fine structure microstructure and vertical mixing processes in the upper ocean in the western weddell sea the upward flux of heat from the subsurface core of warm deep water wdw to the perennially ice covered sea surface over the continental slope in the western weddell sea is estimated using data obtained during february june 1992 from a drifting ice station through the permanent pycnocline the diapycnal heat flux is estimated to be about 3 w m 2 predominantly because of double diffusive convection there is no evidence that shear driven mixing is important in the pycnocline the estimated mean rate of heat transfer from the mixed layer to the ice is 1 7 w m 2 although peak heat fluxes of up to 15 w m 2 are found during storms it is hypothesized that isopycnal mixing along sloping intrusions also contributes to the loss of heat from the wdw in this region however we are unable to quantify the fluxes associated with this process intrusions occur intermittently throughout this experiment but are most commonly found near the boundary of the warm core current and the shelf modified water to the east these heat fluxes are significantly lower than the basin averaged value of 19 w m 2 fahrbach et al 1994 that is required to balance the heat budget of the weddell gyre other studies suggest that shelf processes to the west of the ice station drift track and more energetic double diffusive convection in the midgyre to the east could account for the difference between our flux estimates for this region and those based on the basin scale heat budget

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

a new methodology for the quantitative visualization of coherent flow structures in alluvial channels using multibeam echo sounding mbes 1 in order to investigate the interactions between turbulence and suspended sediment transport in natural aqueous environments we ideally require a technique that allows simultaneous measurement of fluid velocity and sediment concentration for the whole flow field here we report on development of a methodology using the water column acoustic backscatter signal from a multibeam echo sounder to simultaneously quantify flow velocities and sediment concentrations the application of this new technique is illustrated with reference to flow over the leeside of an alluvial sand dune which allows for the first time in a field study quantitative visualization of large scale whole flow field turbulent coherent flow structures associated with the dune leeside that are responsible for suspending bed sediment this methodology holds great potential for use in a wide range of aqueous geophysical flows

turbulent mixing near the yermak plateau during the coordinated eastern arctic experiment during the ice camp component of the coordinated eastern arctic experiment cearex in march april 1989 1500 profiles of temperature conductivity and velocity shear microstructure were obtained near the yermak plateau the dominant signal in isopycnal displacements was the diurnal variability near the plateau consistent with the enhanced diurnal currents found in this region previously from the fram iii and fram iv ice camps the dissipation rate of turbulent kinetic energy e reached maximum values of about 10 6 w kg 1 in two distinct regions the surface mixing layer and the pycnocline between 120 and 220 m there was a significant component of diurnal variability in e in each region in the surface layer e was proportional to the cube of the ice relative current speed at 30 m below the ice and it decayed approximately exponentially with increasing depth major mixing events in the pycnocline were correlated with large amplitude short duration isopycnal displacements the lowest dissipation rates were recorded over the deep nansen basin north of the plateau and in the subsurface core of a submesoscale baroclinic eddy in northern fram strait the time averaged vertical eddy diffusivity near the slope of the plateau was about 2 5 10 4 m2 s 1 in the pycnocline above the atlantic layer implying an upward heat flux of 25 w m 2 although only a small fraction of this heat reached the base of the mixed layer the results confirm that current interactions with steep topography are critical to the modification of atlantic water in the eastern arctic ocean

geochemical characterization of selected western canada oils by c5 c8 compound specific isotope correlation csic abstract forty two oils condensates from the western canada sedimentary basin wcsb ranging in reservoir age from devonian to cretaceous are compared using the stable carbon isotopic ratio of individual hydrocarbons in the gasoline range fraction c 5 c 8 of these oils continuous flow isotope ratio mass spectrometry cf irms using a modified solid dilution purge and trap inletting system can provide reproducible isotopic ratios for the ca 26 dominant n iso and cyclo alkanes and aromatics in the gasoline range the resulting isotopic signatures or gasoline isotopograms for oils condensates provide a diagnostic geochemical technique for oil oil and oil source correlations in many instances the non straight chained hydrocarbons are more diagnostic than n alkanes hierarchical cluster analysis provides a non subjective approach to the treatment of individual isotopic information this study confirms that oils from similar or the same sources produce isotopic signatures that are highly correlated clear carbon isotopic relationships between individual hydrocarbon compounds in the oils suggest a steady state kinetic relationship for the generation of oil and gas as opposed to a thermodynamic equilibrium relationship this mechanism explains the consistent shift in isotopic ratios between similar compounds such as the methylalkanes and dimethylalkanes

relation of inversely graded deposits to suspended sediment grain size evolution during the 1996 flood experiment in grand canyon before glen canyon dam was completed upstream from grand canyon floods scoured sand from the channel bed and deposited sand on bars within recirculating eddies after completion of glen canyon dam in 1963 peak discharge of the mean annual floods dropped from about 2600 to 900 m 3 s and 85 of the sediment supply was eliminated under the postdam flow regime sand bars in eddies have degraded in an experiment to study in part the effects of floods in rebuilding these bars a controlled flood was released from glen canyon dam in late march and early april 1996 although fluvial sequences characteristically fine upward the deposits of the experimental flood systematically coarsen upward measurements of suspendedsediment concentration and grain size and of bed material grain size suggest that the upward coarsening results from the channel becoming relatively depleted of fine grained sediment during the seven days of the high flow experiment predam flood beds of the colorado river also coarsen upward indicating that supply limitation and grain size evolution are natural processes that do not require the presence of a dam

geochemistry of oils in the northern viking graben the composition of crude oils in the northern viking graben area reflects the influence of both the type of organic matter and the thermal maturity of jurassic source rocks in the major basin depocenters referred to as the oseberg and troll kitchens forty four oil samples were analyzed and classified primarily based on chemical composition but with recognition of constraints on origins imposed by geographic and stratigraphic locations five groups are recognized 1 snorre oils 2 stratfjord gullfaks oils 3 brent oseberg beta veslefrikk oils 4 oseberg alpha troll oils and 5 agat and blocks 35 8 and 35 11 oils the composition of oils in the first three groups reflects the large relative proportions of marine organic matter and the lower expulsion temperatures characteristic of oils derived from the draupne formation the composition of oils in the last two groups reflects source rocks having more terrestrial organic matter and higher expulsion temperatures the initial phase of hydrocarbon expulsion and migration from the draupne formation in the northern viking graben began about 56 ma in the troll kitchen and about 45 ma in the oseberg kitchen with continued subsidence and heating of jurassic source rocks gases and condensates were expelled beginning about 40 ma in the trollmore kitchen d about 30 ma in the oseberg kitchen this secondary phase of hydrocarbon generation has mixed with and displaced some of the earlier accumulations less

