applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

human adaptation to mid to late holocene climate change in northeast thailand this article integrates palaeoenvironmental and archaeological sequences covering the mid to late holocene in northeast thailand the former reveal the fluctuating intensity of the asian summer mo

coordinated hydrological regimes in the indo pacific region during the past two millennia instrumental data suggest that major shifts in tropical pacific atmospheric dynamics and hydrology have occurred within the past century potentially in response to anthropogenic warming to better understand these trends we use the hydrogen isotopic ratios of terrestrial higher plant leaf waxes delta d wax in marine sediments from southwest sulawesi indonesia to compile a detailed reconstruction of central indo pacific warm pool ipwp hydrologic variability spanning most of the last two millennia our paleodata are highly correlated with a monsoon reconstruction from southeast asia indicating that intervals of strong east asian summer monsoon easm activity are associated with a weaker indonesian monsoon im furthermore the centennial scale oscillations in our data follow known changes in northern hemisphere climate e g the little ice age and medieval warm period implying a dynamic link between northern hemisphere temperatures and ipwp hydrology the inverse relationship between the easm and im suggests that migrations of the intertropical convergence zone and associated changes in monsoon strength caused synoptic hydrologic shifts in the ipwp throughout most of the past two millennia

the role of bore collapse and local shear stresses on the spatial distribution of sediment load in the uprush of an intermediate state beach abstract spatial variations in sediment load in the swash uprush and textural properties of sediment in transport were evaluated to investigate the mechanisms responsible for sediment transport during wave uprush four streamer traps were deployed at 2 0 m intervals across the swash zone of a sheltered microtidal sandy beach at port beach western australia over a 4 day period during these trapping experiments offshore significant wave heights were 0 3 0 5 m and wave periods were about 10 s the average width of the uprush zone was 6 9 m and the average uprush duration was 5 9 s cross shore distributions of sediment load for 70 uprush events reveal a maximum in sediment load landward of the base of the swash at about 20 of swash width during single events and a maximum closer to mid swash at about 40 of swash width during multiple events characterized by swash interactions settling velocity distributions of trap samples during individual uprush events are similar to distributions found on the beach surface with the lowest settling velocities finest sediments near the base of the swash zone and maximum settling velocities coarsest sediments around the mid swash position it was found that sediment transport during wave uprush occurs through two distinct mechanisms 1 sediment entrainment during bore collapse seaward of the base of the swash zone and subsequent advection of this bore entrained sediment up the beach by wave uprush and 2 in situ sediment entrainment and transport induced by local shear stresses during wave uprush both mechanisms are considered important but the first mechanism is considered most significant during the early stages of wave uprush when sediment is transported mainly in suspension while the second mechanism is likely to dominate the mid to later stages of wave uprush when sediment is transported mainly by sheet flow the relative importance of the two mechanisms will vary between different beaches with the morphodynamic state of the beach reflective versus dissipative expected to play a major role

origin of dolomites in the cretaceous maha sarakham evaporites of the khorat plateau northeast thailand abstract the khorat plateau of northeast thailand and laos was an area of widespread deposition of evaporites and siliciclastics maha sarakham formation during the cretaceous and three types of dolomites are associated with this formation 1 limpid dolomite 2 coarse subhedral and euhedral dolomite and 3 saddle dolomite limpid dolomite is present as isolated crystals in recrystallized clear halite beds while the other two types are only present as authigenic clusters and individual large crystals within the widespread basal anhydrite unit bau 1 1 m which defines the lowest member of the formation the 18 o pdb isotopic values and the 87 sr 86 sr ratios of the limpid dolomite are within the range of cretaceous seawater petrography and carbon and oxygen isotopes suggest that limpid dolomite was formed under shallow burial during times of freshening in a mostly marine fed aggrading halite salina dolomite formation was possibly influenced by bacterial metabolism the coarse crystalline and saddle dolomite types float within a matrix of coarse recrystallized anhydrite in the basal anhydrite the 18 o isotopic values of the coarse subhedral and euhedral dolomite types are more negative than the limpid dolomite and the 87 sr 86 sr ratios are more radiogenic than typical marine dolomite of the cretaceous saddle dolomite has even more negative 18 o isotopic values than the coarse euhedral dolomite the 87 sr 86 sr ratios of the saddle dolomite are also radiogenic the isotopic and petrographic data indicate that the dolomites in the basal anhydrite unit are late and authigenic but do not appear to replace a precursor carbonate rather they appear to have precipitated within the deep burial environment along a 1 2 m thick subsurface mixing interface between warm upwelling basinal brines and dense highly saline brines created by dissolving the underside of the overlying impervious halite bed the upwelling basinal waters presumably rose through the underlying siliciclastics of the khorat group and then moved laterally along the base of the maha sarakham salt the result of this inferred hydrologic process apparently is an accumulation of burial dolomite and recrystallized residual anhydrite in a petrographically complex unit that ultimately appear to be a solution residue the basal anhydrite unit

characteristics of turbulent boundary layers over a rough bed under saw tooth waves and its application to sediment transport article i nfo a large number of studies have been done dealing with sinusoidal wave boundary layers in the past however ocean waves often have a strong asymmetric shape especially in shallow water and net of sediment movement occurs it is envisaged that bottom shear stress and sediment transport behaviors influenced by the effect of asymmetry are different from those in sinusoidal waves characteristics of the turbulent boundary layer under breaking waves saw tooth are investigated and described through both laboratory and numerical experiments a new calculation method for bottom shear stress based on velocity and acceleration terms theoretical phase difference and the acceleration coefficient ac expressing the wave skew ness effect for saw tooth waves is proposed the acceleration coefficient was determined empirically from both experimental and baseline k model results the new calculation has shown better agreement with the experimental data along a wave cycle for all saw tooth wave cases compared by other existing methods it was further applied into sediment transport rate calculation induced by skew waves sediment transport rate was formulated by using the existing sheet flow sediment transport rate data under skew waves by watanabe and sato watanabe a and sato s 2004 a sheet flow transport rate formula for asymmetric forward leaning waves and currents proc of 29th icce asce pp 1703 1714 moreover the characteristics of the net sediment transport were also examined and a good agreement between the proposed method and experimental data has been found

advances in swash zone research small scale hydrodynamic and sediment transport processes abstract extensive research efforts in the last decade have improved knowledge of swash zone processes this paper reviews and synthesizes from 2004 onward the research advances of small scale hydrodynamics and sediment transport processes considering field laboratory and numerical modeling efforts swash zone hydrodynamics are examined by means of shoreline motions fluid velocities pressure gradients flow structure bed shear stress friction coefficients and turbulence subsequently advances related to sediment transport mechanisms and morphological changes are described detailed descriptions of measuring techniques novel findings and the strengths and weaknesses of the different approaches are discussed the review also acknowledges the major advances in the development of instrumentation to collect highly resolved flow and sediment concentration measurements in direct proximity of the bed and the experimental framework for analyzing local dynamics on a wave by wave time scale e g dam break

vertical fluxes of sediment in oscillatory sheet flow time series of vertical sediment fluxes are derived from concentration time series in sheet flow under waves while the concentrations c z t vary very little with time for z 10d50 the measured vertical sediment fluxes qzs z t vary strongly with time in this vertical band and their time variation follows to some extent the variation of the grain roughness shields parameter 2 5 t thus sediment distribution models based on the pickup function boundary condition are in some qualitative agreement with the measurements however the pickup function models are only able to model the upward bursts of sediment during the accelerating phases of the flow they are so far unable to model the following strong downward sediment fluxes which are observed during the periods of flow deceleration classical pickup functions which essentially depend on the shields parameter are also incapable of modelling the secondary entrainment fluxes which sometimes occur at free stream velocity reversal the measured vertical fluxes indicate that the effective sediment settling velocity in the high 0 3 c z t 0 4 concentration area is typically only a few percent of the clear water settling velocity while the measurements of richardson and jeronimo chem eng sci 34 1979 1419 from a different physical setting lead to estimates of the order 20 the data does not support gradient diffusion as a model for sediment entrainment from the bed that is detailed modelling of the observed near bed fluxes would require diffusivities that go negative during periods of flow deceleration an observed general trend for concentration variability to increase with elevation close to the bed is also irreconcilable with diffusion models driven by a bottom boundary condition

hydroclimatic shifts in northeast thailand during the last two millennia the record of lake pa kho the southeast asian mainland is located in the central path of the asian summer monsoon a region where paleoclimatic data are still sparse here we present a multi proxy toc c n delta c 13 bio

