modelling glacial climatic millennial scale variability related to changes in the atlantic meridional overturning circulation a review abstract since the discovery of glacial abrupt variability in greenland and the north atlantic about two decades ago its modelling remains a conceptual and technical challenge while the global climatic signature of heinrich events can reasonably be ascribed to the fresh water discharge related to the massive iceberg armadas released by the laurentide ice sheet in the north atlantic the existence of such a triggering mechanism is elusive as far as dansgaard oeschger type variability is concerned even if other mechanisms have been proposed the majority of modelling attempts to better understand glacial climate variability has assumed it to be linked to abrupt variations in the atlantic meridional overturning circulation amoc in this review we introduce the rationale behind this approach i e the possible existence of several deep ocean circulation equilibria associated with distinct climate signatures we then review the published fresh water hosing experiments and the mechanisms at work to explain the climate differences related to the different amoc states most of these works have been performed under pre industrial boundary conditions the few hosing experiments run under glacial conditions show that the sensitivity of the climate system to fresh water hosing is very dependent on the background climate state in order to rigourously compare several types of experiments equilibrium runs vs transient runs with pre industrial vs glacial boundary conditions we present experiments especially run for this review with two climate models of intermediate complexity uvic and loveclim although there are similarities between the responses simulated by these models there are also many differences which would benefit being compared to reconstructions such as those presented in this special issue however a strict comparison will require to consider boundary conditions as realistic as possible for marine isotopic stage 3 modelling glacial variability to compare model results with paleoclimatic data remains a big challenge

atlantic meridional overturning circulation during the last glacial maximum the circulation of the deep atlantic ocean during the height of the last ice age appears to have been quite different from today we review observations implying that atlantic meridional overturning circulation during the last glacial maximum was neither extremely sluggish nor an enhanced version of present day circulation the distribution of the decay products of uranium in sediments is consistent with a residence time for deep waters in the atlantic only slightly greater than today however evidence from multiple water mass tracers supports a different distribution of deep water properties including density which is dynamically linked to circulation

the deglacial evolution of north atlantic deep convection deepwater formation in the north atlantic by open ocean convection is an essential component of the overturning circulation of the atlantic ocean which helps regulate global climate we use water column radiocarbon reconstructions to examine changes in northeast atlantic convection since the last glacial maximum during cold intervals we infer a reduction in open ocean convection and an associated incursion of an extremely radiocarbon 14c depleted water mass interpreted to be antarctic intermediate water comparing the timing of deep convection changes in the northeast and northwest atlantic we suggest that despite a strong control on greenland temperature by northeast atlantic convection reduced open ocean convection in both the northwest and northeast atlantic is necessary to account for contemporaneous perturbations in atmospheric circulation

effect of stone content on water flow velocity over loess slope non frozen soil abstract stony soils are commonly found worldwide and are considerably studied for their hydrological characteristics and effect on soil erosion water flow velocity is an important parameter in understanding the effect of stone content on hydrodynamics and soil erosion in this study laboratory experiments were used to measure rill flow velocity by using electrolyte tracer method under different hydraulic conditions flow rates of 1 2 4 and 8 l min slope gradients of 5 10 15 and 20 and stone mass contents amounting to 0 10 20 and 50 nine sensors which were 1 m apart along the 8 m long rill were used to measure flow velocity by tracing solute transport measured flow velocity increased with slope gradient and flow rate the highest increase in flow velocity was measured from 15 to 20 which were also affected by flow rate effects of discharge rate on flow velocity presented the largest difference when flow rate increased from 2 l min to 8 l min at slope gradients higher than 5 the effects of different factors were quantified by a regression model with high accuracy of 0 99 maximum flow velocity of water was predicted at 15 23 of stone content flow velocity increased with 0 15 23 of stone content but decreased at higher values this study aims at further understanding the hydrodynamics of soil erosion and sediment transport behaviors in hillslopes with different stone contents to obtain information for quantifying soil erosion on stony slopes

warming of surface waters in the mid latitude north atlantic during heinrich events 1 during the six heinrich events of the last 70 kyr episodic calving from the circum atlantic ice sheets released large numbers of icebergs into the north atlantic these icebergs and associated meltwater flux are hypothesized to have led to a shutdown of atlantic meridional overturning circulation and severe cooling in large parts of the northern hemisphere however due to the limited availability of high resolution records the magnitude of sea surface temperature sst changes related to the impact of heinrich events on the midlatitude north atlantic is poorly constrained here we present a record of u37k based ssts derived from sediments of integrated ocean drilling project site u1313 located at the southern end of the ice rafted debris ird belt in the midlatitude north atlantic 41 n we demonstrate that all six heinrich events are associated with a rapid warming of surface waters by 2 4 c in a few thousand years the presence of ird leaves no doubt about the simultaneous timing and correlation between rapid surface water warming and heinrich events we argue that this warming in the midlatitude north atlantic is related to a northward expansion of the subtropical gyre during heinrich events as a wide range of studies demonstrated that in the central ird belt heinrich events are associated with low ssts these results thus identify an antiphased seesaw pattern in ssts during heinrich events between the midlatitude warm and northern north atlantic cold this highlights the complex response of surface water characteristics in the north atlantic to heinrich events that is poorly reproduced by freshwater hosing experiments and challenges the widely accepted view that within the ird belt of the north atlantic heinrich events coincide with periods of low ssts

