FIGURE 14.61 Calculated temperature changes over the past 100,000 years from the European Greenland Ice Core Program (GRIP) (adapted from Jouzel et al., 1997).

amplitude of the temperature record from the Dye 3 site in Greenland 865 km south of the GRfP site and 730 m lower in elevation was 50% larger than that at the GRIP site.)

Some of the indicators of climate change have shown very rapid changes, over decades or less, during particular time periods in the past. For example, Fig. 14.62 shows ice core measurements of (a) electrical conductivity, (b) snow accumulation rate, and (c) concentration of calcium at the start of the Holocene period some 11,600 years ago (Taylor et al., 1997). Electrical conductivity is a measure of the acidity of the ice, since H+ is the major charge carrier; the direct current is measured between two electrodes that have a voltage difference of several thousand volts. As seen in Fig. 14.62a, such measurements provide excellent spatial and hence time resolution. The transition from the Wisconsin to the Holocene period is seen to be characterized by an increase in electrical conductivity of the ice core and a decrease in calcium. The two are inversely related since high concentrations of CaC03 neutralize strong acids, decreasing the conductivity. The rate of accumulation of snow (Fig. 14.62b) also increases. These changes occurred in less than about two decades. Taylor and co-workers also point out that the data in Fig. 14.62 suggest there is a "flicker" just prior to the rapid transition to the alternate climate state.

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