dense water formation in the aegean sea numerical simulations during the eastern mediterranean transient 1 dense water formation processes in the aegean sea eastern mediterranean are studied using a three dimensional numerical ocean model the simulations cover the period 1979 1994 during which major changes that affected the thermohaline circulation of the whole mediterranean sea were recorded sensitivity studies that focus on the role of freshwater budget are presented and the results are evaluated against available hydrological data of the same period the very cold winters of 1987 1992 and 1993 and the extended dry period 1989 1993 that affected the whole eastern mediterranean sea are the main driving mechanisms corresponding to 50 and 32 respectively of the excessive deepwater volume formed in the aegean after 1987 the reduced black sea water outflow during the same dry period was another important forcing mechanism contributing 18 to the total formation while the increased inflow of saline waters from the levantine sea after 1992 was an additional preconditioning factor the locations and mechanisms of water formation processes are identified with combined analysis of data from the march 1987 oceanographic cruise in the aegean sea and the respective model results for that period deep water is found to be formed mainly through open ocean convection in the central and north aegean sea while the contribution of shelf areas is limited intermediate water is also formed through open ocean convection in the southern aegean sea during cold winters as well as in the central and northern aegean during mild winters the total volume of dense water formed during 1979 1994 corresponds to an annual formation rate of 0 24 sv for deep water and 0 34 sv for intermediate water

the turbidity maximum zone of the yenisei river siberia and its impact on organic and inorganic proxies a general overview of the processes taking place in the summer mixing zone of the fresh yenisei river water with the marine waters of the kara sea is given in this study with special emphasis on the interaction between bulk total suspended matter inorganic fe mn and organic suspended organic carbon suspended nitrogen proxies within the mixing zone a zone of enhanced turbidity maximum turbidity zone was observed comparable to studies in other rivers flocculation of particles due to changes in salinity and hydrography cause this maximum turbidity zone and resuspension additionally enhances the turbidity in the near bottom layers organic matter behaves conservatively in the mixing zone in terms of its percentage of suspended matter it however undergoes degradation as revealed by amino acid data inorganic redox and salinity sensitive proxies mn fe behave non conservatively dissolved iron is removed at low salinities 2 due to precipitation of iron oxyhydroxides and adsorption of manganese on suspended particles enhancing the mn al ratio of the suspended matter in the same zone at higher salinities within the mixing zone fe al and mn al ratios of the suspended particles are depleted due to resuspension of sediment with lower fe al and mn al ratios dissolved manganese concentrations are significantly higher in the near bottom layers of the mixing zone due to release from the anoxic sediment all things considered the yenisei river mixing zone shows patterns similar to other world s rivers

secular variation of the earth s magnetic field in the balkan region during the last eight millennia based on archaeomagnetic data summary the first archaeomagnetic secular variation sv curves for the whole southern balkan peninsula are presented these are based on all data within a 700 km circle centred at thessaloniki 40 60on 23 00oe this data set consists of 325 directional and 625 intensity data mainly from greece bulgaria serbia and southern hungary some data from southern italy are also included the sliding moving window technique was used to calculate a continuous sv curve for intensity while the directional sv curves were calculated using the bivariate extension of the fisher statistics these curves are well constrained and clearly show the main features of the geomagnetic field variation in this region during the last eight millennia comparisons with the predictions of the scha dif 3k and scha dif 8k regional and the cals7k 2 and arch3k 1 global geomagnetic field models show a good agreement for the last 3000 years but differences for older times the balkan sv curves identify several rapid changes of the geomagnetic field in eastern europe and can be used as reference curves for archaeomagnetic dating in the balkan peninsula

recent particulate organic carbon and total suspended matter fluxes from the ob and yenisei rivers into the kara sea siberia the ob and yenisei rivers account for more than one third of the total fresh water supply to the arctic ocean in the past their sediment load and particulate organic carbon poc discharge into the kara sea has been measured at stations in the hinterland far south of the estuaries suspended matter has been sampled in the estuaries and southern kara sea within the framework of the joint russian german sirro program siberian river run off allowing a reliable new estimate of fluxes from the rivers into the kara sea our estimates of annual supplies of sediment 3 76 10 6 t particulate organic carbon 0 27 10 6 t and particulate nitrogen pn 0 027 10 6 t from the ob river to the kara sea are lower than earlier estimates from the northernmost gauging station in the hinterland due to deposition of particulate matter in the ob bay on the other hand our estimates of the yenisei s annual sediment 5 03 10 6 t particulate organic carbon 0 57 10 6 t and particulate nitrogen 0 084 10 6 t supplies to the kara sea are probably too high as they suggest a pure bypass system in the investigated area we differentiate between an area of recent deposition in the south of the kara sea and an area of recent organic matter degradation further north d 2004 elsevier b v all rights reserved

