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.

该奖项全部或部分由2021年美国救援计划法案（公法117-2）资助。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，在那里，深层沃茨是由寒冷和/或含盐的表面沃茨下沉而“形成”的。水团形成期间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，是气-海气体交换物理学的极好示踪剂：它们在海洋内部的丰度告诉我们，当水最后出现在海面时，气体交换的效率如何。另一种示踪剂，溶解氧的“三氧同位素”（TOI）组成（测量氧-16，氧-17和氧-18的相对丰度）对生物学和物理学都很敏感。然而，在现代海洋中，这些重要的海气交换示踪剂中的每一个都仍然研究不足。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惰性气体和TOI进行新的最先进的测量。该项目开发的方法也将使未来的研究机会，利用这些宝贵的样本。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学研究所（WHOI）之间的新伙伴关系编制讲习班和讲座材料的持续努力做出贡献和附近的公立高中，主要是代表性不足的少数民族学生。这个项目的主要目标是量化的幅度和空间变异的两套保守的示踪剂，在深水形成时，每种气体都对海-气气体交换敏感：惰性气体和TOI。对这些示踪剂的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，多项研究一直发现深海中重惰性气体（Ar、Kr和H2O）相对于其在海水中的溶解度平衡浓度存在不饱和现象。然而，虽然存在几种理论，但对于为什么重惰性气体在整个深海中不饱和，也没有任何理由怀疑是单一过程造成的，也没有达成共识。考虑到北方和南方深水形成的机制截然不同，北大西洋和南大西洋之间惰性气体不平衡的空间变化可能为这一悬而未决的问题提供关键线索。然而，到目前为止，分析的局限性限制了强大的检测和量化的水团间的差异不平衡。TOIs还可以提供对深水形成期间的海气不平衡的深入了解，因为氧-17的相对过量（相对于大气氧同位素比率，并因呼吸作用而校正同位素分馏）反映了海气交换和光合作用之间的平衡。惰性气体和TOI一起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稀有气体的不饱和和光合作用氧的积累（从而导致过量氧-17）。然而，在深海中存在的TOI的高质量的测量，由于分析的挑战，尽管TOI作为一个保守的示踪剂的物理和地球化学在深水形成的巨大潜力。拟议的工作将涉及对1980年代在海上提取的存档溶解气体样本进行100次测量，这些样本自收集以来一直储存在坚固的储罐中。这一项目是第一次在大空间范围内测量相同深海样本中的惰性气体和TOI，方法是始终采用相同的方法和仪器，以消除实验室间的偏差。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。这项工作增加了冗余，以提高结果的准确性，方法是用多台仪器测量所有样本，包括成对的相邻台站，并用1980年代收集这些样本时使用的原始设备进行提取实验。例如，将在两个单独的仪器上独立测量重惰性气体元素比率，并将使用惰性气体同位素的高精度（0.01 permil量级）测量来测试和校正样品的完整性。总的来说，这一大组存档的气体提供了一个独特的机会，以更好地了解这些示踪剂，并探索它们可能提供的定量见解，以解决有关深海通风的悬而未决的问题。这个奖项反映了NSF的法定使命，并已被认为是值得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的支持。