Dissolved organic carbon (DOC) plays an important role in the carbon cycle, radiative forcing, and biogeochemistry in cryospheric regions. In this study, concentrations, light-absorption properties and bioavailability of DOC from snow cover in Alaska were characterized. Results indicated that average concentrations of DOC in snow of Alaska (0.17-0.30mg L-1) were lower than that found in Asian mountainous glaciers, but higher that found from polar regions snow. No significant trend of DOC was observed during April to May in 2017 due to the short term study; while the vertical variations generally showed a little higher values in the surface snow than that in the sub-surface snow. An obvious characteristic of DOC light-absorbance in snow between the wavelength of 300 and 700nm indicated the mass absorption cross of DOC at 365nm (MAC(DOC365)) was 0.32 +/- 0.24 and 0.37 +/- 0.32m(2) g(-1) for the snow cover at Barrow site (Arctic Ocean coast) and the other Alaskan regions, respectively. The MAC(DOC365) values increased especially during snow melting, indicating the DOC with high MAC values were prone to retain in snow. The proportion of radiative forcing caused by DOC relative to that by black carbon in snow was approximately 2.3%, indicating that DOC in snow should be considered during the accelerated melt of snow cover. The bioavailability experiment of DOC in snow indicated that DOC may be an important bioavailable source for proglacial and coastal ecosystems in Alaskan Arctic regions. Using backward air mass trajectory analysis, we suggested that DOC deposited in snow at Barrow primarily originates from marine or terrestrial air mass, but the specific contribution of different sources cannot be quantified without data related to the DOC's chemical composition and carbon isotopic signatures. This study highlighted the climatic implications of DOC in snow in the Arctic regions.

Dissolved organic carbon (DOC) plays an important role in the carbon cycle, radiative forcing, and biogeochemistry in cryospheric regions. In this study, concentrations, light-absorption properties and bioavailability of DOC from snow cover in Alaska were characterized. Results indicated that average concentrations of DOC in snow of Alaska (0.17-0.30mg L-1) were lower than that found in Asian mountainous glaciers, but higher that found from polar regions snow. No significant trend of DOC was observed during April to May in 2017 due to the short term study; while the vertical variations generally showed a little higher values in the surface snow than that in the sub-surface snow. An obvious characteristic of DOC light-absorbance in snow between the wavelength of 300 and 700nm indicated the mass absorption cross of DOC at 365nm (MAC(DOC365)) was 0.32 +/- 0.24 and 0.37 +/- 0.32m(2) g(-1) for the snow cover at Barrow site (Arctic Ocean coast) and the other Alaskan regions, respectively. The MAC(DOC365) values increased especially during snow melting, indicating the DOC with high MAC values were prone to retain in snow. The proportion of radiative forcing caused by DOC relative to that by black carbon in snow was approximately 2.3%, indicating that DOC in snow should be considered during the accelerated melt of snow cover. The bioavailability experiment of DOC in snow indicated that DOC may be an important bioavailable source for proglacial and coastal ecosystems in Alaskan Arctic regions. Using backward air mass trajectory analysis, we suggested that DOC deposited in snow at Barrow primarily originates from marine or terrestrial air mass, but the specific contribution of different sources cannot be quantified without data related to the DOC's chemical composition and carbon isotopic signatures. This study highlighted the climatic implications of DOC in snow in the Arctic regions.

Soot aerosols have become the second most important contributor to global warming after carbon dioxide in terms of direct forcing, which is the dominant absorber of visible solar radiation. The optical properties of soot aerosols depend strongly on the mixing mechanism of black carbon with other aerosol components and its hygroscopic properties. In this study, the effects of atmospheric water on the optical properties of soot aerosols have been investigated using a superposition T-matrix method that accounts for the mixing mechanism of soot aerosols with atmospheric water. The dramatic changes in the optical properties of soot aerosols were attributed to its different mixing states with atmospheric water (externally mixed, semi-embedded mixed, and internally mixed). Increased absorption is accompanied by a larger increase in scattering, which is reflected by the increased single scattering albedo. The asymmetry parameter also increased when increasing the atmospheric water content Moreover, atmospheric water intensified the radiative absorption enhancement attributed to the mixing states of the soot aerosols, with values ranging from 1.5 to 2.5 on average at 0.870 mu m. The increased absorption and scattering ability of soot aerosols, which is attributed to atmospheric water, exerted an opposing effect on climate change. These findings should improve our understanding of the effects of atmospheric water on the optical properties of soot aerosols and their effects on climate. The mixing mechanism for soot aerosols and atmospheric water is important when evaluating the climate effects of soot aerosols, which should be explicitly considered in radiative forcing models. (C) 2014 Elsevier Ltd. All rights reserved.