#23: How do ice floes move at the North Pole?

When you think of mathematics, most people probably have equations in mind, dusty blackboards and maybe a calculator. Probably a very one-sided image of mathematics that you had to revise very quickly when you met the mathematician Dr. Carolin Mehlmann. She was on an expedition to the Arctic Ocean in August 2023, together with her colleague Prof. Thomas Richter, for their research on sea ice. In the new episode "Knowledge when you want it", the two talk about the expedition, their sea ice model and all their experiences and new findings.

Today's guest:

Dr. Carolin Mehlmann and Prof. Thomas Richter research and teach at the Faculty of Mathematics. Together they participated in a two-month expedition to the Arctic Ocean with the research vessel "Polarstern" from the Alfred Wegener Institute. Within this time, they have examined the numerical model that will more reliably simulate and predict the precise movement and size of sea ice at the North Pole. With Dr. Mehlmann's new sea ice model, it should be possible in the future to analyze the size and thickness of individual ice floes and their direction of movement in more detail and thus make more precise predictions about their behavior. Following the expedition, the two researchers are organizing a thematic year on mathematics and climate change for schoolchildren and interested parties, starting in November 2023, in order to bring the research to life.


*the audio file is only available in German

The Podcast to Read


Intro voiceover: Knowledge when you want it. The podcast about research at the University of Magdeburg.

Lisa Baaske: When I think of mathematics, the first thing that runs down my spine is a cold shiver. And then I see equations in front of me, dusty blackboards and maybe a calculator. I admit: A very one-sided image of mathematics that I had to revise very quickly when I met the mathematician Dr. Carolin Mehlmann. When I sat in her office about a year ago and she told me that she would be taking part in an expedition to the Arctic Ocean in August 2023, I was immediately hooked on her story and also on her research. My name is Lisa Baaske, I work in the university's press office. And that's what we're going to talk about today: About the sea ice model that Dr. Mehlmann and her colleague Prof. Thomas Richter are developing, about the expedition to the Arctic Ocean in which the two participated, and about all their experiences and new findings. A warm welcome!

As I already mentioned, it is of course unusual for a mathematician to take part in an expedition. What exactly are you researching?

Dr. Carolin Mehlmann: Exactly. My research is about developing models. Models to predict how sea ice will change in the future. These models are mathematical equations, which is where mathematics comes in. And in order to make predictions, we need these equations that describe the physics that we observe.

Prof. Thomas Richter: And I am a professor of numerical mathematics, I come from the field of fluid mechanics. That means I do research on all kinds of topics and in doing so I work with engineers, but also with medical scientists, now also with psychologists. One of my projects is about a large climate model, which is actually being redeveloped in France. And so I'm also getting into the area of ice dynamics, meaning one of my research areas is looking at how to represent the ice surface on the ocean in large climate models.

Lisa Baaske: First of all, it sounds like you have a good point of intersection. What does the work here in Magdeburg look like?

Dr. Carolin Mehlmann: Exactly. So I'm dealing with a particular area of sea ice, and that is the so-called marginal ice zone. That is the transition between the solid ice and the open water. And the marginal ice zone is represented by the fact that there are a lot of small ice floes, and everything is very dynamic. And I'm asking myself in a project of mine the question: how can I describe this mathematically? So how can I develop an equation that describes how these ice floes interact? And how can I then represent this zone, which is not currently in climate models, but which is getting bigger and bigger because of climate change, in climate models? And I'm working on this project together with a PhD student of mine, we're developing this model.

Lisa Baaske: What is special about this model? So why can't current climate models represent it yet?

Dr. Carolin Mehlmann: Current climate models are concerned with how the ice moves on average. So if you have a certain area then you would look at: okay, how is the ice in this area, and you average over the movement of the whole floes and describe statistically on average how that moves. But when you get to the marginal ice zone, you have the problem that there might not be enough floes in that area. You have a lot of open water and only small individual floes. And then this approach, that I want to describe something on average, doesn't make sense anymore.

Lisa Baaske: What does your day in Magdeburg look like?

