paleoceanographic and climatic implications of a new mediterranean outflow branch in the southern gulf of cadiz abstract the presence of contourite drifts in the southern gulf of cadiz goc along the moroccan margin raises questions about the re circulation of mediterranean outflow water mow in the goc and the origin of the currents depositing them here we compare two cores representative of iberian and moroccan contourite drifts covering the last 22 kyr although the whole sequence is contouritic in character it reflects the interaction of distinctive silty contourite facies high flow velocity periods imbedded in muddy contourite facies low flow velocity periods evidence from benthic foraminifera 13c sortable silt grain size oceanographic ctd profiles and numerical simulations indicate the mediterranean water mass as the source of the southern contourite deposits our data therefore suggests an additional branch of upper mow veering southwards off the straits of gibraltar along the moroccan margin during mis marine isotope stage 2 upper mow was a sluggish current while in the holocene upper mow dominated as a fast semi steady flow throughout the deglaciation silty contourites associated with higher flow speeds were deposited in the northern and southern goc during cold events such as heinrich stadial 1 hs1 and the younger dryas forced by global millennial scale climate variability millennial variability also appears to drive the deposition of silty contourites in the holocene we estimated an average duration of 1 ka for the process of depositing a fast contourite unit the case of silty contourite i6 within hs1 allows us to illustrate with extremely high resolution a rapid sequential change in circulation with gradual slow down of dense mediterranean water while surface was freshening hs1 provoking injection of high salinity intermediate waters via contour currents into the goc and hence the north atlantic the subsequent brief collapse of dense water formation in the mediterranean sea triggered a major increase in sea surface temperatures 10 c ka in the goc developing into the next interstadial bolling allerod the impact of mediterranean intermediate waters is manifested here by triggering a substantial rearrangement of intermediate and deep circulation in the north atlantic which would have further impacted the atlantic meridional overturning circulation amoc

field flume reveals aquatic vegetation s role in sediment and particulate phosphorus transport in a shallow aquatic ecosystem abstract flow interactions with aquatic vegetation and effects on sediment transport and nutrient redistribution are uncertain in shallow aquatic ecosystems here we quantified sediment transport in the everglades by progressively increasing flow velocity in a field flume constructed around undisturbed bed sediment and emergent macrophytes suspended sediment 100 m became dominant at higher velocity steps after a threshold shear stress for bed floc entrainment was exceeded shedding of vortices that had formed downstream of plant stems also occurred on that velocity step which promoted additional sediment detachment from epiphyton modeling determined that the potentially entrainable sediment reservoir 46 g m 2 was similar to the reservoir of epiphyton 66 g m 2 but smaller than the reservoir of flocculent bed sediment 330 g m 2 all suspended sediment was enriched in phosphorus by approximately twenty times compared with bulk sediment on the bed surface and on plant stems indicating that the most easily entrainable sediment is also the most nutrient rich and likely the most biologically active

structure of the mediterranean undercurrent and mediterranean water spreading around the southwestern iberian peninsula 1 rafos float and hydrographic data are analyzed to investigate the pathways rates and mechanisms of mediterranean water mw spreading into the north atlantic from the gulf of cadiz with an emphasis on processes other than meddies we find that the transition of the mediterranean outflow from a density current to an intermediate depth jet occurs as it enters portimao canyon south of portugal due to rapidly steepening topography and associated turbulent entrainment this feature was not seen in recent plume model simulations due to their use of smoothed topography in addition to the traditional lower salinity maximum or core a denser deeper continuous vein of mw was also traceable from portimao canyon to cape st vincent the mean velocity structure of the mediterranean undercurrent changes from a 30 km wide jet with peak mean westward speed of 0 2 m s 1 along the southern iberian slope to a broader much weaker northward flow with maximum mean speed of only 0 06 m s 1 along the western iberian slope due in part to changes in the bottom slope lower core mw spread mainly 1 southward into the interior gulf of cadiz 2 northward along the western iberian slope and 3 westward into the deep tagus abyssal plain the average spreading rate was 0 01 0 02 m s 1 toward the west northwest direction meddies forming near the slope were found to have an indirect but profound impact on mw spreading often diverting mw approaching from upstream into the interior the results are compared to recent hydrography based studies of mw spreading pathways

two circulation regimes of the mediterranean outflow revealed by lagrangian measurements the eurofloat experiment was a joint initiative to examine the large scale spreading of mediterranean water mw and labrador sea water in the northeast north atlantic rafos float data from the southern mw portion of the eurofloat experiment have been examined in conjunction with historical float data in order to calculate quasi eulerian means in an effort to separate and quantify the constituents of the spreading of the mw tongue east of the mid atlantic ridge while recent studies focussed chiefly on the role of meddies in the shaping of the mw tongue this analysis also examines the tongue s second constituent that is the background non meddy advective and diffusive flow the results suggest the existence of two regimes approximately to the north and south of the 36 n parallel i e the latitude of the gulf of cadiz which are distinguished by different types of dominant spreading mechanisms for mw to the south of the gulf of cadiz the background flow shows an incoherent and weak mean whereas the mean velocity of the salt enhanced meddies is strong and to the southwest in contrast to the north of 36 n the mean velocity of the meddies seems to be less pronounced and the background flow is shown to be a major component in the northwestward spreading of the mw tongue the two regimes are separated by the azores current which previously has been hypothesized to act as a dynamic barrier to the southward advective spreading of the background regime which the meddies are able to penetrate because of their high kinetic energy overall the meddies are calculated to contribute to approximately half of the total salinity anomaly flux

stress on the mediterranean outflow plume part i velocity and water property measurements abstract in september 1988 six sections were occupied across the mediterranean outflow plume in the gulf of cadiz within 100 km of the strait of gibraltar vertical profiles of temperature and salinity were collected at ctd stations velocity and temperature profiles were collected with expendable current profilers at a subset of these stations at the channel base the plume undergoes geostrophic adjustment and turns northwest to flow along the continental slope there it decelerates and spreads gradually down the slope as friction slows the current and allows it to cross isobaths within the plume downstream velocity and density increase rapidly in the interfacial layer with depth to the velocity maximum or nose 5 150 m above the bottom below the nose in the bottom layer downstream velocity decreases rapidly toward the bottom but the stratification is weak ekman like veering occurs in the interfacial layer local bottom stresses on the plume are estimated by fitting the near bottom velocity prof

