chemistry of uranium thorium and radium isotopes in the ganga brahmaputra river system weathering processes and fluxes to the bay of bengal abstract the most comprehensive data set on uranium thorium and radium isotopes in the ganga brahmaputra one of the major river systems of the world is reported here the dissolved 238u concentration in these river waters ranges between 0 44 and 8 32 1 and it exhibits a positive correlation with major cations na k mg ca the 238 u cations ratio in waters is very similar to that measured in the suspended sediments indicating congruent weathering of uranium and major cations the regional variations observed in the 234 u 238 u activity ratio are consistent with the lithology of the drainage basins the lowland tributaries chambal betwa ken and son draining through the igneous and metamorphic rocks of the deccan traps and the vindhyan bundelkhand plateau have 234 u 238 u ratio in the range 1 16 to 1 84 this range is significantly higher than the near equilibrium ratio 1 05 observed in the highland rivers which drain through sedimentary terrains the dissolved 226ra concentration ranges between 0 03 and 0 22 dpm 1 the striking feature of the radium isotopes data is the distinct difference in the 228ra and 226ra abundances between the highland and lowland rivers the lowland waters are enriched in 228ra while the highland waters contain more 226ra this difference mainly results from the differences in their weathering regimes the discharge weighted mean concentration of dissolved 238u in the ganga at patna and in the brahmaputra at goalpara are 1 81 and 0 63 1 respectively the ganga brahmaputra river system constitutes the major source of dissolved uranium to the bay of bengal these rivers transport annually about 1000 tons of uranium to their estuaries about 10 of the estimated global supply of dissolved uranium to the oceans via rivers the transport of uranium by these rivers far exceeds that of the amazon although their water discharge is only about 20 of that of the amazon the high intensity of weathering of uranium in the ganga brahmapura river system can also be deduced from the 232 th 238 u and 230 th 238 u activity ratios measured in the suspended sediments 230th is enriched by about 19 in the suspended sediments relative to its parent 238u the flux of excess 230th supplied to the bay of bengal via these river sediments is 980 1012 dpm a about six times more than its in situ production from seawater in the entire bay of bengal

fracture propagation to the base of the greenland ice sheet during supraglacial lake drainage surface meltwater that reaches the base of an ice sheet creates a mechanism for the rapid response of ice flow to climate change the process whereby such a pathway is created through thick cold ice has not however been previously observed we describe the rapid 2 hours drainage of a large supraglacial lake down 980 meters through to the bed of the greenland ice sheet initiated by water driven fracture propagation evolving into moulin flow drainage coincided with increased seismicity transient acceleration ice sheet uplift and horizontal displacement subsidence and deceleration occurred over the subsequent 24 hours the short lived dynamic response suggests that an efficient drainage system dispersed the meltwater subglacially the integrated effect of multiple lake drainages could explain the observed net regional summer ice speedup

greenland meltwater as a significant and potentially bioavailable source of iron to the ocean the micronutrient iron is thought to limit primary production in large regions of the global ocean meltwater measurements suggest that the greenland ice sheet serves as a significant source of potentially bioavailable iron to the surrounding coastal ocean

the geochemistry of rhenium and osmium in recent sediments from the black sea abstract the os isotopic composition of recent sediments from the black sea are reported with the concentrations of re os and major and minor elements osmium concentrations range from 0 23 to 0 69 ppb and re concentrations range from 21 to 85 ppb concentrations of both elements are large relative to average crustal material and are positively correlated with organic carbon 187 os 186 os ratios range from 5 7 to 7 1 all of these values are less radiogenic than the estimated 187 os 186 os ratio of seawater and average continental crust material variations in the os isotopic composition of these sediments are attributed to mixing of a hydrogenous component 187 os 186 os ratio between 7 and 9 and a less radiogenic detrital component 187 os 186 os ratio between 1 and 4 a mixing model is used to determine the fraction of os in the sediment associated with each component and the burial fluxes of re and os in the black sea are calculated in addition the data are used to estimate the magnitude of systematic error which such initial os isotopic heterogeneity may introduce into re os age determinations of ancient organic rich sediments

re os isotope systematics and weathering of precambrian crustal rocks implications for the marine osmium isotope record the effects of weathering of freshly exposed precambrian rocks on the mobility of osmium were studied on soils developed on a chronosequence of glacial moraines from the western wind river range in wyoming the os budget of the precambrian granitoid source rocks is dominated by os rich trace phases such as magnetite amongst the major silicates biotite or a trace phase in biotite carries most of the os and re and is also the most radiogenic mineral with 187os 186os of 113 and 187re 186os of 2 000 re os isotope systematics of source rocks and soils indicate that rapid oxidation of magnetite mobilizes os with an isotopic composition similar to the isotopic composition of the bulk soils a very radiogenic fraction of os is mobilized through preferential weathering of biotite radiogenic runoff from precambrian shields inferred from osmium isotope analyses of freshwater fe mn nodules suggests that high latitude precambrian shields are important source areas of radiogenic os in seawater we propose that glacial scouring and weathering of glacial tills exposed after deglaciation of precambrian shields surrounding the north atlantic provides a mechanism for the slightly more radiogenic nature of north atlantic seawater compared to other seawater masses glacial interglacial variations in the osmium isotopic composition of seawater seem plausible and may be triggered by changes in weathering regimes on glacial interglacial time scales in high latitude shield areas surrounding the north atlantic

effects of black shale weathering on the mobility of rhenium and platinum group elements radiogenic os from the continents dominates the late cenozoic marine os budget a variety of proposed radiogenic sources includes organic rich sediments precambrian shields and re rich sulfides identifying the dominant sources of radiogenic os to the oceans has a strong impact on past climate models because weathering of silicates acts as a net sink of co 2 whereas weathering of organic matter acts as a source here we investigate the effects of black shale weathering on the integrity of the re os isotope system and release of re and platinum group elements time correlative pairs of fresh drill core and weathered outcrop black shales of late ordovician age utica shale magnafacies quebec were analyzed for re os ir pt and pd as well as total s n and c as c carb and c org the results indicate that 25 64 of the initial re budget 45 90 of the os budget 14 65 of the ir budget 60 77 of the pt budget 69 86 of the pd budget and 44 96 of the c org budget are lost during weathering we use positive correlations of os pt and pd with c org and n to calculate the respective platinum group element concentrations in the unweathered organic matter end member as 3 ng g os 9 ng g pt and 11 24 ng g pd although black shales make up

seasonal evolution of water contributions to discharge from a greenland outlet glacier insight from a new isotope mixing model the greenland ice sheet gris subglacial hydrological system may undergo a seasonal evolution with significant geophysical and biogeochemical implications we present results from a new isotope mixing model to quantify the relative contributions of surface snow glacial ice and delayed flow to the bulk meltwater discharge from a small 5k m 2 land terminating gris outlet glacier during melt onset may and at peak melt july we use radioactive 222 rn and stable isotopes 18 o deuterium to differentiate the water source contributions atmospherically derived 7 be further constrains meltwater transit time from the glacier surface to the ice margin we show that 1 222 rn is a promising tracer for glacial waters stored at the bed and 2 a quantitative chemical mixing model can be constructed by combining 222 rn and the stable water isotopes applying this model to the bulk subglacial outflow from our study area we find a constant delayed flow stored component from melt onset through peak melt this component is diluted first by snowmelt and then by increasing glacial ice melt as the season progresses results from this pilot study are consistent with the hypothesis that subglacial drainage beneath land terminating sections of the gris undergoes a seasonal evolution from a distributed to a channelized system

the record of sea water 187os 186os variation through the cenozoic the variation of sea water 187os 186os during the cenozoic has been determined by analyzing the hydrogenous os released by acidic hydrogen peroxide leaching of layers in an abyssal north pacific pelagic clay core overall sea water 187os 186os has increased from 3 2 at 58 ma to the present day value of 8 6 this pattern is similar to the well known 87sr 86sr evolution of sea water the increase in the proportion of continental os 187os 186os 10 could be due to enhanced weathering rates of black shales associated with the uplift of the himalayas other elements associated with black shale weathering such as u and p should show effects in the sedimentary record

a field study of the chemical weathering of ancient sedimentary organic matter weathering profiles developed on organic carbon rich black shales were studied to examine the loss and degradation of organic matter om during weathering and its role in the geochemical carbon cycle analysis of weathered shales reveals between 60 and nearly 100 total organic carbon toc loss in highly weathered samples relative to initial unweathered toc content pyrite loss coincides with or precedes organic carbon loss elemental analysis and flash pyrolysis gas chromatography py gc of kerogen concentrates indicate that there is little or no selective enrichment or depletion of norg containing sorg containing alkylaromatic branched alkyl or long chain n alkyl moieties in most profiles during weathering kerogen o c ratios consistently increase with toc and pyrite loss infrared spectroscopy ir reveals an increase in the relative abundance of c c and c o bonds relative to alkyl c h bonds in progressively weathered samples these results suggest a two component model for kerogen weathering largely non selective oxidation and hydration followed by cleavage dissolution of oxidized kerogen fragments the extent of weathering in a given outcrop is likely limited by a combination of the rate of physical erosion and exposure of the rock to oxidizing surface waters with om type composition playing a lesser role

hydro biogeochemical coupling beneath a large polythermal arctic glacier implications for subice sheet biogeochemistry 1 we analyze the interannual chemical and isotopic composition of runoff from a large high arctic valley glacier over a 5 year period during which drainage evolved from a long residence time drainage system feeding an artesian subglacial upwelling sgu at the glacier terminus to a shorter residence time drainage system feeding an ice marginal channel imc increased icemelt inputs to the sgu are thought to have triggered this evolution this sequence of events provides a unique opportunity to identify coupling between subglacial hydrology and biogeochemical processes within drainage systems of differing residence time the biogeochemistry of the sgu is consistent with prolonged contact between meltwaters and subglacial sediments in which silicate dissolution is enhanced anoxic processes e g sulphate reduction prevail and microbially generated co2 and sulphide oxidation drive mineral dissolution solute in the imc was mainly derived from moraine pore waters which are added to the channel via extraglacial streams these pore waters acquire solute predominantly via sulphide oxidation coupled to carbonate silicate dissolution we present the first evidence that microbially mediated processes may contribute a substantial proportion 80 in this case of the total glacial solute flux which includes coupling between microbial co2 generation and silicate carbonate dissolution the latter suggests the presence of biofilms in subglacial ice marginal sediments where local perturbation of the geochemical environment by release of protons organic acids and ligands stimulates mineral dissolution these data enable inferences to be made regarding biogeochemical processes in longer residence time glacial systems with implications for the future exploration of antarctic subglacial lakes and other wet based ice sheet environments

influence of palaeoweathering on trace metal concentrations and environmental proxies in black shales the mineralogical and chemical compositions of lower carboniferous tournaisian marine black shale from the kowala quarry the holy cross mountains poland were investigated this study focuses on disturbances in palaeoenvironmental proxies caused by palaeoweathering which progressively changed the major and trace element abundances palaeomagnetic investigations reveal that the devonian carboniferous succession was weathered during the permian triassic by the infiltration of oxidizing fluids related to karstification following post variscan exhumation the weathering process led to vermiculitization of chlorite partial dissolution of calcite and replacement of pyrite by hematite and goethite moreover the concentrations of some trace metals including co cu pb mo ni as and u significantly decreased consequently some elemental abundance ratios that are used as environmental proxies including u th ni co and v cr were altered elements that are bound to iron sulphides e g mo appear to be especially prone to mobilization by even a lightly weathered black shale the documented weathering including changes in elemental concentrations can potentially create misinterpretations of the original palaeoenvironmental conditions in addition the palaeoweathering of the studied samples appears to have substantially changed the carbon oxygen nitrogen and molybdenum stable isotope values the nitrogen and molybdenum stable isotope ratios in particular appear to be most sensitive to the effects of weathering and therefore are good indicators of palaeo weathering processes the major cause of these changes is the decay of organic matter and pyrite for the organic carbon stable isotopes ratios the main factor that controlls this process appears to be the preferential degradation of labile organic matter a combination of the total organic carbon toc total sulphur ts content mo concentration and stable isotope compositions seems to be the most useful for identify palaeo weathering our results suggest that reductions in ts and mo in tandem with diminished mo stable isotope values in the absence of obvious changes to the toc content provide the most compelling evidence of palaeo weathering

