Table 1 contains statistics of a sample of independent mean estimates for each term, presenting arithmetic means of reported values, their maxima and minima, and standard deviations. When a standard deviation around a mean estimate was reported in one of the many sources, we attempted to incorporate some of this uncertainty in the tabular values of Table 1 by including the mean, mean plus standard deviation, and mean minus standard deviation all as independent estimates contributing to the sample.
Annual precipitation C flux to Africa was estimated from the sum of estimates for dissolved organic and inorganic (DOC and DIC) carbon fluxes from precipitation following the approach in Kempe [70]. For DOC, the flux was calculated as the product of annual precipitation water flux with the maximum or minimum observed continental rainwater DOC reported in Willey et al. [71], where precipitation delivered to Africa was estimated from an FAO rainfall product [72]. Similarly, the DIC flux was calculated as the product of annual African precipitation with a) continental rainwater DIC at a pH of 7.4 and 10°C as in Willey et al. [71], and b) its product with the mean CO2 content of precipitation reported in Miotke [73].
Africa's annual riverine C discharge to oceans was calculated from the sum of riverine DOC and DIC flux estimates also as in Kempe [70]. For DIC the flux was calculated as the product of Africa's riverine discharge [74,75] with DIC content of Africa's river water [74]. For DOC, we used the global ratio of DOC to DIC in river water [74] to estimate DOC content of Africa's river water, which was then multiplied by river water discharge.
When not directly reported, carbon emissions from human-managed fires were estimated by converting biomass burned into carbon emissions based on a common [e.g. [27,28,76]] assumption of biomass to carbon emissions ratio of ~0.45.
Acknowledgements
Funding for this study was provided by the United States National Aeronautics and Space Administration (NASA) Terrestrial Ecology Program (Dr. Diane Wickland), and the National Oceanic and Atmospheric Administration (NOAA) Global Carbon Cycle Program (Dr. Kathy Tedesco). We would like to thank A.J. Dolman of Vrije University, Amsterdam, and Robert B. Jackson of Duke University for providing initial reviews of the draft manuscript.
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