run up of internal waves on a gentle slope in a two layered system this paper describes the dissipative phase of internal wave run up on uniform slopes of 0 030 and 0 054 rad as observed in a series of laboratory experiments the waves were generated continuously at the interface of two miscible layers of differing density as each wave in the perodic train propagated onto the slope it steepened and developed into a solitary like wave before finally overturning surrounding fluid was engulfed into the wave as it overturned and the resulting gravitational instability produced considerable turbulence and mixing the broken wave took the form of a discrete bolus of dense fluid which propagated for some distance up the slope bulk parameters which characterize the nature of the bolus were defined and the dependence of these on the incident wave parameters and their behaviour during the run up phase were examined

internal tides and tidal cycles of vertical mixing in western long island sound in estuaries tidal period variations in the rate of vertical mixing have been observed to result from various causes in liverpool bay and the york river they have been attributed to tidal straining of the along channel density gradient modulating stratification in the hudson river they arise from tidal modulation of the height of the tidal current bottom boundary layer bbl along continental shelves tidal period fluctuations in mixing have been observed to result from the dissipation of internal waves iws western long island sound wlis moored instrument records indicate that large near bottom increases in dissolved oxygen do and heat and a decrease in salt occur during the middle of the flood tide an analysis of water mass signatures indicates that the transport involved is vertical and not horizontal temperature data from a vertical thermistor array deployed in the wlis for 16 days in august 2009 clearly show a tidal cycle of iw activity creating a mean thermocline depression at midflood of approximately 25 of the water depth with individual iw thermocline depressions of as much as 50 of the water depth contemporaneous adcp measurements show increases in shear due to iws during the flood near bottom internal wave activity is maximal at and after midflood and is correlated with near bottom temperature and do tendencies at both tidal and subtidal scales we conclude that internal tides are an important vertical mixing mechanism in the wlis through both increased shear from iws and displacement of the pycnocline into the region of high shear in the bbl

nearshore internal bores and turbulent mixing in southern monterey bay 1 we observed transient stratification and mixing events associated with nearshore internal bores in southern monterey bay using an array of instruments with high spatial and temporal resolution the arrival of the bores is characterized by surging masses of dense cold water that tend to stratify the water column the bore is followed by a gradual drop in the temperature throughout the water column over several hours defined here as the bore period until a sharp warm front relaxation followed by high frequency temperature fluctuations returns the column back to nearly its original state defined here as the mixing period mixing periods revealed increased temperature variance at high frequencies n as well as a greater percentage of events where dynamic instabilities may be present ri 0 25 suggesting active mixing of the stratified water column turbulent dissipation rates in the stratified interior during the mixing period estimated using the technique of isopycnal slope spectra revealed mean values the same order of magnitude as near bed bottom generated turbulence observations indicate that local shear produced turbulent kinetic energy by the warm front relaxations dominates mixing in the stratified interior the non canonical nature of these bore and relaxation events is also investigated with a numerical model and the dynamics are shown to depend on the internal iribarren number our results suggest that nearshore internal bores interacting with local bathymetry dramatically alter local dynamics and mixing in the nearshore with important ecological implications

geochemical characteristics and hydrocarbon generation modeling of the jurassic source rocks in the shoushan basin north western desert egypt abstract the shoushan basin is an important hydrocarbon province in the western desert egypt but the origin of the hydrocarbons is not fully understood in this study organic matter content type and maturity of the jurassic source rocks exposed in the shoushan basin have been evaluated and integrated with the results of basin modeling to improve our understanding of burial history and timing of hydrocarbon generation the jurassic source rock succession comprises the ras qattara and khatatba formations which are composed mainly of shales and sandstones with coal seams the toc contents are high and reached a maximum up to 50 the toc values of the ras qattara formation range from 2 to 54 wt while khatatba formation has toc values in the range 1 47 wt the ras qattara and khatatba formations have hi values ranging from 90 to 261 mghc gtoc suggesting types ii iii and iii kerogen vitrinite reflectance values range between 0 79 and 1 12 vrr rock eval t max values in the range 438 458 c indicate a thermal maturity level sufficient for hydrocarbon generation thermal and burial history models indicate that the jurassic source rocks entered the mature to late mature stage for hydrocarbon generation in the late cretaceous to tertiary hydrocarbon generation began in the late cretaceous and maximum rates of oil with significant gas have been generated during the early tertiary paleogene the peak gas generation occurred during the late tertiary neogene

migration induced compositional changes in oils and condensates of a single field thirty one oils and condensates from the vermilion 39 field offshore louisiana u s gulf coast are examined using techniques of elemental isotopic and molecular geochemistry in an effort to determine the causes of compositional differences among them compositional variability in elemental concentration carbon isotope ratios and molecular distributions suggests that at least two sub groups occur in the sample set the sub groups are characterized by differences in n c 15 content relative to n c 15 pristane phytane ratio 13 c sulfur and nitrogen concentration and s n ratio although the separation into these two sub groups is superficially indicative of distinct sources and or variable levels of thermal maturity interpretation of the data set as a whole indicates that source influences maturity differences and biodegradation do not control observed variations in composition reliable source e g r c 27 29 sterane distribution and maturity e g 20s 20s 20r parameters provide clear evidence of a common source and constant maturity level for all 31 oils condensates the remaining geochemical differences including various molecular pristane phytane isotopic 13 c oil and elemental s n parameters correlate with the extent of migration fractionation that each sample has undergone as measured by the relative amount of n c 15 in each sample the migration fractionation process in the vermilion 39 field is facilitated by fault initiated pressure releases within reservoirs that originally contained full range crudes vertical migration of the released saturated hydrocarbon gases has led to a concentration of lighter components in the most fractionated samples this geochemical interpretation is supported by geologic data inasmuch as the extent of fractionation is least in the deepest samples and greatest in the shallowest samples the results presented here indicate the potential for misinterpretation of geochemical parameters previously considered to be influenced solely by source influence or thermal maturity

numerical investigation of internal wave induced sediment motion resuspension versus entrainment we present numerical simulations of near bed instability induced by internal waves shoaling over topography using a model with an explicit representation of the sediment concentration we find that not all separation bubble bursting events lead to resuspension though all lead to significant transport out of the bottom boundary layer this transport can significantly enhance chemical exchange across the bottom boundary layer when resuspension occurs we find that it is largely due to two dimensional evolution of the separation bubble during the bursting process three dimensionalization occurs once the resuspended sediment cloud is transported out of the bottom boundary layer and hence redeposition is strongly influenced by three dimensional effects we derive a criterion for resuspension over a linearly sloping bottom in terms of two dimensionless parameters that encapsulate the sediment properties

geomorphic characterization of four shelf sourced submarine canyons along the u s mid atlantic continental margin abstract shelf sourced submarine canyons are common features of continental margins and are fundamental to deep sea sedimentary systems despite their geomorphic and geologic significance relatively few passive margin shelf breaching canyons worldwide have been mapped using modern geophysical methods between 2007 and 2012 a series of geophysical surveys was conducted across four major canyons of the us mid atlantic margin wilmington baltimore washington and norfolk canyons more than 5700 km2 of high resolution multibeam bathymetry and 890 line km of sub bottom chirp profiles were collected along the outer shelf and uppermost slope depths of 80 1200 m the data allowed us to compare and contrast the fine scale morphology of each canyon system the canyons have marked differences in the morphology and orientation of canyon heads steepness and density of sidewall gullies and the character of the continental shelf surrounding canyon rims down canyon axial profiles for washington baltimore and wilmington canyons have linear shapes and each canyon thalweg exhibits morphological evidence for recent relatively small scale sediment transport for example washington canyon displays extremely steep wall gradients and contains 100 m wide 5 10 m deep v shaped incisions down the canyon axis suggesting modern or recent sediment transport in contrast the convex axial thalweg profile the absence of thalweg incision and evidence for sediment infilling at the canyon head suggest that depositional processes strongly influence norfolk canyon during the current sea level high stand the north walls of wilmington washington and norfolk canyons are steeper than the south walls due to differential erosion though the underlying cause for this asymmetry is not clear furthermore we speculate that most of the geomorphic features observed within the canyons e g terraces tributary canyons gullies and hanging valleys were formed during the pleistocene and show only subtle modification by holocene processes active during the present sea level high stand

the western desert versus nile delta a comparative molecular biomarker study abstract the western desert and the nile delta are prolific petroleum producing basins the correlation and matching between their petroleum systems have been briefly studied overall geochemical and biological marker analyses of twelve crude oil and condensate samples taken from seven oil gasfields located in the nile delta and the western desert basins of egypt were effective in identifying and geographically defining two major oil families related by age and source rock depositional environment these samples were classified respectively as late cretaceous tertiary and jurassic early cretaceous the source rocks giving rise to the late cretaceous tertiary oils are associated with abundant terrestrial organic matter the source rocks giving rise to jurassic early cretaceous oil are presumably generated from a mixed terrestrial marine source meanwhile the western desert oil samples show prominent c 30 steranes elevated c 27 monoaromatic steroids and a distinct homohopane distribution suggesting this oil type is derived from a more marine influenced source rock than terrigenous sourced oil in the nile delta the most crucial geochemical fingerprinting biomarkers that have been used to differentiate between nile delta and the western desert oil are oleananes highly branched isoprenoids hbi sterane isomerization 24 norcholestanes aromatic steroid hydrocarbons and c 30 24 n propylcholestanes

