coherence of western boundary pressure at the rapid wave array boundary wave adjustments or deep western boundary current advection this study investigates the coherence between ocean bottom pressure signals at the rapid climate change programme rapid west atlantic variability experiment wave array on the western north atlantic continentalslope includingthewoodsholeoceanographicinstitutionlinew highlycoherentpressuresignals propagate southwestward along the slope at speeds in excess of 128 m s 21 consistent with expectations of barotropic kelvin like waves coherent signals are also evidenced in the smaller pressure differences relative to 1000 m depth which are expected to be associated with depth dependent basinwide meridional transport variations or an overturning circulation these signals are coherent and almost in phase for all time scales from 3 6 years down to 3 months coherence is still seen at shorter time scales for which group delay estimates are consistent with a propagationspeedofabout1 m s 21 over990 kmofcontinentalslopebutwithlargeerrorboundsonthespeed this is roughly consistent with expectations for propagation of coastally trapped waves though somewhat slower than expected a comparison with both eulerian currents and lagrangianfloat measurements shows that the coherence is inconsistent with a propagation of signals by advection except possibly on time scales longer than 6 months

propagation of signals in basin scale ocean bottom pressure from a barotropic model 1 the exchange of atmospheric plus oceanic mass between ocean basins is investigated using a global barotropic ocean model we find two particular cases of exchange between two basins at periods of 4 6 days the exchange is between the atlantic and pacific basins and represents a known oscillation forced by atmospheric pressure this mode represents a failure of the inverse barometer relationship due to the large scale and high frequency of atmospheric forcing and the presence of continents significant exchange between atlantic and pacific also occurs at longer periods the second case is most prominent at periods longer than 30 days strongest at periods longer than 100 days and represents a mass exchange between the southern ocean and the pacific the southern ocean part of this exchange is clearly related to the southern mode of fluctuations in antarctic circumpolar transport forced by southern ocean wind stress the reason for the exchange being with the pacific rather than other basins is explored and is found to be related to the balance of wind stress by form stress in drake passage exchange with the atlantic and indian oceans becomes dominant if drake passage topography is removed while recognizing the limitations of a barotropic model we contend that it is necessary to understand the barotropic adjustment process in order to make sense of longer timescale processes accordingly we end with speculation on the possible importance of the barotropic results for global sea level and tropical dynamics

the sulfur isotope signatures of marinoan deglaciation captured in neoproterozoic shallow to deep cap carbonate from south china a b s t r a c t we present high resolution sulfur and carbon isotope records from the cap carbonate of the doushantuo formation south china a unique suite of depositional facies spanning across a pronounced paleo oceanic depth gradient the i34s of carbonate associated sulfate cas decreases across a shelf to slope depth transect we propose that the deeper water slope profile represents syn glacial sulfur isotope compositions of the seawater sulfates with impact of 34 s depleted hydrothermal sulfur inputs while the i 34 s of the shallow inner shelf were dominantly controlled by the 34 s enriched terrigenous input we suggest that the terrigenous sulfur inputs were mainly from weathering and erosion of the pre marinoan datangpo formation glacially ground and then freshly exposed during rapid deglaciation the widespread datangpo formation deposited between the sturtian and marinoan glacial intervals is noted for the unusually high i34s values of its pyrite the low sulfate conditions in the ocean allowed for strong local controls and consequent heterogeneities in seawater chemistry the post marinoan ocean was stratified in the immediate wake of glaciation with anoxic deep waters overlain by an oxic melt water layer during the transgression the shallow water was disturbed by upwelling the oxidation of dissolved organic carbon doc from deep water would lead to transiently enhanced 13c depletions but 34s enrichments in the shallow waters

mineralogy early marine diagenesis and the chemistry of shallow water carbonate sediments abstract shallow water carbonate sediments constitute the bulk of sedimentary carbonates in the geologic record and are widely used archives of earth s chemical and climatic history one of the main limitations in interpreting the geochemistry of ancient carbonate sediments is the potential for post depositional diagenetic alteration in this study we use paired measurements of calcium 44ca 40ca or 44ca and magnesium 26mg 24mg or 26mg isotope ratios in sedimentary carbonates and associated pore fluids as a tool to understand the mineralogical and diagenetic history of neogene shallow water carbonate sediments from the bahamas and southwest australia we find that the ca and mg isotopic composition of bulk carbonate sediments at these sites exhibits systematic stratigraphic variability that is related to both mineralogy and early marine diagenesis the observed variability in bulk sediment ca isotopes is best explained by changes in the extent and style of early marine diagenesis from one where the composition of the diagenetic carbonate mineral is determined by the chemistry of the fluid fluid buffered to one where the composition of the diagenetic carbonate mineral is determined by the chemistry of the precursor sediment sediment buffered our results indicate that this process together with variations in carbonate mineralogy aragonite calcite and dolomite plays a fundamental and underappreciated role in determining the regional and global stratigraphic expressions of geochemical tracers 13c 18o major minor and trace elements in shallow water carbonate sediments in the geologic record our results also provide evidence that a large shallow water carbonate sink that is enriched in 44ca can explain the mismatch between the 44 40ca value of rivers and deep sea carbonate sediments and call into question the hypothesis that the 44 40ca value of seawater depends on the mineralogy of primary carbonate precipitations e g aragonite seas and calcite seas finally our results for sedimentary dolomites suggest that paired measurements of ca and mg isotopes may provide a unique geochemical fingerprint of mass transfer during dolomitization to better understand the paleo environmental information preserved in these enigmatic but widespread carbonate minerals

observed basin scale response of the north atlantic meridional overturning circulation to wind stress forcing abstractthe response of the north atlantic meridional overturning circulation moc to wind stress forcing is investigated from an observational standpoint using four time series of overturning transports below and relative to 1000 m overlapping by 3 6 yr these time series are derived from four mooring arrays located on the western boundary of the north atlantic the rapid western atlantic variability experiment wave array 42 5 n the woods hole oceanographic institution line w array 39 n rapid moc mocha 26 5 n and the meridional overturning variability experiment move array 16 n using modal decompositions of the analytic cross correlation between transports and wind stress the basin scale wind stress is shown to significantly drive the moc coherently at four latitudes on the time scales available for this study the dominant mode of covariance is interpreted as rapid barotropic oceanic adjustments to wind stress forcing eventually forming two counterrotating ekman overturning cells c

zn sr isotope records of the ediacaran doushantuo formation in south china diagenesis assessment and implications abstract recent studies show that zinc isotopes could provide valuable clues to environmental change and biogeochemical cycle of the past oceans this study reports a modified procedure for leaching the carbonate fractions in sedimentary rocks a thorough evaluation of diagenetic effects and systematic variations of zn and sr isotope ratios in lower part of the ediacaran stratigraphic unit deposited in the aftermath of the marinoan glaciation in south china the influence of post depositional diagenesis on zn isotope compositions of the studied samples is assessed by comparing 66zn to other geochemical indexes 87sr 86sr 13c 18o and mn sr ratios in the five studied cap carbonate sections member i of the doushantuo formation dolostones from four sections have 66zn values positively correlated with 18o values and negatively correlated with 87sr 86sr ratios 0 7081 0 7204 these correlations suggest that these cap dolostone samples have been modified by post depositional diagenesis the light 66zn value 0 02 suggests that initial zn isotope ratios of cap dolostones could have been reset by hydrothermal fluids with relatively high zn concentration and low 66zn values by contrast carbonates from member ii of the doushantuo formation above cap dolostones are relatively pristine based on their low 87sr 86sr ratios 0 7079 0 7086 being indistinct from the proposed early ediacaran seawater 87sr 86sr values chemical and isotopic variations in these samples are interpreted to reflect primary signals that record paleo environmental changes of the early ediacaran ocean a rapid increase of 66zn from 0 3 to 1 1 occurs in the middle part of member ii accompanying by relatively invariant 87sr 86sr ratios that imply insignificant changes in input from continental weathering considering the limited change in atmospheric oxygen during this period the rapid 66zn raise indicates an increase in buried organic matters which is consistent with the coupled positive shift of 13ccarb as well as the fossil records found in the same strata these results provide insights into zn cycling in the post marinoan oceans and facilitate the application of zn isotopes in carbonates as a proxy for the fate of marine organic matter

the observed north atlantic meridional overturning circulation its meridional coherence and ocean bottom pressure abstractanalyses of meridional transport time series from the rapid climate change meridional overturning circulation rapid moc array at 26 n and from argo float and altimetry data at 41 n reveal that at semiannual and longer time scales the contribution from the western boundary dominates the variability of the north atlantic meridional overturning circulation moc defined as the transport in the upper 1000 m of the ocean because the variability of the western boundary contribution is associated with a geostrophic overturning it is reflected in independent estimates of transports from gradient of ocean bottom pressure obp relative to and below 1000 m on the continental slope of the western boundary at three nominal latitudes 26 39 and 42 5 n time series of western meridional transports relative to and below 1000 m derived from the obp gradient or equivalently derived from the transport shear profile exhibit approximately the same phase relationship between 26 and 39 42 5 n as the wes

dynamical linkage of tropical and subtropical weather systems to the intraseasonal oscillations of the indian summer monsoon rainfall part i observations the indian summer monsoon rainfall ismr over the western ghats wg and the bay of bengal bob is marked by the intraseasonal oscillations isos with preferred 10 20 day and 30 50 day bands on the basis of pentad climate prediction center merged analysis precipitation and daily sea level pressure and winds at 850 hpa derived from european center for medium range weather forecast reanalysis we present the structure and evolution of the isos linked to the ismr variations over the wg and the bob and the associated anomalies of the atmospheric circulation using the approaches of wavelet analysis bandpass filtering and composite analysis this study reveals that the activities of both the intertropical convergence zone itcz and the western pacific subtropical high wpsh contribute strongly to the structure and propagation of the isos on intraseasonal time scales northward development and propagation of the itcz plays a critical role in the northward propagating isos but not in the westward propagating bob 10 20 day isos the latter isos may be linked instead to the activity of synoptic scale weather systems to the east over the western tropical pacific the enhanced itcz in the tropical indian ocean plays a strong role in the sudden strengthening of the wpsh during the transition from the break to active phase of the 30 50 day isos we find that the strong wpsh in the asian summer monsoon season with generally northward advance and eastward withdrawal promotes the formation of a northwest to southeast tilted anomalous rainfall belt over the east asian tropical summer monsoon region and the western tropical pacific in the 30 50 day low frequency band positive negative elongated rainfall anomalies with an unbroken northwest southeast tilt strong easterly westerly anomalies in the tropical pacific and northward advance and eastward movement of strong weak wpsh are favorable for maintaining the eastward propagation of the 30 50 day isos in the pacific daily high resolution sea surface temperature obtained from the national oceanic and atmospheric administration is used to explain the propagation features of the 10 20 day isos in the indian ocean

