imaging near surface heterogeneities by natural migration of backscattered surface waves s u m m a r y we present a migration method that does not require a velocity model to migrate backscattered surface waves to their projected locations on the surface this migration method denoted as natural migration uses recorded green s functions along the surface instead of simulated green s functions the key assumptions are that the scattering bodies are within the depth interrogated by the surface waves and the green s functions are recorded with dense receiver sampling along the free surface this natural migration takes into account all orders of multiples mode conversions and non linear effects of surface waves in the data the natural imaging formulae are derived for both active source and ambient noise data and computer simulations show that natural migration can effectively image near surface heterogeneities with typical ambient noise sources and geophone distributions

surface wave tomography of the western united states from ambient seismic noise rayleigh and love wave phase velocity maps summary we present the results of rayleigh wave and love wave phase velocity tomography in the western united states using ambient seismic noise observed at over 250 broad band stations from the earthscope usarray transportable array and regional networks all available threecomponent time series for the 12 month span between 2005 november 1 and 2006 october 31 have been cross correlated to yield estimated empirical rayleigh and love wave green s functions the love wave signals were observed with higher average signal to noise ratio snr than rayleigh wave signals and hence cannot be fully explained by the scattering of rayleigh waves phase velocity dispersion curves for both rayleigh and love waves between 5 and 40 speriod were measured for each interstation path by applying frequency time analysis the average uncertainty and systematic bias of the measurements are estimated using a method based on analysing thousands of nearly linearly aligned station triplets we find that empirical green s functions can be estimated accurately from the negative time derivative of the symmetric component ambient noise cross correlation without explicit knowledge of the source distribution the average traveltime uncertainty is less than 1 s at periods shorter than 24 s we present rayleigh and love wave phase speed maps at periods of 8 12 16 and 20 s the maps show clear correlations with major geological structures and qualitative agreement with previous results based on rayleigh wave group speeds

a numerical model study of the alboran sea gyre abstract reduced gravity and two layer numerical models have been used to study the circulation in the westernmost basin of the mediterranean sea the alboran sea circulation is forced by flow through a 20 km wide port in the western boundary representing the strait of gibraltar the reduced gravity model domain is a rectangle measuring 600 km 160 km with 10 km 5 km grid resolution when forced by an eastward on northeastward inflow the model solutions evolve to a steady state which exhibits a meandering current the first meander of the current forms the northern boundary of an anticyclonic gyre horizontal dimensions of the gyre are strongly dependent upon the inflow angle vorticity associated with the incoming current magnitude of the incoming transport and the north south extent of the basin the meandering current is considered a standing rossby wave with a highly distorted vorticity trajectory due to the interaction of the current with the northern and southern boundaries when velocity transport is increased the wavelength increases approximately as v as a result the anticyclonic gyre shifts east as velocity increases and west as velocity decreases these solutions show that bottom topography winds and coastline features are not necessary mechanisms for the formation of the gyre two layer model solutions were obtained using realistic topography geometry and a westward moving lower layer the addition of the lower layer flow and topography distorted the circulation in the upper layer particulary in the southern half of the basin this is caused by the large topographically steered currents along the southern shelf the high variability of the horizontal dimensions and location of the gyre has been observed both experimentally and through satellite imagery model results show that the high variability is caused by variations in the inflow velocity drifter tracks both observational and model derived help determine the circulation in both layers of the alboran sea the close comparison between model and experimental drifters lends credibility to the model circulation and dynamics

interferometric daylight seismic imaging summary claerbout s daylight imaging concept is generalized to a theory of interferometric seismic imaging ii interferometric seismic imaging is defined to be any algorithm that inverts correlated seismic data for the reflectivity or source distribution as examples we show that ii can image reflectivity distributions by migrating ghost reflections in passive seismic data and generalizes the receiver function imaging method used by seismologists interferometric seismic imaging can also migrate free surface multiples in common depth point cdp data and image source distributions from passive seismic data both synthetic and field data examples are used to illustrate the different possibilities of ii the key advantage of ii is that it can image source locations or reflectivity distributions from passive seismic data where the source position or wavelet is unknown in some cases it can mitigate defocusing errors as a result of statics or an incorrect migration velocity the main drawback with ii is that severe migration artefacts can be created by partial focusing of virtual multiples

petrological and organic geochemical investigation of recent peats with known environments of deposition abstract a series of recent peat samples from tropical sub tropical and temperate locations were investigated using coal petrographical and organic geochemical techniques maceral and biomarker compositions were examined to see if they correlated or diverged from the known environment of deposition of the peats the proportion of humotelinite was related to the water depth and the frequency of dry periods the ph and trophic level have a modifying influence on the preservation of tissues furthermore the proportions of sclerotinite in the peats seem to reflected the oxygen status in the mire which was also mirrored in the abundance of humic and fulvic acids a facies diagram was calculated for the peat samples to see how maceral indices would fare in interpreting their known environments of deposition the results proved to be generally unsuccessful as the herbaceous and woody peats did not always give the predicted high humodetrinite and humotelinite compositions respectively the aliphatic hydrocarbon fraction from the extracts of the peat samples show that mainly odd numbered n alkanes are present diterpenoids triterpenoids and hopanoids were found in most samples and were mainly unsaturated in nature the relative proportion of hopanoids in pears appears to be related to bacterial activity in acidic environments de a triterpenoids were also detected in the peat stage of diagenesis in an angiosperm dominated peat type mariscus polycyclic aromatic triterpenoids were present in the aromatic fraction of the extract their occurrence and proportion appears to be related to the degree of humification in a taxodium peat mono di and triaromatic diterpenoids were detected the presence of these aromatic biomarkers indicate the rapid formation of these compounds in the peat stage mainly mediated by microbial activity

