a numerical study of the mediterranean sea circulation abstract a primitive equation ocean model that makes use of a curvilinear orthogonal grid and a sigma coordinate system was used to simulate the mediterranean sea the model was forced with monthly climatological values of wind stress heat and salinity flux with the help of the curvilinear horizontal grid the larger scales of the entire mediterranean sea are modeled and the topography around the narrow and shallow straits of gibraltar is also reasonably well represented the resulting model inflow and outflow seems to mimic the real mediterranean often in considerable detail levantine intermediate water is formed in the levantine basin and exits through the strait of sicily and the strait of gibraltar deep water formation processes are clearly represented by the model the model results indicate that in the western mediterranean the wind stress is very important in establishing the summer northward shift of the atlantic inflow lateral boundary runoff surface salinity and heat fluxes are necessar

vertical profile of artificial radionuclide concentrations in the central arctic ocean abstract the artificial radionuclides 90 sr 137 cs 238 pu 239 240 pu and 241 am have been measured in eight water samples collected in 1979 at intervals from surface to bottom through the ice at the lorex satellite camp ss near the north pole differences in the concentrations and ratios of these nuclides compared with values measured over time in the various water masses that flow into the arctic ocean can be used as semi independent checks on rates of flow to the lorex stations and on residence times in the arctic ocean an unexpected finding was that water labelled with low level liquid waste from the windscale plant on the irish sea is a major component of the 1500 m lorex sample and has reached there in no more than eight to ten years even from this one station in the polar ocean estimation of the inventories of the various radionuclides is good enough to emphasize the importance of horizontal advection of the various supply terms to the arctic

estimation of deep and intermediate water mass formation rates in the mediterranean sea abstract using a simple diagnostic model and climatological surface temperature salinity and air sea fluxes the deep and intermediate water formation sites of the mediterranean sea are determined as well as the annual formation rates for each of them with the same model the t and s characteristics of the water masses are estimated four distinct formation sites are formed one in the western gulf of lions and three in the eastern adriatic northern ionian rhodes gyre area southern aegean basin respectively with well defined water types being produced at each formation site the computed annual production rates compare quite well with other independent estimations found in literature

a snow transport model for complex terrain as part of the winter environment in middle and high latitude regions the interactions between wind vegetation topography and snowfall produce snow covers of non uniform depth and snow water equivalent distribution a physically based numerical snow transport model snowtran 3d is developed and used to simulate this three dimensional snow depth evolution over topographically variable terrain the mass transport model includes processes related to vegetation snow holding capacity topographic modification of wind speeds snow cover shear strength wind induced surface shear stress snow transport resulting from saltation and suspension snow accumulation and erosion and sublimation of the blowing and drifting snow the model simulates the cold season evolution of snow depth distribution when forced with inputs of vegetation type and topography and atmospheric foreings of air temperature humidity wind speed and direction and precipitation model outputs include the spatial and temporal evolution of snow depth resulting from variations in precipitation saltation and suspension transport and sublimation using 4 years of snow depth distribution observations from the foothills north of the brooks range in arctic alaska the model is found to simulate closely the observed snow depth distribution patterns and the interannual variability

the physics of wind blown loess implications for grain size proxy interpretations in quaternary paleoclimate studies abstract loess deposits are recorders of aeolian activity during past glaciations since the size distribution of loess deposits depends on distance to the dust source and environmental conditions at the source during transport and at deposition loess particle size distributions and derived statistical measures are widely used proxies in quaternary paleoenvironmental studies however the interpretation of these proxies often only considers dust transport processes to move beyond such overly simplistic proxy interpretations and toward proxy interpretations that consider the range of environmental processes that determine loess particle size distribution variations we provide a comprehensive review on the physics of dust particle mobilization and deposition furthermore using high resolution bulk loess and quartz grain size datasets from a last glacial interglacial sequence we show that because grain size distributions are affected by multiple often stochastic processes changes in these distributions over time allow multiple interpretations for the driving processes consequently simplistic interpretations of proxy variations in terms of only one factor e g wind speed are likely to be inaccurate nonetheless using loess proxies to understand temporal changes in the dust cycle and environmental parameters requires i a careful site selection to minimize the effects of topography and source distance and ii the joint use of bulk and quartz grain size proxies together with high resolution mass accumulation rate calculations if possible

the residence time of the freshwater component in the arctic ocean the time function of bomb tritium concentrations in river runoff to the arctic ocean has been reconstructed from published data on tritium in precipitation 1959 1975 tritium measurements on oceanic samples through the halocline exhibit strong linear relationships between tritium concentrations tu values and salinity these waters thus look like binary mixtures of atlantic source water and freshwater runoff combining these data the vintage of the freshwater component in the arctic basin has been determined assuming no other major tritium source the relation indicates the average age of the freshwater component to be 11 1 years in the nansen basin and the outflow and somewhat higher in the canada basin according to tritium salinity data a surface layer of 10 60 m is affected by sea ice melting and freezing in the nansen basin and the thickness of this layer increases to 150 170 m toward the canada basin there is tritium also in the deeper waters the unmixed atlantic water which points at residence times for that water not to exceed 17 years the appendix is available with the entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j81 012 1 00 payment must accompany order

a general circulation model for upper ocean simulation abstract a general circulation model gcm of the ocean that emphasizes the simulation of the upper ocean has been developed this emphasis is in keeping with its future intent that of an air sea coupled model the basic model is the primitive equation model of bryan and cox with the additions of optional usage of the mellor yamada level 2 5 turbulence closure scheme and horizontal nonlinear viscosity these modifications are intended to improve the upper ocean simulations particularly sea surface temperature and heat content the horizontal grid spacing is 1 latitude 1 longitude and is global in domain the equatorial region between 10 n and 10 s is further refined in the north south direction to resolution there are 12 vertical levels with six levels in the top 70 m the model incorporates varying bottom topography prior to coupling the ocean model to an atmospheric gcm experiments have been carried out to determine the ocean gcm s performance using atmospheric forcing from observed data

a pv approach for dense water formation along fronts application to the northwestern mediterranean the mechanisms of dense water formation 29 0 kg m 3 at work in the baroclinic cyclonic gyre of the north western mediterranean basin are investigated through a pv budget pv potential vorticity the pv budget is diagnosed from an eddy resolving 1 36 ocean simulation driven in surface by hourly air sea fluxes provided by a non hydrostatic atmospheric model at 2 5km resolution the pv budget is controlled by the diabatic frictional and advective pv fluxes around the gyre the surface diabatic pv flux dominates the pv destruction except along the northern branch of the north current where the surface frictional pv flux is strongly negative in this region the bathymetry stabilizes the front and maintains the current northerly in the same direction as the dominant northerly wind this configuration leads to optimal wind current interactions and explains the preponderance of frictional pv destruction on diabatic pv destruction this mechanical forcing drives a cross front ageostrophic circulation which subducts surface low pv waters destroyed by wind on the dense side of the front and obducts high pv waters from the pycnocline on the light side of the front the horizontal pv advections associated with the geostrophic cyclonic gyre and turbulent entrainment at the pycnocline also contribute to the pv refueling in the frontal region the surface non advective pv flux involves energy exchanges down to 1400 w m 2 in the frontal zone this flux is 3 5 times stronger than atmospheric buoyancy flux these energy exchanges quantify the coupling effects between the surface atmospheric forcing with the oceanic frontal structures at submesoscale this article is protected by copyright all rights reserved

the use of topographic scale models in predicting eolian dust erosion in hilly areas field verification of a wind tunnel experiment abstract eolian erosion of natural dust in an area of 53 ha situated in the northern negev desert is investigated in detail both in the wind tunnel erosion simulations on a topographic scale model and in the field the wind tunnel results and the field results show good agreement indicating that wind tunnel simulations of eolian dust erosion on scale models of complex topography may predict at least to an acceptable level the erosion sensitive areas in a hilly landscape of nearly uniform surface roughness the experiments also indicate that a restricted height distortion of scale models may be acceptable to determine the areas of highest erosion in addition wind tunnel blockage percentages up to 10 may be allowed to obtain acceptable erosion patterns on the model when surface roughness is more or less uniform eolian erosion of dry dusty sediments is almost entirely determined by macro topography if however surface roughness is highly variable over the field the initiation of eolian erosion is also largely a function of local micro topography

wind tunnel experiments and field measurements of aeolian dust deposition on conical hills abstract the spatial pattern of short term aeolian dust deposition on and around cone shaped hills is investigated via the simulation in a wind tunnel of dust storms over a topographic scale model of a conical hill in the negev desert israel the results are tested during a full scale dust storm in the negev the wind tunnel experiments adequately predict the field pattern although some problems may arise on steep windward slopes where the accumulation threshold is more quickly exceeded on the scale model than in the field conical hills create an elongated area of low deposition dust shadow in their lee downwind from the shadow zone a local area of more than normal compared to the undisturbed surroundings deposition occurs on the lateral flanks of the hill and also on the small convex windward slope just upstream of the top and at the top itself dust deposition remains low to very low it is the lowermost concave windward slope that receives the largest amounts of dust the pattern described above refers to short term deposition only water erosion may seriously alter the final accumulation pattern since it will clean the slopes of important amounts of dust that accumulate in the wadis

late holocene landscape reconstruction in the land of seven rivers kazakhstan abstract a landscape reconstruction for the late holocene was carried out in the land of the seven rivers kazakhstan to investigate the environmental conditions during the prehistoric nomadic occupation of the sakes 1st mill bc two sampling locations were sedimentologically analysed a radiocarbon dated late holocene colluvial deposits and b fluvial deposits of assumed late pleistocene to early holocene age the geochemical and mineralogical components icp element analysis carbon contents grain size distributions x ray diffractometry were investigated to identify synsedimentary weathering conditions a modified weathering index mcia was used to evaluate the weathering processes the mcia results were compared with the silt clay ratio as an additional indicator for post depositional soil forming processes differences within the silt clay ratios and mcia indexes revealed that during the late holocene increased erosion processes occurred in the catchment a first tentative geochronology is based on radiocarbon and luminescence ages ranging from 14 5 1 4 ka to 3 23 0 07 cal ka bp for the colluvial deposits this paleoenvironmental reconstruction is supplemented by a detailed geomorphological characterization of the present landscape relief landforms and landscape units close to the sakian graves

