atlantic paleogene biserial heterohelicid foraminifera and oxygen minima through most of the paleogene the planktonic foraminifera called biserial heterohelicids record the most depleted carbon isotope ratios among planktonic foraminiferal species they are interpreted to occupy an oxygen minimum habitat stronger interplanktonic carbon isotope contrasts and more enriched near surface carbon isotope values correspond to higher abundances of biserial heterohelicids this group appears to have preferred latitudes and times when the oxygen minimum was well developed biserial heterohelicid generic and specific diversity are directly related to the interplanktonic carbon isotope contrast minimal specific diversity characterizes the oligocene when interplanktonic and surface to bottom carbon isotope contrasts were consistently low diversity and abundance decreases were coeval with increased oceanic ventilation

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

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

uranium series isotopes in river materials insights into the timescales of erosion and sediment transport abstract the uranium series isotope signatures of the suspended and dissolved load of rivers have emerged as an important tool for understanding the processes of erosion and chemical weathering at the scale of a watershed these signatures are a function of both time and weathering induced fractionation between the different nuclides provided appropriate models can be developed they can be used to constrain the residence time of river sediment this chronometer is triggered as the bedrock starts weathering and the inferred timescale encompasses the residence time in the weathering profile storage in temporary sediment deposits e g floodplain and transport in the river this approach has been applied to various catchments over the past five years showing that river sediments can reside in a watershed for timescales ranging from a few hundreds of years iceland to several hundreds of thousands of years lowlands of the amazon various factors control how long sediment resides in the watershed the longest residence times are observed on stable cratons unaffected by glacial cycles or more generally climate variability and human disturbance shorter residence times are observed in active orogens andes or fast eroding recently glaciated catchments iceland in several cases the residence time of suspended sediments also corresponds to the time since the last major climate change the u series isotope composition of rivers can also be used to predict the river sediment yield assuming steady state erosion is reached by comparing this estimate with the modern sediment yield obtained by multi year sediment gauging it is clear that steady state is seldom reached this can be explained by climate variability and or human disturbance steady state is reached in those catchments where sediment transport is rapid iceland or where the region has been unaffected by climate change and or human disturbance u series are thus becoming an important tool to study the dynamics of erosion

time scale and conditions of weathering under tropical climate study of the amazon basin with u series the rio solimoes amazonas amazon river and its major tributaries have been analyzed for u series nuclides 238 u 234 u 230 th 226 ra disequilibria have been measured in the dissolved 0 2 lm as well as bed sands u series disequilibria are closely related to major and trace element compositions and therefore reflect elemental fractionation during chemical weathering moreover while the dissolved load records present day weathering suspended particles integrate the erosion his tory over much longer time scales 100 ka lowland rivers are characterized by long time scales of chemical erosion p100 ka result ing in a high weathering intensity moreover exchange between suspended particles and the dissolved load may explain the u series signature for these rivers by combining u series and pb isotopes in suspended particles we show that erosion in the rio madeira basin occurred as a multi step process whereby the pristine continental crust was eroded several hundreds of ma ago to produce sediments that have then been integrated in the cordillera by crustal shortening and are currently eroded in contrast recent erosion of a pristine crust is more likely for the rio solimoes amazonas 10 ka the suspended particles of the rivers draining the andes solimoes ama zonas madeira suggest time scales of weathering ranging between 4 and 20 ka this indicates that suspended particles transported by those rivers are not stored for long periods in the andean foreland basin and the tropical plain the sediments delivered to the ocean have resided only a few ka in the amazon basin 6 3 1 ka for the rio amazonas at obidos nevertheless a large fraction of the sediments coming out from the andes are trapped in the foreland basin and may never reach the ocean erosion in the andes is not operating in steady state u series systematics shows unambiguously that rivers are exporting a lot more sediments than predicted by steady state erosion and that is a consequence of soil destruction greater than production by relating this observation to the short time scales of weathering inferred for the andes a few ka it appears that the erosion regime has been recently perturbed resulting in high denudation rates a possible explanation would be the increase in precipitation less than 5 ka proposed by recent paleoclimatic studies our results indicate that erosion responds rapidly to high frequency climatic fluctuations

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

a record of late quaternary continental weathering in the sediment of the caspian sea evidence from u th sr isotopes trace element and palynological data abstract this study presents combined mineralogical chemical isotopic 87sr 86sr and u th disequilibria series and palynological analyses on bulk sediments and on distinct mineral phases carbonates and clays from a 10 m long core drilled in the southern caspian sea and containing a late pleistocene and early holocene record the data allowed identifying 1 the main variations in sedimentation 2 the processes causing these variations 3 the modification of erosion vs weathering and 4 the influence of climatic and or caspian sea level changes in the region since the late pleistocene the chemical and mineralogical results allowed the division of the sedimentary sequence into three main units and a transition zone the lower unit unit u1 primarily consists of silicate and carbonate rich detritus sedimentation characteristics including observation of detritus in secular equilibrium are relatively constant within this unit and reflect mechanical erosion in a cold climate unit u1 probably corresponds to a glacial period when the vegetation cover was sparse and wind and river transport of pollen were strong subsequently global increase in temperatures has greatly modified the sedimentation in the caspian sea south basin biogenic sedimentation is higher in units u2 and u3 and detrital inputs varied from unit u1 variations in detrital input are likely to be caused by decreasing aeolian contribution and by relative changes in river volumes and origins the study of the bulk sediments clays and carbonates reflects an increase in chemical weathering since about 10 14c ka bp ago base of unit u2 in line with an increase in the vegetation cover our results suggest an evolution of continental weathering conditions in the catchment area of the caspian sea from dominantly mechanical physical erosion during the cold period to a continuous increase in weathering since the lateglacial period as climate improved which illustrates the strong relation between climate vegetation cover and weathering processes this paper also highlights how the u th disequilibrium series proxy combined with other geochemical and palynological studies could be a useful tool to record and constrain the modification of weathering regime in response to climatic and environmental changes at regional scale

spatial distribution of dissolved constituents in icelandic river waters summary in this study we map the spatial distribution of selected dissolved constituents in icelandic river waters using gis methods to study and interpret the connection between river chemistry bedrock hydrology vegetation and aquatic ecology five parameters were selected alkalinity sio2 mo f and the dissolved inorganic nitrogen and dissolved inorganic phosphorus mole ratio din dip the highest concentrations were found in rivers draining young rocks within the volcanic rift zone and especially those draining active central volcanoes however several catchments on the margins of the rift zone also had high values for these parameters due to geothermal influence or wetlands within their catchment area the din dip mole ratio was higher than 16 in rivers draining old rocks but lowest in rivers within the volcanic rift zone thus primary production in the rivers is limited by fixed dissolved nitrogen within the rift zone but dissolved phosphorus in the old tertiary catchments nitrogen fixation within the rift zone can be enhanced by high dissolved molybdenum concentrations in the vicinity of volcanoes the river catchments in this study were subdivided into several hydrological categories importantly the variation in the hydrology of the catchments cannot alone explain the variation in dissolved constituents the presence or absence of central volcanoes young reactive rocks geothermal systems and wetlands is important for the chemistry of the river waters we used too many categories within several of the river catchments to be able to determine a statistically significant connection between the chemistry of the river waters and the hydrological categories more data are needed from rivers draining one single hydrological category the spatial dissolved constituent distribution clearly revealed the difference between the two extremes the young rocks of the volcanic rift zone and the old tertiary terrain

transport and exchange of u series nuclides between suspended material dissolved load and colloids in rivers draining basaltic terrains this study presents uranium and thorium concentrations and activity ratios for all riverine phases bedload suspended load dissolved load and colloids from basaltic terrains in iceland and the azores small basaltic islands such as these are thought to account for 25 of co2 consumed by global silicate weathering and for 45 of the flux of suspended material to the oceans these data indicate that u and th in the dissolved and colloidal fractions are strongly controlled by ph and to a much lesser extent by levels of dissolved organic carbon which are low in these environments at high ph basalt glass dissolution is enhanced and secondary mineral formation e g fe oxyhydroxides and allophane is suppressed resulting in high dissolved u and low colloidal u and th indicating a direct chemical weathering control on elemental abundances when the dissolved 234u 238u activity ratio is 1 3 i e when physical weathering groundwater contribution or soil formation are high there is little isotope exchange between dissolved and colloidal fractions at lower activity ratios the dissolved load and colloids have indistinguishable activity ratios suggesting that when chemical weathering rates are high secondary clay formation is also high and colloids rapidly adsorb dissolved u many of the suspended sediment samples have 234u 238u activity ratios of 1 which suggests that uptake of u onto the suspended load is important identical 230th 232th in suspended dissolved and colloidal samples suggests that th like u is exchanged or sorbed rapidly between all riverine phases this particle reactivity combined with poorly constrained contributions from groundwater and hydrothermal water and short term variations in input to soils volcanic and glacial suggests that u series nuclides in riverine material from such basaltic terrains are unlikely to reflect steady state erosion processes

spatial and temporal variability of 234u 238u activity ratios in the shu river central asia this study presents the temporal and spatial variability of 234u 238u activity ratios in the shu river and provides interpretation to explain the downstream changes of uranium and the 234u 238u activity ratios in the study area the positive linear correlation r 2 0 98 p 0 001 between uranium concentration and specific electrical conductance is consistent with rock weathering and leaching as the major contributor of dissolved uranium in the studied area of the river the 234u 238u activity ratio ranged between 1 6 in the upper reaches of the river to 1 15 furthest downstream activity ratios at specific sampling points do not show significant seasonal variability

similarities between planktonic and larger foraminiferal evolutionary trends through paleogene paleoceanographic changes abstract the paleogene evolutionary records of planktonic foraminifera and larger benthic foraminifera show parallel patterns in development that may in part reflect changes in nutrient flux to surface waters following the terminal cretaceous extinctions faunas were dominated by a few cosmopolitan opportunistic species more specialized k strategists in both groups diversified during the paleocene dominating into the early eocene consistent with he globally mild climatic regime and probable limited rates of nutrient flux to surface waters high latitude cooling intensified in the middle eocene promoting diversification of less specialized taxa characteristic of cooler and deeper waters higher latitudes meridional upwelling zones and boundary currents geographic ranges of warm water taxa diminished and fragmented yet many species survived thus global diversities during the middle eocene were the highest in the cenozoic as cooling and increased rates of nutrient flux further intensified in the late eocene extinction rates of warm water planktonic and larger benthic species exceeded origination rates of cooler water and less specialized forms so diversity dropped to intermediate levels where it remained through the late eocene and oligocene previous observations that planktonic foraminiferal faunas dominated by warm water taxa are often replaced by cool water faunas even though oxygen isotopes only recorded relatively minor cooling can be reconciled by the explanation that the biotic communities responded to changes in trophic resources and euphotic habitats that accompany the temperature reduction as well as to temperature change itself

