cenozoic lateritic weathering and erosion history of peninsular india from 40 ar 39 ar dating of supergene k mn oxides since deccan traps extrusion 65 ma ago thick weathering mantles have developed over peninsular india on both the western coastal lowland and adjacent plateau separated by the western ghats escarpment manganiferous lateritic profiles formed by supergene weathering of late archean manganiferous protores are exposed on paleolandsurface remnants on both sides of the escarpment petrological and geochemical characterizations of samples from those mn lateritic profiles allowed identifying cryptomelane k mn oxide dated by 40ar 39ar geochronology the ages obtained document major weathering periods ca 53 50 ma and ca 37 23 ma in the highland and ca 47 45 ma ca 24 19 ma and discrete weathering pulses at 9 ma and 2 5 ma in the lowland old ages of the highland 53 50 ma and the lowland 47 45 ma indicate synchronous lateritic weathering across the escarpment at a time the peninsula started to drift across the equatorial belt intense weathering periods at ca 53 45 and ca 37 23 ma are interpreted to reflect the early eocene climatic optimum and the onset of asian monsoon regimes respectively the ages further indicate that most of the dissection of the highland must have taken place after 23 ma whereas the lowland was weakly incised essentially after 19 ma our results also document divergent erosion and weathering histories of the lowland and the highland after the eocene suggesting installation of a dual climatic regime across the western ghats escarpment

surface area control of shallow cratonic to deep marine carbonate accumulation sites of calcium magnesium carbonate accumulation have been shifting from shallow shelf to deep marine settings since the late cretaceous during this time total area of flooded epicratonic shelf has decreased about 50 and areas of shelf carbonate deposition have declined from 27 106 km to present areas of 1 4 106 km while the maximum extent of platform carbonate accumulation has decreased from about 50 to 28 north latitude in terms of cratonic carbonate this decrease in tropical shelf area has resulted in a sixfold reduction in shoal water limestone accumulation from a cretaceous rate of 0 6 km m y to a present value of about 0 1 106 km m y over the same time period the global carbonate compensation depth has deepened by about 1 5 km attendant with a threefold areal increase of calcite ooze depositionn 40 to 130 106 km this expansion has resulted in an eightfold increase in pelagic limestone accumulation from a cretaceous rate of 0 05 106 km m y to a present rate of about 0 4 106 km m y transfer of accumulation from shallow cratonic to deep marine depositional settings records the central role of sedimentary environment surface area in predicating the differential partitioning of finite carbonate fluxes to phanerozoic global oceans

brittle frictional mountain building 2 thermal structure and heat budget this paper describes a simple thermal model of an actively deforming critically tapered fold and thrust belt the model determines the steady state temperature distribution and heat flow as well as the pressure temperature time histories of rocks that outcrop at the surface the main parameters controlling the thermal structure are the accretion and erosion rates the undisturbed geothermal gradient at the toe and the amount of frictional heating both shear heating on the decollement fault and internal strain heating within the deforming brittle wedge are incorporated in a mechanically consistent manner and they dominate the effect of radiogenic heating except in fold and thrust belts with significantly overpressured pore fluids the mean stresses temperatures and surface heat flow all increase with an increase in the basal and internal coefficients of friction and this dependence is used to constrain the level of friction on the decollement fault beneath the steady state fold and thrust belt in taiwan rocks outcropping in the core of the central mountain range of taiwan experience maximum theoretical temperatures in excess of 400 c and maximum mean pressures in excess of 500 mpa if the coefficient of basal friction is b 0 5 qualitatively these conditions are in good agreement with the observed high greenschist facies metamorphism the theoretical surface heat flow which increases from 95 mw m2 at the front of the fold and thrust belt to 240 mw m2 at the rear is in excellent agreement with the results of a recent geothermal survey of taiwan and theoretical cooling histories are in good agreement with fission track and other geochronologic studies taken together these results provide strong evidence that sliding on the basal decollement fault beneath taiwan is governed by a coefficient of friction in the range of typical laboratory measurements b 0 5 0 2 approximately 35 of the total surface heat flux of 3 gw is heat conducted into the base of the wedge from the top of the basal decollement fault and somewhat more than 30 is heat advected into the toe by accretion the remaining heat is generated internally about 25 by internal strain heating and about 10 by radiogenic heating either an increase in the coefficient of basal friction b or a reduction in the pore fluid pressure ratio b leads to an increase in the surface heat flow because of the increased frictional heating within the wedge and on the basal decollement fault the overall balance of energy in a steady state fold and thrust belt is described by the equation e w g q where is the rate at which both mechanical and heat energy are added from external sources w g is the rate at which work is performed against gravitational body forces in a reference frame attached to the overriding plate and q is the rate at which waste heat flows out of both the upper and lower boundaries the total power input into the taiwan fold and thrust belt is approximately 4 2 gw the mechanical work being done on the base and front of the fold and thrust belt accounts for 3 of these 4 2 gw in addition 0 9 gw of heat are being advected from the subducting plate into the toe by accretion the remaining 0 3 gw are being supplied by in situ radiogenic heating the outgoing energy is dominated by the 3 gw of heat conducted out the top in the surface heat flow however another 0 8 gw are conducted down beneath the rear portion of the basal decollement fault to heat the underlying subducting slab only 0 4 of the incoming 4 2 gw do useful mechanical work against gravity within the wedge the efficiency of brittle frictional mountain building in taiwan is therefore 10

environmental changes since 8 4 ka reflected in the lacustrine core sediments from nam co central tibetan plateau china the tibetan plateau induces and enhances the asian monsoon that influences the plateau itself east china and even the whole of asia pursuing the changing monsoon history and its impact in this environment sensitive area is a key for understanding the climatic changes here we present the initial results from core sed iments in nam co central tibet to elucidate the holocene environment changes in this area the studied lake nam co is the second largest lake with an elevation of 4718 m water area of 2015 km 2 and catchment area of 10 610 km 2 by using echo seismic profiling and hydro echosounding we investigated the bathymetric dis tribution of the whole lake one 332 cm long piston core was successfully taken in the east part of the lake at 60 m water depth twelve ams 14 c dates from top to bottom of this core established a good time sequence toc tn n alkanes grain size clay minerals fe mn sr ba and caco3 content were analysed with sampling intervals from 1 cm to 10 cm results showed that since 8400 yr bp the environment changes in this region indicate three stages the early stage 8400 6900 yr bp was characterized by slight shifting from warm to cold with a cold dry interval at 8100 7800 yr bp the middle stage was from 6900 to 2900 yr bp during which cli mate changed from warm humid to cold dry however around 2900 yr bp the climate once was slightly cold but strongly dry the late stage from 2900 yr bp to present was characterized by a general tendency toward cold dry the first temperature decline was around 1700 1500 yr bp following which temperature increased once before decreasing again around 600 300 yr bp which might be the result of the little ice age

the progressive intensification of northern hemisphere glaciation as seen from the north pacific ocean drilling project odp site 882 50 22 n 167 36 e provides the first high resolution grape density magnetic susceptibility carbonate opal and foraminifera planktonic and benthic stable isotopes records between 3 2 and 2 4 ma in the northwest pacific we observed a dramatic increase in ice rafting debris at site 882 at 2 75 ma which is coeval with that found in the norwegian sea suggesting that the eurasian arctic and northeast asia were significantly glaciated from 2 75 ma onwards prior to 2 75 ma planktonic foraminifera 18o records indicate a warming or freshening trend of 4 c or 2 over 80 ka if this is interpreted as a warm pre glacial pliocene north pacific it may have provided the additional moisture required to initially build up the northern hemisphere continental ice sheet the dramatic drop in sea surface temperatures sst 7 5 c at 2 75 ma ended this suggested period of enhanced sst and thus the proposed moisture pump moreover at 2 79 and 2 73 ma opal mass accumulation rates mar decrease in two steps by five fold and is accompanied by a more gradual long term decrease in caco3 mars evidence from the southern ocean odp site 704 indicates that just prior to 2 6 ma there is a massive increase in opal mars the opposite to what is found in the north pacific this indicates that the intensification of northern hemisphere glaciation was accompanied by a major reorganisation of global oceanic chemical budget possibly caused by changes in deep ocean circulation the initiation of northern hemisphere glaciation occurred in the late miocene with a significant build up of ice on southern greenland however the progressive intensification did not occur until 3 5 3 ma when the greenland ice sheet expanded to include northern greenland following this stage we suggest that the eurasian arctic and northeast asia glaciated at 2 75 ma approximately 100 ka before the glaciation of alaska 2 65 ma and 200 ka before the glaciation of the north east american continent 2 54 ma

rise of angiosperms as a factor in long term climatic cooling by late cretaceous or early tertiary time the diversification and proliferation of angiosperm deciduous ecosystems resulted in higher rates of mineral weathering this increase in the global average weathering rate would have caused a decrease in atmospheric carbon dioxide and hence global cooling the magnitude of this decrease is quantitatively explored here by developing a formulation for global weathering which combines ecosystems that differ in their fractional global coverage and intrinsic rates of weathering incorporating this formulation into models specifically several previously developed global steady state models of the geochemical cycle of carbon between the atmosphere and carbonate rocks gives results that show signifi cant global cooling from the evolution of the angiosperm deciduous ecosystems this cooling may vary from a few degrees up to 10 c in this way deciduous ecosystems with high rates of mineral weathering could have contributed to the evolution during the past 100 m y of a cooler earth and thus were a factor in producing conditions that enhanced their global proliferation

sensitivity of climate and atmospheric co2 to deep ocean and shallow ocean carbonate burial previous models of physical and biogeochemical controls of the evolution of atmospheric co2 and climate over hundreds of millions of years have neglected the effect of variations in the balance between shallow ocean and deep ocean carbonate deposition this is important because the relative proportions of carbonate burial in the two reservoirs have changed over time here i set up a model of the carbonate silicate geochemical cycle that distinguishes carbonate masses produced by the two types of burial and shows that reasonable increases in deep ocean burial could produce substantial warmings over a few hundred million years the model includes exchanges between crust and mantle transients from burial shifts are found to be sensitive to the fraction of non degassed carbonates subducted into the mantle without the habitation of the open ocean by plankton such as foraminifera and coccolithophores today s climate would be substantially colder

phanerozoic atmospheric co2 change evaluating geochemical and paleobiological approaches abstract the theory and use of geochemical modeling of the long term carbon cycle and four paleo pco 2 proxies are reviewed and discussed in order to discern the best applications for each method geochemical models provide pco 2 predictions for the entire phanerozoic but most existing models present 5 10 m y means and so often do not resolve short term excursions error estimates based on sensitivity analyses range from 75 200 ppmv for the tertiary to as much as 3000 ppmv during the early paleozoic the 13 c of pedogenic carbonates provide the best proxy based pco 2 estimates for the pre tertiary with error estimates ranging from 500 1000 ppmv pre devonian estimates should be treated cautiously error estimates for tertiary reconstructions via this proxy are higher than other proxies and models 400 500 ppmv and should not be solely relied upon we also show the importance of measuring the 13 c of coexisting organic matter instead of inferring its value from marine carbonates the 13 c of the organic remains of phytoplankton from sediment cores provide high temporal resolution up to 10 3 10 4 year high precision 25 100 ppmv for the tertiary to 150 200 ppmv for the cretaceous pco 2 estimates that can be near continuous for most of the tertiary its high temporal resolution and availability of continuous sequences is advantageous for studies aiming to discern short term excursions this method however must correct for changes in growth rate and oxygen level at elevated pco 2 750 1250 ppmv this proxy loses its sensitivity and is not useful the stomatal density and stomatal index of land plants also provide high temporal resolution 2 year high precision 10 40 ppmv for the tertiary and possibly cretaceous pco 2 estimates and so also is ideal for discerning short term excursions unfortunately this proxy also loses sensitivity at some level of pco 2 above 350 ppmv which currently is largely undetermined our analysis of the recently developed 11 b technique shows that it currently is not yet well constrained most importantly it requires the assumption that the boron isotopic composition of the ocean remains nearly constant through time in addition it assumes that there are no biological or temperature effects and that diagenetic alteration of the boron isotopic composition does not occur a fifth co 2 proxy based on the redox chemistry of marine cerium has several fundamental flaws and is not discussed in detail here

enhanced cenozoic chemical weathering and the subduction of pelagic carbonate the observed trend of increasing oceanic 87sr 86sr ratios during the late cenozoic led raymo et al 1 to propose that chemical weathering rates increased at this time as a result of enhanced weatherability of silicate rocks they suggested that this was due in turn to continential uplift primarily in the himalayas and the andes because weathering involves the reaction of silicates with atmospheric carbon dioxide considerations of changes in weathering rates must take into account the need to balance the global carbon cycle to maintain this balance on timescales greater than 106yr enhanced weathering requires an increased flux of co2 into the atmosphere2 without such an increased flux weathering rates could not increase and one is then forced to search for other explanations for the observed 87sr 86sr trend such as a changing riverine strontium isotope composition3 6 here i assume that the strontium isotope record does indeed reflect enhanced weathering in the late cenozoic but propose that its cause may have been an increased co2 flux arising from the recycling of pelagic sedimentary carbon at subduction zones since the jurassic sedimentary carbonate accumulation has shifted from primarily cratonic to primarily pelagic environments7 11 because sea floor spreading transports pelagic carbonate to and recycles it through metamorphic environments in subduction zones this shift to pelagic carbonate accumulation would provide the increased co2 flux needed to increase weathering rates12 13

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

equatorial convergence of india and early cenozoic climate trends india s northward flight and collision with asia was a major driver of global tectonics in the cenozoic and we argue of atmospheric co2 concentration pco2 and thus global climate subduction of tethyan oceanic crust with a carpet of carbonate rich pelagic sediments deposited during transit beneath the high productivity equatorial belt resulted in a component flux of co2 delivery to the atmosphere capable to maintain high pco2 levels and warm climate conditions until the decarbonation factory shut down with the collision of greater india with asia at the early eocene climatic optimum at 50 ma at about this time the india continent and the highly weatherable deccan traps drifted into the equatorial humid belt where uptake of co2 by efficient silicate weathering further perturbed the delicate equilibrium between co2 input to and removal from the atmosphere toward progressively lower pco2 levels thus marking the onset of a cooling trend over the middle and late eocene that some suggest triggered the rapid expansion of antarctic ice sheets at around the eocene oligocene boundary

paleoatmospheric consequences of co2 released during early cenozoic regional metamorphism in the tethyan orogen the eocene was the warmest epoch of the cenozoic with published estimates of eocene atmospheric co2 content ranging from two to six times the current value calculations of co2 consumption by silicate weathering show that co2 fluxes to the atmosphere of ca 1018 myr could account for inferred paleocene eocene atmospheric co2 contents and the resulting greenhouse effect would have contributed to eocene warmth extensive portions of the tethyan orogen underwent regional metamorphism culminating in the eocene prograde metamorphism may have been contemporaneous with the late paleocene global warming we calculated the amount of metamorphic co2 produced at depth in the himalayan orogen with data on the timing of the india asia collison duration of prograde regional metamorphism and proportions and bulk compositions of metamorphic co2 source rocks if co2 was generated at a constant rate over a 10 myr period of prograde metamorphism in the himalayan orogen we estimate that ca 1018 1019 moles myr of metamorphic co2 were produced at depth significant expulsion of metamorphic co2 to the atmosphere may have occurred by focused fluid flow along shear zones such as the extensive main central thrust in the himalayan orogen an additional ca 1018 myr could have been contributed by eocene regional metamorphism in the mediterranean tethys i e from the alps to turkey the extensive metamorphism associated with the india asia collision and the closing of tethys may have contributed to co2 greenhouse warming in the early to mid cenozoic

euphotic zone bacterioplankton sources major sedimentary bacteriohopanepolyols in the holocene black sea abstract bacteriohopanepolyols bhps are lipid constituents of many bacterial groups geohopanoids the diagenetic products are therefore ubiquitous in organic matter of the geosphere to examine the potential of bhps as environmental markers in marine sediments we investigated a holocene sediment core from the black sea the concentrations of bhps mirror the environmental shift from a well mixed lake to a stratified marine environment by a strong and gradual increase from low values 30 g g 1 toc in the oldest sediments to 170 g g 1 toc in sediments representing the onset of a permanently anoxic water body at about 7500 years before present bp this increase in bhp concentrations was most likely caused by a strong increase in bacterioplanktonic paleoproductivity brought about by several ingressions of mediterranean sea waters at the end of the lacustrine stage 9500 years bp 15n values coevally decreasing with increasing bhp concentrations may indicate a shift from a phosphorus to a nitrogen limited setting supporting growth of n2 fixing bhp producing bacteria in sediments of the last 3000 years bhp concentrations have remained relatively stable at about 50 g g 1 toc the distributions of major bhps did not change significantly during the shift from lacustrine or oligohaline to marine conditions tetrafunctionalized bhps prevailed throughout the entire sediment core with the common bacteriohopanetetrol and 35 aminobacteriohopanetriol and the rare 35 aminobacteriohopenetriol so far only known from a purple non sulfur proteobacterium being the main components other bhps specific to cyanobacteria and pelagic methanotrophic bacteria were also found but only in much smaller amounts our results demonstrate that bhps from microorganisms living in deeper biogeochemical zones of marine water columns are underrepresented or even absent in the sediment compared to the bhps of bacteria present in the euphotic zone obviously the assemblage of molecular fossils in the sediments does not represent an integrated image of the entire community living in the water column remnants of organisms living in zones where effective transport mechanisms such as the fecal pellet express exist are accumulated while those of others are underrepresented our work shows a high stability of bhps over geological time scales largely uniform distributions and only minor changes in structures like an increasing prevalence of saturated over unsaturated bhps with time were observed consequently sedimentary bhp distributions are less suitable as markers for in situ living bacteria but are useful for paleoreconstructions of bacterioplanktonic communities and productivity changes

provenance sea level and monsoon climate controls on silicate weathering of yellow river sediment in the northern okinawa trough during late last glaciation abstract high resolution multi proxy records including geochemical and grain size data from detrital sediments of iodp site u1429 in the northern okinawa trough provide reliable evidence for constraining sediment source and transport processes they also allow silicate weathering and erosion controlled by sea level change and east asian summer monsoon evolution since 34 ka to be reconstructed provenance proxies indicated that sediments in the northern okinawa trough were mainly supplied by the yellow river middle reach at 34 8 ka the low sea level and proximity of paleo yellow river mouth to the northern okinawa trough were the causes of the dominant yellow river input after 8 ka a retreated yellow river mouth coupled with the blocking effect of the kuroshio current and its branches together with strong east asian summer monsoon precipitation resulted in relatively strong sediment input from kyushu to the northern okinawa trough meanwhile yellow river upper reach supplied more sediments to the study site than that during the 34 8 ka on glacial interglacial scale silicate weathering proxies indicate that the core sediment was more weathered during the last glacial and deglacial than that in the modern yellow river we attribute this to the increased upper reach sediment input which supplied more weak weathered sediment to the study site during the holocene besides composite effect of weathering during glacial and deglacial sediment production and additional weathering upon subaerial exposure of shelf deposits during low sea level stage as well as older weathered sediments reworking during sea level rise could also account for this weathering regime on multi millennial scale from 34 to 18 5 ka silicate weathering was mainly controlled by the east asian summer monsoon with a cooling and drying climate associated with weakened summer monsoon activity this is consistent with the reduced alteration of sediments eroded from the yellow river basin from 18 5 to 8 ka strong reworking of older weathered sediments overwhelmed the east asian summer monsoon in controlling silicate weathering which induced a continuous increase in chemical alteration of the sediments during this period

thermal and kinematic modeling of bedrock and detrital cooling ages in the central himalaya 1 we introduce a new method that convolves detrital mineral cooling ages with digital elevation models to test numerical models of erosion in collisional orogens along a trans himalayan transect in central nepal we develop a kinematic and thermal model to predict variations in bedrock cooling ages in modern himalayan topography the model assumes a thermal steady state and utilizes a simple ramp and flat style decollement representing the main himalayan thrust the model also assumes a topographic steady state such that overthrusting is balanced by erosion to maintain a constant topographic profile erosion rates display strong spatial variations as a function of the angle between the slope of the topographic surface and the trajectories of rock particles approaching the surface to predict the detrital cooling age signal we combine the distribution of bedrock cooling ages within a catchment with the rate of erosion and distribution of muscovite predicted cooling age distributions are compared with detrital 40ar 39ar muscovite data to assess varying tectonic and erosion scenarios such cooling age distributions are very sensitive to how much of the total plate convergence is expressed as erosion of the overthrusting plate the best fit model assigns 4 6 km myr 1 of overthrusting equivalent to as much as 1 5 2 km myr 1 of vertical erosion to the asian plate although a trade off exists between ramp geometry along the decollement and the best fit rate only a narrow range of ramp dips decollement depths and erosionally compensated overthrusting rates are compatible with the observed detrital ages

