Widespread Anthropogenic Nitrogen in Northwestern Pacific Ocean Sediment

Sediment samples from the East China and Yellow seas collected adjacent to continental China were found to have lower δ¹⁵N values (expressed as δ¹⁵N = [¹⁵N:¹⁴N_sample/¹⁵N:¹⁴N_air - 1] × 1000‰; the sediment ¹⁵N:¹⁴N ratio relative to the air nitrogen ¹⁵N:¹⁴N ratio). In contrast, the Arctic sediments from the Chukchi Sea, the sampling region furthest from China, showed higher δ¹⁵N values (2-3‰ higher than those representing the East China and the Yellow sea sediments). Across the sites sampled, the levels of sediment δ¹⁵N increased with increasing distance from China, which is broadly consistent with the decreasing influence of anthropogenic nitrogen (N^ANTH) resulting from fossil fuel combustion and fertilizer use. We concluded that, of several processes, the input of N^ANTH appears to be emerging as a new driver of change in the sediment δ¹⁵N value in marginal seas adjacent to China. The present results indicate that the effect of N^ANTH has extended beyond the ocean water column into the deep sedimentary environment, presumably via biological assimilation of N^ANTH followed by deposition. Further, the findings indicate that N^ANTH is taking over from the conventional paradigm of nitrate flux from nitrate-rich deep water as the primary driver of biological export production in this region of the Pacific Ocean.