radiogenic and stable sr isotope ratios 87 sr 86 sr δ 88 86 sr as tracers of riverine cation sources and biogeochemical cycling in the milford sound region of fiordland new zealand this study reports radiogenic sr isotope ratios 87sr 86sr stable sr isotope ratios 88 86sr and major ion concentrations for river rock sediment soil and plant samples collected from the cleddau and hollyford catchments in the milford sound region of fiordland new zealand the catchments primarily drain gabbro but some tributaries access limestone and volcanogenic sediments the goal of the study was to understand controls on riverine 88 86sr values in a landscape with multiple factors that may influence chemical weathering including dense vegetation high rainfall and abundant freshly eroded holocene fluvio glacial and landslide debris rivers draining gabbro have higher 88 86sr values than bedrock by as much as 0 14 and the 88 86sr values strongly correlate with molar ca sr ratios r2 0 69 leaching of rocks and sediment reveals no evidence for the preferential dissolution of minerals having high 88 86sr values and ca sr ratios in stream sr isotope fractionation seems unlikely because comparison against 87sr 86sr and ca sr ratios demonstrates that riverine 88 86sr values conservatively trace water mass mixing the riverine data are best explained by the input of soil water which is distinct from potential bedrock end members i e silicates and carbonates based on 88 86sr but indistinguishable in terms of ca sr and 87sr 86sr while strontium isotope fractionation during secondary mineral formation and pedogenesis is possible clay mineral formation is minor and most soils are poorly developed instead soil water 88 86sr values more likely reflect plant uptake plant samples yielded a wide range of 88 86sr values but on average they are lower than those for bedrock consistent with the expectation that plants preferentially incorporate lighter sr isotopes mass balance constraints together with 87sr 86sr ratios indicate that soil water 88 86sr values are 0 30 higher than bedrock 88 86sr values and mixing calculations show that the plant fractionated soil water pool contributes 27 of the riverine sr for tributaries accessing limestone and volcanogenic sediments ca sr and 87sr 86sr ratios appear consistent with two component mixing between silicate and carbonate weathering but 88 86sr values reveal a third contribution from soil water inputs similar to gabbro catchments the results of this study suggest that sr isotopes behave conservatively during water mass mixing and stream transport but non conservatively in soil where plant uptake can elevate soil water 88 86sr values relative to bedrock plant uptake or related biogeochemical processes such as ion exchange on organic matter surfaces also appear to modify soil water ca sr ratios many studies use 87sr 86sr and ca sr ratios to apportion riverine solutes between silicate and carbonate weathering but ca sr ratios may be non conservative in densely vegetated areas the stable sr isotope tracer shows promise for resolving riverine cation sources as well as effects from biological cycling

calcium isotope ratios in the world s largest rivers a constraint on the maximum imbalance of oceanic calcium fluxes 1 the oceanic mass balance of calcium ca is defined by a balance between the inputs rivers and hydrothermal and outputs bulk carbonate of ca large rivers were analyzed for ca isotope ratios 44ca 42ca expressed as ca to investigate the source and cycling of riverine ca and to add an isotopic mass balance constraint to the oceanic budget of ca the new data account for approximately one third of the total ca supplied to the oceans by rivers inter sample and seasonal variability was assessed by analyzing more than one sample for many rivers the range in the ca of large rivers at high water stand is extremely narrow at 0 27 variations in ca do not correlate with proxies for carbonate silicate or evaporite derived ca and are more likely related either to inherent variability in the lithological sources of ca or to process related fractionation the spread in riverine ca overlaps with the spread in marine limestone ca consistent with most riverine ca coming from the recycling of limestones the ca isotope composition of continental runoff has an average ca value of 0 38 0 04 identical to recent 5 m yr bulk carbonate ooze 0 33 0 13 2s d isotopic mass balance constrains that the input and output fluxes of ca to and from the oceans are balanced to within 15 over time scales similar to the residence time of ca in the oceans 1 m yr a greater imbalance between the fluxes would result in a detectable difference between the ca value of bulk carbonate and the riverine input at the current level of uncertainty the input and output fluxes could be imbalanced over much shorter time scales such as glacial interglacial cycles in which case the ocean carbonate system will not yet have responded because of the long residence time of ca the maximum current flux imbalance of 15 would be sufficient to account for the total variations in ca concentration over the tertiary such an interpretation is not unique but is the simplest interpretation given the similarity between the input and output isotopic compositions and rules out hypotheses of extreme imbalance in the recent global biogeochemical cycle of ca

effect of calcite precipitation on stable strontium isotopic compositions insights from riverine and pool waters in a karst cave abstract radiogenic and stable sr isotope ratios 87 sr 86 sr 88 86 sr serve as potential tracers for evaluation of weathering sources and associated physicochemical processes in terrestrial environments despite carbonate weathering sourcing two thirds of the total continental sr flux to the ocean however few attempts have been aimed at studying stable sr isotope fractionation in carbonate dominated aquifers here we present a monthly resolved monitoring dataset of major ion concentrations and sr isotope ratios for karst riverine and pool waters at the luofang cave in the central china to understand the potential controls responsible for water 88 86 sr compositions under various climatic conditions with the exception of some pool waters in the dry period significantly heavier 88 86 sr were detected in the riverine and pool waters 0 20 to 0 42 compared to bedrock 88 86 sr 0 24 to 0 28 which can t be interpreted solely by lithology a sequential leaching experiment of the local soils suggests limited stable sr isotope fractionation during incongruent silicate mineral dissolution local plant utilization and biological activity in the soil overlying the cave are possible processes for causing the observed heavier 88 86 sr in cave water however air partial pressure of co 2 in cave monitoring water ph and sr isotopic mass balance calculations suggest that plant utilization is unlikely to be the primary control on the heavier water 88 86 sr on the other hand significant stable sr isotope fractionation was found between the cave dripping waters and calcite precipitates and the 88 86 sr car aq was estimated to be 0 15 0 07 2sd precipitation of secondary calcites might be a potential process responsible for the heavier 88 86 sr in the waters the negative correlation between 88 86 sr and sr na ratios in the cave waters is consistent with a scenario of preferential incorporation of the light sr isotope by solid phase furthermore by combining the calcite saturation states and water ph our results suggest that calcite precipitation is the most likely process controlling 88 86 sr compositions in cave water we demonstrate that secondary calcite precipitation in carbonate dominated catchments could be important in controlling the riverine water 88 86 sr compositions

analysis of high pressure fluid flow in fractures with application to yucca mountain nevada slug test data abstract increases in water pressure if large enough can be sufficient to open existing fractures in a fractured rock water system such large water pressure increases are expected during earthquake activity and are also produced artificially in high pressure hydraulic fracturing and slug injection tests in an in situ slug injection test the slug of water is initially released into a packed off interval of the borehole where the contained fluid is at ambient pressures we recognize three separate stages in the behaviour of the fracture as the water pressure decreases due to drainage namely opening closing and finally completely closed in the first stage the water will initially drain out along conduits between the faces of the opening fracture as the fracture opens and grows it can become long enough to intersect any pre existing network of open joints and fractures if this connection occurs the opened fracture will stop growing and there will be further rapid flow of fluid out along these open conduits even if connection to an open conduit does not occur as the pressure drops the fracture will stop growing and eventually halt at the pressure where the fracture tip begins to close drainage into any open conduits will cease and drainage during fracture closing will thus be by flow into the porous walls of the fracture and borehole this effect of the conduit being shut off may manifest as a kink in the observed height decay of the slug at this pressure due to the effect of the different drainage terms as the water pressure decreases the fracture will continue to close until the water pressure drops below the critical pressure and the fracture becomes completely closed this total closure occurs at the same pressure as that necessary to re open the fracture and has been taken equal to the minimum principal stress this total closure of the fracture also may manifest as a kink in the observed height decay of the slug as below this closure pressure is the third and final stage where drainage is at the usual low pressures controlled by the permeability of the rock just around the packed off interval of the borehole we develop the most general mathematical model for this phenomenon using conservation of mass of the water in the borehole fracture system for each separate pressure stage this model of fracture behaviour with separate flow stages and pressure regimes explains the physical basis for the increasingly used technique in high pressure injection tests of measuring the so called re opening pressure at the sharp change in slope of the rate of change of water height vs height analytic and numerical solutions yield the rate at which the water height drops during the slug test and comparison with high pressure test data confirms the accuracy of the model analysis of data from yucca mountain nevada gives values for the fracture opening pressures that indicate the presence of extensional stresses of significant magnitude and of zones of pre existing open fracture networks in the vicinity of the proposed repository site

stable sr isotope sr ca mg ca li ca and mg li ratios in the scleractinian cold water coral lophelia pertusa the aragonitic skeletons of scleractinian cold water corals can serve as valuable archives in paleoceanographic studies the potential of 88 86sr sr ca mg ca li ca and mg li ratios of the cold water coral lophelia pertusa to record intermediate water mass properties has been investigated here we used samples from several locations along the european continental margin spanning a large temperature range from 6 to 14 c stable strontium isotope measurements were carried out with the recently developed double spike tims technique and our results differ from those obtained with less precise methods in contrast to the strong positive relationship with temperature of previous studies our results suggest that 88 86sr measured in scleractinian cold water corals is not controlled by seawater temperature but reflects the sr isotopic composition of seawater with an offset of 88 86sr 0 196 as found in previous studies the elemental ratios sr ca li ca and mg li measured in corals are significantly related to water temperature and do not correlate with salinity moreover sr ca ratios in l pertusa display the expected inverse correlation with temperature however the variance in the sr ca data severely limits the accuracy of paleotemperature estimates the li ca and mg ca ratios reveal other influences besides temperature such as ph and or growth or calcification rate however corresponding mg li ratios in l pertusa are more tightly related to temperature as they remove these secondary effects in particular the mg li ratio in l pertusa may serve as a new promising paleotemperature proxy for intermediate water masses our dataset represents the most extensive geochemical examination of l pertusa to date revealing a temperature sensitivity of 0 015 mol mmol c for mg li however using this temperature dependence and the precision of 5 3 2sd only temperature variations larger than 1 5 c can be resolved with 95 confidence

