sulfur geochemical constraints on mesoproterozoic restricted marine deposition lower belt supergroup northwestern united states abstract despite nearly a century of study by a diverse group of precambrian workers competing interpretations have persisted that favor both marine and nonmarine depositional settings for the mesoproterozoic belt supergroup of the northwestern united states our data for sedimentary pyrite formation in unmetamorphosed organic rich shales of the newland formation of the lower belt supergroup western montana argue that at least a portion of the belt basin during its early history was characterized by restricted marine conditions with only episodic incursions of seawater this model is supported by ratios of organic carbon corg to pyrite sulfur that once corrected for selective diagenetic and thermal loss of corg and the inferred high reactivity of the corg reservoir in the absence of vascular land plant remains suggest degrees of sulfate limitation consistent with a restricted marine setting the isotopically heavy disseminated pyrite that dominates the black shales shows a broad range of 34s values of bacterial origin 34s ranges from 8 7 to 36 3 mean 7 6 n 41 the pyrite data overlap with the 34s range of coeval barite sulfate within the basin and are similar to independent estimates for the sulfate of mesoproterozoic seawater these relationships have allowed us to delineate a record of bacteriogenic pyrite that formed in a modified marine reservoir where the supply of sulfate was limited a bacterial mechanism is further suggested by the morphological character of this early formed pyrite including the ubiquitous framboids after comparing our results with those from present day localities such as the black sea and sites of lacustrine deposition we conclude that the abundant 34s enriched bacteriogenic disseminated pyrite observed in black shales of the newland formation must record a style of sulfate limitation possible only within an isolated marine basin receiving an intermittent flux of seawater although the entire belt basin likely remained a restricted marine setting throughout deposition of the lower belt supergroup sulfur isotope data from the newland formation at two localities separated by more than 150 km in the eastern belt basin reveal stratigraphic trends in the strength of the marine connection specifically the connection evolved such that inputs of seawater sulfate increased progressively in frequency and possibly strength during deposition of the newland formation overall the hypothesized restricted marine setting when viewed in light of independent tectonic sedimentologic and geochronologic evidence suggests syndepositional and likely episodic continental rifting which helps constrain the proterozoic paleotectonic history of western laurentia

contemporaneous early diagenetic formation of organic and inorganic sulfur in estuarine sediments from st andrew bay florida usa estuarine sediment samples were collected from nine stations in st andrew bay near panama city florida usa contrasting grain size and varying concentration of organic carbon allowed a comparative study of the relationships among organic degradation processes sulfur cycling and diagenetic removal of dissolved sulfide produced by bacterial sulfate reduction abundance and sulfur isotopic composition were determined for dissolved sulfide dissolved sulfate pyrite humic acid sulfur fulvic acid sulfur and elemental sulfur presence of free dissolved sulfide and enrichment in 34s of porewater sulfate in samples from organic rich muddy sediments of st andrew bay indicate high rates of sulfate reduction and anoxic conditions below 5 mm depth such conditions are not reflected in samples from organic poor sandy near shore sediments collected from highly productive areas occupied by seagrass beds in this estuarine system pyrite and fulvic acid sulfur are the largest sinks for sulfide produced by bacterial sulfate reduction strong correlation between abundances of pyrite and fulvic acid sulfur suggests coincident formation in the uppermost 10 cm of sediment large differences in isotopic composition between these two species and consistent enrichment in 34s of the fulvic acid fraction however indicate two different reaction pathways abundance and sulfur isotopic composition of humic acid and fulvic acid sulfur suggest that organic sulfur is derived from mixing between 1 34s depleted sulfur with an unknown oxidation state that was recycled from bacterial hydrogen sulfide and 2 34s enriched sulfur interpreted as primary biosynthetic sulfur originally assimilated from dissolved sulfate samples taken from sandy sediment localities where aquatic vascular plants are rooted in the anoxic zone show a strong depletion in 34s in the fulvic acid sulfur fraction suggesting recycled hydrogen sulfide as the dominant source of organic sulfur

primary productivity and early diagenesis in the toarcian tethys on the example of the mn rich black shales of the sachrang formation northern calcareous alps organic inorganic and isotope geochemical investigations have been performed on 25 samples 20 laminated marl samples and 5 re sediment samples taken from a 27m thick black shale section of early toarcian age cropping out in the northern calcareous alps on the basis of mno fe organic carbon toc contents and hydrogen index hi values the laminated marls of the section can be divided into two parts toc contents and hi values are below 2 and 500 mg hc g toc in the lower mn rich and fe rich part mno between 2 and 16 fe between 3 9 and 6 4 while they range between 5 and 9 and 600 700 mg hc g toc respectively in the upper mn poor and fe poor part mno 1 fe between 1 5 and 3 8 both original amount of organic carbon toc or calculated from toc mno and sulphur contents and cao concentration show a strong upward increase in the lower mn fe rich part of the section toc or and cao are believed to represent planktonic particles hence their simultaneous upward increases are interpreted as the result of an at least 2 5 fold increase of productivity during the first part of the black shale event following the same logic in the second part of the black shale event productivity is believed to have slightly decreased from the previously reached high level stratigraphic variation of the sulphur isotopic ratio support this scenario comparison of organic geochemical and 34 s data of the re sediments with those of the neighbouring marls suggests that increase and decrease of productivity was paralleled by expansion and withdrawal of oxygen depleted waters during the black shale event the extent of the oxygen depleted bottom water was governed by changes in intensity of productivity changes in rates of deposition of mn and fe were not related to those of the productivity but they deeply influenced nature and intensity of bacterial degradation of organic matter and especially the incorporation of sulphur into kerogen the high contribution of mn and fe minerals in the case of the lower mn rich part prevented by both dilution and degradation of om due to mn reduction an intense incorporation of sulphur into om in the upper mn and iron poor part the high initial c org fe ratio led to an important incorporation of sulphur into om and an early termination of sulphate reduction

investigating the mechanisms associated with the evolutions of twin extratropical cyclones over the northwest pacific ocean in mid january 2011

explicit convection and scale aware cumulus parameterizations high resolution simulations over areas of different topography in germany abstractan increase in the spatial resolution of regional climate model simulations improves the representation of land surface characteristics and may allow the explicit calculation of important physical processes such as convection the present study investigates further potential benefits with respect to precipitation based on a small ensemble of high resolution simulations with wrf with grid spacings up to 1 km the skill of each experiment is evaluated regarding the temporal and spatial performance of the simulation of precipitation of one year over both a mountainous region in southwestern germany and a mainly flat region in northern germany this study allows us to differentiate between the impact of grid spacing topography and convection parameterization furthermore the performance of a state of the art convection parameterization scheme in the gray zone of convection is evaluated against an explicit calculation of convection only our evaluation demonstrates the following high resolution si

sensitivities of a flash flood event over catalonia a numerical analysis abstract on 9 and 10 june 2000 the northeastern part of the iberian peninsula was affected by heavy rains that produced severe floods over densely populated areas the zones most affected were the provinces of tarragona and barcelona located in the region of catalonia five people were killed 500 were evacuated and the property losses were estimated to exceed 65 million euros the episode was characterized by the entrance of an atlantic low level cold front and an upper level trough that contributed to the generation of a mesoscale cyclone in the mediterranean sea east of mainland spain the circulation associated with this mesoscale cyclone advected warm and moist air toward catalonia from the mediterranean sea the convergence zone between the easterly flow and the atlantic front as well as the complex orography of the region are shown to be involved in the triggering and organization of the convective systems radar shows the development of two long lived mesoscale convective systems that merged

late pleistocene to holocene environmental changes as recorded in the sulfur geochemistry of coastal plain sediments southwestern taiwan abstract a core drilled at san liao wan in the southwestern coastal plain of taiwan has been analyzed for total sulfur contents isotopic values as well as ratios of pyritic sulfur to organic carbon our results demonstrate a close relationship between late pleistocene sea level change and the proxies generated in this study the inorganic sulfur contents indicate that at our study site the holocene transgression started at 11 ka and remained under seawater for thousands of years until the late holocene corresponding to a depth of 20 m in the study core the uppermost 20 m of core shows relatively high total organic carbon toc and 34s of inorganic sulfur suggesting a transitional environment such as muddy lagoon or marsh before the site turned into a modern coastal plain in the lower part of the core at depths of 110 145 m corresponding ages of 12 30 ka low sulfur contents are recorded probably indicating fluvial sediments deposited during the oceanic isotope stage ois 2 a sea level lowstand the lower part of the core roughly within ois 3 records at least two transgressions although the transgressional signals may be somewhat obscured by subsequent weathering the reworked origin of organic matter reported in previous studies is confirmed by our organic sulfur data however the marine organic source was periodically dominant the modern high sulfate concentrations in pore water have no correlation to the other sulfur species in the sediments probably indicating that the sulfate migrated into the site subsequent to early diagenesis

the central paratethys during oligocene as an ancient counterpart of the present day black sea unique records from the coccolith limestones abstract four isochronous oligocene coccolith limestone horizons from the carpathians were examined in order to reconstruct paleoceanographic conditions in the central paratethys the dominance of small and size uniform pyrite framboids the occurrence of low diversity dinoflagellate cysts and coccolithophorids and the presence of biomarker molecule 28 30 dinorhopane indicate that the water column was stratified with the upper water column being relatively well oxygenated but the bottom water being anoxic the latter is confirmed by the fine and consistent horizontal laminations in various parts of the basin scarcity of benthic organisms and their trace fossils the limestones exhibit typical marine 13c values but are significantly depleted in 18o and enriched in 87sr relative to contemporaneous ocean water these isotopic compositions result from a decreased salinity of the surface waters caused by an increased riverine input this is confirmed by the lack or impoverishment of planktonic foraminifers presence to abundance of goniodomid dinoflagellate cysts and massive occurrence of low diversity nannoplankton assemblages which indicates decreased salinities as low as 17 and high productivity in the upper water column these observations indicate that the limestones were formed during periods when connection of the central paratethys with the global ocean was limited which impeded water exchange causing the development of low salinity conditions of surface water and bottom water anoxia during the deposition of the oldest tylawa horizon primary productivity was enhanced and chemocline was positioned exceptionally high in the water column moreover decreased 13c values in both carbonates and organic matter of this horizon suggest that widespread methane venting took place in the basin during np23 all these data show that during the oligocene the central paratethys experienced similar conditions to those of the current black sea which can be used as a modern analogue especially for the tylawa horizon therefore the tylawa horizon can be perceived as a potential effect of future post depositional processes of coccolith marls analogous to those having been deposited in the black sea for 2 7 kyr

