enhanced riverine carbon flux from carbonate catchment to the ocean a comparative hydrogeochemical study on ishigaki and iriomote islands southwestern japan 1 riverine carbon transportation is an important carbon flux connecting reservoirs of the atmosphere continents and oceans the flux is strongly related to the important roles of rivers such as regulation of climate change and buffering of ocean acidification here to evaluate the linkage of such functions of rivers and geological characteristics of the watersheds we present the results of a comparative hydrogeochemical study conducted on small subtropical watersheds of aluminosilicate dominated iriomote island and carbonate based ishigaki island southwestern japan rivers on ishigaki island exhibited much higher alkalinity than rivers on iriomote island which was even higher than the mean value of major rivers in the world such as the saint lawrence and the mississippi this high alkalinity was the result of carbonate dissolution enhanced by soil originated co2 as a result of this high inorganic carbon input the ratio of inorganic carbon and nutrients of the river water was higher than that of marine organic matter such as the redfield ratio making the coastal seas a potential source of co2 for the atmosphere

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

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

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

evidence for stable sr isotope fractionation by silicate weathering in a small sedimentary watershed in southwestern taiwan abstract radiogenic sr isotopes 87 sr 86 sr are robust for provenance identification in hydrology affected mainly by the age of background lithologies and the degree of chemical weathering however there is limited knowledge concerning the fractionation mechanism of stable sr isotopes 88 sr 86 sr in rivers in this study river water was collected on a weekly to monthly basis throughout dry and wet seasons furthermore to study the variations of radiogenic and stable sr isotopes during intense weathering a major flooding event 2000 mm precipitation in three days typhoon morakot water was captured within a small drainage catchment system 161 km 2 along the hou ku river in southwestern taiwan for a better constraint on the end member compositions bedload sediments suspended particles and several host rocks were sampled for a systematic investigation the carbonate and silicate phases of these solids were chemically separated dissolved major elements indicate that the watersheds were predominated by silicate weathering stable sr isotopes show no significant variation 88 sr 0 24 0 31 temporally and spatially with an average of 0 28 additionally all solids showed lower 88 sr values than the river water while the host rocks had higher 88 sr values 88 sr 0 20 0 26 than the residual weathering products 88 sr 0 08 0 22 indicating preferential leaching of heavy sr into the hydrosphere and leaving light sr in the residual solids results of laboratory acid leaching experiments reveal that dissolution of high 88 sr value minerals occurred at an early stage of weathering the variation of weathering intensity does not alter stable sr isotopes in silicate weathering dominated river water which contains higher stable sr isotopes than the associated sediments the silicatic sedimentary rocks preferentially released higher stable sr isotopes into the hydrosphere during chemical weathering thus leaving lower stable sr isotopes in the residual solids

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

onset and ending of the late palaeozoic ice age triggered by tectonically paced rock weathering the onset of the late palaeozoic ice age about 340 million years ago has been attributed to a decrease in atmospheric co2 concentrations associated with expansion of land plants as plants both enhance silicate rock weathering which consumes co2 and increase the storage of organic carbon on land however plant expansion and carbon uptake substantially predate glaciation here we use climate and carbon cycle simulations to investigate the potential effects of the uplift of the equatorial hercynian mountains and the assembly of pangaea on the late palaeozoic carbon cycle in our simulations mountain uplift during the late carboniferous caused an increase in physical weathering that removed the thick soil cover that had inhibited silicate weathering the resulting increase in chemical weathering was sufficient to cause atmospheric co2 concentrations to fall below the levels required to initiate glaciation during the permian the lowering of the mountains led to a re establishment of thick soils whilst the assembly of pangaea promoted arid conditions in continental interiors that were unfavourable for silicate weathering these changes allowed co2 concentrations to rise to levels sufficient to terminate the glacial event based on our simulations we suggest that tectonically influenced carbon cycle changes during the late palaeozoic were sufficient to initiate and terminate the late palaeozoic ice age the late palaeozoic was characterized by glacial cycles numerical simulations suggest that increased silicate weathering due to mountain uplift and soil removal caused atmospheric co2 to fall below the threshold for glaciation