some comparative marine chemistries of rhenium gold silver and molybdenum abstract four metals re au ag and mo whose dissolved forms in seawater can potentially be reduced to insoluble states have been measured in a variety of solids depositing under anoxic conditions hydrothermal sulfides coastal sediments and phosphorites for comparative purposes these elements have also been determined in ferromanganese minerals and pelagic sediments which have accumulated under oxidizing conditions rhenium appears to be a unique sentinel for identifying reducing depositional environments where enrichments of greater than three orders of magnitude above crustal concentrations are found molybdenum follows re in these sediments but mo is enriched also in those that accumulate under oxidizing conditions the reported mo crustal concentrations appear low in comparison to our measured sedimentary values gold and ag are concentrated in hydrothermal deposits and sulfides appear to be involved in the precipitation of these elements coastal sediments adjacent to a domestic outfall of los angeles california contain extraordinary high accumulations of anthropogenic au ag and pt the study seeks an understanding of the mobilities and sinks of these metals in the marine environment during the major weathering cycle further anthropogenic contributions to their sedimentary concentrations are identified

sr isotope evolution of seawater the role of tectonics we use a high resolution seawater sr isotopic evolution curve for the last 100 m y in conjunction with modern riverine sr flux measurements and also geologic tectonic and geochronological data to make the case for a close relationship between seawater sr isotopic composition and the india asia continental collision using a simple seawater sr budget model we begin by showing that the sr flux associated with alteration of seafloor basalts is too small and does not have the right time evolution to account for much of the seawater sr isotopic curve of the last 100 m y the flux of dissolved sr carried by rivers originating in the himalaya tibet region on the other hand is presently a significant fraction of the global sr budget we calculate how this riverine flux would have had to change with time in order to match the observed seawater sr isotopic curve and find that the riverine flux remains relatively constant prior to the collision of india with asia but then increases very significantly after collision we note that the period of most rapid change in seawater sr isotopic ratio from 20 ma to 15 ma is also a period of exceptionally high erosion in parts of the himalayas and the tibetan plateau as further evidence that sr derived from the collision of india with asia plays a major role in the sr isotopic evolution of seawater we show that the total amount erosion of the himalaya tibetan plateau since collision which we calculate separately represents a total amount of sr that is very nearly the same as the cumulative amount required by the sr isotopic change of seawater since collision the relationship between erosion and riverine sr flux allows us to use the sr isotopic evolution of seawater to reconstruct a history of erosion since collision and we find that the erosion rate accelerates with time since collision with the present having the largest rate when we apply the sr budget model to the entire phanerozoic using a new compilation of deformed continental area versus time we find that we can account for the large scale structure of the seawater sr isotopic curve but fail to reproduce several local maxima and minima especially in the period 100 300 ma the present high s7sr s6sr of seawater and similar highs in the devonian and cambrian do correlate with extensive deformation on the continents

characterization of dissolved organic matter dom from glacial environments using total fluorescence spectroscopy and parallel factor analysis aquatic dissolved organic matter dom is a major reservoir of reduced organic carbon and has a significant influence on heterotrophic biological productivity and water quality in marine and freshwater environments although the forms and transformations of dom in temperate aquatic and soil environments have been studied extensively this is not the case for glacial environments in this study fluorescent excitation emission matrices eems parallel factor analysis parafac and cluster analysis were used to characterize the fluorescing components of dom in ice and water samples from supraglacial englacial subglacial and proglacial environments of seven glaciers in the canadian arctic norway and antarctica at least five significant fluorescent dom fractions were identified which accounted for 98 2 of the variance in the dataset these included four protein like components and one humic like component the predominantly proteinaceous character of dom from these glaciers is very different from the more humic character of dom described previously from lacustrine fluvial estuarine and marine environments dom from the sampled glaciers is broadly similar in character despite their geographically distinct locations different thermal regimes and inter and intra site differences in potential organic matter sources glacier ice samples had a relatively low ratio of humic like protein like fluorescence while meltwater samples had a higher ratio

higher erosion rates in the himalaya geochemical constraints on riverine fluxes the modern erosion rate of continental scale mountains is difficult to estimate and is usually based on measurement of the suspended load flux of rivers combined with assumptions about river bedload transport and sedimentation in flood plains these two parameters are very difficult to measure directly in continental scale basins in this paper we examine the chemical composition of the suspended load bedload and dissolved load of the ganga and brahmaputra rivers and compare them with the average composition of himalayan source rocks a mass balance equation of erosion fluxes shows that a si rich component is needed in addition to suspended and dissolved load fluxes to account for the composition of the source rock it corresponds to bedload sediment and flood plain deposits which are enriched in quartz by mineral sorting during transport the combined budget of si al and fe in the river system allows us to estimate this si rich flux by this method the total himalayan erosion is estimated to be twice the measured flux of suspended load the comparison between the brahmaputra and the ganga shows that the eastern himalaya has a higher erosion rate 2 9 mm yr than the western himalaya 2 1 mm yr this is likely the result of the higher runoff in the brahmaputra basin the intensity of the monsoon acts as a first order control of the erosion rate in the range

basal ice microbiology at the margin of the greenland ice sheet basal ice at the margin of the greenland ice sheet was studied with respect to its physical characteristics and microbiological community the basal ice contained high concentrations of dissolved ferrous fe and must therefore be anoxic oxygen consumption experiments indicate that 50 of the oxidation was due to biological activity while the rest could be attributed to chemical processes most likely weathering reactions with ferrous fe at least six different fe containing mineral sources were detected in basal ice together with potential bioavailable fe nanoparticles an active denitrifier population was identified due to formation of 30 n dinitrogen gas after amendment of anoxic sediment slurries with 15 n no3 sulfate reduction could not be detected the solid ice facies contained an abundant 10 8 cells cm 3 and complex microbial community that harbored representatives of at least eight major phyla within the domain bacteria the clone library was dominated by members of the subdivision of proteobacteria of which the largest proportion was affiliated to the genus rhodoferax that comprises facultative aerobic iron reducers the second most abundant phylum was bacteroidetes the solid ice facies had many physical similarities with the overlying debris rich banded ice facies indicating that they formed by similar subglacial processes and harbor similar microbial communities this study extends our knowledge of life in subglacial environments such as beneath ice sheets genbank accession numbers hm439882 hm439950 hq144215 hq144221

subglacial methanogenesis a potential climatic amplifier 1 subglacial environments are a previously neglected component of the earth s global carbon cycle a reflection of the view held until recently that they are dominated by abiotic and oxic conditions here we provide a realistic assessment of the theory that the basal regions of the ice sheets that formed over north america and europe during glaciations were host to significant populations of anaerobic microorganisms including methanogens able to metabolize organic carbon sequestered during interglacials and overridden during quaternary glacials in doing so we review the current evidence for subglacial methane release during deglaciation estimate the size of the subglacial reservoir of organic carbon soc and assess the amount of soc available to subglacial microbes and the likely pathways and rates of carbon turnover we then discuss the fate of subglacial methane and the potential impact of its release on atmospheric methane concentrations we calculate that the soc equates to 418 610 pg c and includes carbon from terrestrial soils vegetation peatlands lake and marine sediments the soc that is potentially available for microbial conversion to methane is smaller than this estimate due to 1 glacial erosion 2 accumulation of recalcitrant organic carbon compounds over time 3 conversion to carbon dioxide by aerobic anaerobic respiration and 4 incomplete conversion of labile organic matter to methane we estimate that the total soc available for conversion to methane is 63 pg c our estimates of methane production potentials span a wide range because of the current uncertainty surrounding subglacial metabolic rates we believe however that there is a strong likelihood that subglacial microbes could convert 63 pg of soc to methane during a glacial cycle if this were the case release of this methane from the ice sheet margins during retreat would need to be episodic in order to significantly impact atmospheric methane concentrations our findings suggest that it may well be important to consider subglacial environments as active components of the earth s carbon cycle conclusive determination of the potential impact of subglacial methane production on atmospheric methane concentrations during deglaciation however awaits more precise determination of the ability of subglacial microbes to degrade organic carbon components and their associated rates of metabolism under in situ conditions

the cryoconite ecosystem on the greenland ice sheet this paper presents an assessment of biological activity associated with ice surface debris cryoconite at the ice sheet scale estimates of the mass distribution of cryoconite over the greenland ice sheet gis and the biological activity associated with it are presented and then coupled with a surface mass balance model to estimate total carbon fluxes due to respiration and photosynthesis we find an average loading of 66 g m 2 at kangerlussuaq southwest greenland which compares well with recent estimates from kronprins christians land 17 440 g m 2 boggild and others 2010 in northeast greenland we also report a significant microbial biomass in cryoconite at both these places 10 3 10 4 cells mg 1 and carbon fluxes of the order of 1 3 m mcg 1 d 1 for both respiration and photosynthesis the modelling indicates that total respiration and photosynthesis fluxes are likely to be 10 1 10 2 gg c a 1 and thus far from trivial however estimation of the net ecosystem impact across the entire ice sheet on atmospheric co2 concentrations is problematic because photosynthesis rates were almost certainly low during our field campaign therefore like its water balance the carbon balance of the gis is now known to be important but its accurate quantification will remain elusive until more data are forthcoming

calculating the balance between atmospheric co2 drawdown and organic carbon oxidation in subglacial hydrochemical systems in order to constrain co2 fluxes from biogeochemical processes in subglacial environments we model the evolution of ph and alkalinity over a range of subglacial weathering conditions we show that subglacial waters reach or exceed atmospheric pco2 levels when atmospheric gases are able to partially access the subglacial environment subsequently closed system oxidation of sulfides is capable of producing pco2 levels well in excess of atmosphere levels without any input from the decay of organic matter we compared this model to published ph and alkalinity measurements from 21 glaciers and ice sheets most subglacial waters are near atmospheric pco2 values the assumption of an initial period of open system weathering requires substantial organic carbon oxidation in only 4 of the 21 analyzed ice bodies if the subglacial environment is assumed to be closed from any input of atmospheric gas large organic carbon inputs are required in nearly all cases these closed system assumptions imply that order of 10 g m 2 y 1 of organic carbon are removed from a typical subglacial environment a rate too high to represent soil carbon built up over previous interglacial periods and far in excess of fluxes of surface deposited organic carbon partial open system input of atmospheric gases is therefore likely in most subglacial environments the decay of organic carbon is still important to subglacial inorganic chemistry where substantial reserves of ancient organic carbon are found in bedrock in glaciers and ice sheets on silicate bedrock substantial long term drawdown of atmospheric co2 occurs

major ion chemistry of the ganga brahmaputra river system weathering processes and fluxes to the bay of bengal the ganga brahmaputra one of the world s largest river systems is first in terms of sediment transport and fourth in terms of water discharge a detailed and systematic study of the major ion chemistry of these rivers and their tributaries as well as the clay mineral composition of the bed sediments has been conducted the chemistry of the highland rivers upper reaches of the ganga the yamuna the brahmaputra the gandak and the ghaghra are all dominated by carbonate weathering ca mg and hco3 account for about 80 of the cations and anions in the lowland rivers the chambal the betwa and the ken hco3 excess over ca mg and a relatively high contribution of na k to the total cations indicate that silicate weathering and or contributions from alkaline saline soils and groundwaters could be important sources of major ions to these waters the chemistry of the ganga and the yamuna in the lower reaches is by and large dictated by the chemistry of their tributaries and their mixing proportions illite is the dominant clay mineral about 80 in the bedload sediments of the highland rivers kaolinite and chlorite together constitute the remaining 20 of the clays in the chambal betwa and ken smectite accounts for about 80 of the clays this difference in the clay mineral composition of the bed sediments is a reflection of the differences in the geology of their drainage basins the highland rivers weather acidic rocks whereas the others flow initially through basic effusives the ganga brahmaputra river system transports about 130 million tons of dissolved salts to the bay of bengal which is nearly 3 of the global river flux to the oceans the chemical denudation rates for the ganga and the brahmaputra basins are about 72 and 105 tons km yr 1 respectively which are factors of 2 to 3 higher than the global average the high denudation rate particularly in the brahmaputra is attributable to high relief and heavy rainfall