flume experiments for determining rill hydraulic characteristic erosion and rill patterns a series of flume experiments were conducted to understand shallow water hydraulics erosion in rills as well as morphological patterns of a rill as effected by rill bed slopes and inflow rates the soil used was cecil soil a sandy loamy soil four flow rates 3 8 7 6 11 4and 15 2 l min and 4 slopes 1 3 5 and 7 were adopted in the experiments the velocities rill widths and sediment concentrations at the outlet were recorded and analyzed with multivariable regression method as functions of slopes inflow rate and or their interactive terms rill widths changing along the rill with certain periodical patterns were visulally observed a mathematical model was advanced to describe these changing patterns of rill width sampling length for transport capacity was determined with the analysis of both sediment yields and width patterns

comparison of rill flow velocity regimes between developing and stationary rills abstract flow velocity is fundamental in calculating related parameters of physical soil erosion models it has been well known that rill flow velocity varies with developing rill form which complicates and impedes the development of soil erosion models in filed rainfall erosion frequently occurs with pre existing rills not damaged by tillage practices however the rill flow velocity in this case has received little attention in this study we investigated rill flow velocity regimes for both developing and stationary rills using 5 m length plots in the laboratory the experiments included two consecutive rainfalls which had similar runoff rate the first rainfall had an intensity of 90 mm h 1 which generated well developed rills the second had an intensity of 60 mm h 1 and did not damage the rills formed by the first rainfall the results show that for a developing rill rill flow velocity is higher in the lower slope than that in the upper slope and rill flow velocity in the lower slope fluctuates much more over time as a result of the variation of rill morphology following rill development with rill development the rill flow velocity of the lower slope decreased responding to the stabilizing rill channel and exhibited a similar trend to that in upper slope for a stationary rill the rill flow velocities at both sections varied little over time demonstrating that rill flow velocity is primarily influenced by rill morphology hence the results suggested that the strength of fluctuation in rill flow velocity could be used to characterize the instantaneous intensity of soil erosion and active level of rill development the channel of the stationary rill simply acted as transport pathways of sediment supplied by inter rill erosion the physical models of soil erosion should take into account the micro topography on land surface related to the antecedently formed rills

muted change in atlantic overturning circulation over some glacial aged heinrich events several periods of massive iceberg discharge into the north atlantic and widespread cooling marked the last glacial period reconstructions of northward flow along the florida margin suggest that not all cold events were associated with a change in the strength of the atlantic meridional overturning circulation

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

research paperseffect of stone content on water flow velocity over loess slope frozen soil soils in high altitude or latitude regions are commonly rich in stone fragments which are frequently frozen the hydrodynamics of water flow over frozen stony slopes must be investigated to understand soil erosion and sediment transportation the objective of this laboratory experiments was to measure water flow velocity over frozen slopes with different stone contents by using electrolyte trace method the experiments were performed under slope gradients of 5 10 15 and 20 flow discharge rates of 1 2 4 and 8 l min and stone contents of 0 10 20 and 50 on mass basis nine equidistant sensors were used to measure flow velocity along flume from the top of the slope results indicated that stone content significantly affected flow velocity under increasing slope gradient the increase in stone content rapidly reduced the flow velocity the flow velocities over frozen slopes were 1 21 to 1 30 times of those over non frozen slopes under different slope gradients and flow rates when the stone content increased from 0 to 20 proportions gradually decreased from 52 to 25 and 13 additionally flow velocities over frozen and non frozen soil slopes became gradually similar with increasing stone content this study will help elucidate the hydrodynamics soil erosion and sediment transport behaviors of frozen or partially unfrozen hillslopes with different stone contents

testing the utility of paleonutrient proxies cd ca and zn ca in benthic foraminifera from thermocline waters 1 reconstruction of oceanic nutrient concentrations in the past provides information about nutrient cycling and physical circulation and the role these processes have played in past climate changes the cd ca and zn ca of benthic foraminifera have been used successfully to reconstruct past deep ocean nutrient concentrations in this study we test the ability of benthic foraminiferal cd ca and zn ca to detect changes in thermocline nutrient concentrations using a set of 31 multicores collected in the florida straits multicore sites span depths of 173 751 m estimated seawater cd concentrations of 0 02 0 42 nmol kg 1 and estimated seawater zn concentrations of 0 3 3 1 nmol kg 1 cd ca in several taxa of benthic foraminifera captures the regional differences and general shape of the nutricline on either side of the florida straits indicating that it is capable of resolving small changes in upper ocean nutrient concentrations in the past we estimate that the upper ocean partition coefficient for calcitic cd ca may be slightly higher than the established value low seawater zn concentrations combined with low partition coefficients and slight laboratory contamination severely complicated the evaluation of benthic foraminiferal zn ca however at least one species c pachyderma incorporates zn with a relatively high partition coefficient 22 minimizing these complications c pachyderma zn ca reflects the regional differences and general shape of the nutricline on either side of the florida straits and demonstrates potential for thermocline paleoceanography

a method for measuring erosive flow velocity with simulated rill abstract the water flow velocity along an eroding rill is of interests for understanding rill erosion hydrodynamics soil erosion makes the measurement of flow velocity highly variable in this paper a new method is suggested to simulate rills so as to make controllable and efficient measurements of erosive velocity of rill flow a series of comparative flume experiments were conducted to verify the method by measuring the shallow water flow velocity along both the simulated and real rills by using a computerized electrolyte tracer method the experiments involved three flow rates 12 24 and 48 l min and three slope gradients 5 10 and 15 five sensors were used to trace the solute transport processes at 30 60 90 120 and 150 cm from the location where the salt solute was injected into the water flow flow velocities under simulated rill and real conditions were computed by fitting the measured solute transport processes with its analytic solution the results showed that under different flow rates and slope gradients velocities along the simulated rill agreed very well with those along the real rill this demonstrates that the simulated rill well simulates the real rill this method will help further study of the hydrodynamics in eroding rill