lake kumphawapi revisited the complex climatic and environmental record of a tropical wetland in ne thailand kumphawapi which is thailand s largest natural freshwater lake contains a 10 000 year long climatic and environmental archive new data sets stratigraphy chronology hydrogen isotopes plant macrofossil and charcoal records for two sedimentary sequences are here combined with earlier multi proxy studies to provide a comprehensive reconstruction of past climatic and environmental changes for northeast thailand gradually higher moisture availability due to a strengthening of the summer monsoon led to the formation of a large shallow lake in the kumphawapi basin between 10 700 and c 7000 cal bp the marked increase in moisture availability and lower evaporation between c 7000 and 6400 cal bp favoured the growth and expansion of vegetation in and around the shallow lake the increase in biomass led to gradual overgrowing and infilling to an apparent lake level lowering and to the development of a wetland multiple hiatuses are apparent in all investigated sequences between c 6500 and 1400 cal b

formula for predicting bedload transport rate in oscillatory sheet flows abstract at high bed shear stress sheet flows often occur in coastal waters in which high concentration bedload sediments are transported in a thin layer near the bed this paper firstly constructs a theoretical model partial differential equations pdes for the intense transport of non cohesive bedload sediments by unidirectional currents and then seeks a special solution to the pdes to determine the thickness of the bedload particle water mixture which could serve as the reference height that is often invoked in numerical computation and simulation of suspended sediment transport in turbulent flows moreover a modified formula is presented to determine the reference concentration using a uch approach the present study derives a 1d formula for predicting bedload transport rate in sheet flows driven by asymmetric waves with the help of a novel formula for evaluating wave friction factor the new bedload formula can generically take into account slope angle positive and negative wash load concentration in the driving water flow and other factors that affect bedload transport rate it compares well with measured data in a large scale wave flume dohmen janssen c m hanes d m 2002 sheet flow dynamics under monochromatic non breaking waves journal of geophysical research 107 c10 1301 1321 a large scale oscillatory water tunnel hassan w n ribberink j s 2005 transport processes of uniform and mixed sands in oscillatory sheet flow coastal engineering 52 745 770 and in a swash zone of natural beach masselink g hughes m g 1998 field investigation of sediment transport in the swash zone continental shelf research 18 1179 1199

transmission reflection tomography application to reverse vsp data a multiphase tomographic algorithm is presented that allows 2 d and 3 d slowness inverse of velocity and variable reflector depth to be reconstructed simultaneously from both transmission and reflection traveltimes we analyze the ambiguity in the determination of velocity and depth in transmission and reflection data and realize that depth perturbation is more sensitive to reflection traveltime anomalies than slowness perturbation whereas the reverse is true of transmission traveltime anomalies because of the constraints on velocity and depth provided by the different wave types this algorithm reduces the ambiguity substantially between velocity and depth prevalent in reflection tomography and also avoids the undetermined problem in transmission tomography the linearized inversion was undertaken iteratively by decoupling velocity parameters from reflector depths a rapid 2 d and 3 d ray tracing algorithm is used to compute transmission and reflection traveltimes and partial derivatives with respect

hydrodynamics and sediment transport in the swash zone a review and perspectives the dominant hydrodynamic forcing and resulting sediment transport mechanisms in the swash zone are reviewed combined with a discussion of future measurement and modelling requirements the importance of swash zone processes in the overall behaviour of the nearshore littoral zone are identified with the paper subsequently focusing on aspects that directly relate to sediment transport on beaches the review considers analytical and numerical modelling work and both field and laboratory data the hydrodynamics of the swash zone are first discussed with reference to the surf zone boundary swash characteristics forcing mechanisms and shoreline oscillations subsequent sections consider more micro scale processes such as the internal flow kinematics turbulence the bed boundary layer and infiltration exfiltration through permeable beds the second part of the paper outlines the fundamental mechanics of sediment transport in the swash zone followed by a more detailed discussion of sediment transport modes induced by the dominant hydrodynamic conditions modelling concepts are reviewed and the strengths and weaknesses of different approaches identified a final summary and future modelling perspectives conclude the paper

vsp traveltime inversion near surface issues p wave velocity information obtained from vertical seismic profiles vsps can be useful in imaging subsurface structure either by directly detecting changes in the subsurface or as an aid to the interpretation of seismic reflection data in the shallow subsurface p wave velocity can change by nearly an order of magnitude over a short distance so curved rays are needed to accurately model vsp traveltimes we used a curved ray inversion to estimate the velocity profile and the discrepancy principle to estimate the data noise level and to choose the optimum regularization parameter the curved ray routine performed better than a straight ray inversion for synthetic models containing high velocity contrasts the application of the inversion to field data produced a velocity model that agreed well with prior information these results show that curved ray inversion should be used to obtain velocity information from vsps in the shallow subsurface

recent advances in modeling swash zone dynamics influence of surf swash interaction on nearshore hydrodynamics and morphodynamics the role of the swash zone in influencing the whole nearshore dynamics is reviewed with a focus on the interaction between surf and swash zone processes local and global hydromorphodynamic phenomena are discussed in detail and a description of the overall swash zone operation is given the effects of swash zone boundary conditions are highlighted together with the importance of surf zone boundary conditions major emphasis is placed on illustrating the interactions of various hydrodynamic modes which in turn control the swash and surf zone morphology finally methods to account for swash zone processes in coastal models with different temporal and spatial resolutions are proposed

effects of wave shape on sheet flow sediment transport 1 a two phase model is implemented to study the effects of wave shape on the transport of coarse grained sediment in the sheet flow regime the model is based on balance equations for the average mass momentum and fluctuation energy for both the fluid and sediment phases model simulations indicate that the responses of the sheet flow such as the velocity profiles the instantaneous bed shear stress the sediment flux and the total amount of the mobilized sediment cannot be fully parameterized by quasi steady free stream velocity and may be correlated with the magnitude of local horizontal pressure gradient or free stream acceleration a net sediment flux in the direction of wave advance is obtained for both skewed and saw tooth wave shapes typical of shoaled and breaking waves the model further suggests that at critical values of the horizontal pressure gradient there is a failure event within the bed that mobilizes more sediment into the mobile sheet and enhances the sediment flux preliminary attempts to parameterize the total bed shear stress and the total sediment flux appear promising

coarse sediment particle motion under highly asymmetrical waves with implications for swash zone sediment transport abstract hydrodynamics and sediment transport in the swash zone are unique and very complex phenomena acquiring a robust model for predicting sediment motion in the swash zone requires in depth insight about the behavior of sediment particles in highly asymmetric and turbulent waves that continuingly uprush the beach face and retrieve in backwashes in order to consider a physical system of the coarse particle motion in the swash zone with a reduced number of external parameters and capture some of the realism of the situation the experiments are conducted in rather simple conditions to provide some information about the particle responses in terms of jump length against asymmetric waves to be implicated for the swash zone the results show that despite reduction of many external parameters jump length is still a highly skewed stochastic parameter the probability distribution of jump length is quite wide large variance and skewed different from that of saltation length in steady unidirectional flow in which the distribution is close to normal considering integral of excess energy of an arbitrary single wave over its duration as a rational and meaningful representative of flow condition the average jump length j l incremental trends reduces in the higher energy condition resulting in a linear trend in logarithmic scale the j l s due to higher turbulent kinetic energy follow similar trend of less turbulent flow conditions

a bayesian approach for determining velocity and uncertainty estimates from seismic cone penetrometer testing or vertical seismic profiling data conventional processing methods for seismic cone penetrometer data present several shortcomings most notably the absence of a robust velocity model uncertainty estimate we propose a new seismic c

southward movement of the pacific intertropical convergence zone ad 1400 1850 tropical rainfall patterns control the subsistence lifestyle of more than one billion people seasonal changes in these rainfall patterns are associated with changes in the position of the intertropical convergence zone which is characterized by deep convection causing heavy rainfall near 10 n in boreal summer and 3 n in boreal winter dynamic controls on the position of the intertropical convergence zone are debated but palaeoclimatic evidence from continental asia africa and the americas suggests that it has shifted substantially during the past millennium reaching its southernmost position some time during the little ice age ad1400 1850 however without records from the meteorological core of the intertropical convergence zone in the pacific ocean quantitative constraints on its position are lacking here we report microbiological molecular and hydrogen isotopic evidence from lake sediments in the northern line islands galapagos and palau indicating that the pacific intertropical convergence zone was south of its modern position for most of the past millennium by as much as 500km during the little ice age a colder northern hemisphere at that time possibly resulting from lower solar irradiance may have driven the intertropical convergence zone south we conclude that small changes in earth s radiation budget may profoundly affect tropical rainfall

