Yao Tandong

Recent glacial retreat in High Asia in China and its impact on water resource in Northwest China

Under the impact of climatic warming, the glaciers in the High Asia in China have been retreating continuously with negative glacial mass balance in recent several decades. The retreat became more intensive in the past 10 years. The spatial pattern of the glacial retreat in the High Asia in China is that the smallest magnitude of retreat is in the inland of the Tibetan Plateau, the magnitude increases from the inland to the margin of the Tibetan Plateau, and the largest magnitude at the margin of the Tibetan Plateau. The glacial retreat in the High Asia in China has an important impact on the water resource of the arid regions in Northwest China. This study shows that the glacial retreat in the 1990s has caused an increase of 5.5% in river runoff in Northwest China. In the Tarim River basin, the increase of river runoff is higher than 5.5%.

Mid-holocene climates and environments in China

Abstract This paper focuses mainly on the climatic and environmental variations 5 to 3 ka. B.P. with particular reference to one stable warmer and wetter millennium (7.2-6 ka B.P.). Some large-scale centennial warming was accompanied by an increase in precipitation owing to the expansion of the monsoon circulation, e.g. rapid warming during the period from 8.5 to 8.3 ka B.P. and was reflected in the high level of some inland lakes and the sudden expansion of vegetation in pollen diagrams. The growth of the Neolithic culture with agriculture and settlement in the present semi-arid area of Northwest China was undoubtedly related to the dramatic warming and wetting before 8 ka B.P. According to the proxy data of palynological studies, the deviation of annual mean temperature from todays about 7-6 ka B.P. was roughly estimated at about 1°C in South China, 2°C in the Changjiang (Yangtze) Valley, 3°C in North China and Northeast China. The strongest warming by 4–5°C was recorded in Qinghai-Xizang (Tibet) Plateau. The winter temperature rise was much greater than the annual average temperature. In the eastern half of China, the vegetation zones are mainly parallel to the latitude. During the climax of the Holocene warm period, the northern limit of the tropical monsoonal rain forest shifted less than 1° of latitude northward, the subtropical broad-leaved evergreen forest about 1° of latitude, the north subtropical deciduous and evergreen broad-leaved mixed forest about 3° of latitude in the coastal area but only 1–1.5° of latitude in mid-West China and the warm temperate deciduous forest moved 4° of latitude northward, greatly expanding its distribution. Further north, the cool temperate boreal forest withdrew from its southern boundary by about 2° of latitude. Global climatic warming in the mid-Holocene resulted in a sea-level rise. During the period from 6 to 5 ka BP. the sea-level was about 1–3 m higher than the present level. Large area of coastal lowland was submerged by sea water and frequency of occurrence of storm surges also increased during the high sea-level period.

Trends and features of climatic changes in the past 5000 years recorded by the Dunde ice core

A 81BO record from Dunde Ice Cap, located in the Qjlian mountains on the northeastern margin of the Tibetan Plateau, has been analyzed and interpreted. With an ice temperature of 7.3°C at a depth of 10 m and -4.7°C at the bottom of the ice cap, and an accumulation rate of400mma· l , the Dunde core has provided interesting results. The upper part of this core, core D-I, can be easily dated by a combination of 8IBO, microparticle concentration and conductivity. It can also be dated as far back as 4550 BP by counting dust layers in ice. Based on the time scale established by the above methods and on the 8lB Otemperature relation, the OIBO fluctuations in the upper 120 m of the core can be interpreted as mainly due to climatic changes during the past ~ 5000 years. The warmest periods in the past ~ 5000 years in the core were found to be cen tered on the presen t, 3000, and 4100 BP, and the cold er periods center around 500, 1200,4000, and 4500 BP. It is clear from the ice-core record that the Little Ice Age was only one of many cold periods in the past, although it was the cold est period in the past 500 years.

Relationships between δ18O in precipitation and surface air temperature in the Urumqi River Basin, East Tianshan Mountains, China

In order to evaluate the dependency of present-day δ18O in precipitation with temperature, individual precipitation events have been continuously sampled since 1996 at three stations along the Urumqi River Basin, eastern Tianshan mountains, north High China. Both the correlation and the positive slope of δ18O versus temperature increase with elevation for monthly averages, indicating that on long time scales high altitude precipitation δ18O should be a reliable indicator of regional temperature fluctuations, and supporting future ice core drilling.

Monsoon and Dust Signals Recorded in Dasuopu Glacier, Tibetan Plateau

During summer 1997, a 15 m firn core was recovered from Dasuopu glacier (28°23′ N, 85°44′ E; 7000 m a.s.l.) on the northwest margin of Xixabarngma Feng in the central Himalaya. Oxygen isotope values and concentrations of Ca 2+ , Mg 2+ , NH 4 + , SO 4 2− and NO 3 − were measured over the 10 years of snow accumulation captured in the firn core. The seasonal variations of δ 18 O values and major-ion concentrations in the Dasuopu core indicate that summer monsoon and dust signals are clearly recorded in Dasuopu glacier. Annual variations in δ 18 O values are controlled by the amount effect, with more negative (i.e. lighter) δ 18 O values representing summer monsoon precipitation characteristic of tropical regions. Higher concentrations of Ca 2+ , Mg 2+ and SO 4 2− reflect the influx of mineral aerosols from the vast arid and semi-arid desert regions to the north and west during the spring dust-storm period. High spring concentrations of NH 4 + and NO 3 − appear to reflect changes in regional biogenic-source strength.

