geology of panamint valley saline valley pull apart system california palinspastic evidence for low angle geometry of a neogene range bounding fault geological studies support the interpretation that northern panamint valley and saline valley southeast california form paired pull apart basins on opposite sides of the right slip hunter mountain fault zone eight to ten km of late cenozoic net slip can be established on the hunter mountain fault zone palinspastic reconstruction of northern panamint valley indicates that the valley was formed by movement on a shallow crustal low angle normal fault of 0 15 degree west dip during the last 3 0 ma this interpretation appears to contradict the notions that little extension is accomodated in the uppermost crust by low angle faulting and that the most recent extension in the basin and range province is accomodated exclusively by high angle faulting saline valley however is interpreted to have formed by extension on closely spaced rotated planar normal faults thus within one geometric system of paired pull apart basins extension appears to have been accommodated in the shallow crust in two different ways

ca sr and 87sr 86sr geochemistry of disseminated calcite in himalayan silicate rocks from nanga parbat influence on river water chemistry trace amounts of disseminated calcite were identified in gneiss schist and granite bedrock sampled from the raikhot watershed and other locations within the nanga parbat massif of northern pakistan the calcite grains occur interstitially within individual silicate minerals at grain boundaries and as fracture fillings that transect the mineralogic fabric of the rock disseminated calcite composes is 0 29 wt of silicate rocks sampled in the raikhot watershed and has ca sr mol nmol and 87sr 86sr ratios that range from 0 878 to 5 33 and from 0 794 039 to 0 930 619 respectively elsewhere in the nanga parbat region disseminated calcite composes 3 6 wt of the silicate rock samples and has ca sr mol nmol and 87sr 86sr ratios that range from 0 535 to 3 33 and from 0 715 757 to 0 771 244 respectively for all samples the 87sr 86sr ratios of disseminated calcite are similar to the 87sr 86sr ratios measured in the silicate host rock within the partially glaciated raikhot watershed the rapid weathering of disseminated calcite with high ca sr and 87sr 86sr ratios has a strong influence on the chemical composition of stream water and exceeds contributions from silicate mineral dissolution comparisons of disseminated calcite compositions with source water chemistry throughout the himalaya suggest that disseminated calcite may be a more important component of himalayan silicate rocks than previously recognized therefore calculations relating the sr isotope geochemistry of himalayan rivers to atmospheric co2 consumption should consider this widespread and compositionally variable carbonate end member

holocene and pleistocene dissolution cycles in deep sea cores of baffin bay and davis strait palaeoceano graphic implications abstract calcium carbonate dissolution has been studied in several grab samples and piston cores from baffin bay and davis strait ranging in water depth from 200 to 2300 m the intensity of dissolution was determined from examining 1 the ratio of arenaceous to calcareous benthonic foraminifera 2 the ratio of benthonic to planktonic foraminifera 3 the relationships between the dissolution susceptible and dissolution resistant foraminifera 4 the degree of foraminiferal test fragmentation and 5 the relationships between plankton tows and the fauna in the surface sediments all core tops and grab samples from baffin bay surface sediments below 600 900 m water depth demonstrated intense dissolution of calcium carbonate sediments below 900 m were biogenic carbonate free indicating 100 foraminiferal loss due to dissolution possible causes of substantial undersaturation in calcium carbonate of baffin bay bottom water are very low temperatures and higher concentrations of carbon dioxide all cores also demonstrated intense dissolution during interglacial or interstadial isotope stages 1 3 5 7 and 9 similarities in planktonic foraminiferal assemblages suggested the presence of similar bottom water masses during these periods the preservation state of biogenic carbonate debris in glacial isotope stages 2 4 6 8 and 10 is similar to the assemblage found in the water at present

palynomorph distribution in recent sediments from the labrador sea surface sediments from the labrador sea and baffin bay have been examined for their palynomorph content pollen and spore assemblages reflect the vegetation zones of eastern canada although long distance atmospheric transport results in over representation of pinus and spores a linear decrease of pollen input is observed with distance from the source vegetation the abyssal domain receives less than 2 of the initial input the abundance of dinoflagellate cysts reflects a relatively high primary productivity in surface water masses which seems proportional to the benthic productivity as shown by the concentrations of organic linings of foraminifers the relative abundance of dinoflagellate cyst taxa and principal component analysis led to the definition of three assemblages that can be related to sea surface conditions and current pattern the modern distribution of dinoflagellate cysts was used to interpret assemblages recovered in five box cores from the deep labrador sea results reveal important ch

early diagenetic processes in deep labrador sea sediments reactive and nonreactive iron and phosphorus a sequential extraction procedure was applied to separate the oxides and lithogenous phases of iron and manganese and the organic and inorganic phosphorus phases in four box cores and one piston core from the slopes and rises of the labrador sea sedimentation rate rather than the location in the basin appears as a master variable of the diagenetic transformations of fe mn and p high sedimentation rate characteristic of two of the box cores led to the creation of zones near the redox boundary of partial reprecipitation of dissolved fe mn and p released in the deeper reducing portions of the sediments in contrast surficial sediments from box cores with 10 times lower sedimentation rate only have sufficient reductive capacity to remobilize mn hydroxides while leaving the fe oxyhydroxides intact under these conditions there is evidence for a redistribution of reactive inorganic p leading to the crystallization of carbonate fluorapatite in the top 30 cm of the cores gradual transformation of bur

clay mineral signature of the nw atlantic boundary undercurrent abstract surface sediments were sampled along 2 transects across the iceland and irminger basins and in the labrador sea clay mineral assemblages deduced from x ray analyses of the carbonate free

strontium isotopes as tracers of ecosystem processes theory and methods abstract the strontium sr isotope method can be a powerful tool in studies of chemical weathering and soil genesis cation provenance and mobility and the chronostratigraphic correlation of marine sediments it is a sensitive geochemical tracer applicable to large scale ecosystem studies as well as to centimeter scaled examination of cation mobility within a soil profile the 87sr 86sr ratios of natural materials reflect the sources of strontium available during their formation isotopically distinct inputs from precipitation dryfall soil parent material and surface or groundwater allow determination of the relative proportions of those materials entering or leaving an ecosystem the isotopic compositions of labile soil exchange complex and soil solution strontium and sr in vegetation reflect the sources of cations available to plants strontium isotopes can be used to track the biogeochemical cycling of nutrient cations such as calcium the extent of cation contributions from in situ weathering and external additions to soil from dust and rain can also be resolved with this method in this paper we review the geochemistry and isotopic systematics of strontium and discuss the use of this method as a tracer of earth surface processes

solute sources and chemical weathering in the owens lake watershed eastern california 1 chemical and strontium isotope analyses of solutes in a series of streams representing the bulk of the water reaching the 8500 km2 owens lake watershed provide a unique opportunity to evaluate factors that control stream chemistry on a regional scale the streams drain terrain that is dominated by mesozoic granitoids of the sierra nevada batholith but that also contains irregularly distributed roof pendants of paleozoic metasedimentary sequences mass balance modeling indicates that plagioclase feldspar weathering is the dominant contributor to stream chemistry and that carbonate dissolution is also a significant source of solutes for most streams the calculated ratio of plagioclase to carbonate is highly sensitive to the assumed weathering product of plagioclase kaolinite versus smectite and we suggest that the importance of carbonate could be exaggerated in cases where only the plagioclase to kaolinite reaction is considered strontium isotope 87sr 86sr ratios range from 0 70685 to 0 71958 with a flow weighted mean of 0 70911 to the extent that this value represents the water that would be flowing into owens lake were it not diverted by the los angeles aqueduct system the flow weighted mean 87sr 86sr ratio is consistent with ratios measured in owens lake core carbonates ranging in age up to 25 kyr the overall sr budget of the watershed is determined by the relative contributions of carbonate dissolution and plagioclase feldspar weathering and is dominated by reactions related to pyrite oxidation and hydrothermal fluid input from just two subbasins the impact of these processes needs to be considered when modeling regional and global riverine sr budgets climate related shifts in the relative importance of silicate mineral weathering reactions appear to be only second order effects on a regional scale

isotope stratigraphy sedimentation rates deep circulation and carbonate events in the labrador sea during the last 200 ka high resolution stable isotope and accelerator mass spectrometry 14c measurements in 25 box and piston cores from the labrador sea allow the reconstruction of major paleoceanographical changes during the last 200 ka in this basin and also document the links between the interior of the laurentide ice sheet and the north atlantic ocean during this interval two deep circulation regimes are indicated by contrasting sedimentation rates on the slopes i the modern situation is characterized by a gyre of the north atlantic deep water nadw components into the basin which is responsible for the high energy western boundary undercurrent this regime also prevailed during the former true interglacials and possibly during shorter warm intervals e g bolling allerod ii a more frequent nadw free situation during glacial and interstadial intervals is marked by the presence of a vertically homogeneous water mass in the basin sedimentological records also indicate that carbonate events i e pulses of

asynchronous instability of the north american arctic and greenland ice sheets during the last deglaciation abstract the chronology of deglacial meltwater pulses from the laurentide ice sheet is well documented however the deglacial history of the north american arctic north eastern laurentide and innuitian and western greenland ice sheets draining into the labrador sea via baffin bay is less well constrained here we present new high resolution radiocarbon dated records from the central baffin bay spanning 17 to 10 kyr bp and documenting the full deglacial history of baffin bay sedimentological and geochemical data confirm the presence of two periods of enhanced detrital carbonate delivery termed baffin bay detrital carbonate events bbdcs these events are dated to 14 2 13 7 kyr bp and 12 7 11 kyr bp they are synchronous across baffin bay and their mineralogical signature indicates a common source of detrital carbonate from northern baffin bay the first event bbdc 1 postdates heinrich event 1 and the second event bbdc 0 predates the recently revised timing of heinrich event 0 the onset of the bbdc events appears not to be systematically linked to greenland temperature change as they occur during both interstadial and stadial periods this indicates that deglaciation of north american arctic and western greenland ice sheets with the associated iceberg and meltwater discharge were decoupled from the dominant north atlantic climate mode where iceberg discharge events from the laurentide ice sheet occurred during stadial periods

