How deep diving robots are revealing clues to ocean carbon storage

For three years these unique floats called Biogeochemical Argo (BGC-Argo), have revealed how much carbon in the remote southern ocean is stored, how it stores and how it might change in the future.

Biological oceanographer from the Institute for Marine and Antarctic Studies at the University of Tasmania Pete Strutton said through the floats, they found plankton played a key role in their findings.

"Plankton on the ocean's surface absorb atmospheric carbon dioxide and package it into particles that end up deep in the ocean, where they can be stored for thousands of years," Dr Strutton said.

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"It's called the biological carbon pump, and it's a major contributor to the Southern Ocean's capacity to remove carbon dioxide from our atmosphere.

"We knew plankton played a critical role in this, but what wasn't clear until now was whether it was mostly gravity causing those particles to sink, or if there were other processes at work."

For the study, BGC-Argo floats equipped with a rich set of sensors were deployed in the Australian sector of the southern ocean.

Dr Strutton said they spent most of their time drifting at 1000 meters deep.

"Every 10 days they sink down to 2000 meters, and then they come up to the surface," Dr Strutton said.

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"And while they're going from 2000 meters to the surface they're collecting data like temperature, biological and chemical measurements.

"When they get to the surface, they transmit the data via satellite back to the lab and we make it available to whoever wants it within 24 hours."

IMAS adjunct researcher and lead-author Dr Leo Lacour said until now, it was impossible to do extensive observations of the biological carbon pump across vast areas of the Southern Ocean at the same time.

"So over three full years, we've been able to explore different pathways to the deep ocean, such as the changing depths of surface mixing and the rapid water movement in high energy oceans - and how each pathway changes in strength over time," Dr Lacour said.

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Dr Strutton said the southern ocean took up 40 per cent of the carbon dioxide the oceans were taking up.

"It's punching well above its weight," Dr Strutton said.

He said the study revealed that intense and rapid changes in the biological carbon pump are common in the southern ocean.

"These results are important because they help us understand how the southern ocean stores carbon, which means we can better predict how the process might shift as the climate changes," Dr Strutton said.

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