Chemical climate proxies
How far into the past can ice-core records go? Scientists have now identified regions in Antarctica they say could store information about Earth’s climate and greenhouse gases extending as far back as 1. By studying the past climate, scientists can understand better how temperature responds to changes in greenhouse-gas concentrations in the atmosphere. This, in turn, allows them to make better predictions about how climate will change in the future.
Now, an international team of scientists wants to know what happened before that. At the root of their quest is a climate transition that marine-sediment studies reveal happened some 1.
A difficulty in ice core dating is that gases can diffuse through firn, so the location, but their predictions have not always proved reliable.
Results of the discovery are being published this week in the Proceedings of the National Academy of Sciences. The work was funded by the National Science Foundation and the U. Krypton dating is much like the more-heralded carbon- 14 dating technique that measures the decay of a radioactive isotope — which has constant and well-known decay rates — and compares it to a stable isotope.
Unlike carbon- 14 , however, krypton is a noble gas that does not interact chemically and is much more stable with a half-life of around , years. Krypton is produced by cosmic rays bombarding the Earth and then stored in air bubbles trapped within Antarctic ice. It has a radioactive isotope krypton- 81 that decays very slowly, and a stable isotope krypton- 83 that does not decay. Comparing the proportion of stable-to-radioactive isotopes provides the age of the ice.
In their experiment at Taylor Glacier in Antarctica, the researchers put several -kilogram about pounds chunks of ice into a container and melted it to release the air from the bubbles, which was then stored in flasks. The krypton was isolated from the air at the University of Bern, Switzerland, and sent to Argonne for krypton- 81 counting. The researchers determined from the isotope ratio that the Taylor Glacier samples were , years old, and validated the estimate by comparing the results to well-dated ice core measurements of atmospheric methane and oxygen from that same period.
Now the challenge is to locate some of the oldest ice in Antarctica, which may not be as easy as it sounds. There also are special regions where old ice is exposed at the edges of an ice field, Brook pointed out.
Record-shattering 2.7-million-year-old ice core reveals start of the ice ages
The dating of ice sheets has proved to be a key element in providing dates for palaeoclimatic records. Cores show visible layers, which correspond to annual snowfall at the core site. If a pair of pits is dug in fresh snow with a thin wall between them and one of the pits is roofed over, an observer in the roofed pit will see the layers revealed by sunlight shining through. A six-foot pit may show anything from less than a year of snow to several years of snow, depending on the location.
Poles left in the snow from year to year show the amount of accumulated snow each year, and this can be used to verify that the visible layer in a snow pit corresponds to a single year’s snowfall. In central Greenland a typical year might produce two or three feet of winter snow, plus a few inches of summer snow.
For situations in which multiple measurements across suites of cores are possible, zero-error dating is achievable, just as for tree rings. However, this is expensive.
Author contributions: C. Ice outcrops provide accessible archives of old ice but are difficult to date reliably. Here we demonstrate 81 Kr radiometric dating of ice, allowing accurate dating of up to 1. The technique successfully identifies valuable ice from the previous interglacial period at Taylor Glacier, Antarctica. Our method will enhance the scientific value of outcropping sites as archives of old ice needed for paleoclimatic reconstructions and can aid efforts to extend the ice core record further back in time.
We present successful 81 Kr-Kr radiometric dating of ancient polar ice. Our experimental methods and sampling strategy are validated by i 85 Kr and 39 Ar analyses that show the samples to be free of modern air contamination and ii air content measurements that show the ice did not experience gas loss. We estimate the error in the 81 Kr ages due to past geomagnetic variability to be below 3 ka. We show that ice from the previous interglacial period Marine Isotope Stage 5e, — ka before present can be found in abundance near the surface of Taylor Glacier.
Our study paves the way for reliable radiometric dating of ancient ice in blue ice areas and margin sites where large samples are available, greatly enhancing their scientific value as archives of old ice and meteorites. At present, ATTA 81 Kr analysis requires a 40—kg ice sample; as sample requirements continue to decrease, 81 Kr dating of ice cores is a future possibility. Ice cores from the Greenland and Antarctic ice sheets provide highly resolved, well-dated climate records of past polar temperatures, atmospheric composition, and aerosol loading up to ka before present 1 — 3.
