late quaternary evolution of the northern aegean shelf abstract a dense network of 3 5 khz and uniboom seismic profiles revealed the geological evolution of the ierissos alexandroupolis shelf area of the northern aegean during the latest sea level rise near the end of the pleistocene ca 14 000 yr b p the sea was at about 120 m and almost 5300 km2 of shelf was exposed to subaerial erosion two permanet lakes existed in the ierissos and kavalla gulfs as well as a number of ephemeral lakes scattered throughout the rest of the area kavalla gulf was drained by the nestos river which joined the strymon river at the outer strymonikos plateau on the flat samothraki plateau were dune fields marshes and a number of minor seasonal rivers while the evros river flowed east of the plateau by ca 13 000 yr b p the sea had risen to 70 m and covered 30 of the previously exposed shelf the lakes at ierissos and strymonikos gulfs were shallower and the sea approached to within about 5 km of them kavalla gulf and the adjacent eastern strymonikos plateau lay 10 m above sea level while the sea intruded along river mouths at the samothraki plateau during this transgression of the sea river bed gravels and sands were covered by silts and clays at the pleistocene holocene transition ca 10 500 yr b p the sea lay at about 50 m and in areas of steep slope the coast was close to its present position at kavalla gulf the sea advanced along the paleochannel of the nestos river and the island of samothraki was separated from the mainland by ca 7500 yr b p the sea was only 15 m below its present level and the northeastern aegean shelf assumed nearly its present morphology the nestos river changed course to the east and thassos island was separated from the mainland coarse sediment formed wedges nearshore whereas fine grained sediments were distributed widely by current action in many areas relict sediments are present

interaction of lateral baroclinic forcing and turbulence in an estuary 1 observations of density and velocity in a channel in northern san francisco bay show that the onset of vertical density stratification during flood tides is controlled by the balance between the cross channel baroclinic pressure gradient and vertical mixing due to turbulence profiles of velocity salinity temperature and suspended sediment concentration were measured in transects across suisun cutoff in northern san francisco bay on two days over the 12 5 hour tidal cycle during flood tides an axial density front developed between fresher water flowing from the shallows of grizzly bay into the northern side of suisun cutoff and saltier water flowing up the channel north of the front transverse currents were driven by the lateral salinity gradient with a top to bottom velocity difference greater than 30 cm s south of the front the secondary circulation was weak and along channel velocities were greater than to the north the gradient richardson number shows that stratification was stable north of the front while the water column was turbulently mixed south of the front time series measurements of velocity and salinity demonstrate that the front develops during each tidal cycle in estuaries longitudinal dynamics predict less stratification during flood than ebb tides these data show that stratification can develop during flood tides due to a lateral baroclinic pressure gradient in estuaries with complex bathymetry

conference on the last deglaciation timing and mechanism abstract for years paleoclimatologists have held the general view that the last deglaciation began around 17 000 to 15 000 yr ago that the shape of the globally integrated deglacial curve was smoothly sigmoidal with the fastest rate of change centered around 11 000 yr ago and that the deglaciation ended around 7000 to 5000 yr ago recent studies have challenged several aspects of this consensus and have suggested that the mechanisms responsible for the deglaciation are significantly different from those previously proposed as a result an international workshop was held at airlie house in virginia during may 2 6 of 1983 to evaluate a wide range of evidence relevant to this controversy the conference results suggested that 1 the decrease in global ice volume occurred in two steps with the dating of the earlier step still in doubt but the later step occurring at about 10 000 7000 yr ago and 2 the most likely feedback mechanisms for accelerating the initial forcing by orbital variations are delayed bedrock rebound marine downdraw calving and co 2 heating

neural networks and their applications in lithostratigraphic interpretation of seismic data for reservoir characterization modern 3d seismic data and the associated extracted attributes have allowed better description of reservoir heterogeneities and more realistic assessment of hydrocarbons in place however the establishment of a complicated nonlinear relationship between seismic attributes and reservoir properties has been a major challenge for working geoscientists recently supervised neural networks have been used for predicting reservoir properties away from the boreholes in interwell regions after establishing the relationship between seismic attributes and well log data the effectiveness of these neural network techniques in 3d seismic interpretation is demonstrated in this paper through a real data example from india s cambay basin

observations of stratified turbulent mixing in an estuary neap to spring variations during high river flow abstract observations of turbulent mixing stratification and currents were made with a free falling microstructure profiler and a 600 khz adcp in the hudson river off manhattan in may 1994 the ship was anchored in a relatively straight and uniform channel about 15 m deep over 4 days of intense observations from 19 to 24 may 1994 the progression from neap tides to spring tides caused a severe reduction in stratification from an initial top to bottom salinity difference of 18 to 3 6 while low gradient richardson numbers ri occurred only in the weakly stratified bottom layer on flood during neap tides low ri spanned the water column on the second half of ebb during spring tides turbulent dissipation rates varied roughly inversely to ri during neap conditions turbulent mixing was intense only in the bottom layer on flood where eddy diffusivities k reached more than 10 2 m 2 s 1 while mixing was weak in the centre of the halocline near 5 m during spring tides strong mixing occurred throughout the water column during the latter part of ebb with typical k 5 10 3 m 2 s 1 and typical vertical salt flux of 0 0015 kg m 2 s 1 if it existed in isolation this flux would eliminate the haline stratification on a time scale of 4 h ebb time bands of low ri and intense mixing showed increasing phase lag with increasing distance from the bottom the spring tide ebb time internal turbulent stress was relatively uniform with depth with a typical magnitude of 0 4 pa 4 dyne cm 2 turbulent overturning thorpe scales ranged from below 1 cm in the neap tide halocline to a few metres in the weakly stratified bottom layer on flood the strong spring tide ebb time mixing had thorpe scales of typically 0 5 m throughout the water column ozmidov scales tracked thorpe scales except in the weakly stratified layer above the bottom

modulation of the semidiurnal cycle of turbulent dissipation by wind driven upwelling in a coastal embayment with two 25 hour series of turbulent microstructure and currents observations carried out in august 2013 during spring chaos 1 and neap tides chaos 2 we investigated the semidiurnal cycle of turbulent dissipation in an embayment affected by coastal upwelling ria de vigo nw iberia at the time of sampling the bay hosted a net wind driven bi directional positive exchange flow and thermal stratification turbulent kinetic energy tke dissipation e at the interface between upwelled and surface waters was enhanced by two orders of magnitude during the ebbs 10 6 w kg 1 with respect to the floods 10 8 w kg 1 this pattern was caused by the constructive interference of the shear associated with the upwelling and tidal currents the vertical structure of the tidal currents was consistent with a deformation of tidal ellipses by stratification which was tightly coupled to the intensity of upwelling this two pronged interaction resulted in a modulation of the semidiurnal cycle of turbulent dissipation by coastal upwelling thus as a result of the upwelling relaxation conditions experienced during chaos 1 depth integrated interior tke dissipation rates were higher by a factor of 2 compared to chaos 2 by using a simple model we determined that observed variations in turbulent mixing had a limited influence on the tidal variations of stratification which were dominated by straining and advection the mixing mechanism described here is potentially relevant for the ecology of upwelling bays as it can stimulate the transport of nutrients from deep upwelled waters to the sun lit surface layers where primary production takes place

porosity and lithologic estimation using rock physics and multi attribute transforms in balcon field colombia this study presents the results of integrating rock physics seismic inversion and multi attribute transforms to estimate reservoir rock properties of cretaceous aged sandstones from balcon field in the neiva basin upper magdalena valley colombia

intratidal variations in stratification and mixing in the hudson estuary this study represents a detailed examination of intratidal variations in boundary layer structure in a relatively narrow straight section of the hudson river estuary during high river discharge the presence of active mixing is inferred from estimates of the richardson number the maximum height above bed to which mixing occurs is comparable during flood and ebb however the regions of mixing differ in density structure during the flood active mixing is confined to a well mixed near bed layer whereas during the ebb active mixing occurs throughout regions of significant stratification tidal straining maintains stratification during the ebb while it promotes the growth of a uniform bottom mixed layer during the flood in general maximum and minimum near bed stratification occur during late ebb and flood respectively reflecting the dominant role played by tidal straining in determining intratidal variation vertical stretching was also found to be an important term in the stratification balance during the ebb

sedimentological and geoenvironmental evaluation of the coastal area between al khowkhah and al mokha southeastern red sea republic of yemen the increasing anthropogenic activities e g constructing touristic resorts have led to notable changes in the yemeni red sea coastal regions in this context recent sediments have been investigated to infer possible natural and man induced processes on these coastal areas the target area lies between longitudes 43 13 43 30 e and latitudes 13 15 13 55 n it extends about 90 km along the coastline as a part of the tihama plain geomorphologically it forms a long curved stretch with pronounced headlands embayments and bays generally it is covered by recent sediments wadi lagoon beach and spit deposits along with sabkha coastal dunes and mangrove textural studies reveal that most of the studied sediments are mainly poorly to moderately sorted and are composed mainly of sandy fractions with few gravel and mud mostly bimodal with minor unimodal patterns the igneous granites as well as basic basalt andesite and andesitic pyroclastics and acidic dacite and rhyolite volcanic rocks of tertiary age which are exposed to the east of the study area are believed to be the source of pyroxenes amphiboles epidotes biotite sphene zircon tourmaline and rutile in a decreasing order of abundance moreover smectite kaolinite chlorite illite and palygorskite are the predominant clay minerals mainly of detrital origin the total carbonate content fluctuates from 37 41 lagoon sediments to 53 74 sabkha sediments the high amount of sea grasses which covers the tidal flat zone and relates to the fine grained sediments accounts for the high organic matter content the mineralogy of the source rocks has controlled the general distribution of major elements fe mg na k and mn in the beach sediments in such sediments the concentrations of the heavy metals cu zn cd ni pb and co may reflect the sediment pollution using different approaches the enrichment factors efs of the trace metals for most samples reveal values that are greater than 1 referring to three groupings which are moderate to moderately severe zn cu and mn minor to moderate pb and co and zero to minor cd and ni enrichment the efs for pb cd ni and co metals 5 especially in al khowkhah abu zahr moushij zahari ruays yokhtol and mokha localities are possible of anthropogenic contributions

