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 δN values (expressed as δN = [N:N/N:N - 1] × 1000‰; the sediment N:N ratio relative to the air nitrogen N:N ratio). In contrast, the Arctic sediments from the Chukchi Sea, the sampling region furthest from China, showed higher δN values (2-3‰ higher than those representing the East China and the Yellow sea sediments). Across the sites sampled, the levels of sediment δN increased with increasing distance from China, which is broadly consistent with the decreasing influence of anthropogenic nitrogen (N) resulting from fossil fuel combustion and fertilizer use. We concluded that, of several processes, the input of N appears to be emerging as a new driver of change in the sediment δN value in marginal seas adjacent to China. The present results indicate that the effect of N has extended beyond the ocean water column into the deep sedimentary environment, presumably via biological assimilation of N followed by deposition. Further, the findings indicate that N 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.