Laboratory experiment on rip current circulations over a moveable bed: Drifter measurements
This study describes a laboratory experiment on rip current circulations over a moveable bed. Rip current characteristics over eight contrasting nature-like beach morphologies are investigated. The seabed varied from reasonably alongshore uniform to strongly alongshore nonuniform with crescentic patterns and bar-rip morphologies, representative of a full morphological down-state sequence. The same offshore shore-normal waves were generated by the wavemaker for the eight situations with the same mean water level to study the sensitivity of rip current characteristics as a function of the beach morphology only. In each case, a 30 to 60 min video run was used to track a large number of drifters released within the surf zone. Results show the presence of classic rip current patterns with counterrotating cells and a relatively narrow offshore-directed jet varying from shore-normal to strongly skewed. Wave-driven circulations were strongly unstable. Computed standard deviations of flow intensity and direction provide high-resolution information on the spatial variability of rip current instabilities. Highly pulsating and weakly directionally variable offshore-directed flow is observed in the rip neck for well-developed bar-rip morphologies that turns into a weakly pulsating and highly directional variable rip current flow with decreasing beach alongshore nonuniformity. Proposing a definition of rip current intensity based on the rip current circulation geometry, rip current intensity was found to linearly increase with increasing measure of beach alongshore nonuniformity within both the low-energy and moderate-energy rip current regimes. To date, our laboratory experiment provides the first extensive quantitative rip current information during a full down-state sequence for a given wave condition.
(Journal of Geophysical Research. vol. 115, n° 0148-0227, pp. C12008, 28/05/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LEGI, UJF, Grenoble INP, CNRS, Géosciences Montpellier, UAG, INSU - CNRS, UM, CNRS
PREDATION OF MUDFLAT MEIO-MACROFAUNAL METAZOANS BY A CALCAREOUS FORAMINIFER, AMMONIA TEPIDA (CUSHMAN, 1926)
Benthic foraminifera are heterotrophic protists that utilize different trophic mechanisms and nutritional resources. They exhibit a wide range of trophic behaviours: selective (grazing) and indiscriminate herbivory, symbiosis, carnivory, parasitism, uptake of dissolved organic matter, passive suspension feeding and, most commonly, deposit feeding. The benthic foraminifera Ammonia tepida, previously known as an herbivore, fed as a carnivore in laboratory experiments where mobile metazoans were provided. We observed predation on the three types of metazoans provided: nematodes, copepods, and a larval gastropod. This foraminifera used its pseudopodial network to entrap the invertebrates, which were then stripped of their soft internal tissues within 24 hours. Our experiments are the first to demonstrate that Ammonia tepida, despite its limited motility, is able to utilize larger mobile animals as a food source. The great abundance of small metazoans in most marine environments suggests that they are a food source for foraminifera. Further study of foraminiferal feeding strategies will enhance our understanding of their role in marine communities.
(Journal of Foraminiferal Research, n° 0096-1191, 28/05/2026)
LIENSs, INSU - CNRS, ULR, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BIAF, UA, UAG, UPMC, UNS, CNRS
Structural vs functional approaches: A first comparison between WFD indicators and Ecological Network Analysis indices on French estuaries
At summary: general context, issue indicators, material and methods data, results.