spatial and temporal variability of the velocity and hydrographic structure in a weakly stratified system broad sound casco bay maine the velocity and hydrographic structure across broad sound a north south orientated subsystem of casco bay me that lacks continuous coastal boundaries were characterized using velocity observations from two moorings in late summer fall of 2013 and velocity and density observations from a repeat transect ship survey conducted over a tidal cycle during the same period at tidal time scales the system is dominated by a barotropic semidiurnal standing wave with a west to east decrease in tidal amplitude and relatively minimal phase change across the majority of the transect the stratification vertical differences of 0 5 1 0 kg m 3 was generally laterally uniform and stronger during the flood phase which is hypothesized to result from stronger offshore stratification the mean circulation had strong lateral shear with inflow over the deepest point in the bathymetric cross section and eastern slope and outflow over the western slope there was also vertical shearing of the horizontal velocities with stronger northward or northward trending velocities at depth the depth averaged subtidal fluctuations were relatively small 2 3 cm s 1 and uncorrelated between mooring sites suggesting the vertically uniform current response associated with remote wind forcing is of limited importance on the other hand the depth dependent velocity fluctuations at the subtidal time scale were in large part 36 72 driven by wind forcing the net flux ratio a means of quantifying the relative importance of the vertical and lateral shear in the flow field was typically 0 44 indicating the structure of the local wind response favored vertically sheared flow

impact of the depth to width ratio of periodically stratified tidal channels on the estuarine circulation the dependency of the estuarine circulation on the depth to width ratio of a periodically weakly stratified tidal estuary is systematically investigated here for the first time currents salinity and other properties are simulated by means of the general estuarine transport model getm in cross sectional slice mode applying a symmetric gaussian shaped depth profile the width is varied over four orders of magnitude the individual along channel circulation contributions from tidal straining gravitation advection etc are calculated and the impact of the depth to width ratio on their intensity is presented and elucidated it is found that the estuarine circulation exhibits a distinct maximum in medium wide channels intermediate depth towidth ratio depending on various parameters which is caused by a maximum of the tidal straining contribution this maximum is related to a strong tidal asymmetry of eddy viscosity and shear created by secondary strain induced periodic stratification 2sips in medium channels transverse circulation generated by lateral density gradients due to laterally differential longitudinal advection induces stable stratification at the end of the flood phase which is further increased during ebb by longitudinal straining sips thus eddy viscosity is low and shear is strong in the entire ebb phase during flood sips decreases the stratification so that eddy viscosity is high and shear is weak the circulation resulting from this viscosity shear correlation the tidal straining circulation is oriented like the classical gravitational circulation with riverine outflow at the surface and oceanic inflow close to the bottom in medium channels it is about 5 times as strong as in wide quasi onedimensional channels in which 2sips is negligible

mechanisms of sediment transport and deposition sediment sequences and accumulation during the holocene on the thermaikos plateau the continental slope and basin sporadhes basin northwestern aegean sea greece abstract detailed 3 5 khz seismic reflection profiling carried out on the thermaikos plateau the slope and the basin sporadhes basin northwestern aegean has shown that during the holocene the area received fine grained sediments discharged mainly by the rivers axios aliakmon and pinios a well developed oblique sigmoid progradation pattern has been observed on the seismic profiles taken across the deltaic holocene sequences of these rivers three seismic facies have been identified within the oblique sigmoid pattern 1 dark homogeneous facies that represent fine sand deposits along the delta front topsets 2 stratified facies that represent alternating muddier or sandier horizons foresets and 3 transparent facies in which the muddy sediments predominate bottomsets the base of the holocene reflector c has been found beneath the oblique sigmoid pattern the thin homogeneous and transparent seismic facies throughout the slope and the basin has been interpreted as the holocene muddy sediment sequence in the area bottom samples from the outer thermaikos plateau have shown that it is floored by relict terrigenous sand at depths of 90 110 m the sediment and clay mineral distribution and the presence of relict sand confirm that during the holocene period the fine grained sediment dispersion and deposition was effected by the water mass circulation the majority 80 90 of the sediments dispersed from the rivers during the holocene has been captured by the extensive shelf thermaikos plateau having deposited from the near bottom nepheloid layer minor amounts 10 20 of very fine grained material have escaped and deposited from suspension hemipelagic settling in the slope and basin of the studied area

environmental control on shell structure and composition of agglutinated foraminifera along a proximal distal transect in the marmara sea abstract the study of benthic foraminifera in a complex marine system like the marmara sea is a key for understanding the influence of environmental factors on foraminiferal species density assemblage composition and shell construction this kind of study is important for further extensive use of foraminifera based investigation of water mass and sediment exchange between the eastern mediterranean and black sea through the marmara sea based on proximal distal transect from the southwest coast of the erdek bay to the top of canyon close to the north anatolian fault this study aims at defining the geochemical conditions at the seafloor and identifying the sediment constraints that act upon agglutinated test construction for selected species eggerelloides scaber textularia agglutinans textularia sagittula textularia truncata and textularia bocki grain size mineralogical and chemical analyses of their shells were investigated and confronted with the main geochemical conditions prevailing during deposition and within the sediment among grains used to construct the agglutinated foraminiferal tests from available grains both grain size selection and sorting have been evidenced this suggests that the mineralogical composition is related to the species and the sample localization within the basin our observations further suggest that bottom water conditions of the marmara sea do not have a significant influence on agglutinated foraminiferal shell development which is primarily driven by sediment characteristics our results are thus transposable to other environments

high resolution seismic reflection profiles for the reconstruction of postglacial transgressive shorelines an example from greece abstract in 1982 we carried out a shallow penetration high resolution seismic profiling study on the shelf of the southern argolid peloponnesos greece to identify and map the shores of the late pleistocene and holocene and to establish their coastal environments portable equipment and a local boat were used the lowest glacial shore occurs at 115 to 118 m within the range of global values the subsequent rise across the distinct old land surface left behind many shore features scaps beaches and beach ridges channels and lagoons now buried under a few meters of post transgressive deposits these features cluster at a small number of depths below present sea level suggesting that the rise of the sea usually too fast to leave an imprint was episodically interrupted by brief stillstands or even temporary reversals of climatic or tectonic origin the clusters can be roughly dated with reference to a global sea level rise curve after 6000 yr b p sparse archaeological data establish a local curve the seismic profiling technique convenient and not costly holds promise for the identification of postglacial shores elsewhere prior to sampling for dating it has wide application for environmental reconstructions of vanished coastal zones as a basis for prehistoric resource assessments these applications are illustrated with examples from this study

sediment yield studies of headwater catchments in sussex s e england the transport of sediment from six small 0 2 to 17 6 km2 headwater catchments is described the catchments under investigation were located in relation to predominant lithological deposits within the cretaceous rock succession two of the areas were underlain by weald clay two by sandstone ashdown sand and tunbridge wells sand and two by chalk the climate of the region under investigation is temperate with an average annual precipitation 850 mm in excess of potential evapotranspiration 450 mm the transport of suspended material from within the catchments was examined by collecting samples of the water sediment mixture draining the areas using hand held depth integrating and permanently installed stage sampling systems the results of the regularly maintained sampling programme over a two year period are described attempts were made to both measure and compute bed load transport suspended sediment concentrations are compared between catchments and related to hydrological characteristics the nature of the material in transit is examined sediment rating curves are derived for each of the headwater catchments defining the relationship in the form y axb where y suspended sediment concentration mg 1 and x water discharge m3 s annual rating curves are used to derive annual suspended sediment loads by combination with water discharge data using a log incremental computerized approach multiple regression techniques have been used to examine annual loads in terms of hydrological and morphological characteristics of the headwater catchments based on the field information available a generalized model for the relationship between suspended sediment concentration and water discharge is described finally the derived annual loads from the headwater catchments are combined with both limited observations from the larger sussex rivers and data available for other catchment investigations in the british isles to produce a series of prediction equations for catchment yield under temperate climatic conditions