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

glacial interglacial variation in catchment weathering and erosion paces the indian summer monsoon during the pleistocene abstract silicate weathering via co2 consumption is considered to regulate the long term climate change discriminating silicate versus carbonate weathering from sedimentary records is helpful to understand the coupling relationship between weathering and past climate however owing to the paucity of well dated and continuous records of weathering and erosion the relationship between silicate and carbonate weathering and their links with mountain uplift and glacial interglacial climate remain elusive geochemical analysis of a 666 m core from the heqing basin a paleolake situated at the southeastern margin of the tibetan plateau demonstrates silicate versus carbonate weathering and erosion changes under indian summer monsoon ism conditions spanning the entire pleistocene via respective tracing between rb sr and al na ratios the rb sr record is interpreted as reflecting a competition between clayey silicate origin rb versus carbonate origin sr fluxes whereas al na ratio is a balance between weathering and erosion of silicate minerals both pacing the glacial interglacial cycles of the ism during interglacials strong silicate weathering intensity reflected by low al na values is mainly controlled by warmer temperatures with the reduced variability during 1 82 0 92 ma recalling the pacing of the arabian sea surface temperature amplitudes within glacials the weak carbonate leaching and clay erosion within the older and younger intervals are interrupted by strong clay erosion within the middle interval in conclusion the heqing rb sr and al na records reveal the sensitivity of catchment weathering and erosion to ism changes over glacial interglacial timescales with warmer temperature enhancing silicate weathering and clay formation during interglacials and greater physical erosion during glacials

erosion of deccan traps determined by river geochemistry impact on the global climate and the 87sr 86sr ratio of seawater abstract the impact of the deccan traps on chemical weathering and atmospheric co2 consumption on earth is evaluated based on the study of major elements strontium and 87sr 86sr isotopic ratios of the main rivers flowing through the traps using a numerical model which describes the coupled evolution of the chemical cycles of carbon alkalinity and strontium and allows one to compute the variations in atmospheric pco2 mean global temperature and the 87sr 86sr isotopic ratio of seawater in response to deccan trap emplacement the results suggest that the rate of chemical weathering of deccan traps 21 63 t km2 yr and associated atmospheric co2 consumption 0 58 2 54 106 mol c km2 yr are relatively high compared to those linked to other basaltic regions our results on the deccan and available data from other basaltic regions show that runoff and temperature are the two main parameters which control the rate of co2 consumption during weathering of basalts according to the relationship f r f c 0 exp ea r 1 t 1 298 where f is the specific co2 consumption rate mol km2 yr rf is runoff mm yr c0 is a constant 1764 mol l ea represents an apparent activation energy for basalt weathering with a value of 42 3 kj mol determined in the present study r is the gas constant and t is the absolute temperature k modelling results show that emplacement and weathering of deccan traps basalts played an important role in the geochemical cycles of carbon and strontium in particular the traps led to a change in weathering rate of both carbonates and silicates in carbonate deposition on seafloor in sr isotopic composition of the riverine flux and hence a change in marine sr isotopic composition as a result deccan traps emplacement was responsible for a strong increase of atmospheric pco2 by 1050 ppmv followed by a new steady state pco2 lower than that in pre deccan times by 57 ppmv implying that pre industrial atmospheric pco2 would have been 20 higher in the absence of deccan basalts pco2 evolution was accompanied by a rapid warming of 4 c followed after 1 myr by a global cooling of 0 55 c during the warming phase continental silicate weathering is increased globally since weathering of continental silicate rocks provides radiogenic sr to the ocean the model predicts a peak in the 87sr 86sr ratio of seawater following the deccan traps emplacement the amplitude and duration of this spike in the sr isotopic signal are comparable to those observed at the cretaceous tertiary boundary the results of this study demonstrate the important control exerted by the emplacement and weathering of large basaltic provinces on the geochemical and climatic changes on earth

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

lithium isotopes in speleothems temperature controlled variation in silicate weathering during glacial cycles terrestrial chemical weathering of silicate minerals is a fundamental component of the global cycle of carbon and other elements past changes in temperature rainfall ice cover sea level and physical erosion are thought to affect weathering but the relative impact of these controls through time remains poorly constrained this problem could be addressed if the nature of past weathering could be constrained at individual sites in this study we investigate the use of speleothems as local recorders of the silicate weathering proxy li isotopes we analysed 7li and li in speleothems that formed during the past 200 ka in two well studied israeli caves soreq and tzavoa as well as in the overlying soils and rocks leaching and mass balance of these soils and rocks show that li is dominantly sourced from weathering of the overlying aeolian silicate soils speleothem 7li values are ubiquitously higher during glacials 23 than during interglacials 10 implying more congruent silicate weathering during interglacials where congruent means a high ratio of primary mineral dissolution to secondary mineral formation these records provide information on the processes controlling weathering in israel consideration of possible processes causing this change of weathering congruency indicates a primary role for temperature with higher temperatures causing more congruent weathering lower 7lispeleo the strong relationship observed between speleothem 7li and climate at these locations suggests that li isotopes may be a powerful tool with which to understand the local controls on weathering at other sites and could be used to assess the distribution of weathering changes accompanying climate change such as that of pleistocene glacial cycles

