enhanced diapycnal mixing in the south china sea profiles of current velocity temperature and salinity were obtained in the internal wave and mixing experiment in the south china sea scs the luzon strait and the north pacific the observations are examinedforevidenceofenhanceddiapycnalmixinginthescs whichreacheso 10 23 m 2 s 21 inmagnitude resultsfrom independent casts reveal that diapycnal diffusivity in the scs andthe luzon strait is elevatedby two orders of magnitude over that of the smooth bathymetry in the north pacific which are typical of background values in an open ocean the vertical distribution of diapycnal diffusivity is nonuniform in the scs exhibiting higher values at depths greater than about 1000 m this result compares favorably with the direct microstructure measurements at four stations in the scs velocity and density profiles are combined to estimatetheinternaltideenergyfluxgeneratedintheluzonstraitanddirectedintothescs theenergyamounts to 10 gw most of which is rationalized to be the potential energy source for enhanced mixing in the scs

dynamical mechanisms for the south china sea seasonal circulation and thermohaline variabilities abstract the seasonal ocean circulation and the seasonal thermal structure in the south china sea scs were studied numerically using the princeton ocean model pom with 20 km horizontal resolution and 23 sigma levels conforming to a realistic bottom topography a 16 month control run was performed using climatological monthly mean wind stresses restoring type surface salt and heat and observational oceanic inflow outflow at the open boundaries the seasonally averaged effects of isolated forcing terms are presented and analyzed from the following experiments 1 nonlinear dynamic effects removed 2 wind effects removed and 3 open boundary inflow outflow set to zero this procedure allowed analysis of the contribution of individual parameters to the general hydrology and specific features of the scs for example coastal jets mesoscale topographic gyres and countercurrents the results show that the pom model has the capability of simulating seasonal variations of the scs circulation and thermoha

south china sea isopycnal surface circulation this paper investigates the seasonal variabilities of the south china sea isopycnal surface circulations and of the kuroshio intrusion through the luzon strait using the u s navy s climatological temperature and salinity dataset public domain with 83 8 resolution by the p vector method the representative pattern is a persistent basin scale cyclonic circulation away from the surface and a seasonally varying circulation with a weak anticylonic gyre in the summer and a strong cyclonic gyre in the winter near the surface this pattern is consistent with a classical view of mean cyclonic circulation in large stratified lakes and semienclosed marginal seas by emery and csanady and with a recent numerical simulation using the navy s layered ocean model by metzger and hurlburt the computed monthly volume transport through the luzon strait is negative inflow all year round with a minimum value of 213 7 sv in february strongest intrusion and a maximum value of 21 4 sv in september weakest intrusion the annual mean transport is 26 5 sv intrusion

kornerupine sensu stricto associated with mafic and ultramafic rocks in the lutzow holm complex at akarui point east antarctica what is the source of boron

the influence of paleogeography in epicontinental seas a case study based on middle devonian strata from the mackenzie basin northwest territories canada abstract the history of middle devonian sea level changes are recorded in the chinchaga formation lonely bay formation horn plateau formation and the horn river formations that originated in the mackenzie basin which is located in the southern northwest territories canada these strata record an almost consistent sea level rise throughout the middle devonian with punctuated deepenings deposition began in the mackenzie basin in the eifelian with restricted shallow water evaporites and dolomites of the chinchaga formation overlying the chinchaga formation are the open marine carbonates belonging to the lonely bay formation which were overlain by the horn plateau formation buildups pelagic shales of the horn river formation in the late givetian early frasnian later covered these buildups during the early and middle devonian many continental basins in north america had limited interactions with open ocean waters these restricted shallow water basins were vulnerable to the effects of clastic shedding and evaporitic drawdown that commonly caused local lowstands several of these shallow basins including the mackenzie basin have been used to construct devonian sea level curves comparison of the middle devonian strata that formed in the mackenzie basin with well established sea level curves shows that the late givetian regression interpreted from some of those successions is not evident in the succession found in the mackenzie basin this probably reflects the fact that the mackenzie basin was directly linked to the open ocean and was not influenced by the changes in sea level that affected many of the enclosed basins

sedimentary responses to sea level rise and kuroshio current intrusion since the last glacial maximum grain size and clay mineral evidence from the northern south china sea slope abstract we analyzed the terrigenous fraction of a sediment core from the northern slope of the south china sea to better understand the depositional history of the region since the last glacial maximum lgm temporal variations in the grain size and clay mineral composition revealed a complex set of overlapping controls approximately 90 of terrigenous sediment throughout the core ranged in size from 5 5 to 8 5 with the 5 25 6 25 size class being particularly sensitive to environmental changes the proportion of this fraction decreased during deglacial indicating a reduction in the supply of coarser grains due to coastline retreat as the sea level rose toward its present position the relative proportion of clay derived from taiwan increased however the mass accumulation rate of taiwan derived clay decreased suggesting a reduction in the westward bottom current intensity in contrast the relative contribution of clay from the pearl river decreased from 40 during the lgm to 5 when the sea level reached 70 m below its present position the pearl river contribution has remained consistently low throughout the holocene indicating that shore parallel circulation patterns on the shelf resembled their present configuration by 13 ka compared to taiwan and the pearl river the proportion of clay derived from the area east of pearl river epr was relatively minor and less variable a local peak in the relative contribution from this area occurred during a melt water pulse event mwp 1a suggesting that a reservoir of smectite rich clays residing in coastal bays was remobilized by this marine transgression spectral analysis of the relative contributions of the three major clay sources revealed a significant periodicity of 380 years which may reflect changes in solar insolation modulating the flux of clay minerals from taiwan and the pearl river to the deposition site on a centennial scale

the arctic and subarctic ocean flux of potential vorticity and the arctic ocean circulation according to observations the arctic ocean circulation beneath a shallow thermocline can be schematized by cyclonic rim currents along shelves and over ridges in each deep basin the circulation is also believed to be cyclonic this circulation pattern has been used as an important benchmark for validating arctic ocean models however modeling this grand circulation pattern with some of the most sophisticated ocean ice models has been often difficult the most puzzling and thus perhaps the most interesting finding from the arctic ocean model intercomparison project aomip an international consortium that runs 14 arctic ocean models by using the identical forcing fields is that its model results can be grouped into two nearly exact opposite patterns while some models produce cyclonic circulation patterns similar to observations others do the opposite this study examines what could be possibly responsible for such strange inconsistency it is found here that the flux of potential vorticity pv from the subarctic oceans strongly controls the circulation directions for a semienclosed basin like the arctic the pv integral over the whole basin yields a balance between the net lateral pv inflow and the pv dissipation along the boundary when an isopycnal layer receives a net positive pv through inflow outflow the circulation becomes cyclonic so that friction can generate a flux of negative pv to satisfy the integral balance for simplicity a barotropic ocean model is used in this paper but its application to the 3d models will be discussed in the first set of experiments the model with a realistic arctic bathymetry is forced by observed inflows and outflows in this case there is a net positive pv inflow to the basin due to the fact that inflow layer is thinner than that of outflow the model produces a circulation field that is remarkably similar to the one from observations in the second experiment the model bathymetry at fram strait is modified so that the same inflows and outflows of water masses lead to a net negative pv flux into the arctic the circulation is reversed and becomes nearly the opposite of the first experiment in the third experime nt the net pv flux is made to be zero by modifying again the sill depth at fram strait the circulation becomes two gyres a cyclonic one in the eurasian basin and an anticyclonic one in the canada basin to elucidate the control of the pv integral a second set of model experiments is conducted by using an idealized arctic bathymetry so that the pv dynamics can be better explained without the complication of rough topography the results from five additional experiments that used the idealized topography will be discussed while the model used in this study is one layer the same pv integral constraint can be applied to any isopycnal layer in a threedimensional model variables that affect the pv fluxes to this density layer at any inflow outflow channel such as layer thickness and water volume flux can affect the circulation pattern the relevance to 3d models is discussed in this paper

