Polar Researchers Fearan Ecological Collapse in the Arctic

A Forest without Trees

After spending two months on the ice, the team returned to Spitzbergen on September 1. During the expedition, the scientists had spent up to 10 hours each day drilling, filming, measuring and taking samples. They sent up weather balloons and drones, deployed submersible robots and suspended sediment traps beneath the ice. In the evenings, the team would gather in the salon for a beer and to discuss their experiences and findings from the day.

Oceanographers, meteorologists, experts in sea ice physics and ecologists were all part of the team. Marine scientist Zoe Koenig measured currents and turbulence beneath the ice while Sandro Dahlke, the atmospheric physicist, probed clouds with microwaves. The findings produced by biologist Morten Iversen, meanwhile, were something of a riddle. He had joined the team to investigate how the algae growing beneath the sea ice is metabolized over the course of the summer: Which organisms feed on the algae and where the algae itself gets its nutrition.

But Iversen found that there was actually no algae at all in the region between Greenland and Spitzbergen where the Polarstern was operating. In other years, the algae forms the backbone of the Arctic ecosystem. It was almost as though Iversen had come to a forest and realized there were no trees.

In the Arctic, everything is connected to everything else. Perhaps data collected by the others could help explain Iversen’s discovery? Might the algae be missing because the ice melted particularly rapidly this year?

Captain Stefan Schwarze had figured that he would be able to maneuver the Polarstern through the pack ice in August at a speed of around two to three knots. In actuality, though, he was able to travel twice that fast on some days.

Fog hung low over the ice on some days during the expedition, it would rain, and the scientists would trudge through puddles of meltwater and slush. Oceanographer Gunnar Spreen from the University of Bremen complained about the "Bremen weather.” Atmospheric physicist Dahlke, by contrast, was "happy that we were able to see it with or own eyes and study it.” He brought home a data set showing that the rain makes the ice softer and, thus, darker.

As such, the rain contributes to the ice-albedo effect, the feedback mechanism that intensifies the annual loss of sea ice during the Arctic summer. Year after year, the melting process speeds itself up: The more bright, reflective ice melts and the more dark water takes its place, the less heat is reflected and the more rapidly the remaining ice melts. One of the aims of "Contrasts” – as the expedition launched by the Bremerhaven-based Alfred Wegener Institute for Polar and Marine Research (AWI) in Bremerhaven is called – was to study this effect as precisely as possible.

The albedo effect is an important driver of the ongoing disappearance of sea ice in the Arctic. The polar ice cap in the north has been shrinking for decades as a result of climate change, and soon, the North Pole will be almost completely free of ice in the summer.

But when will that future become reality? Forecasts vary and there is a significant lack of knowledge. In this key region, of all places – the location of some of the most important factors in the global climate – there is still a poor understanding of the interaction between sea ice, the ocean and the atmosphere. The concept behind the Contrasts expedition was to enable scientists to study the long-term processes in the Arctic ice in a single season.

Traveling in a Triangle

The Polarstern embarked from the Norwegian town of Tromsø on July 2, heading for three ice floes the team had previously identified on satellite images that were to be examined in detail. They stood for the Arctic’s future, its present and its past.

The Polarstern spent seven weeks sailing in a triangle between the three floes, departing from the particularly stable Floe 3 for the last time on August 29. "We were able to moor at exactly the same spot each time,” says expedition leader Marcel Nicolaus. The weather there was less rainy as well. "Our favorite floe,” the researcher says.

The loss of the station on Floe 1 was a setback, to be sure. For several days, the team could watch the station’s GPS position on the screen in the red salon as it bobbed in Russian waters. But the story had a happy ending. What was left of the ice sheet eventually drifted back into international waters, where the team was able to retrieve it. Only the weather tower had sunk and is now lying on the sea floor in Russian territory.

Nicolaus watched closely as the three floes melted, shrunk and finally broke apart. "First, light blue pools of meltwater form on the ice,” he says. Those are frequently the sites where the ice sheet ultimately breaks apart. "It went quickly,” the expedition leader says. Within four weeks, he says, the floes lost between 30 to 40 centimeters in thickness, becoming darker and grayer with each visit. In late August, the researchers were surprised to note that even Floe 3, which had previously been so stable, had broken apart.

