A Potential Suite of Climate Markers of Long-Chain n-Alkanes and Alkenones Preserved in the top Sediments from the Pacific Sector of the Southern Ocean

Abstract

Investigation of organic compounds in marine sediments can potentially unlock a wealth of new information in these overlooked climate archives. Here we present pilot study results of organic geochemical features of long-chain n-alkanes and alkenones and individual carbon isotope ratios of long-chain n-alkanes from a newly collected, approximately 8-meter long, Pleistocene age sediment core, located in the far reaches of the Pacific sector of the Southern Ocean. We initially analyzed a suite of organic compounds in the core, and the results show abundant long-chain n-alkanes (C29-C35) with predominant odd-over-even carbon preference, which suggests an origin of terrestrial higher plant waxes via long range transport of dust, possibly from Australia and New Zealand. The δ13C values of the C31 n-alkane range from -29.4 to -24.8‰, in which the higher δ13C values suggest more contributions from C4 plants waxes. In the analysis, we found that the mid-chain n-alkanes (C23-C25) have small odd-over-even carbon preference, suggesting that they were derived from marine non-diatom pelagic phytoplankton and microalgae, and terrestrial sources. Furthermore, the C26 and C28 with lower δ13C values (~ -34‰) indicate an origin from marine chemoautotrophic bacteria. We found that the abundances of tetra-unsaturated alkenones (C37:4) in this Southern Ocean sediment core ranges from 11-37%, perhaps a marker of low sea surface temperature (SST). The results of this study strongly indicate that the δ13C values of long-chain n-alkanes and index are potentially useful to reconstruct detailed history of C3/C4 plants and SST change in the higher latitudes of the Southern Ocean.