Evidence of a humid mid- Holocene in the western part of Chinese Loess Plateau

Field works show that the wetland/swamp layers were distributed ubiquitously in the western part of the Chinese Loess Plateau. Universality of the wetland/swampy layer and the consistency of the age reveal that the layer was developed under the humid climatic condition. Dated between 9 and 3.8 kaBP, the wetland/swampy layer is full of aquatic mollusks and has the highest tree and shrub pollen, indicating a humid mid-Holocene. Variations of grain size suggest that winter monsoon weakened during 9—3.8 kaBP while climate change to humid and vegetation cover increased from 9 kaBP onward. After 5.9 kaBP, the humidity declined gradually. In 3.8 kaBP, summer monsoon sharply retreated, and the climate changed to dry.

A carbon- and oxygen-isotope record of recent environ- mental change from Qinghai Lake, NE Tibetan Plateau

A c. 300-year oxygen and carbon isotope record derived from fine-grained and ostracod carbonate from Qinghai Lake testifies to dramatic interannual tointerdecadal limnological change. Fine-grained carbonates, which are mainly authigenic, are likely to have formed in the epilimnion of the lake and their isotopic composition reflects the summer temperature and, more importantly, the isotopic composition of the near-surface waters, which is mainly a function of evaporative concentration. Ostracod shells are secreted in the benthos of the lake, and their isotopic composition reflects summer bottom-water conditions, together with fractionation effects, which may differ between species. Differences betweencontemporaneous values from authigenic carbonates and ostracod shells may provide an indication of stratification within the lake and variations in effective precipitation over the northeast part of the Tibetan Plateau over the past 300 years. A period of moderate evaporative concentration, from about 300 to 100 yr BP, was interrupted by a marked wet phase from ～100 to 40 yr BP, which was in turnfollowed by a return to drier conditions in the most recent part of the record.The increase in ? 18O values in the latter part of the record accords well withinstrumental records of lake-level lowering and salinity increase since about 1955 AD.

Groundwater recharge and climatic change during the last 1000 years from unsaturated zone of SE Badain Jaran Desert

The history of groundwater recharge and climatic changes during the last 1000 years has been estimated and reconstructed using environmental chloride from unsaturated zone profile in the southeast Badain Jaran Desert, NW China. By using a steady-state model for duplicate unsaturated zone chloride profiles, the long-term recharge at the site was estimated to be 1.3 mm yr-1. From one profile, which reached the water table, the climatic change events of 10—20 years duration were well preserved. There were 3 wet phases and 4 dry episodes during the recent 800 years according to the peaks and troughs of recharge rate calculated via chloride concentration and moisture content. There was a dry episode before 1290 AD. At ca. 1500—1530 AD, which is an important date, there was an abrupt change from drought to wet conditions. At the beginning of the 1800s, local climate changed from wet to dry occurred and subsequently deteriorated over the past 200 years. The unsaturated profile was compared with the Guliya ice core records. The agreement of wet and dry phases from 1200 to 1900 AD is quite good, whilst trends diverged during the last 100 years. It seems that the large-scale climate difference took place between mountain regions and the desert basin in NW China during the 20th century, which closely correspond to the water table reduction of some 1 metre.

Late Glacial and Holocene vegetation history and paleoclimate of the Tengger Desert,northwestern China

Sediments spanning the last 30000 yr BP wereobtained from two sections in the southern part of the Teng-ger Desert, northwestern China (3810′46″N, 10245′53″E). The pollen assemblage suggested a Picea forest domination under a wetter and cooler environment from 27580 to 23510 yr BP. During the following period from 23510 to 21880 yr BP a Cyperaceae meadow occurred under a wet and coldclimate. Wetter and cooler conditions returned and a Piceaforest re-occupied this region between 21880 and 20910 yrBP. From 20910 to 15590 yr BP a steppe under a dryenvironment dominated the region. The first temperatureincrease started at ca.15590 yr BP. The pollen assemblagecovering the period between 15590 and 10890 yr BP can be divided into six minor zones, suggesting that the vegetation compositions changed rapidly under unstable climate.Between 10710 and 10370 yr BP the climate became cold and dry again. The climatic conditions became warmer and more humid between 10260 and 9140 yr BP. From 8450 to 7950 yr BP a steppe landscape under a dry climate occupied this region. Between 7950 and 7290 yr BP climate seemed more humid. The following period from 7290 to 5670 yr BP wasgenerally warm. The period between 5670 and 3510 yr BPwas characterized by dramatic climatic oscillations.Relatively cold intervals appeared around 7760 and 7380,6490—6290, 5670—5010, 4470—3510 yr BP. Twopronounced dry events occurred in 6290—5670 and 5010—4470 yr BP with a marked wet spell from 3510 to 3000 yr BP.

