HR: 11:00h
AN: GP22A-03 INVITED     [Abstracts]
TI: Does Rainfall Always lead to Magnetic Enhancement in Topsoils of the World?
AU: * Orgeira, M J
EM: orgeira@gl.fcen.uba.ar
AF: Department of Geological Sciences, FCEN-University of Buenos Aires, and CONICET, Ciudad Universitaria Pab II, Buenos Aires, BA 1425, Argentina
AU: Banerjee, S K
EM: banerjee@umn.edu
AF: Department of Geology and Geophysics and the Institute for Rock Magnetism; University of Minnesota., 108 Pillsbury Hall 310 Pillsbury Drive S.E. , Minneapolis, MN MN 55455, United States
AU: Compagnucci, R H
EM: rhc@at.fcen.uba.ar
AF: Department of Geological Sciences, FCEN-University of Buenos Aires, and CONICET, Ciudad Universitaria Pab II, Buenos Aires, BA 1425, Argentina
AB: We propose a soil geochemical model that aims to explain both magnetic enhancement and depletion found in the topsoil in different climate regimes of the temperate zone. A high degree of correlation has been shown by B. Maher to exist between mean annual rainfall and magnetic enhancement in modern soils developed over loess in China and Russia. However, questions have also been raised about a poor correlation at some other locations such as Argentina, where many areas do not show enhancement. To reconcile both types of observations we propose a soil geochemical model that appeals not to total rainfall but to Potential Water Storage (PWS) of the soils and the presence of organic compounds in the environment. PWS, or total precipitation minus evapotranspiration, plays the major role in our model but other parameters of the soil microenvironment are also important. These are presence of organic ligands, clay and/or silica content, presence of carbonates and local drainage conditions. We compare the different environments in selected sites and find that an effective balance between iron oxide dissolution and authigenesis, driven by PWS and soil chemistry, can explain magnetic enhancements in China and Russia as well as magnetic depletion in Argentina. Rigorous, quantitative testing of our model would go a long way towards a comprehensive understanding of the magnetic effects of pedogenesis in diverse climatic environments.
DE: 1512 Environmental magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly