structure of the upper ocean in the western equatorial pacific the western equatorial pacific has an important role in the el nino southern oscillation climate cycle1 2 and sea surface temperature anomalies in this area are known to affect the global atmospheric circulation3 little is known however about the factors that control the response of the upper ocean and hence sea surface temperature to changes in atmospheric conditions here we present observations of the density and current structure of the upper layers of the western equatorial pacific ocean we observed frontal features with temperature differences of 1 c extending from the surface down to a depth of 150 m a strong salinity front associated with a surface convergence and interleaving of high and low salinity waters in 10 m thick layers that extended for several hundred kilometres in the north south direction the large spatial and temporal variability in temperature and salinity observed must influence heat transport and hence the ocean response to atmospheric forcing in particular the response to westerly wind bursts which are thought to be precursors to an el nino we estimate the horizontal diffusion coefficient of the interleaving which indicates that the observed layering may con tribute to horizontal mixing within the thermocline

radar imaging mechanism of marine sand waves at very low grazing angle illumination caused by unique hydrodynamic interactions 1 the investigations carried out between 2002 and 2004 during six field experiments within the operational radar and optical mapping in monitoring hydrodynamic morphodynamic and environmental parameters for coastal management oroma project aimed to improve the effectiveness of new remote sensing monitoring technologies such as shipborne imaging radars in coastal waters the coastal monitoring radar of the gkss research center geesthacht germany is based on a kelvin hughes rsr 1000 x band 9 42 ghz vertical vv polarized river radar and was mounted on board the research vessel ludwig prandtl during the experiments in the lister tief a tidal inlet of the german bight in the north sea the important progress realized in this investigation is the availability of calibrated x band radar data another central point of the study is to demonstrate the applicability of the quasi specular scattering theory in combination with the weak hydrodynamic interaction theory for the radar imaging mechanism of the seabed radar data have been taken at very low grazing angles 2 6 of flood and ebb tide oriented sand wave signatures at the sea surface during ebb tidal current phases current speeds perpendicular to the sand wave crest 0 6 m s 1 have been measured at wind speeds 4 5 m s 1 and water depths 25 m the difference between the maximum measured and simulated normalized radar cross section nrcs modulation of the ebb tide oriented sand wave is 27 for the flood tide oriented sand wave a difference of 21 has been calculated the difference between the minimum measured and simulated nrcs modulation of the ebb tide oriented sand wave is 10 and for the flood tide oriented sand wave a value of 43 has been derived phases of measured and simulated nrcs modulations correspond to asymmetric sand wave slopes the results of the simulated nrcs modulation show the qualitative trend but do not always quantitatively match the measured nrcs modulation profiles because the quasi specular scattering theory at very low grazing angle is a first order theory

impact of eastern arctic shelf waters on the nansen basin intermediate layers the eurasian shelves supply water to the nansen basin intermediate layers in two ways as buoyancy driven plumes of dense winter water and as permanent inflow of the barents sea branch of atlantic water while the plumes are local and seasonal phenomena the barents sea flow is part of the large scale circulation both interact with atlantic water which enters the arctic ocean through fram strait and moves as a subsurface boundary current eastward along the continental slope during the polarstern cruise ark ix 4 in summer 1993 the fram strait branch was observed as a narrow core within tens of kilometers of the barents sea shelf edge here several patches of cold low salinity water spread across the slope down to about 500 m depth their origin is assumed to be the northern barents sea they mix with the warm saline fram strait branch water fsbw so that the core properties of the latter become modified downstream in the eastern nansen basin the fram strait branch is displaced toward the inner basin by inflow of the barents sea branch of atlantic water bsbw this inflow appears as a broad 200 km wedge extending from 200 to 1300 m depth bsbw is colder and less saline than water of the fram strait branch and it is less dense and less stratified than the ambient water both branches appear to undergo vigorous mixing while spreading eastward so that any eastward continuation of the boundary flow transports about 50 bsbw and 50 fsbw above 600 m and about 80 bsbw and 20 fsbw below that level toward the canadian basin according to available observations the barents and kara seas are the only source areas for shelf waters ventilating the nansen basin below the halocline and these waters constitute a freshwater input rather than a salt input winter shelf water from the laptev sea cannot contribute to layers deeper than the upper halocline

growth and steady state stages of thermohaline intrusions in the arctic ocean thermohaline intrusions are a widespread feature of the arctic ocean pycnocline and may be important for the lateral transport of heat salt and other tracers in an attempt to understand the dynamics of the intrusions we present an analysis of hydrographic observations of a front north of svalbard following intrusions from profile to profile we find that they slope upward toward the cold fresh side of the front however their slope is less than that of the background isopycnals so that the intrusions slope between horizontal and isopycnal surfaces in the wedge of baroclinic instability our analysis proceeds in two stages first to determine what might have caused the initial growth of the intrusions we compare the observed intrusion properties with predictions of an instability theory the results suggest that the intrusions developed as a form of double diffusive interleaving with fluxes dominated by salt fingering and additional forcing by baroclinicity second to investigate the observed finite amplitude interleaving we apply a steady state model to the observations a key result is that diffusive convection not salt fingering must be the dominant form of double diffusion in order to reach steady state this fundamental change in dynamics is discussed in the context of adjustment from the growth stage to an eventual steady state

driving forces of interleaving in the baroclinic front at the equator abstract the different types of instability in the equatorial plane approximation are analyzed by means of a 2d linear stability problem the double diffusive dd and diffusive baroclinic 2d baroclinic and mcintyre instabilities are shown not to develop if contours of the mean salinity density have a parabolic symmetrical relative to the equator shape using modeling results an illustrative scheme of equatorial undercurrent euc regions where different types of instability can develop is presented and subsequently applied to understand the driving forces of the intrusions observed in a closed spaced ctd section located between the equator and 1 n long coherence intrusions are situated within two isopycnal layers aligned to 25 layer 1 and 26 3 layer 2 t where the vertical shear is low it was shown from the model that the layer 1 intrusions being observed in the midlayer of the euc where the mean horizontal gradient of salinity is approximately constant are likely generated by a combined e

radar imaging mechanism of the seabed results of the c star experiment in 1996 with special emphasis on the relaxation rate of short waves due to current variations abstract during the field experiment of the coastal sediment transport assessment using sar imagery project of the marine science and technology program of the european commission an air sea interaction drift buoy asib system was equipped with special sensors and instruments to measure the position the water depth the surface current velocity and direction the modulation characteristics of short wave energies and relevant air sea interaction parameters due to undulations in the seabed the asib system was operated from on board a research vessel and the data were measured while the buoy drifted in the tidal currents across sand waves of the study area all buoy measurements were analyzed by computing frequency spectra of low and high frequency waves scalar spectra between 0 1 and 50 hz the whole range of short water waves was recorded by these in situ measurements on board the buoy which is responsible for the backscattering of commonly used air and spaceborne imaging radars a comprehensive da

evidence for warming of atlantic water in the southern canadian basin of the arctic ocean results from the larsen 93 expedition potential temperature and salinity s data obtained along the perimeter of the southern canadian basin north of the east siberian sea in 1993 aboard the ccgs henry larsen show higher temperatures in waters of atlantic origin than in available climatological data for the canadian basin in particular a front is observed near the mendeleyev ridge which separates the cooler atlantic waters of the canada basin from the warmer atlantic waters observed in the makarov basin the front is further characterized by a change in the s slope of arctic thermocline water and by thermohaline intrusions and s reversals within the atlantic layer the idea that this warm variety of atlantic water has come recently from the eurasian basin is supported by its higher level of the tracer cfc 11

the arctic and subarctic ocean flux of potential vorticity and the arctic ocean circulation according to observations the arctic ocean circulation beneath a shallow thermocline can be schematized by cyclonic rim currents along shelves and over ridges in each deep basin the circulation is also believed to be cyclonic this circulation pattern has been used as an important benchmark for validating arctic ocean models however modeling this grand circulation pattern with some of the most sophisticated ocean ice models has been often difficult the most puzzling and thus perhaps the most interesting finding from the arctic ocean model intercomparison project aomip an international consortium that runs 14 arctic ocean models by using the identical forcing fields is that its model results can be grouped into two nearly exact opposite patterns while some models produce cyclonic circulation patterns similar to observations others do the opposite this study examines what could be possibly responsible for such strange inconsistency it is found here that the flux of potential vorticity pv from the subarctic oceans strongly controls the circulation directions for a semienclosed basin like the arctic the pv integral over the whole basin yields a balance between the net lateral pv inflow and the pv dissipation along the boundary when an isopycnal layer receives a net positive pv through inflow outflow the circulation becomes cyclonic so that friction can generate a flux of negative pv to satisfy the integral balance for simplicity a barotropic ocean model is used in this paper but its application to the 3d models will be discussed in the first set of experiments the model with a realistic arctic bathymetry is forced by observed inflows and outflows in this case there is a net positive pv inflow to the basin due to the fact that inflow layer is thinner than that of outflow the model produces a circulation field that is remarkably similar to the one from observations in the second experiment the model bathymetry at fram strait is modified so that the same inflows and outflows of water masses lead to a net negative pv flux into the arctic the circulation is reversed and becomes nearly the opposite of the first experiment in the third experime nt the net pv flux is made to be zero by modifying again the sill depth at fram strait the circulation becomes two gyres a cyclonic one in the eurasian basin and an anticyclonic one in the canada basin to elucidate the control of the pv integral a second set of model experiments is conducted by using an idealized arctic bathymetry so that the pv dynamics can be better explained without the complication of rough topography the results from five additional experiments that used the idealized topography will be discussed while the model used in this study is one layer the same pv integral constraint can be applied to any isopycnal layer in a threedimensional model variables that affect the pv fluxes to this density layer at any inflow outflow channel such as layer thickness and water volume flux can affect the circulation pattern the relevance to 3d models is discussed in this paper

characteristics of interleaving in the western equatorial pacific 1 the characteristics of intrusive thermohaline features in the thermocline of the western equatorial pacific are examined during two different climatic states the vertical and meridional structure of the features is determined from a total of 12 high resolution meridional sections although there is considerable variability of the broader structure of the flow and temperature salinity fields the spatial scale of the interleaving is found to be persistent over all sections the turner angle and correlations between the spice anomaly and density anomaly suggest that double diffusive processes may be important in the vertical flux of properties the characteristics of the interleaving are compared with the results from the theories of double diffusive interleaving and inertial instability it is found that the observations are consistent with both it is difficult to differentiate between the two theories in explaining the presence of the layers indeed both mechanisms may be playing a role the magnitude of the cross equatorial fluxes of heat and salt due to the features is estimated and shown to be comparable with estimates due to other processes there is a strong potential for the interleaving to impinge on the large scale dynamics of the equatorial pacific ocean

mixing in the west spitsbergen current abstract twenty eight profiles of temperature and salinity down to 1 km depth have been measured in the area north from the coast of svalbard to latitude 84 40 n between 0 and 32 e longitude they show atlantic waters of the west spitsbergen current entering the arctic ocean in a bifilimentary mode one filament following the coastline and the other 300 km farther north apparently following the continental shelf break the profiles show these filaments mixing into the ambient water in a series of intrusive layers which are remarkably uniform over distances of hundreds of kilometers a triple peak structure at the atlantic water maximum is the dominant oceanographic characteristic of the area with salt fingering occurring on the upper surface of the cold intrusions and indications of double diffusive exchanges through the lower surface a system or eddies or meanders is postulated as the mechanism for the production of multiple fronts allowing the intrusive layers to extend to distances much greater t

mapping submarine sand waves with multiband imaging radar 2 experimental results and model comparison on august 16 1989 and on july 12 1991 experiments were performed to study the mapping of submarine sand waves with the airborne imaging radar a polarimetric and in 1991 interferometric airborne p l and c band synthetic aperture radar system the experiments took place in an area 30 km off the coast of the netherlands where the bottom topography is dominated by sand waves with a height between 2 and 6 m and a crest to crest distance of about 400 m at an average depth of 22 m ground measurements were recorded on a nearby platform and on a ship in the test area which also acted as a position fix on august 16 1989 the wind was 5 m s directed toward the northeast while the surface current velocity was around 0 5 m s directed toward the southwest one overflight was made with the flight direction parallel to the sand wave crests and the radar looking upwind at p band the sand waves are clearly visible as dark bands as predicted by theory while at l band the sand waves show up as sawtooth shaped modulations on july 12 1991 wind and surface current had the same opposite directions as in 1989 though the wind was much higher 10 m s three flights were made with the radar pointing upwind cross wind and downwind the upwind and downwind images are very similar despite the high wind speed the sand waves are clearly visible as sawtooth shaped modulations at p band and vaguely visible at l band at c band only wind streaks can be seen all cross wind images show the sand waves as dark bands now with the highest modulations at c band the wind streaks that dominated the upwind and downwind images at c band are much less pronounced in the cross wind images the images are compared with predictions from a new model of the imaging mechanism which includes contribution to the radar cross section of waves moving both from and to the radar wave blocking or wave reflection is treated in an approximate manner for the radar looking upwind or downwind the predicted modulations at p and l band agree well with the observations while those at c band are too high for the radar looking cross wind the model severely underestimates the modulations it is questioned whether a local relaxation source term can describe such a situation the interferogram shows some structure caused by bottom induced surface current variations

the structure and driving mechanisms of the baltic intrusions abstract data from closely spaced ctd profiling performed in the eastern gotland basin after the 1993 inflow event are used to study thermohaline intrusions in the baltic sea two ctd cross sections display abundant intrusive layers in the permanent halocline despite the overwhelming dominance of the salinity stratification diffusive convection is shown to work in the baltic halocline enhancing diapycnical mixing to understand the driving mechanisms of observed intrusions these are divided into different types depending on their structural features only two types of observed intrusions are suggested to be strongly influenced by diffusive convection 1 relatively thin 3 5 m and long up to 8 km intrusions inherent to high baroclinicity regions and 2 relatively thick 10 m and short 2 5 km intrusions inherent to low baroclinicity regions to verify this hypothesis the linear stability models of 3d and 2d double diffusive interleaving in approximation of a finite width front were used it is sh

is interleaving in the agulhas current driven by near inertial velocity perturbations abstract recent observations taken at a number of latitudes in the agulhas current reveal that the water mass structure on either side of its dynamical core is distinctly different moreover interleaving of these distinct water masses is observed at over 80 of the stations occupied in the current particularly within the subsurface density layer between tropical surface water and subtropical surface water masses and within the intermediate layer between the antarctic intermediate water and red sea water masses direct velocity measurements allow for a comparison between the characteristic vertical length scales of the agulhas intrusions and those of velocity perturbations found throughout the current it is found that the interleaving scales match those of the velocity perturbations which are manifest as high wavenumber vertical shear layers and are identified as near inertial oscillations furthermore the properties of the intrusions indicate that double diffusion is not an important process in thei

