morphology of transverse aeolian ridges tars on mars from a large sample further evidence of a megaripple origin abstract using hirise digital terrain models dtms we developed a large morphological dataset to examine the three dimensional shape size and scaling of martian transverse aeolian ridges tars considerable debate exists on the characteristic morphology of tars and the origins of these enigmatic bedforms some researchers suggest polygenesis or multiple classes of similar bedforms reliably characterizing the morphology of tars is an essential prerequisite to developing and evaluating process based models of tar genesis and unraveling aeolian processes on the surface of mars we present measurements of tar morphology from a large dtm derived dataset n 2295 we focused on tars with simple morphologies in order enable more defensible discretization histograms and cumulative log frequency plots of morphometric parameters length width height elongation ratio and wavelength indicate the sample represents a continuum of bedforms from a single population a typical tar from our dataset is 88 5 m long longest planview axis 17 3 m wide shortest planview axis 1 3 m tall and has a wavelength of 25 8 m combined with these data the bulk of evidence presented to date suggests that interpreting tars as megaripples is the most viable working hypothesis

winter time dissolved iron and nutrient distributions in the subantarctic zone from 40 52s 155 160e 1 in hnlc oceanic regions iron fe controls phytoplankton productivity yet large gaps remain in our understanding of iron s biogeochemical cycle here we present the first comprehensive winter dataset for dissolved fe dfe and nitrate no3 distributions 0 1000 m depth between 40s 52s which transects the subantarctic zone saz west of new zealand surface concentrations 0 2 nmol fe kg 1 were conspicuously low i e probably biologically limiting even at winter reserve levels at frontal zones between 43s subtropical front and 51s subantarctic front a fivefold range in fe no3 molar ratios was observed along the transect with subtropical waters where blooms occur having the highest ratios in subsurface waters the major wintertime supply of dfe in the saz is from ekman advection of waters from the south but calculated source water dfe is 0 2 nmol fe kg 1 suggesting that mixed layer dfe concentration is controlled by how long these southern waters remain at the surface 3 years

latitude dependent nature and physical characteristics of transverse aeolian ridges on mars 1 narrow angle images from the mars orbiter camera moc have revealed the common occurrence of small scale 100 m wavelength bright transverse aeolian ridges tars on the surface of mars moc images were used to assess the broad distribution of tars from 90 n to 90 s between 180 e and 240 e to investigate their relationship to latitude elevation thermal inertia geologic units local slopes and surface roughness out of 5112 examined images from the primary mission 520 10 contain evidence of tars 92 of the images with tars are located between 50 latitude and very few occur in the middle to upper latitudes or polar regions of either hemisphere tars are observed at elevations from 5 km to 3 km with the highest frequency 26 between 1 and 0 km there is no systematic relationship between the distribution of tars and global thermal inertia measurements most tars occur in geologic units associated with the channel system materials 39 and the olympus mons aureole 33 at a length scale of 1 85 km pixel the average local slopes for images with and without tars are 1 92 and 1 36 respectively of the parameters investigated the latitudinal trend of tars in both hemispheres appears to be predominantly related to surface roughness with a positive linear correlation between the surface roughness of geologic units and frequency of tars r2 0 87 factors affecting the semiglobal distribution of tars are likely related to the climate and wind regimes in which they formed but do not provide definitive evidence for either saltation or reptation formation mechanisms

longevity of aeolian megaripples abstract megaripples are distinguished from regular ripples by their larger dimensions and bimodal grain size distributions the interplay between wind grain size and ripple morphology height and wavelength controls their development two main mechanisms limit megaripple height the first megaripple flattening due to winds that are above the fluid threshold of the coarse grains destroys the armoring layer of the megaripple the second is megaripple erosion by the impacts of fast moving fine saltating grains that propel the coarse grains constituting the armoring layer for any given wind regime and grain size distribution the potential megaripple dimensions are limited by these two mechanisms here we study the first mechanism and estimate the duration of strong winds sustained above the fluid threshold needed to flatten megaripples strong gusts of wind in contrast cannot destroy the megaripples but can cause ripple migration based on data from previous works on megaripples we find a scaling law between the ripple morphology and the coarse mode of grains at the crest using this scaling relation allows us to calculate the wind velocity and duration needed for megaripple flattening in general the coarser the particles at the megaripple crest the stronger the wind needed to flatten the megaripples moreover the greater the strength of the wind required to flatten the megaripples the lower the recurrence probability taken together these findings increase the longevity of megaripples we apply the results for a megaripple field in the southern arava valley israel

gypsum gravel devils in chile movement of largest natural grains by wind whirlwinds dry convective helical vortices move large gypsum crystals in the andes mountains of northern chile the crystals are entrained from a saline pan surface where they grew in shallow surface brines they are transported as much as 5 km and deposited in large dune like mounds the dune gravel is cemented relatively quickly by gypsum cement precipitating from near surface saline groundwater resulting in gypsum breccia this marks the first occurrence of gravel sized grains moved efficiently in air by suspension provides a new possible interpretation for some ancient breccias and conglomerates and improves understanding of limits of extremity of earth surface environments

wind regime sediment transport and landscape dynamics at a mars analogue site in the andes mountains of northwestern argentina abstract the puna plateau of northwestern argentina is a promising region for analogue investigations of martian aeolian processes owing to its high altitude low atmospheric pressure aridity geology and widespread granular and bedrock aeolian landforms despite a growing body of research about the region s enigmatic aeolian landforms little is known about the contemporary aeolian environment processes and landscape dynamics to address this gap we used a combination of modelled weather data satellite imagery and field measurements to characterize the wind regime aeolian sediment transport and allied surface changes the study focused on the campo de piedra pomez cpp a volcanic landscape with a variety of mars analogue landforms gravel mantled megaripples yardangs ventifacts periodic bedrock ridges and aeolian rat tails modelled weather data from the european center for medium range forecasting s era interim reanalysis dataset confirm the contemporary dominance of northwesterly winds in this region consistent with the primary orientation of yardangs these data also indicate the presence of less frequent southeasterly winds which may explain why re entrant profiles are observed on the southeast flanks of a small portion of the yardang population and why some aeolian rat tails point to the northwest observations from multi temporal satellite imagery indicate that deposition and displacement of small sediment patches overlying ignimbrite bedrock is relatively common across the region samples retrieved from sediment traps deployed over one year in the region suggest a broad range of particle densities are mobilized by wind which implies a wide range of wind speed for fluid entrainment conventional aeolian transport models do not consider the effects of particle density variations on transport processes however in areas with multiple density sediment present our results point towards a need for aeolian models to consider density when quantifying and qualifying sediment transport

identifying regional dust transport pathways application of kinematic trajectory modelling to a trans tasman case pi kinematic trajectory model is used to investigate potential pathways of dust transport from australia to new zealand historically these have been assumed to follow rather direct west east trajectories spanning 2 to 3 days often resulting in red snow events in the southern alps of new zealand however results from the present study which examined the route taken by air parcels originating in southern australia during dust storms on 24 and 25 may 1994 indicate that trans tasman dust transport trajectories are more diverse than previously thought and display considerable variation during single events these mon divergent pathways tie in more closely with aeolian dust sedimentation patterns identified by ocean coring in the tasman sea and may account for the deposition of australian dust on sub antarctic islands located well south of the australian continent copyright 2000 john wiley sons ltd

megaripple flattening due to strong winds abstract megaripples in nahal kasuy in the southern negev desert of israel are characterized by a mean wavelength of about 70 cm and by a bimodal distribution of coarse and fine particle sizes the latter property being a pre requisite for their formation in our three year project megaripple development was monitored using a digital elevation model dem constructed from above ground stereo digital photographs temporal dynamics of wind power drift potential dp were measured and grain size analyses were performed on samples taken from different parts of the megaripple the coarse grains that protect the crest enable the ripple to grow but when ripple height becomes too high the bed shear stress increases thus allowing the wind to move the armoring layer when this happens during strong wind storms the megaripple will flatten and even disappear as was observed in our field study we present measurements that for the first time directly show the megaripple to normal ripple transition and we suggest two possible physical processes as potential causes of this phenomenon megaripple flattening can occur either when the wind exceeds the fluid threshold for a sufficient length of time or after a sequence of storms with winds blowing from the same direction

bias in grain size distribution of deposited atmospheric dust due to the collection of particles in sediment catchers abstract this study investigates how dust deposition samplers affect the grain size characteristics of the sediment they catch sediment samplers act as obstacles in the flow and their collection efficiency varies with the grain size and other factors some particle fractions are collected more efficiently than others resulting in a modification of the original grain size distribution of the sediment this paper presents wind tunnel results for five dust deposition samplers and five wind velocities ranging from 1 to 5 m s 1 the catcher s effect on the grain size was apparent in all experiments dust accumulated in a catcher is finer than undisturbed dust for the dust used in the tests the difference in median grain diameter was of the order of 10 20 but differences up to 40 and more were observed in general the error is higher when the catcher is less aerodynamically shaped the study concludes that grain size data on sediment collected by a catcher should be interpreted with care as they do not necessarily reflect the characteristics of the original sediment

