mangrove forest evolution in a sediment rich estuarine system opportunists or agents of geomorphic change the majority of the world s mangrove forests occur on mostly mineral sediments of fluvial origin two perspectives exist on the biogeomorphic development of these forests i e that mangroves are opportunistic with forest development primarily driven by physical processes or alternatively that biophysical feedbacks strongly influence sedimentation and resulting geomorphology on the firth of thames coast new zealand we evaluate these two possible scenarios for sediment accumulation and forest development using high resolution sedimentary records and a detailed chronology of mangrove forest avicennia marina development since the 1950s cores were collected along a shore normal transect of known elevation relative to mean sea level msl activities for lead 210 pb 210 caesium 137 cs 137 and beryllium 7 be 7 and sediment properties were analysed with pb 210 sediment accumulation rates sars compensated for deep subsidence similar to 8 mm yr 1 used as a proxy for elevation gain at least four phases of forest development since the 1950s are recognized an old growth forest developed by the late 1970s with more recent seaward forest expansion thereafter excess 210pb profiles from the old growth forest exhibit relatively low sars near the top 7 12 mm yr 1 and bottom 10 22 mm yr 1 of cores separated by an interval of higher sars 33 100 mm yr 1 a general trend of increasing sar over time characterizes the recent forest biogeomorphic evolution of the system is more complex than simple mudflat accretion progradation and mangrove forest expansion surface elevation gain in the old growth forest displays an asymptotic trajectory with a secondary depocentre developing on the seaward mudflat from the mid 1970s two to ten fold increases in 210pb sars are unambiguously large and occurred years to decades before seedling recruitment demonstrating that mangroves do not measurably enhance sedimentation over annual to decadal timescales this suggests that mangrove forest development is largely dependent on physical processes with forests occupying mudflats once they reach a suitable elevation in the intertidal copyright c 2015 john wiley sons ltd

near inertial internal wave field in the canada basin from ice tethered profilers abstractsalinity and temperature profiles from drifting ice tethered profilers in the beaufort gyre region of the canada basin are used to characterize and quantify the regional near inertial internal wave field over one year vertical displacements of potential density surfaces from the surface to 750 m depth are tracked from fall 2006 to fall 2007 because of the time resolution and irregular sampling of the ice tethered profilers near inertial frequency signals are marginally resolved complex demodulation is used to determine variations with a time scale of several days in the amplitude and phase of waves at a specified near inertial frequency characteristics and variability of the wave field over the course of the year are investigated quantitatively and related to changes in surface wind forcing and sea ice cover

dynamics of the changing near inertial internal wave field in the arctic ocean abstractthe dynamics of the wind generated near inertial internal wave field in the canada basin of the arctic ocean are investigated using the drifting ice tethered profiler dataset for the years 2005 to 2014 during a decade when sea ice extent and thickness decreased dramatically this time series with nearly 10 years of measurements and broad spatial coverage is used to quantify a seasonal cycle and interannual trend for internal waves in the arctic using estimates of the amplitude of near inertial waves derived from isopycnal displacements the internal wave field is found to be most energetic in summer when sea ice is at a minimum with a second maximum in early winter during the period of maximum wind speed amplitude distributions for the near inertial waves are quantifiably different during summer and winter due primarily to seasonal changes in sea ice properties that affect how the ice responds to the wind which can be expressed through the wind factor the ratio of sea ice drift speed to

inertial currents in the beaufort sea observations of response to wind and shear doppler sonar observations from the arctic internal waves experiment and arctic leads experiment in the beaufort sea are used to examine currents below the ice during spring conditions following two strong wind events the dominant fine scale current consists of both downward and upward propagating near inertial internal waves the downward propagating waves are most evident above 100 m depth while the upward waves are most energetic below this depth the appearance of these waves coincides in time and depth with a westward subinertial current following the winds with maximum speeds of 0 05 m s 1 at 100 m depth simple ray simulations show that the observed subinertial shear can significantly refract near inertial waves with length scales similar to those observed in particular waves that propagate both in the direction of the current and toward the depth of maximum current are enhanced these simulations suggest that the observed near inertial wave enhancement is due in part to wave shear effects rather than solely to surface forcing

validity of uniform flow hypothesis in one dimensional morphodynamic models local uniform flow luf hypothesis is a simplification of the governing equations describing river morphodynamics which is needed to determine the evolution of the bed profile and bed material composition in the case of large time and space scales this paper presents a rigorous analysis of the full one dimensional river hydrodynamic and morphodynamic mathematical model compared to its luf approximation the analysis establishes two criteria to assess the validity of the luf hypothesis 1 a criterion for rivers in equilibrium and 2 a criterion for evolving rivers i e in nonequilibrium the first criterion is based on the concept of the morphological box variations of the river bed longer than the box length are adequately reproduced by the luf hypothesis whereas only spatially averaged values are resolved within the box the second criterion is based on the concept of an evolution window temporal variations represented by wave periods larger than the evolution window can be adequately reproduced by the luf hypothesis whereas variations with shorter periods are averaged within this window the minimum size of morphological box and evolution window that limit the error introduced by the luf hypothesis increases when the froude number decreases further the minimum size of the evolution window increases for decreasing sediment concentration and increasing mixing layer thickness i e for larger bed forms the luf hypothesis is therefore best applied to small mountain rivers for which both the minimum size of the morphological box and the evolution window is relatively small so that spatial and temporal variations can be resolved in more detail applications using the luf hypothesis for large watersheds including the lowland portion of the fluvial network are possible but are limited to simulations over larger spatial and temporal intervals

distribution and sources of bulk organic matter om on a tropical intertidal mud bank in french guiana from elemental and isotopic proxies the mobile french guiana coast is a shoreface region downdrift of the amazon river where enormous quantities of inorganic and organic materials are exchanged with the atlantic ocean the rapid accumulation of these materials forms highly unstable shore attached mud banks which can be temporally emerged and then rapidly colonized and stabilized by microphytobenthos and opportunistic mangroves i e avicennia germinans mud banks are preferential sites for the accumulation and significant remineralization of organic matter om due to intense erosion deposition cycles and potential biological colonization the distribution and sources of bulk sedimentary om were characterized by elemental and isotopic analyses of four sediment cores together with samples from three potential om sources mangrove plants suspended particulate matter spm and microphytobenthos all collected from the landward face of the macouria mud bank french guiana total organic carbon toc and nitrogen tn concentrations in the sediment cores showed that om sources were characterized by spatio temporal variations in this mud bank the relative contributions of mangrove plants spm and microphytobenthos were estimated using a three end member mixing model based on tn toc atomic ratios and 13c values sedimentary om is mostly controlled by spm associated with variable amounts of om derived from mangrove plants and microphytobenthos these variations could be explained by topography and bed elevation which decrease submersion time and increase desiccation higher contributions of microphytobenthos are associated with black om rich laminae identified in sedimentary cores and linked to temporal emersion phases of the mud bank which favor the growth of benthic microalgae this result is confirmed by the calculation of the average sediment accumulation rate around 36 7 14 8 cm yr 1 taking into account the emersion of the study site every spring tide a fortnightly cycle this value is within the range of the previous results from other mud banks in french guiana but is more than ten times greater than values generally obtained in other coastal contexts

sediment pulses in mountain rivers 2 comparison between experiments and numerical predictions 1 mountain rivers in particular are prone to sediment input in the form of pulses rather than a more continuous supply these pulses often enter in the form of landslides from adjacent hillslopes or debris flows from steeper tributaries the activities of humans such as timber harvesting road building and urban development can increase the frequency of sediment pulses the question as to how mountain rivers accommodate pulses of sediment thus becomes of practical as well as academic significance in part 1 cui et al 2003 the results of three laboratory experiments on sediment pulses are reported it was found there that the pulses were eliminated from the flume predominantly by dispersion of the topographic high significant translation was observed only when the pulse material was substantially finer than the ambient load in the river here the laboratory data are used to test a numerical model originally devised for predicting the evolution of sediment pulses in field scale gravel bed streams the model successfully reproduces the predominantly dispersive deformation of the experimental pulses rates of dispersion are generally underestimated largely because bed load transport rates are underestimated by the transport equation used in the model the model reproduces the experimental data best when the pulse is significantly coarser than the ambient sediment in this case the model successfully predicts the formation and downstream progradation of a delta that formed in the backwater zone of the pulse in run 3 the performance of the model is less successful when the pulse is composed primarily of sand this is likely because the bed load equation used in the study is specifically designed for gravel when the model is adapted to conditions characteristic of large sand bed rivers with low froude numbers it predicts substantial translation of pulses as well as dispersion

comment on long waves in erodible channels and morphodynamic influence by stefano lanzoni et al 1 enhanced understanding of information propagation by waves in rivers is essential in the context of fluvial hydraulics and morphodynamics lanzoni et al 2006 are complimented for their interesting contribution which would help to understand the long waves in fluvial flows with sediment transport and morphological evolution the investigation is formulated on the basis of a set of hyperbolic equations under the framework of shallow water hydrodynamics however the continuity equation of the fluid phase features a formal flaw this comment presents the correct continuity equations identifies the flaw and briefly addresses its potential impact on the analysis of fluvial processes

behaviour and taphonomic loss in foraminiferal assemblages of mangrove swamps of french guiana abstract fifty three surface sediment samples were collected in january 1999 july 2000 and december 2000 on mud flats and in mangrove swamps of french guiana sampling stations were selected to provide information on different environmental conditions on the mud flats and in the mangrove forest thirteen samples were also collected at a depth of about 8 12 cm in the sediment additional samples were collected from three long cores in the channel of the kaw river the main parameter controlling the distribution of recent foraminiferal assemblages is the seasonally variable relative influence of coastal water of reduced salinity and low ph low ca river water areas under the influence of coastal water are dominated by calcareous species mainly ammonia tepida and cribroelphidium spp even in mangrove swamps during the dry season river water influences almost all the study area during the rainy season and leads to the dominance of agglutinated species with the nature of the assemblages depending on local environmental characteristics on the mud flats tests are typically well preserved in the 10 cm below the surface that is the most important taphonomically active zone for foraminifera however owing to intense bioturbation the taphonomic processes in the mangrove swamp may result in the total destruction of the microfauna including agglutinated tests this study shows that the preservation of thanatocoenoses in mangrove swamp environments of french guiana only occurs in exceptional circumstances when they are preserved the remaining assemblages even if modified by taphonomic processes give valuable information for paleoenvironmental reconstructions in this environment

