lateral and vertical variations in the wind driven circulation in long shallow lakes solutions are derived for the steady state lateral and vertical variations of horizontal velocity in a long shallow wind driven basin using both linear viscous and mixing length assumptions the bathymetry is represented by a depth distribution function which describes the occurrence of different depths over a cross section of the basin it is shown that the relative importance of the lateral depth integrated and overturning vertically varying circulations is dependent mainly on the bottom roughness and on the shape of the depth distribution for natural bathymetries the lateral circulation is generally dominant and becomes increasingly so as the bottom roughness decreases or as the depth distribution becomes broader it is found that natural bathymetries can be characterized in this context by a single dimensionless number related to the moments of the depth distribution

wind driven subinertial circulation inside a semienclosed bay in the gulf of california abstractmoored current and pressure observations were obtained at bahia concepcion a semienclosed bay located on the eastern side of the baja california peninsula in mexico to describe the wind driven subinertial circulation in winter and early spring the bay is well mixed and forced by persistent winds toward the southeast aligned with the central axis the authors observations show that the sea surface rises downwind in response to wind stress and that there exists a crosswind drift at the surface that is consistent with ekman dynamics this feature is typical of a bay that is deeper than one ekman depth and hence affected by the rotation of the earth there is a persistent along bay circulation toward the end of the bay along its western side with return flow on the opposite side drifters released near the surface across a transect move westward and downwind toward the closed end where they recirculate cyclonically wind driven linear theoretical models successfully predict the observed cross b

impact of restriction of the atlantic mediterranean gateway on the mediterranean outflow water and eastern atlantic circulation during the messinian 1 messinian foraminiferal stable oxygen and carbon isotopes of the montemayor 1 core guadalquivir basin sw spain have been investigated this record is exceptional to study the mediterranean outflow water mow impact on the atlantic meridional overturning circulation amoc and global climate during the messinian because the core is near the guadalhorce corridor the last betic gateway to be closed during the early messinian our results allow dating accurately its closure at 6 18 ma constant benthic 18o values high difference between benthic and planktonic 18o and low sedimentation rates before 6 18 ma indicate the presence of a two layer water column with bottom winnowing due to an enhanced mediterranean outflow current the enhanced contribution of dense mow to the north atlantic ocean likely fostered the formation of north atlantic deep water nadw after 6 18 ma benthic 18o values parallel that of the global glacioeustatic curve the difference between benthic and planktonic 18o is low and sedimentation rates considerably increased this indicates a good vertical mixing of the water column interruption of the mow and a dominant glacioeustatic control on the isotopic signatures according to the role of mow in the modern atlantic thermohaline circulation the reduction of the mow after the closure of the guadalhorce corridor might have resulted in a decreased nadw formation rate between 6 0 and 5 5 ma weakening the amoc and promoting northern hemisphere cooling after the gibraltar strait opening the restoration of the mow and related salt export from the mediterranean could have promoted an enhanced nadw formation

influence of the atlantic inflow and mediterranean outflow currents on late quaternary sedimentary facies of the gulf of cadiz continental margin abstract the late quaternary pattern of sedimentary facies on the spanish gulf of cadiz continental shelf results from an interaction between a number of controlling factors that are dominated by the atlantic inflow currents flowing southeastward across the cadiz shelf toward the strait of gibraltar an inner shelf shoreface sand facies formed by shoaling waves is modified by the inflow currents to form a belt of sand dunes at 10 20 m that extends deeper and obliquely down paleo valleys as a result of southward down valley flow a mid shelf holocene mud facies progrades offshore from river mouth sources but atlantic inflow currents cause extensive progradation along shelf toward the southeast increased inflow current speeds near the strait of gibraltar and the strong mediterranean outflow currents there result in lack of mud deposition and development of a reworked transgressive sand dune facies across the entire southernmost shelf at the outer shelf edge and underlying the mid shelf mud and inner shelf sand facies is a late pleistocene to holocene transgressive sand sheet formed by the eustatic shoreline advance the late quaternary pattern of contourite deposits on the spanish gulf of cadiz continental slope results from an interaction between linear diapiric ridges that are oblique to slope contours and the mediterranean outflow current flowing northwestward parallel to the slope contours and down valleys between the ridges coincident with the northwestward decrease in outflow current speeds from the strait there is the following northwestward gradation of contourite sediment facies 1 upper slope sand to silt bed facies 2 sand dune facies on the upstream mid slope terrace 3 large mud wave facies on the lower slope 4 sediment drift facies banked against the diapiric ridges and 5 valley facies between the ridges the southeastern sediment drift facies closest to gibraltar contains medium fine sand beds interbedded with mud the adjacent valley floor facies is composed of gravelly shelly coarse to medium sand lags and large sand dunes on the valley margins by comparison the northwestern drift contains coarse silt interbeds and the adjacent valley floors exhibit small to medium sand dunes of fine sand because of the complex pattern of contour parallel and valley perpendicular flow paths of the mediterranean outflow current the larger scale bedforms and coarser grained sediment of valley facies trend perpendicular to the smaller scale bedforms and finer grained contourite deposits of adjacent sediment drift facies radiocarbon ages verify that the inner shelf shoreface sand facies sedimentation rate 7 1 cm kyr mid shelf mud facies maximum rate 234 cm kyr and surface sandy contourite layer of 0 2 1 2 m thickness on the cadiz slope 1 12 cm kyr have deposited during holocene time when high sea level results in maximum water depth over the gibraltar sill and full development of the atlantic inflow and mediterranean outflow currents the transgressive sand sheet of the shelf and the mud layer underlying the surface contourite sand sheet of the slope correlate respectively with the late pleistocene sea level lowstand and apparent weak mediterranean outflow current

emplacement of a passive margin evaporitic allochthon in the betic cordillera of spain the triassic section of the external domain of the betic cordillera is rootless and thus allochthonous the frontal accretionary wedge of the guadalquivir allochthon consists dominantly of triassic evaporites and red beds forming a melange with upper cretaceous paleogene deep water sedimentary rocks throughout the unit jurassic rocks are absent it is here proposed that the widespread triassic evaporites of the guadalquivir allochthon were originally emplaced as gravitational allochthonous masses in a passive margin setting much like the widespread allochthonous salt of the texas louisiana gulf of mexico thus on the betic passive margin allochthonous evaporites were first emplaced during the late cretaceous paleogene later during neogene time these evaporites were overthrusted as an accretionary wedge to form the guadalquivir allochthon a schematic reconstructed position of the guadalquivir allochthon places the original passive margin allochthon in its continental slope setting

on the nature of transverse variability in a coastal plain estuary even though estuarine processes are inherently three dimensional most of the previous studies have focused primarily on the axial longitudinal and vertical variabilities recent surveys in the lower delaware bay indicate the presence of significant transverse variability in the salinity distribution and residual circulation pattern conceptual models are developed to examine the mechanisms which might explain the observed transverse structure results indicate that both the gravitational effect and wind forcing are capable of generating substantial transverse structure in drowned river valley estuaries with triangular cross sections

lateral circulation and sediment transport driven by axial winds in an idealized partially mixed estuary 1 a 3d hydrodynamic model roms is used to investigate lateral circulation in a partially mixed estuary driven by axial wind events and to explore the associated transport of sediments the channel is straight with a triangular cross section the model results suggest that driving mechanisms for lateral circulation during axial wind events are different between stratified and unstratified conditions when the water column is largely unstratified rotational effects do not drive significant lateral circulation instead differential advection of the axial salinity gradient by wind driven axial flow is responsible for regulating the lateral salinity gradients that in turn drive bottom divergent convergent lateral circulation during down up estuary winds from the subtidal lateral salt balance it is found that the development of lateral salinity gradient by wind induced differential advection is largely counterbalanced by the advection of salt by lateral circulation itself when the water column is stratified the lateral flow and salinity structures below the halocline closely resemble those driven by boundary mixing and rotational effects are important lateral sediment flux and the event integrated sediment transport are from channel to shoals during down estuary winds but reversed for up estuary winds potential impacts of wind generated waves on lateral sediment transport are evaluated with two cases representing event conditions typical of upper chesapeake bay accounting for wind wave effects results in an order of magnitude increase in lateral sediment fluxes because of greater bottom stresses and sediment resuspension

