observations of turbulence in a tidal beam and across a coastal ridge during a microstructure survey off california in monterey bay we found a midwater beam of strong turbulence emanating from the shelf break along the ray path of the semidiurnal m2 internal tide within the 50 m thick beam the turbulence kinetic energy dissipation rate e exceeded 10 6 w kg 1 and the diapycnal eddy diffusivity k was 0 01 m2 s 1 the beam extended 4 km off the shelf break several factors suggest that this beam of strong turbulence resulted from the breaking of semidiurnal internal tides the beam appeared to originate from the shelf break which is a potential generation site for semidiurnal internal tides the beam closely followed the ray path of the semidiurnal internal tide the average e off the shelf break varied by a factor of 100 with a semidiurnal tidal periodicity the isopycnal displacement confirmed the presence of semidiurnal internal tides processes associated with the breaking of internal tides are intermittent and sporadic at the same location we also observed equally intense turbulence in a 100 m thick layer of stratified water across the ridge of a sea fan this layer of strong turbulence was separated from the bottom and was clearly not generated by bottom friction although less well resolved in time the strong turbulence above the bottom seemed to vary with the semidiurnal tide and existed at the lee of the ridge where the isopycnal surface dipped and rebounded in a pattern resembling that of internal hydraulic jumps on the basis of the behavior of the density field we believe that the deep mixing was most likely produced by the across ridge current of internal tides the breaking of internal tides at middepth where the richardson number is close to the critical value is likely due to shear instability the presence of the coastal ridge provides an alternative pathway for converting energy from internal tides to turbulence via internal hydraulics multiplying the average e in the midwater beam by the length of the global coastline gives 31 gw only a small fraction of the estimated 360 gw dissipated globally by m2 internal tides our observations suggest that either most internal tides are generated away from shelf breaks or most internal tides generated at shelf breaks propagate away from their generation sites rather than dissipate locally and eventually contribute to pelagic mixing

from swallow floats to argo the development of neutrally buoyant floats neutrally buoyant floats have been a vital tool in the exploration of the global ocean circulation and now provide a central element of the in situ ocean observing system through the argo project the paper traces the development of neutrally buoyant floats from their origins in the mid 1950s to the present day and highlights areas of ocean science to which floats made significant contributions

lateral injection of oxygen with the bosporus plume fingers of oxidizing potential in the black sea saline and warm mediterranean water flowing through the bosporus strait maintains a permanent pycnocline with vertical separation of oxic o 2 suboxic absence of o2 and h2s and anoxic h2s zones in the black sea the stable suboxic zone implies restricted vertical mixing of the upper oxic and lower anoxic layers and limited vertical flux of oxygen that cannot balance the upward flux of sulfide we report data that directly confirm massive lateral injections 200 km from the bosporus of oxygen enriched waters of the bosporus plume created by the mixing of shallow cold intermediate layer black sea water with mediterranean water these plume waters are laterally injected into the oxic layer and more importantly into the suboxic and anoxic layers over several small vertical scales fingers of 5 m at water densities st from 15 0 to 16 4 o2 injection oxidizes mn ii to mn iii iv which then oxidizes h2s the onset of h2s detection occurs in deeper waters in the southwest 170 m st 16 4 relative to the west central black sea 110 m st 16 2 and coincides with increased mno2 and s8 formation in the southwest

direct measurement of the deep circulation within the brazil basin abstract in support of the deep basin experiment part of the world ocean circulation experiment a large number of neutrally buoyant floats were released within the brazil basin during the 1990s in an attempt to measure directly the circulation in the deep ocean interior three levels corresponding to the three major subthermocline water masses were selected and results from the deeper two north atlantic deep water nadw and antarctic bottom water aabw are described at this writing processing of acquired tracking data is incomplete hence this paper reports on the progress of the observational program and gives our initial conclusions it appears that the flow in the deep brazil basin is unlike previous conjectures in which the circulation patterns can be characterized as being primarily meridional both along the western boundary and in the interior the existence of a deep western boundary current dwbc is quite clear in the float data at the nadw level but less prominent in the aabw and the interior flow is dominantly zonal with unexpectedly small meridional space scales integral time scales are long of order 20 30 days and eddy kinetic energy levels are low of order 1 cm2 s2 in spite of the low energy levels a surprising number of our floats became caught up in vortices a line of seamounts extending offshore near 20 s known as the vitoria trindade seamounts interrupts the dwbcs and is the location for eddy formation and apparent flow away from the boundary into the interior although it has been speculated that this could feed a narrow zonal current of nadw the namib col current our float trajectories suggest a return to the western boundary rather than a continuation to the east

intermediate and deep currents of the black sea obtained from autonomous profiling floats abstract float trajectories observed at three depths 200 750 and 1550 m in the black sea during a 1 5 yr period offer new insights on the circulation below the permanent pycnocline the float observations for the first time provided direct quantitative evidence for strong currents and a well organized flow structure at intermediate and deep layers in contrast to prior ideas of a rather sluggish deep circulation of the black sea the magnitudes of intermediate and deep currents are typically about 5 10 of the surface currents reaching as much as 5 cm s 1 at 1550 m adjacent to the steep topographic slope on the periphery the combination of float and sea level height altimeter data suggests that a well defined cyclonic circulation extends from the surface to the bottom without reversal in its direction deep currents are steered by the steep topographic slope and well correlated with surface currents at seasonal and longer time scales

major hydrological shifts in the black sea lake in response to ice sheet collapses during mis 6 130 184 ka bp abstract the saalian was one of the largest glaciations during the quaternary with an ice sheet extending considerably wider into the eurasian continent than during other glacials orbital variations caused the ice sheet to switch between growing and shrinking the partial retreat of the ice sheet and meltwater discharge resulted in global sea level rise and increased lake levels of inland seas with broader environmental implications during marine isotope stage 6 mis 6 meltwater entered the formerly enclosed black sea at least twice as documented in a 18o record from anatolian speleothems here we present a sedimentary record from the black sea lake covering mis 6 and provide evidence for three meltwater periods coinciding with insolation maxima bswp 6 1 180 167 ka bp bswp 6 2 160 145 ka bp bswp ii 133 130 ka bp while 18oostracods and sr caostracods point to pronounced meltwater supply and decreasing salinity 87sr 86srostracods shed light on meltwater sources and pathways during all three periods meltwater drained most likely via the dnieper and volga into the black and caspian seas and connected both basins relatively low 87sr 86srostracods values during the oldest meltwater period suggest melting solely of the eastern eurasian ice sheet in contrast during the younger meltwater periods exceptional high 87sr 86srostracods values point towards additional meltwater from the western eurasian ice sheet a surplus from melting glaciers in the tian shan and pamir mountains that finally entered the caspian sea via the amu darya and sry darya probably amplified the input of high radiogenic sr isotope water we also show that higher temperatures and productivity suggest dansgaard oeschger like climate variability during the first half of mis 6

glacial hydrologic conditions in the black sea reconstructed using geochemical pore water profiles abstract chloride and 18 o compositions of interstitial water extracted from a long sediment core retrieved from the nw coast of the black sea allowed us to constrain the main hydrologic changes of the back sea during the late pleistocene and holocene prior to its reconnection with the mediterranean sea through the marmara sea at approximately 9000 calendar yr before present 9 ka cal bp the black sea has evolved as a fresh to brackish water lake at the time of reconnection hydrologic changes were drastic bottom water salinities changed from a few psu practical salinity unit to 22 psu since solutes in the interstitial water column within sediments are advected and diffused the measured concentrations do not reflect those of past bottom waters in order to reconstruct these former concentrations we used an advection diffusion model different scenarios of bottom water chloride and 18 o variations were accounted for in this model in order to simulate present day vertical profiles for concentrations of interstitial water in order to compare them to measured ones the comparison suggests that the glacial black sea was a homogeneous freshwater lake with a 18 o of 10 and a salinity of 1 psu modern hydrologic conditions would only have been reached at 2 ka cal bp concomitant with the onset of coccolith rich thin layers that characterize modern basin sediments such delayed salinization over 7000 yr in the basin may have been due to higher precipitation during the early holocene we also simulated the impact of a catastrophic reconnection and a smoother reconnection both salinity scenarios lead to undistinguishable modelled present day profiles indicating that the precise impact of the last reconnection was lost due to the advection diffusion processes

abrupt changes of temperature and water chemistry in the late pleistocene and early holocene black sea new mg ca sr ca and published stable oxygen isotope and 87sr 86sr data obtained on ostracods from gravity cores located on the northwestern black sea slope were used to infer changes in the black sea hydrology and water chemistry for the period between 30 to 8 ka b p calibrated radiocarbon years the period prior to 16 5 ka b p was characterized by stable conditions in all records until a distinct drop in 18o values combined with a sharp increase in 87sr 86sr occurred between 16 5 and 14 8 ka b p this event is attributed to an increased runoff from the northern drainage area of the black sea between heinrich event 1 and the onset of the bolling warm period while the mg ca and sr ca records remained rather unaffected by this inflow they show an abrupt rise with the onset of the bolling allerod warm period this rise was caused by calcite precipitation in the surface water which led to a sudden increase of the sr ca and mg ca ratios of the black sea water the stable oxygen isotopes also start to increase around 15 ka b p although in a more gradual manner due to isotopically enriched meteoric precipitation while sr ca remains constant during the following interval of the younger dryas cold period a decrease in the mg ca ratio implies that the intermediate water masses of the black sea temporarily cooled by 1 2 c during the younger dryas the 87sr 86sr values drop after the cessation of the water inflow at 15 ka b p to a lower level until the younger dryas where they reach values similar to those observed during the last glacial maximum this might point to a potential outflow to the mediterranean sea via the sea of marmara during this period the inflow of mediterranean water started around 9 3 ka b p which is clearly detectable in the abruptly increasing mg ca sr ca and 87sr 86sr values the accompanying increase in the 18o record is less pronounced and would fit to an inflow lasting 100 a

