夏季东海东北部营养盐的分布变化特征

Two cruises in July 2010 and July 2011 were conducted in the northeastern East China Sea (ECS) to elucidate distribution and variation of nutrients in this area, as well as their responses to the varying Changjiang (Yangtze) River freshwater discharge. The eastward expansion range of Changjiang Diluted Water (CDW, in salinity <31) at surface in July 2010 when monthly water discharge was much greater than normal year, was obviously larger than that in July 2011. However, the expansion range of surface seawater with high NO ₃ -N concentration (e.g., >15μmol/L) was much smaller in July 2010. Concentrations of NO ₃ -N, SiO ₃ -Si, PO ₄ -P at most stations were generally quite low due to surface phytoplankton uptake and water column stratification, and these low values were maintained to the temperature/salinity thermocline and subsurface chlorophyll maximum layer (at depths of 10-40m) where their concentration increased sharply and then showed constant values afterwards. The concentrations of NH ₄ -N at stations in July 2010 were commonly higher than those in July 2011, throughout the water columns and over the whole study area. Molecular ratios of SiO ₃ -Si/NO ₃ -N and PO ₄ -P/NO ₃ -N decreased along the Changjiang River transport pathway northeastwards from the Changjiang River freshwater and estuarine water to the northeastern ECS. The nutrient concentrations of NO ₃ -N, SiO ₃ -Si, and PO ₄ -P in the Kuroshio Subsurface Water and Kuroshio Intermediate Water were quite high, indicating that those water masses, together with CDW, were probably important contributors to the nutrients inventories of the northeastern ECS.