discrepancies between different organic maturity indicators in a coal series affected by an abnormal thermal event visean niger abstract classical petrographical and geochemical approaches have been used to study visean coal seams sampled in two areas 50 km apart in northern niger t max values given by rock eval pyrolysis and individual molecular ratios determined on hopanes and steranes are in agreement with the burial history of the two sets of samples studied the difference of maturity of the two sample sets revealed by these various parameters is consistent with their current difference in burial depth 400 m only small changes of these parameters with depth were observed owing to the small depth interval sampled at both sites 15 and 40 m these variations also appear to be related to normal burial diagenesis no maturity differences between the two sample sets are revealed by vitrinite reflectance data and atomic h c ratios which are in the same range at both sites but display very large variations with depth r v 0 60 1 40 and h c at 0 80 0 90 to 0 55 these data indicate rapid entrance into the oil window this conclusion also being supported by microspectrofluorimetric observations showing oil production and expulsion and by the presence of pyrobitumens containing large devolatilization vacuoles in the deepest samples the abnormally high maturity gradient could have been caused by a hydrothermal event the present observations on coals confirm and supplement previous conclusions drawn from the study of organic materials disseminated in zn pb sulfide ore bearing sedimentary rocks the difference in sensitivity shown by the various maturity indicators is considered very likely to be due to differences in the kinetics of the transformations on which they each depend

biological origin of tetracyclic diterpanes n alkanes and other biomarkers found in lower carboniferous gondwana coals niger abstract the saturated hydrocarbons of coal samples of the anou araren mine tim mersoi basin niger republic have been studied by gc and gc ms chromatograms revealed rather unusual n alkane distributions dominated by compounds in the c 20 c 23 range and showing a rapid and irregular decrease towards higher molecular weights these signatures appear to be typical of the paleozoic gondwana swamps flora unlike typical low maturity terrestrial organic matter characterized by a dominance of odd carbon number n alkanes in the c 27 c 33 range which could be attributed to angiosperms the presence of large amounts of polycyclic diterpanes ent beyerane phyllocladanes and kauranes is unexpected in samples of that age since these compounds are usually thought to be derived from conifers which supposedly had not yet evolved at the time a more likely explanation is that these diterpanes could be derived from biological precursors of the conifers

equations for determining the gas and brine volumes in sea ice samples on a etabli des equations utilisables pour determiner le taux de gaz inclus dans la glace de mer a partir de mesures de densite de salinite et de temperature dans des gammes de temperatures entre 2 c et 30 c inversement ces relations peuvent etre utilisees pour calculer la densite de la glace de mer en fonction de la temperature et de la salinite en prenant en compte a la fois la presence de gaz et de cristaux de sel dans la glace on donne aussi des equations qui permettent le calcul du volume de gaz et d eau salee dans la glace a des temperatures autres que celle pour laquelle la densite a ete determinee

evidence and effects of fluid circulation on organic matter in intramontane coalfields massif central france abstract recent evidence for a late carboniferous hydrothermal event responsible for au as mineralization within the variscan belt of the french massif central adds a supplementary episode to the already rather complex thermal history of this area to better understand this history 45 coal samples from various sites in the massif central were studied petrographically reflectance analysis and geochemically rock eval pyrolysis the results of this study suggest that the studied coal was buried to 1500 m and that the coalification took place within 25 ma probably ending at the boundary between the early and late permian marked by the saalic orogeny two thermal end members basins were identified i the carboniferous of bosmoreau les mines limousin and west graissessac montagne noire showing geothermal paleoflow values between 150 and 180 mw m 2 and ii the stephanian of argentat and detroit de rodez sw massif central with values estimated at between 100 and 120 mw m 2 by plotting the t max and r o values on a diagram the samples were grouped into two populations the first showing a positive correlation between r o and t max and the second with higher t max values than expected after r o values selected samples of the second group are also characterized by a high oxygen index oi that increases with t max these divergence between r o and t max associated with a high oi may be the result of the circulation of slightly oxidizing hot fluids subsequent to coalification the other kind of r o t max divergence seems to be linked to local particularly high thermal activity especially in graissessac and bosmoreau basins it is interpreted as being due to a difference in response of these two maturity indicators respectively to the intensity and duration of the thermal events e g short lived hydrothermal circulation and thermal domes of regional extent