late weichselian deglaciation and early holocene development of a cold water coral reef along the lopphavet shelf northern norway recorded by benthic foraminifera and ostracoda cold water coral cwc settlement in northern norway is strongly related to the outlet glaciers of the fennoscandian ice sheet and dating of known cwc structures show clearly post glacial ages two gravity cores pos391 559 2 277 cm long and pos391 559 3 282 cm long were recovered on a cwc reef in the area of lopphavet northern norway detailed investigations on lithology sediment structures and composition micropaleontology foraminifera and ostracoda and ams 14c dating on the epibenthic foraminifera discanomalina coronata were performed on the two cores phosphorus analyses were performed only on core pos391 559 3 results indicate that the whole core pos391 559 2 is representative of a cwc reef environment the base of the core is dated at 10 600 120 cal yr bp thus representing one of the oldest ages of a norwegian coral reef core pos391 559 3 documents the passage from a proximal glacier environment characterized by fine silty sediments with intercalation of several dropstone layers to a cwc ecosystem the transition from the glacial to the interglacial stage is dated as old as 10 725 205 cal yr bp whereas the base of the core is dated to an age of 15 300 550 cal yr bp diversity of benthic foraminifera is higher within the cwc especially in the intervals containing coral framework five clusters are identified based on the bray curtis similarity term analyses and the interpretation of data shows that they are related to different ecological settings e g fluctuations of the sea ice cover influence of the warmer and more saline atlantic water masses transitional to a fully interglacial environment well oxygenated nutrient rich and high current setting being conducive to cwc ostracod assemblages show that these crustaceans may be also used to characterize sedimentary facies on cwc reefs

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

cenozoic carbon cycle imbalances and a variable weathering feedback abstract the long term stability of earth s climate and the recovery of the ocean atmosphere system after carbon cycle perturbations are often attributed to a stabilizing negative feedback between silicate weathering and climate however evidence for the operation of this feedback over million year timescales and in response to tectonic and long term climatic change remains scarce for example the past 50 million years of the cenozoic era are characterized by long term cooling and declining atmospheric co2 p co 2 during this interval constant or decreasing carbon fluxes from the solid earth to the atmosphere suggest that stable or decreasing weathering fluxes are needed to balance the carbon cycle in contrast marine isotopic proxies of weathering i e 87sr 86sr 7 li and 187os 188os are interpreted to reflect increasing weathering fluxes here we evaluate the existence of a negative feedback by reconstructing the imbalance in the carbon cycle during the cenozoic using the surface inventories of carbon and alkalinity only a sustained 0 25 0 5 increase in silicate weathering is necessary to explain the long term decline in p co 2 over the cenozoic we propose that the long term decrease in p co 2 is due to an increase in the strength of the silicate weathering feedback i e the constant of proportionality between the silicate weathering flux and climate rather than an increase in the weathering flux this increase in the feedback strength which mirrors the marine isotope proxies occurs as transient 1 million year timescales remains invariant to match the long term inputs of carbon over the cenozoic this results in stable long term weathering fluxes even as p co 2 decreases we attribute increasing feedback strength to a change in the type and reactivity of rock in the weathering zone which collectively has increased the reactivity of the surface of the earth increasing feedback strength through the cenozoic reconciles mass balance in the carbon cycle with the marine isotopic proxies of weathering and may explain why there are periods when the earth system is more sensitive to carbon cycle perturbations