petrological and geochemical composition of lignite from the d field kolubara basin serbia abstract the upper miocene lignite from the main coal seam in the d field kolubara basin is a typical humic coal with huminite liptinite and inertinite concentrations of up to 83 7 vol 17 2 vol and 15 5 vol respectively in the huminite group textinite and ulminite are the most abundant macerals with variable amounts of densinite and attrinite liptodetrinite and sporinite are the most common macerals of the liptinite group while inertodetrinite is the most abundant maceral of the inertinite group the mineral matter consists mostly of clay minerals the main sources of organic matter were gymnosperms conifers and microbial biomass followed by angiosperms based on composition of saturated and aromatic diterpenoids it has been established that coal forming plants belonged to the gymnosperm families taxodiaceae podocarpaceae cupressaceae araucariaceae phyllocladaceae and pinaceae peatification occurred in neutral to slightly acidic fresh water environment composition and distribution of biomarkers show that diagenetic changes of the organic matter were mainly governed by bacterial activity in a suboxic to oxic environment based on distribution of aromatic diterpenoids a novel diagenetic pathway for transformation of abietane type precursors under suboxic to oxic conditions is proposed variations in compositions of macerals and biomarkers are in concordance with pronounced seasonality during pontian which caused changes in the water level redox conditions during peatification and to some extent vegetation differences in the paleo plant communities

migration of surface seismic data with vsp green s functions seismic migration is the process by which wavefields recorded on or near the surface are mapped back into the subsurface to form an image of the subsurface structure common to all current migration methods is that they rely on a model of the subsurface for computing green s functions these computed green s functions are approximations of the true green s function in the subsurface the more accurate the method used for computing the green s functions and to some extent also the choice of imaging condition the better image we will get most state of the art migration methods will use green s functions that include multiple arrivals and some finite frequency effects allowing them to image fairly complex geologic structures however the computational model in most cases uses only scalar velocity that is smooth on a wavelength scale thus ignoring scattering effects from small scale structure anisotropy and other intrinsic rock effects further whatever the model is it has to be derived from the dat

rotating flows along indented coastlines the problem of a steady inviscid reduced gracity rotating flow in a wedge around a sharp corner is examined using two or more corner solutions plausible flow streamlines can be generated in more complicated domains as long as no two corners are closer than the rossby radius of deformation this procedure is illustrated with two examples 1 circulation in a channel mouth and 2 flow around a square bump in a coastline

imaging near surface heterogeneities by natural migration of backscattered surface waves field data test abstractwe have developed a methodology for detecting the presence of near surface heterogeneities by naturally migrating backscattered surface waves in controlled source data the near surface heterogeneities must be located within a depth of approximately one third the dominant wavelength of the strong surface wave arrivals this natural migration method does not require knowledge of the near surface phase velocity distribution because it uses the recorded data to approximate the green s functions for migration prior to migration the backscattered data are separated from the original records and the band passed filtered data are migrated to give an estimate of the migration image at a depth of approximately one third each band passed data set gives a migration image at a different depth results with synthetic data and field data recorded over known faults validate the effectiveness of this method migrating the surface waves in recorded 2d and 3d data sets accurately reveals the locations of kn

transition of the tsushima warm current path observed over toyama trough japan abstractmooring ctd and adcp observations were made in 2012 in and around the toyama trough tt cutting across a continental shelf along the japanese coast of the japan sea between noto peninsula np and sado island si to investigate spatiotemporal characteristics of path transition of the coastal branch of the tsushima warm current cbtwc around si downstream of the tt boundary a wavelike alongshore current perturbation accompanied by sea level rise was observed this perturbation occurred after the seasonal amplification of the cbtwc around the np on the upstream boundary of the tt this process was delineated by the results of numerical experiments performed with a two layer model using idealized topography the model showed that a current path of the cbtwc shifted from alongshore mode to offshore mode bridged over the tt in association with the lee eddy development behind the np toward the si over the tt this lee eddy is generated by positive vorticity induced over topographic discontinui

petrographical and organic geochemical study of the kovin lignite deposit serbia abstract the origin of the organic matter om and the characteristics of the depositional environment of lignites from the upper miocene kovin deposit hosting three coal seams of serbia were evaluated based on petrographic data bulk organic geochemical parameters biomarker analysis and stable isotope geochemistry 13c of individual biomarkers samples were collected from four boreholes gd 601 and gd 603 the a field and kb 79 and kb 91 the b field representing different parts of coal seams i ii and iii investigated lignites are typical humic coals the om of lignites is derived from woody vegetation and herbaceous peat forming plants with prevalence of the former in most samples peat forming vegetation is characterized by abundant decay resistant gymnosperm coniferous plants followed by a low amount of angiosperms lignite forming plants mostly belonged to the gymnosperm families cupressaceae taxodiaceae phyllocladaceae and pinaceae slight input of ferns fungi and aquatic macrophyta to lignite om is also evident distributions of hopanoids and isotopic compositions of these biomarkers reflect the activity of various microbial populations represented by methanotrophic chemoautotrophic and heterotrophic bacteria during diagenesis prominent c28 28 30 bisnorneohop 13 18 ene was observed for the first time in the lignite extracts according to the 13c value it was probably derived from chemoautotrophic bacteria c28 28 30 bisnorneohop 13 18 ene could be one of the possible precursors of a series of orphan aromatic hopanoids bearing an ethyl group at c 21 via progressive aromatization peatification proceeded in a fresh water environment under variable redox conditions from anoxic to slightly oxic all three coal seams are heterogeneous the lower parts of the coal seams represent a topogenous fresh water peat mire with open water areas which was subjected to inundations the upper parts of coal seams represent a wet forest swamp with relatively stable conditions despite the observed variations in all three coal seams the mean values of petrographic and organic geochemical parameters suggest general increasing of wetness and establishment of more stable conditions from seam iii to seam i maceral and biomarker data indicate that rapid flooding of the bogs stopped peat growth in all three coal seams relatively frequent variations in all three coal seams followed by repetition of lignite characteristics depict well the pronounced seasonality e g short term cycles of the climate during late miocene in investigated area

a simple model for sheddies ocean eddies formed from shed vorticity abstractrecent studies show that vertical eddy diffusivity is sufficient on its own to introduce intense horizontal shear layers at sloping ocean margins molemaker et al gula et al dewar et al these layers influence mesoscale energy and potential vorticity budgets but cannot be fully represented in models without sloping boundaries no slip boundary conditions and sufficiently high resolution this paper investigates the detachment of these shear layers and their subsequent rolling up into concentrated eddies these shed eddies or sheddies may have significant oceanographic impacts their growth is considered using a simple point vortex model that adapts the brown michael model of vortex shedding to quasigeostrophic flow and allows detailed consideration of the vorticity fluxes the model shows good qualitative agreement with observations and experimental and numerical results it is applied to a number of examples of well known cases of sheddy formation including the agulhas cyclones calif

