Environmental conditions for gravelly and pebbly dunes and sorted bedforms on a moderate-energy inner shelf (Marettimo Island,Italy, western Mediterranean)

Side scan sonar records, sediment textural characteristics, and in-situ field observations were used to study gravelly and pebbly dunes and sorted bedforms on the inner shelf of Marettimo Island, along the northwestern Sicilian shelf. The dunes are composed of coarse sands, gravels and pebbles (D50: 2–16 mm), displaying a symmetrical shape with a wavelength in the range of 1–2.5 m and a height of 0.15–0.30 m. The bedforms are distributed in a patchy pattern in a depth range of 10–50 m, and are described for the first time on a Mediterranean inner shelf. Sorted bedforms are linear morphological features developed almost perpendicular to the coast in the eastern sector of the island between 15 and 50 m water depth. Bottom shear stresses required for sediment entrainment and the generation of the shallower dunes can be reached during strong storms (Hs=5–6 m; Tp=9–11 s), which are not common in the Mediterranean Sea. However, wave storm events recorded in the study area during the last 17 years are not able to generate the coarsest and deeper dunes, suggesting that the stirring mechanism for dune formation is associated with severe storms that have a recurrence interval of more than 17 years. The long-term stability of the coarse bedforms is supported by the permanence of sorted bedforms without significant morphological changes for long periods (>13 years). Therefore, it is shown that processes forming coarse bedforms can occur in tideless and moderate-energy settings like those of the Mediterranean continental shelves, although the morphological features are probably less dynamic and remain unaltered for longer periods than on higher-energy shelves.     

Shelf habitat distribution as a legacy of Late Quaternary marine transgressions: A case study from a tropical carbonate province

The legacy of multiple marine transgressions is preserved in a complex morphology of ridges, mounds and reefs on the Carnarvon continental shelf, Western Australia. High-resolution multibeam sonar mapping, underwater photography and sampling across a 280 km² area seaward of the Ningaloo Coast World Heritage Area shows that these raised features provide hardground habitat for modern coral and sponge communities. Prominent among these features is a 20 m high and 15 km long shore-parallel ridge at 60 m water depth. This ridge preserves the largely unaltered form of a fringing reef and is interpreted as the predecessor to modern Ningaloo Reef. Landward of the drowned reef, the inner shelf is covered by hundreds of mounds (bommies) up to 5 m high and linear ridges up to 1.5 km long and 16 m high. The ridges are uniformly oriented to the north-northeast and several converge at their landward limit. On the basis of their shape and alignment, these ridges are interpreted as relict long-walled parabolic dunes. Their preservation is attributed to cementation of calcareous sands to form aeolianite, prior to the post-glacial marine transgression. Some dune ridges abut areas of reef that rise to sea level and are highly irregular in outline but maintain a broad shore-parallel trend. These are tentatively interpreted as Last Interglacial in age. The mid-shelf and outer shelf are mostly sediment covered with relatively low densities of epibenthic biota and have patches of low-profile ridges that may also be relict reef shorelines. An evolutionary model for the Carnarvon shelf is proposed that relates the formation of drowned fringing reefs and aeolian dunes to Late Quaternary eustatic sea level.     

Wave- and current-induced bottom shear stress distribution in the Gulf of Lions

Simulations of both currents and waves were performed throughout the year 2001 to assess the relative contribution of each to their overall erosive potential on the Gulf of Lions shelf. Statistical analysis of bottom shear stress (BSS) was compared to sediment grain-size distribution on the bottom. The hydrodynamic features of the bottom layer coincide with the distribution of surficial sediments, and three areas with different hydro-sedimentary characteristics were revealed. (i) The sandy inner shelf (<30 m) area is a high-energy-wave dominated area but may be subjected to intense current-induced BSS during on-shore winds along the coast and during continental winds mainly in the up-welling cells. (ii) The middle shelf (30–100 m) is a low-energy environment characterised by deposition of cohesive sediments, where the wave effect decreases with depth and current-induced BSS cannot reach the critical value for erosion of fine-grained sediments. (iii) The outer shelf, which has a higher bottom sand fraction than the middle shelf, may be affected by strong south-westward currents generated by on-shore winds, which can have an erosive effect on the fine-grained sediments.     

