Monthly Variation of Pigment Concentrations and Seasonal Winds in China's Marginal Seas

Abstract

China's marginal seas extend from temperate, subtropical to tropical zones, which encounter different monsoons. This study investigates the monthly variation of phytoplankton pigment concentrations (PC) from 1978 to 1986, and analyzes seasonal winds with sea surface temperatures (SST) among the Bohai Sea, the Yellow Sea, the East China Sea and the northern South China Sea. Nimbus satellite Coastal Zone Color Scanner (CZCS)-derived PC images were averaged into monthly fields for the entire area; we then emphasize the period of one year from November 1979 to October 1980, when CZCS data availability was relatively good. Monthly variability of PC has been compared among three regions (the outlets of the Yellow River, the Yangtze River and the Pearl River). The results revealed well-defined seasonality of PC, wind and SST from north to south in China's marginal seas. In the northern area (Bohai Sea and Yellow Sea), variability in SST (0–28 °C) and PC (0.5–3.5 mg m−3) was high with two peaks of PC appeared in spring–summer and in fall–winter in each year. In the East China Sea, two peaks of PC (1.2 mg m−3 in March and 1.3 mg m−3 in November) were in evidence, where SST variations were ranged 7–28 °C in one year. However, in the southern area (northern South China Sea), variation in SST (15–29 °C) and PC (0.1–0.4 mg m−3) was relatively low; the monthly variation of PC was not so high compared with north area. OCTS derived ocean color data obtained from April 1997 conformed the spatial pattern of Chl-a and colored dissolved organic matter (CDOM), and showed high CDOM and total suspended material (TSS) in the coast waters in the north part of China's marginal seas. Seasonal variation of PC may be related to the reversed monsoon; and spatial variation of PC may be influenced by river discharge, upwelling and coastal currents. High PC areas match good fishing grounds in terms of season and location in the study waters.