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IMAGES BY
ULRIKA LARSSON & LUKASZ LARSSON WARZECHA
ULRIKA LARSSON & LUKASZ LARSSON WARZECHA
PHOTO SERIES | MARCH 2024
PORTRAITS OF ICE CORES
PORTRAITS OF ICE CORES
STORIES TRAPPED
IN ICE
from the collection of the
'ICE CORE LIBRARY', NIELS BOHR INSTITUTE, COPENHAGEN UNIVERSITY
'ICE CORE LIBRARY', NIELS BOHR INSTITUTE, COPENHAGEN UNIVERSITY
The Ice Core Library at the Niels Bohr Institute in Copenhagen, Denmark, is considered a national treasure. The storage facility is known for its extensive collection of ice cores extracted from Greenland, Antarctica, and other places.
These ice cores provide valuable information about past climates, atmospheric composition, and environmental changes over thousands of years. The facility houses a vast archive of ice cores (over 40,000 pieces), carefully stored at sub-zero temperatures to preserve their integrity. Scientists can access these ice cores to further study the climate's history and improve climate models. The ice cores stored in Copenhagen have played a crucial role in advancing our understanding of Earth's climate history and its implications for future climate change. Over the years, the Niels Bohr Institute has facilitated numerous research projects and collaborations worldwide.
Ice cores contain layers of ice formed from snowfall over thousands to hundreds of thousands of years. These layers serve as a chronological record of past climate conditions, allowing scientists to reconstruct temperature variations, atmospheric composition, and other climate parameters over long timescales. Air bubbles trapped within the ice cores provide direct samples of ancient atmospheres. By analyzing the composition of these air bubbles, scientists can determine past concentrations of greenhouse gases such as carbon dioxide and methane, crucial for understanding natural climate variability and the role of human activities in recent climate change. The isotopic composition of water molecules in ice cores can provide information about past temperatures. By measuring the ratio of different isotopes of oxygen and hydrogen, scientists can infer past temperature variations, including changes in polar amplification (the phenomenon where temperature changes are more pronounced at the poles than at the equator).
Ice cores also contain dust particles, aerosols, and various chemical tracers deposited from the atmosphere. These substances can provide information about past atmospheric circulation patterns, volcanic eruptions, biomass burning, and human activities, helping scientists understand the drivers of past climate variability and environmental changes. Ice cores from polar regions like Antarctica and Greenland also provide insights into past ice sheet dynamics and sea level changes. By studying layers of ice and embedded impurities, scientists can reconstruct past ice sheet behaviour, ice melt rates, and sea level fluctuations, which is critical for assessing coastal regions' vulnerability to future sea level rise.
Overall, ice cores are invaluable archives of Earth's climate history. They offer a detailed and comprehensive record of past climate variability. Studying ice core records is essential for understanding the mechanisms and drivers of climate change and improving our ability to predict future climate trends.
NOTE on timekeeping from the 'Ice Core Library' Curator - Prof. Jørgen Peder Steffensen
As most people are aware, the Gregorian calendar is based on the supposed birth date of Jesus Christ.
The Gregorian calendar is clear: The old notation of "AD" (Anno Domini) and "BC" (Before Christ) has, over time, in favour of religious neutrality, shifted to CE (Common Era) and BCE (Before Common Era), but it covers the same. The only funny thing about this system is that it lacks a year "0", which means that the age difference between 2 CE and 2 BCE is three years.
In history, archaeology and tree-ring chronology, where carbon-14 dating is performed, science uses the term B.P. (Before Present). However, the "present" is 1950 CE, which is very confusing. The Carbon-14 method will only work on samples older than 1950 because nuclear bomb tests in the 50s and 60s produced so much carbon-14 that the dating method breaks down for samples younger than 1950 CE.
When we started ice core dating by counting annual layers, we wanted to make sure that our papers did not use carbon-14-based dating. To avoid confusion between carbon-14 dating in tree rings and ice cores, we came up with the term b2k (before 2000 CE), and we still maintain that notation in our papers to distinguish ice cores from other records.