an investigation of the influence of latent heat release on cold frontal motion abstract the effects of condensational heating on cold frontal translation speed are explored through the use of potential vorticity pv diagnostics and model sensitivity experiments it is hypothesized that condensational heating can lead to faster frontal translation speeds in the presence of vertical shear because of the horizontal propagation of the positive pv anomaly associated with the front a case study of a cold front with an evolving precipitation structure is presented a positive correlation existed between the position of condensational heating relative to the frontal zone and frontal translation speed with faster frontal movement occurring when condensational heating was present in the prefrontal zone this front was numerically simulated to see if the hypothesized mechanism for frontal movement was active through the use of a pv budget it was confirmed that condensational heating did contribute to the forward propagation of the cold frontal pv band numerical experiments were performed

comparative study of organic matter preservation in immature sediments along the continental margins of peru and oman part i results of petrographical and bulk geochemical data abstract detailed petrographical and bulk geochemical investigations of organic matter om have been performed on sediments deposited below or close to upwelling areas offshore peru odp leg 112 sites 679 681 688 and oman odp leg 117 sites 720 723 724 in order to obtain a quantitative understanding of its accumulation and degradation microscopical as well as nanoscopical investigations reveal that the om in sediments affected by upwelling mechanisms mainly up to 98 consists of unstructured amorphous organic aggregates without any apparent biological structures in sediments which are not or to a lesser extent affected by upwelling site 720 terrestrial om predominates organic carbon toc contents are highly variable and range between 9 8 in sediments deposited below upwelling cells and 0 2 in sediments outside the upwelling zone the toc sulphur ratios of the sediments scatter widely the samples from the deep water locations sites 688 and 720 show c s ratios of normal marine sediments whereas at the other locations no correlation or even a negative correlation between sulphur and toc concentration exists in most of the upwelling influenced sediments om contains a significant amount of sulphur the incorporation of sulphur into the om followed microbial sulphate reduction and occurred in the upper meters of the sedimentary column below om is still present in vast amounts and relatively hydrogen rich but is nevertheless non metabolizable and becomes the limiting factor for bacterial sulphate reduction according to mass balance calculations 90 99 of the om produced in the photic zone was remineralized and 1 3 was consumed by microbial sulphate reduction the aerobic and anaerobic processes have greatly affected degradation and conservation of om

early diagenetic alteration of organic matter by sulfate reduction in quaternary sediments from the northeastern arabian sea abstract hemipelagic sediments from the northeastern arabian sea off pakistan were analyzed by geochemical and microscopical methods to study the importance of bacterial degradation processes on the quantity and composition of sedimentary organic matter om on the basis of elemental analysis of total organic carbon toc and total sulfur ts the decay of om by sulfate reducing bacteria were calculated concentrations of total iron reactive iron total nitrogen tn total phosphorus tp and hydrogen indices hi were used to assess organic matter reactivity and redox conditions stable sulfur isotopic compositions provided further information about pathway timing and mechanisms of sulfate reduction microscopical observations indicate that throughout the study area om is amorphous 75 95 in almost all samples with only a small contribution of terrigenous om bacterially mediated sulfate reduction leads to continuously decreasing toc ts ratios from 0 4 m to a burial depth of 2 3 m at this depth the anaerobic oxidation of particulate organic matter ceases sulfate reduction in this narrow interval accounts for the decay of up to 70 of the om which has primarily entered the anoxic domain during the bacterially mediated diagenesis preferential consumption of nitrogen and phosphorus containing organic compounds can be observed and quantified the regeneration of up to 60 of tn and more than 50 of tp can lead to a feedback of nutrients to the seawater this recycling process may contribute to the high productivity in the northeastern arabian sea

a shallow convection parameterization for mesoscale models part ii verification and sensitivity studies abstract formulations describing a new shallow convection parameterization intended for mesoscale models have been described in a companion paper part i in the present paper the convection scheme is tested and evaluated against observed datasets in both marine and continental environments additional experiments explore the sensitivity of the scheme to changes in model vertical resolution key parameters of the closure and the cloud dissipation mechanisms the new shallow convection scheme uses a hybrid mass flux closure that adjusts linearly between two closure options based on i boundary layer turbulent kinetic energy tke for very shallow clouds and ii convective available potential energy cape for deep clouds meanwhile cloud mass detrained from convective updrafts acts as the source for a second class of subgrid clouds having nearly neutral buoyancy which can persist for hours performance of the convection submodel is found to be quite reasonable in four cases covering a range of conditi

sea level pressure minimum along the kuroshio and its extension abstractatmospheric effects of sea surface temperature sst fronts along the kuroshio and kuroshio extension k ke are investigated by examining spatial characteristics of the climatological sea level pressure slp surface winds and surface heat flux q fields based on an in situ observation dataset a hydrostatic effect of the sst front is observed during the northwesterly monsoon characterized by a westward extending low slp wedge trough slightly south of the peak in q along the k ke ageostrophic surface westerlies crossing slp isobars toward a trough center are found north of the low slp wedge apparently because of the eastward acceleration by the vertical mixing effect this feature of the ageostrophic winds is less pronounced south of it a north south asymmetry arising as vertical mixing accelerates decelerates eastward ageostrophic winds north south of it while the slp trough near the sst front is found nearly year round except for summer its meridional location seasonally migrates pr

paragneiss assimilation in the genesis of magmatic ni cu co sulfide mineralization at voisey s bay labrador δ34s δ13c and se s evidence the voisey s bay ni cu co deposit is located in ca 1 33 ga troctolitic rocks of the nain plutonic suite northern labrador it is widely regarded as a prime example of sulfide mineralization associated with a magmatic conduit system previous geological and geochemical studies have indicated that the voisey s bay intrusion was contaminated by interaction with both sulfide poor archean gneisses and with paleoproterozoic sulfide bearing tasiuyak metasedimentary gneiss limited sulfur isotope data previously indicated that only one of the four ore zones at voisey s bay is characterized by 34s values outside the range considered normal for uncontaminated mantle derived mafic magmas 0 2 new s isotope data presented here extends the previously reported range in 34s values for the tasiuyak gneiss from 17 0 to 18 3 per mil with an average of 1 4 per mil assimilation of this sulfur followed by isotope homogenization in the magmatic system is consistent with the isotope data from the ore zones and in line with the wealth of evidence that suggests that interaction with tasiuyak gneiss was an essential ingredient for ore formation in all the zones se s values of sulfide minerals in the ore zones at voisey s bay are also in the same range as those of whole rock samples from the tasiuyak gneiss 13c values of both mineralized and nonmineralized parts of the voisey s bay intrusion are anomalous 18 3 to 24 8 and similar to values of graphite in the tasiuyak gneiss both s and c contamination of the voisey s bay intrusion via diffusive transfer in a fluid phase derived from inclusions and wall rocks are considered unlikely because the area had been subjected to granulite grade metamorphism prior to emplacement of the nain plutonic suite either fractional melting or total fusion of xenoliths is considered a more likely mechanism for s addition to the mafic magma via pyrrhotite melting and for c addition in the form of co2 and ch4 produced by reaction of graphite with o and h bearing melt species

an analysis of the landfall of hurricane nora 1997 abstract the changes to the motion and structure of the eastern pacific tropical cyclone nora 1997 during landfall are investigated nora developed south of the mexican coast intensified into a hurricane and made landfall over northwestern mexico and the southwestern united states in this study the authors document the evolution of the structure of nora from a variety of sources observations derived from satellite imagery show the approach of the hurricane to the baja california peninsula and the development of a localized area of mesoscale convection that intensified while moving over the gulf of california the propagation of this convective system became the dominant feature of the landfall and provided heavy precipitation over a region confined to western arizona numerical simulations with the pennsylvania state university national center for atmospheric research mesoscale model version 5 are used to examine the details of the evolution of the observed area of convection over the gulf simulat

sulfurized carbohydrates an important sedimentary sink for organic carbon abstract in contrast to the general belief that carbohydrate carbon ccho is preferentially degraded and is not extensively preserved in the sedimentary record it is shown here that ccho forms a large fraction of the organic matter om of the total organic carbon toc rich upper jurassic kimmeridge clay formation as a result of early diagenetic sulfurization a previously unrecognized pathway of om preservation this is evident from both changes in the molecular composition of the insoluble om and from 13ctoc shifts of 6 with varying ccho contents furthermore experiments simulating the natural sulfurization of the ccho rich alga phaeocystis spp demonstrated that sulfurization can indeed lead to a substantial preservation of ccho with a molecular fingerprint identical to that of the kimmeridge clay and many other recent and ancient marine om rich sediments these results imply that preservation of ccho can exert a fundamental control on 13ctoc in om rich sediments complicating the interpretation of 13ctoc records with regard to estimating terrestrial versus aquatic om fractions reconstruction of past atmospheric co2 levels and global carbon budget models

coupled primary production benthic foraminiferal assemblage and sulfur diagenesis in organic rich sediments of the benguela upwelling system abstract episodically deposited dark organic rich pleistocene and late pliocene sediments from the lower continental slope off southwest africa reveal complex interactions between changes in primary production benthic foraminiferal assemblage and anaerobic microbial processes the organic rich layers contain diatom assemblages characteristic of intense seasonal coastal upwelling whereas stratigraphically adjacent sediments reflect pelagic primary production coastal upwelling dominated depositional intervals coincide with periods of enhanced carbon flux to the seafloor enhanced organic carbon export during dark layer deposition was accompanied by decreases in the diversity of benthic foraminifera to few opportunistic species adapted to high phytodetritus accumulation rates and low o 2 conditions in all sediments the sulfur isotopic composition of pyrite indicates redox cycling of sulfide close to the sediment water interface the sulfur isotopic evidence and the permanent presence of abundant low o 2 adapted benthic foraminifera throughout the organic rich layers suggest an oxygenated benthic environment efficient oxidation of sulfide and removal of sulfide by sulfidization of organic matter inhibited buildup of toxic hydrogen sulfide from bacterial sulfate reduction at the sediment water interface these data imply that in continental slope sediments underneath productive surface waters benthic dysoxic conditions are maintained by the lateral advection of dissolved oxygen to support a small but well adapted benthic community