internal waves in the arctic ocean comparison with lower latitude observations abstract a thermistor chain was moored below the pack ice from 50 150 m in the arctic ocean for five days in 1981 oscillations in temperature are attributed to the vertical dispalcement of internal waves the spectral shape of isotherm dispalcement is consistent with the garrett munk model and other internal wave observations but the spectral level is significantly lower other observations from the arctic ocean also exhibit lower internal wave energy when compared with historical data from lower latitudes the lower energy may be related to the unique generation and dissipation mechanisms present in the ice covered arctic ocean significant peaks in vertical coherence occur at 0 81 and 2 6 cph the peak at 2 6 cph coincides approximately with the high frequency spectral cutoff near the local buoyancy frequency this feature has been observed in many other internal wave experiments the coherent oscillations at 0 81 cph exhibit a node in vertical dispalcement at 75 100 m this is consistent with either

internal wave variability in the beaufort sea during the winter of 1993 1994 1 acoustic doppler current profiler observations were obtained at the sea ice mechanics initiative ice camp as it drifted through the beaufort sea over the winter of 1993 1994 in this paper the variability of the internal wave field is examined initially december 1993 january 1994 the camp drifted westward through the central canada basin 75 n 139 153 w numerous anticyclonic baroclinic eddies were encountered internal wave energy levels averaged 1 25 of the garrett munk gm standard shear variance averaged 1 17 gm during february march 1994 the camp drifted meridionally along 156 w near the northwind ridge reversing direction several times large baroclinic vortices were not detected internal wave energy levels were significantly greater during this period peaking at 1 6 gm shear variance peaked at 1 3 gm the waves were predominantly near inertial resulting from three distinct surface generation events downward vertical energy fluxes ranged from typical values of 0 02 mw m2 to a peak value of 0 15 mw m2 two thirds of the downward flux was associated with waves of vertical scale greater than 55 m the remainder with smaller scale waves upward energy fluxes ranged from 0 02 mw m2 typical to 0 10 mw m2 peak supported almost entirely by the larger scale waves high ice water relative velocities atmospheric storms accompanied by ice deformation appear to be necessary but not sufficient to assure a downward propagating wave generation event the highly variable mesoscale has a significant effect on the near inertial wave field propagation the data suggest that the vertical propagation of near inertial waves is strongly affected by the depth variation of the vertical component of mesoscale vorticity the large beaufort sea vortices appear to have a dual effect on the wave field enhanced vertical propagation speed and decreased energy density is found in the negative vorticity cores propagation into the positive vorticity regions surrounding the cores is inhibited the increase in wave energy experienced as the ice camp left the central beaufort sea is jointly associated with the passage of storms and the absence of large baroclinic vortices over the northwind ridge

wind driven mixing at intermediate depths in an ice free arctic ocean recent seasonal arctic ocean sea ice retreat is a major indicator of polar climate change the arctic ocean is generally quiescent with the interior basins characterized by low levels of turbulent mixing at intermediate depths in contrast under conditions of reduced sea ice cover there is evidence of energetic internal waves that have been attributed to increased momentum transfer from the atmosphere to the ocean new measurements made in the canada basin during the unusually ice free and stormy summer of 2012 show previously observed enhancement of internal wave energy associated with ice free conditions however there is no enhancement of mixing at intermediate depths away from significant topography this implies that contrary to expectations of increased wind induced mixing under declining arctic sea ice cover the stratification in the central canada basin continues to suppress turbulent mixing at intermediate depths and to effectively isolate the large atlantic and pacific heat reservoirs from the sea surface

coastal dynamics and chenier sands in french guiana abstract the holocene coastal plain of french guiana is an open chenier plain the shoreline is characterized by vast migrating shoreface attached mudbanks cheniers develop within the interbank zone these sandbodies which rest on the demerara marine clays have also been observed in the inner parts of the coastal plain this paper deals with the coastal area between mahuri and the maroni rivers in french guiana an overview of the present state of knowledge regarding the coastal research in this area is given and based on new evidence the problem of the provenance of the sandy accumulations will be discussed and further defined

coupled and decoupled numerical modeling of flow and morphological evolution in alluvial rivers existing numerical river models are mostly built upon asynchronous solution of simplified governing equations the strong coupling between water flow sediment transport and morphological evolution is thus ignored to a certain extent an earlier study led to the development of a fully coupled model and identified the impacts of simplifications in the water sediment mixture and global bed material continuity equations as well as of the asynchronous solution procedure for aggradation processes this paper presents the results of an extended study along this line highlighting the impacts on both aggradation and degradation processes simplifications in the continuity equations for the water sediment mixture and bed material are found to have negligible effects on degradation this is however in contrast to aggradation processes in which the errors purely due to simplified continuity equations can be significant transiently the asynchronous solution procedure is found to entail appreciable inaccuracy for both aggradation and degradation processes further the asynchronous solution procedure can render the physical problem mathematically ill posed by invoking an extra upstream boundary condition in the supercritical flow regime finally the impacts of simplified continuity equations and an asynchronous solution procedure are shown to be comparable with those of largely tuned friction factors indicating their significance in calibrating numerical river models it is concluded that the coupled system of complete governing equations needs to be synchronously solved for refined modeling of alluvial rivers

the unified gravel sand tugs model simulating sediment transport and gravel sand grain size distributions in gravel bedded rivers received 9 july 2006 revised 7 august 2007 accepted 14 august 2007 published 30 october 2007 1 this paper presents the unified gravel sand tugs model that simulates the transport erosion and deposition of both gravel and sand tugs model employs the surface based bed load equation of wilcock and crowe 2003 and links grain size distributions in the bed load surface layer and subsurface with the gravel transfer function of hoey and ferguson 1994 and toro escobar et al 1996 a hypothetical sand transfer function and hypothetical functions for sand entrainment infiltration from into the subsurface the model is capable of exploring the dynamics of grain size distributions including the fractions of sand in sediment deposits and on the channel bed surface and is potentially useful in exploring gravel sand transitions and reservoir sedimentation processes simulation of three sets of large scale flume experiments indicates that the model with minor adjustment to the wilcock crowe equation excellently reproduced bed profile and grain size distributions of the sediment deposits including the fractions of sand within the deposits simulation of a flushing flow experiment indicated that the sand entrainment function is potentially capable of simulating the short term processes such as flushing flow events

material exchange between the continental shelf and mangrove fringed coasts with special reference to the amazon guianas coast abstract mangrove fringed coasts are a major coastal environment in the tropics that exchange enormous quantities of inorganic and organic materials and dissolved ions with the adjacent ocean in unique ways the 1 600 km long guiana coast from the amazon river mouth to the orinoco the world s most extensive example is exposed to significant oceanic wave and tidal energy but is almost exclusively composed of mud deposits the huge alluvial discharge of the amazon advected along the inner continental shelf is reworked into 20 25 shore attached and mobile mud banks 10 40 km in length frequent and deep resuspension created by the energetic conditions results in fluid mud suspensions 10 400 g 1 1 that dewater upon re deposition resulting in extreme shoreline progradation rates up to hundreds of metres per year that are equally rapidly mobilized by wave attack biological assemblages mangroves foraminifera diatoms etc and biogeochemical conditions are strongly controlled by the intense recycling of sediments on the shoreface differences in sedimentary ecological and biogeochemical processes are striking when this coast is compared with mangrove fringed deltaic and estuarine coasts elsewhere including those of west africa and southeast asia

millennial to secular time scale impacts of climate and sea level changes on mangroves from the doce river delta southeastern brazil this work integrates geomorphological sedimentological and palynological data with radiocarbon dating as well as 13c 15n and c n from sedimentary organic matter to provide a model of mangrove dynamics during the evolution of a wave dominated delta in southeastern brazil mangrove dynamics are analyzed within the context of millennial and secular climatic and sea level changes tidal flats positioned at highest limit of the intertidal zone along the edge of a lagoon sheltered by beach ridges were occupied by wetlands represented by mangrove and herbaceous vegetation during the mid holocene high sea level after considering the relative sea level fall and relatively higher fluvial sediment discharge during the last 6350 years progradation took place along this shoreline resulting in extensive beach ridge deposits that overlie transgressive muds this process led to loss of mangrove area similar dynamics were repeated at 3043 cal yr bp although in a relatively more distal i e seaward posi

the composition of sedimentary organic matter in relation to the dynamic features of a mangrove fringed coast in french guiana the sedimentary organic matter content of a series of 2 m deep cores was examined in relation to the evolution of mangrove forest on the basis of geochemical analyses and optical observations avicennia dominated forest deposits developing along the highly dynamic coastline of french guiana were collected in five stations based on stage of forest evolution the sedimentary organic matter in the upper sediment of the youngest mangrove swamp is mainly derived from algal mats with low carbon nitrogen ratios c n ratio from 6 to 8 and typical greyish amorphous organic flakes as observed in optical studies indeed rare young avicennia trees are present and effectively geochemical parameters do not give evidence of a litter made up of higher plant debris these rare debris being probably exported by the tides a slight increase with depth in the first decimetres of both total organic carbon toc content and c n ratio results from the development of the radial cable root system of the pioneer avicennia germinans early diagenetic conditions of this young forest are rather controlled by dominant suboxic processes as suggested by high eh values range 200 400 mv and local anoxic processes occurrence of pyrite in micro environments this is mainly due to the oxygen available by roots and crab bioturbation the organic content of the senescent mangrove sediment is mainly derived from higher plant debris in the uppermost 30 cm as indicated by relatively high c n ratios and the predominance of ligno cellulosic debris the strong decrease in hydrogen index values results from the degradation of the higher plant debris losing hydrogen bounds through decay processes moderately acidic ph values low ehs and the presence of pyrite framboids point towards the reducing decay processes in surficial layers of the senescent mangrove mediated by sulphate reducing bacteria whatever the stage of evolution of the forest the geochemical characteristics of the sediment below 30 cm are those of the shoreface one with opaque refractory debris derived from the amazon river detritus discharge the sediment collected from dead mangrove forests subsequently recolonized by pioneer mangroves contains organic markers which predate recolonization recording previous phases of erosion and accretion

