relative weathering intensity of calcite versus dolomite in carbonate bearing temperate zone watersheds carbonate geochemistry and fluxes from catchments within the st lawrence and danube river basins 1 calcite and dolomite solubilities in open weathering environments are proportional to pco2 and inversely proportional to temperature and dolomite solubility is progressively greater than calcite below 25 c the continent scale weathering budget reveals the significance of the northern hemisphere nh to globally integrated riverine fluxes of ca2 mg2 and hco3 the nh contributes 70 of the global hco3 flux while only 54 of the riverine discharge we present results of a comparative hydrogeochemical study of carbonate mineral equilibria and weathering fluxes in two nh carbonate rich river basins surface water geochemistry and discharge were determined for headwater streams in michigan and slovenia within the st lawrence and danube river basins michigan watersheds are established atop carbonate bearing glacial drift deposits derived from erosion of paleozoic strata with thick soil horizons 100 300 cm slovenia watersheds drain mesozoic bedrock carbonates in alpine and dinaric karst environments with thin soil horizons 0 70 cm carbonate weathering intensity is a parameter that normalizes river runoff and hco3 concentration to catchment area meq hco3 km 2 s 1 summing calcite and dolomite contributions and is used to gauge the effects of climate land use and soil thickness on organic inorganic carbon processing rates importantly michigan riverine discharge is one tenth of slovenian rivers providing the opportunity to evaluate the kinetics of carbonate mineral equilibration the study rivers are hco3 ca2 mg2 waters supersaturated for calcite at pco2 values in excess of the atmosphere as discharge varies hco3 concentrations differ by less than 20 for any location and mg2 ca2 remains relatively fixed for michigan 0 5 and slovenia streams 0 4 requiring that dolomite dissolution exceed calcite on a mole basis the ability of calcite and dolomite dissolution to keep pace with increased discharge indicates carbonate weathering is limited only by water flux and temperature dependent solubility in these watersheds carbonate weathering intensity in michigan and slovenia exceeds the world average by factors between 2 and 20 and dolomite weathering intensity estimated from riverine mg2 fluxes exceeds the world average by factors between 2 and 15 thus global fluxes of carbonate related weathering products appear heavily skewed toward carbonate bearing environments at higher latitudes with relatively low mean annual temperatures and high discharge

chemical weathering rates of silicate dominated lithological classes and associated liberation rates of phosphorus on the japanese archipelago implications for global scale analysis abstract lithology is an important characteristic of the terrestrial surface whose properties influence chemical weathering rates specifically non silicate minerals may contribute significantly to the weathering derived fluxes from silicate dominated lithological classes the japanese archipelago consists of predominantly silicate dominated lithologies with a high proportion of volcanics however the spatially explicit representation of chemical weathering rates remains difficult for such a large region because many controlling factors on chemical weathering rates are correlated with each other due to the spatial heterogeneity of lithology a multi lithological model approach to estimate spatially explicit chemical weathering rates for unmonitored areas is applied here to achieve this hydrochemical data of 381 catchments are used to train a set of models recognizing the contribution of a variety of proposed factors influencing chemical silicate rock weathering rates csrwr cations plus dissolved silica flux the monitored catchments cover 44 of the japanese archipelago cation chemical weathering rates excluding si are linearly correlated with csrwr and show outliers if basic volcanics or pyroclastic flows are present due to increased silica release rates lithology and runoff are identified as the strongest predictors for chemical weathering rates temperature and gradient of slope are of less relevance for the regional scale prediction while further proposed factors like soil properties or land cover are not identified as major predictors latter findings are partly attributed to geodata quality low variability of parameter values as well as spatial correlations of proposed controlling factors with lithology or runoff the calculated average csrwr of the archipelago is 25 t km 2 a 1 and ranges from 5 9 to 107 t km 2 a 1 in monitored catchments weathering rates per lithological class as a function of runoff can be grouped into three classes a pyroclastic flows showing the highest chemical weathering rates b alluvial deposits mixed sediments and basic to intermediate volcanics with medium rates and c metamorphics siliciclastic sediments acid volcanics acid plutonics and unconsolidated sediments other than alluvial deposits showing the lowest rates the recognition of lithogenic sulfur would add 9 7 to csrwr of considered catchments results suggest that the lithological classes acid volcanics and unconsolidated sediments contribute above average to the sulfur fluxes possible biases of this observation are discussed the contribution of ca fluxes from non silicate calcic minerals named ca excess ca fluxes in addition to silicate ca fluxes is about 10 of the csrwr on average and is attributed by a wide value range the calculated ratio ca excess to total ca fluxes from chemical weathering averages around 62 75 56 83 and 84 for the lithological classes acid plutonics metamorphics siliciclastic sediments mixed sediments and acid volcanics respectively this suggests a major ca contribution from non silicate calcic minerals for these lithological classes phosphorus release from rocks due to chemical weathering is estimated to be between 1 kg p km 2 a 1 and 390 kg p km 2 a 1 the p release patterns in dependence of runoff per lithological class are different from csrwrs due to differences of applied p content in rocks the identified spatial p release patterns suggest that the consideration of dynamic and spatially resolved p release rates by chemical weathering might improve ecosystem studies later findings may be of importance for analysing the influence of p release from rocks on the climate system via ecosystem functioning on geological time scales a first application of the p release model to the global scale suggests an annual release of 1 6 mt p 13 8 kg p km 1 a 1 by chemical weathering of silicate dominated lithological classes excluding carbonate sedimentary rocks

chemical weathering rates and atmospheric soil co2 consumption of igneous and metamorphic rocks under tropical climate in southeastern brazil abstract chemical weathering rates and atmosphere soil co 2 consumption of igneous and metamorphic rocks under tropical climate in southeastern brazil were evaluated using the chemical composition of surface waters and fresh rocks and soil horizon c in the upper sorocaba river basin surface water samples were collected between june 2009 and june 2010 and analyses were performed to assess ph electrical conductivity ec temperature and total dissolved solids tds including na k ca 2 mg 2 cl so 4 2 po 4 3 no 3 and sio 2 fresh rocks and c horizon samples were also collected taking into account their geological context abundance and spatial density to analyze major elements and mineralogy the concentration of tds and dissolved cations anions and silica increased during the dry period in relation to the wet period and the same behavior was observed for ph ec and temperature after corrections of anthropogenic contributions ca 21 t km 2 yr and atmospheric inputs ca 19 t km 2 yr the annual flux due to chemical weathering involving the igneous and metamorphic rocks was ca 29 t km 2 yr the co 2 atmospheric soil consumption in the upper sorocaba river basin was ca 0 2 10 6 mol km 2 yr and when extrapolated to the entire mantiqueira orogenic belt accounted an estimated consumption of 0 07 10 12 mol yr representing 0 6 of the total co 2 consumption flux derived from global average silicate weathering the chemical weathering rates of igneous and metamorphic rocks in the upper sorocaba river basin were estimated at 15 m my respectively the main weathering process in this watershed was the monossialitization with partial hydrolyses of bedrock minerals except quartz which was not weathered and remained in the soil profile the annual specific flux derived from igneous and metamorphic rocks at upper sorocaba river basin could be compared with watersheds in tropical climates however this value is higher than in other north american european asian and african granitoid watersheds and lower than in montane watersheds

paleozoic plate dynamics current plate motions can be accounted for by a balance of active forces slab pull ridge push and for continental plates trench suction with drag beneath the plate as a resistive force if we assume that the same forces have acted through time we can reconstruct plate motions from the geometry of past plate boundaries paleozoic reconstructions are made with paleomagnetic tectonic climatic and biogeographic data as no ocean floor remains paleomap reconstructions are used to estimate past plate speeds and to test simple dynami cal models in order to determine which ranges of forces best accounts for the observations over the last 600 m y plate speeds averaged over 40 to 100 m y intervals show considerable variation gondwana s speed oscillates from 20 to 60 km m y over a long timescale 200 400 m y with considerable noise superposed over the paleozoic era motions for large continental regions average 28 krn m y force balance models based on present day observations suggest that continental regions without a large attached slab would move 30 mrn yr the opening and closing of the ocean between laurentia and gondwana 560 400 ma is used to test dynamical models and the parameter values assumed in the late precambrian laurentia rifted away from gondwana in the earliest cambrian it was near 40os by late cambrian and ordovician it had moved to the equator during the silurian and devonian laurentia reversed direction and later collided with gondwana at 40os in a model of the forces acting on the plates slab pull ridge push and trench suction are assumed to balance plate drag only certain ranges of ridge push and trench parameters can model both the opening and subsequent closing of the ocean the dynamic models with parameter values inferred from present rates bracket the rates required by the reconstructions

lithium isotope evidence for enhanced silicate weathering during oae 1a early aptian selli event an abrupt rise in temperature forced by a massive input of co2 into the atmosphere is commonly invoked as the main trigger for oceanic anoxic events oaes global warming initiated a cascade of palaeoenvironmental perturbations starting with increased continental weathering and an accelerated hydrological cycle that delivered higher loads of nutrients to coastal areas stimulating biological productivity the end result was widespread anoxia and deposition of black shales the hallmarks of oaes in order to assess the role of weathering as both an oae initiator and terminator via co2 sequestration during the early aptian oae 1a selli event 120 ma the isotopic ratio of lithium isotopes was analysed in three sections of shallow marine carbonates from the pacific and tethyan realms and one basinal pelagic section from the tethyan domain because the isotopic composition of lithium in seawater is largely controlled by continental silicate weathering and high and low temperature alteration of basaltic material a shift to lighter 7li values is expected to characterize oaes the studied sections illustrate this phenomenon 7li values decrease to a minimum coincident with the negative carbon isotope excursion that effectively records the onset of oae 1a a second negative 7li excursion occurs coeval with the minimum in strontium isotopes after the event the striking similarity to the strontium isotope record argues for a common driver the formation and destruction weathering of an oceanic lip could account for the parallel trend in both isotope systems the double spike in lithium isotopes is probably related to a change in weathering congruencies such a chemostratigraphy is consistent with the hypothesis that an increase in silicate weathering in conjunction with organic carbon burial led to drawdown of atmospheric co2 during the early aptian oae 1a