effects of vertical wind shear on the intensity and structure of numerically simulated hurricanes a series of numerical simulations of tropical cyclones in idealized large scale environments is performed to examine the effects of vertical wind shear on the structure and intensity of hurricanes the simulations are performed using the nonhydrostatic pennsylvania state university national center for atmospheric research fifth generation mesoscale model using a 5 km fine mesh and fully explicit representation of moist processes when large scale vertical shears are applied to mature tropical cyclones the storms quickly develop wavenumber one asymmetries with upward motion and rainfall concentrated on the left side of the shear vector looking downshear in agreement with earlier studies the asymmetries develop due to the storm s response to imbalances caused by the shear the storms in shear weaken with time and eventually reach an approximate steady state intensity that is well below their theoretical maximum potential intensity as expected the magnitude of the weakening increases with increasing shear all of the storms experience time lags between the imposition of the large scale shear and the resulting rise in the minimum central pressure while the lag is at most a few hours when the storm is placed in very strong 15 m s21 shear storms in weaker shears experience much longer lag times with th e5ms 21 shear case showing no signs of weakening until more than 36 h after the shear is applied these lags suggest that the storm intensity is to some degree predictable from observations of largescale shear changes in all cases both the development of the asymmetries in core structure and the subsequent weakening of the storm occur before any resolvable tilt of the storm s vertical axis occurs it is hypothesized that the weakening of the storm occurs via the following sequence of events first the shear causes the structure of the eyewall region to become highly asymmetric throughout the depth of the storm second the asymmetries in the upper troposphere where the storm circulation is weaker become sufficiently strong that air with high values of potential vorticity and equivalent potential temperature are mixed outward rather than into the eye this allows the shear to ventilate the eye resulting in a loss of the warm core at upper levels which causes the central pressure to rise weakening the entire storm the maximum potential vorticity becomes concentrated in saturated portions of the eyewall cloud aloft rather than in the eye third the asymmetric features at upper levels are advected by the shear causing the upper portions of the vortex to tilt approximately downshear the storm weakens from the top down reaching an approximate steady state intensity when the ventilated layer can descend no farther due to the increasing strength and stability of the vortex at lower levels

monsoon extratropical circulation interactions in himalayan extreme rainfall extreme precipitation and flood episodes in the himalayas are oftentimes traced to synoptic situations involving connections between equatorward advancing upper level extratropical circulations and moisture laden tropical monsoon circulation while previous studies have documented precipitation characteristics in the himalayan region during severe storm cases a comprehensive understanding of circulation dynamics of extreme precipitation mechanisms is still warranted in this study a detailed analysis is performed using rainfall observations and reanalysis circulation products to understand the evolution of monsoon extratropical circulation features and their interactions based on 34 extreme precipitation events which occurred in the western himalayas weh during the period 1979 2013 our results provide evidence for a common large scale circulation pattern connecting the extratropics and the south asian monsoon region which is favorable for extreme precipitation occurrences in the weh region this background upper level large scale circulation pattern consists of a deep southward penetrating midlatitude westerly trough a blocking high over western eurasia and an intensifying tibetan anticyclone it is further seen from our analysis that the key elements of monsoon midlatitude interactions responsible for extreme precipitation events over the weh region are 1 midlatitude rossby wave breaking 2 west northwest propagation of monsoon low pressure system from the bay of bengal across the indian subcontinent 3 eddy shedding of the tibetan anticyclone 4 ageostrophic motions and transverse circulation across the himalayas and 5 strong moist convection over the himalayan foothills furthermore high resolution numerical simulations indicate that diabatic heating and mesoscale ageostrophic effects can additionally amplify the convective motions and precipitation in the weh region

role of cumulus congestus in tropical cyclone formation in a high resolution numerical model simulation abstractthe role of cumulus congestus shallow and congestus convection in tropical cyclone tc formation is examined in a high resolution simulation of tropical cyclone fay 2008 it is found that cumulus congestus plays a dominant role in moistening the lower to middle troposphere and spinning up the near surface circulation prior to genesis while deep convection plays a key role in moistening the upper troposphere and intensifying the cyclonic circulation over a deep layer the transition from the tropical wave stage to the tc stage is marked by a substantial increase in net condensation and potential vorticity generation by deep convection in the inner wave pouch region this study suggests that tc formation can be regarded as a two stage process the first stage is a gradual process of moisture preconditioning and low level spinup in which cumulus congestus plays a dominant role the second stage commences with the rapid development of deep convection in the inner pouch region after the air colum

role of ocean mesoscale structures in shaping the angola low pressure system and the southern africa rainfall southern african climate is under the influence of both tropical and subtropical systems which result in a complex region where important interactions co exist over a large spectrum of spatiotemporal scales the angola low al situated on boundary between tropical and subtropical southern africa has been diagnosed as a key driver of moisture distribution in the region on daily to seasonal time scales it has been demonstrated that the al pressure system is sensitive to the dynamics of the neighbouring oceans but to date no study has considered the model resolution of air sea interactions required to simulate this sensitivity using sensitivity experiments with a regional atmospheric model which differ only in the mesoscale sea surface temperature sst forcing characteristics either the full spectrum of sst variability or only its large scale components are included we first quantify the importance of sst gradients on the al strength and variability the results suggest that the mesoscale sst variability of the angola benguela frontal zone abfz plays a key role in al activity particularly during the late summer synoptic scale tropical lows which form the al are automatically detected and the results suggest more extreme events occur when the model is forced by mesoscale ssts everywhere and in the abfz area only the rainfall resulting from those events suggests that tropical low episodes are associated with nearly 15 of the total rain in angola and namibia the link between al dynamics and wet spells is also discussed with the former showing a different spatial pattern as well as frequency when the ocean is fully resolved

generation of african easterly wave disturbances relationship to the african easterly jet abstract the relationship between african easterly waves and the background climatology in which they form is studied using a regional climate model the surface and lateral boundary conditions in the model are manipulated to modify the background climatology especially the african easterly jet and the itcz and the behavior of the waves in these different settings is evaluated three climate simulations are presented with monthly mean lateral and surface boundary conditions one has a strong jet and a strong itcz the second has a strong jet and a weak itcz and the third has a weak jet and a strong itcz in these simulations the presence of wave activity is more closely associated with the concentration of the itcz than the strength of the african easterly jet in particular the simulation with a strong jet accompanied by a weak itcz does not produce significant wave activity but a weak jet with a strong itcz has realistic wave disturbances both the charney stern and the fjortoft necessary conditi

sulfur isotopic trends and pathways of iron sulfide formation in upper holocene sediments of the anoxic black sea down core trends for extents of iron sulfidation in upper holocene microlaminated deposits of the black sea abyssal plain imply that most of the pyrite in these sediments is formed in the sulfidic water column and or very close to the sediment water interface sulfur isotopic data for pyrite within microlaminated muds from two localities in the deep basin show striking uniformity between sites and down core with a mean 34scdt value of 37 2 0 9 1 n 18 these isotopic trends support the hypothesis of early pyrite formation isotopic compositions of pyrite sulfur in the microlaminated bottom sediments are similar to those reported for particulate reduced sulfur collected in middepth sediment traps and to 34s values for water column dissolved sulfide within a narrow zone immediately below the o2 h2s interface these three sulfur reservoirs are distinctly different from the isotopic composition of ambient dissolved sulfide of the deep water column 175 m with 34s values for the deep dissolved sulfide reservoir being consistently lower by 2 to 4 these isotopic relationships suggest that iron sulfidation is occurring dominantly within a narrow shallow region at the top of the sulfidic water mass isotopic data from a fine grained turbidite collected in the deep basin and from rapidly accumulating iron monosulfide rich muds on the anoxic upper slope are enriched in34s relative to the microlaminated deposits the enrichments on the basin margin reflect a large component of iron sulfide formed during rapid burial a broad suite of geochemical data including sulfur isotopic results are consistent with an upper slope sediment source for the ubiquitous muddy turbidites of the deep basin the collective effects of reworking transport and redeposition result in a complete conversion of avs to pyrite with little additional iron sulfidation this conclusion is supported by a detailed isotopic mass balance the present isotopic study also highlights fundamental differences in the reactivities of the iron reservoirs distributed throughout the anoxic basin sediments of the upper slope and the genetically linked turbidites of the deep basin show similar extents of iron sulfidation that are significantly lower than those of the microlaminated deposits of the deep basin floor suggesting dramatically shorter timescales of iron reactivity for the microlaminated sediments of the deep basin importantly isotopic patterns from the modern black sea should assist greatly in the recognition and interpretation of ancient anoxia in the stratigraphic record

organic accumulation in the lower chihsia formation middle permian of south china constraints from pyrite morphology and multiple geochemical proxies article i nfo the organic rich chihsia formation middle permian on the yangtze platform western hubei south china is considered to be the major hydrocarbon source rock in south china the lower part of the chihsia formation reported here was deposited in an intrashelf basin and is characterised by black laminated marlstones shales intercalated with dark grey limestones dolomites in which metre scale shallowing or cleaning upward cycles are ubiquitous each cycle is composed of basal marlstone shale and upper lime stone the organic matter is concentrated exclusively in the shaley bases of these cycles and shows system atic cyclic variations in abundance up through the succession an integrated approach of pyrite morphology and multiple geochemical proxies was used to determine the mechanism of organic accumulation in the organic rich sediments many redox proxies including pyrite framboid size distribution c s fe relation ships iron speciation and 34 s values of pyrite suggest deposition beneath the dysoxic bottom water which evolved into a more oxic water body when the organic poor limestones were deposited however the coincidence of increased abundance of total organic carbon toc with increased ba and mo contents in dicates that organic matter accumulation was controlled mainly by primary productivity these data indicate that increased organic accumulation resulted mainly from higher organic carbon export with increased nutri ent flux during superimposed sea level rises of different orders this in turn could have increased the oxygen consumption by respiration of microorganisms and organic matter decay leading to the depletion of oxygen in the water columns furthermore the rapid sedimentation rate further limited bioturbation and organic matter decomposition facilitating the preservation of buried organic matter

the influence of nunataks on atmospheric boundary layer convection during summer in dronning maud land antarctica the effects of nunataks on temperature profiles and wind patterns are studied using simulations from the weather research and forecasting model simulations are compared to hourly observations from an automatic weather station located at the troll research station in dronning maud land areas of bare ground have been implemented in the model and the simulations correspond well with meteorological measurements acquired during the 4 day simulation period the nunataks are radiatively heated during daytime and free convection occurs in the overlying atmospheric boundary layer the inflow below the updraft forces strong horizontal convergence at the surface whereas weaker divergence appears aloft in a control run with a completely ice covered surface the convection is absent in situ observations carried out by a remotely controlled balloon and a small model airplane compare well with model temperature profiles but these are only available over the ice field upwind to the nunatak

