classification of huminite iccp system 1994 abstract in the new classification iccp system 1994 the maceral group huminite has been revised from the previous classification iccp 1971 int handbook coal petr suppl to 2nd ed to accommodate the nomenclature to changes in the other maceral groups especially the changes in the vitrinite classification iccp 1998 the new vitrinite classification iccp system 1994 fuel 77 349 358 the vitrinite and huminite systems have been correlated so that down to the level of sub maceral groups the two systems can be used in parallel at the level of macerals and for finer classifications the analyst now has according to the nature of the coal and the purpose of the analysis a choice of using either of the two classification systems for huminite and vitrinite this is in accordance with the new iso coal classification that covers low rank coals as well and allows for the simultaneous use of the huminite and vitrinite nomenclature for low rank coals

dissolution kinetics of calcium carbonate in equatorial pacific sediments benthic chambers were deployed in the equatorial eastern pacific ocean on a transect along the equator between 103 w and 140 w and on a transect across the equator at 140 w in order to establish the rate of calcium carbonate dissolution on the seafloor dissolution was determined from the rate of alkalinity increase within an incubation chamber measured over an 80 120 hour incubation period dissolution rates were lowest at eastern pacific sites 0 2 0 4 mmol caco3 m2 d and highest at the equatorial 140 w sites 0 5 0 7 mmol m2 d both oxygen consumption rates and the degree of bottom water saturation govern dissolution rates measured dissolution and oxygen consumption rates are used with a numerical model to constrain the value of the dissolution rate constant k formulated according to the equation developed by keir 1980 dissolution rate k 1 n the observed dissolution fluxes are predicted by the model when k 5 to 100 d and n 4 5 this range of k values has important implications regarding the type of carbonate dissolving and its location within the sediment column at low values of k organic carbon rain rates to the seafloor become the dominant driving force of carbonate dissolution at higher values of k the degree of bottom water undersaturation becomes more important dissolution of carbonate within equatorial pacific sediments can be adequately described with k 20 10 d a rate constant much lower than some previously used values dissolution rates do not vary significantly over chamber boundary layer thicknesses between 200 and 800 m indicating that dissolution is not controlled by hydrodynamic conditions chambers acidified with hcl yield very large dissolution rates but for a given degree of acidification the dissolution rate was constant for sites ranging from water depths of 3300 4400 m this implies that there are not more and less easily dissolved forms of caco3 arriving on the seafloor between these depths a budget for alkalinity in the deep pacific predicted by the dissolution model and based on the assumption that all carbonate dissolution takes place in the sediments is within 85 of the input required by a published box model alkalinity budget based on the distribution of nutrients and the water mass transport rates

the role of caco3 compensation in the glacial to interglacial atmospheric co2 change the only viable explanations put forth to date for the glacial to interglacial change in atmospheric co2 content suggested from measurements of the co2 content of gas extracted from ice cores involve changes in the ocean s nutrient cycles any nutrient change capable of creating the 80 atm changes in atmosphere co2 pressure suggested by the ice core results also creates significant change in the deep ocean s co3 content evidence from deep sea sediments suggests that these co3 changes are compensated on the time scale of a few thousand years by reductions or increases in amount of caco3 accumulating in deep sea sediments this compensation process has two important consequences first it significantly increases the magnitude of the co2 change per unit of nutrient forcing second it causes a delay in the response of the atmospheric co2 change while the first of these consequences is a boon to those seeking to explain the co2 change the second may prove to be a curse the ice core co2 record shows no evidence of a significant lag between the co2 response and the polar warming in any case it is important that we improve our knowledge of the magnitude and timing of the caco3 preservation events which mark the close of episodes of glaciation and of the dissolution events which mark the onset of these episodes

glacial carbonate dissolution cycles and atmospheric pco2 a view from the ocean bottom we present a calculation of the global calcium carbonate dissolution response to glacial interglacial changes in seawater carbonate chemistry inferred from cd ca and carbon isotope ratios in benthic foraminifera our model is based on the relationship between the carbonate dissolution flux and the degree of calcite saturation in the three main ocean basins the rate of carbonate dissolution is derived using mechanisms inferred from studies of surface sediment pore water geochemistry the model predicts a change in the relative importance of caco3 burial among the atlantic indian and pacific oceans between glacial and interglacial times chemical rearrangement of deep waters appears to be a viable mechanism for driving interocean differences in carbonate accumulation and observed caco3 burial trends constrain alkalinity changes that accompanied deepwater nutrient redistribution our model predicts atmospheric pco2 lowering during glacial times caused by the carbonate dissolution response to be less than 10 ppm suggesting that this mechanism is not a viable candidate for explaining a large fraction of the observed 80 ppm decrease observed in ice cores

calcite dissolution in sediments of the ceara rise in situ measurements of porewater o2 ph and co2 aq in situ electrode measurements of porewater oxygen and ph from four sites on the ceara rise in the western tropical atlantic unequivocally demonstrate that calcite dissolution driven by metabolic co2 produced within the sediments is a significant part of the diagenesis of sedimentary calcite dissolving at least 20 of the calcite rain to the seafloor the first ever in situ absorbance based measurements of porewater co2 aq support the dissolution estimates based on models of the observed ph distributions and are incompatible with scenarios excluding metabolic co2 driven dissolution our dissolution estimates are consistent with those estimated by an independent study of porewater calcium and alkalinity profiles martin and sayles 1996 at this location the consistency of these disparate porewater measurements and our ability to interpret them with simple models of respiration and dissolution implies that no special mechanism is required to describe this process the calcite dissolution rate constant in the sediments of the deepest station in this study is significantly higher than determined by in situ studies at other locations values approach those determined by early laboratory measurements the dissolution rate constant here must be at least two orders of magnitude higher than for calcite in sediments on the ontong java plateau based on in situ electrode measurements there hales and emerson 1996 the calcite solubility consistent with these data is not compatible with that consistent with the ontong java data the reason for this difference is currently unresolved but may be due to the high order of the empirical dissolution rate law assumed in this study

an evaluation of lohmann s foraminifera weight dissolution index down water column traverses of core top weights for three planktonic species confirm lohmann s 1995 relationship between foraminifera shell weight loss and bottom water carbonate ion content however they also suggest that the initial shell thickness varies with growth habitat and that the offset between bottom water and pore water carbonate ion concentration varies even on small space scales

a new mechanistic model for organic carbon fluxes in the ocean based on the quantitative association of poc with ballast minerals abstract in simulation studies of the ocean s role in the global carbon cycle predicting the depth distribution for remineralization of particulate organic carbon poc is of particular importance following sarmiento et al global biogeochemical cycles 7 1993 417 most simulation models have the power law curve of martin et al deep sea research 34 1987 267 for this purpose the martin et al curve is an empirical fit to data most of which is from shallow floating sediment traps using such a fit implies that all the information necessary for prediction is contained in the carbon flux itself so that the organic carbon flux f oc z at any depth z can be predicted from the flux of organic carbon f oc z 0 at some near surface depth z 0 here we challenge this basic premise arguing that fluxes of ballast minerals silicate and carbonate biominerals and dust determine deep water poc fluxes so that a mechanism based model of poc flux must simultaneously predict fluxes of both poc and ballast minerals this assertion is based on the empirical observation that poc fluxes are tightly linked quantitatively to fluxes of ballast minerals in the deep ocean here we develop a model structure that incorporates this observation and fit this model to us jgofs eqpac data this model structure plus the preliminary parameter estimates we have obtained can be used to explore the implications of our model in studies of the ocean carbon cycle

thorium 230 profiling in deep sea sediments high resolution records of flux and dissolution of carbonate in the equatorial atlantic during the last 24 000 years variations in carbonate flux and dissolution which occurred in the equatorial atlantic during the last 24 000 years have been estimated by a new approach that allows the point by point determination of paleofluxes to the seafloor an unprecedented time resolution can thus be obtained which allows sequencing of the relatively rapid events occurring during deglaciation the method is based on observations that the flux of unsupported 230th into deep sea sediments is nearly independent of the total mass flux and is close to the production rate thus excess 230th activity in sediments can be used as a reference against which fluxes of other sedimentary components can be estimated the study was conducted at two sites ceara rise western equatorial atlantic and sierra leone rise eastern equatorial atlantic in cores raised from three different depths at each site from measurements of 230th and caco3 changes in carbonate flux with time and depth were obtained a rapid increase in carbonate production starting at the onset of deglaciation was found in both areas this event may have important implications for the postglacial increase in atmospheric co2 by increasing the global carbonate carbon to organic carbon rain ratio and decreasing the alkalinity of surface waters and possibly the north atlantic deep water increased carbonate dissolution occurred in the two regions during deglaciation followed by a minimum during mid holocene and renewed intensification of dissolution in late holocene during the last 16 000 years carbonate dissolution was consistently more pronounced in the western than in the eastern basin reflecting the influence of antarctic bottom water in the west this trend was reversed during stage 2 possibly due to the accumulation of metabolic co2 below the level of the romanche fracture zone in the eastern basin

insights into the ecology of epibenthic calcareous foraminifera from a colonization study at 4000 m station m in the ne pacific ocean abstract benthic foraminifera are an abundant and important component of modern and ancient deep sea ecosystems and these single celled organisms generate a fossil record that facilitates the assessment of paleoceanographic changes through time despite recent advances in taxonomic and ecological information about deep sea foraminifera many basic questions remain requiring a better understanding of ecological tolerances morphologic plasticity and distribution of deep sea foraminiferal species this study focuses on the phylogenetics morphology and colonization dynamics of deep sea foraminifera at abyssal station m in the eastern pacific ocean after 368 days at 4000 m on the pacific ocean seafloor 546 foraminifera 80 of which were calcareous species occupied elevated substrate experiments genetic analyses of the most abundant calcareous foraminiferal taxon indicate that this trochospiral species is a morphological variant of cibicidoides wuellerstorfi referred to as c wuellerstorfi var lobatulus although pyrgo and other milioline foraminifera are commonly found within sediments two morphological variants of pyrgo colonized elevated substrates at the station m study site many pyrgo spp and c wuellerstorfi var lobatulus were covered in an organic cyst perhaps as a feeding structure these results suggest that these calcareous foraminifera are able to flourish in deep sea settings where hard substrates are available and may be more widely distributed and diverse in lower bathyal and upper abyssal habitats when elevated substrates are present

late cretaceous cenozoic exhumation of the helanshan mt range western ordos fold thrust belt china insights from structural and apatite fission track analyses abstract the western ordos fold thrust belt is an intracontinental chain predominately formed in the jurassic and subsequently reworked in the late cretaceous and cenozoic the structural deformation of the western ordos fold thrust belt was driven by the force transmitted from the plate boundary of asian collage this study presents new structural analysis apatite fission track and thermal modeling data in the helanshan mt range of the western ordos fold thrust belt the apatite fission track analysis and thermal modeling suggest that the helanshan mt range underwent two stages of cooling and exhumation since the late cretaceous the first fast cooling stage in the late cretaceous 90 70 ma led to ca 1 1 2 km exhumation and the second fast cooling was after ca 30 ma with an exhumation of ca 1 8 2 2 km structural studies indicate that the late cretaceous exhumation was related to nw se compression and the exhumation of after ca 30 ma was associated with wnw ese transtension the wnw ese transtension produced high angle normal faults by reworking the mesozoic pre existing factures comprehensive analyses of the synchronous structures around the boundaries of the asian collage suggest that the late cretaceous exhumation of the helanshan mt range might be the far field results of the convergence between the pacific and eurasian plates the varying rates of the pacific plate subduction may transmit nw sw horizontal stress across the north china plate in contrast the post oligocene