the fluvial geochemistry of the rivers of eastern siberia i tributaries of the lena river draining the sedimentary platform of the siberian craton abstract the response of continental weathering rates to changing climate and atmospheric pco 2 is of considerable importance both to the interpretation of the geological sedimentary record and to predictions of the effects of future anthropogenic influences while comprehensive work on the controlling mechanisms of contemporary chemical and mechanical weathering has been carried out in the tropics and to a lesser extent in the strongly perturbed northern temperate latitudes very little is known about the peri glacial environments in the subarctic and arctic thus the effects of climate essentially temperature and runoff on the rates of atmospheric co 2 consumption by weathering are not well quantified at this climatic extreme to remedy this lack a comprehensive survey has been carried out of the geochemistry of the large rivers of eastern siberia the lena yana indigirka kolyma anadyr and numerous lesser streams which drain a pristine high latitude region that has not experienced the pervasive effects of glaciation and subsequent anthropogenic impacts common to western eurasia and north america the scale of the terrain sampled in terms of area is comparable to that of the continental united states or the amazon orinoco and includes a similarly diverse range of geologic and climatic environments in this paper the chemical fluxes from the western region the very large ancient and geologically stable sedimentary basin precambrian to quaternary of the siberian platform will be presented and compared to published results from analogous terrains in the tropical basins of china while the range in the chemical signatures of the various tributaries included here 60 sampled is large this mainly reflects lithology rather than the weathering environment the areal chemical fluxes are comparable to those of the chinese rivers being dominated by the dissolution of carbonates and evaporites the net consumption of atmospheric co 2 by aluminosilicate weathering is minor as it is in the tropical basins it is much smaller than in active orogenic belts in similar latitudes e g the fraser and yukon but comparable to those of the mackenzie tributaries that drain the eastern slope of the rockies lithology exerts the dominant influence in determining the weathering yield from sedimentary terrains and for a largely carbonate evaporite terrain climate does not have a direct effect

bicarbonate fluxes and co2 consumption by chemical weathering on the japanese archipelago application of a multi lithological model framework abstract prediction of co 2 consumption by chemical weathering is important to understand the global carbon cycle and island arcs are assumed to contribute significantly to the transfer of atmospheric soil co 2 to the oceans previous work established empirical functions for bicarbonate flux and co 2 consumption in dependence of runoff for five to six lithological classes these functions were applied in global studies however it has remained uncertain if improvements can be achieved by considering further factors or by an enhanced lithological classification scheme this study applies a new lithological map of japan with an enhanced lithological classification a hydrochemical data set representing 382 catchments covering 44 4 of the japanese archipelago and a multi lithological model approach to predict bicarbonate fluxes and co 2 consumption by chemical weathering because of significant carbonate contents in sediments different from carbonate sedimentary rocks acid plutonics and metamorphics firstly a bicarbonate flux model approach is established and secondly silicate and carbonate co 2 consumption is estimated based on the geochemical composition of rocks in accordance with previous studies on the catchment scale the most important factors controlling bicarbonate fluxes are lithology and runoff the anion ratio hco 3 so 4 2 cl is identified as the third most important predictor because anion sources and anion composition of river water have a great effect on bicarbonate concentrations and last but not least potential predictors such as gradient of slope temperature and physical erosion explain some part of the observed bicarbonate flux variation these potential predictors have been discussed in literature but quantification of the effects of these factors remains difficult due to their correlation with runoff and lithology however all tested models reproduce a total of observed bicarbonate fluxes within 10 on the regional scale including the simplest model which recognizes only lithology and runoff as predictors model results suggest that bicarbonate flux from the japanese archipelago is about 6 61 t c km 2 a 1 and co 2 consumption by chemical weathering is about 6 05 t c km 2 a 1 91 6 of bicarbonate flux this co 2 consumption rate is 3 2 times above the global average rate the silicate to carbonate co 2 consumption ratio is comparatively high it amounts to 9 9 which is above the global value the latter one being 1 to 1 5 carbonate sedimentary rocks contribute only 1 3 to bicarbonate fluxes due to their low areal proportion 0 2 acid volcanic rocks va show the lowest bicarbonate fluxes on average while basic and intermediate volcanics vb as well as pyroclastics py are in the range of the japanese average value the carbonate weathering contribution to bicarbonate fluxes from mixed sediments siliciclastic sediments metamorphics and acid plutonics is estimated to be 69 2 23 3 63 4 and 24 8 respectively only an average carbonate co 2 consumption per lithological class is calculated because no function based on typical predictors could be established to calculate carbonate weathering contribution to silicate dominated lithological classes this can be attributed to large spatial differences in carbonate content in rocks and to corresponding contributions to bicarbonatefluxes in the following results are compared to bicarbonate flux models of previous studies and identified differences are discussed in conclusion recognition of carbonate abundance in silicate dominated lithological classes including trace calcite is important to calculate silicate carbonate co 2 consumption ratios presented results are relevant for studies modelling co 2 consumption by chemical weathering in context of the global c cycle

physical and chemical weathering rates and co2 consumption in a tropical lateritic environment the upper niger basin the chemical composition of niger river water measured bimonthly at bamako mali during the period 1990 1992 provides an estimate of present weathering rates in the upper niger basin the dominant weathering process is kaolinite formation monosiallitization however seasonal variations promote gibbsite formation in the rainy season september and smectite development in the dry season may the results show that lateritic profiles continue to develop even during very dry episodes the rate of profile development calculated as the difference between the chemical weathering rate at the base of the soil profile and mechanical erosion rate at the soil surface is about 1 3 to 3 7 m myr a comparison between 43 river basins of the world shows that for similar runoff the co2 flux consumed by silicate weathering is about two times lower in lateritic areas than in nonlateritic zones

slab pull and the seismotectonics of subducting lithosphere this synthesis links many seismic and tectonic processes at subduction zones including great subduction earthquakes to the sinking of subducted plate earthquake data and tectonic modeling for subduction zones indicate that the slab pull force is much larger than the ridge push force interactions between the forces that drive and resist plate motions cause spatially and temporally localized stresses that lead to characteristic earthquake activity providing details on how subduction occurs compression is localized across a locked interface thrust zone because both the ridge push and the slab pull forces are resisted there the slab pull force increases with increasing plate age thus because the slab pull force tends to bend subducted plate downward and decrease the force acting normal to the interface thrust zone the characteristic maximum earthquake at a given interface thrust zone is inversely related to the age of the subducted plate the 1960 chile earthquake mw 9 5 the largest earthquake to occur in historic times began its rupture at an interface bounding oceanic plate 30 m y old however this rupture initiation was associated with the locally oldest subducting lithosphere weakest coupling the rupture propagated southward along an interface bounding progressively younger oceanic lithosphere terminating near the subducting chile rise prior to a great subduction earthquake the sinking subducted slab will cause increased tension at depths of 50 200 km with greatest tension near the shallow zone resisting plate subduction plate sinking not only leads to compressional stresses at a locked interface thrust zone but may load compressional stresses at plate depths of 260 350 km provided that the shallow sinking occurs faster than the relaxation time of the deeper mantle this explains k mogi s observations of m 7 thrust earthquakes at depths of 260 350 km immediately downdip and within 3 years prior to five great shallow earthquakes of northern japan the slab pull model explains the lower layer of double seismic zones as due to tension from the deeper sinking plate and the upper layer as due to localized in plate compression as plate motion is resisted by the bounding mantle just downdip of the interface thrust zone there occurs an aseismic 20 50 dip increase of subducted plate this slab bend reflects the summed slab pull force of deeper plate and probably is at the crustal basalt to eclogite phase change resistance to subduction provided by a continually developing slab bend may be an important factor in the size of slab pull force delivered to an interface thrust zone

subduction hinge migration along the izu bonin mariana arc abstract hinge migration or rollback is thought to have a significant influence on the tectonics of trench arc backarc systems where the backarc region is actively opening the hinge is usually either stationary or retreating in a mantle hotspot frame of reference the izu bonin mariana system represents a highly anomalous case in which the hinge is reportedly advancing behind the retreating eastern edge of the overriding philippine sea plate we have re evaluated the motion of the subduction hinge using the best available estimates of the motion of the philippine sea plate and estimated maximum rates of extension within the izu bonin arc if the plate motions have not changed appreciably the subduction hinge of the izu bonin trench has advanced over the last 5 ma the approximate average rate of hinge advance is 0 6 mm a 1 at the north end of the izu bonin arc increasing to 24 30 mm a 1 at 27 n the rate of advance of the mariana hinge at 18 n is 10 20 mm a 1 the dip of the subducted slab is strongly correlated with the motion of the philippine sea plate suggesting that the rapid retreat of the overriding plate affects mantle flow we have found a tentative hinge advance mechanism in a simple newtonian viscous corner flow model though the model has severe geometrical and rheological limitations it suggests that the retreat of the overriding plate gives rise to excess uplift pressures acting on the top surface of the subducted slab if the hinge is not assumed to be fixed the excess pressure will tend to rotate the slab arcward steepening the slab and advancing the subduction hinge thus the westward motion of the philippine sea plate may explain both the advance of the subduction hinge and the observed relationship between the motion of the philippine sea plate and the dip of the subducted slab along the izu bonin mariana trench

carbon river fluxes and weathering co2 consumption in the congo and amazon river basins data on carbon river fluxes recently obtained by the authors for the congo basin within the framework of the pirat program insu cnrs orstom are compared with results previously obtained for the amazon basin a special interest is devoted to the bicarbonate river fluxes and to their relationships with river discharges the flux of atmospheric and soil co2 consumed by rock weathering is estimated to be 3 1 105 and 0 5 105 moles a km2 respectively for the amazon and the congo basin these co2 fluxes represent respectively 67 4 and 74 7 of the total bicarbonate river fluxes a comparison to other large river basins shows that this contribution is directly related to the proportion of carbonate rock areas a transfer function between the weathering co2 flux and the river discharge is calculated for each basin and allows the reconstitution of the variations of this flux using the river discharge fluctuations during the last century these interannual co2 fluctuations present average increasing trends of 10 for amazon basin and only 0 7 for the congo basin during the last century

