biostratigraphy and sedimentology of the fluviatile untere serie early and middle miocene in the central part of the north alpine foreland basin implications for palaeoenvironment and climate the early to middle miocene fluviatile untere serie lithostratigraphic unit of the upper freshwater molasse ufm in the north alpine foreland basin nafb crops out in a 40 m long section at untereichen altenstadt central part of the nafb this section yields a unique superposition of two vertebrate assemblages belonging to different biostratigraphic units early part osm c d karpatian and osm e early badenian detailed taxonomic analyses reveal different diversity patterns in the two assemblages nine small mammal and six ectothermic vertebrate taxa occur in the older level ua 540 m while 20 small mammal and 23 ectothermic vertebrate taxa are recorded for the younger level ua 565 m from the latter locality comes a small sized representative of the biostratigraphically significant megacricetodon lappi lineage this evolutionary level has not been documented previously for the eastern part of the nafb bioclimatic analysis combined with lithofacies and architectural element analysis indicates that significant changes in the fluvial sedimentation style surface water runoff and tectonics occurred between the early karpatian and early badenian a meandering fluvial system marly unit is erosively overlain by sandy braided river deposits sandy unit overbank deposits of the marly unit revealed that the older vertebrate fossil assemblage ua 540 m is deposited in an animal burrow that was presumably produced by owls both reptilian and mammalian taxa are indicative of a relatively open environment and dry probably semi arid climate conversely vertebrates from the sandy unit ua 565 m which are accumulated in channel fill deposits suggest closed as well as open habitats with a subtropical humid climate and mean annual rainfall of about 1 000 mm according to the sequence stratigraphic analysis the marly unit is interpreted as a highstand system tract of the tb 2 2 global 3rd order sequence the new results add support to the hypothesis that the erosional unconformity between both sedimentary units spanning the karpatian badenian transition corresponds to the pre riesian hiatus which has been interpreted as part of the styrian tectonic phase and was previously identified only in the eastern and northeastern part of the nafb the biostratigraphic data further indicate that this hiatus lasted longer in the eastern than in the central part of the basin

the genesis of late hercynian granitoids from galicia northwestern spain inferences from ree studies two mica granites and biotite rich monzogranites and granodiorites constitute the main types of late to post kinematic hercynian intrusions in galicia northwestern iberian massif both rock types exhibit analogous total ree content although the two mica granites have generally more fractionated normalized spectra the hercynian granites studied can be modeled as partial melts which in some cases experienced feldspar dominated fractional crystallization model source materials may be compared to the rocks outcropping in the area studied these granites are not accurately described by the i and s type classification those with s type characteristics two mica granites are derived mainly from an orthogneiss rich model protolith i e i type source whereas those with i type affinities biotite rich granitoids may be modeled from mixtures of orthogneiss and graywacke eastern galicia or from orthogneiss rich protoliths containing only a small proportion of metabasite western galicia the propose

radiocarbon dating and chronology of the early upper paleolithic at kostenki abstract investigations during the last 5 years at kostenki central russia voronezh area have uncovered several new archeological assemblages dating to the earliest phase of upper paleolithic occupation 36 42 ka these discoveries in conjunction with an expanded scope of research at kostenki have forced a reassessment of the east european early upper paleolithic record and generated a set of new questions the paper addresses one of the most important of these questions the problem of two discordant chronological time scales one based on radiocarbon evidences and another on various analyses by pertinent disciplines paleomagnetism palynology tephrochronology and others

ages of some intrusive rocks of southwestern maine u s a whole rock rb sr and u pb zircon age measurements on intrusive rocks in southwestern maine indicate igneous activity at 400 340 and 320 ma these plutonic rocks were emplaced into deformed ordovi

precambrian u pb zircon ages in eclogites and garnet pyroxenites from south brittany france an old oceanic crust in the west european hercynian belt abstract u pb zircon ages have been determined for two eclogites from the vendee and for two garnet pyroxenites from the baie d audierne in an episodic pb loss model the two discordia would give upper intercept ages around 1300 1250 ma and lower intercepts ages of 436 384 ma two interpretations are proposed 1 the 1250 1300 ma ages may reflect an unspecified upper mantle event or process the paleozoic ages correspond to the tectonic emplacement of an eclogitic mantle fragment into the continental crust 2 the protolith may have been extracted from the upper mantle 1250 1300 ma ago and stored in a crustal environment until it was metamorphosed under high pressure conditions around 400 ma ago this latter model is favoured by available geologic and isotopic data consequently we propose that a 1300 ma old oceanic crust was tectonicly incorporated into a sialic basement during the proterozoic this mixture was subsequently subducted during the paleozoic

a heton model of the spreading phase of open ocean deep convection abstract a point vortex heton model of the lateral dispersion of cold water formed in open ocean deep convection is developed and studied as an idealized representation of the sinking and spreading phase of open ocean deep convection the overturning and geostrophic adjustment of dense fluid on and below the radius of deformation scale formed by cooling on the large scale are parameterized in the model by introducing paired discrete point vortices hetons of cyclonic sense in the surface layer anticyclonic below driving a cold baroclinic vortex the convection site is imagined to be made up of many such baroclinic vortices each with a vertically homogeneous core carrying cold convectively tainted waters the point vortices are introduced at a rate that depends on the large scale cooling and the intensity assumed for each vortex the interaction of many cold baroclinic vortices making up a cloud is studied using point vortex green s function techniques the current solenoids of the individual ele

an s coordinate density evolving model of the northwest european continental shelf 1 model description and density structure the proudman oceanographic laboratory three dimensional baroclinic b grid model pol3db has been developed to incorporate features suitable for the modeling of baroclinic processes on the shelf at the shelf slope and in ocean regions to allow long term coupled ocean shelf simulations we test the model on the northwest european continental shelf in the period november 1988 to october 1989 against satellite sea surface temperature measurements against ctd sections both on and off the shelf and in summary against the whole of the north sea project ctd data set the model accurately reproduces the seasonal cycle in the shelf wide spatial temperature structure seen in the observations spatial correlations range from r 0 92 in december to 0 79 in july and the overall rms errors range from 0 8 c in april to 1 6 c in july we demonstrate that the increase in the errors during the summer is due to uncertainties in modeling the vertical temperature structure compared with a climatology the large scale sea surface salinity structure is also well modeled r 0 80 but there is a tendency for the model to overestimate the salinity in the norwegian trench and underestimate it in the kattegat the s coordinates a modified sigma coordinate system allow the formation of a seasonal mixed layer across the shelf break and into the northeast atlantic with a modest vertical resolution the accuracy to which this deep water region is modeled is limited by the initial and boundary conditions and by the extent of the model domain

polynya dynamics a review of observations and modeling 1 polynyas are nonlinear shaped openings within the ice cover ranging in size from 10 to 105 km2 polynyas play an important climatic role first winter polynyas tend to warm the atmosphere thus affecting atmospheric mesoscale motions second ocean surface cooling and brine rejection during sea ice growth in polynyas lead to vertical mixing and convection contributing to the transformation of intermediate and deep waters in the global ocean and the maintenance of the oceanic overturning circulation since 1990 there has been an upsurge in polynya observations and theoretical models for polynya formation and their impact on the biogeochemistry of the polar seas this article reviews polynya research carried out in the last 2 decades focusing on presenting a state of the art picture of the physical interactions between polynyas and the atmosphere sea ice ocean system observational and modeling studies the surface heat budget and water mass transformation within these features are addressed

new insights on the loess paleosol quaternary stratigraphy from key sections in the u s midwest abstract three key quaternary loess paleosol sections were examined in the missouri valley iowa eustis ash pit nebraska and in the wittsburg quarry arkansas to gain insights into the sedimentation environment and climate change of the u s midwest four loess units are present separated by three well developed paleosols crowley s ridge loess oxygen isotope stage ois 8 is pre illinoian in age and is the oldest loess unit investigated a well developed paleosol interpreted as yarmouth soil ois 7 is found in this loess in all three sections overlying the yarmouth soil is loveland loess ois 6 which has been pedogenically altered by the sangamon soil ois 5 it has luvisolic properties but a more clayey pedogenic texture than modern luvisols and has no clear eluvial horizon the overlying roxana silt ois 4 is pedogenically altered at wittsburg and missouri valley the farmdale soil ois 3 is developed in the roxana silt based on pedogenic features we correlate this paleosol to that developed in the gilman canyon formation at eustis in missouri valley and eustis sections the paleosol has chernozemic properties and therefore the gleyic features observed at missouri valley are interpreted as later alterations overlying the farmdale soil is the widespread peoria loess ois 2

eddy shedding from a boundary current around a cape over a sloping bottom abstract the authors discuss laboratory experiments that elucidate the mechanism of formation and westward drift of anticyclonic baroclinic vortices from a buoyant surface current flowing along a lateral boundary and around a cape experiments were carried out with a sloping bottom in order to simulate the topographic effect they showed how a vortex can be generated from the current where it separates and reattaches to the cape and that under some conditions the eddy is able to detach from the cape and drift westward following isobaths two important timescales regulate the flow the time tf that the current takes to generate a vortex and the time td that the vortex takes to drift westward for a distance equal to its radius when these two timescales are either of the same order of magnitude or tf td the vortex was able to form at the cape but it did not detach and drift westward the influence of the depth of the lower layer h0 on the flo

offshore transport of dense shelf water in the presence of a submarine canyon the formation and offshore transport of dense water over a uniformly sloping shelf crosscut by a submarine canyon is examined using a three dimensional primitive equation numerical model a constant negative buoyancy flux is applied in a limited region adjacent to a straight coast to represent brine rejection from ice production in an idealized coastal polynya a sharp density front forms at the edge of the forcing region with surface and bottom intensified jets along the front the flow around the head of the submarine canyon triggers a frontal instability that initially grows only on one side of the canyon the unstable waves on the other side of the canyon are blocked by a localized barotropic flow that develops near the canyon head unstable waves also grow where the forcing region intersects the coast the frontal waves grow rapidly with o 1 day e folding timescales and form eddies with horizontal scales of o 15 km which extract the densest water from the forcing region and carry it offshore directly across isobaths in this way the eddies limit the maximum water density that appears in the model despite continued negative buoyancy forcing some dense water descends into the canyon forming a bottom trapped plume that transports the dense water offshore ahead of the eddies the plume moves relatively slowly i e small froude number with little turbulent entrainment so the advancement and structure of the plume nose can be described successfully as a simple gravity current with an advective diffusive heat balance eddies may slump into the canyon from the side altering both the density anomaly and speed of the canyon plume suggesting that canyon plumes are likely to be highly variable in both space and time

