Collaborative Research: Transparent exopolymer and phytoplankton vertical migration as sources for preformed nitrate anomalies in the subtropical N. Pacific Ocean

合作研究：透明外聚合物和浮游植物垂直迁移作为北太平洋副热带硝酸盐异常的来源

• 批准号: 1923687
• 负责人: Robert Letscher
• 金额: $ 49.13万
• 依托单位: University of New Hampshire
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-09-15 至 2023-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1923687&HistoricalAwards=false
• 关键词: Collaborative; Research; Transparent; exopolymer; phytoplankton

The ocean is usually layered, with light and oxygen in the warmer surface and nutrients at the cooler depths. Biological and physical processes determine this distribution. Marine algae grow in the well-lit upper layers but need nutrients to grow. However, in the subtropics, the ocean's largest biome, the relationship between oxygen and nitrate (a key nutrient required for photosynthesis) is different from expected. Two processes could explain this. Nutrients could be transported upward by migrating giant single-celled algae (phytoplankton). Another explanation is that the production of an organic material called transparent exopolymer (TEP) takes up carbon without using nutrients or exporting carbon to depth, as would occur in photosynthesis. While both processes could be occurring, the relative contribution of migrating phytoplankton versus TEP would tell us whether the observed oxygen pattern in the upper ocean results from photosynthesis. This problem relates to the general question of where and how nutrients reach the well-lit surface waters to enable photosynthesis. These hypotheses are tested at the Hawaii Ocean Time-Series using in-situ camera systems to image and quantify the giant phytoplankton and direct water samples to measure the vertical distribution of TEP. The data are entered into numerical models to calculate the nitrate to oxygen relationships and add information about the carbon cycle. In addition to training of undergraduate students and a postdoctoral fellow, the cruises provide an opportunity to prepare a cadre of communication fellows who will develop materials and media, including videos, to translate this highly complex scientific concepts for the general public. The social media campaign #SaveOur70 provides a valuable venue to reach and engage with the public. Quantifying nutrient transport, utilization, and its relationship to carbon drawdown in the subtropical gyres is fundamental to our understanding of the carbon cycle. Geochemical distributions from the well-characterized time-series sites near Hawaii and Bermuda have long-served to identify previously unknown links between subsurface nitrate fields, summertime dissolved inorganic carbon (DIC) drawdown, and net community production in the absence of known nutrient sources. Two recently suggested processes rise to prominence to explain anomalies in subtropical distributions of dissolved carbon, oxygen, and nitrate in the upper ocean: 1) nutrient transport by giant phytoplankton that vertically migrate, and 2) cycling of low N organic matter between the mixed layer and the upper nutricline as transparent exopolymer particles (TEP) or gel-like organic material (GLOM). While linked at a fundamental level (phytoplankton are TEP producers), the outcome of the two processes are distinct. Vertical migration of phytoplankton is an active transport of nitrate, acquired in the nutricline, to the surface. There is an implication of subsequent reduction, photosynthetic carbon fixation and eventual export. TEP/GLOM cycling results in apparent DIC drawdown but there is no net export out of the surface layer and no requirement for additional nutrient sources in the mixed layer. This project collects the data to quantify the contribution of these two processes to the observed anomalies in nitrate to oxygen distribution at the time-series station at Hawaii (HOT). This is accomplished by enumerating the vertically migrating, aflagellate flora (VMF), implementing a 1-D model on vertical migration, and coupling these results with a 1-D model of the contribution of N-poor carbon cycling patterns in the upper water column derived from TEP and carbohydrate measurements. The combined VMF and TEP/GLOM 1-D models are used to model the dissolved oxygen, carbon, and nitrate budgets at HOT allowing for attribution of both hypothesized processes to the observed preformed nitrate distribution, its formation rate, and summertime inorganic carbon drawdown.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

海洋通常是分层的，在较温暖的表面上有光和氧气，在凉爽的深度处有养分。生物学和物理过程决定了这一分布。海洋藻类在光线充足的上层生长，但需要营养才能生长。但是，在亚热带中，海洋最大的生物群落，氧与硝酸盐之间的关系（光合作用所需的关键营养素）与预期不同。两个过程可以解释这一点。营养物质可以通过迁移巨型单细胞藻类（Phytoplankton）向上运输。另一个解释是，一种称为透明外聚合物（TEP）的有机材料的生产不使用营养或将碳导入深度，就像光合作用中所发生的那样。尽管这两个过程都可能发生，但迁移的浮游植物与TEP的相对贡献会告诉我们上海上观察到的氧气模式是否来自光合作用。 这个问题涉及一个普遍的问题，即养分在何处以及如何到达光线充足的地表水以实现光合作用。 这些假设使用原位摄像头系统在夏威夷海洋时间序列进行了测试，以形象和量化巨型浮游植物和直接水样品，以测量TEP的垂直分布。 将数据输入数值模型，以计算硝酸盐到氧关系并添加有关碳循环的信息。 除了对本科生和博士后研究员的培训外，Cruises还提供了一个机会，可以准备一群交流研究员，他们将开发材料和媒体，包括视频，以向公众翻译这一高度复杂的科学概念。社交媒体活动＃Saveour70提供了一个有价值的场所，可以与公众互动并与之互动。 量化营养转运，利用及其与亚热带回旋中碳缩减的关系是我们对碳循环的理解的基础。 来自夏威夷和百慕大附近特征良好的时间序列地点的地球化学分布已长期以来确定以前未知的硝酸盐领域之间未知的联系，夏季溶解的无机碳（DIC）降低和净社区生产与缺乏已知营养来源的情况下。 最近有两个提出的过程引起了人们的关注，以解释上海中溶解的碳，氧和硝酸盐的亚热带分布的异常情况：1）垂直迁移的巨型植物浮游生物的营养运输，以及2）在混合层和近乎杂质的杂物（Guntricline expopolles expopolles exopolles exopolles exopolys expopolymery（tep expopoly）之间（tep）或旋转的循环（tep）循环。 虽然在基本层面上链接（浮游植物是TEP生产者），但这两个过程的结果是不同的。 浮游植物的垂直迁移是硝酸盐的主动转运，在果皮中获得的硝酸盐迁移到表面。随后的减少，光合碳固定和最终导出的意义。 TEP/GLOM循环导致明显的DIC下降，但没有净出口的表面层，并且不需要混合层中其他营养源。 该项目收集数据，以量化这两个过程对硝酸盐在夏威夷时间序列站（HOT）的硝酸盐中观察到的异常的贡献。 这是通过列举垂直迁移的，脂肪植物（VMF），在垂直迁移的1-D模型中实现的，并将这些结果与来自TEP和碳水化合物测量的上水柱中的N型碳循环模式的1-D模型结合起来来实现。合并的VMF和TEP/GLOM 1-D模型用于建模溶解的氧气，碳和硝酸盐预算，使其在HOT中允许将这两个假设的过程归因于观察到的硝酸盐分布，形成率，其形成率，其夏季Intermime Interit Merit通过评估NSF的构建范围。和更广泛的影响审查标准。