Underneath the frozen sea, below layers of compacted ice and snow, sunlight barely penetrates the waters of the Arctic. And yet, against all the odds, a photosynthesizing algae makes a living, and forms the basis of the food chain in the Arctic Ocean, fuelling the entire ecosystem.
New research published in the Journal of Geophysical Research has found that these algae can carry on photosynthesizing, growing, and living while receiving just 0.02 percent of the light that reaches the surface of the snow 2 meters (6.5 feet) above. This sets the record for the lowest light level ever observed where the algae are still able to go about their business on the underside of the ice.
The ice algae that live in this extreme environment have always been a bit of a mystery. Residing in the small cracks and channels that form on the underside of the ice as the heavier saline water flows out of the ice and into the water, they not only have to deal with the briny environment and sub-freezing temperatures, but also pitch darkness for months on end, and then weak sunlight for the rest of the year.
The team from Aarhus University, Denmark drilled through the meter of ice topped by a meter of snow during the April-May season. They were then able to collect samples of the ice algae, as well as test exactly how much light managed to get through to them. Needless to say, they were surprised by just how little light was necessary for the organisms to grow.
The discovery completely changes the understanding and importance of the role that ice algae play in the Arctic ecosystem, particularly during early spring as the Sun begins to rise above the horizon. As always, however, there is a warning here about how the warming of the Arctic might knock things out of kilter.
“Temperatures are rising in the Arctic," said Lars Chresten Lund-Hansen. "When the snow on top of the ice gets warmer, the algae residing on the underside of the ice receive more light. This may significantly impact the growth of the algae and the extent of the 'spring bloom'. This new knowledge must be considered in the puzzle of how the Arctic will respond to a warmer world.”
Would it mean that there are more nutrients at the bottom of the food chain? Or will the seasons be pushed off balance? And how would any of this affect the creatures higher up the food web, such as fish, seals, whales, and seabirds? These are all questions that need to be considered when we think about the future we’re forging.