Rippled scour depressions on continental shelf bank slopes off Nordland and Troms,Northern Norway

Multibeam bathymetry acquired under the MAREANO programme from the continental shelf off Nordland and Troms, northern Norway, show bedforms that we have interpreted as rippled scour depressions. They occur in three areas offshore on bank slopes facing southeast, more than 15 km from land. They are generally found where the slope gradient is low, in water depths of 70–160 m. Individual depressions are up to 3 km long, 1 m deep and up to 300 m wide. They occur in areas where sediments evolve quickly from glacial deposits on the banks to post-glacial muddy sediments on the glacial troughs. Multibeam backscatter and underwater video data show that depression floors are covered by rippled, gravelly, shelly sand. Ripple crests are parallel or slightly oblique to the depression axis orientation. Sand without bedforms is observed between the depressions. TOPAS seismic lines show that the uppermost seismic unit consists of the sand between the depressions. The base of this unit may be the last transgressive/tidal/wave ravinement surface. Physical oceanographic modelling indicates that maximum current velocities are up to 0.6 m/s in the rippled scour depression areas. Stronger currents appear to inhibit the building of these features. Tidal currents play an important role as they trend parallel to the southeast banks slopes and are likely responsible of the gravelly ripples formation inside the depressions as well as the persistence of these depressions which are not covered by finer sediments. On Malangsgrunnen bank, some of the rippled scour depressions are in the extension of NW–SE furrows located on the bank. Simulated bottom currents indicate currents mainly perpendicular to these furrows, as for the rippled scour depressions on the bank slopes. Nevertheless, these features could also highlight currents coming from the northwest which reach the bank margin and continue down to the areas of the rippled scour depressions. These currents could be responsible for the formation of some of the bedforms, together with tidal currents.     

The effect of asymmetric dune roughness on tidal asymmetry in the Weser estuary

The bed of estuaries is often characterized by ripples and dunes of varying size. Whereas smaller bedforms adapt their morphological shape to the oscillating tidal currents, large compound dunes (here: asymmetric tidal dunes) remain stable for periods longer than a tidal cycle. Bedforms constitute a form roughness, that is, hydraulic flow resistance, which has a large-scale effect on tidal asymmetry and, hence, on hydrodynamics, sediment transport, and morphodynamics of estuaries and coastal seas. Flow separation behind the dune crest and recirculation on the steep downstream side result in turbulence and energy loss. Since the energy dissipation can be related to the dune lee slope angle, asymmetric dune shapes induce variable flow resistance during ebb and flood phases. Here, a noncalibrated numerical model has been applied to analyze the large-scale effect of symmetric and asymmetric dune shapes on estuarine tidal asymmetry evaluated by residual bed load sediment transport at the Weser estuary, Germany. Scenario simulations were performed with parameterized bed roughness of symmetric and asymmetric dune shapes and without dune roughness. The spatiotemporal interaction of distinct dune shapes with the main drivers of estuarine sediment and morphodynamics, that is, river discharge and tidal energy, is shown to be complex but substantial. The contrasting effects of flood- and ebb-oriented asymmetric dunes on residual bed load transport rates and directions are estimated to be of a similar importance as the controls of seasonal changes of discharge on these net sediment fluxes at the Lower Weser estuary. This corroborates the need to consider dune-induced directional bed roughness in numerical models of estuarine and tidal environments.     

Coastal dune fields at the São Francisco River strandplain,northeastern Brazil: morphology and environmental controls

Extensive coastal dune ?elds occur on the Quaternary strandplain associated with the São Francisco River mouth. Two different generations of dunes are identi?ed. One is inactive, already ?xed by vegetation, comprising parabolic dunes. The other generation is active, bordering the present‐day shoreline and transgressing over the inactive dune ?eld. Three morphological provinces in the active coastal dune ?elds are recognized. On the updrift side of the São Francisco River mouth, they are: (a) sand‐sheet with shrub coppice and shadow dunes; (b) isolated dunes of the barchan‐transversal type up to 5 m high, and interdune areas; and (c) a 23 m high compound dune, with superimposed small dunes. The same provinces are recognized on the downdrift side of the river mouth, with two important exceptions: the barchan‐transversal and compound dunes are replaced, respectively, by (i) zibar‐type dunes up to 5 m high, and (ii) a 19 m high precipitation dune, which is associated with numerous blowouts. The prevailing eastern winds from August to January favour the development of the aeolian bedforms and the migration of dunes. The shoreline orientation almost transversal to the winds and the great supply of ?ne‐grained sediments contribute to the formation of barchan‐transversal types and compound dunes in the updrift side. On the other hand, in the downdrift side the shoreline orientation is almost parallel to the prevailing winds. This fact, in association with a coarser grain size in the beachface, favours the formation of zibar‐type and precipitation dunes with numerous blowouts. The rate of migration of individual dunes is about 20 to 24 m per year. This study suggests that the aeolian sedimentation is a relatively recent phenomenon at the Quaternary strandplain of the São Francisco River. The ?rst generation of dune ?elds initiated some time after 3000 years BP and the second generation originated some centuries ago. Copyright © 2004 John Wiley & Sons, Ltd.     

Migration and internal architecture of marine dunes in the eastern English Channel over 14 and 56 year intervals: the influence of tides and decennial storms

Submarine dune dynamics are controlled by tidal currents and wind forces. According to the relative influence of these forces and the nature of dune sediment, different bedform behaviors can be observed. The footprint of the different hydrodynamic agents is recorded into the internal architecture of dunes. This paper is concerned with bedforms that compose the thick sediment wedge located in the eastern English Channel, off the Bay of Somme. This sedimentary archive constitutes an interesting feature to achieve a better understanding of seabed sediment dynamics and its timeline building stages. The dynamics of large submarine dunes, which are organized in fields, are studied thanks to bathymetric and seismic data over the periods 1937–1993 and 1993–2007. Dune morphology presents low lee and stoss side slopes (on average 8° and 3°, respectively) and dune migration rate is not very high. Dune movements are in the direction of residual tidal currents, i.e. toward the east, with mean migration rates around 0·8 to 5 ± 0·25 m yr^?1 and up to 6·6 ± 0·7 m yr^?1, respectively, at multi‐decennial and decennial time scales. The dune internal architecture is complex with superimposed eastward prograding units, displaying locally opposite progradation. Second‐order discontinuities (dip of 0·5°–4° perpendicular to dune crests) constitute dune master bedding. By counting the number of second‐order reflectors between 1937–1993 and 1993–2007, the formation periodicity of these bounding surfaces is estimated to range from 4 to 18 years. These time intervals coincide with the long‐term tidal cyclicities and also with the inter‐annual to decennial variability of storm activity in northern Europe. Two theories were made to interpret the dune internal structures: the second‐order surfaces are interpreted either as the depositional surfaces corresponding to the marks of weak energy periods (weak tidal and storm action), or as erosive surfaces due to an opposite direction of dune migration provoked temporarily by exceptional storms from the northeast. Copyright © 2010 John Wiley & Sons, Ltd.     