sr c and o isotopes in carbonate nodules from the ganga plain evidence for recent abrupt rise in dissolved 87sr 86sr ratios of the ganga abstract the evolution of 87 sr 86 sr ratio of the ganga water during the past 100 ka has been reconstructed in this study the 87 sr 86 sr 13 c and 18 o values have been measured in carbonate nodules from different depths of two sediment cores raised from the indian institute of technology kanpur iitk campus 50 m long and jagdishpur jp 25 m long respectively the 87 sr 86 sr ratios of the carbonate nodules range from 0 7142 to 0 7189 in the iitk and 0 7142 to 0 7367 in the jp cores the nodules in general display significantly lower 87 sr 86 sr ratio compared to contemporary ganga river water at kanpur however values of 87 sr 86 sr ratio are observed in the nodules of the jp core near the surface are consistent with that of the present day ganga water at kanpur as well as groundwater samples from adjacent areas indicate recent abrupt increase in 87 sr 86 sr ratio of the ganga these findings are also consistent with the concomitant increase in 87 sr 86 sr ratio of silicates in contemporary sediments of the ganga at kanpur compared to that of past 100 ka the sudden rise of 87 sr 86 sr ratio of the ganga is probably due to increase in the relative proportion of sr from the lesser himalaya containing silicates and carbonates with higher 87 sr 86 sr ratio the cause for the recent increase in sr contribution from the lesser himalaya is not clear this could be due to enhanced agricultural activities and deforestation and or climatic variability during recent times resulting in more erosion in the lesser himalaya the 13 c and 18 o measured in the nodules from the iitk core vary from 6 8 to 1 6 and 8 3 to 5 4 respectively the co variation of 13 c and 18 o suggest the impact of paleoclimate paleovegetation petrography and chemical composition of carbonate nodules indicate little or no diagenetic alteration

northern latitude chemical weathering rates clues from the mackenzie river basin canada abstract the main scope of this study is to investigate parameters controlling chemical weathering rates for a large river system submitted to subarctic climate more than 110 river water samples from the mackenzie river system northern canada have been sampled and analyzed for major and trace elements and sr isotopic ratios in the dissolved phase the three main morphological units are reflected in water chemistry rivers from the canadian shield are very dilute dominated by silicate weathering millot et al 2002 whereas the rivers of the rocky and mackenzie mountains as well as the rivers of the sedimentary interior platform are dominated by carbonate weathering and are so 4 rich compared to the rivers of the mackenzie and rocky mountains the rivers of the interior plains are organic silica and na rich and constitute the dominant input term to the mackenzie river mainstream rivers of the canadian shield area do not significantly contribute to the mackenzie river system using elemental ratios and sr isotopic ratios a mathematical inversion procedure is presented that distinguishes between solutes derived from silicate weathering and solutes derived from carbonate weathering carbonate weathering rates are mostly controlled by runoff which is higher in the mountainous part of the mackenzie basin these rates are comparable to the carbonate weathering rates of warmer areas of the world it is possible that part of the carbonate weathering is controlled by sulfide oxidative weathering but its extent remains difficult to assess conversely to what was stated by edmond and huh 1997 overall silicate weathering rates in the mackenzie basin are low ranging from 0 13 to 4 3 tons km 2 yr na k ca mg and confirm the negative action of temperature on silicate weathering rates for river basins in cold climates in contrast to what has been observed in other large river systems such as the amazon and ganges rivers silicate weathering rates appear 3 to 4 times more elevated in the plains than in the mountainous headwaters this contradicts the raymo hypothesis raymo and ruddiman 1992 isotopic characterization of suspended material clearly shows that the higher weathering rates reported for the plains are not due to the weathering of fine sediments produced in the mountains e g by glaciers and deposited in the plains rather the relatively high chemical denudation rates in the plains are attributed to lithology uncompacted shales high mechanical denudation and the abundance of soil organic matter derived from incomplete degradation and promoting crystal lattice degradation by element complexation the three to fourfold factor of chemical weathering enhancement between the plains and mountains is similar to the fourfold factor of enhancement found by moulton et al 2000 between unvegetated and vegetated watershed this study confirms the negative action of temperature on silicate weathering for cold climate but shows that additional factors such as organic matter associated with northern watersheds are able to counteract the effect of temperature this acceleration by a factor of 4 in the plains is equivalent to a 6 c increase in temperature

detrital sediment fluxes from continents to oceans abstract detrital sediment is carried from land to the sea by three agents rivers glaciers and winds the shoreline is an arbitrary boundary within the detrital sediment transport system which extends from a site of origin across areas of temporary storage to a site of long term deposition the most important of the agents moving sediment across the land is river transport estimated to be in the order of 20 10 12 kg of sediment annually at present analysis of drainage basins indicates that relief and runoff are the most important factors in determining the sediment load of rivers the competence of rivers to transport sediment is governed by the volume flow gradient and the sediment load itself today most large rivers are fed by snowmelt in highland areas runoff from rainfall in the drainage basin and groundwater inflow along the river course water is lost to evaporation and groundwater infiltration river courses can often be divided into two segments a degradational section in which the gradient is relatively steep and little temporary storage of sediment takes place and an aggradational section where the gradient is sharply reduced through meandering and where large scale temporary sediment storage forms a flood plain lakes trap sediment inland and prevent its transport to the sea today many high and mid latitude rivers are interrupted by lakes of glacial origin there are also some large areas of internal drainage that deliver no sediment to the sea the load carried by rivers has been markedly altered by human activity and may have doubled over the past few thousand years only to be reduced in the past century by the widespread construction of dams the ancient use of fire in hunting and its subsequent use in clearing land has increased erosion extensive deforestation and cultivation processes have also increased the sediment supply dam construction is a relatively new factor and affects the sediment transport system by trapping sediment before it can reach the sea the resulting lower sediment supply from rivers is at least in part compensated by increased coastal erosion glacial erosion is difficult to estimate there is an ongoing controversy whether ice sheets are effective erosive agents or not estimates of the present global flux of glacial detritus range from 0 8 50 10 12 kg annually with the lower value most probable the dust flux is in the order of 0 5 to 0 9 10 12 kg annually but may vary greatly with time

the behavior of natural and anthropogenic osmium in long island sound an urban estuary in the eastern u s abstract the os concentration and 187 os 186 os distributions in surface sediments of long island sound eastern u s provide a way of determining the sources and estuarine transport of os the contribution of anthropogenic os from sewer outfalls from the new york city region supplies a tracer with a characteristic 187 os 186 os of about 1 the os concentration of the bulk surface sediment increases steeply moving toward new york city in the westernmost sound and generally follows the concentration of organic carbon the 187 os 186 os ratio of bulk surface sediment increases from west to east in the westernmost part of the sound and is effectively constant in the central sound we interpret these results as indicating that the surface bulk sediments of the sound contain a low 187 os 186 os component perhaps as a reduced coating associated with organic remains from sewer outfalls the acid hydrogen peroxide leach fraction has an average 187 os 186 os of 9 5 in the central sound significantly higher than both the bulk sediment value and the probable sea water value of about 8 the leach fraction in the westernmost part of the traverse is less radiogenic than the central sound and follows the os wsotope trend of the bulk sediment liquid effluent from a new york city sewer outfall contains 30 pg l 1 of dissolved os with a 187 os 186 os of about 2 5 consistent with its being an end member of the west east sediment pattern recorded in the leach fractions of the westernmost cores the leachable os from the central sound predominantly reflects os in ferromanganese oxyhydroxide coatings from continentally derived sediments with 187 os 186 os ratios more radiogenic than seawater the distribution patterns of anthropogenic and natural os with their characteristic isotopic signatures in the sound and the insights gained from the behavior of other particle reactive species indicates that very little os in solution may pass through the estuarine gauntlet

biogeochemical weathering under ice size matters 1 the basal regions of continental ice sheets are gaps in our current understanding of the earth s biosphere and biogeochemical cycles we draw on existing and new chemical data sets for subglacial meltwaters to provide the first comprehensive assessment of sub ice sheet biogeochemical weathering we show that size of the ice mass is a critical control on the balance of chemical weathering processes and that microbial activity is ubiquitous in driving dissolution carbonate dissolution fueled by sulfide oxidation and microbial co2 dominate beneath small valley glaciers prolonged meltwater residence times and greater isolation characteristic of ice sheets lead to the development of anoxia and enhanced silicate dissolution due to calcite saturation we show that sub ice sheet environments are highly geochemically reactive and should be considered in regional and global solute budgets for example calculated solute fluxes from antarctica 72 130 t yr 1 are the same order of magnitude as those from some of the world s largest rivers and rates of chemical weathering 10 17 t km 2 yr 1 are high for the annual specific discharge 2 3 4 1 10 3 m our model of chemical weathering dynamics provides important information on subglacial biodiversity and global biogeochemical cycles and may be used to design strategies for the first sampling of antarctic subglacial lakes and other sub ice sheet environments for the next decade

carbon dating reveals a seasonal progression in the source of particulate organic carbon exported from the greenland ice sheet surface melt from the greenland ice sheet gris collects particulate organic carbon poc as it drains into subglacial environments and transports it downstream where it serves as a microbial substrate we hypothesized that older poc is entrained by meltwaters as the subglacial drainage network expands upglacier over the summer to test this poc samples were collected from a meltwater river exiting the gris over an ablation season and 14c dated resulting values were compared with meltwater hydrochemistry and satellite observations of the catchment area we found that poc ages increased from 5000 to 9000 years b p until peak discharge and catchment size afterward significant fluctuations in poc age were observed interpreted to result from periods of high and low subglacial hydrological pressure and sediment supply and subsequent exhaustion these observations suggest a seasonal progression in the source of poc exported from the gris and provide evidence for a seasonally evolving subglacial drainage system

the os isotopic composition of himalayan river bedloads and bedrocks importance of black shales re os data are presented for bedrocks and bedloads of selected rivers from the himalayan range in central nepal and bangladesh these data demonstrate that the os isotopic composition of most of the bedrocks is similar to that of the average continental crust notable exceptions to this are the black shales from the lesser himalaya lh which contain large quantities of radiogenic osmium in the black shales the os is not concentrated in the sulfides and may instead be associated with organic matter bedloads collected from rivers which include lh black shales in their catchment basins have notably high os ratios 187os 188os 3 this radiogenic signature persists into the ganga river in contrast the brahmaputra river is less radiogenic suggesting an ophiolite input in the headwater region simple physical mixtures of lh black shales with eroded products from the high range require unreasonably high proportions of black shale to explain the high os ratios observed at the outflow of the range assuming that our bedrock and bedload samples are representative of the source region and the eroded mixture respectively this observation suggests that erosion may not be occurring at steady state in addition mass balance calculations indicate that about 20 of the os and 60 of the re are carried in dissolved form implying that chemical erosion plays an important role in the osmium budget finally the contrast in os isotope ratio between ganga bedloads and bulk sediments in the bengal fan suggests that radiogenic os carried by particulate matter and later remobilized may significantly influence the os composition of seawater

sr and 87sr 86sr in the yamuna river system in the himalaya sources fluxes and controls on sr isotope composition abstract sr and 87 sr 86 sr have been measured in the yamuna river headwaters and many of its tributaries yrs in the himalaya these results with those available for major ions in yrs rivers and in various lithologies of their basin have been used to determine their contributions to riverine sr and its isotopic budget sr in the yrs ranges from 120 to 13 400 nm and 87 sr 86 sr from 0 7142 to 0 7932 streams in the upper reaches draining predominantly silicates have low sr and high 87 sr 86 sr whereas those draining the lower reaches exhibit the opposite resulting from differences in drainage lithology 87 sr 86 sr shows significant co variation with sio 2 tds and na k tz indices of silicate weathering in yrs waters suggesting the dominant role of silicate weathering in contributing to high radiogenic sr this is also consistent with the observation that streams draining largely silicate terrains have the highest 87 sr 86 sr analogous to that reported for the ganga headwaters evaluation of the significance of other sources such as calc silicates and trace calcites in regulating sr budget of these rivers and their high 87 sr 86 sr needs detailed work on their sr and 87 sr 86 sr preliminary calculations however indicate that they can be a significant source to some of the rivers it is estimated that on an average 25 of sr in the yrs is derived from silicate weathering in the lower reaches the streams receive 15 of their sr from carbonate weathering whereas in the upper reaches calc silicates can contribute significantly 50 to the sr budget of rivers these calculations reveal the need for additional sources for rivers in the lower reaches to balance their sr budget evaporites and phosphorites are potential candidates as judged from their occurrence in the drainage basin in general precambrian carbonates evaporites and phosphorites dilute the high 87 sr 86 sr supplied by silicates thus making sr isotope distribution in yrs an overall two end member mixing major constraints in quantifying contributions of sr and 87 sr 86 sr from different sources to yrs rivers are the wide range in sr and 87 sr 86 sr of major lithologies limited data on sr and 87 sr 86 sr in minor phases and on the behavior of sr na and ca during weathering and transport the ganga and the yamuna together transport 0 1 of the global sr flux at the foothills of the himalaya which is in the same proportion as their contribution to global water discharge dissolved sr flux from the yamuna and its mobilization rate in the yrs basin is higher than those in the ganga basin in the himalaya a result consistent with higher physical and chemical erosion rates in the yrs