an extreme cold surge over the greek peninsula summary this paper is devoted to the detailed description of an extreme cold surge that occurred 3 13 march 1987 over greece this event has been rated as the worst snowfall over the last 100 years and duc to its severily and persistence it paralysed the cconornic and communal life of greece for several days emphasis is given to the initiation phase of this event the structural evolution of the cold surge is analysed using both observations and model results model simulations pcrformed with the colorado state university regional atmospheric modelling system provided the necessary data to diagnose the mesoscale structure of the cold outbreak different mechanisms involved in the structural evolution ofthe cold surge are investigated the gustiness of the observed winds and their significant departure from geostrophy are related to the role of an important isallobaric wind the progression of this surge presented characteristics of a density current while near the eastern slopes of the mountain barriers of continental greece cold air damming occurred leading to an accelerated flow parallcl to the mountains heavy snowfall events over greece are often associated with cold air surges prop agating from northern and central europe through the balkans metaxas 1978 livada tselepidaki 1979 prezerakos and angouridakis 1984 these cold surges are accompanied with the passage of a fast moving cold front from the north towards the south very strong winds especially in the gaps between mountains in northern greece and over the aegean sea a sharp temperature decrease over the whole country and a sharp pressure rise the lifetime of these surges is normally from 1 to 3 days extending up to 10 days in exceptional cases their persistence can cause important problems in economic life since the result ing snowfall can prohibit road transportation on the main traffic routes greek forecasters call these cold fronts balkan fronts due to their origin in the frame of this study this terminology will be retained although the classical term cold surge will also be used interchangeably the forecast of the evolution of these fronts as well as the persistence of cold surges over greece is of great importance not only for the impact of snowfall on economic life but also for the safety of navigation in the aegean sea in gale force winds cold surges accompanied by severe weather phenomena have also been reported in the himalayan region nakamura and murakami 1983 over the usa e g bell and bosart 1988 colle and mass 1995 as well as over central america schultz et al 1997 all the aforementioned studies underlined the fact that cold surges are accompanied by strong lower tropospheric northerly winds sharp decreases in temperature and sharp pressure rises in these studies some interesting features accompanying cold surges were also ad dressed mainly cold air damming near mountain barriers as a result of the interaction of the synoptic scale flow with topography bell and bosart 1988 concluded that the component of the pressure gradient force parallel to the mountain was the primary cause for the appearance of an accelerated flow nearly parallel to the mountains colle and mass 1995 demonstrated that pressure ridging east of the mountain barrier caused ageostrophic northerly winds while cold avection of upslope flow led to the damming of cold air schultz et al 1997 showed that the extraordinary equatorial extent of a cold surge was aided by topographic channelling similar to cold air damming

water fluxes through the cretan arc straits eastern mediterranean sea march 1994 to june 1995 abstract five research cruises were undertaken incorporating adcp sections along the cretan arc straits and ctd surveys covering the entire area of the straits and the cretan sea in addition six moorings with 15 current meters were deployed within the straits which monitored flows in the surface 50 m intermediate 250 m and deep 50 m from the bottom layers the adcp cm and ctd datasets enable the derivation of water transports through the cretan arc straits to be assessed flow structure through the cretan arc straits is not the typical flow regime with a surface inflow and deep outflow instead there is a persistent deep outflow of cretan deep water cdw 29 2 with an annual mean of 0 6 sv through the antikithira and kassos straits at depths below 400 m and 500 m respectively cdw outflowing transports are higher 0 8 sv in april june and lower 0 3 sv in october december within the upper water layer 0 400 m the transport and the water exchanges through the straits are controlled by local circulation features which weaken substantially below 200 m the asia minor current amc influences the rhodes and the karpathos straits resulting in a net inflow of water in contrast the mirtoan west cretan cyclone influences the antikithira and kithira straits where there is a net outflow in the kassos strait there is a complex interaction between the east cretan cyclone the ierapetra anticyclone and the westward extension of the rhodes gyre which results in a variable flow regime there is a net inflow in autumn and early winter and a switch to a net outflow in early spring and summer the total inflow and outflow throughout all of the straits ranged from 2 to 3 5 sv with higher values in autumn and early winter and lower in summer the amc carries 2 sv of inflow through the rhodes and karpathos straits and this accounts for 60 80 of the total inflow about 10 15 of the total outflow is of cdw and a further 45 70 occurs through the upper 400 m of the kithira and antikithira straits the kassos strait exhibits a net inflow of 0 7 sv in autumn and early winter with a net outflow of 0 5 sv in early spring and summer

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

recent changes in deep water formation and spreading in the eastern mediterranean sea a review abstract observations of the last decade testify that the characteristics of the deep thermohaline circulation in the eastern mediterranean sea have changed thoroughly the source of the most dense waters of the basin has moved from the adriatic to the aegean sea this new source has proved to be very efficient since the estimated formation rate for the period 1989 95 was more than 1 sv about three times more than the dense water formation rate of the adriatic sea these new waters with hydrological characteristics that are warmer and more saline have replaced almost 20 of the older deep waters of the basin and have uplifted the deep isopycnals by about 500 m this major event can be attributed to important meteorological anomalies in the eastern mediterranean and to changes of circulation patterns the extended dry period of 1988 93 and the exceptionally cold winters of 1987 and 1992 93 created favorable conditions for increased formation of dense water in the aegean furthermore changes in the circulation patterns in the intermediate water range levantine intermediate water liw and cretan intermediate water themselves possibly linked to meteorological anomalies appear to have played an important role in the redistribution of salt as a result of an interruption to exchanges between the ionian and levantine basin the salinities in the latter started to rise high salinity waters were diverted into the aegean malanotte rizzoli p manca b b ribera dacala m theocharis a 1998 the eastern mediterranean in the 80s and in the 90s the big transition emerged from the poem bc observational evidence rapport du commission international de la mer medittanee 35 174 175 and the westward transport of liw was reduced an additional effect of the deep water discharge from the aegean and the resulting uplifting of mid depth waters was to lower salinities in the liw layer this effect is most strongly felt in the ionian sea a 3 d primitive equation numerical model for the eastern mediterranean with a 20 km grid size is used to simulate the observed changes and understand the basic mechanisms which caused them under appropriate atmospheric forcing the model successfully reproduces the main characteristics of the transient these results indicate that the observed changes can be at least partially explained as a response of the eastern mediterranean and more specifically of the aegean to atmospheric forcing variability

changes in the intensity of the geomagnetic field a new more reliable technique has been used to determine the ancient intensity of the earth s magnetic field using samples of baked clay from eight sites in the eastern mediterranean the resultant power spectrum reveals a single strong component with a period of 1430 years the reproducibility of the results obtained with the new method also makes limited archaeomagnetic dating with a precision of between about one and two hundred years between 900 bc and ad 400 possible

re evaluation of greek archaeomagnitudes a new technique is used to determine the secular variation of the geomagnetic ancient field in athens the results indicate that published greek archaeomagnitudes were seriously affected by alteration it is shown that all intensities obtained using modifications of the thellier method may be affected by alteration and are therefore suspect

aegean surface circulation from a satellite tracked drifter array a pilot experiment using an array of 45 drifters to explore the circulation in the north and central aegean sea is described the global positioning system drifters with holey sock drogues provide positions every hour with data recovery through the argos system the drifters were launched in four separate deployments over a 1 yr period the resulting trajectories confirm the existence of a current around the rim of the basin consistent with a buoyancy plume created by the outflow of black sea waters through the dardanelles strait of canakkale in turkish the degree to which this is augmented by an ekman response to the dominant northerly winds is not obvious in the dataset owing to mesoscale dynamics that obscure the existence of any westward ekman flow the mesoscale eddy field involves anticylonic eddies in the current around the rim of the basin consistent with eddies with low salinity water cores cyclones are also seen with the most prominent forming over deep regions in the basin topography the array also documents the interaction of the currents with the straits through the sporades and cyclades island groups these interactions are complicated by the nature of the mesoscale flow and in some trajectories suggest a bernouilli acceleration in straits in others the flow through the island groups appears to be more diffusive and involves deceleration and eddy motions the rapid sampling by the drifters reveals an extremely nonlinear submesoscale eddy field in the basin with length scales less than 4 km and rossby numbers of order 1 a better understanding of the dynamics of these features is of importance for understanding the circulation of the basin