a mixed layer study of the formation of levantine intermediate water a mixed layer model is used to investigate the formation of levantine intermediate water liw over the eastern mediterranean the one dimensional model is initialized with climatological hydrography and integrated over the levantine basin with forcing by climatological surface fluxes realistic and repeated seasonal mixed layer cycles are obtained if the annual surface heat input and water loss are offset by a parameterized horizontal advection the model integrations show that liw is formed during winter in the mixed layer of the northwestern levantine the preferred formation region for liw is found through idealized experiments to be controlled by the preconditioning of the hydrography especially that of the cold cyclonic rhodes gyre rather than by the pattern of the climatological fluxes the annual mean formation rate of liw is estimated to be 1 0 sv using the climatological surface fluxes the magnitude of the annual surface fluxes alters the formation rate and modifies the formation region an additional annual heat flux reduces the formation rate of liw whereas an extra cooling enhances it as well as forming waters denser than liw in the center of the rhodes gyre

calibration of the mdco dust collector and of four versions of the inverted frisbee dust deposition sampler abstract wind tunnel experiments were conducted to determine the efficiency of sediment samplers designed to measure the deposition of aeolian dust efficiency was ascertained relative to a water surface which was considered the best alternative for simulating a perfectly absorbent surface two types of samplers were studied the marble dust collector mdco and the inverted frisbee sampler four versions of the latter catcher were tested an empty frisbee an empty frisbee surrounded by an aerodynamic flow deflector ring a frisbee filled with glass marbles and a frisbee filled with glass marbles and surrounded by a flow deflector ring efficiency was ascertained for five wind velocities range 1 5 m s 1 and eight grain size classes range 10 89 m the efficiency of dust deposition catchers diminishes rapidly as the wind speed increases it also diminishes as the particles caught become coarser adding a flow deflector ring to a catcher substantially improves the catcher s efficiency by up to 100 in some cases the addition of glass marbles to a catcher on the other hand does not seem to increase the efficiency at least not at wind velocities inferior to the deflation threshold for higher velocities the marbles protect the settled particles from resuspension keeping them in the catcher the following five parameters determine the accumulation of aeolian dust in a catcher the horizontal dust flux the weight of the particles atmospheric turbulence resuspension and the dust shadow effect created by the catcher the final accumulation flux depends on the combination of these parameters the catchers tested in this study belong to the best catchers currently in use in earth science and have been the subject of various aerodynamic studies to improve their efficiency nevertheless the catching efficiency remains low in the order of 20 40 for wind speeds above 2 m s 1 other catchers suffer from the same low efficiencies there is thus evidence to believe that dust deposition rates published in the aeolian literature and obtained by collecting the sediment in a catcher largely underestimate the true deposition the errors are considerable of the order of 100 and more a reconsideration of the literature data on aeolian dust deposition measured by catchers is therefore required

cesium 137 transport into the arctic ocean through fram strait cesium 134 and 137cs activities were measured in water samples collected in march april 1981 at the fram 3 ice station located 200 km north of fram strait the water depth profiles of these isotopes reveal the presence of two pathways for the entry of anthropogenic tracers into the arctic ocean through fram strait atlantic water passing across the yermak plateau at the 100 200 m level is labeled by elevated concentrations of 134cs and 137cs associated with inputs from the sellafield reprocessing plant in the united kingdom the 134cs 137cs ratio is consistent with a transit time into the nansen basin from the sellafield united kingdom vicinity of 5 6 years an elevated concentration of 137cs at the 1500 m level is associated with inputs of recently ventilated water from the greenland norwegian seas or as a consequence of brine formation and off shelf transport from the barents sea

sensitivity of time lapse seismic data to pore pressure changes is quantification possible time lapse seismic data have contributed to increased reservoir knowledge and improved hydrocarbon recovery mainly by monitoring changes in fluid saturation seismic signatures of pore pressure changes have been less commonly reported although some observations such as large depletion magnus field and secondary effects such as associated gas out of solution shiehallion field and geomechanical effects in the reservoir and overburden ekofisk valhall and hthp fields have been made quantification of the pore pressure changes from seismic data has rarely been performed to date

mapping the fluid front and pressure buildup using 4d data on norne field norne field in the southern part of the nordland ii area in the norwegian sea approximately 100 km north of aasgard field is producing from an fpso the main field is a horst block approximately 9 3 km figure 1 the reservoir rocks are sandstones of lower and middle jurassic age the hydrocarbon reserves consist of a gas cap 75 m mainly situated in garn formation and an oil leg 110 m mainly situated in ile and tofte formations the sandstones are very good quality with porosities and permeabilities of 25 32 and 200 2000 md respectively net to gross is close to 1 for most reservoir zones oil production started in 1997 the first 4d seismic survey was acquired in 2001 and 4d information has been actively used in subsequent reservoir management

water masses and hydrography during april and june 2016 in the cretan sea and cretan passage eastern mediterranean sea abstract two successive cruises in the cretan sea and cretan passage west levantine basin during april and june 2016 surveyed the physical characteristics of the water masses in these large eastern mediterranean basins data confirm that the hydrographical status is far different from that of the eastern mediterranean transient emt period however the basins have not yet returned to the pre emt status in the cretan sea intermediate water masses of both cretan and levantine origins are detected the stagnating bottom waters of this basin still hold high salinity density and dissolved oxygen values remnant of the emt deep water formation episodes characterised by low salinity and oxygen values transitional waters of mediterranean origin are present between intermediate and bottom layers throughout the cretan sea intermittent weak outflow of warm and saline masses of cretan origin towards the eastern mediterranean is observed at the bottom of both east and west cretan straits in the cretan passage there is no sign of the ierapetra anticyclonic gyre possibly related to the seasonality of the gyre or linked to larger scale eastern mediterranean circulation variability the observed surface circulation in this area is comprised of a series of smaller gyres between the cretan cyclone and the rhodes gyre the bottom waters of the cretan passage present a west to east gradient of increasing salinity and decreasing oxygen related to the propagation of new adriatic deep water from the ionian sea towards the levantine basin

short distance variability in slope bed forms along the southwestern adriatic margin central mediterranean abstract the slope of sw adriatic margin sam is impinged today by two bottom water masses of thermohaline origin that interact constructively along a preferred path the levantine intermediate water liw generated in the eastern mediterranean through intense evaporation and flowing along the contour and the north adriatic dense water naddw formed on the shallow north adriatic and cascading episodically off the shelf these two southward flowing bottom water masses impact the upper slope which is characterized by an irregular physiographic setting and together create the bottom current deposits e g fine grained contourite drifts and sediment waves and related erosional features e g furrows scours comet marks this study is focussed on a small open slope area of the sam ca 35 25 km where high resolution seismic data allow observe elongated contour parallel scours widespread erosion surfaces accompanied by wide crescent shape scours and furrow fields and giant comet marks spatially associated and genetically linked along a common current path further downslope and away from this highly energetic current path a field of sediment waves migrates upcurrent and shows bifurcated crests in some cases the downcurrent limbs of the sediment waves display a well defined erosional character on seismic profiles and furrows on side scan sonar mosaics all bottom current features observed are in equilibrium with the present day oceanographic regime as documented by the available current metre data moreover sediment cores suggest that the sediment waves are actively migrating during the present interglacial possibly implying that bottom waters formation was enhanced after the shallow adriatic shelf was drowned during the late quaternary eustatic rise the sam slope represents therefore an ideal site to improve our understanding of the depositional impact of bottom currents along the mediterranean margins and may provide useful hints on the activity of bottom currents elsewhere on the mediterranean margins

the effect of surface curvature on the deposition of loess a physical model summary a physical model for the deposition of fine dusty material loess on curved surfaces is presented the model is tested in a sedimentation experiment with a symmetrical hill with length axis perpendicular to the flow direction in a wind tunnel it appears both from the model and the experiment that loess deposition will occur preferably on windward slopes and not on leeward ones in contrast to the widespread wind shadow concept below the deflation threshold loess deposition increases as wind speed increases above the deflation threshold an effective accumulation of the loess layer on the surface will occur within a well defined wind speed interval the loess layer on the surface will erode away only if wind speed has exceeded this interval for flat and dry surfaces free of roughness elements the upper limit of the interval is 7 m s free stream velocity for wet surfaces however it may be considerably higher 15 m s and more

discrimination between pressure and fluid saturation changes from time lapse seismic data explicit expressions for computing saturation and pressure related changes from time lapse seismic data have been derived and tested on a real time lapse seismic data set necessary input is near and far offset stacks for the baseline seismic survey and the repeat survey the method has been tested successfully in a segment where pressure measurements in two wells verify a pore pressure increase of 5 to 6 mpa between the baseline survey and the monitor survey estimated pressure changes using the proposed relationships fit very well with observations between the baseline and monitor seismic surveys 27 of the estimated recoverable hydrocarbon reserves were produced from this segment the estimated saturation changes also agree well with observed changes apart from some areas in the water zone that are mapped as being exposed to saturation changes which is unlikely saturation changes in other segments close to the original oil water contact and the top reservoir interface are also estimated and conf

observations with moored acoustic doppler current profilers in the convection regime in the golfe du lion abstract in the golfe du lion south of france favorable conditions for deep winter convection exist and were documented by the medoc experiments during 1969 75 a renewed investigation of that regime with upward looking moored acoustic doppler current profilers adcps was carried out during 24 january 5 march 1987 to record the three dimensional currents associated with the deep mixing while in the earlier studies initial deep convection did not begin until fairly late in the winter season a very strong mistral around 10 january 1987 had already generated a 1arge deep mixed patch homogeneous down to around 2000 m at deployment time three adcps two working at 150 khz and one at 75 khz were moored in a triangle of 15 km sidelength at 550 780 m depth full records at 1 hour ensemble time intervals 400 pings per ensemble 8 m bin lengths were obtained by the 75 khz and one of the 150 khz adcps in mid february a second mistral hit the region with the onset of strong winds and surface cooling the

overburden 4d time shifts induced by reservoir compaction at snorre field abstract interpreting and understanding overburden seismic changes are important to avoid health safety and environmental hse accidents and well drilling problems furthermore overburden time shifts might indicate areas with reservoir compaction and depletion in the snorre sandstone field 4d seismic time shifts of as much as 3 ms are observed in the overburden the cumulative overburden time shifts captured at top reservoir correlate well with pressure depletion areas in the reservoir indicating that the time shifts might be related to changes in stress and strain because of reservoir compaction for further investigation a 2d geomechanical model is built in the area with the most prominent overburden time shifts based on the stiffness of the reservoir and surrounding rocks and simulated reservoir pore pressure changes the geomechanical model predicts a maximum downward displacement at the top reservoir of 0 4 m and maximum seabed subsidence of 0 25 m by defining an appropriate strain sensitiv

