Chao Huang a,b,c , Yin Yang a,b , Fajin Chen a,b,c,* , Deming Kong a,b,c , Jin Xu a,b , Chunqing Chen a,b , Qingmei Zhu a,b,c , Xin Huang a,b,c a Laboratory for Coastal Ocean Variation and Disaster Prediction, College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang, Guangdong 524088, China b Key Laboratory of Climate, Resources and Environment in Continental Shelf Sea and Deep Sea of Department of Education of Guangdong Province, Guangdong Ocean University, Zhanjiang 524088, China c Key Laboratory of Space Ocean Remote Sensing and Application, Ministry of Natural Resources, China

ABSTRACT

Coastal upwelling along the northern South China Sea controls regional marine productivity and thereby influences blue economies. However, centennial-scale upwelling variability and its associated forcing mechanisms are poorly understood, primarily due to the lack of high-resolution upwelling records beyond the instrumental and historical periods. Here we reconstruct monsoon-induced upwelling variations over the past 7000 years, based on a high-resolution (~30 yr) δ15N record from the upwelling zone off the east coast of Hainan Island. δ13C, δ15N, C/N, TOC and biogenic opal are determined to verify the dominant source of marine organic matter in the GH6 core, and δ15N values are used to indicate the variations in nitrate utilization by phytoplankton. The results show distinct centennial-scale variability, which is generally synchronous with solar activity, latitudinal shifts of the Intertropical Convergence Zone (ITCZ), and El Ni? no-Southern Oscillation (ENSO) frequency. We conclude that the centennial-scale upwelling intensity was predominately induced by external solar forcing, with internal feedback such as latitudinal shifts of the ITCZ and ENSO variability as a mediator amplifying the solar variation signal. Our new findings indicate that external forcing mechanisms exerted a significant influence on upwelling variations before the Anthropocene and should be considered when producing future projections of upwelling changes at low latitudes.