Air-sea CO2 exchange in the western Pacific influenced by monsoon and giant diatom (Ethmodiscus rex) blooms during the last deglaciation

The concentration of atmospheric CO₂ increased rapidly during the last deglaciation due to CO₂ outgassing from oceans. However, records of deglacial surface seawater pCO_2-sw are sparse, hindering our understanding of the process and mechanism of air-sea CO₂ exchange and its influence on glacial-interglacial climate change. Here we reconstructed surface seawater pCO_2-sw for the last deglacial period using carbon isotope composition (δ¹³C) of giant diatom (Ethmodiscus rex) frustules from deep-sea sedimentary core collected in the Philippine Sea, western Pacific. Results showed that air-sea CO₂ was fluctuating in the western Pacific during the last deglaciation. The gradients of air-sea CO₂ are dominated by monsoon and biological productivity. The enhanced East Asian winter Monsoon and shallow thermocline during late Heinrich Stadial 1 maintained equilibrium in the air-sea CO₂ exchange balance. During the Bølling period, enhanced East Asian Summer Monsoon has been observed to accelerate the dissolution of eolian-dust and promoted the growth of Ethmodiscus rex, which has been linked to increased primary productivity and, consequently, the uptake of atmospheric CO₂ in the western Pacific. During the Allerød period, continued enhancement of EASM allowed the Philippine Sea to act as a weak CO₂ source releasing CO₂ to the atmosphere. During the Younger Dryas period, as the EASM weaken and the EAWM strengthen, ΔpCO_2(sw-atm) decreased. Our findings highlight the tropical ocean’s role in deglacial air-sea CO₂ exchange and provide insights into the monsoonal and biological drivers of the processes.