alkenone paleothermometry in the north atlantic a review and synthesis of surface sediment data and calibrations despite a clear correlation of alkenone unsaturation and sea surface temperatures sst throughout most parts of the ocean scatter of the regression for various calibration equations has been shown to increase significantly at low ssts in this study we combine previously published n 101 and new n 51 surface sediment data from the northern north atlantic to constrain uncertainties of alkenone paleothermometry at low ssts and to discuss possible sources of the increased scatter in the regression the correlation between alkenone unsaturation and ssts is strongest in particular at the cold end ssts 10 c when the tetra unsaturated alkenones c37 4 are included in the unsaturation index expressed as inline image and regressed against spring summer temperature surface ocean salinity and sea ice cover are not correlated with inline image per se however samples located in regions of permanent winter sea ice cover exhibit a significant warm bias deviation from the linear regression is posited to be related to a number of additional non exclusive factors such as advection of allochthonous material local temperature stratification and uncertainty in the absolute age of surface sediment samples assumed to be equivalent to modern conditions we conclude that alkenone unsaturation allows accurate reconstruction of sst records from many regions of the north atlantic if the factors confounding alkenone paleothermometry detailed here can be excluded

sr isotope tracing of aquifer interactions in an area of accelerating coal bed methane production powder river basin wyoming sr isotope data on groundwater samples from coal and overlying sandstone aquifers in the eastern powder river basin wyoming demonstrate that the sr isotope ratio effectively identifies groundwater from different aquifers where major ion geochemistry and o and h stable isotope data fail groundwaters from sandstone aquifers have a uniform 87sr 86sr ratio of 0 7126 0 7127 waters from coal seams vary from 87sr 86sr ratio 0 7127 near the recharge area to 0 7151 farther into the basin the distinct sr isotope signatures of sandstone and coal aquifers may reflect different sources of sr in these two rock types sr in sandstones is held primarily in carbonate cement whereas coals contain more radiogenic sr in organic matter the sr isotope ratio is useful in identifying wells that contain mixed waters whether due to well construction or to incomplete aquifer isolation measurement and continued monitoring of the sr isotope ratio in groundwaters should provide a powerful tool for characterizing the impact of the burgeoning coal bed methane industry on the hydrology of the powder river basin

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

isotopic variation in the tuolumne intrusive suite central sierra nevada california granitoid rocks of the compositionally zoned late cretaceous toulumne intrusive suite in the central sierra nevada california have initial87sr 86sr values sri and143nd 144nd values ndi that vary from 0 7057 to 0 7067 and from 0 51239 to 0 51211 respectively the observed variation of both sri and ndi and of chemical composition in rocks of the suite cannot be due to crystal fractionation of magma solely under closed system conditons the largest variation in chemistry ndi and sri is present in the outer most equigranular units of the tuolumne intrusive suite sri varies positively with sio2 na2o k2o and rb concentrations and negatively with ndi al2o3 fe2o3 mgo feo cao mno p2o5 tio2 and sr concentrations this covariation of sri ndi and chemistry can be modeled by a process of simple mixing of basaltic and granitic magmas having weight percent sio2 of 48 0 and 73 3 respectively isotopic characteristic of the mafic magma are sri 0 7047 ndi 0 51269 and 18o 6 0 and of the felsic magma are sri 0 7068 ndi 0 51212 and 18o 8 9 the rocks sampled contain from 50 to 80 of the felsic component an aplite in the outer equigranular unit of the tuolumne intrusive suite apparently was derived by fractional crystallization of plagioclase and hornblende from magma with granudiorite composition that was a product of mixing of the magmas described above siliceous magmas derived from the lower crust having a maximum of 15 percent mantle derived mafic component are represented by the inner prophyritic units of the tuolumne intrusive suite

strontium isotope quantification of siderite brine and acid mine drainage contributions to abandoned gas well discharges in the appalachian plateau unplugged abandoned oil and gas wells in the appalachian region can serve as conduits for the movement of waters impacted by fossil fuel extraction strontium isotope and geochemical analysis indicate that artesian discharges of water with high total dissolved solids tds from a series of gas wells in western pennsylvania result from the infiltration of acidic low fe fe 10 mg l coal mine drainage amd into shallow siderite iron carbonate cemented sandstone aquifers the acidity from the amd promotes dissolution of the carbonate and metal and sulfate contaminated waters rise to the surface through compromised abandoned gas well casings strontium isotope mixing models suggest that neither upward migration of oil and gas brines from devonian reservoirs associated with the wells nor dissolution of abundant nodular siderite present in the mine spoil through which recharge water percolates contribute significantly to the artesian gas well discharges natural sr isotope composition can be a sensitive tool in the characterization of complex groundwater interactions and can be used to distinguish between inputs from deep and shallow contamination sources as well as between groundwater and mineralogically similar but stratigraphically distinct rock units this is of particular relevance to regions such as the appalachian basin where a legacy of coal oil and gas exploration is coupled with ongoing and future natural gas drilling into deep reservoirs

late glacial to recent stratigraphy paleontology and sedimentary processes newfoundland continental slope and rise micropaleontology pollen sediment and 18o studies point to considerable variation in sedimentary processes and water mass characteristics on the northeast newfoundland slope and rise during late glacial and holocene time allochthonous shelf and upper slope foraminiferal species suggestive of turbidity current activity occur relatively frequently in rise sediments during a postglacial interval dated by extrapolation from a probable 9300 year old ash horizon a single late glacial turbidity current deposit involved a much larger volume of sediment than that noted for the earlier events and it appears to have originated primarily on the middle slope in conjunction with a widespread late glacial interval of fecal pellet deposition this larger event suggests an increased flux of material in the form of suspended particulate matter to the continental margin following the late wisconsinan glacial maximum oceanographic conditions during late glacial time appear to have stimulated the productivity of zoop

changes in the western boundary undercurrent outflow since the last glacial maximum from smectite illite ratios in deep labrador sea sediments high resolution mineralogical studies were performed on late glacial and deglacial sediments from two deep piston cores from the labrador sea located at the inlet sw greenland rise and outlet labrador rise of the western boundary undercurrent wbuc gyre at the two sites smectites transported from the eastern iceland and irminger basins by the wbuc are observed clay mineral changes are used as proxies for the paleointensity reconstruction of the wbuc on the greenland rise a clay mineral index smectite illite s i ratio is defined a s i ratio of 1 characterized the last glacial maximum it increased after 17 ka and reached a maximum value of 4 during the early holocene the mineralogical changes are gradual and do not show any reversal during the younger dryas this pattern which is confirmed by first order estimations of smectite and illite fluxes suggests gradually increasing sedimentary fluxes and wbuc intensity since the last glacial maximum a peak in the velocity of the wbuc at 9 ka as recorded by clay assemblages is consistent with other regional studies based on pollen foraminifera or grain size measurements a massive dilution of smectites by illite and chlorite s i 3 occurs at 8 5 ka it corresponds to a period of rapid sediment accumulation and reflects an intensified illite rich detrital supply by meltwaters from the southern greenland ice margin on the labrador rise the smectite content varies between 20 and 60 with no obvious trend through time the mineralogical composition is strongly influenced by ice rafted deposition and by the abundance of fast deposit units cf heinrich layers in the north atlantic which contain abundant detrital carbonates spilled over from the north west atlantic mid ocean channel in such layers smectites are present but are diluted by the addition of illites chlorites and kaolinites this provides evidence for a discrete and continuous wbuc supply of fine particles from the irminger and iceland basins as far as the southeastern part of the labrador basin early deglacial smectite rich layers up to 60 are also observed at this site they indicate an increase in the outflow of the wbuc at 13 5 ka bolling allerod as previously reported from grain size or foraminiferal assemblage studies

sr isotope evolution of seawater the role of tectonics we use a high resolution seawater sr isotopic evolution curve for the last 100 m y in conjunction with modern riverine sr flux measurements and also geologic tectonic and geochronological data to make the case for a close relationship between seawater sr isotopic composition and the india asia continental collision using a simple seawater sr budget model we begin by showing that the sr flux associated with alteration of seafloor basalts is too small and does not have the right time evolution to account for much of the seawater sr isotopic curve of the last 100 m y the flux of dissolved sr carried by rivers originating in the himalaya tibet region on the other hand is presently a significant fraction of the global sr budget we calculate how this riverine flux would have had to change with time in order to match the observed seawater sr isotopic curve and find that the riverine flux remains relatively constant prior to the collision of india with asia but then increases very significantly after collision we note that the period of most rapid change in seawater sr isotopic ratio from 20 ma to 15 ma is also a period of exceptionally high erosion in parts of the himalayas and the tibetan plateau as further evidence that sr derived from the collision of india with asia plays a major role in the sr isotopic evolution of seawater we show that the total amount erosion of the himalaya tibetan plateau since collision which we calculate separately represents a total amount of sr that is very nearly the same as the cumulative amount required by the sr isotopic change of seawater since collision the relationship between erosion and riverine sr flux allows us to use the sr isotopic evolution of seawater to reconstruct a history of erosion since collision and we find that the erosion rate accelerates with time since collision with the present having the largest rate when we apply the sr budget model to the entire phanerozoic using a new compilation of deformed continental area versus time we find that we can account for the large scale structure of the seawater sr isotopic curve but fail to reproduce several local maxima and minima especially in the period 100 300 ma the present high s7sr s6sr of seawater and similar highs in the devonian and cambrian do correlate with extensive deformation on the continents

retracted the past valley glacier network in the himalayas and the tibetan ice sheet during the last glacial period and its glacial isostatic eustatic and climatic consequences

smectite composition as a tracer of deep circulation the case of the northern north atlantic abstract the link between smectite composition in sediments from the northern north atlantic and labrador sea and deep circulation is being further investigated through detailed studies of the x ray pattern of smectites and cation saturations this allows clear distinction of dominant terrigenous sources associated to the main components of the modern western boundary undercurrent time variations of smectite characteristics in two piston cores from the inlet and outlet of the western boundary undercurrent gyre in the labrador sea indicate 1 a more southern circulation of north east atlantic deep water during the late glacial 2 a step by step transition to the modern pattern of deep circulation during the late glacial holocene transition with intensification of north east atlantic deep water and davis strait overflow 3 an expansion of davis strait overflow and labrador sea water circulation in relation to ice surges and deposition of detrital layers 4 an intensified circulation of north east atlantic deep water during the younger dryas and 5 a very recent increased influence of denmark strait overflow water beginning between 4 4 and

