This episode introduces the process of finding paleo-temperature
through the analysis of the Greenland ice core by Willi Dansgaard and other scientists.
In the mid-1950s,
when Emilyani was completing a revolutionary achievement using the oxygen isotope ratio of foraminifera,
Billy Dansgaard measured the oxygen isotope ratio by collecting rain and snow from all over the world at the University of Copenhagen in Denmark.
ansgaard was interested in the relationship between daily weather conditions and the oxygen isotope ratio.
While conducting related research,
Dansgaard found a rule of thumb that the relationship between temperature and oxygen isotope ratio in snow falling in high latitudes was unexpectedly simple.
When the annual average temperature is high, the percentage of Oxyzen-18 in the snow in that year is high;
that is, it becomes heavy,
and when the temperature is low, the rate of Oxyzen-18 is low,
that is, it is light.
In other words, the oxygen isotope ratio of snow or ice can be an excellent 'Paleothermometer' for recording past temperatures.
Please look at the linked video for the relationship between the percentage of Oxyzen-18 and the Paleothermometer.
In his 1954 paper titled "Concentration of Fresh Water,"
Dansgaard thought he could use the record of the Greenland ice sheet to reconstruct climate change over the past hundreds of years.
Greenland was a familiar place to Dansgaard,
who worked as an observer at a weather station in Greenland,
far away from town, for a year after graduating from university.
Having joined the ranks of first-rate geochemists at a young age to study oxygen isotope ratios in snow,
Dansgaard learned that a group of US military researchers was excavating the Greenland ice sheet.
Thanks to Greenland, Denmark is considered the country with the largest land area in Europe.
Most of Greenland is located in the Arctic Circle,
except for some parts in the south.
So, in the middle of winter, the sun never shines on the face in almost all areas.
Also, 85 percent of the island's site is covered in thick ice,
the Greenland Ice Sheet.
Because of the ice sheets, people can live only in a few areas near the coast.
In the late 1950s, at the height of the Cold War between the United States and the Soviet Union (now Russia),
a US military base was built in the northwest of Greenland top secret.
The name of the base is 'Camp Century.'
The secret base of this century was built in a place unimaginable by common sense:
the inside of a continental glacier.
However, despite being built in an unconventional location, the base boasted a staggering scale.
The aisle, called Main Street, was about 7 meters in width
and height and more than 400 meters in length, so even a large truck could easily pass through it.
There were tiny sidewalks on both sides of the main street,
and there were 32 convenience facilities next to it,
including a hospital, church, movie theater, gym, and skating rink.
When the base was first built, a mobile nuclear power generator provided the base's power.
During the summer, about 250 US military personnel stayed in the room,
and each room was equipped with a shower.
There was even a bar with fancy bartenders where you could get all your drinks for a quarter coin.
There was a poster of beauties in swimsuits in the bar, but when the church pastor came,
he quickly changed it to a sign with a fishing picture.
The US military carried out various activities at Camp Century in the Greenland continental glacier,
such as research on the structure of the continental glacier and experiments on transporting military supplies into the glacier.
As one such activity, the Lyle Hansen Group of the U.S. Army's Cold Area Engineering Laboratory,
which managed Camp Century, began developing technology to excavate ice cores.
It was an ingenious yet great idea.
To excavate the ice, a structure was erected in the underground base, and in the 1960s, excavation finally began.
Despite numerous technical problems,
the goal was finally achieved in July 1966.
It went down to the bottom of the Greenland continental glacier and excavated a core 1387 meters long.
At the time, the perception that the ice cores excavated at Camp Century would be helpful for past climate change research was vague.
There needed to be a suitable place to store the vast ice core.
In the end, the ice core was transported to the headquarter of Cold Regions Research and Engineering Laboratory in New Hampshire, USA,
and stored there in a freezer.
Even though a full-scale ice core was excavated for the first time in the world,
only some American researchers at the time suggested using this ice core.
Dansgaard, who is Danish, was simply lucky.
Upon learning of the situation,
Dansgaard immediately sent a letter to Chester Langway,
who managed the ice core, and asked for help analyzing the ice core's oxygen isotope ratio.
Langway accepted the offer.
This was the first meeting between Dansgaard and Langway,
who continued their relationship for the next 20 years.
Dansgaard immediately sent a student to New Hampshire's Cold Regions Research and Engineering Laboratory to obtain 86 ice samples.
And Dansgaard, who started analyzing the oxygen isotope ratio of the sample that arrived in Copenhagen,
was surprised by the results.
This is because the selection recorded the cold period,
estimated to be the last ice age, and the warm period before the last interglacial period.
Impressed by this result,
Dansgor sampled the ice cores of Camp Century more closely
and meticulously analyzed the oxygen isotope ratios of 7,500 samples one by one.
The development of the detailed oxygen isotope ratio analysis of the world's first ice core they obtained was overflowing with scientific implications.
Could you look at the graph on the screen?
First, the stable oxygen isotope ratio was maintained from the ice core at nearly 1400 meters to about 1150 meters from the surface layer,
with no significant fluctuations from now until about 10,000 years ago.
Then, although there is some shaking,
the oxygen isotope ratio fluctuates around 29‰
This figure of -29‰ is almost the same as now.
From these results, it can be seen that the climate of Greenland was similar to the present until about 10,000 years ago.
But deeper down, things start to change.
The oxygen isotope ratio decreased rapidly,
and at a depth of 1,200 meters,
estimated to be around 14,500 years ago,
the oxygen isotope ratio decreased to-43‰.
When applied to the relationship between temperature and oxygen isotope ratio previously reported by Dansgaard,
decrease in oxygen isotope ratio of 14‰ corresponds to a temperature drop of more than 20 degrees.
In addition, several exciting signals were found in this ice core.
In the transition from the last glacial to the postglacial,
the climate reached warming through oscillations of seemingly warming and then cooling again.
And that's not all.
Among the ice age records, they found several 'climate changes' of short cycles,
with an oscillation of about 7 degrees Celsius when converted to temperature.
This is because it suggests that Greenland during the ice age was not simply cold but was accompanied by a volatile climate.
This starkly contrasts that oxygen isotope ratios have mostly stayed the same over the past 10,000 years.
The oxygen isotope ratio measurement results of Camp Century ice cores conducted by Dansgaard
proved that ice is a 'tape recorder' that records past climate changes like seabed sediments.
And it had an impact enough for paleotemperature researchers to admit it.
But, the biggest problem is that the essential awareness of the movement of continental glaciers,
which is necessary for determining the age of ice cores,
needed to be improved when the paper was published.
Ice cores, like seafloor sediments, preserve records of older times in the lower parts.
However, continental glaciers have the critical characteristic of slowly flowing down like warmed taffy.
So, the history of the past engraved in the continental glacier has a unique property:
it moves and disappears over time.
In addition, the analysis results of seafloor sediments at the time did not confirm the rapid change in oxygen isotope ratio during the last ice age.
This fact also puzzled many researchers
and caused them to question the results of Camp Century's analysis.
In 1967, the year following the successful excavation to the bottom of the continental glacier,
Camp Century had to be closed inevitably due to the rapid flow of the continental glacier.
Much energy is consumed to keep the base with all facilities comfortable and conduct various military experiments.
Thus, much heat was released, and the ice flow rate around the ground increased.
Nevertheless, camp Century has significantly contributed to opening the way for revolutionary research in science, not the military.
Since then it has been 15 years since an ice core was excavated in Greenland that reached the bottom of the continental glacier.
Just looking at this,
you can see how far ahead of the times Camp Century's paleotemperature research using continental glacier cores is.
And Dansgaard,
who was not immediately recognized for the importance of the results of Camp Century's analysis,
had to wait 15 years before his research was recognized as correct.
He was 44 years old when he successfully excavated Camp Century
and was about to turn 60 when the desired second ice core was excavated.
Before continuing, let's learn more about continental glaciers.
A 'continental glacier' is a block of ice that rests on land.
The continental glaciers are flowing.
Continental glaciers are very dynamic materials that can be described as 'highly viscous liquids.'
It flows from the center of the continental glacier toward the edge at about 1 meter per day and about 10 meters in fast places.
First, let's say you put a small object with the same density as ice on a continental glacier.
As a result of observing the movement of this object for thousands or tens of thousands of years,
it is a streamlined of ice as shown on the screen.
No matter where the thing is placed on the continental glacier,
it is buried a little into the glacier every year.
Ice is continuously supplied to the continental glacier when snow falls.
At the same time, it gradually moves to the edge along the movement of the continental glacier.
The snow that has fallen hardens over time and turns into ice.
The ice at the central summit, which has the shape of an ideal continental glacier,
is pushed in all directions by the weight of the ice that continues to form above it.
So, when an ice core is taken from the center of a continental glacier,
the thickness of the soft layer becomes thinner in the deeper part.
As we go back, ice thickness per chronological age decreases exponentially.
In other words, the lower the continental glacier,
the more age information is contained per unit length.
For example, a 1387-meter-long ice core from Camp Century preserves records spanning about 100,000 years.
More than 90 percent of the past time has been recorded in just 17 percent of the continental glacier floor.
Obtaining detailed climate change records for ages requires more than taking long cores.
Ice must be taken where the bedrock beneath the ice is not tilted,
and there is no irregular flow under the glacier.
Determining the age of ice cores is a complex and laborious task,
different from determining the age of seafloor sediments.
In August 1981,
a second ice core reaching the bottom of the Greenland ice sheet
was taken from the US military radar station Dye 3 in southern Greenland.
This glacial core was collected as part of the Greenland Ice Sheet Project (GISP),
a joint Greenland ice sheet project by the United States, Denmark, and Switzerland that began ten years ago.
Hans Oeschger from the University of Bern, Switzerland,
Chester Langway from the US,
and Billy Dansgaard from Denmark joined Camp Century in this project.
Oeschger is a geochemist who first discovered tritium in the snow by making a detector that measures low-concentration beta rays in the 1950s.
Research using a beta ray counter made by Oeschger
means that snow or ice is a vital recording medium for paleoenvironment research using radioactive nuclides.
