Cryospheric Sciences

Ice-core research

Image of the Week – The Sound of an Ice Age

Image of the Week – The Sound of an Ice Age

New Year’s Eve is just around the corner and the last “image of the week” of 2016 will get you in the mood for a party. If your celebration needs a soundtrack with a suitably geeky touch then look no further. Here is the music for climate enthusiasts: The sound of the past 60,000 years of climate. Scientist Aslak Grinsted (Centre for Ice and Climate, University of Copenhagen, Denmark) has transformed the δOxygen-18 values from the Greenland NorthGRIP ice core and the Antarctic WAIS ice core into music (you can read more about ice cores in our Ice Cores for Dummies post). Using the Greenlandic data as melody and the Antarctic data as bassline, Aslak has produced some compelling music.

You can listen to his composition and read more about his approach here.

The δOxygen-18 values are a measure of the isotopic composition of the ice, and they are a direct indicator of temperature. The image of the week above shows the isotope values for the past 20,000 years as measured by polar ice cores. On the left-hand side, we are in present-day: an inter-glacial. The δOxygen-18 values are high indicating high temperatures. In contrast, on the right-hand side of the figure we are in the last glacial with lower δOxygen-18 values and lower temperatures. One remarkable thing about these curves is how fast the temperature changes in Greenland (top) compared to Antarctica (bottom). This delayed coupling is called the Bipolar Seesaw.

The clefs are our own addition of course. We have not included the time signature because who knows what the rhythm of the climate might be? (Personally, I think it might be in ¾ like a waltz: An unrestrained movement forward with small underlying variations).

The data from Antarctica is published by WAIS Divide Project Members, 2015. The Greenlandic data can be found on the Centre for Ice and Climate website and in publications by Vinther et al., 2006, Rasmussen et al., 2006, Andersen et al., 2006 and Svensson et al., 2006.

Happy New Year!


Ice Cores “For Dummies”

Ice Cores “For Dummies”

Ice cores are important tools for investigating past climate as they are effectively a continuous record of snowfall, which preserves historical information about climate conditions and atmospheric gas composition. In this new “For Dummies” post, we discuss the history and importance of ice-core science, and look at the way we can use ice core chemistry to reconstruct past climate.

Ice sheets, archives of our past

When snow falls on the surface of an ice sheet it begins to compact the snow beneath it – eventually it will be compacted enough to be transformed into ice. Simultaneously, atmospheric air held between the snowflakes is slowly trapped in the ice – forming small air bubbles. In areas where mean annual temperatures at the ice surface remain below 0C, such as Greenland and Antarctica, there is little surface melting, so this snow builds up to form thick ice sheets – up to 3000 metres in some part of East Antarctica! Low surface melt means that the snow that is compressed into ice each year forms a continuous record of the annual snowfall and atmospheric gas concentrations at the time of deposition, but how do we access this record..?

Snow that is compressed into ice each year forms a continuous record of the annual snowfall and atmospheric gas concentrations at the time of deposition

…We drill ice cores – of course!

An ice core is a cylinder of ice that is retrieved from the ice sheet by drilling vertically downwards. The core is drilled in sections from the surface, deep into the ice sheet (Fig. 1) using a rotating drill. Each section of the core is processed at the drill site and often cut further into shorter sections of ~55 cm for more practical transport and analysis in labs. A great deal of equipment is needed to achieve this and drilling is a slow and careful process often taking several field seasons to drill a deep core. An example of a drilling camp is shown in Fig. 2, housing scientists and engineers involved in drilling an ice core on the Fletcher Promontory, West Antarctica.

Figure 1: a) Ice core drill being lowered into the ice on Pine Island Glacier [Credit: Alex P. Taylor] b) Dr Rob Mulvaney processing the Berkner Island ice core, Weddell Sea, Antarctica [Credit: R. Mulvaney]

Figure 2: The layout of the Fletcher Promontory ice-drilling project, Weddell Sea, Antarctica. In the background the large Weatherhaven tent houses the drill rig, the central Weatherhaven tent is used for storage and equipment and a simple shower, the nearest Polarhaven tent is the mess tent, and the Polarhaven tent to the left houses the main generator. The pyramid tents in the foreground are the sleeping tents, and the two to the right are used for toilet facilities [Credit: Mulvaney et al., 2014]

Where to drill an ice core for the best record?