the cenozoic evolution of the strontium and carbon cycles relative importance of continental erosion and mantle exchanges the past variations of the seawater 87sr86sr isotopic ratio are related to changes in the relative contribution of the mantle sr input to the ocean and the sr supply from continental weathering recently it has been postulated that the cenozoic increase in the seawater 87sr86sr isotopic ratio was associated with the uplift of the himalayan and andean mountains at that time these orogenies may have changed the sr isotopic ratio of the continental rocks undergoing weathering as a result of extensive metamorphism increased the river flux of sr through enhanced weathering in these regions and possibly caused the global climatic cooling trend of the cenozoic a model of the major geochemical cycles coupled to an energy balance climate model is used to explore the possible causes of the mesozoic cenozoic fluctuations in the seawater 87sr86sr isotopic ratio the contribution of the mantle exchanges at mid ocean ridges of the recycling of seafloor carbonates through plate margin volcanism and of the alteration of seafloor basalts to the fluctuations of the seawater 87sr86sr isotopic ratio are studied finally this model tentatively describes the impact of the himalayan orogeny on the geochemical cycles of sr and c some possible effects of the extensive metamorphism associated with the india asia collision and of the himalayan uplift are modelled the model reproduces the cenozoic increase of the seawater 87sr86sr isotopic ratio however the impact of the himalayan orogeny on the c cycle appears to be limited and insufficient to generate the global climatic cooling of the cenozoic rather in the model the cenozoic cooling is mostly due to the reduction of the co2 emission from mid ocean ridge volcanism and to changes in the chemical weathering rates in the rest of the world excluding the himalayas

bacteriohopanepolyols preserved in silica sinters from champagne pool new zealand indicate a declining temperature gradient over the lifetime of the vent siliceous sinters from champagne pool cp a geothermal vent in the taupo volcanic zone north island new zealand contained exceptionally well preserved bacteriohopanepolyol bhp distributions bhps were present in a range of sinters deposited over the lifetime of cp 900 yr before present the distributions correlated well with the presence of members of bhp producing bacterial orders known to inhabit cp for example acidothiobacillales burkholderiales and pseudomonadales are known sources of composite bhps with a more complex functional group at c 35 such as bacteriohopanetetrol cyclitol ether found in high relative abundance in each cp sinter analysed the bhp distributions preserved in cp sinters were different from those described previously for any other environmental setting with pentafunctionalised bhps accounting for up to 55 of the total assemblage furthermore composite bhps were the most abundant compound type in each sample and accounted for up to 80 of the total bhp distribution as the age of sinter increased a general increase in bhp abundance was observed similarly in older sinters the complexity of the bhp compounds increased the observations are consistent with a higher temperature of vent water in the past the excellent preservation of bhps in this setting over the lifetime of the vent highlights the usefulness of bhps as biomarkers for reconstructing modern and ancient geothermal vent bacterial communities 2014 published by elsevier ltd

calcium carbonate veins in ocean crust record a threefold increase of seawater mg ca in the past 30 million years chemical sr mg and isotopic 18o 87sr 86sr compositions of calcium carbonate veins ccv in the oceanic basement were determined to reconstruct changes in sr ca and mg ca of seawater in the cenozoic we examined ccv from 10 basement drill sites in the atlantic and pacific ranging in age between 165 and 2 3 ma six of these sites are from cold ridge flanks in basement 46 ma which provide direct information about seawater composition ccv of these young sites were dated using the sr isotopic evolution of seawater for the other sites temperature corrections were applied to correct for seawater basement exchange processes the combined data show that a period of constant low sr ca 4 46 6 22 mmol mol and mg ca 1 12 2 03 mol mol between 165 and 30 ma was followed by a steady increase in mg ca ratios by a factor of three to modern ocean composition mg ca sr ca relations suggest that variations in hydrothermal fluxes and riverine input are likely causes driving the seawater compositional changes however additional forcing may be involved in explaining the timing and magnitude of changes a plausible scenario is intensified carbonate production due to increased alkalinity input to the oceans from silicate weathering which in turn is a result of subduction zone recycling of co2 from pelagic carbonate formed after the cretaceous slow down in ocean crust production rate

variation of ocean sediment thickness with crustal age global ocean sediment thickness and present day ocean sediment accumulation rates are analyzed with respect to the age of the underlying ocean crust trends in average sediment thickness and present day accumulation rate are well fit by cubic polynomials in crustal age for the global ocean and for individual ocean basins sediment thickness and accumulation rates are larger in the north and south atlantic and indian oceans compared to the pacific ocean primarily because the anomalous sediment accumulations that followed continental rifting and collision in the atlantic and indian ocean basins are missing in the pacific ocean modern ocean sediment accumulation rates extrapolated into the past assuming steady state conditions account within uncertainties for the global average sediment thickness on 0 65 ma cenozoic age ocean crust while the profile of anomalously thick sediments on older mesozoic age ocean crust is well fit by adding localized diffusive sediment transport from a steady state source referenced to the adjacent continental margin apart from a distinct 0 5 ma quaternary age sediment pulse deviations in average sediment thickness from this simple model are generally small and are uncorrelated across ocean basins

new constraints on the provenance of hopanoids in the marine geologic record bacteriohopanepolyols in marine suboxic and anoxic environments abstract the abundance and structural diversity of bacteriohopanepolyols bhps was examined in three marine pelagic environments that are characterized by strong vertical redox gradients and water column suboxia or anoxia the abundance and in most instances structural diversity of bhps was highest at depths where conditions were suboxic or anoxic however the majority of the bhp structures that were identified are environmentally cosmopolitan and their biological sources are presently not well constrained an isomer of bacteriohopanetetrol denoted bht ii was observed at all three study sites in association with anoxic and suboxic conditions within the water column based on the absence of bht ii from terrigenous and oxic marine environments studied to date and its strong association with suboxic and anoxic marine pelagic environments we propose that bht ii is a promising candidate biomarker for water column suboxia and anoxia in the marine geologic record the molecular fingerprint of bhps in suspended and sinking particles and core top sediments indicates that hopanoids produced within the water column are exported to marine sediments and that their biological source is most likely associated with settling particles and not the free water phase based on our observations bhps likely represent an important input to the sedimentary hopanoid inventory particularly in upwelling environments characterized by pelagic oxygen minimum zones omz and anoxic marine basins

strontium isotopic variations in jurassic and cretaceous seawater a high resolution seawater strontium isotope curve has been generated through the analysis of well dated and well preserved belemnites and oysters from the middle and upper jurassic and the lower cretaceous of great britain analysis of fe and mn concentrations in these fossils has yielded criteria for eliminating samples that are diagenetically altered the strontium isotope curve remains relatively flat through the aalenian and early bajocian rapidly descends through the late bajocian and bathonian and reaches a minimum in the callovian and oxfordian it then begins a rapid increase in the kimmeridgian and portlandian that continues through much of the early cretaceous the curve levels off in the barremian suddenly dips downwards in the aptian and recovers gradually through the albian the strontium isotopic variations are sufficiently large and the data are presented with sufficient stratigraphic detail to allow precise correlation to the classic ammonite zones and lithologic sections of great britain using the techniques of strontium isotope stratigraphy model results indicate that much of the variation in seawater 87sr86sr between 120 and 40 ma can be explained by changing the intensity of mid ocean ridge hydrothermal fluxes proportionally to estimated mid ocean ridge crustal generation rates it is also possible that the variations during the rest of the mesozoic and the permian are primarily reflections of changing hydrothermal inputs the model results have several important implications first they provide an example in which the variations in the strontium isotope curve are not necessarily driven by changes in fluvial inputs second they suggest that from at least the aptian through the eocene variations in continental weathering were minimal this heightens the importance of the rapid rise in seawater 87sr86sr beginning 40 ma as a significant transition to an extended period of increasing fluvial 87sr fluxes continuing to the present finally the results suggest that several documented short term excursions towards lower 87sr86sr in the latest triassic pliensbachian toarcian callovian oxfordian aptian albian and cenomanian turonian are interpretable as pulses of seafloor hydrothermal activity if so the strontium isotope record offers a means of constraining the timing duration and magnitude of known or proposed hydrothermal events in the geological record

biomarkers for aerobic methanotrophy in the water column of the stratified gotland deep baltic sea filter samples from the oxic zone and suboxic zone of the physically stratified water column and sediment samples of the gotland deep baltic sea were analyzed for bacteriohopanepolyol bhp and phospholipid fatty acid plfa concentrations in total eight bhps were identified with the greatest diversity in the suboxic zone there 35 aminobacteriohopane 31 32 33 34 tetrol aminotetrol and 35 aminobacteriohopane 30 31 32 33 34 pentol aminopentol whose concentrations decreased concurrently from the lower to the upper suboxic zone indicated type i methanotrophic bacteria and thus aerobic oxidation of methane the presence and activity of type i aerobic methanotrophic bacteria was further supported by the presence of 13c depleted plfas specifically 16 1 8c and 16 1 5c 13c as low as 41 2 however the relative amount of methanotroph specific compounds was low aminopentol 0 2 of total bhps 16 1 8c ca 0 5 of total plfas suggesting a minor contribution of aerobic methanotrophic bacteria to the particulate organic matter the distinctive bhp pattern in the suboxic zone including aerobic methanotroph biomarkers and a tentative marker for a pelagic redoxcline putative 22s isomer of the ubiquitous 22r bacteriohopanetetrol bht was mirrored in the sediment samples our data indicate that a major portion of the sedimentary hopanoids of the gotland deep is sourced from the suboxic part of the water column via an effective but unknown transport mechanism

continental pelagic carbonate partitioning and the global carbonate silicate cycle a carbonate silicate geochemical cycle model is developed and used to explore dynamic and climatic consequences of constraints on shallow water carbonate burial and possible carbon loss to the mantle associated with sea floor subduction the model partitions carbonate deposition between shallow water and deep water environments and includes carbon fluxes between the mantle and lithosphere when total lithospheric carbonate mass is constant there are two stable steady states one in which the carbonate burial flux is mostly continental and another in which it is mostly pelagic the continental steady state is characterized by a low metamorphic co2 flux to the atmosphere and predominantly shallow water carbonate burial the pelagic steady state is characterized by a high metamorphic co2 flux and predominantly deep water carbonate burial for reasonable parameter values when total lithospheric carbonate mass is allowed to vary the model oscillates between predominantly continental and predominantly pelagic modes model results suggest that carbonate deposition patterns established during the cenozoic may be pushing the earth system from the continental to the pelagic mode on a time scale of 10 8 yr with a possible consequent order of magnitude increase in the metamorphic co2 flux to the atmosphere

increasing chemical weathering in the himalayan system since the last glacial maximum continental chemical weathering is central in earth s surface biogeochemical cycles as it redistributes elements across reservoirs such as the crust and the oceans however the evolution of weathering through time and its response to external forcing such as changes in climate remain poorly constrained in this work a composite sediment record from the bay of bengal is used to document the evolution of chemical weathering in the himalayan system himalayan range and indo gangetic floodplain the world largest sediment conveyor to the oceans since the last glacial maximum lgm the degree of weathering of the sediments is documented using mobile to immobile ratios such as k si and h2o si as well as detrital calcite abundance robust weathering proxies are derived by correcting the chemical composition of sediment for sorting effects that occur during transport and deposition the bay of bengal record is also further compared to the chemical composition of modern river sediments from the ganga and brahmaputra basin weathering proxies all indicate that the sediments exported by the ganga and brahmaputra rivers became increasingly weathered over the past 21 kyr whereas sr nd and major elements suggest a constant sediment provenance in the system over the last 21 kyr these changes in the degree of weathering of the sediments show that the weathering flux exported by the system to the indian ocean during the lgm was significantly lower than at present and demonstrate that chemical weathering in continental scale basins such as the ganga and brahmaputra responds to late quaternary climate changes