the role of the north aegean in triggering the recent eastern mediterranean climatic changes drastic changes have occurred in the vertical structure of the deep waters of the eastern mediterranean in the early 1990s as dense water of aegean origin has displaced lighter waters of adriatic origin at the bottom of the deep basins this work suggests that the initiation of this process took place in the north aegean in the winter of 1986 1987 and was intensified by another formation event in 1992 1993 the available observations from the north aegean support such a scenario furthermore we propose that the outflow of black sea waters into the aegean through the dardanelles could act as an insulator of the deeper layer from the atmosphere thus absorbing a large part of the heat and salt exchange despite this fact the existence of the densest bottom water of the mediterranean in the north aegean and the continuation of density increase for a large period of time suggests that it is a region of formation thus that the insulation layer may at times be penetrated we suggest that reduced black sea outflow into the north aegean could facilitate dense water formation during the passage of cold atmospheric fronts in the winter

a laboratory examination of floc characteristics with regard to turbulent shearing abstract turbulent shear generated within the water column is recognised as having a controlling influence over both the flocculation of fine grained cohesive sediments within estuarine waters and their respective aggregate break up this study examines the inter relationships between floc characteristics over increasing turbidity 80 200 mg l 1 and turbulent shear 0 0 6 n m 2 environments by the use of a laboratory flume within which a suspension can be sheared at a controlled rate and with an unintrusive macro lens miniature video camera mounted in a viewing port on the flume channel wall the camera enables the direct simultaneous measurement of both floc size and settling velocity from which accurate estimates of floc effective density and porosity can be made measurements were made 120 s after the induced turbulence has ceased the instrument has an upper viewing turbidity limit of 210 mg l 1 and a lower resolution of 20 m the sediment was collected from the inter tidal mudflats at weir quay on the tamar estuary in devon southwest england the results indicated that increasing turbidity at low shear levels encouraged floc growth but the effect of the increasing turbulent shear 0 35 n m 2 together with increasing concentration in suspension causes disruption rather than enhancing the flocculation process at shears up to 0 35 n m 2 the largest size and settling velocity flocs were produced at high concentrations whereas above 0 35 n m 2 disruption caused smaller flocs at higher concentrations the use of algorithms which were based either on a single floc characteristic i e size or settling velocity or a mean fractal dimension were seen not to accurately approximate the experimental data a multiple regression analysis of the experimental data produced the following formula based on mean values of the 20 largest flocs sampled under each of the imposed environmental conditions referred to as max20size mean values settling velocity 0 301 0 00337 rms of the gradient in turbulent velocity fluctuations 0 000606 spm 0 00335 floc size which proved to be the most accurate representation with an r 2 value of 0 95 a similar formula was determined for the average value of the four fastest settling flocs within each sample group max4w s this highlights the importance of modelling algorithms that are developed from data that take into account effective density variations i e simultaneous size and settling velocity measurement

application of copper slag in geomagnetic archaeointensity research 1 paleointensity and archaeointensity studies since the 1950s have produced numerous geomagnetic intensity data for the last seven millennia as a consequence of different experiments and materials there is a complex and internally inconsistent picture of the geomagnetic field behavior in this study we present data using a recently developed experimental design on a heretofore unexploited recording medium copper slag deposits our results based on hundreds of specimens from various archaeometallurgical sites of the southern levant demonstrate the applicability of copper slag material for archaeointensity studies in addition to frequently exhibiting good experimental behavior slag has further advantages such as dense multilayer deposits and in cases embedded charcoals which open the door to data sets with excellent age control and resolution the data presented here augment the high quality database from the middle east and support previously observed periods of rapid change of the intensity of the geomagnetic field