advanced techniques in site characterization and mining hazard detection for the underground coal industry abstract today s highly productive coal mining systems represent large capital investments careful geotechnical planning and design are essential to protect these systems and to help ensure their overall success too often however the ability of the mine operator to adequately characterize the geotechnical environment and keep up with changing geologic conditions lags the advance rate of the mining equipment seismic tomographic imaging based on the same principles as medical computer aided tomography cat scans offers the ability to identify changing geologic conditions loading patterns and the location of nearby abandoned mine workings although seismic tomography has been used for many years in the oil industry until recently its practicality in the mining industry has been limited because the processes involved interfered with mining productivity and were labor intensive in terms of data collection and interpretation new advancements in signal processing have greatly enhanced the speed resolution and range of applications of tomographic imaging in underground coal mine settings many tomography applications in the mining industry use seismic velocity and or attenuation tomography within a volume enclosed by the seismic source and receiver array although results obtained using this geometry work well in many situations recent developments in reflection tomography show promise in eliminating the requirement that the target volume be surrounded by sources receivers for example in seam seismic reflection tomography may now be used to image structures and or old workings from one general location in the mine e g face areas of mains and panel developments well ahead of planned developments largely eliminating the need to probe hole drill on regular intervals these new developments have greatly expanded the ability of the mine operator to cost effectively characterize previously inaccessible areas of the property this paper gives an overview of the theories and processes involved in seismic tomography applicable to coal mine settings recent examples are presented of tomographic imaging applied to a variety of coal mine ground control problems and old works detection in the united states and europe the applicability of both seismic refraction and seismic reflection tomography is discussed

the swash of solitary waves on a plane beach flow evolution bed shear stress and run up the swash of solitary waves on a plane beach is studied using large scale experiments ten wave cases are examined which range from non breaking waves to plunging breakers the focus of this study is on the influence of breaker type on flow evolution spatiotemporal variations of bed shear stresses and run up measurements are made of the local water depths flow velocities and bed shear stresses using a shear plate sensor at various locations in the swash zone the bed shear stress is significant near the tip of the swash during uprush and in the shallow flow during the later stages of downrush in between the flow evolution is dominated by gravity and follows an explicit solution to the nonlinear shallow water equations i e the flow due to a dam break on a slope the controlling scale of the flow evolution is the initial velocity of the shoreline immediately following waveform collapse which can be predicted by measurements of wave height prior to breaking but also shows an additional dependence on breaker type the maximum onshore directed bed shear stress increases significantly onshore of the stillwater shoreline for non breaking waves and onshore of the waveform collapse point for breaking waves a new normalization for the bed shear stress which uses the initial shoreline velocity is presented under this normalization the variation of the maximum magnitudes of the bed shear stress with distance along the beach which is normalized using the run up follows the same trend for different breaker types for the uprush the maximum dimensionless bed shear stress is approximately 0 01 whereas for the downrush it is approximately 0 002

hydroclimatic variability in southeast asia over the past two millennia abstract the spatiotemporal variability of the asian monsoon am over the last two millennia has been attributed to a combination of external solar and volcanic forcing and or internal coupled atmosphere ocean dynamics but the relative importance of these mechanisms remains unresolved the present knowledge of multidecadal to centennial scale am variability over mainland southeast asia is not well constrained despite substantial progress in understanding seasonal to decadal variability from tree ring records here we present the first high resolution stable isotope 13 c and 18 o speleothem record from northern laos spanning the common era 50 bce to 1880 ce the 13 c record reveals substantial centennial scale fluctuations primarily driven by local water balance notably the driest period at our site occurred from 1280 to 1430 ce during the time of the angkor droughts supporting previous findings that this megadrought likely impacted much of mainland southeast asia in contrast variations in stalagmite 18 o reflect changes in rainfall upstream from our study site interestingly the 18 o record exhibits a positive correlation with solar activity that persists after 1200 ce contrary to the findings in previous studies solar forced climate model simulations reveal that these 18 o variations may be driven by solar forced changes in upstream rainout over the tropical indian ocean which modify the 18 o of moisture transported to our study site without necessarily affecting local rainfall amount we conclude that future rainfall changes in mainland southeast asia are likely to be superimposed on multidecadal to centennial scale variations in background climate driven primarily by internal climate variability whereas solar forcing may impact upstream rainout over the indian ocean

indian summer monsoon during the last two millennia abstract the monsoon is a large scale feature of the tropical atmospheric circulation affectingpeople and economies in the world s most densely populated regions future trends due to naturalvariabilityandhuman inducedclimatechangesareuncertain palaeoclimaterecordscanimprove ourunderstanding of monsoon dynamics and thereby reduce this uncertainty palaeoclimate records haverevealed a dramatic decrease in the asian summer monsoon since the early holocene maximum9kabp herewefocusonthelast2ka wheresomerecordsindicateanincreasingtrendinthesummermonsoon analysing globigerina bulloides upwelling records from the arabian sea we nd theweakest monsoon occurred 1500 a bp with an increasing trend towards the present copyright 2010 john wiley sons ltd keywords monsoon holocene tropics india arabian sea introduction earth s climate is changing as a result of both natural andanthropogenic causes one region of the world that isparticularly susceptible to shifts in climate and extremeweather events is the indian subcontinent in this denselypopulated region both droughts and oods as well as trends inthe seasonal receipt of rainfall have the potential to bedevastating from economic agricultural and public healthperspectives the southwest indian monsoon is the maincontributor to india s yearly rainfall budget therefore unravelling past trends of the monsoon rains is critical tounderstanding future monsoon trends india ishome tooneofthelongesttimeseriesofinstrumentalclimate observations the all india monsoon rainfall index spanning 1844 to the present sontaake et al 1993 parthasarathy et al 1994 this record is remarkable bothfor showing an absence of a long term trend and for showing alarge variation in rainfall from one year to the next records ofthe atmospheric circulation such as the indian monsoon index imi based on the arabian sea winds are much shorter andspan only the past 50 a wang et al 2001 these records alsoindicate large variations from one year to the next and do notreveal a trend blending appropriate instrumental records withpalaeo observations from ocean sediments cave deposits orotherproxies canprovidealongerperspectiveonthemonsoonand its natural variability than otherwise would be available the monsoon is the result of both the seasonally changingthermal contrast between the land and ocean and the seasonalmigration of the intertropical convergence zone itcz whichreaches its northernmost location in summer exacerbating thethermally driven pressure gradient gadgil 2003 duringwinter the air over the land is cooler and denser than the airover the water this creates a surface pressure contrast that isenhanced by the position of the itcz over the ocean south ofthe continent of india resulting in a dry northeasterly wind thatblows across the continent in spring the continent warmsquickly compared to the surrounding water the winds thenreverse and a southwesterly wind blows across the arabiansea bringing moisture laden air towards india the south westerly winds that bring the monsoon rains also causeupwelling and sea surface cooling in the arabian sea producing a distinctive fossil record that can be tied to themonsoon winds via well known physical mechanisms a variety of indian and asian summer monsoon indices havebeen developed from instrumental records in general throughout india and asia in summer stronger winds overthe ocean and increased rainfall over land are correlated withthe large scale atmospheric circulation fig 1 the webster yang index wyi is a broad scale index of the monsooncirculation covers a large continuous area 40 1108 e 0 208n and measures the difference in strength between low level 850hpa and upper level 200hpa winds webster and yang 1992 in contrast the imi measures the arabian sea windsby subtracting the low level 850hpa zonal wind over land 20 308 n 60 908 e from the low level 850hpa winds in

summer monsoon precipitation variations in central china over the past 750 years derived from a high resolution absolute dated stalagmite abstract a 2 3 year resolution record of stalagmite oxygen isotope variations from the south flank of the qinling mountains central china has revealed the asian summer monsoon asm precipitation variations in the investigated area over the past 750 years the summer monsoon precipitation gradually increased since 1249 ad reaching its highest values in the period 1535 1685 ad and then decreased with substantial decadal to centennial scale fluctuations the monsoon precipitation increased again between 1920 and 1970 ad three intervals of high monsoon precipitation were identified 1535 1685 ad 1755 1835 ad and 1920 1970 ad three intervals of low precipitation were inferred in 1249 1325 ad 1390 1420 ad and 1890 1915 ad the 18 o composition and lithological features of the stalagmite coincidently indicate a wetter climate during the little ice age lia which is also confirmed by climate records from chinese historical documents within this area a comparison with other high resolution speleothem records indicates regional differences in monsoon precipitation variability from the south to the north of central china in the last 750 years on decadal to centennial scale power spectrum analysis of the 18 o record shows significant 117 8 34 6 14 10 3 and 6 year periodicities these periodicities are widely observed in the climate records from asm controlled areas of china and are consistent with the gleissburg periodicity br ckner periodicity sunspot periodicity of solar activity and el nino southern oscillation enso periodicity these correlations suggest that both solar activity and enso periodicity may have had important influences on asm precipitation in china over the past 750 years

