Brown carbon (BrC) aerosols play a significant role in atmospheric radiative forcing, particularly in the Arctic where they could potentially contribute to surface warming. However, their regional variability and sources in the open ocean remain poorly understood. To address this, we conducted ship-based aerosol measurements aboard the R/V Mirai during the MR18-05C research cruise (October-December 2018), spanning the western North Pacific, Bering Sea, and Arctic Ocean. We examined BrC optical properties alongside PM2.5 chemical composition, trace gases, and meteorological conditions to assess its variability and sources. Our results reveal a drastic northward decline in BrC levels, with light absorption capability in the Bering Sea and the Arctic approximately 50% lower than those in the western North Pacific. The strongest BrC absorption was observed in regions influenced by crop residue burning in Northeast China. In the Arctic, BrC remained low as the main footprint is within the Arctic alongside limited BrC sources, although occasionally affected by long-range transport. Chemical composition analysis highlights biomass burning and fossil fuel emissions as dominant BrC sources in the western North Pacific. Solubility analysis indicated that BrC in the Arctic was predominantly water soluble, increasing its susceptibility to wet scavenging. A strong high-pressure system (1027 +/- 6.2 hPa) over the Arctic (November 9-17) led to aerosol accumulation, although BrC remained low. This study underscores the complex interplay between regional emissions, long-range transport, and atmospheric processing in regulating BrC distributions across latitudinal gradients. Our findings highlight the importance of source-region emissions and transport pathways in determining BrC fate in the Arctic, with implications for understanding its role in climate forcing.

Dissolved organic carbon (DOC) in snow plays an important role in river ecosystems that are fed by snowmelt water. However, limited knowledge is available on the DOC content in snow of the Chinese Altai Mountains in Central Asia. In this study, DOC in the snow cover of the Kayiertesi river basin, southern slope of Altai Mountains, was investigated during November 2016 to April 2017. The results showed that average concentrations of DOC in the surface snowcover (1.01 +/- 0.52 mgL(-1)) were only a little higher than those in glaciers of the Tibetan Plateau, European Alps, and Alaska, but much higher than in Greenland Ice Sheet. Depth variations of DOC concentrations from snowpack profiles indicated higher values in the surface layer. During the observation period, scavenging efficiency for DOC in snow cover is estimated to be 0.15 +/- 0.10, suggesting that DOC in snow can be affected more by the meltwater during ablation season than during accumulation season. The average mass absorption cross at 365 nm and the absorption Angstrom exponent of DOC were 0.45 +/- 0.35 m(2) g(-1) and 2.59 +/- 1.03, respectively, with higher values in March and April 2017. Fraction of radiative forcing caused by DOC relative to black carbon accounted for about 10.5%, implying DOC is a non-ignorable light-absorber of solar radiation in snow of the Altai regions. Backward trajectories analysis and aerosol vertical distribution images from satellites showed that DOC in the snow of the Altai Mountains was mainly influenced by air masses from Central Asia, Western Siberia, the Middle East, and some even from Europe. Biomass burning and organic carbon mixed with mineral dust contributed significantly to the DOC concentration. This study highlights the effects of DOC in the snow cover for radiative forcing and the need to study carbon cycling for evaluation of quality of the down-streams ecosystems. (c) 2018 Elsevier B.V. All rights reserved.