(pp. 22, 28/05/2026)
UR EPBX, CEMAGREF, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LIENSs, INSU - CNRS, ULR, CNRS
Changes in precipitation regimes over North America during the Holocene as recorded by mineralogy and geochemistry of Gulf of Mexico sediments
Changes in terrigenous-transfer patterns from North America toward the Gulf of Mexico via the Mississippi River during the Holocene were investigated using mineralogical and geochemical records from the northern Gulf of Mexico (Pigmy Basin). Clay mineralogy (smectite/illite + chlorite) and geochemical signatures (K and Ti intensities) indicate fluctuations in the detrital sedimentation during the Holocene in the Pigmy Basin. They likely reflect alternations between at least two dominant terrigenous sources: the smectite-rich NW Mississippi watershed, and the illite-and chlorite-rich Great Lakes province and NE Mississippi watershed. These recurring and rapid modifications of erosional processes over this period suggest changes in the hydrological regime via rainfall patterns. Such a modification during the Holocene is likely linked with the rapid atmospheric reorganization following the final collapse of the Laurentide Ice Sheet. Indeed, mineralogical and geochemical proxies indicate east-to-west migrations of the main detrital source (from the Great Lakes and northeastern province toward the northwestern province) associated with Mississippi River megaflood episodes. These modifications of the main detrital sources likely record migrations of the precipitation belt, which are constrained by atmospheric configuration (Jet Stream, Bermuda High and Intertropical Convergence Zone position) and subtropical oceanic hydrological properties (meridional extension of the Atlantic Warm Pool). In the frame of previously published rainfall patterns over the Caribbean and North America, our results highlight some marked modifications of moisture transfer throughout the Holocene. These changes are interpreted as resulting from two atmospheric configurations that have driven alternately the precipitation distribution over North America for the last 10 ka with an apparent cyclicity of~2.5 ka. The coherent common cyclicity between the Gulf of Mexico detrital parameters and Greenland atmospheric proxies over the Holocene suggests that the initial external forcing was rapidly transferred latitudinally through atmospheric processes.
(Global and Planetary Change. vol. 74, n° 0921-8181, pp. 132 - 143, 28/05/2026)
CNRS, LOG, INSU - CNRS, ULCO, CNRS, IRD [Ile-de-France], IUEM, IRD, INSU - CNRS, UBO EPE, CNRS, USF, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
100,000 Years of African monsoon variability recorded in sediments of the Nile margin
Multiproxy analyses were performed on core MS27PT recovered in hemipelagic sediments deposited on the Nile margin in order to reconstruct Nile River palaeohydrological fluctuations during the last 100,000 years. The strontium and neodymium isotope composition of the terrigenous fraction and the major element distribution reveal large and abrupt changes in source, oscillating between a dominant aeolian Saharan contribution during arid periods and a dominant Nile River contribution during pluvial periods. Iron content shows a strong correlation with strontium and neodymium isotopes. This allows the use of a high-resolution continuous Fe record as a proxy of Blue Nile sediment input over the last 100,000 years. The detailed Fe record, with approximately 10 years resolution during pluvial periods, is consistent with subtropical African records of well-dated lake level fluctuations and thus constitutes a first continuous high resolution record of the East African monsoon regime intensity over Ethiopia.;The detailed Fe record shows the two main known pluvial periods attributed to strengthening of the African monsoon over Ethiopia, the Nabtian period from 14 to 8 ka cal BP and the Saharan period from 98 to 72 ka BR For the first time, the last glacial period (Marine Isotope Stage (MIS) 2,3 and 4) is documented with a continuous record showing large oscillations between high and low East African palaeo-monsoon regimes.;The end of the Nabtian period occurred at 8 ka in core MS27PT, i.e. much earlier than on the East Equatorial African region where it ended around 5.5 ka. We interpret this as evidence that the southward shift of the rain belt occurred 3000 years earlier over the Eastern Ethiopian Highland and propose that the gradual southward migration of the rain belt was associated with highly variable intensity and longer rainy seasons from 8 to 5 ka. During the last glacial period, two wet periods are present around 60-50 ka BP and 38-30 ka BP. These two humid periods are in phase with the rise of atmospheric CH4 concentrations suggesting that wetland tropical African area was one of the sources of the atmospheric CH4 during the MIS 3. During the Last Glacial Maximum and MIS 4, high Saharan aeolian influxes in phase with records of aeolian dust deposited in East Antarctica are documented. This study highlights the importance of reconstructions of monsoon rainfall fluctuation at high temporal resolution to better understand the link between low- and high-latitude climate variability at millennial timescales.
(Quaternary Science Reviews. vol. 29, n° 0277-3791, pp. 1342-1362, 28/05/2026)
GEOAZUR 6526, IRD, UPMC, UNS, INSU - CNRS, UniCA, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ETH Zürich, UAG, INSU - CNRS, UM, CNRS
4D CHARACTERIZATION OF METALS BY 3DXRD
The status of 3DXRD microscopy is reviewed, with a special view to applications in metallurgy. Various approaches are compared in terms of perfounance. In addition several recent advances are presented, such as a 3D grain map with an unprecedented spatial resolution of 500 nm, first results from the commissioning of a novel 3D detector set-up and a validation of the box-scan procedure.