potential geologic hazards on the eastern gulf of cadiz slope sw spain abstract geologic hazards resulting from sedimentary oceanographic and tectonic processes affect more than one third of the offshore gulf of cadiz and are identified by interpreting high resolution seismic profiles and sonographs hazards of sedimentary origin include the occurrence of slope instability processes in the form of single or multiple slumps occupying up to 147 km 2 mainly concentrated in the steeper upper slope area besides the presence of steep slopes the triggering of submarine landslides is probably due to seismic activity and favoured by the presence of biogenic gas within the sediment gassy sediments and associated seafloor pockmarks cover more than 240 km 2 in the upper slope hazards from oceanographic processes result from the complex system of bottom currents created by the interaction of the strong mediterranean undercurrent and the rough seafloor physiography the local intensification of bottom currents is responsible for erosive processes along more than 1900 km 2 in the upper slope and in the canyons eroded in the central area of the slope undermining slopes and causing instability the strong bottom currents also create a mobile seafloor containing bedforms in an area of the gulf that extends more than 2500 km 2 mostly in the continental slope terraces hazards of tectonic origin are important because the gulf of cadiz straddles two major tectonic regions the azores gibraltar fracture zone and the betic range which results in diapir uplift over an area of more than 1000 km 2 and in active seismicity with earthquakes of moderate magnitude also tsunamis produced by strong earthquakes occur in the gulf of cadiz and are related to the tectonic activity along the azores gibraltar fracture zone

factors controlling late cenozoic continental margin growth from the ebro delta to the western mediterranean deep sea abstract the ebro continental margin sedimentation system originated with a messinian fluvial system this system eroded both a major subaerial canyon cutting the margin southeastward from the present ebro delta and an axial valley that drained northeastward down valencia trough post messinian submergence of this topography and the pliocene regime of high sea levels resulted in a marine hemipelagic drape over the margin late pliocene to pleistocene glacial climatic cycles drainagebasin deforestation and sea level lowstands combined to increase sediment supply cause the margin to prograde and create a regime of lowstand sediment gravity flows in the deeper margin the depositional patterns of regressive transgressive and highstand sea level regimes suggest that location of the sediment source near the present ebro delta throughout the late cenozoic southward current advection of sediment and greater subsidence in the southern margin combined to cause generally asymmetric progradation of the margin to the southeast thicker less stable deposits filling the messinian subaerial canyon underwent multiple retrograde failures eroded wide gullied canyons and formed unchanneled base of slope sediment aprons in the central margin area other margin areas to the north and south developed a series of channel levee complexes on the basin floor the formation of valencia valley over the messinian subaerial valley and earlier faults led to draining of about 20 of the ebro pleistocene sediment from channel levee complexes through the valley to prograde valencia fan as much as 500 km northeast of the margin thus the ebro margin has two growth directions mainly southeastward during higher sea levels and eastward to northeastward during lower sea levels the northeastward draining of turbidity currents has produced unusually thin and widely dispersed turbidite systems compared to those on ponded basin floors during the past few centuries man s impact has exceeded natural controls on ebro margin growth deforestation of the drainage basin more than doubled the normal holocene sediment supply and construction of dams then reduced the supply by 95 this reduction of the past 50 years has caused erosion of the delta and contamination of bottom sediment because normal holocene sediment discharge is not available to prograde the delta or help dilute pollutants

transverse structure of wind driven flow at the entrance to an estuary nansemond river 1 observations of current velocity profiles were combined with an analytical solution to study the transverse partition of the wind driven flow in an estuary the nansemond river which is a tributary of the james river in the chesapeake bay observations spanned two periods of nearly 3 months in autumn winter of 2003 2004 and spring summer 2004 the wind driven circulation consisted of downwind flow over the shoal and upwind flow in the channel at the entrance to the estuary this pattern developed mainly with landward winds and provided observational evidence that sustains analytical and numerical model results the transverse structure of the flow showed synoptic temporal variability 3 7 days which corresponded to the variability of winds and sea level synoptic variability seemed to be more influential in autumn winter than in springsummer however variability of 1 2 days was persistent in both periods of observation also the transverse structure of the wind driven flows was linked to a counterclockwise recirculation pattern previously observed with survey data part of the flow going into the tributary over the shoal might recirculate and form or enhance the outflow in the channel as suggested by the temporal scale of the wind the recirculation might weaken or even reverse direction every 3 7 days at the entrance to the estuary further detailed studies are needed to better define the extent of this recirculation

late glacial to recent paleoenvironmental changes in the gulf of cadiz and formation of sandy contourite layers planktonic foraminifera and coccoliths were analyzed from six gravity cores obtained on a deep terrace located on the upper continental slope of the gulf of cadiz between 400 and 700 m water depth the lithology of these cores consists mainly of muds with some interbedded sandy or silty foraminifer rich layers that have been reported as contourites originated by the action of the mediterranean outflowing waters mow sweeping the sea bottom today after the last glacial characterized by muddy sedimentation sandy contourites start to deposit in the gulf of cadiz during the bolling allerod 14 11 14c kyr bp climatic optimum this trend was broken during the younger dryas 11 10 14c kyr bp and started again after the end of the younger dryas this pattern is recorded in most of the cores by a single sandy contourite layer formed during the first deglaciation stage bolling allerod time and a sandy contourite interval that initiates immediately after the end of the younger dryas during the second stage of the deglaciation and continues during the holocene the stratigraphy and climatic reconstruction was based on the evolution of the calcareous plankton assemblages during the last climatic transition from the last glacial to the recent holocene the sharp reduction of sinistral n pachyderma along with the reduction of g quinqueloba mark the base of bolling allerod time this is also related to a prominent peak of the subtropical species g sacculifer and g ruber the younger dryas is identified by a reduction in abundance of the subtropical species that again increase just after this period the second step of deglaciation is marked by a sharp decrease in the relative abundance of dextrally coiled n pachyderma in previous papers the sequence of sandy contourites has been related to sea level rise greater gibraltar sill depth and enhanced energy of the mow in this work we suggest that the individual sand layer episodes are condensed layers originating during times of rapid warming and relative sea level rise within the last deglaciation during these times the coastline migrated more rapidly landward and the terrigenous input decreased as it began to be trapped on land and on the shelf resulting in a major drop in sedimentation rate on the upper continental slope in times of low sedimentation rate the particles would have a longer residence time within the upper mixed layer of the near surface sediment and therefore the energy of currents would act longer producing a more efficient winnowing of the sediment at the same time more generations of benthic organisms would rework the mixed layer favoring this winnowing

an interpretation of a prominent magnetic anomaly near the boundary between the eurasian and african plates gulf of cadiz sw margin of iberia abstract the gulf of cadiz is located at the boundary between the eurasian and african plates in the southwestern margin of iberia and it straddles a place of major tectonic events since the mesozoic the gibraltar belt migrated westward into the gulf of cadiz during the miocene while a north south trending margin was built upon allochthonous formations at the western end of the betic rif orogen the geological setting of the gulf allows a study of both the mesozoic and cenozoic evolution of the contact between these two major plates this study reports a regional geophysical survey with an interpretation of the magnetic results using a 2d modelling constrained by recently acquired multichannel seismic profiling mcs and gravity data from the magnetic pattern the area can be subdivided into three sectors which may be the expression of different geological provinces in the eastern sector we find relatively small anomalies 50 nt interpreted as the magnetic expression of the morphological ridges and valleys intersecting the central gulf of cadiz in the southern sector where data are scarce we find a smooth magnetic zone with large wavelength anomalies the western sector dominated by the guadalquivir bank is where the largest magnetic anomalies are observed the guadalquivir bank is a structural high which represents the offshore extension of the hercynian iberian massif we have interpreted a large amplitude magnetic anomaly of more than 300 nt peak to peak with a very steep gradient trending northward to be caused by an intrusive material with an average estimated susceptibility distribution of 0 035 si from the model studies we believe that the magnetic source lies southwest of the guadalquivir bank and is mainly composed of crustal material the material rises up to 4 km depth and probably was uplifted prior to the initial opening extensional stages of the central north atlantic during the triassic

a 120 yr record of widespread contamination from mining of the iberian pyrite belt a metal enriched seawater plume entering the western mediterranean sea through the strait of gibraltar originates 300 km to the west in the rio tinto estuary of southwestern spain mining of rio tinto ore one of the largest metal rich sulfide deposits in the world started well before roman times contemporary rio tinto waters draining the region are highly acidic ph 2 5 with dissolved cadmium zinc and copper concentrations 10 5 10 6 times higher than in uncontaminated surface water of the gulf of cadiz two dated sediment cores from the spanish continental shelf show that metal inputs to the region increased with the onset of intensive mining activities during the second half of the 19th century although the impact of mining may have decreased over the past few decades the tinto river and estuary remain highly contaminated

