High-field magnetic susceptibility ( χHF) as a proxy of biogenic sedimentation along the Antarctic Peninsula

Abstract

High-field mass-normalized magnetic susceptibility ( χ HF) is presented as a proxy for biogenic sedimentation in glacimarine sediment from the western Antarctic Peninsula. χ HF is measured at field strengths that exceed the saturation field of ferrimagnetic minerals. These measurement conditions exclude the contributions of ferrimagnetic iron oxides that dominate low-field volume-normalized susceptibility ( k) measurements. Therefore, χ HF allows for closer examination of paramagnetic and diamagnetic minerals, the latter of which includes biogenic silica and biogenic calcite. In sedimentary sequences from the western Antarctic Peninsula, the main processes affecting the abundance of diamagnetic material in sediment is biological productivity and the subsequent flux of biogenic silica to the seafloor. χ HF profiles were measured on two biosiliceous sediment cores from the western Antarctic Peninsula. Comparisons with quantitative biogenic silica measurements indicate that χ HF tracks % opaline silica very well, and reveals the presence of century-scale cycles in sediment composition in intervals where k appears featureless. χ HF is limited as a quantitative measure of biogenic sediment flux, since terrigenous paramagnetic and diamagnetic minerals also contribute to the measurement. The interpretation of χ HF can also be complicated by the presence of unsaturated high-coercivity minerals such as hematite and goethite, or by the presence of ultra-fine superparamagnetic (SP) particles. However, in sediment sequences where the condition of saturation is met, χ HF is very well suited for the rapid identification of temporal trends in biogenic sedimentation.