integrating geochronologic and instrumental approaches across the bengal basin constraining time is of critical importance to evaluating the rates and relative contributions of processes driving landscape change in sedimentary basins the geomorphic character of the field setting guides the application of geochronologic or instrumental tools to this problem because the viability of methods can be highly influenced by geomorphic attributes for example sediment yield and the linked potential for organic preservation may govern the usefulness of radiocarbon dating similarly the rate of sediment transport from source to sink may determine the maturity and or light exposure of mineral grains arriving in the delta and thus the feasibility of luminescence dating here we explore the viability and quirks of dating and instrumental methods that have been applied in the bengal basin and review the records that they have yielded this immense dynamic and spatially variable system hosts the world s most inhabited delta outlining a framework for successful chronologic applications is thus of value to managing water and sediment resources for humans here and in other populated deltas worldwide our review covers radiocarbon dating luminescence dating archaeological records and historical maps short lived radioisotopes horizon markers and rod surface elevation tables geodetic observations and surface instrumentation combined these tools can be used to reconstruct the history of the bengal basin from late pleistocene to present day the growing variety and scope of bengal basin geochronology and instrumentation opens doors for research integrating basin processes across spatial and temporal scales

geochemical and hydrodynamic controls on arsenic and trace metal cycling in a seasonally stratified us sub tropical reservoir the phase distribution of trace metals and oxyanions including u and as in 2 surface water bodies was investigated within a south texas watershed hosting a high density of surface u mine pits and tailings the objectives of the study were to evaluate the environmental legacy of u mining with particular emphasis on the spatial and temporal variability of water quality in lake corpus christi a downstream reservoir that serves as the major water resource to a population of 350 000 people in the region lyssy pond a livestock pond bordered by u mine tailings was used as a model case study site to evaluate the cycling of u mine derived oxyanions under changing redox conditions although the pond showed seasonal thermal and chemical stratification geochemical cycling of metals was limited to co and pb which was correlated with redox cycling of mn mineral phases and u which suggested reductive precipitation in the pond s hypolimnion uranium levels however were too low to support strong inputs from the tailings into the water column of the pond the strong relationships observed between particulate cr cs v and fe suggest that these metals are associated with a stable particulate phase probably allochthonous alumino silicates enriched in unreactive fe this observation is supported by a parallel relationship in sediments collected across a broad range of sediment depositional processes and histories in the basin arsenic though selectively enriched in the pond s water column was dominated by dissolved species throughout the depth of the profile and showed no sign of geochemical cycling or interaction with fe rich particles arsenic and other oxyanions in the water columns of lake corpus christi and lyssy pond were not affected by the abundant presence of fe rich particles but instead behaved conservatively no evidence was found of anthropogenic impacts of u mines beyond the purely local scale arsenic s presence within the nueces drainage basin is related to interactions between surface and groundwaters with u and as rich geological formations rather than large scale transport of contaminants downstream of the u mine pits and tailings a quantitative mass balance model constructed using monthly hydrological data for the reservoir provides quantitative evidence of seasonal evaporative concentration of as in surface waters demonstrating the predominance of hydrodynamic over geochemical constraints on the cycling of this element

floodplain processes in the bengal basin and the storage of ganges brahmaputra river sediment an accretion study using 137cs and 210pb geochronology floodplain deposits are recognized as potentially large sinks for fluvial sediments yet spatial and temporal patterns of accumulation are not known for many river systems in the tectonically active bengal basin the ganges and brahmaputra rivers coalesce and have formed a large floodplain delta complex where widespread overbank flooding may deposit a significant portion of the river s estimated sediment discharge to investigate the magnitude and distribution of this process accumulation rates were determined by 137cs and 210pb radioisotope geochronology at 60 sites located in three regions of the bengal basin differing in age physiography and river influence these geochronological methods have been applied to floodplain environments in only a few recent studies and the present research offers a revised approach for heterogeneous systems patterns of sediment deposition in the bengal basin reveal three dominant controls on floodplain accretion channel processes overbank flooding and surface runoff accretion is most rapid in the river braidbelt and adjacent floodplain decreasing rapidly with distance from the main channel accumulation rates increase again in low lying distal basins where several meters of annual precipitation and associated runoff rework surrounding floodplain surfaces and transport remobilized sediments to local catchments the extent and magnitude of this process indicate its comparable importance with overbank deposition for floodplain accumulation a sediment budget for the study area reveals that at least 15 of the estimated 1 billion tonnes of fluvial sediment discharge is stored annually and not reaching the oceans as previously assumed extrapolated to the remaining 60 000 km2 of floodplain not covered in this project the sequestered load could rise to 30 of annual sediment discharge

