Organic matter in marine sediment is mainly categorized into three fractions depending on degradability: labile, semi labile and refractory. The degradability of coastal marine sediments depends on the properties of the organic matter contained in the sediments. The purpose of this study was to quantify labile and refractory organic matter in coastal marine sediments with different characteristics collected from the Seto Inland Sea, and to discover the factors controlling the degradability of organic matter. Refractory organic matter content in sediments ranged from 4.7–21.4 mg g⁻¹, a percent composition equivalent to 72–97% of TOC. In contrast, labile and semi-labile content were 0.1–1.4 mg g⁻¹ and 0.1–2.3 mg g⁻¹, respectively, a percent composition equivalent to 0.5–12.9% and 1.8–17.1% of TOC, respectively. Approximately 93% of refractory organic matter was categorized into humin. Organic matter originated from marine phytoplankton settled on the surface of sediments and changed to humin or a refractory organic matter. This study contributes to a better understanding of the organic matter degradation characteristics of coastal marine sediments and provides important parameters for estimating carbon budget and carbon cycling in coastal sea systems.

根据可降解性，海洋沉积物中的有机物主要分为三个部分：不稳定，半不稳定和耐火的。沿海海洋沉积物的可降解性取决于沉积物中所含有机物的性质。这项研究的目的是量化从濑户内海收集的具有不同特征的沿海海洋沉积物中的不稳定和难处理的有机物，并发现控制有机物可降解性的因素。沉积物中难熔有机物含量为4.7–21.4 mg g ^-1，其百分含量相当于TOC的72–97％。相反，不稳定和半不稳定含量分别为0.1–1.4 mg g ^-1和0.1–2.3 mg g ^-1分别占总有机碳的0.5-12.9％和1.8-17.1％的百分比组成。约93％的难熔有机物被归类为腐殖质。源自海洋浮游植物的有机物沉积在沉积物表面，然后变为腐殖质或难处理的有机物。这项研究有助于更好地了解沿海海洋沉积物的有机物降解特性，并为估算沿海海洋系统的碳收支和碳循环提供重要参数。