pedogenic origin of dolomite in a basaltic weathering profile kohala peninsula hawaii we document stoichiometric dolomite occurring in a nonsaline quaternary soil on the kohala peninsula northwestern hawaii geologic constraints and geochemical and isotopic data confirm that this dolomite is not the result of marine influence or wind blown dust the strontium isotopic composition of the dolomite 87sr 87sr 0 7045 0 7048 is indicative of its derivation primarily from the weathering of basaltic parent material rather than from meteoric water or seawater infiltration of soil waters with elevated mg ca 1 derived from alteration of ferromagnesian minerals such as olivine likely led to dolomitization of early precipitated soil calcite and or to direct dolomite precipitation in the profile this demonstrates that well ordered dolomite can form in a nonmarine environment at temperatures 100 c without undergoing burial diagenesis

predictive mapping of seabed substrata using high resolution multibeam sonar data a case study from a shelf with complex geomorphology abstract this study explores the full potential of high resolution multibeam data for the automated and accurate mapping of complex seabed features under a predictive modelling framework for an area of seabed on the carnarvon shelf in western australia morphometric variables and textural measures were derived from multibeam bathymetry and backscatter data several feature extraction approaches were applied to backscatter angular response curves to obtain new features these derivatives and new features were used separately and in combination in the predictions despite the complex distribution of various hard substrata within the study area we achieved a nearly perfect prediction of hard vs soft seabed types with an auc area under curve close to 1 0 the predictions were also satisfactory for gravel sand and mud content with r 2 values that range from 0 55 to 0 73 this study demonstrates that using a full range of derivatives and new features from both multibeam bathymetry and backscatter data optimises the accuracy of seabed mapping from the modelled relationships between sediment properties and multibeam data we confirmed that coarser sediment generally generates stronger backscatter return importantly the results again highlight the advantages of applying proper feature extraction approaches over using original backscatter angular response curves

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

riverine evidence for a fractionated reservoir of ca and mg on the continents implications for the oceanic ca cycle analysis of river water rock travertine and soil from the high altitude negligible vegetation setting of the southern tibetan plateau demonstrates that ca and mg isotope ratios are fractionated during weathering dissolved ca in the two rivers studied is derived primarily by limestone dissolution 44 42ca in the rivers averages 0 43 and is statistically distinct from limestone at 0 31 the range in 44 42ca in these small rivers is 0 43 equivalent to the entire range in 44 42ca recorded in marine carbonate over the last 80 ma precipitation of isotopically light travertine with a 44 42ca of 0 21 enriches solute ca in heavy isotopes the mg isotope composition of the rivers is intermediate between limestone and silicate rock averaging 1 5 silicate soil has a 26mg of 0 03 heavier than silicate rock by 0 5 these fractionations in the soil create a companion groundwater reservoir of heavy ca and light mg seasonal variations in ca and mg isotope ratios in the dissolved load are small but define an array which can be modelled as a mixture between a fractionated groundwater reservoir and surface runoff reflecting the isotopic composition of the lithology fractionation of ca during the weathering of the continents is of importance to the global cycle of ca the riverine input of ca to the oceans dominated by carbonate weathering is controlled not only by the composition of the primary continental crust but also by the size and composition of a fractionated reservoir on the continents the impact on the oceanic cycle of ca depends on the relative residence times of dissolved ca in the ocean and the storage time of fractionated ca

rayleigh fractionation of iron isotopes during pedogenesis along a climate sequence of hawaiian basalt abstract we measured iron isotopic composition of surface 10 20 cm and subsurface 50 70 cm basaltic soil horizons from the island of maui along a climate gradient mcg ranging from 2 2 to 4 2 m mean annual precipitation map all soil forming factors except climate were conserved the mcg has a documented decrease in fe with increasing rainfall that is highly correlated with decreasing mean annual eh values we found that increasing map from 2 8 to 4 2 m resulted in a surface plus subsurface average increase of 0 56 0 09 56fe with the subsurface consistently 0 33 0 06 56fe greater than the surface horizons based on loss of fe relative to nb rayleigh fractionation was observed with 103ln lost retained values of 0 37 0 03 and 0 34 0 04 for the surface and subsurface respectively equivalent 103ln lost retained values for the surface and subsurface soils suggests fe loss is driven by similar mechanisms throughout the soil profile our calculated fractionation factor is about 1 3 the magnitude of laboratory determined fractionation factors for fe reduction suggesting other processes organic complexation fe re precipitation modulate the net fe loss along the mcg these results offer field scale confirmation of laboratory experiments on model systems that show anoxic weathering reactions produce materials enriched in heavy fe isotopes

on the reactivation of extensional fault systems in terranes that have undergone substantial extension three sets of faults dominate a shallow to steep dipping commonly rotational normal faults b a really extensive shallow dipping normal detachment faults and c steep dipping transfer faults that strike at high angles to the normal faults these fault systems may extend through a large fraction of the crust reactivation of these fault systems will depend primarily on the relative strengths of the faults shear zones and their host rock and their orientation in the prevailing stress field it is concluded that reactivation is generally mechanically favoured but that it will probably only take place when the fault shear zones are in near ideal orientations consideration of the tectonic setting of extended terranes and of the limited number of well described examples suggests that reverse thrust reactivation of the normal and detachment faults and wrench reactivation of transfer faults are the most likely styles examples of these styles are described from the bass strait basins of southeastern australia because extended terranes commonly underlie sedimentary basins for example on passive continental margins reactivation of extensional faults may be a key control on the tectonic evolution of such basins i e basin inversion

load strengthening versus load weakening faulting increases in shear stress along a fault during loading to failure cannot generally occur without changes in the normal stress across the fault n the fault loading parameter n n pf distinguishes situations of load strengthening n 0 where the frictional shear strength of faults increases as tectonic shear stress rises from load weakening environments n t6 0 where it decreases compressional faulting in tectonic regimes with v 3 is always load strengthening unless fluid pressure is rapidly increasing extensional faulting in regimes where v 1 is load weakening unless fluid pressure is dropping rapidly strike slip faulting in terrains where v 2 can be either load weakening or load strengthening the particular case where n 0 so that frictional shear strength stays constant during fault loading is a very special situation corresponding to direct shear load strengthening strike slip faulting appears to correlate with tectonic transpression and load weakening with transtension differing loading characteristics of faults in different tectonic regimes must induce varying patterns of cyclic fluid redistribution accompanying the seismic cycle with implications for earthquake recurrence and precursory groundwater phenomena

