seasonal variability of element fluxes in two central siberian rivers draining high latitude permafrost dominated areas in order to constrain the origin and fluxes of elements carried by rivers of high latitude permafrost dominated areas major and trace element concentrations as well as sr and u isotopic ratios were analyzed in the dissolved load of two siberian rivers kochechum and nizhnyaya tunguska regularly sampled over two hydrological cycles 2005 2007 large water volumes of both rivers were also collected in spring 2008 in order to perform size separation through dialysis experiments this study was completed by spatial sampling of the kochechum watershed carried out during summer and by a detailed analysis of the main hydrological compartments of a small watershed from element concentration variations along the hydrological cycle different periods can be marked out matching hydrological periods during winter baseflow period october to may there is a concentration increase for major soluble cations and anions by an order of magnitude the spring flood period end of may beginning of june is marked by a sharp concentration decrease for soluble elements whereas dissolved organic carbon and insoluble element concentrations strongly increase when the spring flood discharge occurs the significant increase of aluminum and iron concentrations is related to the presence of organo mineral colloids that mobilize insoluble elements the study of colloidal ree reveals the occurrence of two colloid sources successively involved over time spring colloids mainly originate from the uppermost organic rich part of soils whereas summer colloids rather come from the deep mineral horizons furthermore u and sr isotopic ratios together with soluble cation budgets in the kochechum river impose for soluble elements the existence of three distinct fluxes over the year a at the spring flood a surface flux coming from the leaching of shallow organic soil levels and containing a significant colloidal component b a subsurface flux predominant during summer and fall mainly controlled by water rock interactions within mineral soils and c a deep groundwater flux predominant during winter which enters large rivers through unfrozen permafrost paths detailed study of the kochechum watershed suggests that the contribution of this deep flux strongly depends on the depth and continuous nature of the permafrost

groundwater modeling for the analysis of active slow moving landslides active slow moving landslides in clayey soils exhibit continuous movements generally controlled both in the accelerating and decelerating phases by the pore water pressure regime that in turn is strictly correlated to the net rainfall regime the paper stresses the importance of a reliable groundwater model to predict these types of movements to this aim a procedure is proposed to define the transient groundwater regime in the slope on the basis of recorded rainfall and monitoring data the model is then used to derive the time dependent shear strength along the main slip surfaces the displacements at selected points along the slip surface are computed using a phenomenological i e empirical relationship between the local factor of safety and the displacement rate at those points the procedure is employed for the analysis of a well documented case history the porta cassia landslide central italy

a linear regression framework for predicting subsurface geometries and displacement rates in deep seated slow moving landslides abstract a new numerical integration linear regression tool is used to investigate kinematic behavior in deep seated sliding surface deeper than 3 m mass movements the technique is developed in the context of real inclinometer records and numerical integration using nine inclinometer case histories from four well documented large landslides carrot river montebestia karya village and pietrapertosa axial metric subsurface geometric deformation rates are predicted and compared for four different case studies from the literature a reactivated composite extremely slow earth slide earthflow a reactivated composite extremely slow debris slide rock fall an active composite very slow earth slide earth flow and a reactivated complex slow earth slide earth spread sensitivity analysis based on sliding surface depth to length d l ratios show that the mobility of these slow moving masses is closely dependent on the mode of sliding the results also show that short term and long term dynamics of slow moving landslides can be captured by geometrical patterns because the parameter determined is a geometric property the technique used in the investigation can be applied in new landslide problems independent of local conditions and triggering mechanisms within the confines of the stipulated boundary conditions hence with this framework also unrelated landslide problems can be analyzed and compared as demonstrated herein additionally this approach is useful for two dimensional reconstructions of subsurface displacement and velocity profiles and thus may act as a precursor to detailed field investigation programs warning systems and mitigation projects at minimal costs

biogeochemistry of stable ca and radiogenic sr isotopes in a larch covered permafrost dominated watershed of central siberia stable ca and radiogenic sr isotope compositions were measured in different compartments stream water soil solutions rocks soils and soil leachates and vegetation of a small permafrost dominated watershed in the central siberian plateau the sr and ca in the area are supplied by basalt weathering and atmospheric depositions which significantly impact the sr isotopic compositions only vegetation significantly fractionates the calcium isotopes within the watershed these fractionations occur during ca uptake by roots and along the transpiration stream within the larch trees and are hypothesised to be the result of chromatographic processes and ca oxalate crystallisations during ca circulation or storage within plant organs biomass degradation significantly influences the ca isotopic compositions of soil solutions and soil leachates via the release of light ca and organic and organo mineral colloids are thought to affect the ca isotopic compositions of soil solutions by preferential scavenging of 40ca the imprint of organic matter degradation on the 44 40ca of soil solutions is much more significant for the warmer south facing slope of the watershed than for the shallow and cold soil active layer of the north facing slope as a result the available stock of biomass and the decomposition rates appear to be critical parameters that regulate the impact of vegetation on the soil water system in permafrost areas finally the obtained 44 40ca patterns contrast with those described for permafrost free environments with a much lower 44 40ca fractionation factor between soils and plants suggesting specific features of organic matter decomposition in permafrost environments the biologically induced ca isotopic fractionation observed at the soil profile scale is not pronounced at the scale of the streams and large rivers in which the 44 40ca signature may be controlled by the heterogeneity of lithological sources

chemical weathering of silicate rocks in aldan shield and baikal uplift insights from long term seasonal measurements of solute fluxes in rivers abstract a reassessment of available information from the russian hydrological survey on long term seasonal measurements of water suspended matter and dissolved major element discharges in 30 small and large watersheds draining acid silicate rocks granites gneisses quartzites shales of the aldan shield and baikal uplift was combined with new data on river water chemistry for three granitic watersheds in order to calculate the fluxes of elements due to chemical weathering in accord with data on world rivers a positive correlation between chemical erosion rate and runoff is observed the majority of cations are removed during summer monsoon the spring flood yields 10 20 of the annual flux and the winter season accounts for only 5 15 the mean multi annual flux of total dissolved solid which is largely dominated by ca 60 80 on the siberian craton is comparable with that of temperate zones but higher than that of the canadian shield for similar runoff values rock composition and annual temperatures important element recycling due to litter degradation and weathering acceleration via organic ligands produced by abundant vegetation over permafrost soils is invoked to explain these results

the magnesium isotope δ26mg signature of dolomites abstract dolomite precipitation models and kinetics are debated and complicated due to the complex and temporally fluctuating fluid chemistry and different diagenetic environments using well established isotope systems 18 o 13 c 87 sr 86 sr fluid inclusions and elemental data as well as a detailed sedimentological and petrographic data set we established the precipitation environment and subsequent diagenetic pathways of a series of proterozoic to pleistocene syn depositional marine evaporative sabkha dolomites syn depositional non marine evaporative lacustrine and palustrine dolomites altered marine mixing zone dolomites and late diagenetic hydrothermal dolomites these data form the prerequisite for a systematic investigation of dolomite magnesium isotope ratios 26 mg dol dolomite 26 mg ratios documented here range from 2 49 to 0 45 26 mg mean 1 75 1 08 n 42 the isotopically most depleted end member is represented by earliest diagenetic marine evaporative sabkha dolomites 2 11 0 54 2 n 14 in comparing ancient compositions to modern ones some of the variation is probably due to alteration altered marine 1 41 0 64 2 n 4 and earliest diagenetic lacustrine and palustrine dolomites 1 25 0 86 2 n 14 are less negative than sabkha dolomites but not distinct in composition various hydrothermal dolomites are characterized by a comparatively wide range of 26 mg ratios with values of 1 44 1 33 2 n 10 by using fluid inclusion data and clumped isotope thermometry 47 to represent temperature of precipitation for hydrothermal dolomites there is no correlation between fluid temperature 100 to 180 c and dolomite mg isotope signature r 2 0 14 nor is there a correlation between 26 mg dol and 18 o dol magnesium isotope values of different dolomite types are affected by a complex array of different mg sources and sinks dissolution precipitation and non equilibrium fractionation processes and overprinted during diagenetic resetting further progress on the use of 26 mg dol as a proxy will require new theoretical and experimental data for 26 mg fluid dol that includes dehydration effects of the free mg aquo ion versus fluid temperature in ancient diagenetic systems complex variables must be considered these include fluid chemistry and physical properties mg sources and sinks temporal changes during precipitation and post precipitation processes including open and closed system geochemical exchange with ambient fluids all of these factors complicate the application of 26 mg dol as proxy for their depositional or diagenetic environments nevertheless the data shown here also indicate that 26 mg dol can in principle be interpreted within a detailed framework of understanding