biogenicity of gold and silver bearing siliceous sinters forming in hot 75 c anaerobic spring waters of champagne pool waiotapu north island new zealand champagne pool a large hot spring at waiotapu in north island new zealand is rimmed by a subaerial sinter dam and a shallow subaqueous shelf that is composed of orange sinter rich in metallic sulphides orange siliceous flocs also rich in sulphides are in constant circulation in the spring pool and form loose sediment on the shelf the orange sinters and flocs are rich in as sb tl and hg and have high concentrations of au 100 ppm and ag 330 ppm most metallic sulphides are amorphous and disseminated throughout the sinter instead of forming distinct mineral phases the shelf sinters are domal and resemble stromatolites the neutral chloride waters ph 5 5 temperature 75 c however are virtually anaerobic examination of the sinters by scanning electron microscopy confirms that they are laminated and contain an abundant low diversity assemblage of filamentous bacilliform and coccoid microbes the flocs are similarly composed of very small silicified filaments silicification involved replacement of the cell walls and extensive encrustation by opal a based on size and morphology these microbes are probably anaerobic bacteria or archaea by providing substrates for nucleation of the silica the microbes are indirectly contributing to the formation of the gold bearing sinters

close mass balance of long term carbon fluxes from ice core co 2 and ocean chemistry records on geological timescales carbon dioxide enters the atmosphere through volcanism and organic matter oxidation and is removed through mineral weathering and carbonate burial an analysis of ice core co2 records and marine carbonate chemistry indicates a tight coupling between these processes during the past 610 000 years which suggests that a weathering feedback driven by atmospheric co2 leads to a mass balance between co2 sources and sinks on long timescales feedbacks controlling long term fluxes in the carbon cycle and in particular atmospheric carbon dioxide are critical in stabilizing the earth s long term climate it has been hypothesized that atmospheric co2 concentrations over millions of years are controlled by a co2 driven weathering feedback that maintains a mass balance between the co2 input to the atmosphere from volcanism metamorphism and net organic matter oxidation and its removal by silicate rock weathering and subsequent carbonate mineral burial1 2 3 4 however this hypothesis is frequently challenged by alternative suggestions many involving continental uplift and either avoiding the need for a mass balance or invoking fortuitously balanced fluxes in the organic carbon cycle5 6 7 8 9 here we present observational evidence for a close mass balance of carbon cycle fluxes during the late pleistocene epoch using atmospheric co2 concentrations from ice cores10 11 12 we show that the mean long term trend of atmospheric co2 levels is no more than 22 p p m v over the past 610 000 years when these data are used in combination with indicators of ocean carbonate mineral saturation to force carbon cycle models the maximum imbalance between the supply and uptake of co2 is 1 2 during the late pleistocene this long term balance holds despite glacial interglacial variations on shorter timescales our results provide support for a weathering feedback driven by atmospheric co2 concentrations that maintains the observed fine mass balance

paleo eolian dynamics in the andean plateau inferences from sedimentology of fossil and modern dunes fil lopez steinmetz romina lucrecia universidad nacional de jujuy instituto de ecorregiones andinas consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet salta instituto de ecorregiones andinas argentina universidad nacional de jujuy argentina consejo nacional de investigaciones cientificas y tecnicas argentina

geochemistry of metals and metalloids in siliceous sinter deposits implications for elemental partitioning into silica phases abstract sinter deposits are formed by precipitation of silica from hydrothermal fluids that have reached the surface environment they are commonly found around hot springs and represent surface expressions of underlying geothermal systems and or low sulfidation epithermal gold silver hydrothermal deposits several studies have reported ppm to weight percent concentrations of metals e g au ag cu and metalloids e g as sb b in sinters capping geothermal systems and epithermal gold silver deposits however the relation between the maturity of the siliceous sinter and its metal enrichment remains unknown here we use geochemical and mineralogical data that link the silica crystallinity degree with trace metal and metalloid contents in sinter in this paper we provide in situ trace element data in metal rich silica sinter samples from the puchuldiza geothermal field in the altiplano of northern chile that record the complete diagenetic sequence from non crystalline opal a to microcrystalline quartz combined sem xrd and la icp ms data show that the concentration of metals and metalloids in sinters from puchuldiza display a strong correspondence with silica crystallinity while arsenic and boron are predominantly enriched in the more amorphous silica phases opal a ct gold and silver show higher concentrations in the more crystalline phases opal c quartz silica structural morphological and geochemical transformations from its initial precipitation to its final maturation after diagenesis are responsible for this differential enrichment during the initial stages gold and silver are incorporated into silica microspheres as cationic species and or metal nanoparticles or colloids while arsenic and boron incorporation is controlled by as bearing accessory minerals and fe oxyhydroxides as diagenesis progresses and the crystallinity of silica increases diffusion driven processes such as ostwald ripening may progressively enrich gold and silver in the sinter while metalloids are depleted owing to the low retention of arsenic by silica these findings indicate that the diagenetic transitions of silica defined by significant structural changes that involve generation of surface defects and the creation of reactive sites may play an important role in elemental uptake by silica in near surface environments

the himalayas organic carbon burial and climate in the miocene cooling ages of rock in the himalayas imply that rapid exhumation between the main central thrust system and the south tibetan detachment system occurred between 21 and 17 ma the generation of relief and enhanced weathering which followed this event may have resulted in a pronounced increase in the delivery of dissolved strontium carbon phosphorus and other chemical weathering products to the ocean richter et al 1992 the increased supply of nutrients stimulated productivity in oceanic upwelling zones and expansion of the oxygen minimum zone leading to enhanced burial and preservation of organic matter in the monterey formation and other deposits from this interval a downdraw of atmospheric co2 associated with enhanced chemical weathering rates and organic matter burial may have led to global cooling and the expansion of the antarctic ice sheet by 15 ma the above scenario differs from the monterey hypothesis of vincent and berger in that co2 downdraw is primarily via silicate weathering rather than organic carbon burial and that organic carbon burial is driven by increased delivery of nutrients to the ocean rather than by stronger upwelling a carbon mass balance calculation which assumes that river fluxes have been increasing over the last 40 ma predicts that absolute organic carbon burial increased over this interval while at the same time the fraction of carbon buried as organic matter versus carbonate decreased this implies that the organic carbon cycle has acted as a net source of co2 to the atmosphere over the late cenozoic

rock based measurement of temperature dependent plagioclase weathering long term 105 years weathering can be quantified by measuring microsopic dissolution of minerals in exposed rock surfaces digital backscattered bse electron microscope images of plagioclase porosity in field exposures of known age resolves weathering at finer scales and over longer time spans than conventional solute budget and laboratory studies rock based bse imaging is therefore a potentially useful tool for quantifying steady state weathering fluxes occurring over geologic time here we compare results of the rock based method against solute budget and experimental data using plagioclase weathering rates from 14c dated basalt flows on hualalai volcano in hawaii usa a rock based field activation energy of 26 2 kcal mol 1 is somewhat higher than solute budget and laboratory measurements of plagioclase weathering

late cenozoic evolution of the eastern margin of the tibetan plateau inferences from 40ar 39ar and u th he thermochronology high topography in central asia is perhaps the most fundamental expression of the cenozoic indo asian collision yet an understanding of the timing and rates of development of the tibetan plateau remains elusive here we investigate the cenozoic thermal histories of rocks along the eastern margin of the plateau adjacent to the sichuan basin in an effort to determine when the steep topographic escarpment that characterizes this margin developed temperature time paths inferred from 40 ar 39 ar thermochronology of biotite multiple diffusion domain modeling of alkali feldspar 40 ar release spectra and u th he thermochronology of zircon and apatite imply that rocks at the present day topographic front of the plateau underwent slow cooling 30 50 c m y coincident with exhumation from inferred depths of 8 10 km at denudation rates of 1 2 mm yr samples from the interior of the plateau continued to cool relatively slowly during the same time period 3 c m y suggesting limited exhumation 1 2 km however these samples record a slight increase in cooling rate from 1 to 3 c m y at some time during the middle tertiary the tectonic significance of this change remains uncertain regardless late cenozoic denudation in this region appears to have been markedly heterogeneous with the highest rates of exhumation focused at the topographic front of the plateau margin we infer that the onset of rapid cooling at the plateau margin reflects the erosional response to the development of regionally significant topographic gradients between the plateau and the stable sichuan basin and thus marks the onset of deformation related to the development of the tibetan plateau in this region the present margin of the plateau adjacent to and north of the sichuan basin is apparently no older than the late miocene or early pliocene 5 12 ma

was the himalayan orogen a climatically significant coupled source and sink for atmospheric co2 during the cenozoic the hypothesis that the himalayan orogen was a climatically significant coupled source and sink for atmospheric co2 during the cenozoic is evaluated in light of the timing duration and co2 fluxes associated with himalayan metamorphism and chemical weathering we suggest that diachronous eohimalayan metamorphism occurred over a 20 m y time span middle eocene to early oligocene with total metamorphic co2 production of 4 10 1018 mol because this is much greater than the amount of carbon stored in the atmosphere and oceans and because uplift and accelerated erosion began at least 5 m y after the peak of metamorphism we conclude that it is implausible that co2 produced by metamorphism in the himalayan orogen was consumed millions of years later by erosion enhanced weathering in this orogen assuming a global climate silicate weathering feedback we estimate that metamorphic co2 degassing from the himalayan orogen would have produced a warming of 0 5 c and enhanced weathering in this orogen would have produced a cooling of 0 2 c thus direct climate effects of this degassing and weathering were likely to have been minor

himalayan tectonics weathering processes and the strontium isotope record in marine limestones the time evolution of the isotopic composition of seawater strontium the ratio of strontium 87 to strontium 86 over the last 500 million years has the form of an asymmetric trough the values are highest in the cambrian and recent 0 7091 and lowest in the jurassic 0 7067 superimposed on this trend are a number of smaller oscillations consideration of the geochemical cycle of strontium and the dynamics of weathering shows that only himalayan style continental collisions can influence the isotope ratio on the scale observed the contemporary himalayan orogeny is by far the largest since the late precambrian pan african event that produced the high in the cambrian

