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个溶解气体样品。这些样本已经存档，可以分析各种气体，这些气体可以提供20世纪80年代深水形成和循环的信息。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，具有众所周知的海洋输入，半衰期为269年，以及2）六氟化硫（SF6），一种化学惰性的人造气体，在过去的60年中一直进入海洋，随着时间的推移，众所周知，几乎线性增加输入。氩-39的半衰期是研究大西洋深海平均环流的理想方法，而SF6则可以追踪最近形成的深海环流。 目前测量海洋中SF6和小水样中氩-39的技术在1980年代还不存在。 这项工作将确定1980年代收集的储存样品是否未受到储存期间泄漏的污染，以及是否可以准确测量样品中的SF6。如果是这种情况，就有可能将对这些样本进行的测量与对今天和将来进行的考察中从同一地点收集的样本进行的测量进行比较。这将提供关于随着地球气候变暖而可能发生的深大西洋环流变化的信息。该项目将雇用两名本科生，为他们提供实验室和研究经验，因为他们学习如何用气相色谱法测量气体。（探索性研究早期概念资助）项目的目的是检查20世纪80年代收集的储存气体样品的完整性，以确定这些样品是否适合SF6测量，制定一个程序，将这些样本的等分试样转移到其他实验室，并将这些样本的所有信息汇集成一个文件，分发给其他调查人员，并张贴在海洋学网站上。样品收集在两种容器中，一种是用于海洋/北大西洋瞬变示踪物研究和热带大西洋研究的2.8升高压钢罐，另一种是用于南大西洋通风实验的4升低压钢罐。调查人员将测试这些样品的完整性，方法是将罐压与收集时的压力进行比较，并测量氮氩比，这将显示大约100个样品的子集是否有任何大气污染。 他们将确定这些样品是否适合进行SF6测量，方法是使用在海上进行此类测量的常规方法测量这一子集的SF6，并将这些测量结果与这些航行中在海上测量的CFC-11和CFC-12进行比较。样本子集将包括约8个站从地面到底部的垂直剖面和约20个站的地面样本。 将把表面样品中的SF6浓度与假定在样品收集时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1980年代收集的样本的完整性，并为使用这些样本调查1980年代大西洋深水环流以及1980年代以来这种环流的变化打开大门。 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。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。

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 These samples have been archived and can be analyzed for a variety of gases that could provide information on deep water formation and circulation in the 1980s.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.