evidence for the inherent unsteadiness of a river plume satellite observations of the niagara river discharge we present satellite data from the niagara river plume showing that a large eddy or bulge forms and grows in the plume near the mouth of the river the plume consists of a semicircular bulge region immediately offshore of the mouth and a narrow current that propagates east along the shoreline during the low wind period from 27 to 29 may 1999 the width of the bulge more than doubled and the current width increased only slightly approximately one third of the niagara river water accumulated in the bulge near the mouth during this period implying that the transport rate in the shore parallel current was reduced to two thirds of the river discharge rate the effective radius and the growth rate of the bulge computed from the satellite images was in good agreement with previous laboratory results and a numerical model of the niagara river plume this is the first field evidence of the unsteadiness of the bulge

observation of a turbid plume using modis imagery the case of douro estuary portugal abstract the douro is one of the longest rivers in the iberian peninsula and represents the most important freshwater input into the atlantic ocean in the northwestern portuguese coast in order to fill the gaps on the comprehension of the spatial variability of the douro estuarine plume an innovative methodology was applied to observe and characterize this plume and its spatial and temporal variability using images of normalized water leaving radiance at 555 nm from modis moderate resolution imaging spectroradiometer in combination with long term concurrent wind tidal and river discharge data 2003 2011 this work evaluates the effect of the main drivers river discharge wind and tide on the plume features expected strong relationships between river discharge and turbid levels were detected a circular pattern is well distinct off douro estuary when the flow exceeds 500 m 3 s 1 under upwelling favorable winds and high river discharge regime an offshore expansion is observed during southerly winds there is a plume confinement to the coast easterly winds produce a bulge formation with an offshore detachment from the coast while westerly winds tend to confine freshwater close to the shoreline and decrease the cross shore advection under high river discharges a remarkable tidal influence in the near field regions is observed close to the coast and near the river mouth

towards a parametrization of river discharges into ocean general circulation models a closure through energy conservation diagnostic methods are defined in order to compare two numerical simulations of ocean dynamics in a region of freshwater influence the first one is a river plume simulation based on a high resolution numerical configuration of the pom coastal ocean model in which mixing parametrizations have been previously defined the second one is a simulation based on the nemo global ocean model used for climate simulations in its half a degree configuration in which a river inflow is represented as precipitation on two coastal grid cells both simulations are forced with the same freshwater inflows and wind stresses the divergence of volumetric fluxes above and below the halocline are compared results show that when an upwelling wind blows the two models display similar behavior although the impact of lack of precision can be observed in the nemo configuration when a downwelling wind blows the nemo global ocean configuration can not reproduce the coastally trapped baroclinic dynamics because its grid resolution is too coarse to find a parametrization to help represent these dynamics in ocean general circulation models a method based on energy conservation is investigated this method shows that it is possible to link the energy fluxes provided by river inflows to the divergence of energy fluxes integrated over the grid cells of ocean general circulation models a parametrization of the dynamics created by freshwater inflows is deduced from this method this enabled creation of a box model that proved to have the same behavior as the fluxes previously computed from the high resolution configuration

enhancement of alongshore freshwater transport in surface advected river plumes by tides abstracta recent numerical study by isobe showed that imposing alongshore tidal forcing on buoyant coastal discharge enhances the net freshwater transport in the coastal currents the mechanisms for this transport enhancement are studied using a three dimensional primitive equation ocean model regional ocean modeling system roms lagrangian drifters are used to trace the freshwater transport paths it is found that the river plume bulge circulation largely follows the rigid body motion i e constant vorticity the buoyant fluid near the bulge s outer edge is thinner and faster behaving as a baroclinic jet the bulge currents then split after impinging on the coast the outer fluid feeds the downshelf flowing coastal currents while the inner fluid recirculates to form the bulge the coastal current transport estimated from the present and prior studies corresponds well to a baroclinic jet theory with the incident angle of bulge currents at the coast being a key parameter without tides the bulg

