影响浮游植物水华物理因子的研究

The “Sverdrup critical-depth model” for the physical driver of the onset of the spring phytoplankton bloom in the North Atlantic considers that the spring bloom begins when the mixed layer become shallower than a critical depth. Satellite and in situ measurements of chlorophyll are used to show that the critical-depth model is indeed flawed. Several papers have appeared recently that suggest a different relationship between the mixed layer depth and spring bloom timing. Nonetheless, the key process, common to all hypotheses of bloom, is the stabilization of the water column that can influence balance among light, nutrients, and phytoplankton losing by grazing and vertical advection. In Yellow Sea and East China Sea, phytoplankton bloom is an important process to influence primary production. To learn the main physical processes that impact phytoplankton bloom the timing and magnitude of phytoplankton bloom fromt the physical side, will help us better understand the blooms response to climate change, so as to provide an indication of the response of ecosystem to external disturbance. This project will start from the “Sverdrup critical-depth model”, focus on the balance among the factors limiting phytoplankton bloom, diagnosticate main physical processes impact the phytoplankton growth, and find the answer that reside in the physical proxy for bloom initiation: what physical indicators best predict bloom timing in Yellow Sea and East China Sea?

Sverdrup临界深度理论被用于解释物理作用对浮游植物水华的驱动，该理论以混合层厚度为指针，强调混合层浅于临界深度是水华发生的条件。近来，卫星和实测叶绿素均显示该理论存在缺陷，几种假说相继被提出，但共识就是浮游植物水华过程是受水体稳定性所影响的光照、营养盐、以及浮游植物消耗间的动态平衡过程。浮游植物水华是我国黄东海初级生产力的重要过程。从物理因素出发，了解影响水体稳定性的物理过程如何影响浮游植物水华的发生时间及强弱，能帮助我们更好得了解浮游植物水华对气候变化的响应，从而为生态系统对外界干扰的响应提供指示作用。本项目拟以Sverdrup临界深度理论为起点，着眼于浮游植物水华过程中各种限制因子的平衡关系，通过对浮游植物生长消耗收支的诊断，判断影响浮游植物浓度变化的主要物理过程，找到物理指标来指示黄东海浮游植物周期性水华发生的条件。

本项目研究了不同物理背景水体中影响浮游植物水华的主要过程。主要针对研究三个代表区域：1.陆架区；2.河口区；3.深海区。针对这三个代表性区域利用长时间序列卫星遥感资料，结合实际观测及数值模拟等多种手段，研究了浮游植物水华的季节特征及年际变化，以及物理影响机制。研究发现，在陆架区域，浮游植物水华主要受季节性层化所影响的真光层和营养跃层的影响，叶绿素的年际变化和影响水体稳定度的混合有较好的相关关系；河口区域，河流冲淡水带来的营养盐效应、层化效应和浊度效应同时影响着浮游植物动力学；热带大洋区域（季风性气候），独特的季风季节性反转所带来的动力学场转变是解释该地区生物学反应机理的基本框架，表针物理场变化的SST能很好的预测特定区域叶绿素的年际异常变化。