ferromanganese oxide deposits from the central pacific ocean i encrustations from the line islands archipelago abstract chemical and mineralogical analyses of a well controlled suite of ferromanganese encrustations from the line islands archipelago central pacific suggest that they represent purely hydrogenous deposits i e they have formed through the slow accumulation of trace metal enriched oxides directly from the water column mineralogically they consist predominantly of mno2 and amorphous feoohxh2o compositionally they are similar to mno2 nodules from adjoining basinal areas but are enriched in both mn mean 20 4 max 29 3 and co mean 0 55 max 1 57 mno2 is the most important trace metal bearing phase strong associations are noted between it and co mo ni zn and cd whilst only be is associated specifically with feooh v sr and pb are partitioned between the authigenic oxide phases whilst ti most probably occurs as tio2xh2o cu is contained in both aluminosilicate contaminant phases and fe oxide phases these relations are considered to reflect the differing scavenging behaviour of mn and fe oxides in the water column crusts from 1 2 km are enriched in mn and the mn related elements and exhibit higher mn fe ratios than deeper crusts which are compositionally constant the higher mn fe ratios may result from a supply of mn from continental borderland sediments at these depths which is transported horizontally by advective diffusive processes since manganophile elements are enriched relative to mn in the 1 2 km crusts it is considered that the supply of mn is scavenged by existing oxides is oxidised and effectively occludes them a higher proportion of oxide particles thus exhibit mn oxide scavenging properties in the 1 2 km depth zone the increased vertical flux of mn resulting from the supply at 1 2 km is not reflected by higher mn fe ratios in deeper crusts so that the vertical flux of oxides is not simply related to the standing crop the mn fe ratios of the crusts thus reflect the composition of suspended oxides at similar depths

surface based transport model for mixed size sediment we present a transport model for mixed sand gravel sediments fractional transport rates are referenced to the size distribution of the bed surface rather than subsurface making the model completely explicit and capable of predicting transient conditions the model is developed using a new data set of 48 coupled observations of flow transport and bed surface grain size using five different sediments the model incorporates a hiding function that resolves discrepancies observed among earlier hiding functions the model uses the full size distribution of the bed surface including sand and incorporates a nonlinear effect of sand content on gravel transport rate not included in previous models the model shares some common elements with two previous surface based transport models but differs in using the full surface size distribution and in that it is directly developed from a relatively comprehensive data set with unambiguous measurement of surface grain size over a range of flow transport rate and sediments

embedding reach scale fluvial dynamics within the caesar cellular automaton landscape evolution model abstract we introduce a new computational model designed to simulate and investigate reach scale alluvial dynamics within a landscape evolution model the model is based on the cellular automaton concept whereby the continued iteration of a series of local process rules governs the behaviour of the entire system the model is a modified version of the caesar landscape evolution model which applies a suite of physically based rules to simulate the entrainment transport and deposition of sediments the caesar model has been altered to improve the representation of hydraulic and geomorphic processes in an alluvial environment in channel and overbank flow sediment entrainment and deposition suspended load and bed load transport lateral erosion and bank failure have all been represented as local cellular automaton rules although these rules are relatively simple and straightforward their combined and repeatedly iterated effect is such that complex non linear geomorphological response can be simulated within the model examples of such larger scale emergent responses include channel incision and aggradation terrace formation channel migration and river meandering formation of meander cutoffs and transitions between braided and single thread channel patterns in the current study the model is illustrated on a reach of the river teifi near lampeter wales uk

a transferable method for the automated grain sizing of river gravels 1 the spatial and temporal resolution of surface grain size characterization is constrained by the limitations of traditional measurement techniques in this paper we present an extremely rapid image processing based procedure for the measurement of exposed fluvial gravels and other coarse grained sediments defining the steps required to minimize the errors in the derived grain size distribution this procedure differs significantly from those used previously it is based around a robust object detection algorithm that produces excellent results on images exhibiting a wide range of sedimentary conditions crucially without any user intervention or site specific parameterization the procedure is tested using a data set comprising 39 images from three rivers with contrasting grain lithology shape roundness and packing configuration and representing a very wide range of textures it is shown to perform more consistently than the best existing automated method achieving a precision equivalent to that obtainable by wolman sampling but taking between one sixth and one twentieth of the time the error in area by number grain size distribution percentiles is typically less than 0 05

calcite dissolution in sediments of the ceara rise in situ measurements of porewater o2 ph and co2 aq in situ electrode measurements of porewater oxygen and ph from four sites on the ceara rise in the western tropical atlantic unequivocally demonstrate that calcite dissolution driven by metabolic co2 produced within the sediments is a significant part of the diagenesis of sedimentary calcite dissolving at least 20 of the calcite rain to the seafloor the first ever in situ absorbance based measurements of porewater co2 aq support the dissolution estimates based on models of the observed ph distributions and are incompatible with scenarios excluding metabolic co2 driven dissolution our dissolution estimates are consistent with those estimated by an independent study of porewater calcium and alkalinity profiles martin and sayles 1996 at this location the consistency of these disparate porewater measurements and our ability to interpret them with simple models of respiration and dissolution implies that no special mechanism is required to describe this process the calcite dissolution rate constant in the sediments of the deepest station in this study is significantly higher than determined by in situ studies at other locations values approach those determined by early laboratory measurements the dissolution rate constant here must be at least two orders of magnitude higher than for calcite in sediments on the ontong java plateau based on in situ electrode measurements there hales and emerson 1996 the calcite solubility consistent with these data is not compatible with that consistent with the ontong java data the reason for this difference is currently unresolved but may be due to the high order of the empirical dissolution rate law assumed in this study

modelling differential catchment response to environmental change the caesar cellular automaton evolutionary slope and river model is used to demonstrate significant differences in coarse sediment transfer and alluviation in medium sized catchments when responding to identical holocene environmental changes simulations for four u k basins the rivers swale ure nidd and wharfe shows that catchment response driven by climate and conditioned by land cover changes is synchronous but varies in magnitude there are bursts of sediment transfer activity generally of rapid removal but with some sediment accumulation dspikest with longer periods of slow removal or accumulation of sediment in different valley reaches within catchments reach sensitivity to environmental change varies considerably some periods are only recorded in some reaches whilst higher potential sensitivity typically occurs in the piedmont areas of the catchments modelled here these differential responses appear to be highly non linear and may relate to the passage of sediment waves by variable local sediment storage and availability and by large and small scale thresholds for sediment transfer within each catchment differential response has major implications for modelling fluvial systems and the interpretation of field data model results are compared with the record of dated alluvial deposits in the modelled catchments d 2005 elsevier b v all rights reserved

a cellular model of river meandering river meandering has been successfully modelled using vector based methods but these can not simulate multiple or braided channels conversely cellular braided river models fail to replicate meandering this paper describes a new method to simulate river meandering within a cellular model caesar a novel technique for determining bend radius of curvature on a cell by cell basis is described that importantly allows regional information on bend curvature to be transferred to local points this local curvature is then used to drive meandering and lateral erosion through two methods key difficulties are identified including the deposition of material on point bars and cut off development but the method illustrates how meandering can be integrated within a cellular framework this demonstrates the potential to produce a single model that can incorporate both meandering and braiding copyright 2006 john wiley sons ltd

the oxidation state of manganese in marine sediments and ferromanganese nodules marine sediments and ferromanganese nodules from the pacific ocean have been analyzed for the omn ratio of solid manganese we tested six chemical methods and concluded that the iodometric and oxalate methods were equivalent and were the best choice in terms of accuracy and precision on natural samples we choose the iodometric method for most of our analyses because the oxalate procedure is a method of differences the ferromanganese nodules that we analyzed were all from manop site h and had mnfe ratios that ranged from 5 6 to 70 these nodules were invariably highly oxidized with omn values ranging from 1 90 to 2 00 our most precise analyses suggest that less than 1 of the total manganese is present as mn ii we also analyzed red clay and hemipelagic sediments from the eastern tropical pacific baja borderland and manop site h and carbonate ooze samples from the equatorial pacific these sediments are also highly oxidized omn 1 90 to 2 00 except when mn ii appears in the interstitial water as dissolved mn ii increases the value of the omn ratio in the solid phase decreases the omn ratio decreases to values as low as 1 40 this decrease appears to be due to a decrease in oxidized manganese by reduction however an increase in reduced manganese in the solid sediments by adsorption or mnco3 formation can not be ruled out in all cases

micromorphological characteristics of a marine ferromanganese crust abstract marine ferromanganese oxide crust fragments sampled from a massive equatorial pacific ocean crust deposit exhibit distinct micromorphological features and a microchemical distribution which have not been previous reported black shiny upper layers of the crust display a prismoidal microstructure and a unique crystallite habit expressed by a mosaic like design of hexagonal and pentagonal columns this columnar arrangement which has been previously reported on a scale of a few millimeters in other marine fe mn deposits extends vertically for several centimeters and is observed throughout the entire horizontal plane of growth of the crust and is the largest scale of morphological regularity observed in marine fe mn deposits to date the polygonal columnar structures which constitute the crust are mainly composed of mn fe and ti oxides aluminium and si rich intercolumnar space lamellae surrounds individual columns and sharply defines each polyhedron additionally the chemical composition of the crust fragments exhibits an unusual uniformity over several centimeters which to our knowledge has not been previously observed in marine fe mn minerals

cellular modelling of river catchments and reaches advantages limitations and prospects the last decade has witnessed the development of a series of cellular models that simulate the processes operating within river channels and drive their geomorphic evolution their proliferation can be partly attributed to the relative simplicity of cellular models and their ability to address some of the shortcomings of other numerical models by using relaxed interpretations of the equations determining fluid flow cellular models allow rapid solutions of water depths and velocities these can then be used to drive usually conventional sediment transport relations to determine erosion and deposition and alter the channel form the key advance of using these physically based yet simplified approaches is that they allow us to apply models to a range of spatial scales 1 100 km 2 and time periods 1 100 years that are especially relevant to contemporary management and fluvial studies however these approaches are not without their limitations and technical problems this paper reviews the findings of nearly 10 years of research into modelling fluvial systems with cellular techniques principally focusing on improvements in routing water and how fluvial erosion and deposition including lateral erosion are represented these ideas are illustrated using sample simulations of the river teifi wales a detailed case study is then presented demonstrating how cellular models can explore the interactions between vegetation and the morphological dynamics of the braided waitaki river new zealand finally difficulties associated with model validation and the problems prospects and future issues important to the further development and application of these cellular fluvial models are outlined 2007 elsevier b v all rights reserved

particle clusters in gravel bed rivers an experimental morphological approach to bed material transport and stability concepts structured gravel river beds clearly exert a major influence on bed stability indexing structural stability by field measurements of bed strength neglects the processes operating to entrain and transport bed material in different parts of each structure this study takes a morphological approach to interpreting the critical processes using particle tracing to determine the movement of individual cluster particles over a range of flood event magnitudes and durations the experiment was carried out on the river south tyne uk it uses flow hydrographs measured nearby and also benefits from previous studies of historical development channel morphology and sediment transport at the same site more than 30 clusters were monitored over a seven month period during which clusters occupied 7 16 per cent of the bed threshold flows delimiting three apparently contrasting bed sediment process regimes for cluster particles are tentatively set at 100 m3 s 1 and 183 m3 s 1 durations of flow at these levels are critical for cluster development rather than flow peak values wake particles are transported most easily flow straightening in the wandering channel planform reduces the stability of clusters since mechanical strength is markedly reduced by this change of direction the overall area covered by clusters between significant transport events varies little implying a dynamic equilibrium condition copyright 2005 john wiley sons ltd

