changing atmospheric δ14c and the record of deep water paleoventilation ages we propose a new calculation method to better estimate the deep water ventilation age from benthic planktonic foraminifera 14 c ages our study is motivated by the fact that changes in atmospheric 14 c through time can cause contemporary benthic and planktonic foraminifera to have different initial 14 c values this effect can cause spurious ventilation age changes to be interpreted from the geologic data using a new calculation method 14 c projection ages we recalculate the data from the pacific ocean contrary to previous results we find that the pacific intermediate and deep waters were about 600 years older than today at the last glacial maximum in addition there are possible signals of ventilation age change prior to ice sheet melting and at the younger dryas however the data are still too sparse to constrain these ventilation transients

paleodrainage and paleochannel morphology of a barakar river early permian in the rajmahal gondwana basin bihar india abstract undisturbed sediments belonging to the barakar formation of the rajmahal basin are commonly coarse to medium grained and feldspathic they display both tabular and trough cross bedding and are commonly interbedded with thin arenaceous and carbonaceous shale and coal the average thickness of crossbedding sets is 28 15 cm with an inclination of 16 5 these features and other evidence suggest that the crossbedded sandstone units are subaqueous in origin the paleodrainage in the basin is deduced by circular directional statistics using a vectorial parameter of 217 foreset planes of crossbedded units from 16 widely separated outcrops dip azimuth distribution is generally unimodal fan shaped and displays a high magnitude of resultant r 0 6448 and a mean paleoflow of 15 48 paleochannel results indicate that the barakar river was about 235 415 m wide and 3 7 5 5 m deep and that it was moderately sinuous p 1 39 and flowed on a slope of about 35 cm km 0 00035 with an average flow velocity of 60 150 cm sec the azimuthal variability smaller value of circular variance together with a high width depth ratio steep slope and paucity of fine clastics suggest fast deposition by an anastomosing stream with bed load channels a possible extension of the rajmahal gondwana basin is discussed in the subsurface into the purnea and darjeeling basins to the north and northern part of bangladesh in the east with a northerly outlet of the barakar river towards a cratonic shore zone

sediment trend models fail to reproduce small scale sediment transport patterns on an intertidal beach a rigorous test is presented of the application of sediment trend models to an intertidal beach environment characterized by bar morphology sediment samples were collected during low tide from a regular grid and their sediment fall velocity distributions obtained using a settling tube were analysed using moment analysis the net sediment transport direction determined from beach surveys hydrodynamic measurements wave ripple observations and sediment transport modelling was compared with predictions by sediment trend models based on the spatial distribution of sediment parameters it was found that the sediment transport pathways and patterns of sedimentation predicted using sediment trend models were at odds with field observations and varied significantly depending on whether surface or sub surface sediment samples were used the sediment trend models are thought to fail because in energetic and morphologically variable beach environments spatial patterns in sediment characteristics are mainly attributed to the presence of different hydrodynamic regions and associated morphology rather than sediment pathways the use of sediment trend models cannot replace the collection of morphological hydrodynamic and sediment transport data in the field to define relationships between flows forms and sedimentation patterns on a dynamic intertidal beach

determining the strength of the deep western boundary current using the chlorofluoromethane ratio abstract the dilution of a passive tracer during deep water formation and the subsequent advection mixing in a deep boundary current is modeled with application to chlorofluoromethanes cfms in the north atlantic two different types of boundary currents are considered a uniform flow and a simple shear flow in each case the core of the flow mixes with surrounding water which continually accumulates cfms in an extreme case the coupled systems predicts that the cfm ratio in the current is unaltered from the ratio of its source water save for a time lag more realistic cases however suggests that the ratio is not a conserved quantity but is substantially altered in both the overflow basin and boundary current matching the model results to cfm data collected near the grand banks gives a predicted average core speed of 5 10 cm s 1 for the deep western boundary current and provides a constraint on the transport and diffusivity of the flow as well

sources and flow patterns of deep ocean waters as deduced from potential temperature salinity and initial phosphate concentration through the deconvolution of ocean chemical data it has been shown that the ratio of o2 utilization to phosphate production in the sea is 175 6 rather than 138 as proposed by redfield et al 1963 we find no evidence that this ratio changes significantly with location or depth in the sea we have used this new ratio to calculate the initial phosphate concentrations for the waters sampled during the geosecs and tto programs the important application of these new results is in constraining the origin and flow patterns of deep waters in the ocean we believe that a strong case can be made that antarctic salinity maximum water i e the common water of montgomery 1958 is produced by the mixing of waters entering the antarctic from mid depths in the indian pacific and atlantic with weddell sea bottom water southern component antarctic common water consists of about 45 weddell sea bottom water 30 intermediate waters from the pacific and indian oceans and 25 deep water originating from the northern atlantic

bed load grain velocities and sediment transport rates theoretical consideration of the dynamics of bed load sediment transport leads to expressions for bed grain velocity and sediment transport rate as respectively ub a u u c and ib a tan u u c 0 c agreeing in form with many previous analyses the grain velocity equation agrees well with all experimentally determined velocities of single grains moving over fixed rough beds if a is allowed to vary with bed roughness and saltation height values of u c for such overriding grains are substantially less than normally accepted values the sediment transport rate equation predicts plane bed experimental data well over five orders of magnitude of ib values of a tan increase significantly from lower to upper stage plane beds due to an increase in a with suspended sediment concentration but also due to a decrease in tan with increasing transport stage and grain size as predicted by bagnold

tantalizing evidence for the glacial north atlantic bottom water the global meridional overturning circulation moc is one of the key components of the global climate system over timescales of 102 to 103 y moc connects the cold carbon rich waters in the deep ocean with warmer carbon poorer surface waters through localized deep water formation and more widespread upwelling of deep water by redistributing heat near the surface and affecting carbon storage at depth and therefore atmospheric pco2 moc exerts a strong control on the global climate a long standing puzzle in paleoclimatology is the configuration of moc in the atlantic basin during the cold climate conditions of the last glacial period the atlantic is of special interest because the north atlantic deep water nadw a key driver of the global moc forms there today in pnas keigwin and swift 1 present intriguing new carbon isotope data from a very deep site in the western north atlantic that indicate the presence of hitherto unidentified bottom water sourced in the glacial north atlantic in the modern ocean two water masses dominate the deep atlantic ocean nadw and the antarctic bottom water aabw fig 1 a nadw is composed of two varieties the upper nadw is formed in the labrador sea by wintertime open ocean convection that may reach as deep as 2 000 m the denser lower nadw originates in the nordic seas through open ocean convection and mixing with arctic ocean water it overflows southward over the greenland iceland scotland ridge both varieties flow southward as the deep western boundary current of the atlantic basin in the depth range of 1 500 m to 4 000 m in contrast aabw originates on the continental shelves of antarctica where brine rejection during sea ice formation in coastal polynyas increases the seawater density aabw flows northward in the atlantic basin beneath nadw fig 1 schematic diagram of amoc 1 1email katsumi at umn edu 1 xref corresp 1 1

evidence from the northeastern atlantic basin for variability in the rate of the meridional overturning circulation through the last deglaciation a first study from the subtropical western atlantic using 231pa 230th ratios as a kinematic proxy for deep water circulation provided compelling evidence for a strong link between climate and the rate of meridional overturning circulation moc over the last deglaciation however these results warrant confirmation from additional locations and water depths because the interpretation of the sedimentary 231pa 230th ratio in terms of circulation vigor can be biased by variations in particle flux and composition we have measured 231pa 230th in a core from the iberian margin in the northeastern atlantic basin and have compared these new results to the data from the western atlantic basin we find that the reduction in the circulation during h1 and yd and the subsequent increases first recognized in the sediment deposited on bermuda rise are also evident in the eastern basin in a totally different sedimentary regime confirming that sedimentary 231pa 230th ratios record basin wide changes in deep water circulation however some differences between the eastern and western records are also recognized providing preliminary evidence to differentiate between renewal rates in the two north atlantic basins and between shallower and deeper overturning our results suggest the possible existence of two sources of glacial north atlantic intermediate deep water gnaiw one in the south labrador sea and another west of rockall plateau both sources contributed to the meridional overturning but the two had different sensitivity to meltwater from the laurentide and the fennoscandian ice sheets during the deglaciation these results indicate that additional information on the geometry and strength of the ventilation of the deep atlantic can be obtained by contrasting the evolution of sediment 231pa 230th in different sections of the atlantic ocean

