coarse bed load transport in an alluvial gravel bed stream dupuyer creek montana coarse bed load was sampled in a gravel cobble bed stream during two major floods in the snowmelt runoff season the channel is characterized by high rates of bank erosion and therefore high rates of sediment supply and bed load flux peak discharge reached four times bank full and bed load was sampled at flows 0 7 1 7 times bank full a large aperture bed load sampler 1 m by 0 45 m captured the largest particles in motion and specifically targeted the coarse bed load size distribution by using a relatively large mesh 32 mm or d25 of streambed surface size distribution bed load flux was highly variable with a peak value of 0 85 kg s m for the coarse fraction above 38 mm bed load size distribution and maximum particle size was related to flow strength entrainment was size selective for particles d70 and larger 88 155 mm while particles in the range d30 d70 35 88 mm ceased to move at essentially the same flow bed load flux was size selective in that coarse fractions of the streambed surface were under represented in or absent from the bed load painted tracer particles revealed that the streambed surface in the riffles could remain stable even during high rates of bed load transport these observations suggest that a large proportion of bed load sediments was sourced from outside the riffles repeat surveys confirmed major scour and fill in pools up to 0 75 m and bank erosion 2 m which together contributed large volumes of sediment to the bed load copyright 2007 john wiley sons ltd

arctic palaeo river discharge and environmental change evidence from the holocene kara sea sedimentary record abstract in this paper we summarize data on terrigenous sediment supply in the kara sea and its accumulation and spatial and temporal variability during holocene times sedimentological organic geochemical and micropaleontological proxies determined in surface sediments allow to characterize the modern riverine terrigenous sediment input ams 14c dated sediment cores from the ob and yenisei estuaries and the adjacent inner kara sea were investigated to determine the terrigenous sediment fluxes and their relationship to paleoenvironmental changes the variability of sediment fluxes during holocene times is related to the post glacial sea level rise and changes in river discharge and coastal erosion input whereas during the late middle holocene most of the terrigenous sediments were deposited in the estuaries and the areas directly off the estuaries huge amounts of sediments accumulated on the kara sea shelf farther north during the early holocene before about 9 cal kyr bp the maximum accumulation at that time is related to the lowered sea level increased coastal erosion and increased river discharge based on sediment thickness charts echograph profiles and sediment core data we estimate an average holocene 0 11 cal kyr bp annual accumulation of 194 106 t yr 1 of total sediment for the whole kara sea based on late holocene modern sediment accumulation in the estuaries probably 12 106 t yr 1 of riverine suspended matter i e about 30 of the input may escape the marginal filter on a geological time scale and is transported onto the open kara sea shelf the high resolution magnetic susceptibility record of a yenisei core suggests a short term variability in siberian climate and river discharge on a frequency of 300 700 yr this variability may reflect natural cyclic climate variations to be seen in context with the interannual and interdecadal environmental changes recorded in the high northern latitudes over the last decades such as the nao ao pattern a major decrease in ms values starting near 2 5 cal kyr bp being more pronounced during the last about 2 cal kyr bp correlates with a cooling trend over greenland as indicated in the gisp 2 ice core extended sea ice cover in the north atlantic and advances of glaciers in western norway our still preliminary interpretation of the ms variability has to be proven by further ms records from additional cores as well as other high resolution multi proxy arctic climate records

long term bedload mobility in gravel bed rivers using iron slag as a tracer abstract bedload dispersion is evaluated in gravel bed rivers using slag elements from ironworks established along rivers in the ardenne region between the fourteenth and the nineteenth centuries large quantities of slag were dumped close to these rivers or even directly into the channels for centuries slag elements were dispersed in the bedload and transported by floods of varying importance consequently slag may be considered as a reliable tracer to analyze bedload dispersion over several centuries the size of slag elements was studied along 16 ardenne rivers the longitudinal size trend of the largest slag particles allows the effective competence of these rivers to be determined between 19 and 129 mm for rivers where specific stream power for the bankfull discharge ranges between 20 and 134 w m a direct relationship doesn t exist between these two parameters as the size of slag elements must be considered with regard to the d 50 of the bed selective transport was analyzed directly downstream of the input sites the sorting distance varies from river to river and depends on the velocity of the coarse elements introduced into the river since the inception of the iron industry downstream of two metallurgic sites the slag propagation fronts were located as the periods of activity at these sites are known from historical studies the virtual velocity of bedload movement in these rivers was estimated to be 2 4 km century

a geochemical investigation of carboxylic acids released via sequential treatments of two surficial sediments from the changjiang delta and east china sea two surface sediments from the delta of the changjiang river the fourth largest river in the world in terms of water discharge and the seventh in terms of sediment discharge and an adjacent area of the east china sea were subjected to sequential treatments in order to obtain complete quantitative and qualitative information on carboxylic acid moieties five successive treatments allowed for the release of all acid moieties occurring in each sample i the unbound acids isolated from extracts ii the oh labile acids released by classical saponification iii the oh ptc labile acids obtained via an additional saponification with a phase transfer catalyst iv the h labile acids released by a subsequent acid hydrolysis and v the tightly bound acids only released by thermolysis these five fractions correspond to distinct pools whose occurrence reflects diaerences in the mode of linkage of the acid moieties and or in the protection provided by the structures to which they are linked such analysis of acid moieties provided information on i the relative contributions from microalgae bacteria and higher plants in the delta and seaward stations ii the degree of early diagenetic alteration for the acids derived from these diaerent sources and iii the types of microalgal and bacterial species implicated these features were also compared with the results of the only previous study where the sequential treatments were applied on surficial sediments from a sharply diaerent environment the lena river delta arctic 2000 elsevier science ltd all rights reserved

effective discharge in rocky mountain headwater streams summary whereas effective discharge q eff in mountain streams is commonly associated with a moderate flow such as bankfull discharge q bf this study found that the maximum discharge q max and not bankfull discharge is the channel forming or effective flow for gravel transport in plane bed streams where partial bed mobility causes steep gravel transport rating curves q eff may approach bankfull flow in some step pool channels where gravel moves over a static cobble boulder bed our conclusions are based on magnitude frequency analyses conducted at 41 gauged rocky mountain headwater streams because these gauged streams lacked gravel transport data as is typical comparable streams with measured transport rates were used to develop scaling relations for rating curve exponents with stream and watershed characteristics those scaling relations were then used to estimate the steepness of gravel rating curves at the 41 gauged but unsampled sites the measured flow frequency distributions were characterized by two fitted power functions the steepness of the flow frequency distributions and the estimated steepness of gravel transport relations were combined in magnitude frequency analyses to compute q eff

coupling primary production and terrestrial runoff to ocean acidification and carbonate mineral suppression in the eastern bering sea water column ph and carbonate mineral saturation states were calculated from dissolved inorganic carbon dic and total alkalinity data collected over the eastern bering sea shelf in the spring and summer of 2008 the saturation states of the two most important carbonate minerals calcite calcite and aragonite aragonite were strongly coupled to terrestrial runoff from the yukon and kuskokwim rivers primary production in the surface waters and remineralization of organic matter at depth over the shelf in spring before ice melt occurred ph over the shelf was largely confined to a range of 7 9 8 1 and calcite and aragonite ranged from 1 5 to 3 0 and 0 8 to 2 0 respectively at the stations closest to river outflows aragonite was undersaturated in the water column from the surface to the bottom during the summer sea ice retreat high rates of primary production consumed dic in the mixed layer which increased ph and calcite and aragonite however calcite and aragonite decreased by 0 3 in the bottom waters over the middle and outer shelf over the northern shelf where export production is highest aragonite decreased by 0 35 and became highly undersaturated the observed suppression and undersaturation of calcite and aragonite in the eastern bering sea are correlated with anthropogenic carbon dioxide uptake into the ocean and will likely be exacerbated under business as usual emission scenarios therefore ocean acidification could threaten some benthic and pelagic calcifying organisms across the bering sea shelf in the coming decades

