Enhanced Primary Production in the Oligotrophic South China Sea Related to Southeast Asian Forest Fires

• Published in: Journal of geophysical research. Oceans 2020-02, Vol.125 (2), p.n/a
• Main Authors: Xiao, Hong‐Wei, Luo, Li, Zhu, Ren‐Guo, Guo, Wei, Long, Ai‐Min, Wu, Jing‐Feng, Xiao, Hua‐Yun
• Format: Article
• Language: English
• Subjects: Biogeochemical cycle; Biogeochemical cycles; Biogeochemistry; Depolarization; Deposition; Ecological function; Ecosystems; Environmental changes; Fertilizers; Fires; Forest & brush fires; Forest ecosystems; Forest fires; Forests; Fossil fuels; Geographical distribution; Geophysics; Levels; Marine ecosystems; Mineral nutrients; Nitrogen; Nitrogen cycle; Nitrogen deposition; Nitrogen isotopes; Nutrients; Oceans; Primary production; Productivity; Rain; Rain water; Smoke; Time; Tropical climate; Tropical forests; Wet deposition
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2019JC015663

Atmospheric reactive nitrogen deposition is an important process in the nitrogen cycle of natural ecosystems, especially in oligotrophic oceans. Increased land‐based atmospheric nitrogen deposition over the ocean changes the stoichiometric balance of marine ecosystems; this causes changes in ecosystem functions and biogeochemical cycles. Current studies have shown that atmospheric reactive nitrogen is mainly derived from land‐based human activities, such as the use of fertilizers, combustion of fossil fuels, and forest fires. Forest fires can provide a vast amount of reactive nitrogen and other nutrients over short time scales and may greatly influence marine ecosystems. Here, we document a large change in nitrogen concentration and primary productivity in upper levels of the South China Sea (SCS), coincident with Indonesian forest fires between August and September of 2012. Using back trajectories, fire spot maps, geographical distributions of the smoke, vertical distributions of the depolarization ratio, and nitrogen isotope values of nitrate in rainwater, we found that the change in nitrogen could be attributed to the forest fires. Our results show that the SCS received about 180 Gg of N as wet deposition during the sampling period. This atmospheric nitrogen deposition caused high primary productivity (40.679 ± 15.852 mg C·m−2·hr−1) in the upper levels of the SCS, which tripled values recorded in other years. This suggests that high nitrogen levels as well as other nutrients derived from tropical Asian forest fires are of great importance to the marine ecosystem of the SCS and also likely affect global marine biogeochemical cycles. Plain Language Summary Atmospheric nitrogen deposition can stimulate primary productivity in nitrogen‐limited marine ecosystems. Tropical forest fires can provide a vast amount of reactive nitrogen and other nutrients over short time scales and may greatly influence marine ecosystems. We document a large change in nitrogen concentration and primary productivity in upper levels of the South China Sea, in which reactive nitrogen was mainly derived from Indonesian forest fires in summer 2012. This suggests that high nitrogen levels as well as other nutrients derived from tropical forest fires are of great importance to the global marine ecosystem. Key Points South China Sea received high N during fires Atmospheric nitrogen deposition from fire caused high primary productivity in the South China Sea