environmental history recorded over the last 70 years in biển hồ maar sediment central highlands of vietnam abstract global warming enhances atmospheric moisture loading and will likely affect the east asian monsoon system across vietnam the absence of a long written climate history from vietnam creates a reliance on geological archives of past monsoon history and regional paleoenvironmental changes to provide a framework for evaluating current climatic trends bi n h lake 14 03 n 108 00 e is a volcanic crater i e maar in vietnam s central highlands that has been accumulating sediment since the pleistocene field campaigns between 2016 and 2018 recovered an abundance of gravity and piston sediment cores extending to a depth of 15 m covering approximately the last 30 ka bp the paleoenvironmental interpretation of pleistocene and holocene sediment requires knowledge of modern lacustrine and sedimentary conditions as well as the origin and transport pathways of the catchment material here we focus on a high resolution sedimentological and geochemical reconstruction of the recent environmental history from 1950 ad to the present based on sediment cores from bi n h maar in direct comparison with local and regional weather and historic records the uppermost sedimentary record reflects a substantial anthropogenic influence such as deforestation military use crater breaching dam and sill construction and reforestation that strongly modified the maar s morphology and hydrology a strong increase in sedimentation rate during the 1960 70s in bi n h cores coincided with u s military activities and water withdrawal a breach in the maar s rim and the connection to a new external reservoir in 1983 1984 ad increased bi n h water level reforestation around most of bi n h s rim in the 1990s curbed erosion and sedimentation rate nutrient availability in bi n h declined in the past 10 years after the installation of a concrete sill between bi n h and the reservoir to limit water exchange with the more nutrient rich reservoir this paper is a calibration study on modern sediment to provide an empirical basis for the interpretation of bi n h s deeper holocene and pre holocene sedimentary record

swash overtopping and sediment overwash on a truncated beach new experimental laboratory data are presented on swash overtopping and sediment overwash on a truncated beach approximating the conditions at the crest of a beach berm or inter tidal ridge runnel the experiments provide a measure of the uprush sediment transport rate in the swash zone that is unaffected by the difficulties inherent in deploying instrumentation or sediment trapping techniques at laboratory scale overtopping flow volumes are compared with an analytical solution for swash flows as well as a simple numerical model both of which are restricted to individual swash events the analytical solution underestimates the overtopping volume by an order of magnitude while the model provides good overall agreement with the data and the reason for this difference is discussed modelled flow velocities are input to simple sediment transport formulae appropriate to the swash zone in order to predict the overwash sediment transport rates calculations performed with traditional expressions for the wave friction factor tend to underestimate the measured transport additional sediment transport calculations using standard total load equations are used to derive an optimum constant wave friction factor of f w 0 024 this is in good agreement with a broad range of published field and laboratory data however the influence of long waves and irregular wave run up on the overtopping and overwash remains to be assessed the good agreement between modelled and measured sediment transport rates suggests that the model provides accurate predictions of the uprush sediment transport rates in the swash zone which has application in predicting the growth and height of beach berms c 2005 elsevier b v all rights reserved

measurements and modeling of swash induced pressure gradients in the surface layers of a sand beach field measurements of swash induced hydraulic pressure gradients in the surface layers of a sand beach are presented and compared to a one dimensional diffusion model the model provides a description of flow through a porous quasi saturated sediment and is driven by the time varying swash depth on the beach surface the field measurements broadly show four different types of pressure propagation behavior which appear dependent on cross shore position in the swash zone the hydraulic gradients within the surface layers of the beach are typically found to be much greater than those likely to be generated by tidally induced groundwater flow in these instances the diffusion model generally provides a good description of the data however very large hydraulic gradients are frequently observed just below the beach surface and these cannot be adequately described by the diffusion model a mechanism is proposed through which these large hydraulic gradients could be generated

persistent multidecadal power of the indian summer monsoon article i nfo the instrumental record of indian summer monsoon ism precipitation displays two complete manifesta tions of an inferred multidecadal cycle hitherto no precipitation sensitive proxy record from the indian subcontinent has had the necessary resolution and length to adequately assess whether this observed feature is an inherent aspect of the ism system on longer timescales here we present compelling evidence for persistence of this cycle using a millennial length ad 600 1550 and sub annually resolved speleothem oxygen isotope record 18 o from dandak cave in east central india the record displays a high degree of correlation with a speleothem based asian monsoon reconstruction from wanxiang cave in north central china on annual to decadal timescales showing theregional significanceof these findings theobserved period inourmonsoonreconstructionissimilartothatassociatedwiththegleissbergsolarcycleandmultidecadalsea surface temperature variability in the north atlantic amo both of which are often cited as the prominent pacemakers of ism variability on multidecadal timescales we document transient coherence between ism precipitation amount and solar variability that persists exclusively in the century prior to and during the medieval climate anomaly nominally ad 950 1300 the non stationary nature of the sfv monsoon relationship presented here may be evidence of the time varying influence of tropical ocean atmosphere dynamics on the solar monsoon link however it is not possible to show with significance that this period of coherenceisanythingmorethananartifactoftwotimeserieswithsimilarspectra wetherefore areinclinedto interpret our record as evidence of a minimal role of solar variability in driving persistent multidecadal variability of the ism multidecadal sst variability in the north atlantic remains as the likely alternative driver for persistence of this cycle regardless of the causative mechanism s the amplitude and regional signature of the observed cycle in ism precipitation highlight its societal importance with respect to forecasting ism precipitation on multidecadal timescales

influence of the intertropical convergence zone on the east asian monsoon a palaeoclimate record spanning the past 16 000 years with nearly annual time resolution has been obtained from lake huguang maar in china the magnetic properties and titanium content of the lake sediments are thought to reflect changes in the east asian winter monsoon strength thus providing a complement to palaeoclimate archives that record the strength of the rain bearing summer monsoon the records point to an anti correlation between winter and summer monsoon strength best explained by migration of the intertropical convergence zone itcz a belt of low pressure air at the equator interestingly the decline of china s tang dynasty and the mayan civilization broadly coincide with drought periods recorded in lake huguang maar and cariaco basin sediments respectively did major shifts in the position of the itcz catalyse simultaneous events in civilizations on opposite sides of the pacific ocean the asian australian monsoon is an important component of the earth s climate system that influences the societal and economic activity of roughly half the world s population the past strength of the rain bearing east asian summer monsoon can be reconstructed with archives such as cave deposits1 2 3 but the winter monsoon has no such signature in the hydrological cycle and has thus proved difficult to reconstruct here we present high resolution records of the magnetic properties and the titanium content of the sediments of lake huguang maar in coastal southeast china over the past 16 000 years which we use as proxies for the strength of the winter monsoon winds we find evidence for stronger winter monsoon winds before the bolling allerod warming during the younger dryas episode and during the middle and late holocene when cave stalagmites suggest weaker summer monsoons1 2 3 we conclude that this anticorrelation is best explained by migrations in the intertropical convergence zone similar migrations of the intertropical convergence zone have been observed in central america for the period ad 700 to 900 refs 4 6 suggesting global climatic changes at that time from the coincidence in timing we suggest that these migrations in the tropical rain belt could have contributed to the declines of both the tang dynasty in china and the classic maya in central america

rainfall variations in central indo pacific over the past 2 700 y tropical rainfall variability is closely linked to meridional shifts of the intertropical convergence zone itcz and zonal movements of the walker circulation the characteristics and mechanisms of tropical rainfall variations on centennial to decadal scales are however still unclear here we reconstruct a replicated stalagmite based 2 700 y long continuous record of rainfall for the deeply convective northern central indo pacific ncip region our record reveals decreasing rainfall in the ncip over the past 2 700 y similar to other records from the northern tropics notable centennial to decadal scale dry climate episodes occurred in both the ncip and the southern central indo pacific scip during the 20th century current warm period cwp and the medieval warm period mwp resembling enhanced el nino like conditions further we developed a 2 000 y long itcz shift index record that supports an overall southward itcz shift in the central indo pacific and indicates southward mean itcz positions during the early mwp and the cwp as a result the drying trend since the 20th century in the northern tropics is similar to that observed during the past warm period suggesting that a possible anthropogenic forcing of rainfall remains indistinguishable from natural variability

backshore coarsening processes triggered by wave induced sand transport the critical role of storm events spatial backshore processes were investigated through field observations of topography and median sand grain size at a sandy beach facing the pacific ocean in japan a comparison of the backshore profile and cross shore distribution of the median sand grain size in 1999 and 2004 revealed an unusual sedimentary process in which sand was coarsened in a depositional area in the 5 year period although sediment is generally coarsened in erosional areas in support of these observations monthly spatial field analyses carried out in 2004 demonstrated a remarkable backshore coarsening process triggered by sedimentation in the seaward part of the backshore during a storm event in order to elucidate mechanisms involved in the backshore coarsening process thresholds of movable sand grain size under wave and wind actions a uniform parameter for both these cases in the onshore and offshore directions were estimated using wave tide and wind data the cross shore distributions of the estimated thresholds provided reasonable values and demonstrated a coarsening mechanism involving the intermediate zone around the shoreline under alternating wave and wind actions as a result of which coarse sand was transported toward the seaward part of the backshore by large waves during storms and then toward the landward part by strong onshore winds the 5 year backshore coarsening is most certainly explained by repetition of short term coarsening mechanisms caused by wave induced sand transport occurring from the nearshore to the intermediate zone copyright 2010 john wiley sons ltd

