Environmental influences over the last 16ka on compound-specific δ¹³C variations of leaf wax n-alkanes in the Hani peat deposit from northeast China

Compound-specific carbon isotope ratios (δ¹³C) of leaf wax n-alkanes (C₂₁-C₃₃ odd carbon numbered n-alkanes) were measured in the Hani peat sequence from northeast China. These data were compared with lipid biomarker compositions to assess changes in local vegetation and paleoclimate for the last 16ka. The δ¹³C values of n-alkanes range between -36.6 and -30.7%, showing that the compounds originate from C₃ plants. Much larger variations (~5.4%) in the n-alkane δ¹³C values than those of atmospheric CO₂ during the last 16ka (< 0.5%) indicate that the isotopic values were affected by environmental factors in addition to the postglacial δ¹³C variations in the atmospheric reservoir. The stratigraphic records of δ¹³C reveal decoupled fluctuations among the individual n-alkanes, particularly between 15.5 and 11.4ka. Synchronous excursions in the δ¹³C offsets among individual n-alkanes (δδ¹³C) and lipid biomarker paleoplant proxies (Paq, and C₂₃/C₃₁ and C₂₇/C₃₁) from 14.9 to 13.2ka and 12.7 to 11.6ka suggest that vegetational changes are the most likely causes for the decoupled δ¹³C variations. Parallel fluctuations of the δ¹³C values of terrestrial higher plant-derived C₂₉ and C₃₁ n-alkanes and the n-alkane average chain-length (ACL) from 11 to 6ka indicate that the δ¹³C variations responded to net evaporation changes. Negative shifts in the n-alkane δ¹³C values coinciding with the ACL decreases at 10.5-9.3ka and 8.1ka indicate the short-term onset and fluctuations of the summer monsoon strength in eastern China during the early Holocene.