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

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

the application of uranium series disequilibrium concepts to sediment yield determination the determination of uranium series disequilibria in fluvial environments is proposed as a method of calculating catchment mass balances the technique is based on two main principles firstly 234u is more mobile than 238u especially during the early stages of weathering secondly uranium is far more mobile than either thorium or protactinium consequently teaching during weathering results in the loss of the uranium found in the fresh rock leaving the two immobile daughters behind the ratio of uranium carried by sediment to that dissolved us uw can therefore be determined from river water and sediment isotopic activity ratios fluxes of uranium can then be calculated from average concentrations in the water and the associated sediment from which a sediment yield can be inferred the witham catchment in lincolnshire has been used to test the proposed method a us uw ratio of between 5 and 7 is determined and a sediment yield of 2 51 2 12 tonnes yr 1 km 2 is proposed although some problems concerning environmental chemistry have arisen the validity of the approach is confirmed by the close correspondence between the results obtained and those inferred by earlier workers using more conventional methods

biochronology and paleoclimatic implications of middle eocene to oligocene planktic foraminiferal faunas abstract planktic foraminiferal assemblages have been analyzed quantitatively in six dsdp sites in the atlantic site 363 pacific sites 292 77b 277 and indian ocean sites 219 253 in order to determine the nature of the faunal turnover during middle eocene to oligocene time biostratigraphic ranges of taxa and abundance distributions of dominant species are presented and illustrate striking similarities in faunal assemblages of low latitude regions in the atlantic pacific and indian oceans a high resolution biochronology based on dominant faunal characteristics and 55 datum events permits correlation between all three oceans with a high degree of precision population studies provide a view of the global impact of the paleoclimatic and paleoceanographic changes occurring during middle eocene to oligocene time planktic foraminiferal assemblage changes indicate a general cooling trend between middle eocene to oligocene time consistent with previously published oxygen isotope data major faunal changes indicating cooling episodes occur however at discrete intervals in the middle eocene 44 43 ma p13 the middle late eocene boundary 41 40 ma p14 p15 the late eocene 39 38 ma p15 p16 the eocene oligocene boundary 37 36 ma p18 and the late oligocene 31 29 ma p20 p21 with the exception of the e 0 boundary faunal changes occur abruptly during short stratigraphic intervals and are characterized by major species extinctions and first appearances the eocene oligocene boundary cooling is marked primarily by increasing abundances of cool water species this suggests that the e 0 boundary cooling which marks a major event in the oxygen isotope record affected planktic faunas less than during other cooling episodes planktic foraminiferal faunas indicate that the e 0 boundary event is part of a continued cooling trend which began during the middle eocene two hiatus intervals are recognized in low and high latitude sections at the middle late eocene boundary and in the late eocene p15 p16 these hiatuses suggest that vigorous bottom water circulation began developing in the middle eocene consistent with the onset of the faunal cooling trend and well before the development of the psychrosphere at the e 0 boundary

atlantic eocene planktonic foraminiferal historical biogeography and paleohydrographic indices abstract analysis of a quantitative and synoptic data base of eocene atlantic planktonic foraminifera has illuminated many facets of foraminiferal faunal structure and composition reflective of bioprovince and useful for empirical establishment of ecologic and paleohydrographic indices tropical indigenes such as the morozovellids turborotaliids subquadrate acarininids and some globigerinathekids dissolve most rapidly along with juveniles of most species tropical faunas are high in diversity and dominance include oxygen minimum indices such as the biserial heterohelicids only in high productivity times such as the middle eocene are dominated by genera with high numbers of species and species consistently typical of warm water regions until the late eocene when faunas include a higher number of middle than lower latitude types truly tropical genera are replaced by subtropical eutrophic indicators such as the globigerinathekids and contract to the florida current region prior to their extinctions at the end of the middle eocene atlantic late paleogene tropical forms first appear in the gulf of mexico at the end of the middle eocene middle latitude faunas include high numbers of chiloguembelinids pseudohastigerinids small and biconvex morozovellids round and globigerinid form acarininids low spired subbotinids in the late middle eocene high spired subbotinids large and typical globigerinids in the late eocene these forms have intermediate dissolution susceptibilities middle latitude faunas are often high in diversity in midddle latitude frontal regions dominance is low even in warm intervals when tropical indigenes increase in number in middle latitude faunas especially in boundary currents low latitude species penetrate temperate areas also during cool eutrophic periods of vigorous circulation such as the late middle eocene typical of temperate slope faunas are high abundances of high spired subbotinids and small sized catapsydracids high latitude faunas are usually low in diversity except in the middle to late eocene when frontal regions were located in the southern labrador sea and over rockall bank typical forms are the low spired subbotinids until the late middle eocene globorotaloids catapsydracids tenuitellids and in the late eocene the biserial heterohelicids indigenous species are the most solution resistant and many are mesopelagic during warmings rare low latitude indices penetrate high latitudes subpolar faunas have greatest affinities with middle latitude faunas at these times

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

chemical evolution of rare earth elements fractionation between colloidal and solution phases of filtered river water abstract within the dissolved fraction of connecticut river water there is large scale fractionation of rare earth elements between colloidal and solution phases colloidal particles carry a large part of the dissolved ree pool filtration through filters with progressively smaller pore size 0 45 0 22 and 0 025 m results in filtrates with lower absolute concentrations of ree and more fractionated compositions with decreasing pore size the filtrates have shale normalized abundances which become systematically more depleted in the lree relative to the hree hence both the solution and colloidal phases are significantly fractionated with respect to the dissolved fraction these conclusions are consistent with previous studies of ree in rivers estuaries and soils and with surface solution speciation models colloids play an important role in the aquatic geochemistry of rare earth elements they are responsible for the fractionation of ree during the estuarine removal of ree the removal of suspended and colloidal particles from river water leaves the solution phase of river water with compositions of ree as evolved as those of surface seawater hence the evolution of the composition of ree in river water and seawater is significantly influenced by colloid formation during chemical weathering on the continents

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

major calcareous nannofossil and foraminiferal events between the middle eocene and early miocene abstract the more significant biostratigraphic events during the time interval from beginning middle eocene to beginning miocene with special emphasis on the eocene oligocene boundary are discussed the microfossils considered are calcareous nannofossils planktic foraminifera and smaller and larger benthic foraminifera areas taken into account include particularly the caribbean trinidad barbados dsdp south atlantic sections cape basin site 360 walvis ridge sites 362a 363 angola basin site 364 the equatorial north atlantic dsdp site 354 and the southern alps possagno in the larger foraminifera the treatment is somewhat different with selected families and genera being considered for their distribution in the eastern and western hemisphere

paleoceanography of the cretaceous tertiary boundary event inferences from stable isotopic and other data we report the results of new stable oxygen and carbon isotope analyses on carbonate fine fraction whole rock and benthic foraminifers caco3 and coarse fraction percentage determinations and trace element sr analyses on carbonate constituents across the cretaceous tertiary k t boundary in deep sea drilling project dsdp sites 47 2 356 384 and 577 and compare them with published results from k t boundary sections in other dsdp sites we used the trace element data and scanning electron microscope examination to evaluate possible diagenetic alteration and relative preservation of the samples analyzed in this study the 18o data when interpreted as isotopic paleotemperatures indicate relative stable surface water and deepwater temperatures in the late maestrichtian followed by somewhat fluctuating temperatures in the early paleocene however there is no indication of either a significant warming or cooling at or following the k t boundary several sites do exhibit somewhat heavier 18o values by about 0 5 across the boundary which might suggest a 2 3 c cooling at most however we interpret these somewhat heavier 18o values as reflecting slightly better preservation of 18o of carbonate constitutents in relatively clay rich intervals e g lower diagentic potential characteristic of the k t boundary the 13c values of carbonate fine fraction and planktonic foraminifers indicate a major negative excursion in surface water total dissolved carbon across the boundary the surface water and deepwater 13c values from benthic foraminifers combined with calculated decreases in carbonate accumulation rates at all sites in the earliest paleocene are consistent with a major decrease in productivity across the k t boundary the decrease in caco3 accumulation rates is due not to increased rates of dissolution but to decreased production in surface waters the low productivity episode lasted at least 1 m y beyond the k t boundary crisis suggesting that hypothesized catastrophic events alone such as impact of an apollo object are not the only explanation for the observed long term decrease in productivity there is also an indication in the 13c curves from several sites that the surface water 13c decrease began in the latest maestrichtian suggesting that the decrease in productivity may have been independent of a hypothesized impact event