transient eastern mediterranean deep waters in response to the massive dense water output of the aegean sea in the 1990s abstract we present a detailed account of the changing hydrography and the large scale circulation of the deep waters of the eastern mediterranean emed that resulted from the unique high volume influx of dense waters from the aegean sea during the 1990s and of the changes within the aegean that initiated the event the so called eastern mediterranean transient emt the analysis uses repeated hydrographic and transient tracer surveys of the emed in 1987 1991 1995 1999 and 2001 2002 hydrographic time series in the southern aegean and southern adriatic seas and further scattered data aegean outflow averaged nearly 3 10 6 m 3 s 1 between mid 1992 and late 1994 and was largest during 1993 when south and west of crete aegean influenced deep waters extended upwards to 400 m depth emt related aegean outflow prior to 1992 confined to the region around crete and to 1800 m depth wise amounted to about 3 of the total outflow outflow after 1994 up to 2001 2002 derived from the increasing inventory of the tracer cfc 12 contributed 20 to the total of 2 8 10 14 m 3 densities in the southern aegean sea deep waters rose by 0 2 kg m 3 between 1987 and 1993 and decreased more slowly thereafter the aegean waters delivered via the principal exit pathway in kasos strait east of crete propagated westward along the cretan slope such that in 1995 the highest densities were observed in the hellenic trench west of crete aegean influenced waters also crossed the east mediterranean ridge south of crete and from there expanded eastward into the southeastern levantine sea transfer into the ionian mostly followed the hellenic trench largely up to the trench s northern end at about 37 n from there the waters spread further west while mixing with the resident waters additional transfer occurred through the herodotus trough in the south levantine waters after 1994 consistently showed temperature salinity t s inversions in roughly 1000 1700 m depth with amplitudes decreasing in time the t s distributions in the ionian sea were more diverse one cause being added aegean outflow of relatively lower density through the antikithira strait west of crete spreading of the aegean influenced waters was quite swift such that by early 1995 the entire emed was affected and strong mixing is indicated by near linear t s relationships observed in various places referenced to 2000 and 3000 dbar the highest aegean generated densities observed during the event equaled those generated by adriatic sea outflow in the northern ionian sea prior to the emt a precarious balance between the two dense water source areas is thus indicated a feedback is proposed which helped triggering the change from a dominating adriatic source to the aegean source but at the same time supported the previous long year dominance of the adriatic the emed deep waters will remain transient for decades to come

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

generation of an estuarine sediment plume by a tropical storm 1 tropical storm lee 2011 caused a record flood in the susquehanna river which discharged about 6 7 million tons of suspended sediments into the bay an amount equal to the input of 6 average years the flood carried sediment produced a large sediment plume that covered one half of chesapeake bay with the maximum suspended sediment concentration exceeding 2500 mg l 1 three stages were identified in the development of the sediment plume corresponding to three dominant forcing mechanisms i e river flow estuarine circulation and sediment settling most of the flood carried sediments were deposited in the bay within 20 days sands were dumped in the susquehanna flats with a maximum thickness of 10 cm while fine grained sediments were dusted over a wide area in the upper bay with a maximum thickness of 4 cm long term simulation of the post storm period showed that a majority of the flood sediments were redistributed to accumulate in the estuarine turbidity maximum region due to flood ebb asymmetry in tidal suspension and advection by estuarine circulation and tidal flows while the rest were transported seaward and deposited in the mid bay it is estimated that the flood delivered 9 months of particulate nitrogen and over 1 year of particulate phosphorus supplies to the estuary this catastrophic event may change the geological history and exacerbate water quality decline in the american largest estuary

can flocs and water stable soil aggregates be differentiated within fluvial systems abstract this paper uses a number of particle structural characterizations and behavioral assessments in an attempt to differentiate flocs formed in the water column from water stable soil aggregates formed in the terrestrial environment but transported to a river by overland flow using discrete populations of flocs and soil aggregates the study successfully illustrated differences in floc structure as defined by fractal dimension sphericity measures density and porosity and behavior as defined by settling velocity flocs were generally found to be porous and irregular in shape with high water content low density and low settling velocity whereas soil aggregates were found to be rounder more compact dense with lower porosity and a higher settling velocity the techniques were however inappropriate for differentiating the two particle forms from river storm samples which are collected at the time when both particle forms are believed to be in suspension results suggest that aggregates once within the river system undergo a quick transformation into hybrid particles aggregate floc combinations due to flocculation processes occurring on the river bed following quick settling or during suspended sediment transport it is also possible that the aggregates undergo flocculation processes during overland flow forming hybrid particles prior to entering the river system or never reach the river altogether ending up in long term depositional areas in the terrestrial environment

two dimensional numerical modeling of storm deposition on the northern california shelf abstract a two dimensional across shelf sediment transport model has been developed to simulate storm deposition on continental shelves this paper describes the structure of the model and related algorithms in the model the time dependent sediment resuspension transportation and deposition and across shelf transport gradients are simulated as responses to storm waves on the eel shelf northern california the simulations show that the pattern of storm deposition on the sandy inner shelf is different from that on the muddy middle and outer shelf storm bed thickness decreases seaward across the inner shelf sandy zone as far as the 50 m isobath farther seaward storm bed thickness increases as the mud component in the sea floor becomes abundant then decreases again as the weakening of bottom wave motion with greater depth becomes the dominant control storm bed thickness in the mud zone thus has a nearly symmetrical cross shelf pattern with the maximum thickness at a water depth of 70 m the pattern suggests that while the sequence of new beds found in february 1995 on the eel shelf may have had a flood source their geometry reflects storm resuspension and transport the new muds found in these beds may have been reworked transported and redeposited several times by storm waves and other oceanic forces numerical simulations illustrate that the critical bottom shear stress for mud erosion e and the coefficient for sand resuspension 0 are more important than other parameters in determining storm depositional patterns on the eel shelf

