on the linkage between antarctic surface water stratification and global deep water temperature the suggestion is advanced that the remarkably low static stability of antarctic surface waters may arise from a feedback loop involving global deep water temperatures if deep water temperatures are too warm this promotes antarctic convection thereby strengthening the inflow of antarctic bottom water into the ocean interior and cooling the deep ocean if deep waters are too cold this promotes antarctic stratification allowing the deep ocean to warm because of the input of north atlantic deep water a steady state deep water temperature is achieved such that the antarctic surface can barely undergo convection a two box model is used to illustrate this feedback loop in its simplest expression and to develop basic concepts such as the bounds on the operation of this loop the model illustrates the possible dominating influence of antarctic upwelling rate and antarctic freshwater balance on global deep water temperatures

circulation mixing and production of antarctic bottom water abstract the antarctic source of bottom water to the abyssal layer of the world ocean is examined as well as its large scale flow pattern and ultimate entrainment rate into the deep water above we make use of the available high quality station data in the southern ocean to construct bottom maps of neutral density and mean property maps including chlorofluorocarbon cfc for the abyssal layer underneath a selected neutral density surface the maximum density at the sill depth of drake passage is used to distinguish between the voluminous deep water mass that is a continuous component of the antarctic circumpolar current from the relatively denser bottom water originated along the antarctic continental margins based on water density antarctic bottom water aabw is defined here generically to include all volumes of non circumpolar water of antarctic origin over the shelf regime multiple localized sources of specific aabw types contribute to the abyssal layer of the adjacent antarctic basins characteristics of these dense bottom waters reflect closely those observed on the parent shelf water mass spreading paths of newly formed deep and bottom waters over the slope regime and their subsequent oceanic circulation patterns are analyzed on the basis of global property maps for the aabw layer interior mixing and interbasin exchanges of aabw are deduced from mean characteristic curves following the southern streamline of the antarctic circumpolar current outflow and mixing of aabw from the weddell sea to the argentine basin is depicted using density and cfc distributions of two zonal hydrographic lines recirculation and mixing of deep and bottom waters within the weddell gyre are also detailed using a meridional section along the greenwich meridian the strength of all localized sources of aabw combined is estimated by two independent approaches an estimate of the total production rate of aabw is calculated based on the oceanic cfc budget for the aabw layer offshore of the 2500 m isobath the sum of all downslope inputs of well ventilated bottom water types underneath the top isopycnal must account for the measured cfc content in the bottom layer the resulting total aabw production rate is about 8 sv which is a conservative figure that neglects the loss of cfc bearing waters across the top isopycnal in recent years whereas about 9 5 sv is calculated assuming a well mixed bottom layer making use of their transient nature cfc distributions at the top of the aabw layer indicate that more direct and rapid entrainment of cfc rich bottom waters below occurs over localized areas with relatively strong upwelling rates and enhanced vertical mixing a second more ad hoc but independent oceanic mass budget of the bottom layer is also constructed a typical basin wide rate of deep upwelling of 3 10 7 m s 1 requires 10 sv 1 sv 106 m3 s 1 of newly formed aabw to sink down the slope around antarctica we have also formulated a spatial distribution of deep upwelling on the isopycnal at the top of the aabw it is expressed as a combination of wind topographic and turbulent components which in turn are functions of the isopycnal depth bottom depth and bottom layer thickness this non uniform upwelling field yields about 12 sv of aabw exported across the top isopycnal fortuitously the overall average of upward speed at the top isopycnal 3 7 10 7 m s 1 compares well with previous estimates of deep upwelling in the northern basins a series of likely sites for strong vertical entrainment of aabw are clearly identified in the modeled distribution of deep upwelling consonant with the observed cfc distributions on the top isopycnal altogether regions with relatively high upwelling rates 5 10 7 m s 1 occupy only a quarter of the total areal extent of the top isopycnal but they account for as much as 45 of the total vertical transport

the pre quaternary history of fire abstract although evidence for land vegetation comes from the silurian and maybe even earlier the first record of fossil charcoal fusain is from the late devonian for this period there are only one or two isolated records not until the early carboniferous is there a record of extensive charcoal deposits mainly preserved in near shore clastic sediments which provide evidence of significant and widespread wildfires by the late carboniferous charcoal was common or abundant in a wide range of facies including tropical wetland peats wildfire played an important role in shaping the environment at this time the latest palaeozoic and early mesozoic records of charcoal are fewer whereas important deposits of late mesozoic age are found worldwide the occurrence of charcoal at the cretaceous tertiary boundary has been highlighted as evidence for a global fire following a meteorite impact but this interpretation is questionable charcoal has been widely reported from tertiary sediments and its appearance in the quaternary and recent is not solely as a result of human impact through the past 400 million years there have been major changes in atmospheric oxygen levels that affected fire intensity and frequency fire systems thus have a long history and their impact on shaping the environment is assessed

magnetostratigraphic constraints on the age of the lower beaufort group western karoo basin south africa and a critical analysis of existing u pb geochronological data we studied three partially overlapping sections with a composite thickness of 600 m in the upper permian fluvial siltstones and fine grained sandstones of the abrahamskraal formation the basal unit of the beaufort group in the karoo basin of western cape province south africa paleomagnetic analysis reveals three components of natural remanent magnetization nrm heating to 180 c removes a remanent magnetization parallel to the present day field which is interpreted as a viscous overprint an intermediate unblocking temperature component is removed by heating to 450 c this direction is always of normal polarity and is identical to a regional overprint imparted during the early jurassic emplacement of the karoo large igneous province a high temperature component isolated above 450 c is of dual polarity and is interpreted as primary on the basis of a positive reversals test the virtual geomagnetic pole position for the abrahamskraal formation computed from the average high temperature characteristic remanent magnetization direction is in agreement with the late permian directions for stable gondwana and with previous results from the lowermost abrahamskraal formation and waterford formation at the ouberg pass section the predominantly normal polarity of this magnetization is in agreement with either a middle late lopingian age ca 254 256 ma or a late guadalupian age ca 262 ma according to the global geomagnetic polarity time scale we integrate these new results with existing magnetostratigraphic biostratigraphic and geochronological results from the karoo basin with particular emphasis on the controversy over zircon age data reported from the underlying ecca group

fluorescing macerals in south african coals abstract maceral microlithotype and fluorescing maceral content were analysed along with the vitrinite relative fluorescence measurements thirty samples from the south africa soutpansberg waterberg and main karoo basins were investigated these results were also compared with previously measured vitrinite reflectance values the application of fluorescence techniques has allowed the identification of much higher liptinite content about 5 as compared with the results of routine maceral analysis in white light results presented provide an explanation of this difference which is caused by difficulties in identifying fine liptodetrinite particles under illumination by the halogen lamp therefore detritic particles of uncertain affinity should be verified under fluorescing light during routine maceral analysis the presence and intensity of the fluorescing vitrinite in south african coals were also studied the occurrence of this component is connected with the rank of coal but could be also affected by the facies sample no b 35 and in situ coal oxidation sample no b 3 the relative fluorescence intensity of vitrinite depends on the rank of the coal but also on its degree of oxidation it seems also to be connected with the expulsion of oil which enhances its intensity the influence of the fluorescing macerals content on some coal properties was proved by the positive correlation between fluorescing vitrinite as well as sum of fluorescing macerals and calorific value 0 66 and 0 74 corr coeff respectively this proves the necessity of fluorescence application in routine maceral analysis carried out for coal quality evaluation

