The Barremian-Aptian arid phase in western Europe

Evidence is presented from nine areas in western Europe (Speeton, Yorkshire; southern North Sea; Channel and Weald Basins, southern England; Jeanne d'Arc, Lusitanian and Aquitanian Basins of the North Atlantic continental margins; Lower Saxony Basin, north Germany; the Paris Basin and southern France) for a phase of aridity which began during the Hauterivian-middle Barremian and continued to dominate the climate of the region until the mid-Aptian, although conditions during this period were not uniformly dry throughout. Criteria for recognising arid environments include the occurrence of evaporites, abundances of carbonate-rich sediments, red beds, firmgrounds, carbonate nodules and pyrite concretions, depletion of kaolinite, spore assemblages of limited morphological diversity, and the presence of numerous coniferalean and cheirolepidiacean pollen grains. The change from generally humid to dry climates during the Barremian is thought to have been linked to a lowering of sea-level. The arid phase clearly falls within the time span of the first Cretaceous Oceanic Anoxic Event.     

Patterns of benthic fauna and benthic respiration on the celtic continental margin in relation to the distribution of phytodetritus

In-situ and shipboard measurements of sediment community oxygen consumption (SCOC), in conjunction with a study of the distributions of macro and megafauna and phytopigments, were used to determine and, where possible, explain the distribution of labile particulate organic matter (POM) on the NE Atlantic continental slope (Goban Spur, SW Ireland). A specific issue concerned the existence of depocentres of labile POM on the slope caused by lateral transport, a phenomenon that has been found previously in the NW Atlantic. The SCOC data from October 1993 and May 1994 showed a steady decrease with increasing water depth. SCOC values ranged from 5.4 mmol m⁻² d⁻¹ at the shelfbreak to 0.3 mmol m⁻² d⁻¹ at 4,500 m depth. No evidence was found for seasonal variation in SCOC. A clear seasonal signal was observed with regard to sediment phytopigments and phytopigment fluxes into sediment traps attached to the benthic lander. The upper- and mid-slope values of both parameters were much higher in May 1994 than in October 1993 and August 1995. This is consistent with the normal spring bloom pattern; but because of the degraded state of the May phytodetritus in the near-bottom water, reflected in the lack of a response in SCOC and the low chlorophyll-a concentrations, it was concluded that the material was not derived from the overlying photic zone, but instead transported from elsewhere in the benthic nepheloid layer (BNL). In August 1995, the lower slope (>3,000 m) had received a strong and fresh phytodetritus pulse (3 g C m⁻²) forming a mucous layer on top of the sediment. Using phytopigments and sterols as molecular markers, it was shown that the pulse was derived from an offshore bloom with an important contribution by dinoflagellates. By contrast, no mucous layer was found on the upper slope stations in August 1995. Macrofauna biomass showed a distinct decline from the upper slope down to the lower slope conforming to the diminishing supply of labile POM. The total wet biomass of megafauna reached relatively high values at the lower slope (>3,500 m) owing to large motile sea cucumbers. The presence of these “vacuum-cleaner” sea cucumbers is considered indicative of the occurrence of phytodetritus pulses. In spite of their assumed adaptation to periodic pulses, the estimated contribution by the sea cucumbers to the total benthic mineralization is minor. When combining data from different years/seasons we observed decoupling between the food supply to the lower slope and the upper and mid slopes. The major pulse to the former comes from an offshore summer bloom. The upper and mid slope appear to be fuelled by spring bloom material which is subsequently redistributed on the upper slope in a BNL. The quality of the seston in the BNL diminished in the offshore direction as indicated by the phytopigment concentrations.     

Effects of TRH and somatostatin on releases of prolactin and growth hormone in vitro by the pituitary of Poecilia latipinna

Summary Pituitary glands from a teleost fish were incubated in the presence of the synthetic hypophysiotropic peptides, thyrotrophin-releasing hormone and somatostatin, in two media of different osmotic pressure.The effects on prolactin and growth hormone cells were detected by electron-microscopic morphometry with the aid of an image analyser. Thyrotrophin-releasing hormone caused changes in prolactin cell ultrastructure consistent with stimulated hormone release and, in the low osmotic pressure medium, appeared to increase synthetic activity. There was no effect on growth hormone cells. After somatostatin treatment, both synthesis and release in prolactin cells appeared to be inhibited, and there was an obvious inhibition of synthesis and release in growth hormone cells. The response of both cell types to somatostatin did not appear to be dependent on the osmotic pressure of the medium.