Climate Research: Reading the Book of Ice

Why climate researchers treat drill cores from the large ice sheets of Antarctica or Greenland as if they had dug them in a gold mine is easy to say: they can be dated relatively well compared to other climate archives. And because it is expensive to drill in places so far away from the home institutes and without any infrastructure, it makes sense to preserve them for research.

Humanity has come up with all sorts of ideas to store things: food warehouses, museums, and even the ancient Egyptians had libraries. But ice cream? How can ice be preserved in our summer latitudes over long periods of time? Hard to imagine. But it does exist: the “Ice Library”, in Bremerhaven as a branch of the Alfred Wegener Institute (AWI) for polar and marine research.

The institute benefited from the fact that, after long disputes, it was founded not in Kiel, but in 1980 at the mouth of the Weser. The city is still a center of fish processing. Prominent companies such as “Frosta” or “Nordsee” have to reserve considerable space for their frozen goods. When the drill cores could no longer be stored in the main building – at that time they were still packed in plastic sleeves and visible individually, which gave the impression of a library – the institute rented a large warehouse from the logistics company Nordfrost. On the outskirts of the city, behind the busy tourist hotspot fishing port. In 2018, a state-of-the-art cold store was installed.

Bracing for the cold in his padded anorak, Johannes Freitag opens the steel gate and stands in the fog that the moist air has brought in. The temperature here is constantly minus 28 degrees Celsius. “Still quite warm,” says glaciologist Freitag, who is interested in the processes that are or have occurred in the ice. This is sufficient for Greenland ice, but in deep drill cores from Antarctica, temperatures can sometimes reach minus 50 degrees, and since they are no longer under pressure, the crystals relax, which affects the examination of trapped air bubbles. That’s why Antarctic drill cores are usually stored at the respective camp.

A warehouse full of ice

An impressively wide hall opens up, a high-bay warehouse whose brightness is further enhanced by thousands of white Styrofoam boxes. Here the ice cream freaks’ treasures rest on pallets that are sorted in and out with a pallet truck. The oldest ice, formed about 800,000 years ago, comes from the EPICA drilling at Dome C, one of the highest points of the East Antarctic ice sheet. It is in smaller boxes because only the remains of the drill core, which has been examined according to all the rules of the art, are kept. Six core segments cut to meter lengths fit into the standardized boxes.

“If we make information visible about what time we are in, that motivates the crew.”

John FridayGlaciologist

Of course, each box has a number so that scientists can use the database to see what is inside. But to be on the safe side, stick labels on the visible sides. On one of them is written in black felt-tip pen: B51. “When I read this, I know immediately: This is the 51st ice core that we at the Alfred Wegener Institute drilled in East Antarctica in 2012,” says Johannes Freitag. »About 200 meters deep, 75 degrees south, 15 degrees east. It says archive here – I know what the pieces look like just from this identifier. I was involved in almost all of the drilling. This is a half core that is divided into quarter cores.«

Analyzes are already taking place on site

Freitag appreciates the special atmosphere at the drilling sites, the “magic moment” when a piece of climate history is brought to light. Because you want to be independent of the weather, you drill in a gymnasium-sized vault under the ice with several corridors to test laboratories and interim storage facilities. The high drill pipe is central there. The journey to great depths and up sometimes takes half an hour. Then the four meter long drill appears. The ten centimeter thick core is carefully pushed out of the steel pipe and divided into meter lengths.

The electrical properties are measured on site; They are different depending on how much and which trace substances are in the core. For example, particles from volcanic eruptions can be perceived. These are clues if you want to date the ice. And because the electrical properties also depend on the orientation of the crystals, one can conclude that deformation processes are occurring. “This means we already know at camp how old the ice is approximately,” says Freitag. »The drilling is strenuous and in the long run – always the same steps – maybe even tiring. If we make information visible about what time we are in, that motivates the crew.«

The first drillings were secret

The first deep drilling in Greenland, initially kept secret, was completed in 1993 at the US military base Century. Six more followed. The last one, EastGRIP (East Greenland Ice Core Project), lasted from 2016 to 2023, interrupted by the Corona period. It reached a depth of 2,664 meters. Last winter, the AWI glaciologists processed the entire core; Ten men and women scurried around in the institute’s minus 20 degree ice laboratory for eight weeks and cut core segments for the upcoming investigations. They were then distributed to special working groups in several countries.

With each new core, scientists hope to be able to more precisely record the climate history of the Greenland ice sheet – and thus a region that influences the entire northern hemisphere. But it’s not the way you might imagine that a particularly meaningful core would be the ultimate. The conditions of the precipitation and what happens to it vary from place to place because the ice flows. There are shear zones, all kinds of folds; all of this has to be taken into account.

The traces of the last warm period

So you can’t say from a single core: the last warm period, the Eem, named after a river in the Netherlands, began 120,000 years ago. On another core, isotope analysis shows the tipping point to be in the warm period, for example 125,000 years ago. The studies show that there is still great uncertainty in the dating of events in the past. The glaciologists have to synchronize the individual measurements and the results of all drill cores in order to be able to limit the likely extravagances of the climate swing. And you need multiple methods to do this because each method has different time scales.

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The Eemian Interglacial – the period between two ice ages – is interesting because it allows comparisons with our current climate system. The era in which Neanderthals still hunted mammoths lasted from around 130,000 to 115,000 years before today. In July 2010, in one of the most difficult to access places on the Greenland ice sheet, the NEEM (North Greenland Eemian Ice Drilling) drilling, which was associated with great expectations, reached the rock bed at a depth of 2537 meters. Scientists from 14 nations were involved in the project. For the first time, the ice layers of the Eem Age could be drilled through and examined. Even material from the previous Ice Age was recovered.

One of the most controversial questions was: Was there ice on Greenland during the last interglacial? Drilling was carried out in north-west Greenland precisely because it was believed that they would come across the remains of a compact Eem ice sheet. “Yes, we found ice, but its stratigraphy was disturbed,” says Freitag. »There has been a mixing. We were also able to determine this from other drill cores. And the spatial distribution was different. This shows again that only the study of all the data leads to overall knowledge.«

Comparing the isotope ratios between heavy and light hydrogen or oxygen – a measure of the temperature at which the snow fell – showed that the Eem was around five degrees warmer than today – temperatures that current civilization will reach at the turn of the next century would if it does not initiate radical countermeasures. What is also alarming is that in certain periods there have been stark climate changes from warm to cold and vice versa, jumps of fifteen to twenty degrees Celsius within just a few decades. The climate crash can happen quickly.

A surprising conclusion was: Despite the higher air temperatures, the ice masses shrank far less than expected compared to today. That’s the good news. The new findings refute all horror scenarios according to which the Greenland ice sheet will completely disappear during a warm period. Conversely, if the sea level was four to eight meters higher during the Eem, this means that more ice melted in Antarctica.

Target: 1.5 million year old ice

A new well is currently being sunk in Antarctica, about 50 kilometers away from the previous one at Dome C, project name: “Beyond-EPICA Oldest Ice”. “In January next year, when the international team arrives on the rock, we hope to have 1.5 million year-old ice on the table,” says Johannes Freitag. He is a little nervous because the top 1,600 meters will be cut next week at the Alfred Wegener Institute. »In the time before the Eemian, the climate variance changed over longer periods of time. Recognizing this is important because we can then use our models to test how the Earth’s climate system works.”

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