magnesium isotope fractionation in biogenic and abiogenic carbonates implications for paleoenvironmental proxies abstract geochemical variations in marine biogenic carbonates that are preserved in the geological record serve as proxies of past environmental change however interpreting most proxies is complicated by biologically mediated vital effects highlighting the need to develop new tools for reconstructing paleoenvironmental change recently magnesium mg isotope variability in carbonates has been explored extensively to determine its utility as a paleoenvironmental proxy we review the results of these works which have yielded valuable information on the factors affecting mg isotope fractionation between carbonates and solution 26mgcarb sol in biogenic and abiogenic carbonate minerals strong evidence exists for a mineralogical control on 26mgcarb sol with the negative offset from 0 following the sequence aragonite 3 mol mol and saturation states 3 that are similar to seawater suggest that 26mgcarb sol has a temperature dependence of 0 01 c 1 and is insensitive to precipitation rate in contrast a significant precipitation rate dependence is observed in calcites precipitated from solutions with relatively low mg ca ratios

characterising the stable δ88 86sr and radiogenic 87sr 86sr isotopic composition of strontium in rainwater rainwater plays a major role in determining the transfer of elements and pollutants to soils and hydrological catchments with compositional variations reflecting the extent of mixing between marine sea salt terrestrial dust and vegetation and anthropogenic aerosols while the radiogenic strontium isotope system 87sr 86sr is often used to help constrain the different sources of atmospheric sr the degree of variability in the stable strontium isotope system 88 86sr remains unresolved in order to determine how atmospheric sr affects the 88 86sr composition of water entering the hydrological cycle this study analysed a suite of rainwater samples collected over the course of a year in central paris rainwater 88 86sr compositions were found to range from 0 13 to 0 32 with 87sr 86sr ratios varying between 0 70796 and 0 71093 no seasonality was observed in 88 86sr whereas 87sr 86sr ratios were observed to be generally more radiogenic in the summer and less radiogenic in the winter strontium enrichment factors significantly above seawater implied a predominantly terrestrial non sea salt origin of sr in rainwater with the 88 86sr and 87sr 86sr composition of this terrestrial fraction consistent with a mixture of sr derived from carbonate dust and agricultural fertiliser evidence for a 0 1 decrease in the 88 86sr composition of the river seine as it passes through paris suggests that anthropogenic pollutants may contribute to significant regional variations in the composition of sr in the hydrological cycle together these results demonstrate that there is significant potential for both temporal and spatial variations in the 88 86sr and 87sr 86sr composition of rainwater that need to be taken into consideration when studying 88 86sr variations in localised catchments

determination of 88sr 86sr mass dependent isotopic fractionation and radiogenic isotope variation of 87sr 86sr in the neoproterozoic doushantuo formation abstract we measured both mass dependent isotope fractionation of 88sr 88sr 86sr and radiogenic isotopic variation of sr 87sr 86sr for the neoproterozoic doushantuo formation that deposited as a cap carbonate immediately above the marinoan related nantuo tillite the 88sr and 87sr 86sr compositions showed three remarkable characteristics 1 high radiogenic 87sr 86sr values and gradual decrease in the 87sr 86sr ratios 2 anomalously low 88sr values at the lower part cap carbonate and 3 a clear correlation between 87sr 86sr and 88sr values these isotopic signatures can be explained by assuming an extreme greenhouse condition after the marinoan glaciation surface seawater mixed with a large amount of freshwater from continental crusts with high 87sr 86sr and lighter 88sr ratios was formed during the extreme global warming after the glacial event high atmospheric co2 content caused sudden precipitation of cap carbonate from the surface seawater with high 87sr 86sr and lighter 88sr ratios subsequently the mixing of the underlying seawater with unradiogenic sr isotope compositions and normal 88sr ratios probably caused gradual decrease of the 87sr 86sr ratios of the seawater and deposition of carbonate with normal 88sr ratios the combination of 87sr 86sr and 88sr isotope systematics gives us new insights on the surface evolution after the snowball earth

87sr 86sr ratios in hydrothermal waters and deposits from the east pacific rise at 21 n abstract 87 sr 86 sr ratios of three hydrothermal waters collected on the east pacific rise at 21 n define a mixing line between seawater and a hydrothermal end member at 0 7030 which is derived by seawater basalt interaction at ca 350 c and water rock ratio of about 1 5 sr concentrations are not affected in the process while mg uptake from seawater is almost complete up to2 3 of this hydrothermal component is involved in anhydrite precipitation while the sr isotopic ratio in sulfides chalcopyrite sphalerite cannot be distinguished from that of sulfate it is estimated that ca 1 10 10 moles of strontium are yearly cycled in the hydrothermal systems of mid oceanic ridges thereby affecting the 87 sr 86 sr budget of seawater mass balance between river runoff limestone precipitation and ridge basalt alteration suggests that the 87 sr 86 sr ratios of the river runoff are in the range 0 7097 0 7113 and are largely dominated by limestone alteration

glacial effects on weathering processes new insights from the elemental and lithium isotopic composition of west greenland rivers greenland is by far the dominant source of glacial runoff to the oceans but the controls on the chemical and isotopic composition of this runoff are poorly known to better constrain glacial effects on weathering processes we have conducted elemental and lithium isotope analyses of glacial and non glacial rivers in gneiss catchments in west greenland the glacial rivers have high total suspended solids 0 5 g l 1 and low total dissolved solids 12 scm 1 relative to the non glacial rivers and they contain a higher proportion of dissolved ca2 and k because of subglacial preferential weathering of trace carbonates and biotite the glacial rivers also have high so42 because of the oxidation of trace sulphides under the ice both glacial and non glacial rivers have high 7li respectively not vert similar 26 and not vert similar 30 relative to the rocks from which the li is derived not vert similar 8 saturation state modelling suggests that this is due to the formation of fe oxyhydroxides in the non glacial rivers with preferential uptake of 6li during inner sphere sorption of li on the fe oxyhydroxide surface glacial rivers however are undersaturated with respect to clay minerals and fe oxyhydroxides nevertheless leaching of suspended sediments indicates that not vert similar 65 of the li in these sediments is associated with fe oxyhydroxide phases and the 7li value of this li is low not vert similar 5 these results suggest that these fe oxyhydroxides formed under the ice as a product of sulphide oxidation with preferential uptake of 6li onto the mineral surface solubilisation of li from these fe oxyhydroxide phases is unlikely to represent a significant flux of li to the oceans moreover because the difference between the 7li values of glacial vs non glacial rivers is small glaciation has not had a significant impact on the li isotopic composition of the riverine flux delivered to the oceans in the past even at the height of the last deglaciation

stable strontium isotopes δ88 86sr in cold water corals a new proxy for reconstruction of intermediate ocean water temperatures abstract zooxanthellate scleractinian corals are known as archives for temporal variations of climate variables such as sea surface temperature salinity or productivity the use of azooxanthellate cold water corals as potential archives for intermediate water mass properties and climate variability was tested recently however the correlation of established proxies such as 18o and 13c with temperature is difficult since there is no direct temperature equation applicable as in shallow water corals other temperature proxies such as sr ca mg ca and u ca are influenced by the complex microstructure of the aragonite skeleton the rate of calcification and other vital effects observed for coral species for the first time we show that the stable strontium isotope ratio 88 86sr incorporated in the skeletons of the cold water coral species lophelia pertusa portrays the ambient seawater temperature the temperature sensitivity from live samples collected along the european continental margin covering a temperature range from 6 to 10 c is 0 026 0 003 c 2 standard error which is a sensitivity similar to the tropical shallow water coral record of pavona clavata this indicates a similar fractionation process of strontium for both zooxanthellate and azooxanthellate corals for coral aragonite the 88 86sr ratio may serve as a new paleo temperature proxy and introduces new perspectives in paleoceanography with respect to intermediate water dynamics

isotopic approaches for quantifying the rates of marine burial diagenesis 1 diagenetic reactions in marine sediments have the potential to alter geochemical proxy records and affect the global carbon cycle over tens of thousands to millions of years this article describes advances in the use of ca sr and u series isotopes in constraining carbonate recrystallization and silicate dissolution rates in marine systems we specifically focus on recent efforts that interpret isotope variability in marine pore fluids using reactive transport models of varying complexity such studies suggest that calcite recrystallization rates are significant over time scales 1 myr approaching exchange rates of 0 4 1 myr 1 over longer time scales isotopic data point to continued exchange between calcite and coexisting pore fluid though at lower rates than in young sediments extrapolating these recrystallization rates over tens of millions of years we quantify the extent to which geochemical climate proxies such as mg ca in calcite can be altered diagenetically in some cases such diagenetic effects significantly affect the interpretation of long term climatic trends as well as determinations of absolute paleotemperatures silicate dissolution rates in siliclastic marine sediments appear to be similar in magnitude to dissolution rates in terrestrial environments 10 7 10 6 yr 1 such estimates suggest that silicate weathering in marine sediments may play an important role in the carbon cycle at least over time scales approaching 400 500 kyr