ca sr and ba stable isotopes reveal the fate of soil nutrients along a tropical climosequence in hawaii abstract nutrient biolifting is an important pedogenic process in which plant roots obtain inorganic nutrients such as phosphorus p and calcium ca from minerals at depth and concentrate those nutrients at the surface here we use soil chemistry and stable isotopes of the alkaline earth elements ca strontium sr and barium ba to test the hypothesis that biolifting of p has been an important pedogenic process across a soil climosequence developed on volcanic deposits at kohala mountain hawaii the geochemical linkage between these elements is revealed as generally positive site specific relationships in soil mass gains and losses particularly for p ba and ca using the ratio of immobile elements titanium and niobium ti nb to link individual soil samples to a restricted compositional range of the chemically and isotopically diverse volcanic parent materials at sites where p is enriched in surface soils relative to abundances in deeper soils the isotope compositions of exchangeable ca sr and ba in the shallowest soil horizons 10 cm depth at those sites is consistently heavier than the volcanic parent materials the isotope compositions of exchangeable ca and sr trend toward heavier compositions with depth more gradually reflecting increasing leakiness from these soils in the order ba

elucidating modern geochemical cycles at local regional and global scales using calcium isotopes abstract in earth s surface environment calcium ca is an important mobile metal that is actively and passively transported in solution and within organic and mineral phases being cycled and recycled during various biogeochemical processes with the development of modern mass spectrometric techniques small variations in the stable and radiogenic isotopic compositions of ca can be measured revealing insight in these complex biogeochemical cycles and tracing and quantifying components across a range of spatial and temporal scales similar to other more routine isotope systems more than three decades of work reveal systematic variations in the partitioning of ca isotopes due to both abiotic and biological processes an overview of processes that fractionate ca isotopes at local regional and global scales is outlined here we present detailed examples of instances in which ca isotopes have provided unique insight into the functioning of earth surface processes and the cycling of ca at multiple scales future studies should target questions for which ca isotopic analysis provide unique insight and when combined with other isotope and trace element multi proxy studies better constrain the system of interest at the same time we challenge the scientific community to explore new frontiers including polar regions and other extreme environments

positive relief over buried post glacial channels great barrier reef province australia abstract continuous seismic profiling on the continental shelf central great barrier reef province australia has delineated a major sub bottom reflector interpreted as the pre holocene surface channels eroded in this surface are infilled and overfilled by post glacial sediments filling is ascribed to estuarine backfilling during sea level rise followed by deposition of delta front deposits in many cases these fills create positive relief over buried channels hence modern shelf morphology may not be an accurate guide to the positions of pleistocene channels across the shelf

precontact vegetation and soil nutrient status in the shadow of kohala volcano hawaii abstracthumans colonized hawaii about 1200 years ago and have progressively modified vegetation particularly in mesic to drytropical forests we use 13 c to evaluate the contribution of c 3 and c 4 plants to deep soil organic matter to reconstruct pre humancontact vegetation patterns along a wet to dry climate transect on kohala mountain hawaii island precontact vegetationassemblages fall into three distinct zones a wet c 3 dominated closed canopy forest where annual rainfall is n2000 mm a dry c 4 dominated grassland with annual rainfall b500 mm and a broad transition zone between these communities characterized by eitherc 3 trees with higher water use efficiency than the rainforest trees or c 3 trees with a small amount of c 4 grasses intermixed thelikelihood of c 4 grass understory decreases with increasing rainfall we show that the total concentration of rock derived nutrientsin the b2 mm soil fraction differs in each of these vegetation zones nutrient losses are driven by leaching at high rainfall and byplant cycling and wind erosion at low rainfall by contrast nutrients are best preserved in surface soils of the intermediate rainfallzone where rainfall supports abundant plant growth but does not contribute large amounts of water in excess of evapotranspiration polynesian farmers exploited these naturally enriched soils as they intensified their upland agricultural systems during the last threecenturies before european contact 2006 elsevier b v all rights reserved

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

classification of seafloor geology using multibeam sonar data from the scotian shelf abstract we describe a method for classifying multibeam sonar data and illustrate the method using data collected with a simrad em1000 sonar on the scotian shelf canada the method involves comparing various attributes of the bathymetry and backscatter with typical examples of specified seafloor types and computing their statistical degree of similarity sediment ponds are identified as areas of low echo amplitude and low topographic gradient and curvature ridges and troughs are identified by fitting a paraboloid to patches of the bathymetry once the sediments ridges and troughs are located we are able to use the database to extract orientations and other characteristics of these features for example the orientation of the topography can be computed from the paraboloid surface and rose diagrams of the ridge and trough orientations reflect the fabric of up turned cambro ordovician sedimentary beds outcropping in this area the unconsolidated sediments ponded within small basins have low topographic gradients with consistent tilts towards the southeast mean 133 which we interpret as due to offshore transport of holocene sediments possibly in response to storms

barium isotopes in cold water corals abstract recent studies have introduced stable ba isotopes 138 134 ba as a novel tracer for ocean processes ba isotopes could potentially provide insight into the oceanic ba cycle the ocean s biological pump water mass provenance in the deep ocean changes in activity of hydrothermal vents and land sea interactions including tracing riverine inputs here we show that aragonite skeletons of various colonial and solitary cold water coral cwc taxa record the seawater sw ba isotope composition thirty six corals of eight different taxa from three oceanic regions were analysed and compared to 138 134 ba measurements of co located seawater samples sites were chosen to cover a wide range of temperature salinity ba concentrations and ba isotope compositions seawater samples at the three sites exhibit the well established anti correlation between ba concentration and 138 134 ba furthermore our data set suggests that ba ca values in cwcs are linearly correlated with dissolved ba in ambient seawater with an average partition coefficient of dcwc sw 1 8 0 4 2sd the mean isotope fractionation of ba between seawater and cwcs 138 134bacwc sw is 0 21 0 08 2sd indicating that cwc aragonite preferentially incorporates the lighter isotopes this fractionation likely does not depend on temperature or other environmental variables suggesting that aragonite cwcs could be used to trace the ba isotope composition in ambient seawater coupled ba and 138 134 ba analysis on fossil cwcs has the potential to provide new information about past changes in the local and global relationship between ba and 138 134 ba and hence about the operation of the past global oceanic ba cycle in different climate regimes