gas charged sediments in the aegean and ionian seas greece abstract during the last fifteen years marine seismic surveys in the aegean and ionian seas have revealed numerous acoustic anomalies i e acoustic turbid zones gas pockets gas plumes enhanced reflectors columnar disturbances wipe outs and meso to micro morphological features such as pockmarks domes mud volcanoes and elongated depressions these are attributed to the presence of gas in sediment interstices the gas charged sediments are found in pleistocene and present day fjord like environments pleistocene and present day deltaic environments lakes and open sea environments the gas found in the quaternary fjord like and deltaic depositional environments is assumed to be of biogenic origin the gas found in the pre quaternary open sea environments is associated with faulting and salt doming and may therefore be of thermogenic origin although the sediment grain size is favourable for the formation of pockmarks the lack of them is probably due to the high seismicity which characterises these regions

geochemical and sedimentological patterns in the thermaikos gulf north west aegean sea formed from a multisource of elements surface sediment samples from thermaikos gulf were analysed for organic carbon cd pb cr cu zn mn ni co and fe and were subjected to grain size analysis the results showed that pb cu and zn had the same source of pollution in the following order of importance the sewage outfall the industrial zone and the axios river the concentration of these metals increased with decreasing mean grain size suggesting their association with the fine fraction of the sediments the clays and the organic matter cadmium was more loosely correlated with the metals of the previous group being derived from the community activities and also from the weathering of land based ophiolitic rocks iron cr ni co and mn are of natural origin the weathering of mafic and ultramafic rocks being responsible for their enrichment this was more apparent in the case of ni which was more enriched in the coarser and better sorted sediments near the delta of the river aliakmon

creation of residual flows in a partially stratified estuary the creation of residual flows in estuaries is examined using acoustic doppler current profiler data sets from northern san francisco bay the data sets are analyzed using principal component analysis to examine the temporal variability of the flows which create the residual circulation it is seen that in this periodically and partially stratified estuary the residual flows are created through a series of pulses with strong variability at the 24 hour timescale through the interaction of shear stratification and mixing this interaction is captured through the use of a dimensionless number the horizontal richardson number rix which is developed to examine the local balance between the stratifying and destratifying forces at the tidal timescale it is seen that rix is a valuable parameter in predicting the onset of the residual creating events with a threshold value of 3 on ebb tides this critical value is argued to be a threshold above which the stratification and shear flow create a feedback effect each further intensifying the other this feedback results in a highly variable exchange flow which creates the estuarine residual in intermittent pulses rather than as a steady flow although typically attributed to baroclinic forcing an argument is made that these pulses of residual creating exchange flow could be created by barotropic forcing in the presence of variable stratification which is asymmetric between flood and ebb tides this result poses a great challenge for turbulence modeling as the timing and magnitude of stratification and shear must be correctly simulated on the tidal timescale in order to reproduce the effects seen in the data sets presented

modern sedimentation in the n w aegean sea abstract the area under investigation is located within 22 45 to 23 45 e and from 39 15 to 40 15 n sedimentological bathymetric and shallow geophysical data were collected from here during the 7 78 cruise of r r s shackleton twenty seven sea bed surface samples were collected using a day grab from different environments these were analysed for grain size distribution carbonate content and clay mineralogy on the basis of the bathymetric and shallow geophysical data the area has been classified into five major physiographic environments according to their bathymetry and topography 1 shelf thermaicon plateau 2 slope 3 marginal plateau 4 the canyon system and valleys and 5 sporades basin based on the sedimentological analyses the surface sediments have been classified into four major provinces as follows 1 province 1 shelf muds 2 province 2 muddy sands 3 province 3 outer margin muds and 4 province 4 outer shelf shelf break it is concluded that modern sedimentation in the n w aegean sea is dominated by the terrigenous river inputs and by the circulation of both high and low salinity masses

evros delta evolution of continental shelf sediments abstract investigations of the continental shelf sediments off the evros river delta involved a study of 40 bottom samples and three short piston cores which were examined concurrently with current measurements aerial photographs and physical oceanographic parameters sedimentological processes are more related to the suspended load discharged from the evros river and near bottom currents rather than to the bathymetry of the area

delta progradation and sediment fluxes since the last glacial in the thermaikos gulf and the sporades basin nw aegean sea greece abstract late quaternary sedimentary cover in the thermaikos gulf consists of three seismic units i the uppermost unit a that represents delta progradation during the last 6000 yr when the sea surface almost reached the present level highstand systems tract hst ii unit b that includes relatively coarse grained sediments deposited in a shallow high energy estuarine environment during the post glacial transgression transgressive systems tract tst and iii the lowest unit c which may represent late glacial prodeltaic deposits and slope to basin turbidites lowstand systems tract lst seismic units a and b overlay a well defined unconformity which resulted from sub aerial erosion during the late glacial sea level fall subtracting the thickness of unit a from the present bathymetry the paleo relief of the late holocene times ca 6000 yr bp sea level up to 20 m was assessed similarly the paleo relief 24 000 yr bp sea level 100 to 120 m was estimated the main morphological feature is the incised valley of a major river that resulted from the confluence of the axios aliakmon loudias gallikos and possibly pinios rivers sediment fluxes in the nw aegean sea were estimated for three time spans of the late quaternary interval i 6000 yr bp present interval ii 18 000 6000 yr bp and interval iii 24 000 18 000 yr bp the terrestrial sediment load supplied by the axios aliakmon pinios and smaller rivers was estimated at 35 4 10 9 t for interval i 93 of this material was deposited on the continental shelf whereas the remaining 7 was transported to the adjacent basin the mean annual terrestrial flux was estimated at 5 5 10 6 t yr 1 during interval ii more than 79 10 9 t of terrestrial sediment were discharged into the area terrestrial flux 6 6 10 6 t yr 1 of which 86 was deposited on the shelf during interval iii the terrestrial load was 40 6 10 9 t terrestrial flux 6 8 10 6 t yr 1 and sediments were predominantly deposited on the slope and basin based on the sediment s carbonate content the biogenic loads and fluxes were also determined the biogenic flux during intervals ii and iii was found to be 2 5 times higher than during interval i

origin of late glacial holocene hemipelagic sediments in the aegean sea clay mineralogy and carbonate cementation abstract four hemipelagic lithological units are identified in the late glacial to holocene sediments in the aegean sea these lithologies are silty clay and clay in texture and include a varying mixture of loose terrigenous sediments supplied from the adjacent landmass gravel to sand sized cemented carbonate clasts and nodules sand to silt sized air born volcanic debris and biogenic remains sediment dispersal during the past 14 000 years was controlled mainly by the fluvial discharge rate by sea level variations which determined the proximity of basins to river mouths and by oceanographic conditions in the aegean sea cemented carbonate clasts and nodules occur in all sediments except unit c sapropel s1 they are well to friably cemented mottled to peloidal micrite or microcrystalline inter granular cement between terrigenous and bioclastic debris and the carbonate is 10 11 mole magnesium calcite during the deposition of sapropel s1 unit c the aegean sea was strongly stratified with colder more saline water masses occupying the deep basins which prevented the development of cemented carbonate nodules and clasts aragonite as pteropods and microcrystalline aragonite is present throughout the cores and together with the cemented carbonate clasts and nodules show that shallow pore waters in the aegean sea have been saturated to supersaturated with respect to both aragonite and magnesium calcite for at least the past 14 000 years results of xrd studies show that unit c sapropel s1 is characterized by lower smectite and kaolinite and higher illite and chlorite than the other units lower smectite illite and kaolinite chlorite ratios in unit c may reflect increased supply of illite and chlorite from european lowland rivers flowing into the black sea from rivers discharging directly into the northern and eastern aegean sea and decreased supply of kaolinite which is mainly of north african origin

the dynamics of a partially mixed estuary measurements of velocity density and pressure gradient in the lower hudson river estuary were used to quantify the dominant terms in the momentum equation and to characterize their variations at tidal and spring neap timescales the vertical momentum flux assumed to be due mainly to turbulent shear stress was estimated indirectly based on the residual from the acceleration and pressure gradient terms the indirect estimates of stress compared favorably to bottom stress estimates using a quadratic drag law supporting the hypothesis that the tidal momentum equation involves a local balance between tidal acceleration pressure gradient and stress divergence estimates of eddy viscosity indicated that there was significant tidal asymmetry with flood tide values exceeding ebb values by a factor of 2 as a consequence of the asymmetry the vertical structure of the tidally averaged stress bore no resemblance to the tidally averaged shear in spite of the asymmetry of vertical mixing the tidally averaged estuarine circulation was found to depend simply on the intensity of bottom turbulence which could be parameterized by a rayleigh drag formulation based on the tidal velocity magnitude and the tidally averaged near bottom flow this seemingly paradoxical result indicates that the estuarine circulation can be modeled without detailed knowledge of the effective eddy viscosity only requiring an estimate of the bottom drag coefficient the tidal forcing conditions and the baroclinic pressure gradient a notable characteristic of this solution is an inverse dependence of the estuarine circulation on the amplitude of the tides

water masses in thermaicos gulf north western aegean sea physical oceanographic data were collected during september 1975 at stations in the shallow water max depth 45 m embayments of salonica bay and thermaicos gulf and comparisons are made with data collected during other seasons the distribution of temperature and salinity in the water column indicated the following features fresh surface water predominantly related to river discharge an intermediate water mass apparently formed by mixing between the fresh and open sea waters a thermocline and deep bottom water open sea characteristics the summer distribution of density in the surface and bottom waters and the seasonal variation in the pattern of surface salinity suggested an anti clockwise water circulation throughout the embayments

axial convergence in a well mixed estuary abstract transverse secondary circulations involving surface convergence observed in a well mixed estuary in north wales are made visible by the collection of surface material along an axial line which extends continuously for many kilometres through the estuary the circulation and axial convergence however are seen only during the flood phase of the tide and no similar behaviour has been observed during the ebb phase convergent circulations in the estuary are associated with small but steady transverse density gradients in the cross section produced by non uniform advection of the longitudinal gradient through the channel a diagnostic model using measured mean distributions of cross sectional density indicates surface transverse velocities 0 1 ms 1 similar to those observed in the estuary the model further predicts appreciable transverse divergent currents at a fractional depth of 0 75 a prediction which has been tested in the estuary using a vertical array of accurately resolving current direction indicators

the geology and geochemistry of the surficial sediments off thraki northern greece abstract a geological and geochemical investigation has been carried out on the surficial sediments of the samothraki plateau an area of some 4600 km 2 off thraki northern greece most of the surface sediments are sands or silty sands but finer grained sediment occurs near the mouths of the main rivers and seawards of the shelf break the sediments are a mixture of several phases modern river run off reworked older sediments and biogenic material modern sedimentation is only important near the main river mouths and in nearshore areas where coastal erosion is taking place the silty sands and sands which cover much of the mid shelf are relict sediments although their fine grained component may have been brought in by recent current action the fe and al contents of the sediments closely reflect the amounts of very very fine sand or silt and clay sized material present the distribution of ti cr and zr largely follows that of fe and al although significant enrichments occur major deposits of ti cr or zr bearing placers do not seem likely in surface sediments in this area on the basis of the present survey

lateral circulation generates flood tide stratification and estuarine exchange flow in a curved tidal inlet abstractcross channel transect measurements of microstructure and velocity in a well mixed and curved tidal inlet in the german wadden sea show the occurrence of significant late flood stratification this stratification is found to be a result of lateral straining this study observes a strong single cell lateral circulation which is strongly pronounced at late flood and absent during most of ebb this tidal asymmetry is caused by a systematic interplay between centrifugal forcing and the lateral baroclinic pressure gradient during flood a positive feedback between the terms generates strong lateral circulation whereas during ebb a negative feedback leads to a suppression of the cross channel exchange a theoretical framework based on vorticity is developed which allows lateral and longitudinal circulation to be studied in a consistent way with this framework it is possible to show that the tidal asymmetry of the lateral flow is a major driver of residual longitudinal estuarine circulation here ide

origin and distribution of clay minerals in the alexandroupolis gulf aegean sea greece the mechanisms of clay mineral distribution in alexandroupolis gulf are studied the annual solid supply of the evros river flowing into the gulf amounts to at least 1 000 000 m3 the surficial bottom sediments are commonly fine grained and are distributed along zones almost parallel to the coastline in the central part of the gulf clay silt size sediments predominate the main clay minerals in the size fractions 2 1 1 0 25 and 0 25 m are illite smectite kaolinite and in small amounts interstratified illite smectite quartz feldspars amphiboles and chlorite occur in traces in the coarser fraction 2 1 m of some samples all the above minerals are the weathering products of the evros river drainage basin as well as of the neogene and quaternary unconsolidated sediments of the coast the hydrodynamic regime and physical grain size are the main mechanisms which control the distribution of the clay minerals in the gulf the low content of kaolinite in all samples and the presence in traces of chlorite and amphiboles in some coarse clay fractions may be due to the unfavourable climatic and physicochemical conditions as well as to the rapid transport and deposition of freshly weathered material

the paleoclimatic interpretation of clay minerals in sediments a review abstract the application of paleoclimatic interpretation to clay minerals from continental and marine sediments is reviewed and the advantages of this method are indicated levels relatively rich in chlorite illite palygorskite and quartz are interpreted as corresponding to relatively dry periods while more humid periods lead to more intensive weathering and consequently to the dominance of clay minerals more advanced in the relative stability scale such as kaolinite smectite is taken to indicate a climate with contrasting seasons and a pronounced dry season using this and similar schemes the paleoclimates of areas adjoining the mediterranean basin north sea north atlantic southern arctic equatorial and north west pacific and north phillipine sea are reconstructed clay minerals in sediments particularly marine sediments can be useful indicators of paleoclimatic conditions while they do not produce direct indications of climatic parameters they provide integrated records of overall climatic impact occasionally they may be superior to the more conventional paleoclimatic methods such as pollen or oxygen isotope analysis the limitations imposed on the paleoclimatic interpretation of clay minerals in sediments are discussed on the basis of examples the distinction between authigenic and detrital clay minerals is shown to be problematic particularly with regard to smectite the relationship between climatic parameters and clay mineral formation is complicated by the intervention of extra climatic factors such as topography geomorphology lithology and time post depositional diagenetic changes may not be recognized differentiation during transport due to size sorting or differential flocculation may overlap climate induced differentiation the association of clay mineral assemblages with specific source areas presents difficulties due to dispersal pathways that are affected by type of transport agency i e water ice or wind transport agencies are not constant with time by an interdisciplinary approach with the paleoclimatic information derived from clay minerals being correlated with that obtained from the analysis of microfossils and oxygen isotope data many of these limitations can be overcome

sliding and regional slope stability in active margins north aegean trough mediterranean continuous seismic air gun sub bottom profiling in the north aegean has revealed a large submarine slide the failure zone extends from a depth of about 300 m down to 850 m and covers an area of 85 km2 the mean thickness of the slide reaches about 55 m and an estimated total volume of 3 8 km3 of late pleistocene sediments has slid a distance of 6 7 km chronostratigraphic analysis of the acoustic reflectors imply that the major and secondary glide planes are the transitional zones between a lower sequence of strongly stratified reflectors stiff relatively coarser sediment layers and the overlying acoustically transparent and or poorly stratified sequence weaker muddy layers with higher water content and lower shear strength these weak transparent layers have been deposited during interglacial high sea level stands isotopic stages 7 5 3 the major glide plane is assumed to have been developed within a muddy layer that was deposited about 170 245 ka bp stratigraphic sedimentological data and ams dates indicate an early holocene age of the major failure event not earlier than about 5 5 ka bp and not later than 7 8 ka bp the regional seismic hazard and slope stability analysis shows that the north aegean marginal upper middle slopes are highly unstable the calculated values of horizontal ground acceleration able to initiate failures kc range from 80 to 300 gal downslope this is lower than what is expected within 50 yr especially in the upper middle slopes

late quaternary sedimentation on the north aegean continental margin greece the late quaternary seismic stratigraphy of the north aegean continental shelf and adjacent basins has been interpreted from boomer and 3 5 khz seismic profiles ages derived from shallow cores and offshore wells and relative offsets on small synsedimentary faults provide chronological control sea level history inferred from seismic stratigraphy correlates with the global eustatic sea level record based on oxygen isotopic curves outer shelf progradation correlates with lowstands of sea level in isotopic stages 2 3 and 6 whereas shelf wide transgression surfaces correspond to the stage 6 5 and 2 1 transitions when rapid deglaciation occurred the present depth of the delta plain formed on the outer shelf during the late stage 6 lowstand provides a dated and originally horizontal marker for estimating rates of tectonic subsidence gross distribution of sediment facies is similar in both tectonically stable and active areas the shelf break formed by delta progradation but is marked by faults in most places because of the accommodation provided by graben subsidence rates of 0 3 1 5 mm yr standard sequence stratigraphic analysis can be applied to these sediments deposited during high amplitude quaternary sea level oscillations high rates of subsidence result in the preservation of an unusually complete record of sea level change major lowstand progradation is dependent on the duration rather than the magnitude of sea level lowstand the long glaciations in isotopic stages 6 12 16 and 22 resulted in the most prominent seaward progradation on the margin sandy lowstand turbidite deposits formed only when there was rapid fall in sea level otherwise sand was trapped on delta tops and silty muds were deposited in deep water

benthic foraminifer palaeoecology of the late quaternary continental outer shelf of a landlocked marine basin in central aegean sea greece abstract north evoikos gulf greece constitutes a landlocked epicontinental and semi enclosed basin connected to the central west aegean sea through a strait probably not allowing full exchange of intermediate and deep water masses benthic foraminifer analyses were carried out on a late quaternary core from the outer shelf of the basin with the aim of tracing palaeoceanographic changes the benthic foraminifer species percentage per sample was used to calculate two main biological proxies the benthic foraminifer oxygen index bfoi and benthic foraminifer high productivity bfhp proxy estimated by grouping benthic foraminifer taxa which are known to flourish under high corg flux the estimated values of bfhp and bfoi were controlled mainly by the abundance of bolivinid species which are generally considered as opportunistic and shallow infaunal species tolerant to low oxygen conditions the statistical analysis q mode cluster analysis singled out four time intervals each characterized by certain levels of oxygenation and food availability time interval 1 8513 8300 cal bp is characterized by a mixed fauna of oxyphilic taxa and taxa that live in suboxic environment indicating the existence of a relatively eutrophic system with a well oxygenated sediment water interface time interval 2 8300 8100 cal bp records a deterioration of conditions on sea floor testified by significant oxygen and biotic diversity decrease benthic foraminifer composition in time interval 3 8100 7000 cal bp depicts environmental conditions still highly variable yet with faunal indication of more stable conditions than during the previous interval finally the benthic foraminifer assemblage of time interval 4 7000 3500 cal bp is related to the high food supply and good bottom circulation the data suggest a strong linkage between the quantity and quality of the organic matter supplies and the diversity and composition of the benthic foraminifer faunas moreover this study clearly demonstrates that vertical tectonic movements need to be taken into account when reconstructing the late quaternary palaeoceanography of this region

