Biology Algae photosynthesize in almost complete darkness

Microalgae in the Arctic Ocean carry out photosynthesis in almost complete darkness under snow-covered sea ice. According to the German Alfred Wegener Institute (AWI), this was "unexpectedly" revealed on Wednesday by measurements from an Arctic mission.

Switzerland was also involved in the Mosaic long-term expedition of the research icebreaker "Polarstern".

According to the AWI, just a few days after the end of the polar night, the tiny algae are already generating energy from photosynthesis and building up biomass even under ice and snow.

The AWI spoke of results of "significance for the entire planet" and the fundamental understanding of biological processes. "Even though our results are specific to the Arctic Ocean, they show what photosynthesis as a whole is capable of," explained AWI expert Clara Hoppe on Wednesday. "If it is so efficient under the challenging conditions of the Arctic, we can assume that organisms in other regions of the oceans have also adapted so well."

According to the AWI, the so-called photosynthetic habitat in the ocean could be much larger than previously thought. Even in deeper layers, there would be enough light to produce energy and oxygen through photosynthesis. This would enable food chains for fish, for example.

One hundred thousandth of the amount of light

According to the results of the study now published in the journal "Nature Communications", the microalgae in the Arctic Ocean only had access to around one hundred thousandth of the amount of light available on the Earth's surface on a sunny day. In order to measure this at all, the researchers first had to freeze newly developed measuring devices in the Arctic sea ice during the month-long Mosaic expedition.

According to the institute, which specializes in marine and polar research, the measurements showed that algae were already building up biomass under the ice just a few days after the end of the month-long polar night. Photosynthesis is "absolutely" necessary for this. The data from the extremely sensitive light sensors also revealed that this was already taking place close to the light minimum that, according to theory, is needed to start photosynthesis.

The German research icebreaker "Polarstern" froze in the central Arctic for a year in 2019 during the so-called Mosaic expedition and drifted through the region with the sea ice during the polar winter. The international expedition, which involved 20 nations, is considered the largest and most complex Arctic exploration to date.