paleohydrology of the upper miocene bicorb lake eastern spain as inferred from stable isotopic data from inorganic carbonates abstract the hydrological evolution of the upper miocene bicorb lake eastern spain has been established based on sedimentology carbonate mineralogy and stable isotopic data from inorganic carbonates from the upper lacustrine unit three main subunits have been recognized in subunit a the sedimentological features suggest a hydrologically closed lake although the isotopic data are not conclusive the isotopic compositions of primary carbonates from subunit b display a distribution typical for a hydrologically closed lake and allow the differentiation of four developmental stages the first stage was defined by the deposition of gypsum lmc dolomite and aragonite indicating large variations in the water mg ca ratio during the second and third stages only lmc was deposited suggesting only minor mg ca fluctuations the 13c and 18o pattern of the second stage shows a well defined covariance r 0 8 while in the third stage the isotopic data display a negative covariant relationship r 0 8 changes in dissolved inorganic carbon composition are considered the main factor to explain the variations from positive to negative covariance in the fourth stage the lake waters underwent large mg ca fluctuations as indicated by the deposition of lmc hmc and aragonite the isotopic trend is also covariant finally subunit c is characterized by lmc and minor amounts of hmc suggesting minor changes in mg ca ratio the isotopic features of this subunit are more congruent with a hydrologically open lake the lowest 13c and 18o values are very similar in the three subunits reflecting the most dilute conditions of the lake water and a uniform isotopic composition of the local meteoric water during these periods the changes in water balance and solute inputs recorded in the mineralogy and isotopic signatures of carbonates were controlled by the diapiric evolution and changes in the e p balance

an inverse modeling study in fram strait part i dynamics and circulation abstract in order to reconstruct the circulation in the northern greenland sea between 77 n and 81 n and the exchanges with the arctic ocean through fram strait a variational inverse model is applied to the density field observed in summer 1984 during the mizex 84 experiment an estimate of the three dimensional large scale pressure field is obtained in which the solution is decomposed into a limited number of vertical modes and the mode amplitudes are described by piece wise polynomials on a finite element grid the solution should be consistent with a frictional depth integrated vorticity balance and with the density data the global model parameters are tuned to ensure agreement between the retrieved geostrophic velocity and independent currentmeter data in a companion paper schlichtholz and houssais 1999b the same method but without dynamical constraint is applied to the same hydrographic dataset to perform a detailed water mass analysis and to estimate individual water mass transports a comprehensive picture of the summer geostrophic circulation in fram strait is obtained in which northward recirculations in the east greenland current egc and various recirculations from the west spitsbergen current wsc to the egc are identified it is suggested that the branch of the wsc following the upper western slope of the yermak plateau turns westward beyond 81 n and recirculates southward along the lower slope then merging with a westward recirculating branch south of 79 n at 79 n a southward net transport of 6 5 sv is found in the egc which combined with a northward net transport of only 1 5 sv in the wsc results in a fairly large outflow of 5 sv from the arctic ocean to the greenland sea the inverse solutions show that in summer the local induction of vorticity by the wind stress curl or by meridional advection of planetary vorticity should be small so that in the egc and in the wsc the vorticity balance is mainly achieved between the bottom pressure torque and dissipation of vorticity through bottom friction a substantial barotropic flow associated with along slope potential energy gradients is indeed identified on both sides of the strait

oxygen and carbon isotope trends and sedimentological evolution of a meromictic and saline lacustrine system the holocene medicine lake basin north american great plains usa abstract the succession of sedimentary subfacies in the medicine lake basin south dakota usa documents numerous changes in total dissolved solids tds lake level and the nature and stability of meromixis during the holocene the lake formed about 10 6 ka b p when coarse clastics and massive fine grained muds were deposited in a well mixed freshwater system subsequently the lake became saline and meromictic depositing a finely laminated unit composed of variegated and gray muds organic facies gypsum and aragonite laminae phototrophic bacterial plate communities bpc at the chemocline were significant producers of pelagic organic matter relatively high lake levels at least 10 m higher than today but saline and meromictic conditions predominated through the early to mid holocene at the end of this phase lake level dropped and stable meromixis was disrupted sands and massive or banded muds were deposited in sublittoral areas and benthic microbial communities bmc spread over the lake replacing bpcs as the predominant microbial producers when lake level rose again massive and laminated units were deposited under less saline conditions another pronounced episode of low lake level and high salinity followed the most recent sediments are sapropels massive or banded muds and littoral sands the 18o record from authigenic aragonite shows more positive values during the arid mid holocene interval with an abrupt increase at the end of this period followed by generally more negative values during the cooler and wetter late holocene the small range of 18o values 3 suggests that the lake was well buffered against high frequency climatic cycles probably as a result of groundwater modulation we postulate that meromixis and the type of photosynthetic microbial communities dominating the basinal region of the lake system either bpcs or bmcs exerted major controls on the carbon cycle and consequently on the development of isotopic trends linking 13c and 18o values more negative 13c values during the early and mid holocene are interpreted as a consequence of the predominance of 12c enriched microbial carbon from bpcs examples of both covariant and inverse covariant isotope trends between 13c and 18o values occur in the medicine lake record inverse covariant trends characterize long periods of stable meromixis when bpcs predominate over bmcs we hypothesize that well developed water stratification caused by greater influx of relatively 18o depleted freshwater induces higher productivity at the chemocline and consequently more positive 13c values in the precipitated carbonates unstable phases of meromixis or holomictic conditions are characterized by a predominance of bmcs or other biogenic producers over bpcs and a number of other factors combine to promote covariant trends the medicine lake record is consistent with the paleoclimatic interpretation for the northern great plains of a more arid early and middle holocene followed by an abrupt transition to a relatively cooler and wetter late holocene the sedimentary succesion in medicine lake documents a much more fluctuating and abrupt climate behavior than suggested by the vegetation paleorecord and suggest a late holocene climate punctuated by arid episodes

long period astronomically forced terrestrial carbon sinks abstract sequestration of organic matter by peat accumulation constitutes a primary sink for carbon in the global carbon cycle the processes that control the formation and storage of peat at geological time scales are poorly understood but are of a non solved issue of fundamental importance for understanding the global climate system we analyzed a 7 million years long terrestrial record of late oligocene age from the as pontes basin in northern spain which demonstrates that minima in the 405 kyr and 2 4 myr eccentricity cycles play a key role in peat formation such nodes exhibit reduced precession amplitudes thus avoiding extremes in seasons and seasonal contrast for a prolonged period of time in the as pontes basin this orbital configuration is associated with a decrease in siliciclastic sedimentation and enhanced peat formation feedbacks between equilibrium landscapes and ecosystem stability will lead to a deceleration of weathering and erosion rates in catchment areas and to minimum and stable sediment flux along the sediment routing system mid latitude peat burial could contribute to disturb the carbon cycle by removing atmospheric carbon at times of minimum eccentricity

paleoclimate of the past 4000 years at lake turkana kenya based on the isotopic composition of authigenic calcite abstract authigenic calcite was analyzed for 13 c and 18 o in a 12 m long core from lake turkana that spans the last 4200 yr the 18 o record is interpreted to reflect lake level history and indicates high stands prior to 4000 yr b p from 1800 to 2000 yr b p and within the last century this coincides better with the history of lake level change reported for other lakes in africa than did the previous lake level curve for lake turkana based on 14 c dates of exposed shoreline deposits the 13 c curve roughly parallels the 18 o curve and may reflect the influence of the omo river plume both of the isotope records are strongly cyclic with periodicites common to both at 80 120 150 and 225 yr other somewhat longer periodicites are nearly equal in the two records and there is close agreement with previously published cycles based on carbonate and lamination thickness analyses in the same turkana core