temporal isotopic variations of dissolved silicon in a pristine boreal river abstract it has previously been concluded that the stable si isotopes are fractionated during geochemical and biogeochemical elemental transfers such as weathering and precipitation of clays and biogenic si which has opened up the possibility of using si as a tracer in natural terrestrial ecosystems furthermore quantification of the biogenic impact on the biogeochemical si cycle has attracted significant scientific interest since biological control has been suggested previous observations of seasonal variations in the dissolved si isotopic pattern further imply that high frequency riverine sampling during main hydrological events might provide important information about natural processes governing the fluvial biogeochemical si cycle therefore temporal variations in the isotopic composition of riverine dissolved si were investigated for the kalix river northern sweden the largest pristine river system in europe based on high frequency sampling during a period of 25 weeks from early april to early october 2006 temporal variations spanning 0 4 for 29si and 0 8 for 30si of dissolved si in the kalix river were observed during the period suggesting that the riverine dissolved si input to the oceans cannot be considered to have a constant si isotopic composition on a short time scale the results implicate biogeochemical si cycling via formation and dissolution of biogenic silica as processes significantly affecting the dissolved si transport in boreal systems during april to early october the si budget in the river system appeared to be controlled by relative si enrichment during high discharge events and relative si depletions in the subarctic mountainous and lake dominated areas the si enrichments and depletions were accompanied by decreasing and increasing riverine 29si and 30si respectively these isotope variations can be explained by release of plant derived silica depleted in heavier si isotopes during the spring snowmelt further increased volumetric contribution from the headwater and losses of dissolved si due to biogenic silica formation by diatoms in the subarctic lakes at a later period are expected to be responsible for the preferential losses of lighter isotopes as further verified by land cover analysis

massive magnesium depletion and isotope fractionation in weathered basalts abstract magnesium isotopes have been shown to fractionate significantly during continental weathering however the degree and direction of fractionation varies from one study to the next and the main factors that control mg isotope fractionation during weathering have yet to be delineated here we report mg contents and isotopic compositions for two 10 m deep drill cores through bauxites developed on columbia river basalts crbs samples from these two drill cores have very low mgo contents 0 12 0 25 wt and variable but high 26mg values from 0 1 to up to 1 8 the heaviest isotopic composition ever reported for mg relative to the average values of fresh crbs 26mg 0 23 0 07 and mgo 5 9 wt these features reflect the near complete loss of mg in the isotopically heavy regolith the most highly weathered bauxites at the tops of the profiles have the lowest 26mg values reflecting the addition of isotopically light eolian dust excluding these samples 26mg in bauxites displays a weak positive correlation with gibbsite abundance suggesting that gibbsite preferentially retains 26mg in the bauxites the integrated mg isotopic fractionation factors between bauxite and fluid 26mgbauxite fluid inferred from rayleigh fractionation calculations vary from 0 05 to 0 4 which is similar to the range inferred from previous studies of igneous rock weathering profiles though none of these previous studies found the extremely heavy 26mg and massive mg depletion seen here collectively studies of weathering profiles suggest loss of isotopically light mg from the continents which must contribute to the very light 26mg seen in river water and seawater

the influence of weathering processes on riverine magnesium isotopes in a basaltic terrain this study presents major trace element and mg isotope data for the dissolved load and suspended particulates of icelandic rivers draining dominantly basaltic catchments including both glacier fed and direct runoff rivers these samples provide the opportunity to understand the behaviour of mg isotopes during chemical weathering where variations due to lithology are not extant given the significant role of mg in the carbon cycle such variations may provide important information on the regulation of earth s climate hydrothermal waters groundwater precipitation glacial ice basalt glass olivine and representative soils have also been analysed the dissolved load shows a wide range of 26mg compositions compared to the parent basaltic glass 26mg 0 29 ranging from 0 96 to 0 64 while precipitation and hydrothermal waters possess 26mg values of 0 83 and 0 85 respectively with lower mg concentrations than the dissolved load biomass activity in vegetation and organic material in soils and rivers colloids appear to have little effect on the mg isotope compositions rather the data suggest that mg elemental and isotopic variations are largely controlled by the formation and stability of secondary phases in response to differing hydrological conditions in some samples seawater in the form of direct precipitation or glacial runoff also appears to be an important source of mg glacier fed rivers groundwaters and some direct runoff rivers with a high ph have higher 26mg than basalt which is most likely due to the incorporation of light mg isotopes in secondary minerals in contrast those direct runoff rivers which have a relatively low ph have low 26mg relative to basalt consistent with preferential incorporation of heavy mg isotopes into secondary phases although it is not possible to rule out some contribution from precipitation riverine suspended particulates are depleted in mobile elements and have 26mg compositions values both higher and lower than unweathered basalt in the glacier fed and direct runoff rivers where the 26mg of the dissolved phase is heavy due to the formation of secondary phases the suspended load is light because it contains more of those phases the opposite is true for the remainder of the direct runoff rivers which have low ph this could be due to dissolution of secondary minerals enriched in light mg which are unstable at low ph or the formation of new secondary phases

chemical weathering of silicate rocks in karelia region and kola peninsula nw russia assessing the effect of rock composition wetlands and vegetation this study is aimed at assessing the effect of factors including lithology forest peatland coverage dissolved organic carbon and vegetation on chemical fluxes and concentrations of major elements in rivers the mean annual element concentrations and dissolved fluxes of acid and basic rock dominated watersheds of the karelia region and kola peninsula nw russia have been estimated from the chemical composition of river water samples collected in the summers of 1996 2000 and from annual discharge and chemical composition data of 16 watersheds collected from 1961 to 1975 the mean annual flux corrected for atmospheric input varies from 0 5 to 5 6 t km2 y and is dominated by alkali metals for the kola alkaline rocks and by calcium for the karelian granito gneisses the pure granitic and pure basaltic river chemical denudation rates in the baltic shield are 0 33 and 2 3 t km2 y respectively the cationic and silica fluxes of both granitic and basaltic watersheds are comparable with those of other boreal regions having similar runoff compositions and climate the cationic flux of the rivers is positively correlated with the basic rock fraction of the watershed whereas the dissolved organic carbon flux increases with the increasing peatland fraction the chemical composition of the river water is controlled by bedrock dissolution during dry periods and by plant litter degradation and washout of organic debris from the topsoil horizon during wet periods taking account the chemical composition of the plant litter and the biological turnover intensity it was estimated that the plant litter degradation in kola and karelia regions provides 10 40 of total annual dissolved riverine element flux

calcium and magnesium isotope systematics in rivers draining the himalaya tibetan plateau region lithological or fractionation control abstract in rivers draining the himalaya tibetan plateau region the 26mg 24mg ratio has a range of 2 and the 44ca 42ca ratio has a range of 0 6 the average 26 mg values of tributaries from each of the main lithotectonic units tethyan sedimentary series tss high himalayan crystalline series hhcs and lesser himalayan series lhs are within 2 standard deviation analytical uncertainty 0 14 the consistency of average riverine 26 mg values is in contrast to the main rock types limestone dolostone and silicate which range in their average 26 mg values by more than 2 tributaries draining the dolostones of the lhs differ in their 44 42 ca values compared to tributaries from the tss and hhcs the chemistry of these river waters is strongly influenced by dolostone solute mg ca close to unity and both 26 mg 1 31 and 44 42 ca 0 64 values are within analytical uncertainty of the lhs dolostone these are the most elevated 44 42 ca values in rivers and rock reported so far demonstrating that both riverine and bedrock 44 42 ca values may show greater variability than previously thought although rivers draining tss limestone have the lowest 26 mg and 44 42 ca values at 1 41 and 0 42 respectively both are offset to higher values compared to bedrock tss limestone the average 26 mg value of rivers draining mainly silicate rock of the hhcs is 1 25 lower by 0 63 than the average silicate rock these differences are consistent with a fractionation of 26 mg values during silicate weathering given that the proportion of mg exported from the himalaya as solute mg is small the difference in 26mg 24mg ratios between silicate rock and solute mg reflects the 26mg 24mg isotopic fractionation factor silicate dissolved mg between silicate and dissolved mg during incongruent silicate weathering the value of silicate dissolved mg of 0 99937 implies that in the tss solute mg is primarily derived from silicate weathering whereas the source of ca is overwhelmingly derived from carbonate weathering the average 44 42 ca value in hhcs rivers is within uncertainty of silicate rock at 0 39 the widespread hot springs of the high himalaya have an average 26 mg value of 0 46 and an average 44 42 ca value of 0 5 distinct from riverine values for 26 mg but similar to riverine 44 42 ca values although rivers draining each major rock type have 44 42 ca and 26 mg values in part inherited from bedrock there is no correlation with proxies for carbonate or silicate lithology such as na ca ratios suggesting that ca and mg are in part recycled however in spite of the vast contrast in vegetation density between the arid tibetan plateau and the tropical lesser himalaya the isotopic fractionation factor for ca and mg between solute and rocks are not systematically different suggesting that vegetation may only recycle a small amount of ca and mg in these catchments the discrepancy between solute and solid ca and mg isotope ratios in these rivers from diverse weathering environments highlight our lack of understanding concerning the origin and subsequent path of ca and mg bound as minerals in rock and released as cations in rivers the fractionation of ca and mg isotope ratios may prove useful for tracing mechanisms of chemical alteration ca isotope ratios of solute riverine ca show a greater variability than previously acknowledged the variability of ca isotope ratios in modern rivers will need to be better quantified and accounted for in future models of global ca cycling if past variations in oceanic ca isotope ratios are to be of use in constraining the past carbon cycle