Prof. Thomas Richter: Well, the semester just started. That means that at the moment I spend a lot of my time with lectures and seminars, but then I also have a whole bunch of PhD students who are working on all the different projects. And in between, I meet with them a lot. In other words, you can say that there is very little time for your own research during the semester. Then there are the trips to workshops or conferences that I sometimes squeeze in. It's all very varied and a lot of fun, but when things are going well, I have a half day every one or two weeks where I can really concentrate on trying to figure things out myself and make progress in mathematics. The other work is also mathematical work, of course, but I don't do that on my own; instead, I guide and collaborate within the teams.

Lisa Baaske: I see. I think that's probably more of a question for Dr. Mehlmann because that's what she's primarily concerned with. But why research on sea ice of all things?

Dr. Carolin Mehlmann: I got into sea ice a bit by chance. I always knew I wanted to do something applied. And I wanted to do mathematics that would be useful to people and that could be used in everyday life. Of course, sea ice is abstract at first. If you were to do a survey in Magdeburg right now to ask: "How important is sea ice to you?", most people would probably say "not that important right now". I got into this research area of sea ice dynamics a bit by chance, also through my doctorate. Then I also worked in Hamburg at the Max Planck Institute, which also develops climate models, and there I was responsible for sea ice. But it could also have been tsunami early warning systems, for example. This scientific factor has always interested me. In the end, it was sea ice, and that is of course a fascinating field of research. You can also go on great expeditions. Of course, that's also something that motivates you even more when you see what you're researching.

Lisa Baaske: Yes, and sea ice is actually not that uninteresting for people in Saxony-Anhalt either.

Dr. Carolin Mehlmann: It's important, but it's still very abstract. Because when we look out of the window, that's not what we see at first.

Lisa Baaske: Yes, absolutely understandable. And how did it finally come about that you both took part in an expedition to the North Pole? What kind of expedition was that?

Prof. Thomas Richter: We were traveling with the ship "Polarstern", which is the German icebreaker that is actually used for research tasks all the time. It always alternates between sailing north in our summer months and south in the winter months, so that the light is always there. And the thing is, there are a lot of people on the ship. That means that you can't just say, "I'm going to get on board and book my trip," but an application is submitted a long time in advance by a so-called cruise director. In our case, the cruise director was the director of the Alfred Wegener Institute, who applied for this trip, and the rough timetable had been fixed for a very long time. I think just about two or three years in advance. And we wrote an application to be able to go on the trip.

Dr. Carolin Mehlmann: Some background, we complement each other very well in terms of content. I just had this project, which is about describing this particular zone. And Thomas complements that quite well in terms of the mathematical method, also for an optimal experimental setup, which we then used on the ship. So it developed a bit in such a way that we participated together.

Lisa Baaske: You "attached" to the expedition, as it were, if I understood correctly. What was the main goal of the expedition? Why did the ship set off in the first place?

Dr. Carolin Mehlmann: The expedition was called "ArcWatch" and the idea is to observe how the Arctic is changing in the wake of climate change. Data had already been collected once in 2012, and the idea was to visit the same points again by ship, collect data and see how the habitat there has changed. It was also a very emotional moment when we reached the North Pole and the captain made a little speech. It was very short, about three or four minutes, but he said that in the early 90s, in order to reach the North Pole, the "Polarstern" still needed the second icebreaker. That means that the ship couldn't just go there to take measurements. And now we have reached the North Pole with only 30% of the ship's engine capacity. He had just described that briefly, and I found that very depressing. When you know that the ship can now just sail there, without much effort and without much difficulty. That was very impressive.

Lisa Baaske: Yes, that does sound pretty scary. You always hear about it, but in the end, you don't get much direct experience. And then you experienced it very much yourself that it is very, very difficult. As you mentioned, you boarded the ship in August. What was the preparation like before that? Not only for your research, but also in general for everything around it, for example the cold.

Dr. Carolin Mehlmann: Yes, there were different stages. At one time we were together at the clothing camp in Bremerhaven, where we were able to borrow special equipment from the Alfred Wegener Institute. We tried on shoes, snow pants, snow jackets and also had a polar bear course.

Prof. Thomas Richter: The reason is that we also left the ship. That means that during the voyage we worked on the ice itself, and polar bears also live up there. They look quite cute from a distance, but you don't want to meet them up close. They are very curious. And the curiosity shows itself then in hitting and biting. They may not mean any harm, but they want to have a taste. And that's why it's important when you're outside to take care of yourself a little bit. That means that whenever a group is outside, for every five people or so, you have to have a so-called polar bear guard. And that means one person does nothing but stand around and watch for polar bears. The person also has a rifle with them and a signal gun. But first of all, you have to say generally nothing happens. I asked several times, and I was told not a single polar bear has ever had to be shot on Alfred Wegener Institute ship expeditions. Fortunately. But still, you have to be prepared for that circumstance, and of course you can't just walk around with a gun. Well, actually you can. It's international territory up there, so it's not really clear what the laws are. But of course you want to handle it responsibly and not just hand a gun to someone. That's why there was a preparatory course beforehand, where you learned mainly in theory: How do you deal with polar bears? How do you even hold a rifle without shooting yourself in the foot and how do you use it in an emergency?

Lisa Baaske: You wouldn't think that if you were going on a North Pole expedition, you'd have to learn how to use a gun first. But of course that makes total sense listening to you now. Was there anything else besides polar bears and clothing?

Prof. Thomas Richter: Of course, you're on the road for a long time. You’d be gone for two months. That means that even when you're not thinking about research, for example, I downloaded enough different books onto my Kindle. I'm not much of a movie watcher, but I downloaded some audiobooks and podcasts beforehand so I could have those with me. It ended up not being boring, but you don't know how it’s going to go in advance. And I’d made sure that I could be confident that I wouldn’t get bored there.

Lisa Baaske: You have to make wise decisions about what to take with you.

Dr. Carolin Mehlmann: Otherwise, it's also a bit of an organizational matter. If you're not here for two months, then you also have to take care of your employees so that they know who to contact. For me, it was a lot of organizing beforehand. You hoped that you really hadn't forgotten anything. It was really a relief when you finally got on the ship. I don't know how many times I was in Bremerhaven this year because that's where the Alfred Wegener Institute is. We also went up to the "Polarstern" once before because we assembled our camera system and checked whether everything was working. Then you go from one course to the next, you have a meeting with the team leadership. With our project we were assigned to the physics team, and we also met with them beforehand. So getting to know each other and discussing a bit how it works. And for me it felt like there was a lot of organization, and only when you were on the ship did you think to yourself, "Now it's finally going to start.”

Lisa Baaske: I can imagine that very well. How many people were generally on the ship?

Dr. Carolin Mehlmann: We were 50 scientists and 50 crew members.

Lisa Baaske: Quite a few people, I would not have thought.

Prof. Thomas Richter: But the ship was big, you would get lost.

Lisa Baaske: Okay, so you didn't have the feeling that you were standing there with 100 people in a very small space.

Prof. Thomas Richter: No. That was one of my worries before, that it might always be annoying because you never have your peace. But that wasn't the case at all, the ship is bigger than you think.

Dr. Carolin Mehlmann: Yes, it has a lot of floors, but the ship was at capacity, even to the last seat for the scientists. There was one room that was occupied by four gentlemen. And I think that was also a very intense time for the four of them, two months together in a very small cabin.

Lisa Baaske: So either a friendship for life was formed, or you never see each other again afterwards. What were you most looking forward to before the trip? And what were you perhaps most anxious about?

Dr. Carolin Mehlmann: Well, I was most excited about sea ice, and that was also a great moment, when you go to the ice, the ocean suddenly becomes very calm, because the waves are dampened by it. And then you really see a streak of bright flashing on the horizon, so to speak, something that shines. And that was really a great moment, driving into the ice. And a little bit of worry that maybe at some point you think I want to go, but you can't go because you're on the ship and you're there for two months, whether you want to or not at that point.

Lisa Baaske: But was there that point?

Dr. Carolin Mehlmann: Sure, yes. I had underestimated that a little bit. The weather is very bad and it's very, very foggy, we had maybe five sunny days in two months. It's like a really heavy November here and then you get to the point where you think: I just want to go outside and see a green tree. So yes, there was that.

