Gas Chromatographic Tuning of the U^k′₃₇ Paleothermometer

The extensive use of the C₃₇ di- and triunsaturated alkenones for the estimation of sea surface temperatures in ancient oceans prompts an investigation of the analytical constraints on reliable gas chromatographic measurements. Several tests reproducing the alkenone amounts currently encountered in high-resolution stratigraphy studies show that no significant errors are specifically related to differences between on-column, splitless, and septum-programmable injection. However, irreversible adsorption on the chromatographic column is one major source of error that has significant effects (temperature deviations higher than 0.5°C) when the total amounts of alkenones introduced into the system are lower than 5-10 ng. These deviations are more important for lower relative proportions of the triunsaturated species (higher temperature). The observed adsorption evidences that, in the practical operating conditions for analysis of large data sets (average of three replicate injections for 1 g of sample), a concentration of 50 ng/g is the lowest limit for reliable paleotemperature estimation.