Origin of an enigmatic regional Mio-Pliocene unconformity on the Demerara plateau

The Demerara plateau, located offshore French Guiana and Suriname, is part of a passive transform continental margin particularly prone to develop slope instabilities, probably in relation to the presence of a free distal border along its steep continental slope. Slope failure occurred at different periods (Cretaceous to Neogene) and shows an overall retrogressive evolution through time. Upslope these failure headscarp, an enigmatic regional MioPliocene unconformity has been discovered through the interpretation of new academic and industrial datasets. The aim of this work is to describe and understand the origin of this surface. Our analysis shows that this unconformity is made of a series of valleys that cross-cut sedimentary strata. Each one of these valleys has a short lateral extent and is closed along two perpendicular directions, which suggests that it could correspond to a highly meandering system, or to some sub-circular depressions. The infill of these features is equivalent to the regional stratigraphic strata found outside the structures, but in a subdued position. This seems to imply that the structures have originated by a local loss of sediments at their base or by sliding processes. Furthermore, these depressions intersect each other through time, while migrating progressively downslope. We discuss a series of hypotheses that try to explain the onset and evolution of these depressions forming the Mio-Pliocene unconformity (Canyons? Slope failures? Contourite moats? Hydrate pockmarks?). Having established that these structures are depressions formed by collapse, and have many similarities with structures recently described in the literature as pockmarks associated with gas hydrate dissolution, we favor this hypothesis. We propose that these hydrate pockmarks form with a mass failure that was triggered by fluid-overpressure development at the base of the hydrate stability zone.

Optimization of growth and bacteriocin activity of the food bioprotective Carnobacterium divergens V41 in an animal origin protein free medium

Optimization of Carnobacterium divergens V41 growth and bacteriocin activity in a culture medium deprived of animal protein, needs for food bioprotection, was performed by using a statistical approach. In a screening experiment, twelve factors (pH, temperature, carbohydrates, NaCl, yeast extract, soy peptone, sodium acetate, ammonium citrate, magnesium sulphate, manganese sulphate, ascorbic acid and thiamine) were tested for their influence on the maximal growth and bacteriocin activity using a two-level incomplete factorial design with 192 experiments performed in microtiter plate wells. Based on results, a basic medium was developed and three variables (pH, temperature and carbohydrates concentration) were selected for a scale-up study in bioreactor. A 23 complete factorial design was performed, allowing the estimation of linear effects of factors and all the first order interactions. The best conditions for the cell production were obtained with a temperature of 15°C and a carbohydrates concentration of 20 g/l whatever the pH (in the range 6.5-8), and the best conditions for bacteriocin activity were obtained at 15°C and pH 6.5 whatever the carbohydrates concentration (in the range 2-20 g/l). The predicted final count of C. divergens V41 and the bacteriocin activity under the optimized conditions (15°C, pH 6.5, 20 g/l carbohydrates) were 2.4 x 1010 CFU/ml and 819200 AU/ml respectively. C. divergens V41 cells cultivated in the optimized conditions were able to grow in cold-smoked salmon and totally inhibited the growth of Listeria monocytogenes (< 50 CFU g-1) during five weeks of vacuum storage at 4° and 8°C.

Otolith shape variation provides a marker of stock origin for north Atlantic bluefin tuna (Thunnus thynnus)

Two stocks of bluefin tuna (Thunnus thynnus) inhabit the north Atlantic; the western and eastern stocks spawn in the Gulf of Mexico and the Mediterranean Sea respectively. Trans-Atlantic movements occur outside spawning time whereas natal homing maintains stock structure. Commercial fisheries may exploit a mixed assemblage of both stocks. The incorporation of mixing rates into stock assessment is precluded by uncertainties surrounding stock discrimination. Otolith shape descriptors were used to characterise western and eastern stocks of Atlantic bluefin tuna in the present study and to estimate stock composition in catches of unknown origin. Otolith shape varied with length and between locations and years. Within a restricted size range (200-297-cm fork length (FL)) the two stocks were distinguished with an accuracy of 83%. Bayesian stock mixture analysis indicated that samples from the east Atlantic and Mediterranean were predominantly of eastern origin. The proportion assigned to the eastern stock showed slight spatial variation; however, overlapping 95% credible intervals indicated no significant difference (200-297 cm FL: central Atlantic, 73-100%; Straits of Gibraltar, 73-100%; Morocco, 50-99%; Portugal 64-100%). Otolith shape could be used in combination with other population markers to improve the accuracy of mixing rate estimates for Atlantic bluefin tuna.