Late Holocene elemental and isotopic carbon and nitrogen records from the East China Sea inner shelf: Implications for monsoon and upwelling

 

Abstract

      The East China Sea (ECS) is characterized by a relatively high riverine martial input that is associated with East Asian monsoon systems. In this study, we investigated a 272 cm-long sediment core (THB-2) from the ECS inner shelf for the AMS 14C dating, grain size, total organic carbon (TOC), total nitrogen (TN), and stable carbon and nitrogen (δ13C and δ15N) isotopes to provide insights into previous changes in the monsoon-climate and the intensity of the coastal upwelling. A three end-member (riverine, deltaic, and marine) mixing model was applied to determine the temporal variations in sedimentary organic matter sources. The transport and burial of the Changjiang riverine organic carbon in the ECS inner shelf is strongly controlled by the combined effects of the monsoon-climate and human activities during the late Holocene. The sedimentary δ15N records of the THB-2 core are more complex and may be best explained by changes in the nutrient utilization in the coastal zone surface waters. The downcore variations of the marine organic matter-δ15N are closely related to the intensity of East Asian summer monsoon during the last 3.6 ka. The stronger East Asian summer monsoon likely favored the intensive coastal upwelling and additional Changjiang discharge during the 3.6–2.7 ka and 0.4–0 ka periods, which triggered the greater relative nitrate utilization in the coastal surface water.