mid eocene alluvial lacustrine succession at gebel el goza el hamra shabrawet area ne eastern desert egypt facies analysis sequence stratigraphy and paleoclimatic implications abstract this study aims to provide the depositional facies sequence stratigraphic and paleoclimatic characteristics of the mid eocene bartonian continental succession exposed at gebel el goza el hamra shabrawet area ne eastern desert egypt the studied succession consists of siliciclastic rocks followed upward by carbonate rocks detailed field observation and petrographic investigation indicate accumulation in floodplain dominated alluvial and shallow lacustrine systems the floodplain dominated alluvial facies 45 m thick is composed mainly of carbonate nodules bearing mottled mudrock with subordinate sandstone and conglomerate beds the conglomerate and pebbly sandstone bodies interpreted as ephemeral braided channel deposits the massive laminated planner cross bedded fine to medium grained sandstone bodies interlayered within mudstone reflect sheet flood deposits the mudrocks associated with paleosols represent distal floodplain deposits the shallow lacustrine facies 15 m thick is made up of an alternation of marlstone micritic limestone dolostone and mudrock beds with charophytes and small gastropods both the alluvial and lacustrine facies show evidence of macro and micro pedogenic features pollen assemblages stable 18 o and 13 c isotopes and paleopedogenic features reflect prevalence of arid to semi arid climatic conditions during the bartonian the sequence stratigraphic framework shows an overall fining upward depositional sequence consisting of low and high accommodation systems tracts last hast and is bounded by two sequence boundaries sb 1 sb 2 conglomerate and pebbly sandstone deposits braided channel and sheet flood deposits of the lower part of the alluvial facies reflect a last mudrock and silty claystone facies distal floodplain deposits of the upper part of alluvial facies and its overlying lacustrine facies correspond to a hast the last hast and sb were formed during different accommodation to sediment supply a s ratio phases the variation in a s ratios was mainly controlled by sea level change as well as by local tectonic subsidence and uplift of the basin coincident with the reactivation of the syrian arc system during the bartonian

isotopic and geochemical composition of marl lake waters and implications for radiocarbon dating of marl lake sediments radiocarbon dates on organic and calcareous fractions of sediment cores from marl lakes may yield anomalous ages due to the assumption of a constant hardwater correction factor along the sediment sequence a study of eight marl lakes in southern ontario that are actively precipitating calcium carbonate was conducted in order to assess those isotopic and aqueous geochemical parameters in modern lakes that may be utilized to estimate the history and extent of variations in the hardwater effect along such sediment sequences results show an increase in the 13c composition of lake dic dissolved inorganic carbon as approach to isotopic equilibrium with atmospheric co2 occurs differences in the extent to which this equilibrium is established also appear responsible for observed differences in the 14c activity of dic between lakes of as much as 20 pmc percent modern carbon these variations have been related to the relative residence times of water in each lake by examination of their corresponding seasona

the palaeohydrological evolution of lago chungara andean altiplano northern chile during the lateglacial and early holocene using oxygen isotopes in diatom silica oxygen isotopes of diatom silica and petrographical characterisation of diatomaceous laminated sediments of lago chungara northern chilean altiplano have allowed us to establish its palaeohydrological evolution during the lateglacial early holocene ca 12 000 9400 cal yr bp these laminated sediments are composed of light and dark pluriannual couplets of diatomaceous ooze formed by different processes light sediment laminae accumulated during short term diatom blooms whereas dark sediment laminae represent the baseline limnological conditions during several years of deposition oxygen isotope analysis of the dark diatom laminae show a general 18o enrichment trend during the studied period comparison of these 18odiatom values with the previously published lake level evolution suggests a correlation between 18odiatom and the precipitation evaporation ratio but also with the evolution of other local hydrological factors as changes in the groundwater outflow as well as shifts in the surface volume ratio of lago chungara the lake expanded probably increasing this ratio during the rising lake level trend due to changes in its morphology enhancing evaporation furthermore the lake s hydrology was probably modified as the groundwater outflow became sealed by sediments increasing lake water residence time and potential evaporation both factors could cause isotope enrichment natural environment research council nerc copyright 2008 reproduced with the permission of nerc published by john wiley sons ltd

water masses and circulation in the eurasian basin results from the oden 91 expedition the oden 91 north pole expedition obtained oceanographic measurements on four sections in the nansen and amundsen basins of the eurasian basin and in the makarov basin of the canadian basin thereby proving the feasibility of carrying out a typical oceanographic program using an icebreaker in the arctic ocean the data show greater spatial variability in water structure and circulation than was apparent from previous data the results show that a clear front exists between the eurasian and canadian basins such that upper halocline water in the canadian basin is almost absent from the eurasian basin the lower halocline water produced in the barents kara sea region permeates much of the eurasian basin and flows along the continental slope into the canadian basin the deeper circulation is strongly influenced by topography three return flows of the atlantic layer are identified one over the nansen gakkel ridge one over the lomonosov ridge and a third flowing from the canadian basin the slight differences observed in salinity and temperature characteristics of the deeper waters of the nansen and amundsen basins do not lead to an obvious explanation of their origin or flow pattern

sedimentary facies depositional environments and palaeogeographic evolution of the neogene denizli basin sw anatolia turkey abstract the denizli basin southwestern anatolia turkey contains a record of environmental changes dating since the early miocene detailed facies analysis of the neogene formations in this half graben enables us to document successive depositional regimes and palaeogeographic settings sedimentation commenced in the early miocene with the deposition of alluvial fan and fluvial facies kizilburun formation at this stage alluvial fans sourced from elevated areas to the south prograded towards the basin centre the middle miocene time saw the establishment of marginal lacustrine and wetland environments followed by the development of a shallow lake sazak formation the uppermost part of this unit consists of evaporitic saline lake and saline mudflat facies that grade upward into brackish lacustrine deposits of late miocene pliocene age kolankaya formation the lake became shallower at the end of the pliocene time as is indicated by expansion shoreface foreshore facies in the early quaternary the denizli basin was transformed into a graben by the activation of ese trending normal faults alluvial fans were active at the basin margins whereas a meandering river system occupied the basin central part oxygen isotope data from carbonates in the successive formations show an alternation of wetter climatic periods when fresh water settings predominated and very arid periods when the basin hosted brackish to hypersaline lakes the neogene sedimentation was controlled by an active ese trending major normal fault along the basin s southern margin and by climatically induced lake level changes the deposition was more or less continuous from the early miocene to late pliocene time with local unconformities developed only in the uppermost part of the basin fill succession the unconformable base of the overlying quaternary deposits reflects the basin s transformation from a half graben into a graben system

diagnostic study of the fram strait marginal ice zone during summer from 1983 and 1984 marginal ice zone experiment lagrangian observations from 1984 marginal ice zone experiment observations in fram strait three main results concerning large scale mesoscale and summer marginal ice zone miz features are presented and discussed in this paper regarding the large scale the main conclusion is that the east greenland current egc is a narrow stable current in contradiction with past results presenting the egc as a broad and unstable current in the mesoscale the west spitsbergen current wsc and the norwegian current are the main generators for eddies in fram strait these eddies propagate northwestward preferentially following topographic features like fracture zones which are quite abundant in this region in our opinion these wsc eddies represent an important part of the atlantic water recirculation in fram strait when approaching the east greenland continental slope they interact with the egc and they form well developed eddies these ice edge eddies associated with ice edge tongues are quite recognizable with remote sensing techniques the summer marginal ice zone in fram strait is clearly characterized by sea ice concentrations from 1 10 to 3 10 and floe sizes limited to 1 km or less there is a well defined limit which separates the pack ice from the miz where no big ice floes are ever recorded the breaking action of waves and swell propagating into the ice are likely to be the only mechanisms explaining such a drastic filtering effect according to their amplitudes and directions winds and eddies act in the miz in shrinking or stretching this zone

