landslide driven erosion and slope channel coupling in steep forested terrain ruahine ranges new zealand 1946 2011 abstract landslides are an important means of conveying sediment from slopes to channels in steepland environments but landsliding is a discontinuous process this means that any single assessment in time of their contribution to the sediment cascade is of limited value to better understand landscape dynamics and the contribution of landslides to slope channel coupling over time this paper quantifies connectivity over a time span of 65 years in small steep headwater catchments in the southern ruahine range new zealand temporal variability in landsliding and slope channel coupling was assessed using six sets of aerial photography flown between 1946 and 2011 from which over 6900 landslides were mapped in arcgis of which up to 78 connected with the stream network estimates of the volume of material delivered by landslide erosion to headwater channels were based on ground survey measurements of selected landslide scars and suggest that between 1946 and 2011 over 5 million m 3 of sediment was delivered from slopes to channels in the 221 km 2 study area forest cover is not sufficient to prevent this erosion these catchment systems are particularly vulnerable to high magnitude storm events which significantly elevate landslide intensity and enhance sediment delivery as occurred in the mid 1970s the legacy of these events remains in these headwater channels with ongoing consequences for stream and hazard management in and adjacent to the ranges

diatom response to the holocene climatic optimum on the north icelandic shelf abstract a diatom record from core md992275 on the north icelandic shelf reveals palaeoclimatic and palaeoceanographic changes during the time interval 9000 to 5600 cal year bp the study period includes the holocene climate optimum hco as widely known in the north atlantic region a comparison with data for the last 2000 years and with the present day surface sediment diatom assemblages shows that there was considerably stronger influence of atlantic water masses in the area during the hco than in the late holocene and today the results of cluster analysis and principal component analysis divide the studied period into three intervals each characterised by a specific diatom assemblage the assemblages indicate changes in the interaction of the relatively warm irminger current ic and the cold east greenland current egc and east icelandic current eic the north icelandic shelf was strongly affected by the ic during the interval 8000 6800 cal year bp which may be the warmest period of the holocene during the intervals 9000 8000 and 6800 5600 cal year bp the influence of the ic was relatively weak and that of the egc and eic increased correspondingly the well known 8200 cal year bp cooling event shown in many records from the north atlantic is reflected by a relatively strong influence of the egc and eic between about 8300 and 8100 cal year bp in our record however the diatom assemblages show that the inferred circulation change did not bring the strength of the ic down to the levels seen at present and during the last two millennia

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

differential recovery from the effects of a 100 year storm significance of long term hillslope channel coupling howgill fells northwest england a 100 year storm that occurred in 1982 caused major geomorphic changes in the main valleys of the northern howgill fells northwest england those changes which were documented at that time involved extensive hillslope gully erosion alluvial fan sedimentation and substantial sediment input to the stream systems the streams channels which had hitherto been dominantly single thread relatively stable channels responded in many reaches by switching to wide shallow unstable locally braided channels over the 20 years since the event there has been a partial recovery to channel geometries similar to the pre flood conditions however the degree of recovery contrasts between two neighbouring valleys bowderdale and langdale the channel of bowderdale beck has largely recovered flood sedimentation zones have largely stabilised and new single thread channels have cut through most of the former braided reaches in some places channel widths remain higher than the pre flood values and locally recovery has been modified by a lagged complex response in langdale recovery is only partial with many reaches demonstrating sustained instability over the 20 year post flood period furthermore the overall spatial patterns suggest some reach to reach transfer of coarse sediment shifting zones of instability downstream the contrasts between the two valleys appear to relate to different hillslope to channel coupling characteristics themselves inherited from late pleistocene conditions these contrasts are also evident in the longer term post 1949 history of channel change and stability in these two streams indicative of the higher intrinsic instability of the langdale system

geomorphic effectiveness a linear concept in a non linear world geomorphic effectiveness has been an influential concept in geomorphology since its introduction by reds wolman and john miller in 1960 it provided a much needed framework to assess the significance of an event by comparing event magnitude to the resultant geomorphic effects initially this concept was applied primarily in river channels under the linear assumption that geomorphic responses to similarly sized flood events will be consistent numerous authors have since attempted to quantify a direct proportional relationship between event magnitude and different forms of geomorphic response in a variety of geomorphic settings in doing so these investigations applied an array of metrics that were difficult to compare across different spatiotemporal scales and physiographic and geomorphic environments critically the emergence of other geomorphic concepts such as sensitivity connectivity thresholds and recovery has shown that relationships between causes events and geomorphic effects responses are often complex and non linear this paper disentangles the complex historical development of the geomorphic effectiveness concept and reviews the utility of various metrics for quantifying effectiveness we propose that total energy joules is the most appropriate metric to use for quantifying the magnitude of disturbance events cause and volumetric sediment flux associated with landform modification is the most appropriate metric for quantifying geomorphic effects while both metrics are difficult to quantify they are the only ones which facilitate comparison across a range of spatiotemporal scales comparability in a variety of geomorphic environments flexibility the geomorphic effectiveness concept can continue to be useful provided that geomorphologists use flexible and comparable metrics today geomorphologists are better prepared to consider the influence of non linear processes on determinations of geomorphic effectiveness allowing investigators to not only determine if a disturbance event was effective but also to explain why or why not copyright

diatoms from the surface sediments of the south china sea and their relationships to modern hydrography abstract a principal components analysis of diatoms in surface sediment samples from the south china sea scs shows a clear relationship between the spatial distributions of diatoms and the current pattern of the region six diatom assemblages are distinguished representing environments with different hydrological characteristics the neritic planktonic species thalassionema nitzschioides is the dominant component in the surface sediment diatoms with relatively small changes throughout the scs suggesting that the water mass exchanges between the scs and the pacific and indian oceans are relatively small the strongest impact of the warm oceanic water occurs in the northeasternmost part of the scs where assemblage v is located with nitzschia marina azpeitia nodulifera azpeitia neocrenulata rhizosolenia bergonii and thalassionema frauenfeldii as main taxa warm oceanic planktonic species n marina r bergonii and a neocrenulata can be used as indicators of warm oceanic waters flowing into the scs in paleoceanographic reconstructions of the area in particular in tracking the water from the western pacific including the kuroshio current it may however be problematic to use another tropical oceanic planktonic species a nodulifera as an environmental indicator because of its strong resistance to dissolution thus possibly further transport

a diatom based transfer function for reconstructing sea ice concentrations in the north atlantic abstract a diatom based sea ice transfer function is developed using 99 surface sediment samples from the north atlantic and the associated modern sea ice concentrations canonical correspondence analysis cca is applied to the species assemblages of the surface sediment samples and the association of the species with two environmental parameters august sea surface temperature and may sea ice concentration is assessed the results of this analysis indicate negative correlation between sea ice and sea surface temperature and that a group of diatom species is strongly associated with sea ice especially may sea ice concentration the results of the cca legitimate the development of a diatom based sea ice transfer function the maximum likelihood method has been applied as the transfer function method as it has been proven most suitable with this particular data set the newly developed transfer function is then used to reconstruct may sea ice concentration in three cases each focusing on a different time period the last glacial maximum the younger dryas and the holocene in all three cases the transfer function produces reasonable results when compared to other paleoclimatic proxy results this suggests that the sea ice concentration reconstructed by the diatom based sea ice transfer function is a valid and reliable method which can be applied as a valid proxy for may sea ice concentration

river terraces and alluvial fans the case for an integrated quaternary fluvial archive abstract the fluvial archive literature is dominated by research on river terraces with appropriate mention of adjacent environments such as lakes despite modern sedimentary basins comprising a significant 88 volume of distributive fluvial systems of which alluvial fans 1 km

air photo based change in channel width in the minnesota river basin modes of adjustment and implications for sediment budget abstract the minnesota river and major tributaries have experienced large increases in discharge over the past century aerial photograph based measurements of channel width were made for the 1938 2015 period at 16 multibend subreaches by digitizing the area between vegetation lines and dividing by centerline length results show considerable increases in width for the main stem 0 62 0 10 y and major tributaries 0 31 0 08 y but are inconclusive for smaller channels width

morphological controls on the downstream passage of a sediment wave in a gravel bed stream sediment waves in river systems have been widely reported although few studies have examined the interaction between these waves and the morphology of the reaches through which they pass this interaction determines how waves are modified as they propagate downstream this study documents the origin and downstream passage of an avulsion generated sediment wave through a 374 m study reach of the allt dubhaig scotland a nested survey framework was adopted with volumes calculated from cross sections spaced between 10 and 40 m apart documenting the origin and downstream passage of the wave the wave moved through an intensively c 1 m cross section spacing monitored 120 m stretch reach a within the study reach allowing assessment of sediment exchanges between the incoming wave and the local morphology successive surveys show the movement of the wave through and out of the reach and also that areas where wave sediment was deposited did not always correspond with areas of subsequent erosion reach a was divided into three morphologically distinct sub reaches 1a 2a and 3a within which sediment fluxes and the three dimensional distribution of erosion deposition were estimated sediment wave input into 1a and 2a relatively stable sub reaches caused forced bar aggradation and erosion of sediment from elsewhere within the reach which then became part of the wave the downstream transfer of this sediment into unstable 3a caused aggradation and in response widespread erosion which increased the magnitude of the sediment wave as it exited reach a sediment exchange between the recipient reach and the wave depends upon local morphological stability and is a crucial process affecting wave magnitude and attenuation the macroscale sediment wave interacted with rather than overwhelmed the recipient morphology 1998 john wiley sons ltd

patterns of sediment slug translation and dispersion following typhoon induced disturbance oyabu creek kyushu japan a six year monitoring programme characterized the migration dispersion patterns of sediment slugs generated following typhoon induced disturbances in 1993 and 1997 along a single thread gravel bed stream oyabu creek on kyushu island japan this laterally con ned creek comprises rif e pool sequences with intervening bedrock outcrops the passage of sediment pulses associated with sediment slug processes re ected and was controlled by the rif e pool structures which provided channel bed roughness the volume of sediment stored along valley oors and the distribution of bedrock outcrops changes to bed material size following major sediment inputs during the disturbance events also exerted an in uence on subsequent sediment slug processes the sequence of rainfall events together with changes to channel bed structure induced different phases in the sediment slug processes the capacity of a reach to store or trap sediment as recorded by the longitudinal structure of the channel varied during these differing phases copyright 2004 john wiley sons ltd

diatom surface sediment assemblages around iceland and their relationships to oceanic environmental variables canonical correspondence analysis of diatoms from surface sediment samples and oceanographic environmental variables shows that summer and winter sea surface temperatures water depth and winter sea surface salinity are the main environmental factors affecting diatom distribution around iceland of these summer sea surface temperature is the most important five diatom assemblages are distinguished and the distribution of these assemblages is clearly correlated with oceanic current patterns in the region the sea ice diatom assemblage is limited to the area where the east greenland current polar water has its strongest influence and the cold diatom assemblage is basically controlled by the less cold east icelandic current modified polar water the mixing diatom assemblage results from the interaction between the cold east greenland and east icelandic currents and the warm irminger current the warm diatom assemblage is located in the area dominated by the irminger current and may be used as an indicator of warm water masses atlantic water the coastal diatom assemblage is the only one strongly influenced by both water depth and summer water temperatures

