sand dune patterns on titan controlled by long term climate cycles linear sand dunes on equatorial titan are shaped by winds the morphologies of smaller dunes that have been reoriented with respect to the linear dune crests suggest that winds shift with long term orbitally driven climate cycles on titan

coherence between solar activity and the east asian winter monsoon variability in the past 8000 years from yangtze river derived mud in the east china sea ams 14 c dating and grain size analysis for core pc 6 located in the middle of a mud area on the inner shelf of the east china sea ecs were used to rebuild the holocene history of the east asian winter monsoon eawm the 7 5 m core recorded the history of environmental changes during the postglacial transgression the core s mud section the upper 450 cm has been formed mainly by suspended sediment delivered from the yangtze river mouth by the ecs winter coastal current ecswcc since 7 6 kyr bp using a mathematical method called grain size vs standard deviatiow we can divide the core pc 6 s grain size distribution into two populations at about 28 mu m the fine population 28 mu m is considered to be transported by the ecswcc as suspended loads content of the fine population changes little and represents a stable sedimentary environment in accord with the present situation thus variation of mean grain size from the fine population would reflect the strength of ecswcc which is mainly controlled by the east asian winter monsoon abrupt increasing mean grain size in the mud section is inferred to be transported by sudden strengthened ecswcc which was caused by the strengthened eawm thus the high resolution mean grain size variation might serve as a proxy for reconstruction of the eawm a good correlation between sunspot change and the mean grain size of suspended fine population suggests that one of the primary controls on centennial to decadal scale changes of the eawm in the past 8 ka is the variations of sun irradiance i e the eawm will increase in intensity when the number of sunspots decreases spectral analyses of the mean grain size time series of core pc 6 show statistically significant periodicities centering on 2463 1368 128 106 100 88 91 7678 and 70 72 years the eawm and the east asian summer monsoon easm agree with each other well on these cycles and the east asian monsoon eam and the indian monsoon also share in concurrent cycles in holocene which are in accord with the changes of the sun irradiance c 2005 elsevier b v all rights reserved

near bed mass flux profiles in aeolian sand transport high resolution measurements in a wind tunnel vertical profiles of the streamwise mass flux of blown sand in the near bed 17 mm region are analysed from high resolution measurements made using an optical sensor in a wind tunnel this analysis is complemented by detailed measurements of mass flux and mean velocity profiles throughout the boundary layer depth 0 17 m using passive chambered sand traps of small dimensions and armoured thermal anemometers respectively the data permit a preliminary analysis of the relations between the observed forms of the profiles of near bed fluid stress and horizontal mass flux within a carefully conditioned boundary layer profiles of mass flux density are found to be characterized by three regions of differing gradient with transitions at about 2 mm and 19 mm above the bed the exponential decay of mass flux with height is confirmed for elevations above 19 mm and when plotted as a function of u 2 g a parameter of mean vertical trajectory height in saltation the gradient of mass flux in this region scales with the wake corrected friction velocity u where u 0 30 m s 1 a separate near bed region of more intense transport below 19 mm is identified which carries 80 per cent of the total mass flux this region is evident in some previous field and wind tunnel data but not in profiles simulated by numerical models ventilated passive sand traps underestimate mass flux in this region by 37 per cent at slow or moderate wind speeds a third significant region below 2 mm is observed these regions are likely to be related to grain populations in successive saltation low energy ejections and intermittent bed contact respectively optical measurements reveal locally high grain concentrations at some elevations below 5 mm these heights scale with transport rate mass flux gradient and wind speed copyright 1999 john wiley sons ltd

barchan dune mobility in mauritania related to dune and interdune sand fluxes 1 we present a 1 year study of 50 dunes in a small field of barchan dunes in mauritania we documented the morphological evolution of the dunes and their migration rates and measured at 10 min intervals the interdune sand transport the wind strength and its direction for the same interval of time the dune heights h 0 range between 2 and 5 m and their celerity c is found to be well approximated by the standard migration law c q 0 h 0 with q 0 50 m 3 m yr from both the interdune sand flux and the migration rate of the dunes we were able to estimate the spatially averaged sand flux at the dune crest as well as the bulk sand flux associated with the mass of sand transported by the dune we found that the sand flux at the crest was about 3 times greater than the interdune mass transport rate whereas the bulk sand flux was surprisingly of the same order as the interdune flux moreover we analyzed carefully the interdune sand transport data which can be well described by the sorensen law the cumulative mass of sand transported during moderate wind events within 1 year was much greater than that transported during strong wind events

multi spatial analysis of aeolian dune field patterns abstract aeolian dune fields are composed of different spatial scales of bedform patterns that respond to changes in environmental boundary conditions over a wide range of time scales this study examines how variations in spatial scales of dune and ripple patterns found within dune fields are used in environmental reconstructions on earth mars and titan within a single bedform type different spatial scales of bedforms emerge as a pattern evolves from an initial state into a well organized pattern such as with the transition from protodunes to dunes additionally different types of bedforms such as ripples coarse grained ripples and dunes coexist at different spatial scales within a dune field analysis of dune field patterns at the intersection of different scales and types of bedforms at different stages of development provides a more comprehensive record of sediment supply and wind regime than analysis of a single scale and type of bedform interpretations of environmental conditions from any scale of bedform however are limited to environmental signals associated with the response time of that bedform large scale dune field patterns integrate signals over long term climate cycles and reveal little about short term variations in wind or sediment supply wind ripples respond instantly to changing conditions but reveal little about longer term variations in wind or sediment supply recognizing the response time scales across different spatial scales of bedforms maximizes environmental interpretations from dune field patterns

