Australian bush fires created an algae bloom east of New Zealand

Friday, 17 September 2021

A plume of bush fire smoke rises over New South Wales in 2019. Smoke clouds passed over New Zealand and out over the Pacific, where they contributed to an algae bloom.

OPINION: Scrolling through my smartphone photos the other day while reminding myself of life before Covid-19, my finger paused on January 5, 2020.

The photo showed some houses in Auckland silhouetted against an apocalyptic orange sky. Before the pandemic monopolised our attention, the big science-related story capturing worldwide attention was the series of massive bush fires in Australia.

During the dry summer of 2019-20 the fires, burning mainly in the southeast of the country, consumed an estimated 46 million acres of land, 5900 houses and claimed 34 human lives. Scientists reckon a staggering 3 billion animals were killed or displaced.

The gigantic smoke cloud that crossed the Tasman and coloured our skies for days became an eerie precursor to what would be a surreal year. But it had a more profound impact too. The cloud passed over us and helped fertilise a bloom of phytoplankton in the Southern Ocean between New Zealand and South America that for a short period was bigger in area than Australia itself.

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Here’s the photo that sparked Peter Griffin’s column this week. It was an “eerie precursor to what would be a surreal year”.

Phytoplankton are microscopic marine algae that form the basis of the food chain in our oceans. Researchers who spotted the bloom using satellites and ocean buoy measurements, published their findings in the journal Nature last week. They say the bloom was “unprecedented in the 22-year satellite record and lasted for four months”.

'All power ... to the Lovelocks of this world,” Stuff science columnist Peter Griffin writes.

How did smoke from the bush fires spark such a flurry of growth? The plume was rich in iron, which is essential to the process of photosynthesis. With three times the usual amount of iron being deposited into the ocean, the growth of phytoplankton went into overdrive.

Phytoplankton don’t just eat iron. They also absorb carbon dioxide. The scientists estimate the massive bloom absorbed an amount of CO2 roughly equivalent to the amount released into the atmosphere by the bush fires.

So could putting iron in the oceans be the key to reducing the CO2 that is contributing to global warming? That’s unlikely. About 20 years ago, our own scientists from Niwa performed an experiment in the Southern Ocean, creating an algal bloom by dissolving iron into the water.

The experiment and others of its kind showed that in the ocean a much lower ratio of carbon is captured by iron added than was observed in lab experiments. Niwa scientist Dr Cliff Law suggests a 100-year iron fertilisation programme could “draw down atmospheric CO2 by 33 parts per million, which is less than 9 per cent of current atmospheric CO2 levels”.

So iron fertilisation is likely to be of very limited use in tackling climate change. We will see more major bush fires, which could have an additional perverse outcome. Algal blooms in lakes and coastal areas can create dead zones, killing off other aquatic life.

“For these kinds of toxic soup, you need three main ingredients: high temperatures, high CO2 and an influx of nutrients,” says Dr Chris Mays, an Australia-based palaeontologist at The Swedish Museum of Natural History Humans.

We are now providing all three in abundance. The result could be an increasingly toxic brew.