Reductions of dry atmospheric inorganic nitrogen deposition and carbon uptake in the Yellow Sea of the Northwestern Pacific Ocean for the COVID-19 period.

Rapid population growth and industrialization in Northeast Asian countries have led to excessive atmospheric nitrogen (N) inputs into the Yellow Sea and the Northwestern Pacific Ocean. Given its location between China and the Korean Peninsula, the Yellow Sea is influenced by anthropogenic emissions from both regions and receives substantial N deposition, which may enhance primary productivity. We monitored dry inorganic N (nitrate; NO3- and ammonium; NH4+) deposition and analyzed the isotopic compositions of δ15N- and δ18O-NO3-, δ13C-total carbon (TC), and δ15N-total nitrogen (TN) in total suspended particle (TSP) samples collected before the COVID-19 (2018) and during the COVID-19 (2021-2022). Reduced human activities such as vehicle exhaust and coal combustion led to a decrease in dry inorganic N deposition from 2.6 mmol N m-2 month-1 in 2018 to 1.4 mmol N m-2 month-1 in 2021-2022. Based on the estimated conversion of deposited N to C, C uptake by phytoplankton in the Yellow Sea decreased by 21.2 to 34.0 Gg C month-1 during 2021-2022 compared to 2018. Our findings indicate that future reductions in N emissions and deposition may affect the ocean's capacity to absorb C.