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The East Asian summer monsoon (EASM) system plays a crucial role in regulating climatic and hydrological variability in East Asia. The hydrological effects of the EASM in eastern China during the Little Ice Age (LIA) remains controversial, however. Here, we established a relatively high-resolution palaeohydrological record over the last 700 years in East China via analyzing n -alkanes from a peat core. Mid- and long-chain (C 21 –C 25 and C 27 –C 31) n -alkanes account for more than 95% of the total odd‑carbon-numbered n -alkanes, with short-chain n -alkanes (C 17 –C 19) accounting for only 2.3% on average, suggesting that organic matter in the peat core originated primarily from vascular plants. Organic geochemical indices, including P aq (an indicator of contributions from aquatic plants), the average chain length (ACL) of long-chain n -alkanes, and C 31 /C 27 and C 23 /C 29 n -alkane ratios, suggest a transition from dry conditions during the middle LIA to wet conditions in the late LIA. Comparing P aq records from the study profile with previous records from the EASM region, we found that the northern and southern parts of eastern China showed contrasting changes in humidity during the LIA. Specifically, the southern part shifted from mid-LIA dry conditions to late-LIA wet conditions, whereas the northern part shifted from mid-LIA wet conditions to late-LIA dry conditions. This spatial heterogeneity in hydroclimate could be attributed to La Niña-like conditions and intense summer monsoons during the middle LIA and El Niño-like conditions and weak summer monsoons during the late LIA. Our study demonstrates the importance of understanding spatial heterogeneity of hydroclimatic changes to probe the mechanisms whereby EASM modulates regional climatic changes during the LIA. • We analyzed alkane proxies from a peatland in SE China to rebuild palaeohydrology. • Organic debris originate from a mixture of terrestrial and aquatic plants. • Alkanes reveal shifts from moderate wet to dry to wet conditions during the LIA. • Northern and southern parts of the EASM region show humidity contrast in the LIA. • This spatial heterogeneity in palaeohydrology may be linked to EASM and ENSO. [ABSTRACT FROM AUTHOR]

Vegetation–climate relationships are often different at varying spatial scales, which is seldom taken into account in reconstructing past climate changes from fossil pollen spectra represent more local vegetation composition but using regional or extra-regional modern pollen–climate calibration set. In this paper, we employ 2620 surface pollen spectra and six pollen sequences from continental East Asia to reconstruct Holocene climate with modern analogue technique. A novel data set of vegetation sensitivity index (VSI) is introduced to examine vegetation–climate relationships in 0.5° search windows around the fossil sites (local) and in the tailored calibration sets (regional). Then, we compare them to the explanatory abilities of (reconstructed) climate variables on explaining the pollen variance in calibration sets and in the fossil pollen data sets using constrained ordination, cross-validation and significance test. By this procedure that we called local–regional–fossil comparison, we can better determine which variable reconstruction is valid and useful. In our cases, moisture variable reconstructions in temperate forest-steppe ecotone at the East Asian summer monsoon margin are reliable. Consistent Holocene moisture variations with a strong monsoon influence during 8.6–4.0 cal ka BP which can help us to better interpret human adaptations along the Great Wall. However, quantitative climate reconstructions at some sites are less reliable due to highly heterogeneous vegetation sensitivities surrounding the site, particularly for areas with complicated topographical contexts. We stress that vegetation sensitivities at local and regional scales both need to be investigated before conducting quantitative climate reconstruction. [ABSTRACT FROM AUTHOR]

Late Miocene and Pliocene climate changes provide an analogue for understanding linkages between variations in precipitation, the intensity of the Asian Monsoon (AM) and vegetation in a warm world with high atmospheric CO 2. This study presents a reconstruction of vegetation and paleoclimate based on a pollen sequence between ~10.8 and 7.2 Ma, in addition to an analysis of pollen assemblages of Pliocene and Pleistocene, from the Weihe Basin, central China. Based on the Coexistence Approach (CA), the reconstruction indicates that the late Miocene and Pliocene climate was warmer and wetter than today, and that the vegetation responded to a strengthened AM prior to the onset of the Northern Hemisphere glaciations (NHG) during the early Pliocene. A significant vegetation shift from forest to grassland occurred at ~9.0 Ma, suggesting a climate shift from warm-wet to cool-dry in central East Asia earlier than previously thought. The quantitative reconstruction suggests that mean annual precipitation exceeded ~800 mm/year and the warm season (June to September) precipitation exceeded ~560 mm during ~10.8–7.2 Ma. Based on pollen analysis, the late Pliocene, however, appears to have been relatively cool and dry, followed by a colder and drier Pleistocene, associated with an overall weakening of the AM. The paleoclimate reconstruction reveals that the AM exhibited phased weakening since ~10.8 Ma, which is consistent with stepwise global temperature variations. It is clear that vegetation variations were mainly driven by the AM precipitation and global cooling in the semi-humid region of the Weihe Basin since the late Cenozoic. This study provides insights into vegetation dynamics under global warming conditions. • A quantitative reconstruction of vegetation and monsoon precipitation was developed. • The late Miocene precipitation was 200 mm greater than the modern situation. • A vegetation shift occurred at ~9.0 Ma suggests the climate shift earlier. • The Asian Monsoon was phased weakening since ~10.8 Ma, responding to global cooling. • Vegetation variation was driven by the Asian Monsoon precipitation in a warm world. [ABSTRACT FROM AUTHOR]