dust a diagnostic of the hydrologic cycle during the last glacial maximum dust concentrations in ice of the last glacial maximum lgm are high in ice cores from greenland and antarctica the magnitude of the enhancements can be explained if the strength of the hydrologic cycle during the lgm was about half of that at present this notion is consistent with a large decrease 5 c in ocean temperature during the lgm as recently deduced from measurements of strontium and calcium in corals

response characteristics of a short range high resolution digital sonar altimeter abstract the datasonics model asa 920 digital sonar altimeter dsa is a compact high frequency 1 mhz short range 0 5 5 m underwater sonar device originally designed as an altimeter for submersibles the dsa has previously been successfully used on a bottom mounted tripod to measure changes in relative bed elevation at a point on the shoreface prior to and during a storm fixed to a rigid mounting on the seabed the dsa produces a digital output that is proportional to the transducer elevation above the bed the purpose of this report is to describe the response characteristics of the dsa tests using a flat steel plate and a flat sand bed as targets showed that the dsa is capable of resolving differences in elevation of at least 0 5 cm a laboratory calibration demonstrated that the instrument response is linear because the acoustic pulse emitted by the transducer has a finite width the dsa is incapable of delineating undulating sand beds when the bedslope taken over the beamwidth is significant this limits the instrument s use over a bed of wave generated ripples in general the altimeter does not see into the troughs of ripples when its height above the bed is more than eight times the ripple wavelength the instrument stability is good over 12 operating hours 14 days of burst sampling the indicated elevation drifted by 0 3 cm in the field the acoustic pulse is susceptible to interference by suspended particulate matter and bubbles during deployment in a water depth of 8 m on the shoreface two problems occurred pulse scattering that caused a loss of echo detection which was manifested as spikes in the record and premature echoes that obscured the actual bed surface a second altimeter with an operating frequency of 300 khz datasonics model psa 900 also gave a linear response but with a reduced accuracy of approximately 1 cm

environmental and climate reconstructions of the fore baikal area during mis 5 1 multiproxy record from terrestrial sediments of the ust oda section siberia russia abstract the ust oda section exposes the structure of a 25 m terrace of the kitoy river the eroded surface of the jurassic sandstones is overlain by the heterogeneous primarily aeolian alluvial upper pleistocene holocene deposits that include buried soils the quaternary part of the section exhibits five main stratigraphic subdivisions ranging from isotopic stage mis 5 to mis 1 reconstructed vegetation composition of the unit 1 formation age is typical for late quaternary interglacial periods and suggests moderately cool and moderately humid climate unit 2 sediments yielded small mammal remains of taiga steppe tundra and hydrophilic species characterizing the fauna as ecologically mixed or disharmonic typical of cold pleistocene epochs in eurasia for example lagurus lagurus and dicrostonyx sp are animal species whose current habitats do not cross and are substantially distant from each other microtheriofauna species composition and structure imply unit 2 formation under the conditions of cold and arid climate together with 14c dating of the overlying strata suggesting its mis 4 age unit 3 sediments contain spore pollen spectra typical for mis 3 interstadial of the pribaikalye area mis 3 climate substantially differed from the modern one average january temperatures might have been 15 c lower than the modern ones and the mean july temperatures 2 3 c lower mean annual precipitation value could be lower than the modern one by 100 mm yr the analysis of the small mammal species ecological requirements suggests domination of tundra steppe landscapes in the area during the formation of the unit 3 theriofauna of the unit 5 allows reconstruction of paleoecological conditions close to modern ones in humidity and temperature

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr

numerical analyses of subsurface flow in a steep hillslope under rainfall the role of the spatial heterogeneity of the formation hydraulic properties 1 the paper aims at analyzing subsurface flow and streamflow generation in steep hillslopes after rainfall the principal scope of the work is to assess the role played by the spatial variability of the hydraulic properties on the subsurface flow patterns and hillslope discharge we try to address this task through a three dimensional numerical model which solves the richards equation under prescribed initial and boundary conditions along an established practice the relevant hydraulic parameters are modeled as random space functions with given statistical properties realistic features of the spatially variable formation parameters and the precipitation data are incorporated into the simulation model it is found that spatial heterogeneity has a significant impact on the movement of water in the hillslope and the streamflow generation in particular the heterogeneous systems are more sensitive to rain input and display an increase of both the water table and saturation which is faster than the homogeneous case the same is for water velocity which is everywhere larger when heterogeneity is considered as a consequence the dynamics of subsurface stormflow recognized as the leading mechanism for streamflow generation in the simulations and the outflow discharge produced by the hillslope after a rain event are enhanced by heterogeneity despite of the possible lack of generality of the numerical experiments they provide useful insight into the complex dynamics occurring in hillslope systems the simulations show the importance of including realistic spatial heterogeneity in hillslope hydrology studies

spatial variability of bottom types in the lower chesapeake bay and adjoining estuaries and inner shelf abstract the spatial distributions of the bed textural and morphologic properties that influence boundary layer roughness characteristics in the lower chesapeake bay the lower portions of the york james and elizabeth rivers and the adjacent inner continental shelf were systematically mapped a high resolution fully corrected side scan sonar mapping system 100 khz was used for remote acoustic detection of bottom roughness supported by ground truthing by direct in situ observations by divers these complementary methods proved to be especially effective in detecting a wide range of roughness controlling bed surface properties at various scales fine scale variations in sediment size and associated bottom texture are considered to be the main source of heterogeneity in nikuradse skin friction roughness a wide variety of small and intermediate scale morphologic elements provide meso scale and small scale distributed form drag roughness depending upon location the distributed roughness may be either biogenic or hydrodynamically induced by currents and waves although anthropogenic roughness prevails in certain instances e g port areas in terms of particular combinations of roughness scales and types combined sonar and diver observation data allow the beds to be systematically but qualitatively classified into 10 bottom types each of which is associated with a particular type of subenvironment

controlling factors of hazardous debris flow in taiwan three unanticipated large scale debris flows occurred in various rock type areas during typhoons that passed through taiwan the present study identifies possible hazard factors and the triggering mechanism several investigative methods relevant to these ends were selected including aerial photo analysis discontinuity patterns and geomaterial characteristics in affected gullies conjoined discontinuities protruded to the point of material slumping and producing large volumes of debris in heavy rainfall such debris tends to flow downward into the gullies discontinuity distribution produces geometric models of potential failure in plane wedge and toppling forms these slumping materials had been introduced and had accumulated along the gullies under study rapidly increasing water pressure caused by heavy precipitation provided a powerful force that triggered the debris flow movement large masses of slurry changed into an effective cutting force to erode the sidewalls resulting in more masses of slumping materials converging in the gully and quickly funnelling down into the lower gullies

