Quantifying the concentration of ferrimagnetic particles in sediments using rock magnetic methods

We have developed a quantification method that uses mainly room temperature rock magnetic measurements to calculate concentrations of ferrimagnetic particles in sediments. Our method uses saturation magnetization (M_s) as a total ferrimagnetic concentration proxy, the saturation remanence ratio (M_rs/M_s) as a magnetic grain-size proxy, the anhysteretic remanence ratio (_a/M_rs) to estimate inter-particle magnetostatic interactions, and the normalized susceptibility of the ferrimagnetic fraction (_f/M_s) to calculate the proportion of ultrafine, superparamagnetic particles. This approach eliminates the effect of dilution of the magnetic properties by weakly magnetic matter, and allows the calculation of direct concentrations (or fluxes for dated sedimentary profiles) of constituent ferrimagnetic components. We test our method on a short sediment core from an urban Minnesota lake, for which we calculate ferrimagnetic fluxes of four magnetic components, and compare their pre- and post-European settlement values. Our quantification technique can be applied for reconstructing past environmental changes in a range of sedimentary environments, and is particularly useful for large sets of samples, where detailed magnetic unmixing methods are unfeasible due to time or instrument constraints.