Geoacoustic provinces of the northern South China Sea based on sound speed as predicted from sediment grain sizes

摘要

The determination of geoacoustic provinces has important applications in assessing the responses of sedimentary environment and processes. Suitable geoacoustic provinces have not yet been identified in the northern South China Sea, which is an excellent study site for examining sediment acoustic properties. To determine the geoacoustic provinces of sediments in the northern South China Sea, 270 position samples were collected and analysed. Two-parameter empirical equations linking sediment grain-size components to sound speed were applied to sediments from the continental shelf and slope to accurately calculate sound speed in seafloor sediments, especially in the absence of site-specific acoustic data. Based on the ratios of sound speed within the sediments, two geoacoustic provinces are identified. Province I, which is characterized by low sound speed, primarily consists of fine-grained sediments discharged from the Pearl River. Province II, which is characterized by high sound speed, can be further divided into Province II-A and Province II-B. Province II-A is composed of mixed modern and relict sediments originating from the Pearl River and the southwest coast of Taiwan during a Pleistocene drop in sea level. Province II-B consists of coarser relict sediments caused by sea level change during the late Quaternary.