Sound speed structure models of seafloor sediments in the Southern South China Sea

Abstract

The various sedimentary environments and the several sediment sources indicate that seafloor sediments in the southern South China Sea have unique acoustic research significance. The direct sound speed measurements of seafloor sediments are particularly valuable for this study sea, which lacks acoustic data. In order to characterize and develop the sound speed structure models locally depending on sedimentary environment and sediment texture in the southern South China Sea, sound speeds and physical parameters of 21 sediment cores were measured, and vertical distributions of sound speeds and physical properties were obtained. The vertical variations of physical properties and sound speeds indicate that there were obvious differences among the seafloor sediments in Sunda Shelf, in the continental slope and in the Nansha Trough. The sound speed structure models were classified in several categories according to the vertical variations of sound speed, texture parameter and stratified structure of sediments. The categories included: the trough-stratified model; trough-unstratified model; slope-stratified model; slope-unstratified model; shelf-stratified model; and, shelf-unstratified model. The comparison of results indicates that the clay-silt sediments have smaller vertical variation gradient, while the silt-clay and sand-silt sediments have larger variation gradient. These sound speed structure models can reveal the unique acoustic environment significance of surface sediments - at the interface of seawater and the seafloor - and will really be of great help to determine the acoustic properties of seafloor sediments and to populate data relating to the study sea area.