[A-CC26] Ice cores and paleoenvironmental modeling

[ACC26-P01] A biomass burning record over the past 350 years in an ice core from Northwest Greenland

*Kumiko Goto-Azuma^1,2, Yoshimi Ogawa-Tsukagawa¹, Yutaka Kondo¹, Remi Dallmayr⁹, Jun ogata¹, Nobuhiro Moteki³, Sho Ohata⁴, Tatsuhiro Mori⁵, Makoto Koike³, Kaori Fukuda¹, Motohiro Hirabayashi¹, Sumito Matoba⁶, Yuki Komuro¹, Akane Tsushima⁷, Naoko Nagatsuka¹, Koji Fujita⁴, Naga Oshima⁸, Kyotaro Kitamura¹, Kenji Kawamura^1,2, Wataru Shigeyama^1,2, Hideaki Motoyama^1,2, Teruo Aoki^1,2 (1.National Institute of Polar Research, 2.SOKENDAI, 3.University of Tokyo, 4.Nagoya Univeristy, 5.Tokyo University of Science, 6.Hokkaido University, 7.Chiba University, 8.Meteorological Research Institute, 9.Alfred Wegner Institute for Polar and Marine Research)

Keywords:Greenland, Black carbon, Biomass burning, Ice core

Black carbon (BC) is one of the major light-absorbing aerosols, which can affect Earth’s radiation budget. BC in the atmosphere absorbs sunlight and heats the atmosphere, whereas BC deposited on snow and/or ice reduces the surface albedo and enhances snowmelt. BC can also act as cloud condensation nuclei and ice nucleating particles, which play important roles in climate change. To understand the role of BC in climate change, we need to know concentrations, size distributions, and spatial and temporal variability in them. However, observations of BC in the atmosphere and snow have been started only recently. There have been no direct observations of BC in the preindustrial time, which was unaffected by anthropogenic input. Ice cores can provide proxy records of the past BC concentration and size distribution in the preindustrial period as well as the industrial period. The records from the preindustrial period are of special importance in understanding the role of BC in the pristine environment.

We analyzed an ice core drilled at SIGMA-D site, Northwest Greenland (Matoba et al., 2015), down to the depth of 113 m using a Continuous Flow Analysis (CFA) system developed at the National Institute of Polar Research. The CFA system enabled us to obtain high-resolution data of BC, stable isotopes of water, microparticles and six elements (Na, K, Mg, Ca, Fe, and Al). For BC analysis, we used a recently developed Wide-range (WR) SP2 (Single Particle Soot Photometer), which can detect BC particles in size range between 70 and 4000 nm (Mori et al., 2016). A combination of WR-SP2 and a high-efficiency nebulizer allowed us accurate measurements of BC concentrations and size distributions. We dated the core by annual layer counting using mainly Na and water stable isotopes. Our ice-core record covers the past 350 years. We divided each year into 12 months and calculated monthly averaged BC concentrations and size distributions.

Concentrations of BC started to increase in the 1870s, reached its maximum in the 1920s - 1930s, and decreased again since then. The increases are likely due to anthropogenic BC, which we as found to deposit mainly in fall and winter months. Before the increases started, the major source of BC was biomass burning, which showed summer peaks in BC concentrations. Based on the different seasonality of anthropogenic and biomass burning BC, we reconstructed temporal variability in biomass burning BC. Except for occasional large biomass burning events, we found relatively stable biomass burning BC concentrations over the past 350 years. We did not find particularly high summer BC concentrations in warm periods.