A 3200‐year weathering record of the Mekong River basin by sediments from the South China Sea

The Mekong River is a mega‐river in East and Southeast Asia, and precipitation in its watershed influences more than 300 million people. However, the controlling factor in precipitation and weathering in the basin remains controversial. Here we present a high‐resolution record of weathering of the Mekong River basin over the past 3200 years by magnesium isotopes (δ 26 Mg) of silicate components in a sediment core from an area off the Vietnam coast in the western South China Sea. The results show that the δ 26 Mg values of silicates in marine sediments range from −0.40 to 0.036‰, and display evident change patterns. Our data support a theory that weathering in the Mekong River basin is controlled by three monsoon systems including the East Asian summer monsoon (EASM), the Indian summer monsoon (ISM), and the Western North Pacific summer monsoon (WNPSM), but the ISM may have played a more important role in the past century.