To get a good record of climate we want to find an area of ice that has many annual layers (good temporal resolution) that has not been disturbed by high ice flow velocities, usually these conditions can be found at an ice dome or divide. An ice sheet is a large plateau with a relatively stable rate of annual snowfall; the dome (or ice divide) is the point in the ice sheet where there is only vertical flow (compression) of ice (Fig. 3). Horizontal flow of ice is greater with the greater distance from the dome. Therefore, domes are the ideal site on the ice sheet or ice cap to drill for an ice core to ensure no interference with the snowfall history at the site. It is reasonable to assume that the ice-core record taken from a site with high annual snowfall will not extend the furthest back in time; similarly, a low annual snowfall and a large ice-sheet thickness will offer a record spanning much further back in time.

Figure 3: Ice flow within the ice sheet showing the zero flow at the ice divide – the ideal site for an ice core [Credit: Snowball Earth]

For Antarctica, the amount of snowfall across the ice sheet depends on the distance from the coast and sources of moisture; the highest mean annual snowfall is found at West Antarctic ice sheet sites whilst the lowest values are inland on the East Antarctic ice sheet, one of the driest deserts on Earth. In addition to the West and East Antarctic ice sheets, the Antarctic Peninsula is the third and final sector of the continent with high mean annual snowfall comparable to West Antarctica. In comparison to Antarctica, the Greenland ice sheet has a relatively high present-day mean annual snowfall, varying across the ice sheet between 10 and 30 cm per year. Therefore, if your aim is to find the oldest ice on Earth, East Antarctica is a good place to start looking, see our post on the quest to drill an ice core that contains ice which is over a million years old. Additionally, for the longest records it is paramount to find a drilling location with no (or at least very low) annual melting at the bedrock.

If your aim is to find the oldest ice on Earth, East Antarctica is a good place to start looking

What does an ice core actually record?

Once an ice core has been drilled and cut into sections, some of the sections are analysed and others are preserved. This is particularly important as some of the analysis is destructive (e.g. melting of the ice to extract water and gas). Therefore an archive of the ice core itself is needed. So, what information can we obtain from analysing the core and how is it done?

Annual layers, past snowfall and past temperatures!

Reconstructing the past surface temperature and snowfall is incredibly useful for understanding climate processes and changes through time in order to assess any present-day local and regional changes in climate. We can do this by:

          • Measuring the thickness of the annual layers: This is done by counting layers in the core, either by visual identification of the peaks in deposition or use of a computer algorithm. The thickness of a specific year depends on how much snow fell at the site and on how much the snowfalls of the following years compacted this specific layer. We can estimate the strain caused by compaction which allows us to extract historical annual snowfall.
          • Past air temperatures (Stable Water Isotope Record): An additional method to reconstruct past snowfall is from the ratios of the stable water isotopes from the water that forms snow and precipitation. The ratio of stable water isotopes has a linear relationship with surface temperature (see box below). Mathematical reconstructions of accumulation using the temperature reconstructions from stable water isotopes are employed in ice core profiles where the compaction of annual snowfall results in an annual layer thickness beyond standard laboratory resolution, such as Antarctic sites. Following the accumulation reconstruction, the rate of compaction of the annual snowfall to ice and subsequent ‘thinning’ of the deposited snowfall layer must be estimated by glaciological modelling.
          • Trace-element analysis: For the upper depths of a deep ice core, or an ice core with an easily-resolvable annual layer thickness, the continuous analysis of an ice core for stable water isotopes offers a sub-annual view of the climate record.

