vulnerability and fate of a coastal sand dune complex rosetta idku northwestern nile delta egypt types distribution and origin of recent sand dunes between rosetta and idku in the western sector of the nile delta egypt were investigated sand samples from the dunes beach and seafloor were studied for grain size distribution and mineralogical composition it has been found that most of the dunes in the study area have been subjected to deterioration and removal due to the construction of buildings and the international coastal highway the remnant constitutes a damaged belt of foredunes that extends from el bouseily village to the west of idku town the dune s origin is interpreted to be the result of coastal drifting and the subsequent transport of sediments of the former canopic nile branch eastward by the predominant longshore current and by aeolian processes the blown sand grains accumulated to form a belt of coastal sand dunes of original longitudinal and crescentic forms urbanization of the coast has severely altered the landscape the study area is considered vulnerable to the impacts of climate change and the expected rise in sea level the outcome of potential sea level rise is serious erosion problems are expected to be exacerbated and vast areas from land and property would be lost thus protection and preservation the remaining dunes in the study area are vital requirements for shore protection

factors determining desert dune type while most observers recognize four elemental types of desert dunes longitudinal transverse barchan and star1 3 there is little agreement about which factors determine these types the angular relationships between the resultant of sand shifting winds and both the crest and principal slipfaces of the elemental types have been discussed qualitatively for many decades these relationships have been quantified but the wide range of dune types that combine the elemental forms and the juxtaposition of different dune types show that wind regime is not the only determinant for example sand availability has been considered important we have now quantified the importance of both wind regime and sand availability as determinants of dune type we show here that the four elemental types occur in areas uniquely defined by both the equivalent sand thickness of sediments held in the dunes and a measure of directional variability of sand moving winds wind strength does not appear to be important vegetation has an ambiguous role and the particle size of dune sediments is unimportant

the cape ghir filament system in august 2009 nw africa in the framework of the canaries iberian marine ecosystem exchanges caibex experiment an interdisciplinary high resolution survey was conducted in the nw african region of cape ghir 30 38 n during august 2009 the anatomy of a major filament is investigated on scales down to the submesoscale using in situ and remotely sensed data the filament may be viewed as a system composed of three intimately connected structures a small shallow and cold filament embedded within a larger deeper and cool filament and an intrathermocline anticyclonic eddy ite the cold filament which stretches 110 km offshore is a shallow feature 60 m deep and 25 km wide identified by minimal surface temperatures and rich in chlorophyll a this structure comprises two asymmetrical submesoscale 18 km fronts with jets flowing in opposite directions the cold filament is embedded near the equatorward boundary of a much broader region of approximately 120 km width and 150 m depth that forms the cool filament and stretches at least 200 km offshore this cool region partly resulting from the influence of cold filament is limited by two asymmetrical mesoscale 50 km frontal boundaries at the ite located north of the cold filament we observe evidence of downwelling as indicated by a relatively high concentration of particles extending from the surface to more than 200 m depth we hypothesize that this ite may act as a sink of carbon and thus the filament system may serve dual roles of offshore carbon export and carbon sink

altimeter derived variability of surface velocities in the california current system 2 seasonal circulation and eddy statistics abstract satellite surface height and temperature fields are used to examine the seasonal surface circulation in the california current system in spring and summer an equatorward jet develops next to the coast with an initial latitudinal structure that responds to the latitudinal distribution of equatorward alongshore winds this jet moves offshore from spring to fall and develops meanders and closed eddies that contribute eddy kinetic energy and water mass properties to the nearby deep ocean higher eke appears first in spring near the coast and moves offshore with the seasonal jet along altimeter tracks parallel to the coastline 200 and 400 km offshore the greatest eke is found in summer and fall respectively with wavelengths of approximately 300 km these are the wavelengths of the largest meanders and the distance between the largest eddies visible in altimeter snapshots of the jet at 600 800 km offshore the wavelengths are generally smaller 100 150 km similar to eddy sizes reported by others for the quiescent northeast pacific some energy with longer wavelengths arrives at the track 600 km offshore in winter and 800 km offshore in spring which we interpret as the most offshore extension of the eke generated by the jet and eddy system closer to the coast in the previous spring and summer a sequence of snapshots from october 1992 to october 1993 shows details of the evolution of the jet and eddy system over one complete annual cycle

moored observations of the current and temperature structure over the continental slope off central california 2 the energetics of the flow off point sur the data from two current meter moorings off point sur california were analyzed to examine the energy transfers over the continental slope in the california current system ccs the method used was to calculate terms in the heat equation at intermediate depths between instruments using the thermal wind relation to estimate the horizontal temperature gradients from the vertical shear time series of u v and t were collected for 17 months may 1989 to october 1990 at site p2 on the 800 m isobath and for 12 months may 1990 to may 1991 at site p3 25 km farther offshore on the 1800 m isobath instrument depths were 100 350 and 500 m at both moorings plus 1000 m at site p3 mean values of the energy conversion terms were computed at sites p2 and p3 at 225 m depth and at site p2 at 425 m depth the local change of eddy potential energy epe was approximately balanced epe t 0 for each case but the dynamics were quite different at p2 225 the sources of epe were advection by the mean flow and baroclinic instability which converted mean potential energy mpe to epe the losses came from eddy advection out of the region and the vertical eddy heat flux vehf which converted epe to eddy kinetic energy eke at p2 425 baroclinic instability provided the major source of epe this plus a small positive contribution from the vehf was balanced by advection of epe out of the region by both the mean flow and the eddies at p3 225 mean advection and baroclinic instability were negligible and the downward eddy heat flux vehf was balanced by advection of heat out of the region by the eddies time series of terms in the epe equation were used to examine high energy transfer events at both moorings events at p2 involved both horizontal and vertical processes and had longer timescales several days to weeks than those at p3 which had much shorter timescales 2 5 days and were dominated by vertical processes compared to the gulf stream the mean baroclinic instability at p2 both depths was smaller by at least a factor of 10 a term by term comparison between the mean values off point sur and the kuroshio extension showed different processes with the eddies gaining strength at the expense of the mean flow off point sur and the opposite occurring in the kuroshio extension

