HR: 16:00h
AN: GP34A-01 INVITED     [Abstracts]
TI: The Concept of Linear Unmixing - a Key for Interpreting Environmental Magnetic Signals
AU: * Spassov, S
EM: simo.spassov@oma.be
AF: Centre de Physique du Globe, Institut Royal M\'et\'eorologique, Dourbes, B-5670 Belgium
AU: Hus, J
EM: jhus@oma.be
AF: Centre de Physique du Globe, Institut Royal M\'et\'eorologique, Dourbes, B-5670 Belgium
AU: Egli, R
EM: egli@geod.baug.ethz.ch
AF: Institute for Rock Magnetism, 291 Shepherd Labs, 100 Union Street S.E., Minneapolis, MN 55455-0128 United States
AU: Heller, F
EM: heller@mag.ig.erdw.ethz.ch
AF: Institut f\"ur Geophysik, ETH H\"onggerberg, Z\"urich, CH-8093 Switzerland
AU: Evans, M E
EM: evans@phys.ualberta.ca
AF: Avadh Bhatia Physics Laboratory, University of Alberta Edmonton, Edmonton, T6G 2J1 Canada
AB: In recent years, environmental magnetism has become a powerful examination method in many research fields. The interpretation of the results, however, requires careful analysis since many simultaneously occurring physical and chemical processes depending on each other and acting over different scales in time and space, may be involved. In order to resolve this complexity, the concept of linear unmixing has become an important empirical interpretation method, which can be used also for quantitative analyses. The basic assumption -- the coexistence of endmembers -- is almost always satisfied. Three examples - ranging from palaeomagnetism to environmental pollution monitoring - will be given, illustrating the importance of the linear unmixing concept. {\it Palaeomagnetism} Continuous records of the palaeomagnetic field are accessible via the measurement of the natural remanent magnetisation of stratified sediments. As the sediment acts as a non-linear filter, the field record may be distorted causing misinterpretation. This distortion depends on the influence of the environment on the magnetic mineralogy of the sediment, which is -- in the case of loess sediments -- composed of coexisting pedogenic and detrital endmembers with specific magnetic properties. Their variable contribution determines the degree of distortion. Transitional polarity records in loess/palaeosol sediments may not always reflect real geomagnetic field behaviour but rather lithological variations. {\it Climate} Proxy records, e.g. magnetic low-field susceptibility, are {\it en vogue} to characterise sediment stratigraphies. They reflect a climatic signal, but in essence, the proxy material has acted as a filter, and the climatic information is resolved just roughly. Using the linear unmixing concept, proxy data can be decoded and valuable information is accessible via the stratigraphic variation of endmembers, (e.g. detrital, pedogenic, biogenic). A profile from a gleyic luvisol has been unmixed resulting in four different remanence components. Their variation through the soil profile allows conclusions about formation and alteration of magnetic phases during the soil development, hence throwing some light on the pedogenic processes. {\it Pollution} Linear mixing (or unmixing) is able to recognise and to quantify natural and anthropogenic components. Several air filters collecting dust from roads with variable pollution degree were investigated. Two remanence components were observed in all filters. One component, which is directly related to the exhaust pipe emissions of motor vehicles, can be used for an empirical quantitative estimate of the mass contribution of exhaust emissions. Independent chemical cross-calibration confirms the magnetic measurements as a fast and inexpensive method for systematic pollution monitoring of wide areas with passive sampling methods.
DE: 1512 Environmental magnetism
DE: 1533 Remagnetization
DE: 1540 Rock and mineral magnetism
DE: 1600 GLOBAL CHANGE (New category)
DE: 0345 Pollution--urban and regional (0305)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting