Mineral magnetic ‘tracing’ of aeolian dust in southwest Pacific sediments

Reliable magnetic signatures were sought to trace aeolian dust in Tasman Sea sediments where the aeolian fraction had also been chemically isolated. Modern dust samples from eastern Australia were found to have a strong ferrimagnetic signal and a weaker antiferromagnetic (AFM) background. The ferrimagnetic component could not be detected in the deep-sea sediments, where a finer biogenic magnetite component prevails over a background AFM and two other ?authigenic components. The modern dust is thought to be unrepresentative of prehistoric dust, probably as the result of contamination from local agricultural soils. The AFM component in the sediments, however, was found to be highly correlated with the independently determined aeolian concentration, except in intervals with a high magnetic susceptibility, high χfd signal, possibly from an authigenic component. Because of the non-aeolian contribution to magnetic hardness (SIRM + IRM−300) and different relationships observed in different cores, the magnetic tracing of aeolian dust is currently only valid as a measure of relative changes in concentration in sediments with similar chemistry and low frequency dependence of susceptibility.