provenance and weathering control on river bed sediments of the eastern tibetan plateau and the russian far east abstract we investigated the petrography and major trace and rare earth element compositions of the bed sediments from the large rivers draining the eastern tibetan plateau etp the huang he yellow chang jiang yangtze hong he red mekong and salween the combined drainage spans tropical temperate and arid climate zones in addition samples from the lena river draining the verkhoyansk and sette daban ranges in an arctic to sub arctic climate zone in siberia were also studied for their major and trace element composition the sub angular texture the quartz feldspar rock fragment classification in the lithic arenite field and the relatively low chemical index of alteration cia 42 79 indicate that these sediments are texturally petrographically and chemically immature and immobile trace elements can be used to obtain some information about the lithologic provenance the etp river sediments are felsic and similar to the upper continental crust with the salween most felsic and the lena most mafic the sediments show a gradation in maturity that is not clearly related to present climatic or physiographic regime this suggests that maturity itself is a relict feature inherited from previous sedimentary cycles the high physical erosion in such high energy and relief systems seems to inhibit intense weathering and manifests a provenance control from local rocks on the sediment compositions

medieval warming little ice age and european impact on the environment during the last millennium in the lower hudson valley new york usa establishing natural climate variability becomes particularly important in large urban areas in anticipation of droughts we present a welldated bi decadal record of vegetation climate land use and fire frequency from a tidal marsh in the hudson river estuary the classic medieval warm period is evident through striking increases in charcoal and pinus dominance from 800 1300 a d paralleling paleorecords southward along the atlantic seaboard higher inputs of inorganic sediment during this interval suggest increased watershed erosion during drought conditions the presence of the little ice age ensues with increases in picea and tsuga coupled with increasing organic percentages due to cooler moister conditions european impact is manifested by a decline in arboreal pollen due to land clearance increased weedy plant cover i e ambrosia plantago and rumex and an increase in inorganic particles to the watershed

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

chemical composition of the zeya river sediments in weathering trend of river sediments of asia the chemical composition of river sediments reflects bedrock geochemistry in the area of erosion and characterizes trend of weathering in the catchment area the article presents data about chemical composition of zeya river sediments this river is one of the largest watercourses in the amur river basin the chemical composition of river sediments was analyzed by x ray fluorescence spectrometry compared with the upper continental crust the river sediments are depleted in almost all analyzed major elements according to the analysis of major element the ratio degree of weathering of river sediments in middle reach of the zeya increases down the river the chemical composition of studied river sediments is close to those in the rivers of northeastern china

comparisons of 210pb and pollen methods for determining rates of estuarine sediment accumulation abstract comparisons of sedimentation rates obtained by 210 pb and pollen analyses of 1 m cores collected throughout the potomac estuary show good agreement in the majority of cores that can be analyzed by both methods most of the discrepancy between the methods can be explained by the analytical precision of the 210 pb method and by the exactness with which time horizons can be identified and dated for the pollen method x radiographs of the cores and the distinctness of the pollen horizons preclude significant displacement by reworking and or mixing of sediments differences between the methods are greatest where uncertainties exist in assigning a rate by one or both methods i e 210 pb trends and or possible horizon assignments both methods show the same relative rates with greater sediment accumulation more common in the upper and middle estuary and less toward the mouth the results indicate that geochronologic studies of estuarine sediments should be preceded by careful observation of sedimentary structures preferably by x radiography to evaluate the extent of mixing of the sediments time horizons whether paleontologic or isotopic are generally blurred where mixing has occurred precluding precise identification whenever possible two methods should be used for dating sediments because a rate albeit erroneous can be obtained isotopically in sediments that are mixed accurate sedimentation rates are also difficult to determine where the time boundary is a zone rather than a horizon where the historical record does not provide a precise date for the pollen horizon or where scouring has removed some of the sediment above a dated pollen horizon

the little ice age and medieval warm period in the sargasso sea sea surface temperature sst salinity and flux of terrigenous material oscillated on millennial time scales in the pleistocene north atlantic but there are few records of holocene variability because of high rates of sediment accumulation holocene oscillations are well documented in the northern sargasso sea results from a radiocarbondated box core show that sst was approximately 1 degree c cooler than today approximately 400 years ago the little ice age and 1700 years ago and approximately 1 degree c warmer than today 1000 years ago the medieval warm period thus at least some of the warming since the little ice age appears to be part of a natural oscillation 39 refs 4 figs 1 tab