the influence of lateral advection on the residual estuarine circulation a numerical modeling study of the hudson river estuary abstract in most estuarine systems it is assumed that the dominant along channel momentum balance is between the integrated pressure gradient and bed stress scaling the amplitude of the estuarine circulation based on this balance has been shown to have predictive skill however a number of authors recently highlighted important nonlinear processes that contribute to the subtidal dynamics at leading order in this study a previously validated numerical model of the hudson river estuary is used to examine the forces driving the residual estuarine circulation and to test the predictive skill of two linear scaling relationships results demonstrate that the nonlinear advective acceleration terms contribute to the subtidal along channel momentum balance at leading order the contribution of these nonlinear terms is driven largely by secondary lateral flows under a range of forcing conditions in the model runs the advective acceleration terms nearly always act in concert with the baroclinic pressure gradie

temporal variations in sedimentation patterns nw aegean sea abstract cores are examined from the northern continental slope environment of the sporadhes basin the western part of the north aegean sea trough three distinct lithofacies have been identified which correspond with similar environments identified elsewhere in the western and southeastern mediterranean these layers turbiditic mud hemipelagic mud calcareous ooze represent late quaternary climatic and eustatic sea level changes and tectonic activity based on benthic foraminiferal evidence from the eastern part of the north aegean sea trough it is suggested that contemporary sediment supply and physical oceanographic conditions in the area under investigation might be conducive to sapropel formation also that the depositional sequence in the cores represents a gradual recovery in the mediterranean sea since its last stagnation and sapropel formation some 8000 years ago

the influence of the evros river on the recent sedimentation of the inner shelf of the ne aegean sea the transboundary evros river discharges into the alexandroupolis gulf located in the inner shelf of the northeastern aegean sea where it has formed an extended delta grain size and mineralogical analyses of five sediment cores collected in the subaqueous delta provide the following information about recent sedimentation processes in the northeastern part of the aegean shelf a river mouth deposits consisting of coarse grained sediments are mainly deposited in front of the active mouth whilst some sandy material is expected to be transported alongshore by nearshore currents b delta front deposits are characterised by fine grained sediments that include evidence of human activities which have taken place in a more intense way since the 1950s and c prodelta deposits are represented by almost uniform riverine mud that cover the pre existed relict sands of the shelf indicating also the limit some 15 km to the sw of the influence of riverine sedimentation on the seabed of the inner shelf of the alexandroupolis gulf

estuarine boundary layer mixing processes insights from dye experiments a series of dye releases in the hudson river estuary elucidated diapycnal mixing rates and temporal variability over tidal and fortnightly time scales dye was injected in the bottom boundary layer for each of four releases during different phases of the tide and of the spring neap cycle diapycnal mixing occurs primarily through entrainment that is driven by shear production in the bottom boundary layer on flood the dye extended vertically through the bottom mixed layer and its concentration decreased abruptly near the base of the pycnocline usually at a height corresponding to a velocity maximum boundary layer growth is consistent with a one dimensional stress driven entrainment model a model was developed for the vertical structure of the vertical eddy viscosity in the flood tide boundary layer that is proportional to u 2 n where u and n are the bottom friction velocity and buoyancy frequency above the boundary layer the model also predicts that the buoyancy flux averaged over the bottom boundary layer is equal to 0 06n u 2 or based on the structure of the boundary layer equal to 0 1nblu 2 where nbl is the buoyancy frequency across the flood tide boundary layer estimates of shear production and buoyancy flux indicate that the flux richardson number in the flood tide boundary layer is 0 1 0 18 consistent with the model indicating that the flux richardson number is between 0 1 and 0 14 during ebb the boundary layer was more stratified and its vertical extent was not as sharply delineated as in the flood during neap tide the rate of mixing during ebb was significantly weaker than on flood owing to reduced bottom stress and stabilization by stratification as tidal amplitude increased ebb mixing increased and more closely resembled the boundary layer entrainment process observed during the flood tidal straining modestly increased the entrainment rate during the flood and it restratified the boundary layer and inhibited mixing during the ebb

quantifying the contributions of tidal straining and gravitational circulation to residual circulation in periodically stratified tidal estuaries abstract this numerical modeling study quantifies for the first time the contribution of various processes to estuarine circulation in periodically stratified tidal flow under the impact of a constant horizontal buoyancy gradient the one dimensional water column equations with periodic forcing are first cast into nondimensional form resulting in a multidimensional parameter space spanned by the modified inverse strouhal number and the modified horizontal richardson number as well as relative wind speed and wind direction and the residual runoff the along tide momentum equation is then solved for the tidal mean velocity profile in such a way that it is equated to the sum of the contributions of tidal straining resulting from the temporal correlation between eddy viscosity and vertical shear gravitational circulation resulting from the depth varying forcing by a constant horizontal buoyancy gradient wind straining and depth mean residual flow resulting from net freshwater runoff this definitio

near bottom turbulence measurements in a partially mixed estuary turbulent energy balance velocity structure and along channel momentum balance abstract a set of moored bottom mounted and shipboard measurements obtained in a straight section of the lower hudson estuary during late summer and early fall of 1995 determine velocity density and along channel pressure gradient throughout the 15 m water column as well as providing direct eddy correlation estimates of reynolds stress and indirect inertial range estimates of dissipation within 3 m of the bottom the analysis focuses on testing 1 a simplified turbulent kinetic energy equation in which production balances dissipation 2 the prandtl karman law of the wall which is a relationship between bottom stress and near bottom velocity gradient and 3 a simplified depth integrated along channel momentum balance involving local acceleration pressure gradient and bottom stress estimates of production and dissipation agree well throughout the entire record the relationship between bottom stress and velocity gradient is consistent with the law of the wall within approximately 1 m of the sea

reducing uncertainty in characterization of vaca muerta formation shale with poststack seismic data the late jurassic early cretaceous vaca muerta vm formation in the neuquen basin has served as an important source rock for many of the conventional oil and gas fields in argentina with the interest in developing and exploiting shale resources in the country many companies there have undertaken characterization of the vm formation in terms of the elements of shale plays among other characteristics shale plays can be identified based on the total organic carbon toc content better toc leads to better production however there is no way of measuring it directly using seismic data and it can be estimated only indirectly considering the influence of toc on compressional and shear velocities and density geoscientists have attempted to compute it using the linear or nonlinear relationship it might have with p impedance understanding the uncertainty in using such a relationship for characterizing the vm formation a different approach has been followed for characterizing it because a linear relationship seems to exist between gamma ray gr and toc in addition to p impedance gamma ray is another parameter of interest for characterizing the vm formation using p impedance and gr volumes a bayesian classification approach has been followed to obtain a reservoir model with different facies based on toc and the associated uncertainty with it as the first step different facies were defined based on the cutoff values for gr and p impedance computed from well log data then gaussian ellipses were used to capture the distribution of data in a crossplot of gr versus p impedance next 2d probability density functions pdfs were created from the ellipses for each of the facies combining these pdfs with gr and p impedance volumes different facies were identified on the 3d volume poststack model based inversion was used to compute the p impedance volume and the probabilistic neural network pnn approach was used to compute gr volume derived p impedance and gr volumes correlated nicely at blind wells on the 3d volume which gave confidence in the characterization of the vm formation an overlay of the discontinuity detail in terms of curvature lineaments on the determined toc content at the level of interest helps in obtaining a more complete picture which is useful for the planning of horizontal wells

late quaternary sea level change sedimentation and neotectonics of the gulf of gokova southeastern aegean sea abstract the sedimentary and tectonic late quaternary evolution of the gulf of gokova located at the southwest anatolia southeastern aegean sea region has been interpreted from 800 line km of 3 5 khz and single channel airgun seismic reflection profiles the older part of the gokova basin is formed by mainly e w trending faults and filled by the latest miocene pliocene quaternary hemipelagic sediments with thickness up to 2 5 km the lycian nappes which primarily cover extreme southwestern anatolia represent the basement rocks for the gokova region younger active faulting so called gokova transfer fault gtf which has not been previously discussed in the literature trends ne in the central part of the gulf of gokova basin and records sinistral strike slip motion broadly parallel to the convergence direction of the aegean anatolian and african plates the continental shelf of the northeastern gulf of gokova is mostly formed by numerous superimposed deltaic successions depositional sequences separated by major erosional unconformities during times of lowered sea level associated with late quaternary glaciations deltas prograded more than 40 km seaward from their present positions foreset progradation terminated with the rise of sea level in interglacial and post glacial times and deltas were relocated far inland these major transgressions resulted in unconformities that are correlated with the beginning of oxygen isotope stages 9 7 5 and 1 and provide chronostratigraphic markers for a detailed analysis of sedimentation patterns in the late quaternary all seismic lines show that the topset to foreset transition of the youngest pleistocene delta system developed around 145 150 ms below present sea level thus the maximum pleistocene sea level lowering 18 000 years bp was about 110 m the positions of maximum regression for isotopic stages 6 8 and 10 were found as 160 190 and 215 m below present sea level respectively paleo shoreline positions during isotopic stages 2 6 and 8 suggest an overall gradual subsidence of gokova basin during the last 0 5 ma in the southeastern aegean sea the seismic sedimentary chronology suggests that the gokova basin is subsiding at 0 3 0 4 mm year three bathymetric low and e w wnw ese directed two main ridges in the gulf area are noticeable from the bathymetric data and are well correlated to the seismic data while the main orientation of the gulf is e w more recent ene wsw and wnw ese structures are remarkable in the western and the mid eastern part of the gulf respectively subsidence rates are greatest in the southern center of the basin and decrease northward so that the northern area is being tilted southward