environments of the russian plain during the middle valdai briansk interstade 33 000 24 000 yr b p indicated by fossil mammals and plants abstract abundant mammal 45 localities and plant 52 sections fossil data collected from the russian plain deposits of the middle valdai briansk interstade indicate a period of noticeable warming these materials were jointly analyzed the data were organized in the database software paradox and then moved to the gis program arc info mathematical methods as well as traditional research methods were used for the analysis the reconstructed biogeographical provinces illustrate the specific environmental and climatic conditions of the briansk interstade analogues of modern natural zones did not exist at this time on the russian plain the briansk landscapes reflect the moderate cool climate of this period when the majority of northern subarctic plant and mammal species extended their ranges considerably to the south to the central russian plain at the same time steppe species penetrated farther north and west this combination shows that the continuous forest zone was destroyed during the briansk inter stade five biogeographical provinces have been reconstructed from the north to the south for the russian plain during the briansk warming on the basis of joint analysis of mammalian and botanical data

on the importance of surface forcing in conceptual models of the deep ocean in the major ocean basins diapycnal mixing upwells dense antarctic bottom water which returns southward and closes the deepest cell of the meridional overturning circulation moc this cell ventilates the deep ocean and regulates the partitioning of co2 between the atmosphere and the ocean the oceanographic community s conceptual understanding of the deep stratification and moc has evolved from classic abyssal recipes arguments to a more recent appreciation of along isopycnal upwelling in the southern ocean consistent with a weakly mixed ocean interior both the deep stratification and the deep moc are shown here to be sensitive to the form of the surface buoyancy forcing in a two dimensional model that includes a circumpolar channel and northern basin for a fixed surface buoyancy condition the deep stratification is essentially prescribed whereas for a fixed surface buoyancy flux the deep stratification varies by orders of magnitude over the range of diapycnal diffusivity observed in the ocean these cases also produce different scalings for the deep moc with in both weak and strong regimes in addition these scalings are shown to be sensitive not only to the type of surface boundary condition but also to the latitudinal structure of the surface fluxes this latter point is crucial as buoyancy budgets and dynamical features of the circulation are poorly constrained along the antarctic margins this study emphasizes the need for caution in the interpretation of simple conceptual models that while useful may not include all mechanisms that contribute to the moc s strength and structure

numerical simulation of the filchner overflow the plume of ice shelf water isw flowing into the weddell sea over the filchner sill contributes to the formation of antarctic bottom water the filchner overflow is simulated using a hydrostatic primitive equation three dimensional ocean model with a 0 5 2 sv isw influx above the filchner sill the best fit to mooring temperature observations is found with influxes of 0 5 and 1 sv below a previous estimate of 1 6 0 5 sv based on sparse mooring velocities the plume first moves north over the continental shelf and then turns west along slope of the continental shelf break where it breaks up into subplumes and domes some of which then move downslope other subplumes run into the eastern submarine ridge and propagate along the ridge downslope in a chaotic manner the next western ridge is crossed by the plume through several paths despite a number of discrepancies with observational data the model reproduces many attributes of the flow in particular we argue that the temporal variability shown by the observations can largely be attributed to the unstable structure of the flow where the temperature fluctuations are determined by the motion of the domes past the moorings our sensitivity studies show that while thermobaricity plays a role its effect is small for the flows considered smoothing the ridges out demonstrate that their presence strongly affects the plume shape around the ridges an increase in the bottom drag or viscosity leads to slowing down and hence thickening and widening of the plume

on the baroclinic instability of cold core coupled density fronts on a sloping continental shelf a theory is presented to describe the linear baroclinic instability of coupled density fronts on a sloping continental shelf the new baroclinic model equations used to study the instability process correspond to an intermediate lengthscale dynamical balance specifically the frontal dynamics while geostrophic is not quasigeostrophic because frontal height deflections are not small in comparison with the frontal scale height the evolution of the frontal height is strongly coupled to the geostrophic pressure in the surrounding slope water through the hydrostatic balance which expresses the continuity of the dynamic pressures across the frontal interface the deeper surrounding slope water evolves quasi geostrophically and is coupled to the front by baroclinic vortex tube stretching compression associated with the perturbed density front allowing the release of mean frontal potential energy and the topographic vorticity gradient associated with the sloping bottom it is shown that the baroclinic stability characteristics are principally determined by a so called non dimensional interaction parameter denoted p which physically measures the ratio of the destabilizing baroclinic vortex tube stretching compression to the stabilizing topographic vorticity gradient for a given along front mode wavenumber it is shown that a minimum p is required for instability several other general stability results are presented necessary conditions for instability growth rate and phase speed bounds the existence of a high wavenumber cutoff and a semicircle theorem for the unstable modes the linear stability equations are solved exactly for a parabolic coupled density front and a detailed description of the spatial and temporal characteristics of the instabilities is given for physically realistic parameter values the instabilities are manifested as amplifying topographic rossby waves in the slope water and on the density front the unstable perturbations take the form of amplifying anticyclones which have maximum amplitude on the offshore side

les eaux thermales des granites de galice espagne des eaux carbogazeuses aux eaux alcalines thermal waters from granites of galicia spain from co2 rich to high ph waters abstract thermal waters from galicia spain range from co 2 rich low ph to high ph sulfide rich waters going through intermediate waters in order to explain the variations of their chemical composition we present a discussion of the major factors governing the water composition we eiscuss especially the isochemical recrystallization of a granite it is shown that the equilibrium mineral association of the water alkali granite system is unique for chalco alkaline granites two different associations are possible depending on the chemical composition of the granite the effect of an addition of co 2 is also discussed some criteria allowing a distinction between fully equilibrated and non equilibrated waters are presented finally the composition of galician waters is explained by different initial co 2 contents and by different values of the degree of the granite water reaction progress

supra regional correlations of the most ancient paleosols and paleolithic layers of kostenki borschevo region russian plain abstract the archaeological site kostenki12 located on the middle don river provides a key stratigraphic profile for regional paleopedological paleoenvironmental geological and cultural sequences containing the oldest known cultural layers of the region layer v paleolithic layer iv upper paleolithic layer iii kostenki strelets culture early phase dating to the early part of mis3 or in chronometric terms to 54 42 ka kostenki12 complements kostenki14 markina gora which is a key profile for the interval 42 27 ka the new data from kostenki12 show that the east european upper paleolithic began 45 ka the stratigraphy exhibits similarities to that of borschevo5 the kostenki12 pollen diagram is correlated with 1 other pollen diagrams from kostenki borschevo region 2 the most detailed climatostratigraphical scale of the russian plain late pleistocene 3 16 o 18 o greenland gisp2 scale 4 13 c 14 c record from stalagmite at villars cave france as well as with pollen records 5 7 from 5 lake monticchio italy 6 southern black sea m72 5 25 gc1 and 7 glinde and moershoofd northern germany the results of the supra regional paleoenvironmental correlations demonstrate that the lowest paleolithic layer v and paleosol d characterized by elm dominance correlate to the second half of the optimum of the glinde interstadial at 51 48 ka corresponding to do 14 the earliest upper paleolithic layer iv and paleosol b characterized by coexistence of elm forests and wet meadows began to form during the second part of the moershoofd interstadial optimum at 46 44 ka correlating with do 12 paleosol a and layer iii kostenki strelets culture began to form after the abrupt end of the moershoofd interstadial 43 5 ka during unstable conditions according to pollen and paleozoological data steppe with horse dominance and later spruce forest tundra with reindeer dominance in paleozoological complex these correlations provide more accurate dating of the paleolithic layers and paleosols at kostenki borschevo suggesting that previously reported radiocarbon dates on units below ci tephra layer are too young but that the osl chronology is generally accurate

generation of a buoyancy driven coastal current by an antarctic polynya descent and spreading of high salinity water generated by salt rejection during sea ice formation in an antarctic coastal polynya is studied using a hydrostatic primitive equation three dimensional ocean model called the proudman oceanographic laboratory coastal ocean modeling system polcoms the shape of the polynya is assumed to be a rectangle 100 km long and 30 km wide and the salinity flux into the polynya at its surface is constant the model has been run at high horizontal spatial resolution 500 m and numerical simulations reveal a buoyancy driven coastal current the coastal current is a robust feature and appears in a range of simulations designed to investigate the influence of a sloping bottom variable bottom drag variable vertical turbulent diffusivities higher salinity flux and an offshore position of the polynya it is shown that bottom drag is the main factor determining the current width this coastal current has not been produced with other numerical models of polynyas which may be because these models were run at coarser resolutions the coastal current becomes unstable upstream of its front when the polynya is adjacent to the coast when the polynya is situated offshore an unstable current is produced from its outset owing to the capture of cyclonic eddies the effect of a coastal protrusion and a canyon on the current motion is investigated in particular due to the convex shape of the coastal protrusion the current sheds a dipolar eddy

rare earth element distribution in some hercynian granitoids from the finisterre region nw spain two series of granitoids are present in the finisterre region one is formed mainly by syn collision two mica leucogranites the other is composed of syn and post collision granodiorites and monzogranites of calc alkaline affinity the emplacement of these granitoids took place during and after the main phases of regional deformation petrographic and geochemical studies on the leucogranites suggests a common crustal origin with the surrounding metamorphic series which includes metasediments and orthogneisses of medium to high grade amphibolite facies the syn and post collision calc alkaline series is associated with basic to intermediate rocks suggesting a lower crustal origin ree data have been used to characterize the two types of granitoids and to model the source areas of generation there is no evidence for an origin of the granitoids by melting of mantle type igneous rocks instead the sequences of granitoids can be explained assuming different degrees of partial melting from a heterogeneo

