Mission belge Antarctique 2018

Category: Observation campaign (Page 1 of 2)

How do we drill an ice core in Antarctica ?

by Jean-Louis Tison.

To answer this question, you first need to know the length (and therefore the time span) of the ice core that you wish to extract from the ice sheet.

If you are only interested by a short core a few to 10 meters long, for example to study the properties of the snow and firn (transition from snow to ice) you can use a simple and lightweighted system, entrained manually or with a small motor at the top.

At the other extreme, if you want to recover 3000 meters of ice, all the way to the bottom of the ice sheet, covering up to 800.000 years, you need to gather all your friends internationally (and a lot of money!) for an international drilling program that might last more than 5 years (summers in the field).

In that case, the drill is much more complex and send down the hole with the motor on top of the drill barrel, which is made of an upper container (tube) to collect the chips from the cutting of the ice, and a lower one to collect the core. At the bottom of the latter is the drilling head, equipped with 2-3 knives, that digs an annular hole, isolating the core from the ice sheet.

The cutting chips are pushed up an “archimede’s screw” on the outside of the inner tube, where the core is collected. The chips are contained by an outer tube and are therefore driven up, to end up in the upper container. When up to 5 meters of core are drilled, the tubes are full, and the drill is brought back to the surface, the chips emptied from the upper container, and the ice core recovered from the inner tube.

Everything is controlled from the surface by a computer connected to the drill motor by way of electrical cables within the hauling metallic cable. The drilling is performed within a drilling fluid slightly denser than the ice (once we are in the ice, ca. 100 m depth), in order to prevent the hole from closing down from one year to the other (the ice deforms under its own weight and closes the hole!). It also prevents mechanical damage of the core by the drill, when the pressure of the ice around gets too big compared to the atmospheric pressure in the hole.

For intermediate depths, like at our Mass2Ant locations (300 m core, several centuries), we use a light-weighted version of the deep drilling system: the Eclipse drill (Canadian made). Because the quality of the cores was degrading under 100m depth last year, we will use a “wet drilling” version of the system, for the first time this year! Cross fingers and wait for the pictures of this year!

In the meantime, some pictures of last year! (photos: T.J. Young and Emmanuel Potvin)

The drill head with 3 knives, in rotation

Extracting the inner barrel (containing the core) from the outer barrel. In this light-weighted version, there is no dedicated chips chamber. The chips reaching the top of the spiral fall on top of the core in the inner barrel.

The drill trench and operators (Emmanuel and Etienne)

A good core

…and a bad (broken in) core!

What do we learn from ice cores?: The Paleothermometre

 by Jean-Louis Tison

One of the most crucial information that we can extract from an ice core is the temperature that existed at the time the snow deposited at the surface of the ice sheet. We will make an attempt today to better understand the principle of this “thermometer of the Past” (Paleo-thermometer).

A little bit of basic chemistry (good old school days!): Ice is solid water (H2O). It is made of an assemblage of atoms of Oxygen and Hydrogen. Atoms are characterized by a core, made of protons and neutrons, and electrons spinning around it. The number of protons (atomic number) in the core define the “name” of the atom: Oxygen has 8 protons in its core and Hydrogen only 1 proton in its core. However, there exist several varieties of atoms of Oxygen and Hydrogen, differing by the number of neutrons in their core. Less neutrons in the core will make the atom lighter, more will make it heavier. We call these various atoms of oxygen or Hydrogen “isotopes”.

To make a long story short, let’s talk about Oxygen only. A similar story could be told for Hydrogen in the water molecule.

