Statistical Models for Use of Palaeosol Magnetic Properties as Proxies of Palaeorainfall
Barbara Maher, Antonio Possolo
The magnetic properties of well-drained, near-neutral modern soils demonstrate strong relationships with mean annual precipitation MAP, averaged over the last 30 years). The pedogenic magnetic susceptibility, for instance, is low under low MAP values ( 300 mm/yr), is increasingly high under higher MAP totals (up to 1500 mm/yr) and declines in association with higher MAP values. These magneto-climatic relationships have been amply documented, characterized quantitatively, and used for Quaternary palaeoclimatic reconstructions. However, neither the uncertainty of the climofunctions derived from such relations, nor the uncertainty of the corresponding estimates of palaeorainfall, have been assessed rigorously and realistically. Using previously published datasets -- from the Great Plains of the United States, from the Chinese Loess Plateau, from arid and tropical areas of Mali, and from Mediterranean and Saharan regions of Morocco -- we illustrate the development and calibration of statistical models that enable the use of magnetic properties of paleosols as proxies for paleorainfall. We also characterize the uncertainty of the estimates that these models produce when they are used for palaeoclimatic reconstructions. The good agreement between Holocene palaeo-rainfall reconstructions for Duowa, Qinghai Province, in the Chinese Loess Plateau, based on two very different calibration datasets, indicates the robustness of the pedogenic magnetic susceptibility as a proxy for past rainfall.