proportions of convective and stratiform precipitation revealed in water isotope ratios distinguishing convective and stratiform rainfall is key to understanding how the water cycle responds to climate change an analysis of satellite and surface data shows that rain isotope ratios reflect the proportions of these types of rain

influences of large scale convection and moisture source on monthly precipitation isotope ratios observed in thailand southeast asia abstract many paleoclimatic records in southeast asia rely on rainfall isotope ratios as proxies for past hydroclimatic variability however the physical processes controlling modern rainfall isotopic behaviors in the region is poorly constrained here we combined isotopic measurements at six sites across thailand with an isotope incorporated atmospheric circulation model isogsm and the hybrid single particle lagrangian integrated trajectory hysplit model to investigate the factors that govern the variability of precipitation isotope ratios in this region results show that rainfall isotope ratios are both correlated with local rainfall amount and regional outgoing longwave radiation suggesting that rainfall isotope ratios in this region are controlled not only by local rain amount amount effect but also by large scale convection as a transition zone between the indian monsoon and the western north pacific monsoon the spatial difference of observed precipitation isotope among different sites are associated with moisture source these results highlight the importance of regional processes in determining rainfall isotope ratios in the tropics and provide constraints on the interpretation of paleo precipitation isotope records in the context of regional climate dynamics

the mathematics of early diagenesis from worms to waves the changes that sediments undergo after deposition are collectively known as diagenesis diagenesis is not widely recognized as a source for mathematical ideas however the myriad processes responsible for these changes lead to a wide variety of mathematical models in fact most of the classical models and methods of applied mathematics emerge naturally from quantification of diagenesis for example small scale sediment mixing by bottom dwelling animals can be described by the diffusion equation the dissolution of biogenic opal in sediments leads to sets of coupled nonlinear ordinary differential equations and modeling organisms that eat at depth in the sediment and defecate at the surface suggests the one dimensional wave equation while the effect of waves on pore waters is governed by the two or three dimensional wave equation diagenetic modeling however is not restricted to classical methods diagenetic problems of concern to modern mathematics exist in abundance these include free boundary problems that predict the depth of biological mixing or the penetration of o2 into sediments algebraic differential equations that result from the fast reversible reactions that regulate ph in pore waters inverse calculations of input functions histories and the determination of the optimum choice in a hierarchy of possible diagenetic models this review highlights and explores these topics with the hope of encouraging further modeling and analysis of diagenetic phenomena

vertical distribution of feeding and particle selective transport of 137cs in lake sediments by lumbriculid oligochaetes lumbriculid oligochaetes are an important member of the conveyor belt deposit feeding species responsible for advective reworking of profundal sediments in the great lakes these threadlike worms ingest sediments over a range of depths 0 5 cm and deposit gut contents at the sediment surface this action results in a depth dependent particle advection rate which can be related to the distribution of their feeding in this study two replicate microcosms of rectangular cross section 3 5 cm containing evenly spaced 1 cm thin layers 0 5 mm of sediment labeled with gamma emitting 137cs were inoculated with the lumbriculid stylodrilus heringianus at a density of 7 9 104 m 2 10 c the subsequent amount of tracer lost from each layer as well as the downward movement of the layers were determined by peiodically scanning the length of the cells with a well collimated gamma detector system during the course of the 600 hour experiment 137cs activities decreased only in layers between 0 and 6 cm depth these decreases were accompanied by the appearance of a new layer at the sediment surface between 80 and 90 of the activity lost from the underlying layers appeared in the emergent surface peak thus indicating that subsurface defecation was minor aspect of conveyor belt transport decreases in 137cs activity within layers were consistent with first order kinetics with a maximum loss rate of about 0 08 hour 1 the vertical distribution of the rate constant was very nearly gaussian with the maximum at 3 3 cm and a spread sd of 1 4 cm the rate of layer burial decreased monotonically but nonlinearly with sediment depth from an extrapolated surface value of about 1 8 10 2 mm h 1 a model based on conservation of mass was developed which relates the tracer feeding distribution to the velocity distribution assuming that the distribution of mass removed through feeding was proportional to the amount of tracer removed the model takes rigorous account of depth dependent porosity and provides an excellent description of the velocity distributions if the transfer of 137cs is taken to be 1 67 times the mass transfer rate this factor termed the feeding selectivity factor is attributed to the selection of fine particles by worms and is important in models describing trace and contaminant diagenesis in sediments reworked by conveyor belt species

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

plutonium and210pb distributions in northeast atlantic sediments subsurface anomalies caused by non local mixing abstract the depth distributions of 210 pb and 239 240 pu measured in a suite of box cores collected from water depths of 4000 5000 m in the northeast atlantic ocean exhibit pronounced subsurface maxima caused by sediment reworking by benthic infauna small scale spatial heterogeneity in bioturbation rates is indicated by large differences in tracer profiles from duplicate cores separated only by a few centimeters 210 pb and 239 240 pu activity distributions from each subcore exhibit a high degree of correlation and most tracer profiles exhibit one or more subsurface maxima one dimensional biodiffusion analogue models do not adequately simulate the principal features of this data set however an inverse conveyer belt mixing model which simulates subsurface egestion or a functionally equivalent process of surficial material which is enriched both in organic debris and radioactive tracers can reproduce the subsurface tracer maxima single event and continuous subsurface egestion models have been formulated and solved for different feeding rates and background biodiffusive fields the single event model provides a better fit to the data and in particular ensures the observed high degree of correlation between the 210 pb and 239 240 pu activity profiles regardless of the different tracer input functions the most likely candidate responsible for subsurface tracer egestion is a large infaunal worm of the phylum sipunculida which dominates the biomass below a depth of 3 cm

strong influence of water vapor source dynamics on stable isotopes in precipitation observed in southern meghalaya ne india to calibrate 18o time series from speleothems in the eastern indian summer monsoon ism region of india and to understand the moisture regime over the northern bay of bengal bob we analyze the 18o and d of rainwater collected in 2007 and 2008 near cherrapunji india d values range from 18 5 to 144 4 while 18o varies between 0 8 and 18 8 the local meteoric water line lmwl is found to be indistinguishable from the global meteoric water line gmwl late ism september october rainfall exhibits lowest 18o and d values with little relationship to the local precipitation amount there is a trend to lighter isotope values over the course of the ism but it does not correlate with the patterns of temperature and rainfall amount 18o and d time series have to be interpreted with caution in terms of the amount effect in this subtropical region we find that the temporal trend in 18o reflects increasing transport distance during the ism isotopic changes in the northern bob surface waters during late ism and vapor re equilibration with rain droplets using an isotope box model for surface ocean waters we quantify the potential influence of river runoff on the isotopic composition of the seasonal freshwater plume in the northern bob temporal variations in this source can contribute up to 25 of the observed changes in stable isotopes of precipitation in ne india to delineate other moisture sources we use backward trajectory computations and find a strong correlation between source region and isotopic composition palaeoclimatic stable isotope time series from northeast indian speleothems likely reflect changes in moisture source and transport pathway as well as the isotopic composition of the bob surface water all of which in turn reflect ism strength stalagmite records from the region can therefore be interpreted as integrated measures of the ism strength

mixing sedimentation rates and age dating for sediment cores abstract analytic solutions to the advection diffusion equation useful as a guide for the interpretation of mixing sedimentation rate and age dating effects in sediment cores have been derived various simplified mixing models appropriate to 14 c and 210 pb measurements have been considered the emphasis has been on a discussion of the various interrelations and dependencies among the mixing coefficient sedimentation rate and radioactive decay constant parameters in determining the 14 c and 210 pb concentrations as a function of depth porosity variations within the sediment column are also considered and the transformed advection diffusion equation including porosity effects is derived

