Thesis or Dissertation Studies on ice core records of dicarboxylic acids, ω-oxocarboxylic acids, pyruvic acid, α-dicarbonyls and fatty acids from southern Alaska since 1665 AD : A link to climate change in the Northern Hemisphere

Pokhrel, Ambarish

Alaskan ice core (180 m long, 343 years) has been analyzed for a homologous series of normal (C2 - C11), branched chain (iC4 - iC6), unsaturated (maleic, fumaric, methylmaleic and phthalic), multifunctional dicarboxylic (malic, oxomalonic and 4- oxopimelic), ω-oxocarboxylic acids (ωC2 - ωC9), pyruvic acid, glyoxal and methylglyoxal using gas chromatography (GC/FID) and GC/mass spectrometry (GC/MS) to understand historical changes in water soluble organic aerosols. Similarly, homologous series of straight chain fatty acids (C12:0 - C30:0) has been detected by using GC/FID and GC/MS system. Predominance of oxalic acid was found followed by adipic and succinic acid. Molecular distributions of ω-oxocarboxylic acids are characterized by the predominance of 9-oxononanoic, followed by 4-oxobutanoic and glyoxylic acids. Historical concentrations of diacids, oxoacids and α-dicarbonyls are formed by the oxidation of precursor compounds emitted from biogenic and biomass burning activities and which are controlled under climate oscillations and similar meteorological parameters. Historical trends of monoterpene and isoprene SOA tracers showed significant concentrations since the 1660s, which are associated with ambient atmospheric temperature and controlled by Aleutine Low. Molecular distributions of fatty acids are characterized by even carbon number predominance with a peak at palmitic (C16:0) followed by oleic (C18:1) and myristic acid (C14:0). The historical trends of short-chain fatty acids, together with correlation analysis with inorganic ions and organic tracers suggest that short-chain fatty acids (except for C12:0 and C15:0) were mainly derived from sea surface micro layers. In contrast, long-chain fatty acids (C20:0 - C30:0) are originated from terrestrial higher plants, soil organic matter and dusts, which are also linked with Greenland Temperature Anomaly (GTA). Hence, this study suggests that Alaskan fatty acids are strongly influenced by Pacific Decadal Oscillation/North Pacific Gyre Oscillation and/or extra tropical North Pacific surface climate and Arctic Oscillation. Organic tracers in ice core were derivatized with N,O-bis-(trimethylsilyl) trifluoroacetamide (BSTFA) with 1% trimethylsilyl chloride (TMCS) and pyridine and the derivatives were analyzed using GC/MS system. Levoglucosan, dehydroabietic and vanillic acid showed higher concentration with many sporadic peaks since 1660s-1830s, 1913, and 2005. Moreover, there are a few discrepancies of higher spikes among them after 1980s with sporadic peaks in 1994-2007 for dehydroabietic acid. Historical trends of levoglucosan, dehydroabietic and vanillic acid showed that biomass burning activities from resin and lignin phenols from boreal conifer trees and other higher plants and grasses were significant before 1840s and after 1980s in the source regions of southern Alaska. Nitrite (NO2 -), nitrate (NO3 -), sulfate (SO4 2-) and methanesulfonate (CH3SO3 -) were determined for an ice core of the Aurora Peak in southeast Alaska using ion chromatograph. They have common periods for higher spike during the years 1665- 2008. They are attributed to the same source regions and similar pathways. Interestingly, we found multi-decadal scale atmospheric transport from lower to higher latitudes in the North Pacific, which is reflected in historical concentration trends of anions. Moreover, correlation of levoglucosan with NH4 +, NO3 - , SO4 2- and NO2 - suggests that these anions and cations are poor tracer of biomass burning activities in the source regions of southern Alaska. Hence, this study revels a new dimension of anions periodic cycles in the North Paficic region, which may alter the concept of other ice core studies in the Northern and Southern Hemisphere.
Hokkaido University(北海道大学). 博士(環境科学)

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