pan african extension and near isothermal exhumation of a granulite facies terrain dronning maud land antarctica t he m uhlig hofmann and filchnerfjella in central dronning maud land antarctica consist of series of granitoid igneous rocks emplaced in granulite and upper amphibolite facies meta morphic rocks the area has experienced high temperature metamorphism followed by near isothermal decompression partial crustal melting voluminous magmatism and extensional exhumation during the later phase of the late neoproterozoic to cambrian pan african event remnants of kyanite garnet ferritschermakite rutile assemblages indicate an early higher pressure metamorphism and crustal overthickening the gneisses experienced peak granulite facies temperatures of 800 900 ca t intermediate pressures breakdown of garnet sillimanite spinel bearing assemblages to cordierite shows subsequent re equilibration to lower pressures an e w foliation dominating the gneisses illustrates transposition of migmatites and leucocratic melts which evolved during the near isothermal decompression occurrence of extensional shear bands and shear zones evolving from the ductile partial melting stage through semiductile towards brittle conditions shows that the uplift persisted towards brittle crustal conditions under tectonic w sw vergent extension late orogenic pan african quartz syenites intruded after formation of the main gneiss fabric contain narrow semiductile to brittle shear zones illustrating that the extensional exhumation continued also after their emplacement the latest record of the pan african event is late magmatic fluid infiltration around 350 400 c and 2 kbar at this stage the pan african crust had undergone 15 20 km exhumation from the peak granulite facies conditions we conclude that the later phase of the pan african event in central dronning maud land is characterized by a near isothermal decompression p t path and extensional structures indicating tectonic exhumation which is most likely related to a late orogenic collapsing phase of the pan african orogen

progressive shape evolution of a mineral inclusion under differential stress at high temperature example of garnet inclusions within a granulite facies quartzite from the lutzow holm complex east antarctica due to the size independency of dislocation creep assuming ggrtqtz 1 0 nm 1 dgb a 1 0 10 12 m 2 s 1 dgb b 1 0 10 11 m 2 s 1 and sa 1 0 mpa the garnet data are fitted to a theoretical curve under condition of sb 1 4 10 2 mpa ta 0 5 myr and

aluminous granulites from the pulur complex ne turkey a case of partial melting efficient melt extraction and crystallisation abstract in the pulur complex ne turkey a heterogeneous rock sequence ranging from quartz rich mesocratic gneisses to silica and alkali deficient fe mg and al rich melanocratic rocks is characterized by granulite facies assemblages involving garnet cordierite sillimanite ilmenite spinel plagioclase quartz biotite corundum rutile and monazite textural evidence for partial melting in the aluminous granulites particularly leucosomes is largely absent or strongly obliterated by a late stage hydrothermal overprint however inclusion relations high peak p t conditions the refractory modes bulk and biotite compositions of the melanocratic rocks strongly support a model of partial melting the melt was almost completely removed from the melanocratic rocks and crystallised within the adjacent mesocratic gneisses which are silica rich bear evidence of former feldspar and show a large range in major element concentrations as well as a negative correlation of most elements with sio2 peak conditions are estimated to be 800 c and 0 7 0 8 gpa subsequent near isothermal decompression to 0 4 0 5 gpa at 800 730 c is suggested by the formation of cordierite coronas and cordierite spinel symplectites around garnet and in the matrix sm nd rb sr and 40ar 39ar isotope data indicate peak conditions at 330 ma and cooling below 300 c at 310 ma

the assessment of ree patterns and 143nd 144nd ratios in fish remains abstract the ree content and isotopic composition of sr and nd have been determined in fish teeth ranging in age from the trias to the present and from various localities mostly around the atlantic these measurements have been carried out on selachian and teleost remains from the same locality in togo and show no appreciable difference which suggests with the help of a mass balance calculation of the ce anomaly that diagenetic effects are not responsible for the ree enrichment of biogenic phosphates one group of fossil teeth has about 3 times the ree abundances of shale and a shale normalized pattern with a minimum at sm it is thought to reflect deposition in the open sea environment a second group has ree concentration about 10 times higher than the first group with either a regular light ree enrichment or more frequently a maximum in the middle ree both being probably indicative of deposition in estuarine or near shore conditions the shape of the ree spectra and the size of the ce anomaly can be used semi quantitatively to determine the depth of deposition the results presented here on late cretaceous eocene fish teeth samples from morocco reflect an increasing influx of deep waters with a lowla yb ratio and strong negative ce anomaly which agrees well with the evolution of sediment chemistry and microfauna associations in contrast nd is typical of the water mass in which the fish debris decayed examples of nearly isolated basins identified with nd isotopes include the south atlantic prior to the lutetian nd 13 5 the miocene persian gulf nd 3 1 and bolivia during the late cretaceous nd 12 8 togo and guinea bissau results suggest that in the south atlantic the meridional oceanic circulation had not started before 45 ma ago combination of ree and nd data suggests that the assignment of jurassic cretaceous samples measured so far to open sea water masses is still ambiguous

internal waves as controlling factor in the development of stromatoporoid rich facies of the apulia platform margin upper jurassic lower cretaceous gargano promontory italy abstract during the late jurassic stromatoporoid rich buildups were developed in south and intra tethys realms these stromatoporoid buildups are mainly characterized by the high percentage of intraclastic bioclastic debris as main components of buildup bodies however the source of hydrodynamic energy resulted in debris production is still a matter of debate this study examines the upper jurassic lower cretaceous stromatoporoid rich buildups of monte sacro limestones msl apulia carbonate platform acp in order to describe the main carbonate facies along the study area as well as the possible source of turbulence three main lithofacies have been distinguished lf1 stromatoporoid rich facies with two subfacies lf1 s1 floatstone with wackestone to fine grained packstone lf1 s2 rudstone floatstone with intraclastic bioclastic packstone grainstone lf2 stromatoporoid coral facies distributed in wackestone to packstone matrix lf2 s1 and tabular stromatoporoid corals surrounded by wackestone matrix lf2 s2 and lf3 stromatoporoid microbial facies these facies were deposited along the mid part of a distally steepened ramp the in situ form of stromatoporoids was developed in a mud dominated matrix lf1 s1 under low energy conditions while the intraclastic bioclastic rich facies lf1 s2 were deposited under a high energy condition the distribution of lf2 and lf3 in muddy matrix suggests occurrence of these lithofacies in quiet environments the biotas were influenced by several factors including nutrient and light availability as well as by hydrodynamism the stromatoporoid rich buildups in acp can be categorized as phototrophic heterotrophic reefs generated in a pure carbonate environment the light penetration was confined resulted in the high development of light independent micro encrusters tubiphytes morronensis in a mesophotic condition where the environment was not ideal for light dependent microencrusters lithocodium bacinella to grow we suggest that debris dominated stromatoporoid rich lithofacies lf1 thrived in meso oligophotic setting along the nutricline and were affected by more than episodic high energy events in a context where the surface waves were not effective in such environments internal waves can be an effective candidate to explain the episodic turbulences to produce the debris rich facies of lf1 s2 moreover internal waves can pump the nutrient rich waters to the buildups and create an ideal setting where these metazoan communities thrived

