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，在温暖的表面有光和氧气，在较冷的深处有营养物质。生物和物理过程决定了这种分布。海藻生长在光线充足的上层，但需要营养来生长。然而，在海洋最大的生物群落亚热带，氧气和硝酸盐（光合作用所需的关键营养素）之间的关系与预期不同。两个过程可以解释这一点。营养物质可以通过迁移的巨型单细胞藻类（浮游植物）向上输送。另一种解释是，一种被称为透明外聚合物（TEP）的有机材料的产生吸收了碳，而不像光合作用那样使用营养物质或将碳输出到深处。虽然这两个过程都可能发生，但浮游植物迁移与TEP的相对贡献将告诉我们，在海洋上层观察到的氧气模式是否是光合作用的结果。 这个问题涉及到营养物质在哪里以及如何到达光照良好的表面沃茨以实现光合作用的一般问题。 这些假设进行了测试，在夏威夷海洋时间序列使用原位相机系统的图像和量化的巨大的浮游植物和直接水样测量TEP的垂直分布。 这些数据被输入到数值模型中，以计算硝酸盐与氧气的关系，并添加有关碳循环的信息。 除了培训本科生和一名博士后研究员外，这次航行还提供了一个机会，培养一批传播研究员，他们将开发材料和媒体，包括视频，为公众解释这一高度复杂的科学概念。社交媒体活动#SaveOur70提供了一个与公众接触和参与的宝贵场所。 量化营养物质的输送、利用及其与亚热带环流中碳排放的关系是我们理解碳循环的基础。 地球化学分布从夏威夷和百慕大群岛附近的特征良好的时间序列站点长期以来一直服务于确定以前未知的地下硝酸盐田之间的联系，夏季溶解无机碳（DIC）下降，在没有已知的营养源和净社区生产。 最近提出的两个过程上升到显着的解释溶解碳，氧，硝酸盐在上层海洋亚热带分布的异常：1）营养盐运输的巨型浮游植物垂直迁移，2）低N有机物质的循环之间的混合层和上层营养层透明的外聚合物颗粒（TEP）或凝胶状有机物质（GLAM）。 虽然在基本层面上相互关联（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将营养层中获得的硝酸盐主动输送到表面。这意味着随后的减少、光合作用固碳和最终的输出。 TEP/GLAM循环导致明显的DIC下降，但没有净输出的表层和不需要额外的营养源的混合层。 该项目收集的数据，以量化这两个过程的贡献，所观察到的异常硝酸盐氧分布在时间序列站在夏威夷（HOT）。 这是通过列举垂直迁移，aflagellate植物群（VMF），实施1-D模型的垂直迁移，并耦合这些结果与1-D模型的贡献氮贫碳循环模式在上层水柱来自TEP和碳水化合物测量。组合的VMF和TEP/GLAM 1-D模型用于模拟HOT下的溶解氧、碳和硝酸盐预算，允许将两个假设过程归因于观察到的预先形成的硝酸盐分布、其形成速率，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查进行评估，被认为值得支持的搜索.