Hello. My name is Benjamin Robin. I'm a researcher at the Alfred Wegener Institute in Germany. Today, I'm going to talk to you about a big Arctic Drift Expedition called MOSAiC, where a ship will drift for a whole year across the Central Arctic. I'm going to focus in particular on the liquid ocean part of that experiment. Here, you can see a map of the Arctic Ocean. It's basically here located between Asia on one side, Europe here in the bottom right, and on the left here you can see North America. That big white thing here, that's Greenland. The MOSAiC drift has actually started already in this central region of the Arctic Ocean in the deep part of the ocean. Is going to drift for a whole year near the North Pole, and then towards the Fram Strait here near Spitsbergen. As you've seen in the map, the Central Arctic is actually quite close to where you may be living. So anything that happens in the Central Arctic could actually get to lower latitudes, like to where you live in a couple of days through the atmosphere, for example, things like cold spells. Another thing is that the ocean is strongly connected to the lower latitudes as well. So on scales of months to a year, those things that happened in the Arctic can reach lower latitudes and vice versa. Here you can see a schematic of the different processes that we're interested in studying during MOSAiC. Now, we're focusing on the smaller scales. By scales, I mean things that are large or small in space. Here, we focus on the things that we can usually not observe with our long-term, large-scale observing systems. So we are particularly trying to study what happens in the atmosphere. Things like cloud formation, how that interacts with the surface, for example, the sea ice and the snow or the ocean below. So the interaction between these different parts is particularly important to us, which includes things like the ecosystem and biogeochemistry. One of the processes that we're really interested in the ocean is, how the currents behave. Now, the currents can be generally larger scale going into a certain direction over hundreds of kilometers. But you can also have little worlds or eddies in the ocean. Those are very important because they can push water that's for example, a little bit warmer into regions which are not so warm. Other processes are fronts that can be, for example, generated if the ice suddenly opens in mid-winter and the ocean it's exposed to extreme cold. Two parameters that are really important for physical oceanographers are temperature and salinity. That means how salty the ocean is, how much salt is in there. By that, I mean something just 35 grams per kilogram. These parameters are particularly important because they determine how stacked up or how well-layered the water is. If you have strong differences in these parameters, then the actual density of the water is very different and the water can be very stable. Conversely, if you increase, for example, salinity near the surface, you would increase the density and eventually would start to mix the upper water column. That's what happens during ice formation. Coming to that, we're very much interested in the mixing of the ocean. So how much different waters in the vertical mix? This can also happen in horizontal of course and a very important parameter there is turbulence. That's the tiny wiggly motion that we get to the ocean over centimeter to meter scales. Some of these processes you can already see in data that we've actually obtained before MOSAiC started. Here's a picture near the starting region of where MOSAiC started, taken a few years earlier by an autonomous drifting buoy. This buoy was actually mounted in the ice and measured in a few 100 meters below in the ocean. This is salinity near the surface and it shows you that there is a large-scale gradient. So on this map where you see North and East, you can see over scales of 100 and more kilometers that salinity is varying. But what you can also see are these really tiny dots that are actually varying on very small scales, something like a few to 10s to 20 kilometers. Those are the kinds of variations that really want to measure and understand in MOSAiC and they could be caused by things like passing eddies in the ocean. Here I show you the kind of rough setup that we have in MOSAiC very schematically. So you have the Polish stir and the big ship drifting next to an ice flow. Since it is fixed to this ice flow, people can work on the ice. There are different devices on the ice, measured in and both and under the ice. A lot of them have to be regularly serviced by people from the ship, and some have to be actually operated directly by somebody standing there. In addition, we've got this autonomous network around us of different buoys on the ice that measure above, in, and under the ice. Those devices can give us measurements like the temperature or the salinity I've just shown you and send this data in near real time back to the satellite, and people can even see it on the ship. That can help us to put everything into the context of a few tens of kilometers around the ship and understand these processes better. Now, where do we actually study? I've already shown you roughly on the map right in the beginning. Here you can see a similar kind of map, only this time you also see a typical ice cover in this particular case from October this year. The little box with the red dots in it, that's where the MOSAiC actually started and the big black arrow is pointing towards it. When you follow the kind of split arrow with the labor called Transpolar Drift, you will see that it passes the North Pole, it's something like 100 kilometers, and then goes towards the Fram Strait, near Svalbard, then eventually go into the Nordic seas. That's the drift track we kind of expect and it's part of a larger current that is marginally driven by the atmosphere pushing the sea ice and the ocean across the Central Arctic. Here, you can see a much more of a zoom-in Polarstern on the bottom right and the sea ice around it. Now, the sea ice is she given in these blue shades and the whitish actually little piled up bits of ice so-called ridges, with the ices crushed together and deformed to give a little mount on the top and below. Those are little white bits and the blue bits are actually much more plain and level ice. In the white circle, you can see ocean city. That's our main workplace on the ice near the ship. Here, you can see a picture just after the setup, and you can actually still see the daylight in the background, something that for the next few months, people will not be experiencing on the ship. In that little tent here, you see the door with a little light inside. That's where we do a lot of our measurements. So the tent is on the ice, but there's actually a big hole in the ice below and the hole in the floor of the tent as well that we can open, to lower devices into the ocean and measure. On the outside, you can see a lot of the logistics around this. For example, the power lines, which tend to be along the main paths to the ship and which allow us to actually run instruments out there and have a data connection. Now here, you see the inside of the tent when one of our main instruments has just come up. This is actually a device we use not just to take water samples, as you can see by the bottles, but put a lot of instrumentation on it that can measure things. For example, temperature, salinity, but also other parameters of biological and biogeochemical nature. Here, you can see a person taking a water sample right after the instrument came up. What have we measured already? Well, here's an example of some of the autonomous systems that I told you about, that are dispersed around Polarstern within tens of kilometers around the ship. Here you can see the drift tracks. So they started roughly in the bottom right of this plot and when more or less North Westward, as a big arrow on the left indicates. The stars are the current locations and the small star that is of slightly different color in the middle that's was Polarstern. This is the status on the 23rd of October this year. Those instruments measured temperature and salinity for us at different depths in the top 100 meters of the water column. You can see that here where I've plotted U-salinity, at 100 meters along the track of one of those devices. Now, you can see there are some smooth gradients here and salinity. So the blues are the low salinity and the greens and yellows, they are the higher salinity values, so saltier water. In addition, you can see that small patchiness where the little dots next to each other very, and those are due to things like this little worlds or eddies in the ocean or it can also be caused by fronts, for example, within the middle of winter, the ice suddenly opens up and the ocean is exposed to extremely cold atmosphere. Those measurements are interesting in its own right, but understanding those processes will also significantly help us to improve numerical weather prediction or climate models that run on large scales over 100 years or longer and they can currently not preserve all those processes. I hope I've given you a bit of an overview of what we do in the ocean team during MOSAiC, and how we interact with the others.