theoretical estimates of light reflection and transmission by spatially complex and temporally varying sea ice covers the reflection absorption and transmission of light at visible and near infrared wavelengths by snow and ice covers is important for a number of geophysical problems the focus of this paper is on the reflection and transmission of light by spatially inhomogeneous and temporally varying sea ice covers this is investigated using a two stream multilayer radiative transfer model in the wavelength region from 400 to 1000 nm the model is computationally simple and utilizes the available experimental data on the optical properties of sea ice the ice cover is characterized as a layered medium composed of selections from nine distinct snow and ice types three case studies are presented illustrating values of spectral albedo transmittance and transmitted photosynthetically active radiation par for 1 a spatially inhomogeneous ice cover 2 a uniform ice cover as it undergoes a melt cycle and 3 a temporally changing spatially variable ice cover results indicate that small scale horizontal variations in snow depth and ice thickness can cause light transmission to change over 3 orders of magnitude dramatic changes in light reflection and transmission are predicted in the early part of the melt season as the ice cover evolves from an opaque snow covered medium to translucent bare or ponded ice

a semianalytical algorithm for quantitatively estimating sediment and atmospheric deposition flux from modis derived sea ice albedo in the bohai sea china quantitative estimates of particulate matter pm concentration in sea ice using remote sensing data is helpful for studies of sediment transport and atmospheric dust deposition flux in this study the difference between the measured dirty and estimated clean albedo of sea ice was calculated and a relationship between the albedo difference and pm concentration was found using field and laboratory measurements a semianalytical algorithm for estimating pm concentration in sea ice was established the algorithm was then applied to modis data over the bohai sea china comparisons between modis derived and in situ measured pm concentration showed good agreement with a mean absolute percentage difference of 31 2 from 2005 to 2010 the modis derived annual average pm concentration was approximately 0 025 g l at the beginning of january after a month of atmospheric dust deposition it increased to 0 038 g l atmospheric dust deposition flux was estimated to be 2 50 t km 2 month similar to 2 20 t km 2 month reported in a previous study the result was compared with on site measurements at a nearby ground station the ground station was close to industrial and residential areas where larger dust depositions occurred than in the sea but although there were discrepancies between the absolute magnitudes of the two data sets they demonstrated similar trends

east antarctic sea ice albedo thickness distribution and snow cover characteristics of springtime sea ice off east antarctica were investigated during a cruise of the australian national antarctic research expedition in october through december 1988 the fractional coverage of the ocean surface the ice thickness and the snow cover thickness for each of several ice types were estimated hourly for the region near the ship these observations were carried out continuously during the 4 weeks the ship was in the ice thin and young ice types were prevalent throughout the region and the observations show a systematic increase in the total area weighted pack ice thickness including open water area from only 0 2 m within 50 km of the ice edge to 0 45 m close to the coast ice thickness averaged over the ice covered region only is also relatively thin ranging from 0 35 m near the ice edge to 0 65 m in the interior these values are probably typical of average winter thickness for the area the average snow cover thickness on the ice increased from 0 05 m near the ice edge to 0 15 m in the interior average ice concentration increased from less than 6 10 near the ice edge to 8 10 in the interior the ship observed concentrations were in good agreement with concentrations derived from passive microwave satellite imagery except in some regions of high concentration in these regions the satellite derived concentrations were consistently lower than those estimated from the ship possibly because of the inability of the satellite sensors to discriminate the appreciable percentage of very thin ice observed within the total area spectral albedo was measured for nilas young grey ice grey white ice snow covered ice and open water at wavelengths from 420 to 1000 nm allwave albedo was computed by using the spectral measurements together with estimates of near infrared albedo and modeled spectral solar flux area averaged albedos for the east antarctic sea ice zone in spring were derived from representative allwave albedos together with the hourly observations of ice types these area averaged surface albedos increased from about 0 35 at the ice edge to about 0 5 at 350 km from the edge remaining at 0 5 to the coast of antarctica the low average albedo is in part due to the large fraction of open water within the pack but extensive fractions of almost snow free thin ice also play an important role

