Collaborative Research: Biogeochemical and physical conditioning of Sub-Antarctic Mode Water in the Southern Ocean

合作研究：南大洋亚南极模式水的生物地球化学和物理调节

• 批准号: 1735846
• 负责人: Matthew Long
• 金额: $ 40.15万
• 依托单位: University Corporation For Atmospheric Res
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-08-01 至 2023-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1735846&HistoricalAwards=false
• 关键词: Collaborative; Research; Biogeochemical; physical; conditioning

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.

南印度洋寒冷的表层水下沉至约 500 米，在黑暗中移动数千英里，约 40 年后在其他洋盆的赤道附近重新出现。这个主要水团被命名为亚南极模式水（SAMW）。据估计，当它变暖并上升到阳光照射的亚热带和热带水域时，它所含有的营养物质可以为那里高达 75% 的微观植物生长提供燃料。在沉没之前，SAMW 的化学性质会因两种常见浮游植物的生长和独特的生理机能而发生改变；壳由二氧化硅制成的硅藻，以及具有碳酸盐壳的颗石藻。当地的物理动态影响这两个浮游植物的生长地点和速度。因此，在 SAMW 形成时建立了不同的营养物和微量化学指纹。该项目是一项极其详细的现场和建模工作，将记录和量化显着的、相互关联的过程，这些过程以化学方式连接两个相距半个地球的重要海洋生态系统。领导该项目的科学家将研究 SAMW 生物和化学调节的复杂性，从而提供有关生物碳泵大规模海洋控制的关键数据，该生物碳泵在千年时间尺度上将大气中的二氧化碳清除到深海。 该项目的科学影响将源于重要的同行评审出版物和改进的预测模型。对一系列学者（包括高中生、本科生和研究生以及技术人员和博士后参与者）的培训将产生社会效益。一名高中教师和科学传播专家将带着该项目出海，并通过社交媒体和预定的网络互动与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水域北部的生产力，一月两次对印度洋东南部的探险将识别、跟踪和研究独特的中尺度涡流，这些涡流作为离散的水块支持丰富的颗石藻或硅藻及其相关微生物群落。将用拉格朗日 Argo 漂流器跟踪涡流，并在数月的时间尺度内准确观察 SAMW 的化学条件（即 Si、N、P、Fe 和碳酸盐化学）。利用这些涡流和相关横断面巡航中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，该项目将实现三个主要目标：(1) 确定 SAMW 颗石藻和硅藻调节碳酸盐的速率化学加上营养物和痕量金属浓度，以及使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、硅酸盐和/或硝酸盐在控制藻类组合和遗传多样性方面的作用，(3) 将这些发现与 SAMW 的埃克曼和涡驱动俯冲相结合，利用观测和全球数值模型来研究生物地球化学对盆地规模的影响。南纬 30 至 60 度的经向调查将用于表征随着 SAMW 俯冲并向北前进，碳酸盐化学、养分分布、生产力、遗传和各种浮游生物群的生物量的更大规模变化。

项目成果

Southern Ocean Calcification Controls the Global Distribution of Alkalinity

南大洋钙化控制着全球碱度分布

• DOI: 10.1029/2020gb006727
• 发表时间: 2020-12
• 期刊: Global Biogeochemical Cycles
• 影响因子: 5.2
• 作者: Krumhardt, K. M.;Long, M. C.;Lindsay, K.;Levy, M. N.
• 通讯作者: Levy, M. N.