sulfur record of rising and falling marine oxygen and sulfate levels during the lomagundi event carbonates from approximately 2 3 2 1 billion years ago show markedly positive 13c values commonly reaching and sometimes exceeding 10 traditional interpretation of these positive 13c values favors greatly enhanced organic carbon burial on a global scale although other researchers have invoked widespread methanogenesis within the sediments to resolve between these competing models and more generally among the mechanisms behind earth s most dramatic carbon isotope event we obtained coupled stable isotope data for carbonate carbon and carbonate associated sulfate cas cas from the lomagundi interval shows a narrow range of 34s values and concentrations much like those of phanerozoic and modern marine carbonate rocks the 34s values are a close match to those of coeval sulfate evaporites and likely reflect seawater composition these observations are inconsistent with the idea of diagenetic carbonate formation in the methanic zone toward the end of the carbon isotope excursion there is an increase in the 34s values of cas we propose that these trends in c and s isotope values track the isotopic evolution of seawater sulfate and reflect an increase in pyrite burial and a crash in the marine sulfate reservoir during ocean deoxygenation in the waning stages of the positive carbon isotope excursion

diurnal shear instability the descent of the surface shear layer and the deep cycle of equatorial turbulence a new theory of shear instability in a turbulent environment is applied to eight days of velocity and density profiles from the upper equatorial pacific this period featured a regular diurnal cycle of surface forcing together with a clear response in upper ocean mixing during the day a layer of stable stratification and shear forms at the surface during late afternoon and evening this stratified shear layer descends leaving the nocturnal mixing layer above it using high resolution current measurements the detailed structure of the descending shear layer is seen for the first time linear stability analysis is conducted using a new method that accountsfortheeffectsofpreexistingturbulenceoninstabilitygrowth shearinstabilityfollowsadiurnalcycle linked to the afternoon descent of the surface shear layer this cycle is revealed only when the effect of turbulence is accounted for in the stability analysis the cycle of instability leads the diurnal mixing cycle typically by 2 3h consistent with the time needed for instabilities to grow and break late at night the resulting turbulence suppresses further instabilities lending an asymmetry to the mixing cycle that has not been noticed in previous measurements deep cycle mixing is triggered by instabilities formed as the descending shear layer merges with the marginally unstable shear of the equatorial undercurrent in the morning turbulence decays and the upper ocean restratifies wind accelerates the near surface flow to form a new unstable shear layer and the cycle begins again

enhanced turbulence and energy dissipation at ocean fronts the ocean surface boundary layer mediates air sea exchange in the classical paradigm and in current climate models its turbulence is driven by atmospheric forcing observations at a 1 kilometer wide front within the kuroshio current indicate that the rate of energy dissipation within the boundary layer is enhanced by one to two orders of magnitude suggesting that the front rather than the atmospheric forcing supplied the energy for the turbulence the data quantitatively support the hypothesis that winds aligned with the frontal velocity catalyzed a release of energy from the front to the turbulence the resulting boundary layer is stratified in contrast to the classically well mixed layer these effects will be strongest at the intense fronts found in the kuroshio current the gulf stream and the antarctic circumpolar current all of which are key players in the climate system

modulation of equatorial turbulence by a tropical instability wave 1 strong modulation of turbulent mixing by a westward propagating tropical instability wave tiw was observed in the stratified shear layer between the equatorial undercurrent euc and the surface mixed layer during october and november 2008 at 0 n 140 w the unique deep diurnal cycle mixing in the stratified layer beneath the equatorial cold tongue was observed where nighttime turbulent mixing was a factor of 10 greater than during daytime the turbulent kinetic energy dissipation rate e was 10 6 w kg 1 and the turbulent heat flux was 500 w m 2 at least 5 10 times greater than observed previously in the central equatorial pacific turbulence mixing varied significantly during the four distinct phases of the meridional flow associated with the tiw observations during the northward to southward transition recorded the largest values of reduced shear squared the thickest nighttime surface mixed layer the deepest penetration of the deep cycle turbulence and the largest turbulent heat flux and largest integrated e in the deep cycle layer dcl during steady southward flow the depth of the bases of the nighttime surface mixed layer and of the dcl were the shallowest a 50 m thick layer of strong turbulence was observed immediately above the euc core during the northward to southward and steady southward phases here the average e exceeded 10 6 w kg 1 the eddy diffusivity exceeded 10 3 m2 s 1 and the turbulent heat flux was 500 w m 2 to parameterize mixing in the central equatorial pacific accurately numerical models must simulate the enhancement of mixing associated with tiws and also the variability of mixing in different tiw phases

role of narrow mountains in large scale organization of asian monsoon convection abstract the asian summer monsoon is organized into distinct convection centers but the mechanism for this organization is not well understood analysis of new satellite observations reveals that narrow mountain ranges are an important organizing agent anchoring monsoon convection centers on the windward side the bay of bengal convection in particular features the heaviest precipitation on its eastern coast because of orographic lifting as the southwest monsoon impinges on the coastal mountains of myanmar also known as burma this is in contrast to the widely held view that this convection is centered over the open ocean as implied by coarse resolution datasets a view that would require an entirely different explanation for its formation narrow in width and modest in height 1 km these mountains are hardly mentioned in conceptual depictions of the large scale monsoon and poorly represented in global climate models the numerical simulations of this study show that orographic rainbands are not a

possible role of warm sst bias in the simulation of boreal summer monsoon in sintex f2 coupled model reasonably realistic climatology of atmospheric and oceanic parameters over the asian monsoon region is a pre requisite for models used for monsoon studies the biases in representing these features lead to problems in representing the strength and variability of indian summer monsoon ism this study attempts to unravel the ability of a state of the art coupled model sintex f2 in simulating these characteristics of ism the coupled model reproduces the precipitation and circulation climatology reasonably well however the mean ism is weaker than observed as evident from various monsoon indices a wavenumber frequency spectrum analysis reveals that the model intraseasonal oscillations are also weaker than observed one possible reason for the weaker than observed ism arises from the warm bias over the tropical oceans especially over the equatorial western indian ocean inherent in the model this warm bias is not only confined to the surface layers but also extends through most of the troposphere as a result of this warm bias the coupled model has too weak meridional tropospheric temperature gradient to drive a realistic monsoon circulation this in turn leads to a weakening of the moisture gradient as well as the vertical shear of easterlies required for sustained northward propagation of rain band resulting in weak monsoon circulation it is also noted that the recently documented interaction between the interannual and intraseasonal variabilities of ism through very long breaks vlbs is poor in the model this seems to be related to the inability of the model in simulating the eastward propagating madden julian oscillation during vlbs

constraints on palaeoenvironments in the lower cretaceous wealden of southern england from the geochemistry of sphaerosiderites abstract sphaerosiderites are millimetre scale concretions of feco 3 that form predominantly in waterlogged environments and are of use in palaeoenvironmental and palaeohydrological studies we present petrographic elemental and stable isotopic 13 c 18 o data from sphaerosiderites collected from the lower cretaceous wealden sediments of southern england the sphaerosiderites are composed of very pure feco 3 with only small amounts of ca mg and mn present suggesting that they are well preserved and were precipitated from fresh groundwater 13 c values display a relatively large range from about 5 to 30 vpdb in contrast 18 o values are relatively invariant 1 0 83 with an average of 3 01 vpdb the relationship between carbon and oxygen suggests that the sphaerosiderites faithfully record palaeo groundwater 18 o likely 18 o values for groundwater were calculated using a published experimentally derived siderite water fractionation equation and plausible assumed values for palaeotemperature the average estimate was 4 9 smow the wealden sphaerosiderite oxygen isotope values are comparable with other early cretaceous data from similar palaeolatitudes but lower than estimated holocene values for equivalent latitudes this observation may indicate greater rainfall at 30 n during the cretaceous relative to the holocene and also suggests relative stability of palaeoclimatic conditions during the early cretaceous at this palaeolatitude

potential vorticity dynamics of tropical instability vortices abstracttropical instability vortices tivs in the equatorial pacific exhibit energetic horizontal and vertical circulation characterized by regions of high rossby number and low richardson number their strong anticyclonic vorticity and vertical shear can influence the broader scale circulation by driving lateral mixing and vertical exchange between the ocean surface and interior the authors use a set of nested high resolution simulations of the equatorial pacific with a finest grid size of 3 km to examine the vortex dynamics associated with tiv core water formation tiv cores are characterized by low values of the ertel potential vorticity pv as the relative vorticity is anticyclonic with magnitude comparable to the local coriolis parameter a study of the variation of pv and other scalars along lagrangian fluid parcel tracks entering the tivs shows that the low pv water in their cores is a mix of equatorial undercurrent euc water and north equatorial counter current necc water the euc water

barotropic rossby waves radiating from tropical instability waves in the pacific ocean abstracttropical instability waves are triggered by instabilities of the equatorial current systems and their sea level signal with peak amplitude near 5 n is one of the most prominent features of the dynamic topography of the tropics cross spectral analysis of satellite altimetry observations shows that there is sea level variability in the pacific ocean as far north as hawaii i e 20 n that is coherent with the sea level variability near 5 n associated with tropical instability waves within the uncertainty of the analysis this off equatorial variability obeys the dispersion relation for nondivergent barotropic rossby waves over a fairly broad range of periods 26 38 days and zonal wavelengths 9 23 of longitude that are associated with tropical instability waves the dispersion relation and observed wave properties further suggest that the waves are carrying energy away from the instabilities toward the north pacific subtropical gyre which together with the observed coherence of the sea

origin of manganese carbonates in jurassic red shale central japan manganese carbonate deposits in japanese jurassic sedimentary rocks were studied petrogeochemically the deposits are characteristically composed of spheroidal micronodules up to 1 mm in diameter and always contain well preserved radiolarian shells chemical elemental composition and mineralogical characteristics indicate that the micronodules contain rhodochrosite in a mixed carbonate phase composition mn86 7 92 2ca2 2 2 9mg2 6 6 7fe2 6 5 6 co3 carbon and oxygen isotope values which range from 7 99 to 4 78 and 4 05 to 0 28 relative to pdb respectively suggest that the manganese carbonate was precipitated in a suboxic zone the micronodules closely resemble agglutinated benthic foraminifera in shape we suggest that agglutinated foraminiferal tests composed of radiolarian shells accumulated selectively on the sediment surface during redeposition of bottom sediments and were replaced by manganese carbonate in suboxic diagenetic conditions of manganese reduction

