Differential timing of C4 plant decline and grassland retreat during the penultimate deglaciation

Abstract Compound-specific stable carbon isotope composition of terrestrial leaf wax n -alkyl lipids (δ 13 C alk ) was measured in sediments from the northern South China Sea (SCS), allowing assessment of vegetation change in the source area within the penultimate glacial cycle during 60–160 kyr. Our δ 13 C alk record suggested a prominent vegetation contrast between the glacial and the interglacial, with more C 4 plant developing during the glaciation and a rapid decline during the glacial termination. This deglacial change in δ 13 C alk was attributed to an increase in humidity caused by the enhancement of the East Asian Summer Monsoon (EASM). However, the inferred deglacial C 4 decline lagged by ~ 4 kyr behind the grass retreat inferred from published pollen record. We argue that the time discrepancy in the two terrestrial plant proxies may have resulted from their differential responses to regional climate change, with grass community structure more sensitive to temperature rise and plant photosynthetic pathway more sensitive to humidity increase. Therefore, an earlier penultimate deglacial warming relative to humidity increase can be inferred from the lead of grass retreat relative to C 4 decline, which implies that EASM may be delayed during the deglacial warming.