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Lake level and its inferred East Asian summer monsoon (EASM) evolution in northern boundary of EASM during the Holocene are highly debated. Here, we present a 15-ka record of glycerol dialkyl glycerol tetraethers (GDGTs) in a closed lake in northern China to address this issue. Surface and downcore sediment data demonstrate sedimentary GDGT-0 and branched GDGTs (brGDGTs) are of aquatic production. Contents of GDGT-0 and brGDGTs increase but brGDGT-based paleo-temperature proxy decreases with water depth in surface sediments along a nearshore to offshore transect. This trend is likely due to an increasingly hypoxic condition, favored by anaerobic microbes producing these GDGT-0 and brGDGTs, in bottom water. Accordingly, brGDGT-derived water temperature and pH would reflect bottom water conditions that are largely regulated by water depth of the lake. Downcore GDGT data and their derived temperature and pH consistently reveal a gradually increasing lake level from the late Pleistocene to the early Holocene, a high level during 9.5–5 ka BP and a decreasing trend afterward. The lake-level records from independent and robust proxies in this study largely agree with pollen records in the region, supporting a mid-Holocene maximum EASM precipitation. [ABSTRACT FROM AUTHOR]

The impact of global warming on the climate of northern China has been investigated intensively, and the behavior of the East Asian monsoon during previous intervals of climatic warming may provide insight into future changes. In this study, we use paleovegetation records from loess and lake sediments in the marginal zone of the East Asian summer monsoon (EASM) to reconstruct the EASM during the interval of warming from the Last Glacial Maximum (LGM) to the Holocene. The results show that during the LGM, desert steppe or dry steppe dominated much of northern China; in addition, the southeastern margin of the deserts east of the Helan Mountains had a distribution similar to that of the present-day, or was located slightly further south, due to the cold and dry climate caused by a strengthened East Asian winter monsoon (EAWM) and weakened EASM. During the last deglaciation, with the strengthening of the EASM and concomitant weakening of the EAWM, northern China gradually became humid. However, this trend was interrupted by abrupt cooling during the Heinrich 1 (H1) and Younger Dryas (YD) events. The EASM intensified substantially during the Holocene, and the monsoon rain belt migrated at least 300 km northwestwards, which led to the substantial shrinking of the desert area in the central and eastern part of northern China, and to the large expansion of plants favored by warm and humid conditions. Paleoclimatic records from the marginal zone of the EASM all show that the EASM reached its peak in the mid-Holocene, and past global climatic warming significantly strengthened the EASM, thereby greatly improving the ecological environment in northern China. Thus, northern China is expected to become wetter as global warming continues. Finally, high resolution Holocene vegetation records are sparse compared with the numerous records on the orbital timescale, and there is a need for more studies of Holocene climatic variability on the centennial-to-decadal scale. [ABSTRACT FROM AUTHOR]

Many lakes exist in southeastern Badain Jaran Desert and its hinterland, including 110 perennial lakes and some seasonal or extinct lakes. Geomorphological, sedimentological, and bioglyph evidence obtained from field investigations on Badain Jaran Desert lake group, alongside measurements and dating performed on lake relic, prove that these lakes expanded while the climate was relatively wet during early and middle Holocene. The dating results suggest that the pan-lake period of the Badain Jaran Desert began at 10 cal kyr BP, before which the limnic peat period occurred (11-10 cal kyr BP). Many lakes reached their maximal water-level during 8.6-6.3 cal kyr BP and retreated or dried up in the late Holocene (about 3.5-0 cal kyr BP). During that period, the precipitation at Badain Jaran Desert may have reached 200 mm yr?1 for 7.7-5.3 cal kyr BP, inferred from both the age and precipitation rate of calcareous root tubes. The water balance calculation shows that wetter and warmer climate and the increase of underground water recharge were key factors in maintaining and developing the lake group at both centennial and millennial time scales. Furthermore, lake surface expansion and the increasing fresh water availability set the background for the prosperous prehistoric culture. [ABSTRACT FROM AUTHOR]

Volatiles erupted from large-scale explosive volcanic activities have a significant impact on climate and environmental changes. As an important ecological factor, the occurrence of fire is affected by vegetation cover, and fire can feed back into both vegetation and climatic change. The causes of fire events are diverse; and can include volcanic eruptions. The amount of charcoal in sediment sequences is related to the frequency and intensity of fire, and hence under good preservation conditions fire history can be reconstructed from fossil charcoal abundance. Until now, little research on the role of fire has been carried out in northeastern China. In this study, through research on charcoal and tephra shards from Gushantun and Hanlongwan, Holocene vegetation change in relation to fire and volcanic events in Jilin, Northeastern China, was investigated. Where tephra shards are present in Gushantun it is associated with low level of both conifers and broadleaved trees, and is also associated with a pronounced charcoal peak. This suggests forest cover was greatly reduced from a fire caused by an eruption of the Tianchi volcano. We also detected one tephra layer in Hanlongwan, which also has the almost same depth with low level forest pollen values and one charcoal peak. This was caused probably by an eruption of the Jinlongdingzi volcano. [ABSTRACT FROM AUTHOR]