structural development of the peregrina huizachal anticlinorium mexico abstract the sierra madre oriental fold belt is a nw se trending contractional belt that spans nearly the entire length of mexico this area underwent triassic middle jurassic rifting and late cretaceous early cenozoic shortening our structural investigation of the peregrina huizachal anticlinorium in east central mexico shows that its development is characterized by two phases of deformation an early thin skinned phase and a late thick skinned phase a detachment developed at the contact between the rift sedimentary rock and overlying limestone during the thin skinned phase deformation of the upper jurassic cretaceous strata is accommodated by a series of detachment folds and faults the rift boundary faults are sub perpendicular to the late stage compression in east central mexico this makes rift related faults prone to be inverted as reverse faults during the thick skinned phase the basement in the rift is uplifted along two opposing reverse faults and experience internal deformation its uplift contributed to the growth of the peregrina huizachal anticlinorium

morphological characterisation of reef types in torres strait and an assessment of their carbonate production coral reefs represent major accumulations of calcium carbonate caco3 the particularly labyrinthine network of reefs in torres strait north of the great barrier reef gbr has been examined in order to estimate their gross caco3 productivity the approach involved a two step procedure first characterising and classifying the morphology of reefs based on a classification scheme widely employed on the gbr and then estimating gross caco3 productivity rates across the region using a regional census based approach this was undertaken by independently verifying published rates of coral reef community gross production for use in torres strait based on site specific ecological and morphological data a total of 606 reef platforms were mapped and classified using classification trees despite the complexity of the maze of reefs in torres strait there are broad morphological similarities with reefs in the gbr the spatial distribution and dimensions of reef types across both regions are underpinned by similar geological processes sea level history in the holocene and exposure to the same wind wave energetic regime resulting in comparable geomorphic zonation however the presence of strong tidal currents flowing through torres strait and the relatively shallow and narrow dimensions of the shelf exert a control on local morphology and spatial distribution of the reef platforms a total amount of 8 7million tonnes of caco3 per year at an average rate of 3 7kg caco3m 2yr 1 g were estimated for the studied area extrapolated production rates based on detailed and regional census based approaches for geomorphic zones across torres strait were comparable to those reported elsewhere particularly values for the gbr based on alkalinity reduction methods however differences in mapping methodologies and the impact of reduced calcification due to global trends in coral reef ecological decline and changing oceanic physical conditions warrant further research the novel method proposed in this study to characterise the geomorphology of reef types based on classification trees provides an objective and repeatable data driven approach that combined with regional census based approaches has the potential to be adapted and transferred to different coral reef regions depicting a more accurate picture of interactions between reef ecology and geomorphology

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

barium isotopic fractionation in seawater mediated by barite cycling and oceanic circulation the marine biogeochemical cycle of ba is thought to be controlled by particulate baso4 barite precipitation associated with the microbial oxidation of organic carbon and its subsequent dissolution in the baso4 undersaturated water column despite many of these processes being largely unique to ba cycling concentrations of ba and si in seawater exhibit a strong linear correlation the reasons for this correlation are ambiguous as are the depth ranges corresponding to the most active baso4 cycling and the intermediate sources of ba to particulate baso4 stable isotopic analyses of dissolved ba in seawater should help address these issues as ba isotopic compositions are predicted to be sensitive to the physical and biogeochemical process that cycle ba we report a new methodology for the determination of dissolved ba isotopic compositions in seawater and results from a 4500 m depth profile in the south atlantic at 39 99 s 0 92 e that exhibit oceanographically consistent variation with depth these data reveal that water masses obtain their ba and ba isotopic signatures when at or near the surface which relates to the cycling of marine baso4 the shallow origin of these signatures requires that the substantial ba isotopic variations in the bathypelagic zone were inherited from when those deep waters were last ventilated indeed the water column below 600 m is well explained by conservative mixing of water masses with distinct ba and ba isotopic compositions this leads us to conclude that large scale oceanic circulation is important for sustaining the similar oceanographic distributions of ba and si in the south atlantic and possibly elsewhere these data demonstrate that the processes of organic carbon oxidation baso4 cycling and ba isotopic fractionation in seawater are closely coupled such that ba isotopic analyses harbor great potential as a tracer of the carbon cycle in the modern and paleo oceans

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

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

calcium isotopes in a proglacial weathering environment damma glacier switzerland the biogeochemical cycling and isotopic fractionation of calcium during the initial stages of weathering were investigated in an alpine soil chronosequence damma glacier switzerland this site has a homogeneous silicate lithology and minimal biological impacts due to sparse vegetation cover calcium isotopic compositions obtained by tims using a 43ca 46ca double spike were measured in the main ca pools during this very early stage of weathering the young soils which have formed 44 42ca 0 44 44 42ca 0 44 were indistinguishable to the rocks from which they were derived 44 42ca 0 44 44 42ca 0 44 and stream water 44 42ca 0 48 44 42ca 0 48 was also within error of the average rock this lack of variation indicates that the dissolution of the bulk silicate rock does not strongly fractionate ca isotopes the only ca pool which was strongly fractionated from bulk rock was vegetation which exhibited an enrichment of light ca isotopes significant ca isotope fractionation between bulk rock and the dissolved flux of ca is likely to only occur where the ca biogeochemical cycle is dominated by secondary processes such as biological cycling adsorption and secondary mineral precipitation

