Marta Ribó

SAND RIDGES IN THE MID-OUTER SHELF AS POTENTIAL SAND BORROWS AREAS (NW MEDITERRANEAN)

The Coastal Sediments ’15 conference, Understanding and Working with Nature, 11-15 May 2015, San Diego, California.-- 13 pages, 6 figures

Modern to glacial age subglacial meltwater drainage at Law Dome, coastal East Antarctica from topography, sediments and jökulhlaup observations

Abstract Rare jökulhlaup events, also known as subglacial lake outburst flood events, have been observed at the Law Dome ice margin and provide an insight into the physical characteristics of subglacial meltwater and drainage. The subglacial topography based on data from the BEDMAP2 and ICECAP projects, together with subsurface transects of the ice margin obtained using ground-penetrating radar, reveal several lakes and lake-like depressions and the drainage pathways of two jökulhlaup events. Oxygen isotope typing of the meltwater during the most recent (2014) jökulhlaup event, combined with ice margin stratigraphy, enable the identification of ice tunnel melt pathways that exploit the 30–90° dipping basal ice layering. The presence of subglacial meltwater beneath Law Dome during the Holocene to Glacial periods is confirmed by the dendritic drainage pattern in the subglacial morphology and extensive layers of basal regelation ice and subglacial carbonate precipitate deposits found within the Løken Moraines sediments. These subglacial carbonates, including ooid layers, formed from the mixing of glacial meltwater and seawater at 72 ka BP. The combined evidence indicates that the ocean discharge of subglacial meltwater may be variable and/or is periodically blocked by basal freezing events near the ice sheet terminus.

Large-Scale Fine-Grained Sediment Waves Over the Gulf of Valencia Continental Slope (NW Mediterranean)

Recently acquired swath bathymetry, high-resolution seismic profiles and bottom sediment samples have revealed the presence of large-scale fine-grained sediment waves over the Gulf of Valencia continental slope. Like many other deep-water sediment waves, these features were previously attributed to gravitational slope failure related to creep-like deformation, and have now been reinterpreted as sediment wave fields extending from 250 m depth to the continental rise at ~850 m depth. Sediment wave lengths range between 500 and 1000 m and maximum wave heights of up to 50 m are found on the upper slope, decreasing downslope to a minimum height of 2 m. Seismic profiles showed continuous internal reflectors and several sediment wave packages were differentiated, being thicker on the crest of each wave and thinner on the downslope flank, indicating that these sediment waves are upslope-migrating. The sediment wave formation process was inferred from contemporary hydrodynamic observations, and internal wave activity is suggested to be the most probable mechanism for the sediment transport and deposition and subsequent maintenance of the sediment waves over the Gulf of Valencia continental slope.

Sand Ridges on the Mid-Outer Valencia Continental Shelf

A sand ridge field with crests oriented NE–SW (52°) located between 55 and 85 m water depth on the Valencia continental shelf (Spain) was mapped with multibeam swath bathymetry and characterized with high-resolution seismic reflection profiling and sediment sampling. Boundary layer hydrodynamic and suspended sediment concentration measurements conducted over a sand ridge at 66 m depth showed evidence of wave and current sediment resuspension during a major storm event. It is argued that these sand ridges developed in a shallow environment and there is no evidence of present-day ridge migration or morphological degradation.