numerical investigation of lake bed seepage patterns effects of porous medium and lake properties abstract three dimensional steady state numerical models were used to investigate the relative significance of several factors controlling lake bed seepage patterns lake depth lake bed slope orientation of an asymmetric lake with respect to a regional hydraulic gradient lake bed sediments and heterogeneity and anisotropy of the porous medium we considered both inflow and flow through lakes and our focus was on the details of seepage flux at the lake bed not on the surrounding porous medium while porous medium factors anisotropy and heterogeneity are important we found several conditions where lake bed factors were nearly as important in controlling the distribution of seepage varying lake bed slope from 0 013 to 0 04 in different simulations had a significant effect on shoreline seepage rates were 10 40 higher for lakes of low slope than lakes of steep slope also significantly elevated seepage in some cases a local maximum was observed offshore at the break in bed slope between the sloping side and flat central portions of the lake bed whenever the surrounding porous medium had a high anisotropy 1000 or 100 for flow through lakes in media of high anisotropy the annual volume of groundwater inseepage was significantly higher about 20 in lakes with steep bed slope compared to those with low slope this effect of slope was smaller at lower anisotropy for an asymmetric flow through lake a lake with a steep bed slope on one side moderate slope on the other the percentage of lake bed experiencing inseepage was greatest when the steep side was downgradient and the effect was larger at higher anisotropy these effects illustrate the complex interaction between lake bed slope and the anisotropy of the surrounding porous medium in controlling lake groundwater exchange adding low conductivity lake sediments and decreasing their conductivity shifted groundwater seepage further offshore in inflow lakes increasing the anisotropy of the surrounding porous medium had the same effect adding sediments and increasing anisotropy also decreased nearshore seepage in flow through lakes but without increasing offshore seepage in this case the net effect was a smaller annual volume of lake groundwater exchange at the same time the percentage of the lake bed experiencing inseepage increased in flow through lakes even as the annual volume of inseepage was decreasing thus for flow through lakes a larger area of inseepage may not be a good indicator of a greater volume of inseepage lake depth did not have a significant effect on the quantity or distribution of seepage to inflow or flow through lakes many of the physical factors investigated here influence the amount of lake groundwater exchange and the proportions of nearshore and offshore seepage therefore they are potentially significant to lake water quality and ecology in addition to hydrology

glacial isostatic adjustment i the forward problem summary the isostatic adjustment of a radially stratified visco elastic spheroid is treated using space time green functions for the associated surface mass load boundary value problem these impulse response functions are convolved with a heaviside function to give the time dependent deformation of the planet which would be produced by a unit point mass brought up from infinity at t 0 and allowed to remain on the surface the resulting heaviside green functions can be employed to simulate all of the important signatures of glacial isostatic adjustment given a space time dependent surface mass load consisting of ice sheet ablation histories and a model of the simultaneous filling of the ocean basins these source terms are simply convolved with the heaviside green function appropriate to a specific response signature a realistic model of the spatial distribution of the main late pleistocene ice loads and of their temporal disintegration is constructed the response of two visco elastic earth models is computed and compared to a global set of relaxation data relative sea level curves on the basis of this initial comparison of theory and observation the possibility that the lower mantle has a viscosity which is significantly in excess of the viscosity of the upper mantle is excluded in addition clear evidence of the presence of the lithosphere has been found in relaxation data from sites which were near the edge of the laurentide ice sheet such data should therefore prove useful as a basis for analysis of lateral variations in lithosphere thickness further extensions of the calculation are suggested

stress observations and driving force models for the south american plate stress observations are compared to predictions of driving force models for the south american plate stress observations have the potential to give detailed information about the forces driving the plates in that sets of forces with the same net torque can produce quite different stress patterns for a two dimensional vertical section model of a plate there are three conditions for dynamical equilibrium the net forces and the net torque about any point must all be zero these conditions are used to estimate the magnitudes of forces as a function of age with ridge push and slab pull as active forces and plate drag and slab resistance as passive forces the results are consistent with earlier published models and indicate that the primary balance for an oceanic plate is between slab pull and the resisting drag forces we generalize the model for the possible forces driving the south american plate and compare with observed stress measurements and kinematics the south american plate has a small slab pull component amounting to about one fifth the ridge push force with the other components reasonably isolated geographically thus the plate balance is largely between ridge push and plate drag this gives an opportunity of resolving the effects of trench suction or collision at the subduction zones most remarkable is the nearly uniform e w orientation of the regional stress field shmax directions which is extensional in the high andes a second feature is the n s orientations in the amazon basin the two dimensional horizontal stress patterns are compared for successive models of combinations of driving forces models with ridge push slab pull at the scotia and caribbean arcs and trench suction near the west coast balanced by plate drag produce similar stress patterns to those observed the magnitude of a possible trench suction force is estimated using a model with an eddy between the nazca slab and the overlying south american plate

ecosystem controlled soil rock pco2 and carbonate weathering constraints by temperature and soil water content carbonate dissolution in soil groundwater systems depends dominantly on ph temperature and the saturation state of the solution with respect to abundant minerals the ph of the solution is in general controlled by partial pressure of co2 pco 2 produced by ecosystem respiration which is controlled by temperature and water availability in order to better understand the control of land temperature on carbonate weathering a database of published spring water hydrogeochemistry was built and analysed assuming that spring water is in equilibrium with the soil water rock atmosphere the soil pco 2 can be back calculated based on a database of spring water chemistry the average soil rock co2 was calculated by an inverse model framework and a strong relationship with temperature was observed the identified relationship suggests a temperature control on carbonate weathering as a result of variations in soil rock pco 2 which is itself controlled by ecosystem respiration processes the findings are relevant for global scale analysis of carbonate weathering and carbon fluxes to the ocean because concentration of weathering products from the soil rock system into the river system in humid high temperature regions are suggested to be larger than in low temperature regions furthermore results suggest that in specific spring samples the hydrochemical evolution of rain water percolating through the soil rock complex can best be described by an open system with pco 2 controlled by the ecosystem abundance of evaporites and pyrite sources influence significantly the chemistry of spring water and corrections must be taken into account in order to implement the inverse model framework presented in this study annual surface temperature and soil water content were identified as suitable variables to develop the parameterization of soil rock pco 2 mechanistically consistent with soil respiration rate findings

chemical weathering and atmospheric soil co2 uptake in the andean and foreland amazon basins abstract this study is a geochemical investigation of the andean and foreland basins of the amazon river at high spatial and time resolution carried out within the framework of the hybam research program hydro geodynamics of the amazon basin monthly sampling was carried out at 27 gauging stations located in the upper tributaries of the amazon basin from north to south the napo maranon ucayali madre de dios beni and mamore rivers the aim of this paper is to estimate the present day chemical weathering rate cwr as well as the flux of co 2 consumption from total and silicate weathering in the andes and foreland amazon basins and to discuss their distribution as a function of geomorphic and structural parameters based on the forward method the napo and other ecuadorian basins present high silicate weathering rates in comparison with the other basins we confirm that the maranon and ucayali rivers control the amazon hydrochemistry due to the presence of salt rocks and carbonates in these basins the madre de dios beni and mamore basins do not contribute much to the amazon dissolved load this north to south cwr gradient can be explained by the combination of decreasing weatherable lithology surface and decreasing runoff rates from the north to the south the foreland part of the basins or mountain lowland transition accounts for nearly the same proportion of the amazon silicate chemical weathering and carbonate chemical weathering fluxes as the andean part this result demonstrates the importance of the sediment accumulation areas in the amazon basin weathering budget and can be explained by the occurrence of a higher temperature the deposition of fresh sediments from andean erosion and a higher sediment residence time than in the upper part of the basin with a total co 2 consumption rate of 744 10 3 moles km year 1 and a silicate co 2 consumption rate of 300 10 3 moles km year 1 the upper amazon river andes foreland part is the most intense part of the amazon basin in terms of atmospheric co 2 consumption by weathering processes it is an important co 2 sink by weathering processes but accounts for only somewhat more than half of the co 2 consumption by silicate weathering of the amazon basin this result points out the importance of the lowland part of the basin in the inorganic c silicate budget the upper amazon accounts for 2 4 of the world s silicate co 2 consumption which is the same proportion as for the southern and southern east himalaya and tibetan plateau

is chemical index of alteration cia a reliable proxy for chemical weathering in global drainage basins the chemical weathering of silicate rocks in continents as an important sink of atmospheric co2 is of great significance for global environmental change rivers play a key role in earth surface processes and are regarded as the most important carrier of terrigenous materials into the sea the chemical index of alteration cia has been widely used as a proxy for chemical weathering in sediment source area in this paper the cia values of suspended particulate matters from 44 rivers worldwide are recalculated the cia values vary significantly with the highest average value occurring in african rivers and the lowest in north american rivers the correlation analyses suggest that on a global scale the cia is sensitive to land surface temperature latitude at river mouth and soil depth in the drainage basins but poorly correlated with drainage area precipitation average elevation and runoff however the cia of the rivers draining east china are closely related to temperature precipita tion latitude and runoff primarily reflecting the dominant control of monsoon climate on chemical weathering in the catchments it is therefore unrealistic to find a simple law of regulating chemical weathering in continents the cia actually reflects the integrated weathering history in the drainage basins and therefore caution should be taken while using it as a direct and quantitative proxy for evaluating the intensity of instantaneous chemical weathering in continents

geochemistry of large river suspended sediments silicate weathering or recycling tracer this study focuses on the major and trace element composition of suspended sediments transported by the world s largest rivers its main purpose is to answer the following question is the degree of weathering of modern river borne particles consistent with the estimated river dissolved loads derived from silicate weathering in agreement with the well known mobility of elements during weathering of continental rocks we confirm that river sediments are systematically depleted in na k ba with respect to the upper continental crust for each of these mobile elements a systematics of weathering indexes of river borne solids is attempted a global consistency is found between all these indexes important variations in weathering intensities exist a clear dependence of weathering intensities with climate is observed for the rivers draining mostly lowlands however no global correlation exists between weathering intensities and climatic or relief parameters because the trend observed for lowlands is obscured by rivers draining orogenic zones an inverse correlation between weathering intensities and suspended sediment concentrations is observed showing that the regions having the highest rates of physical denudation produce the least weathered sediments finally chemical and physical weathering are compared through the use of a simple steady state model we show that the weathering intensities of large river suspended sediments can only be reconciled with the silicate derived dissolved load of rivers by admitting that most of the continental rocks submitted to weathering in large river basins have already suffered previous weathering cycles a simple graphical method is proposed for calculating the proportion of sedimentary recycling in large river basins finally even if orogenic zones produce weakly weathered sediments we emphasize the fact that silicate chemical weathering rates and hence co2 consumption rates by silicate weathering are greatly enhanced in mountains simply because the sediment yields in orogenic drainage basins are higher hence the parameters that control chemical weathering rates would be those that control physical denudation rates

