Summary findings of the fourth international radiocarbon intercomparison (FIRI)(1998–2001)

Abstract

Interlaboratory comparisons have been widely used in applied radiocarbon science. These are an important part of ongoing quality assurance (QA) programmes, which are vital to the appropriate interpretation of the evidence provided by the 14 C record in Quaternary applications (including climate change and environmental reconstruction). International comparisons of laboratory performance are an essential component of the quality assurance process in radiocarbon dating. If the user community is to have confidence in radiocarbon results, it needs to be assured that laboratories world wide are producing measurements that are reliable and in accordance with 'good practice'. The findings from the most recent (completed in 2001) and extensive (more than 90 participating laboratories) radiocarbon intercomparison (FIRI) are reported here. This study was designed (i) to assess comparability, or otherwise, of the results from different laboratories and (ii) to quantify the extent and possible causes of any interlaboratory variation. The results demonstrate that there are no significant differences amongst the main measurement techniques (gas proportional counting, liquid scintillation counting and accelerator mass spectrometry (AMS)) but there is evidence of small laboratory offsets relative to known age samples for some laboratories. There is also evidence in some cases of underestimation of measurement precision. Approximately 10% of all results were classified as extreme (outliers) and these results were generated by 14% of the laboratories. Overall, the evidence supports the fact that radiocarbon laboratories are generally accurate and precise but that, notwithstanding internal QA procedures, some problems still occur, which can best be detected by participation in independent intercomparisons such as FIRI, where the results allow individual laboratories to assess their performance and to take remedial measures where necessary. The results from FIRI are significant in that they show a broad measure of agreement between measurements made in different laboratories on a wide range of materials and they also demonstrate no statistically significant difference between measurements made by radiometric or AMS techniques.

Relationships between calibrated ages and depth in stratigraphical sequences: an estimation procedure by mixed-effect regression

“…These temporal issues have led to a great interest in the fields of 14C dating (Boaretto et al, 2002), 210Pb dating (Appleby, 2001), varved records (Brauer et al, 2001), and other dating methods. These procedures are expensive and timeconsuming, and frequently materials from sediment cores are poor in quality or quantity for particular procedures.…”

The intercept is a poor estimate of a calibrated radiocarbon age

“…Weighted average of the ranges based on their mode is very sensitive to ranges merging as the standard deviation increases. The errors reported for radiocarbon errors do not always re ect the full uncertainty attached to a date, as shown by the radiocarbon laboratory intercomparisons (Boaretto et al, 2002). This has led to the occasional use of 'error multiplier terms'.…”

Constraining circulation changes through the last deglaciation with deep-sea coral radiocarbon and sedimentary 231Pa/230Th

“…The primary standard was NBS Oxalic Acid I (NIST-SRM-4990, henceforth HOxI; Fm¼1.0397). Secondary standards were IAEA C-2 (fraction modern (Fm) 0.4114, Rozanski et al, 1992), TIRI-I (Fm¼0.2524, Scott, 2003, and FIRI-C (Fm¼0.1041, Boaretto et al, 2002) carbonate materials, and a radiocarbon-dead deep-sea coral (ALV-3884-153-003-011, . The blank correction for all reconnaissance coral samples was based on analyses of nine radiocarbon-dead replicates of ALV-3884-153-003-011 analyzed on CFAMS.…”