Taiwan uplift drove the organic carbon sink in the northern South China Sea since the late Pliocene

Petrogenic organic carbon (OCpetro), a critical geological reservoir, plays a vital role in long-term carbon cycling and global climate dynamics. Active orogenic regions serve as hotspots of OCpetro oxidation because of high bedrock denudation rates and substantial OCpetro reserves within the crust. However, limited data and proxies have hindered a comprehensive understanding of the temporal evolution of OCpetro oxidation during orogeny. We semi-quantified the OCpetro oxidation intensity and flux in Taiwan, an active orogen in East Asia, since the late Miocene. Raman spectroscopy and organic carbon-nitrogen (including δ13C and ratio of C/N) were employed to analyze OCpetro in abyssal sediment deposited in the northern South China Sea. The OCpetro oxidation intensity was higher than 50% before 3 Ma, while it sharply declined from ∼50% to ∼20% over the past 3 m.y. Conversely, the OCpetro oxidation flux rose from 0.12 ± 0.03−0.19 ± 0.04 Mt/yr before 3 Ma to 0.23 ± 0.04−0.35 ± 0.07 Mt/yr after 3 Ma. The accelerated uplift of the Taiwan orogen increased erosion rates, which shortened the residence time of OCpetro in the weathering zone and increased the supply of OCpetro for oxidation. As a result, the OCpetro oxidation pattern in Taiwan transitioned from “less supply with high oxidation intensity” to “more supply with low oxidation intensity.” Combined with the flux of the biosphere-immobilized OC, Taiwan transformed from an OC source to a sink during the orogeny. Our study highlights the significant influence of orogenic activity on the preservation and oxidation of OC.