vertical mixing in the ocean the thermohaline circulation of the ocean results primarily from downwelling at sites in the nordic and labrador seas and upwelling throughout the rest of the ocean the latter is often described as being due to breaking internal waves here we reconcile the difference between theoretical and observed estimates of vertical mixing in the deep ocean by presenting a revised view of the thermohaline circulation which allows for additional upwelling in the southern ocean and the separation of the north atlantic deep water cell from the antarctic bottom water cell the changes also mean that much less wind and tidal energy needs to be dissipated in the deep ocean than was originally thought

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

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

aspects of the antarctic circumpolar current dynamics investigated with drifter data interactions between eddies and mean flow are essential to close the momentum budget of the southern ocean as well as to determine the structure of the global meridional overturning circulation both the structure of the antarctic circumpolar current and the eddy dynamics arising at its heart are importantfor water mass circulation and global ocean ventilation and therefore for the global climate however the characterization of the eddy fields of heat and momentum are still poorly sampled by direct observations and are difficult to accurately resolve or parameterize in numerical models here we present observation based eddy statistics and eddy heat flux ehf from a consistent dataset and estimate southern ocean surface ehf from direct measurements without any parameterization assumption observations obtained from near surface drifters represent a very useful dataset to analyze the eddy field because of their ability to catch a large number of scales of motion while providing a quasi synoptic coverage of the investigated area differences between winter and summer distributions of mean velocities mean kinetic energy and eddy kinetic energy are shown to be strongly constrained by bottom topography and suggest a winter shift of the polar front in specific areas around the circumpolar belt overall the flow follows the contours of constant planetary vorticity set by the depth of the ocean and creates anisotropy in eddy dispersion with maximum dispersion along these contours furthermore eddy mean flow interactions are strongly influenced by topography with eddies having a tendency to accelerate jets upstream of ridges and decelerate them further downstream these strong regional variabilities introduced by topography affect the flux of heat induced by eddies and therefore affect formation and subduction of the main surface and intermediate southern ocean water masses integrated over the southern ocean subduction of water masses induced by ehf appears as an order on component for the southern ocean thermocline ventilation our results based on direct observations emphasizes once more the importance of continuing sustained effort to better represent the effect of mesoscale eddies in a coarse climate model if we are to represent and predict future climate

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

spatial variability of turbulent mixing in the abyssal ocean ocean microstructure data show that turbulent mixing in the deep brazil basin of the south atlantic ocean is weak at all depths above smooth abyssal plains and the south american continental rise the diapycnal diffusivity there was estimated to be less than or approximately equal to 0 1 x 10 4 meters squared per second in contrast mixing rates are large throughout the water column above the rough mid atlantic ridge and the diffusivity deduced for the bottom most 150 meters exceeds 5 x 10 4 meters squared per second such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry

eddy variability and energetics from direct current measurements in the antarctic circumpolar current south of australia two year time series measurements of current velocity and temperature in the subantarctic front saf south of australia from 1993 to 1995 provide estimates of eddy fluxes of heat and momentum across the antarctic circumpolar current acc and further insight into the variability of the acc the saf was found to be an energetic meandering jet with vertically coherent fluctuations varying on a timescale of 20 days with typical amplitude 30 cm s21 at 1150 dbar a daily varying coordinate frame that follows the direction of flow allowed mesoscale variability of the saf to be isolated from variability due to meandering of the front and proved very successful for examining eddy fluxes vertically averaged cross stream eddy heat flux was 11 3 kw m 22 poleward and significantly different from zero at 95 for fluctuations in the 2 90 day band zonally integrated this eddy heat flux 50 9 pw is more than large enough to balance heat lost south of the polar front and is as large as cross saf fluxes found in drake passage cross stream eddy momentum fluxes were small not significantly different from zero and of indeterminate sign but tending to decelerate the mean flow a relationship between vertical motion and meander phase identified in the gulf stream was found to hold for the acc eddy kinetic energy levels were similar to those in drake passage and southeast of new zealand eddy potential energy was up to an order of magnitude larger than at other acc sites most likely because meandering of the front is more common here baroclinic conversion was found to be the dominant mechanism by which eddies grow south of australia typical eddy growth time is estimated to be 30 days approximately twice as fast as in drake passage consistent with eddy energy growing rapidly downstream