organic and organo mineral colloids in discontinuous permafrost zone on going permafrost thaw in discontinuous permafrost regions produces significant amounts of small permafrost subsidence and depressions while large lakes are likely to drain into streams and rivers the intensification of permafrost thaw may alter the size distribution and chemical composition of organo fe al colloids in lakes and rivers we used a continuum of surface water bodies from permafrost subsidence small depressions and thaw ponds to large lakes and rivers that drain the western siberia lowland wsl to assess oc major and the trace element size distribution between the 20 m 5 m 1 2 m 0 45 m 0 22 m 0 025 m and 1 kda 1 4 nm size fractions this approach allowed us to distinguish the organic and organo ferric colloids that were responsible for the transport of trace elements in surface waters and address their evolution during possible physico chemical and biological processes both conventionally dissolved 0 22 m and low molecular weight 1 kda fractions exhibited an order of magnitude decrease in doc fe in the landscape continuum depressions and permafrost subsidence thaw ponds thermokarst lakes streams rivers thermodynamic modeling and on site size separation suggested that a number of trace elements tes including alkaline earth elements and several micronutrients zn ba mn and ni decreased the degree of their binding to dom along the landscape continuum whereas the majority of insoluble tes al fe co cd cu pb rees th and u remained complexed with dom in the lmw 1 kda fraction two primary sites of colloid generation included i ground vegetation and peat leaching which supplied dom complexes of divalent metals and organo al entities to thaw ponds and lakes and ii fe2 oxidation and te co precipitation with fe hydroxides in the presence of surface dom at groundwater discharge sites within the riparian hyporheic zones of rivers under a warming climate scenario an increase in the thickness of the thawing depth will intensify the input of inorganic components from deep mineral horizons and possibly underground waters thus producing the enrichment of large lakes in fe rich colloids and particles the speciation of divalent metal micronutrients cu ni and co and toxic metals al cd pb and u that are complexed within dom will most likely remain conservative overall the wsl s surface water colloidal composition may shift from dom rich and dom al rich to fe rich and the export of low soluble trivalent and tetravalent hydrolysates from the soil to rivers will increase

using stable mg isotopes to distinguish dolomite formation mechanisms a case study from the peru margin abstract the magnesium isotope composition of diagenetic dolomites and their adjacent pore fluids were studied in a 250 m thick sedimentary section drilled into the peru margin during ocean drilling program odp leg 201 site 1230 and leg 112 site 685 previous studies revealed the presence of two types of dolomite type i dolomite forms at 6 m below seafloor mbsf due to an increase in alkalinity associated with anaerobic methane oxidation and type ii dolomite forms at focused sites below 230 mbsf due to episodic inflow of deep sourced fluids into an intense methanogenesis zone the pore fluid 26mg composition becomes progressively enriched in 26mg with depth from values similar to seawater i e 0 8 relative to dsm3 mg reference material in the top few meters below seafloor mbsf to 0 8 0 2 within the sediments located below 100 mbsf type i dolomites have a 26mg of 3 5 and exhibit apparent dolomite pore fluid fractionation factors of about 2 6 consistent with previous studies of dolomite precipitation from seawater in contrast type ii dolomites have 26mg values ranging from 2 5 to 3 0 and are up to 3 6 lighter than the modern pore fluid mg isotope composition the enrichment of pore fluids in 26mg and depletion in total mg concentration below 200 mbsf is likely the result of mg isotope fractionation during dolomite formation the 26mg enrichment of pore fluids in the upper 200 mbsf of the sediment sequence can be attributed to desorption of mg from clay mineral surfaces the obtained results indicate that mg isotopes recorded in the diagenetic carbonate record can distinguish near surface versus deep formed dolomite demonstrating their usefulness as a paleo diagenetic proxy

influence of rainfall regime on hydraulic conditions and movement rates in the overconsolidated clayey slope of the orvieto hill central italy the medieval town of orvieto is built on the top of a pyroclastic slab overlying a gentle slope of overconsolidated clays the clayey slope has been constantly affected by landslide phenomena in the form of slow movements and failure events which in turn have periodically caused instability of the marginal areas of the pyroclastic slab since 1982 a number of casagrande type piezometers and inclinometers were installed in the northern slope of the orvieto hill within the area that was involved in the huge porta cassia landslide in 1900 in this paper after a brief description of the geology and the geotechnical properties of the slope data obtained through the monitoring system are illustrated piezometric data are utilized to develop a conceptual model of the hydraulic conditions in the clayey slope and inclinometer measurements are interpreted and correlated with the geotechnical ground profile and slope morphology to understand the present complex evolution of the clayey slope finally the strong

natural variations of δ30si ratios during progressive basalt weathering hawaiian islands abstract silicon stable isotopes can be used to trace the biogeochemical pathways of si as it moves from its continental sources to its sink in ocean sediments along the way si is incorporated into clay minerals taken up by plants where it forms plant opal and leached into rivers the major land to ocean conduit compared to igneous rocks the waters that drain continents are enriched in heavy si isotopes but the mechanisms that control fractionation have not been elucidated we studied si isotope fractionation along a 4 million yr basaltic soil chronosequence on the hawaiian islands using the natural context of these samples in combination with laboratory experiments we demonstrate that the isotopic composition of dissolved si in weathering systems is determined by the combined effects of rock disintegration clay mineral neosynthesis and si biocycling weathering preferentially releases 28si into solution whereas secondary mineral formation preferentially removes 28si from solution in humid environments leached soils have lost large amounts of this soluble si thus creating a net loss of 30si from the entire soil system as soils develop and greater fractions of si reside in neoformed clay minerals 30sibulk soil values change progressively toward more negative values basalt 30si values are about 0 5 but older soils have 30si values up to 2 5 the difference between the solid and solution 30si values remains more or less constant with progressive weathering and therefore soil water from older soils has a more negative 30si composition in the upper horizons of the hawaiian soils this weathering driven 30si shift is modified by the addition of unweathered primary minerals via dust carrying 30si values of about 0 5 and by biocycling of si via plants producing negative 30si values in phytoliths and positive 30si values in soil solutions derived from upper horizons due to the high concentrations of dissolved si in these near surface layers rivers have more positive 30si values than predicted based on the weathering status of the lower horizons when combined with published 30si values from large rivers worldwide we find that the results from hawaii point to weathering control of si isotopes delivered to the oceans and thus to an important continent ocean linkage that warrants further investigation

the effect of permafrost vegetation and lithology on mg and si isotope composition of the yenisey river and its tributaries at the end of the spring flood abstract this work focuses on the behavior of the stable mg and si isotope compositions of the largest arctic river the yenisey river and 28 of its major and minor tributaries during the spring flood period samples were collected along a 1500 km latitudinal profile covering a wide range of permafrost lithology and vegetation despite significant contrasts in the main physico geographical climate and lithological parameters of the watersheds the isotope composition of both dissolved mg and si was found to be only weakly influenced by the degree of the permafrost coverage type of vegetation forest vs tundra and lithology granites basalts carbonates or terrigenous rocks this observation is generally consistent with the lack of chemical uptake of mg and si by soil mineral formation and vegetation during the early spring the radiogenic sr isotope composition of the yenisey and its tributaries varied within a narrow range 0 708 87 sr 86 sr 0 711 reflecting the dominance of phanerozoic rock weathering and or atmospheric deposition on these compositions the mg and si isotopic compositions of riverine samples reflect two main processes with distinct isotopic signatures first isotopically heavier mg 26 mg 1 0 0 2 and isotopically lighter si 30 si 1 0 0 25 are added to the waters by river suspended matter dissolution and leaching from vegetation biomass topsoil litter second isotopically lighter mg 26 mg 1 5 to 1 75 and isotopically heavier si 30 si 1 75 2 0 are delivered to the yenisey s tributaries from deep underground water feeding the rivers via taliks this lighter mg and heavier si isotopic composition is interpreted to originate from precambrian dolomite dissolution and aluminosilicate dissolution coupled with authigenic mineral precipitation respectively in deep underground water reservoirs taking account of the isotopic composition evolution over the course of the year established earlier on mono lithological watersheds of the yenisey basin the average annual isotopic signatures of the yenisey river arriving to the arctic ocean are estimated to be 26 mg 1 58 0 30 and 30 si 1 60 0 25 as the yenisey is the largest river feeding the arctic ocean and as it samples a large variety of environments and lithologies these values may be reasonable estimates for the average mg and si isotopic composition of the dissolved riverine flux to the arctic ocean

