Primary supervisor: Zanna Chase
Co-supervisor: Taryn Noble
Brief project description:
The Southern Ocean plays a critical role in the oceanic silicon cycle, with Southern Ocean sediments responsible for nearly 50% of silicon burial globally (Treguer and De La Rocha 2013; Chase et al. 2015). The abundant and productive diatoms in the Southern Ocean deliver large amounts of silicon to the seafloor in the form of opal frustules. However, only ~1 - 6% of the silicon that reaches the seafloor escapes dissolution and is preserved long term in the sediment (Chase et al 2015; Pondaven et al. 2002; Nelson et al. 2000). Most of the silicon dissolves in the upper tens of cm of the sediment, and returns as silicic acid to the water column, where it can be reincorporated in the biological cycle. The remaining, buried opal, is incorporated into the sediment record. Paleoceanographers use this buried opal in the form of accumulation rates and preserved diatom assemblages to reconstruct ocean productivity and environmental conditions through time.
Despite its importance to global chemical cycles, and to the integrity of paleoceanographic interpretations, many questions remain about what controls the preservation of opal in Antarctic sediments. There is a growing body of evidence that aluminium plays a central role in opal preservation, with opal preservation increasing with a higher proportion of lithogenic material relative to opal in sinking particles (Van Cappellen and Qui 1997; and see summaries in Martin and Sayles 2003 and Sarmiento and Gruber 2006, chapter 7). The relationship appears to be site specific, although the overall lack of data may be obscuring larger trends.
This project will add to our understanding of opal preservation in Antarctic sediments using data and samples collected on a recent voyage to Cape Darnley, East Antarctica (Jan – Feb 2022). The project will use analyses of sediment and sediment pore waters (e.g. see Gallinari et al. 2008 and Sayles et al. 2001) to evaluate the role of lithogenic material in opal preservation, and to test some proposed algorithms to predict opal burial efficiency (e.g. Sayles et al. 2001). Pore water analyses will be completed at sea, and the student will have access to these data. Sediment solids will be analysed at IMAS for concentrations of opal, Th-232, Al and Th-230. These measurements will enable calculations of fluxes of opal and lithogenic material.