biomarker proxy shows potential for studying the entire quaternary arctic sea ice history recently a novel and promising biomarker proxy for reconstruction of arctic sea ice conditions was developed and is based on the determination of a highly branched isoprenoid with 25 carbons ip25 so far ip25 records have been restricted to the last 150 kyr bp here we present a biomarker record from ocean drilling program odp site 912 going back to the pliocene pleistocene boundary and indicating that sea ice of variable extent occurred in the fram strait southern yermak plateau area at least since about 2 2 ma furthermore our data support the idea that a combination of ip25 and open water phytoplankton biomarker data pip25 index may give more reliable and quantitative estimates of past sea ice cover at least for the study area this study reveals that the novel ip25 pip25 biomarker approach has potential for semi quantitative paleo sea ice studies covering the entire quaternary and motivate to carry out further detailed high resolution research on odp iodp material using this proxy

climatic dependence of the organic matter contributions in the north eastern norwegian sea over the last 15 000 years abstract lipids are used for the evaluation of the different organic matter contributions in the north eastern norwegian sea m23258 site 75 n 14 e over the last 15 000 years development of a mass balance model based on the down core quantification of the c 37 alkenones the odd carbon numbered n alkanes a odd and the unresolved complex mixture of hydrocarbons ucm has allowed three main organic matter inputs involving marine continental and ancient reworked organic matter to be recognized the model shows good agreement between measured and reconstructed toc values similarly a strong parallelism is observed between predicted components such as marine toc and carbonate content which was determined independently representation of the model results within a time scale based on 15 ams 14 c measurements shows that the main changes in organic matter constituents are coincident with the major climatic events of the last 15 000 years thus the predominance of reworked organic matter is characteristic of termination ia up to 70 continental organic matter was dominant during the bolling allerod b a and younger dryas yd periods about 85 and a strong increase of marine organic matter occurred in the holocene between 50 and 75 this agreement reflects the main hydrographic changes that determined the deposition of sedimentary materials between 0 and 15 cal ka ice rafted detritus from the barents continental platform ice melting waters from the arctic fluvial system discharging into the barents sea and dominance of north atlantic currents respectively in this respect the high resolution down core record resulting from the mass balance and lipid measurements allows for the identification of millennial scale events such as the increase of reworked organic matter at the final retreat of the barents ice sheet at the end of the deglaciation period termination ib

transport of terrestrial organic carbon to the oceans by rivers re estimating flux and burial rates this study re estimates one important component in the global carbon cycle the modern global fluviatile organic carbon discharge and burial rates according to these results approximately 430 1012 g of terrestrial organic carbon are transported to the ocean in modern times this amount is higher than the latest estimates but takes into account new data from oceania not previously considered in global flux studies however only the minor amount of 10 or approximately 43 1012 gc year 1 is most likely buried in marine sediments this amount is similar to the burial of marine organic carbon in the coastal ocean 55 1012 gc year 1 adding both estimates gives approximately 100 1012 gc year 1 which is the value calculated by berner 1982 for terrestrial deltaic shelf sediments however the results in this study suggest that on a global scale the organic carbon content in coastal ocean sediments is not solely of terrestrial origin but a mixture of nearly equal amounts of marine and terrestrial organic carbon the major part of the terrestrial organic carbon that enters the ocean by rivers approximately 400 1012 gc year 1 seems to be either a remineralised in the ocean whereas the mechanism by which the terrestrial organic carbon is oxidised in the ocean are unknown or b is dispersed throughout the oceans and accumulates in pelagic sediments

dune migration in a steep coarse bedded stream during 1986 and 1987 migrating bed forms composed of coarse sand and fine gravel d50 1 8 to 9 1 mm were documented in the north fork toutle river at kid valley washington at flow velocities ranging from 1 6 to 3 4 m s 1 and depths of 0 8 to 2 2 m the bed forms predominantly lower regime dunes were studied with a sonic depth sounder transducer suspended in the river at a stationary point twelve temporal depth sounding records were collected during storm runoff and nearly steady average streamflow with record durations ranging from 37 to 261 min waveform height was defined by dune front heights which ranged from 12 to 70 cm a weak correlation between flow depth and the standard deviation of bed elevation was noted dune front counts and spectral analyses of the temporal records showed that dune crests passed the observation point every 2 to 5 min dunes were often superposed on larger bed forms with wave periods between 10 and 30 min gradual changes in waveform height and periodicity occurred over several hours during storm runoff the processes of dune growth and decay were both time dependent and affected by changes in streamflow rates of migration for typical dunes were estimated to be 3 cm s 1 and dune wavelengths were estimated to be 6 to 7 m

response of bed surface patchiness to reductions in sediment supply 1 river beds are often arranged into patches of similar grain size and sorting patches can be distinguished into free patches which are zones of sorted material that move freely such as bed load sheets forced patches which are areas of sorting forced by topographic controls and fixed patches of bed material rendered immobile through localized coarsening that remain fairly persistent through time two sets of flume experiments one using bimodal sand rich sediment and the other using unimodal sand free sediment are used to explore how fixed and free patches respond to stepwise reductions in sediment supply at high sediment supply migrating bed load sheets formed even in unimodal sand free sediment yet grain interactions visibly played a central role in their formation in both sets of experiments reductions in supply led to the development of fixed coarse patches which expanded at the expense of finer more mobile patches narrowing the zone of active bed load transport and leading to the eventual disappearance of migrating bed load sheets reductions in sediment supply decreased the migration rate of bed load sheets and increased the spacing between successive sheets one dimensional morphodynamic models of river channel beds generally are not designed to capture the observed variability but should be capable of capturing the time averaged character of the channel when applied to our experiments a 1 d morphodynamic model rte bookagdegnormgravmixpw xls predicted the bed load flux well but overpredicted slope changes and was unable to predict the substantial variability in bed load flux and load grain size because of the migration of mobile patches our results suggest that 1 the distribution of free and fixed patches is primarily a function of sediment supply 2 the dynamics of bed load sheets are primarily scaled by sediment supply 3 channels with reduced sediment supply may inherently be unable to transport sediment uniformly across their width and 4 cross stream variability in shear stress and grain size can produce potentially large errors in width averaged sediment flux calculations

magma productivity and early seafloor spreading rate correlation on the northern voring margin norway constraints on mantle melting abstract continental rifting at the voring margin off mid norway was initiated during the earliest eocene 54 ma and large volumes of magmatic rocks were emplaced during and after continental breakup in 2003 a marine survey collecting ocean bottom seismometer single channel reflection and magnetic data was conducted on the norwegian margin to constrain continental breakup and early seafloor spreading processes the profile described here crosses the northern part of the voring plateau and the crustal velocity model was constructed through a combination of ray tracing and forward gravity modeling the latter corrected for the thermal effects remaining from the seafloor spreading we found a maximum igneous crustal thickness of 18 km decreasing to 6 5 km over the first 6 m y after continental breakup both the volume and the duration of excess magmatism are about twice as large as that of the more margin south of the east jan mayen fracture zone which offsets the two margin segments by 170 km a similar reduction in magmatism occurs to the north over an along margin distance of 150 km to the lofoten margin but without a margin offset both the geochemical data and the mean p wave velocity indicate that there is active mantle upwelling combined with a moderate temperature increase during the earliest mantle melting at the voring margin the mean p wave velocity versus crustal thickness also indicates that there is a transition from convection dominated to temperature dominated magma production 2 m y after breakup the magnetic data were used to derive plate half spreading rates for the northern voring margin which are very similar to that obtained at the more margin there is a strong correlation between magma productivity and early plate spreading rate suggesting a common cause a model for the breakup related magmatism should be able to explain this correlation but also the magma production peak at breakup the along margin magmatic segmentation and the active mantle upwelling proposed end member hypotheses comprise elevated upper mantle temperatures caused by a hot mantle plume or edge driven small scale convection fluxing mantle rocks through the melt zone edge driven convection does not easily explain these observations but a mantle plume model in which buoyant plume material flows laterally to pond in the rift topography at the base of the lithosphere close to breakup time is promising when the continents break apart the hot and buoyant plume material can flow up into the rift zone from surrounding areas as the rift transits to drift and the excess temperature of this material will then cause excess magmatism which dies off as the rift restricted material is spent the buoyancy of the plume material may in addition cause active upwelling which can increase the melting furthermore and also increase the force on the plate boundaries to enhance plate spreading rate this conceptual model explains how both excess magmatism and spreading rate will be reduced similarly with time as the plume material is consumed by plate spreading and thus correlate

