Dust deposits a boon for microscopic ocean life

Australian researchers have found dust blowing into the oceans can help boost the productivity of vital microorganisms in marine ecosystems.

Reviews of more than a decade of sensor data from floats in the Southern Ocean by teams attached to several of the nation’s top Antarctic and climate science research institutions found iron-rich dust particles fertilise the ocean with vital nutrients for tiny marine plants called phytoplankton.

The sensors are suspended around 1km beneath the ocean surface. They drop down a further kilometre and then return to the surface every 10 days and upload biochemical data via satellites.

This data monitors nitrate concentrations within the ocean, which phytoplankton also require for growth. A reduction in nitrates is used as a marker for phytoplankton growth.

Phytoplankton provide the foundation of marine food webs as a primary food source for small animals and large filter feeders (such as baleen whales).

Surprise carbon storage

According to data published today in the journal Nature, enriching oceans with dust particles has been found to support about a third of the Southern Ocean’s phytoplankton productivity.

This process has at least two benefits. Iron is scarce in the Southern Ocean, so windblown dust provides a boost that supports more phytoplankton. It can also boost the capacity of oceans to store carbon, which is one of the two necessary reactants (in the form of carbon dioxide) in photosynthesis.   

“The more phytoplankton grow, the more carbon can be stored in the ocean,” says the study’s lead author Jakob Weis, a biological oceanographer.

“But just like plants on land, phytoplankton require nutrients and light to thrive.”

Weis and his colleagues simulated current and historic dust deposits across the southern hemisphere, calculating that during historic ice ages, a 40-fold greater amount of dust was cast into the Southern Ocean, leading to double the level of phytoplankton growth.

He hopes the models used in these simulations will help climate scientists more accurately understand the role dust-iron deposition has in phytoplankton growth, and what this means for carbon storage.

“What we’re providing with this new relationship is a component that can be integrated into global climate models, making predictions more accurate,” Weis says.

“These models will then give us the bigger picture of how changes in ocean productivity, together with ocean circulation and chemistry, affect the ocean’s ability to store carbon and thereby regulate CO2 levels.”

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