wind formed gravel bed forms wright valley antarctica 1 bed forms composed of gravel size particles 50 of particles 4 mm are observed in the wright valley of the mcmurdo dry valley system in antarctica these bed forms are characterized by a very asymmetrical shape with a mean aspect ratio of 0 025 standard deviation 0 005 mean wavelength of 2 7 m 0 49 m and a mean height of 0 06 m 0 01 m particle size analysis of the bed form sediments shows bimodality with a peak near 9 mm and another between 0 5 mm and 0 25 mm time integrated sediment trap samples of horizontal saltation and creep flux indicate the flux of particles 4 mm during the two year monitoring period was extremely low measurements of the horizontal displacement of tracer particles 14 mm 12 mm 10 mm 8 mm and 6 mm diameter placed onto the bed forms corroborate the low particle flux measurements and limited movement of particles the bed forms share form and grain size characteristics with both ripples and mega ripples showing poor sorting of particles across a single wavelength except for a slight coarsening at the crest similar to ripples but their sinuosity suggest that transverse instabilities affect their formation similar to mega ripples based on the data for the prevailing environmental conditions it can be argued that the wright valley form is an expression of gravel particles moved solely by highly intermittent creep processes this also argues for the need for a very long period of time for their evolution on the order of centuries

distribution of organic walled marine and terrestrial palynomorphs in surface sediments offshore eastern new zealand organic walled dinoflagellate cyst dinocyst and terrestrial spore pollen assemblages are analysed from 38 modern surface sediments offshore eastern new zealand from 33 to 54 s water depths of 79 to 4680 m and spanning the prominent chatham rise the most diverse abundant and best preserved marine and terrestrial assemblages are observed on the northern flank of chatham rise coincident with the subtropical front region being an area of enhanced biological activity and primary productivity dinocyst assemblages are dominated by the gonyaulacoid autotrophic taxa impagidinium nematospheropsis labyrinthus operculodinium centrocarpum spiniferites and peridinioid heterotrophic brigantedinium taxa with preferences for cooler e g selenopemphix antarctica and warmer e g impagidinium strialatum water masses are identified in distribution records and canonical correspondence analysis of the nine environmental parameters measured dinocyst assemblages were strongly correlated to sea surface temperature february and chlorophyll a autumn terrestrial spores and pollen dominate palynomorph assemblages in many sites and primarily reflect the presence of lowland podocarp broadleaf forest of onshore eastern new zealand spores and bisaccate pollen dominate assemblages with angiosperm pollen comprising up to 10 in the chatham rise area pollen from plants restricted to northern regions has been transported south via subtropical surface currents this pilot study shows that palynomorph assemblages offshore new zealand including the high terrigenous input margin of eastern north island can provide suitable proxy records for characterisation of coeval marine and terrestrial changes through time

large scale cenozoic wind erosion in the puna plateau the salina del fraile depression wind erosion is integral to the evolution of arid landscapes on earth and mars but the nature of long term wind erosion of bedrock is poorly understood here we describe the salina del fraile sdf

evidence for different episodes of aeolian construction and a new type of wind streak in the 2016 exomars landing ellipse in meridiani planum mars we present evidence for a complex multigenerational bed form pattern and a new type of wind streak the ripple streak in the landing site ellipse of the 2016 exomars entry descent and landing demonstrator module edm in meridiani planum mars we identified three main groups of bright toned bed forms population 3 represented by ne sw trending bed forms located inside craters was emplaced by winds coming from the nw or the se population 2 emplaced by strong easterlies formed by intracrater transverse aeolian ridges tars and n s trending megaripples plains ripples population 1 consists of a relict bed form pattern emplaced by winds coming from the north or south alternatively population 1 can represent a sand ribbon pattern that formed together with the plain ripples we also report the presence of a new type of wind streak the ripple streak which is formed by the population 2 bed forms clustered in the wake zone of impact craters based on the results of this work we now know the edm module is set to land in a complex aeolian environment data from the dust characterization risk assessment and environment analyser on the martian surface onboard the edm can help to better decipher the wind regime in meridiani planum

aeolian granule ripple deposits namibia granule ripples are a common feature of most dunefields yet they have seldom been recognized in ancient deposits although granule ripples are common in erosional settings such as windward slopes of dunes or scour surfaces in interdunes they nevertheless migrate laterally and leave distinctive deposits that can be recognized in ancient rocks these deposits have characteristics of type b sand sheet deposits including poured in texture curving ripple trough tangential coarse grained foresets irregular silty layers well sorted coarse and fine layers either horizontal or within foresets and fine layers in ripple troughs wind tunnel experiments suggest that under low velocity wind conditions granule ripples grow to a significant degree as parasites dependent on saltation of fine sand grains whose impact moves the larger grains of the granule ripple although the depositional surface of granule ripples is commonly coated with a layer of coarse grains this is in most places only a few grains thick underlying deposits commonly have a poorly sorted or poured in texture this texture results from an admixture of fine grains that fall among the spaces between the larger grains during deposition

live dead comparison of benthic foraminiferal faunas from the rhone prodelta gulf of lions nw mediterranean development of a proxy for palaeoenvironmental reconstructions dead benthic foraminiferal faunas 150 m from the rhone prodelta gulf of lions nw mediterranean were analysed at 41 stations 15 100 m water depth sampled in june 2005 and september 2006 and compared to the living faunas investigated during previous studies at the same stations the comparison between dead and living assemblages enhances the understanding of taphonomic processes that may modify the composition of the dead faunas in this area we observed a loss of individuals from living to dead assemblages of species characterised by a fairly fragile test and therefore more prone to fragmentation or dissolution e g bolivina alata quinqueloculina tenuicollis allochthonous dead and or live specimens may be transported to some parts of the prodelta particularly the shallowest sites where hydrodynamic processes i e river flood storm swells longshore currents are more intense these specimens may originate from relict deltaic structures e g elphidium spp from the lobe of bras de fer or from surrounding areas e g ammonia beccarii forma beccarii from the river opportunistic species e g bulimina marginata cassidulina carinata characterised by high reproductive rates have much higher relative abundances in the dead than in the living fauna cluster analyses based on dead foraminiferal assemblages divide our study area into four main thanatofacies directly related to distinct local environmental conditions prevailing in the prodelta close to the river mouth ammonia beccarii forma beccarii and ammonia tepida are found in sediments subject to a high riverine influence i e bottom currents high organic and inorganic material input of continental origin elphidium species are abundant in the silty sandy relict deltaic lobe west of the river mouth which is characterised by strong longshore currents that disturb the benthic environment nonion fabum rectuvigerina phlegeri and valvulineria bradyana are found along the coast west of the rhone river mouth in the area defined as the river plume thanatofacies in the more stable and deeper prodeltaic area species known to feed on fresh phytodetritus e g bulimina aculeata marginata c carinata hyalinea balthica dominate the faunas since only minor variations in species relative abundances and spatial distributional patterns are observed between the living and the dead faunas we consider that our thanatofacies have not been influenced by substantial transport of dead tests this suggests that fossil benthic foraminifera can provide a reliable tool for investigating the development of the palaeo rhone prodelta

coexisting active travertines and tufas in the southeastern border of the puna plateau abstract the terma los hornos is an active hydrothermal system located in the southeastern border of the andean puna plateau in catamarca province northwest argentina it exhibits a complete range from high to low temperature quaternary carbonate products still actively forming travertines and tufas can be considered lithological end members within the depositional system but the lack of clear boundaries has generated confusion when trying to distinguish them in the fossil record in the terma los hornos a continuum between both extremes is recorded through a transition of different morphologies and dominant but non diagnostic fabrics among which we recognize a variety of crystalline crusts shrubs spheroidal particles encrusted bubbles and reeds lithoclastic grumulous micritic and silty sandy carbonates these were grouped in the following depositional subsystems 1 vents and pinnacles 2 mound apron 3 terraced slope 4 steep slopes and 5 flooding areas and palustrine hydrochemistry results show substantial variabilities ranging from 65 c ph 6 41 1029 ppm alkalinity and 37 ppm calcium concentrations at the vents site to 21 c ph 8 13 and 800 ppm alkalinity and 14 ppm calcium concentrations at 1 km downstream were carbonate precipitation is no longer visible the set of linked subenvironments tend to merge into a larger scale geobody that defines the travertine system with a proximal area dominated by physicochemical processes and a distal extent with pervasive microbial and common macrophyte features the travertine system should not be understood as a fixed model and its limits as well as the existing subenvironments their extents and degree of overlapping will depend mainly on three factors 1 hydrothermal input 2 climate and 3 landscape perched past travertine deposits together with internal architectures and extent of the presently active travertine system allows thinking about constructive and destructive stages respectively thought as dominantly expanding and erosional periods alternation of these two evolutionary stages and their balance will dictate the volume of primary facies and potential reworking products a better understanding of these stages and their litho stratigraphic products will allow developing predictive stratigraphic and correlation models based on a sequence stratigraphic approach

aeolian processes and features in cool climates this review concentrates on the characteristics of wind processes and products in cold lowland deserts its main aims are to show how difficult it can be to separate wind generated from water generated processes and features without detailed study of lamination types to suggest cold aeolian interpretations for some ancient pre quaternary rocks and to encourage students to revisit many ancient deposits with such interpretations in mind although upper quaternary and recent cold climate aeolian deposits have been studied for many years there are very few older examples described martian features are included since mars is now one of the most exciting areas of study