(pp. 101-119, 28/05/2026)
DTU, MATEIS, UCBL, INSA Lyon, INSA, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ESRF
Spatial variability of live benthic foraminiferal faunas on the Portuguese margin
We investigated benthic foraminiferal densities, composition, and microhabitats at three sampling stations on the Portuguese margin, at 980, 1860 and 3125m water depth. For each site, we studied two sets of three replicate cores, sampled during two successive multi-corer deployments. Our results show an overall trend of decreasing foraminiferal densities from the shallowest to the deepest site, in response to a decreasing labile organic matter flux to the sea floor. Faunas at 980m are strongly dominated by Uvigerina mediterranea, which shows a conspicuous faunal density maximum close to the sediment surface. At 1860m, the surface faunas are much poorer, and no longer dominated by a single taxon. Cibicidoides robertsonianus, C. kullenbergi, Uvigerina peregrina, Gavelinopsis translucens and Hoeglundina elegans are present in about equal quantities. The deep infaunal community at these two stations is dominated by Globobulimina affinis, and has comparable densities. At 3125m, the faunas are very poor in 5 of the 6 cores, and mainly consist of agglutinant taxa. At all three stations, important differences are observed between the 6 studied cores. At 980m, the faunal density is about 4 times higher in one of the cores, mainly due to high numbers of Uvigerina mediterranea. This could be explained by the position of this core in a topographical depression, where organic matter concentrates. At 1860m, two sets of three cores, taken during two successive multicorer deployments, contain different amounts of deep infaunal taxa. Finally, at 3125m, one of the 6 cores contains an exceptionally rich deep infaunal community (up to 450 individuals per 50cm), dominated by the calcareous taxa Fursenkoina bradyi, Globobulimina affinis and Chilostomella oolina. The fact that the subrecent fossil faunas of three studied cores from this site are all enriched in these taxa indicates that the observed high infaunal standing stocks are a recurrent phenomenon, in response to a currently unidentified process that strongly concentrates metabolisable organic matter in deeper sediment layers.
(Micropaleontology. vol. 56, n° 0026-2803, pp. 297 - 322, 28/05/2026)
LPG-ANGERS, LPG, UA, UN UFR ST, UN, INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Live benthic foraminiferal faunas along a bathymetrical transect (140–4800 m) in the Bay of Biscay (NE Atlantic)
In a 10-stations bathymetrical transect in the Bay of Biscay, we observed important changes in the density, composition and microhabitats of live foraminiferal faunas from the outer continental shelf to the abyssal plain. Four zones are recognised: (1) at the upper continental shelf (140 m water depth), foraminiferal densities are very high and the superficial sediment is occupied by Bolivina subaenariensis and Valvulineria bradyana. Globobulimina spp., Chilostomella oolina and Nonion fabum dominate the infaunal niches, which are positioned close to the sediment–water interface due to a strong compaction of the vertical succession of redox zones. (2) At the upper continental slope stations (300–1000 m), foraminiferal densities are high and the superficial sediments are dominated by Uvigerina mediterranea/peregrina. Deeper in the sediment, intermediate infaunal niches are occupied by Melonis barleeanus. Due to a deeper oxygen penetration, the deep infaunal taxa Globobulimina spp. and C. oolina live at a considerable depth in the sediment. (3) At the mid and lower slope stations (1000–2000 m) in the superficial sediment Cibicidoides kullenbergi and Hoeglundina elegans progressively replace U. mediterranea. U. peregrina is still a dominant taxon, reflecting its preference for a somewhat intermediate organic flux level. Deep infaunal taxa become increasingly rare. (4) At the lower slope and abyssal plane stations (deeper than 2000 m), faunal densities are very low and the fauna is composed exclusively by shallow infaunal species, such as Nuttallides umboniferus and Melonis pompilioides. The foraminiferal data together with the pore water data in the sediment give evidence of the presence of a trophic gradient from very eutrophic settings at the upper continental shelf towards oligotrophic settings at the abyssal area.
