Collaborative Research: Inventories of Primary Productivity by In-situ Mass Spectrometry in the Upper Ocean

在海洋的大部分地区，从二氧化碳中产生有机物（特别是通过光合生物）和将有机物呼吸转化为二氧化碳（通过各种各样的生物，包括光合生物）几乎处于平衡状态——但也不完全平衡。在一些远离陆地的地区，通过光合作用产生的碳比被呼吸回的二氧化碳要多；在另一些国家，情况正好相反。弄清楚这一点是非常重要的，因为在光合作用超过呼吸作用的地区，海洋生物的食物净产量以及大气中二氧化碳（一种强大的温室气体）的净清除量都在增加。相反，呼吸作用超过光合作用的海洋区域是净食物消耗和向大气释放二氧化碳的区域。在实践中，问题在于这种或那种方式的差异是如此之小，以至于很难区分测量本身和数据中的噪声（即散射）。要解决这个问题需要新的技术，这种技术可以在海洋本身而不是在一瓶取样的海水中进行高精度的必要测量。在这个项目中，研究人员将尝试使用一种通常只在分析实验室中发现的复杂仪器——质谱仪，一种能够对海洋水柱中与光合作用和呼吸有关的溶解氧、二氧化碳和其他物质的数量变化进行超高精度测量的设备。研究人员将支持研究生作为研究团队不可或缺的成员参与研究。此外，还将为中学生提供公共教育外展，让他们有机会参与该项目，获得第一手经验，了解如何利用基础科学解决海洋学问题。在本项目中，一组研究人员将利用原位质谱法评估这些方法学问题的一个方面，以更好地约束净群落产量（NCP）。UMIMS是一种快速响应的水下膜入口质谱仪，可以部署在自主和远程操作的车辆中。在该应用中，UMIMS将被部署在SeaSoar拖曳车上，以获得高分辨率的溶解氧（O2）超过氩（Ar）预算的垂直剖面，这是一种很有前景的海洋表面NCP测量方法。具有UMIMS的配置文件可以提供解决影响NCP预算的整个混合层和光区的过程的能力。在短期内，该团队将利用UMIMS的功能来准确同时获得O2和Ar的混合层剖面图，并将UMIMS的NCP测量值与传统的船上海水O2/Ar预算测量值进行比较。这些比较将用于确定两种方法的局限性，以及它们能够解决导致非固定交换的环境物理过程的程度。从长远来看，研究人员希望在技术和方法上取得必要的进步，将UMIMS部署在拉格朗日浮子和海上滑翔机上。因此，该项目有望在测量海洋代谢平衡和生物泵的近连续时间和空间序列观测方面迈出重要一步，类似于今天Argo浮标测量温度和盐度的方式。

Production of organic matter from carbon dioxide (specifically by photosynthetic organisms) and respiration of organic matter back to carbon dioxide (by a wide variety of organisms, including photosynthesizers) are very nearly in balance over much of the ocean -- but not quite. In some regions remote from land, more carbon is produced through photosynthesis than is respired back to carbon dioxide; in others, just the opposite is true. Figuring out which is exceedingly important because in regions where photosynthesis exceeds respiration, there is a net production of food for marine life as well as a net removal of carbon dioxide (a powerful greenhouse gas) from the atmosphere. Conversely, oceanic regions where respiration exceeds photosynthesis are zones of net food consumption and release of carbon dioxide to the atmosphere. In practice, the problem is that the differences, one way or the other, are so small that it is difficult to distinguish between the measurements themselves and noise (that is, scatter) in the data. Resolution of this problem requires new technology that can make the necessary measurements with very high precision in the ocean itself rather than in a bottle of sampled seawater. In this project, the investigators will attempt to do just that using a sophisticated instrument normally found only in an analytical laboratory -- a mass spectrometer, a device capable of making ultra-high-precision measurements of changes in the amount of dissolved oxygen, carbon dioxide, and other substances associated with photosynthesis and respiration in the marine water column. The investigators will support graduate students to participate as integral members of the research team. There will also be public educational outreach to secondary school students offering them the opportunity to engage with the project to gain first-hand experience seeing how the basic sciences can be used to solve oceanographic problems.In this project, a team of investigators will evaluate one facet of these methodological concerns using in-situ mass spectrometry to better constrain net community production (NCP). The UMIMS is a fast-response Underwater Membrane Inlet Mass Spectrometer that can be deployed in autonomous and remotely-operated vehicles. In this application, UMIMS will be deployed aboard a SeaSoar tow vehicle to make high resolution vertical sections of the excess dissolved oxygen (O2) over argon (Ar) budget, a promising measure of NCP in the surface ocean. Profiles with the UMIMS can provide the capacity to resolve processes throughout the mixed-layer and euphotic zone that affect the NCP budget. In the near term, the team will utilize the capabilities of the UMIMS to make accurate and simultaneous mixed layer profiles of O2 and Ar and compare measurements of NCP from the UMIMS with measurements from the conventional shipboard O2/Ar budget from underway seawater. These comparisons will be used to determine the limitations of both methods and the degree to which they can resolve the ambient physical processes leading to non-stationary exchange. In the long term, the researchers expect to make the technological and methodological advances necessary to deploy the UMIMS on Lagrangian floats and sea gliders. As such, this project is expected to make a significant step toward measuring near-continuous time and space series observations of the oceanic metabolic balance and the biological pump, similar to the way Argo floats measure temperature and salinity today.