analysis of velocity field in the eastern black sea from satellite data during the black sea 99 experiment 1 maximum cross correlation mcc analysis of national oceanic and atmospheric administration noaa advanced very high resolution radiometer avhrr imagery of the eastern black sea in late september 1999 has been used to reconstruct the velocity and vorticity fields of the upper layer of the sea analysis revealed the large scale dynamic features characteristic of the black sea namely the rim current as well as the detailed pattern of mesoscale vortical activity including meanders eddies and dipoles which are often observed on satellite visible infrared or sea color imagery the dynamical character of the pronounced dipole structure in the northeastern part of the black sea was determined by comparison with satellite ir images geostrophic velocities calculated on the basis of conductivity temperature depth ctd casts performed and trajectories of six argos tracked surface velocity program svp drifters deployed during the black sea 99 expedition onboard r v akvanavt on 25 30 september 1999

oceanographic implications of laboratory experiments on diffusive interfaces abstract this paper contains a summary of the results from some laboratory and theoretical studies on the diffusive interface in double diffusive convection paying particular attention to the recent work of fernando a simple model is developed which predicts the thickness of the convecting layers in a thermohaline staircase structure the laboratory buoyancy flux measurements and the model results are extrapolated for oceanic situations and comparisons are made with field measurements

warm intrusions in the intermediate layer 150 500 m of the black sea eastern gyre interior 1 the new ctd data from the r v akvanavt 2002 cruise presented and discussed in this study show that lateral limits of the bosphorus lens penetration into the black sea interior are substantially wider than the earlier observed ones the data reveal unexpectedly thick warm lenses in the 150 500 m depth range within the eastern gyre of the black sea thus we provide observational evidence that the bosphorus warm water penetration into the sea interior is not a local phenomenon confined to the southwestern and central parts of the western gyre the intrusions have been previously observed only there but rather a fundamental basin wide process determining the intermediate layer structure in the black sea as was recently assumed on the basis of the numerical modeling results

formation pathways of light hydrocarbons in deep sediments of the danube deep sea fan western black sea abstract we report on the geochemistry of light hydrocarbons and pore water in sediments down to 147 m below seafloor mbsf at two sites within the gas hydrate stability field of the danube deep sea fan black sea sediments were drilled with marum mebo200 and comprise the transition from limnic to the recent marine stage stable c n ratios mean 5 1 and 5 6 and 13c corg values mean 25 8 v pdb suggest relatively uniform bulk organic matter compositions in contrast pore water 2h and 18o values varied considerably from approx 120 to 30 v smow and from 15 to 3 v smow respectively these data pairs plot close to the global meteoric water line and indicate paleo temperature variations depletions of pore water in 2h and 18o below 40 mbsf indicate low temperatures and likely reflect conditions during the last glacial period s methane was much more abundant than the only other hydrocarbons found in notable concentrations ethane and propane c1 c2 c3 20 000 relatively constant 13c ch4 70 v pdb and 13c c2h6 52 v pdb values with depth indicate that methane and ethane are predominantly of microbial origin and that their formation was not limited by carbon availability in contrast 2h ch4 values varied in a large range approx 310 to 240 v smow with depth and positively correlated with trends observed for 2h h2o isotope separations 13c ch4 co2 2h ch4 h2o substantiate that microbial carbonate reduction cr is the prevalent methanogenic pathway throughout the sediments irrespective of their geochemical history remarkably in 13c ch4 2h ch4 diagrams widely used samples characterized by 2h ch4 values more negative than approx 250 plot out of the field assigned for pure cr we conclude that assignments of microbial methanogenic pathways based on classical interpretations of 13c ch4 2h ch4 pairs can lead to misinterpretations as severe 2h depletions of methane formed through microbial cr can result from 2h depletions of the pore water generated during low temperature climatic periods

residence time of osmium in the oceans 1 estimates of osmium residence time in the oceans that are based on oceanic mass balance calculations 35 50 kyr appear irreconcilable with those inferred from the recent evolution of the osmium isotope composition of seawater 3 4 kyr it is argued that the osmium budget of the oceans is currently close to steady state and thus that the estimates made by the two methods should agree as the inventory of osmium in the oceans is relatively well constrained these disparate residence time estimates imply wildly different osmium input fluxes to the oceans an osmium residence time of 8 10 kyr is proposed by evaluating the uncertainties and limitations of both methods and it is argued that osmium inputs to the ocean are currently underestimated by a factor of 3 this reflects in part the underestimation of the river input of osmium to the oceans owing to a bias within the existing data set and in part the probable existence of sources of osmium to the oceans that have not yet been identified the very short residence time of 3 4 kyr inferred from the postglacial change in seawater composition assuming a single step change in input flux is rejected as it implies unreasonably high osmium input fluxes to the oceans it is concluded that a postglacial spike in osmium flux associated with a meltwater event must have driven part of the change in seawater composition however it is also shown that such a spike cannot be the dominant cause of the most recent shift in seawater 187os 188os

directly measured mid depth circulation in the northeastern north atlantic ocean the circulation of water masses in the northeastern north atlantic ocean has a strong influence on global climate owing to the northward transport of warm subtropical water to high latitudes but the ocean circulation at depths below the reach of satellite observations is difficult to measure and only recently have comprehensive direct observations of whole ocean basins been possible here we present quantitative maps of the absolute velocities at two levels in the northeastern north atlantic as obtained from acoustically tracked floats we find that most of the mean flow transported northward by the gulf stream system at the thermocline level about 600 m depth remains within the subpolar region and only relatively little enters the rockall trough or the nordic seas contrary to previous work our data indicate that warm saline water from the mediterranean sea reaches the high latitudes through a combination of narrow slope currents and mixing processes at both depths under investigation currents cross the mid atlantic ridge preferentially over deep gaps in the ridge demonstrating that sea floor topography can constrain even upper ocean circulation patterns

transform marginal plateaus abstract numerous submarine plateaus form highstanding bathymetric highs at continent to ocean transitions due to their proximity to continents they have been frequently labelled marginal plateaus although this term has not been clearly defined or associated with a specific geology or geodynamic process until now these elevations have been interpreted as submerged thinned continental fragments detached from continents basaltic buildups formed by hotspots volcanic margins or oceanic plateaus many of these plateaus formed at transform margins connecting oceanic basins of contrasted ages we propose for the first time to define and review a class of marginal plateaus related to a specific tectonic setting transform marginal plateaus tmps based on a compilation of 20 tmps around the world we show that most of them have a polyphased history and have undergone at least one major volcanic phase our review highlights in particular a hitherto unrecognized close link between hotspots volcanic activity and transform margins we also propose that due to their polyphased history tmps may contain several successive basins and overlooked long lived sedimentary archives we finally highlight that because these tmps were transform plate boundaries perpendicular or oblique to surrounding rifts many of them were close to last contact points during final continental breakup and may have formed land bridges or bathymetric highs between continents therefore we discuss broader scientific issues such as the interest of tmps in recording and studying the onset and variations of oceanic currents or past biodiversity growth bio connectivity and lineage evolution

double diffusive convection in this paper we present a rather personal view of the important developments in double diffusive convection a subject whose evolution has been the result of a close interaction between theoreticians laboratory experimenters and sea going oceano graphers more recently applications in astrophysics engineering and geology have become apparent in the final section we attempt to draw some general conclusions and suggest that further progress will again depend on a close collaboration between fluid dynamicists and other scientists

palaeo digital elevation models for use as boundary conditions in coupled ocean atmosphere gcm experiments a maastrichtian late cretaceous example abstract palaeogeography specifically palaeotopography and palaeobathymetry provides an essential boundary condition for computer based atmosphere and ocean modelling it also provides the geographic context for understanding surface processes palaeodrainage palaeoweathering and biotic interactions palaeoecology palaeobiogeography with increased model resolution coupled ocean atmosphere general circulation models gcms and the addition of vegetation soil weathering ice and chemical modules there is now a need for more robust detailed palaeotopographies and palaeobathymetries that are fully integrated with the processes being modelled especially the hydrological system here we present a new geographic information system gis based hydrologically correct palaeo digital elevation model dem for the maastrichtian late cretaceous we describe the methods and concepts used to construct the map and draw attention to the limits imposed by scale and uncertainty and how these factors must be considered as part of the error analysis of derived model results the underlying palaeogeography is one of a series of 27 global maps that represent the stages of the cretaceous and sub epochs of the cenozoic each map is generated at a scale of 1 30 million in arcview gis and arcinfo using data from the lead author s own databases of lithologic tectonic and fossil information the lithologic databases of the paleogeographic atlas project the university of chicago a survey of published literature and dsdp odp data interpretations of elevation are derived following the methods outlined in ziegler et al ziegler a m rowley d b lottes a l sahagian d l hulver m l gierlowski t c 1985 paleogeographic interpretation with an example from the mid cretaceous annual review of earth and planetary sciences 13 385 425 an understanding of the tectonic regime and evolution of each feature and the age depth relationship for the ocean the global palaeo dem was derived using the elevation contours from the paleogeography and the suite of hydrological tools available in arcinfo grid the palaeo dem has been constrained by defining areas of internal palaeodrainage palaeoriver mouths and known palaeoriver courses the maastrichtian has been completed first to provide the boundary conditions for a series of coupled atmosphere ocean experiments when integrated with the results of the coupled ocean atmosphere model the result is a powerful tool for understanding surface processes and an important step towards the development of a continuous series representing a fully evolving palaeolandscape