in situ erosion measurements on fine grained sediments from the bay of fundy amos c l daborn g r christian h a atkinson a and robertson a 1992 in situ erosion measurements on finegrained sediments from the bay of fundy mar geol 108 175 196 in situ measurements of the erodibility of fine grained sediments have been made in two regions of the bay of fundy using the benthic annular flume sea carousel the regions were markedly different in benthic biology atmospheric exposure ice loading and wave effects nevertheless remarkable similarities were found in erosion character three patterns of erosion were detected type ia erosion is characterized by an asymptotically decreasing erosion rate with time it is a surface phenomenon associated with the erosion of 1 mm organic pellets formed by the browsing amphipod corophium volutator and was found in regions of high benthic activity only onset of this erosion type is equated with z0 of otsubo and muraoka 1988 type ib erosion also showed asymptotically decreasing erosion with time but erosion generated rip up clasts and aggregates up to 7 mm in diameter type ib erosion occurred at all locations at imposed bed stresses between 1 0 and 4 4 pa peak erosion lasted only 1 3 minutes at any imposed stress level and thereafter ceased this pattern of erosion is the result of a linearly increasing sediment shear strength with depth with an internal friction angle circa 70 onset of this erosion is equated with to2 of otsubo and muraoka 1988 type i erosion occurred only in the uppermost 0 5 mm of the bed below type ii erosion was dominant type ii erosion was constant with time and over the time scales of our experiments was independent of changes in bulk bed shear strength with depth it was found at all locations and was produced by bed shear stresses between 2 and 10 pa type ii erosion succeeded type ib erosion video observations show that type ii erosion is characterized by failure along fine planes of weakness within the sediment probably related to the sediment microfabric generated after deposition a relationship r 2 0 65 n 72 was found between peak erosion rate e of all types and excess bed shear stress of the form proposed by parchure and mehta 1985 ln e e r z zs z 5 kg m s where ef 5 1 x 10 s kg m2 s and t 1 62 m n s this relationship held for all data irrespective of exposure sediment texture or benthic activity notwithstanding similar erosion rates changes in erosion type will have a profound impact on net erosion given its relationship to microfabric erosion type is not predictable using standard laboratory measurements

vertical dispersion of fine and coarse sediments in turbulent open channel flows through using a kinetic model for particles in turbulent solid liquid flows underlying mechanisms of sediment vertical dispersion as well as sediment diffusion coefficient are investigated four hydrodynamic mechanisms namely gravitational settling turbulent diffusion effect of lift force and that of sediment stress gradient coexist in two dimensional 2d uniform and steady open channel flows the sediment diffusion coefficient consists of two independent components one accounts for the advective transport of sediment probability density distribution function due to sediment velocity fluctuations and the other results from sediment eddy interactions predictions of the kinetic model are in good agreement with experimental data of 2d open channel flows in such flows it is shown that 1 the parameter i e the inverse of the turbulent schmidt number may be greater than unity and increases toward the bed being close to unity for fine sediments and considerably large for coarse ones 2 eff

meddies in the mercator north atlantic and mediterranean sea eddy resolving model the new generation of high resolution ocean models offers a new way to investigate the characteristics and the evolution of the ocean mesoscale an analysis of the simulated mediterranean eddies the so called meddies is presented the model used in this study is the mercator north atlantic 9 n 70 n and mediterranean sea prototype pam a high resolution configuration 3 5 8 km horizontal grid based on the opa ocean general circulation model the meddies are coherent structures of warm and salt mediterranean water mw advected in the northeast atlantic a 5 year experiment performed with pam reproduced the main observed characteristics of the meddies thermohaline properties 11 8 c 36 psu sizes radius between 25 and 110 km thickness between 500 and 1000 m westward advection velocities 1 4 cm s 1 angular velocities a period of 20 days a good estimate of the number of meddies in the northeast atlantic 22 and their realistic geographical distribution 80 south of 40 n moreover and in agreement with a previous study based on an observation cruise these modeled meddies represent half of the westward salinity transport of mw

currents and sediment transport in mangrove forests abstract a field study of the tidal currents cohesive sediment dynamics and transport of organic carbon in a highly vegetated mangrove swamp was carried out at middle creek cairns australia the interaction of tidal currents and the vegetation generated jets eddies and zones of stagnant waters which were numerically modelled a high value of the manning friction coefficient n 0 1 was derived by the dense vegetation about 80 of the suspended sediment brought in from coastal waters at spring flood tide was trapped in the mangroves corresponding to about 10 12 kg of sediment m 1creek length spring tide resulting in a rise of the substrate by about 0 1 cm year 1 the selective trapping of clay was caused by flocculation of the finer particles in the mangroves there was an indication of a slight inwelling of organic carbon creek water was readily differentiated from mangrove water by large differences in the molecular weight distribution of the dissolved organic carbon

modeling of hydroecological feedbacks predicts distinct classes of landscape pattern process and restoration potential in shallow aquatic ecosystems article i nfo it is widely recognized that interactions between vegetation and flow cause the emergence of channel patterns that are distinct from the standard schumm classification of river channels although landscape pattern is known to be linked to ecosystem services such as habitat provision pollutant removal and sustaining biodiversity the mechanisms responsible for the development and stability of different landscape patterns in shallow vegetated flows have remained poorly understood fortunately recent advances have made possible large scale models of flow through vegetated environments that can be run over a range of environmental variables and over timescales of millennia we describe a new quasi 3d cellular automata model that couples simulations of shallow water flow bed shear stresses sediment transport and vegetation dynamics in an efficient manner that efficiency allowed us to apply the model widely in order to determine how different hydroecological feedbacks control landscape pattern and process in various types of wetlands and floodplains distinct classes of landscape pattern were uniquely associated with specific types of allogenic and autogenic drivers in wetland flows regular anisotropically patterned wetlands were dominated by allogenic processes i e processes driven by periodic high water levels and flow velocities that redistribute sediment relative to autogenic processes e g vegetation production peat accretion and gravitational erosion these anistropically patterned wetlands are therefore particularly prone to hydrologic disturbance other classes of wetlands that emerged from simulated interactions included maze patterned amorphous and topographically noisy marshes open marsh with islands banded string pool sequences perpendicular to flow parallel deep and narrow channels flanked by marsh and ridge and slough patterned marsh oriented parallel to flow because vegetation both affects and responds to the balance between the transport capacity of the flow and sediment supply these vegetated systems exhibit a feedback that is not dominant in most rivers consequently unlike in most rivers it is not possible to predict the channel pattern of a vegetated landscape based only on discharge characteristics and sediment supply the antecedent vegetation pattern and vegetation dynamics must also be known in general the stability of different wetland pattern types is most strongly related to factors controlling the erosion and deposition of sediment at vegetation patch edges the magnitude of sediment redistribution by flow patch elevation relative to water level and the variability of erosion rates in vegetation patches with low flow resistance as we exemplify in our case study of the everglades ridge and slough landscape feedback between flow and vegetation also causes hysteresis in landscape evolution trajectories that will affect the potential for landscape restoration namely even if the hydrologic conditions that historically produced higher flows are restored degraded portions of the ridge and slough landscape are unlikely to revert to their former patterning as wetlands and floodplains worldwide become increasingly threatened by climate change and urbanization the greater mechanistic understanding of landscape pattern and process that our analysis provides will improve our ability to forecast and manage the behavior of these ecosystems published by elsevier b v

