dynamic relations for the deposition of sediment on floodplains and point bars of a freely meandering river abstract fluvial features such as floodplains and point bars are built by sediment deposition and sculpted by erosion long term measurements 38 yr of the cross section topography of active floodplains and point bars along the freely meandering powder river in southeastern montana usa mean daily discharge of 12 5 m3 s 1 were used to develop dynamic relations between annual sediment deposition and peak flood discharge five floodplain sections and five point bar sections were selected from 24 cross sections along a 90 km study reach at each cross section the sediment deposition volume per unit streamwise distance was computed as the difference between two topographic surveys made in consecutive years snowmelt floods were found to be the dominant annual process however other processes such as flash floods ice breakup floods and autumnal floods were important episodically the dynamic relations were linear for both fluvial features the snowmelt deposition discharge relations showed in general that point bars were about two times more efficient at trapping sediment than floodplains each relation had a discharge threshold that must be exceeded before sediment was deposited although these discharge thresholds for floodplains and point bars had essentially the same mean value 69 and 71 m3 s 1 respectively they represented different processes thresholds for other rivers will probably differ from those for powder river because of different channel geometry and sediment characteristics

modeling framework for sediment deposition storage and evacuation in the floodplain of a meandering river theory 1 a theory for the movement of suspendible sediment through the floodplain of a simple actively migrating river is developed the floodplain is represented as a series of sediment storage reservoirs each incorporating multiple bends of a river independent models for floodplain sediment deposition and for subsequent removal of sediment by lateral channel migration allow the volume of sediment stored in the floodplain and the associated average floodplain elevation to change over time and down the valley at a given quasi steady discharge deposition depends on a simple one dimensional partition between channel and floodplain discharge and on suspended sediment concentration one size class which varies along the reach depending on lateral supply and floodplain history sediment supply is specified at the upstream end of the reach using a suspended sediment rating curve long term average overbank deposition rates are approximated by weighting multiple steady state solutions using a flow duration curve the channel bed elevation of the system is assumed to be fixed and tributaries are handled using simple lateral source terms the interaction between the submodels is such that under constant boundary conditions the channel evolves toward a state of geomorphic equilibrium where the volume of sediment added to the floodplain by overbank deposition just balances the volume removed by channel migration the model is easily adapted to track conservative suspended sediment tracer material concentration as such material moves through the channel floodplain system

a chemical indicator of trade wind reversal in corals from the western tropical pacific historical levels of manganese have been measured in the annual rings of a reef coral from tarawa atoll 1 30 n 173 e in order to assess the temporal variability of this trace element in surface waters of the western tropical pacific seasonal variability associated with vertical mixing is not apparent as is the case in the eastern pacific however mn ca ratios are highly perturbed during three el nino southern oscillation enso events 1965 1972 1976 that occurred within the growth period 1960 1977 for approximately 6 months during each of these events mn ca ratios increase by 50 80 from a background of 27 nmol mn mol ca these features co occur with negative 18o pulses recorded in the same coral which result from anomalously abundant rainfall wet deposition of mn however does not appear to be an adequate source to account for the inferred surface ocean enrichments the most plausible explanation has to do with the transient appearance of westerly winds along the equator during enso periods particularly vigorous westerly wind bursts sometimes averaging 10 m sec or more over 16 hours during the aforementioned years may have generated wind waves of sufficient strength to create an aura of particulate and diagenetically remobilized mn from within the shallow westward facing lagoon of tarawa this interpretation is supported by relatively high mn concentrations measured in pore waters of tarawa lagoon sediments the results suggest a useful new chemical tracer of historical enso conditions in the western pacific basin

