Allochthonous ostracods in the South China Sea and their significance in indicating downslope sediment contamination

摘要

The modern distribution pattern of allochthonousostracods in the South China Sea was analyzed, and theirpalaeoceanographical signifucance in indicating down slopesediment contamination was testified using the sediment record ofa core. General characteristics of allochthonous ostracods insurface sediments of the South China Sea include (1) a distributionlimited to the shelf and slope off southern China and around coralreef-studded shoal areas; (2) a distinct depth range and assemblagecomposition of allochthonous forms between the areas on thecontinental slope and around coral reefs; and (3) a downslopedecline of assemblage abundance, mean shell size and adult tojuvenile ratio, although this tendency is reversed at depths below2000m, probably due to the increased carbonate dissolution andlowered productivity of indigenous ostracods in the deep sea. Thedistribution patterns confirm the idea that post-mortem transportof marine ostracods occurs in a downslope manner, and at thesame time suggests that allochthonous ostracods are suitableindicators of sedimentary source. An analysis of ostracods fromthe core of Sonne-95 Cruise Site 17940, taken from the northernslope of the South China Sea, reveals markedly higheraccumulation rates and abundance of allochthonous forms in thetransitional phases from cold to warm periods than in the quietperiods in between, implying that downslope sediment transportfrom the shelf area was significantly intensified duringtransgression and regression.