upward flow of north pacific deep water in the northern south china sea as deduced from the occurrence of drift sediments 1 reflection seismic profiles show that drift sediments occur in the depth range of 1200 2800 m on the continental margin off southeast china these drift deposits were generated by upward flow near the dongsha islands of the north pacific deep water npdw which enters the south china sea via the bashi channel sill depth 2500 m this flow results in deposition of slope sediments resuspended off east and south taiwan on the slope southeast of the dongsha islands at 1200 m water depth this upward flow probably terminates and the npdw mixes with the surface water sediment ages from odp site 1144 southeast of the dongsha islands show that this process started at least 1 1 m y ago indications for mass wasting in the area of upslope water flow document the simultaneous occurrence of current and gravity controlled sedimentation processes however bottom current related drift sedimentation dominates

evaluation of the application of rare earth elements to paleoceanography anomalous departures of rare earth elements ree from similarity of chemical behaviour are most evident in a comparison of ce with its neighbors under reducing conditions ce3 acts like other ree but oxidized ce4 is adsorbed on mn fe oxyhydroxides or organic particulates and consequently the remaining solution will tend to exhibit a negative ce anomaly in addition more subtle fractionations may emphasize the light or the heavy or the middle ree a pattern of ree may be recorded by immediate diagenesis on a suitable chemical substrate such as apatite fish debris conodonts carbonate or chert this record was originally thought to reflect the paleoredox conditions of primary deposition however any such primary record may be overprinted by late diagenetic alteration early analyses of ree in conodonts from a wide range of sediments suggested a prevalence of reducing conditions no ce anomaly in pre carboniferous oceans and more common oxidation negative ce anomaly in the late paleozoic however recent research by other investigators indicates that variations in cean are more diverse in origin and in particular many are distorted to an unknown extent by late diagenesis in any case it is now clear that geological age does not show a consistent relationship to the level of the ce anomaly the ce anomaly apparently does not play any regular role in the isotopic events that accompany prominent mass extinctions further research is required to understand and thus make useful the controls on the ce anomaly

the behavior of rare earth elements in seawater precise determination of variations in the north pacific water column abstract we present new highly precise and accurate data for ten rare earth elements rees in two water column profiles and in bottom waters from three additional localities in the north pacific our results presented here and in an earlier publication indicate that the water column in the western north pacific is stratified with respect to the isotopic composition of nd as well as nd la sm nd and er la both the nd isotopic and the ree data show that ree transport is strongly influenced by horizontal advection even in the sluggish circulation of the pacific in general rees increase in concentration with depth at mid latitude they reach a maximum concentration at about 3000 m and then decrease to the bottom at high latitude heavy rees reach a maximum concentration near 3000 m whereas light rees continue to increase in concentration with depth the deep water maximum and bottom water depletion is interpreted as an advective feature resulting from the flow of a lower concentration of rees in antarctic bottom water under a higher concentration of rees in the north pacific concentrations of rees do not show a linear relationship with those of si indicating that the ree cycle is not directly coupled to that of the si cycle ree element ratios i e nd la correlate with hydrographie properties which suggests that major features of the ree patterns may be conserved during lateral transport comparison of our ree data to those in previously published reports on pacific seawater shows that the identification of ree distributions affected by advection is only made possible by the high precision analysis we developed for this study the ce concentration we observe is relatively constant over 200 4500 m depth at both sites where we have complete profiles this unique constancy of ce is in contrast to the contiguous rees la and nd which show substantial concentration variations with depth

stability of pargasite during ultrahigh temperature metamorphism a consequence of titanium and ree partitioning orthopyroxene clinopyroxene plagioclase needles and symplectite along the cleavage planes and grain boundaries of fluorine bearing titanian ferroan pargasite from the highland complex sri lanka are interpreted as evidence for dehydration melting at ultrahigh temperature conditions high ti up to 0 4 pfu and f x f up to 0 56 content in pargasite extends its stability to higher temperatures and the composition indicates the dehydration melting reaction may take place at ultrahigh temperatures 950 c at a pressure around 10 kbar close to peak metamorphic conditions the increase of ti content close to the grain boundaries and cleavage planes in pargasite indicates titanium partitioning from the melt during dehydration melting enhanced the stability of the mineral toward ultrahigh temperature conditions the ree content in the pargasite shows a similar behavior to that of titanium the cores with no breakdown assemblage consist of low and flat ree concentrations with respect to the high and eu depleted rim clinopyroxene in symplectite and needle shaped lamellae within the pargasite porphyroblasts have similar ree patterns with slightly low concentrations relative to that of pargasite in the breakdown assemblage lrees are partitioned mainly into plagioclase while the hrees are partitioned into orthopyroxene the ree enrichment in the pargasite rims signals their relative partitioning between pargasite rims and melt modeling of the partitioning of ti and rees associated with pargasite breakdown demonstrates that its stability is greatly enhanced at uht conditions this investigation implies that the stability of hydrous minerals such as amphibole can be extended to uht conditions and expands our knowledge of metamorphism in the lower crust

carbonate systems along nutrient and temperature gradients some sedimentological and geochemical constraints research over the past several decades has clearly demonstrated that changes in the ocean environment have had major impacts on carbonate systems changes in climate ocean circulation and seafloor spreading rates have influenced temperature and seawater chemistry including carbonate saturation state and nutrient availability and thereby have determined boundary conditions for the biota that form carbonate platforms in turn the biota determine accumulation rates and facies zonations thus controlling platform geometry and facies dynamics in the first section of this paper we examine how nutrient availability influences carbonate facies associations we first discuss the role of temperature and nutrient gradients in the modern ocean and their influence on biotic associations then we discuss how carbonate sedimentation can be characterized along nutrient gradients in the second section we review proxies currently used to reconstruct paleoproductivity in open ocean environments and discuss their applicability to neritic carbonate systems we highlight the variety of existing proxies and their limitations and suggest that multiple lines of evidence are needed for valid interpretations our short review discusses sedimentological biogenic and geochemical proxies that can be used to reconstruct past nutrient fluxes and to constrain paleoceanographic controls over the distribution of carbonate associations however it also reveals that more data and case studies are needed that integrate shallow and deep water carbonate sequences and elucidate the links between temperature vs nutrient supplies changes and facies in ancient carbonate sequences