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

late quaternary vegetation dynamics in a biodiversity hotspot the uluguru mountains of tanzania abstract late quaternary vegetation history and environmental changes in a biodiverse tropical ecosystem are inferred from pollen charcoal and carbon isotope evidence derived from a 48 000 yr sedimentary record from the uluguru mountains a component of the eastern arc mountains of kenya and tanzania results indicate that eastern arc forest composition has remained relatively stable during the past 48 000 yr long term environmental stability of the eastern arc forests has been proposed as a mechanism for the accumulation and persistence of species during glacial periods thus resulting in the diverse forests observed today the pollen and isotope data presented here indicate some marked changes in abundance but no significant loss in moist forest taxa through the last glacial maximum thereby providing support for the long term environmental stability of the eastern arc anthropogenic activities including burning and forest clearance were found to play a moderate role in shaping the mosaic of forest patches and high altitude grasslands that characterise the site today however this influence was tempered by the inaccessibility of the mountain

cyclic rapid warming on centennial scale revealed by a 2650 year stalagmite record of warm season temperature 1 a 2650 year bc665 ad1985 warm season mjja may june july august temperature reconstruction is derived from a correlation between thickness variations in annual layers of a stalagmite from shihua cave beijing china and instrumental meteorological records observations of soil co2 and drip water suggest that the temperature signal is amplified by the soil organism co2 system and recorded by the annual layer series our reconstruction reveals that centennial scale rapid warming occurred repeatedly following multicentenial cooling trends during the last millennia these results correlate with different records from the northern hemisphere indicating that the periodic alternation between cool and warm periods on a sub millennial scale had a sub hemispherical influence

late holocene high frequency east asia winter monsoon variability inferred from the environmentally sensitive grain size component in the distal shelf mud area east china sea the b2 b2g and i4 sediment cores recovered from the centre of the distal mud area of the east china sea ecs were analysed for grain size distribution proxies for environmentally sensitive grai

reconstruction of winter monsoon strength by elemental ratio of sediments in the east china sea abstract the east asian winter monsoon eawm transports cold air from the high northern latitudes to the mid and low latitudes thus investigations on its variation pattern and mechanism are essential for acquiring further knowledge on the interplay across the high and low latitudes proxies such as grain size and foraminiferal 18o in marine sediments and elemental ratios in the chinese loess have been used for the reconstruction of eawm strength however more high resolution reconstructions for eawm are required for further understanding the mechanism of climate systems and predicting climate change in this study we present a high resolution time series of the late holocene eawm strength reconstructed by element method comparisons of element concentrations elemental ratios and mean grain size mgs of environment sensitive components in a sediment core from the shelf of the east china sea indicate that k ti ratio is an appropriate proxy for the reconstruction of the eawm strength k ti ratio exhibits similar trends with proxies of sea surface temperature and eawm strength in different regions influenced by the eawm warm and cold periods such as the roman warm period medieval warm period and little ice age are identified in the reconstructed results total solar irradiance anomaly tsi and k ti ratios exhibit comparable tendencies in the last two millennia and frequency spectrum analysis exhibits similar periodicities in the time series of tsi and k ti which confirm that solar irradiance has a significant impact on the easm on centennial time scale

strong coherence between solar variability and the monsoon in oman between 9 and 6 kyr ago variations in the amount of solar radiation reaching the earth are thought to influence climate but the extent of this influence on timescales of millennia to decades is unclear a number of climate records show correlations between solar cycles and climate1 but the absolute changes in solar intensity over the range of decades to millennia are small2 and the influence of solar flux on climate is not well established the formation of stalagmites in northern oman has recorded past northward shifts of the intertropical convergence zone3 whose northward migration stops near the southern shoreline of arabia in the present climate4 here we present a high resolution record of oxygen isotope variations for the period from 9 6 to 6 1 kyr before present in a th u dated stalagmite from oman the 18o record from the stalagmite which serves as a proxy for variations in the tropical circulation and monsoon rainfall allows us to make a direct comparison of the 18o record with the 14c record from tree rings5 which largely reflects changes in solar activity6 7 the excellent correlation between the two records suggests that one of the primary controls on centennial to decadal scale changes in tropical rainfall and monsoon intensity during this time are variations in solar radiation

comparing dune migration measured from remote sensing with sand flux prediction based on weather data and model a test case in qatar this study explores validating and calibrating the wind regime predicted by global circulation models gcm on earth and other planets using optical remote sensing of dune dynamics we use spot 5 images to track the migration of 64 barchan dunes in qatar using the cosi corr technique we estimate the volume of the dunes using a scaling law calibrated from one particular dune which was surveyed in the field using volume and migration rate we determine the sand flux from a single dune q dunes and scale this estimate to the whole dune field we compare the measured sand flux with those derived from wind velocity measurements at a local meteorological station as well as with those predicted from era interim a global circulation model the comparison revealed that the wind velocity predicted by era interim is inappropriate to calculate the sand flux this is due to the 6 h sampling rate and to systematic bias revealed by a comparison with the local wind data we describe a simple procedure to correct for these effects with the proposed correction similar sand flux are predicted using the local and era interim data independently of the value of the value of the shear velocity threshold u t the predicted sand flux is about 65 of q dunes the agreement is best assuming the value u t 0 244 m s which is only slightly larger than the value of u t 0 2612 m s estimated based in the sand granulometry measured from field samples the influence of the dune topography on the wind velocity field could explain the underestimation in any case the study demonstrates the possibility of validating gcm model and calibrating aeolian sand transport laws using remote sensing measurements of dune dynamics and highlights the caveats associated to such an approach

seepage induced penetration of water vapor and dust beneath ripples and dunes 1 we present stratigraphic measurements of humidity and bulk density beneath the surface of a barchan dune obtained with a capacitance probe a model shows that air seeping through the sand bed in response to spatial variations of static pressure along the ripple surface guides water vapor through ripple crests and gradually stores dust beneath troughs the accumulated dust remains trapped beneath the relatively compact trough surface until wind is violent enough to mobilize sand deeply

the sedimentary response to a rapid change in lake level in lake tanganyika abstract we present records of sedimentary organic carbon nitrogen and carbonate and stable isotope records of organic material and carbonate from a series of sediment cores that straddle the permanent chemocline in lake tanganyika sedimentation rates for these cores are consistent among the sites 0 05 0 1 cm y 1 and all records show an increase in sedimentary carbonate aragonite content centered at 1879 the mid 19th century coincides with a major 10 m lake level transgression throughout the period of lake level transgression and subsequent regression the organic matter 13c and 15n records develop a prominent and coincident negative excursion followed by a return to values similar to those prior to the lake level transgression this negative excursion in 15n and 13c is also coincident with an increase in carbonate corrected organic carbon we interpret the 13c results as a decline in primary production during the transgression with the 15n results signaling a concomitant increase in the reliance on nitrogen fixation as the nitrogen source the coincident peak in organic carbon is interpreted as being a result of enhanced preservation driven by the precipitation and burial of aragonite