the eocene oligocene boundary event in the deep sea analysis of middle eocene to early oligocene calcareous and siliceous microfossils shows gradual biotic changes with no massive extinction event across the eocene oligocene boundary biotic changes in the late paleogene appear to reflect changing paleoclimatic and paleoceanographic conditions and do not support suggestions of a catastrophic biotic event caused by a bolide impact at the eocenel oligocene boundary

a new explanation for extreme 234u238u disequilibria in a dolomitic aquifer high 234u238u activity ratios are found in the shallow groundwater of the phreatic transvaal dolomite aquifer the aquifer is uranium poor while the waters are oxygen rich and young tritium and 14c are used to show that the disequilibrium increases the longer the water resides in contact with the dolomite host the 228ra and 222rn isotopes were used as supporting evidence that ion exchange between the 238u series nuclides in the water and the carbonate wall rock is necessary in assisting in the fractionation process the wolkberg cave speleothems preserve a record of the uranium isotopic fractionations that evolved as water flowed through the aquifer extremely variable and elevated 234u238u ratios of 2 12 are characteristic individual caverns may exhibit very large 234u238u variability in their drip water and in derivative carbonate precipitates speleothems deeper chambers where water has spent a longer time in contact with the aquifer tend to exhibit a greater degree of uranium isotopic fractionation in their speleothems the recorded fractionation process has been an ongoing one from at least the middle late pleistocene to the present the speleothem study supports the contention that ion exchange processes that produce sufficient enrichment of uranium on carbonate can provide ideal conditions for generating uranium isotopic fractionation in the water of carbonate aquifers in the absence of redox changes and within a uranium poor environment

platforms of the nicaraguan rise examples of the sensitivity of carbonate sedimentation to excess trophic resources the nicaraguan rise is an active tectonic structure in the western caribbean carbonate accumulation on its platforms has not kept pace with relative holocene sea level rise despite a tropical location remote from terrigenous sedimentation trophic resources apparently exceed levels favoring coral reef development because sponge algal communities dominate the drowning western platforms in contrast to mixed coral algal benthos on pedro bank and well developed coral reefs along the north coast of jamaica concentrations of biotic pigments in sea surface waters show a corresponding west east gradient oceanic waters flowing over the western banks carry nearly twice as much biotic pigment as oceanic waters north of jamaica sources enriching the western caribbean are terrestrial runoff upwelling off northern south america and topographic upwelling over the nicaraguan rise that relatively modest levels of trophic resources can suppress coral reef development holds important implications for understanding carbonate platform drownings in the geologic record

uranium isotopes as proxies of the environmental history of the lake baikal watershed east siberia during the past 150 ka abstract a new experimental method for the determination of the isotopic composition of authigenic uranium in lake baikal siberia sediments has supplied a record of 234u 238u aut ratios during the past 150 ka with a resolution of ca 200 years reconstruction of the 234u 238u aut activity ratio as a proxy for lake water composition shows that the uranium isotope disequilibrium has not stayed constant throughout this period it varied greatly in response to regional climate the 234u 238u activity ratio in lake baikal paleowaters was inferred to be high during interglacial time 1 85 2 during mis 5 5 and the holocene 1 4 1 7 during mis 5 1 and 5 3 and dropped to 1 16 0 01 during glacial time the variability in the deduced 234u 238u ratios of lake baikal waters of the past may have been caused by the climatically modulated redistribution of contributions of riverine discharges from different provinces of the very large catchment of the lake aridity during ice ages was more pronounced in the south of eastern siberia and in northern mongolia relative to that in the northern regions of the lake baikal watershed the southern contribution of riverine input into the lake was essentially absent during glacial periods records of some elements ca k sr rb si al la th u th ciw from the bottom sediments of lake baikal during the last 0 5 myr with a resolution of 2 kyr have also been obtained coupling these data with records of weathering indices shows that not only riverine waters but also terrigenous material delivered into lake baikal from different regions of the very large watershed during interglacial and glacial times glacial erosion delivered fine siliciclastic material glacial milk mainly from the nearest mountain glaciers situated in the northwestern region of lake baikal while during warmer periods terrigenous material was sourced from the surrounding river valleys a conceptual model for the simulation of the fluvial discharge gradient between the northern and southern provinces of the lake baikal watershed is proposed and a first order simulation of past changes in the contribution of the selenga river to the lake water budget is given

pigment distribution in the caribbean sea observations from space abstract the caribbean is a semi enclosed tropical sea which is generally considered oligotrophic but that is influenced by nearly 20 of the annual discharge of the world s rivers amazon and orinoco rivers and by seasonal upwelling along the southern margin to investigate the role of these nutrient sources on the productivity of the region we mapped the distribution of pigments in the eastern caribbean east of 80 w using a series of coastal zone color scanner czcs images collected between november 1978 and december 1982 five additional images were examined for the period 1983 1986 the images revealed a seasonal cycle in the spatial structure of near surface pigment during january may there were high pigment concentrations 0 5 mg m 3 along the continental margin south of 14 n where upwelling occurred very little pigment 3 105 km2 this plume reached puerto rico around september october and drifted westward slowly losing its color signature we estimate that the discharge of the orinoco contributes 2 12 of the daily nitrogen requirements of the phytoplankton growing in the river plume and leads to the fixation of 7 29 105 tons of carbon per year the rest of the nitrogen demand appears to be met by nitrogen cycling the large scale 100 km pigment distribution patterns in the caribbean sea seem to be controlled by wind stress flux of water through the basin and river discharge westward advection of atlantic water probably dominates the flow during the first half of the year restricting the dispersal of blooms to the southern half of the caribbean while flushing the central and northern portions as the influx of atlantic water decreases in the second half of the year local ekman transport driven by the trade winds becomes dominant and surface waters drift northwestward throughout the basin the seasonal sequence of changes in pigment distribution patterns was consistent from year to year except in 1980 and 1984 when wind conditions in the caribbean were anomalous close scrutiny of the 4 years of czcs images did not reveal any evidence of large scale 300 km eastward flowing currents in the central caribbean this supports the view that previous observations of countercurrents were based on partial sampling of eddies of 100 250 km diameter

fluctuations in the trophic resource continuum a factor in global diversity cycles the trophic resource continuum trc in euphotic zones of the world s oceans is the spectrum of conditions from the richest runoff and upwelling areas to the most nutrient deficient subtropical seas that spectral range has likely varied through geologic history as more efficient phytoplankton taxa evolved as oceanic circulation rates changed and in response to oceanic mixing events reduced rates of oceanic turnover should produce regionally intensified eutrophy and oligotrophy that is trc expansion because oceanic waters as a whole are relatively nutrient rich increased rates of oceanic turnover should prevent extremely eutrophic and extremely oligotrophic conditions from developing causing trc contraction global biotic diversities in the oceans are strongly influenced by communities in oligotrophic environments nutrient deficient waters are more stable and more transparent than richer waters permitting higher degrees of specialization sparse nutrient supplies necessitate smaller phytoplankton and longer more complex food chains preservation potential of oligotrophic biotas is also greater because calcareous taxa are more prevalent and because calcium carbonate is less apt to be bioeroded or dissolved fluctuations in the trc should profoundly affect diversity of habitats within the euphotic zone of the oceans the evolutionary response to a trc expansion diversification would occur in a geologic time frame of millions of years while evolutionary responses to a trc contraction including extinction could occur in a biological time frame of generations a simple model indicates that a reduction in the trophic resource continuum from expansion during a major marine transgression down to modern levels could result in loss of 40 of the euphotic habitats how fluctuations in the trc control diversity of euphotic habitats in the oceans provides an hypothesis by which to interpret global taxonomic diversity cycles as well as taxonomically selective extinctions changes in species dominance and some morphologic trends

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

mobility and fluxes of major minor and trace metals during basalt weathering and groundwater transport at mt etna volcano sicily abstract the concentrations and fluxes of major minor and trace metals were determined in 53 samples of groundwaters from around mt etna in order to evaluate the conditions and extent of alkali basalt weathering by waters enriched in magma derived co 2 and the contribution of aqueous transport to the overall metal discharge of the volcano we show that gaseous input of magmatic volatile metals into the etnean aquifer is small or negligible being limited by cooling of the rising fluids basalt leaching by weakly acidic co 2 charged water is the overwhelming source of metals and appears to be more extensive in two sectors of the s sw paterno and e zafferana volcano flanks where out flowing groundwaters are the richest in metals and bicarbonate of magmatic origin thermodynamic modeling of the results allows to evaluate the relative mobility and chemical speciation of various elements during their partitioning between solid and liquid phases through the weathering process the facts that rock forming minerals and groundmass dissolve at different rates and secondary minerals are formed are taken into account at mt etna poorly mobile elements al th fe are preferentially retained in the solid residue of weathering while alkalis alkaline earth and oxo anion forming elements as se sb mo are more mobile and released to the aqueous system transition metals display an intermediate behavior and are strongly dependent on either the redox conditions mn cr v or solid surface related processes v zn cu the fluxes of metals discharged by the volcanic aquifer of etna range from 7 0 10 3 t a th to 7 3 10 4 t a na they are comparable in magnitude to the summit crater plume emissions for a series of elements na k ca mg u v li with lithophile affinity but are minor for volatile elements basalt weathering at mt etna also consumes about 2 1 10 5 t a of magma derived carbon dioxide equivalent to ca 7 of contemporaneous crater plume emissions the considerable transport of some metals in etna s aquifer reflects a particularly high chemical erosion rate evaluated at 2 3 10 5 t a enhanced by the initial acidity of magmatic co 2 rich groundwater

environmental and seasonal controls on riverine dissolved uranium in the hudson james and ungava bays region canada this study documents the spatiotemporal variability of riverine uranium contents and fluxes in rivers discharging into the hudson james and ungava bays hjub samples retrieved during a monitoring program of the koksoak great whale la grande and nelson rivers were analyzed for dissolved uranium concentration u and activity ratio 234u 238u field surveys conducted during baseflow and snowmelt in six other rivers of the hjub basin provided complementary data it is estimated that altogether the studied rivers export 3 4 105 mol year of u towards the hjub with a discharge weighted average 234u 238u of 1 27 two main factors appear to control seasonal fluctuations in dissolved u exports from hjub rivers snowmelt and anthropogenic flow control under natural hydrological regimes the dilution of u caused by snowmelt does not compensate for the associated increase in discharge and riverine u fluxes are intensified during springtime contrastingly the timing of riverine u exports is decoupled

