Estuarine conservation and restoration: the Somme and the Seine case studies (English Channel, France)

Megatidal estuaries such as the Seine and the Somme (North-Western France) are rather well delimited and human impacts on them are well understood. Since the middle of the 19th Century, there has been a slow but irreversible degradation of the state of these English Channel estuaries. However, current conservation and restoration strategies tend to freeze habitats in a particular state, their status being defined, most often, through a patrimonial or utilitarian approach. Connectedness between biotopes (sensu habitat+community) has a tendency to be neglected, especially with regard to main ecological gradients, i.e., salinity. In this paper, evaluation methodologies are proposed with the intention of assessing changes to ecosystem functions, under anthropogenic disturbance, controlled or otherwise. The Seine (a heavily industrialised ecosystem) is compared to the Somme (considered here for its pseudo-natural features) in order to discriminate between oceanic processes (siltation and plugging of estuaries) and anthropogenic influences. Preservation and restoration of habitats rely on a robust scientific methodology. The multi-scale approach adopted in the projects presented here relies on sensitive socio-ecological assessment procedures, tools for evaluating ecological quality, and well-built monitoring programmes based upon pertinent indicators. Such managerial tools were used to refine strategies and make them compatible with the sustainable co-development of resources in a European context. This paper demonstrates how scientists were able to acquire and apply knowledge in the field of rehabilitation and restoration. Jointly with managers and policy-makers, they have brought scientific information and socio-economics together in order to answer questions about the restoration of sites or habitats and to anticipate future propositions in the spirit of Integrated Coastal Zone Management (ICZM).     

SiO2 precipitation in olivine: ATEM investigation of two dunites annealed at 300 MPa in hydrous conditions

Two natural dunites were annealed at pressure P=300 MPa, temperature T=1373, 1473 and 1573 K, and fO₂ within the stability field of olivine. The starting materials contained small amounts of hydroxyls in the form of minor phases of hydrated minerals, which released an aqueous phase during the experiments. A detailed analytical transmission electron microscopy (ATEM) investigation of these materials revealed that small quantities of two types of silica-rich glass formed during heat treatment. The first type of glass, found at triple junctions as rare partially crystallized glass pockets, results from melting dehydration reactions involving the hydrous phases. The second type of glass is found as pure silica precipitates (0.1–0.5 μm in size, for a total of a few 0.1 vol%) within the olivine grains of specimens heated to ≥1473 K. From considerations of the kinetics of the precipitation at 1473 K, we interpret this silica precipitation as resulting from the condensation of olivine metallic vacancies promoted by increasing fluid fugacities during the runs. Our observations, thus, demonstrate that metastable silica can precipitate in olivine from dunites experiencing rapid changes in their thermodynamical environment.     

Eruption and mass-wasting-induced processes during the late holocene destructive phase of Nevado del Ruiz volcano, Colombia

The November 13, 1985, eruption was characteristic of the Arenas eruptive stage of Nevado del Ruiz, the most recent of a series of twelve eruptive stages that have occurred in the past 11,000 years. Eruptive sequences, deposits and processes similar to that of 1985 have characterized the behavior of Nevado del Ruiz during three major prehistorical and historical eruptive stages: the approximately 3300-3100 yr. B.P. Hedionda, the 16th century Azufrado, and the mid-1800's Lagunillas eruptive stages, that partly destroyed the present Ruiz summit.According to the interpretation of the stratigraphic record of prehistorical eruptions and historical accounts, almost every recent magmatic event was small or short-lived. Nevertheless, rockslide-debris avalanches and catastrophic debris flows were triggered in all the eruptions owing to slope failures related to specific tectonic features of Ruiz volcano and/or to significant interactions between pyroclastic debris and the ice cap. Evidence for headward retreat of avalanche scarps during multiple eruptions reinforce the case that large slope failures can occur repeatedly at a large-volume volcano like Ruiz without reconstruction of the edifice. The latest Ruiz eruptions that involved rockslide-debris avalanches resemble in part the Shiveluch 1964 event for which evidence of lateral blast deposits are lacking, but differ in part from this type because non-eruptive and mass-wasting processes also triggered rockslide-debris avalanches.Many factors render the cluster of domes of the Ruiz summit unstable, including: (1) deeply dissected troughs opened toward the north-northeast (Azufrado), east (Lagunillas), and south (Recio) flanks; (2) strongly hydrothermally altered north and east flanks of the summit; (3) currently glaciated or recently deglaciated, high cliffs; (4) steep unstable margins of the ice cap on the north and east.Thus, in light of its past behavior, a small eruption or an earthquake might trigger catastrophic rockslide-debris avalanches. Furthermore, such avalanches as well as glacial outburst-floods and ice avalanches could induce debris flows by mobilizing weathered, water-saturated, and unconsolidated rocks or deposits.     

The effects of non-sphericity in diagnosis of solar and stellar atmospheres

Between the interplanetary medium, filled by winds, magnetic structures, etc., and the interior of stars, opaque, and dominated heavily by the gravitational spherical field, the stellar atmosphere is a place where the true physical equilibrium, on the inside, sufficiently described by the parameters L, M, R, and the chemical composition X, Y, Z, is progressively changing into a situation far for equilibrium, which needs many more parameters to be properly described.The assumption that the equilibrium situation was dominating in the atmosphere has been generally accepted during the first half of this century. Since 1950 or so, we progressively learnt that the thermodynamical equilibrium (TE), and even the local thermodynamical equilibrium (LTE), are far from being actually in existence, that the radiative equilibrium (RE) is not actually perfect, convection, diffusion, magnetism, dissipation processes... playing a non-negligible part in the energy transport, that the hydrostatic equilibrium (HE) is only an approximation, as the convection and the magnetism are affecting the atmospheric layers, that neither the sphericity of atmospheric layers (plane-parallel hypothesis: PP) is achieved, nor the homogeneity of stellar iso- layers. During the 1950s and following decades, we began to suspect these difficulties and their consequences. In this paper, we turn towards a new consequence of the last-mentioned effect: the influence of non-sphericity and inhomogeneity upon the stellar (and solar perhaps) abundances of elements.Dedicated to Cornelis de Jager     

Facies system of the Eastern Barents Sea since the last glaciation to present

Twenty-two sediment cores raised from the central and eastern parts of the Barents Sea have been studied to reconstruct the evolution of the facies system since the Late Weichselian glaciation. Multiproxy records reveal four lithostratigraphic units, which reflect major development stages of paleoenvironments. Age control is provided by 23 AMS ¹⁴C dates for Holocene sections of four cores. Continental moraine deposits of the last glaciation are overlain by proximal glaciomarine facies of the initial deglaciation phase. During this phase, the Barents Sea ice sheet detached from the ground resulting in seawater penetration into troughs, iceberg calving, deposition of IRD and fine-grained glacier meltwater load in newly formed marine basins. The main deglaciation phase is characterized by pulsed sedimentation from various gravity flows resulting in accumulation of distal glaciomarine facies comprising laminated clay and sand sequences with minor IRD. Redistribution of fine-grained suspended matter by bottom currents and brine-induced nepheloid flows combined with biogenic processes and minor ice rafting caused facies diversity of the Holocene marine sediments. The Holocene facies of shelf depressions reflect rather high, but variable productivity responding to climate changes and variations of Atlantic water inflow into the Barents Sea.     

Pasisar: Performances of a High and Very High Resolution Hybrid Deep-Towed Seismic Device

The Pasisar seismic acquisition system combines a source at the sea surface and a deep-towed single channel streamer. This unconventional device geometry reduces the width of the first Fresnel zone which increases the lateral resolution. However, the device acquisition geometry generates artifacts on seismic profiles and induces large incidence angles of the seismic signal. A specific processing sequence must be applied to the data to obtain a readable seismic section. Penetration of the seismic signal depends on the energy of the signal reaching the seafloor and on its incidence angle. Because of smaller source energy, 800 Joules Sparker data cannot be acquired in water depth larger than 1500 m for example, whereas there is no depth limit for the use of this system with air gun sources. Differential acoustic absorption of seismic frequencies (below 1000 Hz) in the water column is negligible when compared with wave fronts expansion. Thus, the horizontal resolution of any seismic system strongly depends on the frequency spectrum of the seismic source and on the travel distances. Pasisar and conventional seismic profiles being usually simultaneously recorded, we illustrate the interest of using a hybrid seismic device by comparing horizontal resolutions as well as signal-to-noise ratio obtained with both the Pasisar and conventional systems. In addition, by carefully picking time arrivals of a reflection on simultaneously recorded surface and deep-towed seismic records, it is possible to estimate the average interval seismic velocity. We present the simplified example of a horizontal reflector.     

