Resultats de dragages et essai de stratigraphie des bancs de Galice,et des montagnes de Porto et de Vigo (marge occidentale Iberique)

Dredged samples have been studied to establish the stratigraphy as well as the probable paleogeographic evolution of the sedimentary cover of Galicia Bank, and Vigo and Porto Seamounts. The sedimentation appears to have been neritic up to the Late Jurassic. These structural features evolved separately from the Iberic continental margin in Late Jurassic to Early Cretaceous times. Part of the sediments is made of calpionellid limestones, which is indicative of open marine conditions in this area of the Atlantic at that time. This also suggests the establishment of marine connections between this area and the “Mésogée”. These open marine conditions would have persisted since the Early Cretaceous.     

Importations et remaniements de thanatofaunes dans les sables de la plate-forme profonde des approches occidentales de la Manche

Macro- and micro-faunas are reported from six gravity cores collected at a mean depth of 150 m in the surficial deposits of the Kaiser sand bank in the Southern Western Channel Approaches. These are bivalves (mainly), gastropods, echinids, crustaceans and foraminifers. These fauna present a very rich association of numerous, well preserved species from various ecological settings. Such an association is commonly reported from the continental shelf of the last transgressive cycle. In addition, the sediment comprises two imported faunal associations. The first one corresponds to thanatocaenoses of Pliocene/lowermost Pleistocene and Weichselian age, reworked respectively from the underlying celtic incised valley fills and the Celtic Sand Banks. The absence of Quaternary fauna prior to the Weichselian suggests that the introduction of Pliocene sources occurred during the last climatic cycle. The second stage of importation took place after the last transgression in the Western Channel, and corresponds to the enrichment of the sediment in coastal fauna derived from western Brittany by the the predominant ebb tidal current. The variations of taxonomic diversity from core to core suggest a sediment transport around the bank that matches the one deduced from the study of tidal bedforms. At the present day, the wave action is highlighted by accumulation of species of the same shape, size and density inside storm beds. However, the survival within these beds of very small, juvenile shells indicate that each storm reworking was short in duration.     

Structure de la marge continentale Norvégienne au débouché de la mer de Barentz

Reconstructions of the continents prior to the opening of the Norwegian sea indicate an overlap between the Greenland and the Norwegian continental margins just west of the Barentz sea and imply that the basement of this area is of oceanic origin. Seismic profiling shows an oceanic-type basement covered by thick Tertiary sediments. The sedimentary supply is related to the geological history of the Barentz sea where only little unconsolidated sediments are known. Further south the structures of the present margin are directly related to the early opening of the Norwegian sea.     

Phytoplancton en baie de Seine. Influence du panache fluvial sur la production primaire

Phytoplankton distribution and primary productivity were investigated in the Bay of Seine (eastern English Channel, France) in spring and early summer of 1992 and 1994. In 1992, the horizontal distribution of phytoplankton species was determined over the whole Bay of Seine. In 1994, species distribution and primary productivity were studied along the salinity gradient of the Seine plume and in the neighbouring marine waters. Phytoplankton distribution was characterised by the permanent diatom dominance from early spring to early summer. The spring bloom did not occur uniformly over the bay, but was initiated in the marine waters, in the middle of the bay and progressed towards the coast where it developed, in June, in the diluted waters of the Seine plume. Phytoplankton distribution was also characterised by the dominance of large diatoms (Rhizosolenia) in marine waters and by the dominance of small species (Skeletonema costatum, Asterionella glacialis) in the plume waters. The greatest abundance of large diatoms was generally encountered below the euphotic zone. This accumulation seemed to be related to cell sedimentation and advection of marine waters below the diluted plume waters. The daily carbon productivity range was 1.4 to 3 g m⁻² d⁻¹. The highest values were measured in the plume waters (S > 28), suggesting the primary productivity in the plume was more controlled by light than by nutrients. The photic zone productivity/ chlorophyll a ratios (P/B; producted carbon per unit of Chla) were close to 40 mg mg⁻¹ d⁻¹ in the plume waters. P/B exceptionally reached 90 mg mg⁻¹ d⁻¹ in early summer. This value corresponded to a fast growing population of S. costatum. In marine waters, P/B varied from 22 mg mg⁻¹ d⁻¹, in spring, to 43 mg mg⁻¹ d⁻¹, in early summer.     

Incidence de la cinetique de decroissance de la temperature apres le choc thermique sur les modifications d'activite des esterases et les possibilites de survie de Scolelepis (malacoceros) fuliginosa (annelide polychete)

Scolelepis fuliginosa reared in the laboratory at 13°C were put through 10-min thermal shocks at 16°C and 18°C and were then submitted to either a slow or a rapid temperature reduction. After the thermal shock, a posterior fragment of each specimen was cut off at intervals, until six days. Samples were submitted to electrophoresis on polyacrylamide gel, esterase activity being determined with α-naphthyl acetate.Enzymograms show that thermal shocks act on esterases in decreasing the activity of the main fractions. Immediate effects result in a very precocious enzymic response; more long-term effects depend on the maximum temperature, the animal's sex and the kinetics of the post-shock thermal reduction.Females are more sensitive than males. For a given Δt, esterase changes are greater and more long-lasting. After a 16°C Δt, a rapid decrease in temperature prevents the loss of activity of the middle and fast fractions in males and delays, by about 10 h, the alteration of female esterases. After 18°C ΔT, loss of activity of the middle and fast fractions occurs in less than 1 h, independently of the thermal kinetics, but survival is only possible—solely for males—with a rapid decrease in temperature which also delays females' deaths by between 24 and 48 h.In conclusion, a rapid decrease in temperature gives organisms a better resistance to thermal shock, as determined by esterase activity and controls the lethality of a high Δt.