Predominance of phytoplankton-derived dissolved and particulate organic carbon in a highly eutrophic tropical coastal embayment (Guanabara Bay, Rio de Janeiro, Brazil)
(Biogeochemistry. vol. 137, n° 0168-2563, pp. 1 - 14, 01/01/2018)
UFF, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, PSL, UVSQ, CEA, INSU - CNRS, X, IP Paris, CNES, SU, CNRS, UPCité
Volcanic influence of Mt. Fuji on the watershed of Lake Motosu and its impact on the lacustrine sedimentary record
(Sedimentary Geology. vol. 363, n° 0037-0738, pp. 200 - 220, 01/01/2018)
ULiège, IRSNB / RBINS, UGent, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GEOPS, UP11, CNRS, AORI, UTokyo
Human-induced river runoff overlapping natural climate variability over the last 150 years: Palynological evidence (Bay of Brest, NW France)
For the first time a very high resolution palynological study (mean resolution of 1 to 5 years) was carried out over the last 150 years in a French estuarine environment (Bay of Brest; NW France), allowing direct comparison between the evolution of landscapes, surface water, and human practices on Bay of Brest watersheds, through continental (especially pollen grains) and marine (phytoplanktonic microalgae: cysts of dinoflagellates or dinocysts) microfossils. Thanks to the small size of the watersheds and the close proximity of the depositional environment to the mainland, the Bay of Brest represents an ideal case study for palynological investigations. Palynological data were then compared to published palaeo-genetic analyses conducted on the same core and to various available instrumental data, allowing us to better characterize past environmental variability since the second half of the 19th century in Western Brittany. We provide evidence of some clues of recent eutrophication and/or pollution that affected phytoplankton communities and which appears linked with increased runoff (higher precipitations, higher percentages of riparian forest pollen, decline of salt marsh-type indicators, and higher values of the XRF Ti/Ca signal), mainly explained by the evolution of agricultural practices since 1945 superimposed on the warming climate trend. We assume that the significant relay observed between dinocyst taxa: Lingulodinium machaerophorum and Spiniferites bentorii around 1965 then followed by Spiniferites membranaceus after 1985, attests to a strong and recent eutrophication of Bay of Brest surface waters induced by high river runoff combined with abnormally elevated air temperatures, especially obvious in the data from 1990. The structure of the dinocyst community has thus been deeply altered, accompanied by an unprecedented increase of Alexandrium minutum toxic form at the same period, as confirmed by the genetic quantification. Despite this recent major anthropogenic forcing, the fossil pollen sequence also records natural climate variability. We highlight, for the first time, a possible connection between climate (AMO modes) and fossil pollen records (especially tree pollination rates) in coastal sediments using tree percentage fluctuations as an indirect proxy for past sea surface and atmospheric temperatures.
(Global and Planetary Change. vol. 160, n° 0921-8181, pp. 109 - 122, 01/01/2018)
LGO, UBS, IFREMER, UBO EPE, CNRS, LEMAR, IRD, IFREMER, UBO EPE, CNRS, DYNECO, IFREMER, GM, IFREMER, IFREMER, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Long-term (1998 vs. 2010) large-scale comparison of soft-bottom benthic macrofauna composition in the Gulf of Lions, NW Mediterranean Sea
We achieved a long term (i.e., 1998 vs. 2010) large scale (i.e., whole Gulf of Lions) study of benthic macrofauna composition in the Gulf of Lions based on the resampling of 91 stations located along 21 inshore-offshore transects. Results show that the 3 main benthic communities identified in 1998 were still present in 2010 although their composition changed. Using only year and station of sampling we found a significant space-time interaction explaining changes in macrofaunal community composition, and, in this study, stations differ primarily in terms of depth and distance to the Rhône river mouth. Temporal changes in benthic macrofauna composition were clearly most important at shallow stations (i.e., in the Littoral Fine Sand community) than at deep ones (i.e., Terrigenous Coastal Mud community). These results are in good agreement with the current paradigm according to which climatic oscillations such as NAO (North Atlantic Oscillation) and WeMO (Western Mediterranean Oscillation) are indirectly (i.e., through changes in the frequency of occurrence and the intensity of storms) controlling benthic macrofauna composition in the Gulf of Lions. This hypothesis is further supported by a meta-analysis of changes in the average and maximal yearly abundances of the polychaete Ditrupa arietina. At last, the spatial modelling of 1998 and 2010 benthic macrofauna compositions both suggested a significant effect of Rhône River inputs on the spatial distribution of benthic macrofauna in the Gulf of Lions.
