Holocene Dust Transport to the Sub-Antarctic – Implications for the mid-latitude westerlies

Understanding the past behaviour of the Southern Hemisphere mid-latitude westerlies in the past is important due to their role in determining precipitation regimes on Southern Hemisphere land masses, advecting heat and influencing carbon cycling in the Southern Ocean and the transport of mineral and biological matter between continents. The aim of this study was to determine how the Southern Hemisphere mid-latitude westerly winds varied in their strength and intensity over the mid to late Holocene (~5500 cal yr BP to present). Australian dust transport to ombrotrophic (rainfall-fed) peat bogs on Campbell Island (52°34’S, 169°09’E) and Stewart Island (47°00’S, 168°50’E) was assessed. Ombrotrophic bogs grow above the surrounding hydrology and so are isolated from local contributions of sediment (fluvial or colluvial). Subsequently, the majority of mineral matter present in the cores analysed in this study was transported from the Australian mainland into the bogs by the westerly winds. Rates of dust deposition were determined by loss-on ignition analysis and the provenance of dust was determined using a mass balance approach which compared the chemistry of samples in the core to a range of over 250 potential source sediments. Rates of dust deposition and the provenance of dust were used to determine palaeo-aridity patterns on the Australian mainland, which were then used to infer the likely latitudinal position of westerly winds at particular points in time. Patterns of changing grain size were used to determine the changing intensity of the westerly winds. From ~5500-4000 cal yr BP, the results of this study indicate a southward displacement and weak nature of the westerlies. From ~4000-1700 cal yr BP, results indicate a northward displacement and strengthening of the westerlies. The westerlies remained in their northerly location after ~1700 cal yr BP, whilst wind intensity fluctuated. Results suggest that overall, the westerly winds have moved northward and increased in intensity since ~5500 cal yr BP.