Marine sinking particulate organic matter (POM), acting as a link between surface primary production and burial of organic matter in marine sediments, undergoes a variety of physical and biochemical alterations on its way to the deep ocean, resulting in an increase in its un-characterizable proportion with diagenesis. Further, the binding ligands in POM for iron, an essential nutrient to marine life and tightly coupled with organic matter, has rarely been studied. In the current study, we employed an approach combining sequential extraction with ultrahigh resolution mass spectrometry (ESI-FTICRMS), in order to explore and unravel the chemical characteristics of organic matter compounds relevant to marine particle flux within the mesopelagic and deep ocean, with a focus on the potential iron-carrying molecules. With increasing depth, POM increases in aliphaticity, and decreases in intensity-normalized O/C ratios, aromatics, and carboxylic-rich alicyclic molecules (CRAM)-like compounds. The potential iron-carrying molecules account for ∼14% of total identified molecules, and appear to have been incorporated into the marine particles via ion complexation, hydrophobic interaction, and/or interlayered “occlusion.” The relative abundance of iron-binding organic molecules in these three operationally-defined categories changes with depth: “surficially-complexed” fraction decreases with depth, the “interlayered-occluded” fraction increases to a comparable extent and “hydrophobic interaction” fraction occurs at all depths. Collectively, the potential iron-carrying organic molecules exhibit a set of unique molecular characteristics: a relatively lower average H/C ratio and a higher O/C ratio compared to bulk POM, a dominance of aromatics, black carbon-like compounds and CRAM-like compounds, and minor amounts of aliphatics. These molecules exhibit partial similar molecular features as precursors formed from photochemical reactions in the surface ocean, but they have been greatly modified by flux processes. Noticeably, a minor fraction of these iron-carrying molecules (<1%) was identified to contain hydroxamate-like moieties [N(OH)-COOH], the key functionality of one of the strongest iron-binding ligands in the dissolved phase. This agrees with improved spectrophotometric results and corroborates their presence in the POM. These hydroxamate-like moieties play an important role in controlling the distributions and fluxes of Fe and particle-reactive radionuclides with similar chemical complexing properties as Fe (e.g., thorium) in the ocean.

海洋下沉的颗粒有机物（POM），是海洋沉积物中地表初级生产与掩埋有机物之间的联系，在通往深海的过程中经历了各种物理和生化改变，导致其沉没度增加。具有成岩作用的可表征比例。此外，很少研究POM中铁的结合配体，铁是海洋生物的必需营养素并与有机物紧密结合。在当前的研究中，我们采用相继萃取与超高分辨率质谱（ESI-FTICRMS）相结合的方法，以探索和揭示与中古海洋和深海中与海洋颗粒通量有关的有机物化合物的化学特性，专注于潜在的载铁分子。随着深度的增加，POM的脂肪族含量增加，强度归一化的O / C比，芳族化合物和富含羧基的脂环族分子（CRAM）样化合物降低。潜在的载铁分子约占已鉴定分子总数的14％，并且似乎已通过离子络合，疏水相互作用和/或层间“阻塞”被掺入海洋颗粒中。在这三个操作定义的类别中，与铁结合的有机分子的相对丰度随深度而变化：“表面复杂”的分数随深度而降低，“层间封闭”的分数以相当的程度增加，而“疏水相互作用”的分数在深度处发生。所有深度。总的来说，潜在的载铁有机分子表现出一系列独特的分子特征：与本体POM相比，平均H / C比相对较低，O / C比较高，芳族化合物，类炭黑化合物和CRAM类化合物占主导地位，脂族化合物含量较低。这些分子与由海洋表面光化学反应形成的前体表现出部分相似的分子特征，但通过助熔剂工艺对其进行了很大的修饰。值得注意的是，这些载铁分子中的一小部分（<1％）被鉴定为含有异羟肟酸酯样部分[N（OH）-COOH]，这是溶解相中最强的铁结合配体之一的关键功能。这与改进的分光光度结果相符，并证实了它们在POM中的存在。