vertical profiles of suspended sand concentration and size from multifrequency acoustic backscatter vertical profiles of suspended sand concentration and size are obtained from multifrequency acoustic profiling data collected in 1989 during a nearshore experiment at stanhope lane beach prince edward island the data were acquired with acoustic sounders operating at 1 2 25 and 5 mhz independent estimates of concentration were made using optical backscatter sensors obss the algorithm for inversion of the three frequency backscatter data to particle size and concentration based on the ratios of the different signals was tested in laboratory experiments with an unconfined high reynolds number suspended sediment jet results from the stanhope beach experiment are presented for three different surface wave energy regimes with significant wave orbital velocities ranging from 0 3 to 0 8 m s and peak wave periods of 4 6 s the acoustic estimates of mean concentration are shown to be within 10 on average of those determined with the obs nearest the bottom at 5 to 10 cm height over time scales ranging from 6 5 min to 4 6 s one wave period the acoustic estimates of suspended sediment size near the bottom are within 5 20 of the bottom sediment mean size the statistical variability of the size estimates is high with standard deviations in the estimates ranging between 30 and 50 of the mean the time averaged concentration profiles exhibit an exponential decrease with height above an o 10 cm thick near bottom region of nonexpo nential decrease in contrast the time averaged mean size profiles decrease approximately linearly with height and rather slowly about 25 in 0 5 m

does rotation influence double diffusive fluxes in polar oceans abstractthe diffusive or semiconvection regime of double diffusive convection ddc is widespread in the polar oceans generating staircases consisting of high gradient interfaces of temperature and salinity separated by convectively mixed layers using two dimensional direct numerical simulations support is provided for a previous theory that rotation can influence ddc heat fluxes when the thickness of the thermal interface sufficiently exceeds that of the ekman layer this study finds therefore that the earth s rotation places constraints on small scale vertical heat fluxes through double diffusive layers this leads to departures from laboratory based parameterizations that can significantly change estimates of arctic ocean heat fluxes in certain regions although most of the upper arctic ocean thermocline is not expected to be dominated by rotation

vertical mixing at intermediate depths in the arctic boundary current microstructure and hydrographic observations during september 2007 in the boundary current on the east siberian continental slope document upper ocean stratification and along stream water mass changes a thin warm surface layer overrides a shallow halocline characterized by a 40 m thick temperature minimum layer beginning at 30 m depth below the halocline well defined thermohaline diffusive staircases extended downwards to warm atlantic water intrusions found at 200 800 m depth observed turbulent eddy kinetic energy dissipations are extremely low epsilon 10 6 w m 3 such that double diffusive convection dominates the vertical mixing in the upper ocean the diffusive convection heat fluxes f dc h 1 w m 2 are an order of magnitude too small to account for the observed along stream cooling of the boundary current our results implicate circulation patterns and the influence of shelf waters in the evolution of the boundary current waters

molecular 13c and 14c evidence for the allochthonous and ancient origin of c16c18 n alkanes in modern soils the heterogeneous isotopic composition of c3 and c4 plants can be used to to follow the fate of plant carbon into soil organic molecules thus after 23 years of cropping of maize c4 on a soil which was previously under c3 vegetation c25 c33 soil n alkanes are 13c enriched up to 9 relatively to the initial c3 soil reflecting the input of 13c enriched n alkanes from maize waxes in sharp contrast c16 c18 soil n alkanes do not show any significant 13c 12c variation over the same time interval this absence of isotopic variation along with consideration of their relative concentration absolute concentration and biodegradability demonstrate that these substances must represent a regular input from an external source evidence of a large contribution of an ancient source amounting to more than 65 of the alkane fraction is given by a 14c age of 8510 yrs bp moreover short chain n alkanes from soils diesel fuel diesel automobile exhaust and petroleum products exhibit similar distributions and 13c values these findings suggests that c16 c18 soil n alkanes represent a non point source pollution of ancient hydrocarbons either carried by aerosols or entering the soil via continuous hydrocarbon seepage from the deep sedimentary rocks of the paris basin

effective diffusivities within oceanic thermohaline staircases a scale for the thickness of layers in regular diffusive type thermohaline staircases derived from dimensional analysis is found to collapse oceanic data combining this scale with laboratory derived double diffusive flux laws we formulate effective diffusivities for salt heat and density the diffusivities depend on the turner number r but are independent of the brunt vaisala frequency for r near 1 the diffusivities for salt and heat are approximately equal 10 4 m2 s 1 they decrease roughly as r 4 and r 2 respectively over the oceanic range 1 r 10

measuring suspended sediment concentrations using acoustic backscatter devices abstract in recent years the requirement to develop a technique for measuring suspended sediment concentration profiles with similar temporal and spatial resolution to that of electromagnetic current meter measurements of the flow has led to the development of an acoustic approach acoustic backscatter devices have been constructed and deployed in marine environments and measurements of backscattered signal profiles obtained however the translation from acoustic returns to suspended load has been an empirical procedure resulting in some uncertainty regarding the accuracy and reliability of the conversion process to address this problem a series of laboratory measurements of acoustic backscattering from marine suspensions were conducted using two acoustic backscatter instruments operating at 3 0 and 5 65 mhz a simple semi empirical backscattering theory has been developed to predict the form of the scattered signal and comparisons have been made of the concentrations predicted from the theory against concentration measurements made in laboratory tanks the results show that the main features of the backscattering signal can be explained and accurate concentration estimates can be made from the acoustic returns it is concluded that acoustic backscatter techniques are potentially powerful tools for examining at high resolution the structure of suspended sediment concentration profiles near the seabed

tide mediated warming of arctic halocline by atlantic heat fluxes over rough topography atlantic water brings heat to the subsurface arctic ocean pan arctic microstructure measurements of energy dissipation suggest that vertical mixing is substantial over the continental slopes tidally induced and insensitive to sea ice cover

compound specific isotope analysis as a tool for characterizing mixed oils an example from the west of shetlands area abstract the origin of an oil accumulation can be difficult to establish when the oil is a mixture from multiple sources or when multiple episodes of charging are involved in this study oils from the clair field west of shetland islands which are mixtures of nonbiodegraded oil added to biodegraded oil are characterized by comparing the carbon isotope ratios of the gasoline range hydrocarbons grh of the oil to the grh released from the pyrolysis of the asphaltenes in the oil this comparison allows characterization of the source of the first versus the second pulse of oil into the reservoir information useful in assessing the source potential of the basin

greater role for atlantic inflows on sea ice loss in the eurasian basin of the arctic ocean arctic sea ice loss is a leading indicator of climate change and can be attributed in large part to atmospheric forcing here we show that recent ice reductions weakening of the halocline and shoaling of the intermediate depth atlantic water layer in the eastern eurasian basin have increased winter ventilation in the ocean interior making this region structurally similar to that of the western eurasian basin the associated enhanced release of oceanic heat has reduced winter sea ice formation at a rate now comparable to losses from atmospheric thermodynamic forcing thus explaining the recent reduction in sea ice cover in the eastern eurasian basin this encroaching atlantification of the eurasian basin represents an essential step toward a new arctic climate state with a substantially greater role for atlantic inflows