variational estimation of effective channel and ungauged anabranching river discharge from multi satellite water heights of different spatial sparsity abstract multi satellite sensing of continental water surfaces ws represents an unprecedented and increasing potential for studying ungauged hydrological and hydraulic processes from their signatures especially on complex flow zones such as anabranching rivers however the estimation of discharge from ws observations only is a very challenging ill posed inverse problem due to unknown bathymetry and friction in ungauged rivers measurements nature quality and spatio temporal resolutions regarding the flow model scales this paper proposes an effective 1d hydraulic modeling approach of sufficient complexity to describe anabranching river flows from sparse multisatellite observations using the hivdi inverse method presented in larnier et al 2019 with an augmented control vector including a spatially distributed friction law k x h depending on the flow depth h it is shown on 71 km of the xingu river anabranching amazon basin with altimetric water height timeseries that a fairly accurate upstream discharge hydrograph and effective patterns of channel bathymetry and friction can be infered simultaneously the coherence between the sparse observation grid and the fine hydraulic model grid is ensured in the optimization process by imposing a piecewise linear bathymetry profile b x which is consistent with thehydraulic visibility ofws signatures garambois et al 2017 montazem et al 2019 the discharge hydrograph q t at observation times and effective bathymetry friction b x k x h patterns are retrieved from 8 years of satellite altimetry envisat at 6 virtual stations vs along flow next the potential of the forthcoming swot data dense in space is highlighted by infering a discharge hydrograph and dense patterns of effective river bathymetry and friction a physically consistent scaling of friction by reaches enables to consider more dense bathymetry controls finally a numerical analysis shows i the importance of an unbiased prior information in the inference of a triplet q b x k x h from ws observations ii the clear signatures of river bottom slope break in low flows and width variations in high flows through the analysis of the friction slope term which is consistent with the findings of montazem et al 2019 from ws curvature analysis

bottom ablation and heat transfer coefficients from the 1983 marginal ice zone experiments bottom ablation in the marginal ice zone miz is a fundamental process that controls the ice edge position in both the winter and the summer during the east and west marginal ice zone experiments mizex west and mizex east in 1983 periodic sonic distance measurements between the overlying ice and transducers fixed on masts below ice floes determined the bottom ablation the melt rates for floes within 15 km of the ice edge ranged from near zero when the ice was in water at the freezing point to 0 5 m d 1 when the ice entered warm water greater than 3 k to the south simultaneous velocity and temperature measurements at 2 m below the ice in mizex west and at 2 m and 10 m below the ice in mizex east show the response of the melt rate to changing oceanographic conditions for the first time the combined oceanographic and ablation measurements allow the direct calculation of the bulk heat transfer coefficient ch between the ice and the ocean at 2 m and 10 m below the ice for the bering sea experiment ch was 8 10 4 while for the fram strait experiment ch varied from 2 10 4 to 4 10 4 within each set of experiments ch remained nearly constant over a wide range of melt rates relative ice water speeds and seawater temperatures

macrofossils in raraku lake easter island integrated with sedimentary and geochemical records towards a palaeoecological synthesis for the last 34 000 years abstract macrofossil analysis of a composite 19 m long sediment core from rano raraku lake easter island was related to litho sedimentary and geochemical features of the sediment strong stratigraphical patterns are shown by indirect gradient analyses of the data the good correspondence between the stratigraphical patterns derived from macrofossil correspondence analysis and sedimentary and geochemical data principal component analysis shows that macrofossil associations provide sound palaeolimnological information in conjunction with sedimentary data the main taphonomic factors influencing the macrofossil assemblages are run off from the catchment the littoral plant belt and the depositional environment within the basin five main stages during the last 34 000 calibrated years bp cal yr bp are characterised from the lithological geochemical and macrofossil data from 34 to 14 6 cal kyr bp last glacial period the sediments were largely derived from the catchment indicating a high energy lake environment with much erosion and run off bringing abundant plant trichomes lichens and mosses into the centre of raraku lake during the early holocene the infilling of the lake basin and warmer conditions favoured the growth of a littoral plant belt that obstructed terrigenous input cladoceran remains and solanaceae seeds are indicative of reduced run off and higher values of n and organic c indicate increased aquatic and catchment productivity from 8 7 to 4 5 cal kyr bp a swamp occupied the entire basin the increase of cyperaceae seeds reflects this swamp development and with oribatid mites and coleopteran remains indicates a peaty environment and more anoxic conditions in raraku at around 4 5 cal kyr bp dry conditions prevented peat growth and there is a sedimentary hiatus about 800 cal yr bp peat deposition resumed finally in the last few centuries a small lake formed within the surrounding swamp evidence of human activity is recorded in these uppermost sediments

forecasting coal resources and reserves in heterogeneous coal zones using 3d facies models as pontes basin nw spain abstract forecasting coal resources and reserves is critical for coal mine development thickness maps are commonly used for assessing coal resources and reserves however they are limited for capturing coal splitting effects in thick and heterogeneous coal zones as an alternative three dimensional geostatistical methods are used to populate facies distribution within a densely drilled heterogeneous coal zone in the as pontes basin nw spain coal distribution in this zone is mainly characterized by coal dominated areas in the central parts of the basin interfingering with terrigenous dominated alluvial fan zones at the margins the three dimensional models obtained are applied to forecast coal resources and reserves predictions using subsets of the entire dataset are also generated to understand the performance of methods under limited data constraints three dimensional facies interpolation methods tend to overestimate coal resources and reserves due to interpolation smoothing facies simulation methods yield similar resource predictions than conventional thickness map approximations reserves predicted by facies simulation methods are mainly influenced by a the specific coal proportion threshold used to determine if a block can be recovered or not and b the capability of the modelling strategy to reproduce areal trends in coal proportions and splitting between coal dominated and terrigenous dominated areas of the basin reserves predictions differ between the simulation methods even with dense conditioning datasets simulation methods can be ranked according to the correlation of their outputs with predictions from the directly interpolated coal proportion maps a with low density datasets sequential indicator simulation with trends yields the best correlation b with high density datasets sequential indicator simulation with post processing yields the best correlation because the areal trends are provided implicitly by the dense conditioning data

holocene climate in the northern great plains inferred from sediment stratigraphy stable isotopes carbonate geochemistry diatoms and pollen at moon lake north dakota abstract seismic stratigraphy sedimentary facies pollen stratigraphy diatom inferred salinity stable isotope 18 o and 13 c and chemical composition sr ca and mg ca of authigenic carbonates from moon lake cores provide a congruent holocene record of effective moisture for the eastern northern great plains between 11 700 and 9500 14 c yr b p the climate was cool and moist a gradual decrease in effective moisture occurred between 9500 and 7100 14 c yr b p a change at about 7100 14 c yr b p inaugurated the most arid period during the holocene between 7100 and 4000 14 c yr b p three arid phases occurred at 6600 6200 14 c yr b p 5400 5200 14 c yr b p and 4800 4600 14 c yr b p effective moisture generally increased after 4000 14 c yr b p but periods of low effective moisture occurred between 2900 2800 14 c yr b p and 1200 800 14 c yr b p the data also suggest high climatic variability during the last few centuries despite the overall congruence the biological diatom sedimentological isotopic and chemical proxies were occassionally out of phase at these times the evaporative process was not the only control of lake water chemical and isotopic composition

optimum and robust 3d facies interpolation strategies in a heterogeneous coal zone tertiary as pontes basin nw spain coal exploration and mining in extensively drilled and sampled coal zones can benefit from 3d statistical facies interpolation starting from closely spaced core descriptions and using interpolation methods a 3d optimum and robust facies distribution model was obtained for a thick heterogeneous coal zone deposited in the non marine as pontes basin oligocene early miocene nw spain several grid layering styles interpolation methods truncated inverse squared distance weighting truncated kriging truncated kriging with an areal trend indicator inverse squared distance weighting indicator kriging and indicator kriging with an areal trend and searching conditions were compared facies interpolation strategies were evaluated using visual comparison and cross validation moreover robustness of the resultant facies distribution with respect to variations in interpolation method input parameters was verified by taking into account several scenarios of uncertainty the resultant 3d facies reconstruction improves the understanding of the distribution and geometry of the coal facies furthermore since some coal quality properties e g calorific value or sulphur percentage display a good statistical correspondence with facies predicting the distribution of these properties using the reconstructed facies distribution as a template proved to be a powerful approach yielding more accurate and realistic reconstructions of these properties in the coal zone