geologic history of natural coal bed fires powder river basin usa abstract coal bed fires ignited by natural processes have baked and fused overlying sediments to form clinker a hard red or varicolored rock through much of the northern great plains of the united states usa the gently dipping coal beds in the region burn when regional downwasting brings them above the local water table the resulting clinker forms a rim along the exposed edge of the coal bed in an ongoing process through geologic time the resistant clinker is left capping buttes and ridges after the softer unbaked strata erode away clinker outcrops cover more than 4100 km2 in the powder river basin prb which lies in wyoming wy and montana mt the clinker in place records tens of billions of tons of coal that have burned releasing gases into the atmosphere the amount of clinker that has eroded away was at least an order of magnitude greater than the clinker that remains in place fission track and uranium thorium helium ages of detrital zircon crystals in clinker and paleomagnetic ages of clinker show that coal beds have burned naturally during at least the past 4 million years ma the oldest in place clinker that has been dated collected from a high isolated clinker capped ridge has a fission track age of 2 8 0 6 ma evidence of erosion and downcutting is also preserved by clinker clasts in gravel terraces one clinker boulder in a terrace 360 m above the yellowstone river has a fission track age of 4 0 0 7 ma coal bed fires are caused by lightning wildfires spontaneous combustion or human activity on coal outcrops and in mines miners government agencies and ranchers have extinguished thousands of coal bed fires but natural ignition continues where fresh coal has access to air at any given time hundreds of fires mostly small are burning in the powder river basin the total amount of coal burned by natural fires in the last 2 ma is one to two orders of magnitude greater than the total amount of coal removed by mining in the past century however current annual rates of coal mining are three to four orders of magnitude greater than estimated prehistoric annual rates of coal consumption by natural fires

optically stimulated luminescence dating of sediments over the past 200 000 years optical dating of sediment using optically stimulated luminescence has become important for studying earth surface processes and this technique continues to develop rapidly a group of closely linked luminescence methods can be used to estimate the time since grains of quartz and feldspar were last exposed to daylight by detecting their subsequent response to environmental ionizing radiation exposure the technique is well suited to the dating of deposits as young as one year to several hundred thousand years recent technical developments have established a dating protocol with improved precision a high degree of reliability and an in built means to detect incomplete signal removal during deposition this approach has been extended to age estimation for single grains opening up a wider range of potential environments and new possibilities for understanding postdepositional grain movement ongoing research offers the possibility of significant age range extension and novel applications including low t

interpreting environmental signals from the coralline sponge astrosclera willeyana coralline sponges sclerosponges have been proposed as a new source for paleo subsurface temperature reconstructions by utilizing methods developed for reef building corals however unlike corals coralline sponges do not have density variations making age determination difficult in this study we examined multiple elemental rations b mg sr ba u in the coralline sponge astrosclera willeyana we also measured skeletal density profiles along the outer living edge of the sponges and this data indicates significant thickening of skeletal material over intervals of 2 3 mm or 2 3 years this suggests that any skeletal recovered environmental record from astrosclera willeyana is an integration of signals over a 2 3 year period sponge sr ca seemed to hold the most promise as a recorder of water temperature and we compared sr ca from 2 sponges in the great barrier reef and one from truk in micronesia to their respective sea surface temperature record the correlations were not that strong approx r 0 5 but they were significant it appears that the signal smoothing due to thickening or perhaps even some biologic control on sr skeletal partitioning limits the use of sr ca as an indicator of water temperature in astrosclera willeyana

diagnostic model of the three dimensional circulation in the upper equatorial pacific ocean abstract to investigate the processes that maintain the large scale annual average thermal structure of the equatorial pacific the three dimensional ocean circulation for a large area is determined from a diagnostic model applied to repeated meridional hydrographic sections along 150 w and 11o w from 5 n to 5 s geostrophic balances are used to determine velocity profiles from 0 to 500 db across the boundaries of the region zonal velocities across 150 w and 110 w at approximately 1 lattitude intervals from 5 n to 5 s and meridional velocities across 5 n and 5 s averaged over the zonal distance between 150 w and 110 w poleward wind driven flows across 5 n and 5 s based on climatological zonal wind stress are added to the geostrophic velocities in the mixed layers to achieve overall mass conservation the reference dynamic height field at 500 db is adjusted at four of the 21 stations by about 1 dyn cm horizontal nondivergence is used to determine meridional velocities between 0 75 and 5 latitudes

stability in the south pacific surface marine 14c reservoir over the last 750 years evidence from american samoa the southern cook islands and the marquesas abstract although minor climatic and sea level changes have been documented for the south pacific during the late holocene our understanding of the consequent impact of these changes on the marine 14 c reservoir and therefore the 14 c content of shellfish is limited ultimately this has implications for documenting the chronology of human movement and adaptation in this region in this paper we compare marine reservoir r data obtained from tightly controlled archaeological proveniences with known age pre ad 1950 shells from the southern cook islands american samoa and marquesas islands results indicate that there has been no significant change in the near shore marine reservoir in these three locations over the last ca 750 years furthermore known age pre ad 1950 shell samples provide more precise r values for use in sample calibration than archaeological paired shell charcoal samples this is attributed in part to the limitations of assigning provenance and age to material from archaeological sites on the basis of these results we conclude that the known age pre ad 1950 shell derived r values can be used to calibrate shell 14 c results from deposits of late holocene age