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

quantifying the relative importance of flow regulation and grain size regulation of suspended sediment transport α and tracking changes in grain size of bed sediment β to predict changes in sediment transport it is essential to know whether transport is regulated mainly by changes in flow or by changes in grain size of sediment on the bed in flows where changes in suspended sediment transport are regulated purely by changes in flow grain size of bed sediment is constant increases in flow strength cause increases in both concentration and grain size of sediment in suspension because stronger flows are able to suspend more sediment and coarser grains under this constraint of constant grain size of bed sediment concentration and median diameter of suspended sediment are positively correlated in contrast where transport is regulated purely by changes in grain size of sediment on the bed concentration and median diameter of suspended sediment are negatively correlated because increasing the median diameter of the bed sediment causes the concentration to decrease while causing the median grain size in suspension to increase where both flow strength and grain size on the bed are free to vary the relation between concentration and grain size in suspension can be used to quantify the importance of grain size regulation relative to flow regulation of sediment transport a measure defined as to predict sediment transport in systems that are regulated dominantly by changes in grain size on the bed it is more useful to measure sediment input events or changes in grain size on the bed than to measure changes in flow more commonly grain size of bed sediment may be secondary to flow in regulating transport but may nevertheless be important the relative coarseness of bed sediment can be measured directly or like can be calculated from measurements of concentration and grain size of suspended sediment

interaction of coal and oil in confined pyrolysis experiments insight from the yields and carbon isotopes of gas and liquid hydrocarbons abstract isothermal confined gold capsule pyrolysis experiments were performed for coal alone oil alone and coal plus oil with oil coal ratios ranging from 0 006 to 0 171 at 315 c 345 c and 375 c respectively and 50 mpa for 72 h in the experiment for coal plus oil the amounts and compositions of hydrocarbon gases are substantially different from those predicted from the results in the experiments for oil alone and coal alone the results of these experiments demonstrate that kerogen and oil do not crack separately in the experiments of coal plus oil the interaction between kerogen and oil components leads to the generation of hydrocarbon gases with oil coal ratio increasing the amounts of individual and total hydrocarbon gases decrease at first and then increase rapidly up to several times those calculated from the yields of these components in the experiments for oil alone and coal alone the c1 c1 5 ratios of hydrocarbon gases decrease and are increasingly lower than those calculated from the yields of hydrocarbon gases in the experiments for oil alone and coal alone the amount and carbon isotopes of individual n alkane demonstrate that the free liquid n alkanes were incorporated into kerogen and replaced the bound liquid n alkanes covalently bonded alkyl groups in kerogen carbon isotopes of hydrocarbon gases further suggest that the bound liquid n alkanes in kerogen preferentially crack into hydrocarbon gases

molecular and isotopic compositions of bitumens in silurian tar sands from the tarim basin nw china characterizing biodegradation and hydrocarbon charging in an old composite basin abstract biodegradation and oil mixing in silurian sandstone reservoirs of the tarim basin one of the largest composite basins in china were investigated by analyzing the molecular characteristics and stable carbon isotopic signatures of low molecular weight lmw saturated hydrocarbons and high molecular weight hmw asphaltenes detection of 25 norhopanes and 17 nortricyclic terpanes in most silurian tar sands from the tabei uplift in the tarim basin suggests a much greater degree of biodegradation here than in the tazhong uplift this explains the relatively more abundant tricyclic terpanes gammacerane pregnane and diasteranes in tar sands from the tabei uplift than in those from the tazhong uplift hence care must be taken when assigning oil source correlations using biomarkers in tar sands because of the biodegradation and mixing of oils derived from multiple sources in such an old composite basin asphaltenes in the tar sands seem to be part of the oil charge before biodegradation depending on the relative anti biodegradation characteristics of asphaltenes the similarity in carbon isotopic signatures for asphaltenes and their pyrolysates and the consistent product distribution for flash pyrolysis and for regular steranes in asphaltene pyrolysates regardless of whether the tar sands were charged with fresh oil according to the relative distributions of regular steranes and the relatively abundant 1 2 3 4 tetramethylbenzene significantly enriched in 13 c the oil sources for asphaltenes in the tar sands might be related to lower paleozoic marine source rocks formed in euxinic conditions nevertheless the relatively low abundance of gammacerane and c 28 regular steranes observed in asphaltene pyrolysates and residual hydrocarbons within limited samples investigated in this work made a direct correlation of oils originally charged into silurian tar sands with those cambrian source rocks reported so far seem not to be possible comparison of carbon isotopic signatures of n alkanes in asphaltene pyrolysates with those of lmw saturated hydrocarbons is helpful in determining if the abundant n alkanes in tar sands are derived from fresh oil charges after biodegradation the limited carbon isotopic data for n alkanes in lmw saturated hydrocarbons from the tar sands can be used to classify oils charged after biodegradation in the composite basin into four distinct groups

molecular and carbon isotopic geochemistry of crude oils and extracts from permian source rocks in the northwestern and central junggar basin china abstract the junggar basin is a major oil producing province in china most oil reservoirs found so far in this basin are in the mahu sag and neighboring uplifts northwestern junggar basin a total of 78 oils and 10 permian source rocks from the northwestern and central junggar basin and two oils and two permian source rocks from the eastern junggar basin were analyzed by gc gc ms and gc irms the 78 oils can be clearly classified into two groups based on these analytical results for group i oils 13c values of individual n alkanes are relatively higher and remain stable with increasing carbon number for group ii oils these values are relatively lower and decrease at first and then increase with carbon number differences in molecular parameters can be also observed between these two groups of oils group i oils generally have 1 higher pr n c17 and ph n c18 ratios and lower pr ph ratio and 2 higher gammacerane c30 hopane gammacerane and carotane carotane c30 hopane ratios compared with group ii oils in addition group i oils mainly have tricyclic terpane distribution patterns with either c20 c21 c23 while group ii oils mainly have the pattern of c20 c23 however molecular parameters overlap to some extent between these two groups of oils group i oils correlate well with the nine source rocks of the lower permian fengcheng formation p1f while group ii oils correlate well with the three source rocks of middle permian age based on carbon isotopic and molecular compositions the occurrence of these two groups of oils in the northwestern and central junggar basin are consistent with facies and thickness variations in the source rocks within the lower permian fengcheng formation p1f and middle permian lower wuerhe formation p2w