experimental studies on new zealand hot spring sinters rates of growth and textural development to study the rate of growth of sinters in new zealand hot springs field experiments were conducted in seven geothermal areas at wairakei fan shaped subaqueous deposits of amorphous silica grow rapidly 350 kg a 1 m 2 of drain wall and are composed of silicified filaments with subordinate bacillus and spirillium shaped organisms characterization of bacteria revealed isolates sharing 97 16s rrna gene sequence homologies affiliated with thermus meiothermus bacillus tepidomonas thermomonas porphyrobacter thermonema and hydrogenophilus spp as well as previously uncultured bacteria at rotokawa microstromatolites have a slow growth rate 0 004 mm day 1 that is attributed to low ph capillary rise and evaporation at champagne pool sinter growth 0 023 mm day 1 is dominated by wave action building alternating microbe rich and microbe poor layers silica sinter was not observed at waikite where slides developed a layer of calcite 0 026 mm day 1 sinter growth at ngatamariki 0 016 mm day 1 forms by capillary rise evaporation and diffusion and at tokaanu subaqueous growth is slow 0 002 mm day 1 and contains silicified microbes textures at orakei korako indicate similar mechanisms to ngatamariki except that growth is more rapid 0 023 mm day 1 due to a splash contribution silica and calcite saturation indices adequately explain the growth of the sinters and calcite indicating that microbes are not inducing precipitation where it should not occur the rate of precipitation is correlated with silica supersaturation but ph effects can alter this relationship the degree of preservation of microbial material is explained by the effect of ostwald ripening on silica spherules subaqueous growth allows coarsening of spherules and poor preservation of smaller microbes while subaerial nucleation is rapid ostwald ripening is inactive and better preservation can be expected

late pleistocene climatic trajectory in the phase space of global ice ocean state and co2 observations and theory we consider the evolution of three main slow response variables describing the state of the climate system during the late pleistocene global ice mass atmospheric carbon dioxide and the ocean state as measured respectively by the specmap 18o record the vostok co2 record and the north atlantic sea surface temperature record at 50 n core k708 1 which is coherent with other ocean state properties their coevolution is portrayed in the form of a trajectory in the phase space of the three variables and its projections on its three phase planes the oscillatory nature and phase lags of the variables are clearly illustrated suggesting a physical process scenario that can account for the observations the basic element of this scenario is a free near 100 kyr period oscillation driven by internal instability involving feedbacks between all three variables under the influence of earth orbital milankovitch forcing and long term tectonic co2 forcing it is shown that a phenomenological theory advanced by the authors emphasizing the role of co2 provides a credible account of the phase space trajectory

metamorphic decarbonation silicate weathering and the long term carbon cycle the seawater 87sr 86sr curve implies a 50 100 myr episodicity in weathering rate which requires a corresponding variation in co2 degassing from the solid earth to the atmosphere it is proposed that this is caused by orogenesis which both produces co2 as a result of metamorphic decarbonation reactions and consumes extra co2 as a consequence of erosion enhanced weathering global climate on the geological time scale is therefore conttolled by the difference between the relatively large and variable orogenic moderated degassing and weathering co2 fluxes

bacteriohopanepolyol signatures of cyanobacterial and methanotrophic bacterial populations recorded in a geothermal vent sinter the distribution of bacteriohopanepolyols bhps in a modern terrestrial geothermal silica sinter has been employed as a proxy for bacterial populations and bacterially mediated processes occurring within the geothermal ecosystem analysis of samples from opaheke pool hot spring in the taupo volcanic zone north island new zealand revealed the presence of a suite of bhps relating to cyanobacteria and type i and type ii methanotrophic bacteria

microbial biomarkers support organic carbon transport from methane rich amazon wetlands to the shelf and deep sea fan during recent and glacial climate conditions abstract we have investigated the delivery of terrestrial organic carbon oc to the amazon shelf and deep sea fan based on soil marker bacteriohopanepolyols bhps adenosylhopane and related compounds and branched glycerol dialkyl glycerol tetraethers gdgts as well as on 14c dating of bulk organic matter the microbial biomarker records show persistent burial of terrestrial oc evidenced by almost constant and high bit values 0 6 and soil marker bhp concentration 80 230 g g toc total oc on the late holocene shelf and even higher bit values 0 8 0 9 but lower and more variable soil marker bhp concentration 40 100 g g toc on the past glacial deep sea fan radiocarbon data show that oc on the shelf is 3 4 kyr older than corresponding bivalve shells emphasizing the presence of old carbon in this setting we observe comparable and unexpectedly invariant bhp composition in both marine sediment records with a remarkably high relative abundance of c 35 amino bhps including compounds specific for aerobic methane oxidation on the shelf avg 50 of all bhps and the fan avg 40 notably these marine bhp signatures are strikingly similar to those of a methane producing floodplain area in one of the amazonian wetland varzea regions the observation indicates that bhps in the marine sediments may have initially been produced within wetland regions of the amazon basin and may therefore document persistent export from terrestrial wetland regions with subsequent re working in the marine environment both during recent and past glacial climate conditions

two cretaceous volcanic episodes in the western pacific ocean stratigraphic analyses of cores recovered by the deep sea drilling project from the western pacific ocean confirm that cretaceous volcanic activity in that region was common and that two separate major episodes of activity can be distinguished the older episode aptian to cenomanian in age resulted in the formation of most of the oceanic plateaus in the western pacific in the younger santonian to maastrichtian episode several island and seamount chains formed especially those in the west central pacific that trend north northwest these volcanic events among the most extensive in the marine geologic record covered an area of at least 30 10 6 km 2 possibly the older episode was responsible for a cretaceous sea level high and concomitant epi continental transgression the younger episode of volcanism certainly covered an extensive area but its effect upon sea level may not have been as great as that of the older event

the early paleozoic carbon cycle a review of o c sr and s isotope trends for the entire phanerozoic shows that the present day values of isotope signals are similar to those at the proterozoic termination the sharp rise in 87sr 86sr since 65 ma has been attributed to an uplift and subsequent metamorphism and erosion associated with the himalayas and tibet this orogenic evolution has been postulated to have influenced the global organic and inorganic carbon cycles and climate as well a similar large scale orogeny the pan african event also dominated the neoproterozoic vendian times and the similarity of modern and neoproterozoic isotope values for seawater may therefore have had a comparable tectonic cause in this contribution we present the results of a numerical model of the coupled c alkalinity s sr cycles suggesting that the early paleozoic from early cambrian to late devonian evolution of sr o c and s seawater isotope signals could have been the consequence of progressive oxidation of a large reduced carbon reservoir exhumed during the pan african orogeny the 18o measured in brachiopod shells is used as a forcing of the model postulating that any change in the oxygen isotopic composition of seawater is the result of a disequilibrium in the organic carbon subcycle through the coupling of the oxygen isotopic and carbon cycles the calculated 13c 87sr 86sr and 34s are in good agreement with the data as is the reasonable calculated history for atmospheric pco2 and its relation to global climate

distribution of hopanoids along a land to sea transect implications for microbial ecology and the use of hopanoids in environmental studies bacteriohopanepolyols bhps are lipid constituents of diverse bacteria and have great potential as taxonomically and environmentally diagnostic biomarkers in order to examine their environmental behavior and potential for tracing biogeochemical processes we analyzed bhps and geohopanoids the diagenetic products of bhps in soils and surface sediments from the middle yangtze river catchment to the east china sea ecs shelf these data are compared to an up to date survey of bhp distributions in soils including regions collectively covering the arctic temperate subtropics and tropics regional climatic differences particularly temperature likely exert an important control on bhp distributions in soils in the aquatic river estuary shelf setting bhp concentrations and structural diversity are substantially lower than in soils suggesting that in aquatic environments either bacterial biodiversity is lower or there is not the same requirement for hopanoid synthesis however different aquatic regimes vary substantially high bhp diversity and enhanced bhp production occur in the biogeochemically dynamic yangtze estuary whereas bhp distribution is uniform with much less structural diversity in the oligotrophic ecs open shelf the rsoil index based on the relative abundances of soil marker bhps against bacteriohopanetetrol is suggested as a new approach to trace soil organic matter input into marine sediments the rsoil indices decrease from the river to the ecs correlating strongly with branched and isoprenoid tetraether indices and moderately correlating with 13c of organic carbon values and the concentrations of higher plant biomarkers demonstrating their ability to trace soil organic matter inputs at least to the ecs

neogene growth of the sedimentary organic carbon reservoir we develop a recycling model using 13c 12c mass balance for net growth loss of the sedimentary organic carbon corg reservoir and apply it to the neogene bulk marine carbonate 13c record the model allows for variations in photosynthetic fractionation factors carbon cycling rates and the isotopic composition of riverine carbon inputs to the oceans the sign of the net flux term is controlled by the difference between fractional corg burial and fractional corg weathering independent of any variations in carbon cycling rate these terms are in turn estimated from the carbon isotope mass balance of newly deposited and weathered sediments respectively the magnitude of the net flux is sensitive to the global carbon cycling erosion deposition rate which may be estimated by the use of the records of radiogenic isotopic variations nd sr in paleoseawater a key observation and input to the model is that photosynthetic carbon isotope fractionation by both marine algae and terrestrial plants has decreased during the cenozoic incorporating time dependent carbon isotope fractionation into the model shows that the sedimentary corg reservoir has grown throughout most of the neogene even as marine 13c values fell after 14 ma a similar result is obtained if the variation in the marine 13c record is largely caused by changes in the carbon isotopic composition of river fluxes to the oceans rather than changes in the organic inorganic ratio of output to the burial sink the growth of the sedimentary organic carbon reservoir requires that the neogene sedimentary carbon cycle was a net source of o2 and a net sink of co2 to the atmosphere at least until the plio pleistocene as a consequence neogene co2 consumption by silicate weathering cannot be balanced by oxidation of sedimentary corg placing a significant constraint on global carbon balance models a related prediction of our model is that atmospheric o2 levels rose during the neogene

synchronous changes in seawater strontium isotope composition and global climate the 87sr 86sr ratio of sea water has increased gradually over the past 40 myr suggesting a concomitant increase in global chemical weathering rates1 6 recently dia et al 7 analysed a 250 kyr 87sr 86sr record and found superimposed on this gradual increase higher frequency 87sr 86sr variations which appeared to follow a 100 kyr cycle this periodicity corresponds to one of the prominent cycles in the earth s orbital parameters which are known to modulate the patterns of solar insolation and hence climate8 10 the resolution of this record was however insufficient to establish the phase relationship between the 87sr 86sr variations and global climate cycles here we present a high resolution seawater 87sr 86sr record spanning the past 450 kyr we find that maxima and minima in 87sr 86sr coincide with minima and maxima respectively in continental ice volume from the specmap oxygen isotope record20 apparently suggesting that there was less chemical weathering in arid glacial periods than in the more humid interglacials during glacial interglacial transitions however seawater 87sr 86sr changes at a rate of 1 p p m kyr 1 approximately three times that evaluated by dia et al 7 mass balance calculations illustrate that simple changes in modern chemical weathering regimes cannot fully account for such rapid changes suggesting that we need to revise current ideas about strontium reservoirs and the mechanisms for exchange between them