an analytical numerical approach to the hydraulics of floating debris in river channels a new simplified approach is developed for the channel flow dynamics under woody debris transport a continuous carpet of debris is considered covering a uniform stationary current due to the floating debris the shear stresses in the fluid domain are affected as a result the velocity profile is different from the free surface flow the simple model proposed here is able to capture the essential features of flow response to woody debris transport velocity and stress profiles are analytically derived for laminar flow and compared with the zero debris condition more realistic turbulent currents are simulated with the reynolds equations where turbulent stresses are modeled by the simple mixing length concept validation is carried out by comparison with experimental velocity profiles and with direct numerical simulation of the navier stokes equations synthetic diagrams are proposed for the calculation of the flow velocity and the bed shear stresses in terms of the relevant non dimensional parameters

on the southward motion of mediterranean salt lenses abstract a new mechanism is proposed to account for the southward motion of salt lenses in the canary basin it relies on the active mixing that is observed at the periphery of such eddies between the warm salty mediterranean waters of the core and the surrounding fresher and cooler atlantic waters intrusions driven by this thermohaline contrast feed on the eddy potential energy and drain off the eddy volume anomaly submitted to the continuous entrainment of its own fluid by the frontal turbulence the salt lens suffers a velocity divergence at its periphery induced by a geostrophic adjustment process this causes in turn a squashing of the density surfaces and the salt lens must then move southward to conserve its potential vorticity a possibility offered by the spherical nature of the earth it appears that mixing may load to the coherent latitudinal displacement of an ensemble of fluid parcels on a plant while at the same time dissipating the energy of the structure itself

merging and migration of two meddies in this study a scenario is developed of two adjacent mediterranean water eddies meddies as they were observed merging and drifting through the iberian basin observations are based on four rafos floats at 850 1050 dbar two hydrographic surveys centered roughly at 38 n 24 w and trajectories of surface drifters drogued at 100 m in april 1991 the meddy a was identified and labeled by surface drifters during the revisit one month later two meddies were encountered b1 and b2 in the vicinity of the former meddy a the coalescence of b1 subsequently identified as a one month older and b2 is inferred from a simple kinematic model describing the observed movement of the rafos floats for up to three months after the second ctd survey the deduced vorticity front radius 15 km within b1 was of insufficient strength to keep the core waters of b1 isolated and prevent the absorption of b1 by b2 the resulting meddy b1 b2 showed a clear near surface dynamical signal its deep root 1800 m could explain the expulsion from the meddy of the remaining rafos float and surface drifter at the time of the meddy s collision with the josephine seamount for the first time a set of lagrangian and hydrographic observations give direct evidence that neighboring meddies can merge as predicted by theoretical considerations

erosional and mechanical strengths of deposited cohesive sediments erosion tests were run on soft cohesive sediment beds freshly deposited from a concentrated slurry in a large rotating annular flume a total of seven tests were carried out with the bed age varying between 1 8 days and 18 9 days a surface type erosion was observed for the applied shear stress range 0 1 1 pa following the increase in the water flow the erosion rate increases quickly to a peak value and then drops off to approximately zero the eroded depth was less than 8 mm for all beds but the resistance to erosion at a given depth and for a given bed structure increased with increasing bed age this phenomenon was attributed to thixotropy the erosional strength of a given sediment layer is found to be one order of magnitude lower than its undrained and drained mechanical shear strengths measured with innovative testing methods hypotheses are given to explain that difference however at constant density and soil water chemistry the erosional and mechanical strengths seem to be affected by the same factors such as bed age structure and temperature

a census of meddies tracked by floats recent subsurface float measurements in 27 mediterranean water eddies meddies in the atlantic are grouped together to reveal new information about the pathways of these energetic eddies and how they are often modified and possibly destroyed by collisions with seamounts twenty meddies were tracked in the iberian basin west of portugal seven in the canary basin during february 1994 14 meddies were simultaneously observed 11 of them in the iberian basin most 69 of the newly formed meddies in the iberian basin translated southwestward into the vicinity of the horseshoe seamounts and probably collided with them some meddies 31 passed around the northern side of the seamounts and translated southwestward at a typical velocity of 2 0 cm s into the canary basin some meddies observed there were estimated to be up to 5 yr old four meddies in the canary basin collided with the great meteor seamounts and three meddies were inferred to have been destroyed by the collision overall an estimated 90 of meddies collided with major seamounts the mean time from meddy formation to a collision with a major seamount was estimated to be around 1 7 yr combined with the estimated meddy formation rate of 17 meddies yr from previous work this suggests that around 29 meddies co exist in the north atlantic therefore during february 1994 we observed about half of the population of meddies

