Paolo Rossi Castelli 14 October 2021 5 min read

A surprising fact: fires ‘fertilise’ oceans

An international team has studied the effects of Australia’s bushfire seasons. Ash released into the air by burning trees becomes food for phytoplankton on the surface of the sea.

The extremely serious wildfires that devastated Australia in the summers of 2019 and 2020 caused huge environmental disasters and numerous casualties, but also had an unforeseen positive effect, at least in the Earth's southern hemisphere.

According to the Argo satellite and marine buoy system, the large quantities of particles released into the atmosphere by burning trees and other vegetation, which are very rich in iron and nitrogen, were carried by the winds and deposited over vast areas of ocean thousands of kilometres away ‘fertilising’ them, particularly the oceans between New Zealand and South America.

The arrival of this ash caused the proliferation of large quantities of phytoplankton (microscopic plants like cyanobacteria and several types of algae, which live on the surface of the water and are essential food for fish). “It was an abnormal bloom, on an unprecedented scale," wrote researchers from Duke University (USA) and other Australian and British institutions, who processed the data thanks to the Barcelona Supercomputing Center, in the scientific journal Nature.

This study, comments Duke University in a press release, is the first to definitively link a large-scale response by marine life to aerosol (micro-particle) fertilisation of substances produced by fire.

But that is not all: according to researchers, the phytoplankton may have absorbed almost all the carbon dioxide (about 95%) produced in excess by the fires and estimated at 715 million tonnes between November 2019 and January 2020. By comparison, all human activities in Australia produce around 530 million tonnes of CO2 per year.

Possible new solutions
So at this point, can we use this information to improve the management of greenhouse gases, particularly CO2, and find new solutions? For many years there have been efforts to study the so-called fertilisation of the sea as a possible solution to excess carbon dioxide in the atmosphere, precisely because the micro-organisms that form plankton are able to convert carbon from CO2 and water into carbohydrates, through photosynthesis, and release oxygen into the air.

However, the idea of ‘fertilising’ the sea with large quantities of iron and other minerals to promote this phenomenon has always been controversial, because while it is, at least in theory, an effective remedy, there are fears that it may have effects that are difficult to control, such as altering the normal balance of marine biomass by introducing large quantities of elements such as iron into the sea. The devastating Australian fires offered, if nothing else, the opportunity to study these phenomena in the field.

Doubts about ‘restored’ CO2
However, it is not clear yet if some of the CO2 removed by phytoplankton is somehow ‘restored’ through the normal metabolic processes of microorganisms. "We need to undertake new studies to clarify this," said Nicolas Cassar, professor of biogeochemistry at Duke University. “That will be our next challenge."


Paolo Rossi Castelli

Journalist since 1983, Paolo has been dealing with scientific divulgation for years, especially in the fields of medicine and biology. He is the creator of Sportello Cancro, the site created by on oncology in collaboration with the Umberto Veronesi Foundation. He collaborated with the pages of the Science of Corriere della Sera for several years. He is the founder and director of PRC-Comunicare la scienza.