Collaborative Research: Automated continuous measurement of CFC and SF6 saturations in surface waters

了解水团的年龄对于估计海洋的人为二氧化碳吸收是很重要的。水团的年龄可以用概率分布函数或渡越时间分布(TTD)来表征，使用CFCs和SF6等瞬变示踪剂来约束TTD。然而，限制TTD的最大不确定性来源之一是缺乏关于表面示踪剂饱和的知识。在海洋环流模型中使用示踪剂调查海洋混合和环流，以及根据示踪剂清单计算水团形成率，也需要了解表面饱和度。为了减少氟氯化碳和SF6饱和的不确定性，夏威夷大学马诺阿分校和哥伦比亚大学拉蒙特-多尔蒂地球天文台的研究人员将建造一个自动分析系统，用于连续测量表层海洋和大气中的氟氯化碳和SF6。尽管测量海水中的氯氟化碳和六氟化硫是相当常规的，但拥有一个由一个人操作的自动化系统将允许在几乎没有人力的情况下从各种船只上获取饱和度数据。新的分析系统将部署在亚极地/极地地区(例如S4P)和亚热带地区(例如A20/A22/A16)的CLIVAR/REPEAT水文邮轮上，最终目标是在未来的CLIVAR/REPEAT水文邮轮上部署该系统，并在冬季出现深水形成且很少进行测量的区域的机会船上部署该系统。通过记录示踪剂饱和水平和环境变量(如温度、盐度、风速、混合层深度)的变化，研究小组希望为社区提供急需的测量，以限制基于示踪剂的人为二氧化碳吸收估计，为使用氟氯化碳和SF6的模型计算提供更好的边界条件，并开始对控制这些气体在表层海洋中饱和的过程有一些深入的了解。更广泛的影响使用瞬时示踪剂研究水团年龄是整体研究海洋环流和海洋吸收燃烧化石燃料向环境释放的大量二氧化碳的能力的一个重要方面。反过来，海洋对二氧化碳的吸收将缓和由于人类干扰而导致的地球气候变化。更好地了解SF6和氟氯化碳饱和度将减少从氟氯化碳和SF6库存确定水团形成率的误差，减少根据SF6和氟氯化碳数据确定的循环时间尺度的误差，对使用这些示踪剂的循环模型提供更严格的约束，并减少根据氟氯化碳和SF6水团年龄确定海洋人为二氧化碳吸收的误差。作为一个教育组成部分，本科生将被雇用在第二和第三个暑假期间参与该项目，以计算从以前的巡航到将通过正在进行的系统获得数据的地区的氟氯化碳饱和度。学生将把这些数据与正在进行的数据进行比较，以确定氯氟化碳饱和度是否随时间变化。在这个过程中，这些学生将学习海洋学，并获得研究我们这个时代最紧迫的全球环境问题之一的经验。

Knowing the age of water masses is important in estimating anthropogenic CO2 uptake by the ocean. The age of a water mass can be characterized by a probability distribution function, or transit time distribution (TTD), and transient tracers such as CFCs and SF6 are used to constrain the TTD. However, one of the largest sources of uncertainty in constraining TTDs is lack of knowledge about surface tracer saturations. Knowledge of the surface saturation is also needed to investigate ocean mixing and circulation using tracers in ocean circulation models and to calculate water mass formation rates from tracer inventories. To reduce the uncertainty in CFC and SF6 saturations, researchers at the University of Hawaii at Manoa and at the Lamont-Dougherty Earth Observatory of Columbia University will construct an automated analysis system for continuous measurements of CFCs and SF6 from the surface ocean and the atmosphere. Even though the measurement of CFCs and SF6 in seawater is fairly routine, having an automated system operated by one person will permit saturation data to be acquired from a variety of ships with little manpower. The new analysis system will be deployed on CLIVAR/Repeat Hydrography cruises in a subpolar/polar region (e.g., S4P) and a subtropical region (e.g., A20/A22/A16), with the eventual goal of deploying the system on future CLIVAR/Repeat Hydrography cruises, and on ships of opportunity to regions during winter when deep water formation occurs and very few measurements have been made. By documenting variations in tracer saturation levels and environmental variables (e.g., temperature, salinity, wind speeds, mixed layer depth), the research team expects to provide the community with much needed measurements to constrain tracer-based estimates of anthropogenic CO2 uptake, provide better boundary conditions for model calculations using CFCs and SF6, and begin to gain some insights into processes controlling the saturations of these gases in the surface ocean. Broader Impacts The study of water mass ages using transient tracers is an important aspect of the overall study of the ocean circulation and of the ability of the ocean to take up the large amounts of CO2 that are being released to the environment by the burning of fossil fuels. The uptake of CO2 by the ocean, in turn, will moderate changes in the Earth's climate due to human perturbations. Better knowledge of SF6 and CFC saturations will reduce errors in determining water mass formation rates from CFC and SF6 inventories, reduce errors in circulation time scales determined from SF6 and CFC data, provide tighter constraints on circulation models that utilize these tracers, and reduce errors in determination of oceanic uptake of anthropogenic CO2 based on CFC and SF6 water mass ages. As an educational component, undergraduate students will be hired to work during the second and third summers on the project to calculate CFC saturations from previous cruises to regions where data will have been acquired with the underway system. The student will compare these data to the underway data to determine if CFC saturations have changed with time. In the process, these students will learn about oceanography and gain research experience working on one of the most pressing global environmental problems of our time.