tropical instability wave energetics observations from the tropical instability wave experiment ocean velocity data from an array of subsurface moorings deployed from may 1990 to june 1991 during the tropical instability wave experiment are used to study the energetics of planetary waves in the vicinity of the equator at 1408w such waves observed from august to december 1990 were initiated by barotropic instability arising primarily from the cyclonic shear region of the south equatorial current and equatorial undercurrent just north of the equator subsequently local barotropic production continued to maintain and modulate these tropical instability waves through a combination of cyclonic shear and meridional velocity component divergence just north of the equator the end of the wave season coincided with the propagation past the array of a large intraseasonal kelvin wave

paleoenvironmental implications of early diagenetic siderites of the paraiba do sul deltaic complex eastern brazil abstract abundant early diagenetic siderites occur as spherulites and rhombohedral microcrystalline and macrocrystalline crystals in the cores of the 2 mu 1 rj well drilled in the paraiba do sul deltaic complex rio de janeiro brazil the host sediments of the siderites are siliciclastic hybrid and carbonate deposits intense pedogenetic processes affected the siliciclastic sediments immediately after deposition comprising clay illuviation plants bioturbation feldspar dissolution and iron oxide hydroxide precipitation siderite and pyrite are the main diagenetic constituents the other diagenetic products are kaolinite smectite argillaceous and carbonate pseudomatrix quartz overgrowths diagenetic titanium minerals jarosite and iron oxides hydroxides early diagenetic siderites were separated into four groups based on their elemental and stable isotopic composition as well as on their paragenetic relationships with the other constituents and with the host sediments spherulitic to macrocrystalline siderites from group 1 are almost pure average 94 7 mol feco3 1 2 mol mgco3 2 3 mol caco3 1 8 mol mnco3 and precipitated from meteoric porewaters in continental siliciclastic rocks under suboxic conditions 18ovpdb values range in 10 28 to 5 57 and the 13cvpdb values in 12 68 to 4 33 microcrystalline rhombohedral siderites from group 2 have zonation due to substantial ca and mg substitution core average 78 5 mol feco3 4 2 mol mgco3 15 7 mol caco3 1 6 mol mnco3 edge average 74 0 mol feco3 9 2 mol mgco3 15 6 mol caco3 1 1 mol mnco3 and 13cvpdb and 18ovpdb values of 0 17 and 1 96 precipitated from marine porewaters in packstones wackestones under methanogenic conditions the group 3 is represented by irregular spherulitic siderites with moderate ca and mg substitutions average 80 2 mol feco3 7 9 mol mgco3 11 3 mol caco3 0 6 mol mnco3 with 18ovpdb values ranging from 5 96 to 7 61 and 13cvpdb values ranging from 5 15 to 10 41 the group 4 microcrystalline siderites are magnesium rich average 57 3 mol feco3 31 4 mol mgco3 9 6 mol caco3 1 7 mol mnco3 13cvpdb 1 43 and 18ovpdb 14 09 the group 3 and 4 siderites were formed from brackish porewater under suboxic conditions in hybrid and siliciclastic rocks these variations in siderites are probably related to the paraiba do sul river dynamics to sea level changes and to climatic variations that took place during the quaternary

formation of siderite mg calcite iron sulphide concretions in intertidal marsh and sandflat sediments north norfolk england concretions cemented mainly by siderite mg calcite and iron monosulphide are common in late holocene marsh and sandflat sediments on parts of the north norfolk coast field experiments have shown that the concretions are actively forming in reduced sediments in which sulphate reducing bacteria are active 13c values ranging from 3 to 11 8 mean 5 9 0 suggest that the carbonate in the concretions is derived partly from marine sources and partly from microbial degradation of organic matter 18o values ranged from 6 4 to 0 8 mean 1 0 suggesting that carbonate precipitated in porewaters ranging from pure sea water to sea water diluted with meteoric water chemical analysis of porewaters showed no evidence of significant sulphate depletion at the depth of concretion formation some concretions have formed around fragments of wood or metal but others contain no apparent nucleus in field experiments siderite fes and mg calcite were precipitated around several different nuclei within a period of six months we suggest that siderite may form wherever the rate of iron reduction exceeds the rate of sulphate reduction such that insufficient dissolved sulphide is available to precipitate all the available dissolved ferrous iron

the indian monsoon and its variability for over 300 years the monsoon has been viewed as a gigantic land sea breeze it is shown in this paper that satellite and conventional observations support an alternative hypothesis which considers the monsoon as a manifestation of seasonal migration of the intertropical convergence zone itcz with the focus on the indian monsoon the mean seasonal pattern is described and why it is difficult to simulate it is discussed some facets of the intraseasonal variation such as active weak cycles break monsoon and a special feature of intraseasonal variation over the region namely poleward propagations of the itcz at intervals of 2 6 weeks are considered vertical moist stability is shown to be a key parameter in the variation of monthly convection over ocean and land as well as poleward propagations special features of the bay of bengal and the monsoon brought out by observations during a national observational experiment in 1999 are briefly described

mechanisms for enso phase change in a coupled gcm the mechanisms leading to el nino onset and termination in the echam4 opa coupled gcm are assessed and compared to observations and existing enso paradigms at the equator as well as off equator the patterns and timing of modeled el nino composites are in good agreement with those observed heat content of the west pacific is confirmed as a precursor to enso phase change and the present work emphasizes the role of its northern off equator part west north pacific wnp region 58 158n 1208 1708e the associated heat content changes appear to be dominated by a local ekman pumping or forced rossby waves rather than the accumulation of remotely generated free rossby waves as proposed by many theories the heat content decrease in the wnp region which triggers el nino termination is due to the negative feedback of the atmospheric gill s response to the increased equatorial sst in the east pacific in agreement with most paradigms delayed recharged west pacific oscillators the present study introduces the advection of the off equator signal to the equatorial waveguide by the mean currents of the western pacific as an additional process a similar feedback with opposite sign also seems to drive the modeled el nino onset favoring a too strong and regular biennial enso in the model this is due to the stronger than observed walker circulation that isolates the wnp region from other remote influences like monsoons the model also exhibits aborted enso events where the warming peaks in late spring instead of late autumn and is quickly terminated by the gill s negative feedback the abort event occurs too frequently in the coupled model due to too strong and too zonal a convergence zone south of the equator double itcz it bears some resemblance to the spring 1993 warming when the southern tropics were also warm the results of this paper provide additional insight into the el nino seasonal phase lock mechanisms

characteristics of a surface buoyant jet tidal outflow from leschenault estuary in winter forms an unsteady surface buoyant jet in koombana bay on each outgoing tide as the water moves away from the exit channel and spreads radially over the bay it assumes a plumelike nature the mean features of this buoyant outflow such as the plume shape frontal celerity internal circulation and the bulk entrainment were measured in an intensive field program these features are shown to compare favorably with results from previous laboratory investigations and predictions from a simple inertia buoyancy force balance which includes entrainment at the front the stability of the plume frontal region was examined and it is shown that subfronts were present but their behavior cannot be explained by reference to previous work

variable methane fluxes in shallow marine systems over geologic time abstract carbon cycling is an important but poorly understood process on passive continental margins in this study we use the ionic and stable isotopic composition of interstitial waters and the petrology mineralogy and stable isotopic composition of authigenic carbonates collected from ocean drilling program odp leg 174a sites 1071 and 1072 to constrain the origin of the carbonates and the evolution of methane on the outer new jersey shelf the pore fluids of the new jersey continental shelf are characterized by 1 a fresh brackish water plume and 2 organic matter degradation reactions which proceed through sulfate reduction however only minor methanogenesis occurs the oxygen isotopic composition of the pore fluids supports a meteoric origin of the low salinity fluids authigenic carbonates are found in nodules thin 1 cm layers and carbonate cemented pavements siderite is the most common authigenic carbonate followed by dolomite and calcite the oxygen isotopic composition of the authigenic carbonates i e 1 3 6 5 peedee belemnite pdb indicates an origin in marine pore fluids the carbon isotopic composition of dolomite cements range from 16 4 to 8 8 pdb consistent with formation within the zone of sulfate reduction siderite 13c values show a greater range 17 67 16 4 but are largely positive mean 2 8 and are interpreted to have formed throughout the zone of methanogenesis in contrast calcite 13c values are highly negative as low as 41 7 and must have formed from waters with a large component of dissolved inorganic carbon derived from methane oxidation pore water data show that despite complete sulfate reduction methanogenesis appears not to be an important process presently occurring in the upper 400 m of the outer new jersey shelf in contrast the carbon isotopic composition of the siderites and calcites document an active methanogenic zone during their formation the methane may have been either oxidized or vented from shelf sediments perhaps during sea level fluctuations if this unaccounted and variable methane flux is an areally important process during neogene sea level fluctuations then it likely plays an important role in long term carbon cycling on passive continental margins

an analysis of tropical instability waves in a numerical model of the pacific ocean 2 generation and energetics of the waves this work was supported by the department of com merce noaa under grant na56gp0026 one of the au thors sm was partially supported by a nasa global change fellowship ngt 30288 another author ab was supported by a ucar postdoctoral fellowship

coupling between northward propagating intraseasonal oscillations and sea surface temperature in the indian ocean using a hybrid atmosphere ocean coupled model it is shown that during the boreal summer northwardpropagating intraseasonal oscillations npisos are strongly coupled to the underlying sea surface temperature sst in the indian ocean sector on the one hand the intraseasonal atmospheric convection changes the sst through solar radiation latent heat flux and mixed layer entrainment on the other the induced sst fluctuations feed back to affect the intraseasonal convection the preferential northward rather than southward propagation of boreal summer isos in the indian ocean is partially explained by an interaction among the summer mean climate state the atmospheric disturbances and the ocean surface temperature a solution to an atmosphere only model forced with daily sst produces much stronger npisos than a similar solution forced with monthly mean sst amip type run the atmosphere only model however even when it is forced by daily sst from the coupled model with a small amount of noise in the initial and or boundary conditions is unable to reproduce the npisos in the coupled case in the coupled system intraseasonal sst anomalies are forced by intraseasonal atmospheric convection and hence are in quadrature with the convection in the stand alone atmospheric model however sst acts only as a boundary forcing and the resultant atmospheric convection has almost the same phase with the underlying sst one consequence is that the intensity of the sst forced intraseasonal convection in the stand alone atmospheric model is considerably weaker than in the coupled model finally solutions indicate that the northward movement of the off equatorial convection in the northern indian ocean is more closely related to local intraseasonal sst anomalies than to the equatorial eastward moving madden julian oscillation positive negative sst anomalies in the northern indian ocean lead the active break phases of the intraseasonal convection by about 2 pentads 10 days therefore intraseasonal sst anomalies in the northern indian ocean are potentially a useful index to forecast active break spells of the south asian summer monsoon

