Unintentional ocean fertilization by anthropogenic iron
co-emitted with sulfur dioxide from smelting facilities

1. Key Points

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Iron released with sulfur dioxide as fine particles into the atmosphere during smelting (anthropogenic iron *1) plays an important role in supplying dissolved iron (*2) to the Southern Ocean.

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Air pollution associated with mineral resource development causes health hazards and plays an important role in providing nutrients (dissolved iron) to the marine environment.

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The results of this study should contribute to future marine conservation measures and associated international joint research (GESAMP, *3).

2. Overview

Akinori Ito and Takuma Miyakawa, senior researchers from the Research Institute for Global Change (RIGC), Japan Agency for Marine–Earth Science and Technology (JAMSTEC), statistically analyzed observational data from multiple oceans along with atmospheric data from Fukue Island, Goto Islands, Nagasaki Prefecture. Using the Global Atmospheric Chemical Transport Model (*4), they were able to predict the anthropogenic supply of iron to the Southern Ocean. In particular, their results showed that anthropogenic iron released to the atmosphere with sulfur dioxide via smelting processes plays an important role in supplying dissolved iron to the Southern Ocean due to a lack of effective air pollution countermeasures.

Iron is an important nutrient for marine phytoplankton, with dissolved iron in atmospheric aerosols being the main source of this nutrient in iron-deficient oceans. Recently, the possibility that anthropogenic iron released into the atmosphere during the smelting of iron-bearing minerals has received attention as a possible source of dissolved iron at the global scale. The details of such release have remained unclear, and it has not been considered an important source of iron to the Southern Ocean, owing to the relatively clean atmosphere in this region. However, past observations show that the influx of anthropogenic iron-bearing aerosols to the Southern Ocean has been underestimated. In the study reported here, JAMSTEC scientists developed a numerical model and statistically analyzed predictions of the release of anthropogenic iron release in the Southern Ocean based on observation data. The results showed that numerical models that employed a low iron emission factor (*5) relative to mineral smelting in the Northern Hemisphere and a high iron emission factor in the Southern Hemisphere reproduced the observation data the best. This finding is consistent with the fact that aerosol emissions are already regulated in the Northern Hemisphere, while such regulations are limited for smelters in parts of the Southern Hemisphere. It was previously reported that the chemical properties of anthropogenic iron change during transport from the atmosphere to the ocean in the form of microparticles (aerosols), making them more water-soluble (Press Releases < JAMSTEC). This supports the analytical results presented here and highlights the importance of anthropogenic iron released by smelting as the source of dissolved iron in the Southern Ocean.

The results of the study reported here indicated that the emission of chemicals to the atmosphere in association with mineral resource development can cause health hazards while also providing nutrients to the marine environment. The study should contribute to future research on marine environmental conservation measures by GESAMP (*3). The results also suggest that improvements are needed to the interactions between Earth’s biogeochemistry and climate in the Earth System Model (*6), which considers the existing interactions between the atmosphere and marine environment.

This study was based on research supported by the JSPS KAKENHI 20H04329 and MEXT-Program for The Advanced Studies of Climate Change Projection (SENTAN) (*7) JPMXD0722681344, and was conducted as a part of an international joint study by GESAMP related to the scientific aspects of marine environmental conservation. The results were published in Environmental Science & Technology on March 1^st (JST).