variability of carbonate diagenesis in equatorial pacific sediments deduced from radiogenic and stable sr isotopes the recrystallisation dissolution precipitation of carbonate sediments has been successfully modelled to explain profiles of pore water sr concentration and radiogenic sr isotope composition at different locations of the global ocean however there have been few systematic studies trying to better understand the relative importance of factors influencing the variability of carbonate recrystallisation here we present results from a multi component study of recrystallisation in sediments from the integrated ocean drilling program iodp expedition 320 321 pacific equatorial age transect peat where sediments of similar initial composition have been subjected to different diagenetic histories the peat sites investigated exhibit variable pore water sr concentrations gradients with the largest gradients in the youngest sites radiogenic sr isotopes suggest recrystallisation was relative rapid consistent with modelling of other sediment columns as the 87sr 86sr ratios are indistinguishable within 2 uncertainties from contemporaneous seawater 87sr 86sr ratios bulk carbonate leachates and associated pore waters of site u1336 have lower 87sr 86sr ratios than contemporaneous seawater in sediments older than 20 2 ma most likely resulting from the upward diffusion of sr from older recrystallised carbonates it seems that recrystallisation at site u1336 may still be on going at depths below 102 5 rmcd revised metres composite depth suggesting a late phase of recrystallisation furthermore the lower sr ca ratios of bulk carbonates of site u1336 compared to the other peat sites suggest more extensive diagenetic alteration as less sr is incorporated into secondary calcite compared to the other peat sites u1336 has an inferred greater thermal gradient and a higher carbonate content the enhanced thermal gradient seems to have made these sediments more reactive and enhanced recrystallisation in this study we investigate stable sr isotopes from carbonate rich deep sea sediments for the first time pore water 88 86sr increases with depth from 0 428 to values reaching up to 0 700 at site u1336 documenting an isotope fractionation process during recrystallisation secondary calcite preferentially incorporates the lighter sr isotope 86sr leaving pore waters isotopically heavy the 88 86sr values of the carbonates themselves show more uniform values with no detectable change with depth carbonates have a much higher sr content and total sr inventory than the pore waters meaning pore waters are much more sensitive to fractionation processes than the carbonates the 88 86sr results indicate that pore water stable sr isotopes have the potential to indicate the recrystallisation of carbonate sediments

positive correlation between li and mg isotope ratios in the river waters of the mackenzie basin challenges the interpretation of apparent isotopic fractionation during weathering during chemical weathering magnesium mg is released by the dissolution of both carbonate and silicate sources the degree to which solute concentrations and isotopic compositions of rivers reflect the relative proportions of these two inputs or cycling by a series of processes associated with weathering is poorly constrained in the river waters of the mackenzie basin canada the mg content is high and mg isotope ratios 26mg 24mg expressed as mg 26 show in excess of one per mil variability part of this variability is attributed to the 3 range in the carbonate and silicate rocks drained despite this inherent lithological control on river water mg 26 values there is also evidence for a fractionation control a linear positive covariation between lithium 7li 6li expressed as li 7 and mg isotope ratios in the river waters of the mackenzie basin is reported this covariation is not expected because previously reported fractionation related to physicochemical processes associated with clays or oxides should induce a negative covariation with mg isotope ratios

assessing the role of climate on uranium and lithium isotope behaviour in rivers draining a basaltic terrain this study presents uranium u and lithium li isotope and major and trace element data for the dissolved load suspended particles and bedload from rivers draining dominantly basaltic catchments on the island of sao miguel in the azores archipelago uranium activity ratios are at secular equilibrium in the bedload but are higher for suspended material suggesting sorption of uranium from the solution onto particle surfaces the 234u 238u of the riverine dissolved phase varies between 1 02 and 1 86 and lies on a mixing trend between the values expected from chemical weathering of basalt high u 234u 238u at secular equilibrium and an endmember with low u and high 234u 238u which probably reflects recoil effects associated with physical weathering and or soil formation lithium isotope ratios are consistently lighter in suspended material than the corresponding bedload suggesting preferential retention of 6li in the suspended load in turn the 7li of the dissolved load is always isotopically heavier ranging from 5 9 to 36 2 although the lightest values are affected by hydrothermal input the lithium isotopic composition of the dissolved load reflects the balance of primary mineral dissolution to secondary mineral formation comparison of the behaviour of u and li isotopes between sao miguel iceland and other basaltic terrains suggests that whilst u isotopes are dominated by weathering regimes dependent on factors such as weathering rates temperature runoff and climate neither weathering intensity nor climate exerts a direct influence on li isotope behaviour rather the formation of secondary minerals which is indirectly controlled by climate weathering primary mineralogy and biology appears to play the dominant role

the stratigraphy of the nicola group in the hedley district british columbia and the chemistry of its intrusions and au skarns the nieola group at hedley british columbia is a late carnian to late norian late triassic sequence of calcareous sedimentary and arc related volcaniclastic rocks it was deposited on a tectonically active paleoslope that marked either the rifted eastern margin of the shallow marine nicola basin or the faulted edge of an intrabasinal platform the lower part of the nicola group comprises a succession of four essentially coeval sedimentary facies from east to west across the district these are informally named the thin approx 200 in shallow marine limestone dominant french mine formation the thicker calcareous siltstone dominant hedley and chuchuwayha formations in the central part of the district and the thick up to 2208 m deeper water and argillite dominant stemwinder formation these facies are all blanketed by the whistle formation a 1200 m thick unit of basaltic tuff and tuffaceous sediment whose base is marked by a gravity slide megabreccia the copperfield breccia the nicola arc at hedley was associated with two plutonic episodes oldest are the hdey intrusions which are related to economic au skarns including the nickel plate deposit which has produced over 71 t of gold from 13 4 mt of ore the hedley intrusions are similar in composition quartz gabbro to quartz diorite and overall metaluminous chemistry to other island arc generated plutons related to many cu and fe skarns in british columbia although they are less evolved they also differ in having lower fe28 fe8 ratios avg 0 23 indicating a reduced oxidation state and higher baila and scinb ratios a slightly younger plutonic episode produced the 193 ma early jurassic brodey batholith and the 194 ma mount riordan stock the latter is associated with the mount riordan crystal peak industrial garnet skarn gold skarns are preferentially developed in areas where the hedley intrusions cut the hedley and french mine formations the aka skarn ore is marked by anomlous as bi te and co values and by high pyrrhotitelpyrite and pyroxeneigarnet ratios it is distinct from the ore of fe cu mo bb zn w and sn skarns by its very low cuiau zniau and aglau ratios avg 97 18 and 12 respectively

determination of temperature dependent stable strontium isotope 88sr 86sr fractionation via bracketing standard mc icp ms stable strontium isotopes here 88sr 86sr are introduced as a new member of the nontraditional stable isotopes we have developed a bracketing standard method for the determination of 88 86sr using an axiom mc icp ms and normalizing to strontium srm nbs987 for individual measurements the external reproducibility is better than about 25 ppm 1 rsd for the iapso seawater standard a 88 86sr value of 0 381 0 010 2sem was determined for the first time a temperature dependent strontium isotope fractionation during calcium carbonate precipitation could be shown aragonite samples inorganically precipitated under temperature control between 10 and 50 c revealed a 88 86sr temperature dependency of 0 0054 5 c r2 0 987 in contrast for natural coral samples pavona clavus from a proxy calibration study 23 to 27 c we did determine 0 033 5 c r2 0 955 the processes causing this sixfold stronger temperature dependency for the natural coral samples have to be studied in more detail in future studies in a first approach the different slopes can be interpreted as effects of kinetic fractionation of strontium ions with or without a hydrate shell of 22 to 29 water molecules

young volcanism and related hydrothermal activity at 5 s on the slow spreading southern mid atlantic ridge the effect of volcanic activity on submarine hydrothermal systems has been well documented along fast and intermediate spreading centers but not from slow spreading ridges indeed volcanic eruptions are expected to be rare on slow spreading axes here we report the presence of hydrothermal venting associated with extremely fresh lava flows at an elevated apparently magmatically robust segment center on the slow spreading southern mid atlantic ridge near 5 s three high temperature vent fields have been recognized so far over a strike length of less than 2 km with two fields venting phase separated vapor type fluids exit temperatures at one of the fields reach up to 407 c at conditions of the critical point of seawater the highest temperatures ever recorded from the seafloor fluid and vent field characteristics show a large variability between the vent fields a variation that is not expected within such a limited area we conclude from mineralogical investigations of hydrothermal precipitates that vent fluid compositions have evolved recently from relatively oxidizing to more reducing conditions a shift that could also be related to renewed magmatic activity in the area current high exit temperatures reducing conditions low silica contents and high hydrogen contents in the fluids of two vent sites are consistent with a shallow magmatic source probably related to a young volcanic eruption event nearby in which basaltic magma is actively crystallizing this is the first reported evidence for direct magmatic hydrothermal interaction on a slow spreading mid ocean ridge

the behaviour of magnesium and its isotopes during glacial weathering in an ancient shield terrain in west greenland the magnesium mg isotope composition of rivers is sensitive to changes in the balance of primary mineral dissolution and secondary mineral formation as these processes are regulated by climate then changes to the earth s climate system such as the onset of glaciation could potentially alter the isotopic behaviour of mg in rivers to investigate how mg isotopes behave during glacial weathering we have determined the mg concentration and mg isotope ratio for the dissolved suspended and bedload phases of glacial and non glacial rivers in west greenland this region is essentially monolithological and there is little biological activity hence isotope variations largely result from differences in weathering processes dissolved mg in rivers is always enriched in the light mg isotopes relative to the bedload 26mg 0 4 and the glacial rivers have lighter mg isotope compositions 26mg 1 to 1 3 than the non glacial rivers 26mg 0 6 enrichment of light mg in the dissolved load is consistent with the preferential uptake of heavy mg from solution during the formation of secondary silicate minerals however evidence from saturation state modelling suggests that little secondary mineral formation is likely to have occurred in the glacial rivers because the concentration of dissolved solids is very low moreover the glacial derived suspended sediment has identical mg isotope ratios to the bedload these observations suggest that the formation of secondary weathering minerals is not controlling the behaviour of mg isotopes in these rivers rather variations in the 26mg value of the dissolved load are attributed to incongruent weathering of the solid phase preferential dissolution of carbonate minerals which have low 26mg 1 1 to 5 2 imparts a more negative 26mg signal to the glacial river waters although our study indicates that the mg isotopic composition of the dissolved load is sensitive to changes in weathering congruence it is unlikely that glaciation will result in major changes in the 26mg composition of continental runoff