climate control on early cenozoic denudation of the namibian margin as deduced from new thermochronological constraints abstract the processes that control long term landscape evolution in continental interiors and in particular along passive margins such as in southern africa are still the subject of much debate e g braun 2018 although today the namibian margin is characterized by an arid climate it has experienced climatic fluctuations during the cenozoic and yet to date no study has documented the potential role of climate on its erosion history in western namibia the brandberg massif an erosional remnant or inselberg provides a good opportunity to document the cenozoic denudation history of the margin using the relationship between rock cooling or exhumation ages and their elevation here we provide new apatite u th sm he dates on the brandberg inselberg that range from 151 12 to 30 2 ma combined with existing apatite fission track data they yield new constraints on the denudation history of the margin these data document two main cooling phases since continental break up 130 myr ago a rapid one 10 c myr following break up and a slower one 1 2 c myr between 65 and 35 ma we interpret them respectively to be related to escarpment erosion following rifting and continental break up and as a phase of enhanced denudation during the early eocene climatic optimum we propose that during the early eocene climatic optimum chemical weathering was important and contributed significantly to the denudation of the namibian margin and the formation of a pediplain around the brandberg and enhanced valley incision within the massif additionally aridification of the region since 35 ma has resulted in negligible denudation rates since that time

enhanced chemical weathering of rocks during the last glacial maximum a sink for atmospheric co2 abstract it has been proposed that increased rates of chemical weathering and the related drawdown of atmospheric co2 on the continents may have at least partly contributed to the low co2 concentrations during the last glacial maximum lgm variations in continental erosion could thus be one of the driving forces for the glacial interglacial climate cycles during quaternary times to test such an hypothesis a global carbon erosion model has been applied to a lgm scenario in order to determine the amount of co2 consumed by chemical rock weathering during that time in this model both the part of atmospheric co2 coming from silicate weathering and the part coming from carbonate weathering are distinguished the climatic conditions during lgm were reconstructed on the basis of the output files from a computer simulation with a general circulation model only the predicted changes in precipitation and temperature have been used whereas the changes in continental runoff were determined with an empirical method it is found that during the lgm the overall atmospheric co2 consumption may have been greater than today by about 20 mainly because of greater carbonate outcrop area related to the lower sea level on the shelves this does not however affect the atmospheric co2 consumption by silicate weathering which alone has the potential to alter atmospheric co2 on the long term silicate weathering and the concomitant atmospheric co2 consumption decreased together with a global decrease of continental runoff compared to present day both by about 10 nevertheless some uncertainty remains because the individual lithologies of the continental shelves as well as their behavior with respect to chemical weathering are probably not well enough known the values we present refer to the ice free continental area only but we tested also whether chemical weathering under the huge ice sheets could have been important for the global budget although glacial runoff was considerably increased during lgm weathering under the ice sheets seems to be of minor importance

major element chemistry in the upper yangtze river a case study of the longchuanjiang river article water samples were collected twice per month over a two year period from the longchuanjiang river yunnan province china to understand monthly variations in major elements and solute fluxes as related to rock weatheringand associatedco2consumption rates solute concentrations were 5 times the medianof 65 mg l for global average total cationic exchange capacity tz

comment on numerical investigation of lake bed seepage patterns effects of porous medium and lake properties by genereux d and bandopadhyay i 2001 journal of hydrology 241 286 303

chemical weathering of monsoonal eastern china implications from major elements of topsoil major element compositions of 36 bulk samples and 41 clay samples which were obtained from 47 topsoils collected in monsoonal eastern china were investigated with conventional wet chemistry and x ray fluorescence xrf spectrometry respectively based on major element analyses the mobility of major elements and latitudinal distributions of sio2 al2o3 ratio chemical index of alteration cia chemical index of weathering ciw and weathering index of parker wip were analyzed meanwhile the suitability of these chemical weathering indices to topsoils in monsoonal eastern china and its controls were discussed these investigations indicate that na k ca mg and si are relatively depleted while mn p fe and ti are relatively enriched in topsoils of the study area by comparison with their contents in the upper continent crust ucc and that alkali metal na k and alkaline earth metal ca mg elements are generally easier to be depleted from their parent materials than other major elements during chemical weathering the latitudinal distributions of cia ciw and wip show that they are suitable to both bulk and clay samples but sio2 al2o3 is only suitable to clay samples not suitable in bulk ones all these investigations indicate a significant dependence of grain size in major element abundance and latitudinal distributions of sio2 al2o3 cia ciw and wip but parent rock type has little effect on them except its impact on the latitudinal distribution of wip in clay samples the significant grain size dependence probably indicates the presence of unaltered minerals in bulk samples thus we suggest that clay samples are more suitable to investigating chemical weathering of sediments on continents than bulk samples the trivial effect of parent rock type probably indicates a relatively uniform chemical weathering on various parent rocks correlation analyses indicate that climate is the dominant control of chemical weathering of topsoils in the study area and the significant latitude effect indicated by the spatial distributions of chemical weathering indices actually reflect the climate control on chemical weathering of topsoils chemical weathering indices actually reflect the integrated weathering history in the study area besides the dominant control of climate other factors like tectonics parent rock biology landform and soil depth and age might also have some effect on the chemical weathering of topsoils in the study area which needs further research c 2013 elsevier ltd all rights reserved

geochemistry of dissolved and suspended loads of the seine river france anthropogenic impact carbonate and silicate weathering this study focuses on the chemistry of the seine river system one of the major rivers in europe and constitutes the first geochemical investigation of both suspended and dissolved loads of this river the seine river drains a typical mesozoic cenozoic sedimentary basin the paris basin constituted of limestones mixed or interbedded with terrigenous sediments derived from the paleoreliefs bordering the mesozoic and cenozoic seas in the context of quantifying the global influence of carbonate and silicate weathering on atmospheric co2 consumption the seine river offers the possibility of examining weathering rates in a flat sedimentary environment under temperate climatic conditions one of the major problems associated with the seine river as with many temperate rivers is pollution we propose in this paper 2 approaches in order to correct the dissolved load of the seine river for anthropogenic inputs and to calculate weathering rates of carbonates and silicates the first uses the dissolved load of rivers and tries to allocate the different solutes to different sources a mixing model based on elemental ratios is established and solved by an inversion technique the second approach consists in using the suspended load geochemistry under steady state conditions we show that the geochemistry of suspended sediments makes it possible to estimate the amount of solutes released during the chemical weathering of silicates and thus to calculate weathering rates of silicates the total dissolved load of the seine river at paris can be decomposed into 2 of solutes derived from natural atmospheric sources 7 derived from anthropogenic atmospheric sources 6 derived from agriculture 3 derived from communal inputs and 82 of solutes derived from rock weathering during high floods the contribution of atmospheric and agriculture inputs predominates the weathering rate of carbonates is estimated to be 48 t km2 yr 25 mm 1000 yr only 10 of carbonates are transported in a solid form the rest being transported in solution co2 consumption by carbonate weathering approaches 400 103 mol km2 yr in the seine river at paris about 2 3 mg l of dissolved cations are found to originate from the chemical weathering of silicates by taking dissolved silica into accounts the total dissolved load derived from silicate weathering is about 6 7 mg l this value is minimal because biological uptake of silica probably occur in the seine river the chemical weathering rate of aluminosilicates is estimated to be 2 t km2 yr the ratio of physical over chemical weathering of silicates range between 1 and 3 and the total chemical and physical erosion rates of sedimentary silicates are about 2 3 mm kyr the co2 consumption by silicate weathering 15 24 103 mol km2 yr and is independent of dissolved silica concentration silicate consumption is thus 20 times less than carbonate consumption in the paris basin compared to the neighboring granitic areas the sedimentary region drained by the seine river has 2 to 3 times lower co2 consumption rates we attribute this difference to the cation depleted nature of the seine basin aluminosilicates which are of sedimentary origin at a world scale the chemical denudation rates found for the seine basin are very low and comparable to those given for tropical lowland rivers draining silicates such as the rivers of the congo and amazon basins in spite of huge climatic differences we attribute this similarity to the low mechanical denudation that characterizes these two types of regions

plate moving mechanisms constraints and controversies the nature of the driving forces for plate tectonics has been a subject for intense often heated debate for more than a quarter of a century on 15 april 1992 peter ziegler delivered the annual william smith lecture to the geological society on the subject of plate moving mechanisms followed by a series of lectures on related themes this thematic set of papers resulting from the meeting covers some of the major issues discussed for more than a quarter of a century earth scientists have debated the nature of the forces which drive the lithospheric plates one of the major problems has been whether mantle convection including the activity of mantle plumes dominates or whether boundary and plate forces such as slab pull and ridge push exert the most important controls on plate motions clearly the relative importance of the different forces involved may vary both in space and time and they may either reinforce or counterbalance each other depending upon the tectonic setting on 15 april 1992 peter ziegler delivered the annual william smith lecture to the geological society on the subject of plate moving mechanisms this was followed by a further eight presentations on related themes by an international group geoscientists from europe and north america of the nine papers presented at the meeting six are included in this thematic set ziegler bott wilson searle et al doglioni pavoni the other speakers were randall m richardson university of arizona tuscon usa john f dewey oxford and sierd cloetingh free university