an agent based model of dune interactions produces the emergence of patterns in deserts 1 crescent shaped barchan dunes are highly mobile dunes which are ubiquitous on earth and other solar system bodies although they are unstable when considered separately they form large assemblies in deserts and spatially organize in narrow corridors that extend in the wind direction collision of barchans has been proposed as a mechanism to redistribute sand between dunes and prevent the formation of very large dunes here we use an agent based model with elementary rules of sand redistribution during collisions to access the full dynamics of very large barchan fields we tune the dune field density by changing the sand load lost ratio and follow the transition between dilute fields where barchans barely interact and dense fields where dune collisions control and stabilize the dune field in this dense regime barchans have a small well selected size and form flocks the dune field self organizes in narrow corridors of dunes as it is observed in real dense barchan deserts

the little ice age and medieval warm period in the sargasso sea sea surface temperature sst salinity and flux of terrigenous material oscillated on millennial time scales in the pleistocene north atlantic but there are few records of holocene variability because of high rates of sediment accumulation holocene oscillations are well documented in the northern sargasso sea results from a radiocarbondated box core show that sst was approximately 1 degree c cooler than today approximately 400 years ago the little ice age and 1700 years ago and approximately 1 degree c warmer than today 1000 years ago the medieval warm period thus at least some of the warming since the little ice age appears to be part of a natural oscillation 39 refs 4 figs 1 tab

controls on terrigenous sediment supply to the arabian sea during the late quaternary the makran continental slope the input of terrigenous sediment along the tectonically active makran continental margin off south western pakistan gulf of oman northern arabian sea is studied on the basis of sediment cores distributed along a transect from the upper slope to the abyssal plain spatial and temporal variations in sediment composition sedimentation rate and turbidite frequency in late pleistocene holocene time last 20 14c ka will be discussed and related to changes in sea level and climate and tectonic activity end member modelling of the grain size distributions of the hemipelagic and turbiditic sediments indicate that the sediments are adequately described as mixtures of three end members which represent turbidite sand turbidite silt or eolian dust and fluvial mud the geochemical and mineralogical compositions of the hemipelagic sediments indicate that the eolian dust was dominantly supplied from the northern arabian peninsula and the persian gulf region and that the fluvial input is from the makran margin the ratio of contributions of eolian and fluvial sediment in the hemipelagic intervals is used as an indicator of continental aridity i e summer monsoon intensity highest holocene turbidite frequencies and sedimentation rates are recorded at the deepest coring sites they are related to the proximity of the deformation front of the accretionary prism turbidite sedimentation on the upper continental slope was most frequent during the last glacial period of sea level lowstand and continued during the entire deglaciation and sea level rise infrequent turbidite sedimentation occurred during the holocene highstand of sea level turbidite sedimentation during the period of late sea level rise and the holocene sea level highstand is inferred to be due to the strong impact of episodic events i e flash floods and earthquakes and because of the narrow shelf of the active makran continental margin

variations in titan s dune orientations as a result of orbital forcing abstract wind blown dunes are a record of the climatic history in titan s equatorial region through modeling of the climatic conditions associated with titan s historical orbital configurations arising from apsidal precessions of saturn s orbit we present evidence that the orientations of the dunes are influenced by orbital forcing analysis of 3 titan general circulation models gcms in conjunction with a sediment transport model provides the first direct intercomparison of results from different titan gcms we report variability in the dune orientations predicted for different orbital epochs of up to 70 although the response of the gcms to orbital forcing varies the orbital influence on the dune orientations is found to be significant across all models furthermore there is near agreement among the two models run with surface topography with 3 out of the 5 dune fields matching observation for the most recent orbital cycle through comparison with observations by cassini we find situations in which the observed dune orientations are in best agreement with those modeled for previous orbital configurations or combinations thereof representing a larger portion of the cycle we conclude that orbital forcing could be an important factor in governing the present day dune orientations observed on titan and should be considered when modeling dune evolution

conservation implications of the provenance of modern sediment on a shell rich platform of lake tanganyika kigoma tz shell rich substrate shell beds in the littoral reaches of lake tanganyika africa form a unique substrate that host a number of endemic organisms including sponges and shell dwelling cichlid fish the predominant gastropod neothauma tanganyensis whose shells comprise the majority of the shell beds are themselves endemic to the lake sedimentologic and observational data suggest that one of these shell beds located between the towns of kigoma and ujiji tanzania on the western side of central lake tanganyika is impacted by modern sedimentation in the northern portion of the study discrete patches of the shell beds between 6 30 m water depth are blanketed by 20 to 50 wt mud in these areas there are few to no sponges nor shell dwelling cichlid fish as evidenced by lack of occurrences of fish nests with shells however in the southern part of the study area within the same depth range the shell beds contain less mud and sponges and fish nests with shells are more common mineralogic and geochemical data suggest the patterns and composition of the sediment are consistent with two sources the sediment accumulating on the shell beds in the northern portion of the study area matches the chemistry of the weathered precambrian metasedimentary rocks in hillslopes adjacent to the lake within a region undergoing severe land use changes the sediment accumulating along the southern portion of the study site particularly in deeper water matches the chemistry of sediment from the luiche river which forms a delta at the southern end of the study site this delta has prograded up to 1 km within the last 40 years however in this setting the bulk of deltaic sediment is shunted into deeper water and so appears to represent a less severe threat to the shallow water shell bed habitat than the local hillslopes this is one of a few detailed studies of the sedimentology of a shell bed habitat in lake tanganyika and the first to tie the sediment to its source this has important implications for conservation of these habitats as methods and practices of conservations vary based on the types of disturbance the study also has implications for biologists interested in community structure as certain species of cichlids appear to be efficient engineers of the substrate forming shelly nests but in areas of high mud content are absent

assessing the martian surface distribution of aeolian sand using a mars general circulation model a sand transport model using white s 1979 sand flux equation and the mars general circulation model pollack et al 1990 was developed to understand the erosional sources transport pathways and depositional sinks of windblown sand on mars an initially uniform distribution of sand 4 mm over the entire surface is regionally transported based on wind stress saltation threshold and percentage of topographic trapping results are consistent with the observed polar and hellespontus dunes and christensen s 1986 modeled block size distribution but only for an extremely low saltation threshold 0 024 n m 2 low thresholds generally result in transport of sand sized particles originating in the northern mid latitudes to the north pole and transport from the northern lower latitudes to the southern hemisphere our results indicate that the polar dune fields could form in 50 000 years consistent with the active polar dunes and lack of longitudinal dunes observed on the surface of mars