a model for atmospheric co 2 over phanerozoic time a new model has been constructed for calculating the level of atmospheric co sub 2 over phanerozoic time which is much simpler mathematically than the blag model but more complex geologically and biologically results suggest that there has been a notable pattern of varying atmospheric co sub 2 level over the past 570 my with high levels during the mesozoic and early paleozoic and low levels during the permo carboniferous and late cenozoic sensitivity analysis shows that within reasonable limits of the principal governing parameters this qualitative trend of varying co sub 2 is relatively insensitive to the actual values chosen for these parameters causes of the co sub 2 variation are multiple and no single geological or biological process can be called upon to explain all co sub 2 variation for all time the calculated trend of co sub 2 over time agrees well with independent estimations of paleoclimates thus the greenhouse theory of paleoclimate on a long geological time scale is supported by the results of the present study

steady and non steady state carbonate silicate controls on atmospheric co2 two contrasting hypotheses have recently been proposed for the past long term relation between atmospheric co2 and the carbonate silicate geochemical cycle one approach berner 1990 suggests that co2 levels have varied in a manner that has maintained chemical weathering and carbonate sedimentation at a steady state with respect to tectonically controlled decarbonation reactions a second approach raymo et al 1988 applied specificlly to the late cenozoic suggests a decrease in co2 caused by an uplift induced increase in chemical weathering without regard to the rate of decarbonation according to the steady state first hypothesis increased weathering and carbonate sedimentation are generally associated with increasing atmospheric co2 whereas the uplift second hypothesis implies decreasing co2 under the same conditions an ocean atmosphere sediment model has been used to assess the response of atmospheric co2 and carbonate sedimentation to global perturbations in chemical weathering and decarbonation reactions although this assessment is theoretical and cannot yet be related to the geologic record the model simulations compare steady state and non steady state carbonate silicate cycle response the e fold response time of the co2 weathering feedback mechanism is between 300 and 400 ka the response of carbonate sedimentation is much more rapid these response times provide a measure of the strength of steady state assumptions and imply that certain systematic relations are sustained throughout steady state and non steady state scenarios for the carbonate silicate cycle the simulations suggest that feedbacks can maintain the system near a steady state but that non steady state effects may contribute to long term trends the steady state and uplift hypotheses are not necessarily incompatible over time scales of a few million years

sr and nd isotopes at the prmian triassic boundary a record of climate change abstract we present a detailed curve of seawater 87sr 86sr for the middle permian to triassic based on analyses of conodonts from overlapping sections in the u s a pakistan correlated using conodont biostratigraphy the isotope ratio decreased in the middle permian at an average rate of 0 000062 ma 1 reached a minimum in the capitanian 257 258 ma and increased in the late permian at an average rate of 0 000097 ma 1 the late permian rate of increase was roughly two and a half times greater than the average increase over the past 40 ma and approximately equal to the highest cenozoic rates which occurred over much shorter time intervals modeling results suggest that decreasing middle permian 87sr 86sr ratios were driven by changes in the riverine sr flux to the oceans while increasing ratios in the late permian triassic are attributed to both increased riverine 87sr 86sr and flux the reduced middle permian riverine flux coincides with extreme continental aridity associated with the formation of pangea and recorded by massive evaporite deposits in addition mountains in the equatorial region of pangea may have created a rain shadow thereby minimizing precipitation in regions that currently contribute the bulk of chemical weathering products to the ocean increasing riverine 87sr 86sr in the late permian is suggested by the observation that 143nd 144nd values decrease at the same time however the source of radiogenic sr is not known frequently cited mechanisms for increasing 87sr 86sr in runoff such as glaciations and continent to continent collisions coincide instead with decreasing seawater 87sr 86sr in the middle permian one possible source may have been deep erosion into older orogens associated with a dramatic increase in chemical weathering in the late permian the cause of enhanced weathering appears to have been increased levels of atmospheric co2 with associated global warming and increased humidity proposed sources of co2 include dissociation of gas hydrates and oxidation of organic matter during extreme sea level regression as well as volcanic emissions from siberian traps eruptions continental floral and faunal distributions are consistent with this interpretation as are oceanic 13c patterns and variations in shallow water sediment lithologies

decoupling of bio and geohopanoids in sediments of the benguela upwelling system bus abstract geohopanoids derive from bacteriohopanepolyol bhp precursors however knowledge of the specific sources and diagenetic fate of both compound classes in marine sediments is fragmentary we studied the relationship between bhps and geohopanoids in a sediment core from the central benguela upwelling system bus including deposits over the last 75 ka the bus is a palaeo oceanographically stable setting where primary production is largely controlled by variation in upwelling intensity and therefore nutrient supply marine production in the bus was generally higher during glacial than during interglacial times as reflected in the levels of sedimentary total organic carbon geohopanoids at the study site consisted mainly of extractable hopanes and hopanols and occurred in the highest amounts during glacial periods a minor but still considerable fraction of geohopanoids was sulfur linked to geomacromolecular organic matter among these s bound hopane moieties 17 h 21 h trishomohopane c33 was the predominant compound suggesting a diagenetic overprint of bhps before linkage among the bhps a rare bacteriohopanetetrol with likely 22s configuration was observed this structural feature was lacking in the geohopanoids which all had the 22r configuration different behaviour of bhp and geohopanoid concentrations as well as 13c discrepancies indicate a decoupling of bio and geohopanoids geohopanoids most likely reflect laterally transported fossil organic matter whereas bhps are indigenous to the upper water column of the study site and may relate to past upwelling intensity nutrient levels hence care has to be taken using geohopanoids and other biomarkers for palaeoreconstruction in settings where sedimentation processes are not fully understood

geyserite in hot spring siliceous sinter window on earth s hottest terrestrial paleo environment and its extreme life siliceous hot spring deposits or sinters typically form in active terrestrial on land volcanic terrains where magmatically heated waters circulating through the shallow crust emerge at the earth s surface as silica charged geothermal fluids geyserites are sinters affiliated with the highest temperature 75 100 c natural geothermal fluid emissions comprising localized lithologically distinctive hydrothermal silica precipitates that develop around geysers spouters and spring vents they demarcate the position of hot fluid upflow zones useful for geothermal energy and epithermal mineral prospecting near vent areas also are extreme environment settings for the growth of microbial biofilms at near boiling temperatures microbial biosignatures e g characteristic silicified microbial textures carbon isotopes genetic material lipid biomarkers may be extracted from modern geyserite however because of strong taphonomic filtering and subsequent diagenesis fossils in geyserite are very rare in the pre quaternary sinter record which in and of itself is patchy in time and space back to about 400 ma only a few old examples are known such as geyserite reported from the devonian drummond basin australia devonian rhynie cherts scotland and a new example described herein from the spectacularly well preserved late jurassic 150 ma yellowstone style geothermal landscapes of patagonia argentina there geyserite is associated with fossil vent mounds and silicified hydrothermal breccias of the claudia sinter which is geologically related to the world class cerro vanguardia gold silver deposit of the deseado massif a part of the chon aike siliceous large igneous province tubular filament like micro inclusions from claudia were studied using integrated petrographic and laser micro raman analysis the results of which suggest a biological origin the putative fossils are enclosed within nodular geyserite a texture typical of subaerial near vent conditions overall this worldwide review of geyserite confirms its significance as a mineralizing geological archive reflecting the nature of earth s highest temperature habitable terrestrial sedimentary environment hot spring depositional settings also may serve as analogs for early earth paleoenvironments because of their elevated temperature of formation rapid mineralization by silica and morphologically comparable carbonaceous material sourced from prokaryotes adapted to life at high temperatures

diverse biohopanoid compositions of non marine sediments abstract biohopanoid compositions were determined for modern sediments from 27 lacustrine environments and 1 near coastal lagoon gc ms analysis of existing hopanols and those produced by a side chain cleavage reaction periodic acid and sodium borohydride of the bacteriohopanepolyols provided quantitative data for bacteriohopanetetrol bht bacteriohopanepentol and composite tetra penta and hexafunctionalised biohopanoids additional analysis of acetylated total extracts by hplc apci ms has allowed us to identify up to seven intact bacteriohopanepolyols in these environments including the first direct observation of 35 aminobacteriohopanepentol in environmental samples this method is complementary to the periodic acid approach in providing more specific compositional information the lacustrine environments exhibit a wide range of compositions many with high inputs of hexafunctionalised biohopanoids up to 60 of total tetra penta and hexafunctionalised biohopanoids indicative of major contributions to the sediment from type i methanotrophic bacteria several methylated biohopanoids were also detected in most of the samples with 2 as the dominant configuration of the methyl group 2 methylbacteriohopanetetrol was by far the most abundant and most commonly occurring compound of this type and comprised the most abundant bacteriohopanepolyol in one saline lake laguna grande spain such compounds are believed to be derived from cyanobacteria currently the only known quantitatively significant source of 2 methylated biohopanoids biohopanoids containing a methyl group at c 3 were also detected in a limited number of environments these data demonstrate the wide variability in bacteriohopanepolyol compositions among depositional environments and the potential of these compounds to preserve bacterial source information and thereby to record environmental change

balancing the cenozoic carbon and alkalinity cycles constraints from isotopic records a simple model of the carbon alkalinity and strontium cycles is built up and used to interpret the carbon and strontium isotopic evolution of seawater over the cenozoic as recorded in marine limestones the idea that weathering fluxes have increased globally over the cenozoic in response to the himalayan uplift is critically examined it is shown that such an increase of global weathering postulated to explain the sharp increase in the 87sr 86sr ratio is not compatible with the carbon isotopic record if the budgets of carbon alkalinity and strontium are considered simultaneously another scenario of the cenozoic evolution of global weathering consistent with the carbon isotopic record is proposed in which the global weathering flux varies only slightly over the cenozoic with a small increase between 15 ma and the present this second scenario appears more consistent with the reconstructed carbonate sedimentation rate and the evolution of the carbon isotopic fractionation in continental and oceanic environments

tertiary paleoceanic chemical variability unintended consequences of simple geochemical models five lines of concrete quantitative evidence about oceanic chemical composition during the past 65 m y can provide insights into the controlling processes and their temporal variations but the system constraints are not yet fully understood the calcium carbonate compensation depth mean carbon isotopic ratio and strontium isotopic ratio have all changed significantly during this time while changes in lithium to calcium and strontium to calcium ratios have been much smaller when these tracers are considered separately simple scenarios of changes in geochemical and geological factors can be used to explain the historical records these factors include 1 increases in continental chemical weathering rates and net continental fluxes to the oceans 2 changes in the isotopic composition of material weathered from continents to the oceans 3 decreases in the proportion of calcium carbonate deposited on continental shelves 4 changes in the deposition or weathering rates of certain types of sediments and 5 changes in hydrothermal circulation because these geochemical cycles are linked to each other and to others such as nutrients and global atmospheric carbon dioxide an explanation invoked for one tracer must satisfy the direction magnitude and timing of the patterns for all the tracers several simple scenarios for geochemical variations have been evaluated for their consequences both intended and unintended and compared to the historical records despite the attractiveness and possible justifications of some simple hypotheses for example decreases in organic carbon burial rates increases in carbonate weathering rates on the continents or increases in all continental weathering rates no one simple scenario appears to be consistent with both the timing and magnitude of the changes observed during the past 65 m y for all tracers considered the contradictions uncovered can be useful in defining what knowledge is crucial to further understanding of oceanic chemical history better knowledge is needed of absolute deep ocean sediment accumulation rates and their temporal variability of the extent and time scale of variability in the net carbon isotope input to the ocean from continental weathering of steady state fluxes for oceanic mass balances and the extent to which these mass balances approach steady state behavior and of the links and interactions between the geochemical cycles of various elements

