Abstract The changes in the structure of XAD-8 isolated dissolved organic matter (DOM) samples along a river (Penobscot River) to estuary (Penobscot Bay) to ocean (across the Gulf of Maine) transect and from the Pacific Ocean were investigated using selective and two dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy coupled with elemental and carbon isotope analysis. The results provide important insights into the nature of relatively stable structures in the river-to-ocean continuum and the enigma of the fate of terrestrial DOM in the marine system. First, lignin and carboxyl-rich alicyclic molecules (CRAMs), which are indistinguishable from mass spectrometry, were clearly differentiated with NMR spectroscopy. NMR unambiguously showed that CRAMs persisted along the river-to-ocean transect and in the Pacific Ocean, while lignin residues dramatically decreased in abundance from the river to the coastal ocean and the Pacific Ocean. The results challenge a previous conclusion that lignin-derived compounds are refractory and can accumulate in the coastal ocean. The loss of terrestrial plant-derived aromatic compounds such as lignin and tannin residues throughout the sequence of riverine, coastal, and open ocean DOM extracts could also partially explain the decreasing organic carbon recovery by XAD-8 isolation and the change in carbon stable isotope composition from riverine DOM (δ 13 C −27.6‰) to ocean DOM (δ 13 C −23.0‰) extracts. The observation, from advanced NMR, of similar CRAM molecules in XAD-8 isolated DOM samples from the Penobscot River to the Penobscot Bay and from the ocean refutes a previous conclusion that XAD-isolated DOM samples from seawater and river are distinctly different. The alicyclic structural features of CRAMs and their presence as the major structural units in DOM extracts from the Penobscot River to Gulf of Maine transect, together with the deduced old 14 C age of CRAMs in the ocean, imply that terrestrial CRAMs may persist on timescales long enough to be transported into the ocean.

中文翻译：

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河流有机物质大量输入海洋的证据

摘要 采用选择性方法研究了沿河流（佩诺布斯科特河）到河口（佩诺布斯科特湾）到海洋（跨越缅因湾）横断面和太平洋的 XAD-8 分离溶解有机物 (DOM) 样品的结构变化。和二维 (2D) 核磁共振 (NMR) 光谱结合元素和碳同位素分析。结果为了解河流到海洋连续体中相对稳定结构的性质以及海洋系统中陆地 DOM 命运之谜提供了重要见解。首先，与质谱法无法区分的木质素和富含羧基的脂环族分子 (CRAM) 与 NMR 光谱法有明显区别。核磁共振明确表明，CRAM 沿着河流到海洋的横断面和太平洋持续存在，而木质素残留量从河流到沿海海洋和太平洋的丰度急剧下降。结果挑战了先前的结论，即木质素衍生的化合物是耐火的，可以在沿海海洋中积累。在整个河流、沿海和公海 DOM 提取物序列中，陆生植物来源的芳香化合物（如木质素和单宁残留物）的损失也可以部分解释 XAD-8 分离导致的有机碳回收率下降和碳稳定同位素组成的变化从河流 DOM (δ 13 C −27.6‰) 到海洋 DOM (δ 13 C −23.0‰) 提取物。来自高级核磁共振的观察结果，来自佩诺布斯科特河到佩诺布斯科特湾和海洋的 XAD-8 分离的 DOM 样品中类似 CRAM 分子的分析反驳了先前的结论，即来自海水和河流的 XAD 分离的 DOM 样品明显不同。CRAM 的脂环结构特征及其作为从佩诺布斯科特河到缅因湾横断面的 DOM 提取物中的主要结构单元的存在，以及推断的海洋中 CRAM 的旧 14 C 年龄，意味着陆地 CRAM 可能在时间尺度上持续很长时间足以运入大海。