            Figure 4: Seasonal deposition of four chemical species in the WAIS Divide ice core. Pink: electrical conductivity measurements; Black: Black Carbon; Red: non-sea salt Sulphur; Blue: Sodium. Each panel, shows the averaged annual record for 2 different periods: the Antarctic Cold Reversal (ACR, 13-14,000 years ago – bold line) and the Holocene, (10-11,000 years ago – thin line) the [Credit: Fig. 2, Sigl et al., 2016 ]

            The deposition of a number of chemical elements increases during the summer season and decreases during the winter.When these elements are measured in the ice core they can be depicted as an almost-sinusoidal record, indicating the historical seasons. High-resolution ice-core profiles can be dated by counting these annual layers, and have been done so across Greenland and at the West Antarctic Ice Sheet (WAIS) Divide ice core site. Fig. 4 shows two annual signals over 24 months for four different chemicals that are deposited in ice cores (Sigl et al., 2016). The peak in seasonal deposition is shown twice for each chemical, at different times in history, but the seasonality of these species remains strong throughout time.
Reconstructing Past Temperatures
We commonly think of water as H2O - a molecule containing two hydrogen atoms and one oxygen atom. However, atoms (i.e. Hydrogen and Oxygen) come in several forms, known as isotopes - atoms with the same number of protons, but differing numbers of neutrons. Those isotopes that don't decay over time and are preserved in the ice core are know as stable water isotopes. It is possible to measure the amount of each different stable water isotope present in an ice core by melting the ice core and using a mass spectrometer to analyse the water produced.

The snow that eventually forms ice cores starts its life as ocean water which is evaporated and transported to the polar regions. Water isotopes with more neutrons are heavier and therefore require more energy to evaporate and transport. The amount of energy available to do this is related to temperature. Therefore heavier isotopes are found in ice cores in higher amounts at warmer periods in the planet's history! Find out more  here!

Atmospheric gas

Ice-core measurements of atmospheric gases correlate well with direct measurements taken from the atmosphere dating back to 1950. As a result of this, ice-core scientists can assume that the atmospheric gas concentrations measured in ice cores reflects the atmospheric conditions at the time the gas was entrapped in the ice core. Hence, ice cores tell us that carbon dioxide concentrations have been relatively stable for the last millennia until around 1800 AD but since then a rise of almost 40% has been measured in both ice cores and direct atmospheric measurements (Fig. 5).

Figure 5: 1000 years of atmospheric CO2 concentrations from various Antarctic ice cores (DML, South Pole, Law Dome and Siple Dome) and the direct measurements in Mauna Loa Observatory [Credit: Ashleigh Massam, compiled from open access data sources]

Carbon dioxide concentrations have been relatively stable for the last millennia until around 1800 AD but since then a rise of almost 40% has been measured

In addition to comparison with present-day measurements, the trapped gases offer a record of direct atmospheric and greenhouse gas concentrations, including methane, carbon dioxide and nitrous oxide (Fig. 6) on a longer timescale – up to 800,000 years (Loulergue et al., 2008). Records show the connection between fluctuations in the atmosphere and long-term global climate variations (e.g. temperature) on a millennial timescale (Kawamura et al., 2007). The long-term trends show a pattern in the gas concentrations that compare well with glacial-interglacial climate. The phasing and timing of the eight glacial cycles covered by this record are dominated by the orbital cycle of the Earth on a 96,000-year periodicity, with a warm, interglacial period between each cold period. However, as we will see later in this blog post, this may not be the case when we look further back in time!

Figure 6: Variations of temperature (from present day mean temperature, black), atmospheric carbon dioxide (in part per million by volume — blue) and methane (in part per billion per volume red) over the past 800,000 years, from the EPICA Dome C ice core in Antarctica. Modern value (of 2009) of carbon dioxide and methane are indicated by arrows. [Credit : Centre for Ice and Climate , University of Copenhagen. Re-used with permission ]

Other climate proxies

Chemistry preserved in the ice also offers a proxy (=a means) to reconstruct other seasonally-deposited tracers:

                        • Information on past sea-ice extent can be obtained from chemicals found in ice cores which are also present in sea salt such as sodium, chlorine and methanesulphonic acid (MSA) (Sommer et al., 2000; Curran et al., 2003; Rothlisberger et al., 2003).
                        • The seasonal deposition of elements such as iron, magnesium and calcium, which are linked to dust from far-afield and the short-term climate variability such as atmospheric circulation (Fuhrer et al., 1999).
                        • Finally, volcanic layers in the ice core such as tephra and sulphate deposit provides a unique timestamp to a specific depth. These layers were deposited at the same time, all over the world and can be pinpointed to a specific volcanic eruption. Deposits of the same layer outside of a glaciated landscape, (e.g. within rock layers ) can often be dated using radiocarbon (Carbon-14) or another radiogenic dating methods. Additional age horizons can be interpreted by events assumed to occur in the world at the same time, such as rapid climate events. Age constraints are beneficial to interpreting deep ice-core records that are not analysed at a sub-annual resolution by offering pinpoint age horizons to an ice-core record.