137cs losses from a loamy surface water gleyed soil inceptisol a laboratory simulation experiment abstract 137 cs was applied with simulated rainfall to 0 25 m 2 soil boxes at an intensity of 20 mm hr 1 for 30 minutes ten simulations were performed on six soil boxes at 2 and 4 slopes soil was compacted in one box to simulate the effects of tractor wheelings the depth distribution of 137 cs was analysed in six soil cores in addition a 1 m long 16 cm wide soil trough was placed under the simulator until a constant rate of overland flow was generated 137 cs was added at four locations at increasing distance from the trough outflow overland flow drainage water and suspended sediments were collected and analysed separately for 137 cs in all experiments at 2 slopes the highest proportion of the 137 cs input was lost by drainage at 4 slopes and with compaction the greatest amount of 137 cs was eroded with sediment approximately 10 of the added 137 cs was lost from the compacted soil over the ten simulations 137 cs retention in the upper 10 cm of the profile ranged from more than 95 compacted soil to less than 45 uncompacted soils results from the trough experiment suggested that 137 cs could be preferentially adsorbed by sediments entrained in overland flow

marine origin of savannah river estuary sediments evidence from radioactive and stable isotope tracers to determine the origin of sediments in the savannah river estuary we have measured 137 cs and stable isotope ratios of c n and s in suspended particles and bottom sediments at several sites in the savannah river and estuary and offshore on the continental shelf the 137 cs and stable isotope data were used with a two endmember mixing model to partition the suspended and bottom sediments at sites along a salinity gradient into riverine and marine fractions results from the 137 cs measurements indicated that 65 of inorganic sediments in suspension or in the top 5 cm of bottom deposits in the estuary were of marine origin stable carbon isotope ratios indicated that 74 of the organic sediments in suspension or on the bottom of the estuary were of marine origin except for sediments at the lowest salinity estuarine site

historical changes in 239pu and 240pu sources in sedimentary records in the east china sea implications for provenance and transportation abstract concentrations and isotopic compositions of plutonium pu are widely used for its source identification and to determine transport processes of pu associated particulate matter and water we investigated the concentrations of 239pu and 240pu and their ratios in a number of sediment samples from the east china sea ecs collected in the summer of 2013 august 6 28 the 239 240pu activity concentrations in surface sediment samples were found to range between 0 048 and 0 492 bq kg 1 and the 240pu 239pu atom ratios showed a similar trend as that of the 239 240pu activities the pu atom ratios ranged from 0 158 to 0 297 and were mostly higher than the mean global fallout value of 0 18 the 239 240pu inventories in the ecs varied widely from 2 to 807 bq m 2 with the highest values commonly found in the coastal areas in the yangtze estuary the mean 239 240pu activity concentration is close to the estimated value of the suspended material from the yangtze river catchment 0 18 bq kg 1 and the 240pu 239pu atom ratio was found to be 0 18 which indicates that the yangtze river input is the dominant source of pu for this area the total annual yangtze river input of 239 240pu was estimated to be 2 4 10 10 bq which is small compared to the total amount of 239 240pu buried 3 1 10 13 bq in the whole ecs the pacific proving ground input appears to be the dominant source of pu to the ecs accounting for 45 52 of the total inventory the fractional amount of 239 240pu scavenged from the total 239 240pu transported by the kuroshio current kc and taiwan warm current twc into ecs sediments is estimated to be 10 our study shows that the 240pu 239pu atom ratio is useful not only to obtain a better insight of the biogeochemistry influenced by the kc but also to trace the long range transport of other particle reactive species besides the sedimentation rates obtained based on the penetration depths of 239 240pu and vertical profiles of excess 210pb agree within uncertainties which suggests that 239 240pu can potentially be used as a chronostratigraphic time marker in the marine environment

