The measurement of D/H ratio in alkenones and their isotopic heterogeneity

The method was applied to purify alkenones in suspended particles and surface sediments from a site in Chesapeake Bay, eastern USA. The hydrogen isotopic composition of di- and triunsaturated C37 and C38 alkenones differed significantly on the basis of chain length and the degree of unsaturation, demonstrating the importance of gas chromatography-isotope ratio-mass spectrometry (GC-irMS) analysis of individual alkenones for accurate paleoenvironmental reconstruction. Constant fractionation factors between alkenones with different chain length but the same degree of unsaturation (αC37:2-C38:2andαC37:3-C38:3=1.01) and those with the same chain length but different degree of unsaturation (αC37:2-C37:3andαC38:2-C38:3=0.97) in all samples suggest that the values may represent hydrogen isotope fractionation associated with elongation and desaturation during alkenone biosynthesis.