silicate rock weathering and atmospheric soil co2 uptake in the amazon basin estimated from river water geochemistry seasonal and spatial variations abstract using the data of the camrex project 1982 1984 on the water geochemistry of the amazon river and its main tributaries it was possible to assess the silicate rock weathering processes and the associated consumption of atmospheric soil co2 taking into account seasonal and spatial variations this study confirms the important role of the andes in the fluvial transport of dissolved and particulate material by the amazon and it shows for the first time that the silicate weathering rate and atmospheric soil co2 consumption are higher in the andes than in the rest of the amazon basin the seasonal variations exhibit the significant role of runoff as a major factor controlling silicate weathering processes and show that the chemical erosion rates vary greatly from low discharge to high discharge the average weathering rate estimated for the whole amazon basin 15 m my is comparable to other estimations made for other tropical equatorial environments a comparison between physical and chemical weathering rates of silicate rocks for the amazon basin and for each tributary basin show that in the andes and in the amazon trough the soil thicknesses are decreasing whereas in the shield the soil profiles are deepening

the significance of mid latitude rivers for weathering rates and chemical fluxes evidence from northern xinjiang rivers rivers draining the sedimentary platform of northern xinjiang the center of asian continent are characterized by low discharge under a temperate and arid climate the influence of rock mineralogy climate relief and human activity on natural water composition and export as a result of weathering is a major scientific concern both at the local and the global scale while comprehensive work on the controlling mechanism of chemical weathering has been less carried out in the sedimentary platform of northern xinjiang thus the effects of climate and rock weathering on the inorganic hydrogeochemical processes are not well quantified at this climatic extreme to remedy this lack a comprehensive survey has been carried out of the geochemistry of the large pristine rivers in northern xinjiang the erlqis yili wulungu jingou and numerous lesser streams which has not experienced the pervasive effects of glaciation and subsequent anthropogenic impacts the scale of the terrain sampled in terms of area is comparable to that of the huanghe and includes a diverse range of geologic and climatic environments in this paper the chemical fluxes from the stable sedimentary basin of the northern xinjiang platform will be presented and compared to published results from analogous terrains in the monsoon basins of china and world overall the fluvial geochemistry of northern xinjiang in westerly climate is similar to that of the chinese rivers huanghe and yangtze in the east asian monsoon climate both in property property relationships and concentration magnitudes the range in the chemical signatures of the various tributaries is large this reflects that lithology exerts the dominant influence in determining the weathering yield from the sedimentary terrains rather than the weathering environment the effect of different rock weathering ranges from rivers dominated by aluminosilicate weathering mainly of granites sandstones and shales to those bearing the signatures of dissolution of carbonates and evaporites and of continental playa deposits carbonates are the general predominant lithology undergoing dissolution particularly within the lesser arid areas the pco2 in the study rivers is out of equilibrium with respect to atmospheric pco2 about up to 20 times supersaturated relative to the atmosphere but not to such an extent as the amazon in the floodplain a roughly positive relationship is observed between solute concentrations and the drought index di for natural waters in the region indicating a coupled mountain basin climate has a direct effect the relative contributions of end member solute sources to the total dissolved cations from each watershed have been quantitatively estimated using dissolved load balance models showing the results as evaporite dissolution carbonate weathering silicate weathering atmospheric input for the whole catchment the areal total dissolved fluxes range from 0 05 to 2 53106mol km2 yr 0 02 2 09106mol km2 yr and 0 01 1 04106mol km2 yr in the yili zhungarer and erlqis respectively comparable to those of chinese and siberia rivers draining sedimentary platforms even though they are in drastically different climatic regimes in general the fluxes from rivers in sedimentary basins are comparable to those from orogenic zones but are much higher than in the shield regions the co2 consumption by aluminosilicate weathering 0 2 284103mol km2 yr is much smaller than in active orogenic belts 19 1750103mol km2 yr in similar latitudes and 143 1000103mol km2 yr in the tropical basins but comparable to those of the chinese 7 106103mol km2 yr and siberia 16 112103mol km2 yr rivers 2013 elsevier b v

the carbonate system geochemistry of shallow groundwater surface water systems in temperate glaciated watersheds michigan usa significance of open system dolomite weathering we present here a field geochemical study of controls on carbonate weathering within rapidly circulating shallow groundwater surface water systems in the glaciated mid continent region groundwaters and surface waters in three watersheds spanning the upper to lower peninsulas of michigan consist of ca 2 mg 2 hco 3 solutions derived from the open system dissolution of calcite and dolomite in soils developed on mixed mineralogy glacial drift the thermodynamic stabilities of calcite and dolomite both decrease with decreasing temperature with dolomite more strongly affected thus the low mean annual temperature of these temperate weathering environments maximizes the absolute solubility of dolomite as well as its solubility relative to calcite many groundwaters in the study area approach equilibrium with respect to the more soluble dolomite and are moderately supersaturated with respect to calcite groundwaters in each watershed have distinct and relatively narrow ranges of carbon dioxide partial pressure p co 2 values which increase significantly from north to south log p co 2 of 3 0 to 2 2 atm suggesting that there are landscape level differences in carbon transformation rates in soil weathering zones increases in weathering zone p co 2 values produce hco 3 concentrations that vary by a factor of five but the mg 2 ca 2 and mg 2 hco 3 ratios of all groundwaters are similar suggesting relatively constant weathering input ratios of calcite and dolomite although surface waters commonly are between 2 and 10 times supersaturated with respect to calcite the mg 2 hco 3 ratios of surface waters are very close to initial groundwater values suggesting that back precipitation of calcite is not a significant process in these systems the enhanced solubility of dolomite at low temperatures coupled with the landscape level differences in carbon cycling suggest that temperate zone weathering reactions in glaciated terrains are significant contributors to continent scale fluxes of both mg 2 and hco 3

direct evidence of the feedback between climate and nutrient major and trace element transport to the oceans abstract climate changes affect weathering denudation and riverine runoff and therefore elemental fluxes to the ocean this study presents the climate effect on annual fluxes of 28 dissolved elements and organic and inorganic particulate fluxes determined over 26 42 year period in three glacial and three non glacial river catchments located in eastern iceland annual riverine fluxes were determined by generating robust correlations between dissolved element concentrations measured from 1998 to 2003 and suspended inorganic matter concentrations measured from 1962 to 2002 with instantaneous discharge measured at the time of sampling in each of these rivers these correlations were used together with measured average daily discharge to compute daily elemental fluxes integration of these daily fluxes yielded the corresponding annual fluxes as the topography and lithology of the studied glacial and non glacial river catchments are similar we used the records of average annual temperature and annual runoff to examine how these parameters and glacier melting influenced individual element fluxes to the oceans significant variations were found between the individual elements the dissolved fluxes of the more soluble elements such as mo sr and na are less affected by increasing temperature and runoff than the insoluble nutrients and trace elements including fe p and al this variation between the elements tends to be more pronounced for the glacial compared to the non glacial rivers these observations are interpreted to stem from the stronger solubility control on the concentrations of the insoluble elements such that they are less affected by dilution the dilution of the soluble elements by increasing discharge in the glacial rivers is enhanced by a relatively low amount of water rock interaction increased runoff due to glacial melting tend to be collected rapidly into river channels limiting water rock interaction it was found that the climate effect on particle transport from the glacial rivers is far higher than all other measured fluxes this observation together with the finding that the flux to the oceans of biolimiting elements such as p and fe is dominated by particulates suggests that particulate transport by melting glaciers have a relatively strong effect on the feedback between continental weathering atmospheric chemistry and climate regulation over geologic time

temperature and co2 dependency of global carbonate weathering fluxes implications for future carbonate weathering research abstract carbonate weathering and transfer of carbon towards the coastal zone is one of the relevant sinks for atmospheric co2 controlled by hydrology ecosystem respiration river water degassing and further factors specifically the connection between the soil rock system to the river systems and instream processes affecting the weathering product fluxes remain under researched based on constraints for soil rock pco2 river pco2 and an identified dependence of river alkalinity on temperature this work tested which controls should be considered at the global scale to accomplish a more holistic carbonate rock weathering model compiled river data suggests that with increasing land temperature above approximately 11 c the amount of instream alkalinity in carbonate catchments decreases due to the temperature effect on the carbonate system while the converse holds true at lower temperatures latter is in accordance with calcite dissolution controlled by soil rock pco2 estimates based on ecosystem respiration in addition the type of the weathering system open semi closed to closed system with respect to co2 was identified to be highly relevant for global weathering estimations open systems seem to be the most dominant boundary condition of calcite weathering in the soil profile tropical areas with thick soil layers however cause the carbonate weathering system to shift from open to semi closed or closed system conditions the findings support that calcite weathering fluxes in the soil profile are higher than the fluxes to the ocean transported by rivers furthermore an increase in mean land temperature does not necessarily translate into an increase of lateral weathering fluxes because it might have an influence on soil development discharge co2 degassing soil respiration and calcite dissolution all these named factors need to be addressed to be able to quantify global carbonate weathering fluxes and to assess the sensitivity of carbonate weathering fluxes on climate variability future works should focus on collecting more temporal river chemistry data mainly in tropical regions to understand the main mechanism causing the observed decrease of alkalinity concentration with temperature

subduction hinge migration abstract it has been argued that back arc tectonics is controlled principally by the absolute motion of the overriding plate and the migration of the hinge of the downgoing plate thus hinge migration rollback is fundamentally important to understanding the geodynamics of back arc regions but even rates of hinge migration are unknown the rate of hinge migration can be estimated if the rate of back arc extension and the motion of the overriding plate are known rates of rollback in a hotspot reference frame range from near zero in the case of the new hebrides arc to 50 70 mm a at the south sandwich arc and may be as high as 100 mm a at the tonga trench but the hinge is actually advancing along the izu bonin trench as evidenced by the fact that there is no significant active extension behind the izu bonin arc the rate of hinge advance increases from north to south along the izu bonin trench and correlates well with the dip of the subducted slab active spreading in the mariana trough may be attributed to a rate of hinge advance which is lower than the rate of retreat of the philippine plate all of the possible motions of overriding plates and subduction hinges which might give rise to back arc opening are represented among the examples considered thus there is no unique circumstance in which back arc extension occurs finally there appears to be no clear correlation between hinge motion and the age of the subducted lithosphere