glacial interglacial changes of southern hemisphere wind circulation from the geochemistry of south american dust abstract the latitudinal displacement of the southern westerlies and associated climate systems is a key parameter for understanding the variations of southern hemisphere atmospheric circulation during the late quaternary period to increase understanding of past atmospheric circulation and of the paleo environmental conditions associated with continental dust sources we dig deeper into dust provenance in paleo archives of the southern hemisphere we present here a sr nd isotopic and rare earth element study of surface sediments collected along a 4000 km latitudinal band from arid and semi arid terrains in southern south america findings from terrains that served as paleo dust suppliers are compared with modern dust collected from monitoring stations along the same latitudinal band which affords a test on how actual present day aeolian compositions compare to those of the past potential source areas moreover the comparison between past and present day datasets is useful for understanding present day atmospheric circulation armed with a new comprehensive dataset we revise previous interpretations of the provenance of dust trapped in the antarctic ice and sediments deposited in the south atlantic sector of the southern ocean these comparisons support multiple source regions in southern south america that changed with climates the findings reveal that although patagonia plays an important role in contributing dust to the higher latitudes central western argentina and to a lesser extent the southern puna region also emerge as potentially important dust sources during glacial times the southern altiplano appears to be a major contributor during interglacial periods as well we rely in part on an understanding of modern wind dust activities to conclude that the possible presence of southern south america source regions other than patagonia in east antarctic ice is consistent with an overall equatorward displacement during glacial times of both the mid latitude westerlies and the subtropical jet stream

the largest wind ripples on earth reply we thank de silva 2010 1 for the opportunity to discuss the origin of the unique megaripples mr found on the puna plateau forman and krohling were invited as co authors of this reply because we produced new data supplied here de silva suggests that the genetic relationship inferred by

spatial and particle size distributions of atmospheric dissolvable iron in aerosols and its input to the southern ocean and coastal east antarctica 1 to characterize atmospheric dissolvable iron over the southern ocean so and coastal east antarctica cea bulk and size segregated 0 056 18 m in diameter aerosols were collected from 34 s 109 e to 69 s 76 e and between 69 s 76 e and 66 s 110 e during a cruise during november 2010 to march 2011 aerosols were analyzed for total dissolvable fe and fe ii by uv visible spectroscopy and total fe by inductively coupled plasma mass spectrometry the average concentrations of total fe were 19 ng m 3 range 10 38 ng m 3 over the so and 26 ng m 3 range 14 56 ng m 3 in cea the average fe ii concentrations were 0 22 ng m 3 range 0 13 0 33 ng m 3 over the so and 0 53 ng m 3 range 0 18 1 3 ng m 3 over cea the total dissolvable fe followed the same trend over the so a single peak size distribution of fe ii existed over cea a bimodal size distribution of fe ii appeared with the first peak at 0 32 0 56 m and the second peak at 5 6 10 m higher fe concentrations over cea than over the so and the existence of coarse mode fe ii over cea suggest potential dust sources in antarctica the fractional fe ii solubility ranged from 0 58 to 6 5 and decreased with total fe concentration increase the estimated atmospheric fluxes of fe ii were 0 007 0 092 mg m 2 yr 1 over the so and 0 022 0 21 mg m 2 yr 1 in cea total dissolvable fe fluxes were 0 007 0 52 mg m 2 yr 1 over the so the atmospheric dissolvable fe input contributes to the dissolved fe pool in the so surface waters

west african monsoon variability during the last deglaciation and the holocene evidence from fresh water algae pollen and isotope data from core kw31 gulf of guinea abstract the study of aquatic and mangrove pollen grains and algae from freshwater environments from core kw31 recovered off the mouth of the niger river 3 31 1 n 05 34 1 e 1181 m water depth documents large scale changes in river discharge linked to variations of atlantic monsoon rainfall during the last glacial interglacial transition and the holocene two main taxa dominate the algal record pediastrum which records the strongest river input from 14 500 to 7100 cal b p and botryococcus which indicates surficial runoff in more arid periods particularly at the onset of the deglaciation and during the younger dryas several dry events punctuated the first and more intense phase of the so called african humid period 14 500 cal b p 9800 cal b p during the younger dryas 13 400 12 100 cal b p then around 11 400 11 200 cal b p indicating major climate instability freshwater discharges decreased after 7100 cal b p and definitely dropped to modern values after 3500 cal b p in agreement with land data the microfossil record of core kw31 shows that the increase in freshwater input to the ocean and correlative rainfall over western tropical africa were gradual in response to insolation forcing at the transition from glacial to interglacial situations

fecycle attempting an iron biogeochemical budget from a mesoscale sf6 tracer experiment in unperturbed low iron waters 1 an improved knowledge of iron biogeochemistry is needed to better understand key controls on the functioning of high nitrate low chlorophyll hnlc oceanic regions iron budgets for hnlc waters have been constructed using data from disparate sources ranging from laboratory algal cultures to ocean physics in summer 2003 we conducted fecycle a 10 day mesoscale tracer release in hnlc waters se of new zealand and measured concurrently all sources with the exception of aerosol deposition to sinks of iron from and rates of iron recycling within the surface mixed layer a pelagic iron budget timescale of days indicated that oceanic supply terms lateral advection and vertical diffusion were relatively small compared to the main sink downward particulate export remote sensing and terrestrial monitoring reveal 13 dust or wildfire events in australia prior to and during fecycle one of which may have deposited iron at the study location however iron deposition rates cannot be derived from such observations illustrating the difficulties in closing iron budgets without quantification of episodic atmospheric supply despite the threefold uncertainties reported for rates of aerosol deposition duce et al 1991 published atmospheric iron supply for the new zealand region is 50 fold i e 7 to 150 fold greater than the oceanic iron supply measured in our budget and thus was comparable i e a third to threefold to our estimates of downward export of particulate iron during fecycle the fluxes due to short term hours biological iron uptake and regeneration were indicative of rapid recycling and were tenfold greater than for new iron i e estimated atmospheric and measured oceanic supply giving an fe ratio uptake of new iron uptake of new regenerated iron of 0 17 i e a range of 0 06 to 0 51 due to uncertainties on aerosol iron supply and an fe ratio biogenic fe export uptake of new regenerated iron of 0 09 i e 0 03 to 0 24

limitation of algal growth by iron deficiency in the australian subantarctic region in march 1998 we measured iron in the upper water column and conducted iron and nutrient enrichment bottle incubation experiments in the open ocean subantarctic region southwest of tasmania australia in the subtropical convergence zone 42 s 142 e silicic acid concentrations were low 1 5 m in the upper water column whereas pronounced vertical gradients in dissolved iron concentration 0 12 0 84 nm were observed presumably reflecting the interleaving of subtropical and subantarctic waters and mineral aerosol input results of a bottle incubation experiment performed at this location indicate that phytoplankton growth rates were limited by iron deficiency within the iron poor layer of the euphotic zone in the subantarctic water mass 46 8 s 142 e low concentrations of dissolved iron 0 05 0 11 nm and silicic acid 1 m were measured throughout the upper water column and our experimental results indicate that algal growth was limited by iron deficiency these observations suggest that availability of dissolved iron is a primary factor limiting phytoplankton growth over much of the subantarctic southern ocean in the late summer and autumn

detailed structure of the subtropical front over chatham rise east of new zealand a detailed description of the subtropical front stf over chatham rise is presented information is provided by conductivity temperature depth ctd profiler temperature and salinity transects high resolution 3 4 km spacing near synoptic expendable bathythermograph surveys shipboard acoustic doppler current profiler measurements a 160 km constant depth undulator tow and satellite sst measurements in austral autumn and spring april and october near 178 30 e detailed sections across the front reveal that the stf can be divided into northern and southern fronts nstf and sstf separated by a frontal zone consistent with observations of the stf elsewhere comparison with a western ctd section along 176 e reveals that this structure breaks down close to the new zealand landmass the dominant impact of seasonally is the formation and decay of a seasonal thermocline of fairly constant depth over the entire region velocity measurements indicate eastward zonal flows on the northern and southern flanks of chatham rise the flow over chatham rise is complicated by stirring processes but has a mean southward trend consistent with the less dense warm salty subtropical water stw overriding the more dense cold fresh subantarctic water saw to the south horizontal length scale analyses of the temperature field for a constant depth tow at 21 m indicate a k 2 4 spectral falloff with no proof of preferential length scales the temperature salinity gradients are largely density compensated in this mixed layer tow the horizontal temperature standard deviation shows subsurface maxima concentrated at the locations of the nstf and sstf vertical length scales vary across the front with large scales 80 100 m in the stw north of the stf and smaller scales 20 40 m in the subtropical frontal zone and saw to the south the surface vertical length scales are dominated by the presence of a seasonal thermocline

pulsating flow dynamics of sustained forced pyroclastic density currents insights from a facies analysis of the campo de la piedra pomez ignimbrite southern puna argentina the quaternary campo de la piedra pomez ignimbrite cppi is a superbly exposed partially indurated rhyolitic ignimbrite emplaced on the southern puna of argentina it is characterized by a variety of facies that record in unprecedented detail the flow dynamics of the parent pyroclastic density currents pdcs detailed facies analysis and internal architecture defined using a sequential stratigraphy approach reveal that cppi was formed by sustained pdcs generated from a low fountain eruptive style boiling over the pdcs had overall flow conditions characterized by high particle concentration and limited capability to surmount topographic obstacles the mobility of the pdcs was largely controlled by high pore pressure and the continuous supply at the source sustained forced convection dominated pdcs the successive forestepping backstepping stacking patterns identified in the cppi reflect a marked unsteadiness of its parent pdcs due to a pulsating discharge rate at the source the lateral facies variations in the cppi record the non uniform character of its parent pdcs as they flowed outward from the base of the collapsing fountain proximal medial areas characterized by steady aggradation rates pass through to distal braided thalwegs with highly variable aggradation rates to frontal edges characterized by the step aggradations of secondary decoupled pumice rich lobes collectively the facies variations in the cppi record the complex dynamics of sustained pdcs that include pulsating discharge rate at the source progressive modification of the original topography and lateral flow transformations