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

routing of heterogeneous sediments over movable bed model development a one dimensional numerical model of sediment routing is derived to simulate erosion transport and deposition of individual size density fractions in the bed material within a relatively straight nonbifurcating alluvial channel the reach of interest is subdivided into a number of longitudinal elements of varying width averaged properties during each time step flow depths and velocities in each element are determined from the gradually varied flow equation using the standard step method for backwater calculations the bedload transport rate of each size fraction is calculated from a modified bagnold equation implementing a novel approach that takes into consideration the effects of turbulent fluctuations in the bed shear stress critical shear stresses for entrainment of particles from the mixed bed are determined using relationships that treat grain protrusion and hiding the transport of particles in suspension is modeled using a convection diffusion sediment continuity equation either explicitly

the western boundary undercurrent off the bahamas abstract two tritium sections through the deep western boundary current east of the bahamas taken in late 1980 and early 1981 are presented tritium from the bomb tests in the late 1950s and early 1960s is used to identify recently formed deep waters in the sections high concentrations are found in the north atlantic deep water low tritium values occur in the labrador sea water found above the core of this deep water this is consistent with the suggestion by talley and mccartney that this water mass has not been ventilated at the temperatures observed in these sections since the mid 1950s tritium in the sections is correlated with maxima in potential vorticity this is inconsistent with deep convection as a direct source for the water mass the potential vorticity maxima may be associated with plume dynamics near the overflow regions or with the dynamics of the deep western boundary current the sections are south of the section discussed by jenkins and rhines where high tritium concentrations were fo

atmospheric14c changes resulting from fossil fuel co2 release and cosmic ray flux variability a high precision tree ring record of the atmospheric14c levels between 1820 and 1954 is presented good agreement is obtained between measured and model calculated 19th and 20th century atmospheric 14c levels when both fossil fuel co2 release and predicted natural variations in14c production are taken into account the best fit is obtained by using a diffusion model with an oceanic eddy diffusion coefficient of 3 cm2 s a co2 atmosphere ocean gas exchange rate of 21 moles m 2 yr 1 and biospheric residence time of 60 years for trees in the state of washington the measured 1949 1951 atmospheric 14c level was20 0 1 2 below the 1855 1864 level model calculations indicate that in 1950 industrial co2 emissions are responsible for at least 85 of the 14c decline whereas natural variability accounts for the remaining 15

is ocean thermohaline circulation linked to abrupt stadial interstadial transitions abstract are the abrupt stadial interstadial s is climate transitions observed in the greenland ice cores also seen in marine climate records literature which shows that the s is events have a large footprint in ocean surface marine properties encompassing the entire northern hemisphere has been reviewed whether this influence extends to the deep circulation is more equivocal on most recent evidence several of the heinrich ice rafting debris events are clearly associated with elimination of north atlantic source waters from the deep atlantic but most cores studied do not resolve the other s is events except for one new record from the bermuda rise which shows all of the major s is cycles in benthic foraminiferal deep sea corals can tell us how rapid these events are in the deep sea

the mean age of ocean waters inferred from radiocarbon observations sensitivity to surface sources and accounting for mixing histories a number of previous observational studies have found that the waters of the deep pacific ocean have an age or elapsed time since contact with the surface of 700 1000 yr numerical models suggest ages twice as old here the authors present an inverse framework to determine the mean age and its upper and lower bounds givenglobaloceandataanalysisproject glodap radiocarbonobservations andthey show that the potential range of ages increases with the number of constituents or sources that are included in the analysis the inversion requires decomposing the world ocean into source waters which is obtained here using the total matrix intercomparison tmi method at up to 2 83 28 horizontal resolution with 11 113 surface sources the authors find that the north pacific at 2500 m depth can be no younger than 1100 yr old which is older than some previous observational estimates accounting for the broadness of surface regions where waters originate leads to a reservoir age correction of almost 100 yr smaller than would be estimated with a two or three water mass decomposition and explains some of the discrepancy with previous observational studies a best estimate of mean age is also presented using the mixing history along circulation pathways subject to the caveats that inference of the mixing history would benefit from further observations and that radiocarbon cannot rule out the presence of extremely old waters from exotic sources the deep north pacific waters are 1200 1500 yr old which is more in line with existing numerical model results

sample site variation in settling velocity distribution subpopulations using curve dissection analysis it is generally believed that grain size distributions can be broken down into subpopulations which may be characteristic of a specific mode of transport some source signature or the nature of sediment packing in the depositional process this paper evaluates the variation at a sample site of subpopulation parameters of settling velocity distributions derived using a non linear least squares algorithm for curve dissection results incorporate artificial samples constructed using spherical glass beads in the 125 840 m range and natural samples collected as close as possible from a single sedimentation unit in marine fluvial and aeolian environments if subpopulation distributions from the same sample site are compared then 90 of artificial bead samples and 65 of natural sands have cumulative curves diverging from each other by less than 20 similarity in means and standard deviations of subpopulations collected at the same site was not easily obtained however if it is important to be able to identify a specific process or source signature correctly then 86 of all subpopulations from the same natural sample site grouped together if subpopulations of grain size distributions are to be used for process identification it is advisable to analyse more than one sample from a site

rapid transient changes in northeast atlantic deep water ventilation age across termination i 1 a sequence of accelerator mass spectrometry ams 14c dates performed on benthic and planktonic foraminifera from a northeast atlantic deep sea core md99 2334k 37 48 n 10 10 w 3146 m permit the reconstruction of deep water 14c ventilation ages across the last deglaciation the records from md99 2334k have been placed on the gisp2 timescale via the synchrony of temperature changes recorded in the greenland ice cores and in north atlantic planktonic 18occ calcite 18o on the basis of a range of estimates for past source water 14c this permits the estimation of 14c projection ventilation ages for comparison with benthic planktonic 14c age differences although the accurate estimation of past ventilation ages is precluded by unknown deep water 14c source signatures and by uncertainty regarding the extent of deep water mixing it is clear that deep water ventilation in the northeast atlantic was significantly reduced during the last glaciation increased abruptly coincident with the bolling allerod warming and rapidly became reduced again during the younger dryas cold reversal the character of these changes is consistent with a varying dominance of north atlantic deep water nadw versus antarctic bottom water aabw parallel benthic 13c deep water temperature tdw and deep water 18o 18odw estimates support this inference the fact that deglacial changes in the deep water radiocarbon content of the northeast atlantic run parallel to opposite changes in atmospheric radiocarbon content and in parallel with greenland temperature fluctuations unequivocally implicates changes in ocean circulation in deglacial climate evolution and illustrates the capacity for the deep ocean to respond and contribute to abrupt climate change

