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

particle transport of 234u 238u in the kalix river and in the baltic sea the role of particles for u isotope transport was investigated in the kalix river watershed a particle poor fe mn rich river in northern sweden and in the baltic sea estuary particles 0 45 m are strongly enriched in u and contain 20 50 of the total riverine uranium budget and 1 of the total u in brackish waters 3 7 psu the particles have high 234 u which is close to that of dissolved u in the associated water indicating that u on particles is dominantly nondetrital and isotopically exchanges rapidly with the ambient dissolved u particles at the river mouth are dominated by nondetrital fe mn oxyhydroxides uranium and fe are strongly correlated clearly demonstrating that secondary fe oxyhydroxide is the major carrier of u in river water there is no evidence for significant association of u with mn oxyhydroxide apparent u distribution coefficients k d fe were calculated for u between the authigenic fe on particles and the solution these values appear to be relatively constant throughout the year this suggests an equilibrium between fe in solution and authigenic fe oxyhydroxides on detrital particles high values of k d fe calculated for one summer as well as high u concentrations in brackish waters can be explained by u scavenging by biogenic phases with low authigenic fe content

impact of spatial averaging on radar reflectivity at internal snowpack layer boundaries microwave radar amplitude within a snowpack can be strongly influenced by spatial variability of internal layer boundaries we quantify the impact of spatial averaging of snow stratigraphy and physical snowpack properties on surface scattering from near nadir frequency modulated continuous wave radar at 12 18 ghz relative permittivity density grain size and stratigraphic boundaries were measured in situ at high resolution along the length of a 9 m snow trench an optimal range of horizontal averaging 4 6 m was identified to attribute variations in surface scattering at layer boundaries to dielectric contrasts estimated from centimetre scale measurements of snowpack stratigraphy and bulk layer properties single vertical profiles of snowpack properties seldom captured the complex local variability influencing near nadir radar surface scattering we discuss implications of scaling in situ measurements for snow radiative transfer modelling and evaluation of airborne microwave remote sensing of snow

the u series toolbox for paleoceanography the geochemistry of marine sediments is a major source of information about the past environment of the many measurements that provide such information those of the u series nuclides are unusual in that they inform us about the rate and timescales of processes oceanic processes such as sedimentation productivity and circulation typically occur on timescales too short to be assessed using parent daughter isotope systems such as rb sr or sm nd so the only radioactive clocks that we can turn to are those provided by cosmogenic nuclides principally 14c or the u series nuclides this makes the u series nuclides powerful allies in the quest to understand the past ocean climate system and has led to their widespread application over the last decade as in other applications of the u series those in paleoceanography rely on fractionation of the nuclides away from secular equilibrium in the oceanic setting this fractionation is generally due to differences in the solubility of the various nuclides the behavior of the u series nuclides in the ocean environment was widely researched in the middle decades of the twentieth century this work established knowledge of the concentrations of the nuclides in the various compartments of the ocean system and of their fluxes between these compartments such understanding was comprehensively summarized in the ivanovich and harmon u series volume 1992 particularly by cochran 1992 understanding of the behavior of the u series nuclides has not advanced very dramatically in the decade since that summary but a major theme of research has been the use of this geochemical understanding to develop u series tools to assess the past environment table 1 view this table table 1 summary of seawater data for u series nuclides with paleoceanographic applications s soluble i insoluble full descriptions of the paleoceanographic uses and references are provided in the text further details of the half

concentrations and fluxes of uranium in two major chinese rivers the changjiang river and the huanghe river abstract we collected samples from january 2010 to december 2011 to determine the concentrations and fluxes of uranium in the changjiang yangtze and huanghe yellow rivers in china the dissolved u concentrations duc were measured by inductively coupled plasma mass spectrometry icp ms at the freshwater end members of the changjiang and huanghe rivers the ducs ranged from 1 32 to 4 06 nmol l and 13 85 to 29 99 nmol l in the changjiang and huanghe rivers respectively the temporal variations of duc followed the seasonal change with high values in the two rivers occurring during the dry seasons and low values during the flood seasons a strong negative correlation was observed between duc and discharge in the changjiang river r2 0 69 but a weak correlation r2 0 35 was found in the huanghe river the correlations between the major ions and the u in the rivers indicated that the primary source of uranium was from the weathering of carbonate and evaporite in the changjiang basin the weathering of evaporite bearing sequences and the erosion of loess dominated the u sources of the huanghe river carbonate ligands in the dry season and phosphate ligands in the wet season were the primary factors controlling the accumulation and transportation of dissolved uranium in the changjiang river the soils of the huanghe basin contained five times more leachable uranium compared to the soils of the changjiang basin which may explain the high duc in the huanghe river the weighted mean concentrations of uranium were 2 78 nmol l in the changjiang river and 22 07 nmol l in the huanghe river this lead to annual dissolved u fluxes duf of 2 3 106 mol yr in the changjiang river and 4 1 105 mol yr in the huanghe river the sum of the u fluxes in the two rivers represented 11 9 of the global u riverine flux into the sea comparing with 2 5 of the global runoff into the sea the 234u 238u activity ratio of the huanghe river had higher values 1 455 1 418 compared to the changjiang river 1 424 1 374 from the dry season to the wet season respectively

observed and modelled effects of ice lens formation on passive microwave brightness temperatures over snow covered tundra abstract immediately before an april 2007 snow survey and passive microwave radiometer field campaign in the northwest territories canada a rain on snow event deposited a thin 3 mm continuous layer of ice on the surface of the snowpack at eight sites the brightness temperature t b of the undisturbed snow pack was measured with a multi frequency dual polarization 6 9 19 37 and 89 ghz ground based radiometer system the ice lens was then carefully removed and the t b s were measured again the individual v pol channels and the 37 v 19 v difference were largely unaffected by the presence of the ice lens exhibiting a systematic shift of about 3 k in comparison the ice lens had a considerable effect on the h pol t b at all frequencies with a mean difference ice lens present ice lens removed of 9 k 5 3 k at 6 9 ghz 40 k 11 3 k at 19 ghz 33 k 7 6 k at 37 ghz and 19 k 8 0 k at 89 ghz the effect of the ice lens on h pol measurements was also observed with spaceborne data from the advanced microwave scanning radiometer amsr e satellite data simulations of t b were produced for each site using a new two layer formulation of the helsinki university of technology hut snow emission model the ice lens was used as the top layer and the underlying snowpack considered as a homogenous second layer the agreement between observations and simulations was variable with agreement strongest at 19 ghz a comparison with simulations produced using the microwave emission model of layered snowpacks memls suggests hut model uncertainty is related not to the ice lens but to difficulties in simulating emission from deep snow overall the observations and simulations suggest h pol measurements are capable of detecting new ice layers across the tundra snowpack while v pol measurements are more appropriate for snow water equivalent swe retrievals due to their relative insensitivity to ice layers