A molecule of water containing lighter isotopes of Oxygen will be lighter than a one containing heavier oxygen isotopes. Nature is such a nice friend to scientists that there is a simple (linear) relationship between the temperature at which the snow accumulates at the surface of the ice sheet and the proportion of light and heavy water molecules in the snow: the colder the temperature, the higher the amount of light water molecules that will be present in the snow and vice-versa. This is illustrated in Figure 1 for the Antarctic and Greenland. Scientists quantify the proportion of light and heavy isotopes in water molecules by the symbol d18O (for Oxygen, where the most abundant heavier version is 18O, as compared to the dominant lighter isotope 16O). When d18O is negative, the snow sample contains less heavy oxygen isotope than the “reference”, which is standard ocean water (the most abundant at the surface of the Earth) and vice versa. So, in brief, the lower the d18O of the snow, the lower the temperature when it fell at the surface of the ice sheet, and the relationship is linear (see Figure 1). The same will be true for d2H (also written dD, D is for Deuterium, the heavy form of Hydrogen, with 2 neutrons in its core).

Figure 1 : the linear relationship between snow d18O (or dD) and the air temperature when it falls at the surface of the ice sheet: the principle of the paleo-thermometer.

For each successive layer in our ice core, we can then measure the proportion of light and heavy oxygen isotopes (d18O) or Hydrogen isotopes (dD) in the snow (that became ice) to reconstruct the temperature that existed at the time that layer of snow was at the surface of the ice sheet: this is the principle of the paleothermometre.

The beauty of the technique is that it works at all timescales: we will for example clearly see the difference between a glacial period (cold period with very negative d18O or dD) and an interglacial period (warm period with less negative d18O or dD) on long time scales. Not only that …we will also be able to discriminate summer (warmer) from winter (colder) each year. This is crucial, since we will then be able to “count the years”, and therefore date the core from those seasonal fluctuations of the water stable isotopes signals (d18O or dD), as shown in the example of Figure 2.

By measuring the thickness of ice that exists between two peaks (or two troughs) of the seasonal d18O or dD signal we will be able to reconstruct the annual snow fall at the surface of the ice sheet, one of the major goals of the Mass2Ant project, as you already know by now!…

Figure 2 : An example of d18O (black curve) and dD (light blue curve) profiles between 20 et 30 m in the Derwael Ice Rise ice core, in the vicinity of the ice coring locations of Mass2Ant (Philippe et al., 2015). This depth interval covers 10-11 years of accumulation, as shown by the seasonal fluctuations of the water stable isotopes (d18O.et dD)….”Rendez-vous” in one of our next blogs to understand what the other profiles mean !

What do we learn from ice cores?: introduction to a series

 by Jean-Louis Tison

Ice cores are the memory of our Climate. They are not the only one, though!… You can read the climate of the past in ocean sediments, corals, tree rings, stalactites in caves, lake deposits, peat deposits and many others. Not all of these archives give you the same amount of information though. Also, some are easily dated (a must for an archive, of course!), other less easily.

Ice cores are extremely wealthy in information, as you will discover here and in the following blogs. They can give you a very detailed record of the Climate and the Environment on several ten thousands of years. However, they have only gone back in time for less than a million year until now, because snow that turns into ice as it is slowly buried in the ice sheet, deforms under its own weight, and flows both downwards to the bedrock and outwards towards the ocean. It thins up so much under these processes, that no ice is left beyond that age limit! The oldest ice dated today in an ice core goes back 800.000 years in time. However, a new project funded by the European Union aims at finding ice older than 1.5 million years old in Antarctica, and this new drilling project will be the next challenge of the coming decades. Other countries are also involved in this challenging task: Russia, Australia, Japan…

In our Mass2Ant project, as you already know, we will be more focused on the last centuries, to document the transition of the Climate into this new geological period that some of us refer to the Anthropocene: a period where the Climate increasingly feels the influence of Mankind (mostly since the Industrial Revolution).