a case study of the cutoff process and latent heating effect in an upper level cold core low during the mei yu season in east asia abstractusing observational data and model sensitivity test the present study diagnosed the evolution of an upper level trough over 2 7 may 1998 during the mei yu season in east asia with a focus on the role of latent heating downstream from the trough on the cutoff process and the formation of the cold core low ccl compared with conceptual models based on dry dynamics the formation process of this cutoff low col was inconsistent with the model of migratory jet streak trough interaction but the evolution of the upper level trough including its narrowing and rotation of axis and the scale of the resultant col generally agreed with the theory of interaction between trough and mean westerly flow with anticyclonic background shear east southeast of the trough active and persistent convection appeared and induced 1 divergent ageostrophic flow near the tropopause 2 an increase in mid to upper level thickness due to effective heating and 3 amplification of an upper level ridge downstream thro

controls on regional marine redox evolution during permian triassic transition in south china abstract although oceanic anoxia is regarded as a leading cause of the permian triassic boundary ptb mass extinction its timing extent and underlying causes remain unclear here we conducted a high resolution fe s c mo geochemical study of the entire changhsingian and lowermost induan succession in a carbonate ramp setting at ganxi western hubei province south china six stratigraphic units representing discrete redox intervals were identified based on integrated fe s c mo data units i iii are of latest wuchiapingian to early changhsingian age with units i and iii characterized by euxinia and unit ii by uncertain redox conditions unit iv of mid changhsingian age records a gradual transition from euxinic to ferruginous conditions units v and vi spanning the latest permian mass extinction lpme to earliest triassic interval were deposited under dominantly ferruginous conditions punctuated by both euxinic and oxic episodes redox variations at ganxi were controlled by contemporaneous oceanographic changes in the upper oceanic thermocline region i euxinia in units i and iii may record elevated marine productivity as suggested by mean organic carbon accumulation rates or ocar of 6 5 and 5 1 mg cm2 kyr respectively that was possibly related to upwelling ii the euxinic to ferruginous transition from unit iv to units v vi can be attributed to a combination of reduced sulfate availability and rising terrigenous iron inputs mean fe of 1 7 and 3 9 respectively for units v iv and vi compared to 1 0 for units i iii and iii transient intervals of euxinia in units v and vi were facilitated by enhanced sulfate fluxes related to episodic volcanism during this interval an integration of the redox data from ganxi with previously published data from the shangsi and xiakou sections suggests that enhanced weathering fluxes were most likely the key factor controlling the marine redox transition from euxinic to ferruginous conditions during the latest permian across the south china region

moist dynamics and orographic precipitation in northern and central california during the new year s flood of 1997 abstract the dynamics of moist orographic flows during the january 1997 floods in northern and central california are investigated using numerical simulations computed with the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 early in the event 31 december 1996 1 january 1997 the low level winds offshore of california s central coast were blocked by the topography of the santa lucia range and the low level winds in the central valley were blocked by the topography of the central sierra nevada range in contrast moisture laden winds along the northern coast ranges and the northern sierra nevada flowed over topographic barriers as the core of humid air migrated to the south over 24 h the low level barrier jets weakened as the atmospheric stability decreased bringing heavy rainfall to the central and southern sierra nevada at the end of the event the heavy precipitation during this event was largely controlled by the interactio

a modeling study of orographic convection and mountain waves in the landfalling typhoon nari 2001 in this study the characteristics of mountain induced gravity waves mgws and orographic convection in typhoon nari 2001 and their impacts on the formation of orographic precipitation as nari moved across taiwan s central mountain range cmr are investigated by analyzing the cloud resolving model simulation results in the distant rain band convective cells were triggered frequently on the steep windward slope of cmr and advected downstream simultaneously mgws could exist on the lee side with stable environmental stratification three phases occurred in the mgws convection interaction including the enhancement of mgws and convection breaking and restoring of mgws when the convective cells and mgws were superposed in out of phase the amplitudes of both mgws and convective cells were increased decreased the vertical wavelength of mgws was also increased during the in phase superposition even inducing the further breaking of mgws for the formation of precipitation on the lee side mgws convection interaction contributes on a smaller scale to offset the reduction effect from the larger scale descending moreover convective cells on the windward slope could contribute a large amount of cloud ice and snow particles aloft to seed hydrometeors over the lee side more cloud water was produced by the mgws convection interaction when their amplitudes were increased during the in phase superposition riming and coalescence processes were responsible not only for the windward slope precipitation enhancement but also the secondary precipitation maximum over the lee side therefore the mgws convection interaction could modify the structure of vertical motion and hydrometeors over the lee side and then affect orographic precipitation when nari passed the cmr as nari s eyewall encountered the northern cmr the terrain generated long lasting strong updrafts at the upslope resulting in a doubled rainfall maximum to that in the no terrain sensitivity experiment the downdraft branch of the mgw produced a rain shadow on the lee side copyright 2011 royal meteorological society

a coupled atmosphere wave ocean modeling system simulation of the intensity of an idealized tropical cyclone abstract a coupled atmosphere wave ocean modeling system cawoms based on the integration of atmosphere wave atmosphere ocean and wave current interaction processes is developed the component models consist of the weather research and forecasting wrf model the simulating waves nearshore swan model and the princeton ocean model pom the coupling between the model components is implemented by using the model coupling toolkit the cawoms takes into account various wave related effects including wave state and sea spray affected sea surface roughness sea spray heat fluxes and dissipative heating in atmosphere wave coupling it also considers oceanic effects such as the feedback of sea surface temperature sst cooling and the impact of sea surface current on wind stress in atmosphere ocean coupling in addition wave current interactions including radiation stress and wave induced bottom stress are also taken into account the cawoms is applied to the simulation of an idealized tropical cyclo

sulfur geochemistry of organic rich sediments from mud lake florida u s a abstract organic rich sediment cores from mud lake florida were analyzed for sulfur species and their isotopic compositions the cores include the upper 4 m of sediment which consist of four major horizons based on petrographic analyses of the organic material from 400 to 300 cm depth the sediment consists of a cladium sawgrass peat from 300 to 200 cm depth the sediment consists mostly of nymphaea water lily peat from 200 to 100 cm depth the sapropel is more consolidated and contains a high proportion of non combustible material mostly from sponge spicules and the sediment consists of an amorphous sapropel above 100 cm depth the total sulfur content of the sediment ranges from 1 53 to 4 95 3 35 10 7 on an ash free and carbonate free basis and is dominated by disulfide pyrite with maxima for both total sulfur and disulfide sulfur at 117 and 365 cm organic sulfur contents are slightly lower than those of disulfides but have a similar depth profile systematic changes in the isotopic composition of sedimentary disulfide and organic sulfur coincide with variations in the sulfur species and vegetation types high disulfide contents and low disulfide isotopic ratio values 34s characterize the saw grass interval indicating high sulfate availability during deposition or during later diagenesis the water lily interval is characterized by a change to higher 34s values for both disulfide and organic sulfur this change may be the result of higher organic matter accumulation accompanied by a higher rate of sulfate reduction and or a slower rate of sulfate supply to the sediment the transition to sapropel is accompanied by a large negative shift in disulfide 34s values consistent with an increase in sulfate availability and a slower rate of sulfate reduction reactive iron availability does not appear to play a major role in limiting the amount of sulfide minerals in these sediments major shifts in 34s values at 117 350 cm depth coincide with maxima in the amount of non combustible material mostly sponge spicules in the sediment these maxima may record refractory material which accumulated around the emergent vegetation at the margins of the wetland at the time of deposition alternatively they may be records of dry periods when refractory material was concentrated in the sediment as organic matter became oxidized upon exposure to air

transport and reduction of sulfate and immobilization of sulfide in marine black shales in fine grained sediments in which the amount of reduced sulfur retained in stable phases substantially exceeds that present initially in pore waters rates of sulfate reduction may have equaled or exceeded rates of sulfate transport resulting in enrichment of sup 34 s in pore waters and reduction products abundance and isotopic compositions of reduced sulfur compounds can be used to calculate the extent of sulfide retention and improve reconstructions of carbon sulfur oxidation reduction redox budgets the miocene monterey formation and upper devonian new albany shale represent distinct types of black shales that accumulated under different conditions of sulfate reduction our results suggest that the rate of sulfate reduction was controlled largely by mass transport in the monterey and by the reduction process itself in the new albany sulfide was more efficiently retained in the monterey thus each mole of sulfide in the new albany represents a greater amount of sedimented organic carbon removed during sulfate reduction 30 refs 4 figs 1 tab

comparison of simulated and observed continental tropical anvil clouds and their radiative heating profiles abstractvertically pointing millimeter wavelength radar observations of anvil clouds extending from mesoscale convective systems mcss that pass over an atmospheric radiation measurement program arm field site in niamey niger are compared to anvil structures generated by the weather research and forecasting wrf mesoscale model using six different microphysical schemes the radar data provide the statistical distribution of the radar reflectivity values as a function of height and anvil thickness these statistics are compared to the statistics of the modeled anvil cloud reflectivity at all altitudes requiring the model to be statistically accurate at all altitudes is a stringent test of the model performance the typical vertical profile of radiative heating in the anvil clouds is computed from the radar observations variability of anvil structures from the different microphysical schemes provides an estimate of the inherent uncertainty in anvil radiative heating profiles all schemes underestima

gravity waves generated by deep tropical convection estimates from balloon observations and mesoscale simulations 1 convective gravity waves in the tropics are studied by analyzing in situ measurements from long duration stratospheric balloons launched during the preconcordiasi campaign 2010 and mesoscale simulations an improved temporal resolution of the observations as well as the balloon quasi lagrangian behavior allow an unprecedented investigation of the whole gravity wave spectrum first a case study of gravity waves generated by a developing cyclone tropical storm gelane february 2010 is carried out using observations complemented by numerical simulations with the weather research and forecast model with a resolution down to 1 km distributions of momentum fluxes obtained from both data show reasonable agreement and emphasize waves with short wavelengths 15 km and short periods 20 min still some differences are also found which can likely be related to errors of the modeled background flow second observations from the whole preconcordiasi flights are analyzed with an emphasis on gravity wave momentum fluxes their phase speed distribution has a robust shape with maximum fluxes with near zero ground based phase speeds yet significant momentum fluxes are also found for larger values yielding a mean phase speed of about 27 ms 1 the momentum fluxes are concentrated in short episodes with intense values and their intermittency is quantified using probability distribution functions and the gini coefficient 0 5 0 6 the relative importance of convective and topographic sources are investigated suggesting comparable intensities but a greater occurrence frequency of convective events waves emitted by tropical storm gelane do not stand out relative to other convective events

