[A-CC33] Ice cores and paleoenvironmental modeling

[ACC33-09] Identification of non-volatile particulates in the 1908 event layer in an ice core of the Southeast Dome of Greenland.

*Mizuki Hirano¹, Iizuka Yoshinori², Kaoru Kawakami², Sumito Matoba², Hiroshi Ohno³, Takuto Ando⁴ (1.Graduate School of Environmental Science Hokkaido University, 2. Institute of Low Temperature Science Hokkaido University, 3.Division of Civil and Environmental Engineering Kitami Institute of Technology, 4.Graduate School of International Resource Sciences Akita University)

Biomass burning influences regional and global climate through the emission of greenhouse gases and particulates (Bowman et al., 2009). Forest fires, one of the biomass burning, plays an important role in the carbon cycle, because it emits CO₂ equivalent to 50% of fossil-fuel combustion per year (Bowman et al., 2009). Some of particulate aerosols produced by forest fires are deposited on polar ice sheets and are preserved in the ice. In this study, we conducted Raman Spectroscopy analysis of non-volatile particles in ice cores from the Southeast Dome of Greenland (SE-Dome ice core) to identify the composition of the past particulate aerosols, including those derived from forest fires.
The SE-Dome ice core was powdered with a ceramic knife, and then the powdered samples were placed on a round stainless-steel plate with a diameter of 10 mm. The stainless-steel plate was set in a cylindrical jig at -50°C. Dry nitrogen was passed through the jig to sublimate all volatile materials including ice in the sample. After sublimation, shape and chemical composition of the residue nonvolatile particles were analyzed with a Raman spectroscopy (HORIBA, XploRA LabSpec6). In this study, 532 nm and 785 nm lasers were used for Raman analysis under the following conditions: a 100× objective lens, laser power 1% or 10%, cumulative exposure time of 10 seconds.
The powdered sample from ice core dated July 1908, which is the highest ammonium ions concentration in the entire ice core (1800-2020), is expected to contain a large amount of organic matter. Raman spectra of nonvolatile particles in the July 1908 samples as well as the 1804 (pre-Industrial Revolution) and 1970 (the peak of anthropogenic SOx and NOx) samples, those two are background without ammonium ion peak, were analyzed in total 382 particles. As a result, particles containing dehydroabietic acid were detected only in the July 1908 sample (33/152 particles). Dehydroabietic acid is a tracer of forest fires produced during the burning of coniferous trees, suggesting a forest fire had occurred in July 1908. The Tunguska event, which occurred on June 30, 1908, in Siberia, Russia and has been debated whether traces of this explosion in the Greenland ice core (Zennaro et al., 2014; Legrand et al., 2016). The finding of dehydroabietic acid particle in this study suggests the July 1908 ammonium ion peak was from not the Tunguska explosion but forest fires in North America as discussed by Legrand et al. (2016).

References
Bowman, D. M., Balch, J. K., Artaxo, P., Bond, W. J., Carlson, J. M., Cochrane, M. A., ... & Pyne, S. J. (2009). Fire in the Earth system. science, 324(5926), 481-484.
Zennaro, P., Kehrwald, N. A. T. A. L. I. E., McConnell, J. R., Schüpbach, S., Maselli, O. J., Marlon, J., ... & Barbante, C. (2014). Fire in ice: two millennia of boreal forest fire history from the Greenland NEEM ice core. Climate of the Past, 10(5), 1905-1924.
Legrand, M., McConnell, J., Fischer, H., Wolff, E. W., Preunkert, S., Arienzo, M., ... & Flannigan, M. (2016). Boreal fire records in Northern Hemisphere ice cores: a review. Climate of the Past, 12(10), 2033-2059.