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

late pleistocene holocene paleoenvironmental changes inferred from the diatom record of the ulleung basin east sea sea of japan abstract the diatom floral record from two piston cores 00ghp 01 and 00ghp 07 taken from the southwestern margin of the ulleung basin east sea sea of japan reveals a series of well defined changes in glacio eustatic sea level and paleoceanographic conditions during the late pleistocene holocene six assemblage zones and two barren zones in 00ghp 01 and four assemblage zones in 00ghp 07 are erected respectively on the basis of frequency of variations in and occurrences of biostratigraphically significant diatom species all assemblage zones have been strongly influenced by the tsushima warm current twc the twc has an important affect on controlling the distribution and composition of diatom flora which in turn reveal the history of the twc in this area the distribution pattern of diatoms in the diatom assemblages reveals sea surface temperature and salinity affected by the sediments type and terrigenous material input diatom temperature td values show that the site of 00ghp 01 in the ulleung basin has been influenced by a relatively enhanced twc twice during the deposition of lowermost and uppermost intervals a relatively weak twc was recorded in the middle interval since the latest pleistocene the diatom assemblages of 00ghp 07 represent an apparently continuous late quaternary record spanning the last glacial maximum bolling allerod younger dyras and holocene high abundance of a low salinity coastal water diatom paralia sulcata may reflect the influx of the east china sea water through the korean strait to the east sea sea of japan during the last glacial maximum the sea level was low enough that selected basin with shallow sills along the margin of the east sea sea of japan became isolated from the pacific ocean salinity also decreased due to increased freshwater input from rivers draining the surrounding lands the density stratified water column may have prevented vertical mixing and resulted in anoxic bottom water conditions

modern distribution of diatoms in sediments from the george v coast antarctica abstract currently little information exists concerning high frequency climate change in the antarctic data that are essential to gaining a more complete understanding of global climate change sediments from the george v coast continental margin potentially contain a high resolution record of the late holocene the relatively high rate of sedimentation 3 mm year and the presence of laminated intervals which contain undisturbed sequences make these sediments valuable for future downcore work in order to utilize diatom assemblages as proxies of paleoclimatic and paleoceanographic parameters a preliminary study of the surface sediment distribution of diatoms from the george v coast continental margin was completed nitzschia curta van heurck hasle and nitzschia kerguelensis o meara hasle present great potential for tracking the holocene retreat of ice across the continental shelf of this region concentrations of n curta an ice related form decreases in an offshore direction whereas n kerguelensis an oceanic species associated with circumpolar flow displays an increase in sediments offshore the genus thalassiosira cleve displays a clear association with areas of open water primary production as has been noted in others parts of the antarctic downcore variability in relative abundance of this genus will be useful in understanding the history of sea ice versus open water production on the george v coast shelf in contrast the distribution of chaetoceros ehrenberg resting spores appears to be more complex but may be related to the position of the stationary ice edge associated with the annual minimal extent of sea ice finally an understanding of the downcore variability of thalassiothrix antarctica schimper ex karsten a species which is very abundant in the laminated sections of the sediment cores will have to rely on studies of its distribution in other areas of the antarctic as it is sparsely distributed along the george v coast today

surface water temperature changes in the high latitudes of the southern hemisphere over the last glacial interglacial cycle a set of numerical equations is developed to estimate past sea surface temperatures sst from fossil antarctic diatoms these equations take into account both the biogeographic distribution and experimentally derived silica dissolution the data represent a revision and expansion of a floral data base used previously and includes samples resulting from progressive opal dissolution experiments factor analysis of 166 samples 124 holocene core top and 42 artificial samples resolved four factors three of these factors depend on the water mass distribution one subantarctic and two antarctic assemblages factor 4 corresponds to a dissolution assemblage inclusion of this factor in the data analysis minimizes the effect of opal dissolution on the assemblages and gives accurate estimates of sst over a wide range of biosiliceous dissolution a transfer function dtf 166 34 4 is derived from the distribution of these factors versus summer sst its standard error is 1 c in the 1 to 10 c summer temperature range this transfer function is used to estimate sst changes in two southern ocean cores 43 s and 55 s which cover the last climatic cycle the time scale is derived from the changes in foraminiferal oxygen and carbon isotopic ratios the reconstructed sst records present strong analogies with the air temperature record over antarctica at the vostok site derived from changes in the isotopic ratio of the ice this similarity may be used to compare the oceanic isotope stratigraphy and the vostok time scale derived from ice flow model the oceanic time scale if taken at face value would indicate that large changes in ice accumulation rates occurred between warm and cold periods

dating of post glacial landforms in the central howgills little is known of holocene landform development in upland britain this paper describes a site at middle langdale in the howgill fells of cumbria where large but now stabilized and inactive gullies cut through periglacial material at the base of the gullies large debris cones have buried earlier alluvial sediments on the valley floor on these sediments and buried by the debris cones is a well developed organic soil from which two 14c dates have been obtained in an attempt to estimate the age range of the soil these dates range from 2580 55 years bp for the fine particulate fraction from the base of the organic horizon to 940 95 years bp for fossil rootlets from the uppermost organic layer immediately below the overlying debris cones the pollen evidence suggests that the valley floor site was initially dominated by alder carr and later by a juncus marsh with birch alder and hazel nearby the pollen from the surrounding upland area suggests woodland on the valley sides dominated by oak and elm that was later replaced by a more open environment rich in heath species and in which disturbed ground species were present the magnetic evidence indicates a stable local environment during soil formation but shows a sudden inwash of unweathered debris at the top of the buried soil the evidence suggests that the valley floor was geomorphologically stable throughout the period of soil formation although there was a local change in valley floor vegetation and a reduction of woodland cover on the valley sides at sometime during the period the evidence then points to major geomorphological changes a wave of soil erosion gully development and debris cone deposition perhaps following the scandinavian introduction of sheep farming in the tenth century a d

variability in the length of the sea ice season in the middle eocene arctic finely laminated middle eocene sediments from the central arctic contain high abundances of the delicate sea ice dwelling fossil diatoms synedropsis spp and sea ice rafted debris sea ice ird establishing an offshore seasonal sea ice regime ca 47 ma synedropsis spp co occur with other diatom taxa and microfossils requiring open water this strongly indicates seasonality nonetheless seasonal reconstruction of the flux cycle cannot be resolved by standard bulk sediment analysis which destroys sedimentary fabrics and averages data within samples here we resolve and reconstruct seasonal scale flux events from these sediments using backscattered electron imagery bsei of resin embedded sediment a nondestructive technique that preserves the integrity of sedimentary microfabrics thus revealing discrete productivity flux events at ultrahigh e g 30 m resolution seasonality is expressed at the submillimeter scale by successions of discrete mono specific laminae and micro lenses of synedropsis spp terrigenous material sea ice ird and open water taxa indicating that first year ice existed in the central arctic further bsei reveals millimeter scale alternation of bundles of laminae and microlenses of two distinct types one characterized by synedropsis spp and terrigenous material the other by mainly open water taxa and little terrigenous material the sedimentation rate and preliminary assessment of annual cycles indicate suborbital variability on the order of multi decadal to centennial duration we argue that this reflects variations in the sea ice season length

late holocene summer sea surface temperatures based on a diatom record from the north icelandic shelf diatom assemblages from a high resolution core on the north icelandic shelf reveal a general late holocene cooling trend which is interrupted by three relatively warm periods diatom data from sur

variations in flood magnitude effect relations and the implications for flood risk assessment and river management abstract in spite of major physical impacts from large floods present river management rarely takes into account the possible dynamics and variation in magnitude impact relations over time in flood risk mapping and assessment nor incorporates feedback effects of changes into modelling using examples from the literature and from field measurements over several decades in two contrasting environments a semi arid region and a humid temperate region temporal variations in channel response to flood events are evaluated the evidence demonstrates how flood physical impacts can vary at a location over time the factors influencing that variation on differing timescales are examined the analysis indicates the importance of morphological changes and trajectory of adjustment in relation to thresholds and that trends in force or resistance can take place over various timescales altering those thresholds sediment supply can also change with altered connectivity upstream and changes in state of hillslope channel coupling it demonstrates that seasonal timing and sequence of events can affect response particularly deposition through sediment supply duration can also have a significant effect and modify the magnitude relation lack of response or deposits in some events can mean that flood frequency using such evidence is underestimated a framework for assessment of both past and possible future changes is provided which emphasises the uncertainty and the inconstancy of the magnitude impact relation and highlights the dynamic factors and nature of variability that should be considered in sustainable management of river channels