albedo of dirty snow during conditions of melt the evolution of spectrally averaged albedo wavelengths between 0 28 m and 2 8 m of snow surfaces treated with known initial concentrations of particles of submicron sized soot and air fall volcanic ash was investigated during conditions of natural melt depending on the particle type and concentration the initial applications reduced the surface albedo to values ranging from 0 18 to 0 41 which were substantially lower than the albedo of the untreated natural snow about 0 61 many of the soot particles flushed through the snowpack with the meltwater and surface concentrations of soot greater than about 5 10 7 kg kg did not persist for more than a few days the migration of particles to depth caused the snow to brighten after the initial application thus limiting the amount of albedo reduction and the consequent effects on melting nevertheless the soot remaining near the surface had a substantial long term effect the residual concentration of 5 10 7 kg kg persisted for several weeks and compared to the untreated surface reduced the albedo by about 30 and increased melting by 50 particles of volcanic ash with diameters larger than about 5 m remained at or near the snow surface although many of the smaller particles flushed through the snow with the meltwater the surface albedo was not changed significantly by their removal the different behaviors of the ash and soot are probably related to the difference in their particle size distributions in relation to the thickness of water films that form the transport paths under conditions of partial saturation that are characteristic of melting snow

evolution of electromagnetic signatures of sea ice from initial formation to the establishment of thick first year ice the spatial and temporal distribution of new and young sea ice types are of particular interest because of the influence this can exert on the heat and mass balance of the polar sea ice the objective of the present work is to characterize the temporal evolution of the electromagnetic em signatures of sea ice from initial formation through the development of first year fy ice on the basis of the temporal variations in the physical properties of the ice the time series of young sea ice signatures including microwave emissivity radar backscatter and visible and infrared spectral albedo has been measured at successive stages in the growth and development of sea ice both under laboratory and field conditions these observations have been accompanied by studies of the physical properties that influence the interaction between radiation and the ice this has resulted in a consistent data set of concurrent multispectral observations that covers essentially all phases of the development of the different types of sea ice from initial formation to thick fy ice mutually consistent theoretical models covering the entire wavelength range of the observations are applied to selected cases and successfully match the observations principal component analysis pca of the data set suggests combinations of the set of frequencies to effectively distinguish among different stages in the temporal evolution of the sea ice

roles of barotropic convective momentum transport in the intraseasonal oscillation both observational data analysis and model simulations suggest that convective momentum transport cmt by cumulus convection may play a significant role in the intraseasonal oscillations iso by redistributing atmospheric momentum vertically through fast convective mixing process the authors present a simple theoretical model for the iso by parameterizing the cumulus momentum transport process in which the cmt tends to produce barotropic wind anomalies that will affect the frictional planetary boundary layer pbl in the model with equatorial easterly vertical wind shear vws it is found that the barotropic cmt tends to select most unstable planetary scale waves because cmt suppresses the equatorial ekman pumping of short waves which reduces the shortwave instability from the pbl moisture convergence and accelerates the shortwave propagation the model with subtropical easterly vws has behavior that can be qualitatively different from the model with equatorial easterly vws and has robust northward propagation the basic mechanism of this northward propagation is that the cmt accelerates the barotropic cyclonic wind to the north of iso which will enhance the precipitation by pbl ekman pumping and favor the northward propagation the simulated northward propagation is sensitive to the strength and location of the seasonal mean easterly vws these results suggest that accurate simulation of the climatological mean state is critical for reproducing the realistic iso in general circulation models

hydrocarbon distribution in coals and in dispersed organic matter of different maceral compositions and maturities more than 60 samples from 5 coal seams and adjacent siltstones and sandstones were selected from a well through westphalian b sediments from northern germany in order to study bitumen generation and migration the cores were drilled between 1200 und 1530 metres depth in this interval vitrinite reflectance rr is increasing from 0 70 to 0 92 results reveal high hydrocarbon generation potentials for all coal samples but not for adjacent clastic rocks although maceral compositions of both are quite similar yields and compositions of thermal extracts from the coals depend on maceral compositions and rank however the bulk of the already generated bitumen has not been removed during natural coalification and is not easily releasable by thermovaporisation a mass balance based on elemental composition of dull coals indicates that in the rather narrow rank interval 0 70 0 92 rr a total mass loss of 20 may have occurred by migration this is evidenced by a loss of about 20 of the original hydrogen the rest being stored in the coals