determining sources and transit times of suspended sediment in the murrumbidgee river new south wales australia using fallout 137cs and 210pb sediment budgets typically require an estimate of the proportional yield from erosion sources to sediments in transport and storage this becomes increasingly difficult as catchments become larger and erosion storage and deposition processes become more complex we demonstrate how fallout radionuclides can be used to estimate the proportional contributions to sediment load from a tripartite classification of erosion sources in a large catchment the mid murrumbidgee 13 500 km2 the three major potential sources of sediment within this catchment are cultivated lands 22 of the surface area uncultivated pastoral lands 78 and the numerous channels and gullies found in this region concentrations of the fallout radionuclides 210pbex and 137cs in representative samples from each of these three sources are significantly different employing these values in a simple mixing model shows that the largest contribution of material is currently derived from subsoil channel gully sources alterations to the suspended sediment 210pbex signature by in situ labeling and decay are also considered applying the model with different concentrations of 210pbex decayed as a function of residence time in channels suggests that the mean residence time of fine grained material within this system is 10 5 years however differences in 137cs concentrations observed between flood and low flow sediments and the presence of the short lived cosmogenic 7be suggest that residence time of some of this fine grained material may be of the order of only weeks to months

anthropogenic stable cesium in water and sediment of a shallow estuary st louis bay mississippi abstract st louis bay slb mississippi is a small shallow estuary with moderate local residential and industrial development dissolved stable cs i e 133 cs was significantly enriched in bay waters up to 1570 nm as compared to river 2 refinery located on the north shore of the bay is the likely source of the cs given that the highest cs concentrations were found in waters and in surface sediments up to 49 g g near the refinery outfall this setting presented a unique opportunity to study remobilization of cs in a shallow estuarine system where sediment resuspension is frequent remobilization up to 3 fold increase of dissolved cs was observed during sediment resuspension events a weak correlation between cs and clay strong correlations among cs silt and particulate organic carbon poc and simple numerical approaches indicate that desorption from resuspended particulate matter is the likely mechanism of cs remobilization cs enriched slb waters can be traced to nearshore mississippi sound waters but not into mississippi bight waters further offshore the findings from this study also suggest that caution needs to be taken when interpreting the radio cesium distribution in shallow estuarine and coastal systems

recent estuarine sedimentation rates from shallow inter tidal environments in western scotland implications for future sea level trends and coastal wetland development during the mid late holocene large sections of the scottish coastline have been characterized by falling relative sea levels resulting from differential glacio isostatic uplift of this region of northern britain the complex interplay between crustal and sea level movements continues to influence the morphological development of the scottish coast a number of geophysical models predict ongoing uplift of the scottish landmass however a number of recent studies based upon the analysis of satellite altimetry data indicate a late 20th century acceleration in the rate of eustatic sea level rise detailed geochemistry radiometric dating and diatom analysis on selected sediment cores from four mature coastal marsh environments in argyll western scotland provides an opportunity to investigate the linkages between twentieth century crustal movements eustatic sea level rise and recent rates of sedimentation recorded within marsh sediments across the proposed scottish glacio isostatic uplift dome solid phase major and trace element geochemistry has been used to examine the extent to which post depositional physical disturbance and or chemical reactions may have influenced the reliability of the radiometric dating methods geochemical data indicate that the evolution of these marsh environments has not been significantly influenced by physical disturbance and overall the supply of minerogenic material to the marshes has been quite uniform vertical distributions of 210pbexcess and 137cs activity have been measured and used to develop models of recent marsh vertical accretion dating of the cores reveals subtle variations in the rates of sediment accumulation over the last c 70 years between sites for much of the last hundred years or so sedimentation rates have been in good overall agreement with various estimations for sea level rise although at the more easterly sites these estimates are generally exceeded however quasi equilibrium between marsh sedimentation and sea level rise for much of the twentieth century is indicated from the diatom analysis over the most recent period of marsh development 10 years a significant increase in the rate of surface sedimentation is recorded at all sites across the study area diatom analysis of these surface layers reveals an increase in the relative abundance of marine polyhalobous taxa in the near surface sediments this signifies a very recent increase in the rate of regional relative sea level rise indicating that a regional threshold in coastal forcing has now been exceeded these findings provide clear evidence that recent relative sea level rise is now outpacing estimated rates of glacio isostatic adjustment gia across the proposed scottish uplift dome