perspectives on proterozoic surface ocean redox from iodine contents in ancient and recent carbonate abstract the proterozoic eon hosted the emergence and initial recorded diversification of eukaryotes oxygen levels in the shallow marine settings critical to these events were lower than today s although how much lower is debated here we use concentrations of iodate the oxidized iodine species in shallow marine limestones and dolostones to generate the first comprehensive record of proterozoic near surface marine redox conditions the iodine proxy is sensitive to both local oxygen availability and the relative proximity to anoxic waters to assess the validity of our approach neogene quaternary carbonates are used to demonstrate that diagenesis most often decreases and is unlikely to increase carbonate iodine contents despite the potential for diagenetic loss maximum proterozoic carbonate iodine levels are elevated relative to those of the archean particularly during the lomagundi and shuram carbon isotope excursions of the paleo and neoproterozoic respectively for the shuram anomaly comparisons to neogene quaternary carbonates suggest that diagenesis is not responsible for the observed iodine trends the baseline low iodine levels in proterozoic carbonates relative to the phanerozoic are linked to a shallow oxic anoxic interface oxygen concentrations in surface waters would have at least intermittently been above the threshold required to support eukaryotes however the diagnostically low iodine data from mid proterozoic shallow water carbonates relative to those of the bracketing time intervals are consistent with a dynamic chemocline and anoxic waters that would have episodically mixed upward and laterally into the shallow oceans this redox instability may have challenged early eukaryotic diversification and expansion creating an evolutionary landscape unfavorable for the emergence of animals

geostrophic dynamics of meridional transport variability in the subpolar north atlantic the north atlantic meridional overturning 6 circulation moc is believed to play an important role in regulating the earth s climate yet there is still much uncertainty regarding the dynamics of the moc and its variability it is well established however that through geostrophy the zonally integrated meridional transport at a particular latitude and depth can be determined from the east west bottom pressure difference across the basin therefore rather than consider the moc as a large scale system this paper focuses on the dynamics of this geostrophic relationship in two numerical ocean models at a single latitude 50 14 n in the sub polar atlantic first it is shown that the bottom pressure on the western boundary is sufficient to recover with high fidelity the interannual meridional transport variability at 50 17 n over a one hundred year period in the climate model hadcm3 it is found that the variability of western boundary pressure is closely associated with density changes over the continental slope these changes lead to a large zonal gradient in potential energy and an unfeasible depth mean velocity over the slope the western boundary pressure from which the meridional transport can be recovered is generated as a compensation to this and limits the depth mean flow this demonstrates that in numerical ocean models at least meridional transport variability is generated as a local response to density changes on the western slope whether this is a true representation of actual ocean variability is uncertain but if it were then meridional transport variability could largely be determined using only the density field on the western slope

zn isotopic evolution in early ediacaran ocean a global signature abstract the zn isotope composition of sedimentary archives reveals key biosphere lithosphere interactions throughout geologic history a recent zn isotope study of ediacaran cap carbonates from south australia revealed that the local isotopic profile reflects global changes in oceanic chemistry to examine this critical assumption this study investigates a high resolution zinc isotope profile of marinoan post glacial cap carbonates from the yangtze platform south china stratigraphic variations in zn isotope data from this study are similar to previously reported sections in south australia and south china the remarkable isotopic similarity between the two sections that were deposited on distant geographically separated continental blocks demonstrates that the zn isotopic variations reflect changing global signatures of the early ediacaran ocean this study highlights the value of zn isotopes in sediments as a global proxy for paleoceanographic studies we interpret the systematic stratigraphic changes in the zn isotope composition of the studied post glacial marinoan carbonates as a global oceanic trend controlled mainly by varying inputs and outputs of zn to the ocean decreasing 66zn values in the lowermost part of the section are attributed to the global precipitation of carbonate enriched in the heavier zn isotope a positive shift in the middle part of the section is explained by the non quantitative removal of isotopically lighter zn by sulfide minerals lower 66zn values in the uppermost part likely reflect the changing contributions of continental weathering and sulfide precipitation our data suggest that non quantitative removal of zn by sulfides is a previously unrecognized sink for zinc in the oceans

spatial variability of sea level rise in twenty first century projections abstract a set of state of the science climate models are used to investigate global sea level rise slr patterns induced by ocean dynamics in twenty first century climate projections the identified robust features include bipolar and bihemisphere seesaws in the basin wide slr dipole patterns in the north atlantic and north pacific and a beltlike pattern in the southern ocean the physical and dynamical mechanisms that cause these patterns are investigated in detail using version 2 1 of the geophysical fluid dynamics laboratory gfdl coupled model cm2 1 under the intergovernmental panel on climate change s ipcc special report on emissions scenarios sres a1b scenario the steric sea level changes relative to the global mean the local part in different ocean basins are attributed to differential heating and salinity changes of various ocean layers and associated physical processes as a result of these changes water tends to move from the ocean interior to continental shelves in the north at

boundary wave communication of bottom pressure and overturning changes for the north atlantic 1 the relationship between changes in sea surface height bottom pressure and overturning is explored using isopycnal model experiments for the north atlantic changes in high latitude forcing are communicated rapidly over the basin through boundary wave propagation along the continental slope involving a hybrid mixture of kelvin and topographic rossby waves as well as spreading more slowly through advection along the western boundary this wave communication leads to coherent signals in sea surface height and bottom pressure variability extending for several thousand kilometers along the continental slope the model results are in broad agreement with altimetric diagnostics and the patterns only alter in detail with the realism of the topography the adjustment in bottom pressure is directly linked to a change in overturning since west east contrasts in bottom pressure are associated with a zonal integral in the meridional geostrophic flow correlation patterns reveal that temporal changes in overturning are primarily connected to the vertical contrast in bottom pressure across the shelf and continental slope along the western boundary

the relationship between convection and sea surface temperature on intraseasonal timescales abstract the relationship between tropical convection surface fluxes and sea surface temperature sst on intraseasonal timescales has been examined as part of an investigation of the possibility that the intraseasonal oscillation is a coupled atmosphere ocean phenomenon the unique feature of this study is that 15 yr of data and the whole region from the indian ocean to the pacific ocean have been analyzed using lag correlation analysis and compositing techniques a coherent relationship between convection surface fluxes and sst has been found on intraseasonal timescales in the indian ocean maritime continent and west pacific regions of the tropics prior to the maximum in convection there are positive shortwave and latent heat flux anomalies into the surface followed by warm sst anomalies about 10 days before the convective maximum coincident with the convective maximum there is a minimum in the shortwave flux followed by a cooling due to increased evaporation associated with enhanced westerl

stratigraphy sedimentology and isotopic geochemistry of australian neoproterozoic postglacial cap dolostones deglaciation delta 13 c excursions and carbonate precipitation abstract thin d13c excursions in the geologic record they are interpreted to record a brief postglacial anomaly in ocean chemistry in australia the marinoan varanger equivalent 600 ma cap dolostone units exhibit many of the characteristics displayed by such deposits elsewhere around the globe including fine grained dolomitic mineralogy lateral persistenc at basinal scales thin laminae graded beds intervals with abundant marine cements crystal fans and a distinctive negative d13c isotopic signature of up to 5 pdb on the basis of these features the australian examples are interpreted here to be deeper water deposits below storm wave base resulting from an anomalous flux of inorganic carbonate to the sea floor during postglacial transgression detailed isotopic analysis of australian cap dolostones indicates d13c values ranging from 1 to 5 and gen rally becoming more depleted in 13c upsection trace element data indicate some diagenetic stabilization but textural evidence and the presence of similar profiles in different basins argue against a pervasive recrystallization event the range in d13c values between sections as well as more negative 13c values appear to correlate with greater paleobathymetry within basins this implies either 1 only partial preservation of the complete oceanic variation of d13c or 2 precipitation of this peculiar facies owes its genesis to basinal specific oceanographic processes such as proximi y of a given section to a postglacial upwelling zone in the later case d13c values would not represent whole ocean values stratigraphic constraints and paleoenvironmental interpretations suggest that much of this excursion lies within the geologically brief period of postglacial transgression this implies that the cause s of d13c variation likely operated on time scales significantly less than the residence time of carbon in the oceans 105 yr the continent wide and perhaps global nature of cap dolostones indicates that large volumes of carbonate were precipitated during the postglacial transgressive period such large scale carbonate precipitation over the hypothesized short time interval of postglacial transgression must have caused or have been the product of profound changes in the carbon cycle and global climate at tha time similar evidence for transgression and increased carbonate deposition in the holocene are attributed to the changing basin shape and ph of the oceans the coral reef hypothesis of berger 1982 cap dolostones may record a proterozoic equivalent of this process with the substitution of abiotic carbonate precipitation for skeletal precipitation by reef organisms

