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 homologousseries 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 andmethylglyoxal 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 beendetected 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 thepredominance of 9-oxononanoic, followed by 4-oxobutanoic and glyoxylic acids.Historical concentrations of diacids, oxoacids and α-dicarbonyls are formed by theoxidation of precursor compounds emitted from biogenic and biomass burningactivities and which are controlled under climate oscillations and similarmeteorological parameters. Historical trends of monoterpene and isoprene SOAtracers showed significant concentrations since the 1660s, which are associated withambient atmospheric temperature and controlled by Aleutine Low.Molecular distributions of fatty acids are characterized by even carbon numberpredominance with a peak at palmitic (C16:0) followed by oleic (C18:1) and myristicacid (C14:0). The historical trends of short-chain fatty acids, together with correlationanalysis 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. Incontrast, long-chain fatty acids (C20:0 - C30:0) are originated from terrestrial higherplants, soil organic matter and dusts, which are also linked with GreenlandTemperature Anomaly (GTA). Hence, this study suggests that Alaskan fatty acids arestrongly influenced by Pacific Decadal Oscillation/North Pacific Gyre Oscillationand/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 pyridineand the derivatives were analyzed using GC/MS system. Levoglucosan,dehydroabietic and vanillic acid showed higher concentration with many sporadicpeaks 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 fordehydroabietic acid. Historical trends of levoglucosan, dehydroabietic and vanillicacid showed that biomass burning activities from resin and lignin phenols from borealconifer trees and other higher plants and grasses were significant before 1840s andafter 1980s in the source regions of southern Alaska.Nitrite (NO2-), nitrate (NO3-), sulfate (SO42-) and methanesulfonate (CH3SO3-)were determined for an ice core of the Aurora Peak in southeast Alaska using ionchromatograph. 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 tohigher latitudes in the North Pacific, which is reflected in historical concentrationtrends of anions. Moreover, correlation of levoglucosan with NH4+, NO3- , SO42- andNO2- suggests that these anions and cations are poor tracer of biomass burningactivities in the source regions of southern Alaska. Hence, this study revels a newdimension of anions periodic cycles in the North Paficic region, which may alter theconcept 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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