These ice cores provide valuable information about past climates, atmospheric composition, and environmental changes over thousands of years. The facility houses a vast archive of ice cores (over 40,000 pieces), carefully stored at sub-zero temperatures to preserve their integrity. Scientists can access these ice cores to further study the climate's history and improve climate models. The ice cores stored in Copenhagen have played a crucial role in advancing our understanding of Earth's climate history and its implications for future climate change. Over the years, the Niels Bohr Institute has facilitated numerous research projects and collaborations worldwide.
Ice cores contain layers of ice formed from snowfall over thousands to hundreds of thousands of years. These layers serve as a chronological record of past climate conditions, allowing scientists to reconstruct temperature variations, atmospheric composition, and other climate parameters over long timescales. Air bubbles trapped within the ice cores provide direct samples of ancient atmospheres. By analyzing the composition of these air bubbles, scientists can determine past concentrations of greenhouse gases such as carbon dioxide and methane, crucial for understanding natural climate variability and the role of human activities in recent climate change. The isotopic composition of water molecules in ice cores can provide information about past temperatures. By measuring the ratio of different isotopes of oxygen and hydrogen, scientists can infer past temperature variations, including changes in polar amplification (the phenomenon where temperature changes are more pronounced at the poles than at the equator).
Ice cores also contain dust particles, aerosols, and various chemical tracers deposited from the atmosphere. These substances can provide information about past atmospheric circulation patterns, volcanic eruptions, biomass burning, and human activities, helping scientists understand the drivers of past climate variability and environmental changes. Ice cores from polar regions like Antarctica and Greenland also provide insights into past ice sheet dynamics and sea level changes. By studying layers of ice and embedded impurities, scientists can reconstruct past ice sheet behaviour, ice melt rates, and sea level fluctuations, which is critical for assessing coastal regions' vulnerability to future sea level rise.
Overall, ice cores are invaluable archives of Earth's climate history. They offer a detailed and comprehensive record of past climate variability. Studying ice core records is essential for understanding the mechanisms and drivers of climate change and improving our ability to predict future climate trends.
NOTE on timekeeping from the 'Ice Core Library' Curator - Prof. Jørgen Peder Steffensen
As most people are aware, the Gregorian calendar is based on the supposed birth date of Jesus Christ.
The Gregorian calendar is clear: The old notation of "AD" (Anno Domini) and "BC" (Before Christ) has, over time, in favour of religious neutrality, shifted to CE (Common Era) and BCE (Before Common Era), but it covers the same. The only funny thing about this system is that it lacks a year "0", which means that the age difference between 2 CE and 2 BCE is three years.
In history, archaeology and tree-ring chronology, where carbon-14 dating is performed, science uses the term B.P. (Before Present). However, the "present" is 1950 CE, which is very confusing. The Carbon-14 method will only work on samples older than 1950 because nuclear bomb tests in the 50s and 60s produced so much carbon-14 that the dating method breaks down for samples younger than 1950 CE.
When we started ice core dating by counting annual layers, we wanted to make sure that our papers did not use carbon-14-based dating. To avoid confusion between carbon-14 dating in tree rings and ice cores, we came up with the term b2k (before 2000 CE), and we still maintain that notation in our papers to distinguish ice cores from other records.
Photography - Lukasz Larsson Warzecha
Art Director - Ulrika Larsson
Special Thanks - Prof. Jørgen Peder Steffensen
Niels Bohr Institute
Art Director - Ulrika Larsson
Special Thanks - Prof. Jørgen Peder Steffensen
Niels Bohr Institute
Air Bubbles and Greenland’s Warm Past
1023 CE or 977 b2k
Ice Core - GRIP
72°34.74′N 37°33.92′W
Depth - 236.9m
1023 CE or 977 b2k
Ice Core - GRIP
72°34.74′N 37°33.92′W
Depth - 236.9m
The ice cores show warmer temperatures in Greenland around 1000 CE, which may explain the Norse peoples' settlement there at that time. The year 1000 CE was 1 degree warmer than 1970—in Greenland—and 1850 was the coldest decade since the ice age. The Scandinavian Stone Age was 2.5 degrees warmer than it was in 1970.