storage filters upland suspended sediment signals delivered from watersheds climate change tectonics and humans create long and short term temporal variations in the supply of suspended sediment to rivers these signals generated in upland erosional areas are filtered by alluvial storage before reaching the basin outlet we quantified this filter using a random walk model driven by sediment budget data a power law distributed probability density function pdf to determine how long sediment remains stored and a constant downstream drift velocity during transport of 157 km yr for 25 km of transport few particles are stored and the median travel time is 0 2 yr for 1000 km of transport nearly all particles are stored and the median travel time is 2 5 m y both travel time distributions are power laws the 1000 km travel time distribution was then used to filter sinusoidal input signals with periods of 10 yr and 10 4 yr the 10 yr signal is delayed by 12 5 times its input period damped by a factor of 380 and is output as a power law the 10 4 yr signal is delayed by 0 15 times its input period damped by a factor of 3 and the output signal retains its sinusoidal input form but with a power law tail delivery time scales for these two signals are controlled by storage in channel transport time is insignificant and low frequency signals are transmitted with greater fidelity than high frequency signals these signal modifications are essential to consider when evaluating watershed restoration schemes designed to control sediment loading and where source area geomorphic processes are inferred from the geologic record

the chronology and stratigraphy of the alluvial terraces of the river dane valley cheshire n w england three groups of alluvial terraces together with the modern floodplain mark the postglacial development of the middle part of the dane valley cheshire these are a high terrace group of late pleistocene age a middle terrace group of late pleistocene to early holocene age a low terrace of mid late holocene age and a modern post ca 1840 ad floodplain a chronology of erosion deposition and landform development since mid holocene times is established in this paper on the basis of terrace morphology stratigraphy sedimentology soil analysis magnetic mineral analysis and four radiocarbon dates after dissection of the middle terrace during the early to mid holocene a long period of lateral activity by the river was followed by a major aggradation phase which formed the low terrace surface this was followed by dissection during the last ca 300 years and the development of the modern floodplain since ca 1840 ad various explanations for the changes during the holocene are considered the low terrace aggradation appears to be related to a major phase of mediaeval soil erosion

caco3 dissolution in sediments of the ceara rise western equatorial atlantic we have used porewater sampling by in situ techniques including whole core squeezing as well as by shipboard sectioning and whole core squeezing to estimate the rates of sedimentary organic matter oxidation and caco3 dissolution at seven sites on the ceara rise in the western equatorial atlantic ocean porewater no3 profiles at all sites show a pattern indicative of active organic matter oxidation in the upper 15 20 cm of the sediments and in a buried organic rich layer the organic c oxidation rate generally decreases with increasing water depth from a value of 22 mol cm2 y at the shallowest site 3279 m to 14 mol cm2 y at the deepest site 4675 m over this depth range the bottomwaters vary from moderately supersaturated with respect to calcite to strongly undersaturated high resolution alkalinity profiles measured in porewaters collected by in situ whole core squeezing yield estimated ca2 fluxes of 11 mol cm2 y at a site located at the depth of the calcite saturation horizon and 7 6 zmol cm2 y at a moderately undersaturated site ca2 fluxes calculated from profiles in porewaters collected by relatively coarse resolution in situ sampling methods clearly indicate that there is caco3 dissolution above the calcite saturation horizon the dissolution of aragonite may contribute to the dissolution flux at the shallowest site these ca2 fluxes as well as fluxes estimated from a model of sedimentary organic matter oxidation and calcite dissolution indicate that 36 66 of the caco3 rain to the seafloor dissolves at sites at and above the calcite saturation horizon while 52 75 of the rain dissolves at sites below this depth when these results are incorporated into the oceanic caco3 budget of milliman 1993 they indicate that 35 of caco3 production is preserved in the deep sea they suggest a caco3 accumulation rate that is 27 lower than that estimated by milliman 1993 our corg oxidation caco3 dissolution model indicates that a large fraction of the caco3 dissolution that is occurring on the ceara rise is attributable to the neutralization of metabolic acids produced during organic matter oxidation the efficiency with which organic matter oxidation dissolves caco3 that is the ratio caco3 dissolution attributable to organic matter oxidation organic matter oxidation rate generally increases as degree of undersaturation of bottomwaters increases however there are deviations from the general trend that can be attributed to site to site variations in the kinetics of organic matter oxidation and calcite dissolution this result indicates that the dissolution of caco3 as a result of organic matter oxidation in the deep sea may mask the effects of variations in surface water caco3 productivity and bottomwater chemistry on the accumulation rate of caco3 in deep sea sediments

geochemistry of ferromanganese nodules from domes site a northern equatorial pacific multiple diagenetic metal sources in the deep sea abstract the major and minor element composition of ferromanganese nodules from domes site a has been determined by x ray fluorescence methods three phases appear to control the bulk compositions mn and fe oxyhydroxides and aluminosilicates relatively wide compositional variations are evident throughout the area nodules with high mn fe ratios high cu mg mo ni and zn concentrations and high todorokite mno 2 ratios have granular surface textures and are confined to an east west trending depression with thin quaternary sediment cover nodules with low mn fe ratios high concentrations of as ca ce co la p sr ti v y and zr and low todorokite mno 2 ratios have smooth surfaces and are confined to shallower areas with relatively thick quaternary sediment to the north and south of the depression all nodules in the area have compositions which are influenced by diagenesis but those with the most marked diagenetic signature high mn fe and cu ni ratios low ce la ratios and more todorokite are found in areas of very slow or non existent sedimentation many of these nodules are actually in contact with outcropping tertiary sediment this paradox may be resolved by postulating by analogy with some shallow water occurrences that the nodules accrete from bottom waters which have enhanced particulate and dissolved metal contents derived from diagenetic reaction in areas remote from the site of nodule formation the metals are supplied in a bottom flow probably antarctic bottom water which also erodes or prevents modern sedimentation in the depression nodules on the flanks of the depression are not evidently affected by this flow and derive at least pan of their constituent metals from diagenetic reaction in the underlying quaternary sediment apparently abyssal diagenetic nodules can have an immediate and a remote diagenetic metal source metal fluxes derived from pore water dissolved metal gradients may not be relevant to particular accreting nodules if a significant fraction of their metals is derived from outside the area in which they form

modelling landscape evolution geomorphology is currently in a period of resurgence as we seek to explain the diversity origins and dynamics of terrain on the earth and other planets in an era of increased environmental awareness yet there is a great deal we still do not know about the physics and chemistry of the processes that weaken rock and transport mass across a planet s surface discovering and refining the relevant geomorphic transport functions requires a combination of careful field measurements lab experiments and use of longer term natural experiments to test current theory and develop new understandings landscape evolution models have an important role to play in sharpening our thinking guiding us toward the right observables and mapping out the logical consequences of transport laws both alone and in combination with other salient processes improved quantitative characterization of terrain and process and an ever improving theory that describes the continual modification of topography by the many and varied processes that shape it together with improved observation and qualitative and quantitative modelling of geology vegetation and erosion processes will provide insights into the mechanisms that control catchment form and function this paper reviews landscape theory in the form of numerical models of drainage basin evolution and the current knowledge gaps and future computing challenges that exist copyright 2010 john wiley sons ltd

coarse sediment connectivity in river channel systems a conceptual framework and methodology identification of coarse sediment connectivity down river channel systems is important for understanding the linkages between river reaches the influence of sediment sources on channel morphology and the mechanisms and liability to propagation of morphological change a conceptual framework is developed in which several types and degrees of connectivity are proposed it is hypothesised that sediment connectivity varies with sediment sources and with stream competence to transport the coarse fractions a method of identifying the status of reaches is developed based on field mapping of morphology and sedimentology the analysis is exemplified by two channels one an ephemeral channel in se spain the other a perennial channel in nw england questions arise over whether reaches that lack channel stores transfer coarse sediment three scenarios are suggested 1 lack of flux due to lack of competence of the reach 2 flushing through of sediment due to high competence and 3 potential transport of coarse sediment but exhaustion or lack of availability changes in connectivity will take place over different time scales depending on the nature of exchange and time scales of storage short term variations in connectivity can be identified by repeated mapping

the influence of the carbonate dissolution rate on the growth and composition of co rich ferromanganese crusts from central pacific seamount areas abstract the metal composition of oceanic ferromanganese deposits occurring in seamount regions line islands chain and mid pacific mountains varies with water depth and age the results of metal determinations of carbonate plankton samples suggest that carbonate dissolution in the water column might have an important influence on the accretion and composition of hydrogenetic precipitates two ferromanganese crust generations of different age have been observed the precipitation of the older crust took probably place during early oligocene the younger crust began to form during middle miocene between the two crust generations periods of carbonate sedimentation and of phosphorite deposition occur the hydrogenetic formation of the crusts is controlled by the metal supply from the water column according to the laws of colloidal surface chemistry dissolution experiments with carbonate plankton samples show that the main fe source for the hydrogenetic crust formation are colloidal fe hydroxide particles being released in the water column from the dissolution of carbonate plankton skeletons in the case of mn maximum dissolved mn occurs in the oxygen minimum zone as the result of in situ break down of organic matter and the in situ reduction of mn bearing solid phases closely beneath the oxygen minimum zone a fe supply mobilized within the oxygen minimum zone has also to be taken into account in the water column below the oxygen minimum zone a mixture of colloidal particles of mn fe oxyhydroxide and colloidal al fe silicate precipitate together on the surface of substratum rocks the mixing ratio of these colloidal phases controlling the metal composition of the ferromanganese precipitates is depth dependent and shows also temporal variations in general mn fe ratio ni and co contents decrease with depth down to the calcite compensation depth the most probable mechanism for the ultimate removal of co and ni from the water column might be a surface reaction mno2 is specifically able to absorb hydrous co2 and ni2 ions because of the surface enrichment of co and the strong electrical field of mn iv a subsequent oxidation of co2 to co3 takes place leading to higher enrichment of co in comparison to ni the most important factor governing the high co enrichment in the ferromanganese crusts is the growth rate the lower the growth rate the higher the co content maximum values of up to 2 co occurring in samples from water depths between 1500 and 1100 m 1 are related to lower carbonate dissolution rates and corresponding lower fe supply the metal supply from the water column is strongly related to distinct environmental factors such as bio productivity range of lysocline and calcite compensation depth rate of carbonate dissolution and activity of the antarctic bottom water thus our model shows that the growth periods and the metal composition of hydrogenetic seamount crusts are controlled by changes in the paleoceanography and reflect distinct environmental conditions

net local removal of floodplain sediment by river meander migration abstract erosion from the banks of meandering rivers causes a local influx of sediment to the river channel most of the eroded volume is usually replaced in nearby point bars however the typical geometry of river bends precludes the local replacement of all eroded material because i point bars tend to be built to a lower elevation than cutbanks and ii point bars tend to be shorter than the eroding portion of cutbanks because of channel curvature in a floodplain that is in equilibrium i e neither increasing nor decreasing in volume sediment eroded from cut banks must be replaced elsewhere on the floodplain the local imbalance caused by differences in bank height should be balanced primarily by overbank deposition while the local imbalance caused by curvature should be balanced primarily by deposition in abandoned stream courses or oxbow lakes estimates of these local imbalances based on remotely sensed measurements of bank geometry and channel migration have been made on four systems in the united states a 91 km reach of the pearl river in louisiana and mississippi a 62 km reach of the bogue chitto river in louisiana a 35 km reach of the neuse river in north carolina and a 2 7 km reach of the vermillion river in minnesota for these systems the total local imbalance integrated over many bends ranged from 0 36 to 2 27 m 3 yr m of valley length 0 15 to 1 32 m 3 yr m of channel length or 7 to 45 of gross cutbank erosion with a typical value of about 17 when compared with gauged suspended sediment data the measurements provide estimates of the relative importance of floodplains for storing material transported by a river system the data suggest that even if the studied systems are near long term mass balance equilibrium as opposed to undergoing net deposition or erosion almost all of the sand and in some cases much of the silt and clay in transit through these systems is likely to have spent some time stored in an upstream floodplain

late pleistocene evolution of the ocean s carbonate system abstract we demonstrate that the carbonate record from a single site ocean drilling program site 1089 in the deep south atlantic represents a qualitative high resolution record of the temporal evolution of the carbonate saturation state of the deep sea the record is especially notable because it is free from many of the complications that limit other records low sedimentation rates blurring by chemical erosion bioturbation etc the pattern of carbonate variability is characteristic of indo pacific cores with high carbonate glacials and low carbonate interglacials wt carbonate lags changes in benthic 18 o by an average of 7 6 kyr and carbonate variations are in phase with the rate of change first derivative of benthic 18 o intense dissolution occurs at the transition from interglacial to glacial periods and increased preservation occurs during deglaciations these observations represent two fundamentally different responses of the marine carbonate system the lagged response of carbonate to 18 o reflects a steady state mass balance process whereby the lysocline adjusts to maintain alkalinity balance between riverine input and marine burial the site 1089 carbonate signal is remarkably similar to inferred changes in the sr ca of seawater for the past 250 kyr which implies that both carbonate dissolution and seawater sr ca may be controlled by sea level induced changes in the location of carbonate deposition shelf basin fractionation during glacial to interglacial cycles the transient change in preservation during the transitions into and out of glacial stages reflects a response of the carbonate system to a redistribution of alkalinity and dic in the ocean i e carbonate compensation comparison of the site 1089 carbonate and vostok p co 2 records suggests a role of deep sea co 3 2 variations for governing at least some second order features of the atmospheric p co 2 signal in order to quantify this role however measurement of indices of dissolution along a true depth transect will be required to estimate the magnitudes of changes in deep sea co 3 2

the chemical and physical speciation of trace metals in fine grained overbank flood sediments in the tyne basin north east england deposition of fine sediment contaminated by heavy metals on floodplains in the tyne basin north east england during a major flood in august 1986 provided an unusual opportunity to investigate the chemical and physical speciation of metals in overbank fines selective extractions and heavy liquid analyses were used to assess the chemical forms of sediment associated metal and the relationship between grain size density and metal concentration and to identify sources of metalliferous material generally the highest concentrations of trace metals were found in the 500 250 m size range and in the heavier density fractions 3 3 gml 1 though more than 60 of metals reported to the lightest 3 3 gml 1 density product the principal source of metals appeared to be reworked alluvium contaminated by historic mining activity metal concentrations in flood sediment decrease downstream from former mining areas though at varying rates depending on the physical propeties and chemical phase of individual metals with the exception of cu dominated by lithogenic fraction metals are primarily associated with fe mn oxides pb zn and to a lesser extent with carbonates cd zn organic matter zn cu and an operationally defined exchangeable cd component in the upper and middle parts of the tyne basin physical processes of downstream sediment metal content reduction were found to predominate while in the lower reaches of the tyne sediment metal transport appears to be governed by chemical sorption desorption processes associated with fe mn oxides and organic material finally the results of the study are discussed in a wider context of particulate metal transport in rivers and recommendations are made for refining density based models of metal dispersal

modeling long term contamination in river systems from historical metal mining heavy metal contamination of sediments within river systems is a major environmental problem around the world deposited as a by product of metal mining contaminated sediments are persistent and widespread frequently affecting large areas of floodplains which makes precise assessments of contamination levels and patterns difficult this paper describes findings from a new generic catchment sediment model called tracer which uses historical mining records to accurately predict present day and future levels and patterns of contamination this model provides detailed views of the extent of contami nation and demonstrates how contaminated sediments form into hot spots which in turn become secondary sources of pollution the exceptional longevity of the contamina tion is also revealed 70 of the deposited contaminants remain within the river system for 200 yr after mine closure simulations of the impact of future climate changes in northern england show that increased flood magnitudes are likely to decrease surface contamination through dilution by cleaner sediment from hillslopes unaffected by mining activity

quantifying fluvial non linearity and finding self organized criticality insights from simulations of river basin evolution abstract a numerical study was undertaken to investigate non linearity and the potential for self organized criticality soc in the evolution of river basins twenty three simulations were carried out using the authors caesar landscape evolution model in which the magnitude of storm events variability of storm events sediment heterogeneity sources of sediment supply and catchment morphology are systematically varied to evaluate their importance as possible drivers for non linear behavior and soc temporal fluctuations in simulated sediment yield show notable non linear behavior storm magnitude and occurrence of landslides appear to have little impact on variability of the sediment yield when compared to the impacts of sediment heterogeneity rainfall variability and catchment morphology particularly it appears that the non linearity of sediment yields results from the manner in which the catchment processes the variable rainfall rather than just the rainfall variability itself the variations in sediment yield show a power law magnitude frequency distribution which is a possible but inconclusive indicator of soc however several other more qualitative arguments can be made to support the case for soc in these simulations specifically we identify the nature of the critical state and suggest two cascade mechanisms by which the system can organize itself around this critical state combined these arguments indicate that simulated evolution of river basins indeed exhibits soc at least with respect to sediment yield the critical state appears to be an indicator of the connectivity of the drainage network thus the simulations indicate that unlike traditional soc systems the critical state of the system can vary in time as sudden changes in drainage network connectivity may result in sudden changes in the soc behavior of the system

australasian microtektites in a substrate a new constraint on ferromanganese crust accumulation rates abstract microtektites belonging to the australasian tektite strewn field are found in the substrate of a ferromanganese crust dredged from the central indian basin they are identified on their physical appearance geographic occurrence and chemical composition the ferromanganese crust has a thickness range of 6 17 mm and its chemistry and mineralogy indicate hydrogenic accretion because the australasian strewn field has an age of 0 77 ma this finding implies that the overlying fe mn crust has minimum accretion rates of 7 8 22 1 mm myr which are much higher than the average growth rates of hydrogenic crusts

cobalt and platinum rich ferromanganese crusts and associated substrate rocks from the marshall islands abstract ferromanganese crusts cover most hard substrates on seafloor edifices in the central pacific basin crust samples and their associated substrates from seven volcanic edifices of cretaceous age along the ratak chain of the marshall islands are discussed the two most abundant substrate lithologies recovered were limestone dominantly fore reef slope deposits and volcanic breccia composed primarily of differentiated alkalic basalt and hawaiite clasts in a phosphatized carbonate matrix the degree of mass wasting on the slopes of these seamounts is inversely correlated with the thickness of crusts crusts are generally thin on limestone substrate away from areas of active mass wasting processes and large atolls crusts may be as thick as 10 cm maximum the dominant crystalline phase in the marshall islands crusts is mno 2 vernadite high concentrations of cobalt platinum and rhodium strongly suggest that the marshall islands crusts are a viable source for these important metals many metals and the rare earth elements vary significantly on a fine scale through most crusts thus reflecting the abundances of different host mineral phases in the crusts and changes in seawater composition with time high concentrations of cobalt nickel titanium zinc lead cerium and platinum result from a combination of their substitution in the iron and manganese phases and their oxidation potential

oxidation state of marine manganese nodules analyses of the bulk oxidation state of marine manganese nodules indicates that more than 98 of the mn in deep ocean nodules is present as mn iv the samples were collected from three quite different areas the hemipelagic environment of the guatemala basin the pelagic area of the north pacific and seamounts in the central pacific results of the study suggest that todorokite in marine nodules is fully oxidized and has the following stoichiometry k na ca ba 33 mg cu ni 76mn5o22 h2o 3 2

interelement relationships in ferromanganese crusts from the central pacific ocean their implications for crust genesis the fine scale chemical variations in ferromanganese fe mn crusts from the central pacific ocean were investigated using a variety of techniques in order to elucidate their genesis thirty seven major minor and trace elements were determined by icp oes and icp ms in sub samples collected at approximately 2 mm intervals throughout the crust sequences an inverse relationship is observed between the logarithm of the elemental distribution coefficients log cmncsw and the mean residence time tr of elements in seawater these associations provide evidence supporting the strong link between seawater and fe mn crust chemistry results of factor analysis reveal that elements in crusts can generally be partitioned into four major groups with selected elements displaying associations with several groups these statistical associations are interpreted to represent hydrogenetic mn ni co cu ce zn biogenic ba zn cu pt fe detrital al si fe and carbonate fluorapatite ca p ree groups a comparison between elemental associations in fine scale data from individual crust sequences and bulk compositional data from samples collected in separate locations reveals very similar elemental associations the similar elemental associations in bulk samples and in fine scale subsamples from individual crusts are consistent with the notions that hydrogenetic crusts exhibit no significant post depositional remobilization of elements and that elemental distributions within crusts reflect the chemistry of oceanic water during the period in which they accreted chemical paleotracks are proposed based on factor scores derived from chemical variations as a function of depth in individual crusts our results show that there is internal consistency between the chemical evolution previously proposed seamount paleotracks and nanofossil biostratigraphy dating results

west antarctic ice sheet retreat driven by holocene warm water incursions glaciological and oceanographic observations coupled with numerical models show that warm circumpolar deep water cdw incursions onto the west antarctic continental shelf cause melting of the undersides of floating ice shelves because these ice shelves buttress glaciers feeding into them their ocean induced thinning is driving antarctic ice sheet retreat today here we present a multi proxy data based reconstruction of variability in cdw inflow to the amundsen sea sector the most vulnerable part of the west antarctic ice sheet during the holocene epoch from 11 7 thousand years ago to the present the chemical compositions of foraminifer shells and benthic foraminifer assemblages in marine sediments indicate that enhanced cdw upwelling controlled by the latitudinal position of the southern hemisphere westerly winds forced deglaciation of this sector from at least 10 400 years ago until 7 500 years ago when an ice shelf collapse may have caused rapid ice sheet thinning further upstream and since the 1940s these results increase confidence in the predictive capability of current ice sheet models

dissolution of calcite in deep sea sediments ph and o2 microelectrode results abstract we present microelectrode profiles of oxygen ph and porosity measured at in situ depth across the sediment water interface from stations above and below the calcite saturation horizon in the equatorial atlantic resistivity electrode data indicate that the diffusion coefficient for solutes is attenuated by nearly a factor of two within the top centimeter of the sediment lattice oxygen and porosity data are used to estimate that the organic carbon respiration rate of the sediment is 10 15 mol cm 2 yr 1 in these locations comparison of the ph data with numerical model results reveals that sedimentary calcite dissolves in response to respiration in the top few centimeters of sediment even above the saturation horizon we calculate that the effective in situ dissolution rate constant for calcite required to explain these data is the neighborhood of 10 100 d 1 although more data are needed to confirm this result it appears to be at least an order of magnitude less than the rate observed in laboratory stirred reactor experiments

a dramatic atlantic dissolution event at the onset of the last glaciation 1 measurements of the caco3 content of the caco3 size index and of foraminifera weights demonstrate that a prominent dissolution event occurred in the western equatorial atlantic at the onset of the last glacial period the decrease in co3 ion concentration appears to have been too large to be accounted for by the ocean acidification associated with the demise of excess interglacial biomass rather it appears to have been the result of a temporary strengthening of the penetration of the glacial equivalent antarctic bottom water into the atlantic the co occurrence of massive ethmodiscus rex deposition in the eastern equatorial atlantic bears witness to a reorganization of circulation in the atlantic this reorganization may well reflect a temporary collapse of conveyor circulation at the onset of the last glaciation