reservoir monitoring of steam assisted gravity drainage using borehole measurements this paper presents the results from a research project focusing on permanent crosswell geophysical methods for reservoir monitoring during steam assisted gravity drainage a feasibility study indicated detectable differences in seismic and electrical reservoir properties based on expected changes in temperature and fluid saturation during the production of extra heavy oil as a result of this a permanent cross well system was installed at the leismer demonstration area located in the athabasca oil sands region in alberta canada baseline data sets including cross well seismic three dimensional vertical seismic profiling and cross well electrical resistivity tomography have been acquired comparisons between conventional surface seismic and downhole seismic data show an increase in resolution and frequency content as expected steam assisted gravity drainage induced time lapse effects are clearly visible in the 3d vertical seismic profiling and electrical resistivity tomography data sets even after a few months of oil production in general the 3d vertical seismic profiling images show a higher resolution than the surface seismic data in particular when dealing with vertical positioning of the time lapse events the electrical resistivity tomography baseline shows clear separation between zones of high and low electrical resistivity and during 23 months of electrical resistivity tomography measurements the maximum reduction of resistivity is 85 time lapse observations from acoustic and electrical borehole data correspond well and are also supported by temperature measurements in the two observation wells emerging technologies updated models improved flexibility and reduced costs will allow future reservoir monitoring with surface and borehole data in combination or even with borehole data exclusively key words borehole geophysics resistivity seismics time lapse

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

a new model of topographic effects on the distribution of loess a model of topographic influence on the regional transport and accumulation of loess in sparsely vegetated landscapes is proposed based on the critical role played by saltating eolian sand in the entrainment and long distance transport of finer grained suspended dust in this model long term accumulation of loess occurs mainly downwind of topographic obstacles that limit eolian transport of sand and associated re entrainment of dust regional and local patterns of distribution of late wisconsinan loess in parts of the upper mississippi river basin are closely related to the distribution of topographic obstacles to sand transport these cases of topographic influence occur in a region where evidence exists for sparse tundra like vegetation during the deposition of loess in the late wisconsinan similar topographic effects may not be evident further south in the missouri and mississippi river basins because vegetation density was generally sufficient to prevent the movement of eolian sand out of source valleys thus topographic obstacles and dense vegetation may have similar effects on loess distribution under different environmental conditions

temporal and spatial trends in the distribution of 137cs in surface waters of northern european seas a record of 40 years of investigations abstract the distribution of anthropogenic 137 cs in surface waters of the ne atlantic ocean resulting from discharges from european nuclear reprocessing plants the chernobyl accident and global fallout has shown decreasing concentrations in most regions in the past 2 decades in proportion to the lessening of its release rates from the sellafield and la hague reprocessing plants in contrast concentrations increased significantly in the baltic sea in 1986 as a result of the chernobyl accident the average 137 cs concentrations in surface water have been estimated for the year 2000 to be 60 50 bq m 3 for the irish sea 3 1 for the celtic sea 2 1 1 2 for the english channel 4 2 for the north sea 50 20 for the baltic sea 2 1 for the norwegian sea 2 4 0 5 for the barents sea and 4 1 bq m 3 for the kara sea on the basis of time series data the corresponding effective half lives of 137 cs in surface water have been estimated to be 4 1 years for the irish sea 2 1 for the celtic sea 1 2 0 5 for the english channel 3 1 for the north sea 13 2 for the baltic sea 4 1 for the norwegian sea 5 1 for the barents sea and 13 4 years for the kara sea the mean transit times of water masses have been estimated to be 0 5 0 1 year from the irish sea to the north channel 2 0 2 years to the north of scotland 2 5 0 2 to the east coast of england 3 0 5 to the southern north sea 4 0 5 to the central and eastern north sea 1 5 0 2 to the celtic sea 2 0 2 to the english channel 5 1 to the baltic sea 4 5 0 5 to the norwegian sea 5 1 to the barents sea and 6 1 years to the kara sea

circulation and hydrography of the levantine basin results of poem coordinated experiments 1985 1986 abstract a brief review of the meteorological setting hydrography and the circulation in the levantine basin of the eastern mediterranean is given the recent high resolution data obtained in poem coordinated experiments of 1985 1986 are then used to optimally estimate the circulation in the basin in two different seasons and to describe the water mass distributions some of the features observed during the experiments support the historical knowledge on the locations of sub basin scale gyres and the general circulation in addition to which some new features are established details of the circulation such as the intensity the multiple scales and the three dimensional structure of the various vortices and the central levantine basin current are displayed extensively a variety of sub basin meso and sub mesoscale vortices occur with highly assymmetric baroclinic vertical structures some eddies split into multiple centres with depth interpreted as indicating possible coalescences a number of long lived eddies were persistent in both surveys the sub surface atlantic water aw is advected by and entrapped within the eddy field the levantine intermediate water liw at intermediate depths is shown to be maintained throughout the year in the northeastern sector of the levantine basin and along the periphery of the rhodes gyre the levantine intermediate water also has a patchy distribution owing to the advection and trapping by the eddy field which it helps to generate through adjustment processes

the contemporary physical and chemical flux of aeolian dust a synthesis of direct measurements of dust deposition abstract the deposition of aeolian or windblown dust is widely recognized as an important physical and chemical flux to ecosystems dust deposition adds exogenous mineral and organic material to terrestrial surfaces and can be important for the biogeochemical cycling of nutrients there have been many studies that characterize the physical and chemical composition of dust however few studies have synthesized these observations in order to examine patterns geochemical fluxes we have compiled observations of dust deposition rates particle size distributions psd mineralogy and bulk elemental and organic chemistry the rates of dust deposition observed across the globe vary from almost 0 to greater than 450 g m 2 yr 1 sites receiving dust deposition can be partitioned into broad categories based on there distance from dust source regions when compared to global dust models our results suggest some models may underestimate dust deposition rates at the regional and local scales the distance from the source region that dust is deposited also influences the particle size distributions mineralogy and chemical composition of dust however more consistent dust sampling and geochemical analyses are needed to better constrain these spatial patterns on average the concentrations of most major elements si al fe mg ca k in aeolian dust tend to be similar 20 to the composition of the upper continental crust ucc but there is substantial variability from sample to sample in contrast some elements tend to be depleted na or enriched ti in dust likely as a result of soil weathering processes prior to dust emissions trace elements especially heavy metals are consistently enriched in dust relative to the ucc ecologically important nutrients such as n and p are also present in dust deposition the geochemical flux attributable to dust deposition can be substantial in ecosystems located proximal to dust source regions we calculate estimates of elemental flux rates based on the average chemical composition of aeolian dust and varying rates of deposition these estimated flux rates are useful as a rough gauge of the degree to which dust deposition may influence biogeochemical cycling in terrestrial ecosystems and should be utilized to better constrain deposition estimates of global dust models

radionuclide tracer profiles at the cesar ice station and canadian ice island in the western arctic ocean abstract water column profiles of naturally occurring 210pb 210po 226ra and fallout 137cs 239 240pu radionuclides measured at the canadian ice island in 1985 1986 and 1989 over the arctic ocean continental shelf were compared to profiles measured at the cesar ice station in the central arctic ocean in 1983 cesium 137 concentrations at cesar decreased from a mean value of 4 2 bq m3 in the surface mixed layer to less than 1 0 bq m3 in the atlantic layer and deep waters cesium 137 concentrations were similar to cesar values in the surface mixed layer at the ice island but in halocline water they were lower than values measured at comparable water depths at cesar indicating that the arrival of fallout 137cs in the ice island halocline had been delayed compared to its arrival in the cesar halocline these data are consistent with a combination of mixing box and lateral advection models with mixing occurring over the russian continental shelves followed by lateral advection through the interior halocline waters of the canada basin dissolved 210pb and 210po concentrations were higher in nutrient maximum water at the ice island compared to cesar low values at cesar are caused by scavenging of particle reactive radionuclides during modification of bering sea water in continental shelf environments the elevated 210pb and 210po concentrations measured in nutrient maximum water at the ice island are assumed to result from ingrowth of 210pb from 226ra during lateral advection of upper halocline water between the cesar and ice island locations a process that is estimated to take approximately 11 years plutonium 239 240 is also depleted relative to 137cs in the surface mixed layer and upper halocline at the ice island owing to its scavenging during modification of pacific water in shelf environments the 239 240 pu 137 cs ratio increases to values approaching fallout levels in lower halocline and atlantic water owing to both reduced 239 240pu removal in source waters and vertical transport of 239 240pu with sinking particles

an insightful parametrization for the flatlander s interpretation of time lapsed seismic data an approximation is developed that allows mapped 4d seismic amplitudes and time shifts to be related directly to the weighted linear sum of pore pressure and saturation changes the weights in this relation are identified as key groups of parameters from a petroelastic model and include the reservoir porosity this dependence on groups of parameters explains the inherent non uniqueness of this problem experienced by previous researchers the proposed relation is of use in 4d seismic data feasibility studies and inversion and interpretation of the 4d seismic response in terms of pore pressure and water saturation changes a further result is drawn from analysis of data from the north sea and west africa which reveals that the relative interplay between the effects of pore pressure and saturation changes on the seismic data can be simplified to the control of a single spatially variant parameter cs cp combining these results with those from published literature we find that cs cp 8 appears to be a generality across a range of clastic reservoirs with a similar mean porosity using this cs cp value an in situ seismic scale constraint for the rock stress sensitivity component of the petroelastic model is constructed considering this component carries the largest uncertainty

on the relationship between the decadal oscillations of the northern ionian sea and the salinity distributions in the eastern mediterranean 1 we study the impact of decadal inversions of the ionian upper layer circulation denominated as adriatic ionian bimodal oscillation system on thermohaline properties of the levantine and cretan seas lagrangian drifter data and surface geostrophic currents show that the atlantic water aw flow is well organized and most intense when the ionian circulation is cyclonic during the ionian anticyclonic phase the aw spreading pathway is the longest contributing to its prolonged mixing and higher salinity once it reaches the levantine thus the levantine basin is subject to less dilution by aw during the anticyclonic surface circulation phase empirical orthogonal function analysis of the sea level shows a large amplitude circular feature in the northern ionian which matches the cyclonic anticyclonic gyre obtained from lagrangian measurements furthermore it reveals the out of phase variability of the north ionian gyre and the aegean and levantine sea levels we further show that the surface salinity of the levantine basin variation is out of phase with that of the ionian surface layers salinity variations of the deepwater column in the aegean are out of phase with the ionian surface salinity values owing probably to a fast transfer of the surface salinity changes via winter deep convection the changing of the levantine and cretan seas salinity parallel to the ionian circulation inversions suggests that the preconditioning for the eastern mediterranean transient emt is driven by internal processes as the ionian inversions are cyclical events we conclude that the emt is not an isolated episode but potentially a recurrent phenomenon

technetium 99 and cesium 134 as long distance tracers in arctic waters in august 1984 134cs originating from the british reprocessing plant sellafield formerly windscale was found in the waters between canada and greenland the transit time from sellafield to baffin bay is approximately eight years the concentration in the surface waters in the south eastern part of baffin bay of a pollutant coming from the north sea is approximately 1 of its concentration in the north sea the conclusions based upon the observations of 134cs are supported by determinations of 99tc in greenland fucoids enhanced discharges of 99tc apparently began in 1970 i e four years earlier than those of radiocesium the unreported annual 99tc discharges in the 1970s prior to 1978 are estimated to be approximately 40 tbq 1 kci

the 1987 aegean dense water formation a streamtube investigation by comparing theoretical model results satellite field and numerical data with contourite distribution abstract we here discuss a detailed investigation of the dense water formation evolution and spreading in the aegean sea during the year 1987 immediately prior to the onset of the eastern mediterranean transient emt we use hydrologic data collected during the lia cruise satellite images for sst sea surface temperature and protheus data a coupled ocean atmosphere numeric model along with theoretical streamtube models these hydrological analyses are related to late quaternary sedimentary drifts in the cyclades plateau and in the myrtoon basin our analysis shows that streamtube dynamics provide a novel model of dense water evolution and spreading in the aegean basin applying this model to dense water masses observed in winter and spring 1987 near samothrace and over the limnos lesbos plateau results in a geostrophic flow of this dense cold water towards the limnos sporades channel in the north aegean sea there it mixes with dense water from the limnos lesbos plateau and finally both move geostrophically towards the cyclades plateau these results indicate that most of the dense water observed near the cyclades formed initially about 3 months earlier at samothrace and limnos shelves during its long pathway it partially mixed with adjacent water masses although our analysis concerns only one year of dense water analyses these results are thought to reflect a more general and recurrent phenomenon in the aegean basin indeed high resolution airgun 10 in seismic reflection data from the cyclades plateau reveal the presence of late quaternary sediment drifts these observations are concordant with results from our theoretical model this suggests a direct link between such a dense water cascading and contourite dynamics the continuation of sediment drifts into the deep basin floor 900 m deep of the myrtoon basin moreover indicates a cascading character of such bottom currents at the flanks of the basin a feature that set further investigations

geochemical profiles in the central arctic ocean their relation to freezing and shallow circulation temperature salinity nutrient tritium and oxygen isotope data collected during the lomonosov ridge experiment along a drift track between the makarov and fram basins over the lomonosov ridge are presented the relationship of these quantities to the processes that maintain the halocline in particular to the production of more saline waters by addition of brines formed during the freezing of seawater is described the results support the idea that the wide continental shelves of the arctic ocean play an important role in maintaining the halocline productivity and to the chemical and physical effects of freezing sea water a comparison of this ocean with its low productivity at least during winter with other oceanic regions should help to elucidate some of the effects of biological activity on marine chemistry for example trace metal cycling and speciation aagaard et al 1981 discussed the way in which the cold waters of the halocline which lie immediately below the surface mixed layer and extend to the top of the warm atlantic layer could be produced on the wide continental margins surrounding the arctic ocean the processes in volve freezing with release of highly saline brines having a temperature close to the freezing point of surface sea water this water flows over the shelves and into the central basin sinking then to the appropriate density surface the distribu tions of various chemical parameters will be affected in predictable ways by these processes as a part of the lomonosov ridge experiment lorex which ran from late march until the end of may 1979 a program was undertaken aimed at describing more accurate ly the hydrography of the central arctic ocean and studying the geochemistry of selected trace elements in this unusual environment to this end water samples were collected from a drifting ice station lorex satellite camp 1 for the measurement of salinity silicate phosphate 5 80 trace metals moore 1981 1983 carbon 14 tritium helium 3 caesium 137 caesium 134 strontium 90 plutonium ameri cium h d livingston et al manuscript in preparation 1983 alkalinity and ph ice cores were collected to investi gate the possibility of deducing the extent of temporal changes in the tritium content of the surface waters

the influence of saharan dust deposits on la palma soil properties canary islands spain abstract the significance of saharan dust deposits for ecosystems has been demonstrated in several studies showing its influence on pedogenesis and soil chemical and physical parameters by the addition of nutrient elements this contribution is especially important for volcanic soils poor in plant available phosphorous as those of the island of la palma canary islands spain thus this study investigates the spatial distribution of saharan dust on the island and determines its influence on soil properties and thus on the ecosystem of the island since silt sized quartz is not autochthonously formed on the island it served as a reliable indicator for saharan dust quartz was identified and quantified using x ray diffractometry the influence of saharan dust additions on soil properties was assessed by texture analyses and analyses of plant available phosphorous an element strongly limiting plant growth on the island due to its fixation in the structure of amorphous volcanic clay a luff lee effect revealed significant influence on dust distribution whereas small geomorphologic structures as hollows and mounds hardly influenced the dust distribution pattern a positive correlation of quartz content with the proportion of the grain size fraction 0 5 10 m demonstrates an influence on soil physical properties apparently influencing available water capacity furthermore our data suggest an increasing content of plant available phosphorous with a rising amount of saharan dust in the soils thus the input of saharan dust influences soil fertility of la palma and is an important factor regarding the fragility of the la palma ecosystems

oceanographic distributions of zinc cadmium copper and aluminium in waters of the central arctic vertical profiles are presented of dissolved cadmium zinc copper and aluminium at the lorex 79 site in the central arctic ocean cd zn and cu show unusually high surface concentrations of 0 3 3 and 5 nmoll 1 respectively these levels are related to contributions from surface run off and from the underlying nutrient rich bering sea winter water al has lower surface concentrations than observed elsewhere and shows no correlation with the nutrients the importance of aeolian supply is questioned and the results point to a major role for inorganic removal of al at least in the arctic ocean

disequilibria between226ra 210pb and 210po in the arctic ocean and the implications for chemical modification of the pacific water inflow abstract measurements have been made of226ra and both dissolved and particulate forms of210pb and210po in a vertical profile at 85 50 n 108 50 w in the arctic ocean in the upper water column226ra shows a concentration maximum that is coincident with one in the nutrients silicate phosphate and nitrate while at the same depth dissolved and particulate210pb and210po all show minimum concentrations it is suggested that the concentration maxima are partly due to sources of the respective elements in the continental shelf sediments the shelf waters being subsequently advected into the arctic ocean basins the210pb and210po minima have similarly been explained by interaction between the shelf sediments and overlying waters an estimate is made of the possible contributions of shelf sediments to the layer of silica rich water which covers the canada basin at a depth of 100 150 m residence times have been calculated for dissolved210pb and210po at various depths in the water column surface water residence times of dissolved and particulate forms of these radionuclides are longer than in surface atlantic waters probably due to lower biological activity in the surface waters of the canada basin an estimatee has been made of the average sinking velocity of particulate material

natural radionuclides and plutonium in sediments from the western arctic ocean sedimentation rates and pathways of radionuclides abstract sediment cores collected during r v polar sea aos94 expedition from the chukchi shelf to the north pole were analyzed for several decay series natural radionuclides and pu isotopes to study sedimentation rates and pathways of radionuclides in the western arctic ocean the measured sedimentation rates vary by more than three orders of magnitude along the transect from 210pb based rates of 200 700 cm kyr 1 over the chukchi shelf and 89 cm kyr 1 at the chukchi slope to 230th based rates of 0 02 0 3 cm kyr 1 at various settings in the deep basin 230thex profiles in the central western arctic basin are characterized by a cyclic pattern and a pronounced sub surface maximum superimposed on an overall decrease with depth sediment inventories of excess 210pb and 230th in the deep basin as a whole cannot account for their in situ production and 210pb fall out the opposite is true at the slope and shallower waters we contend that as with other ocean basins boundary scavenging also exists in the arctic ocean the broad continental shelves and the slope region may have the potential of removing all or most of the particle reactive radionuclides unaccounted for in the deep basin the pu isotope data are consistent with the notion of boundary scavenging sediment inventories and concentrations of pu decrease rapidly offshore isotopic composition of pu suggests mixing of fall out pu which decreases with increasing latitudes and fuels reprocessing pu derived from the russian and atlantic sides of the arctic ocean although fuel reprocessing pu has impinged on the chukchi slope its existence over the chukchi shelf is not evident and probably overshadowed by fall out pu

ekofisk life of field seismic operations and 4d processing abstract in 2010 the world s largest optical permanent reservoir monitoring prm system was installed in the southern part of the norwegian north sea at ekofisk the life of field seismic lofs system consists of 3966 seabed multicomponent sensors along 200 km of mostly trenched fiber optic seismic cables and covering about 60 km2 of ekofisk field seismic data are acquired via a topside recording unit and a containerized source operated on a supply vessel six vintages of data were acquired between the end of 2010 and fall 2013 different aspects of seismic operations at ekofisk include seismic source recording system data transfer quality control and processing one of the key factors in achieving the full value of a prm system is to handle such operations in a safe integrated and efficient manner to deliver high quality seismic volumes for interpretation with rapid turnaround key aspects of the 4d processing sequence include robustness and optimal turnaround integration of the different oper

a four dimensional analysis of the thermal structure in the gulf of lion the theoretical and experimental tomography in the sea experiment thetis 1 took place in the gulf of lion to observe the evolution of the temperature field and the process of deep convection during the 1991 1992 winter the temperature measurements consist of moored sensors conductivity temperature depth and expendable bathythermograph surveys and acoustic tomography because of this diverse data set and since the field evolves rather fast the analysis uses a unified framework based on estimation theory and implementing a kaiman filter the resolution and the errors associated with the model are systematically estimated temperature is a good tracer of water masses the time evolving three dimensional view of the field resulting from the analysis shows the details of the three classical convection phases preconditioning vigourous convection and relaxation in all phases there is strong spatial nonuniformity with mesoscale activity short timescales and sporadic evidence of advective events surface capping intrusions of levantine intermediate water liw deep convection reaching 1500 m was observed in late february by late april the field had not yet returned to its initial conditions strong deficit of liw comparison with available atmospheric flux data shows that advection acts to delay the occurence of convection and confirms the essential role of buoyancy fluxes for this winter the deep mixing results in an injection of anomalously warm water t 0 03 to a depth of 1500 m compatible with the deep warming previously reported

the 4d seismic signature of oil water contact movement due to natural production in a stacked turbidite reservoir combined time lapse reservoir simulation and seismic modelling has been performed on both 1d and 3d models of a channelized turbidite reservoir the models have been built using core log laboratory and seismic data from the nelson field central north sea as a template oil and water movement in the main channels channel margins and interchannel regions is investigated with a particular focus being the effect of poor net to gross the analysis confirms that saturation effects dominate the response whilst stress sensitivity effects play a minor role the trough peak signature in the seismic difference volumes formed by the sweep of the water can be continued and mapped slightly further than the channel margins this characteristic 4d signature remains roughly intact despite the complicated depositional architecture and accurately delineates the area of moved fluid but it needs additional calibration to combat the detrimental influence of the low net to gross signal strength is largely dependent on reservoir quality but is also compromised by the net to gross fluid distribution and more critically by the exact timing of the seismic survey for example a region of bypassed oil zone remains undetected as it forms early during the production this work demonstrates that to understand fully the 4d signature at a quantitative level requires adequate knowledge of the fluid properties but also more critically the geology

ecology and spatial pattern of cyanobacterial community island patches in the atacama desert chile 1 plant landscape ecology studies have been carried out for decades and are fundamental to biological research in contrast few corollary spatial landscape studies exist for microorganisms particularly in extreme environments to address this gap we mapped the abundance and spatial distribution of photoautotrophs colonizing translucent rocks in several sites in the atacama desert including the hyperarid core cyanobacterial communities at all sites are predominantly 75 perilithic confined to the periphery of rocks and occur in non random spatial patterns island patches at multiple scales cyanobacterial patches typically contain 1 5 colonized rocks but in some cases support much higher numbers a high resolution mapping of a single 18 m2 rock cluster at the aguas calientes study site 25 s 69 w revealed colonization of 5 2 49 of 948 quartz rocks and showed colonized rocks to be much larger 2x than the available mean rock size ripley s k and point pattern analyses show that quartz rocks are not selected or occupied by cyanobacteria randomly but that non random processes distinct from those creating the background rock pattern must be invoked to explain microbial patchiness in the atacama desert these processes include physical controls rock size orientation microtopography that reflect resource water limitations and biological dispersal via rainfall fog and wind

aeolian deposition of dust over hills the effect of dust grain size on the deposition pattern wind tunnel experiments were conducted to investigate the effects of topography on the grain size characteristics of aeolian dust deposits experiments were performed on three isolated hills having various size and aspect ratios the longitudinal profile of the median grain diameter was investigated for each hill the longitudinal dust deposition profile was also studied for nine grain size classes of between 10 and 104 m as were wind and dust concentration profiles in the atmosphere upwind of over and downwind of a hill the wind tunnel experiments show that the grain size characteristics of aeolian dust deposits are affected by topography most apparent is the occurrence of a zone of reduced grain size on the leeside of hills which extends from just upwind of the summit to a distance of several times the height of the hill slightly coarser than normal dust is deposited on the concave windward hill slope and in a zone downwind of the area of reduced grain size but the increase in grain size in these zones remains very small although the normalized dust deposition profile for a hill does not vary substantially as a function of grain size systematic trends are observed the most important tendencies are 1 a progressive extension in the downwind direction of a zone of decreased dust deposition on the leeside of a hill the coarser the grains the further downwind the zone of reduced deposition extends 2 a progressive increase in dust deposition immediately upwind of a hill the finer the grains the higher the deposition value upwind of a hill becomes both tendencies are explained by the difference in inertia of the grains which is controlled by grain size copyright 2005 john wiley sons ltd

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

a synthesis of the ionian sea hydrography circulation and water mass pathways during poem phase i abstract in this paper we revisit with a thorough in depth analysis the dataset collected in the hydrographic surveys of the international collaborative programme poem physical oceanography of the eastern mediterranean in the period 1986 1987 the work has two major objectives the first is to refine the dynamic picture of the ionian upper thermocline sub basin scale circulation rather less definitive than the dynamic picture of the levantine sea circulation the second is to identify the pathways of the major water masses of the basin not only in the near surface but also in the intermediate and deep layers to our knowledge this is the first work defining the pathways of the levantine intermediate water liw and of the adriatic deep water adw eastern mediterranean deep water emdw that characterize the intermediate and deep circulations the major novel results can be summarized as follows in the upper thermocline 1 the atlantic ionian stream ais jet entering the sicily straits bifurcates into two main branches at 37 n 17 e it advects the modified atlantic water maw into the ionian sea interior the first branch turning directly southward encloses an overall anticyclonic area comprising multiple centers around which the maw is advected 2 the second ais branch extends further into the northeastern ionian where it too turns southward before crossing the entire ionian sea meridionally advecting maw on its left side and ionian surface water isw on its right this branch of the jet is confined to the ionian margin and does not pass around the pelops gyre 3 a new water mass the lsw is formed in the levantine basin and enters the cretan passage then is first veered cyclonically south of crete by the cretan gyre and successively is entrained anticyclonically around the pelops gyre and then enters the aegean sea 4 a permanent cyclone located in the northeastern ionian determines the pathway of mixed adriatic surface water ionian surface water asw isw 5 a permanent cyclone is found in all the surveys near the tip of the italian boot this novel analysis of the liw pathways shows that 1 the major source of intermediate liw during the period 1986 1987 was actually in the levantine sea liw formed there entered the cretan passage was veered cyclonically by the cretan gyre south of crete and then entered the southern ionian sea the major liw pathway was westward directly to the sicilian straits 2 secondary important liw pathways were determined by the interior structures the strong pelops anticyclone was entraining liw around its periphery and was determining the liw northward pathway that closely followed the eastern greek coastline it was along this pathway that liw entered the otranto strait a further branch of liw was entrained and recirculated around the multiple ionian anticyclones ia of the western ionian sea 3 the cretan cyclone is a feature confined to the upper thermocline intermediate layer it disappears at 400 dbar while the pelops anticyclone is strongly barotropic below the upper 100 dbar and penetrates quite intense down to 800 dbar 4 a further completely novel result concerns the new water mass found in the deep layer that spreads on the 29 15 kg m3 isopycnal surface this water mass characterized by high salinity and high oxygen content is formed inside the aegean sea and is observed to spread out all around the cretan arc straits the final fully novel result is the demonstration of a second pathway for the adw exiting from the otranto strait that is transformed into emdw and occupies the abyssal layers of the ionian sea interior the traditional pathway for emdw is along the isobaths along the western side of italy but adw was observed to be exiting from the otranto strait in the eastern hellenic trench at 39 5 n both during poem on86 and poem as87 this second pathway for emdw follows isobath contours along the western side of greece the two emdw routes converge and merge between 36 n and 35 n so producing a deep layer of emdw that occupies uniformly the abyssal plain of the interior of the ionian sea

a three dimensional numerical study of deep water formation in the northwestern mediterranean sea abstract deep water formation dwf in the northwestern mediterranean sea and the subsequent horizontal circulation are investigated in a rectangular basin with a three dimensional primitive equation model the basin is forced by constant climatological heat and salt fluxes convective motion is parameterized by a simple nonpenetrative convective adjustment process plus richardson number dependent vertical eddy viscosity and diffusivity a homogeneous column of dense water is progressively formed in the forcing area meanders of 40 km wavelength develop at the periphery of the column these features agree with observations energy studies show that the meanders are generated mainly through a baroclinic instability process these meanders and the associated cells of vertical motion contribute to the process of dwf they generate vertical advection while the associated horizontal advection tends to restratify the surface water of the column and thus to inhibit very deep convection just before the end o

seismo stratigraphic characters of paleocontourites along the calabro tyrrhenian margin southern tyrrhenian sea abstract buried contourites located offshore capo suvero calabria southern italy have been investigated using analysis of sparker profiles the deposits onlap an erosional surface produced by a slide in the upper slope pleistocene units the overall seismic characters of the deposits suggest an interpretation as infilling drift deposits formed by the activity of a northward bottom current flowing along the paleoslope the deposits with thickness up to 140 m are made up of 3 units including 8 sub units with an upward convex shape on dip profile and a lenticular shape on strike profile the stacking pattern of sub units highlights a general upslope migration interrupted by two downslope shifts accompanied by erosion a general migration toward the north has also been recognized this evolution could be explained by autocyclic processes due to the seafloor modification during the growth of the deposits otherwise it could also be related to variations of the oceanographic conditions or eventually to sea level changes formation of the deposits located in the present day 110 240 m bathymetric range could have been significantly deeper than present location as a consequence of the regional uplift affecting the area since pleistocene under this hypothesis an intermediate current may be inferred for the formation of the deposits these deposits are quite rare along the tyrrhenian margins and their formation preservation seems to be related to the peculiar morphological setting of the area characterized by a morpho structural high and a slide scar their presence is relevant for the stratigraphy of the eastern tyrrhenian margin as they underline the importance of bottom current processes with implications on paleocirculation reconstructions of the mediterranean basin