geomorphic coupling and sediment connectivity in an alpine catchment exploring sediment cascades using graph theory through their relevance for sediment budgets and the sensitivity of geomorphic systems geomorphic coupling and sediment connectivity represent important topics in geomorphology since the introduction of the systems perspective to physical geography by chorley and kennedy 1971 a catchment has been perceived as consisting of landscape elements e g landforms subcatchments that are coupled by geomorphic processes through sediment transport in this study we present a novel application of mathematical graph theory to explore the network structure of coarse sediment pathways in a central alpine catchment numerical simulation models for rockfall debris flows and hillslope and channel fluvial processes are used to establish a spatially explicit graph model of sediment sources pathways and sinks the raster cells of a digital elevation model form the nodes of this graph and simulated sediment trajectories represent the corresponding edges model results are validated by visual comparison with the field situation and aerial photos the interaction of sediment pathways i e where the deposits of a geomorphic process form the sources of another process forms sediment cascades represented by paths a succession of edges in the graph model we show how this graph can be used to explore upslope contributing area and downslope source to sink functional connectivity by analysing its nodes edges and paths the analysis of the spatial distribution composition and frequency of sediment cascades yields information on the relative importance of geomorphic processes and their interaction however regardless of their transport capacity in the study area the analysis stresses the importance of mass movements and their interaction e g the linkage of large rockfall source areas to debris flows that potentially enter the channel network moreover it is shown that only a small percentage of the study area is coupled to the channel network which itself is longitudinally disconnected by natural and anthropogenic barriers besides the case study we discuss the methodological framework and alternatives for node and edge representations of graph models in geomorphology we conclude that graph theory provides an excellent methodological framework for the analysis of geomorphic systems especially for the exploration of quantitative approaches towards sediment connectivity

catchment scale dis connectivity in sediment flux in the upper hunter catchment new south wales australia abstract dis connectivity within and between landscape compartments affects the extent and rate of transfer of energy and matter through catchments various landforms may impede sediment conveyance in a river system whether laterally to the channel termed buffers or longitudinally along the channel itself termed barriers a generic approach to analysis of landscape dis connectivity using slope threshold analysis in gis tied to air photograph interpretation and field mapping of buffers and barriers is tested in the upper hunter catchment australia under simulated conditions effective catchment area which is a measure of the proportion of a catchment that has the potential to contribute sediment to the channel network varies from 73 to just 3 of the total catchment area for differing subcatchments in the upper hunter this variability can be explained by the spatial distribution and assemblage of buffers and barriers in each subcatchment multiple forms of disconnectivity are evident in some subcatchments such that when one buffer or barrier is breached other features still impede sediment transfer within the system the importance of the position of buffers and barriers within any given subcatchment is emphasised spatial variability in valley width exerts a critical control on catchment connectivity with more efficient sediment conveyance in narrow valleys relative to wider valleys characterised by piedmonts terraces fans and extensive floodplains in which conveyance is impeded this variability reflects the landscape history and geological setting of each subcatchment the framework developed in this paper can be used to assess the impact of natural or human induced buffers and barriers on catchment scale sediment flux in any landscape setting providing a physical template atop which other biogeochemical fluxes could be examined

geomorphic impact and system recovery following an extreme flood in an upland stream thinhope burn northern england uk abstract quantitative assessments of the impacts of extreme floods on channel morphology are rare real time kinematic rtk gps surveys of a 500 m reach of the thinhope burn an upland gravel bed stream in the uk taken in 2003 and 2004 permitted an assessment of geomorphic work whilst the channel was at steady state a large flood that occurred on 17 july 2007 resulted in a catastrophic impact to the thinhope burn valley floor the reach was re surveyed after the event in 2007 and again in 2008 and in 2011 digital elevation models were produced from the survey data which allowed the spatial patterns of erosion and deposition and volumetric changes between surveys to be established a total of 5202 m3 of deposition and 2125 m3 of erosion was recorded in the reach following the flood event field walking of the catchment and comparison of aerial photographs for 2003 and 2007 suggested that most of the material mobilised had originated from existing sediment held in terraces and paleoberms on the valley floor although slope failures were evident including peat slides in the headwaters delivery of sediment from coupling zones to the channel was thought to play a secondary role in the geomorphic response shown by the channel similarly large volumes of erosion and deposition were found after resurveys in 2008 and 2011 suggesting that the system was still in its relaxation phase the results obtained in this investigation coupled with historical information on the flood history of thinhope burn dating back to 1766 suggested that rare large floods are the geomorphically effective flows in the catchment

sediments in arctic sea ice implications for entrainment transport and release despite the arctic sea ice cover s recognized sensitivity to environmental change the role of sediment inclusions in lowering ice albedo and affecting ice ablation is poorly understood sea ice sediment inclusions were studied in the central arctic ocean during the arctic 91 expedition and in the laptev sea east siberian arctic region expedition 1992 results from these investigations are here combined with previous studies performed in major areas of ice ablation and the southern central arctic ocean this study documents the regional distribution and composition of particle laden ice investigates and evaluates processes by which sediment is incorporated into the ice cover and identifies transport paths and probable depositional centers for the released sediment in april 1992 sea ice in the laptev sea was relatively clean the sediment occasionally observed was distributed diffusely over the entire ice column forming turbid ice observations indicate that frazil and anchor ice formation occurring in a large coastal polynya provide a main mechanism for sediment entrainment in the central arctic ocean sediments are concentrated in layers within or at the surface of ice floes due to melting and refreezing processes the surface sediment accumulation in central arctic multi year sea ice exceeds by far the amounts observed in first year ice from the laptev sea in april 1992 sea ice sediments are generally fine grained although coarse sediments and stones up to 5 cm in diameter are observed component analysis indicates that quartz and clay minerals are the main terrigenous sediment particles the biogenous components namely shells of pelecypods and benthic foraminiferal tests point to a shallow benthic marine source area apparently sediment inclusions were resuspended from shelf areas before and incorporated into the sea ice by suspension freezing clay mineralogy of ice rafted sediments provides information on potential source areas a smectite maximum in sea ice sediment samples repeatedly occurred between 81 n and 83 n along the arctic 91 transect indicating a rather stable and narrow smectite rich ice drift stream of the transpolar drift the smectite concentrations are comparable to those found in both laptev sea shelf sediments and anchor ice sediments pointing to this sea as a potential source area for sea ice sediments in the central arctic ocean sea ice clay mineralogy is significantly different from deep sea clay mineral distribution patterns the contribution of sea ice sediments to the deep sea is apparently diluted by sedimentary material provided by other transport mechanisms

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

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

holocene marine diatoms from the faeroe islands and their paleoceanographic implications abstract temporal oceanographic changes based on mid and late holocene marine diatom floras from the faeroe islands region have been studied the four studied coring sites are located in the skalafjord and a more open ocean environment the mouth of the kaldbaksfjord at water depths ranging between 50 and 70 m comparison of the diatom records in the fjord sediments with those from the outer part of the fjord shows that the fjord provides a more optimum potential for paleoceanographic reconstructions the concentrations of marine taxa and relative abundance of freshwater diatom species in the marine environment were analyzed with the aim of relating them to environmental conditions estimated diatom concentrations were very low and ranged from a maximum of 14 4 10 6 valves per gram dry sediment in the inner part of the fjord to a minimum of 0 1 10 6 outside the fjord the freshwater diatom flora that occurred between 1200 and 700 cal yr bp in the inner part of the fjord suggests much higher precipitation during this time and increased freshwater discharge into the fjord presence of actinocyclus normanii which is an indicator of increasing trophy is related to the first human settlement on the faeroe islands maximum likelihood factor analysis mlfa was used to describe the most essential relationship among the diatom species and to employ these relationships for inferring holocene environmental changes in the faeroe islands the first two mlfa factors are related to oceanic influences in the region factor 1 is represented by a warmer water diatom assemblage and is suggested to correspond to inflow of the norwegian atlantic current to the skalafjord whereas factor 2 is an indicator of a colder water diatom assemblage that corresponds to inflow of arctic norwegian water mixing anwm during the 4900 3200 cal yr bp time interval

surface sediment diatom distribution and holocene paleotemperature variations in the greenland iceland and norwegian sea one hundred and four surface sediment samples and two piston cores from the greenland iceland and the norwegian gin sea hopkins 1988 were analyzed diatoms were common to abundant in most surface sediment samples and throughout the holocene q mode factor analysis allowed the definition of six significantly different floral assemblages which explained 91 7 of the total variance mapping of the six factors showed their close affinity to hydrographic regimes these are the norwegian atlantic current assemblage thalassionema nitzschioides paralia sulcata proboscia alata arctic water assemblage thalassiosira gravidaspores sea ice assemblage nitzschia grunowii nitzschia cylindra thalassiosira hyalina arctic norwegian waters mixing assemblage rhizosolenia hebetata f semispina rhizosolenia borealis atlantic assemblage thalassiosira oestrupii and norwegian arctic waters mixing assemblage thalassiosira gravida vegetative cells transfer functions gint2 relating factor distributions to winter february and summer august surface water temperatures were generated the transfer functions have a standard error of estimate of 1 5 c august and 1 0 c february downcore studies of core 52 43 from the norwegian basin and core 57 5 from the iceland plateau revealed diatom abundance and sea surface paleotemperature trends in the area during the holocene the first appearance of diatoms in cores 52 43 and 57 5 occurs within the vedde ash layer 10 600 years b p and the saksunarvatn ash layer 9100 years b p respectively diatom abundances increase steadily throughout the pre boreal atlantic time to 25 and 35 million valves per gram dry sediment in the norwegian basin and iceland plateau cores respectively application of the temperature transfer functions gint2 to the two holocene records revealed higher than present sea surface temperatures during the boreal atlantic chronozones for the iceland plateau and during the middle younger dryas sub boreal chronozones for the norwegian basin core temperatures decreased steadily since then with a slight increase to the present values both the iceland and the norwegian seas experienced a strong influx of temperate atlantic surface waters in the beginning of the holocene sea surface temperatures dropped steadily in the latter part of the holocene as the influx of the atlantic surface waters diminished

