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Assessing the saponification effect on the quantification of long chain alkenones and the U37 paleothermometer

Jong-Ku Gal, Jung-Hyun Kim, Daun Kim, Sujin Kang, Kyung-Hoon Shin
Geochemical Journal, Vol. 52, No. 6, P. 497-507, 2018

ABSTRACT

In this study, we evaluated the saponification effect on alkenone quantification and the U37 paleothermometer using two internal standards (2-nonadecanone and squalane) by analyzing in-house reference sediment and eleven surface sediments taken from the Yellow Sea. The C37:3 and C37:2 alkenone concentrations of the in-house reference sediment showed significant differences between before and after the saponification (ΔC37:3 and ΔC37:2) depending on the internal standards used. However, the differences in the U37 and the estimated sea surface temperatures were insignificant. The ΔC37:3 and ΔC37:2 concentrations were larger when calculating based on 2-nonadecanone (46 ± 26 and 136 ± 67 ng/g, respectively) than those based on squalane (–7 ± 4 and –12 ± 10 ng/g, respectively) in the surface sediments. Interestingly, the ΔC37:3 and ΔC37:2 concentrations based on 2-nonadecanone showed a strong correlation with the loss of 2-nonadecanone that occurred during saponification. Accordingly, our study indicated that preferential loss of internal standards (e.g., 2-nonadecanone) can occur during saponification, which affects alkenone quantification and, thus, attention should be paid when choosing an internal standard.

KEYWORDS

alkenones, U37, sea surface temperature, saponification, Yellow Sea

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