Beschreibung: Biomass burning influences global climate change and the composition of the atmosphere. The drivers, effects, and climate feedbacks related to fire are poorly understood. Many different proxies have been used to reconstruct past fire frequency from lake sediments and polar ice cores. Reconstruction of historical trends in biomass burning is challenging because of regional variability and the qualitative nature of various proxies. Vanillic acid (4-hydroxy-3-methoxybenzoic acid) is a product of the combustion of conifer lignin that is known to occur in biomass burning aerosols. Biomass burning is likely the only significant source of vanillic acid in polar ice. In this study we describe an analytical method for quantifying vanillic acid in polar ice using HPLC with electrospray ionization and tandem mass spectrometric detection. The method has a detection limit of 100 pM and a precision of ± 10% at the 100 pM level for analysis of 100 μl of ice melt water. The method was used to analyze more than 1000 discrete samples from the Akademii Nauk ice cap on Severnaya Zemlya in the high Russia Arctic (79°30’N, 97°45’E) (Fritzsche et al., 2002; Fritzsche et al., 2005; Weiler et al., 2005). The samples range in age over the past 2,000 years. The results show a mean vanillic acid concentration of 440 ± 710 pM (1σ), with elevated levels during the periods from 300-600 and 1450-1550 C.E.

Beschreibung: Biomass burning is a major source atmospheric gases and aerosols, and an important part of the global carbon cycle and radiation budget. The factors controlling centennial and millennial variability in region/global biomass burning are not well understood because there are few well-dated proxy records. We are exploring ice core records of organic compounds resulting from incomplete combustion of lignin as tracers for biomass burning. In this study we investigate the distribution of vanillic acid (VA) in Arctic ice cores. VA is a major product of conifer combustion, but may also be produced from angiosperms. VA was measured in ice core samples using ion chromatography with electrospray MS/MS detection. Here we present measurements of vanillic acid in three Arctic ice cores from Siberia (Akademii Nauk; 0-3 kyr bp), northern Greenland (Tunu; 0-1.75 kyr bp), and Svalbard (Lomonosovfonna; 0-0.75 kyr bp). The Siberian record exhibits 3 strong centennial scale maxima (1200-600 BC, AD 300-800, and AD 1450-1700). All three cores exhibit a smaller feature around 1250, with a subsequent decline in Greenland and Svalbard. VA levels in Greenland and Svalbard are generally smaller than those in Siberia. These results suggest strong input from Asian sources to the Siberian core, and lower Arctic-wide “background” levels at the other sites.

Beschreibung: Biomass burning plays an important role in atmospheric chemistry, the global carbon cycle, and climate. The relationship between burning and climate, and the factors that influence burning emissions over long timescales are not well understood. Therefore, well-dated records are needed to establish a history of biomass burning. In this study we examine the distribution of vanillic (VA) and p-hydroxybenzoic (p-HBA) acids in a Siberian Arctic ice core (Akademii Nauk) covering the past 2800 years. These molecules are produced by the incomplete combustion of lignin, incorporated into atmospheric aerosols, and transported/deposited on ice sheets. VA and p-HBA are generated from the combustion of conifers and grasses, respectively, but are not uniquely derived from these sources. These records should be considered qualitative because a wide range of aerosols is generated from various plant materials under different combustion conditions. The records may also reflect changes in source region locations, transport efficiency, and atmospheric removal prior to deposition. Ice core samples were analyzed using ion chromatography with electrospray MS/MS detection. VA and p-HBA levels were markedly elevated during three time periods. The most recent of these periods occurred from AD 1450-1720 (140-220 m). The timing of two earlier peaks is less well constrained. They are estimated to be from 300-700 AD (400-500 m) and from 800-400 BC (610-670 m). The similarity between VA and p-HBA suggests that the two compounds are derived from a common source. These three periods of elevated VA and p-HBA are not evident in nitrate, ammonium, or black carbon measurements from the same ice core or with high latitude sedimentary charcoal records from North America, Europe, or eastern Siberia.

Beschreibung: Wildfires and their emissions have significant impacts on ecosystems, climate, atmospheric chemistry and carbon cycling. Well-dated proxy records are needed to study the long-term climatic controls on biomass burning and the associated climate feedbacks. There is a particular lack of information about long-term biomass burning variations in Siberia, the largest forested area in the Northern Hemisphere. In this study we report analyses of aromatic acids (vanillic and para-hydroxybenzoic acids) over the past 3145 years in the Eurasian Arctic Akademii Nauk ice core. These compounds are aerosol-borne, semi-volatile organic compounds derived from lignin combustion. The analyses were made using ion chromatography with electrospray mass spectrometric detection. The levels of these aromatic acids ranged from below the detection limit (.01 to .05 ppb) to about 1 ppb, with roughly 30 % of the samples above the detection limit. In the preindustrial late Holocene, highly elevated aromatic acid levels are observed during four distinct periods (1180–660 BCE, 180–220 CE, 380–660 CE, and 1460–1660 CE). The timing of these periods coincides with the episodic pulsing of ice-rafted debris in the North Atlantic known as Bond events. Aromatic acid levels also are elevated during the onset of the industrial period from 1780 to 1860 CE, but with a different ratio of vanillic and para-hydroxybenzoic acid than is observed during the preindustrial period. This study provides the first millennial scale record of aromatic acids. It clearly demonstrates that coherent aromatic acid signals are recorded in polar ice cores that can be used as proxies for past trends in biomass burning.