Lisa Baaske: So when I thought to myself, here in August at 34° C, it would be nice if it got cooler, you probably thought the exact opposite.

Dr. Carolin Mehlmann: Exactly, the sun should really come out again.

Lisa Baaske: I can imagine. And what were you most looking forward to and what were you anxious about?

Prof. Thomas Richter: I think I was looking forward to it being like time off. I actually promised myself a lot of rest. I was also thinking that in between, when we're just cruising with the ship and when there's nothing to work on on the ice, that we'll have a lot of time to work on stuff, like a kind of research sabbatical. I had a little list of tasks that I needed to do for myself, and I thought, well, that's really where I'm going to have the time and peace to do that. It didn't quite turn out that way. It was just a lot more work than I thought it would be. I got a little bit done, but nowhere near what I thought I would. But on the other hand, none of my fears came true. One was that it would be annoying because the ship was always full, but you really had enough peace and quiet. And then I thought to myself, it was almost always light. Towards the end you got towards sunset, but it was always light, and I thought, maybe I wouldn’t be able to sleep there, but that wasn't a problem at all.

Lisa Baaske: Did you have a sleep mask then, or do you just get used to it?

Prof. Thomas Richter: That wasn't necessary at all. We had blinds to pull down, but that was really a thick screen. Nothing could get through.

Lisa Baaske: I see. Very interesting. You rarely say those words, recently me more often than usual because I got in touch with you. But you two are just back from the North Pole. The research vessel "Polarstern" returned in October. How long exactly were you away, and where did the route take you?

Prof. Thomas Richter: We were on the road for two months. We started in Norway, in Tromsø. At the beginning of August, the first, second maybe, we left. And then we just went north. That is, we passed Spitsbergen, there was a short stop for tax reasons and for refueling. I didn't quite understand that. Then we needed a stamp and we had to buy some flour for the trip. And then we went up and that wasn't long at all, that wasn't five days in total. And then we reached the ice and from that point on you were in the ice. And you can imagine it like this: on the trip we had nine ice stations, that's what you call it when the ship chooses a large ice floe. And then we anchor ourselves to that ice floe. So you really anchor yourself to the ice for one or two days in order to be able to work there stationarily. Yes, that's how we made it a very long way. The route with the ship had a fixed destination, we wanted to retrace the expeditions of twelve years ago. That is, we went up and I think it was about the 85th parallel, where we then stayed for quite a long time, and then went very far east. So if you look at the map, we made about a 1/4 turn around the earth. Then we drove straight up to the North Pole and at the North Pole everything falls together, then we drove over the 60th degree of longitude back south. So it was quite a long trip, and every few days there was a two-, three-day stop.

Dr. Carolin Mehlmann: You could estimate that we were really permanently in the ice for altogether about six weeks. And you can imagine our work like this: we anchored, that was about three days of ice station, then we drove two days of transit to the next floe. Then we repeated the whole thing and recorded the data. So there was basically always a change between "We go to the next ice floe", "We are on an ice floe", "We collect data" and then packing equipment, unpacking, cleaning...

Prof. Thomas Richter: Well, maybe it's important that there were only eight people in our team out of 50. And then there were others who also worked on the ice, biologists and chemists. But a lot of research was also done directly from the ship. That is, a great deal of research was also deep-sea research. Then either the seabed, that is, the mud is brought up to be able to examine it on deck, or photographs were taken of the seafloor to get an overview of the animals and plants there. That is, it was not only the ice, there was research being done on the ship all the time, day and night.

Lisa Baaske: But it's also very interesting, because it's so interdisciplinary that you can also look into other research areas to see how they work, right?

Dr. Carolin Mehlmann: Yes, it was also refreshing to see something different. But it was really like that. You can imagine it like a small power plant. Research and work were going on around the clock.

Lisa Baaske: That sounds very, very interesting in any case. You had already mentioned a few things, like it just doesn't get dark. Were there other things you had to get used to? I can imagine that life on a ship has its own peculiarities.

