Collaborative Research: Biogeochemical and Physical Conditioning of Sub-Antarctic Mode Water in the Southern Ocean

南印度洋冰冷的地表水下沉到500米左右，在黑暗中行进数千英里，大约40年后在其他海洋盆地的赤道附近重新浮出水面。这个主要的水团被称为亚南极模式水（SAMW）。当它变暖并上升到阳光照射的亚热带和热带沃茨时，它所含的营养物质估计为那里75%的微观植物生长提供了燃料。在它下沉之前，SAMW的化学性质被两种常见浮游植物的生长和不同的生理学改变;硅藻的外壳由二氧化硅制成，颗石藻的外壳由碳酸盐制成。当地的物理动力学影响这两类浮游植物生长的位置和速度。因此，不同的营养和微量化学指纹建立在SAMW形成的点。这个项目是一个非常详细的领域和建模工作，将记录和量化显着的，相互关联的过程，化学连接两个重要的海洋生态系统相隔半个世界。领导该项目的科学家将研究SAMW生物和化学条件的复杂性，从而提供有关生物碳泵的大规模海洋控制的关键数据，该生物碳泵在千年的时间尺度内将大气中的二氧化碳清除到深海。 该项目的科学影响将来自重要的同行评审出版物和改进的预测模型。社会效益将来自对一系列学者的培训，包括高中生、本科生和研究生，以及技术和博士后参与者。一名高中教师和科学传播专家将与该项目一起出海，并通过社交媒体和预定的网络互动与海岸上的学生分享船上的经验。为了研究SAMW的形成和俯冲如何控制全球沃茨的生产力以及北部，1月的两次印度洋东南部考察将确定，跟踪和研究独特的中尺度漩涡，作为离散的水包裹，支持丰富的颗石藻或硅藻种群及其相关的微生物群落。将用拉格朗日Argo漂移器跟踪涡旋，并将在数月的时间尺度上观察SAMW的化学条件（即Si，N，P，Fe和碳酸盐化学）。该项目将利用从这些涡流和相关样带考察中获得的生态过程与营养物、微量金属和碳酸盐化学之间的反馈数据，实现三个主要目标：（1）确定SAMW颗石藻和硅藻调节碳酸盐化学以及营养物和痕量金属浓度的速率，以及用传统方法和下一代序列DNA/RNA分析评估研究区域的分类和生理多样性，（2）探索铁对生长的限制，硅酸盐和/或硝酸盐在控制藻类组合和遗传多样性，（3）联合收割机结合这些发现与Ekman和涡驱动的SAMW俯冲检查流域尺度上的地球化学影响，使用观测和全球数值模型。将利用南纬30至60度的纬向调查，说明随着SAMW俯冲并向北移动，各种浮游生物群体的碳酸盐化学、营养物分布、生产力、遗传学和生物量的大规模变化。

Cold surface water in the southern Indian Ocean sinks to about 500 meters and travels in the dark for thousands of miles before it resurfaces some 40 years later near the equator in the other ocean basins. This major water mass is named the Sub-Antarctic Mode Water (SAMW). Nutrients it contains when it warms and rises into the sunlit subtropical and tropical waters are estimated to fuel up to 75% of the microscopic plant growth there. Before it sinks, the chemical properties of the SAMW are modified by the growth and distinct physiology of two common phytoplankton; diatoms with shells made of silica, and coccolithophores with carbonate shells. Local physical dynamics influence where and how fast these two phytoplankton classes grow. Consequently, differing nutrient and trace chemical fingerprints are established at the point of SAMW formation. This project is an exceptionally detailed field and modeling effort that will document and quantify the remarkable, interconnected processes that chemically connect two important oceanic ecosystems half a world apart. The scientists leading the project will study the complexity of the biological and chemical conditioning of the SAMW and thus provide critical data about the large-scale oceanic controls of the biological carbon pump that removes atmospheric carbon dioxide to the deep ocean over millennial timescales. Scientific impact from this project will stem from significant peer-reviewed publications and improved predictive models. Societal benefits will develop from training of a range of scholars, including high school, undergraduate, and graduate students, as well as technical and post-doctoral participants. A high school teacher and science communication specialist will go to sea with the project and share experiences from the ship with students on shore via social media and scheduled web interactions. To examine how SAMW formation and subduction controls the productivity of global waters well to the north, two January expeditions to the SE Indian Ocean will identify, track, and study the unique mesoscale eddies that serve as discrete water parcels supporting rich populations of either coccolithophores or diatoms plus their associated microbial communities. The eddies will be tracked with Lagrangian Argo drifters and observations will be made of exactly how SAMW is chemically conditioned (i.e. Si, N, P, Fe, and carbonate chemistry) over time scales of months. Using data obtained on the feedback between ecological processes and nutrient, trace metal, and carbonate chemistry in these eddies and on related transect cruises, the project will have three main goals: (1) determine the rates at which SAMW coccolithophores and diatoms condition the carbonate chemistry plus nutrient and trace metal concentrations, as well as assess taxonomic and physiological diversity in the study area with traditional methods plus next-generation sequence DNA/RNA profiling, (2) explore growth limitations by iron, silicate and/or nitrate in controlling algal assemblages and genetic diversity, and (3) combine these findings with the Ekman- and eddy-driven subduction of SAMW to examine biogeochemical impact on a basin scale, using both observations and global numerical models. A meridional survey from 30 to 60 degrees south latitude will be used to characterize the larger-scale variability of carbonate chemistry, nutrient distributions, productivity, genetics and biomass of various plankton groups as SAMW is subducted and proceeds northward.