The use of single seeding events to evaluate the effect of hail suppression

Summary During the years 1977–82 a randomized hail suppression experiment, Grossversuch IV, was conducted in Central Switzerland, testing a Soviet seeding method, which was called the competing embryo concept. Due to logistical and technical difficulties there were several seeded hail cells with insufficient seeding coverage. This fact complicates a statistically proper evaluation of the experiment.To overcome the problem of insufficient seeding, a method is demonstrated, which takes a single seeding event (in our case one rocket) as the statistical unit instead of the seeded cell. The assumption is made that each rocket, which hit the zone of hail formation, reduces the hail production and can be investigated independently from the others. 19 seed cells with 226 truly fired rockets and 18 control cells with 170 simulated rockets, representing over 90% of the total global kinetic energy of all Grossversuch IV cells, were selected. A randomization test is introduced to test the average differences of the true and simulated seeding events. A highly significant increase of kinetic energy after seeding (p-value around 1%) is observed. This result supports the statistically non-significant trend obtained in the confirmatory analysis.With 4 Figures     

Use of lipids and their degradation products as biomarkers for carbon cycling in the northwestern Mediterranean Sea

Changes in phytoplankton composition and degradation of particulate organic matter (POM) in the northwestern Mediterranean Sea were studied using time-series sediment trap samples collected during the spring of 2003 at the DYFAMED station. Lipid biomarkers (pigments, fatty acids, sterols, acyclic isoprenoids, alkenones and n-alkanols) were used to identify the main contributors to the POM produced during two phytoplankton blooms, while the effects of photooxidation, autoxidation and biodegradation were differentiated using characteristic lipid degradation products. Traps collected material corresponding to pre-bloom, bloom and post-bloom periods. Pigment analyses in the integrated (0-200 m) water column samples indicated that diatoms dominated the initial stages of the bloom event, with smaller amounts of haptophytes and pelagophytes. During the second part of bloom event there was a switch to haptophyte dominance with significant contributions from diatoms and pelagophytes, and an increased contribution from cryptophytes. Fatty acid distributions in the trap samples reflected contributions from marine bacteria, phytoplankton and zooplankton. Photooxidation and autoxidation products of monounsaturated oleic, cis-vaccenic and palmitoleic acids were detected along with photooxidation products from the chlorophyll side-chain. The relatively good correlation between the variation of U₃₇^K′ index and specific phytol autoxidation product percentage allowed us to attribute the alterations of U₃₇^K′ observed during the pre-bloom period and in the deeper traps to the involvement of selective autoxidative degradation processes. A variety of sterol oxidation products formed by biohydrogenation, autoxidation and photooxidation were detected. Sterol degradation products appeared to be less suited than oxidation products of monounsaturated fatty acids for the precise monitoring of the degradation state of POM, but their stable functionalized cyclic structure constitutes a useful tool to estimate the part played by biotic and abiotic processes. In these waters, biotic degradation generally predominates, but abiotic degradation is not negligible and, as expected, the extent of biotic degradation increases with depth. To obtain a more complete picture of POM degradation, the use of a pool of lipid degradation products (i.e. from unsaturated fatty acids, the phytyl side-chain and sterols) should be employed.     

Hindcast of pluvial,fluvial, and coastal flood damage in Houston,Texas during Hurricane Harvey (2017) using SFINCS

Natural Hazards - As demonstrated by recent tropical cyclone events, including U.S. Hurricanes Harvey, Irma, and Maria (2017), and Florence (2018), the destructive potential of flooding driven by...