the importance of colloids and mires for the transport of uranium isotopes through the kalix river watershed and baltic sea the importance of colloids and organic deposits for the transport of uranium isotopes from continental source regions and through the estuarine environment was investigated in the mire rich kalix river drainage basin in northern sweden and the baltic sea ultrafiltration techniques were used to separate uranium and other elements associated with colloids 10 kd and 3 kd from solute uranium and provided consistent results and high recovery rates for uranium as well as for other elements from large volume samples uranium concentrations in 0 45 m filtered kalix river water samples increased by a factor of 3 from near the headwaters in the caledonides to the river mouth while major cation concentrations were relatively constant 234 u 238 u ratios were high 234 u 770 1500 throughout the basin without showing any simple pattern and required a supply of 234 u rich water throughout the kalix river a large fraction 30 90 of the uranium is carried by 10 kd colloids which is compatible with uranium complexation with humic acids no isotopic differences were found between colloid associated and solute uranium within the baltic sea about half of the uranium is removed at low salinities the proportion that is lost is equivalent to that of river derived colloid bound uranium suggesting that while solute uranium behaves conservatively during estuarine mixing colloid bound uranium is lost due to rapid flocculation of colloidal material the association of uranium with colloids therefore may be an important parameter in determining uranium estuarine behavior mire peats in the kalix river highly concentrate uranium and are potentially a significant source of recoil 234 u to the mirewaters and river waters however mirewater data clearly demonstrate that only small 234 u 238 u shifts are generated relative to inflowing groundwater a simple box model of uranium accumulation in peat and transport through the mire that is compatible with the mire data demonstrates that with efficient removal of uranium from solution only small shifts in 234 u 238 u ratios can be generated in mirewater uranium the measurements and model calculations show that mirewaters are not the primary source of the uranium in the river bedrock groundwaters with high 234 u 238 u ratios and uranium concentrations must be the dominant source of riverine uranium

234u 238u ratios and230th ages for hateruma atoll corals implications for coral diagenesis and seawater234u 238u ratios published results for corals that are more than ca 50 ka old from for example barbados and vanuata often yield initial 234u 238u activity ratios that are significantly greater than 1 144 0 004 the value for modern seawater this study reports results for corals from hateruma atoll japan and investigates the effects of diagenesis on the initial 234u 238u ratios of the corals hateruma consists of over 95 reef material of less than 500 ka in age because groundwaters associated with recent carbonates tend not to have elevated 234u 238u ratios the scope for increasing the 234u 238u ratios of hateruma corals through groundwater interaction should be minimal the corals examined range from those which show no petrographic or x ray evidence for diagenetic alteration and are pristine to those containing secondary cements of either aragonite or high or low mg calcite these various phases have been mechanically separated and analysed in agreement with previous assertions the analyses of these separates demonstrates that the presence of calcite should be a cause for rejection of coral samples it is also shown that aragonite cement can form later than coral death and may bias estimates of age and initial 234u 238u ratios of the six pristine corals three have anomalous 230th 238u ratios requiring u loss and or230th addition the remaining fifteen of the eighteen total analyses reported here yield ages from 1 6 ka to 260 ka no evidence for an increase in 234u 238u ratios in past seawater from this period has been found the best estimates for 234u 238u ratios are close to the current seawater value

evaluation of passive microwave melt detection methods on antarctic peninsula ice shelves using time series of sentinel 1 sar abstract passive microwave datasets have been used to quantify the extent and duration of surface melt in greenland and antarctica from 1978 on with daily and near daily intervals these results have important implications for climate analysis and may help evaluate ice shelf stability however the accuracy of passive microwave methods used to detect melt is difficult to quantify especially on the antarctic peninsula here four different melt detection methods are employed including a new formulation of a statistical analysis of brightness temperature time series using a k means clustering algorithm strikingly two of the most widely used passive microwave melt detection methods are found to vary by 48 mean days of melt per year across six different locations on the larsen c wilkins and george vi ice shelves in the absence of ground truth observations time series of sentinel 1 sar observations from 2016 on provide a comparison dataset in topographically flat regions where surface melt is spatially uniform the passive microwave melt detection method based on a k means analysis and the cross polarization gradient ratio method demonstrate the highest agreement and correlation with active radar melt detection methods one issue which has plagued passive microwave analysis is its coarse spatial resolution high resolution sar images are able to demonstrate and quantify the spatial variability of melt within individual passive microwave pixels melt is shown to be suitably uniform in space for passive microwave applications at the study sites on antarctic peninsula ice shelves but not so in other regions of the antarctic peninsula spatial heterogeneity of surface melt on the sub pixel scale is often related to varying surface topography

uranium colloidal transport and origin of the 234u 238u fractionation in surface waters new insights from mount cameroon in order to evaluate the spatial variability of the 234u 238u fractionation and its origin in surface waters 234u 238u activity ratios a r and trace element concentrations were measured in 34 streams and springs draining mount cameroon volcano in addition tangential ultrafiltration techniques were applied to 10 of the samples to assess the role of colloids on the transport of the uranium isotopes u concentration variations in the different ultrafiltered fractions indicate that inorganic colloids can significantly influence the transport of this chemical element even in diluted and organic poor waters such influence which may be related to the chemical and physical nature of colloids does induce fractionations between u and sr along with filter size 234u 238u a r variations among the different ultrafiltered fractions of a sample remain small or even negligible only two samples exhibit a significant isotopic difference between colloid associated and solute u colloids of these two samples seem to correspond to a phase which is distinct from the dissolved and particulate loads of the waters at the scale of the volcano the 234u 238u a r in surface waters is large ranging from 1 038 to 1 397 small 234u 238u fractionations between 1 038 and about 1 10 are attributed to surface and meteoric weathering of the bedrock by contrast the highest 234u 238u fractionations up to 1 397 are associated with groundwater contributions thus variations in the 234u 238u a r could correspond to the water source and not to the surface weathering processes consequently 234u 238u disequilibrium may represent a powerful tool for detecting and quantifying the influence of groundwater inputs on the chemical fluxes carried by surface waters

