response of the chydorid faunas to rapid climatic changes in four alpine lakes at different altitudes abstract the subfossil assemblages of chydoridae from late glacial preboreal sediments of four sites from 603 m to 2290 m asl were analysed to trace the community response to rapid climatic warming that occurred at this period of time in each site distinct signals at the younger dryas preboreal boundary were recorded by density of remains species diversity or community composition however responses varied considerably among the sites this variation was attributed to the situation that the chydorid community structure is determined not only by temporal younger dryas preboreal boundary and spatial among the sites temperature gradients but also by the specific local ecological conditions at the sites in some species the classification with respect to cold tolerance should be reconsidered

cenozoic ice rafting history of the central arctic ocean terrigenous sands on the lomonosov ridge the cenozoic ice rafted debris ird history of the central arctic is reconstructed utilizing the terrigenous coarse sand fraction in iodp 302 cores from 0 to 273 meters composite depth this holocene middle eocene quantitative record of terrigenous sand accumulation on the lomonosov ridge along with qualitative information on grain texture and composition confirms the interpretation that ice initiation sea ice and glacial ice occurred 46 ma in the arctic and provides a long term pattern of arctic ice expansion and decay since the middle eocene ird mass accumulation rates range from 0 to 0 13 g cm2 ka in the middle eocene and from 0 to 0 36 g cm2 ka in the neogene ird mass accumulation rate mar maxima in the miocene and pliocene cooccur with either glacial initiation or intensification in the sub arctic the 46 25 ma ird onset in the central arctic slightly precedes the earliest evidence of ice in the antarctic and compares in timing with a 1000 ppm decrease in atmospheric concentrations of co2 the decline of pco2 in the middle eocene may have driven both poles across the temperature threshold that enabled the nucleation of glaciers on land and partial freezing of the surface arctic ocean especially during times of low insolation

late eocene to early miocene ice sheet dynamics and the global carbon cycle paired benthic foraminiferal trace metal and stable isotope records have been constructed from equatorial pacific ocean drilling program site 1218 the records include the two largest abrupt 1 myr increases in the cenozoic benthic oxygen isotope record oi 1 in the earliest oligocene 34 ma and mi 1 in the earliest miocene 23 ma the paired mg ca and oxygen isotope records are used to calculate seawater 18o w calculated w suggests that a large antarctic ice sheet formed during oi 1 and subsequently fluctuated throughout the oligocene on both short 0 5 myr and long 2 3 myr timescales between about 50 and 100 of its maximum earliest oligocene size the magnitudes of these fluctuations are consistent with estimates of sea level derived from sequence stratigraphy the transient expansion of the antarctic ice sheet at mi 1 is marked in the benthic 18o record by two positive excursions between 23 7 and 22 9 ma each with a duration of 200 300 kyr bottom water temperatures decreased by 2 c over the 150 kyr immediately prior to both rapid 18o excursions however the onset of each of these phases of ice growth is synchronous within the resolution of the records with the onset of a 2 c warming over 150 kyr we suggest that the warming during these glacial expansions reflect increased greenhouse forcing prompted by a sudden decrease in global chemical weathering rates as antarctic basement silicate rocks became blanketed by an ice sheet this represents a negative feedback process that might have operated during major abrupt growth phases of the antarctic ice sheet

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

reconstructing biomes from palaeoecological data a general method and its application to european pollen data at 0 and 6 ka biome models allow the results of experiments with atmospheric general circulation models to be translated into global maps of potential natural vegetation the use of biome models as a diagnostic tool for palaeoclimate simulations can yield maps that are directly comparable with palaeoecological pollen and plant macrofossil records provided these records are biomized i e assigned to biomes in a consistent way this article describes a method for the objective biomization of pollen samples based on fuzzy logic pollen types taxa are assigned to one or more plant functional types pfts then affinity scores are calculated for each biome in turn based on its list of characteristic pfts the pollen sample is assigned to the biome to which it has the highest affinity subject to a tie breaking rule modern pollen data from surface samples reflecting present vegetation across europe are used to validate the method pollen data from dated sediment cores are then used to reconstruct european vegetation patterns for 6 ka the reconstruction shows systematic differences from present that are consistent with previous interpretations the method has proved robust with respect to human impacts on vegetation and provides a rational way to interpret combinations of pollen types that do not have present day analogs the method demands minimal prior information and is therefore equally suitable for use in other regions with richer floras and or lower densities of available modern and fossil pollen samples than europe

effects of earthquake induced landslides on sediment budget and transport over a 50 yr period landsliding during a magnitude 7 7 earthquake in 1929 in northwestern south island new zealand delivered up to 400 000 m 3 km 2 of sediment to stream channels first to third order channels were buried to depths of as much as 10 m with sedimentary rock debris for distances ranging from 2 of the 92 km 2 study area because of the coarse grain size of the sedimentary rock debris and trapping of sediment in numerous landslide dammed lakes sand and pebble sized debris originating from landslides on a 6 6 km 2 area of granite has been transported downstream no more than 10 km at least 50 to 75 of this granitic debris is retained in the fourth order 92 km 2 catchment 50 yr after the earthquake the long retention times of sediment and the volume of debris supplied by landslides during a large earthquake suggest that earthquake induced landsliding is the principal sediment supply mechanism in the region

the equilibrium alluvial river under variable flow and its channel forming discharge when the water discharge sediment supply and base level vary around stable values an alluvial river evolves toward a mean equilibrium or graded state with small fluctuations around this mean state i e a dynamic or statistical equilibrium state here we present analytical relations describing the mean equilibrium geometry of an alluvial river under variable flow by linking channel slope width and bed surface texture the solution holds in river normal flow zones or outside both the hydrograph boundary layer and the backwater zone and accounts for grain size selective transport and particle abrasion we consider the variable flow rate as a series of continuously changing yet steady water discharges here termed an alternating steady discharge the analysis also provides a solution to the channel forming water discharge which is here defined as the steady water discharge that given the mean sediment supply provides the same equilibrium channel slope as the natural long term hydrograph the channel forming water discharge for the gravel load is larger than the one associated with the sand load the analysis illustrates how the load is distributed over the range of water discharge in the river normal flow zone which we term the normal flow load distribution the fact that the distribution of the imposed sediment supply spatially adapts to this normal flow load distribution is the origin of the hydrograph boundary layer the results quantify the findings by wolman and miller 1960 regarding the relevance of both magnitude and frequency of the flow rate with respect to channel geometry

late glacial climatic changes in eastern france lake lautrey from pollen lake levels and chironomids high temporal resolution analyses of pollen chironomid and lake level records from lake lautrey provide multi proxy quantitative estimates of climatic change during the late glacial period in eastern france past temperature and moisture parameters were estimated using modern analogues and plant functional types transfer function methods for three pollen records obtained from different localities within the paleolake basin the comparison of these methods shows that they provide generally similar climate signals with the exception of the bolling comparison of pollen and chironomid based temperature of the warmest month reconstructions generally agree except during the bolling major abrupt changes associated with the oldest dryas bolling allerod younger dryas and the younger dryas preboreal transitions were quantified as well as other minor fluctuations related to the cold events e g preboreal oscillation the temperature of the warmest month increased by not vert similar5 c at the start of bolling and by 1 5 3 c at the onset of the holocene while it fell by ca 3 to 4 c at the beginning of younger dryas the comparative analysis of the results based on the three lautrey cores have highlighted significant differences in the climate reconstructions related to the location of each core underlining the caution that is needed when studying single cores not taken from deepest part of lake basins

gravel bed river evolution in earthquake prone regions subject to cycled hydrographs and repeated sediment pulses sediment often enters rivers in the form of sediment pulses associated with landslides and debris flows this is particularly so in gravel bed rivers in earthquake prone mountain regions such as southwest china under such circumstances sediment pulses can rapidly change river topography and leave the river in repeated states of gradual recovery in this paper we implement a one dimensional morphodynamic model of river response to pulsed sediment supply the model is validated using data from flume experiments so demonstrating that it can successfully reproduce the overall morphodynamics of experimental pulses the model is then used to explore the evolution of a gravel bed river subject to cycled hydrographs and repeated sediment pulses these pulses are fed into the channel in a fixed region centered at a point halfway down the calculational domain the pulsed sediment supply is in addition to a constant sediment supply at the upstream end results indicate that the river can reach a mobile bed equilibrium in which two regions exist within which bed elevation and surface grain size distribution vary periodically in time one of these is at the upstream end where a periodic discharge hydrograph and constant sediment supply are imposed and the other is in a region about halfway down the channel where periodic sediment pulses are introduced outside these two regions bed elevation and surface grain size distribution reach a mobile bed equilibrium that is invariant in time the zone of fluctuation free mobile bed equilibrium upstream of the pulse region is not affected by repeated sediment pulses under the scenarios tested but downstream of the pulse region the channel reaches different fluctuation free mobile bed equilibriums under different sediment pulse scenarios the vertical bed structure predicted by the simulations indicates that the cyclic variation associated with the hydrograph and sediment pulses can affect the substrate stratigraphy to some depth copyright 2017 john wiley sons ltd