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

macro and micro factors affecting coal seam quality and distribution in southern africa with particular reference to the no 2 seam witbank coalfield south africa abstract petrographical and palynological coal quality investigations relating to variations in one of the best known and well researched coalfields in africa the witbank coalfield and one of the most commercially important seams within this coalfield the no 2 seam are highlighted in this paper the investigations were based on 14 channel samples covering a 40 20 km 2 area in the witbank coalfield the results indicate that the coals in the no 2 seam were formed at the stage of major change over from dwyka to ecca floras as illustrated by the progressive dying out of dwyka pollens and spores and the introduction of ecca floral elements this also suggests a rapid amelioration of climate over the period of peat accumulation following a period of continental glaciation furthermore it is proposed that the in seam horizons reflect fluctuating of cyclic environments probably due to changing water level and plant communities due to changing growth environments saccate pollens appear to occur in association with vitrinite rich microlithotypes trilete spores with inertodetrite and carbominerite rich microlithotypes and plicates with inertite semifusite inertodetrite microlithotypes acritarchs nonspinose are present in parts of the seam where inertodetrite is common and in association with unusual suites of trace and major elements possibly indicating changing geochemical environments in high groundwater conditions petrographic results indicate that the coals are medium rank hypobituminous and show wide variations in maceral mineral and microlithotype compositions both vertically and laterally on the basis of microlithotype and mineral group analyses investigations were undertaken to establish vertical subdivisions by the study of historical patterns and possible lateral correlations of these subdivisions in the area under investigation these methods were then compared with distribution of selected chemical and geochemical parameters the evidence suggests that a common sequence of major events and some minor events occurred during the accumulation of the no 2 seam as manifested by petrographic and palynological facies three major periods or zones are recognized these tepresent periods of relatively stability quiescence separated by major in seam disruptive events namely flood deposits bearing high proportions of detrital organic material or minor clastic sedimentation these zones are subdivided into several subzones representing periods of reworking local flooding or rise in ground water levels and or changing geochemical environments these events can be recognized throughout the area under investigation but the manifestation of these events varies from area to area depending upon topographic situation proximity to river channels valley flanks or palaeoshorelines degree of subsidence and compaction geochemical environment and length of time under a specific set of conditions thus channels in close proximity to one another or in similar positions relative to valley flanks or axes appear to be remarkably similar to one another direct correlation of stratigraphic zones and sub zones from sample site of sample site was therefore possible although the methods to achieve this are complex and require the support of several supplementary complementary interpretative techniques coal quality variations and distribution within the original seam are therefore explicable in terms of the detailed factors listed above

depositional environments and coal petrography of the permian karoo sequence witbank coalfield south africa abstract a sedimentological and coal petrographic study of the permo carboniferous karoo sequence in the witbank coalfield south africa has revealed that coal seams formed in fluvial environments are thick and laterally continuous and have higher inertinite and mineral matter contents than coals formed in lower delta plain environments these latter coals are thin and laterally discontinuous twe depositional sequences from witbank coalfield have been interpreted in terms of depositional environments and related to coal thickness distribution and composition the first depositional sequence comprises a sequence of diamictites conglomerates and sandstones deposited by glacial and glaciofluvial processes these deposits are overlain by the no 1 and no 2 coal seams contemporaneous braided fluvial sedimentation during peat accumulation resulted in the splitting of the no 1 and no 2 seams into subseams the second depositional sequence comprises two upward coarsening deltaic sequences capped by the no 3 and no 4 seams respectively the no 3 seam accumulated in a lower delta plain setting while the no 4 seam accumulated in an upper delta plain environment the deposition of fine grained sediment within an embayment and later fluvial sedimentation during the accumulation of the no 4 seam has caused splitting of the no 4 seam into the no 4 upper and no 4 upper a subseams coal seams associated with glaciofluvial and upper delta plain sedimentation such as the no 1 no 2 and no 4 coal seams are thick laterally extensive and generally have high inertinite and low vitrinite contents the no 3 seam which accumulated in a lower delta plain setting is thin laterally discontinuous and has a high vitrinite and low inertinite content

palynological records of the permian ecca group south africa utilizing climatic icehouse greenhouse signals for cross basin correlations abstract the permian formations of the south african karoo basin play a crucial role in understanding gondwana s climate history during this time of major global changes in this paper we present two data sets one from the coal bearing vryheid formation witbank basin and one from the whitehill and upper prince albert formations of the dp 1 78 core ne karoo our main goal was to study the vegetation changes during this period of global warming and test if the climatic signals could be used to correlate the basinal ecca group facies with the fluvio deltaic coal bearing strata of the witbank basin the palynological record of the no 2 coal seam of the vryheid formation indicates a cold climate fern wetland community characteristic of lowland alluvial plains and an upland conifer community in the lower part of the coal seam up section these communities are replaced by a cool temperate cycad like lowland vegetation and gymnospermous upland flora the data set of the dp 1 78 core is interpreted to represent a cool to warm temperate climate represented by a high amount of gangamopteris and glossopteris elements both data sets are very different in their composition which can be explained by the differences in depositional environment however our findings reveal a different age of the studied assemblages and thus also suggest that both data sets represent different stages in the transition from icehouse to greenhouse during permian times as the stratigraphic correlation between the main karroo basin and the peripheral basins is still under discussion this paper provides new data to underpin the stratigraphic placement of the whitehill formation relative to the coal bearing vryheid formation

radiometric dating demonstrates that permian spore pollen zones of australia and south africa are diachronous abstract the well refined permian palynozonation of western and eastern australia is the current standard biostratigraphic scheme for the southern hemisphere but intra gondwanan floristic provincialism means that several stratigraphically useful palynomorph taxa are rare or absent elsewhere in gondwana radio isotopic ages for both australia and the main karoo basin of south africa demonstrate that key marker taxa appear diachronously in the two countries or they are absent in one of the countries the establishment of new plant taxa in the gondwanan permian realm was strongly tied to palaeolatitude with floral distributions primarily affected by temperature precipitation and seasonality this spatio temporal variation of floras hinders global biostratigraphic correlations both south africa and australia have excellent long ranging permo triassic terrestrial sedimentary successions and although vertebrate biostratigraphy has been the focus of much research endeavour in the south african karoo palynological studies have lagged accordingly a new south african palynozonation should be established that is based on the first appearances of key index taxa in the main karoo basin rather than elsewhere in gondwana in the interim the diachronous ranges of palynomorphs must be considered when correlating south african rocks to other global sections by means of the australian spore pollen zonation

effects of the earth s rotation and bottom slope on a density current descending a sloping bottom 1 the dynamic and transport processes associated with the descent of dense water along a sloping bottom are investigated by numerical experiments the focus is on effects of the earth s rotation the coriolis parameter f and bottom slope inclination s before baroclinic instability grows to finite amplitude development stage downslope volume transport agrees roughly with an estimate based on the ekman layer theory the volume transport decreases with increasing f and it is larger in steep slope cases the offshore extension scale of the dense water region is mainly determined by internal radius of deformation which decreases with increasing f and increases with increasing s the growth rate of the baroclinic instability increases with increasing f and s the baroclinic instability is also affected by energy transfer due to reynolds stress especially in the low and mid latitude regions after the instability grows to finite amplitude mature stage the dense water is effectively transported offshore by the eddy flows the eddy transport decreases with increasing f and it is lower in steep slope cases than in gentle slope cases that is although the flow instability becomes stronger with increasing f and s in the development stage the offshore eddy transport of dense water becomes less efficient with increasing f and s in the mature stage the mechanisms of these effects are also examined in detail