degradation et lessivage des hydrocarbures de la formation ordovicienne de thumb mountain encaissant le gite zn pb de polaris territoires du nord ouest canada carbonate rocks of the ordovician thumb mountain formation host to the zn pb polaris deposit contain hydrocarbons that show types of alteration classically attributed to biodegradation and water washing the hydrocarbons of the upper part of this formation and of the overlying irene bay formation indicate alterations due to water washing only the hydrocarbons of the impermeable shales of the overlying cape phillips formation display indices of only higher thermal maturity than the underlying units contrary to classical concepts of hydrocarbon biodegradation n alkanes cyclohexylalkanes even isoprenoids and perhaps also steranes seem to have been degraded simultaneously and not successively in this sequence this alteration process is mainly responsible for a log linear decrease of the amounts of n alkanes and cyclohexylalkanes with increasing depth the severe and uniform alteration of aromatic hydrocarbons throughout the interval which is opposite to the progressive alteration of associated n alkanes can be attributed solely to water washing this conclusion necessitates a reconsideration of previous interpretations attributing the loss of short side chain substituted polyaromatic compounds to microbial activity hopanes tri and tetra cyclic terpanes as well as aromatic steroids and hopanoids seem to have been unaffected by the alteration phenomena the increase in the degree of alteration of the hydrocarbons with increasing depth implies that the responsible migrating fluid circulated per ascensum

the interaction of ultraviolet light with arctic sea ice during sheba the reflection absorption and transmission of ultraviolet light by a sea ice cover strongly impacts primary productivity higher trophic components of the food web and humans measurements of the incident irradiance at 305 320 340 and 380 nm and of the photosynthetically active radiation were made from april through september 1998 as part of the sheba surface heat budget of the arctic ocean program field experiment in the arctic ocean in addition observations of snow depth and ice thickness were made at more than 100 sites encompassing a comprehensive range of conditions the thickness observations were combined with a radiative transfer model to compute a time series of the ultraviolet light transmitted by the ice cover from april through september peak values of incident ultraviolet irradiance occurred in mid june peak transmittance was later in the summer at the end of the melt season when the snow cover had completely melted the ice had thinned and pond coverage was extensive the fraction of the incident ultraviolet irradiance transmitted through the ice increased by several orders of magnitude as the melt season progressed ultraviolet transmittance was approximately a factor of ten greater for melt ponds than bare ice climate change has the potential to alter the amplitude and timing of the annual albedo cycle of sea ice if the onset of melt occurs at increasingly earlier dates ultraviolet transmittance will be significantly enhanced with potentially deleterious biological impacts

natural and artificial maturation of biological markers in a toarcian shale from northern germany steroid and terpenoid biological marker evolution was studied in a maturity sequence of lias toarcian shales and adjacent strata from three shallow boreholes in the hils syncline northern germany excellent facies control within the study area ensures the comparability of the organic matter type among the stratigraphically equivalent samples of the natural maturation series in the early hydrocarbon generation stage 0 68 r0 a strong facies dependence of some sterane and hopane isomerisation values was found within the same borehole at only a few metres depth difference the extent of sterane isomerisation at c 14 and c 17 was close to 80 in the toarcian shale and between about 55 and 65 in the adjacent dogger and lias sediments similar differences were observed for the 17 h hopane moretane and 22 29 30 trisnor 18 h neohopane 22 29 30 trisnor 17 h hopane ratios whereas the 20s 20s 20r sterane isomerisation ratio did not show this difference the observed differences mostly disappear by the end of the main oil generation phase 0 88 ro where several reactions appear to have reached completion hydrous pyrolysis experiments by variations of time and temperature were used to simulate the natural evolution of the biological markers results for sterane isomerisation in the high temperature range were compared to those published by mackenzie and mckenzie geol mag 120 417 470 1983 for natural sediments kinetic data derived for this reaction from the hydrous pyrolysis results alone or from the combination of hydrous pyrolysis and natural data sets differ markedly from those determined by mackenzie and mckenzie 1983 the hydrous pyrolysis data alone yield an activation energy for sterane isomerisation at c 20 of 131 kj mol the combined data of 170 kj mol the frequency factors are in the 105 108 s 1 range the significance of the data is discussed in detail