velocity of water flow along saturated loess slopes under erosion effects abstract rainfall or snow melted water recharge easily saturates loose top soils with a less permeable underlayer such as cultivated soil slope and partially thawed top soil layer and thus may influence the velocity of water flow this study suggested a methodology and device system to supply water from the bottom soil layer at the different locations of slopes water seeps into and saturates the soil when the water level is controlled at the same height of the soil surface the structures and functions of the device the components and the operational principles are described in detail a series of laboratory experiments were conducted under slope gradients of 5 10 15 and 20 and flow rates of 2 4 and 8 l min 1 to measure the water flow velocities over eroding and non eroded loess soil slopes under saturated conditions by using electrolyte tracing results showed that flow velocities on saturated slopes were 17 to 88 greater than those on non saturated slopes flow velocity increased rapidly under high flow rates and slope gradients saturation conditions were suitable in maintaining smooth rill geomorphology and causing fast water flow the saturated soil slope had a lubricant effect on the soil surface to reduce the frictional force resulting in high flow velocity the flow velocities of eroding rills under different slope gradients and flow rates were approximately 14 to 33 lower than those of non eroded rills on saturated loess slopes compared with that on a saturated loess slope the eroding rill on a non saturated loess slope can produce headcuts to reduce the flow velocity this study helps understand the hydrodynamics of soil erosion and sediment transportation of saturated soil slopes

evidence from the florida straits for younger dryas ocean circulation changes 1 the waters passing through the florida straits today reflect both the western portion of the wind driven subtropical gyre and the northward flow of the upper waters which cross the equator compensating north atlantic deep water export as part of the large scale atlantic meridional overturning circulation it has been postulated from various lines of evidence that the overturning circulation was weaker during the younger dryas cold event of the last deglaciation we show here that the contrast in the oxygen isotopic composition of benthic foraminiferal tests across the florida current is reduced during the younger dryas this most likely reflects a decrease in the density gradient across the channel and a decrease in the vertical shear of the florida current this reduced shear is consistent with the postulated reduction in the atlantic meridional overturning circulation we find that the onset of this change in density structure and flow at the start of the younger dryas is very abrupt occurring in less than 70 years

deglacial variability of antarctic intermediate water penetration into the north atlantic from authigenic neodymium isotope ratios 1 understanding intermediate water circulation across the last deglacial is critical in assessing the role of oceanic heat transport associated with atlantic meridional overturning circulation variability across abrupt climate events however the links between intermediate water circulation and abrupt climate events such as the younger dryas yd and heinrich event 1 h1 are still poorly constrained here we reconstruct changes in antarctic intermediate water aaiw circulation in the subtropical north atlantic over the past 25 kyr by measuring authigenic neodymium isotope ratios in sediments from two sites in the florida straits our authigenic nd isotope records suggest that there was little to no penetration of aaiw into the subtropical north atlantic during the yd and h1 variations in the northward penetration of aaiw into the florida straits documented in our authigenic nd isotope record are synchronous with multiple climatic archives including the greenland ice core 18o record the cariaco basin atmosphere 14c reconstruction the bermuda rise sedimentary pa th record and nutrient and stable isotope data from the tropical north atlantic the synchroneity of our nd records with multiple climatic archives suggests a tight connection between aaiw variability and high latitude north atlantic climate change

field measurement of the velocity of overland flow using dye tracing a new method of computing the mean velocity of overland flow using dye tracing is proposed in which a specified cross section is divided into zones of relatively uniform flow characteristics termed partial sections the mean surface velocity for each partial section is determined by timing the passage of injected dye and this figure is multiplied by 0 67 0 70 or 0 80 depending on whether the flow is laminar transitional or turbulent to give mean velocity the mean velocity for the entire cross section is calculated by multiplying the mean velocity of each partial section by its cross sectional area summing the products for all the partial sections and dividing by the total area of the cross section a field test shows that mean velocity derived in this manner differs from mean velocity derived by the discharge method i e by dividing discharge measured volumetrically by cross sectional area by an average of only 7 07 per cent thus the partial section technique appears to provide a reliable method of estimating mean velocity of overland flow

a geostrophic transport estimate for the florida current from the oxygen isotope composition of benthic foraminifera we present a new method for the quantitative reconstruction of upper ocean flows for during times in the past for the warm t 5 c surface ocean density can be accurately reconstructed from calcite precipitated in equilibrium with seawater as both of these properties increase with decreasing temperature and increasing salinity vertical density profiles can be reconstructed from the oxygen isotopic composition of benthic foraminifera the net volume transport between two vertical density profiles can be calculated using the geostrophic method using benthic foraminifera from surface sediment samples from either side of the florida straits florida keys and little bahama bank we reconstruct two vertical density profiles and calculate a volume transport of 32 sv using this method this agrees well with estimates from physical oceanographic methods of 30 32 sv for the mean annual volume transport we explore the sensitivity of this technique to various changes in the relationship between temperature and salinity as well as salinity and the oxygen isotopic composition of seawater

