How smooth should curves be for calibrating radiocarbon ages?

Abstract

We show that smoothed versions of the high-resolution calibration curves should be used when 14C ages are calibrated with large (>~30 14C yr) measurement errors (represented by standard deviation σm) or are mixtures of elements of variable age (natural sample error with standard deviation σn). The degree of smoothing should agree with the standard deviation of total sample error, σt, the square root of the quadratic sum of σm and σn. However, in most cases, σt is not well known, especially due to difficulties in quantifying σn. We present an inverse method that gives a measure of mean σt for different materials that are widely used in (conventional) 14C dating. Calculations with large (>100) data sets of wood, charcoal, ombrotrophic peat and minerotrophic peat/gyttja samples indicate that σt of such materials is generally much larger than previously assumed, mainly because of large values of σn. This means that particularly in organic deposits, strongly smoothed calibration curves should be used where medium-term 14C variations (wiggles) are completely straightened. -from Authors