discussion on the concepts in paleoenvironmental reconstruction from coal macerals and petrographic indices abstract organic facies analyses quantify the coal constituents and plot various associations to discriminate the paleoenvironment for coal bearing successions this allows the relation of coal composition to mire ecosystems or environments coal petrographic models are used extensively to reconstruct the nature of ancient peat forming environments many authors proposed relations between specific maceral assemblages and or micro lithotypes and peat forming environments the key controlling factors which affect peat environment include hydrogeology redox ph vegetation type clastic influx sedimentation and peat accumulation rate etc recent advancements in coal maceral study and organic petrology reveal the pros and cons of the available indices and models the main reasons for the failure of the petrographic models are oversimplification of the effects of humification on tissue preservation vs destruction the use of post diagenetic processes e g geochemical gelification in determining depositional environments changes in petrographic composition related to floral evolution geological age rank increase and compaction lack of distinction between different inertinite maceral in some models here the widely used petrographic indices and models are reviewed based on the observations of several workers and the applicability and concepts of paleo environmental reconstruction are discussed a multi disciplinary approach including petrography palynology chemistry etc has been recommended which is more logical and scientific than the exclusive use of petrographic composition for paleoenvironmental interpretation

hypautochthonous allochthonous coal deposition in the permian south african witbank basin no 2 seam a combined approach using sedimentology coal petrology and palaeontology abstract a suite of techniques including coal petrology micropalynology mesofossil analysis and macroscopic appearance has been used to examine the early permian south african witbank basin no 2 seam from a sample locality near ogies this coal appears to be similar in its palynological and petrographic composition to other coals of this interval from this basin however its accumulation appears to have been largely hypautochthonous or allochthonous evidenced by erosive contacts small scale cross laminations and fine lenticular bodies being recognised within the coal seam profile this ex situ deposition probably in part relates to frequent wildfire activity which may have promoted subsequent run off and erosion and led to the numerous mineral rich horizons observed in the sample seam profile in addition to the sedimentological characters described above the petrology of the seam and its mesofossils most particularly megaspores from a lycopsid parent vegetation indicate saturated peat forming conditions however examination of charred mesofossil fragments indicates periods of low humidity and even drying of the peat itself rendering it liable to combustion these contradictory characters may indicate seasonality and suggest a coldness of the climate at least for part of the year that could account for the retardation of peat decay during these drier intervals these characters can be reconciled with deposition during an interglacial phase as the dwyka glaciation terminates as has previously been proposed for the witbank basin no 2 seam

on the fundamental difference between coal rank and coal type abstract this article addresses the fundamental difference between coal rank and coal type while theoretically settled long ago as being different aspects of coal systems science the two concepts are still often confounded in recent years this has resulted in the publication of several works stating that coal type changes with coal rank coal type refers solely to coals depositional origin and the maceral mineral admixture resulting from that origin coal types typically fall in to two categories humic coals developed from peat and sapropelic coals developed from organic mud either type may be allocthonous or autochthonous and within types further refinement of depositional environment can be made coal rank refers to the changes in geochemistry and resultant changes in reflectance caused by increasing thermal maturity of the coal thus it provides an overprint of maturity on existing coal types with proper techniques such as use of crossed polars and etching maceral forms can be differentiated even at high ranks and the original coal type determined

on the sources of weddell gyre antarctic bottom water in march april 1995 as part of the world ocean circulation experiment section a23 we completed 49 hydrographic stations across the weddell gyre and southern antarctic circumpolar current from the antarctic continental shelf 72 5 s 16 5 w to south georgia 55 s 34 5 w chlorofluorocarbon cfc 11 cfc 12 and cfc 113 data collected at these stations reveal that distinct sources renew the antarctic bottom water defined as waters with potential temperatures less than 0 c of the weddell gyre weddell sea bottom water defined as waters with potential temperatures less than 0 7 c formed in the western weddell sea has cfc concentrations about 5 to 6 times higher in the eastward flowing northern weddell gyre than in the westward flowing southern limb our cfc measurements suggest that distinct sources of weddell sea bottom water exist in the western weddell sea in agreement with previous descriptions based on potential temperature and salinity signals in the northern weddell gyre high cfc concentrations in weddell sea deep water potential temperatures between 0 c and 0 7 c confirm the long recognized sources for this water mass in the western and southwestern weddell sea in the southern weddell gyre at about 20 w and along the antarctic continental slope weddell sea deep water with potential temperatures around 0 45 c shows a deep cfc maximum about 1000 m above the seafloor cfc concentrations in this deep southern core are about 80 of those of new weddell sea deep water in the northern weddell gyre near 30 w the a23 cfc and hydrographic data are not consistent with the hypothesis that weddell sea deep waters are derived from a single source in the western weddell sea instead these tracers suggest that an important portion of the weddell sea deep water in the southern weddell gyre originates outside the western weddell sea probably near the amery basin and environs around 75 e these features of the circulation and renewal of the deep weddell gyre should be carefully considered in simulations dealing with fluxes pathways and formation rates of antarctic bottom water

weddell gyre temperature maximum stratum at depths below 200 m relatively warm salty water spreads poleward from the antarctic circumpolar current acc this deep water mass is cooled through interaction with the atmosphere feeding the formation of dense bottom water which in turn influences much of the world ocean significant poleward spreading is accomplished within the weddell gyre of the atlantic sector of the southern ocean an extensive data set obtained in the 1980s within the weddell gyre provides a detailed view of the subsurface temperature maximum t max stratum defining the top of the deep water mass the seasonal sea ice growth and retreat pattern reflects the t max distribution there is evidence for subdivision of the t max into two cold centers which may reflect secondary circulation features within the gyre the primary inflow of warm deep water is derived from the southern edge of the acc near 20 30 e the inflow spreads to the west along 65 s and is divided into smaller pools of relatively warm water west of maud rise with a cold feature directly over the rise in a manner shown by models of topographically generated eddies variability of the t max stratum in the vicinity of maud rise arising from changes in the vigor of the large scale circulation may influence the regional vertical heat fluxes and be related to interannual variability of the sea ice cover and to the recurring polynya feature typical of the region

flow of bottom water in the northwestern weddell sea the weddell sea is known to feed recently formed deep and bottom water into the antarctic circumpolar water belt from whence it spreads into the basins of the world ocean the rates are still a matter of debate to quantify the flow of bottom water in the northwestern weddell sea data obtained during five cruises with r v polarstern between october 1989 and may 1998 were used during the cruises in the weddell sea five hydrographic surveys were carried out to measure water mass properties and moored instruments were deployed over a time period of 8 5 years to obtain quasi continuous time series the average flow in the bottom water plume in the northwestern weddell sea deduced from the combined conductivity temperature depth and moored observations is 1 3 0 4 sv intensive fluctuations of a wide range of timescales including annual and interannual variations are superimposed the variations are partly induced by fluctuations in the formation rates and partly by current velocity fluctuations related to the large scale circulation taking into account entrainment of modified warm deep water and weddell sea deep water during the descent of the plume along the slope between 0 5 sv and 1 3 sv of surface ventilated water is supplied to the deep sea this is significantly less than the widely accepted ventilation rates of the deep sea if there are no other significant sources of newly ventilated water in the weddell sea either the dominant role of weddell sea bottom water in the southern ocean or the global ventilation rates have to be reconsidered