atmospheric co2 consumption by chemical weathering in north america abstract co 2 consumption by chemical weathering is an integral part of the boundless carbon cycle whose spatial patterns and controlling factors on continental scale are still not fully understood a dataset of 338 river catchments throughout north america was used to empirically identify predictors of bicarbonate fluxes by chemical weathering and interpret the underlying controlling factors detailed analysis of major ion ratios enables distinction of the contributions of silicate and carbonate weathering and thus quantifying co 2 consumption extrapolation of the identified empirical model equations to north america allows the analysis of the spatial patterns of the co 2 consumption by chemical weathering runoff lithology and land cover were identified as the major predictors of the riverine bicarbonate fluxes and the associated co 2 consumption other influence factors e g temperature could not be established in the models of the distinguished land cover classes artificial surfaces dominated by urban areas increase bicarbonate fluxes most followed by shrubs grasslands managed lands and forests the extrapolation results in an average specific bicarbonate flux of 0 3 mmol km 2 a 1 by chemical weathering in north america of which 64 originates from atmospheric co 2 and 36 from carbonate mineral dissolution chemical weathering in north america thus consumes 50 mt atmospheric co 2 c per year about half of that originates from 10 of the area of north america the estimated strength of individual predictors differs from previous studies this highlights the need for a globally representative set of regionally calibrated models of co 2 consumption by chemical weathering which apply very detailed spatial data to resolve the heterogeneity of earth surface processes

stable carbon cycle climate relationship during the late pleistocene a record of atmospheric carbon dioxide co2 concentrations measured on the epica european project for ice coring in antarctica dome concordia ice core extends the vostok co2 record back to 650 000 years before the present yr b p before 430 000 yr b p partial pressure of atmospheric co2 lies within the range of 260 and 180 parts per million by volume this range is almost 30 smaller than that of the last four glacial cycles however the apparent sensitivity between deuterium and co2 remains stable throughout the six glacial cycles suggesting that the relationship between co2 and antarctic climate remained rather constant over this interval

carbon export and hco3 fate in carbonate catchments a case study in the karst plateau of southwestern china abstract the consumption of co 2 due to carbonate weathering is thought to be an important terrestrial sink for atmospheric co 2 however the reaction and fate of weathering products may significantly affect the magnitude of the sink carbon mass balances were determined in hongfeng lake a small artificial lake located in the carbonate plateau of sw china this was accomplished by measuring the concentrations of dic dissolved inorganic c doc dissolved organic c poc particulate organic c and co 2 partial pressure in lake waters inflows and outflows and in surrounding spring waters results show that maximum dic mainly hco 3 derived from carbonate weathering by co 2 to doc ratios in the catchment export load reach 21 implying that as much as 80 of the exported primary production is in the form of hco 3 and therefore the co 2 consumed by carbonate weathering and subsequent dic export is a critical component of the c balance in this ecosystem this exported hco 3 subsidizes c cycling of aquatic ecosystems in the catchment and 32 excluding carbonate derived c returns to the atmosphere as co 2 evasion through the fluvial and lacustrine water air interface and 10 is stored in lake sediment this lake has a small co 2 emission rate 13 2 3 9 mmol m 2 d 1 or 0 097 mol m 2 a 1 relative to catchment area compared to mean values for many reservoirs found in temperate and tropical climatic zones this is likely due in part to low organic c loads supplied by the karst dominated catchment and low lake water doc concentrations the estimate indicates that more c 39 returns to the atmosphere and much less 13 is stored in sediments implying that the c sink of carbonate weathering may not be as significant as once thought

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

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

glacial weathering sulfide oxidation and global carbon cycle feedbacks connections between glaciation chemical weathering and the global carbon cycle could steer the evolution of global climate over geologic time but even the directionality of feedbacks in this system remain to be resolved here we assemble a compilation of hydrochemical data from glacierized catchments use this data to evaluate the dominant chemical reactions associated with glacial weathering and explore the implications for long term geochemical cycles weathering yields from catchments in our compilation are higher than the global average which results in part from higher runoff in glaciated catchments our analysis supports the theory that glacial weathering is characterized predominantly by weathering of trace sulfide and carbonate minerals to evaluate the effects of glacial weathering on atmospheric pco 2 we use a solute mixing model to predict the ratio of alkalinity to dissolved inorganic carbon dic generated by weathering reactions compared with nonglacial weathering glacial weathering is more likely to yield alkalinity dic ratios less than 1 suggesting that enhanced sulfide oxidation as a result of glaciation may act as a source of co 2 to the atmosphere back of the envelope calculations indicate that oxidative fluxes could change ocean atmosphere co 2 equilibrium by 25 ppm or more over 10 ky over longer timescales co 2 release could act as a negative feedback limiting progress of glaciation dependent on lithology and the concentration of atmospheric o 2 future work on glaciation weathering carbon cycle feedbacks should consider weathering of trace sulfide minerals in addition to silicate minerals