estuarine flocs their size settling velocity and density the size and settling velocity of flocs of suspended sediments from the chesapeake bay were measured in laboratory experiments and in the field the curves between floc diameter and settling velocity showed a non stoke s relationship that was best described by the following settling velocity cm s 1 73 floc diameter cm 0 78 furthermore the relationship between floc diameter and settling velocity indicated that the floe density decreased as the floes increased in size in addition to changing density a cylinder shape was found to be the best shape factor

settling speeds of floes in fresh water and seawater the settling speeds of floes of fine grained natural sediments approximately 10 200 m in diameter have been measured in both fresh water and seawater these floes were formed at fluid shears of 100 200 and 400 s 1 and at sediment concentrations of 10 100 and 400 mg l values typical of conditions in the near shore areas of lakes and oceans especially during storm conditions it is demonstrated that the settling speed of a floe is a strong function of fluid shear and sediment concentration as well as of the diameter of the floe but it is a weak function of salinity for the same diameter and salinity floes produced at the lower fluid shears and sediment concentrations have lower settling speeds than do floes produced at higher fluid shears and sediment concentrations if the conditions of fluid shear and sediment concentration under which the floes were produced are unknown or ignored it is shown that the settling speed of a floe is a weak function of diameter and salinity

coagulation rates of clay minerals and natural sediments abstract coagulation experiments conducted using illite kaolinite montmorillonite and four natural sediment samples in blade and couette reactors with solutions of various salinities yielded collision efficiency factors significantly higher than those in the previous literature indicating that coagulation begins at lower salinities 1 2 1 the natural sediments do not generally behave as might be predicted for a mixture of the standards of the minerals of which the natural sediment samples were comprised the half times for coagulation of the particles indicate that in nature the coagulation process would probably be completed in the first few parts per thousand salinity

in situ settling behavior of marine snow1 the settling velocities of undisturbed macroscopic aggregates known as marine snow were measured with scuba in surface waters off southern california and analyzed as a function of aggregate size mass and density the mean settling velocity was 74f39 m d l for aggregates ranging from 2 4 to 75 mm in maximum length sinking rates in the field varied exponentially with aggregate size and dry weight and were consistently up to four times slower than rates measured in the laboratory the excess densities of the 80 aggregates examined were calculated from volume and dry weight and ranged over four orders of magnitude with a median of 1 4 x 1o 4 g cm 3 aggregates of marine snow sank more slowly than predicted for either solid or porous spheres of equivalent volume and density although their velocities were within the range expected for equivalent sinking prolate ellipsoids no relationships between settling velocity and either excess density or particle shape were found drag coefficients of marine snow were also higher than predicted by theory for spheres of equivalent volume and density these deviations from theoretical expectations may be partially explained by errors in the estimation of the excess densities of aggregates variability in the densities of the heterogeneous primary particles comprising marine snow fecal pellets claymineral particlcs phytoplankton molts etc and the potential for buoyancy regulation by individual phytoplankton cells inhabiting aggregates make determination of excess density especially

deposition properties of fine sediment this paper describes depositional properties of the fine portion d 0 075mm of the surficial bed sediments taken from the upper st clair river the experiments were conducted using the circular flume facility at the canada center for inland waters in burlington canada tests were conducted under the same initial conditions which involved mechanical mixing following the application of a very high shear stress that resulted in a solids suspension of 200 g l deposition was allowed to occur under five different shear stresses the deposition rate and the floc size were monitored using a laser based malvern particle size analyzer the results were used to estimate the settling velocity as a function of applied shear stress and lapsed time for the selected shear stress