physical description of an upwelling filament west of cape st vincent in late october 2004 1 the present paper describes the physical characteristics of an upwelling filament off cape st vincent southern iberia in october 2004 based on remote sensing hydrographic adcp and wind data it was associated with a meandering jet similar to eastern pacific or canary filaments though its dynamical features were weaker as a result of the surface trapped top 100 m and weak horizontal density gradients the filament transported 0 9 sv of coastal water offshore of which 8 was due to ekman transport it formed following the destabilization of an alongshore equatorward upwelling jet close to the cape the filament was structurally asymmetric with anticyclonic geostrophic vorticity to the north and more strongly cyclonic to the south as a result of the meanders and existing eddies the filament comprised a sequence of cold submesoscale 30 km diameter cyclones vertical velocities of 15 m d 1 were associated with meanders of the jet the surface and subsurface circulation was coupled at middepths 90 150 m anticyclonic recirculation of northern water seemed associated with a separated older upwelling jet mediterranean water mw was present below 350 dbar as a topographically steered undercurrent and a meddy cyclone dipole these undercurrents contributed to the formation of the october filament through baroclinic instability associated with the enhanced vertical shear

ocean climate of the south east atlantic observed from satellite data and wind models the near coastal south east atlantic ocean off africa is a unique and highly dynamic environment comprising the cool benguela current warm angola current and warm agulhas current strong coastal upwelling and the congo river strongly influence primary production much of the present knowledge of the south east atlantic has been derived from ship borne measurements and in situ sensors which cannot generally provide extensive spatial and temporal coverage similarly previous satellite studies of the region have often focused on small spatial areas and limited time periods this paper provides an improved understanding of seasonal and interannual variability in ocean dynamics along the south east atlantic coast of africa using time series of satellite and model derived data products eighteen years of satellite sea surface temperature data are complimented by 7 years of sea level data three years of chlorophyll a data illustrate the seasonal biological response but the time series is not of sufficient length for investigating interannual variability in chlorophyll biomass modelled wind fields are used to describe atmospheric forcing of the surface ocean this is the first synoptic scale description of the south east atlantic from a suite of large spatial coverage long time series products previous studies of seasonal and interannual variability in the region are reviewed and used to interpret key oceanographic features and processes identified in the satellite data key findings of this study are 1 descriptions of seasonal and interannual variability from these data show climate forcing of the south east atlantic coast of africa from both the northern and southern boundaries bimodal seasonal signals of equatorial origin propagate poleward along the angolan coast while the trade winds and events in the agulhas region dominate the agulhas bank and southern benguela the northern benguela is a mixed regime under the influence of forcing from both directions 2 the benguela nino years of 1984 and 1995 are clearly observed in sea surface temperature and sea level anomalies and correspond to anomalously weak southerly winds at the equator these conditions were also observed in 1999 suggesting this too may have been a benguela nino year 3 consideration of putative nino type events in the equatorial atlantic from this and other studies suggests that the frequency of these events is much higher than previously estimated and may be similar to the frequency of el nino southern oscillation enso events in the pacific ocean furthermore years of anomalously strong southerly winds at the equator occur during pacific enso years c 2003 elsevier ltd all rights reserved

wind forced modeling studies of currents meanders and eddies in the california current system this process oriented study of the california current system ccs uses a high resolution multilevel primitive equation ocean model on a plane to isolate the response of that eastern boundary oceanic regime to temporal and spatially varying wind forcing to study the generation evolution and maintenance of many of the observed features such as currents meanders and eddies in the ccs the model is forced from rest with seasonal climatological winds in response to the prevailing wind direction surface equatorward currents develop along with upwelling of cooler water along the coast and a poleward undercurrent baroclinic barotropic instabilities in the equatorward surface current and poleward undercurrent result in the generation of meanders near the coast as the meanders intensify cold upwelling filaments develop along the coast and subsequently extend farther offshore in time the meanders form both cyclonic and anticyclonic eddies which subsequently propagate farther offshore longer simulation times 3 4 years in which a quasi equilibrium state for the ccs is reached show a seasonal cycle in response to the wind forcing for the coastal currents upwelling and filaments the meanders and eddies however can be quasi permanent as well as seasonal features the quasi permanent features play a significant role in modifying coastal currents upwelling and filaments which leads to large temporal and spatial variability in the ccs in a sensitivity study the results from several numerical experiments are used to examine the dependence of the generation of the currents meanders and eddies on the type of coriolis parameterization wind forcing and coastline geometry both the meridional variability of plane and the alongshore component of the wind stress are shown to be key ingredients for generating realistic vertical and horizontal structures for the cores of the surface equatorward and the subsurface poleward currents with such structures the currents are baroclinically and barotropically unstable resulting in the generation of meanders filaments and eddies irregularities in the coastline geometry are shown to be important for anchoring upwelling and filaments as well as for enhancing the growth of meanders and eddies cyclonic eddies tend to form in the vicinity of capes while anticyclonic eddies tend to form in the coastal indentations between capes the region off cape blanco is identified as the location where the coastal equatorward flow off oregon leaves the coast to develop a meandering jet off california the results from these experiments support the hypothesis that wind forcing and coastline irregularities on a beta plane are important mechanisms for the generation of many of the observed features of the ccs

dunes on the skeleton coast namibia south west africa geomorphology and grain size relationships simple and locally compound transverse and barchanoid dunes dominate the 2000 km2 skeleton coast dunefield in northwestern namibia south west africa dune height and spacing are closely correlated r 0 89 and decrease across the dunefield from southwest to northeast with an accompanying change from transverse to barchanoid ridges and ultimately barchans the dunes are aligned transverse to the dominant strong south and south southwest onshore winds alignment patterns indicate that surface roughness changes between coastal plain and dunes cause dune forming winds to swing to the right over the dunes but resume their original direction beyond grain size and sorting vary at three scales the dune the dune landscape and through the dunefield overall the sands derived from three localities by deflation from beaches supplied by vigorous longshore drift become progressively finer and better sorted across the dunefield paralleling changes in dune height and spacing a statistically significant relationship r 0 65 was established between dune spacing and the phi grain size of the coarser fraction of the dune sands demonstrating the importance of the protective effects of coarse grains and suggesting that the morphometry of simple transverse dunes may be controlled by the scale of turbulence associated with the threshold wind speed required to move the coarsest fraction of the dune sand