origin of strong winds in an explosive mediterranean extratropical cyclone abstractduring 2 3 december 2012 the black sea and east coast of romania were affected by a rapidly deepening mediterranean cyclone the cyclone developed a bent back front along which short lived

john m hayes 1940 2017 father of isotopes in modern and ancient biogeochemical processes biosynthetic carbon and hydrogen isotope fractionation and compound specific isotope analytical techniques john michael hayes professor of chemistry and geology for 26 years at indiana university bloomington until 1996 then director of the national ocean sciences accelerator mass spectrometry facility at woods hole oceanographic institution and adjunct professor at harvard university until 2007 died peacefully at his home in berkeley california on february 3rd 2017

ocean tidal cooling effect on summer sea fog over the okhotsk sea 1 ocean tide is a periodic phenomenon of the rise and fall of the sea level that depends on the bathymetry and positions of the moon and sun relative to the earth in the okhotsk sea the ocean tide causes strong vertical mixing in the upper ocean generating rich structures in summer sst with extraordinarily cold patches on kashevarov bank along the kuril islands northeast of the terpeniya peninsula and inside shelikhov bay the present study analyzes and synthesizes a suite of ship board and satellite observations and numerical simulations to investigate the ocean tidal cooling effect on summer sea fog over the okhotsk sea over the tide induced cold patches atmospheric stability increases and surface wind weakens markedly possibly through suppressed atmospheric vertical mixing our analysis of ship board observations reveals frequent sea fog occurrence over the cold patches with a maximum exceeding 70 along the kuril islands in july august numerical simulations with the weather research and forecasting wrf model support that the cold patches cool air temperature decelerate surface wind and form a strong surface inversion layer up to 0 5 km high creating favorable conditions for sea fog occurrence the wrf simulation without the tidal cooling effect reduces sea fog occurrence by more than 20 over cold patches illustrating the importance of sst products for climate models

iron availability as a dominant control on the primary composition and diagenetic overprint of organic matter rich rocks iron is known to stimulate surface ocean productivity as well as intervene with bacterially mediated processes of organic matter remineralization during early diagenesis in this paper we examine the influence of iron supply on the geochemistry trace metals 34s organic matter of sedimentary rocks deposited in a clastic dominated marine ramp environment to this end we studied two late jurassic formations of the boulonnais area north france both formations were deposited under quite similar conditions but they differ in the reactive iron supply they received only one of the two formations was affected by the particulate iron shuttle process our results indicate that 1 the iron shuttle may be recorded through concomitant enrichments in p mo as and sb 2 a limited reactive iron supply will allow the sulfurization of organic matter even in a context of moderate productivity thus sulfurization can be a factor favoring a noticeable accumulation of organic matter iron may thus be an important agent in the c cycle

impact of surface characteristics on flow over a mesoscale mountain dynamical downscaling of atmospheric flow over iceland has revealed that prominent downslope accelerated flows are not merely extreme events but rather constitute a strong climatological signal over the larger ice caps ice caps are characterised by smooth and cold surfaces and both of these properties have previously been found to enhance downslope flows in this article we investigate the response of downslope accelerated flow over hofsjokull in central iceland to an increase in surface roughness and a change in surface temperature corresponding to the effect of melting hofsjokull s ice cap we do so by exploring the flow over hofsjokull for a summertime case by means of several numerical sensitivity experiments in the experiments we find a stronger downslope flow acceleration with than without the ice cap while an increased surface roughness distinctly dampens the downslope flow the effect of changing the surface temperature is minimal this study is both of general relevance through its exploration of factors affecting downslope acceleration of stably stratified flow and also of interest because glaciers diminish rapidly in a changing climate

identifying global vs basinal controls on paleoproterozoic organic carbon and sulfur isotope records abstract paleoproterozoic sedimentary successions are important archives of the redox evolution of earth s atmosphere and oceans efforts to unravel the dynamics of our planet s early oxygenation from this archive rely on various geochemical proxies including stable carbon and sulfur isotopes however ancient metasedimentary rocks often experienced early and late stage bio geochemical processes making it difficult to discern primary environmental signals from bulk rock 13corg and 34s values such complexity in carbon and sulfur isotope systematics contributes to uncertainty about the redox structure of paleoproterozoic oceans a currently popular idea is that following the great oxidation event global changes led to low oxygen environments and temporally fluctuating ocean redox conditions that lasted until the neoproterozoic the volcano sedimentary rocks of the onega basin have figured prominently in this concept particularly the exceptionally organic rich rocks of the 1 98 ga zaonega formation however a growing body of evidence shows that local depositional processes acted to form the 13corg and pyrite 34s records of the zaonega formation thus calling for careful assessment of the global significance of these isotope records placing new and existing organic carbon and sulfur isotope data from the zaonega formation into the context of basin history and by comparing those results with key paleoproterozoic successions of the francevillian basin gabon the pechenga greenstone belt nw russia and the animikie basin canada we show that the stratigraphic 13corg and pyrite 34s trends can be explained by local perturbations in biogeochemical carbon and sulfur cycling without requiring global drivers despite their temporal disparity we also demonstrate that individual successions share certain geological traits e g magmatic and or tectonic activity hydrocarbon generation basin restriction suggesting that their pyrite 34s and 13corg trends were governed by common underlying mechanisms e g similar basinal evolution and biogeochemical feedbacks and are not necessarily unique to certain time intervals we further show that pyrites in these successions that are most likely to capture ambient seawater sulfate isotopic composition have consistent 34s values of 15 18 which hints at remarkable stability in the marine sulfur cycle over most of the paleoproterozoic era

the pyrite multiple sulfur isotope record of the 1 98 ga zaonega formation evidence for biogeochemical sulfur cycling in a semi restricted basin abstract the pyrite sulfur isotope record of the 1 98 ga zaonega formation in the onega basin nw russia has played a central role in understanding ocean atmosphere composition and inferring worldwide fluctuations of the seawater sulfate reservoir during the pivotal times of the paleoproterozoic era that in turn has led to a concept that earth s atmospheric oxygen levels underwent global scale changes here we present a steady state isotope mass balance model to gain insight into the mechanisms governing the sulfur cycle and sulfate reservoir during deposition of the organic rich zaonega formation we demonstrate that coupling between high microbial sulfate reduction rates and effective sulfate removal by pyrite precipitation can lead to rayleigh distillation of the basinal sulfate reservoir and development of high amplitude positive 34 s excursions this modelling approach illustrates that secular changes in sedimentary pyrite isotope trends can be explained by processes that reflect local basin scale fluctuations in sulfur cycling rather than global mechanisms

the intensification of the low level jet during the development of mesoscale convective systems on a mei yu front abstract during the period of 21 25 june 1991 a mei yu front observed by the post taiwan area mesoscale experiment produced heavy precipitation along the western side of the central mountain range of taiwan several oceanic mesoscale convective systems were also generated in an area extending from taiwan to hong kong numerical experiments using the penn state ncar mm5 mesoscale model were used to understand the intensification of the low level jet llj these processes include thermal wind adjustment and convective inertial and conditional symmetric instabilities three particular circulations are important in the development of the mei yu front first there is a northward branch of the circulation that develops across the upper level jet and is mainly caused by the thermal wind adjustment as air parcels enter an upper level jet streak the upper level divergence associated with this branch of the circulation triggers convection second the southward branch of the circulation with its rising mot

conceptual models of upper level frontogenesis in south westerly and north westerly flow the conceptual model proposed by shapiro as it is applied to the evolution of an upper level frontal zone within a baroclinic wave is reviewed and its limitations are investigated through previous literature and two casestudies presented in this paper the early stages in the evolutions of these two cases are used to examine specific limitations of this conceptual model 1 upper level frontogenesis in south westerly flow that evolves from a state of equivalent barotropy to a state of cold advection along the front and 2 upper level frontogenesis in northwesterly flow with along front variation in the sign of the thermal advection such that warm advection occurs upstream of cold advection in the thermal trough vector frontogenesis diagnostics for the lagrangian rate of change of the magnitude and direction of the horizontal potential temperature gradient including tilting due to vertical motion are derived these diagnostics are applied to the two cases to examine the maintenance of the potential temperature gradient and the development of cold advection along each upper level front the upper level front in south westerly north westerly flow was maintained primarily by deformation tilting frontogenesis in agreement with previous research the increasing cold advection along the upper level front in both cases was related to an upstream vorticity maximum for the case in south westerly flow the pre existing vorticity maximum approached a downstream equivalent barotropic upper level front in a manner similar to an instant occlusion resulting in cold advection along the length of the upper level front for the case in north westerly flow an intensifying vorticity maximum concentrated the cold advection in the base of the thermal trough as warm advection developed upstream these two cases are compared to upper level fronts in previous literature and a climatology of upper level fronts associated with landfalling cyclones over the eastern north pacific ocean the results indicate that these two cases are typical of early evolutions of upper level fronts that can occur in south westerly and north westerly flow therefore a revised version of the shapiro conceptual model is presented that represents more accurately the early evolutions exhibited in the present and previous studies

petrographic and geochemical characteristics of the lacustrine black shales from the upper triassic yanchang formation of the ordos basin china implications for the organic matter accumulation the lacustrine black shales in the chang7 member from the upper triassic yanchang formation of the ordos basin in central china are considered one of the most important hydrocarbon source rocks however the mechanism of organic accumulation in the black shales remains controversial to resolve the controversy with the former paleontological data of yanchang formation and sedimentation rate data of the chang7 black shales we investigated the typical intervals of the chang7 black shales ticbs which were obtained by drilling in yaowan at the southern margin of the ordos basin and performed various sedimentary isotopic and geochemical analysis including the sedimentary petrography pyrite morphology total organic carbon toc and total sulfur ts the ratio of pyritic fe to total fe dopt major and trace elements together with pyritic sulfur isotopes 34spy the high sulfur content enrichment of redox sensitive trace metals and the lower sedimentation rate of the ticbs in addition to the presence of marine spined acritarchs and coelacanth fossils indicate that the ticbs were deposited in a lacustrine environment possibly influenced by seawater the petrographic observations show a thick layer of black shale with interlayers of thin layered siltstone silty mudstone and laminated tuff which were related to the turbidity currents and volcanism respectively the u th c s and mo u covariations pyrite morphology dopt combined with the 34spy suggest that the deposition occurred beneath the anoxic sulfidic bottom waters which was intermittently influenced by the oxygen containing turbidity the ni al and cu al possibly show extremely high to high primary productivity in the water column which might be connected with the substantial nutrients input from seawater or frequently erupted volcanic ash entering the lake in addition the coincidence of an increased abundance of toc with increased p al ni al cu al and u th as well as relatively consistent ti al suggest that the accumulation of the organic matter might be irrelevant to the clastic influx and was mainly controlled by the high primary productivity and anoxic sulfidic conditions further the covariations of toc vs p al and toc vs ba al indicate that the high primary productivity led to the elevated accumulation and burial of organic matter while the anoxic to sulfidic conditions were likely resulted from an intense degradation of the organic matter during the early diagenesis in summary the organic matter accumulation is ultimately attributed to the high primary productivity possibly resulted from seawater or volcanic ash entering the lake