a synthesis of the circulation and hydrography of the south aegean sea and the straits of the cretan arc march 1994 january 1995 abstract four seasonal oceanographic cruises were carried out in the eastern mediterranean sea within the framework of the cec mast mtp project pelagos during 1994 1995 the surveys covered the south aegean sea and the adjacent open sea regions southeastern ionian northwestern levantine analysis of ctd data revealed that a multiscaled circulation pattern prevails in the area it differs from the circulations detected during the 1986 87 thus indicating interannual variability cyclonic and anticyclonic gyres and eddies are interconnected by currents and jets variable in space and time most of the features are persistent others seem transitional or recurrent the hydrological structure is also complex and apart from the upper layer does not present basinwide any significant seasonality dynamical and hydrological regimes are variable in the upper and intermediate layers at the straits of the cretan arc while the deep regime seems rather constant topographic control is evident on the flows through the straits the new very dense deep water mass namely the cretan deep water cdw and a well defined intermediate layer of minimum temperature and salinity the so called transition mediterranean water tmw consists the new important structural elements of the south aegean sea the cdw outflows towards the deep and bottom layers of the eastern mediterranean thus considerably contributing to the formation of the new denser deep and bottom water of the eastern mediterranean which sinks and displaces the eastern mediterranean deep water of adriatic origin in the adjacent sea regions outside the aegean sea

hydrology and circulation in the southern cretan sea during the cincs experiment may 1994 september 1995 this work is a description of the water masses and circulation in the site of the cincs pelagic benthic coupling in the oligotrophic cretan sea experiment in the southern boundary of the cretan sea a region of recently renewed interest with respect to the hydrology of the eastern mediterranean basin analysis of hydrological data from the study area reveals the presence of five water masses local surface water and remotely advected modified atlantic water maw share the surface layers below them are cretan intermediate water ciw between 50 and 150 dbar transition mediterranean waters tmw with its core located between 300 400 dbar and the cretan deep waters cdw occupying the depths below 800 dbar the circulation over the coastal shelf and slope is dictated by the offshore semi permanent mesoscale features that dominated the cretan sea in 1994 1995 forcing locally a shoreward flow the hydrographic observations are verified by current meter measurements from a mooring in the sampling area the recorded velocity is generally towards the se direction seasonally modulated reaching maximum speeds of 27 cm s 1 analysis of the new data set has revealed a previously unobserved feature of the oceanographic characteristics of the region over the base of the cretan slope there occur lenses of water that are warmer and more saline than their surroundings these lenses probably form on the shelf seasonally their waters are rich in oxygen and have a density that is higher than historical cretan deep water values

distribution of the thermohaline characteristics in the aegean sea related to water mass formation processes 2005 2006 winter surveys 1 aiming at portraying the aegean s water mass structure and identifying dense water formation processes two winter cruises were conducted in 2005 2006 across the plateaus and depressions of the aegean sea the most prominent feature of the water mass distribution in the basin is a distinct x shape of the s characteristics suggesting a complicated coupling of the major aegean sub basins the surface and deep waters are relatively decoupled with diverse origin characteristics while the intermediate layers act as connectors of the main thermohaline cells the central aegean seems to play a key role due to formation processes of water masses with densities equal and or higher than 29 2 kg m3 that take place in the sub basin and disperses in the north aegean on the other hand the south aegean appears greatly influenced by the eastern mediterranean circulation and water mass distribution especially under the eastern mediterranean transient status the transitional mediterranean water monitored in the post emt period and characterized by low temperature at 14 2 c low salinity at 38 92 and low dissolved oxygen at 3 97 ml l with its core around 750 m and above the saline 39 06 cretan deep water altered significantly the south aegean structure the pre emt thermohaline pattern of the central and south aegean deep layers were similar while the bottom density of the central basin was higher than that in the south aegean thus it is possible that the deep waters of the central aegean acted as a dense water reserve supply for the deeper part of the southern basin

sedimentary controls on modern sand grain coat formation abstract coated sand grains can influence reservoir quality evolution during sandstone diagenesis porosity can be reduced and fluid flow restricted where grain coats encroach into pore space conversely pore lining grain coats can restrict the growth of pore filling quartz cement in deeply buried sandstones and thus can result in unusually high porosity in deeply buried sandstones being able to predict the distribution of coated sand grains within petroleum reservoirs is thus important to help find good reservoir quality here we report a modern analogue study of 12 sediment cores from the anllons estuary galicia nw spain collected from a range of sub environments to help develop an understanding of the occurrence and distribution of coated grains the cores were described for grain size bioturbation and sedimentary structures and then sub sampled for electron and light microscopy laser granulometry and x ray diffraction analysis the anllons estuary is sand dominated with intertidal sand flats and saltmarsh environments at the margins there is a shallowing fining upwards trend in the estuary fill succession grain coats are present in nearly every sample analysed they are between 1 m and 100 m thick and typically lack internal organisation the extent of grain coat coverage can exceed 25 in some samples with coverage highest in the top 20 cm of cores samples from muddy intertidal flat and the muddy saltmarsh environments close to the margins of the estuary have the highest coat coverage mean coat coverage of 20 2 and 21 3 respectively the lowest mean coat coverage occurs in the sandy saltmarsh 10 4 beyond the upper tidal limit and sandy intertidal flat environments 8 4 close to the main estuary channel mean coat coverage correlates with the concentration of clay fraction the primary controls on the distribution of fine grained sediment and therefore grain coat distribution are primary sediment transport and deposition processes that concentrate the clay fraction in the sediment towards the margins of the estuary bioturbation and clay illuviation mechanical infiltration are secondary processes that may redistribute fine grained sediment and produce grain coats here we have shown that detrital grain coats are more likely in marginal environments of ancient estuary fills which are typically found in the fining upward part of progradational successions