strong sh to love wave scattering off the southern california continental borderland seismic scattering is commonly observed and results from wave propagation in heterogeneous medium yet deterministic characterization of scatterers associated with lateral heterogeneities remains challenging in this study we analyze broadband waveforms recorded by the southern california seismic network and observe strongly scattered love waves following the arrival of teleseismic sh wave these scattered love waves travel approximately in the same azimuthal direction as the incident sh wave at a dominant period of 10 s but at an apparent velocity of 3 6 km s as compared to the 11 km s for the sh wave back projection suggests that this strong scattering is associated with pronounced bathymetric relief in the southern california continental borderland in particular the patton escarpment finite difference simulations using a simplified 2 d bathymetric and crustal model are able to predict the arrival times and amplitudes of major scatterers the modeling suggests a relatively low shear wave velocity in the continental borderland

neogene lake systems of central and south eastern europe faunal diversity gradients and interrelations abstract the gastropod diversity of 12 neogene lake systems is evaluated in total 1184 gastropod taxa from 119 localities are recorded deriving from the early miocene rzehakia lake system the early to middle miocene dinarid lake system lake skopje the paratethyan sarmatian lakes and the south german lakes the late miocene lake pannon the pliocene lakes dacia transylvania slavonia kosovo and sostanj as well as the holocene lake petea each lake system is characterised according to its faunistic inventory and endemism according to their gastropod faunas the lakes may be divided into pyrgulid hydrobiid viviparid and planorbid dominated ones the generally high endemism rate is between 60 and 98 species diversity and generic diversity are strongly correlated in contrast neither endemism nor lake size are tightly linked with diversity outstandingly high diversities such as observed for lake pannon are rather a result of the combined effect of autochthonous evolution in a long lived system and accumulation of inherited elements examples of parallel evolution in lymnaeids and planorbids are presented

laboratory experiments on the interaction of a buoyant coastal current with a canyon application to the east greenland current this paper presents a set of laboratory experiments focused on how a buoyant coastal current flowing over a sloping bottom interacts with a canyon and what controls the separation if any of the current from the upstream canyon bend the results show that the separation of a buoyant coastal current depends on the current width w relative to the radius of curvature of the bathymetry rc the flow moved across the mouth of the canyon i e separated for w rc 1 in agreement with previous results the present study extends previous work by examining both slope controlled and surface trapped currents and using a geometry specific to investigating buoyant current canyon interaction the authors find that although bottom friction is important in setting the position of the buoyant front the separation process driven by the inertia of the flow could overcome even the strongest bathymetric influence application of the laboratory results to the east greenland current egc an arctic origin buoyant current that is observed to flow in two branches south of denmark strait suggests that the path of the egc is influenced by the large canyons cutting across the shelf as the range of w rc in the ocean spans those observed in the laboratory what causes the formation of a two branched egc structure downstream of the kangerdlugssuaq canyon 688n 328w is still unclear but potential mechanisms are discussed

generation of intermediate water vortices in a rotating stratified fluid laboratory model we hypothesize that a formation mechanism of anticyclonic eddies lenses is the outflow of intermediate waters down the canyons of the continental shelf we reproduced in the laboratory the horizontal injection of fluid into the rotating stratified surroundings at the equilibrium density level the experiments demonstrate that such an injection forms an anticyclonic eddy measurements of the velocity field show that the core of the eddy is almost axisymmetric and is in solid body rotation the periphery of the eddy is formed by the jet flow cyclonic satellites were also observed at the periphery of the eddy the main features of the laboratory flow are consistent with those of the young eddy observed recently in the gulf of cadiz

generation and unstable evolution of a density driven eastern poleward current the iberian poleward current 1 the generation and evolution of a density driven eastern poleward current is investigated using a high resolution primitive equation numerical model the simulations focus on the iberian poleward current ipc as a case study the flow is generated by a meridional upper ocean density gradient balanced by an eastward surface intensified flow that adjusts at the coastal margin the resulting current system has a baroclinic character with poleward flow at the surface layer and equatorward flow underneath a few weeks after initialization the sheared along slope flow generates several vorticity structures downstream of the main topographic features in the lee of the topography persistent anticyclones are observed and deep cyclogenesis is induced in relation to the meandering of the upper layer jet these structures evolve preferentially as cyclone anticyclone eddy pairs and after interaction some dipoles are ejected offslope within a period of a few months the initial meridional gradient evolves into a complex system of fronts eddies and slope flows the dynamics of flow topography interaction is analyzed a comparison with satellite imagery of the ipc is conducted and similarity in scales and patterns is noted

a meddy off cape st vincent part i description abstract a meddy an eddy formed from mediterranean source water was surveyed in detail with two types of expendable profilers and a ctd instrument the muddy comprised two distinct vertically aligned tenses with a combined thickness of 650 m both lenses were stratification minima the upper lens was warmer fresher 12 25 c 36 5 psu and more circular the lower lens was cooler more saline 12 1 c 36 65 psu and more elliptical oriented alone a northeast by southwest line the upper lens homogeneous out to a radius of 6 km had a radius of maximum velocity of 9 km its relative vorticity was 0 85 f and its ertel potential vorticity 4 10 12 m s 1 was 17 times below ambient levels due to the combined effects of negative relative vorticity and vortex stretching the meddy contained more kinetic energy than available potential energy energy burger number of 2 5 compared with historical meddies it had a larger burger number and a more negative vorticity rossby number