u pb age and lead isotopic characterization of au bearing skarn related to the andorra granite central pyrenees spain auriferous skarns are associated with post and late kinematic hercynian granites that intruded into cambro ordovician to devonian sediments of the central pyrenees we determined the age of the andorra granite and the associated skarn at 305 3 ma by u pb dating titanite from the endo skarn the sulfur isotopic composition from sulfides in the skarn cardellach et al 1992 shows a significant variation with isotopically light sulfur 34s 3 in the barren skarns and heavy sulfur 34s 11 in the gold bearing skarns outwards it increasingly resembles sulfur from arsenopyrite disseminations in the cambro ordovician sediments the lead isotopic composition from sulfides of the skarns is very homogeneous 206pb 204pb 18 410 207pb 204pb 15 699 208pb 204pb 38 574 in contrast to the one in gold bearing arsenopyrite veins and in arsenopyrite disseminations in the sediments e g 206pb 204pb varies from 18 54 to 30 36 combined sulfur and lead isotope data indicate that the lead in the skarn is dominantly derived from the granite whereas the sulfur is derived at variable portions from both the granite and the sediments

sr z sbnd nd isotopic record of multi stage interactions between mantle derived magmas and crustal components in a collision context the ultramafic granitoid association from vivero hercynian belt nw spain late stage epizonal calc alkaline granitoids of the hercynian belt are often associated with coeval more basic rocks such granitoids have been the focus of special attention when studying the role of mantle derived magmas in granitoid genesis these studies conclude that basic magmas are involved in granitoid production but their contribution to the chemical composition of granitoids is often controversial the vivero massif nw spain includes calc alkaline granitoids and coeval ultramafic and mafic rocks but these granitoids are syntectonic and intruded into middle crustal levels during an early stage scattered major and trace element chemistry together with heterogeneous sr nd isotopic results preclude an origin of this ultramafic to granitoid association by any closed system fractionation process ultramafic rocks include peridotites pyroxenites and homblendites with endi from 3 5 to 1 3 and 87sr86sr i ratio from 0 7059 to 0 7080 they are interpreted as cumulates formed by in situ fractional crystallization from contaminated basaltic magmas particularly by interaction with 87sr enriched fluids mafic rocks comprise biotite amphibole diorites quartz diorites and tonalites with ndi from 3 8 to 0 0 and 87sr86sr i ratio from 0 7058 to 0 7073 they represent either cumulates or more evolved magmas of calc alkaline affinity these rocks display an inverse correlation between the degree of differentiation and the degree of contamination inferred from isotope data this points to wall rock assimilation by thermal erosion during ascent of basic magmas up to the middle crust and supports the participation of mantle sources with positive end and 87sr86sr i 0 7058 granitoids range from amphibole biotite tonalites through biotite granodiorites to monzonitic granites they show an isotopic trend which diverges from that of ultramafic and mafic rocks endi 6 0 to 1 9 decreases while 87sr86sr i ratio 0 7061 to 0 7082 increases from tonalites to monzonitic granites reflecting an increasing contribution of crustal components in more differentiated rocks assimilation and fractional crystallization mixing included account for such an evolution contamination of basic magmas by this process occurring at deeper crustal level produced hybrid tonalites and related mafic magmatic enclaves only monzonitic granites are interpreted as pure crustal melts their hree fractionated patterns gd yb 4 5 suggest equilibrium with a garnet rich residuum partial melting of moderate time integrated rb sr protolith such as greywackes and or meta igneous rocks of intermediate acid composition could account for the isotopic composition of these monozogranites this example shows that at least some calc alkaline granitoids of collisional setting are not produced by pure intra crustal melting they are formed through a complex multi stage hybridization process involving mantle derived magmas crustal components and several concomitant magmatic processes

micromammals from an early holocene archaeological site in southwest china paleoenvironmental and taphonomic perspectives abstract investigations of the well known paleontological and archaeological site of tangzigou in western yunnan province in 2003 and 2006 yielded plentiful mammalian remains and a large number of stone and bone artifacts among the mammalian remains were those of many micromammals representing modern taxa of scandentia insectivora and rodentia the micromammal assemblage is dominated by rodents which constitute 92 of the total number of identifiable elements murids are the most common elements followed by rhizomyids sciurids and hystricids the tangzigou deposits appear to have been created over a period of 200 300 years in the early to middle holocene judging from the tight cluster of ams radiocarbon dates between 9000 and 8745 bp based on the known habitat preferences of the living species most of the tangzigou micromammals were arboreal or dwellers of the forest floor the micromammal assemblage thus indicates that subtropical forest including bamboo dominated the environment around tangzigou the assemblage is remarkable for the near absence of very small micromammal species such as small mice this bias appears to have been introduced by humans who collected the larger bodied species of micromammals for food this interpretation is supported by the presence of a large number of burned elements especially dentaries the analysis of the larger mammals also showed that tangzigou was a place where prehistoric people gathered to butcher the hunted scavenged animals

the age and nature of the basement of southern britain evidence from sr and pb isotopes in granites the isotopic study of granitic intrusions in southern britain provides an indication of the age and geochemical nature of the south british basement which is otherwise generally obscured from observation by sedimentary cover this paper reports pb isotopic compositions of feldspars in granites from sw england lundy mountsorrel and shap in addition to age and initial 87 sr 86 sr data on two of the granites a review of published rb sr age and isotope data for southern britain and consideration of the new pb data using the plumbotectonics model of doe zartman 1979 indicate that the basement to southern britain has an age of 800 ma with an upper limit of 1200 ma the granites studied in this work have substantial components of crustally derived sr and pb

carbonate rhizoliths in loess and their implications for paleoenvironmental reconstruction revealed by isotopic composition δ13c 14c abstract loess paleosol sequences are important terrestrial archives for studying quaternary climate changes they often contain secondary carbonates including e g rhizoliths calcified roots these secondary carbonates are precipitated in isotopic equilibrium with root derived co2 and are therefore used to reconstruct the vegetation present during their formation based on stable carbon isotopic composition 13c usually the chronological context of secondary carbonates in general is not mentioned because it is assumed that they are formed synsedimentary with loess deposition the loess paleosol sequence at nussloch sw germany contains in its youngest part upper wurmian large carbonate rhizoliths with diameters of up to 5 cm and lengths of up to 1 m and more which have not been described in this profile so far we investigated rhizoliths as well as loess adjacent to and distant from rhizoliths for carbonatic carbon ccarb and organic carbon corg contents as well as their isotopic composition 13c radiocarbon dating to identify the rhizolith origin and the time frame of their formation considering the 13c fractionation by carbonate precipitation the 13ccarb values 10 9 0 1 revealed c3 plant origin of the rhizolith carbonate and the absence of large amounts of occluded primary loess carbonate similar 14c ages of rhizolith ccarb and corg 3788 59 years bp and 3150 59 years bp respectively argued for the absence of postsegregational alteration therefore they are suitable for the reconstruction of paleoenvironmental conditions after loess sedimentation the 14c ages clearly indicate that rhizoliths did not form synsedimentary roots penetrated the loess at nussloch after the deposition had ceased at 15 ka bp even in the loess adjacent to the rhizoliths up to a distance of 5 cm 13ccarb values indicate the presence of secondary carbonate deriving from postsedimentary organic matter of origin other than that of the reference loess material hence this postsedimentary input of younger root biomass might have masked the initial plant signal in loess paleosol sequences which could cause uncertainties for paleoenvironmental reconstructions based solely on loess organic matter

eddy formation by dense flows on slopes in a rotating fluid properties of the flow generated by a continuous source of dense fluid on a slope in a rotating system are investigated with a variety of laboratory experiments the dense fluid may initially flow down the slope but it turns under the influence of rotation to flow along the slope and initial geostrophic adjustment gives it an anticyclonic velocity profile some of the dense fluid drains downslope in a viscous ekman layer which may become unstable to growing waves provided that the viscous draining is not too strong cyclonic vortices form periodically in the upper layer and the dense flow breaks up into a series of domes three processes may contribute to the formation of these eddies first initial downslope flow of the dense current may stretch columns of ambient fluid by the taylor column process which we term capture secondly the initial geostrophic adjustment implies lower layer collapse which may stretch the fluid column and thirdly viscous drainage will progressively stretch and spin up a captured water column overall this last process may be the most significant but viscous drainage has contradictory effects in that it progressively removes dense lower layer fluid which terminates the process when the layer thickness approaches that of the ekman layer the eddies produced propagate along the slope owing to the combined effects of buoyancy coriolis balance and beta gyres this removes fluid from the vicinity of the source and causes the cycle to repeat the vorticity of the upper layer cyclones increases linearly with l d where l is the rossby deformation radius the bottom slope and d the total depth reaching approximately 2 f in the experiments presented here the frequency at which the eddy dome structures are produced also increases with while the speed at which the structures propagate along the slope is reduced by viscous effects the flow of dense fluid on slopes is a very important part of the global ocean circulation system and the implications of the laboratory experiments for oceanographic flows are discussed

