the impact of using different modern climate data sets in pollen based paleoclimate reconstructions of north america abstract the use of different modern climate data sets is shown to impact a continental scale pollen based reconstruction of mean july temperature tjul over the last 2000 years for north america data from climate stations physically modeled from climate stations and reanalysis products are used to calibrate the reconstructions results show that the use of reanalysis products produces warmer and or smoother reconstructions as compared to the use of station based data sets the reconstructions during the period of 1050 1550 ce are shown to be more variable because of a high latitude cold bias in the modern tjul data the ultra high resolution worldclim gridded data may only useful if the modern pollen sites have at least the same spatial precision as the gridded dataset hence we justify the use of the lapse rate corrected university of east anglia climate research unit cru based whitmore modern climate data set for north american pollen based climate reconstructions

changes in the parkland boreal forest boundary in northwestern ontario over the holocene abstract changes in vegetation were tracked from a well dated sediment core from a boreal lake lake 239 at 200 year resolution over the holocene this presently oligotrophic lake is located 100 km east from the present day parkland forest ecotone in northwestern ontario near shore sediment core transects from lake 239 have previously shown this lake was at least 8 m lower than present in the mid holocene or 58 less lake volume in comparison to today large shifts were expected in the terrestrial vegetation if the low lake levels were related to climate the core from lake 239 shows increases in the relative abundance and concentration of pollen such as cupressaceae and ambrosia indicating a more open boreal forest between 4500 8000 cal yr bp pollen based inferences of average summer and winter temperatures suggest that temperatures were on average up to 1 2 c warmer than today with winter temperatures up to 4 c warmer the pollen inferences also suggest enhanced precipitation likely in the summer but with an overall increase in evaporation and evapotranspiration resulting in reduced effective moisture to assess regional climate changes pollen based reconstructions of temperature and precipitation were developed and synthesized from sediment cores from eight previously published lakes from which pollen sites were available to both the west and east of lake 239 spanning present day prairie lakes to forested lakes up to 300 km east of the prairie boreal ecotone all sites show shifts in pollen assemblages that indicate a warm mid holocene period prairie sites west of the experimental lakes area ela show mid holocene decreases in precipitation relative to today whereas sites near or east of ela show consistent increases in precipitation but with increased temperatures and enhanced evaporation during the mid holocene

multi temporal uav data for automatic measurement of rill and interrill erosion on loess soil the fragile landscape of the north european loess belt is prone to soil erosion due to soil properties and intense land use of the fertile region exact measurement of surface changes with high temporal and spatial resolution over large areas is necessary to quantify and understand rill and interrill erosion processes high resolution aerial imagery acquired by an unmanned aerial vehicle uav is used to automatically generate precise digital surface models dsms of high spatial resolution by applying structure from motion image processing tools during an investigation period of ten months a 600 m2 field plot is observed during four field campaigns a stable reference system is established for multi temporal comparison the overall accuracy of the dsms generated from uav images is less than 1 cm verified by comparison with terrestrial laser scanner tls data furthermore a method for automatic rill extraction and rill parameter calculation is developed which enables objective rill description with cm accuracy and resolution soil surface roughness and rill development as well as volumetric quantifications are analysed for multi temporal change detection surface changes during winter season are controlled by soil consolidation crusting and sheet erosion during rainy spring season sheet erosion and rill incision occur two thunderstorms in summer season cause dominant rill erosion erosion rills are more dominantly deepening than widening from to 2 to 4 cm depth and from 17 to 23 cm width resulting in average per rill erosion values of 0 03 and 0 07 m3 respectively an orientation dependent lateral rill shift is revealed implying rill widening in eastern direction due to dominant winds from the west volumetric quantifications indicate high erosion volumes reaching up to 121 tha 1 during the summer events highest erosion volumes are due to rill erosion rather than interrill erosion copyright 2014 john wiley sons ltd

pollen based continental climate reconstructions at 6 and 21 ka a global synthesis subfossil pollen and plant macrofossil data derived from 14c dated sediment profiles can provide quantitative information on glacial and interglacial climates the data allow climate variables related to growing season warmth winter cold and plant available moisture to be reconstructed continental scale reconstructions have been made for the mid holocene mh around 6 ka and last glacial maximum lgm around 21 ka allowing comparison with palaeoclimate simulations currently being carried out as part of the fifth assessment report ar5 of the intergovernmental panel on climate change the synthesis of the available mh and lgm climate reconstructions and their uncertainties obtained using modern analogue regression and model inversion techniques is presented for four temperature variables and two moisture variables reconstructions of the same variables based on surface pollen assemblages are shown to be accurate and unbiased reconstructed lgm and mh climate anomaly patterns are coherent consistent between variables and robust with respect to the choice of technique they support a conceptual model of the controls of late quaternary climate change whereby the first order effects of orbital variations and greenhouse forcing on the seasonal cycle of temperature are predictably modified by responses of the atmospheric circulation and surface energy balance

estimates of sea surface temperature in the coral sea at the last glacial maximum the climap 1981 reconstruction of the coral sea found relatively little cooling 2 c in the low latitudes 10 s but a warming off australia at about 25 s the small low latitude changes are of interest because terrestrial pollen and snowline data from the new guinea highlands imply that surface temperatures may have been 6 to 9 c colder at the last glacial maximum lgm the purpose of this paper is to evaluate these conclusions on the basis of additional core sites new oxygen isotope stratigraphy and new sea surface temperature sst estimates using the modern analog technique mat in the northern coral sea planktonic foraminifer assemblages consist of tropical subtropical species that show little change over the past 20 kyr quantitative estimates of sst using the modern analog technique mat confirm the climap 1981 conclusion that little or no temperature change occurred in this tropical region at the lgm thus reinforcing the conflict with terrestrial evidence in the southern region 25 s two cores indicate that foraminifer faunas became more subtropical at the lgm the mat estimates for the lgm are 3 to 4 c colder than modern producing a steeper thermal gradient in the southern coral sea these data remove the warm sst anomaly along the eastern coast of australia and indicate that during the lgm cool high latitude waters were displaced northward along the coast of australia into the southern coral sea

