the meandering gulf stream as seen by the geosat altimeter surface transport position and velocity variance from 73 to 46 w the surface geostrophic velocity field for the gulf stream region was analyzed for the position structure and surface transport of the gulf stream for 2 5 years of the geosat altimeter exact repeat mission synthetic data using a gaussian velocity profile were generated and fit to the sea surface residual heights to create a synthetic mean sea surface height field and profiles of absolute geostrophic currents most of cross track velocity variance was due to the meandering of the gulf stream rather than to rings or complicated velocity profiles which suggested that the simple model parameters are an efficient description of the gulf stream fluctuations an analysis of the model parameters and the actual geostrophic velocity profiles revealed two different flow regimes for the gulf stream connected by a narrow transition region coincident with the new england seamount chain the upstream region was characterized by relatively straight gulf stream paths long eulerian time scales and eastward propagating meanders the downstream region had more large meanders no consistent propagation direction and shorter eulerian time scales a 25 reduction in surface transport occurred in the transition region with a corresponding reduction in current speed and no change in gulf stream width a significant anomaly in surface transport near 69 w suggested the existence of small scale recirculation gyres there the highest variance empirical orthogonal functions of position and surface transport were significantly correlated with larger surface transports leading more northerly positions by a month

variability in the location of the antarctic polar front 90 20 w from satellite sea surface temperature data the path of the antarctic polar front pf is mapped using satellite sea surface temperature data from the noaa nasa pathfinder program the mean path and variability of the pf are strongly influenced by bathymetry meandering intensity is weaker where the bathymetry is steeply sloped and increases in areas where the bottom is relatively flat there is an inverse relationship between meandering intensity and both the width of the front and the change in temperature across it there is a persistent large separation between the surface and subsurface expressions of the pf at ewing bank on the falkland plateau

effects of episodic rainfall on a subterranean estuary numerical simulations were conducted to examine the effect of episodic rainfall on nearshore groundwater dynamics in a tidally influenced unconfined coastal aquifer with a focus on both long yearly and short term daily behaviour of submarine groundwater discharge sgd and seawater intrusion swi the results showed non linear interactions among the processes driven by rainfall tides and density gradients rainfall induced infiltration increased the yearly averaged fresh groundwater discharge to the ocean but reduced the extents of the saltwater wedge and upper saline plume as well as the total rate of seawater circulation through both zones overall the net effect of the interactions led to an increase of the sgd the nearshore groundwater responded to individual rainfall events in a delayed and cumulative fashion as evident in the variations of daily averaged sgd and salt stored in the saltwater wedge quantifying the extent of swi a generalized linear model glm along with a gamma distribution function was developed to describe the delayed and prolonged effect of rainfall events on short term groundwater behaviour this model validated with results of daily averaged sgd and swi from the simulations of groundwater and solute transport using independent rainfall datasets performed well in predicting the behaviour of the nearshore groundwater system under the combined influence of episodic rainfall tides and density gradients the findings and developed glm form a basis for evaluating and predicting sgd swi and associated mass fluxes from unconfined coastal aquifers under natural conditions including episodic rainfall

the influence of evaporation and rainfall on supratidal groundwater dynamics and salinity structure in a sandy beach evaporation has been recognized as a major driving force affecting coastal aquifer systems however its effects on subsurface flow and salinity structure have not been investigated in sufficient detail this paper presents field measurements and numerical simulations of pore water flow and subsurface salinity structure in the supratidal zone of a sandy beach subjected to evaporation as well as rainfall it was found that evaporation significantly increased pore water salinity up to 85 g l within a shallow layer approximately 10 cm below the beach surface the induced density gradient generated salt fingers near the beach surface which caused local groundwater circulation i e fingering flow however unlike inland aquifers the salt fingering was significantly diminished by tidal action that prompted the horizontal mixing of salt in the beach the subsequent precipitation e g rainfall diluted the evaporation induced high saline plume near the beach surface and drove the plume to migrate further downward the plume gradually dispersed and was diluted along the groundwater pathways the simulation results indicated that evaporation as well as precipitation at the beach surface induced complex driving mechanisms for supratidal groundwater flow depending on the intensity at the beach surface evaporation and rainfall significantly altered the pore water flow and associate solute transport processes in the supratidal zone of the beach

tide induced seawater groundwater circulation in shallow beach aquifers summary in this paper we investigated the tide induced seawater groundwater circulation in shallow beach aquifers using the finite element model marun the numerical solutions were generalized using a dimensionless formulation from a dimensionless tidal period and a dimensionless beach slope of 10 we obtained results that apply to a wide range of beach permeabilities from 10 4 m s to 10 3 m s beach slopes from 3 16 to 31 6 tidal amplitude 0 3 m 2 m and period diurnal or semidiurnal the numerical simulations demonstrated the following the maximum darcy velocity always occurs at the intersection of the watertable and the beach surface the offshore beach groundwater is almost stagnant compared with the onshore groundwater flow which may explain the previous observations that the major portion of the seaward groundwater seepage usually occurs in the shallow part of the submerged beach the outflow from the seepage face accounts for 41 97 average 55 of the outflow from the intertidal zone the amount of seawater infiltrating into the intertidal zone in a tidal cycle increases with the beach permeability and decreases when the inland recharge increases and ranges from 35 5 m 3 yr 1 m 1 to 505 8 m 3 yr 1 m 1 for all the cases considered smaller beach slopes smaller inland freshwater recharges and or greater beach permeability lead to larger saltwater plumes in the intertidal zone of the beach the results are in line with the existing results of field observations and numerical simulations by previous researchers a 2008 elsevier b v all rights reserved

a mechanistic study of nonlinear solute transport in a groundwater surface water system under steady state and transient hydraulic conditions two laboratory experiments were conducted to investigate the effects of tides and buoyancy on beach hydraulics in the presence of a seaward groundwater flow due to an elevated regional water table in the first experiment case 1 the difference in concentration between the salt water at sea and the water of the regional aquifer was small 2 4 g l 1 such that it did not engender density gradients the salt acts as a tracer in this case in the second experiment case 2 the difference was 32 0 g l 1 which creates a significant density gradient this case corresponds to the presence of fresh groundwater in the subsurface of the coasts of the continental united states the experiments were numerically simulated by the marine unsaturated marun model a numerical model for density and viscosity dependent flows in two dimensional variably saturated media the long term experimental and numerical results showed that the seawater plume entered the beach from the sea and occupied most of the intertidal zone the maximum depth of the seawater plume was near the midsection of the intertidal zone and it decreased near the low and high tide lines when viewed in the context of case 2 these results indicate an inverted salinity distribution in beaches subjected to tides with salt water from sea overtopping the freshwater lens for both cases water from the regional aquifer moved seaward beneath the seawater in the intertidal zone and pinched out near the low tide mark we also noted that beach hydraulics are highly two dimensional with water entering the beach at a near vertical angle and leaving it at a near horizontal angle which casts doubts on analyses of beach hydraulics based on the dupuit assumption findings from this work have direct implications within the practice of bioremediation of oil spills on beaches we found that applying dissolved nutrients on the beach surface at low tide is superior to applying them in a trench landward of the beach this is because the residence time of the nutrient plume in the bioremediation zone of the beach in the prior situation is longer than that in the latter

estimation of evaporation from the normally dry lake frome in south australia depth profiles of deuterium composition expressed as delta values have been used to make point estimates of evaporation from the floor of the normally dry lake frome a salt lake in northern south australia values from five sites varying between 90 and 230 mm yr 1 have been used to obtain a relatively crude approximation for mean evaporation rate from the lake of 170 mm yr 1 under the assumption that this represents discharge of water from the regional groundwater system the groundwater inflow into the lake is calculated as 5 108 m3 yr 1 two possible models which describe groundwater inflow into the lake are discussed