A climate archive, such as ice cores, always works the same way: you measure a variable/property in the medium (ice for example), what we call a “proxy”, to pull out information on a climate or environmental variable (Temperature, precipitations, winds, air masses circulation, greenhouse gases content of the atmosphere a.s.o..). The Figure here below lists some of these information that you can retrieve from an ice core

Stay with us, and you will learn more on the most important ones as we drill deeper into the ice!…

 

 

 

 

 

 

 

 

 

Back to Princess Elisabeth Station

By Hugues Goosse

We have definitely left our camp on the ice rise that we have named TIR for Tison Ice Rise. We have announced it to our chief scientist for whom it is likely the last mission in Antarctica, during our last evening dinner on the site.

The official choice of the name of a location in Antarctica depend on a specific commission. This is thus complicated and requires a lot of time but, for us, it will remain the TIR.

Jean-Louis next to the wood tower that protects the drilling hole and will be removed next year to perform new measurement.

The dismantlement of the camp was a bit more perturbed than planned as we had a storm over the last days there. It was less strong that the one that hit us late December but, during the removal of the drilling tent, all the skill of our accompanying team and the involvement of the whole group was required to avoid that part of it fly away.

Logistics and organization in Antarctica are full of surprises. We were supposed to leave the camp the 12. After a rumor for the 14th, an announcement for the night from 12 to 13, we finally left the 13 in the evening.

We came back through the camp where we slept a few nights when we made the measurements on the site of last year drilling site (FKIR) and finally arrive at the Princess Elisabeth Station after a 20 hour trip spend in the container that were used as kitchen, talking a bit, playing games but mainly sleeping after all those short nights despite the bumps on the ‘road’.

The team at the arrival at Princess Elisabeth station

The next step was to organize the material and put it in the right boxes to bring them in Belgium according to the custom documents. We sorted our garbage and put it in the right containers here at the station.

We also had to prepare the transport of the ice cores. After we leave, they will be brought to Perseus, an air strip close to Princess Elisabeth Station. They will then fly in an Iliouchine to Cape Town and finally by boat in a container at -25°C towards Anvers. They are expected in Brussels in early March. This step is always a bit stressful as the ice cores should of course not melt during the journey but even not warm up to avoid reactions in the ice that would modify the amount of some components!

The Princess Elisabeth station on a snowy day

For our departure from Princess Elisabeth Station, we should wait for the right weather. Several days were mentioned over the last few days. If everything goes well, it is planned to go back through the Nov air base and then Cape Town as on the in. The departure is expected on the 19th, arriving in Brussels the 21st if everything goes as planned.

Map showing the region north of Princess Elisabeth Station (PEA) with the first camp where we spend a few nights (CAMP), the first ice rise we visited (FKIR) and the second one where we drilled the ice core (TIR)

Map showing the region north of Princess Elisabeth Station (PEA) with the first camp where we spend a few nights (CAMP), the first ice rise we visited (FKIR) and the second one where we drilled the ice core (TIR)

How do you find your way in Antarctica?

By Hugues Goosse and Sainan Sun

The only ‘roads’ in Antarctica are the path taken by snow tractors and snow mobiles. Even if there are indicated by poles, they can be quickly covered by snow. Of course, no sign helps you for directions at the ‘crossroads’.

Out of busy places such as between an airport and a base, you should thus not rely too much on them.

The topography is relatively flat. No building or change in vegetation can be used as a mark to remember your way.

The path followed by tractors out of Novo air base

The path followed by tractors out of Novo air base

In addition, sometimes when snow is blowing or the fog is very thick, you cannot see at a distance of two meters. In this ‘white out’, everything seems white. You cannot even walk five meters between two buildings if you cannot follow a safety rope previously installed in prevision of such extreme conditions.

The security rope in the camp to find our way to the tents even if we have no visibility

The security rope in the camp to find our way to the tents even if we have no visibility

More generally, the best way is to use a navigation system based on satellites like in the GPS of your car. You set the coordinates of your destination and then you just follow the indications.

For some scientific interests, ‘marks’ (e.g. bamboo sticks) are put on ice. First, surface accumulation can be estimated by simply measuring the part of the bamboo that is still out of the snow compared to the last year. Standard handle GPS have an accuracy of about 10 meters, and can be used to find the marks you left in the previous campaign in slowly flowing regions such as ice divides.