reconstruction of late glacial summer temperatures from chironomid assemblages in lac lautrey jura france a chironomid july air temperature inference model based on chironomid assemblages in the surface sediments of 81 swiss lakes was used to reconstruct late glacial july air temperatures at lac lautrey jura eastern france the transfer function was based on weighted averaging partial least squares wa pls regression and featured a leave one out cross validated coefficient of determination r2 of 0 80 a root mean square error of prediction rmsep of 1 53 c and was applied to a chironomid record consisting of 154 samples covering the late glacial period back to the oldest dryas the model reconstructed july air temperatures of 11 12 c during the oldest dryas increasing temperatures between 14 and 16 5 c during the bolling temperatures around 16 5 17 0 c for most of the allerod temperatures of 14 15 c during the younger dryas and temperatures of ca 16 5 c during the preboreal the lac lautrey record features a two step july air temperature increase after the oldest dryas with an abrupt temperature increase of ca 3 3 5 c at the oldest dryas bolling transition followed by a more gradual warming between ca 14 200 and 13 700 bp the transfer function reconstructs a less rapid cooling at the allerod younger dryas transition than other published records possibly an artefact caused by the poor analogue situation during the earliest younger dryas and an abrupt warming at the younger dryas holocene transition during the allerod two centennial scale 1 5 2 0 c coolings are apparent in the record although chronologically not well constrained the first of these cold events may be synchronous with the beginning of the gerzensee oscillation the second is inferred just before deposition of the laachersee tephra at lac lautrey and is therefore coeval with the end of the gerzensee oscillation in contrast to the greenland oxygen isotope records the lac lautrey palaeotemperature reconstruction lacks a clearly defined greenland interstadial gi event 1d and the decreasing temperature trend during the bolling allerod interstadial copyright 2005 john wiley sons ltd

vegetation responses to rapid warming and to minor climatic fluctuations during the late glacial interstadial gi 1 at gerzensee switzerland abstract high resolution pollen analyses made on the same samples on which the ratios of oxygen isotopes were measured that provided the time scale and a temperature proxy after correlation to northgrip 1 a primary succession the vegetation responded to the rapid rise of temperatures around 14 685 yr bp with a primary succession on a decadal to centennial time scale the succession between ca 15 600 and 13 000 yr bp included 1 1 the replacement of shrub tundra by woodland of juniperus and tree birch around 14 665 yr bp 1 2 the response of juniperus pollen to the shift in oxygen isotopes in less than 20 yr 1 3 a sequence of population increases of hippophae rhamnoides ca 14 600 yr bp salix spp ca 14 600 yr bp betula trees ca 14 480 yr bp populus cf tremula ca 14 300 yr bp and pinus cf sylvestris ca 13 830 yr bp 2 biological processes plants responded to the rapid increase of summer temperatures on all organisational levels 2 1 individuals may have produced more pollen e g juniperus 2 2 populations increased or decreased e g juniperus betula later pinus and 2 3 populations changed their biogeographical range and may show migrational lags 2 4 plant communities changed in their composition because the species pools changed through immigration and local extinction some plant communities may have been without modern analogue these mechanisms require increasing amounts of time 2 5 processes on the level of ecosystems with species interactions may involve various time scales besides competition and facilitation nitrogen fixation is discussed 3 the minor fluctuations of temperature during the late glacial interstadial which are recorded in 18o resulted in only very minor changes in pollen during the aegelsee oscillation older dryas biozone gi 1d and the gerzensee oscillation gi 1b 4 biodiversity the afforestation at the onset of bolling coincided with a gradual increase of taxonomic diversity up to the time of the major pinus expansion

supply and removal of sediment in a landslide dominated mountain belt central range taiwan abstract a strong coupling between hillslope and valley systems is often inferred for mountain landscapes dominated by bedrock landsliding we reveal the nature of this link using data sets on landsliding and sediment transport from two montane catchments draining the eastern central range of taiwan here the magnitude frequency distribution of landslides can be modeled by a robust power law but this scale invariance is not mirrored in the sediment discharge at the mountain front instead downstream sediment loads reflect a complex response to both sediment supply and ambient hydraulic conditions the rivers do not transport significant amounts of sediment unless it is provided by hillslope mass wasting in the catchment removal of landslide debris is a function of the transport capacity of the stream at the site of entry thus there is a dual supply and transport control on sediment loads in bedrock floored streams over a monitoring period of 25 yr the bulk of the sediment leaving the mountain bel

younger dryas and allerod summer temperatures at gerzensee switzerland inferred from fossil pollen and cladoceran assemblages linear and unimodal based inference models for mean summer temperatures partial least squares weighted averaging and weighted averaging partial least squares models were applied to a high resolution pollen and cladoceran stratigraphy from gerzensee switzerland the time window of investigation included the allerod the younger dryas and the preboreal characteristic major and minor oscillations in the oxygen isotope stratigraphy such as the gerzensee oscillation the onset and end of the younger dryas stadial and the preboreal oscillation were identified by isotope analysis of bulk sediment carbonates of the same core and were used as independent indicators for hemispheric or global scale climatic change in general the pollen inferred mean summer temperature reconstruction using all three inference models follows the oxygen isotope curve more closely than the cladoceran curve the cladoceran inferred reconstruction suggests generally warmer summers than the pollen based reconstructions which may be an effect of terrestrial vegetation not being in equilibrium with climate due to migrational lags during the late glacial and early holocene allerod summer temperatures range between 11 and 12 c based on pollen whereas the cladoceran inferred temperatures lie between 11 and 13 c pollen and cladocera inferred reconstructions both suggest a drop to 9 10 c at the beginning of the younger dryas although the allerod younger dryas transition lasted 150 160 years in the oxygen isotope stratigraphy the pollen inferred cooling took 180 190 years and the cladoceran inferred cooling lasted 250 260 years the pollen inferred summer temperature rise to 11 5 12 c at the transition from the younger dryas to the preboreal preceded the oxygen isotope signal by several decades whereas the cladoceran inferred warming lagged major discrepancies between the pollen and cladoceran inference models are observed for the preboreal where the cladoceran inference model suggests mean summer temperatures of up to 14 15 c both pollen and cladoceran inferred reconstructions suggest a cooling that may be related to the gerzensee oscillation but there is no evidence for a cooling synchronous with the preboreal oscillation as recorded in the oxygen isotope record for the gerzensee oscillation the inferred cooling was ca 1 and 0 5 c based on pollen and cladocera respectively which lies well within the inherent prediction errors of the inference models

sedimentary impacts from landslides in the tachia river basin taiwan abstract a case study of coseismic landslides and post seismic sedimentary impacts of landslides due to rainfall events was conducted in the tachia river basin taichung county central taiwan about 3000 coseismic landslides occurred in the basin during the ml 7 3 chi chi earthquake in 1999 the deposits from these landslides provided material for numerous debris flows induced by subsequent rainfall events the estimated 4 1 107 m3 of landslide debris produced in the upland area caused sediment deposition in riverbeds and flash floods inundated downstream areas with sediment during torrential rains the landslide frequency size distributions for the coseismic landslides and the subsequent rainfall induced landslides were analyzed to determine the sediment budgets of the post seismic geomorphic response in the landslide dominated basin both the coseismic and the rainfall induced landslides show a power law frequency size distribution with a rollover it was found that the rainfall induced landslide magnitude was smaller than the coseismic one and that both have comparable negative scaling exponents in cumulative form of about 2 0 for larger landslides 10 2 km2 this may be attributed to ongoing movement or reactivation of old landslides and a natural stabilisation of small landslides between 10 4 and 10 2 km2 it is proposed that the characteristics of geological formations and rainfall as well as changes in landslide area are reflected in the power law distribution

quantification of biotic responses to rapid climatic changes around the younger dryas a synthesis to assess the presence or absence of lags in biotic responses to rapid climatic changes we 1 assume that the 18o in biogenically precipitated carbonates record global or hemispheric climatic change at the beginning and at the end of the younger dryas without any lag at our two study sites of gerzensee and leysin switzerland 2 derive a time scale by correlating the 18o record from these two sites with the 18o record of the grip ice core 3 measure 18o records in ostracods and molluscs to check the record in the bulk samples and to detect possible hydrological changes 4 analyse at gerzensee and leysin as well as at two additional sites that lack carbonates and hence a 18o record pollen plant macrofossils chironomids beetles and other insects and cladocera 5 estimate our sampling resolution using the grip time scale for the isotope stratigraphies and the biostratigraphies and 6 summarise the major patterns of compositional change in the biostratigraphies by principal component analysis or correspondence analysis we conclude that at the major climatic shifts at the beginning and end of the younger dryas hardly any biotic lags occur within the sampling resolution of 8 30 years and that upland vegetation responded as fast as aquatic invertebrates we suggest that the minor climatic changes associated with the gerzensee and preboreal oscillations were weakly recorded in the biostratigraphies at the lowland site but were more distinct at higher altitudes individualistic responses of plant and animal species to climatic change may reflect processes in individuals e g productivity and phenology in populations e g population dynamics in spatial distributions e g migrations and in ecosystems e g trophic state we suggest that biotic responses may be telescoped together into relatively short periods 50 to 150 years perhaps disrupting functional interactions among species and thus destabilising ecosystems

climatic reconstruction in europe for 18 000 yr b p from pollen data an improved concept of the best analogs method is used to reconstruct the climate of the last glacial maximum from pollen data in europe in order to deal with the lack of perfect analogs of fossil assemblages and therefore to obtain a more accurate climate reconstruction we used a combination of pollen types grouped according to plant phenology and present climate constraints rather than pollen percentages for each individual taxon the distribution of pollen taxa into plant functional types pfts is aimed to reflect the vegetation in terms of biomes which have a wider distribution than a species the climatic variables are then calibrated on these pfts using an artificial neural network technique the use of pfts allowed us to deal with situations where pollen assemblages have only partial modern analogs the method is applied to the glacial steppic vegetation in europe using 15 pollen records north of the pyrenees alps line the reconstructed temperatures were lower than today 30 10 degrees c for the temperature of the coldest month t c and 12 3 degrees c far the annual mean t ann south of that line t c and t ann anomalies were respectively 15 5 degrees c and 10 5 degrees c the available moisture index and annual precipitation were also lower than present 60 20 north of mediterranean sea 800 100 mm for precipitation in italy and greece the available moisture was 20 lower with a precipitation anomaly of ca 600 200 mm southward the moisture index was close to that at present 20 and precipitation was lower 300 300 mm c 1998 university of washington