Two million-year-old ice cores provide first direct observations of an ancient climate
How are ice cores dated? How, there is some accuracy in linking Taylor Glacier samples to ice accuracy records due to analytical uncertainties and the possible nonuniqueness of the vostok. Second, the ice vostok chronologies themselves are subject to uncertainties. For the last 60 ka, an annual layer-counted age scale is available for Greenland, to which Antarctic records can be tied using globally how-mixed CH 4 ; beyond this age, ice radiocarbon modeling is how used to reconstruct the chronology 39 – The uncertainty in the ice core temperature can be evaluated by comparing them to independently dated speleothem records showing concomitant events 41 – Third, the Kr samples tell a spread in ages due to their finite temperature.
We estimate this last effect is only important for the oldest sample where the layers tell how strongly compressed.
NEWSLETTER OF THE NATIONAL ICE CORE LABORATORY — SCIENCE MANAGEMENT OFFICE. Upcoming accurate dating of the ice cores.” “Using a.
To support our nonprofit science journalism, please make a tax-deductible gift today. Scientists endured bitter winds to retrieve ancient ice from a blue ice field in the Allan Hills of Antarctica. Scientists announced today that a core drilled in Antarctica has yielded 2. Some models of ancient climate predict that such relatively low levels would be needed to tip Earth into a series of ice ages. But some proxies gleaned from the fossils of animals that lived in shallow oceans had indicated higher CO 2 levels.
Although blue ice areas offer only a fragmentary view of the past, they may turn into prime hunting grounds for ancient ice, says Ed Brook, a geochemist on the discovery team at Oregon State University in Corvallis. Ice cores from Greenland and Antarctica are mainstays of modern climate science. Traditionally, scientists drill in places where ice layers accumulate year after year, undisturbed by glacial flows.
The long layer cake records from deep sites in the center of Antarctica reveal how greenhouse gases have surged and ebbed across hundreds of thousands of years. The Princeton-led team went after ancient ice sitting far closer to the surface, in the Allan Hills, a wind-swept region of East Antarctica kilometers from McMurdo Station that is famous for preserving ancient meteorites. Deep, old layers are driven up, while wind strips away snow and younger ice, revealing the lustrous blue of compressed ice below.
Ice core dating using stable isotope data
Thin cores of ice, thousands of meters deep, have been drilled in the ice sheets of Greenland and Antarctica. They are preserved in special cold-storage rooms for study. Glacier ice is formed as each year’s snow is compacted under the weight of the snows of later years. Light bands correspond to the relatively fresh, clean snows that fall in the summer when warmer conditions bring more moisture and precipitation.
Dark bands mark the polar winter season, when little new snow falls on these frigid deserts and blowing snow is mixed with dust, discoloring the white snow. The layers are only millimeters to centimeters thick.
Scientists say they have developed a means of accurately dating Earth’s oldest and densest polar ice.
Ice consists of water molecules made of atoms that come in versions with slightly different mass, so-called isotopes. Variations in the abundance of the heavy isotopes relative to the most common isotopes can be measured and are found to reflect the temperature variations through the year. The graph below shows how the isotopes correlate with the local temperature over a few years in the early s at the GRIP drill site:.
The dashed lines indicate the winter layers and define the annual layers. How far back in time the annual layers can be identified depends on the thickness of the layers, which again depends on the amount of annual snowfall, the accumulation, and how deep the layers have moved into the ice sheet. As the ice layers get older, the isotopes slowly move around and gradually weaken the annual signal.
Read more about – diffusion of stable isotopes – how the DYE-3 ice core has been dated using stable isotope data – how stable isotope measurements are performed – stable isotopes as indicators of past temperatures – how annual layers are identified using impurity data. Move the mouse over individual words to see a short explanation of the word or click on the word to go to the relevant page. For more information on the topic please contact Bo Vinther.
Centre for Ice and Climate. Ice Core Drilling Projects. More information.
Using krypton gas to date the age of ancient ice cores
View the discussion thread. At the bottom of my page How does CO2 respond to temperature? One note of caution. You mix between Antarctic temperature and the global temperature. They are not the same. Antarctic temperature variations are much larger than the global ones.
record to the metronome, a chronostratigraphy of the Vostok ice core is derived with an accuracy of _+ kyr. The developed timescale.
Determining the age of the ice in an ice core can be done in a number of ways. Counting layers, chemical analysis and mathematical models are all used. Annual layers of snowfall recorded in an ice core can be counted — in much the same way that tree-rings can be counted — to determine the age of the ice. This method can present challenges. Many cores come from regions where the yearly snowfall accumulation is too small for the annual layers to be distinguished.
Even in cores where the yearly snowfall produces thick layers, the nature of glacier flow stretches and thins layers as they get buried deeper. This flow-thinning means that annual layer counting eventually becomes impossible in all deep cores. Layers in ice cores can become apparent when the core is analysed for a chemical signal that varies with the seasons.