reply to the comment by r anderson on uranium series disequilibrium sedimentation diatom frustules and paleoclimate change in lake baikal

oxygen and hydrogen isotope systematics of lake baikal siberia implications for paleoclimate studies we interpret oxygen and hydrogen isotope data for water samples from lake baikal siberia its tributaries and other local rivers and local precipitation in terms of the known water budget for the modern lake in order to gain insight into past limnological and climatic processes that influenced the lake lake baikal is remarkably uniform in its isotopic composition i80 15 8 0 2 0 6d 123 f 2 0 and lies slightly to the right of the global meteoric water line which suggests significant evaporation water is supplied to the lake by over 300 rivers and streams the oxygen isotope values 8180 of the rivers in the baikal catchment range from 13 4 to 21 2 0 the hydrogen isotope values sd for the same area range from 103 to 156 0 both these ranges generally conform to the global meteoric water line the weighted average isotopic composition of input to the lake rivers plus precipitation is 15 2 0 for 6 0 and 116 0 for 6d values higher than those of the modern lake therefore the isotopic composition of the modem lake cannot be related to the modern input through simple evaporation instead modeling of the isotopic mass balance of the lake suggests that inputs precipitation and influx from rivers and outputs evaporation and outflow are not at a steady state equilibrium under current climate conditions we found previous input to the lake had lower zy o and 6d values than modern input which reflects cooler climates in the past compared with modern conditions under constant climate conditions steady state conditions are not expected to be reached by the lake for at least 700 yr because of its large size and the long residence time of water in the lake

geostatistical analysis of the borden aquifer hydraulic conductivity field abstract a total of 11 vertical cores spaced 1 m apart along a single transect were extracted from the borden aquifer at a location 60 m north northeast from the site studied by sudicky previously examination of these cores shows the upper 1 5 2 0 m of the aquifer to be comprised of relatively unstructured fine to medium sands underlain by a 0 1 0 8 m thick peaty layer and a 0 1 m thick organic rich horizon between depths of 3 05 and 6 10 m the aquifer is comprised of clean horizontally bedded fine to medium sands similar to those examined by sudicky previously statistical analysis of 642 subsamples of 5 cm length from this interval suggests that the permeability data may follow a log normal distribution with a mean lntransformed permeability m 2 of 25 67 and a variance of 0 585 no consistent trend with depth was detected for ln k or for the mean and variance of ln k on a core by core basis exponential spherical and gaussian models all provided excellent fits to the vertical experimental variogram calculated using the classical estimator without the removal of outliers these fits produced correlation scales ranging from 0 16 to 0 23 m of the three theoretical models only the gaussian model produced a reasonable fit to the horizontal experimental variogram with a correlation scale of 4 8 m a linear model was also found to fit the experimental variogram data well in comparison with earlier results of sudicky and woodbury and sudicky it can be concluded that similar deposits were examined in this study particularly with respect to correlation structure on the basis of statistical tests however it cannot be concluded that the mean and variance of ln k are stationary over the 60 m distance between the cores examined in this study and those of sudicky the results of this study indicate that the borden hydraulic conductivity field is relatively uniform over the scale examined but that it cannot be characterized by a single spatially invariant statistical distribution

response of a residual soil slope to rainfall rainfall induced landslides are a common problem in residual soil slopes of the tropics it is widely known that rainfall induced slope failures are mainly caused by infiltration of rainwater howe

the capillary fringe and its effect on water table response abstract shallow water tables are often observed to respond in a highly disproportionate manner to precipitation events that is the magnitude of the response is often much greater than would be predicted on the basis of the specific yield of the geologic material and the amount of rainfall physical arguments are presented to show that if the capillary fringe the zone of tension saturation extends to ground surface then the addition of a very small amount of water can result in an immediate and large rise in the water table the arguments are supported by a field experiment in which the addition of 0 3 cm of water caused the water table to rise 30 cm in 0 25 min thus demonstrating the large and highly transient influence of the capillary fringe on the position of the water table the evidence in this study as well as recent work of others suggests that the capillary fringe effect could have a major influence on the process of stream flow generation contaminant transport to surface waters and contaminant transport in hydrogeologic regimes having shallow water tables it is further shown that calculations of groundwater recharge and consumptive use based on water table response and an assumed specific yield could be substantially in error

nepheloid and suspended particulate matter in south eastern lake michigan a persistent benthic nepheloid layer with high total suspended matter tsm and high total particulate surface area was observed in south eastern lake michigan the layer thickens from a few metres near the shelf slope boundary to greater than 10 m at the base of the slope when compared to the hypolimnion tsm increases by a factor of 2 20 at 1 m above the bottom the greatest increase detected at the slope basin boundary sediment trap profiles within the nepheloid layer show that the particulate flux increases exponentially from about 10 m above the bottom to 1 m above the bottom suggesting that a large fraction of the collected material came from resuspension a nepheloid layer is created during the formation of the thermal bar and maintained during the stratified period apparently through the action of weak but persistent currents this layer is supplemented by lakeward transport of fine particles resuspended near the shelf slope boundary due to impingement of the thermocline on the bottom or during higher energy events

response of the benthic nepheloid layer to near inertial internal waves in southern lake michigan 1 time series measurements of water transparency water temperature and current velocity were made at a station located in 58 m of water in southern lake michigan during the summer of 1995 currents generated by near inertial internal waves are correlated with variations in the thickness and in the vertical distribution of suspended sediment in the benthic nepheloid layer although a direct causal link between internal wave action and changes in the nepheloid layer could not be established the data suggest that local resuspension by shoaling internal waves maintains the layer during the stratified period the origin and maintenance of the benthic nepheloid layer is most likely the result of local resuspension due to a combination of internal wave action and longer term processes

the major and minor element geochemistry of lake baikal funding for u s participation in the fieldwork and sample collection was provided by the u s national science foundation funding for the analytical work was obtained by various means

the use of234th 238 disequilibrium to examine the fate of particle reactive species on the yangtze continental shelf measurements of234th t1 2 24 1d in water column and seabed samples from an area near the mouth of the yangtze river people s republic of china provide the following information 1 most of the234th in waters near the mouth of the yangtze river is in particulate form and horizontal transport and sedimentation of234th bearing particles dominate the234th budget in this area a model incorporating processes in at least two dimensions is required to understand the fate of particle reactive species on the yangtze continental shelf 2 the residence times of particle reactive species with respect to scavenging range from 0 3 days nearshore to 4 0 days offshore the residence times with respect to removal to the seabed range from 0 5 day nearshore to 11 0 days offshore 3 scavenging residence times for234th decrease as the concentration of suspended particles increases the time for removal of234th to the seabed increases with distance from shore a variable which integrates such factors as scavenging rate bathymetry and frequency of resuspension