Secondly, by measuring the movement of the stick in one year, you can estimate the ice velocity. This requires a high precision in the measure as the shift is often smaller than one meter around the ice divides. The more precise system GNSS (global network of satellite system) is often implemented in this case.

An antenna communicates with satellites in different directions and different heights to interpret the precise coordinates. A static point is often chosen as a reference station (such as the peak of ice divide), the relative movement compared to the reference station can achieve precision of millimeter magnitude by half an hour tracking.

The tripod with the antenna used to measure precisely the position

Looking for the bamboos in this ice environment to determine their position is like searching a needle in a haystack. It may take some time, but the technique works well !

A few centimeters still out of the snow after one year!

What do you need for an observation campaign in Antarctica?

By Hugues Goosse

The first thing that you think about is probably the scientific equipment needed to perform the measurements. This equipment can be relatively light and comes with you in the plane when you travel to Antarctica but it comes more generally separately as cargo or is even stored at the station.

The second element is likely your personal belongings, such as polar clothes, camera, computers to analyses the data, etc.

However, a dominant aspect in the problem, requiring a lot of time, manpower and budget is the logistics. Everything is more complex in Antarctica and thus must be well prepared and organized.

The International Polar Foundation (IPF) is responsible for the operations at the Princess Elisabeth station. This means that they are in charge of organizing the work at the station itself but also the scientific activities related to the station.

This starts first with the preparation of the scientific mission, for instance performing the medical checking of the participants and booking the flights towards South Africa and then Antarctica.

Continue reading

260.1 m !

By Hugues Goosse

Our stay in the field is close to its end now. The drilling has reached this Thursday morning the final depth of 260.1 m. The quality of the ice core is great all along, thanks to the addition of the drilling fluid. We have thus well beaten the value of 208 m reached last year, and this core was of bad quality after 100m.

The deepest core of this season

The deepest core of this season

We have made more radar measurements of the snow layers than planned and we have calculated precisely the position and height of the many bamboo sticks we have planted close to the field camp. Some parts of the area looks now as a kind of dried bamboo forest!

The bamboo stick that remains in the snow indicating the position measured with the GNSS and which will be revisited next year

Next year, some members of the team will come back to measure the part of the bamboos that remains out of the snow and the new positions of those bamboos. They will also redo some radar measurements to see the changes from one year to the next. This will allow us inferring the accumulation of the snow at the surface as well as the ice movements.

We have also plenty of profile of the snow density and surface snow properties.

Nander in a snow pit collecting snow properties.

Continue reading

Ice core borehole measurement: temperature and optical televiewer

By Mana Inoue

One of Sarah and my role in the field is carrying out the ice core borehole temperature measurement and optical televiewer (OPTV) measurement. The OPTV is a kind of camera that films and analyse the snow and ice layers.

Temperature record will give us an idea of the energy budget changes in the ice sheet. OPTV measurement will give us an idea of the density profile through the ice core borehole.

OPTV measurement “the ice fishing”

OPTV measurement “the ice fishing”

OPTV is also able to tell us the vertical strain rate (how much of the snow accumulation in the year is thinning by the weight of another one year of snow accumulation) by comparing the OPTV record from the previous year measurement.

How we do the measurement? Both temperature and OPTV measurement were similar. We put a temperature probe or OPTV probe into the ice core borehole and record what the machine tells us.

Which means there is not much physical movement during this measurement. And if we don’t move much it gets cold quick. To at least protect from wind, we have a tent around us during the measurement. At the result, we look like we are doing ice fishing.

We will do further analysis with the data when we back to our lab. Wait for us for the exciting finding!

OPTV camera view

OPTV camera view

What do you need for an observation campaign in Antarctica?

By Hugues Goosse

The first thing that you think about is probably the scientific equipment needed to perform the measurements. This equipment can be relatively light and comes with you in the plane when you travel to Antarctica but it comes more generally separately as cargo or is even stored at the station.