(Revue de Micropaléontologie. vol. 53, n° 0035-1598, pp. 139 - 162, 28/05/2026)
LPGN, UN, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
A method to calculate sediment fluxes from infrequent data: application to 65 rivers of the French river quality database
Improving knowledge of sediment exports represents one major challenge for environmental sciences considering their role in geochemical cycles and their link with Earth's surface processes. Because suspended sediment (SS) fluxes in rivers reflect the integration of combined erosion, transport and deposition processes that occur within the drained area, their calculation is thus essential in surface processes studies. Suspended sediment fluxes are estimated from discharge measurements and SS concentrations, either by averaging methods or by predicting sediment concentration values from continuous discharge data. In the latter case, a power function (or power law relation) is often defined between the observed SS concentrations and the corresponding discharge data. However it seems unrealistic to consider a single relation between SS concentrations and river discharges. The reason is hat sediment production processes are not homogeneous in time, showing local and seasonal effects for example in agricultural areas where land cover varies inside a year or in mountainous regions where snow melting has a strong influence. Moreover, these processes are also spatially heterogeneous, due to spatial patterns in landscape characteristics, meteorological phenomena and geomorphology. In addition, important gaps persist when calculating SS fluxes, mainly due to SS measurements are not always carried out with high frequency. Based on 65 river basins in France, with various sizes, geomorphologies and land uses, this study aims at testing methods for an estimation of annual sediment loads, based on infrequent SPM concentration data spanning over several decades.
(pp. 12206-1, 28/05/2026)
BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, SISYPHE, UPMC, EPHE, PSL, PSL, CNRS
Highstand vs. lowstand turbidite system growth in the Makran active margin: Imprints of high-frequency external controls on sediment delivery mechanisms to deep water systems
Late Quaternary turbidite system growth along the Makran convergent margin is investigated through a set of deep-sea cores from upper slope and piggy-back basins to deep basin plain settings. High-resolution stratigraphy in these various depositional environments permits reconstruction of the evolution of sand-to-mud ratio, sedimentation rates, frequencies, and thickness of turbidite deposits during the last 25 ka BP. This study demonstrates how tectonics, climate and eustasy can interplay at high resolution (< 20 ka) and control the input of terrigeneous sediment along the tectonically active Makran convergent margin, in a source-to-sink perspective. The Makran turbidite system growth has been continuous throughout sea-level lowstand, transgressive, and highstand conditions. However, the frequency, rates, and nature of sediment supply varied in response to climate, sea-level, and tectonically induced changes in source-to-sink sediment dispersal modes. These changes include conditions of sediment production and availability in the drainage basin, capacity of transport from fluvial systems, and rates of sediment storage on the shelf and upperslope areas. Climate in the hinterland appears as a first-order control on the properties of turbidity currents that feed the turbidite system, controlling the average sand-to-mud ratio in the deep water deposits. The onset of sea-level highstand after ∼ 8 ka BP resulted in a notable change in turbidite system growth, characterized by the occurrence of large volume, thick turbidity currents (> 300 m thick along the continental slope) originated from successive, multiple slide or slump-induced surges. Their related deposits have low recurrence intervals, close to those calculated from the large magnitude earthquake and tsunami record in the Makran area. Comparison with the Nile and Indus turbidite systems growth during the Late Quaternary provides an evaluation of the relative importance of shared forcing parameters (i.e. monsoon-induced phases of arid/humid conditions and post-glacial sea-level rise), in significantly different basin settings. The Indus fan appears mainly controlled by eustasy during the last 25 ka. Inversely, similarities are found between the Nile and Makran turbidite systems, where sea-level changes are modulated by the climate impact on fluvial dynamics in the hinterland. However, the Makran turbidite system growth is continuous through times, because both the uplift in the coastal area and the fluvial dynamics of short, mountainous river systems allow high sediment transfer rates to the marine basin, even though arid conditions and associated low water fluxes. Earthquake-induced highstand turbidite deposits form a thick sedimentary succession in the Oman abyssal plain, and are significant in the geologic record. This study finally illustrates how the complex interplay between external (allogenic) forcings can complicate the interpretation of high-resolution sedimentary successions in turbidite-filled basins.
(Marine Geology. vol. 274, n° 0025-3227, pp. 187 - 208, 28/05/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IFP, VU, SHOM, IFREMER, UNS, UniCA