Relationship between magnetic susceptibility and grain size of sediments in the China Seas and its implications

Although magnetic susceptibility (MS) of sediments is widely used as an indicator in paleoclimate reconstructions, its significance is unclear in short-term environmental change in muddy sediments on the continental shelves of the Yellow Sea and the East China Sea. In the present study, we found positive and negative correlations between MS and the median grain size (MZ) of fine sediments near the Yangtze estuary and in the North Yellow Sea, respectively. These distinct relationships between MS and MZ depend on sources of materials thus can be used to study changes in material sources of sediments in the South Yellow Sea. According to these relationships, the positive correlation between MS and MZ in the central South Yellow Sea Mud before 1920 AD revealed the impact of materials from the Yangtze River; and the negative correlation after 1920 AD could be attributed to the changes of location of the Yangtze trunk stream to the sea. The inference of the geological change around 1920 AD was also supported by the abrupt change in trends of TOC/TN ratio.