Isotopic analysis of the snow cover at an alpine glacier as an indicator of local climatic variations and isotopic homogenization processes

Stratigraphic variations of 18O/16O ratios of winter-accumulated snow at an alpine temperate glacier correspond to temporal pattern of local climatic variations. Although the snow is influenced by percolation and homogenization processes, the isotope stratigraphy in the glacier's accumulation area is not destroyed during the first part of summer. Below the equilibrium line altitude, rapid melting results in isotopic homogenization. Variation of δ 18O values in the firn are relatively small

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

Soluble ionic and oxygen isotopic compositions of a shallow firn profile, Baishui glacier no. 1, southeastern Tibetan Plateau

In the summer of 2004, a firn profile, 18.3 m long, extending down to glacier ice, was recovered in the accumulation area of the largest glacier, Baishui No. 1, on Yulong mountain, the southernmost glacier-covered area in mainland Eurasia. Multivariate empirical orthogonal function (EOF) and statistical correlation analyses of major-ion data from the profile demonstrate that three distinct types of ionic material contribute to the chemical characteristics of firn in this monsoonal region: material of marine origin, which is transported by the Indian southwest monsoon; crustal materials, which come from local sources; and anthropogenic pollutants, which are produced by industrial and agricultural activities in South Asia. Although the influence of post-depositional processes on the seasonal isotopic and soluble ionic compositions is significant, dust layers in the firn profile are clearly visible. Due to the effects of meltwater percolation, the dust layers generally coincide with late-summer snow surfaces. We therefore use the dust layers, combined with the seasonal variations of electrical conductivity (EC), Ca2+ and Mg2+, to establish a depth/age scale for the firn profile. The reconstructed net accumulation has a significant negative correlation with the temperature at Lijiang, whereas the correlation between the net accumulation and the precipitation amount at Lijiang is weak. Although the δ18O time series of the firn profile was modified significantly by meltwater percolation, the correlation between annual mean δ18O values and the Indian southwest monsoon index (WSI1) is significant. This result suggests that δ18O records from monsoon-influenced temperate glaciers can provide a valuable record of past variations of the Indian southwest monsoon.link_to_subscribed_fulltex

The irregular pattern of isotopic and ionic signals in the typical monsoon temperate-glacier area, Yulong mountain, China

Sampling was carried out at Baishui glacier No. 1, the largest glaciet on Yulong mountain, China, during the summers of 1999 and 2000, to investigate the spatial variations of oxygen isotopes in the atmosphere-glacier-river system. The results confirm that there is an apparent inverse relation between the oxygen isotopic composition of precipitation and air-temperature/precipitation amount in this region, with lower δ18O values when the amount of precipitation and air temperature in summer is higher, due to the influence of intense monsoon climate on the study area. There are marked differences in the δ18O values of winter-accumulated snow, glacial meltwater, summer precipitation and the glacier-fed river water. Spatial and temporal variations of isotopic composition arc controlled by varied weather conditions at different altitudes. Isotopic depletion or fractionation occurs during phase changes, snow-to-ice and ice-to-meltwater transformations and runoff processes. Variations of stable isotopes in glacier runoff can indicate variations of sources of supply. Ionic changes occur as a result of meltwater contact with glacier bed materials.link_to_subscribed_fulltex

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.link_to_subscribed_fulltex

Recent variability of the climate and glaciers in China's monsoon region

Climatic data, ice core records, the tree-ring index and recorded glacier variations have been compared, and used to reconstruct a history of climatic and glacial changes in the monsoonal temperate-glacier region of southwestern China during the last 400 years. The results indicate that the region's temperature has increased in a fluctuating manner during the 20th century, after the two cold stages of the Little Ice Age of the 17th-19th centuries, with a corresponding retreat of most of the glaciers during the 20th century, against a background of global warming. Rates of retreat accelerated after the 1980s. The few advancing glaciers that did exist have started to retreat in recent years. The amount, trend and amplitude of variation of precipitation have differed in different parts of the region. The climatic records in the Dasuopu ice core, from the Himalaya area in the western part of the region, show a decreasing trend in precipitation, the converse of the trend in temperature. However, in the Hengduan Mountains and other areas of the eastern part of the region, a rising trend in rainfall has accompanied increasing temperatures, a result of the variable atmospheric circulations from different sources. The data indicate that the Southwest Monsoon, which is the principal controlling factor in the Chinese monsoonal temperate-glacier region, can be classified into two parts. One is the Indian Monsoon from the Arabian Sea, passing across the Indian Peninsula. This transports the vapour for precipitation in the Himalaya area, the western part of the monsoonal temperate-glacier region. The other part is the Bengal Monsoon originating in the Bay of Bengal, passing over Bengal and Burma. This is the major source of precipitation in the Hengduan Mountains and other areas in the eastern part of the region. In addition, the eastern part is influenced by the Southeast Monsoon arriving from the western Pacific, whilst the western part is affected in winter by the southern branch of the westerly circulation. This complex atmospheric situation results in differing patterns of precipitation in the western and eastern zones. Although it is clear that both temperature and precipitation affect the glaciers, further work is needed to confirm which is the major factor influencing present glacier change.link_to_subscribed_fulltex