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

major ion chemistry of the yarlung tsangpo brahmaputra river chemical weathering erosion and co2 consumption in the southern tibetan plateau and eastern syntaxis of the himalaya the yarlung tsangpo brahmaputra river drains a large portion of the himalaya and southern tibetan plateau including the eastern himalayan syntaxis one of the most tectonically active regions on the globe we measured the solute chemistry of 161 streams and major tributaries of the tsangpo brahmaputra to examine the effect of tectonic climatic and geologic factors on chemical weathering rates specifically we quantify chemical weathering fluxes and co2 consumption by silicate weathering in southern tibet and the eastern syntaxis of the himalaya examine the major chemical weathering reactions in the tributaries of the tsangpo brahmaputra and determine the total weathering flux from carbonate and silicate weathering processes in this region we show that high precipitation rapid tectonic uplift steep channel slopes and high stream power generate high rates of chemical weathering in the eastern syntaxis the total dissolved solids tds flux from the this area is greater than 520 tons km 2 yr 1 and the silicate cation flux more than 34 tons km 2 yr 1 in total chemical weathering in this area consumes 15 2 10 5 mol co2 km 2 yr 1 which is twice the brahmaputra average these data show that 15 20 of the total co2 consumption by silicate weathering in the brahmaputra catchment is derived from only 4 of the total land

moderate chemical weathering of subtropical taiwan constraints from solid phase geochemistry of sediments and sedimentary rocks abstract the well known earthquake and storm triggered extremely high physical weathering rate in taiwan is consistent with present geochemical studies of sediments from different subenvironments offshore coastal river and lake and sedimentary rocks of different geological ages indicating a moderate chemical weathering condition major and trace element concentrations normalized to the average upper crust of yangtze craton show that the sediments and the average composition of sedimentary rocks of taiwan are depleted in ca mg na and sr enriched in rb and zr and unchanged with respect to k indicating their moderately altered nature the mean chemical index of alteration cia 71 75 and plagioclase index of alteration pia 81 86 values of coastal and offshore sediments reveal the sediments derivation from sedimentary rocks by moderate silicate chemical weathering processes the mean cia value 62 of sedimentary rocks of taiwan is similar to that for chinese sediment 61 further confirming

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

two unique weathering regimes in the changjiang and huanghe drainage basins geochemical evidence from river sediments the present research reconstructs the histories of chemical weathering in the drainage basins of the changjiang and huanghe based on the chemical compositions of the river sediments the silicate weathering of the changjiang basin is strong and naand ca silicate minerals are considerably dissolved while other silicate minerals are less attacked in comparison the huanghe basin is characterized by very weak silicate weathering and the weathering degree corresponds well with that of the loess which is the predominant source of the huanghe sediment overall the changjiang and huanghe basins constitute a consistent weathering spectrum from the early to intermediate stage the similarity of chemical compositions between upper continental crust and the huanghe sediments as well as the low degree of chemical weathering in the huanghe basin imply that the river sediments can be considered to be the representative of ucc and are suitable for studying the evolution of continental crust our observations indicate that climate is the predominant factor controlling silicate weathering in both river basins while controls by source rocks and relief are subordinate highly erosive river basins such as the huanghe produce poorly weathered materials which casts doubt on the idea that strong physical weathering naturally contributes much to chemical weathering differences in silicate weathering processes between the changjiang and huanghe basins may provide more constraints in estimating atmospheric co2 budget in china d 2003 elsevier b v all rights reserved

geochemistry of loess paleosol sediments of kashmir valley india provenance and weathering abstract middle to late pleistocene loess paleosol sediments of kashmir valley india were analyzed for major trace and ree elements in order to determine their chemical composition provenance and intensity of palaeo weathering of the source rocks these sediments are generally enriched with fe 2 o 3 mgo mno tio 2 y ni cu zn th u sc v and co while contents of sio 2 k 2 o na 2 o p 2 o 5 sr nb and hf are lower than the ucc chondrite normalized ree patterns are characterized by moderate enrichment of lrees relatively flat hree pattern gd cn yb cn 1 93 2 31 and lack of prominent negative eu anomaly eu eu 0 73 1 01 average 0 81 paas normalized ree are characterized by slightly higher lree depleted hree and positive eu anomaly various provenance discrimination diagrams reveal that the kashmir loess paleosol sediments are derived from the mixed source rocks suggesting large provenance with variable geological settings which apparently have undergone weak to moderate recycling processes weathering indices such as cia ciw and pia values 71 87 83 83 and 80 57 respectively and a cn k diagram imply weak to moderate weathering of the source material

