Marine phytoplankton can grow under thick sea ice in near darkness, converting what little light exists into energy, though it is still unclear how these microscopic algae have adapted to grow in these extreme conditions.
It was previously thought that phytoplankton couldn鈥檛 grow in the Arctic until the sea ice began to melt, but Achim Randelhoff at Laval University in Canada and his colleagues found that the microscopic marine algae are able to photosynthesise and grow even in winter, with growth peaking in April and May.
Over two years, the team deployed four autonomous floats in Baffin Bay in the Arctic. The bay is covered with thick sea ice for seven months a year: throughout winter and lasting into July.
Advertisement
The floats are 2.25-metre-long, rod-like robotic devices equipped with sensors to measure temperature, salinity and the reflection of light off various particles, called backscattering. They travel underwater and can detect and avoid ice.
By measuring the amount of chlorophyll 鈥� a green pigment essential for photosynthesis 鈥� in the water, and the amount of particle backscattering, the researchers measured fluctuations in the amount of phytoplankton during winter.
They found that phytoplankton grew slowly in near darkness and that the rate at which it accumulated peaked more than two months before the Arctic sea ice began to retreat, when Baffin Bay was completely covered with thick ice.
Based on the floats鈥� measurements of the amount of light at a given depth and area 鈥� and previous research on how phytoplankton behave under different light levels 鈥� the researchers found that a small amount of photosynthesis was occurring, beginning from February when sunlight returned to the bay.
The reason why marine phytoplankton in the Arctic have adapted to grow under such extreme conditions isn鈥檛 yet clear. 鈥淭his very small growth could support survival of phytoplankton during winter,鈥� says Randelhoff.
The under-ice growth might also contribute to the spring bloom, a surge in the amount of phytoplankton that begins in early spring and lasts until early summer, he adds.
Science Advances
