Hydroclimate variation during the Mystery Interval in the East Asian Summer Monsoon area

Abstract

The inconsistency of paleoclimate records between the mid-low and high latitudes during the Mystery Interval (MI, 17.5–14.5 ka BP) is not well resolved. To provide a mechanism analysis, this study conducts spatial comparisons of hydroclimate changes in the Asian Summer Monsoon (ASM) region during the MI by reconstructing the paleohydrology of the south of East Asian Summer Monsoon (EASM) region using the molecular distributions and carbon isotope ratio of n-alkanes, as well as elemental and isotopic composition of bulk organic matter, in a sedimentary core retrieved from Dingnan (DN) wetland. The multiple indices of the DN core confirmed the occurrence of dry-wet and wet-dry transitions at ca. 17.5 ka BP and 16.0 ka BP, respectively. Synchronous with the dry-wet transition in the DN records, the Indochina Peninsula at a slightly lower latitude became wetter. In contrast, the middle Yangtze region at a more northern latitude became slightly drier, and North China did not show a hydrological variation. Moreover, the wet-dry transition at the mid-MI was strong in the Indochina Peninsula (10–20°N, at about 16.5 ka BP) and the southern EASM region (23–27°N, at about 16.0 ka BP) but was nearly absent in the middle Yangtze region (28–32°N) and North China (35–40°N). The first hydrological transition possibly connects with the synchronous southward movement of the Intertropical Convergence Zone (ITCZ) and the westerly jet caused by the cooling of the Northern Hemisphere. The absence of the second hydrological transition is interpreted as a result of the decoupling of the ITCZ and the westerly jet caused by the delayed formation of the ITCZ due to the warming of the Southern Hemisphere. This study reveals spatial differences in the hydroclimate variations during the MI and highlights the potential influence of coupling between the westerly jet and the ITCZ on rainfall in the ASM region.