vertical heat transfer in the arctic ocean the role of double diffusive mixing 1 microstructure profiles collected in the central amundsen basin are analyzed in order to quantify the role of double diffusive mixing for vertical heat transfer from the atlantic layer in the profiles a persistent but laterally incoherent thermohaline staircase structure is identified in the 200 260 m depth range the staircase contains homogeneous layers with average height of 1 3 m and thin high gradient interfaces with average temperature and salinity jumps of about 0 065 c and 0 015 respectively when inferred from a commonly used diffusive convection parameterization the average vertical heat flux within the staircase is 0 6 w m 2 this is one order of magnitude larger than the molecular diffusion alone and of the same order as the overall heat loss from the atlantic layer in the deep basins of the arctic ocean the parameterization is evaluated using observed turbulent heat fluxes and is found to overestimate diffusive convective fluxes with up to an order of magnitude especially for weak thermal forcing small temperature jumps in staircase staircases coexist with thermohaline intrusions in the vertical temperature and salinity profiles lomonosov ridge is identified as a potential region for formation of intrusions it is found that salt fingering is the dominant process during intrusion growth whereas diffusive convection is the dominant process in maintaining the intrusions at steady state in the deep basins

the relationship between double diffusive intrusions and staircases in the arctic ocean abstractthe origin of double diffusive staircases in the arctic ocean is investigated for the particular background setting in which both temperature and salinity increase with depth motivated by observations that show the coexistence of thermohaline intrusions and double diffusive staircases a linear stability analysis is performed on the governing equations to determine the conditions under which staircases form it is shown that a double diffusive staircase can result from interleaving motions if the observed bulk vertical density ratio is below a critical vertical density ratio estimated for particular lateral and vertical background temperature and salinity gradients vertical background temperature and salinity gradients dominate over horizontal gradients in determining whether staircases form with the linear theory indicating that perturbations to stronger vertical temperature gradients are more likely to give rise to a staircase examination of arctic ocean temperature and salinity measurements

tidally forced lee waves drive turbulent mixing along the arctic ocean margins in the arctic ocean limited measurements indicate that the strongest mixing below the atmospherically forced surface mixed layer occurs where tidal currents are strong however mechanisms of energy conversion from tides to turbulence and the overall contribution of tidally driven mixing to arctic ocean state are poorly understood we present measurements from the shelf north of svalbard that show abrupt isopycnal vertical displacements of 10 50 m and intense dissipation associated with cross isobath diurnal tidal currents of 0 15 m s 1 energy from the barotropic tide accumulated in a trapped baroclinic lee wave during maximum downslope flow and was released around slack water during a 6 hr turbulent event high frequency internal waves were present the full 300 m depth water column became turbulent dissipation rates increased by a factor of 100 and turbulent heat flux averaged 15 w m 2 compared with the background rate of 1 w m 2 plain language summary turbulent mixing in the arctic ocean water column affects sea ice variability through transport of subsurface heat toward the surface this turbulent mixing is concentrated along the margins mainly driven by tidal flow over sloping topography however processes of energy transfer from tides to turbulence in the arctic are poorly understood and the magnitudes and locations of mixing are poorly constrained here we present detailed measurements from the shelf north of svalbard showing a turbulent event driven by moderate tidal currents the energy is trapped and accumulated at the time of maximum downslope flow and is released at the turn of the tide when the entire water column becomes highly turbulent our observations imply that this process is an important source of mixing in the arctic ocean

variation in the isotopic composition of single components in the c4 c20 fraction of oils and condensates abstract determination of the isotopic composition of individual compounds in the c4 c15 range has been difficult due to the lack of suitable instrumentation it has also been suggested that isotopic fractionation during storage might occur with the introduction of online gc irms an instrument is now available to test whether or not isotopic fractionation occurs during storage to test this two condensates were analysed using the gc irms method samples were taken for analysis at regular intervals during storage at elevated temperatures only small changes in isotopic composition were observed during evaporation with a slight enrichment in 13c in some compounds however the changes are so small that even prolonged storage times do not significantly affect the carbon isotopic composition of the compounds as long as there is enough material left for analysis two separate suites of samples one from the central graben the other from the viking graben were used to demonstrate the use of the technique in correlating oils and condensates this study shows that the oil condensates in the central graben are not sourced from a single source rock differing only in maturity as reported earlier but are sourced from various source facies where especially edda differs significantly from the others i e the compounds in edda are 1 2 0 heavier than the rest of the analysed samples in the central graben the analysed viking graben oils and condensates were divided into three groups based on this study

spatial variability of the arctic ocean s double diffusive staircase the arctic ocean thermohaline stratification frequently exhibits a staircase structure overlying the atlantic water layer that can be attributed to the diffusive form of double diffusive convection the staircase consists of multiple layers of o 1 m in thickness separated by sharp interfaces across which temperature and salinity change abruptly through a detailed analysis of ice tethered profiler measurements from 2004 2013 the double diffusive staircase structure is characterized across the entire arctic ocean we demonstrate how the large scale arctic ocean circulation influences the small scale staircase properties these staircase properties layer thicknesses and temperature and salinity jumps across interfaces are examined in relation to a bulk vertical density ratio spanning the staircase stratification we show that the lomonosov ridge serves as an approximate boundary between regions of low density ratio approximately 3 to 4 on the eurasian side and higher density ratio approximately 6 to 7 on the canadian side we find that the eurasian basin staircase is characterized by fewer thinner layers than that in the canadian basin although the margins of all basins are characterized by relatively thin layers and the absence of a well defined staircase a double diffusive 4 3 flux law parametrization is used to estimate vertical heat fluxes in the canadian basin to be o 0 1 wm 2 it is shown that the 4 3 flux law may not be an appropriate representation of heat fluxes through the eurasian basin staircase here molecular heat fluxes are estimated to be between o 0 01 wm 2 and o 0 1 wm 2 however many uncertainties remain about the exact nature of these fluxes this article is protected by copyright all rights reserved

