Ice cores dating

In summary, a number of chemical constituents in polar snow and ice have seasonal concentration variations that make them suitable for dating ice cores by counting annual layers. In... 

Figure 9.2. Generalized trend of the concentration of methane in air extracted from dated ice cores. (After Cicerone and Oremland, 1988.)...

Dansgaard W. and Hammer C.U., Geophysical timescales from absolutely-dated ice cores from Greenland. Fys. Tidsskr. (Denmark), 76, 138-140 (1978). 

This technique of dating ice cores by counting annual layers, identified either visually or isotopically (or both), has been widely used to develop climate histories for the ice sheets in East and West Antarctica. However, the method is limited to about 1,000 years by the progressive thinning of annual layers with depth in the ice sheet. 

Hammer, C. U., Clausen, H. B., Dansgaard, W. et al. (1987). Dating of Greenland ice cores by flow models, isotopes, volcanic debris, and continental dust. /. Glacial. 20,3-26. 

Salamatin, A. N., Lipenkov, V. Y., Barkov, N. I. et al. (1998). Ice core age dating and paleothermometer calibration based on isotope and temperature profiles from deep boreholes at Vostok Station (East Antarctica). /. Geophys. Res. 103(D8), 8963-8977. 

Our experience to-date suggests that current measurement and analysis techniques allow the reliable detection of variations in the atmospheric C02 content of 30 percent or more. Our first measurements have been made on samples covering the last 30,000 years, a period of major climatic change which might possibly have led to a change in the atmospheric C02 content. Ice cores... 

The application of glaciochemical horizons to ice core dating is a recent and rapidly evolving development. A concerted search is under way to determine the impact of known events on the chemical composition of polar snow. So far, two types of universally applicable horizons have been detected in polar ice cores volcanic eruptions and Late Wisconsin dust. 

Other events, evidence of which has not yet been detected in polar ice, may also eventually serve as useful time markers in the future. Large meteors or meteor swarms that ablated in the upper atmosphere may have left a significant chemical impact on succeeding snowfalls. The same may be true for cometary collisions or brushes with a comet s tail. As with ancient volcanic eruptions, such events need not have been historically documented. If identified and accurately dated in one ice core, these events will serve as useful time horizons in other cores. 

The climate has the ability to shift into radically different states according to ice cores extracted from Greenland s massive ice sheet in the early 1990s. These rods of ice are up to three kilometers long and provide a set of climate records for the past 110,000 years. They allow the investigation of annual layers in the ice cores which are dated using a variety of methods. The composition of the ice provides the temperature at which it formed. 

The aerosol and gaseous lead that has settled onto polar ice eventually becomes buried. Thus, ice cores provide an excellent chronological record of lead inputs as shown in Figure 28.25. Humans began smelting lead ores dates back to at least 5000 BC and can be detected in the ice core record. Lead production increased significantly at the start... 

Fig. 4 Depth-age relationship of the ice cores from Fiescherhom glacier [12] and Colle Gnifetti [13, 14], Besides annual layer counting and radiocarbon ( C) dating, two types of time markers were used Saharan dust events (labeled by the year only) and volcanic eruptions (labeled by year and name of volcano). Depth is given in water equivalent. This is the amount of water contained in the ice core which is calculated using fim and ice density, respectively, both increasing with depth...

Geologist Claude F. Boutron and colleagues discovers high amounts of lead in Greenland ice cores dating from Roman times, confirming widespread production and use of lead in this period. 

One approach to elucidating the contribution of natural variability to recent temperature trends is to examine markers for temperature over much longer time scales, prior to the industrial revolution. A major source of such data is ice cores (see also Section B.2a). These ice cores provide a record of climate and atmospheric composition for at least 110,000 years, for which there is agreement among various studies. Data are available for 250,000 years before the present (bp), but there is some uncertainty in the dating of the layers corresponding to these older ice core depths (Chappel-laz et al., 1997). 

Salamatin, A. N., V. Y. Lipenkov, N. I. Barkov, J. Jouzel, J. R. Petit, and D. Raynaud, Ice Core Age Dating and Paleothermometer Calibration Based on Isotope and Temperature Profiles from... 

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