sediment exchange between amazon mudbanks and shore fringing mangroves in french guiana time series remote sensing data sediment cores and water column profiles of fluid properties and suspended sediment concentration were utilized to examine the mechanisms and volumes of sediment exchange between the mangrove fringe and the coastal zone in french guiana remote sensing estimates of sediment yield from mangrove shoreline erosion by wave attack during the 30 year periods when offshore amazon mudbanks are not adjacent to a 30 40 km long section of the shoreline are 6 23 million tons year 1 7be 137cs and 210pb inventories in sediment cores from inner 5 m water depth mudbank areas suggest the mangrove erosion occurs primarily during the january april period of high wave energy and is responsible for the bulk of sediment deposition on the leading edge of the mudbank remote sensing estimates of shoreline accretion associated with onshore flux of sediment from a mudbank are also large 8 26 million tons year 1 radiotracer generated strata age relationships indicate that the lower intertidal zone of the leading depositional edge of the mudbank is a relict surface suggesting the offshore mudbank is decoupled from the shoreline water column profiles and radiochemical signatures point to fluid mud suspensions 10 400 g l 1 as the primary mechanism for delivering sediment across the relict intertidal zone to create the accretion at the shoreline if the estimates of sediment volume involved in shoreline accretion and erosion in the studied area are extrapolated along the entire 1400 km long guianas coastline possessing offshore mudbanks the annual exchange of sediment to and from the mangrove fringe is at least equivalent to the average input of new sediment from the amazon

southward migration of the austral limit of mangroves in south america abstract temperature influences the global distribution of mangroves and global warming may be causing a poleward mangrove expansion sedimentary features pollen and isotopes data from six sediment cores as well as 14c datings indicated a marine transgression during the holocene and it contributed to the expansion of tidal flats occupied by saltmarshes environmental conditions suitable for mangroves development occurred on the study site during the holocene but according to 210pb and 14c dating the establishment of mangroves mainly represented by laguncularia trees only began between 1957 and 1986 ad on the studied tidal flats spatial temporal analysis based on satellite and drone images revealed a mangrove expansion of 10 ha in the study area between 2003 96 1 ha and 2019 106 1 ha nowadays in the study area saltmarshes mainly characterized by spartina and acrostichum are sharing tidal flats with mangroves represented by laguncularia 5 m tall and avicennia 11 m tall probably the absence of mangroves during the holocene followed by their establishment and expansion during the anthropocene in the subtropical zone is associated with a migration of the austral mangrove limit into the temperate zone caused by the gradual increase in winter temperatures this process may be related to a poleward mangrove migration since the late holocene caused by a natural holocene global warming however the industrial era warming must have intensified the mangrove expansion into temperate zones

more on the evolution of bed material waves in alluvial rivers sediment waves or pulses can form in rivers following variations in input from landslides debris ows and other sources the question as to how rivers cope with such sediment inputs is of considerable practical interest experimental numerical and eld evidence assembled by the authors suggests that in mountain gravel bed streams such pulses show relatively little translation instead mostly dispersing in place this research has recently been the subject of discussion in particular it has been suggested that a the equations of ow and sediment mass balance used in the analyses and in most other morphodynamic analyses require correction b the dominance of dispersion appears only because the hyperbolic nature of the governing equations has not been adequately considered and c the sediment transport equation used in the analyses does not lead to generalizable results here we suggest that a the relations for mass balance do not require the indicated correction b the hyperbolic nature of the governing equations does not preclude the result of dispersion dominating translation in mountain streams and c the general behaviour of an appropriate hyperbolic model of sediment waves pulses includes the relative roles of dispersion and translation and is not affected by the precise choice of a sediment transport relation as long as the choice is reasonable for the case in question copyright 2005 john wiley sons ltd

half a century of dynamic coastal change affecting mangrove shorelines of french guiana a case study based on remote sensing data analyses and field surveys the mobile mud banks several kilometres wide and about 30 km long which form the sedimentary environment of the coast of the guianas are a consequence of the huge particulate discharge of the amazon these mud banks shift towards the northwest influenced by the combined action of accretion and erosion a process also affected by periodic variability because of this movement the coastline is unstable and continuously changing such changes determine the structure and composition of mangrove forests the only type of vegetation adapted to this dynamic environment the objectives of this study were to identify coastal changes that took place over the last 50 years and to relate them to natural processes of turnover and replenishment of mangrove forests these objectives have been achieved through a combination of remote sensing techniques aerial photographs and spot satellite images and field surveys in the area of the sinnamary estuary french guiana ground data were collected in representative mangrove forest stands chosen as a function of their growth stages and their structural features from pioneer and young stages to adult mixed and declining formations the coastline changes and the mangrove dynamics over the 1951 1999 period are analyzed through production of synthetic digital maps showing an alternation of net accretion 1951 1966 and erosion periods 1966 1991 followed by the present accretion phase based on this structural functional and historic information a global scenario of mangrove forest dynamics is proposed including a model of forest development forest gap processes and sedimentological dynamics the results of this research are discussed within the context of regional coastal amazonian area and global climate d 2004 elsevier b v all rights reserved

near inertial internal waves and sea ice in the beaufort sea the evolution of the near inertial internal wavefield from ice free summertime conditions to ice covered wintertime conditions is examined using data from a yearlong deployment of six moorings on the beaufort continental slope from august 2008 to august 2009 when ice is absent from july to october energy is efficiently transferred from the atmosphere to the ocean generating near inertial internal waves when ice is present from november to june storms also cause near inertial oscillations in the ice and mixed layer but kinetic energy is weaker and oscillations are quickly damped damping is dependent on ice pack strength and morphology decay scales are longer in early winter november january when the new ice pack is weaker and more mobile decreasing in late winter february june when the ice pack is stronger and more rigid efficiency is also reduced as comparisons of atmospheric energy available for internal wave generation to mixed layer kinetic energies indicate that a smaller percentage of atmospheric energy is transferred to nearinertial motions when ice concentrations are 90 however large kinetic energies and shears are observed during an event on 16 december and spectral energy is elevated above garrett munk levels coinciding with the largest energy flux predicted during the deployment a significant amount of near inertial energy is episodically transferred to the internal wave band from the atmosphere even when the ocean is ice covered however damping by ice and less efficient energy transfer still leads to low arctic internal wave energy in the near inertial band increased kinetic energy below 300m when ice is forming suggests some events may generate internal waves that radiate into the arctic ocean interior

the dominance of dispersion in the evolution of bed material waves in gravel bed rivers bed material waves are temporary zones of sediment accumulation created by large sediment inputs recent theoretical experimental and field studies examine factors influencing dispersion and translation of bed material waves in quasi uniform gravel bed channels exchanges of sediment between a channel and its floodplain are neglected within these constraints two factors influence relative rates of dispersion and translation 1 interactions between wave topography flow and bed load transport and 2 particle size differences between wave material and original bed material our results indicate that dispersion dominates the evolution of bed material waves in gravel bed channels significant translation requires a low froude number which is uncharacteristic of gravel bed channels and low wave amplitude which for a large wave can be achieved only after substantial dispersion wave material of small particle size can promote translation but it primarily increases bed load transport rate and thereby accelerates wave evolution copyright 2001 john wiley sons ltd

reconstructing a sediment pulse modeling the effect of placer mining on fraser river canada gold mining along 525 km of the fraser river between 1858 and 1909 added an estimated 1 1 108 t of tailings half gravel and the rest finer to the river s natural sediment load we simulate the response using a 1 d multigrain size morphodynamic model since premining conditions are unknown and modern data are insufficient for tuning the process representation we devised a novel modeling strategy which may be useful in other data poor applications we start the model from a smoothed version of the modern longitudinal profile with bed grain size distributions optimized to match alternative assumptions about natural sediment supply and compare runs that include mining with control runs that can be used to quantify the effects of deficiencies in process representation and initialization simulations with an appropriate choice of natural supply rate closely match the best available test data which consist of a detailed 1952 1999 gravel budget for the distal part of the model domain the simulations suggest that the main response to mining was rapid bed fining which allowed a major increase in bed load transport rate with only slight 0 1 m mean aggradation within the mining region and most of the excess sediment exported well beyond the mountain front within the mining period or soon afterward we compare this pattern of response by a large powerful river with previous case studies of river adjustment to sediment supply change

brachyuran crab community structure and associated sediment reworking activities in pioneer and young mangroves of french guiana south america this study in french guiana evaluates the changes of crab assemblages and their bioturbation activities between mangrove early stages pioneer and young mangrove and within stages by taking their spatial heterogeneity tidal channels flat areas pools into account the results show differences in crab assemblage structure between and within the early stages of mangrove in relation to microhabitat and sediment characteristics the sediment reworking rates are a function of the biomass or density of particular species ucides cordatus uca cumulanta and burrower functional groups crab species or functional interactions mediate changes in sediment reworking rates suggesting the need to consider entire benthic communities rather than single species this study suggests that the role of the micro habitat in determining the biologically induced sediment reworking rates depends on the age of the mangrove feeding activity results in a sediment turnover of 11 7 9 7 g dw m 2 day 1 and 6 8 3 0 g dw m 2 day 1 in the pioneer and young mangroves respectively burrow maintenance excavates 40 5 7 4 g dw m 2 day 1 and 251 3 419 7 g dw m 2 day 1 in the pioneer and young mangroves respectively upscaling to the studied area sinnamary estuary 6 km 2 shows that 500 tons day 1 and 20 tons day 1 of sediments could be excavated and pelletized respectively during the spring tides of the dry season thus biological sediment reworking would greatly contribute to the sedimentary dynamics of the guianese mangroves under amazonian influence c 2016 elsevier ltd all rights reserved

near inertial wave propagation in the western arctic abstract from october 1997 through october 1998 the surface heat budget of the arctic sheba ice camp drifted across the western arctic ocean from the central canada basin over the northwind ridge and across the chukchi cap during much of this period the velocity and shear fields in the upper ocean were monitored by doppler sonar near inertial internal waves are found to be the dominant contributors to the superinertial motion field typical rms velocities are 1 2 cm s 1 in this work the velocity and shear variances associated with upward and downward propagating wave groups are quantified patterns are detected in these variances that correlate with underlying seafloor depth these are explored with the objective of assessing the role that these extremely low energy near inertial waves play in the larger scale evolution of the canada basin the specific focus is the energy flux delivered to the slopes and shelves of the basin available for driving mixing at the ocean boundaries the energy and