signatures of the mediterranean outflow from a north atlantic climatology 2 diagnostic velocity fields part 1 of this study is a descriptive analysis of the spreading of mediterranean water based on high resolution maps of salinity and density in the eastern basin in this second part of our study velocity fields for two representative isopycnal surfaces of the mediterranean outflow o 0 s 29 70 and o 0 s 29 90 are estimated from a diagnostic model that combines climatological hydrographic data from the national oceanic data center with long term direct measurements of water exchange through the strait of gibraltar the model is constrained by geostrophic dynamics conservation of mass no flux conditions at the continental shelf and specified flow through the strait of gibraltar our principal data source is a recently assembled database of the north atlantic that consists of climatological mean property fields averaged on isopycnal surfaces the mean fields are based on more than 80 years 1909 1990 of data and have a nominal horizontal resolution of 0 5 o to provide boundary conditions at the strait of gibraltar we use the results of a model developed from data collected during the gibraltar experiment in 1985 the estimated velocity fields show mediterranean water exiting the strait of gibraltar following the southern iberian coast and then entering the tagus basin where it turns anticyclonically to create a reservoir of this water mass the flow continues northward along the eastern boundary penetrating into the rockall channel finally the model flow fields do not show a significant westward advection of mediterranean waters into the subtropical gyre

a census of meddies in a long term high resolution simulation the output from a high resolution two decade long mediterranean outflow simulation is analysed here to provide a census of mediterranean water eddies aka meddies both anticyclones and cyclones the formation rate of meddies that survive for at least 90 days is of 12 meddies yr 1 of which 12 are cyclones the rate of formation reaches 40 meddies yr 1 30 cyclones when considering all the meddies living over 15 days about 70 of the population is born along the southwestern iberian slope but several robust meddies also originate in points of convergence of the main pathways into the open ocean the longest lived meddies propagate northwestwards but most of the anticyclones veer southwestwards after a while as the meddies drift away from their birthplace their radius tends to increase gradually from 15 to 30 km the thickness depth difference between isopycnals 27 2 and 27 5 of anticyclones born near cape st vincent contracts by approximately 100 m after travelling 1000 km from their source their mean swirl velocities range from about 21 cm s 1 at z 1000 m up to 27 cm s 1 at z 600 m mean salinity and temperature anomalies are significantly lower for cyclones which in general are also more slowly rotating shallower and thinner than anticyclones cyclones are more easily tracked at 600 m depth where longer trajectories are recorded in the vicinity of portimao canyon cyclones outnumber anticyclones while the reverse happens downstream of cape st vincent

a numerical study on the successive formation of meddy like lenses 1 we present a process study on the sustaining mechanism of lens formation using a series of numerical experiments of a density current over a sloping bottom with a cape along the coastline water parcels in the bottom density current are shed into the offshore region leading to periodic formation of anticyclonic lenses as part of baroclinic dipolar vortices the cyclonic partner is more prominent at the surface and the coupled vortices are carried by the mean current established in the offshore region parameter dependence of dipole generation is examined which suggests that the background current is necessary for the detached eddies to be coherent in the downstream direction and for shedding events to repeat nof and pichevin 1996 it is also shown that the density mixing of the bottom current provides criteria for cyclogenesis at the sea surface a detailed analysis is given by a five layer model forced by a water mass source sink which reproduces the baroclinic dipolar vortices similar to those observed in the preceding z coordinate model we find that the dipole generation is due to the finite amplitude divergence convergence of the baroclinic current passing the cape stern and chassignet 2000 the overall analyses suggest three necessary conditions for successive eddy formation 1 a localized variation in the coastline causing the finite amplitude disturbance 2 mixing of mediterranean water with the surrounding fluids leading to anticyclonic rotation of meddies as well as cyclogenesis at the surface and 3 background currents that advect the detached vortices out of the source region index terms 4255 oceanography general numerical modeling 4219 oceanography general continental shelf processes 4520 oceanography physical eddies and mesoscale processes 4528 oceanography physical fronts and jets keywords eddy shedding dense water plume numerical simulation

evaluation of regional ocean circulation models for the mediterranean sea at the strait of gibraltar volume transport and thermohaline properties of the outflow a set of simulations from different configurations of the nemomed8 nemomed12 and nemomed36 ocean regional circulation models for the mediterranean sea has been studied in order to assess the accuracy of their representation of the exchange through the strait of gibraltar the model volume transport and thermohaline properties of the mediterranean outflow have been compared with observational data collected at espartel sill the westernmost sill of the strait by a permanent station moored since october 2004 in the frame of the ingres projects results show that in terms of volume transport nemomed8 simulations perform a better representation of the exchange while nemomed12 36 underestimate both the mean inflow and outflow the reason for this underestimation is a too low velocity of the flow which could be consequence of an enhanced roughness effect due the flow bathymetry interaction an important improvement in the representation of the exchange seasonality is achieved by the simulations including sea surface height variability of the atlantic area of the domain the results for the themohaline characteristics of the mediterranean outflow are better for nemomed12 and nemomed36 as a consequence of their better representation of the local dynamical processes that leads to a more realistic composition of the mediterranean waters comprising the flow

meddy trajectories in the canary basin measured during the semaphore experiment 1993 1995 as part of the structures des echanges mer atmosphere proprietes des heterogeneites oceaniques recherche experimentale semaphore experiment four mediterranean water eddies meddies were identified in the canary basin and tracked with freely drifting rafos floats one large and energetic meddy discovered 1700 km west of cape saint vincent portugal set a distance and speed record as it translated another 1700 km southwestward at 3 9 cm s during 1 5 years this meddy traveled 57 of the distance from cape saint vincent toward the spot mcdowell and rossby 1978 found a possible meddy north of the dominican republic two meddies were observed to interact with the azores current as they passed underneath or through it three meddies collided with tall seamounts which seemed to disrupt the normal swirl velocity perhaps fatally in two cases one meddy appeared to bifurcate when it collided with seamounts

bathymetric prediction from dense satellite altimetry and sparse shipboard bathymetry the southern oceans south of 30 s are densely covered with satellite derived gravity data track spacing 2 4 km and sparsely covered with shipboard depth soundings hundreds of kilometers between tracks in some areas flexural isostatic compensation theory suggests that bathymetry and downward continued gravity data may show linear correlation in a band of wave lengths 15 160 km if sediment cover is thin and seafloor relief is moderate at shorter wave lengths the gravity field is insensitive to seafloor topography because of upward continuation from the seafloor to the sea surface at longer wavelengths isostatic compensation cancels out most of the gravity field due to the seafloor topography we combine this theory with wiener optimization theory and empirical evidence for gravity noise to signal ratios to design low pass and band pass filters to use in predicting bathymetry from gravity the prediction combines long wavelengths 160 km from low pass filtered soundings with an intermediate wavelength solution obtained from multiplying downward continued band pass filtered 15 160 km gravity data by a scaling factor s s is empirically determined from the correlation between gravity data and existing soundings in the 15 160 km band by robust regression and varies at long wave lengths we find that areas with less than 200 m of sediment cover show correlation between gravity and bathymetry significant at the 99 level and s may be related to the density of seafloor materials in these areas the prediction has a horizontal resolution limit of 5 10 km in position and is within 100 m of actual soundings at 50 of grid points and within 240 m at 80 of these in areas of very rugged topography the prediction underestimates the peak amplitudes of seafloor features images of the prediction reveal many tectonic features not seen on any existing bathymetrie charts because the prediction relies on the gravity field at wavelengths 160 km it is insensitive to errors in the navigation of sounding lines but also cannot completely reproduce them therefore it may be used to locate tectonic features but should not be used to assess hazards to navigation the prediction is available from the national geophysical data center in both digital and printed form