a decomposition of the atlantic meridional overturning a decomposition of meridional overturning circulation moc cells into geostrophic vertical shears ekman and bottom pressure dependent or external mode circulation components is presented the decomposition requires the following information 1 a density profile wherever bathymetry changes to construct the vertical shears component 2 the zonal mean zonal wind stress for the ekman component and 3 the mean depth independent velocity information over each isobath to construct the external mode the decomposition is applied to the third generation hadley centre coupled ocean atmosphere general circulation model hadcm3 to determine the meridional variability of these individual components within the atlantic ocean the external mode component is shown to be extremely important where western boundary currents impinge on topography and also in the area of the overflows the sverdrup balance explains the shape of the external mode moc component to first order but the time variability of the external mode exhibits only a very weak dependence on the wind stress curl thus the sverdrup balance cannot be used to determine the external mode changes when examining temporal change in the moc the vertical shears component allows the time mean and the time variable upper north atlantic moc cell to be deduced at 25 s and 50 n a stronger dependency on the external mode and ekman components between 8 and 35 n and in the regions of the overflows means that hydrographic sections need to be supplemented by bottom pressure and wind stress information at these latitudes at the decadal time scale variability in ekman transport is less important than that in geostrophic shears in the southern hemisphere the vertical shears component is dominant at all time scales suggesting that hydrographic sections alone may be suitable for deducing change in the moc at these latitudes

paleo redox context of the mid devonian appalachian basin and its relevance to biocrises abstract the devonian period witnessed the expansion of vascular land plants and an atmospheric oxygenation event associated with enhanced organic mass burial the deposition of organic rich shales e g black shales of the marcellus subgroup and several biotic crises in the marine realm have been linked to devonian ocean anoxia however it is not clear how redox conditions evolved in different parts of the water column in such a context of dynamic changes in the atmosphere ocean system to address this problem we use the bulk carbonate i ca proxy on core samples from yates county ny in order to reconstruct the water column redox history through the onondaga limestone into the lower marcellus shale on the secular scale the range of i ca values support the notion of a devonian rise in atmospheric oxygen relative to time intervals earlier in the paleozoic in terms of eifelian stage stratigraphic trends i ca ratios are generally stable and high in the onondaga formation but show large fluctuations in lower marcellus strata low i ca ratios are found near the onset of organic rich shale deposition indicating relatively reducing subsurface waters the pattern of redox changes resembles that of contemporaneous sea level changes finally the reconstructed oxygenation changes are correlated to three biotic transitions in devonian marine systems

quasi periodic oscillations in a symmetric general circulation model abstract long lime integrations with a symmetric version of the clas climate model with hydrology have shown that the hadley circulation has well defined strong and weak episodes this oscillation of the hadley circulation seems to occur in two dominant range of periodicities one with periods between 10 and 15 days and another with periods between 20 and 40 days this quasi periodic behavior of the hadley circulation is seen only when the moist convective heating is determined by dynamics if the latent beating in the atmosphere is prescribed and kept artificially fixed this oscillation of the hadley circulation disappears thus this oscillation of the hadley circulation appears as a result of interactions between moist convective and dynamical processes a wave phenomenon is seen in the lower atmosphere that propagates toward the position of maximum radiative beating this wave perturbation has a length scale of about 15 20 degrees latitude in the north south direction this phenomenon has large ampli

development and life cycle of the indian monsoon effect of the 30 50 day oscillation abstract the velocity potential fields generated from the fgge iii b horizontal winds of the european centre for medium range weather forecasts were subjected to an empirical orthogonal function eof analysis to extract the annual cycle and the 30 50 day mode of the divergent circulations we found that the indian monsoon circulation is portrayed by the annual cycle of the divergent circulation and develops as a classical giant sea breeze model on the other hand this monsoon system is modulated by the planetary scale 30 50 day low frequency mode to establish an onset active break revival retreat life cycle this modulation is accomplished through the following interaction process the northeastward propagation of the planetary scale 30 50 day mode over the indian monsoon region induces transient local hadley circulation through this type of circulation the planetary scale 30 50 day mode couples with and steers northward the low level 30 50 day monsoon troughs and ridges that originated around the e

relation between sea level and bottom pressure and the vertical dependence of oceanic variability 1 the relation between large scale sea level and bottom pressure variability is studied using long 50 yr simulations of a general circulation model under realistic forcing admittance and coherence analyses are used to characterize the bottom pressure and sea level relationship as a function of period horizontal spatial scale and location at the model grid scale 1 bottom pressure is found to be essentially equivalent to sea level at periods 60 and in shallow depths 200 m elsewhere bottom pressure and sea level fields can differ significantly results indicate an increase of the importance of baroclinic signals with decreasing latitude and spatial scale with significant baroclinic signals at intra seasonal and longer periods present in many subtropical and mid latitude regions variability is clearly baroclinic at inter annual periods regardless of location and spatial scale results have broad implications for the interpretation and processing of both satellite altimetry and gravity data and for their assimilation into numerical models

determining north atlantic meridional transport variability from pressure on the western boundary a model investigation 1 in this paper we investigate the possibility of determining north atlantic meridional transport variability using pressure on the western boundary focusing on the 42 n latitude of the halifax wave array we start by reviewing the theoretical foundations of this approach next we present results from a model analysis both statistical and dynamic that demonstrate the feasibility of the approach we consider how well we can quantify the meridional transport variability at 42 n given complete knowledge of bottom pressure across the basin and to what degree this quantification is degraded by first ignoring the effect of intervening topography and then by using only bottom pressure on the western boundary we find that for periods of greater than 1 year we can recover more than 90 of the variability of the main overturning cell at 42 n using only the western boundary pressure provided that we remove the depth averaged boundary pressure signal this signal arises from a basin mode of bottom pressure variability which has power at all time scales but that does not in truth have a meridional transport signal associated with it and from the geostrophic depth independent compensation of the ekman transport an additional benefit of the removal of the depth averaged pressure is that this high frequency ekman signal which is essentially noise as far as monitoring the meridional overturning circulation for climatically important changes is concerned is clearly separated from other modes

a window on the deep ocean the special value of ocean bottom pressure for monitoring the large scale deep ocean circulation we show how by focusing on bottom pressure measurements particularly on the global continental slope it is possible to avoid the fog of mesoscale variability which dominates most observables in the deep ocean this makes it possible to monitor those aspects of the ocean circulation which are most important for global scale ocean variability and climate we therefore argue that such measurements should be considered an important future component of the global ocean observing system to complement the present open ocean and coastal elements our conclusions are founded on both theoretical arguments and diagnostics from a fine resolution ocean model that has realistic amplitudes and spectra of mesoscale variability these show that boundary pressure variations are coherent over along slope distances of tens of thousands of kilometres for several vertical modes we illustrate the value of this in the model atlantic by determining the time for boundary and equatorial waves to complete a circuit of the northern basin 115 and 205 days for the first and second vertical modes showing how the boundary features compare with basin scale theoretical models and demonstrating the ability to monitor the meridional overturning circulation using these boundary measurements finally we discuss applicability to the real ocean and make recommendations on how to make such measurements without contamination from instrumental drift

methane derived authigenic carbonate from the lower doushantuo formation of south china implications for seawater sulfate concentration and global carbon cycle in the early ediacaran ocean authigenic carbonate associated with anaerobic oxidation of methane aom usually via microbial sulfate reduction msr or ferric iron reduction is generally characterized by extremely low 13c values 30 vpdb this has been used as one of the major diagnostic features for the recognition of hydrocarbon seep carbonate in the geological past previous reports on precambrian authigenic carbonates are rare limiting our understanding of the effects of their deposition on the earth s carbon isotopic mass balance in this study mainly based on petrographic features and pronounced negative 13c values as low as 38 1 we discovered authigenic calcite cement immediately above the cap dolostone in the basal ediacaran doushantuo formation in the jiulongwan section yangtze gorges area south china our observations not only provide direct evidence for the involvement of aom during carbonate precipitation in the early ediacaran 635 ma but also suggest that the seawater sulfate concentrations in the early ediacaran may have been higher than previously thought

a note on the representation of steric sea level in models that conserve volume rather than mass this note discusses the representation of steric sea level in ocean circulation models changes in steric sea level are caused when changes in the density of the water column imply an expansion or contraction of the column models usually make the boussinesq approximation and conserve volume rather than mass and so do not properly represent expansion or contraction this means that although expansion contraction is included in the equation of state it is not accounted for by the model dynamics in this note we examine the equation governing the time evolution of the sea level displacement it is shown that requiring conservation of mass rather than volume introduces a new term to this equation a simple example is used to show the relationship of the new term to the surface buoyancy flux the equilibrium response to the new term has two parts one part consists of the goldsbrough and stommel gyres for which in the ocean interior vortex stretching due to the local expansion contraction of the water column is balanced by changes in planetary vorticity the other part corresponds to the inverse barometer the effect is to adjust sea level by a globally uniform but timevarying factor determined by the net expansion contraction of the global ocean since this correction is globally uniform it has no dynamical significance both the goldsbrough stommel gyres and the inverse barometer solution are missing from models as currently formulated this does not represent a serious error however if comparison is made with observations of sea level model calculated sea level should be adjusted by a globally uniform time varying factor determined by the net expansion contraction of the global ocean this would be important for assessing the likely rise in sea level in response to global warming

tracing crustal fluids applications of natural 129i and 36cl the two cosmogenic isotopes 129i and 36cl have half lives and geochemical characteristics that make their application of interest in the tracing of crustal fluids oil field brines and geothermal fluids the focus of this review is to compare 129i data from volcanic fluids with those from mud volcanoes and gas hydrate locations associated with the same subduction zone in order to demonstrate that fundamentally different hydrologic systems are present in active margins whereas 129i i ratios in volcanic fluids are site dependent and show a relation to the ages of subducting marine sediments ratios in fore arc fluids are similar in all sites investigated and are independent of the ages of the host sediments and the age of the subducting slab volcanic fluids contain iodine transported in sediments from the trench to the main volcanic zone whereas iodine in fore arc fluids is derived from organic material stored in the upper plates of subduction zones

