Underwater drone maps ice algae in Antarctica

An underwater drone is helping researchers map the distribution of ice algae on the underside of the sea ice in Antarctica.

With the new robot technology, it is now possible to study the underside of sea ice across large distances and explore a world previously restricted to specially trained divers only.

"The drone was actually designed to study the sea bed and map factors such as sediment types, but our Australian colleagues modified the drone so that it now looks up towards the bottom of the sea ice and measures the light coming through the ice with a radiometer," said associate professor Lars Chresten Lund Hansen from the Aarhus University in Denmark.

This is how it works:

A Weddell seal weighing almost 500 kg blocks the hole laboriously sawn out by researchers in the two-metre-thick ice to launch drones under the sea ice.

The seal finally glides back into the water foraging for more fish and the researchers have access to the open water.

The advanced technology drone is then carefully lowered into the icy cold sea.

A tent covers the hole in the ice measuring 3m x 1m, and the researchers send their torpedo-shaped underwater drone down through the hole to map the underside of the sea ice.

Making the hole takes most of the day and requires a major equipment package including an oil burner and steam drill.

Ice algae on the underside of the ice absorb light at certain wavelengths, and the radiometer measures how much or how little light is absorbed at these wavelengths.

Based on the light measurements, the researchers can calculate the amount of algal biomass under the ice, and thereby get an idea of where the ice algae are located and how many there are.

The drone follows a pre-programmed course and it maps the distribution of ice algae over very large areas where studies have not previously been possible.

Ice algae are an important component of the Antarctic ecosystem.

They begin to grow under the ice as soon as the Sun emerges in early spring, and survive on the small amount of sunshine that penetrates the compact layers of ice.