a model for particle selective transport of tracers in sediments with conveyor belt deposit feeders conveyor belt deposit feeding organisms prevalent in both marine and freshwater systems have a profound effect on sediment properties and transport processes these organisms ingest sediments over a range of depths while depositing gut contents from tails protruding above the sediment surface this action results in particle selective transfer of buried materials to the sediment surface and imposes an accelerated rate of sediment and pore water burial within the feeding zone most previous efforts to combine sediment diagenesis with the effects of biogenic reworking characterize mixing as exclusively diffusive and ignore such major advective effects here a model is developed based on fundamental diagenetic equations for transport and reaction for the distribution of tracers in accumulating sediments subject to compaction and diffusive as well as advective redistribution by benthic organisms conveyor belt cb feeding is characterized as a first order process with a depth dependent rate constant which is either localized gaussian or distributed integrated gaussian biogenic diffusivity of bulk sediments is allowed these alternative depth dependences as well the model assumes simple linear adsorption of the tracer between solid and solution phases and uses a time dependent flux at x 0 which is a combination of that originating externally and the depth integrated contributions from feeding particle selectivity is introduced by applying mass conservation separately to transport of the tracer and bulk sediments properties of the model are illustrated for tracers in nondispersive systems strongly bound to sediment solids cb recycling gives rise to transient reflections on passage of a tracer pulse through the zone of bioturbation reflections readily disappear in the presence of various integrative processes the system time resolution is defined in terms of the downward propagation of dual tracer pulses and shown to be systematically degraded by intensified feeding and selective transport a simple expression is developed for estimating the magnitude of particle selective changes in steady state surface concentrations in terms of the particle selectivity factor and the efficiency of sediment reworking unrecognized particle selectivity can lead to false inferences about changes in the rate of delivery of tracers to sediments selective cb recycling can cause a tracer such as 210pb to be retained largely within the bioturbation zone so that relatively little activity reaches the region of sediment useful for geochronological interpretation increased selectivity accentuates the sensitivity of the profile to details of the reworking process the model applied to previous studies of cb deposit feeders in tracer labeled freshwater microcosms shows the need to include particle diffusion as well as advection in the treatment of cb transport

extracting the benthic mixing impulse response function a constrained deconvolution technique abstract benthic mixing or bioturbation acts as a low pass filter on stratigraphic signals altering both the apparent rates and amplitudes of recorded events the mixing process is represented as a time invariant convolution and uses an impulse response function irf parameterized in terms of mixed layer thickness and mixing intensity diffusion coefficient such parameterization facilitates construction of the inverse deconvolution model which is used to examine the effects of incorrect irf characterization on deconvolution results results show that mixing intensity is as important a parameter as mixed layer thickness when unmixing a stratigraphic signal stable oxygen isotope records from two different species of planktonic foraminifers with changing relative abundances in the same core will show apparent offsets in the timing of events due to mixing the offset can be used with the appropriate unmixing equation to constrain mixed layer thickness and mixing intensity based on analysis of actual isotope signals the assumption is that any offsets in the records of the two species are totally a product of the mixing process the technique was applied to a high resolution glacial interglacial record termination ii from an equatorial pacific piston core multiple lateral subsamples were stacked to increase signal to noise ratio a multidimensional nonlinear optimization routine simplex was used to minimize an error function related to stratigraphic offsets between the two species a solution to this problem yielded a mixed layer 5 cm thick and a mixing intensity of 7 cm2 ka 1 this mixed layer thickness is at the low end of estimates based on 14c profiles in box cores from the same geographic area the mixing operator is probably conservative and does not take into account that sedimentation rates were higher during the last glacial period than during the holocene this may explain the inability of the algorithm to completely remove the stratigraphic offset between the two isotope records the unmixed record using the parameters 5 cm and 7 cm2 ka 1 shows a deglaciation overshoot which is distinctly smaller than the meltwater spike proposed earlier i e less than 0 1 versus a range of 0 3 1

active crustal deformation in the marmara sea region nw anatolia inferred from gps measurements deformation in the boundary zone between the anatolian and eurasian plates has been determined by means of repeated global positioning system gps measurements three campaigns 1990 1992 1994 were carried out around the marmara sea the network lies within the active earthquake belt of nw anatolia extending from the western part of the north anatolian fault zone nafz to the aegean extensional province results of the dense network consisting of 52 sites clearly reveal the westward motion of anatolia the rates amount to 17 mm a 3 mm a on average relative to istanbul located at the northeastern edge of the sea of marmara based on the trajectories for the displacements of the observation sites it is concluded that the marmara sea forms a transition zone between the europe fixed region of thrace black sea eurasia and nw anatolia at the western extremity of nw anatolia the motion bends from w to wsw 247 the strain field calculated yields an e w oriented right lateral strike slip movement average 0 12 ppm a maximum 0 41 ppm a accompanied by ne sw extension average 0 12 ppm a maximum 0 52 ppm a at the eastern end of the marmara sea and n s extension at the aegean shore line comparisons with the directions of t axes derived from 65 fault plane solutions of earthquakes show remarkable agreement