suspension and near bed load sediment transport processes above a migrating sand rippled bed under shoaling waves the present study focuses on the fine scale flow and sand transport processes above onshore migrating ripples below skewed surface gravity waves in the shoaling zone a set of acoustic instruments was deployed in the shoaling region of the large scale wave channel at canal d investigacio i experimatacio maritima universitat poltiecnica de catalunya barcelona spain in order to provide high resolution velocity and sediment concentration profiles with an acoustic concentration and velocity profiler acvp measurements are analyzed relative to the positions of the measured nonmoving sand bed and the interface separating the suspension from the near bed load layer this interface is detected here by the application of a novel acoustic bed echo detection method furthermore the use of the dual frequency inversion proposed in the work of hurther et al 2011 allows for the calculation of the sediment concentration profile across both the suspension and near bed load layers the sand bed was covered by quasi two dimensional suborbital ripples migrating onshore as proposed by o donoghue et al 2006 the occurrence of quasi two dimensional ripples is attributed to the fine size sand of d50 250 mm used in the present study under full scale forcing conditions in order to determine the effect of shoaled wave skewness on the ripple vortex entrainment and sediment transport the instantaneous and mean measurements of the flow sediment concentration and sediment flux along the ripple profile are discussed in terms of 1 the occurrence of ripple vortex entrainment on either side of the ripple crest 2 the wave velocity phase lagging driven by the ripple vortex entrainment process and the turbulent bed friction effects in the wave boundary layer 3 phase lagging between velocity and maximum concentration and sediment flux events 4 the structure of bed friction and ripple driven turbulence across the suspension and the near bed load layers and 5 the streaming components the results on these aspects strongly support that the wave velocity skewness effect under shoaling waves is fairly similar to the one obtained in skewed oscillatory water tunnel flows furthermore it is found that the onshore oriented net bed load sediment transport is at the origin of the onshore ripple migration this flux is roughly twice as much as the opposite offshore oriented net suspension flux dominated by the ripple vortex entrainment processes

sediment discharge division at two tidally influenced river bifurcations 1 we characterize and quantify the sediment discharge division at two tidally influenced river bifurcations in response to mean flow and secondary circulation by employing a boat mounted acoustic doppler current profiler adcp to survey transects at bifurcating branches during a semidiurnal tidal cycle the adcp collecting flow velocity and acoustical backscatter data was used to quantify suspended sediment discharge adopting a recently introduced calibration procedure measured profiles of flow velocity and sediment concentration allowed us to compute spatiotemporal distributions of the shear velocity the roughness length and the rouse number spatiotemporal distributions of the settling velocity were obtained by combining the rouse number and shear velocity estimates with in situ measurements from a laser particle size analyzer bed load transport rates were inferred from shear stress estimates the concentration field shows a direct response to bed shear stress stressing the alluvial context of the system the flow in the bifurcation regions is characterized by counter rotating secondary flow cells which stretch over the full width and depth of the cross sections in the downstream branches and persist throughout the entire tidal cycle the pattern of secondary flow suggests the flow approaching the bifurcation is concentrated in two independent threads a two cell structure inhibits the exchange of sediment that would occur in case a single cell would stretch over the full channel width the division of suspended sediment primarily depends on the upstream transverse profile of the suspended sediment concentration which is in turn dependent on geometrical factors such as upstream curvature

broadband acoustic quantification of stratified turbulence high frequency broadband acoustic scattering techniques have enabled the remote high resolution imaging and quantification of highly salt stratified turbulence in an estuary turbulent salinity spectra in the stratified shear layer have been measured acoustically and by in situ turbulence sensors the acoustic frequencies used span 120 600 khz which for the highly stratified and dynamic estuarine environment correspond to wavenumbers in the viscous convective subrange 500 2500 m 1 the acoustically measured spectral levels are in close agreement with spectral levels measured with closely co located micro conductivity probes the acoustically measured spectral shapes allow discrimination between scattering dominated by turbulent salinity microstructure and suspended sediments or swim bladdered fish the two primary sources of scattering observed in the estuary in addition to turbulent salinity microstructure the direct comparison of salinity spectra inferred acoustically and by the in situ turbulence sensors provides a test of both the acoustic scattering model and the quantitative skill of acoustical remote sensing of turbulence dissipation in a strongly sheared and salt stratified estuary

quantitative holocene climatic reconstructions for the lower yangtze region of china quantitative proxy based and high resolution palaeoclimatic datasets are scarce for the lower reaches of the yangtze river lyr basin this region is in a transitional vegetation zone which is climatologically sensitive and as a birthplace for prehistorical civilization in china it is important to understand how palaeoclimatic dynamics played a role in affecting cultural development in the region we present a pollen based and regionally averaged holocene climatic twin dataset for mean total annual precipitation pann and mean annual temperature tann covering the last 10 000 years for the lyr region this is based on the technique of weighted averaging partial least squares regression to establish robust calibration models for obtaining reliable climatic inferences the pollen based reconstructions generally show an early holocene climatic optimum with both abundant monsoonal rainfall and warm thermal conditions and a declining pattern of both pann and tann values in the middle to late holocene the main driving forces behind the holocene climatic changes in the lyr area are likely summer solar insolation associated with tropical or subtropical macro scale climatic circulations such as the intertropical convergence zone itcz western pacific subtropical high wpsh and el nino southern oscillation enso regional multi proxy comparisons indicate that the holocene variations in precipitation and temperature for the lyr region display an in phase relationship with other related proxy records from southern monsoonal china and the indian monsoon influenced regions but are inconsistent with the holocene moisture or temperature records from northern monsoonal china and the westerly dominated region in northwestern china overall our comprehensive palaeoclimatic dataset and models may be significant tools for understanding the holocene asian monsoonal evolution and for anticipating its future dynamics in eastern asia

effects of rock fragments on soil erosion by water at different spatial scales a review this paper reviews the various effects of rock fragments on soil erosion by water since these effects are scale dependent they are investigated at three different nested spatial scales the microplot 4 10 6 100m2 the mesoplot 10 2 102 m2 and the macroplot 101 104 m2 for each scale the corresponding process mechanisms are discussed particular attention is paid to the effects of rock fragment cover on the intensity of soil erosion processes at the mesoplot scale i e on interrill areas rock fragments at the soil surface can have negative as well as positive effects on sediment yield these ambivalent effects are conditioned by the type of fine earth porosity soil surface slope vertical position and size of rock fragments and by the occurrence of horseshoe vortex erosion at the microplot scale i e the soil surface area which is covered by a single rock fragment and at the macroplot scale i e upland areas where both interrill and rill erosion takes place rock fragments at the soil surface have a negative effect on sediment yield in these two scales rock fragments can thus be considered as natural soil surface stabilizers at the macroplot scale the mean decrease of relative interrill and rill sediment yield with rock fragment cover can be expressed by an exponential decay function the scatter of the data indicates that a given rock fragment cover can have different efficiencies in reducing interrill and rill sediment yield depending on the varying intensities of the hydrological and erosion subprocesses these findings have implications for erosion modelling and soil conservation