elastic parameter estimation for the identification of sweet spots vaca muerta formation neuquen basin argentina abstract early identification of zones with possible good production sweet spots in shale plays is important to optimize the return on capital investment analyzing elastic rock properties helps in the identification of sweet spots in the vaca muerta formation the vertical and lateral heterogeneity of total organic carbon toc and carbonate content are two critical factors that partly control the geomechanical response of the rock unconventional reservoirs have low permeability making it necessary to define brittle zones to stimulate the rock and induce fractures to produce this leads to the definition of mineralogy ranges that help discriminate brittle and ductile rock based on rock properties this study is based on a 3d seismic survey and several vertical pilot wells with full log suites horizon interpretations and logs are used to build a low frequency model that together with prestack seismic data is input for seismic inversion inversion results predict poisson s ratio v directly and to

the importance of tidal and lateral asymmetries in stratification to residual circulation in partially mixed estuaries measurements collected in the york river estuary virginia demonstrate the important impact that tidal and lateral asymmetries in turbulent mixing have on the tidally averaged residual circulation a reduction in turbulent mixing during the ebb phase of the tide caused by tidal straining of the axial density gradient results in increased vertical velocity shear throughout the water column during the ebb tide in the absence of significant lateral differences in turbulent mixing the enhanced ebb directed transport caused by tidal straining is balanced by a reduction in the net seaward directed barotropic pressure gradient resulting in laterally uniform two layer residual flow however the channel shoal morphology of many drowned river valley estuaries often leads to lateral gradients in turbulent mixing tidal straining may then lead to tidal asymmetries in turbulent mixing near the deeper channel while the neighboring shoals remain relatively well mixed as a result the largest lateral asymmetries in turbulent mixing occur at the end of the ebb tide when the channel is significantly more stratified than the shoals the reduced friction at the end of ebb delays the onset of the flood tide increasing the duration of ebb in the channel conversely over the shoal regions where stratification is more inhibited by tidal mixing there is greater friction and the transition from ebb to flood occurs more rapidly the resulting residual circulation is seaward over the channel and landward over the shoal the shoal channel segregation of this barotropically induced estuarine residual flow is opposite to that typically associated with baroclinic estuarine circulation over channel shoal bathymetry

lateral variability of sediment transport in the delaware estuary lateral processes contribute significantly to circulation and material transport in estuaries the mechanisms controlling transport may vary spatially such that shallow and deep regions of an estuary contribute differently to the total transport an observational study was conducted to explore the importance of lateral variability in sediment transport mechanisms in the delaware estuary seven moorings were deployed across the channel in the region of the estuarine turbidity maximum etm zone from april to august 2011 time series of along channel sediment transport reveal a consistent pattern of sediment export across the entire estuary during periods of high river discharge followed by a transition to import within the channel and export on the flanks during low river flow there is a persistent divergence of across channel sediment fluxes on the delaware side where sediment from the flank is transported toward both the channel and wetland coast decomposition of the fluxes highlight that across channel sediment transport is driven by mean lateral circulation whereas along channel transport is driven primarily by mean advection with tidal pumping contributing to about 30 of total transport the spatial and temporal variability of mean advection and tidal pumping were generally complementary with both contributing to the observed sediment transport pathways tidal pumping linked to tidal asymmetries in stratification and sediment resuspension was shown to drive both ebb driven export and flood driven import depending on the tidal variability of stratification the spatiotemporal patterns of sediment transport highlight the three dimensional structure of the etm and shed light on the variability of sediment transport mechanisms

late pleistocene holocene sedimentation in the nw aegean sea a palaeoclimatic palaeoceanographic reconstruction sedimentological particle size organic carbon calcium carbonate clay mineralogy and radiocarbon dating and micropalaeontological investigation of 9 cores from the nw aegean sea eastern mediterranean have enabled five main lithological units to be identified the units cover a period from the late pleistocene to the present day on the basis of these results and reference to other studies a palaeo reconstruction is presented for the area the reconstruction takes into account the increase in sea level during the period the decrease in fluvial inputs issuing to the area from the north mediterranean coastline and the possible influence of water issuing from the black sea it is concluded that the sedimentological and oceanographic regimes of the area were strongly influenced by a fluvial component during the late pleistocene and early holocene whereas today the sedimentary record is more indicative of an open oceanic environment

modeling the lateral circulation in straight stratified estuaries the dynamics of lateral circulation in an idealized straight estuary under varying stratification conditions is investigated using a three dimensional hydrostatic primitive equation model in order to determine the importance of lateral circulation to the momentum budget within the estuary for all model runs lateral circulation is about 4 times as strong during flood tides as during ebbs this flood ebb asymmetry is due to a feedback between the lateral circulation and the along channel tidal currents as well as to time varying stratification over a tidal cycle as the stratification is increased the lateral circulation is significantly reduced because of the adverse pressure gradient set up by isopycnals being tilted by the lateral flow itself when rotation is included a timedependent cross channel ekman circulation is driven and the tidally averaged bottom lateral circulation is enhanced toward the right bank when looking toward the ocean in the northern hemisphere this asymmetry in the tidally averaged bottom lateral circulation may lead to asymmetric sediment transport leading to asymmetric channel profiles in straight estuaries for the weakly stratified model run advection due to lateral currents is a dominant term in both the along channel and cross channel momentum equations over a tidal cycle and for the tidally averaged momentum equations in the tidally averaged along channel momentum equation lateral advection acts as a driving term for the estuarine exchange flow and can be larger than the along channel pressure gradient therefore it should not be ignored when estimating momentum budgets in estuaries

role of asymmetric tidal mixing in the subtidal dynamics of narrow estuaries 1 the role of asymmetric tidal mixing atm in subtidal estuarine dynamics is investigated using a series of generic numerical experiments that simulate narrow estuaries under different stratification and external forcing conditions the focus is on quantifying the characteristics of atm induced flow and its contributions to stratification and salt transport the flow induced by atm has a two layer vertical structure in periodically stratified estuaries similar to that of the density driven flow it has a three layer vertical structure in the central regime of weakly stratified estuaries and a reverse two layer structure in highly stratified estuaries the changes in vertical distribution of atm induced flows result from the influence of stratification on the covariance of eddy viscosity and vertical shear such covariance represents the driving force of atm induced flow in the tidally averaged momentum equation compared to density driven flow atm induced flow dominates in periodically stratified estuaries with strong tides has the same order of magnitude in weakly stratified estuaries with moderate tides and is less important in highly stratified estuaries with weak tides in contrast to density driven flow that always increases estuarine stratification and transports salt landward the atm induced flow exhibits different behaviors because of its varying vertical structure in estuaries with strong tides atm induced flow tends to enhance stratification and to transport salt landward similar to density driven flow in estuaries with weak tides atm induced flow tends to reduce stratification and to transport salt seaward

distribution of clay minerals in surface sediments of the aegean sea a compilation extensive published data sets and some new data on the clay mineral composition of surface sediments in the aegean sea northeastern mediterranean sea have been compiled in order to map the distribution patterns of clay mineral assemblages and to decipher source areas and transport paths we distinguished six provinces a northwest aegean province a marmara dardanelles province a west turkey province a southeast aegean province a kithira province and a central aegean province the clay mineral assemblages in the coastal and shelf areas carry the signature of the riverine sediment discharge from southeast europe and turkey respectively the southern aegean sea is probably influenced by the river nile discharge and transport of clay minerals by surface currents the clay minerals in the central aegean sea form a mixed assemblage comprising components of the other assemblages a dispersion and dilution of clay minerals by surface currents is obvious

observations of turbulence in a partially stratified estuary the authors present a field study of estuarine turbulence in which profiles of reynolds stresses were directly measured using an adcp throughout a 25 h tidal day the dataset that is discussed quantifies turbulent mixing for a water column in northern san francisco bay that experiences a sequence of states that includes a weak ebb and flood that are stratified followed by a strong and eventually unstratified ebb and flood these measurements show that energetic turbulence is confined to a bottom mixed layer by the overlying stratification examination of individual reynolds stress profiles along with profiles of richardson number and turbulent froude number shows that the water column can be divided into regions based on the relative importance of buoyancy effects using the measured turbulence production rate p the dissipation rate e is estimated the observed turbulence had values of e nn 2 20 all of the time and e nn 2 200 most of the time suggesting that the observed motions were buoyancy affected turbulence rather than internal waves however at times turbulent froude numbers in much of the upper water column were less than one indicating important stratification effects taken as a whole the data show that stratification affects the turbulent velocity variance q2 most severely that is observed reductions in u9w9 are largely associated with small values of q2 rather than with a dramatic reduction in the efficiency with which turbulent motions produce momentum fluxes finally the dataset is compared to predictions made using the popular mellor yamada level 2 5 closure these comparisons show that the model tends to underestimate the turbulent kinetic energy in regions of strong stratification where the turbulence is strongly inhomogeneous and to overestimate the turbulent kinetic energy in weakly stratified regions the length scale does not appear to compensate for these errors and as a result similar errors are seen in the eddy viscosity predictions it is hypothesized that the underestimation of q2 is due to an inaccurate parameterization of turbulence self transport from the near bed region to the overlying stratification