recording microscale variations in snowpack layering using near infrared photography deposition of snow from precipitation and wind events creates layering within seasonal snowpacks the thickness and horizontal continuity of layers within seasonal snowpacks can be highly variable due to snow blowing around topography and vegetation and this has important implications for hydrology remote sensing and avalanche forecasting in this paper we present practical field and post processing protocols for recording lateral variations in snow stratigraphy using near infrared nir photography a fuji s9100 digital camera modified to be sensitive to nir wavelengths was mounted on a rail system that allowed for rapid imaging of a 10 m long snow trench excavated on the north side of toolik lake alaska 68 3 n 149 36 w post processing of the images included removal of lens distortion and vignetting a tape measure running along the base of the trench provided known locations control points that permitted scaling and georeferencing snow layer heights estimated from the nir images compared well with manual stratigraphic measurements made at 0 2 m intervals along the trench n 357 r2 0 97 considerably greater stratigraphic detail was captured by the nir images than in the manually recorded profiles nir imaging of snow trenches using the described protocols is an efficient tool for quantifying continuous microscale variations in snow layers and associated properties

modeling time series of microwave brightness temperature at dome c antarctica using vertically resolved snow temperature and microstructure measurements time series of observed microwave brightness temperatures at dome c east antarctic plateau were modeled over 27 months with a multilayer microwave emission model based on dense medium radiative transfer theory the modeled time series of brightness temperature at 18 7 and 36 5 ghz were compared with advanced microwave scanning radiometer eos observations the model uses in situ high resolution vertical profiles of temperature snow density and grain size the snow grain size profile was derived from near infrared nir reflectance photography of a snow pit wall in the range 850 1100 nm to establish the snow grain size profile from the nir reflectance and the specific surface area of snow two empirical relationships and a theoretical relationship were considered in all cases the modeled brightness temperatures were overestimated and the grain size profile had to be scaled to increase the scattering by snow grains using a scaling factor and a constant snow grain size below 3 m depth i e below the image derived snow pit grain size profile brightness temperatures were explained with a root mean square error close to 1 k most of this error is due to an overestimation of the predicted brightness temperature in summer at 36 5 ghz

genesis and occupancy of a shell midden on parana state coast brazil abstract the publications related to pedological characterization of shell middens are rare and there are no comprehensive studies the objective of the present study was to understand habits and intensity of seasonal human occupancies and genesis of stratigraphic levels of an archaeological site on parana state coast brazil the formation of the shell midden by hunter fisher gatherer groups over thousands of years followed only a few patterns of interaction with the environment which would facilitate the studies of correlations with other middens of the brazilian coast in addition to strategies of searching food the amerindian also diversified their activities to improve life quality including cooking certain foods and the placement of insulating material on the midden the evolution of the genesis of layers was much more dependent on the depositional period than the post depositional interval during the post depositional period only the formation of silicate in the clay fraction of the more superficial layers was favored

uranium series disequilibrium in river sediments and waters the significance of anomalous activity ratios abstract samples of river water suspended and bottom sediments from the fenland catchment system draining into the wash u k have been analysed for the longer lived u th series radionuclides 238u 234u 230th and 232th the aim of this work was to assess the effects of open system phase transfer on the u series disequilibria observed in the river waters and sediments and to investigate the controls exerted on this phase transfer by the hydrological regime two important aspects of the u series radionuclide mobilisation in this modern river system have been observed 1 u series radionuclides are in a continuous state of flux between river sediments and river water and 2 u sorption on sediment particles is seasonably variable sequential extraction of whole sediments revealed that the u series isotopic characteristics of the ion exchangeable organic bound carbonate amorphous fe mn oxyhydroxides and crystalline fe mn oxides are controlled to a significant degree by the acquisition of u isotopes from the aqueous phase during summer when surface run off and river discharges are generally low the u isotope acquisition by sediment particles results in anomalously high234u 238u activity ratios 1 this is of importance for studies which rely upon the isotopic and elemental separation of u series radionuclides in the weathering system i e mass balance weathering rate and sediment yield assessments

234u 238u activity ratios in freshwaters as tracers of hydrological processes the strengbach watershed vosges france abstract 234u 238u and 87sr 86sr isotopic ratios as well as major and trace u ba sr rb element concentrations were analyzed in dissolved loads of the strengbach stream vosges france in order to constrain the sources of u isotopes 234u 238u to river waters the variations of the 234u 238u activity ratios along the stream indicate a clear dependence between the 234u 238u activity ratios of the surface waters and the different types of rocks forming the watershed with near equilibrium values for the waters draining granites and high 234u 238u disequilibria 1 4 for those flowing over carbonates the high 234u 238u disequilibria are related to a supply of 234u enriched groundwaters located within the carbonate rocks the 234u 238u activity ratios of the waters at the outlet of the catchment collecting the sources of the stream on the granitic lithology decrease from 1 02 to 0 96 when the discharge of the stream increases such a tendency requires mixing between a water body enriched in 234u which weathered the granitic bed rock at secular equilibrium and a water with a 234u 238u activity ratio below unity representing a mobilization of u from material that has already been weathered comparison of the geochemical characteristics of waters collected during the year and those collected during a flood event reveals the involvement of two different weathered end members depending on the hydrological conditions during the year the dissolved u transported by the river originates from bed rock and deep horizons of the weathering profile whereas a significant part of u during the flood event is supplied by superficial horizons of soils probably complexed by organic colloids these results outline the potential of 234u 238u activity ratios to investigate hydrological processes and emphasize that their use as tracers of rock weathering should be made cautiously

