Isotopic and chemical analyses of a temperate firn core from a Chine alpine glacier and its regional climatic significance

Mt. Yulong is the southernmost currently glacier-covered area in Eurasia, including China. There are 19 sub-tropical temperate glaciers on the mountain, controlled by the south-western monsoon climate. In the summer of 1999, a firn core, 10.10 m long, extending down to glacier ice, was recovered in the accumulation area of the largest glacier, Baishui No. 1. Periodic variations of climatic signals above 7.8 m depth were apparent, and net accumulation of four years was identified by the annual oscillations of isotopic and ionic composition. The boundaries of annual accumulation were confirmed by higher values of electrical conductivity and pH, and by dirty refreezing ice layers at the levels of summer surfaces. Calculated mean annual net accumulation from 1994/1995 to 1997/1998 was about 900 mm water equivalent. The amplitude of isotopic variations in the profile decreased with increasing depth, and isotopic homogenization occurred below 7.8 m as a result of meltwater percolation. Variations of δ(18)O above 7.8 m showed an approximate correlation with the winter climatic trend at Li Jiang Station, 25 km away. Concentrations of Ca(2+) and Mg(2+) were much higher than those of Na(+) and K(+), indicating that the air masses for precipitation were mainly from a continental source, and that the core material accumulated during the winter period. The close correspondence of Cl(-) and Na(+) indicated their common origin. Very low concentrations of SO(2-)4 and NO(-)3 suggest that pollution caused by human activities is quite low in the area. The mean annual net accumulation in the core and the estimated ablation indicate that the average annual precipitation above the glacier's equilibrium line is 2400 - 3150 mm, but this needs to be confirmed by longterm observation of mass balance

Winter-Season Climatic Signals in the Recently Deposited Snowpack on a Norwegian Alpine Glacier

Vertical variations of oxygen isotopes in the snow which accumulates during the winter at the Norwegian glacier Austre Okstindbreen are not entirely eliminated after 1-2 months of ablation in the following summer. Survival of isotopic signals closely relates to the re-freezing capacity of snow accumulated in winter when its temperature was below 0°C. The meltwater re-freezes in layers formed in winter hindered subsequent meltwater percolation in summer when snow temperature was at melting point and, therefore, varied isotopic record was reserved between these ice layers. The isotopic record in snowpack can provide an estimate of the approximate trend of the most recent winter season temperatures. The relationship between regional temperature changes and б18O values in the snowpack is affected by many natural factors, but 1989-90 (a glacier balance year) winter air temperatures were reflected in the snow which remained on the glacier Austre Okstindbreen at an altitude of 1,350 m in July 1990. There was larger amplitude of variations of б 18O values in the 4.1 m of snow above the 1989 summer surface, but variations in the underlying firn were relatively small. Meltwater percolation modifies the initial variations of б 18O values in the snowpack. At a site below the mean equilibrium line altitude on Austre Okstindbreen, increased isotopic homogenization within a ten-day period in July accompanied an increase of the mean б 18O value. Although the isotopic record at a temperate glacier is likely to be influenced by more factors than is that at polar glaciers, it can provide an estimate of the approximate trend of recent local temperature variations.</jats:p

Distribution features of stable oxygen isotopes in the typical monsoon temperate glacier region, Mountain Yulong in China

During the summers of 1999 and 2000, sampling was carried out in Mt. Yulong, for the investigation of the spatial distribution of oxygen stable isotope in the atmospheric-glacial-hydro system and similar results obtained in the two years have confirmed our conclusion. There is an evident negative correlation between stable isotopic composition and air temperature precipitation amount, suggesting that there exists a strong "precipitation amount effect" in this typical monsoon temperate-glacier region. There are marked differences between the δ(18)O values in winter accumulated snow, glacial meltwater, summer precipitation and glacier-feeding stream. Under the control of varied climatic conditions, spatial and temporal variations of above glacial-hydro mediums are apparent. Isotopic depletion or fractionation and ionic changes had occurred during the phase change and transformation processes of snow-ice, ice-meltwater, flowing of runoff and contact with bedrock. The variation of stable isotope in a runoff can reflect not only its own flowing process but also its different feeding sources

Winter-season climatic signals in the recently deposited snowpack on a Norwegian alpine glacier

Vertical variations of oxygen isotopes in the snow which accumulates during the winter at the Norwegian glacier Austre Okstindbreen are not entirely eliminated after 1-2 months of ablation in the following summer. Survival of isotopic signals closely relates to the re-freezing capacity of snow accumulated in winter when its temperature was below 0°C. The meltwater re-freezes in layers formed in winter hindered subsequent meltwater percolation in summer when snow temperature was at melting point and, therefore, varied isotopic record was reserved between these ice layers. The isotopic record in snowpack can provide an estimate of the approximate trend of the most recent winter season temperatures. The relationship between regional temperature changes and δ 18O values in the snowpack is affected by many natural factors, but 1989-90 (a glacier balance year) winter air temperatures were reflected in the snow which remained on the glacier Austre Okstindbreen at an altitude of 1,350 m in July 1990. There was larger amplitude of variations of δ 18O values in the 4.1 m of snow above the 1989 summer surface, but variations in the underlying firn were relatively small. Meltwater percolation modifies the initial variations of δ 18O values in the snowpack. At a site below the mean equilibrium line altitude on Austre Okstindbreen, increased isotopic homogenization within a ten-day period in July accompanied an increase of the mean δ 18O value. Although the isotopic record at a temperate glacier is likely to be influenced by more factors than is that at polar glaciers, it can provide an estimate of the approximate trend of recent local temperature variations