Life in the polar ocean is surprisingly active in the dark winter
Even in the constant night of a polar winter, birds such as this black guillemot and plenty of other creatures are surprisingly active, a new study finds.
Prof Geir Johnsen/NTNU
Scientists have long thought that in the supercold, perpetually dark, polar winter, life pretty much shuts down. With no sunlight, there’s no photosynthesis, so phytoplankton wouldn’t be active. That would cut off the base of the marine food web, and there would be no energy entering the system. Everything else would have to enter a resting state, the theories suggested. That would include anything that relied on sight to find food, such as seabirds, since they wouldn’t be able to see their prey.
Wrong.
A group of researchers led by Jørgen Berge of the Arctic University of Norway in Tromsø spent the winters of 2013, 2014 and 2015 sampling the waters and observing seabird communities in Kongsfjorden, Svalbard, which is north of the Arctic Circle. They found a surprisingly active marine community that in some habitats was actually more diverse than what is found in warmer, sunlit months, the scientists report September 24 in Current Biology.
Without light, phytoplankton are indeed inactive, and there are fewer of them than are found in the spring bloom. But when the researchers artificially lit the plankton, they quickly got to work. They weren’t sleeping — just waiting for the sun to return. Zooplankton, meanwhile, were busy munching away the polar winter, the scientists found. And some, such as Calanus copepods, found that the dark made a great time for mating.
On and near the seafloor, life also kept churning. Iceland scallops kept growing. Traps — which rely on invertebrates crawling inside to get bait — captured gastropods, amphipods and crabs. When the scientists tallied up the invertebrates, they found that the animals’ densities were 10 times greater than what is found in the region in May and October.
Cod and haddock had stomachs half-full of food. And seabirds were observed foraging. Their communities had dwindled, as many birds had migrated south or to the open ocean for the winter. But there were little auks, black guillemots, northern fulmars, glaucous gulls and others. And they were managing to find food. Some were surviving on bioluminescent krill, which were presumably easier to find in the dark. But dissections of stomach contents also found evidence that birds had eaten fish and crustaceans (sadly, also plastic in one glaucous gull).
Scientists had assumed that during the quiet, dark winter, the spring phytoplankton bloom dominated processes in the Arctic system. And management of the region — one that is currently undergoing rapid climate change — was based on that assumption, Berge and his colleagues note. But with the discovery that the ecosystem is active throughout the year, some rethinking may be due.