generation of internal solitary waves by lateral circulation in a stratified estuary abstractinternal solitary waves are commonly observed in the coastal ocean where they are known to contribute to mass transport and turbulent mixing while these waves are often generated by cross isobath barotropic tidal currents novel observations are presented suggesting that internal solitary waves result from along isobath tidal flows over channel shoal bathymetry mooring and ship based velocity temperature and salinity data were collected over a cross channel section in a stratified estuary the data show that ekman forcing on along channel tidal currents drives lateral circulation which interacts with the stratified water over the deep channel to generate a supercritical mode 2 internal lee wave this lee wave propagates onto the shallow shoal and evolves into a group of internal solitary waves of elevation due to nonlinear steepening these observations highlight the potential importance of three dimensionality on the conversion of tidal flow to internal waves in the rotating ocean

energy transport by nonlinear internal waves wintertime stratification on oregon s continental shelf often produces a near bottom layer of densefluid that acts as an internal waveguide on which nonlinear internal waves propagate shipboard profiling and bottom lander observations capture disturbances that exhibit properties of internal solitary waves bores and gravity currents wave like pulses are highly turbulent instantaneous bed stresses are 1 n m 2 resuspending bottom sediments into the water column and raising them 30 m above the seafloor the waves cross shelf transport of fluid counters the time averaged ekman transport in the bottom boundary layer in the nonlinear internal waves we have observed the kinetic energy is roughly equal to the available potential energy and is o 0 1 mj per m of coastline the energy transported by these waves includes a nonlinear advection term huei that is negligible in linear internal waves unlike linear internal waves the pressure velocity energy flux hupi includes important contributions from nonhydrostatic effects and surface displacement it is found that statistically huei 2hupi vertical profiles indicate that up z is more important in transporting energy near the seafloor while ue z dominates farther from the bottom with the wave speed c estimated from weakly nonlinear wave theory it is verified experimentally that the total energy transported by the waves hupi huei chei the high but intermittent energyflux by the waves is in an averaged sense o 100 w per m of coastline this is similar to independent estimates of the shoreward energy flux in the semidiurnal internal tide at the shelfbreak

sedimentary processes on the atlantic continental slope of the united states abstract until recently the sedimentary processes on the united states atlantic continental slope were inferred mainly from descriptive studies based on the bathymetry and on widely spaced grab samples bottom photographs and seismic reflection profiles over the past 6 years however much additional information has been collected on the bottom morphology characteristics of shallow subbottom strata velocity of bottom currents and transport of suspended and bottom sediments a review of these new data provides a much clearer understanding of the kinds and relative importance of gravitational and hydrodynamic processes that affect the surface sediments on the rugged slope between georges bank and cape lookout n c these processes include 1 small scale mass wasting within submarine canyons and peripheral gullies 2 density flows within some submarine valleys 3 sand spillover near the shelf break 4 sediment creep on the upper slope and 5 hemipelagic sedimentation on the middle and lower slope the area between georges bank and hudson canyon is further distinguished by the relative abundance of large scale slump scars and deposits on the open slope the presence of ice rafted debris and the transport of sand within the heads of some submarine canyons between cape lookout and southern florida the slope divides into two physiographic units and the topography is smooth and featureless on the florida hatteras slope offshelf sand spillover and sediment winnowing related to gulf stream flow and possibly to storm driven currents are the major processes whereas hemipelagic sedimentation is dominant over the offshore slope along the seaward edge of the blake plateau north of the blake spur slumping generally is absent south of cape lookout although one large slump scarp related to uplift over salt diapirs has been identified east of cape romain future studies concerning sedimentary processes on the atlantic slope need to resolve 1 the ages and mechanisms of mass wasting 2 the accumulation rates and thicknesses of hemipelagic sediments and 3 the causes and variability of offshelf sand spillover sediment winnowing and canyon transport

applications and limitations of mango s light hydrocarbon parameters in petroleum correlation studies mango 1987 reported on the remarkable invariance of four isoheptanes in petroleums regardless of the absolute concentration the ratio of sums of concentration of 2 methylhexane 2 3 dimethylpentane 3 methylhexane 2 4 dimethylpentane remains constant the k1 ratio value being around unity gas chromatographic analyses of an additional 500 oils contradict this invariance as a suite of oils from the cretaceous northwest basin argentina deviate significantly by having a ratio of 1 67 still oils derived from the same structural kerogen have invariant ratios that can vary from a lowest value of 0 79 found for the midland oil set mango 1990 up to a highest value of 1 67 found for the cretaceous northwest basin mango 1990 postulated so called parent daughter schemes having an invariance in the ratio of isoheptanes and dimethylcyclopentanes an invariance unique for a homologous set of oils but possibly distinctly different from another suite of homologous oils it will be shown here that this difference in invariance can be used in oil oil correlation studies and that this technique is especially powerful for oil condensate correlation condensates in which the concentration of biological markers is quite often below the limit of detection further the concentration of light hydrocarbons needed for this approach can be determined from whole oil gas chromatography without any pre treatment thus providing a rapid and cheap tool for correlation studies

evolution of veatch washington and norfolk submarine canyons inferences from strata and morphology abstract investigations of veatch washington and norfolk submarine canyons on the eastern continental margin of the united states resulted in a detailed assessment of their past and present geologic processes norfolk and washington canyons share such characteristics as similar levee geometry stratigraphy and mineralogy veatch canyon differs from norfolk and washington canyons in these respects seismic reflection profiles of all three submarine canyon heads indicate an erosional origin seismic profiles of veatch canyon s lower continental slope indicate a formation by depositional processes in contrast the continental slope profiles of washington and norfolk canyons reveal a history of alternating episodes of deposition and erosion cored sediments from washington and norfolk canyons disclose recent intermittent down canyon transport of sand to the continental rise bathymetric and seismic profiles suggest veatch washington and norfolk canyons have all been subjected to a minimum of two periods of development similar axial trends of washington and norfolk canyons imply a common structural influence

ubiquitous occurrence of high molecular weight hydrocarbons in crude oils abstract for many years the presence of waxes in crude oils has been associated with organic matter derived from terrigenous sources high temperature gas chromatography htgc has been used to establish the ubiquitous presence of high molecular weight hmw hydrocarbons extending as high as c 120 in crude oils hmw hydrocarbons c 40 have been observed in crude oils derived from terrigenous lacustrine and marine source materials modified extraction techniques have also led to the detection of hmw hydrocarbons in source rock extracts the fractions of hmw hydrocarbons are complex mixtures of long chain aliphatic and alkyl aromatic hydrocarbons and can represent up to 8 of a whole oil the carbon preference index cpi of hmw alkylcyclopentanes in the c 42 c 46 range provides useful information on the characteristics of the original depositional environment age maturity and degree of biodegradation do not appear to affect the cpi of alkylcyclopentanes used for evaluating depositional environments differences in the distributions of the hmw hydrocarbons between the source rock extracts and the crude oils in the reservoirs may reflect changes occurring due to migration

hydrocarbon potential and depositional paleoenvironment of a middle jurassic succession in the falak 21 well shushan basin egypt integrated palynological geochemical and organic petrographic approach abstract the topmost lower and middle jurassic formations of organic rich clastics with minor carbonate deposits were recognized as very significant source reservoir rocks in the north western desert of egypt although several studies are devoted to their source rock characteristics and petroleum potential the depositional paleoenvironment and paleoredox conditions are still poorly understood in the current study these sediments were assessed in terms of their organic matter richness hydrocarbon generative potential and thermal maturity total sulfur ts contents and organic petrographic characteristics depositional paleoenvironment was investigated using dinoflagellate cysts dinocysts and the composition of particulate organic matter along with organic petrographic characteristics redox conditions were assessed based on ts total organic carbon toc relationship and type of kerogen that was derived mainly from palynofacies analysis toc contents show fair to excellent generative potential of hydrocarbons mainly of kerogen type iii gas prone the thermal maturity based on tmax and rr indicates mature stage of oil window palynological analysis yielded poor to rich intervals of moderately preserved biostratigraphically useful dinocysts in the upper part of the khatatba formation an assemblage of 81 species belonging to 54 genera of moderately diverse dinocysts spores and pollen grains was identified freshwater algae acritarchs and microforaminiferal test linings are sporadically documented within the studied interval based on the first downhole appearance fda of the recovered marker dinocyts the upper part of the khatatba formation was palynologically dated as late bathonian callovian the depositional environment was interpreted and three environments were deduced the lower interval representing the topmost ras qattara and yakout red shale member was deposited in a fluvial lacustrine environment where oxic conditions prevailed as deduced from the color of reddish brown sandstone and red shale the middle interval spans unit iib kabrit and unit iii which accumulated in a deltaic to shallow marine environment under dysoxic suboxic settings the upper interval covers unit i and unit iia that have been deposited in a fluvio deltaic to shallow marine with high paleoproductivity under suboxic conditions one sample in the upper interval in unit iia reflected anoxic setting

