Jianchen Pu

Recent Glacial Retreat and Its Impact on Hydrological Processes on the Tibetan Plateau, China, and Surrounding Regions

ABSTRACT Glacial retreat on the Tibetan Plateau and surrounding regions is characteristic since the 1960s and has intensified in the past 10 yr. The magnitude of glacial retreat is relatively small in the interior of the Tibetan Plateau and increases to the margins of the plateau, with the greatest retreat around the edges. Glacial retreat in this region is impacting the hydrological processes in the Tibetan Plateau and surrounding regions. The glacial retreat has caused an increase of more than 5.5% in river runoff from the plateau. In some areas, such as the Tarim River basin, the increase in river runoff is greater. Glacial retreat has also caused rising lake levels in the areas with large coverage of glaciers, such as the Nam Co Lake and Selin Co Lake areas. Rising lake levels are devastating grasslands and villages near the lakes.

Glacier variations and climate warming and drying in the central Himalayas

Repeat measurements of glacier terminus positions show that glaciers in the central Himalayas have been in a continuous retreat situation in the past decades. The average retreat rate is 5.5–8.7 m/a in Mt. Qomolangma (Everest) since the 1960s and 6.4 m/a in Mt. Xixiabangma since the 1980s. In recent years, the retreat rate is increasing. Ice core studies revealed that the accumulation rate of glaciers has a fluctuating decrease trend in the last century with a rapid decrease in the 1960s and a relatively steady low value afterwards. Meteorological station record indicates that the annual mean temperature has a slow increase trend but summer temperature had a larger increase in the past 30 a. All these suggest that the glacier retreat results from precipitation decrease in combination with temperature increase, and hence glacier shrinkage in this region will speed up if the climatic warming and drying continues.

Glacier variations and climate change in the central Himalaya over the past few decades

Abstract Glacier variation is one of many indicators of climate change. Repeat measurements of the glacier terminus positions for selected glaciers in the central Himalaya document that they have been in a state of continuous retreat over the past few decades. Since the 1960s the average retreat rate on the north slope of Qomolangma (Mount Everest) is 5.5–9.5ma-1 and on Xixiabangma it is 4.0–5.2ma-1. Many glaciers on the south slope of the central Himalaya have been in retreat, and recently their retreat rate has accelerated. Ice-core studies show that the annual accumulation on these glaciers has fluctuated, but over the last century it has declined. It decreased rapidly in the 1960s and has remained consistently below the long-term mean thereafter. Meteorological station records indicate that the annual mean temperature in the region has slowly increased, particularly during the summer months. The strongest warming has occurred in the last 30 years. These data suggest that the current glacier retreat is due to the combined effect of reduced precipitation and warmer temperatures, and, if these conditions continue, the glaciers in the region will continue to shrink.

Relationship between calcium and atmospheric dust recorded in Guliya ice core

By the analyses of Guliya ice core on the Tibetan Plateau, it was found that the calcium (Ca2+) originated from the terrestrial source is the main cation of soluble aerosol and a good proxy of the atmospheric component and environment in the mountain ice core located in the mid-low latitude arid regions. Evident variation of Ca2+ concentration has been found in the Guliya ice core since the Last Interglaciation with two relatively strong increase periods and two weak increase periods. These variations are generally related to climatic changes: high Ca2+ concentration periods coincide with cold periods and low Ca2+ concentration periods coincide with warm periods. However, Ca2+ concentration does not always decrease (increase) with climate warming (cooling). The magnitude and phase of Ca2+ concentration does not always match temperature either. The changes of atmospheric circulation, land surface condition and atmospheric humidity might be important factors which influence Ca2+ concentration besides temperature.

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 new type of ice formation zone found in the Himalayas

Ice formation was studied on the Dasuopu Glacier located in the Mount Xixabangrna (28°23′ N, 85°43′E) in the Himalayas. Snow pits and shallow ice cores are analyzed to reveal ice formation process. The results show that the ice formation process, or in other words, the process of densitification, on the col (7 000 m a. s. I.) of the Dasuopu Glacier is a stable, slow and gradual process. The snow-ice transformation on the glacier is estimated to be 30–40 m below the surface. The temperature on the Dasuopu Glacier is very low (~ - 14°C at 10 m) and similar to that in polar type ice cap. We, therefore, speculate that the process of snow-ice transformation is undertaken under snow pressure, and that there is a percolation zone on the Dasuopu Glacier. The high altitude of the col and monsoon snow fall accompnied by heavy cloud and high albedo favorite the percolation zone formation.

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.

Fukushima Nuclear Accident Recorded in Tibetan Plateau Snow Pits

The β radioactivity of snow-pit samples collected in the spring of 2011 on four Tibetan Plateau glaciers demonstrate a remarkable peak in each snow pit profile, with peaks about ten to tens of times higher than background levels. The timing of these peaks suggests that the high radioactivity resulted from the Fukushima nuclear accident that occurred on March 11, 2011 in eastern Japan. Fallout monitoring studies demonstrate that this radioactive material was transported by the westerlies across the middle latitudes of the Northern Hemisphere. The depth of the peak β radioactivity in each snow pit compared with observational precipitation records, suggests that the radioactive fallout reached the Tibetan Plateau and was deposited on glacier surfaces in late March 2011, or approximately 20 days after the nuclear accident. The radioactive fallout existed in the atmosphere over the Tibetan Plateau for about one month.

Effects of ion elution on formation of ice core record

PREVIOUS studies have shown that 50%—80% of the pollutant load in the snowpacks can be released with the first 30% of the meltwater. So the ion elution can alter the seasonal-layer distribution of chemical contents deposited in the snowpacks and form a new chemical distribution, which is preserved perpetually as the ice core record. In order to reconstruct the paleoclimate and paleo-environment from the ice core with high accuracy, it is necessary to determine the correlation of the chemical distribution between pre- and post-ion elution processes.