the recognition of reactivation during continental deformation reactivation involves the accommodation of geologically separable displacement events intervals 1 ma along pre existing structures the definition of a significant period of quiescence is central to this phenomenological definition and the duration of the interval chosen represents the resolution limit of reactivation criteria found in most ancient settings in neotectonic environments reactivation can be further defined as the accommodation of displacements along structures that formed prior to the onset of the current tectonic regime this mechanistic definition cannot always be applied to ancient settings due to the uncertainties in constraining relative plate motion vectors four sets of criteria may be used to recognize reactivation in the geological record stratigraphic structural geochronological and neotectonic some structural criteria may not be reliable if used in isolation to identify reactivated structures much of the previously published evidence cited to invoke structural inheritance is equivocal as it uses similarities in trend dip or three dimensional shape of structures numerous fault and shear zone processes can cause significant weakening both synchronously with deformation and in the long term and may be invoked to explain reactivation the collage of fault bounded blocks forming most continents therefore carries a long term architecture of inheritance which can explain much of the observed complexity of continental deformation zones

seismic and field evidence for selective inversion of cretaceous normal faults salta rift northwest argentina abstract northwestern argentina was the site of the continental salta rift in cretaceous to paleogene time the salta rift had a complex geometry with several subbasins of different trends and subsidence patterns surrounding a central high fault trends in the rift were extremely variable there is evidence of normal and or transfer faults trending n ne e and se it is not clear if all these faults were active at the same time indicating a poorly defined extension direction or if they formed in different non coaxial extension phases in either case their trends were very likely influenced by preexisting fault systems beginning in early eocene time the rift basins were superseded by andean foreland basins and later became caught in the andean thrust deformation propagating eastward resulting in the inversion of rift faults due to their different orientations not all faults were equally prone to reactivation as thrusts n to nne trending faults were apparently most strongly inverted probably often to a degree where the traces of their normal fault origin have become obliterated we present seismic evidence of moderately inverted n trending faults in the tres cruces basin and field examples of preserved e trending normal faults however reactivation sometimes also affects faults trending approximately parallel to the main neogene shortening direction indicating short term deviations from the general pattern of neogene thrust deformation these pulses of orogen parallel contraction may be linked to the intermittent activity of oblique transfer zones

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

barium stable isotopes in the global ocean tracer of ba inputs and utilization abstract barium has been used as a biogeochemical tracer for alkalinity productivity and riverine inputs in the ocean but its oceanic cycle remains poorly constrained barium stable isotope measurements may improve the use of ba as a tracer and better constrain the cycling of ba but data are only available in limited regions of the oceans in this study we present dissolved seawater ba isotopic compositions in a sample collection spanning the north atlantic south atlantic north pacific and southern oceans compiled global upper ocean ba data show a relatively constant ba 35 45 nm in the near surface waters throughout the global ocean with the exception of areas near river inputs or strong upwelling the relatively uniform distribution of ba in the upper ocean seawater indicates that ba removal is slow relative to supply and mixing and implies that near surface ba isotope values are controlled by basin scale balances rather than by regional or short term processes seawater ba isotopic compositions show a large variation of 138 134 ba values ranging from 0 24 to 0 65 and a tight relationship with ba this global relationship can be simply modelled assuming a primary deep southern ocean source for ba to yield a maximum isotope fractionation of 1 00058 0 00010 ba seawater 138 134 ba particle 138 134 this suggested isotope fractionation during ba removal from seawater is larger than implied by laboratory measurement during barite formation suggesting additional fractionating phases or a two stage fractionation process riverine input from the rio de la plata to the south atlantic has a signature of 138 134 ba 0 06 0 11 which is too light to explain the heavy values 0 58 observed in the surface open ocean globally the ba isotope composition of the upper ocean waters is correlated with the fraction of ba utilization at the basin scale which varies from 138 134 ba signals in the northern sourced 0 45 and the southern sourced water 0 25 trace mixing and allow identification of non conservative behaviour of ba reflecting additional inputs or sinks of ba during transport most likely addition from sediment or hydrothermal ba isotopes may be useful to trace such inputs in the present and past ocean

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

calcium isotope constraints on the uptake and sources of ca2 in a base poor forest a new concept of combining stable δ44 42ca and radiogenic eca signals abstract plant available reserves of major base cations ca 2 and mg 2 decreased markedly in soils over the past century thus posing a potential threat to forest ecosystem health trees are thought to obtain dissolved ca 2 ions mainly from an easily accessible soil water reservoir also termed the exchangeable cation pool the status of ca reserves in this soil pool is sensitive to anthropogenic perturbations such as soil acidification induced by acid rain and or excessive timber harvesting here we show that in a base poor forest of the northeastern usa i e wachusett mountain massachusetts the exchangeable ca pool of deeper mineral soils has a unique isotope signature that is significantly enriched in the radiogenic 40 ca due to the dissolution of k rich silicate minerals such as biotite using a simple isotope mass balance and assuming that the input of ca from biotite has a e ca signature of 16 the results of our calculation indicate that the weathering of biotite may supply a sizeable fraction up to 25 of ca 2 ions into the exchangeable cation pool of deeper mineral soils importantly samples of local vegetation i e woody tissues of red oak show no detectable excess of the radiogenic 40 ca and based on our model the upper limit of a possible biotite derived ca contribution in vegetation is estimated at 5 we also found no evidence of the radiogenic 40 ca signal in the samples of forest floor and the uppermost organic rich soils 0 15 cm depth which in turn suggest that over the long term development of the forest and its organic matter accumulation the vegetation growth must have also relied primarily on the non radiogenic ca sources based on our experimental data such sources may include i wet atmospheric deposition ii the organically complexed ca in topsoil horizons and iii chemical weathering and or fungal mediated dissolution of apatite and ca rich plagioclase hence our stable and radiogenic ca isotope data indicate that the studied base poor forest is able to bypass the exchangeable cation pool of deeper i e below 15 cm mineral soils and still manages to meet its nutritional requirements with respect to ca another important implication of this study is that the organically complexed ca in the topsoil horizon 0 15 cm depth has to be tightly bound to the ion exchange sites otherwise the large radiogenic 40 ca signatures present in the exchangeable cation pool of deep mineral soils would be swamped by the downward gravitational flux of non radiogenic ca from the decaying organic matter and litterfall hence the limited mobility of the organically complexed ca in soils and its tight biological cycling could explain the lack of a significant impact of vegetation on the ca isotope systematics observed in large rivers

