Huge Blue Carbon Sink Discovered in Great Barrier Reef Could Be Warding Off Climate Change

The Great Barrier Reef has a meadow of deep-water seagrass that acts as a huge blue carbon sink, scientists have discovered. The seagrass, which covers an area twice the size of New Jersey, stores almost 28 million tonnes of organic carbon—and could be helping to ward off climate change.

Blue carbon is a term used for carbon that is captured by marine systems, including mangroves, seagrasses and salt marshes. Peter Macreadie, from Deakin University in Australia, had previously investigated the coastal seagrass in terms of their potential to store carbon.

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During a trip to the Great Barrier Reef, Macreadie was told there was a vast area of deep-water seagrass around the reef: "My natural interest was to propose that we should check if these deep-water seagrasses are also significant carbon sinks," he told Newsweek.

Macreadie, working with Paul York and Michael Rasheed, of James Cook University, Australia, compared carbon stocks from deep-water (deeper than 15 meters), mid-water and shallow-water seagrass. They found the seagrass in the deeper regions contained similar levels of carbon as those in the shallow water.

Publishing their findings in the journal Biology Letters, the researchers worked out that if the deep-water seagrass they analyzed stores a similar amount of carbon as other deep-water meadows in the Great Barrier Reef lagoon, then there is about 27.4 million tonnes of blue carbon locked up there.

"We knew there would be some," Macreadie said, "but not 27.4 million tonnes." He notes that the limitation of the research is in the spatial coverage—they were only able to test a relatively small area, and upscaling that to estimate the entire seagrass area is not ideal. However, the research does indicate there are more blue carbon sinks out there than we previously thought.

"These blue carbon ecosystems are a powerful natural weapon in the fight against climate change," Macreadie said. "This is a good news story—we've discovered another important asset: Another major carbon sink that no-one knew about.

"The carbon cycle is this generation's great big juggling act, and it feels like we're dropping the ball. So to find ecosystems that we didn't know were locking up carbon and putting it in a water grave is splendid news. With this discovery we now must include these ecosystems in our greenhouse gas inventories."

Many scientists are currently worried about the destruction of blue carbon sinks—through aquaculture, agriculture, pollution and the exploitation of mangrove forests. At the moment, little is known about deep-water mangroves and their ability to sustain changing environmental conditions.

"The optimistic side of me would say that they are pretty resilient to disturbances and are more likely to bounce-back than their shallow water counterparts, which are currently facing 'death by a thousand cuts' and are in global decline," Macreadie said.

Great Barrier Reef
File photo: Great Barrier Reef iStock

The team says more research will be needed in order to assess the role deep-water seagrass plays in carbon capture. "Currently, global tropical deep-water seagrasses are poorly quantified, with most discoveries relatively recent and the likelihood that many more areas exist in unsurveyed waters. Our study suggests these areas potentially harbour significant undescribed global seagrass carbon sinks," they wrote.

Grace Cott, a wetland scientist at the University College Dublin, Ireland, commented on the study: "The findings are exciting as the carbon stocks were found to be higher than expected," she told Newsweek. "The findings also highlight the fact that the seagrass species plays an important role in influencing the carbon stocks of the sediments.

"These results point towards the necessity to study deep-water seagrass meadows globally and also to further investigate the role of carbonate material in blue carbon cycling. This will ultimately assist in accurate assessment of the carbon sink potential of these important habitats."