文章利用4种不同的气候态风场Scatterometer Climatology of Ocean Winds(SCOW)、Climate Forecast System Reanalysis(CFSR)、the Interim ECMWF Re-Analysis(ERA-Interim)和NECP[the National Centers for Environmental Prediction(NCEP)/National Center for Atmospheric Research(NCAR)Reanalysis 1]分别驱动区域海洋环流模式(Regional Ocean Modeling System,ROMS)以模拟南海环流,从而比较分析南海上层环流模拟结果的差异及其与风应力场之间的动力联系。结果表明,4种风场均能模拟出南海海盆尺度环流的季节变化特征,但对南海局地环流特征的模拟存在差异。分析显示,局地显著的正风应力旋度是冬季吕宋冷涡产生的根本原因;夏季越南东部海域的上层环流偶极子在模拟试验结果中均显现,但其强度与局地风应力旋度大小有关。海峡通量的模拟结果显示,吕宋海峡水体通量受海峡风场差异影响较小;台湾海峡秋冬季水体通量则有较大差别,强东北季风不利于海峡北向水体输送。此外,台湾海峡冬季较强的北向水体输送有利于南海暖流的生成。研究结果对深入理解南海上层环流对大气强迫的响应有裨益,并且可为不同目的的南海环流数值模拟时的风场选择提供参考。
Nutrient limitation is known to inhibit growth and metabolism and to alter elemental stoichiometric ratios in phytoplankton. In this study, physiological changes in Thalassirosira weissflogii were measured under different dissolved inorganic phosphate (DIP) regimes in semi-continuous cultures to revisit the utility of the Redfield ratio for assessing nutrient limitation. The results showed that cell size increased with decreasing DIP availability. In the P-depleted treatment (f/2-P) the cell size was 1.48 times larger than that in the P-limited (f/100) treatment and 2.67 times larger than that in the P-saturated treatment (f/2 and f/10). The fucoxanthin to chlorophyll a ratio (Fuco/chl a) was relatively stable (about 0.3) in P-saturated cultures and was 10 times higher than that in P-limited and P-depleted cultures. During the experimental period, the photosynthetic efficiency index, ?F/Fm′, was relatively stable at ~0.50 in the P-saturated cultures, but quickly declined with decreasing DIP availability. Although cellular P content showed a significant difference between the P-saturated culture (1.6 pg/cell) and the P-limited culture (0.7 pg/cell), the N/P ratio in T. weissflogii did not show a trend with DIP availability and fluctuated slightly around 25. Our results suggest that cell division in T. weissflogii is not strictly size-gated but is probably regulated by a biochemical, and hence, an elemental stoichiometric ratio threshold, and that deviation of the cellular N/P ratio from the Redfield ratio is not a reliable indicator of algal nutrient stress.