diatom distribution in southern ocean surface sediments atlantic sector implications for paleoenvironmental reconstructions abstract a study of 230 surface sediment samples collected in the atlantic sector of the southern ocean between the southernmost weddell sea and the subtropical zone documents the modern distribution of diatoms revealing patterns of paleoenvironmental significance estimations of diatom valves per gram dry sediment display numbers of 50 200 106 in the zone of high opal burial located between the mean position of the winter sea ice edge and the polar front and maximum values of greater than 200 106 in the near shore sedimentary basins off the antarctic peninsula lowest diatom concentrations and assemblages strongly affected by dissolution were encountered in the weddell basin despite alteration of the diatom assemblages prior to their incorporation into the sediment record the biogeographic distribution and the abundance pattern of most of the 35 studied diatom species shows a close relationship with the surface hydrography water temperature these relationships can be used to estimate past surface water temperatures based on statistical treatments of the assemblages or on simple relations of species occurrences in the geological record another close link occurs between the distribution of sea ice and sea ice related diatoms

catchment hydro geomorphological responses to environmental change in the southern uplands of scotland lake sediment and geomorphic evidence from the loch of the lowes st mary s loch basin in the central southern uplands of scotland provide a multiproxy reconstruction of changing sediment availability and transmission through the catchment interrogation of magnetic geochemical and grain size parameters for lake and catchment materials suggests it is possible to identify independent proxies that reflect both supply availability and discharge capacity controls on the sediment signal chronological control for the lake sediment record is proposed by linking a 210pb 137cs chronology for the last c 120 yr to an age depth profile based on proposed temporal correlations between cyclic hirm lf variability and the north atlantic oscillation geochronological studies on debris cones and alluvial fans yield evidence for episodic hillslope gullying 2000 0 bc with more extensive region wide slope instability ad 700 900 1100 1300 and after ad 1450 1550 and gully stabilization over the last 150 years the latter two episodes coincide with the lake sediment evidence for increased sediment supply from ad 1600 declining after ad 1870 the capacity related lake proxies appear to identify phases of increased flooding ad 1625 1650 1680 1700 1730 1760 1800 1815 1850 1880 1910 1930 1960 1970 and possibly the 1990s close correspondence between the sediment flood archive and historical records of flooding in scotland suggests that lake catchment systems of this type have the potential to yield valuable information on past hydrological response

suspension freezing of bottom sediment and biota in the northwest passage and implications for arctic ocean sedimentation ice observations and sediment collected in a summer transit through the northwest passage provide insights on suspension freezing the most important sediment entrainment mechanism for the arctic ocean no evidence was seen for entrainment by bottom adfreezing bluff slumping river flooding dragging ice keels or significant eolian transport from land to sea lack of eolian sediment loading in the northwest passage together with that already reported for northern alaska eliminates wind as an important source for fine sediment in the pack of the beaufort gyre and related parts of the transpolar drift muddy sediment with pebbles and cobbles algae with holdfasts ostracodes with appendages and well preserved mollusks and sea urchins were collected from two sites in a 50 km long stretch of turbid ice these materials indicate that suspension freezing reaching to a water depth of 25 30 m during the previous fall was responsible for entrainment this mechanism requires rapid ice formation in open shallo

palaeoclimatic significance of late quaternary diatom assemblages from southern windmill islands east antarctica abstract the late quaternary palaeoenvironmental history of the southern windmill islands east antarctica has been reconstructed using diatom assemblages from two long well dated sediment cores taken in two marine bays the diatom assemblage of the lowest sediment layers suggests a warm climate with mostly open water conditions during the late pleistocene during the following glacial the windmill islands were covered by grounded ice preventing any in situ bioproductivity following deglaciation a sapropel with a well preserved diatom assemblage was deposited from 10 500 cal yr bp between 10 500 and 4000 cal yr bp total organic carbon corg and total diatom valve concentrations as well as the diatom species composition suggest relatively cool summer temperatures hydrological conditions in coastal bays were characterised by combined winter sea ice and open water conditions this extensive period of glacial retreat was followed by the holocene optimum 4000 to 1000 cal yr bp which occurred later in the southern windmill islands than in most other antarctic coastal regions diatom assemblages in this period suggest ice free conditions and meltwater stratified waters in the marine bays during summer which is also reflected in high proportions of freshwater diatoms in the sediments the diatom assemblage in the upper sediments of both cores indicates neoglacial cooling from 1000 cal yr bp which again led to seasonally persistent sea ice on the bays the holocene optimum and cooling trends in the windmill islands did not occur contemporaneously with other antarctic coastal regions showing that the here presented record reflects partly local environmental conditions rather than global climatic trends

sedimentary records of bulk organic matter and lipid biomarkers in the bering sea a centennial perspective of sea ice variability and phytoplankton community abstract in this study organic geochemical analyses of two sediment cores bl16 and lv63 23 recovered from the western bering sea were carried out to examine the sea ice variability and its relationship to phytoplankton community evolution over the past century bulk stable organic carbon isotopic composition 13ctoc showed pronounced depletion on the northern shelf since the late 1970s indicating greater terrigenous organic matter om under warming during recent decades variation in sedimentary om in the southward core was closely associated with marine primary productivity and regional deposition processes arctic sea ice proxy ip25 throughout the two cores with different temporal profile patterns demonstrated sea ice presence with the spatio temporal variability across the study area over the past century the phytoplankton marker ip25 index pip25 a proxy for estimating semi quantitatively sea ice concentrations reflected a decreased sea ice cover with more distinct interannual fluctuations between 0 7 and 0 2 especially in core bl16 after the late 1970s coinciding with the recent warming scenario increased concentrations of phytoplankton biomarkers brassicasterol and dinosterol and their ratios as well as the pip25 record in core bl16 indicated a synchronous variability of reduced sea ice cover with the enhancement of phytoplankton productivity since the late 1970s these results suggested a coupled interaction of the sea ice condition and planktonic ecosystem in the north bering shelf our results also revealed recent since the 2000s spatial heterogeneity in sea ice coverage between the northern and southern parts of the bering sea

holocene north atlantic surface circulation and climatic variability evidence from diatom records diatom analyses have been performed on a 425cm long holocene marine sediment sequence from the north atlantic south of iceland and a 920cm sediment core spanning the last c 7500 years from skalafjord faeroe islands additional core data include stable isotopes and results from magnetic susceptibility measurements while chronostratigraphic control has been provided by ams 14c measurements the diatom records reveal distinct changes in north atlantic surface circulation and climate that have been correlated with published terrestrial and marine records initial holocene warming is dated at 9900 14c years bp and after a preboreal cold spell enhanced north atlantic current activity and warming prevailed from 9600 to 8800 14c years bp from 8800 to 8000 4c years bp the advection of warm atlantic water masses weakened presumably under atmospheric circulation conditions characterized by a dominating negative nao prior to the holocene climatic optimum 6000 5000 14c years bp distinct hydrographic gradient

sediment transfer and transformation of an alluvial valley floor the river south tyne northumbria u k the amounts of alluvial storage and the mechanisms responsible for the dispersal of sediment associated with historic metal mining are examined for a 115 year timespan on a 22 km reach of the river south tyne northern england analysis of lateral and vertical channel change over this period the extent of actively reworked gravels and identification of metals in alluvial units show five sedimentation zones separated by more stable reaches aggradation in the late nineteenth century was followed by a period of storage and local reworking and then incision some reaches show short term storage of sediment injected from tributaries which may be dispersed by floods there is some evidence of transfer of sediment bodies downvalley within sedimentation zones and of a sediment wave movement between zones in lower parts of the south tyne investigated present day incision the variation in the area of actively reworked gravel spreads and the widespread dispersal of fine grained toxic metal mining wastes all have practical implications the intricate response of the channel system to historic changes in sediment supply is not readily described by either a complex response model or a simple translatory wave

land sea linkage of holocene paleoclimate on the southern bering continental shelf detailed diatom records within surface and core sediments from the southern bering continental shelf sbcs reveal that the holocene evolution of sea ice distribution is associated with low pressure patterns holocene sea ice distribution over the sbcs was mainly controlled by the location of the aleutian low the corresponding paleoceanographic and paleoclimate conditions can be divided into three stages 1 the early holocene before 7000 cal yr bp was characterized by extensive sea ice distribution under two low pressure cells which covered the western bering sea and the gulf of alaska respectively 2 between 3000 and 7000 cal yr bp the low pressure system over the gulf of alaska became weak causing total sea ice mass over the sbcs to retreat 3 in the past 3000 years prevailing southwesterly winds over the sbcs due to the developing aleutian low have reduced further sea ice cover on the sbcs these paleoclimatic changes were probably a response to enso variation the timings of water mass exchanges on the sbcs coincided with sea level change along the alaskan peninsula as a result subsequent morphologic alterations have also influenced the paleoceanographic condition of the sbcs the effect of the surface coastal water and bottom marine water on the sbcs intensified about 6000 cal yr bp when sea level increased

channel response to sediment wave propagation and movement redwood creek california usa redwood creek north coastal californa usa has experienced dramatic changes in channel confguation since the 1950s a series of large floods in 1955 1964 1972 and 1975 combined with the advent of widespread commercial timber harvest and road building resulted in extensive erosion in the basin and contributed high sediment loads to redwood creek since 1975 no peak flows have exceeded a 5 year recurrence interval twenty years of cross sectional survey data document the downstream movement of a sediment wave in the lower 26 km of this gravel bedded river at a rate of 800 to 1600 m a i durng this period of moderately low flows higher transit rates are associated with reaches of higher unit stream power the wave was initially deposited at a site with an abrupt decrease in channel gradient and increase in channel width the amplitude of the wave has attenuated more than i m as it moved downstream and the duration of the wave increased from eight years upstream to more than 20 years downstream channel aggradation and subsequent degradation have been accommodated across the entire channel bed channel width has not decreased significantly after initial channel widening from large 25 year recurrence interval floods three sets of longitudinal surveys of the streambed showed the highest increase in pool depths and frequency in a degrading reach but even the aggrading reach exhbited some pool development through time the aggraded channel bed switched from functioning as a sediment sink to a significant sediment source as the channel adjusted to high sediment loads from 1980 to 1990 sediment eroded from temporary channel storage represented about 25 per cent ofthe total sediment load and 95 per cent of the bedload exported from the basin