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

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

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

lithium magnesium and uranium isotope behaviour in the estuarine environment of basaltic islands this study presents major and trace elements and uranium u lithium li and magnesium mg isotope data for dissolved and suspended particulate material from estuaries draining dominantly basaltic terrains in iceland borgarfjor ur and sao miguel povoacao in the azores archipelago the concentrations of dissolved sodium na calcium ca potassium k sulphate so4 mg and li and 7li 6li and 26mg 24mg isotope ratios vary directly as a function of the dissolved chloride concentration cl indicating that these species are non reactive in these estuaries however u appears to be affected either by colloid flocculation or the formation of fe oxyhydroxides in borgarfjor ur the major element composition of suspended particulate material in the estuary at borgarfjor ur shows that the detrital silicates delivered to the estuarine mixing zone are relatively unweathered accordingly the 26mg isotope composition of the suspended material is indistinguishable from that of the parent basalts however the 234u 238u activity ratios of the suspended material are significantly different from the parent basalt indicating rapid equilibration of the u isotopes between particles and seawater the li concentration and 7li isotope composition of the suspended load are also observed to increase with increasing cl consistent with ongoing weathering of detrital material and the formation of secondary minerals in seawater depending on the particle residence time in the estuary this process could remove as much as 15 25 of the global riverine input of li to the ocean

238u234u230th chronometry of femn crusts growth processes and recovery of thorium isotopic ratios of seawater abstract comparison of 234 u excess 238 u and 230 th 232 th activity ratios in oceanic fe mn deposits provides a method for assessing the closed system behaviour of 238u 234u 230th as well as variations in the initial uranium and thorium isotopic ratios of the precipitated metal oxides this approach is illustrated using a fe mn crust from lotab seamount marshall islands west equatorial pacific here we report uranium and thorium isotopic compositions in five subsamples from the surface of one large 5 cm diameter botryoid of this crust and from two depth profiles of the outermost rim of the same botryoid the decrease of 234 u excess 238 u and 230 th 232 th activity ratio with depth in the two profiles gives mean growth rates for the last 238u 212th 150 ka of 7 8 2 mm ma and 6 6 1 mm ma respectively all data points surface and core samples but one define a linear correlation in the ln 230 th 232 th ln 234 u excess 238 u diagram this correlation indicates that for all points the u th system remained closed after the fe mn layer precipitated and that the different samples possessed the same initial uranium and thorium isotope ratios furthermore these results show that the preserved surface of this fe mn crust may not be the present day growth surface and that the thorium and uranium isotopic ratios of seawater in west equatorial pacific have not changed during the past 150 ka the initial thorium activity ratio is estimated from the correlation obtained between ln 230 th 232 th ln 234 u excess 238 u

the relationship between riverine u series disequilibria and erosion rates in a basaltic terrain u series isotopes have been measured in the dissolved phase suspended load and bedload of the main rivers draining basaltic catchments in iceland for the dissolved phase 234u 238u and 238u 230th range between 1 08 and 2 2 and 7 4 and 516 respectively for the suspended load and bedload 234u 238u and 238u 230th range from 0 97 to 1 09 and from 0 93 to 1 05 respectively chemical erosion rates calculated from dissolved major elements range between 13 and 333 t km 2 yr 1 physical erosion rates have also been estimated from existing data and range between 21 and 4864 t km2 yr with an average of 519 t km 2 yr 1 u series disequilibria indicate that weathering in iceland operates at close to steady state conditions a model of continuous weathering indicates a maximum weathering timescale of 10 kyr with an average rate of uranium release into water of 1 6 10 4 yr 1 which is significant when compared to granitic terrains located at similar latitudes and to tropical basaltic terrains all river waters display 234u 238u greater than secular equilibrium consistent with the effects of alpha recoil the same dissolved phase 234u 238u exhibit a negative trend with physical erosion rates explained by the dominant effect of close to congruent chemical weathering of hyaloclastites in the younger basaltic terrains therefore chemical erosion rate and mineral weathering susceptibility play a major role in determining 234u 238u disequilibria in basaltic river waters comparison of global data for river basins in which weathering was recently strongly limited indicates a negative correlation between silicate weathering rates estimated with major elements and the age of weathering estimated with u series disequilibria this strongly suggests a key role of time and soil thickness on the chemical erosion of silicates

the distribution of 234u 238u activity ratios in river sediments abstract uranium u isotopes can be used to estimate the comminution age of sediments i e the time elapsed from sediment production on continents via weathering and physical erosion to deposition in the sedimentary record the calculation of this comminution age is based on measured 234u 238u activity ratios in river sediments and inferred time dependent recoil effect which leads to the preferential release of 234u from mineral lattices during erosion processes in this study we report on a large scale 234u 238u investigation of modern river sediments worldwide with the aim to determine the extent to which parameters such as grain size lithology weathering climate and geomorphology may influence the distribution of u isotopes in fine grained sediments our extensive dataset n 64 includes u isotopic measurements for many of the world s largest rivers but also rivers draining particular climatic and geological settings our results indicate that sediments collected from river basins draining mostly igneous metamorphic or volcanic rocks often display 234u 238u ratios 1 with clay size fractions

the eocene oligocene boundary and the psychrospheric event in the tethys as recorded by deep sea ostracods from the massignano global boundary stratotype section and point central italy abstract latest eocene earliest oligocene deep water ostracods from the massignano global boundary stratotype section and point gssp central italy were studied from a palaeoecological perspective to investigate the psychrospheric event in the tethys although quantitative analyses were hampered by the low incidence of fauna the high resolution sampling used in this study 148 samples distributed over a 23 m thick succession spanning 3 m y allowed the following inferences 1 overall features e g abundance diversity composition of the assemblages suggest a middle lower bathyal environment with no significant palaeobathymetrical changes 2 today a similar fauna notably characterised by the common occurrence of the genus agrenocythere would likely be encountered in upper psychrospheric conditions water masses beneath the permanent thermocline with a temperature range of 4 10 c 3 although no noticeable faunal turnover has been recognised throughout the succession minor faunal changes seem to occur in the first part of the section probable appearance of legitimocythere presequenta and to a lesser extent also across the eocene oligocene boundary the presumed appearance of l presequenta latest eocene correlates quite well in timing and possible significance with the faunal changes observed in other microfossil groups foraminifers and dinocysts this event is possibly linked to a cooling pulse which might have been caused by the arrival or increasing advection of cold bottom waters in the study area faunal evolution across the eocene oligocene boundary is thought to be consistent with an intensification of the cooling trend and an increase of primary productivity which fits fairly well with the 13c record relationships between the subtle ostracod faunal changes observed in the massignano gssp and the main late eocene early oligocene psychrospheric event can be only speculative nevertheless we found no evidence that precludes the possibility of interpreting the massignano ostracod pattern as a subdued local expression of this major event although speculative this is a reasonable hypothesis because the investigated area is situated in western tethys far from the main circulation of deep ocean waters

modelling two dimensional steady state groundwater flow and flow sensitivity to boundary conditions in blanket peat complexes this study used a two dimensional steady state finite element groundwater flow model to simulate groundwater flow in two newfoundland blanket peat complexes and to examine flow system sensitivity to changes in water table recharge and aquifer properties the modelling results were examined within the context of peat forming processes in the two complexes modelled flow compared favourably with observed flow the sensitivity analyses suggested that more highly decomposed bog peat along bog margins probably has had a positive impact on net peat accumulation within bog interiors peat with lower hydraulic conductivity along bog margins effectively impedes lateral drainage localizes water table drawdown to extreme bog margins and elevates water tables along bog interiors peat formation and elevated water tables in adjacent poor fens laggs currently rely on placic and ortstein horizons impeding vertical drainage and water flow inputs from adjacent bogs modest reductions in atmospheric recharge were found to govern bog flow system geometries in a way that would adversely affect paludification processes in adjacent fens laggs copyright 2004 john wiley sons ltd

atlantic eocene planktonic foraminiferal paleohydrographic indicators and stable isotope paleoceanography reconstruction of atlantic ocean vertical and meridional water characteristics is based on combined synoptic fossil census data stable isotope records and measurements of individual planktonic foraminiferal species correlations between planktonic foraminiferal indices and specific water types and or chemical conditions are used to trace seven stages in the history of atlantic circulation during eocene climatic changes 1 warm equable probably saline productive ocean of the early eocene characterized by lowest meridional and vertical thermal gradients and the maximal extent of tropical surface water 2 early middle eocene expansion of subtropical waters and faunas accompanying the first climatic cooling and eutrophication of equatorial surface waters 3 maximal partitioning of water types faunas and bioprovinces in middle eocene zone p11 accompanying maximum planktonic foraminiferal diversity accelerated near surface and deepwater cooling and intensified upwelling 4 latest middle eocene zone p14 maximal planktonic foraminiferal evolutionary overturn during accelerated cooling deep and surface water ventilation and transformation of tropical surface water habitat with the expansion of temperate water types and faunas this accompanied the reduction of meridional heat transport in boundary currents 5 late eocene bottom water and middle latitude cooling broadening of meridional temperature gradients and expanded oxygen minimum but faunal homogenization following the decreased import of mediterranean water ourflow 6 weakening and or shoaling of the nutricline an oxygen minimum and the thermocline preceding a diminution of primary productivity at the eocene oligocene boundary and 7 earliest oligocene low productivty ocean marked by diminished vertical thermal contrasts and homogeneous foraminiferal faunas dominated by small sized individuals the increased areal extent of upwelling with the outcropping of cooler waters over large geographic regions provides an important climatic forcing mechanism in the latest middle and late eocene

