Clean-up procedures for the unbiased estimation of C-37 alkenone sea surface temperatures and terrigenous n-alkane inputs in paleoceanography

Sample preparation procedures for the quick determination of C-25-C-33 n-alkanes and the U-37(k) index in small sediment sample amounts (ca. 1 g dry weight) have been developed. Alkaline hydrolysis and silica column fractionation are the two clean-up steps considered. The former eliminates the interferences from the sedimentary wax esters which dominate the lipid composition in high latitude Atlantic Ocean sediments. The latter has been designed to collect both lipid groups (C-25-C-33 n-alkanes and C-37 alkenones) in one single fraction avoiding the interferences from highly polar compounds which affect, in particular, the quantitative determination of the n-alkanes. The whole procedure has been shown not to affect the U-37(k) measurements, even at low C-37 ketone concentrations such as 10 ng which is the minimum threshold of total C-37 alkenones in the gas chromatographic system for avoidance of adsorption-related interferences [1]. As shown with real case examples the usefulness of these clean up methods is highly dependent on the amounts of interfering lipid compounds present in the sediment extracts and their application may not be necessary for the open sea sediments present in most low latitude areas.