A hydrocarbon biomarker record for the last 40 kyr of plant input to Lake Heqing, southwestern China

Multi proxy records relating to climate and vegetation have been obtained for a core spanning the last 40 kyr from the Heqing Lake Basin (26°N, 100°E; 2200 m asl.), Yunnan Province of southwestern China. Compound-specific carbon isotope records for the vascular plant leaf wax hydrocarbons, the C23–C33 n-alkanes, and for the algal hydrocarbons, the C23 and C25 n-alkenes and a C30 cyclobotryococcatriene, all show a shift of circa +3‰ in δ 13C values from MIS 3 to the end of MIS 2, followed by a rapid return to lighter values. This shift (from −32 to −29‰) for the n-alkanes and n-alkenes most likely derives from bicarbonate utilization by aquatic plants in the lake, rather than increased C4 photosynthesis. Thus, both pollen data and hydrocarbon data appear to reveal a rise and fall in the contributions of submerged and/or floating plants during MIS 2.