solar forcing of centennial scale east asian winter monsoon variability in the mid to late holocene abstract centennial scale variability of the east asian winter monsoon during the holocene is poorly understood because suitable archives and proxies are lacking here we present a high resolution 30 yr spacing planktonic foraminiferal o 18 record of neogloboquadrina incompta dextral form which reflects sea surface temperature during the winter season for the last 6000 yrs from marine sediments in the western north pacific stronger winter monsoons indicated by cooler winter ssts correspond to weaker summer monsoons indicated by the cave oxygen isotopes in centennial scale variability the variability also shows good correlation with o 18 records in lake sediments and ice cores from the yukon territory canada spanning the last 4500 yrs suggesting east west climate coupling across the north pacific furthermore the climate changes across the north pacific co vary over widespread regions such as the eastern tropical pacific and the northern red sea and the reconstructed solar activity the cross spectral and wavelet analyses show that the east asian winter monsoon shares some cyclicity with the solar variability our results suggest that the solar activity is a fundamental forcing producing the centennial scale eawm variability mediated by the large scale climate linkages

twentieth century climatic warming in china in the context of the holocene development of an annual mean temperature series of china for the period of ad 1880 1998 indicated that 1998 was thie wanrest year since 1880 during 1998 temperature was 1 38c higher than the normal 1961 90 annual mean temperatures of china were found using a weighted average of 10 regional series whliich covei ed the xvhole lanid ai ea of the coutliry fromii xinjiang and tibet ii the west to tailwan i the ecast gaps in temperatture obseivations were filled by using ice core i 0 and tie iing data for thice regions in the west and docuimenitary data for scven regions in the east since 1 951 only obser x ational data were usecl fiftyyear mean teiimperatture anomnalies were calculated trom the ninth to trwentietlh cernturies the series do not show any conisistenit warm peiliod in west china durinig the mediaeval warmii period ad 900 to 1300 but temiperatures in east china in at 850 1099 anid 1200 99 were abouit 0 2c higher than the average for recent years centurv mean ternperatures combin

late quaternary vegetation reconstruction from the eastern arc mountains tanzania abstract pollen spore macrofossil and stable isotope c and n analyses from a 266 cm sediment core collected from a swamp on the eastern arc mountains tanzania are used to reconstruct vegetation and environmental history an estimated time scale based on five 14c ages records approximately 38 000 yr this palaeorecord is the first from this biodiversity hotspot and importantly extends through the last glacial maximum lgm the altitudinal transition from montane to upper montane forest shifted from 1700 1800 m 38 000 14c yr bp to 1800 1900 m 35 000 29 000 14c yr bp from 29 000 to 10 000 14c yr bp it shifted from 1850 1950 m across the lgm to 1750 1800 m during 10 000 3500 14c yr bp and to present day elevations at 2000 m during the last 3500 14c yr bp the relative ecosystem stability across the lgm may be explained by the indian ocean s influence in maintaining continuous moist forest cover during a period of east african regional climate aridity during the late holocene presence of abundant coprophilous fungi and algal blooms demonstrates increasing human impact neurospora spores indicate frequent fires coinciding with clear signals of decline in podocarpus and psychotria trees that possibly represent selective logging

recent aeolian dune change on mars previous comparisons of martian aeolian dunes in satellite images have not detected any change in dune form or position here we show dome dunes in the north polar region that shrank and then disappeared over a period of 3 04 mars years 5 7 earth years while larger neighboring dunes showed no erosion or movement the removal of sand from these dunes indicates that not only is the threshold wind speed for saltation exceeded under present conditions on mars but that any sand that is available for transport is likely to be moved dunes that show no evidence of change could be crusted indurated or subject to infrequent episodes of movement

basaltic sand ripples at eagle crater as indirect evidence for the hysteresis effect in martian saltation abstract the rover opportunity documented small basaltic sand ripples at the bottom of eagle crater meridiani planum on mars these ripples are composed of fine basaltic sand 100 m diameter and their average wavelength and height are 10 cm and 1 cm respectively present theories on the transition between saltation and suspension predict that such light particles are suspended by turbulence at the fluid threshold which is the minimum wind speed required to initiate saltation consequently the existence of these 100 m ripples on mars indicates that either current suspension theories are incorrect or that saltation can take place at wind speeds substantially below the fluid threshold indeed recent studies point to the occurrence of hysteresis in martian saltation that is once initiated hysteresis can be maintained at much lower wind speeds than the fluid threshold we investigated the possible role of hysteresis in the formation of fine grained ripples on mars by coupling for the first time a detailed numerical saltation model comsalt with a dynamic model for sand ripple formation the results from the coupled model indicate that ripples with properties similar to those observed at eagle crater can be developed by the impact mechanism at shear velocities far below the fluid threshold these findings are consistent with the occurrence of hysteresis in martian saltation and support the hypothesis that hysteresis plays a role in the surprisingly large sand mobility observed at several locations on mars

an advance of soler glacier north patagonian icefield at c ad 1222 1342 soler glacier is a temperate outlet glacier on the eastern side of the north patagonian icee eld in chile the glacier is currently receding from its little ice age maximum position attained sometime between ad 1600 and 1900 across the snout and foree eld of the glacier is an arcuate belt of well sorted granule gravel and coarse sand containing tree remains these sediments are interpreted as reworked glaciolacustrine material elevated to the glacier surface by thrusting and folding radiocarbon dating of samples of tree remains in these reworked glaciolacustrine sediments demonstrates that the glacier overrode this lake bed sometime between ad 904 and ad 1334 in situ tree remains plastered onto a large boulder in front of the glacier constrain this advance to the period between ad 1222 and ad 1342 this advance precedes by several hundred years the maximum little ice age extent of other north patagonian icee eld outlet glaciers suggesting either an early age for the onset of little ice age conditions or a previously unrecognized period of glacier advance prior to the advance at c ad 1222 to ad 1342 soler glacier was more recessed than at present cone rming the dynamic response of patagonian glaciers to holocene climatic e uctuations