organic carbon export from the greenland ice sheet abstract glacial meltwater exports a unique type of organic carbon to marine systems distinct from non glacially derived riverine export potentially capable of stimulating downstream marine primary productivity here we describe for the first time the bulk level dissolved organic carbon doc and particulate organic carbon poc isotopic composition of glacial meltwater draining the greenland ice sheet gris these data in conjunction with an earlier study that investigated the molecular level composition of gris dissolved organic matter collectively describe the concentration radiocarbon content and lability of organic carbon in subglacial discharge from a land terminating outlet glacier during a melt season by scaling up our measurements across the ice sheet we estimate that the annual doc flux from the gris 0 08 tg y is equivalent to that from a small arctic river discharge q 3 y and that the annual poc flux from the gris 0 9 tg y may be comparable to that of a large arctic river q 200 km 3 y the doc flux is derived primarily from beneath the glacier subglacial 75 in the early season and from surface ice melt up to 100 transmitting through the subglacial environment at the peak of the meltseason the poc flux is primarily derived from the subglacial environment throughout the meltseason the early season low flow glacier discharge contains higher doc concentrations 0 5 4 1 mg l 1 and exports more enriched carbon 14 c doc 250 compared to the peak season high flow discharge when the concentrations are lower 0 1 0 6 mg l 1 and the 14 c is more depleted 14 c doc 400 conversely the poc export 1 4 13 2 mg l 1 14 c poc 250 shows no temporal variation in either concentration or radiocarbon content throughout the meltseason dissolved ion loads in concomitant samples reflected the seasonal evolution of the subglacial drainage system confirming the influence of subglacial hydrology on the composition of the bulk carbon pools based on this work we conclude that 1 different mechanisms control the doc and poc flux from glacial systems 2 chemically distinct doc pools are accessed by seasonally evolving hydrological flow paths and 3 the gris can deliver labile carbon which may also be 14 c depleted to downstream proglacial and marine environments

environmental magnetic characterization of the alaknanda and ramganga river sediments ganga basin india abstract the ganga basin represents a network of complex river systems experiencing rapid changes due to natural and anthropogenic activities the alaknanda and ramganga rivers lying adjacent to each other in the nw himalayas represent two unique sub basins of river ganga having distinct physiography climate physical and chemical processes and land use patterns the present study employs mineral magnetic technique to unravel the controlling factors that influence alteration in sediment source composition and transport processes along the routing pathway the variations in magnetic mineralogy and concentrations provide a suite of information discriminating the sediment sources and transport mechanisms the results show dominant ferrimagnetic mineral assemblage in the alaknanda basin whereas an admixture of ferrimagnetic and antiferromagnetic minerals in the ramganga basin the high spatial variability in concentration of magnetic minerals in alaknanda basin indicates the role of felsic and mafic rocks weathering as well as anthropogenic contribution in sediment magnetism the tributaries flowing through peculiar lithology and anthropocentric polluted areas influence the magnetism of main river channels the loss of mafic weathering signatures in downstream sediment of the ramganga floodplains is due to reconstruction of man made dam at kalagarh which traps upstream sediment load the magnetically hard antiferromagnetic minerals in sediments of ramganga floodplain region compared to mountainous region indicate its possible source either from pollution due to extensive land use for industrial and agricultural practices or from more oxidative weathering under low sedimentation and low energy environment the findings signify new aspects of sediment sources accentuate anthropogenic perturbation and demonstrates the applicability of environmental magnetism for developing sediment dispersal mixing and pollution model for the larger ganga basin

recent large increases in freshwater fluxes from greenland into the north atlantic 1 freshwater fw fluxes from river runoff and precipitation minus evaporation for the pan arctic seas are relatively well documented and prescribed in ocean gcms fluxes from greenland on the other hand are generally ignored altogether despite their potential impacts on ocean circulation and marine biology here we present a reconstruction of the spatially distributed fw flux from greenland for 1958 2010 we find a modest increase into the arctic ocean during this period fluxes into the irminger basin however have increased by fifty percent 6 3 0 5 km3 yr 2 in less than twenty years this greatly exceeds previous estimates for the ice sheet as a whole the rate of increase since 1992 is 16 9 1 8 km3 yr 2 the cumulative fw anomaly since 1995 is 3200 358 km3 which is about a third of the magnitude of the great salinity anomaly gsa of the 1970s if this trend continues into the future the anomaly will exceed that of the gsa by about 2025

chemical and strontium oxygen and carbon isotopic compositions of carbonates from the lesser himalaya implications to the strontium isotope composition of the source waters of the ganga ghaghara and the indus rivers samples of precambrian carbonate mostly dolomite outcrops collected across the lesser himalaya have been analysed for their mineralogy chemical composition and isotope ratios of sr o and c to assess the extent of their preservation and their role in contributing to the high radiogenic strontium isotope composition of the source waters of the ganga ghaghara and the indus their sr concentrations range from 20 to 363 ppm 18opdb 1 4 to 12 8 and mn 11 2036 ppm the petrography of the samples their low sr concentrations and wide range of 18o values are suggestive of their postdepositional alteration the 87sr 86sr of the bulk samples and their carbonate fractions are similar to one another with values ranging from 0 7064 to 0 8935 and are generally more radiogenic than that of contemporaneous seawater comparison of the 87sr 86sr and sr ca ratios among the carbonates and silicates from the lesser himalaya and the source waters of the ganga ghaghara and the indus shows that the values for the source waters overlap with those of the silicates but are much higher than those in carbonates an upper limit of carbonate sr in the various source waters is calculated to be between 6 and 43 assuming that all the ca in the rivers is of carbonate origin the results show that on the average weathering of the precambrian carbonates is unlikely to be a major contributor to the highly radiogenic strontium isotope composition of these source waters however they can be a dominant supplier of radiogenic sr to some rivers on a regional scale the silicate sr component in some of the source waters of the ganga bhagirathi bhilangna alaknanda and ganga ghaghara kali and sarju and the indus sutlej was calculated from the ca na sr na ratios and strontium isotope compositions of these rivers and the silicate endmember these calculations suggest that 33 89 of sr in the bhagirathi bhilangna alaknanda ganga and sarju rivers is of silicate origin whereas in the kali and the sutlej it is much lower only 8 the remaining sr to all these waters has to be supplied from other sources such as weathering of carbonates and evaporites this study underscores the importance of weathering of silicates carbonates and evaporites in contributing to the sr mass balance and 87sr 86sr of the source waters of the ganga ghaghara and the indus the present day silicate and carbonate sr contributions to the sr budget of the rivers vary considerably but among the major source waters of the ganga silicate sr exerts a more dominant control on their sr abundance and 87sr 86sr

strontium isotopes and rubidium in the ganga brahmaputra river system weathering in the himalaya fluxes to the bay of bengal and contributions to the evolution of oceanic87sr 86sr the concentrations of rb and sr and87sr 86sr isotopic ratios have been measured in the dissolved load of the ganga brahmaputra g b river system the ganga was sampled extensively from its source at gangotri in the higher himalaya to patna on the alluvial plains the brahmaputra was sampled in its stretch in assam in india the average sr concentration in the ganga at patna is 1 2 mol l and that in the brahmaputra at goalpara is 0 73 mol l the mean87sr 86sr ratios are 0 7239 and 0 7192 respectively the87sr 86sr in the ganga source waters the alaknanda the bhagirathi and their tributaries range between 0 7300 and 0 7986 considerably higher than the global average runoff value of 0 7119 the high87sr 86sr in the ganga source waters result from the intense weathering of precambrian granites and gneisses enriched in radiogenic sr the sr isotope systematics of the ganga waters is dominated by silicate weathering whereas carbonate weathering plays a significant role in their major ion chemistry the g b system transports about 910 million moles of dissolved sr annually to the bay of bengal with an average87sr 86sr of 0 7213 the sr transported by the g b system is about 2 7 of the global dissolved sr flux to the oceans via rivers model calculations reveal that the g b system has contributed significantly to the sr isotope evolution of seawater during the past 20 ma the flux of rb through the g b system is 24 million moles per year this is about 5 of the global river supply of rb to the oceans nearly twice the contribution of water via the g b system to the oceans our study suggests that the marine geochemistries of sr and rb and possibly u may have been influenced considerably by the himalayan orogeny

molecular characterization of dissolved organic matter associated with the greenland ice sheet abstract subsurface microbial oxidation of overridden soils and vegetation beneath glaciers and ice sheets may affect global carbon budgets on glacial interglacial timescales the likelihood and magnitude of this process depends on the chemical nature and reactivity of the subglacial organic carbon stores we examined the composition of carbon pools associated with different regions of the greenland ice sheet subglacial supraglacial proglacial in order to elucidate the type of dissolved organic matter dom present in the subglacial discharge over a melt season electrospray ionization esi fourier transform ion cyclotron resonance ft icr mass spectrometry coupled to multivariate statistics permitted unprecedented molecular level characterization of this material and revealed that carbon pools associated with discrete glacial regions are comprised of different compound classes specifically a larger proportion of protein like compounds were observed in the supraglacial samples and in the early melt season spring subglacial discharge in contrast the late melt season summer subglacial discharge contained a greater fraction of lignin like and other material presumably derived from underlying vegetation and soil these results suggest 1 that the majority of supraglacial dom originates from autochthonous microbial processes on the ice sheet surface 2 that the subglacial dom contains allochthonous carbon derived from overridden soils and vegetation as well as autochthonous carbon derived from in situ microbial metabolism and 3 that the relative contribution of allochthonous and autochthonous material in subglacial discharge varies during the melt season these conclusions are consistent with the hypothesis that given sufficient time e g overwinter storage resident subglacial microbial communities may oxidize terrestrial material beneath the greenland ice sheet

effects of increase glacier discharge on phytoplankton bloom dynamics and pelagic geochemistry in a high arctic fjord arctic fjords experience extremely pronounced seasonal variability and spatial heterogeneity associated with changes in ice cover glacial retreat and the intrusion of continental shelf s adjacent water masses global warming intensifies natural environmental variability on these important systems yet the regional and global effects of these processes are still poorly understood in the present study we examine seasonal and spatial variability in kongsfjorden on the western coast of spitsbergen svalbard we report hydrological biological and biogeochemical data collected during spring summer and fall 2012 our results show a strong phytoplankton bloom with the highest chlorophyll a chla levels ever reported in this area peaking 15 5 g l during late may and completely dominated by large diatoms at the inner fjord that may sustain both pelagic and benthic production under weakly stratified conditions at the glacier front a progressively stronger stratification of the water column during summer and fall was shaped by the intrusion of warm atlantic water t 3 c and sal 34 65 into the fjord at around 100 m depth and by turbid freshwater plumes t 1 c and sal 34 65 at the surface due to glacier meltwater input biopolymeric carbon fractions and isotopic signatures of the particulate organic material pom revealed very fresh and labile material produced during the spring bloom 13c enriched with values up to 22 7 at the highest chl a peak and high in carbohydrates and proteins content up to 167 and 148 g l respectively and a clear and strong continental signature of the pom present during late summer and fall 13c depleted with values averaging 26 5 and high in lipid content up to 92 g l when freshwater melting is accentuated our data evidence the importance of combining both physical i e water mass dominance and geochemical i e characteristics of material released by glacier runoff data in order to understand the timing intensity and characteristics of the phytoplankton bloom in kongsfjorden a continuously changing system due to sustained warming in a scenario where glacial retreat is predicted to increase the impacts of meltwater discharge and associated delivery of organic and inorganic material to the surrounding waters special attention is required in order to predict the consequences for arctic fjords and adjacent shelf ecosystems