temporal variability of uranium concentrations and 234u 238u activity ratios in the mississippi river and its tributaries abstract 234 u 238 u activity ratios and total dissolved uranium concentrations in the lower mississippi river at new orleans la have been analyzed on a bi weekly basis over 2003 2004 during this time period the range in 234 u 238 u activity ratios is approximately 17 from 1 241 to 1 473 while uranium concentrations span an even greater range of 130 0 28 to 1 33 ppb there is no correlation between uranium activity ratio and discharge and only a very weak correlation between uranium concentration and discharge in order to examine the cause of the substantial variability in the lower river concentrations and 234 u 238 u activity ratios we sampled the four major tributaries of the mississippi river ohio missouri upper mississippi and arkansas rivers each river was sampled four times each time representing a unique discharge season in general lithological and climatological parameters in the tributary sub basins exert the greatest control on lower mississippi river uranium concentration and isotope signatures these parameters may also be influenced by groundwater infiltration below the confluences of the major tributaries our temporal analysis suggests that if one were to estimate mississippi river uranium fluxes to the ocean based on single point sampling during 2003 2004 significant over or under estimations of these values would ensue our two year average mississippi river uranium flux values suggest that previous best estimates of the contribution of mississippi river uranium to the global average riverine 234 u 238 u activity ratio are too high by 36 if other major world rivers are as poorly constrained with respect to uranium systematics as the mississippi river then the global average riverine u flux and 234 u 238 u activity ratio need to be revised

uranium isotopes as a tracer of sources of dissolved solutes in the han river south korea abstract the uranium u content and 234u 238u activity ratio were determined for water samples collected from korea s han river in spring summer and winter 2006 to provide data that might constrain the origin of u isotope fractionation in river water and the link between u isotope systematics in river waters and the lithological nature of the corresponding bedrock the large difference in the major dissolved loads between the two major branches of the han river the north han river nhr and south han river shr is reflected in the contrasting u content and 234u 238u activity ratio between the tributaries low u content 0 08 0 75 nm average 0 34 nm and small 234u 238u activity ratio 1 03 1 22 average 1 09 in the nhr and high u content 0 65 1 98 nm average 1 44 nm and large 234u 238u activity ratio 1 05 1 45 average 1 24 in the shr the large spatial differences in u content and 234u 238u activity ratio are closely related to both lithological differences between the two tributaries and groundwater input the low u content and small 234u 238u activity ratio in the nhr arise mainly from a combination of surface and meteoric weathering of the dominant silicate rocks in this branch and congruent dissolution of already weathered secular equilibrium materials in contrast the high u content and large 234u 238u activity ratio in the shr are ascribed to the dissolution of carbonates and black shales along with significant inputs of deep groundwater

u th ra fractionation during weathering and river transport the potential of radioactive disequilibria as tracers and chronometers of weathering processes has been recognised since the 1960 s e g rosholt et al 1966 hansen and stout 1968 this interest results from the dual property of the nuclides of the u and th radioactive series 1 to be fractionated during water rock interactions and 2 to have radioactive periods of the same order of magnitude as the time constants of many weathering processes and chemical transfers to ground and river waters therefore the study of radioactive disequilibria in surface environments should help to bring information about the nature the intensity but also the time scale of the water rock interactions produced during weathering and related chemical transfers these different properties have justified many of the studies on u th series in weathering profiles and river waters rosholt 1982 scott 1982 and osmond and ivanovich 1992 gave a synthesis of the studies of u series in weathering and surface hydrology up to the 1980 s and the 1990 s respectively here we present the main directions taken in these domains over the last decade they were partly stimulated by the analytical developments made in the measurement of the medium half life nuclides of 238u series i e 234u 230th 226ra in the mid 1980 s namely the use of thermal ionisation mass spectrometry tims e g chen et al 1986 edwards et al 1987 cohen et al 1991 chabaux 1993 chabaux et al 1994 and more recently the use of mc icp ms turner et al 2001 robinson et al 2002 for u and th isotope analysis details of these developments are given in this volume goldstein and stirling 2003 compared to the radioactive counting methods previously used the new techniques permit 1 a reduction by one order of magnitude or more of the size of the sample required for

snow stratigraphic heterogeneity within ground based passive microwave radiometer footprints implications for emission modeling two dimensional measurements of snowpack properties stratigraphic layering density grain size and temperature were used as inputs to the multilayer helsinki university of technology hut microwave emission model at a centimeter scale horizontal resolution across a 4 5 m transect of ground based passive microwave radiometer footprints near churchill manitoba canada snowpack stratigraphy was complex between six and eight layers with only three layers extending continuously throughout the length of the transect distributions of one dimensional simulations accurately representing complex stratigraphic layering were evaluated using measured brightness temperatures large biases 36 to 68 k between simulated and measured brightness temperatures were minimized 0 5 to 0 6 k within measurement accuracy through application of grain scaling factors 2 6 to 5 3 at different combinations of frequencies polarizations and model extinction coefficients grain scaling factors compensated for uncertainty relating optical specific surface area to hut effective grain size inputs and quantified relative differences in scattering and absorption properties of various extinction coefficients the hut model required accurate representation of ice lenses particularly at horizontal polarization and large grain scaling factors highlighted the need to consider microstructure beyond the size of individual grains as variability of extinction coefficients was strongly influenced by the proportion of large hoar grains in a vertical profile it is important to consider simulations from distributions of one dimensional profiles rather than single profiles especially in sub arctic snowpacks where stratigraphic variability can be high model sensitivity experiments suggested that the level of error in field measurements and the new methodological framework used to apply them in a snow emission model were satisfactory layer amalgamation showed that a three layer representation of snowpack stratigraphy reduced the bias of a one layer representation by about 50

lithologic and climatologic controls of river chemistry abstract the chemistries of rivers draining a variety of lithologic and climatic regions have been surveyed for the purpose of quantifying the fluxes of bicarbonate and silica from rivers with respect to bedrock lithology and runoff in all 101 different rivers each draining a primary lithology were examined across the united states puerto rico and iceland to minimize seasonal effects only rivers with at least two years of data were used basaltic catchments were examined in the greatest detail in a survey of hawaiian island watersheds the average river chemistries could be related to the distribution of soil associations within each catchment an analysis of cation activity relationships among rivers draining basaltic catchments shows that the river compositions define slopes which are consistent with an equilibrium ion exchange control on cation ratios among different lithologies unique weathering rate relationships were developed with yields at typical present day runoff rates 1 100 cm y increasing in the order sandstones granites basalts shales and carbonates the bicarbonate and silica fluxes for each of these lithologies have been quantified for use in global studies of chemical denudation our study confirms that the dissolved yield of a given drainage basin is determined by a balance between physical and chemical weathering thus a warm wet climate or the presence of abundant vegetation cannot guarantee high rates of chemical denudation unless accompanied by high rates of physical removal