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

ca isotope cycling in a forested ecosystem reports of large ca isotope fractionations between trees and soils prompted this study of a boreal forest ecosystem near la ronge saskatchewan to improve understanding of this phenomenon the results on five tree species black spruce trembling aspen white spruce jack pine balsam poplar confirm that nutrient ca uptake by plants favors the light isotopes thus driving residual ca in plant available soil pools towards enrichment in the heavy isotopes substantial within tree fraction occurs in tissues formed along the transpiration stream with low 44ca values in fine roots 2 mm intermediate values in stemwood and high values in foliage separation factors between different plant tissues are similar between species but the initial fractionation step in the tips of the fine roots is species specific and or sensitive to the local soil environment soil water 44ca values appear to increase with depth to at least 35 cm below the top of the forest floor which is close to the deepest level of fine roots the heavy plant fractionated signature of ca in the finely rooted upper soils filters downward where it is retained on ion exchange sites leached into groundwater and discharged into surface waters the relationship between ca uptake by tree fine roots and the pattern of 44ca enrichment with soil depth was modeled for two ca pools the forest floor litter and the underlying upper b mineral soil six study plots were investigated along two hillside toposequences trending upwards from a first order stream we used allometric equations describing the ca distribution in boreal tree species to calculate weighted average 44ca values for the stands in each plot and estimate ca uptake rates the 44ca value of precipitation was measured and soil weathering signatures deduced by acid leaching of lower b mineral soils steady state equations were used to derive a set of model ca fluxes and fractionation factors for each plot the model reproduces the increase in 44ca with depth found in forest floor and upper b soil waters transient model runs show that the forest ca cycle is sensitive to changes in plant ca uptake rate such as would occur during ontogeny or disturbance accordingly secular records of 44ca in tree ring cellulose have the potential to monitor changes in the forest ca cycle through time thus providing a new tool for evaluating natural and anthropogenic impacts on forest health another model run shows that by changing the size of the isotope fractionation factor and adjusting for differences in forest productivity that the range in ca isotope fractionation in forested ecosystems reported in the literature thus far is reproduced as a quantitative tool the ca cycling model produces a reasonable set of relative ca fluxes for the la ronge site consistent with environment canada s measurements for wet deposition in the region and simulated ca release from soil mineral weathering using the profile model but the sensitivity of the model is limited by the small range of fractionation observed in this boreal shield setting of 1 which limits accuracy if the model were applied to a site with a greater range in 44ca values among the principal ca fluxes it is capable of producing robust and reliable estimations of ca fluxes that are otherwise difficult to measure in forested ecosystems

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

calcium isotopes in the marine environment and the oceanic calcium cycle abstract a systematic investigation of 44 ca 40 ca ratios in the oceanic ca cycle indicates that the average ca isotopic composition of input and output are quite different suggesting that the present ocean is not in a steady state our data show that sea water has uniform 44 ca 40 ca as expected from the long residence time of ca in the oceans it also exhibits the heaviest isotopic composition among all samples measured consistent with recent results by skulan et al 1997 and must be maintained at this value by strong biogenic isotope fractionation during the precipitation of caco 3 our measurements show that the riverine input is variable the most radiogenic river waters we have measured lowest 44 ca 40 ca are from ganges tributaries which also have high 87 sr 86 sr although there does not appear to be a systematic correlation between ca and sr isotopic compositions based on available data there is also significant isotopic variability among samples of caco 3 precipitated from the present ocean with coccolith oozes showing the most highly fractionated isotopic values relative to seawater among foraminifera ca isotopes exhibit species dependent fractionation effects but also appear to display systematic temperature dependent fractionation within inidividual species

extreme lithium isotopic fractionation during continental weathering revealed in saprolites from south carolina the lithium concentration and isotopic composition of two saprolites developed on a granite and diabase dike from south carolina have been measured in order to document the behavior of lithium isotopes during continental weathering both saprolites show a general trend of decreasing d 7 li with increasing weathering intensity as measured by both bulk density and the chemical index of alteration cia the saprolite developed on the granite is isotopically lighter than the fresh igneous rock d 7 li 6 8x to 1 4x vs 2 3x respectively and is generally depleted in lithium these observations are consistent with leaching of lithium via rayleigh distillation during progressive weathering most saprolites fall on a rayleigh distillation curve corresponding to an apparent fractionation factor a of 0 997 however two samples have higher lithium contents than the fresh granite and thus point to additional processes affecting lithium in the saprolite e g sorption of lithium on to clay minerals the saprolite profile developed on the diabase dike shows highly variable d 7 li values ranging down to extremely light compositions 20x previous work has identified a chemical and mineralogical discontinuity at a depth of 2 m but our lithium data show a marked discontinuity at 6 m depth saprolite samples at or above 6 m depth are highly weathered cia 88 95 depleted in lithium having b50 of the original diabase lithium and isotopically light 10x to 20x vs 4 3x for the unweathered diabase most of the data are consistent with leaching of lithium via rayleigh distillation during intense weathering with apparent a values of 0 995 to 0 980 samples experiencing lower apparent a values tend to have higher kaolinite smectite ratios suggesting a mineralogical control on isotopic fractionation however the lightest sample at 20x is only slightly depleted in lithium and would require extremely low a values to explain via rayleigh distilliation this extreme composition remains enigmatic saprolite samples below 6 m have highly variable d 7 li 5x to 14x and importantly lithium concentrations that are higher than that of the unweathered diabase up to 2 4 times the concentration of the fresh diabase these deeper saprolites thus cannot be explained by rayleigh distillation a positive correlation between d 7 li and li

