DW: Professor Christian Haas, you've just completed the second leg of the MOSAiC mission.  The mission's ship, the "Polarstern," has been drifting in the Arctic to measure the effects of climate change since October - most of the time in the midst of the total darkness of the polar night. Have you had any unexpected experiences?

Professor Christian Haas: Well, we are all experienced in Arctic sea ice expeditions and Polarstern cruises but living and working in total darkness for such a long time was new for most of us. We did not know what to expect. We have lights on the ship, including search lights and specially prepared head lamps, that have made working on the ice relatively easy. Most people have dealt with the darkness well, psychologically and health-wise, without having to use daylight lamps or vitamin D supplements much.

That said, we hadn't expected to see a polar bear in the middle of the polar night at such a high latitude. And the fact that we saw only one indicates that they are very rare near the North Pole in winter.

It was also somewhat unexpected to see a seal under the ice in early February. There is little scientific or anecdotal evidence of the presence and behavior of marine mammals near the North Pole in winter.

What is it like in the Arctic? How does the Arctic sound? How does it look — is everything just white? Is there an arctic smell?

In winter, everything is just black or white if it's illuminated, with shades of grey, depending on the age of the ice, for instance where there are cracks, and depending on the snow cover. There are no sounds except during ice deformation. Walking or skiing over the ice and snow creates all sorts of fancy sounds too — squeaky, hollow sounds, with occasional snow collapses that would initiate avalanches if the ice wasn't flat.

Do you notice the drift? Can you feel, hear or see it?

You cannot notice the ice drift with your own senses, but due to real-time GPS positioning that's displayed on all of the ship's data systems we were able to observe the magnitude and changes of drift speed and direction at any time. We see our movements on maps that we make of our so-called "drift track."

Occasionally, cracks would open up in the ice or pressure ridges would form, and if you're nearby when that happens, you can see the relative motion between parts of the ice floe [Ed.: a sheet of floating ice], and you can hear moaning, grinding, hammering, or squeaking sounds. During such events we can watch the deformation of the ice on the ship's radar.

What have been the most surprising discoveries or observations so far?

The most surprising observations may have been our marine mammal observations. There are hundreds of thousands of different plankton in the Arctic, and it takes experienced taxonomists to identify them. Even after consulting experts on land, it is not always exactly clear what kind of animal we've found and how common it is. We found larger numbers of polar cod under the ice, which shows that there is an active eco system even in winter, with enough food for higher species. From early February on we frequently observed a seal under the ice, feeding on the polar cod.

But the goal is to carry out the most complete, most accurate, and most continuous observations of the air, ice, and water in the Arctic, and their interactions, to better understand what governs the growth and melt of the ice and the recent retreat of summer sea ice, and how these have changed in recent decades. So, it's not so much about making new discoveries.

By observing a complete set of atmospheric parameters, including air temperature, humidity, wind profiles, aerosols and clouds, we can evaluate how this affects the growth of the ice, the redistribution of snow, and the cooling and mixing of the water. And our observations show that the average air temperatures are higher than decades ago, that the ice is thinner, and that the cold oceanic surface layer is shallower than before. 

These are signs of the the "new Arctic" scientists are talking about - a changing north polar environment. Does the "old Arctic" still exist?

The ice floe we've seen has been composed of both first-year ice of the new Arctic, and second-year ice of the old Arctic. At the start of the project, the second-year ice was thinner than it used to be and there was only a little difference in the growth rates between the young and old ice. Both the old and the new Arctic are characterized by an absence of sunlight and therefore an absence of solar radiation during the polar night. That means the polar night is still a period of strong surface cooling and ice growth. But the water is storing more heat and there are different greenhouse gas concentrations in the atmosphere.

Now your ship, the Polarstern, of course also pumps emissions into the Arctic. How does your presence there affect the environment - and the results of your surveys?

Polarstern is a modern research vessel that accommodates about 100 people with every comfort of normal daily life. That requires power, heat, and fresh water. The ship uses about 11 tons (12 US tons) of diesel fuel every day. And that creates emissions of heat and soot that get distributed and deposited in the wider environment, depending on wind speed and its direction.

We also have to release processed grey water regularly. We have a novel system that releases that grey water below the ship, via a long hose, at a depth of 150 meters (492 feet). So, the grey water cannot spread immediately below the ice or affect any of our oceanographic and biogeochemical measurements.

The Polarstern emits noise and light, but that doesn't affect our measurements. We take biological ice measurements far from the ship at a "dark site," the most remote observational point, to avoid any impacts of light pollution on biological productivity.

The mission has set two new records for Arctic exploration: Yours is the northernmost mission during the Arctic winter, and it's the first self-powered ship to travel so far north so early in the year. How does it feel to be a part of that?

Science is not only about data but also about exploration, discovery, imagination, and about pushing the limits. Reaching the poles has always been some part of scientific exploration of the Arctic and Antarctic, and the North Pole is also a pole of imagination and destination. Getting as close as possible to the North Pole is part of that challenge. Having set a new record, however special, and being part of it, fills everyone with pride and provides stories to tell, and just demonstrates how extreme and successful our undertaking has been, compared to all earlier, similar efforts.

Professor Christian Haas  is a geophysicist and climate sciences and sea ice physics expert at the Alfred-Wegener-Institute, a Helmholtz centre for polar and marine research in Germany. He is head of MOSAiC expedition's leg 2. The MOSAiC Arctic mission is ongoing until September or October 2020. 

Read more: The Polarstern's journey to South Africa