2 d ray based tomography for velocity layer shape and attenuation from gpr data tomographic inversion for near surface structure from multioffset ground penetrating radar gpr reflection data is implemented the model is parameterized as layers with constant velocity and constant attenuation the solution is divided into two parts first the velocity and shape of each layer are estimated from the observed reflection traveltimes then using this geometry and the corresponding ray paths the attenuation of each layer is estimated from the observed relative amplitudes solution of both tomographic problems is performed by singular value decomposition of the sensitivity matrix to compute information density resolution and covariance matrices as well as the solution tests on synthetic data for which the solution is known show that the algorithm converges efficiently to the neighborhood of the correct solution inversion of multichannel field data in a gpr line from a fluvial eolian environment produces a model that is consistent with structural images and velocity estimates obtai

three simple models of wave sediment transport abstract the process of sediment transport by nonbreaking waves over horizontal rippled beds is presented by three different models which are evaluated through comparison with wave flume data the conclusion from this testing is the simpler the better it is shown that the process in question can in fact be modelled adequately without quantitative consideration of the suspended sediment distribution only a reference average concentration at the bed is needed on the other hand classical diffusion models severely underpredict the transport of coarse sand in suspension because the process is much more organized than diffusion the possibility of adapting the models to conditions involving sheet flow and or breaking waves is discussed

full scale cfd simulation of tsunamis part 2 boundary layers and bed shear stresses abstract this paper presents results from numerical simulations of the propagation and run up of full scale tsunamis using a reynolds averaged navier stokes model with emphasis on the resulting boundary layers and bed shear stresses spatial distributions of the shields and rouse parameters during run up and draw down show that for the tsunamis considered with a sediment grain size corresponding to medium sand considerable sediment transport shields parameter o 10 o 100 can be expected during run up and that the sediment transport can be expected to be dominated by suspended load the results likewise show that the expected sediment transport during draw down will similarly be considerable and dominated by suspension the tsunami induced boundary layers are monitored in time and the observed boundary layer thickness ranges from spanning only a small fraction of the water depth to spanning the entire depth the velocity profiles beneath the tsunamis are shown to have good correspondence with a logarithmic profile within the boundary layer similarly the bed shear stresses beneath the tsunamis are investigated and a new and simple engineering model is developed for predicting the temporal variation of the bed shear stress based only on a free stream velocity signal the new engineering model is shown give better predictions for the bed shear stress than a standard manning approach and is likewise shown in the appendix to produce reasonable predictions for shorter wind scale waves it is finally also shown how the temporal evolution of the boundary layer thickness can be predicted based on the free stream velocity signal alone the results presented here are part 2 of a larger study where part 1 presents the model validation and detailed descriptions of the run up process

eulerian flow velocities in the swash zone field data and model predictions measurements of eulerian flow velocity obtained within the swash zone on a relatively steep beach face gradient 1 23 are compared with an extended ballistic swash model the model only requires a friction factor beach slope and terminal bore velocity as input the following model predictions matched well with observations 1 the maximum eulerian flow velocity is the shoreline velocity when it arrives at the fixed point of interest on the beach face 2 at any location the time of flow reversal occurs prior to the shoreline reaching its maximum landward excursion 3 the maximum flow velocity in the backwash is the velocity recorded as the shoreline recedes past the fixed point of interest and this is less than the maximum uprush velocity and 4 the duration of the uprush flow is shorter than the duration of the backwash flow previous studies have already confirmed that the ballistic swash model including friction can accurately predict shoreline motion and maximum run up on steep beaches this study shows that it is similarly successful in predicting eulerian flow velocities during individual swash events the model does not presently account for interacting swash however and so may be less appropriate on gently sloping beaches

morphodynamical modelling of field scale swash events in the present work data for three single swash events are selected from those available for an accretive tide that occurred at le truc vert beach france during a measurement field campaign at that location these events are primarily chosen because of the different final bed change they produced namely variable accretion seaward erosion landward deposition and variable erosion along the swash zone these data are compared to results obtained from a state of the art numerical fully coupled 1d morphodynamical shallow water solver driven by measurements made of those events in the lower swash inner surf zone it is found that the hydrodynamics is reasonably well represented although the computed results exhibit reduced maximum inundations in comparison with the observed ones the model reproduces the correct order of magnitude of the morphodynamic change after each event and sometimes the pattern of erosion and deposition but this change is generally underestimated sensitivity analyses are conducted with respect to more uncertain physical parameters and assumed initial conditions they suggest that initial spatial distributions for velocity and pre suspended sediment concentration play a key role in the quantitative and qualitative prediction of the bed change

the influence of seaward boundary conditions on swash zone hydrodynamics abstract the influence of the seaward boundary condition on the internal swash hydrodynamics is investigated new numerical solutions of the characteristics form of the nonlinear shallow water equations are presented and applied to describe the swash hydrodynamics forced by breaking wave run up on a plane beach the solutions depend on the specification of characteristic variables on the seaward boundary of the swash zone equivalent to prescribing the flow depth or the flow velocity it is shown that the analytical solution of shen and meyer shen m c meyer r e 1963 climb of a bore on a beach part 3 runup j fluid mech 16 113 125 is a special case of the many possible solutions that can describe the swash flow but one that does not appear appropriate for practical application for real waves the physical significance of the boundary conditions is shown by writing the volume and momentum fluxes in terms of the characteristic variables results are presented that illustrate the dependence of internal flow depth and velocity on the boundary condition this implies that the internal swash hydrodynamics depend on the shape and wavelength of the incident bore which differs from the hydrodynamic similarity inherent in the analytical solution a solution appropriate for long bores is compared to laboratory data to illustrate the difference from the analytical solution the results are important in terms of determining overwash flows flow forces and sediment dynamics in the run up zone

measurement and modelling of the influence of grain size and pressure gradient on swash uprush sediment transport the paper examines the dependency between sediment transport rate q and grain size d i e q dp in the swash zone experiments were performed using a dam break flow as a proxy for swash overtopping on a mobile sediment beach the magnitude and nature of the dependency i e p value is inferred for different flow parameters the initial dam depth or initial bore height do the integrated depth averaged velocity u3 dt and against the predicted transport qp using the meyer peter muller mpm transport model experiments were performed over both upward sloping beds and a horizontal bed the data show that negative dependencies p 0 are obtained for u3 dt this indicates that a given do and qp transport less sediment as grain size increases whereas transport increases with grain size for a given u3 dt the p value is expected to be narrow ranged 0 5 p 0 5 a discernible difference observed between the measured and predicted transport on horizontal and sloping beds suggests different modes of transport the incorporation of a pressure gradient correction dp dx using the surface water slope i e piezometric head in the transport calculation greatly improved the transport predictions on the horizontal bed where dp dx is positive on average the incorporation of a pressure gradient term into the mpm formulation reduces qp in the uprush by 4 fine sand to 18 coarse sand and increases qp over a horizontal bed by 1 fine sand to two orders of magnitude coarse sand the measured transport for fine and coarse sand are better predicted using mpm and mpm dp dx respectively poor predictions are obtained using nielsen 2002 because the pressure gradient in the uprush is of opposite sign to that inferred from velocity data in that paper it is suggested that future swash sediment transport models should incorporate the grain size effect partly through the pressure gradient although the dp dx influence is small for fine sands because of the grain size scaling contained in the stress term

infiltration effects on sediment mobility under waves sediment mobility measurements with a horizontal sand bed under non breaking waves are reported conditions include no seepage and steady downward seepage corresponding to head gradients up to 2 5 the results indicate that infiltration tends to inhibit sediment mobility for a horizontal bcd of 0 2 mm quartz sand exposed to moderated wave induced bed shear stresses the effect is weak for the parameter range of the present study the two opposing effects of shear stress increase due to boundary layer thinning and the stabilizing downward drag are successfully accounted for through the modified shields parameter of nielsen nielsen p 1997 coastal groundwater dynamics proc coastal dynamics 97 plymouth asce dp 546 555 using coefficients derived from independent studies that is from the shear stress experiments of conley conley d c 1993 ventilated oscillatory boundary layers phd thesis university of california san diego 74 pp and the slope stability experiments of martin and aral martin c s and m m aral 1971 seepage force on interfacial bed particles j hydraulics div proc asce vol 97 no hy7 pp 1081 1100 c 2001 elsevier science b v all rights reserved