dependence of simulation of boreal summer tropical intraseasonal oscillations on the simulation of seasonal mean the link between realism in simulation of the seasonal mean precipitation and summer tropical intraseasonal oscillations and their dependence on cumulus parameterization schemes is investigated using the florida state university global spectral model fsugsm forty member model ensemble simulations of the northern summer season are generated for three different cumulus parameterization schemes namely arakawa schubert naval research laboratory nrl zhang and mcfarlane national center for atmospheric research ncar and emanuel massachusetts institute of technology mit the mit scheme simulates the regional pattern of seasonal mean precipitation over the indian monsoon region well but has large systematic bias in simulating the precipitation over the western pacific and the maritime continent although the simulation of details of regional distribution of precipitation over the indian monsoon region by the nrl and ncar schemes is not accurate they simulate the spatial pattern of precipitation over the tropical indo pacific domain closer to observation the nrl scheme seems to captures the observed northward and eastward propagation of intraseasonal precipitation anomalies realistically however the simulations of the ncar and mit schemes are dominated by a westward propagating component the westward propagating mode seen in the model as well as observations is indicated to be an equatorial rossby wave modified by the northern summer mean flow an examination of the relationship between simulation of the model climatology and eastward propagating character of monsoon intraseasonal oscillations isos in a limited sample shows that the scheme that simulates better seasonal mean pattern of rainfall over the tropical indo pacific domain also simulates better intraseasonal variance and more realistic eastward propagation of monsoon isos among the parameters known to be important for meridional propagation of the summer monsoon isos the meridional gradient of mean humidity in the lower atmosphere seems to be crucial in determining the northward propagation in the equatorial indian ocean between 10 s and 10 n for better prediction of the seasonal mean indian monsoon therefore the model climatology should have minimum bias not only over the indian monsoon region but also over the entire indo pacific basin

extension of berner s new geochemical classification of sedimentary environments to ancient sediments using stable isotopes of carbon and oxygen in siderite nodules and lithology of host shales one can recognize geochemical environments proposed by berner in devonian carboniferous sediments of the appalachian basin his oxic post oxic and sulfidic diagenetic environments are well represented sediments of the methanic environment may be present but the evidence is equivocal the sulfidic sediments can be further subdivided into well laminated and bioturbated corresponding to the presence of h 2 s in the overlying water in the first case but confined to the sediment pore waters in the second journal abstract

sulfidation of organic matter associated with gold mineralization pueblo viejo dominican republic the pueblo viejo district is one of the largest producers of precious metals in the world yielding more than 11 000 kg of au annually gold mineralization at pueblo viejo is hosted in spilite and coarse elastic and finely laminated fine grained carbonaceous sedimentary rocks of the lower cretaceous los ranchos formation mineralization was accompanied by sulfidation as evidenced by i the occurrence of siderite distal to mineralization and pyrite proximal to mineralization 2 increased s fe ratios associated with au mineralization 3 the occurrence of native s in and adjacent to mineralization and 4 the presence of sulfidized organic matter organo s compounds in mineralized rocks organic matter in the carbonaceous sedimentary rocks comprises vitrinite and pyrobitumen rock eval pyrolysis data indicate that this organic matter is overmature hi 55 the organic matter is s rich up to 14 wt s in rocks where all fe has been sulfidized to pyrite x ray absorption near edge structure xanes analysis indicates that the c bonded s is thiophenic early disseminated au mineralization is postulated to have occurred in response to sulfidation of ferrous fe to form pyrite the consequent decline in the activity of h2s in the mineralizing fluid would have destabilized au bisulfide complexes and caused deposition of gold the restriction of s rich organic matter to rocks in which all fe occurs as pyrite indicates that sulfidation of organic matter postdates sulfidation of ferrous fe and therefore deposition of much of the au

stable isotopic and carbonate cyclicity in lower cretaceous deep sea sediments dominance of diagenetic effects abstract oxygen and carbon isotopic variability of the dominant m carbonate fraction within bedded organic carbon rich lower cretaceous sediment intervals from various dsdp sites are closely correlated with preservational changes in the carbonates isotopic fluctuations are absent where carbonate contents vary little and where the carbonate fraction is dominated by biogenic phytoplankton remains within each of the studied intervals oxygen and carbon isotopic ratios become increasingly more negative in samples with carbonate contents higher than about 60 in which the proportion of diagenetic microcarbonate increases rapidly carbon isotopic ratios show a trend towards positive values in samples with carbonate contents of less than 40 and strong signs of dissolution the taxonomic composition of nannofossil assemblages varies little within single intervals despite significant differential diagenesis among individual beds this points towards ecological stability of oceanic surface waters during the deposition of alternating beds bedding is however closely related to changing bioturbation intensity indicating repeated fluctuations of the deep water renewal rates and oxygen supply various microbial decomposition processes of organic matter leading to bed specific differential carbonate diagenesis resulted in an amplification of primary bedding features and are considered responsible for most of the observed fluctuations in the stable isotopic ratios and carbonate contents

ironstones and green marine clays in the dongjeom formation early ordovician of korea abstract in the sino korean north china block the occurrence of ironstone is reported for the first time from the lower ordovician dongjeom formation korea the dongjeom formation comprises much quartzose sediment deposited on the extensive carbonate platform and is composed of three coarsening upward sequences ironstone beds are distributed on the tops of the lower two sequences suggesting that they mark approximately maximum flooding events during the relative lowstand of sea level when the dongjeom formation was deposited extensive weathering in the source areas coupled with higher order sea level rises resulted in the formation of the dongjeom ironstones the dongjeom ironstones include much green marine clays ironstones of the lowest sequence are characterized by glaucony facies and those of the middle sequence by chamosite facies chemical compositions of dongjeom glauconies reveal that they were originally nascent to slightly evolved 3 to 5 k 2 o wt and that they were affected by illitization after burial their immature compositions suggest that glauconies were formed in about 10 3 to 10 4 years or less on the seafloor the substrates for glauconitization are interpreted as detrital mineral grains regressions after glauconitization introduced iron oxides to the green grains eventually forming the iron oxide rich band under the most oxidizing conditions the distribution of glauconies in limited horizons suggests that the dongjeom glauconies are autochthonous in origin chamosites have granular shapes and are mixed with quartzose sand grains suggestive of reworking during storms the dongjeom chamosites were transformed from the precursor berthierines the occurrence of glauconies in correlative horizons in korea and north china may indicate that glauconitization in the host sediments which were deposited in far northern gondwana occurred under the influence of a coeval transgressive event

an undulatory discontinuity surface on a gently inclined muddy ramp possible evidence of secondary helical flow from the geological record an unusual somewhat cryptic undulatory discontinuity has been recognized near the basal contact of the wanakah shale member of the middle devonian ludlowville formation in western new york it is in part marked by undulating diagenetic limestone beds and concretionary horizons but can be traced continuously by subtle surfaces of fossil and pyritic lags this surface marks the top of parallel elongate mud ridges trending approximately n s perpendicular to the inferred e w depositional strike of the appalachian basin in western new york these ridges are observed in the field as irregularly spaced mud swells which have up to 1 5 m of relief and vary from 30 to 50 m or more in width the intervening broad flat channel floors are characterized by dense concentrations of diminutive brachiopods with gastropods and styliolinids which are gradually replaced by thin styliolinid horizons with abundant pyrite nodules and pyritized burrows over the tops of the swells traceable shelly horizons are observed to pinch out over the swells suggesting a period of relatively undisturbed sediment filling following the formation of the channellized surface the interval of nearly barren shale below this irregular surface however contains concretionary horizons and rare styliolinid pavements which are themselves irregular possibly indicating a changing topography for this surface through time previous taphonomic and palaeoecological studies of the lower wanakah shale member have disclosed a well defined regressive transgressive cycle with more subtle superimposed subcycles the undulatory surface described here occurs within the early regressive part of this cycle and appears to record an accentuated regressive kick of a lower order subcycle the formation of this surface is therefore interpreted to be a consequence of regressive submarine erosion and sediment bypass together with redeposition from suspension the development of the channels and parallel longitudinal mud ridges was probably controlled by helical flow cells within offshore directed bottom currents they may be the first recorded instance of sedimentary furrows described from the geological record taphonomic and biofacies data indicate relative depths below average storm wave base suggesting that sediment winnowing and redeposition occurred at depths only rarely affected by the direct impact of storm wave agitation

individual and combined influences of enso and the indian ocean dipole on the indian summer monsoon the relative influences of the enso and indian ocean dipole iod events on the indian summer rainfall were studied using observational data and an atmospheric general circulation model agcm the composite analysis of rainfall anomalies demonstrates that the iod while significantly influencing the indian summer monsoon rainfall also significantly reduces the impact of enso on the indian summer rainfall whenever these events with the same phase co occur the agcm experiments have shown that during an el nino event the walker circulation over the tropical indo pacific region is modulated a low level anomalous divergence center over the western pacific and an anomalous convergence zone over the equatorial indian ocean are induced furthermore an anomalous zone of convergence over the myanmar and south china regions is induced during an el nino event these zones of anomalous convergence are complemented by anomalous divergence over the indian region causing anomalous subsidence and weakened rainfall when a strong positive iod event simultaneously occurs with el nino the latter s influence on the indian monsoon is reduced by both poles of the iod through the following mechanism an anomalous divergence center as compared to the summers when an el nino alone occurs is introduced in the eastern tropical indian ocean from this center the anomalous divergent flow crosses the equator and this air while weakening the el nino induced divergence over the western pacific also leads to convergence over the indian monsoon region this results in the reduction of the enso induced subsidence and the related rainfall deficit over the eastern flank of the indian monsoon trough region and adjoining regions to the east on the other hand over the western part of the tropical indian ocean sector part of the anomalous ascending motion from the warm pole of the positive iod event subsides just to the north of the equator moves northward ascends and causes surplus rainfall this reduces the enso induced rainfall deficit over western india the western part of the monsoon trough and parts of pakistan the agcm experiments also demonstrate that positive iod events amplify the enso induced dryness over the indonesian region