a high resolution investigation of temperature salinity and upwelling activity proxies in corals we present a high resolution study of five geochemical components of a new caledonia coral core minor and trace elements sr ca u ca mg ca ba ca together with oxygen isotopes 18o were investigated at near fortnightly resolution geochemical measurements were compared to sea surface temperature ssttsg and salinity ssstsg recorded by a thermosalinograph tsg located less than 10 m from the coral results show that sr ca mg ca and 18o are temperature dependent correlation coefficient to local ssttsg between 0 74 and 0 84 their robustness as sst tracers is tested against a satellite based data set for a 4 year validation period u ca has a more complex behavior and appears to be linked to both ssttsg and ssstsg despite relatively small local sss variations for the first time this salinity related imprint is quantified in a u ca coralline ratio in addition to sst and sss tracers ba ca measurements provide a possible way to investigate upwelling activity occurrences

radiocarbon variability in the western equatorial pacific inferred from a high resolution coral record from nauru island we have generated a high resolution coral delta sup 14 c record spanning the last 50 years to document the seasonal and interannual redistribution of surface waters in the western tropical pacific prebomb 1947 endash 1956 delta sup 14 c values average minus 63 per thousand and have a total range of 30 per thousand values begin to increase in 1957 reaching a maximum of 137 per thousand in mid 1983 large interannual variability of up to 80 per thousand closely follows the el ni tilde n o southern oscillation enso during each enso warm phase delta sup 14 c values begin to increase reflecting the reduction of low sup 14 c water upwelling in the east and the invasion of subtropical water into the western equatorial tropical pacific maximum delta sup 14 c values are in phase or lag the corresponding sea surface temperature maxima in the eastern tropical pacific whereas the rapid return to more negative delta sup 14 c is in phase with eastern pacific enso indices the highest amplitude excursions occur during the 1965 1966 and 1972 1973 events when the sup 14 c contrast is highest between the eastern pacific and subtropics the 1982 1983 el ni tilde n o although a larger enso event has a lower delta sup 14 c amplitude reflecting the penetration of bomb radiocarbon into the equatorial undercurrent and the reduced contrast in delta sup 14 c betweenmore thermocline and subtropical surface waters at that time this coral record demonstrates the potential for using similar radiocarbon time series for documenting variability in pacific shallow circulation over interannual and decadal timescales copyright 1998 american geophysical union less

the atlantic deep western boundary current water masses and transports near the equator the distributions and transports of deepwater masses at the western boundary in the tropical atlantic off brazil have been studied on three surveys along 35 degrees w and 5 degrees s and one at 10 degrees s transports are obtained from direct measurements of the velocity fields pegasus profiling system and lowered acoustic doppler current profiler and from geostrophic computations using chlorofluoromethane cfm and hydrographic distributions four water masses could be identified forming the north atlantic deep water nadw system two of these have a high cfm content the shallow upper nadw sunadw and the overflow lower nadw olnadw these exhibit the highest velocity signals at 35 degrees w where distinct flow cores seem to exist most of the southeastward flow of the sunadw centered around 1600 m occurs 320 km offshore between 3 degrees 09 s and 1 degrees 50 s 9 7 3 3 sv farther north in that section a highly variable reversing flow is found in a second velocity maximum the transport of olnadw centered around 3800 m of 4 6 2 6 sv is guided by the parnaiba ridge at 1 degrees 45 s 35 degrees w the water masses located between the two cfm maxima the labrador sea water lsw and the lnadw old water mass lnadw old did not show any persistent flow features however a rather constant transport of 11 1 2 6 sv was observed for these two layers the total southeastward flow of the nadw at 35 degrees w showed a transport of 26 8 7 0 sv if one neglects the reversing sunadw north of 1 degrees 50 s at 5 degrees s the flow of all deepwater masses shows vertically aligned cores the main southward transport occurred near the coast 19 5 5 3 sv the boundary current is limited offshore by a flow reversal present in all three surveys but located at different longitudes at 10 degrees s a southward transport of 4 7 sv was observed in november 1992 however the section extended only to 32 degrees 30 w so that probably a significant part of the flow has been missed an important result is the large transport variability between single cruises as well as variability of the spatial distribution of the flow at 35 degrees w which could lead to large uncertainties in the interpretation of single cruise observations despite these uncertainties we suggest a circulation pattern of the various deepwater masses near the equator by combining our mean transport estimates with other observations

