Centennial-scale evolution of organic carbon sources and burial in the northern coastal mud area of the Shandong Peninsula and its response to human activities

The mud area off the northern Shandong Peninsula is a critical region for sediment and organic carbon (OC) burial in the Yellow Sea. Based on a sediment borehole with 210Pb-derived sedimentation rate of 0.63 cm/a, multiple proxy parameters including grain size, total organic carbon (TOC), total nitrogen (TN), stable carbon isotope (δ13C), and nitrogen isotope (δ15N) were analyzed to reconstruct centennial-scale OC sources and burial. Results show that the sediments are dominated by clayey silt, with stable grain-size composition over the past century. OC is derived from mixed marine and terrestrial sources, with marine phytoplankton contributing 56.3% on average. TOC content ranges from 0.31% to 0,41%, showing an increasing trend since 1950, with δ¹5N rising from 4.35‰ to 5.41‰, indicating enhanced marine productivity driven by increased nutrient inputs and mariculture. Terrestrial OC contribution decreased from 52.6% to 34.7%, largely due to dam construction on the Yellow River, followed by a slight recovery in recent decades. Compared to the central South Yellow Sea, our study area exhibits lower OC accumulation rates but stronger sensitivity to human activities due to its proximity to the Yellow River source. This study provides scientific evidence for coastal carbon sink assessment under Anthropocene pressures.