88 sr 86 sr fractionation and calcite accumulation rate in the sea of galilee abstract this study used the sea of galilee lake kinneret northern israel as a natural laboratory to investigate the fractionation of the stable sr isotope ratio 88 sr 86 sr during precipitation of inorganic primary calcite from the lake s water it was found that the absolute value of the 88 sr 86 sr fractionation factor 88 86 sr increases as a function of calcite accumulation rate 88 86 sr 0 05 to 0 042 log r mol m 2 d 1 where r is the accumulation rate furthermore the 87 sr 86 sr and 88 sr 86 sr ratios in the freshwater and brines that enter the lake were used to calculate the contributions of these sources to the lake sr budget the 87 sr 86 sr and 88 sr 86 sr ratios were measured in primary calcite aragonite shells of live melanopsis lake water and various water sources to the lake while the lake s 87 sr 86 sr ratios are determined by the mixture of freshwater of the jordan river and saline springs the 88 sr 86 sr ratios of the lake reflect a more complex mass balance that includes the effect of isotopic fractionation associated with the precipitation of primary calcite data analysis suggests that long term accumulation of inorganic calcite depleted in the heavy isotope 88 sr results in an increase of the 88 86 sr value of the lake water by 0 05 in contrast to the primary inorganic calcite biogenic aragonite of the melanopsis shells show a rather constant 88 sr 86 sr water caco 3 fractionation of 88 86 sr 0 21 similar 88 86 sr values were reported for the precipitation of coralline and inorganic aragonite from seawater and the precipitation of inorganic calcite from various continental waters the 88 86 sr value of inorganic calcite is modulated by the rate of carbonate precipitation as noted above and shown by precipitation experiments massive precipitation of primary calcite with a wide spread of accumulation rates occurs during the spring phytoplankton bloom in lake kinneret the bloom dictates the degree of calcite saturation in the lake and hence the stable sr isotopic composition of the precipitating calcite the correlation between 88 sr 86 sr and the calcite accumulation rate can be therefore used as a tool to reconstruct environmental and ecological variations in the historical lake by analyzing the 88 sr 86 sr ratio in the primary caco 3 recovered from the lake s sedimentary archives

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

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

sr stable isotope composition of earth the moon mars vesta and meteorites abstract high precision stable sr isotopic variations 88 sr 86 sr are reported in a variety of terrestrial samples martian and lunar meteorites hed undifferentiated primitive meteorites chondrules and refractory inclusions almost all the whole rock samples are isotopically indistinguishable at a 50 parts per million ppm level the exceptions are cv and co chondrites which are isotopically light and for which we believe that their isotopic composition is controlled by the proportion of refractory material five separated chondrules and one refractory inclusion from allende are isotopically light with 88 86 sr fractionations up to 1 73 whereas the matrix is enriched in the heavy isotopes 88 86 sr 0 66 the depletion in heavy isotopes observed in chondrules and refractory inclusions could be attributed to the condensation of a material already depleted in sr however in that case more than 60 of the original material would be unaccounted we propose instead that isotopic fractionation by electromagnetic sorting of ionized heavy sr from neutral sr in the early solar system for the origin of the fractionation observed in refractory inclusions and redistribution of sr by aqueous alteration for the origin of the fractionation observed in chondrules and matrix we conclude that cv and co chondrites are not the primary building blocks for earth and mars

high precision radiogenic strontium isotope measurements of the modern and glacial ocean limits on glacial interglacial variations in continental weathering existing strontium radiogenic isotope 87sr 86sr measurements for foraminifera over quaternary glacial interglacial climate cycles provide no evidence for variations in the isotope composition of seawater at the 9 13 ppm level of precision however modelling suggests that even within this level of uncertainty significant up to 30 variations in chemical weathering of the continents are permitted accounting for the longer term rise in 87sr 86sr over the quaternary and the apparent imbalance of sr in the oceans at the present day this study presents very high precision 87sr 86sr isotope data for modern seawater from each of the major oceans and a glacial interglacial seawater record preserved by planktic foraminifera from ocean drilling program odp site 758 in the north east indian ocean strontium isotope 87sr 86sr measurements for modern seawater from the atlantic pacific and indian oceans are indistinguishable from one another 87sr 86sr 0 7091792 0 0000021 n 17 at the level of precision obtained in this study 4 9 ppm 2 this observation is consistent with the very long residence time of sr in seawater and underpins the utility of this element for high precision isotope stratigraphy the 87sr 86sr seawater record preserved by planktic foraminifera shows no resolvable glacial interglacial variation 87sr 86sr 0 7091784 0 0000035 n 10 and limits the response of seawater to variations in the chemical weathering flux and or composition to 4 9 ppm or less calculations suggest that a variation of 12 around the steady state weathering flux can be accommodated by the uncertainties obtained here the new data cannot accommodate a short term weathering pulse during de glaciation although a more a diffuse weathering pulse accompanying protracted ice retreat is permissible however these results still indicate that modern weathering fluxes are potentially higher than average over the quaternary and such variations through glacial cycles can also account for the longer term rise in 87sr 86sr over this time interval the very high precision measurements made for the marine 87sr 86sr record in this study place clear limits on the magnitude and timing of changes in the chemical weathering flux during glacial interglacial cycles further constraints must be sought from even higher precision measurement or elements with shorter residence times in the ocean such as osmium os that have the capacity to respond to short term variations in input

the phanerozoic δ88 86sr record of seawater new constraints on past changes in oceanic carbonate fluxes the isotopic composition of phanerozoic marine sediments provides important information about changes in seawater chemistry in particular the radiogenic strontium isotope 87sr 86sr system is a powerful tool for constraining plate tectonic processes and their influence on atmospheric co2 concentrations however the 87sr 86sr isotope ratio of seawater is not sensitive to temporal changes in the marine strontium sr output flux which is primarily controlled by the burial of calcium carbonate caco3 at the ocean floor the sr budget of the phanerozoic ocean including the associated changes in the amount of caco3 burial is therefore only poorly constrained here we present the first stable isotope record of sr for phanerozoic skeletal carbonates and by inference for phanerozoic seawater 88 86srsw which we find to be sensitive to imbalances in the sr input and output fluxes this 88 86srsw record varies from 0 25 to 0 60 vs srm987 with a mean of 0 37 the fractionation factor between modern seawater and skeletal calcite 88 86srcc sw based on the analysis of 13 modern brachiopods mean 88 86sr of 0 176 0 016 2 standard deviations s d is 0 21 and was found to be independent of species water temperature and habitat location overall the phanerozoic 88 86srsw record is positively correlated with the ca isotope record 44 40casw but not with the radiogenic sr isotope record 87sr 86sr sw a new numerical modeling approach which considers both 88 86srsw and 87sr 86sr sw yields improved estimates for phanerozoic fluxes and concentrations for seawater sr the oceanic net carbonate flux of sr f sr carb varied between an output of 4 7x1010mol myr and an input of 2 3x1010mol myr with a mean of 1 6x1010mol myr on time scales in excess of 100myrs the f sr carb is proposed to have been controlled by the relative importance of calcium carbonate precipitates during the aragonite and calcite sea episodes on time scales less than 20myrs the f sr carb seems to be controlled by variable combinations of carbonate burial rate shelf carbonate weathering and recrystallization ocean acidification and ocean anoxia in particular the permian triassic transition is marked by a prominent positive 88 86srsw peak that reflects a significantly enhanced burial flux of sr and carbonate likely driven by bacterial sulfate reduction bsr and the related alkalinity production in deeper anoxic waters we also argue that the residence time of sr in the phanerozoic ocean ranged from 1myrs to 20myrs

coupled δ44 40ca δ88 86sr and 87sr 86sr geochemistry across the end permian mass extinction event abstract we report high resolution high precision 44 40ca 88 86sr and 87sr 86sr records spanning the permian triassic boundary ptb from the meishan and dajiang carbonate successions in south china the goal of the study was to understand the behavior of ca and sr isotopes during a time period in earth history characterized by severe biological and environmental perturbations including a major mass extinction flood basalt volcanism ocean acidification and sea level fluctuations dajiang displays negative 44 40ca and 88 86sr excursions and invariant 87sr 86sr ratios in the