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

discussion predicting rainfall induced landslide potential along a mountain road in taiwan j ching h j liao and j y lee 2011 geotechnique 61 no 2 153 166

a new mechanism for seaward dispersion of midshelf sediments silt to sand size particles may be transported across middle continental shelves by currents forced by the radiation stress of variable amplitude swell with the passage of each group of waves of sufficient amplitude for the high waves in the group to resuspend bottom sediments there is a seaward bias in the return of sediments to the seafloor over a storm season with the passage of many wave groups the net seaward sediment displacement may be 1 5 km

quaternary sedimentation and subsidence history of lake baikal siberia based on seismic stratigraphy and coring the long continuous high latitude stratigraphic record of lake baikal was deposited in three broad sedimentary environ ments defined by high resolution seismic reflection and coring meth ods 1 turbidite depositional systems by far the most widespread characterizing most of the margins and floors of the main basins of the lake 2 large deltas of major drainages and 3 tectonically or topographically isolated ridges and banks holocene sedimentation rates based on radiocarbon ages vary by more than an order of mag nitude among these environments from less than about 0 03 mm yr on ridges and banks to more than about 0 3 mm yr on basin floors ex trapolating these rates with a correction for compaction yields ten tative estimates of about 25 and 11 ma for the inception of rifting in the central and north basins respectively and less than 6 ma for the 200 m sediment depth on academician ridge the selenga delta has the distinctive form of a classic prograding gilbert type delta but its history appears to represent a complex com bination of tectonism and sedimentation the central part of the delta is underlain by prograding shallow water sequences now several hun dred meters below the lake surface these deposits and much of the delta slope are mantled by fine grained deep water hemipelagic de posits whose base is estimated to be about 650 000 years old modern coarse grained sediment bypasses the delta slope through fault con trolled canyons that feed large subaqueous fans at the ends of the south and central basins these relations along with abundant other evidence of recent faulting and the great depths of the central and south basins suggest that these two rift basins have experienced a period of unusually rapid subsidence over the last 650 000 years dur ing at least part of which sedimentation has failed to keep pace

uranium series disequilibrium sedimentation diatom frustules and paleoclimate change in lake baikal abstract the large volume of water approximately one fifth of the total surface fresh water on the planet contained in lake baikal in southeastern siberia is distinguished by having a relatively high concentration of uranium ca 2 nm and together with the surface sediments an unusually high234u238u alpha activity ratio of 1 95 about 80 of the input of uranium to the lake with a234u238u ratio of 2 0 comes from the selenga river profiles of uranium as well as the extent of isotopic disequilibrium in a 9 m sediment core collected on academic ridge generally show high values during interglacial periods corresponding to high diatom frustule numbers difr and biogenic silica bsi data that have been reported elsewhere during glacial periods low difr and bsi uranium progeny 234u and230th were in secular equilibrium with low concentrations of their parent238u radionuclide distributions were interpreted in terms of a quantitative model allowing for adsorption of riverine inputs of uranium onto two classes of sedimenting particles with differing238u232th ratios and uranium progeny in secular equilibrium if the234u238u activity ratio of adsorbed uranium has remained constant mean sedimentation rates can be independently estimated as 3 6 0 6 and 3 7 0 9 cm kyr 1 for the decay of234u and in growth of230th respectively these rates are consistent with a mean rate of 3 76 cm kyr 1 calculated by optimization of the correspondence between adsorbed238u and 18o in dated oceanic sediments the adsorbed uranium apparently tracks variable river flow during interglacials and is drastically reduced during periods of glaciation evidently uranium has not been significantly redistributed within baikal sediments over at least the past 250 kyr and is a unique biologically non essential tracer for climate sensitive processes which provide their own internal geochronometers potentially useful for ages up to 1 myr bp

comment on uranium series disequilibrium sedimentation diatom frustules and paleoclimate change in lake baikal by d n edgington j a robbins s m colman k a orlandini and m p gustin

modes of cross shore sediment transport on the shoreface of the middle atlantic bight the mechanisms responsible for onshore and offshore sediment fluxes across the shoreface zone seaward of the surf zone were examined in a 3 year field study the study was conducted in the southern part of the middle atlantic bight in the depth region 7 17 m using instrumented tripods supporting electromagnetic current meters pressure sensors suspended sediment concentration sensors and sonar altimeters the observations embraced fairweather moderate energy swell dominated and storm conditions cross shore mean flows ranged from near zero during fairweather to 20 cm s 1 during the storm oscillatory flows were on the order of 10 cm s 1 during fairweather and 100 cm s 1 during the storm suspended sediment concentrations at about 10 cm above the bed were 5 kg m 3 during the storm three methods were applied to evaluate the relative importance of incident waves long period oscillations mean flows and gravity in effecting shoreward or seaward sediment flux 1 an energetics transport model was applied to instantaneous near bottom velocity data 2 higher moments of near bottom flows were estimated and compared and 3 suspended sediment fluxes were estimated directly from the instantaneous products of cross shore velocity and suspended sediment concentration the results show that measurable contributions were made by all four of the processes most significantly mean flows were seen to dominate and cause offshore fluxes during the storm and to contribute significantly to onshore and offshore flux during fairweather and moderate energy incident waves were in all cases the major source of bed shear stress but also caused shoreward as well as seaward net sediment advection low frequency effects involving wave groups and long period waves made secondary contributions to cross shore sediment flux contrary to expectations low frequency fluxes were just as often shoreward as seaward whereas cross correlations between suspended sediment concentration and the instantaneous near bottom current speed were high and in phase under storm conditions they were weak and out of phase during fairweather conditions this suggests that simple energetics models are probably inadequate for predicting fairweather transport of suspended sediment

new instrumentation for the investigation of sediment suspension processes in the shallow marine environment abstract an instrumentation system has been developed that continuously measures flow velocity water depth and suspended sediment concentration profiles in the nearshore zone the system consists of four components 1 an array of electronic sensors including an electromagnetic current meter a surface piercing resistance wave gauge and a five element array of optical back scatterance sensors 2 a signal processing electronics unit 3 a guyed mast support structure and 4 a data acquisition system the small size of the sensors and their response characteristics make the array suitable for monitoring sediment transport to within a few centimeters of the bed under moderately large breaking waves 2 m results from an experiment on an exposed ocean beach on the coast of washington u s a indicate that sand suspension events of long duration 15 40 sec relative to the period of incident waves contribute a significant quantity of sand to the total littoral drift work is now in progress to modify the system for self contained operation on the continental shelf field investigations with the modified system will focus on the acquisition of a data set to test the validity of the suspended sediment distribution equation