long term variability of arctic ocean waters evidence from a reanalysis of the ewg data set 1 we have examined interannual to decadal variability of water properties in the arctic ocean using an enhanced version of the 1948 1993 data released earlier under the gore chernomyrdin environmental bilateral agreement that earlier data set utilized gridded fields with decadal time resolution whereas we have developed a data set with annual resolution we find that beginning about 1976 most of the upper arctic ocean became significantly saltier possibly related to thinning of the arctic ice cover there are also indications that a more local upper ocean salinity increase in the eurasian basin about 1989 may not have originated on the shelf as had been suggested earlier in addition to the now well established warming of the atlantic layer during the early 1990s there was a similar cyclonically propagating warm event during the 1950s more remarkable however was a pervasive atlantic layer warming throughout most of the arctic ocean from 1964 1969 possibly related to reduced vertical heat loss associated with increased upper ocean stratification a cold period prevailed during most of the 1970s and 1980s with several very cold events appearing to originate near the kara and laptev shelves finally we find that the silicate maximum in the central arctic ocean halocline eroded abruptly in the mid 1980s demonstrating that the redistribution of pacific waters and the warming of the atlantic layer reported from other observations during the 1990s were distinct events separated in time by perhaps 5 years we have made the entire data set publicly available

observational and laboratory insights into salt finger convection improving observational capabilities in the ocean are revealing a substantial body of evidence that the double diffusive instability known as salt fingers is widely present and plays a significant role in oceanic mixing this evidence includes unique fine and microstructure features in particular regions and distinct patterns in the temperature and salinity variations over large areas laboratory experiments have also advanced our understanding of salt fingers the insights gleaned from both laboratory and ocean are reviewed and related to large scale ocean structure and climate modeling

modulation of radar backscatter from the ocean by a variable surface current abstract calculations of surface wave and radar cross section modulation induced by a spatially varying surface current have been compared with field measurements made with sar x and l bands real aperture radar x band laser slope guage and ccd video camera during the joint canada u s ocean wave investigation project jowip which took place in august 1983 the comparison reveals that i many existing wind relaxation models underpredict the hydrodynamic effect of the current ii simple bragg scattering model underpredicts radar backscatter modulation for higher frequency radars e g x band but appears acceptable at lower radar frequencies e g l band iii the discrepancy between measurements and calculations at high radar frequency is reduced but not eliminated when the effects of long surface waves have been accounted for keywords include radar backscatter surface wave modulations wave current interactions georgia strait experiment and jowip

effect of baroclinicity on double diffusive interleaving although ocean fronts are often baroclinic existing models of double diffusive interleaving have ignored such baroclinic effects as velocity shear and horizontal density gradients to determine the importance of these effects the authors have formulated a linear instability analysis applicable to baroclinic fronts two limiting cases are considered one for fronts with strong vertical and or horizontal shear the other for fronts with weak shear in both limits double diffusive interleaving can be enhanced or suppressed by baroclinicity interleaving motion is enhanced if isopycnals rise toward the fresh side of the front conversely interleaving is suppressed if isopycnals slope downward across the front a significant result is that the salinity gradient along isopycnals is not a good indicator of interleaving strength as an example the model is applied to a mediterranean salt lens the effect of baroclinicity is significant the predicted growth rates are increased by 35 90 the large scale velocity and hydrographic fields indicate that meddy sharon lies somewhere between the high and low shear limits nevertheless the model predictions agree reasonably well with the observed interleaving characteristics

an equivalent barotropic mode in the fine resolution antarctic model abstract both the 6 year time mean flow and the eddy kinetic energy in the fine resolution antarctic model are found to be approximately self similar in the vertical with the velocity showing a rapid decay with depth a simple argument is given as to why this would be expected to occur in this and other numerical models and an analysis is given as to the degree of steering of the mean flow by topography

water masses and circulation in the eurasian basin results from the oden 91 expedition the oden 91 north pole expedition obtained oceanographic measurements on four sections in the nansen and amundsen basins of the eurasian basin and in the makarov basin of the canadian basin thereby proving the feasibility of carrying out a typical oceanographic program using an icebreaker in the arctic ocean the data show greater spatial variability in water structure and circulation than was apparent from previous data the results show that a clear front exists between the eurasian and canadian basins such that upper halocline water in the canadian basin is almost absent from the eurasian basin the lower halocline water produced in the barents kara sea region permeates much of the eurasian basin and flows along the continental slope into the canadian basin the deeper circulation is strongly influenced by topography three return flows of the atlantic layer are identified one over the nansen gakkel ridge one over the lomonosov ridge and a third flowing from the canadian basin the slight differences observed in salinity and temperature characteristics of the deeper waters of the nansen and amundsen basins do not lead to an obvious explanation of their origin or flow pattern

physical and geochemical properties across the atlantic pacific water mass front in the southern canadian basin temperature salinity nutrients oxygen and halocarbon data collected in the arctic ocean reveal a frontal structure previously unrecognized in the hydrography of the canadian basin samples were collected on a 1300 km section extending from the beaufort sea in the canada basin to the east siberian sea in the makarov basin these data collected in 1993 aboard the ccgs henry larsen reveal a lateral boundary between water masses of atlantic and pacific origin the term water mass assembly is introduced to describe the basic arrangement or vertical stacking of water masses found in the arctic ocean recognizing that water mass components within each assembly may differ from basin to basin using historical data two primary water mass assemblies are defined each consisting of three layers an upper layer an atlantic layer and a deep layer these two assemblies are marked by important differences one assembly here defined as the western arctic wa assembly is characterized by an upper layer of relatively fresh high nutrient water of pacific origin below this by an atlantic layer with a core temperature generally below 0 5 c and finally by a deep layer of higher salinities and colder temperatures about 0 5 c than found in the overlying atlantic layer the second assembly here defined as eastern arctic ea assembly is characterized by the absence of pacific water in the upper layer below this by an atlantic layer core as warm as 2 to 3 c and by a colder about 0 9 c deep layer because the presence or absence of pacific origin water is a key characteristic distinguishing the two assemblies we will refer to the water mass boundary between the two assemblies as the atlantic pacific front earlier research indicated that water masses in the arctic ocean were separated by a front above the lomonosov ridge into the canadian and eurasian basins although all larsen 93 stations from the canada basin a1 d1 display classic wa assembly characteristics the makarov basin station e1 shows ea assembly characteristics in the upper and atlantic layers and a wa assembly deep layer this suggests a relocation in the position of the atlantic pacific boundary away from the lomonosov ridge further larsen 93 data show the transition region between the atlantic and deep layers is fresher in the makarov basin than corresponding water in either the canada or eurasian basins implying a source of cold low salinity water perhaps from the laptev and east siberian shelves the front separating these two assemblies lies above the mendeleyev ridge and is marked by large lateral gradients in all measured properties in particular the penetration of anthropogenic halocarbons is 2 to 3 times deeper in the makarov basin than in the canada basin implying enhanced rates of ventilation this suggests that direct exchange between the canadian and eurasian basins has occurred recently near the perimeter and that physical and chemical properties including contaminants may have been transported by boundary currents more quickly from one basin to the other

radar imaging of submarine sand waves in tidal channels the simple theoretical model of alpers and hennings describing the radar imaging of submarine bottom topography in coastal waters with strong unidirectional tidal currents is analytically extended to show the influence of advection the theory applies for l band radar where second order terms in the hydrodynamic interaction can be neglected as a first approximation if future imaging radars from satellites and space platforms as the ers i first european remote sensing satellite the jers i first japanese earth remote sensing satellite and the eos earth observing system are to be used for cartographic applications it is necessary to include the effect of advection to improve accuracy this extension of the model simulates the position of the radar cross section modulation relative to coastal geomorphological bedforms by application of that theory it is possible to map features such as the crests of sandbanks and sand waves