On arrival in an uninhabited southern Greenland, Erik the Red named the land Greenland because it was green and lush along its fjords in contrast to the northeast of Iceland from which he came. The Norse peoples lived in Greenland for 400 years, after which the Little Ice Age occurred.
Due to ice's high thermal capacity and low thermal conductivity, every meter of ice core still "remembers" the temperature it had while it was at the surface.
Prof Dorthe Dahl-Jensen from the Niels Bohr Institute took advantage of this peculiar physical characteristic of ice and measured temperatures in the GRIP borehole after drilling, meter by meter, through 3 km of ice with a thermometer with a precision of 0.01 degrees. The temperature in 1970 CE was -31.7 C, in 1000 CE -30.6 C, in 1650 CE -32.3 C (when the Swedes took over Skåne, Halland and Blekinge), from 3000 to 6000 BCE -29.2 C (Holocene optimum) and from 21,000 BCE to 30,000 BCE -58 C.
These are all Greenland temperatures. While Greenland was 26 degrees colder 25,000 years ago, Kenya and Tanzania were only about 2.5 degrees colder (lake sediment studies), and this means that the difference in global average between 1970 and 1000 could amount to only a fraction of a degree.
This ca. 15 cm long ice core fragment with visible air bubbles represents one year in ice core records.
On arrival in an uninhabited southern Greenland, Erik the Red named the land Greenland because it was green and lush along its fjords in contrast to the northeast of Iceland from which he came. The Norse peoples lived in Greenland for 400 years, after which the Little Ice Age occurred.
Due to ice's high thermal capacity and low thermal conductivity, every meter of ice core still "remembers" the temperature it had while it was at the surface.
Prof Dorthe Dahl-Jensen from the Niels Bohr Institute took advantage of this peculiar physical characteristic of ice and measured temperatures in the GRIP borehole after drilling, meter by meter, through 3 km of ice with a thermometer with a precision of 0.01 degrees. The temperature in 1970 CE was -31.7 C, in 1000 CE -30.6 C, in 1650 CE -32.3 C (when the Swedes took over Skåne, Halland and Blekinge), from 3000 to 6000 BCE -29.2 C (Holocene optimum) and from 21,000 BCE to 30,000 BCE -58 C.
These are all Greenland temperatures. While Greenland was 26 degrees colder 25,000 years ago, Kenya and Tanzania were only about 2.5 degrees colder (lake sediment studies), and this means that the difference in global average between 1970 and 1000 could amount to only a fraction of a degree.
This ca. 15 cm long ice core fragment with visible air bubbles represents one year in ice core records.
'Summer Melt' Episode
1889 CE or 111 b2k
Ice Core - NGRIP
75°6′N 42°18′W
Depth - 34.65m
1889 CE or 111 b2k
Ice Core - NGRIP
75°6′N 42°18′W
Depth - 34.65m
In recent decades, the melting of the Greenlandic Ice Sheet has increased. In fact, Greenland is losing so much ice that its gravity is getting weaker. However, not all the ice loss is due to surface melting.
Only a handful of surface melt layers are found in ice cores covering all of the Greenland Ice Sheet (found in all cores, North to South and East to West). These layers indicate that the air temperature over the entire ice sheet got so warm that the whole of Greenland was melting at the surface.
Four such melting episodes occurred after the year 2000, but only one was detected in 1889, during the thousand years between 1000 CE and 2000 CE. It is visible here as a clear band in the middle of this ice core piece from the North Greenland Ice Core Project.
In the most recent history, on 11 July 2012, nearly the entire ice sheet's surface melted.