seasonal riverine barium isotopic variation in the middle yellow river sources and fractionation abstract barium ba isotopes have been used to trace water mass mixing and export productivity in the oceans however the sources isotopic signature and seasonal variation of dissolved ba in large rivers remain poorly constrained in order to improve our understanding of sources and fractionation of riverine ba isotopes at the continental scale weekly sampling of river water was carried out in the middle yellow river over the full hydrological year of 2013 dissolved ba was mainly sourced from silicate dissolution whose flux was correlated with physical erosion rate in this arid to semi arid basin largely covered by loess more than half of the annual dissolved ba flux was transported during the monsoon season june to mid september in particular during a storm event period accounting for 4 of the annual dissolved ba flux in 4 days the dissolved ba isotopic composition 138barw ranged from 0 17 to 0 46 all higher than 138ba of loess 0 00 0 04 the seasonal variation in 138barw is best explained via an adsorption model of light ba isotopes onto solids in the river which is sensitive to erosion of loess in particular during the storm event and the spring time ice melting intervals with a potential role of barite precipitation in groundwater during the dry seasons with one to three orders of magnitude higher particulate matter fluxes during the monsoon seasons in rivers such as the yellow river desorption of ba could result an unaccounted strong variation of ba concentration and isotopic composition in coastal environments which further study requires

refractory element mobility in volcanic soils refractory trace element concentrations in strongly weathered hawaiian soils ranging in age from 20 to 4100 ka are highly elevated over parent rock values due to extensive mass loss of more soluble major elements during pedogenesis nb and ta exhibit virtually no mobility soil nb ta ratios are within the range of fresh bedrock even when soil nb concentrations are residually enriched by a factor of 10 in contrast al zr and hf are depleted relative to nb in surface soil horizons but are enriched at depth clearly indicating mobility of these elements variations in th nb ratios in soil profiles indicate significant th mobility within the soil column however mass balance calculations require that accretion of th enriched asian dust has resulted in a net increase in th in some soils soils developed on a 150 ka rainfall gradient show that the mobility and loss of zr increase with mean annual precipitation

application of the topographic position index to heterogeneous landscapes topographic position index tpi is an algorithm increasingly used to measure topographic slope positions and to automate landform classifications we applied tpi to a geoarchaeological research project in northwestern belgium but its use led to erroneous landform classifications in this heterogeneous landscape we asked whether deviation from mean elevation dev was a better method for landform classification than tpi we found that it enabled more accurate geomorphological assessment when using northwestern belgium as a case study

accretion of asian dust to hawaiian soils isotopic elemental and mineral mass balances hawaiian soils contain a mixture of material derived from in situ weathering of parent material plus atmospheric inputs including sea salt aerosols and asian dust we use soil mineralogy and radiogenic isotope geochemistry sr and nd to evaluate the impact of asian dust on a chronosequence of hawaiian soils dust becomes an important constituent of soils 20 ky and older near surface 50 cm depth horizons contain as much as 30 quartz a mineral absent from local parent material basaltic sr and nd isotope signatures in these horizons have been completely overprinted by asian dust signatures with 87sr 86sr ratios as high as 0 723 and end values as low as 7 ree patterns in these soils are indistinguishable from that of average upper continental crust quartz abundance and nd isotopes provide two independent tracers of long term dust additions to the chronosequence soils the two tracers indicate a minimum long term average dust accretion rate of 125 mg cm 2 ky 1 at the 150 ka chronosequence site roughly a factor of three higher than holocene dust accumulation rates estimated from north pacific sediment cores we find that the mass of dust preserved in these soil profiles does not increase with age in soils 150 ka and older requiring a loss mechanism for accreted dust on the basis of the geomorphic stability of these sites observed preferential loss of dust derived mica relative to quartz and estimates of soil si leaching rates we argue that chemical weathering is the dominant loss mechanism for dust from these soils dust has a profound effect on the budgets of elements that are susceptible to leaching losses dust becomes the dominant source of soil nutrients si and p in the oldest most intensely weathered soils we calculate a dust derived p input flux of 0 8 mg cm 2 ky 1 and a dust derived si input flux of 35 mg cm 2 ky 1 si leaching fluxes are high 1400 mg cm 2 ky 1 in the youngest 2 ka soils and drop systematically with soil age to a value that closely balances the dust derived si input flux by 4100 ka extremely refractory elements such as nb which are concentrated in soils by residual enrichment processes are much less readily impacted by dust addition although dust has had a pronounced impact on sr and nd isotopic budgets and on soil mineral composition at the 150 ka site dust cannot have contributed 4 of the total nb contained in this soil profile

ca cycling and isotopic fluxes in forested ecosystems in hawaii 1 biogeochemical processes fractionate ca isotopes in plants and soils along a 4 million year developmental sequence in the hawaiian islands we observed that plants preferentially take up 40ca relative to 44ca and that biological fractionation and changes in the relative contributions from volcanic and marine sources produce a significant increase in 44ca in soil exchangeable pools our results imply moderate fluxes enriched in 44ca from strongly nutrient depleted old soils in contrast with high 40ca fluxes in young and little weathered environments in addition biological fractionation controls divergent geochemical pathways of ca and sr in the plant soil system while ca depletes progressively with increasing soil age sr ca ratios increase systematically sr isotope ratios provide a valuable tracer for provenance studies of alkaline earth elements in forested ecosystems but its usefulness is limited when deciphering biogeochemical processes involved in the terrestrial ca cycle ca isotopes in combination with sr ca ratios reveal more complex processes involved in the biogeochemistry of ca and sr

nutrient cycling in a tropical montane rainforest under a supply limited weathering regime traced by elemental mass balances and mg stable isotopes abstract forest ecosystem nutrition and rock weathering are intimately linked through the supply of mineral nutrients and recycling re utilisation of nutrients released from plant litter during mineralisation here we report on novel applications of mg stable isotopes in combination with mass balance calculations to quantify nutrient supply from bedrock atmospheric wet and dry deposition and recycling in a tropical ecosystem characterised by a supply limited weathering regime in the central highlands of sri lanka we measured mg stable isotopes radiogenic sr isotope ratios and element concentrations in the different compartments of the earth s critical zone bedrock saprolite soil soil pore water stream water and vegetation as tracers for element mass fluxes and pathways we find that in the clay rich saprolite mg isotopes are fractionated towards isotopically heavy mg during secondary mineral formation soil pore water and stream water are the complementary isotopically light reservoirs the mg isotope composition of above ground vegetation is on average identical to soil pore water based on these observations we suggest that a tight near surface mineral nutrient loop between plants and soil sustains the tropical forest ecosystem this loop is disconnected from the rock weathering nutrient source in the saprolite beneath soil external atmospheric wet and dry inputs mainly mg and ca strongly contribute to the plant available nutrient budget that the nutrient depleted regolith does not supply these findings based on mg stable isotopes agree with independently obtained information on bio element p k ca mg si recycling this nutrient supply setting contrasts with that reported for the southern sierra nevada usa where a kinetically limited weathering regime prevails our study illustrates the application of new flux estimators based on elemental and metal stable isotope measurements across a range of climate and weathering regimes