alternative modes of quaternary pelagic biosiliceous and carbonate sedimentation a perspective from the east sea japan sea abstract six piston cores 95pc 1 mb97pc 19 ty99 pc18 95pc 3 95pc 4 and 96ebp 4 from the east sea japan sea were examined to assess the fluctuations in carbonate and biogenic silica sedimentation data from four of these cores 95pc 1 mb97pc 19 ty99 pc18 and 96ebp 4 collected from depths above the present carbonate compensation depth ccd clearly show that carbonate content increased during glacial periods and decreased during interglacial periods whereas biogenic silica content shows the opposite pattern the two cores collected below the ccd also show glacial interglacial variations in carbonate and biogenic opal contents with patterns similar to the cores collected above the ccd this study provides strong evidence for cyclic variations of biogenic components corresponding to interglacial glacial cycles even though variations in carbonate and opal contents seem to be affected by dissolution and dilution the inverse correlation between carbonate and biogenic silica contents suggests that two mutually exclusive oceanic modes affected the biogenic sedimentation these modes may have resulted from sea level changes that led to water column stratification during glacial low stands and breakdown of water column stratification and consequent active vertical mixing during interglacial high stands

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

micropaleontological assessment of sediments from buor khaya bay laptev sea abstract the paper presents the first set of micropaleontological data from the buor khaya bay sediments in the southeastern part of the laptev sea obtained from the bottom sediments through permafrost drilling the study of diatoms and spore pollen assemblages in hole 1d 11 and hole 4d 12 high resolution seismic profiling and lithological composition of the sediments have facilitated the identification of two different age strata formed under different conditions and dating to the late pleistocene and holocene the pleistocene strata were composed of assorted sands with inclusions of dense dehydrated silt formed under continental conditions the holocene strata were composed mostly of clayey silt that had formed under transgressive conditions and significant influence of the lena river runoff and arctic tundra vegetation on the coast

river adjustment to changes in sediment load the effects of tin mining on the ringarooma river tasmania 1875 1984 the mining of alluvial tin in the ringarooma basin began in 1875 reached a peak in 1900 20 and had virtually ceased by 1982 during that time 40 million m3 of mining waste were supplied to the main river quickly replacing the natural bed material and requiring major adjustments to the channel based on estimates of sediment supply from more than 50 widely scattered mines and the frequency of flows capable of transporting the introduced load the river s transport history is reconstructed using a mass conservation model because of the lengthy time period 110 years and river distance 75 km involved the model cannot predict detailed change but it does reproduce the main pattern of sediment movement in which successive phases of aggradation and degradation progress downstream peak storage is predicted in that part of the river where braiding and anastomosis are best developed aggradation was most rapid in the upper reaches close to major supply points becoming slower and later with distance downstream channel width increased by up to 300 per cent where the valley floor was broad and braiding became relatively common bridges had frequently to be replaced while bed levels were still rising in lower reaches degradation began in upper ones notably after 1950 and by 1984 had progressed downriver over 30 km rates of incision reached 0 5 m yr 1 especially in the early 1970s when record high flows occurred as a result of degradation the bed material became gravelly through either reexposure of the original bed or lag concentration of coarser fractions also a narrower unbraided channel has developed the river is beginning to heal itself and upper reaches now have reasonably stable beds but at least another 50 years will be required for the river to cleanse its channel of mining debris

from plot to regional scales interactions of slope and catchment hydrological and geomorphic processes in the spanish pyrenees the hydrological and geomorphic effects of land use land cover changes particularly those associated with vegetation regrowth after farmland abandonment were investigated in the central spanish pyrenees the main focus was to assess the interactions among slope catchment basin and fluvial channel processes over a range of spatial scales in recent centuries most mediterranean mountain areas have been subjected to significant human pressure through deforestation cultivation of steep slopes fires and overgrazing depopulation commencing at the beginning of the 20th century and particularly since the 1960s has resulted in farmland abandonment and a reduction in livestock numbers and this has led to an expansion of shrubs and forests studies in the central spanish pyrenees based on experimental plots and catchments in large basins and fluvial channels have confirmed that these land use changes have had hydrological and geomorphic consequences regardless of the spatial scale considered and that processes occurring at any particular scale can be explained by such processes acting on other scales studies using experimental plots have demonstrated that during the period of greatest human pressure mainly the 18th and 19th centuries cultivation of steep slopes caused high runoff rates and extreme soil loss large parts of the small catchments behaved as runoff and sediment source areas whereas the fluvial channels of large basins showed signs of high torrentiality braided morphology bare sedimentary bars instability and prevalence of bedload transport depopulation has concentrated most human pressure on the valley bottoms and specific locations such as resorts whereas the remainder of the area has been affected by an almost generalized abandonment subsequent plant recolonization has resulted in a reduction of overland flow and declining soil erosion at a catchment scale this has caused a reduction in sediment sources and channel incision in the secondary streams at the regional scale the most important consequences include a reduction in the frequency of floods reduced sediment yields increasing stabilization of fluvial channels colonization of sedimentary bars by riparian vegetation and a reduction in the braiding index and stabilization of alluvial fans these results demonstrate the complexity and multiscalar nature of the interactions among land use and runoff generation soil erosion sediment transport and fluvial channel dynamics and highlight the need to adopt a multiscale approach in other mountain areas of the world

dinoflagellate cyst assemblages in surface sediments of the laptev sea region arctic ocean and their relationship to hydrographic conditions the occurrence and distribution of dinoflagellate cysts in surface sediments from the laptev sea shelf and the adjacent continental margin has been studied in relation to surface water conditions assemblages were interpreted by visual inspection and q mode factor analysis the inner laptev shelf is a type area for polar environments because of near absence of relatively warm waters from the pacific or atlantic oceans and an extensive seasonal sea ice cover assemblages are of low diversity and are dominated by the cold water taxon islandinium minutum and related morphotypes the common occurrence of distinctive polykrikoid cyst morphotypes is an indicator of polar environments furthermore strong supply of freshwater in summer influences the surface water conditions and is a major factor controlling the occurrence and distribution of dinoflagellate cysts the dinoflagellate cysts nematosphaeropsis labyrinthus and operculodinium centrocarpum are restricted to the continental margin suggesting a relation to the inflow of relatively warm atlantic waters along the eurasian continental margin an abundance maximum of brigantedinium spp at the shelf break is related to the mean position of the marginal ice zone

coupling between hillslopes and channels in upland fluvial systems implications for landscape sensitivity illustrated from the howgill fells northwest england abstract the sensitivity of upland fluvial systems depends on the magnitude and frequency of sediment and flood producing events modified by the internal coupling characteristics of the system this paper assesses the role of hillslope channel coupling for the sensitivity of upland geomorphic systems using evidence from a 30 year monitoring programme of geomorphic change in the carlingill valley howgill fells northwest england in the hillslope zone there is little sediment supply to the stream system locally slope failures occur in response to extreme events six such events in 30 years within the ca 6 km 2 carlingill valley in the footslope coupling zone basally induced gullies are major sediment sources to the stream sediment production events occur ca 30 times per year feeding sediment to basal debris cones stream floods which can entrain these sediments occur once every ca 2 5 years stream channel morphology is adjusted to this regime downstream of gullies channels are wide and braided elsewhere they are narrow and single thread as the gullies develop however this coupling weakens and the eroding slopes eventually stabilise by revegetation over the 30 year monitoring period there has been a progressive trend towards gully stabilisation and an associated reduction in channel instability massive destabilisation may occur in response to rare extreme flood events such an event return period 100 years occurred in neighbouring langdale and bowderdale valleys in june 1982 that event destabilised the system causing slope failures fan deposition and in some places a switch in channel style to wide braided channels since 1982 there has been a progressive recovery by slope stabilisation and single thread sinuous channels have become reestablished a different style of extreme event occurred in carlingill in october 1998 in response to the wettest week in the 30 year period a slope failure fed debris flows 400 m downslope almost coupling with the channel system future climatic change could render the system prone to destabilisation through either extreme flood events or through major slope failures

hillslope gullying in the solway firth morecambe bay region great britain responses to human impact and or climatic deterioration abstract in the solway firth morecambe bay region of great britain there is evidence for heightened hillslope instability during the late holocene after 3000 cal bp little or no hillslope geomorphic activity has been identified occurring during the early holocene but there is abundant evidence for late holocene hillslope erosion gullying and associated alluvial fan and valley floor deposition interpretation of the regional radiocarbon chronology available from organic matter buried beneath alluvial fan units suggests much of this geomorphic activity can be attributed to four phases of more extensive gullying identified after 2500 2200 1300 1000 1000 800 and 500 cal bp both climate and human impact models can be evoked to explain the crossing of geomorphic thresholds and palaeoecological data on climatic change bog surface wetness and human impact pollen together with archaeological and documentary evidence of landscape history provide a context for addressing the causes of late holocene geomorphic instability high magnitude storm events are the primary agent responsible for gully incision but neither such events nor cooler wetter climatic episodes appear to have produced gully systems in the region before 3000 cal bp increased gullying after 2500 2200 cal bp coincides with population expansion during iron age and romano british times the widespread and extensive gullying after 1300 1000 cal bp and after 1000 800 cal bp coincides with periods of population expansion and a growing rural economy identified during norse times 9 10th centuries ad and during the medieval period 12 13th centuries ad these periods were separated by a downturn associated with the harrying of the north ad 1069 to 1070 the gullying episode after 500 cal bp also coincides with increased anthropogenic pressure on the uplands with population growth and agricultural expansion after ad 1500 following 150 years of malaise caused by livestock and human the black death plagues poor harvests and conflicts on the scottish english border the increased susceptibility to erosion of gullies is a response to increased anthropogenic pressure on upland hillslopes during the late holocene and the role of this pressure appears crucial in priming hillslopes before subsequent major storm events in particular the cycles of expansion and contraction in both population and agriculture appear to have affected the susceptibility of the upland landscape to erosion and the hillslope gullying record in the region therefore contributes to understanding of the timing and spatial pattern of human exploitation of the upland landscape

