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，它们可以测量的范围是：1)天然放射性同位素Ar-39，化学上是惰性的，对海洋的输入众所周知，半衰期为269年；2)六氟化硫(SF6)，一种化学上惰性的人造气体，过去60年来一直以众所周知的、近乎线性的输入随时间增加进入海洋。Ar-39的半衰期是研究大西洋深海平均环流的理想方法，而SF6则跟踪新近形成的深水的环流。目前在海洋中测量SF6和在小水样中测量Ar-39的技术在20世纪80年代还不存在。这项工作将确定在1980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，就有可能将对这些样本进行的测量与在今天和未来进行的邮轮上从相同地点收集的样本的测量进行比较。这将提供有关大西洋深层环流变化的信息，这些变化可能随着地球气候变暖而发生。这个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仪测量气体。这个项目的目标是检查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，开发一种将这些样本的等量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单一文件，可以分发给其他研究人员并发布在海洋学网站上。样品是在两种类型的容器中收集的，2.8升高压钢罐用于海洋/北大西洋研究中的瞬变示踪剂(TTO/NAS)和热带大西洋研究(TTO/TAS)，以及4升低压钢罐用于南大西洋通风实验(SAVE)。调查人员将通过将储罐压力与采集时的压力进行比较，并在大约100个样本的子集上测量氮与氩的比率来测试这些样本的完整性。氮与氩的比率将显示是否存在任何大气污染。他们将确定样品是否适合SF6测量，方法是在这一子集上使用在海上进行这些测量的常规方法测量SF6，并将这些测量结果与在这些巡航中在海上测量的CFC-11和CFC-12进行比较。样本子集将包括大约8个测站从地表到底部的垂直剖面和大约20个测站的地表样本。地表样品中的SF6浓度将与采集样品时假定与大气浓度平衡的预期浓度进行比较。如果测量成功，这些测量将确保1980年代采集的样本的完整性，并为使用这些样本调查1980年代期间大西洋深水循环以及1980年代以来这种循环的变化打开大门。还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。这一奖项反映了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。

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 These samples have been archived and can be analyzed for a variety of gases that could provide information on deep water formation and circulation in the 1980s.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