correlation of crude oils and oil components from reservoirs and source rocks using carbon isotopic compositions of individual n alkanes in the tazhong and tabei uplift of the tarim basin china abstract carbon isotopic compositions were determined by gc irms for individual n alkanes in crude oils and the free adsorbed and inclusion oils recovered by sequential extraction from reservoir rocks in the tazhong uplift and tahe oilfield in the tabei uplift of tarim basin as well as extracts of the cambrian ordovician source rocks in the basin the variations of the 13 c values of individual n alkanes among the 15 oils from the tazhong uplift and among the 15 oils from the triassic and carboniferous sandstone reservoirs and the 21 oils from the ordovician carbonate reservoirs in the tahe oilfield demonstrate that these marine oils are derived from two end member source rocks the major proportion of these marine oils is derived from the type a source rocks with low 13 c values while a minor proportion is derived from the type b source rocks with high 13 c values type a source rocks are within either the cambrian lower ordovician or the middle upper ordovician strata not drilled so far while type b source rocks are within the cambrian lower ordovician strata as found in boreholes td2 and fang 1 in addition the three oils from the cretaceous sandstone reservoirs in the tahe oilfield with exceptionally high pr ph ratio and 13 c values of individual n alkanes are derived or mainly derived from the triassic jurassic terrigenous source rocks located in quka depression the difference of the 13 c values of individual n alkanes among the free adsorbed and inclusion oils in the reservoir rocks and corresponding crude oils reflects source variation during the reservoir filling process in general the initial oil charge is derived from the type b source rocks with high 13 c values while the later oil charge is derived from the type a source rocks with low 13 c values the 13 c values of individual n alkanes do not simply correlate with the biomarker parameters for the marine oils in the tazhong uplift and tahe oilfield suggesting that molecular parameters alone are not adequate for reliable oil source correlation for high maturity oils with complex mixing

mean flow and turbulence structure over fixed two dimensional dunes implications for sediment transport and bedform stability detailed measurements of flow velocity and its turbulent fluctuation were obtained over fixed two dimensional dunes in a laboratory channel laser doppler anemometry was used to measure the downstream and vertical components of velocity at more than 1800 points over one dune wavelength the density of the sampling grid allowed construction of a unique set of contour maps for all mean flow and turbulence parameters which are assessed using higher moment measures and quadrant analysis these flow field maps illustrate that 1 the time averaged downstream and vertical velocities agree well with previous studies of quasi equilibrium flow over fixed and mobile bedforms and show a remarkable symmetry from crest to crest 2 the maximum root mean square rms of the downstream velocity values occur at and just downstream of flow reattachment and within the flow separation cell 3 the maximum vertical rms values occur within and above the zone of flow separation along the shear layer and this zone advects and diffuses downstream extending almost to the next crest 4 positive downstream skewness values occur within the separation cell whereas positive vertical skewness values are restricted to the shear layer 5 the highest reynolds stresses are located within the zone of flow separation and along the shear layer 6 high magnitude high frequency quadrant 2 events ejections are concentrated along the shear layer kelvin helmholtz instabilities and dominate the contribution to the local reynolds stress and 7 high magnitude high frequency quadrant 4 events occur bounding the separation zone near reattachment and close to the dune crest and are significant contributors to the local reynolds stress at each location these data demonstrate that the turbulence structure associated with dunes is controlled intrinsically by the formation magnitude and downstream extent of the flow separation zone and resultant shear layer furthermore the origin of dune related macroturbulence lies in the dynamics of the shear layer rather than classical turbulent boundary layer bursting the fluid dynamic distinction between dunes and ripples is reasoned to be linked to the velocity differential across the shear layer and hence the magnitude of the kelvin helmholtz instabilities which are both greater for dunes than ripples these instabilities control the local flow and turbulence structure and dictate the modes of sediment entrainment and their transport rates

ice tethered profiler observations of the double diffusive staircase in the canada basin thermocline vertical heat fluxes through the staircase are in the range 0 05 0 3 w m 2 only about one tenth of the estimated mean surface mixed layer heat flux to the sea ice it is thus concluded that the vertical transport of heat from the atlantic water in the central basin is unlikely to have a significant impact to the canada basin ocean surface heat budget icebreaker conductivity temperature depth data from the beaufort gyre freshwater experiment show that the staircase is absent at the basin periphery turbulent mixing that presumably disrupts the staircase might drive greater flux from the atlantic water at the basin boundaries and possibly dominate the regionally averaged heat flux

measurements of the relationship between turbulence and sediment in suspension over mobile sand dunes in a laboratory flume 1 the relationship between fluid and particle motions over a mobile dune bed was investigated using a laboratory flume with mobile sand dunes fluid turbulence data from a laser doppler velocimeter ldv and suspended sediment data from an acoustic backscatter system bss were collected from the same sampling volume at a constant position relative to passing sand dunes in a laboratory channel by using a motion control system to follow bed forms through the test section a second bss continually traversed the test section to map the bed profile the data from the ldv and the two bss units were correlated in order to link turbulence data with variations in suspended sediment concentration and position on bed forms local values of suspended sediment concentration were poorly correlated with quadrant classification indicating a weak relationship between local turbulence and sediment in suspension reynolds stress values were not strongly affected by dune size over the scales covered in the experiments sweeps quadrant 4 events were the most numerous but bursts quadrant 2 events generally had higher relative magnitudes bursts were best correlated with changes in suspended sediment concentration and with cumulative sediment suspension

intermittent intense turbulent mixing under ice in the laptev sea continental shelf vertical mixing in the bottom boundary layer and pycnocline of the laptev sea is evaluated from a rapidly sampled 12 h time series of microstructure temperature conductivity and shear observations collected under 100 sea ice during october 2008 the bottom boundary turbulent kinetic energy dissipation was observed to be enhanced 10 4 w m 3 beyond background levels 10 6 w m 3 extending up to 10 m above the seabed when simulated tidal currents were directed on slope upward heat fluxes into the halocline class waters along the laptev sea seabed peaked at 4 8 w m 2 averaging out to 2 w m 2 over the 12 h sampling period in the laptev sea pycnocline an isolated 2 h episode of intense dissipation 10 3 w m 3 and vertical diffusivities was observed that was not due to a localized wind event observations from an acoustic doppler current meter moored in the central laptev sea near the m2 critical latitude are consistent with a previous model in which mixing episodes are driven by an enhancement of the pycnocline shear resulting from the alignment of the rotating pycnocline shear vector with the under ice stress vector upward cross pycnocline heat fluxes from the arctic halocline peaked at 54 w m 2 resulting in a 12 h average of 12 w m 2 these results highlight the intermittent nature of arctic shelf sea mixing processes and how these processes can impact the transformation of arctic ocean water masses the observations also clearly demonstrate that absence or presence of sea ice profoundly affects the availability of near inertial kinetic energy to drive vertical mixing on the arctic shelves

