Early interglacial carbonate-dilution events increased terrigenous organic matter deposition in seamount sediments of the northern South China Sea since the last deglaciation

A thermal maximum in the West Pacific Warm Pool, with La Ni$\stackrel{\sim }{n}$a-like conditions prevailing during the early Holocene, triggered frequent and intensive typhoons affecting Taiwan Island. However, no studies have conclusively demonstrated whether fluvial inputs affected the deposition of terrigenous organic matter (OM) in deep-sea sediments during early interglacial carbonate-dilution events. This study measured dual carbon isotopes (δ¹³C and Δ¹⁴C) of total organic carbon (TOC) and organic compound classes in the seamount Core SCS18–1 to evaluate the influences of the carbonate-dilution events on OM deposition in the northern South China Sea (NSCS). The radiocarbon mass balance revealed greater percentages of terrigenous OM during the early interglacial carbonate-dilution events (30 ± 1 %), suggesting rapid transport of substantial amounts of terrigenous OM from Taiwan Island, driven by intensified typhoon activities. Among organic compound classes, total hydrolysable amino acids have gradually decreased in terrigenous contributions since the last deglaciation, due to the prolonged lateral transport time influenced by rising sea-level. Humic acids had the greatest terrigenous contribution during the carbonate-dilution events (27 %), indicating that they were sensitive to the carbonate-dilution events. Additionally, acid-base insoluble OM and lipids increased in terrigenous sources during the transgression phase, indicating the influences of sea-level rise and the carbonate-dilution events. These carbon isotopic results suggest that OM in seamounts provides reliable paleoclimatic information for deep-sea sediments, underscoring that the large number of seamounts may shed new light on the transport of terrigenous OM from land to ocean on a global scale.