soil geomorphic significance of land surface characteristics in an arid mountain range mojave desert usa abstract mountains comprise an extensive and visually prominent portion of the landscape in the mojave desert california landform surface properties influence the role these mountains have in geomorphic processes such as dust flux and surface hydrology across the region the primary goal of this study was to describe and quantify land surface properties of arid mountain landforms as a step toward unraveling the role these properties have in soil geomorphic processes as part of a larger soil geomorphic study four major landform types were identified within the southern fry mountains in the southwestern mojave desert on the basis of topography and landscape position mountaintop mountainflank mountainflat intra range low relief surface and mountainbase a suite of rock vegetation and morphometric land surface characteristic variables was measured at each of 65 locations across the study area which included an associated piedmont and playa our findings show that despite the variation within types landforms have distinct land surface properties that likely control soil geomorphic processes we hypothesize that surface expression influences a feedback process at this site where water transports sediment to low lying areas on the landscape and wind carries dust and soluble salts to the mountains where they are washed between rocks incorporated into the soil and retained as relatively long term storage recent land based video and satellite photographs of the dust cloud emanating from the sierra cucapa mountains in response to the 7 2 magnitude earthquake near mexicali mexico support the hypothesis that these landforms are massive repositories of dust

effects of rock fragment cover on hydrological response and soil loss from regosols in a semi humid environment in south west china abstract controlling soil hydrological processes and combating soil erosion on agricultural fields are high priorities for crop production and ecological environments in this research the effect of land application of rock fragments on surface runoff subsurface runoff infiltration and soil loss on regosols had been investigated under field conditions using a portable rainfall simulator experimental twin plot two subplot with 1 m wide by 2 m long 32 slope with different rock fragment covers ranging from 0 40 were exposed to three rainfall intensities low 57 2 mm h 1 medium 91 3 mm h 1 and high 122 5 mm h 1 fifteen treatments were conducted in the experiments in duplicates surface runoff subsurface runoff soil moisture and sediment were measured results show that surface rock fragment cover retarded surface runoff increased infiltration and subsurface runoff and diminished sediment concentration and soil loss the final infiltration rates which increased with increasing rock fragment covers were 16 5 42 7 mm h 1 at low intensity 19 7 50 8 mm h 1 at medium intensity and 23 8 56 4 mm h 1 at high intensity compared with bare soils surface runoff rates were reduced to 24 51 and 64 in soils with 40 rock fragment cover at low medium and high intensity rainfall respectively subsurface runoff volume was significantly higher and time to start subsurface runoff was shorter as surface rock fragment cover increased compared with bare soils subsurface runoff coefficients increased to 3 5 3 3 and 2 9 times in soils with 40 rock fragment cover at low medium and high intensity respectively sediment concentrations increased from 9 8 g l 1 for 40 rock fragment cover under high intensity rainfall to 51 5 g l 1 for bare soils with rain falling at high intensity the erosion rate was 15 g m 2 min 1 for bare soils under low intensity the relationship between rock fragment cover and soil loss ratio can be expressed by an exponential function with a high degree of reliability regardless of rainfall intensities overall results indicate the surface rock fragments can be influential in shaping hydrological processes and soil loss from sloping farmland

on the remote acoustic detection of suspended sediment at long wavelengths experimental results are presented which indicate a linear relation between the time averaged amplitude of the envelope of the backscattered acoustic pulse at 192 khz and the square root of suspended sediment concentration in the 10 to 103 mg 1 1 range particle sizes ranged from 2 to 140 m the measurements were made in a negatively buoyant mine tailing discharge plume in a submarine channel at depths of 60 to 90 m in rupert inlet british columbia from the theory of acoustic backscatter from a solid elastic sphere in the rayleigh region it is shown that if the pressure amplitude of the backscattered wave is rayleigh distributed then such a linear relation is to be expected expressions for the optimum acoustic frequency for the detection of dilute suspensions at a given range and for the minimum detectable concentration are obtained assuming a thermal noise background the possibility that bubbles contribute to the backscatter is considered and found to be unlikely on the basis of probable bubble lifetimes

calculation of in situ acoustic sediment attenuation using off the shelf horizontal adcps in low concentration settings the use of off the shelf acoustic doppler velocity profilers adcps to estimate suspended sediment concentration and grain size in rivers requires robust methods to estimate sound attenuation by suspended sediment theoretical estimates of sediment attenuation require a priori knowledge of the concentration and grain size distribution gsd making the method impractical to apply in routine monitoring programs in situ methods use acoustic backscatter profile slope to estimate sediment attenuation and are a more attractive option however the performance of in situ sediment attenuation methods has not been extensively compared to theoretical methods we used three collocated horizontally mounted adcps in the fraser river at mission british columbia and 298 observations of concentration and gsd along the acoustic beams to calculate theoretical and in situ sediment attenuation conversion of acoustic intensity from counts to decibels is influenced by the instrument noise floor which affects the backscatter profile shape and therefore in situ attenuation we develop a method that converts counts to decibels to maximize profile length which is useful in rivers where cross channel acoustic profile penetration is a fraction of total channel width nevertheless the agreement between theoretical and in situ attenuation is poor at low concentrations because cross stream gradients in concentration sediment size or gsd can develop which affect the backscatter profiles we establish threshold concentrations below which in situ attenuation is unreliable in fraser river our results call for careful examination of cross stream changes in suspended sediment characteristics and acoustic profiles across a range of flows before in situ attenuation methods are applied in river monitoring programs