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

control of lower limb overturning circulation in the southern ocean by diapycnal mixing and mesoscale eddy transfer a simple model is developed of the lower limb of the meridional overturning circulation in the southern ocean based on residual mean theory it is hypothesized that the strength of the lower limb overturning is strongly controlled by the magnitude of abyssal diapycnal mixing and that of mesoscale eddy transfer k in particular it is argued that k the scaling and associated theory find support in a suite of sensitivity experiments with an idealized ocean general circulation model this study shows that intense diapycnal mixing is required to close the buoyancy budget of the lower limb overturning circulation in contrast to the upper limb where air sea buoyancy fluxes can provide the required diabatic forcing

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

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

glacial isostatic adjustment constrains dehydration stiffening beneath iceland abstract during melting in the upper mantle the preferred partitioning of water into the melt will effectively dehydrate the solid residue linear extrapolation of laboratory experiments suggests that dehydration can produce a sharp viscosity contrast increase of a factor 500 across the dry solidus in this study we show that the suggested magnitude of dehydration stiffening in a plume ridge setting is incompatible with the present glacial isostatic adjustment gia in iceland using gps observations of current gia in iceland we find that the data are best fit by a viscosity contrast over the dry solidus in the range 0 5 3 a viscosity contrast higher than 10 requires a mantle viscosity below the dry solidus lower than 4 8 10 18 pa s depending on the thickness of the dehydrated layer a viscosity contrast of 100 or more demands a mantle viscosity of 10 18 pa s or less however we show here that a non linear extrapolation of the laboratory data predicts a viscosity contrast as low as a factor 3 29 assuming conditions of constant strain rate to constant viscous dissipation rate this is compatible with our gia results and suggests that the plume ridge interaction beneath iceland is governed by a non linear rheology and controlled by a combination of kinematic and dynamic boundary conditions rather than buoyant forces alone

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

isopycnal averaging and the residual mean circulation abstract the zonally averaged circulation in the atmosphere or ocean can be misleading if the averaging is performed at constant height in the ocean there is apparently anomalously large diapycnal motion forming the so called deacon cell the atmospheric equivalents are the ferrel cells there are two zonal averaging techniques commonly used to avoid these spurious cells one involves averaging at constant density and this technique has been used in both fluids the other technique which has so far been applied only in the atmosphere involves taking into account perturbation correlation terms to form the residual mean circulation using a taylor series expansion we show that these apparently dissimilar techniques are formally equivalent at leading order in perturbation amplitude the equivalence is demonstrated using output from the fram southern ocean numerical model

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

spatial and temporal patterns of small scale mixing in drake passage temperature and salinity profiles obtained with expendable ctd probes throughout drake passage between february 2002 and july 2005 are analyzed to estimate turbulent diapycnal eddy diffusivities to a depth of 1000 m diffusivity values are inferred from density temperature inversions and internal wave vertical strain both methods reveal the same pattern of spatial variability across drake passage diffusivity estimates from inversions exceed those from vertical strain by a factor of 3 over most of drake passage the polar front pf separates two dynamically different regions strong thermohaline intrusions characterize profiles obtained north of the pf south of the pf stratification is determined largely by salinity and temperature is typically unstably stratified between 100 and 600 m depth in the upper 400 m turbulent diapycnal diffusivities are o 10 3 m2 s 1 north of the pf but decrease to o 10 4 m2 s 1 or smaller south of the pf below 400 m diffusivities typically exceed 10 4 m 2 s 1 diffusivities decay weakly with depth north of the pf whereas diffusivities increase with depth and peak near the local temperature maximum south of the pf the meridional pattern in near surface mixing corresponds to local maxima and minima of both wind stress and wind stress variance near surface diffusivities are also found to be larger during winter months north of the pf wind driven near inertial waves strong mesoscale eddy activity and double diffusive convection are suggested as possible factors contributing to observed mixing patterns