Only a handful of surface melt layers are found in ice cores covering all of the Greenland Ice Sheet (found in all cores, North to South and East to West). These layers indicate that the air temperature over the entire ice sheet got so warm that the whole of Greenland was melting at the surface.
Four such melting episodes occurred after the year 2000, but only one was detected in 1889, during the thousand years between 1000 CE and 2000 CE. It is visible here as a clear band in the middle of this ice core piece from the North Greenland Ice Core Project.
In the most recent history, on 11 July 2012, nearly the entire ice sheet's surface melted.
Vedde Ash Layer
10,171 BCE or 12,171 b2k
Ice Core - EGRIP
75°38′N 35°59′W
Depth - 1264m
10,171 BCE or 12,171 b2k
Ice Core - EGRIP
75°38′N 35°59′W
Depth - 1264m
The Vedde ash layer is 0.5 cm thick and approximately 10 cm from the left of the section. All the other layers visible in this ice core section are so-called 'cloudy bands', which are visible due to the high dust content in springtime snow during the ice age. One can almost count annual layers in this section. The annual layers are between 4 and 2 cm thick.
When an ice core is bored all the way to the bottom of the Greenlandic Ice Sheet, only three visible ash layers, which stem from large volcanic eruptions, are found - Saksurnavatn volcanic eruption ash layer from early Holocene, some 10,000 years ago, the Vedde and the NAAZ II ash layers.
There are about 20 layers of crypto-tephras, which are invisible to the naked eye but contain ash particles. One of these is the Alaskan Okmok eruption of 43 BCE (the Caesar volcano); this eruption has been fingerprinted by tiny ash particles.
The Vedde ash layer is one of the most noticeable and stems from a large, unnamed Icelandic volcano that scattered ash across Greenland, the North Atlantic, and Europe. Vedde ash was first found in sediments near Vedde in Zealand and Denmark, hence the name. The discovery of the ash layer in the ice cores allows the Vedde layer in Zealand and other places to be dated very precisely.
When an ice core is bored all the way to the bottom of the Greenlandic Ice Sheet, only three visible ash layers, which stem from large volcanic eruptions, are found - Saksurnavatn volcanic eruption ash layer from early Holocene, some 10,000 years ago, the Vedde and the NAAZ II ash layers.
There are about 20 layers of crypto-tephras, which are invisible to the naked eye but contain ash particles. One of these is the Alaskan Okmok eruption of 43 BCE (the Caesar volcano); this eruption has been fingerprinted by tiny ash particles.
The Vedde ash layer is one of the most noticeable and stems from a large, unnamed Icelandic volcano that scattered ash across Greenland, the North Atlantic, and Europe. Vedde ash was first found in sediments near Vedde in Zealand and Denmark, hence the name. The discovery of the ash layer in the ice cores allows the Vedde layer in Zealand and other places to be dated very precisely.
The World's First White Christmas
1 CE or 1999 b2k
Ice Core - NGRIP
75°6′N 42°18′W
Depth - 383.35m
1 CE or 1999 b2k
Ice Core - NGRIP
75°6′N 42°18′W
Depth - 383.35m
In countries that celebrate Christmas and lie on latitudes where snow falls in winter, the big question leading up to Christmas is always, “Will it be a White Christmas this year?” The first Christmas snow can in fact be found in the ice core — the snow which fell the year Jesus was born, the year from which the dating of the Christian era begins. In the NGRIP ice core from central Greenland, this Christmas snow can be found approximately 380 metres under the ice cap. The ice cap is like a huge sandwich, in which each year can be seen as a layer in the ice.
The Past Tells Us
About the Future
124,000 BCE or 126,000 b2k
Ice Core - NGRIP
75°6′N 42°18′W
Depth - 3081,65m
About the Future
124,000 BCE or 126,000 b2k
Ice Core - NGRIP
75°6′N 42°18′W
Depth - 3081,65m
The Eemian interglacial, which occurred just before the last glacial period, the Weichselian, culminated with temperatures in Greenland that were 7.5°C warmer than today. The Eemian (named after the Dutch river Eem, where they found sediments from this period first) was indeed about 2 C warmer than the Holocene, but not only that. During the Eemian interglacial, sea levels were 6-9 metres higher than today. Deep sea sediments and the Antarctic ice core from Dome C show that the Eemian was warmer than any interglacial in the last 1,000,000 years, which is the period when humans existed. So, a more than 2 C warming will take the world into a new climate situation in the entire history of human civilisation.