Current knowledge from ice-core records

As we have seen, ice core are important because they put the current climate variations into the context of a long-term climate history. Additionally, polar ice cores can allow us to looks at variations between the northern and southern hemisphere. Ice cores also extend back much, much further in time than terrestrial weather stations or satellite records:

Figure 7: Deep ice core locations in Greenland and Antarctica [Credit and more details: NSIDC ]

The current past climate record tells us about glacial and inter-glacial periods (Fig. 6) but also allows us to look at finer detail – i.e. the variability within these periods, which were previously assumed stable.  For example, ice cores have led to the discovery of Dansgaard-Oeschger events; which are are rapid climate fluctuation events, characterised by rapid warming followed by gradual cooling to return to glacial conditions, 25 of these events have happened during the last glacial period.

Records from the Northern and Southern hemisphere also allow us to link these small and large scale changes in climate in the two hemispheres. For example, ice cores analysed from both poles show a ‘call and response’ signal between Dansgaard-Oeschger events in the Northern Hemisphere and events in the Antarctic climate record. The southern hemisphere cooled during the warm phases of Dansgaard-Oeschger events in the northern hemisphere (Buizert et al., 2015), and vice versa during northern hemispheric cooling (see our previous blog post on the subject).

There are already over a dozen ice cores taken from Greenland and Antarctica (Fig. 7), offering a clear and detailed history of the climate during the Late Quaternary period (Fig. 6), going back up to 800,000 years (Quaternary = last 2.6 million years). As we mentioned earlier the timing of glacial and inter-galcial cycles in this 800,000 year old record is dominated by the orbital cycle of the Earth (96,000-year periodicity). However, marine records show that frequency of glacial-interglacial cycles was different before this time (Lisiecki and Raymo, 2005). It is in order to better understand these changes that the quest for the oldest was formed – beginning last month the mission aims to drill an ice core of ice older than 800,000 years to gain detailed information about the climate even further back in time.

Detailed records from high-resolution ice cores improves our understanding of the response of the planet to deglaciation events

The continuous and high-resolution of ice-core records, together with marine and terrestrial records, offers a global view of coupled processes from ice sheet calving events, changes to ocean circulation and heat transport and the subsequent cooling events across the Earth. Detailed records from high-resolution ice cores improves our understanding of the response of the planet to deglaciation events from the large ice sheets that once covered much of the northern hemisphere. Melting ice sheets pose a significant threat to the planet from rising sea levels and the freshwater input leading to inevitable changes in climate.

Edited by Emma Smith and Sophie Berger

Ashleigh Massam is a final-year PhD student based in the Ice Dynamics and Palaeoclimate group at the British Antarctic Survey and with the Department of Geography at Durham University. Her project is developing the age-depth profiles of three ice cores drilled at James Ross Island, Fletcher Promontory and Berkner Island, West Antarctica, by a combination of high-resolution trace-element analytical techniques and modelling ice-sheet processes.

Image of The Week – Ballooning on the Ice

Image of The Week – Ballooning on the Ice
A curious experiment is taking place in Greenland. An experiment involving very large balloons and – of course – a lot of snow. Read on to discover why balloons are an environmentally friendly tool when constructing an ice core drill camp.

Last year, a small team traversed 400km from northwest Greenland to the EastGRIP site (read more about the traverse here). This year another strenuous task is waiting: setting up the camp and getting everything ready to drill through the largest ice stream in Greenland: The North East Greenland Ice Stream.

What about the balloons then?