δ13c δ18c covariance as a paleohydrological indicator for closed basin lakes the relationship between 18o and 13c in a closed basin lake is a function of hydrological change vapor exchange lake productivity and total co2 or carbonate alkalinity concentration covariance of 18o and 13c usually occurs in lake sediments under the condition of hydrological closure for time periods of the order of 5000 yr or longer on shorter time scales however certain subtleties in the use of the 13c 18o covariance as a hydrology history indicator must be recognized the covariant trend may not be found in hyper alkaline lakes because of the insensitivity of 13c to lake volume changes for less alkaline closed basin lakes covariance of 13c 18o will result from relatively rapid increase or decrease of lake volume with the rapid decrease condition giving rise to heavy and narrow ranged isotopic values for both 13c and 18o due to the coupled evaporation productivity effect when the lake volume remains stable as is the case for an over flowing open lake poor 13c 18o covariance will ensue due to the effect of vapor exchange with the atmosphere we have used the measured 13c 18o covariance in carbonate sediments of mono lake california to deduce paleo hydrological and lake water alkalinity and salinity variations and found the results in consonance with holocene lake level history derived from the 18o and other information

branching of atlantic water within the greenland spitsbergen passage an estimate of recirculation atlantic water aw supplies the largest source of heat mass and salt to the arctic ocean via fram strait greenland spitsbergen passage yet it represents only a fraction of the atlantic water that resides in the greenland iceland norwegian and barents seas this is a result of both the branching of the central core of aw along its northward flow and the modification of its t s signature through air sea ice interactions and internal mixing this paper addresses the quantitative analysis of the three dominant atlantic water cores within fram strait and north of 76 n using an 11 year 1977 to 1987 hydrographic database spatial variations of heat volume and salt along its flow path of some 600 km showed that the major core of atlantic water that directly enters the arctic ocean svalbard branch did not extend past 20 e of the 9719 km3 of atlantic water existing within the region one third resided within the svalbard branch the remainder 22 and 45 were held within the return atlantic current and the yermak branches respectively restricting the analysis to a southern limit of 79 n effectively removed the return atlantic current and showed a nearly equal split between the two remaining branches work completed by bourke et al 1988 indicated that the yermak branch is largely recirculated to the south if true this analysis supports rudels 1987 model estimate of a 50 recirculation of aw within this region

the gin sea a synthesis of its physical oceanography and literature review 1972 1985 abstract a synthesis and review of the physical oceanography of the gin sea greenland iceland and norwegian seas is presented an accompanying bibliography is included from 1972 through 1985 some 1986 works are also noted emphasis is placed on describing the gin sea as a major semi enclosed basin that plays a role unique among the world s oceans by providing a strong two way advective exchange between the ice covered polar sea and the north atlantic ocean and at the same time acting as the primary site for northern hemisphere bottom water formation the water masses for the gin sea are defined in a manner as consistent as possible with the literature the large scale oceanographic and meteorological factors influencing the water mass formation and circulation are described a sample calculation of the various horizontal and vertical thermohaline driven exchanges is given

diagenesis of late miocene micritic lacustrine carbonates madrid basin spain mud grade lacustrine limestones of miocene age from the madrid basin spain reveal varied and complex diagenetic histories microporous micrites occur as well as micrites with anhedral mosaics the micrites have recrystallized from a metastable precursor in part under sub oxic meteoric diagenetic conditions probably before extensive karstification in the pliocene the absence of aragonite relics their mainly micritic microfabric low sr content and covariant trend of sr and mg suggest that the micrites formed from mainly high magnesian calcite muds lacustrine micrites can be compared to marine forms and criteria used to assess the composition of the marine precursor muds can be applied to lacustrine limestones to complement other techniques to identify original lake water compositions

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

laboratory simulation of exchange through fram strait laboratory experiments and theory were conducted to observe the flow patterns and transport in both buoyancy driven and wind driven rotating fluids in lock exchange experiments water with one density flows into a second basin after a sliding gate is removed water of a second density flows back into the first basin the size and location of the currents for various values of density difference rotation rate and assorted sidewall geometries was recorded volume flux of the fluid was also measured and compared with a theory for lock exchange flow of a rotating fluid in a separate group of experiments with a passive upper layer easterly winds like those in the arctic ocean drive the upper level water into the arctic ocean and therefore oppose the buoyant exchange westerly winds would drive the water out of the arctic ocean this indicates that the exchange between the arctic ocean and the greenland norwegian sea is likely to be driven by buoyancy rather than by driven by wind crude estimates of the volumetric and fresh water exchange rate from the lock exchange formulas are compared with observed ocean fluxes and approximate agreement is found

saline outflow from the arctic ocean its contribution to the deep waters of the greenland norwegian and iceland seas abstractsince 1985 various investigators have proposed that norwegian sea deep water nsdw is formed by mixing of warm and saline deep water from the arctic ocean with the much colder and fresher deep water formed by convection in the greenland sea gsdw we here report on new observations which suggest significant modification and expansion of this conceptual model we find that saline outflows from the arctic ocean result in several distinct intermediate and deep salinity maxima within the greenland sea the southward transport of the two most saline modes is probably near 2 sv mixing of gsdw and the main outflow core found over the greenland slope derived from about 1700 m in the arctic ocean cannot by itself account for the properties of nsdw instead the formation of nsdw must at least in part involve a source which in the arctic ocean is found below 2000 m the mixing of various saline outflows is diapycnal while significant nsdw production appears to occur in northern fram strait large amounts of saline arctic ocean outflow also traverse the western greenland sea without mixing and enter the iceland sea during the past decade deep convection in the greenland sea has been greatly reduced while deep outflow from the arctic ocean appears to have continued resulting in a markedly warmer slightly more saline and less dense deep regime in the greenland sea american geophysical union 1991

isotope hydrology of early paleogene lake flagstaff central utah implications for cordilleran evolution lacustrine sediments from paleogene foreland basins of the north american cordillera serve as powerful integrators of information on climatic and tectonic conditions but episodes of hydrologic connection between basins may confound straightforward interpretations we use stable isotope ratios of carbon and oxygen in authigenic carbonates of the flagstaff formation in central utah to investigate the history of the lake system which produced these sediments flagstaff limestone and dolostone exhibit isotopic compositions consistent with having formed from the same fluid at surface conditions indicating high evaporative concentration was unnecessary to drive dolomite precipitation isotopic data are consistent with the flagstaff formation having been produced by a large lake which occupied its basin from the late paleocene into the early eocene lake flagstaff was hydrologically distinct from lake uinta to the north but may have been connected to lake claron in the south paleoaltimetry estimates suggest that the mean elevation of lake flagstaff9s catchment in the sevier highlands did not exceed 1 5 km the growing evidence from stable isotope data that cordilleran elevations were relatively low in the early paleogene is in stark contrast to structural and sedimentological evidence for a high nevadaplano and a topographically rugged sevier thrust belt

