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来自《2021年美国救援计划法案》(公法117-2)。气体在大气和海洋内部之间的转移由高纬度地区的过程控制，那里的深水是由寒冷和/或咸水的表层水下沉而形成的。在水团形成过程中影响海-气交换的过程对海洋吸收二氧化碳和其他重要气体起着重要作用。溶解的稀有气体不受化学或生物的影响，是大气-海洋气体交换物理的极好示踪：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，气体交换是多么有效。另一种示踪剂是溶解氧的“三重氧同位素”(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-气交换示踪物中的每一个仍然没有得到充分的研究。该项目旨在对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TOIS进行最新的测量。该项目中开发的方法也将使未来的研究机会能够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研究所(WHOI)和附近一所公立高中之间的新伙伴关系开发研讨会和讲座材料，该高中的少数民族学生人数主要不足。该项目的主要目标是量化两套保守示踪剂的大小和空间变异性，这两套示踪剂在深水形成时分别对海-气交换独立敏感：稀有气体和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，相对于海水中重惰性气体(Ar、Kr和Xe)在海水中的溶解平衡浓度，深海中的重惰性气体处于不饱和状态。然而，尽管存在几种理论，但对于为什么重惰性气体在整个深海都是不饱和的，也没有任何理由怀疑是单一过程造成的，没有达成共识。鉴于北方和南方深水形成机制的巨大差异，南北大西洋之间稀有气体不平衡的空间变异性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对不平衡中水团间差异的可靠检测和量化。TOIS还可以洞察深水形成期间的海-气不平衡，因为氧-17的相对过剩(相对于大气氧同位素比率并经呼吸引起的同位素分馏校正)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稀有气体的不饱和和光合氧的积累(从而导致过剩的氧-17)。然而，由于分析方面的挑战，深海TOI的高质量测量很少，尽管TOI在深水形成过程中作为物理和生物地球化学的保守示踪剂潜力很大。拟议的工作将涉及100个存档的溶解气体样本的测量，这些样本是20世纪80年代在海上提取的，自收集以来一直储存在坚固的储罐中。该项目是通过始终如一地使用相同的方法和仪器消除实验室间的偏差，首次在大范围内测量同一深海样品中的惰性气体和总有机污染物。它涉及三个世界卫生组织实验室的测量，并使用最先进的技术进行每一次独立的示踪剂测量。这项工作建立了冗余，以提高结果的准确性，方法是在多台仪器上测量所有样本，包括成对的相邻站点，并使用1980年代用于收集这些样本的原始设备进行提取实验。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(0.01permil)测量将用于测试和校正样品的完整性。总体而言，这一大套存档气体提供了一个独特的机会，可以更好地理解这些示踪剂，并探索它们可能提供的关于深海通风的悬而未决的问题的量化洞察。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。