sediment resuspension and transport in lake michigan during the unstratified period instrumented moorings were deployed during the winter of 1994 95 at three depths 28 58 and 101 m in southern lake michigan storms during the observation period were not unusually severe so the processes observed are typical of those that occur during an average winter time series observations of water temperature beam attenuation coefficient a measure of water transparency and current velocity show that local resuspension of bottom sediment occurred frequently after the breakdown of the thermocline resuspension was most frequent close to the shore but was also observed at the 58 m station local resuspension did not occur at the 101 m station but advection to the site of material resuspended at shallower sites was observed these observations do not support the hypothesis proposed by previous investigators that local resuspension at depths of 100 m or greater occurs during the unstratified period it is more likely that fine grained material resuspended by storm action in intermediate water depths 30 60 m is transported into the deeper parts of the lake by the general lake circulation

shoreface morphodynamics on wave dominated coasts abstract an open ocean shoreface typical of long wave dominated sandy coasts has been examined through a combination of extensive field measurements of wave and current patterns with computations of marine bedload transport and sedimentation sand transport on the upper shoreface is dominantly controlled by waves with only secondary transport by currents sand on the middle and lower shoreface as well as the inner continental shelf is entrained by storm waves and transported by a complex pattern of bottom boundary layer currents storm events have been studied and modeled for the shoreface off tiana beach long island the dominant effect of coastal frontal storms is to cause significant shore parallel bedload transport with important shore normal secondary components these storms tend to result in net offshore transport of sand removed from the beach and surf zone systems the bedload transport during a storm is convergent on the shoreface leading to accretion most accretion occurs on the upper shoreface with lesser deposits covering the middle and lower shoreface as well as the inner continental shelf longer term equilibrium can be maintained by slow return of sand up the shoreface during non storm conditions annual and geologic time scale budgets of shoreface sand transport and sedimentation yield equilibrium net accretion or net deposition the annual balance results from an integration of the event scale bedload transport patterns and morphologic responses these processes and responses have feedback mechanisms which stabilize the system over longer but not geologic time scales geologic time scale balances are controlled by relative sea level changes and relative availability of sediment supply with the event scale shoreface and transporting processes providing the mechanism to produce the changes in long term morphology and sedimentation patterns in the area of study the long term pattern is one of net shoreface erosion and the permanent loss of sand to the shelf floor

maintenance of the shoreface by wave orbital currents and mean flow observations from the long island coast waves and currents were observed for a total of 36 days in august 1976 and 1977 calculations of wave transport of sediment using a bagnold equation for transport and second order stokes theory show that wave orbital current asymmetry results in landward sediment transport in 10 m or less water depth but does not significantly effect transport at greater depths calculations of sand transport using the madsen grant formulation show that during a 36 day observation period sediment in less than 10 m of water generally moved landward into the breaker and then along coast with the wave driven littoral flow the calculations show that below 10 m the generally upwelling coast parallel mean flow did not move sediment however during two days of a mild summer northeaster storm a downwelling coastal jet developed with 60 cm sec sup 1 maximum current the calculations show that if this flow had been combined with the intense wave regime of the succeeding several days sediment would have been entrained across the lower as well as the upper shoreface movement would have been offshore and alongshore such storm transport is believed to be typical of the more intense winter storms and to be responsible for the erosionalmore shoreface retreat that has caused up to a kilometer of shoreline retreat on the long island coast in the last century less

a rock magnetic record from lake baikal siberia evidence for late quaternary climate change rock magnetic measurements of sediment cores from the academician ridge region of lake baikal siberia show variations related to late quaternary climate change based upon the well dated last glacial interglacial transition variations in magnetic concentration and mineralogy are related to glacial interglacial cycles using a conceptual model interglacial intervals are characterized by low magnetic concentrations and a composition that is dominated by low coercivity minerals glacial intervals are characterized by high magnetic concentrations and increased amounts of high coercivity minerals the variation in magnetic concentration is consistent with dilution by diatom opal during the more productive interglacial periods we also infer an increased contribution of eolian sediment during the colder windier and more arid glacial conditions when extensive loess deposits were formed throughout europe and asia eolian transport is inferred to deliver increased amounts of high coercivity minerals as staining on eolian grains during the glacial intervals variations in magnetic concentration and mineralogy of lake baikal sediment correlate to the specmap marine oxygen isotope record the high degree of correlation between baikal magnetic concentration mineralogy and the specmap oxygen isotope record indicates that lake baikal sediment preserves a history of climate change in central asia for the last 250 ka this correlation provides a method of estimating the age of sediment beyond the range of the radiocarbon method future work must include providing better age control and additional climate proxy data thereby strengthening the correlation of continental and marine climate records

the morphodynamic effects of incident wave groupiness and tide range on an energetic beach abstract the roles played by daily tide range and incident wave groupiness in affecting the short term morphodynamic responses of an energetic beach are examined demodulation of original tide and wave time series from the moderate energy narrabeen beach australia resulted in new time series of daily tide range and a daily grouping factor which expresses the relative amplitude of the alternation between groups of high and low waves using these new time series together with time series of daily beach state and changing breaker conditions statistical analyses were performed aimed at determining the contributions made by tide and groupiness in explaining time varying beach state additional to those made by time varying wave conditions eigenvector analyses of monthly surveyed beach and surf zone profiles provided a set of time series on modes of profile configuration change which were also analyzed to determine the relative effects of waves and tide range on profile shape both tide range and groupiness are significant determinants of beach state the six beach states are reflective low tide terrace transverse bar and rip rhythmic bar and beach longshore bar trough and dissipative wright and short 1984 provided that wave conditions are within the appropriate range to favor beach states at the reflective end of the sequence spring tides will tend to favor the low tide terrace over the transverse bar and rip state higher tide ranges are also associated with more subdued bar trough topography the more accentuated bar trough profiles are developed when tide range is minimal overall higher relative incident wave groupiness favors the more dissipative states incident wave groupiness is the dominant factor determining whether the low tide terrace state or transverse bar and rip state prevails provided incident wave steepnesses permit one or the other of these states groupiness is also important in discriminating between the transverse bar and rip and rhythmic bar and beach states

hydrologic response of catchments to precipitation quantification of mechanical carriers and origins of water 1 precipitation induced overland and groundwater flow and mixing processes are quantified to analyze the temporal event and pre event water and spatial groundwater discharge and overland runoff origins of water entering a stream using a distributed parameter control volume finite element simulator that can simultaneously solve the fully coupled partial differential equations describing 2 d manning and 3 d darcian flow and advective dispersive transport mechanical flow driven by hydraulic potential and tracer based hydrograph separation driven by dispersive mixing as well as mechanical flow are simulated in response to precipitation events in two cross sections oriented parallel and perpendicular to a stream the results indicate that as precipitation becomes more intense the subsurface mechanical flow contributions tend to become less significant relative to the total pre event stream discharge hydrodynamic mixing can play an important role in enhancing pre event tracer signals in the stream this implies that temporally tagged chemical signals introduced into surface subsurface flow systems from precipitation may not be strong enough to detect the changes in the subsurface flow system it is concluded that diffusive dispersive mixing capillary fringe groundwater ridging and macropore flow can influence the temporal sources of water in the stream but any sole mechanism may not fully explain the strong pre event water discharge further investigations of the influence of heterogeneity residence time geomorphology and root zone processes are required to confirm the conclusions of this study

