Surface glaciology at Dome C

Text and pictures © 2005-2024 Guillaume Dargaud
Last updated on 2021/11/05

"Tonight, Hell freezes over !"    — Mr Freeze, from the movie Batman & Robin.

Sampling sessions

Left: Emanuele on his knees away from the station, collecting a snow sample. Snow samples are collected twice daily, at two different location, 1.5km and 0.5km away from the station, with the glacio shelter partway between them.

The official title of Emanuele's research here is: "Paleo-climate and paleo-environment from ice core chemical, physical and isotopic stratigraphies". That's a mouthful. And indeed he was very busy all winter, almost never having time to watch the odd movie at night and running around to his sampling areas several times every day. We estimate that he walked outside more than 1000km, which would have been enough to reach the coast.

Right: Night sampling in a windstorm. Up on the high antarctic plateau the wind is rare and not very fast, but enough to drop the visibility to a few meters and the windchill to a terrifying -110°C. On days like this, there normally wouldn't be any sampling, a well deserved rest for Emanuele who otherwise would walk 6km per day.

The main goal of his research is to study the chemical composition of the aerosols being deposited, depending on the season and particle size. By aerosol we mean any kind of solid particle present in the atmosphere: snowflakes, ice crystals, solid state condensation (aka reverse sublimation)... In other words, what happens at the limit between snow and atmosphere and what happens to the chemicals present in the air as the snow deposits, as well as what happens later as it starts to turn to ice deeper in the ground. A reliable understanding of the present situation is necessary in order to analyze the deep cores going back hundred of thousands of years extracted by the now completed Epica drilling project. The understanding of past climates, ranging 8 full glacial cycles, requires a solid understanding of how the chemicals get there in the first place: re-emission into the atmosphere, chemical transformation, diffusion in the snow layers...

Left: Emanuele getting ready for his snow sampling session in the winter twilight, right at the pole marker. Not stepping anywhere behind the pole allowed to avoid contamination. Due to the distance, the night samplings are always done in two people for security reasons, in addition to using a radio each.

For this purposes, aerosol, hoar, superficial snow and crystal samples are collected all around Concordia. Several basic analyzes are performed on site, for instance nitric, hydrochloric, sulfuric and methanesulphonic acids. The laboratory possesses an ion chromatograph, a laminar flow hood to manipulate sampling devices in contamination-free conditions, a gradient water purification system, technical scales, an ultrasonic cleaning bath...

Right: Collecting snow destined to be melted and analyzed.

Aerosol samples are collected during the winter in a tiny shelter 500m upwind from Concordia using various types of pumps and filters: a preselected cutoff sampler, a multi-stage impactor and a filter-sandwich system. The samples collected by the cutoff devices are smaller than 10 and 2.5 micrometers. The multi-stage device is able to separate and collect aerosols from 10 to 0.4 micrometers in 8 fractions. Such sampling allows to correlate the chemical composition of the Dome C aerosol to its size distribution. Samples are taken continuously for durations of 6 to 8 days and repeated most of the winter.

Left: Emanuele in winter snow sampling garb: plastic gloves on top of pile gloves to avoid contamination, face mask against freezing lungs and serious 'bellylamp' to find his way. Samples are collected inside small vials, sealed, and then analyzed in the lab on the ion chromatograph.

Hoarfrost and superficial snow are collected all year round in several sites around the Concordia Station. During day/night alternation periods (spring and autumn) samples are collected both at night and at noon; this in order to study the effect of sun irradiation on the atmosphere/snow transfer process and on the persistence of some chemical compounds in the superficial snow layers. All those samples will be analyzed in the glacio-chemistry laboratory of the Chemistry Department of the University of Florence for Na+, NH4+, K+, Mg2+, Ca2+, F-, Cl-, NO3-, SO42-, acetate, formate, MSA, stable isotopes, tritium, mercury, trace elements from cosmic material...

Right: A picture taken from Concordia showing the path to the glaciology shelter (the first one). Farther along are one of the 3 magnetism shelters and the seismology shelter hiding the seismology cave and its blue tunnel.

Cursory analysis of those samples is performed inside the Concordia laboratory and will be compared to a more in depth analysis run on those same samples after their return in Europe.

Left: The same view during the winter night, done in long exposure to show Emanuele's lamp lighting his return trip.