late glacial to holocene paleoenvironmental evolution of the black sea reconstructed with stable oxygen isotope records obtained on ostracod shells high resolution stable oxygen isotope d 18 o on ostracod shells xrf scanning and bulk grain size data obtained on a transect of 6 gravity cores from the continental slope in the northwestern black sea give new insight into the hydrological evolution of the black sea since the last glacial maximum lgm stable climatic conditions during the lgm were followed by a series of meltwater pulses between 18 and 15 5 kyr bp that resulted in temporary isotopic depletion of the black sea waters subsequently steadily increasing d 18 o values in all cores are mainly caused by isotopically enriched precipitation at the onset of the allerod bolling warm period a comparison of the major trends in d 18 o at different water depths suggests evaporation driven deep water formation since 14 5 kyr bp while the two shallowest cores from 168 and 465 m water depth were under the influence of increased warming in the upper water column since 14 5 and 12 5 kyr bp respectively the core from 168 m depth seems to be additionally influenced by freshwater input of the danube this core provides a high resolution record from the younger dryas allerod boundary and suggests that a nao like climate mode was governing the interannual variability in the run off of the danube which implies that this climate mode has been a persistent climatic feature over central europe the inflow of saline mediterranean waters occurs between 9 and 8 kyr bp where a merging of all d 18 o records signals an initial homogenisation of the water column

deep convection in the labrador sea as observed by lagrangian floats abstract during the winters of 1997 and 1998 a total of 24 lagrangian floats were deployed in the labrador sea these floats were designed to match the buoyancy and compressibility of seawater they measured temperature and three dimensional position pressure for vertical position and rafos acoustic tracking for latitude and longitude as they followed water motions three dimensionally this data provides direct observation of mixed layer depth and excellent estimates of vertical velocity floats were repeatedly carried across the convecting layer by vertical velocities averaging several centimeters per second with vertical excursions of up to one kilometer in the horizontal several scales of eddy motion were resolved as was a possible float predilection toward remaining in water preconditioned for convection heat flux estimates from this data reveal entrainment and surface heat fluxes similar in magnitude the mixed layer acts as a vertical conveyor belt of temperature transporting heat from depth

dynamics diffusion and geomorphological significance of tidal residual eddies many shallow tidal areas show the occurrence of ebb and flood surplusses organized in cell like structures or tidal residual eddies they seem to arise from a nonlinear transfer of vorticity from the oscillating tidal field to the mean field the irregular structure of the bottom topography or the coastline acting as a catalyst to produce the necessary vorticity gradients the dynamical characteristics of the eddies assist our understanding of the geomorphology of the sea bed

fine scale velocity distribution revealed by datuming of very high resolution deep towed seismic data example of a shallow gas system from the western black seavelocity analysis via deep towed seismic

an abrupt drowning of the black sea shelf abstract during latest quaternary glaciation the black sea became a giant freshwater lake the surface of this lake drew down to levels more than 100 m below its outlet when the mediterranean rose to the bosporus sill at 7 150 yr bp 1 saltwater poured through this spillway to refill the lake and submerge catastrophically more than 100 000 km2 of its exposed continental shelf the permanent drowning of a vast terrestrial landscape may possibly have accelerated the dispersal of early neolithic foragers and farmers into the interior of europe at that time

preliminary results from directly measuring middepth circulation in the tropical and south pacific as part of the world ocean circulation experiment 300 autonomous lagrangian circulation explorer floats were deployed in the tropical and south pacific to measure the general circulation at 900 m depth most floats measured average currents over 25 submerged days between ascents to the surface for locating and data relay by the end of 1997 over 12 500 observations spanning 840 float years were obtained accuracy of the average velocity is limited by variability some of which is found to arise from steady flows with spatial variations smaller than averaging scales observed 25 day velocities are serially uncorrelated except near the equator where energetic zonal variability has seasonal timescales and appears to be described by a data assimilating ocean circulation model run by the national centers for environmental prediction space time averages of float velocities disclose a general pattern of middepth flow that resembles the surface circulation with the strongest flows of o 3 cm s in the deep antarctic circumpolar current and east australian current the weaker elements of the flow including an interior subtropical circulation with o millimeters per second flows are described by an objective analysis whose accuracy is limited by sampling noise rather than uncertainty of the analysis parameters the subtropical circulation has a gyres within a gyre structure including boundary currents along australia and east of new zealand and a concentrated equatorial limb with surprising strength in the western basin this current is also involved in a tropical gyre with generally eastward flow along the equator in the western basin at least because of strong seasonal scale variability the equatorial zonal currents are not well measured yet but data are still being accumulated comparison with reid s 1997 absolute circulation shows more areas of agreement than of disagreement

molybdenum isotope fractionation in pelagic euxinia evidence from the modern black and baltic seas here we present stable isotope data for vertical profiles of dissolved molybdenum of the modern euxinic water columns of the black sea and two deeps of the baltic sea dissolved molybdenum in all water samples is depleted in salinity normalized concentration and enriched in the heavy isotope 98mo values up to 2 9 compared to previously published isotope data of sedimentary molybdenum from the same range of water depths furthermore 98mo values of all water samples from the black sea and anoxic deeps of the baltic sea are heavier than open ocean water the observed isotope fractionation between sediments and the anoxic water column of the black sea are in line with the model of thiomolybdates that scavenge to particles under reducing conditions an extrapolation to a theoretical pure mos42 solution indicates a fractionation constant between mos42 and authigenic solid mo of 0 5 0 3 measured waters with all thiomolybdates coexisting in various proportions show larger but non linear fractionation the best explanation for our field observations is mo scavenging by the thiomolybdates dominantly but not exclusively present in the form of mos42 the mo isotopic compositions of samples from the sediments and anoxic water column of the baltic sea are in overall agreement with those of the black sea at intermediate depth and corresponding sulphide concentrations the more dynamic changes of redox conditions in the baltic deeps complicate the black sea derived relationship between thiomolybdates and mo isotopic composition in particular the occasional flushing mixing of the deep waters affects the corresponding water column and sedimentary data 98mo values of the upper oxic waters of both basins are higher than predicted by mixing models based on salinity variations the results can be explained by non conservative behaviour of mo under suboxic to anoxic conditions in the shallow bottom parts of the basin most pronounced on the nw shelf of the black sea

regional 2d seismic interpretation and exploration potential of offshore deepwater sierra leone and liberia west africa the offshore region of sierra leone and liberia has been underexplored on the continental shelf and unexplored in deepwater however a reconnaissance interpretation of new 2d seismic data in conjunction with a review of the reservoir and geochemical information available to date is positive about the hydrocarbon potential of the region three distinct prospective hydrocarbon basins are present sierra leone basin liberia basin and harper basin figure 1

sedimentary record of a shoaling of the oxic anoxic interface in the black sea abstract recent studies of hydrographic nutrient and geochemical properties in the upper 200 m of the black sea have led to the hypothesis that the oxic anoxic interface chemocline has shoaled by 30 m during the past few decades this conclusion remains disputed however because historical hydrographic data are not sufficient to distinguish between short term variability and a long term net upward displacement in the position of the chemocline sediments deposited on the shelf where the oxic anoxic interface impinges on the sea floor provide a reliable record of the redox conditions of overlying bottom waters sediments deposited under anoxic conditions are invariably laminated whereas sediments deposited under sustained conditions of oxygenated bottom waters are heavily bioturbated a set of five cores collected along a transect across the shelf in the south central black sea was examined for evidence of a shoaling of the oxic anoxic interface results indicate that there has not been a basin wide 30 m shoaling of the interface during the past 20 years as postulated from hydrographic data although brief intervals during which the interface was depressed to a position as much as 30 m deeper than at present may have occurred one core contained a clear record of a shoaling of the interface as indicated by a transition from bioturbated to laminated sediments but this transition occurred 200 years ago

isotopic composition of osmium in terrestrial samples determined by accelerator mass spectrometry interest has revived in the rhenium osmium system due to significant advances in detection methods1 4 and because of its use for the identification of extraterrestrial material at the cretaceous tertiary boundary5 another perhaps more important application is its use as a tracer for the origin of crustal material this application is however severely restricted by the very low concentrations typical of crustal rocks we present here the first results for the isotopes 187os 188os and 189os measured in sub p p b parts per 109 level samples by accelerator mass spectrometry ams our first exploratory measurements on extraterrestrial and crustal material with os concentrations between 2 p p m parts per 106 and 0 006 p p b show a detection limit of 0 01 p p b and a precision of better than 10 the 187os 186os ratios measured for samples for the canyon diablo meteorite and from the east clearwater crater in quebec canada were close to 1 typical of extraterrestrial material in contrast ratios in samples from the ries crater in germany were around 10 which is evidence of predominantly crustal osmium in these rocks

noble gas anomalies related to high intensity methane gas seeps in the black sea dissolved noble gases and tritium were analyzed at a series of high intensity methane gas seeps in the black sea to study the transport and gas exchange induced by bubble streams in the water column these processes affect marine methane emissions to the atmosphere and are therefore relevant to climate warming the seep areas investigated are located in the dnepr paleo delta west of crimea and in the sorokin trough mud volcano area south east of crimea noble gas concentration profiles at active seep sites revealed prominent anomalies compared to reference profiles that are unaffected by outgassing supersaturations of the light noble gases helium and neon observed relatively close to the sea floor are interpreted as effects of gas exchange between the water and the rising bubbles depletions of the heavy noble gases argon krypton and xenon that were detected above an active bubble releasing mud volcano appear to be related to the injection of fluids depleted in noble gases that undergo vertical transport in the water column due to small density differences in both cases the noble gas anomalies clearly document seep specific processes which are difficult to detect by other methods helium is generally enriched in the deep water of the black sea due to terrigenic input although exceptionally high helium concentrations observed in one seep area indicate a locally elevated helium flux most of the seeps studied seem to be negligible sources of terrigenic helium noble gas analyses of sediment pore waters from the vicinity of a mud volcano showed large vertical gradients in helium concentrations the helium isotope signature of the pore waters points to a crustal origin for helium whereas the deep water of the black sea also contains a small mantle type component