a recent turbidity current event hueneme fan california reconstruction of flow properties a recent 100 yr old turbidite is described from hueneme fan california continental borderland dense sampling over the fan surface has allowed excellent delineation of the characteristics of this deposit it exhibits bouna de sequences and has a distinctly bimodal sandy silt grain size distribution through the use of generalized fluid dynamics equations it is possible to reconstruct original flow properties of the current which deposited this material the calculated velocities ranged from 10 90 cm s 1 and excess density above ambient seawater from 0 001 0 005 g cm 3 in the lower midfan and upper fan channel regions respectively height of the current ranged from 5 15 m on slopes from 1 5 to 0 15 a total of 107 m3 of sediment was deposited during 10 days the turbidity current is conjectured to have originated from direct river input during the floods of 1884 an older event is also described which has distinctly different properties and origins the grain sizes of this older deposit are much coarser and sedimentary structures suggest higher flow regimes this turbidite is conjectured to have been deposited from a higher density faster current thought to have been generated by slumping the need for a better understanding of the controls on the characteristics of turbidity currents and their effect on fan morphology is emphasized

seawater carbonate ion δ13c systematics and application to glacial interglacial north atlantic ocean circulation seawater carbonate ion and 13c are affected by many processes including biology air sea exchange alkalinity change and mixing between different water masses study of modern ocean data shows that deep ocean carbonate ion and 13c of dissolved inorganic carbon can be used together as useful tracers for deep water mass reconstructions in the past we present records of deep water carbonate ion concentration co32 changes of the north atlantic ocean water column since the last glacial quantitatively reconstructed using benthic foraminiferal boron calcium b ca ratios records from six cores over 1 to 4 km reveal that the carbonate chemistry of the glacial north atlantic was more stratified than the modern ocean with higher co32 by 20 30 mol kg 1 at 1 2 km and lower co32 by 20 mol kg 1 at sites deeper than 3 5 km producing an 800 m glacial shoaling of calcite saturation horizon comparison with benthic foraminiferal 13c and var epsilonnd of fe mn oxide leachates shows that the deep glacial waters with low co32 are consistent with a southern ocean source while those with high co32 but distinct 13c chemistry were supplied by two endemic sources one being the norwegian greenland sea ngs our carbonate ion results suggest that the glacial boundary between north and south sourced deep waters is at 2 8 km significantly deeper than 2 3 km estimated from benthic foraminiferal 13c weakened surface compensation inflow to the ngs promoted cooling and continental ice growth at north high latitude and a deeper boundary may reduce atmospheric co2 sequestration in the deep atlantic implying a greater role of other parts of the ocean

automatic grain sizing of vertical exposures of gravelly deposits abstract the grain size distribution gsd is a key indicator in stratigraphy and morphology it is a basic tool used by a variety of disciplines geology geomorphology archeology ecology and engineering automatic grain sizing ags has been developed to estimate the gsd of surfaces in a rapid and effortless manner yet the traditional bulk method time consuming and laborious is still in use for the determination of the gsd of coarse grained sedimentary deposits and of the near subsurface of landforms principally river beds the ags technique is examined here in its application to the stratigraphic record and to the subsurface images processed by ags and manual samples of coarse grained deposits in section were compared for evaluation of accuracy and determination of the extent of validation of the ags technique the ags often achieves results very similar to field counting especially when the largest grains are accounted for in the size of the sampling area and when photographs are taken afar without flash best results are provided when two images of the same sediment are taken at close range and also from afar to combine their gsds hence overcoming errors generated by resolution sampling area and grain size the computed errors are larger than those in prior studies yet remain reasonably small even though results are not bias corrected axes exposed in an outcrop very likely differ from those exposed on the surface and sediment properties and lighting conditions vary although results indicate a 25 burial effect the performance of the ags for sections is high unlike prior application of ags for riverbed surface openwork gravels conglomerate sections and the near subsurface include a matrix resulting in a somewhat larger mean irreducible error the technique may be utilized in studies of conglomerate texture allowing the evaluation of entire gsds under difficult sampling conditions an example use of ags to subsurface gsd evaluation is provided among others enabling an easy and fast method to calculate extent of armoring

abyssal water carbon 14 distribution and the age of the world oceans the carbon 14 distribution in the abyssal waters of the world oceans indicates replacement times for pacific indian and atlantic ocean deep waters more than 1500 meters deep of approximately 510 250 and 275 years respectively the deep waters of the entire world ocean are replaced on average every 500 years

constraints on deep water formation from the oceanic distributions of 10be 1 an analysis of the oceanic distribution of cosmogenic 10be shows that deep waters are formed by descending of cold dense surface waters at a rate of 18 sv 106 m3 s 1 in the northern north atlantic and 21 sv of which 17 sv enters the pacific in the antarctic over the last mixing cycle of 800 years lending support to the estimates based on radiocarbon and nutrient distributions it also indicates that deep water production in the northern north atlantic is 50 higher averaging over the recent 100 years than over the last mixing cycle suggesting a possible increase in the thermohaline ventilation of the north atlantic during the past century

response of deep ocean circulation to initiation of northern hemisphere glaciation 3 2 ma carbon isotopic records from benthic foraminifera are used to map patterns of deep ocean circulation between 3 and 2 million years ago the interval when significant northern hemisphere glaciation began the 18o and 13c data from four atlantic sites 552 607 610 and 704 and one pacific site 677 show that global cooling over this interval was associated with increased suppression of north atlantic deep water nadw formation however the relative strength of nadw production was always greater than is observed during late pleistocene glaciations when extreme decreases in nadw are observed in the deep north atlantic our data indicate that an increase in the equator to pole temperature gradient associated with the onset of northern hemisphere glaciation did not intensify deepwater production in the north atlantic but rather the opposite occurred this is not unexpected as it is the warm high salinity characteristic rather than the low temperature of thermocline waters that is critical to the deepwater formation process in this region today

glacial water mass geometry and the distribution of δ13c of σco2 in the western atlantic ocean 1 oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa cibicidoides and planulina from 25 new piston cores gravity cores and multicores from the brazil margin the cores span water depths from about 400 to 3000 m and intersect the major water masses in this region these new data fill a critical gap in the south atlantic ocean and provide the motivation for updating the classic glacial western atlantic 13c transect of duplessy et al 1988 the distribution of 13c of co2 requires the presence of three distinct water masses in the glacial atlantic ocean a shallow 1000 m southern source water mass with an end member 13c value of about 0 3 0 5 vpdb a middepth 1500 m northern source water mass with an end member value of about 1 5 and a deep 2000 m southern source water with an end member value of less than 0 2 and perhaps as low as the 0 9 values observed in the south atlantic sector of the southern ocean ninnemann and charles 2002 the origins of the water masses are supported by the meridional gradients in benthic foraminiferal 18o a revised glacial section of deep water 13c documents the positions and gradients among these end member intermediate and deep water masses the large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation

radiocarbon age of waters in the deep atlantic revisited the authors use a simple box model to evaluate the impact of temporal changes of the atmosphere s sup 14 c c on ventilation fluxes for the deep atlantic calculated from radiocarbon measurements the conclusion is that despite the fact that over the 300 year period from 1650 to 1950 the atmosphere s radiocarbon content declined at the same rate as radiocarbon decays this temporal change has a relatively small impact 10 15 on radiocarbon based estimates of the ventilation rate of the deep atlantic the reason is that the radiocarbon content of the source waters for deep atlantic are reasonably well buffered against changes in atmospheric sup 14 c c

determining the causes of pleistocene stream aggradation in the central coastal areas of western australia summary late pleistocene stream aggradation was widespread in the moresby ranges western australia the general geomorphological characteristics of the drainage basins and the details of the sedimentology paleohydraulics suggest that stream aggradation was due to sediment yields exceeding stream capacity however from a consideration of the mechanics of stream aggradation it is demonstrated that stream aggradation was a response to both sediment supply and base level controls with both processes operating against a background of high sediment yields the study demonstrates that it can be relatively straightforward to establish the causes of stream aggradation

