News in Science

Dust storm triggers ocean bloom

The red dust storm that dumped thousands of tonnes of soil across eastern Australia two weeks ago has caused an explosion in microscopic life in Sydney Harbour and beyond.

Researchers analysing the impact say the finding validates plans to increase fish stocks to feed some of the world's poorest people using ocean fertilisation.

Professor Ian Jones, director of the Ocean Technology Group at University of Sydney, says enriching oceans with nitrogen will also aid the fight against climate change.

Jones' comments follow an analysis of the impact on the sea of the 23 September dust storm that swept across New South Wales and southeast Queensland.

At its peak the storm carried about 140,000 tonnes of soil an hour from central Australia.

Tripling in size

An estimated 4000 tonnes of dust settled on Sydney, while Jones and his colleagues calculate about three million tonnes landed in the Tasman Sea between Australia and New Zealand.

Measurements taken at the Sydney Institute of Marine Science on the harbour's north shore show a tripling of microscopic plant life, or phytoplankton, at the Chowder Bay site and in samples taken 10 kilometres off shore.

The scientists measure the presence of phytoplankton using remote sensing technology that can detect chlorophyll in the plants, which form the base of the ocean food chain.

Jones says phytoplankton needs nutrients such as nitrogen and phosphate to grow, nutrients that are scarce in what he calls Australia's "desert" ocean waters, but were abundant in the topsoil that blew across the country.

Like all plants, phytoplankton take in carbon dioxide from the air, which is carried to the bottom of the ocean when the plants die.

Jones says it is estimated eight million tonnes of CO2 was captured by the extra two million tonnes of phytoplankton that grew in the Tasman Sea, the equivalent of a month's emissions from a coal-fired power station.

He says the dust storm was a natural experiment that supports their work in fertilising the ocean by adding nitrogen-rich urea to the sea.

According to Jones this promotes the growth of phytoplankton near the surface of the ocean, which then leads to an increase in fish numbers.

Further tests

Jones and colleague Associate Professor Rob Wheen, also of Sydney University, are waiting for approval to test the approach in Australian sea waters.

They want to inject 2.5 tonnes of urea into the ocean to increase the amount of phytoplankton in a controlled area.

"More phytoplankton growth means more stocks of fish. I see much promise in ocean nourishment being able to provide economical protein for vast numbers of malnourished people," says Jones.

He says a continuously nourished patch of water about 20 kilometres in diameter could double the income of artisan fishermen in countries such as Morocco, and provide a constant source of protein to local people.

"All this while storing 10 million tonnes per year of carbon dioxide in the deep ocean," he says.

A Nature paper earlier this year questioned the amount of CO2 captured through ocean fertilisation and raised concerns about increases in algal blooms.

Jones says these criticisms were directed at research that used iron to enrich the ocean, rather than nitrogen.

He says the harbour findings show there is little danger to the environment from enriching the sea with nitrogen - five days after the dust storm phytoplankton levels were back to normal.