10Be - 26Al exposure age calculator

For calculating an exposure age when erosion rate is known independently.

Multiple sample form -- Kaplan et al. (2011) Patagonia calibration data set

Uses version 2.2 code. October, 2013.

Written by Greg Balco, balcs@u.washington.edu

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Be-10 calibration data from:

Kaplan, M. and nine others, 2011. In-situ cosmogenic Be-10 production rate at Lago Argentino, Patagonia: implications for late-glacial climate chronology. Earth and Planetary Science Letters, v. 309, pp. 21-32.

Calibration data: Excel spreadsheet

Independent (radiocarbon) age constraints on these sites are minimum and maximum ages (minimum ages only for one site; min and max ages for a second site), rather than exact ages for moraine emplacement. In the source paper, the authors used this information to derive minimum and maximum estimates for the reference Be-10 production rate. Here, single best-fitting values for the reference production rate are estimated using a fitting algorithm that incorporates all the one-sided age constraints. Thus, chi-squared fit values are not meaningful and not reported below. MATLAB code to do this calculation is linked from the higher level page.

Small differences (< 1%) between the reference Be-10 production rates inferred from the calibration data in the table below and those reported in Table 3b in the source paper are due to differences in the code used to do the calculation and, to a lesser extent, rounding errors. To ensure consistency between production rate calibration and exposure-age calculations, the values in the table below are calculated using the same code that is used to compute the exposure ages in the online calculator.

The source paper computed uncertainties for their minimum and maximum limits on reference production rates based on the scatter of the individual measurements at each site (ca. 2-3% uncertainties). These are not applicable to the single best-fitting value for the reference production rate used here. This uses a new estimate of the production rate uncertainty derived from the variation in the value of the fitting parameter with the value of the reference production rate by assuming that the probability distribution of the fitting parameter obeys the chi-square distribution. This isn't exactly appropriate because of the one-sided nature of the constraints. However, this indicates 3-4% uncertainties, which are probably a decent estimate. Note that these samples are all from a fairly small region, so the production rate uncertainty quoted here includes minimal scaling uncertainty. Thus, it probably underestimates the true external uncertainty involved when applying these calibration data at other sites.

Kaplan et al. did not measure Al-26 concentrations. Thus, reference production rates for Al-26 in the table below are calculated from those for Be-10 using (P26 / P10) = 6.75.

Scaling scheme Reference Be-10 Percentage Reduced Reference Al-26
for spallation production rate (atoms/g/yr) uncertainty chi-squared production rate (atoms/g/yr)


Sample data entry:

Enter data block here.

Note change in Version 2.2:

Production rates and decay constants have been updated in this version to reflect the Be-10 restandardization and half-life revision in Nishiizumi et al., 2007. Thus, you must now specify the standard to which your Be-10 and Al-26 measurements have been normalized. This means that two input fields, the Be-10 and Al-26 standard names, have been added. You'll need to add two columns to your spreadsheets before cutting and pasting data. Refer to the new example spreadsheet here. For a list of currently available standards, see this page.

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