The influence of dunes on mixing in a migrating salt‐wedge: Fraser River estuary,Canada

Dune bedforms and salt‐wedge intrusions are common features in many estuaries with sand beds, and yet little is known about the interactions between the two. Flow visualization with an echosounder and velocity measurements with an acoustic Doppler current profiler over areas of flat‐bed and sand dunes in the highly‐stratified Fraser River estuary, Canada, were used to examine the effect of dunes on interfacial mixing. As the salt‐wedge migrates upstream over the flat‐bed, mixing is restricted to the lower portion of the water column. However, as the salt‐wedge migrates into the dune field from the flat bed, there is a dramatic change in the flow, and large internal in‐phase waves develop over each of the larger dunes, with water from the salt‐wedge reaching the surface of the estuary. The friction Richardson number shows that bed friction is more important in interfacial mixing over the dunes than over the flat‐bed, and a plot of internal Froude Number versus obstacle (dune) height shows that the salt‐wedge flow over the dunes is mainly supercritical. Such bedforms can be expected to cause similar effects in interfacial mixing in other estuaries and sediment‐laden density currents, and may thus be influential in fluid mixing and sediment transport. Copyright © 2010 John Wiley & Sons, Ltd.     

Early‐stage aeolian protodunes: Bedform development and sand transport dynamics

Early‐stage aeolian bedforms, or protodunes, are elemental in the continuum of dune development and act as essential precursors to mature dunes. Despite this, we know very little about the processes and feedback mechanisms that shape these nascent bedforms. Whilst theory and conceptual models have offered some explanation for protodune existence and development, until now, we have lacked the technical capability to measure such small bedforms in aeolian settings. Here, we employ terrestrial laser scanning to measure morphological change at the high frequency and spatial resolution required to gain new insights into protodune behaviour. On a 0.06 m high protodune, we observe vertical growth of the crest by 0.005 m in two hours. Our direct measurements of sand transport on the protodune account for such growth, with a reduction in time‐averaged sediment flux of 18% observed over the crestal region. Detailed measurements of form also establish key points of morphological change on the protodune. The position on the stoss slope where erosion switches to deposition is found at a point 0.07 m upwind of the crest. This finding supports recent models that explain vertical dune growth through an upwind shift of this switching point. Observations also show characteristic changes in the asymmetric cross‐section of the protodune. Flow‐form feedbacks result in a steepening of the lee slope and a decline in lower stoss slope steepness (by 3°), constituting a reshaping of protodune form towards more mature dune morphology. The approaches and findings applied here, (a) demonstrate an ability to quantify processes at requisite spatial and temporal scales for monitoring early‐stage dune evolution, (b) highlight the crucial role of form‐flow feedbacks in enabling early‐stage bedform growth, alluding to a fluctuation in feedbacks that require better representation in dune models, and (c) provide a new stimulus for advancing understanding of aeolian bedforms. Copyright © 2017 John Wiley & Sons, Ltd.     

Modeling river dune development and dune transition to upper stage plane bed

Large asymmetric bedforms known as dunes commonly dominate the bed of sand rivers. Due to the turbulence generation over their stoss and lee sides, dunes are of central importance in predicting hydraulic roughness and water levels. During floods in steep alluvial rivers, dunes are observed to grow rapidly as flow strength increases, undergoing an unstable transition regime, after which they are washed out in what is called upper stage plane bed. This transition of dunes to upper stage plane bed is associated with high transport of bed sediment in suspension and large decrease in bedform roughness. In the present study, we aim to improve the prediction of dune development and dune transition to upper stage plane bed by introducing the transport of suspended sediment in an existing dune evolution model. In addition, flume experiments are carried out to investigate dune development under bed load and suspended load dominated transport regimes, and to get insight in the time scales related to the transition of dunes to upper stage plane bed. Simulations with the extended model including the transport of suspended sediment show significant improvement in the prediction of equilibrium dune parameters (e.g. dune height, dune length, dune steepness, dune migration rate, dune lee side slope) both under bed load dominant and suspended load dominant transport regimes. The chosen modeling approach also allows us to model the transition of dunes to upper stage plane bed which was not possible with the original dune evolution model. The extended model predicts change in the dune shapes as was observed in the flume experiments with decreasing dune heights and dune lee slopes. Furthermore, the time scale of dune transition to upper stage plane bed was quite well predicted by the extended model. Copyright © 2015 John Wiley & Sons, Ltd.     