iberian plate kinematics a jumping plate boundary between eurasia and africa the rotation of iberia and its relation to the formation of the pyrenees has been difficult to decipher because of the lack of detailed sea floor spreading data although several models have been proposed1 7 here we use detailed aeromagnetic measurements from the sea floor offshore of the grand banks of newfoundland to show that iberia moved as part of the african plate from late cretaceous to mid eocene time with a plate boundary extending westward from the bay of biscay when motion along this boundary ceased a boundary linking extension in the king s trough to compression along the pyrenees came into existence finally since the late oligocene iberia has been part of the eurasian plate with the boundary between eurasia and africa situated along the azores gibraltar fracture zone

wind modifications to density driven flows in semienclosed rotating basins abstract an analytical two dimensional model is used to describe wind induced modifications to density driven flows in a semienclosed rotating basin wind stress variations produce enhancement inversion or damping of density driven flows by altering the barotropic and baroclinic pressure gradients and by momentum transfer from wind drag the vertical structure of wind induced flows depends on h the nondimensional surface trapping layer where is the inverse of the ekman layer depth d and h is the maximum water depth for h 5 wind driven flow structures are similar to the ekman spiral for h 2 wind driven flows are unidirectional with depth the relative importance of density to wind forcing is evaluated with the wedderburn number w 1 h2d which depends on water density mean depth h a proxy of the baroclinic pressure gradient d and wind stress because d depends on and therefore on the eddy viscosity of water az wind speed and az both modify w moreover wind direction alters w by

new insights into upper mow variability over the last 150kyr from iodp 339 site u1386 in the gulf of cadiz the upper mediterranean outflow water mow paleo oceanographic history in the gulf of cadiz is poorly constrained due to the lack of high resolution records that pre date the last glaciation existing proxy records concentrate on mow variability along the middle slope of the gulf of cadiz here we present a continuous high resolution benthic foraminifera 18o record from the upper mow core at iodp expedition 339 site u1386 in the gulf of cadiz of the past 150 000 years based on 18o grain size and zr al variability comparison of our results with existing mediterranean sea md01 2472 md95 2043 open ocean lr04 and gulf of cadiz md99 2339 records we have gathered new insights into the evolution of the upper mow core on glacial interglacial timescales the influence of the upper mow at site u1386 was strongest during mis 5 and mis 1 similar 18o variability can be seen in the levantine intermediate water liw originating from the levantine basin of the eastern mediterranean sea we found clear indication for a vertical shift of the mow from the upper to the middle slope of the gulf of cadiz during sea level lowstands coinciding with mis 4 and mis 2 but also during mis 3 additionally our results indicate an increased upper mow flow correlated with heinrich events 7 to 10 and the younger dryas and also inversely relate to precession forced monsoonal freshwater inputs into the eastern mediterranean in the context of sapropel formation we could not find conclusive evidence of the proposed mow shutdown in our data

reversing water exchange patterns at the entrance to a semiarid coastal lagoon abstract water velocity and density profiles were obtained in late spring and late winter to document reversing mean circulation patterns at the entrance to a semiarid coastal lagoon the bay of guaymas in the gulf of california mexico the lagoon is shallow but the bathymetry at its entrance is similar to that of temperate estuaries with an asymmetrically positioned channel flanked by shoals in late spring the mean circulation at the entrance to the lagoon was driven by horizontal density gradients that arose from excess evaporation over precipitation in the area as evidenced by water density profiles the lagoon exported relatively warm 25 8 c and salty 36 2 water to the gulf of california through the channel this export was consistent with inverse estuarine circulation influenced by bathymetry in late winter the circulation at the entrance of the lagoon was mostly driven by wind stress that blew from the northwest roughly along the main axis of the lagoon relatively cool 16 0 c and less salty 35 1 water from the gulf of california was driven into the lagoon within the channel density gradients inside the lagoon seem to have played a secondary role in driving the circulation the late winter circulation was then estuarine like with outflow in the direction of the wind over the shallow areas and a compensatory inflow appearing in the channel as expected from theory of wind driven flow over bathymetry this estuarine like circulation developed despite the lack of measurable freshwater input to the lagoon and was the opposite to that observed in late spring these observations then document a reversal in water exchange patterns from season to season in a semiarid coastal lagoon the observations also constitute one of the few reported examples of flow over shoals driven in the same direction as the wind stress with a compensatory flow in the channel

late quaternary seismic facies of the gulf of cadiz spanish margin depositional processes influenced by sea level change and tectonic controls abstract seismic facies and quaternary depositional systems of the gulf of cadiz have been characterized by means of high resolution seismic profiles airguns geopulse and ore 3 5 khz a total of 11 pleistocene and two holocene sequences separated by type 1 or type 2 discontinuities were identified the age of the depositional sequences was determined based on foraminifera ages from boreholes and by correlation with seismic profiles of the slope areas with uniform deposition and without significant discontinuities these seismic units have been mapped throughout the margin allowing to establish the correlation with eustatic sea level curves and global climatic trends the distribution and geometry of the units reveals that most of the sedimentary record was developed during episodes of forced regression ten regressive periods corresponding to 5th order cycles arranged into 4th order were distinguished absolute water depths for the development of coastal deposits in each unit were calculated using depth from present day sea level corrected for tectonic subsidence in the area the model for the evolution of the depositional system of the gulf of cadiz continental margin highlights the strong influence of tectonism in the development of depositional bodies controlling the distribution of deposits generally produced during episodes of sea level fall

glacial holocene salinity changes in the mediterranean sea hydrographic and depositional effects oxygen isotope changes as recorded by pleistocene foraminifera from open ocean sediments are primarily a function of changes in the isotopic composition of the global seawater reservoir caused by ice volume changes with a secondary temperature component1 oxygen isotope records from marginal basins such as the gulf of mexico2 the mediterranean sea3 5 and the red sea6 also exhibit the global signal but are far more complicated owing to the strong overprint of local climate conditions in particular glacial interglacial changes in continental aridity and river runoff produce significant salinity changes in these semi enclosed basins using available oxygen isotope records we estimate that glacial 18 000 yr bp salinities in the eastern and western mediterranean sea were 2 7 and 1 2 higher respectively than at present these elevated glacial salinities played an important part in preconditioning the eastern mediterranean for the eventual accumulation of organic carbon rich sediments sapropels at the end of deglaciation

proximal distal ichnofabric changes in a siliciclastic shelf early pliocene guadalquivir basin southwest spain abstract the lower pliocene deposits cropping out along the atlantic coast of cadiz in the conil cabo roche area formed on a shelf gently deepening towards the w nw up to five types of facies can be recognized distributed in belts from proximal to distal parts of the shelf 1 coarse grained sandstone with trough cross stratification facies on the most proximal parts of the shelf inner shelf deposits 2 medium grained sandstone with low angle planar cross stratification facies deposited in a more distal position due to storm currents transporting sediment offshore this facies intercalates with the previous trough cross bedded sandstone 3 massive fine grained sandstone and siltstone facies laterally and vertically related with the previous facies type and representing sediments formed in the middle shelf close to the storm wave base 4 tabular sandstone bed facies corresponding to storm bed deposits intercalated within the two previous facies 5 greenish bluish shale facies accumulated on the outer shelf below storm wave base three ichnofabrics associated with these facies are recognized 1 the two cross bedded facies are dominated by a macaronichnus ichnofabric characterized by macaronichnus and bichordites traces that represent colonization of a shifting sandy substrate by polychaetes macaronichnus tracemakers and by sea urchins bichordites producers 2 a rosselia ichnofabric consisting of vertical traces of rosselia cross cutting macaronichnus characterizes the interval of massive fine grained sandstone and silt facies and interbedded tabular sandstones this ichnofabric formed under high sedimentation rates with rosselia traces exhibiting stacked patterns that indicate vertical readjustment following deposition 3 massive fine grained sandstone and silt facies are distinguished by a cylindrichnus ichnofabric this fabric was produced by the activity of a moderately diverse community dominated by sessile burrow dwelling probably superficial detritus feeding polychaetes rosselia and cylindrichnus tracemakers and vagile deposit feeding polychaetes planolites producers in addition infaunal deposit detritus feeders producing spreiten structures teichichnus are found in distal areas pervasive indistinct mottling of the sediment of this facies was probably due to the activity of very shallow burrowers in the uppermost sediment tiers this proximal distal replacement of ichnofabrics reflects the change of benthic communities across the shelf this distribution does not fit the traditional seilacherian ichnofacies model for soft ground shallow marine settings in which proximal vertical dwelling burrows of the skolithos ichnofacies dominate high energy environments in the pliocene of cadiz shallow tier burrows of deposit detritus feeders characterize the high energy facies instead which fit better with the cruziana ichnofacies this deviation can be related with the particular palaeoenvironmental conditions thus vagile opportunistic deposit feeders colonized the dune foreset when the dunes were stable and the progradation of the structure favored the preservation of the traces

