sample scale carbon isotopic variability and diverse biomass in the paleoproterozoic zaonega formation russia abstract the stratigraphic record of organic matter in the c 1 97 ga zaonega formation zf onega basin northwestern russia exhibits a distinct negative 13c excursion 13corg from 25 to 40 vpdb which was previously interpreted either to reflect a disturbance in the global carbon cycle after the great oxidation event or to have been caused by an increase in basinal methanotrophic activity in order to assess the nature of primary biomass and the effects of post depositional alteration we here report the sample scale carbon isotopic characteristics of organic matter in two drill cores from the zf covering 500 m of stratigraphy by using secondary ion mass spectrometry sims the results confirm that the organic matter has to a large extent preserved the primary isotopic signatures whereas secondary effects are limited

evidence of an extratropical atmospheric influence during the onset of the 1997 98 el nino the major 1997 98 el nino episode was initiated by a series of very energetic westerly wind bursts in late 1996 and early 1997 downwelling oceanic kelvin waves were subsequently generated and propagated rapidly eastward across the equatorial pacific ocean and induced significant warming in the eastern basin by analyzing newly available wind products derived from ssm i satellite observations we found indications that these westerly wind bursts were embedded within the active phase of the tropical intraseasonal oscillation the madden julian oscillation but their amplitudes were greatly enhanced in the western pacific sector the local enhancement involved the development of equatorial twin cyclones which themselves were induced by northerly cold surges from east asia western north pacific into the tropical pacific demonstrating an extratropical atmospheric influence on tropical processes

decomposition of surface drifter observations in the atlantic ocean 1 surface drifter observations are decomposed into mean seasonal annual and semiannual and eddy components via gauss markov estimation this approach helps separate seasonal fluctuations and mean values in the observationally sparse tropical and south atlantic where monthly mean values cannot be calculated at the spatial scale of the major currents in some regions large differences are found between these means and those obtained by simple binned averaging the differences are attributed to inhomogeneous sampling of seasonal variability and to the inherent bias of lagrangian observations towards periods of low velocity the analysis reveals strong seasonal variations of some surface currents including a significant late spring reversal of the western north equatorial counter current

extreme 13ccarb enrichment in ca 2 0 ga magnesite stromatolite dolomite red beds association in a global context a case for the world wide signal enhanced by a local environment abstract the palaeoproterozoic positive excursion of 13 c carb is now considered as three positive shifts of 13 c carb separated by returns to 0 which all occurred between 2 40 and 2 06 ma this isotopic event is unique in terms of both duration 300 ma and 13 c enrichment up to 18 the mechanism responsible for one of the most significant carbon isotopic shifts in earth history remains highly debatable to date 13 c of 10 to 15 cannot be balanced by organic carbon burial forg as there is no geological evidence for an enhanced corg accumulation prior to or synchronous with the excursion instead termination of these excursions is followed by formation of a vast reservoir of 13 c depleted organic material 45 at shunga and by one of the earliest known oil generation episodes at 2 0 ga none of the three positive excursions of 13 c carb is followed by a negative isotopic shift significantly below 0 as has always been observed in younger isotopic events reflecting an overturn of a major marine carbon reservoirs this may indicate that forg was constant implying that the mechanism involved in the production of corg was different onset of intensive methane cycling resulting in c change is another possibility the majority of sampled 13 c carb rich localities represents shallow water stromatolitic dolostones red beds and evaporites formed in restricted intracratonic basins and may not reflect global 13 c carb values closely spaced drill core samples n 73 of stromatolitic dolostones from the 1980 27 ma tulomozerskaya formation in the onega palaeobasin russian karelia have been analysed for 13 c carb and 18 o carb in order to demonstrate that different processes were involved in the formation of 13 c carb rich carbonates the 800 m thick magnesite stromatolite dolomite red beds succession formed in a complex combination of environments on the karelian craton peritidal shallow marine low energy protected bights barred basins evaporative ephemeral ponds coastal sabkhas and playa lakes the carbonate rocks exhibit extreme 13 c enrichment with 13 c values ranging from 5 7 to 17 2 vs v pdb mean 9 9 2 3 and 18 o from 18 6 to 26 0 vs v smow mean 22 0 1 6 the tulomozerskaya isotopic excursion is characteristic of the global 2 4 2 06 ga positive shifts of carbonate 13 c 12 c although it reveals the greatest enrichment in 13 c known from this interval an external basin s is considered to have provided an enhanced corg burial and global seawater enrichment in 13 c the global background value for the isotopic shift at tulomozero time ca 2 0 ga is roughly estimated at around 5 an explosion of stromatolite forming microbial communities in shallow water basins evaporative and partly restricted environments high bioproductivity enhanced uptake of 12 c and pene contemporaneous recycling of organic material in cyanobacterial mats with the production and consequent loss of co2 and ch4 are believed to be additional local factors which may have enhanced 13 c from 5 up to 17 such factors should be taken into account when interpreting carbon isotopic data and attempting to discriminate between the local enrichment in 13 c and globally enhanced 13 c values we propose that many previously reported 13 c values from other localities where environmental interpretations are not available or have not been taken into account may not represent the global 13 c values

isotopic evidence for a sizeable seawater sulfate reservoir at 2 1 ga abstract the 2 1 ga tulomozero formation deposited on the fennoscandian shield consists of shallow marine carbonate and siliciclastic rocks dissolution breccias and widespread syndepositional marine evaporites now mostly present as pseudomorphs after ca sulfates this study investigates sulfates hosted in three different proxies to constrain the sulfur isotopic composition of seawater sulfate acknowledging the presence of different types of sulfates carbonate associated sulfate cas breccia associated sulfate bas and sulfate relicts rs in a variety of lithologies of the tulomozero formation a widely used and accepted proxy for the ambient seawater sulfate sulfur isotopic composition is carbonate associated sulfate which was extracted from carbonate samples across the entire tulomozero formation in addition sulfate was extracted from a siliciclastic dissolution breccia which is suggested to have formed after dissolution of sulfate evaporites the sulfate sulfur isotopic composition from both lithologies was measured ex situ 34 s cas 10 9 2 7 34 s bas 9 0 1 1 ubiquitous pseudomorphs after ca sulfates occur in the tulomozero formation and contain m size anhydrite and barite relicts their sulfur isotopic composition was measured in situ by secondary ion mass spectroscopy sims 34 s anhydrite 9 6 1 0 34 s barite 11 0 3 1 sulfur isotope data from carbonate rocks breccias and the sulfate relicts match the existing 34 s record of seawater sulfate during that time and show no distinct stratigraphic variations indicating that the seawater sulfate sulfur isotopic composition remained unaffected from environmental changes during the time of deposition of the tulomozero formation physical evidence for widespread precipitation of sulfate rather than abundant chloride suggests a modern style evaporite sequence with carbonates followed by sulfate and then chlorides however this requires a minimum sulfate concentration of 2 5 mm in the ambient seawater consequently the evidence for persistent evaporitic sulfate deposition in the tulomozero formation implies a substantial seawater sulfate reservoir at 2 1 ga according to the estimated minimum depositional time from the thickness of the carbonate rocks of the formation the residence time of seawater sulfate is expected to have been at least 5 ma the available data support the existence of a sizeable seawater sulfate reservoir in the mid paleoproterozoic ocean in fact more than 10 of the modern sulfate reservoir