florida straits deglacial temperature and salinity change implications for tropical hydrologic cycle variability during the younger dryas temperature and d 18 osw a proxy for surface salinity records based on mg ca ratios and oxygen isotope measurements in the planktonic foraminifera globigerinoides ruber from a sediment core located on the western margin of the florida straits as a proxy for meltwater discharge influence on florida straits surface water salinity we also measured ba ca ratios in g ruber from the same core results show that riverine influence on florida straits surface water started by 17 2 ka bp and ended by 13 6 ka bp 600 years before the start of the younger dryas yd cold interval the initiation of the yd is marked by an abrupt increase in florida straits d 18 osw values indicating a shift to elevated sea surface salinity occurring in 130 years most likely resulting from increased regional aridity and or reduced precipitation in order to resolve the timing of tropical atmospheric circulation change relative to amoc variability across this transition we compare the timing of surface water changes to a recently published record of florida current variability in the same core reconstructed from benthic oxygen isotope measurements we find synchronous changes in atmospheric and ocean circulation on the transition into the yd consistent with an abrupt reduction in amoc as the driver of tropical atlantic atmospheric circulation change at this time

variable density flow and solute transport simulation of regional aquifers containing a narrow freshwater saltwater transition zone variable density flow and solute transport simulation of aquifer systems containing narrow transition zones between freshwater and saltwater requires particular attention to certain aspects of the numerical method and its application to be successful typically only cases involving wide transition zones have been simulated with variable density transport models possibly because of inaccuracies in the modeling approaches used the major components of a successful approach are threefold first functionally consistent approximation of terms involved in fluid velocity calculations is necessary in the case of galerkin finite element methodology a significant modification is required to the standard approach in order to achieve consistency second the simulator must be verified in a particular series of tests the usual tests using henry s problem for verification of density dependent transport simulators are inadequate to check for consistency of the velocity approximations and for the accuracy of simulating flow driven by bouyancy forces third adequately fine spatial discretization is required when applying the simulator for spatial stability of the numerical transport solution and to allow accurate representation of narrow transition zones and the effects of low transverse dispersivity the effectiveness of this approach is demonstrated through simulation of the flow of fresh and saline groundwater in the layered basalt aquifer of southern oahu hawaii the transition zone in this regional flow system is narrow except near the discharge area where it is broadly dispersed simulation of this common situation with an inconsistent approximation gives grossly incorrect results while simulation with a consistent model provides a robust tool for analysis of system hydrology

gulf stream trajectories measured with free drifting buoys abstract during 1975 78 35 free drifting buoys measured surface currents in the gulf stream region the buoy trajectories trace numerous paths of the stream and show that the stream is strongly influenced by the new england seamounts this influence is manifested as 1 a quasi permanent 100 km southeastward deflection of the stream and the frequent occurrence of a ring meander over the seamounts 2 large amplitude meanders beginning at the seamounts and extending eastward and 3 small 20 km diameter eddies which appear to be generated locally by individual seamounts a chart of the mean temperature field at a depth of 450 m agrees with several of the patterns seen in the buoy trajectories west of the seamounts the mean path of the gulf stream is eastward over the seamounts the path turns sharply northeastward and the isotherms in the stream abruptly diverge

long term persistence of oil from the exxon valdez spill in two layer beaches oil spilt from the tanker exxon valdez more than 20 years ago still persists in the gravel beaches of prince william sound alaska field data and numerical modelling indicate that some of the oil was trapped in the anoxic environment of the lower layers of the beaches when the water table was low oil spilled from the tanker exxon valdez in 1989 refs 1 2 persists in the subsurface of gravel beaches in prince william sound alaska the contamination includes considerable amounts of chemicals that are harmful to the local fauna3 however remediation of the beaches was stopped in 1992 because it was assumed that the disappearance rate of oil was large enough to ensure a complete removal of oil within a few years here we present field data and numerical simulations of a two layered beach with a small freshwater recharge in the contaminated area where a high permeability upper layer is underlain by a low permeability lower layer we find that the upper layer temporarily stored the oil while it slowly and continuously filled the lower layer wherever the water table dropped below the interface of the two layers as a result of low freshwater recharge from the land once the oil entered the lower layer it became entrapped by capillary forces and persisted there in nearly anoxic conditions that are a result of the tidal hydraulics in the two layered beaches we suggest that similar dynamics could operate on tidal gravel beaches around the world which are particularly common in mid and high latitude regions4 5 with implications for locating spilled oil and for its biological remediation

some observations of the azores current and the north equatorial current the regions containing the two zonal currents of the subtropical gyre in the eastern north atlantic the azores current and the north equatorial current nec have quite different physical characteristics associated with the azores current are strong horizontal thermohaline gradients that can be located easily both at the surface and at depth with temperature data alone thus making satellite ir imagery and expendable bathythermograph profiles suitable for observing it during winter the surface expression of the azores current is often found to the north of the strongest subsurface gradients in contrast to the azores current and to the central water mass boundary just to the south the nec has relatively weak horizontal temperature and salinity gradients requiring density information in order to identify it there is no clear surface manifestation found with the nec common to both currents though is that each transports o 8 sv in the upper 800 m of the ocean near 27 w with the largest velocities being in the upper 400 m

impacts of evaporation on subsurface flow and salt accumulation in a tidally influenced beach we coupled a mass transfer formulation of evaporation to the density dependent variably saturated finite element model marun to predict the salinity under realistic conditions in a beach in the gulf of mexico the results showed that evaporation almost doubled the pore water salt concentration in the intertidal zone in comparison to the case with no evaporation the results also showed that for the relatively wet atmospheric conditions the maximum evaporation did not occur from the supratidal zone rather from the intertidal zone and it was due to the difference in moisture between pore water and atmosphere the highest salinity occurred during the spring tide period and extended into the neap tide period when the atmospheric condition was assumed to be constant and conducive to large evaporation high temperature and low air humidity the maximum salinity region shifted to the supratidal zone and persisted there due to low mixing the maximum salinity value in the intertidal zone for this case was not larger than that of the variable atmospheric condition case however the maximum was more landward than the more realistic variable atmospheric condition case which suggests that accurate characterization of pore water salinity in tidally influenced beaches requires accurate knowledge of atmospheric conditions in addition to beach and hydraulic properties the constant atmospheric condition simulations suggest that antecedent extreme conditions greatly affect the salinity in the supratidal zone but they are dampened in the intertidal zone

gulf of mexico circulation within a high resolution numerical simulation of the north atlantic ocean 1 the gulf of mexico circulation is examined from the results of a high resolution 1 12 north atlantic simulation using the miami isopycnic coordinate ocean model the motivation for this paper is twofold first we validate the model s performance in the gulf of mexico by comparing the model fields to past and recent observations and second given the good agreement with the observed gulf of mexico surface circulation and loop current variability we expand the discussion and analysis of the model circulation to areas that have not been extensively observed analyzed such as the vertical structure of the loop current and associated eddies especially the deep circulation below 1500 m the interval between successive model eddy sheddings is 3 to 15 months the eddy diameters range between 140 and 500 km the life span is about 1 year and the translational speeds are 2 3 km d 1 in good agreement with observations areas of high cyclonic eddy occurrence in the model are southwest of florida the loop current boundary and the western campeche bay area the cyclonic eddy diameters range between 50 and 375 km the orbital speeds range between 1 and 55 cm s 1 the translational speeds range between 0 5 and 14 km d 1 and the eddy life spans range between 1 and 3 months the vertical structure of the temperature and salinity of each modeled eddy from the moment it is shed until it disintegrates in the western gulf of mexico is in agreement with the few available observations below 1500 m deep cyclonic eddies are associated with the surface loop current anticyclones the eddy variability is consistent with rossby waves propagating westward and there is bottom intensification of the flow close to steep topography overall we show that this very high horizontal resolution isopycnic coordinate ocean model which is able to produce a quite realistic surface circulation for the north and equatorial atlantic is also able to reproduce well the smaller scale basin wide intricate dynamics such as the gulf of mexico variability