the alteration of lateral circulation under the influence of human activities in a multiple channel system changjiang estuary abstract extensive coastal engineering activities including channel dredging and constructions of large infrastructure have greatly altered hydrodynamics in the changjiang estuary while the changes in longitudinal circulation have been well documented limited studies have focused on the alteration in lateral circulation and its impact on estuarine circulation in the changjiang estuary lateral circulation in an estuary plays an important role in modulating estuarine circulation sediment transport and morphological change different from many of previous numerical studies we utilize an unstructured grid numerical model configured in a way to allow inundation over dikes and tidal flats numerical model experiments show significant changes in lateral circulation and stratification along the north passage in response to the altered geometry and bathymetry due to the channel deepening and the dike construction both the channel deepening and the dike construction led to an enhanced stratification further analysis suggests that the along channel the lateral and the vertical including up and downwelling and vertical mixing effects are all important in modulating the intra tidal stratification destratification process the channel deepening enhances both the lateral and the vertical effects around the high water slack the construction of dikes that completely blocks the lateral water exchange between the north passage and surrounding tidal flats changes the system from a multiple channel system into a single channel system with dike construction the estuarine circulation tends to have a horizontally sheared pattern with weaker friction and a stronger stratification

geochemistry and mineralogy of the nw aegean sea surface sediments implications for river runoff and anthropogenic impact abstract surface sediments of the nw aegean sea were analyzed for clay mineral composition 94 samples organic c and carbonate content and major and minor elements 112 samples illite is the most abundant clay mineral followed by smectite chlorite and kaolinite clay minerals are preferentially deposited within the continental shelf and slope environment due to the prevailing cyclonic circulation and the formation of flocs in the rivers pro delta areas the spatial distribution of major lithogenic elements si al ti fe is substantially biased by the presence of relict sands located in the central eastern part of the thermaikos gulf continental shelf biogenic elements ca sr are noticeably pronounced on the northern flank of the north sporades islands organic c content and minor elements cu zn as and pb are enriched markedly over the thessaloniki bay and gulf suggesting substantial human impact deriving largely from untreated or partly treated domestic and industrial effluents the terrigenous component of the elements is preferentially contributed from the axios river zn and pb the aliakmon river cr co ni cu and as and to a lesser extent from the pinios river v co ni and cu a considerable part of the metals originates in ultra mafic and volcanic formations which are abundant in the rivers catchment basins carbonate content exhibits great variability with the highest values observed in biogenic sediments of the sporades basin in the latter area mn and fe oxides and hydroxides were found as coatings on calcite the coatings were enriched in cr co ni zn as mo and pb due to adsorption or ion exchange during early diagenesis the combined influence of the river systems the thessaloniki metropolis and the diverse sedimentological background generates great patchiness in the distribution of major and minor elements

recent evolution of a mediterranean deltaic coastal zone human impacts on the inner thermaikos gulf nw aegean sea the inner thermaikos gulf is located in the northwestern aegean sea receiving water and sediment fluxes from the axios aliakmon gallikos and loudias rivers the geomorphological and sedimentological evolution of the system is reconstructed for the last 150 years 1850 2000 on the basis of detailed analysis of historical bathymetric charts late holocene history is considered within the context of changing riverine sediment supply and human activities three evolutionary stages are identified stage i 1850 1916 corresponds to a natural phase of rapid deltaic progradation and sea floor deposition with an average sediment accumulation rate of 6 5 10 6 m 3 a 1 during stage ii 1916 1956 human interference e g artificial changes in river delta plains realignment of channels and land reclamation schemes to the deltaic system increased sediment delivery to the coastal waters by a factor of three this in turn enhanced the progradation of the active river mouth areas in contrast stage iii 1956 2000 is characterized by significant coastline deltaic retreat and erosion of the adjacent sea floor net loss of 2 5 10 6 m 3 a 1 this was as a result of extensive river damming which trapped a significant part of the sediment moving seaward furthermore these human impacts have affected the character of the surficial sea bed sediments of the gulf by reducing the proportion of mud the response of the deltaic margin of the inner thermaikos gulf to various anthropogenic interventions seems to be analogous to that of other deltas in the mediterranean region where large drainage projects the development of irrigation networks and dam construction have taken place within their river basins

the role of advection straining and mixing on the tidal variability of estuarine stratification abstractdata from the hudson river estuary demonstrate that the tidal variations in vertical salinity stratification are not consistent with the patterns associated with along channel tidal straining these observations result from three additional processes not accounted for in the traditional tidal straining model 1 along channel and 2 lateral advection of horizontal gradients in the vertical salinity gradient and 3 tidal asymmetries in the strength of vertical mixing as a result cross sectionally averaged values of the vertical salinity gradient are shown to increase during the flood tide and decrease during the ebb only over a limited portion of the cross section does the observed stratification increase during the ebb and decrease during the flood these observations highlight the three dimensional nature of estuarine flows and demonstrate that lateral circulation provides an alternate mechanism that allows for the exchange of materials between surface and bottom waters even when direct turbu

bottom stress estimates and their prediction on the northern california continental shelf during code 1 the importance of wave current interaction abstract high quality near bottom boundary layer measurements obtained at a midshelf location 90 m water depth in the code region off northern california are described bottom tripod velocity measurements and supporting data obtained during typical spring and early summer conditions june 1981 during code 1 are analyzed to obtain bath velocity profiles and mean bottom stress and bottom roughness estimates during the time period described the mean near bottom 0 997 approximately 30 percent of the time effects induced by unsteadiness from internal waves result in some degradation of the profiles 0 96 r 0 997 the rest of the time mean stress profiles indicate the logarithmic layer is approximately a constant stress layer the near bottom flow field is composed of mean currents and oscillatory currents due to well typing mean u values estimated from measurements greater than 30 cm above the bottom have magnitudes of 0 5 1 0 cm s 1 mean stress valu

late pleistocene unconformity in the gulf of kavalla northern aegean greece abstract a 147 cm core from the gulf of kavalla on the northern aegean shelf displays two different lithologies separated by an erosional contact the upper part 0 128 cm consists of clayey silt to silty clay grading into silty sand and represents a neritic to nearshore marine environment the lower section 128 147 cm is a stiff calcareous mudstone with scattered microcrystalline calcite nodules and probably represents part of a subaerial soil horizon b ca seismic data indicate that at this location the unconformity between the late glacial subaerial surface and the overlying post glacial transgressive deposits occurs at a depth of 150 cm and has apparently been sampled by the core

can hydrocarbon source rocks be identified on seismic data hydrocarbon source rocks contain signifi cant volumes of organic matter are capable of expelling petroleum when heated and have produced most of the world s known oil volumes recently source rocks have also become recognized as unconventional economic reservoirs here we present a new way of identifying characterizing and mapping spatial distributions and variations of thick source rocks 20 m that is based on seismic data only this has a signifi cant impact on the prospect risk assessment of petroleum plays rock property studies of organic rich claystones show that the acoustic impedance ai which is the product of compressional velocity and density decreases nonlinearly with increasing total organic carbon toc percent claystones mixed with low density organic matter toc 3 4 have signifi cant lower ai and higher intrinsic anisotropy than otherwise similar nonorganic claystones this gives the top and base source rock refl ections characteristic negative and positive high amplitudes respectively which dim with increasing refl ection angle in addition the toc profi le which is a smoothed toc percent curve infl uences the top and base amplitude responses an upward increasing toc profi le has the highest amplitude at the top while the opposite asymmetry is observed for downward increasing toc profi les by using seismic data we therefore can map lateral distribution thickness variation in toc profi les and with local well calibration convert ai data to toc percent this approach to mapping source rocks may change the way petroleum systems are evaluated

numerical analysis of stratification and destratification processes in a tidally energetic inlet with an ebb tidal delta stratification and destratification processes in a tidally energetic weakly stratified inlet in the wadden sea south eastern north sea are investigated in this modeling study observations of current velocity and vertical density structure show strain induced periodic stratification for the southern shoal of the tidal channel in contrast to this in the nearby central region of the channel increased stratification is already observed directly after full flood to investigate the processes leading to this different behavior a nested model system using getm is set up and successfully validated against field data the simulated density development along a cross section that includes both stations shows that cross channel stratification is strongly increasing during flood such that available potential energy is released in the deeper part of the channel during flood an analysis of the potential energy anomaly budget confirms that the early onset of vertical stratification during flood at the deeper station is mainly controlled by the stratifying cross channel straining of the density field in contrast to this in the shallow part of the channel the relatively weak cross channel straining is balanced by along channel straining and vertical mixing an idealized analytical model confirms the following hypothesis the laterally convergent flood current advecting laterally stratified water masses from the shallow and wide ebb tidal delta to the deep and narrow tidal channel has the tendency to substantially increase cross channel density gradients in the tidal channel this process leads to stratification during flood