contact spectroscopy for determination of stratigraphy of snow optical grain size we present a technique for in situ measurement of the vertical and spatial stratigraphic distribution of snow optical grain size with a coupled contact illumination probe and field spectroradiometer accurate measurements of optical equivalent grain size are critical for modeling radiative properties of snow such as spectral albedo and microwave emission measurements of the spectral reflectance of the snow pit surface are made at 2 cm intervals in the vertical plane under constant illumination and view geometries we invert the integral of the continuum normalization of the ice absorption feature with maximum at 1 03 mm wavelength for optical equivalent grain size using the validated model of nolin and dozier 2000 that has accuracy of 10 50 mm across the grain size range 50 900 mm results are presented for an alpine site in southwest colorado usa across the ablation season and for a greenland ice sheet site at the onset of snowmelt these results suggest that traditional measurements of grain size using a hand lens are nearly accurate only for rounded grains r 2 0 41 rmse 160 mm for polycrystals and faceted grains the hand lens approach is very inaccurate r 2 0 03 and 0 24 rmse 1206 and 1010 mm respectively we demonstrate an order of magnitude improvement in modeling of shortwave spectral albedo and net shortwave flux with contact spectroscopy measurements of grain size stratigraphy over those from a hand lens

microstructure dependent densification of polar firn derived from x ray microtomography the densification of dry polar snow and firn results in a continuous increase of density with depth accompanied by significant density fluctuations within seasonal layers density measurements of high spatial resolution reveal a persistent minimum of density fluctuations in the vicinity of the snow firn transition 0 55 0 65 g cm 3 in firn core records in this study we give an explanation for the fluctuation minimum by applying a new method of x ray microtomography to obtain three dimensional 3 d structural data of a greenland firn core at 13 different depths between 10 and 78 m a set of 16 samples of 40 cm total length for each depth interval was measured a reconstructed firn segment of 40 cm covers 1 2 years of snow accumulation using digital image analysis techniques different structural parameters are estimated including 3 d pore and particle sizes and specific surface areas it is shown that the densification rates of snow and firn layers consisting of coarse particles are much higher than those consisting of fine particles within the same depth interval this causes a density crossing of fine and coarse grained layers with a minimum of density variations at the crossover point this crossing over implies that formerly dense layers in the seasonal density signal are not of the same origin as dense layers in the deeper part of the firn column and that the seasonal density signal will totally change shape with depth it is speculated that in coarse and fine grained firn the dominant mechanism of densification acts over different regimes of density

relation between grain size and correlation length of snow in the past it has often been difficult to compare results of different types of snow structural information grain size and correlation length are such parameters of granular media and there exist different definitions and different measurement methods for both of them the relation between these parameters is analyzed from theoretical and from experimental points of view considering optical and microwave properties for spherical ice grains the connecting formulas are simple but for other shapes the two parameters are not directly related care must be taken in the measurement procedure especially if grain size is regarded as the maximum extent of connected ice particles the results are likely to lead to extreme overestimates therefore it is concluded that grain size should be complemented by an additional size parameter namely the surface to volume ratio of equivalent spheres i e a measure of the correlation length methods to determine this quantity in the laboratory have been known for a long time methods to obtain such measurements in the field are described here

u isotope ratios as tracers of groundwater inputs into surface waters example of the upper rhine hydrosystem major elements trace elements and sr and u isotopes were analyzed in the dissolved load of water samples collected in the main reservoirs of the rhine graben i e the rhine river its main tributaries and the shallow and deep ground waters in several different aquifers our results confirm that the variations of major elements trace elements especially sr and rb and sr isotope ratios of the water samples are mainly correlated to the lithological variations of the watershed the atmospheric inputs can be considered as a minor cause for the chemical variability of the surface waters in the rhine hydrosystem except for a few chemical elements in the mountain streams human activity in particular the pollution by the exploitation of the alsace potash mines mainly affects the na and cl concentrations of the rhine and the south alluvial groundwaters but remains negligible for the other water samples the specific study of the lauter stream located in the lower triassic sandstones buntsandstein sequences demonstrates the importance of groundwater influences onto the chemical composition of river waters up to 50 of the total dissolved load tds of this stream is supplied by deep waters this contribution significantly modifies the chemical composition of the stream especially the 238u 234u radioactive disequilibrium which in turn can be used as a specific tracer of deep water inputs into surface waters and could be useful to distinguish in the dissolved load of rivers surface weathering fluxes from deeper ones

on the possibility of determining rates of removal of uranium from crystalline igneous rocks using u series disequilibria 1 a u leach model and its applicability to whole rock data the removal of u from granitic rocks is characterised by234u 238u 1 and 230th 234u 1 it is notable from weathered eye dashwa lakes canada granite samples and from the published data that230th 234u ratios seldom exceed a limiting value of about 2 a u leach model is discussed in detail which may account for these observations the model assumes that 230th is practically immobile and that the removal of u can then be measured against the decay rate of the unsupported230th a property of the model is that the isotope ratios reach constant values reflecting a kind of secular equilibrium and this implies that u is seldom removed faster than the decay of230th if the limited230th 234u ratios from the data correspond to secular equilibrium ratios then this allows simple calculation of u leach rates from any given subsurface sample a test for the model using235u 231pa ratios is suggested a comparison of leach rates derivable from u th pb systematics of colorado and wyoming granite samples with the corresponding estimates from the model shows that the latter are high by a factor of 10 50 data from rapidly weathered surface rinds suggests that the presence of labile u restricts the application of the model to subsurface low weathered zones