the summer hydrography and surface circulation of the east siberian shelf sea during the ice free summer season in 1995 the authors deployed and subsequently tracked 39 surface drifters to test the hypothesis that the discharge from the kolyma river forces a buoyancy driven coastal current from the east siberian sea toward bering strait the observed mean flow is statistically significant at the 95 level of confidence but its direction contradicts their initial hypothesis instead of a coastally trapped eastward flow the authors find a laterally sheared westward flow with maximum velocities offshore that correlate only weakly with the local winds at a daily wind dominated timescale the drifter data reveal spatially coherent flows of up to 0 5 m s21 the lagrangian autocorrelation scale is about 3 days and the lagrangian eddy length scale reaches 40 km this spatial scale exceeds the nearshore internal deformation radius by a factor of 3 however it more closely corresponds to the internal deformation radius associated with the offshore ice edge bulk estimates of the horizontal mixing coefficient resemble typical values of isotropic open ocean dispersion at midlatitudes hydrographic observations and oxygen isotope ratios of seawater indicate a low proportion of riverine freshwater relative to sea ice melt in most areas of the east siberian sea except close to the kolyma delta the observations require a reevaluation of the conceptual view of the summer surface circulation of the east siberian sea eastward buoyancy driven coastal currents do not always form on this shelf despite large river discharge instead ice melt waters of a retreating ice edge act as a line source of buoyancy that in 1995 forced a westward surface flow in the east siberian sea

early human occupations in western santa cruz province southernmost south america abstract this paper discusses basic tendencies in the characteristics of the early archaeological record corresponding to human occupation near the eastern flank of the andean range at the southern end of south america lithic artifacts are analyzed within an organization of technology perspective and are discussed according to borrero s ecological model of the peopling of patagonia the characteristics of the lithic artifacts along with raw material provenience at the oldest levels at sites cerro casa de piedra 7 and chorrillo malo 2 match our expectations for an exploration or early colonization phase in the peopling of the space in addition the range of variation of tools is similar to that present at early sites located to the east of the area some differences at these sites are already evident among these are the higher tool deposition rates at sites located close to pampa del asador a known source of black obsidian that was used by early inhabitants of patagonia this poses some new questions that should be addressed regionally taking into account the regional availability of lithic resources

an idealized study of near equatorial river plumes the dynamics of near equatorial river plumes nerps are investigated using a highly idealized model the spreading of a nerp from an eastern boundary is characterized by a continuous shedding of westward propagating eddies this process transfers the bulk of the freshwater discharge to the deep ocean thus distinguishing nerps from their midlatitude counterparts in the long term limit a nerp can be rationalized as a plume emanating from a coastal source the evolution of nerps in an unstratified basin is quite different from that in a stratified one the spin up in an unstratified basin is characterized by the formation of an anticyclonic bulge which spreads westward thus creating a density stratification that favors the subsequent development of smaller and faster moving secondary eddies the collision of the secondary eddies with the leading bulge arrests the effects of mixing thus allowing the further spreading of the buoyancy anomaly in a stratified basin the generation of anticyclonic eddies is accompanied by a concurrent generation of cyclones which pump saltier waters to the surface hence leading to smaller sea surface salinity sss anomalies nerps are sensitive to variations of the freshwater flux qfw and the geomorphological setting larger qfw generates bigger eddies which spread at a rate proportional to the square root of the normalized flux wide shelves allow the interaction of the eddies with the bottom thus promoting a cyclonic shift of the axis of the eddy train the inclination of the coast affects the dynamical balance controlling the near field behavior of nerps

archaeological littoral sites on the northern coast of santa cruz valuable evidence of sea level changes on the continental patagonian coasts argentina geological studies are fundamental to archaeologists as they provide essential data to understand certain processes involved in the present archaeological record when working on marine coastal archaeology the information provided by geomorphologic studies with regards to the evolution and dynamics of coastal marine lines is essential to assess the availability and accessibility of certain marine coastal areas and their resources to human populations of the past this is also the key to reach correct cultural interpretations however on certain occasions archaeological information can also offer valuable alternative data for geologists to reach geological interpretations for instance when working on the evolution and changes of coastal sea lines in this case spatial and temporal scales must be regarded this idea is supported on the experience gained through research done on the patagonian atlantic coast at the two archaeological localities introduced in this paper cabo blanco where we evaluate models of evolution of the coastline with a number of radiocarbon dates from excavated sites and punta medanosa where we discuss the temporal depth of the formation of the coastal ridges for the mid holocene transgression

coastally trapped waves in the presence of a shelf edge density front a numerical model is developed to analyze the stability and propagation characteristics of coastally trapped waves on a shelf with a shelf edge density front the model is applied to the saglek bank on the labrador shelf in an attempt to explain the ice edge undulations observed in noaa 5 satellite images it was found that the instability is suppressed by the bottom slope if the entire shelf slope is below the front however if the front intersects the bottom at about 1000 m depth with an associated current speed of 50 cm s 1 an upper limit for the labrador current the front could be unstable with a wavelength of 70 90 km and phase speed of 30 45 cm s 1 in approximate agreement with the estimates from satellite images furthermore the neutral propagating modes will be modified by the front some modes will be transformed from barotropic shelf waves to bottom trapped frontal waves the presence of a density front on a continental shelf also results in either restricting or eliminating the backward propagation of energy on the shelf and hence has a significant effect on the energy propagation along the shelf

