Ice core - Wikipedia
Formal definition and dating of the GSSP (Global Stratotype Section and . The Greenland ice core from NorthGRIP (NGRIP) contains a proxy. Results for ice cores: DEFINITION: Borings taken from the Arctic and Antarctic polar ice caps, and paleoclimatology and as a method of absolute dating. Define ice cap. ice cap synonyms, ice cap pronunciation, ice cap translation, English dictionary definition of ice cap. or ice cap n. An extensive dome-shaped or.
Some drills have been designed to retrieve a second annular core outside the central core, and in these drills the space between the two cores can be used for circulation. Cable-suspended drills have proved to be the most reliable design for deep ice drilling. Some have been designed for working in cold ice; they have high power consumption and the heat they produce can degrade the quality of the retrieved ice core.
Early thermal drills, designed for use without drilling fluid, were limited in depth as a result; later versions were modified to work in fluid-filled holes but this slowed down trip times, and these drills retained the problems of the earlier models.
In addition, thermal drills are typically bulky and can be impractical to use in areas where there are logistical difficulties. More recent modifications include the use of antifreezewhich eliminates the need for heating the drill assembly and hence reduces the power needs of the drill. The drawbacks are that it is difficult to accurately control the dimensions of the borehole, the core cannot easily be kept sterile, and the heat may cause thermal shock to the core. EM drills are also more likely to fracture ice cores where the ice is under high stress.
The casing has to reach down to the impermeable ice layers. To install casing a shallow auger can be used to create a pilot hole, which is then reamed expanded until it is wide enough to accept the casing; a large diameter auger can also be used, avoiding the need for reaming. An alternative to casing is to use water in the borehole to saturate the porous snow and firn; the water eventually turns to ice.
To address this, work has been done on technology to drill replicate cores: Replicate cores were successfully retrieved at WAIS divide in the — drilling season, at four different depths. The largest projects require years of planning and years to execute, and are usually run as international consortiums. The EastGRIP project, for example, which as of is drilling in eastern Greenland, is run by the Centre for Ice and Climatein Denmark and includes representatives from 12 countries on its steering committee.
A spring-loaded lever arm called a core dog can break off the core and hold it in place while it is brought to the surface. The core is then extracted from the drill barrel, usually by laying it out flat so that the core can slide out onto a prepared surface. The surface that receives the core should be aligned as accurately as possible with the drill barrel to minimise mechanical stress on the core, which can easily break.
The ambient temperature is kept well below freezing to avoid thermal shock. It is usually cut into shorter sections, the standard length in the US being one metre.
The cores are then stored on site, usually in a space below snow level to simplify temperature maintenance, though additional refrigeration can be used.
If more drilling fluid must be removed, air may be blown over the cores. Any samples needed for preliminary analysis are taken.
The core is then bagged, often in polytheneand stored for shipment. Additional packing, including padding material, is added.
When the cores are flown from the drilling site, the aircraft's flight deck is unheated to help maintain a low temperature; when they are transported by ship they must be kept in a refrigeration unit.
These locations make samples available for testing. A substantial fraction of each core is archived for future analyses. Over a depth range known as the brittle ice zone, bubbles of air are trapped in the ice under great pressure. When the core is brought to the surface, the bubbles can exert a stress that exceeds the tensile strength of the ice, resulting in cracks and spall. Some steps can be taken to alleviate the problem.
Liners can be placed inside the drill barrel to enclose the core before it is brought to the surface, but this makes it difficult to clean off the drilling fluid. In mineral drilling, special machinery can bring core samples to the surface at bottom-hole pressure, but this is too expensive for the inaccessible locations of most drilling sites.
Keeping the processing facilities at very low temperatures limits thermal shocks. Extruding the core from the drill barrel into a net helps keep it together if it shatters.Climate change: understanding the facts (Vostok ice core)
Brittle cores are also often allowed to rest in storage at the drill site for some time, up to a full year between drilling seasons, to let the ice gradually relax. For the results of these tests to be useful in the reconstruction of palaeoenvironmentsthere has to be a way to determine the relationship between depth and age of the ice. The simplest approach is to count layers of ice that correspond to the original annual layers of snow, but this is not always possible.
An alternative is to model the ice accumulation and flow to predict how long it takes a given snowfall to reach a particular depth. Another method is to correlate radionuclides or trace atmospheric gases with other timescales such as periodicities in the earth's orbital parameters.
As a result, there are two chronologies for a given ice core: To determine the relationship between the two, models have been developed for the depth at which gases are trapped for a given location, but their predictions have not always proved reliable. The size of a crystal is related to its growth rate, which in turn depends on the temperature, so the properties of the bubbles can be combined with information on accumulation rates and firn density to calculate the temperature when the firn formed.
The CO 2 can be isolated by subliming the ice in a vacuum, keeping the temperature low enough to avoid the loess giving up any carbon.
The results have to be corrected for the presence of 14 C produced directly in the ice by cosmic rays, and the amount of correction depends strongly on the location of the ice core. Corrections for 14 C produced by nuclear testing have much less impact on the results.