transport and release of transition elements during early diagenesis sequential leaching of sediments from manop sites m and h part i ph 5 acetic acid leach sediments from manop sites m and h in the eastern tropical pacific ocean can be partitioned into operationally defined phases by means of a sequential leach procedure this paper reports the results of the first leach in the sequence an acetic acid solution buffered as p h 5 with sodium acetate this leach is designed to remove carbonate bound and sorbed cations the only cation bound in a consistent ratio to calcium in the carbonate is strontium the molar ratio is 2 10 3 in contrast transition metals are sorbed onto the surfaces of other sedimentary particles the proportions sorbed range from 2 to 10 of the total manganese about 10 of the total nickel and copper and less than 1 of the total iron the pool of sorbed metals in surface sediments is sufficiently large and the rate of biological stirring is sufficiently rapid for this metal reservoir potentially to dominate the porewater reservoir in supplying metals to ferromanganese nodules a simple model for nodule growth based upon transfer of metals through this reservoir suggests that only 1 of the sedimentary sorbed metals within a radius of 2 to 9 cm is required to support typical nodule growth rates

ferromanganese deposits from the gulf of alaska seamount province mineralogy chemistry and origin ferromanganese oxide deposits dredged from four seamounts welker miller murray and patton in the gulf of alaska seamount province include poorly crystallized microlaminated crusts on basalt substrate well crystallized mn oxide veins in epiclastic sedimentary rocks and crystalline mn oxide layers and micronodules in phosphorite the principal rock types dredged are alkali basalt pillow fragments and tuffaceous conglomerate and sandstone the glassy rims of pillow fragments the glassy goundmass of large volcanic clasts and the tuffaceous component of the sediment are altered to palagonite other low temperature alteration products include phillipsite smectite and carbonate apatite thick 10 50 mm fe mn crusts consist mainly of 6 mn0 straight and cuspate growth laminae indicate variable growth rates and periods of nondeposition a larger number of detrital particles toward the top of thick crusts record the increasing influence of active volcanoes of the aleutian arc during northwestward movement of the pacific plate thick crusts on basalt substrate have higher mnife ratios and lower co content than fe mn crusts from low latitude seamounts of the central pacific region thin 10 rnm crusts on volcaniclastic substrate contain todorokite and bimessite and have higher mnife ratios ni and cu and lower fe and co than thick gulf of alaska crusts veins of todorokite and cryptomelane with complex internal structure occur in altered tuffaceous sandstone and conglomerate from miller seamount fibrous todorokite has a composition similar to those of other marine examples but may contain up to 7 mn2 in m2 sites microprobe analysis of the marine cryptomelane indicates a composition that is approximately k ba 2 mn4 co 8016 x h20 a third type of fe mn deposit in phosphorite is an intimate mixture of todorokite and minor 6 mn02 bearing layers and micronodules carbonate apatite and phillipsite that encloses grains of altered volcanic glass and lithic fragments the microlaminated structure mineralogy predominantly 6 mn02 and composition mnife ratio and transition metal rare earth element u and th contents of the thick crusts are characteristic of hydrogenetic fe mn crusts elsewhere in the pacific conversely the crystallinity and chemical composition of the mn oxide veins and thin crusts indicate formation during diagenesis of the volcanogenic sediment substrate mn and other transition metals are mobilized during lowtemperature oxidative alteration palagonitization of basaltic volcanic glass the oxidation of fez to fe3 during palagonitization and the dissolution of the dilute biogenic fraction of the sediment combine to lower the eh of ambient pore fluid and enhance the mobility of mn2 diagenesis in the phosphatic sandstone from patton seamount involves organic rich sediment and pore waters elevated in phosphorus owing to upwelling above a large volcanic edifice les cchantillons de dcp6ts de ferromangankse draguks sur quatre monts sous marins welker miller murray et patton dans la province des monts sous marins du golfe de i alaska sont formts de crodtes microlaminces et pauvrement cristallisces sur un substratum de basalte de veines d oxyde de mn bien cristallisc encaisstes dans des roches stdimentaires cpiclastiques et de couches et micronodules d oxyde de mn cristallin dans une phosphorite les principaux types de roches dragutes sont des fragments de coussins de basalte alcalin et de conglomcrat et de grks tufaccs les franges vitrifices des fragments des coussins la matrice vitrifice des gros fragments volcaniques et la composante tufacke du scdiment sont altcr6es en palagonite les autres mincraux d altkration sont phillipsite smectite et carbonate apatite

the effect of ocean alkalinity and carbon transfer on deep sea carbonate ion concentration during the past five glacial cycles abstract glacial interglacial deep indo pacific carbonate ion concentration co 3 2 changes were mainly driven by two mechanisms that operated on different timescales 1 a long term increase during glaciation caused by a carbonate deposition reduction on shelves i e the coral reef hypothesis and 2 transient carbonate compensation responses to deep ocean carbon storage changes to investigate these mechanisms we have used benthic foraminiferal b ca to reconstruct deep water co 3 2 in cores from the deep indian and equatorial pacific oceans during the past five glacial cycles based on our reconstructions we suggest that the shelf to basin shift of carbonate deposition raised deep water co 3 2 on average by 7 3 0 5 se mol kg during glaciations oceanic carbon reorganisations during major climatic transitions caused deep water co 3 2 deviations away from the long term trend and carbonate compensation processes subsequently acted to restore the ocean carbonate system to new steady state conditions deep water co 3 2 showed similar patterns to sediment carbonate content caco3 records on glacial interglacial timescales suggesting that past seafloor caco3 variations were dominated by deep water carbonate preservation changes at our studied sites

sediment residence time and connectivity in non equilibrium and transient geomorphic systems abstract growing empirical evidence shows that many geomorphic systems are in transient state or out of equilibrium with respect to the external driving forces the transient state is often related to the dis connectivity of the many constituent parts of geomorphic systems as a result of sediment storage along the sediment flow path from its source to the final sink the response time of geomorphic systems to external changes is thus dependent on the residence time of sediment in various storage compartments here i present a mathematical concept based on reservoir theory to model residence time of sediment using millennial scale sediment budgets the framework sheds light on the limitation of the sediment delivery ratio which is often used as a measure of sediment connectivity in geomorphic systems and provides analytical information on process type pace of sediment flux and connectivity of storage compartments along the sediment cascade the application of the reservoir theory to geomorphic systems under agricultural land use shows that sediment delivery ratios are linked to the virtual velocity of the eroded sediment the time since the onset of agricultural land use and the size of the studied basins with respect to the temporal evolution of sediment storages that temporarily remove sediment from the conveyor belt the framework aims to estimate the sediment residence time in storages which is linked to the effective time scale of disconnectivity reanalysis of a long term empirical sediment budget from central europe reveals that the response to agricultural land use which started 5000 years bp is mainly buffered by the long residence time of sediment on hillslopes in the order of 10 3 years which results in a delayed floodplain aggradation furthermore the framework was applied to paraglacial mountain systems that inherit striking evidences of pleistocene glacial erosion and still recover from the change from glacial to interglacial conditions as a consequence of the reduced lateral and longitudinal connectivity i show that paraglacial response times of sediment flux in mountain headwater in the canadian rocky mountains range in the order of 100 400 ka the results indicate that response times at the transition from glacial to interglacial conditions are much longer than the return interval of the major glaciations causing a transient behavior of mountain headwater basins during interglacial periods the presented reanalysis of millennial scale sediment budgets of agricultural and mountain geosystems provides an integrative framework to link paleo environmental reconstructions and the connectivity of transient geomorphic system to external changes

calcareous nannofossil biostratigraphic dating of a ferromanganese crust from schumann seamount abstract calcareous nannofossil biostratigraphy was employed to determine the age and growth rates of the different layers within ferromanganese crusts from schumann seamount 200 miles north of the island of kauai hawaii this work is part of a study to reconstruct the paleoceanographic history of crusts using various geochemical indicators the methods are based on the identification of coccolith imprints not actual coccolith remains age constraints on the time span of a particular horizon are defined either 1 by the presence of a species which was extant for only a limited geological time interval or 2 by the presence of two organisms whose time ranges overlapped age resolution is optimized by short time ranges or narrow overlaps in the crust studied there was considerable inter horizon variability in the preservation of coccolith imprints in imprint abundance and in species diversity some of the crust layers examined were narrowly constrained temporally 1 4 myr while others were less so 10 myr our results indicate that the minimum age for the interval at 27 mm depth is at least eocene this is the maximum age many believe any crust can be the position of this interval however is only about one half of the way through the crust while the data support previous estimates of average crust growth rates 0 5 mm myr the actual apparent growth rate appears to have varied by an order of magnitude 0 1 to 2 mm myr

ferromanganese nodules from manop sites h s and r control of mineralogical and chemical composition by multiple accretionary processes abstract the chemical composition of ferromanganese nodules from the three nodule bearing manop sites in the pacific can be accounted for in a qualitative way by variable contributions of distinct accretionary processes these accretionary modes are 1 1 hydrogenous i e direct precipitation or accumulation of colloidal metal oxides in seawater 2 2 oxic diagenesis which refers to a variety of ferromanganese accretion processes occurring in oxic sediments and 3 3 suboxic diagenesis which results from reduction of mn 4 by oxidation of organic matter in the sediments geochemical evidence suggests processes 1 and 2 occur at all three manop nodule bearing sites and process 3 occurs only at the hemipelagic site h which underlies the relatively productive waters of the eastern tropical pacific a normative model quantitatively accounts for the variability observed in nearly all elements zn and na however are not well explained by the three end member model and we suggest that an additional accretionary process results in greater variability in the abundances of these elements variable contributions from the three accretionary processes result in distinct top bottom compositional differences at the three sites nodule tops from h are enriched in ni cu and zn instead of the more typical enrichments of these elements in nodule bottoms in addition elemental correlations typical of most pelagic nodules are reversed at site h the three accretionary processes result in distinct mineralogies hydrogenous precipitation produces mno2 oxic diagenesis however produces cu ni rich todorokite and suboxic diagenesis results in an unstable todorokite which transforms to a 7 a phase birnessite upon dehydration the presence of cu and ni as charge balancing cations influence the stability of the todorokite structure in the bottoms of h nodules which accrete dominantly by suboxic diagenesis na and possibly mn 2 provide much of the charge balance for the todorokite structure limited growth rate data for h nodules suggest suboxic accretion is the fastest of the three processes with rates at least 200 mm 106 yr oxic accretion is probably 10 times slower and hydrogenous 100 times slower since these rates predict more suboxic component in bulk nodules than is calculated by the normative analysis we propose that suboxic accretion is a non steady state process variations in surface water productivity cause pulses of particulate flux to the sea floor which result in transient mn reduction in the surface sediments and reprecipitation on nodule surfaces

effects of phosphatization on the geochemical and mineralogical composition of marine ferromanganese crusts most hydrogenetic ferromanganese crusts in the central pacific consist of two growth generations a phosphatized older growth generation that is impregnated with carbonate fluorapatite cfa and a younger non phosphatized growth generation geochemical and mineralogical investigations of non phosphatized and phosphatized crust layers revealed significant differences that are not simply dilution effects by cfa certain elements are depleted in old crusts compared to young crusts in the order si fe al ti co mn pb others like ni zn cu y and rees rare earth elements are mostly enriched suboxic conditions in the phosphate rich water of the oxygen minimum zone that infiltrated the crusts caused a partial redissolution of crust phases resulting in mobilization of associated elements a partial recrystallization of more stable phases and a secondary input of nutrient type elements the frequent occurrence of todorokite in phosphatized crust layers indicates that mn mobilized from the vernadite crust phase was partially recrystallized as todorokite which is more stable under suboxic conditions incorporating ni cu and zn into the crystal lattice but rejecting co other metals like pb y and rees probably form stable phosphate phases in phosphatized crusts our investigations emphasize that under the influence of phosphatization diagenetic remobilization and reorganization in fe mn crusts took place in contrast to non phosphatized crusts the older phosphatized crust generation no longer represents a complete primary crust precipitate therefore young non phosphatized and old phosphatized crust generations should be considered as two different sample types with respect to geochemical composition mineralogy and evolution we also suggest that most methods for age determination like the 87sr86sr isotopic dating method or co chronometry cannot be used for phosphatized crusts without caution