in situ calcium carbonate dissolution in the pacific ocean over the past several years researchers have been working to synthesize the woce jgofs global co2 survey data to better understand carbon cycling processes in the oceans the pacific ocean data set has over 35 000 sample locations with at least two carbon parameters oxygen nutrients cfc tracers and hydrographic parameters in this paper we estimate the in situ caco3 dissolution rates in the pacific ocean water column calcium carbonate dissolution rates ranging from 0 01 1 1 mmol kg1 yr1 are observed in intermediate and deepwater beginning near the aragonite saturation horizon in the north pacific intermediate water between 400 and 800 m caco3 dissolution rates are more than 7 times faster than observed in middle and deep water depths average 0 051 mmol kg1 yr1 the total amount of caco3 that is dissolved within the pacific is determined by integrating excess alkalinity throughout the water column the total inventory of caco3 added by particle dissolution in the pacific ocean north of 40s is 157 pg c this amounts to an average dissolution rate of approximately 0 31 pg c yr1 this estimate is approximately 74 of the export production of caco3 estimated for the pacific ocean these estimates should be considered tomore be upper limits for in situ carbonate dissolution in the pacific ocean since a portion of the alkalinity increase results from inputs from sediments less

the holocene preservation history of equatorial pacific sediments a model of the sediment mixed layer is used to quantify the glacial holocene changes in calcite preservation productivity minus dissolution at water depths that span the transition between lysocline and calcite compensation depth in the equatorial pacific the mean preservation fluxes required by the model to account for the observed changes in sediment composition indicate in most cases that calcite dissolution exceeds supply and that there has been net removal of calcite from surface sediments over the holocene the sediment mixed layer is therefore not at steady state with respect to caco3 fluxes the model is also used to show that an observed increase in the radiocarbon age of the core top sediments with increasing extent of dissolution cannot be explained by chemical erosion of underlying glacial material dissolution taking place at or just below the sediment water interface is the probable cause of this phenomenon

paleoenvironments of lacustrine coals the occurrence of algae in humic coals abstract according to previous studies there is a significant difference in the thickness and number of coal seams from the foredeep and the intermontane coal basins or basins situated on platforms and cratons recent petrographic and geochemical investigations on selected coal samples from foredeep and intermontane basins of europe carboniferous and tertiary and south america permian show that the coal seams in each of these coal basins have significant differences in their petrographic and geochemical compositions many intermontane coals are characterized by more liptinite than foredeep coals fluorescence studies show that up to 75 of the liptinite macerals of these humic coals can be attributed to alginite and or degradation products of algae this indicates that generally subaquatic conditions occurred more often in the peats that formed within intermontane basins

oligo miocene rift of sardinia and the early history of the western mediterranean basin the geodynamic evolution of the western mediterranean basin in spite of many studies is still uncertain there is some consensus for interpreting this basin as a kind of small oceanic marginal basin its opening has generally been related to a subduction process which was active during the oligocene miocene somewhere east of sardinia corsica1 7 as the margins of the basin are deeply buried below miocene to present sediments direct lithological and stratigraphical data which could explain the events responsible for its formation are rare8 10 or missing altogether to obtain such data detailed field studies have been undertaken in sardinia fig 1 and the first results are presented here this approach is justified by the fact that in that island oligocene and miocene sediments were deposited in a rift fossa tettonica sarda of verdabasso11 which is the easternmost arm of the complex rift system that affected the european plate during oligocene and miocene times one of these arms evolved towards a small oceanic basin the western mediterranean or algero provencal basin while others such as the gulf of valencia and the sardinia rift aborted and remained at the rift stage its exceptional exposures make it possible to examine the sardinia rift to clarify the sequence of events which created it and to establish a sedimentological model which we believe is directly applicable to the western mediterranean basin

association of sinking organic matter with various types of mineral ballast in the deep sea implications for the rain ratio 1 we compiled and standardized sediment trap data below 1000 m depth from 52 locations around the globe to infer the implications of the armstrong et al 2002 ballast model to the ratio of organic carbon to calcium carbonate in the deep sea the rain ratio we distinguished three forms of mineral ballast calcium carbonate opal and lithogenic material we concur with armstrong et al 2002 that organic carbon sinking fluxes correlate tightly with mineral fluxes based on the correlations seen in the trap data we conclude that most of the organic carbon rain in the deep sea is carried by calcium carbonate because it is denser than opal and more abundant than terrigenous material this analysis explains the constancy of the organic carbon to calcium carbonate rain ratio in the deep sea today and argues against large changes in the mean value of this ratio in the past however sediment trap data show variability in the ratio in areas of high relative calcium carbonate export mass caco3 mass ratio 0 4 unexplainable by the model leaving open the possibility of regional variations in the rain ratio in the past

chemical characteristics of liptinite macerals in humic and sapropelic coals abstract according to previous studies alginite does not occur in humic coals however in coals from the saar district f r germany alginite was identified by fluorescencemicroscopy in addition high amounts of an undeterminable liptinite maceral were found and tentatively explained as an alteration product of alginite therefore organic geochemical methods were used to characterize and identify this unknown liptinite maceral organic geochemical parameters such as cpi pristane phytane ratio and methylphenanthrene index show not only a dependence from coal rank but also yield additional information about the type of organic matter input and the depositional environment of the coals a series of coals of different origins around 0 8 vitrinite reflectance were investigated to determine how far the geochemical parameters reflect change in facies the samples included cannel boghead and resinite rich coals as well as isolated durain bands with increasing amounts of alginite in the coal the cpi pristane phytane and c 4 naphthalene phenanthrene ratios of the extracts decrease as illustrated by two representatives samples some resinite and sporinite rich coals show a primarily naphthalene derived aromatic composition whereas some alginite rich coals of the same rank show phenanthrene and its derivatives to be dominant with respect to technological properties most coals from the saar district correspond with a higher rank than indicated by reflectance measurements those coals in general show lower values of the aforementioned ratios in comparison with ruhr coals of similar vitrinite reflectance values

climatic change and caco3 preservation an 800 000 year bathymetric reconstruction from the central equatorial pacific ocean sixteen deep sea cores from the central equatorial pacific are used to reconstruct a continuous 800 000 year 800 kyr record of bathymetric variations in carbonate preservation as measured by calcium carbonate caco3 content the depth of the sedimentary lysocline has fluctuated markedly in conjunction with late pleistocene climate cycles while the carbonate critical depth ccrd which is the water depth where the sediments contain 10 caco3 has remained relatively constant as a result the depth of the lysocline controls the bathymetric position and thickness of the caco3 transition zone defined as the depth from the lysocline to the ccrd modern and interglacial aged sediments show poor caco3 preservation and thick caco3 transition zones glacial aged sediments show good preservation and deep thin zones due to the deepening of the lysocline detailed comparison of the caco3 preservation and oxygen isotope records from the central equatorial pacific confirms the observation that preservation maxima and minima tend to occur during the latter half of glacial and interglacial stages and on climate transitions rather than during the middle of climatic stages during the nine major glacial stages of the last 800 kyr the lysocline deepened by at least 400 to 800 m this deepening indicates an increase in the abyssal carbonate ion concentration co3 and a depression of the calcite saturation horizon best explained by the deeper presence of a more carbonate saturated water mass the bottom of the transition zone has remained at a relatively constant depth during the brunhes chron indicating a balance between caco3 sedimentation and dissolution in the deepest waters of the central equatorial pacific

western equatorial pacific deep water carbonate chemistry during the last glacial maximum and deglaciation using planktic foraminiferal mg ca to reconstruct sea surface temperature and seafloor dissolution 1 we present a reconstruction of deep water carbonate saturation state co32 in the western equatorial pacific for the last glacial maximum lgm and deglaciation based on changes in the mg ca ratio of planktic foraminifers with increased water depth our data suggest there have been changes in bottom water co32 over the past 25 000 years at water depths as shallow as 1 6 km the co32 reconstruction for the lgm suggests co32 was similar or slightly higher than modern values between 1 6 and 2 0 km shifting sharply to lower values an average 30 mol kg lower below 2 5 km the shift in chemistry between 2 0 and 2 5 km supports a hypothesis that pacific overturning circulation occurred deeper during the lgm with a slightly more ventilated water mass above 2 0 km the data are not consistent with enhanced preservation in this region of the deep pacific at depths greater than 2 5 km suggesting that the long held view of better preservation throughout the glacial deep pacific must be reevaluated for the deglaciation we have evidence of a co32 maximum that suggests enhanced deglacial preservation between 1 6 and 4 0 km in comparison to the holocene and the lgm the deglacial co32 was as much as 28 mol kg higher than modern between 1 6 and 4 0 km results suggest carbonate burial rates were 1 5 times greater during the deglacial than the over the past 5 kyr

caco3 dissolution in sediments of the ceara rise western equatorial atlantic we have used porewater sampling by in situ techniques including whole core squeezing as well as by shipboard sectioning and whole core squeezing to estimate the rates of sedimentary organic matter oxidation and caco3 dissolution at seven sites on the ceara rise in the western equatorial atlantic ocean porewater no3 profiles at all sites show a pattern indicative of active organic matter oxidation in the upper 15 20 cm of the sediments and in a buried organic rich layer the organic c oxidation rate generally decreases with increasing water depth from a value of 22 mol cm2 y at the shallowest site 3279 m to 14 mol cm2 y at the deepest site 4675 m over this depth range the bottomwaters vary from moderately supersaturated with respect to calcite to strongly undersaturated high resolution alkalinity profiles measured in porewaters collected by in situ whole core squeezing yield estimated ca2 fluxes of 11 mol cm2 y at a site located at the depth of the calcite saturation horizon and 7 6 zmol cm2 y at a moderately undersaturated site ca2 fluxes calculated from profiles in porewaters collected by relatively coarse resolution in situ sampling methods clearly indicate that there is caco3 dissolution above the calcite saturation horizon the dissolution of aragonite may contribute to the dissolution flux at the shallowest site these ca2 fluxes as well as fluxes estimated from a model of sedimentary organic matter oxidation and calcite dissolution indicate that 36 66 of the caco3 rain to the seafloor dissolves at sites at and above the calcite saturation horizon while 52 75 of the rain dissolves at sites below this depth when these results are incorporated into the oceanic caco3 budget of milliman 1993 they indicate that 35 of caco3 production is preserved in the deep sea they suggest a caco3 accumulation rate that is 27 lower than that estimated by milliman 1993 our corg oxidation caco3 dissolution model indicates that a large fraction of the caco3 dissolution that is occurring on the ceara rise is attributable to the neutralization of metabolic acids produced during organic matter oxidation the efficiency with which organic matter oxidation dissolves caco3 that is the ratio caco3 dissolution attributable to organic matter oxidation organic matter oxidation rate generally increases as degree of undersaturation of bottomwaters increases however there are deviations from the general trend that can be attributed to site to site variations in the kinetics of organic matter oxidation and calcite dissolution this result indicates that the dissolution of caco3 as a result of organic matter oxidation in the deep sea may mask the effects of variations in surface water caco3 productivity and bottomwater chemistry on the accumulation rate of caco3 in deep sea sediments