revisiting internal waves and mixing in the arctic ocean 1 to determine whether deep background mixing has increased with the diminishment of the arctic sea ice we compare recent internal wave energy and mixing observations with historical measurements since 2007 the north pole environmental observatory has launched expendable current probes xcps as a part of annual airborne hydrographic surveys in the central arctic ocean mixing in the upper 500 m is estimated from xcp shear variance and conductivity temperature depth ctd derived brunt vaisala frequency internal wave energy levels vary by an order of magnitude between surveys although all surveys are less energetic and show more vertical modes than typical midlatitude garrett munk gm model spectra survey averaged mixing estimates also vary by an order of magnitude among recent surveys comparisons between modern and historical data reanalyzed in identical fashion reveal no trend evident over the 30 year period in spite of drastic diminution of the sea ice turbulent heat fluxes are consistent with recent double diffusive estimates both mixing and internal wave energy in the beaufort sea are lower when compared to both the central and eastern arctic ocean and expanding the analysis to mooring data from the beaufort sea reveals little change in that area compared to historical results from arctic internal wave experiment we hypothesize that internal wave energy remains lowest in the beaufort sea in spite of dramatic declines in sea ice there because increased stratification amplifies the negative effect of boundary layer dissipation on internal wave energy

coupling between sedimentary dynamics early diagenetic processes and biogeochemical cycling in the amazon guianas mobile mud belt coastal french guiana coastal french guiana lies within the vast mobile mudbelt that characterizes much of the s american inner shelf downdrift of the amazon river approximately 15 20 of the amazon sediment outfall moves nw along the guianas in part as a series of 20 25 coastal mud waves seasonal studies of a representative migrating mudwave located between kourou and sinnamary french guiana demonstrate that diagenetic properties and biogeochemical cycling are closely coupled to sedimentary dynamics and the refluxing of reduced components between the seabed coastal facies and well oxygenated overlying water an unsteady two zone diagenetic regime is typically present in the shallow subtidal and low intertidal regions a surficial layer usually 0 5 1 m thick is nonsulfidic highly reactive and dominated by fe mn cycling this suboxic layer unconformably overlies more consolidated sediment in which net so42 reduction is often observed and contracts shoreward toward the mangrove fringe as sediments stabilize and become bioturbated the relatively stable intertidal flats are also sites of significant benthic primary production despite suboxic conditions over extensive intervals anaerobic remineralization rates are high co2 0 2 0 6 mm day 1 and often show little evidence of attenuation with depth integrated co2 fluxes are 20 235 mmol m 2 day 1 wet dry season average 120 far exceeding diffusive o2 fluxes into the bottom high reactivity 0 08 day 1 and low c n remineralization release ratios 5 3 of decomposing material imply fresh substrate of marine origin most reduced solid phase fe is present as nonpyritic authigenic fe minerals 20 fe ii is in pyrite and low sedimentary c s ratios 6 8 reflect the generally nonsulfidic conditions a broad range of tracers e g 234th t1 2 24 days 210pb t1 2 22 years seasonal cl profiles and nonsteady state diagenetic models of pore water concentrations and oxidant reductant relationships demonstrate that the upper 0 1 1 m of deposits are reworked and exchanged with overlying water on timescales of 10 days to seasonally thus the seafloor acts as a massive suboxic batch reactor entraining and processing reactive marine plankton regenerating fe mn oxides exchanging metabolites and nutrients with the oxygenated water column and generating suites of nonsulfidic authigenic minerals the apparent paradoxical properties of high remineralization rate low reductant content corg 630 mol g 1 and dominance of suboxic metal cycling are a direct consequence of frequent entrainment of highly reactive organic substrate and simultaneous regeneration of the major fe oxidants in oxygenated water the amazon guianas mobile mudbelt is a zone of extraordinarily intense sedimentary and biogeochemical recycling greatly exceeding stable coastal systems such as salt marshes in material exchange with the sea

effects of sea level rise and climatic changes on mangroves from southwestern littoral of puerto rico during the middle and late holocene abstract we evaluated the response to sea level rise and climatic changes of the northeastern caribbean by establishing a palaeoenvironmental reconstruction of the flamenco lagoon located in the coastal side of the guanica dry forest a mab unesco reserve in the semi arid southwestern coast of puerto rico 17 57 10 31 n 66 50 39 30 w the reconstruction was based on pollen records sediments analysis 13 c 15 n c n data and ams 14 c dating of one sediment core the geology of the area is rocky calcareous karst with rocky outcrops and canyons with intermittent streams that move water during periods of high run off conditions the present lagoon is surrounded by rocky outcrops where dry forest vegetation is present on the terrestrial sides and sand dunes on the coastal side we propose that the studied lagoon developed after the stabilization of sea level rise in the region following three main stages 1 before 5400 cal yr bp sediments were accumulated according to small channels dynamics and trees shrubs and herbs were present the sedimentary organic matter was mainly sourced from terrestrial c 3 and c 4 plants 2 between 5400 and 4400 cal yr bp tidal flats were established and mangroves mainly represented by rhizophora trees migrated landward with sea level rise and established in the area and the sedimentary organic matter was sourced from terrestrial c 3 plants 3 around 4400 cal yr bp sea level was near the stabilization the endorheic minibasin was closed when a coastal sand dune was established as a result of drier climatic conditions mangroves were eliminated from the system as a result of the closure of the area by sand dunes and increased salinity in water due to high evaporative demand of the climate the pollen dominance of herbaceous and shrubby vegetation prevails until present throughout the lagoon development sedimentary organic matter was sourced from c 3 and c 4 plants as well as phytoplankton organic matter the closure of the lagoon and the drier conditions prevalent in the region during the late holocene which lasts until the present day and increased the contribution of salinity tolerant phytoplankton that characterizes the current conditions of the flamenco lagoon

management responses to pulses of bedload sediment in rivers abstract rivers can experience sudden pulses of sediment from human and natural erosion processes that can accumulate in the bed abundant studies have examined the sources and dynamics of sediment pulses and problems caused by these pulses particularly flooding avulsions and habitat simplification much less has been written about what managers can do about sediment pulses and that is the purpose of this review the first option for managers is to do nothing and this decision can be informed by many case studies and by theory on the propagation and character of sediment pulses their diffusion translation and celerity doing nothing should be informed by the secondary effects of sediment pulses on channels including widening avulsions and tributary interactions if managers decide that something needs to be done about the sediment they have four options 1 reducing the sediment supply at source 2 trapping sediment in the channel 3 accelerating sediment transport through a reach and 4 directly extracting sediment the most common of these actions is undoubtedly to reduce the supply at source but there are few examples of the consequences of this for sediment pulses there are even fewer examples of trapping accelerating and extracting sediment all of these options have great potential for managing sediment pulses however they also have the potential to trigger incision of tributaries and of the channel behind the passing sediment wave overall the literature equips managers to understand the dynamics of sediment pulses but it does not yet equip them to confidently manage these geomorphic events

origin of amazon mudbanks along the northeastern coast of south america abstract seismic profiles sediment cores and water column measurements were collected along the northeastern coast of brazil to examine the origin of mudbanks in the amazon coastal mud belt these 10 60 km long shore attached features previously had been observed to migrate along the 1200 km coast of the guianas in response to wave forcing chirp 3 5 khz seismic profiles of the shoreface and inner shelf located two mudbanks updrift of the previous eastern limit in french guiana 210 pb geochronology shows that these two banks are migrating to the northwest over a relict mud surface in 5 20 m water depth the mudbanks are 3 4 m thick and are translating over a modern shoreface mud wedge deposited by previous mudbank passage in

the influence of the trade winds on the coastal development of the guianas at various scale levels a synthesis abstract the coastal development of the guianas is dominated by extensive shoreface attached and alongshore westward migrating mudbanks the behaviour of these mudbanks is mainly determined by a combination of the large supply of amazon borne silt and clay and the trade wind generated wave action in the front zone of the mudbanks fluid mud is formed as a result the incoming waves are strongly attenuated and deposition is favoured at their rear side compacted clay deposits are eroded by waves the mudbanks migrating in this manner are the driving mechanism in the development of the smallest coastal unit which consists of a mudbank and the eastward adjacent interbank area eisma et al neth j sea res 28 1991 181 has demonstrated that the frequency of the northeast trade wind which blows towards the coast of the guianas in the windy season january till april shows a systematic change in time for the period 1953 1986 there is evidence that the frequency of winds coming from directions between 50 and 80 roughly east northeast increases the same applies to the wind velocity from that direction in the last 10 years a reversal of these trends appears to occur for a more or less east west directed coastal section e g the coastline of suriname a more easterly direction of the northeast trade wind results in an increased longshore wave energy flux in the coastal waters this causes an increase in length of the mudbanks at the detriment of the usually eroding interbank parts of the coast this is evidenced by the large scale coastal development during the related period demonstrating an increasing length of the mudbanks and consequently an increasing net accretion it is hypothesised that this development will reverse if the new trends in wind direction and velocity develop further at the geological scale it is considered that a coincidence of a systematic increase of more northerly directed wind frequencies and a fall in sea level are responsible for the two erosive interruptions in the generally accreting coastal plain during the young holocene period

turbulent upper ocean mixing affected by meltwater layers during arctic summer abstractevery summer intense sea ice melt around the margins of the arctic pack ice leads to a stratified surface layer potentially without a traditional surface mixed layer the associated strengthening of near surface stratification has important consequences for the redistribution of near inertial energy ice ocean heat fluxes and vertical replenishment of nutrients required for biological growth the authors describe the vertical structure of meltwater layers and quantify their seasonal evolution and their effect on turbulent mixing in the oceanic boundary layer by analyzing more than 450 vertical profiles of velocity microstructure in the seasonal ice zone north of svalbard the vertical structure of the density profiles can be summarized by an equivalent mixed layer depth hbd which scales with the depth of the seasonal stratification as the season progresses and melt rates increase hbd shoals following a robust pattern implying stronger vertical stratification weaker vertical eddy diffusivit

evolution of a sediment wave in an experimental channel the routing of bed material through channels is poorly understood we approach the problem by observing and modeling the fate of a low amplitude sediment wave of poorly sorted sand that we introduced into an experimental channel transporting sediment identical to that of the introduced wave the wave essentially dispersed upstream and downstream without translation although there was inconclusive evidence of translation late in the experiment when the wave was only 10 20 grain diameters high alternate bars migrated through zones of differing bed load transport rate without varying systematically in volume celerity or transport rate sediment that overpassed migrating bars was apparently responsible for dispersion of the wave the evolution of the wave was well predicted by a one dimensional model that contains no adjusted empirical constants numerical experiments demonstrate however that the theory does not predict sediment waves that migrate long distances downstream such waves can only be explained by the following processes not represented by the theory selective bed load transport spatial variations in bar and other form roughness the mechanics of mobile armor and perhaps other mechanisms