modeling the mediterranean sea interannual variability during 1961 2000 focus on the eastern mediterranean transient 1 this work is dedicated to the study of the climate variability of the mediterranean sea in particular the study of the eastern mediterranean transient emt which occurred in the early 1990s simulations of the 1961 2000 period have been carried out with an eddy permitting ocean general circulation model of the mediterranean sea driven by realistic interannual high resolution air sea fluxes using different databases for the river runoff black sea inflow and atlantic thermohaline characteristics at climatological or interannual scales we assess the effects of the non atmospheric hydrological forcings on the simulation of the interannual variations of the mediterranean circulation the evolution of the basin scale heat content is in very good agreement with the observations especially in the surface and intermediate layers while the agreement is lower for the evolution of the salt content convection events in the aegean sea are noticed in the simulations between 1972 and 1976 in the late 1980s and around the emt period the formation rates of cretan deep water cdw are different during these periods allowing or preventing the spreading of cdw into the eastern mediterranean the sequence of the emt events is well reproduced the high winter oceanic surface cooling and net evaporation over the aegean sea in the early 1990s the high amount of dense cdw formed during these winters and then the overflow and the spreading of this cdw in the eastern mediterranean among the preconditioning processes suggested in the literature we find that changes in the levantine surface circulation possibly induced by the presence in the cretan passage of anticyclonic eddies and a lasting period with reduced net precipitation over the eastern mediterranean lead to an increase of the salt content of the aegean sea changes in the black sea freshwater inflow or in the characteristic of the atlantic water entering at the gibraltar strait also modify the thermohaline state of the aegean sea before the emt but as none of these preconditioning factors has a lasting impact on lowering the vertical stratification of the aegean sea we conclude that concerning the emt the major triggering elements are the atmospheric fluxes and winds occurring in winters 1991 1992 and 1992 1993

a real time oceanographic nowcast forecast system for the mediterranean sea we describe here a nowcast forecast system for the entire mediterranean sea designed for real time forecasts and closely resembling operational numerical weather prediction systems the core of the system is a high resolution 10 km three dimensional primitive equation based sigma coordinate numerical circulation model assimilating remotely sensed multi channel sea surface temperature and in situ expendable bathythermograph conductivity temperature depth observational data using an optimal interpolational scheme we present results for 1993 and 1994 from this data assimilation model focusing principally on the mesoscale features prevalent in the western and eastern mediterranean sea we show that the model exhibits considerable skill in simulating both the permanent and transient mesoscale features in the mediterranean in particular hitherto less well known and less well studied circulation features in the adriatic and aegean seas are carefully examined and presented particular care is given to discussing the circulation in the entire mediterranean with particular attention to flows through various straits and their variability

pu 137cs and excess 210pb in russian arctic sediments the activity ratios of pu and radiocesium isotopes have been used to delineate the major sources such as global and close in debris fallout nuclear fuel reprocessing and fabrication plant effluents in the environment we have measured 238pu 239 240pu 137cs and excess 210pb concentrations in 107 surficial sediments as well as in 5 sediment cores collected in the summer months of 1993 and 1994 from the ob and yenisey rivers russia and the kara sea a comparison of the sediment core inventories of 239 240pu and 137cs along with the 238pu 239 240pu activity ratios with those expected from global fallout allows us to estimate the relative amounts if any of reactor derived 238pu and 239 240pu from the dumped reactor sites in the study area in surficial sediment samples collected in 1993 and 1994 the 239 240pu concentrations varied between 4 2 and 856 mbq kg 1 with a mean of 239 mbq kg 1 in samples with a measurable 238pu the 238pu 239 240pu activity ratios varied between 0 010 and 0 069 with an average value of 0 035 0 014 this range can be compared to the average 238pu 239 240pu activity ratio of 0 030 for the year 1993 from nuclear weapons testing and snap fallout obtained from soil studies indicating very little 5 additional sources of 238pu to the sediments in the study area the inventories of pu in the 5 sediment cores from the study area varied between 2 67 0 67 and 24 5 2 2 bq m 2 with a mean value of 8 83 bq m 2 the 137cs concentrations in the upper 3 cm of the sediments varied between below detection limit to 71 4 bq kg 1 with a mean of 14 9 bq kg 1 the 137cs inventories in the 5 sediment cores varied between 156 7 28 3 and 1600 153 3 bq m 2 with a mean value of 583 3 bq m 2 the mean ratio of inventories of pu to that of 137cs 0 015 is comparable to the values in other places in the arctic region there is a significant correlation between total organic carbon and concentrations of 137cs 239 240pu and 210pb suggesting that organic matter enriched fine particles are a likely carrier phase for these nuclides the ratio of 137cs 239 240pu also suggests that most of these nuclides are derived from global fallout

iodine 129 137cs and cfc 11 tracer transit time distributions in the arctic ocean 1 time series measurements of the nuclear fuel reprocessing tracers 129i and 137cs and ventilation tracer cfc 11 were used to determine circulation time scales for atlantic water aw in the arctic ocean measurements in surface water are consistent with an advection model and transit times from the north sea of 1 4 years to the barents sea 3 6 years to the kara sea and 9 12 years to the north pole tracer ages for intermediate waters do not support an advection model because they vary with time the tracer relationships were employed to determine transit time distributions ttd using inverse gaussian functions that implicitly incorporate the effects of mixing in simulating fluid flow tracer concentrations were used to constrain the ratio of the width of the ttd to the mean age a measure of the relative importance of mixing giving values for most intermediate water regimes of 1 these results are in contrast to values 1 typical of the north atlantic indicating the greater relative importance of advection compared to mixing in the arctic ocean mean ages for aw increase from 12 20 years in the southern makarov basin to 30 40 years near the arctic outflow north of greenland a decline in with distance along the direction of aw boundary flow from the makarov into the canada basin may indicate relatively stronger mixing in regimes upstream of the makarov basin but also implies that ttds may differ from inverse gaussian functions for flow in the arctic domain

228ra as a tracer for shelf water in the arctic ocean during its formation on the vast siberian shelves arctic surface water is strongly enriched in 228ra when 228ra of surface samples from the arctic interior is plotted against the river water component fr derived from salinity 180 and silicate as tracers a shelfwater end member can be calculated by extrapolation highest values occur in the core of the transpolar drift indicating rapid transport of surface water comparable to the known ice drift pattern low values at ice island t3 are explained by radioactive decay 5 8 year half life during the long residence time of fresh and shelf influenced water in the beaufort gyre some evidence of decay and consequently prolonged transit times is also observed in the southern nansen basin future research is required to establish the seasonal interannual and spatial variability of 228ra on the shelves in order to determine the full potential of 228ra as a tracer for the origin and transport rates of shelfwater in the arctic basin apart from the usual 228ra signature of bottom waters the tracer is also observed in intermediate layers where it gives evidence of recent contact with slope or shelf sediments the atlantic inflow along the barents slope is enriched down to 2000 m the return flow over the amundsen basin and lomonosov ridge carries a shelf signature of 228ra and 228th down to more than 1200 m depth in agreement with the enrichment observed in 137cs deeper maxima around 1900 2500 m in the nansen basin are interpreted as inflow of bottom water from the norwegian sea through fram strait

scale model simulations of the deposition of loess in hilly terrain the sedimentation of loess in a 40 km2 area on the northern border of the belgian loess belt is investigated by means of wind tunnel experiments loess deposition is simulated on a relief scale model for different wind directions it appears that simulation with northeast winds produces a loess deposition pattern that coincides closely to the field pattern which may be an indication that the loess bearing winds at the end of the weichselian came from the northeast loess deposition occurs preferably on windward slopes and not on leeward ones the wind shadow concept which is important in the case of sand deposition may therefore not necessarily apply to fine materials such as fine silt and clay

temporal evolution of the water mass properties during the eastern mediterranean transient emt in the aegean sea 1 we present time series of temperature and salinity of the aegean sea using the data sets for the period from 1991 to 1996 from 15 oceanographic cruises to depict the temporal variability of the water masses of the aegean sea this period covers an interesting large scale change in the thermohaline circulation in the eastern mediterranean and the aegean sea this change is known as the eastern mediterranean transient emt and was first described during early 1990s our analysis reveals that very dense water formation in the central aegean sea is partially due to the anomalous decrease in winter atmospheric temperature although this alone cannot completely account for the formation of the dense water a synchronous increase in surface salinity accompanied by low temperature values in the winter months is also necessary for the emt event to occur

convection with rotation in a neutral ocean a study of open ocean deep convection abstract the intensity and scale of the geostrophically adjusted end state of the convective overturning of a homogeneous rotating ocean of depth h at a latitude where the coriolis parameter is f induced by surface buoyancy loss of magnitude b0 are studied by numerical experiment the experiments are related to observations and laboratory studies of open ocean deep convection a numerical model based on the nonhydrostatic boussinesq equations is used the grid spacing of the model is small enough that gross aspects of convective plumes themselves can be resolved yet the domain of integration is sufficiently large to permit study of the influence of plumes on the large scale and geostrophic adjustment of the convected water numerical simulations suggest that cooling at the sea surface is offset by buoyancy drawn from depth through the agency of convective plumes these plumes efficiently mix the water column to generate a dense chimney of fluid which subsequently breaks up through the mechanism of bar

tracers and modeling the major tracer activity of the last four years was the completion in 1983 of a survey of the north and tropical atlantic begun in 1981 as part of the transient tracers in the ocean tto project brewer et al 1985 an early set of papers brewer et al 1983 and swift 1984 discussed evidence from these observations for the freshening of the north atlantic due to cessation of overflow across the iceland scotland ridge in the period between geosecs and tto broecker et al 1985a examined observations further south within the deep northeastern atlantic and showed that there was no change of nutrient contents in this region during the same time span consistent with their conclusion that there is no ventilation of this region from the north kawase and sarmiento 1985 and 1986 used the tto data to produce a series of nutrient and salinity maps and property property plots on density surfaces in the thermocline and middepth waters of particular interest in these studies is the evidence from silica salinity observations of strong cross isopycnal mixing and advection in the equatorial region