silicon isotope variations in central siberian rivers during basalt weathering in permafrost dominated larch forests abstract this work is devoted to the characterization of natural mechanisms of silicon isotope fractionation within siberian watersheds and predicting the climate warming effect on si fluxes from the land to the arctic ocean to unravel the different sources of silica generated by basalt weathering in central siberia under permafrost and larch deciduous forest conditions we measured the si isotopic composition of large and small rivers surface flow interstitial soil solutions plant litter and soils the average annual discharge weighted 30 si values of the second largest tributary of the yenissei river nyzhnaya tunguska and its main northern tributary kochechum are equal to 1 08 0 10 and 1 67 0 15 respectively while their average annual si concentrations are very similar 3 46 and 3 50 mg l respectively during summer baseflow the dissolved si isotope composition of both large rivers and a small stream ranges between 1 5 and 2 5 this is much heavier compared to the source basaltic rocks but similar to the fresh litter of larix gmelinii the dominating tree species in this region it could be consistent with litter degradation in the uppermost soil horizons being the dominant source of solutes annually exported by central siberian rivers during spring flood accounting for 60 80 of annual si flux the 30 si of the large rivers dissolved load decreases by 1 1 5 thus approaching the value of the bedrock and the silicate suspended matter of the rivers rsm this may reflect the dissolution of the silicate suspended load at high water mineral ratio the winter 30 si values of the large river dissolved load range between 1 0 and 2 5 during this period contributing to 10 of the annual si chemical flux the interaction between bedrock porous tuffs and deep ground waters occurs at a very high solid solution ratio leading to the precipitation of isotopically light secondary minerals and enrichment of 30 si in the fluids that feed the river through the unfrozen flowpaths results of this study imply that more than a half of the silica transported by siberian rivers may transit through the biogenic pool and that like in other stable basaltic regions bedrock water interactions account for a lesser fraction of the silica flux as a result of projected future climate warming and weathering increases in boreal regions the 30 si isotopic composition of large siberian rivers is likely to shift towards less positive values

the fluvial geochemistry of the rivers of eastern siberia ii tributaries of the lena omoloy yana indigirka kolyma and anadyr draining the collisional accretionary zone of the verkhoyansk and cherskiy ranges fundamental to the global carbon cycle over geologic time scales is the control of atmospheric co2 by aluminosilicate weathering much of the information on the rates of this process comes from rivers in the tropics and subtropics to understand the possible climatic influences systematic studies are needed for the arctic subarctic regions this is the second in a series of papers addressing this problem by systematic studies of the pristine rivers of the russian far east the region to the east of the siberian platform huh et al 1998 is a geologically complex terrain formed by the mesozoic collision and accretion of the siberian and kolyma plates because of the arid continental climate it has not been glaciated in the recent past thus it is possible to study weathering processes in an arctic environment dominated solely by cryogenic interactions without contamination by heterogeneous components derived from scouring glaciers all the major rivers and their tributaries in this area have been sampled on expeditions to individual basins 100 samples on a reconnaissance basis at falling stage usually in july and august the total dissolved cation levels tz are moderate up to 3 100 eq and the major ion chemistry is indicative of ca aluminosilicate and carbonate weathering with significant contributions from black shales in some tributaries the si tz si na k and 87sr 86sr ratios indicate that the weathering is superficial i e only to cation rich secondary minerals the areal total dissolved solid fluxes range from 0 04 to 0 39 106 mol km2 yr up to an order of magnitude lower than for the amazon orinoco draining the andes in the tropics 0 6 4 1 106 mol km2 yr the co2 consumption by aluminosilicate weathering 18 230 103 mol km2 yr is also at the lower end of the range observed in the amazon orinoco headwaters 143 1 000 103 mol km2 yr however as the north american counterparts in similar latitudes and with comparable relief the mackenzie yukon and fraser draining the rockies also have high dissolved solids 0 2 2 9 106 mol km2 yr and co2 19 1 750 103 mol km2 yr fluxes these low values seem to be more a function of lithology than simply climate ice action in cold environments appears to overcome the inhibiting effects of the decreased temperatures and lack of precipitation in producing a high chemical yield but results in superficial weathering in the case of aluminosilicates

myshake initial observations from a global smartphone seismic network myshake is a global smartphone seismic network that harnesses the power of crowdsourcing in the first 6 months since the release of the myshake app there were almost 200 000 downloads on a typical day about 8 000 phones provide acceleration waveform data to the myshake archive the on phone app can detect and trigger on p waves and is capable of recording magnitude 2 5 and larger events more than 200 seismic events have been recorded so far including events in chile argentina mexico morocco nepal new zealand taiwan japan and across north america the largest number of waveforms from a single earthquake to date comes from the m5 2 borrego springs earthquake in southern california for which myshake collected 103 useful 3 component waveforms the network continues to grow with new downloads from the google play store every day and expands rapidly when public interest in earthquakes peaks such as during an earthquake sequence

magnesium isotopes in permafrost dominated central siberian larch forest watersheds abstract to unravel the mg isotope fractionation pathways within the continuous permafrost zone in the larch deciduous forest of central siberia we measured the mg isotopic composition of two large siberian rivers nizhnaya tunguska and kochechum which flow into the yenisey a small forested stream and the major fluid and solid sources of mg in the watershed atmospheric precipitates surface suprapermafrost flow interstitial soil solutions plant biomass litter and mineral soils the obtained results indicate a significant seasonal variation in riverine water mg isotope signatures during the winter baseflow the mg isotope composition of large rivers is significantly lighter than the source basaltic rocks and the atmospheric depositions these differences support the presence of fluids enriched in lighter mg isotopes such as those affected by the mineral precipitation of secondary silicates or fluids that dissolve sedimentary carbonate rocks during the spring flood and in the summer and fall seasons the river fluid 26 mg values increased by 0 2 0 3 and approached the mg isotope composition of the ground vegetation dwarf shrubs mosses and the soil organic horizon overall the riverine waters were 0 3 0 7 lighter than the unaltered bedrock and the deep minerals soil horizons the mg isotopic compositions of larix gmelinii organs i e stem wood roots and needles exhibit a low variability however an enrichment of 0 2 0 3 in the 26 mg of larch needles in the course of the growing season from june to september can be observed this enrichment most likely demonstrates uptake of isotopically heavier mg by the plant in addition to the progressive thawing of the mineral soil deepening of the active layer of the soil overall the mg isotope approach indicates the important contribution of vegetation larch needles mosses and dwarf shrubs to the riverine mg isotope signature and helps to reveal the contribution of isotopically light carbonate rocks in the large rivers of the central siberian plateau

temperature dependent residual shear strength characteristics of smectite bearing landslide soils this paper presents experimental investigations regarding the effect of temperature on the residual strength of landslide soils at slow to moderate shearing velocities we performed ring shear tests on 23 soil samples at temperatures of 6 29 c the test results show that the shear strength of smectite rich soils decreased when temperatures were relatively low these positive temperature effects strength losses at lower temperatures observed for smectite bearing soils are typical under relatively slow shearing rates in contrast under relatively high shearing rates strength was gained as temperature decreased as rheological properties of smectite suspensions are sensitive to environmental factors such as temperature ph and dissolved ions we inferred that temperature dependent residual strengths of smectitic soils are also attributed to their specific rheological properties visual and sem observations of ca bentonite suggest that slickensided shear surfaces at slow shearing rates are very shiny and smooth whereas those at moderate shearing rates are not glossy and are slightly turbulent indicating that platy smectite particles are strongly orientated at slow velocities the positive temperature effect is probably due to temperature dependent micro friction that is mobilized in the parallel directions of the sheet structure of hydrous smectite particles on the contrary the influence of micro viscous resistance which appears in the vertical directions of the lamination is assumed to increase at faster velocities our results imply that if slip surface soils contain high fractions of smectite decreases in ground temperature can lead to lowered shear resistance of the slip surface and trigger slow landslide movement

enhanced landslide investigations through advanced dinsar techniques the ivancich case study assisi italy abstract we extensively exploit advanced differential sar interferometry dinsar techniques for enhanced landslide investigations we focus on the ivancich area assisi central italy which is affected by a deep seated landslide investigated through in situ surveys for this area large data sets of sar acquisitions were collected by the c band ers 1 2 and envisat sensors from april 1992 to november 2010 and by the x band radars of the cosmo skymed csk constellation from december 2009 to february 2012 we concentrate on the advanced dinsar technique referred to as small baseline subset sbas approach benefiting of its capability to generate deformation time series at full spatial resolution and from multi sensor sar data this allows us to present one of the first examples for a landslide area of ers 1 2 envisat deformation time series exceeding 18 years the results allowed characterizing the long term behaviour of the landslide and identifying sectors of the unstable slope affected by different deformation dynamics analysis of the csk data set characterized by a reduced revisit time and improved spatial resolution resulted in a 15 time larger point density with respect to the ers envisat measurements allowing to investigate nearly all the buildings and in many cases portions of buildings in the landslide area lastly we present an innovative modelling approach based on the effective integration of the dinsar measurements with traditional geological and geotechnical information providing deeper insights on the kinematical evolution of the landslide we consider our analysis a prototype example that can be extended to different geological and geotechnical conditions providing significant advances in the understanding of ground deformations induced by active landslides

