Hoppe and colleagues discovered that Arctic microalgae can photosynthesize and grow in incredibly dim light, challenging our understanding of ocean productivity. Their findings suggest that marine life in polar regions and deep waters may be more active than we realized.
The researchers found algal growth resumed under sea ice at daily average light levels of just 0.04 μmol photons m⁻² s⁻¹ in late March. This is 10-100 times lower than previous estimates and approaches the theoretical minimum light requirement for photosynthesis.
As part of the expedition, they froze the German research icebreaker Polarstern in the icepack of the central Arctic for a year in 2019, in order to investigate the annual cycle of the Arctic climate and ecosystem. The team used autonomous light sensors deployed under Arctic sea ice during the year-long expedition. They also tracked algal growth by measuring chlorophyll concentrations and carbon uptake in water samples,
The extremely low light levels supporting net growth were unexpected and suggest marine primary production may occur more extensively than previously thought. The photosynthetic habitat in the global ocean could therefore be significantly larger than previously assumed.
[O]ur threshold would deepen the bottom of the euphotic zone from 23 to 54 m. This substantially increases the vertical extent and thus the total volume of the euphotic zone in the world’s oceans and may change our view on upper twilight zone ecology and biogeochemistry.
Hoppe, C. J. M., Fuchs, N., Notz, D., Anderson, P., Assmy, P., Berge, J., … & Wloka, J. (2024). Photosynthetic light requirement near the theoretical minimum detected in Arctic microalgae. Nature Communications, 15(1), 7385. https://doi.org/10.1038/s41467-024-51636-8
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Cover image: MOSAiC Ocean City during Leg 3. Alfred-Wegener-Institut / Saga Svavarsdottir