organic matter production and preservation and evolution of anoxia in the holocene black sea dating of sediments collected in gravity cores during leg 1 of the 1988 r v knorr expedition to the black sea suggests that the onset of water column anoxia at 7 5 ka was virtually synchronous across the basin over a depth range of 200 2250 m a finely laminated organic carbon oc rich sapropel unit ii was produced as a result of this anoxia the trigger for increased oc production and development of anoxia was the spillover of saline waters through the bosporus that probably began at 9 0 ka and peaked between 7 0 and 5 5 ka this spillover enhanced vertical mixing and nutrient cycling and caused a short term 2 3 kyr burst in surface water productivity during the early part of unit ii deposition continued incursion of saline waters enhanced vertical stability and inhibited mixing of nutrients into surface waters thus limiting primary production and decreasing the oc flux to sediments beginning 5 5 ka concentration accumulation rate and degree of preservation of organic matter all decreased in the upper part of unit ii as a result of decreasing productivity but anoxia persisted throughout most of the water column the end of unit ii sapropel deposition was synchronous across the black sea as the result of the first blooms of the coccolith emiliania huxleyi which presumably marked an increase in surface water salinity above 11 and the beginning of unit i deposition the high coccolith carbonate fluxes that occurred during deposition of unit i diluted the oc concentration in the sediments but oc accumulation rates are about the same as those in upper part of unit ii

post rift stratigraphic architectures along the african margin of the equatorial atlantic part i the influence of extension obliquity abstract we investigated the variability of the first order crustal structure and early post rift stratigraphy of six segments of the african equatorial atlantic margin using sub surface data seismic and wells extension obliquity of the segments varies from 0 for the west ivory coast and ghana transform segments to 30 for the togo benin oblique segment and 75 for the east ivory coast normally divergent segment the sierra leone and liberia segments underwent probably deformation during both the early jurassic rifting of the central atlantic and the early cretaceous rifting of the equatorial atlantic with contrasted divergence obliquities for segments that underwent a single rifting we show that the higher the obliquity the wider the crustal thinning domain this has a major influence on the first order geometry of all the post rift horizons including the present day slope the lower the obliquity the larger the differential subsidence across the margin and the steeper the present day slopes of post rift horizons this also has a major influence on the flexural isostatic response of the lithosphere to thermal and erosion sedimentation driven un loads during the early post rift narrow transform segments underwent higher flexural and or thermal uplifts in the proximal domain than wider divergent segments along the same margin divergent segments therefore may preserve early post rift deposits in their proximal domains whereas they are not preserved on nearby transform segments

observed basin wide propagation of mediterranean water in the black sea mediterranean water entering the black sea through the bosphorus strait forms middepth intrusions that contribute to the salt heat and volume balances of the sea ventilate its water column at intermediate depths and restrain the upward flux of hydrogen sulfide from deeper layers despite the importance for the black sea environment the circulation of mediterranean origin water in the basin is fundamentally underexplored here we use hydrographic data collected from ships and argo profiling floats to identify pathways of the mediterranean intrusions in the general circulation system of the sea while earlier the intrusions were observed primarily near the bosphorus strait we present an evidence for their intermittent extensive propagation throughout the basin we find that the main conduit for the intrusions is the southern limb of the rim current that carries the intruded water from the bosphorus strait eastward a part of this eastward flow recirculates cyclonically into the interior of the sea where traces of the intrusions gradually disappear because of mixing we put forward the hypothesis that the formation of the most prominent intrusions is associated with strong cyclonic storms over the bosphorus strait which lead to abnormally large influx of mediterranean water

changing coastal oceanography of the black sea ii mediterranean effluent abstract the behavior and physical mechanisms during the mediterranean flow entering the black sea from the bosphorus are described using existing field observations and hydrodynamic models for the vertical and along axis circulation in the strait soviet studies in the 1960 1970 s showed that a well defined sill north of the bosphorus does not prevent the overflow of dense mediterranean water onto the shelf even during unfavorable conditions high surface elevation in the black sea and strong northerly winds the stream makes a sharp westward turn after exiting from the strait and then starts its track downward to the shelf slope intensive dispersion of the mediterranean water occurs at a distance of 25 50 km from the strait recent laboratory and mathematical models have been reviewed to describe the behavior of the density and current interfaces in the strait and the role of temporary blockage of the dense flow upon the mediterranean effluent two hypothetic physical mechanisms for sill overflow are discussed one is associated with bifurcation of the coastal flows approaching the strait orifice and formation of a diversion zone in the upper layer which facilitates the flow over the sill another hypothesis suggests that the sill exercises frictionless rotational hydraulic control in the short 4 km continuation of the strait channel persistent northeasterly or southerly winds can substantially affect the intensity of the mediterranean effluent by modifying the average flow fields and density structures in the strait ts analysis of far field property distribution shows that the mediterranean water contributes to the laminated structure of the black sea water column under average conditions the mediterranean waters follow the mainstream of the black sea current system along the turkish coast reaching the deepest strata in the southeastern corner of the sea ongoing soviet diversions of fresh water from the northern slope of the black sea and projected damming of the major estuaries and the azov sea will intensify the mediterranean effluent and at the same time will increase the vertical mixing due to more effective convective overturn these phenomena will lead to partial or complete disappearance of the h2s layer and general warming of the water column

isopycnal lagrangian statistics from the north atlantic current rafos float observations one hundred isopycnal floats were tracked on the 27 2 and 27 5 surfaces in the newfoundland basin nfb from july 1993 to july 1995 to study the current structure and exchanges of waters between the subtropical and subpolar gyres the float mapped mean flow consists of weak flows in the nfb and a strong boundary current the north atlantic current nac which separates from the boundary at the northwest corner becoming a diffusive zonal drift the nac meanders are linked to topography and have similar patterns on the two isopycnals despite the fact that the upper layer velocities are twice as fast as the lower layer ones perturbation velocity from the mean is used to compute isopycnal turbulent dispersion and diffusivity this large data set allows us to resolve a narrow mean nac and results in a gaussian turbulence the turbulence approximately follows the classic taylor dispersion theory integral timescales and length scales and turbulent isopycnal diffusivity are of 1 5 2 5 days 20 30 km and 1 7 103 m2 s 1 respectively the timescale increases with depth and decreases with latitude the length scale decreases with depth and longitude and the diffusivity decreases with depth and from nac to nfb compared to previous results from surface drifters and isobaric floats our isopycnal statistics are more isotropic and agree better with the taylor dispersion theory because 1 the mean velocity has a better resolution and 2 the isopycnal floats are better lagrangian followers the diffusivity scales better with the rms velocity and length scale than with the velocity variance and timescale

postglacial connection of the black sea to the mediterranean and its relation to the timing of sapropel formation the opening of the connection between the mediterranean and black seas as sea level rose above the bosporus sill has long been associated with the formation of the most recent holocene sapropel deposit s1 in the eastern mediterranean but the mechanism has remained elusive we present a model for the opening of the black sea based on hydraulics arguments which demonstrates that increased freshwater flux out of the black sea began 500 1000 years after sea level reached sill depth and that the timescale for the increased freshwater flux that drained the freshwater reservoir of the black sea is about 2500 3500 years we argue that the increased freshwater discharge out of the black sea would lead to decreased deep water formation and higher productivity in the surface waters in the eastern mediterranean two conditions generally associated with sapropel formation the delay in increased freshwater flux after the opening of the black sea and the period of increased freshwater discharge appear to match the onset and duration of sapropel deposits in the eastern mediterranean

evolution of satellite derived mesoscale thermal patterns in the black sea abstract infrared image sequences covering the black sea are examined to investigate the evolution of mesoscale structures on the sea surface during the warm seasons of 1991 1993 wind induced surface mixing and convective mixing are responsible for producing many features the influence of seasonal evolution of the cold intermediate water ciw on the vertical and surface structures of eddies including cold anticyclonic ones in summer is examined the annual variations of the short and long wave structures accompanying the meandering rim current are identified the influence of river inputs to the western shelf area was traced more distinctly as evidence of the maximal outflow after the spring flood satellite data also helped in the interpretation of several peculiarities observed in vector distributions of the acoustic doppler current profiler adcp observations resulting from sub mesoscale dynamic features that were insufficiently resolved by the in situ data the adcp velocity maxima coincide with the temperature gradient of the rim current and the vector directions correspond to the satellite derived flow configuration in april 1993 implying a close correlation between both measurements

observations of mediterranean flow into the black sea mediterranean sea water inflow into the black sea is investigated using acoustic and oceanographic data obtained in the black sea exit region the path of mediterranean water and the resulting spreading on the continental shelf are observed with multibeam echo sounding swath bottom bathymetry measurements high resolution echo sounding images and conductivity temperature depth profiles it is found that the saline mediterranean water is reduced by 6 practical salinity units as it flows and spreads on the shelf before reaching the continental slope where it sinks to a depth appropriate to its density temporal and spatial variability in the flow and their relation to atmospheric and sea level changes are documented it is shown that blockage of the mediterranean undercurrent occurs when the estimated black sea water transport exceeds 25 103 m3 s 1 which corresponds to a relative sea level difference greater than 40 cm mediterranean flow into the black sea is a high reynolds low richardson number flow resulting in a turbulent bottom boundary layer measurements of the path averaged turbulent kinetic energy dissipation rate give values ranging from 1 10 6 to 1 10 4 w kg 1

