Human activities such as industry and fossil fuel burning are likely contributing extra iron to some parts of the world’s oceans, according to a study published June 14 in Nature Communications.

Iron is an important nutrient for the growth of phytoplankton, tiny single-celled plants at the base of the ocean food chain. But iron is not very soluble in seawater and tends to be scarce in marine environments; the lack of this element limits phytoplankton growth in up to one-third of ocean waters worldwide.

These observations have led to proposals to “fertilize” the ocean with iron to stimulate phytoplankton growth. The idea is that the increased phytoplankton growth would remove some of the excess carbon dioxide we’ve released into the atmosphere, and thus help to mitigate climate change.