generation of upwelling circulation under downwelling favorable wind within bottom attached buoyant coastal currents abstracta two dimensional modeling study by moffat and lentz recently reported that downwelling favorable wind can induce cross shore upwelling circulation within a bottom attached buoyant coastal current here we extend the problem to three dimensions the driving mechanism and the sensitivity for the upwelling circulation are studied using a primitive equation ocean model and an analytical model after the initial downwelling adjustment that steepens the isopycnals and compresses the coastal current the cross shore flow can switch to steady upwelling circulation this reverse circulation coincides with a vertically well mixed water column and persists until interrupted by the arrival of river plume bulge from upstream during the upwelling phase the ageostrophic cross shore flow follows the ekman balance the sense of cross shore circulation is governed by a dimensionless parameter the shear ratio which measures the relative size of geostrophic shear and velocity shear supported by the wind in th

buoyant gravity currents along a sloping bottom in a rotating fluid author posting cambridge university press 2002 this article is posted here by permission of cambridge university press for personal use not for redistribution the definitive version was published in journal of fluid mechanics 464 2002 251 278 doi 10 1017 s0022112002008868

the palimpsest problem hearth pattern analysis and middle paleolithic site structure abstract a principal behavioral issue in paleoanthropology centers on the degree to which the behaviors of neanderthals and modern humans may have differed efforts to address this problem have employed the analysis of living floors and site structure in which researchers have traditionally emphasized a dichotomy between the site structures thought to distinguish modern human and neanderthal occupations this thinking links complex site structures characterized by several discrete activity areas to modern humans in contrast to the simple structure of neanderthals as seen in single hearths associated with overlapping generalized activities correlations between prehistoric behaviors and site structures however may be masked distorted and even destroyed by a variety of natural and cultural agencies natural post depositional processes may be associated with bioturbation cryo turbation and the degradation of sediments through wind and water erosion both post and synch deposition disturbance of artifact distributions and features by human activities may involve cleaning scuffage and other site alterations perhaps the most vexing of problems associated with post depositional distortion is from subsequent overlapping occupations in which a smearing or blurring of artifact distributions occurs i e the palimpsest problem using the results of a multi year research program of stratified living floors at the late levantine mousterian rockshelter site of tor faraj southern jordan an introduction to a partial solution of addressing the palimpsest problem through hearth pattern and ring and sector analyses is described here

longshore suspended sediment transport and its implications for submarine erosion off the yangtze river estuary abstract coastal currents that originate from large rivers play a key role in delivering sediment to shelf regions quantifying their transport capability is therefore essential to understanding the sediment budgets and the consequent deposition or erosion of coastal areas in february 2012 we observed the sediment transport carried by the min zhe coastal current that originates from the yangtze river mouth and calculated a flux of 18 7 tons per second on a cross shore section in this period the coastal current was at a typical status which allowed us to estimate a total annual sediment transport of 0 27billion tons southward this result was more than three times the present annual yangtze river sediment discharge suggesting that considerable net sediment removal occurs in the coastal regions the sediment transport 0 27 billion tons year is probably the deposition erosion threshold for the east china sea coast north of our study site analysis of historical yangtze river sediment influx records showed that the onset and acceleration of coastal erosion was closely linked with the operation of the three gorges dam tgd upstream of the yangtze river

observations of shoaling density current regime changes in internal wave interactions abstractwe present in situ and remote observations of a mississippi plume front in the louisiana bight the plume propagated freely across the bight rather than as a coastal current the observed

laboratory experiments simulating a coastal river inflow the dynamics of buoyant water entering a rotating basin are studied using a series of laboratory experiments designed to elucidate the alongshore transport mechanisms in river plumes inflowing water which is discharged perpendicular to the tank wall is observed to form a growing anticyclonic bulge and a coastal current downstream of the bulge detailed simultaneous measurements of the velocity and buoyancy fields in the plume confirm that the bulge momentum is in a gradient wind balance and the coastal current is geostrophic the growth of the bulge and accumulation of fluid within it coincides with a reduction in coastal current transport to approximately 50 of the inflow discharge the bulge is characterized by a depth scale h w hich is proportional to the geostrophic depth hg and two time dependent horizontal length scales yc the displacement of the bulge centre from the wall and rb the effective radius of the bulge these two length scales are proportional to the inertial radius