satellite altimetry observations of the black sea level the paper is devoted to the application of satellite altimetry from the topex poseidon and ers 1 missions to the black sea we use the nasa ocean altimeter pathfinder project collinear data set and monthly climatic hydrography to restore the dynamical sea level that which connected with the black sea circulation two realizations are created from collinear and grid data sets the black sea hydrographic survey data collected by the cooperative marine science programme for the black sea are used for validation of both products the estimated rms accuracy of the black sea dynamical level is about 3 cm the grid data product is used for the analysis of seasonal and mesoscale variability of the black sea level the observations show that the black sea circulation has strong seasonal variation it attenuates in summer to autumn and intensifies in winter to spring this variability is accompanied by a western phase propagation of the sea level a simple two layer model of the wind induced circulation in the rectangular basin provides an interpretation of these results it is shown that the seasonal variability of the geostrophic circulation is most likely produced by the annual changes of the wind stress curl the western phase propagation is treated as the radiation of rossby waves from the eastern coast of the basin typical periods of the mesoscale oscillations of the dynamical sea level are estimated from the topex poseidon altimeter time series in different parts of the black sea by means of a spectral analysis the strongest mesoscale oscillations have periods of about 120 days and are located in the southeastern part of the basin where the rim current bifurcates and off the crimean peninsula where the rim current meanders as a result of the local orography

topographic control of oceanic flows in deep passages and straits saddle points between neighboring deep ocean basins are the sites of unidirectional flow from one basin to the next depending on the source of bottom water flow in these sites appears to be topographically controlled so the interface between the bottom water and the water above adjusts itself to permit bottom water flow from the basin that contains a source of bottom water into the next examples in the atlantic include flow in the romanche fracture zone the vema channel the ceara abyssal plain the anegada jungfern passage and the discovery gap but there are many more theoretical predictions of volume flux using a method that requires only conductivity temperature depth data archives and detailed knowledge of bathymetry near the saddle point are compared with volume flux estimates using current meters and or geostrophic estimates for seven cases the ratio of prediction to volume flux estimate ranges from 1 0 to 2 7 some ocean straits that separate adjacent seas are also found to critically control bidirectional flows between basins theory of the influence of rotation on such critical flows is reviewed predictions of volume flux in eight cases are compared with ocean estimates of volume flux from traditional methods

accretion rate of extraterrestrial particles determined from osmium isotope systematics of pacific pelagic clay and manganese nodules abstract pelagic clay and mn nodules from domes sites in the north pacific and a varved glacial lake deposit from connecticut were analysed for os concentration and isotopic composition by isotope dilution secondary ion mass spectrometry after treatment by nis fusion or oxalic acid leaching bulk pelagic clay from domes site c has 187 os 186 os 6 5 and os 0 14 ng g oxalic acid leaches of this same sediment and of mn nodules from domes sites a and c have more radiogenic 187 os 186 os ratios which average 8 3 bulk glacial lake hitchcock sediment has 187 os 186 os 12 5 and os 0 06 ng g the total os flux to north pacific pelagic clay is 7 to 10 ng os cm2 106 y lake hitchcock sediment provides an integrated value for the local crustal 187 os 186 os ratio the oxalic acid leaches are assumed to attack hydrogenous phases selectively a simple model in which the only sources of os to the ocean are continental crust with the isotopic composition of lake hitchcock 187 os 186 os 12 5 and extraterrestrial particles with 187 os 186 os 1 1 results in a cosmic flux of osmium to the sediment of 4 9 ngos cm2 106 y of which 20 is hydrogenous a model in which the sources of os to the ocean are continental crust with an 187os 186os ratio of 30 from the model of palmer and turekian 1986 oceanic mantle or crust with 187 os 186 os 1 04 and extraterrestrial particles with 187 os 186 os 1 1 results in a cosmic flux of os to the sediment of 5 7 ngos cm2 106 y of which none is hydrogenous these extraterrestrial os fluxes correspond to maximum c 1 chondrite accretion rates of between 4 9 104 and 5 6 104 tonnes y

quasi steady exchange flow in the bosphorus current meter moorings and high resolution surveys in the bosphorus reveal important details of the exchange flow during early september 1994 the flow was quasi steady and demonstrated strong mixing particularly in the surface layer after it entered the principal contraction of the strait composite froude numbers in the contraction are lower than expected consistent with recent modeling that shows friction producing significant deviations from predictions of inviscid two layer hydraulic theory

the circulation and hydrography of the marmara sea abstract a comprehensive set of data collected during 1986 1992 reveal seasonal and interannual variability in the circulation and hydrography of the marmara sea waters which have contrasting properties and originate from the adjacent basins supply the two layer stratified flows in the sea of marmara turbulent entrainment into the upper layer in the exit region of the bosphorus jet and wind stirring in winter both contribute equally to the basin vertical mixing the upper layer circulation of the marmara sea is determined from adcp measurements and from dynamical calculations based on hydrographic data the mean upper layer circulation is anti cyclonic mainly driven by the southward flowing bosphorus jet in the enclosed domain the bosphorus inflow is well defined except during the periods of low discharge in autumn and winter when the jet becomes weaker and tends to become attached to the west coast near the exit mediterranean water entering from the dardanelles supply the suhalocline layer the negatively buoyant plume of well oxygenated water is the only means of renewal of the deep waters partially compensating for the oxygen consumed by the degradation of organic matter sinking from the upper layer into the lower layer yet the subhalocline waters remain permanently deficient in oxygen as a result of the internal balances of diffusion advection and consumption the depth to which the plume penetrates is a function of the seasonal characteristics of the inflow density modified in the strait and the weak interior stratification

pleistocene water intrusions from the mediterranean and caspian seas into the black sea the hydrological balance of the black sea is governed by riverine input and by the exchange with the mediterranean sea a speleothem record from a cave in northern turkey that tracks the isotopic signature of black sea surface water suggests an open connection to the mediterranean sea in at least twelve periods in the past 670 000 years

flow water mass changes and hydraulics in the bosphorus 1 using average sections along the bosphorus taken in september 1994 with a loosely tethered profiler and an acoustic doppler current profiler gregg et al 1999 found the exchange flow between the sea of marmara and the black sea to be quasi steady but far from satisfying the hydraulic control conditions for two layered flows here we examine synoptic sections and use images from an acoustic backscatter system to provide the first detailed look at the flow and water mass changes in the bosphorus and to assess how well the flow satisfies the hydraulic assumptions thirty kilometers long 28 100 m deep and 0 75 3 km wide the bosphorus has bathymetry for more complex than that used in analytic or numerical models of exchange flows the particulars affect dynamics in important ways for instance owing to changes in channel shape the narrowest section known as the contraction is not also the minimum in cross sectional area rather it is a transition between the wider northern half and the narrower southern half of the strait and some places south of the contraction have slightly smaller areas sharp bends occur throughout the strait and often produce flow separations as well as directing upper and lower flows to opposite sides of the channel never 28 of the water column the interface thickens to 75 in the southern half of the strait as a result of intense mixing downstream of the contraction as a consequence of the strong mixing and numerous flow separations we conclude that the exchange flow may be at least partly controlled by friction instead of being a simple hydraulic flow

observations of black sea mesoscale eddies and associated horizontal mixing 1 a large 80 90 km in diameter anticyclonic eddy centered at 43 n 37 38 e has been the subject of complex investigation in the summer autumn of 1999 based on measurements carried out during the black sea 99 expedition on board of r v akvanavt ctd surveys deployment of argos tracked drifters analysis of satellite imagery and using altimetric sea level anomaly maps from merged topex poseidon and ers 2 satellite data the eddy was formed as a nearshore anticyclonic eddy nae in the sochi sukhumi region separated from the coast on 6 9 april 1999 stayed at the center of the eastern basin which is usually characterized by cyclonic circulation during about 8 months and decayed near the turkish coast in december 1999 a compilation of hydrodynamic situations of different years 1993 1997 1999 suggests that similar open sea anticyclonic eddies are frequently the elements of the circulation in the eastern black sea in the warm season april december a positive correlation appears to be between eddies formation and weak macroscale circulation associated with low atmospheric wind forcing long lifetime of open sea anticyclones is likely determined by their interaction with neighboring eddies naes separation from the coast and their transformation into open sea eddies provide horizontal mixing of the upper layer waters and results in deflection of the rim current offshore formation of large meanders of the current around the eddies and its branching when rounding such features an example of calculation of cross shelf water transport relating to an offshore rim current branch is presented it is pointed out that an estimation of the shelf open sea water exchange based on the box balance model does not contradict the assumption that such exchange is considerably determined by naes separation from the coast

a simple evolutionary model for water and salt in the black sea this paper presents a time dependent variable size box model for the total fluid and salinity balances of the black sea in addition to the advective flows due to riverine and mediterranean inputs of water the model accounts for entrainment flows which are parameterized using the theory of ellison and turner 1959 and employs a modified version of the gargett 1984 formulation for eddy diffusivity in describing cross pycnocline mixing flows the variable volume of the boxes permits explicit simulation of the replacement of the preexisting late pleistocene lake water by the inflow of denser mediterranean water our results indicate that the time needed to displace the old deep water with new saltier water is 2000 years or less because of the effects of mixing the salinity of both the surface and deep waters requires a greater time interval to obtain present day values i e 4000 years if the inflow of mediterranean water is constant in time at its present value and 6000 years if this input changes with time in approximation to the rate of sea level rise the occurrence of the marine coccolithophorid emiliania huxleyi in the holocene sapropel layer requires a minimum surface salinity of 11 which takes some 1600 to 3100 years to develop this range is a result of the uncertainty in the history of the mediterranean water input the model is also employed to investigate the freshening of the black sea after cutoff of mediterranean input the salinity of both surface and deep waters is found to fall below 11 in less than 3000 years and the freshening process is complete in 9000 years

