1. Paleoprecipitation Reconstructions for the Brady Soil Based on Rock-Magnetic Analyses Christoph E. Geiss Pooja Shakya Emily Quinton William C. Johnson Joseph Mason

4. Pedogenic Magnetic Component fine grained (d < 0.1 μm) ferrimagnetic minerals (magnetite, maghemite) remarkably consistent in it’s magnetic properties throughout the Midwestern U.S. under certain conditions we can calculate its abundance in a sample

5. estimates of pedogenic magnetic minerals ARM ratios (presented today) –ARM is highly sensitive for fine magnetic particles –easily measured magnetic coercivity distributions –more time consuming, but yields more information about the samples for moderns soils from the Midwestern U.S. both methods yield equivalent results

6. some magnetism basics saturation magnetization (M s ) magnetization of a sample when exposed to a (pretty strong) magnetic field remanent magnetization (M r ) magnetization of a sample in zero field various flavors (ARM, IRM etc.) simple linearized model: M r = α × M s For many natural samples M r is additive M tot = M 1 + M 2

7. 2-component mixing model pedogenic component (fine-grained maghemite) background component (here coarse-grained rest) f ped = relative volume (or mass) fraction of pedogenic component pedogenic contribution to magnetic remanence background contribution to magnetic remanence

8. ARM Ratios (ARM / IRM) Sensitive for fine-grained (SD) ferrimagnets Can write simple model to predict ARM / IRM ratios Note:J s cancels out and if the  ’s are known f ped is the only variable left therefore, can calculate f ped from ARM ratios

9. observed range

10. ARM-ratios of modern enhanced horizons

13. precipitation reconstructions

14. comparison with modern precipitation

15. Caveats ! technique might underestimate ppt –no loss of pedogenic material –magnetic enhancement reaches equilibrium state rapidly magnetic properties of parent material can be distinguished from pedogenic material –inherited pedogenic Fe-oxides / redeposited soils