paleo eolian dynamics in the andean plateau inferences from sedimentology of fossil and modern dunes fil lopez steinmetz romina lucrecia universidad nacional de jujuy instituto de ecorregiones andinas consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet salta instituto de ecorregiones andinas argentina universidad nacional de jujuy argentina consejo nacional de investigaciones cientificas y tecnicas argentina

a wind tunnel investigation of particle segregation ripple formation and armouring within sand beds of systematically varied texture this paper reports on a wind tunnel investigation of particle segregation ripple formation and surface armoring within sand beds of systematically varied particle size distribution from coarsely skewed to bimodal by design the system was closed with no external inputs of mass from an external particle feed particles too coarse to travel in saltation for the given range in wind speed were dyed red in order to distinguish them in optical images from finer sand particles which could be entrained into the unidirectional airflow a 3d laser scanner measured the changing bed topography at regular time intervals during 18 experiments involving varied combinations of wind speed and bed texture image classification techniques were used to investigate the coincident self organization of the two populations of particles as distinguished by their colour as soon as saltation commenced some of the red particles segregated into thin discontinuous patches particle trapping and sheltering on these rough patches was strongly favoured causing them to grow preferentially during the earliest stages of formation bedform growth coincided with i rapid coarsening of the surface texture and ii the merging of proto ripple crests to generate larger rhythmic bedforms of lower frequency consistent with previous work ripple size was observed to increase under stronger winds when not exceeding the threshold for entrainment of the coarse mode or red particles from the crest with declining rates of mass transport and particle segregation as the bed surface armoured and the consequent deceleration of ripple propagation through to the end of each experiment all surfaces eventually attained a steady state morphometry at saturation the largest ripples developed upon beds having the lowest initial concentration of red particles this article is protected by copyright all rights reserved

aerodynamic roughness height for gravel mantled megaripples with implications for wind profiles near tars on mars abstract aerodynamic roughness heights of 1 3 cm were obtained from measured wind profiles collected among fields of gravel mantled megaripples in the high desert of the puna region of northwestern argentina roughness height appears to be relatively insensitive to the angle at which the wind was incident upon the bedforms throughout the study sites the results represent the first wind profiling measurements for large megaripples but they also demonstrate the importance of a careful evaluation of many potential effects that can influence the utility of wind profiling data the same effects that influence collection of fieldwork data must also be considered in any prediction of wind profiles anticipated to occur near transverse aeolian ridges and other aeolian features on mars that are intermediate in scale between wind ripples and small sand dunes

dust provenance in antarctic ice during glacial periods from where in southern south america 1 the origin of dust deposited in east antarctica is not fully understood yet this study demonstrates that contrary to nd sr isotopes are strongly fractionated in the finest sized material representing potential dust sources in south america analysis of nd isotopes suggests that argentine loess southern ocean sediments and antarctic dust may all have a related origin or can represent comparable mechanisms of eolian sediment transport and deposition this analysis also concludes that the patagonian signature can explain a high proportion of the isotopic composition of dust trapped in antarctic ice during glacial periods the puna altiplano plateau emerges as the second possible important sediment contributor explaining the crustal like signature found in east antarctic dust and should be considered as a potential source area when quaternary paleoclimate is reconstructed from argentine loess antarctic dust and south atlantic sediment records

mechanisms limiting the growth of aeolian megaripples megaripples are distinguished from regular ripples by their larger size and bimodal sediment distribution the interplay between wind grain size and morphology controls their development but the exact mechanisms that limit the size of megaripples have been unclear using wind tunnel experiments we found two main mechanisms that limit the height of megaripples the first mechanism is megaripple flattening due to strong enough winds that drive the coarse grains into saltation the second mechanism is megaripple deflation by impacts of faster saltation grains in this latter mechanism the coarse grains are propelled by the impacts of fine saltating grains the occurrence of both these mechanisms depends on the grain size distribution and increases with both megaripple height and wind speed thus for a given wind environment and grain size distribution there exists a limit on the size of megaripples which is determined by these two mechanisms

coastal zone color scanner pigment concentrations in the southern ocean and relationships to geophysical surface features the spatial and seasonal distributions of phytoplankton pigment concentration over the entire southern ocean have been studied for the first time using the coastal zone color scanner historical data set from october 1978 through june 1986 enhanced pigment concentrations are observed between 35 s and 55 s throughout the year with such enhanced regions being more confined to the south in the austral summer and extending further north in the winter north and south of the polar front phytoplankton blooms 1 mg m3 are not uniformly distributed around the circumpolar region instead blooms appear to be located in regions of ice retreat or high melt areas such as the scotia sea and the ross sea in relatively shallow areas e g the patagonian and the new zealand shelves in some regions of ekman upwelling like the tasman sea and near areas of high eddy kinetic energy such as the agulhas retroflection among all features examined by regression analysis bathymetry appears to be the one most consistently correlated with pigments correlation coefficient being about 0 3 for the entire region the cause of negative correlation with bathymetry is unknown but is consistent with the observed abundance of iron in shallow areas in the antarctic region it is also consistent with resuspension of phytoplankton cells by wind induced mixing especially in shallow waters on the other hand in the deep ocean especially at latitudes 30 in average pigment concentration over the entire region during different seasons indicates possible influence of time dependent parameters

atmospheric transport of iron and its deposition in the ocean the atmospheric transport of continental weathering products is responsible for much of the mineral material and fe entering the open ocean and is probably the dominant source of nutrient fe in the photic zone in regions where other nutrients are present in high concentrations the flux of fe from the atmosphere may be a limiting factor in primary productivity due to the larger source regions for dust north of the equator 8 times more atmospheric fe is deposited in the northern hemisphere than in the southern hemisphere the mineral aerosol and fe transport and deposition are highly variable due to the episodic nature of dust generation and its transport and deposition processes between 10 and 50 of the total atmospheric fe entering the world ocean appears to dissolve i e it will pass through a 0 4 m pore size filter rapidly when the mineral matter enters the ocean much of the atmospheric fe is present as fe ii apparently produced as a result of photochemical reduction reactions taking place during atmospheric transport this readily soluble fe ii should be available immediately for use as a nutrient by phytoplankton atmospheric transport from the continents is estimated to supply 3 times as much dissolved fe to the oceans as that delivered via rivers

megaripple migration on mars aeolian megaripples with 5 to 50 m spacing are abundant on the surface of mars these features were repeatedly targeted by high resolution orbital images but they have never been observed to move thus aeolian megaripples especially the bright toned ones often referred as transverse aeolian ridges tars have been interpreted as relict features of a past climate in this report we show evidence for the migration of bright toned megaripples spaced 1 to 35 m 5 m on average in two equatorial areas on mars indicating that megaripples and small tars can be active today the moving megaripples display sand fluxes that are 2 orders of magnitudes lower than the surrounding dunes on average and unlike similar bedforms on earth can migrate obliquely and longitudinally in addition the active megaripples in the two study areas of syrtis major and mawrth vallis show very similar flux distributions echoing the similarities between dune crest fluxes in the two study areas and suggesting the existence of a relationship between dune and megaripple fluxes that can be explored elsewhere active megaripples together with high sand flux dunes represent a key indicator of strong winds at the surface of mars a past climate with a denser atmosphere is not necessary to explain their accumulation and migration

the effect of coastal processes on phytoplankton biomass and primary production within the near shore subtropical frontal zone this study evaluated drivers of phytoplankton net primary production npp rates and chlorophyll a chla concentrations within the coastally oriented subtropical frontal zone stfz off the south island of new zealand time series measurements of hydrographic parameters macronutrients size fractionated npp and chl a were conducted on a bi monthly basis from july 2009 to november 2010 this study found that nutrient limitation in these waters is controlled by the dual influx of silicate inputs from riverine sources in coastal neritic water nw and oceanic inputs of nitrate from the high nutrient low chlorophyll hnlc region of the offshore sub antarctic surface waters sasw total chl a concentrations and primary production rates were perennially higher in near shore nw and modified subtropical waters stw than in the sasw with highest indicators of biological production observed in the austral spring and summer seasons october to march these periods of peak production and biomass were dominated in both parameters by microphytoplankton 20 mm size fractions the coupled dominance by these large phytoplankton and the near depletion of silicate in all characterised waters within the frontal system indicate the importance of silicic diatoms as drivers of bloom production the influence of coastal waters on the stfz system is most pronounced with the intrusion of neritic water beyond the shelf boundary during periods of surface water thermal stratification and riverine dilution through flooding events these two events were notably observed during the spring 2009 sampling cruise in december 2009 and in the flood event in may 2010