new insights into prospectivity of liberia sierra leone basin because of improvements in seismic acquisition and processing this paper examines how the understanding of the prospectivity of the liberia sierra leone basin has developed over the last 40 years largely due to improvements in seismic data over this period a series of basins developed between major transform fault zones associated with the opening of the south atlantic ocean from the early cretaceous onward the liberia sierra leone basin forms part of the west african transform margin that extends from sierra leone to benin early hydrocarbon exploration 1972 1985 was targeted at shelfal structural synrift traps of lower cretaceous age none of the wells drilled in this period was regarded as a discovery in 2001 a new regional 2d seismic survey allowed a new play deepwater upper cretaceous channel fans to be identified more recent 3d seismic using the latest data acquisition and processing technologies including avo has enabled drillable prospects to be identified wells drilled in 2009 2010 offshore sierra leone have established that a working hydrocarbo

experiments with mixing in stratified flow over a topographic ridge the interaction of quasi steady abyssal ocean flow with submarine topography is expected to generate turbulent mixing in the ocean this mixing may occur locally close to topography or via breaking quasi steady lee waves that can carry energy into the ocean interior there is currently no theoretical or empirically derived prediction for the relative amounts of local and interior mixing we report measurements of the mixing rate in laboratory experiments with a topographic ridge towed through a density stratification the experiments span three parameter regimes including linear lee waves nonlinear flow and an evanescent regime in which wave radiation is weak full field density measurements provide the depth dependence of energy loss to turbulent mixing allowing separation of the local mixing in the turbulent wake and remote mixing by wave radiation remote mixing is significant only for a narrow band of forcing parameters where the flow speed is resonant with internal waves in all other parameter regimes local mixing close to the topography is dominant the results suggest that mixing by local nonlinear mechanisms close to abyssal ocean topography may be much greater than the remote mixing by quasi steady lee waves this article is protected by copyright all rights reserved

thermohaline structure transport and evolution of the black sea eddies from hydrological and satellite data abstract combination of altimetry based method of eddy identification and historical hydrological measurements for 1992 2015 is used to analyze the thermohaline and dynamic structure of the black sea eddies and its relation with eddy intensity eddy age and season of a year anticyclonic eddies aes are characterized by negative salinity anomalies which can reach 1 7 psu at the depth of the main halocline the temperature anomalies are positive in their upper layers and negative in the deeper layers because of the vertical displacement of the waters of the cold intermediate layer cil cyclonic eddies ces have the opposite structure with increased salinity colder upper layers and warmer deeper layers thermohaline anomalies in the eddies of both signs are maximal in summer while in winter they are shallowest and minimal the displacement of pycnocline in eddies causes the decrease increase of stratification in the upper layer of aes ces and opposite increase decrease in their deeper layers it also causes the deepening uplift of the layer of maximum geostrophic vertical shear in aes ces the latter is the probable reason of the observed higher intensity and deeper penetration of orbital velocities in aes than in ces the changes of isopycnals positions during the eddies lifetime are used to quantify the evolution of vertical velocity in aes and ces in the beginning of aes life during intensification phase vertical velocity is directed downward while during the decaying phase it change its sign and is directed upward the opposite is observed in ces vertical velocity is maximal at the pycnocline depth of 100 110 m with values changing from 8 to 8 10 6 m s in aes and from 5 to 25 10 6 m s in ces eddies thermohaline structure and altimetry derived orbital velocity is tightly related this relation obtained in the study and altimetry derived data on the distribution of eddy frequency translational speed and orbital velocity is used to quantify eddies salt heat content and transport in the basin the transport velocity of water in the eddies core 2 4 cm s is significantly smaller than the average velocity of the large scale currents 10 40 cm s such slowing causes the relative transport of eddies against the mean flow direction this effect leads to the accumulation of brackish and cold water in the deep layers of east black sea and maintain the observed east west asymmetry of the basin thermohaline fields

geochemical paleogradient in pore waters controlled by aom recorded in an oligocene laminated limestone from the outer carpathians abstract a 20 cm thick laminated limestone of oligocene age from the outer carpathians is composed mainly of coccoliths and authigenic calcite 13 c values unequivocally indicate that the authigenic calcite precipitated as a result of methane oxidation the 13 c and 18 o values change gradually from the base to the top of the bed from 38 0 to 17 6 and from 1 1 to 5 7 respectively this trend reflects a geochemical gradient which developed in the zone of anaerobic oxidation of methane aom due to the consumption of sulfate by methane this gradient was related to an inverse relationship between the concentrations of both compounds in the pore waters of the aom zone methane was the source of isotopically light carbon it was accompanied by heavy oxygen containing water liberated from decomposition of gas hydrates the methane bearing fluids migrated upwards to the base of the sulfate reduction sr zone where methane was oxidized ch 4 so 4 2 hco 3 hs h 2 o and the aom zone developed the bicarbonate produced in this reaction was significantly depleted in 13 c and 16 o in the sr zone organic matter was oxidized by sulfate 2ch 2 o so 4 2 h 2 s 2hco 3 the bicarbonate released in that reaction was the source of isotopically heavier c and lighter o the proportion of bicarbonate produced by oxidation of methane to bicarbonate produced by oxidation of organic matter decreased upwards the resultant isotopic composition of bicarbonate dissolved in the pore waters changed upwards towards higher 13 c and lower 18 o values and has been recorded in the limestone s isotopic composition

co variation of nitrogen isotopes and redox states through glacial interglacial cycles in the black sea abstract in all aquatic environments nitrogen cycling within the water column is strongly influenced by oxygen we hypothesize that the nitrogen isotopic composition 15 n of organic matter deposited in the sediments is a proxy for the redox state of the water column at the time of deposition we tested the hypothesis by measuring the bulk sedimentary 15 n values in a drill core from the black sea a basin that alternates between oxic less saline conditions and anoxic marine conditions on glacial interglacial time scales we reconstructed these changes in black sea redox conditions using sedimentary 15 n total organic carbon toc total nitrogen tn redox sensitive metals and micropaleontological data from a deep sea core dsdp site 380 the sedimentary data reveal that during the transitions between oxic and anoxic conditions 15 n values increased relative to the preceding and succeeding quasi steady state oxic and anoxic periods the results indicate that the reciprocal transitional states from anoxic to oxic conditions were accompanied by intense denitrification during the quasi stable oxic and anoxic states characterized by glacial fresh water and interglacial marine conditions nitrification and complete nitrate utilization respectively dominate the nitrogen cycle while other factors may influence the 15 n record our results support the hypothesis that the variations in nitrogen isotopic composition of organic matter are strongly influenced by changes in redox state in the black sea subphotic zone on glacial interglacial time scales and can be explained by a relatively simple model describing the effects of oxygen on the microbial processes that drive the nitrogen cycle in marine ecosystems our model suggests that the nitrogen isotopic composition of marine sediments on geological time scales can be used to reconstruct the redox state of the overlying water column

mixing on the black sea shelf north of the bosphorus microstructure observations over the black sea shelf and slope north of the bosphorus reveal a very small turbulent diapycnal diffusivity k 10 6 m s 1 in the cold intermediate water during late summer when winds are at their seasonal minimum recent modeling by oguz et al 1998 shows that only with such low diffusivity can the observed separation between dissolved oxygen o2 and hydrogen sulfide h2s be maintained the measurements also provide a reference for mixing over continental shelves where tides are negligible and when winds are light

distribution of deep sea black shales of cretaceous age in the eastern equatorial atlantic from seismic profiling abstract the presence of thick 200 m carbonaceous shales of cretaceous age in the deep waters of the eastern equatorial atlantic was first revealed by drilling at dsdp sites 367 and 368 near the cape verde islands more recent seismic investigations show that black shales are widely distributed in this region in the gambia basin they are associated with a group of seismic reflectors lying at depths of 400 600 m below the sea floor these can be traced southwards from the drill sites into the sierra leone basin and eastwards beneath the african continental rise to depths at which ambient temperatures fall within the oil generation window in the gambia basin the reflectors continue westwards from the cape verde archipelago before terminating on turonian oceanic basement 92 ma south of the guinea fracture zone near 10 n extension of the same seismic sequence on to younger oceanic crust indicates that deep sea carbonaceous deposits formed close to the present equator as late as the early campanian 80 ma long after a series of oceanic anoxic events in the aptian albian oae1 and over the cenomanian turonian boundary oae2 led to widespread accumulation of black shales this late period of deposition may correspond to the more locally developed oae3 high surface productivity in equatorial upwelling zones during the late cretaceous probably played an important role in delivering large amounts of organic carbon to the sea floor when meridional movement of deep water between the south and north atlantic was restricted by closely spaced east west fracture zones in some areas seismic data show that the black shales level out rather than drape pre existing topography implying significant downslope transport of organic rich material from upwelling cells near the african margin

rare earth element exchange through the bosporus the black sea as a net source of rees to the mediterranean sea the bosporus is the only source of seawater to the black sea and helps to maintain the basin wide salinity gradient that caused the black sea to become the largest permanently anoxic basin in the world some 3000 years ago concentrations of dissolved rare earth elements rees in each of the three layers of water that make up the bosporus inflow outflow system substituted into a simple hydrographic model that evaluates the entrainment of outflowing black sea water in the inflowing mediterranean sea water suggest that the black sea acts as a net source of rees to the mediterranean sea this holds true for ce which shows a considerable range of concentrations in the outflowing black sea water even if the lower end of that range is taken to represent the ce concentration of the black sea endmember

oceanography of the black sea a review of some recent results abstract a new synthesis of the black sea oceanography is presented primarily based on studies carried out in the southern black sea as well as on some recent work covering the entire basin obtained in a new era of increasing cooperation between the riparian countries a review of the physical environment is given seasonal and interannual climatic variability of the system are discussed in relation to its hydrology water mass variability and formation are studied with emphasis on the inflow of mediterranean waters pycnocline variability shelf and internal mixing and double diffusive convection the general circulation of the basin and the roles of stratification topography and coastline variations in determining the behaviour of the rapid unstable boundary currents and upwelling along the coast are discussed based on hydrographic data and satellite observations impacts of the physical processes on the ecosystem are discussed

