【作者】 宋洪军；

【导师】 王宗灵； 季如宝；

【作者基本信息】 中国海洋大学 ， 环境科学， 2010， 博士

【摘要】 浮游植物水华作为近海重要的生物过程,其动态变化对生态系统内的营养传递、生产力水平和各生源要素的循环等均有重要影响。随着气候变化对生态系统影响的研究的深入,浮游植物水华生物气候学研究已成为当前生物海洋学研究的热点。论文选择了缅因湾及其邻近海域为研究对象,通过SeaWiFS卫星观测资料和现场观测资料分析以及生态模型数值模拟,研究了缅因湾及其邻近海域浮游植物春季和秋季藻华的空间和年际变化,分析了控制藻华发生时间(以峰值发生时间表示)和藻华强度(以平均叶绿素浓度表示)的主要环境因子,并探讨了与气候变化有关的藻华动态变化可能产生的生态效应。卫星遥感资料分析结果发现,缅因湾及其邻近海域春季藻华发生时间在空间上存在较显著由东向西推移的分布特征,而秋季藻华则相反,呈由西向东推移的整体规律。春季和秋季藻华平均叶绿素浓度的空间分布规律较为一致,即东部的斯科舍陆架区叶绿素浓度较低,而西部的缅因湾区域叶绿素浓度较高。年际变化上,春季藻华发生早的年份,秋季藻华一般发生较晚,二者呈现显著的负相关性(r=-0.235,P<0.05)；但同一年份的春季和秋季藻华的平均叶绿素浓度间无显著相关性。春季藻华发生时间的年际变化与海表盐度的变化显著正相关(r=0.415,P<0.01),但秋季藻华发生时间与海表盐度和海表温度两因子存在显著负相关性(r=-0.28,P<0.05；r=-0.317,P<0.01)。这是由于：海表盐度低,意味着水体垂直结构相对稳定,促进层化作用的形成,这就导致春季藻华发生较早,而秋季藻华发生较晚；海表温度与秋季藻华发生时间之间的相关性,主要是由于低温低盐的表层流的年际变化导致海表温度与海表盐度间的正相关性所致。利用1-D生态模型成功模拟了缅因湾和斯科舍陆架区1984-2007期间的浮游植物水华和浮游生物生产力的年际和年代际变化。模拟结果发现,缅因湾和斯科舍陆架区春季和秋季藻华发生时间和藻华强度均存在显著的年际变化,藻华发生时间的年际变化幅度约为±2-3周,藻华强度的变化范围可高至～1 mg Chl m-3。较早的春季藻华和较晚的秋季藻华主要与盐度较低的表层水或0-50m层间较大的盐度差增加的水体稳定性有关。单因子实验结果表明,盐度是影响春季和秋季藻华动态(尤其是藻华发生时间)的主要环境因子；海表温度和海表风对水体垂直结构的影响不如盐度梯度显著,因而对藻华动态变化影响较弱；营养盐水平控制藻华强度,但对藻华发生时间的影响较弱。此外,模型模拟的初级生产力、中型浮游动物生产力和颗粒输出通量的年际变化幅度较小(标准差小于平均值的10%)。年初级生产力高值一般出现在春季藻华发生较早的年份(缅因湾：r=-0.205；斯科舍陆架：r=-0.51),但初级生产力与藻华发生时间(或水体稳定性)相关性不显著。春季藻华期间大粒径浮游植物占据绝对优势,而秋季藻华则以小粒径浮游植物为主；两季节藻华期间浮游动物生物量均主要由中型浮游动物贡献。缅因湾和斯科舍陆架区藻华发生时间的年际变化范围较大,但浮游生物生产力的年际变化幅度较小,由此可以侧面的得出该区域渔业资源的年际变化主要受藻华发生时间的控制,而不是受每年总的生产力水平的控制。更多还原

【Abstract】 As one of the most important biological processes in coastal oceans, the phytoplankton bloom dynamics can affect the coupling of pelagic food chains, thus can have important ramifications for trophic interactions, overall system productivities and biogeochemical processes. Phytoplankton phenology has been one of the research hot-spots in the field of biological oceanography to understand the impact of climate change on marine ecosystem. In this thesis, Gulf of Maine and its adjacent coastal waters were selected as the study area. Remotely sensed ocean color data (SeaWiFS) and field observations analysis and numerical modeling have been used to study the spatial and inter-annual variability of both spring and fall phytoplankton blooms in the Gulf of Maine (GoM) and its adjacent coastal waters. The main environmental factors controlling the bloom timing and magnitude (peak timing and mean chlorophyll concentration during blooms were selected as the indices) have been identified, and the ecological effects of the climate-change-related bloom dynamics were also discussed.The ocean color data reveal a general pattern of westward progression of spring phytoplankton bloom (SPB), and an eastward progression of fall phytoplankton bloom (FPB) from the Nova Scotian Shelf (NSS) to GoM perspective. The spatial pattern of mean chlorophyll concentration in spring is similar to that in fall, with a lower concentration in the NSS and higher in the GoM. Inter-annually, there is a weak but significant tendency for years with earlier (delayed) SPBs to be followed by delayed (earlier) FPBs (r=-0.235, P<0.05), but the mean chlorophyll concentrations during SPBs are not correlated with that during FPBs. The inter-annual variability of SPB timing is significantly correlated with the sea surface salinity (SSS, r=0.415, P <0.01), but the FPB timing is correlated with both SSS and sea surface temperature (SST) (r=-0.28, P<0.05; r=-0.317, P<0.01). Further analysis shows that low SSS means a relatively stable water column and promotes the formation of stratification, which causes an earlier SPB and a delayed FPB. The correlation between SST and FPB timing is contrary to the theoretic mechanism. In reality, high (low) SST anomalies are often associated with high (low) SSS anomalies in this region. This is mainly due to variations in the advection of cold, fresh waters flowing into the study region.A 1-D ecosystem model, driven by surface heat and wind forcing and relaxed toward observed salinity profiles, was applied to simulate the inter-annual and decadal-scale variability of the phytoplankton blooms and plankton production from 1984-2007 in the Nova Scotian Shelf (NSS) and Gulf of Maine region (GoM). The model captured the mean observed timing and magnitude of the spring phytoplankton bloom (SPB) and fall phytoplankton bloom (FPB) in both systems, as well as observed inter-annual variations in SPB peak timing. Model simulations for both the GoM and NSS exhibited marked inter-annual variability in SPB and FPB timing (±2-3 weeks) and magnitude (up to～1 mg Chl m-3). Earlier SPBs and delayed FPBs are linked to enhanced water column stability generated by less saline surface water or sharper salinity gradients over the top 50m of the water column. The process-oriented numerical modeling experiments suggest that 1) salinity is the main factor influencing the bloom timing and magnitude in the NSS-GoM region, especially for the timing of SPBs; 2) compared to buoyancy forcing induced by vertical salinity gradient, the impact of surface heating and surface wind stress on the blooms variability is much weaker; and 3) the nutrient level controls bloom magnitude, but only has minor effect on bloom timing. Moreover, the modeled variation in annual primary productivity, mesozooplankton productivity, and particle export flux was modest (<10% of the mean). Years with high primary production were weakly associated with early SPBs (GoM: r=-0.205; NSS:r=-0.51), but there was no significant relationship with water column stability. Large phytoplankton is dominant in SPB, while small phytoplankton is dominant in FPB. Mesozooplankton biomass is the main part of zooplankton biomass in both SPB and FPB. Inter-annual variations in fisheries production due to changes in annual productivity are thus likely secondary to profound shifts in fisheries recruitment and production that have been linked to variations in SPB and FPB timing.更多还原