurements and mast measurements have been used to highlight the turbulence dynamics of a case with most unusual flow characteristics the boundary layer had a depth of about 1200 m the thermal stratification was near neutral with small positive heat flux below 300 m and equally small negative heat flux above the entire situation lasted about 6 hours turbulence levels were unexpectedly high in view of the fact that momentum flux was negligible in fact positive in the layers near the surface and buoyancy flux was also small the turbulence was found to scale with the height of the boundary layer giving rise to velocity spectra having the shape of those characteristic of convectively mixed boundary layers analysis of the turbulence budget for the entire planetary boundary layer pbl revealed that energy was produced from shear instability in the uppermost parts of the pbl and was distributed to the lower par