fluctuations in deep western north atlantic circulation on the blake outer ridge during the last deglaciation variations in the mean grain size of the detrital silt fraction from four piston cores along a depth transect on the blake outer ridge were used to examine paleocirculation patterns and intensity between 2650 and 3818 m for the late pleistocene and holocene prior to 12 kyr circulation was focused on the upper part of the ridge above 2700 m and may have corresponded to enhanced levels of intermediate water production in the north atlantic deepwater circulation during deglaciation underwent a two step decrease to minimum speeds from 15 5 to 13 5 kyr followed by a three step increase to maximum speeds at 10 kyr minima in circulation at 13 5 and 12 kyr can be directly associated with oxygen isotopic evidence for advection of reduced salinity surface water to the north atlantic additional circulation minima at 15 and 10 5 kyr may also be the result of reduced salinity from high latitude meltwater discharge evidence for a drop to moderate circulation intensity during the holocene is supported by isolated geochemical records but could also be explained by decoupling of ocean ventilation rates from bottom circulation or a change in sediment provenance at the end of deglaciation

late quaternary alluvial fans and paleosols of the kangra basin nw himalaya tectonic and paleoclimatic implications abstract the paper describes late quaternary pedosedimentary sequences of the alluvial fans from the kangra basin of nw himalayas for tectonic and paleoclimatic implications in the proximal part of the kangra basin three coalescing alluvial fans namely rait rihlu fans 65 km2 kangra fans 200 km2 and palampur fans 170 km2 from west to east evolved due to reactivation of longitudinal and transverse faults and climatic changes during the late quaternary the fans are characterised by subsidence of rait rihlu fans uplift of kangra fans and tilting of palampur fans the thick 90 m pedosedimentary sequences exposed along the rivers characterise the dominant formative processes over the fans the stream flow sediments dominate the rait rihlu fans whereas the debris flow sediments dominate the kangra and palampur fans the fan sequences are also marked by the formation of strongly developed paleosols on loess l1 l3 loess paleosols and weakly developed paleosols on fluvial deposits in response to the tectonics and climate change in nw himalayas formation of the loess in proximal and distal settings of the alluvial fans is related to the cool dry climates during the advance of glaciers in the adjoining areas at 78 ka 44 ka 30 ka and 20 ka when climate was approaching towards the last glacial maxima field characters micromorphology grain size and clay minerals of these loessic deposits suggest strong pedogenesis of the loess during a warm humid climate after the retreat of glaciers in the nw himalayan region and are likely related to marine isotope stages mis4 5 in proximal and mis2 3 in distal the loess paleosols show some degree of syndepositional pedogenesis in upper horizons and are accretionary in nature weakly expressed pedogenic features in fluvial and debris flow deposits suggest rapid sedimentation over unstable surfaces related to the reactivation of main boundary thrust mbt and other regional faults

the strontium isotopic evolution of marcellus formation produced waters southwestern pennsylvania abstract the production of natural gas and natural gas liquids from unconventional tight shale formations involves hydraulic fracturing and subsequent removal of fluids co produced with the gas the chemistry of the returning fluid reflects the original composition of the injection water mobilized constituents in the shale formation and co mingled formation waters liberated by hydraulic fracturing produced water from unconventional gas wells tapping the middle devonian marcellus formation is characterized by high total dissolved solids tds including very high strontium concentrations in this study the strontium isotope composition 87 sr 86 sr was measured in produced waters from four horizontally drilled hydraulically fractured marcellus shale gas wells in southwestern pennsylvania sampled from the first day after commencement of flowback to as much as 27 months later the 87 sr 86 sr of the waters tended to change rapidly over the first few days of water return and then approached but did not reach a constant range of values from 0 7113 to 0 7114 which appears to be characteristic of this part of the marcellus play in contrast the concentration of sr rose more slowly and appeared to hit a steady state value up to 3000 mg l by the end of the first year taken together with results from earlier work these data suggest mixing between injected frac fluid and high tds formation water highly enriched in sr and isotopically relatively uniform throughout the marcellus shale gas play this brine could exist within porous lenses of organic matter in the shale in pre existing fractures within the shale and or originate from fluids that migrated from adjacent formations at some point during the post depositional history of the basin

the strontium isotopic budget of himalayan rivers in nepal and bangladesh abstract himalayan rivers have very unusual sr characteristics and their budget cannot be achieved by simple mixing between silicate and carbonate even if carbonates are radiogenic we present sr o and c isotopic data from river and rain water bedload and bedrock samples for the western and central nepal himalaya and bangladesh including the monsoon season central himalayan rivers receive sr from several sources carbonate and clastic tethyan sediments high himalayan crystalline hhc gneisses and granitoids with minor marbles carbonates and metasediments of the lesser himalaya lh and miocene recent foreland basin sediment from the siwaliks group and the modern flood plain in the tethyan himalaya rivers have dissolved sr 6 mol l and 87sr 86sr 0 717 with a large contribution from moderately radiogenic carbonate rivers draining hhc gneisses are very dilute with sr 0 2 mol l and 87sr 86sr 0 74 lesser himalayan streams also have low sr 0 4 mol l and are highly radiogenic 87sr 86sr 0 78 highly radiogenic carbonates of the lh do not contribute significantly to the sr budget because they are sparse and have very low sr in large rivers exiting the himalaya sr systematics can be modeled as a mixture between tethyan rivers where slightly radiogenic carbonates mean 87sr 86sr 0 715 are the main source of sr and lesser himalaya waters where extremely radiogenic silicates 0 8 are the main source of sr hhc waters are less important because of their low sr rivers draining the siwaliks foreland basin sediments have sr 4 mol l and 87sr 86sr 0 725 weathering of silicates in the siwaliks and the flood plain results in a probably significant radiogenic 0 72 0 74 input to the ganges and brahmaputra g b but quantification of this flux is limited by uncertainties in the hydrologic budget the g b in bangladesh show strong seasonal variability with low sr and high 87sr 86sr during the monsoon sr in the brahmaputra ranges from 0 9 mol l and 0 722 in march to 0 3 mol l and 0 741 in august we estimate the seasonally weighted flux from the g b to be 6 5 108 mol yr with 87sr 86sr 0 7295

dinoflagellate cyst distribution in high latitude marine environments and quantitative reconstruction of sea surface salinity temperature and seasonality a data base of 179 reference sites documents the relations between the assemblages of organic walled dinoflagellate cysts and sea surface temperature salinity and seasonality throughout the north atlantic adjacent subpolar basins labrador sea baffin bay irminger and iceland basins and epicontinental environments off eastern canada estuary and gulf of st lawrence hudson bay principal component analyses show close relationships between dinoflagellate cyst data and sea surface conditions the first component 71 1 of the variance correlates with the winter temperature salinity and seasonal duration of sea ice cover whereas the second component 11 3 of the variance appears mainly related to summer temperature transfer functions using the best analogue method were tested by reconstructing modern sea surface conditions on the basis of the reference dinoflagellate cyst assemblages the correlation coefficient between instrumental averages and reconstructed values ranges from 0 87 august tem

glacial interglacial instabilities of the western boundary under current during the last 365 kyr from sm nd ratios of the sedimentary clay size fractions at odp site 646 labrador sea we present 40 sm nd isotope measurements of the clay size 2 m fractions of sediments from the sout hern greenland rise odp 646 that span the last 365 kyr these data track changes in the relative supply o f fine particles carried into the deep labrador sea by the western boundary under current wbuc back to the fourth glacial interglacial cycles earlier studies reveal ed three general sources of particles to the core s ite i precambrian crustal material from canada greenland and or scandinavia north american shield nas ii palaeozoic or younger crustal material from east gr eenland nw europe and or western scandinavia young crust yc and iii volcanic material from iceland and the mid atlantic ridge mar clay size fractions from glacial sediments have the lowest nd isotopic ratios supplies of young crustal particles were si milar during glacial oxygen isotope stages ois 2 6 and 10 i n contrast the mean volcanic contributions decrease d relative to old craton material from ois 10 to ois 6 and the n from ois 6 to ois 2 the glacial ois 8 interval d isplays a mean sm nd ratio similar to those of interglacials ois 1 5 and 9 compared with other interglacials ois 7 was marked by a higher yc contribution but a similar 3 0 mar supply the overall nas contribution dropped by a factor of 2 during each glacial interglacial tran sition with the mar contribution broadly replacing it during interglacials to decipher between higher supplies and or dilution particle fluxes from each end memb er were estimated glacial nas fluxes were systematically h igher than interglacial fluxes during the time int erval examined fine particle supplies to the labrador se a were strongly controlled by proximal ice margin e rosion and thus echoed the glacial stage intensity in con trast the wbuc carried mar supplies from the eastern basins did not change significantly throughout the last 36 5 kyr except for a marked increase in surface sedi ments that suggests unique modern conditions distal wbuc controlled inputs from the northern and ne north atlant ic seem to have been less variable than proximal suppl ies linked with glacial erosion rate

burial rates of organic matter along the eastern canadian margin and stable isotope constraints on its origin and diagenetic evolution abstract organic carbon oc and nitrogen n contents and 13 c and 15 n values in total organic matter om were measured in sub surface sediments 0 30 cm sub bottom from 21 cores raised from the laurentian channel of the gulf of st lawrence and the labrador sea to document om fluxes and storage along the eastern canadian margin storage rates as high as 2 5 g m 2 yr 1 for oc and 0 2 g m 2 yr 1 for n are observed in the laurentian channel suggesting that the shelf plays a significant role in terms of om storage from 1 to 2 of the primary production based on the isotopic composition of the essentially marine om of the labrador sea 13 c v pdb 21 9 0 4 15 n air 7 6 0 6 n 12 there is no isotopic evidence for a significant relative input of terrestrial om along the laurentian channel 13 c v pdb 21 9 0 4 15 n air 8 0 0 9 n 10 either due to high relative fluxes of marine om and or to the trapping of continental om in the estuary and upstream high storage rates of om are also observed on the continental rise of the labrador sea as high as 1 1 g c m 2 yr 1 and 0 09 g n m 2 yr 1 they contrast with one order of magnitude lower rates on the slope due to low sedimentation rates sr and sediment winnowing by the western boundary undercurrent wbuc reduced early diagenetic alteration of om is observed particularly in the laurentian channel it results in discrete i losses of oc and n ii shifts in c n ratios suggesting preferential removal of n bearing om also highlighted by losses in total hydrolysable amino acids haa in the labrador sea slope records due to low sr om concentration changes linked to long term temporal variations may superimpose on these diagenetic trends and some influence of the wbuc is noticeable