Snow height

Besides the taking of aerosol and snow samples, Emanuele is involved in nivologic and glaciological measurements to determine how the snow deposits on the Dome C plateau which is of primary importance in the calculation of the surface mass balance of the Antarctic ice sheet. In other words: is Antarctica melting or not ? Ice crystals structures affects the quality of satellite measurements because they change the physical properties of the snow surface, such as the albedo, and thus have an influence on the planetary energy budget used in weather forecast and global warming models. Every day, Emanuele takes observations on the amount of deposition and the shape and size of snow crystals with a pocket lens on a raised wood tablet. The main five crystal categories are diamond dust, precipitation particles, blowing snow, air hoarfrost, and surface hoarfrost; all ranging in size from 0.5 to 2mm and forming almost every day. The predominant crystals are constituted by columns and needles, with some variations having interesting names like diamond dust, Shimizu crystals or bullet clusters !

Left: A different kind of glaciology session, done 2 or 3 times a year, to measure snow heights. A few km south of the station, upwind to avoid artificial disturbances, are about 50 poles planted in a cross pattern (the line of poles is visible on the image). Their height above the snow is measured and averaged.

Right: The height of snow is measured precisely because the yearly snow accumulation on the high plateau is only a few centimeters, and most of the snow falls in winter while in summer it tends to sublimate. Actually the snow doesn't fall in the common sense of the term as much as it just 'appears' in a solid state condensation process directly on exposed surfaces. The lidar helps determine how much snow is falling in the form of very thin ice crystals.

Right: Emanuele under his face mask during the long walk. He had to stop often to measure the snow heights, removing his gloves each time, and got really cold this way. Also the temperature was -65°C when we headed out, but had dropped to a near -75°C by the time we got back.

Left: Taking a break on the snow after a non-stop 4 hour walk on snow at sub -70°C temperatures.

By measuring the snow height around a network of 50 poles, it was determined that the snow accumulation was 4cm between autumn and spring. And final thing that Emanuele is taking care of: a geomagnetic observatory from which he downloads data monthly.

Left: No engines in winter: everything is done by foot, possibly pulling a pulka with equipment on top.

Right: One in a series of several surface markers used to regularly measure the movement of the ice. Dome C is defined as the top of the local ice, but it's so flat that it's easier to define it as the place from where the ice flows in every direction, which is the most interesting to deep drilling glaciologists. The station is visible far away on the horizon from this reference pole used yearly by specialized GPS equipment to pinpoint to flow of ice to within a few cm a year horizontally.

Left: After the sampling session, part of the samples are analyzed directly in the lab, but others are put in cold storage before being shipped to Italy in the summer for a more thorough analysis.

Thanks to Emanuele who provided most of the info for this page, as well as posed for the images !

The glaciology shelter

Left: After collecting samples outside, a brief stop into the glaciology shelter to warm up but also to check on the equipment, see if the pumps are still running and possibly change the filters (180° fisheye image).

Right: Emanuele after putting the just collected snow into the ultrasonic bath where it will melt.

Left: Emanuele spent some time to install his shelter at the beginning of the winterover, adding an extra layer of insulating mylar on the walls. Several pumps are seen in the back.

Right: Many different kinds of analyzes are performed for surface glaciology. Besides the direct samples of snow taken from the ground, there's also several pumps taking in outside air and the few crystals of ice it contains. Those crystals are then sorted by dimensions through an impactor filter, and later analyzed for content. The quantity of crystals in the atmosphere is so low that each pumping session has to run for 3 days non-stop, hoping that the wind won't turn and bring smoke from the station's power plant.

Right: Emanuele changing one of the filters on the roof of his shelter.

Left: The correlation between the chemicals present in the atmosphere, those found in the surface snow and those found in the deep ice is very important if you want to be able to figure out what the climate was like long ago from only some chemical traces within the ice. Some chemicals undergo transformations when the snow deposits or when it turns into ice. Others concentrate or on the contrary evaporate and won't stay in the ice. This means analyzing all the possible chemicals, in all the possible circumstances (summer, winter, in the sun, in the dark, with different temperatures or humidity levels, etc...) An overwhelming task.

Right: Here Emanuele holding one of his impactor filters.

Left: Some trouble with a partly dismantled pump: it has stopped for unknown reasons and the smell doesn't forecast anything good.

Right: Once open, it's clear the pump's burnt for good. The high altitude causes problems not only for PC hardware but for anything that needs cooling, and it appears it wasn't enough here: the graphite parts of the engine heated up, broke apart and sent conductive dust into the wiring, shorting the whole thing. Emanuele will finish the winter out of spare pumps, having lost most of them.

Left: Milky Way above the glaciology shelter. Going along Emanuele during his night samplings was one of the best way to enjoy the night sky, provided your glasses weren't fully iced up and fused to your nose !