a two dimensional analytic tidal model for a narrow estuary of arbitrary lateral depth variation the intratidal motion an innovative method is introduced to solve a two dimensional depth averaged analytic model for narrow estuaries or tidal channels with arbitrary lateral depth variations the solution is valid if the lateral variation of the amplitude of tidal elevation a is small i e a a where a is the amplitude of the tidal elevation this assumption is supported by a 60 day observation of elevation in the james river estuary using pressure sensors at both sides of a cross section of the estuary the error introduced by the solution is of the order of a a which has a maximum of 5 in the james river estuary the propagation of the tidal wave elevation is therefore essentially one dimensional along the estuary regardless of the depth distribution whereas tidal velocity has a strong transverse shear and is three dimensional in general dozens of depth functions in six groups of various forms are used to calculate the solution the tidal velocity is highly correlated with the bathymetry the largest amplitude of the along channel velocity is in the deepest water the phase of the along channel velocity in the shallow water leads that in deep water causing a delay in time of flood or ebb in the deep water the transverse velocity is generally small in the middle of a channel but reaches its maximum over the edges of bottom slopes the depth function has a significant effect on the ellipticity and the sense of rotation of the tidal ellipses by fitting the observed phase of semidiurnal tide in the james river estuary to the phase of the momentum equation we have obtained optimal values of the drag coefficient 1 5 10 3 and 1 8 10 3 for the spring and neap tides respectively then we apply these values of the drag coefficient and the model to the james river estuary using the real bathymetry results show remarkable agreement between the observations and the model along the transects for both spring and neap tides the cross channel phase difference of the along channel velocity between the channel and the shoal is found to be 1 hour a value consistent with that from the model the model estimated lateral variation of elevation is 2 5 of the tidal amplitude which is slightly smaller than the observed value

surface facies and sediment dispersal patterns southeastern gulf of cadiz spanish continental margin abstract grain size of 294 samples and mineralogical analysis of 364 surface samples from the spanish continental shelf and upper slope of the gulf of cadiz delineate four sediment facies that derive mainly from siliciclastic sources the northern area is formed by the mud rich prodelta of the guadalquivir river parallel to the coast and progradational towards the southeast it exhibits a typical bulk mineral association of illite smectite kaolinite chlorite in the north central area there is a smaller coarser grained prodelta in the bay of cadiz linked to the guadalete river which offshore becomes connected to the guadalquivir prodelta its mineral association is quartz illite kaolinite chlorite in the southern area where fluvial input is negligible the characteristic coarse grained facies generally corresponds to relict late pleistocene reworked deposits the typical mineral association is quartz calcite aragonite smectite mixed layer clay minerals the fourth area corresponds to the shelf break and upper slope offshore cadiz bay where a westward grain size coarsening differentiates the deposits of the last low sea level stand and no typical mineral association exists the mineralogy of the terrigenous deposits indicates a source area from paleozoic sequences of the sierra morena to the north and the subbetic units and gibraltar flysch to the east the neogene deposits of the guadalquivir depression are an additional source of shelf sediments the surface sediment distribution on the inner continental shelf is largely determined by the southeastern atlantic water flow the terrigenous input from rivers and the shelf physiography sediment dispersal on the outer continental shelf and upper slope in contrast largely reflects the location of low sea level stand the development of palimpset deposits and the location of the mediterranean undercurrent over the margin

latest miocene benthic δ 18 o changes global ice volume sea level and the messinian salinity crisis oxygen isotope evidence indicates high but variable 18o values in benthic foraminiferal calcite during the latest miocene and earliest pliocene these high values may represent increases in global ice volume and associated sea level fall the 18o record resembles glacial interglacial cycles but with only one third the amplitude of the late pleistocene signal this variability may reflect instability in the antarctic ice sheet and palaeomagnetic correlation points to an isotopic event coinciding with the isolation and desiccation of the mediterranean basin during the latest messinian

three dimensional wind driven flow in an elongated rotating basin abstract the wind driven circulation in lakes lagoons estuaries or coastal embayments is described with a linear steady three dimensional barotropic model in an elongated basin of arbitrary depth distribution on an f plane with rotation the vertically averaged velocity scales with the ekman depth rather than the maximum depth h0 as in the case without rotation near the closed ends of the basin the flow turns in viscous boundary layers because the length of the turning areas depends on the sign of the bottom slope and on the ratio of the ekman depth to h0 there is a striking contrast between the turning areas on either side of an observer looking toward the end of the basin in the northern hemisphere the turning area on the left is broad of order 1b where b is the basin half width the turning area on the right is narrow of order b and dynamically equivalent to the western boundary current in models of the wind driven ocean circulation ekman solutions are used to describe the ve

geotechnical characteristics and slope stability in the gulf of cadiz abstract sedimentological and geotechnical analyses of thirty seven core samples from the gulf of cadiz continental margin were used to define the regional variability of sediment properties and to assess slope stability considering the sediment property data set as a whole there is an association between grain size plasticity and water content any one of these properties can be mapped regionally to provide an indication of the dominant surface sediment lithology based on static sediment strength a simplified slope stability analysis showed that only steep slopes 16 for even the most vulnerable sediment can fail under static loading conditions accordingly transient loads such as earthquakes or storms are needed to cause failure on more moderate slopes a regional seismic slope stability analysis of the cadiz margin was performed based on detailed geotechnical testing of four gravity core samples the results showed that the stability of these slopes under seismic loading conditions depends upon sediment density the cyclic loading shear strength the slope steepness and the regional seismicity sediment density and cyclic loading shear strength are dependent upon water content which can act as a proxy for plasticity and texture effects specifically sediment in the water content range of 50 56 is most vulnerable to failure under cyclic loading within the cadiz margin as a result for a uniform seismicity over the region susceptibility to failure during seismic loading conditions increases with increasing slope steepness and is higher if the sediment water content is in the 50 56 range than if it is not the only sampled zone of failure on the continental slope contains sediment with water content in this critical range storm wave induced instability was evaluated for the continental shelf the evaluation showed that a storm having hundreds of waves with a height in the range of 16 m might be capable of causing failure on the shelf however no sediment failures were observed on the shelf that might have been caused by this mechanism

observations of the lateral structure of wind driven flow in a coastal plain estuary abstract wind stress is one of the main drivers of estuarine circulation the lateral structure of wind induced flows in estuaries has been described mainly with analytical and numerical models the aim of this study is to investigate with observations the lateral structure of wind induced flow in a coastal plain estuary the james river virginia such structure was explored with the first empirical orthogonal function eof1 mode derived from month long moored adcps deployed at two cross sections in the estuary mode 1 explained 53 of the variance and was attributed to wind forcing its lateral structure eigenvectors consisted of upwind flow centered in the channel at middle depth downwind flow over the shoals and a vertically sheared bidirectional flow over the channel slope wavelet coherence analysis showed that along estuary wind was highly coherent with mode 1 coherence squared 0 9 especially at the period band between 4 and 6 days the along estuary wind stress and the temporal variation of mode 1 showed an anti phase coherence with the wind stress leading mode 1 persistently in addition an analytical solution showed a lateral structure similar to the eigenvectors obtained with eof1 the conclusion is that the lateral structure described by eof1 was induced by wind stress and was consistent with analytical and numerical model results these results are among the handful available that confirm the theoretical structure of wind driven flows over laterally varying bathymetry