palaeoproterozoic evaporites in fennoscandia implications for seawater sulphate the rise of atmospheric oxygen and local amplification of the δ13c excursion this paper addresses global oxygenation and establishment of a marine sulphate reservoir in the palaeoproterozoic we report syn depositional marine anhydrite containing pseudomorphs after ca sulphates as widespread throughout the tulomozero formation in the se fennoscandian shield implying that surface waters were oxidized and a large so42 marine reservoir was developed as early as 2100 ma the ca sulphates and associated magnesite and halite precipitated syn depositionally from oxidized evolved and modified seawater in coastal playa sabkha and intertidal flat settings sr 87 sr 86 and delta 13 c of associated c 13 rich stromatolitic dolostones were environmentally controlled with the highest ratios occurring in playa and sabkha carbonates the results imply that the palaeoproterozoic delta 13 c carb excursion was amplified by 8 by local environmental factors and calls into question many observations of putative delta 13 c global signals reported previously from similar palaeoproterozoic evaporitic dolostones the local environmental amplification can explain a large regional and intercontinental delta 13 c discrepancy observed in synchronous carbonates

temporal constraints on the paleoproterozoic lomagundi jatuli carbon isotopic event the paleoproterozoic lomagundi jatuli positive 13c excursion in sedimentary carbonates represents an event whose magnitude and duration is unique in earth history although precise absolute chronology of this event remains poorly constrained in northeastern fennoscandia an 1300 m thick sedimentary volcanic succession of the pechenga greenstone belt records decline of this isotopic excursion zircons from sedimentary rocks that occur within the decline have yielded 207pb 206pb dates at 2058 2 ma 6 ma including u decay constant uncertainties and provide the first maximum age constraint on the termination of the lomagundi jatuli event combined with existing constraints these data indicate an 140 m y interval characterized by 13c rich carbonate accumulation

wind driven currents in the tropical pacific abstract an analysis is made of the ensemble mean ageostrophic near surface circulation measured by 1503 lagrangian drifters drogued to 15 m depth in the tropical pacific between 1987 and 1994 it was found that the physical model of the wind driven currents in a weakly stratified upper layer in which the richardson number remains near unity accounts for 40 of the vector variance of the observations in such a model the amplitude of the current is proportional to u n f 1 2 and the depth scale of the wind driven layer is proportional to u n f 1 2 when the ageostrophic currents at 15 m depth are binned by the scaled ekman depth a net rotation of 0 87 radians was observed through the layer depth these measurements suggest that the vertical austausch coefficient of the upper ocean is proportional to u2 n ekman proposed such a model based on two reports of wind driven currents in 1905 at widely separated latitudes

a widespread positive 13ccarbanomaly at around 2 33 2 06 ga on the fennoscandian shield a paradox carbon isotope measurements carried out on 201 carbonate samples from the early proterozoic of the kola peninsula n karelia and norway yield 13c pdb spanning 20 5 to 11 a general 13c secular trend shows that prior to 2 33 ga values are typically normal marine averaging around 3 0 between 2 33 and 2 06 ga in jatulian time there follows a rapid excursion to positive 13c of around 6 post jatulian time is characterized by 13c of sedimentary carbonates fluctuating between 5 and 3 also it is remarkable for the first pronounced development of diagenetic carbonates which have 13c between 14 and 6 the c 6 positive 13c shift with a duration of about 270 myr coincides with a maximum in the diversity and abundance of stromatolites and with widespread development of red beds but does not coincide with the maximum of buried corg mass the fennoscandian shield represents the largest isotoically anomalous carbonate province yet reported and the positive 13c excursion together with a series of major global palaeoenviromental changes seems to be more intense than the precambrian cambrian transition events however it is still not clear what kind of mechanism this phenomenon could be attributed to an increase of the ronov ratio and or broecker ratio and other possible models are discussed as the target for future investigations

sedimentary and volcanic facies recording the neoarchaean continent breakup and decline of the positive δc excursion abstract the palaeoproterozoic kalix greenstone belt at the northern end of the bothnian bay in sweden comprises three groups the lower group a ca 3000 m thick unit of subaerially erupted tholeiitic intraplate basalts interbedded with fluviatile conglomerates represents the volcano sedimentary succession deposited in a rift setting these units are truncated by a break up unconformity above which is the middle group an 800 m thick succession of dolograinstones stromatolitic dolostones arenites volcanoclastic and mafic volcanic rocks stromatolite morphologies and the occurrence of distinctive sedimentary structures including planar and herringbone cross bedding hummocky cross stratification symmetrical and asymmetrical ripples desiccation cracks and tepees indicate markedly variable depositional environments associated with transition from a marine influenced rifted margin to a rimmed carbonate shelf sedimentation was accompanied by subaerial mafic volcanism and syndepositional tectonics the upper group a more than 2000 m thick unit of deep water shales was deposited on the drowned carbonate platform of the middle group in response to tectonically enhanced subsidence this study provides a detailed palaeoproterozoic depositional history of the fennoscandian shield from rifting to passive margin development associated with both dispersal of the neoarchaean supercontinent and decline of the proterozoic positive isotopic excursion of 13 c 12 c in sedimentary carbonates in contrast to many previously reported 13 c rich palaeoproterozoic carbonates which were deposited in non marine to restricted or partly restricted settings the carbonate facies reported herein were well connected to the oceanic realm and thereby represent a good opportunity to test restricted marine versus open marine models for how the carbon cycle functioned in deep time

a 170 year sr ca and ba ca coral record from the western pacific warm pool 1 what can we learn from an unusual coral record 1 a long lived porites coral from new ireland 2 5 s 150 5 e papua new guinea has been analyzed for sr ca and ba ca by laser ablation inductively coupled plasma mass spectrometry la icpms the top 50 years of the core are examined here and compared with instrumental sea surface temperatures ssts for the small range of sst in the warm pool sr ca shows an unusually large response the best estimate for the slope of a temperature calibration is 0 23 0 03 mmol mol per c this strong slope is partly a result of the high resolution sampling but is also due to additional biological mediation of the sr ca ratios which appears to be associated with seasonal changes of calcification rate and limits the prediction skills of this proxy thermometer high density bands synchronous with high sr ca ratios suggest that calcification may be enhanced by beneficial small amounts of nutrients available during el nino transient ba enrichment synchronous with colder than average sst is also observed during el nino and attributed to the shoaling of the new ireland coastal undercurrent the high level of enrichment in particular during upwelling triggered by westerly wind bursts suggests an origin from both dissolved seawater and marine biological barium

the role of oceanic heat advection in the evolution of tropical north and south atlantic sst anomalies abstract the role of horizontal oceanic heat advection in the generation of tropical north and south atlantic sea surface temperature sst anomalies is investigated through an analysis of the oceanic mixed layer heat balance it is found that sst anomalies poleward of 10 are driven primarily by a combination of wind induced latent heat loss and shortwave radiation away from the eastern boundary horizontal advection damps surface flux forced sst anomalies due to a combination of mean meridional ekman currents acting on anomalous meridional sst gradients and anomalous meridional currents acting on the mean meridional sst gradient horizontal advection is likely to have the most significant effect on the interhemispheric sst gradient mode through its impact in the 10 20 latitude bands of each hemisphere where the variability in advection is strongest and its negative correlation with the surface heat flux is highest in addition to the damping effect of horizontal advection in these latitude bands e

an advective reflective conceptual model for the oscillatory nature of the enso recent findings about zonal displacements of the pacific warm pool required a notable modification of the delayed action oscillator theory the current leading theory for the el nino southern oscillation enso simulations with a linearized coupled ocean atmosphere model resulted in 3 to 6 year enso like oscillations with many of the variable model parameters found to be very close to their observed values this simple model suggests that ocean processes that are ignored or underestimated in the delayed action oscillator theory such as zonal current convergence zonal advection of sea surface temperature and equatorial wave reflection from the eastern ocean boundary are fundamental to the development of the enso in particular to its manifestations in the central equatorial pacific

high δ13c paleoproterozoic carbonates from the transvaal supergroup south africa marbles from the transvaal supergroup kaapvaal craton south africa record two positive carbon isotope excursions to average 13 c carbonate values of 6 to 8 relative to v pdb separated by carbonates with normal marine 13 c values 0 2 these elevated values have been preserved through metamorphic devolatilization together with an already documented high 13 c excursion in overlying rocks three separate positive carbon isotope excursions occurred on the kaapvaal craton in the interval 2 43 to 1 93 ga it is not yet clear how many of these excursions reflect global rather than local processes

the 1997 98 el nino evolution relative to previous el nino events abstract the evolution of the 1997 98 el nino is described using ncep sst and olr data ncep ncar reanalysis sea level pressure slp fields and the florida state university surface wind data from november 1996 to january 1997 the eastern pacific is characterized by equatorial cold sst and high slp anomalies while the western pacific is marked by off equatorial warm sst anomalies and off equatorial anomalous cyclones corresponding to this distribution are high olr anomalies in the equatorial central pacific and low olr anomalies in the off equatorial far western pacific the off equatorial anomalous cyclones in the western pacific are associated with a switch in the equatorial wind anomalies over the western pacific from easterly to westerly these equatorial westerly anomalies then appear to initiate early sst warmings around the date line in january february 1997 and around the far eastern pacific in march 1997 subsequently both the westerly wind and warm sst anomalies along with the low olr ano

mineralogical and isotopic characterization of graphite deposits in the western part of the north qaidam orogen and east kunlun orogen northeast tibetan plateau china abstract medium to high grade metamorphic rocks comprising numerous graphite deposits are widely distributed in the periphery of the qaidam basin northern tibetan plateau china we present textural xrd and raman spectroscopy characteristics of graphite 13c results of graphite and cogenetic calcite and 18o results of calcite in three graphite occurrences located at the periphery of qaidam basin graphite displays hexagonal platy flaky irregular polygonal ovate morphologies with occasional spherulitic textures graphite morphologies combined with xrd and raman spectroscopy indicate that graphite has relatively high crystallinity raman microspectroscopy of graphite shows that peak metamorphic temperatures vary between 690 and 801 c graphite 13cv pdb values range between 26 3 and 21 6 indicating organic carbon as the major carbon source for graphite calcite 13cv pdb and calcite 18ov smow values range between 10 8 and 3 9 and between 6 6 and 29 5 respectively calcite 13cv pdb results show that organic carbon was mixed with inorganic carbon which resulted in an increase of 13cv pdb calcite 18ov smow values indicate that the graphite deposits experienced late stage water rock interaction the positive and negative anomalies of calcite 13cv pdb indicate that organic matter oxidation and recycling locally occurred during the final stage of the great oxidation event the wide distribution of regional metamorphic organogenic graphite deposits provides evidence for large scale paleoproterozoic biological activity in the periphery of the qaidam basin

carbon isotopes and the rise of atmospheric oxygen new data for the isotopic composition of carbon in carbonate sediments deposited between 2 6 and 1 6 ga indicate that the value of 13c in these sediments underwent a very large positive excursion between 2 22 and 2 06 ga a reassessment of the earlier 13c data for carbonate sediments shows that this excursion was probably worldwide and that it was preceded and followed by several hundred million years during which the 13c of carbonate sediments differed little from that of modern carbonates the large 13c excursion between 2 22 and 2 06 ga was probably related to an abnormally high rate of organic carbon deposition which generated an abnormally high rate of o2 production we estimate that the total excess o2 produced during the excursion was between 12 and 22 times the present atmospheric o2 inventory the 13c data therefore suggest that the o2 content of the atmosphere increased very significantly between 2 22 and 2 06 ga this inference is supported strongly by several other lines of evidence

anomalous surface currents in the tropical indian ocean an anomalous climate event occurred in 1997 in the indian ocean with severe consequences for the surrounding continental areas in response to an intensification of the trade winds a westward gradient of sst and an anomalous reversal of the eastward surface currents with peak velocity anomalies exceeding 1 m s were evident in boreal autumn a similar but weaker event took place in 1994 in this study we examine the observational record during the 1990s including surface drifter velocities sst and altimeter sea level to confirm these dramatic changes we examine the key momentum balance between wind induced momentum flux and the pressure gradient force as well as the important role of horizontal temperature advection in the mixed layer heat response

secular trend in the near surface currents of the equatorial pacific ocean 1 the westward zonal near surface currents of the equatorial pacific ocean appear to have strengthened during the past 20 years by 9 10 cm s here we document this change in both near surface drifter and moored currents accompanying this increase in surface currents is a shallowing of the equatorial thermocline and a weakening of the zonal component of the equatorial trade winds however a simple model suggests that the most important factor is a reduction by 8 m of the average mixed layer depth over this period

lagrangian study of the panama bight and surrounding regions near surface circulation of the panama bight and surrounding regions 0 9 n 73 w 90 w was studied using satellite tracked drifter trajectories from 1979 2004 this region encompasses three major currents showing typical velocities of 30 cm s 1 1 the eastward north equatorial counter current necc 2 the near circular panama bight cyclonic gyre pbcg and 3 the westward south equatorial current sec we do not observe significant modification of the mean surface circulation during el nino southern oscillation events even if the sec is slightly reinforced during relatively warm el nino periods at seasonal scales the circulation is strongly controlled by the activity of the panama wind jet in boreal winter the currents are stronger and an anticyclonic cell is present west of the pbcg this dipole leads to a strong 200 km wide southward current which then disappears during the rest of the year in summer the three major currents have reduced intensity by 30 40 large scale current vorticity shows that the upwelling associated with the pbcg is also 3 4 times stronger in winter than during summer months the kinetic energy is largely dominated by eddy activity and its intensity is double in winter than during summer ageostrophic motions and eddy activity appear to have a substantial impact on the energy spatial distribution in the necc and sec regions lagrangian scales are anisotropic and zonally enhanced in the direction of the mean currents the typical integral time and length scales of these regions are 2 5 days and 50 60 km in the zonal direction and 1 5 days and 25 30 km in the meridional direction lateral eddy diffusivity coefficients are on the order of 11 14 107 cm2 s 1 zonally and 5 6 107 cm2 s 1 meridionally in contrast in the pbcg region the lagrangian characteristics are isotropic with typical timescales of 1 7 days space scales of 30 km and eddy diffusivity coefficients of 6 107 cm2 s 1 in both directions

paleoproterozoic stark formation athapuscow basin northwest canada record of cratonic scale salinity crisis abstract the paleoproterozoic stark formation a thick breccia unit formed during the transition from marine to non marine foreland basin fill in the athapuscow basin northwest territories canada four types of breccia occur in the stark formation 1 bedded breccias at the base of the unit overlying the basinal facies of the underlying pethei group are interpreted as debris flows 2 massive chaotic breccias occur in the lower part of the stark formation throughout the basin and these are interpreted to be evaporite collapse breccias 3 siltstone and mudstone breccia occurs in the upper part of the stark formation and is also interpreted as evaporite collapse breccia though much less evaporite was involved in its formation than the underlying chaotic breccia and 4 laminar accretionary breccia consisting of laminar carbonate clasts commonly with flat bottoms and convex up upper surface geometries these clasts occur in lenticular pods and are interpreted to form in caves following dissolution of evaporites or carbonates the widespread presence and abundance of evaporite pseudomorphs especially halite in all breccia types the stratigraphic restriction of the stark formation and irregular filling above this unit indicates that all but the bedded breccia formed by the dissolution and collapse of evaporites chaotic breccia directly above underlying pethei group shallow water and deep water carbonates indicates the evaporates formed across the platform and adjacent deep basin foundered megaclasts up to 1 5 km long and 40 m thick in basinal settings suggest cumulative evaporite thicknesses on the order of a few tens to a few hundreds of meters carbonate clasts in all the breccias contain abundant wave ripples planar laminations stromatolites and ooids these structures along with a paucity of subaerial exposure features indicates nearly all carbonate deposition in the stark was subaqueous thus by inference the evaporites in the stark formation were also partially subaqueous displacive halite pseudomorphs are common throughout all facies in the stark formation silicified and dolomite filled halite pseudomorphs are common along the contact between the evaporite collapse breccia and underlying carbonate platform pethei group and surrounding large clasts in basinal settings silicified hopper crystal casts within deep water rhythmites of the uppermost pethei group indicate precipitation of halite over deep waters gypsum pseudomorphs are exceedingly rare and anhydrite pseudomorphs were not observed the dominance of halite features in this basin and two penecontemporaneous basins kilihigok basin and wopmay orogen surrounding the slave craton suggests that relative to the present day seawater at 1 9 to 1 8 ga was oversaturated with respect to calcium carbonate had higher hco3 concentration and possibly was depleted in so42 the dearth of extensive thick bedded marine gypsum in the archean and early paleoproterozoic can be explained by low atmospheric oxygen content prior to 2 ga in conjunction with increased carbonate saturation before 1 6 ga

application of stable carbon isotopes to early biochemical evolution on earth the emergence and early evolution of life on earth have long been intriguing subjects for scientific inquiry and a continuous source of intel lectual excitement current work at this frontier proceeds along a number of different avenues and comprises a variety of disciplinary approaches that together strongly suggest that the earth was inhabited by life as early as almost 4 gyr ago the present state of the field as inferred from the results of a broad interdisciplinary approach has recently been summarized by j w schopf and coworkers cf schopf 1 983 it is with the advantage of such a synoptic view that the present review addresses a single facet of the theme namely the potential isotopic infer ences of the presence of co2 fixing autotrophic organisms for the carbon cycle of the early earth with biologically derived organic carbon as well as carbonates limestone dolomite etc abundantly preserved in sediments relevant isotopic evidence should have been encoded in the geologic record from its onset about 3 8 gyr ago it has been known since the pioneering studies by nier gulbransen 1939 murphey nier 1941 and rankama 1948 that the trans formation of inorganic carbon into living matter entails a marked bias in favor of the light isotope c2c with the heavy species l3c retained in the inorganic reservoir subsequent work performed by many investigators e g craig 1953 park epstein 1960 has confirmed that all common

upper equatorial pacific ocean current and salinity variability during the 1996 1998 el nino la nina cycle the recent el nino la nina cycle exhibited striking patterns of current and salinity variability in the upper equatorial pacific ocean this evolution is described from mid 1996 through 1998 using a remarkable data set of 35 meridional conductivity temperature depth ctd acoustic doppler current profiler adcp sections along with buoy data the sections nominally from 8 s to 8 n between 165 e and 95 w were occupied over the course of 27 months a wide range of current variability was sampled with currents that appeared or disappeared some time during the cycle including an equatorially trapped eastward surface current the equatorial undercurrent the northern branch of the south equatorial current and the north equatorial countercurrent basin wide interannual changes in upper ocean and pycnocline zonal transports were as large as 64 32 106 m3 s 1 changes in the salinity structure included a deep and fresh mixed layer in the central equatorial pacific that built up during the el nino and was then disrupted by upwelled salty water with the onset of la nina a very fresh mixed layer observed in the eastern equatorial pacific late in the el nino and a reduction in the strength of the meridional equatorial salinity gradient within the pycnocline to one third of the usual value during the el nino finally the zonal transports above the thermocline from 5 s to 5 n were well correlated with the rate of change of warm water volume west of the individual ctd adcp sections

nloadf a program for computing ocean tide loading the loading of the earth by the ocean tides produces several kinds of signals which can be measured by geodetic technique in order to compute these most accurately a combination of global and local models of the ocean tides may be needed the program nloadf convolves the green functions for loading with ocean tide models using a station centered grid with fixed dimensions making it easy to combine different ocean models without overlap in the convolution the program computes all the quantities of interest gravity displacement tilt and strain and includes the case where measurements are made beneath the surface of the ocean

intense surface currents in the tropical pacific during 1996 1998 tropical pacific ocean near surface currents and their momentum and temperature balances are investigated using several data sets including drifting buoy velocities and topex poseidon altimetry the data sets are combined to produce monthly surface current estimates on a uniform grid for the 6 year period 1993 1998 using multivariate optimal interpolation the analysis shows dramatic changes in current from december 1996 through august 1998 in response to the recent el nino southern oscillation event eastward current anomalies of 1ms 21 were recorded in december 1996 in the western pacific generated by sporadic westerly wind bursts by april 1997 these equatorial anomalies reached the eastern boundary and in the summer of 1997 a band of strong eastward flow formed across the basin this circulation pattern persisted until the beginning of 1998 when a westward equatorial jet appeared in january april interestingly the reversal of flow occurred prior to the restoration of the trade winds the timing of these events as well as the results of previous dynamical studies raise questions about the relative importance of terms in the zonal momentum and temperature balances we address the first of these questions by examining the applicability of a three term linear zonal momentum balance on the equator in all cases we focus on anomalies from the time mean our results show that local acceleration is reasonably well balanced by the difference between zonal pressure gradient anomaly and wind induced momentum flux this three term balance displays significant basin wide variations and is consistent with the conclusion that the equatorial pacific is not in equilibrium with local wind forcing due to the presence of propagating waves examination of the temperature balance shows that at the beginning of el nino the warming in the central pacific is mainly supported by horizontal temperature transport while the vertical heat exchange and transport become important in the eastern half of the equatorial pacific during the transition from el nino to la nina

geodynamics and earth tides observations from global to micro scale introduction the volume collects papers submitted to pure and applied geophysics following a call on the topic geodynamics and earth tides partly the authors had participated in the 18th geodynamics and earth tides symposium held intrieste italy in june 2016 theearth tides constitute the leading thread through the book since instrumentation sensitive enough to observe them also records a broad spectrum of signals generated by earth dynamic processes

pseudomorphs after evaporitic minerals interbedded with 2 2 ga stromatolites of the yerrida basin western australia origin and significance widespread quartz pseudomorphs after evaporitic minerals are interbedded with stromatolites in 2 2 ga sedimentary rocks in the yerrida rift basin of western australia these deposits preserve diverse original crystal morphologies that grew displacively either as individuals or as clusters within stromatolitic horizons and associated fine grained siliciclastic beds the stromatolites were deposited in shallow marine restricted environments although evaporitic minerals are largely replaced by quartz their crystal shapes include lenticular rosette needle and nodular forms suggesting that they formed from calcium sulfate rich brines textures suggest that replacement by quartz occurred during early alteration of the sediments original calcium sulfate minerals such as gypsum or anhydrite are indicated by the morphologies of the pseudomorphs this concept is supported by anhydrite inclusions in the quartz crystals that form the pseudomorphs and this finding indicates that calcium sulfate existed in early proterozoic sedimentary environments

the importance of the eastward zonal current for generating extreme el nino extreme el nino e g 1983 1983 and 1997 1998 causes severe weather and climate impacts globally but the associated dynamics is not fully understood the present study shows that advection of mean temperature by anomalous eastward zonal current plays an important role in producing such extreme events especially during the early part of the developing period while the climatological direction of the upper oceanic current in the equatorial pacific is westward at times the direction reverses these eastward current events are well distinguished from the normal westward conditions the upper layer zonal current in the equatorial pacific is basically in geostrophic balance and forced by wind stress however in the case of the eastward zonal current events persistent westerly winds are observed in the western pacific and the current becomes synchronized with the westerly wind stress above the advection of the mean temperature by the anomalous zonal current in the early developing period always precedes strong el nino though it does not significantly contribute to the growth of la nina neutral and moderate el nino and is the major contributor of asymmetry in the early developing phase

