Grain-size distribution and frictional behaviour of sediment cores from the Nice Slope

The upper shelf of the landslide-prone Ligurian Margin (Western Mediterranean Sea) off Nice well-known for the 1979 Airport Landslide is a natural laboratory to study preconditioning factors and trigger mechanisms for submarine landslides. For this study low-stress ring shear experiments have been carried out on a variety of sediments from >50 gravity cores to characterise the velocity-dependent frictional behaviour. Mean values of the peak coefficient of friction vary from 0.46 for clay-dominated samples (53 % clay, 46 % silt, 1 %) sand up to 0.76 for coarse-grained sediments (26 % clay, 57 % silt, 17 % sand). The majority of the sediments tested show velocity strengthening regardless of the grain size distribution. For clayey sediments the peak and residual cohesive strength increases with increasing normal stress, with values from 1.3 to 10.6 kPa and up to 25 % of all strength supported by cohesive forces in the shallowmost samples. A pseudo-static slope stability analysis reveals that the different lithologies (even clay-rich material with clay content >=50 %) tested are stable up to slope angles <26° under quasi-drained conditions.

Hydrogen consumption by gills of Bathymodiolus spp. collected at the Comfortless cove and Lilliput hydrothermal vent fields in May 2006

The discovery of deep-sea hydrothermal vents in 1977 revolutionized our understanding of the energy sources that fuel primary productivity on Earth. Hydrothermal vent ecosystems are dominated by animals that live in symbiosis with chemosynthetic bacteria. So far, only two energy sources have been shown to power chemosynthetic symbioses: reduced sulphur compounds and methane. Using metagenome sequencing, single-gene fluorescence in situ hybridization, immunohistochemistry, shipboard incubations and in situ mass spectrometry, we show here that the symbionts of the hydrothermal vent mussel Bathymodiolus from the Mid-Atlantic Ridge use hydrogen to power primary production. In addition, we show that the symbionts of Bathymodiolus mussels from Pacific vents have hupL, the key gene for hydrogen oxidation. Furthermore, the symbionts of other vent animals such as the tubeworm Riftia pachyptila and the shrimp Rimicaris exoculata also have hupL. We propose that the ability to use hydrogen as an energy source is widespread in hydrothermal vent symbioses, particularly at sites where hydrogen is abundant.