What's particularly interesting about this ice core piece is the size of the ice crystals. The light refracting of the ice crystals shows their enormous size. The single crystals are the size of a tennis ball, and that's because the Eemian ice in Greenland sits so deep in the ice sheet and so close to bedrock that geothermal heat warms up the ice from below. In some locations, such as NGRIP, the heating is enough for the ice sheet to melt from below. The ice in this core has not yet reached basal melting, as melting occurs just 30 m below this core, but the temperature is quite high, -3 C, compared to the -30 C of the ice sheet. These high temperatures cause large crystals to grow, thus removing small crystals. Also, as the Eemian ice is very clean, i.e. with less dust and chemical impurities, there are no anchor points for small crystals to remain, and crystal growth is unhindered.
What's particularly interesting about this ice core piece is the size of the ice crystals. The light refracting of the ice crystals shows their enormous size. The single crystals are the size of a tennis ball, and that's because the Eemian ice in Greenland sits so deep in the ice sheet and so close to bedrock that geothermal heat warms up the ice from below. In some locations, such as NGRIP, the heating is enough for the ice sheet to melt from below. The ice in this core has not yet reached basal melting, as melting occurs just 30 m below this core, but the temperature is quite high, -3 C, compared to the -30 C of the ice sheet. These high temperatures cause large crystals to grow, thus removing small crystals. Also, as the Eemian ice is very clean, i.e. with less dust and chemical impurities, there are no anchor points for small crystals to remain, and crystal growth is unhindered.
French Revolution
1783 CE or 217 b2k
Ice Core - NGRIP
75°6′N 42°18′W
Depth - 60,75m
1783 CE or 217 b2k
Ice Core - NGRIP
75°6′N 42°18′W
Depth - 60,75m
In 1783, the Icelandic volcano Laki erupted. The eruption lasted eight months and killed a fifth of Iceland’s population. The gas cloud from the eruption scattered a noticeable layer of sulphuric acid on the ice sheet, leading to falling temperatures in Europe, which affected harvests in the following years. This layer is not visible to the naked eye, but rather in the Electrical Conductivity Measurements (ECM). The ECM spike appears in the left portion of the ice core presented in this image.
In 1789, women walked to Versailles in France to protest the lack of bread and high food prices. This was one of the events that culminated in the French Revolution.
In 1789, women walked to Versailles in France to protest the lack of bread and high food prices. This was one of the events that culminated in the French Revolution.
The Forested Landscape Under the Ice
500,000 - 1,500,000 BCE
Ice Core - NEEM
77°27′N 51°4′W
Depth - 2535m
500,000 - 1,500,000 BCE
Ice Core - NEEM
77°27′N 51°4′W
Depth - 2535m
Time before 450,000 years ago cannot be read in the ice sheet since the drilling of the ice cores reaches the bedrock, and there is no more ice to measure. Using a stone drill, DNA from a forested southern Greenland has been found under the ice, presumed to be half a million years old. From the found DNA, we can reconstruct the landscape as it looked then, with plants, bushes, and insects, but we do not know precisely how old these finds are.
The latest research project, green2ice, funded by the Horizon Europe ERC Synergy grant, is trying to answer this question.
This unique project brings together researchers specialised in various complementary fields. Dorthe Dahl-Jensen brings her expertise in geophysics and modelling, François Fripiat in biogeochemistry on basal ice and frozen sediments, Pierre-Henri Blard in geochemistry and geochronology, and Anders Svensson in ice core measurements and stratigraphy.
The latest research project, green2ice, funded by the Horizon Europe ERC Synergy grant, is trying to answer this question.