a model for 137cs and other tracers in lake sediments considering particle size and the inverse solution abstract a numerical model for the time dependent behavior of particle associated tracers in sediments has been developed the model is based on the advection diffusion equation for a tracer and includes a sediment density that increases with depth as a modified power function and a diffusion coefficient that follows a half gaussian function versus depth with maximal diffusivity at the sediment water interface the solution procedure is based on finite elements or finite differences the density function is developed from soil mechanics concepts and includes mixing effects through a young s modulus that is increased in the top layer according to a half gaussian function the new density function provides a better fit to 15 out of 17 sediment cores from lake michigan than a frequently used exponential expression the tracer model provides an excellent fit for the 137cs distributions in all of the 17 lake michigan cores that were investigated our fit to the 137cs profile of a southern lake michigan core that has been examined by others is significantly better than previous fits particularly near the top of the core from two different forms of the governing equation for a tracer and the resultant fits to experimental data it appears that 137cs is associated with colloidal and 210pb with settling particles a previously developed time domain method to extract the historical input record of a tracer from its sedimentary profile influenced by mixing has been further improved by including m depth and n time intervals where m n and by fitting the influx to a polynomial the improved method is demonstrated for the cd input to a northern lake michigan core nlm84b although the time resolution obtained 5 yr is better than the previous resolution 15 yr it is clear that the method needs to undergo further development in order to decrease the error of the reconstructed influx and particularly to avoid negative fluxes

determination of mixing parameters from tracer distributions in deep sea sediment cores abstract computer optimization and approximate analytical procedures are developed for the determination of the depth of bioturbation mixing d and the mixing coefficient d for instantaneous tracer inputs the methods have been applied to observations of microtektites volcanic ash and pumice in sixteen deep sea sediment cores the values for d are well determined generally with confidence intervals of a few centimeters or less and with an average value of d 11 cm for the sixteen cores the values for d are determined to first figure accuracy at best with values of around 10 cm 2 ka 1 or greater

interpretation procedures for the determination of sediment parameters from time dependent flux inputs abstract a formulation for the effects of a time dependent input flux to a sedimentation system consisting of a diffusive layer underlain by a non diffusive medium has been developed the intent is to provide interpretation procedures for the determination of sedimentation rate diffusion coefficient and mixed layer thickness from observed tracer concentrations they have been applied for illustrative purposes to published137cs and239 240pu measurements

differing source water inputs moderated by evaporative enrichment determine the contrasting δ18ocellulose signals in maritime antarctic moss peat banks 1 oxygen isotope palaeoclimate records preserved in moss tissue cellulose are complicated by environmental influences on the relationships between source water inputs and evaporative conditions we carried out stable isotope analyses of precipitation collected from the maritime antarctic and cellulose extracted from co located chorisodontium aciphyllum dominated moss peat bank deposits accumulated since 1870 a d analyses of stable oxygen and hydrogen isotope composition of summer precipitation on signy island 60 7 s 45 6 w established a local meteoric water line lmwl similar to both the global mwl and other lmwls and almost identical to the hadam3 isotope enabled global circulation model output the oxygen isotopic composition of cellulose 18oc revealed little temporal variation between four moss peat banks on signy island since 1870 however 18oc followed two patterns with sites a and d consistently 3 enriched relative to 18oc values from sites b and c the growing moss surfaces at sites a and d are likely to have been hydrated by isotopically heavier summer precipitation whilst at sites b and c the moss banks are regularly saturated by the isotopically depleted snow melt streams laboratory experiments revealed that evaporative enrichment of c aciphyllum moss leaf water by 5 occurred rapidly following saturation ecologically equivalent to post rainfall or snow melt periods in addition to the recognized source water cellulose fractionation extent of 27 3 such a shift would account for the 32 difference measured between 18o of signy island precipitation and cellulose