With Oeshuger's joining, the research group has become even more powerful.
Dye 3 is more than 1400 kilometers south-southeast of Camp Century.
This is one of the radar bases the United States built from Alaska
to Iceland to monitor aircraft or missiles invading from the north in the 1950s when the East-West Cold War was in full swing.
In addition, there are four radar stations from Dye 1 to Dye 4 across southern Greenland from east to west.
Among them, in Dye 3,
continental glacier excavation was carried out for about three years from 1979 to 1981,
and an ice core with a length of 2037 meters was collected.
The results of analyzing about 9,000 samples were published as a thesis in December 1982,
the year after the excavation of the ice core was completed.
The results were in line with Dansgaard's expectations.
This is the same oxygen isotope ratio record as Camp Century.
In particular, during the Ice Age, which lasted from 110,000 to 20,000 years ago,
warming followed by sudden coldness was repeated several times.
Paleoclimatic researchers skeptical of Camp Century's oxygen isotope ratio records had no choice but to believe this time.
The number of short warm periods, including small ones, reached 24,
later called the Dansgaard-Oeschger event after Billy Dansgaard and Hans Oeschger.
This climate event and the Heinrich event discovered later indicated that climate change is short-lived.
In 1989, a research group from eight European countries initiated another project to collect ice cores at the summit
(3200 meters above sea level),
the highest area of ​​the Greenland ice sheet.
The project is called the Greenland Ice Core Project, or GRIP for short.
A US research group also started an ice core excavation project at around the same time,
just 28 kilometers to the west.
The project was called 'GISP2' after the first letters of the Greenland Ice Sheet Project 2.
It means that it is the second project after the excavation of Dye 3.
The summit, which corresponds to the 'headwater' of continental glacier flow,
is theoretically the place where ice deformation is the smallest because there is almost no flow.
Moreover, because the ice is thick and can be traced back to the past,
it is considered an optimal excavation site for palaeoclimatic restoration research.
Both projects aimed to confirm the results obtained from Camp Century or Dye 3
and restore the climate to an older era and definitive version of Greenland's late Quaternary climate change.
In GISP2,
a new excavation system was used with sensors that can measure 16 physical properties of ice,
such as density, temperature, and pressure.
In addition,
by continuously measuring the number of dissolved substances in the ice that varies with the season and minute changes in impurities such as aerosol particles,
it was possible to accurately count the ice layer formed one sheet per year.
Thanks to this technological innovation,
GISP2 could reasonably accurately determine the age of the ice cores 45,000 years ago.
In August 1992,
three years after excavation,
GRIP succeeded in extracting a 3029-meter ice core that reached the bottom of the continental glacier.
And in July of the following year,
a year later, GISP2 excavated 3053 meters of ice core, including bedrock.
The screen shows the oxygen isotope ratio records of GRIP and GISP2.
Let's take a closer look at this graph,
one of the most influential figures in the study of palaeoclimatic fluctuations over the past 100,000 years.
From 10,000 years ago to the present,
the Holocene indicates a remarkably stable climate,
with measurements of both outcomes moving within -36 ~ -34%.
It shows the same result as Camp Century or Dye 3.
In other words, this result suggests that the climate of Greenland has been relatively stable for the past 10,000 years.
Also, as with previous ice core records,
the interval between 110,000 and 20,000 years ago included several brief warm periods or Dansgor-Osugger events.
There is no longer any doubt that this climate event is a natural climate change across Greenland.
However, analyzing the two ice cores taken from Summit needed more clarity.
The oxygen isotope ratio showed severe fluctuations between 130,000 and 110,000 years ago,
corresponding to the last interglacial period.
As a result of careful examination by researchers afterward,
it was found that irregular ice flow occurred at the bottom of the continental glacier,
and the record was disturbed.
Unfortunately, these two cores did not become definitive for the last interglacial climate.
In 1999,
a joint international team excavated another ice core to clarify the climate change of the 'past interglacial.'
This time, as in GRIP and GISP2,
we carefully selected places where complex ice deformation does not occur.
And a new drilling plan called 'North GRIP'
was carried out about 800 kilometers north of Summit.
About four years later, in July 2003,
the research team succeeded in collecting an ice core with a total length of 3085 meters.
Since the deepest part corresponds to 135,000 years ago,
it was a core that reached the last interglacial, considered a task.
The record for oxygen isotope ratios in the ice-free NorthGRIP
did not show the expected large fluctuations.
The climate of the last interglacial was equally stable as in the Holocene.
Dansgaard retired from research in 1992 after successfully excavating an ice core at GRIP.
Half a century ago,
Dansgaard's dream of analyzing ice cores and restoring the palaeoclimate is now in full bloom,
revealing an essential aspect of the climate change enigma.
However, ice cores mined in Greenland could only determine the climate up to about 140,000 years ago.
Therefore, older ice was needed to determine the environment before 140,000 years.
Undoubtedly, Antarctic glaciers are the largest glaciers on Earth that contain older ice.
Thus, scientists' attention is turned to Antarctica.
The story of this will be introduced in the next episode.
Thank you for watching until the end.
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