Potential of Leaf Wax Lipids for Synchronization of Marine Sediments and Polar Ice Cores

The waxy coating of vascular plants contains a series of C27-C33 n-alkanes with a characteristic prevalence of odd over even-numbered carbon chains. These species are relatively abundant and well-preserved in the marine environment. In this study, the lipid components of sediments from the Bermuda Rise were extracted and the leaf wax n-alkanes were analyzed by GC-MS. A characteristic fragment (m/z 85) of the mass spectra was used to quantitate the presence of each n-alkane in the sediment. The sediments analyzed spanned the transition from cold stadial to warm interstadial conditions, and back to stadial conditions, 40-36 kyr ago (IS-8). The concentration of leaf wax n-alkanes had an inverse relationship with sea surface temperature during this transition. Total C27-C33 n-alkane levels ranged from 200 ng/g of sediment in the interstadial to 700 ng/g in the stadial periods. The results of these analyses are consistent with an increase in aeolian deposition or detrital load during colder periods. Techniques were also developed for the clean extraction and analysis of trace levels of naturally occurring lipids in polar ice. Pilot samples from a glacial (MIS 3) section of the Greenland GISP2 ice core had very low abundances of total C27-C33 odd n-alkanes ranging from 80-700 ng/kg of ice after subtraction of a blank that represented 10-50% of the n-alkanes present. The pilot samples exhibited an unexpected distribution of C27-C33 n-alkanes, with approximately equal abundances of even and odd-numbered n-alkane chains (as opposed to the approximately 5-fold excess of odd over even chains expected for leaf wax). The peak of the n-alkane distribution was between C28-C31. We will evaluate the prevalence and significance of the n-alkane distribution in additional ice samples spanning the same time interval we analyzed in the Bermuda Rise sediment to determine if leaf waxes can be used to synchronize the chronologies of marine sediment and polar ice cores.