Long-range transport of continentally-derived particulate carbon in the marine atmosphere: evidence from stable carbon isotope studies

Abstract

Since 1979, we have investigated marine and non-marine sources of particulate carbon in the marine atmosphere from measurements of carbon concentration and isotopic composition 13 C/ 12 C). Aerosol samples were collected, mostly during the Sea/Air Exchange (SEAREX) Program experiments, in the northern and southern hemispheres (Sargasso Sea, Enewetak Atoll, Peru upwelling, American Samoa, New Zealand, Amsterdam Island). The concentration and the isotopic composition of particulate carbon of marine origin are about the same in both hemispheres (C mean =O.O7 μgC m -3 , δ 13 C mean C = -21‰) This component is primarily associated with large sea-salt particles (diameter > 3 μm). Particulate carbon of continental origin displays a variable isotopic composition (δ 13 C range: - 23 to - 28‰,) and is primarily found attached to the smallest aerosol particles (diameter < 1 μm). This continental component shows little temporal variability, but its concentration is much lower in the southern hemisphere (0.06 μgC m -3 ) than in the northern hemisphere (0.45 μgC m -3 ). Also, the northern hemisphere samples appear strongly depleted in 13 C compared to those from the southern hemisphere. This can be explained on the basis of our isotopic data over various continental areas (Paris region, Ivory Coast, Congo) as due to the predominance in the northern hemisphere of carbonaceous aerosols of anthropogenic origin derived either from industrial combustion processes or from biomass burning. On the other hand, our data set from the southern hemisphere appears to reflect primarily natural land-derived biogenic emissions. DOI: 10.1111/j.1600-0889.1986.tb00184.x