Collaborative Research: Contribution of allochthonous dissolved organic nitrogen to biological nitrogen demand in the subtropical North Pacific

合作研究：北太平洋副热带地区外来溶解有机氮对生物氮需求的贡献

• 批准号: 2343222
• 负责人: Robert Letscher
• 金额: $ 39.9万
• 依托单位: University of New Hampshire
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2024
• 资助国家: 美国
• 起止时间: 2024-07-01 至 2027-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2343222&HistoricalAwards=false
• 关键词: Collaborative; Research; Contribution; allochthonous; dissolved

Vast stretches of the ocean, covering almost 60% of its surface, are ‘deserts' where life struggles to survive due to nutrient scarcity. Located in the central gyres of the subtropical ocean, these regions are too remote to receive significant nutrient inputs from land or from deeper waters by vertical mixing. The low supply of nutrients should result in reduced levels of photosynthesis and less complex food webs. However, observations instead indicate that life grows at rates similar to regions which receive higher nutrient supplies. Our project seeks to determine what the missing sources of nutrients are that help sustain these ecosystems. This work will focus on nitrogen bound within dissolved organic molecules that are produced in nutrient-rich regions, including coastal California, and then transported laterally to the ‘ocean desert’ of the subtropical North Pacific Ocean. A one-month research expedition will leave from San Diego, CA and end in Honolulu, HI USA to study the production, accumulation, chemical composition, and utilization of dissolved organic nitrogen (DON) and link it to photosynthesis occurring across the North Pacific. The new knowledge gained about the role of DON in satisfying the nutrient requirements of the subtropical North Pacific will be used to construct computer models that gauge the global importance of this nutrient source to subtropical ocean ecosystems. Additional nitrogen (N) sources beyond subsurface nitrate (NO3-) and N2 fixation fluxes are required to explain observed net community production (NCP) within subtropical ocean ecosystems. Numerical models indicate that laterally supplied allochthonous DON may support 10-60% of NCP in oligotrophic subtropical gyres, but with large uncertainties. The proposed work will field test hypotheses concerning the biological production and consumption of marine DON, and whether allochthonous DON is a significant organic nutrient source sustaining NCP. A North Pacific cruise will use observations of DON concentration, chlorophyll a concentration, and N isotopes [DON's 15N/14N ratio, and NO3-'s 15N/14N ratio] to identify regions of net DON production and consumption in the context of net and gross biological productivity estimated using O2/Ar and triple Oxygen isotopic measurements, respectively. Novel organic geochemistry tools will be used to identify the molecular composition of the allochthonous DON. The influence of depth on DON consumption will be investigated using ship-board incubations that expose surface DON collected across gradients in surface NO3- to microbial communities from several depth intervals. Finally, a new semi-labile DON tracer will be encoded in a global ocean biogeochemistry model, fashioned to behave like the allochthonous DON characterized from the field observations. The DON and isotopic data sets will serve to constrain model parameterizations of semi-labile DON cycling. The state-of-the-art model of semi-labile DON cycling will be used to quantitatively assess the portion of NCP sustained by allochthonous DON delivery to the North Pacific subtropical gyre and extend this assessment across the global ocean.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.

大片海洋覆盖了近 60% 的表面，是“沙漠”，由于营养匮乏，生命在这些地区艰难生存。这些区域位于亚热带海洋的中央环流，距离陆地太远，无法获得大量营养输入。或通过垂直混合来自更深的水域。 营养物质供应不足会导致光合作用水平降低和食物网复杂性降低。 然而，观察结果表明，生命的生长速度与我们项目寻求的营养物质供应量较高的地区相似。以确定有助于维持这些生态系统的营养物质的缺失来源。这项工作将重点关注在营养丰富的地区（包括加利福尼亚州沿海地区）产生的溶解有机分子中的氮，然后横向运输到美国的“海洋沙漠”。为期一个月的亚热带北太平洋研究考察将从加利福尼亚州圣地亚哥出发，最终抵达美国夏威夷州檀香山，研究溶解有机氮 (DON) 的产生、积累、化学成分和利用，并将其与光合作用联系起来。发生在整个北方太平洋地区关于呕吐毒素在满足北太平洋亚热带营养需求方面的作用的新知识将用于构建计算机模型，以衡量这种营养源对亚热带海洋生态系统以外的额外氮源的全球重要性。需要硝酸盐 (NO3-) 和 N2 固定通量来解释亚热带海洋生态系统中观察到的净群落生产 (NCP)。数值模型表明横向供应的异源 DON 可能支持这一观点。 10-60% 的 NCP 存在于副热带低营养环流中，但具有很大的不确定性。拟议的工作将现场测试有关海洋 DON 的生物生产和消耗的假设，以及异源 DON 是否是维持 NCP 的重要有机营养源。将使用 DON 浓度、叶绿素 a 浓度和 N 同位素 [DON 的 15N/14N 比率和 NO3- 的15N/14N 比率]，以分别使用 O2/Ar 和三氧同位素测量估算的净生物生产力和总生物生产力来确定 DON 净生产和消耗区域。将使用新型有机地球化学工具来确定 DON 的分子组成。异源 DON 的影响将通过船载培养进行研究，该培养将表面 NO3- 梯度收集的表面 DON 暴露于多个深度区间的微生物群落中。新的半不稳定 DON 示踪剂将被编码在全球海洋生物地球化学模型中，其行为类似于根据现场观察表征的异源 DON。DON 和同位素数据集将用于约束半不稳定 DON 循环状态的模型参数化。最先进的半不稳定 DON 循环模型将用于评估通过异地 DON 输送到北太平洋而定量维持的 NCP 部分该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。