particle size variation of aeolian dune deposits in the lower reaches of the heihe river basin china abstract the grain size characteristics of aeolian dune and gobi sands in the lower reaches of the heihe river desert basin ejina of northwestern china in central asia were investigated aimed at a sedimentological study of the dune sediments and their response to aeolian processes and source area grain size parameters mean standard deviation skewness and kurtosis were determined for sand samples from dune crests interdunes and gobi areas the aeolian dunes are mainly composed of medium and fine grained sand sorting improves with decreasing grain size a clear relationship occurs between skewness and sorting in that sands become progressively zero skewed sk1 0 as sorting improves suggesting that improved sorting is accomplished by loss of both relatively coarser and finer grains in the desert in comparison with many other desert areas the dunes in the ejina are composed of relatively coarse sands are poorly sorted and relatively platykurtic in log probability grain size distributions most dune sands in the ejina are composed of two distinctive saltation populations truncated at about 1 8 and 2 5 this represents two differing aeolian transport conditions and presumably produces two separate saltation populations in opposite air flow directions sand dunes exhibit grain size and sorting patterns in which sands become finer better sorted and more finely skewed from interdune to crest which is a similar pattern to that in the namib desert this pattern can be best explained by differential movement of sand in creep and saltation populations at a regional scale dune sands tend to become finer from southwest to northeast in the desert basin which coincides with the basin hydrological setting but not with the compound direction of the basin wind system it appears that local scale factors such as hydrological processes and source materials rather than regional aeolian processes are responsible for the grain size variations of dune sands in the ejina desert

demographics of mesoscale eddies in the california current 1 demographics and variability of persistent mesoscale eddies in the california current have been investigated in a systematic manner using a decade 1995 2004 of merged satellite altimeter data the number of persistent eddies formed each year varied almost 3 fold 4 fold for cyclones anticyclones and was strongly modulated by the 1997 1998 el nino event over the 10 year period cyclone formation was maximum in both winter and summer while maximum anticyclone formation occurred only in winter the majority of long lived eddies 70 day lifespan originated seaward of the 1000 m isobath and with the exception of 2 anticyclones did not form between 45 and 50 n maximum westward propagation of long lived eddies was almost 800 km with similar mean propagation speeds for cyclones and anticyclones

reconstruction of linear dunes from ancient aeolian successions using subsurface data permian auk formation central north sea uk abstract a series of well logs and cores penetrating the predominantly aeolian auk formation permian rotliegend group central north sea uk have been evaluated to determine the morphology and style of migratory behaviour of the original dune bedforms the overall depositional environment and to assess implications for reservoir heterogeneity this has been achieved by detailed facies analysis of subsurface datasets and by comparison of the observed sedimentary styles of accumulation to analogous modern aeolian dune fields aeolian bedform type morphology detailed migratory behaviour and the nature of the accumulation surface have been interpreted analysis of the facies architecture of preserved cross bedded sets and cosets indicates accumulation on a dry substrate via the migration and climb of large linear bedforms that possessed low angle inclined lower plinths up to 15 m thick dune plinth elements are dominated by wind ripple and reworked wind ripple strata and were preferentially preserved as successive bedforms migrated over one another at low angles packages of grainflow dominated strata representative of accumulation on the higher part of the bedform lee slope are less common and tend to be preserved mostly in the upper parts of large cosets of strata 30 m thick large linear bedforms were separated by dry interdune areas although the primary direction of sand transport was along the elongated crests of the bedforms a secondary component of transverse motion enabled the lateral migration and preferential preservation of lee slope deposits that arose from a minor oblique component of bedform migration in places the architecture records the preservation of small barchanoid dune deposits either within interdune depressions or superimposed on the lower flanks of the large linear bedforms the preserved aeolian facies types exert a primary control on reservoir quality few previous studies have documented linear dunes in ancient successions these findings represent a valuable case example

grain size characteristics of dune sands in the central taklimakan sand sea abstract compared with the sand grain size of the other sand seas central taklimakan sand sea has some of the finest sands seen globally the dunes are composed of fine and very fine sands with a diameter between 2 00 and 4 00 0 25 0 063 mm there are differences in the grain size distributions for different dune types mean grain size of the compound complex crescent dune sands is 3 08 the compound dome dunes 3 21 the compound complex linear dune sands between 2 63 and 3 41 and the star dunes 2 81 from the northern edge of the sand sea towards southern edge the components of fine and very fine sands increase closely related to the wind regimes time scale for dune development and underlying sediments compared with the foregoing there are some differences for the compound complex linear dunes in the centre of taklimakan though the pattern of coarser crests does exist the sorting parameters indicate that the sands on the west flank of compound complex linear dunes are better sorted than that on the east flank and crest sampling on the superimposed dunes developed on the surface of the complex linear dunes suggests that the patterns of finer crest coarser crest all existed in central taklimakan under the conditions of low energy wind regime when fine sand is available the frequency of the pattern for finer crest and better sorting will increase sampling on the simple crescent dunes developed on the interdunes suggests that the simple dunes are developed originally with nearly the same grain size distributions and parameters with the development of the dunes and evolution of the dune morphology the grain size distributions of the dune sands varied under the actions of the wind regimes time scale and underlying sediments

multiple dipole eddies in the alaska coastal current detected with landsat thematic mapper data seventeen dipole eddies including five large well formed ones three second generation eddies and two double eddies were observed in the alaska coastal current near kayak island in one single scene of the landsat thematic mapper tm on april 22 1985 the digital landsat tm satellite data were computer analyzed to extract details in the near coastal circulation in the northern gulf of alaska enhancement techniques were applied to the visible and thermal ir bands the features are evident only in the visible bands because of the ability of these bands to detect the distribution of sediments in the near surface these eddies did not have a significant thermal signature the sources of these sediments are the glacial streams found throughout the gulf of alaska coast eddies of this configuration and frequency have never been observed here previously however the oceanographic and meteorological conditions are typical for this time of year these eddies should be important to the cross shelf mixing processes in the alaska coastal current and are an indicator that the flow here can be unstable at certain times of the year