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

annually resolved coral skeletal δ138 134ba records a new proxy for oceanic ba cycling abstract barium calcium ratios in the skeletons of scleractinian shallow water corals have been used as proxies for coastal and oceanic processes such as river discharge oceanic upwelling and surface ocean productivity however the variations in ba ca ratios in aragonitic coral skeletons remain difficult to interpret as an environmental proxy this difficulty is mainly due to the influence of internal biomineralization and multiple external environmental processes on ba incorporation into coral skeletons and these processes are hard to constrain with ba ca alone here we present the first annually resolved records of the ba isotopic compositions 138 134ba in shallow water corals porites collected alive in the field supplemented by the analysis of ba ca ratios seven coral cores were recovered at different oceanic settings in the south china sea extending from the northern inner shelf to the central and southern deep basin the annual 138 134ba records of six corals fell within a narrow range from 0 24 0 03 to 0 38 0 03 2sd with a mean value of 0 33 0 08 2sd n 21 one single inner shelf coral revealed low 138 134ba values 0 10 0 11 0 03 which might reflect the influence of terrestrial water sediment in contrast the coral ba ca ratios showed a wide range of intercolony differences from 2 to 14 mol mol this variation is too large to be ascribed to the changes in the ba concentrations of seawater or other environmental parameters rayleigh fractionation between corals and seawater during biomineralization was proposed to explain the anomalous variations in the ba ca ratios observed in coral skeletons however this result is incompatible with the relatively constant ba isotopic compositions in coral instead we suggest that the probable precipitation of witherite baco3 within the domains of aragonite under oversaturated calcifying fluid could explain the large variability in the coral ba ca ratios the coral 138 134ba records from diverse oceanic settings were largely unaffected by biomineralization processes and temperature and displayed a relatively constant negative offset from typical surface seawaters our results suggest that ba isotopes in porites could be a proxy for reconstructing the 138 134ba of seawater and hence provide new insights into ba cycling in the upper oceans in the past

from a black to a gray box a mass balance interpretation of pedogenesis we utilize chemical elements as tracers in a mass balance analysis that provides functional relationships among soil chemical composition bulk density and volume change in relation to parent material these analytical functions are based on the principle of conservation of mass and include a term quantifying mass flux into out of the soil and between horizons we apply the technique to the oldest member of a chronosequence developed on marine terraces in northern california it is an alfisol that evolved from beach sand to its present state nearly one third of its weight is composed of secondary clay minerals in about 240 ky aside from large increases in organic carbon desilication is the dominant factor in soil evolution 29 50 83 g cm 2 si was leached from the beach sand during pedogenesis the rate of desilication is roughly 2 1 t km 2 yr 1 0 21 g cm 2 ky 1 an order of magnitude slower than that implied by the si denudation rate calculated for the mattole river watershed weathering of primary minerals and synthesis of secondary minerals is relatively well advanced suggesting that the rate of desilication may be declining the local beach is composed of quartz and sodic plagioclase with smaller amounts of chlorite mica and kaolinite the soil has substantially different mineralogy sand is dominated by quartz and clay is dominated by kaolinite halloysite chloritic intergrades and gibbsite bases are also leached though the total mass was much less 57 2 55 g cm 2 of na in the beach sand was lost as plagioclase weathered by focusing on elemental and mineralogical gains and losses we emphasize the essential connection between the pedologic environment and the external hydrochemical environment

mapping reef features from multibeam sonar data using multiscale morphometric analysis classification of seafloor habitats from geomorphological proxies is increasingly being applied to understand the distribution of benthic biota particularly as more and larger datasets collected with high resolution multibeam echo sounders are becoming available with increased capacity to collect and use sonar data there is a need for automated approaches to identify seafloor structures and habitats for a survey area of approximately 2 5 2 5 km a generic feature extraction algorithm similar to terrestrial topographic analysis has been developed and applied to a spatially complex submerged mid shelf reef in the great barrier reef lagoon multibeam data collected with a reson seabat 8101 was gridded at 1 m resolution and an automated feature extraction method was applied that analyses the seafloor geomorphology to predict reef features from geomorphological proxies quadric surface fitting was used to determine various surface parameters based on multiple spatial scales subsequently 6 morphometric feature types plane channel ridge pass pit and peak were derived for all mapping scales weighted multiscale fuzziness was then applied to extract the dominant morphometric feature classes finally seafloor morphology patterns in combination with seafloor rugosity measurements were analysed in order to predict reef features these reef features cover significant patches of bioturbation beyond the submerged platform reef as well as the dominant reef features such as outer reef crest and inner reef flat layback corrected and manually classified towed video transects support the classification algorithms used to extract the reef features