generation and emplacement of shear related highly mobile crustal melts the synkinematic leucogranites from the variscan tormes dome western spain the tormes dome consists of s type granites that intruded into ordovician augen gneisses and neoproterozoic lower cambrian metapelites metagreywackes at different extents of migmatization s type granites are mainly equigranular two mica granites occurring as 1 enclave laden subvertical feeder dykes 2 small external sill like bodies with size and shape relations indicative for self similar pluton growth and 3 as large pluton bodies emplaced at higher levels than the external ones these magmas were highly mobile as it is inferred from the high contents of fluxing components the disintegration and alignment of pelitic xenoliths in feeder dykes and at the bottom of some sill like bodies field relations relate this 311 ma magmatism u pb monazite to the regional shearing of the d3 variscan event partial melting modeling and the relatively high estimated liquidus temperatures indicate biotite dehydration partial melting 800 840 c and 400 650 mpa rather than water fluxed melting implying that there was no partial melting triggered by externally derived fluids in the shear zones instead the subvertical shear zones favored extraction of melts that formed during the regional migmatization event around 320 ma nd isotope variation among the granites might reflect disequilibrium partial melting or different protoliths mass balance and trace element partial melting modeling strongly suggest two kinds of fertile crustal protoliths augen gneisses and metapelites slight compositional variation among the leucogranites does not reflect different extent of protolith melting but is related to a small amount of fractional crystallization 13 for the equigranular granites which is generally more pronounced in shallower batholitic leucogranites than in the small and homogeneous sill like bodies the lower extent of fractional crystallization and the higher pressure emplacement conditions of the sill like bodies support a more restricted movement through the crust than for batholitic leucogranites

extensional flow produces recumbent folds in syn orogenic granitoids padron migmatitic dome nw iberian massif this contribution provides a case example on the generation of large scale recumbent folds in syn orogenic granitoids we analyze the progressive reworking of extension related structures into later ones after a period of crustal thickening the padron migmatitic dome formed after the climax of the gondwana laurussia collision in the late paleozoic petrostructural analysis carried out in the eastern flank of this dome reveals that extensional flow resulted in progressive exhumation of mainland gondwana which rested under peri gondwanan allochthonous terranes and a suture zone during maximum crustal thickening exhumation proceeded up to upper crust levels andalusite stability field along with partial melting of the middle lower crust and with the generation of granitoid laccoliths during an early extensional stage newly formed lithological and mechanical anisotropies such as the presence of variably sized sheet shaped bodies of syn orogenic granitoids provided a favorable rheological setting for fold nucleation during the intermediate stages of extension in extending orogenic crust whether recumbent folds occur after significant melt production depends on the lateral vertical flow ratio and on the orientation of deforming bodies with regard to kinematic strain axes we suggest that subhorizontal extensional flow dominated over vertical flow during the early and intermediate stages of the evolution of the padron dome a component of vertical diapiric flow caused progressive tilting of the sheet like bodies and obliquity respect to strain axes this resulted in the development of regional scale folds at the expense of syn orogenic granitoids such as in the case of the portomouro recumbent synform extensional ductile flow was oblique to the trend of the orogen during the whole process and directed to the nnw during the formation of recumbent folds non coaxial shearing favored an nnw sse elongate shape for the syn kinematic granitic massifs as well as the subsequent nucleation of recumbent folds deformation concentrated along discrete detachments during the late stages of extension

the cadomian orogeny in saxo thuringia germany geochemical and nd sr pb isotopic characterization of marginal basins with constraints to geotectonic setting and provenance abstract the cadomian basement and the cambro ordovician overstep sequence in saxo thuringia is characterized by clastic sedimentation from the late neoproterozoic to the ordovician magmatism in the avalonian cadomian arc preserved in saxo thuringia occurred between ca 570 and 540 ma peri gondwanan basin remnants with cadomian to early palaeozoic rocks are exposed as very low grade metamorphosed rocks in six areas schwarzburg anticline berga anticline doberlug syncline north saxon anticline lausitz anticline and elbe zone a hiatus in sedimentation between 540 and 530 ma cadomian unconformity is related to the cadomian orogeny a second gap in sedimentation occurred during the upper cambrian 500 to 490 ma and is documented by a disconformity between lower to middle cambrian rocks and overlying tremadocian sediments major and trace element signatures of the cadomian sediments reflect an active margin continental arc those of the ordovician sediments a passive margin the cambrian sediments have inherited the arc signature through the input of relatively unaltered cadomian detritus initial nd and pb isotope data from the six saxo thuringian areas demonstrate that there is no change in source area with time for each location but that there are minor contrasts among the locations 1 cadomian sediments from the lausitz anticline the doberlug syncline and the elbe zone have lower 207pb 204pb than all other areas 2 the core of the schwarzburg anticline which is overprinted by greenschist facies conditions and detached is isotopically heterogeneous one part of its metasedimentary units has less radiogenic nd than sediments from other low grade units of similar age in the same area 3 cadomian sediments from the schwarzburg anticline show an input of younger felsic crust 4 the rothstein group shows distinct input of young volcanic material also 5 cadomian sediments from the lausitz anticline the elbe zone and parts of the north saxon anticline are characterized by input from an old mafic crust nd isotope data of the remaining areas yield average crustal residence ages of the sediment source of 1 5 1 9 ga which suggests derivation from an old craton as found for other parts of the iberian armorican terrane collage similarly the pb isotope data of all areas indicate sediment provenance from an old craton the rapid change of lithologies from greywacke to quartzite from the late neoproterozoic cadomian basement to the ordovician does not reflect changes in sediment provenance but is essentially due to increased reworking of older sediments and old weathering crusts that formed during various hiatus of sedimentation this change in sediment maturity takes its chemical expression in lower overall trace element contents in the quartzite dilution effect by quartz and relative enrichment of some trace elements zr mree hree due to detrital zircon and garnet the rb sr systematics of the quartzites and one ordovician tuffite was disturbed most likely during the variscan orogeny which suggests a lithology controlled mobility of alkali and calc alkali elements by comparison with available data it seems unlikely that only nd tdm model ages are useful to distinguish between west african and amazonian provenance nd tdm model ages of 1 5 to 1 9 ga in combination with paleobiogeographic aspects age data from detrital zircon and palaeogeographic constraints especially through tillites of the saharan glaciation in the hirnantian strongly indicate a provenance of saxo thuringia from the west african craton

lead isotopic composition of hercynian granitic k feldspars constrains continental genesis lead isotope compositions have been determined in many k feldspars from granitic rocks emplaced during the variscan hercynian orogeny sensu lato around 300 myr in various parts of europe and the eastern us the ratios show a regular geographical pattern with contours arched around southern france and parallel to the atlantic coast of the us this distribution parallels predriftpalaeogeographical zones during the palaeozoic the lead isotope pattern of variscan granitic rocks is similar to that of some orogenic volcanic suites but is better explained by crustal melting than by an hercynian mantle crust material mixing the continental crust from these areas must be older than 3 000 myr large scale fluid circulation in the crust during orogenic processes apparently explains the observed geographical patterns of lead isotopes

manaslu leucogranite a collision signature of the himalaya a model for its genesis and emplacement the manaslu pluton is one of 10 leucogranites that formed in the overthrusted higher himalaya after the indo eurasian collision field and analytical data indicate that the underlying migmatites of the tibetan slab may be where the leucogranitic melts were generated the himalayan crustal thrusting of a hot slab over a rather cold volcano sedimentary pile le fort 1975a provides the necessary release of fluids these fluids cross the main central thrust mct induce the partial anatexis of the overheated tibetan slab and produce a leucogranitic magma the emplacement of the magma at first is located along the main disharmonic plane above the mct between the infrastructure and the superstructure there it generates a convective hydrothermal system extending very far laterally according to the stratification of permeabilities progressive emplacement of the granite proceeds as the convected fluids including the fluids released by the saturated magma dissolve the mainly calcareous host rocks of tibetan sedimentaries a frozen image of this caving out progression is given by the extensive network of granitic dikes outside the pluton the two quite independant fluid cycles of the generation and of the emplacement were triggered or guided by the tectonics due to collision this two fold model dominated by fluid activity may be of importance for other leucogranites and granites

the distribution and formative processes of latent heat polynyas in east antarctica a study of polynya characteristics in east antarctica was undertaken using ice concentrations derived from special sensor microwave imager data for the period july 1987 august 1994 the areas of polynyas were defined as having an ice concentration 75 the analysis revealed a total of 28 coastal polynyas within the study region the spatial and temporal variability in areal extent was quantified the timing of mean maximum areal extent varied from june to october the bathymetry and wind regime at each polynya site was examined to gauge the relative importance of these parameters in polynya formation and maintenance in 20 locations shallow banks and shoals form grounding zones for icebergs and anchoring sites for fast ice which form barriers to the predominantly westward drift of the pack ice elsewhere north south coastal protrusions or alignments form similar barriers the subsequent removal of newly formed sea ice from the lee of such barriers by katabatic and synoptic winds maintains areas of reduced ice concentration and open water very few coastal polynyas are attributed solely to katabatic outflow the combined influence of bathymetry topography and winds is responsible for the characteristics of the majority of polynyas many were considered to be marginal characterised by occasional periods when the ice concentration falls below 75 an analysis of annual winter totals of areas with ice concentrations 75 shows no trends in total polynya areal extent over the period 1987 94 known locations of emperor penguin aptenodytes forsteri rookeries were also found to be associated with the locations of coastal polynyas

a numerical study on the successive formation of meddy like lenses 1 we present a process study on the sustaining mechanism of lens formation using a series of numerical experiments of a density current over a sloping bottom with a cape along the coastline water parcels in the bottom density current are shed into the offshore region leading to periodic formation of anticyclonic lenses as part of baroclinic dipolar vortices the cyclonic partner is more prominent at the surface and the coupled vortices are carried by the mean current established in the offshore region parameter dependence of dipole generation is examined which suggests that the background current is necessary for the detached eddies to be coherent in the downstream direction and for shedding events to repeat nof and pichevin 1996 it is also shown that the density mixing of the bottom current provides criteria for cyclogenesis at the sea surface a detailed analysis is given by a five layer model forced by a water mass source sink which reproduces the baroclinic dipolar vortices similar to those observed in the preceding z coordinate model we find that the dipole generation is due to the finite amplitude divergence convergence of the baroclinic current passing the cape stern and chassignet 2000 the overall analyses suggest three necessary conditions for successive eddy formation 1 a localized variation in the coastline causing the finite amplitude disturbance 2 mixing of mediterranean water with the surrounding fluids leading to anticyclonic rotation of meddies as well as cyclogenesis at the surface and 3 background currents that advect the detached vortices out of the source region index terms 4255 oceanography general numerical modeling 4219 oceanography general continental shelf processes 4520 oceanography physical eddies and mesoscale processes 4528 oceanography physical fronts and jets keywords eddy shedding dense water plume numerical simulation