The very small quantities typically found require at least g of ice to be used, limiting the ability of the technique to precisely assign an age to core depths. It is more difficult to connect the timescales in different hemispheres.
Meaning of "stadial" in the English dictionary
Oceanic Cores In this method one compares certain inclusions in dated ocean cores with related inclusions found in the ice-core of a still undetermined age. Examples of such inclusions are a decrease or increase in temperature over a period of years that can be determined from flora and fauna found in the oceanic core and a decrease increase in the 18O enrichment over this same period of years.
Another example is volcanic ash. Hyde has posted separately some of the relationships between ocean core data and their astronomical causes. These are the primary "inclusions" that are compared.
ice core in a sentence - how to use "ice core" in a sentence - ichacha sentence maker
I apologize for my use of nondescript terminology here. The major disadvantages of this method are that one must compare different signatures of climatic change that correspond to the same event and that one is not certain of the lag times if any between oceanic reactions and glacial reactions to the same climatic changes.
Volcanic Eruptions After the eruption of volcanoes, the volcanic ash and chemicals are washed out of the atmosphere by precipitation. These eruptions leave a distinct marker within the snow which washed the atmosphere. We can then use recorded volcanic eruptions to calibrate the age of the ice-core. Since volcanic ash is a common atmospheric constituent after an eruption, this is a nice signature to use in comparing calibrated time data and an ice-core of undetermined age.
Another signature of volcanism is acidity. The major diasadvantage of this method is that one must previously know the date of the eruption which is usually not the case. Furthermore the alkaline precipitants of the ice ages limits this measure to approximately BC. Ph Balances One unique marker of periods of glaciation is that precipitation during the ice ages are markedly alkaline. This is due to the fact that the ice ages tied up a large quantity of the available water thus exposing a larger portion of the continental shelves.
From these shelves huge clouds of alkaline dusts primarily CaCO3 were blown across the landscape. The major disadvantage of this method is that it gives only very approximate age ranges i. Furthermore, the lag time between the onset of glaciation and increased alkalinity are uncertain. Paleoclimatic Comparisons In this method, one compares long range climatic changes e. Radioactive Dating of Gaseous Inclusions In this method one melts a quantity of glacial material from a given depth, collects the gases that were trapped inside and use standard 14C and 36Cl dating.
The major disadvantage of this method is that a huge amount of ice must be melted to gather the requisite quantity of gases. Ice Flow Calculations In this method, one measures the length of the ice core and calculates how many years it must have taken for a glacier of that thickness to form.
This is the most inaccurate of the methods used for dating ice-cores. First one must calculate how the thickness of the annual layer changes with depth. After this one must make some assumptions of the original thickness of the annual layer to be dated i. The Vostok Ice-Core To demonstrate the methods used in dating ice-cores I will use the Vostok ice-core as an example because I found plenty of literature on it and because it is an Antarctic ice-core which was what the original post was about.
The Vostok Ice-Core is 2, meters long and was collected in two portions: The total depth of the ice sheet from which the core was collected is approximately 3, meters. Experimental Methodology The ice core was sliced into 1. A discontinuous series sampled every 25 meters and a continuous series from 1, to 2, meters were then sent in solid form to Grenoble, France for further analysis.
At Grenoble the ice was put into clean stainless steel containers. The samples were crushed and then melted with the gases given off collected and saved for further analysis. The melt water was tested for chemical composition and then electrolysised. The results determined from these various samples were consistent between the continuous and discontinuous slices within the sections that overlapped.
They were also consistent with Greenland ice-cores, other Antarctic ice-cores, dated volcanic records, deep sea cores, and paleoclimatic evidence. Results While unable to provide specific dates within a milleniathe analysis show definate evidence of the the last two ice ages.
It should be noted that all of the methods listed above were consistent with the above results. Conclusions In this section I will provide a brief review of how the ice-core data effects both the age of the earth question and the Velikovskian catastrophism.
This original post was written at a time when both Bob Bales and Ted Holden were frequent posters to talk. Bob Bales has argued that the age of the Earth is about 50, years, and you are probably aware that Ted Holden is a proponent of the Velikovskian Catastrophism. Thus, these conclusions are reader specific. To maintain an age for the earth of 50, years, one would need to describe a mechanism that allows more than 2 false ice layers to form per year.
Search Results | Archaeology Wordsmith
It should be noted that one also needs to describe why this mechanism has ceased to function in historic times since the Vostok ice-core demonstrates a number of the historically recorded volcanism at the correct periods of time.
Velikovsky and the Noachian deluge. Such a mass of water would have provided sufficient buoyancy to float the polar caps off their beds. No way to drop them exactly back onto their original location, or to regrow them. In fact, the Greenland ice cap would not regrow under modern last 10 ky climatic conditions.
By this I mean no petroleum, no vermin, no weird Venus gasses, no red snow, no manna in amongst the layers.