Taking to the skies to shade corals using new technologies

Published 26 August 2021
Plume of seawater droplets from sprayer rises into the sky Plumes of seawater droplets generated by the jet sprayer rise into the sky (credit Brendan Kelaher/Southern Cross University).

Southern Cross University-led field trials of an innovative new technique that aims to prevent coral bleaching by spraying microscopic seawater particles into the air is producing exciting preliminary results.

Made possible with the support of the partnership between the Australian Government’s Reef Trust and the Great Barrier Reef Foundation, the technique known as Cloud Brightening enhances the clouds by helping them to reflect solar energy away from the Reef; in turn helping protect coral from bleaching.

An initial trial of the prototype Cloud Brightening equipment in 2020 has proved it is feasible to pump seawater and atomise it into tiny droplets at a rate of hundreds of trillions per second.

The Cloud Brightening project team, led by Dr Daniel Harrison of Southern Cross University, completed a second trial this year which gathered critical data on the behaviour of the atmosphere over the Great Barrier Reef during the summer months, when corals are most at risk of bleaching.

DR DAN HARRISON, CLOUD BRIGTENING PROJECT LEADER: Last year out here we conducted a proof of concept experiment where we showed that it's technically feasible to pump seawater and atomize it into trillions per second of tiny little seawater droplets which in theory can go on to help brighten clouds and cool the reef. This year what we're really interested in looking at is the behaviour of that plume of sea salt droplets as it drifts away from the boat. There's a few critical questions around that how many of those droplets make it up to cloud height and how does the atmospheric turbulence and the winds spread those droplets. And these questions will help us to design a system for the future that may be able to work over the whole reef. This fieldwork mission has several components. One of the components is to collect background atmospheric data. So we have a whole lab set up on the ship that's sampling air from up at the front of the boat the wind before it hits the boat and we're looking at all the background properties of particles that are naturally floating around in the air out here on the reef. Another part further back on the ship is the cloud brightening prototype and that's mark-2 this year so it's producing around twice as many droplets as last year and we're very interested in in how those droplets are spreading through the atmosphere. So we have a big focus this year on using drones as sampling platforms to measure the plume not just in a horizontal dimension but also in a vertical dimension. So one of the great advances that we've made from last year is really our sampling platforms. So the boat that we're using for sampling downwind is now larger and much more capable and we're actually able to launch drones and retrieve drones off of that boat.

USOP DRAHM, MANDUBURRA TRADITIONAL OWNER: As well as being important to the indigenous people of Australia we realise it's important to all Australians. We love the coast we love our water let's look after it together.

DR DAN HARRISON, CLOUD BRIGTENING PROJECT LEADER: Cloud brightening is just one of a whole suite of ideas that we're examining in the Reef Restoration and Adaptation Program and the overarching goal of all of this research is to look into all of the possible ways we can think of that we might be able to help the Reef to survive climate change.

“Marine cloud brightening sees microscopic sea water droplets sprayed into the air, creating a plume of salt crystals which interacts with cloud to reflect solar energy away from the reef waters when heat stress is at its maximum,” says Dr Harrison.

“It’s effectively boosting a natural process because cloud droplets form over the ocean when moisture gathers around salt crystals and other minute particles, stirred up by winds from the ocean’s surface.”

They also mapped the movement of the atomised sea salt plume to better understand how cloud brightening could be most effectively deployed over the Reef.

“This year what we were really interested in looking at was the behaviour of that plume of sea salt droplets as it drifted away from the boat and mixed towards the clouds. We hope this critical information we’ve collected will help us to design a system for the future that will enable us to show a brightening response in the clouds,” Dr Harrison says.

Both expeditions were both conducted at Broadhurst Reef, 100km offshore from Townsville on the central section of the Reef. It involved researchers from Southern Cross University and QUT in partnership with SIMS (Sydney Institute of Marine Science), University of Melbourne, University of Sydney, Ron Allum Deepsea Services, Australian Institute of Marine Science, Riverside Marine, EmiControls, and Quaternium.

Dr Harrison said Cloud Brightening has the potential to protect the entire Great Barrier Reef from coral bleaching in a relatively cost-effective way, buying precious time for longer-term climate change mitigation.

“What’s unique about this technique is that can be used intermittently when required as an emergency response to protect corals from bleaching during marine heatwaves,” he said.

Great Barrier Reef Foundation managing director Anna Marsden says it is crucial to pioneer new techniques to help save our Reef from a growing combination of threats.

“The greatest threat to our Reef is climate change and we’re already seeing the effects, with three mass bleaching events in five years,” Ms Marsden says.

“The rate at which bleaching events are now occurring on the Reef is a matter of huge concern but there is hope, and the time to act is now.

“That’s why, through the Reef Restoration and Adaptation Program we’re bringing together people and science to pioneer new solutions, such as cloud brightening, to restore coral reefs and help them adapt at unprecedented scales.”

Seawater sprayer jets close up

Jet sprayer releases seawater plume off the back of the vessel (credit Alejandro Tagliafico/Southern Cross University).

Dr Harrison says cloud brightening has the potential to protect the entire Great Barrier Reef from coral bleaching in a relatively cost-effective way, buying precious time for longer-term climate change mitigation.

“What’s unique about this technique is that it can be used intermittently when required as an emergency response to protect corals from bleaching during marine heatwaves.

“Cloud Brightening has the advantage of being very scalable. The Reef is huge, 2500km long, an area the size of Italy. Cloud Brightening is one of the ideas that, if it scales up how we hope it may, it is potentially usable over the entire reef and can help all the coral and all the ecosystem.”

Manduburra traditional owner Usop Drahm, who has joined both expeditions, says he welcomes this scientific research, which has seen Indigenous people and other Australians work together to maintain the Reef ecosystem for future generations.

“This technology might help prevent bleaching and we like that it uses no chemicals and relies on natural processes,” Mr Drahm says.

The Reef Restoration and Adaptation Program is funded by the partnership between the Great Barrier Reef Foundation and the Australian Government’s Reef Trust. It is delivered by a collaboration between the Australian Institute of Marine Science, the Great Barrier Reef Foundation, CSIRO, The University of Queensland, QUT, Southern Cross University and James Cook University.

Read the related feature article in Nature Can artificially altered clouds save the Great Barrier Reef?

Media contact: Sharlene King, media office at Southern Cross University +61 429 661 349 or scumedia@scu.edu.au