HR: 08:00h
AN: GP41A-01 INVITED     [PDF]
TI: Magnetic Mineral Concentrations of Recent Lake Sediments as Recorders of Climate Variations
AU: * Kodama, K P
EM: kpk0@lehigh.edu
AF: Lehigh University, Department of Earth and Environmental Sciences, 31 Williams Drive, Bethlehem, PA 18015-3188 United States
AU: Kim, B
EM: bak4@lehigh.edu
AF: Lehigh University, Department of Earth and Environmental Sciences, 31 Williams Drive, Bethlehem, PA 18015-3188 United States
AB: We have been studying the mechanism by which the variation of magnetic mineral concentrations in recent lake sediments could record local climate variations. Our earliest work showed that magnetic mineral concentrations in lakes of different productivity (eutrophic, mesotrophic, and oligotrophic) from the Pocono Mountains of northeastern Pennsylvania showed a correlation to historic records of regional rainfall over the past 100-200 years. The robustness of these correlations was hampered by the reliance on $^{210}$Pb dating of the lake sediments. The varve chronology of sediments from Lake Ely in northeastern Pennsylvania afforded a more accurate downcore comparison between magnetic mineral concentrations and a local historic rainfall record. The observation of a positive correlation between ARM and SIRM and the local rainfall record over the past 60 years suggested a model in which increased precipitation supplied more nutrients to a postulated magnetotactic bacteria population in the lake and enhanced the production of magnetosomes that were preserved in the lake sediments. A detailed study of the mineral magnetism of water filtered from the water column and recent lake sediments of Lake Ely indicates that magnetosomes are definitely present at the oxic-anoxic transition in the water column and in recent lake sediments. Comparison of the ARM intensity of water column filtrate with the ARM intensity of material collected six months later from a sediment trap, does give some support to the rainfall-nutrient model, but the correlation recorded over this short period is not strong and is incomplete. Comparison of the magnetic data to the historic temperature record suggests that the duration of lake ice cover may be a mitigating factor in the magnetic mineral recording of rainfall variation, i.e. colder winters with longer periods of ice cover would minimize mixing of lake waters by wind and allow larger populations of magnetotactic bacteria to develop in the following spring and summer. Based on our studies, the best lake from which to obtain a record of climate variations using magnetic mineral concentration is one with a magnetic mineralogy dominated by magnetosomes, i.e. where the detrital input to the lake has a easily distinguished, different magnetic mineralogy from the magnetosomes or has a much lower magnetic mineral concentration. In addition, the magnetic mineral concentrations may record a combination of precipitation and temperature variations.
DE: 1505 Biomagnetism
DE: 1512 Environmental magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting