Interaction Between Organic Carbon Conversion and Microbial Metabolism in Marginal Seas Sediments During Hydrodynamic Sorting Processes

Hydrodynamic sorting processes control the transport of marine sediments in benthic environments of marginal seas, affecting the distribution of associated microbes and organic carbon (OC) composition in marine sediments. However, microbial characteristics variations and their impacts on OC stability during hydrodynamic sorting processes remain insufficiently understood. Here, we analyzed the concentrations and carbon isotopes of phospholipid fatty acids (PLFAs), and conducted the thermal stability analysis on OC in grain-size fractionated sediments retrieved along the classical transport pathway from the Yellow River delta to the Yellow Sea. We find that the relative abundance of anaerobic bacterial PLFAs has positive correlations with the proportion of pre-aged OC and negative correlations with the proportion of refractory OC compounds, and bioavailable OC become more limited along the transport pathway. We suggest that the decreasing refractory OC and the increasing pre-aged OC may facilitate the increasing abundance of anaerobic bacteria, and the metabolism of microbes can utilize the refractory OC during resuspension of marine sediments. The metabolism of microbes attached to resuspension sediments may produce by-products including pre-aged OC, which may promote the pre-aged OC burial in benthic environments, with important environmental implications such as carbon sequestration in marginal seas sediments.