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

seasonality and meridional propagation of the mjo abstract the madden julian oscillation mjo is known to have a substantial impact on the variability of the asian australian summer monsoons an important but not well understood aspect of the mjo monsoon connection is the meridional propagation of bands of enhanced or reduced precipitation that are especially pronounced during the northern summer in this study the nature of the seasonality of the mjo is examined with a focus on the meridional propagation using both observations and simulations with an atmospheric general circulation model agcm a key result is that the agcm when forced with idealized eastward propagating equatorial dipole heating anomalies reproduces the salient features of the observed seasonality in the precipitation and wind fields associated with the mjo including meridional propagation into the indian and australian summer monsoon regions an analysis of the simulations and observations shows that the off equatorial precipitation anomalies are initiated by surface fricti

early diagenesis and its relationship to depositional environment and relative sea level fluctuations upper cretaceous marshybank formation alberta and british columbia early diagenesis of the upper cretaceous late coniacian to early santonian marshybank formation was controlled by depositional environment composition of depositional water fe and organic content of the sediment sedimentation rate proximity to the shoreline and influx of meteoric water related to relative sea level fall five depositional environments each characterized by a distinct early diagenetic mineral assemblage have been recognized offshore shelf sediments that were deposited in a dysaerobic environment are characterized by abundant framboidal pyrite and rare septarian concretions composed of early calcite and siderite intense sulphate reduction promoted by the dysaerobic depositional water was the primary influence on early diagenesis offshore shelf sediments deposited under aerobic conditions are characterized by abundant concretions composed of two generations of siderite s1 and s2 in this environment methanogenesis rather than sulphate reduction was more important early diagenesis of the inner shelf sands was generally limited however in sands deposited proximal to the shoreline mixing of marine and meteoric waters promoted crystallization of fe rich chlorite and siderite the shoreface was characterized by dissolution of detrital minerals in the upper portion and precipitation of kaolinite or illite smectite in the lower portion in the coastal plain environment brackish water and early reducing conditions resulted in formation of abundant euhedral pyrite ankerite rather than siderite is the typical early diagenetic carbonate the 18o values of the earliest cements i e early calcite siderite s1 inner shelf siderite indicate crystallization from a low 18o marine derived porewater assuming crystallization at 25 c a 18o value of about 7 smow can be estimated for the seaway during marshybank formation time similar calculations for the overlying dowling member puskwaskau formation suggest that the 18o value of the seaway increased to about 4 smow consistent with its transgressive nature very low 18o values are exhibited by siderite s2 these results indicate crystallization during intermediate diagenesis 60 c from meteoric water 15 smow that entered the marshybank formation during sea level lowstand

influence of indian ocean dipole on poleward propagation of boreal summer intraseasonal oscillations abstract the influence of the indian ocean dipole iod on the poleward propagation of boreal summer intraseasonal oscillations bsisos is examined using observed datasets this study finds that coherent incoherent poleward propagation of precipitation anomalies from 5 s to 25 n are observed during negative positive iod years disorganized poleward propagation of bsiso in the south equatorial indian ocean is observed during positive iod years the rationale behind such an anomaly in the poleward propagation of bsiso in contrasting iod years is identified based on the theory of northward propagating bsiso which suggests the influential role of air sea interaction on the genesis and propagation of bsiso it is found that the mean structure of moisture convergence and meridional specific humidity distribution undergoes radical changes in contrasting iod years which in turn influences the meridional propagation of bsiso this study assumes significance considering the critical role of bsiso in modulat

relation between eurasian snow cover snow depth and the indian summer monsoon an observational study abstract satellite derived snow cover data for 22 yr and snow depth data for 9 yr over eurasia have been analyzed to reexamine the possible relation of snow with the indian summer monsoon in contrast to the previous studies that use snow cover averaged over all of eurasia as a single number the frequency of occurrence of snow at each grid point over eurasia is correlated with the indian summer monsoon rainfall thus specific geographical regions over eurasia that are responsible for the well known inverse relationship between eurasian snow cover and indian monsoon rainfall are delineated it is found somewhat surprisingly that western eurasia is the only geographical region for which a significant inverse correlation exists between winter snow cover and subsequent summer monsoon rainfall however composites for high and low snow cover over eurasia show spatially homogeneous large scale patterns of snow cover and surface temperature anomalies winters of high and low snow cover for eurasia are found t

effects of air sea coupling on the boreal summer intraseasonal oscillations over the tropical indian ocean the effects of air sea coupling over the tropical indian ocean tio on the eastward and northward propagating boreal summer intraseasonal oscillation bsiso are investigated by comparing a fully coupled ctl and a partially decoupled indian ocean pdio experiment using sintex f coupled gcm air sea coupling over the tio significantly enhances the intensity of both the eastward and northward propagations of the bsiso the maximum spectrum differences of the northward eastward propagating bsiso between the ctl and pdio reach 30 25 of their respective climatological values the enhanced eastward northward propagation is related to the zonal meridional asymmetry of sea surface temperature anomaly ssta a positive ssta appears to the east north of the bsiso convection which may positively feed back to the bsiso convection in addition air sea coupling may enhance the northward propagation through the changes of the mean vertical wind shear and low level specific humidity the interannual variations of the tio regulate the air sea interaction effect air sea coupling enhances reduces the eastward propagating spectrum during the negative indian ocean dipole iod mode positive indian ocean basin iob mode and normal years during positive iod and negative iob years such phase dependence is attributed to the role of the background mean westerly in affecting the wind evaporation sst feedback a climatological weak westerly in the equatorial indian ocean can be readily reversed by anomalous zonal sst gradients during the positive iod and negative iob events although the ssta is always positive to the northeast of the bsiso convection for all interannual modes air sea coupling reduces the zonal asymmetry of the low level specific humidity and thus the eastward propagation spectrum during the positive iod and negative iob modes while strengthening them during the other modes air sea coupling enhances the northward propagation under all interannual modes due to the persistent westerly monsoon flow over the northern indian ocean

a whirling ecosystem in the equatorial atlantic 1 the equatorial pacific and atlantic oceans exhibit remarkable meridional undulations in temperature and chlorophyll fronts visible from space over thousands of kilometers and often referred to as tropical instability waves here we present new observations of an ecosystem ranging through three trophic levels phytoplankton zooplankton and small pelagic fish whirling within a tropical vortex of the atlantic ocean and associated with such undulations cold nutrient and biologically rich equatorial waters are advected northward and downward to form sharp fronts visible in all tracers and trophic levels the equatorward recirculation experiences upwelling at depth with the pycnocline and ecosystem progressively moving toward the surface to reconnect with the equatorial water mass the observations thus indicate that it is a fully three dimensional circulation that dominates the distribution of physical and biological tracers in the presence of tropical instabilities and maintains the cusp like shapes of temperature and chlorophyll observed from space

geology of the early devonian oolitic iron ore of the gara djebilet field saharan platform algeria abstract the oolitic iron ore of the gara djebilet field occurs within the early devonian sediments of the tindouf basin algerian sahara particularly in the upper djebilet formation of pragian age three large lenses form three individual deposits extending e w for about 60 km namely gara west gara center and gara east the mineralization is interbedded with argillaceous to sandy sediments and it can be related to a barrier island palaeoenvironment bordered by an inner lagoon or shallow embayment and an epicontinental sea trapped by palaeozoic shoals the oolitic sediments show a mineralogy marked mainly by magnetite hematite goethite maghemite chamosite bavalite siderite apatite and quartz three paragenetic associations present a vertical distribution with a lower non magnetitic ore a magnetitic ore and an upper non magnetitic ore three petrographical facies types have been defined a cemented facies foc a detrital facies fod and a non detrital facies fond chemical data for the whole field show a difference between the lower non magnetitic ore fe 54 6 the magnetitic ore fe 57 8 and the upper non magnetitic ore fe 53 the magnetitic ore which corresponds mainly to the workable ore cutoff grade at 57 has the following composition sio2 4 9 al2o3 4 2 fe2o3 61 43 feo 19 2 and p2o5 1 8 the corresponding calculated economical ore reserves are 985 106t with 57 8 fe regarding the genesis of the oolitic iron ore a southern source is suggested for the iron with deposition taking place in a quiet environment there the ooids developed by an intrasedimentary accretion mechanism around detrital grain within an iron rich mud the gara djebilet field is an important occurrence of the north african palaeozoic ironstone belt extending from the zemmour to libya which also includes ironstones of ordovician silurian and devonian age

diagenesis of ferriferous phases in the northampton ironstone in the cowthick quarry near corby england berthierine siderite and pyrite are the major ferriferous phases in the northampton ironstone nis mineralogical and chemical data suggest a formation of these phases in a diagenetic marine environment changing from post oxic to sulphidic conditions berthierine was formed first when the fe 2 activity in the diagenetic system increased later this phase was partially replaced by siderite and or pyrite a second stage of the diagenetic development in the nis with increasing co 2 partial pressure p co 2 is documented by siderite the isotopic composition 18 o mean value 1 7 pdb 13 c mean value 8 6 pdb points to siderite precipitation from a marine porewater environment with a microbial co 2 source the shift from post oxic to sulphidic conditions is indicated by the occurrence of pyrite and can be considered as a final stage the diagenetic processes in the marine environment and the formation of the ferriferous phases were stopped by the influx of brackish or fresh water when the midland shelf turned estuarine

buoyant gravity currents released from tropical instability waves abstracttwo extremely sharp fronts with changes in sea surface temperature 0 4 c over lateral distances of 1 m were observed in the equatorial pacific at 0 140 w and at 0 75 n 110 w in both c

growth mechanisms and geochemistry of carbonate concretions from the cambrian wheeler formation utah usa carbonate concretions provide unique records of ancient biogeochemical processes in marine sediments typically they form in organic rich mudstones where a significant fraction of the bicarbonate required for carbonate precipitation is supplied from the decomposition of organic matter in the sediments as a result carbonates that comprise concretions are usually characterized by broad ranges in 13c and include values that are significantly depleted relative to seawater this article reports results from a physical petrographic and geochemical analysis of 238 concretions from the wheeler formation cambrian series 3 utah usa which are unusual in several respects most prominently they formed in organic poor mudstones total organic carbon 0 1 to 0 5 and are characterized by a narrow range of 13c that onlaps the range of contemporaneous seawater values subtle centre to edge trends in 13c demonstrate that concretion precipitation was initiated by local chemical gradients set up by microbial activity in the sediments but was sustained during growth by a large pool of inorganic bicarbonate probably derived from alkaline bottom waters the large inorganic pool appears to have been important in facilitating rapid precipitation of the concretion matrix which occurred via both displacive and replacive carbonate precipitation during early diagenesis stable isotope data from cogenetic pyrite 34s and silica 18o phases provide insight into the evolution of biogeochemical processes during concretion growth and suggest that concretions were formed almost entirely during sulphate reduction with only minor modification thereafter concretions of the wheeler formation appear to represent an end member system of concretion formation in which rapid growth was promoted by ions supplied from sea water as such they offer insight into the spectrum of processes that may influence the growth of carbonate concretions in marine sediments