arctic ocean heat impact on regional ice decay a suggested positive feedback abstractbroad long living ice free areas in midwinter northeast of svalbard between 2011 and 2014 are investigated the formation of these persistent and reemerging anomalies is linked hypothetically with the increased seasonality of arctic sea ice cover enabling an enhanced influence of oceanic heat on sea ice and in particular heat transported by atlantic water the memory of ice depleted conditions in summer is transferred to the fall season through excess heat content in the upper mixed layer which in turn transfers to midwinter via thinner and younger ice this thinner ice is more fragile and mobile thus facilitating the formation of polynyas and leads when openings in ice cover form along the atlantic water pathway weak density stratification at the mixed layer base supports the development of thermohaline convection which further entrains warm and salty water from deeper layers convection induced upward heat flux from the atlantic layer retards ice formation either keeping ice thick

mooring based observations of double diffusive staircases over the laptev sea slope abstracta yearlong time series from mooring based high resolution profiles of water temperature and salinity from the laptev sea slope 2003 04 2686 m depth 78 26 n 125 37 e shows six remarkably persistent staircase layers in the depth range of 140 350 m encompassing the upper atlantic water aw and lower halocline despite frequent displacement of isopycnal surfaces by internal waves and eddies and two strong aw warming pulses that passed through the mooring location in february and late august 2004 the layers preserved their properties using laboratory derived flux laws for diffusive convection the authors estimate the time averaged diapycnal heat fluxes across the four shallower layers overlying the aw core to be 8 w m 2 temporal variability of these fluxes is strong with standard deviations of 3 7 w m 2 these fluxes provide a means for effective transfer of aw heat upward over more than a 100 m depth range toward the upper halocline these findings suggest that double diffusion is an imp

winter convection transports atlantic water heat to the surface layer in the eastern arctic ocean a 1 yr 2009 10 record of temperature and salinity profiles from ice tethered profiler itp buoys in the eurasian basin eb of the arctic ocean is used to quantify the flux of heat from the upper pycnocline to the surface mixed layer the upper pycnocline in the central eb is fed by the upward flux of heat from the intermediate depth 150 900m atlanticwater aw layer thisfluxisestimatedtobe 1wm 22 averaged over one year release of heat from the upper pycnocline through the cold halocline layer to the surface mixed layer is however seasonally intensified occurring more strongly in winter this seasonal heat loss averages 3 4wm 22 between january and april reducing the rate of winter sea ice formation this study hypothesizes that the winter heat loss is driven by mixing caused by a combination of brine driven convection associated with sea ice formation and larger vertical velocity shear below the base of the surface mixed layer sml enhanced by atmospheric storms and the seasonal reduction in density difference between the sml and underlying pycnocline

carbon and hydrogen isotopic compositions of n alkanes as a tool in petroleum exploration compound specific isotope analysis csia of individual organic compounds is a powerful but underutilized tool in petroleum exploration when integrated with other organic geochemical methodologies it can provide evidence of fluid histories including source maturity charge history and reservoir processes that can support field development planning and exploration efforts the purpose of this chapter is to provide a review of the methodologies used for generating carbon and hydrogen isotope data for mid and high molecular weight n alkanes we discuss the factors that control stable carbon and hydrogen isotope compositions of n alkanes and related compounds in sedimentary and petroleum systems and review current and future applications of this methodology for petroleum exploration we discuss basin specific case studies that demonstrate the usefulness of csia either when addressing particular aspects of petroleum exploration e g charge evaluation source rock oil correlation and investigation of maturity and in reservoir processes or when this technique is used to corroborate interpretations from integrated petroleum systems analysis providing unique insights which may not be revealed when using other methods csia of n alkanes and related n alkyl structures can provide independent data to strengthen petroleum systems concepts from generation and expulsion of fluids from source rock to charge history connectivity and in reservoir processes

the diffusive regime of double diffusive convection the diffusive regime of double diffusive convection is discussed with a particular focus on unresolved issues that are holding up the development of large scale parameterizations some of these issues such as interfacial transports and layer interface interactions may be studied in isolation laboratory work should help with these however we must also face more difficult matters that relate to oceanic phenomena that are not represented easily in the laboratory these lie beneath some fundamental questions about how double diffusive structures are formed in the ocean and how they evolve in the competitive ocean environment

observational validation of the diffusive convection flux laws in the amundsen basin arctic ocean the low levels of mechanically driven mixing in many regions of the arctic ocean make double diffusive convection virtually the only mechanism for moving heat up from the core of atlantic water towards the surface in an attempt to quantify double diffusive heat fluxes in the arctic ocean a temperature microstructure experiment was performed as a part of the north pole environmental observatory npeo 2013 field season from the drifting ice station barneo located in the amundsen basin near the lomonosov ridge 89 5 n 75 w a diffusive convective thermohaline staircase was present between 150 and 250 m in nearly all of the profiles typical vertical heat fluxes across the high gradient interfaces were consistently small o 10 1 w m 2 our experiment was designed to resolve the staircase and differed from earlier arctic studies that utilized inadequate instrumentation or sampling our measured fluxes from temperature microstructure agree well with the laboratory derived flux laws compared to previous studies which could find agreement only to within a factor of two to four correlations between measured and parameterized heat fluxes are slightly higher when using the more recent flanagan et al 2013 laboratory derivation than the more commonly used derivation presented in kelley 1990 nusselt versus rayleigh number scaling reveals the convective exponent to be closer to 0 29 as predicted by recent numerical simulations of single component convection rather than the canonical 1 3 assumed for double diffusion however the exponent appears to be sensitive to how convective layer height is defined

application of pyrolysate carbon isotope and biomarker technology to organofacies definition and oil correlation problems in north sea basins abstract detailed sampling of apparently homogeneous potential source rock intervals frequently indicates unsuspected variations in organic facies which may or may not be reflected in the wireline logs carbon isotope analyses of pyrolysates provide a useful technique in these investigations which are essential for valid oil to source correlations in the jurassic of a north sea viking graben well the rich source shales at the top of the draupne formation are significantly depleted in 13 c and correlate with the oils from this area thus suggesting that this interval has acted as the primary source of the viking graben crudes a quite different pattern is evident in a well from the central graben and the data not only explain why the oils of the greater ekofisk area are relatively enriched in 13 c but also demonstrate that the variations within these oils are facies controlled pyrolysate carbon isotopes provide an excellent correlation between the middle devonian upper caithness flagstones of the inner moray firth and the beatrice crude oil this correlation is supported by the biomarker data and there is no need to appeal to a contribution from either an upper or middle jurassic source to achieve a match with the beatrice oil

