Collaborative Research: Phlorotannins - An Important Source of Marine Chromophoric Dissolved Organic Matter?

有色溶解有机物(CDOM)是过滤后的水中吸收阳光的成分，在海洋和淡水生态系统的研究中非常重要，因为它可以用来追踪表层水的混合，作为碳循环和其他生物地球化学过程的替代品。尽管在过去几十年里，CDOM在海洋研究中的重要性已经得到了坚定的确立，但海洋中CDOM的来源和结构组成仍然不清楚，并继续是一个有争议的主题。马尾藻是一种褐藻，广泛分布于温带和亚热带海域，可能是马尾藻丰富的马尾藻海和墨西哥湾CDOM的重要来源。本项目将调查大型褐藻衍生化合物对海洋CDOM池的贡献。这项研究的结果将对海洋碳循环和海洋颜色的卫星遥感产生影响，以评估表层水团和生物地球化学过程的混合。该项目将为博士后学者提供教育机会，夏季本科生实习(通过当地NSF赞助的本科生研究经验(REU)计划)，以及为当地高中生提供研讨会和研究机会。海洋CDOM的来源仍然存在争议，全面了解其来源、分布和命运一直很困难。海洋CDOM，特别是“类腐殖质”成分，被认为来自陆地来源，主要是木质素。然而，最近的证据表明，大型褐藻产生的邻氯单宁的渗出可能对海洋CDOM池有重要贡献。邻单宁是一类多酚，只有在马尾藻等大型褐藻中才能发现并持续分泌，它强烈地吸收紫外线，在某些地理位置对海洋CDOM池的贡献可能被低估了。在部分氧化后，这些特定化合物的光吸收在可见光中延伸到更长的波长，产生类似于木质素的吸收光谱。这些邻苯二甲酸单宁及其转化产物吸收光线，这可能在一定程度上解释了在公开海洋环境中观察到的“类腐殖质”特征。本研究旨在表征马尾藻CDOM的光学性质和分子组成，包括其有氧氧化和光化学行为，并对马尾藻CDOM进行量化，以更好地估计其对马尾藻海和墨西哥湾CDOM池的可能贡献。

Chromophoric dissolved organic matter (CDOM), the sunlight absorbing components in filtered water, is important in the study of marine and freshwater ecosystems as it can be used to trace the mixing of surface waters, as a proxy for carbon cycles, and other biogeochemical processes. Although its importance in ocean studies has been firmly established over the last several decades, sources and structural composition of CDOM within the oceans remains unclear and continues to be a subject of debate. Sargassum, a brown alga, is widely distributed in temperate and subtropical marine waters and may be important source of CDOM to the Sargasso Sea and Gulf of Mexico where Sargassum is abundant. This project will investigate the contribution of macro brown algae-derived compounds to the marine CDOM pool. Results from this study will have implications for the marine carbon cycle and satellite remote sensing of ocean color to assess mixing of surface water masses and biogeochemical processes. The project will provide educational opportunities for a postdoctoral scholar, summertime undergraduate internships (through a local NSF-sponsored Research Experiences for Undergraduates (REU) program), and workshop and research opportunities for local high schools students.Sources of marine CDOM remain debatable and a comprehensive understanding of its origins, distribution and fate have been difficult. Marine CDOM, and in particular the "humic-like" component, have been suggested to originate from terrestrial sources, primarily lignins. However, recent evidence indicates that the exudation of phlorotannins produced by macro brown algae may contribute significantly to the marine CDOM pool. Phlorotannins, a class of polyphenols that are only found in, and continuously exuded by macro brown algae such as Sargassum, strongly absorb ultraviolet light and may have been underestimated in their contribution to the marine CDOM pool within certain geographic locales. Upon partial oxidation, light absorption by these specific compounds extends into longer wavelengths in the visible creating an absorption spectrum similar to that of lignin. These phlorotannins and their transformation products absorb light that might explain in part the "humic-like" signatures observed in open ocean environments. This study aims to characterize the optical properties and molecular composition of Sargassum-derived CDOM including its aerobic oxidation and photochemical behavior, as well as quantify Sargassum-derived CDOM to better estimate its possible contribution to the CDOM pool in the Sargasso Sea and Gulf of Mexico.