quaternary glaciation of mount everest abstract the quaternary glacial history of the rongbuk valley on the northern slopes of mount everest is examined using field mapping geomorphic and sedimentological methods and optically stimulated luminescence osl and 10 be terrestrial cosmogenic nuclide tcn dating six major sets of moraines are present representing significant glacier advances or still stands these date to 330 ka tingri moraine 41 ka dzakar moraine 24 27 ka jilong moraine 14 17 ka rongbuk moraine 8 2 ka samdupo moraines and 1 6 ka xarlungnama moraine and each is assigned to a distinct glacial stage named after the moraine the samdupo glacial stage is subdivided into samdupo i 6 8 7 7 ka and samdupo ii 2 4 ka comparison with osl and tcn defined ages on moraines on the southern slopes of mount everest in the khumbu himal show that glaciations across the everest massif were broadly synchronous however unlike the khumbu himal no early holocene glacier advance is recognized in the rongbuk valley this suggests that the khumbu himal may have received increased monsoon precipitation in the early holocene to help increase positive glacier mass balances while the rongbuk valley was too sheltered to receive monsoon moisture during this time and glaciers could not advance comparison of equilibrium line altitude depressions for glacial stages across mount everest reveals asymmetric patterns of glacier retreat that likely reflects greater glacier sensitivity to climate change on the northern slopes possibly due to precipitation starvation

direct dating of the oxygen isotope record of the last deglaciation by 14c accelerator mass spectrometry major trends of quaternary global climate are reflected in the continental ice volume changes which have been reconstructed by oxygen isotope analysis1 2 18o records from deep sea sediments show that the net glacial build up occurs relatively slowly3 but that the end of an ice age occurs quickly in less than 10 000 yr implying a nonlinear response4 5 to simple milankovitch theory6 the latter observation suggests that the cause of the most recent deglaciation was the maximum in summer calorific radiation at the upper latitudes of the northern hemisphere centred around 11 000 yr ago a view supported by early studies7 later work has produced conflicting dates the main source of confusion being problems with obtaining accurate and reliable dates here by using accelerator mass spectrometry we have measured 14c for various species of foraminifera to produce a reliable timescale for the oxygen isotope record our results show that at the end of the last ice age continental ice sheets began to melt more than 4 000 yr before the northern hemisphere maximum of summer calorific radiation

climatic solar oceanic and geomagnetic influences on late glacial and holocene atmospheric 14c 12c change late glacial and holocene 14c12c ratios of atmospheric co2 vary in magnitude from a few per mil for annual decadal pertubations to more than 10 for events lasting millennia a data set illuminating 10 to 104 yr variability refines our understanding of oceanic climatic versus geomagnetic or solar forcing of atmospheric 14c12c ratios most of the variance in the holocene atmospheric 14c12c record can be attributed to the geomagnetic millennia time scale and solar century time scale influence on the flux of primary cosmic rays entering the atmosphere attributing the observed atmospheric 14c12c changes to climate alone leads to ocean circulation and or global wind speed changes incompatible with proxy records climate ocean related 14c redistribution between carbon reservoirs while evidently playing a minor role during the holocene may have perturbed atmospheric 14c12c ratios measurably during the late glacial younger dryas event first order corrections to the radiocarbon time scale 12 000 30 000 14c yr b p are calculated from adjusted lake sediment and tree ring records and from geomagnetically defined model 14c histories paleosunspot numbers 100 9700 cal yr b p are derived from the relationship of model 14c production rates to sunspot observations the spectral interpretation of the 14c12c atmospheric record favors higher than average solar activity levels for the next century minimal evidence was found for a sun weather relationship

isotopic evidence of enhanced carbonate dissolution at a coal mine drainage site in allegheny county pennsylvania usa stable isotopes were used to determine the sources and fate of dissolved inorganic c dic in the circumneutral ph drainage from an abandoned bituminous coal mine in western pennsylvania the c isotope signatures of dic 13cdic were intermediate between local carbonate and organic c sources but were higher than those of contemporaneous pennsylvanian age groundwaters in the region this suggests a significant contribution of c enriched in 13c due to enhanced carbonate dissolution associated with the release of h2so4 from pyrite oxidation the sr isotopic signature of the drainage was similar to other regional mine waters associated with the same coal seam and reflected contributions from limestone dissolution and cation exchange with clay minerals the relatively high 34sso4 and 18oso4 isotopic signatures of the mine drainage and the presence of presumptive so4 reducing bacteria suggest that so4 reduction activity also contributes c depleted in 13c isotope to the total dic pool with distance downstream from the mine portal c isotope signatures in the drainage increased accompanied by decreased total dic concentrations and increased ph these data are consistent with h2so4 dissolution of carbonate rocks enhanced by cation exchange and c release to the atmosphere via co2 outgassing

limits on the ventilation rate for the deep ocean over the last 12000 years in this paper we present accelerator radiocarbon measurements on hand picked benthic and planktonic foraminifera separated from two deep sea cores raised from the south china sea from the benthic planktonic age differences we are able to place limits on the extent to which the ventilation rate of the deep pacific ocean has changed over the last 12000 years while much work remains to be done before any definitive answers for the global oceans can be given these results on cores with sedimentation rates suitably high to avoid major corrections for bioturbation effects suggest that the ventilation rate of the deep pacific ocean has remained nearly the same throughout holocene time further there is no suggestion that the rate was slower during the period of major glacial retreat these results confirm that the changes in atmospheric14c c ratio over the last 10000 years owe their origin to radiocarbon production rate changes

reconstruction of sea surface temperature salinity and sea ice cover in the northern north atlantic during the last glacial maximum based on dinocyst assemblages past sea surface conditions over the northern north atlantic during the last glacial maximum were examined from the study of 61 deep sea cores the last glacial maximum time slice studied here corresponds to an interval between heinrich layers h2 and h1 and spanningabout 20 16 ka on a 14c time scale transfer functions based on dinocyst assemblages were used to reconstruct sea surface temperature salinity and sea ice cover the results illustrate extensive sea ice cover along the eastern canadian margins and sea ice spreading only during winter over most of the northern north atlantic on the whole much colder winter prevailed despite relatively mild conditions in august 10 15 c at most offshore sites thus suggesting a larger seasonal contrast of temperatures than today lower salinity than at present is reconstructed especially along the eastern canadian and scandinavian margins likely because of meltwater supply from the surrounding ice sheets these reconstructions contrast with those established by climap on the basis of planktonic foraminifera these differences are discussed with reference to the stratigraphical frame of the last glacial maximum which was not the coldest phase of the last glacial stage the respective significance of dinocyst and foraminifer records is also examined in terms of the thermohaline characteristics of surface waters and the vertical structure of upper water masses which was apparently much more stratified than at present in the northern north atlantic thus preventing deep water formation

benthic foraminiferal assemblages in labrador sea sediments relations with deep water mass changes since deglaciation surface sediment samples from the labrador sea and the irminger and iceland basins have been analysed for their benthic foraminiferal content to define the relationship between benthic foraminiferal assemblages and bottom water characteristics on the shelf 301 530 m and the upper slope 1364 and 1980 m the distribution of assemblages is complex and appears related to diversified microhabitats in the deep sea domain 2600 m three main assemblages have been identified the first dominated by epistominella exigua is related to the north east atlantic deep water neadw the second characterized by the co dominance of cibicides wuellerstorfi and e exigua seems to characterize the north west atlantic bottom water nwabw the third marked by the occurrence of nuttalides umbonifera is recorded at depths greater than 3500 m and is associated with the northern extent of the antarctic bottom water aabw microfaunal and isotopic analyses of two cores from the greenland slope 90 013 011 2800 m and

a 200 ka geomagnetic chronostratigraphy for the labrador sea indirect correlation of the sediment record to specmap abstract a chronostratigraphic framework for the last 200 ka based on relative variations of geomagnetic paleointensity has been derived for the labrador sea where 18o stratigraphies are compromised by lack of benthic foraminifera and environmental perturbations of the planktic record relative paleointensity records derived from three labrador sea piston cores are correlated to a recently developed 200 ka paleointensity composite sint 200 y guyodo j p valet earth planet sci lett 143 1996 23 36 the chronology for sint 200 was derived by correlating oxygen isotope stratigraphies from individual paleointensity records to the specmap chronostratigraphy the correlation of sint 200 to labrador sea paleointensity records allows the specmap chronology to be imported into the labrador sea although comparisons of the chronostratigraphy based on paleointensity correlations with those derived from ams 14c dates and 18o data indicate significant discrepancies support for the new chronostratigraphic framework is provided by 1 consistent correlation of labrador sea detrital layers to north atlantic heinrich layers 2 general consistency between planktic 18o values and the specmap reference curve and 3 feasible prediction for the age of ash layer 2 as the new chronostratigraphy is tied to specmap labrador sea sediment cores can now be directly compared with any specmap dated record