oxygen and carbon isotopic composition of marine carbonate concretions an overview abstract compilation of stable isotope data 18o and 13c for marine calcite siderite and dolomite concretions from a large number of studies reveals consistent and unanticipated isotopic trends although many of the dolomites have 18o values that are compatible with precipitation from unaltered seawater at low temperatures most of the calcites and siderites are far too depleted in 12o for such an origin this is surprising as most of the concretions appear to have formed very early in the diagenetic history of the sediments often within several meters of the sediment water interface the most likely cause of the anomalously depleted oxygen values is a decrease in pore water 18o values during early diagenesis a result perhaps of a significant influx of meteoric water into the marine shelf environment or water mineral interaction e g precipitation of 18o enriched minerals the carbon isotopic field for dolomite is quite different from that for calcite and siderite highly positive 13c values are fairly common only for dolomites this indicates that while dolomite concretions often form in sediments where methanogenesis is rapid precipitation of calcite and siderite concretions is restricted to sediments where either n methanogenesis takes place or where methanogenesis is not extensive enough to generate highly positive pore fluid 13c values this variation in carbon isotopic composition among the different minerals suggests that the rates of organic carbon oxidation and sedimentation may control the mineralogy of carbonate concretions high organic carbon oxidation rates favor dolomite and lower oxidation rates favor calcite or siderite

the three dimensional structure of an upper ocean vortex in the tropical pacific ocean in the equatorial pacific ocean easterly trade winds and the earth s rotation combine to drive surface currents away from the equator thereby causing cold nutrient rich subsurface water to upwell the front1 that forms between this upwelled water and warmer waters north of the equator is sometimes visible as a spectacular line in the sea 2 between 2 and 6 n westward propagating cusp shaped disturbances observed along this front3 have been attributed to the effect of dynamical instabilities in the system of zonal equatorial currents4 11but the connection between these phenomena remains unclear here we report extensive measurements from shipboard sensors satellite and drifting buoys which reveal the three dimensional structure of an anticyclonic eddy or vortex 500 km in diameter and centred at 4 n we suggest that cusp shaped disturbances of the front are caused by trains of large amplitude vortices which are driven by instability of the mean zonal shear we show that these vortices not only play an important role in the meridional transport of heat salt and momentum but are also associated with regions of intense horizontal convergence along the front where dramatic concentrations of marine life are observed

tropical 45 day oscillations during the 1979 northern hemisphere summer abstract based on fgge 1 cvel iiib data the structural features of 45 day perturbations over a tropical belt 15 n 15 s during the 1979 summer are detailed at the equator 45 day perturbations which are primarily associated with the zonal wind components of wavenumber 1 propagate eastward 8 of longitude per day and upward 0 7 km per day probably indicating downward energy flux in the southern hemisphere tropics 0 15 s the 45 day zonal mean wind perturbations propagate downward with an approximate phase speed of 0 8 km per day in the northern hemisphere tropics they are largely of standing character with the maximum amplitude 3 m s 1 near 200 mb at 15 n there exists a strong association between monsoon activity over south asia and changes in the intensity of the equatorial walker circulation when active monsoons occur over south asia the walker circulation becomes stronger than usual with prominent 850 mb easterlies 200 mb easterlies over the eastern pacific east of the date line an

sea surface cooling at the equator by subsurface mixing in tropical instability waves changes in the sea surface temperature of equatorial waters have critical effects on the large scale atmospheric circulation shipboard measurements of turbulence kinetic energy dissipation rate indicate that seasonal surface cooling in the central equatorial pacific may be largely caused by mixing induced by tropical instability waves

the zonal momentum balance of the equatorial undercurrent in the central pacific abstract current velocity data from an array of subsurface moorings deployed during the tropical instability wave experiment from may 1990 to june 1991 are used to diagnose the upper ocean zonal momentum balance at 0 140 w the flow field and associated zonal momentum flux divergence are fully three dimensional over the upper 250 m consistent with the earliest descriptions and theoretical ideas of the equatorial undercurrent euc estimates of the vertical stress divergence show dynamical flow regimes that change between the surface and the base of the euc being essentially linear modified by nonlinearity near the surface weakly nonlinear at the euc core and fully nonlinear below the core the vertical stress divergence is much larger over the lower portion of the euc than previously reported but this is consistent with the observed downstream deceleration of the euc and the idea that vertical mixing is important in maintaining the thermostad nonlinearity becomes increasingly important with dec

observation and analysis of shear instability in the fraser river estuary 1 we investigate the occurrence of shear instability in the fraser river estuary instabilities observed with an echo sounder are compared with a linear stability analysis based on observed velocity and density profiles we find that each set of observed instabilities coincides with an unstable mode predicted by the taylor goldstein equation each of these instabilities occurs in a region where the gradient richardson number is less than the critical value of 1 4 both the taylor goldstein predictions and the echo soundings indicate the instabilities are concentrated either above or below the density interface this one sidedness is in contrast to the archetypal kelvin helmholtz instability although the dominant source of mixing in the estuary appears to be caused by shear instability when the tide produces strong near bed velocities small scale overturning due to boundary layer turbulence is apparent throughout the depth

mesoscale to submesoscale transition in the california current system part ii frontal processes this is the second of three papers investigating the regime transition that occurs in numerical simulations for an idealized equilibrium subtropical eastern boundary upwelling current system similar to the california current the emergent upper ocean submesoscale fronts are analyzed from phenomenological and dynamical perspectives using a combination of composite averaging and separation of distinctive subregions of the flow the initiating dynamical process for the transition is near surface frontogenesis the frontal behavior is similar to both observed meteorological surface fronts and solutions of the approximate dynamical model called surface dynamics i e uniform interior potential vorticity q and diagnostic force balance in the intensification of surface density gradients and secondary circulations in response to a mesoscale strain field however there are significant behavioral differences compared to the surface dynamics model wind stress acts on fronts through nonlinear ekman transport and creation and destruction of potential vorticity the strain induced frontogenesis is disrupted by vigorous submesoscale frontal instabilities that in turn lead to secondary frontogenesis events submesoscale vortices and excitation of even smaller scale flows intermittent submesoscale breakdown of geostrophic and gradient wind force balance occurs during the intense frontogenesis and frontal instability events

structures and mechanisms of the northward propagating boreal summer intraseasonal oscillation abstract the spatial and temporal structures of the northward propagating boreal summer intraseasonal oscillation bsiso are revealed based on the analysis of both the echam4 model simulation and the ncep ncar reanalysis the bsiso structure and evolution characteristics simulated by the model bear many similarities to those derived from the ncep ncar reanalysis the most notable features are the remarkable meridional asymmetries relative to the bsiso convection in the vorticity and specific humidity fields a positive vorticity perturbation with an equivalent barotropic structure appears a few latitude degrees north of the convection center the maximum specific humidity also shows a clear northward shift in the lower troposphere two internal atmospheric dynamics mechanisms are proposed to understand the cause of the northward propagation of the bsiso the first is the vertical shear mechanism the key process associated with this mechanism is the generation of barotropic vorticity due to the couplin

high resolution calcareous nannoplankton palaeoecology as a proxy for small scale environmental changes in the early miocene within a 5 5 m thick succession of upper burdigalian cnp zone nn4 shallow neritic sediments from the north alpine foreland basin in lower austria a high resolution section of finely laminated sediment with a thickness of 940 5 mm was logged the section was continuously sampled resulting in 100 samples covering a thickness of 10 mm each an integrated approach was applied to these samples in order to study proxy records including calcareous nannoplankton geochemical and geophysical data multivariate statistics on the autochthonous assemblage were used to evaluate the ecological preferences of each taxon and to rule out possible contamination of the signal by taphonomic processes in order to assess changes in the assemblage composition throughout the section three taphogroups were defined using both the autochthonous and allochthonous nannofossils based on the distribution of these taphogroups five distinct intervals were defined that are indicative of centennial to decadal changes in palaeoenvironmental conditions combining these results with other proxies geochemistry geophysics we were able to reconstruct short term small scale variations in terms of temperature primary productivity bottom water oxygenation organic matter flux freshwater influx and changes in relative sea level in a highly dynamic shallow marine setting this study represents the first such high resolution analysis performed on a marine succession of late burdigalian age it is also a first attempt to analyse outcrop data on such a high resolution sub milankovitch scale with respect to calcareous nannoplankton in conjunction with geochemical and sedimentological data

sequence stratigraphic context of extensive basin margin evaporites middle jurassic gypsum spring formation wyoming u s a abstract ancient marine evaporites are commonly far more extensive than any known modern evaporite system this is true not only for basin central saline giants but also for evaporites that occur in basin margin settings and the origin of these basin margin systems is unclear extensive basin margin evaporites of the middle jurassic gypsum spring formation are well exposed along the eastern flank of the bighorn basin in wyoming usa and a facies and sequence stratigraphic analysis was undertaken to understand the origin of these evaporites and associated deposits the gypsum spring formation was deposited on a northwestward dipping mixed evaporate carbonate siliciclastic ramp with facies and depositional environments that include distal ooid shoal grainstone open marine shallow subtidal peloidal skeletal wackestone to packstone restricted shallow subtidal laminated lime mudstone peritidal dolostone and microbialite as well as red mudstone and gypsum deposited on mud flats sabkhas and salinas three depositional sequences are present with the j 1 j 1a and j 1b sequence boundaries characterized locally by chert pebble lags silicified horizons and iron rich paleosols evaporites accumulated in a basin margin position with 1 6 m beds of gypsum forming in salinas and sabkhas and nodular anhydrite and gypsum forming in red mudstones deposited on sabkhas and mud flats the limited lateral extent of salina type gypsum beds and the variable number of these beds among the exposures indicates substantial autocyclic control on the formation of salinas salinas are well developed in the tst of the j 1 sequence and sabkhas and mud flats are well developed in the j 1 hst the j 1a hst and the j 1b tst the great lateral extent of the gypsum spring evaporites reflects the original expanse of the depositional environment in which they formed and is not the result of diachroneity of a narrow evaporite precipitating belt such as the modern day coastal sabkhas of the trucial coast the great lateral extent of gypsum spring evaporites suggests that they were precipitated mainly from continental brines on an expansive desert mudflat

