It is nearly noon in mid-January, and despite the full moon, the mountains and glaciers around me are cloaked in darkness. I’m in a small boat cruising a remote fjord of the Svalbard archipelago, halfway between mainland Norway and the North Pole, following a motorized kayak as it putts back and forth across the choppy water. Through the blackness, I can just barely see the kayak, called a Jetyak, as it occasionally rams into ice along its pre-programmed course.
This is the second time the Jetyak—laden with high-tech gear—has been dispatched to collect information about the tiny organisms living in the frigid water, and it’s about to yield some remarkable data for the scientists with me on this boat.
Since 2012, the biologists Jørgen Berge of the Arctic University of Norway (UiT) and Geir Johnsen of the Norwegian University of Science and Technology (NTNU) have made regular trips aboard the research vessel Helmer Hanssen to explore the marine life that survives in the dead of the polar night, the darkness that envelops the Arctic from November to February. Berge is the leader of the research team, which also includes scientists from the U.S. and the U.K.; Johnsen is in charge of submersibles and other equipment.
Berge first discovered the wintertime patterns of Arctic marine life by accident while on a research expedition in 2007. “We went [north of here] on this ship to take up a mooring,” Berge tells me in his cabin aboard the boat. “It was the spring that was of importance to us, but when we looked at the winter, we thought that something was wrong, that this can’t be correct. We saw something that we had never imagined.”
The mooring carried an acoustic Doppler instrument for profiling ocean currents, but after downloading its data, Berge happened to notice odd acoustic backscatter that showed masses of zooplankton on the move—odd for that time of year. Specifically, the data was suggesting a phenomenon called diel vertical migration (DVM), the daylight-synchronized rise and fall of zooplankton, small fish, and krill, which rise to the surface at night to feed on algae and dive back down during the day.
DVM is common year-round in warmer waters with more abundant sunlight, but to find it in the Arctic in the middle of winter—with no algae and no light—was startling. Scientists had always assumed that the polar night was a time of icy stasis, when marine life died off or ate little for months at a time, awaiting the return of springtime’s 24-hour daylight and the accompanying algal bloom.
After his initial discovery, Berge went back and examined 15 years of acoustic winter data in Svalbard, comparing it with similar records that other researchers had collected from sites in Canada, Greenland, Russia, and the North Pole. The results were all the same: The telltale acoustic backscatter indicated that marine life had always been there. Berge began organizing polar night expeditions each January to understand why Arctic marine life stayed locked into a daily rhythm, even with no sunlight. As his teams would soon discover, zooplankton thrive throughout winter even without algae to eat.
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On a trip to this same fjord last year, Berge and Johnsen spotted a glowing fish in the water and scooped it into a coffee cup over the side of their rubber dinghy. Johnsen explains that it was a species of lantern fish normally found in much warmer North Atlantic waters at depths of 200 meters. Finding it in shallow water this far north, he said, was mind-boggling.
“It told us that the deep ocean is at the surface here in the polar night,” says Johnsen.
To identify all the species they spot, Johnsen and his colleagues at NTNU have developed an imaging system based on a camera that geologists normally use for aerial analysis of soil minerals on land. Called a hyperspectral camera, it captures light-wavelength signatures for each object it sees. To collect their aquatic data, the researchers attach it to a submersible vessel called a remote-operated vehicle, or ROV.
The day after chasing the Jetyak, I huddle in a freight container packed with video monitors on the Helmer Hanssen deck with Johnsen and Berge watching live footage from the ROV they have just launched. A young graduate student, rigid with concentration, sits next to them, holding the remote-control console that operates the ROV.
“You see the unseen,” Johnsen excitedly says as he points to the footage on a separate monitor dedicated to the hyperspectral camera. “For instance, if you have one green leaf and one plastic leaf, both of those are green for us, but in a hyperspectral image, per image pixel, you will see the absorption of peaks of chlorophyll. The plastic leaf will not have this optical fingerprint.” With specialized software, Johnsen can identify scores of species by cross-referencing their spectral “fingerprints” to a database he has already compiled.
He and Berge help the ROV operator navigate across the seafloor toward a site at the mouth of the fjord. Using a robotic arm, the grad student drops a metal plate on the seafloor as a place marker. Over the next five minutes, he sends the ROV surveying in all directions, expertly flying the craft over a submarine cliff and past some juvenile rockfish and skittish ghost shrimp.
