Keqin Duan

Geochemical analyses of a Himalayan snowpit profile: implications for atmospheric pollution and climate

Abstract Organic compounds, extracted from snow and ice from the Dasuopu glacier, on the Qinghai-Tibetan Plateau in Southwest China at an altitude of 7000 m above sea level (asl), were identified through pre-enrichment, solvent extraction and subsequent GC–MS analysis. The average concentration of the extractable organic matter reached 45.4 μg/l. C15–C33 n-alkanes, C6–C18 n-alkanoic acids, C24–C31 n-alkan-2-ones and esters were derived from subtropical higher plants, as well as marine algae and bacteria. Organic compounds, indicative of petroleum residues such as automobile and diesel exhaust were also unexpectedly identified in the glacial snow. These included n-alkanes, alkylcyclohexanes, pristane, phytane, extended C19–C29 tricyclic terpanes, a C24 tetracyclic terpane, C27–C35 αβ hopanes, and C27–C29 steranes. Their presence indicates that the remote mountainous region and, to some extent, the middle-upper troposphere are polluted by human activities. Concentrations of some organic compounds, and total extractable organic matter, display a weak seasonal variation, postulated to be related to the location of middle-upper troposphere. The C17 n-alkane abundance and some molecular ratios exhibit a stronger seasonal variation, which may signify strong climatic change.

Five decades of shrinkage of July 1st glacier, Qilian Shan, China

A survey of July 1st glacier, Qilian Shan, China, was carried out in 2002. Previously, the glaciers boundary had been recorded in 1956, and further research had been carried out in the mid- 1970s and 1980s. Our survey reveals that area shrinkage and surface lowering have accelerated in the past 15 years. Surface elevation changes can result from changes in accumulation, surface melting and emergence velocity. The contributions of these elements to surface lowering are evaluated at the lower part of the glacier from observations of surface velocity, ice thickness and precipitation, and from temperature data near the glacier. Apart from the effect of glacier ice redistribution, our analysis reveals quantitatively that the recent accelerated glacier shrinkage has been caused by increasing temperature. Furthermore, it is established that meltwater discharge from the glacier in the past 17 years has increased due to glacier shrinkage, by about 50% over that from 1975 to 1985.

A shallow ice core re-drilled on the Dunde Ice Cap, western China: recent changes in the Asian high mountains

A 51?m deep ice core was re-drilled on the Dunde Ice Cap of western China in 2002, 15 years after the previous ice core drilling in 1987. Dating by seasonal variations in ?18O and particle concentration showed that this 51?m deep ice core covered approximately the last 150 years. The stratigraphy and density showed that more than 90% of the ice core was refrozen ice layers, which comprised less than 5% of the annual accumulation in the older core. This indicates that the ice cap had experienced a more intense melting since 1987, possibly due to climate warming in this region. Mean net accumulation since the last drilling (2002?1987) was 176?mm?a?1, which was considerably smaller than that obtained from the 1987 core (390?mm?a?1, 1987?1963), indicating a significant decrease of net accumulation on the ice cap in the more recent period. The ?18O record showed an increasing trend in the late 19th century and the highest in the 1950s, which is consistent with the previous core findings. However, there has been no significant increase in ?18O during the last two decades, in contrast to the warming trends suggested by the melt features and other climate records. This discrepancy may be due to the modification of ?18O records by melt water runoff, percolation, and refreezing on the ice cap. Results strongly suggest recent significant mass loss of glaciers in the Asian high mountains and serious shortage of water supply for local people in this arid region in the near future.

Response of monsoon vari- ability in Himalayas to global warming

Reconstructed annual net accumulation from the Dasuopu ice core recovered in Himalayas, with a good correlation to Indian monsoon, reflects a major precipitation trend in central Himalayas. The Dasuopu accumulation (DSP An) also shows a strong correlation to the Northern Hemispheric temperature. Generally, as the Northern Hemispheric temperature increases by 0.1 K, the accumulation decreases by about 90 mm and vise versa. Under the condition of global warming, especially since 1920, the Northern Hemispheric mean temperature has increased by about 0.5 K, whereas accumulation in Dasuopu ice core has decreased by about 450 mm. According to the relationship between accumulation and temperature, a scenario prediction of monsoon rainfall in central Himalayas is made.