The Yellow Sea, positioned between China and the Korean Peninsula, receives high atmospheric nitrogen (N) deposition driven by intense regional industrialization, which strongly impacts marine primary productivity. In this study, we investigated dry inorganic N deposition (NO₃^– and NH₄⁺) alongside isotopic signatures (δ¹⁵N- and δ¹⁸O-NO₃^–, δ¹³C-TC, and δ¹⁵N-TN) in total suspended particle (TSP) samples collected before (2018) and during the COVID-19 pandemic (2021–2022). Due to reduced human activities, including vehicle emissions and coal burning, dry inorganic N deposition declined sharply from 2.6 mmol N m^–2 month^–1 in 2018 to 1.4 mmol N m^–2 month^–1 in 2021–2022. Converting the deposited N into carbon uptake revealed that phytoplankton C uptake in the Yellow Sea dropped by 21.2–34.0 Gg C month^–1 during the pandemic period. These results demonstrate that future anthropogenic N emission controls could substantially influence the carbon sequestration capacity of the ocean.