A few days later, Johnsen suits up to do some traditional underwater photography closer to shore.“You give this man a camera, and send him underwater,” Berge says, “and he will return with pictures that are magic.” That evening, Johnsen shows me images he has taken on various cruises, capturing bioluminescent copepods blinking like Christmas trees and whelk eggs shimmering like jewels.
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Each research cruise yields its own surprises. In 2012, Berge and Johnsen followed the Helmer Hanssen in a skiff through ice-clogged waters. They were dazzled by what the big ship left in its wake.
“There was something so immensely beautiful and gripping about that sight,” Berge recalls. “We were literally just hanging over the side of the boat looking down and saw all these blue lights blinking and shining in all dimensions.”
Bioluminescence, the chemical glow produced by many marine organisms, is frequently found in warmer waters, but is rare to see in the Arctic winter.
“The fact that such a large fraction of the arctic zooplankton is able to produce light—and that they are up at the surface and they do produce light—says something about the activity levels of the system during the polar night,” Berge says. “And that’s the key thing. What we have learned, above all, is that this is a light climate, not a temperature climate. Light rules here.”
Berge points out that the biggest explosion of Arctic Ocean biomass occurs with the return of sunlight in April, even though air temperatures are still bitter and sea ice is still near its maximum. Understanding how large masses of zooplankton survive in the absence of sunlight, and why they follow a daily DVM pulse, remains a major goal of Berge’s team.
“There are quite a lot of species that have the ability to switch between modes and that makes them quite successful in food webs,” Nicole Aberle-Malzahn, an NTNU biological oceanographer and microbiologist, tells me in the ship’s lab. “If conditions are good … and there are enough nutrients available, they do photosynthesis. But if light conditions are bad, like right now at this time of the year,” they switch to other food sources, helping prolong a viable food web rather than dying off.
Aberle-Malzahn also notes that microbes like single-celled protozoa may be as important as zooplankton in driving the food web in late winter. While larger zooplankton take a month to double in number, microzooplankton can do it in a day, frantically feeding on spring’s algal bloom and becoming, in turn, food for their larger neighbors.
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Some zooplankton, like the ubiquitous Calanus genus—tiny copepods with oversized antennae—use the polar night for romance. Males fertilize the females in the dark of winter and then die off. The females survive till spring on their substantial fat reserves, and their winter egg production provides abundant food for zooplankton at the surface. At midday, though, the zooplankton dive for darker waters to avoid being spotted by predators like krill, whose eyes work in the faintest of light.
According to Jonathan Cohen, a visual ecologist from the University of Delaware aboard the ship, krill eyes are over one million times more sensitive than our own. To them, the nearly imperceptible daylight at noon in the polar night is 100 times stronger than light from the brightest full moon.
In the ship’s lab, Cohen works behind a heavy curtain at a large, black Plexiglas cube that contains a small water chamber in which individual krill are tested for light sensitivity in total darkness. A fiber optic rod directs electronic flash into the pure dark chamber, while a needle inserted in the eye measures electrical responses to the flash.
“One of the major implications of climate change in the Arctic is thinning ice and a changing light climate,” says Cohen. He notes that this particular fjord has seen a dramatic decrease in winter ice over the past decade, allowing more light to penetrate deeper into the sea. “A warmer, brighter Arctic means, from a krill’s perspective, less sensitivity to light,” he adds.
On this cruise, Cohen is focused on how much a krill’s light sensitivity is influenced by an internal body clock. Do they see as well at midnight as at noon? His preliminary results indicate that sensitivity varies with time of day, decreasing at noon regardless of the actual amount of daylight. As predators, krill have evolved to be in the right place at the right time, but new Jetyak data suggest that their prey, zooplankton, respond more to light disconnected from any internal clock, fleeing the surface when light makes them more visible. The krill and their prey have each evolved to their own survival strategies, cued to light changes that are nearly imperceptible to humans.
For Berge’s team, it is now clear that there is enormous biological activity during the polar night, driven by light that is invisible to our eyes. It is also increasingly clear that deep sea species can become shallow sea phenomena at these latitudes at this time of year, and that Atlantic species are moving farther north into the Arctic, where temperatures are rising twice as fast as the global average. What is not clear—and may remain forever unknown—is what Arctic marvels we may lose before we even knew we had them.
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