the impact of climate on the biogeochemical functioning of volcanic soils abstract rainfall and the amount of water available to leach ions from soil are among the most important features determining mineral weathering secondary mineral synthesis and soil chemical properties along an arid to humid climosequence on kohala mountain hawaii we sampled 16 soil profiles and found that weathering and soil properties change in a nonlinear fashion with increased rainfall the lavas are influenced by a strong rain shadow with mean annual precipitation map averaging 160 mm near the coast and rising to 3000 mm near the summit a temperature decline from 24 to 15 c with increasing elevation is matched by lower potential evapotranspiration et a water balance model monthly precipitation minus monthly et defines three broad climate zones along the sampling transect an arid zone with moisture deficit in every month an intermediate zone with moisture deficit during low rainfall summer months and moisture surplus during high rainfall winter months and a humid zone with moisture surplus during every month the annualized water balance can be ratioed with the integrated porosity of the top meter of soil to provide a leaching index the index reaches 1 total filling of the pore space on an annual basis at about 1400 mm map index values 1 imply intense leaching conditions because of pore water replacement in these 170 ka soils leaching losses of soluble base cations and si are nearly complete at index values 1 whereas only 60 of al has been lost at index values 1400 mm soil buffering capacity has been totally exhausted leading to low ph and low ecec the nonlinear decline in ecec is irreversible under natural conditions base cation depleted soils will remain so even if the climate shifts to drier conditions in contrast a climate shift to wetter conditions can drastically modify surface chemical properties existing in the drier soils as weathering depletes primary minerals elements are lost to leaching and surface chemistry is modified there is a time dimension implied in climate gradient studies soils forming in recently rejuvenated landscapes contain more primary minerals and should experience loss of buffering capacity at higher rainfall loss of buffering capacity means that biological acidity will move more deeply into the vadose zone or into the aquatic system the details of this transfer depend on present and past climate and the age and erosional stability of landscapes

geochemistry of the hawi lavas kohala volcano hawaii hawi lavas form the late stage alkalic cap on kohala volcano and range in composition from hawaiite to trachyte new detailed field mapping of kohala and reinterpretation of previously published age data suggest that there was no significant eruption hiatus between the hawi and underlying pololu shield lavas as was previously suggested mineral and whole rock chemical data are consistent with a crystal fractionation origin for the hawaiite to trachyte compositional variation observed within the hawi lavas plagioclase clinopyroxene ti magnetite olivine and apatite fractionation are needed to explain this variation the clinopyroxene fractionation may have occurred at moderate pressure because it is virtually absent in these lavas and is not a near liquidus phase at pressures of less than 8 kb plagioclase would be buoyant in the hawi hawaiite magmas so a mechanism like dynamic flow crystallization is needed for its fractionation and to account for the virtual absence of phenocrysts in the lavas hawi lavas are distinct in sr and nd isotopic ratios and or incompatible element ratios from the pololu lavas thus they were derived from compositionally distinct sources compared to other suites of hawaiian alkalic cap lavas hawi lavas have anomalously high concentrations of phosphorus and rare earth elements these differences could be due to greater apatite content in the source for the hawi lavas

detachment folding in the central and eastern zagros fold belt iran salt mobility multiple detachments and late basement control abstract detachment folding has been studied on the basis of field and subsurface examples from the central and eastern zagros iran we discuss different aspects of detachment folding well illustrated in the studied area in particular we focus on salt mobility multiple decollements and late basement control salt mobility concerns the hormuz basal detachment and the gachsaran upper detachment for the latter it is shown that mobility results not only from folding related diapirism but also from early gravity driven migration from growing anticlines towards intervening synclines concentric folding between two detachment levels is directly observed in the izeh zone central zagros where it is shown that the wave length depends on the distance between the two active decollements and that the fold shape is a function of the level of erosion throughout the zagros detachment folds mainly developed during an initial thin skinned phase of deformation which was followed by the current thick skinned stage this succession is particularly well expressed in the eastern zagros where basement faults cut early detachment folds obliquely

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

morphological characterization of coral reefs by combining lidar and mbes data a case study from yuanzhi island south china sea the correlation between seafloor morphological features and biological complexity has been identified in numerous recent studies this research focused on the potential for accurate characterization of coral reefs based on high resolution bathymetry from multiple sources a standard deviation std based method for quantitatively characterizing terrain complexity was developed that includes robust estimation to correct for irregular bathymetry and a calibration for the depth dependent variablity of measurement noise airborne lidar and shipborne sonar bathymetry measurements from yuanzhi island south china sea were merged to generate seamless high resolution coverage of coral bathymetry from the shoreline to deep water the new algorithm was applied to the yuanzhi island surveys to generate maps of quantitive terrain complexity which were then compared to in situ video observations of coral abundance the terrain complexity parameter is significantly correlated with seafloor coral abundance demonstrating the potential for accurately and efficiently mapping coral abundance through seafloor surveys including combinations of surveys using different sensors

the impact of biotic abiotic interfaces in mineral nutrient cycling a study of soils of the santa cruz chronosequence california abstract biotic abiotic interactions between soil mineral nutrients and annual grassland vegetation are characterized for five soils in a marine terrace chronosequence near santa cruz california a mediterranean climate with wet winters and dry summers controls the annual cycle of plant growth and litter decomposition resulting in net above ground productivities of 280 600 g m 2 yr 1 the biotic abiotic a b interface separates seasonally reversible nutrient gradients reflecting biological cycling in the shallower soils from downward chemical weathering gradients in the deeper soils the a b interface is pedologically defined by argillic clay horizons centered at soil depths of about one meter which intensify with soil age below these horizons elevated solute na ca mg ca and sr ca ratios reflect plagioclase and smectite weathering along pore water flow paths above the a b interface lower cation ratios denote temporal variability due to seasonal plant nutrient uptake and litter leaching potassium and ca exhibit no seasonal variability beneath the a b interface indicating closed nutrient cycling within the root zone whereas mg variability below the a b interface denotes downward leakage resulting from higher inputs of marine aerosols and lower plant nutrient requirements the fraction of a mineral nutrient annually cycled through the plants compared to that lost from pore water discharge is defined their respective fluxes fj plants qj plants qj plants qj discharge with average values for k and ca fk plants 0 99 fca plants 0 93 much higher than for mg and na fmg plants 0 64 fna plants 0 28 the discrimination against rb and sr by plants is described by fractionation factors ksr ca 0 86 krb k 0 83 which are used in rayleigh fractionation mixing calculations to fit seasonal patterns in solute k and ca cycling krb k and k 24 mg 22 mg values derived from isotope data in the literature fall within fractionation envelopes bounded by inputs from rainfall and mineral weathering ksr ca and k 44 ca 40 ca fractionation factors fall outside these envelopes indicating that ca nutrient cycling is closed to these external inputs small net positive k and ca fluxes 6 14 mol m 2 yr 1 based on annual mass balances indicate that the soils are accumulating mineral nutrients probably as a result of long term environmental disequilibrium

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