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

Investigating organic compounds in marine sediments can potentially unlock a wealth of new information in these 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 m long, located in the far reaches of the Pacific sector of the Southern Ocean. We analyzed a suite of organic compounds in the core. The results show abundant long-chain n-alkanes (C-29-C-35) with predominant odd-over-even carbon preference, suggesting an origin of terrestrial higher plant waxes via long-range transport of dust, possibly from Australia and New Zealand. The delta C-13 values of the C-31 n-alkane range from -29.4 to -24.8 parts per thousand, in which the higher delta C-13 values suggest more contributions from C-4 plant waxes. In the analysis, we found that the mid-chain n-alkanes (C-23-C-25) have a small odd-over-even carbon preference, indicating that they were derived from marine non-diatom pelagic phytoplankton and microalgae and terrestrial sources. Furthermore, the C-26 and C-28 with lower delta C-13 values (similar to-34 parts per thousand) indicate an origin from marine chemoautotrophic bacteria. We found that the abundances of tetra-unsaturated alkenones (C-3(7:)4) in this Southern Ocean sediment core ranges from 11 to 37%, perhaps a marker of low sea surface temperature (SST). The results of this study strongly indicate that the delta C-13 values of long-chain n-alkanes and U-37(k) index are potentially useful to reconstruct the detailed history of C-3/C-4 plants and SST change in the higher latitudes of the Southern Ocean.

Automated summary

The study analyzed organic compounds in sediment core from the Southern Ocean, revealing long-chain n-alkanes potentially transported from Australia and New Zealand. Different carbon chain lengths of n-alkanes came from various sources such as marine phytoplankton, microalgae, terrestrial plants, and chemoautotrophic bacteria. This research highlights the potential use of delta C-13 values of long-chain n-alkanes and U-37(k) index for reconstructing the history of C-3/C-4 plants and sea surface temperature changes in the Southern Ocean.