biotic responses to rapid warming about 14 685 yr bp introduction to a case study at gerzensee switzerland abstract the late glacial climatic warming indicated in the greenland ice core record about 14 685 years before 1950 ad belongs to a type of very rapid high amplitude warming similar the onsets of dansgaard oeschger events during marine isotope stage 3 mis 3 in order to estimate the nature and rates of change of biotic responses to such a major climatic shift we need a reliable time scale as well as climatic indicators independent of the biota both are provided by a high resolution oxygen isotope record from precipitated carbonates of lake marl in gerzensee switzerland van raden et al 2013 this issue on the basis of the assumption of synchronous climatic changes between greenland and gerzensee the close correlation of the oxygen isotope changes at the two sites allows the use of the ngrip gicc05 timescale at gerzensee with the zero point at 1950 ad to maintain comparability with the numerous radiocarbon dates in europe the 18o record measured in precipitated carbonates is checked and refined by the 18o measured in mono specific ostracod samples von grafenstein et al 2013 in this issue the shift of 3 6 18o pdb in only about 112 years at the end of the gs 2 represents a very rapid temperature increase of at least 6 2 c this increase is confirmed by reconstructions based on transfer functions for pollen and chironomids by lotter et al 2012 possibly 4 7 c in the annual mean and 2 5 c in summer temperatures after this major shift the greenland late glacial interstadial gi 1 corresponding to the regional biozones bolling and allerod 18o records of both greenland and gerzensee exhibit four minor fluctuations about 1 0 1 2 18o of which the second and the fourth are especially clearly correlated with several of terrestrial records in the northern hemisphere the oxygen isotope record is used as a template for all these sediment and bio stratigraphies the biotic responses may include at least five types of process 1 changes in productivity of individuals within a year or two 2 changes in populations usually somewhat slower depending on life cycles and environmental constraints 3 changes due to migration often rather slow depending again on life cycles and environmental constraints 4 changes in the terrestrial and aquatic communities and 5 changes on the level of ecosystems including pedogenesis nutrient cycling and species interactions these biotic responses to the early rapid warming about 14 685 ka bp are elaborated in subsequent papers for plants chironomids ostracods and cladocera ammann et al 2013 a brooks and heiri in this issue von grafenstein et al in this issue novakova et al 2013 this issue in addition lake levels are reconstructed by magny 2013 this issue and vegetation dynamics and n2o emissions are modelled lischke et al 2013 pfeiffer et al 2013 the changes in the mammal fauna of the swiss plateau are summarized by nielsen 2013 this issue

numerical study of alternate bars in alluvial channels with nonuniform sediment rivers typically present heterogeneous bed material but the effects of sediment nonuniformity on river bar characteristics are still unclear this work investigates the impact of sediment size heterogeneity on alternate bars with a morphodynamic numerical model the model is first used to reproduce a laboratory experiment showing alternate bar formation with nonuniform bed material subsequently the influence of sediment size heterogeneity on alternate bars is investigated distinguishing hybrid from free bars definition based on the presence absence of morphodynamic forcing considering the results of nine scenarios in four of them a transverse obstacle is used to generate forcing the computations are carried out with the telemac mascaret system solving the two dimensional shallow water equations with a finite element approach accounting for horizontal and vertical sediment sorting processes the results show that sediment heterogeneity affects free migrating and hybrid bars in a different way the difference lies in the presence absence of a migration front so that distinct relations between bed topography bed shear stress and sediment sorting are obtained sediment sorting and associated planform redistribution of bed roughness only slightly modify free migrating bar morphodynamics whereas hybrid bars are greatly impacted with decreased amplitude and increased wavelength increased sediment size heterogeneity increases the degree of sediment sorting while the sorting pattern remains the same for both free and hybrid bars moreover it produces averagely higher longer and faster free bars while in the case of hybrid bars their wavelength is increased but no general trend can be determined for their amplitude

late glacial fossil midge stratigraphies insecta diptera chironomidae from the swiss alps abstract chironomid midges insecta diptera chironomidae are sensitive indicators of environmental change but relatively few studies have been made of the response of european midge faunas to the high amplitude climatic oscillations of the late glacial in this study late glacial assemblages of chironomid midges from four swiss lakes or former lakes gerzensee 603 m leysin 1230 m regenmoos 1260 m and heremence 2300 m were compared and contrasted the study focused on the response of chironomid assemblages to the beginning and end of the younger dryas cold interval c 12 690 11 485 cal yr bp and to minor cold climatic fluctuations gerzensee oscillation c 13200 12800 cal yr bp and preboreal oscillation c 113 65 11 100 cal yr bp the durations of these climatic fluctuations were defined climato stratigraphically based on oxygen isotope boundaries and the chronology was derived by correlation with grip oxygen isotope records major differences in the composition of the four lakes chironomid assemblages reflected differences in altitude and local environmental conditions nevertheless each lake fauna showed a marked response to the major and minor climatic oscillations demonstrating that large scale temperature change had an overriding influence on the distribution of chironomid midges

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

experimental evidence for the effect of hydrographs on sediment pulse dynamics in gravel bedded rivers 1 gravel augmentation is a river restoration technique applied to channels downstream of dams where size selective transport and lack of gravel resupply have created armored relatively immobile channel beds augmentation sediment pulses rely on flow releases to move the material downstream and create conditions conducive to salmon spawning and rearing yet how sediment pulses respond to flow releases is often unknown here we explore how three types of dam releases constant flow small hydrograph and large hydrograph impact sediment transport and pulse behavior translation and dispersion in a channel with forced bar pool morphology we use the term sediment pulse generically to refer to the sediment introduced to the channel the zone of pronounced bed material transport that it causes and the sediment wave that may form in the channel from the additional sediment supply which can include input sediment and bed material in our experiments we held the volume of water released constant which is equivalent to holding the cost of purchasing a water volume constant in a stream restoration project the sediment pulses had the same grain size as the bed material in the channel we found that a constant flow 60 greater than the discharge required to initiate sediment motion caused a mixture of translation and dispersion of the sediment pulse a broad crested hydrograph with a peak flow 2 5 times the discharge required for entrainment caused pulse dispersion while a more peaked hydrograph 3 times the entrainment threshold discharge caused pulse dispersion with some translation the hydrographs produced a well defined clockwise hysteresis effecting sediment transport as is often observed for fine sediment transport and transportlimited gravel bed rivers the results imply a rational basis for design of water releases associated with gravel augmentation that is directly linked to the desired sediment behavior

responses to rapid warming at termination 1a at gerzensee central europe primary succession albedo soils lake development and ecological interactions the transition from the oldest dryas to the bolling around 14 685 cal yr bp was a period of extremely rapid climatic warming from a single core of lake marl taken at gerzensee switzerland we studied the transition in stable isotopes of oxygen and carbon on bulk sediment and charophyte remains as well as on monospecific samples of ostracods after pisidium a in addition pollen chironomids and cladocera were analyzed the 18o record serves as an estimate of mean air temperature and by correlation to the one from ngrip in greenland it provides a timescale the timing of responses the statistically significant zone boundaries of the biostratigraphies are telescoped at the rapid increase of about 3 in 18o at the onset of bolling biotic responses may have occurred within sampling resolution 8 to 16 years although younger zone boundaries are less synchronous gradual and longer lasting responses include complex processes such as primary or secular succession during the late glacial interstadial of bolling and allerod two stronger and two weaker cool phases were found biological processes involved in the responses occurred on levels of individuals e g pollen productivity of populations increases or decreases immigration or extinction and on the ecosystem level species interactions such as facilitation or competition abiotic and biotic interactions include pedogenesis nitrogen fixation nutrient cycling catchment hydrology water chemistry of the lake and albedo controlled by the transition from tundra to forest for the swiss plateau this major change in vegetation induced a change in the mammal fauna which in turn led to changes in the tool making by paleolithic people

the quasi equilibrium longitudinal profile in backwater reaches of the engineered alluvial river a space marching method an engineered alluvial river i e a fixed width channel has constrained planform but is free to adjust channel slope and bed surface texture these features are subject to controls the hydrograph sediment flux and downstream base level if the controls are sustained or change slowly relative to the timescale of channel response the channel ultimately achieves an equilibrium or quasi equilibrium state for brevity we use the term quasi equilibrium as a shorthand for both states this quasi equilibrium state is characterized by quasi static and dynamic components which define the characteristic timescale at which the dynamics of bed level average out although analytical models of quasi equilibrium channel geometry in quasi normal flow segments exist rapid methods for determining the quasi equilibrium geometry in backwater dominated segments are still lacking we show that irrespective of its dynamics the bed slope of a backwater or quasi normal flow segment can be approximated as quasi static i e the static slope approximation this approximation enables us to derive a rapid numerical space marching solution of the quasi static component for quasi equilibrium channel geometry in both backwater and quasi normal flow segments a space marching method means that the solution is found by stepping through space without the necessity of computing the transient phase an additional numerical time stepping model describes the dynamic component of the quasi equilibrium channel geometry tests of the two models against a backwater exner model confirm their validity our analysis validates previous studies in showing that the flow duration curve determines the quasi static equilibrium profile whereas the flow rate sequence governs the dynamic fluctuations