a sr isotopic comparison between thermal waters rocks and hydrothermal calcites long valley caldera california abstract the 87 sr 86 sr values of thermal waters and hydrothermal calcites of the long valley caldera geothermal system are more radiogenic than those of young intracaldera volcanic rocks five thermal waters display 87 sr 86 sr of 0 7081 0 7078 but show systematically lighter values from west to east in the direction of lateral flow we believe the decrease in ratio from west to east signifies increased interaction of deeply circulating thermal water with relatively fresh volcanic rocks filling the caldera depression all types of pre syn and post caldera volcanic rocks in the west and central caldera have 87 sr 86 sr m between about 0 7060 and 0 7072 and values for sierra nevada granodiorites adjacent to the caldera are similar sierran pre intrusive metavolcanic and metasedimentary rocks can have considerably higher sr isotope ratios 0 7061 0 7246 and 0 7090 0 7250 respectively hydrothermally altered volcanic rocks inside the caldera have 87 sr 86 sr m slightly heavier than their fresh volcanic equivalents and hydrothermal calcites 0 7068 0 7105 occupy a midrange of values between the volcanic plutonic rocks and the sierran metamorphic rocks these data indicate that the long valley geothermal reservoir is first equilibrated in a basement complex that contains at least some metasedimentary rocks reequilibration of sr isotope ratios to lower values occurs in thermal waters as convecting geothermal fluids flow through the isotopically lighter volcanic rocks of the caldera fill

quaternary soils and dust deposition in southern nevada and california eoliandustconstitutesmuchofthepedogenic material in late pleistocene and holocene soils of many arid regions of the world comparisonofthecompositionsand influx rates of modern dust with the eolian component of dated soils at 24 sites in southern nevada and california yields informationon 1 thecompositionandinflux rate of dust in late pleistocene and holocene soils 2 paleoclimate and its effects on the genesis of aridic soils especially with regard to dustfall events 3 the timing and relative contribution of dust from playa sources versus alluvial sources and 4 the effects of accumulation of dust in soil horizons the 2mmfractionsofaandbhorizons of soils formed on gravelly alluvial fan deposits in the study area are similar to moderndustingrainsize contentofcaco3and salt majoroxides andclaymineralogy thus they are interpreted to consist largely of dust the major oxide compositions of the shallow soil horizons are nearly identical to that of the modern dust but the compositions of progressively deeper horizons approachthatoftheparentmaterial theclay mineralogyofmoderndustatagivensiteis similar to that of the av horizons of nearby holocene soils but is commonly different from the mineralogies of deeper soil horizonsandoftheavhorizonsofnearbypleistocenesoils theseresultsareinterpretedto indicate that dust both accumulates and is transformed in av horizons with time changes in soil accumulation rates provide insights into the interplay of paleoclimate dustsupply andsoil formingprocesses modern dust deposition rates are more than large enough to account for middle and late holocene soil accumulation rates at nearly all sites however the early holocene soil accumulation rates in areas near late pleistocene pluvial lakes are much higher than modern rates and clearly indicate a dust deflation and deposition event that caused rapid formation offine grained shallow soil horizons on uppermost pleistocene and lower holocene deposits we interpret late pleistocene soil accumulation rates to indicate that dust deposition rates were low during this period but that increased effective moisture during the late wisconsinan favored translocation of clay andcaco3fromnearthesurfacetodeeper inthesoilprofile pre latepleistocenerates are very low in most areas mainly due to a pedogenic threshold that was crossed when accumulations of silt clay and caco3 began to inhibit the downward transport of eolian material but in part due to erosion

coal fly ash interaction with environmental fluids geochemical and strontium isotope results from combined column and batch leaching experiments abstract the major element and sr isotope systematics and geochemistry of coal fly ash and its interactions with environmental waters were investigated using laboratory flow through column leaching experiments sodium carbonate acetic acid nitric acid and sequential batch leaching experiments water acetic acid hydrochloric acid column leaching of class f fly ash samples shows rapid release of most major elements early in the leaching procedure suggesting an association of these elements with soluble and surface bound phases delayed release of certain elements e g al fe si signals gradual dissolution of more resistant silicate or glass phases as leaching continues strontium isotope results from both column and batch leaching experiments show a marked increase in 87 sr 86 sr ratio with continued leaching yielding a total range of values from 0 7107 to 0 7138 for comparison the isotopic composition of fluid output from a fly ash impoundment in west virginia falls in a narrow range around 0 7124 the experimental data suggest the presence of a more resistant highly radiogenic silicate phase that survives the combustion process and is leached after the more soluble minerals are removed strontium isotopic homogenization of minerals in coal does not always occur during the combustion process despite the high temperatures encountered in the boiler early released sr tends to be isotopically uniform thus the sr isotopic composition of fly ash could be distinguishable from other sources and is a useful tool for quantifying the possible contribution of fly ash leaching to the total dissolved load in natural surface and ground waters

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

smnd signature of modern and late quaternary sediments from the northwest north atlantic implications for deep current changes since the last glacial maximum abstract nd isotopes and sm nd concentrations have been investigated in the clay size fraction of surface and late quaternary sediments of the northern north atlantic four sources of nd have been identified in the surface sediments 1 a radiogenic nd typical of the iceland volcanism 2 a pan african nd issued from eastern greenland 3 a variscan nd derived from the arctic ocean 4 an old unradiogenic nd related to the north american shield in the iceland and irminger basins the major sources of nd are the variscan nd derived from the arctic ocean and the iceland nd except in the western irminger basin where the pan african nd originating from eastern greenland is dominant and labels sedimentary supplies linked to the denmark strait overflow water nd derived from icelandic volcanism is never clearly dominant even on the reykjanes ridge and the nd derived from the american shield becomes dominant only in the labrador sea sediments lying in the pathway of the western boundary undercurrent have nd isotopic compositions which are shifted towards more radiogenic values indicating an input of material from the eastern basins carried by this deep current late quaternary sediments were cored from the southern greenland rise core 90 013 013 and eastern labrador rise orphan knoll core 91 045 094 in core 90 013 013 nd values during the last glacial maximum are as low as 20 but subsequently rose to 9 in the modern sediments indicating that the sedimentary material during the last glacial maximum was dominated by unradiogenic nd from the north american shield this may be related to a lesser outflow of the western boundary undercurrent in core 91 045 094 located along the labrador current trajectory a dominant supply of north american shield nd is recorded perhaps originating at least partially from the hudson strait the sm nd data are compatible with smectite vs illite studies at the same sites which suggest a continuous but more modest western boundary undercurrent supply during last glacial maximum

application of lp icp ms to benthic foraminifers abstract a laser microprobe coupled with an inductively coupled plasma mass spectrometer lp icp ms was used to determine mg mn sr and ba contents of benthic foraminifers in the solid state calcite shells of cibicides wuellerstorfi oridorsalis umbonatus pyrgo spp and aragonite tests of hoeglundina elegans which were taken from the surface sediments of the northwestern north atlantic ocean were ablated by a laser beam multiple measurements were achieved on single tests since the diameters of ablation pits 20 50 m are significantly smaller than those of the shells 250 m mg ca mn ca and ba ca of the ablated materials are significantly affected by fe mn oxide coatings and extraneous ba bearing phases and sr ca is not noticeably influenced by those contaminants there is no substantial variation of sr ca within and between shells of a foraminiferal species on the contrary sr ca is species dependent sr ca of pyrgo spp is three times as high as that of h elegans and nearly twice as high as those of c wuellerstorfi and o umbonatus

tracing the interaction of acid mine drainage with coal utilization byproducts in a grouted mine strontium isotope study of the inactive omega coal mine west virginia usa abstract in order to ameliorate acidic discharge the inactive omega coal mine west virginia was partially filled by injection of a grout consisting of 98 coal utilization byproducts cub including fluidized bed combustion ash and fly ash and 2 portland cement in this study discharge chemistry and sr isotope ratios were determined to identify and quantify the extent of interaction between mine waters and the cub cement grout eight sampling sites were monitored around the downdip perimeter of the mine the major and trace element chemistry of the discharges was generally not sufficient to distinguish between discharges that interacted with grout and those that did not elements that showed the most separation include k and as which were elevated in some waters that interacted with cub cement grout in contrast the sr isotope ratios clearly distinguished discharges from grouted and non grouted areas discharges that bypassed the grouted portions had 87 sr 86 sr ratios ranging from 0 71510 to 0 71594 while two discharges that interacted with grout had ratios in the range of 0 71401 0 71456 the treatment inlet which includes both grouted and ungrouted discharges yielded intermediate isotopic ratios leaching experiments on cub cement grout coal and surrounding rocks are consistent with the isotopic trends observed in the discharges based on these results waters that interacted with grout received 30 40 of their sr from the cub cement grout material these results suggest that the grout material is chemically eroding at a rate of approximately 0 04 per year this novel application of the sr isotope system illustrates its ability to sensitively track and quantify fluid interaction with coal and cub based grout

paleoceanography of the deep western boundary undercurrent on the north american continental margin for the past 25 000 yr temporal fluctuations of silt mean particle size and foraminiferal indices were used to examine fluctuations in velocity and position of the axis of the deep western boundary undercurrent dwbuc on the north american continental margin from 25 to 17 ka the dwbuc axis was 500 m shallower and farther inshore than its present position on the lower rise current speed was high from 25 to 20 ka and then waned until 17 ka between 17 and 7 ka the major axis of the dwbuc shallowed to 4000 m current speed increased from 17 to 11 ka but slowed from h to 7 ka since 7 ka the dwbuc axis has deepened to its modern position at 4900 m the zone of maximum carbonate dissolution remained below the dwbuc the most intense dissolution was from 22 to 9 ka and 5 to 2 ka highest abundance of uvigerina and highest percent benthic foraminifera were immediately above the dwbuc from 22 to 7 ka after which values of both parameters fell to near zero

