Human-made iron intake five times higher than estimated

Iron is released by burning biomass as well as fossil fuel combustion into the atmosphere and then transported to oceans. Credit: Reiko Matsushita

In addition to controlling CO2 emissions, land and ocean storage is also a factor in determining how rapidly the gas may be removed from the atmosphere. In order for marine ecosystems to produce chemical energy through photosynthesis, the micronutrient iron is essential (known as iron fertilization). CO2 is converted to O2 and organic molecules in this process.

Most scientists believe that natural processes are the primary source of iron entering the ocean from the atmosphere. Human-made iron contributes far more to the Southern Ocean than previously assumed, according to a study published in npj Climate and Atmospheric Science, which was headed by Nagoya University’s Graduate School of Environmental Studies, together with Cornell and Colorado universities. It’s possible that it’s five times as high. In the future, this could have an impact on environmental management.

Due to fossil fuel combustion, the majority of human-made iron can be found in the atmosphere and then carried to remote ocean areas. Scientists used an improved global atmospheric model in conjunction with data from aeroplane measurements to better understand how human activities affect iron concentrations.

There is evidence to suggest that the Southern Ocean region’s iron supply is being boosted significantly by human-made iron (up to 60%). Contrary to earlier research which predicted that just 10% of iron came from human-made iron, the proportion of human-made sources has now been found to be significantly higher.

Iron supply to oceans in this region is predicted to diminish dramatically, which could have unanticipated repercussions for the future climate. Phytoplankton photosynthesis may decline as a result of a drop in iron in the atmosphere, resulting in a decrease in marine CO2 uptake. Global warming has been linked to rising amounts of carbon dioxide (CO2) in the atmosphere.

To sustain ocean phytoplankton growth and primary production in the Southern Ocean, Dr. Matsui stated, iron is a critical micronutrient. It adjusts atmospheric CO2 levels. In the next decades, tighter limitations on global fossil fuel emissions could reduce iron availability, which could limit marine ecosystems’ ability to store carbon and worsen global warming.

Achieving global carbon neutrality by lowering fossil fuel consumption in the next few decades would have a significant impact on human-made emissions. As the atmosphere warms, this could have an effect on the global climate. The importance of human-made sources in iron fertilisation in the Southern Ocean must be taken into account in future models.

Further information: Mingxu Liu et al, The underappreciated role of anthropogenic sources in atmospheric soluble iron flux to the Southern Ocean, npj Climate and Atmospheric Science (2022). DOI: 10.1038/s41612-022-00250-w

Source: Nagoya University