Enhanced short-term sediment deposition within the Nazaré Canyon, North-East Atlantic

Abstract

Abstract In January and May 1999, interface sediments were sampled within the Nazare Canyon, a large submarine canyon that deeply indents the western Iberian continental margin (NE Atlantic) at around 39°35N. Excess 234Th profiles were established with high resolution to calculate inventories and bioturbation coefficients. A northern transect at 42°N is briefly presented as a reference for the Western Iberian margin. Synthesis of these parameters is used to examine short-term deposition within the Nazare Canyon. 234Thxs was always detected with significant activities on surface in most of the samples. Along the reference transect and in the adjacent area, surface 234Th excesses are about 10–20 dpm g−1. In contrast, 234Thxs reaches very high levels (up to 170 dpm g−1) in the canyon. There is a large range of variability in inventories and bioturbation rates, in relation with depth and location. These results show a preferential deposition in the canyon and focus in the upper and middle part of the canyon. On a monthly time scale the Nazare Canyon appears as a significant locus of sedimentation for the Western Iberian margin.