A NEW PRECIPITATION PROXY FROM SOIL MAGNETICS: IMPLICATIONS FOR EXPANDING PALEOCLIMATE RECONSTRUCTIONS

Describing precipitation patterns and changes in the hydrological cycle during periods of past global change is crucial for providing an understanding of terrestrial climate systems and predicting impacts of future climate change such as shifting water availability. While a host of proxies and climofunctions exist including depth to Bk, CIA-K, CALMAG and others, all of the available tools for predicting paleoprecipitation are plagued either by limited precipitation ranges (effective only for low-precipitation regimes; e.g., depth to Bk, CIA-K) or relevance to a limited range of paleosols (single-pedotype relationships; e.g., CALMAG). Here we measure the acquisition of isothermal remanent magnetization in soil material to describe the ratio of pedogenic magnetic minerals goethite and hematite, and use the relationship between these soil magnetic properties and water availability in modern soils to describe a new proxy for precipitation. By compiling both literature-derived and measured goethite-hematite (G/H) ratios and mean annual precipitation estimates for a global suite of modern soils (n = 70), we describe a strong (R² = 0.95) linear relationship between the G/H ratios of soil B-horizons and mean annual precipitation. Based on this relationship, we present a new paleosol climofunction for estimating paleoprecipitation values for a wide range of climatic regimes (100–3300 mm yr^-1) and soil types (Inceptisols, Alfisols, Ultisols, Oxisols, Mollisols, Aridisols, Spodosols). We also present a case study and apply this novel climofunction to paleosols from the Eocene of Wyoming, and show that estimates based on G/H ratios compare favorably to previously published estimates utilizing alternative methods (e.g., depth to Bk and CIA-K).