Discriminating dusts and dusts sources using magnetic properties and hematite:Goethite ratios of surface materials and dust from North Africa, the Atlantic and Barbados

Abstract

Magnetic measurements and Diffuse Reflectance Spectroscopy are used in an attempt to differentiate dusts and dust sources in North Africa, over the Atlantic and in Barbados. Special attention is paid to dusts and to lacustrine clay and diatomite samples from the Bodele Depression, in view of its alleged importance in trans-Atlantic and global dust generation. The results indicate that dusts from the Bodele Depression can be distinguished from other dusts and potential sources in Niger, Chad, Burkina and Mali on the basis of their magnetic properties, notably their low magnetic concentrations, negligible frequency dependent magnetic susceptibility and distinctive IRM demagnetization characteristics. Dust from over the Atlantic and from Barbados, obtained from meshes in the 1960s and ’70s have high frequency dependent susceptibility values, are quite distinctive from the Bodele Depression samples and are more closely comparable to samples from elsewhere in the Sahara and especially the Sahel. The Diffuse Reflectance Spectroscopy data, though of limited value here, are not inconsistent with the inferences based on the magnetic measurements. Overall, the results obtained point to a wide range of sources for dusts both over North Africa itself and across the Atlantic. They do not offer support to the view that dusts from the Bodele Depression have dominated supply across the Atlantic over the last five decades.