carbon isotope evidence for a northern source of deep water in the glacial western north atlantic the prevailing view of western atlantic hydrography during the last glacial maximum lgm calls for transport and intermixing of deep southern and intermediate northern end members however 13c and 14c results on foraminifera from a sediment core at 5 0 km in the northern subtropics show that there may have also been a northern source of relatively young very dense nutrient depleted water during the lgm 18 ky to 21 ky ago these results when integrated with data from other western north atlantic locations indicate that the ocean was poorly ventilated at 4 2 km with better ventilation above and below that depth if this is a signal of water mass source and not nutrient storage it would indicate that a previously unrecognized deep water end member originated along the western margin of the labrador sea analogous to dense water formation today around antarctica and in the okhotsk sea

dissolved iron in the tropical and subtropical atlantic ocean 1 detailed depth profiles and surface transects of dissolved iron dfe defined by 0 4 m filtration were investigated on three cruises in the subtropical and tropical atlantic ocean where dust deposition varied by 3 orders of magnitude surface dfe and dissolved mn concentrations reflected dust deposition trends but are not proportional to the estimated inputs using estimates of the atmospheric flux of dfe surface dfe residence times were calculated to be on the order of 1 to 5 months deepwater dfe concentrations varied with water masses depending on their source age and transit pathways at a site located on the edge of the equatorial system 10 n 45 w high dfe 1 nmol kg was associated with an oxygen minimum zone at depths of 130 to 1100 m dfe concentrations in north atlantic deep water nadw decreased by 30 from sites in the north atlantic to a site in the south atlantic 24 5 s 37 w and dfe was lower in the antarctic derived water masses 0 4 nmol kg than in nadw at the south atlantic site an estimate of deepwater scavenging residence time for dfe was 270 140 years based on decreasing dfe along the nadw flow path

use of sedimentological information for geometric simulation of natural porous media structure a geometric simulation method was used to develop a three dimensional highly detailed synthetic representation of point bar sediments in the wabash river system geometric simulation methods in comparison to well known second order stochastic methods offer the advantage of being more closely related to depositional processes which are often similarly conceptualized i e described in terms of shapes of discrete bed forms trends in grain size and spatial relationships of defined geologic facies multiple scales of geometric variation were defined within a sedimentologically prescribed framework and shapes of discrete geometric elements were established at each scale the selected shapes were based on published field studies including sedimentological bed form studies and trench studies in active point bar sediments the parameterization of the shapes allowed for random variability of the shape descriptors discrete shapes were then generated and assimilated by computer hydraulic conductivity values were assigned to the discrete elements based on reports of observed variations in grain size and field measurements of hydraulic conductivity the synthetic model referred to as a numerical aquifer is being used as the basis for extensive numerical experimentation to study the relationship between natural spatial structure and subsurface flow and transport

depositional mechanisms as revealed from grain size measures of the palaeoproterozoic kolhan siliciclastics keonjhar district orissa india abstract the depositional mechanisms of the palaeoproterozoic kolhan siliciclastics have been examined using grain size analytical approaches grain size distributions of different lithofacies reveal a somewhat diversified paralic depositional environment including nearshore beach macrotidal estuary and inland dunes these inferences arise from different ways of analysing grain size data such as cumulative curves bivariant plots linear and multigroup discriminant functions and sediment trend matrix analyses sediment trend matrix analysis of various lithofacies taken together appears to be most effective for synthesizing the relationship between facies and sub environments taking into account the regional and local variations of lithofacies distribution and primary sedimentary structures grain size distributions and sediment transport paths as revealed from the above statistical parameters suggest overall hydraulic control of the grain size distribution of the kolhan siliciclastics in a fluvio beach shallow marine depositional setup

differential bed sedimentology and the maintenance of riffle pool sequences abstract riffle pools are the characteristic reach scale bedforms of gravel and mixed bedded channels of low to moderate slope the purpose of this paper is to clarify several aspects of the sedimentology of riffle pool sequences and to suggest how these both reflect and control riffle pool stability in the presence of spatial differences in the turbulent near bed flow field high frequency velocity measurements obtained using an array of electromagnetic current meters are combined with results from grid and transect sampling of bed sediments from 9 sites on 3 small upland rivers in n exmoor u k riffle sediments are shown to possess greater development of microtopographic structuring than adjacent pools which enhances riffle stability and which may reflect greater turbulent kinetic energy there over most of the flow range data on surface sediment arrangement and turbulent flow characteristics can be combined with different transport threshold equations to explain the maintenance of riffle pool sequences with respect to a particle queuing kinematic wave model without recourse to a competence reversal as conventionally assumed

suspended sediment distribution and residual transport in the coastal ocean off the ganges brahmaputra river mouth abstract an examination of suspended sediment dispersal in the coastal ocean off the ganges brahmaputra river system using shipboard and satellite data reveal distinct patterns of sediment distribution and sediment motion which help explain the dynamics of the world s largest sediment dispersal system during the low discharge period suspended sediment concentration distribution is mainly a function of tidal energy and the sediments are primarily transported as a suspension population satellite and sea bed data indicate that transport of river sediments is largely restricted to an area landward of about the 20 isobath during the low discharge period a simplistic estimate of residual transport and its separation into tidal and non tidal components indicate that non tidal transport contributes about 47 of the total transport and has transport directions mostly southwestward during the northeast monsoon the tidal residual transport which contributes about 53 of the total transport however does not show any particular direction for most of the stations although some landward stations show shoreward transport although few water column measurements were made during the high discharge period data from this and previous studies suggest that the dominant transport direction is to the southwest for most of the year

variability in oceanic dissolved iron is dominated by the colloidal fraction abstract oceanic surface and deep iron distribution and size fractionation were investigated on three cruises in the sub tropical and tropical atlantic ocean detailed profiles and transects were collected and analyzed for dissolved fe dfe 0 4 m filtered and soluble fe sfe 0 02 m filtered the difference between dfe and sfe is inferred to be the colloidal fraction of fe cfe sfe concentration distributions and profiles showed little variability in the atlantic ocean with slightly lower concentrations of sfe in the upper ocean than the relatively uniform concentrations observed in deep water 0 3 to 0 4 nmol kg in contrast variability in the atlantic dfe was dominated by variability in cfe dfe and cfe followed dust deposition trends and observed surface maxima in dfe profiles were always due to maxima in the cfe fraction where dust deposition and surface dfe were low i e the south atlantic the cfe fraction of dfe was low and frequently negligible in surface waters below the surface maxima in cfe and dfe cfe always decreased to negligible levels at 30 80 m remained low or negligible throughout the pycnocline and increased with depth below the pycnocline at a site located on the edge of the equatorial system 10 n high dfe and cfe concentrations were associated with an oxygen minimum zone omz at depths of 130 to 1100 m deep water dfe and cfe concentrations varied between water masses depending on the source age and path of the water masses dfe in nadw decreased by 30 from the north atlantic to the south atlantic site with most of the decrease due to loss of cfe at the south atlantic site nadw had higher dfe and a higher fraction of cfe than the antarctic water masses