This unique project brings together researchers specialised in various complementary fields. Dorthe Dahl-Jensen brings her expertise in geophysics and modelling, François Fripiat in biogeochemistry on basal ice and frozen sediments, Pierre-Henri Blard in geochemistry and geochronology, and Anders Svensson in ice core measurements and stratigraphy.
Pleistocene - Holocene
9,703 BCE or 11,703 b2k
Ice Core - NGRIP
75°6′N 42°18′W
Depth - 1492,45m
9,703 BCE or 11,703 b2k
Ice Core - NGRIP
75°6′N 42°18′W
Depth - 1492,45m
Ice core dating is an independent method of absolute dating based on counting individual annual layers in large ice sheets.
The official boundary between the Pleistocene and Holocene can be observed well in ice core records. This boundary marks the very beginning of warmer climates.
The boundary is precisely 10 cm to the left of the break in the middle. It is only 1-2 cm thick and marks the last year of the last ice age. It also marks the end of the last minor glacier advance, the Younger Dryas, which lasted a little more than 1000 years.
Following this year, temperatures in Greenland rose by 16 C in 20 years, dust concentrations dropped by a factor of 10 in fewer than 10 years, and the annual snowfall more than doubled in three years.
The official boundary between the Pleistocene and Holocene can be observed well in ice core records. This boundary marks the very beginning of warmer climates.
The boundary is precisely 10 cm to the left of the break in the middle. It is only 1-2 cm thick and marks the last year of the last ice age. It also marks the end of the last minor glacier advance, the Younger Dryas, which lasted a little more than 1000 years.
Following this year, temperatures in Greenland rose by 16 C in 20 years, dust concentrations dropped by a factor of 10 in fewer than 10 years, and the annual snowfall more than doubled in three years.
'Mammoth's Shit' - NAAZ II Ash Layer
53,400 BCE or 55,400 b2k
Ice Core - GRIP
72°34.74′N 37°33.92′W
Depth - 2431m
53,400 BCE or 55,400 b2k
Ice Core - GRIP
72°34.74′N 37°33.92′W
Depth - 2431m
The North Atlantic Ash Zone (NAAZ) II. The volcanic source of the layer is known to be situated in Thórsmörk in southern Iceland. The ash layer is widespread in the North Atlantic region and serves as an important time marker linking ice cores with marine and lake sediment records beyond the range of C-14 dating. According to the Greenland ice-core chronology, the ash layer is 55,400 years old, whereas a recent Ar-Ar dating of the ash layer based on material from Iceland suggests an age of 56,100 years. The difference between the two dating methods is well within dating uncertainty.
In the ice core, the NAAZ II ash layer is one of the most prominent out of a handful of visible ash layers in the 120,000 years covered by the ice cores. The brownish ash layer, which is a few mm thick, appears somewhat reworked in the core with an agglomeration of smaller particles. This may be a result of ice deformation in this deep part of the ice sheet. One has to imagine the entire Greenland ice sheet being covered by ash at the time of the eruption. Not the type of eruption that we would like to experience today. It doesn’t take much imagination, either, to see this layer of ash for what it could be. There is a common joke among the scientific community referring to this particular layer as mammoth shit.
In the ice core, the NAAZ II ash layer is one of the most prominent out of a handful of visible ash layers in the 120,000 years covered by the ice cores. The brownish ash layer, which is a few mm thick, appears somewhat reworked in the core with an agglomeration of smaller particles. This may be a result of ice deformation in this deep part of the ice sheet. One has to imagine the entire Greenland ice sheet being covered by ash at the time of the eruption. Not the type of eruption that we would like to experience today. It doesn’t take much imagination, either, to see this layer of ash for what it could be. There is a common joke among the scientific community referring to this particular layer as mammoth shit.
Prof. Jørgen Peder Steffensen
Niels Bohr Institute
Ice Core Library Curator
Niels Bohr Institute
Ice Core Library Curator