modeling radiotracers in sediments comparison with observations in lakes huron and michigan a comprehensive model for the activity of radionuclides in sediments is presented the model is based on the advection diffusion equations for sediment solids and a radioactive tracer mixing caused by deposit feeders is taken into account by a half gaussian hg integrated gaussian ig or exponential ex diffusion coefficient with a maximum value d0 at the sediment water interface and an effective mixing depth m where m hg zm ig or a ex compaction is described by an exponential bulk sediment density the differential equations are solved by finite differences in particular the crank nicolson method for the time dependent case cs 137 estimation of the mixing parameters d0 and m is carried out efficiently by minimizing chi square for measured and calculated steady state pb 210 activities the derived mixing depths of zm 4 6 0 1 cm station 14 and a 0 8 0 1 cm station 18 for the cores from lake huron are in good agreement with the organism distributions the corresponding d0 values are 12 2 and 1 5 0 5 cm2 yr respectively where the latter number is lower than a previous lower limit estimate 3 3 cm2 yr based on 1974 data these diffusion coefficients are in excellent agreement with those inferred from the densities of pontoporeia and tubificid oligochaetes 9 3 and 1 6 cm2 yr respectively compared with southern lake michigan there appears to be less sediment focusing in northern lake michigan where the ratios of measured to atmospheric cs 137 inventories have an average value of 0 89 and range from 0 32 to 1 41 for six cores from the deep basin when these ratios are used to correct the pb 210 fluxes we obtain an atmospheric pb 210 flux of 0 99 0 06 dpm cm2 yr because of its more realistic activity profiles we consider the present model to be generally better than previous models

modeling reactive transport in sediments subject to bioturbation and compaction current bioturbation models are marked by confusion in their treatment of porosity different equations appear to be needed for different biodiffusion mechanisms i e interphase mixing where biological activity causes bulk mixing of sediment affecting both tracer and porosity profiles versus intraphase mixing where the solid components are intermixed but the porosity is left unchanged another issue is whether the model depends upon the particle type with which tracers are associated e g 137 cs on small clay particles versus 210 pb on larger grains this uncertainty has lead to conflicting conservation equations for radiotracers and in particular to the question whether the porosity should be placed inside or outside of the differential term that governs the biodiffusive flux we have reexamined this situation in the context of multiphase multicomponent continuum theory most importantly we prove that under the assumption of steady state porosity there exists only one correct form of the steady state conservation equation for a radiotracer regardless of biodiffusion mechanism and particle type i e

atmospheric fluxes of lead zinc and cadmium from frequency domain deconvolution of sedimentary records a frequency domain deconvolution method to extract past input fluxes of particle associated pollutants from their sedimentary records is developed the method is based on the assumption of a mixing layer below which no further mixing takes place from the latter historical layer a filtered time record is obtained also from known steady state sedimentation parameters a response to a unit impulse input is calculated by forward finite difference programs the unknown input flux is then generated by taking fourier transforms of the two time series forming the ratio of the transforms and applying the inverse frequency transform the method has been tested for internal consistency and applied to pb zn and cd in several sediment cores from lake michigan the results are consistent with those obtained previously with a time domain method however at the present stage of development the time resolution in the frequency method 1 year is considerably better than in a general time domain method 15 years the effects of deconvolution are to sharpen peaks to generate peaks where none were present in the unprocessed record and to shift the onset time of pollution towards more recent times in most cases there is a remarkable agreement between reconstructed input records and alternative source functions for example maxima around 1969 for pb and cd in deconvolved input records are confirmed by the atmospheric loading data for the great lakes region pb and u s consumption figures cd

nonlinear parameter estimation for sediment cores abstract nonlinear parameter estimation techniques are applied to three distinctly different sediment cores for which concentrations of tracers with steady and time dependent flux inputs are available the mathematical model employed consists of a diffusive upper layer of finite depth underlain by a semi infinite nondiffusive medium confidence regions and intervals are reported for sedimentation rate diffusion coefficient and mixed layer depth based on ordinary least squares criteria for each tracer conflicting estimates are resolved using a weighted least squares procedure which combines observations of the individual tracers and exploits their strengths and weaknesses

a model for radionuclides in sediments influenced by mixing and compaction a model for the activity of radionuclides in sediments has been set up based on the one dimensional advection diffusion equation the model considers sedimentation mixing and compaction observed distributions of deposit feeding organisms and the nature of physical disturbances indicate that a gaussian diffusion coefficient may be appropriate two layer models with constant and gaussian mixing respectively in the upper layer are compared with measured pb 210 profiles for two cores from green bay lake michigan and it is found that the maximal diffusion coefficient d0 in the gaussian model is considerably greater than the constant d value e g d0 4 versus d 0 2 cm2 year if compaction effects are neglected the solution for the gaussian model is based on an approximate power series method compaction can be taken into account by using an exponential sedimentation rate or bulk sediment density by comparing with measured data for a lake ontario core it is seen that compaction alone can give an appreciable flattening of the activity curves near the top layers