three dimensional groundwater flow to a shallow pond an explicit solution summary steady groundwater flow near a shallow disk shaped pond the bottom of which is in direct hydraulic contact with a confined homogeneous aquifer is studied analytically by the fabrikant method of l operators for the case of a unidirectional flow at infinity a rigorous and explicit expression for the hydraulic head and specific discharge components are obtained depending on the ambient specific discharge aquifer conductivity pond radius and the pond bottom head three regimes gaining losing and flow through of pond water groundwater interaction are explicitly demarcated the hinge line on the pond bottom for the flow through regime is shown to be a straight line the only stagnation point in the gaining regime is found from a simple nonlinear equation closed form expressions for the total pond seepage rate and inflow outflow rates are presented streamlines and isochrones of groundwater travel time are found by a particle tracking method the capture and release zones of the pond are outlined

paleomagnetic tests of pacific plate reconstructions and implications for motion between hotspots the plate motion circuit through the south pacific and antarctica is shown to fail paleomagnetic tests of consistency these failures imply that reconstructions of pacific basin plates relative to surrounding plates inferred from this circuit are systematically in error and that estimates of motion between hotspots inferred from this circuit are probably too large therefore the motions between hotspots remain poorly known and may be much smaller than previously estimated

riverine hydrochemistry and co2 consumption in the tropic monsoon region a case study in a granite hosted basin hainan island china to evaluate the carbon sink capacity caused by rock chemical weathering processes and its controlling factors in the tropical monsoon region the hydrochemistry of the granite hosted changhuajiang river chjr basin in hainan island china were systematically investigated by collecting water samples from the river mouth to headwater in the dry season and the wet season respectively the results show that na ca2 and hco3 are dominant in the chemical runoff of the chjr the spatial and temporal variations of major ions imply the influence of the multi sources the concentrations of ca2 mg2 hco3 and dsi mainly sourcing from rock silicates and carbonates weathering are lower in the wet season than those in the dry season however the concentrations of k cl so4 2 and no3 mainly sourcing from the atmospheric precipitation and human activities are significantly controlled by the monsoon rainfall and hydrological stage in the chjr basin the contributions of the silicates chemical weathering human activities atmospheric input evaporites dissolution and carbonates chemical weathering to the chemical runoff are 82 62 9 05 5 24 2 05 and 1 05 in the chjr respectively the chemical weathering rates of silicates carbonates and evaporites are 16 25 0 40 and 0 62 t km 2 year 1 respectively chemical weathering rates in global granite hosted basins significantly correlate with temperatures p 10 c on a regional scale we find that the chemical weathering rates in the southern china appear a weak positive correlation with normalized differential vegetation indexes ndvi which need to be confirmed by enough data the flux of atmospheric co2 consumption from rock weathering in the chjr basin is 2 71 105 mol km 2 year 1 by the discharge water of 2014 with being close to that 2 9 105 mol km 2 year 1 in the other tropical basins and far from that 5 06 105 mol km 2 year 1 calculated by the averaged discharge water of over years in the chjr the silicates weathering intensity lies at the moderate phase implying that the weathering processes are still developing in global tropical granite basins hence how the atmospheric co2 consumption from rock weathering will change with increasing the atmospheric co2 level and dam construction altering water cycle in the tropical monsoon area is expected to be deserved

impact of atmospheric co2 levels on continental silicate weathering 1 anthropogenic sources are widely accepted as the dominant cause for the increase in atmospheric co2 concentrations since the beginning of the industrial revolution here we use the b witch model to quantify the impact of increased co2 concentrations on co2 consumption by weathering of continental surfaces b witch couples a dynamic biogeochemistry model lpj and a process based numerical model of continental weathering witch it allows simultaneous calculations of the different components of continental weathering fluxes terrestrial vegetation dynamics and carbon and water fluxes the co2 consumption rates are estimated at four different atmospheric co2 concentrations from 280 up to 1120 ppmv for 22 sites characterized by silicate lithologies basalt granite or sandstones the sensitivity to atmospheric co2 variations is explored while temperature and rainfall are held constant first we show that under 355 ppmv of atmospheric co2 b witch is able to reproduce the global pattern of weathering rates as a function of annual runoff mean annual temperature or latitude for silicate lithologies when atmospheric co2 increases evapotranspiration generally decreases due to progressive stomatal closure and the soil co2 pressure increases due to enhanced biospheric productivity as a result vertical drainage and soil acidity increase promoting co2 consumption by mineral weathering we calculate an increase of about 3 of the co2 consumption through silicate weathering mol ha 1 yr 1 for 100 ppmv rise in co2 importantly the sensitivity of the weathering system to the co2 rise is not uniform and heavily depends on the climatic lithologic pedologic and biospheric settings

a simple global model of plate dynamics and mantle convection cooling and thickening of lithospheric plates with age and subduction result in large scale horizontal density contrasts tending to drive plate motions and mantle flow we quantify the driving forces associated with these density contrasts to determine if they can drive the observed plate motions first two dimensional models are computed to evaluate the effects of assumed rheologies and boundary conditions we are unable to obtain platelike behavior in viscous models with traction free boundary conditions the piecewise uniform velocities distinctive of plate motion can be imposed as boundary conditions and the dynamic consistency of the models evaluated by determining if the net force on each vanishes if the lithosphere has a newtonian viscous rheology the net force on any plate is a strong function of the effective grid spacing used leading to ambiguities in interpretation incorporating a rigid plastic lithosphere which fails at a critical yield stress into the otherwise viscous model removes these ambiguities the model is extended to the actual three dimensional spherical plate geometry the observed velocities of rigid plastic plates are matched to the solution of the viscous stokes equation at the lithosphere asthenosphere boundary body forces from the seismically observed slabs from the thickening of the lithosphere obtained from the actual lithospheric ages and from the differences in structure between continents and oceans are included interior density contrasts such as those resulting from upwellings from a hot bottom boundary layer are assumed to occur on a scale small compared to plate dimensions and are not included the driving forces from the density contrasts within the plates are calculated and compared to resisting forces resulting from viscous drag computed from the three dimensional global return flow and resistance to deformation at converging boundaries the rms residual torque is 30 of the driving torque the density contrasts within the plates themselves can reasonably account for plate motions body forces from convection in the interior may provide only a small net force on the plates at converging boundaries the lithosphere has a yield stress of 100 bars drag at the base of the plates is 5 bars and resists plate motion the net driving forces from subducting slabs and collisional resistance are localized and approximately balance driving forces from lithospheric thickening are distributed over the areas of the plates as is viscous drag the approximate balance of these two forces predicts plate velocities uncorrelated with plate area as observed the model represents a specific case of boundary layer convection the dynamical results are consistent with either upper mantle or mantle wide convection

plates and their motions the last reviews which covered research in plate motions were those of herron and pitman 1975 on marine magnetic anomalies and dewey 1975 on plate tectonics both reporting on research for the period 1971 1974 in the last 12 years there has been considerable refinement of relative motion models as well as further development of global models also major effort has gone into defining reference frames for the study of plate motions and discriminating between them more recently the role of errors in individual plate rotations and the associated uncertainties in reconstructions have received attention in this report i concentrate on work published in the last 4 years 1983 1986 citing a minimum of publications from previous years however some papers in press for early 1987 have been included this report first reviews work on relative plate motions for the present and past and reconstructions and then models for these motions global ones for driving forces and local ones determining subduction history and back arc spreading the problem of reference frames both hotspot and paleomagnetic is discussed next i end with a review of work on the errors in plate motions

the geochemical characteristics of the parana river suspended sediment load an initial assessment most water in the parana river drainage basin is supplied by the tropical upper parana over 60 of the total annual water discharge 550 km3 the total suspended solids tss load c 80 106 t year 1 however is essentially furnished 50 70 by the mountainous arid and mostly sediment mantled upper bermejo river drainage basin this characteristic suggests that the parana river solid load tss 600 km upstream from the mouth is largely recycled sedimentary material whose discharge weighted mean chemical index of alteration is c 71 the extended ucc normalized multi elemental diagrams are similar to those of other world rivers nevertheless the detailed inspection of ucc normalized rare earth element ree spidergrams reveals a lithological source for the parana river tss that might be compatible with either tholeiitic flood basalts widespread in the upper drainage or with young andean intermediate volcanic rocks in view of the bermejo river s dominant role as a sediment contributor we feel that the signature preserved in the parana s tss is the latter conversely the uruguay river tss ree signature is certainly determined by the extensive weathering products of jurassic cretaceous tholeiitic basalts copyright 2003 john wiley sons ltd

modelling of atmospheric co2 consumption by chemical weathering of rocks application to the garonne congo and amazon basins modelling of atmospheric co consumption by chemical weathering of rocks application to the garonne congo and amazon basins

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

plate driving forces over the cenozoic era plate reconstructions are used to estimate plate torques for the cenozoic era assuming a dynamical balance between active torques slab pull and ridge push and plate drag as the passive torque in a published one dimensional model for the motion of an oceanic plate the plate drag balances slab pull and ridge push expressing each of these forces in terms of age and sub duction rate and using values at 15 trenches coefficients are found which give a least squares fit here we have retained a common age factor which gives a greater weight to older more rapidly moving plates and the contribution due to ridge push is larger than that found in the previous study but still much smaller than the slab pull force this one dimensional force model is generalized to two dimensional plates moving over the earth s surface and we obtain a torque balance equation in which slab pull and ridge push torques are proportional to boundary chord vectors with the weights depending on powers of subduction velocity at the middle of the chords for each plate we find the unique angular velocity which satisfies the torque balance requirement and this balance torque is compared with the plate drag torque obtained from the plate s geometry and reconstructed angular velocity comparison of the torques is made for two published models for present day plate motions as well as six published reconstructions for time intervals spanning the cenozoic for the present the mismatch between the balanced torque and drag torque is about the same as the difference between the two alternative published models torques are fairly stable throughout the cenozoic with the misfit increasing systematically for earlier reconstructions

