Discrimination of Hydrate and Diagenetic Methane Inputs to the Ocean with Measurements of Natural 14CH4

甲烷包合物水合物是目前全球甲烷收支中的一个主要未知数。对全球甲烷水合物储量的独立估计表明，它含有1019克甲烷，相当于地球大气甲烷储量的2000倍，约为海洋DIC储量的30%。黑海水柱甲烷浓度、氧化速率和稳定同位素分布表明，黑海甲烷周转迅速（~20 y），黑海沉积物中已知水合物是重要的水柱甲烷源。黑海的有限环流允许将其作为生物地球化学桶来整合甲烷输入并获得基础水合物解离率的估计。在这个项目中，加州大学欧文分校的研究人员将尝试测量天然14CH4，以区分水合物（放射性碳死亡）甲烷和成岩产生的（现代或有限时代）甲烷，增加我们对水合物解离的理解，以及基础水合物分解对全球甲烷预算的重要性。他们将使用Cariaco盆地作为无水合物的比较环境，以提供一种了解黑海多种甲烷来源的方法，并将在那里进行d13C-CH4， d2H-CH4和14CH4的平行测量。通过稳定同位素和14CH4测量对黑海各个喷口以及北美西海岸和墨西哥湾的喷口进行表征。最后，他们将测量北太平洋东部热带水域的14CH4，以验证该地区存在的甲烷最大值的较深区域可能是陆架渗漏和喷口输入的结果。研究人员已经开发的低空白、低背景的方法将允许在低至2nM的甲烷浓度下，在100升海水中测量14CH4。更广泛的影响：甲烷水合物作为一种可能的未来能源正在被认真考虑之中。重要的是要有一个像14CH4这样的特定的、容易理解的示踪剂来评估天然水合物通量的变化，以及评估与商业开发相关的潜在损失。这个项目将涉及一名研究生和一名本科生。

ABSTRACTOCE-0327776Methane clathrate hydrates are a major unknown in the present global methane budget. Independent estimates of the global methane hydrate reservoir size indicate that it contains 1019 g of methane, equivalent to 2000-times the Earth's atmospheric methane reservoir, or about 30% of the ocean DIC reservoir. Methane concentration, oxidation rate, and stable isotope distributions in the Black Sea water column indicate that methane turnover in the Black Sea is rapid (~20 y) and that hydrates, which are known to be present in Black Sea sediments, are an important water column methane source. Restricted circulation in the Black Sea allows using it as a biogeochemical bucket to integrate methane inputs and to obtain an estimate of the basal hydrate dissociation rate.In this project, researchers at the University of California - Irvine will attempt measurements of natural 14CH4 to discriminate between hydrate (radiocarbon-dead) methane and diagenetically-produced (modern or finite age) methane, increasing our understanding of the dissociation of hydrates and the importance of basal hydrate decomposition to the global methane budget. They will use the Cariaco Basin as a hydrate-free comparison environment to provide a means of understanding the multiple methane sources in the Black Sea and will undertake parallel measurements of d13C-CH4, d2H-CH4, and 14CH4 there. Vent inputs will be characterized with stable isotope and 14CH4 measurements on individual Black Sea vents as well as vents from the western coast of North America and the Gulf of Mexico. Finally, they will measure 14CH4 in waters in the Eastern Tropical North Pacific to test the suggestion that the deeper zone of the methane maximum present in this region may result from shelf seep and vent inputs. The low-blank, low-background method already developed by the investigators will permit measurement of 14CH4 in as little as 100 liters of seawater with a methane concentration as low as 2nM. Broader Impacts: Methane hydrates are under serious consideration as a possible future energy source. It is important to have a specific, well-understood tracer like 14CH4 to assess changes in natural hydrate fluxes as well as to assess potential losses associated with commercial development. This project will involve one graduate student and an undergraduate.