Si Cycling and Si Control of New Production and Organic Carbon Export in the Southern Ocean and the Sargasso Sea: A JGOFS Synthesis

最近在马尾藻海、赤道太平洋和南大洋等非常不同的系统中进行的几项研究表明，硅藻是地表水中大部分新生产和出口生产的原因。这些观察结果，结合硅藻对硅（Si）的绝对生长需求，表明溶解硅的可用性可能会调节大部分海洋的新生产和出口生产。因此，如果上层海洋的碳和氮循环模型的目标是预测海洋对自然和人为强迫的生物反应，就必须将硅对硅藻生产力和有机物输出的控制纳入其中。由于缺乏有关调节硅循环的因素的数据（例如硅的生产速率、硅的溶解速率和硅藻生产率的硅限制），这项任务目前在大多数海洋中是不可能完成的。pi将综合在美国和法国JGOFS项目中获得的几个大型数据集，并使用新开发的物理/生物地球化学模型，其中明确包括硅藻生产力的二氧化硅调节，从而首次基于数据确定控制海洋上层200-500 m Si循环的因素。他们将研究硅循环特征的变化如何影响硅藻从地表水中输出碳和氮的能力。通过数据综合和数值模拟的结合，pi将：1)确定那些是上层海洋硅循环特征的最强决定因素的过程，2)评估硅循环的差异如何影响硅藻促进新生产和出口生产的能力。该结果将为下一代海洋碳循环的全球生物地球化学模型奠定基础，该模型必须明确纳入硅对硅藻生产力受硅限制的系统中碳和氮输出的调节。

Several recent studies in very different systems, such as the Sargasso Sea, Equatorial Pacific and Southern Ocean, have shown that diatoms are responsible for much of the new and export production in surface waters. Those observations, combined with the diatoms' absolute growth requirement for silica (Si), suggest that the availability of dissolved SI may regulate new and export production in much of the sea. Models of carbon and nitrogen cycling in the upper ocean must therefore incorporate Si control of diatom prodctivity and organic-matter export if their goal is to predict the biological response of the oceans to natural and anthropogenic forcing. That task is currently impossible for most of the ocean due to the scarcity of data regarding factors regulating Si cycling (e.g. Si production rates, Si dissolution rates and Si limitation of diatom productivity).The PIs will synthesize several large data sets obtained during the U.S. and French JGOFS programs and use a newly developed physical/biogeochemical model, which explicitly inclues silica regulation of diatom productivity, to make the first data-based determination of the factors controlling the cycling of Si in the upper 200-500 m of the ocean. They will investigate how changes in the character of the Si cycle affect the ability of diatoms to contribute to carbon and nitrogen export from surface waters. Through a combination of data synthesis and numerical modeling the PIs will: 1) identify those processes that are the strongest determinants of the character of the Si cycle in the upper ocean, and2) assess how the resulting differences in the Si cycle affect the ability of diatoms to contribute to new and export production.The results will establish a foundation for the next generation of global biogeochemical models of marine carbon cycling, which must explicitly incorporate Si regualtion of carbon and nitrogen export in systems where diatom productivity is limited by Si.