lake level history of lake tanganyika east africa for the past 2500 years based on ostracode inferred water depth reconstruction assemblages of ostracodes from sediment cores illuminate lake level history at decadal to centennial timescales during the late holocene at lake tanganyika east africa the ostracode based lake level curves for several cores resemble both each other and the only previously published lake level record of comparable resolution for lake tanganyika during this interval successfully reconstructing known highstands improving the chronology of known lowstands and contributing new information on late holocene lake level variability at this important tropical african location in agreement with other late holocene records from east africa the surface level at lake tanganyika reflects predominantly arid conditions throughout this interval interrupted by relatively brief episodes of higher precipitation and lake level the most pronounced lowstand in the record occurs at v200 0 bc with other significant lowstands dating to the intervals v200 500 ad v700 850 ad the medieval warmperiod mwp v1050 1250 ad at lake tanganyika and the latter part of the little ice age lia v1550 1850 ad the most important wet intervals in the lake level record are centered on v500 ad v1500 ad and v1870 ad the highstands and lowstands reported here for lake tanganyika appear to be fairly coherent with other records of rainfall throughout east africa during the mwp and the lia prior to the mwp paleoclimate records are apparently less coherent although this may be a reflection of the resolution and abundance of recent paleoclimatic data available for this climatically complex region

timescale dependence of aeolian sand flux observations under atmospheric turbulence 1 the transport of sand in saltation is driven by the persistently unsteady stresses exerted by turbulent winds based on coupled high frequency observations of wind velocity and sand flux on a desert dune during intermittent saltation we show here how observations of saltation by natural winds depend significantly on the timescale and method used for determining shear stress and sand flux the correlation between sand flux and excess shear stress stress above a threshold value systematically improves for longer averaging timescale t and is better for stress determined by the law of the wall versus the reynolds stress method fitting parameters for the stress flux relationship do not converge with increasing t which may be explained by the nonstationary nature of wind velocity statistics we show how it may be possible based on the scale dependent statistics of stress fluctuations to rescale saltation flux predictions for wind observations made at different timescales however our observations indicate hysteresis and time lags in thresholds for initiation and cessation of saltation which complicate threshold based approaches to predicting sediment transport at different timescales

aeolian saltation on mars at low wind speeds laboratory experiments indicate that the fluid threshold friction speed u tf required to initiate fully developed aeolian saltation is much higher on mars than on earth a discrepancy exists between mars climate models that do not predict winds this strong and observations that sand sized particles are indeed moving this paper describes how wind friction speeds well below u tf but above the impact threshold u ti required to sustain saltation can initiate sustained saltation on mars but at relatively low flux numerical experiments indicate that a sand grain on mars mobilized sporadically between u ti and u tf will develop over fetch lengths longer than generally available within low pressure wind tunnels trajectories capable of splashing grains that propagate saltation and collectively form a cluster of saltating grains that migrate downwind together the passage of a saltation cluster should leave behind a narrow zone of affected surface grains the cumulative effect of many clusters represents a low flux phenomenon that should produce slow changes to aeolian bedforms over periods in which winds remain close to u ti and never or rarely reach u tf field evidence from small impact ripples along rover traverses is consistent with effects of saltation at these low friction speeds without obvious evidence for events u tf the potential utility of this grain mobility process is that it can operate entirely at more common winds well below u tf and so help explain widespread sand movements observed on mars wherever evidence might be mostly absent for u tf being exceeded

variability of the apparent von karman parameter during aeolian saltation 1 the variability of the apparent von karman parameter a during aeolian saltation was evaluated in a field experiment at jericoacoara brazil to test this variability velocity profiles reynolds stress and sand transport data were gathered and analyzed we used 15 data sets with sand laden airflow and 2 runs with clear airflow results indicated an inverse linear relationship between a and bulk gravimetric sand concentration r2 0 746 and sand transport rate r2 0 577 we found values of a as low as 0 26 this means that using the von karman constant 0 40 rather than the variable a to estimate shear velocity based on the slope of the velocity profile will lead to over estimation of shear velocity averaging about 20 in this study this in turn produces an over estimation of wind blown sand transport rates based on models that have terms with shear velocity cubed

a centennial scale variability of tropical north atlantic surface hydrography during the late holocene abstract sea surface temperature sst and sea surface salinity sss fluctuations in the northeastern caribbean have been reconstructed through the last 2000 yr using an artificial neural network and 18 o analyses of planktonic foraminifera a warmer period prevailed in the ne caribbean from ad 700 950 which may reflect the occurrence of stronger and or more frequent el nino events a 2 c cooling of winter ssts from ad 1400 to 1550 coincides with the occurrence of reduced solar output the sporer event episodes of lower ssss with marked minima at the onsets of the dark ages in europe ad 500 600 and little ice age ad 1400 are cyclically recurrent at intervals of 200 400 yr and coincide with drier periods in mexico this may indicate that the tropical atlantic evaporation precipitation budget and ssss are affected by a centennial scale modulation involving the freshwater export import from into the atlantic ocean coeval changes recorded in the deep north atlantic circulation indicate that low latitude sss anomalies may be advected polewards by the north atlantic current system thus affecting deep ocean convection and strength of the thermohaline circulation

martian aeolian activity at the bagnold dunes gale crater the view from the surface and orbit the first in situ investigation of an active dune field on another planetary surface occurred in 2015 2016 when the msl curiosity rover investigated the bagnold dunes on mars hirise images show clear seasonal variations that are in good agreement with atmospheric model predictions of intra annual sand flux and migration directions that together indicate that the campaign occurred during a period of low wind activity curiosity surface images show that limited changes nevertheless occurred with movement of large grains particularly on freshly exposed surfaces two occurrences of secondary grain flow on the slip face of namib dune and a slump on a freshly exposed surface of a large ripple these changes are seen at sol to sol time scales grains on a rippled sand deposit and unconsolidated dump piles show limited movement of large grains over a few hours during which mean friction speeds are estimated at 0 3 0 4 m s 1 overall the correlation between changes and peak rems winds is moderate with high wind events associated with changes in some cases but not in others suggesting that other factors are also at work the distribution of rems 1 hz wind speeds show a tail up to the 20 m s 1 showing that even higher speed winds occur non aeolian triggering mechanisms are also possible the low activity period at the dunes documented by curiosity provides clues to processes that dominated in the martian past under conditions of lower obliquity