extension of carbon flux estimation to oxic sediments based on sulphur geochemistry and analysis of benthic foraminiferal assemblages a case history from the eocene of hungary abstract the amount and type of organic matter om chemical and mineralogical compositions and the amount and isotopic ratio of sulphur were measured and benthic foraminiferal assemblages were analysed in a 70 m thick core section comprising marine marls from the eocene of hungary on the basis of benthic foraminiferal oxygen index bfoi the studied sediments were deposited under a range of anoxic to oxic bottom water conditions the amount of corg mineralised during early burial was calculated in two steps first carbon mineralised by sulphate reduction was calculated from the amount of sedimentary sulphur corrected for escaped oxidised h2s by taking into account the isotopic composition of sulphur then on analogy of recent sediments which are deposited with a similar rate of sedimentation and beneath bottom waters of similar o2 content carbon loss by aerobic respiration was estimated a good stratigraphic control and knowledge of variation of mineralogical composition along the section permitted to estimate past variation of local organic carbon flux cflux from calculated original corg contents during deposition of the studied strata cflux first decreased from 1 16 to 0 41 g corg m2 y then it progressively increased to 1 81 g corg m2 y changes in local cflux are explained by changes in water depth flux of terrestrial organic components and availability of nutrients liberated by alteration of products of the coeval pyroclastic activity

application of scale selective data assimilation to tropical cyclone track simulation tropical cyclone track is strongly controlled by the large scale environmental circulation in limited area models lams driven by global analyses or forecasts through a conventional lateral boundary nesting approach the global analyses are often distorted by the use of sponge zone or interpolation when they are passed into the lam in this study a dynamical downscaling approach based on scale selective data assimilation ssda is applied to a limited area numerical weather prediction model with emphasis on tropical cyclone track simulation the idea of the ssda approach is to drive the lam not only from the lateral boundary but also from the model domain interior the large scale flow from global analyses or forecasts is assimilated into the regional model using 3 d variational data assimilation the large scale features in the lam are thus constrained to follow the global analyses while allowing the regional model itself to develop the regional and small scale characteristics the results from the case study of hurricane katrina 2005 show that both large and small scale flows in the regional model benefited from the ssda approach leading to an improvement in the accuracy of storm track simulation when provided with an accurate large scale circulation from global analyses in addition the ssda procedure is shown to be an effective method to construct a nested grid regional modeling system that reduces model sensitivity to model domain geometry and location

iron limitation in the western interior seaway during the late cretaceous oae 3 and its role in phosphorus recycling and enhanced organic matter preservation the sedimentary record of the coniacian santonian oceanic anoxic event 3 oae 3 in the north american western interior seaway is characterized by a prolonged period of enhanced organic carbon oc burial this study investigates the role of fe in enhancing organic matter preservation and maintaining elevated primary productivity to sustain black shale deposition within the coniacian santonian aged niobrara formation in the usgs 1 portland core iron speciation results indicate the development of a reactive fe limitation coeval with reduced bioturbation and increased organic matter preservation suggesting that decreased sulfide buffering by reactive fe may have promoted enhanced organic matter preservation at the onset of oae 3 an fe limitation would also provide a feedback mechanism to sustain elevated primary productivity through enhanced phosphorus recycling additionally our results demonstrate inconsistencies between fe based and trace metal redox reconstructions iron indices from the portland core indicate a single stepwise change whereas the trace metal redox proxies indicate fluctuating redox conditions during and after oae 3 using fe speciation to reconstruct past redox conditions may be complicated by a number of factors including fe sequestration in diagenetic carbonate phases and efficient sedimentary pyrite formation in a system with limited fe supply and high levels of export production

sulfur and carbon isotope geochemistry of coal and derived coal combustion by products an example from an eastern kentucky mine and power plant abstract the isotopic compositions of s 34 s and c 13 c were determined for the coal utilized by a power plant and for the fly ash produced as a by product of the coal combustion in a 220 mw utility boiler the coal samples analyzed represent different lithologies within a single mine the coal supplied to the power plant the pulverized feed coal and the coal rejected by the pulverizer the ash was collected at various stages of the ash collection system in the plant there is a notable enrichment in 34 s from the base to the top of the coal seam in the mine with much of the variation due to an upwards enrichment in the 34 s values of the pyrite variations in 34 s and in the amount of pyritic s in the coal delivered to the plant show that there was a change of source of coal supplied to the plant between week one and week two of monitoring supporting a previous study based on metal and sulfide geochemistry for the same plant the fly ash has a more enriched 34 s than the pulverized coal and in general the 34 s is more enriched in fly ashes collected at cooler points in the ash collection system this pattern of 34 s suggests an increased isotopic fractionation due to temperature with the fly ash becoming progressively depleted in 34 s and the flue gas s containing components becoming progressively enriched in 34 s with increasing temperatures substantially less variation is seen in the c isotopes compared to s isotopes there is little vertical variation in 13 c in the coal bed with 13 c becoming slightly heavier towards the top of the coal seam an 83 93 loss of solid phase c occurs during coal combustion in the transition from coal to ash owing to loss of co 2 despite the significant difference in total c content only a small enrichment of 0 44 0 67 in 13 c in the ash relative to the coal is observed demonstrating that redistribution of c isotopes in the boiler and convective passes prior to the arrival of the fly ash in the ash collections system is minor

relationship between amazon and high andes rainfall 1 a regional climate model is used to study the connections between amazon and high andes rainfall the modeling effort focuses on understanding the rainfall response during the last glacial maximum lgm 21 000 years ago as paleoproxy evidence generally suggests that the high andes were wet during this period while conditions over the amazon were drier although there is more uncertainty about the latter analysis of the yearlong present day and full lgm integrations reveals that the delayed onset of amazon convection in the lgm during austral spring is associated with an enhancement of rainfall over the high andes in the absence of convection over the amazon in the austral spring zonal geopotential height gradients over the amazon strengthen resulting in anomalous easterly flow between the amazon and the high andes instead of the low level flow paralleling the andes e g northwesterly the flow impinges more directly onto the eastern slopes of the andes during the lgm where it rises and transports moisture from the amazon up into the mountains enhancing convection over the andes this circulation mechanism explains how the moisture and rainfall over the high andes of peru and bolivia can increase such as the case for the lgm despite large scale drying over south america present day observations are then explored for 1984 2002 and 2003 to identify whether mechanisms identified in the paleoclimate modeling are observable in the present day climate comparison of these particular springs reveals a response analogous to the lgm model response suggesting that this mechanism that connects tropical atlantic sea surface temperatures amazon convection and high andes rainfall is operating in the present climate

reexamining the cold conveyor belt abstract despite the popularity of the conveyor belt model for portraying the airflow through midlatitude cyclones questions arise as to the path of the cold conveyor belt the lower tropospheric airflow poleward of and underneath the warm front some studies beginning with carlson s analysis of the eastern u s cyclone of 5 december 1977 depict the cold conveyor belt moving westward reaching the northwest quadrant of the storm turning abruptly anticyclonically rising to jet level and departing the cyclone downstream hereafter the anticyclonic path other studies depict the cold conveyor belt reaching the northwest quadrant turning cyclonically around the low center and remaining in the lower troposphere the cyclonic path to clarify the path of the cold conveyor belt the present study reexamines carlson s analysis of the cold conveyor belt using an observational and mesoscale numerical modeling study of the 5 december 1977 cyclone this reexamination raises several previously unappreciated

convective snowbands downstream of the rocky mountains in an environment with conditional dry symmetric and inertial instabilities abstract convective snowbands moved slowly over wyoming and northern colorado on 16 17 february 2007 and produced up to 71 mm 2 8 in of snow that was unpredicted by operational numerical weather prediction models and human forecasters the northwest southeast oriented bands lasted for over 6 h comprising both a single major band more than 30 km wide and multiple minor bands about 10 km wide the convective bands initiated within the ascending branch of a secondary circulation associated with both near surface and elevated frontogenesis but the bands remained nearly stationary while the near surface frontogenesis moved quickly equatorward the bands occurred downstream of complex terrain on the anticyclonic shear side of a midlevel jet streak where conditional dry symmetric negative potential vorticity and inertial negative absolute vorticity instabilities were present to determine the mechanisms responsible for the development and organization of these bands simulations using a convectio

multiple sulphur isotope records tracking basinal and global processes in the 1 98 ga zaonega formation nw russia abstract the exceptionally organic rich rocks of the 1 98 ga zaonega formation deposited in the onega basin nw russia have refined our understanding of earth system evolution during the paleoproterozoic rise in atmospheric oxygen these rocks were formed in vent or seep influenced settings contemporaneous with voluminous mafic volcanism and contain strongly 13c depleted organic matter here we report new isotopic 34s 33s 36s 13corg and mineralogical major element total sulphur and organic carbon data for the upper part of the zaonega formation which was deposited shortly after the termination of the lomagundi jatuli positive carbon isotope excursion the data were collected on a recently obtained 102 m drill core section and show a 13corg shift from 38 to 25 sedimentary sulphides have 34s values typically between 15 and 25 reflecting closed system sulphur isotope behaviour driven by high rates of microbial sulphate reduction high sulphate demand hydrothermal activity and hydrocarbon seepage four intervals record 34s values that exceed 30 we interpret these unusually 34s enriched sulphides to be a result of limited sulphate diffusion into pore waters due to changes in sedimentation and or periods of basinal restriction additionally there are four negative 34s excursions that are interpreted to reflect changes in the open closed system behaviour of sulphate reduction or availability of reactive iron our findings highlight the influence of basinal processes in regulating sulphur isotope records and the need for care before interpreting such signals as reflecting global conditions

