Alpine Mountain’s Ice Core Records of Dicarboxylic Acids, ω-Oxocarboxylic Acids, and α-Dicarbonyls from Southern Alaska Since 1665 to the Present

Abstract

Ice cores can provide insights into the paleogeochemical cycle and allow us to determine how and why geochemical cycles changed in the past. By understanding how the paleogeochemical cycle changed in the past, we are able to improve predictions of how climate will change in the future. The sensitivity of atmospheric oxidizing capability can be reflected in a homologous series of normal (C₂–C₁₁), branched chain (iC₄–iC₆), unsaturated, multifunctional structures of diacids, together with ω-oxoacids (ωC₂–ωC₉) and α-dicarbonyls (glyoxal and methylglyoxal). We analyze the Alaskan ice core (180 m long, 343 years, 30 species) to understand the historical changes of water-soluble organic aerosols transported over the Aurora Peak facing the Gulf of Alaska. We found a predominance of oxalic acid (C₂), followed by adipic (C₆) and succinic (C₄) acids. Interestingly, similar concentration levels are recorded for 9-oxononanoic (ωC₉), 4-oxobutanoic (ωC₄), and glyoxylic acids (ωC₂). Such molecular distributions are different from those of continental and marine aerosols in mid-latitudes. These polar compounds are likely formed by atmospheric oxidation of unsaturated fatty acids (e.g., C_18:1) and isoprene, which are emitted from the lower latitudes of the northern North Pacific rim (NPR). The concentration ratios of C₃/C₄ and those of other species, which are connected to the atmospheric oxidizing capability of the Northern Hemisphere, exhibit associations with a multidecadal cycle of climate oscillations and periods of the primary and secondary sources. Multidecadal variations of C₃/C₄ ratios may be coupled with sea ice retreat and advance in the Bering Sea and Gulf of Alaska, where the Aleutian Low is significant in the NPR.