holocene evolution in weathering and erosion patterns in the pearl river delta sediments in the pearl river delta have the potential to record the weathering response of this river basin to climate change since 9 5 ka most notably weakening of the asian monsoon since the early holocene approximate to 8 ka cores from the pearl river delta show a clear temporal evolution of weathering intensity as measured by k al k rb and clay mineralogy that shows deposition of less weathered sediment at a time of weakening monsoon rainfall in the early mid holocene 6 0 2 5 ka this may reflect an immediate response to a less humid climate or more likely reduced reworking of older deposits from river terraces as the monsoon weakened human settlement of the pearl river basin may have had a major impact on landscape and erosion as a result of the establishment of widespread agriculture after around 2 5 ka weathering intensity sharply increased despite limited change in the monsoon but at a time when anthropogenic pollutants e g cu zn and pb increased and when the flora of the basin changed sr 87 sr 86 covaries with these other proxies but is also partly influenced by the presence of carbonate the sediments in the modern pearl river are even more weathered than the youngest material from the delta cores we infer that the spread of farming into the pearl river basin around 2 7 ka was followed by a widespread reworking of old weathered soils after 2 5 ka and large scale disruption of the river system that was advanced by 2 0 ka

late quaternary tectonic and sedimentary history of outer izmir and candarli bays western turkey abstract air gun and 3 5 khz seismic profiles from the eastern aegean sea off turkey show that the continental shelf of outer izmir and candarli bays is formed by several superimposed deltaic sequences during times of lowered sea level associated with late quaternary glaciations deltas prograded seaward more than 60 km from their present positions foreset progradation ceased with the rise of sea level in interglacial and post glacial times and deltas were reestablished far inland in drowned river valleys these major transgressions resulted in unconformities within the superimposed prograded delta sequences the most recent three unconformities are correlated with the beginning of oxygen isotope stages 5 3 and 1 and provide chronostratigraphic markers for a detailed analysis of sedimentation patterns in the late quaternary the coastal shelf and basins are subsiding at an average rate of about 1 m per 1000 years this tectonic subsidence manifests itself as widespread normal block faulting which can be related to the pre miocene structural framework of the region

geomechanical and geometric seismic attributes in an interpretation workflow for characterization of unconventional reservoirs conventional seismic attributes often provide satisfactory results especially in the characterization of conventional reservoirs such as sandstones this is not so evident with more compact low permeability and apparently uniform reservoirs which comprise substantial reserves in amounts unthinkable a few decades ago and whose development seemed almost impossible until very recently unconventional reservoirs considered in this article are located in a predominantly jurassic cretaceous rifted depositional basin the basin shifted into an early sag phase during the late jurassic and early cretaceous resulting in the accumulation of a thick series of carbonates and shales tithonian berriasian and valanginian rocks compose the segment of the geologic column under consideration the studied sedimentary sequence is a highly prolific oil prone source rock with total organic carbon toc up to 8 wt and amorphous organic matter type i ii kerogen deposited in a euxinic paleoenvironment which generated s

role of straining and advection in the intratidal evolution of stratification vertical mixing and longitudinal dispersion of a shallow macrotidal salt wedge estuary 1 a month of flow observations in the snohomish river estuary reveals the complex intratidal and fortnightly stratification mixing and dispersion dynamics in this macrotidal shallow salt wedge estuary system both salt wedge propagation and concomitant straining of the density field dominate temporal and spatial variations in stratification leading to intratidal variability of shear and mixing that differs in important ways from observations in partially mixed estuaries bottom generated turbulent kinetic energy production is enhanced during spring tides and acts in concert with straining to counteract advection and minimize vertical stratification during the spring flood tides this bottom generated mixing contributes to a buoyancy flux near the top of a well mixed layer during strong flood tides during strong ebb tides interfacial shear production and buoyancy flux occur along the sharp straining enhanced interface just before the system becomes well mixed longitudinal dispersion is less sensitive to the spring neap cycle yet exhibits strong intratidal variability reduced longitudinal dispersion is observed during the large floods relative to the rest of the tidal cycle behavior we attribute to a lack of vertical shear overall ebb tide advection and straining enhance stratification and longitudinal dispersion and allow for interfacial mixing intratidal variability which varies on the spring neap scale is a dominant feature of this estuary suggesting the importance of intratidal processes and tidally varying mixing coefficients in similar strongly stratified strongly forced estuaries

microstructure observations of turbulent mixing in a partially mixed estuary part i dissipation rate variations of turbulent mixing in the water column and in the benthic boundary layer were observed with a microstructure profiler in the hudson river estuary during two cruises in summer and fall of 1995 variability patterns of stratification shear richardson number ri and turbulent dissipation rates e were similar to those of earlier observations with strong turbulence in the weakly stratified bottom layer weak turbulence in the halocline during neap tides and low ri and high e spanning the water column during spring ebbs depthintegrated turbulent dissipation rates re dz approximately equaled the work done by the tidal pressure gradient force adjusted for the change in tidal kinetic energy alternatively a suitable scaling for re dz is also provided by the product of bottom shear stress and depth average velocity t by a relationship that fails at slack tide however at heights above bottom of z 0 3 m and again excepting slack tides observed e were highly correlated with a law of the wall dissipation rate eb 5 kz ratios e eb were close to 1 here the friction 3 u

clay mineral distribution in last glacial holocene sediment cores from the eastern marmara sea cinarcik basin izmit gulf transition nw turkey multisources and transport paths in a two way flow system abstract the regional variations in grain size xrd bulk and clay mineral distribution in 97 sediment samples from 6 gravity cores obtained from 20 to 300 m water depths have been investigated to reveal source and transportation patterns as well as the effects of climatic and sea level changes during the last 25 000 14 c bp in the eastern marmara sea ems nw turkey the major proportions of sediments in the ems consist of silt 20 83 and clay 17 90 whereas sand and gravel abundances rarely exceed 10 of the bulk minerals 10 a micas 23 55 and feldspars 17 55 dominate over quartz 10 21 and calcite 10 26 smectites 23 62 illite 18 36 chlorites 6 21 kaolinite 2 20 and 14s 14c mixed layer minerals 0 27 constitute the principal clay mineral assemblages both bulk and clay mineral assemblages in the ems are similar to those found in the izmit gulf on the southern marmara shelf at the marmara aegean approaches and the southern black sea this would suggest that there is no distinct source for mineral assemblages of the study area outside the marmara basin the concentrations of clay fractions and clay mineral assemblages tend to increase or decrease with depth in the cores but this is limited to some intervals and not to entire sections in the cores this distribution pattern therefore represents rather local sources of provenance and surrounding fluvial drainage basins together with dilution and distribution effects by current transport processes rather than the expected paleoclimatic features and sedimentary input by inflowing black sea and aegean sea water masses throughout the last glacial to holocene

longitudinal versus lateral estuarine dynamics and their role in tidal stratification patterns in lower south san francisco bay author s hoang olivia abstract the dynamics of shoal channel estuaries require consideration of lateral gradients and transport which can create significant intratidal variability in stratification and circulation when the shoal channel system is strongly coupled by tidal exchange with mudflats marshes or other habitats the gradients driving intratidal stratification variations are expected to intensify to examine this dynamic hydrodynamic data was collected from january 27 2017 february 10 2017 in lower south san francisco bay a small subembayment fringed by extensive shallow vegetated habitats during this deployment salinity variations were captured through instrumentation of 6 stations arrayed longitudinally and laterally allowing for mechanisms of stratification creation and destruction to be calculated directly and compared with observed time variability of stratification at the central station we present observation based calculations of longitudinal straining longitudinal advection lateral straining and lateral advection the time dependence of stratification was observed directly and calculated by summing measured longitudinal and lateral mechanisms we found that the stratification dynamics switch between being longitudinally dominated during the middle of ebb and flood tides to being laterally dominated during the tidal transitions this variability is driven by the interplay between tidally variable lateral density gradients and turbulent mixing relatively constant along estuary density gradients are differentially advected during flood and ebb tides resulting in maximal lateral density gradients around tidal transitions simultaneous decrease in turbulent mixing at slack tides allows lateral density driven exchange to stratify the estuary channel at the slack after flood at the end of ebb barotropic forcing drives negatively buoyant shoal waters towards the channel plain language summary san francisco bay sits within a highly urbanized area the dense population creates large wastewater effluent resulting in high nutrient levels scientists wonder why there have not been annual phytoplankton blooms like observed in other estuaries with lower nutrient levels some have hypothesized it is due to high turbidity levels and tidal breakdown of stratification creating nonideal environments for phytoplankton growth however decadal trends show that the estuary is becoming less turbid and with changes in climate patterns there is potential for persistent stratification we observed development of stratification over the ebb tide and destratification in two distinct events as the tide reverses over the flood tide at the reversal of the tides water in the shoals exchange with the water in the channel creating a pulse of salty water to the channel at the ebb to flood transition and a pulse of fresh water at the flood to the ebb transition destratification occurs in the early flood tide due to a pulse of saline water received from the shoals then due to the advection of less stratified water being pulled to the center channel of the estuary finally stratification is destroyed completely due to longitudinal straining and turbulent mixing