Form drag is a major component of bed shear stress associated with tidal flow in the vicinity of an isolated sand bank,Torres Strait,northern Australia

Tidal current and elevation data were collected from five oceanographic moorings during October 2004 in Torres Strait, northern Australia, to assess the effects of large bedforms (i.e., sand banks) on the drag coefficient (C_D) used for estimating bed shear stress in complex shallow shelf environments. Ten minute averages of tidal current speed and elevation data were collected for 18 days at an on-bank site (<7 m water depth) and an off-bank site (<10 m). These data were compared to data collected simultaneously from two shelf locations (<11 m) occupied to measure regional tidal behaviour. Overall C_D estimates at the on- and off-bank sites attained 7.0±0.1×10⁻³ and 6.6±0.1×10⁻³, respectively. On-bank C_D estimates also differed between the predominant east–west tidal streams, with easterly directed flows experiencing C_D=7.8±0.18×10⁻³ and westerly directed flows C_D=6.4±0.12×10⁻³. Statistically significant differences between the off-bank and on-bank sites are attributed to the large form drag exerted by the sand banks on the regional tidal currents, and statistically significant differences between the westward and eastward flows is ascribed to bedform asymmetry. Form drag from the large bedforms in Torres Strait comprises up to 65% of the total drag coefficient. When constructing sediment transport models, different C_D estimates must therefore be applied to shelf regions containing steep bedforms compared to regions that do not. Our results extend the limited inventory of seabed drag coefficients for shallow shelf environments, and can be used to improve existing regional seabed mobilisation models, which have direct application to environmental management in Torres Strait.     

南海北部东沙海域巨型水下沙丘的分布及特征

本文基于多波束测深和高分辨率多道反射地震数据研究了东沙海域深水巨型水下沙丘的特征.巨型水下沙丘发育在230~830m水深的上陆坡范围内,呈斑块状分布.NW-SE向的近海底流体运动不仅冲蚀地层,形成了三条与水下沙丘间隔分布的冲蚀带,为水下沙丘提供了沉积物来源,同时也为水下沙丘的形成提供了动力源.研究区水下沙丘波长(L)范围55~510m,波高(h)范围1.5~20m,二者呈指数关系分布.沙丘的波长随水深增大而增大,波高则在500~700m水深范围内最大.水下沙丘NE—SW向展布的脊线和几何参数关系是与现今水动力条件相平衡的结果.     

Observation and numerical modeling of tidal dune dynamics

Tidal sand dune dynamics is observed for two tidal cycles in the Arcachon tidal inlet, southwest France. An array of instruments is deployed to measure bathymetric and current variations along dune profiles. Based on the measurements, dune crest horizontal and vertical displacements are quantified and show important dynamics in phase with tidal currents. We observed superimposed ripples on the dune stoss side and front, migrating and changing polarity as tidal currents reverse. A 2D RANS numerical model is used to simulate the morphodynamic evolution of a flat non-cohesive sand bed submitted to a tidal current. The model reproduces the bed evolution until a field of sand bedforms is obtained that are comparable with observed superimposed ripples in terms of geometrical dimensions and dynamics. The model is then applied to simulate the dynamics of a field of large sand dunes of similar size as the dunes observed in situ. In both cases, simulation results compare well with measurements qualitatively and quantitatively. This research allows for a better understanding of tidal sand dune and superimposed ripple morphodynamics and opens new perspectives for the use of numerical models to predict their evolution.     