on the reactivation of a large landslide induced by rainfall in highly fissured clays abstract the paper discusses the field investigations geotechnical characterization and time evolution of horizontal displacements in a wide landslide the latter triggered by an earthquake occurring in september 2002 is located in sicily and involves a thick body of stiff and highly fissured clays belonging to a varicoloured clay formation in order to characterise the reactivation of landslide mechanisms induced by rainfall a three year monitoring programme 2008 2011 was implemented to measure rain pore water pressures and deep and superficial displacements the monitoring data made it possible to recognize three distinct landslides which evolve at variable rates in different directions within the overall landslide area the landslides were reactivated by the increase in pore water pressures in the period autumn 2009 spring 2010 the data clearly show the mechanical role of pore water pressures in the stability of the slope and point out the dependence of the time evolution of the horizontal displacement on the pore water pressure variation induced by rainfall back analysis carried out on the single landslides confirmed that they are reactivated ones since the residual shear strength is mobilised on the pre existing sliding surfaces the pore water pressure variation and the landslide body displacement rates can be effectively related to 5 month cumulative rainfall by simple models characterised by three parameters these models calibrated on the period october 2009 september 2010 made it possible to predict the horizontal displacement rates in the ensuing time period the displacements forecasted by the model in the period september 2010 may 2011 agree very well with the measured ones

co variation of mg and c isotopes in late precambrian carbonates of the siberian platform a new tool for tracing the change in weathering regime abstract this study reports significant mg isotopic variations in 32 samples of late precambrian dolomites from various parts of the siberian platform exhibiting a range of 13 c from 10 to 6 v pdb in the ediacaran dolomites from the n and ne part of the patom paleobasin a systematic increase of 26 mg from 2 3 0 2 to 0 8 0 3 dsm3 along with a 13 c decrease from 6 to 10 26 mg 0 072 13 c 1 83 with a correlation coefficient of r 2 0 73 n 20 are observed within the stratigraphic sequence of ediacaran and ediacaran lower cambrian transition successions all positive c isotope excursions co vary with negative mg isotope shifts and vice versa other samples from the siberian platform lay on this regression with r 2 0 66 n 28 except for 4 samples probably diagenetic dolostones that exhibit a positive 26 mg 13 c correlation the enrichment of sedimentary dolomite in heavy carbon and light mg isotopes may be interpreted as a result of a complex interplay of contrasting sedimentation conditions sea regression versus sea transgression regime yielding different weathering regimes and relative contributions of carbonate versus silicate rocks the enrichment of both oceanic water and carbonate sediments by 26 mg could occur during transgression and would coincide with sedimentation of low 13 c carbonates whereas sedimentation of the depleted in 26 mg and enriched in 13 c carbonates could happen under regression regime when exposed carbonate platforms and coastal planes are subjected to intense weathering

seasonal sensitivity of weathering processes hints from magnesium isotopes in a glacial stream seasonal changes in river chemistry offer the potential to assess how weathering processes respond to changing meteorological parameters and ultimately how chemical weathering might respond to climatic parameters systematic seasonal variations in magnesium isotope ratios the 26mg 24mg ratio expressed as 26mg in per mil units are reported in stream waters from a mono lithological granitic weathering limited first order catchment from the swiss alps damma glacier rain ground and pore waters in addition to plants rocks mineral separates and soil are also reported the concentration response of the river waters is attenuated compared to the large changes in discharge however the systematic trends in the isotope data imply that either the source of the mg changes in a systematic manner or that the process by which mg is released into solution changes as a function of discharge the two first order observations in the data that need to be explained are 1 the systematic enrichment in 24mg in the stream waters compared to the granitic rocks they drain and 2 a systematic increase in 26mg in the waters during the summer melt season both observations which are similar to many other rivers draining silicate rock can either be accounted for by 1 conservative mixing between at least two different sources of mg in addition to precipitation inputs or 2 process related fractionation if the stream water compositions can be rationalised by multi component mixing there is at least one unidentified component with a 26mg 1 2 this is considered unlikely multiple physicochemical processes could fractionate mg isotope ratios such as 1 preferential leaching of 24mg 2 exchange of mg onto or from mineral surfaces and into interlayer sites of clays 3 uptake by plants and 4 26mg could be preferentially retained during the formation of secondary phases such as clays amorphous phases or oxides these processes are not mutually exclusive and distinguishing between them at a field scale is not trivial but significant biological uptake is improbable at this site unless there is a non identified external input of mg 26mg must be accumulating in solid phase residues in the catchment because of at least one physicochemical process such processes are likely well described at least in the first order by a rayleigh distillation model simple calculations illustrate how much 26mg would accumulate in the catchment per unit time in the first order the isotopic enrichments in the solids are so small that they would not be detectable for the time scales that are relevant to this field site in spite of the marked impact on the water chemistry the seasonal signal detected by mg isotope ratios is promising for using them with a better understanding of fractionation mechanisms to quantify how specific weathering processes impact upon both export fluxes and retention of elements within catchments

the silicon isotope composition of the upper continental crust the upper continental crust ucc is the major source of silicon si to the oceans and yet its isotopic composition is not well constrained in an effort to investigate the degree of heterogeneity and provide a robust estimate for the average si isotopic composition of the ucc a representative selection of well characterised continentally derived clastic sediments have been analysed using high precision mc icpms analyses of loess samples define a narrow range of si isotopic compositions 30si 0 28 to 0 15 this is thought to reflect the primary igneous mineralogy and predominance of mechanical weathering in the formation of such samples the average loess 30si is 0 22 0 07 2 s d identical to average granite and felsic igneous compositions therefore minor chemical weathering does not resolvably affect bulk rock 30si and loess is a good proxy for the si isotopic composition of unweathered crystalline continental crust the si isotopic compositions of shales display much more variability 30si 0 82 to 0 00 shale si isotope compositions do not correlate well with canonical proxies for chemical weathering such as cia values but do correlate negatively with insoluble element concentrations and al si ratios this implies that more intensive or prolonged chemical weathering of a sedimentary source with attendant desilicification is required before resolvable negative si isotopic fractionation occurs shale 30si values that are more positive than those of felsic igneous rocks most likely indicate the presence of marine derived silica in such samples using the data gathered in this study combined with already published granite si isotope analyses a weighted average composition of 30si 0 25 0 16 2 s d for the ucc has been calculated

quantifying the impact of riverine particulate dissolution in seawater on ocean chemistry the quantification of the sources and sinks of elements to the oceans forms the basis of our understanding of global geochemical cycles and the chemical evolution of the earth s surface there is however a large imbalance in the current best estimates of the global fluxes to the oceans for many elements in the case of strontium sr balancing the input from rivers would require a much greater mantle derived component than is possible from hydrothermal water flux estimates at mid ocean ridges current estimates of riverine fluxes are based entirely on measurements of dissolved metal concentrations and neglect the impact of riverine particulate dissolution in seawater here we present 87sr 86sr isotope data from an icelandic estuary which demonstrate rapid sr release from the riverine particulates we calculate that this sr release is 1 1 7 5 times greater than the corresponding dissolved riverine flux if such behaviour is typical of volcanic particulates worldwide this release could account for 6 45 of the perceived marine sr budget imbalance with continued element release over longer timescales further reducing the deficit similar release from particulate material will greatly affect the marine budgets of many other elements changing our understanding of coastal productivity and anthropogenic effects such as soil erosion and the damming of rivers

influence of infiltration on the periodic re activation of slow movements in an overconsolidated clay slope in orvieto central italy overconsolidated clay slopes are affected by intermittent slow movements at the top of the clay formation and within the landslide debris cover monthly data from inclin

reassessing the stable δ88 86sr and radiogenic 87sr 86sr strontium isotopic composition of marine inputs the stable strontium isotope system 88 86sr has recently been suggested to be a suitable proxy for determining variations in the strength of the marine carbonate system the principal output flux of oceanic sr however in order to be able to interpret carbonate driven variations in 88 86srseawater a robust understanding of 88 86srinput is required surprisingly only a limited amount of 88 86sr data currently exists for rivers and hydrothermal fluids thus this study assesses the variability of 88 86sr and 87sr 86sr in global rivers hydrothermal fluids and porewaters as well as minor marine sr sources such as continental dust rainwater and glacial ice our analyses broadly confirm the findings of krabbenhoft et al 2010 and reveal flux weighted 88 86srriverine and 87sr 86srriverine compositions of 0 32 and 0 71299 respectively the hydrothermal fluids analysed in this study are consistent with an end member 88 86srhydrothermal composition that is the same as the oceanic crust at 0 24 although three samples that display 88 86sr compositions offset from the seawater hydrothermal mixing trend suggest that the precipitation of alteration phases such as anhydrite may drive 88 86srhydrothermal to higher values porewater fluids obtained from sediment cores in the atlantic and pacific oceans have 88 86sr compositions within error of seawater 0 39 implying that the diagenetic flux of sr may not significantly affect the 88 86sr composition of seawater continental loess samples have 88 86sr compositions that are consistently lighter than or equal to terrestrial silicates with their tendency to lower values thought to reflect the preferential removal of heavier sr isotopes into solution during weathering finally rainwater and glacial ice samples have 88 86sr compositions that are also isotopically lighter than their associated water sources a factor that may be attributed to interaction with isotopically light loess and additional sr contributions from the bedrock together the principal marine inputs define flux weighted oceanic 88 86srinput and 87sr 86srinput compositions of 0 32 and 0 71161 these values are consistent with an elevated supply of riverine sr to the oceans due to increased post glacial weathering but require the enhanced weathering of exposed carbonate shelves during glacial periods or significant changes in the rate of carbonate burial to match observed changes in the 87sr 86sr ratio of seawater our results confirm that providing a diagenetically robust proxy can be found the 88 86sr and 87sr 86sr isotope systems should provide a useful proxy for investigating changes in the marine carbonate system through time

