Assessing the saponification effect on the quantification of long chain alkenones and the U37K’ paleothermometer

In this study, we evaluated the saponification effect on alkenone quantification and the U-37(K') 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 C-37:3 and C-37:2 alkenone concentrations of the in-house reference sediment showed significant differences between before and after the saponification (Delta C-37:3 and Delta C-37:2) depending on the internal standards used. However, the differences in the U-37(K') and the estimated sea surface temperatures were insignificant. The Delta C-37:3 and Delta C-37:2 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 Delta C-37:3 and Delta C-37:2 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.This study was supported by the project titled "The Study of Marine Geology and Geological Structure in the Korean Jurisdictional Seas" funded by the Ministry of Oceans and Fisheries (MOF), and by a National Research Foundation of Korea (NRF) grant funded by the Ministry of Science and ICT (MSIT) (NRF-2016R1A2B3015388, PN17100)