deterministic coastal morphological and sediment transport modeling a review and discussion 1 modern coastal ocean modeling systems are now capable of numerically simulating a variety of coastal and estuarine problems and can thus provide useful information for managing coastal zones here we review state of the art eulerian implementations of bottom up sediment transport and morphological change in coastal ocean hydrodynamic models in order to investigate the fate of suspended sediment in coastal and estuarine waters as well as the evolution of sea or river beds sediment dynamics need to be represented at a scale relevant to the numerical discretized solution and significant effort is devoted to parameterize sediment processes we discuss boundary layer hydrodynamics and the computation of the bed shear stress we also focus on approaches used to represent near bed processes such as bed load transport and sediment erosion and deposition sediment diffusivities settling velocities and cohesive processes such as flocculation all have an impact on suspended sediment throughout the water column we then describe the implementation of process parameterizations in coastal hydrodynamic models explicitly reviewing five widely used systems the approaches implemented in these coastal models may present distinct strengths and shortcomings with regard to some important issues for coastal zones both numerical and physical while these detailed limitations need to be considered as part of model assessment more general issues also hinder present state of the art models in particular sediment transport is inherently highly empirical which is further compounded by issues arising from turbulence closure schemes we conclude by suggesting some possible directions toward improving sediment dynamics understanding and coastal scale predictive ability

aegean sea water masses during the early stages of the eastern mediterranean climatic transient 1988 90 abstract the aegean water masses and circulation structure are studied via two large scale surveys performed during the late winters of 1988 and 1990 by the r v yakov gakkel of the former soviet union the analysis of these data sheds light on the mechanisms of water mass formation in the aegean sea that triggered the outflow of cretan deep water cdw from the cretan sea into the abyssal basins of the eastern mediterranean sea the so called eastern mediterranean transient it is found that the central aegean basin is the site of the formation of aegean intermediate water which slides southward and depending on their density renews either the intermediate or the deep water of the cretan sea during the winter of 1988 the cretan sea waters were renewed mainly at intermediate levels while during the winter of 1990 it was mainly the volume of cdw that increased this aegean water mass redistribution and formation process in 1990 differed from that in 1988 in two major aspects i during the winter of

in channel surficial fine grained sediment laminae part i physical characteristics and formational processes an in channel surficial depositional feature surficial fine grained laminae composed of loosely bound fine sediment deposited during low flow conditions has often been observed in river systems in south western ontario the physical characteristics of this feature have been determined by a direct observation image analysis system this sediment consists primarily of flocculated fine grained material the size distributions of surficial fine grained laminae and suspended sediment were not significantly different each distribution is bimodal in nature and shows a characteristic grain size deficiency in the 4 5 m size range this observation suggests that flocculation and not low discharge or low competence is the dominant mechanism for the formation of surficial fine grained laminae under conditions of low flow in fluvial systems of south western ontario a quantitative assessment of this feature shows its potential importance as a source of fine grained sediment and associated contaminants for downstream transport

climatic changes in the aegean sea influence the eastern mediterranean thermohaline circulation 1986 1997 recent changes of water mass characteristics in the south aegean sea have considerably influenced the eastern mediterranean thermohaline circulation a combination of salinity increase 1987 92 and temperature drop 1992 94 caused massive dense water formation and strong outflow towards the deep and bottom parts of the eastern mediterranean this climatic shift the most important since the existence of observations in the basin is a combined effect of extreme meteorological events superimposed on large scale trends it has initiated a series of modifications in the hydrology and dynamics of the entire eastern mediterranean with possible influence on the mediterranean outflow in the north atlantic ocean