dolomitization of the middle devonian winnipegosis carbonates in south central saskatchewan canada the middle devonian winnipegosis carbonate unit in south central saskatchewan is partially to completely dolomitized two major types of replacive dolomite are distinguished microcrystalline to finely crystalline dolomite type 1 displays nonplanar a to planar s textures mimetically replaces the precursor limestone accounts for about four fifths of dolomite phases volumetrically and mainly occurs in the winnipegosis mounds and the lower winnipegosis member directly underlying the mounds medium crystalline dolomite type 2 shows planar s to planar e textures commonly occurs in the lower winnipegosis and brightholme members and decreases upward in abundance the 87 sr 86 sr ratios of type 1 dolomite 0ae70795 to 0ae70807 fall within the estimated sr isotopic range for middle devonian marine carbonates stratigraphic petrographic and geochemical data constrain the formation of type 1 dolomite to hypersaline sea water in a near surface environment after marine cementation and sub aerial diagenesis and prior to precipitation of the middle devonian leofnard salts movement of dolomitizing fluids could be driven by density differences and elevation head the shift to lower d 18 o values of type 1 dolomite 7ae 4t o 5ae1 vienna pee dee belemnite vpdb is interpreted as the result of recrystallization at elevated temperatures during burial type 2 dolomite has higher 87 sr 86 sr ratios 0ae70809 0ae70928 suggesting that the dolomite probably formed from basinal fluids with an increased richness in the radiogenic sr isotope in type 2 dolomite sr 2 concentrations are lower and fe 2 and mn 2 concentrations are higher compared with the associated limestone and type 1 dolomite type 2 dolomite is interpreted as having been formed from upward migrating basinal fluids during latest devonian and carboniferous period

sapphirine quartz association in garnet implication for ultrahigh temperature metamorphism at rundvagshetta lutzow holm complex east antarctica

sulfide evolution in high temperature to ultrahigh temperature metamorphic rocks from lutzow holm complex east antarctica the high temperature ht to ultrahigh temperature uht metamorphic rocks from lutzow holm complex east antarctica show a systematic difference between sulfide assemblages in the rock matrix and those found as inclusions in the silicates stable in high temperatures matrix sulfides are commonly pyrite with or without pentlandite and chalcopyrite on the other hand inclusion sulfides are pyrrhotite with or without pentlandite and chalcopyrite lamellae when recalculated into integrated single phase sulfide compositions inclusion sulfides from the uht region showed a wider range of solid solution composition than the inclusion sulfides from the ht region the host minerals of the sulfides with extreme solid solution compositions are those stable at the peak of metamorphism such as orthopyroxene and garnet one of the most extreme ones is included in orthopyroxene coexisting with sillimanite quartz which is the diagnostic mineral assemblage of uht metamorphism these observations suggest that sulfide inclusions preserve their peak metamorphic compositions pyrrhotite did not revert to pyrite because of the closed system behavior of sulfur in inclusion sulfides on the other hand in the rock matrix where the open system behavior of sulfur is permitted original sulfides were partly to completely altered by the later fluid activity

the geochemistry of late archaean microbial carbonate implications for ocean chemistry and continental erosion history trace element concentrations and combined sr and nd isotope compositions were determined on stromatolitic carbonates microbialites from the 2 52 ga campbellrand carbonate platform south africa shale normalised rare earth element and yttrium patterns of the ancient samples are similar to those of modern seawater in having positive la and y anomalies and in being depleted in light rare earth elements in contrast to modern seawater and microbialite proxies the 2 52 ga samples lack a negative ce anomaly but possess a positive eu anomaly these latter trace element characteristics are interpreted to reflect anoxic deep ocean waters where unlike today hydrothermal fe input was not oxidised and scavenged and rare earth elements were not coprecipitated with fe oxyhydroxides the persistence of a positive eu anomaly in relatively shallow campbellrand platform waters indicates a dramatic reversal from hydrothermally dominated archaean to continental erosion dominated phanerozoic rare earth element flux ratio the dominant hydrothermal input is also expressed in the initial sr and nd isotope ratios there is collinear variation in sr nd systematics which range from primitive values 87sr 86sr of 0 702386 and end of 2 1 to more evolved crustal ratios mixing calculations show that the range in trace element ratios e g y ho and initial isotope ratios is not a result of contamination by trapped sediment but that the chemical and isotopic variation reflects carbonate deposition in an environment where different water masses mixed calculated nd flux ratios yield a hydrothermal input into the 2 52 ga oceans one order of magnitude larger than continental input such a change in flux ratio most likely required substantially reduced continental inputs which could in turn reflect a plate tectonic causation e g reduced topography or expansion of epicontinental seas

fluctuations in the trophic resource continuum a factor in global diversity cycles the trophic resource continuum trc in euphotic zones of the world s oceans is the spectrum of conditions from the richest runoff and upwelling areas to the most nutrient deficient subtropical seas that spectral range has likely varied through geologic history as more efficient phytoplankton taxa evolved as oceanic circulation rates changed and in response to oceanic mixing events reduced rates of oceanic turnover should produce regionally intensified eutrophy and oligotrophy that is trc expansion because oceanic waters as a whole are relatively nutrient rich increased rates of oceanic turnover should prevent extremely eutrophic and extremely oligotrophic conditions from developing causing trc contraction global biotic diversities in the oceans are strongly influenced by communities in oligotrophic environments nutrient deficient waters are more stable and more transparent than richer waters permitting higher degrees of specialization sparse nutrient supplies necessitate smaller phytoplankton and longer more complex food chains preservation potential of oligotrophic biotas is also greater because calcareous taxa are more prevalent and because calcium carbonate is less apt to be bioeroded or dissolved fluctuations in the trc should profoundly affect diversity of habitats within the euphotic zone of the oceans the evolutionary response to a trc expansion diversification would occur in a geologic time frame of millions of years while evolutionary responses to a trc contraction including extinction could occur in a biological time frame of generations a simple model indicates that a reduction in the trophic resource continuum from expansion during a major marine transgression down to modern levels could result in loss of 40 of the euphotic habitats how fluctuations in the trc control diversity of euphotic habitats in the oceans provides an hypothesis by which to interpret global taxonomic diversity cycles as well as taxonomically selective extinctions changes in species dominance and some morphologic trends

deep south china sea circulation 1 the analysis of an updated monthly climatology of observed temperature and salinity from the u s navy generalized digital environment model reveals a basin scale cyclonic circulation over the deep south china sea scs the cyclonic circulation lies from about 2400 m to the bottom the boundary current transport of the cyclonic circulation is around 3 0 sv our results suggest that the cyclonic circulation is mainly forced by the luzon overflow with bottom topography playing an important role the structures of potential temperature salinity and potential density in the deep scs are consistent with the existence of the cyclonic circulation specifically low salinity water is found in the interior region west of luzon island and surrounded by saline pacific water in boundary current regions to the north west and southwest our results show the potential density distribution and the corresponding cyclonic circulation in deep scs are primarily controlled by salinity variations in the deep basin

