Collaborative Proposal: Biomarkers in Diatom Frustules: Development and Application of a New Compound-Specific Isotope Analysis Method to Understand the Present and Past Ocean

硅藻是一种微小的单细胞浮游植物，在有机模板上分泌二氧化硅壁，称为晶胞体。生长硅藻的结晶体及其有机模板记录了它们生长的环境条件。一旦结晶体下沉并成为沉积物，古海洋学家就可以利用它们的化学和同位素组成来研究过去的养分利用（15N/14N比）和生产力（13C/12C比），并确定沉积结晶体的放射性碳年龄。目前，在分析与沉积体相关的大块有机质的元素和同位素组成之前，沉积体是物理隔离和化学清洗的。不幸的是，通过这些流行方法得到的记录导致了对过去海洋环境的模糊重建。出于这个原因，华盛顿大学和俄勒冈州立大学的研究人员将开发几种新的、更可靠的方法来分析与硅藻体相关的有机物质的分子和同位素特征。具体来说，科学家团队将通过液相色谱联用质谱法来表征来自培养物、浮游生物拖曳和沉积物的硅藻体中的有机物。研究了在缺铁和补铁条件下，断口清洗和部分溶解对断口结合有机化合物和断口生物标志物的绝对相对丰度的影响。此外，研究小组还将纯化个体的挫折生物标志物。通过改进与硅藻体相关有机质的分子和同位素特征分析方法，提高全新世富硅藻样品的定年精度，合理评价岩心完整性，改进硅藻体中13C/12C、15N/14N和C/N比值的测定方法。至于更广泛的影响，这项工作不仅将为古海洋学开辟全新的途径，而且还将使人们更好地了解过去的气候条件和海洋生物地球化学循环对未来人为影响的反应。该项目还将支助和培训一名女研究生和一名或两名本科生。

ABSTRACTOCE-0525829OCE-0525968Diatoms are microscopic, single-celled phytoplankton, that secrete walls of silica, called frustules, on an organic template. The frustules of growing diatoms and their organic template record the environmental conditions in which they grow. Once frustules sink and become sediment, paleoceanographers are able to use their chemical and isotopic composition to study past nutrient utilization (15N/14N ratio) and productivity (13C/12C ratio), as well as determine the radiocarbon age of sedimentary frustules. Currently, sedimentary frustules are physically isolated and chemically cleaned prior to the analysis of the elemental and isotopic composition of bulk organic matter associated with the frustules. Unfortunately, the records that have been through these prevailing methods have lead to ambiguous reconstructions of past oceanographic environments. For this reason, researchers at the University of Washington and Oregon State University will develop several new, more reliable methods for analyzing the molecular and isotopic signatures of organic matter associated with diatom frustules. Specifically, the team of scientists will characterize the organic matter in diatoms frustules from cultures, plankton tows and sediments by using liquid chromatography coupled to mass spectrometry. The influence of frustule-cleaning and partial dissolution on frustule-bound organic compounds and the absolute relative abundance of biomarkers in frustules under iron limited and iron replete conditions will also be examined. In addition, the team of researchers will also purify individual frustule-bound biomarkers. By improving the methods for analyzing the molecular and isotopic signature of organic matter associated with diatom frustules, the dating of diatom-rich samples of Holocene age will be more accurate, the core integrity will be properly assessed, and the methods for measuring 13C/12C, 15N/14N and C/N ratios in diatom frustules will be improved. As regards broader impacts, the work will not only open up entirely new avenues in paleoceanography, but also lead to a better understanding of past climate conditions and the ocean's biogeochemical cycles response to future anthropogenic impacts. The project will also provide for the support and training of one female graduate student and one or two undergraduate students.