readjustments of a sinuous river during the last 6000 years in northwestern europe cher river france from an active meandering river to a stable river course under human forcing abstract palaeomeanders are characteristic features of meandering river floodplains some were abandoned several millennia ago and can be used as evidence for past fluvial patterns despite many observations of changes undergone by meandering rivers little is known about long term morphological adjustment of meanders this paper reports on investigations conducted in two reaches located in the middle valley of the cher river northwestern europe france to examine the readjustments of lowland meanders during the second half of the holocene the aim of our study was to provide new insights into the complex dynamics that control low energy meandering rivers lidar dem spatial analyses coupled with geophysical surveys and observations of sediments enabled the identification and dating of thirteen palaeomeanders embedded in coarse sediments sand and gravel while the whole floodplain is covered by silty overbank deposits sedimentological geochemical and pollen analyses combined with radiocarbon and osl dating allowed us to reconstruct the chronology of the cutoff and the filling of palaeochannels no palaeochannels older than ca 6000 yr cal bp and no palaeochannels younger than the eleventh thirteenth centuries cal ad were identified this allowed us to distinguish two periods of meandering processes 1 our observations demonstrate the multi millennia persistence of an active meandering pattern in a context of land use changes ca 6000 yr cal bp eleventh thirteenth centuries cal ad the preserved mobility of the river can be mainly interpreted as the result of the low cohesiveness of the bank material too few fine sediments were delivered during the proto historical and historical periods to help stabilize the river course 2 following the eleventh thirteenth centuries cal ad the fluvial system underwent a laterally stable phase the many medieval and modern hydraulic engineering works reduced the specific stream power and prevented lateral erosion the drastic decrease in the river s capacity to generate new meanders resulted in the disappearance of floodplain lakes and loss of habitat diversity

ferromanganese crusts from necker ridge horizon guyot and s p lee guyot geological considerations abstract necker ridge horizon guyot and s p lee guyot in the central pacific were sampled seismically surveyed and photographed by bottom cameras in order to better understand the distribution origin and evolution of ferromanganese crusts necker ridge is over 600 km long with a rugged crest pods of sediment to 146 m thick slopes that average 12 to 20 and debris aprons that cover some of the lower flanks substrate lithologies are mostly hyaloclastite volcaniclastic breccia and minor alkalic basalt horizon guyot 300 km long and 75 km wide is capped by at least 160 m of sediment which buries stepped terraces substrate lithologies are similar to those on necker ridge although previous workers sampled much tholeiitic basalt on horizon s p lee guyot 125 km long and 80 km wide is capped by at least 300 m of sediment and contains talus aprons along its lower flanks ferromanganese encrusted rocks were recovered in every dredge and are thickest on necker ridge crust thicknesses average about 2 5 1 5 and 0 8 cm for necker horizon and s p lee respectively crusts range from smooth or porous surfaces to knobby and botryoidal the entire crust is laminated however two distinct layers commonly exist separated by a paper thin layer of phosphorite the dominant mineral of all crusts is vernadite mno 2 while quartz feldspar apatite and in three rocks todorokite are minor phases quartz and feldspar decrease with decreasing latitude of occurrence and is suggested to be related to eolian input on the average apatite also increases within the crusts with decreasing latitude of occurrence which may be related to high biological productivity in the zone of equatorial upwelling phosphorite substrates are more abundant on necker ridge and s p lee guyot than they are on horizon guyot seamount ferromanganese nodules are distinct from abyssal nodules in their chemistry and internal structure

regional variation of manganese nodule facies on the wake tahiti transect morphological chemical and mineralogical study abstract during the gh80 1 cruise of rv hakurei maru january to march 1980 conducted by the geological survey of japan a significant regional variation of manganese nodule facies was found on the 4000 km long transect from wake to tahiti more than 190 bottom samplings and 120 sea bed photography using box corer free fall grab and piston corer revealed three characteristic nodule facies each extending over hundreds of kilometers in the northern central pacific basin and the mid pacific mountains area zeolitic pelagic clay surface sediment discoidal to irregular shaped smooth surface nodules are dominant they consist of inner fragmented older nodules composed of mno2 and surrounding 2 5 mm thick layers of mno2 and 10 a manganate mn fe and cu ni are low averages 1 4 and 0 85 wt consistent with mineralogy in the central to southern central pacific basin siliceous clay or ooze surface sediment spherical and rough surface nodules with concentric structure predominate each concentric layer consists of 10 a manganate yielding high mn fe and cu ni averages 4 1 and 2 41 wt in the penrhyn basin zeolitic clay surface sediment spherical to discoidal shaped smooth surface nodules of simple internal structure are distributed they consist mostly of mno2 and consequently mn fe and cu ni are low averages 1 3 and 0 85 wt the manihiki plateau covered with thick calcareous sediments is a barren area these regional variation in surface and internal structures and chemical characteristics are principally due to preferential growths of the two ferromanganese minerals the mode of regional variation of the minerals and its close relationship to surface sediments variability are consistent with the two supply route model of these minerals the 10 a manganate forming rough surface dominantly developed within surface sediments as a result of diagenesis of siliceous sediments in the central and southern central pacific basin whereas mno2 develops through direct supply of metal elements from the overlying bottom waters forming smooth surface nodules in the northern central pacific basin and penrhyn basin

quantitative models of sedimentary basin filling summary quantitative modelling of the filling of sedimentary basins was begun in earnest in the 1960s dozens of themes and variations have been proposed since then and have yielded an abundance of idealized stratigraphic patterns as functions of both imposed changes and basin properties post plate tectonic modelling began with rigid lid models which show the stratigraphic signature of subsidence variation this work introduced the connection between stratigraphy and the rheology of the lithosphere rigid lid models are the simplest type of geometric model in which the sediment surface is assigned prescribed geometries usually corresponding to different depositional environments these can reproduce many aspects of overall stratal geometry but are formally restricted to relatively long timescales for which quasi steady surface topography can be assumed so called dynamic models attempt to represent the morphodynamics of the sediment surface by abstracting and averaging short term transport processes most of the dynamic models proposed to date can be seen as special cases of a single general morpho dynamic equation the most important result of the first wave of quantitative basin filling models is that even relatively simple models can produce reasonable stratal patterns we now have a wide array of tools for exploring scenarios searching for general behaviours and effects and making initial quantitative predictions we have also learned that basin response to external forcing as recorded in stratigraphy can be as sensitive to the characteristics of the basin as to the forcing the main brake on the development of basin modelling is not computing power but lack of methods and data for testing the models we have already developed physical experiments which are only just beginning are one means of doing this experimental stratigraphy is a bridge to quantitative field tests which will require collaboration among academic researchers from a wide range of areas and between academia and industry on projects of greater scale and degree of integration than we have seen so far the advancement of quantitative sedimentary geology will also require significant changes in the way the subject is taught at all levels

glacial deep water carbonate chemistry inferred from foraminiferal mg ca a case study from the western tropical atlantic we explore using changes in planktonic foraminiferal mg ca with water depth in a single region to infer relative changes in deep water carbonate chemistry the mg ca ratio in foraminiferal calcite is quantitatively lowered by dissolution we exploit this dissolution effect to generate a profile of carbonate ion concentration co32 for the deep waters of the tropical atlantic during the last glacial maximum we generated mg ca data for three species g ruber g sacculifer and n dutertrei from three cores located along a depth transect 2 8 to 4 0 km on the ceara rise in the western equatorial atlantic we attribute lower mg ca in glacial intervals from the shallow core to changes in sea surface temperature sst the even lower glacial mg ca values in the deeper cores are attributed to dissolution and are used to reconstruct a paleo co32 profile our down core mg ca data for g ruber and g sacculifer confirm that these species are more resistant to mg loss due to dissolution than n dutertrei the greater susceptibility of n dutertrei s mg content to dissolution limits the utility of this species in thermocline temperature reconstructions to cores above the lysocline but significant to this study makes n dutertrei useful in quantifying changes in deep water co32 our paleo co32 reconstruction based on n dutertrei suggests the last glacial maximum co32 gradient in the atlantic was much steeper than today implying that the boundary between deepwater masses in the atlantic was shallower during the last glacial maximum our results suggest comparison of mg ca from multiple cores from one region could similarly provide constraints on changes in carbonate chemistry in other basins and other time periods

floodplain dynamics of a wandering river dendrochronology of the morice river british columbia canada dendrochronological techniques are used to develop a history of flood occurrence and relative stage for the middle section of the morice river based on flood scars bank undercutting dates and tree establishment dates on fluvial features the morice river is the major tributary of the bulkley river skeena river system northwest british columbia canada reach 2 of the morice river drainage area 3499 km2 is forested and little disturbed by human activity it is presently a wandering multiple channel river and shows evidence of frequent channel changes which have reworked most of the floodplain several times in the last 180 years airphoto analysis and dendrochronology demonstrate that many channels show evidence of two or more periods of activity reoccupation and re excavation of pre existing channel segments is more frequent than development of new channels thirty one significant floods over the past 105 years were detected through dendrochronology of flood scarred trees on the morice river flood scars are predominantly caused by flood transported logs abundant log transport results in damage to channel margin trees during events only slightly above bankfull discharge the record of flood scars on channel margin trees and establishment dates of forest stands on abandoned channels and surfaces show that the morice river has maintained its present regimen for the past 115 years during the neoglacial the morice river was more active than in recent times and its channels occupied twice the present area tree establishment dates show that neoglacial surfaces and channels of the morice river were abandoned during the 1820 s the modern floodplain configuration was assumed by 1870