observations of internal wave reflection off sloping bottoms current and temperature spectra exhibit intensification and polarization near sloping bottoms over a band of frequencies centered at the local internal wave critical frequency examples are drawn from a variety of island seamount and continental slope observations waves propagating down from mid depth change energy density wave number and azimuth when they reflect off the bottom providing a natural perturbation to the deep ocean interior internal wave spectrum deviations from linear theory are interpreted as evidence for dissipation through subsequent shear instability and or nonlinear interaction topographic features appear likely to be energy sinks for internal wave energy

the effect of wave induced turbulence on the ocean mixed layer during tropical cyclones field observations on the australian north west shelf 1 field observations of water temperature on the australian north west shelf eastern indian ocean with the support of numerical simulations are used to demonstrate that the injection of turbulence generated by the wave orbital motion substantially contributes to the mixing of the upper ocean measurements also show that a considerable deepening of the mixed layer occurs during tropical cyclones when the production of wave induced turbulent kinetic energy overcomes the contribution of the current generated shear turbulence despite a significant contribution to the deepening of the mixed layer the effect of a background current and atmospheric forcing are not on their own capable of justifying the observed deepening of the mixed layer through most of the water column furthermore variations of a normally shallow mixed layer depth are observed within a relatively short timescale of approximately 10 hours after the intensification of wave activity and vanish soon after the decay of storm surface waves this rapid development tends also to exclude any significant contribution by wave breaking as small rates of vertical diffusivity for wave breaking induced turbulence would require longer timescales to influence the depth of the mixed layer

internal bores and breaking internal tides on the oregon continental slope abstractobservations of breaking internal tides on the oregon continental slope during a 40 day deployment of 5 moorings along 43 12 n are presented remotely generated internal tides shoal onto the slope steepen break and form turbulent bores that propagate upslope independently of the internal tide a high resolution snapshot of a single bore is captured from lowered acoustic doppler current profilers ladcp ctd profiles in a 25 h time series at 1200 m the bore is cold salty over 100 m tall and has a turbulent head where instantaneous dissipation rates are enhanced e 10 6 w kg 1 and sediment is resuspended at the two deepest slope moorings 1452 and 1780 m similar borelike phenomena are observed in near bottom high resolution temperature time series mean dissipation rates and diapycnal diffusivities increase by a factor of 2 when bores are present w kg 1 and m s 1 and observed internal tides are energetic enough to drive these enhanced dissipation rates globally the authors estimate

small and mesoscale processes and their impact on the large scale an introduction abstract great progress has been made in understanding the role of small and mesoscale processes on the large scale structure and circulation of the oceans however many questions remain regarding the sensitivity of the large scale ocean circulation and hence the earth s climate to rates of stirring mixing and dissipation supported by ocean eddies internal waves and boundary layers although such relatively small scale oceanic phenomena are ubiquitous we lack detailed knowledge about their interaction with the large scale motions as well as their interactions amongst themselves contributions are presented from observational theoretical and modeling studies that focus on small and mesoscale ocean processes and some parameterizations of these processes for use in studies of the large scale circulation the range of topics is relatively broad with most focus on internal wave generation flow topography interaction and small and mesoscale processes involved in ocean mixing general conclusions emphasize the notion of localized mixing and the importance of interaction between waves eddies and topography and the importance of interactions between oceanic motions and the background density stratification

gravity currents facilitate formation of high frequency internal solitons and bores at the base of the fraser delta in the southern strait of georgia

peruvian sediments as recorders of an evolving hiatus for the last 22 thousand years highlights review of sediment archives from the peruvian margin since the lgm focus on the evolutionary feature of the hiatus found in archives modern analogue for current dominated environments for paleo reconstructions new results for erosional potential of the non linear internal waves nliws abstract the peruvian continental margin is characterized by the presence of one of the strongest and most distinct oxygen minimum zones omzs in today s oceans therefore it has long been in the focus of oceanographic and geological investigations observations indicate that omzs are expanding in relation with currently changing climate to advance understanding of the temporal evolution of omzs and climate change complete paleoceanographic and palaeoclimatological reconstructions are needed however the development of paleoenvironmental scenarios for the period since the last glacial maximum at this region was hampered by a ubiquitous hiatus and short term interruptions of the stratigraphical record in the present study we combined the stratigraphical information from 31 sediment cores from the peruvian margin located between 3 and 18 s and water depths of 90 to 1300 m within and below today s omz in order to determine the extent of the hiatus and assess the responsible mechanisms a widespread unconformity and related erosional features omission surfaces and phosphorites were observed in sediment cores from the area south of 7 s depicting a prograding feature on the continental slope from south to north during the deglaciation combining recent oceanographic and sedimentological observations it is inferred that tide topography interaction and resulting non linear internal waves nliws shape the slope by erosion carry sediments upslope or downslope and leave widespread phosphoritic lag sediments while the peru chile undercurrent pcuc transports the resuspended sediments southward causing non deposition this exceptional sedimentary regime makes the peruvian margin a modern analogue for such environments overall our compilation of downcore records showed that enhanced bottom currents due to tide topography interaction were progressively evolving and affected a wider area with the onset of the last deglaciation elevated tidal amplitudes and variability of mid depth water masses i e density changes and hydrodynamics in relation with changing climate were potential reasons of this evolving feature of erosion and reworking additionally erosion and non deposition was observed widest and even was encountered on the continental shelf during the early holocene potentially indicating a strong phase of the pcuc mirroring today s el nino like conditions

observations of nonlinear internal waves on the outer new england continental shelf during the summer shelfbreak primer study observations are presented of nonlinear internal waves on the outer new england continental shelf during the summer shelfbreak primer study conducted between july 26 and august 5 1996 current and temperature measurements were made with an upward looking acoustic doppler current profiler adcp located on the 147 m isobath near the shelfbreak and three vertical thermistor moorings located upshelf data from the adcp and two nearby thermistor chains show energetic internal tides propagating at roughly 0 9 m s 21 to the north northwest nearly perpendicular to the local topography with 10 15 cm s 21 horizontal currents and 15 30 m vertical displacements these waves evolve rapidly within a 5 8 km range into an undular internal tidal bore cross isobath barotropic tidal currents responsible for generating the internal tides are in the 5 12 cm s 21 range the bore formation is highly variable there is evidence of a correlation between internal tide steepening and a shelfbreak front jet orientation that is oppositely directed to the internal tide propagation there is no correlation between steepening and the jet s vertical shear statistics of the undular bores show rms travel time fluctuations from 0 8 to 1 7 hours and average tidal bore durations from 12 to 9 hours the average undular bore speed is 0 9 m s 21 with an rms fluctuation of 0 4 m s 21 the number of high frequency waves in the bore varies from 0 to 8 near the shelfbreak and increases to 30 waves 26 7 km upshelf the observed distribution function of temporal spacing between high frequency internal waves is spread between 4 and 20 min

the pressure disturbance of a nonlinear internal wave train observations from a lander fixed to the seafloor over the continental shelf in 124 m of water provide highly resolved velocity measurements through nonlinear internal waves of elevation from these measurements we determine for the first time the non hydrostatic pressure disturbance p nh in nonlinear internal waves for near bottom waves of elevation ranging in amplitude a from 12 to 33 m the value of p nh evaluated at the seafloor changes sign from 0 to and back in accordance with weakly nonlinear theory peak values of vert p nh vert range from 25 to 90 n m 2 the external hydrostatic pressure disturbance due to the surface displacement eta h is inferred from horizontal accelerations for elevation waves eta h peak values range from 0 1 to 9 mm 1 to 90 n m 2 the internal hydrostatic pressure perturbation p wh caused by isopycnal displacement is inferred from measured streamlines and an ambient density profile its value at the seafloor is 0 for elevation waves peak values range from 100 to 300 n m 2 vert eta h vert and seafloor values of vert p nh vert p wh all increase monotonically with a since vert p nh vert and p wh increase at roughly the same rate with a no clear trend arises in the degree to which waves become more or less non hydrostatic as a changes a distinct bottom pressure signature is determined for bottom trapped nonlinear waves of elevation a wave train consisting of a sequence of positive pressure perturbations dominated by p wh by inference a train of surface trapped nonlinear internal waves of depression will consist of a sequence of negative pressure perturbations a result of this analysis is that significant properties of the waves can be discerned from a simple adequately resolved bottom pressure measurement

near bottom current speed maxima in north atlantic contourite environments inferred from current induced bedforms and other seabed evidence abstract seabed acoustic data e g deep tow side scan sonar together with information from seabed photography is presented for estimating near bottom current speed maxima in north atlantic contourite environments these include the southern iceland faroe ridge flank the southeast and southwest greenland margin and the greater antilles outer ridge in the southwestern part of the north atlantic geomorphological response to north atlantic deep water circulation is expressed in a variety of dynamic bedforms and other current controlled seabed features various types of dynamic bedforms reflect different hydraulic energy levels maximum near bottom flow speed of almost 1 0 m s or more is illustrated by infinite sand ribbons found on lag sediment while a much lower maximum of near bottom water flow speed

