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Understanding the distribution and relevant controlling factors of organic carbon in the ocean is of great significance to study the global carbon cycle and tackle climate change. Here, surface sediment samples were collected from the Bohai Sea and the Yellow Sea. For illustrating the source composition, distribution pattern, and their constraints, material characterization such as specific surface area, total organic carbon, nitrogen, sulfur contents and their isotopes (TOC, TN, TS, S2‒, δ13C, δ15N, and δ34S), as well as pigment biomarkers and thermos-gravimetric analysis were conducted. The results showed that the TOC and TN contents were lower in the nearshore but higher in the offshore region due to stronger hydrodynamics nearshore. The specific surface area had significant impacts on the distribution of organic carbon. The sediments contain a mixture of organic carbon from land plants, soil, and marine algae. Three-endmember mixing model suggested that sediments near the Huanghe River mouth and the shallower region along the Liaodong Peninsula in the Bohai Sea were dominated by soil-derived organic carbon with a smaller carbon reactivity index, while marine phytoplankton contributed mostly to the southern Yellow Sea with increasing carbon reactivity index. Significant correlation between TOC and TS in the Bohai Sea and northern Yellow Sea indicated significant linkages between organic carbon degradation and sulfate reduction. The negative δ34S indicated the process of sulfate reduction-sulfide oxidation-seawater sulfate diffusion at the sediment-water interface, which hinted the oxidation of organic carbon from oxic to anoxic condition. Pigment degradation potentially resulted in its weak correlation with the TOC content. As the risk of harmful algal bloom and hypoxia is becoming more severe, it is essential to monitor the coupling relationship of water chemistry and elemental cycling in the sediment to comprehensively understand the role of the continental shelf on organic carbon burial.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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