channel response to an extreme flood and sediment pulse in a mixed bedrock and gravel bed river we exploit a natural experiment caused by an extreme flood 500 year recurrence interval and sediment pulse derived from more than 2500 concurrent landslides to explore the influence of valley scale geomorphic controls on sediment slug evolution and the impact of sediment pulse passage and slug deposition and dispersion on channel stability and channel form sediment slug movement is a crucial process that shapes gravel bed rivers and alluvial valleys and is an important mechanism of downstream bed material transport further increased bed material transport rates during slug deposition can trigger channel responses including increases in lateral mobility channel width and alluvial bar dominance pre and post flood lidar and aerial photographs bracketing the 2007 flood on the chehalis river in south western washington state usa document the channel response with high spatial and temporal definition the sediment slug behaved as a gilbert wave with both channel aggradation and sequestration of large volumes of material in floodplains of headwaters reaches and reaches where confined valleys enter into broad alluvial valleys differences between the valley form of two separate sub basins impacted by the pulse highlight the important role channel and channel floodplain connectivity play in governing downstream movement of sediment slug material finally channel response to the extreme flood and sediment pulse illustrate the connection between bed material transport and channel form specifically the channel widened lateral channel mobility increased and the proportion of the active channel covered by bars increased in all reaches in the study area the response scaled tightly with the relative amount of bed material sediment transport through individual reaches indicating that the amount of morphological change caused by the flood was conditioned by the simultaneous introduction of a sediment pulse to the channel network copyright 2015 john wiley sons ltd

numerical simulation of downstream fining by selective transport in gravel bed rivers model development and illustration a numerical model has been developed for the routing of gravel sized sediment along a river channel which is free to adjust both its long profile and surface texture hydraulic calculations use a step backwater approach and sediment transport is predicted with the method of parker 1990a which uses a low degree of size selectivity exchange of sediment between the surface and subsurface is described using the modified exner equation of parker and sutherland 1990 the model is applied to an idealized channel based on the highly concave allt dubhaig scotland in which fining by particle wear is minor the rapid downstream fining observed in this river is closely matched by model predictions after a time equivalent to 102 years under the present flow regime of the river the evolution of the fining pattern during the model run and associated changes in sediment transport and bed aggradation are described it is concluded that strong profile concavity can force rapid downstream fining even though bed load transport is only slightly size selective this run of the model serves as a basis for testing of the sensitivity of downstream fining to alternative choices of parameter values and boundary conditions which are summarized here and will be described in a subsequent paper

transient water and sediment storage of the decaying landslide dams induced by the 2008 wenchuan earthquake china article earthquake triggered landslide dams are potentially dangerous disrupters of water and sediment flux in mountain rivers and capable of releasing catastrophic outburst flows to downstream areas we analyze an inventory of 828 landslide dams in the longmen shan mountains china triggered by the mw 7 9 2008 wenchuan earthquake this database is unique in that it is the largest of its kind attributable to a single regional scale triggering event 501 of the spatially clustered landslides fully blocked rivers while the remainder only partially obstructed or diverted channels in steep watersheds of the hanging wall of the yingxiu beichuan fault zone the size distributions of the earthquake triggered landslides landslide dams and associated lakes a can be modeled by an inverse gamma distribution b show that moderate size slope failures caused the majority of blockages and c allow a detailed assessment of seismically induced river blockage effects on regional water and sediment storage monte carlo simulations based on volumetric scaling relationships for soil and bedrock failures respectively indicate that 14 18 of the estimated total coseismic landslide volume of 6 4 14 6 10 9 m 3 was contained in landslide dams representing only 1 4 of the 60 000 slope failures attributed to the earthquake these dams have created storage capacity of 0 6 10 9 m 3 for incoming water and sediment about 25 of the dams containing 2 of the total river blocking debris volume failed one week after the earthquake these figures had risen to 60 20 and 90 90 within one month and one year respectively thus also emptying 92 of the total potential water and sediment storage behind these dams within one year following the earthquake currently only 0 08 10 9 m 3 remain available as natural reservoirs for storing water and sediment while 0 19 10 9 m 3 i e about a third of the total river blocking debris volume has been eroded by rivers dam volume and upstream catchment area control to first order the longevity of the barriers and bivariate domain plots are consistent with the observation that most earthquake triggered landslide dams were ephemeral we conclude that the river blocking portion of coseismic slope failures disproportionately modulates the post seismic sediment flux in the longmen shan on annual to decadal timescales

sea level and salinity fluctuations during the paleocene eocene thermal maximum in arctic spitsbergen palaeoenvironmental manifestations of the palaeocene eocene thermal maximum petm 56 ma are relatively well documented in low to mid latitude settings and at high southern latitudes but no documented high northern latitude sites record the entire hyperthermal event we present high resolution multi proxy records from a petm succession on spitsbergen in the high arctic palaeolatitude 75 n by comparing our results with those from integrated ocean drilling program site 302 4a we document regional palaeoenvironmental variations in the expression of the petm with evidence for major differences in basin margin vegetation and water column oxygen depletion sedimentological palynological and geochemical data demonstrate a pre petm sea level rise in spitsbergen before the delta13ctoc excursion which culminated in maximum flooding during the peak of the event the appearance of the dinoflagellate cyst apectodinium before the onset of the carbon isotope excursion cie corroborates environmental change in the arctic had begun prior to the cie sedimentological and palynological evidence indicate that elevated terrestrial runoff resulted in water column stratification providing further evidence for an intensification of the hydrological cycle during the petm

fluvial evacuation of landslide material from bedrock confined channels under controlled experimental conditions abstract the supply of sediment from hillslopes to channels is rarely constant with discrete events e g landslides known to transfer large volumes of sediment in geologically short periods of time especially in tectonically active areas understanding the rates and patterns of subsequent sediment evacuation is important for understanding variability of landscape evolution as well as mitigating the risk of geohazards associated with bed aggradation and the loss of channel capacity to convey flood waters here we performed a series of controlled laboratory flume experiments to explore the controls on sediment transport after a single sediment input in scenarios with i different initial input volumes 4 25 kg under constant flow conditions 40 l s ii a constant initial input volume 12 kg under different flow magnitudes 5 60 l s and iii a repeat of the input sediment volumes in scenario i but with the same volume of water delivered using a ramped hydrograph 0 60 0 l s we find the presence of sediment piles impacts the flow hydraulics with a backwater effect developing upstream of the pile that causes a flow acceleration around the location of the pile for a given discharge larger sediment piles have a greater impact on the flow hydraulics which in turn induces higher rates of sediment transport and erosion of the pile in all cases sediment remains at the initial pile input location for the duration of the sediment evacuation acting to protect the bed from erosion we highlight the role of geomorphic hydraulic interactions in controlling the sediment evacuation and suggest there is an optimal combination of pile size and flow conditions flow magnitude and hydrograph shape for accelerated rates of sediment transport which are important for the short term and long term channel dynamics and the landscape evolution variability

recognition of cyclic and non cyclic environmental changes in the mediterranean pliocene a palynological approach the interval between 2 8 and 2 3 ma b p from the south italian singa section has been investigated for its dinoflagellate cyst and sporomorph contents in order to facilitate palaeoenvironmental interpretation the following curves are derived from the data the ratios sporomorphs dinoflagellate cysts protoperidinioid gonyaulacoid dinoflagellate cysts warm cold water indicating dinoflagellate cysts inner neritic oceanic dinoflagellate cysts outer neritic oceanic dinoflagellate cysts and the reworked dinoflagellate cysts per gram of sediment furthermore the already available 18o curve has been used calibration of changes in the sporomorph dinoflagellate ratio against the computed astronomical insolation curve leads to an improved age assessment for the section frequency analysis on the curves shows the 23 41 and 100 ka frequency components to be most important phase and amplitude differences between the filtered 23 41 and 100 ka frequency components are used for environmental interpretation the 23 ka frequency band is best explained by changes in runoff induced transport the 41 ka frequency components are classified in a group with short response time to orbital forcing and a group with longer response time those signals having a short response time are attributed to local precipitation induced changes in runoff those signals having a longer response time are mainly attributed to changes in global temperature and to a lesser extent to changes in global ice volume finally longer term cyclic and non cyclic changes are mainly attributed to temperature and sea level variation

n2o and ch4 variations during the last glacial epoch insight into global processes 1 greenhouse gas measurements along polar ice cores provide important insight into the former composition of the atmosphere its natural variations and the responses to fast climatic changes in the past we present high resolution nitrous oxide n2o and methane ch4 records measured along two ice cores from central greenland covering part of marine isotope stages 3 and 4 in the last glacial epoch the n2o data confirm the hypothesis that n2o shows variations in phase to fast climatic changes observed in the northern hemisphere the so called dansgaard oeschger d o events variations exist not only for events with a long duration 1500 years and more but also for the shorter ones the comparison with ch4 unveils interesting differences between the response of ch4 and n2o to d o events while the average amplitudes of ch4 oscillations associated with d o events are similar to those of the northern hemisphere summer insolation the magnitude of the n2o concentration change instead correlates with the duration of the d o events the records give further insight into the timing of concentration changes at the beginning of d o events they show that for long lasting events the n2o concentration starts to increase before both the sharp increase in the ch4 concentration and the temperature reconstructed for greenland

