Li Huilin

Preliminary results from measurements of selected trace metals in the snow-firn pack on Urumqi glacier No. 1, eastern Tien Shan, China

We present preliminary results on the occurrence of Pb, Cd, Zn, Al and Fe in dated samples collected from snow-firn packs at an altitude of 4130 m on Urumqi glacier No. 1, eastern Tien Shan. Extreme precautions for avoiding contamination were taken throughout the sampling, processing, transportation and analysis procedures. The concentrations of trace metals were determined by a double-focusing inductively coupled plasma mass spectrometer in an ultra-clean room. The average concentrations for these metals in surface snow are (in ng g -1 ): Pb, 2.4; Cd, 0.05; Zn, 10.0; Al, 100.0; and Fe, 130.0. These are higher concentrations (especially for Pb and Zn) than those in the polar and/or low- latitude remote areas. The data show that the input of trace metals to the snow has a clear seasonal change. Lower concentrations in surface snow can be found in July through September and higher concentrations from October to March, with an exception for January. The mean concentrations of the elements in the snow-firn pack also indicate seasonal variations and show a marked inverse relationship with temperature, possibly a result of meltwater percolation in the snow-firn pack.

Development of depth hoar and its effect on stable oxygen isotopic content in snow–firn stratigraphy on Ürümqi glacier No. 1, eastern Tien Shan, China

Abstract We report on the development of depth hoar and its relation to stable oxygen isotopic content in snow–firn stratigraphy in the percolation zone of Ürümqi glacier No. 1, eastern Tien Shan, China, during the period September 2004–August 2006. The essential condition for the development of depth hoar in the snow–firn pack is the temperature gradient. When the temperature gradient of the snow–firn pack reaches a maximum value of 13.0˚Cm–1 in mid-October, depth hoar begins to develop. By the end of March, the depth hoar might account for 25% of the total snow–firn pack depth. From April to June, as the weather becomes warm, the transport of water vapor diminishes and melting– regelation metamorphism replaces metamorphism caused by the temperature gradient. As a result, the depth hoar turns into coarse-grained firn. Fractionation of the oxygen isotopic content also occurs during formation of the depth hoar. The bottom 15 cm of the depth-hoar δ18O values were depleted in the lighter isotopic species as the snow sublimated from the lower to the upper crystals, and the δ values increased from –9.4% to –7.0% from 8 September 2004 to 25 January 2005. The upper 10 cm of the depth-hoar δ18O values were enriched in the lighter isotopic species and the δ values decreased from –6.8% to –9.3% during the same period.

Changes in CH4 and CO2 emissions from soils under flooded conditions after being exposed to FACE (free-air CO2 enrichment) for three years

To evaluate the variations of CO2 and CH4 emissions from FACE (free-air CO2 enrichment, F) soils three years after rice-wheat rotation FACE treatment, incubation experiments in the laboratory with laboratory and elevated CO2 concentration (1000 μl L−1) were carried out under flooded conditions at 25°C. Results show that soil organic carbon is increased by 11% after exposure to FACE treatment for three years. The results indicate that at laboratory and elevated CO2, the cumulative CO2 emissions from FACE soils are 35% and 22% higher than those from the ambient soils, whereas the cumulative CH4 emissions from FACE soils are 2.6 and 2.3 times that of ambient soils. Thus, there is a larger ratio of cumulative emissions of CH4 to CO2 in the soil F. The elevated CO2 concentration during the incubation stimulates the cumulative CO2 emission significantly, but its stimulation on CH4 emission is not statistically significant. The results indicate that the elevated atmospheric CO2 concentration stimulates the turnover rates of soil organic matter, with a net increase in soil organic matter content, and alters the CH4/CO2 ratio.

Depositional characteristics of NH4+ on Ürümqi glacier No. 1, eastern Tien Shan, China

Abstract Investigation into the depositional and post-depositional processes of atmospheric NH4 + on Ürümqi glacier No. 1 (UG1), China, was implemented within the Program for Glacier Processes Investigation (PGPI) campaign. Aerosol and surface snow samples were collected concurrently on a weekly basis from March 2004 to March 2005 in the UG1 accumulation zone at the headwaters of the Ürümqi river, eastern Tien Shan. All samples were analyzed for NH4 + and other chemical species. This paper investigates the seasonal variations of NH4 +. A significant linear relationship (R 2 = 0.70, N = 21, P < 0.01) between NH4 + concentrations in surface snow and aerosol was found during spring and summer, indicating that the warm–wet condition facilitates the air–snow exchange of NH4 +. Humidity was found to be a significant meteorological factor influencing NH4 + in deposition in autumn and winter. The NH4 + concentration in aerosol clearly shows a trend similar to that in surface snow, suggesting that the variation of atmospheric NH4 + might have been preserved in the surface snow. The possible source of NH4 + is discussed in this paper.