rare earth element geochemistry of late devonian reefal carbonates canning basin western australia confirmation of a seawater ree proxy in ancient limestones rare earth element and yttrium ree y concentrations were determined in 49 late devonian reefal carbonates from the lennard shelf canning basin western australia shale normalized sn ree y patterns of the late devonian samples display features consistent with the geochemistry of well oxygenated shallow seawater a variety of different ancient limestone components including microbialites some skeletal carbonates stromatoporoids and cements record seawater like ree y signatures contamination associated with phosphate fe oxides and shale was tested quantitatively and can be discounted as the source of the ree y patterns co occurring carbonate components that presumably precipitated from the same seawater have different relative ree concentrations but consistent ree y patterns clean devonian early marine cements n 3 display ree y signatures most like that of modern open ocean seawater and the highest y ho ratios e g 59 and greatest light ree lree depletion average nd sn yb sn 0 413 sd 0 076 however synsedimentary cements have the lowest ree concentrations e g 405 ppb non contaminated devonian microbialite samples containing a mixture of the calcimicrobe renalcis and micritic thrombolite aggregates in early marine cement n 11 have the highest relative ree concentrations of tested carbonates average total ree 11 3 ppm stromatoporoid skeletons unlike modern corals algae and molluscs also contain well developed seawater like ree patterns samples from an estuarine fringing reef have very different ree y patterns with lree enrichment nd sn yb sn 1 possibly reflecting inclusion of estuarine colloidal material that contained preferentially scavenged lree from a nearby riverine input source hence devonian limestones provide a proxy for marine ree geochemistry and allow the differentiation of co occurring water masses on the ancient lennard shelf although appropriate partition coefficients for quantification of devonian seawater ree concentrations from out data are unknown hypothetical devonian canning basin seawater ree patterns were obtained with coefficients derived from modern natural proxies and experimental values resulting devonian seawater patterns are slightly enriched in lree compared to most modem seawaters and suggest higher overall ree concentrations but are very similar to seawaters from regions with high terrigenous inputs our results suggest that most limestones should record important aspects of the ree geochemistry of the waters in which they precipitated provided they are relatively free of terrigenous contamination and major diagenetic alteration from fluids with high non seawater like ree contents hence we expect that many other ancient limestones will serve as seawater ree proxies and thereby provide information on paleoceanography paleogeography and geochemical evolution of the oceans copyright c 2004 elsevier ltd

archaean cambrian crustal development of east antarctica metamorphic characteristics and tectonic implications abstract the east antarctic shield consists of a variety of archaean and proterozoic cambrian high grade terranes that have distinct crustal histories and were amalgamated at various times in the precambrian cambrian high grade pan african tectonism at 600 500ma is recognized from four distinct belts the dronning maud land lutzow holm bay prydz bay and denman glacier belts these high grade belts juxtapose distinct mesoproterozoic and neoproterozoic crustal provinces maud rayner and wilkes the rauer terrane and have also marginally affected archaean cratonic remnants in the napier complex and southern prince charles mountains the wilkes province experienced its principal tectonothermal events prior to 1130ma and was not affected by the younger events that characterize the maud province 1150 and 1030 990ma the rayner province 990 920ma and the rauer terrane 1030 990ma these differences between the isotopic event records of the basement provinces now separated by the pan african belts require that the older provinces were not formerly parts of a continuous grenville belt as proposed in the sw us east antartic model east antarctica was not a single unified crustal block within either east gondwana or rodinia until the cambrian which is now demonstrated to be the key phase of high grade and ultrahigh temperature uht metamorphism associated with supercontinent assembly the high grade pan african tectonism is characterized by extensive infracrustal melting clock wise p t paths rapid post peak exhumation along isothermal decompression paths to shallow or mid crustal levels by 500 ma and the generation at least locally of uht conditions a significant flux of heat from the mantle into the deep and initially overthickened crust is required to produce these observed metamorphic effects whilst the thermal evolution can be explained by models that invoke the removal of most of the lithospheric mantle following crustal thickening and prior to rapid extension of the remaining crust these one dimensional models are inconsistent with present crustal thicknesses of 25 35km in the pan african domains of the east antarctic shield

upper layer circulation in the south china sea abstract upper layer circulation is investigated by using all available historical temperature profiles combined with climatological temperature salinity relationships in the south china sea two cyclonic eddies are revealed one is located east of vietnam called the east vietnam eddy and the other is off northwest luzon called the west luzon eddy both local ekman pumping and remotely forced basin scale circulation are important mechanisms controlling these two eddies the luzon strait transport relative to 400 db is estimated to be of the order 3 0 sv 1 sv 1 106 m3 s 1 in the mean and has a seasonal cycle dominated by the annual signal with a maximum 5 3 sv in january february and a minimum 0 2 sv in june july pressure gradients are also examined to explore the dynamics of the intrusion of waters from the pacific into the south china sea through the luzon strait

the effects of thermohaline circulation on wind driven circulation in the south china sea abstractthe dynamic influence of thermohaline circulation on wind driven circulation in the south china sea scs is studied using a simple reduced gravity model in which the upwelling driven by mixing in the abyssal ocean is treated in terms of an upward pumping distributed at the base of the upper layer because of the strong upwelling of deep water the cyclonic gyre in the northern scs is weakened but the anticyclonic gyre in the southern scs is intensified in summer while cyclonic gyres in both the southern and northern scs are weakened in winter for all seasons the dynamic influence of thermohaline circulation on wind driven circulation is larger in the northern scs than in the southern scs analysis suggests that the upwelling associated with the thermohaline circulation in the deep ocean plays a crucial role in regulating the wind driven circulation in the upper ocean

carbon isotopic evidence for photosynthesis in early cambrian oceans were the first metazoan reefs ecologically similar to modern tropical reefs enabling them to persist under oligotrophic conditions we tested the hypothesis of ecological similarity by employing a geochemical approach petrography cathodoluminescence trace elements and stable isotope analyses of primary precipitates of the lower cambrian ajax limestone south australia indicate preservation of original c isotopic composition all primary carbonate components exhibit c isotopic values similar to the composition of inorganically precipitated fibrous marine cements suggesting that archaeocyaths and the calcimicrobe epiphyton precipitated skeletal carbonate in equilibrium with ambient seawater in the absence of vital effects such data do not support the contention that archaeocyaths possessed photosymbionts however a 0 55 shift in 13 c occurs in reefs developed under shallower water conditions relative to deeper reefs this shift suggests the stratification of primary production in early cambrian oceans the pattern is similar to that seen in the modern ocean whereby significant photosynthesis modulates the c isotopic composition of the photic zone