pacific ventilation of the arctic ocean s lower halocline by upwelling and diapycnal mixing over the continental margin 1 pacific winter waters a major source of nutrients and buoyancy to the arctic ocean are thought to ventilate the arctic s lower halocline either by injection isopycnal or penetrative of cold saline shelf waters or by cooling and freshening atlantic waters upwelled onto the shelf although ventilation at salinity s 34 psu has previously been attributed to hypersaline polynya waters temperature salinity nutrient and tracer data suggest instead that much of the western arctic s lower halocline is in fact influenced by a diapycnal mixing of pacific winter waters with s 33 1 psu and denser eastern arctic halocline atlantic waters the mixing taking place possibly over the northern chukchi shelf slope estimates from observational data confirm that sufficient quantities of atlantic water may be upwelled to mix with the inflowing pacific waters with volumes implying the halocline over the chukchi borderland region may be renewed on timescales of order a year

changes in temperature and tracer distributions within the arctic ocean results from the 1994 arctic ocean section abstract major changes in temperature and tracer properties within the arctic ocean are evident in a comparison of data obtained during the 1994 arctic ocean section to earlier measurements 1 anomalously warm and well ventilated waters are now found in the nansen amundsen and makarov basins with the largest temperature differences as much as 1 c in the core of the atlantic layer 200 400 m thus thermohaline transition appears to follow from two distinct mechanisms narrow order 100 km topographically steered cyclonic flows that rapidly carry new water around the perimeters of the basins and multiple intrusions 40 60 m thick which extend laterally into the basin interiors 2 altered nutrient distributions that within the halocline distinguish water masses of pacific and atlantic origins likewise point to a basin wide redistribution of properties 3 distributions of cfcs associated with inflows from adjacent shelf regions and from the atlantic demonstrate recent ventilation to depths exceeding 1800 m 4 concentrations of the pesticide hch in the surface and halocline layers are supersaturated with respect to present atmospheric concentrations and show that the ice capped arctic ocean is now a source to the global atmosphere of this contaminant 5 the radionuclide 129i is now widespread throughout the arctic ocean although the current level of 129i level poses no significant radiological threat its rapid arrival and wide distribution illustrate the speed and extent to which waterborne contaminants are dispersed within the arctic ocean on pathways along which other contaminants can travel from western european or russian sources

double diffusive interleaving part i linear stability analysis abstract quasi horizontal interleaving between water masses is frequently observed in the frontal regions between different water masses where there are significant compensating isopycnal gradients of temperature and salinity it is believed that these intrusions are driven by double diffusive convection which transports salt heat and density across sharp quasi horizontal interfaces i e across regions of large vertical property gradients stern and other investigators have parameterized the vertical flux of salt in these intrusions by an eddy diffusivity multiplied by the vertical gradient of salinity whereas laboratory experiments show that sharp interfaces tend to occur by double diffusive convection and that the vertical fluxes of properties depend on the property contrasts across the interfaces in this paper it is assumed that the vertical fluxes of double diffusive convection are proportional to the salinity contrast across the sharp interfaces that occur between the quasi horizontal intrusio

origin of thermohaline staircases hypotheses concerning the origin of thermohaline staircases in salt fingering regions are reviewed and assessed one such hypothesis that staircases arise from thermohaline intrusions is developed into a quantitative theory it is shown that growing intrusions evolve toward staircases when the background density ratio lies below a threshold value and nonlinear computations confirm that staircases are viable intrusion equilibria staircase properties such as step heights lateral density ratios and layer slopes lie closest to observed values when salt fingers are assumed not to contribute to shear stress and when turbulent mixing rates are smaller than usual thermocline values

a theory of the ka band radar imaging mechanism of a submerged wreck and associated bed forms in the southern north sea the ka band radar imaging mechanism of the submerged wreck sand ribbon of the motor vessel m v birkenfels in the southern north sea is investigated by applying the quasi specular scattering theory and considering the capillary as well as the gravity wave ranges of the wave energy density spectrum for the imaging of wrecks and other oceanographic and meteorological phenomena at the sea surface it is assumed that quasi specular scattering becomes dominant at higher radar frequencies like ka and x band and wind speeds 7 8 m s 1 multibeam echo sounder images of the birkenfels wreck and associated sand ribbons as well as other available environmental in situ data have been analyzed the formation of sand ribbons at the sea bed and the manifestation of its radar signatures at the water surface are caused by an elliptical vortex or helical flow cell triggered by unidirectional tidal current flow interacting with the wreck the difference between simulated and measured normalized radar cross section nrcs modulation as a function of the space variable is less than 31 6 results are presented for nrcs simulations dependent on position for different effective incidence angles unidirectional current speeds wind speeds and relaxation rates the calculated current gradient or strain rate of the imaging theory has the same order of magnitude as those obtained for marine sand waves this implies that the responsible hydrodynamic interaction mechanism is able to produce radar signatures of submerged wrecks sand ribbons and make them visible at the sea surface

renewal and circulation of intermediate waters in the canadian basin observed on the scicex 96 cruise during the summer of 1996 the nuclear submarine uss pogy occupied a line of stations extending through the middle of the canadian basin between about 88 n 44 w lomonosov ridge and about 78 n 144 w center of the canada basin ctd niskin bottle casts extending to 1600 m were carried out at eight stations providing the first high quality temperature salinity cfc tritium and 3he data obtained from this region although xctd data had previously been collected in this region these data along with data from stations at the basin boundary to the south and west reveal the presence of well ventilated intermediate water beneath the halocline in the center of the canada basin indicating renewal times of the order of 1 2 decades the least ventilated intermediate water was observed at the northern end of the canada basin along the southern flank of the alpha ridge intermediate water is derived from the atlantic ocean and enters the arctic ocean through fram strait and the barents sea it flows around the arctic basins in boundary currents and splits in the eastern amundsen basin with one branch crossing the lomonosov ridge and flowing along the east siberian continental slope and the other flowing along the eurasian flank of the lomonosov ridge from the 1996 scientific ice expedition scicex 96 observations we conclude that the branch that flows along the east siberian continental slope transports this water to the chukchi rise where it apparently enters the central canada basin with some flow continuing along the boundary to the southern canada basin the fram strait branch water mixes extensively with waters from the canadian basin during its transit along the east siberian continental slope being diluted by a factor of about 5 by the time it reaches the central canada basin the barents sea branch water does not undergo such extensive mixing and is diluted by a factor of only about 2 when it reaches the central canada basin

near inertial wave propagation in the western arctic abstract from october 1997 through october 1998 the surface heat budget of the arctic sheba ice camp drifted across the western arctic ocean from the central canada basin over the northwind ridge and across the chukchi cap during much of this period the velocity and shear fields in the upper ocean were monitored by doppler sonar near inertial internal waves are found to be the dominant contributors to the superinertial motion field typical rms velocities are 1 2 cm s 1 in this work the velocity and shear variances associated with upward and downward propagating wave groups are quantified patterns are detected in these variances that correlate with underlying seafloor depth these are explored with the objective of assessing the role that these extremely low energy near inertial waves play in the larger scale evolution of the canada basin the specific focus is the energy flux delivered to the slopes and shelves of the basin available for driving mixing at the ocean boundaries the energy and