a diatom based sea ice reconstruction for the vaigat strait disko bugt west greenland over the last 5000 yr abstract a diatom based sea ice concentration sic transfer function was developed by using 72 surface samples from west of greenland and around iceland and validated against associated modern sic canonical correspondence analysis on surface sediment diatoms and monthly average of sic indicated that april sic is the most important environmental factor controlling the distribution of diatoms in the area justifying the development of a diatom based sic transfer function the agreement between reconstructed sic based on diatoms from west greenland and the satellite and modelled sea ice data during the last 75 yr suggests that the diatom based sic reconstruction is reliable for studying the palaeoceanography off west greenland relatively warm conditions with a strong influence of the irminger current ic were indicated for the early part of the record 5000 3860 cal yr bp corresponding in time to the latest part of the holocene thermal maximum between 3860 and 1510 cal yr bp april sic oscillated around the mean value 55 and during the time interval 1510 1120 cal yr bp and after 650 cal yr bp was above the mean indicating more extensive sea ice cover in disko bugt agreement between reconstructed april sic and changes in the diatom species suggests that the sea ice condition in disko bugt was strongly influenced by variations in the relative strength of two components of the west greenland current i e the cold east greenland current and the relatively warm ic further analysis of the reconstructed sic record suggests that solar radiation may be an important forcing mechanism behind the historic sea ice changes

recent arctic marine diatom assemblages from bottom sediments in baffin bay and davis strait abstract this study investigates the present geographical boundaries and environmental limits of the diatom flora in the baffin bay and davis strait area seventy four sea floor surface samples were examined the raw data were analyzed with the cabfac factor analysis program five factor assemblages explaining 87 of the observed variance emerged from this test the statistically most important assemblage is the baffin current assemblage composed ofthalassiosira gravida spores the second assemblage is the summer pack ice assemblage consisting ofactinocyclus curvatulus with a lesser contribution ofthalassiosira trifulta a third assemblage dominated bythalassiosira hyalina is located along the southwest coast of greenland indicating low ice concentration the fourth assemblage consists ofporosira sp spores and indicates fast ice conditions the fifth assemblage is dominated bythalassionema nitzschioides andporosira glacialis vegetative cells and indicates the coastal environment diatoms found in the sediment belong to discrete assemblages which reflect differences in water masses such as salinity and ice conditions these findings should assist in the interpretation of paleoceanographic conditions in the region when diatom assemblages are studied in piston core sediments

geometry and kinematics of the nuncios detachment fold complex implications for lithotectonics in northeastern mexico 1 using recent geologic mapping combined with digital elevation data aerial photo interpretation and cross section balancing we describe the three dimensional 3 d geometry and kinematics of the nuncios fold complex in the monterrey salient of northeastern mexico this map scale evaporite cored detachment fold structure involves upper jurassic through cretaceous rocks deformed during the laramide orogeny and comprises two westward plunging anticlines and an intervening eastward plunging syncline seven balanced cross sections and a 3 d model of this north vergent structure document substantial along strike variations in both fold geometry and detachment depth suggesting that 3 d flow of the detachment layer may have occurred during folding comparison of folds in the monterrey salient with those in the neighboring parras basin suggests that the latter south vergent folds root to a shallower detachment we suggest that northward transport of the monterrey salient folds on the lower evaporite detachment may have been inhibited by a thick sequence of foreland basin rocks in the northeastern parras and southern la popa basins and that the smaller south verging folds formed where the lower detachment was abandoned and slip was transferred to the shallower detachment forming a triangle zone at the front of the sierra madre orogenic wedge

processes controlling the accumulation of diatoms in sediments a model derived from british columbian fjords the transformation of biocoenosis to taphocoenosis of diatom assemblages was examined using monthly sediment traps over a 3 year period at four sites in the fjords of british columbia the fjords were chosen as a natural laboratory where productivity is high and seasonally variable and where geological rates of sediment accumulation approach the biological rates of production and flux the composition of trap samples from different depths was quantified and compared with the surface sediment recovered by box cores fragmentation caused by zooplankton grazing preferentially destroys 20 50 of the early spring and 50 75 of the late spring and early summer production grazing activity and incorporation into pellets does not otherwise affect preservation differential dissolution occurs during settling through the water column taxa with a high surface to volume ratio are preferentially lost low level lateral advection tends to concentrate heavy robust taxa while strong advection affects all particles equally and has no net biasing effect the interaction of these processes results in a sediment assemblage in which winter and fall taxa are more common than they are in the plankton while the early spring bloom is badly underrepresented multivariate analyses indicate that the sediment is dominated by the early summer bloom but caution must be exercised in this interpretation because the bloom is characterized by a species skeletonema costatum which is common at all seasons of the year and therefore is not a reliable indicator of a single period of production the end result is a decrease in seasonal contrast and at some sites a reordering of seasonal proportion in the sediment while the seasonal composition can still be identified there is also evidence of homogenization of sediment assemblages with some of the original spatial variability obscured taken to an extreme a unique fossil assemblage may be produced which cannot be statistically related to any combination of seasons of production three factors which might affect preservation of deep sea assemblages water depth accumulation rate and degree of bioturbation do not have a measurable effect in fjord environments strong modification of assemblages can occur within the upper 500 m deep sea monitoring programs which do not include this interval may lead to erroneous conclusions concerning production and flux to the sediments

the coupling status of alluvial fans and debris cones a review and synthesis alluvial fans and debris cones link two zones of the fluvial system e g hillslope gully systems to stream channels mountain catchment sediment source areas to main river systems or to sedimentary basins and therefore have important coupling or buffering roles these roles may be both functional and preservational the functional role includes debris cone coupling which controls sediment supply from hillslope gully systems to stream channels influencing channel morphology coupling through larger alluvial fans expressed by fanhead trenching causes a distal shift in sedimentation zones or when expressed by through fan trenching causes complete sediment by pass the preservational role stems from the fact that fans and cones are temporary sediment storage zones and may preserve a record of source area environmental change more sensitively than would sediments preserved further downsystem fan coupling mechanisms include distally induced coupling basal scour toe cutting marginal incision and proximally induced coupling fanhead and midfan trenching these mechanisms lead initially to partial coupling either extending the immediate sediment source area to the stream system or shifting the focus of sedimentation distally complete coupling involves transmission of sediment from the feeder catchment through the fan environment into the downstream drainage or a sedimentary basin the implications of coupling relate to downstream channel response fan morphology sedimentation patterns and vertical sedimentary sequences temporal and spatial scales of coupling are related and with increasing scales the dominant controls shift from storm events to land cover to climatic and base level change and ultimately to the relationships between tectonics and accommodation space finally future research challenges are identified modern dating techniques and sophisticated analysis of remotely sensed data can greatly improve our understanding of fan dynamics and should lead to better cross scale integration between short term process based approaches and long term sedimentological applications while maintaining high quality field based observations copyright 2011 john wiley sons ltd

the gravel sand transition in a disturbed catchment abstract more than 40 million cubic metres of mining waste were supplied to the ringarooma river between 1875 and 1984 leading to successive phases of aggradation and degradation the natural bed material is gravel but given the volume of introduced load and the fact that much of the input was less than 5 mm in diameter the size composition of the bed changed from gravel to sand during the phase of downstream progressive aggradation a very sharp gravel sand transition developed in which median grain size decreased from over 30 mm to under 3 mm in less than 500 m with upstream supplies of mining debris becoming depleted first degradation followed the same downstream progressive pattern as aggradation causing the transition to migrate downstream by 1984 the river could be regarded as a series of zones each characterized by a particular bed condition a natural cobble gravel bed unaffected by mining inputs 0 32 km pre disturbance bed re exposed by degradation over 35 40 years 32 53 km sandy substrate with a gravel armour produced by differential transport during degradation 53 65 km sand dominated but with developing surface patches of coarser material 65 75 km sandy bed reflecting the size composition of the original mining input 75 118 km although the gravel sand transition itself is sharp the transitional zone is lengthy 53 75 km as degradation continues the gravel sand transition is expected to progress downstream but it has remained in a stable position for 12 years indeed two major floods during the period released large quantities of sand from the sub armour layer and newly formed banks of mine tailings causing fining both above and below the transition surface grain size is an adjustable component in the transitional zone as the river strives to recover from a major anthropogenic disturbance

diatom evidence of hydrographic changes and ice conditions in igaliku fjord south greenland during the past 1500 years biostratigraphic diatom analyses were carried out on two sediment cores from igaliku fjord south greenland in order to reconstruct hydrographic and climatic fluctuations during the late holocene ad 550 to present pronounced differences in hydrographic setting of the coring sites provide palaeoenvironmental information of both local and more regional character five diatom zones were identified from the subfossil diatom records each describing a hydrographic setting two major climate periods the mediaeval warm period ad 800 1250 and the little ice age ad 1580 1850 that were separated by a variable transitional period were recognized prior to these periods a cold and presumably moist climate regime prevailed between ad 500 and 700 cooling events were identified during the mediaeval warm period in the period ad 960 to 1140 the diatom data demonstrate that marked hydrographic changes occurred in the course of a relatively short timespan beginning at about ad 1300 and culminating around