satellite altimeter derived geostrophic currents in the western tropical pacific during 1992 1993 and their validation with drifting buoy trajectories topex poseidon satellite altimeter measurements from the western tropical pacific 15 s 20 n 125 e 165 w are used to make monthly sea surface topography maps for the period october 1992 to october 1993 the altimeter data were processed using standard corrections to estimate along track sea surface height anomalies which were interpolated to monthly 1 10 resolution maps to convert these surface height anomalies to absolute sea surface height a 0 1000 dbar mean seasonal dynamic height climatology was computed from the same input data used by levitus 1982 to compute his dynamic height climatology with less spatial smoothing by adding the appropriate monthly altimeter heights to these seasonal means we produce 12 approximately monthly sea surface topography maps from 36 cycles of altimeter data the corresponding monthly geostrophic surface currents were compared with the tracks of nearly coincident satellite tracked drifting buoys and were found to agree well in most cases the velocity components zonal and meridional were plotted separately with respect to the velocities estimated from the buoy positions and correlations of these two data sets are very high the seasonal variability of the surface geostrophic currents in this region is depicted by the monthly maps of sea surface height

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

marine carbon reservoir corg ccarb coupling and the evolution of the proterozoic carbon cycle the post 2 0 ga proterozoic c isotope record reveals two distinct yet interrelated trends a stepwise increase in average 13c from 0 calculated with respect to the peedee belemnite isotope standard prior to ca 1 3 ga to 5 in the neoproterozoic and a concomitant increase in the magnitude of isotopic excursions steady state and non steady state models suggest that these fundamental changes are best explained by a combination of evolving burial fluxes and a secular decrease in the size of the marine dissolved inorganic carbon dic reservoir the dic reservoir size affects the sensitivity of the isotopic system to biogeochemical perturbation major rearrangements of carbon cycling during the proterozoic in part related to the evolving marine carbon reservoir permit elevated 13c values to be sustained for geologically long time spans recognition of this dependence on dic reservoir size provides for the first time a direct link between changing carbonate precipitation styles and the marine c isotope record and may help constrain estimates of proterozoic p co2

multiple causes of earth s earliest global glaciation in the context of earth system evolution the causal factors driving the palaeoproterozoic huronian global glaciations occupy a central position the rise of o2 at 2320 ma which eliminated most of the methane was not apparently a single cause triggering the glaciation at c 2450 ma mantle plume driven continental uplifts led to the emplacement of voluminous continental flood basalts in low latitudes that were subsequently dissected by rifting major topographical features and continental drainage patterns were most likely similar to those in younger continental flood basalt provinces and would have enabled deep weathering and erosion of extensive basalt covered continental areas intense consumption of atmospheric co2 by silicate weathering of fresh basaltic surfaces would have been further amplified by a constant organic carbon burial rate these factors similar to those of younger glacial periods in combination with the diminished ch4 greenhouse led to an onset of global cooling at the million year timescale

c o sr and nd isotope systematics of carbonates of papaghni sub basin andhra pradesh india implications for genesis of carbonate hosted stratiform uranium mineralisation and geodynamic evolution of the cuddapah basin abstract the cuddapah basin cb is one of a series of proterozoic basins that overlie the archaean cratons of india and contains a unique stratiform carbonate hosted uranium mineralisation in the present work we discuss stable c o and radiogenic nd sr isotope systematics of carbonates of the papaghni sub basin in order to understand uranium ore forming processes and geodynamic evolution of the cb uranium mineralised dolomites umds of the basal vempalle formation show a significantly lighter 1 5 c isotope signature compared to that of open marine stromatolitic sub tidal facies suggesting input of isotopically lighter carbon through in situ remineralisation of organic matter om this implies deposition in a hydrologically restricted redox stratified lagoonal basin wherein exchange with open oceanic dissolved inorganic carbon dic was limited persistent bottom water anoxia was created and maintained through consumption of dissolved oxygen do by decaying om produced in oxidised surface water zone significantly more radiogenic end t of umd 6 31 0 54 compared to that of dharwar upper crust 8 64 3 11 indicates that dissolved constituents did not originate from the dharwar craton rather were derived from more juvenile exotic sources possibly from a continental arc dissolved uranyl ions u 6 were introduced to the basin through fluvial run off and were reduced to immobile uranous ions u 4 at the redox interface resulting in precipitation of pitchblende and coffinite carbonate horizons of upper vempalle formation and tadpatri formation show progressively more radiogenic nd isotope compositions signifying increased juvenile arc contribution to the papaghni sub basin through time which is also corroborated by the presence of younger zircons 1923 22 ma in pulivendla quartzites we propose that the papaghni sub basin opened as a back arc extensional basin at 2 ga as a result of westerly directed subduction of oceanic crust beneath the eastern indian continental margin the papaghni back arc basin eventually evolved to upper cuddapah foreland basin with collision of the dharwar craton and napier block of antarctica at 1 6 ga possibly during the final stage of amalgamation of the columbia supercontinent

use of the geostrophic approximation to estimate time varying zonal currents at the equator moored thermistor chains at 2 n and 2 s and current temperature moorings at 0 are used to examine the accuracy of geostrophically estimated zonal velocity on the equator in the eastern 110 w and western 165 e pacific the meridionally differentiated form of the geostrophic balance is used to eliminate large errors due to wind balanced cross equatorial pressure gradients statistical analyses indicate that for time scales longer than 30 50 days the observed and geostrophically estimated zonal velocities are similar correlation coefficients of 0 6 0 9 and comparable amplitudes thus low frequency equatorial current oscillations are reasonably well represented by the geostrophic approximation however the mean currents are poorly resolved with the available array in the eastern pacific the mean zonal speed difference over the 10 month comparison period is 25 cm s 1 at 25 m and increases to 60 cm s 1 at 125 m at 165 e mean differences in the upper 250 m are typically 50 cm s 1 over a 4 month record the principal reason for these large mean differences is that the meridional scale of the mean currents is smaller than the spacing of the moorings comparison of observed and geostrophic velocity profiles obtained from shipboard sampling indicates that meridional spacing of about 1 latitude would be optimum for estimating the zonal velocity

interannual geostrophic current anomalies in the near equatorial western pacific abstract a network of island tide gauges is used to estimate interannual geostrophic current anomalies gcas in the western pacific from 1975 to 1997 the focus of this study is the zonal component of the current averaged between 160 e and 180 and 2 to 7 north and south of the equator in the mean flow regions associated with the north equatorial countercurrent necc and the south equatorial current sec respectively the tide gauge gca estimates agree closely with similarly derived currents from topex poseidon sea level anomalies the gcas in the western pacific relate to a basin scale adjustment associated with the el nino southern oscillation characterized here using empirical orthogonal functions of tide gauge and supporting sea surface temperature and heat storage data the dominant eof mode describes the mature phase of enso events and correlates 0 8 with the gca south of the equator the second mode describes transitions to and from enso events and correlates 0 9 with the gca north of th

