INFLUENCE OF VEGETATION AND SOIL TYPE ON THE MAGNETIC PROPERTIES OF SOILS DEVELOPED UNDER UNIFORM CLIMATE ACROSS THE FOREST-PRAIRIE ECOTONE IN NW MINNESOTA: IMPLICATIONS FOR CLIMOFUNCTIONS

Non-detrital magnetic minerals occur in soils as a result of a complex set of processes that are controlled by soil forming factors during pedogenesis. Magnetic climofunctions rely on the assumption that climate is the major control on soil magnetism and the effects of topography, vegetation, parent material, and time are secondary. We present magnetic data from a 11 km transect of anthropogenically unaltered soils that span the forest-to-prairie ecotone in NW Minnesota to evaluate the influence of vegetation on magnetic mineral assemblages. Forest soils (Alfisols), prairie soils (Mollisols), and transitional soils in this study developed on relatively uniform topography, glacial till parent material, under a uniform climate, and presumably over similar time intervals. Our preliminary results suggest that magnetic isolation of the pedogenic fraction of magnetic minerals in soils removes the influence of soil type, vegetation, and possibly parent material. Coercivity unmixing results show that ~45% of remanence in magnetically enhanced horizons is carried by a low-coercivity pedogenic component (likely magnetite) regardless of ecotone and soil type. Enhancement ratios for magnetic susceptibility and low-field remanences, often used as indicators of pedogenically produced magnetic minerals, are more variable but remain statistically equivalent across the transect. Finally, testing of an existing magnetic paleoprecipitation proxy developed on loessic soils of the Great Plains produces surprisingly reliable estimates of annual rainfall (within ~7% of the observed value) given that the soils studied here developed on glacial till. These results support the hypothesis that pedogenically produced magnetic minerals in soils mostly reflect ambient climatic conditions and can be consistent regardless of vegetation, soil type, and potentially parent material. In addition, our work highlights the utility of magnetism as a tool to sensitively differentiate magnetic minerals in soils, which helps to improve our ability to model complex pedogenic processes. Future efforts to isolate the pedogenic fraction of magnetic minerals in the deep past and to expand modern calibrations and models should be targeted to advance the development of more widely applicable magnetic climofunctions.