evolution and variability of the asian monsoon system state of the art and outstanding issues the asian monsoon is comprised of the indian and east asian subsystems these two components are linked to one another in varying degrees by regions of strong sensible heating indo asian landmass and strong latent heat export the western pacific warm pool and the southern subtropical indian ocean variability within the indian and east asian subsystems interactions among them and the extent to which they interact with other climate phenomena e g enso are current topics of modern and paleoclimate research this work provides an overview of past and current paleomonsoon research on tectonic to interannual time scales with a primary focus on marine sediment records while past and current work has contributed greatly to our understanding of paleomonsoon variability at all time scales additional efforts are required to make further progress in two critical areas 1 additional efforts are needed in terms of proxy development and evaluation requiring concerted efforts at long term sediment trap deployments in key monsoon influenced regions as well as development of adequate and widely available core top databases these are necessary to assess the impact of modern oceanographic and seafloor processes on potential monsoon proxies 2 additional effort is also needed in acquiring a sufficient geographic distribution of downcore records to assess linkages among the subsystems and their role in the context of extratropical climate change these records should have high sedimentation rates including varved sections this requires substantial survey support to identify the most appropriate coring and drilling targets c 2004 elsevier ltd all rights reserved

concepts in gravel beach dynamics abstract the dominant processes in gravel beach dynamics are reviewed highlighting some common themes which unify the various components of the gravel beach system the repercussions of which impart on how gravel beach dynamics might be understood conceptually in particular gravel beach dynamics are thought to be highly dependent on the temporal and spatial variation in grain size and the continual adjustments made by an active beach step both of which act not only as the expression of changing morphodynamic conditions but also as a controlling influence morphodynamics the notion that the exchanges on beaches between the hydrodynamics sediment transport and morphological change takes the form of reciprocal relationships which are mediated through feedback mechanisms in such a way that they cannot be thought of or studied independently is not a new one yet it appears that for the gravel beach morphodynamics must be re defined to describe conditions where variations in sediment size are thought to deserve parity rather than as merely a sequent entity or boundary condition morpho sedimentary dynamics is a phrase coined to intuit such cause and effect detailing the co evolution of morphology hydro hydraulics and sediment properties whilst acknowledging causative pluralism feedbacks and multiplier effects this is the recommended conceptual framework within which to crystallise thought and organise further research for the gravel beach essentially it increases the minimum number of parameters needed to describe the state of the gravel beach as a physical system therefore it is advised that simplicity will be most expedient in our future modelling efforts if complexity is to be adequately encapsulated

integral properties of the swash zone and averaging part 3 longshore shoreline boundary conditions for wave averaged nearshore circulation models the aim of the present work final of a three part series is to analyse in detail flow motions within the swash zone and define suitable shoreline boundary conditions for the longshore flow for wave averaged circulation models the analyses of parts 1 and 2 are extended to cover horizontally two dimensional flows an analytical solution for the longshore motion representing the drift velocity of the whole swash zone water mass is found this is seen to be approximated well by the ratio between the time integral of the longshore momentum flux crossing the swash lower boundary and the swash zone net water volume further a complete set of shoreline boundary conditions taking into account wave wave interactions is obtained on the basis of fully numerical solutions of the nonlinear shallow water equations the main focus of the work is to clarify the structure of the shoreline boundary conditions for the longshore flow but attention has also been paid to their derivation and assessment from the numerical solutions the latter have been obtained on the basis of a fairly broad range of input wave conditions which though biased towards those typical of reflective beaches are believed to cover conditions also typical of moderate dissipative beaches two main terms are found to contribute to the longshore drift velocity i a term proportional to the shallow water velocity accounting for short wave interactions frictional swash zone forces and continuous forcing due to non breaking wave nonlinearities and ii a drift type term representing the momentum transfer due to wave breaking

incipient motion of surf zone sediments incipient motion of surf zone sediments incipient motion experiments were conducted with natural gravel acetate beads and coarse gravel sized electronic grains called smart sediment grains in a small oscillatory flow tunnel measurements of fluid velocity were made using particle image velocimetry the strength of the fluid shear stresses and the pressure gradients were examined for a range of oscillatory flow conditions at the onset of motion of the sediment particles to determine which mechanism had induced particle motion the three sediment types utilized in these experiments facilitated an assessment of the effects of sediment grain size diameter shape and density on incipient motion results suggested that the onset of sediment motion was dominated by the pressure gradients for flows with small orbital excursion amplitudes by the shear stresses for flows with large orbital excursion amplitudes and by the combined effects for intermediate flows the denser angular gravel required greater free stream accelerations to trigger sediment motion than the spherical less dense acetate beads and smart sediment grains a combined parameter for incipient motion that accounts for the simultaneous effects of both shear stresses and pressure gradients while depending on the static coefficient of friction and the packing concentration of the mobile bed layer was evaluated for accuracy using a range of sediment types the results suggested that the combined parameter may be a better indicator of sediment mobilization under oscillatory flows than the typically assumed shear stress criterion

a 40 000 year palynological record from north east thailand implications for biogeography and palaeo environmental reconstruction abstract there are few palaeoenvironmental data from the indo chinese peninsula that document environmental and climatic conditions prior to the holocene this study of pollen and spores from a small peat swamp in north east thailand provides a record of vegetation change covering ca 40 000 years b p before present these data indicate that the region supported a fagaceous coniferous forest similar to contemporary vegetation described from south west china climatic conditions were cooler and probably drier than present day climates in thailand levels of biomass burning are relatively high throughout this period tropical broad leaf deciduous forest becomes dominant at the pleistocene holocene boundary with the fragmentation of fagaceous coniferous forest in response to increased temperatures

contrasting the indian and east asian monsoons implications on geologic timescales the surface winds over the arabian sea and south china sea are meaningful indicators for the strength of the indian monsoon and east asian monsoon respectively paleo monsoon variability has been studied through analysis of sediment records from these two monsoon regions to facilitate interpretation of these records we focus on the impacts of internal and external forcing of the monsoon system by contrasting the annual cycle and interannual variability of two subsystems the monsoon over the indian sector 40 105 e and over the east asian sector 105 160 e differences in the annual cycle within these subsystems arise primarily from the different land ocean configurations that determines atmospheric response to the solar forcing thus factors that drive intensities of the monsoonal annual cycle share common features with the external geographic and orbital forcing that controls paleomonsoon variability we show that the differences in interannual variations between the two monsoon subsystems are primarily due to internal factors of the coupled atmosphere ocean land system such as remote impacts of el nin o la nin a and local monsoon ocean interactions the mechanisms that operate on interannual to interdecadal timescales may differ fundamentally from that on geologic orbital timescales the low level flows over the east asia and australia are essentially established by geographic forcing the amplification of the australia summer monsoon during increased solar precession is likely caused by an enhanced east asian winter monsoon rather than following an enhanced indian summer monsoon as on the interannual timescale it is also found that el nin o influences the low level flow moderately over the arabian sea but to a greater extent over the south china sea as such large changes in the pacific thermal conditions may significantly alter the intensity of the east asian monsoon but not the indian monsoon

prolonged monsoon droughts and links to indo pacific warm pool a holocene record from lonar lake central india abstract concerns about the regional impact of global climate change in a warming scenario have highlighted the gaps in our understanding of the indian summer monsoon ism also referred to as the indian ocean summer monsoon and the absence of long term palaeoclimate data from the central indian core monsoon zone cmz here we present the first high resolution well dated multiproxy reconstruction of holocene palaeoclimate from a 10 m long sediment core raised from the lonar lake in central india we show that while the early holocene onset of intensified monsoon in the cmz is similar to that reported from other ism records the lonar data shows two prolonged droughts pd multidecadal to centennial periods of weaker monsoon between 4 6 3 9 and 2 0 6 cal ka a comparison of our record with available data from other ism influenced sites shows that the impact of these pd was observed in varying degrees throughout the ism realm and coincides with intervals of higher solar irradiance we demonstrate that i the regional warming in the indo pacific warm pool ipwp plays an important role in causing ism pd through changes in meridional overturning circulation and position of the anomalous walker cell ii the long term influence of conditions like el nino southern oscillation enso on the ism began only ca 2 cal ka bp and is coincident with the warming of the southern ipwp iii the first settlements in central india coincided with the onset of the first pd and agricultural populations flourished between the two pd highlighting the significance of natural climate variability and pd as major environmental factors affecting human settlements