rock fragments in top soils significance and processes this introductory paper reviews various aspects of rock fragments in top soils such information is required for various reasons and in particular for predicting the impact of climatic or landuse changes on the response of these soils particular attention is paid to the definition and measurement of rock fragment content in top soils the density of soils containing rock fragments the spatial distribution and movement of rock fragments in top soils the effects of rock fragments on some key hydrological processes thermal properties of top soils physical soil degradation soil erosion and soil productivity

bubble clouds and temperature anomalies in the upper ocean the processes of mixing in the upper few metres of the ocean are poorly known and largely unqualified1 but are a vital element in ocean atmosphere interaction playing a key part in the transfer and dispersion of heat gases and nutrients here we report results from a towed instrument used to measure simultaneously water temperature and the sound scattered from bubble clouds produced by breaking waves dominant features in the records are correlated intense sound scattering or bubble clouds being associated with warmer water and large positive temperature gradients with the onset of increased scattering the observations provide a more complete picture of the structure and nature of bubble clouds and establish their assocition with dynamical processes of turbulent diffusion in the upper ocean boundary layer

a pollen study of a late quaternary peat bog south central adirondack mountains new york a series of cores from a 7 ha glacial kettle 600 m above sea level provides information on the development of a sphagnum peat bog and the late quaternary vegetation and climate history of the south central adirondack mountains new york within the kettle stratified drift that dates to about 11 000 yr b p is overlain by varved glacial lake sediment gyttja and peat the fossil pollen samples at brandreth bog were compared with 1 618 modern pollen samples using squared chord distance the degree of similarity between fossil and modern pollen samples was calibrated using comparisons among modern samples from different vegetation regions modern pollen analogs were identified for all of the fossil samples at brandreth bog and the vegetation and climate associated with these modern analogs were used to interpret the vegetation and climate history near the site the numerically derived pollen assemblage zones at brandreth bog are broadly similar to those for other sites in the region a forest similar to the current boreal forest succeeded treeless vegetation and spruce woodland around brandreth bog before about 10 200 yr b p a pine dominated forest was present by 9 600 yr b p continued warming of the climate allowed a hemlock rich mixed conifer hardwood forest to grow around brandreth bog after 7 000 yr b p and spruce and fir became less plentiful after a sharp decline in the amount of hemlock around brandreth bog at 4 700 yr b p birch maple beech and pine became the primary forest constituents spruce and fir trees increased in number near brandreth bog after 4 000 yr b p a development indicative of a reversal of the general warming trend that typified the early holocene by 2 000 yr b p a bog mat had closed over the lake basin a rise in the abundance of ragweed pollen about 125 yr b p reflected european settlement probably to the south correlation among five cores at the study site provided evidence of sediment focusing in the former lake basin

pollen plant macrofossils and microvertebrates from mid holocene alluvium in east central iowa usa comparative taphonomy and paleoecology abstract pollen plant macrofossils and micromammals are commonly used in paleoecological interpretations but rarely are found associated because of distinctly separate taphonomic pathways into the fossil record the lilienthal local biota dating between 5920 60 and 6300 80 14 c b p is a rare exception as the site contains all three proxies juxtaposed in alluvium impounded upstream from a fossil log near the headwaters of mud creek east central iowa u s a a variety of taphonomic processes can strongly influence the composition of fossil assemblages this paper compares the taphonomic framework for each fossil group interprets the paleoecologic signal from each and then compares the three interpretations pollen and plant macrofossils are found in organic silts indicating deposition in a quiet water environment microvertebrates ordinarily occur in sand sized sediments and show evidence of fluvial transport despite these different pathways all lilienthal assemblages indicate that a largely closed mesic deciduous forest grew along mud creek in mid holocene time therefore a narrow north south ecotone must have existed between the forest and tall grass prairie biomes in eastern iowa this robust data set provides a detailed picture of the paleoecology and paleogeography of this past environment

the influence of wind induced bubbles on echo integration surveys an investigation of attenuation of acoustic energy caused by gas bubbles in the surface layers has been carried out this was done primarily to study the effect on echo integration of fish abundance when using hull mounted transducers two different approaches have been used the first examines the variation of the echo intensity from an acoustically stable bottom layer and the second measures the total volume reverberation as a function of depths the bubble density size distribution and the attenuation caused by the bubbles is estimated from the measurements done under different weather conditions the results show that the acoustic attenuation caused by wind induced gas bubbles in the surface layers appear at a lower wind force and at a greater magnitude than earlier reported and expected the attenuation is found to increase rapidly with increasing frequency the results are also used to find the minimum towing depths of a transducer as a function of the wind speed necessary in order to keep the attenuation due to the bubbles below a given number

a sharp view on river dune transition to upper stage plane bed sandy river beds are dominated by rhythmic features known as dunes experimental investigations of turbulent flow and sediment transport over dunes have predominantly focused on equilibrium flows that are rare in natural rivers using a novel acoustic instrument over migrating dunes in a laboratory setting we quantify a number of dynamical properties that are crucial in our understanding and modeling of dune morphology and kinematics particularly under nonequilibrium flows during dune transition to upper stage plane bed measured sediment transport distributions reveal a positive spatial lag between dune crest and maximum sediment transport rate that eventually caused washing out of dunes bed load was entirely captured in dune troughs contributing to dune translation where most of suspended load was advected further downstream contributing to dune deformation measured bypass fraction was about 76 which means that only 24 of the total sediment load at the dune crest contributed to dune migration

applying plant functional types to construct biome maps from eastern north american pollen data comparisons with model results abstract global biome models like biome1 convert climate model simulations of past climates into biome distributions and thus facilitate comparison of both climate and biome model results with biomes estimate from paleoecological data we adapted a biomization method recently developed for european pollen data for use with pollen data in eastern north america and then compared its estimated biomes with those derived from applying biome1 to the climate simulations from the ncar ccm1 national center for atmospheric research community climate model version 1 for 6000 years ago 6 ka we first tested the biomization method by seeing how well the biomes inferred from modern pollen data match observed biomes we found that modifications to the method were necessary in part to account for physiological differences between north american and european taxa and in part to cope with our choice of using just 23 major pollen taxa our modifications significantly improved the match between observed modern biomes and pollen derived biomes as measured by the kappa statistic we tested our tuning of the biomization method by matching its inferred 6 ka biomes to biomes estimated from pollen data using the modern analog technique the degree of agreement at 6 ka is close to that for today showing that 1 the biomization method and modern analog technique when applied to the same pollen data produce consistent results and 2 the modifications made to the biomization method are robust back to 6 ka we then used the results of the biomization method to test the biome maps simulated by biome1 which derives biome distributions from observed climate values for today and from the climatic simulations of the ccm1 for 6 ka only a fair agreement is seen and significant offsets exist in the placement of biomes by biome1 for today biome1 simulates the boundary between the temperate deciduous and cool mixed forests to be too far south and the steppe forest boundary to be too far west these model biases are also evident in the simulations at 6 ka despite the fact that ccm1 simulates warmer than present temperatures in the central united states to the north however biome1 correctly simulates the cool mixed forest and taiga boundary at 6 ka as more northwestward than at present