extending the database of permian palaeo wildfire on gondwana charcoal remains from the rio do rasto formation parana basin middle permian rio grande do sul state brazil abstract macroscopic charcoal has been recovered from a bonebed from the barro alto outcrop middle permian guadalupian rio do rasto formation in the southernmost part of the parana basin brazil during this time a global biotic crisis was taking place and changes in the palaeofloristic composition can be observed records of palaeowildfires from the guadalupian period are scarce on a global scale in the parana basin low plant diversity compared to the entirety of gondwana persists and just a few plant bearing localities have so far been described from the northern part of the basin in the studied locality macroscopic charcoal could be detected in an outcropping bonebed and the occurrence of palaeo wildfires was confirmed besides representing the first palaeobotanical data for the guadalupian of the southern part of the parana basin the charcoal remains analyzed here are also a significant record of the local environmental conditions during the increase in aridity observed during the guadalupian and lopingian in gondwana this contributes to the understanding of regional changes that took place during this interval

water table shapes and drain flow rates in shallow drainage systems abstract a relationship between drain flow rate elevation and shape of the water table and recharge intensity in shallow drainage systems is developed from an analytical spatial integration of the boussinesq equation in transient conditions drain flow rates are shown to be the sum of three terms the first one is proportional to the maximum water table elevation and more generally to the steady state flow rate at the same water table elevation the second one is a fraction of the recharge rate of the water table depending on the water table shape the third one accounts for possible changes in water storage in the water table due to its shape changes drain flow rates in shallow drainage systems are shown to be fully predicted by one unique variable that is a function of a combination of the hydraulic conductivity k the drainable porosity f and the drain spacing 2l namely k f2l2 this variable also determines the dynamics of changes in the water table shape and in turn the respective parts of the three terms in the equation it is shown that drainage systems with values of 1 m 1 h 1 respond very fast to recharge events water table shape changes occur very quickly so that the third component of the drain flow can be neglected in that case the equation results in a simplified analytical relationship the reliability of the complete and simplified equations to predict drain flow rates in transient conditions is discussed in relation to in situ measurements

the karoo basin of south africa type basin for the coal bearing deposits of southern africa abstract the coal bearing sediments and coal seams of the karoo basin southern africa are described and discussed the karoo basin is bounded on its southern margin by the cape fold belt onlaps onto the kaapvaal craton in the north and is classified as a foreland basin coal seams are present within the early permian vryheid formation and the triassic molteno formation the peats of the vryheid formation accumulated within swamps in a cool temperate climatic regime lower and upper delta plain back barrier and fluvial environments were associated with peat formation thick laterally extensive coal seams have preferentially accumulated in fluvial environments the coals are in general inertinite rich and high in ash however increasing vitrinite and decreasing ash contents within seams occur from west to east across the coalfields the triassic molteno coal seams accumulated with aerially restricted swamps in fluvial environments these molteno coals are thin laterally impersistent vitrinite rich and shaly and formed under a warm temperate climatic regime palaeoclimate depositional systems differential subsidence and basin tectonics influence to varying degrees the maceral content thickness and lateral extent of coal seams however the geographic position of peat forming swamps within a foreland basin coupled with basin tectonics and differential subsidence are envisaged as the primary controls on coal parameters the permian coals are situated in proximal positions on the passive margin of the foreland basin here subsidence was limited which enhanced oxidation of organic matter and hence the formation of inertinitic coals the coals in this tectonic setting are thick and laterally extensive the triassci coals are situated within the tectonically active foreland basin margin rapid subsidence and sedimentation rates occurred during peat formation which resulted in the preservation of thin laterally impersistent high ash vitrinite rich shaly coals

evidence of deep and bottom water formation in the western weddell sea abstract during ice station polarstern ispol r v polarstern cruise ant xxii 2 november 2004 january 2005 hydrographic and tracer observations were obtained in the western weddell sea while drifting closely in front of the larsen ice shelf these observations indicate recently formed weddell sea bottom water which contains significant contributions of glacial melt water in its upper part and high salinity shelf water in its lower layer the formation of this bottom water cannot be related to the known sources in the south the filchner ronne ice shelf we show that this bottom water is formed in the western weddell sea most likely in interaction with the larsen c ice shelf by applying an optimum multiparameter analysis omp using temperature salinity and noble gas observations helium isotopes and neon we obtained mean glacial melt water fractions of about 0 1 in the bottom water on sections across the weddell gyre farther north melt water fractions are still on the order of 0 04 using chlorofluorocarbons cfcs as age tracers we deduced a mean transit time between the western source and the bottom water found on the slope toward the north 9 3 years this transit time is larger and the inferred transport rate is small in comparison to previous findings but accounting for a loss of the initially formed bottom water volume due to mixing and renewal of weddell sea deep water a formation rate of 1 1 0 5 sv in the western weddell sea is plausible this implies a basal melt rate of 35 19 gt year or 0 35 0 19 m year at the larsen ice shelf this bottom water is shallow enough that it could leave the weddell basin through the gaps in the south scotia ridge to supply antarctic bottom water these findings emphasize the role of the western weddell sea in deep and bottom water formation particularly in view of changing environmental conditions due to climate variability which might induce enhanced melting or even decay of ice shelves

paleodepositional environments and tectonosedimentary controls of the postglacial permian coals karoo basin south africa abstract coal deposits of the karoo basin in south africa are contained within an 80 250 m thick clastic sequence designated the vryheid formation this formation constitutes part of the ecca group of the karoo sequence and contains several mineable bituminuos coal and anthracite beds and sporadic coking coal seams the sedimentary succession was deposited during the early permian following the late carboniferous dwyka ice age paleoclimate initially influenced the paleodepositional environments which for the lowermost stages comprised glaciofluvinal outwash braided plain deposits overlying minor deltaic and glaciolacustrine fill the early permian floral assemblages attest to a cool temperature climatic regime in the extreme northern parts of the basin the lowermost coals frequently directly overlie dwyka diamictite or pre karoo basement paleodepositional systems associated with the coals above the glaciogenic succession consisted predominantly of regressive fluviodeltaic facies assemblages in the northern regions regressive deltaic lobes prograded rapidly basinward across the relatively shallow intracratonic platform in the northeast areas greater subsidence rates were accompanied by multiple stacking of regressive deltaic cycles in several areas of the coalfields peat accumulation was associated with the bed load braided fluvial systems these subsequently modified the underlying deltaic deposits by intense and deep erosion that removed portions of the underlying stratigraphy smaller scale syndepositional anastomosed rivers which were contemporaneous with certain peat swamps locally controlled seam distribution and adversely affected coal seam quality coal distribution was directly controlled a the tectonic setting b the nature of the pre karoo basement lithologies c the basement paleotopography and d the paleodepositional systems associated with and following peat formation the coalfields are restricted to a relatively small area in the northern and northeastern parts of the karoo basin where a stable intracratonic shelf provided a suitable tectonic setting for peat accumulation resistant basement lithologies orthoquartzite and felzite produced positive topographic relief while easily weatehred archean granite basement terrain left residual topographic depressions that were later extensively filled by sediment differential compaction of fine sediment mud and silt deposited over the diverse basement topography provided further subtle controls on coal seam thickness sediments and coal overlying basement highs compacted significantly causing thinning and a draping effect of the sedimentary cover in contrast paleovalleys contained substantial thickness of sediment and host some of the thickest seams these coals can however thin and shale out against the adjacent elevated valley flanks the paleovalley coals were further affected by multiple seam splits produced by fluvial channels that contemporaneously occupied the lowland areas

