Text published in Newspaper Jan Mot, no. 125, Jan. 2021.
This text is the first part of a series of contributions to the newspaper by Heiko Goelzer, a friend and a scientist working in climate research. He studies the role of ice sheets in the climate system on various timescales in past, present and future and their contribution to sea-level change. Goelzer’s contributions are written on the occasion of our participation in GALLERIES CURATE: RHE, an international exhibition project organised by 21 galleries on the theme of water. Please see also our interview with the author in the previous issue of the gallery’s newspaper.
About water – part 1
By Heiko Goelzer
Oslo, Jan. 6
Our local pond would freeze over in the winters and was only a few minutes by foot from the house I grew up in. Long before my time and before the advent of electric refrigeration units, the pond was created by the local brewery so they could use the ice for cooling. For me, it was the place where I took my first steps on solid ice and learned to skate. Many years thereafter, we went with the whole family every Sunday to an ice-skating rink, where we had artificial but consistent conditions most of the year.
That natural bodies of water freeze over when it gets cold enough for long enough, providing opportunities for ice-skating enthusiasts, may seem like a trivial and unspectacular event. But in fact, it is a remarkable and intriguing phenomenon that is worth a second look. While the density of most other liquids increases when cooled towards the freezing point, water reaches its maximum density around 4 °C. Further cooling beyond that point decreases the density, which makes that the coldest water is always on top and ice can form there. Without this density anomaly of water, our ponds and lakes would freeze from the bottom up, with dire consequences for the plants and animals living there. Whatever the underlying reason for the anomaly (a completely satisfying scientific explanation has yet to be found), it is not only at the root of facilitating the ice-skating experience on natural ice, but pretty much facilitating life itself.
A layer of ice on top of a lake reduces the heat loss to the air above it quite considerably, so that the heat is trapped in the water and ice grows much slower than it would otherwise. And the thicker the ice, the better the separation. This insulating effect of ice on a body of water allows the coexistence of liquid water and air of several tens of degrees below zero, only separated by a few centimetres of ice, which again can be understood as protecting the life beneath it.
It needs a couple of days well below zero to freeze over a lake thick enough with ice to walk on. The famous speed-skating event Elfstedentocht in the Netherlands is only held when the ice everywhere on the almost 200 km long track on a network of connected canals, rivers and lakes is at least 15 cm thick. This only happened in three of the last 50 winters and the last time in 1997, with a near miss for the Elfstedentocht in 2002. For this event, the ice needs to safely support up to 15000 skaters passing through on that one particular day, hence the strict requirements. More risk-tolerant Nordic Skaters on remote lakes, for whom probing that threshold has become part of the sport, have found an ice thickness of around 3 cm as the absolute lowest supporting limit. Close to that threshold, the ice is visibly bending and emitting laser-like sounds as the skater passes over it.
Most of the ice that forms by freezing of water in our environment is called “ice one h” (Ice Ih) and is one of the currently 18 known forms of crystalline ice made from water. The subscript h refers to the hexagonal crystalline structure that we know from our images of snowflakes. Most of the other forms of water ice only occur under conditions very different from our daily experience, high in the atmosphere, in outer space or in the laboratory. The ice that I am working with does not form by freezing of lakes and rivers overnight, it is created over years of snow accumulation high up in the mountains. Every year a new layer of snow is deposited, and lower layers are compressed under the weight of the new snow above. Over time, the air in the snowpack escapes or is compressed as the snow is compacted into solid glacier ice.
The first time I really got in contact with such ice was during a family summer holiday in Switzerland. The hike we did that day started at the Morteratsch railway station at 1900 m down in the valley and got up to the Diavolezza cable-car station at almost 3000 m elevation. On a sunny day, the view up there of the mountain range to the south, marking the border to Italy, is breathtakingly beautiful. On the way up, the key attraction of the hike and reason for my father picking out the route was the crossing of the Morteratsch glacier at around 2500 m. Close to the ice, we had to rope up and put crampons on for the traverse. I had good practice with the climbing harness, and I knew how to tie myself into the rope, but something didn’t feel right. I can still remember the harness much too tight around my chest, I couldn’t breathe well.
Stepping out on the ice is a curious and daunting experience. It may feel as solid as rock under your feet, but there is something uncomfortable, a sensation like fear of height when looking into the abyss. Is the fear transferred from the experience of walking on a frozen lake, not knowing how thick the ice is, if it will hold and what is underneath? It was probably to the better at the time that I didn’t know about the ice actually moving under our feet, even if it was only by several tens of meters a year. But there was also water on the glacier, a lot of it! In the summer this part of the glacier can be free of snow and the ice is melting in the heat of the day. Small streams of melt water collect into bigger streams of water and into rivers on the surface of the glacier. We had to jump over two or three of those on our way. We followed one of the rivers downstream to see where it went. And at some point it abruptly just disappeared from the surface and fell into a big hole in the ice with a screaming and grinding sound. In my imagination, I pictured myself being washed down the river and down the hole to disappear forever in the glacier.
The holes in the glacier are called moulins or glacier mills and form part of the network of conduits and channels that transport the meltwater from the glacier down the valley, on the surface, inside the glacier and under the ice. Walking towards the glacier along the valley floor in the summer, one finds a huge mouth in the glacier front where the water exits. I once met a group of researchers on the glacier that had just returned from exploring part of the internal network of channels. They had ropes and other climbing equipment with them that had allowed them to access the system through a dry moulin similar to the one I had pictured myself being washed down on my first visit to the glacier as a kid. I had mixed feelings about their choice of research method.
It was many years later that I came back to the Morteratsch glacier as part of the annual field trips we did with the research group of my post-doc position in Brussels. We would visit the glacier in early fall just before the first winter snow to measure ice velocity, ice thickness and the amount of melt at the surface. The process involves drilling several-meter deep holes in the ice and planting long plastic stakes that freeze in over the winter. Coming back the next year, the new stake positions are used to determine the ice velocity, while the height of the stake above the surface records the amount of ice that has melted. To plant the stakes and find back the ones from the year before, we would walk all over the glacier, and I had plenty of opportunities to revisit the places of my first encounter with the glacier. But even after years of going back and spending many days on the glacier, the first steps on the ice were always taken with a certain respect that never went away.
The glacier also holds memories well beyond our own timeline. The snow and everything else that is buried with it is well preserved in the upper part of the glacier, where the amount of snowfall exceeds the snow melt. Old ice from a glacier can therefore be used to reveal information about the past. The air trapped in small bubbles in the ice can even serve as direct sample of the atmospheric composition at the time of deposition. For very big, old and slow glaciers, such information can be preserved for hundreds of thousands of years back in time. In our case, the glacier flow transports the ice and enclosed material within a few decades to lower elevations where it eventually melts out. On our excursions, we regularly passed the rusted remains of an airplane wreck from World War II and other signs of human presence on the glacier, including the result of what must have been a more recent fatal skiing accident.
Over the seven years I went to visit the glacier, we documented and experienced an accelerating thinning and retreat of the glacier that was clearly visible from year to year. Places on the glacier tongue we had worked on one year were gone the next. Massive meandering meltwater canyons were carved out of the retreating glacier front. And it was getting more and more difficult to access the shrinking ice from the sides over steepening walls of rocks and debris left behind by the retreating glacier. Based on our measurements and related results from other glaciers, one of my colleagues recently projected that the glacier volume of the entire European Alps will be halved by the year 2050. For the Morteratsch glacier, a further retreat of several hundred meters has to be expected. The hundred meters thick ice I had walked over as a child will then be gone, and the path to the other side will instead go along the rocky valley floor.