distribution of fluid muds on the amazon continental shelf abstract a comprehensive study of suspended sediment transport on the amazon shelf was conducted as part of the amasseds project a multidisciplinary amazon shelf sediment study to understand the link between physical processes and the fate of amazon river sediment a small instrumented tripod was used to measure the fluid flow and suspended sediment characteristics throughout the water column on varying time scales e g semidiurnal fortnightly seasonal dense nearbed suspensions or fluid muds suspended sediment concentration 10 g l on the order of a few meters in thickness were found on the inner and middle shelf covering an area ranging from 5 700 km2 during falling and low river discharge to 10 000 km2 during rising and high discharge fluid muds generally observed in the region of bottom salinity fronts extend across the topset beds to the foreset beds during rising and high discharge salinity and temperature anomalies frequently observed in fluid muds imply that often the muds do not result from erosion and resuspension from the seabed but from trapping processes at the bottom salinity front and transport across the shelf the vertical structure of fluid mud varies in space and tune variability close to the river mouth is predominantly fortnightly related to the location and structure of the bottom salinity front on the open shelf the variability appears to be related to seasonal differences in river and sediment discharge and the location of the bottom salinity front the total suspended sediment inventory on the shelf during the season of high discharge is approximately equal to the annual sediment discharge from the river 1 2 109 tons yr and 90 of that inventory is within fluid mud suspended sediment transport on the shelf is dominated by fluid mud

morpho dynamics of the brahmaputra jamuna river bangladesh abstract the jamuna river is the downstream continuation of the brahmaputra in bangladesh it is one of the largest sand bed braided rivers in the world and every year it erodes thousand hectares of mainland floodplain rendering tens of thousands of people landless and or homeless understanding the morpho dynamics of this river and its responses to the various drivers of morphological change that act on it is essential to improving the livelihoods of millions of floodplain dwellers in bangladesh especially given the threats posed by climate change reliable data information and knowledge of river process are sparse and so progress in linking the impacts of multiple drivers including neo tectonics earthquakes large scale avulsions and engineering interventions to complex morphological responses depends on making best use of historical maps time series satellite images hydro morphological data expert judgment and local knowledge this paper draws on all these sources to chronicle the morphological evolution of the jamuna river since the avulsion that created it about 200 years ago and to establish temporal trends and spatial patterns in the changes that have characterized process response mechanisms in this fluvial system since then the understanding gained from these investigations then supports deeper analyses to explain how historical migration of the river westward has produced significant contrasts between left and right west bank material properties elucidate the relationships between discharge fluvial processes anabranch instability and floodplain erosion rates and identify causal links between drivers and morphological responses at a variety of time and space scales finally the new knowledge generated by the analyses developed herein are combined with existing conceptual and empirical process response models for the jamuna to predict possible future morphological adjustments in ways helpful in identifying appropriate strategies for climate change adaptation in bangladesh the enhanced knowledge gained from these historical and contemporary investigations may also be useful in assessing the impacts of natural and anthropogenic drivers on other large braided rivers

numerical model of sediment pulses and sediment supply disturbances in mountain rivers sediment pulses in rivers can result from many mechanisms including landslides entering from side slopes and debris flows entering from tributaries artificial sediment pulses can be caused by the removal of a dam this paper presents a numerical model for the simulation of gravel bedload transport and sediment pulse evolution in mountain rivers a combination of the backwater and quasi normal flow formulations is used to calculate flow parameters gravel bedload transport is calculated with the surface based bedload equation of parker in 1990 the exner equation of sediment continuity is used to express the mass balance at different grain size groups and lithologies as well as the abrasion of gravel the river is assumed to have no geological controls such as bedrock outcrops and immobile boulder pavements the results of nine numerical experiments designed to study various key parameters relevant to the evolution of sediment pulses are reported here results of the numerical runs indicate that the evol

ekman veering internal waves and turbulence observed under arctic sea ice the ice ocean system is investigated on inertial to monthly time scales using winter 2009 10 observations from the first ice tethered profiler itp equipped with a velocity sensor itp v fluctuations in surface winds ice velocity and ocean velocity at 7 m depth were correlated observed ocean velocity was primarily directed to the right of the ice velocity and spiraled clockwise while decaying with depth through the mixed layer inertial and tidal motions of the ice and in the underlying ocean were observed throughout the record just below the ice ocean interface direct estimates of the turbulent vertical heat salt and momentum fluxes and the turbulent dissipation rate were obtained periods of elevated internal wave activity were associated with changes to the turbulent heat and salt fluxes as well as stratification primarily within the mixed layer turbulent heat and salt fluxes were correlated particularly when the mixed layer was closest to the freezing temperature momentum flux is adequately related to velocity shear using a constant ice ocean drag coefficient mixing length based on the planetary and geometric scales or rossby similarity theory ekman viscosity described velocity shear over the mixed layer the ice ocean drag coefficient was elevated for certain directions of the ice ocean shear implying an ice topography that was characterized by linear ridges mixinglengthwasbestestimatedusingthewavenumber ofthebeginningoftheinertialsubrangeoravariable drag coefficient analyses of this and future itp v datasets will advance understanding of ice ocean interactions and their parameterizations in numerical models

mixing across the arctic ocean microstructure observations during the beringia 2005 expedition 1 turbulent scale temperature and conductivity were measured during the pan arctic beringia 2005 expedition the rates of dissipation of thermal variance and diapycnal diffusivities are calculated along a section from alaska to the north pole across deep flat basins canada and makarov basins and steep ridges alpha mendeleev and lomonosov ridges the mixing rates are observed to be small relative to lower latitudes but also remarkably non uniform relatively elevated turbulence is found over deep topography confirming the dominant role of bottom generated internal waves measured patterns of mixing in the arctic are also associated with other mechanisms such as double diffusive structures and deep overflows a better knowledge of the distribution of mixing is essential to understand the dynamics of the changing arctic environment

unsteady diagenetic processes and sulfur biogeochemistry in tropical deltaic muds implications for oceanic isotope cycles and the sedimentary record abstract sedimentary s cycling is usually conceptualized and interpreted within the context of steadily accreting 1 d transport reaction regimes unsteady processes however are common in many sedimentary systems and can result in dramatically different s reaction balances and diagenetic products than steady conditions globally important common examples include tropical deltaic topset and inner shelf muds such as those extending from the amazon river 1600 km along the guianas coast of south america these deposits are characterized by episodic reworking of the surface seabed over vertical depths of 0 1 3 m reworked surface sediments act as unsteady suboxic batch reactors unconformably overlying relict anoxic often methanic deposits and have diagenetic properties largely decoupled from net accumulation of sediment despite well oxygenated water and an abundant reactive organic matter supply physical disturbance inhibits macrofauna and benthic communities are dominated by microbial biomass across immense areas in the surficial suboxic layer molecular biological analyses tracer experiments sediment c s fe compositions and 34s 18o of pore water so 4 2 indicate close coupling of anaerobic c s and fe cycles 18o so 4 2 can increase by 2 3 during anaerobic recycling without net change in 34s so 4 2 demonstrating so 4 2 reduction coupled to complete anaerobic reoxidation to so 4 2 and a 18o so 4 2 reduction reoxidation fractionation factor 12 summed magnitudes s reoxidation must be coupled to fe oxide reduction contributing to high dissolved fe2 1 mm and fe mobilization export the reworking of amazon guianas shelf muds alone may isotopically alter 18o so 4 2 equivalent in mass to 25 of the annual riverine delivery of so 4 2 to the global ocean unsteady conditions result in preservation of unusually heavy 34s isotopic compositions of residual cr reducible s ranging from 0 to 30 in physically reworked deposits in contrast bioturbated facies adjacent to physically reworked regions accumulate isotopically light s 34s to 20 in otherwise similar decomposition regimes the isotopic patterns of both physically and biologically reworked regions can be simulated with simple diagenetic models heavy s isotopic signatures are largely a consequence of unsteady diffusion and progressive anaerobic burndown into underlying deposits whereas isotopically depleted bioturbated deposits predominantly reflect biogenic diffusive scaling and isotopic distillation diffusive pumping associated with reoxidation in burrow walls immediately adjacent to reduced zones the s isotopic transition from unsteady physically controlled regions of the amazon delta moving laterally into bioturbated facies mimics the transition of s isotopic patterns temporally in the geologic record during the rise of bioturbation no special role for s disproportionation is required to explain these differences the potential role of unsteady suboxic diagenesis and dynamic reworking of sediments has been largely ignored in models of the evolution of surficial elemental cycling and interpretations of the geologic record

on evolution of bed material waves in alluvial rivers field and laboratory measurements have shown distinct characteristics of bed sediment waves under differing conditions whilst their theoretical interpretation has emerged to be equivocal this note aims to clarify the interpretation of evolution of bed material waves the complete set of governing equations for the flow sediment morphology system is deduced to demonstrate its universally hyperbolic nature irrespective of the sediment transport functions implemented to close the equations the hyperbolic nature can admit not only attenuating bed material waves but also shock like waves that are not unusual in the real world it is suggested that the theory of dispersion diffusion is not universally appropriate for evolution of bed material waves

near inertial mixing in the central arctic ocean observations were made in april 2007 of horizontal currents hydrography and shear microstructure in the upper 500m from a drifting ice camp in the central arctic ocean an approximately 4 day long time series collected about 10 days after a storm event shows enhanced near inertial oscillations in the first half of the measurement period with comparable upward and downward propagating energy rough estimates of wind work and near inertial flux imply that the waves were likely generated by the previous storm the nearinertial frequency band is associated with dominant clockwise rotation in time of the horizontal currents and enhanced dissipation rates of turbulent kinetic energy the vertical profile of dissipation rate shows elevated values in the pycnocline between the relatively turbulent underice boundary layer and the deeper quiescent water column dissipation averaged in the pycnocline is near inertially modulated and its magnitude decays approximately at a rate implied by the reduction of energy over time observations suggest that near inertial energy and internal wave induced mixing play a significant role in vertical mixing in the arctic ocean

decadal scale morphological evolution of a muddy open coast analysis of the long term morphological evolution of a muddy open coast sediment transport suggests a growth of mudbanks migrating along the coast cross shore exchange of sediment is equally significant as longshore transport mudbank and shoreline erosion accretion trends are reversed