factors influencing the distribution of subantarctic deep sea benthic foraminifera campbell and bounty plateaux new zealand abstract we investigate the combination of environmental factors that influence the distribution patterns of benthic foraminiferal tests 63 m in a topographically varied region crossed by both the subtropical and subantarctic fronts south east of new zealand seafloor sample sites extending from outer shelf 50 m to abyssal 5000 m depths are bathed by five different water masses and receive phytodetritus from subtropical subantarctic and circumpolar surface water masses eight mappable associations are recognised by q mode cluster analysis of the benthic foraminiferal census data similar associations are identified using cluster analysis based solely on the presence or absence of species canonical correspondence analysis and a correlation coefficient matrix were used to relate the faunal data to a set of environmental proxies these show that factors related to water depth especially decreasing food supply with increasing depth are the most significant in determining the overall foraminiferal distribution other contributing factors include surface water productivity and its seasonality bottom water ventilation energetic state of the benthic boundary layer and resulting substrate texture and bottom water carbonate corrosiveness three shallow water associations 50 700 m dominated by cassidulina carinata trifarina angulosa globocassidulina canalisuturata gavelinopsis praegeri and bolivina robusta occur in coarse substrates on the continental shelf and on the crests and upper slopes of four seamounts under well oxygenated high energy regimes and high food input three mid bathyal to upper abyssal associations 500 3300 m dominated by alabaminella weddellensis c carinata and epistominella exigua occur in biopelagic sandy mud beneath a region of strongly seasonal food supply with their composition influenced by total food flux ventilation oxygen minimum zone and bottom current strength an unusual lower bathyal association 1200 2100 m dominated by t angulosa and ehrenbergina glabra occurs in a belt of coarser sandy substrate that runs along the crest of the submarine plateaux slopes beneath the strongly flowing subantarctic front related currents a deep abyssal association 3500 5000 m dominated by nuttallides umbonifer and globocassidulina subglobosa occurs on the abyssal plain beneath oligotrophic lower circumpolar water south east of the subantarctic front and is strongly influenced by the cold carbonate corrosive conditions the faunal composition of this subantarctic region is most similar to adjacent southern new zealand but with the addition of a few significant antarctic elements e g e glabra globocassidulina crassa

bedform spacing from defect dynamics spacing is a time varying characteristic of bedform fields deriving from the behavior of defects ends of crest lines in the bedform pattern in a model based on this hypothesis crest line length is lost and spacing increases because bedform defects which are smaller in height and faster migrating than surrounding bedform crest lines merge with larger bedforms as defects migrate through bedform fields spacing in large bedform fields asymptotically increases with the logarithm of time as pairs of oppositely facing defects meet and annihilate spacing in small bedform fields such as flumes exponentially approaches a fixed value as defects are eliminated at the boundaries of the field model predictions are compatible with observed spacing of transverse bedforms ripples formed under waves and linear dunes calling into question the widespread assumption that bedform spacing approaches a steady state value characteristic of fluid flow and sediment transport over two dimensional bedforms

a terrestrial analog for transverse aeolian ridges tars environment morphometry and recent dynamics abstract transverse aeolian ridges tars are a distinct aeolian bedform found on mars the formative processes evolution and geological significance of tars is poorly understood fundamentally it is unknown whether tars are dunes mega ripples or another bedform type we examined aeolian bedforms in the lut desert of iran as a terrestrial analog for martian tars from an objective sampling strategy with high resolution satellite imagery we developed a large morphometric dataset for comparison with existing martian tars we also examined the dynamics of the lut bedforms between 2004 and 2012 to determine if they were static or migrating results indicate that the range in the dimensions length width height and wavelength of the lut bedforms and martian tars overlap suggesting lut bedforms are a viable terrestrial tar analog our sample yielded median values of 55 18 m 9 80 1 02 m and 20 m for length longest planview axis width shortest planview axis height and wavelength respectively cumulative log frequency plots of morphometric parameters suggest the sample is from a single population and process mechanism although the vast majority of lut bedforms examined were static between 2004 and 2012 some migrated up to 0 09 myr 1 on average this is much slower than nearby dunes 4 12 myr 1 but is explained by the existence of a surface lag of coarse particles on the tar like bedforms the combination of morphometry surface sedimentology and slow migration rate indicate the lut bedforms are mega ripples which provides evidence supporting interpretation of martian tars as mega ripples testing the mega ripple hypothesis for martian tars requires measurements of their sedimentology which may be possible with the mars science laboratory rover curiosity as well as expanded measurements of tar morphometry to constrain their size shape and scaling

seasonal variations in foraminiferal flux in the southern ocean campbell plateau new zealand abstract time incremental sediment trap moorings were deployed at two sites across campbell plateau new zealand one in the relatively quiet waters of the plateau interior pukaki rise and the other at the antarctic circumpolar current swept margin eastern campbell flank a continuous record of particle flux over 416 days identifies marked differences in faunal composition and seasonal occurrence in response to these two dynamically different southern ocean settings in the shallow and thermally isolated interior of the pukaki rise site the flux of foraminifera was closely linked to the austral spring pulse of primary production at which time 97 of the total foraminiferal production for the year occurred this seasonal flux of foraminifera at pukaki rise was dominated by the species globorotalia inflata and globigerina bulloides the collapse of phytoplankton production at the end of spring was most likely a result of a co limitation of iron and silicic acid over the deep and dynamic eastern flank of campbell plateau there were four seasonal pulses of foraminiferal flux the largest in spring when almost half of the foraminiferal production occurred most of the spring flux at this site consisted of globorotalia inflata and globigerinita glutinata summer at eastern campbell flank exhibited the lowest flux of foraminifera but the highest species diversity while autumn and winter fluxes were dominated by the deep dwelling globorotalia truncatulinoides although there was only a single pulse of foraminiferal flux at pukaki rise its mass g m 2 d 1 was still greater than that which occurred over the flank summed across all four seasons however the overall standing stock tests m 2 d 1 on the flank was more than twice that which occurred at the pukaki rise site an examination of core top material taken from gravity cores collected in the vicinity of the sediment trap locations revealed typical southern ocean foraminiferal assemblages that were markedly dissimilar in proportion to those observed in the sediment traps

zebra stripes in the atacama desert revisited granular fingering as a mechanism for zebra stripe formation abstract although a number of studies have pointed out the remarkable slowness of earth surface processes in the atacama desert process mechanisms under such extremely limited water availability are poorly understood and process rates remain unknown this paper revisits the discussion on the formation of the prominent atacama specific hillslope zebra stone stripes previously interpreted to result from palaeo overland flow owen et al 2013 compared to this study our data document different stripe characteristics with regard to stripe form and orientation as well as sorting and bedding patterns of stripe confining surface gravel units we found a remarkable form concordance between zebra stripes and deposits from experiments on segregation induced granular fingering hence we propose a combination of seismic shaking and instantaneous dry granular free surface flows as the key mechanism for zebra stripe formation our findings underline the potential significance of seismicity in shaping atacama landscapes which bear important analogies to extra terrestrial surfaces

first data on volume and type of deflated sediment from southern puna plateau and its role as source of the chaco pampean loess abstract this paper presents the first attempt at qualitatively and quantitatively evaluating the sedimentary contribution of the puna plateau to the loess and soils of the argentinean pampas the origin of the pampean sediment has been traditionally ascribed to northern patagonia but new evidence supports a dual supply western central andes north patagonia and puna altiplano plateau three different lines of evidence show here that puna dust supply is active and produces significant sedimentary deposition up to places like buenos aires city the first evidence is meteorological and we show here one event related to an abnormal rainfall that deposited large quantities of a reddish brownish silt eroded out from the puna calling the attention of the environmental agency of buenos aires city the second evidence is the sampling of active wind transport collecting extremely coarse material carried out in the saltation layer suggesting the fine grained material escapes the area as fugitive dust this also demonstrates that observed gravel bearing bedforms of the puna are active and that the transport system seems to be activated by polar fronts only results show that the saltation curtain is abnormally thick and coarse suggesting that the kinetic energy peaks ca 7 10 times higher than for normal saltation while the transported grain size coincides with the lagged sediment in this basin composing different bedforms varying between sandy gravel and gravelly sand the third evidence is the quantification of the exported material by defining a reference surface as the initial time of evolution and the present day surface the initial surface is an alluvial surface of an estimated age of 11 12 ka bp volume balance was achieved by a detailed topographic stratigraphic and geophysical survey reconstructing old alluvial and present surfaces two gridding methods were used and more conservative results of the volume balance indicate a total erosion of ca 3 386 hm 3 of sediment in 72 ha spliced in 0 963 hm 3 of sediment that was left within the place forming gravel dunes while the remaining volume of ca 2 423 hm 3 is sediment truly exported from the surveyed area results imply a continuous blanket of ca 4 m thick of sediment exported out of this basin in the holocene these findings prove that the puna contribution to the chaco pampean plain is significant although not unique thus true proportions of sediment contribution to soils and loess from these multiple sources should be better evaluated in future studies

surface ocean lower atmosphere interactions in the northeast pacific ocean gyre aerosols iron and the ecosystem response 1 here we report measurements of iron and aluminum in surface and subsurface waters during late march and late may of 2001 on transects between central california and hawaii a large cloud of asian dust was detected during april 2001 and there was a clear signal in surface water iron due to aerosol deposition on the may transect iron and aluminum concentrations increased synchronously by 0 5 and 2 nm along the southern portion of the transect which includes the hawaii ocean time series hot station from background values in march 0 1 to 0 2 nm fe these changes occurred in a ratio that is close to the crustal abundance ratio of the metals which indicates a soil aerosol source a vertical profile of dissolved iron was also measured at the hot station in late april and this profile also shows a large increase near the surface direct observations of aerosol iron concentration at mauna loa observatory on hawaii indicate that aerosol concentrations were significantly lower than climatological values during this period soil aerosol concentrations along the transect were estimated using the real time navy aerosol analysis and prediction system naaps the naaps results show a large meridional gradient with maximum concentrations in the boundary layer north of 30 n however the deposition of iron and aluminum to surface waters was highest south of 25 n near hawaii there were only weak signals in the ecosystem response to the aerosol deposition

