Australia: The Land Where Time Began

A biography of the Australian continent 

Oxygen Decline Accelerated in the Tropical Pacific over the Past Decades by Aerosol Pollutants

Over the past several decades in the mid-depth of the tropical Pacific Ocean the dissolved oxygen concentration has declined (Stramma et al., 2008). The expansion of the oxygen minimum zone that has resulted has consequences for the ecosystem (Seibel, 2010) and biogeochemical cycles (Codispoti et al., 2001) of the region, though the causes of this decline are yet to be fully understood. In this paper Ito et al. have presented the results of their study of the combining of models of atmospheric chemistry, ocean circulation and biogeochemical cycling to test the hypothesis that over the Pacific Ocean the redistribution of oxygen in deeper waters was contributed to by atmospheric pollution. In the study Ito et al. simulated the atmospheric enhancement of soluble iron and deposition of fixed nitrogen that was enhanced by atmospheric pollution, as well as the impacts of this pollution on ocean productivity and biogeochemical cycling for the late 20^th century. The magnitude and large-scale pattern of the oxygen changes from the 1970s to the 1990s that are observed are reproduced by the model, the reinforcing effects of the pollution-enhanced deposition of iron and natural variability of the climate, are revealed by the sensitivity experiments. The effects of the aerosol deposition are largest in the mid-latitudes, though its effects on oceanic oxygen are most pronounced in the tropics, which have led to an increased regional productivity, respiration and oxygen depletion in the subsurface waters. It is suggested by these results that anthropogenic pollution can interact and amplify impacts that are climate driven on ocean biogeochemistry, even in remote ocean biomes.

Sources & Further reading

Ito, T., A. Nenes, M. S. Johnson, N. Meskhidze and C. Deutsch (2016). "Acceleration of oxygen decline in the tropical Pacific over the past decades by aerosol pollutants." Nature Geosci 9(6): 443-447.