bedload sheets in heterogeneous sediment field observations in streams with beds of coarse sand and fine gravel have revealed that bedload moves primarily as thin migrating accumulations of sediment and coarse grains cluster at their leading edge these accumulations are one or two coarse grains high and are much longer 0 2 0 6 m long in sand 0 5 2 0 m in fine gravel than their height the authors propose the term bedload sheet for these features and the authors argue that they result from an instability inherent to bedload movement of moderately and poorly sorted sediment in essence coarse particles in the bedload slow or stop each other trap finer particles in their interstices and thus cause the coarse particles to become mobile again bedload sheets develop on the stoss side of dunes causing the dune to advance incrementally with the arrival of each sheet successive deposition of coarse sediment from the leading edge followed by fine sediment may generate the grain size sorting that distinguishes cross bedding available flume experiments and field observations indicate that bedload sheets are a common but generally unrecognized feature of heterogeneous sediment transport

understanding spatio temporal barrier dynamics through the use of multiple shoreline proxies abstract at the coast risk arises where and when static human developments are situated within dynamic surroundings barrier islands are often sites of heightened coastal risk since they frequently support substantial human populations and undergo extensive morphological change owing to their low lying form and persistence in energetic hydrodynamic and meteorological conditions using the mixed sand gravel barrier of blakeney point this study argues that to avoid an only partial understanding of coastal zone processes it is necessary to make use of multiple shoreline proxies capturing processes operating both at different timescales and different cross shore positions here five shoreline proxies were extracted from three data sources shoreline error was quantified and compared to observed shoreline change rates to establish proxy specific appropriate timescales for shoreline change analysis the map derived mean high water line at blakeney point revealed landward retreat of 0 61 m a 1 over the past 130 years with a shift from drift towards swash alignment of the barrier since 1981 over the past 24 years the high water line ridge line and vegetation line reveal proxy specific response to management regime change the termination of barrier reprofiling of the eastern section of the barrier has resulted in increased sediment release to the downdrift barrier terminus buffering retreat there at the expense of the updrift section the vegetation line represents an effective proxy for storm driven overwash with maximum shoreline retreat during surge events of 172 m illustrating a strong event driven component to barrier morphodynamics by comparison to the other proxies the lidar light detection and ranging derived mean high water line offers relatively limited insights into barrier dynamics emphasising the importance of multi proxy approaches in the face of technological advance we demonstrate the continued importance of critical attention towards the dependencies that exist between shoreline proxy selection and the processes that can be observed as a result

dynamics of a fringe mangrove forest detected by landsat images in the mekong river delta vietnam mangrove forests dominate many tropical coastlines and are one of the most bio diverse and productive environments on earth however little is known of the large scale dynamics of mangrove canopies and how they colonize intertidal areas here we focus on a fringe mangrove forest located in the mekong river delta vietnam a fast prograding shoreline where mangroves are encroaching tidal flats the spatial and temporal evolution of the mangrove canopy is studied using a time series of landsat images spanning two decades as well as shuttle radar topography mission srtm elevation data our results show that fast mangrove expansion is followed by an increase in normalized difference vegetation index ndvi in the newly established canopy we observe three different dynamics of the mangrove fringe in the southwest part of the fringe near a deltaic distributary where the fringe boundary is linear the canopy expands uniformly on the tidal flats with a high colonization rate and high ndvi values in the northeast part of the fringe near another distributary the canopy expands at a much lower rate with low ndvi values in the fringe center far from the river mouths the fringe boundary is highly irregular and mangroves expansion in characterized by sparse vegetated patches displaying low ndvi values we ascribe these different dynamics to wave action and southwest longshore transport triggered by energetic northeasterly monsoons during winter we further link the large scale dynamics of the fringe to small scale physical disturbances waves erosion and deposition that might prevent the establishment of mangrove seedlings based on these results we include mangrove encroachment in an already published conceptual model of progradation of the mekong river delta we conclude that high ndvi values and a constantly linear vegetation water interface are indicative of stable mangrove canopies undergoing fast expansion probably triggered by sediment availability at the shore our results can be applied more generally to mangrove forests growing in minerogenic and high tidal range environments with high sediment inputs copyright 2016 john wiley sons ltd

geomorphic response to gravel augmentation and high flow dam release in the trinity river california the geomorphic effect of introducing a gravel augmentation totaling 520 m3 into a gravel bed stream during a dam controlled flood in may of 2015 was monitored with bedload transport measurements an array of seismometers and repeated topographic surveys half of the augmented gravel was injected into the flow with front end loaders on the rising limb of the flood and the other half was injected on the first day of the peak virtually all of the gravel transported past the injection point was deposited within about 7 to 10 channel widths of the injection point most of the injected gravel deposited along the left bank of the river whereas the right half of the channel bed was dominated by scour the downstream third of the depositional area consisted of a small dune field that developed prior to the second gravel injection and subsequently migrated about one channel width downstream a second depositional front was observed upstream from the gravel injection point where a delta like wedge of bed material developed in the first hours of the flow release and changed little over the remainder of the release these two depositional areas represent small scale bed material storage reservoirs with the potential to accumulate and periodically release packets of bed material interactions with such storage reservoirs are hypothesized to cause large bed material pulses to disperse by fragmenting into multiple smaller pulses as a refinement to the conceptual model that views sediment pulse evolution in terms of dispersion and translation the concept of pulse fragmentation has practical implications for gravel management it implies that gravel augmentations can produce morphologic changes at locations that are separated from the augmentation point by arbitrarily long reaches and it highlights the dependence of pulse propagation rates on the nature and distribution of the bed material storage reservoirs in the channel system copyright 2017 john wiley sons ltd

studies of a mangrove basin tuff crater new zealand i mangrove biomass and production of detritus abstract the mangrove avicennia marina var resinifera in a tidally flooded explosion crater tuff crater near the southern latitudinal limit of mangroves in new zealand adopts two distinct growth forms taller tree like mangroves up to 4 m tall along the banks of the tidal creek and low stunted shrub mangroves less than 1 m tall on the mudflats twelve trees were felled and on the basis of a biomass height relationship for the taller trees and a biomass canopy width relationship for the lower above ground biomass excluding pneumatophores was estimated average above ground biomass for the taller mangrove was estimated to be 104 1 t ha 1 and for the lower 6 8 t ha 1 while the value for the taller mangroves is similar to figures reported for more complex tropical mangroves the fact that 94 of the basin is covered by low generally sparse mangroves means that total biomass for the basin is estimated to be 153 t an average of only 7 6 t ha 1 litter fall beneath the taller mangroves is estimated as 7 6 2 5 t ha 1 a 1 and beneath the lower mangroves 3 3 0 5 t ha 1 a 1 the value for the taller mangroves is similar to that reported from mangroves in many other parts of the world but because of the extensive low sparse mangroves the total for the basin is estimated as 53 7 t a 1 an average rate of 2 7 t ha 1 a 1 a very low rate of litter fall when compared with elsewhere decomposition of mangrove leaves occurs relatively rapidly with leaves losing half their dry weight in 10 weeks and then continuing to degrade but at a slower rate substrate sediment samples contain high organic matter content and although some organic matter appears to be exported via the tidal creek a proportion of the detrital production is evidently recycled in situ

migration of mud banks and changing coastline in french guiana abstract the french guiana coast is characterized by migrating mud banks which act not only as markers of hydrodynamic and climatic processes but also have an important impact on coastal evolution the role of mud banks was documented by vertical aerial photographs taken in 1979 1982 and 1984 these allow the delineation of the intertidal parts of the banks at low tide and at identical tidal ranges the following results were obtained 1 six mud banks separated by interbank eroding areas are present along the french guiana coast the intertidal parts of three of these banks are cut by river mouths 2 between 1979 and 1984 the intertidal parts of the banks migrated to the west northwest along the coast at rates ranging from 320 to 1220 m yr mean rate 900 m yr 3 in the same period the extent of the intertidal areas colonized by new mangroves 60 km 2 was nearly the same as that of the areas bearing older mangroves 58 km 2 that were lost by erosion while the nature of the surface covered by the intertidal parts of the banks remained nearly the same in spite of the migration of these banks these results suggest the existence of hydrodynamic circulation cells linked to large coastal mud banks along northeastern south america additionally historical data 1955 1972 show long term variations in the velocity of mud bank migration

the wavenumber frequency spectrum of vortical and internal wave shear in the western arctic ocean abstract upper ocean velocity and shear data were obtained from doppler sonars operated at the surface heat budget of the arctic ocean sheba ice camp during the camp s year long drift across the western arctic ocean these are used to estimate wavenumber frequency spectra of shear e z during three selected time intervals the arctic shear spectra are similar in form to typical oceanic spectra except that they have roughly an order of magnitude less variance the slope of the frequency dependence is also steeper 3 4 for 10 m and time scales 1 h are deemed significant at subinertial frequencies a vortical quasigeostrophic contribution to the shear spectrum is seen the vertical wavenumber depe

sediment pulses in mountain rivers 1 experiments 1 sediment often enters rivers in discrete pulses associated with landslides and debris flows this is particularly so in the case of mountain streams the topographic disturbance created on the bed of a stream by a single pulse must be gradually eliminated if the river is to maintain its morphological integrity two mechanisms for elimination have been identified translation and dispersion according to the first of these the topographic high translates downstream according to the second of these it gradually diffuses away in any given river both mechanisms may operate this paper is devoted to a description of three controlled experiments on sediment pulses designed to model conditions in mountain streams each of the experiments began from the same mobile bed equilibrium with a set rate and grain size distribution of sediment feed in one experiment the median size of the pulse material was nearly identical to that of the feed sediment in the other two the pulse material differed in grain size distribution from the feed sediment being coarser in one case and finer in the other case in all cases the mode of pulse deformation was found to be predominantly dispersive a result that constitutes the main conclusion of this paper the pulses resulted in a notable but transient elevation of sediment transport rate immediately downstream when the pulse was coarser than the ambient sediment the bed downstream remained armored and a migrating delta formed in the backwater upstream when the pulse was finer than the ambient sediment translation was observed in addition to dispersion the presence of the finer material notably elevated the transport of ambient coarse material on the bed downstream in part 2 cui et al 2003 the experimental results are used to test a numerical model