the late pleistocene evolution of palaeo megalake bungunnia southeastern australia a sedimentary record of fluctuating lake dynamics climate change and the formation of the modern murray river abstract the ephemeral lacustrine carbonates of the bungunnia limestone deposited in palaeo megalake bungunnia preserve a detailed record of pleistocene palaeoenvironmental and palaeoclimatic change in southeastern australia five distinct lake shorelines lake levels 0 4 are visible on digital elevation models ranging in elevation from around 70 m to 30 m above sea level the bungunnia limestone is preserved on the three lowest terraces ranging over 20 m in elevation lake levels 2 4 on the two higher of these terraces bungunnia limestone contains ooids and stromatolites and is calcite and aragonite dominated whereas on the lower terrace level bungunnia limestone is dolomite gypsum and magnesite dominated and preserves tepee structures and mud cracks thus lacustrine conditions are interpreted to have become increasingly saline and evaporitic over time reflecting an overall trend to more arid climatic regimes the highest lake level level 0 at around 70 m above sea level appears to relate to a period of significantly increased rainfall that allowed the lake to overflow for the first time marking the initiation of the modern murray river subsequently the lake fluctuated between 1 a steady state open lake system where water was overflowing across the padthaway high spillpoint and active gorge cutting was proceeding and 2 a closed lake system with no overflow that resulted in carbonate precipitating conditions during 1 shoreline erosion was occurring within the basin providing the terraces on which the bungunnia limestone carbonates were deposited during 2 in this 1 is likely to correspond with significantly wetter late pleistocene interglacial and 2 with arid glacial conditions the formation of the modern murray river and the demise of palaeo megalake bungunnia were therefore consequences of a combination of gorge cutting and increasing aridity resulting from interglacial glacial climate oscillation superimposed on significant overall climatic change

stable isotope characterization of the miocene lacustrine systems of los monegros ebro basin spain palaeogeographic and palaeoclimatic implications the lacustrine carbonate facies from three allostratigraphic units n1 n2 and n3 of miocene age in the los monegros region ebro basin are characterized isotopically the dominant facies are marls laminated limestones stromatolitic limestones massive limestones and bioturbated limestones these are associated with lacustrine sulphate deposits and distal alluvial facies palaeohydrological reconstructions of the study area are supported by the isotopic and the mineralogical composition of the carbonates massive and bioturbated limestones occupy a very similar compositional domain and have the lowest isotopic compositions of all the facies 9 18opdb 4 5 and 6 4 13cpdb 0 4 reflecting a short residence time of the water and variable commonly high influence of biogenic co2 laminated limestones and stromatolites define a comparatively enriched domain with 18o values ranging from 6 to 0 and 13c values ranging from 3 5 to 0 these values indicate stronger evaporation and enhanced 12c assimilation due to intense biological activity during periods of longer water residence time marls have isotopic values intermediate between these two domains and correspond to periods of lacustrine dilution dolomite bearing samples mainly laminated and stromatolitic facies show a 18odol cal 7 5 with respect to calcite from the same facies while 13c values show very little enrichment up to 1 the positive correlation r 0 85 between 18o and dolomite contents suggests that dolomite resulted from the progressive evaporative concentration of a single water mass and not from the mixing of waters of different compositions the dolomite is thought to be primary or at most the product of very early diagenetic processes the isotopic composition of the facies and their spatial and temporal variations depend on the depositional environment and were constrained by changing regional paleogeography isotopic trends from units n1 to n3 upper agenian vallesian period display a regular depletion in heavy isotopes that indicates a climatic change towards wetter conditions

an inverse modeling study in fram strait part ii water mass distribution and transports abstract a water mass analysis is carried out in fram strait between 77 15 and 81 15 n based on three dimensional large scale potential temperature and salinity distributions reconstructed from the mizex 84 hydrographic data collected in summer 1984 combining these distributions with the geostrophic flow field derived from the same data in a companion paper schlichtholz and houssais 1999 the heat fresh water and volume transports are estimated for each of the water masses identified in the strait twelve water masses are selected based on their different origins among them the polar water pw enters fram strait from the arctic ocean both over the greenland slope and over the western slope of the yermak plateau in the atlantic water aw range four modes with distinct geographical distributions are indentified in the deep water range the eurasian basin deep water ebdw is confined to the lena trough and to the molloy deep area where it is involved in a cyclonic circulation the warm and shallower mode of the norwegian sea deep water nsdw concentrated to the west is mainly seen as an outflow from the arctic ocean while the cold and deeper mode essentially observed to the east enters the strait from the greenland sea apart from the ebdw there is a tendency for all water masses of polar origin to flow along the greenland slope the two most abundant water masses the aw and the nsdw occupy as much as 67 of the total water volume the southward net transport of pw through fram strait is about 1 sv at 78 9 n at the same latitude the net transport of aw is southward and equal to about 1 7 sv only the transport of the warm mode aww is northward amounting to 0 2 sv the overall net outflow of the deep waters to the greenland sea is about 2 6 sv two upper water masses the fresh aw f and the cold awc mode of the aw and one deep water mass the nsdw appear to be produced in the strait with production rates between 77 6 and 79 9 n of about 0 2 1 0 and 1 7 sv respectively a southward net fresh water transport through the strait of about 2000 km 3 yr 1 relative to a salinity of 34 93 is mainly due to the pw the net heat transport relative to 0 1 c is northward but undergoes a rapid northward decrease suggesting an area averaged surface heat loss of 50 100 w m 2 in the strait

isotopic composition of siderite as an indicator of depositional environment compilation of available oxygen and carbon isotopic data for siderites from different depositional environments indicates that marine and continental siderites are characterized by distinctive compositional fields the most notable difference between the fields is the generally higher 13 c values of continental vs marine siderites this difference appears to reflect the fact that marine sediments generally undergo a more extensive period of sulfate reduction than do the continental sediments in which siderite forms analysis of siderite geochemistry may assist in determination of depositional environment in cases where the available sedimentological evidence is ambiguous

modern dolomite deposition in continental saline lakes western victoria australia microcrystalline dolomite forms a major constituent of holocene sediments of numerous continental saline playa lakes in southeastern australia the lake waters are highly supersaturated with respect to dolomite as well as other mg carbonates but undersaturated or near saturation with respect to calcite and aragonite the dolomite shows no replacement textures and most likely formed by direct precipitation conditions in these lakes that appear conducive to the precipitation of dolomite are 1 high salinity 2 high mg ca ratios and 3 high alkalinity the moderate sulfate levels of the brines do not seem to be inhibiting carbonate precipitation

composition of inland waters with marine like fauna and inferences for a miocene lake in spain abstract knowledge of the ionic composition of athalassic non marine waters where marine like organisms currently live allows to evaluate their ionic and total dissolved solid tds tolerance ranges together with other ecological data these chemical parameters can be used to interpret hydrological and hydrochemical conditions in ancient lake basins where analogous faunas have been recorded an example of such a utilization of the biological record is presented for miocene clastic dominated lacustrine deposits of the tertiary ebro basin of ne spain which contain marine like fossils comparison of the deduced chemical parameters for the miocene lake waters with the chemical composition of recent groundwaters and saline springs in the same area allows us to infer a similar mode of solute acquisition this implies that there were important cl so 4 saline inflows to the miocene lakes