The containers with the equipment, the ice core storage and the drilling tent.

The second element is likely your personal belongings, such as polar clothes, camera, computers to analyses the data, etc.

However, a dominant aspect in the problem, requiring a lot of time, manpower and budget is the logistics. Everything is more complex in Antarctica and thus must be well prepared and organized.

The International Polar Foundation (IPF) is responsible for the operations at the Princess Elisabeth station. This means that they are in charge of organizing the work at the station itself but also the scientific activities related to the station.

This starts first with the preparation of the scientific mission, for instance performing the medical checking of the participants and booking the flights towards South Africa and then Antarctica.

Before our arrival at the station, the IPF team organized the convoy for the field campaign in order to provide us with all the infrastructure necessary for the scientific experiments and to make our stay in the field as comfortable as possible. The food for 4 weeks in the field also had to be prepared.

For instance, IPF team has installed solar panels on the container we use as a kitchen so that we can rely on a renewable source of energy and not just on a generator for our electricity. They also have added a shower in the bathroom-container, finishing the last details only a few hours before we left Princess Elisabeth station.

The containers including the kitchen, the bathroom and the toilets, with the solar panels

Some adaptations of the scientific equipment had also to be carried out at the station, such as installing the radar antenna on one of the skidoos. The update of a software may seem simple for most of us but becomes much more complex if the connection is very slow. The help of people knowing the method to overcome the problem is thus very much appreciated.

All of this requires a wide range of skills in the team as, if you are not able to do something, it is impossible to call a specialist nearby to help you.

The field mission itself implies heavy infrastructures, with two containers put on sledges for the equipment, one containers for the storing of the ice cores and two containers for the kitchen, bathroom and toilets. Two snow tractors are required for pulling the convoy and we brought six snow mobiles for our travels on site.

The parking for the skidoos and the snow tractor.

The generator and solar panels provide energy to warm up the containers (in particular the kitchen and  the bathroom) and electricity for the scientific equipment, especially the drill.

Pierrick, our mechanics, working with the drill

Material is important for the campaign, but some specialised personal from IPF is also essential. A field guide and a mechanics are accompanying us in the field to be sure that we avoid dangerous unmapped regions, help us if any trouble would occur and to take care of the equipment that suffers a lot in this harsh environment. Both of them also help us greatly for the scientific measurements thanks to their experience.

Christophe, our field guide, in the kitchen.

This part of the work is sometimes hidden in the discussion of scientific research and logistic constrains may sometimes be difficult to understand, even for us. Nevertheless, we are grateful that it is handled properly here otherwise our scientific campaign would not be possible!

Snow measurements

By Nander Wever

Earlier, we wrote how important snow is in the mass balance of Antarctica. During the campaign, we regularly survey the snow structure. We are particularly interested in the snow density.

The classical way would be to dig snow pits. However, snow pits are very time consuming, and you basically only get information from one specific spot.

We know that snow in Antarctica is highly variable. Not only is there a difference between snow in the interior of Antarctica and near the coast, even at meter distance the snow can be very different due to wind erosion and deposition.

We use a special device to survey the snow microstructure, called a Snow-Micro-Penetrometer (SMP). Whenever possible, we take SMP measurements. For example during our traverses to the drilling sites, regular stops to rest, eat, refuel are done every 30 km. We then quickly take about 10 to 20 samples of snow density in the upper 1 meter of the snowpack, spaced 4-5 meter apart.

Nander doing a snow survey with the SMP during a refuelling stop for the tractors pulling our field camp. The photo also shows that the snow cover is variable in the area

Nander doing a snow survey with the SMP during a refuelling stop for the tractors pulling our field camp. The photo also shows that the snow cover is variable in the area

Continue reading

« Older posts

© 2020 Bel Antar 2018

Theme by Anders NorénUp ↑