the burning of gondwana permian fires on the southern continent a palaeobotanical approach abstract fossil charcoal has widely been accepted as a direct indicator for the occurrence of palaeo wildfires in upper palaeozoic sediments of euramerica and cathaysia records of these remains are relatively common and regionally and stratigraphically more or less homogeneously distributed in terrestrial sequences on the other hand just a few records have been published for the permian of gondwana and only recently has it been demonstrated that macroscopic charcoals are also common here most permian macroscopic charcoal from gondwana is gymnospermous and has been reported from coal bearing strata macroscopic charcoal occurrences are spread out in different sequences and also in distinct stratigraphic intervals in the permian e g parana basin sakmarian artinskian of brazil karoo basin artinskian of south africa damodar basin lopingian of india and dead sea area changhsingian of jordan they range from peri glacial post glacial to warm temperate climatic systems throughout the permian macro and micro charcoal occurrences are compared to inertinite incidences to support the pyrogenic origin for these coal macerals and to provide an up to date overview on the known evidences of permian wildfires on gondwana in space and time

seasonal simulation of the southern ocean coupled ice ocean system the southern ocean ice ocean system is investigated using a coupled model developed at princeton university the ocean model uses the primitive equations and solves the second moment closure for turbulent mixing the snow ice model uses a three level thermodynamic scheme resembling semtner s 1976 model the focus here is to study the seasonal variability of the ice covered areas and water mass formation the model simulates reasonably well the seasonal cycle of the ice cover in the southern ocean the annual rapid advance of the ice extent is tied to the ice advection away from the coast toward the antarctic circumpolar current acc where it melts rapidly with the increase of radiative fluxes in the austral spring the european center for medium range weather forecasts climatology tends to produce too little ice in the pacific sector for which the primary cause is a weak meridional wind stress the oceanic heat fluxes are up to 100 w m 2 in open water areas and along the coastal areas except in the weddell and ross seas which are occupied by a year round sea ice cover and have average heat flux of 20 w m 2 or less however there is a small region in the ross sea with high heat loss suggesting deep convection the meridional and zonal heat fluxes are in reasonable agreement with observational estimates the atlantic meridional heat flux is zero at 34 s northern boundary of the model which is an inadequacy in the model in the indian ocean sector the flux is southward while in the pacific sector it is weak and equatorward from the water mass balance we can deduce that the antarctic bottom water aabw t 27 85 annual production is 12 sv in the atlantic sector and 5 sv in the ross sea the total production of 17 sv is in excellent agreement with the observational estimates of 10 20 sv intermediate water types are produced in the indian ocean sector where some of the aabw is lost during that conversion in the atlantic sector 6 sv of the annually formed aabw is advected north across the acc in the pacific sector the northward aabw flow is 7 5 sv which is in excess of the ross sea production suggesting that a considerable portion of the aabw formed in the weddell sea is contributing to that flux

a numerical model of the weddell sea large scale circulation and water mass distribution a circumpolar model for regional studies of the wind driven and thermohaline circulation of the southern ocean including the major sub ice shelf areas is described a first series of numerical experiments focusing on the weddell sea reveals a pronounced and persistent double cell structure of the weddell gyre with a maximum transport of 60 sv in agreement with observations experiments with artificial passive tracers point to the shallow shelf areas off the filchner ronne ice shelf as main locations for bottom water production the trajectories of lagrangian floats are used to determine the pathways and timescales of water mass spreading in the model in addition the effect of sub ice shelf forcing on the water mass characteristics is evaluated it is shown that water modified in the sub ice cavities contributes significantly to the deep and bottom water formation along the continental slope and affects the water mass characteristics throughout the weddell sea by increasing the stability of the near surface stratification and preventing deep convection

a comparison of temperate and boreal peats from ontario canada possible modern analogues for permian coals abstract peat profiles were sampled from a raised bog and an interior fen located in the boreal james bay lowlands northern ontario and a cold temperate swamp and a cold temperate bog in the great lakes st lawrence lowlands southern ontario an examination of the micromorphology and maceral compositions of the peats indicates that considerable differences exist between environments the boreal bog and fen both consist predominantly of relatively unaltered textinite commonly sphagnum derived with higher liptinite contents in the fen profile attributable to the more diverse vegetation both the cold temperate swamp and bog show high levels of humification at the surface possibly partially attributable to recent climatic warming trends causing a decline in water table elevation in all profiles funginite was persistent ranging from 2 to 10 of the total maceral content indicating that aerobic conditions generally prevailed at the surface at the time of deposition the influence of depositional environment and vegetation type on the resulting peat was born out in plots of tissue preservation index vs gelification index the petrographic study also demonstrated that none of the profiles contained high inertodetrinite semifusinite contents comparable to those within cold climate cratonic permian gondwana coals since the oxidation processes leading to the formation of inertinite are considered to take place at the peat stage if the peats studied were to contain a similar maceral assemblage upon coalification inertinite precursors may be present in the peat the lack of petrographic similarity between the holocene peats and the permian coals may be related to a number of factors the decrease in water table elevation possibly responsible for the inertinization of the permian coals may have occurred following the cessation of peat formation not concurrently with accumulation and is potentially attributable to long term factors such as climatic warming the change in the peat forming vegetation from permian glossopteris and gangamopteris dominated communities to holocene sphagnum and coniferous vegetation alters the characteristics of the initial botanical starting materials and some aspects of the ecology particularly trophic and ph conditions which control the post depositional alteration of the plant materials and the resulting maceral assemblages

controls on peat accumulation in the permian vryheid formation in a part of northern natal south africa abstract the early permian vryheid formation is a fluviodeltaic tongue of sediment deposited on the passive northern margin of an asymmetric intracontinental linear trough karoo basin in the study area these strata attain a maximum thickness of about 270 m comprising three informal lithostratigraphic members lower zone coal zone and upper zone the coal zone is characterized by arkosic coarse to very coarse pebbly sandstones and subordinate fines arranged in upward fining sequences many of which are coal capped these units are interpreted as distal outwash fan deposits sedimentation patterns in the upper and lower zones are dominated by superimposed upward coarsening sequences representing repeated wave fluvially dominated fan delta progradation peat accumulation in the cool seasonal climate which prevailed during vryheid formation sedimentation was slow significant peat thicknesses were deposited only in areas of low basin compaction subsidence in the coal zone during a period of general stability extensive upper delta plain and alluvial plain peats formed on broad platforms created by abandonment of braided channel systems the thickest peats accumulated in raised swamps where vegetation stabilized contemporaneous channels promoted a high water table peat erosion by later channel activity was slight since channel widening rather than stream bed erosion prevailed coals thin split and contain more ash near loci of contemporaneous channel activity upper delta plain coals were not marine influenced some lower delta plain coals also formed on broad abandoned deltas and are likewise extensive rapid compaction subsidence rates attracted channel activity or marine incursions and the seams are thin peats also accumulated in restricted emergent interdistributory bays during delta construction these coals are thin discontinuous marine influenced and contain numerous clastic partings