structural control and geological significance of the zn pb ores formed in the benasque pass area central pyrenees during the post late ordovician extensional event of the gondwana margin abstract the benasque pass area central pyrenees is located in the eastern part of the variscan lys caillaouas massif where cambro ordovician rocks of the hesperian massif crop out in the area several zn pb deposits are located in variscan structures lead isotopes indicate a late ordovician early devonian model age for the deposits in the region an unconformity between pre late ordovician and late ordovician rocks has been defined by several authors and has been identified in the study area the first structures observed in the benasque pass area consist of a pre variscan cleavage which only affects the pre late ordovician rocks in the study area the main structures correspond to two variscan generations i e w trending north verging folds which are associated with the main foliation s 1 d 1 ii e w trending upright folds and associated small south directed thrusts d 2 d 2 structures are the ones hosting the zinc lead ore in the benasque pass area d 1 and d 2 variscan structures have developed under low grade metamorphic conditions some faults observed in the north and the south of the study area may have alpine movement in the benasque pass area the strongly silicified and brecciated zinc lead ore is mainly developed in the d 1 short limb of the mina peak syncline within which s 1 foliation is intensely folded and cross thrust by d 2 structures taking into account their model age all these zinc lead deposits seem to be stratiform stratabound or filling open spaces in origin and related to the pre variscan extension described for the central pyrenees however the zinc lead ore is hosted in strongly silicified and brecciated variscan structures the 34 s isotopic composition of sulfides indicates that the metamorphism and deformation did not completely obliterate the original isotopic composition suggesting that sulfur in the benasque pass has mainly come from the reduction of marine sulfate extracted from the rocks of the metasedimentary sequence in the benasque pass area the lead isotope ratios are homogeneous and have a pre variscan model age which is also the age of the host rocks in the case of the benasque pass the deposits occurred in variscan structures making it impossible to recognize their original pre variscan characteristics indicated by lead isotopes model age the correlation between the pb isotope data for deposits from the benasque pass and aran valley also located in the central pyrenees and those for other deposits from the southern european gondwana is evident and the isotopic data set closely fits the two stage pb evolution model for sardinia terrane the coherence of the pb isotope trends in all the deposits suggests that pb was extracted at various times from sources with similar time averaged u pb th pb and th u values through a process of leaching of the basement rocks by large volumes of hydrothermal fluids in the case of the pyrenees central and eastern the lead and other metals present in the deposit were extracted by hydrothermal fluids from the upper crust rocks during the post late ordovician extensional event of the gondwana margin

geochemical and ndsrpb isotopic composition of alleghanian granites of the southern appalachians origin tectonic setting and source characterization abstract we report major element trace element and nd and sr isotopic ratios for 35 samples of late mississippian early permian alleghanian granites that intrude the carolina terrane eastern slate belt inner piedmont and kiokee belt of the southern appalachians major element compositions indicate that most plutons are high potassium k 2 o 4 metaluminous granites initial e nd depleted mantle model ages and initial 87 sr 86 sr ratios respectively of the plutons range from 8 2 to 3 4 940 1020 ma and 0 70642 0 72798 for the inner piedmont 2 3 to 2 0 660 1130 ma and 0 70421 0 71035 for the kiokee belt 2 7 to 2 4 660 870 ma and 0 70353 0 70816 for the eastern slate belt and 6 7 to 1 9 690 1140 ma and 0 70391 0 70739 for the carolina terrane the chemical and isotopic data are most consistent with formation of the granites by anatexis of continental crust rather than derivation from a depleted mantle source rocks of the carolina terrane have e nd 300 ma values and pb isotopic ratios indistinguishable from those of most alleghanian granites suggesting it is a likely source some alleghanian granites within the carolina terrane require a more evolved source than exposed carolina terrane rocks suggesting that evolved crust possibly grenville basement occurs structurally below or within the terrane the chemical and isotopic compositions of granites intruding the kiokee belt eastern slate belt and carolina terrane are similar suggesting that these terranes are geochemically similar in contrast alleghanian granites within the inner piedmont have higher initial 87 sr 86 sr and lower 143 nd 144 nd ratios indicating that their sources are isotopically more evolved the virtual absence of alleghanian plutons with mafic intermediate compositions and the lack of geographic trends in chemical and isotopic composition across the orogen makes a subduction origin for the granites unlikely the consistency of the geochemical data with a crustal anatectic origin of the granites together with the observation that they intruded synchronously with alleghanian thrusting in the valley and ridge province suggests strongly that they are collisional in origin the crustal heating events that produced the granites might have been caused by delamination of mantle lithosphere during collision of laurentia with gondwana 1 2 alternatively adequate heating may have occurred by crustal thickening during emplacement of thrust sheets 3

wind effects on the buoyancy driven general circulation in a closed basin using a two level model abstract wind effects on buoyancy driven circulation in a two level rectangular basin are studied the ocean is driven by positive and negative buoyancy fluxes in the northern and southern portions as well as wind stress of constant curl in a model with a flat and frictionless bottom a barotropic component is determined only by wind forcing a baroclinic component of the wind driven circulation associated with horizontal density gradient is reduced by horizontal diffusion i e the wind driven circulation is more barotropic with stronger diffusion meridional overturn induced by buoyancy fluxes is modified by the wind driven circulation for example the southward upper level flow produced by positive and negative buoyancy fluxes in the northern and southern portions greatly shifts to the western eastern boundary by cyclonic anticyclonic wind driven circulation with realistic intensity relative importance of the wind driven circulation to the buoyancy driven circulation for meridional density

krotovinas pedogenic processes and stratigraphic ambiguities of the upper palaeolithic sites kostenki and borshchevo russia abstract the excavations of the upper palaeolithic sites of kostenki and borshchevo located in the middle russian plain bear several meters of loess derived colluvial deposits of the middle and late valdai which cover alluvial sediments of the don floodplain at least four cultural layers and more than three paleosol units occur within the colluvial deposits a high number of krotovinas is most obvious mainly the burrows of cricetus cricetus and lagurus lagurus which on first view seem only to disturb sediment and soil stratigraphy to disprove this assumption the present paper investigates the significance of krotovina fillings within soil research by applying micromorphological analysis the study gives insight into different filling materials soil forming processes inside abandoned and filled burrow systems and surrounding material in some cases krotovina fillings in this part of the middle russian plain can be areas of bulking and compaction of preferential paths of infiltration followed by calcium carbonate depletion and of drying followed by secondary calcification further burrows are paths for second and third generations of soil faunal activities

investigations into the potential effects of pedoturbation on luminescence dating much effort has been focussed on understanding the luminescence properties of natural minerals to achieve a reliable accurate and precise dating technique however some field related aspects such as the influence or effect of post depositional disturbance on luminescence dates are as yet underexplored in the case of pedoturbation depending on its intensity the rate of sedimentation and unit thicknesses potentially the whole sedimentary record at a site can be affected this may lead to distorted osl chronologies and erroneous sediment burial ages pedoturbation can result in sediment mixing and or exhumation that affect luminescence both at the bulk and single grain level effects of these two principle processes on luminescence ages are examined using standard multigrain and single grain protocols high resolution sampling of surface gopher mounds was used to determine the efficiency of bio exhumation in resetting luminescence signal results show this is an inefficient mechanism for onsite sediment bleaching the effects on luminescence signal of bio mixing were explored by comparing a sample collected from within a krotovina infilled burrow to an adjacent undisturbed sample results show the difficulties in identifying pedoturbated samples at the single aliquot level and the possible inaccuracies in using the lowest palaeodose values to calculate osl ages where pedoturbation of samples is suspected use of probability plots of palaeodoses data is recommended from these plots it is proposed that only data falling within a normal distribution centred on the peak probability be used to calculated osl ages and to mitigate problems arising from pedoturbation

cascades of dense water around the world ocean dense water overflow off continental shelves cascading is one of the contributing processes of shelf deep ocean exchange and of topical interest to climate studies and nutrient fluxes dense water originating from cooling evaporation freezing and salinization on a shallow shelf spills over the shelf edge and may develop as near bottom gravity current or an intermediate depth intrusion it is difficult to observe in nature due to its intermittent character this paper provides an extensive inventory of observed cases of water cascades around the world ocean summarises their locations and individual properties and provides statistics of the identified cases the search for cascading was carried out using oceanographic databases and a literature review this study identified 61 confirmed cases world wide including 25 cases in the arctic seas 12 at mid latitudes seven in sub tropical and tropical regions and 17 off the antarctic shelves eighteen cascades had not been reported before we analyze a set of numerical parameters of dense water cascades allowing us to quantify compare and contrast the properties of water cascades the overall average density contrast between the confirmed cascades and ambient water is 0 37 kg m3 it can be as much as 2 kg m3 on some arctic shelves frequently initiated by strong cooling at the surface cascades often remain colder through the descent thus supplying the deep ocean with colder and fresher water in non dimensional variables the data from all climate zones fit well to a unique curve which represents a relationship between a cascade s internal structure and the parameters describing its forcing on average the down slope volumetric flux provided by dense water cascades is estimated as 0 05 to 0 08 sv per 100 km of shelf edge regional terms arctic antarctic north atlantic ocean barents sea mediterranean sea skagerrak tasman sea sea of okhotsk

determination of the rare earth element abundances in 29 international rock standards by instrumental neutron activation analysis a critical appraisal of calibration errors abstract a standard additions method has been used to calibrate an in house multi element rock standard for the analysis of the rare earth elements ree and th ta hf and co by instrumental neutron activation analysis this preliminary calibration with a precision of typically better than 7 1 has been refined by comparing our analyses of the four u s g s standard rocks agv 1 bcr 1 g 2 and gsp 1 with compiled analyses obtained by a critical survey of over 70 published references our standard calibration was adjusted by the average discrepancy between our analyses and published analyses for each element for all four u s g s standards the accuracy of this final calibration is estimated to be better than 5 absolute and it has been used to determine the above elemental abundances in 29 international rock standards five of the ree have been determined by interpolation from chondrite normalised plots

