Interview: Understanding Antarctica’s Ice
Freshly returned from the Antarctic Winter, to the cold Belgian spring, glaciologists Frank Pattyn and Reinhard Drews from the Université Libre de Bruxelles (ULB) tells us about their work in the field during this year's BELARE campaign at Princess Elisabeth Antarctica.
Frank Pattyn, ULB professor and researcher in the IceCon project, which aims to gain a better understanding of the rate of the loss of ice – now and in the past - from the Antarctic ice sheet in the Dronning Maud Land area.
Did you accomplish all your goals for the season?
The IceCon project is a multi-year programme. This means that we took measurements this season and we'll have to take measurements in future seasons. We managed to do everything that we wanted to do this season. We even did more than we wanted, in fact.
This was in spite of major time constraints?
There was as lot to do. Logistically, it was a very complicated programme. There was not much time to spare. But we were very well-prepared. We spent a lot of time at Princess Elisabeth station setting everything up and testing all the equipment. So when we went into the field, we could get started right away.
What did you accomplish this season?
First of all, we installed two continuous GPS stations. One was put on top of Seal Nunatak (a nunatak is a rocky outcrop sticking above the ice), which is 65 km from Princess Elisabeth Antarctica and 10 km from Romnoesfjellet Nunatak, close to where the former Japanese station Asuka was located.
The continuously-functioning GPS station will measure over a four-year period the position of the nunatak it sits on. The nunatak's position is likely to change horizontally due to tectonic movements in the Earth's crust. But more importantly, we're interested in how its position will change vertically as the ice sheet loses ice mass.
During the last glacial maximum (LGM) some 20,000 years ago, the Antarctic Ice Sheet was significantly thicker. From the start of the last deglaciation, which began 11,700 years ago until the present, the ice sheet has been losing mass. The continental crust rebounds as the weight of the ice on top of it diminishes. Ice loss was much greater at the beginning of the deglaciation. But the process is still ongoing. This kind of rebound is also happening in Scandinavia, for instance.
The measurements we're taking with the GPS station will help us learn more about the volume of the Antarctic Ice Sheet during the LGM.
How many GPS stations did you install?
We didn't install just one GPS station (what we installed is similar to what we've installed at Princess Elisabeth a few years ago) - we also installed a GPS station near the coast, on the Derwael Ice Rise.
But have to take into account is the fact that the GPS does not sit on top of rock, but rather on top of flowing ice.
One problem you have for GPS measurements is that there's not a lot of exposed rock available in Antarctica. About 98% of the whole continent is covered by snow and ice. So sometimes you don't have the option of installing instruments on solid rock. You have to manage with putting them on the flowing ice. So you need to take into account variations due to the motion of the ice. This requires not only setting up a continuous GPS station, but also extra measurements that allow you to measure that extra signal.
What kinds of extra measurements did you have to make?
Several kinds. We had to drill some ice cores as much as 120 metres deep around the ice rise. This drilling allowed us to analyze the ice in the ice rise. My colleague Jean-Louis Tison was responsible for the drilling. It was very successful. The ice cores were stored for transport and are being shipped to Brussels. We expect to get them later in spring.
What will you look at in the ice cores?
One of the things we need to look at is the density of the ice along an entire profile in the region. Another thing is that the ice is compressed. It moves vertically as well as horizontally. In order to measure its vertical displacement, we drilled a series of boreholes – not with the ice core drill, but with a hot water drill, like they use to drill into subglacial lakes, only on a much smaller scale.
We used the holes to measure the change in position of the ice between the bottom of the hole and the surface of the ice. We do this by lowering an anchor down to the bottom of the borehole and connecting it with a steel cable to the surface, putting tension on the cable. Over the next several years we'll see how much the length of the cable has changed. The length of the cable between the bottom of the borehole and the surface should become smaller over time because the ice becomes compressed.
The guys from Princess Elisabeth Antarctica devised the anchor system we're using. It worked very well. It was a major achievement.
And what about the horizontal displacement of the ice?