contrasting sulfur geochemistry and fe al and mo al ratios across the last oxic to anoxic transition in the cariaco basin venezuela an abrupt transition from oxic to anoxic sulfidic euxinic marine bottom waters occurred in the cariaco basin in response to increasing productivity resulting from the late pleistocene post glacial rise in sea level and corresponding increase in surface water nutrient availability the microlaminated sediments of the euxinic interval which span the last f14 5 ky suggest a predominance of water column syngenetic pyrite formation based on 1 high pyrite sulfur spy concentrations in the surficial sediment layers 2 values for degree of pyritization dop that generally do not increase appreciably with increasing burial 3 ratios of total iron fet to al that are elevated above the continental baseline recorded in the underlying oxic sediments and 4 spy isotope trends that largely mimic the d 34 shsof the modern water column intermediate dop values in the microlaminated deposits and fet al ratios that are slightly above continental levels indicate an iron reservoir controlled by scavenging during syngenetic pyrite formation in combination with intermediate rates of fe bearing siliciclastic accumulation as predicted from the relative rates of siliciclastic delivery fet al and dop data lie between end member values observed in the modern black sea as viewed broadly fet al and dop relationships in euxinic sediments reflect the balance between syngenetic fe scavenging and temporal and spatial gradients in siliciclastic input pyrite concentrations are generally low in the underlying oxic marine deposits because of limitations in the supply of organic carbon corg however the upper 80 cm of the fe rich corg poor bioturbated sediment show evidence for a strong diffusional hsoverprint from the overlying fe limited euxinic marine environment this post glacial transition manifests in pyrite overprints that are strongly 34 s depleted relative to those in restricted presently euxinic marine settings elsewhere in the world such as the black sea where the sedimentary sequence spanning the last glacial interglacial transition begins with a shift from freshwater to corg poor oxic marine deposition and thus dominantly sulfate diffusion trends for mo al ratios in the microlaminated sediments suggest that mo is enriched by roughly two orders of magnitude above the continental levels recorded in the oxic deposits organic matter plays a role by enhancing hsproduction and or by providing a substrate for mo scavenging significant mo enrichment via diffusion into the upper portion of the bioturbated zone was not observed despite hs rich pore waters as recorded in the heavy iron sulfide overprint we have

high resolution model based investigation of moisture transport into the pacific northwest during a strong atmospheric river event abstracta series of precipitation events impacted the pacific northwest during the first two weeks of november 2006 this sequence was punctuated by a particularly potent inland penetrating atmospheric river ar that produced record breaking precipitation across the region during 5 7 november the precipitation caused destructive flooding as far inland as montana s glacier national park 800 km from the pacific ocean this study investigates the inland penetration of moisture during the event using a 4 1 33 km grid spacing configuration of the weather research and forecasting wrf modeling system a high resolution simulation allowed an analysis of interactions between the strong ar and terrain features such as the cascade mountains and the columbia river gorge cr gorge moisture transport in the vicinity of the cascades is assessed using various metrics the most efficient pathway for moisture penetration was through the gap i e cr gap between mt adams and mt hood which includes the cr gorge w

numerical analysis of a mediterranean hurricane over southeastern italy abstract the presence of a subsynoptic scale vortex over the mediterranean sea in southeastern italy on 26 september 2006 has been recently documented by the authors the transit of the cyclone over land allowed an accurate diagnosis of the structure of the vortex based on radar and surface station data showing that the cyclone had features similar to those observed in tropical cyclones to investigate the cyclone in greater depth numerical simulations have been performed using the weather research and forecasting wrf model set up with two domains in a two way nested configuration model simulations are able to properly capture the timing and intensity of the small scale cyclone moreover the present simulated cyclone agrees with the observational analysis of this case identifying in this small scale depression the typical characteristics of a mediterranean tropical like cyclone an analysis of the mechanisms responsible for the genesis development and maintenance of the cyclone has also been p

evaluation of high frequency paleoenvironmental variation using an optimized cyclostratigraphic framework example for c s fe analysis of devonian mississippian black shales central appalachian basin u s a abstract stratigraphic successions are rarely sampled at sufficiently dense spacing to permit evaluation of paleoenvironmental variation at the shortest fundamental frequency operative in the depositional system of interest often because that frequency remains undetermined here we provide an example of a sampling strategy optimized for recovery of high frequency paleoenvironmental signals based on 1 full core analysis using a continuous survey tool such as x radiography followed by 2 fine sampling of selected small scale cycles that record significant short term paleoenvironmental variation we show that this strategy results in recovery of high frequency paleoenvironmental signals that are completely missed by low density sampling protocols permitting key insights into depositional and early diagenetic processes that may otherwise by overlooked the present case study is based on c s fe systematics of the cleveland and sunbury shales which belong to the upper devonian lowermost carboniferous black shale succession of the central appalachian basin in eastern north america in these units the fundamental scale of paleoenvironmental variation is recorded by pervasive decimeter scale 5 to 20 cm thick compositional cycles that are readily visible in outcrop in which high organic layers weather out as resistant ledges we identified these cycles in drillcores using x radiography which proved to be an effective proxy for compositional variation owing to control of bulk density primarily by total organic carbon toc content we then sampled selected dm scale cycles n 21 at a centimeter spacing generating short high resolution multiproxy chemostratigraphic records including toc sulfur and fe concentrations fepy fehr a redox proxy 34spyrite and organic maceral content this analysis yielded the novel insight that all proxies related to authigenic iron sulfides e g stotal and spyrite fetotal and fepyrite fepy fehr and 34spyrite covary negatively with toc within the dm scale cycles we interpret the unusual pattern of negative toc pyrite covariation in the cleveland and sunbury shales to have resulted from differential distributions of labile organic matter om which drove h2s production via microbial sulfate reduction msr and reactive fe which controlled pyrite formation labile om was concentrated in high toc layers whereas reactive fe was concentrated in low toc layers possibly as fe oxyhydroxide coatings on silt grains as a consequence of which part of the h2s generated in the high toc layers diffused upward into the low toc layers before becoming fixed as pyrite this process is evidenced by several contrasts between high toc and low toc layers 1 higher spyrite concentrations and fepy fehr values in the latter 2 concentration of pyrite in the lower part of low toc layers immediately above high toc layers and 3 higher 34spyrite values in the latter reflecting late diagenetic formation of the h2s that diffused upward into the low toc layers to our knowledge this process has not been documented previously in ancient marine shales probably owing to insufficiently high resolution analysis in earlier studies

pre rodinian mesoproterozoic supercontinental rifting along the western margin of laurentia geochemical evidence from the belt purcell supergroup abstract recent efforts at supercontinental reconstruction for the late precambrian e g the sweat hypothesis moores 1991 have commonly invoked an uncertain lacustrine interpretation for deposition of the mesoproterozoic belt purcell supergroup with the belt basin placed centrally within the assembled landmass the utility of the belt purcell system in addressing proterozoic continental configurations has improved with refined constraints on the timing and setting of deposition contrary to a lacustrine interpretation elemental carbon sulfur c s relationships and stratigraphic s isotope trends for black shales of the helena embayment of western montana the easternmost extension of belt deposition reveal that the early belt basin received at least episodic fluxes of open marine water into a variably restricted setting in the present study this model of restricted marine deposition was tested and corroborated by generation of an analogous s isotope stratigraphy for the time equivalent prichard formation located to the west of the embayment within the main belt basin data for both pyrite and coexisting pyrrhotite show comparatively high 34 s values and systematic s isotope shifts in excess of 20 over stratigraphic intervals spanning several hundred meters suggesting limited and temporally varying sulfate availability in a bacterially driven marine system additional geochemical and sedimentological proxies e g 13 c of carbonate lithologies diagnostic abiotic carbonate precipitates and the presence of glauconite further support a repeated or continued marine linkage throughout belt deposition a model for a restricted marine setting when viewed in light of independent tectonic evidence i e syndepositional mafic magmatism with peaks in activity at approximately 1470 and 1370 ma hydrothermal activity mineralization along basin bounding high angle normal faults and high rates of sedimentation that resulted in sediment thicknesses of up to 16 km defines a history of active and likely episodic rifting for the belt basin collectively these observations are temporally consistent with new models for precambrian supercontinent cyclicity and suggest a complex history for western laurentia that includes both episodes of convergence and at least incipient rifting prior to the final assembly of rodinia this relationship reflects a stepwise continental assembly perhaps analogous to the formation of gondwana and the subsequent assembly of pangea

upward increase of kerogen δ13c in the peru margin upper oligocene possible implications for the cenozoic evolution of atmospheric co2 abstract carbon isotopic composition of predominantly marine kerogen in latest oligocene mudstones of the peru margin odp 682a hole shows an about 3 5 increase with decreasing age py gc and elemental c n ratio analysis of the kerogen plus sulphur isotopic study together with earlier knowledge on geological setting and organic geochemistry results in a better understanding of depositionary environment and allows to separation of the influence of concentration of water dissolved carbon dioxide ce on kerogen 13c from that of other factors bacterial degradation sea surface temperature dic 13c productivity and admixture of land plant om based on this analysis the major part of the kerogen shift is considered as a result of the latest oligocene decrease of marine photosynthetic carbon isotopic fractionation in the peru margin photic zone which in turn possibly reflects a simultaneous drop in atmospheric co2 level uncertainties in the evaluation of the factors affecting the marine photosynthetic carbon isotopic fractionation and the extent of ocean atmosphere disequilibrium do not permit calculation of the decrease of the atmospheric co2

inorganic geochemistry of albian sediments from the lower saxony basin nw germany palaeoenvironmental constraints and orbital cycles abstract within the international albicore project upper albian sediments from a 245 m core kirchrode i drilled in hannover were studied by inorganic geochemical methods more than 650 samples minimum sample spacing 0 5 m were analysed for major and minor element concentrations this chemical database was used to reconstruct the depositional environment and to investigate the influence of high frequency milankovitch cycles on the chemical composition of the sediments the chemical composition of the sedimentary sequence is primarily controlled by variations in carbonate content corresponding to ca al ratios variations in both ti al and si al ratios are interpreted as fluctuations in detrital composition resulting from increases in smectite and quartz content in the upper section of the core high amounts of reactive iron but low pyrite concentrations the lack of enrichment of redox sensitive trace elements v cr and high mn concentrations indicate oxic bottom water conditions and the absence of an oxygen minimum zone for the upper albian at the kirchrode site the nutrient related trace elements ba p zn suggest a generally oligotrophic setting with slightly elevated productivity only in the uppermost upper albian only one layer was identified as containing volcanogenic material at 87 20 m this layer is characterised by elevated montmorillonite zr and nb mass balance calculations for the entire core suggest that the high mn values cannot be explained by riverine input alone therefore a coastal oxygen minimum zone south of the kirchrode site is postulated as an additional mn source cyclic variations in both carbonate content and al normalised concentrations of predominantly detrital elements like si and ti are seen in a 60 m interval 40 100 m where sedimentological palaeontological and geochemical data suggest stable depositional conditions although carbonate cyclicity cyclicity in detrital input and nutrient related element abundances do not correlate with each other three strong peaks in the results of spectral analysis of these chemical data for this interval appear to correspond to milankovitch frequencies in the eccentricity obliquity and precession bands