the shaping of continental slopes by internal tides the angles of energy propagation of semidiurnal internal tides may determine the average gradient of continental slopes in ocean basins 2 to 4 degrees intensification of near bottom water velocities and bottom shear stresses caused by reflection of semi diurnal internal tides affects sedimentation patterns and bottom gradients as indicated by recent studies of continental slopes off northern california and new jersey estimates of bottom shear velocities caused by semi diurnal internal tides are high enough to inhibit deposition of fine grained sediment onto the slopes

internal tides in the strait of gibraltar abstract analysis of moored current measurements in the strait of gibraltar is provided here the vertical internal displacements double amplitudes with a semidiurnal frequency are extremely large and sometimes exceed 200 m it is found that these displacements are associated with forced tidal internal waves over camarinal sill which crosses the strait the separation of tidal components showed that the amplitude of internal tide with m2 frequency is 69 m while the amplitudes of other components of the internal tide s2 k1 o1 are 3 5 times smaller the amplitudes of the waves decrease with the distance from the sill and at a distance of 50 km from the sill the amplitudes are 3 times smaller than over the sill the energy of internal tides is transferred to internal bore and turbulent mixing the wavelength of the internal tide was estimated on the basis of moored measurements the wavelength of the east propagated wave is 90 km while the west propagated wave is 60 km numerical modeling demonstr

classification and thermal history of petroleum based on light hydrocarbons abstract classifications of oils and kerogens are described two indices are employed termed the heptane and isoheptane values based on analyses of gasoline range hydrocarbons the indices assess degree of paraffinicity and allow the definition of four types of oil normal mature supermature and biodegraded the values of these indices measured in sediment extracts are a function of maximum attained temperature and of kerogen type aliphatic and aromatic kerogens are definable only the extracts of sediments bearing aliphatic kerogens having a specific thermal history are identical to the normal oils which form the largest group 41 in the sample set this group was evidently generated at subsurface temperatures of the order of 138 149 c 280 300 f defined under specific conditions of burial history it is suggested that all other petroleums are transformation products of normal oils

wind induced currents and bottom trapped waves in the santa barbara channel the santa barbara channel sbc is a coastal basin about 100 km long bounded by the southern california mainland on the north and by a chain of islands on the south the sbc is at most 50 km wide and just over 600 m deep the nature of current and wind variance peaks in the 2 4 day and 4 6 day bands in the channel are analyzed from january to july 1984 for both bands the dominant empirical mode of the currents is highly coherent with the dominant empirical mode of the winds over this region surface intensification of currents is revealed by measurements made between 25 and 300 m in contrast the deeper currents are characterized by bottom trapping evidence for baroclinic bottom trapped topographic rossby waves is found on the northern shelf at the western mouth of the channel in both frequency bands at 30 m the distribution of phases shows currents at the center of the western mouth leading the southern interisland passes by about 0 3 day and the eastern mouth by about 0 6 day in both bands co and quadrature vectors of currents and winds describe this wind current system in detail it is speculated from spatial and temporal eigenfunctions of currents and winds and from available satellite images that the dominant current mode described above is a channelwide response to upwelling north of point conception northwestward of the sbc the upwelling related currents cause a net inflow of mass into the western end of the channel which is compensated by an outflow passing through both the interisland passes and through the eastern mouth of the channel as a result of the narrowness and shallowness of the passes and of the shallowness of the southern shelf in general high flow speeds are attained there that the authors speculate seem to force deep high frequency motions both at the center of the sbc and at the northern half of its western mouth

a statistical analysis of extreme events in current variations due to internal waves from the australian north west shelf measurements of current fluctuations due to internal waves obtained from two fixed point moorings on the australian north west shelf have been analyzed with the aim of calculating the probability of short scale large amplitude internal waves exceeding particular values such waves are generated as a result of breaking or hydrodynamical instability of the semidiurnal internal tide the statistical stationarity of each record has been checked and it is shown that the records can be used for the calculation of the frequency by which currents exceed a particular value for wave heights double amplitudes of less than 60 cm s 1 the theoretical forms for exceedance frequency from the theory of extreme statistics have been checked and it is shown that for one location a power asymptotic provides a slightly better descriptor of the statistics than an exponential asymptotic and for the other location an exponential asymptotic is found to provide the better fit the exceedance frequency for internal waves near the australian north west shelf is found to be less than 1 3 waves per hour the exceedance probability for each location has been calculated using poisson statistics

hydraulic jump and undular bore formation on a shelf break abstract the evolution of the semidiurnal internal tide as it propagates across the australian north west shelf is discussed analytically as the tide is of long wavelength and small amplitude this evolution is described by a perturbed extended korteweg de vries equation it is found that the flow is dominated by nonlinearity and hence is hydraulic except in the neighborhood of any shocks predicted by hydraulic theory hydraulic theory predicts the formation of two shocks in each period of the tide the inclusion of dispersion in boundary layers around the shocks results in one of these shocks breaking up into an undular bore good agreement is found with observations by holloway of the semidiurnal internal tide on the australian north west shelf

a nonlinear model of internal tide transformation on the australian north west shelf a numerical solution to the generalized korteweg de vries k dv equation including horizontal variability and dissipation is used to model the evolution of an initially sinusoidal long internal wave representing an internal tide the model shows the development of the waveform to the formation of shocks and solitons as it propagates shoreward over the continental slope and shelf the model is run using observed hydrographic conditions from the australian north west shelf and results are compared to current meter and thermistor observations from the shelf break region it is found from observations that the coefficient of nonlinearity in the k dv equation changes sign from negative in deep water to positive in shallow water and this plays a major role in determining the form of the internal tide transformation on the shelf there is strong temporal variability in the nonlinear coefficient due to both background shear flow and the large amplitude of the internal tide which distorts the density profile over a wave period both the model and observations show the formation of an initial shock on the leading face of the internal tide in shallow water the change in sign of the coefficient of nonlinearity causes the shock to evolve into a tail of short period sinusoidal waves after further propagation a second shock forms on the back face of the wave followed by a packet of solitons the inclusion of bottom friction in the model is investigated along with the dependance on initial wave amplitude and variability in the coefficients of nonlinearity and dispersion friction is found to be important in limiting the amplitudes of the evolving waves

high frequency internal waves in lake geneva trains of high frequency internal waves have been observed in the thermocline of lake geneva within a few hours after the passing of disturbances which cause a rapid increase or jump in the depth of the thermocline three possible mechanisms for the source of the internal waves are proposed and compared with available data i that the waves are a soliton packet following the jump ii that the waves are generated as the jump passes over or around a local region of rough topography and iii that the jump produces a moving disturbance near the shoreline with internal waves forming a wake behind it the investigation of the last possibility involves the solution of the problem of the form of an internal wave wake in the presence of mean currents which vary in depth both in their strength and direction the wave pattern of the wake in the observed current distribution and stratification of the lake is described and compared with that in the absence of shear an expression for the energy of internal waves propagating in a shear flow is also derived and it is found that the rate of energy loss from the jump to the waves is small the minimum richardson number resulting from the co existence of the mean shear and the internal waves is marginally greater than 1 4 suggesting that the waves may be limited by shear flow instability however none of the mechanisms for their generation and propagation is fully compatible with the available data

application of tetracyclic polyprenoids as indicators of input from fresh brackish water environments abstract c30 tetracyclic polyprenoids tpp are most prominently observed in samples derived from low salinity i e fresh to brackish lacustrine environments and are generally present in low levels in samples derived from saline i e marine and saline lacustrine environments a near shore facies of the chonta formation peru that has no marine palynomorphs but abundant chlorococcalean green algal nonmarine palynomorphs has high levels of tpp suggesting green algae or chlorophyta are a possible source for the tpp compounds the ratio between a c30 tpp compound and 27 norcholestanes is useful for assessing this nonmarine algal input moderate elevations of tpp above what is common in marine derived samples were found in ostensibly marine source rocks and oils from certain basins of western and northern south america middle magdalena colombia maracaibo venezuela and trinidad basins this is likely due to transport from the nonmarine to the marine environment because of an influx of fresh water into the near shore marine environment alternatively oils from these basins may have inputs from near shore shallow marine algae with chemistry similar to that found in lacustrine settings the tpp ratio in conjunction with other environmental indicators such as 4 methyl steranes or hopane sterane ratio is useful for differentiating marine and nonmarine influences in pre salt oils and source rocks of west africa the tpp ratio used with other environmental indicators gammacerane c29 steranes c30 steranes and age diagnostic biomarkers dinosteranes 4 methylsteranes can be useful in differentiating among nonmarine source facies for example in the turpan hami basin china permian saline lacustrine and jurassic lacustrine deltaic facies can be discriminated

internal solitons on the pycnocline generation propagation and shoaling and breaking over a slope in part 1 a study is made of the internal solitary wave on the pycnocline of a continuously stratified fluid a korteweg de vries kdv equation for the interfacial displacement is developed following benney s method for long nonlinear waves experiments were conducted in a long wave tank with the pycnocline at several different depths below the free surface while keeping the total depth approximately constant a step like pool of light water trapped behind a sliding gate served as the initial disturbance condition the number of solitons generated was verified to satisfy the prediction of inverse scattering theory the fully developed soliton was found to satisfy the kdv theory for all ratios of upper layer thickness to total depth in part 2 of this study we investigate experimentally the evolution and breaking of an internal solitary wave as it shoals on a sloping bottom connecting the deeper region where the waves were generated to a shallower shelf region it is found through quantitative measurements that the onset of wave breaking was governed by shear instability which was initiated when the local gradient richardson number became less than the internal solitary wave of depression was found to steepen at the back of the wave before breaking in contrast with waves of elevation two slopes were used with ratios 1 16 and 1 9 and the fluid was a boussinesq fluid with weak stratification using brine solutions

