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The Taklamakan Desert (TD) is a major source of mineral dust emissions into the atmosphere. These dust particles have the ability to darken the surface of snow on the surrounding high mountains after deposition, significantly impacting the regional radiation balance. However, previous field measurements have been unable to capture the effects of severe dust storms accurately, and their representation on regional scales has been inadequate. In this study, we propose a modified remote-sensing approach that combines data from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite and simulations from the Snow, Ice, and Aerosol Radiative (SNICAR) model. This approach allows us to detect and analyze the substantial snow darkening resulting from dust storm deposition. We focus on three typical dust events originating from the Taklamakan Desert and observe significant snow darkening over an area of >2100, >600, and >630 km2 in the Tien Shan, Kunlun, and Qilian Mountains, respectively. Our findings reveal that the impact of dust storms extends beyond the local high mountains, reaching mountains located approximately 1000 km away from the source. Furthermore, we observe that dust storms not only darken the snowpack during the spring but also in the summer and autumn seasons, leading to increased absorption of solar radiation. Specifically, the snow albedo reduction (radiative forcing) triggered by severe dust depositions is up to 0.028-0.079 (11-31.5 W m-2), 0.088-0.136 (31-49 W m-2), and 0.092-0.153 (22-38 W m-2) across the Tien Shan, Kunlun, and Qilian Mountains, respectively. This further contributes to the aging of the snow, as evidenced by the growth of snow grain size. Comparatively, the impact of persistent but relatively slow dust deposition over several months during non-event periods is significantly lower than that of individual dust event. This highlights the necessity of giving more attention to the influence of extreme events on the regional radiation balance. Through this study, we gain a deeper understanding of how a single dust event can affect the extensive snowpack and demonstrates the potential of employing satellite remote38 sensing to monitor large-scale snow darkening. [ABSTRACT FROM AUTHOR]

Although water-soluble organic carbon (WSOC) in the cryosphere can significantly influence the global carbon cycle and radiation budget, WSOC in the snowpack has received little scientific attention to date. This study reports the fluorescence characteristics, absorption properties, and radiative effects of WSOC based on 34 snow samples collected from sites in northeastern China. Sampling sites were divided into five groups, comprising southeastern Inner Mongolia (SEIM), northeastern Inner Mongolia (NEIM), the south of northeastern China (SNC), the north of northeastern China (NNC), and the Changbai Mountain area (CBM). Together, these groups represent a significant degree of regional WSOC variability, with concentrations ranging from 0.50 ± 0.19 to 5.70 ± 3.68 μg g−1 (mean = 3.59 ± 3.19 μg g−1). We then identified the three principal fluorescent components of WSOC as (1) a high‑oxygen humic-like component (HULIS-1) of terrestrial origin, (2) a low‑oxygen humic-like component (HULIS-2) of mixed origin, (3) and a protein-like component (PRLIS) derived from autochthonous microbial activity. In SEIM, a region dominated by desert and exposed soils, the WSOC content exhibits the highest humification index (HIX) but the lowest fluorescence (FI) and biological (BIX) indices; the fluorescence signal is mainly attributed to HULIS-1, and thus implicates soil as the primary source. By contrast, the HIX (FI and BIX) value was the lowest (highest) and PRLIS most intense in the remote grasslands and forested areas of NEIM, suggesting a primarily biological source. For SNC and NNC, both of which are characterized by intensive agriculture and industrial activity, the fluorescence signal is dominated by HULIS-2 and the HIX, FI, and BIX values are all moderate, indicating mixed origins for WSOC (anthropogenic activity, microbial activity, and soil). We also observed that, throughout northeastern China, the light absorption of WSOC is dominated by HULIS-1, followed by HULIS-2 and PRLIS. The contribution of WSOC to albedo reduction (average concentration 3.6 μg g−1) in the ultraviolet–visible (UV–vis) band is approximately half that of black carbon (BC: average concentration 0.6 μg g−1); radiative forcing is 3.8 (0.8) W m−2 in old (fresh) snow, equating to 19 % (17 %) of the radiative forcing of BC. These results indicate that WSOC has a profound impact on snow albedo and the solar radiation balance. [ABSTRACT FROM AUTHOR]

Water-soluble organic carbon (WSOC) in the cryosphere has important impact on the biogeochemistry cycling and snow/ice surface energy balance through changes in the surface albedo. This work reports on chemical characterization of WSOC in 28 representative snowpack samples collected across regional area of northern Xinjiang, northwestern China. We employed multi-modal analytical chemistry techniques to investigate both bulk and molecular-level composition of WSOC and its optical properties, informing the follow-up radiative forcing (푅퐹) modeling estimates. Based on the geographic differences and proximity of emission sources, the snowpack collection sites were grouped as urban/industrial (U), rural/remote (R), and soil-influenced (S) sites, for which average WSOC total mass loadings were measured as 1968±953 ng g-1 (U), 885±328 ng g-1 (R), and 2082±1438 ng g-1 (S), respectively. The S sites showed the higher mass absorption coefficients at 365 nm (푀퐴퐶365) of 0.94±0.31 m² g-1 compared to those of U and R sites (0.39±0.11 m² g-1 and 0.38±0.12 m² g-1, respectively). Bulk composition of WSOC in the snowpack samples and its basic source apportionment was inferred from the Excitation-Emission Matrices and the Parallel Factor analysis featuring relative contributions of two humic-like (HULIS-1 and HULIS-2) and one protein-like (PRLIS) components with ratios specific to each of the S, U, and R sites. Additionally, a sample from site 120 showed unique pollutant concentrations and spectroscopic features remarkably different from all other U, R, and S samples. Molecular-level characterization of WSOC using high-resolution mass spectrometry (HRMS) provided further insights into chemical differences among four types of samples (U, R, S, and 120). Specifically, much more reduced S-containing species with high degree of unsaturation and aromaticity were uniquely identified in U samples, suggesting an anthropogenic source. Aliphatic/proteins like species showed highest contribution in R samples, indicating their biogenic origin. The WSOC components from S samples showed high oxygenation and saturation levels. A few of unique CHON and CHONS compounds with high molecular weight were detected in the 120 sample, which might be anthraquinone derivatives from plant debris. Modeling of the WSOC- induced 푅퐹 values showed warming effects of 0.04 to 0.59 W m-2 among different groups of sites, which contribute up to 16% of that caused by BC, demonstrating the important influences of WSOC on the snow energy budget. [ABSTRACT FROM AUTHOR]