stable runoff and weathering fluxes into the oceans over quaternary climate cycles the effect of glacial interglacial cycles on surface weathering rates has been unclear a beryllium based proxy for weathering shows minimal variations in the input of silicate weathering products to the oceans for the past two million years

potential origins of 400 500 kyr periodicities in the ocean carbon cycle a box model approach 1 cenozoic proxy records of both the isotopic composition of dissolved inorganic carbon in the oceans 13cdic and deep ocean carbonate preservation show significant periodicities in the range 400 500 kyr sensitivity analysis of the ocean carbon cycle to potential variability on this timescale in patterns of global oceanic primary productivity and or continental weathering fluxes is performed using a 7 box ocean atmosphere model the data constraints imposed by plio pleistocene proxy records of 13cdic carbonate preservation and atmospheric pco2 variability allow different scenarios to be evaluated forcing with the global oceanic primary production ratio of inorganic and organic carbon leads to the relative phases of response most consistent with the proxy data however only when changes also occur in total marine primary production can the observed relative amplitudes of 13cdic and pco2 variability also be reproduced this scenario is consistent with oscillations between a highly productive coccolithophore rich global ocean and a less productive diatom rich one such oscillations have been proposed to originate from the orbital eccentricity cycle leading to changes in seasonality and thus silica utilization in the southern ocean however the period of response in model 13cdic is always close to that of the forcing function used and thus a significant discrepancy remains between the orbital eccentricity cycle period of 413 kyr and the observed 500 kyr 13cdic periodicity seen in the pleistocene

chemical weathering and associated co2 consumption in the mahanadi river basin india abstract chemical weathering of continents is one of the major geochemical processes which consumes atmospheric co2 and exerts a strong impact on the global climate the major ion chemistry of the mahanadi river basin one of the largest river basins in india is determined to investigate the sources of major ions and their spatio temporal variability chemical weathering rates and associated co2 consumption in the basin the results reveal that the ions in the basin are dominated by ca and hco3 the total dissolved solids 215 mg l 1 in monsoon and 270 mg l 1 in pre monsoon and total cation concentration 2367 eq in monsoon and 3214 eq in pre monsoon in the basin are relatively higher than the global average the dissolved loads in the basin are dominantly controlled by rock weathering particularly chemical weathering of silicates and carbonates the estimated chemical weathering rates based on the forward model are 44 94 t km 2 yr 1 in monsoon and 2 45 t km 2 yr 1 in pre monsoon with annual average chemical weathering rate of 23 7 t km 2 yr 1 the contribution of silicate weathering rates in the basin is 32 and 1 55 t km 2 y 1 during monsoon and pre monsoon period respectively the estimated co2 consumption rate associated with chemical weathering in the basin is 13 3 105 mol km 2 yr 1 during monsoon and 0 66 105 mol km 2 yr 1 during pre monsoon period with an average annual rate of 6 9 105 mol km 2 yr 1 which is higher than the global average the net rate of co2 consumption by silicate weathering is estimated to be approximately 4 78 105 mol km 2 yr 1 it is observed that the runoff and lithology are the major factors influencing chemical weathering in the basin however the basin elevation has a good negative correlation with chemical weathering rate

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

a simple model for the caco3 saturation state of the ocean the strangelove the neritan and the cretan ocean 1 a simple model of the caco3 saturation state of the ocean is presented it can be solved analytically and is intended to identify the fundamental controls on ocean carbonate ion concentration it should also attract researchers unfamiliar with complex biogeochemical models despite its limitations the model calculated caco3 saturation state of today s ocean agrees well with observations in general the model reveals three distinctly different modes of operation the strangelove ocean of high supersaturation which is dominated by inorganic caco3 precipitation 2 the neritan ocean of indefinite saturation dominated by biogenic shallow water caco3 precipitation and 3 the cretan ocean of low saturation dominated by biogenic pelagic caco3 precipitation in the latter mode the deep ocean co32 is remarkably stable provided that the biogenic production of caco3 exceeds the riverine flux of ca2 and co32 this explains the overall constancy of the saturation state of the ocean documented over the last 100 ma the model is then used to address diverse questions one important result is that the recovery of the oceanic carbonate chemistry from fossil fuel neutralization in the future will be accelerated due to expected reduced biogenic calcification