palaeoenvironmental history of lake baikal during the last 23000 years abstract a sediment core recovered from lake baikal was studied in an attempt to elucidate the palaeoenvironmental history of an intra continental lake under the control of last glacial to post glacial climatic fluctuations the lake conditions were characterised by subdued primary production and increased turbidity conditions during the last glacial maximum terrestrial vegetation and the development of soil layers were reduced in the drainage areas the deglaciation suggested by increased terrigenous sand influx and biological productivity took place at around 18 000 yr b p responding to the increased insolation in the northern hemisphere high latitude the onset of wet and warm conditions at ca 12 000 yr b p brought on a maximum of aquatic production and forestal expansion between 7 000 and 6 000 yr b p since 5 000 yr b p enhanced blooming of diatoms has occurred due to an increased nutrient supply and dissolved silica input into the lake

sediment flux to lake baikal siberia russia modeling approach preliminary results of modeling of annual variability in suspended particle matter spm in lake baikal are presented together with outline of major present day sedimentary environments and variation in sedimentation patterns in drilled sections spanning several million years from the lake the model predicts the spm concentration sedimentation resuspension mixing and mineralization in the lake on a monthly basis using parameters describing the lake geometry and the climate in the catchment results of the modeling are generally in agreement with empirical data and indicate that the model accounts well for the relatively large volume and variable conditions occurring in lake baikal the model also seems to have large potential in predicting variability of sediment flux and mass balance in the lake in the past

vertical and horizontal particle transport in the coastal waters of a large lake an assessment by sediment trap and thorium 234 measurements 1 the horizontal and vertical flux of particulate material in the nearshore of southern lake michigan 0 40 m was estimated with the naturally occurring radionuclide 234th horizontal fluxes of 234th supplemented apparent vertical fluxes of 234th in the water column based on local 234th 238u disequilibria by a factor of 7 14 reinforcing the importance of lateral transport in coastal environments calculated onshore transport of particulate material across the 40 m isobath was as high as 1 1 106 kg km 1 d 1 and exceeds estimates of terrigenous riverine and bluff erosion loading estimates of onshore flux of organic carbon exceeded areal primary productivity by as much as 300 and should be considered in nearshore carbon budgets bottom tethered sediment traps placed 5 m above the bottom measured sedimentation rates that were 1 order of magnitude lower than 234th derived mass fluxes from the water column and 2 orders of magnitude lower than 234th derived mass fluxes to the lakebed we ascribe this difference to under collecting by the sediment trap either because of trap hydrodynamics or flux occurring below the trap capture plane cross shore fluxes showed a periodicity of 4 days and correlated strongly with a topographic vorticity wave that is present throughout the year in southern lake michigan the impact of this wave as a driver of bidirectional cross shore flux on biogeochemical cycling and both nearshore and offshore food webs has not yet been explicitly considered

does 234th 238u disequilibrium provide an accurate record of the export flux of particulate organic carbon from the upper ocean the magnitude of the flux of biogenic particulate organic carbon poc exported from the surface waters of the world ocean and remineralized at depth is critical to constraining models of the global carbon cycle yet remains controversial the use of upper ocean sediment traps is still one of the primary tools for determining this export flux although trap fluxes have been shown to vary significantly because of hydrodynamic and sample collection biases over the past decade 234 th increasingly has been used as a tracer to estimate poc export from the euphotic zone by multiplying the depth integrated 234 th flux by the poc 234 th ratio of sinking particles the accuracy of this technique is highly dependent on the natural variability in the poc 234 th ratio and 234 th flux yet the significance of this variability to estimates of poc export remains uncertain based on an analysis of new 234 th and poc data from the labrador sea and a review of 25 previous independent field studies we report that poc export fluxes can vary 2 10 times or more solely because of variability in the poc 234 th ratio and procedures used to estimate the 234 th flux recommended improvements include studies of the biological chemical and physical mechanisms controlling 234 th organic matter interactions in seawater detailed comparisons of poc 234 th ratios in size fractionated and sediment trap material increased spatial and temporal sampling density of 234 th and more standardized procedures to calculate the 234 th export flux

uranium series chronology for sediments of lake hovsgol mongolia and the 1 ma records of uranium and thorium isotopes from the hdp 04 drill core abstract uranium and thorium isotopes in an 81 m long sediment core hdp 04 of lake hovsgol mongolia were measured to investigate their downcore distributions and to explore potential linkage to paleoenvironmental changes three dimensional isochron techniques using isotope ratio diagrams in 238u 234u 230th 232th system presented by ludwig and titterington were applied to age date the lake sediments at the depths of 11 42 14 71 and 14 83 m in the hdp 04 section the estimated ages of these horizons are 66 8 122 11 and 128 22 ka respectively the 238u concentration throughout the entire section fluctuated by a factor of 12 ranging from 19 9 to 232 1 mbq g with anomalously high 238u peak at 23 8 m in depth while the 232th concentration varied only by a factor of about two between 24 3 and 54 0 mbq g the discrimination of the bulk 238u into authigenic and terrigenous 238u fractions was attempted based on the measured 232th as a correction index for terrigenous materials in the upper 24 m corresponding to the last 250 ka the authigenic 238u was higher in interglacials and lower in glacials this depth profile of authigenic 238u contents was almost identical pattern with that found in a sediment core ver98 1 6 from the academician ridge lake baikal further this profile can be correlated well with that of photosynthetic pigment contents one of proxies of paleoproductivity suggesting that the variation of authigenic 238u contents were associated with the environmental change around lake hovsgol

an energetics total load sediment transport model for a plane sloping beach bagnold s energetics based total load sediment transport model for streams is used as a basis for the development of a total load model of time varying sediment transport over a plane sloping bed in both the bedload and suspended load the transport rate vectors are found to be composed of a velocity induced component directed parallel to the instantaneous velocity vector and a gravity induced component directed down slope the model is applied to idealized surfzone conditions leading to estimates of the local longshore and onshore offshore sediment transport rates as well as the equilibrium beach slope as a function of the local wave and current conditions the model is combined with a nonlinear longshore current model and spatially integrated to obtain predictions of the total longshore transport rate as a function of the incident wave conditions the results support the general form of the wave power equation except that the wave power coefficient is no longer constant but is instead a complex function of the incident wave and beach characteristics

