Researchers from Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), in collaboration with the University of Oxford and the University of Reading, have developed a new mathematical model to explain how a massive bloom of phytoplankton is growing under the Arctic sea ice, where it is normally far too dark for anything requiring photosynthesis to survive.

Their findings, published in the journal Science Advances, showed that sea ice thickness and melt ponds are responsible for creating an environment suitable for the bloom of phytoplankton.

"The meter decline in sea ice thickness in the Arctic in the past 30 years has dramatically changed the ecology in that area," said Chris Horvat, a graduate student in applied mathematics in SEAS and first author of the paper, in a press release.

"All of a sudden, our entire idea about how this ecosystem works is different. The foundation of the Arctic food web is now growing at a different time and in places that are less accessible to animals that need oxygen," he added.

Usually, the bloom of phytoplankton occurs every summer, when the sunlight hits the open water of melt ponds. However, the researchers observed phytoplankton blooming under the ice, which is physically impossible before because the ice reflects most sunlight back into space, blocking it from reaching the waters below.

With the help of mathematical modeling, the researchers found that the Arctic ice that remains frozen during summer is thin and getting thinner. Thinner ice allows more sunlight to penetrate and reach the waters below. 

The researchers found that nearly 30 percent of the ice-covered Arctic Ocean is thin enough to allow sub-ice blooms of phytoplankton during the summer months. The amount of thin ice that allows sub-ice blooms today is significantly higher than it was about 20 years ago, in which only about three to four percent of Arctic sea ice is thin enough to allow massive colonies of phytoplankton to bloom under the ice.