the behavior of double diffusive intrusion in a rotating system the effects of earth s rotation on the stability of a thermohaline front of finite width are studied by means of a linear theory it is found that when the rotation is present two different types of unstable modes are possible when the front is narrow and a rossby radius of deformation based on ruddick and turner s 1979 vertical scale is large in comparison with the width of the front the fastest growing intrusion is nearly two dimensional nonrotational mode and its vertical scale is given by ruddick and turner s scale when the rossby radius becomes small in addition to the nonrotational mode there appears another unstable mode the rotational mode which has a smaller vertical wave number than the nonrotational mode with the introduction of rotation the fastest growing mode has nonzero along frontal wave number that is the intrusion becomes tilted in the along frontal direction when the rossby radius of deformation is sufficiently small in comparison with the width of the front transition from the nonrotational mode to the rotational one occurs the transition from nonrotational to rotational mode becomes less pronounced when the width of the front is increased for fixed horizontal density compensating gradients of temperature and salinity for a wide front the growth rate and vertical wave number for both modes becomes similar which agrees with the results of previous studies for infinite fronts that rotation does not modify the behavior of the intrusion except for the occurrence of along frontal tilt

mapping submarine sand waves with multiband imaging radar 1 model development and sensitivity analysis in 1989 and 1991 unexpected modulations caused by submarine sand waves were observed with the airborne imaging radar air a p l and c band synthetic aperture radar the measurements were performed in a sand wave area off the dutch coast the sand waves have an asymmetric sawtooth shaped profile with the steep slope oriented toward the northeast during the experiments wind and current had opposite directions the wind was directed toward the northeast and the current toward the southwest under these conditions existing models for the imaging mechanism predict that the modulation depth decreases with increasing radar frequency and that the steep slopes show up as dark lines in radar images the air images show a relation between modulation depth and radar frequency as predicted however only the p band image of 1989 shows the steep slopes of the sand waves as dark lines the p band image of 1991 and the l band images of 1989 and 1991 show a sawtooth shaped modulation which cannot be explained by existing theory a new model is developed that is one dimensional in position space and fully two dimensional in wavenumber space the radar cross section is calculated using both first order bragg and an integral equation scattering model in which the cross section originates from a spectral band rather than a single value the new model contains two improvements over previous ones first wave blocking or better wave reflection is included though in an approximate manner it is shown to be of importance at p band only second the contribution to the radar cross section from waves moving both to and from the radar is included whereas some previous models consider only one of these contributions this explains the observed modulations at least qualitatively under the assumptions that the angular distribution of short waves is almost constant and that waves moving against the wind have small relaxation rates

oligo miocene rotation of sardinia kar ages and paleomagnetic data of tertiary volcanics abstract conventional k ar dating was carried out on mineral separates mostly plagioclases from middle tertiary volcanics of sardinia along with paleomagnetic studies the close agreement of dates from the two methods establishes the rotation age of sardinia relative to europe within a rather short time span of 1 5 ma between 20 5 and 19 ma from correlation of our results with the geomagnetic time scale it is suggested that the rotation took place shortly after the magnetic anomaly 6

ocean sand ridge signatures in the bohai sea observed by satellite ocean color and synthetic aperture radar measurements abstract satellite measurements from synthetic aperture radar sar and the moderate resolution imaging spectroradiometer modis onboard the aqua platform are used to study the ocean sand ridges in the eastern bohai sea in china even though the imaging mechanisms for sar and modis aqua remote sensing are different the sand ridges are shown to have exactly the same patterns in images from both sensors therefore the location extension and coverage of the ocean sand ridges can be detected and cross examined by both sar and modis aqua observations satellite images show quite different sand ridge distribution pattern from the published bathymetry map based on in situ data that shows six sand ridges in the area 10 finger shaped sand ridges are identified from satellite observations the tidal current sand ridge interaction driven physical and optical changes are assessed and evaluated the existence of sand ridges causes enhanced water diffuse attenuation coefficient k d 490 and elevated normalized water leaving radiance at the red and near infrared nir wavelengths the sea surface over the sand ridges experiences significant seasonal variability of water turbidity and shows remarkable differences from nearby ocean regions during winter k d 490 values are about 2 3 m 1 over the ridges while the maximum k d 490 in the neighboring oceans is approximately 1 5 m 1 in summer the enhancement of the sea surface turbidity is less significant than that which occurs in winter

observed changes in arctic ocean temperature structure over the past half decade ocean temperature data obtained from the central arctic ocean during 1995 1999 show interannual changes in the temperature of the warm atlantic water core widespread warming continued from 1995 until 1998 but had ceased during 1998 1999 and was replaced by a slight cooling the timing of these changes differed regionally as the warming had occurred prior to 1995 in the nansen and amundsen basins and between 1995 to 1998 in the makarov basin the regional phase differences are consistent with advection along mid ocean ridges from the eurasian margin slope current which provides the source for warm atlantic water anomalous behaviors were associated with the arctic mid ocean and lomonosov ridges and probably reflected the presence of overlying topographically trapped circulations

aeromagnetic constraints on the geostructural interpretation of the southern part of the sardinian rift italy abstract aeromagnetic data are interpreted to better understand the relationship between the southern part of the oligo miocene rift and the plio quaternary campidano graben on sardinia particular reference is made to the geostructural location of the campidano graben the aeromagnetic data have been interpreted by applying three different methods to the original survey data spectral analysis analytical signal and werner deconvolution the results of this study give first order estimates of the depth of the magnetic basement and position of major dykes in the study area and on the efficiency of the inversion methods used

the canada basin 1989 1995 upstream events and far field effects of the barents sea 1 the effects of upstream events on southern canada basin waters were examined using physical and geochemical data collected at one location between 1989 and 1995 these events included atlantic layer warming relocation of the atlantic pacific water mass boundary and increased ventilation of boundary current waters early signals of change in the canada basin first appeared in 1993 along the continental margin and by 1995 were evident in the basin interior and farther downstream differences in physical and geochemical properties nutrients oxygen 129i and cfcs were observed between 150 and 1600 m of the water column by 1995 the boundary between pacific and atlantic origin water was shallower and atlantic origin water occupied more of the canada basin water column atlantic origin lower halocline water was colder and more ventilated fram strait branch water was colder fresher and more ventilated and barents sea branch water was warmer fresher more ventilated and occupied a larger volume of the water column than in previous years water mass analysis showed that the composition of atlantic origin water in the canada basin in 1995 included 20 more water from the barents sea two related events upstream appear to be the source of this change an atmospheric regime shift in 1989 that increased cyclonic circulation a transition unprecedented within the latter half of the 20th century in magnitude geographic reach and apparent oceanographic impacts and a large volume of dense water flowed from the barents sea to the arctic ocean between 1988 and 1989 these two phenomena illustrate the close relationship between atmospheric and oceanic events whose combined influence was evident 6 years later and 5100 km downstream in the canada basin at depths 1000 m

distribution of atlantic and pacific waters in the upper arctic ocean implications for circulation the atlantic and pacific oceans provide source waters for the arctic ocean that can be distinguished by their differing nitrate and phosphate concentration relationships using these relationships we estimate the amount of atlantic and pacific waters in the surface layer top 30 m of the arctic ocean atlantic source water is dominant in most of the eurasian basin and is present in significant amounts in the makarov basin north of the east siberian sea pacific source water is dominant in most of the canadian basin and is present in significant amounts in the amundsen basin north of greenland we deduce circulation patterns from the distributions of atlantic and pacific source waters in the surface layer of the arctic ocean and conclude that the flow within the surface layer differs from ice drift along the north american and european boundaries of the polar basin