reverse sediment transport induced by amplitude modulated waves abstract amplitude modulated waves can induce bedload and suspended load transports of sediment in the reverse direction of the wave propagation the reverse transport rate is mainly controlled by the magnitude of the bottom orbital velocity the mechanism is most effective in transporting silts and fine sands offshore but not clays the sorting characteristic may be amplified when non uniform size sediments are present in the sea bed the mechanism provides a feasible explanation for two shelf sedimentation patterns difficult to understand using conventional seaward sediment transport models

centennial to millennial scale climate shifts in continental interior asia repeated between warm dry and cool wet conditions during the last three interglacial states evidence from uranium and biogenic silica in the sediment of lake baikal southeast siberia abstract we observed timescale dependent changes in the correlations between biogenic silica biosi and uranium concentrations of bulk sediment from the buguldeika saddle lake baikal there was a positive correlation for the glacial interglacial 100 kyr scales over the 180 kyr with inverse correlations for centennial to millennial scales during the last three interglacial states mis 5 3 and 1 the distinction of these correlations between the time scales suggests that the sedimentation processes of biosi and u differ from each other the baikal biosi concentration record is generally regarded as a paleotemperature proxy reflecting the diatom production of the lake on the other hand we concluded that the temporal variation of the u concentration in the sediment reflected the weathering intensity in the south of lake baikal watershed associated with changes in the rainfall moisture levels based on the paleoclimate proxies from lake baikal climates in continental interior asia are identified as having dry and wet conditions during the glacial and interglacial periods respectively this accounts for the rhythms in growth and retreat of ice sheets in eurasia on glacial interglacial scales in the interglacial periods mis 5 3 and 1 the continental interior is contrary to the glacial interglacial climate changes characterized by alternating warm dry and cool wet climates with periods in tens of thousands years in particular such shifts in the climate stand out prominently at the beginning of mis 5d the detrended u record for the last 5 2 kyr shows wet events at 4 3 3 7 3 2 2 3 1 8 1 2 and 0 8 0 3 kyr these events coincide with the timing of the north atlantic ice rafted debris events which were possibly related to solar activity all this evidence suggests that climate in the continental interior followed significantly different fluctuation patterns in the glacial interglacial and shorter time scales

predicting rainfall induced landslide potential along a mountain road in taiwan this paper gives a brief introduction on the background and current status of rainfall induced landslides along a mountain road route t 18 in taiwan and presents a detailed analysis based on the gaussian process model for predicting locations and occurrence times of future landslides using post chi chi earthquake historical data based on inherent and man made features of failed and not failed slopes locations of possible future landslides owing to rainfall along route t 18 are predicted together with historical rainfall data a rainfall fragility graph is established the analysis results show that the gaussian process model is effective in predicting landslide potentials and probabilities comparisons of the gaussian process analysis and the discriminant function analysis are made which show that the former outperforms the latter in many respects the results are valuable for predicting where and when landslides would occur along route t 18 in future heavy rainfalls

an energetics bedload model for a plane sloping beach local transport bagnold s energetics based sediment transport model for streams is used as a basis for the development of a model for the time varying transport of bedload over a plane sloping bed the sediment transport vector is found to consist of two components the velocity induced transport directed parallel to the instantaneous velocity vector and the gravity induced transport vector directed downslope the model is applied to the case of sediment transport within the surf zone for the separate cases of weak and strong longshore currents relative to the wave bore oscillatory water velocity the results suggest the bagnold s oscillatory sediment transport model which forms the basis for a number of longshore sediment transport models is only correct for the special case of weak longshore currents and near normal incident waves for an artibrary strength longshore current v and a local incident wave angle a the longshore transport rate is found to be proportional to sina v 1 sin sup 2 a v sup 3 where u is the wave induced oscillatory water velocity the model also predicts the onshore offshore sediment rate for weak longshore currents and near normal incident waves the predicted equilibrium beach slope is equal to tanf strong longshore currents and or significant local wave angle conditions however cause amore change in this equilibrium beach slope less authors bailard j a inman d l publication date 1981 03 20 osti identifier 6767919 resource type journal article resource relation journal name j geophys res united states journal volume 86 c3 research org scripps institution of oceanography university of california la jolla california 92093 country of publication united states language english subject 58 geosciences shores sedimentation coastal waters gravitation sediments silt velocity water currents currents surface waters 580500 oceanography 1980 1989

circulation during winter and northerly storm events in southern lake michigan 1 moored observations of winds currents and temperature made off the southeastern lake michigan shore during 1998 to 2000 winter spring periods are studied to describe the mean winter circulation and episodic circulation during northerly storms in lake michigan late winter spring sediment plumes in southeastern lake michigan were attributed to these episodic circulation features the winter spring currents in southeastern lake michigan are quite depth independent and the mean currents flow predominantly alongshore and toward the north the observed currents show the signature of a forced two gyre circulation in the southeastern basin the interannual variability of mean and fluctuating currents is mainly due to the variability of prevailing wind forcing the intermittent episodic circulation influenced by northerly storms causes significant asymmetry to the mean circulation during northerly storm episodes the mean current speeds increased significantly and the currents within 10 km of shore followed the surface wind stress while farther offshore the circulation was oppositely directed during these episodes it is also observed that the combination of directly wind forced currents and northward propagating vorticity wave generates significant offshore transport in this region

rare earth element geochemistry of lake baikal sediment its implication for geochemical response to climate change during the last glacial interglacial transition sediments deposited on the bottom of lake baikal have contributed to the understanding of a long term environmental history of continents rare earth elements rees along with major elements and loss on ignition loi of baikal sediments were determined with the aim of evaluating their suitability for a new paleoenvironmental proxy our interest is concentrated on paleoenvironmental change during the last glacial interglacial transition lgit chondrite normalized ree patterns for baikal sediments show a similar variation to those for typical upper continental crustal materials three parameters of la yb n n chondrite normalized value ratio sree tio2 and eu anomaly were used to express detailed characteristics of baikal sediments depth profile of la yb n ratio shows abrupt change whose timing corresponds to the beginning of climatic warming inferred from the profiles of sio2 tio2 and loi in addition la yb n ratio sree tio2 and the degree of eu anomaly correlate with each other this suggests that inflow process of particulate materials into the lake may have changed during the lgit the analytical results of this study lead to the conclusion that ree is a useful paleoenvironmental proxy in the baikal region r 2007 elsevier ltd all rights reserved

