Loads and ages of carbon from the five largest rivers in South Korea under Asian monsoon climates

•The C yield of the 5 river basins in S. Korea was about twice the global mean C yield.•DIC accounted for ~80% of the total riverine carbon loads.•34–45% for DIC, 37–50% for DOC, and 33–47% for POC were exported in summer monsoon.•Modern to old (up to 1020 ybp) carbon was released from the five river basins.•The Δ14CDIC, Δ14CDOC, and Δ14CPOC were the most enriched during the summer.