Photosynthesis can occur in natural settings, even when light levels are extremely low. This insight comes from a study investigating the growth of Arctic microalgae at the end of the polar night. Findings indicate that photosynthesis in oceans can happen under much dimmer light conditions and at greater ocean depths than previously thought.
Photosynthesis can occur in nature, even with very limited light. This conclusion comes from an international study examining the growth of Arctic microalgae during the end of the polar night. Measurements taken during the MOSAiC expedition at a latitude of 88° north revealed that microalgae can begin to build biomass through photosynthesis as early as the end of March, even in the very northernmost regions where the sun barely breaks the horizon. At this time, the habitat of these microalgae remains almost completely dark beneath the snow and ice cover of the Arctic Ocean. The findings, published in the journal Nature Communications, indicate that photosynthesis can occur in the ocean under much lower light levels and at much greater depths than had been believed.
Photosynthesis transforms sunlight into energy that living organisms can use, forming the foundation of life on Earth. However, earlier assessments of how much light is necessary for photosynthesis have always indicated levels significantly higher than the theoretically possible minimum. A new study published in the scientific journal Nature Communications shows that biomass can indeed be generated with light quantities very close to this minimum.
The researchers drew upon data from the international MOSAiC research project for their investigation. During this expedition, which took place in 2019, the German research icebreaker Polarstern was intentionally frozen into the Arctic pack ice for a year to study the yearly cycles of the Arctic climate and ecosystem. Led by Dr. Clara Hoppe from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), the team focused on phytoplankton and ice algae, the primary contributors to photosynthesis in the central Arctic. Surprisingly, measurements showed that just days after the polar night ended, plant biomass accumulation began again, which relies on photosynthesis. High-sensitivity light sensors placed in the ice and water made it possible to accurately gauge the available light.
These results were especially striking because photosynthesis was occurring under snow-covered sea ice, which allows only a minimal amount of sunlight to penetrate: microalgae had access to merely one hundred-thousandth of the light available on a sunny day at the Earth’s surface. “It’s remarkable to observe how effectively the algae can utilize such minimal amounts of light. This illustrates the impressive adaptability of organisms to their environments,” noted Clara Hoppe.
The success of this study relied on collaborative efforts among researchers from various fields. Sea ice specialists Dr. Niels Fuchs and Prof. Dirk Notz from the Institute of Marine Research at the University of Hamburg were instrumental in merging light field measurements with biological data. “To measure such low light levels in the harsh conditions of the Arctic winter, we needed to embed specially designed instruments within the ice during the polar night,” Niels Fuchs explained. His colleague, Dirk Notz, emphasized the challenges posed by the irregularities in the light field beneath the ice due to varying ice thickness and snow cover: “Ultimately, we could confirm: there was simply no more light.”
The findings of this study are significant on a global scale. “Although our results pertain specifically to the Arctic Ocean, they demonstrate the potential of photosynthesis. If it can be so effective in the harsh Arctic conditions, we can infer that organisms in other oceanic regions have also adapted remarkably well,” Clara Hoppe contextualized the findings. This suggests that even in deeper ocean areas, there may be enough light to harness usable energy and oxygen through photosynthesis, which could then benefit marine life such as fish. Consequently, the potential photosynthetic habitat in the world’s oceans might be far larger than previously thought.