modern organic carbon deposition in the laptev sea and the adjacent continental slope surface water productivity vs terrigenous input sediment samples from the laptev sea taken during the 1993 rv polarstern expedition ark ix 4 and the rv ivan kireyev expedition transdrift i were investigated for the amount and composition of their organic carbon fractions of major interest was the identification of different processes controlling organic carbon deposition i e terrigenous supply vs surface water productivity long chain unsaturated alkenones derived from prymnesiophytes and fatty acids derived from diatoms and dinoflagellates were analysed by means of gas chromatography and mass spectrometry first results on the distribution of these biomarkers in surface sediments indicate that the surface water productivity signal is well preserved in the sediment data this is shown by the distribution of the 16 1 n 7 and 20 5 n 3 fatty acids indicative for diatoms and the excellent correlation with the chlorophyll a concentrations in the surface water masses and the biogenic opal content and increased hydrogen indices of the sediments the high concentration of these unsaturated fatty acids in shallow water sediments shows the recent deposition of the organic material in deep sea sediments on the other hand the concentrations are low this decreased content is typical for phytoplankton material which has been degraded by microorganisms or autoxidation in general the alkenone concentrations are very low suggesting low production rates by prymnesiophytes only at one station from the lower continental margin influenced by the inflow of atlantic water masses were some higher amounts of alkenones determined long chain n alkanes as well as high c n ratios and low hydrogen indices indicate the importance of fluvial supply of terrigenous organic matter

biomarker distributions in surface sediments from the kara and laptev seas arctic ocean indicators for organic carbon sources and sea ice coverage studies of spatial and temporal changes in modern and past sea ice occurrence may help to understand the processes controlling the recent decrease in arctic sea ice cover here we determined concentrations of ip25 a novel biomarker proxy for sea ice developed in recent years phytoplankton derived biomarkers brassicasterol and dinosterol and terrigenous biomarkers campesterol and sitosterol in the surface sediments from the kara and laptev seas to estimate modern spatial seasonal sea ice variability and organic matter sources c25 hbi dienes and trienes were determined as additional palaeoenvironmental proxies in the study area furthermore a combined phytoplankton ip25 biomarker approach pip25 index is used to reconstruct the modern sea ice distribution more quantitatively the terrigenous biomarkers reach maximum concentrations in the coastal zones and estuaries reflecting the huge discharge by the major rivers ob yenisei and lena maxima in phytoplankton biomarkers indicating increased primary productivity were found in the seasonally ice free central part of the kara and laptev seas neither ip25 nor pip25 however shows a clear and simple correlation with satellite sea ice distribution in our study area due to the complex environmental conditions in our study area and the transportation process of sea ice diatom in the water column differences in the diene ip25 and triene ip25 ratios point to different sources of these hbis and different environmental conditions the diene ip25 ratio seems to correlate positively with sea surface temperature while negatively with salinity distributions

analysis of flow competence in an alluvial gravel bed stream dupuyer creek montana 1 critical shear stress and unit discharge flow competence models were tested against coarse bed load data from dupuyer creek montana united states maximum particle sizes sampled dmax and d50 to d90 percentiles in the bed load grain size distribution were well correlated with both shear stress and unit discharge bed load grain sizes became coarser with increasing flow strength for the dmax curve shields dimensionless parameter for the surface d50 was estimated at 0 044 and the exponent for relative particle size di d50 was 0 59 in the unit discharge criterion the critical flow to entrain the surface d50 was poorly predicted flow competence relationships based on dmax are prone to the influence of outliers and sample mass variability the mean of the three largest particles dmax 3 is more sensitive to changes in flow strength than the d50 to d90 bed load grain sizes and may represent a good compromise

the non layering of gravel streambeds under ephemeral flood regimes abstract the two layer format common to perennial streambeds in which a relatively coarse armour overlies a finer subarmour develops as a function of both the ingress and subsequent near surface winnowing of interstitial material and the selective non entrainment or slower transport velocity of coarse clasts ephemeral streams appear to lack such vertical layering or are characterized by weak layer development some of this may be due to the degree of mixing associated with the scour and fill process however continuous monitoring of bedload discharge in the nahal yatir in the northern negev desert reveals that sediment transport rates are extremely high so that the chance of armour layer development through selective non entrainment is much reduced indeed a comparison of the bedload and bed material size distributions confirms a high degree of similarity and hints at equal mobility regardless of clast size the monitoring programme also indicates that the bed becomes highly mobile at comparatively modest fluid shear so that practically all floods are associated with high transport rates consequently the winnowing that might be brought about by low transport rate events does not occur even within a single event winnowing is precluded by the rapid nature of flow recession that is so characteristic of flash floods the high degree of bed material mobility is attributable in part to the lack of strength that would otherwise be a corollary of armour development however it also highlights the divergent nature of the feedback loops that govern the relationship between flow and channel deposit in ephemeral and perennial systems

alkane and pah biomarkers as tracers of terrigenous organic carbon in arctic ocean sediments abstract we present the first sedimentary biomarker study encompassing the entire arctic ocean a large data set of organic markers for terrigenous petroleum and combustion inputs alkanes hopanes and steranes parent and alkyl polycyclic aromatic hydrocarbons pahs is examined for patterns in space and time using principal components analysis pca and partial least squares pls biomarker patterns reveal the central arctic ocean basin sediments to be compositionally distinct from those of the mackenzie river beaufort sea and barents sea but similar to those of the laptev sea pah distributions reflected in pah ratios and pca projections demonstrate that arctic ocean sediment is dominated by natural inputs to the extent that anthropogenic combustion pahs are not significant we find only modest changes between the glacial and post glacial sediments for atmospherically transported hydrocarbon biomarkers while particle associated biomarkers were captured strongly at basin edges during the glacial period and much more evenly transported across basins during the post glacial period the orders of magnitude decreases in particle associated petrogenic alkanes and pahs in central basins during glacial times coupled with the uniformity of most petrogenic biomarker parameters for most basin and shelf locations reflect a massive reduction in ice transport that makes the margins the most likely source of petrogenic material for the pleistocene holocene central arctic basins the proximity of large coal deposits of various maturity levels along the lena river the overlap in pah and biomarker composition of the laptev sea and surficial sediments from the central arctic ocean and the location of the laptev sea at the origin of the main transpolar drift all point to eroded coals from the lena river laptev sea as the likely source of petrogenic hydrocarbons to the central arctic ocean the ubiquitous presence of allochthonous coal in arctic ocean surface sediments provides a major constraint on the use of petrogenic biomarkers to infer the presence of subsurface petroleum reserves

paleogene biomarker records from the central arctic ocean integrated ocean drilling program expedition 302 organic carbon sources anoxia and sea surface temperature 1 during integrated ocean drilling program expedition 302 arctic coring expedition acex a more than 200 m thick sequence of paleogene organic carbon oc rich black shale type sediments was drilled here we present new biomarker data determined in acex sediment samples to decipher processes controlling oc accumulation and their paleoenvironmental significance during periods of paleogene global warmth and proposed increased freshwater discharge in the early cenozoic specific source related biomarkers including n alkanes fatty acids isoprenoids carotenoids hopanes hopenes hopanoic acids aromatic terpenoids and long chain alkenones show a high variability of components derived from marine and terrestrial origin the distribution of hopanoic acid isomers is dominated by compounds with the biological 17 h 21 h configuration indicating a low level of maturity on the basis of the biomarker data the terrestrial oc supply was significantly enriched during the late paleocene and part of the earliest eocene whereas increased aquatic contributions and euxinic conditions of variable intensity were determined for the paleocene eocene thermal maximum and eocene thermal maximum 2 events as well as the middle eocene time interval furthermore samples from the middle eocene are characterized by the occurrence of long chain alkenones high proportions of lycopane and high ratios 0 6 of n c35 lycopane n c31 the occurrence of c37 alkenenones which were first determined toward the end of the azolla freshwater event indicates that the oc becomes more marine in origin during the middle eocene preliminary u37k based sea surface temperature sst values display a long term temperature decrease of about 15 c during the time interval 49 44 5 ma 25 to 10 c coinciding with the global benthic 18o cooling trend after the early eocene climatic optimum at about 46 ma parallel with onset of ice rafted debris sst interpreted as summer temperatures decreased to values 15 c for the late early miocene a sst of 11 15 c was determined most of the middle eocene acex sediments are characterized by a smooth short chain n alkane distribution which may point to natural oil type hydrocarbons from leakage of petroleum reservoirs or erosion of related source rocks and redeposition

