The discoveries have been been pouring in for the CSIRO after its research vessel, Investigator, made another major discovery off the coast of Narooma.
Last weekend, scientists on board the vessel used multi-beam technology to map the underwater features of the sea floor south of Montague Island.
Earlier this week, the team reported the finding of an extinct underwater volcano off the Narooma coast. Now, crews have discovered more ancient marvels under the sea.
Through multi-beam sonar technology, the ship identified two submerged mountains that rose 1300m above the sea floor.
The tops of both mountains are 1500m below the surface.
The trio of scientists - Associate Professor Martina Doblin, Professor Iain Suthers, and Amy Nau, of the CSIRO Marine National Facility - wanted to put the sheer scale of the underwater mountains into context.
The two mountains are about 50 per cent bigger than Mount Gulaga, a prominent Narooma landmark.
It is 868m above sea level and the spiritual home of the Yuin people.
“It’s likely we’ll keep making more discoveries using the advanced multi‑beam sonar on the vessel,” said Chief Scientist on the voyage, Associate Professor Martina Doblin.
The initial discovery was made south of Montague Island last weekend.
“The reef appears to be the remnant of an old volcano, submerged more than 110m below current sea level.
“At the top of the reef is a circular depression approximately 200m across, only 15m above the surrounding continental shelf,” Ms Nau said.
Prof Suthers is excited by its history.
“It’s entirely feasible that this ancient eroded feature hosted indigenous Australians over 10,000 years ago, when sea level was lower during the last ice age,” Professor Suthers said.
“It’s also remarkable that such a shallow rocky reef can influence the distribution of pelagic fish. Clearly the reef generates an ecosystem.”
It is that crater that is a bounty for larval fish, Prof Doblin said.
“It creates an upwards lift in the water and helps feed the reef with nutrients,” she said. “It stimulates plankton and larval fish feed on the plankton.”
The bottom survey forms part of a wider study on linking the oceanography of the region with ecosystem functioning and the marine food web.
“Currents may sweep plankton into the southern lee of the island, where baitfish and fairy penguins may forage,” Professor Suthers said.
“The plankton and bio-acoustic data collected by Investigator will be used to examine this.”