Collaborative Research: Planktonic Sources of Chromophoric Dissolved Organic Matter in Seawater

有色溶解有机物(CDOM)是海洋碳库中很小但很重要的一部分，它与太阳辐射相互作用，从而影响海洋中的许多光化学和生物过程。尽管海洋CDOM很重要，但其形成的化学基础仍不清楚。CDOM的形成可能有两种来源：1)初级生产力的异养细菌转化(浮游生物来源)，或2)陆源来源。该项目将通过利用一种强大的新技术来测量颗粒有机物的吸光度和荧光，对浮游CDOM的可能前体进行离散的化学测量，以及酶分析，来研究浮游植物作为海洋CDOM来源的作用。这一研究结果将为浮游CDOM的来源、产生以及异养细菌对其转化提供新的认识。这项关于CDOM的研究将通过北卡罗来纳州水族馆的一个模块广泛分享，并将船上活动的现场直播传输到小学教室。陆地和海洋溶解有机物(DOM)的化学成分不同。实验室和远洋观察表明，浮游植物DOM的细菌转化产生了类似腐殖质的CDOM信号，在视觉上与陆地CDOM中的信号相似。然而，以前对海洋CDOM的吸光度和荧光研究符合电子相互作用(EI)模型，即在腐殖质中发现的部分氧化的陆地分子中常见的供体和受体分子之间的分子内电荷转移(CT)反应。该项目将检验这样一个假设，即浮游植物和细菌提供了供体和受体的来源，这些供体和受体是通过微生物转化和连接的，使它们之间能够进行CT接触，并创建海洋CDOM。为了解决这个问题，研究人员将系统地研究浮游植物的生长，包括海洋积雪的形成。一种新的测量碱基提取的POM(BEPOM)吸光度和荧光的技术将被用于将浮游CDOM结果纳入EI模型，并补充其可能的化学前体的测量。这些实验将提高对海洋中CDOM的产生与浮游CDOM形成的光学和化学联系的理解。在相同的浮游植物生长实验中，确定异养细菌转化浮游植物POM和DOM的时间进程和程度，将有助于深入了解海洋中与雪有关的浮游有机物的细菌转化如何驱动整个海洋CDOM的产生。

Chromophoric dissolved organic matter (CDOM) is a small but important fraction of the marine carbon pool that interacts with solar radiation and thus affects many photochemical and biological processes in the ocean. Despite its importance, the chemical basis for the formation of oceanic CDOM remains unclear. CDOM may be formed from two possible sources: 1) heterotrophic bacterial transformations of primary productivity (plankton-derived), or 2) terrestrially-derived. This project will examine the role of phytoplankton as a source of CDOM in the ocean by utilizing a powerful, new technique to measure particulate organic matter absorbance and fluorescence, discrete chemical measurements of probable precursors to planktonic CDOM, and enzymatic assays. Results of this research will provide new insights into the origin and production of planktonic CDOM and its transformation by heterotrophic bacteria. This research on CDOM will be shared broadly through a module at a North Carolina Aquarium, and streaming live feeds of shipboard activities to elementary school classrooms.Terrestrial and oceanic dissolved organic matter (DOM) differ in their chemical composition. Laboratory and open-ocean observations suggest that bacterial transformation of phytoplankton DOM produces humic-like CDOM signals that are visually similar to those in terrestrial CDOM. However, prior studies of oceanic CDOM using absorbance and fluorescence fit an electronic interaction (EI) model of intramolecular charge transfer (CT) reactions between donor and acceptor molecules common to partially-oxidized terrestrial molecules found in humic substances. This project will test the hypothesis that phytoplankton and bacteria provide a source of donors and acceptors that are microbially-transformed and linked, enabling CT contacts between them and creating oceanic CDOM. To address this, researchers will systematically study phytoplankton growth, including marine snow formation. A new technique for measuring base-extracted POM (BEPOM) absorbance and fluorescence will be used to incorporate planktonic CDOM results into the EI model, and supplemented with measurements of its probable chemical precursors. These experiments will improve understanding of how the production of CDOM in the ocean is linked to the optics and chemistry of planktonic CDOM formation. Determining the time course and extent of phytoplankton POM and DOM transformation by heterotrophic bacteria during the same phytoplankton growth experiments will provide an in-depth understanding as to how bacterial transformation of marine snow-associated planktonic organic matter drives CDOM production throughout the ocean.