mediterranean undercurrent sandy contourites gulf of cadiz spain abstract the pliocene quaternary pattern of contourite deposits on the eastern gulf of cadiz continental slope results from an interaction between linear diapiric ridges that are perpendicular to slope contours and the mediterranean undercurrent that has flowed northwestward parallel to the slope contours and down valleys between the ridges since the late miocene opening of the strait of gibraltar coincident with the northwestward decrease in undercurrent speeds from the strait there is the following northwestward gradation of sediment facies associations 1 upper slope facies 2 sand dune facies on the upstream mid slope terrace 3 large mud wave facies on the lower slope 4 sediment drift facies banked against the diapiric ridges and 5 valley facies between the ridges the southeastern sediment drift facies closest to gibraltar contains medium fine sand beds interbedded with mud the adjacent valley floor facies is composed of gravelly shelly coarse to medium sand lags and large sand dunes on the valley margins compared to this the northwestern drift contains coarse silt interbeds and the adjacent valley floors exhibit small to medium sand dunes of fine sand further northwestward sediment drift grades to biogenous silt near the faro drift at the portuguese border because of the complex pattern of contour parallel and valley perpendicular flow paths of the mediterranean undercurrent the larger scale bedforms and coarser grained sediment of valley facies trend perpendicular to the smaller scale bedforms and finer grained contourite deposits of adjacent sediment drift facies the bottom current deposits of valleys and the contourites of the cadiz slope intervalley areas are distinct from turbidite systems the valley sequences are not aggradational like turbidite channel levee complexes but typically exhibit bedrock walls against ridges extensive scour and fill into adjacent contourites transverse bedform fields and bioclastic lag deposits both valley and contourite deposits exhibit reverse graded bedding and sharp upper bed contacts in coarse grained layers low deposition rates and a regional pattern of bedform zones textural variation and compositional gradation the surface sandy contourite layer of 0 2 1 2 m thickness that covers the gulf of cadiz slope has formed during the present holocene high sea level because high sea level results in maximum water depth over the gibraltar sill and full development of the mediterranean undercurrent the late pleistocene age of the mud underlying the surface sand sheet correlates with the age of the last sea level lowstand and apparent weak mediterranean undercurrent development thus the cyclic deposition of sand or mud layers and contourite or drape sequences appear to be related to late pliocene and quaternary sea level changes and mediterranean water circulation patterns since its pliocene origin the contourite sequence has had low deposition rates of

periodic wind driven circulation in an elongated and rotating basin abstract an idealized model is developed for the three dimensional response of a coastal basin e g lagoon bay or estuary to time periodic wind stress this model handles basins that are deeper and or shallower than an ekman depth with wind forcing frequencies ranging from subinertial to superinertial here the model is used to describe how the response current and sea level of a basin deeper than one ekman depth depends on the wind forcing frequency at low subinertial frequencies the response is similar to the steady wind case and is hence called quasi steady there is a near surface ekman transport to the right of the wind balanced by a return flow at depth lateral bathymetric variations introduce an along basin circulation that decays with increasing frequency and sets the extent of the quasi steady response in the frequency domain at the inertial frequency the wind forces a damped resonant response with large vertical shear and weak depth integrated flow this result is potentially impor

late pleistocene raised beaches of coastal estremadura central portugal abstract we present new stratigraphic sedimentological and chronological data for a suite of tectonically raised beaches dating to marine isotope stages 5 4 and 3 along the estremadura coast of west central portugal the beach deposits are found in association with ancient tidal channels and coastal dunes pollen bearing mud and peat and middle paleolithic archaeological sites that confirm occupation of the coastal zone by neanderthal populations the significance of these deposits is discussed in terms of the archaeological record the tectonic and geomorphic evolution of the coast and correlation with reconstructions of global climate and eustatic sea level change direct correlation between the estremadura beach sections is complicated by the tectonic complexity of the area and the age of the beach deposits which are near or beyond the limit of radiocarbon dating evidence from multiple sites dated by ams radiocarbon and optical luminescence methods suggests broad synchroneity in relative sea level changes along this coast during marine isotope stage 3 two beach complexes with luminescence and radiocarbon age control date to about 35 ka and 42 ka recording a rise in relative sea level around the time of heinrich event 4 at 39 ka depending on assumptions about eustatic sea level at the time they were deposited we estimate that these beaches have been uplifted at rates of 0 4 4 3 mm yr 1 by the combined effects of tectonic halokinetic and isostatic processes uplift rates of 1 2 mm yr 1 are likely if the beaches represent sea level stands at roughly 40 m below modern as suggested by recent eustatic sea level reconstructions evidence from coastal bluffs and the interior of the study area indicates extensive colluvial fluvial and aeolian sedimentation beginning around 31 ka and continuing into the holocene these geomorphic adjustments are related to concomitant changes in climate and sea level providing context that improves our understanding of late pleistocene landscape change and human occupation on the western iberian margin

recent influence of man on the ebro margin sedimentation system northwestern mediterranean sea abstract man s recent activities such as construction of reservoirs dams and irrigation channels have changed the natural dynamics of the ebro margin sedimentation system the amount of sediment supplied by the ebro river is presently less than 5 of the amount supplied 50 60 years ago suspended sediment supplied by the river at the present time has a higher proportion of clay minerals than before the construction of the dams and reservoirs at present only the finer particles escape the dams leaving the remaining sediment and apparently a large proportion of heavy metal inputs coming from inland cities and industries trapped behind them in the lower part of the river heavy metal pollution in the suspended matter is relatively low heavy metal anomalies in the shelf muds suggest that present day sedimentation is restricted mainly to the proximal mud belt area near the mouth of the river abnormally high concentrations of heavy metals in suspended matter have been detected at the shelf break and on the upper continental slope of the ebro system these polluted particles come from rivers and cities located north of the ebro mouth and are transported by the general southward flow along the slope some pollutants can be used as tracers for particle dynamics on the ebro margin the present supplies and fluxes of suspended sediment are significantly different from those which occurred before management of the river and coast began

high resolution stratigraphy of the mediterranean outflow contourite system in the gulf of cadiz during the late pleistocene the impact of heinrich events abstract a detailed high resolution stratigraphic analysis of the mediterranean outflow contourite system at the continental slope of the gulf of cadiz has been carried out through the correlation between a dense network of seismic reflection profiles sparker airgun 3 75 khz and parametric echosounder topas calypso giant piston and standard gravity cores from such correlation we determine a stacking pattern constituted by four main seismic units a d that are internally structured into ten subunits each subunit shows a single sequence formed by transparent seismic facies at the base to smooth parallel reflectors of moderate to high amplitude facies at the top being well correlated in the cores with a coarsening upward sequence the latest pleistocene holocene deposits form glacial interglacial depositional sequences related to cycles with a frequency range below the milankovitch band that corresponds to millennial timescale climatic changes such as dansgaard oeschger 1 5 ka and bond cycles 10 15 ka oxygen isotope records of planktonic foraminifera and the occurrence of ice rafted debris ird in the most recent contourite subunits show clear evidence of the influence of the north atlantic climatic conditions especially the climatic heinrich events h in the slope sedimentation of the gulf of cadiz and then in the circulation of the mediterranean outflow water mow the coarser contourite deposits are mostly associated with the last glacial maximum younger dryas and heinrich events on the central area of the middle slope during globally cooler conditions the mow was denser so that it was more active in deeper areas than today on the other hand during warm periods the mow became less dense favoring an increased intensity of the mow on the distal area of the upper slope therefore spatial and vertical fluctuations of the mow contourite system are strongly affected by global climate and oceanographic changes being clearly influenced by iceberg discharges and probably also by the resumption of thermohaline circulation in the north atlantic ocean during ice melting periods

large deep water coral banks in the porcupine basin southwest of ireland the porcupine basin southwest of ireland was one of the earliest sites from where the deep water corals lophelia sp and madrepora sp were recovered these deep water corals have since been found all along the atlantic margins of europe in water depths ranging from 50 to more than 2000 m recent geophysical studies have demonstrated the mound building potential of deep water corals available data indicate that three major provinces of coral bank occurrences can be identified in the porcupine basin 1 high relief surface mounds which have a dimension of 1 by 5 km and a height up to 200 m hovland mounds flanked to the north by 2 a swarm of buried mounds somewhat smaller up to 90 m and with more irregular shapes than those recognised in area 1 magellan mounds and 3 outcropping or buried conical mounds single or in elongated clusters up to 150 m high occurring on the southeastern slope of the basin belgica mounds as far as can be inferred from shallow cores the surface lithology predominantly consists of an upper layer rich in foraminiferal sand and terrigenous silty clay with intercalations of biogenic rubble the banks host a remarkable number of colonies of living and dead lophelia pertusa and madrepora oculata the living and dead assemblages are underlain by a significant layer of coral debris in a muddy matrix deep water coral debris together with a living association of the same species covers the surface of the belgica and hovland mounds which may suggest that these corals have played a significant role in the development of the mound structures the capacity for mound formation by scleractinian corals in the aphotic zone has been known for some time examples are found at different locations along the shelves and the continental margins of the north atlantic the role of the corals in these deep water build ups is still a point of debate though the genesis and initial control of mound settings in this basin might be related to hydrocarbon seeps it appears that the major development of the porcupine coral banks in recent geological times has most likely been controlled by oceanic circulation and dynamics in water masses and nutrient supply