paleo oxygenation in tertiary epeiric seas evidence from dinoflagellate cysts the dinoflagellate cyst record from an epeiric setting in the oligocene of southwest germany exhibits major changes associated with variations in paleo oxygenation inferred from benthic foraminifera dinoflagellate cyst diversity and equitability strongly decline in the case of extreme oxygen depletion the relative abundance of the dinoflagellate cyst thalassiphora pelagica inversely correlates with the availability of benthic oxygen the t pelagica spectrum consists of different morphotypes which are considered to represent different stages within the cystal part of the t pelagica life cycle following the concept of benedek and gocht the distribution of these morphotypes is also linked to oxygen availability horizons with highest t pelagica abundances are characterized by the occurrence of t pelagica specimens representing an early stage in cyst formation a model is proposed that uses t pelagica as a proxy to assess oxygenation both at the sediment surface and in the water column the occurrence of t pelagica specimens representing an early stage in cyst formation is interpreted to reflect the extension of oxygen depletion upwards into the water column because t pelagica is an easily recognized globally distributed element of paleogene and early neogene dinoflagellate cyst assemblages the application of this model may be of importance in the reconstruction of paleo oxygenation in epeiric settings from these times its sensitivity to changes in benthic oxygenation can be as high as if not higher than that of the approach based on foraminifera moreover it is applicable to decalcified sediments

translation and dispersion of sediment pulses in flume experiments simulating gravel augmentation below dams 1 the effectiveness of gravel augmentation as a river restoration strategy depends on the extent and duration of the topographic and bed texture changes created by the pulse of added sediment previous work has emphasized the strong tendency for natural sediment waves to propagate primarily by dispersion however pulse translation may occur for gravel additions to armored channels downstream of dams where added sediments are finer than the preexisting bed material here we report results of a laboratory investigation in which we created an immobile armored bed and documented the spatial and temporal evolution of the bed topography and bed texture in response to gravel pulses of various volumes and grain sizes the introduced sediment waves evolved by a combination of translation and dispersion with a significant translational component pulse translation and dispersion can be readily discerned on a graph of the time evolution of the downstream cumulative distribution of elevation differences from the preexisting bed topography translation was most evident for smaller volumes of added sediment pulses of finer grained gravel moved through the flume more rapidly resulting in a larger magnitude but shorter duration of bed fining more work is needed to understand the influence of bar pool topography and flow magnitude and duration before the grain size and volume of gravel additions can be selected to achieve optimal patterns of pulse propagation

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

vegetational response to climatic changes recorded in swiss late glacial lake sediments abstract high resolution pollen analysis at five lakes on an altitudinal transect in switzerland gerzensee 603 m leysin 1230 m regenmoos 1260 m zeneggen 1510 m heremence 2290 m focused on the vegetational response to the rapid climatic changes at the end and beginning of the younger dryas and to the minor gerzensee and preboreal climatic oscillations an absolute time scale transferred from the greenland grip ice core to the gerzensee and leysin records by wiggle matching the oxygen isotope stratigraphies facilitates the estimation of pollen influx and rates of change the climatic warming at the end of the younger dryas indicated by increases in oxygen isotope values and or the beginning of organic sedimentation in the lakes was immediately reflected in the vegetation at all the sites investigated the time lags at sites situated above the timberline during the younger dryas are considered to be migrational lags at the onset of the younger dryas a time lag of several decades occurred between the oxygen isotope record of climatic cooling and the major response of the vegetation whereas minor vegetation changes occurred with or without short time lags betula reacted earlier to the new environmental conditions within about 40 50 yr at gerzensee and within less than 36 yr at leysin than pinus and artemisia about 170 yr suggesting that time lags are due to the ecological requirements of the different taxa for the gerzensee and preboreal oscillations little or no change can be observed in the pollen record from gerzensee whereas at leysin both climatic oscillations produced a statistically significant vegetational response to both climatic oscillations generally the vegetation responses to climatic changes are more pronounced near vegetation ecotones at medium and higher altitudes than in the lowlands

forest dynamics during the transition from the oldest dryas to the bolling allerod at gerzensee a simulation study the aim of this study was to explore potential causes and mechanisms for the sequence and temporal pattern of tree taxa specifically for the shift from shrub tundra to birch juniper woodland during and after the transition from the oldest dryas to the bolling allerod in the region surrounding the lake gerzensee in southern central europe we tested the influence of climate forest dynamics community dynamics compared to other causes for delays for this aim temperature reconstructed from a 18o record was used as input driving the multi species forest landscape model treemig in a stepwise scenario analysis population dynamics along with pollen production and transport were simulated and compared with pollen influx data according to scenarios of different 18o temperature sensitivities different precipitation levels with without inter specific competition and with without prescribed arrival of species in the best fitting scenarios the effects on competitive relationships pollen production spatial forest structure albedo and surface roughness were examined in more detail the appearance of most taxa in the data could only be explained by the coldest temperature scenario with a sensitivity of 0 3 c corresponding to an anomaly of 15 c once the taxa were present their temporal pattern was shaped by competition the later arrival of pinus could not be explained even by the coldest temperatures and its timing had to be prescribed by first observations in the pollen record after the arrival into the simulation area the expansion of pinus was further influenced by competitors and minor climate oscillations the rapid change in the simulated species composition went along with a drastic change in forest structure leaf area albedo and surface roughness pollen increased only shortly after biomass based on our simulations two alternative potential scenarios for the pollen pattern can be given either very cold climate suppressed most species in the oldest dryas or they were delayed by soil formation or migration one taxon pinus was delayed by migration and then additionally hindered by competition community dynamics affected the pattern in two ways potentially by facilitation i e by nitrogen fixing pioneer species at the onset whereas the later pattern was clearly shaped by competition the simulated structural changes illustrate how vegetation on a larger scale could feed back to the climate system for a better understanding a more integrated simulation approach covering also the immigration from refugia would be necessary for this combines climate driven population dynamics migration individual pollen production and transport soil dynamics and physiology of individual pollen production

new magnetobiostratigraphic chronology and paleoceanographic changes across the oligocene miocene boundary at dsdp site 516 rio grande rise sw atlantic new magnetobiostratigraphic data for the late oligocene through early miocene at deep sea drilling project dsdp hole 516f provide a significantly revised age model which permits reevaluation of developments that led to the mi 1 glacial event at the oligocene miocene boundary our new high resolution paleomagnetic study which is supported by quantitative calcareous nannofossil and planktonic foraminiferal analyses significantly refines previous age models for oligocene miocene sediments from dsdp hole 516f with ages that are systematically younger than those previously determined in some parts of the oligocene the discrepancy with previous studies exceeds 450 kyr based on this new age model we infer a progressive increase in sedimentation rate and paleoproductivity between circa 23 9 ma and circa 22 9 ma with the highest rate coinciding with the mi 1 glacial event at the oligocene miocene boundary this productivity increase would have resulted in higher rates of carbon burial and in turn a drawdown of atmospheric co2 immediately afterward an abrupt decrease in sedimentation rate and paleoproductivity suggests that the mi 1 deglaciation was associated with decreased carbon input into the ocean elevated sedimentation rates are also documented at 24 5 ma coincident with the oi2d glacioeustatic event the presence of volcanic material within the sediments during these glacial events is interpreted to have resulted from redeposition of sediment scoured from nearby sites on the rio grande rise due to transient variations in bottom water flow patterns

the wurmian late glacial in lowland switzerland a synthesis is provided of late glacial 14 9 ka bp environmental changes in lowland switzerland the swiss plateau the chronology of deglaciation and subsequent developments in vegetation cov

stochastic forcing of sediment supply to channel networks from landsliding and debris flow sediment influx to channel networks is stochastically driven by rainstorms and other perturbations which are discrete in time and space and which occur on a landscape with its own spatial variability in topography colluvium properties and state of recovery from previous disturbances the resulting stochastic field of sediment supply interacts with the topology of the channel network and with transport processes to generate spatial and temporal patterns of flux and storage that characterize the sedimentation regime of a drainage basin the regime varies systematically with basin area we describe how the stochastic sediment supply is generated by climatic topographic geotechnical and biotic controls that vary between regions the general principle is illustrated through application to a landscape where sediment is supplied by mass wasting and the forcing variables are deterministic thickening of colluvium random sequences of root destroying wildfires and random sequences of rainstorms that trigger failure in a population of landslide source areas with spatial variance in topography and colluvium strength landslides stop in channels or convert to scouring debris flows depending on the nature of the low order channel network sediment accumulates within these channels for centuries before being transferred downstream by debris flows time series of sediment supply transport and storage vary with basin scale for any combination of climatic topographic and geotechnical controls in a companion paper benda and dunne this issue we use simulations of timing volumes and locations of mass wasting to study the interaction between a stochastically forced sediment supply and systematic changes of storage and flux through channel networks

orbitally paced climate oscillations across the oligocene miocene boundary the late oligocene and early miocene periods some 21 to 27 million years ago have generally been viewed as times of moderate global warmth and ice free conditions yet several lines of evidence suggest that this interval was punctuated by at least one and possibly several episodes of high latitude cooling and continental glaciation1 2 3 here we present stable isotope and per cent coarse fraction data from an equatorial western atlantic deep sea sediment core that provide high resolution records of the climate variability across the oligocene miocene transition 22 5 25 7 million years ago a strong 40 kyr periodicity in the oxygen isotope record is consistent with a high latitude orbital obliquity control on ice volume and temperature orbital influences are also apparent at precession and eccentricity frequencies including a series of 400 kyr oscillations that culminate in distinct maxima at the oligocene miocene boundary about 23 7 million years ago covariance between the carbon and oxygen isotope records suggests that the oceanic carbon cycle may have contributed to global cooling during the 400 kyr cycles particularly at the oligocene miocene boundary

