On 16 May, RV Polarstern left the MOSAiC floe, which an international team of experts has been researching since last October, to pick up the crew for the next leg of the expedition off the coast of Svalbard. To reach her destination, RV Polarstern had to pass through a belt of multiyear pack ice in Fram Strait. The ship is now making her way back to the MOSAiC floe. Just how long this will take depends on more than just how thick the ice is. In the following interview with meereisportal.de, Captain Thomas Wunderlich and Cargo Officer Felix Kentges talk about their experiences with icebreaking and explain why open leads in the ice, as well as the snow on the floes, are important aspects.
meereisportal.de: Icebreaking at this time of year, mid-June, is a difficult undertaking, because the ice is still very thick. What factors have the most influence on the ship’s progress?
Mr Wunderlich: When we break through the ice, we take a very tactical approach and always look for the best possible route, which can sometimes mean taking a detour. For instance, it’s very important that the region includes leads of open water: when we break the ice, there has to be somewhere for it to go. Of course, the ice thickness is also important, since thicker ice slows us down.
Mr Kentges: The snow cover on the floes also influences how much headway we make. We break the ice by heading for a floe and then using the ship’s own weight to break through the ice. But if there’s too much snow on the ice, which might still be wet and sticky, we can get bogged down in the snow and can’t break so much ice at one go. It’s like when you’re bicycling and go through a puddle with lots of mud, so you barely get back out the other side.
meereisportal.de: What information do you use to plan the course for the next several hours?
Mr Wunderlich: The most important thing is to know under which ice conditions we can safely continue with the RV Polarstern. And then we can plot our course accordingly, using the latest sea-ice charts available. They’re mostly based on satellite images, which can show us where, for instance, there are patches of open water, but also where the particularly large floes are. The images from satellites like the German Aerospace Center’s Terra-SAR-X offer such excellent resolution that we can use them just like a roadmap. Weather permitting, we also use our onboard helicopters to make scouting flights, helping us find the best course for the next several hours. And for orientation in our immediate vicinity, we use images from our own radar, which show us the locations of major pressure ridges and large floes. In the future, aerial photos taken by drones may also become a valuable tool.
meereisportal.de: Before starting a journey like this one, how do you prepare for the ice conditions you’ll encounter?
Mr Kentges: Ice conditions can change rapidly, for instance, due to a storm. That’s why we only plan our route a few days at a time. But before every journey we inform ourselves about the seasonal ice situation, like the position of the ice edge at the time of maximum sea-ice extent in March (meereisportal.de entry here), and exchange notes with our colleagues who made the latest Polarstern expedition to the region. Nevertheless, you never know what the conditions will really be like until you look out the window.
meereisportal.de: The MOSAiC floe is currently at 82.79°N, 7°41 E. You were in the same region a number of years ago, during expedition PS92. How would you describe the conditions this year?
Mr Wunderlich: That’s right; on PS92, too, we had serious difficulties making our way so far north, and the current situation is very similar. Back then we had to contend with several extremely large ice floes, and then time considerations forced us to turn back. Of course, things are very different now, since we have a great deal more time, and now the ice will become thinner and thinner, the closer we get to summer. So the initial conditions are much better this time around.
meereisportal.de: As the ship’s captain, do you get the feeling that the ice conditions have changed so radically that the navigability has improved, at least in summer?
Mr Kentges: For the sake of long-term observations, we always travel to specific regions at the same time of year, which allows us to compare the ice conditions. In recent years, we’ve had to break through less and less ice on our way to the Neumayer III station in Antarctica (see also the meereisportal.de entry). Of course this means we can get to our destination faster, but the changes are also very troubling.
Mr Wunderlich: In the Arctic, I’ve especially noticed the dramatic loss of sea ice off the eastern coast of Greenland. In the past we had to fight with extensive floe systems, but in the last few years we’ve been able to reach the coast with little trouble. For me, the PS115/1 cruise was especially impressive. We penetrated to the northern coast of Greenland, which is very unusual to say the least, since the local ice is normally extremely thick and several years old. But in 2018 an ice-free corridor had formed, which we took advantage of (see also the meereisportal.de entry).
I also found it to be one of the most challenging ice cruises, as we had poor visibility and were only able to make a very few ice scouting flights with the helicopters. At the same time we were in a part of the ocean that was largely uncharted.
meereisportal.de: Thanks kindly for the interview!
On Tuesday, 9 June 2020 at 11.40 a.m. ship’s time, RV Polarstern entered the pack-ice belt in the northern Greenland Sea and set course for the MOSAiC floe, where the international team of experts had left behind autonomous monitoring stations, ensuring further data would be gathered during their absence. Once back on site, the team will continue their drift with the floe and resume their field research.
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