The cooling-rate effect on microwave archeointensity estimates

Author(s)

Poletti, Wilbor ^{[1, 2]} ; Hartmann, Gelvam A. ^[2] ; Hill, Mimi J. ^[1] ; Biggin, Andrew J. ^[1] ; Trindade, Ricardo I. F. ^[2]

Affiliation

^[1] Univ Liverpool, Dept Earth Ocean & Ecol Sci, Geomagnetism Lab, Liverpool L69 3BX, Merseyside - England

^[2] Univ Sao Paulo, Dept Geofis, Inst Astron Geofis & Ciencias Atmosfer, BR-05508090 Sao Paulo - Brazil

• Document type: Journal article
• Source: Geophysical Research Letters; v. 40, n. 15, p. 3847-3852, AUG 16 2013.
• Web of Science Citations: 8

Abstract

New microwave (MW) paleointensity data on historical bricks from Northeast Brazil presented a bias toward higher fields when compared to previous cooling-rate corrected double-heating paleointensity estimates; the same relates to the previously reported values for pottery from Southwestern Pacific islands. A simple theoretical approach suggests that the MW bias in both collections is due to a cooling-rate effect on MW estimates. We then experimentally corrected the MW cooling-rate effect on Brazilian fragments, increasing the degree of consistency between the previous and new results (reducing discrepancies from 25% to 8%). Results indicate similar experimental behavior between microwave and thermal procedures despite the different ways in which the energy is transferred into the spin system. Finally, they allow cooling times of less than 90s to be empirically estimated in most of these MW experiments highlighting the need for systematic cooling-rate corrections to be applied in similar MW paleointensity studies in the future. (AU)

• FAPESP's process: 10/10754-4 - Evolution of the Earth Magnetic Field in South America for the past 500 years
• Grantee: Gelvam André Hartmann
• Support Opportunities: Scholarships in Brazil - Post-Doctoral