Principal component analysis (PCA) and mineral associations of litoraneous facies of continental shelf carbonates from northeastern Brazil

The distribution of mineral phases according to the provenance of carbonate and terrigenous facies of carbonate sediments from a large area of the continental shelf of northeast Brazil was investigated using a major element multivariate analysis approach. Heavy minerals such as ilmenite are restricted to the litoraneous facies of the continental shelf of the states of Paraíba and Pernambuco, and clay minerals are found in distal facies of the continental shelf of the State of Ceará. In the carbonate fraction, composed essentially by Mg-calcite and aragonite, there is co-variation between CaO/MgO and bathimetry in part of the studied continental shelf from depths between 15 and 20 m, apparently due to influence of the seawater temperature, degree of oxygenation and luminosity. The terrigenous facies are mainly composed of quartz, clay minerals, K-feldspars and micro-micaceous minerals, having Fe and Ti oxide and hydroxide minerals as major accessory phases. Major element behavior attests to the presence of arenaceous quartz-rich relict sediments in the 35, 60 and 80 m isobaths of the continental shelf of the state of Ceará which is here interpreted as a proxy of ancient coast lines during the Flandrian transgression.     

A continuous model for sand dunes: Review,new developments and application to barchan dunes and barchan dune fields

Basically, sand dunes are patterns resulting from the coupling of hydrodynamic and sediment transport. Once grains move, they modify the surface topography which in turns modifies the flow. This important feedback mechanism lies at the core of continuous dune modelling. Here we present an updated review of such a model for aeolian dunes, including important modifications to improve its predicting power. For instance, we add a more realistic wind model and provide a self‐consistent set of parameters independently validated. As an example, we are able to simulate realistic barchan dunes, which are the basic solution of the model in the condition of unidirectional flow and scarce sediments. From the simulation, we extract new relations describing the morphology and dynamics of barchans that compare very well with existing field data. Next, we revisit the problem of the stability of barchan dunes and argue that they are intrinsically unstable bed‐forms. Finally, we perform more complex simulations: first, a barchan dune under variable wind strength and, second, barchan dune fields under different boundary conditions. The latter has important implications for the problem of the genesis of barchan dunes. Copyright © 2010 John Wiley & Sons, Ltd.     

Storm-driven shelf-to-canyon suspended sediment transport at the southwestern Gulf of Lions

Shelf-to-canyon suspended sediment transport during major storms was studied at the southwestern end of the Gulf of Lions. Waves, near-bottom currents, temperature and water turbidity were measured on the inner shelf at 28-m water depth and in the Cap de Creus submarine canyon head at 300 m depth from November 2003 to March 2004. Two major storm events producing waves H_s>6 m coming from the E–SE sector took place, the first on 3–4 December 2003 (max H_s: 8.4 m) and the second on 20–22 February 2004 (max H_s: 7 m). During these events, shelf water flowed downcanyon producing strong near-bottom currents on the canyon head due to storm-induced downwelling, which was enhanced by dense shelf water cascading in February 2004. These processes generated different pulses of downcanyon suspended sediment transport. During the peak of both storms, the highest waves and the increasing near-bottom currents resuspended sediment on the canyon head and the adjacent outer shelf causing the first downcanyon sediment transport pulses. The December event ended just after these first pulses, when the induced downwelling finished suddenly due to restoration of shelf water stratification. This event was too short to allow the sediment resuspended on the shallow shelf to reach the canyon head. In contrast, the February event, reinforced by dense shelf water cascading, was long enough to transfer resuspended sediment from shallow shelf areas to the canyon head in two different pulses at the end of the event. The downcanyon transport during these last two pulses was one order of magnitude higher than those during the December event and during the first pulses of the February event and accounted for more than half of the total downcanyon sediment transport during the fall 2003 and winter 2004 period. Major storm events, especially during winter vertical mixing periods, produce major episodes of shelf-to-canyon sediment transport at the southwestern end of the Gulf of Lions. Hydrographic structure and storm duration are important factors controlling off-shelf sediment transport during these events.     