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

on the unsteady separation intrusion of the gaspe current and variability in baie des chaleurs modeling studies a numerical model has been used to study separation intrusion of an unsteady baroclinic coastal jet the gaspe current gc and its impact on dynamics and thermodynamics of the baie des chaleurs bdc gulf st lawrence canada the model has 2 layers with primitive equation dynamics and an embedded bulk mixed layer ml model it is forced with observed atmospheric fluxes as well as the gc the simulations show that the variability in the baie des chaleurs is controlled by the characteristics of the unsteady gc separation intrusion on the basis of the dynamic and vorticity balance analyses it is found that the separation is related to the adverse pressure gradient force which is induced by the ageostrophic terms in the momentum equations and to local vorticity intensification due to the inertial effect in the flow the simulations demonstrate characteristics of unsteady separation the presence of separation in an accelerating current as well as in a linear current with strong deceleration when momentum advection is neglected gives new insight into the mechanisms of unsteady boundary current separation unsteady separation or intrusion occurrence depends on the magnitude of the gc transport as well as its rate and duration of deceleration or acceleration the gc intrusion generates cyclonic circulation in the bdc prevailing westerly winds reduce the cyclonic circulation inside the bay but have little effect on separation intrusion near the entrance the gc either intrudes along the coastline attachment or after separation reattachment increasing vertical shear of the gc and offshore movement of the gc axis reduces the tendency to separate the finding of an asymmetric response of gc separation intrusion to symmetric gc forcing explains the monthly mean features seen in observations taken in the bay

transient eddy formation around headlands eddies with length scales of 1 10 km are commonly observed in coastal waters and play an important role in the dispersion of water borne materials the generation and evolution of these eddies by oscillatory tidal flow around coastal headlands is investigated with analytical and numerical models using shallow water depth averaged vorticity dynamics eddies are shown to form when flow separation occurs near the tip of the headland causing intense vorticity generated along the headland to be injected into the interior an analytic boundary layer model demonstrates that flow separation occurs when the pressure gradient along the boundary switches from favoring accelerating to adverse decelerating and its occurrence depends principally on three parameters the aspect ratio b a where b and a are characteristic width and length scales of the headland h cda where h is the water depth cd is the depth averaged drag coefficient and uo a where uo and are the magnitude and frequency of the far field tidal flow simulations with a depth averaged numerical model show a wide range of responses to changes in these parameters including cases where no separation occurs cases where only one eddy exists at a given time and cases where bottom friction is weak enough that eddies produced during successive tidal cycles coexist interacting strongly with each other these simulations also demonstrate that in unsteady flow a strong start up vortex forms after the flow separates leading to a much more intense patch of vorticity and stronger recirculation than found in steady flow

miocene depositional environment and climate in western europe the lignite deposits of the lower rhine basin germany abstract miocene lignites representing a depositional history of about 7 million years 18 11 ma before present have been studied by organic petrological and organic geochemical methods including analysis of stable carbon and oxygen isotopes the three lignite seams investigated morken frimmersdorf garzweiler developed from peats which grew in a nutrient depleted paralic environment situated close to the sea all seams have low ash mineral matter contents but seam frimmersdorf is richer in sulfur as compared to seams morken and garzweiler sulfur richness and distribution in seam frimmersdorf might be due to the diagenetic effect of sulfate reduction and pyrite precipitation following flooding by the sea and deposition of the marine neurath sands on top of seam frimmersdorf geochemical palaeotemperature analysis gdgt revealed a warm climate during deposition of the peats representing lignite seams morken and frimmersdorf which shifted towards lower temperatures 2 3 c during deposition of the uppermost seam garzweiler i e at about 13 11 ma before present this trend is basically supported by cellulose oxygen isotope values which show a significant scatter however carbon isotope values are less variable indicating predominance of angiosperms in the peat vegetation and rather stable environmental conditions as well as floral assemblage organic petrological studies reveal predominance of small plants and a nutrient depleted environment a modified groundwater index gwiac was applied suggesting deposition above the general groundwater level

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

molecular and isotopic biogeochemistry of the miocene clarkia formation hydrocarbons and alcohols the miocene lacustrine deposit at clarkia northern idaho u s a is well known for its rich and exceptionally well preserved higher plant leaf fossils in the present study the distributions abundance and isotopic compositions of aliphatic hydrocarbons and alcohols isolated from two sediment samples and from two associated fossils magnolia latahensis and platanus dissecta are investigated the general similarity of these characteristics in the sediments suggests a relatively uniform depositional environment and consistent terrestrial input the sediment hydrocarbons are comprised mainly of compounds derived from higher plants and bacteria whereas the alcohols reflect contributions from both higher plants and algae a notable feature of the higher plant derived terpenoid hydrocarbons is the prevalence of des a triterpenes largely in the absence of their pentacyclic precursors indicating the dominance of a ring degradation for these pentacyclic triterpenoids the des a triterpenes include several novel compounds namely 19 h and 19 h 28 nor des a lup 17 ene and des a oleana 9 13 18 diene the sediment samples contain high abundances of c24 c32 long chain alkanediols consisting of a series of diols 1 diols 1 15 diols and an unusual series of 1 3 diols both fossil leaves show clear differences in their compound distributions and concentrations from the associated sediments which suggests that they retain a composition distinct from the sediment groundmass the 13c values of c25 c33 n alkanes and c24 c32 n alcohols in sediments and fossils are consistent with an origin from terrestrial c3 higher plants algal lipids in the two sediments are represented by dinostanol 24 6 and 25 9 inherited from dinoflagellates and long chain 1 15 alkanediols 26 4 to 29 7 derived from microalgae the long chain 1 and 1 3 alkanediols are more enriched in 13c 21 8 to 26 4 suggesting an origin from sources other than higher plants probably aquatic photoautotrophic organisms the 13c depletion of some hopanoids 35 9 to 61 0 attests to contributions from methanotrophic bacteria and suggests an active methane cycle at the time of deposition

carbon isotopic compositions of 28 30 bisnorhopanes and other biological markers in a monterey crude oil abstract an immature tar like oil api 3 13 c 23 6 vs pdb from the miocene monterey formation offshore california was selected for a study of carbon isotopic signatures of individual biomarkers the three principal stereoisomers of 28 30 bisnorhopane c 28 have within analytical precision identical carbon isotopic compositions average 13 c 32 3 0 4 and are considerably depleted in 13 c compared to the whole oil these 28 30 bisnorhopanes bnh differ isotopically from c 29 and c 30 17 h hopanes 25 8 and 26 1 and c 31 c 35 extended hopanes 13 c 27 7 and suggest different precursors for the c 28 hopanes than for c 29 c 35 hopanes the relative depletion of bnh of almost 9 compared to the isotopic composition of the whole oil suggests that these hopanes derive from chemoautotrophic bacteria possibly not yet identified h 2 s oxidizers which utilize 13 c depleted substrates the c 29 and c 30 hopanes are within analytical precision isotopically identical 26 and similar to algal derived compounds e g c 27 steranes 25 9 which is consistent with a cyanobacterial source for these hopanes an archaebacterial biomarker 1 1 biphytane 13 c 25 5 likely derived from methanogens is also isotopically similar to c 27 sterane norpristane pristane and phytane liberated by desulfurization of the aromatic and polar maltene fractions show isotopic compositions similar to the same isoprenoids in the free lipids of the bitumen total range from 24 5 to 27 5 this isotopic similarity supports a common origin for the free and sulfur bound forms of these isoprenoids this origin could be algal and or archaebacterial lipids which both show isotopic compositions within the range of the c 18 c 20 isoprenoids like other marine derived organic matter this monterey oil does not show the strong 13 c depletion typical for methylotroph derived compounds characteristically found in organic matter of lacustrine origin this may indicate fundamental differences of methane recycling processes in marine sulfate dominated as compared to lacustrine environments