the three dimensional overturning circulation of the southern ocean during the woce era a box inverse model of the southern ocean during the world ocean circulation experiment is constructed to investigate the three dimensional structure of the regional overturning circulation in that era the model has many features in common with various preceding inverse studies but also contains several novel elements that make it well suited for addressing many of the significant uncertainties that surround the circulation at present the net overturning circulation of the southern ocean is found to consist of two well defined cells of similar strength the upper cell consists of a northward transport of 18 8 5 5 sv of surface mode and intermediate waters lighter than the 27 5 kg m 3 isoneutral and an equivalent southward flow in the approximate 27 5 27 9 kg m 3 neutral density range encompassing the bulk of the upper circumpolar deep water the lower cell involves the northward export of 18 6 0 9 sv of antarctic bottom water and lower circumpolar deep water denser than 28 08 kg m 3 and an opposing transport in the lighter classes of that water mass substantial structural differences between the overturning circulations of the atlantic indian and pacific basins are indicated by the model s solution overall the diagnosed southern ocean circulation shares many qualitative and some quantitative features with previous inverse estimates particularly as regards the large scale depth integrated lateral circulation and associated energy fluxes in the subtropics and in the antarctic circumpolar current and the strength of the upper overturning cell however it also suggests several significant adjustments to current views of the regional circulation most notable amongst these are the subpolar circulation of the southern ocean is more vigorous and zonally interconnected than generally thought the associated lower overturning cell is more intense than indicated by most preceding estimates contrary to common perception sub surface mixing processes play a role of comparable importance to air sea ice exchanges of buoyancy in underpinning the dianeutral closure of the southern ocean overturning even at shallow mode and intermediate water levels and the connection between north atlantic deep water formation and southern ocean upwelling is fundamentally three dimensional such that deep waters from the north atlantic must upwell dianeutrally before being returned to the permanent pycnocline of the northern oceans

the deacon cell and the other meridional cells of the southern ocean abstract the meridional circulation cells of the southern ocean are investigated using the results from a fine resolution primitive equation model zonal integration along depth levels shows the classical series of meridional cells but integration along density layers shows a number of differences including the virtual disappearance of the deacon cell to investigate the differences the meridional transport is calculated as a function of both density and depth the results show that the deacon cell is associated with systematic changes in the depth of density surfaces between the western boundary current region off south america and the return flow in the interior of the ocean water flowing on each density surface produces a meridional cell with a vertical excursion of a few hundred meters thew cells combine without water crossing density surfaces to produce a single integrated deacon cell extending from the surface to below 2000 m the results also show that at each latitude water on each of the

methods for making point estimates of eddy heat flux as applied to the antarctic circumpolar current yearlong measurements of current and temperature are used to examine the characteristics of eddy heat flux and its distribution in drake passage this seemingly straightforward calculation can produce misleading results when measurement errors are not corrected and when careful consideration is not given to the nature of the time series under study and the coordinate system used when moorings blow over during periods of high current speeds eddy heat fluxes produced from the resulting records may be overestimated by as much as 20 if not corrected by using concomitant pressure time series and vertical temperature gradients although short time scale processes such as tides internal waves and inertial oscillations are routinely eliminated from heat flux estimates by low pass filtering low frequency contamination of eddy heat fluxes is not usually considered long period events can impose unwanted dominating cross correlation eddy heat flux between fluctuation temperature and velocity in drake passage low frequency variability in some current records is associated with sporadic lateral shifts of the fronts within the antarctic circumpolar current defining an effective eddy time scale 40 hours to 90 days and band passing the current records before calculating eddy heat flux results in values that are more homogeneous consistent with one another in direction and have higher statistical significance finally we consider the coordinate system used for the eddy heat flux calculations relative to the dynamic processes under study for the circumpolar current we define poleward eddy heat flux as that component perpendicular to the axis of the current that forms a continuous but distorted band encircling antarctica since the current direction varies in time across stream eddy heat flux is calculated relative to the 90 day low pass direction the resulting heat fluxes from all deep instruments are small about 1 kw m2 whereas those at depths less than 1000 m in the northern passage are an order of magnitude larger the average across stream flux for all available instruments is 3 7 kw m2 and directed to the right poleward of the 90 day low pass current cospectra of fluctuation temperature and velocity show that heat flux is separated on the average into two frequency bands with corresponding periods between 100 and 40 days and 16 and 10 days this pattern is strongly influenced by the records from shallow instruments and those in the northern passage and compares favorably with the cospectrum from a 5 year bridged record from the central passage comparison with previous estimates in this region shows considerable differences partly as a result of the use of different techniques however analysis of five 1 year records from a single location shows that interannual variability is large which urges caution when interpreting the significance of isolated short term estimates of eddy heat flux

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

vertical structure and transport of the antarctic circumpolar current in drake passage from direct velocity observations 1 the structure of the antarctic circumpolar current acc in drake passage is examined using 4 5 years of shipboard acoustic doppler current profiler adcp velocity data the extended 1000 m depth range available from the 38 khz adcp allows us to investigate the vertical structure of the current the mean observed current varies slowly with depth while eddy kinetic energy and shear variance exhibit strong depth dependence objectively mapped streamlines are self similar with depth consistent with an equivalent barotropic structure vertical wavenumber spectra of observed currents and current shear reveal intermediate wavenumber anisotropy and rotation indicative of downward energy propagation above 500 m and upward propagation below 500 m the mean observed transport of the acc in the upper 1000 m is estimated at 95 2 sv or 71 of the canonical total transport of 134 sv mean current speeds in the acc jets remain quite strong at 1000 m 10 20 cm s 1 vertical structure functions to describe the current and extrapolate below 1000 m are explored with the aid of full depth profiles from lowered adcp and a 3 year mean from the southern ocean state estimate sose a number of functions including an exponential are nearly equally good fits to the observations explaining 75 of the variance fits to an exponentially decaying function can be extrapolated to give an estimate of 154 38 sv for the full depth transport