heat flux partitioning in open ocean convection abstract cold air blowing out over a warm ocean leads to convection over an isolated region of the ocean basin this phenomenon known as open ocean convection is often simulated by convective forcing from a circular disk much smaller than the dimension of the domain an important feature of these simulations is the development of eddies at the edge of the disk that serve to transport heat horizontally this has sparked interest in the heat flux characteristics of such a system this paper deals with the thermodynamic properties of this type of convective flow using a rotating tank with bottom mounted hotplate as the experimental apparatus experiments are performed in an initially unstratified fluid for a set of values of the nondimensional forcing parameter rc b1 2 hf3 2 where b is the buoyancy flux h is the fluid depth and f is the coriolis parameter the ratio of the frontal eddy size to the hotplate radius is shown to be an important parameter the experiments reported are for the regi

a numerical investigation of the transport process of dense shelf water from a continental shelf to a slope we investigate the offshore transport process of dense shelf water using a three dimensional primitive equation model we focus on the effects of bottom a dee topography in particular inclination of a bottom slope from a continental shelf to a deep basin for the numerical domain we use an idealized bottom topography in which the bottom deepens gradually from a shallow continental shelf region to a steep slope region in the continental shelf region we use a salt flux which represents the typical brine rejection in a coastal polynya results of the numerical experiments show that dense shelf water is transported offshore by eddy flux and a dense plume the transport by eddy flux occurs mainly over a continental shelf while that by the dense plume occurs over a continental slope a boundary between the regions where the above two processes are dominant corresponds locally to a shelf break a salinity front is developed in the boundary over the shelf break separating the dense shelf water from the offshore water we also investigate the stability of the surface westward current over the shelf break front using a simple analytical model the analytical model investigation shows that shelf break topography plays an important role in determining a neutral point of the stability of the shelf break current and preventing dense shelf water from being transported farther offshore by eddy flux we suggest that eddy activity on a continental shelf contributes not only to the development of the shelf break front but also to the water exchange between a continental shelf and a slope region

ichnology of a late pleistocene ichnofabric nebraska usa abstract the citellus zone is a regionally extensive biohorizon with abundant burrows and remains of ground squirrels spermophilus citellus and other rodents one hundred and four outcrops were evaluated to determine the stratigraphic relationship of the zone and to confirm its geographic extent citellus zone bioturbation exists over the entire 1700 km2 study area in south central nebraska and was synchronous with mid wisconsinan gilman canyon loess deposition altonian and farmdalian substages since burrow abundances are constant throughout its thickness calculations based upon maximum burrow abundance and the known digging rates of the burrowers confirm that the zone could have been produced during gilman canyon deposition in the lower part of the zone decline in burrow abundance with increasing depth in the loveland formation sangamonian and illinoian stages suggests that this unit predates burrowing thomomys sized geomyid trace fossils become proportionally less common with increasing depth consistent with the transition from fodinichnia to domichnia as spermophilus richardsonii sized spermophiline and prairie dog domichnia become more common

recycling processes in granite granodiorite complex genesis the querigut case studied by ndsr isotope systematics abstract using the isotopic rb sr and sm nd petrogenetic tracers we have studied the calc alkaline plutonic complex of querigut pyrenees france which is famous for its acid to mafic rock association and is a typical post tectonic hercynian granitoid its age of 280 m y is already known 2 23 24 and our purpose is to examine the relationship between its different petrographic units and the problem of their source composition the sm nd isotopic results rule out any genetic process involving a unique homogeneous source and imply the presence of old recycled continental materials in contrast the rb sr isotope system seems to have been homogenized by hot fluids maybe post magmatic this is also true for pb isotopes as shown previously by michard vitrac et al 18 on the basis of the isotopic results and the major element data a model of combined fractional crystallization assimilation of country rocks is proposed for the basic part of the complex in contrast acid parts are mainly the result of the continental anatexis this study also constrains the basement s age 1200 1900 m y of the area and suggests a scheme for the gological history of the eastern pyrenees

three dimensional simulations of overflows on continental slopes abstract three dimensional features and instabilities of dense overflows from marginal seas onto continental slopes are investigated using a three dimensional primitive equation numerical ocean model the numerical simulations reveal important instability and three dimensional features of the overflow plumes that have not been included in previous simulations with a one dimensional streamtube model and a two dimensional plume model it is shown that the large primary plume breaks into a number of smaller subplumes on the offshore side of the plume due to instabilities manifested as growing topographic rossby waves over the slope the observed high temporal and spatial variabilities in the denmark strait overflow could be caused by the inherent dynamic instabilities as revealed by the numerical simulations the simulations indicate that the initial overflow velocity and width the properties of the source water the planetary rotation and the slope steepness play major roles in determining the scales of

importance of melt fraction and source rock composition in crustal genesis the example of two granitic suites of northern portugal in the montalegre area northern portugal two varieties of syn to late tectonic hercynian aluminous granitoids are distinguished 1 1 muscovite rich two mica granites forming many successively emplaced bodies with little chemical variation the chemical characteristics of these units suggest partial melting of various crustal rocks under distinct p t and water saturation conditions there has been no homogenization between the different melt batches the rocks contain very few restitic minerals segregation processes may have operated either in the source rock or in an early magmatic stage 2 2 a cordierite biotite and muscovite bearing granitic body its mineralogical composition is extremely heterogeneous and it contains many xenoliths the genesis of this granite results essentially from partial melting of peraluminous orthogneisses the melt fraction was higher than the rheological critical melt percentage rcmp during anatexis the rigid framework of the source rock broke down leading to migration of both melt and residual minerals towards upper crustal levels the heterogeneity of the resulting granite is mostly related to an incomplete separation of residual crystals and melt the existence of biotite and cordierite rich samples is the result of accumulation of residual minerals during the magma emplacement this study emphasizes the role of the source rock composition which controls the degree of partial melting at given p t and water saturation conditions during crustal melting the strong geochemical differences between the two kinds of granitoids are related to the near absence of residual minerals in the muscovite rich granites and to the presence of residual minerals in the cordierite bearing granite it is suggested that the muscovite rich granites are mostly low melt fraction rcmp the presence of many residual crystals alkali feldspars and plagioclases as well as dark minerals in the cordierite granite implies a high viscosity of the melts and therefore water undersaturated melting conditions

effects of along shore wind on dsw formation beneath coastal polynyas application to the sea of okhotsk 1 it is known that salinity anomaly under a polynya reaches and remains an equilibrium value s after termination of its initial increase associated with brine rejection at the surface in this paper we investigate effect of along shore downwelling favorable wind on the equilibrium salinity anomaly by idealized numerical calculations and scale based estimates numerical calculations showed that high saline water beneath polynya is advected downstream by wind driven circulations over the shelf besides baroclinically developed eddies which consequently induces a decrease in s beneath polynya the downwelling favorable wind generates an offshore overturning flow through lower layers referred to as ekman compensation flow ecf which causes a great offshore salinity flux as well as an along shore current we also constructed an equation for estimation of s from the viewpoint of salinity budget over the polynya region in which lateral salinity fluxes caused by ecf along shore wind driven current and baroclinic eddies are scaled the solution s was also verified by a series of numerical calculations furthermore we investigated the effects of along shore wind on dense water generation beneath the okhotsk coastal polynyas we conducted simplified numerical experiments assuming the okhotsk situation in which fs and offshore width b of polynya are predicted by a thermodynamic polynya model with ecmwf meteorological variables the simulated salinity shows a good agreement with the direct measurements the theoretical estimates for s was also applied to two okhotsk polynyas northwestern polynya nwp and northern polynya np in conclusion we found that the along shore wind causes greater salinity decrease in np than in nwp whose variations substantially depend on the aleutian low activity

a numerical study of dense water formation and transport on a shallow sloping continental shelf the circulation and transport of dense water generated by an idealized coastal polynya is studied using a three dimensional primitive equation model starting with a homogeneous quiescent ocean a constant negative buoyancy flux is imposed at the surface over a half elliptical region adjacent to the coastal boundary on a gently sloping continental shelf the flow response can be divided into the following three phases geostrophic adjustment instability and offshore eddy transport during geostrophic adjustment the fluid within the forcing region becomes denser and the flow at the edge of the forcing region accelerates in response to the strong density gradient there eventually the flow at the leading edge of the forcing region relative to kelvin wave propagation becomes unstable and a train of counterrotating eddies develops these eddies then form a complex three dimensional flow field and rapidly transport dense water offshore across isobaths the density within the forcing region reaches a maximum which remains fairly constant after the eddies begin to transport the dense fluid offshore the results are qualitatively insensitive to weakening of the negative buoyancy forcing and to changing the bottom slope eddy scales and velocities are consistent with observations in the arctic the results suggest that instability processes and eddy fluxes are important in transporting dense water off continental shelves and into marginal seas

eastern european rodent rodentia mammalia faunas from the early middle pleistocene transition abstract the rodent faunas from nine sites on the russian plain and taman peninsula corresponding to the early middle pleistocene transition have been analyzed these localities are situated in the dnieper don dniester and danube drainage basins and in the northern regions of the black and azov seas seven of the sites are associated with the upper part of matuyama reversed polarity chron and located between the beginning of jaramillo event and the brunhes matuyama boundary one of the sites was recovered from the chauda marine deposits of the black sea and referred to the very beginning of brunhes epoch the species composition of the rodent fauna sequence has been established the faunas referred to the jaramillo event 1 1 1 0 ma contain the advanced mimomys steppe lemmings prolagurus pannonicus and lagurodon arankae and allophaiomys pliocaenicus faunas were recovered from korotoyak ostrogozhsk suite roksolany zapadnye kairy and ushkalka localities the more advanced rodent faunas of the morozovian assemblage port katon site include also the first representatives of terricola karai dubina and shamin localities have been found below the brunhes matuyama boundary 0 85 ma including the first representatives of microtus microtus ex gr oeconomus and microtus arvalinus the pitymys like voles microtus stenocranius hintoni steppe lemming p pannonicus and yellow steppe lemming eolagurus argyropuloi compose the core of these faunas the litvin locality located in the deposits of the chauda transgression of the black sea and corresponding to the very beginning of the middle pleistocene contains a rodent fauna closely resembling the shamin one it yielded the remains of mimomys savini advanced a pliocaenicus p pannonicus microtus stenocranius hintoni microtus ex gr oeconomus and mcirotus arvalinus thus numerous data permit elucidation of the history of rodent faunas of the russian plain during early middle pleistocene transitions and reveal the definitive stages in their evolution