the source of 90 day oscillations at wake island energetic 90 day oscillations of sea level have been intermittently observed at wake island in the western tropical pacific during the past 2 decades the oscillations tend to occur about 1 5 years after el nino southern oscillation events to have amplitudes of 10 15 cm and to persist for about 1 year sea surface heights from the geosat altimeter are used to establish that these signals take the form of rossby waves and have an energy source near the big island of hawaii which lies 40 of longitude to the east sea level and upper layer currents from an eddy resolving numerical model are examined and suggest that the energy source is eddies generated off the big island of hawaii these eddies appear to be associated with westward currents that intermittently impinge on the island several alternate hypotheses are also discussed and rejected

inner shelf circulation patterns and nearshore flow reversal under downwelling and stratified conditions off a curved coastline 1 the role of a curved coastline and associated bathymetry in the development of downwelling circulation in a stratified inner shelf is examined through a number of numerical experiments different scenarios include constant versus variable wind forcing and variations in bottom friction the three dimensional response of the shelf within the domain embayment enclosed by capes is associated with the generation of a velocity pycnocline disturbance at the upstream cape and its subsequent downstream advection this disturbance is more pronounced under variable wind conditions its downstream advection through the bay exhibits different patterns depending on the competition between inertia and bottom friction near the cape when inertia dominates the disturbance separates from the cape and travels downwind with an enhanced downstream flow offshore and a countercurrent inshore the separation occurs at a low rossby number ro 0 15 which is attributed to the positive curvature of the coastline forming the cape when friction dominates the advection path is constrained along the coastline resulting in an alongshore temperature gradient and a transient thermal front running almost perpendicular to the coast isobaths simulations with spatially variable bottom friction with higher friction toward the coast result in the generation of eddy like features the numerical results are in agreement with both observations and surface temperature imagery from long bay south carolina an embayment enclosed by two capes and emphasize the role that coastline and associated shelf morphology can play in enhancing cross shelf transport and exchange

palaeoclimate and vegetation change in serbia during the last 30 ma abstract in the present study 14 published megafloras from the serbian cenozoic are analyzed with respect to vegetation type palaeoclimate and palaeogeographic settings the floras cover a time span from the oligocene to the late miocene the results obtained are compared with continental climate records from other parts of europe and discussed in the context of global climate change to obtain a quantitative palaeoclimate record a total of seven different climate variables is calculated for each of the floras using the coexistence approach it is shown that basic patterns of vegetation change such as the immigration of arcto tertiary deciduous floristic elements during the early miocene and the decreasing diversity of laurophyllous taxa during the late miocene are ruled by climate change and a changing palaeogeography the serbian cenozoic climate record shows a steep cooling gradient during the oligocene that is most probably is connected to a northward movement of tectonic plates the globally observed middle miocene climate optimum and the late miocene cooling are well reflected according to the palaeotemperatures calculated a warm temperate climate existed in serbia throughout the time span examined the late miocene cooling is most pronounced in winter temperatures and is connected to increasing seasonality precipitation rates obtained for the serbian cenozoic especially those of the warmest and wettest months tend to be lower when compared to the central european cenozoic according to climate analysis and the interpretation of vegetational data there is evidence for regionally drier conditions and increased seasonality of precipitation in the time span from the late badenian to the early sarmatian

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

reconstructed mediterranean salt lens trajectories the existence of energetic anticyclonic mid depth vortices of mediterranean water meddies questions the validity of a conventional advective diffusive balance in the eastern atlantic subtropical gyre a mesoscale experiment in the azores madeira region reveals a link of these meddies to large scale subsurface meanders for the first time it is shown that meddies may have strong surface vorticity indicative of a generation process involving the azores current a deep reaching near surface jet

polar aromatic biomarkers in the miocene maritza east lignite bulgaria aromatic and polar compounds of lignite lithotype bitumens maritza east were analyzed diterpenoid phenols and ketophenols i e mainly ferruginol sugiol hinokione and products of their diagenetic transformations were identified as the dominant biomarkers a variety of sesquiterpenoids was present as well these compounds provided evidence for the assumption that members of the cupressaceae s 1 are the coal precursors polar triterpenoids i e lupeol lupenone adiantone and hopanones were present in subordinate quantities in the humoclarain sample these biomarkers support an input of deciduous angiosperm vegetation to the peat swamp source matter three diagenetic transformation schemes for the diterpenoid phenols ketophenols are proposed 1 ferruginol and or sugiol alteration through dehydrogenation demethylation and ring b cleavage 2 hinokione aromatization to simonellite and 3 7 ketototarol change through 7 ketototar 5 enol to 20 nor 3 oxo totara 5 10 6 dienol the identified diterpenoids demonstrated the presence of gymnospermae in the coal forming community furthermore the phenolic diterpenoids indicated a specific input of organic matter from conifers of the cupressaceae taxodiaceae or podocarpaceae as the most abundant trees in the coal forming swamp

a sensitivity study of reduced gravity channel flows with application to the alboran sea abstract the reduced gravity response of an hydraulically forced flow in a rectangular channel is examined numerically the model parameters were set by observed features of the circulation in the westernmost basin of the mediterranean sea the alboran sea numerical experiments reveal that the solution depends critically on the inclusion of the momentum advection terms and on the form of the boundary condition on the domain s sidewalls in particular while free slip conditions show a coastally trapped current on the model s southern boundary no slip conditions cause the formation of an anticyclonic gyre upon the flow s entry into the basin