a currents of removal approach for interpreting carbonate sedimentary processes abstract this study develops a currents of removal methodology to examine and quantify the nature of physical transport processes affecting the formation of bioclastic deposits in the cocos keeling islands an indian ocean atoll this approach is based on the hydraulic settling and threshold of entrainment characteristics of bioclastic deposits and measured current energy potential mobility pm analysis of 157 samples quantifies the proportion of deposits able to be transported in each geomorphic zone results show that under mean energy conditions wave induced currents entrain and transport sediment within the atoll and show that transport of sediment is not solely reliant on storm energy conditions gradients of pm values are used to reconstruct sediment transport pathways from the reef flat 85 100 pm through shallow passages 75 100 pm to sand aprons 50 75 pm and shallow 0 20 pm and deep lagoon 0 pm comparison of settling velocity distributions of bed material and sediment retained in sediment trap experiments show that actual mobility levels correspond with pm estimates potential mobility analysis also identifies the immobile portions of deposits which increase lagoonward constituent analysis of immobile fractions and analysis of settling frequency distributions are used to differentiate the importance of physical and biological processes in the formation of deposits throughout cocos and identify the role of each geomorphic zone in the transport system the pattern of sediment is controlled by physical processes between the reef flat the primary sediment production zone with sediment transported through the shallow passage conduits to the sand aprons the formation of shallow and deep lagoon deposits is controlled by autochthonous sediment production and storm deposition potential mobility analysis is a powerful tool enabling physical transport processes within bioclastic sedimentary environments to be quantified the ability to examine an individual deposit s hydraulic behaviour and development also enables depositional processes to be examined at a much finer resolution than previously attempted using conventional textural approaches

discussion bulk sampling of coarse clastic sediments for particle size analysis gale and hoare 1992 have provided a figure relating maximum particle diameter in a coarse clastic sediment to the size of sample required to generate a reproducible measure of the particle size distribution of that sediment however they fail adequately to justify the basis for the criterion of sample adequacy adopted in their proposal additionally there is a range of separate issues neglected by gale and hoare 1992 which makes their conclusion inapplicable in many situations a fundamental issue that they neglect is the purpose lying behind a grain size analysis this issue determines what grain size measures are appropriate rather than the empirical seemingly purpose independent approach of gale and hoare 1992

antimony and arsenic biogeochemistry in the western atlantic ocean the subtropical to equatorial atlantic ocean provides a unique regime in which one can examine the biogeochemical cycles of antimony and arsenic in particular this region is strongly affected by inputs from the amazon river and dust from north africa at the surface and horizontal transport at depth from highlatitude northern e g north atlantic deep water and southern waters e g antarctic bottom and intermediate waters as a part of the 1996 intergovernmental oceanographic commission s contaminant baseline survey data for dissolved as iii v as iii mono and dimethyl arsenic sb iii v sb iii and monomethyl antimony were obtained at six vertical profile stations and 44 sites alongthe 11 000 km transect from montevideo uruguay to bridgetown barbados the arsenic results were similar to those in other oceans with moderate surface depletion deep water enrichment a predominance of arsenate 85 as v and methylated arsenic species and as iii in surface waters that are likely a result of phytoplankton conversions to mitigate arsenate stress toxicity perhaps the most significant discovery in the arsenic results was the extremely low concentrations in the amazon plume as low as 9 8 nmol l that appear to extend for considerable distances offshore in the equatorial region the very low concentration of inorganic arsenic in the amazon river 2 8 nmol l about half those in most rivers is probably the result of intense iron oxyhydroxide scavenging dissolved antimony was also primarily in the pentavalent state 95 antimonate but sb iii and monomethyl antimony were only detected in surface waters and displayed no correlations with biotic tracers such as nutrients and chlorophyll a unlike as iii v s nutrient type vertical profiles sb iii v displayed surface maxima and decreased into the deep waters exhibitingthe behavior of a scavenged element with a strongatmospheric input while surface water sb had a slight correlation with dissolved al it is likely that atmospheric sb is delivered with combustion byproducts and not from mineral aerosols in the amazon plume antimony concentrations dropped substantially and an amazon river sample had a concentration 0 25 nmol l that was less than one fourth those found in other major rivers usingthese river data and estimates of atmospheric fluxes based on

geochemical variability induced by entrainment sorting quantified signals for provenance analysis abstract a substantial part of the mineralogical and chemical heterogeneity of clay poor sands at the bed scale results from tractive redistribution of the grains in the bedload since coarse and light particles are more easily entrained than denser and smaller heavy minerals the latter commonly concentrate in grain scale lags that alternate with sand depleted in these minerals when sampled and analysed at the centimetre scale this primary heterogeneity translates into nice geochemical covariations between the minor trace elements that concentrate in some heavy minerals zr ti p cr v y ce among others regressing these variations allow us to derive two chemical fingerprints of the sand one records the proportions between some heavy minerals the other the average composition of framework grains i e a sand composition corrected from the contribution of heavy minerals both relate to provenance and allow different sand beds to be compared in appropriate spider diagrams the construction of these diagrams their potential use and their limitations are discussed using two contrasting examples continental channel sandstones from the ravenscar group middle jurassic yorkshire uk illustrate how these geochemical fingerprints vary from the local to the group scales and how robust they are against diagenetic overprint at ravenscar the zr vs ti v cr covariations record the presence of ti oxides and magnetite together with zircon and of volcanic lithoclasts at the deposition stage despite a high degree of diagenetic alteration overbank sandstones lateral to channels from the deep marine gres d annot formation eocene oligocene alps illustrates how apatite and monazite delivered by a dominantly granitic source generate covariations between zr and p y ce and th contents with characteristically steep slopes

occurrence and formation of water laid placers a placer is a deposit of residual or detrital mineral grains in which a valuable mineral has been concentrated by a mechanical agent the agent is usually running water and the valuable mineral is usually denser than quartz for example gold diamond cassiterite ilmenite or chromite it is difficult to overemphasize the importance of placers as sources of mineral wealth the witwatersrand south africa paleoplacers discovered in 1886 alone have provided over half of all the gold ever mined in the world pretorius 1976 and alluvial placer deposits of cassiterite in southeast asia presently are the world s major source of tin toh 1978 the earliest evidence of placer mining comes from stone carvings in egypt dated at 2500 b c macdonald 1983 and as early as 7 b c strabo pointed out that in turdetania spain more gold was procured from washing sand in the rivers than by digging in the mines given the economic importance of water laid placers and the long history oftheir exploitation it is remarkable that they have received so little attention in sedimentary research mining and exploration practices for the most part have been guided by empirical rules of thumb that are locally useful but lack any firm physical basis of understanding see bateman

rate limited mass transfer or macrodispersion which dominates plume evolution at the macrodispersion experiment made site we present a model of solute transport that explains the large scale behavior of the solute tracer test plumes at the macrodispersion experiment made site as the result of advection and rate limited mass transfer between mobile and small scale immobile domains this model does not consider the process of dispersion and yet provides an alternative explanation of the evolution of the observed concentration profiles compared to the macrodispersion model the mass transfer model better represents the change in mobile dissolved mass with time the peak of the concentration profile and the profile asymmetry specifically unlike the macrodispersion model the mass transfer model explains the facts that the observed mass of the plume was greater than the injected mass in early snap shots of the plume and less than the injected mass at late times we suggest that the injected mass advects through the mobile domain and diffuses into and out of the immobile domain the immobile domain consists of a combination of low permeability zones on the scale of centimeters to decimeters the darcy scale immobile domain and intragranular porosity dead end pores and surface sorption the pore scale immobile domain we suggest that the mobile domain was sampled preferentially when water was extracted therefore at early times relatively clean water in the immobile domain was not sampled and incorrectly assumed to contain high solute concentrations similarly the mass at late times was underestimated because solute trapped in the pore scale immobile domain was not extracted during sampling and therefore ignored the combination of advection and slow mass transfer is consistent with the fact that the peak of the plume migrated only 5 m by the termination of the experiment as well as the different behavior of bromide and tritium tracers

radiocarbon based circulation age of the world oceans 1 the distributions of deep ocean 14c data are often used to illustrate the rate of deep ocean circulation the associated conventional 14c ages show a difference of 1000 years between the north atlantic and the southern ocean and a difference of another 1000 years between the southern ocean and the north pacific these differences may be interpreted directly and mistakenly as the timescale of circulation the characterization of the deep ocean circulation being millennial is common using objectively gridded natural 14c data of key et al 2004 i recast 14c in terms of circulation by accounting for 1 long surface ocean reservoir 14c ages and 2 two sources of deep water formed in the north atlantic and around antarctica the new distribution of circulation 14c ages is more consistent with the deep ocean being characterized by a centennial timescale than a millennial timescale also the role of the southern sourced deep water is now made more obvious by accounting for the two important controls on oceanic 14c that are not well known outside the field of chemical oceanography the new map will be useful as an illustration of global deep ocean circulation to the wider scientific community and as a pedagogical tool to new students in earth sciences and oceanography