lipid distribution in surface sediments from the eastern central arctic ocean abstract during the arctic 91 expedition with rv polarstern numerous short multicorer and long cores kastenlot cores including surface sediments were recovered along a transect crossing the eastern part of the arctic ocean in this paper we present data on the concentration and distribution of short c17 c19 and long chain c27 c29 c31 n alkanes as well as fatty acids 16 0 16 1 18 0 18 1 in the surface sediments from this transect these compounds among others have been used to distinguish between autochthonous marine organic matter and allochthonous terrigenous organic matter supply changes in short chain n alkane as well as fatty acid contents of the sediments allow us to distinguish between regions characterized by higher or lower marine productivity organic carbon contents of the surface sediments are generally high and vary between 0 3 and 2 in general the high organic carbon content of the sediments is derived from a high input of terrigenous organic matter marine productivity in the arctic ocean is mainly controlled by reduced sea ice cover which allows a higher production rate of phytoplankton regions with a higher marine organic matter content are the area nw of svalbard the yermak plateau a part of the lomonosov ridge and makarov basin and the morris yesup rise the pattern of distribution of long chain n alkanes in arctic ocean surface sediments is mainly controlled by sea ice and or direct transport from the adjacent shelf areas although dilution by turbidites influences the deep basins

equal mobility of gravel in streams the remains of the day 1 the concept of equal mobility of gravel transport is 2 decades old the weak form of the hypothesis states that in order to transport the coarse half of the mean annual gravel load through a river reach at a rate equal to the fine half the coarser material must be overrepresented on the bed surface giving rise to a mobile bed armor the degree of mobile bed armoring necessary to accomplish this diminishes with increasing bed shear stress the strong form of the hypothesis states that the grain size distribution of the gravel portion of the bed load should be similar to that of the substrate and finer than that of the surface layer here the hypothesis is subjected to a rigorous test in the laboratory under controlled conditions which are nevertheless chosen to be as representative as possible of actual field conditions the grain size distributions used in the experiment included both model gravel and model sand at the end of the experiment the entire surface layer and a significant depth of substrate were removed from an entire reach of the channel and sieved the results of the experiment confirmed the weak form of equal mobility the surface layer was significantly coarsened compared with the bed load even when the sand was excluded from the size distributions the strong form of equal mobility was also supported by the experiment in that the size distribution of the gravel substrate was nearly identical to the size distribution of the gravel portion of the load the gravel substrate was however slightly but measurably coarser than the gravel load a tendency that has been observed in the field in cases for which the strong form is not satisfied

size selective entrainment of bed load in gravel bed streams entrainment of mixed size gravel bed material was studied in nine reaches of three high power streams in scotland and norway paired measurements of at a point shear stress estimated from velocity profiles and bed load transport by hand held sampler were made they extended to very high values 400 n m 2 3 5 kg m x s x analyses of maximum bed load diameter mean bed load diameter transport rates of individual size fractions and tracer pebble movements all show some dependence of threshold shear stress for entrainment on absolute particle size despite strong relative size effects precise equal mobility of all sizes was approached in the data set with the highest shear stresses and transport rates size selective transport in the streams studied is also indicated by clear downstream and downbar reductions in surface sediment size over distances too short for abrasion to be significant

grain sorting in gravel bed streams and the choice of particle sizes for flow competence evaluations flow competence assessments of floods have been based on the largest particle sizes transported and yield either the mean flow stress mean velocity or discharge per unit flow width the use of extreme particle sizes has potential problems in that they may have been transported by debris flows rather than by the flood it may be difficult to locate the largest particles within the flood deposits and there are questions concerning how representative one or a few large particles might be of the transported sediments and therefore of the flood hydraulics such problems would be eliminated for the most part if competence evaluations are based on median grain sizes of transported sediments or perhaps on some coarse percentile that is established by a reasonable number of grains in order to examine such issues the gravel transport data of milhous from oak creek oregon and of carling from great eggleshope beck england have been analysed in terms of changing grain size percentiles with varying flow stresses a comparison between these two data sets is of added interest because the bed material in oak creek is segregated into well developed pavement and subpavement layers while such a layering of bed materials is largely absent in great eggleshope beck the analyses show that the trend of increasing sizes of the largest particles in the bedload samples diameter dm with increasing flow stresses is consistent with similar dependencies based on sieve percentiles ranging from the medians d50 to the 95th percentiles d95 this indicates that the largest particles are an integral part of the overall distributions of bedload grain sizes and respond to changing flow hydraulics along with the rest of the size distribution in oak creek the median grain size shows the largest change with increasing flow stresses followed by d60 and so on to d95 which shows the smallest change the variations in dm continue this trend and are similar to those for d95 this systematic variation of grain size percentiles in oak creek is consistent with changes in the overall distributions which tend to be symmetrical and gaussian for low discharges but become skewed rosin distributions for high discharges in contrast in great eggleshope beck the several percentiles and dm show the same rate of shift to coarser sizes as flow stresses increase this results in part from differences in sampling techniques wherein the bedload samples from great eggleshope beck represent a complete flood event while shorterterm samples at a specific flow stage were obtained in oak creek as a result of the integrated sampling in great eggleshope beck the bedload grain size distributions are more complex commonly with a bimodal pattern however after accounting for differences in sampling schemes in the two streams contrasting patterns in changing grain size distributions remain and these are concluded to reflect grain sorting differences as the bedload grain size distributions approach the distributions of the bed materials it is surprising that if criteria commonly employed to demonstrate the equal mobility of different grain sizes are used in the comparison then great eggleshope beck is far closer to this condition in spite of its minimal development of a pavement it is concluded that the respective shapes of the bed material grain size distributions in particular their degrees of skewness are more important to the observed sorting patterns than are the effects of a pavement layer regulating grain entrapment to produce an equal mobility of different grain sizes therefore the comparison has established that flow competence relationships will differ from one stream to another depending on the pattern of grain sorting which is a function of the bedmaterial grain size distribution

assessing the importance of terrestrial organic carbon in the chukchi and beaufort seas abstract the western arctic ocean is a unique part of the world s oceans and is an area undergoing significant climate changes the effects and possible climate feedbacks of these changes are not yet fully understood decreased sea ice cover could lead to increased productivity in the water column or a reduction in total productivity through the loss of sea ice algal contributions climate change could also alter the patterns of terrestrial inputs from rivers and coastal erosion in order to better understand the balance of organic material inputs in the western arctic ocean this report presents carbon and nitrogen elemental and isotopic compositions from 19 surface sediment samples and 7 cores from 4 shelf to basin transects as evidence of the sources of organic matter buried in the sediments of the chukchi and alaskan beaufort seas the c n ratios for surface sediments were between 5 3 and 11 5 mean 9 0 1 3 the mean toc was 1 2 0 3 and mean tn was 0 16 0 02 the highest toc contents were observed in the barrow canyon transect likely reflecting heightened overlying productivity the 13 c of this preserved material varied from 22 1 to 16 7 mean 19 4 1 3 a trend to depletion in 13 c and higher c n in eastern sites was observed among the surface samples 15 n varied from 4 1 to 7 6 mean 5 7 1 1 an evaluation of the inputs of organic matter to the western arctic sediment was accomplished using 13 c and 15 n values with the novel technique of a bayesian analysis multi source mixing model this model was used to estimate proportional contributions of sea ice algae water column phytoplankton and terrestrial organic matter we conclude that water column productivity is the source of between 50 and 70 of the organic carbon buried in this portion of the western arctic the remaining 25 35 of carbon is mainly supplied by sea ice algal productivity with at most 15 of sedimentary carbon derived from terrestrial inputs