abundance and structural diversity of bacteriohopanepolyols in suspended particulate matter along a river to ocean transect abstract the concentration and structural diversity of a suite of bacteriohopanepolyols bhps was measured in suspended particulate matter spm from six stations along a river ocean transect off the pacific coast of panama riverine spm contained bhps diagnostic of soil input consistent with a terrigenous source the concentration of bhps was 10 times greater in riverine spm than marine spm demonstrating that terrigenous om exported to marine sediments could provide a significant contribution to the marine sedimentary hopanoid inventory given the rich structural diversity of bhps in terrigenous spm interpretations of the sedimentary record of hopanoids in coastal marine settings must resolve inputs from marine pelagic and terrigenous sources

ocean crustal dynamics the study of oceanic crust continues to be important because of the presence of economic resources in oceanic areas and because many fundamental problems of geologic evolution are best solved from studies of the ocean although modeling and syntheses of existing data remain important key breakthroughs in the future will come from the application of new technology such as multichannel towed seismic arrays deep towed side scan sonars improved thermal probes deep drilling and satellite altimeters

spatially averaged long term erosion rates measured from in situ produced cosmogenic nuclides in alluvial sediment spatially averaged erosion rates of small catchments can be accurately inferred from the concentrations of cosmogenic nuclides in stream sediment here we test this technique at two catchments by comparing erosion rates inferred from cosmogenic nuclides with rates of alluvial fan deposition over the past 16 000 years these two independent estimates agree within one standard error demonstrating that cosmogenic nuclide signatures of stream sediment can be used to measure spatially averaged long term erosion rates using this technique we show that long term erosion rates are an exponential function of average hillslope gradient at these sites

geochemical consequences of increased late cenozoic weathering rates and the global co2 balance since 100 ma large imbalances in the relative net co2 flux over the last 100 m y are obtained from independently derived estimates of co2 uptake by weathering and organic carbon burial and of co2 outgassing assumed proportional to the mean mid ocean ridge mor spreading and mantle plume production mpp rates increasing the river flux of ca mg p and c by 50 since 30 ma to parallel the proposed increase in the sr river flux needed to explain the sr isotopic evolution of seawater richter et al 1992 has a large impact on the global carbon cycle by reducing the excess net co2 imbalance in the late cenozoic co2 uptake is calculated by assuming that 19 of the ca river flux and 60 of the mg river flux are derived from weathering silicates and that mg is removed in the oceans by 1 1 molar exchange reactions with calcsilicates an increase in the mg river flux combined with an overall decrease in the mor spreading rate predicts as much as a factor of 2 increase in the seawater mg concentration since 100 ma the net organic carbon burial flux burial minus weathering largely reflects changes in the bulk carbonate 13c record and to a lesser extent variations in the net carbonate burial flux and mean 13c value of the carbonate weathering flux organic carbon burial efficiency is markedly less than that of p from the middle middle miocene to the present because of early diagenetic transfer of organic p to francolite and oxidation of organic carbon during reworking of margin sediments by sea level fluctuations the large co2 imbalance of the late cretaceous requires significantly less carbonate subduction or greater weathering rates a co2 balance can be achieved in the miocene by decreasing the proposed increase in river fluxes by up to half or by variably increasing the amount of carbonate subducted variations in shallow water carbonate burial and hence the global carbonate record are currently too poorly known to differentiate between the above possibilities the decrease in the excess co2 flux generally parallels the trend to cooler climate inferred from the 18o record but periods of large co2 imbalance generally precede 18o shifts by several million years

global change in the late devonian modelling the frasnian famennian short term carbon isotope excursions a model of the global biogeochemical cycles coupled to a energy balance climate model the combine model is used to identify the causes of two large n 13 c value excursions across the frasnian famennian f f boundary we test a scenario that links the sea level rise to stratification of the proto tethys ocean through the formation of warm saline deep waters in extended epicontinental seas even though this scenario can produce dysoxia below 100 m depth it fails to increase the global burial flux of organic carbon and thus seawater n 13 c values since stratification of the ocean leads to decreased productivity in surface waters several scenarios postulating a continental origin of the perturbations in the late devonian biogeochemical cycles are then tested we found that weathering of platform carbonates exposed during the early famennian sea level fall can account for a maximum positive shift in n 13 c value of 0 7x at the end of the sea level fall episode another 1 0x increase in n 13 c might originate from rapid spreading of vascular land plants near the f f boundary postulating that higher plants globally increased the weatherability of continental surface and that colonized continental area increased by 30 across the f f boundary finally the n 13 c excursion observed at the base of upper rhenana zone and the rapid increase of the carbon isotope ratios at the f f boundary require an increase of phosphorus delivery to the ocean by 40 coeval with the sea level rises once the calculated n 13 c values are in agreement with the measured data the combine model calculates a decrease in atmospheric pco2 from pre perturbation 2925 ppmv in the lower rhenana conodont zone to 1560 ppmv in the upper triangularis zone this decrease in pco2 is due to the increase in burial of organic matter during the kellwasser events and increased continental weatherability triggered by the spreading of continental vascular plants these changes occur within 4 million years the corresponding global climatic cooling reaches 4 4 c at the pole and 2 1 c at the equator f 2003 elsevier b v all rights reserved

history of seawater carbonate chemistry atmospheric co 2 and ocean acidification humans are continuing to add vast amounts of carbon dioxide co2 to the atmosphere through fossil fuel burning and other activities a large fraction of the co2 is taken up by the oceans in a process that lowers ocean ph and carbonate mineral saturation state this effect has potentially serious consequences for marine life which are however difficult to predict one approach to address the issue is to study the geologic record which may provide clues about what the future holds for ocean chemistry and marine organisms this article reviews basic controls on ocean carbonate chemistry on different timescales and examines past ocean chemistry changes and ocean acidification events during various geologic eras the results allow evaluation of the current anthropogenic perturbation in the context of earth s history it appears that the ocean acidification event that humans are expected to cause is unprecedented in the geologic past for which sufficiently well preserved records are available

two types of rifting dependence on the condition of extension abstract rifting of continental lithosphere occurs in two ways 1 1 through continuous extension and subsequent sinking 2 2 in a series of pulses separated by quiet periods sometimes of considerable duration in the first case rifting is not accompanied by significant uplifts in the second uplifts of various sizes from 100 to 2000 km are typical rifting of the first type takes place when continental fragments are freely dispersed as was the case with pangea during its late triassic early jurassic break up in the cenozoic rifts developed in the course of continental collision when relative plate motion was restricted and occurred in short pulses uplift is caused by accumulation of anomalous mantle at the base of the crust during the intervals between phases of extension geological evidence is not consistent with the idea of rifting being directly related to a local source of energy in the mantle mantle plumes and diapirs it is produced by regional stresses in the lithosphere which in their turn may have different origins the lithospheric inhomogeneities observed below the present day rifts are not the cause but a consequence of extension

occurrence and abundance of soil specific bacterial membrane lipid markers in the tet watershed southern france soil specific bhps and branched gdgts recently four bacteriohopanepolyols bhps adenosylhopane and structurally similar adenosylhopane type 1 2 methyl adenosylhopane and 2 methyl adenosylhopane type 1 have been suggested to be characteristic of soil microbial communities and therefore can serve as molecular markers for soil organic matter om supply in river lake and marine sediments in this study we analyzed bhps in peats and soils collected in the tet watershed southern france and compared them with branched glycerol dialkyl glycerol tetraethers gdgts a more established molecular tracer of soil om adenosylhopane type i is identified in all of the samples from the study area except one collected near the tet river mouth with up to three of the related compounds also frequently present particularly in the surface samples the concentrations of soil specific bhps in peat environments have been shown to increase with lower delta 15 n values providing evidence that n 2 fixing bacteria are probably a major source of soil specific bhps in acidic environments it seems likely that soil ph is a major factor controlling bhp occurrence based on statistical analysis of environmental parameters and bhp concentration data the comparison of the soil specific bhp concentrations with those of branched gdgts shows no clear relationship in the tet river system supporting the concept that these two groups of soil specific compounds are synthesized by different microbial organisms living in different niches in the soil profile e g oxic top versus anoxic deep

bacteriohopanepolyol distribution in yenisei river and kara sea suspended particulate matter and sediments traces terrigenous organic matter input abstract bacteriohopanepolyols bhps are ubiquitous bacterial membrane lipids encountered in soils river and marine suspended particulate matter spm and sediments their abundance and distribution provides a direct means to identify bacterial inputs and can be used to trace soil derived bacterial organic matter om and in some cases the presence of bacterial groups and their activities in aquatic systems we have studied the bhp distribution in the spm of a major siberian river yenisei river that crosses a large latitudinal gradient draining a large part of mongolia and siberian russia the yenisei river is the main river to flow into the kara sea a shelf sea of the arctic ocean we show that the bhp distribution and concentration of spm and surface sediments of the yenisei outflow in the kara sea allow to trace soil marker bhps and evaluate the performance of the r soil index a proxy developed to trace bacterial soil derived om soil marker bhps are present in the yenisei river and their concentration decreases from the yenisei river outflow into the offshore marine sediments the r soil correlates well with an independent proxy for bacterial om the bit index r2 0 82 and has a moderate correlation with the 13corg values a bulk om proxy for terrigenous input r2 0 44 consequently the r soil index performs well in the kara sea strengthening its application for tracing bacterial om in the arctic ocean both in modern and downcore sediments furthermore a suite of bhps that are characteristic for methanotrophic bacteria i e 35 aminobacteriohopane 30 31 32 33 34 pentol aminopentol and 35 aminobacteriohopane 31 32 33 34 tetrol aminotetrol is encountered in the yenisei outflow sediments these components are partly sourced from terrigenous sources but are likely also produced in situ in the marine sediments the distribution of the pentafunctionalized cyclitol ether bhp in the marine systems is noteworthy and indicates that it can possibly be applied as a marker for cyanobacterial biomass in marine sediments