winter oceanographic conditions in the fram strait yermak plateau region temperature salinity and currents were measured in the yermak plateau and northern fram strait region during march april 1989 an isothermal upper layer was near the freezing point everywhere except seaward of the ice edge near western svalbard temperatures in the underlying atlantic water layer decreased in general toward the northwest from maximum values in the west spitsbergen current west of svalbard mesoscale features were superimposed on this trend and the most apparent of these was a middepth 200 300 m warm filament overlying the northwestern flank of the plateau currents in the warm filament were northward at 2 4 cm s for a 10 day period in april providing a possible advective explanation for presence of the filament the mechanism for these currents may involve topographic control over a western extension of the north flowing west spitsbergen current or alternately rectification of diurnal currents which are enhanced by the bottom topography of the plateau our data favor the tidal rectification mechanism a warm core anticyclonic eddy associated with the filament contained atlantic water which was virtually unmodified from that occurring more than 200 km farther south characteristics of this eddy were consistent with an origin in the west spitsbergen current in the upper layer a generally cyclonic baroclinic circulation was present about the plateau measured upper layer current speeds were greatest 8 cm s in the southward flowing east greenland current where they exceeded the baroclinic currents by approximately 1 cm s which may represent a southward barotropic component farther to the northeast both measured and baroclinic upper layer currents were weak and variable

late miocene to plio pleistocene fluvio lacustrine system in the karacasu basin sw anatolia turkey depositional paleogeographic and paleoclimatic implications abstract the sedimentary record of the late cenozoic karacasu basin a long lived continental half graben from southwestern turkey is characterized by siliciclastic and carbonate deposits sedimentation was controlled by an active nw se trending major normal fault along the basin s southern margin and by climatically induced lake level changes detailed facies analysis subdivides the entire neogene quaternary basin fill into three distinct litostratigraphic units representing paleogeographic changes and sedimentation patterns throughout the basin evolution sedimentation commenced in the late miocene with the deposition of proximal medial alluvial fan and fluvial facies damdere formation fa1 at this stage alluvial fans developed in elevated areas to the south prograding towards the basin center at the beginning of the pliocene fresh to slightly alkaline shallow lake deposits fa2a of the karacaoren formation formed the lake became open and meromictic conditions developed fa2b pollen data from the fa2b facies show that climate was arid to humid climate probably changed cyclically through time producing alternation of artemisia steppe cold and dry periods and more forested vegetation warm and wet the open lake facies passes upwards into lake margin facies fa2c but it was still dominated by alkaline to slightly saline lake conditions sedimentation was almost continuous from the late miocene to pleistocene in the early quaternary the basin was dissected by the re activation of basin bounding faults the unconformable base of the overlying quaternary deposits karacasu formation fa3 reflected the basin s transformation from a half graben into a full graben system oxygen isotope data from carbonates show an alternation of humid climatic periods when freshwater settings predominated and semiarid arid periods in which the basin hosted alkaline and saline water lakes neotectonic activity has rejuvenated many of the basin bounding faults causing development of talus aprons and local alluvial fans the basin was progressively incised by modern rivers that have largely smoothed out the topographic relief of the graben margins

current regimes across the east greenland polar front at 78 40 north latitude during summer 1984 four weeks of concurrent temperature and current observations from three moorings across the east greenland polar front at approximately 78 40 n showed pronounced differences between the current regimes on either side of the front east of the front vertical shear was minimal mean flow was not statistically significant and fluctuations showed evidence of wind influence west of the front vertical shear and southward mean flow were significant however observed fluctuations were not strongly influenced by local winds the mean current and density structure of the front was similar to that of a two layer boundary current model with constant potential vorticity current fluctuations west of the front were in part related to mesoscale features generated farther north and subsequently advected downstream by the east greenland current or to eddylike features apparently generated through potential vorticity conservation local instabilities of the front most likely account for the remainder of the mesoscale variability seen in the records

pollen and non pollen palynomorphs of lake chalco as indicators of paleolimnological changes in high elevation tropical central mexico since mis 5

tectonic palaeoenvironmental forcing of clay mineral assemblages in nonmarine settings the oligocene miocene as pontes basin spain two small alluvial lacustrine subbasins developed during the early restraining overstep stages of the oligocene miocene as pontes strike slip basin nw spain later the basin evolved into a restraining bend stage and an alluvial swamp dominated depositional framework developed the palaeobiological record demonstrates that the oligocene miocene palaeoclimate in nw spain was subtropical warm and humid to subhumid the metamorphic and igneous basin catchment yielded clay assemblages made up by kaolinite illite and al smectite illite occurred as an original mineral in the source rock area whereas kaolinite and al smectite resulted mainly from weathering of feldspar and clinochlore respectively this detrital primary clay assemblage remained preserved in the colluvial alluvial fan and shallow lacustrine facies whose early diagenesis was influenced by diluted poorly evolved pore waters with neutral to slightly alkaline ph the original clay assemblage was mildly to strongly transformed under early diagenetic conditions in the lacustrine and swampy environments where significant hydrochemical and eh ph changes took place a fibrous magnesium rich clay mineral dominated assemblage palygorskite and sepiolite formed in shallow saline lakes and palustrine zones under the influence of magnesium rich alkaline waters moreover kaoliniteenriched assemblages formed in deep lacustrine swamp and swamp related alluvial zones under the influence of slightly to highly acidic pore waters pore water acidic conditions characterising environments with organic matter accumulation led to early diagenetic transformation of al smectite into kaolinite this process was relatively limited in some environments such as organic matter rich bottoms in meromictic lacustrine zones whereas it was pervasive in peat forming swamp zones the stratigraphic relationships between the diverse clay mineral assemblages in the as pontes basin fill demonstrate the coeval development of rather diverse clay compositions this clearly reflects the influence on clay assemblages of palaeoenvironmental changes forced by the morphological and tectonic evolution of the catchment basin system the interplay between climate and tectonic processes in the source areas did not result in major variations of the clay minerals fed into the basin conversely this tectonic sedimentation interplay influenced the evolution of the drainage and the water balance in the depositional zones causing a complex environmental hydrochemical evolution to occur as a consequence drastic early

large scale oceanography in fram strait during the 1984 marginal ice zone experiment the pattern of large scale circulation in fram strait during summer 1984 is inferred from hydrographic data and water mass analysis and direct current observations by use of surface and subsurface floats the west spitsbergen current carrying warm and salty atlantic water splits into several branches two flowing northward into the arctic ocean and two turning westward causing a recirculation across the main axis of fram strait the individual flow paths are topographically controlled suggesting a strong barotropic component of the circulation

lake qinghai china closed basin like levels and the oxygen isotope record for ostracoda since the latest pleistocene abstract in 1985 a sino swiss limnogeological expedition to china s largest inland lake recovered seismic profiles and piston cores to help calibrate palaeoclimatic models of monsoon and insolation fluctuations over the northern tibet qinghai plateau since the last glacial maximum lake qinghai a perennial lake with an area of 4278 km2 1985 at 3194 m above sea level receives drainage from 30 000 km2 of catchment near the northwest corner of the plateau the 26 5 m deep terminal lake 1985 with brackish alkaline magnesium sulphate rich waters 14 g 1 1 tds has not overflowed since the last glacial but its levels have responded to climatic and hydrologic changes seismic reflection profiles for the sub bottom sediment structures revealed a complex topography with channels relict terraces tectonic tilting and deformation in deposits buried under a 4 6 m packet of mainly flat bedded sediments from which core samples were recovered the lowermost cored material 14 500 yr b p comprises mainly water lain loess deposited in a smaller flood plain lake of up a few metres depth under cold arid climatic conditions ams radiocarbon dating indicates average sedimentation rates for latest pleistocene and holocene deposits in central basin regions of 0 3 0 5 mm yr 1 the 18o values of fossil ostracod valves provide a record of changes in the isotopic chemistry of the lake waters that can be related to the precipitation evaporation budgets which have controlled the palaeo levels for lake qinghai the precipitation evaporation budget for the lake qinghai region is largely determined by the asian monsoon system the lake qinghai sediment record shows that there was no large influx of glacoer melt waters into the lake basin during the post glacial the regional climate remained arid until at least 12 500 yr b p when an incipient monsoon was possibly initiated river transported silts first reached the basin centre at 11 800 yr b p when the lake depth may have increased to 5 m possibly a monsoonal weakening for several centuries after 10 800 yr b p europe younger dryas caused a further period of aridity at 10 200 yr b p the basin began filling towards modern lake dimensions in response to a permanent strengthening of the asian monsoon substantial lake level rises probably characterised the periods 10 200 9800 9500 8500 8300 7200 yr b p and through perhaps a century at about 6800 yr b p decreasing levels probably characterised the intervening intervals short term lake level fluctuations through the mid holocene climatic optimum were minimal indicating a very stable climatic hydrologic regime an isotopic steady state for the lake waters since 3000 500 yr b p obscures the climatic hydrologic regime dependent 18o gradient but there is little stratigraphic evidence to suggest that the lake level has been significantly below its present level since that time three negative 18o excursions for the lake waters may correspond to known glacier advances on the plateau at 3000 2000 and 1500 yr b p during china s neoglacial