the study of detachment and deposition on a hillslope using a magnetic tracer soil erosion by water involves the processes of detachment transport and deposition of soil materials by the erosive forces of raindrops and surface flow of water the redistribution of sediment within a field sized area is important in estimating the effect of erosion and deposition on productivity in helping the conservation planner to target efforts to reduce erosion and to evaluate erosion models the objective of this study was to use a magnetic tracer with size and density similar to soil aggregates to study detachment and deposition on a hillslope two interconnected plots were established on a hillslope two rainfall intensities 35 and 70 mm h 1 combined with two different inflow rates 4 and 10 l min 1 were applied to the upper of the two plots no rain or water was applied to the lower plot which was used to study the deposition of eroded sediments from the upper plot a 5 concentration of magnetic tracer was placed in the upper plot and mixed to depth of 3 cm from this initial condition areas of tracer detachment and deposition were identified using a magnetic sensor areas of detachment were associated with a decrease in magnetic signal while areas of deposition were associated with an increase in the magnetic signal in the lower plot deposition of tracer correlated well with the magnetic susceptibility readings results indicated that the tracer was effective for identifying areas of net detachment and deposition however the tracer to soil ratio did not remain constant for all treatments for this reason a wider range of sizes and densities of the tracer should be tested if the method is to be useful to quantify erosion rates d 2002 elsevier science b v all rights reserved

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

glacial interglacial circulation changes inferred from 231pa 230th sedimentary record in the north atlantic region 1 studies from the subtropical western and eastern atlantic ocean using the 231pa 230th ratio as a kinematic proxy for deep water circulation provided compelling evidence for a strong link between climate and the rate of meridional overturning circulation moc over the last deglaciation in this study we present a compilation of existing and new sedimentary 231pa 230th records from north atlantic cores between 1710 and 4550 m water depth comparing sedimentary 231pa 230th from different depths provides new insights into the evolution of the geometry and rate of deep water formation in the north atlantic during the last 20 000 years the 231pa 230th ratio measured in upper holocene sediments indicates slow water renewal above 2500 m and rapid flushing below consistent with our understanding of modern circulation in contrast during the last glacial maximum lgm glacial north atlantic intermediate water gnaiw drove a rapid overturning circulation to a depth of at least 3000 m depth below 4000 m water renewal was much slower than today at the onset of heinrich event 1 transport by the overturning circulation declined at all depths gnaiw shoaled above 3000 m and significantly weakened but did not totally shut down during the bolling allerod ba that followed water renewal rates further decreased above 2000 m but increased below our results suggest for the first time that ocean circulation during that period was quite distinct from the modern circulation mode with a comparatively higher renewal rate above 3000 m and a lower renewal rate below in a pattern similar to the lgm but less accentuated moc during the younger dryas appears very similar to ba down to 2000 m and slightly slower below

using a thermal tracer to estimate overland and rill flow velocities flow velocity is a basic hydraulic property of surface flows and its precise calculation is necessary for process based hydrological models such as soil erosion and rill development models as well as for modelling sediment and solute transport by runoff this study presents a technique based on infrared thermography to visualize very shallow flows and allow a quantitative measurement of overland flow and rill flow velocities laboratory experiments were conducted to compare the traditional dye tracer technique with this new thermal tracer technique by injecting a combined tracer heated dye into shallow flowing surface water the leading edge tracer velocities estimated by means of infrared video and by the usual real imaging video were compared the results show that thermal tracers can be used to estimate both overland and rill flow velocities since measurements are similar to those resulting from using dye tracers the main advantage of using thermography was the higher visibility of the leading edge of the injected tracer compared with the real image videos copyright 2013 john wiley sons ltd

an improved method for shallow water flow velocity measurement with practical electrolyte inputs summary the measurement of shallow water flow velocity is of interest to hill slope hydrology and soil erosion mechanics lei et al lei t xia w zhao j 2005 method for measuring velocity of shallow water flow for soil erosion with an electrolyte tracer journal of hydrology 301 139 145 proposed an electrolyte pulse method for the purpose but found that the velocity measured at short distances from the salt injector was not as well estimated as those further away from the injector though it is desirable to estimate velocity at short distances for the purpose of portable device development in this study the system was improved over the previous development an additional sensor was added at the salt injection location to register the input signal as the actual boundary condition function instead of using the pulse assumption two function forms a normal distribution function normal model and a sine function sine model were suggested to approximate the measured boundary conditions these two determined boundary models were used to fit the experimentally obtained data using the least square method to determine the model parameters of the boundary conditions the determined normal model and the sine model were both used to solve the transport processes as the convolution integrals of the pulse response and the actually determined boundary functions so as to determine the shallow water flow velocity laboratory experiments were conducted to get data to verify the proposed methods and computational procedures the experiment device included a flume 4 m long and 15 cm wide a solute injector a data logger for control and data acquisition and a computer with specially designed software for data measurement and velocity estimation the experiments involved three flow rates 12 24 and 48 l min 1 and three slope gradients 4 8 and 12 six sensors were used to measure the solute transport processes at 5 30 60 90 120 and 150 cm from the location where the salt solute was injected into the water flow the solutions of both the normal model and sine model fitted the measured data very well for all the experimental conditions the velocities at different distances from the salt solution injector and under different flow rates and slope gradients as computed by the two models were almost identical which indicated the feasibility of the method and the computational procedures as well as the two suggested models for velocity estimation the velocity values estimated by the normal and sine models agreed also with those measured by using the floating objects and the volumetric method these demonstrated the rationality of the improved methods for shallow water flow velocity measurement the results will be useful to design a practical system for the measurement of shallow water flow velocity

