Collaborative Research: Probing the Ventilation Efficiency of the Deep Ocean with Conservative Dissolved Gas Tracers in Archived Samples

合作研究：利用存档样本中的保守溶解气体示踪剂探测深海的通风效率

• 批准号: 2122427
• 负责人: Alan Seltzer
• 金额: $ 66.92万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2122427&HistoricalAwards=false
• 关键词: Collaborative; Research; Probing; Ventilation; Efficiency

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).The transfer of gases between the atmosphere and the interior of ocean is controlled by processes in the high latitudes, where deep waters are “formed” by the sinking of cold and/or salty surface waters. The processes that affect air-sea gas exchange during water mass formation play an important role in the uptake of carbon dioxide and other important gases by the ocean. Dissolved noble gases, which are not affected by chemistry or biology, are excellent tracers of the physics of air-sea gas exchange: their abundances in the ocean interior tell us about how efficient gas exchange was when water was last at the sea surface. Another tracer, the “triple oxygen isotope” (TOI) composition of dissolved oxygen (a measure of the relative abundances of oxygen-16, oxygen-17, and oxygen-18) is sensitive to both biology and physics. However, each of these important tracers of air-sea exchange remains understudied in the modern ocean. This project aims to make new state-of-the-art measurements of noble gases and TOIs in 100 archived gas samples from the North and South Atlantic. The methods developed in this project will also enable future research opportunities that take advantage of these valuable samples. The project will support the training of a PhD student and multiple undergraduates, while contributing to ongoing efforts to develop workshop and lecture materials for a new partnership between Woods Hole Oceanographic Institution (WHOI) and a nearby public high school that has a primarily underrepresented minority student body.The primary objective of this project is to quantify the magnitude and spatial variability of two sets conservative tracers that are each independently sensitive to air-sea gas exchange at the time of deep-water formation: noble gases and TOIs. A deeper understanding of these tracers will provide insight into the physical mechanisms that regulate the efficiency of deep-ocean ventilation. Over recent decades, multiple studies have consistently found undersaturation of the heavy noble gases (Ar, Kr, and Xe) in the deep ocean, with respect to their solubility equilibrium concentrations in seawater. However, while several theories exist, there is no consensus on why the heavy noble gases are undersaturated throughout the deep ocean nor any reason to suspect that a single process is responsible. The spatial variability in noble gas disequilibrium between the North and South Atlantic may provide key clues to this open question, given the vastly different mechanisms of northern and southern deep-water formation. However, to date, analytical limitations have limited the robust detection and quantification of inter water-mass differences in disequilibrium. TOIs may also provide insight into air-sea disequilibrium during deep-water formation, as the relative excess of oxygen-17 (with respect to the atmospheric oxygen isotope ratios and corrected for isotopic fractionation due to respiration) reflects the balance between air-sea exchange and photosynthesis. Together, noble gases and TOIs provide useful constraints to elucidate fundamental mechanisms. For example, sea-ice cover in regions of deep-water formation will simultaneously lead to undersaturation of noble gases and accumulation of photosynthetic oxygen (and thus excess oxygen-17). However, few high-quality measurements of TOI in the deep ocean exist, due to analytical challenges, despite the great potential of TOI as a conservative tracer of physics and biogeochemistry during deep-water formation. The proposed work will involve 100 measurements of archived dissolved gas samples that were extracted at sea in the 1980s and stored in robust tanks since collection. This project is the first effort to measure noble gases and TOI in the same deep-ocean samples across a wide spatial range, by consistently employing the same methodology and instrumentation to eliminate inter-laboratory biases. It involves measurements in three WHOI labs and makes use of state-of-the-art techniques for each independent tracer measurement. This work builds in redundancy to improve the accuracy of results by measuring all samples on multiple instruments, including pairs of adjacent stations, and carrying out extraction experiments with the original equipment used in the 1980s to collect these samples. For example, heavy noble gas elemental ratios will be measured independently on two separate instruments, and high-precision (order 0.01 permil) measurements of noble gas isotopes will be used to test and correct for sample integrity. Overall, this large set of archived gases offers a unique opportunity to better understand these tracers and explore the quantitative insight they may offer into outstanding questions about the deep-ocean ventilation.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.

