Tiny particles of iron in the smoke and ash carried by the wind seem to have fertilized the seawater, as it were.

In 2019 and 2020, Australia was ravaged by disastrous bushfires. The fire spread furiously, turning green areas into blackened landscapes, estimated to have killed more than a billion animals. But now it turns out, strikingly enough, that these devastating forest fires did not only bring much destruction. Because thousands of kilometers away it caused an explosive ‘bloom’ of phytoplankton.

More about the Australian bushfires
The Australian bushfires of 2019-2020 were arguably the worst ever. Although wildfires in Australia are an annual occurrence, this time the fires were really merciless. This was mainly due to the scorching heat in Australia with average temperatures of 40 degrees Celsius. The period between January and November went down in the books as the second hottest and driest period ever. As the fire continued to spread untamed, a state of emergency was declared in several parts of the country. Ultimately, thousands of people were displaced from their homes and the fires killed at least 30 people and a billion animals.

The Australian bushfires of the summer of 2019/2020 had far-reaching consequences. The fires, for example, pumped an estimated 715 million tons of carbon dioxide into the atmosphere. The released smoke and ash then traveled thousands of miles through the air, turning the glaciers in New Zealand brown. The smoke even reached South America. Finally, after traveling thousands of miles, the particles settled on seawater in the Southern Ocean.

Phytoplankton

Researchers in a new study have now discovered something surprising. Because the wind-borne smoke and ash now appear to have caused an immense bloom of phytoplankton – tiny algae that form the basis of the food chain – in the ocean between New Zealand and South America. Phytoplankton suddenly bloomed in abundance over an area larger than the entire Australian continent. “We have not seen such a bloom of phytoplankton in the last 22 years,” said researcher Peter Strutton. “The flowering lasted about four months.”

Forest fires

According to the researchers, this bizarre observed algal bloom can be traced directly to Australia’s devastating bushfires. “What makes it special is that the blooms suddenly appeared at the normally seasonal low,” Strutton explains. “But the smoke from the Australian bushfires turned things around completely.”

Iron

How did the phytoplankton bloom? The smoke from the Australian bushfires contained low but significant concentrations of iron. And that’s vital for phytoplankton to thrive. The small particles of iron in the smoke and ash carried by the wind thus seem to have fertilized the seawater, as it were. In fact, the wildfires dropped three times as much iron into the ocean as normal, delivering nutrients on a scale unprecedented for the region. And the response of phytoplankton was lightning fast.

carbon dioxide

On the one hand, this unprecedented algal bloom has some advantages. Phytoplankton absorb carbon dioxide during photosynthesis. And that happens to such a degree that it can make quite a difference in our atmosphere. This is why fertilizing the ocean with iron to stimulate phytoplankton growth has often been suggested as a method of combating climate change. It is estimated that the immense and unexpected growth of phytoplankton significantly removed some carbon dioxide from the atmosphere; roughly equivalent to the amount released during the Australian bushfires. “Our results provide strong evidence that iron from smoke from wildfires can make oceans fertile, potentially leading to a significant increase in carbon uptake by phytoplankton,” said study researcher Nicolas Cassar. However, the question is whether all that carbon dioxide is actually stored permanently. That depends on numerous factors. “How much of it is safely stored in the ocean and how much is released back into the atmosphere is the next challenge to investigate,” Cassar said.

Deadly

On the other hand, the explosive bloom of plankton can also be deadly to animals. “A single bloom can wipe out countless animals in a matter of days, leaving ‘dead zones’ in freshwater lakes and along coastal areas,” said study researcher Chris Mays, commenting on the study. “For such a poisonous soup you need three main ingredients: high temperatures, high CO2 concentrations and an influx of nutrients. Man supplies the first two. And now the study shows that fires can provide the nutrients. The increase in plankton blooms will put additional pressure on freshwater and coastal ecosystems that are already suffering from a host of other stressors, such as overfishing and extreme warming.”

The study illustrates the enormous impact that smoke and ash particles can have thousands of miles away. “With the increasing risks of wildfires in some areas and the potential impact on the climate, this research shows that we need to focus on the impact of fires on a global scale,” concluded Strutton. Because while the researchers focused on the impact of wildfires in the Southern Ocean in their study, other regions — including the North Pacific and areas near the equator — are likely also responding to the particles released into the water from wildfires. “We need a much more comprehensive representation of wildfires in climate models and targeted studies to understand their impact on marine ecosystems,” concludes Strutton.