a review of lamellae lamellae bands of increased silicate clay and iron are globally ubiquitous in quaternary sands and have been studied for almost a century however their study is hampered by confusion in the literature a researcher who only reads a single case study may be misled into thinking that these features form in only one way this paper reviews recent research on these confusing features outlining three general formation pathways pedogenic petrogenic and pedo petrogenic and within these numerous specific evolutions the review will be useful to geomorphologists that have lamellae in their field areas but whose research is focused elsewhere and those interested in determining local lamellae genesis it will help quaternary scientists understand that lamellae are confusing features and should not be assumed to have climatic significance or indicate buried soils when encountered at depth

clay transformation and pedogenic calcite formation on a lithosequence of igneous rocks in northwestern iran abstract knowledge about the pathways of pedogenic calcite formations and clay transformations on igneous rocks in semiarid regions plays a vital role in the commentary of soil development on these rocks the present study was conducted to explore the weathering stages and pathways for the formation of pedogenic calcite in soils developed on selected plutonic and volcanic rocks in a semiarid climate in north western iran the soils developed on plutonic rocks were found to be in the primary stage of weathering with very few pedogenic calcites except for soil developed on alkali granite which contained few calcitic pedofeatures calcitic crystallitic b fabrics and calcitic pedofeatures were found in all soils developed on volcanic rocks in situ weathering of ca bearing minerals such as plagioclases amphiboles and pyroxenes could be the possible explanation for the accumulation of pedogenic calcite in the absence of calcareous parent rocks in the studied area micritic calcite was observed to be the dominant form in most of the soils developed on volcanic rocks indicating a rapid precipitation of calcium carbonate smectite kaolinite and mica illite were present in the soils developed on plutonic rocks and the clay content in these soils was less than that of the volcanic rocks feldspars plus mica were supposed to be the most likely source minerals for the formation of pedogenic illite which could be consequently transformed into smectite in these semi arid environments smectite mica illite and kaolinite were the most abundant clay minerals in the soils developed on dacite and andesite rocks while a minor quantity of vermiculite occurred only in andesite derived soils smectite as the dominant mineral and some kaolinite with fairly constant variation in content with depth were observed in the soils formed on hornblende andesite and pyroxene andesite this could indicate that the smectite had the authigenic origin and was formed most likely from the weathering of plagioclase hornblende and pyroxene in general in situ crystallization of pedogenic carbonates and high quantities of smectite in the clay fraction confirmed that the soils formed on volcanic rocks were more developed than those on plutonic rocks in the studied semiarid region moreover our results showed that releasing calcium from ca bearing minerals in igneous rocks in conjunction with biological activities resulted in pedogenic calcite formation

impact of historic land use change on sediment delivery to a chesapeake bay subestuarine delta historic land use in the chesapeake bay drainage basin induced large fluxes of fluvial sediment to subestuarine tributaries stratigraphic and palaeoecologic analyses of deltaic deposits may be used to infer changes on the landscape but are not sufficient to quantify past sediment supply when viewed as an inverse boundary value problem reconstruction of the sediment supply function may be achieved by combining deltaic sedimentation chronologies with an equation governing delta progradation we propose that the diffusion equation is appropriate for simulating delta progradation and obtaining the sediment supply function provided a suitable diffusion constant d can be determined three new methods for estimating d are presented for the case of estuarine deltas when the inverse boundary value technique was applied to otter point creek a tidal freshwater delta at the head of bush river in upper chesapeake bay d values ranged from 3763 to 6199 m2 a 1 delta growth simulations showed a 1740 1760 initial pulse a 1760 1780 erosive redistributive interval a 1780 1920 growth period and a 1920 present erosive redistributive era coupling of simulated delta elevations with an empirical plant habitat predictive equation allowed for comparison of predicted versus actual relative habitat areas also the model yielded reconstructed watershed erosion rates and stream suspended sediment concentrations that could be useful for development of water quality regulations copyright 2001 john wiley sons ltd

the ciw index a new chemical index of weathering abstract a new chemical index of weathering that can be applied to modern soils and precambrian paleosis is proposed ciw al2o3 the value of this index increases as the degree of weathering increases and the difference between ciw index values of the silicate parent rock and soil or sediment reflects the amount of weathering experienced by the weathered material

late holocene climate and ecosystem history from chesapeake bay sediment cores usa palaeoclimate records from late holocene sediments in chesapeake bay the largest estuary in the usa provide evidence that both decadal to centennial climate variability and european colonization