barrier island evolution middle atlantic shelf u s a part i shoreface dynamics abstract in part i of this paper near bottom fluid velocity and sediment concentration measurements from the shoreface of a middle atlantic barrier long island coast are analyzed to provide insight into the dynamics of erosional shoreface retreat in part ii these data are combined with observations of coastal stratigraphy in order to construct a model for the evolution and behavior of middle atlantic barriers wave motions on the long island shoreface tend to drive sediment onshore calculations of the onshore sediment flux driven by asymmetrical shoaling waves show that for the wave states commonly encountered on the middle atlantic shelf values become strongly positive landward of approximately 10 m water depth upper shoreface but drop to very low values shortly seaward of that isobath on the lower shoreface and inner shelf floor fair weather wave current interaction tends to cause a landward creep of sediment even though the wave orbital component of the near bottom velocity field is nearly symmetrical this movement occurs because the wave approach direction generally lies within 90 of the direction up coast or down coast of the alongshore wind driven current therefore fluid shear stress acting on the sediments tends to be reinforced during the shoreward stroke of the wave orbital motion and partially cancelled during the seaward stroke during major storms the rate of sediment transport increases by at least an order of magnitude and the role of wind driven currents becomes important much more sediment is resuspended by the wave orbital current component because storm waves are more powerful than fair weather swells but the wind driven flow component is also much stronger and is now available for transporting the resuspended sediment storm flows over the shoreface occur in distinct dynamic zones surf zone friction dominated zone transition zone geostrophic zone the zones are defined by dynamical considerations and expand or contract with the intensity of the causative wind stress during peak flow events the characteristic length scales of the friction dominated and geostrophic zones tend to correspond with the morphologic zones of the shoreface and inner shelf the storm intensified wind driven alongshore flows of the lower shoreface are frequently jet like in nature and may be upwelling or downwelling wind driven coastal flows with a strong downwelling component occur during most storms on the long island coast and are particularly important to the coastal sand budget during these events sand is entrained by the storm intensified upper shoreface circulation system of wave driven alongshore currents and rip currents and is fed into the main wind driven coastal current because of the offshore component of bottom flow sand is swept down the lower shoreface and onto the adjacent inner shelf fair weather processes may be unable to return storm deposited sand to the beach from such an offshore position the shoreface transport regime of the long island barrier coast thus consists of long periods of time months during which sand moves slowly toward the beach punctuated by short intense periods hours or days during which sand is transferred from the shoreface to the adjacent inner shelf the long term sense of movement of the shoreface whether retreating the long island case or prograding must depend on the loss or gain of sand by shoreface with respect to the inner shelf the data shows that the coastal sand budget is controlled not only by the upper shoreface cycle withdrawl of sand from the beach prism storage in the breakpoint bar and its subsequent return to the beach but by a cycle of larger spatial and temporal scale in which sand is exchanged between the shoreface as a whole and the adjacent inner shelf

continental climate response to orbital forcing from biogenic silica records in lake baikal changes in insolation caused by periodic changes in the earth s orbital parameters provide the primary forcing for global ice ages1 6 but it is not clear to what extent the climates in continental interiors are controlled directly by regional variations in insolation and to what extent they are driven instead by the highly nonlinear response of the oceans and ice sheets here we investigate this question using the record of biogenic silica in lake baikal as a proxy for climate change in this high latitude mid continental region we find a good correlation between this record and that of marine oxygen isotopes4 over the past 250 kyr the baikal record exhibits both a strongly nonlinear component manifested in a 100 kyr periodicity and weaker direct insolation components manifested in the 41 kyr obliquity and 23 and 19 kyr precession orbital cycles these results show that even though extreme continental climates such as this are influenced directly by insolation variations they are dominated by the nonlinear rhythm of the oceans and ice sheets

bar generating cross shore flow mechanisms on a beach random waves normally incident on a dissipative beach induce a variety of cross shore flows such as asymmetric oscillatory flow wave grouping induced long wave flow breaking induced turbulent flow and momentum decay induced undertow these flows are identified analyzed and hindcasted in a set of laboratory experiments with the aim of revealing the role of each of the flow mechanisms in the two dimensional case of bar generation on a beach

10be record and magnetostratigraphy of a miocene section from lake baikal re examination of the age model and its implication for climatic changes in continental asia 1 we determined the concentration of the cosmogenic radionuclide be in the miocene section of a sediment core 5 12 my bp retrieved from lake baikal bdp98 hole2 that had been previously dated by the magneto stratigraphic ms method using our new 10 be geochronology we reexamined the ms age depth assignments and found inconsistencies we therefore reexamined the ms record and propose a new model which is consistent with the 10 be data with an age of 8 4 my bp at a depth of 600 meters accepting the revised ms ages we found the profile of the decay corrected 10 be concentration which shows ca 50 decreases of 10 be during the periods 0 2 7 my bp and 5 3 5 8 my bp we also detected considerable increases of the 10 be flux into sediments before 4 5 my bp

90y 90sr disequilibrium in surface waters investigating short term particle dynamics by using a novel isotope pair abstract we demonstrate the use of the disequilibrium between 90 sr t 1 2 29 1 yr and its particle reactive daughter 90 y t 1 2 64 h to estimate particle removal rates and settling velocities in the epilimnion of a freshwater lake during varying conditions of stratification caused by seasonal changes the estimated rates of removal obtained from the 90 sr 90 y disequilibrium showed good agreement with a measured rates of mass removal obtained from settling particle fluxes in sediment traps and the inventories of suspended material and b independently obtained removal coefficients for the scavenging behavior of two different isotopes of particle reactive plutonium present in the water column because of different processes because 90 sr is widespread and readily measurable in freshwater systems as a result of fallout from nuclear weapons testing the 90 sr 90 y disequilibrium is a potentially valuable resource for examining particle dynamics in surface waters

a year of internal poincare waves in southern lake michigan 1 a unique set of full year deep water observations from the middle of lake michigan s southern basin are analyzed to quantify the seasonal variability of the dominant near inertial internal poincare wave at this mid lake location the poincare wave is seen to describe more than 80 of the observed surface current variability for much of the year with characteristic near inertial frequency and clockwise rotating velocities the dominance of the near inertial seiche on the flow decreases with depth the wave persists during the stratified period roughly may through late december and is supported by as few as 1 2 degrees of thermal stratification over 150 m only after complete water column mixing does the wave go dormant for january through april the strongest poincare wave activity is seen to correspond to the period of strongest summer thermal stratification august in spite of the relatively weak winds at this time a simple inertial slab model optimized with linear friction is shown to capture the seasonal variability of the near inertial energy at this location reasonably well the vertical structure of the wave shows good agreement with that calculated with a standard normal modes formulation which is in turn used to characterize the potential shear and mixing caused by the wave late spring and summer events of elevated poincare wave activity are shown to generate sufficiently strong shear with persistent periods of sub 1 richardson numbers within the thermocline suggesting that the near inertial seiche is likely generating thermocline instabilities in the lake s interior