correction factors in the determination of mean velocity of overland flow the velocity of overland flow has been conventionally measured using tracers but it is difficult to measure the mean flow velocity directly because the centroid of the tracer plume is not easily identified consequently previous investigators have measured the velocity of the leading edge of the plume and multiplied it by a correction factor to obtain an estimate of mean velocity an alternative method is to measure the velocity of the peak concentration in the tracer plume and multiply this velocity by another correction factor to estimate mean velocity to investigate the controls of and and develop predictive models for these correction factors 40 experiments were performed in a flume with a mobile sand bed multiple regression analyses reveal that both and vary inversely with slope and directly with reynolds number the derived regression equations may be used to calculate the mean velocity of other shallow overland flows at least within the range of slope and reynolds number for which the equations were developed in the experiments slope ranged from 2 7 to 10 and reynolds number from 1900 to 12 600

precise multielemental ratios in small foraminiferal samples determined by sector field icp ms inductively coupled plasma mass spectrometry icp ms holds two main advantages over other techniques for the measurement of foraminiferal elemental ratios 1 numerous trace metals may be precisely and simultaneously measured and 2 smaller samples may theoretically be used methods are presented for the precise determination of mg ca sr ca cd ca zn ca li ca u ca mn ca and fe ca by sector field icp ms analytical precision is largely independent of sample size over the range of 5 to 125 g caco3 eliminating the need for narrow target dilutions long term 1 precisions are as follows mg ca 0 54 sr ca 0 57 cd ca 1 8 zn ca 3 2 li ca 0 88 u ca 1 9 mn ca 0 97 and fe ca 1 4 for mg ca actual foraminiferal samples appear to give reliable results below 10 g caco3 postcleaning mass

timing of deglacial amoc variability from a high resolution seawater cadmium reconstruction a new high resolution record of benthic seawater cd cdw was generated from a florida straits sediment core at 546 m water depth the record provides additional evidence for cdw below modern values in this channel during the younger dryas and heinrich stadial 1 climatological periods associated with ice sheet melt lower cdw values are interpreted as a weakening of the atlantic meridional overturning circulation amoc reflecting a decreased northward transport of southern sourced higher nutrient intermediate waters by the surface return flow of amoc comparison of this new cdw record with previously published neodymium isotope and 18o records from the same core shows synchronous transitions further illustrating the connection between cdw levels and amoc strength in the florida straits an increase in cdw near 16 ka bolsters existing evidence for a resumption of upper branch amoc strength approximately midway through heinrich stadial 1

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

method for measuring velocity of shallow water flow for soil erosion with an electrolyte tracer abstract measurement of the velocity of shallow water flow on a hill slope is of great importance in soil erosion studies electrolyte tracers have been tried to estimate mean velocity of water flow with the velocity of the leading edge of the solute propagation multiplied with a somewhat arbitrary correction factor in this study an analytical solution of solute tracer transport was formulated to serve as the mathematical foundation for measuring shallow water flow velocity to estimate the flow velocity a procedure was advanced in the procedures the analytical solution is fitted with the measured propagation curve and given the the least square estimation of velocity a detailed mathematical description is outlined for this purpose experimental results are given to show the feasibility of the method including the analytical solution and the estimation procedures this study provides the theoretical foundation for measuring the velocity of shallow water flow and for studies of overland solute transport

meteorites evidence for the interrelationships of materials in the solar system of 4 55 ga ago abstract members of the five major chemical groups of chondrites are samples of rocks which have remained essentially unaltered for 4 55 ga the ordinary chondrites are often regarded as primitive in both chemical and temporal senses however the presence of noritic and anorthositic inclusions in a few ordinary chondrites of great age indicates that at least some unequilibrated ordinary chondrites are not primitive in a temporal sense the eucrites are differentiated basaltic rock types which have ages indistinguishable from those of the oldest chondrites members of three groups of iron meteorites too appear to be equally old it is concluded that the period of formation of ordinary chondrites continued until after differentiation had occurred within some planetary bodies such early melting may have been caused by the decay of 26 al some of the differentiated materials were probably incorporated as plastic rocks liquid chondrules and solid clasts into the accreting parent bodies of the ordinary chondrites

sensitivity of the atlantic intertropical convergence zone to last glacial maximum boundary conditions 1 recent paleoproxy records suggest that the mean latitude of the atlantic intertropical convergence zone itcz varied synchronously with north atlantic climate over a range of timescales throughout the holocene and last glacial maximum we show that the present day meridional mode of atmosphere ocean variability in the tropical atlantic is a potentially useful model for understanding these paleoclimate changes the tropical atlantic in a coupled atmospheric general circulation and slab ocean model responds to last glacial maximum conditions with a southward displacement of the itcz this response arises primarily through the land ice sheet that forces increased north atlantic trades analogous to the forcing on the present day meridional mode changes to sea ice coverage and to ocean heat transport associated with a weakened atlantic thermohaline circulation also cause a meridional mode response though through different mechanisms our results highlight the potential for tropical atlantic paleoclimate to be driven from the high latitude influences in particular land ice on glacial interglacial timescales