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

evolution of atlantic thermohaline circulation early oligocene onset of deep water production in the north atlantic the flow of deep water masses is a key component of heat transport in the modern climate system yet the role of deep ocean heat transport during periods of extreme warmth is poorly understood the present mode of meridional overturning circulation is characterized by deep water formation in both the north atlantic and the southern ocean however a different mode of meridional overturning circulation operated during the extreme greenhouse warmth of the early cenozoic during which time the southern ocean was the dominant region of deep water formation the combination of general global cooling and tectonic evolution of the atlantic basins over the past 55 m y ultimately led to the development of a mode of overturning circulation characterized by both southern ocean and north atlantic deep water sources the change in deep water circulation mode may in turn have affected global climate however unraveling the causes and consequences of this transition requires a better understanding of the timing of the transition new nd isotope data from the southeastern atlantic ocean indicate that the initial transition to a bipolar mode of deep water circulation occurred in the early oligocene ca 33 ma the likely cause of significant deep water production in the north atlantic was tectonic deepening of the sill separating the greenland norwegian sea from the north atlantic

how canyons evolve by incision into bedrock rainbow canyon death valley national park united states incising rivers may be confined by low slope erodible hillslopes or steep resistant sidewalls in the latter case the system forms a canyon we present a morphodynamic model that includes the essential elements of a canyon incising into a plateau including 1 abrasion driven channel incision 2 migration of a canyon head knickpoint 3 sediment feed from an alluvial channel upstream of the knickpoint and 4 production of sediment by sidewall collapse we calculate incision in terms of collision of clasts with the bed we calculate knickpoint migration using a moving boundary formulation that allows a slope discontinuity where the channel head meets an alluvial plateau feeder channel rather than modeling sidewall collapse events we model long term behavior using a constant sidewall slope as the channel incises our morphodynamic model specifically applies to canyon rather than river hillslope evolution we implement it for rainbow canyon ca salient results are as follows 1 sediment supply from collapsing canyon sidewalls can be substantially larger than that supplied from the feeder channel on the plateau 2 for any given quasi equilibrium canyon bedrock slope two conjugate slopes are possible for the alluvial channel upstream with the lower of the two corresponding to a substantially lower knickpoint migration rate and higher preservation potential 3 knickpoint migration occurs at a substantially faster time scale than regrading of the bedrock channel itself underlying the significance of disequilibrium processes although implemented for constant climactic conditions the model warrants extension to long term climate variation

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

chronology of the last glacial cycle in the european alps chronological data for glacier advances in the european alps between the last interglacial eemian and the holocene are summarised 115 to 11 ka during this time glaciers were most extensive extending tens of kilometres out onto the forelands between 30 and 18 ka that is synchronous with the global ice volume maximum of marine isotope stage mis 2 evidence for ice expanding to just past the mountain front for an earlier major glacier advance comes from swiss sites where advances have been luminescence dated to mis 5d 100 ka and mis 4 70 ka up to now no such evidence has been found in the eastern alps by 18 ka more than 80 of the late wurmian ice volume had gone subsequently glaciers readvanced reaching into the upper reaches of the main valleys during the lateglacial gschnitz stadial which likely occurred around 17 ka with final moraine stabilisation no later than 15 4 ka the link of the egesen stadial with the younger dryas climate deterioration is supported by exposure ages from four sites as well as minimum limiting radiocarbon dates from bogs within former glacier tongue areas key questions on the spatial and temporal variability of ice extents throughout the last glacial cycle have yet to be answered copyright 2008 john wiley sons ltd

nearly synchronous climate change in the northern hemisphere during the last glacial termination the climate of the north atlantic region underwent a series of abrupt cold warm oscillations when the ice sheets of the northern hemisphere retreated during the last glacial termination 17 7 11 5kyr ago evidence for these oscillations which are recorded in european terrestrial sediments as the oldest dryas bolling older dryas allerod younger dryas vegetational sequence1 2 has been found in greenland ice cores3 4 the geographical extent of many of these oscillations is not well known5 6 but the last major cold event the younger dryas seems to have been global in extent7 8 9 10 here we present evidence of four major oscillations in the hydrological balance of the owens basin california that occurred during the last glacial termination dry events in western north america occurred at approximately the same time as cold events recorded in greenland ice with transitions between climate regimes in the two regions taking place within a few hundred years of each other our observations thus support recent climate simulations which indicate that cooling of the north atlantic ocean results in cooling of the north pacific ocean11 which in turn leads to a drier climate in western north america12

a model to predict the evolution of a gravel bed river under an imposed cyclic hydrograph and its application to the trinity river 1 major changes in the morphology of the trinity river in california such as narrowing of the cross section and sedimentation of fine sediment in pools occurred after the closure of a system of dams these changes caused a dramatic reduction in the salmonid population and a resulting decline of the fishery gravel augmentation regulated flood releases and mechanical channel rehabilitation are currently being implemented to help restore the aquatic habitat of the river the present paper describes a tool named the spawning gravel refresher for designing and predicting the effects of gravel augmentation in gravel bed rivers the tool assumes an imposed cycled hydrograph the model is calibrated and applied to the regulated reach of the trinity river in four steps 1 zeroing runs to reproduce conditions of mobile bed equilibrium as best can be estimated for the predam trinity river 2 runs to compare the predictions with the results of previous studies 3 runs at an engineering time scale to reproduce the effects of the dams and 4 runs to design gravel augmentation schemes in the fourth group of runs the combined effects of engineered flood flow releases and gravel augmentation are predicted at an engineering time scale the model indicates that the fraction of fine sediment in the surface layer and in the topmost part of the substrate should decrease when subjected to these two restoration measures with a consequent improvement of the quality of the spawning gravel

sediment flux from a mountain belt derived by landslide mapping in humid uplands landsliding is the dominant mass wasting process in the western southern alps of new zealand landslides are scale invariant and have a power law magnitude frequency distribution independent studies from other regions suggest that this is a general property of landsliding this observation is of critical importance to the evaluation of the impact of events of different length scales over different time intervals on landscape evolution it is particularly useful when estimating regional geomorphic rates because it constrains the frequency and overall significance of extreme events which cannot otherwise be evaluated by integrating the complete response of the system we estimate the regional denudation rate due to landsliding to be 9 4 mm yr 1 sediment discharge from the western southern alps is dominated by landslide derived material

the onset of major northern hemisphere glaciations and their impact on dinoflagellate cysts and acritarchs from the singa section calabria southern italy and dsdp holes 607 607a north atlantic abstract the climatic deterioration related to the onset of northern hemisphere glaciations circa 2 52 ma b p must have lead to reorganization and relocation of species associations and may have enhanced species turnover the present study investigates how this deterioration affects the dinoflagellate cyst and acritarch assemblages from two locations dsdp site 607 north atlantic and the singa section southern italy the records from these locations cover the interval from 2 8 to 2 2 ma with at least a 5 ka resolution and they have been correlated to the milankovitch periodicities on a cycle to cycle basis by means of integrated high resolution stable isotope calcium carbonate foraminiferal palynological and magnetostratigraphical datasets in the present study this high resolution stratigraphic framework is used for a detailed correlation of events occurring in each of the depositional sequences it also enables further assessment of the palaeoenvironmental preferences of some dinoflagellate cyst forms comparison of the two palynological records reveals a close correspondence in the timing of major assemblage changes and extinction events confirming their milankovitch cycle based correlation a close link between periods of northern hemisphere cooling at oxygen isotope stages 110 104 and 100 96 and increased dinoflagellate cyst turnover appears to be present for both dsdp site 607 and the singa section the turnover events can also be recognized in the records of planktic foraminifera and calcareous nannoplankton comparison of the singa section with site 607 and with other time equivalent marine palynological data sets shows that some oceanic taxa respond similarly over a large area the biostratigraphical implications are discussed notably the last occurrence of invertocysta lacrymosa appears to be a valuable marker for isotope stage 110 in the mediterranean and north atlantic

macrofossils as records of plant responses to rapid late glacial climatic changes at three sites in the swiss alps plant macrofossils from the end of the younger dryas were analysed at three sites gerzensee 603 m asl leysin 1230 m asl and zeneggen 1510 m asl for the first two sites an oxygen isotope record is also available that was used to develop a time scale schwander et al this volume dates refer therefore to calibrated years according to the grip time scale around gerzensee a pine forest with some tree birches grew during the younger dryas with the onset of the isotopic shift initiating the rapid warming about 11 535 cal years before 1950 the pine forest became more productive and denser at leysin no trees except some juniper scrub grew during the younger dryas tree birches pine and poplar immigrated from lower altitudes and arrived after the end of the isotopic shift about 11 487 b p i e at the beginning of the preboreal at about 11 420 b p zeneggen is situated somewhat higher than leysin but single tree birches and pines survived the younger dryas at the site at the beginning of the preboreal their productivity and population densities increased simultaneously shifts from nitella to chara and from silt to gyttja are recorded all indicating rapidly warming conditions and higher nutrient levels of the lake water and probably of the soils in the catchment at gerzensee the beginning of the younger dryas was also analysed the beginning of the isotopic shift correlates within one sample about 15 years to rapid decreases of macrofossils of pines and tree birches