sea surface temperature variability in southern okinawa trough during last 2700 years 1 most of the temperature reconstructions for the past two millennia are based on proxy data from various sites on land here we present a bidecadal resolution record of sea surface temperature sst in southern okinawa trough for the past ca 2700 years by analyzing tetraether lipids of planktonic archaea in the odp hole 1202b a site under the strong influence of kuroshio current and east asian monsoon the reconstructed sst anomalies generally coincided with previously reported late holocene climate events including the roman warm period sui tang dynasty warm period medieval warm period current warm period dark age cold period and little ice age however the medieval warm period usually thought to be a historical analogue for the current warm period has a mean sst of 0 6 0 8 c lower than that of the roman warm period and sui tang dynasty warm period despite an increase since 1850 ad the mean sst in the 20th century is still within the range of natural variability during the past 2700 years a close correlation of sst in southern okinawa trough with air temperature in east china intensity of east asian monsoon and the el nino southern oscillation index has been attributed to the fluctuations in solar output and oceanic atmospheric circulation

concepts of sediment deposition and accumulation applied to the continental shelf near the mouth of the yangtze river a fundamental understanding of how sedimentary strata form requires distinction between deposition and accumulation of particles deposition refers to the temporary emplacement of particles on the seabed accumulation is the net sum of many episodes of sediment deposition and removal the difference between rates of deposition and accumulation affects the ability of an environment to record sedimentary events radionuclide profiles of 234 th and 210 pb within the seabed can be used to determine 100 day deposition rates and 100 yr accumulation rates respectively on the continental shelf near the mouth of the yangtze river short term deposition rates are about 4 4 cm month whereas accumulation rates integrated over a century are an order of magnitude less about 5 4 cm yr

the sand seas of titan cassini radar observations of longitudinal dunes the most recent cassini radar images of titan show widespread regions up to 1500 kilometers by 200 kilometers of near parallel radar dark linear features that appear to be seas of longitudinal dunes similar to those seen in the namib desert on earth the ku band 2 17 centimeter wavelength images show 100 meter ridges consistent with duneforms and reveal flow interactions with underlying hills the distribution and orientation of the dunes support a model of fluctuating surface winds of 0 5 meter per second resulting from the combination of an eastward flow with a variable tidal wind the existence of dunes also requires geological processes that create sand sized 100 to 300 micrometer particulates and a lack of persistent equatorial surface liquids to act as sand traps

a late holocene paleoclimatic history of lake tanganyika east africa abstract a nearshore core lt03 05 from the north basin of lake tanganyika provides diatom pollen and sedimentary time series covering the last ca 3800 yr at 15 36 yr resolution a chronology supported by 21 ams dates on terrestrial and lacustrine materials allows us to account for ancient carbon effects on 14c ages and to propose refinements of the region s climatic history conditions drier than those of today were followed after ca 3 30 ka by an overall wetting trend several century scale climate variations were superimposed upon that trend with exceptionally rainy conditions occurring 1 70 1 40 ka 1 15 0 90 ka 0 70 0 55 ka and 0 35 0 20 ka around 0 55 0 35 ka during the sporer sunspot minimum drier conditions developed in the northern tanganyika basin while more humid conditions were registered at lakes victoria and naivasha this indicates significant variability in the nature and distribution of near equatorial rainfall anomalies during much of the little ice age

effects of land use change on aquatic biodiversity a view from the paleorecord at lake tanganyika east africa population growth and watershed deforestation in northwestern tanzania threaten the biodiversity of lake tanganyika through erosion and habitat degradation we used cores collected offshore from gombe stream national park and a deforested watershed to reconstruct how land use changes in the gombe stream area since a d 1750 have affected lake biodiversity paleoenvironmental and paleoecological data reveal substantial changes in mass accumulation rates for sediment and organic matter nitrogen stable isotope values and benthic species composition offshore from the deforested watershed since 1880 comparable changes were not observed offshore from the park

a continuous model for sand dunes review new developments and application to barchan dunes and barchan dune fields basically sand dunes are patterns resulting from the coupling of hydrodynamic and sediment transport once grains move they modify the surface topography which in turns modifies the flow this important feedback mechanism lies at the core of continuous dune modelling here we present an updated review of such a model for aeolian dunes including important modifications to improve its predicting power for instance we add a more realistic wind model and provide a self consistent set of parameters independently validated as an example we are able to simulate realistic barchan dunes which are the basic solution of the model in the condition of unidirectional flow and scarce sediments from the simulation we extract new relations describing the morphology and dynamics of barchans that compare very well with existing field data next we revisit the problem of the stability of barchan dunes and argue that they are intrinsically unstable bed forms finally we perform more complex simulations first a barchan dune under variable wind strength and second barchan dune fields under different boundary conditions the latter has important implications for the problem of the genesis of barchan dunes copyright 2010 john wiley sons ltd

winds measured by the rover environmental monitoring station rems during the mars science laboratory msl rover s bagnold dunes campaign and comparison with numerical modeling using marswrf abstract a high density of rems wind measurements were collected in three science investigations during msl s bagnold dunes campaign which took place over 80 sols around southern winter solstice ls 90 and constituted the first in situ analysis of the environmental conditions morphology structure and composition of an active dune field on mars the wind characterization investigation was designed to fully characterize the near surface wind field just outside the dunes and confirmed the primarily upslope downslope flow expected from theory and modeling of the circulation on the slopes of aeolis mons in this season the basic pattern of winds is upslope from the northwest heading up aeolis mons during the daytime 09 00 17 00 or 18 00 and downslope from the southeast heading down aeolis mons at night 20 00 to some time before 08 00 between these times the wind rotates largely clockwise giving generally westerly winds mid morning and easterly winds in the early evening the timings of these direction changes are relatively consistent from sol to sol however the wind direction and speed at any given time shows considerable intersol variability this pattern and timing is similar to predictions from the marswrf numerical model run at a resolution of 490 m in this region although the model predicts the upslope winds to have a stronger component from the e than the w misses a wind speed peak at 09 00 and under predicts the strength of daytime wind speeds by 2 4 m s the namib dune lee investigation reveals blocking of northerly winds by the dune leaving primarily a westerly component to the daytime winds and also shows a broadening of the 1 hz wind speed distribution likely associated with lee turbulence the namib dune side investigation measured primarily daytime winds at the side of the same dune in support of aeolian change detection experiments designed to put limits on the saltation threshold and also appears to show the influence of the dune body on the local flow though less clearly than in the lee using a vertical grid with lower resolution near the surface reduces the relative strength of nighttime winds predicted by marswrf and produces a peak in wind speed at 09 00 improving the match to the observed diurnal variation of wind speed albeit with an offset in magnitude the annual wind field predicted using this grid also provides a far better match to observations of aeolian dune morphology and motion in the bagnold dunes however the lower overall wind speeds than observed and disagreement with the observed wind direction at 09 00 suggest that the problem has not been solved and that alternative boundary layer mixing schemes should be explored which may result in more mixing of momentum down to the near surface from higher layers these results demonstrate a strong need for in situ wind data to constrain the setup and assumptions used in numerical models so that they may be used with more confidence to predict the circulation at other times and locations on mars