coastal sabkha dolomites and calcitised sulphates preserving the lomagundi jatuli carbon isotope signal palaeoproterozoic tulomozero formation carbonates of the onega basin were targeted by icdp far deep hole 10b the recovered rocks contain abundant evidence for palaeoproterozoic gypsum and anhydrite particularly in the form of pseudomorphs of inclusion containing nodules swallow tail twinned crystals and evaporite dissolution breccias similarly sand patch fabric indicates the former presence of surface covering salt crusts in the palaeoproterozoic atmospheric oxygen and seawater sulphate levels at that time must have been sufficient to allow such sulphates to form carbonate 13c values are considered sedimentary or early diagenetic predating greenschist facies metamorphism associated with the svecofennian orogeny these carbonate 13c values range from 7 7 to 15 7 with the highest and lowest values found in dolostones the dolostones as well as calcitised calcium sulphates record the lomagundi jatuli signal however evidence for activity of sulphate reducing and or methanogenic bacteria seems to be lacking dolomite precipitation or dolomitisation calcium sulphate calcitisation and production of the high 13c values processes which typically involve such bacteria in the phanerozoic are thus inferred to have proceeded without the direct influence of sulphate reducers and methanogens the most plausible explanation for the lomagundi jatuli excursion seems to remain significant sequestration of organic carbon in a location yet to be identified

genesis of a giant paleoproterozoic strata bound magnesite deposit constraints from mg isotopes abstract giant strata bound magnesite deposits are absent in modern and most phanerozoic sedimentary environments but occur predominantly in precambrian strata these deposits may have formed directly through precipitation of evolved mg rich seawater in an evaporative shallow marine setting or alternatively by epigenetic hydrothermal replacement of the mg rich carbonate precursor to test these hypotheses we obtained the first mg isotope data from the world s largest strata bound magnesite deposit belt hosted by the ca 2 1 ga dashiqiao formation in northeast china the mg isotope compositions 26 mg of most magnesite ores in the huaziyu deposit are heavier 0 75 0 26 than most proterozoic sedimentary dolostones the mg isotope compositions and major and trace element data indicate that the magnesites are probably not of hydrothermal origin instead a mg rich carbonate precursor precipitated from evaporating seawater in a semi closed system diagenetic brines altered the mg rich carbonate precursor to magnesite subsequently recrystallization during regional metamorphism produced coarsely crystalline and saddle magnesite these interpretations are consistent with the geological features and other geochemical data element concentrations and c and o isotopes for the magnesite ores hence we interpret the formation of the huaziyu magnesite deposit to be dominated by evaporative sedimentation and brine diagenesis

isotopic composition of organic and inorganic carbon from the mesoproterozoic jixian group north china implications for biological and oceanic evolution a b s t r a c t analyses of marine carbon isotope profiles have provided much of our current understanding of the evolution of earth surface environments particularly in the latter portion of the proterozoic eon earlier mesoproterozoic successions however have received comparatively little attention due to the relatively subdued nature of carbon isotope variation in this study we present high resolution isotopic profiles from three sections in the yanshan basin north china craton that combined comprise the entirety of the early mesoproterozoic 1600 1400 ma calymmian period jixian group high resolution profiles of both carbonate and organic carbon provide critical data for global comparison and permit us to better con strain both the pattern and origin of isotopic variation in the mesoproterozoic marine carbonate rocks of the jixian group show generally muted isotopic variation with average values near 0 consistent with previous observations from the early mesoproterozoic data furthermore record an increase in isotopic variation through the succession that is interpreted to reflect a long term decrease in pco2 and conse quently in the isotopic buffering capacity of marine dissolved inorganic carbon dic by contrast the isotopic composition of marine organic matter suggests facies dependent differences in carbon cycling organic carbon compositions suggest a dominance of autotrophic carbon fixation and aerobic decom position in shallow water environments and increased remineralization by anaerobic heterotrophs in deeper water environments correlation between organic carbon composition and depositional environ ment are interpreted to reflect differences in carbon cycling within benthic microbial mats under low oxygen conditions and dynamically maintained stratification of marine waters

surface drifter pathways originating in the equatorial atlantic cold tongue 1 subtropical cells stcs connect subduction zones of the eastern subtropics of both hemispheres to the equatorial current systems via equatorward flow in the thermocline some of this thermocline water is converted back into warm near surface water in the eastern equatorial cold tongue from whence it is exported poleward here we examine the export pathways from the cold tongue in the atlantic based on recently available near surface drifter data we find that similar to its pacific counterpart water upwelled in the atlantic cold tongue follows multiple pathways back into the subtropics but not directly to the subduction zones thus the subtropical cells are open to extensive influence from and exchange with the subtropical and midlatitude ocean

on the influence of diurnal and subdiurnal signals in the normal vector on large ring laser gyroscope observations the ring laser gyroscope rlg technique has been investigated for over 20 years as a potential complement to space geodetic techniques in measuring earth rotation however rlgs are also sensitive to changes in their terrestrial orientation therefore in this paper we review how the high frequency band i e signals shorter than 0 5 cycle per day of the known phenomena causing site deformation contribute to the rlg observable the sagnac frequency we study the impact of solid earth tides ocean tidal loading and non tidal loading phenomena atmospheric pressure loading and continental hydrosphere loading also we evaluate the differences between available models of the phenomena and the importance of the love numbers used in modeling the impact of solid earth tides finally we compare modeled variations in the instrument orientation with the ones observed with a tiltmeter our results prove that at the present accuracy of the rlg technique solid earth tides and ocean tidal loading effects have significant effect on rlg measurements and continental hydrosphere loading can be actually neglected regarding the atmospheric loading model its application might introduce some undesired signals we also show that discrepancies arising from the use of different models can be neglected and there is almost no impact arising from the use of different love numbers finally we discuss differences between data reduced with tiltmeter observations and these reduced with modeled signal and potential causes of this discrepancies

interferometric water level tilt meter development in finland and comparison with combined earth tide and ocean loading models a modern third generation interferometric water level tilt meter was developed at the finnish geodetic institute in 2000 the tilt meter has absolute scale and can do high precision tilt measurements on earth tides ocean tide loading and atmospheric loading additionally it can be applied in various kinds of geodynamic and geophysical research the principles and results of the historical 100 year old michelson gale tilt meter as well as the development of interferometric water tube tilt meters of the finnish geodetic institute finland are reviewed modern earth tide model tilt combined with schwiderski ocean tide loading model explains the uncertainty in historical tilt observations by michelson and gale earth tide tilt observations in lohja2 geodynamic station southern finland are compared with the combined model earth tide and four ocean tide loading models the observed diurnal and semidiurnal harmonic constituents do not fit well with combined models the reason could be a result of the improper harmonic modelling of the baltic sea tides in those models

the rise of oxygen and siderite oxidation during the lomagundi event the paleoproterozoic lomagundi event is an interval of 130 250 million years ca 2 3 2 1 billion years ago in which extraordinarily 13c enriched 10 limestones and dolostones occur globally the high levels of organic carbon burial implied by the positive 13c values suggest the production of vast quantities of o2 as well as an alkalinity imbalance demanding extremely low levels of weathering the oxidation of sulfides has been proposed as a mechanism capable of ameliorating these imbalances it is a potent sink for o2 as well as a source of acidity however sulfide oxidation consumes more o2 than it can supply co2 leading to insurmountable imbalances in both carbon and oxygen in contrast the oxidation of siderite feco3 proper as well as other fe2 bearing carbonate minerals produces 4 times more co2 than it consumes o2 and is a common although often overlooked constituent of archean and early proterozoic sedimentary successions here we propose that following the initial rise of o2 in the atmosphere oxidation of siderite provided the necessary carbon for the continued oxidation of sulfides burial of organic carbon and most importantly accumulation of free o2 the duration and magnitude of the lomagundi event were determined by the size of the preexisting archean siderite reservoir which was consumed through oxidative weathering our proposal helps resolve a long standing conundrum and advances our understanding of the geologic history of atmospheric o2

