Increased Heavily Silicified Diatoms Modulate the Biogenic Silica Deposition in the Yellow Sea

Diatoms are the most important organisms driving the marine biogenic silica (bSi) cycle, but their biomass and species composition have undergone substantial changes in the modern ocean. How their variations affect the marine bSi cycling remains unclear. Here, we estimated the seasonal relationship between diatom assemblages and bSi content, using the data from the sediment trap, in situ observations, and surface sediments in the Yellow Sea. Monthly sediment trap data revealed a significantly positive correlation between the proportion of heavily silicified diatom Paralia sulcata and bSi content, indicating the contribution of diatom silicification to bSi production. Seasonal observations revealed higher bSi content and burial efficiency in summer (1.13 ± 0.38%, 57.4 ± 25.7%) than in spring (0.86 ± 0.17%, 25.3 ± 5.2%), although spring diatom concentrations are 1.5 to 2 times higher. In contrast to spring hydrodynamic conditions, which can enhance the vertical mixing and favor bSi recycling, summer stratification constrains abundant P. sulcata and other diatoms living below the mixed layer. This not only promotes bSi production but also facilitates their deposition and burial in sediments. The results provide important insights into the effects of diatom species shifts on bSi cycling and indicate that the seasonal dominance of heavily silicified species in the diatom community, associated with hydrodynamic sedimentary conditions, could greatly affect the bSi cycling in the modern ocean.