(Journal of Sea Research (JSR). vol. 131, n° 1385-1101, pp. 32-45, 01/01/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LECOB, SU, CNRS, OOB, SU, CNRS, LEMAR, IRD, IFREMER, UBO EPE, CNRS
Modeling analysis of tidal bore formation in convergent estuaries
Despite the recognized impact of tidal bores on estuarine ecosystems, the large scale mechanism of bore formation in convergent alluvial estuaries is still under investigation. So far, field data exist only for a small number of estuaries, while numerical simulations employ the shallow water equations mainly focusing on the small-scale and local processes. In this work, firstly we apply the fully nonlinear weakly dispersive Serre-Green–Naghdi equations to simulate the tide propagation in a convergent estuary of idealized form, verifying that the local dispersion effects, responsible for the appearance of the secondary waves, do not influence the tidal bore onset, which only results from the large scale processes of amplification/damping and distortion of the incoming wave. In a second part, we numerically investigate (225 runs) the estuarine parameter space in order to identify the physical conditions that lead to tidal bore generation. In this parameter space, we determine a critical curve which divides estuaries according to tidal bore occurrence. As a result of this investigation we have shown that bore formation is controlled by the competition between two physical processes: (a) the knee-shaped distortion of the tidal wave, with flood dominance and eventually bore inception; (b) the dissipation of the tidal wave, which is unfavorable to bore formation. We also provide evidence that amplification due to topographic convergence is not a necessary condition for tidal bore generation and that there exist estuaries which display both wave damping and bore development. Finally, the validity of the results has been also assessed in the presence of freshwater river discharge, showing that for low river discharge, its effect on estuarine dynamics can be neglected.
(European Journal of Mechanics - B/Fluids, n° 0997-7546, 01/01/2018)
CARDAMOM, IMB, UB, Bordeaux INP, CNRS, Inria, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Are deep-sea ecosystems surrounding Madagascar threatened by land-use or climate change?
(Deep Sea Research Part I: Oceanographic Research Papers. vol. 131, n° 0967-0637, pp. 93-100, 01/01/2018)
IFREMER, JAMSTEC, GM, IFREMER, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, RIKEN
The balance of canopy and soil effects determines intraspecific differences in foundation species’ effects on associated plants
The impact of plant–plant interactions on species diversity patterns has been broadly addressed in stressful environments, such as alpine ecosystems, where foundation species promote species richness by creating habitat for other species. However, foundation species with contrasting phenotypes might modify the microhabitat differently, which would alter the subordinate community composition, and coincide with distinct feedback effects of those subordinate species on the foundation species. However, the precise interaction mechanisms that facilitate species are not fully understood, especially the relative contribution of above- and below-ground compartments of foundation species to subordinate species and the potential feedbacks they receive. We explored whether two contrasted canopy phenotypes (tight and loose) of the shrub Cytisus galianoi differed in their effects on the microhabitat and on subordinate plant community composition in a dry subalpine system. We also experimentally distinguished the relative contribution of above- (canopy) and below-ground (soil) effects of C. galianoi on the most frequent subordinate species, Festuca indigesta, as well as the reciprocal effects of F. indigesta on C. galianoi. We performed observational and manipulative experiments to assess the influence of phenotypic differences of the shrub on understorey microhabitat and subordinate plant community composition. Reciprocal effects were assessed by removing either F. indigesta from the understorey of the two shrub phenotypes or the C. galianoi canopy from the immediate vicinity of F. indigesta. The two C. galianoi phenotypes differed in mean values of functional traits (like stem density or plant height), modified their understorey microhabitats differently and hosted distinct subordinate communities. Loose phenotypes had more positive effects on community composition and diversity than tight phenotypes. In addition, tight phenotypes simultaneously showed both more positive above-ground and more negative below-ground effects on F. indigesta than loose phenotypes. There were no significant feedback effects of F. indigesta on C. galianoi. The two phenotypes of the foundation species C. galianoi showed contrasting effects on the subordinate plant community: Compared to the tight phenotype, the loose phenotype had higher associated species diversity and reduced reciprocal interaction intensities above- and below-ground with the subordinate species F. indigesta. This highlights the impact of phenotypic variation for plant interactions and community-level diversity.