quantitative model of the growth of floodplains by vertical accretion a simple one dimensional model is developed to quantitatively predict the change in elevation over a period of decades for vertically accreting floodplains this unsteady model approximates the monotonic growth of a floodplain as an incremental but constant increase of net sediment deposition per flood for those floods of a partial duration series that exceed a threshold discharge corresponding to the elevation of the floodplain sediment deposition from each flood increases the elevation of the floodplain and consequently the magnitude of the threshold discharge resulting in a decrease in the number of floods and growth rate of the floodplain floodplain growth curves predicted by this model are compared to empirical growth curves based on dendrochronology and to direct field measurements at five floodplain sites the model was used to predict the value of net sediment deposition per flood which best fits in a least squares sense the empirical and field measurements these values fall within the range of independent estimates of the net sediment deposition per flood based on empirical equations these empirical equations permit the application of the model to estimate of floodplain growth for other floodplains throughout the world which do not have detailed data of sediment deposition during individual floods copyright 2000 john wiley sons ltd

radiocarbon in annual coral rings from the eastern tropical pacific ocean sixty radiocarbon measurements were performed on aragonite from annually banded corals collected from three sites in the galapagos islands preanthropogenic 14c values of coral that grew around a d 1930 averaged 70 this is substantially lower than average values previously reported 51 for corals from florida and belize in the western north atlantic ocean a decrease of 6 was noticed in coral that grew from 1930 to 1954 this decrease could be interpreted as a suess effect in surface ocean water the 100 increase in 14c for coral that grew from 1954 to 1973 is the result of bomb produced 14c that was introduced to the surface ocean waters the 14c levels in corals that grew during el nino years were considerably higher than those for normal years these higher values are attributed to the absence of up welling at the equator during el nino events

ontogeny of a flood plain the ontogeny of five flood plain segments is described for a period of 18 yr following a major flood in 1978 on the powder river in southeastern montana the flood plains developed on relatively elevated sand and gravel deposits left within the channel by the 1978 flood in cross section the flood plains resemble benches with well developed natural levees flood plain growth occurred as sediment was draped onto preexisting surfaces in layers of sand and mud a few centimeters to decimeters thick resulting in some lateral but mostly vertical accretion annual and biannual measurements indicated that as the flood plain segments grew upward the annual rate of vertical accretion decreased as the partial duration recurrence interval for the threshold or bankfull discharge increased from 0 16 to 1 3 yr it is clear that a constant recurrence interval for overbank flow cannot be meaningfully assigned to this type of flood plain ontogeny these flood plains did not grow on migrating point bars and vertical accretion at least initially occurred within the channel rather than across the valley flat during extensive overbank flows sediments of these flood plains define narrow elongated stratigraphic units that border the active channel and onlap older flood plain deposits these characteristics are considerably different from those of many facies models for meandering river deposits facies similar to those described in this paper are likely to be preserved thereby providing important evidence in the geologic record for episodes of periodic channel expansion by ancient rivers

floodplain sedimentation quantities patterns and processes this paper presents the result of measurements of floodplain sedimentation using sediment traps the study was carried out on two embanked floodplains along the rivers rhine and meuse in the netherlands during a 3 day flood in january 1993 raster maps of sediment accumulation were made by interpolating the measurements from the traps using block kriging the sediment maps show clear patterns in sediment accumulation together with the estimated interpolation errors average sediment accumulation ranges between 0 57 and 1 0 kg m 2 high sediment accumulation is found on the levees 4 kg m 2 or more and on low lying areas 1 6 kg m 2 sediment accumulation decreases with distance from the main channel the sedimentation patterns are related to floodplain topography and sediment transporting mechanisms sediment transport by turbulent diffusion as well as by convection can be recognized also flood duration and the process of sediment settling out in ponding water in closed depressions are important the applied method allows comparison of the results with raster based sedimentation models

