Variation of soil magnetism across the Russian steppe: its significance for use of soil magnetism as a palaeorainfall proxy.

Modern soils across the Chinese Loess Plateau exhibit strong but disputed correlation between their pedogenic magnetic content and annual rainfall. A soil magnetism/rainfall transfer function could provide a quantitative proxy of Quaternary rainfall for this region. However, some argue that �magnetic dilution�, through spatially varying fluxes of weakly magnetic dust, controls the soil magnetic properties. Here, we test the soil magnetism/rainfall couple by examining 22 Russian steppe soils (free of present dust accumulation) across a climatic transect. From the semi-arid Caspian region to the more humid Caucasus, the soils display systematic increases in topsoil ferrimagnetic concentrations. With the exception of climate (and its co-variant, vegetation), soil-forming factors are essentially constant across this stable area. Hence, the soil magnetic variations dominantly reflect climate and from statistical analysis, principally rainfall. Further, the Russian steppe magnetic/rainfall relationship matches that observed for the Chinese Loess Plateau. These independent data thus substantiate the soil magnetism/rainfall climofunction and, by inference, eliminate �dust dilution� as a significant magnetic factor