Impact of the Phaeocystis globosa spring bloom on the intertidal benthic compartment in the eastern English Channel: a synthesis

From 1999 to 2005, studies carried out in the frame of regional and national French programs aimed to determine whether the Phaeocystisglobosa bloom affected the intertidal benthic communities of the French coast of the eastern English Channel in terms of composition and/or functioning. Study sites were chosen to cover most of the typical shore types encountered on this coast (a rocky shore, an exposed sandy beach and a small estuary). Both the presence of active Phaeocystis cells and their degradation product (foam) did have a significant impact on the studied shores. The primary production and growth rates of the kelp Saccharina latissima decreased during the bloom because of a shortage of light and nutrient for the macroalgae. On sandy sediments, the benthic metabolism (community respiration and community primary production), as well as the nitrification rate, were enhanced during foam deposits, in relation with the presence of bacteria and active pelagic cells within the decaying colonies. In estuarine sediments, the most impressive impact was the formation of a crust at the sediment surface due to drying foam. This led to anoxic conditions in the surface sediment and resulted in a high mortality among the benthic community. Some organisms also tended to migrate upward and were then directly accessible to the higher trophic level represented by birds. Phaeocystis then created a shortcut in the estuarine trophic network. Most of these modifications lasted shortly and all the systems considered came back to their regular properties and activities a few weeks after the end of the bloom, except for the most impacted estuarine area.     

The 15 August 2007 Peru Earthquake and Tsunami: Influence of the Source Characteristics on the Tsunami Heights

The tsunami caused by the 2007 Peru earthquake (M_w 8.0) provoked less damage than by the seismic shaking itself (numerous casualties due to the earthquake in the vicinity of Pisco). However, it propagated across the Pacific Ocean and small waves were observed on one tide gauge in Taiohae Bay (Nuku Hiva, Marquesas, French Polynesia). We invert seismological data to recover the rupture pattern in two steps. The first step uses surface waves to find a solution for the moment tensor, and the second step uses body waves to compute the slip distribution in the source area. We find the slip distribution to consist of two main slip patches in the source area. The inversion of surface waves yields a scalar moment of 8.9 10²⁰ Nm, and body-wave inversion gives 1.4 10²¹ Nm. The inversion of tsunami data recorded on a single deep ocean sensor also can be used to compute a fault slip pattern (yielding a scalar moment of 1.1 10²¹ Nm). We then use these different sources to model the tsunami propagation across the Pacific Ocean, especially towards Nuku Hiva. While the source model taken from the body-wave inversion yields computed tsunami waves systematically too low with respect to observations (on the central Pacific Ocean DART buoy as on the Polynesian tide gauge), the source model established from the surface-wave inversion is more efficient to fit the observations, confirming that the tsunami is sensitive to the low frequency component of the source. Finally we also discuss the modeling of the late tsunami arrivals in Taiohae Bay using several friction coefficients for the sea bottom.     

First experiments on the maternal transfer of metals in the cuttlefish Sepia officinalis

The aim of this study was to provide a first insight on the incorporation of eight metals in the eggs of the cuttlefish Sepia officinalis via maternal transfer, using radiotracer techniques ((110m)Ag, (241)Am, (109)Cd, (60)Co, (134)Cs, (54)Mn, (75)Se and (65)Zn). The cuttlefish was fed daily with radiolabelled crabs for two weeks; it then started to spawn every three days. Among the eight tracers, only (110m)Ag, (75)Se and (65)Zn were significantly transferred to the eggs. The radiotracer distribution among the egg compartments showed that (75)Se and (65)Zn were accumulated mainly in the vitellus whereas (110m)Ag was found in similar proportion in the vitellus and the eggshell. During the embryonic development, (75)Se and (65)Zn contained in the vitellus were progressively transferred to the embryo, likely to supply its metabolic needs in these essential elements. Although it has no known biological functions, Ag contained in both vitellus and eggshell was also transferred to the embryo. Overall, our results showed that transfer of Ag, Se, and Zn does actually occur from a female cuttlefish to its eggs, at least during the last two weeks before spawning.     

Vlora-Elbasani-Dibra (Albania) transversal fault zone and its seismic activity

The transversal fault zone Vlora-Elbasan-Dibra (VED)with Northeastern strike dislocated the structure ofAlbanides along all their width. This transversalfault is distinguished by the flexure of Lushnja, thediapire dome of Dumrea, the transversal Quaternarydepression of Elbasani, the belt of transversalstructure of Labinoti, and then it continues towardsNortheast with transversal horst of Golloborda andgoes toward FYROM in NE direction. In the Southwesternpart of this transversal fault, near Fieri town, themolasse subsided toward North. The structures ofIonian and Kruja zone, near this transversal fault,also subsided and uplifted more toward North. Throughmarine investigation a transversal fault with ENEstrike direction was discovered near the Northern partof Sazani Island (Aliaj et al., 1996). We think itmay belong to the big transversal fault zone VED.The transversal fault zone VED is clearlyoutlined by the location of strong and weakearthquakes, migration of foci along this fault, themacroseismic field and focal mechanisms. Generally,along this transversal fault it is the transtensionalstrike-slip dextral motion that dominates.In our studies the transversal fault zoneVlora-Elbasani-Dibra was considered to be the mostpotential transversal seismogenetic belt in Albaniaand nearby. It has played, and is still playing,an important role in seismotectonics in Albania andits surrounding regions.     

A quick and low-cost technique to identify layers associated with heavy rainfall in sediment archives during the Anthropocene

Long-term records are needed to investigate the impact of extreme events in the current framework of global change. Sedimentary reconstruction with a high resolution remains difficult without conducting expensive, destructive and/or time-consuming analyses. In this study, high resolution CT-scan profiles (0·6 mm resolution) were used to investigate their potential for detecting flood deposits induced by heavy rainfall events. This method was applied to a sediment core dated with fallout radionuclides – covering a 120 year period – collected in a pond draining a small forested catchment (French Massif Central – Central France). Between 1960 and 2017, 28 layers were deposited. Seventy-six percent of these deposits were correlated to the occurrence of heavy rainfall (>50 mm) recorded during one or two consecutive days. The remainder of the deposits detected with the Computer Tomography (CT) scanner (n = 5) were not correlated to weather events. They mainly occurred in response to landscape management operations (for example, afforestation works as a result of the major 1999 storm). This period was indeed characterized by an increase in the delivery of ¹³⁷Cs-enriched sediment, demonstrating a greater topsoil contribution to sediment during major forest management operations. The intensity of detrital layers has significantly decreased throughout time after a major land use change that took place in 1948 and land abandonment. The frequency of heavy rainfall and associated detrital deposits has nevertheless increased by 60% and 75%, respectively, between the years 1960 and 2017. These results outline the potential of CT-scan for reconstructing long-term flood deposits associated with heavy precipitation.