tracking the onset of phanerozoic style redox sensitive trace metal enrichments new results from basal ediacaran post glacial strata in nw canada abstract a global rise in oxygen levels has been proposed to coincide with the ediacaran to cambrian radiation of animals yet the precise timing and nature of this change remains unresolved one hypothesis is that the ocean atmosphere system became temporarily well oxygenated in the earliest ediacaran directly following the marinoan snowball earth glaciation 635 ma the evidence for oxygenation is based on large enrichments of redox sensitive trace elements in black shale from south china presumably deposited under a euxinic water column these enrichments meet or exceed the bulk concentrations of redox sensitive trace elements found in phanerozoic shale deposited under euxinic water columns here we test the early ediacaran post snowball oxygenation hypothesis with new data from a high resolution multi proxy geochemical and sedimentological study of three stratigraphic sections in the earliest ediacaran sheepbed formation of the mackenzie and wernecke mountains nw canada iron speciation data from all sections suggest that the local water column was dominantly ferruginous with a notable exception of probable euxinic conditions recorded in part of one section redox sensitive elements show no appreciable enrichments in the basal sheepbed formation with maximum concentrations of molybdenum vanadium uranium and chromium only slightly above world average shale values the lack of substantial elemental enrichments within the sheepbed formation is consistent with results from coeval ferruginous strata in svalbard the dominance of local ferruginous conditions in nw canada cannot alone account for the muted redox sensitive element enrichments as v u and cr are thought to be enriched under these conditions and samples deposited under euxinic conditions also lack phanerozoic style enrichments these contrasting results from different localities highlight a need to further investigate the veracity of trace metal enrichments in all localities as representing global redox conditions as the results have important implications for the timing of oxygenation with respect to early animal evolution

reconstructing paleoceanographic conditions during the middle ediacaran evidence from giant ooids in south china abstract the ediacaran was a period of intense environmental change in earth history transient pulses of oxygenation and shifts in ocean chemistry have been interpreted from a range of geochemical proxies including rare earth elements and yttrium rey but it is still a challenge to reconstruct paleoceanographic conditions due to the scarcity of reliable recorder in this study we explore the possibility that a newly discovered deposit of giant ooids in the nanshanping outcrop in south china contains a relatively intact record of the ree composition of ediacaran seawater providing an important window into the redox state of the surface ocean at this time these ooids are relatively large in size 1 6 mm and exhibit densely banded laminae a regional chemostratigraphic correlation shows that the giant ooid bearing succession in south china is in the upper part of the second ediacaran positive carbon isotopic shift ep2 and thus its occurrence was not associated with the shuram excursion additionally the occurrences of giant ooid bearing oolites in different blocks were not synchronous during the middle ediacaran in situ laser ablation analysis of giant ooid cortices reveals that the shale normalized rey patterns are similar to those of modern seawater including depleted light rees superchondritic y ho ratios and positive la anomalies yet no ce anomalies 1 0 0 15 in numerous ooid cortices seems to indicate a suboxidized condition of surface ocean in south china at that time the petrographic and geochemical evidence support the weak diagenetic alteration of the pure giant ooids during burial they formed in open ocean settings with energetic hydrodynamic environments and were affected by early dolomitization that might preserve mostly original petrographic fabrics and rey signatures from further diagenetic overprinting the characteristics of ce anomalies and rey compositions acquired from the giant ooids indicate that the surface ocean was suboxidized in south china during the late stage of ep2 implying the very low atmospheric o2 level at that time our results suggest that giant ooids may be a reliable analytical target that provide a snapshot into palaeoceanographic conditions during this crucial period of dynamic changes in early earth history

northwestward propagation of the intraseasonal oscillation in the western north pacific during the boreal summer structure and mechanism abstract the convection of the intraseasonal timescale in the western north pacific during the boreal summer tends to propagate northwestward in the philippine sea to near 20 n and then continues propagating westward the formation of enhanced convection in the western north pacific is a result of the merging of a convective system moving eastward along the equator and a westward propagating low level convergence anomaly which is located to the east of a vortex in the subtropics a positive feedback between the anomalous circulation and convection leads to a rapid enhancement of the system the strengthened southwesterly associated with the vortex enhances evaporation over the oceans e g the eastern indian ocean the bay of bengal and the south china sea and transports moisture northeastward the moisture converges at the northwestern corner of the convection and results in a potentially unstable atmosphere the result is the northwestward propagation of the coupled circulation convection system in

an early diagenetic deglacial origin for basal ediacaran cap dolostones abstract the beginning of the ediacaran period 635 ma is marked by conspicuous dolostone units that cap marinoan glacial deposits worldwide the extent and sedimentary characteristics of the cap dolostones indicate that anomalous carbonate over saturation coincided with deglacial sea level rise and ocean warming however the geochemical variability within cap dolostones both between continents across single continental margins and within individual stratigraphic sections has been difficult to reconcile with depositional models using a compilation of new calcium and magnesium isotope measurements in marinoan cap dolostone successions worldwide we show that the geochemical variability can be explained by early diagenetic dolomitization of aragonite along a spectrum of fluid and sediment buffered conditions dolostones from the outer platform formed under fluid buffered conditions whereas dolostones on the inner platform and foreslope environment formed under sediment buffered conditions this spatial pattern of dolomitizing conditions is consistent with buoyant recirculation of glacial seawater within carbonate platforms driven by the deglacial sea level rise and development of a meltwater surface ocean using a numerical diagenetic model to evaluate the geochemical differences between sediment and fluid buffered cap dolostone units we constrain the chemical and isotopic composition of both the dolomitizing fluid glacial seawater 13 c 0 2 the meltwater lens 13 c 11 and the primary aragonite sediment 13 c 6 to 3 these model end members do not imply that primary geochemical variability did not exist but demonstrates that it is not necessary to change the chemistry of seawater to explain the global stratigraphic variability in the geochemistry of basal ediacaran cap dolostones our results provide a novel framework for understanding the geochemical variability of cap dolostone units including large excursions in carbon isotopes and how this variability is the product of local diagenetic processes expressed globally in continental margin environments following the last snowball earth

ocean oxidation during the deposition of basal ediacaran doushantuo cap carbonates in the yangtze platform south china abstract precipitation of cap carbonate lithologies is a key feature of cryogenian global glaciations negative carbonate carbon isotopic compositions 13ccarb of these cap carbonates have been variably interpreted as massive drawdown of atmospheric co2 via extensive continental chemical weathering methane oxidation or postglacial upwelling each of these interpretations argues a non steady state of carbon cycle in the aftermath of marinoan global glaciation to further explore the postglacial marine carbon cycle we measured 13ccarb of cap carbonates from six localities in the yangtze platform south china the studied cap carbonates were deposited in a variety of sedimentary environments ranging from the open shelf slope to basin facies cap carbonates deposited in different environments show distinct stratigraphic trends of 13ccarb in the open shelf 13ccarb profile of the songlin section remains almost constant 3 to 4 while the 13ccarb of the jiulongwan section records a negative excursion decreasing from 3 5 to 7 13ccarb of cap carbonates deposited in the slope environment does not show stable stratigraphic trend in the basin environment 13ccarb demonstrates a sharp decline in the middle part of cap carbonates to the nadir value of 11 the negative 13ccarb excursion is best interpreted in terms of oxidation of dissolved organic carbon doc thus recording a pulse of ocean oxidation during cap carbonate precipitation clearly absence of negative 13ccarb excursion in all slope and most open shelf sections may imply that such oxidation event was not ubiquitous in the yangtze platform we speculate that the renewed thermohaline circulation during deglaciation brought oxic surface water into ocean interior which oxidized the basin environment of the yangtze platform however the deglacial thermohaline circulation was not strong enough to cause complete oxidation of the ocean the sporadic oxidation in the open shelf on the other hand might result from the terrestrial influx of oxidant from postglacial continental weathering our study suggests that ocean oxidation though sporadic might have occurred during cap carbonate precipitation and predated the first appearance of putative animal embryos

iodine content of the carbonates from the doushantuo formation and shallow ocean redox change on the ediacaran yangtze platform south china abstract the ediacaran period 635 541 ma is characterized by remarkable carbon isotope 13c excursions significant ocean redox changes and rapid diversification of eukaryotes including early animals these biological and geochemical events are commonly thought to be linked but their causal relationships remain controversial a particular point relates to the shallow ocean redox change across the negative 13c excursions most existing geochemical proxy data focused on tracking the redox conditions of deep or bottom water columns and provided limited information about the surface ocean ratios of iodine to calcium magnesium i ca mg from carbonates represent one of the few redox proxies that track the oxidation state of the shallow oceans here we report paired carbonate carbon isotopes 13ccarb and i ca mg ratios of the doushantuo formation from a drillcore section at daotuo paleogeographically located at the slope of the ediacaran yangtze platform south china in addition we compare the i ca mg ratios across the shuram upper doushantuo 13ccarb excursion in four sections of a shelf to slope transect in the slope section at daotuo the 13ccarb of the doushantuo formation shows three negative anomalies that are correlatable with those documented from the yangtze gorges area shelf and the siduping section slope the i ca mg ratios of the doushantuo formation from the drillcore are dominated by low but non zero

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

low frequency equatorial waves in vertically sheared zonal flow part i stable waves abstract the mechanism by which a vertically sheared zonal flow affects large scale low frequency equatorial waves is investigated with two level equatorial plane and spherical coordinates models vertical shears couple barolinic and barotropic components of equatorial wave motion affecting significantly the rossby wave and westward propagating yanai wave but not the kelvin wave this difference results from the fact that the barotropic component is a modified rossby mode and can be resonantly excited only by westward propagating internal waves the barotropic components emanate poleward into the extratropics with a pronounced amplitude while the baroclinic components remain equatorially trapped a westerly vertical shear favors the trapping of rossby and yanai waves in the upper troposphere whereas an easterly shear tends to confine them in the lower troposphere as such their westward propagation is slowed down by both westerly and easterly shears when the strength of the vertical shear varies w

global view of the intraseasonal oscillation during northern winter abstract in this study svd analysis is applied to a normalized 200 mb streamfunction olr covariance matrix to extract the most recurrent coupled pattern in the northern winter after the removal of the climatological seasonal cycle and seasonal means for each winter the first two singular vectors are on an intraseasonal timescale and the combination of the two forms an oscillation it is characterized by eastward propagation in the indian ocean and the western pacific standing oscillations in both the tropics and the extratropics and the poleward propagation of a zonally symmetric structure although there exists an eastwardly propagating pattern the phase relationship between geopotential wind and streamfunction fields is inconsistent with that of equatorial kelvin waves eastward propagation is most evident in the tropics of the southern hemisphere while the signals in the northern hemisphere are characterized by standing oscillations the distinct characteristics of the northern and southern he

