Underwater drone maps ice algae in Antarctica

Researchers have developed an underwater drone to map the distribution of ice algae on the underside of the sea ice in Antarctica.
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.
"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 Aarhus University in Denmark.

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.
An important part of the project is controlling the drone's measurements by conventional methods where ice cores are drilled out.

The algae are scraped off the underside of the cores and a chlorophyll measurement shows the number of algae. The chlorophyll figures are subsequently compared with the drone's radiometer measurements.

The aim of these investigations is to understand which factors regulate the distribution of the algae. There are some indications that the rough texture on the underside of the ice plays an important role in the algal colonisation of the sea ice.
On the underside of some areas of the ice, there are thin plate-like ice crystals protruding 5 to 10 centimetres out of the bottom. The crystals are wedged between each other, forming a large surface that provides a good habitat for the diatoms that make up the bulk of the ice algae community.
The Antarctic is completely white above the ice, but there is an abundance of colour below the ice. The small greenish-brown unicellular diatoms can grow into large colonies that form entire mats on the underside of the ice.

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.
They are also the year's first producers of food for krill and other zooplankton in the food chain. They get life going so to speak under the ice, where small creatures can frolic in the hanging garden and feast on the algae and bacteria associated with algal life.