topex poseidon the 2 cm solution the unprecedented accuracy of topex poseidon t p altimeter data warrants a new evaluation of the methods typically used to form time series of sea level change whereas explicit removal of orbit error has always been required as a first step in altimeter data processing the t p analysis presented here is based simply on unadjusted monthly averages this approach has the advantage of retaining the large scale ocean signal which would be distorted by orbit adjustment using 16 months of data we have evaluated the t p monthly means on spatial scales ranging from mesoscale to global in the tropical pacific comparisons with 17 island tide gauge records and dynamic height derived from 36 thermistor moorings show that the altimeter data have an accuracy of approximately 2 cm when averaged over spatial scales of a few hundred kilometers on basin scales in the northern hemisphere similar agreement is found between the t p data and the dynamic height climatology of levitus 1982 these new altimeter observations are thus providing the first reliable view of global sea level changes on seasonal to interannual timescales

multivariate reconstruction of missing data in sea surface temperature chlorophyll and wind satellite fields 1 an empirical orthogonal function based technique called data interpolating empirical orthogonal functions dineof is used in a multivariate approach to reconstruct missing data sea surface temperature sst chlorophyll a concentration and quikscat winds are used to assess the benefit of a multivariate reconstruction in particular the combination of sst plus chlorophyll sst plus lagged sst plus chlorophyll and sst plus lagged winds have been studied to assess the quality of the reconstructions the reconstructed sst and winds have been compared to in situ data the combination of sst plus chlorophyll as well as sst plus lagged sst plus chlorophyll significantly improves the results obtained by the reconstruction of sst alone all the experiments correctly represent the sst and an upwelling downwelling event in the west florida shelf reproduced by the reconstructed data is studied

sr isotopic composition of paleoproterozoic 13c rich carbonate rocks the tulomozero formation se fennoscandian shield abstract rb sr systematics has been studied in 13c rich carbonate rocks of the paleoproterozoic 2 09 0 07 ga tulomozero formation in the northern onega lake area the se fennoscandian shield the formation is divided into eight members a f consisting of greenschist facies grade variegated sandstones siltstones mudstones stromatolitic dolostones and subordinate crystalline limestones samples of carbonate rocks were obtained from two overlapping drillholes intersecting the entire thickness of the tulomozero formation prior to isotope analysis the rocks powders were treated with 1n ammonium acetate for partial removal of the late epigenetic carbonate phases major resetting of the rb sr systems in the tulomozero carbonate rocks appears to take place during the svecofennian regional metamorphic event and it was screened by using mn sr fe sr mg ca and 18o 16o ratios high sr content up to 2080 g g in limestones and 530 g g in dolostones coupled with low fe mn 0 40 in dolostones of the upper part of member b and of members g and h is indicative of seawater influxes sea transgression into the tulomozero basin the 87sr 86sr values in the least altered mn sr

chemostratigraphy of paleoproterozoic carbonate successions of the wyoming craton tectonic forcing of biogeochemical change the archean wyoming craton is flanked on the south and east by belts of paleoproterozoic supracrustal successions whose correlation is complicated by lack of geochronologic constraints and continuous outcrop however carbonate units in these successions may be correlated by integrating carbon isotope stratigraphy with lithostratigraphy the 10 km thick paleoproterozoic snowy pass supergroup in the medicine bow mountains was deposited on the present day southern flank of the wyoming craton it contains three discrete levels of glacial diamictite correlative with those in the huronian supergroup on the southern margin of the superior craton the nash fork formation of the upper snowy pass supergroup is significantly younger than the uppermost diamictite and was deposited after the end of the paleoproterozoic glacial epoch carbonates at the base of the nash fork formation record remarkable 13 cenrichment up to 28 v pdb whereas those from overlying members of the lower nash fork formation have d 13 c values between 6 and 8 carbonates from the upper nash fork formation above the carbonaceous shale have carbon isotope values ranging between 0 and 2 5 the transition from high carbon isotope values to those near 0 in the nash fork formation is similar to that at the end of the ca 2 2 2 1 ga carbon isotope excursion in fennoscandia this chemostratigraphic trend and deposition of bifs mn rich lithologies carbonaceous shales and phosphorites at the end of the global ca 2 2 2 1 ga carbon isotope excursion are likely related to ocean overturn associated with the final breakup of the kenorland supercontinent correlative carbonates from the slaughterhouse formation in the sierra madre wy and from the whalen group in the rawhide creek area in the hartville uplift wy have highly positive carbon isotope values in contrast carbonates from other exposures of the whalen group in the hartville uplift and all carbonate units in the black hills sd have carbon isotope values close to 0 combined with existing geochronologic and stratigraphic constraints these data suggest that the slaughterhouse formation and the succession exposed in the rawhide creek area of the hartville uplift are correlative with the lower and middle nash fork formation and were deposited during the ca 2 2 2 1 ga carbon isotope excursion the estes and roberts draw formations in the black hills and carbonates from other exposures in the hartville uplift postdate the ca 2 2 2 1 ga

carbonate deposition in the palaeoproterozoic onega basin from fennoscandia a spotlight on the transition from the lomagundi jatuli to shunga events abstract several deep drillholes were made in the onega palaeobasin by the fennoscandian arctic russia drilling early earth project far deep of the international continental scientific drilling program icdp these provided fresh core material documenting the lomagundi jatuli isotopic event ljie its termination and the start of the shunga event she of an enhanced accumulation of organic matter the cored section represents the most complete known record of the end of the ljie the late phase of the ljie recorded in far deep core 11a is represented by the upper part of the tulomozero formation tf a 300 m thick unit composed of variegated dolostones siltstones and shales accumulated under oxic conditions on a shallow water carbonate platform the tf hosts the earliest known thick formations of halite and massive anhydrite low temperature greenschist facies metamorphism caused partial recrystallisation of the rocks however a primary carbonate phase the dolomite exhibits a negligible degree of post depositional alteration of the carbon isotope system the dataset of 46 bulk carbonate analyses of carbon and oxygen isotopes yielded 13 c carb ranging between 6 8 and 11 8 and revealed a positive excursion from 8 to 11 8 followed by a decline to 8 towards the top of the 300 m thick succession the cored part of the overlying zaonega formation zf recovered in holes 12ab and 13a is an 800 m thick unit composed of mixed siliciclastic carbonate facies with numerous mafic lava flows and tuff beds intruded by gabbro sills the formation represents an unprecedented episode of enhanced accumulation of organic rich rocks and preserves the earliest known supergiant petrified oilfield all typifying the she the sedimentological petrographic geochemical and c and o isotopic study of over 800 m of core throughout the zf suggests that the initial carbonate deposition occurred in a lacustrine environment then rapidly proceeding through a lagoonal setting to a rifted deepwater shelf and finally to a carbonate platform both the deepwater shelf and the platformal settings are marked by organic rich environments the primary dolomite was potentially exposed to syn and post depositional hydrothermal metasomatic alterations organic matter diagenesis metamorphic mineral reactions co 2 degassing and finally a low temperature post metamorphic calcitisation resulting in overall large fluctuations of 13 c carb between 22 and 8 the dataset of over 413 bulk carbonate analyses of carbon and oxygen isotopes screened petrographically and geochemically against post depositional alteration revealed 28 least altered samples within three stratigraphic intervals suggesting multiple positive and negative 13 c carb excursions throughout over 1000 m of stratigraphy a shift from 5 to 9 followed by a drop to near zero values marks the lower part of the zf a 13 c carb decline from 8 to below zero in the middle and upper part of the zf defines the end of the ljie a subsequent prominent negative excursion down to 6 does not show convincing isotopic evidence for influence of methanogenesis and hence appears to be of primary depositional origin an erratic positive excursion in the uppermost part of the drilled section indicates return of 13 c carb to a near normal marine value