For measuring the horizontal displacement, we used GPS markers. Reinhard Drews can say more about this. But basically, we made a network of stakes in the vicinity of this GPS station so we can measure over time the horizontal displacement of these stakes to see how much the ice is moving horizontally.
You also took radar measurements form what I understand.
The last type of measurement we did was taking high-frequency radar to see how the snow and ice accumulation in that area varies. Accumulation is a factor that influences the motion of the ice. These measurements also allow us to draw a link between the deeper layers of ice and the spatially varying patterns in the ice to the 120 metre ice core we drilled.
You accomplished a lot in two weeks.
We only had two weeks in the field to accomplish everything we needed to do. As you can see, we accomplished a lot. We accomplished even more than we needed to get done.
There was another team that worked with us on the IceCon project. But they split from us and went to the ice shelf within the framework of the Be:Wise project. Reinhard Drews, who's having his research funded by the InBev-Baillet Latour Fellowship, has been working on this project. He can tell you more.
Reinhard Drews, post-doc researcher and InBev-Baillet Latour laureate working on the Be:Wise project, aims to improve understanding of ice-shelf flow dynamics by focusing on the buttressing role of ice rises and pinning points – small offshore mountains which support Antarctic ice shelves from underneath.
What field work were you doing while Frank was working at the Derwael Ice Rise?
There was two of us working on the Be:Wise project, which piggybacked on the logistics for the IceCon project. We took the same traverse from Princess Elisabeth station to the coast with them. We joined them for a few days on the Derwael Ice Rise. This was very useful for the Be:Wise project, because we were able to take measurements with low-frequency radar, which helped us visualize the stratigraphy of the ice. This can help us reconstruct past ice flow in the region. This is something we're interested in because the main objective of Be:Wise is to investigate the buttressing effect of ice shelves, its internal stratigraphy, and changes in it. The internal stratigraphy of the Derwael Ice Rise gives some useful information.
During the first few days, we did low-frequency radar surveys at the Derwael Ice Rise. Then we took radar and GPS instruments (we shared them with IceCon members). Five of us – Kinichi Matsuka (NPI), Denis Callens (ULB glaciology laboratory), together with field guides Alain Hubert and Raphael Richard – took the instruments to the ice shelf and we set up a camp there.
Were you able to make good progress in your research?
One highlight was that we were able to access the pinning point (where the bottom of the ice shelf touches rock from the seabed protruding upwards, slowing its flow towards the sea). This was the main target of the survey. We wanted to investigate how this pinning point buttresses the ice shelf. In the first day after setting up the camp, the field guides went to the ice shelf, which is quite dangerous because there are a lot of crevasses. Alain and Raphael spent a lot of time mapping out safe gateways for us to have access to the pinning point. They were able to do it very quickly, which allowed us to collect radar data on the ice in both the floating ice shelves and the pinning point. We were able to do radar mapping for nearly five days thanks to them.
At the same time, we installed what we call strain markers. It's very similar to what we did on the Derwael Ice Rise. The idea is you put a pole in the ice and you measure its position via GPS very precisely. Next year we will have to come back and re-measure its position so we can see how much it has been displaced in relationship to all the other markers due to the ice flow. All together, we put out 26 markers so we can completely map out the strain and deformation of the ice shelf as it flows towards the pinning point.
On top of all this data, we also collected continuous GPS measurements. We left some GPS antennae on the ice for four days to measure the ice flow and the vertical displacement of the ice shelves due to the tides.
Now we need to process the data and combine it into a coherent picture. I'm really happy that we could collect all of this data.
Were you surprised by the amount of work you were able to accomplish?
We collected a lot more data than I thought we would be able to collect. First of all, we had very good logistical support from the Princess Elisabeth Antarctica team. Secondly, we had very good weather this season compared to previous seasons. We never had a day where we had to stay in the camp. We could always go outside and take measurements. I've never had a more productive season in Antarctica!
You had all of your equipment with you this season?
Yes. We took all our equipment with us. We stayed at the station for one week to prepare everything for the field expedition. It was enough time to test everything and set it up. So once we were in the field, we could get to work right away.
We didn't have any major problem. Usually on scientific expeditions in Antarctica, there is something that goes wrong. But this time we had no problems.