delineation of the distinctive nature of tertiary coal beds abstract floral character in mires has changed progressively through time in the carboniferous pteridophytes sphenophytes and lycophytes were dominant but by the permian gymnosperms were an important component of mire flora during the early mesozoic gymnosperms remained the characteristic mire vegetation together with pteridophytes and conifers became dominant during the jurassic cretaceous and paleocene vegetation are similar with taxodiaceous flora being important in mire vegetation from the eocene onwards however angiosperms were increasingly dominant in mire communities and in the miocene herbaceous vegetation began to play a significant role together with these changes in floral character at least three aspects of coal character also appear to vary sequentially with time and are distinctive in the tertiary 1 proportions and thickness of vitrain banding 2 coal bed thickness and 3 proportions of carbonised material a compilation has been made of data from the coal literature comparing older coals with those of the tertiary in order to give a perspective in which to examine tertiary coals it was found that only tertiary coals contain significant proportions of coal devoid of vitrain bands in addition tertiary coals are the thickest recorded coal beds and generally contain low percentages of carbonised material many less than 5 as compared to older coals it is interesting to note that paleocene coal beds are similar to cretaceous coals in that they tend to be thinner and contain higher proportions of carbonised material than do younger tertiary coals the absence of vitrain bands in some tertiary coal beds is thought to result from the floras dominated by angiosperms which are relatively easily degraded as compared to gymnosperms the thickness of tertiary coals may be related to an increase in biomass production from the carboniferous through to the tertiary as plants made less investment in producing lignin an energy intensive process in addition with less lignin in plants easier degradation of biomass may have facilitated nutrient recycling which in turn led to greater biomass production increased biomass production may have also diluted the carbonised material present in some tertiary peats leading to lower proportions in the coal another possible cause of decreased carbonised components in tertiary coal is that decreasing lignin content resulted in decreased charring during fires as lignin is particularly prone to charring a third possibility is that the carbonised component of peat may be concentrated during coalification so that tertiary coals generally of lower rank than mesozoic or paleozoic coals contain a smaller fraction of carbonised plant material it is not at present clear which of these mechanisms may have affected carbonised material in peat and coal but it is clear that lignin type and content has had an important role in determining peat and coal character since the paleozoic

current measurements near ronne ice shelf implications for circulation and melting we present the first year long current meter records ever obtained near the floating filchner ronne ice shelf in the weddell sea the currents are steered along the ice front but in the lower layer where the bottom topography is descending toward the west the current has a component toward the ice front of about 3 cm s 1 during winter the temperature stayed near the surface freezing point while the salinity increased indicating that ice was formed and brine released the seasonal variation in salinity was 0 15 0 05 psu corresponding to the formation of 1 2 m of ice on a shelf depth of 400 m the transport of high salinity shelf water hssw into the ice shelf cavity was found to be of the order 0 5 106 m3 s 1 the production of this water due to oscillating tides and off shelf winds was found to be of the same order of magnitude in contact with glacial ice at great depths and because of the depression of the freezing point the hssw is transformed to ice shelf water isw by cooling and melting processes the melting rate was estimated to 1 1011 ton yr 1 this corresponds to the melting of 0 2 m ice per year if the melting is evenly distributed over the filchner ronne ice shelf if the melting is concentrated along a path from the berkner shelf around the berkner island to the filchner depression then melting rates up to 7 m yr 1 must be expected a comparison of hssw characteristics in the ronne depression our winter observations on the berkner shelf and the isw flowing out of the filchner depression indicates that very little water passes through the cavity from the ronne to the filchner depression it appears that most of the isw originating from processes on the berkner shelf escapes the cavity in the filchner depression this leaves the berkner shelf as the important source of isw and subsequently of the weddell sea bottom water formed from isw

a possible 20th century slowdown of southern ocean deep water formation chlorofluorocarbon 11 inventories for the deep southern ocean appear to confirm physical oceanographic and geochemical studies in the southern ocean which suggest that no more than 5 x 10 6 cubic meters per second of ventilated deep water is currently being produced this result conflicts with conclusions based on the distributions of the carbon 14 carbon ratio and a quasi conservative property po 4 in the deep sea which seem to require an average of about 15 x 10 6 cubic meters per second of southern ocean deep ventilation over about the past 800 years a major reduction in southern ocean deep water production during the 20th century from high rates during the little ice age may explain this apparent discordance if this is true a seesawing of deep water production between the northern atlantic and southern oceans may lie at the heart of the 1500 year ice rafting cycle

bathymetry depth to magnetic basement and sediment thickness estimates from aerogeophysical data over the western weddell basin we estimated the bathymetry and sediment thickness of a remote and difficult to access portion of the antarctic continental margin using aerogeophysical surveying techniques the u s argentina chile aerogeophysical survey collected magnetic and gravity data over the basins surrounding the antarctic peninsula thirty seven of these flight lines were used to estimate bathymetry and depth to magnetic basement for the western weddell basin a wavenumber technique was applied to individual magnetic anomaly profiles in an automated fashion to obtain estimates of the depth to magnetic basement the bathymetric estimates were obtained by admittance inversions of the gravity field the results were then gridded at a 40 km interval for the region 64 w 44 w 73 s and 62 s bathymetric estimates and depth to magnetic basement estimates were differenced at each grid point to obtain a regional estimate of the thickness of nonmagnetic overburden assumed to be sediment subsequent spot measurements of topography in the estimated region of the continental margin generally agree to about 52 m the estimated magnetic basement deepens from the antarctic peninsula margin eastward to a maximum of 10 12 km near 54 w we also postulate the existence of two moderately large basins flanking the eastward continuation of the jason peninsula farther east the basement steps upward with a correspondent thinning of the sedimentary layer along the east coast of the peninsula results agree well with seismic studies on james ross island and magnetotelluric studies on marambio island and the larsen nunatak as well as the british antarctic survey basement estimates from aeromagnetic data this study further demonstrates the utility of combined application of airborne and satellite geophysical techniques in the study of structure and tectonic evolution of continental margins and marine basins

watermass properties of the antarctic slope front a simple model abstract in the antarctic dense shelf water is formed in coastal polynyas and is differentiated from the fresher surface water by the wind induced ice motion that displaces offshore the ice melt from production zones where the shelf water discharges into the deep ocean the antarctic slope front asf is v shaped separating the shelf and surface waters referred to as frontal waters from the circumpolar deep water cdw to elucidate basic constraints on frontal properties a minimal model of homogeneous water masses forced by offshore wind and freshwater input in a perpetual winter is considered with the surface water stirred by and hence aligned with the ice cover there is little leakage of ice or meltwater from the frontal system so ice production and melt merely redistribute heat and salt between frontal waters as such the heat loss to the atmosphere needs to be supplied by entraining cdw which then necessitates the shelf water discharge on account of the mass balance because of the fresh

the international dovetail program abstract the deep ocean ventilation through antarctic intermediate layers dovetail program is an international field and modeling study of the dense deep and bottom waters of the northwestern weddell sea a primary program goal has been to estimate the volume transport and pathways of these waters long considered to be a major source of antarctic bottom water as they escape from the weddell sea over and through the south scotia ridge into the scotia sea corollary goals are to assess modification of the stratification during passage through the narrow steep sided and irregular channels that transect the ridge the program has evolved since its start in 1997 as a primarily process oriented project into a multiyear observational study of the northwestern weddell sea southern scotia sea including the weddell scotia confluence region an additional program goal therefore has become the estimation of interannual variability in the physical system this volume contains a collection of papers that present recent field and model derived results from the dovetail program

