B. Grigholm

Twentieth century dust lows and the weakening of the westerly winds over the Tibetan Plateau

Understanding past atmospheric dust variability is necessary to put modern atmospheric dust into historical context and assess the impacts of dust on the climate. In Asia, meteorological data of atmospheric dust is temporally limited, beginning only in the 1950s. High-resolution ice cores provide the ideal archive for reconstructing preinstrumental atmospheric dust concentrations. Using a ~500 year (1477–1982 A.D.) annually resolved calcium (Ca) dust proxy from a Tibetan Plateau (TP) ice core, we demonstrate the lowest atmospheric dust concentrations in the past ~500 years during the latter twentieth century. Declines in late nineteenth to twentieth century Ca concentrations significantly correspond with regional zonal wind trends from two reanalysis models, suggesting that the Ca record provides a proxy for the westerlies. Twentieth century warming and attendant atmospheric pressure reductions over northern Asia have potentially reduced temperature/pressure gradients resulting in lower zonal wind velocities and associated dust entrainment/transport in the past ~500 years over the TP.

Atmospheric soluble dust records from a Tibetan ice core: Possible climate proxies and teleconnection with the Pacific Decadal Oscillation

record (1935–2005). Statistical analysis of major ion time series suggests that atmospheric soluble dust species dominate the chemical signature and that background dust levels conceal marine ion species deposition. The soluble dust time series have interspecies relations and common structure (empirical orthogonal function (EOF) 1), suggesting a similar soluble dust source or transport route. Annual and seasonal correlations between the EOF 1 time series and National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis climate variables (1948–2004) suggest that the Mt. Geladaindong ice core record provides a proxy for local and regional surface pressure. An approximately threefold decrease of soluble dust concentrations in the middle to late 1970s, accompanied by regional increases in pressure and temperature and decreases in wind velocity, coincides with the major 1976–1977 shift of the Pacific Decadal Oscillation (PDO) from a negative to a positive state. This is the first ice core evidence of a potential teleconnection between central Asian atmospheric soluble dust loading and the PDO. Analysis of temporally longer ice cores from Mt. Geladaindong may enhance understanding of the relationship between the PDO and central Asian atmospheric circulation and subsequent atmospheric soluble dust loading.

Chemical Records in Snowpits from High Altitude Glaciers in the Tibetan Plateau and Its Surroundings.

Glaciochemistry can provide important information about climatic change and environmental conditions, as well as for testing regional and global atmospheric trace transport models. In this study, δ18O and selected chemical constituents records in snowpits collected from eight glaciers in the Tibetan Plateau and adjacent areas have been investigated. Drawing on the integrated data, our study summarized the seasonal and spatial characteristics of snow chemistry, and their potential sources. Distinct seasonal patterns of δ18O values in snowpits indicated more negative in the south TP controlled by Indian monsoon, and less negative in the north TP and Tien Shan. Overall increasing concentrations of microparticles and crustal ions from south to north indicated a strength of dust deposition on glaciers from semi-arid and arid regions. Principal component analysis and air mass trajectories suggested that chemical constituents were mainly attributable to crustal sources as demonstrated by the high concentrations of ions occurring during the non-monsoon seasons. Nevertheless, other sources, such as anthropogenic pollution, played an important role on chemical variations of glaciers near the human activity centers. This study concluded that air mass transport from different sources played important roles on the spatial distributions and seasonality of glaciochemistry.

A Twentieth Century Major Soluble Ion Record of Dust and Anthropogenic Pollutants from Inilchek Glacier, Tien Shan

Using a high-resolution (~18 samples/year) major soluble ion record (Na+, K+, Mg2+, Ca2+, Cl-, NO3- and SO42-) covering the period 1908-1995 AD from the Inilchek Glacier, Tien Shan, Kyrgyzstan we provide a detailed climate and environmental proxy record for the region. Chemical concentrations, empirical orthogonal function analyses and non-crustal excess calculations are used to identify natural and potential anthropogenic depositional trends. Dominant dust proxy species (i.e. Ca2+) reveal highest concentrations during the 1950s-1970s, with declining decadal trends through the end of the record. These trends likely reflect decreases in central Asian dust storm activity post-1950, which has been associated with coupled atmospheric circulation variability and anthropogenic activities. Comparison between Ca2+ and ERA-interim (1979-1995) climate reanalysis data indicates a strong relationship to spring (March, April and May) geopotential height patterns in northwest China and southern Siberia associated with the Siberian High. Non-crustal contribution (excess) estimates of NO3-, K+, SO42-, and Cl- concentrations suggest discernable anthropogenic inputs began between the 1950s-1970s, increased into the mid/late1980s and declined in the 1990s. Excess trends coincide with Former Soviet Union (FSU) consumption, production and emission of fossil fuels and fertilizers, reflecting the rapid growth of agriculture and industry, as well as economic declines in the mid-late 1980s/early 1990s. Excess-Cl- trends reflect timings that coincide with the construction of the Pavlodar Chemical Plant and the military production of Cl2 in Kazakhstan. NOAA HYSPLIT back-trajectory frequency analysis suggests eastern Uzbekistan (e.g. Fergana Valley), Kyrgyzstan and southern Kazakhstan as the primary pollutant sources to the study region.

Twentieth-century warming preserved in a Geladaindong mountain ice core, central Tibetan Plateau

Abstract High-resolution δ18O records from a Geladaindong mountain ice core spanning the period 1477-1982 were used to investigate past temperature variations in the Yangtze River source region of the central Tibetan Plateau (TP). Annual ice-core δ18O records were positively correlated with temperature data from nearby meteorological stations, suggesting that the δ18O record represented the air temperature in the region. A generally increasing temperature trend over the past 500 years was identified, with amplified warming during the 20th century. A colder stage, spanning before the 1850s, was found to represent the Little Ice Age with colder periods occurring during the 1470s–1500s, 1580s–1660s, 1700s–20s and 1770s–1840s. Compared with other temperature records from the TP and the Northern Hemisphere, the Geladaindong ice-core record suggested that the regional climate of the central TP experienced a stronger warming trend during the 20th century than other regions. In addition, a positive relationship between the Geladaindong δ18 O values and the North Atlantic Oscillation index, combined with a wavelet analysis of δ18 O records, indicated that there was a potential atmospheric teleconnection between the North Atlantic and the central TP.