why deposits of longitudinal dunes are rarely recognized in the geologic record dunes that are morphologically of linear type many of which are probably of longitudinal type in a morphodynamic sense are common in modern deserts but their deposits are rarely identified in aeolian sandstones one reason for non recognition of such dunes is that they can migrate laterally when they are not exactly parallel to the long term sand transport direction thereby depositing cross strata that have unimodal cross bed dip directions and consequently resemble deposits of transverse dunes dune parallel components of sand transport can be recognized in ancient aeolian sands by examining compound crossbedding formed by small dunes that migrated across the lee slopes of large dunes and documenting that the small dunes migrated with a component in a preferred along crest direction over the large dunes

modeling grain size variations of aeolian gypsum deposits at white sands new mexico using aviris imagery abstract visible and near infrared vnir through short wavelength infrared swir 0 4 2 5 m aviris data along with laboratory spectral measurements and analyses of field samples were used to characterize grain size variations in aeolian gypsum deposits across barchan transverse parabolic and barchan dunes at white sands new mexico usa all field samples contained a mineralogy of 100 gypsum in order to document grain size variations at white sands surficial gypsum samples were collected along three transects parallel to the prevailing downwind direction grain size analyses were carried out on the samples by sieving them into seven size fractions ranging from 45 to 621 m which were subjected to spectral measurements absorption band depths of the size fractions were determined after applying an automated continuum removal procedure to each spectrum then the relationship between absorption band depth and gypsum size fraction was established using a linear regression three software processing steps were carried out to measure the grain size variations of gypsum in the dune area using aviris data aviris mapping results field work and laboratory analysis all show that the interdune areas have lower absorption band depth values and consist of finer grained gypsum deposits in contrast the dune crest areas have higher absorption band depth values and consist of coarser grained gypsum deposits based on laboratory estimates a representative barchan transverse dune transect 1 has a mean grain size of 1 16 449 m the error bar results show that the error ranges from 50 to 50 m mean grain size for a representative parabolic dune transect 2 is 1 51 352 m and 1 52 347 m for a representative barchan dune transect 3 t test results confirm that there are differences in the grain size distributions between barchan and parabolic dunes and between interdune and dune crest areas the t test results also show that there are no significant differences between modeled and laboratory measured grain size values hyperspectral grain size modeling can help to determine dynamic processes shaping the formation of the dunes such as wind directions and the relative strengths of winds through time this has implications for studying such processes on other planetary landforms that have mineralogy with unique absorption bands in vnir swir hyperspectral data

application of satellite visible band data to high latitude oceans abstract remote sensing of high latitude oceans differs from oceans of tropical and subtropical latitudes because of the decoupling of the water s temperature structure from the flow dynamics at low water temperatures sea surface thermal patterns are useful here as tracers of the flow only without a direct link to the circulation dynamics oceanic flow responds to water density contrasts and at high latitudes the density is controlled by salinity distributions though density contrasts are not ordinarily detectable with remote sensors freshwater discharge in the northeast pacific contains very fine sediments glacial flour that can be detected using landsat thematic mapper tm and multi spectral scanner mss imagery from the tm data we have discovered several new coastal circulation features in the northern gulf of alaska flow around a coastal island produces a myriad of dipole eddies which are important to the cross shelf transport of salt and heat they also serve as sites to test numerical models to allow a better understanding of coastal flows and eddy formation elsewhere detection of these dipole eddies from their sediment distributions has allowed the comparison of different spectral bands from six imaging satellite sensors for their abilities to describe these features we conclude that in addition to the tm sensor s capability the sediments can be detected with the mss and coastal zone color scanner czcs sensors but not with avhrr or defense meteorological satellite program dmsp as a consequence of this comparison of satellite visible data we have confirmed that the dipole eddies here exist under low flow conditions 3 s

upwelling filaments off cap blanc interaction of the nw african upwelling current and the cape verde frontal zone eddy field 1 the hydrographical and dynamical properties of the upwelling filaments forming off cap blanc mauritania are investigated using remotely sensed and in situ data collected in april may 2009 during the strongest upwelling season the area is situated at the southern edge of the nw african upwelling system where the cape verde frontal zone cvfz separates warmer saltier north atlantic central water nacw and cooler fresher south atlantic central water sacw sea surface temperature images indicated the presence of an upwelling filament extending 280 km offshore rooted over the cap blanc promontory and entrained around a warm core anticyclonic eddy after this filament started to decay a new cold filament developed at the approximate same location high resolution moving vessel profiler mvp and acoustic doppler current profiler adcp surveys of these mesoscale structures revealed that both filaments were carrying south atlantic central water sacw offshore through an intense jet like flow similarity of the relative vorticity structure across the filament with that of the tangent eddy suggested that the latter was responsible for the offshore current tracking of this eddy in altimetric data demonstrated that it originated from the cvfz as implied by its hydrographic structure altimetric data also revealed that another anticyclonic structure centered over the cap blanc promontory was responsible for the northwestward advection of sacw into the base of the filament the results support the idea that some upwelling filaments can be produced by the interaction of an external eddy field including topographic eddies with the upwelled water

satellite observations and modeling of meanders in the california current system off oregon and northern california abstract infrared satellite images from the west coasts of oregon and northern california are used to identify meander patterns in sea surface temperature which appear as large cold tongues extending offshore two relatively long series of images from 1982 and a few examples from 1980 and 1983 demonstrate the evolution of the cold tongues from an initial variety of scales 60 200 km to the fastest growing waves 110 130 km and then finally to tongues with longer wavelengths 400 km this is observed to occur over periods of about three months in summer and fall when the coastal circulation is composed of a southward surface current over a northward undercurrent the initial shorter scale features are believed to be excited by the interaction between the mean current and the coastal topography baroclinic instability associated with the vertical shear between the surface current and the undercurrent is found to be responsible for the growth of the features observed in the satellite imagery a nonlinear

