Photosynthesis miracle: Arctic algae thrive with just 100,000th of daylight

An international research team has made a groundbreaking discovery about photosynthesis in the Arctic. Their study reveals that Arctic microalgae can continue to produce biomass even in extremely low light conditions.

This research was part of the MOSAiC expedition, which took place at 88° northern latitude. The findings show that photosynthesis can occur much deeper and in darker conditions than previously thought.

During the MOSAiC expedition, researchers studied microalgae under the snow and ice cover of the Arctic Ocean, where sunlight is minimal. The study found that these microalgae could still build up biomass by the end of March, when the sun is barely visible above the horizon.

This surprising result demonstrates the algae’s ability to perform photosynthesis under conditions that were thought to be too dark for such processes.

Light levels and photosynthesis

Photosynthesis is the process by which sunlight is converted into energy that supports life on Earth. Traditionally, it was believed that photosynthesis required much more light than what was available in the Arctic. However, the new study shows that microalgae can thrive with light levels close to the theoretical minimum.

Dr. Clara Hoppe from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), led the research team. They used data from the MOSAiC project, where the German research icebreaker Polarstern was frozen in the Arctic ice for a year in 2019.

The team focused on phytoplankton and ice algae , crucial for photosynthesis in the Arctic. Their measurements revealed that, just days after the polar night ended, microalgae began to build up biomass again.

The study employed extremely sensitive light sensors placed in the ice and water to gauge the light levels. Despite the snow-covered sea ice blocking most of the sunlight, the microalgae managed to use the very limited light—about one hundred thousandth (0.001%) of what is available on a sunny day—to grow.

“It is very impressive to see how efficiently the algae can utilize such low amounts of light. This shows once again how well organisms are adapted to their environment,” says Hoppe in the press release.

Challenges and implications

The study’s success was due to the close collaboration between researchers from various fields. Sea ice experts Dr. Niels Fuchs and Prof. Dirk Notz from the University of Hamburg played a crucial role in this effort. They combined measurements of light levels with biological data, overcoming significant challenges posed by the harsh Arctic winter.

“To measure such low light levels under the harsh conditions of the Arctic winter, we had to freeze special, newly developed instruments into the ice in the middle of the polar night,” explains Fuchs in the press release.

The research team had to navigate irregularities in the light field caused by variations in ice thickness and snow. Notz notes, “It was particularly difficult to take into account irregularities in the light field under the ice. But in the end, we could be sure: There was just not more light.”

These findings have global implications. “Even though our results are specific to the Arctic Ocean, they show what photosynthesis is capable of. 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,” says Hoppe.

This suggests that photosynthesis could occur in deeper ocean regions with minimal light, potentially providing energy and oxygen for marine life. The photosynthetic habitat in the global ocean might be much larger than previously understood.

The study is published in the journal Nature Communications .