comparison of rill flow velocity over frozen and thawed slopes with electrolyte tracer method summary freeze thaw erosion is the primary soil water erosion form in high altitude and or high latitude regions the water flow velocity along an eroding rill over frozen and thawed slopes is vital to understanding of rill erosion hydrodynamics this study experimentally measured rill flow velocity over frozen and thawed slopes using electrolyte trace method under pulse boundary model the experiments used three flow rates of 1 2 and 4 l min 1 three slope gradients of 5 10 and 15 the temperature of the rill flow water was supplied at 0 c as controlled with ice water mixture seven sensors were used to measure flow velocity by tracing the solute transport process at 10 110 210 310 410 510 and 610 cm distances from the electrolyte injection position the measured velocity became steady at a distance of about 3 m from the electrolyte injection location where the effect of the pulse boundary condition on the analytic solution to the partial differential equation becomes negligible results showed that flow velocity increased with slope gradient and flow rate on frozen slopes a significant effect was observed on the steepest slope or at the highest flow rate over the thawed slope which changed slightly on the gentle slopes and low flow rates flow velocity was about 25 30 and 40 higher on the frozen soil than on the thawed slope at 5 10 and 15 slopes and about 30 higher over the frozen slope at all flow rates this study demonstrates that water over a frozen slope flows much faster than over a thawed slope this study helps in the study and further understanding of the hydrodynamics of soil erosion and sediment transport behaviors of frozen and thawed slopes

the influence of air and sea exchange on the carbon isotope distribution in the sea we explore here the influence of the temperature dependence of isotope fractionation between atmospheric co2and ocean co2 on the distribution of carbon isotopes in the ocean this is accomplished by an analysis of departures from the expected redfield tie between po4 and 13c we find that for the surface ocean the temperature influence largely compensates for the biologic influence in the deep ocean the temperature influence imprinted at the sites of deepwater formation reduces somewhat the biologically induced difference between the carbon isotope ratios for deep waters produced in the northern atlantic and in the antarctic these same features are reproduced in the hamburg ocean model in order to assess the impact of changes in the ratio of ocean mixing rate to wind speed we have made a model run in which co2 exchange rates between air and sea were everywhere doubled as expected the influence of the thermodynamic effect on the oceanic carbon isotope distribution is magnified

rill hydraulics on a semiarid hillslope southern arizona seventy field experiments were conducted in seven rills located on a semiarid rangeland hillslope underlain by gravelly soils at walnut gulch arizona the rills which are characterized by wide shallow cross sections and gravel covered beds have mean at a station hydraulic geometry exponents of b 0 33 f 0 34 and m 0 33 although the differences between these values and typical values of b 0 30 f 0 40 and m 0 30 for cropland rills are not statistically significant they are thought to be real as cropland rills often have more rectangular cross sections and steeper sides than the rangeland rills under study for rills formed in silty loamy soils govers developed an empirical relation between mean flow velocity and discharge emphasizing the generality of this relation he suggested that it may be used as a simple means of routing runoff through rills he also noted that this relation appeared to be unaffected by either slope or soil materials the present data represent rills underlain by coarser and somewhat more varied gravel rich soils these data do not conform to govers relation and a multiple regression analysis reveals that slope and soil materials either directly or indirectly through bed roughness exert almost as much influence on flow velocity as does discharge three alternative methods are developed for predicting flow velocity in the rills under study all three methods give good results with the largest root mean square deviation being 3 115 cm s 1

rill erosion and morphological evolution a simulation model a mathematical model is advanced to simulate dynamically and spatially varied shallow water flow and soil detachment transport and deposition in rills the model mimics the dynamic process of rill evolution including variable rates of sediment redistribution along the bed and changes in local bed morphology the sediment source term in the model uses a point scale probabilistic relationship based on turbulent flow mechanics and a recently developed sediment transport relationship for rills based on stream power the interdependent feedback loops between channel bed morphology local flow hydraulics and local scour and deposition within the framework of the full hydrodynamic equations with inertial terms constitute a mathematical model with the capacity to represent spatial variability and temporal evolution of the rill finite elements were applied to numerically solve the hydrodynamic and sediment continuity equations a series of laboratory flume experiments were performed to evaluate the model initial bed slopes were 3 5 and 7 with step increases of water inflow rates of 7 6 11 4 and 15 2 l min 1 the soil material used in the flume was a kaolinitic sandy clay loam the rill model equations were solved for increasingly complex cases of spatial and temporal variabilities the model followed measured patterns of morphological changes as the rill evolved which suggests that the feedback loops in the model between erosion bed morphological changes and hydraulics were adequate to capture the essence of rill evolution

effect of plant basal cover on velocity of shallow overland flow abstract accurate estimation of mean flow velocity is imperative for the prediction of hydrographs and sediment yield the chezy and manning equations are the most widely used for calculating flow velocity in runoff and erosion models the suitability of both equations for overland flow on bare land has been evaluated and conflicting results were obtained in previous studies the suitability of these equations for overland flow on a planted slope requires further investigation the purposes of this study were to evaluate the suitability of the chezy and manning equations under planted conditions and evaluate quantitative effect of vegetation on manning s n and then on flow velocity flume experiments were conducted at the plant basal cover ranging from 0 to 30 slope gradient varying from8 8 to 25 9 and flow discharge ranging from 0 5 to 2 0 10 3 m3 s 1 the flow depth and flow velocity were measured the coefficient of determination r2 and nash sutcliffe model efficiency nse were used to compare the performance accuracy of both equations the results showed that both equations provided a bad accuracy when plant basal cover was greater than 15 on a planted slope the nse values were negative for manning equation and close to 0 for chezy equation it indicates that manning and chezy equations were not suitable for the planted slope manning s n decreased with the flow depth for 0 plant basal cover and increased with flow depth for plant basal cover greater than 1 25 thus a new equation for calculating manning s n was developed based on plant basal cover and flow depth and was used in the manning equation the new flow velocity equation including plant basal cover provided satisfactory accuracy with a nse of 0 995 the results indicate that the manning s n was significantly affected by flow depth and plant basal cover

