A Greenland ice core record of low molecular weight dicarboxylic acids, ketocarboxylic acids, and α-dicarbonyls: A trend from little ice age to the present (1540 to 1989 A.D.)

Abstract

A homologous series of α,ω-dicarboxylic acids (C2-C10), ω-oxocarboxylic acids (C2-C9), pyruvic acid, and α-dicarbonyls (C2-C3) were measured in the ice core samples (206 m long, ∼450 years old) taken from Site-J (Greenland) using a capillary gas chromatography and mass spectrometry. The measurements have been made on a basis of discontinuous sampling (sampling frequency is roughly 8% of the total ice core length). Molecular distributions of the diacids showed a predominance of succinic acid (C4), followed by oxalic (C2) and malonic (C3) acids, whereas those of ω-oxoacids showed a predominance of C4 or C3 species. Concentration ranges of the total diacids, ω-oxoacids, and α-dicarbonyls were 3.1-32.5 ng g-1, 0.13-2.8 ng g-1, and 0.09-1.7 ng g-1, respectively. Relative abundances of total diacid carbon contents in total organic carbon (TOC; 0.7-5.7 μgC g-1) ranged from 0.04% to 1.3%. The relative abundance of major diacids smoothly fluctuated with maxima at ∼1580, 1780, 1840, 1940, and 1980 years and minima at ∼1680, 1820, 1860, and 1970 years. This trend is generally in good agreement with the changes in the recorded and reconstructed air temperature in the Northern Hemisphere. Temporal trends of the diacids can be explained in terms of the past changes in the sea-to-air emissions of marine organic matter, which is subsequently subjected to a photochemical oxidation in the atmosphere during long-range transport toward the Greenland ice sheet. Further, it was found that the historical trend of oxalic acid-C/TOC correlates with the reconstructed solar irradiance since 1600, suggesting that oxalic acid is more efficiently produced in the past atmosphere by photochemical oxidation of biogenic species during periods characterized by enhanced solar radiations. Oxalic acid signals were also suggested to be modulated by the frequency of biomass burning inputs.