** Progress in Earth and Planetary Science is the official journal of the Japan Geoscience Union, published in collaboration with its 50 society members.
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Interdisciplinary research
202104202104
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
Xin Chen, Xiaodong Liu, Da-Cheng Lin, Jianjun Wang, Liqi Chen, Pai-Sen Yu, Linmiao Wang, Zhifang Xiong, Min-Te Chen
Southern Ocean, Pacific Ocean, n-alkane, Carbon isotopic, SSTUk37
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 (C29–C35) 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 δ13C values of the C31n-alkane range from −29.4 to −24.8‰, in which the higher δ13C values suggest more contributions from C4 plant waxes. In the analysis, we found that the mid-chain n-alkanes (C23–C25) 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 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 to 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 the detailed history of C3/C4 plants and SST change in the higher latitudes of the Southern Ocean.
