Chuck Bednar for redOrbit.com – Your Universe Online
An Aarhus University-led team of researchers are developing and testing underwater drones capable of mapping the distribution of ice algae on the underside of Antarctic sea ice.
Lars Chresten Lund Hansen, Brian Sorrell and PhD student Bibi Ziersen of the Denmark university, along with colleagues from Australia and New Zealand, are working in the frigid conditions at the southernmost continent, sending their torpedo-shaped robot through a three-meter by one-meter hole in the ice in order to map what lies underneath the frozen water.
The 2.5-meter-long underwater drone is ready to be launched through the hole in the sea ice. (Credit:Lars Chresten Lund Hansen)
“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,” Lund Hansen, an associate professor at Aarhus University, explained in a statement Monday.
Ice algae on the underside of the ice can absorb light at certain wavelengths, the researchers said, and the radiometer on the drone can measure the amount of light that is absorbed. Based on those measurements, scientists can calculate the amount of algal biomass beneath the ice, which allows them to determine where the algae are located and how many there are.
The new drone is given a pre-programmed course, and as it travels, it maps the distribution of ice algae over large areas where such investigations had previously been impossible. Measurements obtained by the drone can be compared to those taken using conventional methods, a process that involves ice cores being drilled out and algae being scraped off of their underside.
Chlorophyll measurements reveals the total number of algae there and are then compared to those obtained using the robot’s radiometer. The goal is to understand which factors regulate the distribution of the algae, as there are some indications that the rough texture of the underside of the sea ice plays a key role in its algal colonization, the researchers explained.
There are thin plate-like ice crystals protruding five to 10 centimeters out of the bottom of some of the ice, they added. Those crystals are wedged between one another, forming a surface large enough to provide a good habitat for the diatoms that comprise most of the ice algae community.
While the Antarctic is completely white in color above the ice, there is far more color located beneath it, as these diatoms are greenish-brown and can grow into large colonies that can come together in sheet-like formations on the underside.
“Ice algae are an important component of the Antarctic ecosystem,” the university said. “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,” it added. “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.”
Sorrell reports that the ice algae account for as much as 20 percent of the primary production in the Antarctic sea-ice area, and are especially important because they utilize weak light in spring when there are no other producers that can provide food and energy to other creatures.
The researchers call the initial data provided by the underwater drone “promising,” and said that they plan to expand the project to Arctic locations in the upcoming field season. Station North in Greenland or north of Svalbard on the research vessel R/V Lance are among the locations being considered for that expansion, they added.
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