sedimentary evolution of the pliocene and pleistocene ebro margin northeastern spain abstract the pliocene and pleistocene deposits of the spanish ebro margin overlie a regional unconformity and contain a major disconformity these unconformities named reflector m and reflector g mark the bases of two seismic sequences except for close to the upper boundary where a few small channel deposits are recognized the lower sequence lacks channels the upper sequence contains nine channel levee complexes as well as base of slope aprons that represent the proximal part of the valencia turbidite system diverse geometries and variations in seismic units distinguish shelf slope base of slope and basin floor facies four events characterize the late miocene to pleistocene evolution of the ebro margin a formation of a paleodrainage system and an extensive erosion to depositional surface during the latest miocene messinian b deposition of hemipelagic units during the early pliocene c development of canyons during the late pliocene to early pleistocene and d deposition of slope wedges channel levee complexes and base of slope aprons alternating with hemipelagic deposition during the pleistocene sea level fluctuations influenced the evolution of the sedimentary sequences of the ebro margin but the major control was the sediment supply from the ebro river

depositional history of estuarine infill during the last postglacial transgression gulf of cadiz southern spain abstract the late pleistocene and holocene evolution of the estuaries in the gulf of cadiz is interpreted for the first time using drill cores logs trenches and 38 new radiocarbon data and the results compared with the shelf the odiel tinto and guadalete rivers deposited conglomerates during a highstand that did not reach the present sea level dated at ca 25 30 ka isotopic stage is 3 corresponding to a relatively humid period in the area rivers incised these coarse grained deposits during the last main lowstand at ca 18 ka when sea level dropped to 120 m and the coastline lay 14 km seawards from the present the erosional surface is a sequence boundary and the flooding surface of the postglacial eustatic rise overlain by the valley fill deposits of the transgressive and highstand phases of the last fourth and fifth order depositional sequences recognised in the shelf the first marine influence in the estuaries during the transgression occurs at 25 30 m at ca 10 000 years bp according to fossil assemblages the transgressed basins changed from brackish to more open marine as the sea rose until ca 6500 years bp when it reached the maximum flooding and the sandy estuarine barriers ceased to retrograde toward the muddy central basins then the rate of eustatic rise decreased drastically and the estuarine filling followed a two fold pattern governed by the progressive change from vertical accretion to lateral centripetal progradation at ca 4000 years bp the fluvial input surpassed the already negligible rate of rise causing partial emergence of tidal flats and spit barriers in the largely filled estuarine basins prevalence of coastal progradation upon vertical accretion at ca 2400 years bp caused accelerated expansion of tidal flats and rapid growth of the sandy barriers further changes since the 16th century reflect widespread anthropic impacts

the effects of a deep channel on the wind induced flushing of a shallow bay or harbor wind driven circulation in a shallow bay or harbor is greatly influenced by bottom bathymetry as a result the wind induced flushing time of the system can be significantly reduced by a deep channel dredged along the prevailing wind direction in koombana bay on the coast of southwest australia there exists a navigation channel of this type its effective flushing of the bay is studied here by current meter and drogue deployments the use of hf radar to measure surface transport and simulations with idealized long basin models and two dimensional and three dimensional numerical models

circular plumes in lake pontchartrain estuary under wind straining circular shaped density plumes of low turbidity low fecal indicator escherichia coli and enterococci concentrations and high salinity have been observed near the industrial canal in lake pontchartrain north of the city of new orleans a conceptual model in polar coordinates and a numerical model are developed together with data analysis to illustrate the dense plume it is demonstrated that the northward expansion of the plume occurs under northerly winds the northward expansion of the plume occurs under northerly winds that drive downwind flow at the surface and upwind radial flow at the bottom northerly wind induced straining similar to tidal straining promotes vertical stratification as a result the water becomes stratified near a thin bottom layer 1 m within which density currents are facilitated the stability of the stratified plume suppresses wind induced turbulent mixing inside the plume the bottom water outside of the plume is more effectively stirred by the wind the result being that the suspended sediment concentration outside of the plume area is much higher than inside this contrast in mixing makes the plume visible from the surface by satellites even though the stratification is at the bottom laterally wind stress produces a torque vorticity in areas of non uniform depth such that upwind flow is developed in deep water and downwind flow in shallow water the continuity requirement produces an upwind flow along the axis of the industrial canal ic the upwind flow is balanced by the downwind flow over the shallower peripheral areas along the coast

seismic stratigraphy of the gulf of cadiz continental shelf a model for late quaternary very high resolution sequence stratigraphy and response to sea level fall

gas hydrates in the ginsburg and yuma mud volcano sediments moroccan margin results of chemical and isotopic studies of pore water abstract two active mud volcanoes on the atlantic continental margin of morocco were sampled during a 1999 expedition on the r v professor logachev the active mud volcanoes named yuma and ginsburg are each about 4 km in diameter rise 150 250 m above the seafloor and are the first active methane related mud volcanoes identified in this region gravity cores from the crest of the active mud volcanoes recovered methane hydrates clathrates thirty five pore water samples were extracted and analyzed from seven gravity cores taken in and around the active mud volcanoes estimated gas hydrate content in mud volcano sediments is 2 11 by volume and 4 19 by pore space chloride ion concentrations of the original mud volcano water are similar to those of surrounding seawater but are isotopically different the water is very high in oxygen to 35 and light in hydrogen to 70 pore water with these features has not been previously described in the published literature

spatial variation of cold front wind driven circulation and quasi steady state balance in lake pontchartrain estuary abstract circulation in a low salinity estuary with restricted openings to the ocean is mainly driven by wind and to a lesser extent by water level fluctuations at the open boundaries numerical model experiments are conducted using a baroclinic finite volume community ocean model fvcom for wind driven circulations during a period encompassing a total of 16 cold fronts in the lake pontchartrain estuary the work is focused on the examination of the spatial structure of circulation in response to local and remote winds a quasi steady state balance between the surface slope and wind stress is further analyzed the accuracy of the balance is evaluated by comparing the fvcom calculated surface slope with that from the steady state balance equation results show that this balance is more accurate in the cross estuary direction than that in the along estuary direction r2 0 94 vs 0 60 this difference in the accuracy of the quasi steady state balance between the cross and along estuary directions is caused by the open boundary a tidally induced mean slope exists in addition even if the tidal effect is removed the accuracy still decreases toward the open end for slopes in both directions remote wind effect and residual flow through the eastern open boundary tend to introduce a departure from the quasi steady state balance in both along and cross estuary directions remote wind effect decreases into the interior due to bottom friction local wind effect tends to produce downwind flows in coastal shallow water regions and on the surface but upwind flows near the bottom a result consistent with barotropic wind driven circulations while the remote wind effect is important mostly near the open boundary furthermore quasi steady state balance is more accurate in the along estuary direction before cold front passages then after because of the relatively higher occurrence of the wind in that direction before the cold fronts than after in contrast this quasi steady state balance is less accurate in the cross estuary direction before cold front passages than after because of the relatively lower occurrence of the wind in that direction before the cold fronts than after

wind induced circulation in semienclosed homogeneous rotating basins the wind induced circulation over laterally varying bathymetry was investigated in homogeneous systems using the three dimensional regional ocean model system roms the investigation focused on the influence of the earth s rotation on the lateral distribution of the flow with particular emphasis on the transverse circulation along basin wind stress with no rotation caused a circulation dominated by an axially symmetric transverse structure consisting of downwind flow over the shoals and upwind flow in the channel along the whole domain transverse circulation was important only at the head of the system where the water sank and reversed direction to move toward the mouth the wind induced flow pattern under the effects of the earth s rotation depended on the ratio of the maximum basin s depth h to the ekman depth d the solution tended to that described in a nonrotating system as h d remained equal to or below 1 for higher values of h d the longitudinal flow was axially asymmetric maximum downwind flow was located over the right shoal in the northern hemisphere looking downwind the transverse component of velocity described three gyres the main gyre was clockwise looking downwind and occupied the entire basin cross section as expected from the earth s rotation and the presence of channel walls the other two gyres were small and localized and were linked to the lateral distribution of the along channel velocity component which in turn was dictated by bathymetry these results compared favorably with a limited set of observations and are expected to motivate future measurements

