Sedimentary organic matter (SOM) plays an important role in marine carbon and nitrogen cycling, but the sources, degradation states and fates of SOM are not well understood. In the present study, we determined the total organic carbon (TOC), total nitrogen (TN), stable carbon isotope (δ¹³C), and total hydrolysable amino acids (THAA) to elucidate the sources and degradation states of SOM in the South Yellow Sea (SYS) and the East China Sea (ECS). THAA concentrations ranged from 4.90 to 29.13 μmol/g, with a mean of 11.03 ± 5.06 μmol/g. The distribution pattern of THAA was similar to that of TOC (r = 0.782, P < 0.01) and TN (r = 0.865, P < 0.01), with higher THAA concentrations in the coastal areas. Based on the two end-member mixing model, the fraction of terrestrial organic matter (F_t) ranged from 12.11% to 51.34% (average: 30.17 ± 9.61%), with much higher variability at the nearshore stations compared to the offshore stations. The C/N ratios and the δ¹³C values showed the different distribution trend, and there was a negative correlation between them (r = −0.479, P < 0.05). Based on the C/N ratios and δ¹³C values, the SOM in the study area was a mixture of marine organic matter (OM) and soil-derived OM. In addition, our study showed that SOM was dominated by diatomaceous OM compared to carbonate-derived OM and that terrestrial inputs and primary production were the dominant factors controlling the distribution of OM in the study area. Carbon and nitrogen-normalized yields of THAA (THAA-C% and THAA-N%) showed that relatively fresh OM tended to occur in the coastal areas off the Shandong Peninsula. However, the generally low degradation index (DI) values revealed that all SOM in the study area had undergone significant degradation. Glycine increased in relative abundance as the SOM was degraded, while aromatic amino acids (Tyr and Phe) and neutral amino acids (Leu, Ile and Val) had consistently decreasing trends following SOM degradation.

沉积有机物（SOM）在海洋碳和氮循环中起着重要作用，但尚不清楚其来源，降解状态和命运。在本研究中，我们确定的总的有机碳（TOC），总氮（TN），稳定的碳同位素（δ ¹³ C），和总的可水解氨基酸（THAA）阐明SOM的源极和退化状态在南方黄海（SYS）和东海（ECS）。THAA浓度范围为4.90至29.13μmol/ g，平均值为11.03±5.06μmol/ g。THAA的分布模式与TOC（r = 0.782，P  <0.01）和TN（r = 0.865，P <0.01），沿海地区的THAA浓度较高。根据两个末端成员混合模型，陆地有机物的比例（F _t）为12.11％至51.34％（平均值：30.17±9.61％），与近海站相比，近岸站的变异性更高。的C / N比和δ ¹³ C值显示出不同的分布趋势，并有在它们之间的负相关（r = -0.479，P  <0.05）。基于C / N比和δ ¹³C值表示研究区域的SOM是海洋有机物（OM）和土壤来源的OM的混合物。此外，我们的研究表明，与碳酸盐衍生的OM相比，SOM以硅藻类OM为主，而地面投入和初级生产是控制OM在研究区域中分布的主要因素。THAA的碳和氮归一化产率（THAA-C％和THAA-N％）表明，相对较新鲜的OM倾向于在山东半岛以外的沿海地区发生。但是，一般较低的降解指数（DI）值表明，研究区域中的所有SOM都经历了明显的降解。随着SOM降解，甘氨酸的相对丰度增加，而SOM降解后，芳香族氨基酸（Tyr和Phe）和中性氨基酸（Leu，Ile和Val）一直呈下降趋势。