sedimentation de la matiere organique dans le nord est du bassin de paris consequences sur le depot des argilites carbonees du toarcien inferieur organic matter sedimentation in the northeast of the paris basin consequences on the deposition of the lower toarcian black shales abstract a borehole realised by the agence nationale pour la gestion des dichets radioactifs andra near the village of montcomet aisne in the paris basin allowed to core about 1 km of jurassic series the organic matter om associated to the drilled series has been characterised by various well proven methods rock eval pyrolysis palynofacies study and saturated hydrocarbon analysis the series received variable but notable amounts of inputs of om of terrestrial origin during all the jurassic these inputs probably originated from the ardennes massif near the study area the conditions of preservation of these inputs being poor during the early jurassic improved markedly at the beginning of the domerian and then apparently remained rather constant at least up to the callovian during three distinct and rather well limited periods important amounts of algae derived om added to the background of terrestrial om the most important and the best known of these episodes corresponds to the black shales of the base of the lower toarcian lateral equivalent of the well known schistes carton these results suggest that in the paris basin the deposition of om rich sediments occurred during episodes of high planktonic production happening when medium conditions were favourable to om preservation the quantitative and qualitative fluctuations of the om all along the studied series accompany and describe three of the large transgression regression cycles recently evidenced in the paris basin guillocheau 1991 late carnian toarcian aalenian bathonian and callovo oxfordian one episode of accumulation of planktonic om appears to have occurred in each of these cycles in the neighbourhood of transition transgression regression in the present state of knowledge only the confinement behind sills in a structured basin seems capable of explaining the triggering of episodes of planktonic production in the paris basin these conditions of confinement appear to have mainly resulted from a notable structuration of the platforms and of the adjacent troughs due to 1 subsidence during the tectonic cycles and 2 to distensive tectonic activity during tectono eustatic cycles

the role of shortwave radiation in the summer decay of a sea ice cover heat balance models of ice leads and the underlying water column were used to investigate the role of shortwave radiation in the summer decay of a sea ice cover because of the potential importance of positive feedback between decreasing ice concentration and increasing solar input to the ocean particular emphasis was given to the treatment of heat transfer and lateral melting in leads the rate of heat loss to floe edges was calculated from lead temperatures using an empirical boundary layer parameterization coefficients for this parameterization were obtained from field measurements in the dynamically active ice cover of the greenland sea during the 1984 marginal ice zone experiment and in the static ice of mould bay northwest territories field coefficients were found to be considerably larger than those previously obtained in the laboratory suggesting that heat transfer rates near floe edges were controlled more by winds and currents than by local density differences model studies of individual leads indicate that heat losses to the atmosphere cause lateral melt rates to asymptotically approach a constant value as lead size increases thus although very wide leads transmit considerable energy to the underlying ocean they have relatively little effect on lateral melting other results provide information on the relative importance of horizontal heat transfer rates ice thickness floe perimeter atmospheric forcing and oceanic heat flux in general the calculations indicate that much of the shortwave radiation entering the ocean is absorbed below the ice where it contributes to bottom ablation rather than lateral melting this suggests that previous work has seriously overestimated the magnitude of the feedback between ice concentration and incident shortwave radiation

optical properties of melting first year arctic sea ice the albedo and transmittance of melting first year arctic sea ice were measured during two cruises of the impacts of climate on the eco systems and chemistry of the arctic pacific environment icescape project during the summers of 2010 and 2011 spectral measurements were made for both bare and ponded ice types at a total of 19 ice stations in the chukchi and beaufort seas these data along with irradiance profiles taken within boreholes laboratory measurements of the optical properties of core samples ice physical property observations and radiative transfer model simulations are employed to describe representative optical properties for melting first year arctic sea ice ponded ice was found to transmit roughly 4 4 times more total energy into the ocean relative to nearby bare ice the ubiquitous surface scattering layer and drained layer present on bare melting sea ice are responsible for its relatively high albedo and relatively low transmittance light transmittance through ponded ice depends on the physical thickness of the ice and the magnitude of the scattering coefficient in the ice interior bare ice reflects nearly three quarters of the incident sunlight enhancing its resiliency to absorption by solar insolation in contrast ponded ice absorbs or transmits to the ocean more than three quarters of the incident sunlight characterization of the heat balance of a summertime ice cover is largely dictated by its pond coverage and light transmittance through ponded ice shows strong contrast between first year and multiyear arctic ice covers