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

what sets the mean transport through drake passage twelve experiments with two coarse resolutions of a global ocean model using a variety of surface forcings are analyzed to address the question of what sets the mean transport through drake passage seven of the experiments do not have an active sea ice model but the remaining five do previous theories have suggested that the drake passage transport is governed by the cape horn sverdrup transport or alternatively is proportional to the square root of the meridional ekman transport at the latitude of drake passage the results presented here do not support either of these theories the drake passage transport depends quite strongly on the isopycnal diffusivity parameter in the model and less strongly on the background vertical diffusivity and horizontal viscosity parameters however when the magnitudes of these parameters are fixed the results show a very strong correlation between drake passage transport and both the strength of the meridional ekman transport at the latitude of drake passage and the thermohaline circulation off the antarctic shelf the relationships are monotonic but not linear the best estimate is that the meridional ekman transport drives 100 sv of drake passage transport while the remaining 30 sv are driven by the global thermohaline circulation

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

how wind forcing and air sea heat exchange determine the meridional temperature gradient and stratification for the antarctic circumpolar current mesoscale oceanic eddies have a profound effect on the meridional circulation in the antarctic circumpolar region previous studies have shown that eddies transport heat poleward to balance the heat lost by the ocean to the atmosphere in the waters around antarctica and also transport eastward momentum downward at a rate comparable to the amount of momentum put into the water column by the wind stress using the poleward eddy heat fluxes to relate air sea heat loss and wind stress we find that the meridional temperature gradient in the circumpolar region is determined by the ratio of the air sea heat loss to the zonal wind stress including a widely used parameterisation where poleward eddy heat fluxes are proportional to the mean meridional temperature gradient we find that the slope of isotherms or isopycnals across the circumpolar zone is determined by the wind stress further assuming no cross isopycnal mixing in the interior ocean we find that the stratification in the deep ocean is determined by the ratio of air sea heat loss to zonal wind stress squared the poleward eddy heat fluxes also represent a southward eddy mass transport in the upper water column in density coordinates the vertical gradient of this eddy mass transport is the meridional component of the eddy stokes drift which is equal to the difference between the lagrangian and eulerian mean velocities in the circumpolar region because there can be no zonally averaged geostrophic eulerian meridional velocity across the circumpolar region above the topography this southward eddy stokes drift provides a mechanism by which circumpolar deep water can flow southward across the circumpolar zone eddy heat fluxes which are central to the mass momentum heat and energy balances in the circumpolar region provide a catalyst for relating the roles of wind and buoyancy forcing in setting the overall circulation for the southern ocean

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

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

the ventilated ocean abstractadiabatic theories of ocean circulation and density structure have a long tradition from the concept of the ventilated thermocline to the notion that deep ocean ventilation is controlled by westerly winds over the southern ocean this study explores these ideas using a recently developed lagrangian ocean model lom which simulates ocean motions by computing trajectories of water parcels a unique feature of the lom is its capacity to model ocean circulations in the adiabatic limit in which water parcels exactly conserve their densities when they are not in contact with the ocean surface the authors take advantage of this property of the lom and consider the circulation and stratification that develop in an ocean with a fully adiabatic interior with both isopycnal and diapycnal diffusivities set to zero the ocean basin in the study mimics that of the atlantic ocean and includes a circumpolar channel the model is forced by zonal wind stress and a density restoring at the surface despite the

the role of eddy transfer in setting the stratification and transport of a circumpolar current abstract high resolution numerical experiments of a circumpolar current are diagnosed to study how lateral and vertical transfer of buoyancy by geostrophic eddies balances advection by a meridional circulation driven by surface wind stresses and buoyancy fluxes a theory is developed in the framework of the residual circulation to relate the vertical and horizontal stratification set up to the transfer properties of eddies and the patterns of imposed wind and buoyancy forcing simple expressions are found for the depth of penetration stratification baroclinic transport and residual circulation of the current finally the ideas are applied to the antarctic circumpolar current acc and yield predictions for how its properties depend on wind and buoyancy forcing