seawater 234 u 238 u during the last 800 thousand years abstract constraining the history of seawater 234u 238u is important because this ratio is used to assess the validity of u th ages and because it provides information about the past rate of physical weathering on the continents this study makes use of u rich slope sediments from the bahamas in an attempt to reconstruct seawater 234u 238u for the last 800 kyr for the last 360 kyr u th dating of these sediments provides ages and initial 234u 238u values sixty seven samples largely from marine highstands have initial 234u 238u which scatter somewhat about the modern seawater value 1 145 but neither this scatter nor the average value increases with age of sample these data contrast with published coral data and suggest that seawater 234u 238u has remained within 15 of the modern value for the last 360 kyr this confirms the rejection of coral u th ages where the initial 234u 238u is significantly different from modern seawater data from older highstands dated with 18o stratigraphy or by the presence of the brunhes matuyama b m reversal at 780 kyr allow seawater 234u 238u to be assessed prior to the range of the 230th chronometer unfortunately diagenetic scatter in the data between the b m reversal and 360 kyr is rather large probably relating to low u concentrations for these samples but there is no indication of a trend in seawater 234u 238u with age high u samples from close to the b m reversal show less diagenetic scatter and an initial 234u 238u that averages 1 102 this lower value can be explained by lower seawater 234u 238u at the time of the b m reversal or by progressive loss of 234u from the sediment by recoil a simple box model is presented to illustrate the response of seawater 234u 238u to variations in riverine input such as might be caused by changes in continental weathering comparison of the bahamas 234u 238u data with model results indicates that riverine 234u 238u has not varied by more than 65 for any 100 kyr period during the last 360 kyr it also indicates that the ratio of physical to chemical weathering on the continents has not been higher than at present for any extended period during the last 800 kyr

behavior and budget of dissolved uranium in the lower reaches of the yellow huanghe river impact of water sediment regulation scheme abstract the water sediment regulation scheme wsrs is an important water conservancy project in the yellow river basin which is usually operated annually from june to july to control water and sediment release from the xiaolangdi reservoir in the middle reaches as a greatly concentrated period of delivering terrigenous materials from the yellow river to the sea the wsrs can serve as a natural laboratory to examine the geochemical behavior of elements during their transport along the river uranium isotopes 234u and 238u were measured in yellow river waters at stations xiaolangdi located in the middle reaches of the yellow river and lijin the last hydrologic station near the yellow river estuary during the wsrs 2012 compared with station xiaolangdi dissolved uranium concentration at station lijin was markedly higher showing a significant impact from the wsrs budget calculation for dissolved uranium during the wsrs indicated that two major sources of new added dissolved uranium in the section of the yellow river between xiaolangdi and lijin suspended particles 46 and porewater of bottom sediment 45 the flux of dissolved uranium from the yellow river to the sea was estimated to be 2 40 107 g during the wsrs 2012

rapid mineral surface weathering beneath the greenland ice sheet shown by radium and uranium isotopes abstract glaciated watersheds are regions of intense physical and chemical weathering in order to gain new insight on subglacial weathering processes we measured uranium and radium isotopes from a proglacial river draining the greenland ice sheet gris time series samples were collected from the spring to mid summer a time period during which subglacial drainage pathways are thought to transition from slow inefficient distributed to fast efficient channelized systems the 228ra 226ra activity ratio of the dissolved load varied from 5 2 0 9 16 9 3 6 which was significantly higher than the 228ra 226ra ratio of a suspended sediment load sample of 2 1 0 07 and crustal values of 1 the high 228ra 226ra in the dissolved load relative to the source rock material is indicative of mineral surface weathering induced by rapid and continuous flushing of the subglacial drainage network during the course of the melt season and those prior the 234u 238u ratio 234u varied between 33 and 106 with a discharge weighted mean of 67 the seasonal evolution of 234u did not correlate to geochemical indicators of subglacial meltwater storage time an experiment designed to measure changes in 234u with increasing meltwater storage times found that 234u in the dissolved phase decreased rapidly with increasing storage time similarly samples collected along a transect moving downstream from the ice sheet terminus had decreasing 234u values from 63 to 15 further indicating that with increased weathering the 234u of meltwater decreases coupled with the relatively low 234u and high 228ra 226ra u appears to be impacted by rapid chemical weathering of subglacial and suspended sediments the leverett river discharge weighted u concentration was 0 13 nm if this system is considered representative of the broader gris then the total dissolved u flux from the gris would be on the order of 6 4 104 mol y using a similar set of assumptions the dissolved 228ra and 226ra flux from the gris was 1 1 1014 dpm y and 5 5 1013 dpm y respectively these estimates suggest that the 226ra flux to the ocean from the gris is globally significant and that the 228ra flux in particular is larger than most river inputs

uranium isotopes in rivers estuaries and adjacent coastal sediments of western india their weathering transport and oceanic budget the two major river systems on the west coast of india narbada and tapti their estuaries and the coastal arabian sea sediments have been extensively studied for their uranium concentrations and 238u238u activity ratios the 238u concentrations in the aqueous phase of these river systems exhibit a strong positive correlation with the sum of the major cations na k mg ca and with the hco3 ion contents the abundance ratio of dissolved u to the sum of the major cations in these waters is similar to their ratio in typical crustal rocks these findings lead us to conclude that 238u is brought into the aqueous phase along with major cations and bicarbonate the strong positive correlation between 238u and total dissolved salts for selected rivers of the world yield an annual dissolved 238u flux of 0 88 1010g yr to the oceans a value very similar to its removal rate from the oceans 1 05 1010g yr estimated based on its correlation with hco3 contents of rivers in the estuaries both 238u and its great grand daughter 234u behave conservatively beyond chlorosities 0 14 g l these data confirm our earlier findings in other indian estuaries the behavior of uranium isotopes in the chlorosity zone 0 02 0 14 g l was studied in the narbada estuary in some detail the results though not conclusive seem to indicate a minor removal of these isotopes in this region reexamination of the results for the gironde and zaire estuaries martin et al 1978a and b also appear to confirm the conservative behavior of u isotopes in unpolluted estuaries it is borne out from all the available data that estuaries beyond 0 14 g l chlorosities act neither as a sink nor as a source for uranium isotopes the behavior in the low chlorosity zones warrants further detailed investigation a review of the uranium isotope measurements in river waters yield a discharge weighted average 238u concentration of 0 22 g l with a 234u238u activity ratio of 1 20 0 06ismissing the residence time of uranium isotopes in the oceans estimated from the 238u concentration and the 234u238u a r of the rivers yield conflicting results the material balance of uranium isotopes in the marine environment still remains a paradox if the disparity between the results is real then an additional 234u flux of about 0 25 dpm cm2 103 yr into the oceans about 20 of its river supply is necessitated

