Technical Report NTB 84-36

Surveillance of the north-eastern Atlanic dumpsite for low-level radioactive wasteThe Swiss oceanographic research program PROSPER

This report describes the results of the research undertaken within the CRESP program by the Swiss group PROSPER, for the surveillance of the current dumpsite for low-level radioactive waste in the North-Eastern Atlantic. About 100 nephelometric profiles obtained during three cruises in the vicinity of the site provide a sound basis for the description of the benthic nepheloid layer structure. Statistical analyses show that the last 1000m of water above the bottom are influenced by resuspension processes or by lateral advection of particles detached from the surrounding relief. A mapping performed over a large area (200 x 200 km) confirms the accumulation of particles in topographic lows. Geochemical analysis of suspended matter and surficial sediment has been carried out in order to compare their elemental composition, and to determine the classes of particles which are more likely to be resuspended. The discrepancy between BNL and local sediment composition suggests that advective transport or resuspension of older bottom sediment, exposed following slumping from the hill slopes, could act in addition to the local resuspension of recent sediment.