Five shallow ice cores have been recovered from the summit of the Gregoriev Ice Cap (Photo2)(41.98 °N; 77.92 °E; 4609 m a.s.l.) between 1990 and 2003. The 1990 ice core has been analyzed for stable isotopes, microparticle concentration, major ions (K+, Na+, Ca2+, Mg2+, SO42-, NO3-, Cl-) and total beta-activity (Fig. 2). The 2001 and 2003 ice cores have been analyzed for stable isotopes and concentration of radionuclides (40K, 226Ra, 232Th, 235U, 238U, 137Cs, 90Sr) (Fig. 3). These ice cores have been dated on the base of set of reference horizons and annual microparticle concentrations. The detailed stratigraphic records for the top sections of the 1990 and 2001 cores indicate that 3.8 m of snow/firn accumulated in the 11 years. The mean annual net accumulation derived from this comparison is 0.35 m in ice equivalent (i.e.) (260 mm w.e.) for the period from 1990 to 2001. The net accumulation from 1963 to 1990 was 0.42 m i.e. (320 mm w.e.). Moreover decrease of firn pack depth from 9 to 6 meters has been observed at 4450 m site between 1962 and 2003. Over the same period infiltration ice concentration has been increased as a result of more intensive melt water percolation. Considerable enrichment in stable isotope composition for the top section of the 1990 and 2003 ice cores has been measured. Local meteoric water line is compared with global one. The relationship between d18O in ice cores and mean summer air temperature has been determined (Fig. 4).
Temperatures were measured in the boreholes on the top of the Gregoriev Ice Cap (4609 m) in 1990, 2001 and 2003. Their comparison shows an approximate 1°C warming at 10 m depth between 1990 and 2003. Likewise considerable warming has been measured in boreholes drilled at 4450 m in 1962 and 2003. The temperature rise is ~2.5°C at 10m and 0.5°C at 30 m depth (Fig. 5).
The comparison of airborne images from 1956 and 1988 and satellite image from 2001 show considerable retreat of glacier terminus since 1956 (Fig. 6, 7). This regional warming marked by changes of ice content and stable isotopic composition of the ice cores along with increasing glacier temperatures is consistent with data from the Tien Shan meteorological station.
Photo 2.Gregoriev Ice Cap, 2003. Photo by V.Mikhalenko
|Fig. 2. Profiles of the 0.1-m averages of the total b-activity, d18O, (2),total particles, large particles (³ 0.63 mм), electrical conductivity, NO3-, SO42-, and Cl- in Gregoriev Ice Cap ice core in 1990|
|Fig. 3. Gregoriev Ice Cap. Variations of radionuclides in 2001 ice core: 1 – measured activity, 2 – primary activity||Fig. 4. The relationship between d18O in ice cores and mean summer air temperature|
|Fig. 5. Depth-temperature profiles in the boreholes at 4440 m a.s.l. in 1962 and 2003||Fig. 6. Glacier area has been changed since 1860 from 9.8 km2 to 9.46 km2 in 1956, and to 8.9 km2 in 1988|
Fig. 7. The comparison of airborne images from 1956 and 1988 show considerable retreat of glacier terminus since 1956.
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Thompson, L.G., Mikhalenko, V., Mosley-Thompson, E. et al., 1997. Ice core recent climatic variability: Gregoriev and It-Tish Ice Caps in Central Tien Shan , Central Asia . - Data of Glaciological Studies, Vol. 81, pp. 100-109. (PDF)
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Mikhalenko, V.N., Kutuzov S.S., Faizrakhmanov F.F. et al., 2005. Glacier recession in the Tien Shan Mountains , Central Asia: ice-core and borehole temperature evidence. - Data of Glaciological Studies, Vol. 98, pp. 175-182 (in Russian with English summary) (PDF)
Nagornov, O.V., Konovalov, Yu.V., 2005. Forecast of development of Gregoriev Glacier ( Tien Shan ). pp. 183-193 (in Russian with English summary) (PDF)
Nagornov, O. V., Sokolov, E. S., Sergienko, O. V., 2006. Formation of annual layer structures in glaciers with strong summer melting. - Data of Glaciological Studies, Vol. 100 (in Russian with English summary) (PDF)