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

interaction between the summer monsoons in east asia and the south china sea intraseasonal monsoon modes abstract the summer monsoons in east and southeast asia are characterized respectively by the mei yu in eastern china baiu in japan front mbf and by the monsoon trough stretching from northern indochina to the philippine sea these two major monsoon elements are separated by the north pacific anticyclone as indicated by the 850 mb zonal wind and cumulus convection over some key areas a distinct opposite phase intraseasonal variation exists between the two monsoon elements two approaches are adopted to explore the cause of this opposite phase variation which reflects the coupling between the two monsoon components 1 the correlation coefficient patterns between the 850 mb zonal wind monsoon index and the 850 mb streamfunction field and 2 the composite 850 mb streamline charts and the 120 e zonal wind cross sections it is shown that the opposite phase variation between the two monsoon elements is caused by the anomalous circulation associated with the northward migrating 30 60 day monsoon tr

the relationship between sea level and bottom pressure variability in an eddy permitting ocean model we investigate the relationship between sea level after application of an inverse barometer correction and ocean bottom pressure in an eddy permitting ocean model we find the presence of eddies can disrupt this relationship even on timescales as short as 10 20 days but only in the regions of most energetic eddy variability away from eddies the relationship is similar to that seen in a coarserresolution model with a tight relationship between sea level and bottom pressure at high frequencies but with significant correlations between sea level and bottom pressure at interannual timescales seen only in shelf sea regions in the deep ocean regions where sea level and bottom pressure remain related out to the longest timescales are in the arctic ocean and regions of the southern ocean where particularly large amplitude barotropic fluctuations are found but where the mesoscale signal is weak

oceanic angular momentum and torques in a general circulation model abstract the ocean s angular momentum m and torques about the polar axis are analyzed using output from the global eddy resolving model of semtner and chervin seasonal variability in m is dominated by the annual cycle whose magnitude appears capable of helping explain the residual in the solid earth atmosphere annual momentum budget planetary m and relative mr ocean angular momentum components have comparable seasonal amplitudes most of the mean signal in mr results from flows in the antarctic circumpolar current region but flows as far north as approximately 30 s am needed to explain the seasonal cycle local1y the strongest variability in relative angular momentum is found in the tropics at all depths a manifestation of the zonal recirculating character of the tropical circulation the time rate of change of m is very small compared to the applied wind torque calculation of bottom pressure torques using the geostrophic relation reveals a dominant balance between them and the surface wi

particle geochemistry in the rainbow hydrothermal plume mid atlantic ridge we report the analysis of 18 large volume 500 1500 l in situ filtered samples of particulate material from the largest hydrothermal plume on the mid atlantic ridge overlying the ultramafic hosted rainbow hydrothermal field at 36 deg 14 n measured particulate iron concentrations reach 614 nm high concentrations of particulate fe oxyhydroxides result from the extremely high fe concentration 24 mm and fe h2s ratio 24 of the vent fluids and persist to at least 10 km away from the vent site due to the advection of plume material with the ambient along axis flow two of the nine pairs of pump deployments appear to have intercepted the buoyant or otherwise very young portion of the hydrothermal plume these samples are characterized by anomalously compared to neutrally buoyant plume samples high concentrations of mg u and chalcophile elements and low concentrations of mn ca v y and the rare earth elements ree within the neutrally buoyant plume elemental distributions are largely consistent with previously observed behaviors preferential removal of chalcophile elements conservative behavior of oxyanions p v and u and continuous scavenging of y and the ree this consistency is particularly significant in light of the underlying differences in fluid chemistry between rainbow and other studied sites chalcophile elements are preferentially removed from the plume in the order cd zn co cu phosphorus iron and vanadium iron ratios for the neutrally buoyant plume are consistent with global trends with respect to the concentration of dissolved phosphate in ambient seawater comparison of buoyant and neutrally buoyant plume ratios with data from hydrothermal sediments underlying the rainbow plume cave et al 2002 indicates however that while p fe ratios are indeed constant v fe ratios increase progressively from early stage plume particles to sediments ree distributions in the buoyant and neutrally buoyant plume appear most consistent with a continuous scavenging process during dispersion through the water column

contrasting characteristics between the northward and eastward propagation of the intraseasonal oscillation during the boreal summer abstract this study investigates the structural and evolutionary characteristics of the eastward and northward propagating intraseasonal oscillation iso in the indian ocean and western pacific during the boreal summer along the equator the near surface moisture convergence located to the east of the deep convection region appears to result in the eastward propagation of the iso consistent with the frictional wave cisk conditional instability of the second kind mechanism proposed in previous studies the eastward propagation is characterized by sequentially downstream development of deep convection occuring mainly in certain regions such as 60 95 120 and 145 e and the date line the northward propagation of deep convection can be attributed to the low level moisture convergence located to the north this convergence is a deep structure extending from the surface to the middle troposphere near surface convergence appears only after the systems approach the landmass in the north it is sugges

organic carbon isotope constraints on the dissolved organic carbon doc reservoir at the cryogenian ediacaran transition abstract prominent negative carbonate carbon isotope 13 c carb anomalies from some ediacaran successions are accompanied by invariant or decoupled organic carbon isotope 13 c org values and have been interpreted as resulting from the remineralization of a large dissolved organic carbon doc reservoir capable of buffering carbon isotopes of organic matter this inferred oceanic doc reservoir was thought to have initiated with the onset of cryogenian glaciations ca 720 ma and lasted for millions of years until the late ediacaran period 13 c org around 26 vpdb and relatively low 13 c 22 2 and 2 the overlying organic rich black shale and shaly dolostone have more negative 13 c org 28 to 35 and higher 13 c 28 30 both 13 c carb and 13 c org show a 6 shift within a 4 m thick interval overlying the doushantuo cap carbonate the 13 c org values of the cap carbonate are associated with low toc mostly 13 c carb and 13 c org following cap carbonate deposition is best interpreted as resulting from a rapid increase in organic carbon burial which may have resulted in the rise of oxygen and heralded the first appearance of animals a few meters above the doushantuo cap carbonate the data suggest that a large oceanic doc reservoir did not exist in the early ediacaran ocean excess oceanic doc required to explain the ediacaran shuram and upper doushantuo 13 c excursions if it existed had to be developed during the ediacaran period after cap carbonate deposition

north atlantic meridional overturning circulation variations from grace ocean bottom pressure anomalies concerns about north atlantic meridional overturning circulation namoc changes imply the need for a continuous large scale observation capability to detect changes on interannual to decadal time scales here we present the first measurements of lower north atlantic deep water lnadw transport changes using only time variable gravity observations from gravity recovery and climate experiment grace satellites from 2003 until now improved monthly gravity field retrievals allow the detection of north atlantic interannual bottom pressure anomalies and lnadw transport estimates that are in good agreement with those from the rapid climate change meridional overturning circulation and heatflux array rapid mocha concurrent with the observed amoc transport anomalies from late 2009 through early 2010 grace measured ocean bottom pressures changes in the 3000 5000 m deep western north atlantic on the order of 20 mm h2o 200 pa implying a southward volume transport anomaly in that layer of approximately 5 5 sverdrup our results highlight the efficacy of space gravimetry for observing amoc variations to evaluate latitudinal coherency and long term variability

iodine to calcium ratios in marine carbonate as a paleo redox proxy during oceanic anoxic events periods of globally distributed extreme oxygen depletion so called oceanic anoxic events oaes have been recognized in the mesozoic geological record and appear to be characteristic of episodes of extreme warmth here we explore the application of iodine calcium ratios i ca in marine carbonate as a new geochemical proxy to constrain seawater redox change and provide additional insights into the response of ocean chemistry to ancient climatic warming iodine has long been known as a redox sensitive and biophilic element mainly present as iodate and iodide in seawater iodate converting to iodide under anoxic conditions laboratory experiments growing calcite crystals from solutions spiked with iodate show that this is the ionic species incorporated into the carbonate structure likely substituting for the co 3 2 ion a fall in the i ca ratio measured in carbonates formed in shallow water by marine calcifiers during the early toarcian and cenomanian turonian oaes is interpreted both as a response to a decrease in the iodate iodide ratio in ocean waters and the drawdown of the global iodine inventory under conditions of accelerated organic matter burial the results suggest that i ca ratios in carbonates may be used to monitor seawater oxidation levels throughout earth history

geochemistry of ediacaran cap dolostones across the yangtze platform south china implications for diagenetic modification and seawater chemistry in the aftermath of the marinoan glaciation cap dolostones of the ediacaran doushantuo formation yangtze platform south china from various palaeo water depths were studied to evaluate the extent of their diagenetic alteration and to assess temporal and spatial variations of seawater chemistry in the aftermath of the marinoan glaciation diagenetic fluid overprint is common in cap dolostone lithologies however the mobilization of trace elements and the modification of sr and o isotopic compositions are variable and were controlled by multiple stages of fluid overprint the highest 87 sr 86 sr ratios up to 0 7246 occur in cap dolostones from the palaeo slope environment at the huanglianba section whereas cap dolostones deposited in platform settings and in one of the distal basinal settings reveal 87 sr 86 sr ratios close to the proposed late neoproterozoic seawater composition 0 7077 shale normalized ree y patterns of carbonate leachates display enrichments of heavy over light ree and superchondritic y ho ratios typical of seawater however y ho ratios in the cap dolostones are always lower than modern seawater values which is interpreted to reflect dilution of the seawater signal by continent derived meltwater influx during deglaciation negative ce anomalies in carbonate leachates from platform and slope sections suggest that oxidized conditions existed in shallow marine environments shortly after the marinoan glaciation whereas positive or no resolvable ce anomalies in basin settings indicate that the latter remained anoxic redox stratification of the yangtze margin at the beginning of the ediacaran is further supported by the relative enrichment of redox sensitive trace metals in basinal sections these data may indicate moderately anoxic less than 10 m dissolved o 2 and presumably manganous conditions during the deposition of cap dolostones in the deeper realms of the yangtze basin supplementary material supplementary data for this paper are available at https doi org 10 6084 m9 figshare c 3770957