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

the role of nutrient availability in bioerosion consequences to carbonate buildups abstract zooxanthellate organisms which are among the major carbonate producers on coral reefs are highly adapted to nutrient deficient conditions and tend to be outcompeted by filamentous or fleshy algae if nutrients are abundant reef dwelling bioeroding organisms on the other hand seem to increase in abundance with increasing availability of nutrient and food resources maximum rates of calcium carbonate production in a reef system are comparable in magnitude to maximum rates of bioerosion the dynamic interplay between accretion destruction of coral reefs is therefore likely to be strongly influenced by nutrient availability nutrient availability may also influence development of carbonate facies in reef systems that develop in oligotrophic waters skeletal sands and framework should dominate carbonate buildups in systems that develop in mesotrophic waters enhanced bioerosion should reduce much of the skeletal material to carbonate muds increasing the prevalence of mud rich facies eutrophic conditions should result in bioeroded hardgrounds and carbonate depositional hiatuses when carbonate accumulation rates fail to equal or exceed rates of local relative sea level rise reefs drown bored and lithified pavements with crusts of ferromanganese oxides phosphates or glauconite often separate shallow reef from overlying deeper water deposits nondeposition bioerosion and evidence for low redox potentials at the sediment water interface all implicate excess nutrient availability as a factor in reef drowning some carbonate depositional hiatuses and bioerosional surfaces are local phenomena evidence of responses to local increases in nutrient availability resulting from submergence of soils runoff or topographic upwelling others appear to reflect regional or worldwide events because many carbonate producing organisms have life history strategies specialized to nutrient deficient conditions they are unable to compete when nutrients become plentiful events that triggered ocean turnover or sharp increases in the rate of deep ocean circulation would have increased sea surface nutrient availability worldwide such eutrophication could have caused widespread extinctions in reef communities because eutrophication promotes bioerosion details of the fossil records of those events are probably lost in bioerosional hiatuses

coupling uranium series and 10be cosmogenic radionuclides to evaluate steady state soil thickness in the betic cordillera abstract on earth the critical zone is the near surface environment where interactions between the atmosphere lithosphere hydrosphere and biosphere take place the development of the regolith mantle is controlled by the downwards propagation of the weathering front into the bedrock and denudation at the surface of the regolith by mass movements water and wind erosion when the removal of surface material is approximately balanced by the production of weatherable material at the bottom of the regolith profile the soil system is assumed to be in steady state although recent literature on chemical weathering often assumes that soils have a steady state thickness the concept has rarely been validated with empirical field data in this study we present and compare analytical data from two independent isotopic techniques in situ produced cosmogenic nuclides and u series disequilibria to constrain soil development under semi arid climatic conditions three soil profiles were sampled across the betic ranges at the ridge crest of zero order catchments with distinct topographic relief hillslope gradient and 10be derived denudation rate soil production rates determined based on u series isotopes 238u 234u 230th and 226ra are of the same order of magnitude as 10be derived denudation rates suggesting steady state soil thickness in two out of three sampling sites our results show the potential of a combined u series disequilibria and in situ 10be isotope approach to evaluate steady state soil thickness our study also illustrates the frontiers in applying u series disequilibria to track soil production in environments characterized by weak soil development

eolian contribution to soils on mount cameroon isotopic and trace element records abstract we determined sr nd and pb isotopic compositions and major and trace element compositions of soil samples recovered from three soil profiles developed on relatively young pyroclastic deposits less than 10 000 years old of the mount cameroon volcano the time elapsed since then is short compared with the half lives of rb sm u and th suggesting that radioactive decay can be neglected we therefore assumed that i these polyphase soils developed on isotopically homogenous substrates and ii any isotopic variation within such profiles cannot be due to selective dissolution of primary minerals with isotopic compositions different from that of bulk bedrock any sr nd or pb isotopic variation would therefore record an allochtonous input occurring either in a solid or dissolved state sr and nd isotope compositions change systematically with depth in the soil profile in particular 87 sr 86 sr ratios are far greater in the humic horizons than in the underlying horizons except in the ca9h soil profile although smaller than for sr isotope compositions 143 nd 144 nd ratios displayed an inverse relationship with a decrease towards the uppermost organic rich horizons these isotope shifts correlate with changes in sr and nd contents suggesting an allochtonous input characterized by significantly different isotope compositions and slightly lower sr contents but higher nd contents pb isotopic compositions and pb concentrations in the uppermost horizons were distinct from those of underlying horizons in the soil sequences since an anthropogenic contamination such as from leaded petrol cannot explain the pb shifts a natural source has to be invoked for pb as well as for sr and nd considering both the wind paths in west africa and the isotopic shifts registered in the uppermost horizons saharan dust appears to be the best candidate to explain such variations these inputs probably happened in winter when dry warm harmattan wind blows from the northeast a maximum of 8 of saharan dust accretion was calculated for the mount cameroon soils this corresponds to average dust deposition rates between 1 3 and 0 8 g cm 2 ka 1 values that are much higher than those found in hawaiian soils by kurtz et al kurtz a c derry l a chadwick o a 2001 accretion of asian dust to hawaiian soils isotopic elemental and mineral mass balances geochim cosmochim acta 65 1971 1983 and are probably related to shorter distance between dust source and deposit any elemental mass balance calculated in the upper organic rich horizons should be then corrected from allochtonous wind borne saharan dust before evaluating weathering linked chemical mobilities

weathering rates from top to bottom in a carbonate environment abstract this study investigates u series sr isotopes major and trace elements in a chalk aquifer system located in eastern france soil and rock samples were collected along depth profiles down to 45 m in four localities as an attempt to investigate the weathering processes in the soil the unsaturated zone and the saturated zone of the aquifer interstitial water was extracted from soils and rocks by a centrifugation technique u series offer a powerful tool to calculate weathering rates because the relative mobility of the u and th isotopes can be precisely measured and it does not require the determination of a reference state as in other approaches as expected the data show very large mobile element depletion in the soil with large 230 th excess relative to 238 u while the rocks show more limited but not insignificant mobile element depletion the u series data have been used to constrain weathering rates based on a 1 d reactive transport model weathering rates in the near surface are about 10 100 times faster than at depth however when integrated over the depth of the cores including the unsaturated and the saturated zones this underground weathering represents more than 30 of the total weathering flux assuming congruent dissolution of carbonates the 234 u 238 u ratios in interstitial water are consistent with solid samples showing 234 u depletion near the surface and an excess 234 u at depth a leaching experiment performed on chalk shows that the excess 234 u in natural waters percolating through carbonate rocks results both from preferential 234 u leaching and direct recoil in the interstitial water a new approach was used to derive the recoil ejection factor based on bet measurements and the fractal dimension of chalk surface consideration of preferential leaching and recoil allows a more accurate modeling of weathering rates

paleogene calcareous nannoplankton biostratigraphy of northwestern europe abstract the classic paleogene stages thanetian cuisian lutetian bartonian ludian and stampian defined in the epicontinental deposits of the anglo paris basin s are placed within a standard biostratigraphic framework based on an analysis of their calcareous nannoplankton floras relatively precise biostratigraphic correlations can be made with some chronostratigraphic units e g lutetian while biostratigraphic resolution of others e g ludian is limited important hiatuses are recognized between certain chronostratigraphic units only the base of the lutetian late np14 and bartonian mid np16 stages can be precisely determined in terms of calcareous nannoplankton zones with the recent study of the magnetic polarity history of the paleogene of southern england and recent advances in magnetobiostratigraphic correlations in deep sea cores it is possible to interpret the paleogene history of the anglo paris basin s in a synoptic global framework in which paleomagnetic stratigraphy provides the chronologic and eustatic variations the graphic units of northwestern europe within rather than at the boundaries of i e at dynamic element redefinition of the boundaries of the standard paleogene chronostratigraphic unconformities eustatically controlled depositional cycles would result in more precise correlations in terms of standard calcareous nannoplankton biostratigraphy