impact of diagenetic alteration on brachiopod shell magnesium isotope δ26mg signatures experimental versus field data due to their thermodynamically stable low mg calcite mineralogy the shells of brachiopods are often counted among the most reliable archives of the physicochemical conditions that occurred during the phanerozoic in marine waters consequently traditional and non traditional isotope and elemental proxy data from brachiopod valves have been analyzed in numerous studies and results obtained have been placed in context with ancient seawater properties this paper tests the sensitivity of brachiopod shell magnesium isotope 26mg data to diagenetic alteration we apply a dual approach by i performing hydrothermal alteration experiments using meteoric marine and burial reactive fluids and ii comparing these data to naturally altered ancient brachiopod shells the degree of alteration of individual shells is assessed by a combination of fluorescence and cathodoluminescence microscopy the absence of luminescence might indicate both well preserved shell material but also the secondary enrichment of quenching elements such as iron along diagenetic pathways complementary oxygen isotope data provide insight into the question of open versus closed system behavior of brachiopod shells brachiopod shell magnesium isotope values respond to differential fluid temperature chemistry and experiment durations the patterns observed are complicated by the interplay of kinetic and thermodynamic patterns and the presence of variable amounts of water soluble and water insoluble organic matter within these biominerals generally the range in bulk 26mg from experimentally altered 1 52 and that of bulk samples from ancient diagenetically altered brachiopod valves 1 53 exceed the geochemical variability of 26mgbrachiopod bulk values of most recent specimens 1 26 in the lower and upper range more 26mg enriched 0 8 and more 26mg depleted 0 7 values respectively are found in altered shells in comparison to unaltered ones the data shown here are considered significant for those aiming to reconstruct palaeoenvironmental parameters based on brachiopod archives consequently we propose tentative guidelines for magnesium isotope research applied to ancient carbonates

investigating the behaviour of mg isotopes during the formation of clay minerals abstract we present elemental and isotopic data detailing how the mg isotope system behaves in natural and experimentally synthesized clay minerals we show that the bulk mg isotopic composition 26 mg of a set of natural illite montmorillonite and kaolinite spans a 2 range and that their isotopic composition depends strongly on a balance between the relative proportions of structural and exchangeable mg after acid leaching these natural clays become relatively enriched in isotopically heavy mg by between 0 2 and 1 6 results of exchange experiments indicate that the mg that has adsorbed to interlayer spaces and surface charged sites is relatively enriched in isotopically light mg compared to the residual clay the isotopic composition of this exchangeable mg 1 49 to 2 03 is characteristic of the isotopic composition of mg found in many natural waters further experiments with an isotopically characterized mgcl 2 solution shows that the clay minerals adsorb this exchangeable mg with little or no isotopic fractionation although we cannot discount the possibility that the uptake of exchangeable mg does so with a slight preference for 24 mg to characterize the behaviour of mg isotopes during clay mineral formation we synthesized brucite mg oh 2 which we consider to be a good analogue for the incorporation of mg into the octahedral sheet of mg rich clay minerals or into the brucitic layer of clays such as chlorite in our experiment the brucite mineral becomes enriched in the heavy isotopes of mg while the corresponding solution is always relatively enriched in isotopically light mg the system reaches a steady state after 10 days with a final fractionation factor solid solution of 1 0005 at near neutral ph this result is consistent with the general consensus that secondary clay minerals preferentially take up isotopically heavy mg during their formation however our results also show that exchangeable mg is an important component within bulk clay minerals and can have an important influence over the bulk clay 26 mg value modeling shows that in certain soils or sediments where the percentage of exchangeable mg is 30 and the isotopic composition of the exchangeable mg is around 2 the generation of bulk 26 mg values of 26 mg values that are closer in composition to the ucc despite this results of modeling together with experimental observation suggests that the uptake of exchangeable mg into these clay rich sediments could cause a decrease in the bulk 26 mg value by up to 0 3 0 4 this should be accounted for when assessing the 26 mg value of sediments on a crustal scale

the magnesium isotope budget of the modern ocean constraints from riverine magnesium isotope ratios we have measured the magnesium mg isotope ratios in 45 rivers including 16 of the largest rivers in the world covering a range of geologic tectonic and climatic drainage basin environments the range in riverine 26mg is 2 5 half the variation in terrestrial rock although the mg isotopic composition of the source rock is important for small rivers at a global scale lithology is of limited significance for mg isotope ratios in rivers part of the variability at a global scale may be attributed to fractionation in the weathering environment the rivers analysed constitute 30 of the global mg riverine flux to the oceans and a flux weighted mg isotope composition of global runoff has been estimated at 1 09 even taking into account uncertainty this is distinct from seawater at 0 82 this difference arises either from the fractionation of mg isotope ratios in the ocean and or a mg budget which is not at steady state the difference is consistent with fractionation by carbonate precipitation in the simplest steady state scenario where the oceanic mass balance is maintained by riverine input and hydrothermal and dolomite output mg isotope ratios imply a minimum dolomite mg flux of 9 of the total output mg flux the implications of the distinct isotopic composition of the riverine flux from modern seawater is that the mg isotope ratio of seawater has probably varied outside of current analytical uncertainty mg isotope ratios may therefore provide a valuable new tracer in palaeo oceanography

magnesium isotope systematics of the lithologically varied moselle river basin france abstract magnesium and strontium isotope signatures were determined during different seasons for the main rivers of the moselle basin northeastern france this small basin is remarkable for its well constrained and varied lithology on a small distance scale and this is reflected in river water sr isotope compositions upstream where the moselle river drains silicate rocks of the vosges mountains waters are characterized by relatively high 87sr 86sr ratios 0 7128 0 7174 in contrast downstream of the city of epinal where the moselle river flows through carbonates and evaporites of the lorraine plateau 87sr 86sr ratios are lower down to 0 70824 magnesium in river waters draining silicates is systematically depleted in heavy isotopes 26mg values range from 1 2 to 0 7 relative to the value presently estimated for the continental crust and a local diorite 0 5 in comparison 26mg values measured in soil samples are higher 0 0 this suggests that mg isotope fractionation occurs during mineral leaching and or formation of secondary clay minerals on the lorraine plateau tributaries draining marls carbonates and evaporites are characterized by low ca mg 1 5 3 2 and low ca sr 80 400 when compared to local carbonate rocks ca mg 29 59 ca sr 370 2200 similar to other rivers draining carbonates the most likely cause of the mg and sr excesses in these rivers is early thermodynamic saturation of groundwater with calcite relative to magnesite and strontianite as groundwater chemistry progressively evolves in the aquifer 26mg of the dissolved phases of tributaries draining mainly carbonates and evaporites are relatively low and constant throughout the year from 1 4 to 1 6 and from 1 2 to 1 4 respectively within the range defined for the underlying rocks downstream of epinal the compositions of the moselle river samples in a 26mg vs 87sr 86sr diagram can be explained by mixing curves between silicate carbonate and evaporite waters with a significant contribution from the vosgian silicate lithologies 70 temporal co variation between 26mg and 87sr 86sr for the moselle river throughout year is also observed and is consistent with a higher contribution from the vosges mountains in winter in terms of runoff and dissolved element flux overall this study shows that mg isotopes measured in waters rocks and soils coupled with other tracers such as sr isotopes could be used to better constrain riverine mg sources particularly if analytical uncertainties in mg isotope measurements can be improved in order to perform more precise quantifications

lithium and its isotopes in major world rivers implications for weathering and the oceanic budget abstract the outstanding problem in the lithium geochemical cycle is the lack of an isotopic mass balance in the ocean the 6li compositions of fresh basalts 4 the hydrothermal fluids derived from them average 9 and seawater significantly heavier at 32 are well understood but only very sparse river input data are available for li mass balance calculations in an attempt to rectify the situation we have measured the lithium concentrations and isotopic compositions of major world rivers draining representative geological terrains this helps both to constrain the river endmember and to understand the behavior of lithium isotopes in the continental weathering environment fluvial isotopic compositions display a very large range 6 0 to 32 2 there is no definitive relationship between 6li and lithology but in general rivers draining marine evaporites are 20 to 22 carbonates 26 to 32 black shales 26 shields 6 6 to 19 and mixed siliceous terrains 6 to 28 the flow weighted mean concentration of the measured rivers is 215 nm at 23 this updated riverine 6li value responsible for 30 of the global riverine discharge does not solve the isotopic imbalance if the measured li concentrations and isotopic compositions are representative of all rivers the presence of a yet unidentified sink with a higher fractionation factor 1 023 than determined for low temperature basalt alteration 1 019 is required for an isotopic steady state of li in the ocean authigenic clays are a possible candidate as clays are known to be enriched in both lithium and in the light isotope preferentially alternatively the hydrothermal flux must be much less than half of that estimated by the 3he inventory and the oceanic budgets for 87sr 86sr and mg the relationship of 6li to the major ions and 87sr 86sr suggests that the important processes affecting river dissolved lithium isotopic compositions are fractionation between solution and secondary minerals and thus the intensity of weathering

