The influence of mesoscale eddies on sedimentary processes in the western South China Sea since 32 kyr BP

Abstract

Mesoscale eddies play an important role in the transport of heat, salt and other chemical substances. However, the influence of these eddies on the sediment distribution has not been thoroughly explored. Here, we discuss the influence of eddies on sediment transport in the western South China Sea (WSCS), where the eddy kinetic energy is strong, using sedimentary records of the grain size, clay mineral assemblage and total organic carbon (TOC) since 32 kyr BP. Our results reveal that the mesoscale eddies that influence the sedimentation process are controlled by both sea level fluctuations and summer monsoon variations. During the glacial period, fluvial sediments from the Mekong River, Red River and central Vietnam mountainous rivers were mixed offshore of southeastern Vietnam, as indicated by the strong influence of these river-loaded sediments in gravity core 18XB47 (112.480°E, 15.442°N, water depth 1895 m). During that time, the particles could not effectively settle due to sea-water upwelling in the cold eddy region, while sea-water sinking in the warm eddy region promoted particle settling because the particles in the WSCS were confined by mesoscale eddies offshore of southeastern Vietnam. In contrast, during the last deglacial period when the activity of the Vietnam eddy dipole was reinforced by the rising sea level and strengthening of the summer monsoon, the particles from the WSCS could not be easily transported to the location of core 18XB47 because the eastern Vietnam upwelling moved closer to the coastal area.