234u 238u in a boreal stream network relationship to hydrological events groundwater and scale uranium isotopes u 234 u 238 were measured in eight well studied boreal streams of different sizes and characters and in seven deep groundwater wells up to 11m deep adjacent to these streams t

rey th u solute dynamics in the critical zone combined influence of chemical weathering atmospheric deposit leaching and vegetation cycling mule hole watershed south india the source and proportion of rey th and u exported by groundwater and by the ephemeral stream along with the elemental proportions passing through vegetation have been assessed in the sub humid tropical forested czo of mule hole southern india the study relies on a pluri annual hydro geochemical monitoring combined with a hydrological model the significant difference between the soil input si and output so solute fluxes mmol km2 yr of lree si so 13250 1500 hree 1930 235 th 64 12 and u 63 25 indicates a strong uptake by roots carried by canopy and forest floor processes the contribution of atmospheric dust leaching can reach about 60 of lree and 80 of hree at the watershed scale the u solute flux exported by groundwater 180 mmol km2 yr mainly originates from the breakdown of primary u bearing accessory minerals and dominates by a factor of 25 the stream flux the precipitation of authigenic u bearing phases and adsorption onto fe oxides and oxyhydroxides plays a significant role for limiting the u mobility in the groundwater the plagioclase chemical weathering is efficiently traced by the positive eu anomaly the very low rey to nil th contents are explained by the precipitation of authigenic phases in the stream flow dominated by the overland flow 87 of the yearly stream flow the solute exports in mmol km2 yr of rey 1080 for lree and 160 for hree and of th 14 dominate those by groundwater their mobility is enhanced by chelation with organic ligands produced by forest floor and canopy processes

erosion timescales derived from u decay series measurements in rivers the relative importance of the factors influencing weathering of continental rocks has been a topic of debate for the last few decades the principal reasons are the lack of reliable proxies for chemical weathering and the difficulty in constraining actual physical denudation rates in this study 234u 238u 230th 238u and 226ra 238u were measured by tims and by mc icp ms in the dissolved and suspended loads of rivers from the mackenzie basin northwest territories canada the data show a complementary nature between 234u 238u 230th 238u in the dissolved and suspended loads while 226ra is characterized by a more complex behavior modeling of fractionation of u series nuclides in the particulate matter and the corresponding dissolved phase permits us to constrain the duration of chemical erosion for the suspended load currently sampled in the watershed 9 28 10 ka as well as the rates of release of u series nuclides the results also imply significant recent changes of chemical erosion rates and underline the impact of the last glaciation on current continental fluxes of northern latitude rivers such as the mackenzie river

isotopic and distributional evidence of a planktonic habit for the foraminiferal genusstreptochilus bro nnimann and resig 1971 abstract oxygen and carbon isotope analyses show that the biserial foraminiferal genusstreptochilus which was originally described from pelagic sediments on the eauripik rise and ontong java plateau lived deep in the upper water column within the oxygen minimum layer the species ofstreptochilus average from 4 to 19 of the foraminiferal assemblages in which benthic forms compose less than 1 or 2 specimens ofstreptochilus are selectively dissolved when in contact with the bottom water mass their rapid evolutionary turnover of less than a few million years and their wide areal distribution in the equatorial indo pacific are indicative of planktonic foraminifera aside from usefulness of the species ofstreptochilus as stratigraphic indices these neogene biserial planktonic foraminifera are potential indices of paleoceanographic stratification

uranium isotopes as tracers of groundwater evolution in the complexe terminal aquifer of southern tunisia abstract the complexe terminal ct multi layer aquifer is formed by neogene paleogene sand deposits upper senonian campanian maastrichtian limestones and turonian carbonates the chemical composition and isotopes of carbon and uranium were investigated in groundwater sampled from the main hydrogeological units of the ct aquifer in southern tunisia we paid special attention to the variability of uranium contents and isotopes ratio 234u 238u to provide a better understanding of the evolution of the groundwater system uranium concentrations range from 1 5 to 19 5 ppb typical of oxic or mildly reducing conditions in groundwaters the lowest concentrations are found southeast of the study area where active recharge is supposed to take place when looking at the isotope composition it appears that all the samples including those from carbonate levels are in radioactive disequilibrium with significant 234u excess a clear cut distinction is observed between turonian and senonian carbonate aquifers on the one hand with 234u 238u activity ratios between 1 1 and 1 8 and the sandy aquifer on the other hand showing higher ratios from 1 8 to 3 2 the distribution of uranium in this complex aquifer system seems to be in agreement with the lithological variability and are ultimately a function of a number of physical and chemical factors including the uranium content of the hosting geological formation water rock interaction and mixing between waters having different isotopic signatures significant relationships also appear when comparing the uranium distribution with the major ions composition it is noticeable that uranium is better correlated with sulfate calcium and magnesium than with other major ions as chloride or bicarbonate the 14c activities and 13c values of dic cover a wide range of values from 1 1 pmc to 30 2 pmc and from 3 6 to 10 7 respectively 14c model ages estimated by the fontes and garnier model are all younger than 22 ka and indicate that the recharge of ct groundwater occurred mainly during the end of the last glacial and throughout the holocene

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

control on 234u 238u in lake water a study in the dry valleys of antarctica abstract the 234 u 238 u ratio in surface waters is generally higher than secular equilibrium due to nuclide recoil during alpha decay of 238 u the size of the deviation from secular equilibrium contains information about the environment in which the water is found this potential tool for environmental reconstruction has previously been studied in rivers groundwater and sediment pore water here we conduct a first assessment of the controls on 234 u 238 u in lakewaters thirty three waters from glacial melt streams and lakes of the mcmurdo dry valleys antarctica were analysed for u concentration and isotope ratio glacial melt has a low u concentration and a 234 u 238 u identical to seawater suggesting that u in antarctic ice is largely sourced from sea salt aerosols stream waters have higher u concentration 0 009 to 1 282 ppb and 234 u 238 u 1 280 to 1 832 due to chemical weathering of sediment in stream channels and 234 u recoil from this sediment average 234 u 238 u is 1 502 close to the average of observations from other surface waters worldwide the absence of groundwaters in the dry valleys indicates that reasonably high 234 u 238 u ratios do not require groundwater sources of u so care should be taken before using high 234 u 238 u as an indicator of groundwater inputs to stream waters lakewaters have u concentrations ranging from 0 027 to 46 ppb i e up to 14 times the seawater concentration and 234 u 238 u from 1 05 to 4 50 young lakes have 234 u 238 u which reflects the sources of u in one case lake joyce a 234 u 238 u lower than seawater may suggest u sourced from melting of old ice in which 234 u excess has partially decayed in older lakes 234 u 238 u is significantly higher than that in the inputs due to addition of recoil 234 u from sediments underlying the lake the size of the deviation from secular equilibrium can only be explained however if recoil from a large area of sediment is considered this is reasonable for the two lakes with particularly high 234 u 238 u bonney vanda which are both relicts of much larger lakes present during the last glacial period on the basis of this study the addition of recoil 234 u to lake water is expected to be a general feature and to cause a noticeable increase in 234 u 238 u for lakes with a u residence time of more than a few thousand years

chemical weathering in the drainage basin of a tropical watershed nsimi zoetele site cameroon comparison between organic poor and organic rich waters abstract this study deals with the weathering processes operating at the scale of a small catchment nsimi zoetele cameroon and is focused on the role of organic colloids on mineral weathering and transport of elements in natural waters samples of river spring and groundwaters from nsimi zoetele were filtered through membranes of decreasing pore size 0 22 m 0 025 m or 300 000 da 5000 da to separate colloidal fractions from the truly dissolved one major and trace elements and dissolved organic carbon doc were analysed in each fraction two kinds of waters can be distinguished in the catchment clear and coloured waters clear waters exhibit low concentrations of major and trace elements and doc elements are carried in these solutions in a true dissolved form except al and rare earth elements rees by contrast the higher abundances of al fe and trace elements in coloured waters are controlled by the colloidal fraction thermodynamic equilibrium calculations show that clear waters are in equilibrium with kaolinite and iron oxi hydroxide which are major minerals in the weathered soil for coloured waters the aqueous speciation of ca mg cu fe al la and th was calculated taking into account the complexes with humic acids speciation calculations for cu fe al la th show a strong complexation with humic acids in good agreement with the results of the filtration experiments by contrast although filtration experiments show a strong control of major cations by organic matter for example 75 for ca speciation calculations reveal that their complexes with humic ligands do not exceed a few percent of total dissolved elements this discrepancy is explained as an artefact induced by the organic colloids and occurring during the filtration procedure finally both filtration experiments and speciation calculations show that organic matter plays an important role in natural doc rich waters organic acids increase significantly the dissolution rates of silicates and oxi hydroxides and thus the amounts of solutes and of complexed elements leaving the catchment

uranium series isotopes in colloids and suspended sediments timescale for sediment production and transport in the murray darling river system abstract we have measured 238u 234u 230th radioactive disequilibria in five size fractions of colloids and suspended sediments for four rivers from the murray darling river basin se australia continuous compositional trends of composition are observed for 234u 238u and 230th 238u activity ratios over the range of size fractions studied they are explained by the variable contribution of two components detrital alumino silicates and organic matter using relationships between activity ratios and the loss on ignition it is possible to estimate the u series isotopic composition of both detrital and organic end members which provide the best estimate for the composition of the true detrital phase i e controlled only by the removal of elements through weathering and the true dissolved phase i e colloid free respectively when performing a single filtration at 0 2 m it appears that size fractions and

