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

Hong Wei Xiao, Li Luo, Ren Guo Zhu, Wei Guo, Ai Min Long, Jing Feng Wu, Hua Yun Xiao

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Abstract

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.

Original languageEnglish (US)
Article numbere2019JC015663
JournalJournal of Geophysical Research: Oceans
Volume125
Issue number2
DOIs
StatePublished - Feb 1 2020
Externally publishedYes

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ASJC Scopus subject areas

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology

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