an osmium based method for assessing the source of dissolved rhenium and molybdenum to archean seawater abstract authigenic enrichments of re and mo in 2 7 2 5 ga organic rich mudrocks orm indicate that dissolved re and mo were present in late archean seawater however it can be difficult to determine if the dissolved re and mo were sourced from oxidative crustal weathering or magmatic hydrothermal extraterrestrial mhe inputs comparison of re mo and 192 os non radiogenic os isotope concentrations and initial 187 os 188 os isotope compositions from re os isochron regressions of orm can shed insight on the source of re and mo to archean seawater seawater 187 os 188 os reflects the relative contributions of radiogenic crustal versus unradiogenic mhe os inputs to seawater during the phanerozoic transient increases in magmatic hydrothermal activity marked by unradiogenic 187 os 188 os excursions and higher 192 os concentrations in orm are accompanied in some cases by higher re concentrations these unradiogenic os sources could thus have played a greater role in the archean marine re and possibly mo budget given that the riverine re and mo flux at that time was likely smaller than the phanerozoic flux hence a positive correlation between re mo and 192 os concentrations in archean orm that yields unradiogenic initial 187 os 188 os may reflect a mhe origin for dissolved re and mo in the overlying paleo seawater local oxidative weathering in the presence of photosynthetic o 2 of mafic ultramafic rocks and crustal sulfide minerals with low re os ratios is an alternative explanation but the two scenarios cannot be readily distinguished on the basis of initial 187 os 188 os by contrast an initial 187 os 188 os from archean orm that is statistically higher than the mhe baseline of 0 10 0 11 points to oxidative mobilization of re os and mo from crustal sulfide minerals rhenium and mo concentrations that are negatively correlated with 192 os concentrations in archean orm yielding unradiogenic initial 187 os 188 os suggests that some re and mo were derived from oxidative weathering such negative correlations may reflect an increased marine os sink adsorption to oxide minerals during a mild increase in local environmental o 2 levels these concepts may help trace the onset of photosynthetic o 2 production and accumulation along archean ocean margins

the osmium isotopic composition of the continental crust osmium isotopic compositions and concentrations have been determined for deltaic and continental shelf sediments from three major rivers the amazon changjiang and mississippi and for two loesses from the upper mississippi river valley the loesses have heavy mineral and clay compositions characteristic of mississippi river and delta sediment concentrations range from 15 to 120 pg os g and 187os 186os ratios range from 8 2 to 10 9 sediments which are polluted surface sediment from the changjiang estuary or which have scavenged metals from seawater gulf of mexico slope surface sediment and distal amazon shelf sediment have high osmium concentrations and less radiogenic isotopic compositions purely terrigenous sediments have 15 90 pg os g and 187os 186os 10 0 10 9 north american loess and mississippi delta sediment osmium isotopic compositions are indistinguishable we believe that 187os 186os 10 11 is a good average for currently eroding upper continental crust these sediments have neodymium isotopic compositions close to the global mean for river sediment terrigenous 187os 186os is significantly more radiogenic than seawater 187os 186os 8 6 requiring a nonriverine source of osmium to seawater terrigenous osmium is also significantly more radiogenic than bulk pelagic clay osmium we use the improved estimate of terrigenous 187os 186os to recalculate the flux of extraterrestrial osmium to pacific marine sediment if the residence age of osmium in an upper crustal region is similar to the neodymium model age of a sediment derived from that region a model dependent upper crustal 187re 186os ratio can be calculated for the model ages of the sediments analyzed in this study tdm 1 5 1 7 ga model 187re 186os ratios are 340 360 and can be used to correct for bias resulting from the preferential erosion of young crust the 187os 186os ratio of 2 2 ga crust with 187re 186os 400 is 14 2 we have also used the data from this study to estimate upper crustal osmium and rhenium concentrations of 50 pg g and 390 pg g respectively

documenting the suboxic zone of the black sea via high resolution real time redox profiling we coupled an in situ electrochemical analyzer to a ctd pump profiler system to measure redox species across the oxic anoxic interface of the black sea water column voltammetry was performed using gold amalgam working electrodes to measure simultaneously oxygen and dissolved sulfur species s8 sx2 hs h2s both in situ at 1 m vertical intervals and in an on deck flow cell attached to the outflow of a pump profiler vertical resolution of about 1 5 m in situ data agreed with measurements made in the flow cell and with measurements made from samples collected by rosette bottle casts in situ voltammetry provided undisturbed high resolution measurements and revealed significant yet subtle features not seen by traditional methods because of small spatial separation between the features and the measurements layers of oxygen intrusion 5 m thick from 10 to 150 m o2 were present within the suboxic zone of the southwest black sea that are not present in the west central and northeast black sea oxygen injection also occurs at other depths throughout the southwest and corresponds with small temperature anomalies suggesting influence by bosporus inflow up to 150 km from its entrance to the black sea such an inflow of oxygen as well as spatial variations of the halocline affect both manganese and subsequently sulfide oxidation for a large portion of black sea intermediate water h2s onset occured 60 m deeper in the southwest as compared to the west central in situ voltammetric analyses provided rapid redox information thus enabling more accurate targeting of specific geochemical features by the ctd rosette package

the diffusive regime of double diffusive convection the diffusive regime of double diffusive convection is discussed with a particular focus on unresolved issues that are holding up the development of large scale parameterizations some of these issues such as interfacial transports and layer interface interactions may be studied in isolation laboratory work should help with these however we must also face more difficult matters that relate to oceanic phenomena that are not represented easily in the laboratory these lie beneath some fundamental questions about how double diffusive structures are formed in the ocean and how they evolve in the competitive ocean environment

clues to the nature of the impacting bodies from platinum group elements rhenium and gold in borehole samples from the clearwater east crater canada and the boltysh impact crater ukraine seven large 10 g impact melt rock samples from boreholes from the boltysh impact crater ukraine and six samples from the east clearwater crater canada were analyzed for os ir ru rh pd re and au by the nickel sulfide technique in combination with neutron activation earlier analyses of clearwater east impact melt rocks have shown that they are strongly enriched in ir os pd and re in this work i confirm earlier findings and demonstrate similarly high enrichments of rh and ru the average os ir ru ir pd ir rh ir and ru rh ratios of the melt rock samples from clearwater east are ci chondritic and yield an average ir content of 25 2 6 5 ng g relative to an average upper crust concentration of 0 03 0 02 ng g ir the amount of meteoritic component corresponds to 4 to 7 of a nominal ci component for clearwater east the impact melt rock samples from a bore hole from boltysh are low in ir with an average of 0 2 0 1 ng g the ci normalized abundances increase from the refractory to the more volatile siderophile elements os ir ru rh pd au ni co because of the low ir anomaly and uncertainties in making corrections correlations are weak for indigenous siderophile elements no clear projectile assignment can be made

the african plate a history of oceanic crust accretion and subduction since the jurassic we present a model for the jurassic to present evolution of plate boundaries and oceanic crust of the african plate based on updated interpretation of magnetic gravity and other geological and geophysical data sets location of continent ocean boundaries and age and geometry of old oceanic crust jurassic and cretaceous are updated in the light of new data and models of passive margin formation a new set of oceanic palaeo age grid models constitutes the basis for estimating the dynamics of oceanic crust through time and can be used as input for quantifying the plate boundary forces that contributed to the african plate palaeo stresses and may have influenced the evolution of intracontinental sedimentary basins as a case study we compute a simple model of palaeo stress for the late cretaceous time in order to assess how ridge push slab pull and horizontal mantle drag might have influenced the continental african plate we note that the changes in length of various plate boundaries especially trenches do not correlate well with absolute plate motion but variations in the mean oceanic crust age seem to be reflected in acceleration or deceleration of the mean absolute plate velocity

energetics of semienclosed basins with two layer flows at the strait examination of the energy budget for semienclosed seas with two layer exchange flow at the strait shows that the energy flux at the open portion of the boundary the strait is proportional to the surface buoyancy fluxintegratedoverthebasinarea withtheconstantofproportionalitygivenbytheinterfacedepth whenthe surface buoyancy flux is positive the energy flux is negative these types of basins have an estuarine circulation antiestuarine basins have a negative surface buoyancy flux which provides a positive energy flux augmenting the wind work in powering the circulation the energy budget for the semienclosed seas with vertically separated flows at the strait is examined using reanalysis products for four major semienclosed basins the mediterranean and red seas antiestuarine and the black and baltic seas estuarine important differencesintherelativecontributiontotheenergybudgetofthewindworkversusthesurfacebuoyancyflux are found within basins of the same type and these differences help explain some qualitative aspects of the basins flow

pycnocline and deep mixing in the black sea stable isotope and transient tracer measurements abstract the peculiar mixing processes at the pycnocline and deep regions of the black sea are reviewed in addition to the wind stirring and convective mixing active in the upper pycnocline the other important mechanism that results in limited ventilation of the anoxic waters of the black sea is the mediterranean dense water inflow from the bosphorus modified by the entrainment of surface and intermediate waters introduced into the interior through double diffusive intrusions this inflow aided by the surface ekman flux divergence boundary processes and internal wave breaking is the main mechanism for the mixing and renewal of the sub pycnocline waters in the black sea interior a review of these mixing processes is complemented by results from isotope measurements with improved accuracy and reduced noise compared to earlier experiments measurements of the stable isotopes oxygen 18 18 o and deuterium 2 h confirm the origin of the water masses in the black sea and in the turkish straits including the sea of marmara to be a continuous mixture with variable fractions of salty mediterranean waters with inflowing fresh waters tritium 3 h measurements confirm very little penetration of the transient signal to the sub pycnocline and deep waters of the black sea in comparison to the better ventilated mediterranean waters filling the lower layer of the marmara sea the comparison of stable and transient tracer isotopes shows the effects of fresh waters originating from the north western shelf and the difference between the renewal mechanisms of the marmara and black seas as well as those between the upper and lower pycnocline of the black sea