potential vorticity dynamics of coastal outflows abstracta simple quasigeostrophic model is used to examine the outflow from a river estuary or strait into a coastal ocean as shown by johnson et al these quasigeostrophic outflows are accurately described by analytical long wave solutions this paper first uses these solutions and contour dynamics simulations to discuss the behavior of coastal outflows second it extends the model and the long wave theory to consider the effects of ambient currents tides winds or a variable source flux third consideration of the momentum flux at the source is used to understand the turning of the current showing that steady solutions conserve momentum hence resolving the momentum imbalance paradox of pichevin and nof finally a new numerical scheme to compute steady outflow boundaries is developed the model focuses on the key dynamics driven by the source velocity and the generation of vorticity as the buoyant fluid adjusts the simplicity of the model and insight given by the long wave solutions enables

on the transport of buoyant coastal plumes abstract the role of discharge conditions and shelf geometry on the transport of coastal plumes is studied with a fully nonlinear primitive equation hydrodynamic model the physical setting is an estuarine channel with a small discharge rossby number by simulating different discharge magnitudes buoyant plumes are shown to be succinctly described by a simple coastal front model three results emerge from the model analysis first the plume transport is given by t 0 g ph2 2f where 0 is a parameter dependent on the ratio of the front and the plume widths g p is the plume reduced gravity h is the plume maximum depth and f is the coriolis parameter second this model links the plume transport directly to upstream river conditions with t qr where qr is the river outflow and is a parameter that relates to entrainment the geometry of the plume front and shelf slope and the fraction of freshwater carried downshelf third these equations reduce to analytic results previously established for

alero 4 rock shelter north coast of deseado estuary patagonia argentina hunter gatherer mobility strategies during the late holocene abstract the alero 4 site is a rock shelter located in the vicinity of the northern edge of the deseado river in the santa cruz province of patagonia argentina the stratigraphic studies recorded evidence of human occupation assignable to late holocene stone artifacts bones malacological and anthracological remains were identified based on the study of these items the features and functionality of this type of site in the context of coastal occupations so far recorded in the lower basin of the deseado river are discussed mostly shell middens on coastal dunes the study of the archaeological record of the alero 4 site suggests that human hunter gatherer groups who occupied the lower basin of the deseado estuary and its vicinity during the late holocene used rock shelters in a complementary and synchronously manner with the occupations with shell middens on dunes

dynamics of an equatorial river plume theory and numerical experiments applied to the congo plume case abstractthe congo river has the second largest rate of flow in the world and is mainly responsible for the broad tongue of low salinity water that is observed in the gulf of guinea despite their importance near equatorial river plumes have not been studied as thoroughly as midlatitude plumes and their dynamics remain unclear using both theory and idealized numerical experiments that reproduce the major characteristics of the region the authors have investigated the dynamics of the congo river plume and examine its sensitivity to different forcing mechanisms it is found that near equatorial plumes are more likely to be surface trapped than midlatitude plumes and the importance of the effect in describing the strong offshore extent of the low salinity tongue during most of the year is demonstrated it is shown that the buoyant plume constrained by the geomorphology is subject to the pulling of nonlinear structures and wavelike equatorial dynamics the wind is found to strengthen the intrinsic buoy

river forced estuarine plumes abstract the development maintenance and dissipation of river forced estuarine plumes with and without seaward sloping bottom are studied by use of a three dimensional primitive equation model inside the estuary discussion is focused on how the coriolis force induces lateral asymmetries in the circulation four physical processes dictate the transient as well as the quasi steady circulation in moderately stratified estuaries 1 upper layer convergence during the transient spinup phase 2 upward entrainment leading to the two layer steady circulation pattern 3 upward stretching of the lower layer vortex during the spindown period and 4 in the presence of a seaward bottom slope the left bounded tendency of the landward undercurrent for all phases of development deviations from the laterally averaged circulation pattern caused by these processes are discussed over the shelf various types of plumes are defined according to the visual appearance of the surface salinity field the four types of p

relating river plume structure to vertical mixing abstract the structure of a river plume is related to the vertical mixing using an isohaline based coordinate system salinity coordinates offer the advantage of translating with the plume as it moves or expanding as the plume grows this coordinate system is used to compare the relative importance of different dynamical processes acting within the plume and to describe the effect each process has on the structure of the plume vertical mixing due to inertial shear in the outflow of a narrow estuary and wind mixing are examined using a numerical model of a wind forced river plume vertical mixing and the corresponding entrainment of background waters is greatest near the estuary mouth where inertial shear mixing is large this region is defined as the near field with the more saline far field plume beyond wind mixing increases the mixing throughout the plume but has the greatest effect on plume structure at salinity ranges just beyond the near field wind mixing is weaker at high salinity classes tha