mixed signals of the source and thermal maturity for petroleum accumulations from light hydrocarbons an example of the beryl field abstract we have investigated compositional variations of light hydrocarbons in crude oils from the beryl and adjacent fields of the north sea in combination with carbon isotopic ratios of light hydrocarbons and biomarker properties of oils although there appears to be a strong source influence on various light hydrocarbon maturity parameters this is a consequence of the mixing of hydrocarbons derived from the kimmeridge clay formation as well as from the heather formation and brent coal at varying thermal maturity levels light hydrocarbon parameters based on mango s reaction scheme involving 3 ring and 5 ring intermediates are supported by carbon isotopic ratios of light hydrocarbons however there also is evidence that iso and cyclo heptane precursors exist that contribute c 7 light hydrocarbons independent of mango s model the ratio of 2 4 dimethylpentane to 2 3 dimethylpentane 2 4 dmp 2 3 dmp and other related parameters appear to be reliable indicators of thermal stress but must be interpreted within a complete understanding of the petroleum system under study

stable carbon isotope compositions of crude oils application to source depositional environments and petroleum alteration the carbon isotopic composition of the c15 saturate and aromatic hydrocarbon fractions and the gas chromatographs of the c15 saturate fraction of 339 oils were geochemically and statistically evaluated results of this study show that the average isotopic compositions of the c15 aromatic hydrocarbon fractions of oils sourced from terrigenous or marine organic matter are identical the average isotopic composition of the c15 saturate fraction of oils derived from terrigenous organic sources is slightly more negative 0 9 pmil than the average for marine oils but this difference is insufficient to be used as a reliable source indicator reports in the literature stating that marine oils are isotopically more positive than te rigenous oils and that the difference can be utilized to distinguish between the two are therefore not supported by this study the isotopic differences between oils sourced from terrigenous and marine organic matter do not manifest themselves in the range of absolute values of one oil fraction but rather in the isotopic relationship between the saturate and aromatic hydrocarbon fractions the isotopic relationship is the following oils of terrigenous organic source dgr13caro 1 12 dgr13csat 5 45 oils of marine organic source dgr13caro 1 10 dgr13csat 3 75 the difference between the two equations was evaluated statistically and a statistical parameter cv the canonical variable cv 2 53 dgr13csat 2 22 dgr13caro 11 65 was used to distinguish between marine and terrigenous oils cv values larger than 0 47 indicate predominantly a terrigenous organic source for the oil whereas cv values smaller than 0 47 indicate mostly a marine organic source thermal maturity differences in oils and isotopic variations in the source beds can cause as much as 2 pmil variations in the isotopic composition of one family of oils finally stable carbon isotopes can in some situations help correlate biodegraded oils to their nondegraded counterparts

stable carbon isotope variation of n alkanes in central graben oils while isotope analysis of bulk fractions is a well tried and useful tool in oil correlation use of compound specific isotope ratio mass spectrometry cs irms of individual hydrocarbons is still in its infancy this technique has been developed over the past few years as a useful research tool but its potential in petroleum exploration has yet to be demonstrated in this paper both bulk fraction and individual hydrocarbon isotopic data were acquired their use was evaluated and compared with traditional geochemical measurements such as gas chromatography and gc ms data on 72 oils from the norwegian sector of the central graben were acquired data include 13c isotope composition of whole oil and topped oil as well as saturated and aromatic hydrocarbon nso and asphaltene fractions and 13c isotopic composition of individual n alkanes in the range nc4 to nc35 the same samples were also analysed by capillary gc and gc ms gc gc ms and bulk fraction isotope data suggest that many of the analysed greater ekofisk oils e g valhall edlfisk i e within the lindesnes ridge inversion zone have more than one source facies outside of this area particularly towards the northwest oils are probably mainly from a single source facies the isotopic compositions of individual hydrocarbon compounds also reveal the same divisions in addition several further features were observed the normal alkanes of many of the greater ekofisk oils are more depleted in 12c between nc20 nc25 than at higher or lower molecular weight possibly representative of the original microbial precursors other oils have relatively uniform n alkane isotope profiles with n alkanes which are enriched in 12c relative to the n alkanes of oils with the other type of profile the two different isotope profiles are interpreted as being separate source facies the least mature greater ekofisk oils also become more enriched in 12c with decreasing molecular weight mature oils from this area tend to have very similar n alkane isotope values throughout the measured n alkane range the higher maturity oils and condensates have n alkanes nc8 the tentative interpretation of this is that the highly mature oils condensates are sourced only from highly mature source rocks i e of a condensate window maturity and are not products of thermal alteration in the reservoir

reevaluating dune scaling relations abstract in sand bedded rivers dunes dominate sediment transport and flow resistance dunes are also commonly preserved in fluvial deposits as cross stratified units that record their size shape and migration rates prediction of dune dimensions is therefore important for forecasting modern river channel dynamics as well as reconstructing past fluvial environments on earth and other planets predictions are often made by assuming that the formative flow depth h sets dune dimensions with height scaling as 1 6h and length as 5h yet there is a suite of other scaling relations that link dune dimensions to other variables like grain size transport stage and froude number here we present a new compilation of flow and dune dimension data to evaluate scaling relations the data reveal approximately two orders of magnitude variation in dune height and length at any given flow depth dune heights in shallow flows 2 5 m are often more symmetric have lower lee angles are relatively shorter in height than 1 6h and have a wider range of observed heights for a given depth none of the scaling relations predict the observations exceptionally well likely because of natural variability in dune dimensions and because they do not explicitly account for the apparent scaling break that occurs at 2 5 m we propose new simple depth scaling relations with added statistical uncertainty for the prediction of dune height and length from flow depth as well as flow depth from dune height we conclude that shallow and deep flow dunes exhibit different scaling due to a change in the dominant process controls as dunes get larger

size of suspended sediment over dunes 1 samples of suspended sediment were collected at four elevations simultaneously over two dimensional mobile dunes in two mixtures of 0 5 mm sand in a laboratory flume channel a constant sampling position relative to the dunes was maintained by adjusting the translation rate of the sampling carriage to be the same as the migration rate of the dunes the rate of change of concentration of the suspended sediment with distance from the bed for individual grain sizes was found to be related to the part of the dune over which the samples were collected the suspended sediment concentration over the lowest third of the flow depth was nearly constant over the trough of the bed forms while concentration varied rapidly with depth over the brink point with intermediate rates of change similar to measurements over a flat bed over the rest of the dune the concentration of coarser grains was reasonably explained by assuming they were in intermittent suspension from the brink point of one dune to that of the next differences between the vertical changes in grain size were reduced when the sizes were plotted relative to the mean crest elevation of the dunes rather than the local bed elevation the rouse equation was found to yield accurate predictions of median grain sizes above the crest level using a reference sample while median grain size was found to be nearly constant below the level of the crest