velocity measurement of water flow within gravel layer with electrolyte tracer method under virtual boundary condition summary the measurement velocity of water flow along gravel rich hill slope is of great interest for hydrological simulation and prediction in alpine watersheds the alpine terrain is often covered by rock debris of different origin size and type here summarized as gravel for the sake of simplicity to do this water flow velocity within a gravel layer was measured using the electrolyte tracer method under virtual boundary conditions an improved method over pulse electrolyte tracer method models employing two virtual boundary conditions a sine function and a normal distribution function are suggested as preferable for determining flow velocity by simulating the transport processes of electrolytes along a gravel covered flume at different flow rates 3 6 and 12 l min 1 and slope gradients 4 8 and 12 flow velocities as well as determination coefficients and mean square errors were calculated at five measurement locations 0 3 0 6 0 9 1 2 and 1 5 m using model simulation the feasibility and accuracy of velocity measurements for water flow within gravel layers are justified to the extent that the two models fit well with the experimental data the velocity values predicted by the two models are almost identical and finally the relations between velocity and discharge and between velocity and slope gradient are rationally explained the estimated velocity results also agree well with those previously measured by commonly used methods such as the pulse boundary method and the conventional dye tracer method our results show that the virtual boundary conditions method when used to measure water flow velocity within a gravel layer predicts the flow velocity more rationally than the pulse boundary and dye tracer methods and with greater precision this study suggests that this method is not only readily applicable for obtaining water flow velocity measurements within gravel layers but also for understanding hydrodynamics in typical watershed

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

comparison of thermal salt and dye tracing to estimate shallow flow velocities novel triple tracer approach abstract the accurate measurement of shallow flow velocities is crucial to understand and model the dynamics of sediment and pollutant transport by overland flow in this study a novel triple tracer approach was used to re evaluate and compare the traditional and well established dye and salt tracer techniques with the more recent thermal tracer technique in estimating shallow flow velocities for this purpose a triple tracer i e dyed salted heated water was used optical and infrared video cameras and an electrical conductivity sensor were used to detect the tracers in the flow leading edge and centroid velocities of the tracers were measured and the correction factors used to determine the actual mean flow velocities from tracer measured velocities were compared and investigated experiments were carried out for different flow discharges 32 1813 ml s 1 on smooth acrylic sand stones and synthetic grass bed surfaces with 0 8 4 4 and 13 2 slopes the results showed that thermal tracers can be used to estimate shallow flow velocities since the three techniques yielded very similar results without significant differences between them the main advantages of the thermal tracer were that the movement of the tracer along the measuring section was more easily visible than it was in the real image videos and that it was possible to measure space averaged flow velocities instead of only one velocity value with the salt tracer the correction factors used to determine the actual mean velocity of overland flow varied directly with reynolds and froude numbers flow velocity and slope and inversely with flow depth and bed roughness in shallow flows velocity estimation using tracers entails considerable uncertainty and caution must be taken with these measurements especially in field studies where these variables vary appreciably in space and time

decreased influence of antarctic intermediate water in the tropical atlantic during north atlantic cold events abstract antarctic intermediate water aaiw is a key player in the global ocean circulation contributing to the upper limb of the atlantic meridional overturning circulation amoc and influencing interhemispheric heat exchange and the distribution of salinity nutrients and carbon however the deglacial history of aaiw flow into the north atlantic is controversial here we present a multicore top neodymium isotope calibration which confirms the ability of unclean foraminifera to faithfully record bottom water neodymium isotopic composition e nd values in their authigenic coatings we then present the first foraminifera based reconstruction of e nd from three sediment cores retrieved from within modern aaiw in the western tropical north atlantic our records reveal similar glacial and interglacial contributions of aaiw and a pronounced decrease in the aaiw fraction during north atlantic deglacial cold episodes heinrich stadial 1 hs1 and younger dryas yd our results suggest two separate phases of reduced fraction of aaiw in the tropical atlantic during hs1 with a greater reduction during early hs1 if a reduction in aaiw fraction also reflects reduced amoc strength this finding may explain why in many regions there are two phases of hydrologic change within hs1 and why atmospheric co2 rose more rapidly during early than late hs1 our result suggesting less flow of aaiw into the atlantic during north atlantic cold events contrasts with evidence from the pacific where intermediate depth e nd records may indicate increased flow of aaiw into the pacific during the these same events antiphased e nd behavior between intermediate depths of the north atlantic and pacific implies that the flow of aaiw into atlantic and pacific seesawed during the last deglaciation

a detailed east asian monsoon history surrounding the mystery interval derived from three chinese speleothem records the mystery interval mi 17 5 14 5 ka was the first stage of the last deglaciation a key interval for understanding mechanisms of glacial interglacial cycles to elucidate possible causes of the mi here we present three high resolution precisely dated oxygen isotope records of stalagmites from qingtian and hulu caves in china reflecting changes in the east asian summer monsoon easm then based on well established chronologies using precise 230th dates and annual band counting results the two cave 18o profiles of 7 yr resolution match well at decadal timescales both of the two cave records document an abrupt weakening 2 of 18o rise within 20 yr in the easm at 16 1 ka coinciding with the transition of the two phased mi reconstructed from new mexico s lake estancia our results indicate that the maximum southward displacement of the intertropical convergence zone and associated southward shift of polar jet stream may generate this two phase feature of the mi during that time we also discover a linear relationship among decreasing easm intensity rising atmospheric co2 and weakening atlantic meridional overturning circulation between the mi and younger dryas episodes suggesting a strong coupling of atmospheric oceanic circulations in response to the millennial scale forcing which in turn regulates global climate changes and carbon cycles