the hydraulics of conduit flow in carbonate aquifers abstract analysis of the morphology of dissolution bedform assemblages and hydraulically transported sediments found within conduits in carbonate aquifers in north america and the british isles has allowed the hydraulic conditions under which conduit flows occur to be established mean values of flow velocity boundary shear stress conduit reynolds number conduit froude number boundary friction factor boundary roughness and flow power have been calculated the values obtained are in agreement with other evidence in the conduits and are comparable to those obtained from other similar hydraulic systems

determining paleoceanographic circulations with emphasis on the last glacial maximum the inference from radiocarbon and other data that the north atlantic ocean circulation during the last glacial maximum was reduced is examined because glacial periods are thought to be windier than non glacial ones a reduced circulation is difficult to rationalize a first step is to note that the circulation of mass is unlikely to correspond simply to the circulation of heat or freshwater salt by merely permitting an enhanced input of southern hemisphere water into the north atlantic one can accommodate significantly increased radiocarbon ages such an input is equally interpretable as owing to an increased mass circulation rather than a decreased one inferred estimates from paleo shear estimates in the florida current are re interpreted as producing an indeterminate net flow there determination of the paleocirculation rates is not simpler than the problem in the modern ocean it is fully three dimensional and requires an adequate data base to determine the mass flux rates

radiocarbon decay and oxygen utilization in the deep atlantic ocean a parameter based on the sum of the concentrations of po4 and o2 divided by the redfield coefficient o2 po4 is used to separate the contributions of the northern and southern components to deep waters in the atlantic this separation allows the amount of radiocarbon lost by radiodecay and the amount of oxygen lost to respiration during residence in the deep atlantic to be calculated maps of these quantities reveal strong west to east gradients and weak north to south gradients consistent with ventilation along the western boundary from both ends of the ocean coupled with mixing outward from the boundary the o2 and 14c deficiences are highly correlated suggesting an o2 utilization rate of 12 m kg per century the apparent mean isolation time of water in the deep atlantic is about 200 years

traditional and multivariate techniques in the interpretation of floodplain sediment grain size variations the vertical and horizontal variation of sedimentary fades is the raw data for the interpretation of flood plain history from which palaeohydrological inferences are frequently drawn mixed and fine floodplain sediments present problems of interpretation because of a large grain size range and frequent polymodality caused by the mixing of process associated grain size components this paper discusses the use of traditional grain size statistics and the use of the mode and multivariate statistics the mode although much neglected is indicative of up profile grain size changes and has practical advantages over the mean for mixed and fine floodplain sediments constrained cluster analysis and principal components analysis are used directly on coulter counter results these techniques can rapidly divide a floodplain profile into grain size units and indicate the principal vectors of grain size variation which will be related to the changing processes of deposition principal components analysis reveals the importance of the medium to fine silt category in accounting for grain size variations suggesting that a critical factor in determining the type of alluvial unit deposited is the degree to which it has received fine suspended material grain size data from the lower severn are used to construct a cm diagram which is compared with a texture triangle from both the cm and multivariate analysis a generalized backswamp profile is constructed which shows the existence of a coarser top unit caused by the addition of a fine to medium sand component to the underlying sediment during the late holocene

sediment characteristics and transportation dynamics of the ganga river abstract understanding of river systems that have experienced various forcing mechanisms such as climate tectonics sea level fluctuations and their linkages is a major concern for fluvial scientists the 2525 km long ganga river derives its fluvial flux from northern part of the indian subcontinent and drops in the ganga brahmaputra delta and the bengal fan regions this paper presents a study of the ganga river sediments for their textural properties grainsize characteristics and transportation dynamics a suite of recently deposited sediments 189 bedload samples and 27 suspended load samples of the river and its tributaries was collected from 63 locations dry and wet sieve methods of grainsize analysis were performed and folk and ward s parameters were calculated transportation dynamics of the sediment load was assessed by means of channel hydrology flow sediment rating curves bedform mechanics grainsize images and cumulative curves textural properties of the bedload sediments of the ganga river tributaries originating from the himalaya orogenic belt the northern indian craton and the ganga alluvial plain regions are characterised by the predominance of fine to very fine sand medium to fine sand and very fine sand to clay respectively downstream textural variations in the bedload and suspended load sediments of the ganga river are therefore complex and are strongly influenced by lateral sediment inputs by the tributaries and channel slope at the base of the himalaya a very sharp gravel sand transition is present in which median grainsize of bedload sediments decreases from over 0 16 to 2 46 within a distance of 35 km downstream decline in mean grainsize of bedload sediments in the upper ganga river within the alluvial plain can be expressed by an exponential formula as mean grainsize in 0 0024 distance in kilometres from the himalayan front 1 29 it is a result of selective transport phenomena rather than of abrasion the condition attributed to channel competence with low gradient of 70 to 25 cm km coarsening of the bedload sediments in the middle segment of the river develops due to the coarse bedload sediments mean grainsize 1 8 2 2 supply from the tributaries of the northern indian craton region and increased unit stream power the ganga river sediments show a wide range of grainsize parameters bedload sediments mean grainsize 1 5 3 8 standard deviation 0 3 0 7 skewness 0 2 0 5 and kurtosis 0 8 2 4 suspended load sediments mean grainsize 2 9 5 0 standard deviation 0 6 1 6 skewness 0 6 0 4 and kurtosis 0 7 4 6 mean grainsize of the bedload sediments is 2 6 which is 1 3 units coarser than the suspended load sediments the cumulative grainsize curves of the bedload sediments show a distinct break in slope representing nearly 80 of the bedload sediment transported as graded suspension during the peak monsoon discharge most of the bedload sediments are transported as the discontinuous fine sandy graded suspension by the unidirectional unsteady shooting flow at a high transport rate about 8 106 tons d a model of sedimentation transportation at river channel is proposed the ganga river mobilises a total of 729 106 tons of sediments annually through a narrow zone within its river valley under the present hydrogeological conditions the river sedimentation is climatically controlled and is predicted to produce a 2000 km long 2 to 40 km wide and 25 to 50 m thick ribbon shaped well sorted symmetrically skewed fine sand body

cadmium and delta13c paleochemical ocean distributions during the stage 2 glacial maximum changes in heat and salt transport by ocean currents have been implicated in ice age climate cycles weyl 1 968 newell 1 974 broecker et al 1 990b in addition to the direct physical effects of the ocean on climate the ocean carbon system controls atmospheric co2 and the co2 fluctuations documented in ice core bubbles barnola et a1 1 987 neftel et a1 1 988 are thought to be a significant factor in climate oscillations hansen et al 1 984 dramatic changes in oceanic circulation patterns and carbon system chemistry have occurred during the late quaternary glacial interglacial global climate cycles boyle keigwin 1 982 curry lohmann 1 983 shackleton pisias 1 984 boyle keigwin 1 987 duplessy et al 1 988 curry et al 1 988 broecker et al i 990a these changes in the ocean system may be significant driving forces in the progression of ice age co2 cycles toggweiler sarmiento 1 985 ennever mcelroy 1 985 wenk siegenthaler 1 985 boyle 1 988a b broecker peng 1 990 the oceanic distributions of c513c cd and other carbon system linked properties are controlled by the interaction between biological uptake and decomposition with the general circulation of the ocean because records of past oceanic cd and c5 1 3c are preserved in shells of planktonic and benthic foraminifera