kuroshio intrusion and the circulation in the south china sea 1 the princeton ocean model is used to study the circulation in the south china sea scs and its seasonal transition kuroshio enters leaves the scs through the southern northern portion of the luzon strait the annually averaged net volume flux through the luzon strait is 2 sv into the scs with seasonal reversals the inflow season is from may to january with the maximum intrusion of kuroshio water reaching the western scs during fall in compensation of summertime surface offshore transport associated with coastal upwelling from february to april the net transport reverses from the scs to the pacific the intruded kuroshio often forms an anticyclonic current loop west of the luzon strait the current loop separates near the dongsha islands with the northward branch continuously feeding the south china sea warm current scswc near the shelf break and the westward branch becoming the south china sea branch of kuroshio on the slope which is most apparent in the fall the scswc appears from december to february on the seaward side of the shelf break flowing eastward against the prevailing wind diagnosis shows that the onshore ekman transport due to northeasterly monsoon generates upwelling when moving upslope and the particular distributions of the density and sea level associated with the cross shelf motion supports the scswc

regional dynamics of seasonal variability in the south china sea abstract dynamics of the seasonal cycle of sea surface height ssh in the south china sea scs are studied using observations as well as numerical and theoretical models seasonal variability of the scs is interpreted in light of large scale dynamics and rossby waves it is found that the seasonal cycle over most of the scs basin is determined predominantly by the regional ocean dynamics within the scs the ssh variability is shown to be forced mainly by surface wind curl on baroclinic rossby waves annual baroclinic rossby waves cross the basin in less than a few months leaving the upper ocean in a quasi steady sverdrup balance an anomalous cyclonic anticyclonic gyre is generated in winter summer by the anomalous cyclonic anticyclonic wind curl that is associated with the northeasterly southwesterly monsoon in addition surface heat flux acts to enhance the wind generated variability the winter surface cooling warming cools warms the mixed layer especially in the central scs reducing

rare earth element and nd isotopic variations in regionally extensive dolomites from the burlington keokuk formation mississippian implications for ree mobility during carbonate diagenesis abstract marine carbonates of the burlington keokuk fm miss of the midcontinent region have been subject to two major episodes of regionally extensive 100 000 km2 dolomitization previous studies of the cathodoluminescent petrography sr c and o isotopic compositions and sr fe mn and ca concentrations of burlington keokuk dolostones outline a diagenetic history in which lime mud was pervasively dolomitized by a seawater dominated fluid at many localities this early dolomite generation dolomite i was recrystallized by nonmarine diagenetic fluids at shallow burial depths to produce dolomite ii dolomites i and ii have similar rare earth element ree patterns and abundances and a narrow range of initial 143nd 144nd isotope ratios of 0 511906 0 000025 1 this consistency in the nd isotope ratios and ree patterns along with the presence of anomalously low abundances of cerium in the dolomites cherts glauconite pellets fish apatite and crinoids suggests that 1 seawater derived ree dominated the system and 2 the extensive water rock interaction that produced profound textural and compositional changes during the formation of dolomite ii did not significantly alter the ree patterns or nd isotopic signatures of the dolomites the results of quantitative modeling of isotopic and trace lement exchange during water rock interaction in carbonate systems indicate that extremely large water rock ratios are required to alter the ree signatures of diagenetic carbonates such large water rock ratios can reflect either 1 large extents of fluid flow during carbonate recrystallization or 2 minimal interaction between diagenetic fluids and host rocks during carbonate cement crystallization late vug filling calcite and dolomite have low sm nd and high ce nd n ratios relative to the dolostones such distinct ree signatures probably reflect limited interaction between late diagenetic fluids and burlington keokuk host rocks penecontemporaneous clastic sediments have similar initial 143nd 144nd isotope ratios 0 511857 0 511877 and lower sm nd ratios compared to the dolomites suggesting 1 a common crustal source of ree for the clastics and carbonates and 2 ree fractionation during the formation of carbonate apatite glauconite and other authigenic phases in the marine environment

observation of luzon strait transport using recently collected current and hydrographic data we provide a high resolution picture of the subinertial flow and estimate the volume transport through the luzon strait the distribution of the subinertial flow shows a strong westward flow around 100 m in the northern part of the luzon strait while the eastward flow is confined to the deeper layers mostly at depths around 1000 m the total volume transport is estimated to be 6 3 sv during the period of observations from october 4 to 16 2005 the observations also confirm that the luzon strait transport has a sandwiched vertical structure the net westward volume transport in the deep 1500 m layer of the luzon strait reaches 2 sv

deepwater overflow through luzon strait 1 this study examines water property distributions in the deep south china sea and adjoining pacific ocean using all available hydrographic data our analysis reveals that below about 1500 m there is a persistent baroclinic pressure gradient driving flow from the pacific into the south china sea through luzon strait applying hydraulic theory with assumptions of zero potential vorticity and flat bottom to the luzon strait yields a transport estimate of 2 5 sv 1 sv 106 m3 s 1 some implications of this result include 1 a residence time of less than 30 years in the deep south china sea 2 a mean diapycnal diffusivity as large as 10 3 m2 s 1 and 3 an abyssal upwelling rate of about 3 10 6 m s 1 these quantities are consistent with residence times based on oxygen consumption rates the fact that all of the inflowing water must warm up before leaving the basin implies that this marginal sea contributes to the water mass transformations that drive the meridional overturning circulation in the north pacific density distributions within the south china sea basin suggest a cyclonic deep boundary current system as might be expected for an overflow driven abyssal circulation

timing and rate of isothermal decompression in pan african granulites from rundvagshetta east antarctica geochronological data combined with field and petrological evidence constrain the timing and rate of near isothermal decompression at granulite facies temperatures in rocks from the lutzow holm complex of east antarctica granulite facies gneisses from rundvagshetta in lutzow holm bay experienced a peak metamorphic temperature of over 900 c at c 11 kbar as evidenced by primary orthopyroxene sillimanite bearing assemblages and secondary cordierite sapphirine bearing assemblages in metapelites peak metamorphic assemblages show strong preferred mineral orientation interpreted to have developed synchronously with pervasive ductile deformation zircon from a syndeformational leucosome has a u pb age of 517 9 ma which is interpreted as a melt crystallization age this age provides the best estimate of the time of peak metamorphic conditions the post peak metamorphic history is characterized by near isothermal decompression recorded by mineral textures in a variety of rock compositions field and textural relations indicate that decompression post dated pervasive ductile deformation k ar and 40ar 39ar ages from hornblende and biotite represent closure ages during cooling subsequent to decompression and indicate cooling to temperatures between c 350 and 300 c by c 500 ma thus placing a lower time limit on the duration of the high temperature isothermal decompression episode the combination of the zircon age from a syndeformational melt with k ar and 40ar 39ar closure ages indicates that near isothermal decompression from c 11 to c 4 kbar at granulite facies temperatures followed by cooling to c 300 c took place within a time interval of 20 10 myr simple one dimensional models for exhumation controlled cooling indicate that these data require exhumation rates of the order of c 3 km myr 1 for several million years then cessation of exhumation followed by relatively isobaric cooling during thermal re equilibration