planktogenic eustatic control on cratonic oceanic carbonate accumulation data on mass age distributions and latitudinal limits of mesozoic cenozoic shelf carbonate on cenozoic deepening of the ccd in all major ocean basins and on the abundance of pelagic chalk in epicontinental carbonate sequences indicate that the primary locus of global limestone deposition has gradually shifted from shallow cratonic to deep oceanic settings since jurassic time this change is generally coincident with progressive emergence of continents during global regression as well as with taxonomic diversification of calcareous plankton and implicates one or both processes as the primary control on carbonate sediment partitioning between shallow and deep marine reservoirs widespread pelagic carbonate does not occur with phanerozoic ophiolite sequences until the late mesozoic and generally corresponds to origins of planktonic foraminifera and diversification of coccolithophorids similarly cratonic chalk is largely re stricted to cretaceous sections correlation of mesozoic cenozoic positions of t

diagenetic degradation products of bacteriohopanepolyols produced by rhodopseudomonas palustris strain tie 1 abstract hopanoids are pentacyclic triterpenoids commonly found in soils and sediments and are used as biomarkers for recent or past bacterial communities while hopanes are the ultimate degradation products of bacteriohopanepolyols bhps only a few bhps such as 32 35 anhydrobacteriohopanetetrol anhydrobht have been identified as early diagenetic degradation products here we report on diagenetic degradation products of bhps produced by rhodopseudomonas palustris strain tie 1 after exposure to elevated pressure and temperature while bacteriohopanetetrol bht was degraded to various anhydrobht isomers new n containing degradation products were discovered and tentatively assigned as anhydroaminotriols

rates of continental erosion and mountain building the first objective of this work was to obtain values for the rates at which continental erosion can smooth out or remove the topographic expression produced by orogeny the dominant part is played by mechanical erosion which acts most strongly in regions of large topographic expression chemical erosion depends strongly on precipitation or runoff in individual river drainage basins but because most continents have very similar average rainfall chemical erosion is fairly uniform for continental sized areas and will succeed in planing down all continents to a level peneplain if given enough time the exception to this rule is australia which has a very low chemical erosion rate because of its dryness the time constants for mechanical and chemical erosion so obtained vary between about 30 and 300 my depending on the continent and the assumptions made mountain building occurs throughout the geological time scale but at a non uniform rate although there will not be a balance between erosion and mountain building over a short time scale due to the non uniform rate of mountain building the long term situation must be that the two phenomena should balance out it is shown that the freeboard of continents will respond to the long term balance between mountain building and erosion an expression has been derived for the average continental elevation in which the rate of mountain building depends on the rate of radiogenic heat production within the earth it is shown that relatively small changes in average elevation above sea level of a few hundred metres are predicted to have occurred since the beginning of the proterozoic as mountain building is predicted to decrease on average with time because of the reduction in internal heat generation and as erosion is dependent on the average elevation this average elevation will decrease slowly through time the opposite of what some workers have predicted a more complicated model of mountain building is then investigated in which one component of mountain building has a sinusoidal signal the oscillations in average elevation depend on the period of the sinusoid being smaller for shorter periods finally an average continental elevation is derived using a list of real orogenic events although this list of orogenies is incomplete there is some indication that the actual continental elevation as seen in the flooding history of the continents is similar to that derived in this paper

a comparison of spatially resolved and global mean reconstructions of continental denudation under ice free and present conditions we assess the impact of continental scale processes on global denudation through the use of spatially resolved information for both an ice free paleoclimate and the present climate runoff from general circulation modeling cases representing the early eocene is superimposed upon an eocene paleogeologic reconstruction and this information is combined with chemical denudation rates for silica dissolved moles si and bicarbonate dissolved moles hco3 global fluxes of silica and bicarbonate to the global ocean are then calculated a parallel procedure is carried out with present day distributions of lithology and model derived runoff this work demonstrates that fluxes produced by a simple model such as the one used here are significantly different when calculated with spatially uniform runoff values versus those calculated with a spatially varying runoff distribution having the same global mean value use of a uniform runoff distribution produces denudation rates that are significantly higher than the global results derived from a spatially varying runoff distribution we show that present day fluxes of silica calculated by our model containing spatially varying runoff and lithology are similar to observations of current fluxes suggesting that our model captures the first order relationship accurately however the bicarbonate value compares less well to observations comparison of eocene and present day flux results shows that present day fluxes of si are greater than eocene values while calculated present day hco3 fluxes are greater than or equal to eocene values this result occurs despite the existence of greater global mean annual runoff for the eocene cases and despite the existence of ice covered areas by definition not contributing to chemical weathering in our model in the present case the increase in si global denudation fluxes from the eocene to the present are caused primarily by the large increase in exposed granitic basaltic and shale lithologies and a decrease in exposed sandstone areas between the eocene and present

weathering flux and co2 consumption determined from palaeosol sequences across the eocene oligocene transition abstract rates of base cation depletion are determined for late eocene and early oligocene alluvial palaeosols pacific northwest of north america from pedogenic mass balance geochemistry and time estimates of palaeosol sequences pedogenic strain volume change and mass transfer of base cations silica and other pertinent elements are calculated from the geochemical differences between palaeosol horizons and parent material parent material compositions are determined by identification of the least altered alluvial strata in the sequence time spans of sequences of palaeosols are estimated from 40ar 39ar age dates of interbedded tuff beds and from time of formation estimates of palaeosols based on their degree of development palaeosol sequences from the mid latitude setting of central oregon document a significant decrease in the degree of weathering of individual palaeosols across the eocene oligocene transition as the climate became cooler and drier this decrease in the degree of weathering is accompanied by an increase in the accumulation rate of alluvial soils as indicated by sedimentation rates of stratigraphic packages according to these calculations and estimates the weathering flux of base cations in the john day basin measured in grams per 1000 years per square centimetre increased across the eocene oligocene transition these results when attributed to climate change indicate that weathering flux at this local increased as climate changed from warm humid late eocene conditions to cooler drier oligocene conditions furthermore the extrapolation of these weathering flux results to other mid latitude settings with similar climate change history may help to explain the severe climate change of the eocene oligocene boundary it is proposed that in some mid latitude settings greater quantities of less weathered silicate material were exposed during the early oligocene than during the late eocene thus causing an increase in flux of weathered product increased weathering flux during this time in certain regions of the mid latitudes may have increased both co2 consumption and bicarbonate transport to the ocean and contributed to atmospheric pco2 drawdown and global cooling

late cenozoic ge si record of marine biogenic opal implications for variations of riverine fluxes to the ocean we have determined germanium silicon ratios in purified diatoms and radiolarians from siliceous sediments in holocene core tops one late pleistocene piston core and four high latitude southern ocean deep sea drilling project dsdp sites ranging in age from holocene to oligocene high latitude holocene diatoms in the 10 to 38 m size fraction ge si opal 0 693 0 039 10 6 faithfully record the present oceanic ratio ge si seawater 0 699 0 004 10 6 this confirms that diatoms from siliceous oozes are monitors of seawater ge si and may record past changes in rates of delivery of weathering products to the sea from continental and seafloor weathering large diatoms and radiolarians display ratios much lower than ge si seawater suggesting that ge si opal to some extent displays the effects of biological fractionation from 0 to 2 5 m y b p ge si opal in diatoms from dsdp sites ranges from about 0 54 to 0 70 10 6 similar to the range observed in one late pleistocene piston core over the last 25 kyr from 2 5 to 6 m y b p the ratio is more variable while prior to 10 m y b p ratios are clearly higher averaging about 0 9 10 6 in the early to middle miocene low values of the ratio are consistent with global weathering regimes dominated by river silica input to the sea while higher ratios suggest periods of enhanced hydrothermal input or reduced fluvial contribution nevertheless an oceanic one box model with variable river and hydrothermal inputs and biogenic opal output cannot adequately account for the magnitude or the timing of changes observed in the record suggesting the existence of other sources sinks for inorganic germanium and or silicon to or from the sea

novel type of crust produced during continental rifting a normal oceanic crust cannot be generated after continental crust splitting of rifts filled by a thick pile of young sediments the magma released by the rising mantle is trapped mainly in these sediments as basalts sills and plugs the sediments are themselves metamorphosed by the heat flux from the underlying mantle a metasedimentary crust is formed in direct contact with an abnormal mantle vp 7 5 km s l produced by partial serpentinization

mechanistic links between the sedimentary redox cycle and marine acid base chemistry the redox state of earth s surface is controlled on geological timescales by the flow of electrons through the sedimentary rock cycle mediated largely by the weathering and burial of c s fe phases these processes buffer atmospheric po at the same time co influxes and carbonate burial control seawater acid base chemistry and climate over long timescales via the carbonate silicate cycle however these two systems are mechanistically linked and impact each other via charge balance in the hydrosphere here we use a low order earth system model to interrogate a subset of these connections with a focus on changes that occur during perturbations to electron flow through the sedimentary rock cycle we show that the net oxidation or reduction of the earth s surface can play an important role in controlling acid base processes in the oceans and thus climate and suggest that these links should be more fully integrated into interpretive frameworks aimed at understanding earth system evolution throughout precambrian and phanerozoic time

bacteriohopanepolyols in hydrothermal vent biogenic silicates abstract biogenic silicates from the taupo volcanic zone north island new zealand are shown to contain a number of unusual polyfunctionalised bacteriohopanepolyols hopanoid fractions isolated from the rotokawa hot spring 80 82 c contained significant amounts of 32 35 anhydrobacteriohopanetetrol and two isomers of a related trihydroxylated compound the origin of these unusual hopanoid side chains is unclear and they may result either from novel biosynthetic or diagenetic transformation pathways of known biohopanoid precursors such as bacteriohopanetetrol via cyclisation or reductive removal of adenine from adenosylhopane

modelling the phanerozoic carbon cycle and climate constraints from the 87sr 86sr isotopic ratio of seawater a numerical model describing the coupled evolution of the biogeochemical cycles of carbon sulfur calcium magnesium phosphorus and strontium has been developed to describe the long term changes of atmospheric carbon dioxide and climate during the phanerozoic the emphasis is on the effects of coupling the cycles of carbon and strontium various interpretations of the observed phanerozoic history of the seawater 87sr 86sr ratio are investigated with the model more specifically the abilities of continental weathering volcanism and surface lithology in generating that signal are tested and compared it is suggested that the observed fluctuations are mostly due to a changing weatherability over time it is shown that such a conclusion is very important for the modelling of the carbon cycle indeed it implies that the conventional belief that the evolution of atmospheric carbon dioxide and climate on a long time scale is governed by the balance between the volcanic input of co2 and the rate of silicate weathering is not true rather carbon exchanges between the mantle and the exogenic system are likely to have played a key role too further the increase of the global weathering rates with increasing surface temperature and or atmospheric co2 pressure usually postulated in long term carbon cycle and climate modelling is also inconsistent with the new model other factors appear to have modulated the weatherability of the continents through time such as mountain building and the existence of glaciers and ice sheets based on these observations a history of atmospheric carbon dioxide and climate during phanerozoic time consistent with the strontium isotopic data is reconstructed with the model and is shown to be compatible with paleoclimatic indicators such as the timing of glaciation and the estimates of cretaceous paleotemperatures