deep flows in the yucatan channel and their relation to changes in the loop current extension 1 the first attempt to establish a relation between the loop current extension and deep flows in yucatan channel was made by maul et al 1985 it was unsuccessful probably because of the low spatial resolution of their observations from september 8 1999 to june 17 2000 eight moorings with acoustic doppler current profilers current meters and thermometers were deployed across the yucatan channel the data from these arrays were used to compute time series of the transports below the level of the deepest isotherm observed in the florida straits as required by a simple box model that restricts deep exchanges with the gulf of mexico to the yucatan channel the surface extension of the loop current was inferred from 3 day advanced very high resolution radiometer imagery from october to may when temperature gradients were sufficient to map the warm water unambiguously the deep transports appear at first unrelated to the rate of change of the loop current extension but filtering the series with a 20 day running mean increases the correlation between the low pass series to 0 62 and up to 0 83 with a lag of 8 5 days with loop current changes leading the deep flows the cumulative deep transport a quantity that favors lower frequencies is very well related correlations 0 9 to the surface extension of the loop current also with a lag of about a week these lags are not statistically significant but suggest a timescale for internal adjustment processes in the gulf of mexico the empirical orthogonal function of the current best related to the area extension of the loop current represents a unidirectional flow across the entire deep section flowing either toward or from the gulf of mexico and includes a strong expression of the yucatan undercurrent

a statistical description of the mean circulation and eddy variability in the northwestern atlantic using sofar floats abstract velocity data obtained from trajectories of sofar floats launched as part of several experiments carried out in the northwest atlantic during the last two decades are used to give a statistical description of the mean gulf stream and its recirculation the distribution of eddy variability in the region is also presented a mean gulf stream which bifurcates between 55 and 45 w to feed the north atlantic current and a southern recirculation can be clearly identified a weak interior sverdrup flow is also suggested the spatial distribution of eddy variability is consistent with previous descriptions showing a maximum near the gulf stream

numerical modeling of subsurface release and fate of benzene and toluene in coastal aquifers subjected to tides abstract a numerical study was undertaken to investigate subsurface release and fate of benzene and toluene in a tidally influenced beach the simulations were conducted by using a numerical model biomarun which coupled a multi monod kinetic model biob to a density dependent variably saturated groundwater flow model marun the fate and transport of the contaminant plume were characterized by computing its centroid trajectory spreading area and percentage of biodegradation in beach saturated and unsaturated zone respectively key factors likely affecting this process were investigated including tide amplitude capillarity and hydraulic conductivity it was found that aerobic biodegradation was the major fate of the contaminant plume in the beach tidal action twisted the centroid of the contaminant plume during its migration in the beach which increased the residence time of the plume in the beach high tidal range significantly altered the spatial distribution of the contaminant biodegradation in the beach in contrast the capillary fringe had impacts on the percentage of benzene biodegraded in the saturated and unsaturated zone of the beach the increase in capillary fringe enhanced the percentage of the contaminant biodegraded in the unsaturated zone up to 40 which is comparable to that in the saturated zone hydraulic conductivity seemed to have large impacts on the biodegradation rate of the contaminant in the beach higher hydraulic conductivity induced faster contaminant biodegradation in the beach

convection in groundwater below an evaporating salt lake 2 evolution of fingers or plumes the downward convection of salt fingers or plumes developed from the unstable boundary layer of an evaporating dry salt lake is examined using a numerical model and hele shaw cell experiments in the convecting layer the early small waves evolve into fingerlike or plumelike formations the number of fingers or plumes decreasing with time owing to differential growth and or coalescence comparison of intermediate formational stages of this pattern with the pattern generated by a two dimensional numerical simulation shows good qualitative agreement however there is a significant mismatch of the growth rates at long times in the computer simulation the plume length develops approximately twice as rapidly as it does in the experimental case a simple numerical experiment independent of the salt lake boundary conditions is compared to previously published laboratory scale measures of plume development in hele shaw cells which confirms the retardation of hele shaw plumes by a factor of approximately 50 this departure is attributed to the differences in dimensionality between the hele shaw flow domain and the model domain the data indicated that leading plumes develop isolated behavior at long times and may not be adequately represented in hele shaw analog models and numerical simulation provides a more accurate simulation of field scale behavior

errors in the anisotropy of magnetic susceptibility and magnetic remanence of unconsolidated sediments produced by sampling methods samples from glacial varves were obtained by cutting cubes and by pushing plastic cubical containers into the sediment the anisotropy of magnetic susceptibility results show that the mean angular difference in the kmax direction can be altered by 32 by pushing in the sample containers in a north to south versus an east to west direction the values of lineation and q are raised or lowered dependent upon the direction of push and the original fabric direction mean remanence directions can deviate by as much as 43 in a single clay layer dependent upon the direction in which the sample containers are inserted into the sediment corresponding changes in mean intensity of the remanence also demonstrate that the remanence has been affected by pushing in sample containers the overall results underline the need to adopt trustworthy procedures for the sampling of soft sediments deposited by settling and traction

an analysis of loop current frontal eddies in a atlantic ocean model simulation abstractthe loop current frontal eddies lcfes refer to cyclonic cold eddies moving downstream along the outside edge of the loop current in the eastern gulf of mexico they have been observed by in situ measurements and satellite imagery mostly downstream of the campeche bank continental shelf their evolution simulated by a primitive equation and 37 level atlantic ocean general circulation numerical model is described in detail in this study some of the simulated lcfes arise with the passage through the yucatan channel of a caribbean anticyclonic eddy as weak cyclones with diameters less than 100 km near the yucatan channel they then grow to fully developed eddies with diameters on the order of 150 200 km while moving along the loop current edge modeled lcfes have a very coherent vertical structure with isotherm doming seen from 50 to 1000 m depth the caribbean anticyclone and lcfe are two predominant features in this numerical model simulation which account for 22 and 10 respectively

variations of the gulf stream s north wall east of cape hatteras abstract twelve years 1977 1988 of noaa infrared imagery data were used to study the variations of the north wall displacements of the gulf stream east of cape hatteras i e between 74 w and 65 w the variations of the north wall displacements were compared with the variations in the straits of florida transport which was estimated using a multifrequency model based on the sea level differences between siboney cuba and key west florida for the period 1977 1988 and with transport measurements based on the submarine cable between jupiter florida and settlement point in the bahamas for the period 1982 1988 the north wall reached a maximum northward position in 1985 when the cable data indicated that the straits of florida transport was a maximum the north wall reached a maximum southward position in 1981 cable data were not available before 1982 but the available data suggested that there may have been a minimum transport in 1981 a weak annual cycle of the north wall was found with a maximum northward position in the fall and a maximum southward position in the spring no relationship was found between the annual cycle of the gulf stream s north wall and the annual cycle of the straits of florida transport

numerical modeling of water flow below dry salt lakes effect of capillarity and viscosity abstract we investigate numerically the effects of capillarity and viscosity on density dependent flows below dry salt lakes the numerical model marun boufadel m c suidan m t venosa a d 1999a a numerical model for density and viscosity dependent flows in two dimensional variably saturated media j contam hydrol 37 1 20 is used to assess the combined and separate effects of capillarity and concentration engendered viscosity on the groundwater dynamics of a two dimensional system simulating a dry lake we found that accounting for concentration engendered viscosity effects under saturated water flow conditions gives totally different groundwater dynamics from the case where these effects are neglected however concentration dependent viscosity effects were minor when unsaturated water flow conditions were present under variably saturated flow conditions capillarity effects gave totally different hydraulics in the porous domain from the saturated flow case upwelling regions observed under saturated flow conditions were downwelling when capillarity effects were present a mesh orientation study revealed that density dependent flows were susceptible to the orientation of the diagonals of the triangular elements a discussion on the accuracy and the efficiency of the marun model in the context of density and viscosity dependent flows in two dimensional variably saturated media is also provided

