Collaborative Research: RUI: Investigating Gas Exchange Processes using Noble Gases in a Controlled Environment

大气和海洋之间气体交换的精确描述尚未完全开发，但它是理解气候变化和生态系统动力学的关键过程。当评估气泡在空气-海洋气体交换中的重要作用时，特别是在大风和海浪使直接测量极其困难的偏远海洋地区，这一点尤其成问题。该项目旨在通过使用大型、最先进的风波罐，提供所需的基础、高风波气体交换测量。在这里，pi可以应用他们对稀有气体（氖、氩、氪和氙）的新测量来计算精确控制条件下的总气体通量。这种水箱设置允许系统地定义物理和化学参数（温度、盐度、pH值、风速、湍流、气泡大小分布等），以构建更准确的模型，而不需要在风暴条件下从船上进行类似测量所固有的巨大不确定性。这项研究的一个重要成果，除了提高对空气-海洋气体交换的理解之外，还可以大大提高对光合作用和呼吸作用之间关键生态平衡的估计。目前的方法使用溶解在海水中的二氧化碳和氧气作为生物活性的指示，但不能区分生物过程和大气交换，并且在强气泡注入的大风和海浪条件下估计尤其不准确。这项研究将提高我们在评价海水溶解气体时分离生物和物理过程的能力。此外，该项目将为韦尔斯利学院的15名女本科生提供令人兴奋的现场研究经验，使用迈阿密大学最先进的水箱设施，研究结果将纳入普通和高级化学课程。此外，政府亦会支持学生制作短片及举办其他公众外展活动，以宣传海洋气体交换的重要性。海洋和大气之间气体交换过程的研究一直受到缺乏数据的阻碍，这些数据无法定义在各种风、波和温度条件下气泡过程的定量关系。目前的气体交换模型在对气泡过程进行参数化时往往高度不可靠。在很大程度上，这是由于在偏远地区进行传统的海上测量很难在明确的条件下进行，特别是在大风大浪的情况下。通过使用大型SUSTAIN风浪箱（23米x 6米x 2米），该项目的研究人员计划大大提高我们对风、波和温度变化对气体传输的影响的理解。使用最近开发的现场便携式平衡质谱计，可以几乎连续测量稀有气体比率（Ne, Ar， Kr和Xe），这将导致这些SUSTAIN罐实验在10到40米/秒的不同风速下提供精确表征的气体通量数据。此外，水下阴影系统将对气泡进行成像，使研究人员能够量化气泡大小分布，这是气泡模型中缺失的关键因素。目前的模型使用了一种极大简化的、两种大小级别的气泡表示；本研究将重新评估这一方法，以期更好地参数化气泡大小对气体通量的作用，从而改进用于海洋和气候应用的海气交换模式。

An exact description of gas exchange between the atmosphere and the ocean is not fully developed, yet it is a critical process for understanding climate change and ecosystem dynamics. This is particularly problematic when evaluating the important role of bubbles in air-sea gas exchange, especially in remote ocean locations where high winds and waves make direct measurements extremely difficult. This project seeks to provide needed fundamental, high wind/wave gas-exchange measurements by using a large, state-of-the-art, wind-wave tank. Here the PIs can apply their novel measurements of noble gases (neon, argon, krypton, and xenon) to calculate overall gas fluxes under precisely controlled conditions. This tank setting allows a systematic approach to define the physical and chemical parameters (temperature, salinity, pH, wind speed, turbulence, bubble size distribution, etc.) required to construct more accurate models without the great uncertainties inherent in making similar measurements from a ship in storm conditions. A significant outcome of this study, beyond improved understanding of air-sea gas exchange, could be greatly improved estimates of the critical ecological balance between photosynthesis and respiration. Current methods use carbon dioxide and oxygen dissolved in seawater as an indication of biological activity, but cannot distinguish between biological processes and atmospheric exchange, and estimates are especially inaccurate under high wind and wave conditions with strong bubble injection. This study will improve our ability to separate biological and physical processes in evaluation of dissolved gasses in seawater. Also, this project will provide 15 female undergraduate students at Wellesley College with an exciting, on-site research experience using a state-of-the-art tank facility at the University of Miami, and results will be incorporated into general and advanced chemistry classes. The production of student-created, short format videos, and other public outreach activities will also be supported to disseminate information on the importance of marine gas exchange.The study of gas exchange processes between the ocean and the atmosphere has been hindered by the lack of data required to define quantitative relationships that account for bubble processes under a variety of wind, wave, and temperature conditions. Current gas exchange models tend to be highly unreliable in their parameterization of bubble processes. In large part, this is due to the difficulty of making traditional measurements at sea in remote locations within well-defined conditions, especially with high winds and waves. By using the large SUSTAIN wind-wave tank (23 m x 6 m x 2 m), the researchers in this project plan to greatly advance our understanding of the effect of wind, wave, and temperature variability on gas transfer. The use of a recently developed, field-portable equilibrator mass spectrometer that allows nearly continuous measurements of noble gas ratios (Ne, Ar, Kr, and Xe) will result in these SUSTAIN tank experiments providing precisely characterized gas flux data under varying wind speeds from 10 to 40 m/s. In addition, an underwater shadowgraph system will image bubbles, allowing the researchers to quantify bubble size distributions, a key factor missing from bubble models. Current models use a greatly simplified, two size-class representation of bubbles; an approach that this research will re-evaluate in hopes of creating better parameterizations of the role of bubble size on gas flux, and consequently improved air-sea gas exchange models for oceanic and climatic applications.