dynamics of fingering convection part 1 small scale fluxes and large scale instabilities received and in revised form double diffusive instabilities are often invoked to explain enhanced transport in stablystratified fluids the most studied natural manifestation of this process fingering convection commonly occurs in the ocean s thermocline and typically increases diapycnal mixing by two orders of magnitude over molecular diffusion fingering convection is also often associated with structures on much larger scales such as thermohaline intrusions gravity waves and thermohaline staircases in this paper we present an exhaustive study of the phenomenon from small to large scales we perform the first three dimensional simulations of the process at realistic values of the heat and salt diffusivities and provide accurate estimates of the induced turbulent transport our results are consistent with oceanic field measurements of diapycnal mixing in fingering regions we then develop a generalized mean field theory to study the stability of fingering systems to large scale perturbations using our calculated turbulent fluxes to parameterize small scale transport the theory recovers the intrusive instability the collective instability and the instability as limiting cases we find that the fastest growing large scale mode depends sensitively on the ratio of the background gradients of temperature and salinity the density ratio while only intrusive modes exist at high density ratios the collective and instabilities dominate the system at the low density ratios where staircases are typically observed we conclude by discussing our findings in the context of staircase formation theory

a simple criterion for gyre formation by the surface outflow from a strait with application to the alboran sea a survey of relevant numerical laboratory and observational studies combined with our own laboratory experiments suggests that the surface outflow from a strait generally forms a gyre in the adjacent sea if the exit corner is sharp the gyre grows from an initial separation bubble of radius u f where u is the current speed and f the coriolis frequency the criterion for the maintenance of a coastal jet along a curved coast instead of separation and gyre formation seems to be that the rossby number u frw 1 1 with rw the radius of curvature of the exit corner so that the coriolis force can hold the current to the coast this synthesis disregards factors such as the variation of u across the current but applied to the flow through the strait of gibraltar into the alboran sea suggests that a gyre should always form as the exit corner is sharp we suggest though that the relevant curvature is that where the interface between the two layers intersects the seafloor rather than where the sea surface meets the coast if this is the case supercritical flow or some subcritical flows at the eastern end of the strait should still always lead to gyre formation but the observed replacement of the gyre by a coastal jet along the moroccan coast could be related to subcritical flow that is reduced below its normal value by a barotropic fluctuation or by changes in the interface depth in the mediterranean

intrusions what drives them abstract the driving mechanism for the observed interleaving of water masses is generally assumed to be double diffusive mixing however some observations of intrusions have been made in regions where the mean stratification is stable to double diffusive mixing it has been hypothesized that a finite amplitude disturbance must occur to produce regions where the stratification allows double diffusive mixing or that an instability due to differences in the molecular diffusivity of salinity and temperature produces the desired stratification for double diffusive mixing to start there is also the possibility of a differential vertical flux of salt and heat due to incomplete mixing by turbulence the basis of this idea is described in this paper growth rates vertical scales and cross frontal slopes of intrusions predicted by this process are compared to those predicted by double diffusive mixing

arctic warming evolution and spreading of the 1990s warm event in the nordic seas and the arctic ocean 1 observations in the arctic ocean revealed changes in oceanic temperature salinity and ice cover of the 1990s as compared with earlier data with a numerical model we favorably reproduce the development and subsequent propagation of temperature anomalies in water of atlantic origin in the 1980s and 1990s these propagated into the arctic ocean via the barents sea and the fram strait two warm anomalies entered the arctic ocean through these passages while the first smaller anomaly only warmed up the western eurasian basin the second large anomaly spread far into the eastern eurasian basin and across the lomonossov ridge into the western arctic basins intensified boundary currents during the high nao state in the first half of the 1990s significantly influenced the amplitude and speed of propagation of the temperature anomalies inside the arctic ocean in contrast to the notion of a continuous warming process during the 1990s our model results suggest the warming of the atlantic layer in the arctic ocean occurred in the form of events the event with the largest anomalous heat input during the modeled period entered the arctic between 1989 and 1994 it is possible to trace back the additional heat input into the arctic to an increased volume inflow via the faroer scotland passage and reduced heat loss to the atmosphere in the early 1990s after a weaker warm inflow in the second half of the 1990s the most recent observations and the model results point to a recurring warm anomaly in the inflow from 1999 onward

waters of the makarov and canada basins abstract hydrographic measurements from the 1994 arctic ocean section show how the makarov and canada basins of the arctic ocean are related and demonstrate their oceanographic connections to the eurasian basin the inflow into the makarov basin consists largely of well ventilated water within a broad band of densities from a boundary flow over the siberian end of the lomonosov ridge the boundary flow contains a significant component of dense shelf water likely originating in the barents kara and laptev seas earlier ice camp data show that the canada basin is relatively more isolated from this ventilation source in the canada basin shelf sources influenced by bering sea water appear to add cold waters with high silicate concentrations to the halocline and deeper in 1994 the halocline silicate maximum over the central makarov basin was absent evidence of the recent displacement of the upper s 33 1 halocline water from the chukchi east siberian sea region by water from the eurasian basin much of the makarov basin water in and below the halocline is in fact from the eurasian basin with admixture of waters from the canada basin suggested by their higher silicate concentrations mid depth eddies may transport anomalous properties into the central arctic and create property gradients or fronts in mid depth and deep waters the complex topography of the mendeleyev ridge chukchi plateau region also may assist spreading of water from the boundary into the interior atlantic layer characteristics in 1994 differed from previous general depictions in particular the core temperatures at the chukchi mendeleyev boundary were at least 0 2 c warmer on average than indicated in earlier work the recent warming at intermediate depth has resulted from inflow of atlantic waters that have been cooled relatively little during their transit of the norwegian sea

intrusions in double diffusively stable arctic waters evidence for differential mixing abstract intrusions like those observed in double diffusively stable regions of the arctic ocean can grow from uniform ambient temperature and salinity gradients if diapycnal mixing of these two components differs assuming this to be the driving mechanism the observed 40 60 m intrusion heights constrain the turbulent diffusivity for heat to be less than about 0 01 cm2 s 1 and the salt to heat turbulent diffusivity ratio to be greater than about 0 6 if the diffusivities are constant observations indicate that the intrusions slope across isopycnals in a sense that is consistent with such a scenario although the along intrusion density ratio is greater than that predicted by linear theory for the fastest growing intrusions numerical solutions for growing intrusions resemble observed temperature and salinity profiles

upper ocean velocities in the beaufort gyre a 23 month time series of upper ocean velocities in the beaufort gyre was obtained from an autonomous drifting buoy equipped with an acoustic doppler current profiler the buoy was deployed in the beaufort sea and drifted over the canada basin chukchi shelf and chukchi plateau time evolving spectral analysis was used to examine velocity variability in three frequency bands an eddy band 2 5 day periods a diurnal band and a semidiurnal band the eddy band and the semidiurnal band dominated the horizontal kinetic energy although eddy energy was clearly confined to the beaufort sea and canada basin eddies were found further to the south and west than in previous observations the semidiurnal band was dominated by near inertial motions with amplitude that varied seasonally largest in late summer and smallest in late winter diurnal tides were weak 1 cm s 1 except over a shallow portion of the chukchi shelf

sun glitter imaging of submarine sand waves on the taiwan banks determination of the relaxation rate of short waves natural science foundation of china 40476023 40876031 chinese ministry of science and technology 2009cb421205

nonlinear equilibration of thermohaline intrusions abstract the nonlinear behavior of thermohaline intrusions on a wide front is investigated using a one dimensional numerical model the model is used to follow the evolution of a field of intrusions from infinitesimal amplitude to a large amplitude state characterized by inversions in temperature and salinity it is thus possible to extend the analytical studies of toole and georgi and others to large amplitude allowing for the effects of amplitude dependent diffusivities and for the appearance of stably stratified diffusively stratified and statically unstable regions in the water column as the intrusions grow the model runs are initialized with infinitesimal disturbances that grow exponentially in time until inversions in temperature and salinity occur after inversions appear the intrusions evolve toward an equilibrium state in which friction balances buoyancy forces for both finger and diffusive sense basic state stratifications these equilibrium states are characterized by statically unstabl