deep and bottom water of the weddell sea s western rim oceanographic observations from the ice station weddell 1 show that the western rim of the weddell gyre contributes to weddell sea bottom water a thin 300 meters highly oxygenated benthic layer is composed of a low salinity type of bottom water overlying a high salinity component this complex layering disappears near 66 s because of vertical mixing and further inflow from the continental margin the bottom water flowing out of the western rim is a blend of the two types additionally the data show that a narrow band of warmer weddell deep water hugged the continental margin as it flowed into the western rim providing the continental margin with the salt required for bottom water production

a progress report on the alpern coal classification abstract the alpern coal classification has already been largely utilized and successfully applied both to laurasian north atlantic and gondwana coals it was accepted on basic principles by the international committee for coal petrology and as the official contribution of france it has been recently also partly adopted by the economic commission for europe of the united nations in geneva 1988 this paper deals with the improvement of the previous versions of the classification mainly by introducing new statistical data in order to establish more accurately proposed rank limits a ternary division for rank is maintained with the categories low rank coal or lignite instead of brown coal because high rank lignites may be black not brown medium rank coal or bituminous coal and high rank coal or anthracite the prefixes hypo meso and meta are used for rank subdivision thus avoiding non coherent previous prefixes such as sub bituminous and semi anthracite the selected rank parameters are moisture holding capacity ash free and calorific value moist ash free for lignites mean random reflectance for bituminous coals and anthracites correlations for bed moisture ash free and calorific value dry ash free are given for lignites correlations for volatile matter content mean maximum vitrinite reflectance and hydrogen content are also given for bituminous coals and anthracites type is determined from maceral data and is divided into vitric vitrinite v 60 fusic v liptinite l and liptic v i the ash content and the washability potential at 10 ash level are used to determine grade or facies and allow the distinction between transportable clean coals and non washable coals the run of mine ash content dry basis permits the division between coal middlings and shale if the type is liptic the subdivisions sapropelic coals and oil shales are used these are not washable but are solid fuels with a positive energy potential if the coals to be classified are clean or washed the vertical axis becomes free and can be used for example for swelling properties in bituminous coals the system has been recently computerized and allows for data to be displayed effectively for all relevant fields of application computer output examples are presented for coals from a euramerican and a gondwana basin

maceral types in some permian southern african coals abstract a suite of permian gondwana coals from southern africa exclusive of the republic of south africa were examined petrographically with the exception of a single low volatile bituminous semi anthracite coal from mozambique the coal rank is high volatile bituminous c most coals were dominated by inertinite group macerals primarily semifusinite and detrital inertinite inertodetrinite but with significant secretinite in some cases vitrinite group macerals were absent in several zambian coals when considering these coals it becomes apparent that not all gondwana maceral types determined necessarily fit the iccp definitions

the effect of depositional environment on coal distribution and quality parameters in a portion of the highveld coalfield south africa abstract eight successive lithofacies associations are identified and described they are each laterally continuous and represent a certain depositional phase throughout the study area these are related to sedimentary processes from which a three dimensional paleoenvironmental model is derived subsequently coal distribution and coal quality characteristics are linked to the depositional features of the model the identified depositional phasescommenced with subglacial glaciofluvial and glaciolacustrine settings with associated gilbert type deltas these are followed by meandering and minor braided fluvial settings characterized by laterally and vertically highly variable lithofacies in which the main coal bearing strata were formed coal distribution and quality parameters ash and volatile matter content calorific value are closely related to paleoenvironmental characteristics major changes of coal distribution and quality parameters are mainly associated with active and abandoned channels and these parameters are less variable in floodplain settings

peat forming history of the ancestral souris mire palaeocene ravenscrag formation southern saskatchewan canada analysis of the palaeocene souris lignite northern williston basin using coal petrology and palynology reveals the existence of seven different mire types forming six cycles of varying thickness and composition the order of mire types within the individual cycles allows an idealized mire type succession to be defined the principle factor driving the idealized mire type succession is decreasing water depth within the peat forming environment terrestrialization which leads to an increase in species diversity and a change in floral character from ferns angiosperms gymnosperms increases in water depth are the primary agent responsible for the termination of individual cycles in the ancestral souris mire changes in nutrient status of the mire may also promote major changes in the floral assemblage contributing to cycle termination comparison of densinite ulminite ratios for the central part of the souris seam shows an overall decrease in the degree of humification south westward indicating increa

palaeoenvironmental control on coal formation distribution and quality in the permian vryheid formation east witbank coalfield south africa abstract the no 1 and no 2 coal seams from the permian vryheid formation in the east witbank coalfield south africa are described with respect to their distribution thickness and quality these two coal seams accumulated in a postglacial climatic environment and peat accumulation was closely associated with and influenced by deposition in a braided river system the fluvial channels that were syndepositional with peat accumulation have resulted in thinning of coal below and above channel axes and pinch out of coal adjacent to channel margins low ash coal originated from peat which accumulated in areas away from the influence of clastic sedimentation in contrast higher ash coals are situated adjacent and parallel to channel margins where interbedded channel sand and silt contaminated the peat the lower no 1 seam peat originated under near optimum conditions in a lacustrine swamp which blanketed an underlying platform of glaciofluvial braided river sediment this peat swamp was not subjected to syndepositional clastic contamination and as a result is of superior quality lower ash higher calorific value and volatile matter than the overlying no 2 coal seam the no 2 seam is split by a clastic parting produced by a braided fluvial channel which transected the swamp midway through peat accumulation this fluvial clastic parting deleteriously affected coal thickness and quality a comparison of the gondwanan permian peat forming conditions with those from carboniferous northern hemisphere counterparts suggests that the differences in coal characteristics between these two regions are probably related to different palaeoclimatic conditions and basin tectonics cool temperate climatic conditions which prevailed over the permian peat swamps resulted in less species diversification of vegetation at these high latitude settings than the diverse floral assemblages of the carboniferous swamps a stable intracronic basin platform caused lateral dispersion of sedimentary facies rather than the stacking of vertical facies which occurred in rapidly subsiding depositories partial exposure of the permian peat swamps during peat accumulation may account for the relatively higher inertinite content of the coals

observations and modeling of a pulsating density current 1 we investigate density current formation and flow in the northern gulf of eilat red sea using in situ observations and a high resolution nonhydrostatic general circulation model these density currents occur in relatively warm water 20 c and are probably the warmest in the world ocean we demonstrate the intrinsic nonlinearity of density currents by comparing two high resolution simulations forced by different heat flux this nonlinearity which is poorly represented in global models is shown here to affect the properties of simulated density currents such a bias in simulating density currents in global models may lead to significant biases on the larger scale global ocean circulation and water mass distribution

petrology and palynology of select coal samples from the permian waterberg coalfield south africa abstract the petrology and palynology of coals from the permian aged waterberg coalfield situated in the limpopo province of south africa are considered the waterberg coalfield contains a significant portion of the country s coal reserves but is still comparatively underexplored detailed maceral analyses combined maceral microlithotype analyses mean random and maximum vitrinite reflectance analyses etching and palynology studies were undertaken on coals from four productive horizons there is a general upward trend in vitrinite content through the sequence 15 59 vol mineral matter free dominated by collotelinite along with a slight decrease in coal rank the lower vryheid formation coal has a comparatively low mineral matter and high inertinite content dominated by inertodetrinite the upper grootegeluk formation samples contain above 35 vol mineral matter and liptinite contents ranging from 14 to 21 vol the use of blue light fluorescence in conjunction with incident light single scan method revealed that liptinite is intimately associated with inertodetrinite and mineral matter specifically clays and occasionally pyrite it is evident that the liptinite maceral content has previously been under reported in the waterberg coals the palynofloras correlate with the well studied witbank coalfield the petrography along with the palynology essentially confirm the palaeoenvironment of the karoo basin as progressing from a cooler more oxidising environment to a wetter seasonal environment