organic petrology of selected oil shale samples from the lower carboniferous albert formation new brunswick canada incident light microscopy was used to describe maturation and composition of organic material in oil shale samples from the lower carboniferous albert formation of new brunswick the maturation level was determined in normal white light by measuring vitrinite reflectance and in fluorescent light by measuring fluorescence spectra of alginite b results indicate low to intermediate maturation for all of the samples composition was determined by maceral analysis alginite b is the major organic component in all samples having significant oil potential oil yields obtained from the fischer assay process and oil and gas potentials from rock eval analyses correlate to the amounts of alginite b and bituminite determined in the samples in some of the samples characterized by similar high concentrations of alginite b decrease in fischer assay yields and oil and gas potentials is related to an increase in maturation as expressed by increase in the fluorescence parameter lgrmax and red green quotient of alginite b incident light microscopy particularly with fluorescent light offers a valuable tool for the identification of the organic matter in oil shales and for the evaluation of their oil and gas potentials end of article last page 494

coalification pattern and thermal modelling of the permo carboniferous saar basin sw germany abstract palaeo heat flow values and thicknesses of eroded permo carboniferous sediments in the saar basin were evaluated using one dimensional thermal modelling techniques thermal burial and erosion histories for 16 wells were calibrated by comparing measured and calculated vitrinite reflectance using the kinetic easy r o algorithm and by comparing measured and calculated temperature data on the basis of 37 wells coalification maps were constructed revealing a syn kinematic coalification pattern thermal maturity of the sediments can only be explained by deep burial and moderate heat flows during time of maximum burial i e in the permo carboniferous calculated heat flow data range between 50 and 75 mw m 2 which implies a crustal thickness between 30 and 40 km during the time of maximum burial these values are in accordance with the geodynamic setting of the basin the influence of the permo carboniferous volcanism on the palaeo temperature distribution was overwhelmed by the subsequent deep burial during permian times between 1800 and 3000 m of permo carboniferous sediments were eroded different sedimentation and erosion histories are characteristic for anticlines and synclines respectively

evidence in support of first order dissolution kinetics of calcite in seawater abstract re examination of an experimental determination of the dissolution rate of reagent grade calcite in seawater shows that the original conclusion of rate law with 4 5 order dependence on undersaturation was very sensitive to uncertainties in the saturation state of the seawater with respect to calcite c in particular use of an erroneously high value of the calcite stoichiometric solubility product generated correspondingly low values of the saturation state extrapolation of the experimental measurements to a rate of zero dissolution indicates that the calcite solubility was about 20 lower than that used in the original study similar to more recent estimates if the lower solubity is used for recalulation of the experimental saturation states the dissolution rate rd c day 1 is adequately described by the rate experssion rd c 38 1 omega c 1 in situ measurements of ph in the pore waters of calcite rich sea floor sediments are more consistent with first order kinetics than with 4 5 order kinetics interpretation of pore water ph data using the 4 5 order rate expression requires dissolution rate constants that are different by at least two orders of magnitude and stoichiometric calcite solubility products that are different by several percent between two otherwise similar sites application of the first order dissolution reduces the variability in the rate constant to less than one order of magnitude and all in situ observations are consistent with a single estimate of calcite solubility first order kinetics do not reduce the discrepancy between the laboratory determined rate constants and those based on pore water measurements dissolution rate constants constrained by the in situ ph measurements are at least two orders of magnitude less than the laboratory results

organic carbon flux and organic carbon to calcite flux ratio recorded in deep sea carbonates demonstration and a new proxy 1 theoretical considerations indicate that degree of bottom water calcite saturation organic carbon flux and the ratio of that flux to the calcite flux all are reflected in the carbonate preservation record of deep sea sediments separating the influence of these various factors on the record depends first on estimating the percent of the calcite flux which is dissolved at the seabed we have developed a new proxy for percent dissolved calcite by calibrating a foraminiferal fragmentation index to biogeochemical model derived data application of our proxy combined with geochemical modeling to the surface sediments of the eastern equatorial pacific eep demonstrates the need for all three of the variables listed above to account for the observations further we used reverse modeling to map the ratio of the biotic fluxes across the eep we observe a coherent regional pattern with highest ratio values as expected associated with areas of upwelling particularly along south america our proxy appears to be unaffected by carbonate sediment properties such as percent calcite in samples or the amount of coarse fraction 63 m in the calcareous portion of the sediments therefore it reflects primarily the geochemical environment rather than characteristics of seabed deposits

investigations on the petroleum generation potential of bituminous coals from the saar region abstract the saar basin contains bituminous coals high volatile a and b five coals of westphalian and stephanian age with distinctly varying maceral compositions were analysed by soxhlet extraction and supercritical extraction with different solvents and microscopically from the data obtained it is concluded that the oldest coals have a potential for oil generation whereas the younger coals do not this conclusion is explained by varying liptinite contents and varying adsorption capacities of different vitrinite macerals for bitumen

organic matter oxidation in deep sea sediments distribution in the sediment column and implications for calcite dissolution abstract this study uses pore water profiles of no3 and o2 from 34 deep sea study sites from five oceanic regions encompassing broad ranges of sediment composition and organic matter oxidation rate to analyze the depth distribution of organic matter oxidation within the sediment column while the results are consistent with those of hammond et al 1996 and hales 2003 the broader range of environmental variables considered in this study allows us to show that the depth of oxidation varies systematically with the integrated sedimentary organic matter oxidation rate the scale length for oxidation varies from large values of about 4 cm when the organic matter oxidation rate is 5 mol cm2 y to about 0 35 cm at oxidation rates above 20 mol cm2 y we have included this variability of organic matter oxidation depth in models of calcite dissolution our results show that variations in oxidation depth at a constant degree of supersaturation may result in changes in metabolic dissolution efficiency that are similar in magnitude to those resulting from basin wide variations in the degree of supersaturation with respect to calcite the model shows that when the ratio of sedimentary organic matter oxidation rate to calcite rain rate is held fixed at 0 8 mol mol metabolic dissolution is likely to be significant at all bottom water saturation levels and may result in dissolution of up to 50 of the calcite rain at the calcite saturation horizon

paleomagnetism of jurassic carbonate rocks from sardinia no indication of post jurassic internal block rotations 1 several paleomagnetic studies on carboniferous and permian sedimentary and volcanic rocks from sardinia and corsica have recently demonstrated 1 the tectonic coherence between southern corsica and northern sardinia and 2 significant rotations between individual crustal blocks within sardinia itself the geodynamic significance of these rotations however is not clearly understood mainly because of uncertainties in defining their timing and causes in order to contribute to these issues a pioneering paleomagnetic study on jurassic carbonates from the baronie supramonte region of eastern central sardinia has been extended regionally and stratigraphically a total of 280 oriented drill cores were taken from 44 sites of middle and late jurassic age in the nurra baronie supramonte barbagia sarcidano and sulcis regions despite generally weak remanent magnetization intensities on the order of less than 1 ma m thermal and alternating field demagnetizations were successfully applied to define a characteristic remanent magnetization component in about 60 of the samples site mean directions show rather good agreement after correction for bedding tilt and yield middle and late jurassic overall mean directions of d 269 7 and i 45 0 95 8 0 k 14 and n 25 sites and d 275 5 and i 50 7 95 7 2 k 45 3 and n 10 sites positive regional and local fold and reversal tests demonstrate the primary character of the natural magnetic remanence which is carried by magnetite these results indicate only insignificant amounts 10 of post jurassic rotations within the island of sardinia the resulting middle and late jurassic paleopoles latitude lat 16 5 longitude long 299 1 dp 6 4 and dm 10 1 and lat 23 4 long 301 2 dp 6 5 and dm 9 7 corrected for the opening of 1 the liguro provencal basin and 2 the bay of biscay using rotation parameters from the literature fall near the coeval segment of the european apparent polar wander path these results constrain the timing of large differential block rotations found in late carboniferous permian rocks to a pre middle jurassic age and lead us to exclude tectonics related to the alpine orogeny for such rotations

caco3 dissolution in california continental margin sediments the influence of organic matter remineralization in situ benthic flux chamber and oxygen microelectrode and shipboard porewater results have been used to quantify sea floor dissolution of caco3 on the continental rise adjacent to central california usa the porewater distributions and benthic fluxes of o2 no3 ta ca2 13c and tic are interpreted using a numerical simulation of organic matter remineralization and caco3 dissolution in marine sediments the processes considered in the simulation include organic matter oxidation by o2 no3 and so42 caco3 dissolution and precipitation hs and nh4 oxidation and sediment mixing and sediment accumulation calculated benthic fluxes of o2 no3 ta tic 13c and ca2 porewater concentrations of o2 no3 and nh4 and sediment distributions of organic carbon caco3 excess 210pb and 14c agree well with the measurements benthic fluxes of alkalinity and inferred caco3 dissolution rates cannot be explained on the basis of dissolution driven solely by bottom water undersaturation if the influence of metabolically produced co2 is included benthic fluxes are fully reconciled however this is in agreement with benthic chamber ca2 and 13c results that independently imply substantial caco3 dissolution in these sediments the above observations are in contrast to those reported by jahnke et al 1994 for the west african continental rise and the western equatorial pacific where 1 g diagenetic models predict dissolution fluxes larger than observed with benthic flux chambers we conclude that the extent of metabolic caco3 dissolution may vary regionally numerous factors such as the depth of metabolic co2 production and caco3 dissolution kinetics are known or predicted to influence metabolic dissolution among the factors that should be considered in reconciling these observations are l the extent to which sulfate reduction and reoxidation reactions may influence acid base properties in surface sediments and 2 the total sedimentary caco3 content of the sites that may influence porewater acidity through surface exchange reactions at the mineral surface

coal as a source rock for oil a review the geological debate about whether and to what extent humic coals have sourced oil is likely to continue for some time despite some important advances in our knowledge of the processes involved it is clear that not only liptinites but also perhydrous vitrinites have the potential to generate hydrocarbon liquids in the course of natural coalification some liptinites especially alginite cutinite and suberinite contain a higher proportion of aliphatic moieties in their structure than other liptinites such as sporinite and resinite and are therefore more oil prone it is of potential value to be able to predict the several environments of deposition in which coals with high liptinite contents or containing perhydrous vitrinites may have been formed review of the distribution of oil prone coals in time and space reveals that most are jurassic tertiary with key examples from australia new zealand and indonesia methods based both on experimental simulations and the examination of naturally matured samples have been used to determine the order of generation of hydrocarbons from different macerals results are not entirely consistent among the different approaches and there is much overlap in the ranges of degradation but it seems probable that in the natural environment vitrinites begin to generate early followed by labile liptinites such as suberinite then cutinite sporinite and finally alginite petroleum potential may be determined by experimental simulation of natural coalification or inferred through various micro techniques especially fluorescence and infrared ir spectroscopy or bulk techniques such as elemental analysis and 13c nmr spectroscopy the latter three techniques enable a measure of the polymethylene component of the coal which now appears to be one of the best available approaches for determining petroleum potential no method of experimental simulation of petroleum generation from coals is without criticism and comparative results are highly variable however hydrous pyrolysis confined pyrolysis and forms of open system hydrous pyrolysis approach acceptable simulations whether and to what degree generated liquid hydrocarbons are expelled has long been the central problem in oil from coal studies the structure of vitrinite was believed until recently to contain an interconnected microporous network in which generated oil would be contained until an expulsion threshold was attained recent studies show the pores are not interconnected combined with a dynamic model of pore generation it now seems that expulsion of hydrocarbons is best explained by activated diffusion of molecules to maceral boundaries and ultimately by cleats and fractures to coal seam boundaries the main reason for poor expulsion is the adsorption of oil on the organic macromolecule which may be overcome 1 if coals are thin and interbedded with clastic sediments or 2 if the coals are very hydrogen rich and generate large quantities of oil the existence of oil in vitrinite is attested to by solvent extractions fluorescence properties and by microscopic observations of oil and bitumen experimental simulation of expulsion of oil from coals has only recently been attempted the relative timing of release of generated co2 and ch4 could have considerable importance in promoting the expulsion of liquid hydrocarbons but the mechanism is unclear as it is universally agreed that dispersed organic matter dom in some shales readily generates and expels petroleum it is curious that few consistent geochemical differences have been found between coal macerals and dom in interbedded shales unambiguous evidence of expulsion from coals is limited and in particular only a few commercial oil discoveries can be confidently correlated to coals these include upper cretaceous fruitland formation coals in the usa from which oil is produced new zealand tertiary coals and middle jurassic coals from the danish north sea it is likely that coals have at least contributed to significant oil discoveries in the gippsland basin australia in the turpan basin china and in the kutei and ardjuna basins in indonesia but this remains unproven early reports that early jurassic coals in mid norway were a major source of the reservoired oils have been shown to be inaccurate none of the proposed rules of thumb for generation or expulsion of petroleum from coals seem particularly robust decisions on whether a particular coal is likely to have been an active source for oil should consider all available geological and geochemical information the assumptions made in computational models should be well understood as it is likely with new understandings of processes involved that some of these assumptions will be difficult to sustain