lacustrine sedimentation in active volcanic settings the late quaternary depositional evolution of lake chungara northern chile lake chungara 18 15 s 69 09 w 4520 m above sea level is the largest 22ae5 km2 and deepest 40 m lacustrine ecosystem in the chilean altiplano and its location in an active volcanic setting provides an opportunity to evaluate environmental volcanic vs climatic controls on lacustrine sedimentation the late quaternary depositional history of the lake is reconstructed by means of a multiproxy study of 15 kullenberg cores and seismic data the chronological framework is supported by 10 14c ams dates and one 230th 234u dates lake chungara was formed prior to 12ae8 cal kyr bp as a result of the partial collapse of the parinacota volcano that impounded the lauca river the sedimentary architecture of the lacustrine succession has been controlled by i the strong inherited palaeo relief and ii changes in the accommodation space caused by lake level fluctuations and tectonic subsidence the first factor determined the location of the depocentre in the nw of the central plain the second factor caused the area of deposition to extend towards the eastern and southern basin margins with accumulation of high stand sediments on the elevated marginal platforms synsedimentary normal faulting also increased accommodation and increased the rate of sedimentation in the northern part of the basin six sedimentary units were identified and correlated in the basin mainly using tephra keybeds unit 1 late pleistocene early holocene is made up of laminated diatomite with some carbonate rich calcite and aragonite laminae unit 2 mid holocene recent is composed of massive to bedded diatomite with abundant tephra lapilli and ash layers some carbonate rich layers calcite and aragonite occur unit 3 consists of macrophyte rich diatomite deposited in nearshore environments unit 4 is composed of littoral sediments dominated by alternating charophyterich and other aquatic macrophyte rich facies littoral carbonate productivity peaked when suitable shallow platforms were available for charophyte colonization clastic deposits in the lake are restricted to lake margins units 5 and 6 diatom productivity peaked during a lowstand period unit 1 and subunit 2a and was probably favoured by photic conditions affecting larger areas of the lake bottom offshore carbonate precipitation reached its maximum during the early to mid holocene ca 7ae8 and 6ae4 cal kyr bp this may have been favoured by increases in lake solute concentrations resulting from evaporation and calcium input because of the compositional changes in pyroclastic supply diatom and pollen data from offshore cores suggest a number of lake level fluctuations a late pleistocene deepening episode ca 12ae6 cal kyr bp four shallowing episodes during the early to mid holocene ca 10ae5 9ae8 7ae8 and 6ae7 cal kyr bp and higher lake levels since the mid holocene ca 5ae7 cal kyr bp until the present explosive activity at parinacota volcano was very limited between c 12ae8 and 7ae8 cal kyr bp mafic rich explosive eruptions from the ajata satellite cones increased after ca 5ae7 cal kyr bp until the present

the origin of norwegian sea deep water a nearly homogeneous water mass the norwegian sea deep water is found below 2000 m depth in the norwegian and lofoten basins of the norwegian sea recent observations indicate that this water is a mixture of relatively cold and fresh greenland sea deep water with warmer saltier eurasian basin deep water from the arctic ocean we have found this mixture along the western and southern periphery of the greenland sea near the level where the pressure compensated densities of the parent water masses are equal the along isopycnal mixing produces a remarkably uniform water mass which can be traced only a short distance away from its entry into the norwegian sea through gaps in the mid ocean ridge north of jan mayen island direct measurements of flow through these gaps confirm motion in the proper sense to accomplish this connection

the coal bearing cenozoic as pontes basin northwestern spain geological influence on coal characteristics lignite deposits in the cenozoic as pontes strike slip basin northwestern spain were formed as a function of specific paleoclimatic conditions and tectonic evolution of the basin during the early evolutionary stages the presence of active normal faults and thrusts inside the basin resulted in two subbasins with distinct differences in sedimentary records with respect to lignite seam occurrence thickness area1 extent and lithotype development in contrast during the late evolutionary stages the basin was not split and a more homogeneous sedimentary record in terms of coal seam occurrence and lithotype characteristics developed a total of 26 lignite samples distributed along the basin infill were analyzed by organic petrography and geochemistry all are lignite b astm the lignites deposited during lower basin infill sedimentation units 1 and 2 are dark matrix rich mainly huminitic brown coals with minor bright liptinitic rich coal lithotypes the dark huminitic coals in these units show sedimentological and paleontological evidence of lacustrine influence persistent relatively moderate to low tissue preservation index tpi values and high average gelification index gi values are characteristic of these limno telmatic coals lignites in the upper basin infill unit 4 are almost exclusively matrix rich huminitic brown coals persistent widespread low tpi values and variable but low average gi values are also characteristic of these telmatic coals the overall coal petrological data trend tpi gi and widespread development or absence of liptiniteenriched lignite layers recorded from the lower to the upper basin infill units agrees with the stratigraphic and sedimentological data which show a trend of increasingly drier conditions development of bright liptinite enriched lignite layers was widespread during the early basin evolutionary stages and was influenced by punctuated water table oscillations sedimentological petrological and organic geochemical data point to the conclusion that although the paleoenvironments where peat deposition took place did not undergo dramatic changes they were affected by distinguishable