multiscale flow vegetation sediment feedbacks in low gradient landscapes abstract low gradient fluvial landscapes 1 50 cm km 1 occupy diverse settings inland tidal and deltaic wetlands large river floodplains lowland streams but share many commonalities because of low flow energies these landscapes have abundant vegetation that is submersed or frequently inundated their sediment loads are predominantly fine with large loads transported in suspension the complexities of fluvial vegetation interactions and fine sediment transport have made these landscapes relatively poorly studied in the field of geomorphology yet the importance of understanding their dynamics is paramount these landscapes will be among the first inundated by rising seas and or are presently the focus of the world s largest restoration projects in this synthesis interactions between flow vegetation and sediment documented in inland and tidal marshes chalk and coastal plain streams large river floodplains and deltas are reviewed and classified into feedback processes occurring over a range of five spatiotemporal scales despite different morphologic appearances the feedback processes governing the coevolution of landscapes and vegetation are broadly consistent across settings though modified in their effects by life history traits of vegetation characteristics of the sediment supply external boundary forcing and initial conditions longitudinally elongated patches are common in many settings arising from stress divergence feedbacks however their ultimate morphology is strongly dependent upon the activation of patch or multipatch scale feedbacks which depends on initial densities at the time of colonization generally flow vegetation sediment feedbacks play a dominant role in landscape morphology when the setting is depositional and little initial topographic differentiation is present in that case these feedbacks can explain the apparently paradoxical emergence of high sinuosities or parallel drainage in very low gradients importantly for management flow vegetation sediment interactions may activate a chain of positive feedbacks that engages progressively larger scales resulting in massive destruction of marsh vegetation or topographic homogenization interrupting these feedbacks requires intervention over all scales activated

a model analysis of the behavior of the mediterranean water in the north atlantic abstract the behavior of the mediterranean water in the north atlantic ocean sector of a global ocean general circulation model is explored starting from its entry point at the strait of gibraltar the analysis focuses primarily on one experiment in which explicit watermass exchange between the mediterranean sea and the atlantic at the strait of gibraltar is permitted the model produces an exchange rate of approximately 1 sv sv 106 m3 s 1 this is comparable to estimates derived from field measurements the density of the mediterranean outflow however is lower than observed mainly because of its high temperature more than 2 c higher than in reality the lower density of the outflow and the model s inadequate representation of the entrainment mixing in the outflow region cause the mediterranean water to settle in a depth range 800 1000 m in the north atlantic about 200 m shallower than observed here an interesting current system forms in response to the intrusion of the mediterranean water i

eddy activity in the four major upwelling systems from satellite altimetry 1992 2007 eddy activity in the four major eastern boundary upwelling systems ebus is investigated using 15 years of satellite altimetry data based on the analysis of more than 4000 long lived eddy trajectories in every ebus we show that mesoscale structures are mainly generated along the continental coasts and south of the main archipelagos and propagate westward with velocities increasing toward the equator these mesoscale eddies having radii of 70 160 km are then frequently observed along the coastal transition zones and frontal regions and some large oceanic areas are preferentially populated by cyclonic or anticyclonic eddies temporal variations of the number of newly formed eddies and the associated eddy activity index defined as the mean eddy energy density are finally examined at seasonal and interannual scales the strongest seasonal interannual respectively variations are observed in the california benguela upwelling systems the proposed indices also exhibit contrasted long term trends in each ebus which suggests that eddy activity might be sensitive to a warming climate

modeling the deep eddy field in the southwestern mediterranean the life cycle of sardinian eddies during the mater experiment an eddy characterized by marked levantine intermediate water liw in its core at intermediate depth and called sardinian eddy se has been observed in the algerian basin located in the western mediterranean sea here results from a numerical simulation allow to investigate thoroughly such structures the formation of ses and their life cycle in the model are detailed and compared to in situ observations the formation of ses is associated with the detachment from the continental slope of sardinia of the large scale cyclonic gyre found in the algerian basin once formed ses leave the slope westwards they are strongly barotropic and about 3 to 4 ses are created each year at a later stage ses develop a baroclinic component as revealed by an emerging surface signature about 1 month after their formation coalescence processes and merging of these eddies are documented between minorca and sardinia where these eddies accumulate

modeling the deep convection in the northwestern mediterranean sea using an eddy permitting and an eddy resolving model case study of winter 1986 1987 1 in the northwestern mediterranean sea winter 1986 1987 was particularly cold inducing a strong open ocean convection event in order to investigate the impact of numerical models spatial resolution on the convection representation and the effects of deep convection on the northwestern mediterranean circulation we perform two numerical three dimensional simulations eddy permitting versus eddy resolving models are forced at the surface by the era40 atmospheric fluxes with a simple heat flux correction to better mimic the observed value we examine the characteristics of the deep convection mixed layer water masses characteristics convection zone and mesoscale structures and perform temporal analysis of this event in terms of kinetic energy buoyancy equilibrium and deep water dw evolution the convection characteristics are similarly represented on a global scale by both models and are in good agreement with observations except for the size of the convection region however the eddy resolving model better reproduces the mesoscale structures whose role in the dw formation mixing and transport is shown to be essential the boundary circulation and the overturning are enhanced during the convection event sixty six percent of the dw spreading is due to the bleeding effect into the catalan sea during the convection event whereas 33 is due to the mesoscale structures southwestward advection after the event sixty percent of the restratification with respect of the water column initial structure occurs before july 1987 and is due to light water advection afterward restratification is due to the mixing and is not complete before next year convection

