Storms impacts on a sandy beach including seasonal recovery: alongshore variability and management influences
Despite a global context of shoreline retreat, coastal areas and in particular sandy coasts are increasingly attractive. To handle the problem of coastline retreat different management strategies are deployed and among them soft methods as windbreakers or hard ones as seawalls. But all those methods are known to interfere in the natural evolution of the beach/dune systems at different timescales. To underline potential influences of management strategies on erosion and recovery periods, high frequency DGPS surveys coupled with video images are recorded at a workshop-site exhibiting various management strategies, Biscarrosse beach (SW of France) from November 2015 until September 2016. Results for the winter 2016 highlight a global erosion of the beach associated to a dune foot retreat and an alongshore variability in the beach response to events. The same patterns can be observed during the seasonal recovery period (April to August), in particular a lag in the berm reconstruction in front of the seawall. The LVI (Longshore Variation Index) reflects possible sediment processes taking place between the different sections of the beach: while recovery seems to be dominated by cross-shore exchanges in the unmanaged section, longshore sediment processes seem to be the origin of the recovery in the managed section. This variability could be linked to a permanent rip current visible (98% of observation) in front of the seawall that could cause an offshore sediment export explaining both the lag in term of recovery timescale and the different sediment processes involved during the recovery period. During the erosion season, sediment exchanges between the beach and the dune are limited due to the presence of seawalls and beach erosion and dune retreat in the two ends on the wall accelerated.
(Revue Paralia. vol. 11, n° 1760-8716, pp. n02.1-n02.16, 01/01/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
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
Spatio-temporal dynamics of hydrographic reorganizations and iceberg discharges at the junction between the Northeast Atlantic and Norwegian Sea basins surrounding Heinrich event 4
(Earth and Planetary Science Letters. vol. 481, n° 0012-821X, pp. 236 - 245, 01/01/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, CLIMAG, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Spatial and temporal patterns of shoreline change of a 280-km high-energy disrupted sandy coast from 1950 to 2014: SW France
(Estuarine, Coastal and Shelf Science. vol. 200, n° 0272-7714, pp. 212-223, 01/01/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LIENSs, INSU - CNRS, ULR, CNRS
Multi-Satellite Altimeter Validation along the French Atlantic Coast in the Southern Bay of Biscay from ERS-2 to SARAL
Monitoring changes in coastal sea levels is necessary given the impacts of climate change. Information on the sea level and its changes are important parameters in connection to climate change processes. In this study, radar altimetry data from successive satellite missions, European Remote Sensing-2 (ERS-2), Jason-1, Envisat, Jason-2, and Satellite with ARgos and ALtiKa (SARAL), were used to measure sea surface heights (SSH). Altimetry-derived SSH was validated for the southern Bay of Biscay, using records from seven tide gauges located along the French Atlantic coast. More detailed comparisons were performed at La Rochelle, as this was the only tide gauge whose records covered the entire observation period for the different radar altimetry missions. The results of the comparison between the altimetry-based and in-situ SSH, recorded from zero to five kilometers away from the coast, had root mean square errors (RMSE) ranging from 0.08 m to 0.21 m, 0.17 m to 0.34 m, 0.1 m to 0.29 m, 0.18 m to 0.9 m, and 0.22 m to 0.89 m for SARAL, Jason-2, Jason-1, ENVISAT, and ERS-2, respectively. Comparing the missions on the same orbit, ENVISAT had better results than ERS-2, which can be accounted for by the improvements in the sensor mode of operation, whereas the better results obtained using SARAL are related to the first-time use of the Ka-band for an altimetry sensor. For Jason-1 and Jason-2, improvements were found in the ocean retracking algorithm (MLE-4 against MLE-3), and also in the bi-frequency ionosphere and radiometer wet troposphere corrections. Close to the shore, the use of model-based ionosphere (GIM) and wet troposphere (ECMWF) corrections, as applied to land surfaces, reduced the error on the SSH estimates.
(Remote Sensing. vol. 10, n° 2072-4292, pp. 93, 01/01/2018)
GET, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LEGOS, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS, SYRTE, INSU - CNRS, CNRS, PSL, SU, CNRS, ECOLA, LEGOS, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS
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