When drilling an ice core it is convenient to set up the drill in a place that is sheltered, so that the drilling operation is not hampered by bad weather. It is also best if the ice core is handled in areas where the temperature is not too high. The obvious solution is to dig out caves under the surface of the ice sheet. They provide both a shelter for the weather and a natural cold room. At previous camps, the underground caves or “trenches” have been constructed with wooden beams as a ceiling. However, after several years of snowfall the beams will start to collapse under the weight of the newly accumulated snow.

This year, scientists at the EastGRIP project are attempting a different and completely new approach. Relying on the fact that a dome-shaped ceiling is a very stable construction, the trenches are built using very large balloons. The construction process is quite simple although like all polar fieldwork it also requires hard work.

Pictures by S. Kipfstuhl combined to show the construction of the balloon trenches.

Pictures by S. Kipfstuhl combined to show the construction of the balloon trenches.

First, trenches are dug out of the snow with snowblowers. The balloons are then laid out in the trenches and inflated. Once they are fully inflated they are covered in snow and the snow is left to settle for a couple of days. The balloons are then deflated and beautiful caves appear. After a bit of tidying up, the caves can be outfitted with drills, equipment and other necessities.

A look into the beautiful caves left behind when the balloons were deflated. Credit: S. Kipfstuhl.

A look into the beautiful caves left behind when the balloons were deflated. Credit: S. Kipfstuhl.

And the environmentally-friendly part?

Transporting material into the middle of an ice-sheet is an expensive process that is done via aircrafts fitted with skis. The heavier the material the more fuel is needed for the transport. The wooden beams previously used are heavy and therefore require a lot fuel to transport. On the other hand, balloons are substantially lighter, can be reused for building new trenches and are not left behind as waste. An ingenious solution to a very unique problem!

The EastGRIP project is a lead by Centre for Ice and Climate, University of Copenhagen, Denmark with several international partners and air support from the US Office of Polar Programs, National Science Foundation. You can follow the camp on twitter for photos and updates on daily life on the @egripcamp twitter account.

A balloon ready to get inflated. Credit: S. Kipfstuhl.

A balloon ready to get inflated. Credit: S. Kipfstuhl.

An Antarctic Road Trip

An Antarctic Road Trip

Working in the Arctic and Antarctic presents its own challenges. It is perhaps easy to imagine how a station situated close to the coast is resupplied: during the summer, one or more ships will arrive bringing fuel, food and equipment, but what about stations inland? Flying in supplies by aircraft is expensive and, in the case of large quantities of fuel, unsustainable. Besides, many stations are closed during the winter season, so there is nowhere for a plane to land until the skiway has been reestablished. The answer is of course that you drive. In other words, you go on a polar road trip, and one such road trip is the traverse that starts every year from the German Neumayer III station. The route is almost 800km long and it typically takes the traverse team 10 days to make their way across the East Antarctic Ice Sheet to their goal: Kohnen station at 75 degrees S, 0 degrees W and 2.9km altitude.

This year I got the chance to join the traverse and do a bit of science along the way with my colleague Anna Winter. Read below for a riveting tale of hardships, drilling and bamboo poles!

Map of our traverse route starting at the Neumayer III station on the coast. Credit: Anna Winter.

Who is holding up the traverse?

If you were to look at the traverse from above, you would see six large “Pisten bullies” pulling several sledges, each leaving a track across the ice sheet. However, you would also see two people on a tiny vehicle; a skidoo with two small sledges. Some times the skidoo will be in front of the traverse train, but often it will be trailing behind, and you would definitely notice that the people on the skidoo are stopping frequently. The two people are Anna and myself. We had set out to investigate how much snow is falling in this part of the Antarctic, and to do this we used a range of equipment from highly advanced radar instruments to bamboo sticks and a measurement tape.

Drilling into the past

The Antarctic ice sheet has a long memory. When snow falls, the old snow is buried, so when you drill down into the surface you go back in time and can look into the past. This is how we know what the climate was like in the past. Drilling an ice core all the way to the bottom of Antarctica takes a very long time: often 3 – 5 years or more, but since we want to know something about the very recent changes, we do not have to drill very far.

Drilling a firn core requires patience, focus and sturdy gloves. Credit: Anna Winter.

