Deep carbon sink in the East Asian mantle and its impact on atmospheric CO2 drawdown since the Cretaceous

The western Pacific oceanic slab has been deeply subducted into the mantle beneath East Asia since the early Cretaceous, eventually stagnating within the mantle transition zone (410–660 km). Here we present the first quantitative estimate of the flux of deeply subducted carbon beneath East Asia related to the Pacific slab and evaluate its impact on atmospheric CO₂ levels (pCO₂) since the Cretaceous. We compiled chemical and zinc isotopic data for the widely distributed East Asian intercontinental basalts (EAIBs; N = 399), which originated from partial melting of the upper mantle above the stagnated western Pacific slab. By using a melt CO₂ degassing correction and a "melting-mixing" model, we show that the formation of EAIBs involved ubiquitous magma mixing between silicate melts and carbon-rich melts. Consequently, the mantle source of EAIBs is estimated to have an unexpectedly high carbon content (297 ± 118 μg/g; 1σ), about three times the average carbon in the convecting mantle (110 ± 40 μg/g), primarily due to subducting carbon input from the western Pacific slab. Based on paleogeographic reconstruction models, we show that two peak periods of subducting carbon influx into the mantle transition zone sparked the deep carbon sink beneath East Asia. There is a gap of approximately 26 Ma between peak carbon subduction and widespread EAIB eruptions. This gap suggests that deep carbon sink beneath East Asia, due to inefficient mantle carbon outgassing, may have significantly contributed to the drawdown of atmospheric pCO₂ since the Cretaceous.