a monitoring design for the atlantic meridional overturning circulation 1 current hydrographic data can provide snapshots but no continuous timeseries of the meridional overturning circulation moc using output from two eddy permitting numerical ocean models we test the feasibility of a monitoring system for the moc in the north atlantic the results suggest that a relatively simple arrangement using moorings placed across a longitude depth section and the zonal wind stress is able to capture most of the moc strength and vertical structure as a function of time being closely related to the transport of energy to the north atlantic measuring the moc would open the prospect of having continuous information about a key element of northern hemisphere climate

the 1985 86 intraseasonal oscillation and the role of the extratropics abstract an intraseasonal oscillation that occurred in the 1985 86 northern winter is documented in this study the tropical convection of this event is dominated by the mixture of a standing oscillation over the maritime continent and an eastward moving feature from the indian ocean into the central pacific the time evolution of the upper tropospheric circulation patterns instead of propagating eastward along the equator as suggested in the existing composites of the intraseasonal oscillation is characterized by a series of wave patterns in the northern hemisphere and does not complete the cycle around the globe the familiar moist kelvin wave explanation for the intraseasonal oscillation receives little support from diagnosis of this event using zonal wind height field streamfunction and potential vorticity only in the lower troposphere near the date line is the convincing evidence for its existence found a scenario for the intraseasonal oscillation which is suggested by the analysis includes

late neoproterozoic cap carbonates mackenzie mountains northwestern canada precipitation and global glacial meltdown the 3 27 m thick cap carbonate overlying marinoan ice brook formation glacigene sediments and keele formation carbonate and terrigenous clastic rocks consists of two distinctive stratigraphic units a lower splintery buff weathering microcrystalline dolostone of extensive lateral uniformity comprises mm laminated peloidal sediment with local low angle hummocky like cross stratification micro ridges and synsedimentary tepees all elongated per pendicular to depositional strike this dolostone is unconformably overlain by an upper limestone that exhibits pro nounced facies variation from inboard peloidal lime grainstone and mudstone to shelf edge cementstone to outboard lime wackestone and mudstone calcite cementstones range from isolated crystal fans in laminated limestone to huge decimetre scale crystal arrays to hemispherical and elongate crystal stromatolites wholly composed of acicular crystals that form decametre scale reeflike structures crystal stromatolites are precipitates and replaced microbiolites that con structed biostromes and bioherms like those on many flat topped reef rimmed platforms the calcite crystals have all the physical and chemical attributes of neomorphosed aragonite this aragonite extensively replaced sediment and microbiolite just below the sea floor and grew upward into the overlying water column such interpreted massive synsedimentary replacement is rare in geological history and attests to the highly saturated state of the immediate postglacial ocean all sediment is interpreted to have been caco3 originally low and constant 18 o values reflect diagenetic modification of these carbonates although chemical attributes such as sr and c isotopes in some lithologies are near pristine lower dolostones virtually identical to most other coeval marinoan caps worldwide were part of a global precipitation event of remarkable similarity upper limestones are a more local phenomenon deposited during sea level rise in an aragonitic sea returning to equilibrium after global glaciation low 87 sr 86 sr ratios and varying 13 c values with carbonate sedimentary facies indicate that both units must have formed relatively rapidly prior to significant flu vioglacial runoff or that the influence of this runoff on the chemistry of seawater along continental shelves was mini mal the cap carbonate is thus interpreted to have formed in two steps 1 during initial marine ice melting accompanied by oceanic overturn and upwelling preceding continental margin rebound and 2 during initial stages of sea level rise accompanying continental deglaciation while confirming brief but extensive carbonate precipitation from an ocean highly perturbed by global glaciation the rocks also suggest that this event did not permanently affect either late neoproterozoic ocean chemistry or the contained marine biosphere 1262

trace metal records of regional paleoenvironmental variability in pennsylvanian upper carboniferous black shales abstract regional geochemical differences within a laterally continuous cyclic pennsylvanian upper carboniferous shale in midcontinent north america are interpreted in light of models of glacioeustatic forcing and new views on water column paleoredox stability and trace metal behavior in black shale environments specifically we characterize differences in transition metal fe mn mo v ni zn pb and u concentrations in black shales of the hushpuckney shale member of the swope limestone in iowa and equivalent black shale beds of the coffeyville formation in oklahoma although c s fe systematics and uniform 34 s depleted isotope ratios of pyrite indicate pervasive euxinic deposition anoxic and sulfidic bottom waters for these shales regional variations can be inferred for the efficiency of mo scavenging and for the rates of siliciclastic sedimentation as expressed in spatially varying fe al ratios black shales in iowa show mo enrichment roughly five times greater than that observed in coeval euxinic shales in oklahoma by contrast fe al ratios in oklahoma shales are as much as five times greater than the continental ratio of 0 5 observed in the over and underlying oxic facies and in the coeval black shales in iowa recent work in modern marine settings has shown that enrichments in fe commonly result from scavenging in a euxinic water column during syngenetic pyrite formation in contrast to fe the concentrations of other transition metals mo v ni pb zn u are typically more enriched in the black shales in iowa relative to oklahoma the transition metal trends in these paleozoic shales are reasonably interpreted in terms of early fixation in organic rich sediments due to euxinic water column conditions however regional variations in 1 rates of siliciclastic input 2 organic reservoirs including relative inputs of terrestrial versus marine organic matter and 3 additional inputs of metals to bottom waters from contemporaneous hydrothermal vents are additional key controls that lead to geographic variation in the extent of metal enrichments preserved in ancient organic rich sediments

experimental observations of marine iodide oxidation using a novel sparge interface mc icp ms technique abstract iodine speciation is used as a redox indicator and water mass tracer however the kinetics and mechanisms of oxidation of the reduced iodine species iodide i in seawater remain largely unresolved here we provide constraints on i oxidation rates from seawater incubation experiments using a sensitive radiotracer incubation approach with high precision mass spectrometry samples are inoculated with iodine 129 as i incubated under controlled conditions then oxidized and reduced iodine species are isolated using liquid chromatographic separation samples are subsequently aspirated using a novel sparging interface and the 129i 127i ratio of both iodine species is determined via multi collector inductively coupled plasma mass spectrometry this highly sensitive analytical approach is optimized for estimating the predicted slow rates of iodine redox transformations in small volume seawater samples at marine relevant total iodine concentrations application of this method to coastal samples from martha s vineyard sound usa evidences the heretofore elusive oxidation of i under marine analogue conditions our results demonstrate an increase in the 129i 127i of aqueous oxidized iodine species in unamended seawater most likely due to formation of hypoiodous acid and then dissolved organic iodine at rates of 118 189 nm yr these rates are comparable to those inferred from previous open ocean mass balance approaches but have the benefit of directly linking iodine speciation changes to in situ i oxidation though our treatment experiments do not definitively isolate the oxidation mechanism they provide preliminary insight into important roles for both abiotic and biotic factors as well as iodine transformations between dissolved particulate and gaseous forms ultimately the derived rates and novel experimental technique have potential to improve marine iodine cycling models and provide constraints on the importance of in situ processes in setting patterns of iodine speciation

why western boundary currents in realistic oceans are inviscid a link between form stress and bottom pressure torques it is shown that wind stress curl is balanced by bottom pressure torque in a zonal integral over any strip wide enough to smooth out the effect of nonlinear terms typically about 3 of latitude the derivation is completely general as long as the zonal wind stress is balanced by form stress at each latitude as is known to be the case in the ocean this implies that viscous torques are not important in western boundary currents their place being taken by bottom pressure torques the prediction is confirmed in the context of a global eddy permitting numerical ocean model this link between form stress and bottom pressure torques makes it easier to consider southern ocean dynamics and subtropical gyre dynamics in the same conceptual framework with topographic interactions being important in both cases

time variations in ocean bottom pressure from a few hours to many years in situ data numerical models and grace satellite gravimetry in situ ocean bottom pressure obp obtained from 154 different locations irregularly scattered over the globe is carefully processed to isolate signals related to the ocean general circulation and large scale sea level changes comparison against a global numerical ocean model experiment indicates poor correspondence for periods below 24 hr possibly related to residual tidal signals and small timing errors in the atmospheric forcing applied to the ocean model correspondence increases rapidly for periods between 3 and 10 days where wind driven dynamics are already well understood and consequently well implemented into numerical models coherence decreases again for periods around 30 days and longer where processes not implemented into ocean general circulation models as barystatic sea level changes become more important correspondence between in situ data and satellite based obp as obtained from the gravity recovery and climate experiment grace german research centre for geosciences rl05a gravity fields critically depends on the postprocessing of level 2 stokes coefficients that also includes the selection of appropriate averaging regions for the grace based mass anomalies the assessment of other available grace level 2 products indicates even better fit of more recent solutions as itsg grace2016 and the center for space research and jet propulsion laboratory rl05 mascons in view of the strong high frequency component of obp however a higher temporal resolution of the oceanic grace products would be rather advantageous

oxygenation history of the neoproterozoic to early phanerozoic and the rise of land plants there has been extensive debate about the history of earth s oxygenation and the role that land plant evolution played in shaping earth s ocean atmosphere system here we use the rare earth element patterns in marine carbonates to monitor the structure of the marine redox landscape through the rise and diversification of animals and early land plants in particular we use the relative abundance of cerium ceanom the only redox sensitive rare earth element in well preserved marine cements and other marine precipitates to track seawater oxygen levels our results indicate that there was only a moderate increase in oceanic oxygenation during the ediacaran average cryogenian ceanom 1 1 average ediacaran ceanom 0 62 followed by a decrease in oxygen levels during the early cambrian average cryogenian ceanom 0 90 with significant ocean anoxia persisting through the early and mid paleozoic average early cambrian early devonian ceanom 0 84 it was not until the late devonian that oxygenation levels are comparable to the modern average of all post middle devonian ceanom 0 55 therefore this work confirms growing evidence that the oxygenation of the earth was neither unidirectional nor a simple two stage process further we provide evidence that it was not until the late devonian when large land plants and forests first evolved that oxygen levels reached those comparable to the modern world this is recorded with the first modern like negative ceanom values 0 6 occurring at around 380 ma frasnian this suggests that land plants rather than animals are the engineers responsible for the modern fully oxygenated earth system