axial wind effects on stratification and longitudinal salt transport in an idealized partially mixed estuary abstract a 3d hydrodynamic model regional ocean model system roms is used to investigate how axial wind influences stratification and to explore the associated longitudinal salt transport in partially mixed estuaries the model is configured to represent a straight estuarine channel connecting to a shelf sea the results confirm that wind straining of the along channel salinity gradient exerts an important control on stratification two governing parameters are identified the wedderburn number w defined as the ratio of wind stress to axial baroclinic pressure gradient force and the ratio of an entrainment depth to water depth hs h here w controls the effectiveness of wind straining which promotes increases decreases in stratification during down estuary up estuary wind the ratio hs h determines the portion of the water column affected by direct wind mixing while stratification is always reduced by up estuary wind stratification shows an increase then decrease transition when down estuar

diatoms of the fortuna basin southeast spain evidence for the intra messinian inundation the fortuna basin in southeast spain part of the betic strait was one of the connecting pathways between the atlantic ocean and the mediterranean sea during the late miocene the basin contains a remarkable record of messinian marine sediments two well laminated marly diatomaceous sections were examined the 1 m thick el fenazar section f section and the 36 m thick rio chicamo diatomite member rcd section both sections are intercalated with gypsum horizons the diatoms in the rio chicamo diatomite suggest an atlantic origin and strong coastal upwelling associated with high productivity on the basis of event stratigraphy the diatomites correlate to the intra messinian inundation of the mediterranean sea during the messinian salinity crisis four biostratigraphically useful species nitzchia jouseae thalassiosira oestrupii t praeoestrupii denticulopsis hustedtii and asterolampra acutiloba occur in the west pacific between 5 35 and 4 5 ma lower reversed gilbert chron this interpretation places the subsequent upper evaporite deposition into the lower reversed gilbert chron our results indicate 1 the existence of a marine connection between the atlantic ocean and the mediterranean sea through the betic strait southeast spain during the messinian salinity crisis 2 a possible earlier first appearance of nitzchia jouseae in the betic strait compared to the atlantic and pacific oceans according to the stratigraphy of the fortuna basin and 3 the probability that many of the tripolilike and younger diatomites in the mediterranean are local deposits and diachronous with each other

dependence of wind driven current on wind stress direction in a small semienclosed homogeneous rotating basin abstract the dependence of wind driven current wdc on wind stress direction in a small semienclosed homogeneous rotating basin is investigated using a linear steady state analytical model based on ekman solutions the model is applicable to the middle of the basin midbasin and the current is driven by a constant wind stress of an arbitrary direction the wdc is made up of wind stress driven current wsdc and pressure driven current pdc components the laterally varying water depth of the basin confines the total volume transport in the longitudinal direction while the wind stress driven volume transport changes direction according to the wind stress direction therefore the pressure driven volume transport or equivalent the pressure gradient depends on the wind stress direction the relationship between the pressure gradient and the wind stress is anisotropic as a result the midbasin wdc is also dependent on the wind stress direction the dependence varies according to the lateral position a

the influence of eddy viscosity formulation bottom topography and wind wave effects upon the circulation of a shallow bay abstract a three dimensional hydrodynamic model taking account of enhanced bed stress due to wave current interaction is used to examine the wind induced circulation and flushing time of an idealized homogeneous bay or estuary the model uses a spectral approach in the vertical and hence computes a continuous current profile from sea surface to seabed calculations show that in the case of an estuary of nearly constant cross sectional depth with an along estuary wind the intensity of differential flow in the vertical is critical in determining the flushing time in this case the three dimensional circulation and hence flushing time is sensitive to the formulation of vertical eddy viscosity and in the case of a tidal estuary its variation over the spring neap cycle and with wind intensity must be included for an estuary with a deep central channel horizontal rather than vertical circulations dominate the flow is more uniform in the vertical and hence the circulation is fairly insensitive to ed

a review of the physical oceanography of the mediterranean outflow abstract the physical oceanography of the mediterranean sea is reviewed with particular emphasis on the mediterranean outflow in the gulf of cadiz in this region the dense mediterranean water forms a high velocity bottom current that interacts strongly with the sea floor the major energy source for the plume comes from the release of potential energy as the plume descends the continental slope and the major energy sink is work against bottom stress which is as large as 4 pa where the plume begins to descend the continental slope in this region the current makes a nearly inertial turn that would otherwise appear to be steered by the underlying topography the mediterranean plume entrains the overlying north atlantic central water and thereby loses much of its density anomaly the mixed mediterranean water becomes neutrally buoyant in the lower portion of the north atlantic thermocline near cape st vincent there are then two preferred transport modes having somewhat different temperature and salinity whose distinct characteristics can be found far into the open north atlantic the temperature salinity and volume of the mediterranean water in the strait of gibraltar and in the gulf of cadiz appear to be roughly constant since modern measurements have been made the estimated westward transport of mediterranean water has gone down considerably as direct measurement techniques have been applied a recent estimate is that the westward transport of pure mediterranean water is only about a half a sv 1 sv 106 m3 s 1 the transport of mixed mediterranean water in the western gulf of cadiz is larger by about a factor of three or four because of the entrainment of north atlantic water

geologic evolution of the betic cordilleras in the western mediterranean miocene to the present abstract the betic cordilleras were formed during the eo meso and neo alpine evolution of the western mediterranean area during the neo alpine stage the northward subduction of the african plate took place and the algerian provencal basin opened with the creation of oceanic floor associated space problems produced the expulsion and extensive stretching of the internal zones to the west which in turn disrupted and deformed the external zones of the betic and rif cordilleras these occurrences essentially took place in the burdigalian and continued with diminished intensity into the middle miocene following the suturing of the transcurrent contact between the internal and external zones important n60 90 e and nw se faults occurred the betic cordilleras are characterized as having been deformed by regional horizontal shortening compression oriented wnw ese or nw se which gradually rotated to the nnw sse in the late miocene when its most important intramontane neogene basins were formed the alboran basin with a thinned continental crust was formed as a western prolongation of the opening of the algerian provencal basin with its basic features already apparent in the burdigalian the volcanism present in the southeast of the betic cordilleras and in northeast morocco crossing the alboran basin is mainly late miocene in age it is linked to fracturing and exhibits chemistry related to the different thickness of the crust

very coarse grained beaches as a response to generalized sea level drops in a complex active tectonic setting pleistocene marine terraces at the cadiz coast sw spain abstract the studied pleistocene deposits at the cadiz coast are located on the current intertidal zone or at cliffs parallel to the actual coast 6 50 m a s l from the localities of el puerto de santa maria to chiclana five sequences of very coarse grained beaches have been recognized and dated they unconformably overlie pliocene units and are formed by clast supported conglomerate and coarse grained sandstone chronological ages 87 sr 86 sr and ams 14 c analysis and stratigraphic correlation stand that the oldest marine terrace is the one placed topographically higher and towards the se of cadiz city dated as early pleistocene 1 3 ma after it the sea retreatment produces subaerial exposure of sequence 1 and the development of several calcrete profiles and a paleokarst subsequent sea level rises allow the sedimentation of sequences 2 3 and 4 during early middle pleistocene 1 to 0 8 ma in areas close to cadiz city with subaerial exposure recorded at the top of sequences 3 and 4 during the very upper pleistocene sedimentation of sequence 5 occurs towards the se of cadiz city based on the spatial position of sequence 5 we can conclude that this area constituted a downthrown block during the latest pleistocene in relation to neotectonic processes and diapirism sandstone framework hybrid arenites reveals that main source areas for these marine terraces include units from the betic orogene betic external zones triassic and jurassic rocks and the gibraltar arc the guadalquivir basin passive margin iberian massif the guadalquivir foreland basin marine miocene and pliocene record and local inputs of pleistocene units the siliciclastic supplies from sources were mainly constant during the sedimentation of all set of sequences suggesting maturation processes as reworking and recycling of homogenized sediments during transport early diagenetic processes have been identified as carbonate cementation neomorphism and dissolution outlining the deduced sea level fluctuations during deposition of pleistocene sequences the marine terraces arrangement and its comparison with regionally adjacent areas allows to deduce that the southern and central portuguese coast iberian massif and of the southern and southeastern spanish coast betic orogene were predominantly tectonically raising during pleistocene however the cadiz gulf coast formerly guadalquivir foreland basin was mainly sinking during the same time interval