fluxes of high versus low temperature water rock interactions in aerial volcanic areas example from the kamchatka peninsula russia abstract volcanic areas play a key role in the input of elements into the ocean and in the regulation of the geological carbon cycle the aim of this study is to investigate the budget of silicate weathering in an active volcanic area we compared the fluxes of the two major weathering regimes occurring at low temperature in soils and at high temperature in the active volcanic arc of kamchatka respectively the volcanic activity by inducing geothermal circulation and releasing gases to the surface produces extreme conditions in which intense water rock interactions occur and may have a strong impact on the weathering budgets our results show that the chemical composition of the kamchatka river water is controlled by surface low temperature weathering atmospheric input and in some limited cases strongly imprinted by high temperature water rock reactions we have determined the contribution of each source and calculated the rates of co 2 consumption and chemical weathering resulting from low and high temperature water rock interactions the weathering rates between 7 and 13 7 t km 2 yr for cations only and atmospheric co 2 consumption rates 0 33 0 46 10 6 mol km 2 yr for kamchatka river due to rock weathering in soils low temperature are entirely consistent with the previously published global weathering laws relating weathering rates of basalts with runoff and temperature in the kamchatka river co 2 consumption derived from hydrothermal activity represents about 11 of the total hco 3 flux exported by the river the high temperature weathering process explains 25 of the total cationic weathering rate in the kamchatka river although in the rivers non affected by hydrothermal activity the main weathering agent is carbonic acid reflected in the abundance of hco 3 in rivers in the region most impacted by hydrothermalism the protons responsible for minerals dissolution are provided not only by carbonic acid but also by sulphuric and hydrochloric acid a clear increase of weathering rates in rivers impacted by sulphuric acid can be observed in the kamchatka river 19 of cations are released by hydrothermal acids or the oxidative weathering of sulphur minerals our results emphasise the important impact of both low and high temperature weathering of volcanic rocks on global weathering fluxes to the ocean our results also show that besides carbonic acid derived from atmospheric co 2 hydrochloric acid and especially sulphuric acid are important weathering agents clearly sulphuric acid with hydrothermal activity are key parameters that cause first order increases of the chemical weathering rates in volcanic areas in these areas accurate determination of weathering budgets in volcanic area will require to better quantify sulphuric acid impact

u series disequilibria in suspended river sediments and implication for sediment transfer time in alluvial plains the case of the himalayan rivers 238u 234u 230th radioactive disequilibria were analyzed in suspended sediments collected at different depths from the ganges river and one of its main tributaries the narayani gandak river results associated with bedload sediment data suggest that uranium series u series disequilibria in river sediments of the ganges basin vary with grain size and sampling location the range of observed u series disequilibria is explained by a mixing model between a coarse grained sediment end member represented by bedload and bank sediments and a fine grained end member that both originate from himalaya but undergo different transfer histories within the plain the coarse grained sediment end member transits slowly i e several 100 s ky in the plain whereas the fine grained sediment end member is transferred much faster 20 25 ky as indicated by the absence of significant variations in th isotope composition of the fine grained sediment end members these results show that u series isotopes can be used to quantify the various transfer times of river sediments of different sizes and infer that there can be an order of magnitude of difference or more between the transfer time of suspended and bedload sediments this underlines that a good knowledge of the proportion of suspended vs bedload sediments transported in the river is required to accurately assess how fast erosion products are transferred in a catchment and how fast a catchment is likely to respond to external forcing factors

influence of eolian deposition and rainfall amounts on the u isotopic composition of soil water and soil minerals 230th u dating of secondary deposits such as speleothems and pedogenic carbonate and opal provides information about the original 234u 238u composition of the waters the minerals precipitated from as a result these types of deposits often display temporal variations in initial 234u 238u that could reflect environmental variability past variations in soil water 234u 238u may reflect changes in the flux of water through the soil weathering rates or dust inputs in order to evaluate these potential influences we analyzed modern soil water chemistry and u isotopic compositions of fluids and solids from three soil sequences in nevada modern soil pore waters from diamond valley newark valley and fish lake valley nevada show significant 234u 238u differences between sites as a result of differing soil parent material newark valley pore waters are more heavily influenced by carbonate weathering and display much more enriched 234u 238u values than diamond and fish lake valley pore waters which are dominated by silicate weathering newark valley and diamond valley although located very near to each other have significantly different pore water 234u 238u values suggesting that deposition of distantly sourced dust does not exert a dominant influence on pore water 234u 238u at these sites pore water 234u 238u values also vary systematically along a rainfall gradient at fish lake valley where sites with lower rainfall display higher soil water 234u 238u values the results of this modern soil water chemistry study were used to parameterize two models that investigate the relative influence of dust content recoil and weathering on pore water 234u 238u in the upper layer of the soil and at depth under changing infiltration rates these models suggest that while the composition of soluble dust entering a soil profile is an important consideration the pore water 234u 238u at depth and thus the initial 234u 238u of minerals that precipitate from pore waters should be highly sensitive to changes in the infiltration flux through the soils as infiltration flux is closely tied to rainfall the initial 234u 238u of soil minerals at these sites should provide information about past rainfall variability

low productivity and slow deep water circulation in mid cretaceous oceans paleofertility estimates are derived from organic carbon accumulation rates determined in nonbioturbated mid cretaceous deep sea deposits using organic carbon preservation factors observed in laminated sediments from anoxic holocene environments the estimated mid cretaceous primary production rates are as much as an order of magnitude lower than those measured in today s oceans an evaluation of dissolved oxygen budgets using a simple oceanic circulation model indicates very low deep water renewal rates in mid cretaceous oceans 28 references 2 tables 4 figures

chemical mobilizations in laterites evidence from trace elements and 238u 234u 230th disequilibria geochemical and mineralogical investigations including measurements of major and trace elements sr isotope ratios and 238u 234u 230th activity ratios were made on an old african laterite to reconstruct its formation steps and assess recent chemical mobilization the present data support a scenario of discontinuous formation for the laterite with different bedrock weathering conditions during the formation of each unit rather than a scenario of continuous formation absolute accumulation of fe u and lanthanides in the uppermost ferruginous unit suggests an autochthonous origin of this iron cap by leaching of an older overlying profile present chemical distributions of lanthanides as well as of rb k ba and sr within the profile cannot be linked to the mineralogical distribution of both relictual primary and authigenic secondary phases complementary lanthanide patterns indicate that these elements were primarily accumulated in the uppermost ferruginous unit before further remobilization and accumulation in the underlying horizons these redistribution processes may be related to the chemical instability of the ferruginous cap the 238u 234u 230th disequilibria indicate that recent u mobilization occurs in the whole profile and that as for lanthanides there is a vertical redistribution of u from the uppermost ferruginous unit to the underlying horizons moreover these data show that both u losses and gains exist at each level of the profile a simple modeling of this double u mobilization process is proposed to interpret the 238u 234u 230th data differences in the mobilization and fractionation intensities of the u input and removal processes can account for the two evolution trends which distinguish the ferruginous unit from the underlying ones furthermore on the basis of this modeling the profile appears to be in a transient state because of recent changes in the u mobilization conditions which could correspond to major pleistocene climatic variations

the distribution of rare earth elements in groundwaters assessing the role of source rock composition redox changes and colloidal particles rare earth element ree dissolved organic carbon doc and trace element al mn fe sr ba u and th concentrations were measured in fourteen well water samples 0 22 m and one spring located along two transects set up in a catchment from western europe kervidy coet dan catchment france previous hydrological and hydrochemical no3 so42 investigations demonstrated that three chemically and spatially distinct groundwater types are present in this catchment which is fully confirmed by the ree and doc results these include i a shallow organic rich groundwater 4 4 doc 34 6 mg l from the wetland areas close to the river network this first groundwater type characterized by the development of temporary reducing conditions records high and variable ree contents 2 ree 16 ppb and displays slight or no negative ce anomaly ce ce 0 8 1 05 ii a shallow organic poor doc 3 mg l no3 rich groundwater type 86 8 no3 155 mg l located in the weathered schists below the hillslope domains this second type corresponds to recently recharged oxidized water and displays also high and variable ree concentrations 2 ppb ree 15 ppb but distinguish from the former by the occurrence of very strong negative ce anomalies ce ce 0 05 0 10 finally iii a deep organic poor doc 1 mg l nitrate poor no3 close to 0 2 mg l detection limit groundwater this third type corresponds to reduced water flowing into the deep fresh schists and yields low to very low ree contents ree 0 15 ppb as well as slight negative ce anomaly ce ce 0 8 to 0 9 temporal ree concentration variations were assessed using samples regularly collected over a six month period results show that the spatially distributed ce anomaly and ree pattern signatures are preserved throughout the studied period by contrast ree concentrations are quite variable through time especially in the wetland waters where the ree concentrations are seen to vary in phase with both redox changes and doc fe u and th content variations three ree rich water samples one doc rich and two doc poor were also filtered through membranes of decreasing pore size 100 000 d 30 000 d 5 000 d the results show that between about 40 to 65 of the ree present in the shallow doc poor groundwater samples are controlled by the colloidal fraction which is likely to consist in these inorganic waters of a mixture of mineral phases in the wetland groundwaters the fraction of ree controlled by microparticles is higher than 65 which confirms the predominant role of organic colloids as major ree carriers in wetland waters using the above data set in conjunction with analyses of soil samples we show that the deep ce anomalies found in the upper non organic part of the aquifer are probably not source rock inherited features most likely these anomalies arise from the oxidative precipitation of ce the very low ree content displayed by waters flooding the deep fresh schists is interpreted as due to the combined effects of i ph variation ii secondary sulfate mineral precipitation and iii the trapping of colloids borne ree by the aquifer rock pores data from wetland groundwaters show that the ree fe u and th budgets of these waters are mainly controlled by seasonal changes in redox conditions and organic matter content however unlike organic poor waters it appears difficult to relate the ce behaviour in these organic rich waters solely to redox conditions it is likely that the complexation of ce by organic colloids in the organic rich waters may mask redox changes by inhibiting the development of negative ce anomalies