lagrangian measurements of incipient motion in oscillatory flows incipient motion of coarse gravel sized sediment was investigated under a range of oscillatory flows this article examines the relative significance of shear stresses and pressure gradients in triggering motion which was directly measured with electronic smart sediment grains ssgs the data suggest that incipient motion was induced by the pressure gradients in flows with large accelerations by the shear stresses in flows with low accelerations and greater shear and by the combined effects in intermediate flows a modified incipient motion criterion was evaluated accounting for the combined effects of the shear stresses and pressure gradients which may be more widely applicable in the marine environment

a numerical empirical approach for evaluating morphodynamic processes on gravel and mixed sand gravel beaches abstract pedrozo acuna et al pedrozo acuna a simmonds d j otta a k and chadwick a j 2006 on the cross shore profile change of gravel beaches coastal engineering 53 4 335 347 presented a numerical empirical investigation of the processes that control sediment transport in the swash zone on steep gravel beaches this was based on a sensitivity analysis of a sediment transport profile model driven by a highly non linear boussinesq model lynett p j wu t r and liu l f p 2002 modelling wave run up with depth integrated equations coastal engineering 46 89 107 which was compared to near full scale measurements performed in the gwk flume in hanover in this paper we have extended our analysis to compare these earlier results with those relating to a mixed sediment gravel and sand beach the parametric sensitivity analysis also incorporates a discussion of the effects of acceleration about which there is much debate the sensitivity analysis suggests that fluid acceleration can contribute to the onshore movement of sediment that causes steepening of initially flat beach faces composed of coarse sediment however acceleration alone cannot be the cause of the observed berm growth during the gwk tests instead a complex balance of processes is responsible for the profile evolution of coarse grained beaches with no single dominant process

suspended sediment transport in the swash zone of a dissipative beach abstract simultaneous high frequency field measurements of water depth flow velocity and suspended sediment concentration were made at three fixed locations across the high tide swash and inner surf zones of a dissipative beach the dominant period of the swash motion was 30 50 s and the results are representative of infragravity swash motion suspended sediment concentrations loads and transport rates in the swash zone were almost one order of magnitude greater than in the inner surf zone the vertical velocity gradient near the bed and the resulting bed shear stress at the start of the uprush was significantly larger than that at the end of the backwash despite similar flow velocities this suggests that the bed friction during the uprush was approximately twice that during the backwash the suspended sediment profile in the swash zone can be described reasonably well by an exponential shape with a mixing length scale of 0 02 0 03 m the suspended sediment transport flux measured in the swash zone was related to the bed shear stress through the shields parameter if the bed shear stress is derived from the vertical velocity gradient the proportionality coefficient between shear stress and sediment transport rate is similar for the uprush and the backwash if the bed shear stress is estimated using the free stream flow velocity and a constant friction factor the proportionality factor for the uprush is approximately twice that of the backwash it is suggested that the uprush is a more efficient transporter of sediment than the backwash because the larger friction factor during the uprush causes larger bed shear stresses for a given free stream velocity this increased transport competency of the uprush is necessary for maintaining the beach otherwise the comparable strength and greater duration of the backwash would progressively remove sediment from the beach

free stream velocity descriptions under waves with skewness and asymmetry abstract in shallow water when waves shoal their orbital velocities exhibit skewness velocity skewness and asymmetry acceleration skewness in response to corresponding changes in the free surface near the bed changes in the skewness and asymmetry of the time varying velocities have important consequences for the residual velocities spun up by the bottom friction and for sediment transport in the wave boundary layer where the largest sediment transport often occurs there is a need to represent the free stream velocity the orbital velocity at the edge of the wave boundary layer in a systematic way such that it can be mimicked in wave tunnel experiments and wave boundary layer models which usually do not represent the free surface since there is no readily accessible dynamical theory for shoaling waves that includes both skewness and asymmetry it is necessary to synthesize the shoaling effect in a free stream velocity description that is general enough to fit observed velocity time series this paper reviews previous free stream velocity descriptions including the description of abreu et al 2010 and introduces a new description based on generalising a sawtooth wave shape the paper quantifies all the relevant measures of skewness and asymmetry for each description it then demonstrates that abreu et al s 2010 description represents the most general one and improves upon their fitting techniques to observed free stream velocities to further simplify it when this description is used in conjunction with a characterisation of the velocity for irregular waves such as that of elfrink et al 2006 it is possible to relate velocity skewness and asymmetry directly to the non dimensional wave and beach parameters wave height surface wavelength and surf similarity parameter as a proxy for beach slope matlab scripts are provided for the improved description of abreu et al 2010 and elfrink et al s 2006 characterisation

a 900 year 600 to 1500 a d record of the indian summer monsoon precipitation from the core monsoon zone of india 1 we present a near annually resolved record of the indian summer monsoon ism rainfall variations for the core monsoon region of india that spans from 600 to 1500 a d from a 230th dated stalagmite oxygen isotope record from dandak cave our rainfall reconstruction which spans the medieval warm period mwp and the earliest portion of the little ice age lia indicates that the short instrumental record of ism underestimates the magnitude of monsoon rainfall variability periods of severe drought lasting decades occurred during the 14th and mid 15th centuries and coincided with several of india s most devastating famines

first break vertical seismic profiling tomography for vinton salt dome building laterally depth varying velocity models for vertical seismic profiling vsp imaging is challenging because of the narrow ray angle coverage of vsp data especially if only first arrivals are used this study explores the potential of a new deformable layer tomography dlt for building velocity models with a vsp data set acquired over the vinton salt dome in southwestern louisiana the dlt method uses first breaks to constrain the geometry of velocity interfaces from an initial model of flat constant velocity layers parameterized using a priori geologic and geophysical information a progressive multiscale inversion loop gradually updates the interface geometry the final solution model containing 3d geometry is well supported by resolution and reliability tests and closely matches the long wavelength trends of area sonic logs the presence of velocity anisotropy is also indicated

on the transport of suspended sediment by a swash event on a plane beach we develop solutions for the transport of suspended sediment by a single swash event following the collapse of a bore on a plane beach and we investigate the morphodynamical role that such transport may play although the intrinsic asymmetry between uprush and backwash velocities tends to encourage the export of sediment we find that swash events may be effective in distributing across the swash zone much or all of the sediment mobilised by bore collapse additionally settling lag effects may promote a weak onshore movement of sediment we quantify both effects in terms of the properties of the sediment and of the swash event and comment on the relationship between our findings and recent field studies of swash zone sediment transport

unified view of sediment transport by currents and waves i initiation of motion bed roughness and bed load transport attention is given to the properties of sediment beds over the full range of conditions silts to gravel in particular the effect of fine silt on the bed composition and on initiation of motion critical conditions is discussed high quality bed load transport data sets are identified and analyzed showing that the bed load transport in the sand range is related to velocity to power 2 5 the bed load transport is not much affected by particle size the prediction of bed roughness is addressed and the prediction of bed load transport in steady river flow is extended to coastal flow applying an intrawave approach simplified bed load transport formulas are presented which can be used to obtain a quick estimate of bed load transport in river and coastal flows it is shown that the sediment transport of fine silts to coarse sand can be described in a unified model framework using fairly simple expressions the proposed model is fully predictive in the sense that only the basic hydrodynamic parameters dep

continental scale temperature variability during the past two millennia past global climate changes had strong regional expression to elucidate their spatio temporal pattern we reconstructed past temperatures for seven continental scale regions during the past one to two millennia the most coherent feature in nearly all of the regional temperature reconstructions is a long term cooling trend which ended late in the nineteenth century at multi decadal to centennial scales temperature variability shows distinctly different regional patterns with more similarity within each hemisphere than between them there were no globally synchronous multi decadal warm or cold intervals that define a worldwide medieval warm period or little ice age but all reconstructions show generally cold conditions between ad 1580 and 1880 punctuated in some regions by warm decades during the eighteenth century the transition to these colder conditions occurred earlier in the arctic europe and asia than in north america or the southern hemisphere regions recent warming reversed the long term cooling during the period ad 1971 2000 the area weighted average reconstructed temperature was higher than any other time in nearly 1 400 years

climate and hydrographic variability in the indo pacific warm pool during the last millennium planktonic foraminiferal mg ca and delta o 18 derived sea surface temperature and salinity records from the makassar strait indonesia show a long term cooling and freshening trend as well as considerable centennial scale variability during the last millennium the warmest temperatures and highest salinities occurred during the medieval warm period mwp while the coolest temperatures and lowest salinities occurred during the little ice age lia these changes in the western pacific along with observations from other high resolution records indicate a regionally coherent southern displacement of the inter tropical convergence zone during the lia with more arid conditions in the northern tropics and wetter conditions in the southern tropics