marine geochemical cycles of the alkali elements and boron the role of sediments abstract we have analysed the concentrations of li k rb cs and b and the isotopic ratios of li and b of a suite of pore fluids recovered from odp sites 1037 leg 169 escanaba trough and 1034 leg 169s saanich inlet in addition we have analysed dissolved k rb and cs concentrations for estuarine mixing of the ganges brahmaputra river system together these data sets have been used to assess the role of sediments in the marine geochemical cycles of the alkali elements and boron uptake onto clay minerals during estuarine mixing removes 20 30 of the riverine input of dissolved cs and rb to the oceans prior to this study the only other recognised sink of rb and cs was uptake during low temperature alteration of the oceanic crust even with this additional sink there is an excess of inputs over outputs in their modern oceanic mass balance pore fluid data show that li and rb are transferred into marine sediments during early diagenesis however modeling of the li isotope systematics of the pore fluids from site 1037 shows that seawater li taken up during marine sedimentation can be readily returned to solution in the presence of less hydrated cations such as nh4 this process also appears to result in high concentrations of pore fluid cs relative to local seawater due to expulsion of adsorbed cs from cation exchange sites flux calculations based on pore fluid data for a series of odp sites indicate that early diagenesis of clay sediments removes around 8 of the modern riverine input of dissolved li although nh4 rich fluids do result in a flux of cs to the oceans on the global scale this input only augments the modern riverine cs flux by 3 nevertheless this may have implications for the fate of radioactive cs in the natural environment and waste repositories

reversible ion exchange fixation of cesium 137 leading to mobilization from reservoir sediments abstract the radioactive fission product 137cs has been observed to mobilize from bottom sediments of two south carolina reservoirs during summer thermal stratification and hypolimnetic anoxia mobilization is attributed to ion exchange displacement of 137cs from sediments by cations such as nh 4 fe 2 and mn 2 released under anaerobic conditions three types of 137cs binding sites to sediment clay minerals are identified 1 surface and planar sites from which 137cs is generally exchangeable by all cations studied na nh 4 h cs ca 2 mg 2 fe 2 and mn 2 2 wedge sites where 137cs exchange is sterically limited to cations of similar size and charge nh 4 cs k and perhaps h3o 3 interlayer sites from which 137cs is not readily exchanged more than 15 years after final 137cs inputs the reservoir sediments we studied showed the following percentage distribution of sites 2 to 9 surface sites 6 to 13 wedge sites and 78 to 85 interlayer sites in contrast lake and stream sediments near oak ridge tennessee receiving 137cs inputs more than 20 years earlier had greater than 99 of their 137cs associated with non exchangeable interlayer sites the difference is attributed to the paucity in the south carolina sediments of weathered micaceous clay minerals with their abundant interlayer sites such interlayer deficient clays are dominant in the atlantic and gulf coastal plains of the united states and elsewhere this suggests that 137cs will be physically and chemically more mobile in such areas as well as more biologically available mobility will be enhanced in regimes where cation inputs favoring 137cs exchange occur subsurface waste disposal sites where anaerobic conditions develop with nh 4 production and fe 2 and mn 2 release might be such a regime

