Observational research for iron, biological productivity, and carbon cycle in the subarctic northwestern Pacific

2003 - 2006年，利用高时空分辨率的方法，对亚北极西北太平洋海域铁的二维分布进行了研究。观测到的铁的季节和年际变化提供了以下信息：1）Oyashio混合层中溶解铁（DFe）月平均浓度与硝酸盐浓度的变化趋势一致，其最大值出现在Kosa季节之前。DFe与硝酸盐的比值全年基本恒定（ΔDFe/ΔN=27×10^<-6>[mol/mol]），与北太平洋中层水（NPIW）的比值相似。根据这些观测结果和一个简单的模式计算，得出的结论是，在Oyashio混合层的Dfe的季节变化主要是由春夏生物消耗和冬季循环NPIW。来自灰尘沉积的铁输入对混合层铁循环的影响很小，尽管局部铁沉积有时可能会产生小规模的高铁斑块。2]在水华终止期在Oyashio混合层观察到的DFe数据中有一半以上显示出大致恒定的0.25 nM值，这意味着水华形成硅藻在低于该铁水平时会产生显著的铁限制。在春季，铁比硝酸盐更快地达到这个下限，在春季水华结束时形成铁限制的生态系统条件。然而，在夏季，混合层硝酸盐的最终耗尽发生在7月比DFe，形成硝酸盐限制的生态系统在夏季Oyashio域。

2-D iron distribution in the subarctic northwestern Pacific was investigated repeatedly from 2003 to 2006 with high spacio-temporal resolution equally to major nutrients. Seasonal and interannual variations of iron observed in the Oyashio domain brought us the following information :1] Monthly-mean concentration of dissolved iron (DFe) in the Oyashio mixed layer varies in parallel with nitrate, with its maximum anteceding the Kosa season. Ratio of DFe to the nitrate is fairly constant throughout the year (ΔDFe/ΔN=27×10^<-6>[mol/mol]), and this ratio resembles those of North Pacific intermediate water (NPIW). Based on these observation results and a simple model calculation, it is concluded that the seasonal variation of Dfe in the Oyashio mixed layer is mainly governed by spring-summer biological consumption and winter recirculation from the NPIW. Iron input from the dust deposition is implied to have small effect to the mixed-layer iron cycle, although small-scale high iron patch might sometimes be generated by local iron deposition.2] More than half of the DFe data observed in Oyashio mixed layer at the bloom-termination period shows roughly constant value of 0.25 nM, implying that the bloom-forming diatoms incur significant iron limitation below this iron level. In spring, iron reaches this lower-limit faster than nitrate, forming iron-limited ecosystem conditions at the end of spring bloom. In summer, however, the ultimate depletion of mixed layer nitrate occurs faster than that of DFe at July, forming nitrate-limited ecosystem in the summer Oyashio domain.