Age a BP

Figure 1.7. Speleothem data: oxygen isotope record from stalagmite Q5 from southern Oman over the past 10,300 years. Along the growth axis of the nearly 1 m long stalagmite, every ~ 0.7 mm about 5 mg material (CaCO3) was drilled, yielding n = 1345 samples. The carbonate powder was analysed with an automatic preparation system linked to a mass spectrometer to determine the ¿18O values. (The (18O/16O) ratio is given relative to the Vienna Pee Dee Belemnite (VPDB) standard analogously to the description in Fig. 1.3.) The timescale (years before 1950) is based on 18 U/Th mass-spectrometric ages, obtained on separated and purified material. Dates for samples between absolutely dated positions were obtained by linear interpolation. Time runs from right to left. The ¿18O scale is inverted "in paleoclimatic manner" so that the transition from the last glacial to the present Holocene interglacial at around 10 ka is "upwards." Note that growth of stalagmite Q5 ceased at ~ 2740 a b.p. Climatological questions associated with the data are whether the transition to the Holocene occurred synchronously with climatic transitions in other locations and whether there exist solar influences on the variations in monsoon rainfall (indicated by ¿18O variations, low ¿18O reflecting strong monsoon). (Data from Fleitmann et al. 2003.)

1.4 Spacing

Archives other than documentary collections or climate models require measurements on the archive material. Material-size requirements lead in many cases to a constant length interval, L(i), from which material for one measurement is taken, and also the length spacing, l(i), between the measurement mid-points on the length axis is often constant (Fig. 1.13). Dating transfers from length into the time domain with the "sample duration," D(i), and the temporal spacing, d(i) = t(i) — t(i — 1), here in this book briefly denoted as "spacing." The spacing is frequently noncon-stant: archives normally accumulate not at a constant rate. They might also be subject to postdepositional length distortions such as compressing in the case of ice cores. Archives that allow pre-sampling (visual)

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