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Earth and Space Sciences · Glossary

What is Age model; annual layer counting?

Also known as: age model · annual layer counting

Definition 24.9 University Earth and Space Sciences — Year 2 · Chapter 24 — Climate Archives and Proxies

An age model is the function that assigns an age, with its uncertainty, to every depth of an archive. Annual layer counting builds an age model by counting, from the top down, the layers that each record one year (ice layers, varves, bands), each layer whose annual nature is doubtful being counted as half a year plus or minus half a year.

The GICC05 chronology at 18 climate events from the start of the Holocene to 59.44\, ka: (a) depth in the NorthGRIP core against age; the curve flattens as the annual layers thin with depth, each thousand years taking up fewer metres of ice; (b) the maximum counting error, and the error the same number of uncertain layers would give if their errors were independent (); logarithmic scale. Data: Svensson et al. (2008), Table 1.
The GICC05 chronology at 18 climate events from the start of the Holocene to 59.44 ka59.44\,\mathrm{ka}: (a) depth in the NorthGRIP core against age; the curve flattens as the annual layers thin with depth, each thousand years taking up fewer metres of ice; (b) the maximum counting error, and the error the same number of uncertain layers would give if their errors were independent (Proposition 24.11); logarithmic scale. Data: Svensson et al. (2008), Table 1.
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