60 myr records of major elements and pb nd isotopes from hydrogenous ferromanganese crusts reconstruction of seawater paleochemistry we compare the time series of major element geochemical and pb and nd isotopic composition obtained for seven hydrogenous ferromanganese crusts from the atlantic indian and pacific oceans which cover the last 60 myr average crust growth rates and age depth relationships were determined directly for the last about 10 myr using be 10 be 9 profiles in the absence of other information these were extrapolated to the base of the crusts assuming constant growth rates and constant initial be 10 be 9 ratios due to the lack of additional information co contents have also been used previously to estimate growth rates in co rich pacific and atlantic seamount crusts puteanus and halbach 1988 a comparison of be 10 be 9 and co based dating of three co rich crusts supports the validity of this approach and confirms the earlier chronologies derived from extrapolated be 10 be 9 based growth rates back to 60 ma our data show that the flux of co into co poor crusts has been considerably lower the relationship between growth rate and co content for the co poor crusts developed from these data is in good agreement with a previous study of a wider range of marine deposits manheim 1986 the results suggest that the co content provides detailed information on the growth history of ferromanganese crusts particularly prior to 10 12 ma where the be 10 based method is not applicable the distributions of pb and nd isotopes in the deep oceans over the last 60 myr are expected to be controlled by two main factors a variations of oceanic mixing patterns and flow paths of water masses with distinct isotopic signatures related to major paleogeographic changes and b variability of supply rates or provenance of detrital material delivered to the ocean linked to climate change glaciations or major tectonic uplift the major element profiles of crusts in this study show neither systematic features which are common to crusts with similar isotope records nor do they generally show coherent relationships to the isotope records within a single crust consequently any interpretation of time series of major element concentrations of a single crust in terms of paleoceanograghic variations must be considered with caution this is because local processes appear to have dominated over more basin wide paleoceanographic effects in this study co is the only element which shows a relationship to pb and nd isotopes in pacific crusts a possible link to changes of pacific deep water properties associated with an enhanced northward advection of antarctic bottom water from about 14 ma is consistent with the pb but not with the nd isotopic results the self consistent profiles of the pb and nd isotopes suggest that postdepositional diagenetic processes in hydrogenous crusts including phosphatization events have been insignificant for particle reactive elements such as pb be and nd isotope time series of pb and nd show no systematic relationships with major element contents of the crusts which supports their use as tracers of paleo seawater isotopic composition

sediment load and floodplain deposition rates comparison of the fly and strickland rivers papua new guinea 1 rates of aggradation and infilling of accommodation space along lowland channels in response to postglacial sea level rise should depend on sediment supply the strickland and fly rivers join at just 6 m above sea level and have experienced the same holocene sea level rise historically the strickland has carried about 7 times the sediment load and 1 4 times the water discharge as the fly therefore we hypothesize that the lowland strickland floodplain should be more developed and consequently should presently be capturing proportionately less sediment than the floodplain of the lowland fly river we use mine derived elevated pb and ag concentrations in 111 shallow 1 m floodplain cores collected in 2003 to determine deposition rates across the lower strickland floodplain sediment deposition rates decrease across the floodplain with distance from the channel bank and the average rate of deposition is 1 4 cm a over the first 1 km overbank deposition along the lowland sandbedded strickland results in 13 loss of the total load 0 05 km of channel length of the main stem deposition rates over the first 1 km from the channel bank on the strickland are about 10 times those on the fly for estimated natural sediment loads however the proportional loss per channel length on the strickland is less than that on the fly 0 09 km of main stem channel length because of an extensive network of tributary and tie channels that convey sediment to the floodplain on the fly furthermore the lateral migration of the strickland channel is 5 times that on the fly such that most overbank deposits on the strickland are returned to the channel causing the net loss of sediment to the floodplain to be small we conclude that the strickland river which has a much higher overbank deposition rate than the fly river as a function of distance from channel bank nonetheless has significantly less net accumulation than the fly because 1 a large proportion of the sediment load is conveyed up tributaries and tie channels on the fly and 2 lateral migration which presumably results from the higher load on the strickland sweeps sediment back into the channel hence our field observations support our initial hypothesis though the primary reason for this is because of active lateral migration rather than low overbank deposition rates

growth response of a deep water ferromanganese crust to evolution of the neogene indian ocean abstract a deep water ferromanganese crust from a central indian ocean seamount dated previously by 10 be and 230 th excess was studied for compositional and textural variations that occurred throughout its growth history the 10 be 9 be dated interval upper 32 mm yields an uniform growth rate of 2 8 0 1 mm ma frank m o nions r k 1998 sources of pb for indian ocean ferromanganese crusts a record of himalayan erosion earth planet sci lett 158 pp 121 130 which gives an extrapolated age of 26 ma for the base of the crust at 72 mm and is comparable to the maximum age derived from the co model based growth rate estimates this study shows that fe mn oxyhydroxide precipitation did not occur from the time of emplacement of the seamount during the eocene 53 ma until the late oligocene 26 ma this paucity probably was the result of a nearly overlapping palaeo ccd and palaeo depth of crust formation increased early eocene productivity instability and reworking of the surface rocks on the flanks of the seamount and lack of oxic deep water in the nascent indian ocean crust accretion began older zone with the formation of isolated cusps of fe mn oxide during a time of high detritus influx probably due to the early miocene intense erosion associated with maximum exhumation of the himalayas op cit this cuspate textured zone extends from 72 mm to 42 mm representing the early miocene period intense polar cooling and increased mixing of deep and intermediate waters at the close of the oligocene might have led to the increased oxygenation of the bottom water in the basin a considerable expansion in the vertical distance between the seafloor depth and the ccd during the early miocene in addition to the influx of oxygenated bottom water likely initiated fe mn crust formation pillar structure characterises the younger zone which extends from 40 mm to the surface of the crust i e 15 ma to present this zone is characterised by 25 higher content of oxide bound elements than in the older zone possibly corresponding to further increased oxygenation of bottom waters increased stability of the seamount slope and gradually reduced input of continental detritus from the erosion of the himalayas middle miocene antarctic glaciation which peaked 12 13 ma ago increased the oxic bottom water influx to the basin resulting in accretion of the crust with low detritus therefore the younger crust started to accrete in response to a shift in bottom water circulation towards the contemporary pattern which produced a uniform growth rate and pillar structure up to the present

the radiocarbon age of calcite dissolving at the sea floor estimates from pore water data abstract we measured the radiocarbon content and stable isotopic composition of pore water and bottom water co2 sedimentary organic carbon and caco3 at two sites on the ceara rise one underlying bottom water that is supersaturated with respect to calcite site b the other underlying undersaturated bottom water site g the results were combined with pore water o2 co2 and ca2 profiles martin and sayles 1996 to estimate the radiocarbon content of the caco3 that is dissolving in the sediment mixed layer at site g the caco3 that is dissolving in the upper 2 cm of the sediments is clearly younger richer in 14c than the bulk sedimentary caco3 indicating that nonhomogeneous caco3 dissolution occurs there the case for nonhomogeneous dissolution is much weaker at the site underlying supersaturated bottom water the results indicate that nonhomogeneous dissolution occurs in sediments underlying undersaturated bottom water that the dissolution is rapid relative to the rate of homogenization of the caco3 in the mixed layer by bioturbation and that the dissolution rate of caco3 decreases as it ages in the sediment mixed layer the results support the hypothesis based on solid phase analyses that the preferential dissolution of young i e radiocarbon rich caco3 leads to a pattern of increasing radiocarbon age of mixed layer caco3 as the degree of undersaturation of bottom water increases keir 1984 broecker et al 1991

self organized criticality in river basins challenging sedimentary records of environmental change for many years researchers have linked increases in sediment and bedload from drainage basins to external factors such as increased rainfall however natural systems have always shown a high degree of scatter or nonlinearity in this response which has made prediction of sediment yields difficult we identify and describe a mechanism for self organized criticality in the bedload sediment output from a simple drainage basin evolution model this implies that identical floods will give considerably different sediment yields which effectively renders the system unpredictable therefore existing empirical methods for estimating sediment yields may need to be radically reevaluated furthermore sedimentary records used to infer past climate or environmental conditions could simply reflect the internal system dynamics instead of external drivers

modelling long term basin scale sediment connectivity driven by spatial land use changes changes in land use can affect local geomorphology and sediment dynamics however these impacts could conceivably lead to changes in geomorphological processes beyond the area of land use change thereby evidencing a geomorphic connectivity in the landscape we conduct a numerical modelling experiment using the caesar landscape evolution model to investigate the extent and nature of such connectivity in the river swale basin six simulations are run and analysed two of these are reference simulations where the basin has a hypothetical total grassland cover or total forest cover in the other four simulations half of the basin is subjected to either deforestation or reforestation during the simulation simulations are analysed for temporal trends in sediment yield and for spatial trends in erosion and deposition across the basin results show that deforestation or reforestation in one half of the basin can indeed affect the geomorphology of the other half thus implying a geomorphological connectivity across the basin this connectivity is locally very high with significant morphological impacts close to where de or re forestation occurs changes are observed both downstream and upstream of the areas where the land use changes occurred the impacts are more pronounced in the downstream direction and are still apparent in the basin scale sediment yields as deforestation of half the basin can increase decadal sediment yields by over 100 whilst reforestation of half the basin can lead to 40 decreases however our results also indicate a reverse connectivity whereby erosion and deposition in upstream headwaters and tributaries can for the first time be conclusively attributed to land use changes several kilometres downstream due to alterations in the valley floor base level resulting from incision and alluviation

channel pattern and river floodplain dynamics in forested mountain river systems channel pattern effectively stratifies the dynamics of rivers and floodplains in forested mountain river systems of the pacific northwest usa straight channels are least dynamic with relatively slow floodplain turnover and floodplains dominated by old surfaces braided channels are most dynamic with floodplain turnover as low as 25 years and predominantly young floodplain surfaces island braided and meandering channels have intermediate dynamics with moderately frequent disturbances erosion of floodplain patches maintaining a mix of old and young surfaces return intervals for the erosion of floodplains increase in the order of braided island braided meandering and straight 8 33 60 and 89 years respectively a threshold for the lateral migration of a channel occurs at a bankfull width of 15 20 m the most likely mechanism underlying this threshold is that larger channels are deep enough to erode below the rooting zone of bank vegetation above this threshold channels not confined between valley walls exhibit channel patterns distinguishable by slope and discharge and slope discharge domains can be used to predict channel patterns meandering and braided patterns are most consistently identified by the model and prediction errors are largely associated with indistinct transitions among channel patterns that are adjacent in plots of slope against discharge locations of straight channels are difficult to identify accurately with the current model the predicted spatial distribution of channel patterns reflects a downstream decline in channel slope which is likely correlated with a declining ratio of bed load to suspended load ecological theory suggests that biological diversity should be highest where the intermediate disturbance regime of island braided channels sustains high diversity of habitat and successional states through time

a possible 20th century slowdown of southern ocean deep water formation chlorofluorocarbon 11 inventories for the deep southern ocean appear to confirm physical oceanographic and geochemical studies in the southern ocean which suggest that no more than 5 x 10 6 cubic meters per second of ventilated deep water is currently being produced this result conflicts with conclusions based on the distributions of the carbon 14 carbon ratio and a quasi conservative property po 4 in the deep sea which seem to require an average of about 15 x 10 6 cubic meters per second of southern ocean deep ventilation over about the past 800 years a major reduction in southern ocean deep water production during the 20th century from high rates during the little ice age may explain this apparent discordance if this is true a seesawing of deep water production between the northern atlantic and southern oceans may lie at the heart of the 1500 year ice rafting cycle

local variability of manganese nodule facies on small abyssal hills of the central pacific basin abstract local variability of manganese nodule facies and associated sediments were studied around abyssal hills 60 60 km 2 located in the equatorial zone of the central pacific basin small scale variations in nodule occurrence mineralogy chemistry and internal structure are discussed in relation to seismic records and sediment lithology the slow sedimentation rate from the late tertiary to the quaternary appear to have promoted formation of nodules around the abyssal hills although the plio pleistocene hiatus at depths below sediment surface suggests no clear evidence of increased growth of nodules during the period in the area of rapid and continuous sedimentation away from the hill areas nodules are rare probably because of insufficient lifting force for nodules mineralogical and chemical studies reveal that the two principal nodule morphologies smooth and rough surfaces result from preferential deposition of hydrogenous or diagenetic manganese minerals in relation to early diagenesis of surface siliceous sediments regional variability of nodule surface morphology and composition suggests a very local change in sedimentary conditions in space and internal mineral variation suggests changes in sedimentary conditions with time the geological factors controlling the small scale variability of nodule facies seem to be similar to those controlling regional scale variations

a cellular model of holocene upland river basin and alluvial fan evolution coulthard t j macklin m g kirkby m j 2002 a cellular model of holocene upland river basin and alluvial fan evolution earth surface processes and landforms 27 3 269 288