a radiative transfer model for sea ice with vertical structure variations a radiative transfer model designed for application to snow covered sea ice with vertical layering is presented which removes several of the computational problems associated with media whose optical properties are strong functions of wavelength and depth with this model it is possible to treat the effects of biological activity in the ice as well as vertical variations in brine volume and bubble density transmission spectra can also be calculated as a function of depth in the water column beneath the ice accurate results are achieved for both direct and diffuse incident irradiance for single scattering albedos ranging from 0 0 to 0 99999999 calculated albedos and extinction coefficients for snow and sea ice are consistent with both observations and previous models and the model results resolve apparent inconsistencies among certain observational data sets refraction is included for all layer interfaces and is found to reduce the albedo while the transmissivity responds to changes in the optical depth in addition to redirection of the radiation for bare sea ice ignoring refraction can introduce albedo errors as great as 24 and transmissivity errors of more than 70 absorption by algae in the ice is shown to reduce the transmitted radiation by more than a factor of 10 at certain visible wavelengths the predicted azimuthal dependence of the emergent radiances is very weak even for large solar incidence angles

state of the art of research in kinetic modelling of oil formation and expulsion abstract the last ten years have seen a rapid development in the understanding of petroleum generation and expulsion by a combined use of natural series and experimental simulation this knowledge is now used to develop mathematical models which reproduce the kinetics of petroleum generation and migration in the purpose of basin evaluation by a combination of observation of homogeneous geochemical series experimental simulation and mathematical modelling it has been now established that parameters governing the quantity and composition of petroleum are temperature type of organic matter time or heating rate catalysis by clay minerals which would produce important amounts of isoalkanes is not necessary to produce petroleum the role of minerals although still controversial is rather to retain the heavy fraction of petroleum pressure seems to have a limited influence within the range for effective source rocks kerogen is a tremendously complex macromolecule which is now insufficiently characterized to develop fundamental predictive models of thermal cracking i e involving intermediates such as radicals and olefins such models presently apply only to the cracking of simple molecules hexane hexadecane at limited degrees of cracking for this reason kinetic models are still empirically calibrated on pyrolysis experiments and or on natural maturation trends the most popular models involve a series or a continuous distribution of parallel reactions to describe primary cracking i e direct formation of mobile compounds from kerogen these are generally calibrated against open system pyrolysis with various temperature programs consideration of natural maturation trends i e decrease in petroleum potential may be used also for calibration but discrepancies of organic matter properties availability of deep samples and uncertainties on thermal history limit the effectiveness of such methods whatever the method main activation energies are found in the range 45 60 kcal mol secondary cracking which refers generally to cracking of mobile compounds cannot be modelled from open system pyrolysis nor from natural series unknown residence times but only from closed system pyrolysis although models of primary and secondary cracking still need experimental improvements and more realistic kinetic schemes their ability to predict quantities and composition of petroleum depends primarily on migration which is poorly known indeed migration controls the residence time of petroleum in hot zones of sedimentary basins and thus determines the extent of oil conversion into gas as reproduced by recent numerical models preliminary studies documenting the interactions between thermal cracking and expulsion are shown from haltenbanken area and paris basin in the last few years a kind of agreement has been reached that primary migration was most likely occuring in a separate phase from water and that a sufficient concentration of petroleum must be generated for expulsion to start indeed high expulsion efficiencies over 50 are systematically found for rich and mature source rocks a further understanding of primary migration requires observations of natural series petrophysical studies of source rocks porosities under 10 permeabilities in the nanodardy range thermodynamic investigation of unconventional multiphase organic systems kerogen liquid s gas and experimental simulation under stress this on going research should enable models to track correctly migration paths and thermal history of petroleum fluids as necessary to model their composition