What are your priorities for when you return to Antarctica?
For Be Wise, we need to go back to where the pinning point is an re-measure all the stakes. This will be our priority. What else we'll do hasn't been decided yet.
And for you, Frank?
I'll be back to visit the Derwael Ice Rise for the next few years.
Did your field season go as smoothly as Reinhard's?
We had a few issues with the drilling. Ice core drilling does not always go according to plan. The drill can get stuck, or you can lose an ice sample,. The people in our team working on the drilling had a lot of discussions about what to do if something goes wrong.
But there were some neat ideas that came up that were really useful. We had all these different people with different backgrounds, and this helps you get different ideas for solving problems.
If you drill an ice core a lot in the same spot, you create a lot of what we call “chips”. Chips are crushed ice that is liberated during the drilling process. In an ice drill, you have a thick barrel with threads on the outside and the core you're taking on the inside. As the barrel of the ice drill turns, this crushes ice around it.
You can't drill too much and have the holes too close to one another. So you need to fill in the holes you've already drilled. One thing to do is to consolidate the ice chips. You do this by adding water to the whole and waiting until the whole thing refreezes.
In our situation, we needed to get water into the drill hole. Everyone proposed different ideas for getting the water down there. If you pour it down there form the surface, it can stick to the walls of the bore hole and never reach the bottom, especially if you have a hole that's 60 metres deep.
Raphael, the field guide, came with a great idea. It's an idea a mountain guide would typically think of. Using a rope system that field guides use, we lowered down plastic bags attached to the ropes. Raphael would open up the plastic bag when it reached the bottom, so we were able to effectively plug up the hole again. We as scientists would have never thought of doing something like this. But since Raphael knew how to make a rope system, we were able to solve the problem.
It's great to see that if you have such a diversity of people, you manage to find solutions more easily. It took some time, but we managed. Each viewpoint can bring a new perspective to solving the problem. This is the strength of Antarctic field work. If you work with a mix of people, you get a mix of ideas to solve problems.
And now that you're back in Belgium, you're going to start looking at the data, I imagine?
Yes, we're starting to look at the data. It will take a while before we can report on anything conclusive.
We're already starting to plan for next season. We need to analyze the data to know what we need to do for next season. There's quite a lot of data to analyze.
The field work is only a fraction of the work that needs to be done. The field work requires a lot of preparation. The field work itself is the easy part. And after you collect the data, it takes a lot of time to analyze the data.
We're confident the data analysis will go well. There might be some good things that come out of the analysis in the near future. Watch this space.
Warming of the Southern Ocean is an issue that is contributing to the melt of outlet glaciers in west Antarctica, according to research. Have you observed any warming of the ocean in the Dronning Maud Land region of East Antarctica in your research?
It depends where you are.
For example, near the Derwael Ice rise, we have observations of what's going on with the circulation of the oceans in the region. In one area, we measured and calculated the amount of melt that was happening at the grounding line of the ice shelf (the point where the ice flowing off the continent leaves the bedrock and starts flowing out over the water). There was a very low amount of melting, though. We found that there is a circulation underneath the ice shelf, but that is a very weak circulation.
On the contrary, to the west, it's a completely different picture. There, we found there's an upwelling of warmer water. The problem is that we have no observation yet that this is having an effect on the flow of ice off the ice sheet. Since we've only just started observing this area, we don't know whether this phenomena has been there a long time, if it's something new, or if it's something that happens only every so often.
You haven't been observing this area for too long, though.
No. But we have satellites that have been observing the area. They take a lot of measurements, even if they're not in-situ.
But another thing about the Dronning Maud Land region is that ice accumulation in the region has increased over the last decade. And that of course this influences the signal you get from satellites. So if you can get an increase in ice mass in the area which is not at all compensated by mass loss. It's very difficult if you have an increase in mass due to accumulation and at the same time a decrease in mass due to outflow, and the two balance one another. In that case you probably don't see much.
Picture: Checking out the drilling equipment used by the Icecon scientific team at the Field Camp. - © International Polar Foundation