wind relaxation and a coastal buoyant plume north of pt conception ca observations simulations and scalings in upwelling regions wind relaxations lead to poleward propagating warm water plumes that are important to coastal ecosystems the coastal ocean response to wind relaxation around pt conception ca is simulated with a regional ocean model roms forced by realistic surface and lateral boundary conditions including tidal processes the model reproduces well the statistics of observed subtidal water column temperature and velocity at both outer and inner shelf mooring locations throughout the study a poleward propagating plume of southern california bight water that increases shelf water temperatures by 5 c is also reproduced modeled plume propagation speed spatial scales and flow structure are consistent with a theoretical scaling for coastal buoyant plumes with both surface trapped and slope controlled dynamics plume momentum balances are distinct between the offshore 30 m depth region where the plume is surface trapped and onshore of the 30 m isobath within 5 km from shore where the plume water mass extends to the bottom and is slope controlled in the onshore region bottom stress is important in the alongshore momentum equation and generates vertical vorticity that is an order of magnitude larger than the vorticity in the plume core numerical experiments without tidal forcing show that modeled surface temperatures are biased 0 5 c high potentially affecting plume propagation distance and persistence

the east greenland coastal current structure variability and forcing abstract the subtidal circulation of the southeast greenland shelf is described using a set of high resolution hydrographic and velocity transects occupied in summer 2004 the main feature is the east greenland coastal current egcc a low salinity high velocity jet with a wedge shaped hydrographic structure characteristic of other surface buoyancy driven currents the egcc was observed along the entire greenland shelf south of denmark strait while the transect north of the strait showed only a weak shelf flow this observation in conjunction with water mass considerations and other supporting evidence suggests that the egcc is an inner branch of the east greenland current egc that forms south of denmark strait it is argued that bathymetric steering is the most likely reason why the egc apparently bifurcates at this location repeat sections occupied at cape farewell between 1997 and 2004 show that the alongshelf wind stress can have an influence on the structure and strength of the egcc and egc on timescales of 2 3 days accounting for the wind induced effects the volume transport of the combined egcc egc system is roughly constant 2 sv over the study domain from 68 n to cape farewell near 60 n the corresponding freshwater transport increases by roughly 60 over this distance 59 96 msv referenced to a salinity of 34 8 this trend is consistent with a simple freshwater budget of the egcc egc system that accounts for meltwater runoff melting sea ice and icebergs and net precipitation minus evaporation

a tidally dependent plume bulge at the pearl river estuary mouth abstract both observations and numerical simulations have proven the existence of a plume bulge at the trumpet like pearl river estuary pre the formation dynamic of the pre plume bulge during the southeasterly wind period is investigated with numerical model simulations based on the regional ocean modelling system roms the results indicate that the formation and evolution of the pre plume bulge is strongly modulated by the tidal cycle the bulge is sustained by the strong jet flow along the longitudinal lantau channel which is induced by the ebb current and transports freshwater offshore its size is significantly modulated by spring neap cycle being large during spring tide and very small during neap tide besides the existence of abundant freshwater in the estuary is a precondition for the formation of bulge the ebb jet flow could be strengthened by lateral buoyancy forcing which is induced by the accumulated freshwater in the estuary thus guarantees the offshore extension of bulge the input momentum flux by the river runoff however makes no significant contribution the work indicates a new mechanism of plume bulge formation at a wide estuary and evaluates the impact of different forcings

shelf impact on buoyant coastal current instabilities abstractthe impact of shelf slope on the linear stability of buoyant coastal currents and on the nonlinear formation of coastal meanders and eddies is investigated the authors consider a simplified two layer stratification in cylindrical geometry where a buoyant surface current flows along the coast above a denser water with a flat bottom or steep shelves simulations were performed using the nucleus for european modelling of the ocean nemo ocean global circulation model the initial state of these simulations was defined according to laboratory experiments performed in the same configuration comparisons between laboratory and numerical results highlight the role of momentum diffusion and of the initial perturbations amplitude the authors results confirm that the topographic parameter to ratio between the shelf slope and the isopycnal slope of the current is the relevant parameter to quantify the shelf impact on the linear and nonlinear dynamics of the surface current when the evolution of the b

