Investigating the characteristics and transformation of water-soluble carbonaceous matter in the cryosphere regions is important for understanding biogeochemical process in the earth system. Water-soluble carbonaceous matter is a heterogeneous mixture of organic compounds that is soluble in aquatic environments. Despite its importance, we still lack systematic understanding for dissolved organic carbon (DOC) in several aspects including exact chemical composition and physical interactions with microorganisms, glacier meltwater. This review presents the chemical composition and physical properties of glacier DOC deposited through anthropogenic emission, terrestrial, and biogenic sources. We present the molecular composition of DOC and its effect over snow albedo and associated radiative forcings. Results indicate that DOC in snow/ice is made up of aromatic protein-like species, fulvic acid-like materials, and humic acid-like materials. Light-absorbing impurities in surface snow and glacier ice cause considerable albedo reduction and the associated radiative forcing is definitely positive. Water-soluble carbonaceous matter dominated the carbon transport in the high-altitude glacial area. Owing to prevailing global warming and projected increase in carbon emission, the glacial DOC is expected to release, which will have strong underlying impacts on cryosphere ecosystem. The results of this work have profound implications for better understanding the carbon cycle in high altitude cryosphere regions. A new compilation of globally distributed work is required, including large-scale measurements of glacial DOC over high-altitude cryosphere regions, to overcome and address the scientific challenges to constrain climate impacts of light-absorbing impurities related processes in Earth system and climate models.

Brown carbon (BrC)/water-soluble organic carbon (WSOC) plays a crucial role in glacier melting. A quantitative evaluation of the light absorption characteristics of WSOC on glacier melting is urgently needed, as the WSOC release from glaciers potentially affects the hydrological cycle, downstream ecological balance, and the global carbon cycle. In this work, the optical properties and composition of WSOC in surface snow/ice on four Tibetan Plateau (TP) glaciers were investigated using a three-dimensional fluorescence spectrometer and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The total light-absorption of WSOC in snow/ice at 250-400 nm (ultraviolet region) and 400-600 nm (visible region) accounted for about 60.42% and 27.17% of the light absorption by the total organics, respectively. Two protein-like substances (PRLIS), one humic-like substance (HULIS), and one undefined species of chromophores in snow/ice on the TP glacier surfaces were identified. The lignins and lipids were the main compounds in the TP glaciers and were presented as CHO and CHNO molecules, while CHNOS molecules were only observed in the southeast TP glacier. The light absorption capacity of WSOC in snow/ice was mainly affected by their oxidizing properties. PRLIS and undefined species were closely linked to microbial sources and the local environment of the glaciers (lignins and lipids), while HULIS was significantly affected by anthropogenic emissions (protein/amino sugars). Radiative forcing (RF)-induced by WSOC relative to black carbon were accounted for about 11.62 +/- 12.07% and 8.40 +/- 10.37% in surface snow and granular ice, respectively. The RF was estimated to be 1.14 and 6.36 W m- 2 in surface snow and granular ice, respectively, during the melt season in the central TP glacier. These findings contribute to our understanding of WSOC's impact on glaciers and could serve as a baseline for WSOC research in cryospheric science.

Investigating the characteristics and transformation of water-soluble carbonaceous matter in the cryosphere regions is important for understanding biogeochemical process in the earth system. Water-soluble carbonaceous matter is a heterogeneous mixture of organic compounds that is soluble in aquatic environments. Despite its importance, we still lack systematic understanding for dissolved organic carbon (DOC) in several aspects including exact chemical composition and physical interactions with microorganisms, glacier meltwater. This review presents the chemical composition and physical properties of glacier DOC deposited through anthropogenic emission, terrestrial, and biogenic sources. We present the molecular composition of DOC and its effect over snow albedo and associated radiative forcings. Results indicate that DOC in snow/ice is made up of aromatic protein-like species, fulvic acid-like materials, and humic acid-like materials. Light-absorbing impurities in surface snow and glacier ice cause considerable albedo reduction and the associated radiative forcing is definitely positive. Water-soluble carbonaceous matter dominated the carbon transport in the high-altitude glacial area. Owing to prevailing global warming and projected increase in carbon emission, the glacial DOC is expected to release, which will have strong underlying impacts on cryosphere ecosystem. The results of this work have profound implications for better understanding the carbon cycle in high altitude cryosphere regions. A new compilation of globally distributed work is required, including large-scale measurements of glacial DOC over high-altitude cryosphere regions, to overcome and address the scientific challenges to constrain climate impacts of light-absorbing impurities related processes in Earth system and climate models.

Atmospheric brown carbon (BrC) is an important constituent of light-absorbing organic aerosols with many unclear issues. Here, the light-absorption properties of BrC with different polarity characteristics at a regional site of Pearl River Delta Region during 2016-2017, influenced by sources and molecular compositions, were revealed using radiocarbon analysis and Fourier transform ion cyclotron resonance mass spectrometry. Humic-like substance (HULIS), middle polar (MP), and low polar (LP) carbon fractions constitute 46 +/- 17%, 30 +/- 7%, and 7 +/- 3% of total absorption coefficient from bulk extracts, respectively. Our results show that the absorption proportions of HULIS and MP to the total BrC absorption are higher than their mass proportions to organic carbon mass, indicating that HULIS and MP are the main light-absorbing components in water-soluble and water-insoluble organic carbon fractions, respectively. With decreases in non-fossil HULIS, MP, and LP carbon fractions (66 +/- 2%, 52 +/- 2%, and 36 +/- 3%, respectively), the abundances of unsaturated compounds and mass absorption efficiency at 365 nm of three fractions decreased synchronously. Increases in both nonfossil carbon and levoglucosan in winter imply that the enhanced light-absorption could be attributed to elevated levels of biomass burning organic aerosols (BBOA), which increases the number of light-absorbing nitrogencontaining compounds. Moreover, the major type of potential BrC in HULIS and MP carbon fractions are oxidized BBOA, but the potential BrC chromophores in LP are mainly associated with primary BBOA. This study reveals that biomass burning has adverse effects on radiative forcing and air quality, and probably indicates the significant influences of atmospheric oxidation reactions on the forms of chromophores.