evaluation of topex and basin wide tropical ocean and global atmosphere tropical atmosphere ocean sea surface topographies and derived geostrophic currents fields of topex derived sea level anomalies are validated against and compared with fields of tropical ocean and global atmosphere tropical atmosphere ocean toga tao dynamic height anomalies for the first 470 days of the topex poseidon mission at periods longer than 35 days topex sea level anomalies compare extremely well with toga tao dynamic height anomalies throughout the whole basin with a mean correlation of 0 79 and mean rms differences of 2 6 cm zonal geostrophic current anomalies are then derived from both data sets and validated against in situ current meter measurements at the equator topex derived geostrophic current anomalies at the equator are in good agreement with in situ currents at 0 165 e 0 170 w 0 140 w and 0 110 w toga tao derived current anomalies compare well with in situ currents at 0 110 w 0 140 w and 0 170 w but poor comparisons at 0 165 e are thought to be linked to the absence of instantaneous salinity measurements in the dynamic height calculation despite localized discrepancies basin wide toga tao geostrophic currents compare reasonably well with topex derived geostrophic currents the discrepancies in the comparison between topex and tao are shown to be mostly associated with gaps in toga tao space time sampling and subsequent gridding procedures

variation of initial 230th 232th and limits of high precision u th dating of shallow water corals one hundred eighty u th data including 23 isochrons on 24 pristine modern and holocene corals and 33 seawater samples were analyzed using sector field mass spectrometry to understand the variability of initial 230th 232th 230th 232th0 this dataset allows us to further assess the accuracy and precision of coral 230th dating method by applying quality control including careful sampling and subsampling protocols and the use of contamination free storage and workbench spaces the resulting low procedural blanks give an equivalent uncertainty in age of only 0 2 0 3 yr for 1 2 g of coral sample using site specific 230th 232th0 values or isochron techniques our study demonstrates that corals with an age less than 100 yrs can be 230th dated with precisions of 1 yr six living subtidal coral samples were collected from two continental shelf sites nanwan off southern taiwan in the western pacific and son tra off central vietnam in the south china sea one coral core was drilled from an open ocean site santo island vanuatu in the western tropical pacific and modern and fossil intertidal coral slabs 17 in total were cut from six sites around the islands of simeulue lago north pagai and south pagai of sumatra in the eastern indian ocean the results indicate that the main source of thorium is the dissolved phase of seawater with variation of 230th 232th0 depending on local hydrology with intense input of terrestrial material low 230th 232th0 atomic ratios of 4 9 10 6 and 3 2 10 6 with a 10 variation are observed in nanwan and son tra respectively at the santo site we find a value of 5 6 10 6 at 4 horizons and one high value of 24 10 6 in a sample from ad 1974 6 0 5 likely due to the upwelling of cold water during a la nina event between ad 1973 and 1976 the natural dynamics of 230th 232th0 recorded in the intertidal corals at sites in the sumatran islands are complicated so that this value varies significantly from 3 0 to 9 4 10 6 three of the 141 modern coral 230th ages differ from their true ages by 23 to 4 indicating the presence of detrital material with anomalous 230th 232th values duplicate measurement of coeval subsamples is therefore recommended to verify the age accuracy this improved high precision coral 230th dating method raises the prospects of refining the age models for band counted and tracer tuned chronologies and of advancing coral paleoclimate research

deposition and early alteration of evaporites summary the depositional settings for primary and early diagenetic evaporite deposits generally fall into three categories marginal mixed shallow subaqueous and subaerial shallow and deep subaqueous these three environmental groupings hold for both marine and nonmarine settings although the details of continental evaporites may be far more complex than in most marine fed water bodies the primary evaporite morphologies from many continental playa hypersaline marine and marine marginal depositional settings are reasonably well understood because of the numerous detailed studies of recent holocene and cenozoic deposits that serve as models for sedimentary interpretation the sedimentological features that develop in deeper water settings are inferred based on examination of unaltered cenozoic deposits each environmental setting develops characteristic depositional features and patterns and one facies grades into the next because there may be significant physiochemical changes in water composition during deposition as well as sudden change s in both water depth and basinal circulation description and interpretation of evaporative rocks should not be based on mineralogy alone but on the distinct sedimentary characteristics of each part of a deposit in cases where sediments still reflect their primary mineralogy and morphology most of the environments can now be recognized however geochemical studies are commonly required to determine the source s of the original water the determinative geochemical techniques that presently serve as a support to sedimentologic study include studies of fluid inclusions bromine content of chloride salts and the stable isotopes of strontium sulphur carbon and oxygen only after these and perhaps other chemical analyses are considered can the full depositional history of a region be reasonably unravelled

discussion of the article by a c lasaga and h ohmoto on the oxygen geochemical cycle dynamics and stability geochim cosmochim acta 66 361 381 2002

palaeoproterozoic magnesite lithological and isotopic evidence for playa sabkha environments magnesite forms a series of 1 to 15 m thick beds within the 2ae 0g a palaeoproterozoic tulomozerskaya formation nw fennoscandian shield russia drillcore material together with natural exposures reveal that the 680m thick formation is composed of a stromatolite dolomite red bed sequence formed in a complex combination of shallow marine and non marine evaporitic environments dolomite collapse breccia stromatolitic and micritic dolostones and sparry allochemical dolostones are the principal rocks hosting the magnesite beds all dolomite lithologies are marked by d 13 c values from 7ae1 to 11ae6 v pdb and d 18 o ranging from 17ae4 to 26ae3 v smow magnesite occurs in different forms finely laminated micritic stromatolitic magnesite and structureless micritic crystalline and coarsely crystalline magnesite all varieties exhibit anomalously high d 13 c values ranging from 9ae0 to 11ae6 and d 18 o values of 20ae0 25ae7 laminated and structureless micritic magnesite forms as a secondary phase replacing dolomite during early diagenesis and replaced dolomite before the major phase of burial crystalline and coarsely crystalline magnesite replacing micritic magnesite formed late in the diagenetic metamorphic history magnesite apparently precipitated from sea water derived brine diluted by meteoric fluids magnesitization was accomplished under evaporitic conditions sabkha to playa lake environment proposed to be similar to the coorong or lake walyungup coastal playa magnesite magnesite and host dolostones formed in evaporative and partly restricted environments consequently extremely high d 13 c values reflect a combined contribution from both global and local carbon reservoirs a 13 c rich global carbon reservoir d 13 c at around 5 is related to the perturbation of the carbon cycle at 2ae0 ga whereas the local enhancement in 13 c up to 12 is associated with evaporative and restricted environments

oxygen overshoot and recovery during the early paleoproterozoic abstract during the lomagundi event ca 2 22 to 2 06 ga marine carbonates recorded the largest and longest uninterrupted positive carbon isotope excursion the earliest extensive marine sulfate evaporites were deposited and the average ferric iron to total iron expressed as fe 2 o 3 fe fe2o3 ratio of shales increased dramatically at the end of the lomagundi event the first economic sedimentary phosphorites were deposited and the carbon isotope values of marine carbonates returned to 0 vpdb thereafter marine sulfate evaporites and phosphorites again became scarce while the average fe 2 o 3 fe fe2o3 ratio of shales decreased to values intermediate between those of the archean and lomagundi age shales we propose that the large isotopic and chemical excursions during the lomagundi event were caused by a positive feedback between the rise of atmospheric o 2 the weathering of sulfides in the pre 2 3 ga continental crust and the flux of phosphate to the oceans cf holland 2002 the rise in the terrestrial phosphate flux led to an increase in the burial rate of organic carbon and a major transfer of oxygen from the carbon to the sulfur cycle the end of the lomagundi event was probably caused by a decrease in the terrestrial phosphate flux related to the weathering of low pyrite sediments that were deposited during the lomagundi event the rate of deposition of organic matter and the precipitation of sulfate evaporites decreased the isotopic and chemical excesses of the lomagundi event were eliminated and the ocean atmosphere system entered the period frequently called the boring billion