the influence of organic matter diagenesis on caco3 dissolution at the deep sea floor abstract in situ benthic flux chamber measurements were performed at seafloor locations in the atlantic and pacific oceans where the bottomwaters were supersaturated approximately saturated and undersaturated with respect to calcite there was no evidence of significant dissolution at or above the saturation horizon below the saturation horizon however significant benthic fluxes of titration alkalinity and calcium out of the sediments were observed indicating appreciable dissolution where observed the rate of dissolution is consistent with a rate expression of reaction order 4 5 and a rate constant in the range of 0 05 to 0 5 per day a numerical simulation was constructed to represent organic matter and caco3 diagenesis at the seafloor at the supersaturated and near saturation sites the model over predicts the influence of metabolically produced co2 on the extent of caco3 dissolution it is possible that these results can be reconciled by a better understanding and parameterization of organic matter mineralization and porewater transport processes in surface sediments the primary factors to be considered include 1 the oxidation state of the carbon being oxidized 2 the vertical distribution of oxidation rates including the role of doc in sediment remineralization 3 the influence of nondiffusive transport of near surface porewaters and 4 the influence of episodic depositional events on organic and inorganic carbon cycling

calcium carbonate dissolution in deep sea sediments reconciling microelectrode pore water and benthic flux chamber results abstract we report the benthic fluxes of o2 titration alkalinity ta ca2 no3 po43 and si oh 4 from in situ benthic flux chamber incubations on the ceara rise and cape verde plateau and compare them to previously published results we find within analytical uncertainty that the ta flux is twice the calcium flux suggesting that dissolution precipitation of caco3 is the principal mechanism controlling benthic ta and ca2 fluxes at sites where the sediments contain significant 35 caco3 and the overlying waters are supersaturated with respect to caco3 the ratios of the total dissolution rate to the remineralization rate are significantly less than at all other study sites we propose that these observations can be explained by precipitation of fresh caco3 at the supersaturated sediment surface followed by redissolution deeper in the sediments because of metabolically produced co2 a numerical simulation is presented to demonstrate the feasibility of this explanation in addition surface exchange reactions in high caco3 sediments coupled with high rates of particle mixing may also impact rates of metabolic dissolution and depress chamber derived estimates of carbonate alkalinity and calcium benthic fluxes these results suggest that at supersaturated high caco3 locations previous models of sediment diagenesis may have overestimated the impact of metabolic dissolution on the preservation of caco3 deposited on the sea floor

the global ocean flux of particulate organic carbon areal distribution and magnitude the magnitude and distribution of the particulate organic carbon poc rain rate to the seafloor in the atlantic pacific and indian ocean basins between 61 n and 61 s has been estimated from benthic oxygen flux estimates for water depths 1000 m only the calculation utilizes the extensive data sets of sedimentary organic carbon caco3 and accumulation rate to extrapolate between individual benthic flux measurement sites using an empirically derived correlation between the seafloor oxygen flux and these parameters the poc flux through the 1000 m depth horizon was then estimated from published correlations between sediment trap determined fluxes and water depth total oxygen utilization in the deep ocean is estimated to be 1 2 1014 mol o2 yr 1 a value that agrees well with previous estimates which were based on surface water primary productivity sediment trap and depth relationships and with deep water respiration rates estimated from apparant oxygen utilization aou 14c relationships on the basis of the derived global ocean flux distribution it is concluded that 1 dissolved organic carbon doc inputs are not required to account for estimated deep water respiration rates 2 the majority of the poc input to the deep ocean occurs within 30 of the equator 3 the proportion of primary production that reaches the deep sea does not vary greatly with latitude 4 gyre and continental margin regions contribute roughly equally to the deep poc flux with a relatively minor contribution from the equatorial divergence region 5 of the estimated 7 2 1013 mol c yr 1 of poc that sinks below the 1000 m depth horizon 45 3 3 1013 mol c yr 1 reaches the seafloor where it is oxidized 6 when normalized to basin area average deep flux rates in the atlantic and pacific are similar while highest rates are observed in the indian ocean and 7 the results can be fully reconciled only if the benthic flux of doc is significantly less than the benthic o2 flux

glacial interglacial rain ratio changes implications for atmospheric co2 and ocean sediment interaction abstract a reduction of the carbonate carbon to organic carbon export rain ratio during glacial times has been advanced to explain the glacial interglacial atmospheric co 2 variations this hypothesis is tested and implications for the dynamics of sedimentary carbonate preservation and dissolution are explored with a multi box model mbm of the ocean carbon cycle fully coupled to a new transient early diagenesis model called medusa a peak reduction of the rain ratio by 40 at the last glacial maximum lgm was found to produce a net atmospheric p co 2 reduction of about 40 ppm changing shelf carbonate accumulation rates and continental weathering inputs produced a 55 60 ppm reduction the combination of the two mechanisms generates a p co 2 change of 90 95 ppm which compares well with the observed data however the resulting model sedimentary record does not conform to actual sedimentary records the changes related to continental shelf processes and variable weathering flux depress the calcite saturation horizon csh by about 1 km at the lgm if rain ratio variations are also considered that depression increases by another km in addition to this large amplitude for the csh possibly due to the adopted box model approach the changing rain ratio also leads to transition zone changes in the model sedimentary record that are opposite in phase with data based reconstructions realistic changes in the aragonite fraction of the carbonate rain were found to have only a minimal impact on atmospheric p co 2 finally chemical erosion of deep sea sediment was shown to reduce the amplitude of variation of the sedimentary ccd by about 10 20 it may provide a mechanism to improve the model data agreement

dissolution of calcite in deep sea sediments ph and o2 microelectrode results abstract we present microelectrode profiles of oxygen ph and porosity measured at in situ depth across the sediment water interface from stations above and below the calcite saturation horizon in the equatorial atlantic resistivity electrode data indicate that the diffusion coefficient for solutes is attenuated by nearly a factor of two within the top centimeter of the sediment lattice oxygen and porosity data are used to estimate that the organic carbon respiration rate of the sediment is 10 15 mol cm 2 yr 1 in these locations comparison of the ph data with numerical model results reveals that sedimentary calcite dissolves in response to respiration in the top few centimeters of sediment even above the saturation horizon we calculate that the effective in situ dissolution rate constant for calcite required to explain these data is the neighborhood of 10 100 d 1 although more data are needed to confirm this result it appears to be at least an order of magnitude less than the rate observed in laboratory stirred reactor experiments

thermochronological evidence for mesozoic tertiary tectonic evolution in the eastern sardinia apatite fission track analyses on samples from eastern sardinia document a complex tectonic history whose reconstruction is problematic because of the reactivation of faults and structures at different times from jurassic to miocene the oldest ages 150 154 ma have been detected on the southern margin of the gulf of orosei and are related to the extensional tectonics that characterize the european passive margin during early and middle jurassic times thermal modelling of these data allows reconstruction of the burial history of the mesozoic basin and estimation of a sedimentary thickness of 2000 m part of these sediments was eroded during the following uplift documented by mid cretaceous fission track ages a further exhumation episode of eocene age has been revealed by fission track data on granite samples and has been inferred to be related to the alpine orogenic phase this tectonic episode caused the exhumation of crustal blocks bound by faults that were finally reactivated during the late oligocene early miocene

extensional tectonics on sardinia italy insights into the arc back arc transitional regime although the tectonic features and stress regime typical for accretionary complexes and back arc domains have been widely documented so far few are known on the transitional zone separating these two systems here we report on structural analysis and anisotropy of magnetic susceptibility ams results from eocene pliocene sediments exposed in western sardinia from late oligocene to middle miocene the studied area was located between the alpine apennine wedge to the east which was undergoing shortening and accretion and the liguro provencal basin undergoing extension and spreading we find that prior to the formation of the liguro provencal basin the middle eocene lower oligocene sediments cropping out at the southwesternmost edge of sardinia were subjected to ne sw shortening in present day coordinates in agreement with recently reported geological information conversely the upper oligocene pliocene sedimentary sequences record a different evolutionary stage of extensional processes upper oligocene middle upper burdigalian sediments clearly show a n s oriented magnetic lineation that can be related to extensional direction along the prevalent e w oriented normal faults on the other hand no magnetic lineation has been detected in upper burdigalian serravallian sediments which mark the end of the first rifting process in sardinia which likely coincides with the rift to drift transition at the core of the liguro provencal basin finally a ne sw extension is observed in two tortonian pliocene sites at the northwestern margin of the nnw sse oriented campidano graben our study confirms that ams may represent a valuable strain trajectory proxy and significantly help to unravel the characters of temporally superimposed tectonic events

calcite dissolution in sediments of the ontong java plateau in situ measurements of pore water o2 and ph we present in situ electrode measurements of sediment resistivity pore water oxygen and pore water ph from three stations between 2300 and 3000 m depth on the ontong java plateau in the western equatorial pacific one of these stations is also the site of a concurrent benthic chamber incubation experiment jahnke et al 1994 the pore water oxygen data and a steady state diffusion and reaction model constrain the depth dependent rate of oxic respiration in the sediments and imply a diffusive flux of oxygen to the sediments of 10 21 mol cm 2 yr 1 given these respiration rates the pore water ph data cannot be explained without calcite dissolution driven by metabolically produced co2 the dissolution necessary to explain the observations quantified by a statistical approach is 3 5 6 mol cm 2 yr 1 which corresponds to at least 20 40 of the calcite rain to these sediments over 65 of the total dissolution is driven by metabolic co2 oxygen fluxes and net calcite dissolution constrained by the electrode data are compatible with the benthic chamber measurements of jahnke et al 1994 the dissolution flux while a significant part of the early diagenesis of calcite in these sediments is less than would be predicted by earlier models of dissolution and jahnke et al 1994 probably could not distinguish it from zero with the benthic chamber technique the dissolution rates found in this study are lower than previous estimates because the respiration reaction is concentrated near the sediment water interface and the calcite dissolution rate constants are very small the statistical evaluation of the pore water ph data and model constrain the calcite dissolution rate constant to 0 005 0 16 d 1 following the general trend of lower values determined by in situ techniques rather than by laboratory methods