interfacial and structural relaxations of snow under isothermal conditions we investigated the morphological evolution of laboratory snow under isothermal conditions at 3 9a nd 19 c using x ray tomography we employed a two point density correlation function to measure spatial fluctuations of the density of the bicontinuous ice vapor system at different length scales length scales were derived from the correlation function to distinguish between interfacial coarsening due to the minimization of surface energy on the smallest scales and anisotropic structural re arrangements due to gravity on larger scales on the smallest scales our data suggest a crossover between t 9a nd 19 c from evaporation condensation to surface diffusion as the dominant transport mechanism anomalous growth was found for the slope of the correlation function at the origin and it was similar to those reported for the coarsening of fractal clusters this is consistent with the observed persistence of dendritic structures throughout an entire year the dynamics of large scale morphology was characterized by the first zero crossing of the correlation function which displays a nonmonotonic evolution with a pronounced anisotropy between the direction of gravity and horizontal directions since the correlation function naturally emerges in problems of scattering of radiation in snow our results appear to be important for optical and remote sensing methods

uranium isotopes in the platte river drainage basin of the north american high plains region abstract the north and south platte rivers contribute sigficant concentrations of dissolved uranium to the platte river system from the weathering of uraniferous rocks at their headwaters in colorado and wyoming uranium isotopes measured in three groups of samples collected from the platte river and its major tributaries exhibted a wide range of concentrations 0 27 31 7 g l and activity ratios 1 03 1 72 reflecting variations in the contributions of different sources under differing flow conditions locally elevated uranium concentrations and higher activity ratios were associated with groundwater sources during low flow periods uranium concentrations in surface runoff were lower than in baseflow and correlated significantly with dissolved solids uranium activity ratios in runoff were closer to equilibrium values than those in baseflow suggesting that dissolved uranium in runoff is less affected by disequilibrium processes mixing calculations using uranium concentrations and activity ratios indicate considerable variations in longitudinal and transverse mixing of tributary water with plate river water and temporal variations of groundwater contributions baseflow and irrigation return flow in the plate river system

the indus river system india pakistan major ion chemistry uranium and strontium isotopes the indus river is one of the large river systems draining the himalaya we report in this paper the major ion chemistry sr and u isotope systematics of the indus system particularly its headwaters the results show that 1 on an average about a third of the cations in the waters can be from silicate weathering however most of the ca mg is likely to be from the weathering of carbonates and evaporites 2 the 87sr86sr of the waters ranges between 0 7085 and 0 7595 the higher values 0 72 are typical of the tributaries draining the precambrian granite gneissic terrains the 87sr86sr of the indus main channel throughout its entire stretch shows only minor variations 0 7104 0 7116 the indus transports 8 8 106 mol sr to the arabian sea annually with a 87sr86sr of 0 7111 if our results of sr concentration and 87sr86sr measured at thatta can be considered typical of the indus throughout the year and 3 the u concentration in the indus and its tributaries is generally high 0 37 10 3 g 1 1 the source for the high uranium can be the weathering of granites zones of uranium mineralisation and black shales the indus results when compared with our earlier data on the ganga brahmaputra show that in all these three river systems carbonate weathering is the dominant source of ca mg and hco3 and that u concentrations are high in the case of 87sr86sr the indus waters are less radiogenic however its tributaries draining the precambrian granites gneisses have 87sr86sr in excess of 0 72 similar to that in the rivers of the ganga system the low 87sr86sr of the indus 0 7111 suggests that its contribution to the sr isotope evolution of oceans since the cenozoic is less significant than that of the ganga brahmaputra

measuring specific surface area of snow by near infrared photography the specific surface area ssa is considered an essential microstructural parameter for the characterization of snow photography in the near infrared nir spectrum is sensitive to the ssa we calculated the snow reflectance from calibrated nir images of snow pit walls and measured the ssa of samples obtained at the same locations this new method is used to map the snow stratigraphy the correlation between reflectance and ssa was found to be 90 calibrated nir photography allows quantitative determination of ssa and its spatial variation in a snow profile in two dimensions within an uncertainty of 15 in an image covering 0 5 1 0 m 2 even layers of 1 mm thickness can be documented and measured spatial maps of ssa are an important tool in initializing and validating physical and chemical models of the snowpack

uranium isotopes in surface waters from southern africa abstract the 234 u 238 u activity ratio in river water in southern africa is generally higher than that reported for rivers in other regions of the world this is interpreted as due to the prevailing environmental conditions in this warm dry region mechanical weathering predominates over chemical weathering causing the isotope activity ratio of leached uranium to be on average 2 03 0 42 as compared to a ratio of 1 20 for river water in the more humid tropical and temperate regions the isotopic composition of leachable uranium from river sediment is similar to that in the water rivers draining the witwatersrand gold and uranium mining area clearly show pollution inputs characterised by high uranium content and low activity ratios

the importance of colloids for the behavior of uranium isotopes in the low salinity zone of a stable estuary particle mediated removal processes of u isotopes were investigated during spring flood discharge in the low salinity zone lsz up to 3 practical salinity units psu of a stable estuary a shipboard ultrafiltration cross flow filtration cff technique was used to separate particles 0 2 m and colloids between 3000 daltons 3 kd and 0 2 m from ultrafiltered water 3 kd containing dissolved species sediment traps were used to collect sinking material concentration of fe and organic c which are indicators of the major u carrier phases were used to interpret the behavior of 234 u 238 u during estuarine mixing colloids dominated the river water transport of u carrying 90 of the u on entering the estuary colloids accounted for the dominant fraction of u to about a salinity of 1 psu but only a minor fraction 1 psu there is a general correlation between u and salinity in all filtered fractions the 234 u 238 u ratios in different filtered fractions and sinking particles were generally indistinguishable at each station and showed enrichment in 234 u compared with secular equilibrium 234 u 266 567 this clearly shows that all size fractions are dominated by nondetrital u consideration of u isotope systematics across the estuary reveals that substantial u exchange must occur involving larger particles at least to 1 psu and involving colloids at least to 1 5 psu further exchange at higher salinities may also occur as the proportion of u on colloids decreases with increasing salinity this may be due to decreasing colloid concentration and increasing stabilization of uranyl carbonate complexes during mixing in the estuary the results show that although u is a soluble element that shows generally conservative mixing in estuaries removal occurs in the very low salinity zone and this zone represents a significant sink of u variation in composition and concentration of colloidal particles between different estuaries might thus be an important factor for determining the varying behavior of u between estuaries

