Atmospheric nitrate (NO₃⁻​) plays a crucial role in marine biogeochemical cycles, yet its sources and the extent of their contributions vary significantly across different oceanic regions. This study investigates the isotopic composition (δ¹⁵N−NO₃⁻​) and the source apportionment of nitrate across six distinct oceanic regions: the Bohai Sea & Yellow Sea, East China Sea, northern South China Sea, northwest Pacific Ocean, west Pacific Ocean, and Indian Ocean.

The results reveal significant spatial heterogeneity in the sources of nitrate, driven by regional atmospheric transport and local anthropogenic activities. Pie charts for each region illustrate the relative contributions of various sources, including industry, power generation, residential emissions, road traffic, shipping, biomass burning, soil-derived nitrate, and natural sources such as lightning. For instance, in the Bohai Sea and Yellow Sea, industrial and power generation activities dominate the nitrate sources, accounting for 34.5% and 16.4%, respectively, whereas shipping emissions are prominent in the northwest Pacific Ocean, contributing up to 70.5%. The Indian Ocean, on the other hand, shows a more balanced contribution from various sources, with biomass burning and shipping playing notable roles.

These findings underscore the influence of human activities on nitrate deposition in coastal and open ocean regions and highlight the importance of regional policy measures to mitigate atmospheric pollution. The spatial variability also reflects the influence of atmospheric transport patterns and the proximity of emission sources to marine environments. Understanding these spatial patterns is essential for predicting the environmental impact of nitrate deposition and its role in oceanic nutrient cycles.