radiocarbon profiles of the nw pacific from the lgm and deglaciation evaluating ventilation metrics and the effect of uncertain surface reservoir ages during the last deglaciation the ventilation of the subarctic pacific is hypothesized to have changed dramatically including the rejuvenation of a poorly ventilated abyssal water mass that filled the deep ocean and fluctuations in the strength of north pacific intermediate and deep water formation at millennial timescales foraminiferal radiocarbon reconstructions of past ventilation changes in the pacific are valuable but are hampered by poor carbonate preservation low sediment accumulation rates bias from bioturbation and poorly constrained past surface reservoir age in this study we present paired benthic planktonic radiocarbon measurements from the okhotsk sea and emperor seamounts we take advantage of large contemporaneous peaks in benthic abundances from the last glacial maximum bolling allerod ba and early holocene to produce time slices of radiocarbon from 1 to 4 km water depth we explore the impact of uncertain surface reservoir age and evaluate several approaches to quantifying past ocean radiocarbon distribution using our nw pacific data and a compilation of published data from the north pacific both the calendar age and the absolute value of an ocean radiocarbon estimate depend on the assumed surface reservoir age but for a time slice from a small geographical area with radiocarbon independent stratigraphic correlation between cores the shape of a water column profile is independent of surface reservoir age the nw pacific profiles are similar in shape to the compilation profiles for the entire north pacific which suggests that deglacial surface reservoir age changes across the n pacific did not diverge dramatically across the areas sampled the last glacial maximum lgm profile 2 km spans a wide range of values ranging from values similar to today to lower than today however by the ba the profile has a similar shape to today ultimately local surface reservoir ages end member water mass composition and mixing ratios must each be constrained before a radiocarbon activity reconstruction can be used to confidently infer ventilation changes

muddled or mixed inferring palaeoclimate from size distributions of deep sea clastics abstract one of the outstanding problems of palaeoclimate reconstruction from physico chemical properties of terrigenous deep sea sediments stems from the fact that most basin fills are mixtures of sediment populations derived from different sources and transported to the site of deposition by different mechanisms conventional approaches to palaeoclimate reconstruction from deep sea sediments do not distinguish between provenance and dispersal related variations and therefore often fail to recognise the true significance of variations in sediment properties we formulate a set of requirements that each proposed palaeo environmental indicator should fulfil and focus on the intrinsic coupling between grain size and chemical composition a critical review of past achievements in grain size analysis serves to introduce a conceptual model of spatio temporal grain size variation based on dynamic populations each dynamic population results from a characteristic combination of production and transport mechanisms that corresponds to a distinct subpopulation in the data analysed the mathematical statistical representation of the conceptual model can be obtained by means of the end member modelling algorithm emma applications of the model to several ocean basins are discussed as well as methods to examine the validity of grain size based palaeoclimate reconstructions palaeoclimate reconstructions of a high and low latitude basin illustrate the common degree of complexity of deep sea grain size records

significance of porosity for stratigraphy and textural composition in subsurface coarse fluvial deposits boise hydrogeophysical research site recognition and quantitative characterization of subsurface stratigraphic units in coarse unconsolidated fluvial deposits are difficult because large grain size and the large scale of sedimentary structures make direct interpretation from core difficult or impossible in this paper we use porosity data from well logs and grain size distribution gsd data from core to investigate four pebble and cobble dominated units that have been identified in porosity logs in deposits at a research well field boise hydrogeophysical research site lacking direct observation at an appropriate scale questions about distribution of parameters and textural composition in these units are analyzed with statistical tests the four pebble and cobble dominated porosity stratigraphic units may be grouped into two types 1 units 1 and 3 have low porosity mean 0 17 0 18 and low porosity variance and 2 units 2 and 4 have higher porosity mean 0 23 0 24 and higher porosity variance based on gsd data core samples are subdivided into five lithotypes the five lithotypes occur in different proportions and have different vertical transition probability characteristics in the two types of units 1 units 1 and 3 have only framework gravel dominated lithotypes and have random vertical transition probability between these two lithotypes and 2 units 2 and 4 consist of both framework gravel dominated and sand or matrix dominated lithotypes and have structured vertical transition probability the two framework gravel dominated lithotypes occur in all four stratigraphic units but have distinctly lower porosity in units 1 and 3 i e tighter packing than in units 2 and 4 looser packing considering the repeated stratigraphic occurrence of and the statistical significance of differences between the two types of units both the individual unit distinctions and the two unit groupings appear to be valid it is reasonable to interpret that the observed packing differences associated with units 1 and 3 compared with units 2 and 4 are related to different sedimentary processes that produce different bedforms or grain fabrics perhaps under different bedload transport rates

how much deep water is formed in the southern ocean three tracers are used to place constraints on the production rate of ventilated deep water in the southern ocean the distribution of the water mass tracer po4 phosphate star in the deep sea suggests that the amount of ventilated deep water produced in the southern ocean is equal to or greater than the outflow of north atlantic deep water from the atlantic radiocarbon distributions yield an export flux of water from the north atlantic which has averaged about 15 sv over the last several hundred years cfc inventories are used as a direct indicator of the current production rate of ventilated deep water in the southern ocean although coverage is as yet sparse it appears that the cfc inventory is not inconsistent with the deep water production rate required by the distributions of po4 and radiocarbon it has been widely accepted that the major part of the deep water production in the southern ocean takes place in the weddell sea however our estimate of the southern ocean ventilated deep water flux is in conflict with previous estimates of the flux of ventilated deep water from the weddell sea which lie in the range 1 5 sv possible reasons for this difference are discussed

grain size analysis of the lower cambrian lower cretaceous clastic sequence of jordan sedimentological and paleo hydrodynamical implications abstract 356 sand sized samples ranging in age from early cambrian epoch to late cretaceous epoch of known depositional environments were analyzed mechanically to obtain the grain size parameters of mode median mean and sorting the constructed grain size distribution curves for the various paleozoic and mesozoic formations were interpreted in terms of the paleo hydrodynamic processes prevailing through transportation and deposition the study proved that the grain size parameters of sand sized sediments most sensitive to paleo depositional environmental recognition were the graphic mean grain size and the inclusive graphic sorting mean grain size values below 1 77 of a sand sized sample could indicate a fluvial channel paleo depositional environment whereas the mean grain size values above 2 8 are indicative to a shallow marine paleo depositional environment sorting values above 1 1 may indicate a fluvial channel paleo depositional environment a bivariate discriminatory plot of mean grain size versus sorting yields two fields that can successfully discriminate between the fluvial channel paleo depositional environment and the shallow marine paleo depositional environment a new grain size parameter termed the mean sorting index was introduced in this study and calculated by dividing the mean grain size value over the sorting value it is recorded here that the mean sorting index is more sensitive to paleo depositional environment recognition than the individual mean grain size and sorting parameters

deep ocean biogeochemistry of silicic acid and nitrate 1 observations of silicic acid and nitrate along the lower branch of the global conveyor belt circulation show that silicic acid accumulation by diatom opal dissolution occurs at 6 4 times the rate of nitrate addition by organic matter remineralization the export of opal and organic matter from the surface ocean occurs at a si n mole ratio that is much smaller than this almost everywhere cf sarmiento et al 2004 the preferential increase of silicic acid over nitrate as the deep circulation progresses from the north atlantic to the north pacific is generally interpreted as requiring deep dissolution of opal together with shallow remineralization of organic matter broecker 1991 however sarmiento et al 2004 showed that the primary reason for the low silicic acid concentration of the upper ocean is that the waters feeding the main thermocline from the surface southern ocean are depleted in silicic acid relative to nitrate by implication the same southern ocean processes that deplete the silicic acid in the surface southern ocean must also be responsible for the enhanced silicic acid concentration of the deep ocean we use observations and results from an updated version of the adjoint model of schlitzer 2000 to confirm that this indeed the case