post glacial variability of sea ice cover river run off and biological production in the western laptev sea arctic ocean a high resolution biomarker study abstract multi proxy biomarker measurements were applied on two sediment cores ps51 154 ps51 159 to reconstruct sea ice cover ip25 biological production brassicasterol dinosterol and river run off campesterol sitosterol in the western laptev sea over the last 17 ka with unprecedented temporal resolution the absence of ip25 from 17 2 to 15 5 ka in combination with minimum concentration of phytoplankton biomarkers suggests that the western laptev sea shelf was mostly covered with permanent sea ice very minor river run off and restricted biological production occurred during this cold interval from 16 ka until 7 5 ka a long term decrease of terrigenous riverine organic matter and a coeval increase of marine organic matter reflect the gradual establishment of fully marine conditions in the western laptev sea caused by the onset of the post glacial transgression intensified river run off and reduced sea ice cover characterized the time interval between 15 2 and 12 9 ka including the bolling allerod warm period 14 7 12 9 ka prominent peaks of the dip25 index coinciding with maximum abundances of subpolar foraminifers are interpreted as pulses of atlantic water inflow on the western laptev sea shelf after the warm period a sudden return to severe sea ice conditions with strongest ice coverage between 11 9 and 11 ka coincided with the younger dryas 12 9 11 6 ka at the onset of the younger dryas a distinct alteration of the ecosystem reflected in a distinct drop in terrigenous and phytoplankton biomarkers was detected during the last 7 ka the sea ice proxies reflect a cooling of the laptev sea spring summer season this cooling trend was superimposed by a short term variability in sea ice coverage probably representing bond cycles 1500 500 ka that are related to solar activity changes hence atmospheric circulation changes were apparently able to affect the sea ice conditions on the laptev sea shelf under modern sea level conditions

long chain unsaturated ketones and esters in living algae and marine sediments abstract series of c37 c39 di and triunsaturated ketones and methyl and ethyl esters of hexatriacontadienoic acid c36 2 have been previously identified in marine sediments and the coccolithophorid emiliania huxleyi these compounds have now been found in four further species of the isochrysidales prymnesiophyta which are not known to bear coccoliths suggesting that they are more widely distributed in living algae than previously thought in addition the ketones have been recognised in sediments of eocene age ca 45 ma which greatly extends their known geological time range and increases their potential as molecular markers for algal input heptatriacontatetraen 2 one c37 4 octatriacontatetraen 3 one c38 4 methyl and ethyl esters of hexatriacontatrienoic acid c36 3 and the ethyl ester of hexatriacontatetraenoic acid c36 4 have also been identified in varying amounts in these algae by gas chromatography and computerised gas chromatography mass spectrometry

late pleistocene changes in terrestrial biomarkers in sediments from the central arctic ocean abstract biomarkers in late pleistocene sediments collected from the integrated ocean drilling program iodp arctic coring expedition acex hole m0004c central arctic ocean were investigated the major biomarkers are long chain n alkanes n fatty acids and n alkan 1 ols indicating fresh organic matter om derived predominantly from higher plants the dominance of terrestrial biomarkers is attributed to severe om degradation caused by slow sedimentation in oxygen rich benthic water and or low primary production due to permanent sea ice coverage hopanes representing thermally altered om tend to be abundant in samples with abundant ice rafted debris ird an om rich dark grey layer deposited during marine isotope stage mis 6 contains a significant amount of branched glycerol dialkyl glycerol tetraethers branched gdgts suggesting ice erosion of organic rich continental soil followed by transportation to the central arctic by drifting ice the labile refractory index i e the abundance ratio of long chain n alkan 1 ols to the sum of long chain n alkanes and long chain n alkan 1 ols decreases above the dark grey layer indicating that the om became more refractory this change suggests that coverage of the source region by om rich soil decreased because of extensive glacial erosion during mis 6

oceanic and atmospheric variations during the last deglaciation in the fram strait arctic ocean a coupled high resolution organic geochemical and sedimentological study abstract from a high sedimentation rate core obtained from the yermak slope arctic ocean we deduced short term climatic fluctuations of the last deglaciation lasting from 17 000 to 9000 years bp by using a coupled organic geochemical and sedimentological approach we reconstructed near bottom current conditions and assessed their significance in relation with comparable global thermohaline circulation patterns and surface water conditions highest concentrations and fluctuations of specific marine phytoplankton biomarkers were obtained in the bolling allerod when the major deglaciation of the svalbard barents sea ice sheet sbis occurred the marine biomarker record and the sedimentological record are consistent with climate reconstructions obtained from greenland ice cores and thermohaline circulation variations however beginning with the younger dryas yd episode bottom currents decreased during this time period but surface waters remained very productive the atmospheric conditions of the western fram strait reconstructed from biomarker data and thermohaline circulation signals reconstructed from sedimentological data were decoupled in the yd maximum insolation values of solar radiation and fohn like winds enabled open water conditions and increased productivity values in the northern fram strait at least in summer

evaluation of long term bedload virtual velocity in gravel bed rivers ardenne belgium abstract in many gravel bed rivers bed material transfer has been interrupted or perturbed by anthropogenic activities currently restoration projects are being conducted in many countries in order to re establish bedload continuity however until now few studies have provided indications of the velocity of bed material over the long term at least decade to century time scale in the context of river restoration projects e g weir removal addition of spawning gravel these data are nevertheless crucial to predict the downstream propagation of the geomorphological and biological benefits e g supply transport equilibrium morphological and substratum diversity in our study pit tag tracers were used in eight medium sized gravel bed rivers ardenne region belgium to propose a flow competence relationship based on specific stream power on the one hand and to determine the long term virtual velocity of the bed material corresponding to the median diameter d 50 of the surface layer of riffles on the other hand after each flow event that exceeded the threshold for sediment entrainment tagged particles were sought and located even when they were buried in the subsurface layer afterwards all of the data were used to estimate the virtual velocity of the bed material over the long term using three approaches finally the results were compared with long term transport estimations based on iron slag dispersed by the rivers since the end of the middle ages

climate forcing of fine grained deep marine systems in an active tectonic setting middle eocene ainsa basin spanish pyrenees abstract a multi proxy approach to understand environmental change in deep time was undertaken on about 150 m of core from a 230 m long middle eocene core from the ainsa basin spanish pyrenees representing deep marine siliciclastic sediments using detailed sedimentary logging high resolution multi element xrf geochemistry total organic carbon and stable carbon isotopes the well a6 was drilled as part of an industry university consortium through siltstones fine very fine grained sandstone turbidites and hemipelagic structureless mudstones that were deposited as overbank and off axis deposits from a sandy submarine fan and interfan deposits for comparative mineralogy between the sandstone turbidites and siltstones scanning electron microscopy sem and x ray diffraction xrd were undertaken on selected samples the sandstone turbidites show enrichment of detrital elements such as si zr and ti that can be linked to greater quartz and heavy mineral content compared with adjacent siltstones structureless hemipelagic mudstones comprise mainly clay minerals and carbonate we interpret the sandstone turbidites as from hyperpycnal flows during high river sediment discharge whilst hemipelagic mudstones resulted from the suspension fall out of hypopycnal flows cyclostratigraphic analysis of the core reveals milankovitch cyclicity at frequencies of 0 03 cycles m short eccentricity 0 09 cycles m obliquity 0 15 cycles m precession couplet and 0 19 cycles m precession couplet orbital parameters appear to have controlled the cyclic delivery of coarser grained sediment by turbidity currents two equally plausible depositional models both as milankovitch driven can explain the cyclical changes in the deep marine sediments 1 climatic cycles with humid periods of enhanced chemical weathering increased storminess and greater riverine run off leading to high sediment flux to the deep basin as sandstone turbidites 2 climatic cycles with cooler conditions linked to high frequency small scale eustatic sea level fluctuations with lowstand shelf edge delta progradation resulting in greater volumes of coarse detrital sediment to the seafloor by hyperpycnal flows this study provides an insight into the likely depositional effects of orbitally induced climate change on the nature and delivery of terrigenous sediment into deep marine environments