controls on the solute geochemistry of subglacial discharge from the russell glacier greenland ice sheet determined by radiogenic and stable sr isotope ratios abstract we used radiogenic and stable sr isotope ratios 87sr 86sr and 88 86sr to examine controls on solute acquisition in subglacial discharge from the russell glacier a land terminating lobe of the greenland ice sheet gris located in western greenland the study focused on two melt seasons in 2014 and 2015 subglacial discharge 87sr 86sr ratios are 13 000 ppm higher than those measured for bedload and suspended sediment digests and are more similar to those of bedload sediment leachates these results point to the preferential dissolution of minerals with high 87sr 86sr ratios analyses of mineral separates from bulk rocks demonstrate that biotite chlorite hornblende and k feldspar have relatively high 87sr 86sr ratios subglacial discharge 88 86sr values are 0 10 higher than those for bedload and suspended sediment digests isotope fractionation during secondary mineral formation and or adsorption cannot account for the difference between subglacial discharge and bedrock 88 86sr values as suspended and bedload sediment leachates and digests produced similar 88 86sr values and are within the range for bulk silicate earth consistent with the interpretation of 87sr 86sr ratios we attribute the difference to the preferential dissolution of minerals with high 88 86sr values mineral separates display a wide range of 88 86sr values 0 40 those having high 88 86sr values include hornblende and k feldspar as well as apatite and titanite taken together the preferential weathering of predominately silicate minerals explains the sr isotope geochemistry of subglacial discharge subglacial discharge from the russell glacier feeds the proglacial akuliarusiarsuup kuua river akr along a 32 km transect of the akr from the gris margin toward the coast riverine 87sr 86sr ratios increase from 0 722 to 0 747 in an approximately step wise pattern that corresponds to point source inputs of additional subglacial discharge major cation concentrations and 87sr 86sr ratios minimally vary along lengths of the transect with no hydrological inputs this suggests that proglacial chemical weathering is negligible and likely does not contribute significantly to gris solute fluxes in general this study supports the recent contention that silicate mineral weathering dominates the solute geochemistry of gris subglacial discharge in contrast to valley glaciers which typically show substantial contributions from carbonate and sulfide weathering regardless of primary bedrock composition ice sheet subglacial chemical weathering may therefore have a greater impact on long term atmospheric co2 drawdown than previously realized

characterizing nutrient pathways in quebec canada vineyards insight from stable and radiogenic strontium isotopes abstract soils are a crucial interface of earth s critical zone responsible for the biogeochemical cycling of mineral nutrients while the sources of essential nutrients such as ca and sr in plants have been widely studied the processes by which these nutrients are transferred from the soil to the plants is less clear we present new evidence for systematic nutrient fractionation between soils grapes and wines from five vineyards from the quebec terroir canada using the novel stable sr 88 86sr isotope system we coupled this approach with traditional radiogenic 87sr 86sr measurements on the same samples bulk soils labile fraction of these soils whole grapes and wines from five vineyards from the quebec terroir canada to ensure that variations in 88 86sr values were provoked by processes involved in sr transfer instead of mixing between different sources the 88 86sr values generally decrease from the bulk to the labile fractions of the soils to the grapes a decrease in the difference between the soil fractions 88 86srbulk labile with increasing 88 86sr values in the labile fraction is interpreted to reflect increasing pedogenic mineral precipitation and higher soil fertility the depleted 88 86sr values of the grapes are consistent with a preferential uptake of lighter isotopes by plants this effect is magnified in soils showing higher secondary mineral precipitation an increase in the 88 86sr values from the grapes to the wines reflects the separation of the skin seeds and the juice pulp enriched in 88sr in the winemaking process this mixing relationship is supported by a correlation between the sr concentrations and the 88 86sr values of the wines and grapes these findings suggest promising new applications of stable sr isotopes values for studying soil fertility and the impact of nutrient availability for plant growth in agricultural ecosystems as well as the impact of the maceration processes in the production of wine the overall similarity of 87sr 86sr ratios of the labile soil fractions grapes and wines from the same vineyard support the hypothesis of a same sr source from the soil solution to its transfer to the grape and wine and confirm the potential of the 87sr 86sr ratios as a proxy for geographic provenance of wine however slightly lower 87sr 86sr ratios in the grape pulps by 0 00040 on average compared to the skins and seeds suggest that the sources of nutrients available for plant uptake vary during the vegetative cycle the grape seeds and skins formed in the early growth cycle are characterized by rapid growth due to enhanced rhizosphere activity enhanced mineral dissolution providing higher nutrient levels the enhanced mineral solubility results in higher 87sr 86sr ratios in the skin and seeds derived from enhanced dissolution of 87sr enriched silicate minerals in contrast the pulp develops later in the growth cycle when rhizosphere activity and mineral solubility is reduced resulting in a lesser contribution from silicate minerals and thus reflect a higher proportion of dissolved carbonate contributing to the lower 87sr 86sr ratios of the pulps

strontium stable isotopes fractionate in the soil environments abstract this study shows that the stable isotopic composition of strontium the 88sr 86sr ratio expressed as 88 86sr value relative to the nbs987 standard varies significantly in sedimentary terrestrial environments the abundances of 86sr 88sr isotopes were analyzed by mc icp ms nu plasma all studied rocks and waters show 88 86sr values that are distinctly different from the measured nbs987 standard yielding 0 01 0 05 all errors are reported as 2 modern corals from the northern gulf of aqaba red sea yielded significantly different value than seawater 88 86sr 0 22 0 07 compared to 0 35 0 06 respectively in an excellent correlation with the 88 86sr analyses reported by fietzke and eisenhauer fietzke j eisenhauer a 2006 determination of temperature dependent stable strontium isotopes 88sr 86sr fractionation via bracketing standard mc icp ms geochm geophys geosyst 7 no 8 on other coral samples all carbonate samples that originated in the marine environment corals porites and acropora from the northern gulf of aqaba cretaceous limestone and runoff from the judea mountains as well as lacustrine evaporitic aragonite dead sea and red sea and atlantic seawater yield an average 88 86sr value of 0 26 0 1 on the other hand secondary materials products of chemical weathering from the terrestrial environment of the judea mountain such as terra rossa soil and speleothem calcite that derives its sr from the above lying soil yielded significantly lower 88 86sr value of 0 17 0 06 this indicates that strontium isotopes fractionate in the soil environment calling for a possible development of strontium isotopes as a tracer for processes of chemical weathering and pedogenesis

enrichment of 88 sr in continental waters due to calcium carbonate precipitation abstract 88 86sr data published over the last few years suggest that continental waters are enriched with 88sr as compared to the rocks in their drainage basins in an attempt to understand this phenomenon this study established the fractionation in the 88sr 86sr ratio during precipitation of continental carbonates i e carbonates precipitated on land from surface pedogenic or ground waters and evaluated the contribution of this process to the 88sr enrichment in rivers for this stable and radiogenic sr isotopes 88sr 87sr and 86sr were measured in calcite samples and their precipitating waters collected in various continental environments such as soil cave streams and groundwater the results indicate that continental carbonates are 88sr depleted relative to their precipitating waters placing them as one of the most 88sr depleted reservoirs on earth the average difference in 88 86sr values between waters and solid caco3 tufas or speleothems that they precipitate is carb water 0 218 0 014 1sd an even larger fractionation e carb water 0 285 0 02 was measured in groundwater with particularly high carbonate alkalinity and high carbonate precipitation rate that depleted 65 of the sr in the groundwater resulting in substantial 88sr enrichment in the residual dissolved sr sr 88 86 0 656 results also suggest that pedogenic carbonate precipitation in soil profile removes 50 85 of the sr from the recharging soil water thereby increasing the 88 86sr value of the soil water from 0 18 to 0 3 0 6 similar 88sr enrichment was observed in drip water from a karst cave a maximum removal flux of sr into continental carbonates of about 20 gmol sr y 1 is required to yield the reported 88sr enrichment in global rivers sr 88 86 0 32 relative to their rock sources when using the fractionation factor derived in this study carb water 0 218 and the published 88 86sr composition of marine carbonates of 0 16 this surprisingly large flux requires that 40 of the originally weathered sr should co precipitate with continental carbonates this calculation may suggest that caco3 precipitation is a significant mechanism in the continental sr cycle it is possible however that other mechanisms such as sr uptake by plants or incongruent weathering of silicates could also contribute to the riverine 88sr enrichment alternatively the average 88 86sr value of marine carbonate rock sections undergoing weathering is higher than suggested in current literature it is concluded that additional 88 86sr data on marine carbonate rock sections should be collected to resolve the enigma of the high value of riverine 88 86sr

controls over the strontium isotope composition of river water abstract strontium concentrations and isotope ratios have been measured in river and ground waters from the ganges orinoco and amazon river basins when compared with major element concentrations the data set has allowed a detailed examination of the controls over the strontium isotope systematics of riverine input to the oceans in the following environments 1 1 typical drainage basins containing limestones evaporites shales and alumino silicate metamorphic and igneous rocks 2 2 shield terrains containing no chemical or biogenic sediments and 3 3 the floodplains that constitute the largest areas of many large rivers the strontium concentration and isotope composition of river waters are largely defined by mixing of strontium derived from limestones and evaporites with strontium derived from silicate rocks the strontium isotope composition of the limestone endmember generally lies within the phanerozoic seawater range which buffers the 87 sr 86 sr ratios of major rivers a major exception is provided by the rivers draining the himalayas where widescale regional metamorphism appears to have led to an enrichment in limestones of radiogenic strontium derived from coexisting silicate rocks the strontium isotope systematics of rivers draining shield areas are controlled by the intense transportlimited nature of the weathering reactions and thereby limits variations in the strontium flux from these terrains floodplains are only a minor source of dissolved strontium to river waters and precipitation of soil salts in some floodplains can reduce the riverine flux of dissolved strontium to the oceans the most effective mechanisms for altering the isotope ratio and flux of riverine strontium to the oceans are increased glaciation and large scale regional metamorphism of the type produced during continental collision both mechanisms provide a means for increasing the 87 sr 86 sr ratio of the global riverine flux