kinematic wave modelling of vertical movement of snowmelt water through a snowpack vertical movement of snowmelt water through snowpacks is modelled by applying the kinematic wave theory analytical solutions are obtained for moisture flux particle velocity time history and velocity of meltwater front and total moisture content for a single melt event assuming that the melt rate is constant these solutions are extended to the case involving more than one event

superheavy pyrite δ34spyr δ34scas in the terminal proterozoic nama group southern namibia a consequence of low seawater sulfate at the dawn of animal life sulfur isotope analysis 34 s of well preserved carbonates spanning an 10 ma interval of the terminal proterozoic nama group reveals that disseminated pyrite is consistently enriched in 34 s relative to coeval seawater sulfate as preserved in carbonate associated sulfate cas this observation is not consistent with the current paradigm for interpreting the geologic record of sulfur isotopes which assumes that pyrite 34 s 34 s pyr will be equal to or less than co occurring cas 34 s 34 s cas due to the kinetic isotope effect of bacterial sulfate reduction bsr that favors the lighter isotope of sulfur 32 s during sulfur oxygen bond breakage although the precise mechanism of pyrite sulfur isotope enrichment is debatable our combined observations of extremely 34 s enriched pyrite low bulk rock concentrations of sulfur from cas and pyrite and high frequency fluctuations in 34 s cas and 34 s pyr throughout the nama group carbonates point to very low concentrations of sulfate in portions of the terminal proterozoic ocean the additional occurrence of 34 s enriched pyrite in contemporaneous terminal proterozoic sections from poland and canada reveal that low seawater sulfate may have been widespread in the oceans at this time however the absence of such extremely 34s enriched pyrite from well preserved coeval carbonate sections in oman suggests that such conditions were not globally uniform low geographically varied concentrations of marine sulfate in terminal proterozoic time are consistent with elevated geographically varied concentrations of reactive nonpyritized iron in marine shales recently reported for this interval suggesting that high dissolved fe ii and low o 2 persisted in a range of marine facies as late as 543 ma tens of millions of years after the origin of animals yet prior to their major diversification in early cambrian time

trace sulfate in mid proterozoic carbonates and the sulfur isotope record of biospheric evolution concentrations of oceanic and atmospheric oxygen have varied over geologic time as a function of sulfur and carbon cycling at or near the earth s surface this balance is expressed in the sulfur isotope composition of seawater sulfate given the near absence of gypsum in pre phanerozoic sediments trace amounts of carbonate associated sulfate cas within limestones or dolostones provide the best available constraints on the isotopic composition of sulfate in precambrian seawater although absolute cas concen trations which range from those below detection to 120 ppm sulfate in this study may be compromised by diagenesis the sulfur isotope compositions can be buffered sufficiently to retain primary values stratigraphically controlled 34 s measurements for cas from three mid proterozoic carbonate successions 1 2 ga mescal limestone apache group arizona usa 1 45 1 47 ga helena and newland formations belt supergroup montana usa and 1 65 ga paradise creek formation mcnamara group nw queens land australia show large isotopic variability 9 1 to 18 9 1 1 to 27 3 and 14 1 to 37 3 respectively over stratigraphic intervals of 50 to 450 m this rapid variability ranging from scattered to highly systematic and overall low cas abundances can be linked to sulfate concentrations in the mid proterozoic ocean that were substantially lower than those of the phanerozoic but higher than values inferred for the archean results from the belt supergroup specifically corroborate previous arguments for seawater contributions to the basin limited sulfate availability that tracks the oxygenation history of the early atmosphere is also consistent with the possibility of extensive deep ocean sulfate reduction the scarcity of bedded gypsum and the stratigraphic 34 s trends and 34 s enrichments commonly observed for iron sulfides of mid proterozoic age copyright 2005 elsevier ltd

origins of pyrites in the 2 5 ga mt mcrae shale the hamersley district western australia abstract the mt mcrae shale is the footwall rock unit of the brockman iron formation 2 5 ga in age in the hamersley basin australia it is characterized by a high concentration of organic carbon 2 8 wt an abundance of disseminated pyrite 1 to 10 wt s in the bulk rocks and abundant pyrite nodules 1 10 cm radius we have examined microscale 200 m to 1 cm variations in sulfur isotopic compositions of pyrite and s and c contents in six rock samples from a 27 m drill core section of the base of the mt mcrae shale at the whaleback mine the microanalyses of sulfur isotope compositions were performed in situ on single or aggregates of pyrite crystals eighty four analyses using a nd yag laser microprobe the carbon contents of thirty powdered samples drilled from different parts of the six rock samples are similar 2 to 8 wt c with the exception of one sample 0 5 wt however the occurrence morphology abundance and 34s value of pyrite reveal distinct differences between the two samples from the upper part and the four samples from the lower part of the drill core section pyrite crystals in the upper part occur mostly as disseminated fine grains 5 m the pyrite s contents are uniform within each sample but the 34s values vary from 6 3 to 7 1 these data suggest that pyrite crystals in the upper section were formed by bacterial reduction of seawater sulfate pyrite crystals of the lower section occur in the form of veinlets nodules or laminae of coarse grains 200 m the pyrite contents are highly variable within each specimen 0 to 10 wt and the 34s values vary from 2 2 to 11 8 the formation process of pyrites in the lower section appears to have been complicated pyrite laminae were first formed by bacterial sulfate reduction during early diagenesis and then some of the early pyrites were dissolved and reprecipitated to form pyrite nodules by later diagenetic or hydrothermal solutions in a closed system the sulfur isotope data obtained in this study can be best explained by a model postulating that the seawater about 2 5 ga ago in the hamersley basin had the 34s value of 10 to 15 and that the kinetic isotope effects accompanying bacterial sulfate reduction were 8 13 and 16 21 respectively during the deposition of the lower and upper sections of the mcrae shale the variable 34s values of microscale area and the magnitudes of the kinetic isotope effects suggest that 1 the sulfate concentration of the 2 5 ga seawater was already more than one third of the present seawater value and 2 the activity of sulfate reducing bacteria in the 2 5 ga ocean was generally higher than that in the modern ocean suggestion 1 further implies that by 2 5 ga 3 the atmosphere became oxic and 4 the chemical and isotopic characteristics of sulfur in the earth s near surface reservoirs oceans and sediments were controlled by the phanerozoic style biogeochemical cycles rather than by the mantle buffer i e magmatic mechanism suggestion 2 may imply that 5 the archean oceans were generally warmer compared to the modern oceans and 6 they produced a higher abundance of organic matter that were easily metabolized by sulfate reducing bacteria

superheavy pyrite in the upper cretaceous mudstone of the songliao basin ne china and its implication for paleolimnological environments abstract the widely developed dark mudstone in the upper cretaceous nenjiang formation of the songliao basin is a natural archive for reconstructing the palaeoenvironment a time series sulfur isotope study on the nenjiang formation reveals that authigenic pyrite from the paleo lake is enriched in 34s relative to coeval marine sulfate in the lower nenjiang member i and basal nenjiang member ii the occurrence of 34s enriched pyrite must be explained to understand the paleolimnological environment and the sulfur cycling during this period for which several explanations can be advanced based on a comparison of various mechanisms for superheavy pyrite formation we consider the presence of an anaerobic sulfate minimum zone smz in the paleo lake as the most likely scenario in this zone sulfate was enriched in 34s through microbial sulfate reduction msr and this heavy sulfate became the source for pore water or bottom water from which superheavy pyrite was produced the conceptual model for formation of the superheavy pyrite in the nenjiang formation indicates that the distribution range of the smz was variable in the different sedimentary stages of the nenjiang formation these variations were likely related to successive inputs of sulfate from continental weathering which led to partial mixing of sulfate and attenuation of the smz in the basal nenjiang member ii

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen

relationships between porosity organic matter and mineral matter in mature organic rich marine mudstones of the belle fourche and second white specks formations in alberta canada abstract this study presents approaches for evaluating hybrid source rock reservoirs within tight rock petroleum systems the emerging hybrid source rock reservoir shale play in the upper cretaceous second white specks and belle fourche formations in central alberta canada is used as an example to evaluate organic and inorganic compositions and their relationships to pore characteristics nineteen samples from a 77 5 m long core were analyzed using organic petrography organic geochemistry several methods of pore characterization and x ray powder diffraction xrd the lower part of the studied section includes quartz and clay rich mudrocks of the belle fourche formation with low carbonate content whereas the upper portion contains calcareous mudrocks of the second white specks formation strata are mineralogically composed of quartz plus albite 18 56 wt carbonates calcite dolomite ankerite 1 65 wt clays illite kaolinite chlorite 15 46 wt and pyrite 2 12 wt petrographic examinations document that organic matter represents marine type ii kerogen partly biodegraded with limited terrestrial input vitrinite reflectance r o 0 74 0 87 t max values 438 446 c and biomarkers indicate mid maturity within the oil window the relatively poor remaining hydrocarbon potential expressed as an s2 value between 2 1 and 6 5 mg hc g rock may result from an estimated 60 83 of the original kerogen having been converted to hydrocarbons with the bulk having migrated to adjacent sandstone reservoirs however the present day remaining total organic carbon toc pd content remains relatively high 1 7 3 6 wt compared with the estimated original toc o of 2 4 5 0 wt the calculated transformation ratio of 60 83 suggests that the remaining 17 40 wt of kerogen is able to generate more hydrocarbons the studied section is a tight reservoir with an average swanson permeability of 3 37 10 5 md measured on two samples and total porosity between 1 7 and 5 0 vol 3 vol on average the upper part of the sandy belle fourche formation with slightly elevated porosity values 3 5 5 vol likely represents the interval with the best reservoir properties in the studied core interval total pore volume ranges between 0 0065 and 0 0200 cm 3 g measured by a combination of helium pycnometry and mercury immersion mesopores 2 50 nm are the most abundant pores and occupy 34 67 of total porosity or a volume of 0 0030 0 0081 cm 3 g in comparison micropores 3 g and macropores 50 nm reach up to 57 with the exception of some samples failing to indicate the presence of this pore fraction volume 0 0000 0 0107 cm 3 g macroporosity is mostly responsible for variations in total porosity as suggested by macroporosity s strongest correlation with total porosity within the section the relatively narrow ranges of toc and minerals contents among measured samples limit our ability to further deconvolute factors that influence changes in total porosity and pore size distribution