comparative behavior of authigenic re u and mo during reoxidation and subsequent long term burial in marine sediments the trace element re is enriched in mildly reducing suboxic sediments close to or slightly later in the redox sequence than u and before reduction of mo in more reducing sulfidic sediments this work investigates the behavior of authigenic re during oxidation and long term burial in the sediments of several turbidites from the madeira abyssal plain exposure to bottom water o2 clearly remobilizes authigenic re as found in previous work but reimmobilization occurs in reducing sediments below the oxidation front over a depth range of 0 5 3 m the large spread of the re burndown peak must be kinetically controlled perhaps influenced by the corg content once reimmobilized however the authigenic re signal remains immobile for at least 3 4 myr authigenic u in contrast consistently forms peaks 0 5 m broad whereas authigenic mo is lost on oxidation and does not appear to be refixed unless authigenic pyrite is formed these results imply that any paleoenvironmental significance of authigenic re will be compromised in low sedimentation rate environments 10 cm kyr where there is significant exposure of authigenic re to bottom water o2 however authigenic re records from rapidly accumulating continental margin sediments with much less exposure to bottom water o2 still offer considerable potential as high fidelity recorders of past reducing conditions

source and biolability of ancient dissolved organic matter in glacier and lake ecosystems on the tibetan plateau the tibetan plateau is the world s largest and highest plateau and holds the largest mass of ice on earth outside the icesheets of greenland and antarctica as well as abundant lakes this study examined the molecular and isotopic signatures of dissolved organic matter dom along with its biolability in glacier ice glacier fed streams and alpine lakes on the tibetan plateau the aim was to assess the sources of dom and the potential of dom to provide a carbon subsidy to downstream ecosystems tibetan glaciers and glacier streams exhibited low dissolved organic carbon doc concentrations 17 7 27 9 lm and ancient doc radiocarbon ages 749 2350 ybp the optical properties stable carbon isotope ratios d 13 cdoc and the molecular composition fourier transform ion cyclotron resonance mass spectrometry of tibetan glacier dom are consistent with data from other glacier systems around the world the geochemical signatures and the ancient apparent ages of tibetan glacier dom suggest a significant fraction is derived from the atmospheric deposition of pre aged possibly fossil fuel derived organics within the tibetan alpine lakes doc was also ancient 525 675 ybp due to either inputs of pre aged organics from glacier runoff direct deposition or due to the aging of organics in situ i e a radiocarbon reservoir effect the glacier ice and glacier stream sites exhibited high biolability of doc and so provide a carbon subsidy to downstream environments that will change as glaciers on the tibetan plateau recede

potential field signatures of buried precambrian basement in the western canada sedimentary basin an internally consistent levelled compilation of magnetic data is derived for alberta and northeastern british columbia with bouguer gravity data this compilation is used to refine the definition of precambrian basement domains within the western canada sedimentary basin magnetic data are draped at a constant distance above the mapped basement surface to reduce the effects of varying magnetic source depths automated interpretation methods that effectively map outlines of magnetic sources are used to characterize the internal structure of the domains and to aid in their delineation the basement domain map thus derived differs from previous interpretations in the extension of domains further to the southwest due mainly to the availability of new public domain magnetic data and the more precise definition of domain boundaries based on the magnetic source location maps the nahanni hottah chinchaga thorsby vulcan and kiskatinaw domains are weakly magnetic and characterized by magnetic sources tha

the isotopic composition of leachable osmium from river sediments the 187os186os ratios of acidic hydrogen peroxide leaches of river sediments are inferred to be representative of the isotopic composition of os delivered to sea water from the continents the 187os186os values for river sediment leaches from the eastern and central u s the ganges river and the rio maipo range from 10 1 to 21 5 these results suggest that the 187os186os of the soluble river load delivered from the major continental areas to the oceans is on average more radiogenic than average currently eroding continental crust 10 5 sediment leaches from three rivers from the western u s that drain ophiolitic peridotites have distinctly lower 187os186os values 1 4 7 1 such rivers may be significant contributors to sea water of the relatively unradiogenic osmium required to yield the contemporary oceanic 187os186os of 8 6

trickle or treat the dynamics of nutrient export from polar glaciers cold based polar glacier watersheds contain well defined supraglacial ice marginal and proglacial elements that differ in their degree of hydrologic connectivity sources of water e g snow ice and or sediment pore water meltwater residence times allochthonous and autochthonous nutrient and sediment loads we investigated 11 distinct hydrological units along the supraglacial ice marginal and proglacial flow paths that drain joyce glacier in the mcmurdo dry valleys of antarctica we found that these units play unique and important roles as sources and or sinks for dissolved inorganic nitrogen and dissolved inorganic phosphorus and for specific fractions of dissolved organic matter dom as waters are routed from the glacier into nutrient poor downstream ecosystems changes in nutrient export from the glacial system as a whole were observed as the routing and residence times of meltwater changed throughout the melt season the concentrations of major ions in the proglacial stream were inversely proportional to discharge such that there was a relatively constant trickle of these solutes into downstream ecosystems in contrast no3 concentrations generally increased with discharge resulting in delivery of episodic pulses of dissolved inorganic nitrogen rich water treats into those same ecosystems during high discharge events dom concentrations or fluorescence did not correlate with discharge rate but high variability in dom concentrations or fluorescence suggests that dom may be exported downstream as episodic treats but with spatial and or temporal patterns that remain poorly understood the strong nutrient specific responses to changes in hydrology suggest that polar glacier drainage systems may export meltwater with nutrient compositions that vary within and between melt seasons and watersheds because nutrient dynamics identified in this study differ between glacier watersheds with broadly similar hydrology climate and geology we emphasize the need to develop conceptual models of nutrient export that thoroughly integrate the biogeochemical and

the osmium riverine flux and the oceanic mass balance of osmium the osmium concentration os and isotopic composition were determined in a set of 17 of the largest rivers of the world os varies between 4 6 and 52 1 pg kg and the 187os 188os ratio varies between 0 64 and 2 94 measurement of rainwater samples shows that there is no input of oceanic os to the continent through rain assuming a negligible anthropogenic os input in the dissolved load the natural average river water has an os concentration of 7 9 pg kg and a mean 187os 188os ratio of 1 54 the total riverine flux of os to the ocean is estimated to be 295 kg yr the dissolved os flux from island arcs and oceanic islands represents less than 5 of the total riverine flux and is not further considered the continental os flux to the ocean is then represented by the riverine flux as dissolved os from eolian dust and glacial sediments is negligible assuming steady state it is possible to estimate a maximum unradiogenic flux to the ocean of 126 kg yr cosmic dust or mantle derived and an oceanic residence time between 2 5 104 and 5 4 104 with a mean of 3 5 104 year the estimation of the flux of dissolved cosmic particles shows that their contribution to the seawater os would be 14 of the contribution of the unradiogenic component which means that the mantle derived flux should contribute a major part the first results on water from high temperature axial hydrothermal systems indicate that their input is probably negligible which would necessitate that dominant contribution from the low temperature alteration of the oceanic crust and or of the ultramafic exposures contributes dominantly to the input of unradiogenic os to the seawater we show that it would be necessary to leach 1 3 of the os contained in the volume of ultramafic exposures accessible to seawater to account for all of the unradiogenic component contribution another simpler but less likely possibility is that the dissolved cosmic dust represents the only source of dissolved unradiogenic os to the ocean in which case the riverine input represents 94 of the total dissolved flux to the ocean instead of 70 the modern global dissolved os flux to the ocean would then have a 187os 188os ratio of 1 44 instead of 1 06 and the system would be far from steady state

rhenium molybdenum and uranium in groundwater from the southern great basin usa evidence for conservative behavior abstract dissolved re mo and u concentrations and the concentrations of the major cations and anions were measured in groundwaters from twenty three springs in the southern great basin usa from june 1992 through march 1994 rhenium concentrations ranged from 5 1 pmol kg to 190 20 pmol kg the highest re values were observed in the saline groundwater of saratoga spring in death valley and cold spring in ash meadows whereas the lowest re concentrations were found in nevares spring in death valley the mean re concentration for all of the spring waters sampled is 44 33 pmol kg the concentrations of re differs dramatically for groundwaters that discharge from the regional paleozoic carbonate aquifer and for local groundwaters from felsic volcanic rocks the mean re concentration for groundwaters issuing from the carbonate aquifer is 37 14 pmol kg which is similar to the average re value reported for seawater i e 39 8 0 2 pmol kg whereas for the spring waters that discharge from the felsic volcanic aquifers the mean re concentration is 18 3 5 pmol kg the overall mean concentrations of u and mo in these groundwaters are 18 12 nmol kg and 120 60 nmol kg respectively differences in the u and mo concentrations for groundwaters from the carbonate aquifer and those from the volcanic aquifer are also observed such that the mean u and mo concentrations in the carbonate groundwaters are 13 5 nmol kg and 106 40 nmol kg respectively and the mean u and mo concentrations in the volcanic spring waters are 31 5 4 nmol kg and 94 12 nmol kg respectively by comparison u and mo concentrations reported for seawater are 13 9 nmol kg and 107 nmol kg respectively in the oxygenated groundwaters of the great basin re mo and u appear to be acting conservatively as in seawater as evidenced by the covariance observed between re mo and u with chloride sodium and sulfate groundwaters discharging from the regional carbonate aquifer in ash meadows typically exhibit a u re ratio of about 300 while groundwaters that discharge in death valley from local felsic volcanic sources have ratios of about 1700 waters in the remainder of the death valley springs are intermediate and may result from the mixing of the carbonate and volcanic derived waters the re mo and u concentrations in addition to the major solute chemistry indicates that dissolution of carbonate rocks is of primary importance in the groundwaters from ash meadows whereas the weathering of felsic volcanic rocks contributes substantially to the chemical signatures of the death valley groundwaters the differences between u re ratios and different aquifer materials suggest that there is a relationship between the dissolved u re ratios and the aquifer materials similar re mo u ratios for the groundwaters from the carbonate aquifer and seawater are strongly suggestive of quantitative uptake of these trace elements from seawater by carbonate mineral precipitation and subsequent quantitative release of these trace elements during dissolution of the carbonate rocks by groundwater the substantially larger salinity normalized re mo and u concentrations in the groundwaters compared to seawater rule out the possibility that these groundwaters represent simple mixing of dilute terrestrial waters and seawaters or reconstitution of evaporite deposits by groundwater dissolution

effect of oxygen co injected with carbon dioxide on gothic shale caprock co2 brine interaction during geologic carbon sequestration abstract co injection of oxygen a significant component in co 2 streams produced by the oxyfuel combustion process can cause a significant alteration of the redox state in deep geologic formations during geologic carbon sequestration the potential impact of co injected oxygen on the interaction between synthetic co 2 brine 0 1 m nacl and shale caprock gothic shale from the aneth unit in utah and mobilization of trace metals was investigated at 10 mpa and 75 c a range of relative volume percentages of o 2 to co 2 0 1 4 and 8 were used in these experiments to address the effect of oxygen on shale co 2 brine interaction under various conditions major mineral phases in gothic shale are quartz calcite dolomite montmorillonite and pyrite during gothic shale co 2 brine interaction in the presence of oxygen pyrite oxidation occurred extensively and caused enhanced dissolution of calcite and dolomite pyrite oxidation and calcite dissolution subsequently resulted in the precipitation of fe iii oxides and gypsum caso 4 2h 2 o in the presence of oxygen dissolved mn and ni were elevated because of oxidative dissolution of pyrite the mobility of dissolved ba was controlled by barite baso 4 precipitation in the presence of oxygen dissolved u in the experimental brines increased to 8 14 g l with concentrations being slightly higher in the absence of oxygen than in the presence of oxygen experimental and modeling results indicate the interaction between shale caprock and oxygen co injected with co 2 during geologic carbon sequestration can exert significant impacts on brine ph solubility of carbonate minerals stability of sulfide minerals and mobility of trace metals the major impact of oxygen is most likely to occur in the zone near co 2 injection wells where impurity gases can accumulate oxygen in co 2 brine migrating away from the injection well will be continually consumed through the reactions with sulfide minerals in deep geologic formations