radiogenic and stable strontium isotopes in provenance studies a review and first results on archaeological wood from shipwrecks abstract different approaches are used to study wood provenance but most of them are based on tracers in wood that are generally controlled by climatic factors the strontium isotopic ratio 87 sr 86 sr in trees and soils is related to the signature of the local bedrock despite being used in diverse archaeological studies sr isotopes have rarely been used to trace the provenance of archaeological wood and especially wood from shipwrecks in addition recent analytical advances have allowed the detection of mass dependent fractionation of sr isotopes during biogeochemical processes as reflected in the variation of 88 86 sr values between different environmental materials the 88 86 sr values could be used in conjunction with the 87 sr 86 sr isotope ratio to improve constraints on the sources of sr in the archaeological materials being studied this paper discusses the potential and limitations of using both of these sr isotope ratios to trace the provenance of wood from shipwrecks we review the 87 sr 86 sr and 88 86 sr variations in rocks waters soils plants and other living organisms and discuss how to determine the local sr isotopic signature of potential sites we also compile a list of known wood post mortem modifications in seawater possible implications in terms of the modification of the original sr isotope ratios of wood during storage in seawater are illustrated through preliminary observations this paper points out some limitations and perspectives for using sr isotopes in provenancing wood from shipwrecks and suggests future research to test and apply this approach for tracing the origin of archaeological wood

isotopic constraints on the source of argentinian loess with implications for atmospheric circulation and the provenance of antarctic dust during recent glacial maxima we present rare earth element ree and sr nd isotopic data for argentinian loess 28 38 s with two aims 1 to examine the source regions of argentinian loess and the constraints that these put on palaeo wind directions 2 to further investigate the source of antarctic ice core dust and to test the hypothesis that some of it could be derived from a region to the north of patagonia into which the dry dusty westerly dominated patagonian climate expanded during quaternary glacial maxima sr nd isotopic data for argentinian loess from north of 37 s are distinct from patagonian loess compositions in that they have more radiogenic sr 87sr 86sr 0 7059 0 7123 and less radiogenic nd nd 0 8 to 6 4 ree patterns and sr nd isotopic values are relatively homogeneous for multiple samples taken from single loess sections but show significant differences between sections in general there is a northward change from patagonia like ree patterns and isotopic values away from volcanogenic signatures and towards those that are more like the continental crust the latitudinal nd isotopic pattern is remarkably similar to that for andean volcanic rocks and suggests derivation of loess from the andes by more or less direct westerly transport for loess sections in the north the data imply a contribution from palaeozoic gneisses to the northwest in the chilean altiplano sr nd data for extra patagonian argentinian loess north of 37 s do not support a significant role for this source region in supplying dust to antarctica at the last glacial maximum this conclusion contrasts with previous studies that suggest a significant northward shift in the climatic belts and in particular the westerlies and the antarctic polar front during quaternary glacial maxima very systematic relations between the sr nd isotopic composition of loess and their andean source highlights shifts in the sr isotopic composition of loess to more radiogenic values and strongly suggests that the slight offset between patagonian loess and ice core dust identified by previous workers is due to grain size differentiation effects

high temperature strontium stable isotope behaviour in the early solar system and planetary bodies abstract this study presents comprehensive strontium stable isotope 88sr 86sr data measured by multiple collector inductively coupled plasma mass spectrometry mc icp ms for a suite of carbonaceous chondrites differentiated meteorites lunar martian and terrestrial samples carbonaceous chondrites comprise a mixture of refractory inclusions and chondrules that have light 88sr values between 0 35 to 0 05 and matrix material that possesses a heavy 88sr composition of 0 65 confirming the results of earlier studies consequently bulk carbonaceous chondrites are relatively heterogeneous in composition ranging from 0 12 to 0 35 most likely reflecting clast matrix variability the light 88sr compositions of the refractory inclusions are consistent with mass dependent fractionation of other refractory elements ca and eu and are most likely produced by non equilibrium fractionation undercooling in the nebula gas during condensation of hibonite from the solar nebula simon and depaolo 2010 stable calcium isotopic composition of meteorites and rocky planets earth planet sci lett 289 457 466 carbonaceous chondrites angrites and martian meteorites have indistinguishable compositions at the level of analytical uncertainty of this study however statistical analysis indicates that melts derived from the earth s mantle have heavier 88sr values than bulk carbonaceous chondrites and martian meteorites but compositions indistinguishable from eucrites 88sr 0 26 0 12 moreover terrestrial basalts and andesites have restricted 88sr values 0 30 0 07 suggesting that mantle melting delivers rather homogenous melts to the earth s surface with respect to 88sr in contrast glasses from evolved terrestrial rocks and lunar basalts extend to very light 88sr values 0 20 the sr stable isotope composition covaries with europium anomaly eu eu as an index of plagioclase fractionation and 88sr can be successfully modelled by the heavy isotopes of sr being preferentially partitioned into plagioclase with a fractionation factor of 1 0007 for 88sr 86sr our results demonstrate that sr stable isotopes may be significantly fractionated at high temperatures and their measurement can provide insights into planetary evolution and magmatic processes

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

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

revised middle upper jurassic strontium isotope stratigraphy abstract a study is conducted to supplement the uppermost lower jurassic lowermost cretaceous marine strontium isotope dataset and to present new statistical fits of the middle late jurassic seawater strontium isotope curve based on a numerical time scale and a detailed biostratigraphical zonal scheme the use of the stratigraphical scheme allows reduction of dating errors related to uncertainty of numerical age determinations the presented correlation charts enable direct calibration between strontium isotope stratigraphy and regional biostratigraphical frameworks new strontium isotope data have been obtained from well preserved lower bajocian uppermost callovian oxfordian kimmeridgian and upper volgian belemnite rostra the presented seawater 87 sr 86 sr curve is characterized by reliable 95 confidence limits mean width of 0 000007 which take into account precision of dating of particular data points a decrease of seawater 87 sr 86 sr ratio from ca 0 70730 to ca 0 70683 is observed throughout the middle aalenian early oxfordian 172 1 160 8 ma ago the steepest phanerozoic fall of the ratio with a rate of change of up to 0 00015 per 1 ma is recorded in the bajocian segment of the strontium isotope curve the phanerozoic minimum of the marine 87 sr 86 sr ratio occurred at the early middle oxfordian transition the 87 sr 86 sr ratio increased starting from the middle oxfordian till the end of the jurassic 160 8 145 7 ma reaching a value of ca 0 70720 at the jurassic cretaceous transition the middle earliest late jurassic decrease in seawater 87 sr 86 sr ratio is interpreted as a result of the increased hydrothermal activity of the seafloor during the breakup of gondwana and the formation of new atlantic tethyan oceanic basins the successive rise of the ratio is probably related to the decelerated hydrothermal venting of the oceanic crust although a partial increase in radiogenic strontium input from continental weathering cannot be excluded

weathering processes catchment geology and river management impacts on radiogenic 87sr 86sr and stable δ88 86sr strontium isotope compositions of canadian boreal rivers abstract radiogenic 87sr 86sr and stable 88 86sr strontium isotope compositions spanning a calendar year are reported for rivers from across subarctic canada that drain contrasting lithologies ranging from precambrian bedrock koksoak great whale and la grande rivers of northern quebec to carbonate and clastic phanerozoic sedimentary rocks of the western interior platform nelson river of central and western canada the 87sr 86sr isotopic compositions of the river waters reflect the underlying geology with rivers draining the precambrian shield having higher 87sr 86sr ratios 0 727 0 734 than the phanerozoic dominated nelson river 0 713 the stable strontium isotope values 88 86sr range from 0 26 to 0 39 with the values for the nelson river overlapping those of the other three rivers that have not been developed for hydroelectric power show a seasonal variation in the 87sr 86sr ratios whereas those that have been diverted or dammed show little or no seasonal variation due to increased residence time of their water in hydroelectric reservoirs the three rivers from northern quebec show discrete ranges in their 87sr 86sr and 88 86sr isotope compositions that correlate with the ca sr and na sr ratios of the river water these correlations are interpreted to reflect differential chemical weathering of felsic versus mafic source rocks and or of surficial sediment vs bedrock sources

