- Scientists conducted a series of extensive surveys in Kongsfjorden in Svalbard, Norway, during three consecutive winters from 2013 to 2015.
- Despite the sunless skies during polar winters, various animals — from tiny plankton to large seabirds — seem to be up and moving in the Arctic Ocean, according to the study.
- Most animals in the ocean continued to feed, grow, and reproduce during the polar nights, and some species were more abundant in winter than at other times of the year, the study found.
Winters in the Arctic are long, cold and dark. Nights can last for many days — sometimes even months — plunging some areas into long periods of unbroken darkness. While it might be easy to presume that marine life lies dormant during these prolonged chilly polar nights, researchers have now discovered that the Arctic Ocean is instead host to a buzzing ecosystem during the winters, teeming with animal activity.
Despite the sunless skies, various animals — from tiny plankton to large seabirds — seem to be up and moving in the Arctic Ocean during winters, according to a study published today in Current Biology.
Before this, research of the Arctic Ocean during polar nights have been narrow in scope. “All studies until now have been limited to certain taxa, groups or phenomena,” Jørgen Berge of the Arctic University of Norway and the University Centre in Svalbard, Norway, told Mongabay. “This is the first ecosystem approach that looks at all elements of the food chain.”
About five years ago, Berge and his colleagues were out on a small open boat in Kongsfjorden, a fjord located on the north-west coast of Svalbard in the Arctic Ocean. The team was studying tiny aquatic animals called zooplankton on a polar night when a sight took their breath away, Berge said.
Many zooplankton had lit up the ocean water with their bioluminescence into a “three-dimensional ‘up-side-down’ sky with moving blue-green lights in all forms and sizes,” he said.
This suggested that there was possibly more biological activity during the long periods of winter darkness in the Arctic waters than previously documented. “There and then I decided that we would start investigating what is really going on during the polar night,” he added.
In a series of extensive surveys spanning three consecutive winters from 2013 to 2015, over 100 researchers studied the biodiversity and biological activities of different animal species in Kongsfjorden in the Arctic Ocean. Polar nights there can last for over three months.
In the past, people have presumed that because polar nights are marked by a lack of sunshine and photosynthesis, there would be little biological activity in the ocean during this period owing to a lack of food in the system. But the team found that despite the dark skies, most animals in the ocean, including herbivores, continued to feed, grow, and reproduce during the Arctic polar nights. In fact, some animal species were more abundant during the winters than at other times of the year, the study found.
A particularly surprising finding, according to Berge, was that many species of Arctic seabirds — such as little auks (Alle alle), black guillemots (Cepphus grylle), and glaucous gulls (Larus hyperboreus) — seemed to be actively seeking food in the continuous darkness. How these birds detect their prey during the polar nights remains a mystery, the researchers write.
They have, however, proposed some ideas that could explain the birds’ feeding success.
“Some of the prey items such as Thysanoessa species (krill) are known to be bioluminescent, which might act as a cue for detecting these organisms in the dark,” the researchers write in the paper.
But these observations need to be investigated in much more detail, Berge said.
The researchers also submerged cameras into the chilly waters of Kongsfjorden and recorded a time-lapse video of various zooplankton, snails, fish and crabs feeding on an Atlantic cod the team had set out as bait.
“The fact that the entire system is turned on is new, and has many important implications,” Berge said.
For example, with the climate changing and sea ice melting, Arctic waters are opening up to shipping, fisheries, and other human activities. This makes it important to understand the biological processes and patterns that occur during the polar night, and the mechanisms that drive them, the researchers write.
“We can’t simply assume that the dark polar night is a ‘safe’ period when things are not turned on,” Berge said in a statement. “Rather, it turns out that the dark polar night is an important period for reproduction in a number of organisms, and, as such, it is probably more sensitive than other parts of the year.”
Citations:
- Berge et al (2015) Unexpected Levels of Biological Activity during the Polar Night Offer New Perspectives on a Warming Arctic. Current Biology. http://dx.doi.org/10.1016/j.cub.2015.08.024