evolution of progradation erosion along the french guiana mangrove coast a comparison of mapped shorelines since the 18th century with holocene data the problems in mapping the mangrove shoreline of french guiana are reviewed the present variability of the coastline due to the shifting mudbanks with avicennia mangroves on their shoreface attached upper fringe is extended to the historical period two and a half centuries ago by means of ancient maps and nautical charts in selected sites around the sinnamary river and the mana river estuaries cayenne peninsula the earliest reported shoreline before 1765 compared with other 18th and 19th century maps is relatively stable demonstrating that erosion repeatedly counterbalanced progradation on a centennial time scale this data contrasts with the 20th century initiation of a sedimentary regime that results in very high local progradation rates an examination of the entire holocene sediment record in preserved in french guiana including palynological evidence suggests that most of the holocene progradation may have occurred by different accretion processes than have formed the historical and recent mudbanks settled by avicennia mangals

evolution of a landslide induced sediment wave in the navarro river california a streamside landslide delivered 60 000 m3 of mixed size sediment to the navarro river a sinuous gravel bed channel drainage area 535 km2 at the end of the annual high runoff period in spring 1995 the deposit formed a 9 m high dam that partially breached within several hours but recessional flows entrained little material until the following high runoff season the landslide afforded the opportunity to measure the evolution of a sediment wave from its inception to near obliteration and particularly to test relative tendencies for translation and dispersion of a sediment wave in a natural gravel bed channel this study represents a simple case the wave originated from a single input the preexisting channel was relatively uniform and resistant banks prevented adjustments in width we surveyed channel topography over a 1 5 4 5 km reach centered on the landslide dam each year from 1995 to 1999 and we sampled bed material downstream of the dam in 1995 and 1997 landslide material was coarser than ambient bed material but all sizes were mobilized by subsequent peak flows abrasion of weathered and fractured graywacke sandstone landslide material was roughly an order of magnitude greater than the ambient river gravel the sediment wave dispersed and mostly disappeared within a few years with no measurable translation sediment filled the reservoir created by the eroding landslide dam until throughput of bed load was restored in 1998 the stationary wave crest eroded until in 1999 it was 1 m higher e mail dsutherl fs fed us than the preslide elevation as the wave profile flattened its detectable leading edge extended downstream from 620 m in 1995 to 1600 m in 1997 downstream advance of the wave was associated with coarsening of bed material the sediment wave created a longitudinal disturbance in sediment transport by using the dam as a reference datum of zero bed load transport we computed longitudinal variations in annual bed load and suspended sediment transport rates in 100 m increments downstream of the dam these longitudinal variations were controlled by scour and fill of the bed and by abrasion of bed load particles bed load transport rates in the first and second years after the landslide increased in the landslide vicinity and then decreased downstream as sediment deposited behind the advancing leading edge of the wave the location of peak bed load transport rate advanced from the first year 400 m to the second 800 m we used a physically based one dimensional model cui et al 2002b to hindcast annual changes in transversely averaged bed elevation over the study reach agreement between measured and predicted bed elevations was very good this result supports our conclusion that once emplaced sediment waves in gravel bed rivers tend to disperse with little or no translation

differentiating the relative importance of land cover change and geomorphic processes on fine sediment sequestration in a logged watershed abstract timber harvest often results in accelerated soil erosion and subsequent elevated fine

sediment pulse evolution and the role of network structure abstract sediment pulses are triggered through a variety of mechanisms from landslides to land use change how do these pulses move through the fluvial system and how do they evolve in a system with perfect sediment connectivity the erosional response to a perturbation and the resulting signal at the river mouth would match however this rarely occurs many studies have addressed reach scale dynamics of sediment pulses and how they translate or disperse downstream at the watershed scale network structure and storage become more important in modulating the sediment signal here we review the current literature on sediment pulse behavior and then address the role of network structure on maintaining dispersing or transforming sediment pulses in a fluvial system we use a reduced complexity network routing model that simulates the movement of bed material through a river basin this model is run in the greater blue earth river gber basin in minnesota usa first with spatially uniform inputs and then with inputs constrained by a detailed sediment budget once the system reaches equilibrium a sediment pulse is introduced first at a single location and then throughout the system and tracked as it evolves downstream results indicate that pulses able to translate downstream disperse in place upon arriving at over capacity reaches as sediment goes into storage in the gber basin these zones occur just upstream of a knickpoint that is propagating upstream through all mainstem channels as the pulses get caught in these sediment bottlenecks there is a decoupling of the original pulse of sediment and the resulting bed material wave these results show that the network structure both in terms of network geometry and the spatial pattern of transport capacity can play a dominant role in sediment connectivity and should be considered when predicting sediment pulse behavior at the watershed scale

internal waves and mixing in the marginal ice zone near the yermak plateau observations were made of oceanic currents hydrography and microstructure in the southern yermak plateau in summer 2007 the location is in the marginal ice zone at the arctic front northwest of svalbard where the west spitsbergen current wsc carries the warm atlantic water into the arctic ocean time series of approximately 1 day duration from five stations upper 520 m and of an 8 day duration from a mooring are analyzed to describe the characteristics of internal waves and turbulent mixing the spectral composition of the internal wave field over the southern yermak plateau is 0 1 0 3 times the midlatitude levels and compares with the most energetic levels in the central arctic dissipation rate and eddy diffusivity below the pycnocline increase from the noise level on the cold side of the front by one order of magnitude on the warm side where 100 m thick layers with average diffusivities of 5 3 10 25 m 2 s 21 lead to heat loss from the atlantic water of 2 4 w m 22 dissipation in the upper 150 m is well above the noise level at all stations but strong stratification at the cold side of the front prohibits mixing across the pycnocline close to the shelf at the core of the svalbard branch of the wsc diffusivity increases by another factor of 3 6 here nearbottom mixing removes 15 w m 22 of heat from the atlantic layer internal wave activity and mixing show variability related to topography and hydrography thus the path of the wsc will affect the cooling and freshening of the atlantic inflow when generalized to the arctic ocean diapycnal mixing away from abyssal plains can be significant for the heat budget around the yermak plateau it is of sufficient magnitude to influence heat anomaly pulses entering the arctic ocean however diapycnal mixing alone is unlikely to be significant for regional cooling of the wsc

the amazon influenced muddy coast of south america a review of mud bank shoreline interactions the 1500 km long coast of south america between the amazon and the orinoco river mouths is the world s muddiest this is due to the huge suspended sediment discharge of the amazon river 106 754 tons yr 1 9 part of which is transported alongshore as mud banks mud bank formation is controlled by the physical oceanography of the continental shelf seaward of the amazon river mouth an initial seafloor storage area for much of the suspended sediment discharged from the river in this area rapid and sustained fluid mud concentration and trapping are associated with fresh water salt water interaction and estuarine front activity on the shelf due to the enormous amazon water discharge ca 173 000 m3 s 1 at obidos 900 km upstream of the mouth fluid mud is transported shoreward and then along the coasts of the guianas by a complex interaction of wave and tidal forcing and wind generated coastal currents the mud banks which may number up to 15 or more at any time are up to 5 m thick 10 to 60 km long and 20 to 30 km wide and each may contain the equivalent mass of the annual mud supply of the amazon as the banks migrate alongshore their interaction with waves results in complex and markedly fluctuating shorelines that are associated with space and time varying depositional bank phases and erosional inter bank phases bank zones are protected from wave attack as a result of wave energy dampening by mud and undergo significant albeit temporary coastal accretion accompanied by rapid mangrove colonization the dampening of waves in bank areas as they propagate onshore is accompanied by the shoreward recycling of mud commonly in the form of individual mud bars these bars progressively undergo desiccation and consolidation and thus constitute a major pathway for rapid and massive colonization by mangroves erosion by waves propagating across relatively mud deficient shoreface zones in inter bank areas can lead to muddy shoreline retreat rates of tens of metres to several kilometres over a few months to a few years accompanied by massive removal of mangroves notwithstanding the higher incident wave energy on inter bank shores inter bank shorefaces are permanently muddy due to the pervasive influence of the amazon muddy discharge inter bank and transitional bank to inter bank phases are associated with both periodic sandy chenier formation and extreme forms of rotation of rare headland bound sandy beaches the high mud supply from the amazon has been the overarching geological control on the quaternary evolution of the northeastern south american coast having led to the growth of a muddy shelf clinoform at the mouth of the amazon and more or less important progradation throughout this coast net progradation reflects an imbalance in favour of deposition during each mud bank inter bank cycle the high mud supply has presumably blanketed shelf sand deposited by smaller rivers during eustatic lowstand phases the shelf clinoform structure at the mouth of the amazon and the muddy coastal progradation throughout the coast of the guianas and into venezuela provide analogues of the geological record on muddy shorefaces

trade wind waves and mud dynamics on the french guiana coast south america input from era 40 wave data and field investigations the south american coast between brazil and venezuela is affected by longshore migrating mud banks derived from the fine grained amazon sediment discharge onshore mud migration prevails over shallow bank areas alternating alongshore with deeper inter bank areas the transport on the inner shelf and attachment to the shoreline of this migrating mud has been attributed mainly to wind waves however the lack of in situ data on waves hampers understanding of the relationship between waves and mud dynamics a 44 yr record 1960 2004 of the era 40 wave dataset generated by the european centre for medium range weather forecasts ecmwf was used in conjunction with field investigations in french guiana to define both event scale and longer term patterns of mud mobilisation induced by waves the ratio h03 t2 combining wave height h and period t and the angle of wave incidence were singled out as the most relevant parameters for describing wave forcing typical bank and inter bank profiles and corresponding mud densities and a 3 month record of changes in the thickness of the fluid mud layer in an estuarine navigation channel were monitored by echo sounding from october 2002 to january 2003 an 80 day record of bed level changes in the intertidal zone was obtained from august to november 2004 using a pressure transducer the results on the wave regime of french guiana confirm a distinctly seasonal pattern and highlight an increase in h03 t2 over the 44 yr period related to an increase in trade wind velocities determined from corresponding trends in atlantic wind pseudo stress off the south american coast wave forcing over bank areas leads to the liquefaction of a 1 3 m thick layer of mud that is transported onshore and alongshore by the longshore component of wave energy the episodic nature of high wave energy events generally results in the formation of mud bar features from the shoreward mobilisation of gel like fluid mud the effect of waves on mud is particularly marked following long periods of low energy and especially at the onset of the high wave energy season october to may when even moderate wave energy events can lead to significant mobilisation of mud significant phases of increased wave energy are attended by higher long term annual rates of longshore mud bank migration but the correlation is rather poor between the wave forcing parameter h03 t2 and migration rates because stronger wave forcing is generally associated with low angles of wave incidence this suggests a complementary role of other hydrodynamic mechanisms such as geostrophic and tidal currents in longshore mud bank migration