the influence of wind forcing on the chesapeake bay buoyant coastal current observations of the buoyant coastal current that flows southward from chesapeake bay are used to describe how the thickness width and propagation speed vary in response to changes in the along shelf wind stress three basic regimes were observed depending on the strength of the wind for weak wind stresses from 0 02 to 0 02 pa the buoyant coastal current was relatively thin the front slope was not steep and the width was variable 1 20 km for moderate downwelling southward wind stresses 0 02 0 07 pa wind driven cross shelf advection steepened the front causing the plume to narrow and thicken for stronger downwelling wind stresses greater than 0 07 pa vertical mixing dominated bulk richardson numbers were approximately 0 25 isopycnals were nearly vertical and the plume front widened but the plume width did not change plume thickness and width were normalized by the theoretical plume scales in the absence of wind forcing normalized plume thickness increased linearly from 1 to 2 as downwelling wind stresses increased from 0 to 0 2 pa normalized plume widths were approximately 1 for downwelling wind stresses from 0 02 to 0 2 pa the observed along shelf propagation speed of the plume was roughly equal to the sum of the theoretical propagation speed and the wind driven along shelf flow

bathymetric effects on estuarine plume dynamics 1 the influence of bathymetry on an estuary plume at an estuary shelf transition is studied with a three dimensional ocean circulation model to understand the response of the plume to bathymetry several types of estuarine shapes and shelf geometries were adopted in this numerical study the channel s shape and its width to depth aspect ratio affected the fate of the plume by determining flow characteristics inside the estuary moreover the bathymetry of the shelf such as the shelf slope and the direction of a submarine channel defined the plume characteristics on the shelf an estuarine channel with a triangular cross section generated relatively stronger exchange flows at midestuary than a rectangular cross section which resulted in a larger surface plume over the shelf the extension of the submarine channel onto the shelf favored increased plume water transport out to the shelf a result of reduced frictional effects on the shelf the orientation of the submarine channel changed the direction of the plume over the shelf with no additional external forces two fronts developed at the edges of the submarine channel because of enhanced lateral shears in the flow when the estuary was relatively wide compared to the internal rossby radius kelvin number ke 5 or when the relative strength of the freshwater discharge compared to the estuary width was weak rossby number ro 0 05 the coastal plume did not expand up shelf in fact results indicated that freshwater up shelf transport in a coastal current moving against coriolis accelerations was proportional to ro

the influence of tide and wind on the propagation of fronts in a shallow river plume in this study we used field data and radar images to investigate the influence of winds and tides on the propagation of tidal plume fronts the measurements were collected in a shallow shelf region off the dutch coast 10 km north of the rhine river mouth and they clearly show the passage of distinct freshwater lenses and associated fronts at the surface that propagate all the way to the coastline these fronts are observed as a sudden drop in near surface salinity accompanied by high cross shore shear with onshore velocities at the surface we determined the arrival time to our measurement site frontal propagation speed and structure of the fronts by combining the in situ data and radar images frontal froude numbers show a wide range of values with an average of 0 44 our results show that fronts during spring tides are thinner more mixed and move faster relative to the ground during calm spring tides when compared to calm neap tides downwelling winds during spring tides result in thicker and faster fronts however the intrinsic frontal propagation speed indicates that the wind and tide control the frontal propagation mainly due to advection rather than by changing the frontal structure strong return currents in the near bed layer resulting from fast and thick fronts increase near bed turbulence and bed stresses these high stresses suggest that the passage of fronts in shallow coastal areas can initiate sediment resuspension and contribute to transport processes

spreading dynamics of small river plumes off the northeastern coast of the black sea observed by landsat 8 and sentinel 2 abstract we use near simultaneous ocean color satellite imagery from nasa s landsat 8 and esa s sentinel 2 missions to reconstruct surface currents along the northeastern shore of the black sea and study the spread of a small river plume formed in this area several times a year landsat 8 and sentinel 2 satellites both pass over the study area within a time interval of

a simple theory for the fate of buoyant coastal discharges abstract a simple theory that predicts the vertical structure and offshore spreading of a localized buoyant inflow onto a continental shelf is formulated the theory is based on two competing mechanisms that move the buoyant fluid offshore 1 the radial spread of the lighter water over the ambient water being deflected by the coriolis force and producing an anticyclonic cyclostrophic plume and 2 offshore transport of buoyant water in the frictional bottom boundary layer that moves the entire plume offshore while maintaining contact with the bottom the surface expression of the cyclostrophic plume moves offshore a distance ys 2 3g h0 2i 2g h0 2i 1 2f where g is reduced gravity based on the inflow density anomaly h0 is the inflow depth i is the inflow velocity and f is the coriolis parameter the plume remains attached to the bottom to a depth given by hb 2l ih0f g 1 2 where l is the inflow width both scales are based solely on parameters of the buoyant inflow at its source there