density specific surface area and correlation length of snow measured by high resolution penetrometry precise measurements of snow structural parameters are crucial to understand the formation of snowpacks by deposition and metamorphism and to characterize the stratigraphy for many applications and remote sensing in particular the area wide acquisition of structural parameters at high spatial resolution from state of the art methods is however still cumbersome since the time required for a single profile is a serious practical limitation as a remedy we have developed a statistical model to extract three major snow structural parameters density correlation length and specific surface area ssa solely from the snowmicropen smp a high resolution penetrometer which allows a meter profile to be measured with millimeter resolution in less than 1 min the model was calibrated by combining smp data with 3 d microstructural data from microcomputed tomography which was used to reconstruct full depth snow profiles from different snow climates alpine arctic and antarctic density correlation length and ssa were derived from the smp with a mean relative error of 10 6 16 4 and 23 1 respectively for validation we compared the density and ssa derived from the smp to traditional measurements and near infrared profiles we demonstrate the potential of our method by the retrieval of a two dimensional stratigraphy at kohnen station antarctica from a 46 m long smp transect the result clearly reveals past depositional and metamorphic events and our findings show that the smp can be used as an objective high resolution tool to retrieve essential snow structural parameters efficiently in the field

variations in productivity and eolian fluxes in the northeastern arabian sea during the past 110 ka abstract high resolution one to two samples ka radionuclide proxy records from core 93kl in the northeastern arabian sea provide evidence for millennial climate variability over the past 110 ka we interpret 230th normalized 232th fluxes as a proxy for eolian input and authigenic uranium concentrations as a proxy for past productivity we attribute orbital and suborbital variations in both proxies to changes in the intensity of the southwest indian ocean monsoon the highest 230th normalized 232th fluxes occur at times that are consistent with the timing of the younger dryas heinrich events 1 7 and cold dansgaard oeschger stadial events recorded in the gisp2 ice core such high dust fluxes may be due to a weakened southwest monsoon in conjunction with strengthened northwesterlies from the arabian peninsula and mesopotamia authigenic uranium concentrations on the other hand are highest during warm dansgaard oeschger interstadials when the southwest monsoon is intensified relative to the northwesterly winds our results also indicate that on orbital timescales maximum average eolian fluxes coincide with the timing of marine isotopic stage mis 2 and 4 while minimum fluxes occur during mis 1 3 and 5 although the forcing mechanism s controlling suborbital variabilities in monsoonal intensity is still debated our findings suggest an atmospheric teleconnection between the low latitude southwest monsoon and north atlantic climate

worldwide distribution of continental rock lithology implications for the atmospheric soil co2 uptake by continental weathering and alkalinity river transport to the oceans 1 the silicate rock weathering followed by the formation of carbonate rocks in the ocean transfers co2 from the atmosphere to the lithosphere this co2 uptake plays a major role in the regulation of atmospheric co2 concentrations at the geologic timescale and is mainly controlled by the chemical properties of rocks this leads us to develop the first world lithological map with a grid resolution of 1 1 this paper analyzes the spatial distribution of the six main rock types by latitude continents and ocean drainage basins and for 49 large river basins coupling our digital map with the gem co2 model we have also calculated the amount of atmospheric soil co2 consumed by rock weathering and alkalinity river transport to the ocean among all silicate rocks shales and basalts appear to have a significant influence on the amount of co2 uptake by chemical weathering

238u234u and232th230th in the baltic sea and in river water the concentration c of dissolved238u 234u 232th and230th in fresh and brackish waters from the baltic sea were determined using tims the brackish waters range in salinity from that of sea water sw to 2 5 c238u in oxygen saturated surface waters is well correlated with salinity and shows quasi conservative behavior as does sr samples from the redox water interface show depletion in c238u demonstrating that dissolved u is being removed by femn oxyhydroxides from a simple mixing relationship for the brackish water 234u 1000 was calculated for the fresh water source in the northern baltic a study of the kalixalven river over an annual cycle yields high 234u during spring and summer discharge and lower values during fall and winter showing that different sources contribute to the u load in the river during different seasons c232th and c230th in river water are governed by the discharge reflecting the importance of the increased abundance of small particles 0 45 m for the232th230th load at high discharge 232th 238u in river water is about 40 times less than in detrital material in the brackish water c232th drops 2 orders of magnitude in the low salinity region 5 reaching a value close to that of sea water at a salinity of 7 5 almost all of the riverine232th must be deposited in the low salinity regions of the estuary the230th 232th in river waters is about twice the equilibrium value for232th 238u 3 8 in the brackish waters 230th 232th is greater by a factor of 10 100 than both river water and sw the big increase in230th 232th in the baltic sea waters over the riverine input indicates that the th isotopes enter the estuary as a mixture of two carrier phases we infer that about 96 of232th in river water is carried by detrital particles whereas the other phase solution colloidal has a much higher232th 232th entering the estuary the detrital particles sediment out rapidly whereas the non detrital phase is removed more slowly causing a marked increase in230th 232th in the brackish water in sw 230th 232th is closer to river input and detrital material than in brackish water we conclude that in the deep sea 232th is almost exclusively dominated by windblown dust and can be used to monitor dust flux the230th excess in baltic rivers is produced in u rich 232th poor peatlands and trapped in authigenic particles and transported with the particles time scales for producing the230th excess are 2000 8000 yr this is younger than but comparable to the time of the latest deglaciation which ended some 9000 yr ago when the mires were forming these results have implications for the possible mobility of actinides stored in repositories