Dr. Carolin Mehlmann: Several. For example, what was interesting to me at the beginning was that there were fixed mealtimes. It's not like you go to the cafeteria with your colleagues at some point. It shifts a bit every day, depending on the situation. And there were really fixed mealtimes, which were sometimes very early for our understanding. Lunch was always at 11:30 a.m. and dinner at 5:30 p.m., then in between there was a cake time, a breakfast time... you first had to settle into this everyday life on board. Once a week there was a store where you could buy chocolate, and you had to make sure you didn't forget it. There was another day for when you needed toothpaste again. You also had to get used to a certain rhythm. The interesting thing is that the crew continues to sail, not only with us. The "Polarstern" is still sailing, we got on in Tromsø, and they are all already in their rhythm. So you come onto the ship as a guest and first have to settle into the daily rhythm.

Prof. Thomas Richter: Yes, and what's funny, of course, is that we sailed through the ice almost permanently, which means that you constantly have a small crash in front of the ship. It wasn't that loud most of the time, but it's different to when you travel on a ship normally. It's not a swaying, but rather random movements. Once the ship hits the thicker ice, it kind of sags to the side a little bit. It was a bit irritating, but after a couple of days you actually hardly noticed it. What was maybe weird is that life on the ship is very vertical. It was 100 m long, but you rarely go from front to back. So you walk a surprising amount. You can see that on your phone these days if you look at it. I think I still got to 8,000 steps a day. But I averaged over 35 floors a day. You were constantly moving from top to bottom.

Lisa Baaske: Awesome. Did you actually know beforehand that you would definitely not get seasick?

Dr. Carolin Mehlmann: I was on an expedition before, I knew that.

Prof. Thomas Richter: I assumed that I wouldn't have a problem because I also don't have a problem reading on the bus. I was a bit nervous because in the end you don't know how you will react. But everything went well.

Lisa Baaske: That's good, then. I think that's the worst moment, when you're on it and think: Oh God, this isn't going to work. You've already told us a bit about everyday life. Many, many stairs, obviously. What else did everyday life on the ship look like? Please take us through a day with you!

Prof. Thomas Richter: Yes, in the morning it started with breakfast. To be honest, if we didn't have to go on the ice, I skipped breakfast. That was too early for me, and there was too much to eat anyway. You could actually get a snack all the time in between if you wanted to. And then it just depended. Let's say it was a day where we didn't have ice work. Then it was usual that you had normal office work, like here at the university. Our team had a small, nice office up on the ship and then I just worked there. Actually, it wasn't very different from the university, I just didn't have my PhD students with me. And then it started. Then came lunch, and after that time was running out. After lunch there was a little time to work, but mostly the planning started then. For example, if ice work was scheduled for the next day, then we had to coordinate and plan, we had to pack sleds with all the equipment we needed. Then it went on, then we had cake. Immediately after eating the cake, there was usually the so-called science meeting. That means this was the big meeting with all the people from science where the planning was done for the next part of the journey, but then first results were also presented. We had to evaluate our findings. Maybe it took longer for us, but we were also able to present something. But for example the biologists could directly show some pictures. Right after that there was already dinner. So there was very little time. And then you either worked a little bit, or there was also a small gym, there was a sauna and a small swimming pool. It was more like a paddling pool, but it was enough to play a little water polo. So the days actually went by quite quickly, but also with, this was a surprise to me, a lot of work. It wasn't as quiet as I thought it would be.

Lisa Baaske: And the constants were obviously the food, very interesting!

Dr. Carolin Mehlmann: Yes, because you always have these appointments. There are also lots of containers on the ship and all the things are stored in those containers. They are large containers like you might see in the port of Hamburg. First you stand in front of a container like that, and quite honestly, you don't even know how to open it. And then you learn how to open containers, how to build a large ice drill. What parts does it actually consist of? Which parts do I have to pack into my sled? After that, you always have to clean everything, always hose it down, and stuff like that. So it was always very busy, especially around the ice station.

Lisa Baaske: And what did an ice day look like then?