location and dynamics of the antarctic polar front from satellite sea surface temperature data the location of the antarctic polar front pf was mapped over a 7 year period 1987 1993 within images of satellite derived sea surface temperature the mean path of the pf is strongly steered by the topographic features of the southern ocean the topography places vorticity constraints on the dynamics of the pf that strongly affect spatial and temporal variability over the deep ocean basins the surface expression of the pf is weakened and the pf meanders over a wide latitudinal range near large topographic features width and temperature change across the front increase and large scale meandering is inhibited elevated mesoscale variability is seen within and downstream of these areas and may be the result of baroclinic instabilities initiated where the pf encounters large topographic features the strong correlations between topography and pf dynamics can be understood in the context of the planetary potential vorticity ppv or f h field mean ppv at the pf varies by more than a factor of 2 along its circumpolar path however at the mesoscale the pf remains within a relatively narrow range of ppv values around the local mean away from large topographic features the pf returns to a preferred ppv value of 25 10 9 m 1 s 1 despite large latitudinal shifts the mean paths of the surface and subsurface expressions of the pf are closely coupled over much of the southern ocean

the effect of the new england seamounts on gulf stream meandering as observed from satellite ir imagery abstract it is commonly held belief that meandering of the gulf stream increases dramatically downstream of the new england seamount chain in fact this appears not to be the case the envelope of gulf stream northern edges derived from 30 months of satellite data remains constant from 65 to 58 w only the mean of the integrated path length normalized by the mean path length appears to increase downstream of the seamounts but at very nearly the same rate as upstream of them

prediction of the gulf stream path from upstream parameters a linear wiener least squares optimal filter is used to predict the path of the gulf stream in the region between cape hatteras and 70 w using upstream inlet conditions as filter inputs although position angle curvature geostrophic velocity and curvature vorticity measured at 73 w were tested as multiple inlet parameters it was found that inlet position alone was the best predictor with inlet position as the predictor this filter is equivalent to propagating meanders downstream with a typical phase speed and growth rate forecasts of the downstream path position are produced more accurate than persistence 12 days in advance at 140 km from the inlet 24 days in advance at 240 km from the inlet and 28 days in advance at 340 km from the inlet

frequency of ring separations from the loop current in the gulf of mexico a revised estimate the most energetic events in the circulation of the gulf of mexico are the separation of large anticyclonic rings from the loop current building on previous work the authors examine all the apparent rings since july 1973 this new dataset includes the satellite altimetry since 1992 providing a set of 34 consecutive ring formations the primary advantage of altimetry is that the data remain available in the summer one finding is that the ambiguity of whether or not a ring has separated is reduced but not eliminated the uncertainty with which separation events can be specified remains approximately 4 weeks even with nearly continuous data primary peaks in the distribution of separation intervals are found at 6 and 11 months with a smaller peak at 9 months if the spectrum is smoothed heavily enough a peak in the distribution can be formed nearer 12 months but this near annual peak is a result more of the smoothing than of the data

climatology of ocean features in the gulf of mexico using satellite remote sensing data a climatology of various ocean features in the gulf of mexico gom was developed using the combination of satellite remote sensing and in situ data that spanned periods as long as 32 years twelve separate statistics were created some of which described characteristics of the loop current while others are involved with warm core rings that separate from the loop current and cold core rings these statistics examined the frequency with which the loop current was found in the gom the orientation of the loop current the frequency of intrusion of loop current water onto the west florida shelf and into the gom common water region ring separation period from the loop current ring dissipation ring speed ring path frequency of ring water in the western gom and the frequency of warm and cold core rings wcrs and ccrs respectively in the gom the results indicate that ccrs were principally responsible for mass and heat redistribution in the eastern gom egom and wcrs are responsible for mass and heat redistribution in the western gom wgom the average period for wcr separation from the loop current was 11 months and the range from 5 to 19 months wcrs moved through the wgom most often using the central path i e their trajectory was found between 24 and 26 n latitude and they decreased to about 55 of their initial size when they reach the western wall of the gom ccrs were most often found in the egom and their frequency of occurrence in the egom surpassed that of wcrs anywhere in the gom

convection in groundwater below an evaporating salt lake 1 onset of instability convective groundwater motion can be generated in aquifers beneath and adjacent to saline lakes such motions strongly control the subsurface distribution of salts the formation of saline minerals and the distribution of contaminants that may be disposed of in the saline lake in particular schemes to use saline lakes as evaporation basins for irrigation waste waters must consider the groundwater dynamics associated with convection the convection is driven by the evaporative concentration of salts at the land surface leading to an unstable distribution of density however the evaporative groundwater discharge can dynamically stabilize this saline boundary layer and inhibit convection in this work we investigate the nature and onset of convection for a range of boundary conditions typically found in saline lakes processes involved in the accumulation of salt at the surface of a groundwater discharge zone and in the gravitational instability of the near surface groundwater are considered results of theoretical stability analysis are applied through laboratory and numerical experimentation to the more complex geometries typically found in the field these comparisons indicate that for large saline lakes the stability of the saline boundary layer can be parameterized by traditional rayleigh criteria in which the aquifer permeability and the evaporation rate from the lake bed are principal controlling factors for typical saline lake environments convection will dominate in sediments whose permeability exceeds approximately 10 14 m2 below this threshold permeability the boundary layer should be stabilized by the evaporative flux resulting in the accumulation of salts and evaporites at the land surface these results provide insight into the predictive behavior of groundwater dynamics and solute distributions in many natural systems

western boundary currents and frontal air sea interaction gulf stream and kuroshio extension abstract in the northern hemisphere midlatitude western boundary current wbc systems there is a complex interaction between dynamics and thermodynamics and between atmosphere and ocean their potential contribution to the climate system motivated major parallel field programs in both the north pacific kuroshio extension system study kess and the north atlantic climate variability and predictability clivar mode water dynamics experiment climode and preliminary observations and analyses from these programs highlight that complexity the gulf stream gs in the north atlantic and the kuroshio extension ke in the north pacific have broad similarities as subtropical gyre wbcs but they also have significant differences which affect the regional air sea exchange processes and their larger scale interactions the 15 yr satellite altimeter data record which provides a rich source of information is combined here with the longer historical record from in situ data to describe and compare the curr

the climatology of the north atlantic abstract data from approximately 144 000 hydrographic stations in the north atlantic have been retrieved from the national oceanic data centre and analysed to produce maps of mean pressure temperature salinity and oxygen on selected potential density surfaces for the domain bounded by 0 85 w and 0 65 n the data span the period from 1904 to 1990 with the majority of the data from the last four decades the data set for this region is 60 larger than that used in the production of levitus climatological world atlas this increase in stations coupled with smoothing scales specific to the north atlantic rather than the global ocean considerably improves the resolution of the basin s features the mean property fields and their associated standard deviations are resolved on a one degree grid with little smoothing contrasting with the levitus atlas where properties although presented on a one degree grid have been smoothed on the order of 1000km another important feature of this database is the process by which irregularly spaced data are averaged onto a regular grid in a significant departure from the levitus analysis which averaged on depth surfaces these data were averaged on potential density surfaces thus eliminating an artificial mixing of water mass properties the database is used to describe the baroclinicity of well known features such as the gulf stream the north atlantic current and the deep western boundary current and to elucidate the recirculations associated with these currents it additionally resolves several new features in the intermediate and deep north atlantic these features include the signature of a large scale deep recirculation that extends southwestward from the eastward extension of the north atlantic current to the separation point of the gulf stream near cape hatteras this recirculation which spans approximately 2000m of the water column encompasses more local recirculations and potentially mixes subpolar and subtropical waters furthermore in the upper thermocline this database reveals a coherent azores current that stretches from the gulf stream system south of the tail of the grand banks to madeira this flow is marked by divergences to the south and convergences from the north such that its downstream transport is not much changed

a model study of the vertically integrated transport variability through the yucatan channel role of loop current evolution and flow compensation around cuba 1 in the paper a model study of the vertically integrated transport variability through the yucatan channel role of loop current evolution and flow compensation around cuba by lin et al journal of geophysical research 114 c08003 doi 10 1029 2008jc005199 2009 in the last sentence of paragraph 31 the word westward in drives enhanced westward should be eastward