late holocene temperature fluctuations on the tibetan plateau abstract proxy data of palaeoclimate like ice cores tree rings and lake sediments document aspects of climate changes on the tibetan plateau during the last 2000 years the results show that the tibetan plateau experienced climatic episodes such as the warm intervals during ad 800 1100 and 1150 1400 the little ice age between ad 1400 and 1900 and an earlier cold period between the 4th and 6th centuries in addition temperatures varied from region to region across the plateau a warm period from ad 800 to 1100 in the northeastern tibetan plateau was contemporaneous with cooling in the southern tibetan plateau which experienced warming between ad 1150 and 1400 large scale trends in the temperature history from the northeastern tibetan plateau resemble those in eastern china more than the trends from the southern plateau the most notable similarities between the temperature variations of the tibetan plateau and eastern china are cold phases during ad 1100 1150 1500 1550 1650 1700 and 1800 1850

simulation of the effect of wind speedup in the formation of transverse dune fields a computer simulation model for transverse dune field dynamics corresponding to a uni directional wind regime is developed in a previous formulation two distinct problems were found regarding the cross sectional dune shape namely theerosionintheleeofdunesandthesteepnessofthewindwardslopes thefirstproblemissolvedbyintroducingnoerosion inshadowzones thesecondissueisovercomebyintroducingawindspeedup shearvelocityincrease factor whichcanbe accountedforbyaddingatermtotheoriginaltransportlength whichisproportionaltothesurfaceheight byincorporating these features we are able to model dunes whose individual shape and collective patterns are similar to those observed in nature moreoverweshowhowtheintroductionofanon linearshear velocity increasetermleadstothereductionofdune height andthismayresultinanequilibriumdunefieldconfiguration thisisthoughttobebecausethenon linearincreaseof thetransportlengthmakesthesandtrappingefficiencylowerthanunity evenforhigherdunes sothattheincomingandthe outgoingsandfluxareinbalance tofullydescribetheinter dunemorphologymoreprecisedynamicsintheleeofthedune must be incorporated copyright 2000 john wiley sons ltd

linking watershed disturbance with nearshore sedimentation and the shell beds of lake tanganyika mahale mountains tanzania extensive deposits of shell rich sediments in the nearshore environment of lake tanganyika africa form a unique habitat for a diverse group of endemic gastropods crustaceans fish and sponges among other organisms anthropogenic alteration of the lake s hinterland from deforestation fires and agriculture threaten this crucial habitat through sediment pollution of the littoral environment this study examines the sedimentology of these nearshore shell beds along a study area north of the mahale mountains tanzania to test whether varying levels of watershed disturbance determined by analysis of satellite imagery within three moderately sized watersheds 100 km2 results in sedimentological differences offshore the results show that shell beds adjacent to disturbed watersheds lagosa and rukoma contain more fine grained sediment compared to shell beds offshore of the undisturbed watershed katumbi widespread burning clearance and land cultivation and rains of the wet season are causal factors that result in significant differences in fine grained sedimentation larger sediment plumes offshore and increased shoreline progradation in areas most affected by sedimentation sponges are largely absent and shell coverage which is a measure of fish nesting capabilities is lower the discovery of a small population of live neothauma tanganyicense offshore of the katumbi river suggests that the presence of shell bed forming gastropods in front of a relatively low disturbance watershed and their conspicuous absence offshore of the other two watersheds could be related to recent watershed disturbance and increased sedimentation the increased fine grained sedimentation and limited shell production by the reduced modern gastropod populations may signal that the shell bed ecosystem of lake tanganyika is at risk

effects of historical land use on sediment yield from a lacustrine watershed in central chile sediment yield in the san pedro lake watershed inferred from sedimentation in the lake can be related to land use changes shown on aerial photographs taken during the period 1943 1994 in this watershed which covers 4 5 km2 of mountainous terrain in san pedro county central chile the area of native forest species decreased from 70 per cent in 1943 to 13 per cent in 1994 during this same period the area of pine plantations increased from 4 to 46 per cent to study effects of these changes we took a core from the centre of the lake and estimated sedimentation rates by 210pb dating which we checked with 137cs and pine pollen the results show that sedimentation rate ranged from 5 mg cm 2 a 1 in the late 1800s to 60 mg cm 2 a 1 in the late 1960s these rates together with assumptions about the production and delivery of the sediment give corresponding figures for sediment yields with maximum values close to 1 t ha 1 a 1 sediment yield between 1955 and 1994 closely tracks the total land use change that can be detected irrespective of land use type on sets of aerial photographs taken four to 18 years apart however this measure of land use change while convenient and successful as a predictor of historical erosion may be unreliable because it probably excludes many changes that occurred in long intervals between successive photographs copyright 2001 john wiley sons ltd