Drilling a firn core requires patience, focus and sturdy gloves. Credit: Anna Winter.

On the 31st of January the traverse stopped a bit earlier than usual, and while the drivers tended to the vehicles and the cook prepared the New Years Eve dinner, We started drilling a firn core (firn is old snow that is not ice yet) with the help of Alexander and Torsten. In order to drill a firn core,  you need a drill that can capture the firn inside, a small engine for powering the drill and several extensions so you can go as deep as you like (see photo). It is not an easy process and many things can go wrong. For example, it should not be too warm when you drill. A few metres into the snow the temperature is no longer the same as the air, but instead it is the average annual temperature. Since we are drilling in the summer time this means that the firn we retrieve will be maybe 20 degrees colder than the temperature at the surface. When the drill comes up the metal gets warm and the core will get stuck inside the drill. A real nightmare! This is also the reason why we drilled during the evening even if that cut our New Years Eve celebrations short. Fortunately, we did manage to get a break and enjoyed a delicious New Years Eve meal, before finishing the drilling ten minutes before midnight. We celebrated the success of the drilling and the New Year with a whisky, before the cores were packed in boxes so they can be shipped to Germany for more analyses at the Alfred Wegener Institute.

Measuring a the height of a bamboo pole includes high-technology equipment, namely, another bamboo pole with peanut-can and a measurer tape stuck to it. Credit: Nanna B. Karlsson.

Measuring a the height of a bamboo pole includes high-technology equipment, namely, another bamboo pole with peanut-can and a measurer tape stuck to it. Credit: Nanna B. Karlsson.

The endless row of bamboos

So, how do the bamboo poles fit in the picture? The firn core tells us a lot about the snowfall in the place where it was drilled, but we also want to know what is happening along the route of the traverse, and what is happening right now. Therefore, last year, bamboo poles were set up every 1km along the first part of the traverse. Our task was to increase the number of bamboo poles to one pole every 500m. We also measured the height of the old poles, and compared it to their original height. The further we got from the coast, the taller the bamboo poles were. This is what we expected since we know that very little snow falls in these parts of Antarctica, maybe less than half a metre a year! From our measurements, we now know directly how much snow has fallen since last year. Next year, other people will measure the height of the old bamboo poles and the new ones we put up, and we will know even more about the snowfall. It is a laborious and hard process: the traverse route is almost 800km so it is almost an endless row of bamboo poles. If only they could be seen from space they would make an impressive sight.

This blog post was originally brought on the website of the Alfred Wegener Institute in German. You can see more photos and read the originals here and here.

Tea break with Kottas Mountains in the background. For once we were ahead of the rest of the traverse. Credit: Anna Winter.

Tea break with Kottas Mountains in the background. For once we were ahead of the rest of the traverse. Credit: Anna Winter.

(Edited by Sophie Berger and Emma Smith)

Image of the Week: The Bipolar Seesaw

Image of the Week: The Bipolar Seesaw

The colourful graphs above show how the climate changed in the period from 65 to 25 thousand years ago when Earth was experiencing an ice age. A wealth of information on the dynamics of our climate is embedded in the curves, especially how the northern and southern hemisphere interact, and how fast climate can change.

The figure represents thousands and thousands of hours of work by scientists, technicians and logistics personnel.  It shows the latest results from analyses of an ice core drilled in the middle of the West Antarctic Ice Sheet: The WAIS ice core.


What are we looking at?

In the top part of the figure, the blue curve shows oxygen-isotope values from the North Greenland Ice Core Project. The curve represents temperature in the northern hemisphere where the peaks are high temperatures.

→  First take home message: During the last ice age, the temperatures in Greenland changed very abruptly from cold to warm temperatures. These changes are marked with yellow lines in the figure.

The green curve shows the amount of methane gas in the Antarctic WAIS core. The shape of the methane curve is very similar to the blue temperature (oxygen-isotope) curve from Greenland. The rapid changes in temperatures in Greenland are reflected in the amount of methane in Antarctica.

→ Second take home message: Methane is a “well-mixed” atmospheric gas. This means that if you measure the amount of methane in the air anywhere on Earth, you will get a good indication of the amount of methane on a global level.

The third and fourth curves show the oxygen-isotope values from WAIS (yellow) and the temperatures (purple). In contrast to the Greenland temperatures, the temperatures in Antarctica do not show very fast changes. Instead, we see a slow cycle of rising and falling temperatures.

→ Third take home message: When Greenland experiences a fast warming, Antarctica slowly begins to cool. When Greenland slowly cools, Antarctica begins to warm.


But what does it all mean?

It means that changes in temperature in the northern hemisphere affect the southern hemisphere but with a mechanism that is slightly delayed. This mechanism is of course the ocean. In climate science, this up-and-down pattern is called “the bipolar seesaw” (read more here).


Why is it important?

It is important because it tells us something about how the climate system reacts to abrupt changes. A change in the northern hemisphere is transmitted to the southern hemisphere but not necessarily immediately.


Want to know more?

Read the whole paper here.

Edited by Emma Smith and Sophie Berger

Image of the Week: Atmospheric CO2 from ice cores

Image of the Week: Atmospheric CO2 from ice cores

The measurements of atmospheric CO2 levels at Manu Loa, Hawaii read 401.01ppm on the 7th of December this year. To understand the significance of this number, you just need to look at the figure above from the 4th IPCC report. It shows the changes in CO2 concentrations during the past 800,000 years based on ice core measurements. Values have fluctuated between 190ppm and 280ppm. In other words, both the level of present-day atmospheric CO2 and the rapidity of the increase is unprecedented.

The figure also shows the projections from the IPCC AR4 report for different emission scenarios. Which scenario will turn out to be the most likely might be determined at COP21 in Paris right now.

Read more:

Measurements at Manu Loa, Hawaii

Image of the Week: GISP II Borehole

Image of the Week: GISP II Borehole

Climate records from ice cores have helped scientists understand the past changes in climate.The GISP II (Greenland Ice Sheet Project Two) ice core was more than 3km long and was drilled during a five year period in the 1990s. After the drilling ended the casing of the borehole was extended above the surface, so that the borehole can still be accessed for remeasurements of, for example, temperature and changes in shape.

Science and Shovels: Traversing across the Greenland Ice Sheet.

Science and Shovels: Traversing across the Greenland Ice Sheet.

Moving 150 tonnes of equipment more than 450km across the Greenland Ice Sheet sounds like a crazy idea. In that context, moving a 14-metre high, dome-shaped, wooden structure seems like a minor point, but it really is not. I do not think I realised what an awesome and awe-inspiring project I was part of, until I was out there, in the middle of the blindingly white ice sheet, and I saw the enormous, black structure moving slowly towards our first stop for the night.

Traverse route from NEEM to EGRIP.

Traverse route from NEEM to EGRIP. Topographic map from Bamber et al., 2001, JGR.

Why are we doing this? 

Our field camp NEEM has been inactive since 2012, when the last samples were retrieved from the 2.5km deep borehole. In the following 3 years, scientists and traverse teams have visited the deserted camp occasionally. Now it was time to move everything and start all over on a new drilling project, EGRIP (East Greenland Ice core Project) in Northeast Greenland.

Helle, Paul and Anna readying one of the sledges for the traverse.

Helle, Paul and Anna readying one of the sledges for the traverse. Credit: N. B. Karlsson.

How do you move an entire camp?

In 2012, most of the equipment was packed down on big sledges ready to move, and the dome was fitted with four big skis. The first task this year was to check that everything was in order for the traverse. Let me start by saying that one cannot overestimate exactly how much snow can pile up during three years. The key piece of equipment is therefore a shovel. To be precise, you need a whole bunch of shovels. The two garage tents also had to be taken down. It turned out that they were encased in ice, so add some spades and a couple of sledgehammers to the required equipment.

Freeing the dome

Finally, the skis under the dome had to be freed. The shape of the dome means that the snow drifts around it instead piling up, but the skies under the dome were covered in a mixture of ice and snow. When I look at the photos now, it seems almost unbelievable that we manually cut free and moved away that amount of ice. The piles of ice blocks grew and grew during the two days, where people were working away with chainsaws, shovels and hands to clear the skis. In the meantime, Sverrir, our Icelandic mechanic, displaced tonnes of snow in front of the dome, in order to build a ramp for dragging up the dome.