abrupt increase in precipitation and weathering of soils in east siberia coincident with the end of the last glaciation 15 cal kyr bp abstract an abrupt increase in the temperature in greenland in the wake of the initiation of the bolling allerod warm phase at ca 15 cal kyr bp was followed after a few decades by a dramatic increase in the concentration of methane in the atmosphere of the earth resulting from an increase in humidity in the tropics j p severinghaus e j brook science 286 1999 930 934 analysis of a sediment core from lake baikal east siberia spanning the end of the last glacial period and the holocene revealed an abrupt stepwise 1 3 3 4 fold decrease in the concentration of several soluble elements such as na k mg ca and si in hot nitric acid extracts of small intervals 3 cm this chemical change appears to have occurred over the same time span based on similarities in the profiles of silica and diatoms found in other 14 c dated cores this suggests that the calcium rich mammoth steppe landscape r d guthrie quat sci rev 20 2001 549 573 of siberia created during the last glaciation underwent a dramatic transformation at the end of this period at the beginning of the bolling allerod warm phase due to an increase in precipitation within a time interval of less than 300 yr

last glacial to post glacial 10be fluctuations in a sediment core from the academician ridge lake baikal 10be concentrations sediment composition and sediment accumulation rates were determined in a sediment core from the academician ridge of lake baikal the 10be concentrations vary from 5 07 108 atoms g in the last glacial section to 11 25 108 atoms g in the section representing the post glacial climate stage 10be fluxes on the other hand increase toward the last glacial stage coinciding with an increase of the sediment accumulation rate these facts imply that climate related sedimentation is related to both flux and concentration of the nuclide in the sediment core during the last glacial stage arid conditions in the lake s watershed caused a marked increase in flux of clay particles with low 10be content to the lake resulting in an increased flux but lowered concentration of 10be in the sediments it is suggested that the 10be record of the bottom sediments of lake baikal can be used as a proxy indicator of climate change in central asia

bars bumps and holes models for the generation of complex beach topography in shallow water any two waves of the same frequency are shown to produce complex patterns of drift velocity above the sea bed if the longshore components hi h of the wave numbers of the two waves are different these steady flow patterns exhibit a longshore periodicity of wave number hi h irrespective of whether the waves propagate in the same direction say hi he positive or in opposite directions he negative the interaction of two edge wave modes is examined in detail the drift velocities are calculated and a simple sediment transport model is used to predict the beach topography that would be in equilibrium with these flow patterns as expected crescentic sand bars are produced by the special case of standing edge waves hi h intriguingly for all other cases a combination of complex transverse bars plus meandering or straight offshore bars result patterns that are surprisingly reminiscent of many published descriptions of complex rhythmic topography the extension of the model to three or more waves produces topography that appears to be very irregular although the pattern should repeat over sufficiently long distances along the beach even with only three waves these distances may be very large compared to the scale of the bars

particle delivery to the benthos of coastal lake michigan a 2 d non steady state model was applied to measured profiles of 234th 238u and 90y 90sr disequilibria in a shallow 22 m water column of coastal lake michigan downward fluxes of 234th and 90y were primarily driven by onshore horizontal advection concordance between 234th and 90y derived mass flux estimates from the water column could only be realistically achieved under a nuclide scavenging scenario dominated by direct sorption on bottom or near bottom sediment and vertical convection in the water column not sinking particles an estimated vertical 234th 90y flux ratio of 0 31 in the water column agreed with measured 234th 90y activity ratios on collected ejecta from bottom dwelling dreissenid mussels 0 26 0 05 and not with water column particles 3 3 1 3 a similar 238u 90sr parent nuclide activity ratio of 0 30 0 02 suggests that both 234th and 90y are scavenged in toto below the maximum sampling depth 17 m and near the sediment water interface determining the mechanism by which particles are transported to the bottom is important for understanding not only how benthos are supplied with water column material but also how particle fluxes should be measured and calculated

short term changes in the morphodynamic states of beaches and surf zones an empirical predictive model a time series of 6 5 years of daily observations of beach states and wave characteristics from southeastern australia was analyzed with the aim of determining the degree to which time varying beach state can be explained and predicted the six commonly occurring beach states dissipative longshore bar trough rhythmic bar and beach transverse bar and rip low tide terrace and reflective discussed earlier were related by means of discrete discriminant analyses to the parameter hb wst where hb is breaker height ws is the fall velocity of the beach sand and t is peak breaker period using a total of 1545 cases two values were used in the analyses the immediate value occurring on the day the particular state was observed and a weighted mean value expressing recently antecedent conditions the immediate value made a negligible contribution to explaining day to day beach state observations however the antecedent conditions showed a strong relationship and provide a successful means of prediction by examining cases where the time derivatives of both state and were near zero it was possible to define the equilibrium conditions associated with each state directions of change erosional or accretionary are predicted in terms of departures of from the equilibrium value appropriate to the beach state prevailing at the time change begins

sedimentation processes and new age constraints on rifting stages in lake baikal results of deep water drilling with this paper we present a first attempt to combine the direct results on lithology composition and age dating in the boreholes bdp 93 bdp 96 and bdp 97 with geological and seismic data from the areas where those sections were drilled the sedimentary environments represented by the bdp boreholes are markedly different and possess characteristic lithological features the results of the deep drilling provide the essential means for testing numerous age models used in geological reconstructions of the lake baikal rifting dynamics neither the basin wide unconformity interpreted from seismic data nor the interpreted change from shallow water to deep water facies at the boundary of the seismic stratigraphic complexes were found in the bdp 96 boreholes on academician ridge also lithology does not support the proposed reconstructions of intense lake level fluctuations and transgressions during the pliocene at academician ridge the continuous deep water hemipelagic sedimentation at academician ridge has existed for the past 5 ma the beginning of an intense rifting phase of the neobaikalian sub stage and related drastic changes in sedimentation processes were interpreted on seismic sections as the basin wide unconformity b10 different age estimates for this boundary ranged from late pliocene 3 5 ma to plio pleistocene boundary as shown by bdp 96 borehole b10 is associated with a lithological change from diatomaceous ooze to dense silty clay and not with an erosional contact the new age for this boundary in bdp 96 is approximately 2 5 ma this new age constraint suggests that the upper sedimentary strata of northern baikal 1 5 1 7 km thick have formed during the past 2 5 ma with average sedimentation rates of 60 70 cm ka the bdp 93 boreholes at buguldeika suggest that uplift in primorsky range took place prior to 1 07 1 31 ma a date which exceeds the age of previous geological models