different sources and degradation state of dissolved particulate and sedimentary organic matter along the eurasian arctic coastal margin the amount of organic carbon oc present in siberian arctic permafrost soils is estimated at twice the amount of carbon currently in the atmosphere the shelf seas of the arctic ocean receive large amounts of this terrestrial oc from eurasian arctic rivers and from coastal erosion degradation of this land derived material in the sea would result in the production of dissolved carbon dioxide and may then add to the atmospheric carbon dioxide reservoir observations from the siberian arctic suggest that transfer of carbon from land to the marine environment is accelerating however it is not clear how much of the transported oc is degraded and oxidized nor how much is removed from the active carbon cycle by burial in marine sediment using bulk geochemical parameters total oc d13c and d14c isotope composition and specific molecular markers of plant wax lipids and lignin phenols the abundance and composition of oc was determined in both dissolved and particulate carrier phases the colloidal oc coc part of the dissolved oc particulate oc poc and sedimentary oc soc statistical modelling was used to quantify the relative contribution of oc sources to these phases terrestrial oc is derived from the seasonally thawing top layer of permafrost soil topsoil oc and frozen oc derived from beneath the active layer eroded at the coast commonly identified as yedoma ice complex deposit oc yedoma icd oc these carbon pools are transported differently in the aquatic conduits topsoil oc was found in young doc and poc in the river water and the shelf water column suggesting long distance transport of this fraction the yedoma icd oc was found as old particulate oc that settles out rapidly to the underlying sediment and is laterally transported across the shelf likely dispersed by bottom nepheloid layer transport or via ice rafting these two modes of oc transport resulted in different degradation states of topsoil oc and yedoma icd oc terrestrial cuo oxidation derived biomarkers indicated a highly degraded component in the coc in contrast the terrestrial component of the soc was much less degraded in line with earlier suggestions the mineral component in yedoma icd functions as weight and surface protection of the associated oc which led to burial in the sediment and limited oc degradation the degradability of the terrestrial oc in shelf sediment was also addressed in direct incubation studies molecular markers indicate marine oc from primary production was more readily degraded than terrestrial oc degradation was also faster in sediment from the east siberian sea where the marine contribution was higher compared to the laptev sea although terrestrial carbon in the sediment was degraded slower the terrestrial component also contributed to carbon dioxide formation in the incubations of marine sediment these results contribute to our understanding of the marine fate of land derived oc from the siberian arctic the mobilization of topsoil oc is expected to grow in magnitude with climate warming and associated active layer deepening this translocated topsoil oc component was found to be highly degraded which suggests degradation during transport and a possible contribution to atmospheric carbon dioxide similarly the yedoma icd oc and or old mineral soil carbon may become a stronger source with accelerated warming but slow degradation may limit its impact on active carbon cycling in the siberian shelf seas

contrasts in arctic shelf sea ice regimes and some implications beaufort sea versus laptev sea the winter ice regime of the 500 km from the mainland than in the beaufort sea as a result the annual freeze up does not incorporate old deep draft ice and with a lack of compression such deep draft ice is not generated in situ as on the beaufort sea shelf the laptev sea has as much as 1000 km of fetch at the end of summer when freezing storms move in and large 6 m waves can form also for the first three winter months the polynya lies inshore at a water depth of only 10 m turbulence and freezing are excellent conditions for sediment entrainment by frazil and anchor ice when compared to conditions in the short fetched beaufort sea we expect entrainment to occur yearly different from the intensely ice gouged beaufort sea shelf hydraulic bedforms probably dominate in the laptev sea corresponding with the large volume of ice produced more dense water is generated in the laptev sea possibly accompanied by downslope sediment transport thermohaline convection at the midshelf polynya together with the reduced rate of bottom disruption by ice keels may enhance benthic productivity and permit establishment of open shelf benthic communities which in the beaufort sea can thrive only in the protection of barrier islands indirect evidence for high benthic productivity is found in the presence of walrus who also require year round open water by contrast lack of a suitable environment restricts walrus from the beaufort sea although over 700 km farther to the south we could speculate on other consequences of the different ice regimes in the beaufort and laptev seas but these few examples serve to point out the dangers of exptrapolating from knowledge gained in the north american arctic to other shallow arctic shelf settings

determination of bedload transport using naturally magnetic tracers first experiences at squaw creek gallatin county montana pebbles and cobbles constitute an important part of the sediment discharge of many streams data on the movement of this coarse bedload is important to a variety of studies including analysis of total sediment yield resevoir filling rates bridge erosion and trout spawning habitat despite the importance of knowledge regarding coarse bedload transport measurement remains difficult and unreliable a new detector has been constructed which records the movement of naturally magnetic pebbles and cobbles the detector was installed at a log sill in the bed of squaw creek gallatin county montana to evaluate the detector under natural conditions during a flood in may 1981 the detector recorded the passage of magnetic particles larger than 32 mm extrapolation of the data allows estimation of total bedload transport based on the composition of an unvegetated gravel bar upstream of the detector and on measurements of turbidity during the flood bedload accounted for approximately 66 of the solid material leaving the drainage basin since many coarse bed streams probably contain material as magnetic as the andesitic rocks in squaw creek the procedure should be widely applicable

temporal variations in bedload transport rates associated with the migration of bedforms temporal variations in bedload transport rates that occur at a variety of timescales even under steady flow conditions are accepted as an inherent component of the bedload transport process rarely however has the cause of such variations been explained clearly we consider three data sets obtained from laboratory experiments that refer to measurements of bedload transport made with continuously recording bedload traps each data set is characterized by a predominant low frequency oscillation on which additional higher frequency oscillations generally are superimposed the period of these oscillations as isolated through the use of spectral analysts ranged between 0 47 and 168 minutes and was associated unequivocally with the migration of bedforms such as ripples dunes and bars the extent to which such oscillatory behaviour may be recognized in a data set depends on the duration of sampling and the length of the sampling time with respect to the period of a given bedform several theoretical probability distribution functions have been developed to describe the frequency distributions of relative bedload transport rates that are associated with the migration of bedforms einstein 1937b hamamori 1962 carey and hubbell 1986 these distribution functions were derived without reference to a sampling interval we present a modification of hamamori s 1962 probability distribution function generated by monte carlo simulation which permits one to specify the sampling interval in relation to the length of a bedform comparisons between the simulated and observed frequency distributions that were undertaken on the basis of the data described herein are good significant at the 90 per cent confidence level finally the implications that temporal variability which is associated with the migration of bedforms have for the accurate determination of bedload transport rates are considered

bed load bias comparison of measurements obtained using two 76 and 152 mm helley smith samplers in a gravel bed river 1 we assess how the size of the helley smith hs bed load sampler nozzle affects the accuracy of bed load sampling semitheoretical considerations show that the larger grains resident on the streambed can influence the sample either by blocking the sampler entrance or by causing the sampler to rest in a perched position probabilities for interference can be derived from the distribution of grain sizes but they do not capture the actual complexity of the influence of the bed on sampler performance we therefore make an empirical comparison of sediment trapped by hs samplers with 76 and 152 mm intakes during floods in the gravel bed lower ebro river most bed load rates appeared higher when sampled with the hs152 the largest clasts collected by the hs76 also tend to be smaller than those obtained with the hs152 at the same flow analyzing paired bed load samples we find the probability of a bed load sample collected with the hs152 to be biased is around 43 in the conditions of the present study whereas 65 of samples were biased when obtained with the hs76 the analysis emphasizes the influence of bed material texture over sampler performance and demonstrates that the use of samplers with intake size much larger than bed grain size i e 5d will increase the accuracy of bed load grain size distributions and the precision of annual load estimates in gravel bed rivers