nonlinear motions at the internal tide source 1 oceanic internal tidal wave generation is commonly modeled via interaction of a sinusoidal barotropic vertical velocity w with topography however general w above slopes are predominantly nonlinear as appears in some nonhydrostatic models here 1 2 hz sampled observations are presented from 2 84 m above the bottom mab at 1400 m at the bay of biscay continental slope fronts are observed that all propagate upslope having heights 50 mab and more or less 5 occurring at the tidal periodicity they are accompanied by o 10 min pulses of w 0 10 m s 1 w and irregular small scale waves superimposed on an asymmetric tidal signal this nonlinearity is further exemplified by variations in frontal arrival and steepness height form and is causing i internal tidal intermittency of 10 tidal periods ii nonlinear generation of internal tidal higher harmonics at the source the observations suggest internal tide generation in a broadband instead of a monochromatic beam

a downslope propagating thermal front over the continental slope in the ocean internal frontal bores above sloping topography have many appearances depending on the local density stratification and on the angle and source of generation of the carrier wave however their common characteristics are a backward breaking wave strong sediment resuspension andrelatively cool denser water moving more or less upslope underneath warm less dense water in thispaper we present a rare example of a downslope moving front of cold water moving over near bottomwarm water large backscatter is observed in the downslope moving front s trailing edge rather than theleading edge as is common in upslope moving fronts time series observations have been made during afortnight in summer using a 101 m long array of high resolution temperature sensors moored with anacoustic doppler current profiler at 396 m depth in near homogeneous waters near a small canyon in thecontinental slope off the malin shelf west scotland uk occurring between fronts that propagate upslopewith tidal periodicity the rare downslope propagating one resembles a gravity current and includes strongconvective turbulence coming from the interior rather than the more usual frictionally generated turbulencearising from interaction with the seabed its turbulence is 3 10 times larger than that of more commonupslope propagating fronts as the main turbulence is in the interior with a thin stratified layer close tothe bottom little sediment is resuspended by a downslope propagating front the downslope propagatingfront is suggested to be generated by oblique propagation of internal tidal waves and flow over a nearbyupstream promontory

connecting wind driven upwelling and offshore stratification to nearshore internal bores and oxygen variability this study utilizes field observations in southern monterey bay ca to examine how regional scale upwelling and changing offshore shelf conditions influence nearshore internal bores we show that the low frequency wind forcing e g upwelling relaxation time scales modifies the offshore stratification and thermocline depth this in turn alters the strength and structure of observed internal bores in the near shore an internal bore strength index is defined using the high pass filtered potential energy density anomaly in the nearshore during weak upwelling favorable conditions and wind relaxations the offshore thermocline deepens in this case both the amplitude of the offshore internal tide and the strength of the nearshore internal bores increase in contrast during strong upwelling conditions the offshore thermocline shoals toward the surface resulting in a decrease in the offshore internal tide amplitude as a result cold water accumulates in the nearshore nearshore pooling and the internal bore strength index decreases empirical orthogonal functions are utilized to support the claim that the bore events contribute to the majority of the variance in cross shelf exchange and transport in the nearshore observed individual bores can drive shock like drops in dissolved oxygen do with rapid onset times while extended upwelling peri ods with reduced bore activity produce longer duration low do events

sediment transport processes on an active submarine fault escarpment gulf of corinth greece abstract sediment transport processes on the escarpment of a listric fault in the tectonically active and terrigenous sediment dominated corinth graben in greece are studied using 3 5 khz and airgun profiles and sidescan sonar images the whole of the slope area is affected by gravitational mass movements slumps debris mud flows and liquified and turbidity flows in canyon fan systems large volumes of sediment are transported through slumping debris mud and turbidity flows into the basin here they build coalescing fans which consist of intercalations of debris flow deposits and turbidites in delta front slope fan apron systems sediments are transported radially downslope through slumping debris mud flows liquified flows and high density turbidity flows into the basin where they build coalescing fan aprons these consist of massive homogenized deposits fluxoturbidites in shelf slope systems retrogressive rotational slumping is the dominant instability feature however due to the sharp increase in the slope gradient caused by the slumping debris and turbidity flows are triggered the major factors responsible for triggering gravitational mass movements in the region are earthquakes high sedimentation rates off the river mouths and heavy rainfalls and high seas these mass movements appear to occur at least once every 2 yrs as indicated by the failure of submarine cables

internal wave breaking at concave and convex continental slopes abstract internal wave reflection from a sloping topographic boundary may lead to enhanced shear if the topographic angle to the horizontal is close to that of the internal wave group velocity vector previous analytic studies have suggested that shear enhancement is reduced at concave slopes as compared with convex and planar slopes near the critical angle here the internal wave reflection from concave and convex slopes that pass through the critical angle is investigated numerically using the nonhydrostatic massachusetts institute of technology general circulation model mitgcm overturning shear instability and resultant mixing are examined results are compared with simulations of wave reflection from planar slopes with angles greater than less than and equal to the critical angle in contrast to the analytic predictions no reduction in mixing is found for the concave slope as compared with the other slopes in all cases stratification is eroded in a band above the slope bounded at its outer

exchange through the strait of gibraltar to measure the exchange between the atlantic and mediterranean through the strait of gibraltar an array of current meter moorings was deployed for a year in the strait during 1985 1986 a novel aspect of these measurements is the inclusion of conductivity as well as temperature and pressure sensors on each current meter so that the salinity of the flows could be monitored continuously these salinity measurements determine the water mass characteristics of the flows crossing the sill they allow definition of the 37 psu isohaline as the interface between inflowing fresher atlantic water and outflowing saltier mediterranean water and they enable time series to be developed for the depth of this interface for the upper layer inflow and for the lower layer outflow from these measurements the time averaged outflow of mediterranean water is estimated to be 0 68sv 1sv 1 106m3s 1 and the outflow salinity transport defined to be the outflow times the salinity excess above a basic atlantic water salinity of 36 1 psu is estimated to be 1 50 103m3s 1 1sv 1psu 1 103m3s 1 equivalent to a net evaporation over the mediterranean basin of 52cm y 1 extrapolated measurements of the inflow from current meters generally deployed below 100m depth yield an estimate for the time averaged inflow of 0 93sv which is believed to be unrealistically high in view of the better measured outflow and net evaporation thus a more realistic estimate of the inflow is 0 72sv equal to the sum of the outflow and net evaporation as required by the mass budget for the mediterranean sea such estimates of the exchange are smaller by almost a factor of 2 than previous values for the exchange by lacombe and richez 1982 the exchange across the gibraltar sill is found to be due in nearly equal parts to the mean currents and to the tidal fluctuations the mean currents are smaller than had been expected reaching a peak value of only about 60 cm s 1 in the deep outflow over the sill the tidal exchange is due to a strong correlation over the tidal period between the depth of the interface and the strength of the inflowing currents for the m2 tide at the sill the amplitude of the interface depth is 51 m and the amplitude of the tidal currents is 1 2m s 1 furthermore the inflow and interface depth have similar phases as a consequence the upper layer is deep on the inflowing tide so that a large slug of atlantic water crosses the sill into the mediterranean on the outflowing tide the interface is shallow so that a large slug of mediterranean water crosses the sill into the atlantic similar processes occur for the s2 o1 and k1 tides though the amplitude are smaller in this manner tidal oscillations lead to a time averaged exchange of water masses across the gibraltar sill the inflow and outflow defined to be the instantaneous transports above and below the 37psu isohaline interface exhibit m2 tidal amplitudes of 2 3 sv and 1 3sv respectively thus the tides are large enough to reverse the mean upper layer inflow and lower layer outflow daily averaged inflow and outflow transports exhibit low frequency fluctuations with standard deviations of 0 37sv and 0 22sv respectively such low frequency fluctuations have been shown previously to be associated with barotropic flows through the strait of gibraltar compensating for sea level variations over the mediterranean due to atmospheric pressure fluctuations candela winant and bryden 1989 finally from these measurements there appear to be little fortnightly or annual period fluctuations in the exchange through the strait of gibraltar

application of an internal tide generation model to baroclinic spring neap cycles 1 a numerical internal tide generation model is used to study the behavior of baroclinic spring neap cycles in open basins and channels the motivation for this study comes from an observation on tidal currents in faeroe shetland channel which is briefly described a surprisingly large baroclinic semidiurnal tidal signal is found in the lower part of the water column above the slope on the shetland side concurring with barotropic neap tides the numerical model results indeed show that the baroclinic spring neap cycle may have a phase shift with respect to the barotropic spring neap cycle and that the phase of the baroclinic cycle may vary strongly within short distances it is also shown that even small changes in the background conditions e g stratification can provoke a large phase shift in the baroclinic cycle a possible connection to intermittency is discussed