a freshwater jet on the east greenland shelf in august 1997 rrs discovery cruise 230 world ocean circulation experiment woce section a25 ran a hydrographic section into cape farewell on the southern tip of greenland the closest approach to the shore was 2 nm in a water depth of 160 m over the east greenland shelf analysis of the hydrographic data conductivity temperature depth ctd vessel mounted acoustic doppler current profiler and thermosalinograph has revealed a current flowing southwestward 15 km wide 100 m deep and centered 10 km offshore we believe it to be driven by meltwater runoff from greenland this feature which we call the east greenland coastal current egcc carries a little less than 1 sv 106 m3 s 1 with peak current speeds of 1 m s 1 at the surface the center of the egcc lies on a salinity front with maximum salinity contrast 4 practical salinity units psu between coast and shelf break and between surface and bottom a spot value of freshwater transport is 0 06 sv 1800 km3 yr 1 which is equivalent to 30 of the arctic freshwater gain the presence of the egcc and its continuity up the east greenland coast as far as denmark strait is confirmed in satellite sea surface temperature images and surface drifter tracks we estimate the sensitivity of its freshwater flux to changes in melt season mean surface air temperature to be 25 per 1 c

eddy driven exchange between the open ocean and a sub ice shelf cavity the exchange between the open ocean and sub ice shelf cavities is important to both water mass transformations and ice shelf melting here we use a high resolution 500 m numerical model to investigate to which degree eddies produced by frontal instability at the edge of a polynya are capable of transporting dense high salinity shelf water hssw underneath an ice shelf the applied surface buoyancy flux and ice shelf geometry is based on ronne ice shelf in the southern weddell sea an area of intense wintertime sea ice production where a flow of hssw into the cavity has been observed results show that eddies are able to enter the cavity at the southwestern corner of the polynya where an anticyclonic rim current intersects the ice shelf front the size and time scale of simulated eddies are in agreement with observations close to the ronne ice front the properties and strength of the inflow are sensitive to the prescribed total ice production flushing the ice shelf cavity at a rate of 0 2 0 4 106 m3 s 1 depending on polynya size and magnitude of surface buoyancy flux eddy driven hssw transport into the cavity is reduced by about 50 if the model grid resolution is decreased to 2 5 km and eddies are not properly resolved

the dispersal of dense water formed in an idealized coastal polynya on a shallow sloping shelf abstractthis study examines the dispersal of dense water formed in an idealized coastal polynya on a sloping shelf in the absence of ambient circulation and stratification both numerical and laboratory experiments reveal two separate bottom pathways for the dense water an offshore plume moving downslope into deeper ambient water and a coastal current flowing in the direction of kelvin wave propagation scaling analysis shows that the velocity of the offshore plume is proportional not only to the reduced gravity bottom slope and inverse of the coriolis parameter but also to the ratio of the dense water depth to total water depth the dense water coastal current is generated by the along shelf baroclinic pressure gradient its dynamics can be separated into two stages i near the source region where viscous terms are negligible its speed is proportional to the reduced gravity wave speed and ii in the far field where bottom drag becomes important and balances the pressure gradient the velocity i

akhalkalaki the taphonomy of an early pleistocene locality in the republic of georgia as part of our investigations into the potential of the republic of georgia for providing information on early hominin occupation of eurasia we report here on akhalkalaki a large late early pleistocene locality located along the lower slopes of a miocene andesitic cone originally excavated in the 1950s as a palaeontological site it was re opened in the 1990s and stone tools were found associated with the fauna suggesting that it is also an archaeological occurrence excavations in the 1950s and 1990s uncovered thousands of bones of an early galerian fauna including the remains of new species of hippopotamus equus and canis vekua 1962 1987 and dominated by the remains of equus

re evaluation of lead isotopic data southern massif central france three independent pb isotope homogenizing processes operating on large volumes of rock material during limited intervals in the phanerozoic have been used to define a unique evolutionary curve for rock and ore lead isotopic compositions of the southern massif central france the model is begin gathered text x text t 18 641 text text 9 text 56 e text l1 t 1 text hfill text y text t 15 678 text text 0 text 06934 e text l2 t 1 text hfill text z text t 38 701 text text 30 text 8 e text l3 t 1 text hfill end gathered where xt yt and zt are the calculated isotopic ratios 206pb 204pb 207pb 204pb and 208pb 204pb respectively at time t years ago and l1 l2 and l3 are the decay constants of 238u 235u and 232th respectively the model gives the following ages for averages of the three sets of data used in its generation age of mineralization for carbonate hosted lead zinc ore of les malines ca 150 ma emplacement of the saint guiral liron granite ca 290 ma and an estimated average age of a group of cambrian syngenetic deposits ca 520 ma these ages are in close agreement with ages determined by independent methods

effects of ambient stratification and shelfbreak topography on offshore transport of dense water on continental shelves the transport of dense water offshore from an idealized coastal polynya is examined using a primitive equation numerical model first the prior scaling of the equilibrium density of water produced within the polynya is extended to include the effects of linear bottom slope next ambient linear stratification is added the equilibrium density is modified slightly by the density at the bottom at the initial time next shelfbreak topography is included with both weak and strong ambient stratification for the case of weak stratification dense water carried to the shelfbreak within eddies moves rapidly downslope and is trapped near the bottom the along shelf scale of the dense water cascading down the slope is set by the diameter of the dense water eddies that form along the periphery of the coastal polynya for the case of strong stratification dense water is carried offshore across the shelfbreak at an intermediate depth injecting water originally within the polynya across the shelf and over the continental slope a bottom trapped current flowing near the shelfbreak in the direction of coastal trapped wave propagation also forms these results suggest that water formed within coastal polynyas over arctic shelves may be capable of ventilating the continental slope regions and possibly central basins of the arctic ocean via eddy fluxes

baseline determination of the atmospheric pb sr and nd isotopic compositions in the rhine valley vosges mountains france and the central swiss alps abstract the pb sr and nd isotopic compositions of biomonitors lichen moss bark and soil litter from different regions in the rhine valley as well as of

stratigraphy and environmental reconstruction at the middle wisconsinan gilman canyon formation type locality buzzard s roost southwestern nebraska usa abstract the middle wisconsinan gilman canyon formation at the buzzard s roost type locality in southwestern nebraska was investigated to document the stratigraphy and to reconstruct the environmental and climate record the gilman canyon formation was subdivided into three loess units and three soils with radiocarbon ages constraining it between about 40 ka and 25 ka stable carbon isotope ratios magnetic susceptibility and carbon content were used to define and characterize soils within both the gilman canyon formation and underlying illinoian loveland loess at the height of soil development within the gilman canyon formation climate was supporting c4 dominated grassland with july temperatures equal to or exceeding those of today soil forming intervals within the loveland loess including the sangamon soil also exhibited relative increases in c4 biomass climate as recorded in the gilman canyon formation is corroborated by regional proxy data the formation accumulated during mis 3 and concurrent soil formation coincided with a summer insolation maximum

krotovinas soil archives of steppe landscape history abstract krotovinas the burrows of small mammals are common phenomena in steppe landscapes and for a long time they have been a major point of discussions about the genesis of holocene chernozems in addition krotovinas provide a very valuable archive of the biological activities of soil which is essential when stratigraphical ambiguities are to be solved despite this krotovinas have received little attention within pedostratigraphical research using the example of the upper palaeolithic excavations kostienki and borshchevo in the middle russian steppe an integrative soil scientific approach highlights the importance of burrowing small mammals and of krotovina fillings resulting from both bioturbation and soil erosion in the late pleistocene based on field and laboratory data of sediments inside and outside krotovinas and 14c dating results from two sections this systematic approach demonstrates the high value of the burrow fillings black and humus speckled fillings belong to deep burrows of hamsters dating to the period of early holocene chernozem formation at the very beginning of the preboreal 10 8 ka cal bc greyish sediments originate either from ag bg horizons of the gmelin soil 25 22 ka or from other as yet unknown late valdai paleosols these fillings are the result of the activities of shallow burrowing lemmings in addition burrow fillings have provided optimal material for worms also fossil bones and teeth found within krotovina fillings give new insights into the occurrence of cricetus cricetus and lagurus lagurus in this part of the middle russian steppe

dynamics of isolated convective regions in the ocean abstract an initially resting ocean of stratification n is considered subject to buoyancy loss at its surface of magnitude b0 over a circular region of radius r at a latitude where the coriolis parameter is f initially the buoyancy loss gives rise to upright convection as an ensemble of plumes penetrates the stratified ocean creating a vertically mixed layer however as deepening proceeds horizontal density gradients at the edge of the forcing region support a geostrophic rim current which develops growing meanders through baroclinic instability eventually finite amplitude baroclinic eddies sweep stratified water into the convective region at the surface and transport convected water outward and away below setting up a steady state in which lateral buoyancy flux offsets buoyancy loss at the surface in this final state quasi horizontal baroclinic eddy transfer dominates upright plume convection by using parcel theory to consider the energy transformations taking place it is shown that the de