interaction of tectonic and depositional processes that control the evolution of the iberian gulf of cadiz margin abstract this study provides an integrated view of the growth patterns and factors that controlled the evolution of the gulf of cadiz continental margin based on studies of the tectonic sedimentologic and oceanographic history of the area seven sedimentary regimes are identified but there are more extensive descriptions of the late cenozoic regimes because of the larger data base the regimes of the mesozoic passive margin include carbonate platforms which become mixed calcareous terrigenous deposits during the late cretaceous early tertiary the oligocene and early miocene terrigenous regimes developed in contrast over the active and transcurrent margins near the african iberian plate boundary the top of the gulf of cadiz olistostrome emplaced in the late miocene is used as a key horizon to define the post orogenic depositional regimes the late miocene progradational margin regime is characterized by a large terrigenous sediment supply to the margin and coincides with the closing of the miocene atlantic mediterranean gateways the terrigenous drift depositional regime of the early pliocene resulted from the occurrence of high eustatic sea level and the characteristics of the mediterranean outflow currents that developed after the opening of the strait of gibraltar the late pliocene and quaternary regimes are dominated by sequences of deposits related to cycles of high and low sea levels deposition of shelf margin deltas and slope wedges correlate with regressive and low sea level regimes caused by eustasy and subsidence during the highstand regimes of the holocene inner shelf prograding deltas and deep water sediment drifts were developed under the influence of the atlantic inflow and mediterranean outflow currents respectively a modern human cultural regime began 2000 years ago with the roman occupation of iberia human cultural effects on sedimentary regimes may have equalled natural factors such as climate change interplay of tectonic and oceanographic controls dominated the evolution of the cadiz margin during the cenozoic depositional sequences formed where the tectonic setting provided the accommodation space and the shape of the deposits has been greatly influenced by the strong unidirectional atlantic inflow currents on the shelf and mediterranean outflow currents on the slope the entire cycle of the inflow and outflow deposition along the margin has been controlled first by the tectonic evolution of the betic and rif gateways which become closed during the late miocene and after the messinian by the opening of the strait of gibraltar strong current development during eustatic sea level highstands of the pliocene and quaternary has controlled deposition because of maximum sill depths at gibraltar for water circulation lowstand sea levels slowed circulation and resulted in mud drapes over the slope and regressive stratigraphic sequences over the shelf more recently the human industrial revolution has caused heavy metal contamination of sediment and water over the cadiz margin human activity also has affected sedimentation rates because of deforestation that caused increased depositional rates near undammed rivers and decreased rates where rivers have been dammed future research efforts will need to focus on 1 the effect of increased mediterranean outflow caused by river damming plus global warming and the increased outflow as a potential trigger for new ice ages 2 assessments of geologic hazards for planning man made shoreline structures developing offshore petroleum resources and maintaining undersea communications cables and 3 confirmation of the general geologic history of the cadiz margin

the betic orogen and the iberian african boundary in the gulf of cadiz geological evolution central north atlantic abstract the study of the gulf of cadiz on the basis of multichannel seismic profiles and wells illustrates the stratigraphy and tectonics the evolution of the southern iberian margins was more complex than in most north atlantic margins since it entailed several phases of rifting convergence and strike slip motions three main tectonic provinces surround the internal zones of the gibraltar arc orogenic belt these include in the iberian margin of the gulf of cadiz the flysch units of the campo de gibraltar complex the betic external zones and the neogene basins of the guadalquivir valley fault bounded blocks of flysch and subbetic units crops out over large areas of the southeastern iberian shelf the basement of the northwestern area in contrast is represented by the paleozoic rocks of the hercynian massif of iberia half graben structures determined the main structural trends of the margin during the mesozoic which were affected by inversion structures during the neogene compressional stages the mesozoic and lower cenozoic units are best observed in wells and seismic profiles from the northern area these units are either obscure below a thick olistostrome deposit or are absent in most of the rest of the gulf of cadiz seven lithoseismic units from triassic to upper oligocene and another seven neogene and quaternary units are identified based on the relationship to the depositional sequence and the emplacement of the olistostrome the first tectonic phase was characterized by a passive margin which was controlled by the development of half graben extensional structures and carbonate platforms this evolution comprises the mesozoic and early cenozoic ocean spreading in the north atlantic induced extensional tectonics which deformed the cretaceous syn tectonic post aptian deposits increased amounts of terrigenous materials were supplied to the margin from aptian to albian times controlling depositional patterns while terrigenous siliciclastic facies replaced the jurassic carbonate platforms from middle eocene to early miocene the margin was influenced by the relative motions of iberia and africa and the development of the alpine orogeny the iberian african boundary in the gulf of cadiz experienced transpression and the mesozoic basins probably underwent subduction the emplacement of an olistostrome took place in the gulf of cadiz towards the central atlantic basin plains during the tortonian the end of the olistostrome emplacement during the late miocene coincides with accelerated tectonic subsidence while thick progradational and aggradational depositional sequences were developed the occurrence of closely juxtaposed regions of compression and extension during the miocene may reflect the westwards progression of the gibraltar arc mountain front over a subducting thinned tethys crust when the motion between iberian and africa was n s to nnw sse oriented the migration of the arcuate mountain front into the eastern gulf of cadiz is attributed to a mechanism of collision induced delamination of the mantle lithosphere in contrast to the betic rif belts however there is no geophysical evidence to postulate that continental collision took place in the gulf of cadiz during the cenozoic

high resolution seafloor images in the gulf of cadiz iberian margin in the gulf of cadiz the hydrodynamic process acting on particle transport and deposition is a strong density driven bottom current caused by the outflow of the saline deep mediterranean water at the strait of gibraltar the mediterranean outflow water mow new high resolution acoustic data including em300 multibeam echo sounder deep towed acoustic system sar and very high resolution seismic completed by piston cores collected during the cadisar cruise allow to improve the understanding of the hydrodynamics of the mow in the eastern part of the gulf of cadiz interpretation of data corrects the previous model established in this area and allows for the first time the accurate characterization of various bedforms and erosive structures along the mow pathway and the precise identification of numerous gravity instabilities the interaction between the mow the seafloor morphology and the coriolis force is presently the driving force of the sedimentary distribution pattern observed on the gulf of cadiz continental slope

subsidence in the northeastern nile delta rapid rates possible causes and consequences holocene fluvial and marine deposits have accumulated in a graben like structure on the northeastern margin of the nile delta this part of the delta which includes lake manzala port said and the northern suez canal has subsided rapidly at rates of up to 0 5 centimeter per year since about 7500 years ago this subsidence has diverted at last four major distributaries of the nile river into this region the combined effects of continued subsidence and sea level rise may flood a large part of the northern delta plain by as much as 1 meter by the year 2100 the impact of continued subsidence now occurring when sediment input along the coast has been sharply reduced because of the aswan high dam is likely to be substantial particularly in the port said area and as far inland as south of lake manzala

facies evolution of nearshore marine clastic deposits during the tortonian transgression granada basin betic cordilleras spain abstract the 35 meter thick succession of nearshore coastal deposits near alhama de granada represents the first evidence of the tortonian transgression on the betic orogenic basement in the southeastern part of the granada basin the transgressive sequence is represented by the following facies units in ascending order 1 1 a basal marine facies unit deposited on a shelf 2 2 an estuarine facies unit comprising coarse sand and gravel in which three subfacies can be distinguished a channel subfacies a shoal or bar subfacies and a bioturbated estuarine subfacies 3 3 a beach facies unit in which backshore foreshore and shoreface subfacies can be distinguished 4 4 a sandwaves facies unit comprising sand with gravel and bioclastic lenses 5 5 a shelf facies unit consisting of bioclastic calcarenites which overlie all other facies units the nearshore facies evolution representing a gradual tortonian marine transgression also displays a change from predominantly siliciclastic sedimentation to predominantly bioclastic sedimentation this change reflects a gradual reduction in tectonic uplift in the source area