sorption of cs to micaceous subsurface sediments from the hanford site usa the sorption of cs was investigated over a large concentration range 10 9 10 2 mol l on subsurface sediments from a united states nuclear materials site hanford where high level nuclear wastes hlw have been accidentally released to the vadose zone the sediment sorbs large amounts of radiocesium but expedited migration has been observed when hlw a nano3 brine is the carrier cs sorption was measured on homoionic sediments na k ca2 with electrolyte concentrations ranging from 0 01 to 1 0 mol l in na electrolyte concentrations were extended to near saturation with nano3 s 7 0 mol l the sediment contained nonexpansible biotite muscovite and expansible vermiculite smectite phyllosilicates the sorption data were interpreted according to the frayed edge planar site conceptual model a four parameter two site high and low affinity numeric ion exchange model was effective in describing the sorption data the high affinity sites were ascribed to wedge zones on the micas where particle edges have partially expanded due to the removal of interlayer cations during weathering and the low affinity ones to planar sites on the expansible clays the electrolyte cations competed with cs for both high and low affinity sites according to the trend k na ca2 at high salt concentration cs adsorption occurred only on high affinity sites na was an effective competitor for the high affinity sites at high salt concentrations in select experiments silver thiourea agtu was used as a blocking agent to further isolate and characterize the high affinity sites but the method was found to be problematic mica particles were handpicked from the sediment contacted with cs aq and analyzed by electron microprobe to identify phases and features important to cs sorption the microprobe study implied that biotite was the primary contributor of high affinity sites because of its weathered periphery the poly phase sediment exhibited close similarity in ion selectivity to illite which has been well studied although its proportion of high affinity sites relative to the cation exchange capacity cec was lower than that of illite important insights are provided on how na in hlw and indigenous k displaced from the sediments may act to expedite the migration of strongly sorbing cs in subsurface environments

high cesium concentrations in groundwater in the upper 1 2 km of fractured crystalline rock influence of groundwater origin and secondary minerals abstract dissolved and solid phase cesium cs was studied in the upper 1 2 km of a coastal granitoid fracture network on the baltic shield aspo hard rock laboratory and laxemar area se sweden there unusually high cs concentrations up to 5 6 g l 1 occur in the low temperature 1 median laxemar 3 7 g l 1 and groundwater with marine origin aspo hrl 4 2 g l 1 overall lower but variable cs concentrations were found in other types of groundwater the similar concentrations of cs in the saline groundwater which had a residence time in the order of millions of years and in the marine groundwater which had residence times in the order of years shows that duration of water rock interactions is not the single and primary control of dissolved cs in these systems the high cs concentrations in the saline groundwater is ascribed to long term weathering of minerals primarily cs enriched fracture coatings dominated by illite and mixed layer clays and possibly wall rock micaceous minerals the high cs concentrations in the groundwater of marine origin are in contrast explained by relatively fast cation exchange reactions as indicated by the field data and predicted by 1d solute transport modeling alkali cations with low energy hydration carried by intruding marine water are capable of nh 4 in particular and k to some extent replacing cs on frayed edge fes sites on illite in the fracture coatings the result is a rapid and persistent at least in the order of decades buildup of dissolved cs concentrations in fractures where marine water flows downward the identification of high cs concentrations in young groundwater of marine origin and the predicted capacity of nh 4 to displace cs from fracture solids are of particular relevance in the disposal of radioactive nuclear waste deep underground in crystalline rock

mobile mud dynamics in the east china sea elucidated using 210pb 137cs 7be and 234th as tracers mobile mud mm which has fine grain size distribution 90 clay silt and 2 5 in south inshore indicates that the sediment focusing resulted in the increased mass flux the residence time of mm is estimated as 3 6 years both by mass balance of mm and 210pbex in mm

the structural stability of lunar lava tubes abstract mounting evidence from the selene lro and grail spacecraft suggests the presence of vacant lava tubes under the surface of the moon grail evidence in particular suggests that some may be more than a kilometer in width such large sublunarean structures would be of great benefit to future human exploration of the moon providing shelter from the harsh environment at the surface but could empty lava tubes of this size be stable under lunar conditions and what is the largest size at which they could remain structurally sound we address these questions by creating elasto plastic finite element models of lava tubes using the abaqus modeling software and examining where there is local material failure in the tube s roof we assess the strength of the rock body using the geological strength index method with values appropriate to the moon assign it a basaltic density derived from a modern re analysis of lunar samples and assume a 3 1 width to height ratio for the lava tube our results show that the stability of a lava tube depends on its width its roof thickness and whether the rock comprising the structure begins in a lithostatic or poisson stress state with a roof 2 m thick lava tubes a kilometer or more in width can remain stable supporting inferences from grail observations the theoretical maximum size of a lunar lava tube depends on a variety of factors but given sufficient burial depth 500 m and an initial lithostatic stress state our results show that lava tubes up to 5 km wide may be able to remain structurally stable