neodymium and strontium isotopic dating of diagenesis and low grade metamorphism of argillaceous sediments the behaviour of the rb sr and sm nd isotopic systems with increasing degree of hercynian metamorphic overprint was studied along a transect in cambrian shales of northwestern morocco clay fractions of 0 2 to 2 6 m size from five samples were investigated representing a range from nonmetamorphic to epizonal metamorphic conditions the samples were washed in cold l n hc1 prior to digestion to separate soluble exchangeable rb sr sm and nd from amounts of these elements fixed in the crystallographic sites of the minerals and to analyze both components separately the results reveal that the rb sr isotopic system is dominated by sr hosted by clay mineral phases both detrital and authigenic illite and chlorite and carbonate hosted soluble sr isotopic homogenization of sr occurred during hercynian metamorphism yielding ages between 309 and 349 ma the sm nd isotopic system on the other hand is dominated by cogenetic apatite and fe oxide hydroxide both having high contents of leachable rees the leachates yield a sm nd isochron age of 523 72 ma indicating diagenetic equilibrium between apatite and fe oxide hydroxide fine grained clay fractions of 0 2 m show inheritance of a detrital nd component the study demonstrates that the diagenesis of the investigated argillaceous sediments can be dated by the sm nd chronometer in authigenic cement phases the isotopic system of these minerals apatite fe hydroxide oxide was homogenized during authigenic mineral growth in a sediment that was flushed by diagenetic fluids and had abundant primary or secondary interconnected pore space the hercynian metamorphic overprint caused partial isotopic rehomogenization of the adsorbed and clay hosted portion of the sr as well as of the carbonate hosted sr the sm nd system in the cement phases survived this metamorphism this results in decoupling of the two isotopic systems and allows the dating of diagenesis on the one hand sm nd and metamorphism on the other hand rb sr

himalayan tectonics weathering processes and the strontium isotope record in marine limestones the time evolution of the isotopic composition of seawater strontium the ratio of strontium 87 to strontium 86 over the last 500 million years has the form of an asymmetric trough the values are highest in the cambrian and recent 0 7091 and lowest in the jurassic 0 7067 superimposed on this trend are a number of smaller oscillations consideration of the geochemical cycle of strontium and the dynamics of weathering shows that only himalayan style continental collisions can influence the isotope ratio on the scale observed the contemporary himalayan orogeny is by far the largest since the late precambrian pan african event that produced the high in the cambrian

strontium isotopic characterization of soils and coal ashes abstract the 87 sr 86 sr isotopic ratios and rb and sr concentrations were measured for a number of soils and samples of coal derived fly and bottom ashes fly and bottom ashes from a given coal rank are similar in their concentrations of rb and sr and their 87 sr 86 sr ratios values of 87 sr 86 sr isotopic ratios of ashes decrease in the order bituminous subbituminous lignitic reflecting the decreasing rank of parent coals the 87 sr 86 sr isotopic ratios of soils vary widely differing significantly only from the ratios observed for lignitic ashes the results indicate that the 87 sr 86 sr values may be used as a tracer for detecting dispersion of lignitic ashes on soils in these coal ashes the 87 sr 86 sr ratios of the biogeologically available fraction of sr are linearly correlated with the logarithm of the sr concentrations the logarithm of the rb sr ratios and the rb concentrations

size dependent isotopic composition of planktic foraminifers from chukchi sea vs nw atlantic sediments implications for the holocene paleoceanography of the western arctic abstract in arctic and sub arctic seas shell growth and or secondary calcite overgrowth of neogloboquadrina pachyderma left coiled npl occur along the pycnocline and their 13c and 18o values are size and weight dependent however whereas the npl 18o data from the nw atlantic indicate near equilibrium conditions with ambient waters and a positive relationship between shell weight and 18o content assemblages from box cored sediments of the chukchi sea western arctic are depleted by 2 with respect to equilibrium values with modern conditions and depict a negative relationship between shell weight and its 18o value 0 15 0 03 g on vpdb scale a similar feature is also depicted by the dextral form of n pachyderma npd we associate the reverse shell size or weight vs 18o relationship to the reverse temperature gradient observed along the thermocline between the surface cold and dilute water layer and the underlying near 3 c warmer saline north atlantic water mass the analysis of two late to post glacial sedimentary sequences from the chukchi sea indicates that such a water mass stratification with a reverse thermocline persisted throughout the holocene thus reflecting an early onset of the modern like linkage between the arctic ocean and the north atlantic moreover lower 18o values in both npl and npd together with larger 18o gradients between the different shell sizes at ca 9 7 ka bp suggest 3 c higher temperatures in the upper north atlantic water mass in comparison with the present approximately 1 c at the study site thus likely a higher inflow rate of this water mass during the early holocene

accelerator mass spectrometry radiocarbon stratigraphies in deep labrador sea cores paleoceanographic implications foraminiferal accelerator mass spectrometry ams 14c ages and benthic planktonic age differences in surface layer sediments of labrador sea are influenced by bioturbation and by changes in the relative abundance of foraminiferal species carrying the 14c signal using benthic mixing models we demonstrate that inverse benthic planktonic age differences can be generated when the effect of benthic mixing and abundance change exceeds apparent age differences between surface water and deep water ams 14c ages obtained put constraints on the timing of major paleoceanographic changes in the basin notably on the history of the western boundary undercurrent which was clearly reinitiated during the mid deglaciation and intensified during the last 2 3 ka

detrital carbonate rich sediments northwestern labrador sea implications for ice sheet dynamics and iceberg rafting heinrich events in the north atlantic much of the bed of the central and eastern sectors of the laurentide ice sheet was underlain by paleozoic carbonates we propose that pulses of detrital carbonate rich sediments in two cores from the northwestern labrador sea reflect episodes when an ice stream from the hudson strait extended to the shelf break and delivered sediment onto the slope and deep sea plain atomic mass spectroscopy 14 c dating of planktonic foraminifera in cores hu75 009 iv 55 2 4 km water depth and hu87 033 009 1 4 km water depth and 150 km north northwest indicates that the youngest event occurred between ca 14 and 15 ka and another occurred between 19 and 21 ka the two carbonate intervals in northwestern labrador sea cores are coeval with heinrich events 1 and 2 in the eastern north atlantic lat 45 50 n long 20 w where they are associated with an increase in lithic fragments and a drastic reduction in the numbers of foraminifera these changes have been linked with the massive production of icebergs associated with ice sheet surges our evidence indicates that heinrich events 1 and 2 are associated with the dynamics of the hudson strait ice stream and denote considerable glaciological instability

late pleistocene relative geomagnetic paleointensity from the deep labrador sea regional and global correlations abstract three long piston cores from the deep labrador sea appear to record late pleistocene variations of relative paleointensity of the geomagnetic field two cores extend at least into isotope stage 6 the other into stage 5 in addition to 18o 13c and ams 14c stratigraphies correlation between cores is facilitated by the presence of rapidly deposited high detrital carbonate dc and low detrital carbonate ldc layers some of which correlate to the north atlantic heinrich events hysteresis ratios and rock magnetic parameters indicate that the magnetic assemblage in the cores is pseudo single domain magnetite except for deglacial intervals and dc and ldc layers normalized remanence records show strong correlation for a range of normalizers k karm and sirm and no correlation with bulk magnetic parameters paleointensity records from the three cores are consistent when only dc and ldc layers are used for correlation suggesting that relative paleointensity can be used as a regional correlation tool consistent paleointensity features from the labrador sea indian ocean and mediterranean sea suggest that the sediments are recording dipole field variations although the composite record from two labrador sea cores is strongly correlated to a composite of the mediterranean indian ocean records the chronologies are inconsistent indicating apparent discrepancies in the isotopic and ams 14c chronologies used in the mediterranean indian ocean and labrador sea respectively

radiogenic isotopes systematics and applications to earth surface processes and chemical stratigraphy radiogenic isotopes have wide application to chemical stratigraphy geochronology provenance studies and studies of temporal changes in earth surface processes this paper briefly reviews the principles of radiogenic isotope geochemistry and the distribution of a number of elements of interest in the environment and then uses this information to explore the range of applications to chemical stratigraphy and other fundamental subjects of sedimentary geology many of these applications center on the reconstruction of secular variations in paleoseawater isotope signals these seawater isotope curves can be used for stratigraphic correlation and to assess changes through earth history in processes such as tectonic uplift climate change biogeochemical cycling ocean circulation crustal growth and surface water evolution understanding the modern biogeochemical cycle of the element isotope system of interest is essential for gaining the maximum information regarding the operation of ancient cycles the main sources of uncertainty for reconstructing seawater isotope curves involve diagenetic alteration sample impurities and errors in age assignments rigorous sample selection criteria and pretreatment methods are keys to reconstructing the most accurate seawater isotope curves applications are discussed for the rb sr sm nd la ce lu hf re os u th pb k ar and cosmogenic isotope systems d 2003 elsevier b v all rights reserved

high resolution rock magnetic study of a late pleistocene core from the labrador sea a high resolution rock magnetic study of a late pleistocene core from the labrador sea north of the eirik ridge on the greenland rise reveals three main features in the downcore variation of the

u th and pa insights into sedimentological and paleoceanographic changes off hudson strait labrador sea during the last 37 ka with special attention to methodological issues 231 pa and 230 th excess calculation abstract a 9 m long sediment core spanning the last 37 ka has been raised from the lower labrador continental slope off the hudson strait shelf edge it has been analyzed for its u th and pa isotope contents along with current sedimentological parameters as a means to retrieve information about sedimentological changes in response to northeastern laurentide ice sheet lis margin instabilities the sequence yielded a high resolution record of subglacial detrital carbonate pulses from hudson strait assigned to heinrich events h2 and h1 whereas h0 was missing large variations in bulk sediment u and th contents as well as in 234 u 238 u activity ratio are observed throughout the sequence leading to large uncertainties when calculating excesses in 231 pa and 230 th 231 paxs and 230 thxs over their supported and in growth

quantitative strontium isotope models for weathering pedogenesis and biogeochemical cycling abstract isotopes of strontium sr are a useful tracer for weathering atmospheric fluxes cation biocycling and pedogenesis we present basic models for application of strontium isotopes to the soil vegetation atmosphere system the mathematical formulations fall into the general categories of 1 steady state models in which isotopic ratios remain constant over the time scale of interest and 2 time dependent models in which isotope ratios change through time in the steady state models fluxes of sr and other elements to the system are constant steady state models can be used to infer short term weathering rates from river and stream isotope compositions to determine fluxes to a single or multiple layer soil exchange solution system and to quantify nutrient fluxes to vegetation time dependent models involve a change in isotopic ratio from some initial value to a new value over the time period of interest in some cases the change may represent a shift from one steady state situation to a new one after a shift in one or more of the fluxes feeding the system examples of applications of time dependent models include identifying the dominant cation sources to an evolving soil exchange solution system and calculating weathering rates by measuring the isotopic compositions of primary soil minerals we use time dependent models to explain differences in the isotopic ratios of labile and carbonate sr from arid sites in hawaii with a basalt parent material isotopic signature and new mexico with an atmospheric isotopic signature these models suggest that the difference is due to a combination of low atmospheric strontium fluxes and high weathering rates in the hawaiian profile compared to the new mexico calcrete profile

