Smoke From 2019-20 Wildfires Triggered A Phytoplankton Bloom Bigger Than Australia

Himawari 8 satellite image showing the January 2020 aerosol plume stretching over the South Pacific. Image credit: van der Velde et al 2021

Wildfires wreak havoc on any area, tearing down habitats and fatally burning any living thing in its path, but new research has found that their smoke carries wider world consequences, too.  The study found that smoke from the 2019-20 Australian bushfires took to the skies and traveled thousands of miles before settling on the water. Far from fading from existence, it appears to have triggered a phytoplankton bloom bigger than Australia itself.

Published in the journal Nature, the study sought to ascertain if the enormous fires could be connected to a months-long bloom of phytoplankton in an area of the world where, at that time of year, these microscopic organisms are usually in low supply.

“The phytoplankton bloom in this region was unprecedented in the 22-year satellite record and lasted for around four months,” said co-author Professor Peter Strutton in a statement from Australia's ARC Centre of Excellence for Climate Extremes (CLEx).

“What made it more extraordinary is that the part of the season when the bloom appeared is usually the seasonal low point in phytoplankton, but the smoke from the Australian bushfires completely reversed that.”

Researchers tracked the plumes from the bushfires to investigate if their movements could account for the unexpected bloom and combined this with satellite data and information from autonomous floats deployed across the region. The results indicated that an influx of iron was the most likely culprit, having hitched a ride on the smoke, which peaked at altitudes of 16 kilometers before settling in the Southern Ocean.

Iron is crucial for photosynthesis and phytoplankton growth, so when the smoke dumped three times the amount usually found in the area (as estimated by the researchers) it’s perhaps unsurprising the resident phytoplankton made the most of it. The boom was swift, kicking off in some instances just days after the fire that caused the smoke.

So, what does it all mean? While anything happening at a magnitude measured in continents might fill you with dread, a phytoplankton bloom isn’t necessarily a bad thing. The tiny organisms actually carry out a monumental chore for planet Earth in sequestering carbon through photosynthesis. Sprinkling iron into the ocean has actually been suggested as a means of tackling climate change.

In a second paper, researchers found that while the fires themselves are estimated to have released enough CO2 to surpass Australia’s average annual emissions by 80 percent, the subsequent carbon sink attributed to this explosion of phytoplankton could well have matched what was released. However, without data on the depth to which the carbon sank, it’s impossible to draw firm conclusions. The existing information paints an insightful picture as to the connectedness of wildfires, ocean ecosystems, and climate change.

“With increasing risks of bushfires in some areas, and the potential impact on climate, this research shows that we need to turn our attention to the consequences of fires at a global scale,” said Strutton.

“We need a far more comprehensive representation of wildfires in climate models and targeted studies to understand their influence on marine ecosystems. Our capacity to adapt to future climate change depends on it.”

 
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