a method of sampling clast rich laminated diamictons for magnetic analyses the sampling of nonlithified diamictons for magnetic analyses anisotropy of magnetic susceptibility and paleomagnetic remanence has been restricted to samples that are either massive clay rich sediments or fine grained ones with very low pebble contents a new method was developed that produced standard sized 2 2 2 cm cubes of sediment from a laminated clay poor diamicton from southern denmark the sampling procedure did not affect the sample or its magnetic characteristics in any observable manner

on the meridional surface profile of the gulf stream at 55 w nine month records from nine inverted echo sounders iess are analyzed to describe the mean baroclinic gulf stream at 55 w ies acoustic travel times are converted to thermocline depth which is optimally interpolated kinematic and dynamic parameters gulf stream meridional position velocity and vorticity are calculated primary gulf stream variability is attributed to meandering and changes in direction a mean stream coordinate relative to gulf stream instantaneous position and direction meridional profile is derived and compared with results presented by other investigators the mean velocity is estimated at 0 84 m s 1 directed 14 to the right of eastward and the thermocline 12 c drops 657 m north to south corresponding to a baroclinic rise of the surface of 0 87 m the effect of gulf stream curvature on temporal mean profiles is found to be unimportant and of minimal importance overall the derived downstream current profile is well represented by a gaussian function and is about 190 km wide where it crosses zero surface baroclinic transport is estimated to be 8 5 104 m2 s 1 and maximum shear flanking the maximum is 1 2 10 5 s 1 results compare well with other in situ observational results from the same time period on the other hand analyses by others of concurrent satellite altimetry geosat suggest a considerably narrower more intense mean gulf stream

numerical modeling of water flow and salt transport in bare saline soil subjected to evaporation summary a numerical study based on a density dependent variably saturated groundwater flow model marun was conducted to investigate subsurface flow and salt transport in bare saline aquifers subjected to evaporation which was simulated using the bulk aerodynamic formulation as evaporation was assumed to depend on the pore moisture the evaporation flux evolved gradually causing a gradual increase in the pore salinity this is in contrast to prior studies where the high salinity was imposed instantaneously on the ground surface key factors likely affecting subsurface hydrodynamics were investigated including saturated hydraulic conductivity capillary drive relative humidity in the air and surrounding groundwater replenishment the simulations showed two temporal regimes where the first consists of rapid evaporation for a duration of hours followed by slow evaporation until evaporation ceases in the absence of surrounding groundwater replenishment evaporation induced density gradient generated an upward water flow initially and then the flow decreased at which time a high density salt finger formed and propagated downwards capillary properties and atmospheric condition had significant impacts on subsurface moisture distribution and salt migration in response to the evaporation the results also suggested that the presence of subsurface water replenishment to the evaporation zone tended to produce a steady evaporation rate at the ground surface

gulf stream surface transport and statistics at 69 w from the geosat altimeter geosat altimeter height measurements for the gulf stream for three subtracks from the exact repeat mission were processed to remove the geoid and mean gulf stream height a gaussian model for the gulf stream velocity profile was used to predict the form of the residual height profiles seen by geosat and the mean height profile using estimates of the width and position derived from the height residuals estimates of the maximum surface velocity and the surface transport were obtained by a least squares fit of the synthetic height profiles to the data location statistics from the geosat data were in good agreement with values obtained from infrared images of the gulf stream maximum surface velocities were typically between 1 2 and 2 0 m s 1 the time series showed that surface transport is correlated primarily with the magnitude of the surface velocities although an anomalously large increase in surface transport in the winter of 1987 1988 was caused by an increase in the width of the gulf stream an analysis of the average annual signal in transport showed maximum values in the late fall and minimum transport in the late spring maximum minimum surface transport generally occurred when the gulf stream was north south of its mean position

magnetic and pebble fabrics of glaciomarine diamictons in the champlain sea ontario canada glaciomarine diamicton ite s that contain articulated unbroken shell remains are usually assumed to have been deposited by the settling out of suspended mud with additions of coarse clasts derived

salt freshwater dynamics in a subterranean estuary over a spring neap tidal cycle this paper presents field measurements and numerical simulations of pore water salinities and groundwater flow in the intertidal zone of an unconfined coastal aquifer over a spring neap tidal cycle the study provides insight into the extent and time scales of mixing between fresh groundwater and recirculating seawater in a tidally influenced subterranean estuary salt freshwater dynamics in subterranean estuaries are currently not well understood despite their potentially important implications for fluxes of chemicals to coastal waters via submarine groundwater discharge the data and simulation results show that changes in the tidal shoreline excursion over the spring neap cycle induce significant variations in the intertidal salinity structure observed higher frequency salinity fluctuations demonstrate further the intensity and complexity of the salt freshwater mixing process in contrast with the salinity variations fresh groundwater was found to discharge around a distinct intertidal beach slope break throughout the spring neap period this suggests that the slope break may affect significantly groundwater flow and salt transport near the shore measurements of ph and dissolved oxygen distributions revealed important biogeochemical zonations in the system these zonations are expected to strongly influence the fate of many reactive chemicals in the nearshore aquifer and their subsequent discharge to coastal waters

on the recent destabilization of the gulf stream path downstream of cape hatteras mapped satellite altimetry reveals interannual variability in the position of initiation of gulf stream meanders downstream of cape hatteras the longitude where the gulf stream begins meandering varies by 1500 km there has been a general trend for the destabilization point to shift west and 5 of the last 6 years had a gulf stream destabilization point upstream of the new england seamounts independent in situ data suggest that this shift has increased both upper ocean deep ocean interaction events at line w and open ocean shelf interactions across the middle atlantic bight mab shelf break mooring data and along track altimetry indicate a recent increase in the number of deep cyclones that stir deep western boundary current waters from the mab slope into the deep interior temperature profiles from the oleander program suggest that recent enhanced warming of the mab shelf may be related to shifts in the gulf stream s destabilization point

the surface circulation of the caribbean sea and the gulf of mexico as inferred from satellite altimetry the surface circulation of the caribbean sea and gulf of mexico is studied using 13 years of satellite altimetry data variability in the caribbean sea is evident over several time scales at the annual scale sea surface height ssh varies mainly by a seasonal steric effect interannually a longer cycle affects the ssh slope across the current and hence the intensity of the caribbean current this cycle is found to be related to changes in the wind intensity the wind stress curl and el nino southern oscillation at shorter time scales eddies and meanders are observed in the caribbean current and their propagation speed is explained by baroclinic instabilities under the combined effect of vertical shear and the b effect then the loop current lc is considered focusing on the anticyclonic eddies shed by it and the intrusion of the lc into the gulf of mexico through time twelve of the 21 anticyclonic eddies observed to detach from the lc are shed from july to september suggesting a seasonality in the timing of these events also a relation is found between the intrusion of the lc into the gulf of mexico and the size of the eddies shed from it larger intrusions trigger smaller eddies a series of extreme lc intrusions into the gulf of mexico when the lc is observed as far as 928w are described the analyses herein suggest that the frequency of such events has increased in recent years with only one event occurring in 1993 versus three from 2002 to 2006 transport through the straits of florida appears to decrease during these extreme intrusions

eddy energy and shelf interactions in the gulf of mexico sea surface height anomaly data from satellite are continuously available for the entire gulf of mexico surface current velocities derived from these remotely sensed data are compared with surface velocities from drifting buoys the comparison shows that satellite altimetry does an excellent job resolving gulf eddies over the shelf rise depths between 200 and 2000 m if the proper length scale is used correlations between altimeter and drifter derived velocities are statistically significant r 0 5 when the surface slope is computed over 125 km indicating that remotely sensed sea surface height anomaly data can be used to aid the understanding of circulation over the shelf rise velocity variance over the shelf rise from the altimetry data shows regions of pronounced eddy energy south of the mississippi outflow south of the texas louisiana shelf and in the northwest and northeast corners of the gulf these are the same locations where surface drifters are most likely to cross the shelf rise suggesting gulf eddies promote cross shore flows this is clearly exemplified with both warm and cold eddies finally the contribution of gulf eddies and wind stress to changes in the mean circulation are compared results indicate that the eddy generated vorticity flux to the mean flow is greater than the contribution from the surface wind stress curl especially in the region of the loop current and along the shelf rise base in the western gulf future modeling efforts must not neglect the role of eddies in driving gulf circulation over the shelf rise