an eddy permitting model of the atlantic circulation evaluating open boundary conditions as part of the french clipper project an eddy permitting model of the atlantic circulation has been run for 22 years the domain has open boundaries at drake passage and at 30 e from africa to antarctica the simulated mean circulation as well as the eddy activity is satisfactory for a 1 3 model resolution and the meridional heat transport at 30 s is within the range estimated from observations we use the mixed open boundary algorithm of barnier et al 1998 which has both a radiation condition and a relaxation to climatology the climatological boundary forcing strongly constrains the solution in the whole domain the model heat balance adjusts through the surface heat flux retroaction term more than the open boundaries the radiation phase velocities calculated within the algorithm are analyzed this shows quite surprisingly that both the eastern and western boundaries have a similar behavior regardless of the preferred directions for advection mainly eastward and wave propagation mainly westward our results confirm that open boundary algorithms behave differently according to the dynamics of the region considered the passive boundary condition that penduff et al 2000 applied successfully in the north eastern atlantic does not work in the present south atlantic model we emphasize the need for a careful prescription of the climatology at the open boundary for which a new approach based on synoptic sections is implemented

signatures of the mediterranean outflow from a north atlantic climatology 1 salinity and density fields using historical data from the national oceanic data center the climatology of the eastern north atlantic basin has been investigated for the purpose of detailing the mediterranean outflow water in terms of its salinity density and flow patterns part 1 of this work is a descriptive analysis of the fate of the mediterranean water once it flows out of the strait of gibraltar tracing the salinity and density signatures high resolution maps of the climatological outflow are presented with an emphasis on the continuity of the water from its source from the climatological fields a continuous signal of mediterranean water is tracked northward to 50 20 n yet its westward advection is limited to the tagus basin recirculations of mediterranean water in the gulf of cadiz and in the bay of biscay deduced from property signals are also detailed iorga and lozier this issue present absolute velocity fields from a diagnostic model constrained by geostrophic dynamics conservation of mass and no flux boundary conditions

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

inssev an instrument to measure the size and settling velocity of flocs in situ abstract an instrument has been developed to observe the settling of individual flocs in turbid water in order to measure size and settling velocity spectra of estuarine cohesive suspended sediments inssev in situ settling velocity instrument is bed mounted and comprises a computer controlled decelerator chamber that collects a sample of water from which some of the suspended matter is allowed to enter the top of a settling column the settling flocs are viewed using a miniature video system subsequent analysis of video tapes can provide direct measurements of size and settling velocity of individual flocs down to 20 m from this information floc density can be estimated the main feature of the instrument is its ability to video flocs in situ irrespective of the concentration in the estuary with as little disturbance to their hydrodynamic environment as possible preliminary field testing in the tamar estuary has given useful results in flow velocities up to 0 4 m s 1 and in concentrations up to 200 mg 1 1 the video recordings show large numbers of low density flocs with multiple structures linked by fine organic fibres

baroclinic eddy interaction with isolated topography point vortex and finite difference methods are used to study baroclinic eddies advected into weak and strong encounters with topography it is argued that weak interactions often scatter radially symmetric eddies into generalized hetons the dipole moments so generated within the eddy result in eddy propagations at various angles to the current strong interactions can result in the complete separation of the upper and lower layer circulations subsequent evolution in this case depends on many factors although strong topographic obstacles i e seamounts permit a reorganization of the centers into a coherent structure weaker topography confined to the deep ocean can disrupt the lower center although the upper center typically survives disassociation of the centers with both retaining their integrity is also possible heton generation can occur for eddies with weak lower layer expressions demonstrating a potentially strong control of shallow eddy propagation by deep sea bathymetry analytical and numerical estimates of the induced propagation speeds are sizable arguing topographic scattering is a potentially powerful mechanism influencing eddy propagation

dynamics and evolution of a northern meddy abstract a meddy was discovered in april 1997 off the northwestern corner of spain near 45 n 11 30 w it was tracked during 18 months with lagrangian floats and deep drogued buoys and several cruises were set to collect further hydrological and lowered adcp measurements on it the meddy named ulla was a one core lens with maximum values of temperature and salinity of 11 5 c and 36 17 psu near 1000 m depth yielding anomalies above 2 5 c and 0 5 psu compared to its environment its rotation frequency was close to 1 loop every 5 days the maximum azimuthal velocities of 15 20 cm s 1 were reached near a 15 km radius the meddy had a wide remote influence notably up to the surface and was associated with a total azimuthal volume transport of around 10 sv sv 106 m3 s 1 of which around 2 sv was trapped in the core a widening of the radial structure with decreasing depth was notable in august 1997 meddy ulla was significantly elliptic for most of the time and depending on the periods the main el

the influence of an upper thermocline current on intrathermocline eddies abstract in this study the effect of an upper layer current on the propagation of intermediate vortices such as mediterranean water eddies is investigated the author discusses the advection mechanism proposed by hogg and stommel and shows how the vertical shear of the mean current can also modify the dynamics of an eddy acting as a gradient source of background potential vorticity

new observations of meddy movement south of the tejo plateau mediterranean salt lenses meddies are a dominant factor in the salt budget of the atlantic at middepth in spite of their important role their juvenile migration has not yet been directly observed for the first time two rafos float trajectories show strong evidence of a meddy along the iberian continental slope off lisbon over six weeks we obtained drift observations from two levels 629 847 dbar both instruments recorded a series of loops with an azimuthal speed o 30 cm s 1 at a radius of about 25 km relatively high propagation speeds of several centimeters per second indicate the meddy was probably carried along with the undercurrent of mediterranean water the tejo plateau a prominent feature of the continental slope and a natural obstacle for the spreading mediterranean water tongue appears to act as a deflector for advected meddies possibly formed by interaction of the undercurrent with the canyon rich topography farther south