Temperature variations on the Tibetan Plateau over the last two millennia

The paleoclimate data recovered from ice cores, tree rings and lake sediments indicate regional features of climatic change on the Tibetan Plateau (TP) during the last 2000 years. The composite temperature reconstructions indicate that several main climatic episodes, such as the 揕ittle Ice Age?between 1400 and 1900, the 揗edieval Warm Period?in 1150—1400, a less warm period in 800—1100, and an earlier cold period between the 3rd and 5th centuries, occurred in the TP. In addition, temperature varied from region to region. The period from AD 800 to 1100, which was warm in northeastern TP, was contemporaneous with cooling in the western and southern TP. The southern TP experienced warming between 1150 and 1400. For western TP, the d 18O records of the Guliya ice core indicate that the period 1250—1500 witnessed a clear warming. Large-scale trends in the temperature history from northeastern TP are more similar to those in eastern China than are the trends from the Guliya ice cap far to the west and southern TP. The most prominent similarities between the temperature variations of the TP and eastern China are such cold phases as 1100—1150, 1500—1550, 1650—1700 and 1800—1850, and the latter three cold events match with three widespread glacial advances which occurred on the TP during the Little Ice Age.

A mid-Holocene drought interval as evidenced by lake desiccation in the Alashan Plateau,Inner Mongolia,China

The mid-Holocene in China is traditionally thought to be a warm and humid period with a strong summer monsoon, and is often termed the Holocene Climatic Optimum or Megathermal Period. Here we present lake geomorphologic and lithological evidence from the Alashan Plateau, part of the Mongolian Plateau, that indicates strong lake desiccation during the mid-Holocene. High resolution pollen data from Zhuyeze Lake, at the present summer monsoon margin, is also presented. These data show that present lakes and wetlands in the Juyanze Lake basin west of the Badain Jaran desert, in the Zhuyeze Lake basin between the Badain Jaran and Tengger deserts, and in lakes in the eastern Tengger desert, dried or experienced low lake levels in the mid-Holocene around 5000—7000 cal yr BP. Pollen data further indicate that the vegetation cover declined in both the local areas and in the Qilian Mountains, suggesting the climate was drier than that associated with the present Asian summer monsoon. This mid-Holocene drought interval was present throughout a quite large region of the south Inner Mongolian Plateau. The period was also probably colder, at least in the high Asian plateaus and mountains.

Precipitation variability in central Himalayas and its relation to Northern Hemisphere temperature

A 149.8-m-long ice core was drilled at theaccumulation area of Dasuopu glacier (28?3′N, 85?3′E, 7100 m a.s.l.) in the central Himalayas in 1997. The ice core was analyzed continuously for stable isotopes (d 18O), cations (Na+, K+, Mg2+, Ca2+) and anions (Cl-, 24SO,-3NO-) throughout the core. Cycles indicated by d 18O, cations and anions were identified and counted as seasonal fluctuations as annual increment from maximum to maximum values.Reconstructed 300-year annual net accumulation from thecore reveals a major precipitation trend for the central Himalayas with an average precipitation 750 mm per year. The trend, separated from the time series, shows a strongcorrelation to global temperature. Generally, as northernglobal temperature increases 0.1℃, the accumulationdecreases about 80mm and vise versa. This may suggests that monsoon precipitation in Himalayas have decreasedcontinuously in past decade as a response to global warming.

Formate and acetate as recorded in a mid-latitude glacier in west China

Formate and acetate are ubiquitous in the troposphere. Their occurrence is closely related to processes in the biosphere and contributes to an understanding of carbon biogeochemical cycles. A 43-year record of formate and acetate in an ice core from Glacier 1 (43?6′N, 86?9′E) at Urumqi river head, Tianshan, west China was investigated. Fluctuating between 22.7 ng·g-1 and 2830.7 ng·g-1, acetate concentration averages 373.2 ?376.1 ng·g-1 (mean ?1s, N = 541) and is the highest anion in the record. Next to acetate, the concentration for formate varies between 2.1 ng·g-1 and 795.5 ng·g-1 and averages 61.1 ?89.0 ng·g-1 (N = 541). The formate to acetate ratio averages 0.22 ?0.25 (N = 541), indicating that the chief source is from fossil fuel combustion, coal burning in particular. The two species co-varied in the past four decades and exhibited periods of high concentration from the early 1960s to the middle of 1970s and from the early 1980s to the middle of 1990s, separated by a time of the lower concentration between 1975—1980. These variations may reflect the local/regional anthropogenic pollution to the atmosphere as well as the economic development of northwestern China.