sun glitter radiance and radar cross section modulations of the sea bed aircraft and satellite borne multispectral sensors such as ocean color scanners spectrometers and scanning lidar s have proved to be effective in detecting submarine shallow water bottom topography in clear coastal waters for such studies the blue green band of the visible electromagnetic spectrum wavelength between 400 and 580 nm is used because natural light in this range has the deepest penetration into the water column however if the water becomes turbid the reflection from the submarine sea bed disappears in this case the only possible mechanism available in the optical range of the electromagnetic spectrum for detecting surface signatures of shallow water bottom topography is through the observation of direct sunlight specularly reflected from a roughened sea surface known as sun glitter radiance as the tidal flow over irregularities on the submarine sea bed creates surface roughness variations sun glitter imagery can be used to detect such features in this paper a first order theory of the sun glitter imaging mechanism of submerged sand waves is presented the results of sun glitter radiance modulations are compared with simulations of p band radar cross section modulations and with experimental data calculations of both the constant background sun glitter radiance and the sun glitter radiance modulation show that these parameters are very sensitive to wind speed to view angle with respect to acquisition time and to observation geometry as a whole

circulation features in the central arctic ocean revealed by nuclear fuel reprocessing tracers from scientific ice expeditions 1995 and 1996 measurements of the tracer radionuclides 129 i and 137 cs were conducted on seawater samples collected during the scientific ice expedition cruises to the arctic ocean of the u s navy nuclear submarines uss cavalla and uss pogy in 1995 and 1996 respectively these radionuclides are derived mainly from discharges from the sellafield england united kingdom and la hague france nuclear fuel reprocessing plants and are subsequently transported with atlantic water into the arctic ocean through fram strait and the barents sea iodine 129 results from halocline waters water depths of 59 and 134 m collected virtually synoptically throughout the central arctic ocean during the uss cavalla cruise clearly show the front between atlantic origin water having high 129 i levels 100 10 7 atoms l 1 and pacific origin water labeled mainly by fallout 30 10 7 atoms l 1 measured in central regions of the canada basin indicate that the interior is more efficiently ventilated than previously thought possibly by separation from boundary currents flowing over the continental margin north of the chukchi plateau the 129 i and 137 cs data were interpreted using a transit time model that provided estimates of 6 7 years 0 5 years for the passage of halocline and atlantic water from the norwegian coastal current 60 n to the continental slope of the makarov basin and a lower limit of 8 years for transport to interior regions of the makarov and amundsen basins

investigation of subsurface water flow along the continental margin of the eurasian basin using the transient tracers tritium 3he and cfcs during august september 1993 the r v polarstern expedition ark ix 4 was made to the eurasian continental margin of the arctic ocean sections of oceanographic stations leading from the outer shelf over the continental slopes toward the deep eurasian basin were occupied north of the barents and laptev seas the distributions of the transient tracers cfc 11 cfc 12 tritium and 3he were measured along these sections and are discussed in relation to water mass distribution and circulation along the continental margin of the eurasian basin the tracer data strongly corroborate the temperature and salinity data schauer et al 1997 clearly showing the inflow of atlantic water in two branches the fram strait branch and the barents sea branch high cfc and tritium concen trations extended down to 1300 m over the laptev continental slope indicating strong inflow of the barents sea branch between franz josef land and severnaya zemlya the apparent ages of water in the fram strait branch were estimated to be about 2 years north of the barents sea and 6 years at the eastern end of the nansen basin which corresponds to an apparent mean current speed of about 1 cm s 1 the age of the core of the barents sea branch was also estimated to be about 6 years over the laptev slope region and to increase by 0 5 years as it flowed through this region a lower limit for the inflow of newly formed barents sea branch water was estimated to be 0 5 sv and an overall transport for the sum of fram strait branch plus barents sea branch flow of 4 sv was estimated from this aging in the deep water there was clear evidence for the inflow of norwegian sea deep water through fram strait but there appeared to be no significant input of shelf derived water from the santa anna trough if there was any shelf derived input to eurasian basin bottom water it entered at a deeper depth than was sampled on the slope sections in the laptev sea or its flow is intermittent and was not occurring during the ark ix 4 expedition

fast mapping of magnetic basement depth structure and nature using aeromagnetic and gravity data combined methods and their application in the paris basin assessment of deep buried basin basement relationships using geophysical data is a challenge for the energy and mining industries as well as for geothermal or co2 storage purposes in deep environments few methods can provide geological information magnetic and gravity data remain among the most informative and cost effective methods here in order to derive fast first order information on the basement basin interface we propose a combination of existing and original approaches devoted to potential field data analysis namely we investigate the geometry i e depth and structure and the nature of a deep buried basement through a case study sw of the paris basin joint processing of new high resolution magnetic data and up to date gravity data provides an updated overview of the deep basin first the main structures of the magnetic basement are highlighted using euler deconvolution and are interpreted in a structural sketch map the new high resolution aeromagnetic map actually offers a continuous view of regional basement structures and reveals poorly known and complex deformation at the junction between major domains of the variscan collision belt second werner deconvolution and an ad hoc post processing analysis allow the extraction of a set of magnetic sources at or close to the basin basement interface interpolation of these sources together with the magnetic structural sketch provides a werner magnetic basement map displaying realistic 3d patterns and basement depths consistent with data available in deep petroleum boreholes the last step of processing was designed as a way to quickly combine gravity and magnetic information and to simply visualize first order petrophysical patterns of the basement lithology this is achieved through unsupervised classification of suitably selected gravity and magnetic maps and as compared to previous work provides a realistic and updated overview of the cartographic distribution of density magnetization of basement rocks altogether the three steps of processing proposed in this paper quickly provide relevant information on a deep buried basement in terms of structure geometry and nature through petrophysics notwithstanding limitations of the proposed procedure are raised in the case of the paris basin for instance this study does not provide proper information on pre mesozoic basins some of which have been sampled in deep boreholes

hydrographic changes in the canada basin of the arctic ocean 1979 1996 hydrographic surveys of the southern canada basin have been conducted in winter almost annually since 1979 coverage has extended 100 200 km beyond the shelf to water depths of 2000 3000 m water properties in the upper 1500 m have fluctuated over intervals of a few years and progressive changes have taken place during the 17 years of this study at depths below the warm core of the atlantic layer water is warmer and fresher now than in the early 1980s these changes reflect a thickening of the warm core at its lower boundary by more than 100 m the maximum temperature of the atlantic water has decreased by 0 06 c and the salinity at the maximum has decreased by 0 027 above the atlantic layer the lower halocline 34 5 isohaline has cooled by 0 12 c a change which may indicate that ventilation of this level on the european side of the arctic has been more effective in recent years a good correlation between temperature fluctuations on the 34 5 isohaline and depth fluctuations of the lower 0 c isotherm suggests common forcing of both parameters variation in the flow through the barents sea into the arctic is proposed as that common influence the upper halocine has warmed by 0 15 c on the 33 5 isohaline this trend could be a consequence of decreasing ventilation of the upper halocline over the broad shallow shelves on the pacific side of the arctic ocean and may be related to the decrease in the strength of the siberian high during the same time the net result of changes in the hydrography of the canada basin has been an increase of 0 2 gj m 2 in stored sensible heat an amount sufficient to melt about 0 7 m of sea ice the bulk of the increase results from the thickening of the atlantic layer below 500 m