the role of turbulence stress divergence in decelerating a river plume 1 turbulence controls the composition of river plumes through mixing and alters the plume s trajectory by diffusing its momentum while believed to play a crucial role in decelerating river source waters the turbulence stress in a near field river plume has not previously been observationally quantified in this study finely resolved density velocity and turbulence observations are combined with a control volume technique to describe the momentum balance in the columbia river s near field plume during 10 tidal cycles that encompass both large and small river flow turbulence stress varies by 2 3 orders of magnitude both within a given ebb and between ebbs with different tidal or river forcing its magnitude scales with the strength of the instantaneous ebb outflow i e high stresses occur during peak flow of strong ebbs during these periods the momentum equation is represented by a balance between stress divergence and plume deceleration as the flow relaxes the stress divergence weakens and other terms pressure gradient and coriolis may become appreciable and influence plume deceleration while the momentum balance could not be closed during these weaker flow periods during strong tidal pulses the time scale for decay based on observed stress is significantly less than a tidal half period indicating that stress divergence plays a fundamental role in the initial deceleration of the plume

a convergent instability wave front in the central tropical pacific abstract a narrow front encountered at 2 1 n 140 w was characterized by high productivity and a 2 c temperature drop satellite sea surface temperature sst imagery showed this front to extend over 400 km from just north of the equator to 5 n along the western leading edge of a tropical instability wave cold cusp during 3 days of observations the front propagated westward at 64 cm s 1 while oriented sw ne water velocities and densities around the front were measured using a shipboard acoustic doppler current profiler and hydrographic stations these data showed warm fresh northern water moving southward at speeds of up to 50 cm s 1 to encounter cold salty equatorial water moving northward at up to 40 cm s 1 both slabs were embedded in the south equatorial current here a uniform 100 m deep westward flow of 90 cm s 1 at their meeting a net convergence of 30 cm s 1 across the 1 km wide front drove intense downselling of up to 0 9 cm s 1 both t s relations and velocity fields indicate that cold water subducted beneath the warmer water and continued northward to beyond 3 n deepening to 120 m for analysis the data were gridded in a co ordinate system centered on the front and moving with it the dynamics near the front consisted of a balance between pressure gradient and non linear advection the coriolis force was smaller and associated mostly with the broader scale flow thus the front itself was not geostrophic but rather the leading edge of a density driven flow that can be accurately modeled as a dissipative lock exchange the subduction released potential energy at the rate of 5290 230 w m 1 of front length comparable to previous estimates of large scale energy conversion nevertheless the kinetic energy gain by the larger scale instability was only 840 31 w m 1 implying that the rest of the energy was lost to the large scale flow turbulent dissination as derived from the rate of mixing accounted for only 500 300 w m 1 of this loss on the full 100 km scale of the layered flow the coriolis force became important the orientation of the surface front and the angle of the interface s northward deepening produced a pressure gradient that balanced the meridional flow geostrophically

the madden julian oscillation in echam4 coupled and uncoupled general circulation models the madden julian oscillation mjo dominates tropical variability on timescales of 30 70 days during the boreal winter spring it is manifested as an eastward propagating disturbance with a strong convective signature over the eastern hemisphere the space time structure of the mjo is analyzed using simulations with the echam4 atmospheric general circulation model run with observed monthly mean sea surface temperatures ssts and coupled to three different ocean models the coherence of the eastward propagation of mjo convection is sensitive to the ocean model to which echam4 is coupled for echam4 opyc and echo g models for which 100 years of daily data is available monte carlo sampling indicates that their metrics of eastward propagation are different at the 1 significance level the flux adjusted coupled simulations echam4 opyc and echo g maintain a more realistic mean state and have a more realistic mjo simulation than the nonadjusted scale interaction experiment sintex coupled runs the sintex model exhibits a cold bias in indian ocean and tropical west pacific ocean sea surface temperature of 0 5 c this cold bias affects the distribution of time mean convection over the tropical eastern hemisphere furthermore the eastward propagation of mjo convection in this model is not as coherent as in the two models that used flux adjustment or when compared to an integration of echam4 with prescribed observed sst this result suggests that simulating a realistic basic state is at least as important as air sea interaction for organizing the mjo while all of the coupled models simulate the warm cold sst anomalies that precede succeed the mjo convection the interaction of the components of the net surface heat flux that lead to these anomalies are different over the indian ocean the echam4 opyc model in which the atmospheric model is run at a horizontal resolution of t42 has eastward propagating zonal wind anomalies and latent heat flux anomalies however the integrations with echo g and sintex which used t30 atmospheres produce westward propagation of the latent heat flux anomalies contrary to reanalysis it is suggested that the differing ability of the models to represent the near surface westerlies over the indian ocean is related to the different horizontal resolutions of the atmospheric model employed

geochemistry of carbonate cements in the sag river and shublik formations triassic jurassic north slope alaska implications for the geochemical evolution of formation waters carbonate cements calcite siderite dolomite and ankerite formed throughout the diagenetic history of the sag river and shublik formations the trace element and isotopic geochemistry of these cements varies as a function of the timing of precipitation earliest calcites formed prior to significant compaction of the sediment are relatively enriched in mg up to 4 4 mol and have 87sr 86sr values mean 0 707898 compatible with the original marine pore waters later calcites are relatively fe rich up to 5 0 mol and are characterized by increasing 87sr 86sr values up to 0 712823 and sr content with decreasing age the fe content of zoned siderite and dolomite ankerite rhombs increases towards the outside of the rhombs i e increasing fe content with decreasing age these geochemical variations appear principally to result from changes in pore water chemistry during diagenesis the increase in 87sr 86 sr and sr content of the cements is most likely due to interaction between pore waters and 87 sr rich clay and possibly feldspar in ellesmerian mudrocks whole rock 87sr 86 sr signatures for the mudrocks are 0 716 pore water fe2 concentration was probably controlled by diagenetic alterations involving fe bearing minerals e g pyrite precipitation a reconnaissance examination of carbonate cements in the overlying kingak shale indicates that similar alterations occurred in the kingak the low 18 o value of some calcite cements 11 96 pdb suggests that an influx of meteoric water may have occurred in the mid neocomian though the low value could also result from an abnormally high geothermal gradient associated with mid neocomian rifting

diagenesis of the kimmeridge clay formation onshore uk study of sedimentology carbonate geochemistry and clay mineralogy of four laterally continuous beds from the outcrop of the kimmeridge clay formation indicates strong lateral variations in the depositional and early diagenetic processes reflecting the basin and swell topography of the depositional basin the mudstones from the swell environment with low sedimentation and subsidence rates are shelly and carbonate rich with thin poorly developed oil shales they were deposited under dysaerobic conditions with consequent poor organic matter preservation early diagenetic processes were limited to the sulphate reduction and methanogenesis zones with the formation of discrete horizons of concretions the shallow burial depths attained are reflected by the immaturity of the organic matter in the mudstones although ordered illite smectites are present sediments from other locations comprise black organic rich mudstones the thick beds and good organic matter preservation indicating deposition under high sedimentation and subsidence rates with anoxic bottom waters in a basinal environment these indurated mudstones contain a few shell fragments and much pyrite indicating intense reaction in the sulphate reduction zone carbonates were precipitated in the methanogenesis and decarboxylation zones as ferroan calcites and dolomites the much greater burial depths are indicated by the higher maturity of the organic matter and by the ordered nature of the illite smectites and the loss of kaolinite

a frontal challenge for climate models the ocean surface is filled with a convoluted web of fronts that separate waters of different temperatures and salinities see the figure just as thin ducts in the lung called alveoli facilitate the rapid exchange of gases when breathing fronts are the ducts through which heat carbon oxygen and other climatically important gases enter into the deep ocean a lack of observations however has hampered progress in understanding the dynamics of fronts which can be as narrow as hundreds of meters and as wide as tens of kilometers global satellite measurements of ocean surface velocities and air sea fluxes for instance are only available at resolutions of a few hundred kilometers although shipboard researchers can sample vertical ocean profiles down to centimeter scales only rarely do they collect profiles that are less than 100 km apart on page 318 of this issue d asaro et al 1 present a breakthrough in observing ocean fronts providing direct observations of the workings of the kuroshio front off japan on scales from kilometers to millimeters this detailed and wide ranging portrait was made possible by the development of towed instruments that continuously sample the waters behind a steaming ship the deployment of freely drifting instruments that follow ocean currents and the exercising of a great deal of ingenuity in keeping all these tools along the front for a few weeks in 2007

spherulitic siderites in the holocene coastal deposits of korea eastern yellow sea elemental and isotopic composition and depositional environment abstract siderite concretions are recovered from both freshwater unit ii and tidal unit i deposits in the holocene macrotidal flat of kyunggi bay west coast of korea siderites from both units show a spherulitic and well rounded texture and well developed equant rhombs on the external surfaces the size of the concretions in unit ii 50 150 m in diameter is normally larger than that in unit i 10 20 m the siderites in unit ii are chemically pure and highly enriched in fe whereas those of unit i are relatively impure and distinctly zoned demarcating high mn up to 69 1 mol in the core and high fe up to 75 9 mol in the margin within siderites of unit i substitution for fe by ca and mg reaches up to 20 3 mol mean 15 1 mol and 16 1 mol mean 12 6 mol respectively bulk 18 o values 0 7 to 1 3 peedee belemnite pdb for siderites in unit i are relatively higher than those 7 1 to 0 5 pdb in unit ii regardless of units siderite 13 c values 21 3 to 11 2 pdb are persistently low indicating microbially mediated precipitation at shallow burial depth extensive mn ca and mg substitution coupled with enrichment of 18 o in the siderites of unit i seems to reflect marine influence during the holocene transgression the occurrence of early diagenetic siderites provides supporting evidence on the depositional environment marine vs non marine of the holocene muddy coastal deposits of korea eastern yellow sea

