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

尽管经过数十年的研究，海洋颗粒和溶解有机物（POM和DOM）的分子组成仍然不确定。详细的色谱分析能够识别来自地表水的POM中高达80%的组成分子，但在颗粒落入深海水和沉积物后，不到20%的POM。到目前为止，不同的分析方法也产生了不同的，有时是不相容的，关于影响保存或下沉过程中成分变化的因素的结果。DOM的组成受到了更好的约束，但主要基于核磁共振的研究尚未通过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应用现有的氢同位素分析方法来研究海洋POM和DOM，以帮助限制这些材料的生化组成。氢同位素分析将对这些材料的分子组成提出三种新的限制。脱矿有机材料和选定的生化组分中的氢碳元素比（H/C）应该能够区分新鲜生物分子（H/C 1.5）与来自沉积物和黑碳的干酪根（H/C 1.0）。其次，水中易受快速同位素交换影响的有机氢主要是O-和n -结合的氢，在氨基酸和碳水化合物中的比例（30-50%）远高于在脂质和碳氢化合物中的比例（5%）。第三，生物分子中非交换性氢（8dn）的同位素组成在脂类（通常为-150%）、石油烃（~-100%）、氨基酸和碳水化合物（通常为-50%）之间存在很大差异。氢数据将由一套辅助分析补充，如GCMS，热解-GCMS， SEM和有机硫定量。将从圣佩德罗盆地（加利福尼亚海岸）、M站（东部深海太平洋）和世界各地的其他地点检查样品。样品将在为期5天的研究巡航期间获得，以及通过合作和其他巡航的支持。这项研究将首次测量海洋浮游植物和异养细菌生物化学类别之间的D/H分异，并将检查伴随藻类生物量降解的分异，这两者都可能对碳循环研究有用。pi将探索使用可交换性剖面（即，可交换H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，这一特性对生物化学家或聚合物化学家也很有用。更广泛的影响之一是氢同位素分析方法向海洋应用的转移。研究人员还将开发更自动化和更灵敏的方法来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。它将为至少一篇博士论文和两个本科生暑期实习提供基础，并将为一名高中志愿者提供化学海洋学的介绍。

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.