suspension of bed material over sand bars in the lower mississippi river and its implications for mississippi delta environmental restoration 1 understanding specific pathways for sand transport in the lower reaches of large rivers including the mississippi is a key for addressing multiple significant geologic problems such as delta building and discharge to the oceans and for environmental restoration efforts in deltaic environments threatened by rising sea levels field studies were performed in the mississippi river 75 100 km upstream of the gulf of mexico outlet in 2010 2011 to examine sand transport phenomena in the tidally affected river channel over a range of discharges methods included mapping bottom morphology multibeam sonar cross sectional and longitudinal measurements of water column velocity and acoustic backscatter suspended sediment sampling and channel bed sampling substantial interaction was observed between the flow conditions in the river boundary shear stress channel bed morphology size and extent of sandy bedforms and bed material sand transport quantity transport mode and spatial distribution a lateral shift was observed in the region of maximum bed material transport from deep to shallow areas of subaqueous sand bars with increasing water discharge bed material was transported both in traction and in suspension at these water discharges and we posit that the downriver flux of sand grains is composed of both locally and drainage basin sourced material with distinct transport pathways and relations to flow conditions we provide suggestions for the optimal design and operation of planned river diversion projects

floodplain sedimentation in the upper mississippi valley natural versus human accelerated abstract understanding the time scales and pathways for response and recovery of rivers and floodplains to episodic changes in erosion and sedimentation has been a long standing issue in fluvial geomorphology floodplains are an important component of watershed systems because they affect downstream storage and delivery of overbank flood waters and they also serve as sources and temporary sinks for sediments and toxic substances delivered by river systems here 14c and 137cs isotopic dating methods are used along with ages of culturally related phenomena associated with mining and agriculture to determine rates of sedimentation and morphologic change for a reach of the upper mississippi river and adjacent tributaries in southwestern wisconsin and northwestern illinois the most important environmental change that influenced fluvial activity in this region during last 10 000 years involved the conversion of a late holocene mosaic of prairie and forest to a landscape dominated by cropland and pastureland associated with euro american settlement results presented herein for the upper mississippi valley umv show that the shift from pre agriculture natural land cover to landscape dominance by agricultural land use of the last 175 200 years typically increased rates and magnitudes of floodplain sedimentation by at least an order of magnitude accelerated overbank flooding led to increased bank heights on tributary streams and in turn contributed to more frequent deep flows of high energy these high energy flows subsequently promoted bank erosion and lateral channel migration and the formation of a historical meander belt whose alluvial surface constitutes a new historical floodplain inset against the earlier historical floodplain the new historical floodplain serves as a flume like channel that provides efficient downstream transport of water and sediment associated with moderate and large magnitude floods floodplains on lower tributaries however continue to experience rates of overbank sedimentation that are of anomalously high magnitude given improved land cover and land conservation since about 1950 this lower valley anomaly is explained by minimal development of historical agriculture period meander belts because of relatively low stream power in these channel and floodplain reaches of relatively low gradient in general long term pre agriculture rates of vertical accretion between about 10 000 and 200 years ago averaged about 0 2 mm yr 1 in tributary watersheds smaller than about 700 km2 and about 0 9 mm yr 1 on the floodplain of the upper mississippi river where the contributing watershed area increases to about 170 000 km2 on the other hand rates of historical vertical accretion during the period of agricultural dominance of the last 200 years average between 2 and 20 mm yr 1 with short episodes of even higher rates during times of particularly poor land conservation practices significant hydrologic effects of mining and agricultural started by the 1820s and became widespread in the study region by the mid 19th century the hydrologic and geomorphic influences of mining were relatively minor compared to those related to agriculture high resolution dating of floodplain vertical accretion deposits shows that large floods have frequently provided major increments of sedimentation on floodplains of tributaries and the main valley upper mississippi river the relative importance of large floods as contributors to floodplain vertical accretion is noteworthy because global atmospheric circulation models indicate that the main channel upper mississippi river should experience increased frequencies of extreme hydrologic events including large floods with anticipated continued global warming instrumental and stratigraphic records show that coincident with global warming a shift to more frequent large floods occurred since 1950 on the upper mississippi river and these floods generally contributed high magnitudes of floodplain sedimentation