the intrusion of a density current along the coast of a rotating fluid when light rotating fluid spreads over heavier fluid in the vicinity of a vertical wall coast a boundary jet of width forms the leading edge or nose of which propagates with speed along the coast a certain fraction 8 of the boundary transport is not carried by the nose but is deflected backwards detrained and left behind the propagating nose theoretical and experimental results for and are given for a quasi equilibrium constant regime over longer time intervals the laboratory observations suggest that the nose slows down and stagnates whereupon the trailing flow separates from the coast and an intermittent boundary current forms these processes may be relevant to the mixing of oceanic coastal currents and the maintenance of the mean current

local migration with extrapolated vsp green s functions we have developed a novel vertical seismic profile vsp imaging method that requires only a local velocity model around the well this method is denoted as a local migration where the model based forward propagation and backward propagation operators are computed using a local velocity model between the well and the target body the velocity model for the complex overburden and salt body is not needed and the source side statics are automatically accounted for in addition kinematic and dynamic effects including anisotropy absorption and other unknown undefined rock effects outside of this local velocity model are mostly accounted for numerical tests on an acoustic 2d sigsbee vsp data set an elastic salt model and offset 2d vsp data in the gulf of mexico partly validate the effectiveness of this method by accurately imaging the sediments next to the vertical well

a boom in boomless seismology taking advantage of cheap long lasting sensors developed by the oil and gas industry seismologists are increasingly exploring the top 10 kilometers of the crust with dense surveys of hundreds or even thousands of seismometers what s more the surveys are being operated passively which means that ambient noise from earth is used to illuminate the subsurface passive surveys are cheaper and easier to permit than active surveys which rely on explosives or vibrations from special thumper trucks seismologists predict that the dense surveys will yield precision imaging of magma chambers underneath volcanos and earthquake rupture zones along faults

the effects of clastic sedimentation on organic facies development within a tertiary subbituminous coal bed powder river basin montana u s a abstract the anderson dietz coal is a 25 m thick bed that splits eastward into three benches the anderson dietz 1 and dietz 2 each separated from the other by as much as 45 m of detrital sedimentary rocks petrographic and chemical analyses of the anderson and dietz 1 coal benches suggest that detrital sediments now lithified between the benches were introduced after the peat surface had subsided as a result of either fire or differential compaction of underlying sediments sediments associated with this event had a limited effect upon the quality of the anderson and dietz 1 coal benches ash yields and sulfur contents are elevated only at the very top and bottom of the benches in areas where the benches are not split sulfur content and maceral types indicating degradation increase only in a thin zone 1 m thick that is laterally equivalent to the split sediments however ash yields in this interval increase only slightly 2 5 this indicates that while little sedimentation occurred the peat which formed the coal was inundated by higher ph surface and ground water causing the degradation of plant material

separation of a midlevel density current from the bottom of a continental slope the high salinity water flowing out of the mediterranean sea descends to mid depths in the density stratified ocean continues as a narrow jet along the iberian continental slope and intermittently detaches large scale eddies called meddies this process is important because it maintains the relatively high mean salinity of a major water mass the mediterranean intermediate water in the north atlantic our simplified model of this jet consists of a moving layer with intermediate density 2 sandwiched between motionless layers of density 1 2 the inshore anticyclonic portion of the midlevel jet in the 2 water rests on an inclined bottom the continental slope whereas the cyclonic offshore portion rests on the density interface of the stagnant deep 3 layer an inviscid steady and finite amplitude longwave theory is used to show that if the cross stream topographic slope increases gradually in the downstream direction then the 2 jet is deflected off the bottom slope and onto the upper density interface of the 3 layer the computed magnitude of this separation effect is such as to produce an essentially free jet which is removed from the stabilizing influence of the continental topography it is therefore conjectured that time dependent effects baroclinic instability will produce further amplification causing an eddy to detach seaward from the branch of the jet remaining on the slope

tracking three meddies with sofar floats abstract three meddies were tracked for up to two years in the canary basin using neutrally buoyant sofar floats these meddies have cores of warm salty mediterranean water and are approximately 100 km in diameter 800 m thick and are centered at a depth of 1100 m meddy 1 was tracked for two years 1984 86 with five floats as it drifted 1090 km southward with a mean velocity of 1 8 cm s 1 four shipboard surveys made during these two years revealed the nearly total decay of meddy 1 by gradual mixing processes meddy 2 drifted 530 km southwestward over 8 5 months with a mean velocity of 2 3 cm s 1 until it collided with hyeres seamount near 31 n 29 w the floats trapped in this meddy then stopped looping abruptly implying a major disruption of this meddy meddy 3 drifted 500 km southwestward for a year and a half with a mean translation velocity of 1 1 cm s 1 a comparison of the velocity of meddies to the velocity of nearby floats at 1100 m depth outside of the meddies shows clearly that all three m

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

comparative study of serbian miocene coals insights from biomarker composition abstract the origin of the organic matter om and the characteristics of the paleoenvironment of serbian brown coals covering a time span from the lower to the upper miocene were evaluated and compared based on comprehensive petrological and biomarker analyses investigated coals are typical humic coals peat forming vegetation is characterized by abundant decay resistant gymnosperm coniferous plants followed by variable amount of angiosperms coal forming plants belonged to the gymnosperm families taxodiaceae podocarpaceae cupressaceae araucariaceae phyllocladaceae and pinaceae peatification proceeded in fresh water environment under variable eh settings from anoxic to slightly oxic condition upper miocene lignites were formed in neutral to slightly acidic environment whereas lower and middle miocene coals were deposited under neutral to slightly alkaline and more reductive conditions which is the result of calcium rich surface waters derived from the surrounding jurassic to cretaceous calcareous country rock and higher water column level diagenetic changes of the om were governed by bacterial activity rather than thermal alteration biomarker pattern does not significantly differ in serbian coals of different ages the main differences between upper middle and lower miocene coals are expressed by higher gelification index gi proxy ratio p aq n c 23 n c 27 n c 31 and pimarane 16 h phyllocladane ratio as well as lower relative abundance of c 31 r hopane of the latter one om of lower miocene coals is more mature corresponding to immature early mature stage huminite vitrinite reflectance 0 45 whereas om of upper miocene lignites is in immature diagenetic phase huminite reflectance 0 3 consequently higher gelification of lower miocene coals is probably an effect of higher rank however high humidity wet climate and low acidity within the mire could not be excluded a good correlation between biomarker parameters and paleoclimate data is observed indicating that biomarker patterns represent a valuable tool that reflect even slight paleoclimate changes in serbia during miocene