gulf stream transport and mixing processes via coherent structure dynamics the gulf stream has been characterized as either a barrier or blender to fluid transfer a duality relevant to gyre scale climate adjustment however previous characterization depended on relatively sparse lagrangian in situ observations the finite time lyapunov exponent ftle is calculated from satellite altimetry to identify lagrangian coherent structures lcs in the gulf stream region these lcs provide dense sampling of flow and capture distinct regions associated with mixing independent observations of ocean color contain similar flow dependent structures providing verification of the method and highlighting transport and mixing processes that influence sea surface temperature and chlorophyll among other water properties diagnosed lcs support the existing bower kinematic model of the gulf stream but also highlight novel behavior of comparable importance these include vortex pinch off and formation of spiral eddies clearly identified by lcs and which may be explained by considering changes to flow topology and the dynamics of shear flow instability at both small and large rossby number such processes seen though lcs may further enable validation of climate models the spatial distribution of these intermittent processes is characterized in terms of the criticality of jet dynamics with respect to rossby wave propagation and whether the jet is in an unstable or wave maker regime the generation and connectivity of hyperbolic trajectories in the flow appears to play an important role in governing large scale transport and mixing across the gulf stream

hydrodynamics in a gravel beach and its impact on the exxon valdez oil 1 this paper investigated the interaction of groundwater and seawater in a tidally influenced gravel beach field observations of water table pore water salinity were performed the two dimensional finite element model marun was used to simulate observed water table and salinity based on field observations and model calibrations a two layered beach structure was identified which is characterized by a high permeability surface layer underlain by a low permeability lower layer the salt wedge seaward of the low tide line was almost invariant in comparison with the strong fluctuations of the salinity plume in the surface layer of the intertidal zone the presence of the two layers prevented the presence of a freshwater discharge tube between the upper saline plume and salt wedge this is in contrast with the previous works where freshwater discharge tube was observed the tide induced submarine groundwater discharge sgd was estimated at 9 m3 d 1 m 1 a large value that is probably due to the large tidal range of 4 8 m and the very permeable surface layer the freshwater seawater dynamics revealed here may provide new insights into the complexity intensity and time scales of mixing between fresh groundwater and seawater in tidal beaches the simulated water table of the beach was higher than the interface between the surface layer and the lower layer which prevented exxon valdez oil from penetrating into the lower layer in 1989

observations on the long period variability of the gulf stream downstream of cape hatteras to examine the long period variability of the gulf stream sea level residuals relative to a 2 year mean sea level in the gulf stream downstream of cape hatteras between 75 w and 60 w longitude are used residuals as derived from geosat altimetry between november 1986 and december 1988 were gridded in space and time at a temporal resolution of 10 days and spatial resolution of 1 4 complex empirical orthogonal function ceof analysis was applied to the data set to extract the spatially correlated signal with the original data sub sampled to 1 2 in addition to determining the space time scales and propagation characteristics of the different modes wavenumber frequency spectral techniques were used to separate the variability into propagating and stationary components the ceof technique applied to the data set indicated that the first four ceof modes accounted for 60 of the variability and were found to be above the noise level 99 of the time ceof 1 was associated with westward propagation at 5 km d at a wavelength of 2000 km and eastward propagation at 1 2 km d centered at a 500 km wavelength this first ceof is in good agreement with thin jet equivalent barotropic models which predict westward propagation for wavelengths greater than 1130 km a deflection of the wavelike pattern at 65 w also indicates a possible topographic effect a simple scaling of the effect of topography indicates that for length scales longer than the internal rossby radius of deformation the topographic term is at least of the same order of magnitude as the beta effect the second ceof was more broadbanded in wavenumber space with eastward propagation occurring in a wavenumber frequency band between 300 and 1400 km and 0 5 and 2 0 cycles yr the third ceof is similar in structure to the first but with less energy ceof 4 was clearly identifiable with higher frequencies than the first three with westward propagation at 4 km d the spatial location of this mode along with the westward propagation indicates possible influences from eddy stream interactions thus topography rossby wave dynamics and eddy stream interactions all appear to have a significant role in determining the space time scales and propagation properties of the long period response of sea level in the gulf stream

the relationship between variations in the gulf of mexico loop current and straits of florida volume transport abstract twelve years of monthly mean positions of the northern boundary of the loop current in the eastern gulf of mexico from satellite and in situ data have been compared with coincident 1977 1988 estimates of volume transport in the straits of florida in the subseasonal frequency band 15 1 to 5 1 cycles per month volume transport estimated from cuba minus florida sea level difference in this frequency band accounts for 69 of the variance in volume transport estimated from the florida grand bahama island submarine cable on average the loop current has a dominant period of 11 months whereas the volume transport is dominated by annual spectral energy little significant coherence squared occurs between them the maximum northward penetration of the loop current occurs on average in winter when the volume transport is a minimum but this is an artifact of the sampling epoch this negative relationship is most pronounced for 1979 1981 when transport is characterized as unimodal but for 1984 1985 and 1

a comparison of surface eddy kinetic energy and reynolds stresses in the gulf stream and the kuroshio current systems from merged topex poseidon and ers 1 2 altimetric data analyses of surface eddy kinetic energy eke inferred from 5 years of merged topex poseidon and ers 1 2 altimetric data are presented in the gulf stream gs and the kuroshio ks current systems focusing on anisotropy and eke seasonal interannual and long term variations as well as reynolds stresses for both gs and ks a descriptive analysis of the eke field shows that it is anisotropic along the path of the currents and assesses the close relationship between the spatial distribution of eke high levels and bottom topography a striking ocean feature is found in the gs shaped as a zonal double blade structure in the eke field centered at 37 n 71 5 w that likely corresponds to a regular and permanent lateral displacement of the mean path of the current at this geographical location maps of eke seasonal means for years 1993 1996 and 1997 provide a detailed description of the surface variability meanders pinched off eddies etc and show strong interannual variations in the ks eke monthly mean changes in the ks reveal a well marked seasonal cycle during the first 3 years 1993 1995 with eke peaking in july august this is followed by a constant increase of its level from the beginning of year 1996 till the beginning of 1997 during this increase the zonal velocity variance u 2 is up to 30 higher than its meridional counterpart suggesting a zonal acceleration of the eastward flow eke seasonal changes are also found in the ks current 30 35 n 130 140 e and also show a regular annual cycle during the first 3 years which precedes by 2 months the eke seasonal cycle in the ks extension maximum in may june the maximum in eke in both regions precedes by 2 months the maximum surface transport found by qiu et al 1991 and zlotnicki 1991 occurring in july and late september respectively no such annual cycle is found in the gs region during the first 3 years year 1996 is anomalous in both current systems with mean eke level that increases by more than 20 compared to the other years also eke monthly mean changes in the ks reveal a well marked positive tendency in the eastern part of the current of more than 300 cm2 s 2 yr 1 and a negative tendency both in its eastern part and in the ks current this feature is absent from the gs at last eddy mean flow interaction is presented both the spatial averaging of turbulent quantities and the relative contribution of the different terms of the horizontal momentum fluxes are discussed a tentative explanation is given for the anomalously large u 2 at the end of 1996 in the ks extension