occurrence formation and micromorphology of gypsum in soils from the central german chernozem region occurrence of gypsum in soils from loess of the central german chernozem region indicates that local climatic conditions with low precipitation average 500 mm a 1 and a real evaporation between 450 and 460 mm do not allow leaching of weakly soluble gypsum from soils at a site close to the strip mine etzdorf gypsum is accumulated in the ck horizon of a haplic chernozem down to a depth of about 1 5 m its distribution being nonuniform calculated total gypsum in the haplic chernozem amounts from 10 20 t ha 1 the highest accumulation of gypsum obviously by solution transport and evaporation can be observed in a profile exposed to the air since about 1960 in this profile maximum so42 values however are not found on the surface of the outermost aggregates with whitish efflorescence but at 20 cm depth in the profile in a eutric podzoluvisol the precipitation of gypsum developed on living roots as well as in pores of former roots in a buried chernozem large euhedral gypsum crystals with a diameter of up to 1 5 cm were found gypsum crystals occur in different shapes and sizes such as euhedral lenticular rosette like and equigranular ones even soils having undergone leaching processes reveal unusual increases of so42 at 40 50 cm depth this may be an indicator of more recent so42 input due to atmospheric deposition since the beginning of industrialization it is supposed that gypsum is formed by the reaction of atmogenic sulfuric acid with different ca sources in the soil

pre hercynian mantle lead transfer to basement rocks as indicated by lead isotopes of the schwarzwald crystalline sw germany ii lead isotope evolution of the european hercynides

isotopic evidence of lead sources in loire river sediment sediments along the loire river central france were investigated by means of pb isotopes determined on the labile sediment fraction or acid extractable matter aem the combination of trace elements and pb isotopes allows deciphering the origin of the elements i e natural or anthropogenic and their history in the sediment from two small watersheds one draining basalt the other one granite gneiss both in present day suspended matter in loire river water and in sediment from the loire estuary crustal weathering as confirmed by the pb isotope ratios for most sample points is the main source of pb in the upstream part of the loire river as well as that transported in the middle part of the basin and in the estuary among anthropogenic sources the use of pb isotopic compositions shows an influence of agriculturally derived pb inputs and a major input of pb derived from gasoline particularly in the estuary due to harbor activities

geochemical investigations of the origin of the manaslu leucogranite himalaya nepal the himalayan orogeny is characterized by an intraplate subduction zone the thrusting of the tibetan slab over the foreland is probably responsible for the origin of the manaslu type leucogranites this geochemical study tries to examine the crustal origin of the granite to verify whether the paragneisses of the tibetan slab are the most probable parent material and to determine the subsequent petrogenetic processes the rb sr systematics suggest that 1 1 the scatter of data points in the 87sr86srvs 87rb86sr diagram may be due to the heterogeneity of the initial 87sr86sr ratios 2 2 the initial isotopic ratios are very high 0 730 0 760 and are in agreement with those of the gneisses of the tibetan slab at the time of the melting pb isotopic ratios are homogeneous they are also consistent with a crustal prehistory the ree and th contents are unexpectedly low in comparison with the much higher contents of the parent material monazite left in the residue of melting or more probably extracted in an early stage of the magmatic history may explain the observed ree and th abundances alternatively field observations show that the emplacement of the granite has been accompanied by a very strong hydrothermal activity in consequence the low ree and th contents of the granite could also be due to the loss by solution during prolonged fluid circulation throughout the granitic melt and the sr and pb isotope distribution to the effect of late to post magmatic fluids the isotopic character of which was determined by the underlying tibetan slab

the destruction of lenses and generation of wodons abstract since midocean eddies migrate westward they eventually reach the western boundaries it is therefore of interest to find out what happens after the eddies collide with the walls an isopycnic two layer primitive equation model on a plane and a simple analytical model on an f plane are constructed to investigate the meridional migration of an oceanic eddy along a western wall on a plane three factors determine the eddy s migration along a western meridional wall first the image effect pushes an anticyclonic cyclonic eddy northward southward second the force resulting from the larger coriolis force on the northern side of the eddy pulls an anticyclonic cyclonic eddy southward northward third after an anticyclonic cyclonic eddy collides with the wall parts of the anticyclonic eddy s interior fluid leak out southward northward along the wall forming a thin jet in an analogy to a rocket this jet pushes the eddy northward southward our aim is to investigate in whi

the quartz diorites of limousin elemental and isotopic evidence for devono carboniferous subduction in the hercynian belt of the french massif central a chain of late devonian early carboniferous intrusions on the western margin of the french massif central the limousin tonalite belt consists of quartz diorites which are unusual among french hercynian granitoids in their low silica contents 53 68 wt sio2 and abundant hornblende they represent the earliest and most primitive plutonism post dating the main phase of hercynian metamorphism and have chemical characteristics strongly resembling andesitic lavas of calc alkaline affinity they differ from other massif central hercynian granitoids in their low 87sr86sr360 0 7047 0 7059 and high nd360 0 7 to 1 8 their initial pb composition was rather homogeneous 206pb204pb360 18 15 18 38 207pb204pb360 15 57 15 62 208pb204pb360 38 06 38 26 and their 207pb204pbi values are significantly lower than those of other hercynian granitoids the limousin quartz diorites are considered to have originated from an enriched mantle with characteristics modified by subduction of oceanic crust and terrigenous sediments the primitive quartz dioritic magmas were then contaminated in the lower continental crust by an afc process involving acid metaigneous or metasedimentary lithologies the occurrence of such plutons in the earliest phase of hercynian plutonism in the massif central is probably related to minor subduction at an active continental margin

pre hercynian mantle lead transfer to basement rocks as indicated by lead isotopes of the schwarzwald crystalline sw germany lead isotopes of k feldspars from five granites of the se schwarzwald and from metamorphites are positively correlated in 207 204 as well as 208 204 vs 206 204 diagrams

a two level wind and buoyancy driven thermocline model abstract a simple two level model is designed to simulate the thermocline equations applicable for large scale steady oceanic flow the model serves two functions first it replaces problems with the interpretation of slablike dynamics e g luyten et al 1983 by using continuously horizontally varying buoyancy but at the cost of reducing the vertical resolution drastically the equations used are geostrophy plus a small linear drag to close a stommel like western boundary layer mass conservation and buoyancy conservation with a small but necessary horizontal diffusion inclusion of vertical diffusion has little effect the ocean is driven by an ekman layer whose functions are to provide a given surface input of mass through ekman pumping and buoyancy through a specified buoyancy in the ekman layer i e to maintain the same boundary conditions as in classical thermocline studies sidewall conditions are not well understood and are almost certainly over specified in this formulation s

generation of submesoscale vortices a new mechanism small scale intense vortices composed of water with anomalous values of quasi conservative tracers have been observed in many oceans they are particularly numerous in the beaufort gyre of the arctic ocean possible mechanisms responsible for the generation of these features are examined conservation of temperature salinity and nutrients requires that beaufort sea vortices be created from water that flows into the arctic ocean from the pacific ocean across the broad shallow chukchi sea much of this water passes through barrow canyon near point barrow alaska observations in the canyon show the generation of vortices of approximately the same size as those observed in the beaufort sea barrow canyon is therefore a likely site for the generation of beaufort sea vortices most observed beaufort sea vortices have a central potential vorticity near zero because of a relative vorticity close to their chukchi sea source water is typically stratified with little relative vorticity so that its potential vorticity is nonzero a key step in the generation of the vortices is therefore the reduction of the potential vorticity of chukchi sea water to nearly zero it is proposed that this occurs through the action of frictional torques occurring as the chukchi sea water flows through barrow canyon rather than througji the action of vertical mixing because this flow is driven by a downstream pressure gradient it is concentrated on the right hand wall of the canyon by the coriolis force the frictional torques thus preferentially reduce the potential vorticity of the fluid anticyclonic vortices are therefore preferentially generated it is suggested that a similar scenario may play a role in the generation of submesoscale vortices containing water from the mediterranean and labrador seas

pb isotope systematics and time integrated th u of se asian continental crust recorded by single k feldspar grains in large rivers abstract to elucidate time integrated th u and pb isotope characteristics of the se asian continent 159 individual k feldspar grains from the rivers mekong salween irrawaddy and red river were analyzed earlier u pb dating and hf isotope results of zircon and baddeleyite from the same river sands have established its crustal growth and recycling history also showing that these heavy minerals are sufficiently representative for the evolution of large continental regions geochim cosmochim acta 64 2000 2067 we therefore consider k feldspar populations in these sands to be the best possible way to investigate pb isotope systematics on the continental scale and analyzing individual grains overcomes the averaging effect of multi grain measurements to test the basic condition that u pb ratios are very low in k feldspar pb concentration were measured in all grains and u in about 10 of them corroborating pb concentrations between 4 and 292 ppm with a mean value of 80 40 ppm and u and th well below 0 1 and 0 4 ppm respectively in situ decay of u can therefore be neglected in all grains and measured pb isotope ratios are those acquired by the magmatic or metamorphic host material at the time of k feldspar crystallization relative to the model evolution of 206 pb 204 pb in upper continental crust model ages range between 0 5 and 0 2 ga whereas many 207 pb 204 pb are significantly more radiogenic than any type of phanerozoic crust this confirms important recycling of precambrian crust into the k feldspar source material such as already observed by hf signatures for the heavy mineral source lithologies an important observation is that none of the k feldspars has preserved precambrian pb isotope signature and in consequence detrital sediments covering the se asian continent must essentially originate from phanerozoic orogenic belts where k feldspars have been re equilibrated by metamorphic reactions or crystallization in newly formed melts to dominate delivery of detrital material to such a large extent on the continental scale these phanerozoic orogenies must have generated important high mountains ranges to be subsequently flattened by erosion today topographic highs are exclusively due to uplift in relation to the india asia collision concerning 232 th 208 pb and time integrated th u ratios only 4 out of 159 grains plot on the model curves for continental crust with all other ratios being significantly more radiogenic in 208 pb 204 pb indicating high th u source material if these time integrated th u ratios are modeled in the frame of the known crust formation events th u ratios lie at 4 15 4 22 plotting significantly higher than th u deduced for fine grained sediments or predicted by classical models for average or upper continental crust

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