sea surface manifestation of along tidal channel underwater ridges imaged by sar a group of submerged ocean bottom sand ridges in the bohai sea china are shown in radarsat 1 and envisat synthetic aperture radar sar images the sand ridges appear as fingerlike quasi linear features in the sar images examining the detailed local bathymetry chart we find that these features coincide with the satellite images the heights of the sand ridges are less than 10 m and the water depth is between 10 and 30 m the spacing of the sand ridges is about 10 km and the length of the sand ridges is about 20 km the same sand ridges are also visible on a moderate resolution imaging spectroradiometer modis true color image the semidiurnal and diurnal tidal currents in this area are almost parallel to the major axis of these sand ridges these observations cannot be explained using the existing 1 d sar imaging model which is not applicable to sand ridges parallel to the tidal current in this paper we consider the shallow water current bathymetry in a 2 d space an analytical ocean model was applied to demonstrate the temporal variations of the current divergence and convergence that are induced by the along sand ridge direction current and ridge interaction a radar simulation model is used to simulate the variation of normalized radar cross section nrcs induced by the ocean surface current the simulated nrcs variation is similar to that extracted from the calibrated sar image simulation results also show that the nrcs variation becomes negligible when the ocean current is set to about half of the maximum tidal current

causes and development of repeated arctic ocean warming events 1 a model hindcast for 1948 2002 shows several warming events in the atlantic layer of the arctic ocean the most recent warming event in the 1990s spread from fram strait to the lomonosov ridge and into the canadian basin only a warming event in the 1960s can also be followed into the eastern eurasian basin these two warming events are reinforced by anomalously warm flow from the barents sea while warming events in the 1970s and 1980s encounter average or below normal temperatures in the barents sea branch of the atlantic water the warm barents sea outflow in the 1960s is caused by extensive ice cover and a melt water induced halocline in the barents sea that reduced heat loss from the atlantic water in the 1990s however the warm inflow from the nordic seas was responsible for warmer than normal flow from the barents sea into the arctic ocean

mechanics of thermohaline interleaving beyond the empirical flux laws the article of record as published may be found at http dx doi org 10 1017 s0022112011000061

atlantic water circulation over the mendeleev ridge and chukchi borderland from thermohaline intrusions and water mass properties 1 hydrographic and tracer data from 2002 illustrate atlantic water pathways and variability in the mendeleev ridge and chukchi borderland cblmr region of the arctic ocean thermohaline double diffusive intrusions zigzags dominate both the fram strait fsbw and barents sea branch waters bsbw in the region we show that details of the zigzags temperature salinity structure partially describe the water masses forming the intrusions furthermore as confirmed by chemical tracers the zigzags peaks contain the least altered water allowing assessment of the temporal history of the atlantic waters whilst the fsbw shows the 1990s warming and then a slight cooling the bsbw has continuously cooled and freshened over a similar time period the newest boundary current waters are found west of the mendeleev ridge in 2002 additionally we show the zigzag structures can fingerprint various water masses including the boundary current using this tracer data and the advection of the 1990s warming we conclude the strongly topographically steered boundary current order 50 km wide and found between the 1500 m and 2500 m isobaths crosses the mendeleev ridge north of 80 n loops south around the chukchi abyssal plain and north around the chukchi rise with the 1990s warming having reached the northern but not the southern northwind ridge by 2002 pacific waters influence the atlantic layers near the shelf and over the chukchi rise the northwind abyssal plain is comparatively stagnant being ventilated only slowly from the north there is no evidence of significant boundary current flow through the chukchi gap

radar surface signatures for the two dimensional tidal circulation over phelps bank nantucket shoals a comparison between theory and experiment a comparison is made between real aperture radar rar measurements and simulations based on modeled tidal currents of radar cross section over a complicated tidal basin in the vicinity of the phelps bank region of the nantucket shoals in order to more fully understand the origin of radar signatures that are observed at the ocean surface as a consequence of variations in the topography of the ocean bottom the phelps bank region was mapped under two extreme wind speed conditions in high winds in excess of 15 m s and in low winds of the order of 2 3 m s for the light wind case the measured radar cross section over the west side of the phelps bank was enhanced by as much as 20 db relative to the clutter background for the high wind case no discernible bathymetric signature was found in the highclutter background numerical results for the two dimensional m2 semidiurnal tidal currents over the phelps bank greenberg et al 1989 with min of arc resolution are used as input to the surface signature models the alpers and hennings 1984 first order bragg relaxation model a generalized form of this relaxation model in which wind directional effects are incorporated in an approximate manner and the full spectrum model of lyzenga and bennett 1988 comparisons between the models which do not include wave breaking and an extreme case of 2 3 m s winds where strong wave breaking could become important reveal that although the models predict correlation between variations in bottom topography and surface signature they significantly underpredict the magnitude of the observed effect the model calculations also are very sensitive at low 2 m s wind speeds to the functional form that is assumed for the wind wave forcing in the wave action equation prior visual observations and measurements of wave spectra and wave shoaling in the vicinity of phelps bank strongly suggest that the deficiencies of the modeled results that occur explicitly at light winds are due to wave breaking a number of additional experiments and measurements are suggested for more normal environmental conditions for further theory assessments

oceanic thermohaline intrusions observations intrusions are commonly observed in the upper deep and coastal oceans and are closely linked to lateral fluxes of heat salt and momentum this is a review of observations of intrusions and the results of comparisons of properties such as scale slopes microstructure activity and fluxes with theoretical models a summary of estimates of lateral heat fluxes indicates a wide range of lateral diffusivities we conclude by noting that our present knowledge is insufficient to predict the structure length scales and lateral fluxes of thermohaline intrusions with confidence and list a number of unresolved questions suggestions are made for compilation of existing data into a database for exploratory analysis and testing of theoretical hypotheses an outline is given of a potential collaborative field experiment using ctd fluorescent dye and microstructure observations

effects of turbulent mixing and horizontal shear on double diffusive interleaving in the central and western equatorial pacific abstract the effects of small scale turbulence and the horizontal shear on double diffusive interleaving are treated in the framework of a linear stability problem in the equatorial plane approximation the model predicts the decrease of the vertical wavenumber mmax and growth rate max for the fastest growing intrusion with the increase in the turbulent diffusivity and predicts increased max and decreased mmax with the horizontal shear of the mean zonal flow the effects of turbulent mixing are analyzed at different values of the prandtl number and the criteria of instability are obtained analytically for some simple cases special attention is focused on the influence of the horizontal shear on instability as with the f plane models of interleaving the ctd profiling data obtained from korean and russian research vessels are used to prove the model a closely spaced ctd section across the equator at 176 16 w shows several intrusive layers with high lateral coherence throughout the section whic

an improved composite surface model for the radar backscattering cross section of the ocean surface 2 model response to surface roughness variations and the radar imaging of underwater bottom topography in the companion paper we have presented an improved composite surface model for the calculation of normalized radar backscattering cross sections nrcs of the ocean surface the proposed model accounts for the impact of the full two dimensional ocean wave spectrum on the radar backscatter and was shown to reproduce measured absolute nrcs values for a variety of radar configurations and wind speeds satisfactorily after some reasonable tuning of the input ocean wave spectrum this paper focuses on the modulation of the nrcs in the presence of spatially varying surface currents first the sensitivity of the nrcs to intensity variations of different ocean wave spectral components is investigated then the hydrodynamic modulation of the wave spectrum over underwater bottom topography in tidal waters is computed in different ways and the resulting radar signatures are discussed the composite surface model yields comparable radar signatures at high 10 ghz x band and low 1 ghz l band radar frequencies which is in much better agreement with experimental results than the predictions of a first order bragg scattering model on the other hand measured variations of the nrcs at high radar frequencies appear to be still underestimated in some cases which may be due to shortcomings of our description of the wave current interaction by conventional weak hydrodynamic interaction theory possible improvements of the theory are discussed and requirements for future experiments are formulated