Dr. Carolin Mehlmann: An ice day probably started around 8:00 or 9:00 a.m. Around 7:00 a.m., the head of the ice physics team went to the captain on the bridge and used satellite images and the radar on the ship to select a floe large enough for all the teams to work on. That's in the kilometer range in terms of size, I would say. And then anchoring was done, that is this ice anchor was put on the floe. Then there is an explorer team that goes out onto the ice floe and checks that the ice is thick enough, then paths are marked, and a camp is set up. Where is it okay to walk? What measurements are taken in which area? This drags on a bit until everything is checked. Then we get on the floe with our sleds probably between 10:00 and 11:00 am. They are packed the night before. Then 15 maybe 20 scientists get on their sleds and all walk onto the floe. You then go to the different stations; we were mainly also supporting the ice team. There, a huge hole, about 1.5 m by 1.8 m, was dug into the ice so that a diving robot could be lowered down there. That means that on the first day, you were actually busy digging this hole and setting up a grid. You had to put flags and markers under the ice so that the robot knew where to dive.

Lisa Baaske: So that also means a lot of physical work, right?

Dr. Carolin Mehlmann: Yes, this ice hole always had to be dug and drilled in a four- or five-day rhythm, which was very physically demanding, I would say. After that, there was diving. That was the second day. At the ice station, it was mainly this robot that was dived, we were busy with the camera system. And on the third day, everything had to be dismantled again, the sleds pulled back... that was also very physical again.

Prof. Thomas Richter: Well, digging a hole did make you sweat. I always called it gardening in winter. The ice was between 1 and 1.5 m thick and you had to move a lot of ice, which is also very hard. And to drill through it and saw through it was very exhausting. On the other days it was often the case that the ship was not there. On the first day, the ship was always there because there are various safety regulations. When the ship is not at the floe, a maximum of nine people is allowed on the ice, so that in emergencies you can bring everyone back on the helicopter. But on the first day, it was always very busy with a lot of teams. And that's when the ship was there, and everyone really poured out. And on the other days, there was often only our team and a second team, where longer examinations were carried out. And those days were very quiet in part. On the one hand, the noisy ship was gone, we had generators for the diving robot on the ship, but nevertheless it was relatively quiet and less happened. One of the main tasks, this sounds very boring, was for example that you stand at the hole of the diving robot and do the bear watch, and maybe once an hour you get the message by radio that the robot is coming back. Then you hooked it up briefly, but otherwise not much happened. Sounds very boring, but that can also be very nice, because that's an atmosphere where you otherwise never get to go. Yes, and then that can go differently. It can be a couple of hours, but it can also be that maybe something doesn't go very well with the others. For example, if the ship has problems retrieving any deep-sea equipment, then that's delayed. And I think one time it was like, instead of 8:00 in the evening, then you didn't get picked up until 4:00 at night. But that didn't make that much difference, it was still light. It was still very nice, and it was simply unique. You had to put up with that for a while.

Dr. Carolin Mehlmann: It was always a very nice moment when the ship returned. It was very foggy, like here in November, and then you see the "Polarstern" emerge from the fog. For example, you've heard over the radio: okay, we'll be back in an hour, and then you can imagine it's like waiting for a bus. If it was the day of the dismantling, the scientists already had everything together, and then nine people in red suits sit there and wait. And then the ship arrives and picks up the scientists again.

Lisa Baaske: Sounds like very, very special moments in any case. Yes, that's basically already the next question. So was there anything that happened during the expedition, any moment, or maybe several, that you still remember very vividly and where you say, I'll still tell my great-grandchildren about that later?

Dr. Carolin Mehlmann: We actually had two encounters with polar bears. Once in a transit moment between two ice floes, meaning the ship was traveling from station X to Y, and once at an ice station. I was on bridge watch, because when scientists are out working on the ice, someone always has to be on the bridge with binoculars, too, to see if polar bears are arriving in the distance. I came on duty on the bridge at 8:00 in the morning and then I was already told that there was a polar bear 3.5 km away. So the one who did it before me did it very well and really saw a polar bear at a great distance. And that was very exciting and thrilling. Then it was my job, with another person, to track this polar bear with binoculars and to let them know when it was close enough to the ship. Because at the same time there were scientists out on the ice doing their work. And then at some point a mechanism is triggered that says: no, you have to come back now, the polar bear is close enough. And of course that's also a big responsibility, because if a polar bear swims a little bit, then it's just a little white dot swimming from one ice floe to the next. So that was a very exciting and impressive moment. And it really came. The polar bear had come from these 3.5 km to the measuring stations, because for it this is of course interesting. I will never forget that.

