Jeomshik Hwang

Introduction The biological carbon pump (BCP) is a suite of processes collectively leading to the net uptake of atmospheric CO2. It transfers dissolved inorganic carbon to organic carbon through photosynthesis by phytoplankton in the sunlit surface ocean at a rate of ~50 GtC/yr (Chavez et al., 2011; Johnson and Bif, 2021), and then delivers part of the produced particulate organic carbon (POC) into the ocean interior (Sigman and Boyle, 2000).

Introduction Oceans represent the second important natural source of the climatically important trace gas nitrous oxide (N2O), a compound that plays a pivotal role in the global greenhouse effect and atmospheric chemistry generally (Stocker et al., 2013). Observations and models estimate global oceanic N2O emissions of 2.5–4.2 Tg N yr–1, which is believed to contribute about 20% of the global N2O emissions (Buitenhuis et al., 2018; Tian et al., 2020; Yang et al., 2020).

The salinity ranged from 25.33 to 33.99 (avg. 29.79 ± 1.99) in the surface waters of the study region (Supplementary Table S1). The salinity distribution in the surface waters shows that the low-salinity (<31) water is widely distributed over the East China Sea (Fig. 1), due to the influence of CDW24. A patch of low-salinity water (<28) was observed in the southwestern region of Jeju Island, which seems to be detached from the Changjiang plume21,25.