Testing methods for marine sediment characterisation from a nearshore environment: Davis Station, Australian Antarctic Territory

This study tested and assessed several methods for identifying and describing physical and chemical characteristics of nearshore sediments in East Antarctica. The study emphasised non-destructive techniques that can be used with small volumes of sample. There were three key aims: 1. Provide information about analytical techniques that are non-destructive and can be used on small-volume samples, 2. Apply these techniques to a set of samples where sufficient material is available and compare the results with the outcomes of traditional geochemical techniques, and, 3. Gain additional information on sedimentary processes in the nearshore environment in East Antarctica. Sediment samples from the Antarctic region are especially difficult to collect because of large logistical requirements and are thus highly valuable. Sediment traps are an example of samples with typically small volumes. Such samples provide valuable information about the nature and quantity of marine sediment in the water column and are highly sought after by researchers. By testing characterisation methods on larger samples, this scoping study provides recommendations for analysing small-volume samples, using non-destructive techniques and techniques that can provide additional information to traditional analysis. In this study, laser Raman spectroscopy and infrared spectroscopy were used to provide qualitative mineralogy for calcite, aragonite, and biogenic silica. Microtextural analysis of quartz grains was undertaken with a scanning electron microscope to provide information on the physical transport processes that the sediment has undergone. With this technique we were also able to identify chemical weathering features. Raman spectroscopy is a relatively rapid technique and has simple sample preparation requirements. The technique can target individual grains but can also measure bulk mineralogy. It is a promising technique for distinguishing mineral polymorphs but scope for quantification is limited for multi-component mixtures compared to traditional mineralogical methods like x-ray diffraction (XRD). Infrared spectroscopy is also quick and sample preparation is minimal. The technique requires more sample than will probably be recovered from sediment traps or sediment cores, at least 15 grams. For samples with large proportions of terrigenous sediment, distinguishing biogenic minerals is difficult because of low concentrations. Acquisition of more reference spectra for minerals of interest in marine substrates (particularly biogenic minerals) would be useful for comparing with sample spectra. Microtextural analysis provides detailed information about potential transport processes but sample preparation and analysis is time-consuming when compared to geochemical analysis. The technique is also somewhat destructive as quartz grains need to be cleaned and mounted. We recommend that an absolute minimum of 20 quartz grains is required for microtextural analysis. Microtextural analysis of sediments from near Davis Station suggests reworking of sediments in a subaqueous environment and minimal aeolian transport. There is also evidence of secondary silica precipitation and minor dissolution of quartz grains.