two twentieth century mlh 7 5 earthquakes recorded in annually laminated lake sediments from sary chelek western tian shan kyrgyzstan central asia is highly vulnerable to large earthquakes yet existing records of past seismic activity in this area are still insufficient to reliably assess regional earthquake hazard on longer timescales within this study the sediments of sary chelek a mountain lake in the western kyrgyz tian shan were investigated to explore its potential as a natural paleoseismic archive the lacustrine deposits are characterized by a succession of annually laminated varved sediments overlying event deposits that consist of large scale turbidites and distorted lake sediments similar to earthquake related deposits described from other lake sediment records microscopic sediment analysis furthermore revealed distorted varves in the laminated sequence that closely resemble earthquake related soft sediment deformation structures varve counting and radiometric dating determine the formation of the distorted varves and the emplacement of the large scale event deposits to the early 1990s and mid 1940s respectively this is in good temporal agreement with the occurrence of two large earthquakes that struck western kyrgyzstan in ad 1992 and ad 1946 these results and particularly the precise age control of the sary chelek sediment record highlight its potential for establishing a long and precisely dated record of regional earthquake activity

caesium 137 in sandy sediments of the river loire france assessment of an alluvial island evolving over the last 50 years recent sedimentological and morphological evolution of an island in the river loire france was investigated using the 137cs method this study describes the morphological adjustment of the island in the last 50 years which corresponds to the increased bed incision of this sandy multiple channel environment because of among other things the increase in sediment extraction up to 1995 the results show that some 137cs can be retained by sandy particles potentially in clay minerals forming weathering features included in detrital sand grains from a morphological perspective significant lateral erosion can be observed in the upstream part of the island while a weak lateral accretion occurs in its downstream section data about 137cs and aerial photographs show that the morphology of the island margins has undergone significant changes leading to a lateral migration while the centre of the island has remained relatively stable or is slowly eroding the migration of the island depends on 1 the withdrawal of inherited preincision morphological units such as levees or the development of new units such as a channel shelf 2 water and sediment supply from surrounding channels during flood events 3 preferential sediment trapping 20 mm year 1 from the presence of riparian vegetation on the bank of the secondary channel that is subject to narrowing the sedimentological and morphological response of the island in the context of incision of the loire river bed is expressed mainly by lateral migration and secondarily by a low vertical adjustment

episodic deposition and 137cs immobility in skan bay sediments a ten year 210pb and 137cs time series abstract a geochronology time series provides a powerful tool for elucidating sedimentary processes such as episodic deposition and diffusive mobility of particle reactive constituents depth distributions of 210 pb and 137 cs from skan bay alaska were determined for sediment cores collected in 1980 1984 1987 and 1990 sediment x radiographs reveal distinct layers indicating that sediments were not continuously mixed by bioturbation however the geochronology time series is inconsistent with an undisturbed steady state sediment column profiles from 1980 1984 and 1990 reveal subsurface regions in which 210 pb activity is relatively constant in addition the depth of the primary 137 cs maximum reflecting the 1963 peak in atmospheric bomb testing does not increase in a regular fashion between 1980 and 1990 the 210 pb and 137 cs geochronologies can be reconciled by removing the effects of an instantaneous depositional event the average 210 pb sedimentation rate corrected for episodic deposition in cores that were collected over a ten year period 0 241 0 006 g cm 2 yr 1 is in excellent agreement with the average 137 cs sedimentation rate 0 258 0 008 g cm 2 yr 1 calculated from three stratigraphic markers peak fallout 1963 first appearance in the sediment record 1952 and the chernobyl accident 1986 the mobility of bomb derived 137 cs under in situ conditions was evaluated by a time dependent numerical model applied to the 137 cs time series the model indicates that bomb derived cesium is immobile in skan bay sediments with a solid liquid distribution coefficient k d of 10 5 ml g 1