late holocene vegetation and climate change on the southeastern tibetan plateau implications for the indian summer monsoon and links to the indian ocean dipole abstract the indian summer monsoon ism is one of the most important climate systems whose variability and driving mechanisms are of broad interest for academic and societal communities here we present a well dated high resolution pollen analysis from a 4 82 m long sediment core taken from basomtso in the southeastern tibetan plateau tp which depicts the regional climate changes of the past millennium our results show that subalpine coniferous forest was dominant around basomtso from ca 867 to ca 750 cal yr bp indicating a warm and semi humid climate the timberline in the study area significantly decreased from ca 750 to ca 100 cal yr bp and a cold climate corresponding to the little ice age lia prevailed since ca 100 cal yr bp the vegetation type changed to forest meadow with rising temperatures and moisture ordination analysis reveals that the migration of vegetation was dominated by regional temperatures and then by moisture further comparisons between the basomtso pollen record and the regional temperature reconstructions underscore the relevance of the basomtso record from the southeastern tp for regional and global climatologies our pollen based moisture reconstruction demonstrates the strong multicentennial scale link to ism variability providing solid evidence for the increase of monsoonal strengths over the past four centuries spectral analysis indicates the potential influence of solar forcing however a closer relationship has been observed between multicentennial ism variations and indian ocean sea surface temperature anomalies ssts suggesting that the variations in monsoonal precipitation over the southeastern tp are probably driven by the indian ocean dipole on the multicentennial scale

high resolution x ray fluorescence core scanning analysis of les echets france sedimentary sequence new insights from chemical proxies the les echets sediment sequence has recently been the subject of a high resolution multi proxy study which revealed shifts in lake productivity linked to greenland stadials and interstadials over the last 40 ka wohlfarth et al 2008 rapid ecosystem response to abrupt climate changes during the last glacial period in western europe 40 16 ka geology 36 407 410 here we present new elemental data for this sequence as acquired using an x ray fluorescence core scanning system which provides in situ high resolution continuous multi element analyses it was found that the strength of associations between the studied elements ti rb k zr si ca sr mn and fe varied over time with changes in lake status which are ultimately driven by changes in climate increases in fine grained detrital input as indicated by ti rb k and zr rb overlap with independently established periods of lower lake productivity and are interpreted to represent more arid conditions several of these arid periods are coincident with low diatom concentrations and the timing of heinrich events h4 h3 and h2 the duration of the environmental impacts linked to the h events varied by proxy with elemental data ti and zr rb estimating shorter events than the diatom data periods of lower detrital input and coarser grain sizes agreed in time with periods of higher lake productivity the elemental data provide new insights into hydrological changes and related sediment processes within the catchment and highlight the need for multi element and multi proxy approaches when reconstructing climate change using lacustrine sediment sequences copyright 2011 john wiley sons ltd

holocene environmental change at inle lake shan state myanmar and its implications for the regional development of agriculture abstract we report pollen charcoal and diatom records from the upper 4 m of a core from inle lake myanmar spanning the entire holocene to investigate the changing palaeoenvironments in which early agriculture developed from 12 000 to 10 500 cal yr bp a grass swamp existed until it was flooded by rising lake levels indicated by the onset of marl deposition at the site the onset of higher lake levels coincided with a transition from conifer rich forest to mixed deciduous evergreen forest and a reduction in local biomass burning lake levels remained high until 6400 cal yr bp thereafter fluctuating with possible dry phases at 4050 2400 and 1100 cal yr bp increased burning is apparent from 2200 cal yr bp inferred to represent the onset of human forest clearance to its very reduced state today the inle lake record compares with holocene sequences in china thailand and india and marine cores south of myanmar which similarly show a regional pattern of drier conditions in the early greenlandian stage followed by maximum lake levels in the early northgrippian stage fluctuating lake levels are evident in the later northgrippian and meghalayan stages after 6000 cal yr bp this pattern coincides with precessional reduction in summer insolation in the region which weakens the asian monsoon the present day bare catchments of inle lake probably mostly resulted from forest destruction over the last 2000 years although hints of human presence can be inferred throughout the older record

shear stress and sediment transport calculations for swash zone modelling it is shown that the observed difference in sediment transporting efficiency by the swash uprush compared with the downrush could be mainly due to greater bed shear stress for a given velocity in the more abruptly accelerated uprush the bed shear stress generated by an arbitrary free stream velocity time series is modelled in terms of usual wave boundary layer models plus a phase lead phi tau of the bed shear stress compared with the free stream velocity at the peak frequency with this approach the total transport amounts in uprush and downrush can be modelled satisfactorily with the same sediment transport formula without the need for different uprush and downrush coefficients while the adaptation of sediment transport formulae from steady flow can thus lead to the right total amounts of sediment moved by this method the timing of the instantaneous sediment transport rates are probably not accurately modelled due to the highly unsteady nature of the swash and the presence of pre suspended sediment in the uprush nevertheless the proposed method is a useful intermediate step before we have a complete understanding of sediment transport under very rapid accelerations and of the relative contribution of pre suspended sediment to the onshore sediment transport in swash zones c 2002 published by elsevier science b v

swash zone sediment suspension and transport and the importance of bore generated turbulence a study of swash zone sediment transport was conducted at gleneden beach oregon during february 25 28 1994 the data collected included suspended sediment concentration ssc sea surface elevation and velocity initially 4 and 8 cm above the bed at three cross shore locations within the swash zone spanning high tides ensemble averages of 6 9 and 12 s duration swash events showed that the uprush suspension was high concentrated in the leading edge and nearly vertically uniform above the lower 1 2 cm of the water column shortly after the sensors were inundated by run up the sediment rapidly settled out of the water during flow reversal the ssc was small but increased again in the backwash backwash vertical profiles were markedly different from uprush profiles with much of the suspension being confined to very near the bed where strong vertical gradients in ssc existed these marked differences show that the backwash is not simply the reverse of the uprush implying significant differences in the underlying fluid dynamics and sediment transport mechanisms backwash sediment suspension increased with flow duration however ensemble averaged ssc profiles of varying duration showed that the backwash concentrations were not consistent at the same temporal phases which suggests that water depth in addition to flow duration may be a controlling factor strong cross shore gradients in ssc suggest that bore derived turbulence may affect local sediment transport specifically our data show this bore generated turbulence turbulent kinetic energy directly influences local sediment suspension hence standard bed shear bagnold type sediment transport models may no longer be valid in the vicinity of the bore in the vicinity of the bore a higher correlation between bore generated turbulence and suspended sediment transport was found than between a bagnold type formulation and suspended sediment transport

lake kumphawapi an archive of holocene palaeoenvironmental and palaeoclimatic changes in northeast thailand the long term climatic and environmental history of southeast asia and of thailand in particular is still fragmentary here we present a new c 14 dated multi proxy sediment record toc c n cns

the leading mode of indian summer monsoon precipitation variability during the last millennium 1 the internally generated intraseasonal variability of the indian summer monsoon is characterized by intermittent periods of enhanced active and deficient break precipitation which produce a quasi east west precipitation dipole over the indian subcontinent here we present multicentennial length and near annually resolved reconstructions of monsoon precipitation inferred from absolute dated and instrumentally calibrated speleothem oxygen isotope records from regions central and northeast india that have diametric responses to active break monsoon circulation patterns on centennial timescales ad 1400 2008 precipitation variability from these two regions exhibit opposing behavior oscillating between periods with a persistently active dominated ad 1700 to 2007 and a break dominated ad 1400 to 1700 regime the switch between these regimes occurs abruptly within decades at a time ad 1650 1700 when a proxy record of upwelling intensity from the arabian sea suggest an abrupt increase in the monsoon winds on the basis of these observations we hypothesize that the frequency distribution of active break periods varies on centennial timescales implying a leading role of internal dynamics in governing the ism response to slowly evolving changes in the external boundary conditions

boundary layer dynamics in the swash zone under large scale laboratory conditions this paper presents the results of a laboratory experiment of swash hydrodynamics on a coarse sand barrier beach backed by a lagoon boundary layer dynamics have been analyzed using the high resolution near bed velocities measured by acoustic doppler velocity profilers deployed in the swash zone swash events have been ensemble averaged in order to study mean hydrodynamic patterns a proposed velocity gradient criterion allowed identification of the boundary layer growth during the backwash phase but it was unable to characterize boundary layer variability during uprush cross shore velocity profiles were well represented by the logarithmic model for a large portion of the ensemble averaged swash duration uprush and backwash logarithmic estimated friction factors were of the same order of magnitude with a strong variability related to the boundary layer growth during the backwash the momentum integral method provided smaller bed shear stresses than the logarithmic model a result possibly related to either the assumptions involved in the momentum integral method or to an underestimation of the boundary layer thickness during uprush a decrease of friction coefficients for increasing reynolds numbers at the early backwash was observed this behavior is consistent with traditional results for steady and uniform flows in a transitional regime