Unravelling the Secrets of the Subantarctic Auckland Island Inlets: An Environmental Magnetic Study of a Holocene Sediment Core

Einvik-Heitmann, Vegar

A sediment core (14PL001 – 39P4), collected from the Hanfield Inlet on the subantarctic Island of Auckland Island by a scientific research group from the University of Otago, have been subject to an environmental magnetic study by the use of u-channel samples. Lithostratigraphic analyses was carried out on the core, which contain the transition from a lacustrine environment to a marine environment through an inter-bedded sequence which was correlated to regional sea-level curves, indicating a date of ~8ka. High-resolution magnetic measurements of natural remanent magnetisation intensity, anhysteric remanent magnetisation intensity and magnetic susceptibility, and a stepwise alternating field demagnetisation were performed on the u-channels. Declination, inclination and median destructive field were determined throughout the core by the use of a principal component analysis of orthogonal component vectors. Chemical alteration of titanomagnetites and authigenic growth of pyrrhotite and greigite dominated a larger interval, complicating environmental interpretations. Magnetic mineralogy were therefore further investigated on sub samples by measuring thermomagnetic behaviour and isothermal remanent magnetisation together with energy dispersive spectroscopy. A proxy sensitive to magnetic grain size changes, related to the Holocene westerly wind variability was developed by plotting the measurements of the anhysteric remanent magnetisation intensity on the magnetic susceptibility measurements. The proxy together with sedimentary and mineralogical observations support the suggested pattern of a strong core in the westerly winds for the early Holocene, succeeded by a weak core for the late Holocene.

86 pages A4

2014Einvik-Heitmann

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