Erosión y desertificación.-Atmospheric dust additions as a soil formation factor

Abstract

ABSTRACT The Mediterranean area is distinguished by at least four features that determine the nature of its soils. These are its climate, its mountains, the addition of exogenous dust and ongoing anthropogenic effects.

We here present three cases in which the influence of atmospheric dust additions can be detected in the soils of representative circum-Saharan contexts – the Canary Islands, Betic intramontane depressions, and the Sierra Bermeja peridotite massif (Málaga).

The unique position of the Canary Islands determines important rates of dust deposit, largely depending on position on the relief. The nature of the dust contrasts with the rocky substratum of the islands, and the marine and volcanic context can also affect the nature of the deposits.

The numerous, extensive intramontane basins of the Betic Cordilleras act as large captors of atmospheric dust, with rates similar to those found in the Canary archipelago. The carbonate content of these exogenous additions represents a significant component that should be taken into account when establishing the carbonate accumulation regime in these soils.

Sierra Bermeja is a rather different case. It constitutes the first abrupt relief in the area of the Strait of Gibraltar which, together with the prevailing winds, leads to anomalous concentrations of silica and carbonates in the upper horizons of its soils, unlike the ultrabasic nature of its substratum. Here, the texture and composition of supplies suggest an origin in the Campo de Gibraltar, rather than in the desert. Instances of contamination have recently been confirmed as having this origin.