glacial to holocene climate changes in the se pacific the raraku lake sedimentary record easter island 27 s abstract easter island se pacific 27 s provides a unique opportunity to reconstruct past climate changes in the south pacific region based on terrestrial archives although the general climate evolution of the south pacific since the last glacial maximum lgm is coherent with terrestrial records in southern south america and polynesia the details of the dynamics of the shifting westerlies the south pacific convergence zone and the south pacific anticyclone during the glacial interglacial transition and the holocene and the large scale controls on precipitation in tropical and extratropical regions remain elusive here we present a high resolution reconstruction of lake dynamics watershed processes and paleohydrology for the last 34 000 cal yrs bp based on a sedimentological and geochemical multiproxy study of 8 cores from the raraku lake sediments constrained by 22 ams radiocarbon dates this multicore strategy has reconstructed the sedimentary architecture of the lake infilling and provided a stratigraphic framework to integrate and correlate previous core and vegetation studies conducted in the lake high lake levels and clastic input dominated sedimentation in raraku lake between 34 and 28 cal kyr bp sedimentological and geochemical evidences support previously reported pollen data showing a relatively open forest and a cold and relatively humid climate during the glacial period between 28 and 17 3 cal kyr bp including the lgm period colder conditions contributed to a reduction of the tree coverage in the island the coherent climate patterns in subtropical and mid latitudes of chile and eastern island for the lgm more humid conditions suggest stronger influence of the antarctic circumpolar current and an enhancement of the westerlies the end of glacial period occurred at 17 3 cal kyr bp and was characterized by a sharp decrease in lake level conducive to the development of major flood events and erosion of littoral sediments deglaciation termination 1 between 17 3 and 12 5 cal kyr bp was characterized by an increase in lake productivity a decrease in the terrigenous input and a rapid lake level recovery inaugurating a period of intermediate lake levels dominance of organic deposition and algal lamination the timing and duration of deglaciation events in easter island broadly agree with other mid and low latitude circum south pacific terrestrial records the transition to the holocene was characterized by lower lake levels the lake level dropped during the early holocene ca 9 5 cal kyr bp and swamp and shallow lake conditions dominated till mid holocene partially favored by the infilling of the lacustrine basin during the mid to late holocene drought phases led to periods of persistent low water table subaerial exposure and erosion generating a sedimentary hiatus in the raraku sequence from 4 2 to 0 8 cal kyr bp the presence of this dry mid holocene phase also identified in low andean latitudes and in patagonian mid latitudes suggests that the shift of storm tracks caused by changes in the austral summer insolation or forced by el nino like dominant conditions have occurred at a regional scale the palm deforestation of the easter island attributed to the human impact could have started earlier during the 4 2 0 8 cal kyr bp sedimentary gap our paleoclimatic data provides insights about the climate scenarios that could favor the arrival of the polynesian people to the island if it occurred at ca ad 800 it coincided with the warmer conditions of the medieval climate anomaly whereas if it took place at ca ad 1300 it was favored by enhanced westerlies at the onset of the little ice age changes in land uses farming intensive cattle during the last century had a large impact in the hydrology and limnology eutrophication of the lake

hydraulic visibility using satellite altimetry to parameterize a hydraulic model of an ungauged reach of a braided river what hydraulic information can be gained from remotely sensed observations of a river s surface in this study we analyze the relationship between river bed undulations and water surfaces for an ungauged reach of the xingu river a first order tributary of the amazon river this braided reach is crosscut more than 10 times by a envisat environmental satellite track that extends over 100 km rating curves based on a modeled discharge series and altimetric measurements are used including the zero flow depth z0 parameter which describes river s bathymetry river widths are determined from jers japanese earth ressources satellite images hydrodynamic laws predict that irregularities in the geometry of a river bed produce spatial and temporal variations in the water level as well as in its slope observation of these changes is a goal of the surface water and ocean topography satellite mission which has a final objective of determining river discharge first the concept of hydraulic visibility is introduced and the seasonality of water surface slope is highlighted along with different flow regimes and reach behaviors then we propose a new single thread effective hydraulic approach for modeling braided rivers flows based on the observation scales of current satellite altimetry the effective hydraulic model is able to reproduce water surface elevations derived by satellite altimetry and it shows that hydrodynamical signatures are more visible in areas where the river bed morphology varies significantly and for reaches with strong downstream control the results of this study suggest that longitudinal variations of the slope might be an interesting criteria for the analysis of river segmentation into elementary reaches for the surface water ocean topography mission that will provide continuous measurements of the water surface elevations the slopes and the reach widths

sedimentological and palaeohydrological responses to tectonics and climate in a small closed lacustrine system oligocene as pontes basin spain a small closed lacustrine system developed during the restraining overstep stages of the oligocene as pontes strike slip basin spain the increase in basin accommodation and the headward spread of the drainage which increased the water input triggered a change from shallow holomictic to deeper meromictic conditions the lower shallow lacustrine assemblage consists of mudstone carbonate cycles recording lacustrine palustrine ramp deposition in a saline lake high sr content in some early diagenetic calcites suggests that aragonite and calcite made up the primary carbonate muds early dolomitization took place together with widespread pedogenic activity the upper deep freshwater lacustrine assemblage includes bundles of carbonate clay rhythmites and fine grained turbidite beds primary calcite and diagenetic siderite make up the carbonate laminae the mg content of the primary carbonates records variations in mg ca ratios in lacustrine waters d 18 o and d 13 c covariance trends in calcite reinforce closed drainage conditions d 18 o data indicate that the lake system changed rapidly from short lived isotopically light periods i e from seasonal to pluriannual to longer steadystate periods of heavier d 18 o i e from pluriannual to millennial the small d 13 c changes in the covariant trends were caused by dilute inflow changing the contributions of dissolved organic carbon in the system and or internal variations in lacustrine organic productivity and recycling in both shallow and deep carbonate facies sulphate reduction and methanogenesis may account respectively for the larger negative and positive d 13 c shifts recorded in the early diagenetic carbonates calcite dolomite and siderite the lacustrine system was very susceptible to high frequency climatically forced water balance variations these climatic oscillations interfered with the lowfrequency tectonic and morphological changes in the basin catchment this resulted in the superposition of high order depositional mineralogical and geochemical cycles and rhythms on the lower order lacustrine infill sequence

comparisons of observed and modeled elastic responses to hydrological loading in the amazon basin in large hydrological basin water mass loading can produce significant crustal deformation we compare the monthly vertical component of 18 gps sites located in the amazon basin with the deflection models derived from grace observations in the one hand and derived from hydl a global hydrological model in the other hand the gps dataset includes the largest deflections by hydrological loading ever recorded at two stations located in the center of the basin the main result of the study is that the grace solution produced by grgs groupe de recherche en geodesie spatiale toulouse france produces the best agreement with the gnss series with a correlation coefficient up to 0 9 in the center of the basin although 70 at best of the rms variation in the gps series is accounted

estimation of multiple inflows and effective channel by assimilation of multi satellite hydraulic signatures the ungauged anabranching negro river abstract with the upcoming swot satellite mission which should provide spatially dense river surface elevation width and slope observations globally comes the opportunity to assimilate such data into hydrodynamic models from the reach scale to the hydrographic network scale based on the hivdi hierarchical variational discharge inversion modeling strategy larnier et al 2020 this study tackles the forward and inverse modeling capabilities of distributed channel parameters and multiple inflows in the 1d saint venant model from multisatellite observations of river surface it is shown on synthetic cases that the estimation of both inflows and distributed channel parameters bathymetry friction is achievable with a minimum spatial observability between inflows as long as their hydraulic signature is sampled next a real case is studied 871 km of the negro river amazon basin including complex multichannel reaches 21 tributaries and backwater controls from major confluences an effective modeling approach is proposed using i ws elevations from envisat data and dense in situ gps flow lines moreira 2016 ii average river top widths from optical imagery pekel et al 2016 iii upstream and lateral flows from the mgb large scale hydrological model paiva et al 2013a the calibrated effective hydraulic model closely fits satellite altimetry observations and presents real like spatial variabilities flood wave propagation and water surface observation frequential features are analyzed with identifiability maps following brisset et al 2018 synthetic swot observations are generated from the simulated flowlines and allow to infer model parameters 436 effective bathymetry points 17 friction patches and 22 upstream and lateral hydrographs given hydraulically coherent prior parameter values inferences of channel parameters carried out on this fine hydraulic model applied at a large scale give satisfying results using noisy swot like data at reach scale inferences of spatially distributed temporal parameters lateral inflows give satisfying results as well with even relatively small scale hydrograph variations being inferred accurately on this long reach this study brings insights in i the hydraulic visibility of the signatures of multiple inflow hydrographs at a large scale with swot ii the simultaneous identifiability of spatially distributed channel parameters and inflows by assimilation of satellite altimetry data iii the need for prior information iv the need to further tailor and scale network hydrodynamic models and assimilation methods to improve the fusion of multisource information and potential information feedback to hydrological modules in integrated chains