the boreal summer intraseasonal oscillation relationship between northward and eastward movement of convection the summertime intraseasonal oscillation iso is an important component of the south asian monsoon lagged regressions of intraseasonally filtered 25 80 days outgoing longwave radiation olr reveal that centers of convection move both northward and eastward from the central equatorial indian ocean subsequent to the initiation of an iso eastward movement of convection is also seen at indian subcontinent latitudes 10 8 208n based on the regression results the summertime iso convection signal appears as a band tilting northwestward with latitude and stretching from the equator to about 208n viewed along any meridian convection appears to propagate northward while equatorial convection propagates to the east to examine the robustness of the connection between eastward and northward movement individual isos are categorized and composited relative to the strength of the large scale eastward component of convection in the central equatorial indian ocean it is found that the majority of isos that exhibit northward movement onto the indian subcontinent 42 out of 54 isos or 78 also exhibit eastward movement into the western pacific ocean it is also found that when convection in the central indian ocean is not followed within 10 20 days by convection in the western pacific ocean 12 out of 54 isos or 22 the independent northward movement of convection in the indian ocean region is somewhat stunted the link between the eastward and northward movement of convection is consistent with an interpretation of the summertime iso in terms of propagating equatorial modes the northward moving portion of convection is forced by surface frictional convergence into the low pressure center of the rossby cell that is excited by equatorial iso convection a similar convergence pattern is seen for the northern winter iso but it does not generate poleward movement due to relatively cool ssts underlying the surface convergence

downward lee wave radiation from tropical instability waves in the central equatorial pacific ocean a possible energy pathway to turbulent mixing turbulent mixing in the equatorial pacific ocean is an important process that controls diapycnal heat transport and hence affects the air sea interactions and global climate it is recently shown that in the eastern equatorial pacific strong mixing is induced in the thermocline by enhanced vertical shear associated with tropical instability waves tiws which propagate westward along the equator at a speed of 0 5 m s 1 with a wavelength of 1000 km in this study using a high resolution ocean general circulation model we show that the tiws can play an important role in inducing turbulent mixing in the thermocline also in the central equatorial pacific although the thermocline is too deep to be directly affected by the vertical shear of the tiws the front of the tiw is clearly manifested as a narrow strip of strong convergence of horizontal surface flow from which area downward and westward propagating internal waves are intermittently emanated these internal waves can be interpreted as lee waves generated by the surface flow convergence zone which acts like an inverted obstacle moving along the stratified ocean surface by inducing downward flow the associated downward energy flux below the surface mixed layer increases as the tiw structure becomes deeper toward the central equatorial pacific so that the energy pathway to turbulent mixing in the thermocline can be created the downward energy flux integrated over the entire equatorial pacific and averaged during january 2011 amounts to 8 1 gw occupying a significant fraction of the energy input to the tiws

gold deposition by sulfidation of ferrous fe in the lacustrine sediments of the pueblo viejo district dominican republic the effect of fe c s diagenesis on later hydrothermal mineralization in a maar diatreme complex abstract the pueblo viejo district located in the cordillera central of the dominican republic contains large au ag deposits associated with acid sulfate alteration within spilites conglomerates and carbonaceous sedimentary rocks that were deposited in a maar diatreme complex much of the au mineralization occurs in pyritic carbonaceous siltstones of the pueblo viejo maar diatreme member of the cretaceous los ranchos formation pyrite is the only fe bearing phase in mineralized rock whereas siderite is the dominant fe bearing phase in siltstones distal to mineralization disseminated pyrite occurs as framboids cubes pyritohedra concretions and cement early framboids occur throughout the district au occurs as inclusions in later non framboid disseminated pyrite nfdp an occurrence that is interpreted to be indicative of contemporaneous deposition pyrite framboids exhibit a wide range of 34s cdt values 17 5 to 4 8 and are interpreted to have formed during biogenic reduction of pore water sulfate the nfdp yield restricted 34s cdt values x 5 2 s 2 4 n 43 similar to those obtained from later vein pyrite x 6 4 s 1 5 n 12 alunite and barite have 34s values ranging from 18 8 to 21 6 the interpretation that the nfdp vein pyrite alunite and barite and possibly even the framboidal pyrite share a common source of igneous sulfur is supported by the 34s data siderite occurs as concretions and cement contains abundant mg fe0 75mg0 19mn0 03ca0 02co3 and has 13c pdb and 18o smow values ranging from 2 5 to 1 1 and 14 6 to 19 5 respectively these data are consistent with the interpretation that the siderite formed in lacustrine sediments and that the carbonate in the siderite is probably methanogenic although contributions from oxidation of organic matter during biogenic sulfate reduction thermal decarboxylation of organic matter or magmatic vapor cannot be ruled out disseminated au mineralization in the sedimentary rocks formed when a hydrothermal fluid encountered reactive fe2 in diagenetic siderite the ensuing pyrite deposition consumed h2s and destabilized the au hs 2 complex leading to precipitation of au the capacity of the sedimentary rocks to consume h2s and precipitate au was controlled by the amount of non pyrite fe present as siderite the abundance of siderite was controlled by the extent of pyrite formation during diagenesis

petrography and geochemistry of dispersed organic matter in the oligocene source rocks of the central western part of the getic depression romania abstract the aims of this study include the evaluation and interpretation of oligocene source rocks from the central western part of the getic depression romania and the identification of their maturation and their hydrocarbon potential 24 argillite samples belonging to the source rocks were studied using organic petrography and geochemistry methods including rock eval pyrolysis and the following sets of results were obtained maceral diversity values of vitrinite reflectance thermal alteration index and organic geochemical values the oligocene disperse organic matter contains both humic and terrestrial organic matter as well as sapropelic marine algal matter represented by telalginite and lamalginite several anoxic deep marine water intervals were recorded in the getic depression the samples are immature with tmax values ranging between 415 c and 434 5 c and random vitrinite reflectance of 0 32 and 0 53 the samples yield a total organic content between 0 55 and 5 71 with a hydrogen index between 9 and 379 mg g showing two types of kerogen a mixed type ii iii kerogen indicating a generative potential for hydrocarbon and gas and b type iii kerogen indicating a gas generative potential

influence of indian ocean dipole on boreal summer intraseasonal oscillations in a coupled general circulation model 1 the role of indian ocean dipole iod on poleward propagation of boreal summer intraseasonal oscillations bsiso is examined using long simulation of a coupled ocean atmosphere general circulation model the model sintex f1 simulates the salient features of bsiso realistically it is found that coherent incoherent poleward propagation of precipitation anomalies from 5 s to 25 n are observed during negative positive iod years the probable mechanisms behind such an anomaly in poleward propagation of bsiso in contrasting iod years are identified we find that the mean structure of meridional specific humidity distribution undergoes cardinal changes in contrasting iod years which in turn influences the meridional propagation of bsiso enhanced decreased air sea interaction in negative positive iod years also supports coherent incoherent poleward propagation of bsiso anomalies this study has important implications considering the critical role of bsiso in modulating the seasonal mean summer monsoon rainfall

a thermodynamic model for water column precipitation of siderite in the plio pleistocene black sea it has been hypothesized that finely disseminated soft wheat like grains of siderite in the sideritic muds of the plio pleistocene section of the black sea are sub aqueous precipitates hsu and kelts 1978 in an attempt to quantify this hypothesis we 1 investigated the chemistry mineralogy and isotopic composition of the siderites and associated calcite and 2 developed a thermodynamic model of endogenic siderite precipitation that is directly precipitated from the water column driven by sequential evaporative concentration of acidic dissolved or anic carbon and iron rich waters considering the average com position of the present day satilla drainage of the southeastern umted states as approximating the composition of the waters that fed the neogene black sea and allowing this water to evaporate isothermally at 25 c in equilibrium with atinospheric c02 pc02 l 0 3 5 attn we calculated the aqueous concentrations at which various carbonate phase5 would precipitate out of the system it is shown that evaporation of this water to roughly one twelfth of its original volume can result in precipitation of the pure endmember siderite alone relating our geochemical and modeling results to the details of black sea climatostratigraphic and evolutionary history dur ing the times of deposition of the siderite units we corroborate the qualitative arguments of hsu and kelts 1978 we also conclude that climate was the chief forcing function in transforming episodically the calcite precipitating eutrophic water masses of the plio pleistocene basin to one of siderite ptecipitation based on our model calculations of the thickness of siderite precipitated per cm2 of basin area we further predict that the observed laminae interbeds of siderite could be a composite of several microlayers of siderite and clays

phanerozoic ironstones an introduction and review s u m m a r y ironstones particularly ooidal ironstones have long fascinated sedimentary geologists and have generated an enormous variety of interpretations but have remained poorly understood a recent upsurge in interest in this group of rocks has generated much new information derived from many different disciplines within the earth sciences the first part of this introduction examines recent advances and attempts to produce a synthesis of them with particular reference to the genesis of marine ooidal ironstones current models for the formation of marine oolitic ironstone formations are discussed and a working model based on various lines of recent research is proposed this model invokes the intrasedimentary formation of berthierine ooids in marine environments during postoxic diagenesis the ooids may be mechanically modified and mineralogically transformed by reworking as well as by later diagenesis goethite ooids may be oxidized berthierine ooids reworked lateritic ooids or primary grains the formation of oolitic ironstoneformations is favoured by a break in clastic sediment supply continued supply of iron and physical reworking many sedimentary environments may supply these parameters but changes in sea level leading to the flooding of land masses and the reworking of suitable terrestrial soils may be both an important source for the iron and provide a break in clastic sediment supply in the second part of this introduction the terminology and classification are discussed and conventions proposed the term berthieroid is introduced as a non specific term for material of undetermined berthierine or chamosite composition the term ironstone is proposed as a petrological term and as an informal lithostratigraphic term a deposit composed of ironstones may be termed an ironstone formation it is recommended that a dunham style of classification is employed petrographically with ironstone replacing the stone of the original carbonate classification the nomenclature of allochems in ironstones is also discussed a glossary of ironstone terminology is provided

evolution of indian ocean dipole and its forcing mechanisms in the absence of enso the evolution of indian ocean dipole iod and its forcing mechanisms are examined based on the analysis of coupled model simulations that allow or suppress the el nino southern oscillation enso mode of variability the model can reproduce the most salient observed features of iod even without enso including the relationships between the eastern and western poles at both the surface and subsurface as well as their seasonality this suggests that enso is not fundamental for the existence of iod it is demonstrated that cold warm sea surface temperature sst anomalies in the eastern indian ocean associated with iod can be initiated by springtime indonesian rainfall deficit surplus through local surface wind response the growth of the sst anomalies depends on the initial local subsurface condition both the air sea interaction and surface subsurface interaction contribute to the development of iod the evolution of iod can be represented by two leading extended empirical orthogonal function eeof modes of tropical surface subsurface indian ocean temperatures one stationary and the other non stationary the onset growth and termination of iod as well as the transition to an opposite phase can be interpreted as alternations between the non propagating mode eeof1 and the eastward propagating kelvin wave eeof2 the evolution of iod is also accompanied by a westward propagating rossby wave which is captured in the eeof1 of the subtropical surface subsurface indian ocean temperatures therefore both bjerknes feedback and a delayed oscillator operate during the evolution of iod in the absence of enso also