slowing of the atlantic meridional overturning circulation at 25 n the atlantic meridional overturning circulation carries warm upper waters into far northern latitudes and returns cold deep waters southward across the equator its heat transport makes a substantial contribution to the moderate climate of maritime and continental europe and any slowdown in the overturning circulation would have profound implications for climate change a transatlantic section along latitude 25 n has been used as a baseline for estimating the overturning circulation and associated heat transport here we analyse a new 25 n transatlantic section and compare it with four previous sections taken over the past five decades the comparison suggests that the atlantic meridional overturning circulation has slowed by about 30 per cent between 1957 and 2004 whereas the northward transport in the gulf stream across 25 n has remained nearly constant the slowing is evident both in a 50 per cent larger southward moving mid ocean recirculation of thermocline waters and also in a 50 per cent decrease in the southward transport of lower north atlantic deep water between 3 000 and 5 000 m in depth in 2004 more of the northward gulf stream flow was recirculating back southward in the thermocline within the subtropical gyre and less was returning southward at depth

interannual and interdecadal oscillation patterns in sea level relative sea level height rslh data at 213 tide gauge stations have been analyzed on a monthly and an annual basis to study interannual and interdecadal oscillations respectively the main tools of the study are singular spectrum analysis ssa and multi channel ssa m ssa very low frequency variability of rslh was filtered by ssa to estimate the linear trend at each station global sea level rise after postglacial rebound corrections has been found to equal 1 62 0 38 mm y by averaging over 175 stations which have a trend consistent with the neighboring ones we have identified two dominant time scales of el nino southern oscillation enso variability quasi biennial and low frequency in the rslh data at almost all stations however the amplitudes of both enso signals are higher in the equatorial pacific and along the west coast of north america rslh data were interpolated along ocean coasts by latitudinal intervals of 5 or 10 degrees depending on station density interannual variability was then examined by m ssa in five regions eastern pacific 25 s 55 n at 10 resolution western pacific 35 s 45 n at 10 equatorial pacific 123 e 169 w 6 stations eastern atlantic 30 s 0 and 30 n 70 n at 5 and western atlantic 50 s 50 n at 10 throughout the pacific we have found three dominant spatio temporal oscillatory patterns associated with time scales of enso variability their periods are 2 2 5 3 and 4 6 y in the eastern pacific the biennial mode and the 6 y low frequency mode propagate poleward there is a southward propagation of low frequency modes in the western pacific rslh between 35 n and 5 s but no clear propagation in the latitudes further south however equatorward propagation of the biennial signal is very clear in the southern hemisphere in the equatorial pacific both the quasi quadrennial and quasi biennial modes at 10 n propagate westward strong and weak el nino years are evident in the sea level time series reconstructed from the quasi biennial and low frequency modes interannual variability with periods of 3 and 4 8 y is detected in the atlantic rslh data in the eastern atlantic region we have found slow propagation of both modes northward and southward away from 40 45 n interdecadal oscillations were studied using 81 stations with sufficiently long and continuous records most of these have variability at 9 13 and some at 18 y two significant eigenmode pairs corresponding to periods of 11 6 and 12 8 y are found in the eastern and western atlantic ocean at latitudes 40 n 70 n and 10 n 50 n respectively

frictional moisture convergence in a composite life cycle of the madden julian oscillation abstract a composite life cycle of the madden julian oscillation mjo is constructed using an index based on the first two eofs of the bandpass filtered 20 80 days 850 mb zonal wind averaged from 5 n to 5 s every 2 5 around the equator precipitation 1000 mb convergence 850 mb wind and 200 mb wind are composited for the period 1979 95 water vapor integrated from the surface to 300 mb is composited for the period 1988 92 frictional moisture convergence at the equator is shown to play an important role in the life cycle of the madden julian oscillation mjo regions of boundary layer convergence foster growth of positive water vapor anomalies to the east of convection this convergence coincides with 850 mb easterly wind anomalies as is consistent with kelvin wave dynamics drying of the atmosphere occurs rapidly after the passage of convection with the onset of 850 mb westerly perturbations possible mechanisms for this drying include boundary layer divergence and subsidence or horizontal advect

seawater buffered diagenesis destruction of carbon isotope excursions and the composition of dic in neoproterozoic oceans carbonate sediments of nonglacial cryogenian 659 to 649 ma and early ediacaran 635 to 590 ma age exhibit large positive and negative 13ccarb excursions in a shallow water marine platform in northern namibia the same excursions are recorded in fringing deep sea fans and in carbonate platforms on other paleocontinents however coeval carbonates in the upper foreslope of the namibian platform and to a lesser extent in the outermost platform have relatively uniform 13ccarb compositions compatible with dissolved inorganic carbon dic in the modern ocean we attribute the uniform values to fluid buffered diagenesis that occurred where seawater invaded the sediment in response to geothermal porewater convection this attribution which is testable with paired ca and mg isotopes implies that large 13ccarb excursions observed in neoproterozoic platforms while sedimentary in origin do not reflect the composition of ancient open ocean dic

multi scale interactions of equatorial waves associated with tropical cyclogenesis over the western north pacific the tropical cyclone tc centric approach developed in previous studies tends to overemphasize the direct impact of tropical waves and underestimates their large scale modulation of western north pacific wnp tropical cyclogenesis tcg to overcome these limitations this study proposes a new approach based on empirical orthogonal function analyses to re examine associations of multiple waves including the madden julian oscillation mjo quasi biweekly oscillation qbwo convective equatorial rossby er waves and synoptic scale waves ssws with wnp tcg events there is a close association between wnp tcg events total of 273 tcs in this study and ssws 64 mjo 68 qbwo 64 and er 65 waves these suggest that ssw is critical for many tcg events and all of these intra seasonal waves significantly modulate tcg events a majority of tcs 79 were found to be related to more than one wave type indicating an important role for a combination of dynamic and thermodynamic conditions associated with multiple waves in tcg events further analyses show that ssw activity is strongly modulated by the mjo and er waves while the qbwo has no significant impact on ssws during convectively active mjo and er phases stronger ssw trains with more distinct southeast northwestward aligned structures can be found compared to convectively inactive phases similar intra seasonal modulation of the transition from the mixed rossby gravity waves from the equatorial central pacific to the ssw trains over the wnp by the three waves is noted with such transitions largely favored during convectively active mjo and er phases

trace and rare earth elemental investigation of a sturtian cap carbonate pocatello idaho evidence for ocean redox conditions before and during carbonate deposition abstract this study examines the trace element and ree y geochemistry of a thin pink dolomite in the scout mountain member of the pocatello formation idaho the pink dolomite meets the criteria of a cap carbonate and provides an opportunity to examine ocean redox state and hydrothermal inputs on the margin of laurentia at the terminal stages of the sturtian glaciations here high resolution chemostratigraphy of the dolomite shows that the local marine conditions were rapidly changing during cap emplacement normalized trace metal concentrations of zn cd cu cr mn and ni suggest that transiently reducing conditions prevailed immediately following the initial deposition of the pink dolomite enrichments in eu suggest a hydrothermal vent source for marine waters present during deposition the pink dolomite lacks evidence for persistent sulfide mineralization and its associated enrichments in mo suggesting that anoxia was restricted to areas below the sediment water interface no notable enrichments are recorded in the glacial diamictite though the signal might be masked by high rates of sedimentation our data suggest that the deposition of the pink dolomite progressed through 1 the overturn of local ocean containing a strongly stratified hydrothermally influence water column 2 the delivery of micronutrients to the shallow ocean 3 a biotic bloom in response to micronutrient availability and 4 related organic matter scavenging of metals finally we argue that this period of anoxia was brief and conditions quickly returned to an environment of oxic deposition

near 5 day nonisostatic response of the atlantic ocean to atmospheric surface pressure deduced from sub surface and bottom pressure measurements 1 nonisostatic ocean responses to atmospheric pressure have been observed in tropical regions of the pacific and atlantic oceans at periods near 5 days barotropic ocean model simulations coupled to atmospheric forcing predicted that this nonisostatic ocean response is driven not regionally but globally by the rossby haurwitz wave to date little observational evidence has been provided to support the model simulations especially at extratropical latitudes here we present the basin scale nature of the nonisostatic response in the atlantic ocean near 5 day periods using four historical long term 1 5 year sub surface and bottom pressure measurements spanning from 16 s to 37 n joint analysis of them together with global gridded atmospheric pressure reveals a basin scale nonisostatic sea level fluctuation in the north and tropical atlantic oceans near 5 day periods with almost uniform phase it also confirms that the driving force for this near 5 day fluctuation is the westward propagating rossby haurwitz wave

