University of the Littoral Opal Coast

About: University of the Littoral Opal Coast is a education organization based out in Dunkirk, France. It is known for research contribution in the topics: Catalysis & Dielectric. The organization has 1242 authors who have published 2383 publications receiving 46230 citations. The organization is also known as: ULCO.

Initiation of winter phytoplankton blooms within the Gironde plume waters in the Bay of Biscay

Abstract: Thermostratification and seasonal light increase are generally considered the first causes of phytoplankton spring blooms in temperate waters. The objective of this study is to confirm the existence of winter phytoplankton blooms, responsible for the early exhaustion of phosphate, within the Gironde plume waters (southeast Bay of Biscay), and to understand what may initiate them so early. Two cruises, BIOMET 2 and BIOMET 3, were carried out respectively in early (8 to 21 Jan- uary) and late winter 1998 (25 February to 11 March). An increase of phytoplankton biomass (chl a) between the 2 cruises and non-conservative nutrients observed in late winter confirm an early phyto- plankton growth both in the Gironde plume and adjacent oceanic waters. Among factors that possi- bly initiate these blooms, light availability seems to be the best candidate. First, the status of available light for phytoplankton changed dramatically between the 2 cruises when comparing the instanta- neous depth-averaged irradiance (Em) received by phytoplankton with the light saturation parameter Ek determined from P versus E curves. Light was limiting for phytoplankton growth in early winter according to systematically lower values of Em than Ek in the daytime. However, light was not limit- ing during a large part of the day in late winter since Em was above Ek during 40% of the daylight. The estimated critical depth from the Nelson & Smith (1991; Limnol Oceanogr 36:1650-1661) refor- mulation of the Sverdrup (1953; J Cons Perm Int Explor Mer 18:287-295) equation was much shallower (4 to 13 m) than the mixed layer depth (15 to 50 m) in early winter in the whole Gironde plume up to oceanic waters. On the contrary, it was much deeper (35 m) than the mixed layer depth (9 m) in late winter for the intermediate plume (salinity range 33 to 35) and similar for oceanic waters (S > 35.5) with a bottom depth of 60 to 70 m. Therefore, according to the Sverdrup model, available light is the triggering factor of winter phytoplankton blooms in the Gironde plume and adjacent oceanic waters. Moreover, Riley's (1957; Limnol Oceanogr 2:252-270) empirical critical irradiance of 20.9 W m -2 could be applied in these waters to predict the onset of blooms since it was reached in late winter but not in early winter. The establishment of halostratification and/or decrease of the light vertical attenuation coefficient prevail in the initiation process of winter phytoplankton blooms.

Co–Mg–Al Hydrotalcite Precursors for Catalytic Total Oxidation of Volatile Organic Compounds

Abstract: Co–Mg–Al hydrotalcite type solids were synthesized as precursors of catalysts for the total oxidation of toluene. After calcination at 500 °C, different mesoporous mixed oxides were obtained with high specific surfaces. The comparison of the catalytic activities of the calcined hydrotalcites with those of calcined hydroxides evidenced the superiority of the first oxides explained meanly by higher specific surfaces and more easily reducible particles. DRIFT “operando” allowed to follow the oxidation reaction and the formation of light coke and carbonate species.