late holocene variability in florida current surface density patterns and possible causes 1 planktonic foraminiferal 18o time series from three well dated high sedimentation rate cores near the florida keys 24 4 n 83 3 w exhibit repeated centennial to millennial scale oscillations during the late holocene isotopic shifts of 0 2 0 3 over the past 5200 years represent changes in sea surface temperature sst of 1 0 1 5 c or salinity variability of 1 2 psu the largest significant isotopic events are centered at approximately 200 2000 3200 and prior to 4000 calendar years bp high florida current 18o during the little ice age lia correlates with published records of high 18o in the sargasso sea and low sst off the coast of west africa an interval of generally low 18o in the florida straits from 1800 to 500 years bp is synchronous with the medieval warm period off west africa but leads low 18o in the sargasso sea by several hundred years synchronous cooling across the subtropical gyre during the lia is difficult to explain using interannual north atlantic oscillation patterns but may be consistent with the simulated effects of reduced solar irradiance at frequencies between 1 1000 and 1 300 years during the late holocene florida current 18o is coherent with a published estimate of 14c production rate radiocarbon production seems to lead 18o at these frequencies but uncertainty in the phase calculation precludes a clear lead lag relationship at frequencies lower than 1 300 years florida current 18o is coherent and in phase with atmospheric 14c the coherence of 14c and 18o at periods 1000 years implies oceanic circulation may play a role in modulating atmospheric radiocarbon on millennial timescales

analysis of flow variability in the yucatan channel 1 the structure and variability of the velocity and temperature fields in yucatan channel are analyzed using data from an eight mooring array deployed from august 1999 to june 2000 the area averaged kinetic energy and transport fluctuations spectra show that the extrema of these quantities do not coincide and that flow variability is dominated by highly energetic processes with weak transport contributions transport fluctuations peak in the 20 40 and 5 10 day period bands but show no clear correlation with the local wind stress forcing empirical orthogonal function eof analysis of the along channel velocity component shows that approximately 55 of the total velocity variance is retained in the first two eofs which depict tripolar the center of the channel is out of phase with the sides and dipolar structures a multivariate complex eof analysis of low passed temperature and velocity components suggests the tripole dipole structures are the components of irregular oscillations of the flow related to the northwestward propagation of anticyclones and cyclones through the channel the weak transport signal in these modes is consistent with the eddies being advected by the mean flow in contrast to other western boundary current regions the passage of eddies provides the predominant explanation for the variability in the yucatan channel however the processes controlling transport variability remain unclear

sea surface topographic variability near the new england seamounts an intercomparison among in situ observations numerical simulations and geosat altimetry from the regional energetics experiment intercomparisons are made among three sets of results for two regions of the gulf stream upstream and downstream of the new england seamount chain nesc observational records from 12 inverted echo sounders with pressure gauges ies pgs concurrent geosat altimeter crossover point differences and results from a primitive equation model of the region standard deviations of sea surface topography show generally good agreement for the three data sources no significant difference between the upstream and downstream regions is observed in the actual data ies pg records and geosat topographic variability have values of about 30 cm on both sides of the nesc although model results show a discrepancy in the eastern region barotropic fluctuations account for about 30 of the total surface topographic variability and are only partially correlated with baroclinic fluctuations

saltwater freshwater mixing dynamics in a sandy beach aquifer over tidal spring neap and seasonal cycles the biogeochemical reactivity of sandy beach aquifers is closely linked to physical flow and solute transport processes thus a clearer understanding of the hydrodynamics in the intertidal zone is needed to accurately estimate chemical fluxes to the marine environment a field and numerical modeling study was conducted over a 1 year timeframe to investigate the combined effects of tidal stage spring neap variability in tidal amplitude and seasonal inland water table oscillations on intertidal salinity and flow dynamics within a tide dominated microtidal sandy beach aquifer measured and simulated salinities revealed an intertidal saline circulation cell with a structure and cross sectional mixing zone area that varied over tidal spring neap and seasonal time scales the size of the circulation cell and area of the mixing zone were shown for the first time to be most affected by seasonal water table oscillations followed by tidal amplitude and tidal stage the intertidal circulation cell expanded horizontally and vertically as the inland water table declined displacing the fresh discharge zone and lower interface seaward over monthly spring neap cycles the center of the circulation cell shifted from beneath the backshore and upper beachface to the base of the beach salinity variations in the intertidal zone over semidiurnal tidal cycles were minimal the dynamics of the circulation cell were similar in simulations with and without a berm the highly transient nature of intertidal salinity over multiple time scales may have important implications for the types and rates of chemical transformations that occur in groundwater prior to discharge to the ocean

gulf stream path analysis near the new england seamounts as part of the naval ocean research and development activity s regional energetics experiment 12 inverted echo sounders iess were deployed from june 1985 to july 1986 in two arrays across the historical mean path of the gulf stream near 67 w and 58 w slightly upstream and downstream of the new england seamount chain gulf stream positions and directions were computed at half day intervals for adjacent ies pairs levels of variability at the two array locations were similar but the characteristics of the meanders in terms of propagation and current direction were quite different evidence was found for a quasi stationary meander near 58 w features deduced from ies measurements are compared with concurrent infrared air dropped expendable bathythermograph and geosat altimetry observations

energetics of eddy mean flow interactions in the gulf stream region a detailed energetics analysis of the gulf stream gs and associated eddies is performed using a highresolution multidecadal regional ocean model simulation the energy equations for the time mean and timevaryingflowsarederivedasatheoreticalframeworkfortheanalysis theeddy meanflowenergycomponents and their conversions show complex spatial distributions in the along coast region the cross stream and cross bump variations are seen in the eddy mean flow energy conversions whereas in the off coast region a mixed positive negative conversion pattern is observed the local variations of the eddy mean flow interaction are influenced by the varying bottom topography when considering the domain averaged energetics theeddy meanflowinteractionshowssignificantalong streamvariability upstreamofcapehatteras the energy is mainly transferred from the mean flow to the eddy field through barotropic and baroclinic instabilities upon separating from the coast the gs becomes highly unstable and both energy conversions intensify when the gs flows into the off coast region an inverse conversion from the eddy field to the mean flow dominates the power transfer for the entire gs region the mean current is intrinsically unstable and transfers 28 26gw of kinetic energy and 26 80gw of available potential energy to the eddy field the mesoscaleeddykineticenergyisgeneratedbymixedbarotropicandbaroclinicinstabilities contributing28 26 and 9 15gw respectively beyond directly supplying the barotropic pathway mean kinetic energy also provides 11 55gw of power to mean available potential energy and subsequently facilitates the baroclinic instability pathway

gulf stream path and thermocline structure near 74 w and 68 w the synoptic ocean prediction synop experiment had the goal of providing a physical understanding of energetic mesoscale eddy processes in the gulf stream in the synop inlet array off cape hatteras and in the central array near 68 w modred observations were collected from october 1987 through august 1990 the inlet array measured the surface path and bottom currents where the gulf stream leaves the continental margin to enter the deep water regime small amplitude propagating and growing meanders characterized the variability there the central array measured velocity and temperature as a proxy for density at four levels in the water column as well as the upper and deep level streamfunctions all with mesoscale resolution near 70 w the path envelope exhibited a relative node confined within a 40 km band 55 of the time near 68 w the path envelope was over 3 times as wide due to several elongated steep meander troughs and relatively steep meander crests the crests typically propagated downstream without much growth the troughs often stalled near 68 w steepened and persisted for one to several months two cases evolved into s shaped paths and subsequently formed rings even the time averaged fields showed a small trough in the mean path and thermocline structure whereas meanders of 20 to 60 day periods had similar spectral levels throughout 70 67 w meanders with long periods 85 day accounted for the local minimum in variance at 70 w bottom pressure and velocity observations revealed repeated periods of intense swirl speeds 0 30 m s 1 abyssal eddies the time averaged deep currents exhibited a mean cyclone centered 30 km offshore and downstream of the upper layer mean trough the cross stream slope of the thermocline steepened linearly with path curvature consistent with gradient wind balance structures are illustrated in the mapped fields consistent with baroclinic instability wherein troughs steepen and rings form

