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This paper aims to achieve an improved understanding of the long-term change trends of precipitation δD and δ 18 O values (δD p and δ 18 O p ) in the Asian monsoonal region and their relationship with the corresponding humidity trends during the Holocene. To do this we first review the observed modern spatial pattern of summer precipitation distribution in the East Asian summer monsoon (EASM) region under different EASM intensities, and the relationship between modern observed δ 18 O p values and corresponding precipitation amounts on monthly and inter-annual timescales in the EASM and Indian summer monsoon (ISM) regions. Second, we compare Holocene lacustrine and marine compound-specific hydrogen isotopic records of n -alkanes/ n -alkanoic acid (δD n ), lacustrine authigenic carbonate and cave stalagmite oxygen isotopic records (δ 18 O c and δ 18 O s ) from the Asian monsoonal region, all of which are closely related to δD p and δ 18 O p variations. The results demonstrate that in both the ISM and EASM regions, all of these isotopic records exhibit roughly similar long-term characteristics, i.e. they were all more negative during the early-Holocene and early mid-Holocene (ca. 11–6 ka B.P.; B.P. means before present, present = 1950 AD), and then became more positive towards the late-Holocene. Third, we compare representative paleo-humidity records from the Asian monsoonal region; the results confirm that, in the ISM region, a humid interval occurred in the early-Holocene and early mid-Holocene (ca. 11–6 ka B.P.) and subsequently the climate became more arid towards the late-Holocene. This indicates an enhanced ISM during the early-Holocene and early mid-Holocene (ca. 11–6 ka B.P.), and an ISM of decreasing intensity towards the late-Holocene. On a Holocene orbital scale, both δ 18 O p and δD p appear to be controlled by an “amount effect” in the ISM region, consistent with the region's inter-annual modern δ 18 O p data. This evidence indicates that both δ 18 O p and δD p paleo-records are significantly related to paleo-humidity in the ISM region. In contrast, Holocene humidity variations in the EASM region exhibit clear spatial differences: a humid mid-Holocene interval (ca. 8–3 ka B.P.) occurred in southern and northern China, but an arid interval from ca. 7–3 ka B.P. occurred in central China, in the middle reaches of the Yangtze River. Based on precipitation distribution patterns under different EASM intensities in the EASM region over the past few decades, we conclude that EASM intensity was enhanced during the mid-Holocene (ca. 8–3 ka B.P.). Relative to the ISM intensity, the response of EASM intensity to summer insolation was relatively slow. In the EASM region the relationship between climate and δ 18 O p and δD p is more complex, consistent with analyses of regional inter-annual modern δ 18 O p data. This evidence demonstrates that both δ 18 O p and δD p paleo-records cannot be used directly as paleo-humidity (i.e. precipitation amount or EASM intensity) indicators in the EASM region. Further comparison and analyses demonstrate that the coupled variations in west–east Equatorial Pacific temperature gradients and the West Pacific subtropical high (WPSH) played an important role in determining EASM intensity during the Holocene. [ABSTRACT FROM AUTHOR]

Alpine lakes not only provide internationally important habitats for endangered species, they also play a crucial role in the regional water balance. Unfortunately, a rapid loss of alpine lakes in China has occurred in recent decades; however, intensive human activities, together with regional differences in the responses of lakes to climate change, has impeded our understanding of the contribution of climate change to the loss of these lakes. To better understand how alpine lakes will evolve with continuing global warming, we used the analysis of new sedimentary proxies from Lake Gonghai, an undisturbed alpine lake, together with a review of published records, to reconstruct variations in integrated lake status since the last deglaciation. From 14,660–11,890 cal. yr BP the lake was in the most unstable state, indicated by the highest amplitude fluctuations in lake level and the within-lake environment. The lake status experienced clear millennial-scale changes. During the early and middle Holocene (11,890–3200 cal. yr BP), the most stable lake status occurred, consistent with the highest precipitation levels. Owing to the highest level of freshwater influx in the middle Holocene (8–5 ka), the lake water was the deepest and most acidic. At this time, the dense vegetation cover resulted in maximum catchment stability and the lowest level of soil erosion, and hence the lowest sediment accumulation rate. From 3200 cal. yr BP, decreasing mean annual precipitation resulted in a moderately stable lake status, a shallow water depth and more alkaline lake water. The sparse vegetation cover caused a dramatic increase in the erosion rate and hence in the sediment accumulation rate. We infer that variations in local humidity were the major control on the integrated lake status during the last ~14,600 cal. yr BP. With the anticipated progression of global warming, the status of the alpine lakes in the region may continue to deteriorate and appropriate mitigation strategies are imperative. [ABSTRACT FROM AUTHOR]

Monsoon precipitation over China exhibits large spatial differences. It has been found that a significantly enhanced East Asian summer monsoon (EASM) is characterized by increased rainfall in northern China and by reduced rainfall in southern China, and this relationship occurs on different time scales during the Holocene. This study presents results from a diverse range of proxy paleoclimatic records from northern China where precipitation variability is traditionally considered as an EASM proxy. Our aim is to evaluate the evolution of the EASM during the Holocene and to compare it with all of the published stalagmite δ 18 O records from the Asian monsoon region in order to explore the potential mechanism(s) controlling the Chinese stalagmite δ 18 O. We found that the intensity of the EASM during the Holocene recorded by the traditional EASM proxy of moisture (or precipitation) records from northern China is significantly different from the Chinese stalagmite δ 18 O records. The EASM maximum occurred during the mid-Holocene, challenging the prevailing view of an early Holocene EASM maximum mainly inferred from stalagmite δ 18 O records in eastern China. In addition, all of the well-dated Holocene stalagmite δ 18 O records, covering a broad geographical region, exhibit a remarkably similar trend of variation and are statistically well-correlated on different time scales, thus indicating a common signal. However, in contrast with the clear consistency in the δ 18 O values in all of the cave records, both instrumental and paleoclimatic records exhibit significant spatial variations in rainfall on decadal-to-centennial time scales over eastern China. In addition, both paleoclimatic records and modeling results suggest that Holocene East Asian summer monsoon precipitation reached a maximum at different periods in different regions of China. Thus the stalagmite δ 18 O records from the EASM region should not be regarded as a reliable indicator of the strength of the East Asian summer monsoon. Furthermore, modern observations indicate that the moisture for precipitation in the East Asian monsoon region is mainly derived from the Indian Ocean. The moisture transport route from the Indian Ocean to the East Asian monsoon region during the Holocene is almost identical to that of modern precipitation. Therefore the strong correlation of δ 18 O records in the EASM and Indian summer monsoon (ISM) regions, and the similarity of the pattern of latitudinal changes in δ 18 O values in stalagmites and in modern meteoric precipitation along the water vapor transport route, further suggests that the stalagmite δ 18 O records from the EASM region are essentially a signal of the isotopic composition of precipitation, which is determined mainly by changes in the δ 18 O of atmospheric vapor in the upstream source region over the Indian Ocean and Indian Monsoon region via the upstream depletion mechanism. Finally, the main trends of the stalagmite δ 18 O records are strongly correlated with the known evolution of the ISM, and therefore these records reflect the history of the ISM rather than that of the EASM. Our findings support the conclusion that EASM variability is mainly controlled by Northern Hemisphere summer insolation and was strongly modulated by ice volume during the last deglaciation and early Holocene, which delayed the response of the EASM maximum to peak insolation forcing. [ABSTRACT FROM AUTHOR]