| Biomass burning and fossil fuel combustion produce black carbon (BC), which has a long planetary residence time. In pre-1880 samples, 14C can be used to identify BC carbon pool residence times. In modern BC samples 14C can be used to distinguish between fossil and biomass carbon sources. I have optimized a chemical oxidation technique for radiocarbon measurements of BC (Cr2O7=/H 2SO4 oxidation), and used this technique to measure mass and carbon isotopic signatures of BC in sediments from the abyssal northeast Pacific, the coastal Pacific, the Southern Ocean, and in particulate matter discharged from a California river. Mass results indicate that BC is a significant component of the refractory carbon stored in Pacific and Southern Ocean sediments, as well as in the particulate material exported by a small California river.; Isotopic results indicate that before deposition in ocean sediments, BC spends thousands of years in intermediate carbon pools, including soils. Indirect evidence suggests that the ocean's dissolved organic carbon pool may also play a role in the storage and transport of BC. The identification of old, non-fossil BC in sediments and river carbon suggests a role for biomass burning in the long-term storage of organic carbon. Additionally, the measurement of old carbon in river particulate matter suggests a larger role for riverine C in the ocean's carbon cycle. |
