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Muztagata. Dunde. Tanggula. Dasuopu. Everest. Grain size, concentration, flux and composition of Asian dust in snow and ice cores on Tibetan Plateau Guangjian Wu, Tandong Yao, Baiqing Xu, Lide Tian, Chenglong Zhang, Xuelei Zhang

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Grain size, concentration, flux and composition of Asian dust in snow and ice cores on Tibetan Plateau

Guangjian Wu, Tandong Yao, Baiqing Xu, Lide Tian, Chenglong Zhang, Xuelei Zhang

(Institute of Tibetan Plateau Research, Chinese Academy of Sciences.


(The Third Pole Environment)

Introduction: The multi-year record of dust particles in ice cores, analyzed by the consistent method methodology and over the same particle size range, which makes inter-regional comparisons far more reliable, shows regional differences in the grain size, concentration and flux. The dust isotopic composition is also presented in purpose of provenance tracing, transport pathway detecting, and regional contribution to remote sites. The physical and chemical properties of dust particles from Tibetan Plateau ice cores, which are well analogue of the long-range transported Asian dust in the mid- and upper troposphere, give a comprehensive understanding on the its climatic impact.

2. Dust Concentration and Flux

Figure 2-1. Plots of dust flux versus accumulation and dust flux versus mass concentration in ice cores. A previous study suggested that at any particular location the variation in atmospheric loading is the main cause of year-to-year variation in dust deposition, while the dust flux appears to be relatively independent of annual snow accumulation (Wake et al., 1994). However, flux is tightly correlated with accumulation at Muztagata (7010 m) and Everest, albeit this correlation is not significant at Tanggula (whose accumulation is lowest).

Table 2. Dust concentration, flux and accumulation in ice cores from the Tibetan Plateau

1. Volume-grain size distribution

3. Dust Composition: isotope tracing for Dunde dust

Figure 2-2. The calculated multi-year (March 2000–February 2009) average MODIS AOD index over and near the Tibetan Plateau. The regional AOD distribution is in accordance with the dust flux in ice cores.

Fig. 1-1 Volume size distributions (in 50 channels on logarithmic scale) of microparticles in low- and high concentration samples (black curves) from the Muztagata and Dunde ice cores. Only the high concentration samples obey the log-normal distribution (fitted by red curves). Only particles of 1–30μm diameter were measured.

Fig. 3.1 The Sr−Nd isotopic composition of dust from a shallow Dunde ice core (38º06'N, 96º24'E, 5325 m), Northern China, is analyzed in order to trace its source regions and the provenance of long-range transported Asian dust. Dunde dust samples show similar Sr (87Sr/86Sr averages 0.719982) and Nd (εNd(0) averages −10.6) isotope to desert sand from Taklimakan and Qaidam, revealing that the Tarim and Qaidam Basins are the most possible source areas for Dunde dust, while the contribution from Badain Jaran and Tengger seems very small or unlikely.

Log-normal Fitting Formula: D is the particle diameter, Dm the mode, σthe standard deviation (SD) and VTotal the total volume.

4. Summary

1. Only high-concentration samples obey the log-normal distribution in volume, with mode sizes ranging from 3 to 16 mm. The log-normal distribution was largely attributed to the mid-sized particles between 3~15 mm, which contribute a majority (>70%) of the total volume.

2. The coarse particles are common in the upper-level troposphere over the Tibetan Plateau, suggesting that the lifetime of silt particles in atmosphere, especially for the large particles, might still be underestimated in current climate models.

3. Dust flux in ice cores from the Tibetan Plateau strongly depends on mass concentration, while the correlation between accumulation and flux varies at different sites, but they are not independent of each other.

4. Dust flux over the Tibetan Plateau decreases from the northwest to the southeast, suggesting a major dust transport route. The northern Tibetan Plateau experiences the highest dust flux, which is about 10 times higher than that in the southern Plateau. The calculated dust flux in ice cores is in accordance with satellite results.

5. The Sr–Nd isotopic composition of Dunde dust indicate that Tarim and Qaidam Basins are the most possible provenance. Dunde dust resembles that of North Pacific and Greenland dust in isotope composition, indicating that the important provenance of end members of the Asian dust seems to be Taklimakan on a regional scale.

Fig. 3.2 The Sr–Nd isotopic composition of Dunde dust, Chinese loess, and the end members of Asian dust. The similarity between Dunde and Greenland dust suggests that their same provenance on decadal to century timescale, although the seasonal variation is cleare for the latter.

Table 1. Statistical results for the log-normal fitting parameters for particles in ice cores from the Tibetan Plateau