absorption optical depths associated with these vertical profiles were large as evidenced by a vertical profile over the Norwegian arctic where absorption optical depths of 0.023 to 0.052 were calculated respectively for external and internal mixtures of black carbon with the other aerosol components. Optical depths of these magnitudes lead to a substantial change in the solar radiation balance over the highly reflecting Arctic snow surface during the March–April time frame of these measurements modeled the Arctic aerosol for an absorption optical depth of 0.021 (which is close to the average of an internal and external mixtures for the AGASP flights), under cloud-free conditions. These heating effects were viewed at the time as potentially one of the major causes of Arctic warming trends as described in Archives of Dept. of Energy, Basic Energy Sciences Accomplishments. Presence in soils Typically, black carbon accounts for 1 to 6% but also up to 60% of the total organic carbon stored in soils is contributed by black carbon. Especially for tropical soils black carbon serves as a reservoir for nutrients. Experiments showed that soils without high amounts of black carbon are significantly less fertile than soils that contain black carbon. An example for this increased soil fertility are the Terra preta soils of central Amazonia, which are presumably human-made by pre-Columbian native populations. Terra preta soils have on average three times higher soil organic matter (SOM) content, higher nutrient levels and a better nutrient retention capacity than surrounding infertile soils. In this context, the slash and burn agricultural practice used in tropical regions does not only enhance productivity by releasing nutrients from the burned vegetation but also by adding black carbon to the soil. Nonetheless, for a sustainable management, a slash-and-char practice would be better in order to prevent high emissions of and volatile black carbon. Furthermore, the positive effects of this type of agriculture are counteracted if used for large patches so that soil erosion is not prevented by the vegetation. Presence in waters Soluble and colloidal black carbon retained on the landscape from wildfires can make its way to groundwater. On a global scale, the flow of black carbon into fresh and salt water bodies approximates the rate of wildfire black carbon production. Emission sources By region Developed countries were once the primary source of black carbon emissions, but this began to change in the 1950s with the adoption of pollution control