Laser-based method for black carbon determination in lake sediment cores and black carbon deposition in Greenland since 300 CE
Black carbon (BC) is a conservative tracer for industrial combustion and open biomass burning that has a significant contribution to Earth's radiative budget. Because BC is a dark, light-absorbing particle, BC is estimated by the Intergovernmental Panel on Climate Change (IPCC) to have a forcing of 0.7 watts/meter2, the third largest radiative forcing behind only carbon dioxide and methane. The radiative effects of BC are particularly notable when deposited on bright surfaces, such as snow and ice, and during atmospheric transport. Historical records of BC, such as those measured in ice cores, can be used to reconstruct forest fire history over past millennia. Thus, quantifying BC's role in the climate system is important for understanding both fire history and Earth's radiative budget. This study presents a new method for measuring BC in lake sediment cores using a laser-based instrument that has small sample requirements and high sample throughput. The method has low detection limits and is highly reproducible with proper sample preparation. This method is then applied to a lake from southern Greenland and, in conjunction with BC data from seven Greenland ice cores, used to evaluate Northern Hemisphere BC deposition and fire history since 300 CE. Deposition of BC in Greenland parallels Northern Hemisphere temperature, with higher BC flux during the warmer eras of the past 1700 years.
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