Hong Wu

Thesis Approved:

Black Carbon in Polar Ice Cores: the Palaeo- record of Forest Fire Activity over the Past 13,000 Years

Black carbon in ice cores provides a good indicator of the palaeohistory of the magnitude of biomass burning (Chylek et al. 1992). This record of biomass burning may indicate the level of global biomass storage and does offer a means of investigating the interrelationship between biomass burning and climate. The climate is influenced by biomass burning through production of greenhouse gases and black carbon aerosol - products that affect the global radiation balance. Conversely, the level of biomass burning is influenced by climate both through the effect of climate on amount of biomass available for burning and through conditions that affect the tendency for fire formation. The goal of this study is to measure the black carbon concentration in ice cores from Dye 3, Greenland and Byrd Station, Antarctica, and to explore the relationship between biomass burning and other climate factors.

In making these measurements ice core samples were melted and the particulate impurities were filtered onto quartz filters. These filters were then heated to 670 C to oxidize the black carbon, while changes in light transmittance of the filters provided an indication of the black carbon content.

The experimental results showed that the 15 ice core samples from Dye 3, Greenland, ages covering 3400 B.P. to 900 B.P., had a mean black carbon concentration of 2 *g/kg. This value is within the range of results for modern surface snow at Dye 3. The six ice core samples from 750 B.P. to 100 B.P., the Little Ice Age, had a mean black carbon concentration of 0.6 *g/kg, -a level that very likely reflects a reduction in local biomass burning as well as reduction in forest fire activity that would supply black carbon for long distance transport.

The 18 Byrd Station ice core samples with ages covering the whole Holocene and ranging in age from 750 B.P. to 10,500 B.P., had an average black carbon concentration of 0.50 *g/kg - a concentration that is in agreement with measurements for modern Antarctic snow. The four pre-Holocene ice core samples possessed an average black carbon concentration of 0.10 *g/kg, a level significantly lower than the Holocene mean. These black carbon data from Byrd Station are well correlated with profiles of *18O, an indicator of surface temperature of the earth, and CO2 and CH4, which are, similarly, biosphere derived components of the atmosphere.