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

signature of the atlantic meridional overturning circulation in sea level along the east coast of north america in this letter we examine the relationship between the north atlantic meridional overturning circulation moc and sea level sl along the east coast of north america in the eddy permitting ocean model occam we find a distinctive topography following pattern of sl variability in the western north atlantic that is closely linked with the changing strength of the moc with a 2 cm drop in sl along the us east coast corresponding to a 1sv increase in the moc we find a similar pattern of sl variability in the altimetry record and show that this meridionally coherent sl mode dominates interannual sl variability at tide gauges along the north american east coast between 40 50n hence we conclude that north american coastal sea level may indeed be a useful indicator of moc variability on interannual timescales allowing an observationally based estimate of the likely range of interannual moc fluctuations to be determined citation bingham r j and c w hughes 2009 signature of the atlantic meridional overturning circulation in sea level along the east coast of north america geophys res lett 36 l02603 doi 10 1029 2008gl036215

mechanisms of monsoon low frequency variability surface hydrological effects abstract observations indicate that monsoon systems are characterized by orderly large scale and low frequency variations with a time scale of two weeks and sometimes longer regions of ascending motion are observed to form to the north of the equator and propagate slowly northward across southeast asia the propagation appears to be associated with the active break sequence of the summer monsoon which acts as a modulator on the activity of the synoptic scale disturbances a zonally symmetric non linear two layer model containing an interactive ocean and a continent poleward of 18 n is used to investigate the mechanisms which produce the observed low frequency variability only when a full hydrology cycle is considered does the model product variations which resemble the observed structures mechanisms are traced to include the interaction of the components of the total heating function the sensible heat input in the boundary layer although considerably smaller than the other heating components de

topographic influence on the mjo in the maritime continent abstract this study demonstrates that during the passage of the mjo through the maritime continent in the boreal winter the corresponding deep convection and near surface wind anomalies tend to skirt around mountainous islands flow bifurcation around elongated mountainous islands such as new guinea is clearly seen topographic blocking generates distinctive vorticity and convergence distributions in this specific domain mountain wave like structures are also observed throughout the maritime continent with a clear spatial relationship with the high terrains in sumatra sulawesi and new guinea the existence of topography seems to create extra lifting and sinking within the large scale circulation and thus the convective system exhibits quasi stationary features near the major topography during the mjo passage through the maritime continent it is suggested that resolving the detailed topographic effects may play a key role in simulating realistic characteristics of the mjo in the maritime continent

the 30 50 day mode at 850 mb during monex abstract the analyzed wind field at 850 mb during the summer monsoon experiment monex is subjected to a time series analysis to confirm the existence of a peak in the time range of 30 50 days having established that this study presents a mapping of the motion field for this time scale in this short paper we illustrate the steady meridional propagation of a train of troughs and ridges that seem to form near the equator and dissipate near the himalayas the meridional scale of this mode is around 300 km and its meridional speed of propagation is 0 75 latitude per day the amplitude of the wind for this mode is around 3 6 m s 1 the salient contributions here are the mapping and the demonstration of a very regular behavior of this mode its existence is here noted from a period well before the onset of monsoon i e from early may to late july three major storms during monex were noted to form within the trough line of this system and the period of major cessation of rains over the indian subconti

propagating and standing components of the intraseasonal oscillation in tropical convection abstract two questions related to the intraseasonal variability of tropical convection and circulation remain controversial 1 to what degree is the convective component of the madden julian oscillation mjo a standing oscillation 2 is the eastward propagating circulation anomaly of the mjo coherent with a standing oscillation in convection in an attempt to settle these issues the authors undertake a series of statistical analyses of gridded outgoing longwave radiation and winds to quantify the magnitudes of the propagating and standing components of convection and their coherence with the propagating component of the circulation they demonstrate that no dominant standing oscillation in convection can be identified instead intraseasonal variability of convection is dominated by an eastward propagating mode which the authors interpret as the convective signal of the mjo this propagating component accounts for almost all of the convective variance that is coherent with the eastward propagating di

a theory for the surface atlantic response to thermohaline variability abstract the response of the upper warm limb of the thermohaline circulation in the north atlantic to a rapid change in deep water formation at high latitudes is investigated using a reduced gravity ocean model changes in deep water formation rate initiate kelvin waves that propagate along the western boundary to the equator on a timescale of months the response in the north atlantic is therefore rapid the southern hemisphere response is much slower limited by a mechanism here termed the ldquo uatorial buffer since to leading order the flow is in geostrophic balance the pressure anomaly decreases in magnitude as the kelvin wave moves equatorward where the coriolis parameter is lower together with the lack of sustained pressure gradients along the eastern boundary this limits the size of the pressure field response in the southern hemisphere interior adjustment is by the westward propagation of rossby waves but only a small fraction of the change in thermohaline circulation strength is commun

temporal variability of the atlantic meridional overturning circulation at 26 5 n the vigor of atlantic meridional overturning circulation moc is thought to be vulnerable to global warming but its short term temporal variability is unknown so changes inferred from sparse observations on the decadal time scale of recent climate change are uncertain we combine continuous measurements of the moc beginning in 2004 using the purposefully designed transatlantic rapid climate change array of moored instruments deployed along 26 5 n with time series of gulf stream transport and surface layer ekman transport to quantify its intra annual variability the year long average overturning is 18 7 5 6 sverdrups sv range 4 0 to 34 9 sv where 1 sv a flow of ocean water of 106 cubic meters per second interannual changes in the overturning can be monitored with a resolution of 1 5 sv

chromium isotope stratigraphy of ediacaran cap dolostones doushantuo formation south china abstract the yangtze platform in south china is considered a key site for studying neoproterozoic ocean oxygenation comprehensive cr concentration and isotopic signatures are presented from cap dolostones of the doushantuo formation from a deep water and a shallow marine carbonate section that have previously been used to constrain the redox evolution of ediacaran seawater in space and time employing major and trace element abundances as well as sr o and c isotope compositions the majority of the studied samples yield elevated cr concentrations and negatively fractionated 53 cr signals due to i detrital contamination consistent with cr signatures of other post marinoan cap dolostones ii diagenetic carbonate alteration and post depositional remobilization of cr al concentrations were used as indicator of detrital contamination and to calculate authigenic cr concentration and isotope signatures when the detrital contribution of cr was 18 o carb signals that correlate with low cr concentrations and negatively fractionated 53 cr values post depositional remobilization of cr results in the loss of heavy cr isotopes and consequently light cr isotopes are retained during precipitation of secondary carbonates however some samples might still show pristine ediacaran seawater signals two samples pertaining to the deep water cap dolostone section at yanwutan and one sample pertaining to the shallow water section at jijiawan yield slightly positively fractionated 53 cr signals particularly when corrected to presumably authigenic signals 53 cr auth these values are consistent with those from other neoproterozoic carbonate sections deposited in an oxygenated environment this short sequence of positively fractionated 53 cr auth is concurrent with a cap dolostone 87 sr 86 sr signal close to ediacaran seawater values with relatively high sr and cr concentrations with decreased detrital contamination and with a pronounced negative ce anomaly they indicate either light pulses of enhanced oxidative weathering or inferred from a few least altered samples prevailing oxic conditions during cap dolostone deposition the cr isotopic composition of ediacaran cap dolostones pertaining to the doushantuo formation reveals fine scale fluctuations in post glacial detrital contamination and diagenesis balanced against a clear signal of oxidative weathering cr isotopes have the potential to further enhance our understanding of neoproterozoic weathering regimes and past ocean oxygenation however before the cr isotope system can be faithfully applied to delineate changes in redox conditions recorded in ancient marine carbonates possible diagenetic alteration of the cr signal as well as cr contribution from detrital contamination need to be taken into consideration

the shift of convection from the indian ocean to the western pacific ocean during a 30 60 day oscillation abstract a strong 30 60 day oscillation during november december 1981 is studied using analyzed winds from the national meteorological center outgoing longwave radiation and satellite low level moisture data the outgoing longwave radiation and 150 mb velocity potential for five adjacent events are also examined consistent features include the slow 5 m s 1 propagation of convective energy over the indian ocean western pacific ocean and the fast 15 m s 1 propagation of 150 mb tropical velocity potential in regions remote from the oceanic warm pool the individual events have characteristics of the seasonal and anomalous base state within which they are embedded for the november december 1981 event we concentrate on the details of the shift of convection from the eastern indian ocean to the western pacific ocean an intense cold surge and accompanying convective increase near 110 e precede the shift cast by about 12 days the regional 150 mb circulation responds to the enhanced convection with an i

positive cerium anomaly in the doushantuo cap carbonates from the yangtze platform south china implications for intermediate water column manganous conditions in the aftermath of the marinoan glaciation abstract oxygenation exerted an important control on the emergence and diversification of metazoans in the aftermath of the marinoan glaciation however the relationship between the oceanic dissolved o2 do levels and early metazoan evolution remains equivocal to provide a temporal and spatial reconstruction of the redox conditions for this critical interval this study investigates the early ediacaran cap carbonate deposits within intra shelf facies at three localities in the three gorges area the yangtze platform south china trace and rare earth elements are sequentially extracted from the carbonate fraction for pristine temporal seawater signals the member ii dolostones of the duoshantuo formation which overlies the cap carbonates show a negative ce anomaly no ce anomaly is observed in the lower units of the cap carbonates in contrast positive ce anomalies ce ce 1 3 in the uppermost part of the cap carbonates are observed in all studied sections these positive ce anomalies are accompanied by high mn fe ratios ranging from 5 04 to 14 96 and slightly positive mree anomalies suggesting that a fe mn oxyhydro oxide coparticipation occurred during the cap carbonate deposition the positive ce anomalies may result from the reductive dissolution of the ce enriched mn oxyhydro oxides across a mn iv mn ii redoxcline in a distinct manganous water wedge that was sandwiched between well oxygenated and anoxic ferruginous deep water layers this wedge may have exhibited low oxygen conditions with approximately 10 m do dissolved oxygen in comparison to the 90 m do expected in an oxic setting and 0 m do in an anoxic setting therefore the presence of a positive ce anomaly in the uppermost part of the cap carbonates indicates a new intermediate manganous condition and further elucidates the water column redox structure that existed following the end of the marinoan glaciation early ediacaran metazoans were possibly restricted to fully oxygenated conditions and were absent in the manganous or ferruginous rich environments

iodine records from the ediacaran doushantuo cap carbonates of the yangtze block south china abstract late neoproterozoic cap carbonates formed following the cryogenian glaciations may record information about the significant climate change and ocean chemistry evolution immediately after the snowball earth events large negative carbon isotope anomalies and enigmatic sedimentary structures have been identified from the post marinoan cap carbonates across the globe but their formation mechanism remains debatable due to difficulties of distinguishing overlapped chemical signatures and diagenetic alterations in this study we present i ca mg profiles of four sections from a shallow to deep water transect of the basal doushantuo cap carbonates one of the most extensively studied ediacaran units in south china most samples have i ca mg values lower than 1 mol mol with a few exceptions in the shelf sections up to 2 5 mol mol all calcite samples with extremely low 13c have iodine signal below detection limit suggesting carbonate precipitation from anoxic seawater or diagenetic fluids among the four sections the slope section has the lowest i ca mg values suggesting that it may have experienced more extensive fluid buffered diagenesis and more severe loss of io3 in combination with available major trace rare earth element and isotope data the temporal i ca mg variations support freshwater mixing and deep water upwelling in proximal sites and transient oxidation during deposition of the doushantuo cap carbonates