strontium isotope fractionation of planktic foraminifera and inorganic calcite we have investigated the strontium isotope fractionation 88 86srcarb aq between inorganic calcite and aqueous sr2 ions by precipitation experiments at a constant temperature of 25 c and precipitation rates r ranging from 102 3 to 104 2 mol m2 h strontium isotope ratios were measured using the 87sr 84sr double spike technique it was found that strontium isotope fractionation in these calcites is strongly dependent on the precipitation rate view the mathml source the measured 88 86sr values are significantly correlated with previously measured 44 40ca and sr ca values of the same calcite samples 88 86srcarb aq 0 18 44 40cacarb aq 0 01 view the mathml source the slope of 88sr 86sr versus 44ca 40ca fractionation is 0 18 0 04 and compatible with a kinetic fractionation during dehydration of the strontium and calcium ions but not with isotope fractionation in a diffusive boundary layer using published equilibrium 44 40cacarb aq and view the mathml source values we estimate the equilibrium isotope fractionation of strontium to be very close to zero 88 86sreq carb aq 0 01 0 06 this estimate is confirmed by strontium isotope values of natural inorganic calcites that precipitated very slowly in basalts of the ocean crust the results from the inorganic calcites are used to explain strontium isotope fractionation of planktic foraminifera specimens of two warm water species globigerinoides ruber and globigerinoides sacculifer were picked from the holocene section of a caribbean sediment core we found no significant difference in 88 86sr between the two species in addition g ruber specimens from marine isotope stage 2 in the same core show 88 86sr values identical to the holocene specimens the strontium isotopes of both foraminifera species are strongly fractionated 88 86srcarb aq 0 248 0 005 when compared to published data of other major marine calcifiers applying the results from the inorganic precipitation experiments we find that the strong foraminiferal strontium isotope fractionation can be explained by calcification in a largely open system at high precipitation rates comparable in magnitude to rates known from scleractinian reef corals this interpretation is in good agreement with the kinetic calcification model for planktic foraminifera by kisakurek et al 2011 which was based on calcium isotopes and elemental sr ca ratios

geochemical indicators in western mediterranean messinian evaporites implications for the salinity crisis abstract the messinian salinity crisis msc led to deposition of one of the youngest saline giant on earth the increasing restriction of the connections between the mediterranean the atlantic ocean and the freshwater paratethyan basins resulted in the deposition of massive amounts of evaporites gypsum anhydrite halite and potash salts in shallow marginal basins as well as in deep mediterranean basins here we show that each gypsum unit in the circum mediterranean marginal basins in sicily and spain is characterized by a narrow range of sulfate isotopic values 34s 23 and 18o 14 in the lower gypsum 34s 23 and 18o 17 in the upper gypsum sulfate isotope compositions found in msc evaporites from a variety of circum mediterranean basins are homogenously high relative to expected late miocene marine evaporites 34s 22 and 18o 12 this points to a stratified mediterranean sea with a high salinity dense and anoxic bottom water mass an intermediate depth gypsum saturated brine flooded marginal basins from which selenite deposits formed during the msc stage 1 primary lower gypsum and msc stage 3 upper gypsum messinian brines were gradually affected by biogenic redox processes and isotopically differentiated from global seawater values the homogeneity of isotopic signatures between distant synchronous gypsum deposits further supports the deep basin deep water model for the mediterranean during the entire msc event

strontium isotopes trace biological activity in the critical zone along a climate and vegetation gradient abstract weathering and ecosystem nutrition are intimately linked through the supply of fresh mineral nutrients from regolith and bedrock the geogenic nutrient pathway however the prominence of this link is dependent on the efficiency of nutrient recycling from plant litter the organic nutrient cycle isotope ratios of strontium sr an element that behaves similarly to ca in ecosystems confer two types of information radiogenic sr isotopes inform as to the sources of sr and the degree of weathering while stable sr isotopes constrain partitioning between compartments of the critical zone bedrock water secondary solids and plants to date however neither the reactions nor the mass balance between compartments that fractionate sr isotopes nor the fractionation factors involved are well understood here we present geochemical budgets of sr using radiogenic and stable sr isotopes and ca sr ratios at four sites along a substantial climate and primary production gradient in the coastal mountains of chile we found that sr release through weathering is isotopically congruent and released sr is not strongly isotopically fractionated either during secondary mineral formation or transfer into the exchangeable pool despite this the 88sr 86sr ratio of bio available sr which should reflect the ratio of dissolved sr is higher than that of rock and regolith we propose that this offset is caused by plants while 88sr 86sr in plant organs at the four study sites systematically increased from roots towards their leaves whole plant sr isotope compositions indicate preferential uptake of light sr into plants with a fractionation of up to 0 3 relative to the bio available pool despite this strong biological fractionation 88sr 86sr ratios in bio available sr do not covary with biomass production across our study sites because with greater plant growth sr is recycled more times after release by weathering an isotope neutral process rather the loss of sr from the ecosystem in solid organic material sets the isotope ratio of dissolved or bio available sr organic solids thus appear to constitute a significant export path of elements released during weathering with the removal of solid plant debris reducing the recycling factor of sr and possibly that of other mineral nutrients too

insights into combined radiogenic and stable strontium isotopes as tracers for weathering processes in subglacial environments this study reports stable and radiogenic strontium isotope behaviour in the dissolved load and suspended sediments from the subglacial outflow of the lemon creek glacier juneau ice field alaska over a single melt season in situ measurements discharge total alkalinity ph and conductivity are combined with elemental concentrations x ray diffraction xrd analysis and radiogenic strontium isotope measurements to interpret the variations observed in stable strontium isotopic ratios the stable sr isotope composition 88sr 86sr ratio expressed as 88 86sr of the dissolved load averages 0 31 0 05 and is heavier than both the suspended sediment 0 18 0 03 as well as local bedrocks 0 20 to 0 26 we attribute the enrichment of heavier isotopes in the dissolved load to the uptake of lighter sr isotopes by secondary weathering minerals driving the dissolved load to heavier values x ray diffraction xrd analysis confirms the presence of clays in the suspended sediments and thermodynamic modelling suggests the presence of iron oxy hydroxide phases although it is not possible to completely rule out the effect of dissolution of primary minerals in controlling sr isotopic compositions of the dissolved load our data indicate that the extent of secondary mineral formation likely plays a significant role the preferential weathering of minerals such as biotite consistent with the mineralogical assemblages found in the suspended sediments as well as the potential presence of radiogenic calcites from metacarbonates derived from the yukon tanana terrain may be driving the small seasonal shifts in 87sr 86sr of the dissolved load to more radiogenic compositions from 87sr 86sr dl 0 71048 to 0 710647 using the combination of stable and radiogenic strontium isotopes to investigate weathering processes shows that radiogenic sr isotopes provide information regarding weathering of primary phases while the stable sr isotope data appear to record information regarding the extent of secondary mineral formation where secondary minerals incorporate the light isotopes driving the dissolved load to heavy values

permian strontium isotope stratigraphy cvu acknowledges funding from the leopoldina german national academy of sciences grant no lpds 2014 08

constraining the marine strontium budget with natural strontium isotope fractionations 87sr 86sr δ88 86sr of carbonates hydrothermal solutions and river waters we present strontium sr isotope ratios that unlike traditional 87sr 86sr data are not normalized to a fixed 88sr 86sr ratio of 8 375209 defined as 88 86sr 0 relative to nist srm 987 instead we correct for isotope fractionation during mass spectrometry with a 87sr 84sr double spike this technique yields two independent ratios for 87sr 86sr and 88sr 86sr that are reported as 87sr 86sr and 88 86sr respectively the difference between the traditional radiogenic 87sr 86sr normalized to 88sr 86sr 8 375209 and the new 87sr 86sr values reflect natural mass dependent isotope fractionation in order to constrain glacial interglacial changes in the marine sr budget we compare the isotope composition of modern seawater 87sr 86sr 88 86sr seawater and modern marine biogenic carbonates 87sr 86sr 88 86sr carbonates with the corresponding values of river waters 87sr 86sr 88 86sr river and hydrothermal solutions 87sr 86sr 88 86sr hydend in a triple isotope plot the measured 87sr 86sr 88 86sr river values of selected rivers that together account for not vert similar18 of the global sr discharge yield a sr flux weighted mean of 0 7114 8 0 315 8 the average 87sr 86sr 88 86sr hydend values for hydrothermal solutions from the atlantic ocean are 0 7045 5 0 27 3 in contrast the 87sr 86sr 88 86sr carbonates values representing the marine sr output are 0 70926 2 0 21 2 we estimate the modern sr isotope composition of the sources at 0 7106 8 0 310 8 the difference between the estimated 87sr 86sr 88 86sr input and 87sr 86sr 88 86sr output values reflects isotope disequilibrium with respect to sr inputs and outputs in contrast to the modern ocean isotope equilibrium between inputs and outputs during the last glacial maximum 10 30 ka before present can be explained by invoking three times higher sr inputs from a uniquely glacial source weathering of shelf carbonates exposed at low sea levels our data are also consistent with the weathering peak hypothesis that invokes enhanced sr inputs resulting from weathering of post glacial exposure of abundant fine grained material

controls on stable strontium isotope fractionation in coccolithophores with implications for the marine sr cycle abstract the controls on stable sr isotope fractionation into the calcite produced by the coccolithophore species emiliania huxleyi coccolithus pelagicus spp braarudii and gephyrocapsa oceanica are investigated each species has been cultured under controlled laboratory conditions at a range of temperatures 10 25 c to test the potential of 88 86 sr as a proxy for growth rate and or sea surface temperature coccolithophores are one of the most abundant pelagic calcifiers since sr substitutes to some degree for ca in their calcite coccoliths coccolithophores represent a significant output of sr from seawater potentially influencing the 88 86 sr mass balance in the modern oceans the coccoliths are investigated for their 88 86 sr sr ca and 18 o measured as function of temperature as temperature is increased all species show a negative stable sr isotopic fractionation related to a temperature controlled growth rate we infer the shift of 88 86 sr to lighter values as indicative of a kinetic control on the isotope fractionation revealing the potential of 88 86 sr as a proxy for growth rate which in these experiments is primarily dictated by temperature the results from these experiments indicate that coccolithophore calcite incorporates sr with a very light 88 86 sr isotope composition as low as 0