the interior shelves of the arctic ocean physical oceanographic setting climatology and effects of sea ice retreat on cross shelf exchange abstract the interior shelves of the arctic mediterranean are the shelves of the kara sea laptev sea east siberian sea and beaufort sea they comprise approximately 40 of the total arctic shelf area 2 5 10 6 km 2 and are distinguished from inflow and outflow shelves by their principal forcing dynamics along their southern continental boundary the interior shelves are dominated by the major arctic rivers receiving over 80 of the total freshwater input to the arctic ocean in the mid shelf region wind and ice motion surface stresses dominate mixing and circulation resulting in high variability along their northern seaward boundary they are forced by upwelling and downwelling favourable surface stresses which drive shelf basin exchanges with atlantic and pacific origin cyclonic boundary currents over the upper slope shelf basin exchange is further modified by shelf break morphometry e g canyons valleys headlands and bottom slope here we review the physical oceanographic settings and forcing of the interior shelves and then focus on shelfbreak exchange and supply of nutrients for new primary production due to upwelling across the shelfbreak as a proxy for this nutrient supply we show seasonal and annual time series of along shelfbreak surface stress due to wind and ice motion from 1979 to 2011 we apply this analysis to the shallow shelves from the kara sea to the beaufort sea and comment on recent increases due to atmospheric changes and sea ice retreat

dynamics of the block island sound estuarine plume abstractbuoyant discharge of freshwater from long island sound lis forms a seasonal buoyant plume outside block island sound bis between the coast of long island and the denser shelf waters the plume s seasonal variability and its response to tides winds and surface heating are investigated through a series of process oriented experiments using the regional ocean modeling system roms results show the importance of river discharge wind directions and surface heating in the seasonal variation of the bis buoyant plume in winter and spring the plume is intermediate with a large surface offshore extension detached from the bottom from winter to spring the river discharge increases meanwhile upwelling favorable winds keep dominating they compete with the increase of surface heating and generate a broader buoyant plume in spring than in winter in summer the plume is bottom advected with most of its width in contact with the bottom and is featured with the steepest isopycnals and narrowest pl

impact of variable inflow on the dynamics of a coastal buoyant plume the impact of buoyant discharge variations on the dynamics of coastal buoyancy driven currents is studied using a primitive equation numerical model spem5 first variable discharge is introduced as harmonic fluctuations of the inflow velocity at the tidal period 12 hours and subinertial period 10 days frequencies tidal fluctuations produce only minor effects on the buoyant plume compared to the case of constant inflow while subinertial fluctuations substantially modify the anticyclonic bulge a partially detached anticyclonic plume forms when discharge subsides after reaching its peak value such a plume has maximum offshore extension some distance downstream of the mouth with the lightest water separated from the coast a secondary bulge forms during the low runoff interval when high discharge resumes this secondary bulge is shifted offshore and enhanced for some time an individual high discharge event is next considered where both the net transport of the inflow and the absolute value of its density anomaly increase and then return to their initial background values over 5 and 10 day time intervals this event also generates a partially detached plume especially with the 10 day duration in this case the lightest water occupies the downstream part of the bulge and is separated not only from the coast but also from the mouth the effect of variable discharge is more dramatic with a uniform downstream current of 0 1 m s under such conditions constant buoyant discharge does not form a well pronounced anticyclonic bulge in contrast variable discharge produces an almost circular anticyclone during the high runoff interval as runoff decreases this anticyclone separates from the source and either continues to propagate downstream as an individual eddy or is modified by the next cycle of increasing discharge observational evidence for both the partially detached bulge near the mouth and the anticyclone propagating downstream from its source is presented in this study one feature was observed at the mouth of the columbia river estuary the second feature was observed off the southern new jersey coast 150 km south of its source the hudson estuary

on the alongshelf evolution of an idealized density front abstract observations reveal a strong tendency for fronts to locate over the outer continental shelf and the upper portions of the continental slope in this paper we consider a model of the alongshelf evolution of a quasi steady density front which separates relatively light nearshore water from the offshore results show how in the absence of any external forcing the frictional stress associated with bottom geostrophic velocities can result in the cross shelf migration of a front as one progresses down the shelf in the direction of long coastal trapped wave propagation the primary results are derived for the hypothetical case of a flat shelf adjoining a very deep offshore region in this case the rate of cross shelf migration of a density front is similar to that of a passive scalar front in a barotropic fluid the offshore displacement of a front separating the lighter inshore from the heavier offshore water increases exponentially in the direction of shelf wave propagation on the frictional dec