Embryo dune development on a large,actively accreting macrotidal beach: Calais,North Sea coast of France

Sediment budget data from an 18‐month topographic survey were analysed with data from brief experiments on wind parameters, beach moisture contents, bedforms and sand mobilization in order to monitor conditions and patterns of embryo dune development over a flat 150–1000 m wide accreting upper beach. The surface conditions over the upper beach locally affect aeolian transport, but net dune development over time depends on sustained strong winds and their orientation. Incoming marine sand supplied by storms and onshore winds is reorganized by the dominant offshore to longshore winds into elongated embryo dunes over this upper beach, imprinting a regional morphology of long‐term longshore dune ridge development. Copyright © 2006 John Wiley & Sons, Ltd.     

Nannofossil age constraints for the northern KwaZulu-Natal shelf-edge wedge: Implications for continental margin dynamics, South Africa, SW Indian Ocean

Samples collected from the shelf-edge wedge using surface grab samples and the Jago submersible constrain the KwaZulu-Natal shelf-edge wedge to a late Pliocene age on the basis of the absence of Gephyrocapsa oceanica s.l. and Discoaster brouweri, and the presence of Calcidiscus macintyrei. This correlates with proposed Tertiary sea-level curves for southern Africa and indicates relative sea-level fall during the late Pliocene coupled with hinterland uplift. Exposed failure scarps in the upper portions of submarine canyons yield sediment samples of early Pleistocene ages, indicating the uppermost age of deposition of clinoform topsets exposed in the scarp walls. Partially consolidated, interbedded silty and sandy deposits of similar age outcrop in the thalweg of Leven canyon at a depth of 150 m. These sediments provide an upper age limit of the shelf-edge wedge of early Pleistocene, giving a sedimentation rate of this wedge of 162–309 m/Ma. The distribution of widespread basal-most Pleistocene sediments on the upper slope indicates that these sediments escaped major reworking during sea-level falls associated with Pleistocene glaciations and remain as relict upper slope veneers. The absence of more recent sediments suggests that this area has been a zone of sediment bypass or starvation since the early Pleistocene. Areas where younger sediments mantle deposits of early Pleistocene ages represent areas of offshore bedload parting, re-distributing younger Holocene sediment offshore and downslope.     

Suspended sediment transport in the Gulf of Lions (NW Mediterranean): Impact of extreme storms and floods

In situ observations were combined with 3D modeling to gain understanding of and to quantify the suspended sediment transport in the Gulf of Lions (NW Mediterranean Sea). The outputs of a hydrodynamic–sediment transport coupled model were compared to near-bottom current and suspended sediment concentration measurements collected at the head of seven submarine canyons and at a shallow shelf site, over a 6-month period (November 2003–May 2004). The comparisons provide a reasonable validation of the model that reproduces the observed spatial and time variations. The study period was marked by an unusual occurrence of marine storms and high river inputs. The major water and sediment discharges were supplied by the Rhone, the largest Mediterranean river, during an exceptional flood accompanying a severe marine storm in early December 2003. A second major storm, with moderate flooding, occurred in February 2004. The estimate of river input during the studied period was 5.9 Mt. Our study reveals (i) that most of the particulate matter delivered by the Rhone was entrapped on the prodelta, and (ii) that marine storms played a crucial role on the sediment dispersal on the shelf and the off-shelf export. The marine storms occurring in early December 2003 and late February 2004 resuspended a very large amount of shelf sediment (>8 Mt). Erosion was controlled by waves on the inner shelf and by energetic currents on the outer shelf. Sediment deposition took place in the middle part of the shelf, between 50 and 100 m depth. Resuspended sediments and river-borne particles were transported to the southwestern end of the shelf by a cyclonic circulation induced by these onshore winds and exported towards the Catalan shelf and into the Cap de Creus Canyon which incises the slope close to the shore. Export taking place mostly during marine storms was estimated to reach 9.1 Mt during the study period.