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

lithium isotopes in large rivers reveal the cannibalistic nature of modern continental weathering and erosion abstract the erosion of major mountain ranges is thought to be largely cannibalistic recycling sediments that were deposited in the ocean or on the continents prior to mountain uplift despite this recognition it has not yet been possible to quantify the amount of recycled material that is presently transported by rivers to the ocean here we have analyzed the li content and isotope composition li 7 of suspended sediments sampled along river depth profiles and bed sands in three of the largest earth s river systems amazon mackenzie and ganga brahmaputra rivers the li 7 values of river sediments transported by these rivers range from 5 3 to 3 6 and decrease with sediment grain size we interpret these variations as reflecting a mixture of unweathered rock fragments preferentially transported at depth in the coarse fraction and present day weathering products preferentially transported at the surface in the finest fraction only the finest surface sediments contain the complementary reservoir of li solubilized by water rock interactions within the watersheds li isotopes also show that river bed sands can be interpreted as a mixture between unweathered fragments of igneous and sedimentary rocks a mass budget approach based on li isotopes li al and na al ratios solved by an inverse method allows us to estimate that for the large rivers analyzed here the part of solid weathering products formed by present day weathering reactions and transported to the ocean do not exceed 35 li isotopes also show that the sediments transported by the amazon mackenzie and ganga brahmaputra river systems are mostly sourced from sedimentary rocks 60 rather than igneous rocks this study shows that li isotopes in the river particulate load are a good proxy for quantifying both the erosional rock sources and the fingerprint of present day weathering processes overall li isotopes in river sediments confirm the cannibalistic nature of erosion and weathering

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

seasonal changes in the radiogenic and stable strontium isotopic composition of xijiang river water implications for chemical weathering seasonal changes in strontium sr isotopic systematics in large rivers can effectively track temporal variations in regional chemical weathering and help to better constrain the sr isotopic budget of global oceans however such records are scarce here we present a year long time series of both radiogenic and stable sr isotope measurements 87sr 86sr and 88sr from river water at guiping in the middle reaches of the xijiang river south china temporal changes in chemical weathering in the drainage basin were investigated by recording seasonal changes in the composition of both sr isotopes and major ions in the river water river water 87sr 86sr values range from 0 708487 to 0 710336 with most values being 0 7092 are generally accompanied by high rb sr ratios and low ph and 13c of dissolved inorganic carbo dic and occur during periods of large river flux this indicates that the contribution to the chemistry of river water from the weathering of silicate rocks is enhanced during rainy seasons seasonal variation in river water 88sr is large from 0 147 to 0 661 with higher 88sr values generally corresponding to higher 87sr 86sr values again low 88sr values 0 3 suggest a dominant contribution from the weathering of carbonate rocks whereas the high 88sr values may represent a contribution from intensive weathering of silicate rocks using the time series data we estimated the flux weighted averages of sr concentration 87sr 86sr and 88sr for the xijiang river to be 1 00 mol l 0 70960 and 0 38 respectively the sr concentration and 87sr 86sr results are close to previous estimates while the 88sr value is amongst the highest recorded for the large rivers of the world and is close to that of seawater our results indicate that large rivers draining through tropical sub tropical regions could play an important role in regulating the stable sr isotopic budget of global oceans

seawater 87sr 86sr ratios along continental margins patterns and processes in open and restricted shelf domains abstract to better constrain the sr isotope budget in marginal domains without any fluvial inputs we analyzed the chemical composition and 87sr 86sr ratio of waters and shells from four locations two coastal lagoons one hemipelagic platform and one open marine shelf our results highlight homogeneous 87sr 86sr ratios typical of oligotrophic oceanic waters oow i e 0 709172 0 000023 in the pacific tatakoto atoll and along a mediterranean shore to offshore transect 25 km off banyuls sur mer bsm this attests that oceanic inputs from oligotrophic areas remain the main sr source in open shelf areas compared with submarine groundwater discharges sgd or particulate dissolution influences in bsm only foreshore data are more radiogenic possibly due to rainwater mixing local groundwater springs or more efficient particle dissolution in the intertidal zone in restricted areas we report variable 87sr 86sr ratios between the salses leucate france and oualidia morocco lagoons the first one has homogeneous 87sr 86sr ratio typical of oow except close to sgd in oualidia 87sr 86sr ratios decrease by 1 2 10 3 from oow values close to the atlantic inlet to progressively less radiogenic ones upstream within the interior of the lagoon these differences depend on several factors including the leaky restricted or choked morphology of lagoons modulating the oceanic sr inputs but also sgd fluxes whose 87sr 86sr ratios and sr concentrations are highly variable according to the nature of rocks leached in karstic aquifer in oualidia the low 87sr 86sr ratios correspond to high sr concentrations up to 150 mol l 1 issued from the dissolution of mesozoic evaporites leading to sgd fluxes accounting for 60 of the local sr budget through data compilation we show that similar 87sr 86sr gradients and processes prevail at the whole mediterranean scale finally we postulate that high coastal water retention times can also account for anomalous coastal 87sr 86sr ratios and that the combination of water mass restriction sgd bioadsorption and early diagenetic processes could decrease seawater sr concentrations in some marginal areas

riverine behaviour of uranium and lithium isotopes in an actively glaciated basaltic terrain this study presents u and li isotope and major and trace element data for the dissolved load suspended particulates and bedload for icelandic rivers draining predominantly basaltic catchments physical erosion rates range from 920 to 2084 t km2 yr with the higher values associated with glacier fed rivers chemical erosion rates range from 45 to 91 t km2 yr with lower rates being associated with glacier fed rivers uranium activity ratios 234u 238u are close to secular equilibrium in the suspended and bedloads but all dissolved load samples show values greater than unity ranging from 1 13 to 2 41 the highest 234u 238u values are found in glacier fed rivers and can be attributed to recoil effects as grinding by glaciers locally enhances rates of physical weathering activity ratios in glacial rivers decrease with distance from the glacial source due to input from non glacial tributaries which have high levels of dissolved uranium and lower activity ratios in contrast in non glacial rivers uranium activity ratios increase with distance downstream due to continued weathering in soils and of bedrock the 7li value of the suspended load is always lower than that of the bedload due to preferential retention of 6li in secondary minerals during weathering in turn the 7li value of the dissolved load is always greater than that of the bedload ranging from 17 0 to 43 7 7li for the dissolved load decreases with increasing levels of dissolved silicon and the saturation index of secondary minerals which suggests that 7li decreases with increasing chemical weathering there is no correlation between 7li values and uranium activity ratios for the dissolved load for non glacial rivers but for glacier fed rivers there is an increase in 7li with increasing 234u 238u suggesting that where physical comminution of mineral grains by glaciers is high chemical weathering is suppressed and vice versa

calcium isotopes in the global biogeochemical ca cycle implications for development of a ca isotope proxy abstract at the earth s surface calcium ca is a critical element at a variety of scales it is soluble in natural waters a biological nutrient and a major constituent of the dominant mineral sink for carbon in the ocean caco3 there is a 4 variation in the ca isotopic composition 44ca 40ca expressed as 44ca of various ca reservoirs on earth suggesting ca isotopes as a promising tracer of ca cycling in both the present and the past fifteen years of high precision ca isotope measurements has revealed much about the behavior of ca isotopes in the earth surface environment but there remain fundamental questions concerning how ca isotopes are used to elucidate the marine and terrestrial ca cycles the current work presents a data compilation of over 70 published ca isotope studies totaling over 2600 measurements presented on a common delta scale that includes data on rivers and groundwater dust soils and soil pore fluids vegetation rainwater silicate minerals rocks and authigenic marine minerals carbonates sulfates and phosphates both modern and ancient the data compilation suggests that 1 there is a significant difference between carbonate 0 60 and silicate 44ca 0 94 2 riverine 44ca 0 88 does not simply reflect the compiled carbonate 44ca and 3 terrestrial vegetation exhibits the largest range of ca isotopic compositions 3 5 in the terrestrial setting we discuss these observations in the context of the global ca cycle exploring the extent to which seawater 44ca variability is feasible and how we can achieve accurate reconstructions of seawater 44ca over geologic time scales the current study presents simple mass balance models that quantify the leverage of inputs to change the ca isotopic composition of the ocean as this directly impacts the manner in which ca isotopes are interpreted although ca fractionates isotopically in the modern system during continental cycling the 44ca range of riverine inputs to the ocean is considerably smaller than the variability observed in putative seawater proxies such as nannofossil ooze and marine barite in the terrestrial realm plants exhibit a wide 44ca range and there is evidence that ca fluxes via biomass degradation are significant at the catchment scale we therefore assess the ability of the continental biosphere to influence riverine and consequently seawater 44ca a steady state biosphere has little leverage to alter riverine 44ca except in cases where the 44ca of the recycling flux is isotopically distinct from the 44ca of the uptake flux a non steady state biosphere can substantially impact both soil and riverine 44ca driving exchangeable ca either heavier or lighter depending on the magnitude of the recycling flux relative to the uptake flux based on estimates of the size of the global biosphere 1 5 1015 mol ca we suggest a decaying biosphere has the potential to impact riverine 44ca by tenths of a permil over time scales in the marine realm we evaluate the effect of a variable fractionation factor accompanying global removal of ca from the ocean on seawater 44ca and suggest methods by which such a mechanism can be recognized in the rock record experimental data suggest that there is considerable leverage