dynamic characterization of the hill of civita di bagnoregio viterbo central italy for seismic response analysis abstract located on the top of a volcanic butte civita di bagnoregio is one of the most beautiful villages in central italy this hamlet which dates back to the etruscan era is a medieval cluster of enchanting beauty and a massive tourist attraction that counted more than six hundred thousand visitors in 2016 the peculiar combination of geological conditions regional seismicity and the impressive touristic flow caused the city to be listed among the 100 world s most endangered sites the definition of a reliable geophysical and geotechnical model of the subsurface is essential for any quantitative evaluation of seismic hazard which is the key for knowledge based decisions to design the proper stabilization measures in order to preserve the historical centre several geophysical techniques ambient noise recordings surface wave methods electrical resistivity tomography and seismic downhole were performed to assess the geometry and the low strain stiffness properties of the different geological units and to provide continuous subsurface imaging throughout the urbanized area the surface geophysical investigations were complemented by borehole seismics and geotechnical laboratory testing to provide a detailed dynamic cyclic characterization of the lithotypes which was used for investigating seismic site effects the integration of different investigation techniques allowed circumvention of logistic limitations imposed by the historical center which are a potential source of over simplified earthquake engineering models with no or limited experimentally determined seismic properties thus resulting in unrealistic seismic response estimates the investigation approach used in this case study can be extended to historical centers with similar geotechnical conditions to enhance the safety and resilience as a common basis for a sustainable future

adsorption and desorption controlled magnesium isotope fractionation during extreme weathering of basalt in hainan island china magnesium isotopic compositions of a set of clay rich saprolites developed on the neogene tholeiitic basalt from hainan island in southern china have been measured in order to document the behavior of mg isotopes during continental weathering compared with unaltered basalts 26mg 0 36 the overlying saprolites are strongly depleted in mg i e th mg 99 1 to 92 9 and display highly variable 26mg ranging from 0 49 to 0 40 magnesium concentration and 26mg value of the saprolites display a general increasing trend upwards in the lower part of the profile but a decreasing trend towards the surface in the upper part the variations of mg concentration and isotopic composition in this weathering profile can be explained through adsorption and desorption processes 1 adsorption of mg to kaolin minerals kaolinite and halloysite with preferential uptake of heavy mg isotopes onto kaolin minerals and 2 desorption of mg through cation exchange of mg with the relatively lower hydration energy cations in the upper profile evidence for adsorption is supported by the positive correlation between 26mg and the modal abundance of kaolin minerals in saprolite of the lower profile while negative correlations between 26mg and concentrations of lower hydration energy cations e g sr and cs in the upper profile support the desorption process our results highlight that adsorption and desorption of mg on clay minerals play an important role in behavior of mg isotopes during extreme weathering which may help to explain the large variation in mg isotopic composition of river waters

strontium and its isotopes in canadian rivers fluxes and global implications systematic sampling of the 39 largest canadian rivers shows that the weighted average 87sr86sr ratio in the dissolved load is 0 7111 similar to previous measurements on such large rivers as the amazon and mississippi consequently we believe that the above estimate is likely representative of the global average this imposes a limit of 6 5 1011g yr 1 on the amount of sr exchanged with basalts in hydrothermal cells on mid oceanic ridges evaluation of geological information suggests that sr from silicate sources is of considerable importance for all but the largest canadian rivers the latter have chemical and isotopic composition consistent with 4 1 carbonate vs silicate derivation of sr but such interpretation is not unique in terms of their water discharge the 39 canadian rivers studied account for 4 2 of the world total and their weighted average concentrations for other dissolved solutes are tds 176 ppm ca 18 ppm cl 6 8 ppm and sr 84 ppb

rapid earthquake characterization using mems accelerometers and volunteer hosts following the m 7 2 darfield new zealand earthquake we test the feasibility of rapidly detecting and characterizing earthquakes with the quake catcher network qcn that connects low cost microelectromechan ical systems accelerometers to a network of volunteer owned internet connected com puters following the 3 september 2010 m 7 2 darfield new zealand earthquake we installed over 180 qcn sensors in the christchurch region to record the aftershock se quence the sensors are monitored continuously by the host computer and send trigger reports to the central server the central server correlates incoming triggers to detect when an earthquake has occurred the location and magnitude are then rapidly esti mated from a minimal set of received ground motion parameters full seismic time series are typically not retrieved for tens of minutes or even hours after an event we benchmark the qcn real time detection performance against the gns science geonet earthquake catalog under normal network operations qcn detects and characterizes earthquakeswithin9 1softheearthquakeruptureanddeterminesthemagnitudewithin 1 magnitude unit of that reported in the gns catalog for 90 of the detections

weak impact of landscape parameters and rock lithology on mg isotope composition of the yenisey river and its tributaries abstract constraining the mechanisms controlling the riverine flux of major cations and their isotopes including that of mg to the world ocean is one of the challenges in earth surface isotope geochemistry in an attempt to identify the main factors affecting the mg isotopic composition of large rivers including vegetation climate and lithology of the watershed we studied the largest in terms of discharge siberian river yenisey and 20 of its main tributaries during spring flood summer flow and winter the working hypothesis was that the influence of bedrock composition is most pronounced in winter when the soils are frozen and the rivers are fed by deep underground waters thus we anticipated that the presence of permafrost will help to distinguish the impact of surface processes linked to biological uptake and release and deep soil underground transport of mg from mineral sources in contrast to these expectations no sizable differences in the mg isotope composition of the river water 0 1 for both the yenisey tributaries and its main channel has been observed between the spring flood may and the winter march period those two periods are characterized by the differences of discharge and degree of lithological impact on element source in the river water regardless of the season there was no straightforward control of lithology relative abundance of carbonates basalts granites and sedimentary rocks on 26mg in the main tributaries of the yenisey river our findings suggest that the use of riverine mg isotope signature for tracing weathering mechanisms and dominant lithological impact is not straightforward at the scale of large rivers whose watersheds present multiple lithologies variable climatic conditions and vegetation types

inter mineral mg isotope fractionation during hydrothermal ultramafic rock alteration implications for the global mg cycle abstract both riverine and ocean waters are enriched in 24 mg compared to the homogeneous chondritic mg isotopic composition of the earth s mantle requiring a fractionation step that is generally attributed to low temperature continental crust weathering here we present new observations that indicate that this 24 mg enrichment of surface waters may originate from mg isotope fractionation during the hydrothermal alteration of primary silicate minerals mineral separates of hydrothermally altered ultramafic rocks were collected from three different localities in norway coexisting olivine and serpentine exhibit invariant mg isotope ratios suggesting that serpentinization does not fractionate mg isotopes in contrast carbonation results in significant inter mineral mg isotope fractionation between the antigorite magnesite and talc the carbonation of the natural samples is constrained by o isotope thermometry at 275 c and hence closes the temperature gap between previous investigations of the natural distribution of mg isotopes during surface weathering and magmatic processes the precursor antigorite has an isotopic composition of 26 mg dsm 3 0 11 0 05 whereas the talc is enriched in 26 mg with mean mg 26 0 17 0 08 and the magnesite is depleted in 26 mg with mean mg 26 0 95 0 15 as carbonate minerals dissolve faster than silicate minerals the chemical weathering of carbonated ultramafic and by analogy mafic rocks on the continents will yield isotopically lighter mg to natural surface waters consistent with field observations moreover the mg fractionation observed in this study suggests that sub seafloor hydrothermal carbonation may be a significant contribution to the mg isotopic composition of ocean water

chemical denudation rates of the western canadian orogenic belt the stikine terrane we report in this paper major element and sr isotopic ratio analyses for 19 rivers draining the stikine province in the western canadian cordillera dissolved solutes suspended sediments and river sands were analyzed the aim of the paper is to calculate chemical denudation rates for this uplifted accretionary prism mainly dominated by volcanics and volcanic derived sedimentary rocks the major chemical features of the stikine rivers are their dilute character and the excess of ca mg and sr in the dissolved load with regards to na molar ca na ratios from 2 to 14 mean value of 5 4 are observed although the region is dominated by silicate rocks suspended sediments show ca na ratios close to 0 4 isotopically most of the rivers investigated display lower sr isotopic ratios in the dissolved load compared to the suspended load which is very unusual to account for the excess of cations three different hypotheses are tested by an inversion method allowing us to determine the origin of each major solute the first scenario assumes that the excess of ca and mg is due to the dissolution of unradiogenic carbonates the second scenario supposes that the excess of base cations is derived from the preferential dissolution of ca and mg rich minerals such as amphiboles in the third scenario all solutes are assumed to derived from silicate weathering the cationic weathering rates of silicates although imprecise are in the order of 2 5 tons km2 year for the two first hypotheses if all solutes are taken into account denudation rates are between 9 and 15 tons km2 year on a global scale these numbers are among the lowest found for rivers draining basaltic rocks they are however found to be consistent with the global law for chemical weathering rates established for basaltic rocks showing that chemical denudation rate are linearly correlated to runoff and depend on temperature according to an arrhenius law the rivers draining the complex assemblage of volcanic and volcanic derived rocks in the subduction collision geological context of the stikine province thus respond similarly to the other volcanic provinces of the world this does not seem to be true for associated co2 consumption rates the abundance of sulfate ions in the dissolved load possibly derived from oxidative weathering of sulfides may indeed provide a non negligible part of the protons necessary for chemical weathering within canada the stikine geologic province is one whose silicates weather at a high rate the order of chemical weatherabilty of canadian geological province from the lowest to the highest is established as follows granites shales of the rockies volcanics of the western cordillera shales of the interior platform carbonates

