EAGER: Measurement of Sulfur Hexafluoride and Argon-39 on Archived Samples from the Atlantic Ocean Collected in the 1980s

在20世纪80年代，从大西洋各地的250升水样中收集了大约1200个溶解气体样本。这些样本已被存档，可以分析各种气体，这些气体可以提供20世纪80年代深水形成和环流的信息。特别是，它们可以测量1)天然放射性同位素氩-39，它是化学惰性的，对海洋有众所周知的输入，半衰期为269年；2)六氟化硫（SF6），一种人造气体，化学惰性，在过去的60年里一直进入海洋，众所周知，随着时间的推移，输入几乎呈线性增加。氩-39的半衰期对于研究大西洋深处的平均环流是理想的，SF6追踪了最近形成的深水环流。目前测量海洋中SF6和小水样中argon-39的技术在20世纪80年代是不可用的。这项工作将确定在20世纪80年代收集的储存样品在储存过程中是否没有受到泄漏的污染，以及样品是否可以准确地测量SF6。如果是这样的话，就有可能将这些样品的测量结果与今天和将来在同一地点进行的巡航中收集的样品的测量结果进行比较。这将提供关于随着地球气候变暖而可能发生的大西洋深层环流变化的信息。该项目将雇用两名本科生，为他们提供实验室和研究经验，让他们学习如何用气相色谱法测量气体。这个EAGER（探索性研究早期概念资助）项目的目标是检查20世纪80年代收集的储存气体样本的完整性，确定这些样本是否适合SF6测量，制定将这些样本的配额转移到其他实验室的程序，并将这些样本的所有信息汇编成一个文件，可以分发给其他研究人员并发布在海洋学网站上。样品收集于两种类型的容器中，一种是2.8升高压钢罐，用于海洋/北大西洋研究（TTO/NAS）和热带大西洋研究（TTO/TAS）中的瞬态示踪剂，另一种是4升低压钢罐，用于南大西洋通风实验（SAVE）。调查人员将通过比较储罐压力和收集时的压力，以及测量氮氩比来测试这些样品的完整性，这将显示大约100个样品的子集是否有任何大气污染。他们将通过使用常规的海上测量方法测量SF6，并将这些测量结果与海上测量的CFC-11和CFC-12进行比较，来确定样品是否适合进行SF6测量。样本子集将包括大约8个站点从地面到底部的垂直剖面和大约20个站点的地面样本。表面样品中的SF6浓度将与样品收集时假定与大气浓度平衡的预期浓度进行比较。如果成功，这些测量将确保20世纪80年代收集的样品的完整性，并为使用这些样品调查20世纪80年代大西洋深水环流以及20世纪80年代以来环流的变化打开大门。人们也可能有兴趣进行其他示踪剂和化学测量，这在20世纪80年代是不可能的。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

During the 1980s about 1200 dissolved gas samples were collected from 250-liter water samples at locations throughout the Atlantic Ocean. These samples have been archived and can be analyzed for a variety of gases that could provide information on deep water formation and circulation in the 1980s. In particular, they could be measured for 1) the natural radioactive isotope, argon-39, which is chemically inert, has a well-known input to the ocean, and half-life of 269 years, and 2) sulfur hexafluoride (SF6), a man-made gas that is chemically inert and has been entering the ocean for the past 6 decades with a well-known, nearly linear increasing input through time. The argon-39 half-life is ideal for investigation of the mean circulation of the deep Atlantic Ocean and SF6 traces the circulation of recently formed deep water. The current technology to measure SF6 in the ocean and argon-39 on small water samples was not available in the 1980s. This work will determine if the stored samples collected in the 1980s are uncontaminated by leakage during storage and if the samples can be accurately measured for SF6. If this is the case, it will be possible to compare measurements made on these samples to measurements on samples collected from the same locations on cruises carried out today and in the future. This will provide information on changes in the deep Atlantic circulation that may be occurring as the Earth's climate warms. This project will employ two undergraduate students, providing them laboratory and research experience as they learn how to measure gases with gas chromatography.The objectives of this EAGER (Early Concept Grant for Exploratory Research) project are to check the integrity of the stored gas samples collected in the 1980s, to determine if these samples are suitable for SF6 measurements, to develop a procedure for transferring aliquots of these samples to other labs, and to assemble all of the information on these samples into a single file that can be distributed to other investigators and posted on oceanographic websites. The samples were collected in two types of containers, 2.8-liter high pressure steel tanks for the Transient Tracers in the Ocean/North Atlantic Study (TTO/NAS) and Tropical Atlantic Study (TTO/TAS) and 4-liter low pressure steel tanks for the South Atlantic Ventilation Experiment (SAVE). The investigators will test the integrity of these samples by comparing the tank pressures to the pressure at the time of collection and by measuring the nitrogen to argon ratio, which will show if there is any atmospheric contamination, on a subset of about 100 samples. They will determine if the samples are suitable for SF6 measurements by measuring SF6 on this subset using the method used routinely to perform these measurements at sea, and comparing these measurements to CFC-11 and CFC-12 measured at sea on these cruises. The sample subset will include vertical profiles from surface to bottom at about 8 stations and surface samples from about 20 stations. SF6 concentrations in the surface samples will be compared to the expected concentrations assuming equilibrium with the atmospheric concentration at the time of sample collection. If successful, these measurements will ensure the integrity of samples collected in the 1980s and open the door for using these samples to investigate deep water circulation in the Atlantic Ocean during the 1980s and changes in this circulation since the 1980s. There may also be interest in making other tracer and chemical measurements that were not possible in the 1980s.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.