Prof. Thomas Richter: Yes, and that's where it went perfectly. That's exactly how it should be. We were far from having to shoot at it. You could see it really far, it was very controlled, but there was also good visibility, and the bridge is 20 to 25 meters high, so you can see quite well. Another less nice or rather funny experience: quite early we passed a cruise ship. It was a French cruise ship, and they offer a trip to the North Pole every two weeks in the summer, where you can go there for a lot of money. And of course that's okay somewhere, but it still feels very strange that you have an area where you think you should actually leave it alone. Even as a scientist, you feel a bit like an intruder. It seems strange to you. And besides, it's also a sign that the ice is no longer what it used to be. If you can just go there like that.

Lisa Baaske: Absolutely. I actually didn't know that at all. Of course, it's typical of humans that everything is turned into a tourist attraction. You were there because you wanted to check whether your model actually depicts how the floes move. Does it? How did you investigate this?

Dr. Carolin Mehlmann: We tracked the movement with a camera and then evaluated and described it. And we found that there are situations where this works. But there are also situations where it doesn't work. Our Earth is even more complex than the model I proposed. For me, this means that we have to expand it even further in order to be able to represent all the different situations. That's the way it is in research, too; sometimes you just have to keep thinking and keep working. But it is a partial success.

Prof. Thomas Richter: Maybe I can explain that a little bit. Roughly speaking, the ice floes are driven by the wind. The very rough rule goes back to Fridtjof Nansen from a long time ago. The ice floes are driven by the wind and they have about 2 to 4% of the speed of the wind speed. But this does not go in the same direction, because of the rotation of the earth. This is a force that always acts on everything that moves, the Coriolis force. And that's why the rule is, they're moving at 2% to 4% of the speed, and they're deflected maybe 20 to 40 degrees clockwise if you're in the northern hemisphere. And that's because of the Earth's rotation. Our idea was actually that we narrow that down a little bit, that we understand what is that 2% to 4%, where does that 20 to 40 degrees of deflection come from? How does that depend maybe on the floe size? But we found out that can also be 100 degrees difference. The velocity matched quite well, but the deflection didn't match at all. And it's not like you can just say that's a failure because of that. Not at all. But the work is not done, it's really just starting now. The bottom line is that we found out – which is maybe not so confusing and so special – that the environment is quite important. If a small ice floe of maybe 10 m in diameter moves next to a very large covered area, then this large area has a strong influence on it. And we can explain that as well. The question now for the future: how do you build that into Carolin's model? Because the explanation we have is much too complex, it couldn't be built into a computer model. So that's where the research is really starting now. It's not quite as simple as we imagined, but that doesn't mean it's boring.

Lisa Baaske: Basically you went on the expedition to see whether what you are theoretically considering here in Magdeburg works. And that's basically quite good when you realize that it works, but you have to readjust it.

Dr. Carolin Mehlmann: Exactly, in which situations does that work? If the ice floes are all very small, the same size, and the conditions are all in a similar direction, then it works. But if it's not so homogeneous, coarse and very many small floes, then they do influence each other very strongly. And we have to integrate that into the model now.

Lisa Baaske: What data, impressions or new ideas will you take with you from the expedition? So when you go into the office tomorrow, what are the first results that you are working on now?

Dr. Carolin Mehlmann: The first results are that we have understood that in some situations it works, and we know what those are, and in others it doesn't, as Thomas just described. And then, however, that means that we have to process a lot of data. A huge pile of data.

Prof. Thomas Richter: Yes, these are individual images. And that's probably about a terabyte.

