Researchers have found a "surprising" level of carbon sequestration by a deep water seagrass bed the size of Switzerland in the Great Barrier Reef.

Scientists from Deakin and James Cook Universities have been studying the unknown seagrass bed, more than 15 metres below the surface of the water, since 2014.

Researcher Peter Macreadie said it was the world's first study looking at the role of deep water seagrass in the carbon cycle.

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"When we first started reporting these deep water seagrasses, we thought that might not be providing the same ecosystem services to humanity that the shallow water seagrasses do," Dr Macreadie said.

"What was really surprising for us were the levels of carbon being sequestered by these systems."

Researchers on the Great Barrier Reef donned their scuba gear to take soil samples. ( Supplied: Peter Macreadie )

Mangroves, seagrass meadows and tidal wetlands are known as blue carbon coastal systems.

They are named for their place at the boundary between land and sea, and their unmatched ability to suck CO2 out of the atmosphere and store it in the ground below.

Capturing carbon Coastal plants capture CO2 through photosynthesis and land-based carbon sources

Coastal plants capture CO2 through photosynthesis and land-based carbon sources Carbon can be stored in the soil of blue carbon habitats for thousands of years

Carbon can be stored in the soil of blue carbon habitats for thousands of years When these habitats are damaged or destroyed the carbon can be released as CO2 back into the atmosphere

The data was collected by scientists scuba diving into deep water and taking soil samples which were compared to other carbon collecting ecosystems.

Dr Macreadie said the study found the deep water seagrass played a more integral role in the carbon cycle than first thought.

"Many of us think of trees as being one of these key ecosystems for removing carbon-dioxide and producing the oxygen that we breathe," he said.

"That is still true to this day but this [research] has led to the discovery that seagrasses, salt marshes, and mangroves are among the world's most powerful carbon sinks on the planet."

Dr Macreadie says he wants to know what else deep water seagrasses are doing. ( Supplied: Peter Macreadie )

'Just scratching the surface' of research

While the study found that deep water seagrasses played a significant role in the carbon cycle, Dr Macreadie is planning to do more research into the topic.

"I feel like we're just scratching the surface," he said.

"So we've worked out yes, they're important for carbon sequestration but what else are they doing?

"Are they important as a food source for dugongs and turtles? Are they helping to buffer against ocean acidification?

"Who knows what's ahead of us here."