The Particle Dynamics In The Twilight Zone In Northern South China Sea

The aggregation, disagregation, remineralization and export rates of POC in the twilight zone is one of the weakness items of the ocean carbon cycling study. Stepped-up research in the twilight zone is helpful for understanding the role of biological pump in modulating CO2 level in the atmosphere. More and more attention has been concentrated on the dynamics of particles in the twilight zone in recent years.Samples for the analysis of size-fractionated 228Th, 234Th and dissolved 228Th, 234Th, 228Ra were collected at 9-11 vertical depth intervals at station A1 in the northern South China Sea in February and July 2004 with large volume in-situ pump. Small-volume seawater samples (4-10 L) for the analysis of total and particulate 234Th were collected at the same depth by using Go-Flo bottles. Then each sample were measured with peculiar analysis technique on board and in land-based laboratory. Also derived were profiles of nutrients (NO3- +NO2-, PO43-), dissolved oxygen (DO) and particulate organic carbon (POC).The purpose of this study is to evaluate the particle cycling and export flux of POC in the euphotic and twilight zone in the northern South China Sea. Rate constants of Th and particle cycling were derived by using a reversible particle and Th cycling steady-state model while transport and diffusion terms were neglected. POC export...