new aspects of organic carbon deposition and its paleoceanographic implications along the northern barents sea margin during the last 30 000 years we studied variations in terrigenous tom and marine organic matter mom input in a sediment core on the northern barents sea margin over the last 30 ka using a multiproxy approach we reconstructed processes controlling organic carbon deposition and investigated their paleoceanographic significance in the north atlantic arctic gateways variations in paleo surface water productivity are not documented in amount and composition of organic carbon the highest level of mom was deposited during 25 23 ka as a result of scavenging on fine grained reworked and tom rich material released by the retreating svalbard barents sea ice sheet during the late weichselian a second peak of mom is preserved because of sorptive protection by detrital and terrigenous organic matter higher surface water productivity due to permanent intrusion of atlantic water and high suspension load release by melting sea ice during 15 9 11 2 ka

the nahal yatir bedload database sediment dynamics in a gravel bed ephemeral stream the nahal yatir bedload transport database arises from the northern negev river sediment monitoring programme and represents the first body of bedload information to be collected during flash floods in desert gravel bed streams bedload flux was established automatically with three slot samplers of the birkbeck type this was complemented by hydraulic measurements that allow sediment transport to be rated against channel average shear stress and specific stream power bed material and bedload grain size distributions are also provided the database is given in both printed and electronic tabular format

threshold of coarse sediment transport in broad and narrow natural streams the threshold of coarse sediment transport has been examined in natural streambeds in an upland pennine u k area threshold values of the total boundary shear stress t0 for a given grain size in a narrow natural stream w d 11 efficiency in the entrainment process is related not only to the overall channel geometry but also varies as a function of discharge in channels characterized by compound roughness empirical curves relating t0 and a mean grain size d5 are presented but are limited in application to streams of similar physical and hydraulic characteristics as the ones examined in this investigation considerable divergence is noted between these empirical functions and a summary empirical function for general application obtained from a published source the reasons for this divergence are discussed the influence of grain shape was found not to be important in the initiation of motion criterion this conclusion may reflect the limited range of natural grain shapes in the study streams but might reasonably apply to other field investigations of similar streams modifications of the shields and yalin diagrams are suggested for practical applications in shallow streams with poorly graded bed material the shields parameter may be regarded as an inverse function of the relative protrusion of individual grains in the shallow flow depth d5 d the increased importance of augmented drag forces in the entrainment process in shallow flows is suggested as the physical explanation for the reduced values of the shields parameter however the relationships presented should not be applied to laboratory experiments concerned with well graded sediments therefore beds with little deviation in level in which the shields parameter may be regarded as constant at high reynolds grain numbers consistent estimated field values of a threshold sediment transport parameter might be used to compare field data to threshold values derived from statistical arguments and laboratory experiments reported in the literature

tracking nutrient and productivity variations over the last deglaciation in the arctic ocean we have reconstructed the surface water environment of the arctic ocean over the last 50 000 years using measurements of the organic nitrogen and carbon isotope ratios carbonate and total organic carbon concentrations toc and terrestrial biomarkers lignin and long chain n alkanes in four multicores variations in nitrogen isotope ratios that are concordant with toc and carbonate concentrations representing foraminifera and excluding ice rafted debris reflect differences in relative nutrient utilization of phytoplankton in the surface waters however 15n variations also appear to be dependent on the stratification of the water column and therefore potentially track the exchange of nutrients between deep and surface waters low last glacial maximum lgm 15n values and higher holocene values are opposite to those recorded in the southern ocean the arctic ocean with higher nutrient utilization today compared to the lgm therefore acts as a counterpart to the southern ocean although the global impact on carbon dioxide variations compared to the southern ocean is probably low

partial transport in a natural gravel bed channel 1 partial transport is documented in the gravel bed channel of carnation creek using magnetically tagged stones for four flood peaks the active proportion of surface grains was used to map streambed areas into distinct units of three different levels of grain entrainment in partially mobile regions of the bed the active proportion of surface grains declines with grain size as flow increases areas of partial transport grow at the expense of inactive areas and fully active areas replace areas with partial mobility approximately 25 50 of the bed remained in a state of partial mobility during a flood with a 2 year return period indicating that inactive regions of the bed surface typically persist from year to year during a flood with a 7 year return period surface grain entrainment was nearly complete indicating that full mobilization of surface grains is not a frequent event

on why gravel bed streams are paved bedload transport in poorly sorted gravel bed streams downstream of dams is considered bedload and typical bed material subpavement size distributions are observed to be similar it follows that the coarse half of the subpavement moves through a reach at a rate near that of the fine half since coarser grains are intrinsically less mobile than fine grains it follows that some mechanism must act to nearly equalize mobility it is hypothesized that the pavement seen in gravel bed streams at low flow is in fact in place during typical transport events capable of moving all available sizes this pavement can provide the equalizing mechanism by exposing proportionally more coarse grains to the flow field data are used to quantify this concept and to develop a predictive relation for river pavement the model indicates that pavement should be absent in most sand bed streams in agreement with observation

alkane distributions in arctic ocean sediments reply to alkane and pah biomarkers as tracers of terrigenous organic carbon in arctic ocean sediments by mark b yunker robie w macdonald lloyd r snowdon brian r fowler comment by vera petrova and co authors

bacterial hopanoids as tracers of organic carbon sources and processing across the western arctic continental shelf tracing the inputs of bacterial organic carbon to marine systems has been constrained by the lack of distinguishing geochemical tracers and limited contribution in sediments compared to other sources of organic matter bacteriohopanepolyols bhps provide a direct means to identify bacterial inputs which also reflect potential bacterial groups and their activities in aquatic systems we applied recent analytical approaches to identify and quantify bacterial derived carbon contributions to surface sediments from the western arctic ocean using bhps the abundance and distribution of bhps resemble trends of water column primary production and suggest active heterotrophic recycling of in situ production with some component of long term preservation bhps proposed as terrestrial derived signatures i e adenosylhopanes were also abundant in western arctic sediments and reflect offshore trends of other terrigenous lipid signatures with a fraction representing their degradative products analysis of bhps in organic rich peat and surface sediments from two arctic rivers showed the highest inputs of adenosylhopanes implying active bacterial recycling of recalcitrant terrigenous material bhps observed in western arctic surface sediments reveal significant contributions of bacteria associated with organic carbon from multiple sources

molecular stratigraphy a new tool for climatic assessment variations in sea surface temperatures over the past 500 000 years are inferred from the relative abundance behaviour of two organic compounds c37 alkenones over the upper 8 metres of a sediment core from the eastern equatorial atlantic this molecular record ascribed to contributions from prymnesiophyte algae correlates well with the variations in the 18 signal for the calcareous skeletons of certain planktonic foraminifera thus providing the first demonstration of a new stratigraphical technique which may be especially valuable where methods based on carbonate 18 fail

dimensionless critical shear stress in gravel bed rivers this paper first compiles critical shear stress values from 26 studies of gravel bed rivers gbrs worldwide the most frequently proposed value of the shields criterion c is 0 045 but three major groups with c values ranging from 0 100 were identified second dimensionless critical shear stresses the shields criterion were evaluated for 14 gbrs 18 sites with watershed areas ranging from 12 to 3000 km2 different approaches were used to identify the initial movement of the bed material painted and pit tag pebbles sediment traps and bedload samplers the shields criterion c was estimated using the total shear stress and the grain shear stress several shear stresses were also estimated using shear velocities for bedload transport we obtained an average shields criterion c of 0 040 the values were higher in small rivers 0 050 than larger rivers 0 030 because of more significant bedform shear stresses the shields criterion c was lower when the grain shear stress was used and only reached 0 019 different values are also proposed in relation to the type of mobilization the c value for partial transport was 0 025 and exceeded 0 040 for full transport usually reached in association with discharges with a 10 year return period the values based on the results of sediment traps and a bedload sampler were greater than those obtained using tracers but these differences are smaller than those usually reported in the literature