can deep ocean carbonate preservation history inferred from atmospheric pco2 account for 14c and caco3 profiles on the ontong java plateau abstract bulk 14c and 210pbexcess measurements were made on box cores from water depths of 2300 and 4200 m from the equator on the ontong java plateau a sediment mixed layer thickness of approximately 6 cm and a mixing rate of 20 45 cm2 kyr are inferred from these radionuclide measurements and model simulations of their depth profiles using these sediment mixing characteristics the model is then forced with a deep sea carbonate preservation history derived from an ice core atmospheric pco2 record in order to examine whether the derived history can account for depth profiles of 14c age and caco3 content from the deep western equatorial pacific results show that 14c and caco3 data from the deep site can be simulated simultaneously with some success using the assumed carbonate preservation history and a time varying non carbonate flux function however the model is unable to use the same forcing functions to simulate the 14c and caco3 data from the shallower core these results suggest that local carbonate accumulation is not driven simply by generalized deep water carbonate chemistry inferred from atmospheric pco2 potentially important local processes and aspects of the model that may have contributed to the results are also discussed

the role of the global carbonate cycle in the regulation and evolution of the earth system we review one of the most ancient of all the global biogeochemical cycles and one which reflects the profound geochemical and biological changes that have occurred as the earth system has evolved through time that of calcium carbonate caco3 in particular we highlight a mid mesozoic revolution in the nature and location of carbonate deposition in the marine environment driven by the ecological success of calcareous plankton this drove the creation of a responsive deep sea sedimentary sink of caco3 the result is that biologically driven carbonate deposition provides a significant buffering of ocean chemistry and of atmospheric co2 in the modern system however the same calcifying organisms that under pin the deep sea carbonate sink are now threatened by the continued atmospheric release of fossil fuel co2 and increasing acidity of the surface ocean we are not yet in a position to predict what the impact on caco3 production will be or how the uptake of fossil fuel co2 by the ocean will be affected this uncertainty in the future trajectory of atmospheric co2 that comes from incomplete understanding of the marine carbonate cycle is cause for concern

the relationship between track shortening and fission track age reduction in apatite combined influences of inherent instability annealing anisotropy length bias and system calibration abstract the relationship between reduced track density 0 and reduced mean confined track length l l 0 during annealing has been studied for both spontaneous and induced tracks in four apatite samples with different chemical composition compositional range and origin and with spontaneous tracks giving mean confined track lengths varying from 14 5 m down to 12 3 m in all four apatites induced tracks show a relationship between l l 0 and 0 composed of two regions at higher values the two appear to be equal while at lower values l l 0 is greater than 0 this can be understood qualitatively in terms of the anisotropy of annealing and the bias against revelation of short tracks data from three apatites of uniform composition show near identical relationships in a sample showing a range of apatite compositions the point of divergence from the 1 1 relationship is somewhat higher than in the uniform composition apatites because individual grains anneal at different rates and the presence of highly annealed grains affects the track density more strongly than the mean track length spontaneous tracks show similar relationships to those observed for induced tracks in each sample when the data are renormalised to allow for the natural annealing present in the spontaneous tracks previous studies which led to the idea of length reduction without density reduction for spontaneous tracks did not renormalise density data as well as length data thereby distorting the apparent relationship data for the multi compositional apatite sample where annealing has taken place in geological conditions also agrees with the laboratory annealing data for both spontaneous and induced tracks this consistency suggests that a single process is responsible in all three cases implying that a laboratory based description of annealing can be applied to geological conditions with confidence recognition that spontaneous tracks in apatite are commonly annealed suggests that in general the fission track age should be interpreted as a reflection of both the time over which tracks have been retained and the distribution of etchable track lengths since the latter is a manifestation of the thermal history the fission track age should be interpreted in similar terms

exploring the dissolution effect on the intrashell mg ca variability of the planktic foraminifer globigerinoides ruber the mg ca ratio of the planktic foraminifer globigerinoides ruber is widely used for reconstructing past sea surface temperatures the shell mg ca ratio is also lowered by dissolution which results in lower sea surface temperature estimates in partially dissolved shells here we use an electron microprobe image mapping technique to map the intrashell variability of the mg ca ratio in g ruber white sensu stricto shells to explore changes in the intrashell mg ca ratio associated with dissolution we examine shells from shallow and deep cores ceara rise western tropical atlantic from the holocene and last glacial maximum that represent a preservational gradient image map results show that the mg ca ratio is highly variable both within a single shell and among samples obtained from the same sediment interval our results show that intrashell mg ca variability is retained in samples that have undergone dissolution quantitative analysis of the data from mg ca mapping suggests that preferential loss of high mg ca calcite alone cannot account for the difference in intrashell mg ca variability of shells from shallow and deep cores in both time periods rather the data imply that in g ruber analyzed in this study there is a loss of high mg ca ratios accompanied by a more uniform lowering of mg ca over the range of intershell mg ca variability of shells subjected to dissolution at the 1 m resolution of the microprobe analysis in this study

short term dissolution response of pelagic carbonate sediments to the invasion of anthropogenic co2 a model study 1 this study addresses the potential for and the quantification of dissolution of marine calcium carbonate caco3 sediments occurring on century timescales in response to the invasion of anthropogenic co2 it presents results obtained with the global biogeochemical model pisces interactively coupled to a global sediment model the latter represents the principal reactions involved in early diagenesis of biogenic opal caco3 and organic matter the model reproduces observed distributions of core top caco3 content and bottom water carbonate chemistry e g co32 starting from the climatological state a model experiment is carried out according to the standard cmip scenario of atmospheric pco2 increasing at a rate of 1 per year from 286 to 1144 ppm over a 140 year time period the invasion of anthropogenic co2 results in a strong decrease in bottom water co32 reaching 100 m in areas of deep water formation in the north atlantic and mode and intermediate water formation in the southern hemisphere the concomitant decrease in calcite saturation state of bottom waters drives the dissolution of caco3 the absolute caco3 content averaged over the top first centimeter decreases by up to 6 while the change in advection calculated at the base of the bioturbated layer 10 cm is indicative of net erosion the predicted changes in bottom water chemistry are discussed in terms of their potential impact on benthic communities

paleomagnetic data from late paleozoic dykes of sardinia evidence for block rotations and implications for the intra pangea megashear system paleomagnetic studies of dyke swarms from the variscan belt of europe can be used to reconstruct internal postorogenic rotations within the fold belt here we present paleomagnetic data from 13 late variscan dykes from sardinia ranging in age from 298 5 to 270 10 ma the dykes can be grouped on the basis of their different directions in strike in a northern a central eastern and a south eastern province paleomagnetic component directions have been obtained using thermal and alternating field demagnetization techniques which give reproducible results the paleomagnetic mean directions differ significantly between northern sardinia and south eastern and central eastern sardinia the latter two regions yielding statistically similar paleomagnetic mean directions these results indicate that sardinia fragmented into two arguably three crustal blocks after emplacement of the dykes which experienced differential relative rotations as is also indicated by the differences in overall strike directions the determination of timing sense and magnitude of these rotations has major implications for the reconstruction of the geodynamic evolution of the region in post carboniferous times we argue that the observed block rotations occurred during the permian as the result of post variscan intra pangea mobility possibly related to the transformation of an early permian pangea b to a late permian pangea a

interface dissolution control of the 14c profile in marine sediment abstract the process of carbonate dissolution at the sediment water interface has two possible endmember boundary conditions either the carbonate particles dissolve mostly before they are incorporated into the sediment by bioturbation interface dissolution or the vertical mixing is rapid relative to their extermination rate homogeneous dissolution in this study a detailed radiocarbon profile was determined in deep equatorial pacific sediment that receives a high rate of carbonate supply in addition a box model of sediment mixing was used to simulate radiocarbon carbonate content and excess thorium profiles that result from either boundary process following a dissolution increase results from homogeneous dissolution imply a strong very recent erosional event while interface dissolution suggests that moderately increased dissolution began about 10 000 years ago in order to achieve the observed mixed layer radiocarbon age increased homogeneous dissolution would concentrate a greater amount of clay and 230th than is observed while for interface dissolution the predicted concentrations are too small these results together with small discontinuities beneath the mixed layer in 230th profiles suggest a two stage increase in interface dissolution in the deep pacific the first occurring near the beginning of the holocene and the second more recently roughly 5000 years ago

the cause of the glacial to interglacial atmospheric co2 change a polar alkalinity hypothesis in an attempt to create a scenario for the cause of the glacial to interglacial co2 change recorded in air trapped in polar ice we call on an increase in the alkalinity of polar surface waters in this way we circumvent a major deficiency of the polar nutrient scenarios of sarmiento and toggweiler 1984 siegenthaler and wenk 1984 and knox and mcelroy 1984 namely our scenario does not require a drop in the nutrient content of polar surface waters in conformity with the demonstration by boyle 1988a b that the cadmium content of planktonic foraminifera from polar regions did not decrease from late glacial to holocene time the rise in alkalinity required by our model is a natural consequence of the demise during glacial time of north atlantic deep water as a major force in ocean circulation and of the nutrient maximum deepening of boyle 1988b rather than being original our hypothesis builds on the concept basic to the polar nutrient hypotheses namely that the co2 partial pressure in polar waters controls that for both the atmosphere and warm surface ocean it also requires the alkalinity increase in surface waters produced by boyle s nutrient deepening

reconstructing past particle fluxes in the tropical atlantic ocean using a research strategy analogous to modern sediment trap studies sediment accumulation patterns on submarine rises can be interpreted in terms of past ocean chemistry and circulation we have followed this research strategy to reconstruct the history of surface water productivity and deep water chemistry and circulation in the eastern equatorial atlantic sierra leone rise and western equatorial atlantic ceara rise during the last glacial maximum 18 000 b p on shallow sections of these rises at depths with little carbonate particle degradation we assume that the accumulation of skeletal carbonate approximates the carbonate production rate in surface water during the last glacial maximum the rate of carbonate productivity was lower in the eastern atlantic than it is today while the western atlantic exhibited no glacial interglacial difference in carbonate productivity based on the difference in carbonate accumulation rates between shallow and deep cores on the rises we observed greater dissolution in both basins during the last glaciation the eastern atlantic always had a lower rate of dissolution than the western atlantic despite having deep water with a lower 13c during the last glacial maximum organic carbon accumulation in the eastern atlantic increased with depth in the water column during the last glaciation suggesting that there was a bathymetric decrease in dissolved oxygen concentration at that time these observations are consistent with a glacial decrease in the production rate of northern source deep water during the last glaciation at that time the mixing zone between northern source and southern source deep water migrated to the north in the atlantic resulting in a greater proportion of corrosive southern source deep water in the western atlantic and entering the eastern atlantic through low latitude fracture zones today the ratio of northern and southern components entering the eastern atlantic is about 4 1 based on 13c and carbonate accumulation our best estimate of this ratio during the last glaciation is 1 1

modeling the calcite lysocline a numerical model of calcite dissolution in contact with sediment pore water is used to predict the depth and shape of the calcite lysocline in the deep sea model results are compared with lysocline data from 13 regions in the atlantic pacific and indian oceans the model lysocline shape is sensitive to the calcite dissolution rate constant the calcite organic carbon and refractory material rain rates and the rates of oxic versus anoxic organic carbon degradation in the sediment the model is able to reproduce the observed lysocline within the constraints of the sediment trap and calcite accumulation data using a calcite dissolution rate constant of 30 100 d 1 a molar ratio of organic carbon to calcite rain rates of 0 5 1 0 and an initial caco3 fraction of 90 excluding organic carbon this rate constant is consistent with microelectrode results presented by archer et al 1989 the model predicts that 30 50 of the calcite rain to the sea floor at the saturation horizon dissolves in response to organic carbon respiration consistent with previous modeling studies the range in the best fit value of the organic inorganic carbon rain rates arises from model sensitivity to uncertainty in the rate of anoxic carbon degradation in the sediment and in the rain rate of refractory material rather than from scatter in the data lysocline data from the western equatorial atlantic are anomalous to the rest of the data this anomaly may be explained by high rates of refractory material sedimentation from the amazon river

