The Radiocarbon Sample Archive of Trondheim

Abstract

Atmospheric CO2 samples have been collected by the Trondheim Radiocarbon Laboratory since the 1960s. The remaining material from the measurements has been precipitated as CaCO3 and stored in glass containers. We investigated some of the stored samples to assess whether the material could still be used for remeasurements of atmospheric radiocarbon (14C) content, or if it has been contaminated during the years of storage. We attempted different methods to clean the carbonate and release the CO2 for new measurements. The results indicate that the older samples before 1970 show a significant change in 14C content compared to the original measurements, and that our cleaning methods have only little effect. Later samples from the 1970s, which were archived in glass containers with a different lid, show a lower contamination that, however, still leads to an added uncertainty of several pMC and makes these samples unreliable.

RADIOCARBON STEP-COMBUSTION OXIDATION METHOD AND FTIR ANALYSIS OF TRONDHEIM CaCO3 PRECIPITATES OF ATMOSPHERIC CO2 SAMPLES: FURTHER INVESTIGATIONS AND INSIGHTS

“…These included (i) a 14 C two-step thermal oxidation to remove adsorbed/ absorbed CO 2 and/or labile organic carbon (OC) from CaCO 3 precipitate powders, and (ii) Fourier-transform infrared spectroscopy (FTIR) analysis of the step-combustion treated and untreated CaCO 3 powders. While our new efforts did not produce Nydal's historical 14 C results, offsets were still similar to those obtained by Seiler et al (2023), we provided new insights on the carbon contaminant of Nydal's CaCO 3 precipitate archive.…”

“…There is a vast array of atmospheric CO 2 samples in CaCO 3 powder stored at NTNU that has not been measured yet (> 1000 samples; see Seiler et al 2023 for details). Even though efforts to reproduce Nydal's historical 14 C results (Nydal and Lövseth 1983) after CaCO 3 powder chemical cleansing were disappointing (Seiler et al 2023), further investigations were performed here to gain insight on possible contamination sources, and maybe secure its removal. Assuming that the contaminant was somewhat sensitive to heat treatments at lower temperatures (e.g., lower than 375ºC, a temperature setting that is high enough to remove labile organic carbon, but sufficiently low to avoid charring, Currie et al [2002] or Szidat et al [2013]), additional analyses were carried out.…”

“…An archive of atmospheric CO 2 (as calcium carbonate-CaCO 3 -precipitates) from Lindesnes site (58°N, 7°E), stored at the National Laboratory for Age Determination (NTNU), formerly Trondheim Radiocarbon Laboratory has been evaluated through radiocarbon ( 14 C) analysis for its reliability (Seiler et al 2023). Carbonate precipitates were sampled as described in Nydal and Lövseth (1983).…”

“…The CaCO 3 powders have been stored since the 1960s in distinct glass vials with closures (Figure 1). The 1980s jars and lids (type B1 and B2) seem to offer better seal (Seiler et al 2023). Still, containers were found in a room without climate controls.…”

“…Still, containers were found in a room without climate controls. A thorough 14 C investigation conducted by Seiler et al (2023), commenced by using different chemical cleansing procedures (e.g., hydrochloric acid-HCl and/or hydrogen peroxide-H 2 O 2 ), indicated the presence of a contaminant. Regardless of multiple chemical attempts for contamination removal and different methods to evolve its carbon content, offsets from expected atmospheric 14 C values were as high as 160‰.…”