the diversification of paleozoic fire systems and fluctuations in atmospheric oxygen concentration by comparing silurian through end permian 250 million years myr charcoal abundance with contemporaneous macroecological changes in vegetation and climate we aim to demonstrate that long term variations in fire occurrence and fire system diversification are related to fluctuations in late paleozoic atmospheric oxygen concentration charcoal a proxy for fire occurs in the fossil record from the late silurian 420 myr to the present its presence at any interval in the fossil record is already taken to constrain atmospheric oxygen within the range of 13 to 35 the fire window herein we observe that as predicted atmospheric oxygen levels rise from 13 in the late devonian to 30 in the late permian so too fires progressively occur in an increasing diversity of ecosystems sequentially data of note include the occurrence of charcoal in the late silurian early devonian indicating the burning of a diminutive dominantly rhyniophytoid vegetation an apparent paucity of charcoal in the middle to late devonian that coincides with a predicted atmospheric oxygen low and the subsequent diversification of fire systems throughout the remainder of the late paleozoic first fires become widespread during the early mississippian they then become commonplace in mire systems in the middle mississippian in the pennsylvanian they are first recorded in upland settings and finally based on coal petrology become extremely important in many permian mire settings these trends conform well to changes in atmospheric oxygen concentration as predicted by modeling and indicate oxygen levels are a significant control on long term fire occurrence

southern ocean winter mixed layer austral winter 1986 observations from the polarstern along the greenwich meridian from the ice edge to the antarctic margin show the mixed layer beneath the winter sea ice cover to be significantly depressed in oxygen saturation incorporation of weddell deep water wdw into the winter mixed layer responsible for this undersaturation also introduces heat and salinity into the surface layer which strongly influences the mixed layer sea air exchanges and sea ice formation processes the total wdw transfer into the mixed layer averages 45 myr 1 implying a residence time for the surface water of 2 5 years the associated winter heat flux is 41 w m 2 which limits ice thickness to about 0 55 m agreeing quite well with observations the air temperatures during the cruise are just sufficient to remove the wdw heat input in the presence of observed ice thickness and concentration this suggests that the sea ice cover and wdw heat input into the mixed layer are in approximate balance by midwinter the annual heat flux from wdw to the surface layer and hence into the atmosphere is estimated as 16 w m 2 extrapolation of the greenwich meridian wdw entrainment value to the full circumpolar 60 70 s belt yields total up welling of 24 106 m3 s 1 similar extrapolation of the heat flux value gives a circumpolar total of 2 8 1014 w as a consequence of circulation topography interaction the maud rise water column stands out as an anomaly relative to the surrounding region with a significantly more saline and dense mixed layer below the mixed layer the water column over the crest of the rise is identical to that over the flanks if the latter water column is upwelled by 400 m this uplifting is believed to be a response of the upstream flow encountering the rise increased upstream flow would be expected to increase maud rise upwelling and the dependent salinity density of the mixed layer slight increases in the mixed layer density could trigger a convective mode and generation of a polynya it is hypothesized that spin up of the weddell gyre s barotropic circulation induced by an increase of the regional wind stress curl would enhance the probability of polynya development over maud rise

south africa s coalfields a 2014 perspective abstract for well over a century and a half coal has played a vital role in south africa s economy and currently bituminous coal is the primary energy source for domestic electricity generation as well as being the feedstock for the production of a substantial percentage of the country s liquid fuels it furthermore provides a considerable source of foreign revenue from exports based on geographic considerations and variations in the sedimentation origin formation distribution and quality of the coals 19 coalfields are generally recognised in south africa this paper provides an updated review of their exploration and exploitation histories general geology coal seam nomenclature and coal qualities within the various coalfields autocyclic variability is the norm rather than the exception whereas allocyclic variability is much less so and allows for the correlation of genetically related sequences during the mid jurassic break up of gondwana most of the coal bearing successions were intruded by dolerite these intrusions are important as they may cause devolatilisation and burning of the coal create structural disturbances and related seam correlation problems and difficulties in mining operations whilst many of the coalfields have been extensively explored and exploited those in the north of the country have until recently received much less attention four coalfields occur partly or wholly within the limpopo province of south africa and these may contain as much as 70 of south africa s remaining coal resources these coalfields in particular have been the focus of recent exploration due to the presence of large coking and thermal coal resources as well as for their coal bed methane potential and these resources need to be unlocked with regards to creating maximum benefit and minimal environmental degradation south africa s coals have also been recently addressed as palaeoclimate archives recording gondwana s postglacial climate amelioration by major changes in land plant communities and proving high resolution palyno stratigraphy as a crucial tool to decipher climate change during the permo carboniferous this aspect of the coals of south africa is also reviewed

how much deep water is formed in the southern ocean three tracers are used to place constraints on the production rate of ventilated deep water in the southern ocean the distribution of the water mass tracer po4 phosphate star in the deep sea suggests that the amount of ventilated deep water produced in the southern ocean is equal to or greater than the outflow of north atlantic deep water from the atlantic radiocarbon distributions yield an export flux of water from the north atlantic which has averaged about 15 sv over the last several hundred years cfc inventories are used as a direct indicator of the current production rate of ventilated deep water in the southern ocean although coverage is as yet sparse it appears that the cfc inventory is not inconsistent with the deep water production rate required by the distributions of po4 and radiocarbon it has been widely accepted that the major part of the deep water production in the southern ocean takes place in the weddell sea however our estimate of the southern ocean ventilated deep water flux is in conflict with previous estimates of the flux of ventilated deep water from the weddell sea which lie in the range 1 5 sv possible reasons for this difference are discussed

baroclinic instability of density current along a sloping bottom and the associated transport process numerical experiments with a three dimensional nonhydrostatic ocean model have been carried out to investigate the dynamic processes of downslope density current and associated transport of dense water focusing on the effects of bottom slope for the range of slope inclination s from 0 to 0 04 bottom slope has two effects on baroclinic instability of the flow one is the stabilizing effect due to the topographic effect and to offshoreward increase in water depth the other is the destabilizing effect due to steepened inclination of isopycnal surface which increases available potential energy since the destabilizing effect over the upper slope overcomes the stabilizing one in the early stage unstable waves develop more rapidly with increasing s nonlinear energy conversion due to reynolds stresses also affects the flow stability and then the growth rate of instability increases linearly with s in this stage after the unstable waves have finite amplitudes in the mature stage the stabilizing effect of bottom slope becomes dominant especially over the lower slope thus vigorous unstable eddies are confined to the upper slope region in steep slope cases while they cover the whole slope region in gentle slope cases and this difference in the eddy field causes a drastic change in downslope transport of dense water in gentle slope cases efficiency of the transport becomes higher with increasing s since the destabilizing effect overcomes the stabilizing one as a whole on the contrary the efficiency becomes lower with increasing s in steep slope cases since the stabilizing effect surpasses the destabilizing one as a result the most effective transport is realized in the case with s 0 005 although the transport due to eddies in steep slope cases becomes weak over the lower slope it is still larger than that due to the bottom ekman current since the eddy transport occurs in the bottom layer with a thickness of 100 200 m which is 4 8 times the ekman layer thickness