dinoflagellate cysts from two sediment traps east of new zealand abstract two discontinuous sediment trap records of organic walled dinoflagellate cyst dinocyst flux each sampling 300 days within the years 2005 2009 were derived from two time incremental traps deployed at 1500 m water depth east of new zealand the traps sampled flux from beneath two distinct surface water masses on either side of the subtropical front i warm seasonally macronutrient depleted subtropical and ii cold micronutrient limited subantarctic waters nineteen dinocyst taxa or taxonomic groups were identified from the trap samples trap assemblages at both sites were dominated by cysts of protoperidiniaceae notably brigantedinium spp which comprised almost 98 of the dinocyst flux the seasonality of the dinocyst flux differed between the traps with a pronounced spring flux in the subtropical trap while seasonal variation in the subantarctic trap was relatively muted in subtropical waters moderate correlation was observed between protoperidiniaceae cyst flux and chlorophyll a concentrations in surface waters in the 3 4 weeks prior to sampling in subantarctic waters there was a weak correlation between protoperidiniaceae cyst flux and reduced intensity of storm induced turbulence during the preceding 2 3 weeks there was a large discrepancy between dinocyst assemblages in the traps and those observed in nearby sea floor sediments protoperidiniaceae dinocysts particularly echinidinium and brigantedinium were highly under represented in the sea floor assemblages these forms are more susceptible to degradation in oxygenated sediments than other dinocysts but inter annual variability in cyst flux or short term variation not covered by sampling discontinuities in the current study could also have contributed to this discrepancy the major differences in the seasonality of dinocyst fluxes between the two water masses examined in this initial study suggest that mean annual rather than seasonal climatologies are more appropriate for dinocyst based quantitative palaeoenvironmental reconstructions in the new zealand region

southwest pacific sea surface conditions during marine isotope stage 11 results from dinoflagellate cysts abstract dinoflagellate cyst dinocyst assemblages are examined from three sw pacific marine sediment cores covering marine isotope stage 11 mis11 423 ka 380 ka md06 2988 and md06 2989 are in the east tasman sea north of the subtropical front stf whilst dsdp594 is in subantarctic surface waters saw off eastern new zealand sea surface temperature sst estimates from dinocyst assemblages indicate that the east tasman sea was 2 5 c warmer than present during the peak warmth of mis11 in the east tasman sea north of the stf there is a two step warming into mis11 in cores md06 2988 and md06 2989 east of new zealand and south of the stf at core site dsdp594 dinocyst sst estimates suggest that mis11 was an extended warm period similar to or slightly warmer than present conditions although data from the early phase prior to 417 ka may be compromised due to insufficient modern analogues at all sites glacial interglacial climatic fluctuations were accompanied by large assemblage changes glacial intervals were characterised by higher abundances of assemblages typical of saw nematosphaeropsis labyrinthus selenopemphix antarctica brigantedinium spp subtropical surface water stw assemblages dominated during the interglacial in the east tasman sea including impagidinium aculeatum i patulum and spiniferites mirabilis whilst assemblages consistent with continued saw influence remained during the interglacial at core site dsdp594 albeit with reduced cold water indicators such as s antarctica the changes are particularly pronounced in the east tasman sea where the stf is inferred to have been located further north during glacials mis12 and mis10 the influence of stw at dsdp594 during mis11 and the holocene is inferred to have been less than during mis5e a qualitative dinocyst based index likely reflecting primary productivity also influenced by oxygen concentration on the sea floor is broadly anti phased with sst on glacial interglacial timescales at all sites

granule ripples in the kumtagh desert china morphology grain size and influencing factors granule ripples are found mainly in four regions of the kumtagh desert in china they are characterized by an asymmetrical shape with gentle lower slopes on both sides and abrupt crests the ripples tend to be oriented perpendicular to the prevailing winds except when they form near obstacles such as yardangs the wavelengths range between 0 31 m and 26 m and heights h range from 0 015 m to 1 m the relationship between wavelength and height can be described by a simple linear function and the mean ripple index h is about 20 4 for the study sites the sediments are poorly sorted with negative to very negative skewness at lee and stoss slopes and between ripple troughs which confirms the poured in and shadow appearance described by previous researchers the bimodal or trimodal distributions of grains with modes of 1 16 0 5 and 3 16 and the enrichment of coarse particles at the ripple surface with coarse granule contents ranging between 5 2 and 62 1 indicate that the underlying layer is the original sediment source and that the granule ripples resist erosional processes although the impact of saltating particles and consequently the creep and reptation of coarse grains are responsible for granule ripple initiation at a micro scale however the characteristics of local sediments wind regimes and topographical obstacles as well as the feedbacks among bedform and airflow more strongly affect the development and alignment of granule ripples at a macro scale

dissolved fe in the upper waters of the pacific sector of the southern ocean the concentration of dissolved fe was determined in upper ocean waters along 170 degreesw between 53 and 72 degreess during four cruises between october 1997 and march 1998 as part of the us jgofs southern ocean antarctic polar frontal zone cruises fe concentrations were extremely variable in both space and time as a result of advection of meso scale eddys through the region observed values ranged from a maximum of 0 34 nm at 64 degreess in november next to the retreating ice edge to 0 075 nm in march at 71 degreess in the northern ross sea gyre in general the highest average mixed layer fe concentrations and the largest seasonal changes were observed in the two frontal zones at similar to 60 degreess and similar to 64 degreess formation of deep mixed layers during winter and the entrainment of sub surface waters enriched in fe is the primary source of this element to surface waters in this region of the southern ocean additionally upwelling of circumpolar deep water in the circumpolar current along its northern boundary at the polar front and its southern boundary at the southern antarctic circumpolar current front is an important mechanism supplying fe to surface waters in these areas throughout the summer comparison of integrated fe concentrations and th derived poc export and n drawdown all suggest that the maximum changes in these properties are comparable to those that would be predicted by fe availability fe concentrations determined by shipboard flow injection analysis measures et al mar chem 50 1995 3 were significantly higher than those found in replicate samples determined by shored based flameless atomic absorption spectrophotometry after preconcentration by chelation solvent extraction johnson et al mar chem 57 1997 137 the concentration differences which appear to be restricted to the upper 200 300 m do not appear to arise from different sampling or handling processes but instead are believed to result from the different sensitivity of the methods to organic fractions of fe in seawater c 2001 elsevier science ltd all rights reserved

sea surface temperature variability in the north western mediterranean sea gulf of lion during the common era this study investigates the multidecadal scale variability of sea surface temperatures ssts in the convection region of the gulf of lion nw mediterranean sea over the full past 2000 yr common era using alkenone biomarkers our data show colder ssts by 1 7 c over most of the first millennium 200 800 ad and by 1 3 c during the little ice age lia 1400 1850 ad than the 20th century mean 17 9 c although on average warmer those of the medieval climate anomaly mca 1000 1200 ad were lower by 1 c we found a mean sst warming of 2 c 100 yr over the last century in close agreement with the 0 22 and 0 26 c decade values calculated for the western mediterranean sea from in situ and satellite data respectively our results also reveal strongly fluctuating ssts characterized by cold extremes followed by abrupt warming during the lia we suggest that the coldest decades of the lia were likely caused by prevailing negative ea states and associated anticyclone blocking over the north atlantic resulting in cold continental northeasterly winds to blow over western europe and the mediterranean region

a biogeochemical study in the bellingshausen sea overview of the sterna 1992 expedition abstract a general overview and background of a two ship study to examine biogeochemical fluxes in the marginal ice zone of the bellingshausen sea 65 70 s 80 87 w se pacific sector of the southern ocean is presented the major feature studied was an intense band of chlorophyll that was found geographically close to a receding ice edge however the bloom appeared not to be a result of a shallow mixed layer caused by ice melt stabilisation but rather associated with an oceanic front that coincided with the ice edge details of the hydrographic conditions existing along the 85 w meridian from the ice edge to open water to the north and detailed surveys of surface hydrographic conditions are presented

soil abrasion and eolian dust production implications for iron partitioning and solubility 1 eolian dust is a source of iron for phytoplankton in many ocean areas and there are complex pathways of atmospheric processing from soil to ocean overlooked parts of the pathways are the impact of large 10 m grains including a role as proxies for the behavior of smaller grains and the effect of multiple cycles of uplift and abrasion in the dust source region partitioning readily released acid leachable and refractory and dissolution rates of iron were determined for an artificial dust produced by abrading an australian soil untreated soil abraded soil after production of the artificial dust and a natural australian eolian dust sample taken during a dust storm readily released iron is not created during abrasion and therefore the amount of readily released iron in a dust or dust derived soil depends on processing events since the dust or soil last experienced an abrasion event our study develops a method for the partitioning of iron within airborne dusts and appears to be the first to consider the effect of multiple uplift events on iron partitioning

gravel mantled megaripples of the argentinean puna a model for their origin and growth with implications for mars gravel megaripples in the puna of argentina are the most extreme aeolian megaripples on earth and are useful analogs for aeolian processes on mars field observations supplemented by experimental and numerical constraints on wind characteristics and aeolian transport reveal their conditions of formation and growth to be an aeolian geomorphology perfect storm the bedforms are formed on a substrate of weakly indurated ignimbrite aeolian deflation of which yields a bimodal lag of lithics and pumice clasts onto an undulating surface under normal wind conditions in this region the lithics are organized into bedforms on local upslopes and highs through creep induced by the impact of saltating sand and pumice the gravel bedforms grow through shadowing and trap sand and silt that is gradually kinetically sieved down to lift the gravel mantle upwards to form the megaripples these observations connote that the largest features are not ripples in the sense of migrating bedforms but rather nucleation sites of wind transported sediment strong control by bedrock topography means that the largest bedform wavelengths are not a result of particle trajectories and this complicates their comparison with other ripples and may require a new classification of relevance to mars the puna megaripples are morphologically and contextually similar to small ripple like transverse aeolian ridges tars moreover the puna gravels have similar equivalent weight mg to those composing granule ripples at meridiani planum and their local origin may have implications for the origin of sediment in martian aeolian bedforms finally the stable yet dynamic character of the puna megaripples could help reconcile current models of tars with periodic bedrock ridges that may be produced by aeolian erosion

stability of organic carbon accumulating in spartina alterniflora dominated salt marshes of the mid atlantic u s abstract organic carbon sequestration in salt marsh soils is a function of factors that influence both spatial variability and chemical stability of accumulating carbon refractory carbon slowly decomposed may be the most important in terms of long term sequestration and is widely referred to in models of carbon storage however little information exists about the quantity and variability of refractory carbon accumulation in marshes in this study total c t labile c l and refractory c r organic carbon accumulation rates were measured for spartina alterniflora dominated marshes representing different geomorphological settings with a range of vertical accretion rates three 50 cm long cores were collected in each of three marshes in barnegat bay and three marshes in delaware estuary usa rates of c accumulation were calculated using cesium 137 dating and the relative stability of soil organic carbon was quantified using acid hydrolysis c t accumulation ranged over fourfold among marshes from 72 to 346 g m 2 yr 1 c t and c l accumulation increased with increasing mineral sediment accumulation while c r accumulation was uniform across cores averaging 78 5 g m 2 yr 1 similar rates of c r accumulation across marsh areas with different accretion and mineral sediment accumulation rates was associated with a decline in the c r c l density ratio as mineral volume increased our results suggest that carbon accumulation is higher in salt marshes with higher mineral sedimentation due primarily to the burial of labile carbon and that there is a limit on the rate of chemically recalcitrant carbon accumulation in marsh soils

episodic enhancement of phytoplankton stocks in new zealand subantarctic waters contribution of atmospheric and oceanic iron supply 1 around 30 of oceanic waters are high nitrate low chlorophyll hnlc where low iron levels limit algal growth hnlc waters have mainly been studied using shipboard and lab experiments since 1997 remote sensing of phytoplankton via seawifs ocean color has permitted monitoring of the constancy of this hnlc condition i e spatial homogeneity and low temporal variability of chlorophyll over annual cycles these trends can be exploited as episodic iron inputs should be conspicuous by subsequent expression as iron elevated algal stocks subantarctic sa waters near new zealand are hnlc and the proximity of the arid australian landmass and the iron rich subtropical front provide natural laboratories to detect episodic atmospheric and oceanic iron supply respectively two approaches were used oceanic supply was inferred from episodic increases in chlorophyll concentrations in sa waters detected using ocean color archives additional archives were used to confirm the oceanic provenance of iron supply and identify supply mechanism s atmospheric supply was assessed using data on source areas and loads for dust storms monitored in central australia dust transport and its fate was assessed using air mass forward trajectories and seawifs ocean color and aerosol optical depth maps during 1997 2001 episodic elevated chlorophyll events occurred in sa waters southeast of new zealand there was no evidence of these events being mediated by atmospheric iron supply however neither wind driven lateral advection or vertical mixing alone could account for these episodes dust storms over this period sent plumes either into high iron subtropical st waters or into sa waters in early spring when cells are probably light rather than iron limited

the largest wind ripples on earth comment the dominance of aeolian features on the surface of mars requires a better understanding of potential terrestrial analogs to provide constraints on models of origin in his timely article milana 2009 1 describes the largest wind ripples on earth from the puna plateau of argentina inverting

reconstruction of paleo particulate organic carbon fluxes for the campbell plateau region of southern new zealand using the zinc content of sponge spicules 1 the zinc concentration of siliceous sponge spicules was determined from spicules recovered from four sediment cores spanning the last 160 kyr from the campbell plateau region southeast of new zealand zinc si results showed little difference between holocene and glacial aged spicules an increase in zn si was observed for core y14 where zn si peaked at about 0 6 mol mol during marine isotope stages 5a 5b to better understand the role carbon export has on sponge zn si we explored the strong relationship observed between surficial sediment particulate organic carbon poc and the zn si of sponge silica and related this to sediment trap poc flux estimates conversion of the zn si records to benthic poc fluxes suggests that there has been little change in the amount of poc reaching campbell plateau sediments over the past 30 kyr these results suggest that surface productivity over the campbell plateau has remained relatively low over the past 160 kyr and suggests that glacial productivity was not significantly higher than the present day finally this work reveals that living marine sponges appear to act as the biological equivalents of moored sediment traps recording the flux of poc to the seafloor by archiving zinc associated with sinking poc in the growing silica skeleton

radiolarian based sea surface temperatures and paleoceanographic changes during the late pleistocene holocene in the subantarctic southwest pacific abstract a high resolution record of radiolarian faunal changes from site y8 south of the subtropical front stf offshore eastern new zealand provides insight into the paleoceanographic history of the last 265 kyrs quantitative analysis of radiolarian paleotemperature indicators and radiolarian based sea surface temperature sst estimates reveal distinct shifts during glacial interglacial g i climate cycles encompassing marine isotope stages mis 8 1 faunas at site y8 are abundant and diverse and consist of a mixture of species typical of the subantarctic transitional and subtropical zones which is characteristic of subantarctic waters just south of the stf during interglacials diverse radiolarian faunas have increased numbers of warm water taxa 15 while cool water taxa decrease to 11 of the assemblage warmest climate conditions occurred during mis 5 5 and the early holocene climatic optimum hco at the onset of mis 1 where ssts reach maxima of 12 8 and 12 9 c respectively this suggests that temperatures during the hco were comparable to the eemian one of the warmest interglacial intervals of the late quaternary glacials are characterized by less diverse radiolarian faunas with cool water taxa increasing to 49 of the assemblage coolest climate conditions occurred in mis 4 and 2 where ssts are reduced to 5 4 c and 4 3 c respectively radiolarian faunal changes and sst estimates clearly identify major water masses and oceanic fronts in the offshore eastern new zealand area during warmest mis 5 5 and early mis 1 substantial influence of northern sourced subtropical surface water stw is evident at site y8 this implies southward incursions of stw around the eastern crest of chatham rise with the stf displaced towards higher latitudes and spinning off eddies as far south as campbell plateau additionally increased flow of the southland current sc might have enhanced the local occurrence of warm water radiolarians derived from the subtropical tasman sea coolest glacials are marked by a strong inflow of cool southern sourced waters at site y8 indicating a more vigorous flow along the subantarctic front saf

a theoretical model for aeolian impact ripples new insights into the grain bed impact process arising from both numerical and physical experiments involving single grain impacts lead to a more complete conceptual model of the aeolian saltation process that in turn allows a simple model of aeolian impact ripples to be developed the saltating population may be idealized as consisting of 1 long trajectory high impact energy constant impact angle successive saltations and 2 short trajectory low impact energy reptations it is argued that the spatial variations in mass flux due to the reptating population lead to the growth and translation of impact ripples using the sediment continuity equation an expression for the spatial variation in the ejection rate of reptating grains from a sinusoidally perturbed bed and a probability distribution for the reptation lengths a simple stability analysis demonstrates that the flat bed is unstable to small amplitude perturbations a fastest growing wavelength emerges that is roughly six times the mean reptation length and is only weakly dependent upon the detailed shape of the probability distribution of reptation lengths the results match well with the observed initial wavelengths in wind tunnel experiments

wind blown sandstones cemented by sulfate and clay minerals in gale crater mars gale crater contains mount sharp a 5km thick stratigraphic record of mars early environmental history the strata comprising mount sharp are believed to be sedimentary in origin but the specific depositional environments recorded by the rocks remain speculative we present orbital evidence for the occurrence of eolian sandstones within gale crater and the lower reaches of mount sharp including preservation of wind blown sand dune topography in sedimentary strata a phenomenon that is rare on earth and typically associated with stabilization rapid sedimentation transgression and submergence of the land surface the preserved bedforms in gale are associated with clay minerals and elsewhere accompanied by typical dune cross stratification marked by bounding surfaces whose lateral equivalents contain sulfate salts these observations extend the range of possible habitable environments that may be recorded within gale crater and provide hypotheses that can be tested in situ by the curiosity rover payload

largest wind ripples on earth unique wind ripples attaining heights to 2 3 m wavelengths to 43 m and a crest maximum grain size of 19 mm occur on the argentine puna plateau at 4000 m altitude these are the largest ripples reported on earth comparable only to mars counterparts they form in the presence of high proportions of low density pumice clasts 0 91 g cm 3 although crests are exclusively composed of varnished normal density clasts 2 43 g cm 3 mature ripple profiles are partly excavated on bedrock so they form by a combination of deflation winnowing of finer grains minor wind drift of fine gravel and lagging of clasts 4 cm the large ripple size appears to be related to strong winds dense saltation layers and a long time for evolution ripple sizes are smaller on obstacles as compared to flat terrain there is a lack of correlation between clast size wavelength and the extreme ripple size in spite of the thin atmosphere all of which suggest that while small scale gravel ripples may form according to a reptation model their evolution into large scale types may relate to aerodynamic instabilities originating at the saltation curtain air interface

