Increasing Net Community Production in Western North Pacific Marginal Seas Due to Anthropogenic Nitrogen

Abstract Anthropogenic nitrogen emissions and deposition have substantially increased seawater nitrate concentrations in the western North Pacific. However, their influence on net community production (NCP)—a primary driver of organic carbon export from the euphotic zone—remains one of the least constrained components governing oceanic CO 2 uptake. Using over 190,000 nitrate observations, we reconstructed four decades (1980–2022) of warming period (wp) NCP in the western North Pacific marginal seas (25°N–45°N, 120°E−148°E) at 1° × 1° resolution, based on seasonal mixed‐layer nitrate drawdown and a C:N ratio of 7.3. Distinct increases in nitrate‐based NCP (N‐NCP) were observed in regions strongly influenced by anthropogenic nitrogen inputs. In the Yellow Sea, N‐NCP nearly tripled from 0.6 to 1.7 mol C m −2 wp −1 , with comparable increases downstream of the Changjiang River plume near the Ieodo Ocean Research Station (0.8–1.7 mol C m −2 wp −1 ) and in the East Sea off Korea (1.3–2.5 mol C m −2 wp −1 ), before stabilizing or declining after the mid‐2000s. These trends corresponded closely with changes in anthropogenic nitrogen loading. In contrast, no significant long‐term trends were detected in the open‐ocean East Sea near Oki Island (1.5 ± 0.3 mol C m −2 wp −1 ) or in the central and southern East China Sea (0.2 ± 0.1 mol C m −2 wp −1 ), highlighting the spatial heterogeneity of anthropogenic influence. Overall, the results confirm that anthropogenic nitrogen plays a regionally uneven role in regulating ocean carbon sequestration through NCP in the western North Pacific coastal and marginal seas.