depressional storage for markov gaussian surfaces processes during rain events such as infiltration runoff soil erosion and crust formation are influenced in part by depressional storage and surface roughness if the surface topography is known its potential depressional storage can be calculated the objective of this paper was to relate the statistical parameters for quantifying surface roughness to depressional storage analysis of topographic data sets digitized at millimeter grids by a laser scanner showed that soil roughness can be quantified by a markov gaussian m g type random process a monte carlo simulation procedure was used to find the mean ponding characteristics from simulated m g surfaces depressional storages were found to be functions of two m g parameters two sample length scales and the slope steepness the markov parameters are the global variance 2 and the correlation length scale l and the sample length scales are grid spacing x and side length ls after proper scaling all storage functions collapsed into two nondimensional relationships 1 storage at zero slope as a function of relative sample length scale and 2 storage as a function of scaled slope when l 0 simulated surfaces followed the random gaussian model and the nondimensional storage was only a function of scaled slope storages calculated from digitized elevation data sets with m g type statistics agreed well with results obtained from simulated surfaces

pollen response surface estimates of late quaternary changes in the moisture balance of the northeastern united states abstract quantitative estimates of late quaternary climate in the northeastern united states are reconstructed from fossil pollen data to evaluate changes in the regional moisture balance inferred from water level fluctuations we use environmental response surfaces to calibrate modern pollen data for 17 different taxa to an index of effective soil moisture and mean annual precipitation we apply these response surfaces to fossil pollen data from 60 sites in the region to reconstruct changes in soil moisture and mean annual precipitation at 3000 yr intervals from 12 000 yr b p to present the mapped reconstructions of soil moisture and mean annual precipitation illustrate how the regional moisture balance of the northeast may have changed over the last 12 000 yr in response to changing climate reconstructions of annual precipitation show a gradual increase from 30 below modern values at 12 000 yr b p to near modern values by 6000 yr b p and then remain relatively constant thereafter reconstructed changes in the index of effective soil moisture however show a pattern of near modern values at 12 000 6000 and 3000 yr b p with significantly lower values estimated for 9000 yr b p the time of maximum pine pollen abundances in the northeast this pattern of change is similar to the change in regional moisture balance inferred from stratigraphic records of water level fluctuations these results confirm previous interpretations based on records of water level fluctuations that conditions in the northeast were significantly drier during the early to middle holocene than at other times during the last 12 000 yr

reconstructing palaeoclimatic variables from fossil pollen using boosted regression trees comparison and synthesis with other quantitative reconstruction methods abstract we test and analyse a new calibration method boosted regression trees brts in palaeoclimatic reconstructions based on fossil pollen assemblages we apply brts to multiple holocene and lateglacial pollen sequences from northern europe and compare their performance with two commonly used calibration methods weighted averaging regression wa and the modern analogue technique mat using these calibration methods and fossil pollen data we present synthetic reconstructions of holocene summer temperature winter temperature and water balance changes in northern europe highly consistent trends are found for summer temperature with a distinct holocene thermal maximum at ca 8000 4000 cal a bp with a mean t jja anomaly of ca 0 7 c at 6 ka compared to 0 5 ka we were unable to reconstruct reliably winter temperature or water balance due to the confounding effects of summer temperature and the great between reconstruction variability we find brts to be a promising tool for quantitative reconstructions from palaeoenvironmental proxy data brts show good performance in cross validations compared with wa and mat can model a variety of taxon response types find relevant predictors and incorporate interactions between predictors and show some robustness with non analogue fossil assemblages

a multi frequency acoustic concentration and velocity profiler acvp for boundary layer measurements of fine scale flow and sediment transport processes the use of acoustics to measure sediment transport boundary layer processes has gained increasing acceptance over the past two decades this has occurred through the development of increasingly sophisticated measuring systems and theoretical developments which have enabled flow and suspended sediment parameters to be obtained from acoustic data with a high degree of accuracy until relatively recently separate acoustic systems were used to measure flow and suspended sediment concentration over the past few years however the technology has become sufficiently advanced so that flow and sediment measurements can be integrated into a single system this integration provides quasi instantaneous non intrusive co located high temporal spatial resolution measurements of benthic flow and sediment processes here the development of such an instrument the acoustic concentration and velocity profiler acvp is described the theory underpinning its application is outlined new approaches to velocity de aliasing and suspended sediment inversion instabilities using multi frequency capabilities are presented and the application of the system to sediment transport processes over a sandy ripple bed is illustrated the observations clearly show the value of such instrumentation for studying the dynamical interaction between the bed the flow and the sediments at and within the bottom boundary layer

quantitative interpretation of fossil pollen spectra dissimilarity coefficients and the method of modern analogs abstract dissimilarity coefficients measure the difference between multivariate samples and provide a quantitative aid to the identification of modern analogs for fossil pollen samples how eight coefficients responded to differences among modern pollen samples from eastern north america was tested these coefficients represent three different classes 1 unweighted coefficients that are most strongly influenced by large valued pollen types 2 equal weight coefficients that weight all pollen types equally but can be too sensitive to variations among rare types and 3 signal0to noise coefficients that are intermediate in their weighting of pollen types the studies with modern pollen allowed definition of critical values for each coefficient which when not exceeded indicate that two pollen samples originate from the same vegetation region dissimilarity coefficients were used to compare modern and fossil pollen samples and modern samples so similar to fossil samples were found that most of three late quaternary pollen diagrams could be reconstructed by substituting modern samples for fossil samples when the coefficients indicated that the fossil spectra had no modern analogs then the reconstructed diagrams did not match all aspects of the originals no modern analogs existed for samples from before 9300 yr b p at kirchner marsh minnesota and from before 11 000 yr b p at wintergreen lake michigan but modern analogs existed for almost all holocene samples from these two sites and brandreth bog new york

