Silica Cycling and the Role of Diatoms in the North Pacific Subtropical Gyre

对大西洋硅循环的研究表明，副热带环流占全球海洋二氧化硅产量的13%，但来自北太平洋副热带环流（NPSG）的最新数据显示，二氧化硅产量要高得多，这意味着副热带环流的贡献增加。初步结果还表明，两个环流的季节性二氧化硅生产周期彼此相差数月。与马尾藻海的硅藻在春季定期开花以响应冬季对流翻转不同，永久分层阻止了NPSG的春季硅藻开花事件。每年的硅藻华确实在NPSG中发生，但令人不解的是，它们发生在夏季，这时分层最强，养分浓度处于季节性最低。这些神秘的夏季水华对NPSG的碳和氮输出有重要贡献，它们可能主导着年度硅循环。在这个项目中，来自加州大学圣巴巴拉分校的一名研究人员将研究Si限制强度和二氧化硅溶解的季节性变化如何调节NPSG中二氧化硅生产的年周期，并有助于其独特的季节性。他的假设是，夏季藻华期间的高净二氧化硅产量主要是由NPSG中存在的藻华硅藻物种非常有效的硅酸吸收系统驱动的，该系统使它们能够克服硅的限制并利用低浓度的硅酸。将与HOT计划合作进行时间序列速率测量，以确定ALOHA站的年度硅周期。该项目还将与夏威夷大学新成立的“微生物海洋学研究与教育中心”（CMORE）科技中心合作，研究夏季藻华。就更广泛的影响而言，拟议的项目将扩大我们对控制硅藻对开放海洋生态系统元素循环贡献的机制的理解。拟议的Si循环研究结合了ALOHA站正在进行的C、N和P循环研究，将首次有机会对在少营养环流中同时进行的所有四种元素的循环进行协调分析。该项目还将开发新的方法，通过二氧化硅产量实验来量化32Si。研究生和本科生都将接受培训，PI将与UCSB的海洋科学研究所（MSI）合作，通过MSI的“海洋到课堂”计划，开发与生物碳泵和硅藻在海洋生态系统中的重要性相关的K-12教育材料。

OCE-0648130Studies of the silicon cycle in the Atlantic Ocean have suggested that subtropical gyres account for 13% of global marine silica production, but more recent data from the North Pacific Subtropical Gyre (NPSG) show much higher rates of silica production that imply an increased contribution of subtropical gyres. Preliminary results also reveal that the seasonal silica production cycles of the two gyres are several months out of phase with each other. Unlike the Sargasso Sea where diatoms bloom regularly in spring in response to winter convective overturn, permanent stratification prevents spring diatom blooms events in the NPSG. Annual diatom blooms do occur in the NPSG, but enigmatically they occur during summer when stratification is strongest and nutrient concentrations are at their seasonal minimum. These enigmatic summer blooms contribute significantly to carbon and nitrogen export in the NPSG and they likely dominate the annual silicon cycle.In this project, a researcher from the University of California at Santa Barbara will investigate how seasonal changes in the intensity of Si limitation and silica dissolution regulate the annual cycle of silica production in the NPSG and contribute to its unique seasonality. His hypothesis is that high rates of net silica production during summer blooms are driven mainly by the extraordinarily efficient silicic acid uptake systems of bloom diatom species present in the NPSG that allow them to overcome Si limitation and exploit low concentrations of silicic acid. Time series of rate measurements will be made in collaboration with the HOT program to define the annual silicon cycle at station ALOHA. The project will also collaborate with the new "Center for Microbial Oceanography: Research and Education" (CMORE) Science and Technology Center at the University of Hawaii to study summer blooms.In terms of broader impacts, the proposed project will expand our understanding of the mechanisms controlling the contribution of diatoms to elemental cycling in open ocean ecosystems. The proposed research on Si cycling combined ongoing studies of C, N and P cycling at station ALOHA will allow, for the first time, an opportunity for a coordinated analysis the cycling of all four of these elements simultaneously in an oligotrophic gyre. The project will also develop new methods to quantify 32Si from silica production rate experiments. Both graduate students and undergraduate students will be trained and the PI will work with UCSB's Marine Science Institute (MSI) to develop K-12 educational materials related to the biological carbon pump and the importance of diatoms in marine ecosystems through MSI's "Oceans to Classroom" program.