a novel determination of calcite dissolution kinetics in seawater we present a novel determination of the dissolution kinetics of inorganic calcite in seawater we dissolved 13 c labeled calcite in unlabeled seawater and traced the evolving 13 c composition of the fluid over time to establish dissolution rates this method provides sensitive determinations of dissolution rate which we couple with tight constraints on both seawater saturation state and surface area of the dissolving minerals we have determined dissolution rates for two different abiotic calcite materials and three different grain sizes near equilibrium dissolution rates are highly nonlinear and are well normalized by geometric surface area giving an empirical dissolution rate dependence on saturation state of rate g cm 2 day 7 2 0 6 10 4 1 3 9 0 1 this result substantiates the non linear response of calcite dissolution to undersaturation the bulk dissolution rate constant calculated here is in excellent agreement with those determined in far from equilibrium and dilute solution experiments plots of dissolution versus undersaturation indicates the presence of at least two dissolution mechanisms implying a criticality in the calcite seawater system finally our new rate determination has implications for modeling of pelagic and seafloor dissolution nonlinear dissolution kinetics in a simple 1 d lysocline model indicate a possible transition from kinetic to diffusive control with increasing water depth and also confirm the importance of respiration driven dissolution in setting the shape of the calcite lysocline

in situ measurements of calcium carbonate dissolution rates in deep sea sediments benthic fluxes of alkalinity carbon dioxide and oxygen have been measured using an in situ incubation chamber at three sites manop sites c and s and pacflux site sc in the central equatorial north pacific at two carbonate rich sites c and sc a budget for oxygen alkalinity and tco2 fluxes indicate a net caco3 dissolution rate of approximately 0 4 mmol m 2 day 1 this rate is only 20 of previous estimates but is consistent with a dissolution rate constant predicted from laboratory experiments with deep sea sediments and derived from in situ flux measurements in sediments of the southern california borderland organic matter oxidation in the sediment column provides the acid for 60 100 of the calcium carbonate dissolution occurring at these sites with the remainder derived from undersaturated bottom water at a low carbonate site s no carbonate dissolution in the sediment or on the sea floor is apparent although sediment traps indicate a rain of caco3 through 3400 m the rates of remineralization relative to resuspension or erosion at this site must differ for organic carbon and calcium carbonate so that carbonate grains reaching the sea floor are physically removed by erosion or resuspension before they dissolve while organic carbon is largely oxidized before it can be physically removed

revisiting diagenesis on the ontong java plateau evidence for authigenic crust precipitation in globorotalia tumida the calcite tests of foraminifera lie in marine sediments for thousands to millions of years before being analysed to generate trace element and isotope palaeoproxy records these sediments constitute a distinct physio chemical environment from the conditions in which the tests formed storage in sediments can modify the trace element and isotopic content of foraminiferal calcite through diagenetic alteration which has the potential to confound their palaeoceanographic interpretation a previous study of g tumida from the ontong java plateau western equatorial pacific found that preferential dissolution of higher mg chamber calcite and the preservation of a low mg crust on the tests significantly reduced whole test mg ca and sr ca brown and elderfield 1996 here we revisit these specimens with a combination of synchrotron x ray computed tomography sxct and electron probe micro analyses epma to re evaluate the nature of their diagenetic alteration the dissolution of higher mg calcite with depth was directly observed in the sxct data confirming the inference of the previous study the sxct data further reveal a thickening of the chemically and structurally distinct calcite crust with depth we propose that these crusts have a diagenetic origin driven by the simultaneous dissolution of high mg chamber calcite and precipitation of low mg crust from the resulting modified pore water solution while the breadth of the study is limited by the nature of the techniques the observation of both dissolution and re precipitation of foraminiferal calcite serves to demonstrate the action of two simultaneous diagenetic alteration processes with significant impacts on the resulting palaeoproxy signals

a data driven model of the global calcite lysocline gridded maps of sediment calcium carbonate calcite concentration and overlying water saturation state archer 1996 are combined with maps of benthic oxygen fluxes and sediment accumulation rates from jahnke 1996 and cweink 1986 to drive a diagenetic model of calcium carbonate preservation in deep sea sediments the only model input for which we cannot draw a detailed map is the rain rate of calcite to the seafloor so i use the model to calculate the calcite rain rate required to simulate the observed distribution of calcite concentration on the seafloor the predictive power of the model can be checked by searching for input parameters to which the model is sensitive and comparing the model requirements with independent data the model is sensitive to the ratio of organic carbon to calcite rain rates the rain ratio and within the constraint of pelagic sediment trap rain ratio data is unable to reproduce the calcite field without respiratory dissolution the promotion of calcium carbonate dissolution by the oxic degradation of organic carbon however relative to variability in sediment trap data the required model rain ratio is insensitive to the extent of anoxic respiration the stoichiometric ratio of o c during respiration the bioturbation rate the dissolution rate constant the effect of borate chemistry and small offsets in the saturation state for caco3 the model is sensitive to the accumulation rate of non caco3 material and predicts an atlantic pacific difference in non caco3 rain rate which is consistent with observations the model predicts that the dissolution flux of caco3 from sediments is 25 40 1012 mol yr 1 roughly half of the total deep sea caco3 dissolution rate estimated from the water column alkalinity distribution broecker and peng 1987 archer and maier reimer 1994 wollast 1994 the model also predicts that only 20 30 of the flux of caco3 to the seafloor globally escapes dissolution

the role of vertical chemical fractionation in controlling late quaternary atmospheric carbon dioxide the 30 decrease in atmospheric carbon dioxide during glacial maxima must be driven by some change in the chemical circulation of the ocean here a new model for late quaternary co2 variability is presented which resolves some problems occurring in previous models including the timing of carbon dioxide response and changes in the oxygen content of the deep ocean the primary driving factor in this model is a rearrangement of chemical distributions in the ocean whereby labile nutrients and metabolic co2 are concentrated in deep waters rather than in intermediate waters as observed in the modern ocean this new bottom heavy chemical structure does not affect atmospheric carbon dioxide directly instead co2 induced acidity lowers the deep ocean carbonate ion concentration and temporarily increases carbonate dissolution rates oceanic alkalinity then rises until the deep ocean carbonate ion is restored to its steady state value the resulting increase in oceanic alkalinity draws co2 out of the atmosphere into the ocean alkalinity and atmospheric co2 lag several thousand years behind the change in oceanic chemical structure this delayed response is determined by the limited rate of continental weathering and deep ocean carbonate dissolution relative to the oceanic alkalinity inventory it is proposed that characteristic deglacial and preglacial states of the ocean are leading factors driving glacial interglacial climate changes this concept reinterprets the carbon isotope contrast between surface water and deep waters 13c p b as due to a shift of light metabolic carbon from intermediate waters into deep waters the process is illustrated here by a simple equilibrium five box ocean model the observed intermediate depth nutrient depletion is not sufficient in itself to determine which of several possible mechanisms are operating and some mechanisms are not as effective in changing atmospheric co2 as others the largest response is seen from deepening the regeneration cycle of organic carbon the least response is seen from converting north atlantic deep water into intermediate water

an atlas of the distribution of calcium carbonate in sediments of the deep sea historical observations of the concentration of calcium carbonate in global deep sea sediments are compiled and compared with a new gridded field of seawater co3 concentration to reveal regional variations in the calcite lysocline the most obvious mode of variability of the calcite lysocline is the thickness of the lysocline defined here as the difference in overlying water carbonate saturation co3 between high and low calcite sediments with a thicker lysocline in the atlantic than in the pacific i attribute this variation to differences in the delivery rate of terriginous material a recent model for the lower glacial atmospheric pco2 proposed to change the relationship between the depth of the lysocline and the co3 of the water column by changing the rain rate ratio of organic carbon to calcite production the rain ratio model archer and maier reimer 1994 i search the data set for analogs to the proposed glacial world by looking for a link between the regional climate at the sea surface and the depth of the lysocline below the co3 at the carbonate compensation depth ccd in the tropics appears to be 10 20 mol kg 1 co3 more undersaturated than in high latitudes but this is smaller than the 40 mol kg 1 shift required by the model in addition the general resemblance of the glacial lysocline to the present day requires that the proposed shift in co3 at the ccd be globally uniform rather than locally variable as climate forcing would probably generate i conclude that the rain ratio model would probably require some globally uniform perturbation during glacial time such as a change in ocean si content if it is to explain the entire pco2 decrease observed in the glacial atmosphere finally i grid the sedimentary data to estimate that the inventory caco3 which is available to neutralize fossil fuel co2 is approximately 1600 gt carbon a quantity which may be exceeded by fossil fuel release in the next several centuries

geological controls on the coal quality of the mequinenza subbituminous coal deposit northeast spain abstract the results of geological petrographical geochemical and mineralogical studies performed to determine the coal forming paleo environmental conditions which gave rise to anomalous enrichments in organic sulphur molybdenum and uranium in the oligocene mequinenza subbituminous coal deposit of northeastern spain are summarized this paper demonstrates the major influence exerted by the paleohydrology of the depositional framework on the early diagenetic evolution of the precursor peat deposits the s mo and u enrichments the preservation of aragonite and chlorophillinite and the high degree of gelification of the mequinenza coal are a consequence of alkaline syngenetic conditions in the depositional environment similar conditions can be inferred for many mesozoic and tertiary coal deposits in the mediterranean region mallorca sardinia hungary bulgaria serbia greece and turkey however the source of sulphur may have been different and have included triassic and early jurassic sulphate recycling scenarios or volcanic sources whatever the source sulphur enrichment is always influenced by the alkaline depositional environments developed in basins generated during the alpine cycle in circum mediterranean mobile belts

variability of apatite fission track annealing kinetics ii crystallographic orientation effects a method is presented that permits the length of any horizontal confined fission track inclined at a specified angle to the crystallographic c axis in apatite to be converted to an equivalent track length parallel to the crystallographic c axis the model is based on the results of annealing experiments for six selected apatites five calcian fluorapatites and durango apatite representing a subset of the 15 total apatite specimens studied an iterative process of calculation is required to project fission track lengths onto the c axis and computer source code implementing the solution to this problem is presented this method of projecting apatite fission track lengths onto the crystallographic c axis is shown to remove effectively fission track length variation within single fission track populations due to anisotropic track length reduction for all 15 apatites studied in addition a model is developed that offers predictions that closely reproduce published experimental data concerning the relationship between fission track density etched fission tracks per unit area of apatite surface and the arithmetic mean fission track length finally it is shown that natural fission track populations exhibit fission track length anisotropy similar to that of fission track populations created and annealed in the laboratory this observation implies that the same process by which apatite fission tracks anneal in the laboratory is responsible for annealing of apatite fission tracks in the geological environment

the radiocarbon age of calcite dissolving at the sea floor estimates from pore water data abstract we measured the radiocarbon content and stable isotopic composition of pore water and bottom water co2 sedimentary organic carbon and caco3 at two sites on the ceara rise one underlying bottom water that is supersaturated with respect to calcite site b the other underlying undersaturated bottom water site g the results were combined with pore water o2 co2 and ca2 profiles martin and sayles 1996 to estimate the radiocarbon content of the caco3 that is dissolving in the sediment mixed layer at site g the caco3 that is dissolving in the upper 2 cm of the sediments is clearly younger richer in 14c than the bulk sedimentary caco3 indicating that nonhomogeneous caco3 dissolution occurs there the case for nonhomogeneous dissolution is much weaker at the site underlying supersaturated bottom water the results indicate that nonhomogeneous dissolution occurs in sediments underlying undersaturated bottom water that the dissolution is rapid relative to the rate of homogenization of the caco3 in the mixed layer by bioturbation and that the dissolution rate of caco3 decreases as it ages in the sediment mixed layer the results support the hypothesis based on solid phase analyses that the preferential dissolution of young i e radiocarbon rich caco3 leads to a pattern of increasing radiocarbon age of mixed layer caco3 as the degree of undersaturation of bottom water increases keir 1984 broecker et al 1991