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

complex fluid flow revealed by monitoring co2 injection in a fluvial formation 1 at cranfield mississippi united states a large scale carbon dioxide co2 injection through an injection well 3 080 m deep was continuously monitored using u tube samplers in two observation wells located 68 and 112 m east of the injector the lower tuscaloosa formation injection zone which consists of amalgamated fluvial point bar and channel fill deposits presents an interesting environment for studying fluid flow in heterogeneous formations continual fluid sampling was carried out during the first month of co2 injection two subsequent tracer tests using sulfur hexafluoride sf6 and krypton were conducted at different injection rates to measure flow velocity change the field observations showed significant heterogeneity of fluid flow and for the first time clearly demonstrated that fluid flow evolved with time and injection rate it was found the wells were connected through numerous separate flow pathways co2 flowed through an increasing fraction of the reservoir and sweep efficiency improved with time the field study also first documented in situ component exchange between brine and gas phases during co2 injection it was found that ch4 degassed from brine and is enriched along the gas water contact multiple injectate flow fronts with high ch4 concentration arrived at different times and led to gas composition fluctuations in the observation wells the findings provide valuable insights into heterogeneous multiphase flow in rock formations and show that conventional geological models and static fluid flow simulations are unable to fully describe the heterogeneous and dynamic flow during fluid injection

natural and anthropogenic radionuclide distributions in the nansen basin artic ocean scavenging rates and circulation timescales abstract determination of the naturally occurring radionuclides 232 th 230 th 228 th and 210 pb and the anthropogenic radionuclides 241 am 239 240 pu 134 cs and 137 cs in water samples collected across the nansen basin from the barents sea slope to the gakkel ridge provides tracers with which to characterize both scavenging rates and circulation timescales in this portion of the arctic ocean large volume water samples 15001 were filtered in situ to separate particulate 0 5 m and dissolved th isotopes and 241 am thorium 230 displays increases in both particulate and dissolved activities with depth with dissolved 230 th greater and particulate 230 th lower in the deep central nansen basin than at the barents sea slope dissolved 228 th activities also are greater relative to 228 ra in the central basin residence times for th relative to removal from solution onto particles are 1 year in surface water 10 years in deep water adjacent to the barents sea slope and 20 years in the eurasian basin deep water lead 210 in the central basin deep water also has a residence time of 20 years with respect to its removal from the water column this texture of scavenging is reflected in distributions of the particle reactive anthropogenic radionuclide 241 am which shows higher activities relative to pu in the central nansen basin than at the barents sea slope distributions of 137 cs show more rapid mixing at the basin margins barents sea slope in the south gakkel ridge in the north than in the basin interior cesium 137 is mixed throughout the water column adjacent to the barents sea slope and is present in low but detectable activities in the eurasian basin deep water in the central basin at the time of sampling 1987 the surface water at all stations had been labeled with 134 cs released in the 1986 accident at the chernobyl nuclear power station in the 1 year since the introduction of chernobyl 134 cs to the nansen basin it had been mixed to depths of 800 m at the barents sea slope and to 300 m in the central basin prechernobyl inventories of 137 cs as well as 239 240 pu are 10 times those expected from global atmospheric fallout from nuclear weapons testing and are derived principally from releases from the sellafield u k nuclear fuel reprocessing facility on the irish sea based on the sources of 137 cs to the nansen basin mixing time scales are 9 18 years for the upper water column to 1500 m and 40 years for the deep water these mixing time scales combined with more rapid scavenging at the basin margin relative to the central basin produce residence times of particle reactive radionuclides in the nansen basin comparable to other open ocean areas e g north west atlantic despite the presence of permanent ice cover and long periods of low light levels that limit productivity in the arctic

wind tunnel experiments of aeolian dust deposition along ranges of hills wind tunnel experiments of aeolian dust deposition on topographic scale models of ranges of hills were conducted different hill sizes and hill spacings were used and comparisons with the deposition patterns over single isolated hills were made dust profiles over ranges of hills differ from the profiles over identical but isolated hills on isolated hills the sedimentation maximum on the windward hillslope is always single and located on the concave part of the slope in the case of ranges of hills the maximum is either single or double with the second peak on the convex part of the windward slope in the latter case the local sedimentation maximum on the convex leeslope which is rather unimportant on isolated hills is much more developed in multiple hill topography also dust deposition on the leeslopes is significantly higher in multiple hill topography than on isolated hills dust patterns on ranges of hills may be affected by the dust shadow created by the most upstream located hill if hills succeed each other quickly they are located within the shadow zone and are protected from important dust deposition the plume of high air dust concentration that is created by a hill largely determines the dust pattern on the next hill as a result of the supply of dust from above by the descending plume areas that are normally devoid of dust now experience significant dust deposition

historical changes in 239pu and 240pu sources in sedimentary records in the east china sea implications for provenance and transportation abstract concentrations and isotopic compositions of plutonium pu are widely used for its source identification and to determine transport processes of pu associated particulate matter and water we investigated the concentrations of 239pu and 240pu and their ratios in a number of sediment samples from the east china sea ecs collected in the summer of 2013 august 6 28 the 239 240pu activity concentrations in surface sediment samples were found to range between 0 048 and 0 492 bq kg 1 and the 240pu 239pu atom ratios showed a similar trend as that of the 239 240pu activities the pu atom ratios ranged from 0 158 to 0 297 and were mostly higher than the mean global fallout value of 0 18 the 239 240pu inventories in the ecs varied widely from 2 to 807 bq m 2 with the highest values commonly found in the coastal areas in the yangtze estuary the mean 239 240pu activity concentration is close to the estimated value of the suspended material from the yangtze river catchment 0 18 bq kg 1 and the 240pu 239pu atom ratio was found to be 0 18 which indicates that the yangtze river input is the dominant source of pu for this area the total annual yangtze river input of 239 240pu was estimated to be 2 4 10 10 bq which is small compared to the total amount of 239 240pu buried 3 1 10 13 bq in the whole ecs the pacific proving ground input appears to be the dominant source of pu to the ecs accounting for 45 52 of the total inventory the fractional amount of 239 240pu scavenged from the total 239 240pu transported by the kuroshio current kc and taiwan warm current twc into ecs sediments is estimated to be 10 our study shows that the 240pu 239pu atom ratio is useful not only to obtain a better insight of the biogeochemistry influenced by the kc but also to trace the long range transport of other particle reactive species besides the sedimentation rates obtained based on the penetration depths of 239 240pu and vertical profiles of excess 210pb agree within uncertainties which suggests that 239 240pu can potentially be used as a chronostratigraphic time marker in the marine environment

distribution of 137cs and other radioactive tracers in the eastern mediterranean relationship ot the deepwater transient 1 the time evolution of 137cs distribution in the eastern mediterranean in the period 1977 1999 is discussed in relation to water circulation and in particular to the eastern mediterranean transient emt tritium data are used to reconstruct the spatial distribution of 137cs before the emt and the chernobyl accident relatively high concentrations characterized the surface and intermediate waters of the whole basin and the levels gradually decreased toward the bottom tracer concentrations in the deep waters decreased from west to east reflecting the spreading of the core of the eastern mediterranean deep water formed in the adriatic sea in the 1990s a significant change was induced by the intrusion of new deep water of aegean origin in the bottom layers of the ionian and levantine basins marked by a relatively high 137cs concentration around 2 5 bq m 3 as a result in 1999 the levels were almost homogeneous in the whole deep ionian sea in the past the oldest waters of the eastern mediterranean were found around 1500 m characterized by a tracer minimum layer during the emt this layer was displaced upward to 750 1500 m and was also much thinner than previous the analysis of vertical profiles and ratios of 137cs and 90sr shows that a chernobyl contribution is present in the surface intermediate and deep waters of the ionian sea but not in the tracer minimum layer and in the deep adriatic sea the analysis of tritium helium ages in this area indicates a decreased convective renewal of basin waters in the period 1987 1999 that also explains the absence of a chernobyl signal

going quantitative with 4d seismic analysis it is demonstrated that time lapse seismic signatures can be directly calibrated with historical data from producing and injecting wells via a reservoir simulator material balance calculation or simply using the hard data when this procedure is applied to a field over which two or more repeat surveys have been shot at different calendar times the correlation coefficients that link the seismic difference signatures to the reservoir s pressure and saturation variations are determined by utilizing several seismic attributes that respond differently to reservoir perturbations pressure and saturation changes are then independently estimated the approach is tested on synthetic data and then on data from the schiehallion field on the uk continental shelf with favourable results

quantifying wind erosion at landscape scale in a temperate grassland nonignorable influence of topography abstract revised wind erosion equation rweq is widely applied to determining wind erosion and achieves reliable results however the spatial variability of wind erosivity and wind erosion has not been sufficiently investigated in previous studies in this paper rweq was used to determine wind erosion and its spatial variation at the landscape scale in the xilingele grassland which is a typical temperate grassland in north china suffering from increasing wind erosion problems based on field investigation and laboratory measurement land surface parameter data were obtained computational fluid dynamics cfd wind modelling was integrated to acquire the spatial variation of wind data which considers the influence of topography and land use these data were used to determine the five factors of rweq and wind erosion modulus results showed that the mean wind erosion modulus was 5 33 t ha 1 yr 1 and 97 16 of the area had light or no wind erosion which was mostly distributed in the low plains and the leeward areas however there were hotspots of wind erosion which were mainly distributed in the windward slopes and the summit areas there were no significant differences among the wind erosion moduli of different land uses but land use affected the influence of topography on wind erosion the maximum modulus varied greatly from 0 to 259 41 t ha 1 yr 1 for different land uses and the most severe wind erosion occurred in moderately grazed grassland mg followed by heavily grazed grassland hg arable land al lightly grazed grassland lg and ungrazed grassland ug statistical tests indicated that topography had a significant influence on wind erosion which was not detected in previous studies due to the lack of high resolution topography and wind data the combination of rweq and cfd wind modelling suggests that future wind erosion studies should further consider the important influence of topography to achieve sustainable development in temperate grassland rational grazing is critical and special attention should be paid to windward slopes and high elevation areas

a wind tunnel simulation and field verification of desert dust deposition avdat experimental station negev desert the deposition of natural dust in an area of 53 ha situated in the northern negev desert is investigated in detail both in the wind tunnel dust storm simulations over a topographic scale model and in the field the wind tunnel results and the field results show a high degree of agreement indicating that scale model simulation may be considered an important technique for future loess and desert research more dust settles on windward slopes than on leeward slopes which is in contradistinction with the widespread wind shadow concept air flow separation zones immediately downwind of steep windward slopes have an important impact on dust deposition too in the case of dust deposition on topographic scale models a restricted height distortion of the model will not necessarily lead to serious problems in addition wind tunnel blockage percentages up to 13 may be allowed in order to obtain acceptable dust deposition patterns for the scale model a mean gross dust deposition of about 200 250 g m 2 year 1 is calculated for the northern negev desert for 1987 thus if the settled dust can be protected against erosion in the cultivated areas in the negev the dust content of the top soil will markedly increase with time however it has to be borne in mind that cultivation activities themselves may also contribute to a higher soil erosion and hence to a higher dust content in the atmosphere at any rate a higher dust content in the top soil will unquestionably have an important positive effect on agricultural yields from the air dust concentration data and the dust deposition data a deposition velocity of 4 7cms 1 can be calculated for avdat dust