on the use of high resolution satellite data to describe the spatial and temporal variability of sea surface temperatures in the new zealand region a new high resolution 1 1 km regional data set of satellite derived sea surface temperatures sst is developed and validated against drifting and moored buoy data analysis of 5 years of monthly means and related statistics suggests that there is often a coherent relationship between the sst patterns and oceanographic features identifiable relationships are detailed then used to indicate the temporal and spatial characteristics of watermasses fronts and currents for example a gradient analysis suggests that the subtropical front east of new zealand and west of 177 w is bathymetrically locked to the southern flank of the chatham rise near 44 s beyond 177 w it loops southward to a mean position close to 47 s on the northern edge of the bounty plateau adjacent to the subantarctic front near 48 s harmonic analysis of the 60 months of data suggests that spatial variability in the amplitude of the sst annual cycle is related to circulation water mass features and varies from less than 1 c in subantarctic waters to more than 4 c in new zealand nearshore neritic waters the antarctic circumpolar east auckland and east cape currents also display coherent annual cycle amplitude signatures that differ from adjacent water masses however the amplitude of the annual cycle in subantarctic waters south of the chatham rise and north of the pukaki rise and bounty plateau is significantly different from that of this water mass at other similar latitudes an empirical orthogonal function eof analysis of seasonal anomalies shows that 90 of sst variance can be associated with the annual cycle however four eofs are required to explain 50 of the variance in sst monthly anomalies the first of these 25 4 of the variance indicates that anomalies north and east of new zealand are negatively correlated with those in the subantarctic the second eof represents a tasman sea mode and suggests that the tasman sea has been in a warming phase since december 1996 to at least april 1998 this might explain the exceptional size and sign of the sst anomaly in new zealand waters during the 1998 el nino where in february 1998 it reached 3 5 c in northern new zealand waters similar to the amplitude of the annual cycle

composition and temporal variability of particle fluxes in an insular canyon of the northwestern mediterranean sea abstract particle fluxes have been widely studied in canyons located in continental margins conversely particle fluxes in canyons in sediment starved margins incising small island margins have received very little attention and remain poorly understood the menorca canyon is the largest canyon system in the balearic archipelago despite the high oligotrophic conditions of the balearic archipelago the canyon and surrounding areas host diverse communities dominated by benthic suspension feeders understanding the magnitude and variability of environmental factors influencing these communities thus remain crucial in order to characterize the temporal variability of particle fluxes analyze its geochemical and macroscopic composition and identify the main processes that modulate particle fluxes in the menorca canyon one instrumented line with a sediment trap and a current meter was deployed at 430 m water depth from september 2010 to october 2012 particle fluxes ranged between 190 and 2300 mg m2 d 1 being one of the lowest ever registered in a mediterranean submarine canyon s head the caco3 fraction was the major constituent contrasting with the general trend observed in other mediterranean canyons macroscopic constituents fecal pellets posidonia oceanica detritus and pelagic and benthic foraminifera presented a wide variability throughout the sampling period and were not significantly correlated with the total mass flux the low magnitude of the registered fluxes and the lack of correlation with the observed environmental variables e g currents winds wave height chlorophyll a biomass suggest that there is no evident controlling mechanism however we could infer that resuspension processes and the presence of different hydrodynamic features e g eddies interchange of water masses condition the magnitude and composition of particle fluxes

australian dust storms in 2002 2003 and their impact on southern ocean biogeochemistry during late 2002 and early 2003 southern australia was in the grip of drought and experienced one of its most active dust storm seasons in the last 40 years with large dust plumes frequently advected over the adjacent southern ocean we use meteorological records of dust activity satellite ocean colour and aerosol optical depth data and dust transport modeling to investigate the transport and deposition of mineral dust from australia over adjacent ocean regions and to correlate it with biological response in phytoplankton standing stock as measured by chlorophyll a concentration in five degree latitude bands from 40 60 s seasonal maxima in mean surface chlorophyll a of 0 5 mg m 3 were not achieved until late jan 2003 or during february in the more southerly bands which when compared with a 9 year satellite mean climatology suggests the phenology of the bloom in 2002 03 was atypical contemporaneous field data on co2 fugacity collected on transects between tasmania and antarctica show that significant atmospheric co2 drawdown occurred as far south as 60 s during february 2003 our results provide strong evidence for a large scale natural dust fertilization event in the australian sector of the southern ocean and highlight the importance of dust derived nutrients in the marine carbon cycle of the southern ocean

ground satellite observations and atmospheric modeling of dust storms originating in the high puna altiplano deserts south america implications for the interpretation of paleo climatic archives 1 this study provides a detailed description of the sources transport dispersion and deposition of two major dust events originating from the high altitude subtropical puna altiplano plateau 15 26 s 65 69 w in south america a long and severe drought provided the right conditions for the onset of both events in july 2009 and 2010 dust was transported se and deposited over the pampas region and was observed to continue to the atlantic ocean dust monitoring stations located downwind recorded both events and samples were characterized through chemical and textural analysis through a combination of meteorological data and satellite observations calipso and modis detectors we estimate the emission flux for the 2010 event this estimate was used to constrain the hybrid single particle lagrangian integrated trajectory hysplit transport model and simulate the dust event both satellite imagery and model results agree in the location and extension of the dust cloud calipso detected dust between 6000 and 8500 m a s l which remained at this height during most of its trajectory the dust cloud mixed with a strong convective system in the region and the associated precipitation brought down significant amounts of dust to the ground dust particle size analysis for both events indicates that near the sources dust samples show median modes of 12 4 14 1 m similar to modes observed 1300 km away chemical composition of sediments from potential dust sources shows distinct signatures within the puna altiplano plateau the puna sector being clearly different from the altiplano area in addition both sources are markedly different from the patagonian chemical fingerprint these results have important implications to improve the interpretation of paleo environmental archives preserved on the argentine loess antarctic ice cores and southern ocean marine sediments

the role of aeolian dust in ecosystems abstract the recent upsurge in research attention to aeolian dust has shown that dust transport systems operate on very large spatial and temporal scales and involve much larger quantities of sediment than was previously realized an inevitable consequence of this is that researchers from a range of neighbouring disciplines including ecology are beginning to realize that this new knowledge has important implications for their study areas in the present paper we examine the ecological implications real and potential of this expanding knowledge of dust transport systems with a particular emphasis upon the australian dust transport system we track these ecological effects from source to sink at source wind erosion soil vegetation relationships are often dominated by temporal changes in rainfall nine years of measurements in the channel country of the lake eyre basin australia show that vegetation and soils in dune fields can recover from drought whereas on inter fluve grasslands uni directional and negative successional vegetation changes can result from wind erosion during drought on floodplains both wind erosion and vegetation responses are complicated by flood frequency up to 1999 flooding of saline claypans did not increase vegetation but did increase wind erosion through the supply of alluvial fines however after three floods within as many months vegetation became established and wind erosion rates were dramatically reduced wind erosion research attention is now gradually turning from the physical to the organic content of eroded dusts in australia organic matter content can reach 65 by mass but this cannot be explained by removal of soil organic matter alone biological soil crusts not only stabilize soils against wind erosion but contribute to some of the organic dusts the role of dust as a vector for pathogens is an area which deserves greater research attention in the future downwind from source we show that dust contributions to soils are more widespread and more variable in time and space than earlier work on dust derived loess soils has suggested recent studies also show positive dust impacts upon nutrient budgets within distant forest ecosystems and significant contributions to river nutrient loads especially in the arid sectors of internally draining river basins the number of studies of dust impacts upon marine ecosystems is increasing dramatically studies of dust within antarctic ice cores combined with dust modelling provide compelling evidence that increased soluble iron rich dust inputs to the southern ocean have stimulated phytoplankton populations modern process studies are however yet to clearly demonstrate these relationships finally we examine the potential for major dust impacts upon global climates using its positive and negative effects upon solar radiation and precipitation as examples of the complexity and importance of this new research area

wind ripples in an active drift sand area in the netherlands a preliminary report two types of wind ripples are distinguished in an active drift sand area near hulshorst in the veluwe central netherlands the common type has amplitudes of about 0 5 cm and wavelengths of some 11 cm the atypical ripple has amplitudes of about 1 cm and wavelengths of some 16 cm in both cases the sand grains in the crests are coarser than those in the troughs however the coarseness of the grains in the crests of the higher ripples is much more pronounced than that of the lower it is tentatively suggested that wind ripples are initiated by a regular downwind alternation in the impact energy of the descending grains in saltation possibly due to fixed gravity waves in the sheared flows of air with grains which have strong density gradients with height

periodic bedrock ridges on mars 1 evidence for sediment transport and erosion by wind is widespread over the surface of mars today and was likely a major geomorphic process for much of its geological past although martian surface features resembling aeolian dunes and ripples have been recognized since the mariner and viking missions such features have been interpreted previously as active indurated or exhumed sedimentary forms here we report evidence based on high resolution imaging science experiment images that show some megaripple forms are eroded into cohesive substrate rather than being composed of loose granular material or fossilized dunes exposure of stratigraphic continuity within layered cohesive material extending crest to trough through features with mean wavelengths of 18 to 51 m demonstrates the primarily erosional formation of what we term periodic bedrock ridges pbrs hence some surfaces on mars previously considered to be covered by wind deposited material are actually wind carved exposures that offer windows into martian history pbrs lack the distinctive streamlining associated with wind parallel yardangs and comparison of pbr orientation to yardangs megayardangs and active sedimentary dunes in the same vicinity confirm that these pbrs formed transverse to prevailing winds observed wavelengths of pbrs are comparable to those predicted by a simple model for erosional wavelengths of periodic transverse bed forms owing to the spacing of flow separations within the flow recognition of these transverse aeolian erosional forms brings up the question of how widespread martian pbrs are and how many have been misinterpreted as active or indurated fossilized sedimentary dunes