respiration dissolution and the lysocline 1 here i synthesize the results of several types of measurements of organic carbon respiration and calcium carbonate dissolution rates in pelagic seafloor sediments measurements of pore water oxygen demonstrate that most of the respiration takes place very near the sediment water interface with a scale depth of a few millimeters the remainder of the oxic respiration occurs much deeper in the sediments with a scale depth of several centimeters all measures of respiration from locations as disparate as the tropical pacific and atlantic and the subtropical north atlantic agree that pelagic seafloor rates of oxic respiration of organic carbon are relatively independent of depth and location with the exception of sediments beneath the pacific eastern equatorial upwelling zone calcite dissolution in seafloor sediments requires forcing by respiration produced co2 and rates are consistent with a first order dependence on pore water undersaturation solubility as determined by mucci 1983 at atmospheric pressure and locally variable mass specific dissolution rate constants respiration driven calcite dissolution fluxes predicted by this combination of respiration and dissolution rate expressions are significantly lower than many previous estimates comparison of dissolution fluxes in the oligotrophic open ocean measured by other researchers with benthic chamber incubation techniques with those predicted by this combination of rate expressions is within stated uncertainties in agreement in all but one case questioning the need for complicated mechanisms such as surface buffering or authigenic precipitation to explain seafloor calcite diagenesis applying these kinetics to a simple one dimensional steady state model of the bulk calcite content and sediment accumulation rates of the sediment mixed layer yields results consistent with observations of the seafloor lysocline the region of transition from high calcite to low calcite sediments on the ceara rise in the western tropical north atlantic and the ontong java plateau in the western equatorial pacific scenarios ignoring dissolution driven by respiration produced co2 in pore waters and using the high order dependence on undersaturation and very large dissolution rate constants implied by some earlier laboratory studies do not simulate these observations while the scheme represented here does in fact imply a strong shift in the locus of carbonate dissolution toward the sediment water interface as bottom water saturation decreases as implied by the observations of martin et al 2000 no simple combination of sediment transport coefficients and reaction kinetics can reproduce the observation of increasing 14c age as dissolution progresses these results emphasize the importance of accurate knowledge of the kinetics of respiration and dissolution to interpretation of either the present day or paleolysocline

factors controlling the flux of organic carbon to the bathypelagic zone of the ocean 1 particle fluxes measured with time series sediment traps deployed below 2000 m at 68 sites in the world ocean are combined with satellite derived estimates of export production from the overlying water to assess the factors affecting the transfer of particulate organic matter from surface to deep water multiple linear regression is used to derive an algorithm suggesting that the transfer efficiency of organic carbon defined as the settling flux of organic carbon normalized to export production increases with the flux of carbonate and decreases with water depth and seasonality the algorithm predicts 80 of the organic carbon transfer efficiency variability in diverse oceanic regions the influence of the carbonate flux suggests that the ballasting effect of this biogenic mineral may be an important factor promoting export of organic carbon to the deep sea by increasing the density of settling particles however the lack of a similar effect for biogenic opal suggests that factors other than particle density also play a role the adverse effect of increasing seasonality on the transfer efficiency of carbon to the deep sea is tentatively attributed to greater biodegradability of organic matter exported during bloom events in high latitude opal dominated regions with high f ratios and seasonality while a higher fraction of net production is exported a higher fraction of the exported organic matter is remineralized before reaching bathypelagic depths on the other hand in warm low latitude carbonate dominated regions with low f ratios and seasonality a higher fraction of the exported organic matter sinks to the deep sea

effects of seafloor and laboratory dissolution on the mg ca composition of globigerinoides sacculifer and orbulina universa tests a laser ablation icpms microanalysis perspective article i nfo partial or selective dissolution of planktonic foraminiferal tests on the seafloor has been shown to alter original test mg ca compositions and thus may limit the accuracy of mg ca based thermometry for reconstructions of past sea surface temperatures we have employed laser ablation icpms to determine the extent of dissolution caused changes in mg ca distribution across individual chamber walls of the planktonic foraminifera globigerinoides sacculifer and orbulina universa g sacculifer samples collected from a core top depth transect in the ne indian ocean and laboratory dissolution experiments show little if any evidence of preferential removal of mg rich calcite layers by progressive dissolution of the tests we attribute the absence of selective dissolution to the banded distribution of mg across the chamber walls of these foraminiferal species and to the minimal presence of calcite crusts with relatively low mg composition on the outer surfaces of tests mg ca microanalyses of g sacculifer from core top samples further indicate that for samples collected above the calcite lysocline the effect of postdepositional dissolution on mg ca sample mean values is minimal and within the uncertainty of mg ca thermometry i e 0 4 mmol mol 0 8 c at 28 c comparison with previously published results for g sacculifer supports these observations simple modelling of g sacculifer test dissolution indicates that selective removal of calcite with high mg ca values from within the final chamber of g sacculifer test appears insufficient to cause the 10 decrease in mg ca values observed above calcite lysocline these changes in test composition might be related to development removal as a function of co3 2 of a thin diagenetic surface coating which has a relatively high mg ca

equatorial pacific calcite preservation cycles production or dissolution in the equatorial pacific ocean the depth and shape of the calcite lysocline appears to have changed significantly in response to climate forcing farrell and prell 1989 taking the farrell and prell record at face value the lysocline apparently became steeper during each of the last eight glacial stages also the accumulation rate of calcite during the last glacial maximum was 2 4 times higher than it was during the previous interglacial arrhenius 1952 1988 broecker 1971 farrell 1991 a numerical model for calcite dissolution in sediment is used to interpret these observations the model was validated by comparison with observations from the present day ocean these results are presented elsewhere if the lysocline fluctuations in the equatorial pacific are primarily a dissolution record then changes in the glacial pacific co3 of 20 40 m can be inferred here i offer the alternative explanation that cycles in equatorial production are responsible for the observations higher rates of calcite and organic carbon rain to the sediment in the equatorial region would have depressed the calcite lysocline and increased the calcite accumulation rate as observed a twofold increase in glacial production appears to be adequate to explain the observations but a precise determination is prevented by uncertainties in some of the model parameters

understanding the causes and consequences of past marine carbon cycling variability through models abstract on geological time scales the production and degree of recycling of biogenic carbon in the marine realm and ultimately its removal to sediments exerts a dominant control on atmospheric co 2 and hence variability in climate this is a highly complex system involving a myriad of inter connected biological chemical and physical processes for this reason alone linking observations often highly abstracted in the form of proxies to the primary processes involved and ultimately to explanatory hypotheses for specific geological events and transitions is challenging the past few decades have seen a progressive improvement in theoretical and process based understanding of the various components that make up the marine carbon cycle and hand in hand with this the development of numerical model representations of the complete system models have also been designed and or adapted with paleoclimate questions in mind and applied to quantitatively explore the role of the marine carbon cycle in both perturbations and long term geologic evolutionary trends in global climate and possible feedbacks between them however we must ask whether paleoclimate models incorporate sufficiently appropriate representations of the dynamics and sensitivities of the marine carbon cycle and indeed whether in the geological context we really know what these dynamics are here we provide a comprehensive overview of how marine carbon cycling and the biological carbon pump is treated in available paleoclimate models with the aim of critically evaluating their ability to help interpret past marine carbon cycle and climate dynamics to this end we first provide an overview of commonly used paleoclimate models and some of their associated paleo applications drawing from a wide range of global carbon cycle box models and earth system models of intermediate complexity emics secondly we review and evaluate the three dominant processes involved in the cycling of organic and inorganic carbon in the marine system and how they are represented in models namely biological productivity at the ocean surface remineralisation dissolution of particulate carbon within the water column and the benthic pelagic coupling at the seafloor we generate and employ illustrative examples using the model genie to show how different parameterisations of water column and sediment processes can lead to significantly different model projections our compilation reveals the prevalence of static parameterisations of marine carbon cycling among existing paleoclimate models which are commonly empirically derived from present day observations although such approaches tend to represent carbon transfer in the modern ocean well they are potentially compromised in their ability to reflect the true degree of freedom and strength of feedbacks with respect to past climate events particularly those characterised by environmental boundary conditions that differ fundamentally from today finally we discuss the importance of using models of different complexities and how questions of model uncertainty may start to be addressed

deepwater carbonate ion concentrations in the western tropical pacific since 250 ka evidence for oceanic carbon storage and global climate influence we present new size normalized weight snw co32 core top calibrations for three planktonic foraminiferal species and assess their reliability as a paleo alkalinity proxy snws of globigerina sacculifer and neogloboquadrina dutertrei can be used to reconstruct past deep pacific co32 whereas snws of pulleniatina obliquiloculata are controlled by additional environmental factors based on this methodological advance we reconstruct snw based deepwater co32 for core wp7 from the western tropical pacific since 250 ka secular variation in the snw proxy documents little change in deep pacific co32 between the last glacial maximum and the holocene further back in time deepwater co32 shows long term increases from marine isotope stage mis 5e to mis 3 and from early mis 7 to late mis 6 consistent with the coral reef hypothesis that the deep pacific ocean carbonate system responded to declining shelf carbonate production during these two intervals during deglaciations we have evidence of co32 peaks coincident with terminations 2 and 3 which suggests that a breakdown of oceanic vertical stratification drove a net transfer of co2 from the ocean to the atmosphere causing spikes in carbonate preservation i e the deglacial ventilation hypothesis during mis 4 a transient decline in snw based co32 along with other reported co32 and or dissolution records implies that increased deep ocean carbon storage resulted in a global carbonate dissolution event these findings provide new insights into the role of the deep pacific in the global carbon cycle during the late quaternary

microelectrode studies of organic carbon degradation and calcite dissolution at a california continental rise site fine scale porewater profiles of resistivity o2 ph and pco2 were measured in situ with microelectrodes at a site on the california continental rise they are reported here with more traditional measurements of shipboard porewater no3 alkalinity and tco2 and sediment organic c and caco3 profiles a numerical model encompassing diffusion advection and multiple reaction terms is applied to these data to characterize organic carbon degradation and caco3 dissolution processes near the sediment water interface a benthic o2 flux of 58 mol cm 2 yr 1 over the top 1 mm sediment is estimated based on one measured sub mm depth scale o2 profile the numerical model indicates that this high o2 consumption rate is related to a very labile fraction of organic c which has a degradation rate constant of approximately 4 5 10 8 s 1 1 4 yr 1 and which is not mixed downward by biological mixing seasonality in the benthic o2 consumption rate of this site may be attributed to variations in the input rate of this highly labile organic c degradation rate constants of the bulk organic c by oxygen reduction and by nitrate reduction are estimated to be about the same 1 10 9 s 1 the organic c rain rate responsible for the bulk organic c is estimated to be 53 mol cm 2 yr 1 this estimate exceeds the average rain rate determined by sediment trap collections at this site saturation state profiles calculated from the in situ ph and pco2 data and from modelling the in situ o2 and ph data both indicate that the porewater is undersaturated with respect to calcite to a depth of at least 8 cm the dissolution rate constant of calcite in this caco3 poor station is determined to be 5 10 day 1 assuming the reaction order is 4 5 which is close to the minimum estimates for environments richer in calcite a uniform calcite dissolution rate constant therefore may be adequate for representing carbonate dissolution in global scale models of ocean chemistry