high resolution late glacial chronology for the gerzensee lake record switzerland δ18o correlation between a gerzensee stack and ngrip oxygen isotope variations were analyzed on bulk samples of shallow water lake marl from gerzensee switzerland in order to evaluate major and minor climatic oscillations during the late glacial to highlight the overall signature of the gerzensee 18o record 18o records of four parallel sediment cores were first correlated by synchronizing major isotope shifts and pollen abundances then the records were stacked with a weighting depending on the differing sampling resolution to develop a precise chronology the 18o stack was then correlated with the ngrip 18o record applying a monte carlo simulation relying on the assumption that the shifts in 18o were climate driven and synchronous in both archives the established chronology on the gicc05 time scale is the basis for 1 comparing the 18o changes recorded in gerzensee with observed climatic and environmental fluctuations over the whole north atlantic region and 2 comparing sedimentological and biological changes during the rapid warming with smaller climatic variations during the bolling allerod period the 18o record of gerzensee is characterized by two major isotope shifts at the onset and at the termination of the bolling allerod warm period as well as four intervening negative shifts labeled gi 1e2 d c2 and b which show a shift of one third to one fourth of the major 18o shifts at the beginning and end of the bolling allerod despite some inconsistency in terminology these oscillations can be observed in various climatic proxies over wide regions in the north atlantic region especially in reconstructed colder temperatures and they seem to be caused by hemispheric climatic variations

sea level and surface water change in the western north atlantic across the oligocene miocene transition a palynological perspective from iodp site u1406 newfoundland margin abstract the oligocene miocene transition omt 23 1 ma terminates the late oligocene warming trend and is marked by a transient large amplitude expansion of antarctic ice sheets the associated glacial maximum which is expressed by a 1 positive shift in benthic foraminiferal oxygen isotope values is commonly referred to as the mi 1 isotope event whereas the causes for the glacial maximum at the omt are intrinsically connected to southern hemisphere ice sheet dynamics the behavior of the surface ocean in the northern hemisphere during this time is poorly known to contribute to a better understanding of the paleoceanographic evolution during the omt in the higher latitude north atlantic we have analysed both marine and terrestrial palynomorphs from integrated ocean drilling program iodp site u1406 offshore newfoundland this site has yielded a complete omt section and exhibits a high quality magnetostratigraphy that provides precise age control and allows reliable correlation to other records beyond newfoundland our palynological data which span the interval from 23 3 to 22 5 ma and have a mean temporal resolution of 11 9 kyrs show strong 110 kyr eccentricity paced oscillations during the earliest miocene these oscillations are in phase with similar cyclicity identified in previously published benthic foraminiferal oxygen isotope records more specifically a pronounced sea level variability is documented by the abundances of neritic dinoflagellate cysts dinocysts and terrigenous palynomorphs which both reach maxima during peak glacial intervals as inferred from previously published south atlantic benthic oxygen isotope data a decline in the abundance of warmer water dinocysts suggests a surface water cooling offshore newfoundland from the latest oligocene onwards surface water productivity as derived from the ratio between heterotrophic and autotrophic dinocysts remained generally low throughout the studied interval notably this ratio does not exhibit any correlation with changes in surface water temperature which is estimated from the ratio of warm water over cold water dinocysts together with the consistently low surface water productivity the lack of a correlation between surface water productivity and temperature makes it highly unlikely that the observed paleoceanographic change was caused by a southward migration of the arctic front instead we argue that our data may document an enhanced influence of the proto labrador current on surface waters offshore newfoundland during the earliest miocene that suppressed the influence of the gulf stream in this region of the northwest atlantic we speculate that the enhanced influence of the proto labrador current was triggered by cooling of the northern hemisphere and possibly modulated by high latitude sea ice expansion

coarser and rougher effects of fine gravel pulses on experimental step pool channel morphodynamics understanding how steep mountain rivers respond to natural and anthropogenic sediment supply perturbations is important for predicting effects of extreme events e g floods and landslides and for restoring rivers to more natural conditions using flume experiments we show that stabilized step pool like channel beds can respond to pulses of finer gravel by becoming even coarser and rougher than before adding finer gravel initially reduces bed roughness and also increases the mobility of previously stable bed grains small and intermediate diameter clasts are then preferentially winnowed from the bed surface leaving behind higher concentrations of even larger clasts ultimately this results in both a coarser and rougher bed our experiments demonstrate that steep river beds become stable through the coevolution of bed roughness and surface grain size distribution and that these morphological variables can be sensitive to the history of upstream sediment supply

mid to late eocene organic walled dinoflagellate cysts from odp leg 171b offshore florida mid to late eocene organic walled dinoflagellate cysts from odp leg 171b offshore florida

orbitally forced climate change in late mid eocene time at blake nose leg 171b evidence from stable isotopes in foraminifera previous stable oxygen isotopic data from surface dwelling foraminifera indicate that eocene tropical sea surface temperatures ssts were significantly lower than at present here we show that stable isotopic analyses 180 13c of the late mid eocene mixed layer dweller morozovella spinulosa are consistent with in mid eocene mid latitudes ssts close to or slightly lower than modern temperatures at blake nose western north atlantic in contrast isotopic analyses of the benthic foraminiter nuttalides truempyi reveal a gradual fall in mean bottom water temperatures from 8 to 7 c over c 500 ka years these deep intermediate water temperatures are significantly higher than modern ones and are similar to intermediate and bottom water temperatures recorded from earlier in palaeogene and late cretaceous time large shifts arc seen in the 18o and 13c values of the planktonic foraminifers of up to 1 and 2 6 respectively that probably reflect temperature and nutrient fluctuations controlled by regional changes in upwelling intensity and runoff the surface to benthos 18o gradient decreases from 3 pdb to a minimum of c 0 5 pdb over 400 ka which could relate to the intensity of upwelling spectral analysis reveals precessional forcing in the foraminiferal 18o records which shows the direct influence of low latitude insolation on surface water stratification monsoonal wind systems may have forced the upwelling cycles and or freshwater input the benthic foraminifer 18o record also contains the obliquity cycle in addition to the precessional cycles indicating the inheritance of mid and high latitude forcing to subtropical deep waters

atmospheric nitrous oxide during the last 140 000 years article i nfo reconstructions of past atmospheric concentrations of greenhouse gases provide unique insight into the biogeochemical cycles and the past radiative forcing in the earth s climate system we present new measurements of atmospheric nitrous oxide along the ice cores of the north greenland ice core project and talos dome sites using records of several other ice cores we are now able to establish the first complete composite nitrous oxide record reaching back to the beginning of the previous interglacial about 140 000 yr ago on the basis of such composite ice core records we further calculate the radiative forcing of the three most important greenhouse gases carbon dioxide methane and nitrous oxide during more than a full glacial interglacial cycle nitrous oxide varies in line with climate reaching very low concentrations of about 200 parts per billion by volume during marine isotope stages 4 and 2 and showing substantial responses to millennial time scale climate variations during the last glacial a large part of these millennial time scale variations can be explained by parallel changes in the sources of methane and nitrous oxide however as revealed by high resolution measurements covering the dansgaard oeschger events 17 to 15 the evolution of these two greenhouse gases may be decoupled on the centennial time scale carbon dioxide and methane concentrations do not reach interglacial levels in the course of millennial time scale climate variations during the last glacial in contrast nitrous oxide often reaches interglacial concentrations in response to both glacial terminations and dansgaard oeschger events this indicates from a biogeochemical point of view similar drivers in both temporal cases while carbon dioxide and methane concentrations are more strongly controlled by climate changes in high latitudes nitrous oxide emissions changes may mainly stem from the ocean and or from soils located at low latitudes accordingly we speculate that high latitudes could play the leading role to trigger glacial terminations

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

lateglacial and early holocene insect assemblages from sites at different altitudes in the swiss alps implications on climate and environment insect analyses from four sites at differentaltitudes in the swissalps are presented the dominant insect group considered here is coleoptera beetles though other insect orders are also recorded

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

can magic sand cause massive degradation of a gravel bed river at the decadal scale shi ting river china abstract massive bed degradation 20 m in 7 years has been observed in the shi ting river sichuan province china since the 2008 wenchuan ms 8 0 earthquake the reason for the massive bed degradation has not been well understood a hypothesis has been proposed that relates bed degradation to the augmentation of sand supply after the earthquake the effect of sand on gravel mobility magic sand effect has long been observed in laboratory experiments in this paper we study whether the augmentation of sand supply and its magic sand effect can lead to the observed massive degradation at decadal scales a one dimensional river morphodynamic model is implemented to study the problem in general at field scale and in context of the gravel bed shi ting river sediment transport is calculated with the wilcock and crowe 2003 relation in which the magic sand effect is explicitly embedded in terms of a function relating reference shields number to the surface sand fraction we find that the augmentation of gravel supply leads to bed aggradation whereas the augmentation of sand supply can indeed lead to bed degradation and surface fining the magnitude and timescale of bed degradation are not sensitive to the sand supply rate but are sensitive to the flood intermittency factor i e the fraction of time the river is in flood however an unrealistic flood intermittency factor 0 3 would be required in order to match the observed timescale of bed degradation thus indicating that the magic sand effect might not be the governing reason for massive bed degradation in the shi ting river and by implication in gravel bed rivers in general our simulation results also indicate that despite the fact that magic sand effects are not explicitly included in most sediment transport relations they are at least partly built in via the hiding function that is contained in most sediment transport relations for gravel sand mixtures while here we use the shi ting river as an example our results have applicability to gravel bed rivers subjected to augmentation in sand supply in general