evidence for mass dependent isotopic fractionation of strontium in a glaciated granitic watershed abstract the stable isotope composition of strontium expressed as 88 86sr may provide important constraints on the global exogenic strontium cycle here we present 88 86sr values and 87sr 86sr ratios for granitoid rocks a 150 yr soil chronosequence formed from these rocks surface waters and plants in a small glaciated watershed in the central swiss alps incipient chemical weathering in this young system whether of inorganic or biological origin has no resolvable effect on the 87sr 86sr ratios and 88 86sr values of bulk soils which remain indistinguishable from bedrock in terms of sr isotopic composition although due in part to the chemical heterogeneity of the forefield the lack of a resolvable difference between soil and bedrock isotopic composition indicates that these soils have thus far witnessed minimal net loss of sr a low degree of chemical weathering is also implied by bulk soil chemistry the isotopic composition of sr in streamwater is more radiogenic than median soil reflecting the preferential weathering of biotite in the catchment streamwater 88 86sr values however are indistinguishable from bulk soil 88 86sr values implying that no resolvable fractionation of sr isotopes takes place during release to the weathering flux in the damma forefield analyses of plant tissue reveal that plants rhododendron and vaccinium preferentially assimilate the lighter isotopes of sr such that their 88 86sr values are significantly lower than those of the soils in which they grow additionally 88 86sr values of foliar and floral tissues are lower than those of roots contrary to observations for ca for which sr is often used as an analogue in weathering studies we suggest that processes that discriminate against sr in favour of ca due to the different nutritional requirement of plants for these two elements are responsible for the observed contrast

ecotone or ecocline ecological boundaries in estuaries abstract two main ecological boundaries ecotone and ecocline have been defined in landscape ecology at this scale the estuary represents a boundary between rivers and the sea but there has been no attempt to fit empirical data for estuaries to these boundary models an extensive data set from the thames estuary was analysed using multivariate techniques and species range analysis in order to investigate whether the ecocline or the ecotone model was most relevant to this estuary data for periods of high and low freshwater flow allowed the impact of large scale fluctuations implicit in both models to be determined a continuum of assemblages existed along the salinity gradient from freshwater river to the north sea with shifts in the ranges of organisms apparent in response to changes in freshwater flow this pattern closely fits an ecocline model however the estuary differs from previously defined ecoclines in having two overlapping gradients in the major stressor from river to mid estuary for freshwater species and from sea to mid estuary for marine species we propose therefore that the estuary represents a two ecocline model with fauna inhabiting the mid estuary being either freshwater or marine species at the edge of their range rather than true estuarine organisms this allows a redefinition of the remane diagram with estuarine species removed and supports previous arguments that brackish water species do not exist such two ecocline models may also exist in other marine systems such as rocky shores

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

enhanced weathering and co2 drawdown caused by latest eocene strengthening of the atlantic meridional overturning circulation on timescales significantly greater than 105 years atmospheric pco2 is controlled by the rate of mantle outgassing relative to the set point of the silicate weathering feedback the weathering set point has been shown to depend on the distribution and characteristics of rocks exposed at the earth s surface vegetation types and topography here we argue that large scale climate impacts caused by changes in ocean circulation can also modify the weathering set point and show evidence suggesting that this played a role in the establishment of the antarctic ice sheet at the eocene oligocene boundary in our simulations tectonic deepening of the drake passage causes freshening and stratification of the southern ocean strengthening the atlantic meridional overturning circulation and consequently raising temperatures and intensifying rainfall over land these simulated changes are consistent with late eocene tectonic reconstructions that show drake passage deepening and with sediment records that reveal southern ocean stratification the emergence of north atlantic deep water and a hemispherically asymmetric temperature change these factors would have driven intensified silicate weathering and can thereby explain the drawdown of carbon dioxide that has been linked with antarctic ice sheet growth we suggest that this mechanism illustrates another way in which ocean atmosphere climate dynamics can introduce nonlinear threshold behaviour through interaction with the geologic carbon cycle during the latest eocene declining atmospheric co2 levels led to the inception of the antarctic ice sheet simulations suggest that the deepening of the drake passage caused climate changes that enhanced continental weathering and co2 drawdown

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