The marginal seas are important biologically dynamic places of the ocean, and the nitrogen cycle in these regions is closely related to ecological system. In the biggest marginal sea of western Pacific, South China Sea (SCS), the records of bulk sedimentary nitrogen isotope (δ¹⁵N_bulk) show different trends since last glacial-interglacial cycle, indicating complex environmental information. Here, we provide a δ¹⁵N_bulk record of an intermediate-depth core (KT-1, 16°54′N，110°11′E, 1329 m) from the SCS with stable sedimentation rates. Our record shows a relatively significant glacial-interglacial change, exhibiting higher values at 5.0-5.5‰ in the MIS 1 and MIS 3 and lower values at about 4.0-4.5‰ in the MIS 2. The terrestrial input of organic matter, constrained by TOC and TN contents, suggests a limited influence on the bulk organic materials. The higher TOC contents during the glacials than the interglacials could be a result of better preservation, probably due to lower oxygenation in the water column. The increase of δ¹⁵N_bulk from glacial to interglacial periods could be best explained by enhanced organic matter oxidation by better oxygenation of the intermediate waters in the SCS.
 

South China Sea,bulk sedimentary nitrogen isotope,glacial-interglacial cycle