models for convergence subduction and back arc development plate motions boundary forces and horizontal temperature gradients implications for the driving mechanism abstract largely because of the wide variety of observational constraints which must be satisfied the search for a viable driving mechanism is perhaps the most perplexing problem related to plate tectonics the mechanism must be compatible with the rigid behavior of lithospheric plates and with a wide range of plate sizes shapes and motions it must be consistent with complex configurations of plate boundaries and equally complex boundary interactions such as the destruction of ridges at subduction zones the mechanism must produce steady state relative and absolute plate motions which persist for tens of millions of years but must also account for sudden dramatic changes finally the plate driving mechanism must be consistent with the non newtonian properties of olivine and with the fabrics of upper mantle peridotites mounting evidence suggests that plate motions result from forces associated with plate boundaries and that the principal resisting force is drag at the base of the lithosphere particularly beneath continents several investigators have suggested that gravitational forces acting on thermally induced lateral density variations in the upper mantle are the principal driving forces for plate tectonics if so plate motions are ultimately controlled by the temperature distribution in the upper mantle and plate tectonics represents a state of dynamic equilibrium in which plate motions are both the cause and the consequence of temperature and density variations in the mantle this concept requires that average absolute plate velocities be predictable from the characteristics of individual plates and that plates tend to move down horizontal temperature gradients a simple linear relation which includes contributions from ridge push rp slab pull sp trench suction ts and continental drag cd cm y 2 6 0 4 4 8 1 8 rp 14 3 1 7 sp 3 5 2 5 ts 5 1 0 7 cd predicts plate velocities with an rms error of 0 44 cm y and a correlation coefficient of 0 98 that plate velocities can be accurately predicted from their own boundary configurations and proportions of continental lithosphere is strong evidence that plate motions result from negative buoyancy forces associated with plate boundaries

the 1977 sumba earthquake series evidence for slab pull force acting at a subduction zone the great 1977 sumba earthquake occurred at the eastern sunda trench just west of the collision of australian continental lithosphere with the island arc the length of the aftershock zone of this normal faulting earthquake is about 200 km aftershocks are concentrated 65 115 km east of the main shock epicenter with very few aftershocks in a 50 km long segment that spans the main shock epicenter relocated hypocenters and focal mechanism data are consistent with normal faulting throughout the upper 28 km of the oceanic lithosphere there is no evidence for thrust faulting of the deeper aftershocks these data imply that the neutral bending surface must be at least 35 40 km deep a second aftershock zone about 180 km northwest of the main shock became active immediately following the main shock but events were concentrated during days 50 52 this zone is a 70 km long lineation that trends toward the main shock epicenter and reflects right lateral strike slip faulting within the subducted oceanic plate seismicity exists to a depth of about 650 km in the very old plate beneath the sunda banda arc and that plate s negative buoyancy causes very large slab pull forces great interface thrust earthquakes are absent at the sumba region and slab pull forces are inferred to have partially decoupled the subducted plate from the overriding plate this decoupling permits slab pull stresses to be guided updip to the region of the sumba main shock such shallow acting slab pull provides a bending moment at the trench and explains the deformation and timing observed for the entire sumba earthquake series in this model slab pull forces stretch the subducted plate until the increasing stresses at the shallow subduction zone lead to a subduction zone earthquake postseismically the released oceanic plate undergoes a pulse of downdip strain returning the plate to a less extended state the moment of this downdip plate motion could exceed the seismic moment of the main shock

chemical weathering in a tropical watershed luquillo mountains puerto rico i long term versus short term weathering fluxes abstract the pristine rio icacos watershed in the luquillo mountains in eastern puerto rico has the fastest documented weathering rate of silicate rocks on the earth s surface a regolith propagation rate of 58 m ma 1 calculated from iso volumetric saprolite formation from quartz diorite is comparable to the estimated denudation rate 25 50 ma 1 but is an order of magnitude faster than the global average weathering rate 6 ma 1 weathering occurs in two distinct environments plagioclase and hornblende react at the saprock interface and biotite and quartz weather in the overlying thick saprolitic regolith these environments produce distinctly different water chemistries with k mg and si increasing linearly with depth in saprolite porewaters and with stream waters dominated by ca na and si such differences are atypical of less intense weathering in temperate watersheds porewater chemistry in the shallow regolith is controlled by closed system recycling of inorganic nutrients such as k long term elemental fluxes through the regolith e g si 1 7 10 8 moles m 2 s 1 are calculated from mass losses based on changes in porosity and chemistry between the regolith and bedrock and from the age of the regolith surface 200 ma mass losses attributed to solute fluxes are determined using a step wise infiltration model which calculates mineral inputs to the shallow and deep saprolite porewaters and to stream water pressure heads decrease with depth in the shallow regolith 2 03 m h2o m 1 indicating that both increasing capillary tension and graviometric potential control porewater infiltration interpolation of experimental hydraulic conductivities produces an infiltration rate of 1 m yr 1 at average field moisture saturation which is comparable with libr tracer tests and with base discharge from the watershed short term weathering fluxes calculated from solute chemistries and infiltration rates e g si 1 4 10 8 moles m 2 s 1 are compared to watershed flux rates e g si 2 7 10 8 moles m 2 s 1 consistency between three independently determined sets of weathering fluxes imply that possible changes in precipitation temperature and vegetation over the last several hundred thousand years have not significantly impacted weathering rates in the luquillo mountains of puerto rico this has important ramifications for tropical environments and global climate change

long term controls on continental scale bedrock river terrace deposition from integrated clast and heavy mineral assemblage analysis an example from the lower orange river namibia abstract establishing relationships between the long term landscape evolution of drainage basins and the fill of sedimentary basins benefits from analysis of bedrock river terrace deposits these fragmented detrital archives help to constrain changes in river system character and provenance during sediment transfer from continents source to oceans sink thick diamondiferous gravel terrace deposits along the lower orange river southern namibia provide a rare opportunity to investigate controls on the incision history of a continental scale bedrock river clast assemblage and heavy mineral data from seven localities permit detailed characterisation of the lower orange river gravel terrace deposits two distinct fining upward gravel terrace deposits are recognised primarily based on mapped stratigraphic relationships cross cutting relationships and strath and terrace top elevations and secondarily on the proportion of exotic clasts referred to as proto orange river deposits and meso orange river deposits the older early to middle miocene proto orange river gravels are thick up to 50 m and characterised by a dominance of karoo supergroup shale and sandstone clasts whereas the younger plio pleistocene meso orange river gravels 6 23 m thick are characterised by more banded iron formation clasts mapping of the downstepping terraces indicates that the proto gravels were deposited by a higher sinuosity river and are strongly discordant to the modern orange river course whereas the meso deposits were deposited by a lower sinuosity river the heavy minerals present in both units comprise magnetite garnet amphibole epidote and ilmenite with rare titanite and zircon grains the concentration of amphibole epidote in the heavy minerals fraction increases from the proto to the meso deposits the decrease in incision depths recorded by deposit thicknesses above strath terraces and the differences in clast character size and roundness and type between the two units are ascribed to a more powerful river system during proto orange river time rather than reworking of older deposits changes in provenance or climatic variations in addition from proto to meso orange river times there was an increase in the proportion of sediments supplied from local bedrock sources including amphibole epidote in the heavy mineral assemblages derived from the namaqua metamorphic complex this integrated study demonstrates that clast assemblages are not a proxy for the character of the matrix and vice versa because they are influenced by the interplay of different controls therefore an integrated approach is needed to improve prediction of placer mineral deposits in river gravels and their distribution in coeval deposits downstream

chemical weathering and co2 consumption in the xijiang river basin south china monthly samples of riverine water were collected and analyzed for the concentrations of major ions ca2 mg2 k na hco3 so42 cl no3 dissolved silicon and total dissolved solids tds at wuzhou hydrological station located between the middle and lower reaches of the xijiang river xjr from march 2005 to april 2006 more frequent sampling and analysis were carried out during the catastrophic flooding in june 2005 stoichiometric analysis was applied for tracing sources of major ions and estimating co2 consumption from the chemical weathering of rocks the results demonstrate that the chemical weathering of carbonate and silicate rocks within the drainage basin is the main source of the dissolved chemical substances in the xjr some 81 20 of the riverine cations originated from the chemical weathering processes induced by carbonic acid 11 32 by sulfuric acid and the other 7 48 from the dissolution of gypsum and precipitates of sea salts within the drainage basin the co2 flux consumed by the rock chemical weathering within the xjr basin is 2 37 x 10 11 mol y 1 of which 0 64 x 10 11 mol y 1 results from silicate rock chemical weathering and 1 73 x 10 11 mol y 1 results from carbonate rock chemical weathering the co2 consumption comprises 0 38 x 10 11 mol during the 9 d catastrophic flooding the co2 consumption from rock chemical weathering in humid subtropical zones regulates atmospheric co2 level and constitutes a significant part of the global carbon budget the carbon sink potential of rock chemical weathering processes in the humid subtropical zones deserves extra attention c 2008 elsevier b v all rights reserved

experimental determination of natural carbonate rock dissolution rates with a focus on temperature dependency abstract the denudation of carbonate rocks at landscape scale is controlled by factors like mineral composition temperature precipitation runoff fracture spacing and vegetation cover knowledge on carbonate denudation is important in order to understand landscape development and long term terrestrial marine carbon transport but there are few laboratory studies done on weathering rates of natural carbonate rocks under the low temperatures relevant for glacial interglacial periods to enhance the understanding of carbonate dissolution kinetics we studied low temperature dissolution reactions of various natural triassic carbonate rocks belonging to the lower muschelkalk in germany we conducted batch and flow through experiments investigating the direct correlation of dissolution rates with temperature and to establish whether the fine grained carbonate rocks micrite are more reactive than the coarser grained sparitic limestones by increasing the temperature from 5 to 26 c far from equilibrium dissolution rates of micritic and sparitic limestone samples increased from 2 42 10 07 to 10 88 10 07 and 4 19 10 07 to 7 74 10 07 mol m 2 s 1 respectively specific surface areas ssa of about 0 006 0 01 m 2 g the dissolution rates of dolomite rock samples varied only slightly from 1 06 10 07 to 2 02 10 07 mol m 2 s 1 ssa approximately 0 002 m 2 g in the temperature range 5 25 c at circum neutral ph the obtained apparent activation energies are in the range of earlier experiments done at higher temperatures but there is a distinct difference between the calcite in the micrite 51 kj mol and sparitic 20 22 kj mol lithologies indicating that the dissolution mechanisms are not the same using these activation energies in modelling of natural carbonate denudation we see that there is a clear effect of changing temperature but this is mostly through the increased solubility at lower temperatures and not through the increasing far from equilibrium dissolution rates at higher temperatures formation of fluid pathways by preferential dissolution of framework calcite crystals is suggested to form infiltration pathways and affect denudation rates the difference in crystal size between the micritic and sparitic limestones will affect the formation of such pathways larger crystals may create fewer and larger conduits and this is expected to be more important for the long term denudation than the differences in activation energies