how plausible are high frequency sediment supply driven cycles in the stratigraphic record abstract this paper is an attempt to quantify the plausible time scales of clastic sediment supply variations at the entrance of sedimentary basins our approach is based on the sedimentary system concept which simplifies natural systems by dividing them into three zones of dominant processes the erosion the transfer and the sedimentation subsystems we examine recent results from geomorphology which show that frequent climate changes can induce high frequency sediment flux variations at the outlet of the source area we put forward the crucial role of the transfer subsystem which conveys sediment from the erosion zone to the basin by applying a diffusive model to a number of worldwide rivers we extend from large 1000 km to intermediate 300 km rivers the previous finding that the transfer subsystem acts as a buffer for short periods sediment pulses tens to hundreds of kiloyears this implies that high frequency stratigraphic cycles in clastic accumulations fed by large drainage systems are unlikely to reflect sediment supply cycles of tens to hundreds of thousands of years of periodicities

distal deposition of tephra from the eyjafjallajokull 2010 summit eruption the 2010 eyjafjallajokull lasted 39 days and had 4 different phases of which the first and third 14 18 april and 5 6 may were most intense most of this period was dominated by winds with a northerly component that carried tephra toward europe where it was deposited in a number of locations and was sampled by rain gauges or buckets surface swabs sticky tape samples and air filtering in the uk tephra was collected from each of the phases 1 3 with a combined range of latitudes spanning the length of the country the modal grain size of tephra in the rain gauge samples was 25 mu m but the largest grains were 100 mu m in diameter and highly vesicular the mass loading was equivalent to 8 218 shards cm 2 which is comparable to tephra layers from much larger past eruptions falling tephra was collected on sticky tape in the english midlands on 19 20 and 21st april phase 2 and was dominated by aggregate clasts mean diameter 85 mu m component grains 10 mu m sem eds spectra for aggregate grains contained an extra peak for sulphur when compared to control samples from the volcano indicating that they were cemented by sulphur rich minerals e g gypsum caso4 center dot h2o air quality monitoring stations did not record fluctuations in hourly pm10 concentrations outside the normal range of variability during the eruption but there was a small increase in 24 hour running mean concentration from 21 24 april phase 2 deposition of tephra from phase 2 in the uk indicates that transport of tephra from iceland is possible even for small eruption plumes given suitable wind conditions the presence of relatively coarse grains adds uncertainty to concentration estimates from air quality sensors which are most sensitive to grain sizes 10 mu m elsewhere tephra was collected from roofs and vehicles in the faroe islands mean grain size 40 mu m but 100 mu m common from rainwater in bergen in norway 23 91 mu m and in air filters in budapest hungary 2 6 mu m a map is presented summarizing these and other recently published examples of distal tephra deposition from the eyjafjallajokull eruption it demonstrates that most tephra deposited on mainland europe was produced in the highly explosive phase 1 and was carried there in 2 3 days

influence of flow variability on floodplain formation and destruction little missouri river north dakota resolving observations of channel change into separate planimetric measurements of floodplain formation and destruction reveals distinct relations between these processes and the flow regime we analyzed a time sequence of eight bottomland images from 1939 to 2003 along the little missouri river north dakota to relate geomorphic floodplain change to flow along this largely unregulated river at the decadal scale floodplain formation and destruction varied independently destruction was strongly positively correlated with the magnitude of infrequent high flows that recur every 5 10 yr whereas floodplain formation was negatively correlated with the magnitude of frequent low flows exceeded 80 of the time at the century scale however a climatically induced decrease in peak flows has reduced the destruction rate limiting the area made available for floodplain formation the rate of destruction was not uniform across the floodplain younger surfaces were consistently destroyed at a higher rate than older surfaces suggesting that throughput of contaminants would have occurred more rapidly than predicted by models that assume uniform residence time of sediment across the floodplain maps of floodplain ages produced by analysis of sequential floodplain images are similar to maps of forest ages produced through dendrochronology confirming the assumption of dendrogeomorphic studies that riparian tree establishment in this system is limited to recent channel locations

residence time of alluvium in an aggrading fluvial system relationships between the surface area and age of alluvial deposits were used to estimate the residence time of alluvium in the 2205 km2 waipaoa river basin new zealand the contemporary waipaoa river is an efficient transporter of sediment to the continental shelf but the basin has been characterized by rapid channel and valley aggradation in the historic period and by extensive mid to late holocene alluvial storage in the lower reaches the area weighted mean age of alluvial deposits in the lower part of the river basin is 4400 yr these deposits comprise terrace remnants isolated by downcutting and holocene to recent sediments that are potentially remobilizable by the modern river even though the amount of storage is small relative to downstream transport the majority of the potentially remobilizable alluvium is likely to remain in storage for 100 yr and its half life time for 50 per cent removal is 2000 yr within the confines of the flfloodplain the apparent loss of older deposits is due primarily to burial but losses of the most recent deposits are due almost entirely to remobilization 30 40 per cent with the remainder preserved in the alluvial record for at least 104 yr most of this sediment is likely to remain in storage until there is a shift to a degradational state copyright 2006 john wiley sons ltd

ferromanganese deposits in the hawaiian archipelago abstract dredge sampling and bottom photography of submarine terraces in the hawaiian archipelago find that ferromanganese deposits encrust rock outcrops and form widespread pavements these deposits are economically interesting because of their cobalt content and location within the 200 mile zone ferromanganese crusts and pavements are most prevalent on two deep terrace levels the laualualei 370 560 m and waho 900 1200 m recognized throughout the archipelago although crust thickness and element content vary considerably on both regional and local scales the characteristic variability in crust thickness and element content suggests that environmental conditions vary on small spacial and temporal scales we find no relationship between substrate composition and crust thickness or element content indicating that ferromanganese oxides are deposited from seawater and accumulate on any exposed hard substrate surface we speculate that structural and sedimentary processes regulate the exposure of resistant substrate as a prerequisite for crust layers deposited during intermittent accretion episodes an enrichment in cobalt is correlated to mn fe ratio and the relative proportions of mno2 and feooh which are the principal crust components cobalt content cannot be correlated to water depth crust thickness or basement age of the deep terrace localities since crust thickness and cobalt content generally increase along the archipelago to the northwest deposits found on the wide terraces of the leeward archipelago have the most economic potential this study concludes that hydrogenous deposition of ferromanganese oxides from seawater is affected considerably by local environmental conditions during the evolution of deep terraces on the submarine of slopes of the hawaiian archipelago

flood plain and channel dynamics of the quinault and queets rivers washington usa abstract comparison of historic channel migration rates modern planform conditions and overall sediment wood and flow conditions and interactions for the quinault river and queets river in the western olympic peninsula washington reveals decadal to century scale interactions between gravel bed channels and forested flood plains in temperate maritime environments the downstream alluvial portions of these two rivers can be divided into three reaches of different slope flow sediment and wood regimes i the upper quinault river is aggrading behind lake quinault a natural lake that traps most sediment and wood transported from the olympic mountain headwaters ii the lower quinault river downstream of lake quinault transports only sediment and wood derived from reworking of flood plain deposits and contributed from valley margins iii the queets river has unimpeded movement of sediment and water from the mountainous headwaters to the pacific ocean measurements of channel planform characteristics and historic migration rates and patterns show that these three reaches have correspondingly distinct channel and flood plain morphologies and dynamics the aggrading and sediment rich upper quinault river has the widest flood plain widest active channel greatest number of low flow channels and flanking gravel bars and an average channel migration rate of 12 7 3 3 m year between 1900 and 1994 the comparatively sediment poor lower quinault river has the narrowest flood plain narrowest active channel and lowest channel migration rate 4 0 1 2 m year and most flow is through a single channel with few adjacent gravel bars the queets river has attributes intermediate between the lower and upper quinault rivers including an average channel migration rate of 7 5 2 9 m year flood plain turnover rates are similar for all three reaches with channels eroding the flood plain at the rate of about 0 2 of the flood plain area per year and with corresponding flood plain half lives of 300 to 500 years observations from this study and previous studies on the queets river show that channel and flood plain dynamics and morphology are affected by interactions between flow sediment and standing and entrained wood some of which likely involve time frames similar to 200 500 year flood plain half lives on the upper quinault river and queets river log jams promote bar growth and consequent channel shifting short distance avulsions and meander cutoffs resulting in mobile and wide active channels on the lower quinault river large portions of the channel are stable and flow within vegetated flood plains however locally channel spanning log jams have caused channel avulsions within reaches that have been subsequently mobile for several decades in all three reaches log jams appear to be areas of conifer germination and growth that may later further influence channel and flood plain conditions on long time scales by forming flood plain areas resistant to channel migration and by providing key members of future log jams appreciation of these processes and dynamics and associated temporal and spatial scales is necessary to formulate effective long term approaches to managing fluvial ecosystems in forested environments

formation of ferromanganese crusts on northwest intertropical pacific seamounts electron photomicrography and microprobe chemistry abstract seven ferromanganese crusts from the northwest intertropical pacific seamounts were analyzed for photomicroscopic growth structures microprobe chemistry and ages based on co chronometer growth rate the crusts on the marshall islands seamounts are thick and are divided into phosphatized lower older and nonphosphatized upper younger growth generations the older crust consists of compact laminations and columns impregnated with carbonate fluoapatite cfa whereas the younger crust is characterized by porous botryoids and columns of mno2 and fe oxyhydroxide the crusts on the federated states of micronesia fsm and palau islands seamounts are thin and are often incorporated with inorganic opal a in the uppermost part comprising the younger generation some crusts show scours and fractures although the growth of crusts has been often interrupted by mass failure of slope sediments the crusts on the marshall islands seamounts are estimated to have grown at rate of about 3 mm ma since the middle eocene and to have been phosphatized in the late oligocene during the host seamounts were located beneath the equatorial zone of high productivity prolonged infiltration of the oxygen minimum zone omz water into shallower water older crusts redistributed crust composition by precipitating cfa enriching subsequent amounts of mn and ni and removing some co the younger crust has formed at slower rate about 2 mm ma under the stronger influence of bottom water circulation in the north of the equatorial zone concentrating abundant co in the uppermost part of some crusts siliceous skeletons transform with burial to inorganic opal a and si rich fe oxyhydroxide suggesting that biosilica diagenesis can enhance crust growth

accuracy assessment of georectified aerial photographs implications for measuring lateral channel movement in a gis aerial photographs are commonly used to measure planform river channel change we investigated the sources and implications of georectification error in the measurement of lateral channel movement by testing how the number 6 30 and type human versus natural landscape features of ground control points gcps and the order of the transformation polynomial first second and third order affected the spatial accuracy of a typical georectified aerial photograph error was assessed using the root mean square error rmse of the gcps as well as error in 31 independent test points the rmse and the mean and median values of test point errors were relatively insensitive to the number of gcps above eight but the upper range of test point errors showed marked improvement i e the number of extreme errors was reduced as more gcps were used for georectification using more gcps thus improved overall georectification accuracy but this improvement was not indicated by the rmse suggesting that independent test points located in key areas of interest should be used in addition to rsme to evaluate georectification error the order of the transformation polynomial also influenced test point accuracy the second order polynomial function yielded the best result for the terrain of the study area gcp type exerted a less consistent influence on test point accuracy suggesting that although hard edged points e g roof corners are favored as gcps some soft edged points e g trees may be used without adding significant error based upon these results we believe that aerial photos of a floodplain landscape similar to that of our study can be consistently georectified to an accuracy of approximately f5 m with 10 chance of greater error the implications of georectification error for measuring lateral channel movement are demonstrated with a multiple buffer analysis which documents the inverse relationship between the size of the buffers applied to two channel centerlines and the magnitude of change detected between them this study demonstrates the importance of using an independent test point analysis in addition to the rsme to evaluate and treat locational error in channel change studies d 2005 published by elsevier b v