effective timescales of coupling within fluvial systems this paper presents a review of the coupling concept in fluvial geomorphology based mainly on previously published work coupling mechanisms link the components of the fluvial system controlling sediment transport down the system and the propagation of the effects of base level change up the system they can be viewed at several scales at the local scale involving within hillslope coupling hillslope to channel coupling and within channels tributary junction and reach to reach coupling at larger scales coupling can be considered as zonal coupling between major zones of the system or as regional coupling relating to complete drainage basins these trends are illustrated particularly by the examples of hillslope to channel coupling in the howgill fells northwest england badland systems in southeast spain alluvial fans in spain usa and uae and base level induced dissection of neogene sedimentary basins in southeast spain as the spatial scales increase so do the timescales involved effective temporal scales relate to magnitude and frequency characteristics recovery time and propagation time the relative importance changing with the spatial scale for downsystem coupling at the local scale the first two are important with propagation time increasing in importance in larger systems especially in those involving upsystem coupling related to base level change the effective timescales range from the individual event with a return period of decades through decadal to century timescales for downsystem coupling to tens to hundreds of thousands of years for the basinwide response to base level change the effective timescales influence the relative importance of factors controlling landform development

a diatom based reconstruction of early holocene hydrographic and climatic change in a southwest greenland fjord abstract a diatom based reconstruction of surface water paleoclimatic and paleoceanographic changes in ameralik fjord southwest greenland is presented for the holocene interval 8800 to 3600 cal yrs b p a minor episode of cold surface water conditions is found at ca 8000 7800 cal yrs b p this may be due to the local conditions in the fjord and linked to the culmination of a strong melt water outflow rather than reflecting the widespread north atlantic 8 2 ka cooling event warming of surface water condition from 7800 to 7100 cal yrs b p probably corresponding to the early and warmest part of the holocene thermal maximum htm in this region is reflected in the diatom assemblages and supported by other proxies the west greenland current wgc influences the fjord strongly during this interval indicating enhanced advection of atlantic water masses derived from the irminger current ic a major sedimentary change with a hiatus between 6800 and 4400 cal yrs b p prevents a reconstruction of mid holocene paleoceanograpy the final and less prominent part of the htm is found after 4400 cal yrs b p previous studies from the same site have shown this final stage of the htm to end at 3200 cal yrs b p with the onset of the neoglaciation our study provides further evidence that the marine sedimentary record from west greenland fjords yields paleoenvironmental information reflecting a significant link between local and large scale north atlantic oceanographic and climatic changes

distribution patterns of diatom surface sediment assemblages in the laptev sea arctic ocean abstract the modern diatom distribution in the laptev sea arctic ocean was investigated in 89 surface sediment samples diatom concentrations are relatively low showing values between 0 01 10 6 and 6 7 10 6 valves per gram dry sediment based on a factor analysis using seventeen taxa or taxa groups five diatom surface sediment assemblages can be defined the ice diatom assemblage of the central region of the laptev sea the chaetoceros assemblage of the eastern and southeastern shelf the thalassiosira antarctica assemblage of the continental slope and deep sea the freshwater diatom assemblage in the vicinity of river mouths and deltas and the thalassiosira nordenskioeldii assemblage which shows a patchy occurrence on the central laptev sea shelf the distribution pattern of diatom assemblages in surface sediment is significantly related to oceanographic conditions of surface water masses the main factors controlling the distribution of diatoms in the laptev sea are the riverine freshwater input during the summer which strongly affects the salinity conditions and the sea ice extent furthermore the composition of the thalassiosira antarctica assemblage of the continental slope is largely influenced by dissolution and lateral transport processes

coupling between landslides and eroding stream channels reconstructed from spruce tree rings examples from the carpathians and sudetes central europe the analysis of the positive feedback between landslides and erosion requires determination of the precise temporal and spatial relations between events of colluvium delivery and fluvial erosion in our study we use decennial datasets on the occurrence of landsliding and erosion achieved through dendrochronological methods four sites covering areas of landslide slopes and adjacent valley floors with stream channels were studied landsliding on slopes was dated from the tree ring eccentricity developed in stems tilted due to bedrock instability erosion in channels was dated using the wood anatomy of roots exposed by erosion of the soil cover analysis of the temporal relations between dated landsliding erosion and precipitation record has revealed that two types of repeating sequences can be observed 1 rainfall landsliding erosion 2 rainfall erosion landsliding these sequences are an indication of the occurrence of slope channel positive feedback in the sites studied in the first type landsliding triggered by rainfall delivers colluvia into the valley floor and causes its narrowing which in turn causes increased erosion in the second type erosion triggered by rainfall disturbs the slope equilibrium and causes landsliding landsliding and erosion once triggered by precipitation can occur alternately in years with average precipitation and reinforce one another bidirectional coupling between landsliding and channel erosion was shown notably through the effects of channel shifting and forced sinuosity and by increased erosion of the slopes opposite the active landslides observations also suggest that the repetition of sequences described over longer periods of time can lead to a general widening of the valley floor at the expense of slopes and to a gradual change of the valley cross profile from narrow v shaped into a wide flat bottomed thus landsliding erosion coupling positive feedback was recognized as an important factor shaping hillslope valley topography of the mid mountain areas studied copyright 2014 john wiley sons ltd

the nahal oz reservoir dam break flood geomorphic impact on a small ephemeral loess channel in the semi arid negev desert israel abstract the nahal oz reservoir in the coastal semi arid southwestern israel was designed to enhance local irrigation of crops using reclaimed sewage water during the dry summer months on march 2001 part of the western dike of the reservoir was breached and generated a flow release of 3 5 106 m3 of secondary irrigation water that was channeled down the 1st order ephemeral loess stream nahal yare akh the consequent 12 hour flood surge with an estimated peak discharge of 1000 m3s 1 inflicted severe loess erosion agricultural property and infrastructural damage downstream 6 million post flood mapping documented the geomorphic response to the flood which included channel scour and widening along the initial 2 km downstream of the reservoir where a spillway channel was formed the increase in the cross sectional area was about 60 and had an estimated 170 000 m3 of sediment bed bank and floodplain erosion calculated maximum shear stress and stream power along this section are estimated at 300 nm 2 and 900 wm 2 respectively the peak discharge at the end of this segment was estimated at 800 m3s 1 indicating only minor attenuation along this segment two km downstream of the breach a wide braided fan indicated deposition of the eroded sediments at the end of this segment the floodwater diverged into several watercourses and inundated tilled agricultural fields and neighborhoods downstream 9 km from the reservoir the discharge attenuated to 100 m3s 1 slightly above bankfull further downstream and upon reaching the large shikma stream the flow was already very low this reduction in discharge is attributed to the anthropogenic infrastructure roads neighborhoods and agricultural fields and the large transmission losses typical of sandy ephemeral streams the study shows that channels within erodible materials respond to high peak discharges very locally erosional thresholds that severely incised the channel are only maintained for 2 km below the breached reservoir and as distance from the source area increases available energy is substantially reduced due to high transmission losses gentler valley gradients very wide shallow flow and the ability of the drainage network to accommodate large discharges consequently the geomorphic impact was limited to the first 2 6 km with only minor erosional or depositional evidence downstream the current natural flow regime has only minor impact on the newly formed channel geometry below the breached dam accordingly the channel geometry may be preserved for a relatively long time however channel recovery in this segment was rapid and within a few years all bare loess surfaces exposed during the flood have been covered by dense vegetation the analysis also shows that nahal oz reservoir s dam break flood transmission losses and flood attenuation rates were extreme in comparison to other case studies this artificial flood event in a desert environment offers a rare opportunity to quantify channel and bank erosion evolution processes during an extremely high magnitude flood within highly erodible fine sediment as well as to detect the recovery processes a few years later

sedimentologic and geomorphic variations in storm generated alluvial fans howgill fells northwest england in june 1982 a storm with a return period greater than 100 yr but lasting less than 2 5 hr destabilized hillslopes and produced a suite of geomorphologically and sedimentologically diverse alluvial fans thirteen major fans were deposited at the tributary junctions between small 2 catchments and two north flowing headwater streams of the river lune northwest england storm generated fans spread over or became inset into older stable fans and produced localized vertical accretion of as much as 3 m and lateral accretion of as much as 100 m sedimentary processes operating during deposition involved debris flow transitional flow and streamflow six facies types are recognized on the basis of depositional topography sedimentary texture and fabric and matrix content viscous debris flow d1 dilute debris flow d2 transitional flow t1 fluvial bars and lobes s1 s2 and fluvial sheet gravels s3 regionally streamflow deposition prevails over debris flow deposition and type s3 facies has the greatest areal extent temporal and spatial variations in facies deposition during the storm however resulted from water sediment ratio variations fan deposition involved an early phase of debris flow to transitional flow due to large inputs of sediment from hillslope failures this was followed by a systematic change to more dilute conditions resulting in streamflow deposition and eventually in channel incision a significant amount of geomorphic work and complex variations in sedimentary processes during the storm resulted in part from extensive overland flow and hillslope destabilization discriminant analyses indicate that catchment size channel gradient and percentage of area eroded during the storm controlled whether debris flow or streamflow facies dominated a fan sequence smaller steeper catchments had a greater percentage of the area yielding sediment and are dominanted by debris flows whereas larger catchments produced more runoff resulting in dilution and streamflow the results indicate that the facies sequences and fan entrenchment in the howgill fells which are typically considered products of longer term climatic change or tectonics in other localities are here primarily affected by thresholds related to catchment geomorphology by the type of sediment available and by the position within the storm cell

sediment core from beneath the amery ice shelf east antarctica suggests mid holocene ice shelf retreat the stability of floating ice shelves is an important indicator of ocean circulation and ice shelf mass balance a sub ice shelf sediment core collected during the austral summer of 2000 2001 from site am02 69 42 8 s 72 38 4 e on the amery ice shelf east antarctica contains a full and continuous record of glacial retreat the am02 core site is 80 km south of the floating ice shelf edge and contains a 0 5 m thick holocene surface layer of siliceous mud and diatom ooze of marine origin core data are supportive of sub ice shelf circulation models that predict the landward flow of oceanic water and prove that the landward transport of hemipelagic sediments occurs beneath floating ice shelves over distances of at least 80 km an increase in sea ice associated diatom deposition in the upper part of the holocene suggests that a major retreat of the amery ice shelf to at least 80 km landward of its present location may have occurred during the mid holocene climatic optimum

