The balance between biogenic silica production and its dissolution in the surface ocean

利用硅稳定同位素示踪剂同时测定了北太平洋亚北极西部表层生物源二氧化硅（硅藻）的生成和溶解速率，探讨了生物源二氧化硅的生成和溶解之间的平衡。建立了高分辨率电感耦合等离子体质谱法测定硅同位素比值的新方法。通过对背景Si峰进行校正，获得了与热电离质谱法相似的分析精度和灵敏度。本方法用于测定北太平洋亚北极西部的大潮地表水中生物源二氧化硅的生成和溶解速率。生物源二氧化硅的柱积分溶解速率超过了绿光层内硅藻的产酸速率，说明颗粒状生物源二氧化硅溶解的活性硅酸被表面混合层的硅藻利用。在实验室中还进行了从亚北极北太平洋西部获得的硅藻体的批量溶解实验，以研究优势硅藻群之间溶解动力学的差异。对溶出速率的观察表明，不同硅藻种类和不同硅藻体位置的硅藻体的溶解度不同。硅藻囊体在溶解过程中的形态变化似乎是影响囊体表面积/体积比进而影响其溶解速率的重要因素。根据这些结果，硅藻产生的大部分生物源二氧化硅被估计在海洋表面回收。然而，深层硅藻体的存在意味着硅藻的快速下沉应该被认为是海洋硅循环的另一个重要过程。

Production and dissolution rates of biogenic silica (diatom frustules) in the surface waters were determined simultaneously using silicon stable isotope tracer to investigate balance between biogenic silica production and its dissolution in the surface waters of the western subarctic North Pacific Ocean. New analytical method for the determination of silicon isotope ratios was developed using a high-resolution Inductively Coupled Plasma-Mass Spectrometry. By correcting background Si peaks, analytical precision and sensitivity similar to those of the thermal ionization mass spectrometry were obtained. This method was used for the determination of the rates of biogenic silica production and dissolution in the Oyashio surface water of the western subarctic North Pacific. Column integrated dissolution rate of biogenic silica exceeded production rate by diatoms within the euphotic layer, suggesting active silicic acid dissolved from particulate biogenic silica and its utilization by diatoms in the surface mixed layer. Batch dissolution experiments of diatom frustules obtained from the western subarctic North Pacific were also conducted in the laboratory to investigate differences in dissolution kinetics between the dominant diatom groups. Observed dissolution rates indicated that degree of solubility of diatom frustules is different between the diatom species as well as the site of the frustules. Morphological changes of diatom frustules during the dissolution process seem to be an important factor affecting surface/volume ratio of the frustules and consequently its dissolution rate. From these results, most of the biogenic silica produced by diatoms was estimated to be recycling in the surface ocean. However, existence of diatom frustules in the deep layers implies that rapid sinking of diatom containing feral pellets should be considered as another important process in the marine silicon cycles.