Freeing the dome using shovels, chainsaws and a pisten-bully. The skies are beginning to emerge from under the dome. The skis support the "bike wheel" (blue) that the dome is mounted on.

Freeing the dome using shovels, chainsaws and a pisten-bully. The skies are beginning to emerge from under the dome. The skis support the “bike wheel” (blue) that the dome is mounted on. Credit: N. B. Karlsson.

“It’s going to topple”

I do not think I will ever forget the nerve-wracking moment when the dome was first jolted free. As it moved slightly forward one of the skis lifted completely off the ground, and for a brief, alarming second I thought, “It is going to topple”. Then with a thud, the ski reconnected with the ground and the dome moved slowly up the ramp towards its first stop on the way to EGRIP.


Once the traverse started, the days passed in a blur. You get up early, and some days you wait for hours before setting out because there is a problem with one of the vehicles. Other days, everything works perfectly and you scramble to get everything you need out of the dome, before the ladder is hoisted up and the traverse is on its way. Our convoy was a very mixed lot of vehicles; the big Case tractor driven by Pat pulled the dome. Two Pisten-Bullies pulled sledges containing everything from fuel and extra living quarters to our old forklift. Then we had two Flexmobiles, the elderly gentlemen of the convoy, going at a nice, sedate speed, and finally three skidoos, the science teams.

Anna is checking the radar equipment as one of the pisten-bullies is approaching.

Anna is checking the radar equipment while one of the pisten-bullies is approaching. Credit: N. B. Karlsson.

The freedom of skidooing

Driving a skidoo, we had a lot more freedom than the heavy vehicles. It is easier to make a quick stop on a skidoo and it is often necessary, if there are problems with the equipment. The downside is that it is significantly colder to spend all day on a skidoo than inside a nice, warm cabin. Temperatures were often below -20 degrees Celsius, and although we were fortunate and did not have high winds, it still gets chilly at the end of the day. The solution is to dress warm, in a ridiculous number of layers, and to eat a lot. After a few days we were experts in identifying food that do not freeze easily (salami, fat cheese, brownies), or food that does freeze but is still tasty frozen (smoked halibut, ham).

The Science

At the end of the traverse, Helle, Paul and Sepp had collected numerous samples of the surface snow, dug several metre-deep snow pits and drilled three shallow cores, one of them 15m deep. Simultaneously, Anna and I collected radar data along (almost) the entire traverse route. The data have not been analysed yet but we are looking forward to see the exciting results of our combined efforts.

Helle and Paul are drilling a shallow core while Anna is waiting for the traverse train to pass. Credit: N. B. Karlsson.

Although our traverse is over, the EGRIP project is just beginning. The aim of the project is to investigate the dynamics of fast-flowing ice streams by drilling an ice core through the Northeast Greenland Ice Stream. The EGRIP camp will run until 2020 and next year the camp infrastructure will be set up and drilling will start. Exciting times ahead!

On the traverse we were Dorthe, Helle, Joel, Jørgen Peder, Paul, and myself from CIC (Centre for Ice and Climate, University of Copenhagen, Denmark), Anna and Sepp from AWI (Alfred Wegener Institute, Bremerhaven, Germany), Sverrir, our Icelandic mechanic, Matthias the medic, and Pat Smith from the Greenland Inland Traverse, GrIT, a logistics operations funded by the US National Science Foundation. We were 11 participants, 7 men and 4 women, representing 5 different nationalities, and we had an amazing time!

The project would not be possible without support from the A.P. Møller Foundation, University of Copenhagen, the Alfred Wegener Institute (Germany), Bjerkness Centre (Norway) and the National Science Foundation (USA), who provided staff and a tracked vehicle.

More information:

Read the press release here announcing our arrival at the EGRIP camp.

All our field diaries are available here.

The whole traverse train poses for the end-of-traverse photo. Credit: NEEM field diary.

The whole traverse train poses for the end-of-traverse photo. Credit: NEEM field diary.