geologic control of sr and major element chemistry in himalayan rivers nepal our study of the seti river in far western nepal shows that the solute chemistry of the river and its tributaries is strongly controlled by geology the seti flows through four distinct terranes starting with the tethyan sedimentary series tss and greater himalayan series ghs tss ghs waters display 87 sr 86 sr ratios of 0 73 and high sr and ca consistent with the composition of limestone and marble common in these terranes the 87 sr 86 sr ratio and mg increase markedly as the river passes into the lesser himalayan series lhs where tributaries have 87 sr 86 sr ratios from 0 75 to 1 02 and high sr ca and mg the high mg in lhs waters correlate with high 87 sr 86 sr ratios which we attribute to weathering of highly radiogenic 0 71 0 82 dolostones tributaries to the seti river draining the largely carbonate free dadeldhura thrust sheet dts have ratios near 0 74 but low sr ca and mg and therefore have little impact on seti mainstem chemistry mass balance calculations and camg weathering indices show that carbonate weathering accounts for 70 of total dissolved solids to the seti river sr ca ratios of river waters provide a minimum estimate of the carbonate weathering contribution to sr due to partitioning of sr and ca during incongruent dissolution and reprecipitation of calcite overall we attribute high 87 sr 86 sr ratios in the seti river and its tributaries to the weathering of metacarbonates especially dolostones in the upper nawakhot group which have exchanged sr with silicates during metamorphism our modeling of sr fluxes in the seti river indicates that the tss ghs accounts for 36 39 of the sr the lhs for 40 53 and 8 23 for the dts prior to exposure of lhs rocks at 12 ma tss and ghs carbonates with low 87 sr 86 sr ratios dominated himalayan rivers we attribute the elevated 87 sr 86 sr ratios of himalayan paleorivers during the late miocene and pliocene to exposure and weathering of lhs metacarbonates copyright 2000 elsevier science ltd

correlation of carboniferous strata using a hierarchy of transgressive regressive units carboniferous strata can be described interpreted and correlated using six scales of allocyclic transgressive regressive t r units these t r units are inferred to be the net result of deposition during cycles of sea level change all pennsylvanian and lower permian strata constitute one second order t r unit or synthem the pennsylvanian system contains third fourth fifth and sixth order t r units that can be correlated across both marine and nonmarine facies in the appalachian basin this permits differentiation of allocyclic t r units from autocyclic t r units or fluvial autocyclic units the hierarchical approach is also useful for predicting the location of marine horizons coals claystones and various types of stratigraphic breaks a hierarchical scheme of allocyclic t r units could be combined with biostratigraphic radiometric and magnetostratigraphic data to form a practical chronostratigraphic framework for the carboniferous

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

preliminary estimates for the radiocarbon age of deep water in the glacial ocean radiocarbon ages for benthic and planktonic foraminifera from the late glacial sections of two atlantic and two pacific cores are reported the differences for benthic planktonic pairs suggest that the radiocarbon age for deep atlantic water was somewhat larger than today s i e 600 250 as opposed to 400 years and that the radiocarbon age for deep pacific water was also slightly larger than today s 2100 400 as opposed to 1600 years our results suggest that during glacial time the deep pacific was as it is today significantly depleted in radiocarbon relative to the deep atlantic as many questions remain unanswered regarding the reliability of this approach these conclusions must be considered to be preliminary

the role of disseminated calcite in the chemical weathering of granitoid rocks accessory calcite present at concentrations between 300 and 3000 mg kg 1 occurs in fresh granitoid rocks sampled from the merced watershed in yosemite national park ca usa loch vale in rocky mountain national park co usa the panola watershed ga usa and the rio icacos puerto rico calcite occurs as fillings in microfractures as disseminated grains within the silicate matrix and as replacement of calcic cores in plagioclase flow through column experiments using de ionized water saturated with 0 05 atm co2 produced effluents from the fresh granitoid rocks that were dominated by ca and bicarbonate and thermodynamically saturated with calcite during reactions up to 1 7 yr calcite dissolution progressively decreased and was superceded by steady state dissolution of silicates principally biotite mass balance calculations indicate that most calcite had been removed during this time and accounted for 57 98 of the total ca released from these rocks experimental effluents from surfically weathered granitoids from the same watersheds were consistently dominated by silicate dissolution the lack of excess ca and alkalinity indicated that calcite had been previously removed by natural weathering the extent of ca enrichment in watershed discharge fluxes corresponds to the amounts of calcite exposed in granitoid rocks high ca na ratios relative to plagioclase stoichiometries indicate excess ca in the yosemite loch vale and other alpine watersheds in the sierra nevada and rocky mountains of the western united states this ca enrichment correlates with strong preferential weathering of calcite relative to plagioclase in exfoliated granitoids in glaciated terrains in contrast ca na flux ratios are comparable to or less than the ca na ratios for plagioclase in the subtropical panola and tropical rio icacos watersheds in which deeply weathered regoliths exhibit concurrent losses of calcite and much larger masses of plagioclase during transport limited weathering these results indicate that the weathering of accessory calcite may strongly influence ca and alkalinity fluxes from silicate rocks during and following periods of glaciation and tectonism but is much less important for older stable geomorphic surfaces

surface oceanographic changes in the eastern labrador sea nannofossil record of the last 31 000 years abstract calcareous nannofossils in two ams 14c dated piston cores from the eastern labrador sea yield oceanographic information of the last 31 kyr moderate nannofossil productivity and abundance of north atlantic warm water taxa in the southern labrador sea core 91 045 094p suggest cool surface ocean condition between 31 and 26 thousand years ago ka the irminger current was absent in this interval thus we attribute this cool condition to weak advection of north atlantic water from the southeast we found evidence of cold and or seasonally ice covered surface conditions between 26 and 13 ka in the southern labrador sea and between 31 and 12 6 ka in the northeastern labrador sea core 90 013 013p increase of nannofossil productivity and abundance of north atlantic taxa at about 10 7 ka in core 91 045 094p suggests that the southern labrador sea was influenced by warm north atlantic surface water the polar water of the labrador current had little or no influence on the surface ocean in this area before 9 ka the labrador current started to flow or intensify after 9 ka and became strong by 8 4 ka the northeastern labrador sea remained cold until 8 4 ka perhaps because of discharge of cold meltwater from the greenland ice sheet at this time productivity increased sharply and the assemblage of nannofossils changed these suggest a significant improvement in surface ocean conditions and the establishment of the warm irminger current which marked the onset of the modern circulation pattern characterized by warm west greenland current and strong labrador current

transfer function between surface sediment diatom assemblages and sea surface temperature and salinity of the labrador sea abstract q mode factor analysis cabfac of 38 diatom species in 66 surface sediment samples from the labrador sea allowed the definition of six assemblages explaining 95 69 of the total variance the first assemblage 40 12 of the total variance is represented by thalassiothrix longissima a species characteristic of the irminger current and associated with the west greenland current the second assemblage 34 52 of the total variance is represented by thalassiosira gravida resting spores a cold water species associated with the labrador current a third assemblage 11 43 of the variance represented by chaetoceros spp is concentrated in the northeastern section of the labrador sea and associated with upwelling and high productivity the fourth the fifth and the sixth assemblages represented respectively by coscinodiscus marginatus coscinodiscus oculus iridis and coscinodiscus divisus and nitzschia frigida are less significant and account respectively for 4 95 2 62 and 2 04 of the total variance transfer functions derived by relating factor assemblages to surface water temperature and salinity august and february give standard errors of estimate of 0 93 c august and 0 64 c february for temperature and of 0 58 august and 0 45 february for salinity high correlations between the measured and estimated parameters confirm the validity of the paleoecological equations for the reconstruction of the labrador sea paleoclimate

application of portland cement to control acid mine drainage generation from waste rocks abstract cement has been little investigated as a control for acid mine drainage despite having advantages over cheaper alternatives leaching column experiments set up in triplicate investigated the effect of applying portland cement slurries with three different water cement w c ratios 0 8 1 0 1 2 to pyrite bearing waste rock from brukunga mine in southeastern australia after application of the cement leachate from the cemented columns showed a reduction in acidity compared to the control columns of 85 and 100 for w c ratios of 0 8 and both 1 0 and 1 2 respectively this was due to direct neutralisation of acidity by cement dissolution and encapsulation of the pyrite bearing rock fragments by the cement as shown by a reduction in oxygen consumption rates of up to 70 in columns with the higher w c ratios 1 0 1 2 the cement slurry penetrated to the base of the columns and greatly decreased the permeability the greater coverage of the waste rock by the cement and increased contact time between the leachate and cement meant that no acid drainage leached from these columns ph 7 8 fe al mn zn and cu concentrations rarely above detection limits in columns with a w c ratio of 0 8 the cement slurry was mostly retained in the upper 30 50 of the waste rock leaving a large fraction of the waste rock below without any cement coverage leachate drained relatively quickly from these columns probably through a small number of pathways through the cement plug and carried relatively small loads of acidity and metals from uncemented waste rock beneath the cement thus cement may be a viable method for controlling acid mine drainage generation from waste rock dumps and could be applied with both lower and higher w c ratios could be used to achieve an optimal balance between deep penetration and surficial retention

an evaluation of trace element release associated with acid mine drainage the determination of trace element release from geologic materials such as oil shale and coal overburden is important for proper solid waste management planning the objective of this study was to determine a correlation between trace element residency and concentration to trace element release using the following methods 1 sequential selective dissolution for determining trace element residencies 2 toxicity characteristic leaching procedure tclp and 3 humidity cell weathering study simulating maximum trace element release two eastern oil shales were used a new albany shale that contains 4 6 percent pyrite and a chattanooga shale that contains 1 5 percent pyrite each shale was analyzed for elemental concentrations by soluble adsorbed organic carbonate and sulfide phases all leachates were analyzed to determine total trace element concentrations