quantitative estimation of bioclimatic parameters from presence absence vegetation data in north america by the modern analog technique abstract the method of modern analogs is widely used to obtain estimates of past climatic conditions from paleobiological assemblages and despite its frequent use this method involved so far untested assumptions we applied four analog approaches to a continental scale set of bioclimatic and plant distribution presence absence data for north america to assess how well this method works under near optimal modern conditions for each point on the grid we calculated the similarity between its vegetation assemblage and those of all other points on the grid excluding nearby points the climate of the points with the most similar vegetation was used to estimate the climate at the target grid point estimates based the use of the jaccard similarity coefficient had smaller errors than those based on the use of a new similarity coefficient although the latter may be more robust because it does not assume that the fossil assemblage is complete the results of these analyses indicate that presence absence vegetation assemblages provide a valid basis for estimating bioclimates on the continental scale however the accuracy of the estimates is strongly tied to the number of species in the target assemblage and the analog method is necessarily constrained to produce estimates that fall within the range of observed values we applied the four modern analog approaches and the mutual overlap or mutual climatic range method to estimate bioclimatic conditions represented by the plant macrofossil assemblage from a packrat midden of last glacial maximum age from southern nevada in general the estimation approaches produced similar results in regard to moisture conditions but there was a greater range of estimates for growing degree days despite its limitations the modern analog technique can provide paleoclimatic reconstructions that serve as the starting point to the interpretation of past climatic conditions

rock fragment distributions and regolith evolution in the ouachita mountains arkansas usa rock fragments in the regolith are a persistent property that reflects the combined influences of geologic controls erosion deposition bioturbation and weathering the distribution of rock fragments in regoliths of the ouachita mountains arkansas shows that sandstone fragments are common in all layers even if sandstone is absent in parent material shale and sandstone fragments are produced at the bedrock weathering front but the shale weathers rapidly and intact fragments are rare in the solum sandstone is weathered from ridgetop outcrops and transported downslope some of these fragments are moved downward by faunalturbation and by transport into pits associated with rotting tree stumps upward movement by treethrow is common resulting in a net concentration of rocks near the surface however the highest fragment concentrations are in the lower regolith indicating active production at the weathering front the regolith is a dynamic feature reflecting the influences of vertical and horizontal processes of active weathering at the bedrock interface and of surficial sediment movements the role of trees in redistributing rock fragments suggests that significant regolith mixing occurs over time scales associated with forest vegetation communities and that forest soils have likely been extensively mixed within holocene and historic time copyright 2005 john wiley sons ltd

pollen based summer temperature reconstructions for the eastern canadian boreal forest subarctic and arctic pollen based paleoclimate reconstructions using response surface and modern analog methods reveal an 8000 year record of july temperature fluctuations for 25 eastern canadian lake sites located from the forest tundra to the high canadian arctic postglacial conditions characterized by warmer than present summer temperatures prevailed in baffin island and ne labrador beginning about 7500 and 7000 14c yr bp respectively resulting in warmer than present conditions throughout the region by 6000 14c yr bp 0 5 c to 1 c further south in quebec and w labrador july temperatures were 1 2 c colder than present until after 6000 14c yr bp and only reached modern values after all residual laurentide ice had melted increased summertime insolation and the final disappearance of laurentide ice during the middle holocene probably caused july temperatures throughout eastern canada to peak between approximately 5000 and 3500 14c yr bp mid holocene warming relative to today was more pronounced in baffin island and ne labrador 1 c to 2 c compared to the boreal and subarctic regions of quebec and w labrador 1 c over the past 4000 years decreasing summertime insolation and colder sea surface temperatures in the davis strait and labrador sea contributed to a decline in july temperatures of 1 2 c throughout baffin island and the tundra regions of n quebec and labrador the absence of similar cooling in the records from the boreal forest may support the notion that the mean position of the summertime polar front blocked the colder arctic air during the late holocene

pollen based quantitative reconstruction of holocene climate changes in the daihai lake area inner mongolia china vegetation around the daihai lake northern china is very sensitive to climate changes in this paper pollen based quantitative climate reconstructions using three methods weighted averaging partial least squares method wapls modern analog technique mat and pollen response surface method prs were conducted to obtain robust reconstructions of holocene climate changes in the daihai lake area the result obtained by the three methods all consistently show the annual precipitation to have been 50 100 mm lower in the early holocene 100 200 mm higher in the mid holocene and 50 100 mm lower again in the late holocene than at present the wapls and the mat methods also show quasi synchronous oscillations of the mean annual temperature ta 18 28c lower in the early holocene and 18 38c higher in the midholocene than today the time period from 6200 to 5100 cal yr bp was the wettest and the warmest interval with an annual precipitation pa greater than 550 mm and mean annual temperature ta higher than 6 58c several cold and dry events can be identified to occur about 8200 6000 and 4400 cal yr bp with an annual precipitation less than 400 mm and a mean annual temperature colder than 4 58c respectively the mean temperature of the warmest month tw as reconstructed using both wapls and mat methods was relatively stable during the holocene fluctuating about 628c relative to the present level but the prs method suggests more varied tw values in both amplitude and frequency after 1500 cal yr bp no consistent pattern can be observed from these three different analyses probably because of the impact of intensified human disturbances on the natural vegetation the fluctuations of annual precipitation pa correspond to that observed in dongge cave in southern china the differences might be linked to indian monsoon and east asia monsoon climates or caused by the different degree of dating precision different temporal resolution and different sensitive response of climate proxies to the climate variations