该奖项的全部或部分资金根据《2021 年美国救援计划法案》（公法 117-2）提供。大气和海洋内部之间的气体转移受高纬度地区的过程控制，其中深水是由寒冷和/或含盐的地表水下沉“形成”的。水团形成过程中影响海气交换的过程在海洋吸收二氧化碳和其他重要气体方面发挥着重要作用。溶解的惰性气体不受化学或生物学的影响，是空气-海洋气体交换物理的极好示踪剂：它们在海洋内部的丰度告诉我们当水最后一次出现在海面时气体交换的效率如何。另一种示踪剂，溶解氧的“三重氧同位素”(TOI) 成分（氧 16、氧 17 和氧 18 相对丰度的测量）对生物学和物理学都很敏感。然而，现代海洋中的每一种重要的海气交换示踪剂仍未得到充分研究。该项目旨在对来自北大西洋和南大西洋的 100 个存档气体样本中的稀有气体和 TOI 进行新的最先进的测量。该项目开发的方法还将为未来利用这些有价值的样本的研究机会提供机会。该项目将支持一名博士生和多名本科生的培训，同时为伍兹霍尔海洋研究所 (WHOI) 与附近一所公立高中之间的新合作伙伴关系持续努力开发研讨会和讲座材料，该高中的少数族裔学生人数主要不足。该项目的主要目标是量化两组保守示踪剂的幅度和空间变异性，这两组保守示踪剂对空气-海洋气体交换独立敏感 深水形成时：稀有气体和TOI。对这些示踪剂的更深入了解将有助于深入了解调节深海通风效率的物理机制。近几十年来，多项研究一致发现深海重惰性气体（Ar、Kr 和 Xe）在海水中的溶解度平衡浓度存在欠饱和度。然而，虽然存在多种理论，但对于为什么整个深海中的重惰性气体不饱和，尚未达成共识，也没有任何理由怀疑单一过程是造成这一现象的原因。鉴于南北深水形成的机制截然不同，北大西洋和南大西洋之间稀有气体不平衡的空间变化可能为这个悬而未决的问题提供关键线索。然而，迄今为止，分析的局限性限制了不平衡中水团间差异的稳健检测和量化。 TOI 还可以深入了解深水形成过程中的海气不平衡，因为氧 17 的相对过量（相对于大气氧同位素比，并针对呼吸作用引起的同位素分馏进行校正）反映了海气交换和光合作用之间的平衡。惰性气体和 TOI 共同为阐明基本机制提供了有用的约束。例如，深水形成区域的海冰覆盖将同时导致惰性气体的不饱和和光合氧的积累（从而导致过量的氧17）。然而，尽管 TOI 作为深水形成过程中物理和生物地球化学的保守示踪剂具有巨大潜力，但由于分析方面的挑战，深海 TOI 的高质量测量很少。拟议的工作将涉及对存档的溶解气体样本进行 100 次测量，这些样本是 20 世纪 80 年代在海上提取的，收集后储存在坚固的储罐中。该项目是首次在广泛的空间范围内测量相同深海样本中的稀有气体和 TOI，通过一致采用相同的方法和仪器来消除实验室间偏差。它涉及三个 WHOI 实验室的测量，并利用最先进的技术进行每个独立的示踪剂测量。这项工作通过在多个仪器（包括成对的相邻站点）上测量所有样本，并使用 20 世纪 80 年代用来收集这些样本的原始设备进行提取实验，建立了冗余，以提高结果的准确性。例如，重惰性气体元素比率将在两台单独的仪器上独立测量，惰性气体同位素的高精度（0.01 permil量级）测量将用于测试和校正样品完整性。总体而言，这一大批存档气体提供了一个独特的机会，可以更好地了解这些示踪剂，并探索它们可能为有关深海通风的突出问题提供的定量见解。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优点和更广泛的影响审查标准进行评估，被认为值得支持。