New Zealand scientists are monitoring a possible "catastrophic" 3.5m Antarctic sea-level rise.

GNS Science has been part of an international team of researchers mapping the sea floor under the Ross Ice Shelf.

The shelf is twice the size of New Zealand and helps to slow the flow of Western Antarctica's grounded sea ice into the ocean.

"Most of the ice in West Antarctica sits on ground below sea level and is particularly vulnerable to increases in ocean temperature," GNS Science says.

"If all of this marine-based ice were released into the ocean, global sea level would rise by at least 3.5 metres in the coming centuries."

The researchers used a dynamic gravimeter, which measures the earth's gravitational force from a moving aeroplane, to model the shape of the sea floor.

They found a previously unmapped geological boundary was making the seafloor much deeper on one side, affecting the way the ocean water circulates under the ice shelf.

GNS Science's environment and climate leader Richard Levy says the research will help develop new ways of monitoring the health of Antarctic ice sheets.

"We can use this research to help determine where to place instruments to observe ocean currents that circulate beneath the ice shelf," he says.

"These observations can then guide computer models to predict how the Ross Ice Shelf and the West Antarctic Ice Sheet will change as our climate warms."

Newshub.