a new type of shelf margin deposit rigid microbial sheets and unconsolidated grainstones riddled with meter scale cavities middle cambrian microbial limestone contains a network of unusual predominantly horizontal cavities up to 2 m in length and 0 5 m in height the microbialite experienced rapid syndepositional lithification but adjacent grainstone sediments remained unlithified during deposition this juxtaposition contributed to sediment instability resulting in fracturing and brecciation of the lithified microbialite while unconsolidated grainstones underwent slumping and injection into some cavities remaining space within the cavities was colonized by a series of encrustations thin crusts 2 8 mm of laminated algal mats followed by several generations of calcified renalcis like cyanobacteria up to 45 mm thick remaining void space was partially filled by internal sediment and then sequentially occluded by banded radiaxial fibrous calcite herringbone calcite and finally saddle dolomite cements the radiaxial and herringbone calcite cements precipitated from porewaters derived from seawater that became anoxic through the breakdown of organic matter in the microbialite noteworthy is the presence of herringbone calcite cement not as a seafloor precipitate but as an early cavity fill we propose that the unusual bedding parallel fractures were caused by gravity collapse along a shallow platform margin coeval foreslope sediments show syndepositional slumping faulting and mass flow deposits these redeposited sediments contain boulders of microbialite and grainstone of platform margin provenance 1999 elsevier science b v all rights reserved

anatomy and dynamics of a floodplain powder river montana u s a abstract centimeter scale measurements on several powder river floodplains provide insights into the nature of overbank depositional processes that created the floodplains during a 20 year period after a major flood in 1978 rising stages initially entered across a sill at the downriver end of the floodplains later as stages continued to rise water entered the floodplains through distinct low saddles along natural levees the annual maximum depth of water over the levee crest averaged 0 19 m from 1983 through 1996 and the estimated flow velocities were approximately 0 15 m s 1 water ponded in the floodplain trough a topographic low between the natural levee and the pre flood riverbank and mud settled as thin layers of nearly constant thickness mud layers alternated with sand layers which were relatively thick near the channel together these beds created a distinctive natural levee in some locations individual flood deposits began as a thin mud layer that gradually coarsened upwards to medium grained sand coarsening upwards sequences form initially as mud because only the uppermost layers of water in the channel supply the first overbank flows which are rich in mud but starved of sand at successively higher stages fine sands and then medium sands increase in concentration in the floodwater and are deposited as fine and medium sand layers overlying the initial mud layer theoretical predictions from mathematical models of sediment transport by advection and diffusion indicate that these processes acting alone are unlikely to create the observed sand layers of nearly uniform thickness that extend across much of the floodplain we infer that other transport processes notably bedload transport must be important along powder river even with the centimeter scale measurements of floodplain deposits daily hydraulic data and precise annual surface topographic surveys we were unable to determine any clear correspondence between the gauged flow record of overbank floods and the depositional layers mapped in the floodplain these results provide a detailed example of floodplain deposits and depositional processes that should prove useful for interpreting natural levee deposits in a variety of geologic settings

terrace aggradation during the 1978 flood on powder river montana usa abstract flood processes no longer actively increase the planform area of terraces instead lateral erosion decreases the area however infrequent extreme floods continue episodic aggradation of terraces surfaces we quantify this type of evolution of terraces by an extreme flood in may 1978 on powder river in southeastern montana within an 89 km study reach of the river we 1 determine a sediment budget for each geomorphic feature 2 interpret the stratigraphy of the newly deposited sediment and 3 discuss the essential role of vegetation in the depositional processes peak flood discharge was about 930 m 3 s 1 which lasted about eight days during this time the flood transported 8 2 million tons of sediment into and 4 5 million tons out of the study reach the masses of sediment transferred between features or eroded from one feature and redeposited on the same feature exceeded the mass transported out of the reach the flood inundated the floodplain and some of the remnants of two terraces along the river lateral erosion decreased the planform area of the lower of the two terraces 2 7 m above the riverbed by 3 2 and that of the higher terrace 3 5 m above the riverbed by 4 1 however overbank aggradation on average raised the lower terrace by 0 16 m and the higher terrace by 0 063 m vegetation controlled the type thickness and stratigraphy of the aggradation on terrace surfaces two characteristic overbank deposits were common coarsening upward sequences and lee dunes grass caused the deposition of the coarsening upward sequences which had 0 02 to 0 07 m of mud at the base and in some cases the deposits coarsened upwards to coarse sand on the top lee dunes composed of fine and very fine sand were deposited in the wake zone downstream from the trees the characteristic morphology of the dunes can be used to estimate some flood variables such as suspended sediment particle size minimum depth and critical shear velocity information about depositional processes during extreme floods is rare and therefore the results from this study aid in interpreting the record of terrace stratigraphy along other rivers