chemical weathering and associated co2 consumption in the godavari river basin india abstract the study gives insight into the source of major ions concentration and their seasonal variability chemical weathering rates and associated co 2 consumption in the godavari river basin grb the results show that the godavari river basin water was mildly alkaline with a wide range of tds 40 to 550 mgl 1 the most dominant anion was hco 3 followed by cl and the most dominant cation was ca 2 followed by na for all three sampling seasons the average molar ratio of cl na was 0 59 in pre monsoon 0 51 for post monsoon and 0 66 in monsoon which is lower than the values reported in earlier studies the range of precipitation corrected molar ratio for ca 2 na was 0 20 to 1 84 in pre monsoon 0 59 to 1 59 in post monsoon and 0 35 to 2 09 in monsoon season mg 2 na was 0 26 to 1 18 0 24 to 0 62 and 0 17 to 1 42 in pre monsoon post monsoon and monsoon respectively while hco 3 na was 2 08 to 7 0 in pre monsoon 1 98 to 4 05 in post monsoon and 1 67 to 5 79 in monsoon which indicated the influence of basalt weathering on river water chemistry factor analysis indicated the vital role of silicate and carbonate weathering along with atmospheric and anthropogenic input that govern the water chemistry of the grb the chemical weathering rate of grb varied from 17 61 to 68 16 tkm 2 y 1 with an average of 39 49 tkm 2 y 1 in pre monsoon from 27 94 to 65 67 with the average of 42 02 tkm 2 y 1 in post monsoon season and from 17 53 to 62 95 tkm 2 y 1 with an average value of 34 69 tkm 2 y 1 in monsoon the associated co 2 consumption rate due to chemical weathering in the grb was 0 25 10 12 mol y 1 which is 1 04 of the annual global co 2 consumption 24 10 12 mol y 1 by chemical weathering of silicate and carbonate rocks the average annual co 2 drawdown by deccan trap area 5 10 5 km 2 based on co 2 consumption rate due to silicate weathering determined in this study was 0 29 10 12 mol y 1 2 48 of the annual global co 2 consumption 11 7 10 12 mol y 1 by silicate weathering gaillardet j dupre b allegre c j 1999 global silicate weathering and co 2 consumption rates deduced from the chemistry of large rivers chemical geology 159 3 30 the present study was the first attempt to calculate weathering rate of deccan trap using major ion chemistry of the godavari river water the third largest river in india the study further provides the inventory for co 2 consumption on river basin scale which is an important consideration from the point of view of global warming

boundary forces and plate velocities the notion that plate motions result from forces associated with plate boundaries implies that average plate velocities in a mantle hot spot frame of reference are systematically related to the nature and geometry of plate boundaries and to the proportion of continental lithosphere included in the plates several simple linear models relating plate velocity v to net ridge push rp slab pull sp trench suction ts and continental drag cd have been evaluated by multiple linear regression ridge push slab pull and continental drag are found to be vitally important trench suction may be a real force but because effective trench lengths are small and only three of the twelve plates considered are affected it is not a statistically significant contributor to plate motions the preferred relation v cm yr 2 7 4 5 2 1 9 rp 13 2 1 6 sp 4 7 6 cd is a remarkably good predictor of average plate velocities with an rms error of 0 50 cm yr and a correlation coefficient of 0 97 the implied balance between these net forces is generally consistent with the results of force balance models the constant term includes all forces not explicitly considered and suggests that the combined effects of such forces are about equal for all plates finally because the parameters used for any particular plate are independent of all other plates the success of this simple model strongly suggests that the forces which drive plate motions are intimately related to the plates themselves

coupling of tectonic loading and earthquake fault slips at subduction zones because of the viscoelastic behaviour of the earth accumulation of elastic strain energy by tectonic loading and release of such energy by earthquake fault slips at subduction zones may take place on different spatial scales if the lithospheric plate is acted upon by distant tectonic forces strain accumulation must occur in a broad region however an earthquake releases strain only in a region comparable to the size of the rupture area a two dimensional finite element model of a subduction zone with viscoelastic rheology has been used to investigate the coupling of tectonic loading and earthquake fault slips a fault lock and unlock technique is employed so that the amount of fault slip in an earthquake is not prescribed but determined by the accumulated stress the amount of earthquake fault slip as a fraction of the total relative plate motion depends on the relative sizes of the earthquake rupture area and the region of tectonic strain accumulation as well as the rheology of the rock material the larger the region of strain accumulation is compared to the earthquake rupture the smaller is the earthquake fault slip the reason for the limited earthquake fault slip is that the elastic shear stress in the asthenosphere induced by the earthquake resists the elastic rebound of the overlying plate since rapid permanent plate shortening is not observed at subduction zones there must be either strain release over a large region or strain accumulation over a small region over earthquake cycles the former can be achieved only by significant aseismic fault slip between large subduction earthquakes the most likely mechanism for the latter is the accumulation of elastic strain around isolated locked asperities of the fault which requires significant aseismic fault slip between asperities

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

worldwide distribution of continental rock lithology implications for the atmospheric soil co2 uptake by continental weathering and alkalinity river transport to the oceans 1 the silicate rock weathering followed by the formation of carbonate rocks in the ocean transfers co2 from the atmosphere to the lithosphere this co2 uptake plays a major role in the regulation of atmospheric co2 concentrations at the geologic timescale and is mainly controlled by the chemical properties of rocks this leads us to develop the first world lithological map with a grid resolution of 1 1 this paper analyzes the spatial distribution of the six main rock types by latitude continents and ocean drainage basins and for 49 large river basins coupling our digital map with the gem co2 model we have also calculated the amount of atmospheric soil co2 consumed by rock weathering and alkalinity river transport to the ocean among all silicate rocks shales and basalts appear to have a significant influence on the amount of co2 uptake by chemical weathering

spatial characteristics and controlling factors of chemical weathering of loess in the dry season in the middle loess plateau china hydrochemistry methods were used to decipher the weathering and geochemical processes controlling solute acquisition of river waters in the dry season in the middle loess plateau mlp one of the most severely eroded areas and turbid riverine systems in the world river waters were neutral to slightly alkaline with ph varying from 7 6 to 9 6 the total dissolved solids decreased from northwest to southeast with a mean value of 804 mg l much higher than the global average and other large rivers in china ternary diagram showed that river waters were dominated by na hco3 and cl with the main water type of hco3 cl na saturation index values mg2 ca2 and hco3 analyses indicated the preferential ca2 removal by calcite precipitation gibbs plots and stoichiometry plots indicated that the dissolved solutes were mainly derived from rock weathering with minor anthropogenic and atmospheric inputs samples in the northwestern basin are also influenced by evaporation a forward model of mass budget calculation showed that owing to high soluble characteristics evaporite dissolution was a major feature of river waters and contributed 41 to the total dissolved cations on average while carbonate and silicate weathering contributed 28 and 25 on average respectively besides evaporite dissolution cation exchange is also responsible for the high concentrations of na in river water spatial variations showed that evaporite dissolution and silicate weathering were higher in the northern basin whereas carbonate weathering was higher in the southern basin different from most rivers in the world the physical erosion rates varying from 117 7 to 4116 6 t km2y are much higher than the chemical weathering rates varying from 3 54 to 6 76 t km2y in the mlp because of the loose structure of loess and poor vegetation in the basin in the future studies on comparison of water geochemistry in different seasons and on influence of different types of land use and soil salinization on water geochemistry denudation rates and water quality should be strengthened in the mlp these results shed some lights on processes responsible for modern loess weathering and also indicate the importance of time series sampling strategy for river water chemistry copyright 2016 john wiley sons ltd

δ13c pattern of dissolved inorganic carbon in a small granitic catchment the strengbach case study vosges mountains france abstract the transfers and origins of dissolved inorganic carbon dic were studied for a year in a soil spring stream system in the strengbach catchment vosges mountains france this 80 ha experimental research basin is located on the eastern side of the mountains at an altitude ranging from 883 to 1146 m a s l and is mainly covered by spruce 80 brown acid and podzolic soils developed on a granitic basement and as a result the dic originates solely from co2 generated by oxidation of soil organic matter the 13 c dic in catchment waters is highly variable from about 22 in the springs and piezometers to about 12 in the stream at the outlet of the catchment in the springs pronounced seasonal variations of 13 c dic exist with the dic in isotopic equilibrium with the soil co2 that has estimated 13 c of about 24 in winter and 20 in summer these seasonal variations reflect an isotopic fractionation that seems only induced by molecular diffusion of soil co2 in summer in stream water seasonal variations are small and the relatively heavy dic 12 on average is a result of isotopic equilibration of the aqueous co2 with atmospheric co2

hydrogeochemical and isotopic investigations of the han river basin south korea summary the han river the largest river in south korea draining approximately 26 000 km 2 comprises two major tributaries the north and the south han rivers seasonal and spatial variations in the major ion chemistry and isotope compositions of the han river were monitored for one year at 14 23 locations covering about 80 of the entire drainage basin compared to the south han river shr the north han river nhr was much lower in total dissolved solids tds sr and major ion concentrations but higher in si concentration 34 s so 4 values and 87 sr 86 sr ratios these observations suggest strong influence of prevailing rock types in the drainage basins on the chemical and isotopic compositions of the river waters these are silicate rocks in the nhr basin and carbonate rocks in the shr basin the headwaters of the nhr basin where several flood control dams have been constructed show enrichment in deuterium and oxygen 18 indicating evaporative loss the 34 s so 4 data suggest dissolved sulfates in the nhr and shr are mostly derived from atmospheric deposition and variable mixtures of atmospheric deposition and sulfide oxidation respectively the 87 sr 86 sr ratios are much higher in the nhr 0 71793 0 72722 than in the shr 0 71495 0 71785 with one exception indicating weathering of precambrian and mesozoic granitic rocks and marine carbonates respectively