microfabric mineralogy and early diagenetic history of the whitby mudstone formation toarcian cleveland basin u k the whitby mudstone formation in northeast england contains three shale facies normal restricted and bituminous which have previously been differentiated on the basis of sedimentary structures and faunal assemblages this paper shows that the three facies can also be differentiated by mineralogical geochemical and microtextural criteria determined using bsem edxra xrd and xrf the bituminous shale facies consists of finely laminated shales containing an early diagenetic mineral assemblage dominated by pyrite calcite and dolomite the weakly laminated restricted facies shales contain an early diagenetic assemblage dominated by pyrite the normal facies shales are very weakly laminated and contain siderite in addition to pyrite the geochemical conditions which left a dominant early diagenetic imprint on the three facies are interpreted to be carbon rich sulphidic carbon poor sulphidic and very carbon poor sulphidic respectively

an oxygen minimum palaeoceanographic signal from early toarcian cavity fills moderately deep marine toarcian sedimentary rocks of the medianes nappe alpine front ranges switzerland comprise calcarenites and lime mudstones they were deposited under storm and fairweather conditions in the dysaerobic zone near the storm wave base these remnants of the northern margin of the tethyan ocean show facies where primary sediment 9deep water9 stromatolitic micrite was reworked during early diagenesis stromatactis like cavities were formed by carbonate dissolution near the sediment water interface suboxic early diagenetic conditions are indicated by corroded pyrite and newly formed glauconitic oncoids carbon and oxygen stable isotope data indicate cavity stabilization and cementation above the sulphate reducing zone oceanographic conditions during the time of cavity development are reconstructed from the carbon and oxygen isotope composition of cavity cements of bulk sediment and of associated ammonites 13 c values of up to 4 are related to the oceanic anoxic event of the early toarcian and oxygen isotope values from cements and ammonites define a shallow toarcian thermocline

termination of indian ocean dipole events in a coupled general circulation model abstract using 200 yr of coupled general circulation model cgcm results causes for the termination of indian ocean dipole iod events are investigated the cgcm used here is the scale interaction experiment frontier research center for global change sintex f1 model which consists of a version of the european community hamburg echam4 6 atmospheric model and a version of the ocean parallelise opa8 2 ocean general circulation model this model reproduces reasonably well the present day climatology and interannual signals of the indian and pacific oceans the main characteristics of the intraseasonal disturbances isds oscillations are also fairly well captured by this model however the eastward propagation of isds in the model is relatively fast in the indian ocean and stationary in the pacific compared to observations a sudden reversal of equatorial zonal winds is observed as a result of significant intraseasonal disturbances in the equatorial indian ocean in november december of iod events

a model for the boreal summer intraseasonal oscillation abstract the tropical intraseasonal oscillation iso exhibits pronounced seasonality the boreal summer iso is more complex than its winter counterpart due to the coexistence of equatorial eastward off equatorial westward and northward propagating low frequency modes and their interactions based on observational evidence and results obtained from numerical experiments a mechanism is proposed for the boreal summer iso in which the northern hemisphere summer monsoon nhsm circulation and moist static energy distribution play essential roles with a climatological july mean basic state the life cycle of model low frequency waves consists of four processes an equatorial eastward propagation of a coupled kelvin rossby wave packet an emanation of moist rossby waves in the western pacific a westward propagation and amplification of the rossby waves in south asian monsoon regions and a reinitiation of the equatorial disturbances over the central indian ocean the life cycle spans about one month and p

origin and depositional environment of ordovician stratiform iron mineralization from zamora nw iberian peninsula the ordovician stratiform iron deposits at zamora nw iberia are arranged in several levels ranging between 0 2 and 1 5 m in thickness which are interstratified in the upper member of the pielgo quartzites formation arenig the sandy nature and trace fossils corresponding to the ichnogenus cruziana and daedalus together with major and trace element contents of this formation suggest an inter and subtidal shallow marine depositional environment which on a global scale formed part of a broad shelf situated in the northern margin of the gondwana continent the iron mineralization displays a foliated and banded structure due to the alternation of quartzitic phosphatic apatite chamositic chamositic biotitic and ferriferous magnetite and hematite beds they have high tio2 ta sc v nb co zn and y contents the magnetite contains unusually large amounts of tio2 v cr and ni there is also a clear depletion in eu and the eu sm cn ratio is 1 the chamosite contains high concentrations of cr and v these results suggest that iron was supplied from the weathering of a continental source in combination with volcanic activity such as within basin basic volcanism or the presence of basic volcanic rocks in the exposed land the physicochemical conditions of iron mineral crystallization calculated from chamosite compositions are the following log f o2 38 8 to 30 7 log f s2 13 2 to 9 5 and t 200 to 330 c these results together with the 18o value 2 of the magnetite suggest that chamosite and magnetite were crystallized during later diagenesis and early low grade metamorphism under redox conditions below the magnetite hematite buffer

microbial influence on the oxygen isotopic composition of diagenetic siderite abstract numerous early diagenetic siderite concretions previously described have been interpreted as the results of microbially mediated reactions interpretation of oxygen isotope data for such material requires an understanding of the effect of temperature on fractionation processes however whilst equilibrium fractionation of oxygen isotopes between siderite and water has been measured down to 33 c extrapolation to lower temperatures may be invalid furthermore inorganic measurements may not be applicable to microbial systems the specific iron reducing microorganism geobacter metallireducens has been cultured anaerobically in the laboratory using acetate as an organic substrate and amorphous feooh as an electron acceptor the acetate is oxidised to co2 with concurrent iron reduction and extracellular siderite precipitation rhombohedral siderite crystals up to 25 m in size have been precipitated over a range of temperatures 18 40 c stable isotopic analysis of these crystals and the solutions from which they precipitate shows that this microbial precipitation of siderite has an associated isotopic fractionation different from the published equilibrium and which is not simply a function of temperature in all cases 18o values of siderite are lower than predicted by inorganic equilibrium fractionation data this may explain the numerous anomalously low 18o values reported for early diagenetic marine siderites and previously attributed to mechanisms such as mixing with meteoric water sediment water interaction recrystallisation or variable isotopic fractionation despite a lack of supporting evidence

a modeling study of the impact of tropical instability waves on the heat budget of the eastern equatorial pacific a numerical simulation is used to investigate the mixed layer heat balance of the tropical pacific ocean including the equatorial cold tongue and the region of vortices associated with tropical instability waves tiws the study is motivated by a need to quantify the effects that tiws have on the climatological heat budget of the cold tongue mixed layer there has been some discrepancy between observations indicating very large equatorward heat transport by tiws and models that disagree on the full three dimensional budget validation of the model reveals that the tiw induced circulation patterns are realistic but may have amplitudes about 15 weaker than those in the observations the sst budget within tropical instabilities is first examined in a frame of reference moving with the associated tropical instability vortices tivs zonal advection of temperature anomalies and meridional advection of temperature by current anomalies dominate horizontal advection these effects strongly heat the cold cusps and slightly cool the downwelling areas located at the leading edge of the vortices cooling by vertical mixing is structured at the vortex scale and almost compensates for horizontal advective heating in the cold cusps in contrast to some previous studies tiw induced vertical advection is found to be negligible in the sst budget cooling by this term is only significant below the mixed layer the effect of tiws on the climatological heat budget is then investigated for the region bounded by 2 s 6 n 160 90 w where instabilities are most active tiwinduced horizontal advection leads to a warming of 0 84 c month 1 which is of the same order as the 0 77 c month 1 warming effect of atmospheric fluxes while the mean currents and vertical mixing cool the upper ocean by 0 59 c month 1 and 1 06 c month 1 respectively the cooling effect of tiw induced vertical advection is also negligible in the long term surface layer heat budget and only becomes significant below the mixed layer the results above and in particular the absence of cancellation between horizontal and vertical tiw induced eddy advection are robust in three other sensitivity experiments involving different mixing parameterizations and increased vertical resolution

rock magnetic and geochemical evidence for authigenic magnetite formation via iron reduction in coal bearing sediments offshore shimokita peninsula japan iodp site c0020 sediments recovered at integrated ocean drilling program iodp site c0020 in a forearc basin offshore shimokita peninsula japan include numerous coal beds 0 3 7 m thick that are associated with a transition from a terrestrial to marine depositional environment within the primary coal bearing unit 2 km depth below seafloor there are sharp increases in magnetic susceptibility in close proximity to the coal beds superimposed on a background of consistently low magnetic susceptibility throughout the remainder of the recovered stratigraphic sequence we investigate the source of the magnetic susceptibility variability and characterize the dominant magnetic assemblage throughout the entire cored record using isothermal remanent magnetization irm thermal demagnetization anhysteretic remanent magnetization arm iron speciation and iron isotopes magnetic mineral assemblages in all samples are dominated by very low coercivity minerals with unblocking temperatures between 350 580 c that are interpreted to be magnetite samples with lower unblocking temperatures 300 400 c higher arm higher frequency dependence and isotopically heavy 56fe across a range of lithologies in the coal bearing unit between 1925 1995 mbsf indicate the presence of fine grained authigenic magnetite we suggest that iron reducing bacteria facilitated the production of fine grained magnetite within the coal bearing unit during burial and interaction with pore waters the coal peat acted as a source of electron donors during burial mediated by humic acids to supply iron reducing bacteria in the surrounding siliciclastic sediments these results indicate that coal bearing sediments may play an important role in iron cycling in subsiding peat environments and if buried deeply through time within the subsequent deep biosphere

indian ocean monsoon coupled interactions and impending monsoon droughts 1 monsoon droughts over the indian subcontinent emanate from failures in the seasonal june september monsoon rains while prolonged dry spells monsoon breaks pervade on sub seasonal intra seasonal time scales the underlying causes for these long lasting anomalies remain elusive based on analyses of a suite of observed data sets we report an ocean atmosphere dynamical coupling on intra seasonal time scales in the tropical indian ocean which is pivotal in forcing extended monsoon breaks and causing droughts over the subcontinent this coupling involves a feedback between the monsoonal flow and thermocline depth in the equatorial eastern indian ocean eeio in which an anomaly of the summer monsoon circulation induces downwelling and maintains a higher than normal heat content the near equatorial anomalies induce strong and sustained suppression of monsoon rainfall over the subcontinent it is concluded that the intra seasonal evolution of the ocean monsoon coupled system is a vital key to unlocking the dynamics of monsoon droughts