on the sedimentological origin of down core variations of bulk sedimentary nitrogen isotope ratios 1 the bulk sedimentary nitrogen isotopic composition of two cores from nearby sites on the northern slope of the south china sea site 17940 and ocean drilling program odp site 1144 differs by up to 2 during the last glacial period given their close proximity both core sites are located in the same biogeographic zone and nutrient regime and it is thus unlikely that this offset is due to a true gradient in surface ocean conditions in an attempt to resolve this offset we have investigated the possible effects of two sedimentological parameters that can affect bulk sedimentary 15n namely the variable contribution of inorganic n to bulk n in the sediment and the grain size dependence of bulk 15n we find that neither effect singly or in combination is sufficient to explain the significant 15n offset between the two down core records by elimination the most likely explanation for the observed discrepancy is a different origin of both the organic and inorganic nitrogen at each site this study adds to the growing body of evidence highlighting the complex nature and origin of the sedimentary components in sediment drifts such as odp site 1144

the geochemical balance of the rare earth elements and neodymium isotopes in the oceans profiles of ree concentrations and neodymium isotope measurements in the western indian ocean are consistent with published data from the other major oceans ree concentrations show a strong hydrographic control the influence of intermediate water masses is particularly significant surface water concentrations vary with salinity paniculate rees are less than 5 of dissolved concentration except for ce where up to 20 of total rees are present as 0 4 m particles in contrast to dissolved profiles concentration profiles of paniculate rees including ce all increase with depth ree concentrations correlate with silica over all but the deepest waters although in detail correlations are complex the neodymium isotopic composition of indian ocean seawater avg nd 0 8 3 is intermediate between that for the atlantic and pacific oceans comparison of ree data from the major oceans shows that the hrees behave more like si than do the lrees sm nd ratios are near constant for all oceans whereas ernd ratios vary between the atlantic indian and pacific oceans the fractionation of the rees in surface seawaters can be explained by fractionation factors relative to silica from 0 12 for la to 0 05 for er use of a seven box model shows that the interoceanic variations in neodymium isotopic compositions and nd concentrations cannot be reconciled unless particle water exchange is invoked the degree of exchange required is consistent with particle residence times of 1 10 yr

the implication of the oxygen isotope records in coexisting cherts and phosphates 18 o values have been determined for 53 coexisting chert phosphate pairs from the phanerozoic and precambrian in addition 18 o values were also determined for 18 biogenic phosphates from the phanerozoic the oxygen isotope data for the chert phosphate pairs permit the calculation of the temperatures of formation of the chert phosphate pairs as well as the 18 o of the waters in which they equilibrated in turn the calculated 18 o of the waters permit the calculation of temperatures from the isotopic data of the biogenic phosphates the temperatures for the tertiary and mesozoic samples are compatible with the literature values determined from oxygen isotope data for well preserved calcareous marine skeletal remains the temperatures calculated from the chert phosphate pairs of the paleozoic are usually higher and vary in cycles of about a 150 million year period the early precambrian temperatures are as high as 80 c and decrease with time the use of chert phosphate pairs for temperature determinations are sufficiently promising to warrant further investigations of this type on well preserved chert phosphate or carbonate phosphate pairs

crystal size distribution of garnet in quartzo feldspathic gneisses from the lutzow holm complex at skallen east antarctica

ecological controls on devonian stromatoporoid dominated and coral dominated reef growth in the mackenzie basin northwest territories canada the horn plateau formation composed of isolated reefs is part of the devonian strata that formed in the mackenzie basin in the northwest territories canada the reefs stretch over a 350 m north

compositions of foraminifera rich turbidite sediments from the shenhu area on the northern slope of the south china sea implication for the presence of deep water bottom currents abstract the sediments in gravity core dh 1 collected from shenhu area on the northern slope of the south china sea are composed of two dark grey clay silt layers a1 and a3 and two foraminifera rich layers a2 and a4 a1 is the top layer and a4 is the bottom layer major and trace metal contents along with grain size and mineralogic data suggest that these silt layers represent background hemipelagic sedimentation unlike silt layers the intervening foraminifera rich layera4 exhibits a fining upward trend is distal turbidite grain size cm diagram and the sharp contacts between the foraminifera rich layer a2 and the upper and lower layers suggest layer a2 is the result of depositional interaction between turbidite and bottom currents ams 14c dating of planktonic foraminifera indicate the age of the turbidite in a2 is between15 3 ka and 22 6 ka we hypothesize that turbidite formation in this period was related to the increase supply of terrigenous matter since the last glacial maximum the rapid deposition of each turbidite led to reduced rates of oxygen diffusion into the sediment allowing anoxic conditions develop in sediments and fostering u enrichment 3 1 g g in foraminifera rich layer a4b in contrast decrease concentration of u and u mo ratios in foraminifera rich layera2 which is possibly due to u remobilization as a consequence of downward penetration of the oxidation front from the oxygen rich bottom currents these new data suggest that authigenic u was quite sensitive to the inflow of bottom currents and u mo ratios may indicate the depositional environmental change in relation to the bottom current action on the turbidite

sensitive high resolution ion microprobe u pb dating of prograde and retrograde ultrahigh temperature metamorphism as exemplified by sri lankan granulites ultrahigh temperature uht granulites of the central highland complex sri lanka underwent some of the highest known peak temperatures of crustal metamorphism zircon and monazite u pb systems in granulites near kandy the highest grade region 1050 c 0 9 gpa preserve both a record of the timing of prograde and retrograde phases of uht metamorphism and evidence for the ages of older protolith components zircon grains from a quartz saturated granulite containing relics of the peak uht assemblage have remnant detrital cores with dates of ca 2 5 0 83 ga date clusters of ca 1 7 and 1 04 0 83 ga record episodes of zircon growth in the source region of the protolith sediment two generations of overgrowths with contrasting th u record metamorphic zircon growth at 569 5 and 551 7 ma probably in the absence and presence of monazite respectively the age of coexisting metamorphic monazite 547 7 ma is indistinguishable from that of the younger low th u zircon overgrowths zircon from a quartz undersaturated monazite absent uht granulite with a mainly retrograde assemblage is mostly metamorphic 551 5 ma the ca 570 ma zircon overgrowths in the quartz saturated granulite probably record partial melting just before or at the metamorphic peak the ca 550 ma zircon in both rocks and the ca 550 ma monazite in the quartz saturated sample record post peak isothermal decompression a possible model for this pressure temperature time evolution is ultrahot collisional orogeny during the assembly of gondwana locally superheated by basaltic underplating followed by fast extensional exhumation