hydraulic interpretation of grain size distributions using a physical model for bedload transport abstract grain size distributions of bedload sediment are modelled by considering the time variation of sediment transport in a unidirectional turbulent flow a frequency distribution of instantaneous bed shear stress is divided into a large number of shear stress ranges with mean values of oi each oi is capable of transporting a range of sediment sizes as bedload the maximum size is just at its entrainment threshold the minimum size is just too large to be suspended rates of bedload transport are calculated for each size range using a theoretical bedload function and the proportion of time that these rates occur is obtained by integrating the frequency distribut on between the boundaries of each shear stress range the relative weights of sediment transported in particular size ranges determined for all oi values constitutes the grain size distribution obtained from bedload sampling at a fixed point on the bed cumulative grain size curves have been simulated using the model in order to demonstrate the effects of the various model parameters e g mean bed shear stress viscosity all curves show a distinct break in slope which represents the maximum grain size transportable in suspension when the shear stress attains its maximum fluctuating value examination of many natural bedload distributions shows close qualitative and quantitative agreement with the model and reasons for discrepancies can be fully explained typical grain size distributions of deposited sediments can be obtained by mixing of different flow related bedload distributions in various proportions thus although deposited sediments may primarily result from bedload transport during a steady flood flow flow unsteadiness also plays a part the effects of some deposition directly from suspended load can also be surmised

distribution of grain sizes across a transgressive shoreface abstract distributions of seventeen grain sizes in the sand fraction of the shoreface sediments south of long island new york can be categorized into middle and lower shoreface species very fine sand upper shoreface species fine sand shoreface depleted species medium sand and swash zone species coarse sand the long term fair weather wave base of the study area at a depth of about 16 m is determined on the basis of the characteristic response of grain sizes to the average shoreface hydrodynamics the crosshore deviations from the mean distribution for each grain size were examined by using empirical orthogonal function eof analysis these results show differential associations of grain size deviations with various dynamic zones on the shoreface the hydrodynamic processes of the modern shoreface are speculated to winnow out fine and very fine sands and transport them onshore leaving behind on the lower shoreface and inner continental shelf a lag deposit of transgressive sand sheet composed mainly of medium sand

sortable silt and fine sediment size composition slicing parameters for palaeocurrent speed and palaeoceanography fine sediment size 63 ixm is best measured by a sedimentation technique which records the whole size distribution repeated size measurement with intermediate steps of removal of components by dissolution allows inference of the size distribution of the removed component as well as the residue in this way the size of the biogenic and lithogenic noncarbonate fractions can be determined observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 ixm the dynamics of sediment erosion deposition and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10 1xm grain size and noncohesive above that size thus silt coarser than 10 ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed silt that is f mer than 10 ixm behaves in the same way as clay 2 xm useful parameters of the distribution are the 10 63 ixm mean size and the percentage 10 63 ixm in the fine fraction we cannot use size distributions to distinguish the nature of the currents therefore to infer water mass advection speeds i e the mean kinetic energy of the flow ku regions of high eddy kinetic energy ke must be avoided at the present such abyssal regions lie under the high surface k e of major current systems gulf stream kuroshio agulhas antarctic circmpolar current and brazil falldand currents in the argenthe basin this is probably a satisfactory guide for the pleistocene with regard to the carbonate subfraction of the size spectrum size modes due to both cocco iths and foramlnlferal fragments can be recognized and analyzed with the boundary between them again at about 10 lm the flux of less than 10 lm carbonate at pelagic sites above the lysocline is another candidate for a productivity indicator

environments of deposition paleocurrents and provenance of tertiary deposits along kachemak bay kenai peninsula alaska abstract grain size distributions and sedimentary structures of tertiary strata along kachemak bay indicate a variety of inchannel and overbank fluvial facies a markov analysis indicates cyclicity of these facies probably caused by repeated and regular channel migration during subsidence fossils indicate a cool temperate climate and probable freshwater deposition paleocurrent directions and sandstone composition suggest a metamorphic and sedimentary clastic provenance during homerian time with the addition of pyroclastics during clamgulchian time the homerian stage beds represent facies of braided meandering streams whereas the clamgulchian stage beds represent facies of meandering streams these streams flowed westward and northwestward from the chugach kenai mountains onto wooded low gradient alluvial plains

reduced deep ocean ventilation in the southern pacific ocean during the last glaciation persisted into the deglaciation abstract marine radiocarbon 14c is widely used to trace ocean circulation and the 14c levels of interior ocean water masses can provide insight into atmosphere ocean exchange of co2 the since the last glaciation using tephras as stratigraphic tie points with which to estimate past atmospheric 14c we reconstructed a series of deep radiocarbon ages for several time slices from the last glaciation through the deglaciation and holocene in the southwestern pacific glacial ventilation ages were much greater in magnitude than modern and had a strong mid depth 14c minimum centered on 2500 m glacial radiocarbon ages of intermediate depth waters 600 1200 m were 800 to 1600 14c years about twice modern and persisted through the early deglaciation notably in the glaciation shallower depths were significantly more enriched in 14c than waters between 1600 and 3800 m which were 4000 to 6200 14c years or about 3 5 times older than modern abyssal waters deeper than 4000 m were also more 14c rich than the overlying deep water with radiocarbon ages of 1800 2300 14c years this was similar to modern values in the early deglaciation 14c depleted waters were flushed from shallower depths first and replaced with progressively younger waters such that by 18 ka the deep to intermediate age difference was reduced by half and by 14 ka a modern type 14c profile for deep ocean water masses was in place our results 1 confirm a deep 14c depleted water mass during the lgm and early deglaciation and 2 constrain the extent of this old water in the southern pacific as between 1600 m and 3800 m the availability of atmospheric ages from tephras reveals that the presence of older surface reservoir ages in the glaciation caused the estimation of ventilation ages from simple benthic planktonic offsets to significantly underestimate the depletion of 14c in deep waters this may have had a role in masking the large change in reservoir ages since the glaciation when using benthic planktonic reservoir age estimates

event based stratigraphic simulation of wave dominated shallow marine environments abstract the presence of event beds in the shallow marine stratigraphic record indicates formation is governed by high magnitude low frequency processes rather than low magnitude high frequency processes in this paper a 2 d multiple grain size process response model barsim is presented which uses event deposition to simulate stratigraphic response to changes in sea level and sediment supply barsim uses variable time steps to simulate individual storm event and fair weather periods deposition during storm conditions solely consists of reworked shoreface sediment while fair weather deposits consist of reworked shoreface sediment combined with sediment supplied by littoral drift and suspension simulations using variations in sea level sediment supply both amount and grain size and wave height regime result in distinct depositional patterns stratal geometry and bed characteristics model results indicate that both wave height regime and grain size of supplied sediment have considerable effect on shoreface morphology and stratal characteristics unraveling coastal evolution from the shallow marine stratigraphic record may therefore be more difficult than previously assumed as both variables are expected to vary over geologic time scales

visualization of the turbulent flow structure in a gravel bed river a novel technique for visualizing turbulent flow data from a gravel bed river is presented the time development of flow velocity and shear stress at three heights is displayed using a computer program this can be used to observe how the fluctuations of velocity and shear stress interact both spatially and temporally we highlight examples of flow events which are important for the understanding of flow dynamics the visualization suggests that the turbulent flow field is characterized not only by coherence over time at a point but also by spatial interdependence between points we suggest that this new visualization approach will assist further interpretation of statistical analyses of turbulent signals as well as focusing future measurement strategies by providing a clearer spatio temporal picture of the flow structure