Holocene climate variability archived in the Puruogangri ice cap on the central Tibetan Plateau

Abstract Two ice cores (118.4 and 214.7 m in length) were collected in 2000 from the Puruogangri ice cap in the center of the Tibetan Plateau (TP) in a joint US-Chinese collaborative project. These cores yield paleoclimatic and environmental records extending through the Middle Holocene, and complement previous ice-core histories from the Dunde and Guliya ice caps in northeast and northwest Tibet, respectively, and Dasuopu glacier in the Himalaya. The high-resolution Puruogangri climate record since AD 1600 details regional temperature and moisture variability. The post-1920 period is characterized by above-average annual net balance, contemporaneous with the greatest 18O enrichment of the last 400 years, consistent with the isotopically inferred warming observed in other TP ice-core records. On longer timescales the aerosol history reveals large and abrupt events, one of which is dated ∼4.7 kyr BP and occurs close to the time of a drought that extended throughout the tropics and may have been associated with centuries-long weakening of the Asian/Indian/African monsoon system. The Puruogangri climate history, combined with the other TP ice-core records, has the potential to provide valuable information on variations in the strength of the monsoon across the TP during the Holocene.

Evidence for Recent Climate Change from Ice Cores in the Central Himalaya

Abstract Comparison of the terminus locations of Rongbuk Glacier, Mount Everest, measured in 1966 and 1997 shows that in the past 30 years the glacier has retreated 170–270 m equivalent to a retreat speed of 5.5–8.7 m a–1 . During summer 1997, a 15 m firn core was recovered from Dasuopu glacier (28°23’ N, 85°44’ E; 7000 m a.s.D on the northwest margin of Xixabangma Feng, Xizang (Tibet). The seasonal variations of δ 18O values in the core indicate that monsoon signals are clearly recorded in the glacier. δ18O values are controlled by the amount effect in the monsoon season; more negative δ18O is representative of the monsoon season in snow layers. Analysis of the relationship between ice-core δ18O, sampled from 6500 m a.s.l. on the north side of Mount Everest, and instrumental series representing regional-scale precipitation, atmospheric circulation and temperature suggests a change in the relative influence of these parameters on δ18O since the 1940s. The results of the comparison add to and lengthen the sparse array of instrument data available for the Tibetan (Qinghai-Xizang) Plateau and demonstrate a recent decline in moisture flux for at least the southern part of the plateau. Glacier retreat, associated with a recent increase in temperature in the region, is coincident with this period of decreased moisture flux.

Relationship between δ D and δ 18 O in precipitation on north and south of the Tibetan Plateau and moisture recycling

The local meteoric water line (MWL) has been established from north to south of the Tibetan Plateau based on the measured results of δD and δ18O in precipitation and river water, and the relationship between MWL and moisture origins discussed. The spatial and seasonal variations ofd in precipitation and river water on the Tibetan Plateau have been studied. Results show that the spatial and seasonal variations ofd between north and south of the Tanggula Mountains are related to different moisture origins and water recycling.

Superimposed ice in glacier mass balance on the Tibetan Plateau

The relations betw een mass bal ance and meltwater refre ezing were examined on the basis of glac iolo gical obse rvations carried out in summer 1993 on Xiao Dongkemadi Glacier, Tanggula Mountai ns, central Tibetan Plateau. On this glacier, a part of melt water refreezes at the snovv/ice int erface as superimp osed ice. The amount of supe rimp osed ice formation was determ ined by both meltw ater supply and temperat ure condit ion of the glaci er. Snow-lay er thic kness on the glacier ice body is less than 2 m, even in the higher accu mulat ion zone. About 60% of meltw ater generate d in the accumula tion zone for the period ?v1ay-September was trapped at the snow/ice interface by refre ezing , and was not dis charged out of the glacie r. About 26% of accumulated snow to the glacier surface was repl aced on the snow/ice interface by refreez ing in the accumulation zone. These facts indicate that superim posed ice formation is quit e signifi cant for water retention in glaciers unde r low-pre cipitation conditions.

Mass balance of Xiao Dongkemadi glacier on the central Tibetan Plateau from 1989 to 1995

Abstract Data on the mass balance of Xiao Dongkemadi glacier in the Tanggula mountains, central Tibetan Plateau, were obtained over 5 5 years from 1989 to 1995. These are the first continuous mass-balance data for a continental-type glacier on the Tibetan Plateau, where the glacier accumulates during the summer monsoon (summer-accumulation-type glacier). Mass-balance vs altitude profiles were steeper in the negative than in the positive mass-balance years. This is considered to have resulted from the effect of summer accumulation. The annual mass balance is compared with air temperature, precipitation, and black-body temperature in the area including the glacier, which is calculated from infrared radiation observations by theJapanese Geostationary Meteorological Satellite. It was found that the interannual variation in the glacier mass balance was not closely related to maximum monthly mean air temperature, while it did have a relatively good correlation with maximum monthly mean black-body temperature.