spatial and temporal dynamics of sediment accumulation and exchange along strickland river floodplains papua new guinea over decadal to centennial timescales 1 we investigated the processes of sediment exchange between the strickland river and its lowland floodplain documenting 1 the rates textures and distributions of sediment accumulation 2 temporal variations in these rates 3 the remobilization of sediment by erosive processes and 4 whether net storage is significant over century timescales we used 210pb geochronology of floodplain cores from 11 transects to measure deposition rates over the past 65 years finding a decline from 5 5 cm a 0 10 m distance from the channel to 0 9 cm a 400 m to 0 1 cm a 1 km rates are elevated along curved sections of channel and are stable over time and episodic accumulation is prevalent and may be correlated to floods integrated temporally and spatially the average rate is 1 6 cm a integrating along both sides of 318 river km we studied for the lowland strickland we calculate 12 19 mt of annual sediment accumulation 0 05 mt km or 0 07 of the annual load per km of river length representing 17 27 of the total annual sediment flux we used georeferenced landsat images 1972 2001 to quantify channel migration and the resulting return of sediment to the channel mean lateral migration was 5 1 0 8 m a given the floodplain width of 10 km this implies a waiting time of 1 ka between floodplain formation and subsequent reentrainment of the bank as the channel migrates laterally this raises the possibility that the net return of material from the floodplain due to channel migration could balance the overbank deposition we observed the exchange flux between cut bank erosion and point bar deposition is 20 40 mt highlighting the significance of sediment recycling 50 of the total load such sediment trapping and recycling affects the transport storage and evolution of biogeochemically reactive particles the evolution of the floodplain and the morphodynamics of basin infilling

comparing landscape evolution models with quantitative field data at the millennial time scale in the belgian loess belt this study compares three landscape evolution models and their ability to correctly simulate measured 2500 year landscape evolution in two small catchments in the belgian loess belt watem lt and lapsus both model tillage and water erosion and deposition and have detachment limited descriptions for water erosion and deposition equations in lapsus are more mechanistic than those in watem lt watem ltt resembles watem lt but is a transport limited model all three models are dem based calibration and validation simulations were performed forward in time on 1d transects for four spatial resolutions and backward in time for 2d catchments at 20 m resolution for transects model outputs were compared with discretized observations of transect shape for catchments outputs were compared with point observations of palaeo altitude averaged over landscape element classes for transects the three models performed well resulting in model efficiency factors of 0 92 to 0 99 for calibration and 0 62 to 0 96 for validation however for catchments simulations showed that the transport limited watem ltt model could not realistically simulate long term landscape evolution performance of watem lt and lapsus at catchment scale was similar to that on transects although lapsus has problems with backward calculation tests demonstrate that a transport limited approach cannot be used to model long term landscape evolution in the belgian loess belt which is in agreement with theoretical and empirical understanding of soil erosion processes in this environment the difference in performance between transport limited and detachment limited models is clear only when the models are evaluated in a 2d catchment the lack of such distinction when models were applied in a 1d transect highlights the importance of evaluating landscape evolution models in a 2d setting so that effects of flow convergence divergence can be accounted for copyright 2011 john wiley sons ltd

ferruginous vernadite in an indian ocean ferromanganese nodule select area electron diffraction and microanalysis of the optically dark component of a ferromanganese nodule from the south east indian ocean manganese field indicate that this is composed of a random stratification of crystallites of vernadite mno 2 r 2 o ro r 2 o 3 x y h 2 o where r represents elements such as k ba na ca mg and a disordered hydrated iron oxide possibly ferrihydrite 5fe 2 o 3 9h 2 o or feroxyhyte feooh whether the dark component is an irregular mixed layer hybrid mineral or a layered accumulation resulting from epitaxy of the above phases is uncertain

a need to improve reconstructions of the fluctuations in the calcite compensation depth over the course of the cenozoic reconstructions based on back tracked depths of the transition between caco3 bearing and caco3 depleted sediment suggest that over the last 65 million years the ocean s caco3 compensation depth ccd has remained within the range 4 0 0 6 km taken at face value these results indicate that depth of the calcite saturation horizon and hence also the product of the ca and co3 concentrations have remained nearly constant in turn this suggests that the ratio of calcite production to ingredient supply has not undergone large changes in this paper the method used to reconstruct the temporal fluctuations and interocean differences in the depth of the calcite saturation horizon is scrutinized the basis for my concern is that offset between the depth of the calcite saturation horizon and the depth where dissolution reduces the caco3 content to 20 i e the ccd can vary by a half kilometer or so depending on the rain rates of caco3 and non caco3 when observations on modern ocean sediments are used to test the reliability of these reconstructions the result is that when averaged over a full glacial cycle the depth of the ccds in the pacific and indian oceans fall within the long term range reliable documentation of fluctuations around this long term average requires that additional measurements such as extent of fragmentation be used to supplement those of caco3 content

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

sediment connectivity a framework for understanding sediment transfer at multiple scales a major challenge for geomorphologists is to scale up small magnitude processes to produce landscape form yet existing approaches have been found to be severely limited new ways to scale erosion and transfer of sediment are thus needed this paper evaluates the concept of sediment connectivity as a framework for understanding processes involved in sediment transfer across multiple scales we propose that the concept of sediment connectivity can be used to explain the connected transfer of sediment from a source to a sink in a catchment and movement of sediment between different zones within a catchment over hillslopes between hillslopes and channels and within channels using fluvial systems as an example we explore four scenarios of sediment connectivity which represent end members of behaviour from fully linked to fully unlinked hydrological and sediment connectivity sediment travel distance when combined with an entrainment parameter reflecting the frequency magnitude response of the system maps onto these end members providing a coherent conceptual model for the upscaling of erosion predictions this conceptual model could be readily expanded to other process domains to provide a more comprehensive underpinning of landscape evolution models thus further research on the controls and dynamics of travel distances under different modes of transport is fundamental copyright 2014 john wiley sons ltd

distribution of carbonate ion in the deep ocean support for a post little ice age change in southern ocean ventilation 1 the distribution of co3 ion concentrations in the deep sea proves difficult to reconcile with a steady state thermohaline circulation the problem is that assuming steady state we cannot come up with any satisfactory explanation for the 28 mol kg deficiency of co3 ion concentration in deep pacific and indian ocean water relative to that for the source water mix however following broecker et al 1999 if we assume that during the little ice age deep water formation in the southern ocean was not only much stronger than now but also had lower po4 and co3 concentrations then this anomaly can be explained

evolutionary trajectory of channel morphology and controlling factors in a large gravel bed river abstract interpretation of channel changes is not always straightforward since it requires a detailed reconstruction of the evolutionary trajectory of channel morphology a quantitative analysis of controlling factors and finally identification of links between evolutionary trajectories and controlling factors the aim of this paper is to explain channel adjustments and controlling factors in the tagliamento river a large gravel bed river in northeastern italy traditional methods for studying historical channel changes i e use of aerial photos topographic data were employed but numerical modelling turned out to be very useful for the quantification of bedload transport and for supporting interpretation of past changes and likely future channel evolution river channel underwent three main phases of adjustment over the last 200 years the first two phases from the end of the nineteenth century to the early 1990s were characterized by narrowing channel width decreased from 1250 to 540 m and incision about 1 m and the third phase from the 1990s to present day by widening from 540 to 600 m and slight aggradation about 0 2 m combining evolutionary trajectories of channel morphology and analysis of controlling factors we argue that the long term channel evolution of the tagliamento river was driven mainly by human intervention at the reach scale i e sediment mining and channelization changes in sediment supply in the catchment area had no or minor effects in the study reach the most recent changes i e widening and slight aggradation are explained as a response to past disturbances that have produced a remarkable change of channel geometry and an increase of unit stream power in the reach magnitude and frequency of formative discharges are a key driving factor of the intensity of recent changes while this was not the case during the previous phases of adjustment

geochemistry of ferromanganese crusts and nodules from the south tasman rise southeast of australia abstract eighteen samples of ferromanganese oxide crusts up to 15 cm thick and nodules have been dredged or cored from elevated parts of the seafloor south of tasmania ferromanganese deposits overlie a variety of basement rocks nodules are dominantly ellipsoidal and mononucleate and range up to 13 cm in diameter surface textures for both crusts and nodules range from smooth to rough gritty or botryoidal typically internally laminated the ferromanganese deposits are dominantly ferruginous vernadite while quartz plagioclase fluorapatite phillipsite goethite and in five samples todorokite are minor phases both crusts and nodules show enrichment of fe co and pb and depletion of mn ni cu and zn to be expected with a vernadite dominated mineralogy cobalt and pb content increase with decreasing water depth with highest values in the range 1 2 km the mineralogy chemistry and physical appearance of the deposits indicate a hydrogenetic origin probably in an environment swept by strong erosive and oxygenated bottom currents the samples analyzed are similar in composition to seamount and ridge crusts and nodules from elsewhere in the southwest pacific they are markedly different to those described from the north pacific and in particular are generally much lower in co one co rich crust from a seamount on the south tasman rise water depth 1700 m does not fit in the distribution of co in ferromanganese deposits of the southern pacific and may reflect a local zone of oxygen depletion associated with the subtropical convergence its significant enrichment in co 0 8 1 0 suggests a detailed survey may be warranted to fully assess the economic potential of this material

is the magnitude of the carbonate ion decrease in the abyssal ocean over the last 8 kyr consistent with the 20 ppm rise in atmospheric co2 content 1 changes in the extent of shell fragmentation the wall thicknesses of foraminifera shells and the bulk caco3 content of deep pacific sediments demonstrate that the extent of dissolution has steadily increased during the past 8 kyr on the basis of measurements on sediment core top material from a range of water depths on the ontong java plateau these dissolution proxies have been calibrated allowing the extent of the decrease in carbonate ion concentration to be quantified the results suggest that the decrease was larger than that of 6 mol km expected to accompany the 20 atm rise in atmospheric co2 content that occurred during this time interval however the inconsistency between the magnitude of the change based on the decrease in shell weight on one hand and that based on the increase in fragmentation on the other hand is problematic if indeed the drop in carbonate ion concentration has been larger than expected then 8 kyr ago either a change in the pattern of thermohaline circulation or in the strength of the biological pump must have kicked in and become ever stronger as the millennia passed if thermohaline circulation is the villain then a possible explanation is that the strength of deepwater formation in the northern atlantic has weakened relative to that in the southern ocean

millennial lag times in the himalayan sediment routing system abstract any understanding of sediment routing from mountain belts to their forelands and offshore sinks remains incomplete without estimates of intermediate storage that decisively buffers sediment yields from erosion rates attenuates water and sediment fluxes and protects underlying bedrock from incision we quantify for the first time the sediment stored in 38 000 mainly postglacial himalayan valley fills based on an empirical volume area scaling of valley fill outlines automatically extracted from digital topographic data the estimated total volume of 690 242 452 km 3 is mostly contained in few large valley fills 1 km 3 while catastrophic mass wasting adds another 177 31 km 3 sediment storage volumes are highly disparate along the strike of the orogen much of the himalaya s stock of sediment is sequestered in glacially scoured valleys that provide accommodation space for 44 of the total volume upstream of the rapidly exhuming and incising syntaxes conversely the step like long wave topography of the central himalayas limits glacier extent and thus any significant glacier derived storage of sediment away from tectonic basins we show that exclusive removal of himalayan valley fills could nourish contemporary sediment flux from the indus and brahmaputra basins for 1 kyr though individual fills may attain residence times of 100 kyr these millennial lag times in the himalayan sediment routing system may sufficiently buffer signals of short term seismic as well as climatic disturbances thus complicating simple correlation and interpretation of sedimentary archives from the himalayan orogen its foreland and its submarine fan systems