developing a magnetic tracer to study soil erosion abstract soil erosion is commonly measured as the quantity of sediment leaving a plot or watershed the techniques for measuring soil erosion patterns and sediment redistribution within plots or watersheds by direct monitoring are very limited the objective of this study was to develop a direct and non intrusive tracer method to study the sources patterns and rates of erosion and deposition of sediments in erosion plots the magnetic tracer developed in this study consisted of polystyrene plastic beads embedded with a magnetic powder magnetite the magnetized beads with a mean weight diameter of 3 2 mm and particle density of about 1 2 g cm 3 were uniformly mixed with soil and tested in the laboratory using simulated rainfall and inflow studies to simulate the interrill and rill components of soil erosion respectively in the interrill and rill experiments the tracer was transported in the same proportion it was initially mixed with the soil given this fact a magnetometer which measures the soil s magnetic susceptibility could be used to identify areas of deposition or detachment the magnetic susceptibility would be increased or reduced depending on whether deposition or detachment occurs to simulate detachment and deposition a magnetometer was tested for different tracer concentrations and different thickness of soil containing the tracer the magnetometer promises to be a sensitive accurate and useful tool to study the spatial variation of soil erosion when magnetic tracers are used

deglacial variability in the surface return flow of the atlantic meridional overturning circulation 1 benthic foraminiferal cd ca from a florida current sediment core documents the history of the northward penetration of southern source waters within the surface return flow of the atlantic meridional overturning circulation amoc cd seawater estimates cdw indicate that intermediate depth southern source waters crossed the equator and contributed to the florida current during the bolling allerod warm period of the last deglaciation consistent with evidence of only a modest amoc reduction compared to today the cdwestimates also provide the first paleoceanographic evidence of a reduction in the influence of intermediate depth southern source waters within the florida current during the younger dryas a deglacial cold event characterized by a weak north atlantic amoc our results reveal a close correspondence between the northward penetration of intermediate depth southern source waters and the influence of north atlantic deep water suggesting a possible link between intermediate depth southern source waters and the strength of the atlantic amoc

rare earth element transport in the western north atlantic inferred from nd isotopic observations the isotopic composition of nd in the water column from several western north atlantic sites and formational areas for north atlantic deep water shows extensive vertical structure at all locations in regions where a thermocline is well developed large isotopic shifts 2 to 3 units are observed across the base of the thermocline regions without a thermocline are characterized by much more gradual shifts in isotopic composition with depth in general the data reveal an excellent correlation between the nd isotopic distribution in the western north atlantic water column and the distribution of water masses identified from temperature and salinity characteristics nadw as identified from t s properties is also characterized by a well defined isotopic composition having nd 0 13 5 0 5 this signature is associated with waters identified as nadw from high latitudes near formational areas in the labrador sea down to the equatorial region the isotopic signature of nadw would appear to be formed by a blend of more negative waters originating in the labrador sea nd 0 18 and more positive waters originating in the overflows from the norwegian and greenland seas nd 0 8 to 10 and is consistent with classical theories on the formation of nadw the isotopic signature of nadw is propagated southward to the equator where it is gradually being thinned out by mixing from above and below with more radiogenic nd associated with northward spreading antarctic intermediate and bottom waters the preservation of the isotopic signature of nadw over these large distances indicate that the ree undergo extensive lateral transport the isotopic composition of nd is largely conservative over the time scales of mixing within the atlantic in spite of the intrinsic nonconservative behavior of neodymium nd concentration gradients generally show surface waters to be depleted in nd relative to deep waters which must require vertical transport processes however isotopic differences in the water column preclude the local downward transport of ree from the surface into underlying deep waters as a simple explanation of the concentration gradient the apparent decoupling of ree in nadw from overlying local surface waters and the increasing concentration with depth provide a conflict with simple vertical transport mechanisms that is not yet resolved

hydrographic changes in the tropical and extratropical pacific during the last deglaciation fine scale paired mg ca 18o profiles globigerinoides ruber white sensu lato from the san lazaro basin slb at 25 n in the northeast pacific reveal a transition from a predominant presence of tropical subtropical waters during the last glacial termination t1 to an increasing influence of fresh and cold california current waters toward the holocene changing atmospheric circulation patterns over the northeast pacific in step with the demise of the northern hemisphere ice sheets and or with a shift from el nino to la nina like conditions toward the holocene are prime candidates to explain this water mass change 18osw ivc increases of 0 5 0 7 during the younger dryas yd and heinrich stadial 1 hs1 at the slb are observed in a number of 18osw ivc records from the tropical pacific more directly influenced by changes in the position of the intertropical convergence zone itcz conditioning by itcz migration of the tropical pacific ocean towards salinity increase during yd and hs1 and the subsequent advection of those water masses as far north as 25 n likely accounted for the reconstructed hydrographical changes at the slb a larger influence of tropical water masses as far north as 25 n plausibly contributed to changes in the atmospheric moisture transports to western north america and affected the regional hydrological cycle across t1 finally the fine scale resolution of our 18osw ivc record allows pinpointing a shift from relative salty to fresh surface conditions at 16 2 ka signaling that the two phase structure of hs1 is plausibly a ubiquitous feature of the northern tropical to extratropical ocean atmosphere dynamics