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

了解水团的年龄对于估算海洋人为吸收的二氧化碳非常重要。水团的年龄可以用概率分布函数或传递时间分布（TTD）来表征，而瞬态示踪剂（如CFCs和SF6）用于约束TTD。然而，限制TTDs的最大不确定性来源之一是缺乏对表面示踪剂饱和度的了解。为了在海洋环流模型中使用示踪剂研究海洋混合和环流，并根据示踪剂库存计算水团形成率，还需要了解表面饱和度。为了减少CFC和SF6饱和度的不确定性，夏威夷大学马诺阿分校和哥伦比亚大学Lamont-Dougherty地球观测站的研究人员将构建一个自动分析系统，用于从海洋表面和大气中连续测量CFC和SF6。尽管测量海水中的氟氯化碳和六氟化硫是相当常规的，但如果有一个由一个人操作的自动化系统，就可以在很少人手的情况下从各种船只上获得饱和数据。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 Hydrography巡航上，最终目标是在未来的CLIVAR/Repeat Hydrography巡航上部署该系统，以及在冬季深水形成并且很少进行测量的地区的机会船上部署该系统。通过记录示踪剂饱和度水平和环境变量（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数据，以限制基于示踪剂的人为二氧化碳吸收估计，为使用CFCs和SF6的模型计算提供更好的边界条件，并开始对控制海洋表面这些气体饱和度的过程有所了解。更广泛的影响使用瞬态示踪剂对水团年龄的研究是海洋环流和海洋吸收化石燃料燃烧释放到环境中的大量二氧化碳的能力的整体研究的一个重要方面。反过来，海洋对二氧化碳的吸收将缓和人类活动造成的地球气候变化。更好地了解SF6和CFC饱和度将减少从CFC和SF6清单确定水团形成速率的误差，减少从SF6和CFC数据确定的环流时间尺度的误差，为利用这些示踪剂的环流模型提供更严格的约束，并减少基于CFC和SF6水团年龄确定海洋人为CO2吸收的误差。作为一个教育组成部分，本科生将在第二个和第三个夏天在该项目中工作，计算从以前的巡航到正在进行的系统将获得数据的地区的氯氟烃饱和度。学生将这些数据与正在进行的数据进行比较，以确定CFC饱和度是否随时间而变化。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研究经验。

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.