geomorphic and geologic controls of geohazards induced by nepal s 2015 gorkha earthquake the gorkha earthquake m 7 8 on 25 april 2015 and later aftershocks struck south asia killing 9 000 and damaging a large region supported by a large campaign of responsive satellite data acquisitions over the earthquake disaster zone our team undertook a satellite image survey of the earthquakes induced geohazards in nepal and china and an assessment of the geomorphic tectonic and lithologic controls on quake induced landslides timely analysis and communication aided response and recovery and informed decision makers we mapped 4 312 co seismic and post seismic landslides we also surveyed 491 glacier lakes for earthquake damage but found only 9 landslide impacted lakes and no visible satellite evidence of outbursts landslide densities correlate with slope peak ground acceleration surface downdrop and specific metamorphic lithologies and large plutonic intrusions

the effect of abrupt climatic warming on biogeochemical cycling and n2o emissions in a terrestrial ecosystem the large rapid increase in atmospheric n2o concentrations that occurred concurrent with the abrupt warming at the end of the last glacial period might have been the result of a reorganization in global biogeochemical cycles to explore the sensitivity of nitrogen cycling in terrestrial ecosystems to abrupt warming we combined a scenario of climate and vegetation composition change based on multiproxy data for the oldest dryas bolling abrupt warming event at gerzensee switzerland with a biogeochemical model that simulates terrestrial n uptake and release including n2o emissions as for many central european sites the pollen record at the gerzensee is remarkable for the abundant presence of the symbiotic nitrogen fixer hippophae rhamnoides l during the abrupt warming that also marks the beginning of primary succession on immature glacial soils here we show that without additional nitrogen fixation climate change results in a significant increase of n2o emissions of approximately factor 3 4 from 6 4 1 9 to 21 6 5 9 mg n2o n m 2 yr 1 each additional 1000 mg m 2 yr 1 of nitrogen added to the ecosystem through n fixation results in additional n2o emissions of 1 6 mg n2o n m 2 yr 1 for the time with maximum h rhamnoides coverage our results suggest that local reactions of emissions to abrupt climate change could have been considerably faster than the overall atmospheric concentration changes observed in polar ice nitrogen enrichment of soils due to the presence of symbiotic n fixers during early primary succession not only facilitates the establishment of vegetation on soils in their initial stage of development but can also have considerable influence on biogeochemical cycles and the release of reactive nitrogen trace gases to the atmosphere c 2012 elsevier b v all rights reserved

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

oxygen isotopes of lake marl at gerzensee and leysin switzerland covering the younger dryas and two minor oscillations and their correlation to the grip ice core the ratio of oxygen isotopes is a temperature proxy both in precipitation and in the calcite of lacustrine sediments the very similar oxygen isotope records from greenland ice cores and european lake sediments during the last glacial termination suggest that the drastic climatic changes occurred quasi simultaneously on an extra regional probably hemispheric scale in order to study temporal relations of the different parameters recorded in lake sediments for example biotic response times to rapid climatic changes a precise chronology is required in unlaminated lake sediments there is not yet available a method to provide a high resolution chronology especially for periods with radiocarbon plateaux alternatively an indirect time scale can be constructed by linking the lake stratigraphy with other well dated climate records new oxygen isotope records from gerzensee and leysin with an estimated sampling resolution of between 15 and 40 years match the greenlandic isotope record in many details under the assumption that the main variations in temperature and thus in oxygen isotopes occurred about simultaneously in greenland and switzerland we have assigned a time scale to the lake sediments of gerzensee and leysin by wiggle matching their stable isotope records with those of greenland ice cores which are among the best dated climatic archives we estimate a precision of 20 to 100 years during the last glacial termination

how rivers react to large earthquakes evidence from central taiwan earthquakes and bedrock river incision are fundamental processes in the evolution of tectonically active landscapes yet little work has focused on understanding how a bedrock river responds to a single large earthquake data from the 1999 m w 7 6 chi chi earthquake in central taiwan show dramatic differences in river response that depend on the proximity to the rupture zone near the fault scarp vertical ground deformation intensifi es river incision on a time scale of years to decades while distal to the fault landslides induced by the earthquake mantle bedrock on the river bed with sediment impeding incision for decades to centuries as the material is evacuated this surprising spatial and temporal variability in bedrock incision caused by earthquakes has implications for the paleoseismic interpretation of bedrock terraces and for the evolution of tectonically active landscapes

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales

stochastic forcing of sediment routing and storage in channel networks the stochastic field of sediment supply to the channel network of a drainage basin depends on the large scale interactions among climatically driven processes such as forest fire and rainstorms topography channel network topology and basin scale during infrequent periods of intense erosion large volumes of colluvium are concentrated in parts of a channel network particularly near tributary junctions the rivers carry bed material and wash load downstream from these storage sites at different rates the bed material travels slowly creating transient patterns of sediment transport sediment storage and channel morphology along the channel network as the concentrations of bed material migrate along the network their waveforms can undergo changes by diffusion interference at tributary junctions and loss of mass through temporary sediment storage in fans and terraces and through particle abrasion which converts bed material to wash load we investigated how these processes might influence the sediment mass balance in channels of third and higher order in a 215 km 2 drainage basin within the oregon coast range over a simulated 3000 year period with a climate typical of the late holocene we used field measurements and a simulation model to illustrate interactions between the major controls on large scale processes functioning over long periods of time in complex drainage basins

the oxygen and carbon isotopic signatures of biogenic carbonates in gerzensee switzerland during the rapid warming around 14 685 years bp and the following interstadial abstract the stable isotope signature of ostracods molluscs and charophyte remains from the late glacial section of a shallow core from lake gerzensee switzerland is analyzed along with the bulk carbonate isotope composition in a multi proxy study aiming to document the biotic responses to the first strong warming ca 14 6 ka ago after full glacial conditions the main goal of our contribution is to understand the climatic significance of the oxygen isotope variations in and between the different carbonate species and ideally provide a quantitative estimate of the oxygen isotopic composition of meteoric precipitation which then could be translated to mean temperature estimates corrected for the respective vital offsets the different carbonates show almost identical oxygen isotope ratios for the time preceding and after the rapid transition from greenland climate stages gs2 to gi1 indicating low and seasonally constant water temperatures at the sediment water interface for this period in the following the difference between cold season and warm season carbonates increases gradually pointing to a summer winter temperature difference of roughly 10 k at the end of gi1 we conclude that this gradual water temperature increase is independent of climate and is mainly due to sedimentation shallowing the sediment water interface eventually accentuated by a gradual decrease of gerzensee s water level during gi1 corrected for the isotope fractionation induced by the long term trend of such water temperature change the higher resolved 18o record from the bulk carbonates allows calculation of the presumed oxygen isotope ratio of former lake water 18ol which shows striking similarity to the record from ammersee introducing a tentative hydrological correction close to the present day offset between 18ol and the oxygen isotopes in meteoric precipitation 18op we propose a quantitative 18op and mean air temperature record for the gerzensee region

large floods alluvial overprint and bedrock erosion depending on their behaviour during extreme floods streams can be divided into two distinct classes which derive from a simple threshold model of transport dynamics flood cleaning streams erode during high flows and deposit during small and medium flows flood depositing streams deposit during high flows and erode during small and medium flows using published descriptions of the geomorphic effects of large floods rivers with a wide range of drainage areas and other characteristics are classified as either flood cleaning or flood depositing in bedrock channels this behaviour can lead to a feedback effect the overprint effect between sediment transport processes and bedrock erosion which can modulate long term bedrock erosion rates the overprint effect arises when alluvium covers the bedrock and typical alluvial channel forms e g meandering or braiding patterns armour layers or bedforms develop which influence sediment transport rates this effect may accelerate or decelerate sediment export from a reach causing increased or decreased long term bedrock erosion rates the overprint effect is illustrated using field data from the erlenbach switzerland and its implications for channel dynamics and bedrock erosion are discussed copyright 2012 john wiley sons ltd

dust transport and palaeoclimate during the oldest dryas in central europe implications from varves lake constance this paper evaluates evidence for seasonal loess deposits in peri alpine lake constance at the end of the last glacial oldest dryas chronozone the usefulness of such lacustrine deposits for palaeoclimatic interpretations is discussed the sedimentology of laminated couplets comprising yellow and grey silts has been investigated to test the hypothesis that the couplets are varves i e annual rhythmites comprising alternations of loess and glacial silt and clay the laminae are mostly less than 1 mm thick and include from bottom to top 1 a matrix of well sorted non graded fine yellow silt with sand size intraclasts 2 coarsening upward grey silt with a cap of fining upward silt to clay the latter is typical for varves in modern proglacial lakes and reflects summer and winter deposits silt and clay respectively we propose that the lack of grading and the matrix supported fabric is indicative of aeolian transport and therefore interpret the yellow laminae as loess deposits volcanic glass intraclasts in the loess layers are probably derived from volcanic terrain to the west of the lake indicating an easterly palaeowind direction deposition of loess in the lake occurred regularly at the beginning of each annual cycle suggesting that the palaeowinds were associated with winter and or spring conditions two transport scenarios are suggested to explain the sand grains scattered in this deep water lacustrine record 1 the grains may have been transported as bedload over the annual winter ice cover of the lake under moderate wind strengths frozen into the ice and released for deposition during spring melt 2 the sand grains were blown directly out onto the lake water by very strong winds during spring the first scenario is contrary to the general view that loess was transported during summer and that loess deposits thus reflect summer conditions only loess input to the lake shows a transitional decrease after ca 14 3 kyr bp and cessation at ca 14 kyr bp probably as a result of a change of wind behaviour increased humidity and or vegetational changes during the oldest dryas in central europe