isotopic tracing of the dissolved u fluxes of himalayan rivers implications for present and past u budgets of the ganges brahmaputra system u activity ratios have been measured in the dissolved loads of selected rivers from the himalayan range in central nepal and from the bangladesh as well as in some rain waters a few european and asian rivers have also been analyzed for their u activity ratios the data confirm the negligible effect of rainwater on the budget of dissolved u in river waters the results also indicate that rivers on each himalayan structural unit have homogeneous and specific u isotope compositions i 234u 238u activity ratios slightly lower than unity in the dissolved load of the streams draining the tethyan sedimentary series tss ii values slightly higher than unity for waters from the high himalaya crystalline hhc and the lesser himalaya lh iii systematically higher 234u 238u activity ratios for waters from the siwaliks thus u activity ratios in association with sr isotopic ratios can be used to trace the sources of dissolved fluxes carried by these rivers coupling of u with sr isotope data shows 1 that the u carried by the dissolved load of the himalayan rivers mainly originates from u rich lithologies of the tss in the northern formations of the tibetan plateau and 2 that the elemental u and sr fluxes carried by the himalayan rivers at the outflow of the highlands are fairly homogeneous at the scale of the himalayan chain rivers flowing on the indian plain define a different trend from that of the himalayan rivers in the u sr isotopic diagram indicating the contribution of a specific floodplain component to the u and sr budgets of the ganges and the brahmaputra the influence of this component remains limited to 10 to 15 percent for the u flux but can contribute 35 to 55 of the sr flux the variations of the sr and u fluxes of the ganges brahmaputra river system in response to climatic variations have been estimated by assuming a temporary cut off of the chemical fluxes from high altitude terrains during glacial episodes this scenario would significantly decrease the dissolved u flux of the ganges brahmaputra river system and increase its u activity ratio such a climatic dependence of the himalayan u flux could induce a periodic variation of the mean u activity ratio of the world rivers on glacial interglacial timescales

deep sea benthonic foraminiferal faunal turnover near the eocene oligocene boundary abstract eocene oligocene deep sea benthonic foraminifera in d s d p site 277 in the southwest pacific have been analyzed to determine the benthonic foraminiferal response to the development of the psychrosphere near the eocene oligocene boundary biostratigraphic ranges of 41 taxa show that 23 taxa are found throughout the late eocene to early oligocene sequence while 18 taxa exhibit first or last occurrences comparison of the faunal changes in site 277 with a benthonic foraminiferal oxygen isotope record shows that the development of the psychrosphere did not have a profound effect upon the benthonic foraminifera and the overall faunal change preceding and subsequent to the bottom water circulation event occurred gradually the inferred water mass event affected the relative abundance of one species epistominella umbonifera the lack of major faunal changes at the eocene oligocene boundary in site 277 probably reflects either wide environmental tolerances of the benthonic foraminifera or a bottom water temperature change less than 3 c examination of previously published benthonic foraminiferal biostratigraphic data from d s d p sites 167 171 357 360 363 and 400a and deep sea ostracode data from d s d p leg 3 show faunal changes occurred during discrete intervals in the middle eocene early oligocene the faunal patterns from these data and from site 277 show that the eocene oligocene cooling event did not cause rapid catastrophic changes of the benthonic faunas of the open ocean although significant faunal changes are associated with the water mass event in sites 167 171 and 400a the benthonic faunal changes in middle eocene early oligocene time are consistent with the gradual decrease of inferred bottom water temperatures based on previously published oxygen isotopic data the 18 o eocene oligocene enrichment of 0 76 is a major event in the southern ocean oxygen isotopic record but is considerably less in magnitude than the 1 75 2 00 change that occurred gradually from mid early eocene to the eocene oligocene boundary the benthonic foraminiferal and isotopic data indicate that bottom water circulation may have developed during the middle eocene to early oligocene interval with the 3 c bottom water cooling near the eocene oligocene boundary representing part of this development

processes controlling 234u and 238u isotope fractionation and helium in the groundwater of the st lawrence lowlands quebec the potential role of natural rock fracturing abstract the goal of this study is to explain the origin of 234 u 238 u fractionation in groundwater from sedimentary aquifers of the st lawrence lowlands quebec canada and its relationship with 3 he 4 he ratios to gain insight regarding the evolution of groundwater in the region 234 u 238 u activity ratios or 234 u 238 u act were measured in 23 groundwater samples from shallow quaternary unconsolidated sediments and from the deeper fractured regional aquifer of the becancour river watershed the lowest 234 u 238 u act 1 14 0 01 was measured in ca hco 3 type freshwater from the quaternary shallower aquifer where bulk dissolution of the carbonate allows u to migrate into water with little 234 u 238 u isotopic fractionation the 234 u 238 u act increases to 6 07 0 14 in na hco 3 cl type groundwater preferential migration of 234 u into water by recoil is the underlying process responsible for this isotopic fractionation an inverse relationship between 234 u 238 u act and 3 he 4 he ratios has been observed this relationship reflects the mixing of newly recharged water with 234 u 238 u act close to the secular equilibrium and containing atmospheric tritiogenic helium and mildly mineralized older water 14 c ages of 6 6 kyrs with 234 u 238 u act of 6 07 and large amounts of radiogenic 4 he in excess of the steady state amount produced in situ the simultaneous fractionation of 234 u 238 u act and the addition of excess 4 he could be locally controlled by stress induced rock fracturing this process increases the surface area of the aquifer matrix exposed to pore water from which produced 4 he and 234 u can be released by recoil and diffusion this process would also facilitate the release of radiogenic helium at rates greater than those supported by steady state u th production in the rock consequently sources internal to the aquifers could cause the radiogenic 4 he excesses measured in groundwater

neritic southern extratropical foraminifera and the terminal eocene event abstract if the terminal eocene event tee records a major bolide impact or other extraterrestrial happening then there ought to be disruption of benthonic foraminiferal communities especially in rather shallow neritic environments we record the arrivals and departures of 180 species in a composite succession through the later middle eocene late eocene and earliest oligocene in southern australia the rate of new arrivals increases at each of several transgressions each of which also marks a climatic amelioration the sharpest increase in rate of departure is found at a regional regression within the latest eocene there is no evidence of major disruption of the fauna at the end of the eocene the tee on this data was not extraterrestrial in origin and was hardly cataclysmic the study suggests instead that the origins of late eocene biotic change should be sought through earthly configurations of climate and sea level

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

chemical and physical weathering in south patagonian rivers a combined sr u be isotope approach abstract we investigated physical and chemical weathering in south patagonia encompassing both the tectonically active andes with alpine glaciers and the quiescent seaboard plain with arid climate chemical denudation rates determined from riverine dissolved major elements were 0 07 5 10 5 tons year 1 and the long term rates of co 2 consumption by alkaline earth silicates were 0 03 0 5 10 5 mol km 2 year 1 commensurate with the average global co 2 consumption rate 0 25 10 5 mol km 2 year 1 unradiogenic strontium isotope ratios indicated that the source of silicate weathering was volcanic sedimentary cover basin average total denudation rates based on 10 be measured in active streambed sediments ranged from 0 009 to 0 6 mm year 1 uranium series disequilibria suggested that there is significant redistribution of nuclides between the dissolved and suspended material when applying the simultaneous gain and loss model to the u series data of the suspended load sediment residence times of 10 150 ky were obtained comparison of the dissolved load based chemical denudation rate and 10 be based total denudation rate revealed that some basins are dominated by chemical and some by physical denudation

uranium thorium chronometry of weathering rinds rock alteration rate and paleo isotopic record of weathering fluids abstract the potential of 238u 234u 230th chronometry for constraining the formation rate of weathering rinds developed on fresh rocks is assessed by analyzing a weathering rind on a basaltic clast from a 125 kyr old costa rican alluvial terrace eighteen subsamples were collected from one section of the clast by drilling cores 4 mm in diameter and 5 mm depth along two transects straddling the core rind boundary variations of major and trace element concentrations along the two transects point out a intense loss of alkaline and alkaline earth elements b conservative behaviour of elements such as zr hf and th and c external input of u into the rind without any evidence of u loss during basalt weathering in addition variations in u concentrations along the transects show that the main u th fractionation process associated with the weathering of the basaltic clast is an external input of u without addition nor loss of th in the basalt rind transition zone and that once deposited u is immobile in the weathering rind in the frame of this interpretation scheme a weathering rate of 0 5 0 2 mm kyr can be calculated for the studied clast which is consistent with geological and isotopic evidence constraining the depositional ages of the terraces in addition the variations in the 234u 238u ratio along the analysed transects as well as the increase in sr isotopic ratios within the weathering rind are best explained by temporal variation of the u activity ratios and sr isotope ratios of the soil solutions brought into the rind this work highlights how well detailed u th chronological studies of weathering rinds can 1 constrain the formation rates of weathering systems and 2 record the time variation of isotopic composition of weathering fluids

paleoclimatic analyses of middle eocene through oligocene planktic foraminiferal faunas quantitative faunal analyses and oxygen isotope ranking of individual planktic foraminiferal species from deep sea sequences of three oceans are used to make paleoceanographic and paleoclimatic inferences species grouped into surface intermediate and deep water categories based on 18o values provide evidence of major changes in water mass stratification and individual species abundances indicate low frequency cool warm oscillations these data suggest that relatively stable climatic phases with minor cool warm oscillations of 0 5 m y frequency are separated by rapid cooling events during middle eocene to early oligocene time five major climatic phases are evident in the water mass stratification between middle eocene through oligocene time phase changes occur at p14 p15 p15 p16 p20 p21 and p21 p22 zone boundaries and are marked by major faunal turnovers rapid cooling in the isotope record hiatuses and changes in the eustatic sea level a general cooling trend between middle eocene to early late oligocene is indicated by the successive replacement of warm middle eocene surface water species by cooler late eocene intermediate water species and still cooler oligocene intermediate and deep water species increased water mass stratification in the latest eocene p17 indicated by the coexistence of surface intermediate and deep dwelling species groups suggest that increased thermal gradients developed between the equator and poles nearly coincident with the development of the psychrosphere this pattern may be related to significant ice accumulation between late eocene and early late oligocene time