sm nd in marine carbonates and phosphates implications for nd isotopes in seawater and crustal ages this study explores the possibility of establishing nd isotopic variations in seawater over geologic time calcite aragonite and apatite are examined as possible phases recording seawater values of nd modern biogenic and inorganically precipitated calcite and aragonite from marine environments were found to have nd concentrations of from 0 2 to 70 ppb showing that primary marine caco 3 contains little ree and that nd ca is not greatly enhanced relative to seawater during carbonate precipitation very young marine limestone and dolomite containing no continental detritus have 200 ppb nd all the carbonates are lree enriched 0 16 sm nd 0 45 modern and very young atlantic and pacific carbonates have nd in the range of shallow atlantic and pacific seawater respectively implying that they derive their ree from local seawater the nd in well preserved carbonate fossils is 4 10 4 ppb much greater than in their modern counterparts but like the high values found for carbonates in other studies we believe the high ree contents at the 500 ppb level in some detritusfree carbonates are due to ree rich fe hydroxide in on the carbonate in favorable cases such material may record seawater nd values however introduction of extraneous ree may obscure the original isotopic composition of pure caco 3 because of its very low intrinsic primary ree abundance modern biogenic apatite is also shown to have very low ree content 150 ppb nd but appears to quickly scavenge ree from seawater inorganically precipitated apatite from phosphorites has high concentrations of seawater derived ree young phosphorite apatite from the atlantic and pacific oceans has nd in the range of the seawater from these oceans older apatite samples of similar age from different localities bordering common oceans record similar values of nd t sedimentary apatite has sr t values in good agreement with the curves for 87 sr 86 sr of seawater as a function of time individual conodonts from a single formation yield the same sr t and nd t other workers have shown that sedimentary apatite preserves seawater ree patterns these characteristics suggest that sedimentary apatite can be used to determine nd t in ancient seawater the seawater values so inferred range between 1 7 and 8 9 over the last 700 my and lie in the range of modern seawater showing no evidence for drastic changes high values of seawater nd t in the triassic and latest precambrian may correlate with the breakup of large continental landmasses the initial nd t 15 0 of a 2 ae old phosphorite implies the presence of 1 5 ae old continental crust at 2 ae ago the approach outlined here can be used to constrain the age of the exposed crust as a function of time

thermohaline circulation in the deep south china sea basin inferred from oxygen distributions 1 on the basis of the historical oxygen data available distributions of dissolved oxygen were analyzed in detail to investigate the thermohaline circulation in the south china sea scs the analyses confirmed the existence of a layer of minimal oxygen content at intermediate depths of the basin which shows a low oxygen 1 6 ml l 1 core in the southern basin with water ages shorter than 100 years after entering the scs and which appears isolated from its counterpart of the western philippine sea north to the core along the northern slope there is a band of oxygen rich water in both upper and intermediate layers above 700 m the band can be attributed to the intrusion of high oxygen water through the luzon strait while vertical flux appears to be responsible between 700 and 1500 m the oxygen distribution provides additional evidence for a sandwiched vertical structure in transports through the luzon strait with outflows in the intermediate layer and inflows above and below while the abyssal water of the scs is being replenished by the deep inflows an abrupt change of water properties was observed in both upper and intermediate layers across the luzon strait suggesting possible domination of local vertical mixing over horizontal spreading of inflows in the northern scs a four cell conceptual model was proposed for the thermohaline circulation which consists of a three layer cross basin exchange cell in the luzon strait an active ventilation cell in the upper and intermediate layers along the northern slope an abyssal replenishment cell in the deep and a cyclonic recirculation cell in the interior basin

a three layer alternating spinning circulation in the south china sea abstractunderstanding of the three dimensional circulation in the south china sea scs is crucial for determining the transports of water masses energy and biogeochemical substances in the regional and adjacent larger oceans the circulation s kinematic and dynamic natures however are largely unclear results from a three dimensional numerical ocean circulation model and geostrophic currents derived from hydrographic data reveal the existence of a unique three layer cyclonic anticyclonic cyclonic cac circulation in the upper 1500 m layers in the scs with differing seasonality an inflow outflow inflow structure in luzon strait largely induces the cac circulation which leads to vortex stretching in the scs basin because of a lateral planetary vorticity flux in each of the respective layers the formation of joint effects of baroclinicity and relief jebar is an intrinsic dynamic response to the cac circulation the jebar arises from the cac flow topog

extreme crustal metamorphism during a neoproterozoic event in sri lanka a study of dry mafic granulites abstract garnet clinopyroxene quartz granulites of the central highland complex of sri lanka preserve textural and compositional features indicative of high pressure ultrahigh temperature hp uht crustal metamorphism and multistage retrogression grains of the peak metamorphic assemblage garnet clinopyroxene quartz are commonly separated and embayed by late orthopyroxene plagioclase symplectites however in some domains rare grain to grain associations of the peak assemblages are still preserved thermodynamic modeling in the cao na2o k2o feo mgo al2o3 sio2 system indicates peak metamorphic conditions of 12 5 kbar at 925 c the temperature estimates using garnet and clinopyroxene core compositions are in the range 844 982 c in agreement with the thermodynamic modeling in conclusion the textural geochemical and thermodynamic modeling and thermobarometric data indicate a multistage decompression after hp uht metamorphism u pb zircon laser ablation inductively coupled plasma mass spectrometry

on the dynamics of the south china sea deep circulation 1 in the south china sea scs the deep water is confined to a bowel type trench and the maximum depth is approximately 4700 m the luzon strait is the only deep connection between the scs and the pacific ocean with the deepest sill at about 2400 m in the bashi channel using the hybrid coordinate ocean model this study gives a good description of the scs deep circulation the most obvious features are basin scale cyclonic gyre and western intensification the gyre is elliptical shaped and its major axis is northeast southwest a numerical experiment is designed to investigate what could be possibly responsible for the scs deep circulation the results reveal that the deepwater overflow through the luzon strait controls over the basin scale circulation structure in the deep scs basin the driving mechanism is elucidated based on the potential vorticity pv integral constraint which means the pv inflow across the boundary is balanced by the net pv dissipation along the boundary

environmental and physiological influences on isotopic and elemental compositions of brachiopod shell calcite implications for the isotopic evolution of paleozoic oceans abstract brachiopods from the demissa bed middle devonian hamilton group biologically regulated the incorporation of mg sr and na into their shell calcite significant taxonomic differences in the elemental contents of three species athyris spiriferoides mediospirifer audacula and mucrospirifer mucronatus may be related to differences in calcification processes in contrast no significant difference or vital effects were observed between the isotopic values of mediospirifer audacula and athyris spiriferoides from erie 18o 0 03 p 0 949 13c 0 76 p 0 083 and genessee counties 18o 0 39 p 0 471 13c 0 06 p 0 854 this suggests that these brachiopods did not exert a biological control over their isotopic compositions and that their shell calcites reflect ambient physicochemical conditions isotopic compositions in unaltered shell calcites of brachiopods from genessee county which was close to the basin depocentre are heavy for carbon 13c x 5 01 pdb and oxygen 18o x 2 85 pdb compared to the species sampled at the basin s edge erie county 13c x 2 79 pdb 18o x 3 83 pdb there is a significant separation in isotopic values between the deeper and shallower water brachiopods of the basin 18o 0 98 p 0 0005 13c 2 22 p 0 0005 the 18o variation suggests a temperature salinity change with water depth whereas the change in 13c composition probably records an enrichment depletion of organic matter with water depth this observation has significant implications for paleozoic ocean isotopic evolution studies because many global changes in marine 18o and 13c are based on isotopic shifts of similar magnitude