夏季东海东北部营养盐的分布变化特征

DYNAMICS OF NUTRIENTS IN THE NORTHEASTERN EAST CHINA SEA IN SUMMER

分别于2010年7月和2011年7月,在沿长江冲淡水扩散方向的东海东北部海域进行了典型站点CTD参数的测定和营养盐样品的采集,旨在了解长江不同径流量条件下该区域对长江冲淡水的响应过程及其中营养盐的分布变化特点。结果显示:在长江径流量较大的2010年7月,长江冲淡水(盐度<31)在研究区域表层自西向东的扩散范围明显大于径流量较小的2011年7月。而含有高浓度NO_3-N(如>15μmol/L)海水扩散范围在两个航次的变化却相反。由于海水层化以及表层浮游植物的吸收,各站表层NO_3-N、SiO_3-Si、PO_4-P等浓度一般较低,温盐跃层和次表层叶绿素最大值层以下其浓度升高并逐渐趋于稳定。2010年7月NH_4-N在研究区域各站贯穿整个深度的浓度明显大于2011年7月。与长江冲淡水和长江口相比,东海东北部水体表层SiO_3-Si/NO_3-N和PO_4-P/NO_3-N等营养盐摩尔比值明显降低。黑潮次表层水和黑潮中层水等水团含有较高的营养盐浓度(NO_3-N,SiO_3-Si及PO_4-P),与长江冲淡水相比,可能构成了东海东北部另一个重要的营养盐来源。

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 NO3-N concentration（e.g., 15μmol/L） was much smaller in July 2010. Concentrations of NO3-N, SiO3-Si, PO4-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 NH4-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 SiO3-Si/NO3-N and PO4-P/NO3-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 NO3-N, SiO3-Si, and PO4-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.