the iron isotopic composition of subglacial streams draining the greenland ice sheet abstract in this study we present the first measurements of iron fe stable isotopic composition 56 fe of subglacial streams draining the greenland ice sheet gis we measure the 56 fe values 56 fe 56 fe 54 fe sample 56 fe 54 fe standard 1 10 3 of both dissolved and suspended sediment fe in subglacial outflows from five distinct land terminating glaciers suspended sediments have 56 fe values that lie within the crustal array 56 fe 0 in contrast the 56 fe values of dissolved fe in subglacial outflows are consistently less than 0 reaching a minimum of 2 1 in the outflow from the russell glacier the 56 fe values of dissolved fe vary geographically and on daily time scales major element chemistry and mineral saturation state modeling suggest that incongruent silicate weathering and sulfide oxidation are the likely drivers of subglacial stream fe chemistry and that the extent of chemical weathering influences the 56 fe of dissolved fe the largest difference in 56 fe between dissolved and suspended load is 2 1 and occurs in the subglacial system from the russell glacier southwest gis major element chemistry indicates this outflow to be the least chemically weathered while more mature subglacial systems i e that exhibit greater extents of subglacial weathering have dissolved loads with 56 fe that are indistinguishable from suspended sediments 56 fe suspended dissolved 0 ultimately the dissolved fe generated in some subglacial systems from the gis is a previously unrecognized source of isotopically light fe into the hydrosphere the data illustrate that the dissolved fe supplied by subglacial weathering can have variable 56 fe values depending on the degree of chemical weathering thus fe isotopes have potential as a proxy for subglacial chemical weathering intensity or mode finally based on our regional fe concentration measurements from each glacial outflow we estimate a flux weighted continental scale dissolved iron export of 2 1 gg fe yr 1 to the coastal ocean which is within the range of previous estimates

the role of trace minerals in chemical weathering in a high elevation granitic watershed estibere france chemical and mineralogical evidence we investigated chemical weathering in a high elevation granitic environment in three selected watersheds located in the pyrenees france the sites were located on glacial deposits derived from similar hercynian 300 ma granites characterized by the occurrence of zoned plagioclases and trace calcic phases epidote prehnite sphene apatite the surface waters at those sites show high ca na molar ratios 1 which could not be explained by the dissolution of the major plagioclase oligoclase present in the rocks the coupled approach of investigating stream water chemistry and the mineralogy and chemistry of rocks and soils allowed us to explore the role of the weathering of trace calcic minerals in calcium export at the watershed scale the weathering of the trace calcic minerals which represent 1 of the total rock volume are responsible for more than 90 of the calcium export at the sites annual cationic fluxes 23 104 eq km2 yr calculated for the estibere watershed are among the highest reported for high elevation systems draining granitic rocks and 80 of this annual cationic flux can be attributed to the weathering of trace calcic phases calculations based on isotopic values 87sr 86sr go in the same direction except apatite the trace calcic phases appear to be mainly silicates thus the type of chemical weathering observed in the estibere watershed may have an influence on atmospheric co2 consumption by granite weathering however comparison with other watersheds draining granitic environments worldwide and with the two other sites in the pyrenees indicate that the role of trace calcic phases is important in most young environments exposed to chemical weathering e g high elevation catchments on glacial deposits other factors such as the date of glacial retreat the physical denudation rate the hydrological functioning of the watershed and the nature and structure of the soil cover are also important

last interglacial mis5e hydrographic shifts linked to meltwater discharges from the east greenland margin abstract proximal evidence of the surface ocean response to size reduction of the greenland ice sheet gis during the last interglacial mis5e and preceding glacial termination t2 remains largely elusive using a new sediment record from the western iceland sea the behavior of the northeastern gis and its relation to the subpolar north atlantic surface hydrography is examined extremely light oxygen isotopic 18o values are found off central east greenland during early mis5e and point to enhanced meltwater release potentially from the northeastern sector of the gis data from downstream the cold east greenland current egc and its eastward branches suggest a far reaching effect of this meltwater not only in the nordic seas but also in the se labrador sea in particular whereas an early mis5e warming at 128 5 126 5 ka in the two regions coincided with the relative reduction of meltwater input into the egc the subsequent cooling noted at 126 5 ka followed a renewed major freshwater event off central east greenland our data further indicate persistent freshwater influence from the east greenland margin over the entire mis5e interval and in addition also reveal a late mis5e meltwater event the latter event occurred just prior to the last glacial inception and emphasizes the importance of greenland meltwater as forcing factor on interglacial climates

re os isotope systematics in black shales from the lesser himalaya their chronology and role in the 187os 188os evolution of seawater abstract re and os abundances and os isotope systematics have been measured in a number of black shales sampled from outcrops and two underground phosphorite mines maldeota and durmala in the lesser himalaya the re and os concentrations in these samples exhibit wide range 0 2 to 264 ng g and 0 02 to 13 5 ng g respectively with a mean re os of 25 the 187 os 188 os of these samples also show a broad range 1 02 to 11 6 with many of them far more radiogenic than the currently eroding continental crust the black shales from the maldeota and durmala mines collected a few meters above the krol tal pc c boundary and occurring in the same stratigraphic horizon yield 187 re 187 os isochron ages of 554 16 and 552 22 ma respectively consistent with fossil evidences and those assigned for the pc c boundary at various other locations these results indicate closed system behaviour of re and os in these mine samples and reaffirm the validity of 187 re 187 os pair to date organic rich sediments the age of these mine samples from the outer belt seems to be a few hundred millions of years younger than the preliminary re os age of 839 138 ma for black shales from theog collected from the inner belt these initial results lean toward the hypothesis that the inner belt sediments were deposited earlier than the outer belt however more analyses of black shales are needed to confirm this the role of weathering black shales from the himalaya in contributing to the os isotope evolution of seawater over the past 25 ma was assessed using a simple budget model for seawater os and assuming values for os fluxes and 187 os 188 os based on the available limited data on os concentration and its 187 os 188 os in rivers and oceans these calculations indicate that the required contributions from black shale weathering to account for the entire increase in oceanic 187 os 188 os over the past 16 ma is difficult to satisfy by varying only the os flux from htp rivers 187 os 188 os kept constant at 1 324 or their 187 os 188 os 188 os flux constant at today s value 131 moles yr the requirements to balance os isotope budget in ocean through weathering of black shales however is easier to accommodate if both the os flux from htp himalayan tibetan plateau rivers and their 187 os 188 os are allowed to vary measurements of os abundance in htp rivers and its isotopic composition are needed to test the validity of the model results

the osmium isotopic composition of the continental crust osmium isotopic compositions and concentrations have been determined for deltaic and continental shelf sediments from three major rivers the amazon changjiang and mississippi and for two loesses from the upper mississippi river valley the loesses have heavy mineral and clay compositions characteristic of mississippi river and delta sediment concentrations range from 15 to 120 pg os g and 187os 186os ratios range from 8 2 to 10 9 sediments which are polluted surface sediment from the changjiang estuary or which have scavenged metals from seawater gulf of mexico slope surface sediment and distal amazon shelf sediment have high osmium concentrations and less radiogenic isotopic compositions purely terrigenous sediments have 15 90 pg os g and 187os 186os 10 0 10 9 north american loess and mississippi delta sediment osmium isotopic compositions are indistinguishable we believe that 187os 186os 10 11 is a good average for currently eroding upper continental crust these sediments have neodymium isotopic compositions close to the global mean for river sediment terrigenous 187os 186os is significantly more radiogenic than seawater 187os 186os 8 6 requiring a nonriverine source of osmium to seawater terrigenous osmium is also significantly more radiogenic than bulk pelagic clay osmium we use the improved estimate of terrigenous 187os 186os to recalculate the flux of extraterrestrial osmium to pacific marine sediment if the residence age of osmium in an upper crustal region is similar to the neodymium model age of a sediment derived from that region a model dependent upper crustal 187re 186os ratio can be calculated for the model ages of the sediments analyzed in this study tdm 1 5 1 7 ga model 187re 186os ratios are 340 360 and can be used to correct for bias resulting from the preferential erosion of young crust the 187os 186os ratio of 2 2 ga crust with 187re 186os 400 is 14 2 we have also used the data from this study to estimate upper crustal osmium and rhenium concentrations of 50 pg g and 390 pg g respectively

pge re os and mo isotope systematics in archean and early proterozoic sedimentary systems as proxies for redox conditions of the early earth abstract re os data and pge concentrations as well as mo concentrations and isotope data are reported for suites of fine clastic sediments and black shales from the barberton greenstone belt south africa fig tree and moodies groups 3 25 3 15 ga the belingwe greenstone belt zimbabwe manjeri formation ca 2 7 ga and shales from the witwatersrand ventersdorp and transvaal supergroups south africa ranging from 2 95 to 2 2 ga moderately oxidizing conditions are required to mobilize re and mo in the environment mo fractionation only occurs in solution and these parameters thus have potential use as paleoredox proxies for the early earth pge re abundance patterns of barberton greenstone belt sediments are uniform and very similar in shape to those of komatiites this indicates 1 that the pge came from a source of predominantly ultramafic composition and 2 that pge were transported and deposited essentially in particulate form sediments from the younger belingwe greenstone belt show more fractionated pge re patterns and have re os ratios 10 to 100 higher than those of barberton sediments their pge abundance patterns and re os ratios are intermediate between those of the mid archean shales and neoproterozoic to recent black shales they reflect scavenging of re from solution in the sedimentary environment 98 95 mo values of black shales of all ages correlate with their concentrations the barberton greenstone belt samples have 1 3 ppm mo similar to a granitoid basaltic source this mo has 98 95 mo between 1 9 and 2 4 relative to present day mean ocean water molybdenum momo and is thus not isotopically fractionated relative to such a source similar to the pge this indicates transport in solid form sediments from the belingwe greenstone belt show in part enhanced mo concentrations up to 6 ppm and mo isotope fractionation 98 95 mo up to 1 4 relative to momo the combined pge re and mo data show mainly reducing conditions in the mid archean and suggest that by 2 7 ga the atmosphere and oceans had become more oxidizing substantially younger samples from the transvaal supergroup to ca 2 2 ga surprisingly have mainly low mo concentrations around 1 ppm and show no significant mo isotope fractionation relative to the continental source among possible explanations for this are a return to reducing atmospheric conditions after 2 7 ga reservoir effects or mo removal by sulfide precipitation following sulfate reduction in early proterozoic oceans

geochemical weathering at the bed of haut glacier d arolla switzerland a new model waters were sampled from 17 boreholes at haut glacier d arolla during the 1993 and 1994 ablation seasons three types of concentrated subglacial water were identified based on the relative proportions of ca 2c h co 3 and so4 2 to si type a waters are the most solute rich and have the lowest relative proportion of si they are believed to form in hydrologically inefficient areas of a distributed drainage system most solute is obtained from coupled sulphide oxidation and carbonate dissolution so cd it is possible that there is a subglacial source of o2 perhaps from gas bubbles released during regelation because the high so4 2 levels found up to 1200 eq l are greater than could be achieved if sulphides are oxidized by oxygen in saturated water at 0 c c 414 eq l a more likely alternative is that sulphide is oxidized by fe 3c in anoxic environments if this is the case exchange reactions involving fe iii and fe ii from silicates are possible these have the potential to generate relatively high concentrations of hco3 with respect to so4 2 formation of secondary weathering products such as clays may explain the low si concentrations of type a waters type b waters were the most frequently sampled subglacial water they are believed to be representative of waters flowing in more efficient parts of a distributed drainage system residence time and reaction kinetics help determine the solute composition of these waters the initial water rock reactions are carbonate and silicate hydrolysis and there is exchange of divalent cations from solution for monovalent cations held on surface exchange sites hydrolysis is followed by so cd the so4 2 concentrations usually are 414 eq l although some range up to 580 eq l which suggests that elements of the distributed drainage system may become anoxic type c waters were the most dilute yet they were very turbid their chemical composition is characterized by low so4 2 h co3 ratios and high ph type c waters were usually artefacts of the borehole chemical weathering environment true type c waters are believed to flow through sulphide poor basal debris particularly in the channel marginal zone the composition of bulk runoff was most similar to diluted type b waters at high discharge and was similar to a mixture of type b and c waters at lower discharge these observations suggest that some supraglacial meltwaters input to the bed are stored temporarily in the channel marginal zone during rising discharge and are released during declining flow little of the subglacial chemical weathering we infer is associated with the sequestration of atmospheric co2 t he progression of reactions is from carbonate and silicate hydrolysis through sulphide oxidation by first oxygen and then fe iii which drives further carbonate and silicate weathering a crude estimate of the ratio of carbonate to silicate weathering following hydrolysis is 4 1 we speculate that microbial oxidation of organic carbon also may occur both sulphide oxidation and microbial oxidation of organic carbon are likely to drive the bed towards suboxic conditions hence we believe that subglacial chemical weathering does not sequester significant quantities of atmospheric co2 and that one of the key controls on the rate and magnitude of solute acquisition is microbial activity which catalyses the reduction of fe iii and the oxidation of fes2 copyright 2002 john wiley sons ltd