the degeneration of large scale interfacial gravity waves in lakes mechanisms for the degeneration of large scale interfacial gravity waves are identified for lakes in which the effects of the earth s rotation can be neglected by assuming a simple two layer model and comparing the timescales over which each of these degeneration mechanisms act regimes are defined in which particular processes are expected to dominate the boundaries of these regimes are expressed in terms of two lengthscale ratios the ratio of the amplitude of the initial wave to the depth of the thermocline and the ratio of the depth of the thermocline to the overall depth of the lake comparison of the predictions of this timescale analysis with the results from both laboratory experiments and field observations confirms its applicability the results suggest that for small to medium sized lakes subject to a relatively uniform windstress an important mechanism for the degeneration of large scale internal waves is the generation of solitons by nonlinear steepening since solitons are likely to break at the sloping boundaries leading to localized turbulent mixing and enhanced dissipation the transfer of energy from an initial basin scale seiche to shorter solitons has important implications for the lake ecology

sediment resuspension and mixing by resonantly generated internal solitary waves the observation of internal solitary waves isws propagating upstream along a strongly stratified bottom layer on the california shelf is reported an increased concentration of particulates in the water column accompanies the passage of these isw packets the estimated local richardson number in the bottom vicinity is around 1 4 and a vertical coefficient of eddy diffusivity of order 1022 m2 s21 is associated with the upstream propagating leading isw the leading isw gave rise to reversed flow in an 8 m layer above the bottom it is argued that the upstream propagating isws were generated by resonant flow over bottom topography internal waves generated in this way seem to be frequent in the record of a month long experiment model results suggest that the isws can carry up to 73 of such generated long wave energy the ocean conditions at the site are similar to those of other coastal sites which suggests that the phenomenon described here may be common

transport by breaking internal gravity waves on slopes we use the results of a direct numerical simulation dns with a particle tracking model to investigate three dimensional transport by breaking internal gravity waves on slopes onshore transport occurs within an upslope surge of dense fluid after breaking offshore transport occurs due to an intrusion of mixed fluid that propagates offshore and resembles an intermediate nepheloid layer inl entrainment of particles into the inl is related to irreversible mixing of the density field during wave breaking maximum onshore and offshore transport are calculated as a function of initial particle position and can be of the order of the initial wave length scale for particles initialized within the breaking region an effective cross shore dispersion coefficient is also calculated and is roughly three orders of magnitude larger than the molecular diffusivity within the breaking region particles are transported laterally due to turbulence that develops during wave breaking and this lateral spreading is quantified with a lateral turbulent diffusivity lateral turbulent diffusivity values calculated using particles are elevated by more than one order of magnitude above the molecular diffusivity and are shown to agree well with turbulent diffusivities estimated using a generic length scale turbulence closure model based on a favourable comparison of dns results with those of a similar two dimensional case we use two dimensional simulations to extend our cross shore transport results to additional wave amplitude and bathymetric slope conditions

sediment resuspension mechanisms associated with internal waves in coastal waters 1 large amplitude vertically trapped internal waves can induce sizable velocities and trigger hydrodynamic instabilities in the bottom boundary layer thereby contributing to the resuspension of sediments and the maintenance of sediment concentration in the water column we discuss numerical simulations of several different situations in which the boundary layer in the wave footprint undergoes hydrodynamic instability with a resultant increase in the incidence of spatiotemporal structures that could facilitate sediment resuspension for the case of internal solitary waves we provide bounds in parameter space separating regions in which internal waves can be expected to efficiently resuspend sediment from those in which the boundary layer in the wave footprint is both laminar and stable a notable finding is that the onset of instability is a strong function of the background current the lagrangian transport of passive particles due to the instability is explored and some quantitative measures of the efficiency of the particle transport process are provided we subsequently discuss the evolution of the power spectra of the bottom shear stress with time and find that while the general characteristics of the instability are robust lowering either the reynolds number or the strength of the background current leads to an increase in the typical length scales associated with the mature instability finally we discuss instabilities during the internal wave generation process and alternative instability mechanisms when the bottom is not flat

spatio temporal evolution of sediment waves developed on the gulf of valencia margin nw mediterranean during the plio quaternary abstract several fields of large scale sediment waves have been observed along the gulf of valencia continental margin nw mediterranean the largest sediment waves develop on the continental slope extending from 250 to 850 m water depth with wavelengths ranging between 500 m and 1000 m and wave heights from 2 m to 50 m on the lower part of the slope sediment waves are quasi stationary vertically accreting becoming up slope migrating towards the mid and upper part of the slope a second group of sediment waves have developed over the outer continental shelf with wavelengths of 400 to 800 m and heights of 2 to 4 m also displaying an up slope migrating pattern multi channel seismic lines crossing the continental margin show that the sediment waves over the continental slope region have been continuously developed on the foreset region of the prograding margin clinoform several units of sediment waves have been identified in the sedimentary record evolving in accordance with the margin progradation detailed analysis of single channel sparker seismic profiles revealed the presence of several sediment depositional subunits over the outer continental shelf some of them with successive development of sediment waves being truncated by erosive surfaces likely related to quaternary eustatic sea level oscillations these erosional surfaces can be followed downslope into paraconformable strata of the sediment waves on the continental slope where constant bedform growth is observed without being affected by sea level changes based on geophysical data the thickness of the sediment waves mapped units show that the largest sediment waves in wave ratio length and height develop where sediment deposition rates are the highest coinciding with the upper part of the continental slope foreset clinoforms confined by the presence of structural highs the development of these sediment waves has been previously explained by the interaction of internal waves over the continental slope because sediment waves are preserved in the sedimentary record since the lower pliocene internal waves activity could have been present in this part of the margin shortly after the zanclean reflooding of the mediterranean basin following the messinian desiccation event 5 6 my ago deep water hydrodynamic conditions were re established at that time modulating sediment transport and deposition over the continental slope and outer continental shelf

flow separation and resuspension beneath shoaling nonlinear internal waves 1 laboratory observations are presented showing the structure and dynamics of the turbulent bottom boundary layer beneath nonlinear internal waves nliws of depression shoaling upon sloping topography the adverse pressure gradient beneath the shoaling waves causes the rear face to steepen flow separation to occur and wave induced near bottom vortices to suspend bed material the resuspension is directly attributed to the near bed viscous stress and to near bed patches of elevated positive reynolds stress generated by the vortical structures these results are consistent with published field observations of resuspension events beneath shoaling nliws elevated near bed viscous stresses are found throughout the domain at locations that are not correlated to the resuspension events near bed viscous stress is thus required for incipient sediment motion but is not necessarily a precursor for resuspension resuspension is dependent on the vertical velocity field associated with positive reynolds stress and is also found to occur where the mean wave averaged vertical velocity is directed away from the bed the results are interpreted by analogy to the eddy stress and turbulent bursting resuspension models developed for turbulent channel flows

bottom pressure observations of deep sea internal hydrostatic and non hydrostatic motions in the ocean sloping bottom topography is important for the generation and dissipation of internal waves here the transition of such waves to turbulence is demonstrated using an accurate bottom pressure sensor that was moored with an acoustic doppler current profiler and high resolution thermistor string on the sloping side of the ocean guyot great meteor seamount water depth 549 m the site is dominated by the passage of strong frontal bores moving upslope once or twice every tidal period with a trail of high frequency internal waves the bore amplitude and precise timing of bore passage vary every tide a bore induces mainly non hydrostatic pressure while the trailing waves induce mainly internal hydrostatic pressure these separate internal wave pressure terms are independently estimated using current and temperature data respectively in the bottom pressure time series the passage of a bore is barely visible but the trailing high frequency internal waves are a bore is obscured by higher frequency pressure variations up to similar to 4 x 10 3 cpd approximate to 80n cpd cycles per day n the large scale buoyancy frequency these motions dominate the turbulent state of internal tides above a sloping bottom in contrast with previous bottom pressure observations in other areas infra gravity surface waves contribute little to these pressure variations in the same frequency range here such waves do not incur observed pressure this is verified in a consistency test for large reynolds number turbulence using high resolution temperature data the high frequency quasi turbulent internal motions are visible in detailed temperature and acoustic echo images revealing a nearly permanently wave turbulent tide going up and down the bottom slope over the entire observational period the spectral slope and variance of bottom pressure are equivalent to internal hydrostatic pressure due to internal waves in the lower 100 m above the bottom by non hydrostatic pressure due to high frequency internal waves and large scale overturning the observations suggest a transition between large scale internal waves small scale internal tidal waves residing on thin similar to 1 m stratified layers and turbulence

high frequency internal waves in large stratified lakes observations are presented from lake biwa and lake kinneret showing the ubiquitous and often periodic nature of high frequency internal waves in large stratified lakes in both lakes high frequency wave events were observed within two distinct categories 1 vertical mode 1 solitary waves near a steepened kelvin wave front and vertical mode 2 solitary waves at the head of an intrusive thermocline jet were found to have wavelengths 64 670 m and 13 65 m respectively and were observed to excite a spectral energy peak near 10 23 hz 2 sinusoidal vertical mode 1 waves on the crests of kelvin waves vertically coherent in both phase and frequency and bordering the thermocline jets in the high shear region trailing the vertical mode 2 solitary waves vertically incoherent in both phase and frequency were found to have wavelengths between 28 37 and 9 35 m respectively and excited a spectral energy peak just below the local maximum buoyancy frequency near 10 22 hz the waves in wave event categories 1 and 2 were reasonably described by nonlinear wave and linear stability models respectively analysis of the energetics of these waves suggests that the waves associated with shear instability will dissipate their energy rapidly within the lake interior and are thus responsible for patchy turbulent events that have been observed within the metalimnion conversely the finite amplitude solitary waves which each contain as much as 1 of the basinscale kelvin wave energy will propagate to the lake perimeter where they can shoal thus contributing to the maintenance of the benthic boundary layer