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

kinetic and mineralogic controls on the evolution of groundwater chemistry and 87sr 86sr in a sandy silicate aquifer northern wisconsin usa abstract substantial flowpath related variability of 87sr 86sr is observed in groundwaters collected from the trout lake watershed of northern wisconsin in the extensive shallow aquifer composed of sandy glacial outwash groundwater is recharged either by seepage from lakes or by precipitation that infiltrates the inter lake uplands 87sr 86sr of groundwater derived mainly as seepage from a precipitation dominated lake near the head of the watershed decreases with progressive water chemical evolution along its flowpath due primarily to enhanced dissolution of relatively unradiogenic plagioclase in contrast 87sr 86sr of groundwater derived mainly from precipitation that infiltrates upland areas is substantially greater than that of precipitation collected from the watershed due to suppression of plagioclase dissolution together with preferential leaching of sr from radiogenic phases such as k feldspar and biotite the results of a column experiment that simulated the effects of changing residence time of water in the aquifer sand indicate that mobile waters obtain relatively unradiogenic sr whereas stagnant waters obtain relatively radiogenic sr nearly the entire range of strontium isotope composition observed in groundwaters from the watershed was measured in the experimental product waters the constant mobility of water along groundwater recharge flowpaths emanating from the lakes promotes the dissolution of relatively unradiogenic plagioclase perhaps due to effective dispersal of clay mineral nuclei resulting from dissolution reactions in contrast episodic stagnation in the unsaturated zone along the upland recharge flowpaths suppresses plagioclase dissolution perhaps due to accumulation of clay mineral nuclei on its reactive surfaces differences in redox conditions along these contrasting flowpaths probably enhance the observed differences in strontium isotope behavior this study demonstrates that factors other than the calculated state of mineral saturation must be considered when attempting to simulate chemical evolution along flowpaths and that reaction models must be able to incorporate changing contributions from reacting minerals in the calculations

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

paleoglaciological reconstructions for the tibetan plateau during the last glacial cycle evaluating numerical ice sheet simulations driven by gcm ensembles abstract the tibetan plateau is a topographic feature of extraordinary dimension and has an important impact on regional and global climate however the glacial history of the tibetan plateau is more poorly constrained than that of most other formerly glaciated regions such as in north america and eurasia on the basis of some field evidence it has been hypothesized that the tibetan plateau was covered by an ice sheet during the last glacial maximum lgm abundant field and chronological evidence for a predominance of local valley glaciation during the past 300 000 calendar years that is 300 ka coupled to an absence of glacial landforms and sediments in extensive areas of the plateau now refute this concept this furthermore calls into question previous ice sheet modeling attempts which generally arrive at ice volumes considerably larger than allowed for by field evidence surprisingly the robustness of such numerical ice sheet model results has not been widely queried despite potentially important climate ramifications we simulated the growth and decay of ice on the tibetan plateau during the last 125 ka in response to a large ensemble of climate forcings 90 members derived from global circulation models gcms using a similar 3d thermomechanical ice sheet model as employed in previous studies the numerical results include as extreme end members as an ice free tibetan plateau and a plateau scale ice sheet comparable in volume to the contemporary greenland ice sheet we further demonstrate that numerical simulations that acceptably conform to published reconstructions of quaternary ice extent on the tibetan plateau cannot be achieved with the employed stand alone ice sheet model when merely forced by paleoclimates derived from currently available gcms progress is however expected if future investigations employ ice sheet models with higher resolution bidirectional ice sheet atmosphere feedbacks improved treatment of the surface mass balance and regional climate data and climate reconstructions

dissolved load of the loire river chemical and isotopic characterization the loire river with one of the largest watersheds in france has been monitored just outside the city of orleans since 1994 physico chemical parameters and major and trace elements were measured between 2 day and 1 week intervals according to the river flow the sampling site represents 34 of the total loire watershed with 76 silicate rocks and 24 carbonate rocks elements are transported mainly in the dissolved phase with the ratio of total dissolved salts tds to suspended matter sm ranging between 1 6 and 17 4 chemical weathering of rocks and soils are thus the dominant mechanisms in the loire waters composition the highest tds sm ratios are due to dissolved anthropogenic inputs the database shows no link between no3 content and river flow the na k mg2 so42 and cl concentrations are seen to decrease with increasing discharge in agreement with a mixing process involving at least two components the first component during low flow is concentrated and may be related with input from the groundwater and sewage station water the second component during high flow is more dilute and is in agreement with bedrock weathering and rainwater inputs a geochemical behaviour pattern is also observed for hco3 and ca2 species their concentrations increase with increasing discharge up to 300 m3 s after which they decrease with increasing discharge the sr isotopic composition of the dissolved load is controlled by at least five components a series of natural components represented by a waters draining the silicate and carbonate bedrock b groundwater and c rainwaters and two kinds of anthropogenic components the aim of this study is to describe the mixing model in order to estimate the contribution of each component finally specific export rates in the upper loire watershed were evaluated close to 12 t year 1 km 2 for the silicate rate and 47 t year 1 km 2 for the carbonate rate

foraminifer isotope study of the pleistocene labrador sea northwest north atlantic iodp sites 1302 03 and 1305 with emphasis on paleoceanographical differences between its inner and outer basins article i nfo coresraisedduringiodpexpedition303offsoutherngreenland eirikridgesite1305 andoffthelabradorcoast orphanknollsite1302 1303 wereanalyzedtoestablishanisotopestratigraphy respectivelyforthe inner and outer basins of the labrador sea ls these isotopic data also provide information on the atlantic meridional overturning circulation amoc notably with regard to the intensity of the western boundary under current wbuc which is tightly controlled by the production of denmark strait overflow water dsow and the production of labrador sea water lsw in the inner basin through winter cooling and convection the upper 184 m of sediment at eirik ridge spans marine isotope stages mis 32 to 1 at this site two distinct regimes are observed prior to mis 20 the isotopic record resembles that of the open north atlantic records of the interval

structure of the upper water column in the northwest north atlantic modern versus last glacial maximum conditions 1 during the last glacial maximum the northwestern north atlantic constituted a major conduit for labrador and greenland ice sheet meltwaters vertical density gradients in its upper water masses have been reconstructed by combining information from transfer functions based on dinocysts and from oxygen isotope measurements 18o in planktonic foraminifera transfer functions yield temperature and salinity and thus potential density for the warmest august and coldest february months in the photic zone the 18o values in different size fractions of epipelagic globigerina bulloides and mesopelagic neogloboquadrina pachyderma left coiled npl foraminifera allow us to assess gradients through the pycnocline between surface and intermediate waters based on the calibration of a versus 18o relationship from transfer function reconstructions the size and density of npl shells provide further constraints on these gradients the results show the development of a very strong pycnocline during the lgm with a difference of about 3 summer to 1 5 winter units between surface and underlying waters they indicate conditions unfavorable for vertical convection and support the hypothesis of the spreading of a shallow low salinity buoyant layer over the northern north atlantic this layer depicted a strong e w gradient with maximum seasonal contrast and minimum absolute values westward

instabilities in the labrador sea water mass structure during the last climatic cycle in the modern labrador sea the north atlantic deep water components are found below the 2 km deep intermediate labrador sea water lsw mass which is renewed locally through winter convective mixing this water mass structure remained relatively stable since 9 5 14 c ka bp as indicated by isotopic studies of foraminifer assem blages from deep sea cores almost constant differences in 18 o values are observed between major species these av erage 0 5 between the epipelagic species globigerina bulloides and the mesopelagic species neogloboquadrina pachyderma left coiled and 1 between neogloboquadrina pachydermaand the benthic species cibicides wuellerstorfi after correction for cibicides wuellerstorfi specific fractionation these isotopic compositions represent thermohaline conditions in surface waters in the pycnocline with the lsw and in the deep component of the north atlantic deep water respectively a drastically different structure characterized the glacial labrador sea differences in 18 o values of 2 to 2 5 are then observed between globigerina bulloides and benthic species indicative of a strong halocline between the corresponding water masses thus for reduced production of intermediate waters during the same interval neogloboquadrina pachydermashows 13 c and 18 o fluctuations of 1 to 1 5 amplitude in phase with heinrich bond events and higher frequency climate oscillations the 18 o values in neogloboquadrina pachyderma vary between those of globigerina bulloides and of benthic foraminifers suggesting large amplitude bathymetric fluctuations of the halo thermocline above and below the bathymetric range occupied by neogloboquadrina pachyderma minimum 18 o values in neogloboquadrina pachydermamatch intervals of maximum ice rafting deposition such as the late heinrich events thus intervals with a deeper more dilute buoyant surface water layer

benthic foraminiferal δ13c and accumulation rates of organic carbon uvigerina peregrina group and cibicidoides wuellerstorfi the glacial to interglacial 13c records of the benthic foraminifera cibicidoides wuellerstorfi and the uvigerina peregrina group from deep sea cores cannot be adjusted by a generally valid constant the 13c values of the u peregrina group largely correlate with the accumulation rates of organic carbon suggesting a local habitat effect those of c wuellerstorfi vary independently with respect to the carbon flux and record fluctuations in the 13c of the ambient bottom water isotopic composition

early diagenetic processes in labrador sea sediments uranium isotope geochemistry the concentration and isotopic composition of u dissolved in pore waters from hemipelagic sediments of the labrador sea were determined by thermal ionization mass spectrometry in two 30 cm long box cores the present fluxes of seawater u that diffuses across the sediment seawater interface are on the order of 2 4 g cm2 ka this diffusion imposes decreasing gradients of dissolved u downwards but the u concentration in pore waters immediately below the surface is much lower than that of open ocean seawater this is a primary feature that cannot be explained by carbonate precipitation due to decompression during core retrieval more likely it reflects the presence of a stagnant benthic boundary layer above the sediment water interface in which molecular diffusion of u is slower than in the overlying turbulently mixed seawater and or of microzones near the interface where u is bioaccumulated uranium is adsorbed at depths onto the solid phase in response to changes in the redox conditions within the