Methane Oxidation Rates by AMS: Use of low-level 14C-CH4 and Accelerator Mass Spectrometry to Determine Rates of Water Column Aerobic and Anaerobic Methane Oxidation

我们对海洋甲烷地球化学的理解在很大程度上取决于对好氧和缺氧沃茨和沉积物中甲烷氧化速率的测量。相对较少的氧化率测量可用于海水，其中具有低甲烷浓度（~10 nM至10 uM）。由于14 C-CH 4的比活度，涉及添加这种示踪剂的速率测量需要在高于环境浓度的浓度下添加，并将在几个浓度下测量的速率外推回原位浓度。位于欧文的加州大学的一个研究小组正着手克服这些分析局限性。在这笔赠款的支持下，他们将利用加速器质谱法（AMS）的高灵敏度来测量甲烷氧化率，而甲烷池的大小只有很小的变化。这种方法还将示踪剂14 C-CH 4浓度的活性水平降低到接近免于涵盖放射性同位素的运输和处理的法规的水平。 他们希望在使用14 CCH 4确定甲烷氧化率方面取得两项进展：1）在Cariaco盆地进行甲烷氧化率的平行测量，涉及低水平14 C-CH 4和已建立的3 H-CH 4示踪技术，以及2）开发方法，允许在低于危险废物规定的放射性水平下使用14 C-CH 4。在今后的测量中使用这些低示踪剂活动将简化运输，放宽在配备同位素货车的大型船舶上进行放射性同位素示踪剂实验的要求，并应允许在偏远地点和时间序列测量中更广泛地应用这些测量。该项目将产生一些更广泛的影响。 这项研究将涉及一名研究生和一名本科生。高级首席研究员是积极作为太平洋海洋保护研究所的长滩水族馆的董事会成员。MCRI致力于在种族多元化的长滩社区开展外联和教育，这将有助于与社区团体和学生的接触。初级首席研究员和她的其他同事开发了一个短期课程，向年轻科学家介绍放射性碳在碳循环科学中的应用。该课程的目标是（1）教育一批新的年轻科学家了解全球碳（C）循环科学，（2）向他们介绍AMS放射性碳测量技术和放射性碳在C循环研究中的应用。

ABSTRACTOCE-0622759Our understanding of methane geochemistry in the ocean depends to a large extent on measurements of methane oxidation rates in oxic and anoxic waters and sediments. Relatively few oxidation rate measurements are available for seawater, which has low methane concentrations (~10 nM to 10 uM). Because of the specific activity of 14C-CH4, rate measurements involving addition of this tracer require additions at concentrations higher than ambient and extrapolation of rates measured at several concentrations back to in situ concentrations. A research team at the University of California at Irvine is setting out to overcome these analytical limitations. With support from this grant, they will exploit the high sensitivity of Accelerator Mass Spectrometry (AMS) to measure methane oxidation rates with only small changes in the CH4 pool size. This approach also lowers the activity level of tracer 14C-CH4 concentrations to levels that are close to being exempt from regulations covering transportation and handling of radioisotopes. They expect to make two advances in the use of 14CCH4 in determination of methane oxidation rates: 1) conducting parallel measurements of methane oxidation rate in the Cariaco Basin involving low-level 14C-CH4 and established 3H-CH4 tracer techniques, and 2) developing methods that will allow the use of 14C-CH4 at activity levels that are below those regulated as hazardous waste. The use of these low tracer activities in future measurements will simplify shipping, relax the requirement that radioisotope tracer experiments be performed on large ships with isotope vans, and should permit wider application of these measurements in remote locations and time series measurements. This project will have a number of broader impacts. The research will involve one graduate student one undergraduate student. The senior principal investigator is active as a board member of the Long Beach Aquarium of the Pacific's Marine Conservation Research Institute. MCRI's commitment to outreach and education in the ethnically-diverse Long Beach community should facilitate contact with community groups and students. The junior principal investigator and her other colleagues have developed a short course to introduce young scientists to the use of radiocarbon in carbon cycle science. The goals of the course are (1) to educate a new group of young scientists in the science of the global carbon (C) cycle and (2) to introduce them to the technology of AMS radiocarbon measurements and the applications of radiocarbon to C cycle studies.