spatial and temporal variability in vegetation and coal facies as reflected by organic petrological and geochemical data in the middle miocene cayirhan coal field turkey abstract coal channel samples of middle miocene age are collected from the first tv and second tb seams from underground mines and from exploration boreholes within the cayirhan coal field in the beypazari basin turkey they are investigated in order to detect spatial and temporal changes in maceral and molecular composition of coal and to relate them to changes in vegetation and depositional environment the mean random reflectance values of ulminite 0 40 rr indicate a lignite to subbituminous c coal in rank maceral composition and biomarker ratios of the samples from both seams at the cayirhan deposit argue for coal formation in a limno telmatic environment under dysoxic to anoxic conditions alkaline surface waters of changing ph values and a high and unstable water level at the palaeomire are evidenced by moderate to high gelification index gi and ground water influence gwi values as well as high sulphur contents variations in tissue preservation index tpi and vegetation index vi values point to minor variations in the palaeovegetation during peat formation herbaceous plants dominated in both tb and tv palaeomires low tpi and vi values whereas in the surroundings arboreal vegetation were predominant the decreasing trends in pristane phytane ratios and carbon preference index cpi values towards the ne are suggested to reflect oxygen deficient conditions during peat formation due to a higher ground water level in this part of the basin the occurrence of c 29 diasterenes in low abundances provides evidence for periods of lower ph in the mire the borehole samples from the ne show slightly enhanced contributions of n alkanes from algal and microbial sources the terpenoid hydrocarbons present in the lignite argue for a major contribution of angiosperms to peat formation and slightly enhanced proportions of gymnosperms in the tv palaeomire in the ne based on the high concentrations of lupane type triterpenoids in the coal seams from the underground mine a higher density of betulaceae in the arboreal vegetation in the sw is indicated

the contiguous panarctic riverine coastal domain a unifying concept the riverine coastal domain rcd is a narrow 15 km shallow 10 m contiguous feature that is primarily forced driven by an aggregate of continental runoff sources and which extends clockwise 10 103 km around northern north america we hypothesize that a similar feature extends around northern eurasia the rcd carries a terrestrial signal that affects light nutrient and carbon regimes and provides a coastal pathway for the dispersal and migration of marine biota the physical and biogeochemical variables within the rcd yield a contiguous gradient of environmental conditions along and across the panarctic coastal zone the rcd acts as the initial connector between terrestrial and marine ecosystems and may become even more prominent as terrestrial runoff permafrost thawing and local ice melt are assumed to increase in the near future climate

aliphatic and aromatic triterpenoid hydrocarbons in a tertiary angiospermous lignite abstract the hydrocarbon biomarker assemlage of a liptinite rich early tertiary angiospermous lignite has been characterized the biomarker fistribution for the lignite confirms the low maturity and previous paleobotanic interpretations the aliphatic hydrocarbon fraction consists predominantly of n alkanes showing a strong odd carbon predominance and numerous de a triterpenoids and triterpenoids derived from higher plants bacterially derived triterpenoids were represented primarily by homohopanes and hopenes the aromatic hydrocarbon fraction contains a series of mono di and triaromatic de a triterpenoids and mono tri and tetraaromatic triterpenoids derived from higher plants the concentration and abundance of monoaromatic triterpenoids containing one to three additonal degress of unsaturation have not seen previously observed in a single deposit as such a diagenetic scheme for angiosperm derived triterpenoids is presented which confirms and extends previous hypothesis

synoptic flow and density observations near an arctic shelf break analyses of data from three shipborne surveys describe the quasi synoptic density and velocity fields near barrow canyon alaska the canyon parallels the northwestern coast of alaska and contains three different water masses these are 1 warm and fresh alaskan coastal waters that originate from the bering strait 2 cold and moderately salty waters that originate from the chukchi shelf and 3 warm and salty waters that originate from the atlantic layer of the arctic ocean a halocline separates the chukchi shelf and atlantic layer waters the halocline slopes upward into the canyon where it is then twisted to slope across the wide canyon an intensification of the beaufort gyre near the shelf break just seaward of barrow canyon raises the halocline more than 100 m toward the surface locally upwelling favorable winds raise the arctic halocline which thus is ventilated within barrow canyon adjacent to the coast in the absence of winds the halocline slopes acrosscanyon in the thermal wind sense due to a northward flowing coastal current velocity measurements from a towed acoustic doppler current profiler reveal a northward flowing jet that transports about 0 3 sv sv 106 kg m23 of bering sea summer water into the arctic ocean at speeds that exceed 0 7 m s21 total northward transports through the canyon exceed 1 0 sv the warm waters of this coastal current supply more than 100 w m22 of heat to the atmosphere the jet separates both from the bottom and from the coast hence a laterally and vertically sheared jet forms which breaks into three branches at about 71 88n latitude

observations and laboratory modeling of meddy generation at cape st vincent abstract the amuse canigo and ampor observations provided a large amount of subsurface float data showing evidence of several distinctly different flow behaviors within the mediterranean water layers in the vicinity of cape st vincent southwest portugal some of the floats followed the coastline and moved northward and some were trapped either in anticyclonic lenses of mediterranean water meddies generated at cape st vincent or in cyclonic structures these observations clearly indicated that the anticyclones were accompanied by cyclones at least during their early stages as the dipolar structure moves away from the cape the cyclone tends to shift slowly away from the anticyclone while decaying so that after some time only the meddy persists these in situ observations are compared with large scale laboratory experiments and the agreement between the two sets of observations is remarkably good near the cape and shortly after the generation the nondimensional radius relative vorticity and r