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

the west spitsbergen current disposition and water mass transformation recent work suggests that the west spitsbergen current which provides the principal contribution to the arctic ocean of salt and sensible heat as well as of a variety of anthropogenic tracers is a rather complex circulation feature north of 79 n where the isobaths diverge markedly the current contains two separate warm cores that follow different isobaths the western core carried by the offshore branch of the current follows the western flank of the yermak plateau and north of 80 n at least part of this flow detaches from the plateau probably to contribute to the recirculation in fram strait in contrast the inshore branch follows the shelf break into the arctic ocean it is this inshore branch that provides the primary focus in this paper during the transit of the inshore waters past northwestern spitsbergen the core properties change primarily through vertical heat flux which during ice free conditions in winter is estimated to be of the order of 200 w m 2 from the core layer alone together with some freshening within the arctic ocean this process is responsible for fully transforming the original atlantic water into arctic intermediate water within about 600 km of fram strait

late neogene climate evolution of the central arctic ocean abstract because no sediment of post eocene to late miocene or pliocene age has been recovered from the central arctic ocean oceanographic conditions during the middle cenozoic are unknown the oldest late cenozoic sediment is glacial marine and contains agglutinated foraminifera a few calcareous organisms are present in the oldest late cenozoic sediment with an age of 2 4 ma but at approximately the time as deposition of lithostratigraphic unit f sometime between 2 0 and 1 5 ma there was an abrupt and dramatic increase in calcareous species diversity and abundance in the central arctic ocean many of the newly introduced species are atlantic in origin preliminary evidence suggests that the introduction of a moderately large and diverse calcareous fauna at this time corresponds to the lowering of the arctic ocean ccd level and this may be explained by increased circulation with the northern greenland sea details of the change in threshold values in the fram strait required for the introduction of relatively warmer and carbonate rich water into the central arctic ocean are unknown there is evidence that spreading rates along the north atlantic nansen ridge system increased during the pleistocene and this may have permitted increased circulation between the north atlantic and the central arctic ocean this important change in arctic ocean circulation corresponds to increased pleistocene seasonality in the northern hemisphere

dry aeolian dust accumulation in rocky deserts a medium term field experiment based on short term wind tunnel simulations the spatial pattern of medium term a few months dry aeolian dust accumulation in rocky deserts is predicted using short term deposition and erosion experiments in a wind tunnel the predictions are tested in a field experiment set up in the northern negev desert of israel the results show that superimposing wind tunnel deposition and erosion maps usually leads to correct predictions of medium term dust accumulation the predictions are somewhat less confident near the inflection lines of windward hillslopes where small scale irregularities in the local topography make it difficult to locate the exact position of the areas of little accumulation elsewhere in the topography predictions are good and the method works satisfactorily highest accumulation occurs on concave windward slopes and to a lesser extent on slopes parallel to the wind little accumulation occurs on the convex windward slopes and in dust separation bubbles the smallest accumulation rates are observed immediately upwind of the top of pronounced hills and on leeslopes the rate of dry dust accumulation measured during the field experiment varied from 17 to 93 g m 2 a 1 depending on the topographic position of the accumulation plots for most plots it was of the order of 30 60 g m 2 a 1

low frequency current variability at the straits of crete eastern mediterranean current meter data from six moorings are analyzed to study current variability at the straits of the cretan arc which connect the south aegean sea with the eastern mediterranean the three layers in which the current meters were deployed show different current characteristics the upper layer shows evidence of the asia minor current in the rhodes strait and a clockwise eddy in the karpathos strait water in the middle layer moves slowly into the south aegean the bottom current meters in kassos and antikithira straits recorded currents steady in amplitude and direction with speeds equal to or higher than those observed in the upper layer the observations suggest a significant outflow 0 5 sv of cretan dense water cdw to the levantine and ionian seas rotary empirical orthogonal functions are used to extract and describe the coherent part of the variability forty four percent of the total variability is described by the first three empirical orthogonal functions less than 20 of the current variability of the western strait is coherent with variability of the eastern straits the coherent part of the variability refers mainly to periods longer than 20 days the current meter data are compared with atmospheric pressure showing good correlation during the first period of the measurements when a major atmospheric pressure low passed over the aegean

mobile mud dynamics in the east china sea elucidated using 210pb 137cs 7be and 234th as tracers mobile mud mm which has fine grain size distribution 90 clay silt and 2 5 in south inshore indicates that the sediment focusing resulted in the increased mass flux the residence time of mm is estimated as 3 6 years both by mass balance of mm and 210pbex in mm

a process study of the adriatic ionian system baroclinic dynamics the driving mechanisms behind the decadal reversal of the ionian sea upper layer circulation recently sparked a considerable discussion in the mediterranean scientific community it has been suggested that the reversal can be driven by variations in wind stress curl over the basin baroclinic dynamics acting within the adriatic ionian system aisys or baroclinic dynamics driven by thermohaline properties at the aisys eastern boundary here we perform numerical simulations in order to assess the relative importance of remote forcings wind stress thermohaline fluxes thermohaline open boundary conditions on the vorticity and energy budget of the ionian sea a mechanistic understanding of the aisys dynamics is achieved with an approach based on an increasing complexity in the model forcings and domain our experiments suggest that wind stress does not play a leading role in the vorticity and energy budgets of the ionian sea wind stress can reinforce or weaken the circulation but it is not able to reverse its sign its role becomes dominant only in the absence of inflows through the antikythira strait and cretan passage instead reversals in the upper layer circulation of the ionian sea take place only in the presence of an active boundary on the aegean sea levantine basin side and appear to be correlated with substantial exchanges of availalble potential energy between the two basins as observed at the end of the eastern mediterranean transient from an energetic point of view aisys can be explained therefore only if the role of the aegean sea is explicitly condidered this article is protected by copyright all rights reserved

silicoflagellates in the eastern mediterranean and black seas seasonality distribution and sedimentary record abstract silicoflagellate populations and fluxes were analyzed from water samples and sediment traps in several basins of the eastern mediterranean and black sea to show species distribution in response to ecological factors and compared with the quaternary records of the region in the eastern mediterranean dictyocha stapedia was the most abundant species represented by two varieties var stapedia smaller and with an apex spine that dominated in the pelagic settings and var aspinosa larger and lacking an apex spine that dominated in the north adriatic sea dictyocha aculeata was the second most abundant species octactis pulchra was seasonally dominant in the adriatic sea stephanocha speculum occurred sporadically in the adriatic sea with 6 sided normal sized specimens but was nearly absent from pelagic assemblages in the black sea assemblages and fluxes were characterized by larger 7 sided skeletons of d speculum with apex spines and a lower abundance of o pulchra

intra survey reservoir fluctuations implications for quantitative 4d seismic analysis during the time taken for seismic data to be acquired reservoir pressure may fluctuate as a consequence of field production and operational procedures and fluid fronts may move significantly these variations prevent accurate quantitative measurement of the reservoir change using 4d seismic data modelling studies on the norne field simulation model using acquisition data from ocean bottom seismometer and towed streamer systems indicate that the pre stack intra survey reservoir fluctuations are important and cannot be neglected similarly the time lapse seismic image in the post stack domain does not represent a difference between two states of the reservoir at a unique base and monitor time but is a mixed version of reality that depends on the sequence and timing of seismic shooting the outcome is a lack of accuracy in the measurement of reservoir changes using the resulting processed and stacked 4d seismic data even for perfect spatial repeatability between surveys a spatially variant noise floor is still anticipated to remain for our particular north sea acquisition data we find that towed streamer data are more affected than the ocean bottom seismometer data we think that this may be typical for towed streamers due to their restricted aperture compared to ocean bottom seismometer acquisitions even for a favourable time sequence of shooting and spatial repeatability importantly the pressure signals on the near and far offset stacks commonly used in quantitative 4d seismic inversion are found to be inconsistent due to the acquisition timestamp saturation changes at the boundaries of fluid fronts appear to show a similar inconsistency across sub stacks we recommend that 4d data are shot in a consistent manner to optimize aerial time coverage and that additionally the timestamp of the acquisition should be used to optimize pre stack quantitative reservoir analysis

modeling the dispersal of levantine intermediate water and its role in mediterranean deep water formation this paper demonstrates the importance of levantine intermediate water liw in the deep water formation process in the mediterranean using the modular ocean general circulation model at 0 25 resolution 19 vertical levels over the entire mediterranean with an open gibraltar strait liw formation is strongly prescribed in the rhodes gyre region by haney 1971 relaxation while in other regions surface salinity relaxation is much reduced by applying the mixed thermohaline surface boundary conditions isopycnal diagnostics are used to trace water mass movements and volume fluxes are monitored at straits low viscosity and diffusion are used to permit baroclinic eddies to play a role in water mass dispersal the overall water budget is measured by an average flux at gibraltar of 0 8 sv of which 0 7 sv is exchanged with the eastern basin at sicily liw density around 28 95 spreads rapidly after formation throughout the entire levantine due to baroclinic eddies toward the west liw accumulates in the northern and central ionian with some entering the adriatic through otranto and some mixing southward in eddies and exiting to the western mediterranean through sicily liw is converted to deep water in the south adriatic at an average rate of 0 4 sv water exchange through the otranto strait appears to be buoyancy driven with a strong bias to the end of winter march april while at sicily the exchange has a strong symmetric seasonal cycle with maximum transport of 1 1 sv in december indicating the effects of wind driving liw pathways in the west are complex and variable in the tyrrhenian intermediate water becomes uniform on isopycnal surfaces due to eddy stirring west of sardinia two liw boundary currents are formed in the balearic basin one flows northward up the west coast of sardinia and corsica and one westward along the northern african coast the northward current is consistent with observations while the westward current is intermittent for the first 10 years often breaking up into eddies which enter the basin interior some observations of high salinity waters near the african coast may support this interpretation liw retains a subsurface salinity maximum of 38 4 38 5 practical salinity units psu when reaching the northwestern mediterranean contrasting with surface waters fresher than 38 0 psu west mediterranean deep water is formed below 1500 m depth with climatological characteristics when it is mixed and cooled during winter convection in lions gyre

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