Collaborative research: Hydrogen isotopic studies of marine dissolved and particulate organic matter

尽管经过几十年的研究，海洋颗粒物和溶解有机物（POM和DOM）的分子组成仍然不确定。详细的色谱分析能够识别多达80%的POM的组成分子从表面沃茨，但不到20%的POM从颗粒后，他们已经落入深海沃茨和沉积物。迄今为止，不同的分析方法也产生了不同的，有时不一致的结果，影响保存或下沉过程中的成分变化的因素。DOM的组成是更好的约束，但主要基于NMR的研究还没有被独立的方法进行测试。在这个项目中，来自加州理工学院和伊利诺伊大学的研究人员将把现有的氢同位素分析方法应用于海洋POM和DOM的研究，以帮助限制这些物质的生物化学组成。氢同位素分析将对这些物质的分子组成施加三种新的限制。脱矿质有机材料和所选生物化学组分中氢碳元素比（H/C）应允许区分新鲜生物分子（H/C 1.5）与来自沉积物和黑碳的油母质（H/C 1.0）。第二，有机氢在水中易于快速同位素交换的部分主要代表O-和N-结合的H，并且在氨基酸和碳水化合物中（30-50%）比在脂质和烃中（5%）高得多。第三，生物分子中不可交换的H（8Dn）的同位素组成在脂质（通常为约150%）、石油烃（约100%）以及氨基酸和碳水化合物（通常为约50%）之间显著不同。氢数据将通过一套辅助分析（如GCMS、热解-GCMS、SEM和有机硫定量）进行补充。将对来自不同地点的样品进行检查，如圣佩德罗盆地（加利福尼亚州沿海）、M站（太平洋东部深海）和世界各地的其他地点。样品将在为期5天的研究巡航中获得，以及通过合作和搭载其他巡航获得。这项研究将首次测量海洋浮游植物和异养细菌生化类之间的D/H分馏，并将研究伴随藻类生物量降解的分馏，这两者都可能对碳循环研究有用。PI将探索使用交换机配置文件（即，可交换氢的分数作为时间或温度的函数）来表征有机大分子中三级结构的紧密性和交联性，这一性质对生物化学家或聚合物化学家也应该是有用的。 研究人员还将开发更自动化和更灵敏的方法，用于使用元素分析仪技术测量Dn，这一成就将对基于有机D/H构建高分辨率古气候记录具有重要意义。该项目还将为两所主要研究型大学的本科生和研究生提供一系列教育机会。它将提供至少一个博士学位的基础。本课程将提供博士论文和两个本科生暑期实习机会，并将为高中志愿者提供化学海洋学介绍。

Despite decades of research, the molecular compositions of marine particulate and dissolved organic matter (POM and DOM) remain uncertain. Detailed chromatographic analyses are able to identify up to 80% of the constituent molecules in POM from surface waters, but less than 20% of POM from particles after they have fallen into abyssal waters and sediments. Different analytical methods have also thus far produced disparate, and sometimes incompatible, results concerning factors affecting preservation or compositional changes during sinking. The composition of DOM is better constrained, but the primarily NMR-based studies have not been tested by independent methods. In this project, researchers from California Institute of Technology and from University of Illinois will apply existing methods for hydrogen-isotopic analysis to the study of marine POM and DOM in order to help constrain the biochemical composition of these materials. Hydrogen-isotopic analyses will place three new kinds of constraints on the molecular composition of these materials. The elemental ratio of hydrogen to carbon (H/C) in demineralized organic materials and selected biochemical fractions should allow distinction of fresh biomolecules (H/C 1.5) versus kerogen derived from sediments and black carbon (H/C 1.0). Second, the fraction of organic H that is susceptible to rapid isotopic exchange in water represents primarily O- and N-bound H, and is much higher in amino acids and carbohydrates (30-50%) than in lipids and hydrocarbons (5%). Third, the isotopic composition of non-exchangeable H ( 8 Dn) in biomolecules differs substantially between lipids (typically Dn -150% ), petroleum hydrocarbons (~-100%), and amino acids and carbohydrates (typically -50%). The hydrogen data will be complemented by a suite of ancillary analyses such as GCMS, pyrolysis-GCMS, SEM, and quantification of organic sulfur. Samples will be examined from a variety of locations such as the San Pedro Basin (coastal CA), Station M (eastern abyssal Pacific), and other locations around the world. Samples will be acquired during a 5-day research cruise, as well as via collaborations and piggy-backing on other cruises. This research will measure, for the first time, D/H fractionations between biochemical classes in both marine phytoplankton and heterotrophic bacteria, and will examine fractionations accompanying the degradation of algal biomass, both potentially useful for carbon-cycle studies. The PIs will explore the use of exchangeability profiles (i.e., the fraction of exchangeable H as a function of time or temperature) to characterize the compactness and cross-linking of tertiary structure in organic macromolecules, a property that should also be useful to biochemists or polymer chemists.Among the broader impacts is the transfer of H-isotopic analytical methods to marine applications. The researchers will also develop more automated and sensitive methods for measuring Dn using elemental analyzer technology, an achievement that will have important benefits for constructing high-resolution paleoclimate records based on organic D/H. The project will also provide a range of educational opportunities for undergraduate and graduate students at two major research universities. It will provide the basis for at least one Ph.D. dissertation and two undergraduate summer internships, and will provide an introduction to chemical oceanography for a high school volunteer.