A biometrical analysis of the dinoflagellate cyst Lingulodinium machaerophorum (Deflandre and Cookson 1955) Wall, 1967 in 144 globally distributed surface sediment samples revealed that the average process length is related to summer salinity and temperature at a water depth of 30 m by the equation (salinity/temperature) = (0.078*average process length + 0.534) with R² = 0.69. This relationship can be used to reconstruct palaeosalinities, albeit with caution. The particular ecological window can be associated with known distributions of the corresponding motile stage Lingulodinium polyedrum (Stein) Dodge, 1989. Confocal laser microscopy showed that the average process length is positively related to the average distance between process bases (R²=0.78), and negatively related to the number of processes (R²=0.65). These results document the existence of two end members in cyst formation: one with many short, densely distributed processes and one with a few, long, widely spaced processes, which can be respectively related to low and high salinity/temperature ratios. Obstruction during formation of the cysts causes anomalous distributions of the processes. From a biological perspective, processes function to facilitate sinking of the cysts through clustering.

The shape and infilling of the submerged parts of valleys incised along the southern coast of Brittany (France) have been investigated using very high-resolution seismics and a small number of piston cores. The valley location and morphology are found to be controlled mostly by submarine topography, which is marked by a well-developed fault zone that lies between the modern coast and a prominent basement-cored island and shoal complex located 5-15 km offshore. The faults controlled the shape of the valley networks and the amount of incision along the valley profile. They were probably active until the end of incision, because the valley thalwegs show scarps up to 10 meters high where they are crossed by these faults. The valleys were incised during the Quaternary lowstands of sea level, and most of the fill was emplaced during the last postglacial sea-level rise. The valley fills form a transgressive succession, consisting mainly of fluvial deposits at the base (possibly amalgamated from older sequences) overlain by tide-dominated estuarine deposits and capped by offshore muds. The most prominent internal surfaces are the tidal-and wave-ravinement surfaces. The valley-fill architecture is strongly dependent on the valley morphology (depth of incision, width of the valleys, and extent of estuarine intertidal areas). Estuarine deposits inside narrow and linear valleys are mostly aggrading muds, whereas those inside large and dendritic valleys dominantly comprise sandier, tidal-channel and bar deposits.

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The Bay of Quiberon (NW France), which is protected by the Quiberon Peninsula, provides well-preserved sedimentary archives for high-resolution reconstruction of Holocene climate variability. Very-high-resolution seismic profiles were obtained from two Seistec boomer seismic campaigns conducted in the bay. The seismic surveys reveal the deposition of five distinct sedimentary units. This succession is correlated with radiocarbon-dated sediments sampled in a long CASQ core (MD08-3204CQ). The analysis of the sediments shows significant changes in grain size, indicating a complex series of palaeo-climate events dated at 8800, 8600, 4270, 3860, 2470 and 1060 cal. yr BP. These may be correlated with millennial timescale climate variability corresponding to the phases of Holocene rapid climate changes (RCCs), associated with negative North Atlantic Oscillation (NAO) index and usually characterized by weaker winter storms. On the contrary, periods between RCCs are characterized by the predominance of westerly winds and stormy conditions for Brittany (i.e. positive NAO). However, only storm events occurring during the RCCs have been preserved in the Bay of Quiberon. This paper aims to reconstruct the Holocene sedimentary infill of the bay, highlighting the role of episodic acceleration phases of the sea-level rise on the preservation of sedimentary archives. Thus, the Bay of Quiberon provides substantially a complete sedimentation record of the last 10,000 years characterized by a series of complex palaeo-environmental changes.

Abstract. The evolution of eutrophication parameters (i.e., nutrients and phytoplankton biomass) during recent decades was examined in coastal waters of the Vilaine Bay (VB, France) in relation to changes in the Loire and Vilaine rivers. Dynamic linear models were used to study long-term trends and seasonality of dissolved inorganic nutrient and chlorophyll a concentrations (Chl a) in rivers and coastal waters. For the period 1997–2013, the reduction in dissolved riverine inorganic phosphorus (DIP) concentrations led to the decrease in their Chl a levels. However, while dissolved inorganic nitrogen (DIN) concentrations decreased only slightly in the Vilaine, they increased in the Loire, specifically in summer. Simultaneously, phytoplankton in the VB underwent profound changes with increase in biomass and change in the timing of the annual peak from spring to summer. The increase in phytoplankton biomass in the VB, manifested particularly by increased summer diatom abundances, was due to enhanced summer DIN loads from the Loire, sustained by internal regeneration of DIP and dissolved silicate (DSi) from sediments. The long-term trajectories of this case study evidence that significant reduction of P inputs without simultaneous N abatement was not yet sufficient to control eutrophication all along the Loire–Vilaine–VB continuum. Upstream rivers reveal indices of recoveries following the significant diminution of P, while eutrophication continues to increase downstream, especially when N is the limiting factor. More N input reduction, paying particular attention to diffuse N sources, is required to control eutrophication in receiving VB coastal waters. Internal benthic DIP and DSi recycling appears to have contributed to the worsening of summer VB water quality, augmenting the effects of anthropogenic DIN inputs. For this coastal ecosystem, nutrient management strategies should consider the role played by internal nutrient loads to tackle eutrophication processes.

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