Spatial Patterns of Organic Sulfur and Its Limited Association With Bacterial Communities in the Bohai and Yellow Seas

While the importance of organic sulfur for marine bacteria is widely recognized, how it relates to bacterial community composition, particularly in coastal environments, remains poorly understood. In this study, we quantified dissolved organic sulfur (DOS) and particulate organic sulfur (POS) in the Bohai and Yellow Seas. DOS ranged from 1.7 to 6.8 μM in surface waters and 0.9–5.4 μM in bottom waters, while POS ranged from 0.3 to 1.7 μM in surface waters and 0.2–1.6 μM in bottom waters. In the Bohai Sea, particulate and dissolved C:S ratios averaged 57 ± 38 and 41.4 ± 7.5, respectively, with minimum sulfur inventories of 0.039 ± 0.025 (POS) and 0.300 ± 0.058 Tg S (DOS). In contrast, the Yellow Sea had a lower particulate C:S ratio (25 ± 17) but a comparable dissolved ratio (46.5 ± 12.5), alongside minimum inventories of 1.14 ± 0.69 (POS) and 1.91 ± 0.52 Tg S (DOS). In contrast to previously reported data from the open ocean, the Bohai and Yellow Seas are characterized by distinctly higher organic sulfur concentrations and lower molar C:S ratios. Bacterial communities differed significantly between surface and bottom waters in terms of diversity and network complexity. However, path analysis showed no significant association of organic sulfur with bacterial community composition in either layer. These findings suggest that despite high total organic sulfur concentrations in these coastal waters, its low concentration of bioavailable fractions and taxon‐specific utilization may explain its limited association with bacterial community.