synergic use of satellite and ground based remote sensing methods for monitoring the san leo rock cliff northern italy abstract the historic town of san leo emilia romagna region northern italy is located on top of an isolated rock massif above the marecchia river valley hillside on february 27th 2014 a northeastern sector of the massif collapsed minor structural damages were reported in the town and a few buildings were evacuated as a precautionary measure although no fatalities occurred and the san leo cultural heritage suffered no damage minor rock fall events kept taking place on the newly formed rock wall worsening this hazardous situation in this framework a monitoring system based on remote sensing techniques such as radar interferometry both spaceborne and ground based and terrestrial laser scanning was planned in order to monitor the ground deformation of the investigated area and to evaluate the residual risk in this paper the main outlines of a 1 year monitoring activity are described including a pre event analysis of possible landslide precursors and a post event analysis of the displacements of both the collapse affected rock wall sector and the rock fall deposits

magnesium retention on the soil exchange complex controlling mg isotope variations in soils soil solutions and vegetation in volcanic soils iceland understanding the biogeochemical cycle of magnesium mg is not only crucial for terrestrial ecology as this element is a key nutrient for plants but also for quantifying chemical weathering fluxes of mg and associated atmospheric co2 consumption requiring distinction of biotic from abiotic contributions to mg fluxes exported to the hydrosphere here mg isotope compositions are reported for parent basalt bulk soils clay fractions exchangeable mg seasonal soil solutions and vegetation for five types of volcanic soils in iceland in order to improve the understanding of sources and processes controlling mg supply to vegetation and export to the hydrosphere bulk soils 26mg 0 40 0 11 are isotopically similar to the parent basalt 26mg 0 31 whereas clay fractions 26mg 0 62 0 12 exchangeable mg 26mg 0 75 0 14 and soil solutions 26mg 0 89 0 16 are all isotopically lighter than the basalt these compositions can be explained by a combination of mixing and isotope fractionation processes on the soil exchange complex successive adsorption desorption of heavy mg isotopes leads to the preferential loss of heavy mg from the soil profile leaving soils with light mg isotope compositions relative to the parent basalt additionally external contributions from sea spray and organic matter decomposition result in a mixture of mg sources on the soil exchange complex vegetation preferentially takes up heavy mg from the soil exchange complex 26mgplant exch 0 50 0 09 and changes in 26mg in vegetation reflect changes in bioavailable mg sources in soils this study highlights the major role of mg retention on the soil exchange complex amongst the factors controlling mg isotope variations in soils and soil solutions and demonstrates that mg isotopes provide a valuable tool for monitoring biotic and abiotic contributions of mg that is bioavailable for plants and is exported to the hydrosphere

basalt weathering in central siberia under permafrost conditions chemical weathering of basalts in the putorana plateau central siberia has been studied by combining chemical and mineralogical analysis of solids rocks soils river sediments and suspended matter and fluid solution chemistry altogether 70 large and small rivers 30 soil pore waters and groundwaters and over 30 solids were sampled during july to august 2001 analysis of multiannual data on discharge and chemical composition of several rivers of the region available from the russian hydrological survey allowed rigorous estimation of mean annual major element concentrations and dissolved and suspended fluxes associated with basalt weathering for the rivers tembenchi and taimura that drain monolithologic basic volcanic rocks the mean multiannual flux of total dissolved cations tds c ca mg na k corrected for atmospheric input is 5 7 0 5 t km 2 yr for the largest river nizhniya tunguska draining essentially basic rocks the tds c is 6 1 1 5 t km 2 yr the overall co2 consumption flux associated with basalt weathering in the studied region 700 000 km 2 achieves 0 08 10 12 mol yr which represents only 2 6 of the total co2 consumption associated with basalt weathering at the earth s surface the fluxes of suspended matter were estimated as 3 1 0 5 9 0 0 8 and 6 5 2 0 t km 2 yr for rivers taimura eratchimo and nizhniya tunguska respectively based on chemical analyses of river solutes and suspended matter the relative dissolved versus particulate annual transport of major components is cinorg corg na k ca mg si fe mn ti al which reflects the usual order of element mobility during weathering according to chemical and mineralogical soil and sediment analyses alteration of basalt consists of 1 replacement of the original basaltic glass by si al fe rich amorphous material 2 mechanical desegregation and grinding of parent rocks leading to accumulation of primary hydrothermal trioctahedral smectite and 3 transformation of these trioctahedral oxy smectites and mixed layer chlorite smectite into secondary dioctahedral smectite accompanied by removal of ca mg and fe and enrichment in al no vertical chemical differentiation of fluid and solid phases within the soil profile was identified all sampled soil pore waters and groundwaters were found to be close to equilibrium with respect to chalcedony gibbsite halloysite and allophanes but strongly supersaturated with respect to goethite nontronite and montmorillonite over the annual cycle the contribution of atmospheric precipitation permafrost melting underground reservoirs litter degradation and rock and soil mineral weathering for the overall tds c transport in the largest river of the region nizhniya tunguska is 9 3 3 10 5 10 5 5 25 20 and 45 30 respectively in the summertime direct contribution of rocks and soil mineral weathering via solid fluid interaction does not exceed 20 the main unknown factors of element mobilization from basalt to the river is litter degradation in the upper soil horizon and parameters of element turnover in the vegetation copyright 2005 elsevier ltd

mechanisms of magnesium isotope fractionation in volcanic soil weathering sequences guadeloupe magnesium mg stable isotopes are increasingly used as a weathering proxy in soils and rivers but the impact of the mineralogy of secondary phases on isotopefractionation remains obscure a better understanding of the behaviour of mg isotopes during weathering processes is a mandatory step toward deployment of this new tracer for understanding chemical fluxes exported from the critical zone here we investigate isotopic variations in 26mg in bulk soils and clay fractions relative to their parent andesite in three soilweatheringsequences from guadeloupe formed under contrasting climatic conditions soils formed in drier conditions low precipitation contain smectite whereas soils formed under wet conditions high rainfall are characterized by halloysite and fe oxides or kaolinite all clay fractions have mg isotopic compositions 26mg 0 41 to 0 10 similar to or heavier than their parent andesite 26mg 0 47 supporting the preferential incorporation of heavy mg isotopes in secondary mg bearing clay minerals with the first direct measurements on clay fractions soils with lighter mg isotope compositions have greater quantities of exchangeable mg the data support a contribution from sea spray to the exchangeable mg pool correlated to the soilweathering degree this study highlights for the first time that the soil 26mg not only depend on 26mg of the parent rock and on any fractionation that might occur but also on the mg retention on the exchange complex which could in turn be controlled by external inputs such as sea spray

seasonal movement of the slumgullion landslide determined from global positioning system surveys and field instrumentation july 1998 march 2002 abstract measurements of landslide movement made by global positioning system surveys and extensometers over a 3 5 year period show that the slumgullion landslide in the san juan mountains of southwest colorado moved throughout the monitoring period but that daily velocities varied on a seasonal basis landslide velocities peaked in the early spring and summer in response to snowmelt and summer thunderstorms respectively velocities were slowest in mid winter when air and soil temperatures were coldest and precipitation was generally low and or in the form of snow with a low water content we hypothesize that the seasonal variability in velocities is due to ground water levels and corresponding pore pressures that decrease when surface water is unavailable or cannot infiltrate frozen landslide material and increase when surface water from melting snow or rainfall infiltrates unfrozen landslide material we also suggest that patches of bouldery debris and fractures created by continuous movement of the landslide are conduits through which surface water can infiltrate regardless of the frozen or unfrozen state of the landslide matrix material therefore the availability of surface water is more important than landslide temperature in controlling the rate of landslide movement this hypothesis is supported by field instrumentation data that show 1 landslide velocities coinciding with precipitation amounts regardless of the depth of freezing of landslide material 2 spring and annual landslide velocities that were greatest when the depth of freezing was also the greatest and 3 a rapid several weeks or less velocity and pore pressure response to rainfall the persistent but seasonally variable movement of the landslide fits the bathtub model for landslide movement described by baum and reid baum r l reid m e 2000 ground water isolation by low permeability clays in landslide shear zones in bromhead e n dixon n ibsen m l eds landslides in research theory and practice proc 8th int symp on landslides cardiff wales vol 1 139 144 in their model the landslide is isolated both mechanically and hydrologically from adjacent materials by low permeability clays these clays cause the landslide to retain water our data support this model by suggesting that pore pressures at the basal landslide surface are always adequate to maintain landslide movement and that any infiltration of water at the surface of the landslide is adequate to rapidly increase landslide velocity