freshwater distribution in the arctic ocean simulation with a high resolution model and model data comparison 1 a high resolution numerical simulation of the arctic ocean is analyzed in order to study the fate of river runoff and freshwater fluxes in the arctic ocean the model is driven by realistic winds and thermodynamic forcing from the european centre for medium range weather forecasting ecmwf reanalysis data set dye tracers have been added to visualize the pathways followed by low salinity water from the major arctic rivers and bering strait inflow the model is spun up using repeated forcing with the 1979 annual cycle for 20 years then the 1979 through 1998 atmospheric forcing is applied under the influence of the 1979 through early 1980s winds a large plume of river runoff exits the broad eurasian shelf seas along the lomonosov ridge starting in about 1985 the locus of shelf to basin transport shifts eastward to the alpha mendeleyev ridge complex this shift in the model output is related to changes in the sea surface height ssh fields which we attribute primarily to shifts in surface wind stresses model resolution runoff inputs and relaxation terms in the lena river delta region are analyzed in detail to expose issues with model performance at boundaries with freshwater inflow suggestions are made for improving future simulations of river runoff in basin scale models

breaking surface wave effects on river plume dynamics during upwelling favorable winds this study examines the dynamics of a buoyant river plume in upwelling favorable winds concentrating on the time after separation from the coast a set of idealized numerical simulations is used to examine the effects of breaking surface gravity waves on plume structure and cross shore dynamics inclusion of a wavebreaking parameterization in the two equation turbulence submodel causes the plume to be thicker and narrower and to propagate offshore more slowly than a plume in a simulation with no wave breaking in simulations that include wave breaking the plume has much smaller vertical gradients of salinity and velocity than in the simulation without breaking this leads to decreased importance of shear dispersion in the plumes with wave breaking much of the wideningrate of the plume is explainedby divergentekmanvelocities at the off and onshore edges some aspects of plume evolution in all cases are predicted well by a simple theory based on a critical richardson number and an infinitely deep ocean however because the initial plume in thesesimulationsisincontactwiththeseafloorintheinnershelf somedetailsarepoorlypredicted especially around the time that the plume separates from the coast

classification of buoyant river plumes from large aspect ratio channels abstractthe dynamics of the grand river plume a major tributary of lake michigan was studied in the vicinity of the grand haven coast on the east side of the lake the river spread laterally from the mouth and formed a thin surface buoyant plume with various shapes that have not been previously reported to understand the influence of different driving forces primarily wind buoyancy and ambient currents extensive field experiments were carried out over four periods in august and june 2006 and june and july 2007 they included aerial photography over the plume acoustic doppler current profiler adcp deployments meteorological buoys drifters sf6 and rhodamine wt tracer releases three dimensional 3d ctd profiling over the plume and ctd casts at the river mouth the results showed more flow classes than included in previous studies a modified classification scheme based on the relative magnitude of the plume crossflow length scale and a richardson number were devised that includes longshore c

structure and dynamics of the columbia river tidal plume front 1 time dependent buoyant plumes form at the outflow of tidally dominated estuaries when estuary discharge velocity exceeds plume internal wave speed c a sharp front forms at the plume s leading edge that expands from the time dependent source using observations of the columbia river tidal plume from multiple tidal cycles we characterize time evolving plume structure and quantify front speed uf plume internal wave speed c front curvature and ultimate extent we identify three distinct stages of propagation 1 initially the plume is strongly influenced by shallow bathymetry near the river mouth 2 as the front advances offshore the plume detaches from the bottom and expands as a freely propagating gravity current with relatively constant uf c and frontal froude number f uf c ambient currents explain intracycle variability in uf and winds alter front shape variability in ambient stratification associated with previous cycles plume remnants leads to complex fronts and internal waves 3 finally the plume decelerates adjusts toward geostrophy and may radiate additional internal waves using a simple kinematic model we suggest that constant frontal propagation speed uf 0 9 0 1 m s during stage 2 is primarily controlled by linearly increasing volume flux from the columbia river mouth as this discharge rate subsides the plume expands as a fixed volume with decreasing front speed stage 3 the plume s final extent is controlled by the rossby radius which scales with a length based on the total volume discharged this provides an integral description of plume front evolution based on the time dependent estuary discharge