Laminated diatom mats (LDMs) deposition, formed by the aggregation of giant diatoms (e.g., ), are recognized as a crucial driver of the global carbon and silicon cycles due to their substantial contribution to the flux of organic carbon and biogenic silica. The biogenic silica-rich sediment is one of the typical sediment types in the deep-sea setting of the tropical Pacific Ocean. Here, we analyzed the concentrations of pore-water dissolved organic carbon (DOC) and phosphate (PO), the optical properties, and molecular compositions of dissolved organic matter (DOM) in the two LDMs cores and one non-LDMs core retrieved from the southern Mariana Trench. Our results showed that the LDMs sediments with higher total organic carbon (TOC) contents have lower concentrations of DOC and chromophoric dissolved organic matter (CDOM), compared to the non-LDMs core. Meanwhile, the LDMs samples exhibited lower relative intensity of fluorescent proteins-like, molecular lability boundary (MLB%) and higher values for humification index (HIX) and aromaticity modification (AI) compared to the non-LDM core, indicating a higher level of stability and recalcitrance of DOM likely resulting from microbial degradation of relatively labile DOM compounds. Furthermore, the LDMs samples were characterized by a high abundance of CHO-containing DOM components and a low abundance of nitrogen- and sulfur-containing components, potentially linked to microbial degradation of hydrocarbon compounds that were enriched in the LDMs sediments. Additionally, the unique formulas in the LDMs samples demonstrated higher degree of recalcitrance suggested by higher aromaticity and fraction of CRAM, which may be attributed to microbial transformation of DOM. These findings add to our limited knowledge of the optical properties and molecular composition of DOM in the deep-sea opal-rich sediments, and have implications for understanding DOM cycling in the deep oceans.

中文翻译：

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探讨马里亚纳海沟南部层压硅藻垫中沉积溶解有机物的光学和分子特性

由巨型硅藻（例如）聚集形成的层压硅藻垫（LDM）沉积被认为是全球碳和硅循环的关键驱动因素，因为它们对有机碳和生物硅的通量做出了巨大贡献。生物富硅沉积物是热带太平洋深海沉积物的典型类型之一。在这里，我们分析了两个 LDMs 岩心和一个非 LDMs 岩心中孔隙水溶解有机碳 (DOC) 和磷酸盐 (PO) 的浓度、光学性质和溶解有机质 (DOM) 的分子组成。马里亚纳海沟南部。我们的结果表明，与非LDMs岩心相比，总有机碳（TOC）含量较高的LDMs沉积物的DOC和发色溶解有机物（CDOM）浓度较低。同时，与非 LDM 核心相比，LDM 样品表现出较低的类荧光蛋白相对强度、分子不稳定性边界 (MLB%) 以及较高的腐殖化指数 (HIX) 和芳香度修饰 (AI) 值，表明较高水平的DOM 的稳定性和顽抗性可能是由于相对不稳定的 DOM 化合物的微生物降解造成的。此外，LDMs 样品的特征是含有高丰度的 CHO DOM 成分和低丰度的含氮和硫成分，这可能与 LDMs 沉积物中富集的碳氢化合物的微生物降解有关。此外，LDM 样品中的独特配方表现出更高程度的不顺从性，这表明较高的芳香度和 CRAM 分数，这可能归因于 DOM 的微生物转化。这些发现增加了我们对深海富含蛋白石沉积物中 DOM 的光学性质和分子组成的有限了解，并且对于了解深海中 DOM 循环具有重要意义。