sedimentological modal analysis and geochemical studies of desert and coastal dunes altar desert nw mexico sedimentological compositional and geochemical determinations were carried out on 54 desert and coastal dune sand samples to study the provenance of desert and coastal dunes of the altar desert sonora mexico grain size distributions of the desert dune sands are influenced by the colorado river delta sediment supply and wind selectiveness the desert dune sands are derived mainly from the quartz rich colorado river delta sediments and sedimentary lithics the dune height does not exert a control over the grain size distributions of the desert dune sands the quartz enrichment of the desert dune sands may be due to wind sorting which concentrates more quartz grains and to the aeolian activity which has depleted the feldspar grains through subaerial collisions the desert dune sands suffer from little chemical weathering and they are chemically homogeneous with chemical alteration indices similar to those found in other deserts of the world the desert sands have been more influenced by sedimentary and granitic sources this is supported by the fact that ba and sr concentration values of the desert sands are within the range of the ba and sr concentration values of the colorado river quartz rich sediments the sr values are also linked to the presence of ca bearing minerals the zr values are linked to the sedimentary sources and heavy mineral content in the desert dunes the golfo de santa clara and puerto penasco coastal dune sands are influenced by long shore drift tidal and aeolian processes coarse grains are found on the flanks whereas fine grains are on the crest of the dunes high tidal regimens long shore drift and supply from colorado delta river sediments produce quartz rich sands on the beach that are subsequently transported into the coastal dunes outcrops of quaternary sedimentary rocks and granitic sources increase the sedimentary and plutonic lithic content of the coastal dune sands the chemical index of alteration cia values for the desert and coastal dune sands indicate that both dune types are chemically homogeneous the trace element values for the coastal dune sands are similar to those found for the desert dune sands however an increase in sr content in the coastal dune sands may be due to more caco3 of biogenic origin as compared to the desert dune sands correlations between the studied parameters show that the dune sands are controlled by sedimentary sources e g colorado river delta sediments since heavy minerals are present in low percentages in the dune sands probably due to little heavy mineral content from the source sediment grain sizes in the dune sands are coarser than those in which heavy minerals are found and or the wind speed might not exert a potential entrainment effect on the heavy mineral fractions to be transported into the dune a cluster analysis shows that the el pinacate group is significantly different from the rest of the dune sands in terms of the grain size parameters due to longer transport of the sands and the long distance from the source sediment whereas the puerto penasco coastal dune sands are different from the rest of the groups in terms of their geochemistry probably caused by their high caco3 content and slight decrease in the cia value copyright 2006 john wiley sons ltd

mineralogical maturity in dunefields of north america africa and australia studies of dunefields in central and western north america show that mineralogical maturity can provide new insights into the origin and evolution of aeolian sand bodies many of the world s great sand seas in africa asia and australia are quartzdominated and thus can be considered to be mineralogically mature the algodones california and parker arizona dunes in the southwestern united states are also mature but have inherited a high degree of mineralogical maturity from quartz rich sedimentary rocks drained by the colorado river in libya sediments of the zallaf sand sea which are almost pure quartz may have originated in a similar fashion the fort morgan colorado and casper wyoming dunefields in the central great plains of north america and the namib sand sea of southern africa have an intermediate degree of mineralogical maturity because their sources are large rivers that drained both unweathered plutonic and metamorphic rocks and mature sedimentary rocks mojave desert dunefields in the southwestern united states are quite immature because they are in basins adjacent to plutonic rocks that were their sources other dunefields in the great plains of north america those in nebraska and texas are more mature than any possible source sediments and therefore reflect mineralogical evolution over time such changes in composition can occur because of either of two opposing long term states of the dunefield in one state dunes are stable for long periods of time and chemical weathering depletes feldspars and other weatherable minerals in the sediment body in the other state which is most likely for the great plains abrasion and ballistic impacts deplete the carbonate minerals and feldspars because the dunes are active for longer periods than they are stable d 2003 elsevier b v all rights reserved

j m hunt 1995 petroleum geochemistry and geology 2nd ed xx 743 pp new york w h freeman price 27 95 hardcovers isbn 0 7167 2441 3

depth and seasonality of alkenone production along the california margin inferred from a core top transect alkenone unsaturation indices uk 37 of marine sediment could prove particularly useful on organic rich continental margins where carbonate dissolution hampers the use of other paleoclimatic proxies mccaffrey et al 1990 kennedy and brassell 1992 forty core top samples of recent sediment from a latitudinal transect 23 40 n along the california margin yield uk 37 values that correlate linearly with modern mean annual sea surface temperatures ssts in the range of 12 23 c reproducibility of the unsaturation value in closely spaced cores is near analytical error uk 37 data define a relationship to temperature nearly identical to the prahl et al 1988 laboratory cultures of emiliania huxleyi the close agreement is particularly significant in light of the nannofossil composition of the sediments where the abundance of the coccolith taxon gephyrocapsa oceanica known to synthesize alkenones equals or exceeds that of e huxleyi comparison with seasonal temperature variations at different depths indicates that little if any alkenone production occurs at depths 30 m along the continental margin water depths 2 km sediments in more pelagic locations exhibit small but consistent biases toward winter and or subsurface production similar to previously reported sediment trap and core top data from the oregon margin prahl et al 1993 doose et al 1997

grain size variations on a longitudinal dune and a barchan dune abstract the grain size characteristics of the sand upon two dunes a 40 m high longitudinal dune in the central namib desert and a 6 0 m high barchan in the jafurah sand sea of saudi arabia vary with position on the dunes on the longitudinal dune median grain size decreases sorting improves and the grain size distributions are less skewed and more normalized toward the crest though sand at the windward toe is distinct elsewhere on the dune the changes in grain size characteristics are gradual an abrupt change in grain size and sorting near the crest as described by bagnold 1941 pp 226 229 is not well represented on this dune coarse grains remain as a lag on concave slope units and small particles are winnowed from the sand on the steepest windward slopes near the crest avalanching down slipfaces at the crest acts only as a supplementary grading mechanism on the barchan dune median grain size also decreases near the crest but sorting becomes poorer though the grain size distributions are more symmetric and more normalized the dune profile is a gaussian curve with a broad convex zone at the apex upon which topset beds had accreted prior to sampling grain size increases and sorting improves down the dune s slipface however this grading mechanism does not influence sand on the whole dune because variations in wind regime bring about different modes of dune accretion on both dunes height and morphology appear to influence significantly the grain size characteristics