spectral albedos of sea ice and incident solar irradiance in the southern beaufort sea spectral albedos and incident spectral irradiances have been measured over the wavelength range 400 to 2400 nm on the sea ice near the naval arctic research laboratory narl at pt barrow alaska the observation interval extended from mid may when the ice was still relatively cold until mid june when summer melting was fully established the temporal dependence of albedo for the available surface types was obtained over this time interval showing a general decrease from snow and snow covered ice to blue ice and melt ponds data were also obtained for glacier ice on the athabasca glacier for melting lake ice and for certain other nonice surfaces in the vicinity of narl snow and ice albedos are characteristically highest at visible wavelengths decreasing strongly in the infrared because of the increase in absorption by ice and water local maxima in the spectra correspond to minima in the ice and water absorption variations in albedo are due primarily to differences in the vapor bubble density crystal structure and free water content of the upper layers of the ice incident spectral shortwave radiation was measured as a function of cloudiness and the optical thickness of arctic clouds is significantly less than the thickest clouds at lower latitudes the decrease of the infrared component relatiave to the visible portion of the irradiance with increasing cloud cover is determined this can give rise to an increase in wavelength integrated albedos of as much as 15 using the present data a graphical method is outlined by which visible near infrared satellite imagery can be used to distinguish among melt ponds open leads and other spring and summer sea ice surface types

a theoretical model of radiative transfer in young sea ice a four stream discrete ordinates photometric model including both anisotropic scattering and refraction at the boundaries is presented which treats the case of a floating ice slab the effects of refraction and reflection on the redistribution of the incident radiation field as it enters the ice are examined in detail using one and two layer models theoretical albedos and transmittances are compared to values measured in the laboratory for thin salt ice with an experimentally determined three parameter henyey greenstein phase function comparisons at 650 nm yield single scattering albedos ranging from 0 95 to 0 9997 the models are then used to compare the effects of diffuse and direct beam incident radiation to investigate the dependence of spectral albedo and transmittance on ice thickness and to determine the influence of very cold and melted surface layers

chemical transformations of type iii organic matter associated with the akouta uranium deposit niger geological implications abstract pure vitrinites from the akouta uranium deposit niger have been characterized using rock eval pyrolysis c h o analysis infrared and raman spectroscopies and reflectance measurements the organic matter sampled in the sandy guezouman formation is land derived type iii elemental analyses plotted in a h c vs o c diagram define three types of evolution the first one corresponds to a maturation trend and has been related to a w e geothermal gradient the second one corresponds to a slow rate diagenetic oxidation affecting organic matter located far from the ore zone the third one can be compared with a late oxidation it is related to the mineralizing process and results from both oxidation reduction and radiolysis effects the different alteration trends have been compared to mineralogical and microthermometric data in order to draw geological implications

microfluorimetry applied to organic diagenesis study abstract microfluorimetric analyses using new procedures have been applied on three sedimentary basins each of them exhibiting a specific thermal history the results have been compared to other optical and geochemical maturity parameters it appears that the spectral fluorescence parameters cannot be used as rank parameters because of their complex evolution with increasing diagenesis however they are better parameters than vitrinite reflectance for thermal maturity assessment as far as hydrocarbon generation is concerned for instance it is shown that different types of fluorescent materials release hydrocarbons at different levels of thermal evolution in a given series on the other hand alteration analyses appear to be efficient and objective tools for the punctual detection of hydrocarbons in a sample

theory of the optical properties of lake ice a radiative transfer model is developed to illustrate the processes which determine the spectral albedo and transmission of lake ice the calculated spectral albedo is dominated by specular reflection from the ice surface in the near infrared whereas multiple scattering by bubbles below the surface dominates the visible albedo adding a snow cover to lake ice will normally increase the visible albedo but may reduce the albedo in some regions of the near infrared if the sun is low by reducing the specular reflection in a preliminary test of the model spectral albedo was measured on the natural ice cover of a frozen lake the measurements are explained using the radiative transfer model applied to the air bubble size distribution measured in the same ice the uncertainty in measurement of bubble size distribution leads to uncertainty in the theoretical albedo which is much larger than the error due to approximations used in derivation of the model