Sea-temperature anomalies and population dynamics variations: effects on growth and density of three bivalves

The demographic structure of stable populations is usually modelled by a simple exponential decay mode. For 3 mollusc species, this model has been improved by taking inlo account monthly sea-temperature anomalies calculated on a 20 yr daily temperature chronicle. For the 3 species examined, Tapes rhomboïdes, Glycymeris glycymeris and Spisula ovalis, from the southern part of the Western English Channel, only temperature anomalies during the 2 mo following the major spawning period were positively eorrelated with density anomalies, probably in eonneetion with larval stage sensitivity. Comparison of temperature anomalies and mean annual growth va riability suggests an apparent positive effeet of temperature during autumn or winter months, significant for T. rhomboïdes only. ln spring and summer, temperature anomalies were negatively correlated with annual growth; although this phenomenon did not reach statistieal significanee, it may be linked with the well-known competition between gonadie development and somatie growth

Temporal evolution over ten years in the macrobenthos of muddy sands in the Bay of Concarneau (France)

The temporal evolution of the Amphiura filiformis community of two stations in the Bay of Concarneau was followed during a period of ten years (1970-1979). A concomitance has been found between the demographic fluctuations of the community and the effects of climatic and hydrodynamic factors occurring in the bay throughout the observation period. At the end of the decade a decline of the Amphiura filiformis population and some qualitative changes in the community are observed

Pelagic and benthic trophic chain coupling in a semi-enclosed coastal system, the Bay of Brest (France): a modelling approach

International audienceDuring the 2 last decades several studies have analysed the response of phytoplankton dynamics and benthic trophic webs to increasing anthropogenic eutrophic conditions in the Bay of Brest, France. The present project couples 2 models, a pelagic and a benthic one, to synthesise both these approaches to this ecosystem. This model shows that in spite of net carbon production being more than 10-fold lower than phytoplankton production benthic suspension feeders partly control the phytoplankton dynamics in the Bay. Computation of the nitrogen fluxes reveals the role of the benthic trophic chain in nutrient recycling. It is possible to show that an increase in nitrogen loading in the Bay would have limited consequences on the ecosystem, with the excess nitrogen being transferred to shelf waters without entering the trophic chain. The problem of toxic bloom events that can affect benthic suspension feeders, and consequently the total ecosystem, will have to be thoroughly studied

Modelling Seasonal Dynamics of Biomasses and Nitrogen Contents in a Seagrass Meadow (Zostera noltii hornem). Application to the Thau Lagoon (French Mediterranean Coast).

Abstract not availableJRC.H-Institute for environment and sustainability (Ispra

Deep eddy kinetic energy in the tropical Pacific from Lagrangian floats

At the ocean surface, satellite observations have shown evidence of a large spectrum of waves at low latitudes. However, very little is known about the existence and properties of the deep variability. Most of the subsurface observations rely on localized measurements, which do not allow for a global estimation of this variability. In this study, we use velocity estimates, provided by Argo float drifts at 1,000 m, to analyze the spatial and temporal distribution of the deep eddy kinetic energy (EKE) and its spectral signature with an unprecedented time and space coverage. In the tropical Pacific, high EKE is found along the equator, at the western boundary and poleward of 7 degrees N. EKE meridional distribution is also found to vary at the scale of the meridionally alternating mean zonal jets: it is higher inside eastward currents. We develop an original statistical scale analysis to determine the temporal and spatial scale dependence of this deep EKE footprint. We show the presence of periodic features whose characteristics are compatible with theoretical equatorial waves dispersion relations. Annual and semiannual Rossby waves are observed at the equator, as well as similar to 30-day Yanai waves, consistent with surface tropical instability waves. The location and intensification of these waves match the downward energy propagation predicted by ray tracing linear theory. Short-scale variability (with similar to 70-day periods and 500-km wavelength) has also been detected poleward of 7 degrees N. The generation mechanisms of this variability are discussed, as well as its potential importance for the mean circulation. Plain Language Summary Energy in the deep ocean is important as it is a potential driver of the deep circulation, which has important climate feedbacks. Because of its singular dynamics, the equatorial ocean is a preferential region of transfer of energy from the surface to the interior of the ocean. Very little is known, however, about the energy content in the deep equatorial oceans. In this study, we use the large number of floats, called Argo floats, drifting at 1,000-m depth in the ocean to describe the deep kinetic energy in equatorial regions. We show that various energetic waves are present at 1,000m in the tropical Pacific, and we discuss their potential generation mechanisms as well as their implications for the circulation. These new observations may help to validate some theories or numerical simulations of the deep equatorial and tropical circulation

Cyclones and Anticyclones in Seismic Imaging

Nearly all the subsurface eddies detected in seismic imaging of sections in the northeast Atlantic have been assumed to be anticyclones containing Mediterranean Water (MW). Fewer MW cyclones have been observed and studied. In this study, the work of previous numerical studies is extended to investigate some characteristics of layering surrounding MW cyclones, using a primitive equation model with equal diffusivities for salinity and temperature to suppress the effects of double diffusion. It is shown that, after a stable state is reached, both anticyclones and cyclones display similar patterns of layering: stacked thin layers of high acoustic reflectivity located above and below the core of each vortex, which do not match isopycnals. The authors conclude that it should not be possible to distinguish between MW cyclones and anticyclones based on their signature in seismic imaging alone. Complementary information is needed to determine the sense of rotation

The Evolving Concept of Eutrophication

Third International Symposium on Research and Management of Eutrophication In Coastal Ecosystems. EUTRO 2010 15–18 June 2010 Nyborg, DenmarkIn 1907 Weber referred to the vegetation of German peat bogs as 'eutraphent' if it needed high concentrations of essential elements. Naumann (1919) applied the term eutrophic, with the meaning of 'good nourishment', to Swedish lakes with a rich algal content. Limnologists subsequently developed a paradigm in which oligotrophic lakes become eutrophic as a result of increased nutrient loading, and came to see this development as undesirable. From about 1970 onwards the paradigm began to be applied to the sea. It was incorporated in international law, for example in the European 'Urban Waste Water Treatment' Directive (1990), and clarified for example by decisions by the European Court of Justice (2004, 2009). The European 'Marine Strategy Framework' Directive (2008) requires that “human-induced eutrophication is minimised, especially adverse effects thereof, such as losses in biodiversity, ecosystem degradation, harmful algae blooms and oxygen deficiency in bottom waters.” We build on earlier definitions, and on advances in scientific understanding, to propose that “Eutrophication is a process driven by enrichment of water by nutrients, especially compounds of nitrogen and/or phosphorus, leading to: increased growth, primary production and biomass of algae; changes in the balance of organisms; and water quality degradation. The consequences of eutrophication are undesirable if they appreciably degrade ecosystem health and/or the sustainable provision of goods and services.” We'll explore how this definition applies to the Baltic, Mediterranean, and North, Seas, and discuss it in relation to definitions based on organic enrichmentPeer Reviewe