evolution and structure of a coastal squirt off the mississippi river delta northern gulf of mexico in early october 1992 satellite derived sea surface temperature data revealed a 200 km long and 10 to 30 km wide stream of cool water flowing toward the southwest from the mississippi river delta region satellite imagery and in situ measurements have enabled a detailed study of the squirt s kinematics and subsurface characteristics over a 2 week period in its early stages the squirt appeared as a narrow high speed 75 cm s jet of water which flowed westward over the mississippi canyon forcing a semi submersible drilling rig to suspend operations from october 2 to 4 after crossing back onto the shelf the squirt spread laterally yielding a mushroom shaped feature 75 km wide which consisted of counter rotating vortices northeasterly wind forcing averaging 10 15 m s and water level setup east of the delta appear to have been the primary mechanisms for evolution of the high velocity currents satellite and in situ measurements demonstrate that the dipole eddy was comprised of a cool low salinity low density water mass at least 26 m deep in the center and 16 m deep along its margins this event demonstrates that strong northeasterly winds over the northern gulf of mexico can initiate along shelf and off shelf flows of cooler coastal waters contributing significantly to seasonal cooling and freshening of the continental shelf and to shelf slope exchanges of water during this event approximately 100 km3 of inner shelf and river water was transported off the continental shelf a volume equivalent to 17 of the average annual discharge of the mississippi and atchafalaya rivers

seasonal variability of flow instabilities in the strait of sicily the eastern and western mediterranean seas are connected by the strait of sicily the mean flow conditions comprise a near surface flow of atlantic water aw into the eastern mediterranean and an outflow of levantine intermediate water liw below we present results of a numerical model investigating the stability of currents in the strait the model is nonlinear and uses a hybrid quasi isopycnic vertical coordinate the model domain is a periodic channel with horizontal dimensions of 400 200 km and different bathymetries as initial conditions we use seasonal climatological density fields varying only in cross channel direction external forcing is not applied combining three different bathymetries with both summer and winter climatological data we show the results of six model integrations in all cases the flow is baroclinically unstable the most unstable waves being 100 and 133 km wavelength in summer and 67 km in winter a cross channel parabolic bottom profile instead of a flat bottom stabilizes the flow in the north on the sicilian side of the strait but causes further destabilization in the south on the african side further modification of the bathymetry in terms of shallow shelf sea areas to the south of sicily leads to a deflection of the summer flow in both the aw and the liw range and to the generation of stationary eddies in agreement with observations the final kinetic and eddy kinetic energies of the model are higher in winter than in summer in all model runs from an inspection of satellite images evidence was found for unstable waves of similar wavelength as predicted by the model records from moored current meters support enhanced flow instability on the african side of the strait the position and circulation sense of the stationary eddies in the aw range are found to be consistent with climatology and previously known patches of low sea surface temperature

abrasion derived sediments under intensified winds at the latest pleistocene leading edge of the advancing sinai negev erg abstract quaternary desert loess and sandstone loessite relationships in the geological record raise questions regarding causes and mechanisms of silt formation and accretion in the northern sinai negev desert carbonate terrain only sand abrasion in active erg could have produced the large quantities of quartzo feldspathic silts constituting the late quaternary northwestern negev loess in the continuum of source medium to fine sand of dunes to sink silts in loess the very fine sand is unaccounted for in the record this weakens the sand abrasion model of silt formation as a global process here we demonstrate that as predicted by experiments abrasion by advancing dunes generated large quantities of very fine sand 60 110 m deposited within the dune field and in close proximity downwind this very fine sand was generated 13 11 ka possibly synchronous with the younger dryas under gusty sand dust storms in the southeastern mediterranean and specifically in the northern sinai negev erg these very fine sands were washed down slope and filled small basins blocked by the advancing dunes outside these sampling basins it is difficult to identify these sands as a distinct product we conclude that ergs are mega grinders of sand into very fine sand and silt under windy quaternary and ancient aeolian desert environments

a test of granulometric control of desert dune geometry i g wilson s hypothesis of coarse tail grain size control of dune spacing was derived from three dunefields in the sahara and although it was supplemented by measurements of spacing from other parts of the world the grain size data come only from north africa in this paper the hypothesis is tested in the australian dunefields australian dunes do not form separate categories on a p20 s twentieth percentile spacing plot and when placed on wilson s diagram the australian data form a continuum between dunes and draas ripples maintain their identity suggesting that the average saltation length of sand controls ripple wavelength while dunes and wilson s draas are formed by secondary flow of some kind in australia the spread of data on the p20 s diagram indicates that grain size is not the prime control on s data from australia and the sahara indicate that direct linear relationships between s and h dune spacing and height means respectively for blocks of dunes occur but they have different slopes in different areas these differences possibly reflect variations in vegetation and substrate as well as differences in wind regime the separation of dunes from draas in the sahara reflects the greater role of grain size in an area where coarse grains frequently occur in dune crests the relative paucity of coarse grains in australian dune crests may reflect the fine grained alluvium from which the dunes are derived these differences may be ascribed to differing topography in australia and the sahara

lagrangian observations of the along slope path of the california undercurrent abstract the flow of the california undercurrent cuc along the continental slope and its interaction with deeper offshore waters is studied using trajectories of 53 isobaric rafos the floats were launched off central california and data collected between 1993 and 2009 the mean pressure for the float measurements was 382 dbar the trajectories were broken into 126 segments of continuous alongshore drift over the continental slope poleward drift occurred 88 of the time the mean length of the poleward equatorward drift segments was 262 km 98 km and the exit time for these distances was 32 3 2 3 days 16 1 2 2 days five poleward drift segments exceeded 500 km in length the longest segment stretched from central california to central oregon a distance of 966 km locations where floats left or joined the along slope flow occurred at most latitudes between 35 5 n to 42 5 n here the mean rate at which floats left joined along slope drift was 5 3 3 5 per 50 km of coastline each year locations favored for leaving the undercurrent included the northern edge of the gulf of the farallones 37 5 n and between cape mendocino and cape blanco 41 5 42 n a location favored for joining the undercurrent was the northern edge of the santa lucia bank 35 5 n no floats were observed to join the alongshore flow immediately north of cape mendocino 40 5 41 n longer 290 day float missions often included offshore excursions into the northeastern pacific ocean thirty one westward excursions of the undercurrent were observed with a mean duration of 88 days and a mean offshore distance of 199 km the character of the excursions varied but included offshore and onshore transport in jets cyclonic and anticyclonic eddies and interaction with cold filaments the longest excursion lasted 587 days and extended 1007 km to the west

oceanic variability off the central california coast abstract mesoscale variability off the central california coast is strongly influenced by coastal upwelling and related processes off point sur there is significant space time variability in oceanic properties over periods of days and distances of several tens of km however the internal density field averaged over space ca 120km alongshore and time ca 18 days reveals the expected characteristics of a coastal upwelling regime including an equatorward surface jet 25km to 40km offshore and weaker poleward flow below 150m and within 20km of the coast upper ocean circulation is strongly influenced by the bathymetry offshore to water depths of at least 1000m based on repeated horizontal grids of oceanographic stations horizontal correlation scales for temperature are of the order of 30km in the upper 100m hence a horizontal sampling rate of ca 10km is desirable vertical correlation scales for temperature are of the order of 100m hence a vertical sampling rate of ca 10m is desirable similarly there are indications of a temporal correlation scale of a few weeks hence a temporal sampling rate of ca a few days is desirable empirical orthogonal functions eofs in the cross shore vertical plane suggest the influence of coastally trapped motions within 40km of the coast with an intense alongshore near surface transient coastal jet located ca 20km offshore sudden spring transitions to coastal upwelling conditions are often pronounced in coastal temperature records and they may precede the offshore migration of the major upwelling front by at least a month or more the spring transitions occur over a period of about a week in 1980 the spring transition propagated poleward along the california coast at a speed of ca 64km d 1 during spring and summer movement of a coastal upwelling front often located between 15km and 50km offshore is a major contributor to cross shore variability the upwelling front meanders with an alongshore scale of about 80km a time scale of 30 to 40 days and an amplitude scale of 10km rms based on satellite infrared ir imagery the along shore mean position of the major upwelling front migrates offshore during spring and summer offshore displacement of the front may be caused by ekman transport over periods of days to weeks and by rossby wave dispersion over longer periods during summer a time dependent offshore scale based on rossby wave dynamics was more appropriate than the baroclinic rossby radius every three to four years during 1971 through 1984 el nino episodes produced interannual variability in coastal sea surface temperature sst off central california most of the warming occured during fall and winter el nino episodes were often followed by major spring transitions the recent 1982 1983 episode was 2 to 3 c warmer than the three previous episodes over the past 14 years and its influence lasted almost twice as long

relations between morphology air flow sand flux and particle size on transverse dunes taklimakan sand sea china field experiments on two isolated transverse dunes with different scales in the taklimakan sand sea show that particle size and slope control the threshold shear velocity and sand flows on the stoss of the dunes the decreased threshold shear velocity and the unsaturated sand flows are the main reasons why sands are not deposited at the toe of the dunes the particle size controls sand flux through its influence on the aerodynamic roughness elements and threshold shear velocities the sand flux is different for dune surfaces with different particle size distributions under the control of the medium to low stress of the drifting sand winds the results of the field experiments and particle size analysis showed that sand transport had little influence on the particle size distributions the mean particle size being transported on the stoss is lower than that on the dune surface it is difficult to determine whether or not the wind is fully saturated with sands when sand flux calculation is mainly dependent on the shear velocity and the mean particle size the sands within some range of the particle size are transported and developed into simple transverse dunes and then the interdune surface is coarsened and alternated with the draas in the taklimakan sand sea copyright 2002 john wiley sons ltd

grain size characteristics of linear dunes in the southwestern kalahari abstract linear dunes in the southwestern kalahari sand sea exhibit characteristic grain size and sorting patterns in which sands become coarser better sorted and more finely skewed from interdune to crest in addition at a regional scale sands tend to become finer and better sorted in the direction of transport these patterns can best be explained in terms of the differential movement of sand in creep and saltation populations whereby the saltating population moves more rapidly and is concentrated downwind and in dunes slower moving creep populations remain close to source areas and in interdunes the fines will tend to be concentrated in interdunes because they can penetrate between coarse grains where they are protected from further movement this type of model probably explains most grain size and sorting relationships in desert sand seas

dynamic processes of a simple linear dune a study in the taklimakan sand sea china samples of dune sands surveys of the morphology and field measurements of wind velocity and direction of a simple linear dune in taklimakan sand sea show that the airflow and sand flux vary with the change of wind direction on the dune surface decrease of the airflow stress on the lee flank does not result in much decrease of the sand flux because of the low threshold shear velocities and the airflow conditions there are no significant relations between the sand flux on the lee flank and the angle of incidence of the airflow the low threshold shear velocities and the maintenance of the sand flux at the lee flank are the main mechanisms keeping the linear shape of the dunes measurements of the sand flux shows that it reaches a maximum on the crest of the dune the grain size of the transported sands has some differences compared to that of the dune surface the sands transported are finer than that on the dune surface but better sorted under the influence of the medium to low wind activity the field experiment results exhibit that it is possible for the dunes to be shaped as linear dunes during the processes of accumulation and elongation

aspects of the mean wintertime circulation along australia s southern shelves numerical studies abstract a high resolution numerical model is used to study the mean wintertime shelf slope circulation between the gulfs of south australia and the west coast of tasmania the mean downwelling favorable winds for the region result in a continuous eastward coastal current cc extending from cape leeuwin to the eastern coast of tasmania the magnitude of the cc is generally largest over the shelf break has speeds of more than 40 cm s 1 transport 2 4 sv sv 106 m3 s 1 and is generally in good agreement with observations the relative importance of the leeuwin current zonal winds and density gradients to the shelf circulation is established within bass strait the eastward circulation is in good agreement with observations and simple models show that about 30 of the transport arises from local winds and the remainder from the cc the total transport through the strait 0 95 sv is shown to be controlled by sea level on the east coast of tasmania a current of up to 10 cm s 1 is also found to flow