molecular characterization of suspended and sedimentary organic matter in an arctic delta curie point pyrolysis gas chromatography cupy gc and curie point pyrolysis gas chromatography mass spectrometry cupy gc ms were used to characterize the macromolecular organic content of suspended particles in surface waters at intermediate water depths and in the surface sediments of the lena delta and the adjacent laptev sea eastern siberia the chromatograms of the pyrolysates of the lena river particles revealed several compound classes of biogenic significance polysaccharides phenolic substances and lipid constituents of higher plants the pyrolysates of the surface suspended particles of the laptev sea suggested mixed inputs some fatty acids phytadienes and n alkylnitriles were assigned to planktonic organisms pyrolysis products from terrigenous material encountered in the river were also present at intermediate water depths major differences with respect to the surface particles were evident in all cases we observed a substantial decrease of the precursors of phytadienes and the fatty acids that undergo biotransformation processes a peculiar pattern of three series of c14 c16 and cl8 alkanes and alkenes normal alkane the alki ene the e alk 2 ene and the z alk 2 ene was the prominent feature of these pyrolysates further investigations of the particle solvent extract and the corresponding residue suggested that these alkenes as well as the fatty acids derived from wax esters the composition of the sedimentary material in the laptev sea indicated preservation of the refractory terrigenous constituents however the presence of some algal constituents suggested that a fraction of marine derived macromolecules9 is resistant to degradation the arctic ocean is unique because of its ice cover and limited water exchange with surrounding oceans the marginal seas occupy 70 of this area and their physiography is such that broad shallow continental shelves coincide with the outflow of major rivers arctic environments have been poorly investigated in this respect the role of the arctic ocean and adjacent marginal seas in the global carbon budget has been neglected among other high latitude ecosystems the siberian aquatorium is of interest because of considerable discharge of major world rivers such as the lena yana ob and yenisei the lena river ranked the eighth largest world river discharging to the ocean has an annual water discharge entering the laptev sea of 525 km3 and a sediment discharge of 17 6 x 1 o6 t yr l which corresponds to an

holocene paleoenvironmental implications of diatom and organic carbon records from the southeastern kara sea siberian margin diatom assemblages and organic carbon records from two sediment cores located within an estuarian bay of the inner kara sea trace changes in yenisei river runoff and postglacial depositional environments paleosalinity and sea ice reconstructions are based on modern relationships of local diatom assemblages and summer surface water salinity approximately 15 500 cal yr b p rivers and bogs characterized the study area when sea level reached the 38 to 40 m paleo isobath approximately 9300 cal yr b p the coring site was flooded from 9300 9100 cal yr b p estuarine conditions occurred proximal to the depocenter of fluvially derived material and salinity was 7 8 paleosalinity increased to 11 13 by 7500 cal yr b p following postglacial sea level rise and the southward shift of the siberian coast sharp decreases in diatom accumulation rates total sediment and organic carbon also occurred suggesting the presence of brackish conditions and greater distance between the coast and study site maximum paleosalinity up to 13 was recorded between 7500 and 6000 cal yr b p which was likely caused by the enhanced penetration of atlantic waters to the kara sea stepwise decreases to modern salinity levels happened over the last 6000 cal yr

variation in the reference shields stress for bed load transport in gravel bed streams and rivers 1 the present study examines variations in the reference shear stress for bed load transport r using coupled measurements of flow and bed load transport in 45 gravel bed streams and rivers the study streams encompass a wide range in bank full discharge 1 2600 m3 s average channel gradient 0 0003 0 05 and median surface grain size 0 027 0 21 m a bed load transport relation was formed for each site by plotting individual values of the dimensionless transport rate w versus the reach average dimensionless shear stress the reference dimensionless shear stress r was then estimated by selecting the value of corresponding to a reference transport rate of w 0 002 the results indicate that the discharge corresponding to r averages 67 of the bank full discharge with the variation independent of reach scale morphologic and sediment properties however values of r increase systematically with average channel gradient ranging from 0 025 0 035 at sites with slopes of 0 001 0 006 to values greater than 0 10 at sites with slopes greater than 0 02 a corresponding relation for the bank full dimensionless shear stress bf formulated with data from 159 sites in north america and england mirrors the relation between r and channel gradient suggesting that the bank full channel geometry of gravel and cobble bedded streams is adjusted to a relatively constant excess shear stress bf r across a wide range of slopes

particle size variations between bed load and bed material in natural gravel bed channels particle sizes of bed load and bed material that represent materials transported and stored over a period of years are used to investigate selective transport in 13 previously sampled natural gravel bed channels the ratio d of median particle size of bed material to the transport and frequency weighted mean of median bed load size decreases to unity with increasing drainage area bank full discharge dimensionless stream power and bed material sorting in channels with high values of d significant volumes of fine bed load are transported during discharges that are less than bank full which is commonly associated with general entrainment of the coarse pavement in many gravel bed channels this indicates transport of fine bed load over a more stable substrate of coarser bed material the apparent breakdown in equal mobility of the bed as a whole may be caused by areal segregation of poorly sorted bed material into superiorly sorted patches of varying mean size likely sources of selectively transported fine bed load include fine patches that have low entrainment thresholds and high virtual particle velocities a simple sediment budget applied to measurements from three channels indicates that velocities of material from fine patches in pools relative to velocities of average bed material are high in low order channels and decrease distally as more bed material that represents the bed as a whole is accessed for bed load by deeper annual scour

appraisal of tex86 and tex86l thermometries in subpolar and polar regions tex86 tetraether index of tetraethers consisting of 86 carbon atoms is a sea surface temperature sst proxy based on the distribution of archaeal isoprenoid glycerol dialkyl glycerol tetraethers gdgts in this study we appraise the applicability of tex86 and view the mathml sourcetex86l in subpolar and polar regions using surface sediments we present tex86 and view the mathml sourcetex86l data from 160 surface sediment samples collected in the arctic the southern ocean and the north pacific most of the sst estimates derived from both tex86 and view the mathml sourcetex86l are anomalously high in the arctic especially in the vicinity of siberian river mouths and the sea ice margin plausibly due to additional archaeal contributions linked to terrigenous input we found unusual gdgt distributions at five sites in the north pacific high gdgt 0 crenarchaeol and gdgt 2 crenarchaeol ratios at these sites suggest a substantial contribution of methanogenic and or methanotrophic archaea to the sedimentary gdgt pool here apart from these anomalous findings tex86 and view the mathml sourcetex86l values in the surface sediments from the southern ocean and the north pacific do usually vary with overlaying ssts in these regions the sedimentary tex86 sst relationship is similar to the global calibration and the derived temperature estimates agree well with overlaying annual mean ssts at the sites however there is a systematic offset between the regional view the mathml sourcetex86l sst relationships and the global calibration at these sites temperature estimates based on the global view the mathml sourcetex86l calibration are closer to summer ssts than annual mean ssts this finding suggests that in these subpolar settings a regional view the mathml sourcetex86l calibration may be a more suitable equation for temperature reconstruction than the global calibration

the incidence and nature of bedload transport during flood flows in coarse grained alluvial channels a continuous record reveals that the incidence of bedload in a coarse grained river channel changes from flood to flood long periods of inactivity encourage the channel bed to consolidate sufficiently so that bedload is largely confined to the recession limb of the next flood wave but when floods follow each other closely the bed material is comparatively loose and offers less resistance to entrainment in this case substantial amounts of bedload are generated on the rising limb this is confirmed by values of bed shear stress or stream power at the threshold of initial motion which can be up to five times the overall mean in the case of isolated floods or those which are the first of the season this produces a complicated relationship between flow parameters and bedload and explains some of the difficulties in establishing bedload rating curves for coarse grained channels besides this the threshold of initial motion is shown to occur at levels of bed shear stress three times those at the thresholds of final motion this adds further confusion to attempts at developing predictive bedload equations and clearly indicates at least one reason why equations currently in use are unsatisfactory bedload is shown to be characterized by a series of pulses with a mean periodicity of 1 7 hours in the absence of migrating bedforms it is speculated that this well documented pattern reflects the passage of kinematic waves of particles in a slow moving traction carpet the general pattern of bedload including pulsations is shown to occur more or less synchronously at different points across the stream channel