(Functional Ecology. vol. 32, n° 0269-8463, pp. 2253-2263, 26/04/2026)
EEZA, CSIC, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Approche bayésienne pour estimer les paramètres d'un modèle biodynamique chez les invertébrés benthiques d'eau douce
Les modèles biodynamiques classiques ont été validés pour formaliser la variabilité de la bioaccumulation de contaminants par différentes espèces d'organismes. La bioaccumulation est alors décrite comme la résultante des processus d'absorption et d'élimination (Luoma et Rainbow, 2005). Chez les invertébrés benthiques, ces modèles ont été développés à l'origine pour les métaux, puis pour quelques contaminants organiques, en considérant l'organisme comme un compartiment unique et en ne prenant en compte généralement qu'une seule voie d'exposition. Toutefois, il est crucial de tenir compte dans de tels modèles de tous les processus impliqués dans la bioaccumulation de contaminants, tels que différentes voies d'absorption et notamment la voie trophique, la croissance de l'organisme, mais aussi les effets de saturation et/ou de biotransformation. Ces phénomènes sont d'autant plus importants à prendre en compte pour les invertébrés benthiques, dans la mesure où ils jouent un rôle clé dans le transfert des contaminants puisqu'ils se situent souvent à la base des réseaux trophiques aquatiques. Par ailleurs, l'estimation des paramètres de ces modèles est couramment effectuée par une approche fréquentiste, en deux étapes : premièrement en estimant les paramètres liés à l'élimination, et dans un second temps l'estimation des paramètres liés à l'absorption. Cette méthode nécessite la plupart du temps de fixer certains paramètres lorsque tous ne peuvent pas être estimés simultanément, induisant un biais puisqu'il n'est pas exclu que ces paramètres soient corrélés. L'inférence Bayésienne permet (i) de pallier le problème d'estimation simultanée de tous les paramètres d'un modèle à partir de données de nature différente ; (ii) d'utiliser l'information disponible sur les paramètres (à partir de la littérature, d'expériences préliminaires ou d'avis d'experts) ; et (iii) de fournir une estimation des incertitudes à travers les distributions a posteriori de chaque paramètre, issue de la distribution jointe de tous les paramètres estimés simultanément (incluant donc la corrélation éventuelle). L'objectif de cette étude est de développer un cadre Bayésien générique pour estimer simultanément les paramètres d'un modèle biodynamique chez des espèces d'invertébrés aquatiques variées exposées à divers contaminants, si possible peu connus ou émergents. La distribution a posteriori obtenue pour tous les paramètres permettra une évaluation plus précise de l'incertitude de la bioaccumulation. Nous illustrons cette approche avec des données expérimentales obtenues en conditions contrôlées de cinétiques d'accumulation et d'élimination chez Gammarus fossarum et Chironomus riparius exposés à des sédiments ou des feuilles contaminées en PCB 153 ou en hexabromocyclododécane (retardateur de flamme).
(pp. 20, 26/04/2026)
IRSTEA, LBBE, UCBL, VAS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Geoarchaeology of the Roman port-city of Ostia: Fluvio-coastal mobility, urban development and resilience
Ostia is one of the most extensively excavated cities of the Roman period. The port-city of Rome, which today lies 4 km from the coastline, was established in a very constrained environment at the mouth of the River Tiber. Based on a review of the geoarchaeological and archaeological research at Ostia, 4 new cores analysed through palaeoenvionmental methods, and 21 new radiocarbon dates, we propose a new model of the fluvio-coastal landscape of Ostia from its origin: (1) the coastline shifted rapidly westward between the 8th and the 6th c. BCE followed by a slow progradation and possible erosion phases until the end of the 1st c. CE; (2) the castrum of Ostia (c. late 4th–early 3rd c. BCE) was founded away from the river mouth but close to the River Tiber; (3) between the 4th and the 1st c. BCE, the River Tiber shifted from a position next to the castrum, below the northern Imperial cardo of Ostia, to 150 m to the north; (4) a possible harbour was established to the north of the castrum during the Republican period; (5) the city expanded and a district was built over the harbour and the palaeochannel between the Republican period and the beginning of the 2nd c. CE, showing that Ostia was a dynamic and resilient city during that time. Finally, we suggest the possibility to combine urban fabric analysis (the orientation of the structures) and palaeoenvironmental analysis for reconstructing the evolution of the city in relation to the fluvio-coastal mobility.
(Earth-Science Reviews, n° 0012-8252, pp. 265-283, 26/04/2026)
LIVE, UNISTRA, CNRS, Archéorient, UL2, CNRS, ULiège, IGAG, CNR, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, INP, CEPAM, UNS, CNRS, BSR
Ocean as the main driver of Antarctic ice sheet retreat during the Holocene
Ocean-driven basal melting has been shown to be the main ablation process responsible for the recession of many Antarctic ice shelves and marine-terminating glaciers over the last decades. However, much less is known about the drivers of ice shelf melt prior to the short instrumental era. Based on diatom oxygen isotope (δ18Odiatom; a proxy for glacial ice discharge in solid or liquid form) records from western Antarctic Peninsula (West Antarctica) and Adélie Land (East Antarctica), higher ocean temperatures were suggested to have been the main driver of enhanced ice melt during the Early-to-Mid Holocene while atmosphere temperatures were proposed to have been the main driver during the Late Holocene. Here, we present a new Holocene δ18Odiatom record from Prydz Bay, East Antarctica, also suggesting an increase in glacial ice discharge since ~4500 years before present (~4.5 kyr BP) as previously observed in Antarctic Peninsula and Adélie Land. Similar results from three different regions around Antarctica thus suggest common driving mechanisms. Combining marine and ice core records along with new transient accelerated simulations from the IPSL-CM5A-LR climate model, we rule out changes in air temperatures during the last ~4.5 kyr as the main driver of enhanced glacial ice discharge. Conversely, our simulations evidence the potential for significant warmer subsurface waters in the Southern Ocean during the last 6 kyr in response to enhanced summer insolation south of 60°S and enhanced upwelling of Circumpolar Deep Water towards the Antarctic shelf. We conclude that ice front and basal melting may have played a dominant role in glacial discharge during the Late Holocene.
(Global and Planetary Change. vol. 166, n° 0921-8181, pp. 62-74, 26/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CERFACS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GLACCIOS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, IACT, CSIC, UGR, UCL-ASTR, UCLouvain, MERMAID, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA