For almost three years a robot was hard at work in the Southern Ocean, diving several kilometres and surfacing every 10 days to transmit data.
The "argo" float was recently retrieved by scientists who hope the information can be used to better understand how much carbon the ocean stores.
The float sent data via satellite about water temperature, salinity, algal concentration, suspended matter, oxygen, nutrients, light and pH levels.
CSIRO scientist Christina Schallenberg said the float, the biggest ever deployed by the organisation, also took vision of particles in the water column.
"While the float is only able to transmit counts of particles, it should have stored the actual images," Dr Schallenberg said.
"Now we've recovered the float, we'll get access to the images.
"Not only will this tell us the size of particles, but what they are - faecal pellets, fresh plankton, other (debris).
"(This) is crucial for knowing how the sinking of these particles moves carbon from the surface to the deep ocean."
The two-metre-long 100kg float was picked up by the CSIRO research vessel Investigator after being dropped off roughly 500km south of Tasmania in late 2020.
It floated at a "parking" depth of 1000m and would dive a further 1000m before surfacing every 10 days, recording information on the way.
The float performed the dive cycle 290 times.
Benoit Legresy, CSIRO oceanographer and research voyage chief scientist, said the float still had battery life for further dives.
"But if we hadn't got it before winter, it wouldn't have lasted another year," Dr Legresy said.
"The rich data it contains is priceless. I'm excited by this recovery."
He said the wider use of such autonomous instruments offered great potential for more scientific breakthroughs in the Southern Ocean.
Scientists aboard the Investigator are also gathering data about "leaks" in Southern Ocean currents which act as a buffer between Antarctica and warmer waters.