high frequency variability of western boundary currents using ers 1 three day repeat altimeter data ers 1 three day repeat altimeter ocean products have been analyzed from september 3 to december 9 1991 in the high mesoscale energy areas of the world ocean the obtained height variability is comparable to that derived from 2 years of geosat altimeter data 17 day repeat while it is slightly lower elsewhere the data reveal some high frequency variability of western boundary currents but not the seasonal signals nor the low frequency mesoscale signal which dominates elsewhere isocorrelation maps show that the e folding time is around 10 to 15 days in strong currents the sea height variance integrated over all wavelengths in the frequency wavenumber spectrum corresponds to less than 5 of the total 3 month variance for periods shorter than 20 days up to 15 of this variance for periods shorter than 34 days which are respectively the nyquist frequencies of the topex poseidon and geosat data this signal covers a whole range of wavelengths that cannot be obtained from current meter data in the gulf stream area the total dynamic height signal is estimated by adding a climatological dynamic topography to the mesoscale variability near 60 w the height variations apparently correspond to meanders with periods of 30 to 40 days and latitudinal extension about 200 km they are consistent with westward propagation at about 10 cm s and their surface transport varies by about 50 on this timescale which is in agreement with in situ observations

tide induced groundwater level fluctuation in coastal aquifers bounded by l shaped coastlines 1 this paper presents an analytical solution to describe tidal groundwater level fluctuations in an aquifer bounded by two water land boundaries that form a right angle the aquifer configuration can represent the situation of a right angle corner in an island when the tidal boundaries are the same along both boundaries or the estuary situation if the amplitude damps with distance along one boundary river and the amplitude along the other boundary sea does not change spatially the two dimensional flow equation subject to periodic boundary conditions is changed into a time independent elliptic problem using complex transform the elliptic problem is then solved using the green s function method li et al 2000 obtained a nonperiodic solution to the same problem with an additional hypothetical initial condition their solution includes a time dependent integral the solution presented here is a significant improvement over theirs in the sense that the solution is periodic and computationally efficient since the integral involved is independent of time an approximate solution without integral is also derived an error analysis and a case study in hong kong demonstrate that the approximate solution is adequate for most field problems index terms 1829 hydrology groundwater hydrology 1832 hydrology groundwater transport 1899 hydrology general or miscellaneous 3384 meteorology and atmospheric dynamics waves and tides keywords periodic groundwater flow analytical solution coastal aquifer sea tide l shaped coastline

origin and magnetic fabric of glacial varves nottawasaga river ontario canada an examination of the glacial varved clays that crop out in the banks of the nottawasaga river ontario shows that both the silt and clay layers are composed of sublaminae an analysis of the magnetic fabric and remanent magnetization of the varves shows that the current directions are the same for the clay and silt layers and that the magnetic fabric in the clay layer was not influenced by the earth s magnetic field this indicates that bottom currents were active during the winter period and were of sufficient strength to align the particles of magnetite parallel to the current directions this conclusion is not unique to the nottawasaga varves but serves to illustrate that the conceptual model of glacial varve deposition requires modification

stochastic dynamics of sea surface height variability sea surface height anomalies measured by the ocean topography experiment topex poseidon satellite altimeter indicate high values of skewness and kurtosis except in a few regions including the gulf stream the kuroshio extension and the agulhas retroflection that display bimodal patterns of sea surface height variability kurtosis is uniformly greater than 1 5 times the squared skewness minus an adjustment constant this relationship differs substantially from what standard gaussian or double exponential noise would produce however it can be explained by a simple theory in which the noise is assumed to be multiplicative meaning that a larger background state implies larger random noise elements the existence of multiplicative noise can be anticipated from the equations of motion if ocean dynamics are split into a slowly decorrelating deterministic component and a rapidly decorrelating contribution that is approximated as noise such a model raises the possibility of predicting the probabilities of extreme sea surface height anomalies from first physical principles and may provide a useful null hypothesis for non gaussian sea surface height variability

five year climatological survey of the gulf stream system and its associated rings a 5 year climatological survey of the gulf stream system s landward surface edge defines the mean standard deviation extreme limits annual and interannual variabilities and frequency distributions along 0 5 longitudinal transects from 91 to 44 w the climatology covers the loop current in the gulf of mexico and the gulf stream in the northwest atlantic ocean autocorrelations and power spectra are derived for longitudinal transects between 79 5 and 57 5 w the study also investigates the observed warm core ring and cold core ring movements and their areal extent the observed data are compiled from the oceanographic analysis charts produced by the national oceanic and atmospheric administration which utilize infrared satellite imagery and in situ observations east of cape hatteras the gulf stream system landward surface edge exhibits both interannual and annual signals the interannual variability is equal to the annual variability the mean monthly gulf stream position for the longitudinal band 70 44 w shifts from farthest north in september to farthest south in february the magnitude of the annual shift is largest near the grand banks frequency distributions of the gulf stream system position are quasi normal nearly everywhere autocorrelation plots from the 5 year time series of gulf stream positions at longitudinal transects 79 5 57 5 w exhibit three well defined e folding time regimes with a maximum time of 10 weeks at 72 w power spectrums from 79 5 to 57 5 w are red spectrums having dominant peaks of 1 year period or greater the largest total spectra energies are found at 61 w the loop current sheds rings at two apparent spatial scales which are labeled major 307 km mean and minor 185 km mean warm core rings annually the loop current sheds about one major warm core ring which translates into the western basin of the gulf of mexico and one minor warm core ring which is usually reabsorbed by the loop current the major loop current warm core ring sheddings have no seasonal preference loop current warm core rings have a mean velocity of 2 4 km d west southwest an average of 22 gulf stream warm core rings are formed and absorbed annually between 75 and 44 w the largest frequency of warm core ring formations is seen near the new england seamounts while the largest frequency of warm core ring absorptions is found near cape hatteras gulf stream warm core rings can absorb each other as occurred in 14 of the absorption cases with the highest frequency just upstream of the new england seamounts the gulf stream warm core rings have a surface diameter decay rate of 0 026 per week loop current warm core rings are similar the gulf stream warm core rings have a mean velocity of 2 4 km d west southwest cold core rings have a mean cool core surface diameter of 105 km and a mean velocity of 1 km d southwest more definitive conclusions on cold core rings are not possible as ring identification and tracking by satellite infrared imagery is tentative

effects of wave forcing on a subterranean estuary wave and tide are important forcing factors that typically co exist in coastal environments a numerical study was conducted to investigate individual and combined effects of these forces on flow and mixing processes in a near shore subterranean estuary a hydrodynamic model based on the shallow water equations was used to simulate dynamic sea level oscillations driven by wave and tide the oscillating sea levels determined the seaward boundary condition of the coastal aquifer where variably saturated variable density flow was modeled the simulation results showed that waves induced an onshore upward tilt in the phase averaged sea level wave set up the resulting hydraulic gradient generated pore water circulations in the near shore zone of the coastal aquifer which led to formation of an upper saline plume usp similar to that due to tides however mixing of recirculating seawater in the usp with underlying fresh groundwater was less intensive under the high frequency wave oscillations in the case of combined forcing wave induced circulations coupled with the intra tidal flows strengthened the averaged circulating pore water flows in the near shore zone over the tidal period the circulating flows increased exchange between the subterranean estuary and ocean contributing 61 of the total submarine groundwater discharge for the simulated condition in comparison with the 40 and 49 proportions caused by the same but separate tidal and wave forcing respectively the combined forces also created a more extensive usp with the freshwater discharge zone shifted further seaward the freshwater flow paths in the intertidal subterranean estuary were altered with a significant increase of associated transit times the interplay of wave and tide led to increased mixing between discharging fresh groundwater and recirculating seawater these results demonstrated the complexity of near shore groundwater systems and have implications for future investigations on the fate of land sourced chemicals in the subterranean estuary prior to discharge to the ocean

variability in the slope water and its relation to the gulf stream path 1 sea surface temperature sst and sea surface height ssh data for 1993 2007 for the north atlantic are combined with hydrographic data at 69w to investigate the relation between the gulf stream gs position and the slope water properties sst anomalies north of the gs are correlated with changes in its path the lag of this correlation is such that positive temperature anomalies precede northward shifts of the gs and suggests that sst anomalies move westward with speeds of several cm s eof analysis of the sst and ssh fields shows that cooling and strengthening of the sw flow are in phase over the slope water which is mirrored in the vertical structure of these fields at 69w indicating larger transports in the deep western boundary current lead to southward shifts of the mean gs path this relation between the slope water and the gs path provides some predictability for the latter