The clearest dating is obtained when several seasonal signals are examined and compared. Where layer-counting is not possible, dating generally relies upon mathematical models of ice flow. Another useful technique is to identify events that are verified by other types of climate records, such as historical, tree ring and sedimentary records.
These all have independent methods of dating, and so the timing of a major climate shift or volcanic eruption can be used to synchronise the age scales.
Ice core dating accuracy
It is not uncommon to read that ice cores from the polar regions contain records of climatic change from the distant past. Research teams from the United States, the Soviet Union, Denmark, and France have bored holes over a mile deep into the ice near the poles and removed samples for analysis in their laboratories. Based on flow models, the variation of oxygen isotopes, the concentration of carbon dioxide in trapped air bubbles, the presence of oxygen isotopes, acid concentrations, and particulates, they believe the lowest layers of the ice sheets were laid down over , years ago.
The accurate and precise dating of polar ice cores is important for various studies, including investigations of past climate change and the recent history of the.
Based on an early Greenland ice core record produced back in , versions of the graph have, variously, mislabeled the x-axis, excluded the modern observational temperature record and conflated a single location in Greenland with the whole world. More recently, researchers have drilled numerous additional ice cores throughout Greenland and produced an updated estimate past Greenland temperatures. This modern temperature reconstruction, combined with observational records over the past century, shows that current temperatures in Greenland are warmer than any period in the past 2, years.
However, warming is expected to continue in the future as human actions continue to emit greenhouse gases, primarily from the combustion of fossil fuels. Climate models project that if emissions continue, by , Greenland temperatures will exceed anything seen since the last interglacial period , around , years ago. Widespread thermometer measurements of temperatures only extend back to the mids.
How do scientists use ice cores to determine past climates?
An ice core is a cylinder shaped sample of ice drilled from a glacier. Ice core records provide the most direct and detailed way to investigate past climate and atmospheric conditions. Snowfall that collects on glaciers each year captures atmospheric concentrations of dust, sea-salts, ash, gas bubbles and human pollutants. Analysis of the.
Ice core driller Tanner Kuhl works with the blue ice drill on Taylor Glacier in Antarctica. Argonne scientists used a newly developed technique.
Ice-core records show that climate changes in the past have been large, rapid, and synchronous over broad areas extending into low latitudes, with less variability over historical times. These ice-core records come from high mountain glaciers and the polar regions, including small ice caps and the large ice sheets of Greenland and Antarctica. As the world slid into and out of the last ice age, the general cooling and warming trends were punctuated by abrupt changes.
Climate shifts up to half as large as the entire difference between ice age and modern conditions occurred over hemispheric or broader regions in mere years to decades. Such abrupt changes have been absent during the few key millennia when agriculture and industry have arisen. The speed, size, and extent of these abrupt changes required a reappraisal of climate stability.
Records of these changes are especially clear in high-resolution ice cores.
Scientists successfully use krypton to accurately date ancient Antarctic ice
Princeton University-led researchers have extracted 2 million-year-old ice cores from Antarctica that provide the first direct observations of Earth’s climate at a time when the furred early ancestors of modern humans still roamed. Gas bubbles trapped in the cores — which are the oldest yet recovered — contain pristine samples of carbon dioxide, methane and other gases that serve as “snapshots” of prehistoric atmospheric conditions and temperatures, the researchers recently reported in the journal Nature.
The cores were collected in the remote Allan Hills of Antarctica. First author Yuzhen Yan, who received his Ph. The cores he and his co-authors retrieved are like scenes collected from a very long movie that do not show the whole film, but convey the overall plot.
Inverse dating methods applied for several cen- tral east Antarctic deep ice cores have confirmed the valid- ity of the isotope-based reconstructions within 20 to 30.
I was wondering how ice cores are dated accurately. I know Carbon 14 is one method, but some ice cores go back hundreds of thousands of years. Would other isotopes with longer half-lives be more accurate? Also, how much does it cost to date the core? How are samples acquired without destroying the ice? I imagine keeping the ice intact as much as possible would be extremely valuable. Some of the answers to these questions are available on the Ice Core Basics page.
Ice cores can be dated using counting of annual layers in their uppermost layers. Dating the ice becomes harder with depth. Usually multiple methods are used to improve accuracy. Common global stratigraphic markers are palaeo-events that occur worldwide synchronously, and can allow wiggle-matching between ice cores and other palaeo archives e.
For the ice matrix, these global stratigraphic markers can include spikes in volcanic ash each volcanic eruption has a unique chemical signature , or volcanic sulfate spikes.