holocene moisture evolution across the mongolian plateau and its surrounding areas a synthesis of climatic records abstract based on the review of 26 high standard holocene climatic reconstructions mainly pollen based from the mongolian plateau and its surrounding areas temporal and spatial patterns of the holocene moisture evolution are synthesized the regionally averaged moisture history from the summer monsoon influenced semiarid belt in china i e region a demonstrates that the moisture index curve is broadly in agreement with the synthesized east asian monsoon strength curve both following the general trend of the west tropical pacific sst that is in turn the delayed response to the northern hemispheric summer solar insolation the regionally averaged moisture indices from the winter monsoon dominated southern siberia including lake baikal area and the altai mountains i e region b exhibit a general declining trends since 10 6 9 6 cal kyr bp being largely consistent with the trends of the annual precipitation and the warm season temperature in the russian plain the consistency might be attributable to the holocene declining trend of the warm season temperature in north atlantic region the predominant feature of the regionally averaged moisture index from the westerlies affected northern xinjiang i e region c is a persistent increasing trend since 8 cal kyr bp the wetting trend of northern xinjiang during the past 8000 years might be attributable to the increasing trend of winter insolation and to the associated increasing trend of cold season temperature in northwestern europe the chronological correspondences between dry phases and warm intervals in the arid areas of the mongolian plateau i e northern mongolian plateau within mongolia and southern mongolian plateau within china region d lend a support to the proposal that the mid holocene dry phase was most likely the result of mid holocene high warm season temperature

the implications of laser diffraction measurements of sediment size distributions in a river to the potential use of acoustic backscatter for sediment measurements we construct vertical profiles of the acoustic attenuation and back scattering properties of a river column from measured particle concentration and size distribution profiles the particle size and concentration data were collected in situ in the cowlitz river in washington u s using a laser diffraction instrument lisst sl the particle size distribution was bimodal comprising a vertically well mixed washload and a suspended load that was similar to rouse profiles we then explore how well the results of converting these synthetic profiles to recover an acoustic equivalent sediment concentration and acoustic equivalent size compare with laser data in this bimodal environment the acoustic scattering and attenuation properties are computed for four distinct frequencies 0 5 1 3 and 5 mhz it is seen that at the lowest frequency 500 khz the acoustic attenuation throughout the water column is nearly constant and determined primarily by particles of size smaller than 30 microns i e the washload at the next higher frequency 1 mhz the suspended load also contributed to attenuation but even so attenuation remained nearly constant over the vertical profile thus at the two lower frequencies attenuation was decoupled from scattering making the inverse problem explicit for inversion in contrast at the two highest frequencies scattering of sound by the suspended mode became the dominant contributor to attenuation and attenuation varied by an order of magnitude over river depth as for backscatter the computed acoustic backscatter strength was determined by a combination of the washload and suspended sediment mode at all four frequencies a fairly narrow monotonic relationship was found between total sediment concentration and locally computed backscatter effectively providing a calibration between local backscatter signal strength and suspended sediment concentration such a relationship existed throughout the water column for every frequency the sediment concentration derived from backscatter at a pair of frequencies was within 50 of the value measured by laser diffraction however the acoustic equivalent diameter exceeded the laser volume mean diameter by up to an order of magnitude the robustness of these results for application to other flow regimes or rivers remains to be investigated

use of adcps for suspended sediment transport monitoring an empirical approach a horizontally mounted 300 khz acoustic doppler current profiler was deployed in fraser river at mission british columbia to test its capability to detect size classified concentration of suspended sediment bottle samples in beam provide a direct calibration of the hadcp signals we also deployed a 600 khz vertically mounted adcp from a boat in combination with bottle samples fraser river at mission is 525 m wide with moderate suspended sediment concentration up to 350 mg l 1 in our measurements mostly silt and a modest sand load only at high flows we use an entirely empirical approach to calculate the sediment load using adcps to test the reliability of acoustic methods when assumptions embedded in the sonar equation about the relation between suspended sediment size and concentration and acoustic signals are violated vadcp calibration using matched individual bottle samples and acoustic backscatter departed from the expected theoretical relation calibration using depth averaged sediment concentration and acoustic backscatter more closely matched theoretical expectations but varied through the season hadcp calibrations conformed with theoretical expectations and did not exhibit seasonal variation silt and sand were successfully discriminated however silt dominates the correlations we found no coherent relation between acoustic attenuation and silt concentration in beam results are extended by correlation to estimate mean sediment concentration and total suspended flux in the entire channel this auxiliary correlation cancels any calibration bias and permits monitoring of size classified suspended sediment in absence of detailed information of sediment grain size distribution

the hydrological response of soil surfaces to rainfall as affected by cover and position of rock fragments in the top layer rainfall experiments have been conducted in the laboratory in order to assess the hydrological response of top soils very susceptible to surface sealing and containing rock fragments in different positions with respect to the soil surface for a given cover level rock fragment position in the top soil has an ambivalent effect on water intake and runoff generation compared to a bare soil surface rock fragments increase water intake rates as well as time of runoff concentration and decrease runoff volume if they rest on the soil surface for the same cover level rock fragments reduce infiltration rate and enhance runoff generation if they are well embedded in the top layer the effects of rock fragment position on infiltration rate and runoff generation are proportional to cover percentage micromorphological analysis and measurements of the saturated hydraulic conductivity of bare top soils and of the top layer underneath rock fragments resting on the soil surface reveal significant differences supporting the mechanism proposed by poesen 1986 i e runoff generated as rock flow or as horton overland flow can partly infiltrate into the unsealed soil surface under the rock fragments provided that they are not completely embedded in the top layer hence rock fragment position beside other rock fragment properties should be taken into account when assessing the hydrological response of soils susceptible to surface sealing and containing rock fragments in their surface layers a simple model based on the proportions of bare soil surface soil surface occupied by embedded rock fragments and soil surface covered with rock fragments resting on the soil surface describes the runoff coefficient data relatively well

