The spatio-temporal pattern of Asian summer monsoon during glacial Termination II recorded by Chinese stalagmite δ18O

Abstract

The difficulty in constraining the large-scale Asian summer monsoon (ASM) variability in the Chinese monsoon region (CMR) during glacial Termination II lies in our limited knowledge of the western part, primarily due to sparse paleoclimate records. To get a better picture of the ASM during Termination II, we examined a precisely dated stalagmite δ18O record between 133.1 and 127.0 kyr B.P. from Wanxiang Cave located at the ASM's northern edge in western China. In combination with published δ18O data from this cave, we have identified the ‘Weak Monsoon Interval’ (WMI) in the Wanxiang δ18O record and confirmed that the Heinrich 11 cold event in the North Atlantic caused the weakened ASM over the CMR via reorganization of the large-scale ocean-atmospheric circulation. However, the post-WMI change in δ18O is gradual, in contrast with the abrupt shift shown in the other cave records from southern and northeastern China. The rapid northward migration of the westerly jet relative to the Qinghai-Tibet Plateau is probably responsible for this discrepancy. This northward-positioned westerly jet prevented the more 18O-depleted moisture from the Indian Ocean from reaching the study site. Simultaneously, it facilitated the earlier northward movement of the East Asian summer monsoon (EASM) rainband that carries positive precipitation δ18O to obscure the abrupt decrease in our δ18O record. After the onset of the last interglacial, no obvious Younger Dryas (YD)-like event was recorded in Wanxiang Cave. This result is consistent with most stalagmite δ18O records in the CMR and further suggests a minimal impact of the YD-like event on ASM variabilities. The relatively large amplitude of δ18O variations observed in Wanxiang Cave between the late penultimate glacial and the last interglacial corresponds to a dominant control of the Indian summer monsoon (ISM), whereas smaller δ18O amplitudes were recorded in cave sites mainly under the influence of both ISM and EASM. Therefore, we posit that the heterogeneity of the hydroclimate in the CMR during Termination II resulted from a combination of multiple processes, that is, the westerly jet, ISM and EASM, rather than a single one.