organic geochemical palynofacies and petrographic analyses examining the hydrocarbon potential of the kharita formation albian in the matruh basin northwestern egypt abstract a recent study of selected samples from the cretaceous albian kharita formation of egypt revealed very good to excellent source rock sr potential for six intraformational organic rich intervals this work investigates the sr potential of the entire kharita formation across the matruh basin using samples from two wells the abu tunis 1x well from the central part of the basin and the siqeifa 1x well drilled on the eastern margin of the basin more strongly reducing conditions were developed in the centre of the basin and resulted in the deposition of more organic rich shales by comparison to the less reducing conditions that prevailed on the eastern basin margin where the shales contain less organic matter deltaic intraformational shales and carbonates in the kharita formation of abu tunis 1x constitute a significant 120 m net of the potential sr the lower kharita formation contains 34 m net shale sr of good to very good excellent organic richness yielding values of 1 14 11 59 wt total organic carbon toc the organic matter has low hydrogen index hi values 184 389 mg hc g toc and amorphous organic matter aom and relatively high non opaque phytoclast frequencies indicating mainly gas oil prone organofacies kerogen types iii ii the upper kharita is rather important containing 86 m net shale carbonate sr that has fair to good organic richness 0 8 1 8 wt toc and lower hi 126 250 mg hc g toc a dominance of non opaque phytoclasts and subordinate aom frequencies which together indicate gas oil prone organofacies kerogen iii ii in the siqeifa 1x well kharita deltaic intraformational shales and shaley dolostones comprise 80 m net sr which has mainly fair to good to less very good organic richness 0 8 2 1 wt toc whilst low hi 93 220 mg hc g toc dominance of non opaque phytoclasts and subordinate aom indicate gas prone organofacies kerogen type iii a relative upward increase in deposition of lignite and coaly carbonaceous material supports a gas prone organofacies whilst thermal maturity indices only point to immature to early mature pre to early oil window srs in both the abu tunis 1x and siqeifa 1x wells hydrocarbon exploration focussing on this potential source rock may be justified in areas to the southeast of the matruh basin where modelling indicates this unit may have reached the late mature oil to main gas generation windows

egypt far western desert basins petroleum charge system as defined by oil chemistry and unmixing analysis abstract source rock analysis and maturity modeling in egypt s far western desert basins indicates that several jurassic and cretaceous petroleum source rocks could be mature and expelling hydrocarbons over much of the area highly variable oil characteristics suggest that more than one charge system may be present reservoir crude oil chemistry indicates that the fluids originated from a single source facies generated over a wide range of organic maturity secondary alteration mechanisms include water washing biodegradation and evaporative fractionation crude oils in the upper reservoirs tend to be most affected by biodegradation and water washing condensates and light crude oils in the deepest reservoirs appear to be the residual phase from evaporative fractionation the broad variation in fluid properties and chromatogram character can be attributed to a multi end member mixing system early mature waxy oil later high maturity volatile oil low level biodegradation migrated phase evaporative fractionation and residual phase evaporative fractionation a statistical unmixing algorithm was used to determine end member compositions and relative mixing proportions for each crude oil sample remigration and mixing of the products from multi phase generation and alteration results in complex reservoir fluid compositions such that no single reservoired oil represents a compositional end member rather the oil samples are mixtures of various amounts of multiple end members mixing proportions show regional trends and variations in different reservoirs within a single field the crude oil geochemical data and unmixing analysis support a complex charge history from a single source rock rather than mixing of oils from two source rocks

sub inertial wave boundary turbulence in the gulf of valencia the bottom boundary layer above sloping topography can be highly turbulent even in deep seas this is demonstrated here using high resolution 1 hz sampling temperature sensors that were moored for 5 months every 0 5 m between 6 5 and 61 m above a 572 m deep seafloor promontory on the continental slope off valencia spain using these data turbulence parameters have been estimated with time and in the vertical values vary over four orders of magnitude they have a dominant local inertial period which is modulated by an about 11 day periodicity associated with variations in a baroclinic unstable boundary current when this current is strong and eastward the upslope phase of inertial wave generates convective turbulence which reaches closest to the bottom and therefore can effect sediment dispersal in late winter equally strong shear induced turbulence in 50 m high kelvin helmholtz k h overturns is forced by 0 2 m s 1 off downslope motions which are preceded by periods of warming of a few 0 01 degrees c before the cooler near bottom water is suddenly flushed over the promontory into the basin such anomalously large k h overturns occurred 6 times in the investigated winter period

burst resuspension of seabed material at the foot of the continental slope in the rockall channel to better understand the relationship between near bottom hydrodynamics and sediment resuspension in the transition zone between the continental slope and the abyssal plain an array of three moorings equipped with near bottom sediment traps and current meters was deployed in a triangular configuration of at the foot of the south east slope of the rockall channel north atlantic in addition a fast sampling adcp was moored in the centre of the triangle microscopic observations combined with grain size analysis revealed that the material intercepted by the traps was mainly composed of loose phytodetritus and aggregates organic carbon and 13corg analyses further indicate that this material is relatively fresh and hence probably only transported over short distances the total mass flux measured by the traps suggests input from either laterally advected or resuspended material during the deployment period the measured flux was variable in time and space with a strong increase at the deepest site at the very foot of the slope the measured flux did not correlate significantly with daily averaged current speed suggesting that processes other than those related to elevated bed shear stress are involved in the resuspension mechanism rapid changes in the hydrodynamics probably related to internal motions are evidenced by abrupt bursts in the current velocity and in the near bottom turbidity their occurrence at slack tidal waters appears to be at the origin of the resuspension observed at the foot of the slope of the rockall channel high resolution current velocity measurements suggest that resuspension is dominated by energetic highly localised and short term resuspension events despite the abyssal depths part of these events resemble in many ways the solibores which have been previously observed to enhance sediment transport at much shallower depths over the continental slope while others rather appear to be associated to gravity waves

near bed solibores over the continental slope in the faeroe shetland channel abstract on two occasions within a 12 day measurement period in the faeroe shetland channel strongly nonlinear wave trains were observed at the sea bed propagating up the continental slope in water depths 450 m the events were separated by a period of 4 days and whilst resembling in appearance a density current running up a slope are termed solibores displaying the properties of both turbulent internal bores and nonlinear internal solitary waves isw each solibore displays a steep leading edge followed by a train of nonlinear waves with amplitudes of o 10 m and periods of 5 20 min wave induced particle velocities are consistent with isw whilst a zone of strong horizontal convergence at the leading edge of the solibores causes the formation of a rotor with flow in the opposite sense to a forward overturning surface wave in both cases upward vertical velocities 10 cm s 1 are immediately followed by a return downward flow of equal magnitude a ctd and microstructure transect conducted during the passage of the first solibore illustrates its behaviour as an up slope intrusion of cold dense water with concurrent rates of turbulent dissipation e of o 10 7 w kg 1 and resulting in short term maximum vertical diffusivities kz of o 10 1 m2 s 1 in the long term however kz 140 days which again indicate intermittency in periods of enhanced sediment flux the solibores are consistent with the results of numerical and laboratory experiments on hydraulic jumps resulting from shoaling isw the influence of the slope is proposed to be the reason for their slightly different forms and effects on sediment transport thus the first solibore propagating directly up the slope is proposed to result from an overturning hydraulic jump caused by kinematic instabilities and which subsequently forms a horizontal density intrusion the second solibore represents a dispersive wave train due its oblique direction of propagation which reduces the effective bottom slope allowing dispersion to balance nonlinear effects and prohibiting overturning

the island scale internal wave climate of moorea french polynesia 1 analysis of five year records of temperatures and currents collected at moorea reveal strong internal wave activity at predominantly semi diurnal frequencies impacting reef slopes at depths 30 m around the entire island temperature changes of 1 5 c to 3 c are accompanied by surges of upward and onshore flow and vertical shear in onshore currents superimposed on annual temperature changes of approximately 3 c internal wave activity is high from oct may and markedly lower from jun sep the offshore pycnocline is broadly distributed with continuous stratification to at least 500 m depth and a subsurface fluorescence maximum above the strong nutricline at approximately 200 m minimum buoyancy periods range from 4 8 to 6 min with the maximum density gradient occurring at 50 to 60 m depth in summer and deepening to approximately 150 to 200 m in winter the bottom slope angle around all of moorea is super critical relative to the vertical stratification angle suggesting that energy propagating into shallow water is only a portion of total incident internal wave energy vertical gradient richardson numbers indicate dominance by density stability relative to current shear with relatively limited diapycnal mixing coherence and lagged cross correlation of semi diurnal temperature variation indicate complex patterns of inter site arrival of internal waves and no clear coherence or lagged correlation relationships among island sides semi diurnal and high frequency internal wave packets likely arrive on moorea from a combination of local and distant sources and may have important impacts for nutrient and particle fluxes in deep reef environments