shoreline reconstructions for the persian gulf since the last glacial maximum abstract sea level change in the persian gulf since the time of the last maximum glaciation at about 18 000 yr bp is predicted to exhibit considerable spatial variability because of the response of the earth to glacial unloading of the distant ice sheets and to the meltwater loading of the gulf itself and the adjacent ocean models for these glacio hydro isostatic effects have been compared with observations of sea level change and palaeoshoreline reconstructions of the gulf have been made from the peak of the glaciation until about 14 000 yr bp the gulf is free of marine influence out to the edge of the biaban shelf by 14 000 yr bp the strait of hormuz had opened up as a narrow waterway and by about 12 500 years ago the marine incursion into the central basin had started the western basin flooded about 1000 years later momentary stillstands may have occurred during the gulf flooding phase at about 11 300 and 10 500 yr bp the present shorelines was reached shortly before 6000 yr ago and exceeded as relative sea level rose 1 2 m above its present level inundating the low lying areas of lower mesopotamia these reconstructions have implications for models of the evolution of the euphrates tigris karun delta as well as for the movements of people and the timing of the earliest settlements in lower mesopotamia for example the early gulf floor would have provided a natural route for people moving westwards from regions to the east of iran from the late palaeolithic to early neolithic

storm generated surface waves and sediment resuspension in the east china and yellow seas abstract surface winds derived from atmospheric pressure fields are used as input to a finite depth wind wave model to predict the sea state during a cold air frontal passage over the yellow and east china seas which occurred 15 18 november 1983 the predicted maximum wave stress field near the bottom is used to examine the concept of turbulent wave intensities causing sediment resuspension the temporal variability of the wave field at three sites is used to illustrate the dependence of the bottom response on depth within the yellow sea maps of the temporal and spatial distribution of index for initiation of sediment movement are computed for different noncohesive sediment materials during this storm period and compared to sedimentological results for this region this study demonstrates that wave action is a mechanism which can significantly influence the sediment transport pattern induced by the regional circulation existing in this marginal sea the results also identify regions where winter storm g

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

a two species model of aeolian sand transport the transport of sand by wind results from the equilibrium between the erosion of grains dragged by the flow and the resulting slow down of the wind velocity the dynamical mechanisms governing the saturation of the sand flux are investigated theoretically we first demonstrate that previous models based on the assumption that all the grains have the same trajectory are either not self consistent or lead to unstable solutions a model based on a discrete number of states is derived which solves these problems two well defined species of grain appear which correspond to saltons high energy grains and reptons grains ejected from the sand bed by the impact of saltons they play specific roles the negative feedback of the transport on the wind is limited to the reptation layer while most of the transport is due to saltation the model is further simplified benefiting from the existence of these two species and the dependencies of the threshold velocity the saturated flux the aerodynamic roughness and the saturation length are derived and compared to experimental measurements

earth like sand fluxes on mars strong and sustained winds on mars have been considered rare on the basis of surface meteorology measurements and global circulation models raising the question of whether the abundant dunes and evidence for wind erosion seen on the planet are a current process recent studies showed sand activity but could not determine whether entire dunes were moving implying large sand fluxes or whether more localized and surficial changes had occurred here we present measurements of the migration rate of sand ripples and dune lee fronts at the nili patera dune field we show that the dunes are near steady state with their entire volumes composed of mobile sand the dunes have unexpectedly high sand fluxes similar for example to those in victoria valley antarctica implying that rates of landscape modification on mars and earth are similar

grain size distribution function of polymodal sediments in hydraulic and aeolian environments and numerical partitioning of the sedimentary components most continental sediments are polymodal composed of overlapping components of which the grain size generally obeys some type of natural distribution the grain size components and their function types can be determined from frequency and cumulative curve plots in order to define the function formula of the grain size distribution the function parameters can be estimated by fitting a defined function formula to the measured grain size data of the sample which simultaneously achieves numerical partitioning of the sedimentary components genetic analysis of grain size components of hydraulic and aeolian sediments demonstrates the following environmental implications fluvial sediment is composed of isolated saltation and suspension components the sediments in closed lake basins are dominated by a suspension silt clay component with a small proportion of saltation sand the fine sand component makes up the majority of desert sand overlapping with a small proportion of fine dust aeolian loess is composed of two overlapping components a short suspension time silt component and a long suspension time fine component aeolian material in the north pacific deep sea sediments is dominated by long suspension time fine dust the fine component in aeolian sediments shows a consistent grain size distribution and genetic connection from the desert sand loess of northern china to the north pacific ocean which is mainly transported by westerly winds and is dispersed in the atmosphere forming a background dust c 2002 elsevier science b v all rights reserved

pervasive aeolian activity along rover curiosity s traverse in gale crater mars the nasa mars science laboratory msl rover curiosity has safely landed near a 35 km long dark dune field in gale crater on mars this dune field crosses the landing site from the northeast to the southwest and lies along curiosity s traverse to aeolis mons here we present the first evidence of recent aeolian activity in the form of ripple and dune migration and further estimate wind directions within the dune field through analysis of ripple and dune morphologies and the mars regional atmospheric modeling system mrams we measured a minimum ripple migration rate of 0 66 m per earth year and dune migration rate of 0 4 m per earth year in the southwest portion of the field a strongly bidirectional ripple crestline orientation nearly orthogonal dune slipfaces and linear seif or oblique dunes indicate a bidirectional wind regime with winds mainly coming from the ene and from the northwest however mrams results indicate primary winds from the ene our constraints on the wind regime provide the unique opportunity to use ground measurements from msl to test the accuracy of winds predicted from orbital data

mean sediment residence time in barchan dunes when a barchan dune migrates the sediment trapped on its lee side is later mobilized when exposed on the stoss side then sand grains may undergo many dune turnover cycles before their ejection along the horns but the amount of time a sand grain contributes to the dune morphodynamics remains unknown to estimate such a residence time we analyze sediment particle motions in steady state barchans by tracking individual cells of a 3 d cellular automaton dune model the overall sediment flux may be decomposed into advective and dispersive fluxes to estimate the relative contribution of the underlying physical processes to the barchan shape the net lateral sediment transport from the center to the horns indicates that dispersion on the stoss slope is more efficient than the convergent sediment fluxes associated with avalanches on the lee slope the combined effect of these two antagonistic dispersive processes restricts the lateral mixing of sediment particles in the central region of barchans then for different flow strengths and dune sizes we find that the mean residence time of sediment particles in barchans is equal to the surface of the central longitudinal dune slices divided by the input sand flux we infer that this central slice contains most of the relevant information about barchan morphodynamics finally we initiate a discussion about sediment transport and memory in the presence of bed forms using the advantages of the particle tracking technique