the weathering of basalt and relative mobilities of the major elements at belbex france abstract a basalt and its weathered profile have been analysed for major elements graphical examination shows al fe and ti to have been essentially immobile determining mobility sequences for this deposit is complicated by the long pedogenetic history of the area three different sequences are presented two for different stages of weathering integrated over time and one that reflects the weathering regime of the present day

climatic and tectonic controls on weathering in south china and indochina peninsula clay mineralogical and geochemical investigations from the pearl red and mekong drainage basins 1 results of clay mineralogy major element geochemistry and sr and nd isotopes in 93 argillaceous samples collected from drainage basins of the pearl red and mekong rivers reveal different degrees of chemical weathering in southeast asia despite similar climate conditions across these regions the kaolinite illite ratio illite chemistry index and illite crystallinity can be used as indicators of chemical weathering intensity these mineralogical proxies combined with the k2o na2o cao molar ratio chemical index of alteration cia and weathering trends observed from major element results indicate intensive silicate weathering in the pearl river basin moderate to intensive in the mekong river basin and moderate in the red river basin although a significant modification of epsilon nd 0 values in our riverine sediments during chemical weathering and transport is unlikely sr 87 sr 86 ratios are controlled by various states of chemical weathering of high sr minerals such as plagioclase rich in na and ca with a linear decrease trend from the pearl mekong to red river basins our results suggest that it is not the warm climate with heavy monsoon precipitation but tectonics playing the most significant role in controlling weathering and erosion processes in south china and indochina peninsula strong physical erosion caused by tectonic activities and river incision along the eastern margin of the tibetan plateau and along the red river fault system is responsible for high contents of primary minerals in the lowlands of red and mekong river basins

detrital fine grained sediment contribution from taiwan to the northern south china sea and its relation to regional ocean circulation article i nfo results of clay mineralogy in 140 samples collected in major rivers and lakes in southwestern taiwan and on the seafloor off taiwan in the northeastern south china sea scs combined with clay mineral records of the pearl river drainage basin rivers in luzon and the south china shelf and slope are used to semi quantitatively evaluate the detrital fine grained sediment contribution of taiwan to the northern scs the clay mineral assemblage of the taiwan sourced sediments consists dominantly of illite average 56 and chlorite 41 with very scarce kaolinite and smectite their respective distribution from the rivers and lakes to the seafloor off taiwan does not show obvious basin wide differences linear correlations of illite chemistry index with illite crystallinity and of illite crystallinity with kaolinite present two end members of provenances the pearl river and taiwan for the south china shelf and slope assuming that kaolinite in the northern scs is provided completely from the pearl river the contribution of taiwan in clay minerals is evaluated as 29 to the south china shelf and 23 to the south china slope respectively accordingly the contribution of the pearl river to the south china shelf and slope is 52 and 31 respectively the luzon arc accounts for the rest of clay mineral components for the northern scs mainly by providing smectite the bashi strait crossed branches of the southward deep north pacific deep water and the northward surface kuroshio current in the western pacific may transport taiwan sourced suspended sediments westwards to the northern scs

particle motion and the theory of charcoal analysis source area transport deposition and sampling principles from particle motion physics were applied to recurring problems of the interpretation of stratigraphic charcoal data 1 fires within catchments of lakes often produce no record in fossil charcoal curves and 2 periods characterized by no local fire e g 20th century fire suppression often display as much charcoal as times when local fire was frequent quantitative theory on source area transport deposition and sampling of charcoal shows the relationship between particle sizes counted by alternative methods of charcoal analysis pollen slides for particles 5 80 m in diameter petrographic thin sections for particles 50 10 000 m diameter and charcoal diagrams the relationship between diameter and critical and deposition velocities results in fundamental aerodynamic differences between the sizes of particles quantified by the two methods charcoal recorded on pollen slides is of a size that is difficult to lift but once entrained it remains in suspension thin section charcoal is lifted at relatively low wind velocities but it is not suspended at normal surface wind speeds thermal buoyancy during fire lofts charcoal above the forest canopy depending on particle size and wind speed pollen slide charcoal sizes are underrepresented near the fire because they remain in suspension and are preferentially exported from the burn area thin section charcoal is convected to lower heights on average and is deposited nearby following fire thin section charcoal is redistributed locally by wind and thus may enter lakes because of cohesive forces and aerodynamics more pollen slide charcoal remains on the ground and less enters lakes source areas for pollen slide charcoal are subcontinental to global and diagrams of pollen slide charcoal are biased toward nonlocal charcoal they can be used to interpret importance of fire for broad spatial and temporal scales thin section charcoal represents the catchment fire regime simulation models that generate charcoal during fire mix sediments and then sample at specified intervals indicate that 1 in the absence of sediment mixing the pollen slide method should consistently resolve individual fires that occur with an expectation of 30 50 yr 2 unless samples are continuous neither method will produce useful estimates of fire frequency and 3 even a modest amount of sediment mixing will obscure the signal

