Methane, Ethylene, and Dissolved Organic Phosphorus Cycling in the Western North Atlantic Ocean

“海洋甲烷悖论”指的是在海洋表层水域观察到高浓度甲烷，尽管这些水域含氧量高，硫酸盐含量高，但这两个特征通常都不利于甲烷的产生。本项目旨在阐明这一悖论的原因。根据初步结果，研究人员确定了溶解有机物的微生物循环刺激甲烷生产的潜力。多糖(碳酸盐，如淀粉)是高分子量溶解有机物(HMWDOM)的主要成分，它们可以结合甲基膦酸酯，这可能允许在地表水中产生甲烷。当这些HMWDOM多糖被引入海水样本时，研究人员发现甲烷的产生具有反常的稳定碳同位素比率，与富含甲烷的矛盾的表层水域中的情况相当。通过对北大西洋西部的痕量气体、HMWDOM磷酸盐和稳定碳同位素的测量，研究人员和他的合作者将重新评估初步数据和这些结果对整个海洋甲烷循环的影响。教育和外展工作都包括在内。对于教育部分，一名博士后、一名研究生和暑期本科生将参与该项目，而对于外展活动，倡导者计划为高中生开发基础科学和海洋学课程，在研究巡航中包括一名高中教师，并将成果整合到有机地球化学课程中，该课程的讲座将在网上公开。该项目旨在评估“海洋甲烷悖论”，即高硫酸盐、高含氧量地表水中甲烷过饱和的可能性，是由溶解有机物(DOM)的微生物循环引起的。已经有大量的初步证据支持这一理论。例如，用纯化的高分子量DOM(HMWDOM)多糖对来自ALOHA站的样品进行修饰，并刺激甲烷、乙烯和丙烯的产生。HMWDOM多糖含有甲基膦酸酯(MPN)、2-羟乙基膦酸酯(2-HEP)和其他次要的膦酸酯，它们可能有助于甲烷、乙烯和丙烯的产生。碳同位素数据支持这一理论是海相甲烷悖论背后的过程；富含HMWDOM多糖的样品产生的甲烷的d13C值与与过饱和地表水有关的异常值符合得很好。只有一小部分HMWDOM多糖可以很容易地解释海洋甲烷悖论，这个过程很容易完全改变目前对海洋和大气之间大规模甲烷循环的理解。研究人员将评估初步证据，并通过对痕量气体和HMWDOM磷酸盐进行配对，以及在北大西洋西部进行稳定的碳同位素测量，来评估微生物DOM循环理论。

The "marine methane paradox" refers to observations of high concentrations of methane in surface waters of the ocean, even though these waters are well-oxygenated and high in sulfate, both features which generally do not favor the production of methane. This project aims to elucidate on the cause of this paradox. Based on preliminary results, the investigator identified the potential for methane production stimulated by microbial cycling of dissolved organic matter. Polysaccharides (carbonates such as starch) are a major component of high molecular weight dissolved organic matter (HMWDOM) and they can incorporate esters of methylphosphonate, which may be allowing for the production of methane in surface waters. When these HMWDOM polysaccharides were introduced to seawater samples, the researchers saw production of methane with an anomalous stable carbon isotope ratio comparable to what is seen in the paradoxical surface waters enriched in methane. By making measurements of trace gases, HMWDOM phosphonate, and stable carbon isotope measurements in the western North Atlantic Ocean, the investigator and his collaborators will reassess the preliminary data and the implications of these results for the entire oceanographic cycling of methane. Both educational and outreach efforts have been included. For the educational component, a postdoc, a graduate student, and summer undergraduate students will be work on the project, whereas for the outreach activities, the proponent plans to develop curricula on basic science and oceanography for high school students, include a high school teacher in the research cruise, and integrate results into an organic geochemistry course, the lectures of which will be publically available online. This project seeks to evaluate the possibility that the "marine methane paradox", or the super-saturation of methane in high sulfate, well-oxygenated surface waters, is caused by microbial cycling of dissolved organic matter (DOM). There has been a great deal of preliminary evidence to support this theory. For example, samples from station ALOHA were amended with purified high molecular weight DOM (HMWDOM) polysaccharides, and methane, ethylene, and propylene productions were stimulated. HMWDOM polysaccharides incorporate esters of methylphosphonate (MPn), 2-hydroxyethylphosphonates (2-HEP), and other minor phosphonates, which are likely facilitating the production of methane, ethylene, and propylene. Carbon isotope data supports that this theory is the process behind the marine methane paradox; the d13C value of methane produced from HMWDOM polysaccharide enriched samples agrees well with the anomalous value associated with the super-saturated surface water. Only a small fraction of HMWDOM polysaccharides can easily explain the marine methane paradox, and this process could just as easily fully revise the current understanding of large scale methane cycling between the ocean and atmosphere. The researchers will assess the preliminary evidence and evaluate the microbial DOM cycling theory by making paired trace gas and HMWDOM phosphonate, as well as stable carbon isotope measurements in the western North Atlantic Ocean.