surface roughness evolution of soils containing rock fragments soil surface roughness is a dynamic property which determines to a large extent erosion and infiltration rates although soils containing rock fragments are widespread in the mediterranean region the effect of the latter on surface roughness evolution is yet poorly understood therefore laboratory experiments were conducted in order to investigate the effect of rock fragment content rock fragment size and initial moisture content of the fine earth on the evolution of interrill surface roughness during simulated rainfall surface elevations of simulated plough layers along transects of 50 cm length were measured before and after simulated rainfall totalling 192 5mm z 70mm h with a laser microreliefmeter the results were used to investigate whether systematic variations in interrill surface roughness along stony hillslopes in southeastern spain could be attributed to rock fragment cover and rock fragment size soil surface elevations were measured along the contour lines 50 cm long transects with a contact microreliefmeter roughness was expressed by two parameters related to the height and frequency of roughness elements respectively standard deviation of de trended surface elevations random roughness rr and correlation length l derived from exponential fits of the autocorrelation functions the frequently used assumption that surface roughness rr of cultivated topsoils decreases exponentially with cumulative rain is not valid for soil surfaces covered by rock fragments the rr of soils containing small rock fragments 1 72 7 cm increased with cumulative rainfall after an initial decrease during the first 17 5 mm of rainfall for soils containing large rock fragments 7 7 cm rr increased with rainfall above a threshold rock fragment content by mass of 52 per cent for a given rainfall application rr increased non linearly with rock fragment content the correlation length for soils containing small rock fragments decreases with rock fragment content and is significantly lower than for soils with large rock fragments soils covered with small rock fragments large rr and small l are thus well protected against raindrop impact by a water film in the depressions between the rock fragments on abandoned agricultural fields along hillslopes in southeastern spain rock fragments cover increases non linearly with slope owing to selective erosion of finer particles on steep slopes the increase of surface cover by large rock fragments 25 mm is even more pronounced the simultaneous increase of rock fragment cover and rock fragment size with slope explains the non linear increase of rr with slope these relationships differ for soils covered by platy misaschists and those covered with cubic andesites the variations in correlation length along the hillslopes are not clear probably owing to a simultaneous increase in rock fragment cover and rock fragment size these findings may provide a better prediction of soil surface roughness of interrill areas covered by rock fragments using slope angle and lithology

evidence for warm wet heinrich events in florida analyses of pollen and plant macrofossils from a new core spanning the past 60 000 years from lake tulane florida show a strong antiphase relationship in temperature between florida and the north atlantic region during the pleistocene oak scrub and prairie phases were coeval with long intense dansgaard oeschger interstadials warm periods that initiated bond cycles pine phases were coeval with the north atlantic long stadials cold periods that ended bond cycles and were terminated by heinrich events lake levels were higher during pine phases and climate was wetter however climate in florida was also warmer during these phases which were cold periods in the north atlantic perhaps diminution of thermohaline circulation before and during heinrich events reduced northward heat transport and retained warmth in the subtropical atlantic and gulf of mexico

conservation of soil moisture by different stone covers on alpine talus slopes lassen california abstract this study reports on the influence of stone covers with different clast sizes on the soil moisture of alpine talus slopes in lassen california fifteen four plot sets were sampled in the dry season july 1990 in sandy areas and in talus covered with pebbles cobbles or blocks between 2740 and 2775 m three depths 0 5 5 10 10 15 cm were sampled field moisture content increased gradually with depth in all soil profiles and also in plots covered by increasingly larger rocks surface soils in sand areas were very dry but under rocks had water contents 6 to 14 times greater differences among plots decreased with depth but subsoil samples in sand were still drier than those beneath any stone cover at similar depths blocks were most effective in conserving moisture water content below them was higher than even in deep 10 15 cm sand soils soil temperatures were recorded in sand and under blocks for an 11 day period minima were not significantly different but average maxima were 5 6 c lower under blocks than in sand which reached highs 4 4 c lower than the air differences in soil moisture among talus types are ascribed to lower evaporation losses under stones due to both disruption of capillarity by the coarse particles which prevented water flow to the talus surface and to their efficient reduction of maximum temperatures an irrigation experiment was conducted at 2110 m on a steep talus on the chaos crags from july 18 to aug 2 1993 four 100 75 cm plots with the same surface types than at lassen received 22 5 mm water moisture content was then periodically sampled watering produced similar water distributions among soil depths and talus types to those in lassen evaporation occurred quickly in bare soils due to high air and soil temperatures the sand surface was already dry 2 days after watering but stone covered plots remained moist until day 15 when soils under blocks still retained 77 97 of the water content percent by weight at the start of the test

late quaternary paleoclimate of western alaska inferred from fossil chironomids and its relation to vegetation histories abstract fossil chironomidae assemblages with a few chaoboridae and ceratopogonidae from zagoskin and burial lakes in western alaska provide quantitative reconstructions of mean july air temperatures for periods of the late middle wisconsin 39 000 34 000 cal yr b p to the present inferred temperatures are compared with previously analyzed pollen data from each site summarized here by indirect ordination paleotemperature trends reveal substantial differences in the timing of climatic warming following the late wisconsin at each site although chronological uncertainty exists zagoskin lake shows early warming beginning at about 21 000 cal yr b p whereas warming at burial lake begins 4000 years later summer climates during the last glacial maximum lgm were on average 3 5 c below the modern temperatures at each site major shifts in vegetation occurred from 19 000 to 10 000 cal yr b p at zagoskin lake and from 17 000 to 10 000 cal yr b p at burial lake vegetation shifts followed climatic warming when temperatures neared modern values both sites provide evidence of an early postglacial thermal maximum at 12 300 cal yr b p these chironomid records combined with other insect based climatic reconstructions from beringia indicate that during the lgm 1 greater continentality likely influenced regions adjacent to the bering land bridge and 2 summer climates were at times not dominated by severe cold

spatial distribution of surface rock fragments along catenas in semiarid arizona and nevada usa improved techniques for estimating soil erosion by water have shown that soil surface cover is a major component in the estimate of soil loss erosion prediction models require the user to input slope gradient and soil profile descriptions if equations expressing the relations between slope gradient soil profile rock fragment content and surface rock fragment cover were embedded in these models then direct user input could be reduced field measurements of slope gradient soil profile rock fragment content surface rock fragment cover and vegetation type and cover were made on 12 soil slope complexes on catenas in southeastern arizona usa correlation analysis showed that both slope gradient and soil profile rock fragment content were significantly p 0 01 correlated to surface rock fragment cover additional analysis indicated that the combined effects of slope gradient and soil profile rock content were better defined by a soil slope factor ssf two equations were developed to estimate surface rock fragment cover a logarithmic relation using slope gradient as the independent variable and a hyperbolic equation using the ssf as the independent variable these equations were used to estimate surface rock fragment cover from a soil slope complex in southern nevada the ssfrfc equation gave better estimates of the measured surface rock fragment cover these relations developed for catenas in southeastern arizona may be site specific but they do show that a relation exists for this semiarid area and suggest that similar relations may exist in areas with similar geology and climate such as parts of africa asia australia and south america development of simple relations describing important erosion processes will improve erosion estimates while simultaneously decreasing time and costs associated with using erosion prediction models