hydrogen isotopic compositions of individual alkanes as a new approach to petroleum correlation case studies from the western canada sedimentary basin isotopic compositions of carbon bound hydrogen in individual n alkanes and acyclic isoprenoid alkanes from a number of crude oil samples were measured using gas chromatography thermal conversion isotope ratio mass spectrometry the precision of this technique is better than 3 for most alkanes compared to the large range of d variation among the samples up to 160 the oils were selected from major genetic oil families in the western canada sedimentary basin with source rocks ranging in age from ordovician and possibly cambrian to cretaceous the hydrogen isotopic composition of alkanes in crude oils is controlled by three factors isotopic compositions of biosynthetic precursors source water d values and postdepositional processes the inherited difference in the lipid s biosynthetic origins and or pathways is reflected by a small hydrogen isotopic variability within n alkanes but much larger differences in the d values between n alkanes and pristane phytane the shift toward lighter hydrogen isotopic compositions from paleozoic to upper cretaceous oils in the wcsb reflects a special depositional setting and or a minor contribution of terrestrial organic matter the strong influence of source water d values is demonstrated by the distinctively lower d values of lacustrine oils than marine oils and also by the high values for oils with source rocks deposited in evaporative environments thermal maturation may alter the d values of the alkanes in the oil to some extent but secondary oil migration does not appear to have had any significant impact the fact that oils derived from source rocks that could be of cambrian age still retain a strong signature of the hydrogen isotopic compositions of source organic matter and source water indicates that d values are very useful for oil source correlation and for paleoenvironmental reconstructions

compound specific carbon isotope analysis of natural and artificially generated hydrocarbons in source rocks and petroleum fluids from offshore mid norway stable carbon isotope signatures of individual hydrocarbon components provide important information on the source rock facies of oils as well as their asphaltene fractions despite maturity variations and secondary processes such as phase fractionation and biodegradation our study is based upon petroleum fluids and source rock samples from offshore mid norway where the main source rock is the marine shales of the upper jurassic spekk formation an alternative source is provided by coals and coaly shales of the lower jurassic are formation in terms of maturity the source rock samples are distributed throughout the main phase of oil generation in this study compound specific carbon isotope analysis has been performed on thermal extracts and kerogen pyrolysates of the source rocks as well as on the oils and the pyrolysis products of their asphaltenes we demonstrate that trends of absolute isotope data and specific isotopic fingerprints after normalizing the data are useful for petroleum source rock correlations the carbon isotope ratios of the n alkanes separate the are from the spekk formation samples in both thermal extracts and kerogen pyrolysates becoming less negative with increasing terrestrial input the spekk samples also tend to become isotopically heavier with increasing maturity while the are samples do not show any systematic difference with increasing maturity the carbon isotope ratios of the n alkanes also discriminate between the oils as well as the asphaltenes from the fluids the individual components generated by pyrolysis of kerogens are isotopically heavier than those from the thermal extracts this is expected from models of kinetic isotope effects which predict that the isotopically lightest products are generally released at an earlier stage in the maturation process a similar isotopic difference is also observed between the pyrolysis products of asphaltenes and the original oils derived from the same source rock type however in a sample where the oil and its asphaltene fraction originate from two different source rocks the opposite relationship between the carbon isotope composition of the oil and its asphaltene fraction is observed bulk isotope data of kerogen concentrates pyrolysates and the residue after pyrolysis of the source rock samples as well as bulk isotope data of whole oils are also presented we show that besides separating are from spekk the bulk carbon isotope values of the spekk samples are considerably heavier than the n alkanes from the thermal extracts whereas those of the are samples are almost equal

predicting the migration rates of subaqueous dunes in this paper we develop a simple physically based method for predicting what fraction of sediment moving over the crests of dunes will bypass their lee faces the bypass fraction is found by calculating a characteristic excursion length for every grain size making up a particular train of dunes all particles with excursion lengths greater than the downstream span of the lee face of the average dune are assumed not to contribute to dune propagation bypass fractions based on distributions of excursion lengths account for the discrepancies between total sediment discharge and dune migration rate measured by stein 1965 and guy et al 1966 in laboratory flumes as well as by us in the north loup river of nebraska calculations and these data agree over sediment transporting conditions associated with the entire stability field for dunes composed of medium sand the two laboratory studies show that commonly 30 60 of all sand moving over fully developed dunes is not deposited on slip faces measurements from the north loup river reveal that of all sediment moving over the dune crests there roughly 45 is not being captured on lee faces even though 99 of sediment is transported within 2 cm of the bed the method developed herein successfully estimates measured values for the bypass fraction from 0 to 80 our analysis indicates that the division between grains that are deposited versus those that are bypassing falls within the range of sand sizes making up the suspended load at dune crests

eastern arctic ocean diapycnal heat fluxes through large double diffusive steps abstractthe diffusive layering dl form of double diffusive convection cools the atlantic water aw as it circulates around the arctic ocean large dl steps with heights of homogeneous layers of

formulas for sediment porosity and settling velocity several existing formulas for the initial porosity and settling velocity of sediment have been tested by using extensive data collected from different countries and regions and modified to achieve better reliability or convenience in use

field measurements of flow fields and sediment transport above mobile bed forms 1 field measurements of hydrodynamic conditions bed forms and suspended sediments obtained using a suite of approximately colocated sensors above a mobile bed composed of coarse sand d50 1 28 mm in a strong tidal current with superimposed waves are used to investigate the mean and turbulent flow fields bed forms and the resuspension and transport of sediments in suspension and as bed load while there is no evidence for flow separation properties of the local turbulent flow field are found to vary spatially in response to the bed morphology time averaged suspended sediment concentration profiles c profiles are found to be spatially variable with higher concentrations observed in the trough regions between bed form crests well known expressions used to predict c profiles are found to agree well with measured time averaged c profiles the instantaneous suspended sediment concentration field sscf is found to comprise a series of semiperiodic resuspension events interspersed by relatively quiescent periods using a modified quadrant analysis scheme these events are shown to be correlated closely with times when current and wave induced flows combine and exceed the threshold for suspension the effectiveness of a given combined wave current flow event in resuspending bed sediments is found to depend upon its location relative to bed morphology it is considered that local bed response may be influenced by spatial differences in grain size and compaction brought about by the processes of bed load transport over the bed forms the total mass of sediment in suspension is found to be less than the potential transport capacity of the flow suggesting strongly that the supply of fine sediments is source limited while measured bed form geometry agrees well with predicted dimensions for ripples grain size alone suggests only dunes should be present these were not detected bed load transport qb calculated from measured bed form migration speeds and the measured suspended sediment flux qs was found to agree favorably with empirical predictions