history of the greenland ice sheet paleoclimatic insights abstract paleoclimatic records show that the greenland ice sheet consistently has lost mass in response to warming and grown in response to cooling such changes have occurred even at times of slow or zero sea level change so changing sea level cannot have been the cause of at least some of the ice sheet changes in contrast there are no documented major ice sheet changes that occurred independent of temperature changes moreover snowfall has increased when the climate warmed but the ice sheet lost mass nonetheless increased accumulation in the ice sheet s center has not been sufficient to counteract increased melting and flow near the edges most documented forcings and ice sheet responses spanned periods of several thousand years but limited data also show rapid response to rapid forcings in particular regions near the ice margin have responded within decades however major changes of central regions of the ice sheet are thought to require centuries to millennia the paleoclimatic record does not yet strongly constrain how rapidly a major shrinkage or nearly complete loss of the ice sheet could occur the evidence suggests nearly total ice sheet loss may result from warming of more than a few degrees above mean 20th century values but this threshold is poorly defined perhaps as little as 2 c or more than 7 c paleoclimatic records are sufficiently sketchy that the ice sheet may have grown temporarily in response to warming or changes may have been induced by factors other than temperature without having been recorded

himalayan uplift and osmium isotopes in oceans and rivers previous studies have shown that 187 os 188 os in seawater has become increasingly radiogenic over the last 40 ma in a manner analogous to strontium this rapid rise in the marine 187 os 188 os over the last 17 ma has been attributed to an increase in the bulk silicate weathering rates resulting from the rise of the himalayas and or selective weathering and erosion of highly radiogenic organic rich ancient sediments the key test of this hypothesis is the 187 os 188 os and the total osmium concentration of the himalayan rivers we report the concentration and isotopic composition of osmium in the ganges the brahmaputra and the indus rivers the 187 os 188 os of the ganges close to its source at kaudiyal 30 05 n 78 50 e is 2 65 and os 45 fm kg a second sample of the lower reaches of the ganges at patna 25 30 n 85 10 e gives 187 os 188 os 1 59 and os 171 fm kg the 187 os 188 os of the brahmaputra at guwahati 26 10 n 91 58 e is 1 07 and os 52 fm kg a sample of the indus besham 34 55 n 72 51 e has a 187 os 188 os of 1 2 and os 59 fm kg we infer that the himalayas do not provide either a high flow of osmium or a highly radiogenic osmium component to the oceans the overall trend for osmium and strontium could be explained by a regularly increasing input of global continental weathering sources but the himalayas themselves appear not to be the dominant source

chemical weathering across the western foreland of the greenland ice sheet abstract proglacial streams deliver melt water and chemical weathering products including nutrients and radiogenic isotopes from continental ice sheets to the ocean weathering products are also delivered to the ocean in non glacial streams that form following ice sheet retreat and are disconnected from ice sheet meltwater by hydrologic divides if weathering reactions differ in non glacial and proglacial stream catchments the streams could deliver different types and magnitudes of solutes to the ocean depending on relative discharge volumes unlike proglacial streams however little is known of non glacial stream solute compositions or discharge here we show specific discharges are similar from a proglacial stream draining the greenland ice sheet gris with several streams disconnected from the ice sheet we also evaluate weathering reactions across a 170 km transect in western greenland that contains one proglacial stream draining the gris and two coastal ice distal and three inland ice proximal areas with non glacial streams non glacial streams exhibit solute compositions and offsets between dissolved and bedload sr isotope ratios that indicate weathering increases toward the coast with exposure age and precipitation major element mass balance calculations show weathering reactions shift from predominately carbonic acid weathering of carbonate minerals inland near the ice sheet to predominately sulfuric acid weathering of carbonate minerals near the coast strontium concentrations and isotopic ratios of the proglacial stream reflect mixing of at least two subglacial sources and minor in stream weathering that consumes co2 about 5 times less co2 is consumed per liter in the proglacial than inland non glacial streams however arid conditions inland suggest limited discharge from the ungauged inland streams leads to less total co2 weathering than proglacial stream one coastal area consumes less co2 per liter than the proglacial stream and another coastal area exhibits net co2 production these results indicate estimates for glacial foreland solute fluxes and co2 weathering consumption and production should include estimates from both non glacial and proglacial streams understanding weathering fluxes from these two types of streams will be important for evaluations of past ice sheet retreat and predictions of future solute and co2 fluxes associated with continued ice sheet retreat

rhenium in the black sea comparison with molybdenum and uranium rhenium concentrations were measured in the black sea to determine the behavior of this redox sensitive element in an anoxic basin under reducing conditions re is removed from solution leading to its depletion from black sea deep waters compared with uranium water column re and mo profiles show evidence of removal from mid depths suggesting that these elements are scavenged either in the water column or slope sediments to a greater degree than u black sea surface waters are enriched in re reflecting re in rivers draining into the northern black sea that are enhanced up to 80 fold over other large world rivers this enrichment is most likely anthropogenic and may be due to coal burning in the region a simple two box model is used to demonstrate that re concentrations in the black sea are not in steady state with respect to current riverine inputs and authigenic fluxes riverine inputs of u and mo are not as significant perhaps reflecting the fractionation of re from the other elements during a high temperature combustion process re2o7 is volatile above 270 c

lithologic controls on osmium isotopes in the rio orinoco abstract the seawater 187 os 188 os ratio has been increasing over the last 50 ma and at present is 1 06 reflecting that about 80 of os in the oceans is derived from the continents that provide os with an average 187 os 188 os ratio of about 1 26 whether the past variations in seawater os isotopes record changes in the bulk os flux with an average isotopic composition or the changes in the average 187 os 188 os ratio of the continental inputs or a combination of these two pathways is not clear the fundamental importance of lithology in controlling continental weathering rates and dissolved ion yields has been well established for the major cations it is dramatically manifested in the sr isotopes of rivers that are affected by selective dissolution of carbonates accordingly for os isotopes it has been proposed that disproportionate contributions of os with extremely high 187 os 188 os ratio come from weathering of organic rich black shales here we examine the effect of the weathering of specific lithologies on osmium isotopic composition and concentration in water samples of the orinoco river basin a major river basin draining both black shales exposed in the northern andes and granites of the precambrian guyana shield the northern andes was uplifted 17 ma which corresponds to the time of a dramatic rise in 187 os 188 os ratio the osmium isotopic composition and concentrations vary considerably in the tributaries and the main stem of the orinoco the highest os concentrations are observed in the rivers draining the andes however waters draining the andes are not highly radiogenic 187 os 188 os 187 os 188 os ratio of seawater during the last 17 million years

dissolved rhenium in the yamuna river system and the ganga in the himalaya role of black shale weathering on the budgets of re os and u in rivers and co 2 in the atmosphere extensive measurements of dissolved re and major ion abundances in the yamuna river system yrs a major tributary of the ganga have been performed along its entire stretch in the himalaya from its source near the yamunotri glacier to its outflow at the foothills of the himalaya at saharanpur in addition re analysis has been made in granites and precambrian carbonates some of the major lithologies of the drainage basin these data coupled with those available for black shales in the lesser himalaya allow an assessment of these lithologies contributions to the re budget of the yrs the re concentrations in the yrs range from 0 5 to 35 7 pm with a mean of 9 4 pm a factor of 4 higher than that reported for its global average concentration in rivers dissolved re and cations na k ca mg are strongly correlated in the yrs indicating that they are released to these waters in roughly the same proportion throughout their course the re cations in most of these rivers are one to two orders of magnitude higher than the re na k mg ca measured in granites of the yamuna basin this leads to the conclusion that on average granites crystallines make only minor contributions to the dissolved re budget of the yrs on a basin wide scale though they may be important for rivers with low dissolved re similarly precambrian carbonates of the lesser himalaya do not seem to be a major contributor to dissolved re in these rivers as their re ca mg is much less than those in the rivers the observation that re concentrations in rivers flowing through black shales and in groundwaters percolating through phosphorite black shale carbonate layers in phosphorite mines are high and that re and so4 are significantly correlated in yrs seems to suggest that the bulk of the dissolved re is derived from black shale carbonaceous sediments material balance considerations based on average re of 30 ng g 1 in black shales from the lesser himalaya require that its abundance in the drainage basin of the yrs needs to be a few percent to yield average re of 9 4 pm furthermore the positive correlation between re and cations would require that these re rich sediments e g black shales and re poor lithologies e g crystallines precambrian carbonates contribute re and cations in roughly the same proportion throughout the drainage basin the available data on the abundance and distribution of black shales in the basin are not adequate to test if these requirements can be met the annual fluxes of dissolved re at the base of the himalaya from the yamuna are 150 mol at batamandi and 100 mol at saharanpur compared to 120 mol from the ganga at rishikesh the total flux from the yamuna and the ganga account for 0 4 of the global riverine re flux much higher than their contribution to global water discharge this is also borne out from the mobilization rate of re 1 to 3 g km 2 y 1 in the ganga and yamuna basins in the himalaya compared to the global average of 0 1 g km 2 y 1 black shale weathering can also significantly influence the budgets of os and u in rivers and co2 in rivers and the atmosphere using dissolved re in rivers as a proxy it is estimated that 6 9 108 kg y 1 of black shales are being weathered in the ganga and yamuna basins in the himalaya weathering of such amounts of black shales can account for the reported concentrations of os and u in these rivers furthermore if the weathering results in the conversion of organic carbon in the black shales to co2 it would release 2 105 mol of co2 km 2 y 1 in the yamuna and ganga basins in the himalaya comparable to the co2 consumption from silicate weathering

widespread bacterial populations at glacier beds and their relationship to rock weathering and carbon cycling bacterial populations found in subglacial meltwaters and basal ice are comparable to those in the active layer of permafrost and orders of magnitude larger than those found in ice cores from large ice sheets populations increase with sediment concentration and 5 24 of the bacteria are dividing or have just divided suggesting that the populations are active these findings 1 support inferences from recent studies of basal ice and meltwater chemistry that microbially mediated redox reactions may be important at glacier beds 2 challenge the view that chemical weathering in glacial environments arises from purely inorganic reactions and 3 raise the possibilities that redox reactions are a major source of protons consumed in subglacial weathering and that these reactions may be the dominant proton source beneath ice sheets where meltwaters are isolated from an atmospheric source of co 2 microbial mediation may increase the rate of sulfide oxidation under subglacial conditions a suggestion supported by the results of simple weathering experiments if subglacial bacterial populations can oxidize and ferment organic carbon it is important to reconsider the fate of soil organic carbon accumulated under interglacial conditions in areas subsequently overridden by pleistocene ice sheets

the geochemistry of redox sensitive trace metals in sediments abstract we analyzed the redox sensitive elements v mo u re and cd in surface sediments from the northwest african margin the u s northwest margin and the arabian sea to determine their response under a range of redox conditions where oxygen penetrates 1 cm or less into the sediments mo and v diffuse to the overlying water as mn is reduced and remobilized authigenic enrichments of u re and cd are evident under these redox conditions with the onset of sulfate reduction all of the metals accumulate authigenically with re being by far the most enriched general trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes oxic reducing where oxygen penetrates 1 cm and anoxic conditions using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations we calculate the area of sediments below 1000 m water depth in which oxygen penetration is 1 cm to be 4 of the ocean floor we conclude that sediments where oxygen penetrates 1 cm release mn v and mo to seawater at rates of 140 260 60 150 and 5 10 of their respective riverine fluxes using the authigenic metal concentrations and accumulation rates from this work and other literature these sediments are sinks for re cd and u with burial fluxes of 70 140 30 80 and 20 40 respectively of their dissolved riverine inputs we modeled the sensitivity of the response of seawater re cd and v concentrations to changes in the area of reducing sediments where oxygen penetrates 1 cm our analysis suggests a negligible change in seawater re concentration whereas seawater concentrations of cd and v could have decreased and increased respectively by 5 10 over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10 20 if the area increased by a factor of 3 the concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of cd ca and v ca ratios observed in foraminifera shells over the last 40 kyr this implies that the area of reducing sediments in the ocean deeper than 1000 m 4 has not been greater than twice the present value in the recent past