Dr. Carolin Mehlmann: Yes, it has to go completely through algorithms, and then we can continue working. And these first results that we have now are data that we have already processed during the time on the ship, whenever we have managed to do so in terms of time. And then we have already seen as a first impression, this works, this does not work, but that means now first of all to process really a lot of data. And when you have an overview of the data, then you can adjust the model and the equation.

Lisa Baaske: For you it was already the second expedition. Are there any more expeditions coming up in the near future? What are the plans for the future?

Dr. Carolin Mehlmann: Now I really have a lot of data. I would say, before I do the next expedition, I should definitely utilize and process these things first. So for now, no next expedition is planned.

Prof. Thomas Richter: I've had enough for now, even though it was really a lot of fun. But the time commitment of two months is of course extreme. Life goes on and that catches up with you now. The semester starts without any preparation. Yes, the work with all the other projects has been left behind a bit. And the whole thing only worked out by chance anyway because the trip was right during the semester break. Otherwise it would have been very difficult for me. And then I also think to myself that time is something very valuable. It was really exciting. I had a lot of fun. But the next time I do something like this, I would like to see something completely different. Antarctica is supposed to be very beautiful. But maybe there are also interesting research areas where you can get around, where it's a bit warmer. That wouldn't be bad either.

Lisa Baaske: Maybe into the desert or jungle, who knows. What is also in the near future is the "Climate Change and Mathematics" theme year that you are launching. Tell us a little bit more about it. Who is it aimed at and what can people expect?

Dr. Carolin Mehlmann: We are now in the final preparatory stages of the theme year, then the project should start in 3 to 4 weeks. And the main group is students, their parents and family, so to speak. The idea is that we offer a working group and then they can come to the university. It's not so obvious what mathematics has to do with climate change. I think it's the case that many people wouldn't connect it at all. And the idea of the working group is to show how important mathematical methods are in order to be able to deal with the situation we are in, namely climate change, and to create understanding. We also have to do mathematics in order to deal with such a difficult and complex situation. And that is part of this theme year.

Prof. Thomas Richter: Exactly, we really want to show that mathematics can be quite interesting and exciting and also diverse. That mathematics is not just the image you often see in movies of some very introverted pale person sitting in front of a computer. Maybe there's a little lamp on, maybe he just has a pen and paper, and he ponders for days and weeks. And at some point, he is happy that he has proven something that nobody understands. That really exists, that's part of mathematics. But to be honest, we have nothing to do with it. For us, mathematics usually means, in this case with the sea ice, that there are some problems. And the problems don't come from mathematics, they come, for example, from medicine or, in this case, from climate science. And you need mathematics to understand the problems and hopefully to be able to solve them. And that's what we're trying to convey, that you can also work practically with mathematics and that it's just extremely versatile. So we hope that, of course, on the one hand we create attention for the topic and an interest in people. But we also hope that we can really work a bit on the image of mathematics and maybe even persuade people in the long term to go into it a bit more deeply after school.

Dr. Carolin Mehlmann: Exactly. And to reinforce this point, in addition to the working group, we also have a series of lectures in which we invite various scientists who also work in the climate field to come to Magdeburg. They then give lectures, but those are designed in such a way that they are also aimed at the broader public. So you don't have to be a mathematician or physicist to attend the lectures. We are already looking forward to our first speaker on Nov. 16th, that is Dirk Notz. He is a climate researcher and has also contributed to the Assessment Report of the Intergovernmental Panel on Climate Change. And he is also looking forward to getting schoolchildren excited about this environmental issue. I think that's great.

Lisa Baaske: That sounds super interesting. I hope the podcast also helped to show a little bit that mathematicians do totally cool things. It definitely worked for me, that I thought to myself, gosh, mathematics isn't that bad. Many, many thanks for being here!

Dr. Carolin Mehlmann: Yes, my pleasure!

Lisa Baaske: So, I hope we'll hear a lot from each other again, perhaps when the next expedition to the desert is coming up, so please feel free to get in touch. So, dear listeners, I hope you enjoyed it and will tune in again next time. Stay healthy!

Outro voice: Knowledge when you want it. The podcast about research at the University of Magdeburg.



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