Role of internal waves in the generation of nepheloid layers on the northwestern Alboran slope: Implications for continental margin shaping

Abstract

The role of internal waves in the sediment dynamics of the northwestern Alboran continental slope was investigated in a selected area around the Guadiaro submarine canyon. Nepheloid layer distribution was identified using closely spaced CTD/transmissometer profiles collected during two hydrographic surveys. A well-defined pattern of suspended sediment distribution consisting of surface, intermediate, and near-bottom nepheloid layers was found. Intermediate and bottom nepheloid layers were always observed within the canyon and on the adjacent continental slope, spanning mainly from 200 to 500 m depth. In addition, a current meter with a turbidimeter was deployed in the lower section of the Guadiaro Canyon at 600 m depth, 25 meters above the seafloor. Time series analysis indicated that the currents, temperature, and turbidity within the canyon fluctuate mainly at semidiurnal tidal frequencies, suggesting the presence of semidiurnal internal tides affecting the near-bottom suspended sediment concentration along the canyon axis. High-resolution bathymetry from the study area was used to evaluate the internal wave reflection conditions at semidiurnal tidal frequency for the entire continental slope region. Critical slope conditions were reached on the upper continental slope and along the canyon axis, coinciding with the region in which nepheloid layers were observed. This region also coincides with a zone of erosion on the upper continental slope of the study area previously identified by Hernández-Molina [1993]. These results indicate that the generation of intermediate and bottom nepheloid layers, as well as the erosion and shaping of the northwestern Alborán continental slope, may result from the interaction of internal waves and the seafloor morphology. Copyright 2004 by the American Geophysical Union.