the significance of particle aggregation in the overbank deposition of suspended sediment on river floodplains abstract the effects of suspended sediment aggregation on rates of overbank deposition and on the grain size composition of deposited sediment were investigated using a combined field measurement and numerical modelling approach measurements of the in situ grain size characteristics of the suspended sediment load termed the effective size distribution of the river culm devon were obtained using a custom built water elutriation system samples of suspended sediment and of sediment deposited on the floodplain were analysed in the laboratory to determine the size distributions of their constituent discrete mineral particles termed the ultimate size distribution interpretation of these field data was aided by the development of a two dimensional finite difference model of flood hydraulics and suspended sediment dispersion and deposition field measurements and model predictions show that particle aggregation results in higher relative contributions of fine size fractions to overbank deposits aggregation may also provide a mechanism for explaining the poor agreement between theoretical and observed trends in relationships between mean deposit grain size and distance from the main channel suspended sediment aggregation is shown to cause significant increases in rates of floodplain deposition increases in deposition rates resulting from aggregation may however be less than expected because of the effects of aggregate shape and density the latter may offset increases in particle size so that the settling velocities of the largest aggregates do not increase appreciably with particle diameter

large lenses of highly saline mediterranean water isolated compact anticyclonic eddies or salt lenses were found in the canary basin hydrographic surveys of three such lenses show large anomalies of salinity and temperature 0 8 2 5 c they are centered at 1100 m have a vertical extent of up to 900 m and radii of 50 km current meter records indicate anticyclonic velocities up to 29 cm s 1 fine structure with vertical scales of 20 m and less possibly due to intrusive decay appears at the outer edges of the lenses whereas the centers are free of such structure the probability of finding a salt lens at any station in the canary basin is fairly high 0 08

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

hydrogeomorphology of the hyporheic zone stream solute and fine particle interactions with a dynamic streambed 1 hyporheic flow in streams has typically been studied separately from geomorphic processes we investigated interactions between bed mobility and dynamic hyporheic storage of solutes and fine particles in a sand bed stream before during and after a flood a conservatively transported solute tracer bromide and a fine particles tracer 5 m latex particles a surrogate for fine particulate organic matter were co injected during base flow the tracers were differentially stored with fine particles penetrating more shallowly in hyporheic flow and retained more efficiently due to the high rate of particle filtration in bed sediment compared to solute tracer injections lasted 3 5 h after which we released a small flood from an upstream dam one hour later due to shallower storage in the bed fine particles were rapidly entrained during the rising limb of the flood hydrograph rather than being flushed by the flood we observed that solutes were stored longer due to expansion of hyporheic flow paths beneath the temporarily enlarged bedforms three important timescales determined the fate of solutes and fine particles 1 flood duration 2 relaxation time of flood enlarged bedforms back to base flow dimensions and 3 resulting adjustments and lag times of hyporheic flow recurrent transitions between these timescales explain why we observed a peak accumulation of natural particulate organic matter between 2 and 4 cm deep in the bed i e below the scour layer of mobile bedforms but above the maximum depth of particle filtration in hyporheic flow paths thus physical interactions between bed mobility and hyporheic transport influence how organic matter is stored in the bed and how long it is retained which affects decomposition rate and metabolism of this southeastern coastal plain stream in summary we found that dynamic interactions between hyporheic flow bed mobility and flow variation had strong but differential influences on base flow retention and flood mobilization of solutes and fine particulates these hydrogeomorphic relationships have implications for microbial respiration of organic matter carbon and nutrient cycling and fate of contaminants in streams

overland flow in wetlands vegetation resistance emergent wetland vegetation frequently provides most of the resistance to flow of surface water stems are typically spaced many diameters apart therefore fluid friction should be computed from drag on single objects not channel or packed bed equations complication arises from vertical variation of vegetation density and nonoriented spatial variation of soil elevations further flows are often in the transition region between laminar and turbulent and the manning equation is therefore not appropriate a detailed approach requires knowledge of statistical distributions of wetland ground elevation depth and velocity ground slopes are typically in the range of 0 1 100 cm km however the depth range is small so the combined effects recorrelate to a simple power law equation for dense emergent vegetation with spatial uniformity on the scale of 10 m parameters in the model can be estimated with sufficient accuracy from vegetation and soil surveys combined with relatively little hydrologic data dat

controls on floc size in a continental shelf bottom boundary layer simultaneous in situ observations of floc size waves and currents in a continental shelf bottom boundary layer do not support generally accepted functional relationships between turbulence and floc size in the sea in september and october 1996 and january 1997 two tripods were deployed in 70 m of water on the continental shelf south of woods hole massachusetts on one a camera photographed particles in suspension 1 2 m above the bottom that had equivalent circular diameters larger than 250 m and on the other three horizontally displaced acoustic current meters measured flow velocity 0 35 m above the bottom the tripods were separated by 150 m typically maximal floc diameter stayed relatively constant around 1 mm and it showed a dependence on turbulence parameters that was significantly weaker than that predicted by any model that assumes that turbulence induced stresses limit floc size occasionally when waves and currents generated intense near bed turbulence flocs were destroyed these precipitous decreases in maximal floc size also were not predicted by conventional models the correlation in time between episodes of floc destruction and elevated combined wave current stresses provides the first quantitative support for the hypothesis that floc size throughout bottom boundary layers can be controlled by breakup in the intensely sheared near bed region these observations demand a reassessment of the forces limiting floc size in the sea and they indicate the potential for significant simplifying assumptions in models of floc dynamics

hydrological and dynamical characterization of meddies in the azores region a paradigm for baroclinic vortex dynamics the structure des echanges mer atmosphere proprietes des heterogeneites oceaniques recherche experimentale semaphore oceanographic experiment surveyed a 500 500 km2 domain south of the azores from june to november 1993 and collected hydrological data float trajectories and current meter recordings this data exhibited three intrathermocline eddies of mediterranean water meddies two of them being repeatedly sampled their hydrological and dynamical properties are quantified here by an isopycnic analysis for the three meddies intense temperature and salinity anomalies up to 4 c and 1 1 practical salinity units psu are observed extending vertically over up to 1000 m and centered around 1000 m horizontally these anomalies spread out to radii of 50 60 km while the maximum azimuthal velocities 30 cm s 1 as computed by geostrophy lie only at 35 40 km from the central axis these meddies followed curved trajectories with drift velocities up to 7 5 cm s 1 under the influence of the neighboring mesoscale features cyclonic vortices or azores current meanders the three dimensional structure of potential vorticity in and around these features evidences their complex interactions northwest of the domain a meddy was coupled to a subsurface anticyclone forming an aligned vortex it later interacted with the azores current creating a large amplitude northward meander by vertical alignment of vorticity in the southeastern part of the domain another meddy was vertically aligned with an anticyclonic meander of the azores current and horizontally coupled with a cyclone of large vertical extent these two features as well as a small warm and salty fragment in their vicinity seem to result from the southward crossing of the meddy under the azores current these observations illustrate previous theoretical studies of baroclinic vortex dynamics