use of simulated drifter tracks to investigate general transport patterns and residence times in the coastal transition zone general transport patterns and residence times in the upper 100 m of the coastal transition zone ctz were studied using simulated lagrangian drifter experiments the circulation fields used for the drifter experiments were obtained from a regional primitive equation model that incorporates coastal geometry and bottom topography that is representative of the ctz region the simulated circulation fields show velocity patterns that are consistent with those associated with the filaments and jets observed in the ctz region drifters were released at 880 points in the model domain in a pattern that bracketed both horizontally and vertically the region in which offshore flowing filaments were observed to form at each location drifters were released at depths of 30 60 90 m and tracked for 30 days the depth of these drifters varied along their trajectories in response to the vertical velocities experienced by the drifters an additional set of drifters was released at 30 m and was constrained to remain at this depth the composite drifter trajectories show that transport patterns and residence times in the upper 100 m are determined by the proximity of the drifter release point to the offshore flowing filament drifters released inshore of the filament are transported southward with the mean flow of the model california current drifters released near the region in which the filament originates are transported rapidly offshore the point at which this difference in drifter fate occurs is approximately 100 km offshore the time required for a drifter to be transported from the nearshore region to the outer boundary of the area covered in the ctz model domain is approximately 20 days comparison of the free floating drifters with the 30 m fixed depth drifters shows that the deeper drifters are displaced southward as they are transported offshore in the jet the magnitude of the southward displacement for the 90 m drifters is about 15 km implying substantial cross jet exchange comparison of the simulated drifter trajectories with the trajectory followed by a drifter released during the 1988 ctz field sampling program support the hypothesis that the deepening of the abundance maxima observed in the distributions of dolioletta gegenbauri juvenile forms of euphausia pacifica and eucalanus californicus resulted from these populations being downwelled as they were transported offshore by the flow associated with the filament observed in 1988

filaments on the western iberian margin a modeling study coastal upwelling filaments off the western iberian margin detected in avhrr satellite imagery and in a realistic roms simulation of sea surface temperature were studied in the upwelling seasons may october of 2001 2010 sea surface temperature data were retrieved from avhrr satellite imagery and from a realistic roms numerical simulation the development and variability of the observed filaments were characterized and analyzed during each upwelling season of the 10 year period filaments were generally found anchored to the main bathymetric and coastal features but off the more regular northern coast of the western iberian margin their locations were more variable the results from the modeling analysis reproduced well the general features of filament development moreover results of model and observation showed very similar characteristics as those found in the earlier study of haynes et al 1993 the model output was used to relate filament patterns eddy activity and wind forcing there was a clear relation between upwelling favorable wind strength and number and length of filaments although the relation was weaker in the north of the region model filaments were clearly related to eddies only during periods of weak winds the filament detection method was also applied to a climatologically forced roms simulation which reproduced only gross features of the observed and interannually forced model filament development this suggests that direct wind forcing and its spatial structure are highly important

grain size characteristics of namib desert linear dunes the results of a systematic sampling of linear dunes in the northern namib sand sea show that they are composed of two distinct groups of sands a fine well sorted near symmetrical crest and slip face population and a coarse moderately sorted positively skewed plinth population these may be explained in terms of the aeolian sorting processes operative on the dunes which involve differential rates of movement of creep and saltation load on windward flanks and avalanching on leeward slopes leading to the concentration of coarse sands towards the dune base

enhancement of fronts by vertical mixing microstructure observations near upwelled fronts indicate considerable variation in the structure of vertical mixing across the frontal region observations of cool filaments off northern california indicate that within the cool dense core of filaments the raised pycnocline inhibits the penetration to middepths of surface generated mixing the microstructure profiles are used to estimate the available wind energy for mixing as a function of pycnocline or mixed layer depth a greater portion of energy input at the surface is available for entrainment of dense fluid through the pycnocline and into the surface mixed layer where the pycnocline is shallow hence surface forced mixing may cause a more rapid increase in mixed layer density within the cool filament than outside the filament resulting in an enhanced horizontal density gradient in the mixed layer assuming the flow adjusts towards geostrophy the enhanced horizontal density gradient at the front could result in an accelerated mixed layer in the direction of the preexisting geostrophic flow proportions relating the gain in potential energy to the wind energy vary with pycnocline depth and differ by as much as an order of magnitude from the findings of denman and miyake 1973 and davis et al 1981 horizontal variability of pycnocline erosion may not be properly taken into account in some models and should more realistically be parameterized by including dependence on pycnocline depth during spring and early summer april july the northerly winds along the california coast induce coastal upwelling bringing anomalously cool st 2oc saline 5s 2 0 water to the surface raising the pycnocline over the continental shelf satellite images have revealed large cool features extending offshore beyond the shelf break often hundreds of kilometers seaward of the upwelling region e g bernstein et al 1977 ikeda and emery 1984 flament et al 1985 these anomalous features are believed to play a crucial role in the exchange of properties across the coastal transition zone the region between the nearshore upwelling area and the offshore ocean mooers and robinson 1984 these features were the focus of the coastal transition zone ctz experiment the fronts observed were located west of point arena california seaward of the continental shelf during upwelling conditions isopycnals dome over the shelf and the southward flowing california current develops along the continental shelf break huyer 1983 brink 1983 the strong current found along the sloping isopycnals is not confined to the shelf slope region and often features resembling meanders squirts jets and eddies form on the western edge of the upwelled front bernstein et al 1977 the cause of these features and the resulting influences that they impose on the local ocean are not understood it is believed these features modify the exchange of water between the nearshore upwelling region and the offshore ocean direct transport increased mesoscale eddy formation turbulent diffusion and intrusions near the frontal region are some of the possible mechanisms by which these variable structures enhance diffusion across the transition zone observations of micro scale processes indicate that the rate of surface induced mixing may vary with proximity to the front and that the horizontal density gradients thus established may act to accelerate the mixed layer at the front a series of detailed transects across a meander indi