Asynchronous Holocene climatic change across China

A review of Holocene climatic variations in different parts of China shows that they were asynchronous. Proxy data from ice cores, pollen, loess, lacustrine sediments, and changes of sea and lake levels demonstrate that many warm and cold oscillations have occurred in China during the Holocene, including a most important climatic event known as the "Holocene optimum," a milder and wetter period, and that the duration and amplitude of the optimum period, as well as its start and end times, differed in different parts of China. Uplift of the Tibetan plateau over the past millions of years led to the development of the monsoon climate and to complex atmospheric circulation over continental China during the Holocene. As a result, the Holocene optimum began and terminated earlier in high-altitude regions of western China than at lower elevations in eastern China, and the amplitude of the variations was lower in the east. This suggests that the western higher-altitude areas were more sensitive to climatic change than were the eastern lower-altitude areas. Holocene climatic records in the Dunde and Guliya ice cores do not correspond. Inverse δ 18O variations between the two cores indicate that the effects of climate and atmospheric processes on the stable isotopes at the two sites differed. The correlation between the isotopic composition of carbonates in lake deposits in western China and climatic variations is similar to that in the ice cores. The climatic resolution in ice cores and lake sediments is higher than that in other media. The lack of precise correspondence of climatic records constructed on the basis of proxy data from different parts of China is a result of the different locations and elevations of the sampling sites, the different resolutions of the source material, and the varied climatic conditions within China. Further work is needed to confirm both the conclusions and the inferences presented here. © 2003 University of Washington. All rights reserved.link_to_subscribed_fulltex

Spatial and temporal variations of oxygen isotopes in snowpacks and glacial runoff in different types of glacial area in western China

In order to improve understanding of spatial and temporal variations of stable isotopes in atmospheric precipitation, snow cover and glacier meltwater in different regions of China, samples were collected for isotopic analysis in four areas: Yulong mountain, Yunnan Himalaya (temperate-glacier area); Samdain Kangsang mountain, Nyainqêntanglha Shan (subpolar-glacier area); the headwater area of the Ürümqi river, Tien Shan (subpolar-glacier area); and Muztag mountain, Pamirs (polar-glacier area). Sampling was undertaken in both summer and winter between 2000 and 2003. The δ 18O values show a 'temperature-altitude effect' in new winter snow on Yulong mountain, reflecting the condensation and fractionation processes associated with the winter monsoon, but a different, more complex pattern in residual snow deposited during the summer monsoon; this old snow is influenced by the 'precipitation amount effect', solar radiation and evaporation, and the water content of the snowpack. The summer precipitation at Samdain Kangsang mountain is associated with the summer monsoon. There is a marked precipitation amount effect during the long passage of the southwest/India monsoon from the distant moisture source to Samdain Kangsang mountain, and the summer precipitation is strongly depleted of the heavy isotope. Above 6000 m, the high radiation flux causes much evaporation from the snow surface. The associated 18O enrichment of the snow is reflected in a 'reverse altitude effect'. The δ 18O values in the summer snowpack of the Tien Shan and Muztag mountain decrease with increasing altitude and decreasing air temperature, indicating a temperature-altitude effect. Post-depositional processes cause isotopic changes during the transformation of snow/firn/ice to meltwater; the effects are much stronger at temperate than at polar glaciers. Moreover, changes in the isotopic signal at both temperate and polar glaciers can result from evaporation, sublimation, ablation and drifting.link_to_subscribed_fulltex