chemical indices cia and wip as proxies for integrated chemical weathering in china inferences from analysis of fluvial sediments abstract rivers play a key role in earth surface processes by weathering and eroding the upper continental crust under variable climate regimes how to quantitatively determine the chemical weathering intensity in the drainage basins using geochemistry of fluvial sediments remains unclear the chemical index of alteration cia and the weathering index of parker wip have been used worldwide as proxies to evaluate the chemical weathering intensity in large watersheds and in specific weathering profiles in this study concentrations of major oxides in the suspended particulate matter spm and fine grained floodplain sediments from 13 major rivers in china from north to south were analysed and compiled for the estimation of chemical weathering in china the gradual increase in cia and decrease in wip values with decreasing latitude of the catchments suggest enhanced weathering intensity in these river basins a combined monsoon climate effect of temperature runoff and precipitation primarily controls the chemical weathering in china the provenance rock types and relief play minor roles in weathering whereas an active tectonic setting and typhoon events play key roles in the weathering process in taiwan the cia values of the finer spm samples within a given river are overall greater than those in the corresponding coarser floodplain sediments underscoring the effect of sediment grain size on cia values the irregular seasonal variation of the cia within a specific river further confirms the notion that the cia does not reflect the instantaneous chemical weathering on continents although it is impossible to build a general model for regulating the chemical weathering of continents this study reveals that the integrated chemical weathering intensity in large latitudinal watersheds can with careful application be quantitatively estimated using the proper geochemical proxies of river sediments

major ion chemistry in the headwaters of the yamuna river system chemical weathering its temperature dependence and co 2 consumption in the himalaya abstract the yamuna river and its tributaries in the himalaya constitute the yamuna river system yrs the yrs basin has a drainage area and discharge comparable in magnitude to those of the bhagirathi and the alaknanda rivers which merge to form the ganga at the foothills of the himalaya a detailed geochemical study of the yrs was carried out to determine i the relative significance of silicate carbonate and evaporite weathering in contributing to its major ion composition ii co2 consumption via silicate weathering and iii the factors regulating chemical weathering of silicates in the basin the results show that the yrs waters are mildly alkaline with a wide range of tds 32 to 620 mg l 1 in these waters the abundances of ca mg and alkalinity which account for most of tds are derived mainly from carbonates many of the tributaries in the lower reaches of the yamuna basin are supersaturated with calcite in addition to carbonic acid sulphuric acid generated by oxidation of pyrites also seems to be supplying protons for chemical weathering silicate weathering in yrs basin contributes on average 25 molar basis of total cations on a basin wide scale silicate weathering however does not seem to be intense in the basin as evident from low si na k in the waters 1 2 and low values of chemical index of alteration cia in bed sediments 60 co2 drawdown resulting from silicate weathering in the yrs basin in the himalaya during monsoon ranges between 4 to 7 105 moles km 2 y 1 this is higher than that estimated for the ganga at rishikesh for the same season the co2 consumption rates in the yamuna and the ganga basins in the himalaya are higher than the global average value suggesting enhanced co2 drawdown in the southern slopes of the himalaya the impact of this enhanced drawdown on the global co2 budget may not be pronounced as the drainage area of the yrs and the ganga in the himalaya is small the co2 drawdown by silicates in the yrs basin is marginally higher than the reported values of co2 release from oxidation of organic rich sediments estimated using re as a proxy this comparison shows the need to constrain co2 sources and sinks better to balance its budget in a regional scale the results also show that silicate weathering rate in the yrs basin is 10 mm ky 1 and on the ganga basin it is 5 mm ky 1 which are several times lower than the carbonate weathering rates the significantly higher silicate weathering rate observed in the yrs basin seems to be governed by rapid physical erosion in this region the apparent activation energy for overall silicate weathering in the yrs basin derived from na and si concentrations and water temperature ranges from 50 to 80 kj mol 1 these values are comparable to those reported for granitoid weathering in natural watersheds and feldspar weathering in laboratory experiments this study brings to light the sources contributing to major ions enhanced chemical weathering rates in the yamuna river basin and interdependence of silicate weathering on physical erosion and temperature