For his own research project, Nicolaus had measured the radiative flux through the ice: How much light falls on the surface and how much penetrates into the ocean?

Together with his team, he deployed a submersible robot through a hole in the ice. From a nearby shelter, the pilot was able to steer the submersible beneath the ice. Particularly spectacular are the structures up to 15 meters deep, which resemble upside-down reefs and bear witness to past collisions between ice floes.

The Changing Face of the Arctic

The physics of ice is Thomas Krumpen’s specialty. He plays an animated video clip that compresses just over 30 fateful years in the Arctic into less than three minutes. It shows the sea ice growing year after year far into the North Atlantic every fall and winter before then receding in the spring. White and undulating, the old ice formed in the Beaufort Sea stands out from the gray-colored ice mass of the Arctic, circling there for years until it drifts toward Greenland and the Atlantic Ocean.

But the amount of this old ice has decreased significantly, shrinking far faster than the total amount of ice, colored gray. In 1984, the video shows the Arctic mostly white, but 30 years later, the white areas had almost completely vanished.

Video: Arctic Sea Ice from 1984 to 2016

The total amount of sea ice shrank quickly after 2007. In September 2012, when strong southerly winds pushed the remaining ice together at the pole, only 3.48 million square kilometers of the ocean were covered by ice, still a record low.

"It looks as though a process is taking place in steps,” says Krumpen. "We are waiting for the next great export.” And nobody, he says, can predict when that might come. But the scientist believes it will mark the Arctic’s next great step towards an ice-free summer.

Because the type of ice is changing, says Krumpen, the entire Arctic is taking on a different character. Old ice is rough and variegated. It is marked by "pressure ridges,” scars left over the years by collisions of large ice floes. These ridges, two to three meters in height, generate swirling air currents above the ice and intensify the turbulence of the water below it. More than anything, though, the cracks and crevices provide habitat for small organisms. In January, Krumpen and his team described the changes linked to the loss of such pressure ridges in the journal Nature Climate Change.

His first great surprise came on Floe 1: "Zero” was the algae count he received. Iversen thought it was an outlier, perhaps the result of the ice beginning to melt particularly early this year. Maybe the algae had already separated from the ice, he thought.

But he found the same result on Floe 2 and Floe 3. In other years, the ice algae had grown like thick grass on the underside of the floes, even coloring the ice entirely in some areas. But this year, Iversen found nothing. He was also unable to find any algae floating in water where it should have been present. Typically, they form small gas bubbles that keep them afloat for a long time after separating from the ice.

Drastic Reduction in Ice Algae

The ice algae is essential for the Arctic ecosystem, as analyses performed by AWI scientists have shown. In the fall, when the seawater freezes, the algae is frozen into the ice off the Siberian coast. Only when light begins penetrating the ice after the polar night comes to an end does the algae bloom, forming long filaments stretching for up to several meters with which they can filter the scarce nutrients from the water.

These algae mats provide nourishment to sea butterflies, amphipods, copepods and other miniscule creatures, with their footprint found throughout the food chain, even into the depths of the ocean. AWI research has found that much of the carbon in the Arctic Ocean is funneled into the ecosystem through the ice algae. They are the organisms that keep the life cycle in the ice-locked sea going.

Once the North Pole becomes ice free, as ecologists have long been saying, the ice algae underneath the ice will also disappear. And the ecosystem will collapse. But might it be that this future scenario has already become reality?

A former Polarstern expedition already gathered evidence two years ago of a dramatic reduction in the amount of ice algae. Now, Contrasts appears to have confirmed this finding.

Iversen is still hesitant about speaking of an ecosystem collapse. He first wants to examine the sediment samples he took from the ocean floor 4,000 meters below the surface. He wants to know if he might find evidence there of freshly sunken algae.

But Iversen does think it possible that the ice-free future may already have begun for the Arctic environment. And he has already taken a look at how this future might look. In sediment traps suspended beneath the ice, large quantities of tiny fecal pellets have accumulated. They come from pteropods, small marine animals that filter bacteria from seawater while encased in a gelatinous coating. They seem to be the big winners of the ongoing ecological transformation.

Iversen sees them as a reassuring message. "Nature,” he says, "always finds a way.”