behavior of re and os during low temperature alteration results from himalayan soils and altered black shales re os analyses were performed on five soil profiles developed on silicate lithologies in the narayani drainage basin of the himalayas as well as on several altered black shales and associated alteration phases the results indicate that all of these samples have lost large amounts of re this re loss approached 100 in the black shale derived soils which also most probably lost substantial quantities of os the near constancy of os and re concentrations with depth indicates that this loss occurred quite early in the alteration process rather than progressively during the course of soil development a slight decrease in 187os 188os was observed toward the surface of the two black shale soil profiles possibly indicating a minor preferential mobility of radiogenic 187os for this lithology in the black shale derived saprolite and soils the loss of re and os was related to the loss of organic carbon the importance of this phase is underscored by the fact that organic material separated from a black shale sample accounted for nearly all of the os contained in the whole rock analysis of alteration phases from the surface of a weathered black shale showed that os liberated during alteration was partially reprecipitated in fe oxides with os isotopic compositions very similar to that of the original rock whereas re was removed with the fluid phase these results demonstrate the disproportionately large role that black shale weathering may play in determining the re and os contents of continental runoff and thus ultimately of seawater but they also emphasize the possible complexity of this process the data suggest that a large fraction of the os contained in black shales is released during chemical alteration which is apparently not the case for most other silicate rocks therefore the potential contribution of black shales to the dissolved os budget of runoff and river water may be even greater than that expected from the high os concentrations of these rocks the extent to which this os will affect the seawater os composition depends on how efficiently it is recaptured by secondary phases such as fe mn oxides in situ or during transport these results also underscore the high mobility of re with respect to os at every stage in the erosional process thus explaining the order of magnitude increase in re os ratio from the black shale source rocks to seawater

rhenium and osmium isotopes in black shales and ni mo pge rich sulfide layers yukon territory canada and hunan and guizhou provinces china rhenium and osmium abundances and osmium isotopic compositions were determined by negative thermal ionization mass spectrometry for samples of devonian black shale and an associated ni enriched sulfide layer from the yukon territory canada the same composition information was also obtained for samples of early cambrian ni mo rich sulfide layers hosted in black shale in guizhou and hunan provinces china this study was undertaken to constrain the origin of the pge enrichment in the sulfide layers samples of the ni sulfide layer from the yukon territory are highly enriched in re os and other pge with distinctly higher re 192os but similar pt re compared to the black shale host re os isotopic data of the black shale and the sulfide layer are approximately isochronous and the data plot close to reference isochrons which bracket the depositional age of the enclosing shales samples of the chinese sulfide layers are also highly enriched in re os and the other pge re 192os are lower than in the yukon sulfide layer re os isotopic data for the sulfide layers lie near a reference isochron with an age of 560 ma similar to the depositional age of the black shale host the osmium isotopic data suggest that re and pge enrichment of the brecciated sulfide layers in both the yukon territory and in southern china may have occurred near the time of sediment deposition or during early diagenesis during the middle to late devonian and early cambrian respectively

precise re os ages of organic rich mudrocks and the os isotope composition of jurassic seawater rhenium and osmium isotope and abundance data have been obtained on precisely located samples from three suites of immature organic rich mudrocks from jurassic coastal outcrops in england the data provide accurate whole rock ages of 207 12 ma 181 13 ma and 155 4 3 ma for suites of hettangian toarcian exaratum subzone and kimmeridgian sensu anglico wheatleyensis subzone samples these new re os ages are indistinguishable within the assigned analytical uncertainties from interpolated depositional ages estimated from published geological timescales and establish the importance of the re os dating technique for chronostratigraphic studies early diagenetic pyrite nodules possess levels of re and os which are 1 2 orders of magnitude lower than in the enclosing organic rich mudrocks indicating that these elements had already been removed from sediment pore waters at the time of nodule formation thus the re os isotope system in these organic rich mudrocks has been closed since or from very soon after the time of sediment deposition because most of the re 98 and os 95 99 8 in the mudrocks is shown to be hydrogenous the 187os 188os i of the samples is interpreted to be that of contemporaneous seawater the data thereby provide the first estimates of the os isotope composition of jurassic seawater during the earliest jurassic hettangian the seawater 187os 188os ratio was extremely unradiogenic 0 15 it had increased to 0 8 at the end of the early jurassic toarcian 20 ma later while in the late jurassic kimmeridgian the seawater 187os 188os ratio was 0 59 the most likely explanation for the unradiogenic os isotope composition of hettangian seawater is that the contribution of unradiogenic os to the oceans from the hydrothermal alteration of oceanic crust greatly exceeded the input of radiogenic os from the continents at that time this interpretation is in line with observations suggesting that global weathering rates were low in the hettangian and that increased hydrothermal and volcanic activity preceded the break up of pangea the re os ratios of hettangian mudrocks and by inference of contemporaneous seawater are similar to those of mudrocks deposited at later times during the jurassic and argues against the unradiogenic os in hettangian seawater being derived from extraterrestrial meteoritic sources

transformation of organic matter in a barents sea sediment profile coupled geochemical and microbiological processes process based mechanistic investigations of organic matter transformation and diagenesis directly beneath the sedimentwater interface swi in arctic continental shelves are vital as these regions

application of the 187re 187os system to black shale geochronometry the decay of 187re to 187os provides a tool for determining depositional ages of black shales re and os concentrations and os isotopic compositions of whole rock samples of the bakken shale a mississippian devonian boundary black shale yield a whole rock isochron with an age of 354 49 ma this age is in agreement with the accepted age of the bakken shale 360 ma the initial 187os186os ratio of the isochron is 6 2 3 3 this value is indistinguishable from the 187os186os ratios observed in modern black sea sediments the concentration of common os in bakken shale samples is strongly correlated with total nitrogen indicating that a large fraction of the os in these samples is associated with a hydrogenous component which overwhelms any os supplied to the sediment in association with detrital material or cosmic dust the dominance of the hydrogenous component imparts a relatively homogeneous initial 187os186os ratio to the sediment at the time of deposition the degree of scatter about the isochron exceeds the degree of scatter expected from either analytical error or from the estimated degree of initial isotopic heterogeneity the pattern of scatter is consistent with postdepositional mobilization of re and or os on a small spatial scale we suggest that this mobilization may be a consequence of petroleum formation and migration in the bakken shale

osmium isotope geochemistry in the mackenzie river basin the cenozoic marine osmium isotope record is largely driven by changes in the continental input we aid its interpretation by supplying direct measurements of present day riverine os in known geological and environmental settings we analyzed os concentrations and isotopic ratios in the dissolved suspended and bed materials of the mackenzie river in canada and smaller rivers draining the western cordillera into the pacific ocean rhenium content was measured for suspended and bed materials to provide further constraint dissolved 187os 188os ratios range from 0 74 to 4 5 and are controlled to first order by age and lithology of the bedrock the rivers draining jurassic volcanic rocks are unradiogenic as low as 0 74 and those draining the precambrian canadian shield are radiogenic as high as 3 5 the headwaters of the mackenzie left bank tributaries draining metamorphic carbonates in the eastern cordillera and paleozoic black and gray shales in the transition zone and the interior platform are especially radiogenic 3 0 4 5 with relatively high concentrations of os these latter rivers are responsible for the mackenzie being above world average in os concentration and yield mol os km2 year as well as in 187os 188os the dissolved load is more radiogenic than the suspended or bed loads and constitutes a significant fraction of total fluvial os

the geochemical cycle of rhenium a reconnaissance rhenium re is one of a suite of elements including uranium and molybdenum that display conservative behavior in seawater and are enriched in anoxic sediments the decay of187re to187os provides a geochronometer in ancient sedimentary rocks and gives rise to os isotopic variations in nature in order to better characterize its sources to seawater re was measured in three major rivers amazon orinoco ganges brahmaputra and some of their tributaries re concentrations span four orders of magnitude from 0 02 to 400 pmol kg with the highest concentrations found in rivers draining black shales in the venezuelan andes mainstream re levels in the three rivers are between 1 and 10 pmol kg with a flux weighted average of 2 3 pmol kg the residence time for re in the oceans is estimated to be 750 000 yr with respect to river inputs re profiles from the atlantic and pacific oceans confirm that re behaves conservatively in seawater with no significant uptake onto particles and or recycling within the water column this is also true in the anoxic water column of the black sea re removal into anoxic sediments occurs at or below the sediment water interface as demonstrated in sediment pore waters from chesapeake bay in oxic sediments re is not cycled with manganese oxides and it is not enriched in very slowly accumulating pelagic sediments with a large hydrogenous iron and manganese component or in manganese nodules burial of re in anoxic sediments which accumulate on 0 3 of the ocean floor removes approximately 50 of the riverine re flux to the oceans hence oceanic re concentrations may be very sensitive to changes in the area of anoxic sedimentation

seasonal evolution of subglacial drainage and acceleration in a greenland outlet glacier an acceleration of ice mass loss has been observed near the margin of the greenland ice sheet partly as a result of faster ice motion observations by gps receivers reveal high seasonal variability in ice motion with summer motion up to 220 higher than winter background levels the greenland ice sheet contains enough water to raise sea levels by 7 m however its present mass balance and future contribution to sea level rise is poorly understood1 accelerated mass loss has been observed near the ice sheet margin partly as a result of faster ice motion2 3 4 surface melt waters can reach the base of the ice sheet and enhance basal ice motion5 6 however the response of ice motion to seasonal variations in meltwater supply is poorly constrained both in space and time here we present ice motion data obtained with global positioning system receivers located along a 35 km transect at the western margin of the greenland ice sheet throughout a summer melt season our measurements reveal substantial increases in ice velocity during summer up to 220 above winter background values these speed up events migrate up the glacier over the course of the summer the relationship between melt and ice motion varies both at each site throughout the melt season and between sites we suggest that these patterns can be explained by the seasonal evolution of the subglacial drainage system similar to hydraulic forcing mechanisms for ice dynamics that have been observed at smaller glaciers

a multisatellite study of a pseudo substorm onset in the near earth magnetotail this paper reports the multisatellite and ground observations of two pseudo substorm onset events that occurred successively at 0747 ut and 0811 ut may 30 1985 with more attention to the 0747 ut onset the distinguishing features of the 0747 ut event are as follows 1 the substorm associated tail reconfiguration started in a very localized region in the near earth magnetotail 2 the magnitude of the current disruption decreased markedly as the disruption region expanded tailward 3 on the ground the onset of a very small negative bay 40 nt was observed simultaneously with the onset of the current disruption but over a much wider local time sector than the near earth tail reconfiguration positive bay onsets at mid latitudes also had a longitudinally wide distribution from these features we infer that in the present event the current disruption took place filamentarily near ampte cce at 8 8 re it is also inferred that pseudo substorm onsets are distinguished from standard substorm onsets by the absence of a global expansion of the current disruption and that the spatial scale of the onset region in the magnetosphere is not a major difference between the two the present study suggests that the spatial distribution of the magnetic distortion before onsets is an important factor to determine the expansion scale of the current disruption it is also suggested that the current disruption is basically an internal process of the magnetosphere

correction to an experimental study of permeability and fluid chemistry in an artificially jointed marble by chris marone james rubenstone and terry engelder

osmium behavior in estuaries the lena river example the behavior of dissolved osmium at the river ocean interface was studied in the lena river estuary dissolved osmium removal is observed at very low salinities the loss is estimated to be 28 of the dissolved concentration of the river the removal cannot be related to the flocculation of iron oxide organic matter colloids but occurs simultaneously with the loss of aluminum the proposed mechanism is the adsorption of dissolved osmium on suspended particles in the maximum turbidity zone if this is correct then the removal of osmium in estuaries is probably a common phenomenon no contribution of osmium from the sediments is detected but neither the samples nor the stratified nature of the estuary are favorable to the study of a flux from sediments if this finding can be generalized the estimated global riverine flux of osmium to the ocean has to be recalculated and the osmium residence time in the ocean would change from 3 3 104 yr to 4 6 104 yr

hydrochemistry of ice stream beds evaporitic or microbial effects recently new data have been acquired on the chemical composition of waters within the glacial till beneath the kamb ice stream kis formerly ice stream c and the bindschadler ice stream bis formerly ice stream d two of the arteries of ice loss from the antarctic ice sheet ais we compare this water chemistry with basally stored subglacial waters from arctic and alpine glaciers and the only other measurements of sub ice sheet chemistry to date that emerging from beneath law dome near casey station sw antarctica during a jokulhlaup we find that the chemistries pose significant questions about the hydrology and biogeochemistry of ice sheet beds copyright 2010 john wiley sons ltd