modelling flood hydraulics and overbank deposition on river floodplains this paper outlines a numerical model for the prediction of floodplain inundation sequences overbank deposition rates and deposit grain size distributions the model has two main components first a simplified hydraulic scheme which predicts floodwater flow depths and velocities and second a sediment transport element which employs a mass balance relation describing suspended sediment dispersion by convective and diffusive processes and sediment deposition as a function of particle settling rates these relationships are solved numerically on a finite difference grid that accurately replicates the complex topographic features typical of natural river floodplains the model is applied to a 600 m reach of the river culm devon u k using data derived from a range of field and laboratory techniques continuous records of river stage and suspended sediment concentration provide the model s upstream boundary input requirements these are supplemented by measurements of the in situ settling characteristics of the suspended sediment load the model s sediment transport component is calibrated with the aid of a dataset of measured overbank deposition amounts derived from flood events over a 16 month period the model is shown to predict complicated floodwater inundation sequences and patterns of suspended sediment dispersion and deposition which are largely a product of the complex topography of the floodplain these results compare favourably with observations of overbank processes and are an improvement over those of previous models which have employed relatively simple representations of floodplain geometry 1997 by john wiley sons ltd

the distribution of bomb radiocarbon in the ocean water column inventories are calculated for bomb radiocarbon at all the stations occupied during the geosecs and norpax expeditions and for the available tto stations the pattern of global inventories obtained in this way suggests that a sizable portion of the bomb radiocarbon that entered the antarctic the northern pacific and the tropical ocean has been transported to the adjacent temperate zones a strategy for utilizing these inventory anomalies as constraints on global ocean circulation models is presented essential to this strategy are the improvement of our knowledge of the pattern of wind speed over the ocean the establishment of the wind speed dependence of the rate of gas exchange between the atmosphere and sea and the continued mapping of the distribution of bomb produced radiocarbon in the sea

on the radiocarbon record in banded corals exchange parameters and net transport of 14co2 between atmosphere and surface ocean we have made radiocarbon measurements of banded hermatypic corals from florida belize and the galapagos islands interpretation is presented here of these previously reported results these measurements represent the 14c 12c ratios in dissolved inorganic carbon dioc in the surface ocean waters of the gulf stream and the peru current at the time of coral ring formation a depletion in radiocarbon concentration was observed in coral rings that grew from a d 1900 1952 it was caused by dilution of existing 14c levels with dead co2 from fossil fuel burning the suess effect or se the observed depletion of radiocarbon was greater in corals from the gulf stream 11 than in corals from the peru current 6 a similar trend was observed in the distribution of bomb produced 14c in corals that had grown during the years following a d 1952 the concentration of bomb produced radiocarbon was much higher in corals from temperate regions florida belize hawaiian islands than in corals from tropical regions galapagos islands and canton island a linear relationship appears to exist between the preanthropogenic 14c values and the se values measured in the individual corals because the 14c in corals is derived from two different carbon reservoirs 1 the atmosphere and 2 the subsurface ocean a linear relationship is also observed between the preanthropogenic 14c values and the concentration of bomb produced 14c in the individual corals during a d 1973 the apparent radiocarbon ages of the surface waters in temperate and tropical oceans during the preanthropogenic period range from about 280 to 520 years b p 40 to 69 at all investigated locations it is likely that waters at subsurface depths have the same apparent radiocarbon age of about 670 years b p from the change of oceanic 14c in the surface ocean during post bomb times the approximate annual rate of net input of 14co2 to the ocean waters is calculated to be about 8 of the prevailing 14c difference between atmosphere and ocean from this input and from preanthropogenic 14c values found at each location it can be seen that vertical mixing of water in the peru current is about 3 times greater than that in the gulf stream

shell midden sclerochronology abstract sclerochronological analysis of shell midden faunal remains offers a unique opportunity to study climate and environmental change in relation to human activity middens exist near most aquatic habitats almost worldwide for much of the late pleistocene and holocene they afford good preservation of accretionary calcium carbonate remains such as mollusk shells and fish otoliths in comparatively well dated contexts as such midden samples are a source of sequential proxy records of past climate and environmental conditions and may provide detailed pictures of human environment interaction however midden samples present several challenges to the development and application of sclerochronological proxies including unique taphonomic concerns here these challenges are outlined within descriptions of the major applications of midden sclerochronology archeological concerns including season of capture reconstructing the history of anthropogenic environmental impacts and paleoclimate environment proxy reconstructions