baroclinic eddy generation at a sharp corner in a rotating system laboratory experiments were conducted to investigate the generation of anticyclonic gyres by separation of a surface current from a coast in a rotating two layer system the experiments were motivated by the hypothesis that the flow of coastal currents around capes can generate oceanic eddies as well as by the observation of gyres at the mouths of various straits in the experiments the gyre is formed when the current which flows with the coast to its right if one is oriented in the downstream direction encounters a sharp convex corner the current overshoots the corner loops to the right and reattaches to the coast downstream of the corner between the current loop and the coast is an anticyclone whose width grows with time if a countercurrent flows under the surface current a similar separation in the lower layer results in the generation of a cyclone as well under some circumstances the cyclone and anticyclone advect each other away from the coast as a heton previous studies on related systems found that the corner must be sufficiently sharp for a gyre to form i show that for a very sharp corner the angle made by the corner must be above a critical value of between 40 and 45 for a gyre to form this is in contrast to nonrotating flows of comparable rayleigh number which will separate from a sharp corner at virtually any angle for angles below the critical value the current profile downstream of the corner changes as a function of corner angle indicating that it is the stagnation of the flow nearest the wall which causes the anticyclone to form this stagnation is reminiscent of the two dimensional nonrotating picture of viscous boundary layer dynamics forcing separation of a boundary current however the gyre grows more slowly when the lower layer is much thicker than the upper layer indicating that baroclinic processes are at least quantitatively important in the generation of the gyre by varying the initial condition of the current it is shown that the gyre formation is not a product of the interaction of the nose of the current with the corner in conclusion the experiments indicate that the basic mechanism of gyre formation may be viscous boundary effects as in nonrotating systems but that rotation tends to inhibit eddy generation while baroclinic effects tend to enhance it

wind stress curl forcing of the coastal ocean near point conception california near point conception california the atmospheric flow separates from the coast and a large wind stress curl results direct spatial wind field observations from 20 aircraft overflights in the spring of 1983 suggest that ekman pumping of on average 4 m day21 contributes to the local dynamics during strong and persistent upwelling events the curl driven ekman pumping reaches up to 20 m day21 a single complex empirical orthogonal function explains more than 72 of the spatial and temporal wind stress variance it reveals large wind stress curl at the center of the western santa barbara channel entrance this dominant mode correlates strongly r 2 5 0 79 with the wind stress observed at a moored buoy the location of largest ekman pumping in the ocean indicated by this mode coincides with the location of a laterally sheared cyclonic flow cold upwelled waters enter the santa barbara channel along its southern perimeter while warm and thus buoyant waters from the southern california bight exit the channel along its northern perimeter buoy wind stress and lateral current shear at 30 m depth correlate significantly at periods of about 3 5 and 6 days with phase lags of about 0 5 and 2 days respectively hydrographic observations from 1983 do not however indicate effects of ekman pumping on the internal mass field as winds vary in speed and direction at daily timescales this contrasts with 1984 observations that do indicate strong doming of isopycnals over the center of the channel at its western entrance winds prior to and during hydrographic observations in the spring of 1984 were both stronger and more steady than they were in 1983 cyclonic shears reach 0 4 f at the entrance of the santa barbara channel near point conception here f is the planetary vorticity the thermal wind balance explains the lateral shear of the alongchannel surface flow rather well

dynamics of a buoyancy driven coastal jet the gaspe current a primitive equation ocean model is applied to the process study of the gaspecurrent and cyclonic circulation over the northwestern gulf of st lawrence nwg the model is driven by river discharge and barotropic boundary flows two types of model domains are used an idealized basin with a flat bottom and piecewise coastline and a realistic basin with model resolved nwg bathymetry the model domains are initially filled with horizontally uniform but vertically stratified waters the river discharge is expressed in terms of lower salinity and a weak barotropic inflow in the upper waters at the estuary head the early developments of the estuarine plume and coastal current system driven by the river discharge are qualitatively similar in both basins after a short period adjustment a buoyant plume is developed near the estuary mouth with a surface intensified coastal current advecting the estuarine water seaward in the direction of kelvin wave propagation the coastal current initially follows the coastline closely but later becomes unstable with backward breaking waves developed along the outer edge of the current the kinetic energy analysis reveals that the plume current system is baroclinically unstable with the transient motions resulting primarily from the mean available potential energy with the river discharge at the head as the only driving force the offshore front of the estuarine plume expands continuously seaward leading to a large scale anticyclonic circulation over the nwg the addition of a barotropic westward jet along the quebec shore however is able to restrain the seaward expansion of the offshore front of the plume and therefore form a large scale cyclonic motion over this region

the dynamics of pressure and form drag on a sloping headland internal waves versus eddies topographically generated eddies and internal waves have traditionally been studied separately even though bathymetry that creates both phenomena is abundant in coastal regions here a numerical model is used to understand the dynamics of eddy and wave generation as tidal currents flow past three tree point a 1 km long 200 m deep sloping headland in puget sound wa bottom pressure anomalies due to vertical perturbations of the sea surface and isopycnals are used to calculate form drag in different regions of the topography to assess the relative importance of eddies versus internal waves in regions where internal waves dominate sea surface and isopycnal perturbations tend to work together to create drag whereas in regions dominated by eddies sea surface and isopycnal perturbations tend to counteract each other both phenomena are found to produce similar amounts of form drag even though the bottom pressure anomalies from the eddy have much larger magnitudes than those created by the internal waves topography like three tree point is common in high latitude coastal regions and therefore the findings here have implications for understanding how coastal topography removes energy from tidal currents

generation of submesoscale vortices a new mechanism small scale intense vortices composed of water with anomalous values of quasi conservative tracers have been observed in many oceans they are particularly numerous in the beaufort gyre of the arctic ocean possible mechanisms responsible for the generation of these features are examined conservation of temperature salinity and nutrients requires that beaufort sea vortices be created from water that flows into the arctic ocean from the pacific ocean across the broad shallow chukchi sea much of this water passes through barrow canyon near point barrow alaska observations in the canyon show the generation of vortices of approximately the same size as those observed in the beaufort sea barrow canyon is therefore a likely site for the generation of beaufort sea vortices most observed beaufort sea vortices have a central potential vorticity near zero because of a relative vorticity close to their chukchi sea source water is typically stratified with little relative vorticity so that its potential vorticity is nonzero a key step in the generation of the vortices is therefore the reduction of the potential vorticity of chukchi sea water to nearly zero it is proposed that this occurs through the action of frictional torques occurring as the chukchi sea water flows through barrow canyon rather than througji the action of vertical mixing because this flow is driven by a downstream pressure gradient it is concentrated on the right hand wall of the canyon by the coriolis force the frictional torques thus preferentially reduce the potential vorticity of the fluid anticyclonic vortices are therefore preferentially generated it is suggested that a similar scenario may play a role in the generation of submesoscale vortices containing water from the mediterranean and labrador seas