the role of internal waves in the late quaternary evolution of the israeli continental slope abstract internal waves are widely present in world s oceans propagating in stratified ocean layers such as the seasonal pycnocline at continental shelves and slopes breaking of internal waves may create turbulence of sufficient energy to erode and transport sediments in this study we investigate the late pleistocene to recent impact of internal waves on the morphology of the israeli mediterranean continental slope based on mooring data we show that the internal wave spectrum on the upper slope contains significant energy at near inertial and semidiurnal tidal frequencies sediment subbottom profiler data show two fields of nearly contour parallel sediment waves located in water depths of 80 m 130 m and 190 m 350 m respectively a zone of flat seafloor morphology and remarkably constant slope inclination of 1 0 1 2 separates both sediment wave fields the entire stretch of seafloor between 80 m and 350 m corresponds to depths of major ocean density stratification supporting the propagation of internal waves in addition this area is critically inclined with respect to semidiurnal internal tides and supercritically inclined with respect to near inertial waves two scenarios previously related to internal wave breaking we propose that breaking internal waves control the inclination of the israeli continental slope and contribute to sediment starvation within the zone of flat seafloor morphology the formation of sediment waves is attributed to high frequency trailing internal waves of similar wavelengths as sediment waves observed within a seismic image of the water column we correlate subbottom profiler data to a radiocarbon dated sediment core no sediment waves formed from 16 cal ka 8 cal ka indicating that the seafloor impact of internal waves ceased during a time of rapid sea level rise and fresh water input in the eastern mediterranean realm the end of this period coincides with the formation of sapropel s1

application of biological markers in the recognition of the geochemical characteristics of some crude oils from abu gharadig basin north western desert egypt abstract the objective of this study is to establish the relationship between the hydrocarbons recovered from the abu gharadig basin and middle jurassic khatatba formation as well as the previously established upper cretaceous abu roash f member a suite of fourteen crude oil and condensate samples from the mesozoic reservoirs jurassic cretaceous of the abu gharadig basin western desert egypt was analyzed and geochemically compared with extracts from source rocks of the middle jurassic khatatba formation and the upper cretaceous abu roash f member based on molecular indicators of organic source input depositional environment and age diagnostic biomarkers at least two petroleum systems operate in the abu gharadig basin those derived from late cretaceous marine shales and jurassic early cretaceous non marine organic rich shales as source rocks and possibly a third system appears to be a mixture of them both the correlation of some abu gharadig oils to a late cretaceous source establishes a petroleum system involving these marine cretaceous source rocks

mechanisms of sediment transport and dispersion in a tectonically active submarine valley canyon system zakynthos straits nw hellenic trench abstract physical oceanographic and geophysical data sets are used to examine sediment transport processes currents were directed generally along the axis of the valley canyon system and in an area of low tidal range are attributed to regional weather patterns near bed and near surface currents are opposed both in terms of instantaneous observations and net lagrangian drift near bed down canyon water movement provides a mechanism for the offshore movement of fine grained sediment slope failures have been identified in the geophysical records and are considered to be controlled by earthquakes and salt diapirism in a tectonically active area these failures as mass displacement or slow down slope creep result in debris infill and the generation of turbidity currents fine grained sediments resuspended by the turbidity currents would be transported down canyon by the slowly moving near bed residual water movement hence the dominant transport mechanisms in the valley canyon system are 1 frequent mass sediment failure and 2 nearly continuous down channel fine grained suspended sediment movement

organic geochemical characteristics and interpreted depositional environment of the khatatba formation northern western desert egypt the middle jurassic khatatba formation in the northern western desert of egypt was evaluated in terms of organic matter abundance type and thermal maturity as well as for some organic petrographic characteristics depositional environments were interpreted based on organic geochemical rock eval pyrolysis extract analysis and biomarker distributions and organic petrological methods organic carbon contents range between 1 0 and 32 5 wt the khatatba shale and coaly shale samples have hydrogen index values in the range of 63 to 261 mg hydrocarbon hc g total organic carbon with mixed types 2 3 and 3 kerogens mean vitrinite reflectance ro between 0 77 and 1 07 is in reasonably good agreement with pyrolysis tmax temperature at maximum of s2 peak data 438 459c organic rich sediments of the middle jurassic khatatba formation have very good source rock generative potential and have obtained thermal maturity levels equivalent to the oil window the main generation products are gas with very limited liquid hcs oil or condensate seven shale and coaly shale samples from khatatba formation were characterized using gas chromatography gc and gc mass spectrometry techniques the khatatba samples are characterized by the predominance of c14 c24 alkanes a pristane phytane ratio of less than 2 abundant c27 regular steranes and the presence of tricyclic terpanes these are consistent with the suboxic marine environment conditions for the khatatba source rock biomarker parameters for these samples generally indicate a mixture of land as well as marine derived organic matter input the maturity indicators based on c32 22s 22s 22r homohopane and c29 20s 20s 20r and sterane ratios reveal that the khatatba samples are thermally mature and have reached the peak oil window maturity supporting the ro data

internal lee waves and baroclinic bores over a tropical seamount shark hot spot abstract oceanographic observations were made with a subsurface oceanographic mooring over the summit and flanks of two neighbouring seamounts in the tropical indian ocean to identify processes that may be responsible for the aggregation of silvertip sharks carcharhinus albimarginatus in the deep water drop off surrounding the summits the seamounts which are in the chagos archipelago in the british indian ocean territories are narrow in horizontal extent 15 sides that rise from depths of 600 m and flat summits at a depth of 70 m they are subjected to forcing at subinertial basin scales and local scales that include a mixed tidal regime and storm generated near inertial waves at the drop off at a depth of between 70 and 100 m isotherms oscillate at both diurnal and semidiurnal frequencies with amplitudes of 20 30 m the waves of tidal origin are accompanied by short period 5 min internal waves with amplitudes o 10 m and frequencies close to the local buoyancy frequency n within the thermocline which is the maximum frequency possible for freely propagating internal waves the tidal oscillations result from internal lee waves with 30 m vertical wavelength generated by the prevailing currents over the supercritical seamount flanks whereby the bottom slope is greater than the internal tide wave slope the near n waves are due to enhanced shear associated with the hydraulic jumps that form from the lee waves due to the abrupt transition from steeply sloping sides to a relatively flat summit the jumps manifest themselves as bottom trapped bores that propagate up the slope towards the summit further observations over the summit reveal that the bores subsequently flush the summits with cold water with tidal periodicity the bores which have long wave phase speeds more than double that of the bore particle velocities are characterised by intense vertical velocities 0 1 m s 1 and inferred local resuspension but relatively little turbulence based on temperature overturns our results strongly implicate lee waves as the dynamic mechanism of leading order importance to the previously observed accumulation of biomass adjacent to the supercritical slopes that are commonplace throughout the archipelago we propose that further investigation should identify the spatiotemporal correlation between internal wave activity and fish schooling around the summit and whether such schooling attracts predators

tidal mixing processes amid small scale deep ocean topography the nature of tide topography interaction reflects the topographic scales experienced by water parcels during their tidal excursions in the deep ocean these scales are typically subkilometer yet direct observations of tidal processes on such scales are lacking at one site a saddle amid steep and complex mid atlantic ridge topography observations reveal tidally pulsed bottom trapped fronts overflows and lee waves in response to a tide combined with a mean flow of similar amplitude the tidal pulsing of the fronts and overflows was only evident locally and their phase became unpredictable over scales of hundreds of meters enhanced turbulence in a 100 200 m thick bottom boundary layer had an estimated dissipation rate of 2 6 10 2 w m 2 exceeding the large scale average of tidal dissipation in mid ocean ridge environments but by less than an order of magnitude this site was not a dissipation hotspot and the processes observed could provide widely distributed mixing to the meridional overturning circulation

the origin and accumulation of multi phase reservoirs in the east tabei uplift tarim basin china abstract a giant deep strata oil gas field with complex fluid characteristics was recently discovered in the hade yuke area of the east tabei uplift tarim basin nw china the deep fluids show a lateral co existence of several gas condensate and oil phase reservoirs characterized through the integration of complimentary geochemical e g bulk composition biomarker and stable carbon isotope and geological data typical features of the gas and condensate reservoirs which were mainly distributed in the eastern parts of the study site included high gor gas to oil ratio hydrocarbon gases with relatively heavy 13c values and crude oils with high wax content in contrast oil reservoirs which mostly occurred in more westerly locations had lower gor values lighter 13c values and lower wax content indicating gradual change of fluid characters the petroleum accumulations derive from two hydrocarbon charge events an early oil charge in the late hercynian and a later gas charge in the late himalayan which migrated from east to west leading to a gradual variation in fluid phase and characteristics alteration of paleo oil reservoirs by this secondary gas charge was therefore primarily responsible for the complex fluid character and multi phase reservoirs presently in place secondary condensates were formed from the retrograde condensation of paleo reservoirs our re construction of the hydrocarbon accumulation process encourages future exploration endeavours to target commercially viable gas accumulations in the deep east strata and oil reservoirs in the west