Iron content in forest fire smoke is a plus for the carbon cycle in the Southern Ocean

(ORDO NEWS) — As smoke from the 2019-2020 Australian bushfires spread across the Southern Ocean, the iron-rich particles it deposited in the ocean caused algae blooms larger than Australia and had a rapid and lasting impact on the Southern Ocean marine ecosystem and its carbon cycle.

In a new study from the Institute for Marine and Antarctic Research (IMAS), scientists have found that iron from devastating wildfires has been recycled inside the bloom, allowing it to last for an unprecedented nine months.

The sudden increase in iron also triggered distinct physiological responses in the cells of phytoplankton, the microscopic “drift plants” at the bottom of the ocean food chain.

“The Southern Ocean plays a vital role in the global carbon cycle and is responsible for nearly half of the annual transfer of carbon from surface water to the ocean depths,” says IMAS PhD and lead author Jacob Weiss.

Phytoplankton are known to play a key role in this transfer through a process called the ocean’s biological carbon pump, which captures and transports carbon to the deep ocean in the form of sinking ocean plants and animals.

“The problem is that phytoplankton need iron to thrive, and the Southern Ocean lacks this important trace element.

Therefore, its biological carbon pump is not as efficient as it could be, and this is where wildfire ash and desert dust come into play.

We know that wildfire ash and mineral dust are rich in iron, and as we have seen from recent wildfires, phytoplankton growth is stimulated when these particles settle on the surface of the Southern Ocean.

But the full impact of this on marine ecosystems has not yet been measured.” – says the scientist.

Intense single fertilization by bushfires in Australia has given scientists the opportunity to study the physiological response of phytoplankton to wildfire emissions and their ability to survive on their own recycled iron.

Chemical oceanographer and co-author of IMAS, Professor Zannah Chase, said the reactions identified by the research team could be directly related to wildfire emissions.

The research team found that phytoplankton blooms survived wildfires by almost six months, enduring long periods when iron was only sporadically supplied by wildfire emissions and mineral dust.

“The iron that sustains the bloom comes from iron recycling, which happens when it is released back into the water. The phytoplankton cell dies to be engulfed by new cells,” said Professor Chase.


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