Submarine landslides, Gulf of Mexico continental slope: insights into transport processes from fabrics and geotechnical data

Ursa Basin on the Gulf of Mexico continental slope is a site of extremely fast sedimentation, building thick sequences of underconsolidated and overpressured muds and clays. Frequent sliding created mass transport deposits (MTD). In a study of strength, frictional behaviour, and fabrics of IODP Expedition 308 drillcores we find that mass transport is governed by very low friction coefficients and peak shear strengths of the sediments. The majority of the samples shows velocity weakening, enabling runaway instabilities in the sediment once deformation has started. While sediments at the bases of MTD seem to strengthen by the sliding, those below the bases remain weak, constraining a hazard for slide reactivation. Submarine sediment sliding leaves a strong and irreversible imprint, changing fabric geometries, and reducing the pore space. This is a transport phenomenon leading to expulsion of large amounts of pore fluids during sliding. MTD transport is probably as cohesive bodies, defining a considerable geohazard potential

Baited remote underwater video as a promising nondestructive tool to assess fish assemblages in clearwater Amazonian rivers: Testing the effect of bait and habitat type

Baited remote underwater video (BRUV) systems are being used in marine ecosystems as a nonextractive, cost-effective method of assessing the fish fauna with minimal species bias. This technique has had limited applications in freshwater ecosystems. Rheophilic fish assemblages of the Xingu River, a clearwater Amazonian river in Northern Brazil, were sampled with BRUV systems. Two-hour video recordings were collected using five different bait treatments (sardine, croaker, cat food, sweet corn, and no bait) in two lotic habitat categories (rocky and sandy bottoms). A total of 2460 fish from 56 taxa and 13 families were recorded from the 80 BRUV deployments. Significantly different fish assemblages, species richness, and abundance were detected between habitat types and among treatments. Our results suggest that the use of crushed sardines as a standardized bait optimizes the sampling recording the highest species richness, relative abundance, and number of exclusive species of rheophilic fish in clearwater Amazonian rivers. The data also highlight the unique fish diversity of the Xingu River prior to the expected large-scale environmental degradation resulting from the forthcoming operation of the Belo Monte hydroelectric power plant