Impact of anthropogenic activities on global land oxygen flux.

Atmospheric oxygen (O₂) is one of the predominant features that enable Earth as a habitable planet for active and diverse biology. However, observations since the late 1980s indicate that O₂ content in the atmosphere is falling steadily at part-per-million level. Although a scientific consensus has emerged that the current decline is generally attributed to the combustion of fossil fuel, a quantitative assessment of the anthropogenic impact on the O₂ cycle on both global and regional scale is currently lacking. This paper quantifies the anthropogenic and biological O₂ flux over land and provides a quantitative and dynamic description of land O₂ budget under impacts of human activities on grid scale. It is found that total anthropogenic O₂ flux over land has risen from 35.6 Gt/yr in 2000 to 46.0 Gt/yr in 2013, while the compensation from land (11.5 Gt/yr averaged from 2000 to 2013) displays a faint increase during the same period. High anthropogenic fluxes mainly occur in Eastern Asia, India, North America and Europe caused by fossil fuel combustion and in Central Africa caused by wildfire. Due to strong heterotrophic soil respiration under higher temperature conditions, the positive O₂ flux in the tropics is not significant. Instead, boreal forest and Tibetan plateau become the most important sources of atmospheric O₂ in the Anthropocene. [ABSTRACT FROM AUTHOR]