detrital fission track analysis and sedimentary petrofacies as keys of alpine exhumation the example of the venetian foreland european southern alps italy sedimentary petrography and detrital apatite fission track analysis of sediments from the oligo miocene venetian foreland succession ne italy reveal a multi stage evolution of the alpine source areas during the first stage of sedimentation chattian to langhian the foreland basin was filled by sediments derived from erosion of mainly crystalline austroalpine units exhumed north of the periadriatic lineament these sediments are characterized by litharenites with mean quartz content of about 61 and by a mean detrital apatite fission track peak of about 30 ma the permian paleogene sedimentary cover of the southalpine crystalline basement dolomite region was bypassed by the sediments and made only a minor input from the serravallian onwards the foreland basin was incorporated into the southalpine thrust belt the compressional events of the valsugana phase resulted in thrusting and uplift of the southalpine domain as documented by tortonian fission track ages in the hanging wall of the major regional thrust valsugana thrust fault the southalpine crystalline basement unaffected by alpine metamorphism and its sedimentary cover became the main source of sediments as revealed by the increase in extrabasinal carbonate grains and detrital apatite grains with late triassic jurassic fission track ages during this final stage of basin evolution about 3000 m of sediments were deposited these strata subsequently have been uplifted and eroded since the pliocene indicating a southward migration of the alpine deformation front

caco3 size distribution a paleocarbonate ion proxy lysocline reconstructions play an important role in scenarios purporting to explain the lowered atmospheric co2 content of glacial time these reconstructions are based on indicators such as the caco3 content the percent of coarse fraction the ratio of fragments to whole foraminifera shells the ratio of solution susceptible to solution resistant species and the ratio of coarse to fine caco3 all assume that changes with time in the composition of the input material do not bias the result however as the composition of the input material does depend on climate none of these indicators provides an absolute measure of the extent of dissolution in this paper we evaluate the reliability of the ratio of 63 m caco3 to total caco3 as a dissolution indicator we present here results that suggest that in today s tropics this ratio appears to be determined solely by co3 ion concentration and water depth i e the saturation state of bottom waters this finding offers the possibility that the size fraction index can be used to reconstruct co3 ion concentrations for the late quaternary ocean to an accuracy of 5 mol kg 1

burial and exhumation of corsica france in the light of fission track data 1 the mesozoic and cenozoic exhumation and cooling history of corsica is reconstructed by fission track ft data on basement and sedimentary rocks apatite ages are 105 16 ma zircon ages are 160 145 ma the jurassic and cretaceous ages show that parts of the variscan basement escaped alpine influence the basement was thermally affected by rifting prior to jurassic opening of the ligurian piedmont ocean then it cooled to near surface temperatures in paleocene eocene times subduction buried parts of the basement and overlying flysch to greater depth in the oligocene both collapse of the nappe stack and rifting prior to opening of the ligurian provencal basin affected the apatite ft system of the basement in different partly overlapping areas causing a complex age pattern the study shows that thorough analysis of ft data and thermal modeling allow to assign age populations to distinct cooling processes even when several thermotectonic events contributed to generate an intricate age pattern

pseudo dissolution of marine calcite abstract an enigma exists regarding observations aimed at determining the extent of calcite dissolution on the ceara rise in the western equatorial atlantic based on pore water gradients for ca alkalinity ph 13 c and 14 c a strong case can be constructed that at a depth of 3 3 km about 30 of the calcite rain dissolves martin and sayles geochim cosmochim acta 60 1996 243 263 hales and emerson geochim cosmochim acta 61 1997 501 514 martin et al geochim cosmochim acta 61 2000 1391 1404 however benthic chambers deployed at this site record no ca or alkalinity flux jahnke and jahnke geochim cosmochim acta 2002 in press further there is no evidence for shell weight loss or shell breakup between 2 8 and 4 1 km water depth on the ceara rise broecker and clark global geochem cycles 2002 in press a possible scenario which accounts for all but the 14 c observations martin et al geochim cosmochim acta 61 2000 1391 1404 is that coatings formed on the calcite are stirred downward into the respiration co 2 rich core top mixed layer and there redissolve we term this phenomenon pseudo dissolution

spatial variability of surface sediment porewater ph and related water column characteristics in deep waters of the northern south china sea abstract this study analyzes the ph of surface sediment porewater i e 2 3 cm below the water sediment interface and concentrations of caco3 and organic carbon oc in 1192 sediment cores from the northern south china sea in water depths ranging from 137 to 3702 m this is the first study in the literature to analyze the large scale spatial variability of deep water surface sediment ph over a large ocean basin the data showed strong spatial variations in ph the lowest ph values

cenozoic denudation of corsica in response to ligurian and tyrrhenian extension results from apatite fission track thermochronology 1 the island of corsica france occupies a unique position in the western mediterranean since it has recorded both the cenozoic alpine orogenic history of the area as well as subsequent extensional collapse and oceanic basin formation we present 41 new apatite fission track aft ages and 23 measurements of track length distributions from corsica in order to elucidate its cenozoic thermal and morphological evolution aft ages vary from 10 5 0 8 ma to 53 8 4 1 ma and form a clear spatial pattern oldest ages are encountered in the southwest of the island with a broad band of ages between 20 and 30 ma running across the mountainous central area and ages 20 ma confined to the eastern half of the island samples along the western and northwestern coasts record kilometer scale erosional denudation linked to rifting in the ligurian provencal basin whereas samples from close to the extensionally inverted alpine deformation front record a later cooling phase related to tyrrhenian extension the eastward younging pattern of aft ages suggests the migration of a wave of erosional denudation from west to east across the island apparently controlled by the migrating locus of extension our aft data therefore support models of mediterranean extension controlled by slab roll back

the dissolution kinetics of major sedimentary carbonate minerals abstract among the most important set of chemical reactions occurring under near earth surface conditions are those involved in the dissolution of sedimentary carbonate minerals these minerals comprise about 20 of phanerozoic sedimentary rocks calcite and to a significantly lesser extent dolomite are the major carbonate minerals in sedimentary rocks in modern sediments aragonite and high magnesian calcites dominate in shallow water environments however calcite is by far the most abundant carbonate mineral in deep sea sediments an understanding of the factors that control their dissolution rates is important for modeling of geochemical cycles and the impact of fossil fuel co 2 on climate diagenesis of sediments and sedimentary rocks it also has practical application for areas such as the behavior of carbonates in petroleum and natural gas reservoirs and the preservation of buildings and monuments constructed from limestone and marble in this paper we summarize important findings from the hundreds of papers constituting the large literature on this topic that has steadily evolved over the last half century our primary focus is the chemical kinetics controlling the rates of reaction between sedimentary carbonate minerals and solutions we will not attempt to address the many applications of these results to such topics as mass transport of carbonate components in the subsurface or the accumulation of calcium carbonate in deep sea sediments such complex topics are clearly worthy of review papers on their own merits calcite has been by far the most studied mineral over a wide range of conditions and solution compositions in recent years there has been a substantial shift in emphasis from measuring changes in solution composition to determine batch reaction rates to the direct observation of processes occurring on mineral surfaces using techniques such as atomic force microscopy afm however there remain major challenges in integrating these two very different approaches a general theory of surface dissolution mechanisms currently lacking although see lasaga and luttge science 291 2001 2400 is required to satisfactorily relate observations of mineral surfaces and the concentration of dissolved components studies of aragonite high magnesian calcites magnesite and dolomite dissolution kinetics are much more limited in number and scope than those for calcite and provide at best a rather rudimentary understanding of how these minerals are likely to behave in natural systems although the influences of a limited number of reaction inhibitors have been studied probably the greatest weakness in application of experimental results to natural systems is understanding the often profound influences of foreign ions and organic matter on the near equilibrium dissolution kinetics of carbonate minerals

core top 14c ages as a function of latitude and water depth on the ontong java plateau radiocarbon measurements on core tops from the ontong java plateau confirm a previous finding by berger and killingley 1982 that at any given water depth cores taken on the equator have higher accumulation rates and younger core top ages than their off equator counterparts further these new results fortify the conclusion by broecker et al 1991 that the increase in core top radiocarbon age with water depth rules out homogeneous dissolution within the pore waters as the dominant mechanism either most of the dissolution must occur prior to burial or it must occur during the first pass through the respiration co2 rich upper pore waters after which the calcite grains become armored against further dissolution a puzzling aspect of this new data set is that despite the sizable difference in accumulation rate the extent of dissolution as measured by either the caco3 content or the ratio of caco3 in the 150 m size fraction to that in the 63 m fraction is no different off than on the equator in order to reconcile the results of this study with those obtained by hales and emerson 1996 using in situ electrodes it is necessary to call upon calcite armoring

box cores from the equatorial pacific 14c sedimentation rates and benthic mixing abstract carbon 14 determinations on box cores of calcareous ooze from the western and eastern equatorial pacific suggest that patterns of mixed layer ages sedimentation rates and mixed layer thicknesses are controlled by gradients of carbonate dissolution and fertility and by small scale redeposition processes mixed layer ages range from 3000 to 7000 years with a mode between 4000 and 5000 years sedimentation rates range from 0 8 to 2 4 cm 1000 years mixed layer depths calculated according to the box model of mixing range from 7 cm to 16 cm observed thicknesses are about one fourth smaller than calculated ones

global calcite cycling constrained by sediment preservation controls 1 we assess the global balance of calcite export through the water column and burial in sediments as it varies regionally we first drive a comprehensive 1 d model for sediment calcite preservation with globally gridded field observations and satellite based syntheses we then reformulate this model into a simpler five parameter box model and combine it with algorithms for surface calcite export and water column dissolution for a single expression for the vertical calcite balance the resulting metamodel is optimized to fit the observed distributions of calcite burial flux we quantify the degree to which calcite export saturation state organic carbon respiration and lithogenic sedimentation modulate the burial of calcite we find that 46 of burial and 88 of dissolution occurs in sediments overlain by undersaturated bottom water with sediment calcite burial strongly modulated by surface export relative to organic carbon export we find surface calcite export skewed geographically toward relatively warm oligotrophic areas dominated by small prokaryotic phytoplankton we assess century scale projected impacts of warming and acidification on calcite export finding high sensitive to inferred saturation state controls with respect to long term glacial cycling our analysis supports the hypothesis that strong glacial abyssal stratification drives the lysocline toward much closer correspondence with the saturation horizon our analysis suggests that over the transition from interglacial to glacial ocean a resulting 0 029 pgc a 1decrease in deep atlantic indian and southern ocean calcite burial leads to slow increase in ocean alkalinity until pacific mid depth calcite burial increases to compensate

the influence of caco3 dissolution on core top radiocarbon ages for deep sea sediments radiocarbon ages on caco3 from deep sea cores offer constraints on the nature of the caco3 dissolution process the idea is that the toll taken by dissolution on grains within the core top bioturbation zone should be in proportion to their time of residence in this zone if so dissolution would shift the mass distribution in favor of younger grains thereby reducing the mean radiocarbon age for the grain ensemble we have searched in vain for evidence supporting the existence of such an age reduction instead we find that for water depths of more than 4 km in the tropical pacific the radiocarbon age increases with the extent of dissolution we can find no satisfactory steady state explanation and are forced to conclude that this increase must be the result of chemical erosion the idea is that during the holocene the rate of dissolution of caco3 has exceeded the rain rate of caco3 in this circumstance bioturbation exhumes caco3 from the underlying glacial sediment and mixes it with caco3 raining from the sea surface