effect of sediment pulse grain size on sediment transport rates and bed mobility in gravel bed rivers 1 sediment supply to gravel bed river channels often takes the form of episodic sediment pulses and there is considerable interest in introducing sediment pulses in stream restorations to alter bed surface grain size distributions and bed mobility a series of laboratory experiments was conducted in order to examine how sediment pulse grain size and volume affects the mobility of bed material in gravel bed channels pulses used in the experiments were composed of either the fine tail or the median of the subsurface bed material grain size distribution bed material refers to sediment in the channel prior to the pulse introduction exclusively both types of pulse were finer than the bed material surface median two pulse sizes were used which were either equivalent to the volume of sediment required to cover the entire bed one median subsurface bed material grain diameter deep full unit or 1 4 of this volume 1 4 unit the latter was designed to produce a transitory pulse with the exception of the 1 4 unit coarse pulse introduction of the sediment pulses to the channel caused dramatic increases in the bed load flux the coarse sediment pulses fine the bed surface and coarsen the bed load finer pulses also fine the surface but the bed load fines while the bed material load that excludes pulse material coarsens the greatest effects on the fractional transport occurred during the full unit fine pulse where the pulse covered the greatest bed surface and effectively smoothed the bed increasing near bed velocity and mobilizing the coarse particles overall the coarse pulses were not very effective at mobilizing bed material the large fine pulse mobilized 35 of the bed material surface 35 of its input weight and was most effective at mobilizing the surface however the small fine pulse mobilized 50 of its input weight as it passed through the channel making it the most efficient at mobilizing the bed material

rates and mechanisms of shoreface progradation and retreat downdrift of the amazon river mouth field surveys of the 350 km shoreline adjacent to the amazon river mouth reveal three distinct types erosional mud accretionary sand and accretionary mud formation of these zones is controlled by the delivery of amazon suspended sediment mediated by the hydrodynamic regime erosional mud shorelines extend from rio araguari near the amazon river mouth northwestward 280 km to 3 5 n near cabo cassipore shoreface 5 m water depth retreat annually yields 1 4 106 tons of fine grained sediment deposited during an earlier phase of shoreface progradation sandbodies up to 5 m thick overlie erosional mud shorefaces for 10 30 km downdrift of small rivers the sand is supplied from these rivers and released by shoreline retreat of the river mouth areas amazon river sand is restricted in the coastal zone from its mouth north to the cabo norte shoal area where it mixes with sand carried by rio araguari from the guiana highlands north of 3 5 n mud aggradation and progradation is taking place on underconsolidated low gradient tidal flats backed by mangrove swamps 210pb and 14c geochronology of vibracores from the mudflats indicate that sediment accumulation is rapid 0 24 2 0 cm yr landward of the 2 m isobath supplied from a thick 50 150 cm seasonal surface layer shoreface progradation is episodic separated by decadal hiatuses fine grained suspended sediment flux from the amazon and minor amounts of sand and mud from the local rivers supply sediment to the mudflats shore normal tidal currents and solitary waves rework the surface mud layer preferentially transporting available sand landward into the mangrove fringe and producing very fine grained accumulation on the tidal flat 10 12 mean grain size lateral accretion of features 10 100 km long termed mudcapes produces tens of kilometers of seaward coastal plain addition along the northern coast similar features are identified downdrift along the guianas coast as far as the orinoco river 1600 km the northern amapa shoreface deposits are a locus of modern sediment accumulation which progrades over subaqueous deltaic strata

kinematic wave model of bed profiles in alluvial channels 1 a mathematical model based on the kinematic wave kw theory is developed for describing the evolution and movement of bed profiles in alluvial channels the model employs a functional relation between sediment transport rate and concentration a relation between flow velocity and depth and velikanov s formula relating suspended sediment concentration to flow variables laboratory flume and field data are used to test the model transient bed profiles in alluvial channels are also simulated for several hypothetical cases involving different water flow and sediment concentration characteristics the model simulated bed profiles are found to be in good agreement with what is observed in the laboratory and they seem theoretically reasonable for hypothetical cases the model results reveal that the mean particle velocity and maximum concentration maximum bed form elevation strongly affect transient bed profiles

transient scour and fill the case of the pilcomayo river abstract transient scour and fill refers to the general scour and fill in a riverbed due to flood passage it was given much attention in times of leopold and maddock 1953 and colby 1964 from records of outstanding case studies field data from a station in a contracted long reach of the large sand bed pilcomayo river 1192 newly typed in forms are presented with sediment concentration in the database up to 60 kg m 3 mostly wash load water surface rises and falls during a flood event whereas streambed evolves in reverse it renders the analogy to an accordion streambed scouring accounts for 36 of the change in flow area during floods and data reveal scouring up to 4 m from the streambed elevation when flood starts velocity data display large hysteresis loops inexplicable by unsteady flow only once streambed starts to fall river bed scour is self sustaining water depth gradient appears to be a crucial variable in a novel equation for transient scour and fill derived from exner equation it turns out that flow non uniformity is relevant to explain transient scour and fill in contrast to flow unsteadiness which is not quasi steady gradually varied flow equation solved along the contracted reach is the base for a model that captures well the recorded bed evolution the model explains most of the transient scour and fill by the downstream expansion but the non uniform flow and the bed material suspended load also play a role the model fails on the days of highest sediment concentrations

evolution of a canada basin ice ocean boundary layer and mixed layer across a developing thermodynamically forced marginal ice zone a comprehensive set of autonomous ice ocean measurements were collected across the canada basin to study the summer evolution of the ice ocean boundary layer iobl and ocean mixed layer oml evaluation of local heat and freshwater balances and associated turbulent forcing reveals that melt ponds mps strongly influence the summer iobl oml evolution areal expansion of mps in mid june start the upper ocean evolution resulting in significant increases to ocean absorbed radiative flux 19 w m 2 in this study buoyancy provided by mp drainage shoals and freshens the iobl resulting in a 39 mj m 2 increase in heat storage in just 19 days 52 of the summer total following mp drainage a near surface fresh layer deepens through shear forced mixing to form the summer mixed layer sml in late summer basal melt increases due to stronger turbulent mixing in the thin sml and the expansion of open water areas due in part to wind forced divergence of the sea ice thermal heterogeneities in the marginal ice zone miz upper ocean led to large ocean to ice heat fluxes 100 200 w m 2 and enhanced basal ice melt 3 6 cm d 1 well away from the ice edge calculation of the upper ocean heat budget shows that local radiative heat input accounted for at least 89 of the observed latent heat losses and heat storage partitioned 0 77 0 23 these results suggest that the extensive area of deteriorating sea ice observed away from the ice edge during the 2014 season termed the thermodynamically forced miz was driven primarily by local shortwave radiative forcing

generation of internal waves by sea ice observations in the greenland sea marginal ice zone suggest that when strong stratification occurs near the surface momentum flux into the internal wave field of the upper ocean can be a major component of the force balance that governs ice drift since energy is radiated away by the internal waves turbulent mixing and heat flux are also affected we investigate the downward flux of momentum and energy by internal waves in an ice covered ocean with an idealized model comprising a mixed layer overlying a deep uniformly stratified layer a buoyancy jump separates the mixed layer from the pycnocline drag from a single wave number component of the under ice roughness spectrum is derived as the product of a drag coefficient based on ice speed under ice roughness wave number and amplitude and uniform stratification to the ice ocean interface times an attenuation factor that depends additionally on mixed layer depth and the buoyancy jump at the base of the mixed layer the model is extended to a plausible spectrum of under ice roughness by integration over wave number space internal wave effects are parameterized in terms of the drag coefficient from the integrated spectrum and incorporated into an upper ocean turbulence model model calculations show that plausible values for the peak wave number of the idealized spectrum and roughness variance can account for 1 decreased ice velocity relative to the wind 2 decreased heat exchange coefficient between the ice and ocean and 3 lack of mixed layer deepening all of which were observed during the last week of the 1984 marginal ice zone experiment

quantification of refractory organic material in amazon mudbanks of the french guiana coast abstract sub oxic overturning mudbanks originating in the amazon outlet and traveling northwestward along the coast of south america store 3 5 tg organic carbon on the amazon shelf annually the predominance of old soil carbon burial associated with the sediment has been supported by relatively old bulk radiocarbon ages 2200 3200 14 c y reported but this amount has yet to be quantified for this dynamic setting here we employ ramped pyrolysis radiocarbon dating to mudbank sediments from three cores to further constrain the amount of refractory sedimentary organic carbon present using radiocarbon age as a proxy for reactivity we find that at least 36 of this organic carbon is pre aged refractory terrestrial organic carbon likely sourced from terrestrial soils and averaging ages of 16 100 300 14 c y this implies significant preservation of pre aged terrestrial soil material in this marine environment despite the mobility and oxygen availability in the muds concurrently an average of 77 of this organic material is aged over 1000 14 c y consistent with previous estimates that the majority of organic carbon buried along the shelf is refractory analyses of extracted lignin phenols and terrestrial humic acids also support this preservation of refractory terrestrial material these data indicate that sediment discharged from the amazon river may preserve refractory terrestrial carbon in marine sediments at a minimum of 3 1 tg c y which is more efficient than originally thought

reply to comment by cao and hu on long waves in erodible channels and morphodynamic influence 1 we thank cao and hu 2008 very much for their comment we must honestly say that at first sight we felt that their point reproducing that raised by cao and carling 2003 to challenge the formulation of the 1 d governing equations proposed by lisle et al 2001 had already been proven to be erroneous by cui et al 2005 however after more careful examination of the matter we have concluded that both the final forms of the continuity equation derived by cao and hu 2008 hereinafter referred to as ch and lanzoni et al 2006 hereinafter denoted as lsfs are not wholly correct indeed while the main point raised by ch is definitely correct they reach slightly incorrect conclusions employing a framework which ignores the distinction between bed load and suspended load on the other hand the lsfs derivation is also incorrect in that it will be seen to ignore the defect of water flux due to the presence of particles transported as bed load an effect which turns out to be of the same order of magnitude as that of the retained contributions this effect modifies the final form of the continuity equation for the fluid phase which does indeed include a sediment transport correction whose structure will be seen to be intermediate between the one derived by lsfs and that suggested by ch while as shown in section 4 this modification does not affect the treatment of one dimensional long sediment waves presented by lsfs the issue is of conceptual importance we are therefore grateful to ch for motivating us to provide a hopefully more conclusive clarification of the matter we are confident that the analysis presented below will be instructive for the reader as it was for us