new angles on south atlantic opening existing models of relative motion between the south america and africa plates significantly misrepresent the azimuth of lower cretaceous seafloor spreading in the south atlantic ocean an improved model is derived from fits of fracture zones magnetic reversal anomalies and the edges of a rifted large igneous province at the northeast georgia rise and agulhas plateau an absolute date for this rifting event is not known but by assuming least change in spreading rates during magnetic chron c34 rifting can be estimated to have occurred at 100 ma this modelling demands a plate divergence history that involves diachronous opening of the south atlantic consistent with published estimates of the ages of breakup from sedimentary basins on the south american and african passive margins the diachronous opening lasts approximately 40 million years during which time it must be accommodated by significant intracontinental deformation a reconstruction using the intra c34 rotation also illustrates the earliest possibility for direct deep water connection between the central and south atlantic oceans one further consequence of this model is that a total reconstruction derived from it and closure of the central atlantic between north america and africa suggests that the venezuelan and gulf of mexico basins may be conjugates formed during the earliest opening of the central atlantic and not separate marginal basins

modeling of hydraulically controlled exchange flow in the bosphorus strait abstract recent hydrographic observations obtained in the bosphorus strait illustrate several features of the flow that may be related with the internal hydraulics a two layer numerical model indicates that the two way exchange flow may indeed be subject to a series of internal hydraulic adjustments along the strait due to morphological features such as sills a contraction and abrupt expansion of the width of the strait the model identifies three distinct regions of the supercritical flow the lower layer flow of the marmara sea origin is directed to the north towards the black sea in a progressively thinning layer and is controlled by the sill located near the black sea entrance of the strait the upper layer water of the black sea origin flows in the opposite direction and is controlled upon reaching the constricted region located about 10 12 km away from the marmara end of the strait the upper layer flow is then matched to the subsequent subcritical conditions by undergoing an internal hydraulic ju

seasonal interannual and mesoscale variability of the black sea upper layer circulation derived from altimeter data 1 topex poseidon and ers altimeter data comprising the period from may 1992 to may 1999 are assimilated into a shallow water model for providing a dynamically consistent interpretation of the sea surface height variations and estimation of the temporal and spatial characteristics of the upper layer circulation in the black sea these 7 year long observations offer a new capability for interpretation of major transient and quasi permanent features of the upper layer circulation the instantaneous flow fields involve a complex eddy dominated system with different types of structural organizations in which the eddies and the gyres of the interior cyclonic cell interact continuously among themselves and with meanders and filaments of the rim current the circulation possesses a distinct seasonal cycle whose major characteristic features repeat every year with some year to year variability an organized two gyre winter circulation system disintegrates gradually into a series of interconnecting eddies in the summer and autumn months which are also characterized by more pronounced and complex mesoscale activity in the peripheral flow system our analyses suggest a revised schematic circulation picture of the major quasi permanent and recurrent elements of the black sea

holocene and late glacial palaeoceanography and palaeolimnology of the black sea changing sediment provenance and basin hydrography over the past 20 000 years abstract the elemental geochemistry of late pleistocene and holocene sediments of the black sea recovered in box cores from the basin margins and a 5 m gravity core from the central abyssal region of the basin identifies two terrigenous sediment sources over the last 20 kyrs one source region includes anatolia and the southern caucasus the second region is the area drained by rivers entering the black sea from eastern europe alkali metal al and heavy light rare earth element ratios reveal that the relative contribution of the two sources shifted abruptly every few thousand years during the late glacial and early holocene lacustrine phase of the basin the shifts in source were coeval with changes in the lake level as determined from the distribution of quartz and the heavy mineral hosted trace elements ti and zr the geochemistry of the abyssal sediments further recorded a sequence of changes to the geochemistry of the water column following the lacustrine phase when high salinity mediterranean water entered the basin beginning 9 3 kyrs bp bottom water that had been oxic throughout the lake phase became anoxic at approximately 8 4 kyrs bp as recorded by the accumulation from the water column of several redox sensitive trace metals mo re u the accumulation of organic carbon and several trace nutrients cd cu ni zn increased sharply ca 0 4 kyrs later at 8 0 kyrs bp reflecting an increase of primary productivity its increase was coeval with a shift in the dinoflagellate ecology from stenohaline to euryhaline assemblages during this profound environmental change from the lacustrine to the marine phase the accumulation rate of the lithogenous sediment fraction decreased as much as 10 fold in response to the rise of the water level in the basin from a low stand ca 9 3 ka to its current level

estimation of continental 187os 186os values by using 187os 186os and 143nd 144nd ratios in marine manganese nodules abstract the relationship between 187os 186os and 143nd 144nd in different manganese nodule fields is used to determine the 187os 186os ratio of the continental terrains bounding the major ocean basins the atlantic ocean drainages yield 187os 186os of about 11 the pacific ocean between 25 and 36 and the western indian ocean 20 by assuming a two component continental crust composed of ultramafic rocks high os concentration low 187os 186os and granite with only radiogenic 187os produced in accessory re bearing molybdenite the ultramafic contribution to weathering is about 0 2 some or most of this may come from the alteration of oceanic ultramafics

the upper layer circulation of the black sea its variability as inferred from hydrographic and satellite observations quasi synoptic hydrographic data and satellite imagery are used to describe the circulation and the structural variability of the black sea with particular emphasis on the turkish coast the circulation is indicated to involve a variable cyclonic circulation with no apparent central locus and a well defined cyclonic rim current containing meanders and interacting eddy fields confined to the shelf slope interspersed between the coastal eddies are filaments and intense jets often with dipole eddies at their termina the extension of these features across the shelf slope into the central basin offshore waters implies important dynamical processes related to the shelf deep basin exchanges these features are often steered by the topography and evolve continuously through the mixed baroclinic barotropic instability of the rim current

a point source of heat in a stable salinity gradient when a salinity gradient is heated at a single point a hot plume is formed with a series of layers around and above it in a christmas tree flow pattern qualitative visual observations of the development of this system are reported three kinds of layers are observed the first kind is formed above the basic plume from a hierarchy of secondary plumes on top of the basic one the second develops around the upper part of the basic plume and is driven by the same mechanism as the layers in sidewall heating experiments and the third forming around the lower part of the basic plume is of the same nature as the second type but also has something in common with double diffusive intrusions a characteristic feature for all the three kinds of layers is the existence of systematic shearing motions and vortices quantitative estimates for the plume height and the thickness of the layers are obtained

variability of the near surface eddy kinetic energy in the california current based on altimetric drifter and moored current data low pass filtered velocities obtained from world ocean circulation experiment woce surface drifters deployed in the california current off northern california during 1993 1995 have been compared with surface geostrophic velocity estimates made along subtracks of the topex poseidon altimeter and with moored acoustic doppler current profiler adcp data to obtain absolute geostrophic velocities a mean sea surface height ssh field was estimated using the mean drifter velocities and historical hydrographic data and was added to the altimetric ssh anomalies the correlation between collocated drifter and altimetric velocities is 0 73 significant at the 95 level the component of the drifter velocity which was uncorrelated with the altimetric velocity was correlated with the wind in the ekman transport sense monthly averages of eddy kinetic energy eke estimated using all drifter and altimeter data within the domain 124 132 w 33 40 5 n show energy levels for the drifters that are about 13 greater than those for the altimeter drifter altimeter and adcp measurements all exhibit similar seasonal cycles in eke with the altimeter data reaching maximum values of about 0 03 m 2 s 2 in late summer fall wavenumber spectra of the altimeter velocity indicate that the velocity fluctuations were dominated by features with wavelengths of 240 370 km while the adcp data suggest that the temporal scales of these fluctuations are at least several months between 36 and 40 5 n the region of monthly maximum eke migrates westward to about 128 w on a seasonal timescale this region of maximum eke coincides with the maximum zonal ssh gradient with increased eke associated with increased southward flow a simple model shows that much of the seasonal cycle of the ssh anomalies can be produced by linear processes forced by the curl of the wind stress although the model cannot explain the offshore movement of the front

role of physical processes controlling oxycline and suboxic layer structures in the black sea 1 a one dimensional coupled physical biogeochemical model together with reanalysis of the available data are used to provide a new perspective for identification and interpretation of the suboxic layer sol of the black sea while the lower boundary appears to be stable at t 16 15 0 10 kg m 3 the upper boundary is found not to be isopycnally uniform as asserted previously it is found to vary depending on the intensity of vertical diffusive and advective oxygen fluxes across the oxycline its position therefore does not always correspond to a distinct density surface irrespective of the circulation characteristics instead it changes from t 15 55 0 1 in cyclonic to t 15 9 0 1 kg m 3 in anticyclonic regions whereas its position in the peripheral rim current transition zone occurs at intermediate density values these findings imply that vertical oxygen variations cannot be expressed in terms of density without taking into account physical characteristics of the water column the presence of very strong density stratification is found to prevent ventilation of the sol even intense turbulent mixing generated by a large buoyancy loss during an exceptionally cold winter season is unable to generate sufficiently dense water to overturn and temporarily supply oxygen into the suboxic zone

187os 186os in marine manganese nodules and the constraints on the crustal geochemistries of rhenium and osmium during their formation marine manganese or more properly ferromanganese oxide nodules include and commonly concentrate elements dissolved in seawater this attribute makes them especially valuable recorders of the isotopic composition of elements supplied to the oceans having radiogenic isotopes for these can be used in exploring crustal composition and evolution1 5 from measurements of 187os 186os ratios in marine manganese nodules and comparison with the 143nd 144nd ratios of the same nodules we have calculated the os isotopic composition and the osmium and rhenium concentrations of the weatherable portion of the continental crust together with the proportions of ultra mafic and granitic rock that constitute this crustal mass