diatom inferred salinity records from the arctic siberian margin implications for fluvial runoff patterns during the holocene diatom assemblages were employed to study temporal changes of siberian river runoff on the laptev sea shelf using a correlation between freshwater diatoms in core top sediments and summer surface water salinities from the inner kara sea salinity conditions were reconstructed for a site northeast of the lena river delta present water depth 32 m since 9 calendar years cal ka the reconstruction indicate a strong near coastal and river influenced environment at the site until about 8 6 cal ka corroborated by comparison with other proxy records from further to the east surface salinities increased from 9 to 14 until about 7 4 cal ka owing to ongoing global sea level rise and synchronous southward shift of the coastline although riverine water became less influential at the site since then salinities still varied between 12 5 and 15 particularly during the last 3 5 kyr these more recent salinity fluctuations agree well with reconstructions from just north of the lena delta emphasizing the strong linkage between shelf hydrography and riverine discharge patterns in arctic siberia

dissolution and preservation of antarctic diatoms and the effect on sediment thanatocoenoses abstract comparison of southern ocean diatom populations from i surface ocean production ii underlying antarctic sediments and iii laboratory dissolution experiments demonstrates that dissolution can account for the temporal and spatial variations in sedimentary diatom assemblages observed in southern ocean sediments increasing dissolution causes relative depletions in n kerguelensis k enrichments in t lentiginosa l and slight enrichments in e antarctica a this reflects the relative susceptibility to dissolution of the three species that dominate antarctic sediments we have devised a preservation index for the southern ocean based on the ratio k k l to estimate relative extents of dissolution and applied it to natural assemblages holocene southern ocean sediments display increasing opal preservation toward higher latitudes but south of the antarctic polar front preservation decreases in the order well preserved se indian s atlantic sw indian se pacific poorly preserved dissolution also accounts for the pattern of diatom assemblages in the last glacial maximum lgm sediments of the indian and pacific sectors but in the atlantic increased e antarctica abundances at lgm must have resulted from an increase in surface ocean production of this species holocene and lgm diatoms in atlantic and pacific sector sediments are equally well preserved but in the indian sectors holocene sediments are better preserved than those of lgm age paleoceanographic and paleoclimatic transfer functions derived from factor analyses of variations in the sedimentary abundances of these three diatoms have ignored the effects of differential dissolution on thanatocoenosis and thus should be interpreted with caution

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

multidisciplinary approach to sediment connectivity between debris flow channel network and the dolra river mazeri valley southern caucasus georgia abstract the mazeri valley in the southern caucasus mountains georgia is characterized by a highly dynamic landscape with several active mass wasting processes the spatial and temporal dynamics of these geomorphic processes have over time resulted in the formation of large cones and fans in this context the coupling between the hillslope and the channel plays a fundamental role in controlling the catchment sediment dynamics the sediment produced at higher altitudes on hillslopes may occasionally reach the debris flow channel network and downstream propagation may have significant effects on the fluvial environment and create potential hazards for the population and infrastructure in this regard we report a tree ring based chronology of the debris flow activity on a large cone to shed light on sediment connectivity and better understand the coupling between the main debris flow channel and a bedload river in this remote area under global climate change and glacial retreat the 161 sampled trees demonstrated the appearance of 12 significant events over the last 65 years with all of the events involving possible sediment input into the stream system of the dolra river these successional events with a return interval of 5 4 years have partially destabilized the fluvial system and locally induced a switch in the channel style to a braided channel surficial sedimentary characteristics such as morphometric indices have enabled the discrimination between sediments from the debris flow activity and river dynamics alluvium inputs finally most of the reconstructed event years are characterized by at least one month of above average rainfall

diatoms in the gulf of california seasonal flux patterns and the sediment record for the last 15 000 years flux and taxonomic composition of the diatom assemblage was determined for biweekly sediment traps in the central gulf of california over a 2 year period fluxes and relative abundance of taxa are not significantly different in traps from the eastern side of the guaymas basin and the western side of the carmen basin indicating that patterns of diatom production are uniform across the central gulf at all seasons of the year the annual maximum in diatom flux occurred during the winter season of both years either as a sustained event over many weeks 1990 or as a series of short blooms 1991 1992 of the most abundant taxa only hyalochaete chaetoceros species showed a clear seasonal cycle with a flux maximum in the spring of both years factor analysis defines five assemblages representing 1 summer and fall conditions of surface stratification and nutrient limitation 2 winter bloom triggered by onset of strong northwesterly winds 3 late spring to summer production probably related to sporadic events during periods of weak southeasterly winds 4 spring 1991 inferred to reflect the distal edge of a coastal upwelling phase 5 lateral advection of resuspended sediments from the continental shelf possibly resulting from trapped coastal waves during summer hurricanes and from storms during the 1991 1992 el nino southern oscillation enso the diatom data support the inference that subtropical pacific water penetrates deeper into the gulf during enso events in order to compare the sediment trap record to a sediment core a second factor analysis was done using only the taxa which are preserved in the sediment and omitting the most abundant taxa which showed little downcore variation this produces five factors representing 1 summer fall low production 2 early winter bloom 3 late winter spring upwelling 4 enso conditions and 5 a late spring summer assemblage of uncertain significance variation of species characterisic of each factor was examined in piston core atlantis ii 125 8 56jpc taken from the oxygen minimum zone in guaymas basin correlation to nearby deep sea drilling project hole 480 indicates that the core penetrates to about 15 ka with laminated sediments in the holocene 0 10 ka and late deglacial 11 13 ka and massive nonlaminated sediments around younger dryas time 10 11 ka and before 13 ka downcore variations in the diatom assemblage do not correspond directly to presence of laminations implying that the processes controlling bottom water oxygen content are not determined by conditions of surface water production presence of calcareous nannofossils downcore correlates inversely with two diatom assemblages enso and winter bloom indicators and not with occurrence of laminations suggesting that occurrence of calcareous nannofossils in the sediment is at least partly a function of surface water production prior to 12 ka production was lower than at present during all seasons implying weaker winds throughout the year subtropical waters extended to the midgulf as they do today during enso events between 11 and 12 ka conditions were similar to those of the present with relatively high winter and spring production resulting from northwesterly winds enso events were still common although less so than during the preceding period younger dryas time was one of transition with intermediate conditions a slackening of winter spring northwesterly winds and reduction of total annual production and increased occurrence of enso conditions in the early to middle holocene winter northwesterlies increased to a maximum resulting in very high production but apparently did not persist into spring subtropical waters mostly disappeared from the gulf in the late holocene northwesterly winds have supported high production during both winter and spring seasons

sediment continuity through the upland sediment cascade geomorphic response of an upland river to an extreme flood event hillslope erosion and accelerated lake sedimentation are often reported as the source and main stores of sediment in the upland sediment cascade during extreme flood events while upland valley floodplain systems in the transfer zone have the potential to influence sediment continuity during extreme events their geomorphic response is rarely quantified this paper quantifies the sediment continuity through a regulated upland valley fluvial system st john s beck cumbria uk in response to the extreme storm desmond 4 6 december 2015 flood event a sediment budget framework is used to quantify geomorphic response and evaluate sediment transport during the event field measurements show 6500 710 t of sediment was eroded or scoured from the river floodplains banks and bed during the event with 6300 570 t of sediment deposited in the channel or on the surrounding floodplains 6 of sediment eroded during the flood event was transported out of the 8 km channel floodplain sediment storage was seen to be restricted to areas of overbank flow where the channel was unconfined results indicate that rather than upland floodplain valleys functioning as effective transfer reaches they instead comprise significant storage zones that capture coarse flood sediments and disrupt sediment continuity downstream

paleoceanographic reconstructions of surface ocean conditions in the greenland iceland and norwegian seas through the last 14 ka based on diatoms prior reconstructions of the last glacial maximum and the holocene did not include detailed paleoclimate data from the greenland iceland and norwegian gin seas which cover sensitive areas for oceanographic boundaries sea ice distribution and deep water formation in order to fill this gap we studied nine well dated sediment cores from this area and reconstructed the paleoceanographic conditions of the surface gin seas at 2000 year intervals since 13 400 bp based on the diatom record results show that a n s extending sea ice free corridor had opened along norway already at 13 400 bp indicating a northward flow of a branch of the north atlantic drift possibly caused by a change in the jet stream flow due to the decreased height of the north american ice sheet a major change of climatic conditions occurred over the gin seas as the insolation anomaly reached its maximum around 9000 bp when the sea ice cover and the oceanic fronts retreated to a northwesterly position along greenland and the ocean temperatures rose the first half of the holocene is recorded as the warmest period during the last 13 400 bp in the gin seas the duration of this climatic optimum decreased both toward the north and toward the margins of the area the second half of the holocene is characterized by a cooling trend in step with the decreasing insolation these results support the proposal of imbrie et al 1992 that the gin seas region acts as an initial responder to insolation changes

lena river discharge events in sediments of laptev sea russian arctic abstract to reconstruct the variability of freshwater discharge to the arctic via the lena river 22 gravity cores were collected along two transects that extend from the delta floodplain onto the laptev sea shelf high magnetic susceptibility ms signals appear to be good indicators for river sediment deposition sedimentation of this terrestrial material forms fluvial units distinguished by coarse grain size and high ms signal produced by the magnetic properties from the river derived material the criteria to distinguish marine units are low magnetic susceptibility signals when compared with fluvial units lithological descriptions and granulometric analyses sedigraph granulometric analyses in combination with wet sieving analyses grain size 4 reveal changes in grain size distributions along the cores that are well correlated with magnetic susceptibility data fluvial and marine units were found to alternate sequentially along the cores data from cores comprising two transects in the laptev sea revealed 17 total fluvial events during the last 2000 years the lena river derived sediment bedload could be traced 34 5 47 5 km far from the delta edge of bykovskaya branch showing direct impact of lena river discharge to the laptev sea