Right: Besides all the chemical analyzes, Emanuele is also tasked with visual inspection of freshly deposited snow crystals. Twice a day with a lens he takes a look at the multitudes of shapes and tries to figure out a shape and size distribution: how much ice/snow, size of the crystals, their shape, what proportion of each... See below for some sample pictures.

The six main crystals categories identified at Dome C are diamond dust, precipitation particles, blowing snow, air hoar, surface hoar and rime. Snow deposit is frequent but most of it is thin, between 0.5 and 2mm. Equidimensional crystals are rare among precipitation particles, the main ones being columns and needles which sometimes assume extreme shapes (very long crystals known as 'Shimizu crystals'). Composite crystals, such as 'bullet clusters' or combinations of columns, are often found.

Left: Examining the shape and distribution of snow crystals in winter is not easy: bulky facewear, lack of light, holding your breath to avoid contamination of fragile crystals...

Right: And this is what you see on the accumulation table.

Left: Back in the lab for chemical analysis on the ion chromatograph.

Surface hoar crystals form under quiet condition and clear skies, they grow in the direction the water vapor comes from, the most frequent shapes being hollow columns and needles, often disposed in bundles. Blowing snow occurs when wind get faster than about 5m/s and is composed of small rounded grains with dimensions from 0.1 to 0.2 mm. Snow deposits, besides being an essential input parameter in mass balance studies, are correlated with the superficial atmospheric conditions, and the temporal distribution of the different types can therefore be representative of the meteorological conditions.

Above: Panorama of the glaciology laboratory on the 3rd floor of the quiet building. Emanuele is sorting his filters under the laminar flow hood to avoid contamination.

Thin snow wall

Left: Summer preparation of thermal sensors to return continuous subsurface fluxes and temperatures throughout the winter.

Right: A hole is dug to study surface layers. Another hole will be dug just next to it, leaving a thin wall of snow between both...

Left: The size of my glove shows that the yearly deposits of snow are no more than 10~20cm on the surface. After they get covered by newer snows, the weight tends to expel most of the air slowly turning the snow into compact ice around 100m deep. At that depth a yearly layer is compressed to no more than a few cm and what air is left gets isolated into small bubbles which can be extracted and analyzed. Past climate information is at hand, provided you can reach deep enough.

Right: ...and then one hole is covered to keep it in darkness while the light shines through the wall of snow, showing very obvious yearly layers.

Ice and snow crystals

Left: Some hoar frost on the lab window.

Right: More window frost. Windows of the Concordia buildings are made with a triple outer pane, 20cm of space, and another double pane. Most times in winter some frost would form in the middle space.

Left: Going down into the underground storage area, in the back of the underground garage. This area is closed up most of the year, and for some unknown reasons accumulates large ice crystals on the ceiling. It is a common sightseeing destination at Dome C.

Right: Ribs of ice crystals formed on the underground garage ceiling.

Right: More ice sticking to the garage ceiling.

Left: The storage area, illuminated by flash and lamp. The high humidity forms the crystals, some more than 40cm long. The boxes contain the reference half of the Epica ice core samples, in case something happens to the others during shipping to the european labs.

Right: Long exposure of the same storage area, using whatever available light there is.

Left: Some of the very delicate ice crystals to be found in the cave. If you as much as touch them, they dissolve into ice dust.

Right: Large crystal hanging from the ceiling.

Left: And the same one, backlit with a red LED light.

Right: Ice crystals forming outdoors on the top of the american tower. What surprised us during the winter was the heavy formation of ice away from the ground. The american tower had about one meter thick of ice on the top of its structure in early september, with no ice at all at the base. Within a month it was all but gone from the sun warming up (!) the structure.

Left: Sastrugi seen as far as the eye can carry.

Right: Sastrugi seen vertically down from the tower. At Dome C they do not exceed 10cm in height, but in other wore windy parts of Antarctica they can easily reach over a meter and impede travel even with large vehicles.

Left: Curious area of snow with a different light reflectance index. Studies are underway to measure the exact albedo of Antarctica, the albedo being the proportion of sunlight reflected by the surface. Because Antarctica is so reflective (white snow), small differences in reflection can change a lot the amount of energy accumulated by the planet. This value needs to be precisely quantified before being integrated into global atmospheric models.

Left: Surface snow as seen on Emanuele's collection plate. On this image and the following ones, many different shapes can be seen: needles, bullets, balls, flakes, cylinders...

Right: Surface snow crystals.

Left: Snow crystals after being exposed to the sun for a while.

Right: More snow crystals.

Left: Even more snow crystals. It could go one for much longer as there's an official list of about 4000 ice crystal shapes !

Additional bibliography: The Snowflake by Kenneth G. Libbrecht.