The research was supported in part by National Science Foundation of China (No. 40706060, 40606043);Dragon Project (ID 5292);High-tech Research Development Program of China (No. 2006AA09A310);State Oceanic Administration (SOA) of China (No. 200705027, 2008401, and 908-01-ST11);First Institute of Oceanography (No. 2007B05)