morphologic and transport properties of natural organic floc 1 the morphology entrainment and settling of suspended aggregates floc significantly impact fluxes of organic carbon nutrients and contaminants in aquatic environments however transport properties of highly organic floc remain poorly understood in this study detrital floc was collected in the florida everglades from two sites with different abundances of periphyton for use in a settling column and in racetrack flume entrainment experiments although everglades flocs are similar to other organic aggregates in terms of morphology and settling rates they tend to be larger and more porous than typical mineral flocs because of biostabilization processes and relatively low prevailing shear stresses typical of wetlands flume experiments documented that everglades floc was entrained at a low bed shear stress of 1 0 x 10 2 pa which is considerably smaller than the typical entrainment threshold of mineral floc because of similarities between everglades floc and other organic floc populations floc transport characteristics in the everglades typify the behavior of floc in other organic rich shallow water environments highly organic floc is more mobile than less organic floc but because bed shear stresses in wetlands are commonly near the entrainment threshold wetland floc dynamics are often transport limited rather than supply limited organic floc transport in these environments is therefore governed by the balance between entrainment and settling fluxes which has implications for ecosystem metabolism materials cycling and even landscape evolution

a three dimensional simulation of the formation of anticyclonic lenses meddies by the instability of an intermediate depth boundary current the evolution of a buoyancy driven intermediate water current along an idealized continental slope is investigated using a three dimensional primitive equation ocean model the outflow current originating in a marginal sea flows northward along a linear sloping bottom where it undergoes considerable mixing for a parameter range resembling the mediterranean outflow the flow becomes hydrodynamically unstable the intruding relatively dense outflow water interacts with the overlaying slope water by inducing vortex compression and stretching the phase relation between the upper layer and lower layer perturbations indicates that baroclinic instability is the driving mechanism in the initial destabilization as the disturbances grow to large amplitude dipoles are formed and move away from the boundary current in a westward direction while the amplifying anticyclones wrap around the intruding low potential vorticity water the cyclones usually entrain ambient water and decrease in strength isolated anticyclones finally separate from the boundary current and develop a southward translation component in some cases dipolar structures remain intact and propagate to the west in the slope water strong cyclones and somewhat weaker anticyclones are formed periodically and travel in the direction of the bottom flow the upper layer flow shows surface expressions of the middepth lenses that develop as meddies these penetrate into the ambient slope water and gain a barotropic velocity component the adjustment process is discussed in terms of potential vorticity conservation the instability mechanism discussed here does not require any topographic irregularities sensitivity experiments however suggest that canyons or capes introduce an additional source of vorticity and may lead to the observed localization of spawning events

lagrangian observations of meddy formation during a mediterranean undercurrent seeding experiment mediterranean eddies meddies play an important role in maintaining the temperature and salinity distributions in the north atlantic but relatively little is known about their early life histories including where how often and by what mechanism they form a major field program called a mediterranean undercurrent seeding experiment has been carried out to directly observe meddy formation and the spreading pathways of mediterranean water into the north atlantic between may 1993 and march 1994 49 rafos floats were deployed sequentially in the mediterranean undercurrent south of portugal and tracked acoustically for up to 11 months the float deployments were accompanied by high resolution xbt sections across the undercurrent nine meddy formation events were observed in the float trajectories six near cape st vincent at the southwestern corner of the iberian peninsula and three near the estremadura promontory along the western portuguese continental slope meddy formation thus occurs where the continental slope turns sharply to the right when facing in the downstream direction of the undercurrent after conditionally sampling the float dataset to identify floats that were well seeded in the undercurrent the authors have estimated a meddy formation rate of 15 20 meddies per year the timescale for meddy formation at cape st vincent was found to be 3 7 days shorter than previous estimates based on the volume of larger meddies meddies were observed to form most frequently when the speed of the mediterranean undercurrent was relatively fast the meddy formation process at cape st vincent resembles the conceptual model of e a d asaro whereby anticyclonically rotating eddies are formed by separation of a frictional boundary layer with negative relative vorticity at a sharp corner comparison of the relative vorticity in the anticyclonic shear zone of the undercurrent and that of the newly formed meddies shows that much of the anticyclonic relative vorticity in meddies can be accounted for by the horizontal shear in the undercurrent this confirms earlier work suggesting that the classical mechanism for the generation of submesoscale coherent vortices by collapse and geostrophic adjustment of a weakly stratified fluid injected into a stratified ocean may not be the principle mechanism at work in the formation of meddies at cape st vincent

impact of the spatial distribution of the atmospheric forcing on water mass formation in the mediterranean sea the impact of the atmospheric forcing on the winter ocean convection in the mediterranean sea was studied with a high resolution ocean general circulation model the major areas of focus are the levantine basin the aegean cretan sea the adriatic sea and the gulf of lion two companion simulations differing by the horizontal resolution of the atmospheric forcing were compared the first simulation med16 era40 was forced by air sea fields from era40 which is the ecmwf reanalysis the second simulation med16 ecmwf was forced by the ecmwf analyzed surface fields that have a horizontal resolution twice as high as those of era40 the analysis of the standard deviations of the atmospheric fields shows that increasing the resolution of the atmospheric forcing leads in all regions to a better channeling of the winds by mountains and to the generation of atmospheric mesoscale patterns comparing the companion ocean simulation results with available observations in the adriatic sea and in the gulf of lion shows that med16 ecmwf is more realistic than med16 era40 in the eastern mediterranean although deep water formation occurs in the two experiments the depth reached by the convection is deeper in med16 ecmwf in the gulf of lion deep water formation occurs only in med16 ecmwf this larger sensitivity of the western mediterranean convection to the forcing resolution is investigated by running a set of sensitivity experiments to analyze the impact of different time space resolutions of the forcing on the intense winter convection event in winter 1998 1999 the sensitivity to the forcing appears to be mainly related to the effect of wind channeling by the land orography which can only be reproduced in atmospheric models of sufficient resolution thus well positioned patterns of enhanced wind stress and ocean surface heat loss are able to maintain a vigorous gyre circulation favoring efficient preconditioning of the area at the beginning of winter and to drive realistic buoyancy loss and mixing responsible for strong convection at the end of winter

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