Hendrik Heijnis

Quaternary aminostratigraphy of eolianite on Lord Howe Island, Southwest Pacific Ocean

Abstract Amino acid racemization (AAR) dating of the eolianite on Lord Howe Island is used to correlate several disparate successions and provides a geochronological framework that ranges from Holocene to Middle Pleistocene time. The reliability of the AAR data is assessed by analysing multiple samples from individual lithostratigraphic units, checking the stratigraphic order of the D/L ratios and the consistency of the relative extents of racemization for a suite of seven amino acids. Three aminozones are defined on the basis of the extent of racemization of amino acids in land snails (Placostylus bivaricosus) and ‘whole-rock’ eolianite samples. Aminozone A includes Placostylus from modern soil horizons (e.g. mean D/L-leucine ratio of 0.03±0.01) and whole-rock samples from unconsolidated lagoonal and beach deposits (0.10±0.01–0.07±0.03). Aminozone B includes Placostylus (0.45±0.03) and whole-rock samples from beach (0.48±0.01) and dune (0.45±0.02–0.30±0.02) units of the Neds Beach Formation, deposited during OIS 5. The oldest, Aminozone C, comprises Placostylus recovered from paleosols (0.76±0.02) and whole-rock eolianite samples (0.62±0.00) from the Searles Point Formation, which indicate the formation was likely deposited over several Oxygen Isotope Stages (OIS), during and prior to OIS 7. These data support independent lithostratigraphic interpretations and are in broad agreement with U/Th ages of speleothems from the Searles Point Formation and corals from the Neds Beach Formation, and with several TL ages of dune units in both formations. The AAR data reveal that eolianite deposition extends over a significantly longer time interval than previously appreciated and indicate that the deposition of the large dune units is linked to periods of relatively high sea level.

Mud, mines and rainforest: a short history of human impact in western Tasmania, using pollen, trace metals and lead-210

Lead-210, pollen and trace-element analyses of a finely sampled 7.5-cm sediment core from a subalpine tarn in western Tasmania have provided a detailed record of post-colonial human impact in the region. Lead-210 analysis indicated that the record extends back to about 1811 AD, with several changes in sediment rates evident. These have been tentatively related to disturbance in the catchment associated with ore prospecting. The regional vegetation has been reconstructed for this period using pollen abundances. Prior to 1860 AD, there appears to have been little disturbance in the regional vegetation, with relatively high taxon diversity and pollen concentrations. Important communities included rainforest dominated by Nothofagus cunninghamii and subdominated by Phyllocladus and Eucryphia, eucalypt-dominated mixed and wet sclerophyll forest and subalpine and/or alpine complexes. From the 1860s, the evidence suggests an overall reduction in the extent of regional forests, particularly rainforest and subalpine woodland. Initially, this appears to have been associated with both elevated charcoal levels and minor increases in concentrations of trace metals, particularly lead, tin, arsenic and copper. By the 1950s, however, significant reductions in taxon diversity and pollen abundance (particularly for rainforest and subalpine woodland) were strongly associated with rapidly increasing concentrations of trace metals. This evidence corresponds with historic records of mineral prospecting and mining in the region, especially around Queenstown where significant deforestation occurred due to logging and pollution from smelters. Interestingly, the evidence for the most significant impacts coincided with the escalation of open-cut mining from the 1950s to the 1970s, rather than earlier phases of smelter-produced pollution.

Palynology, aminostratigraphy and U-series dating of marine gortian interglacial sediments in cork harbour, Southern Ireland

Abstract Palynological analysis, amino acid epimerization analysis and uranium thorium disequilibrium age determination of three Irish interglacial cores support the suggestion that there may have been more than one Holsteinian-style temperate interval in Europe. The cores were taken from estuarine deposits beneath glacial diamicton in Cork Harbour, southwest Ireland. The pollen records an incomplete temperate stage. The biotic signature is similar to those from several interglacial sites in Ireland and is considered part of the Gortian group. The pollen signature is Holsteinian/Hoxnian in character. Amino acid epimerization analysis suggests the deposits to be Oxygen Isotope Stage 7 in age, whereas uranium–thorium disequilibrium suggests a minimum Stage 5 age. Possible correlatives of the Gortian group in Europe are suggested.

Centennial-scale trends in the Southern Annular Mode revealed by hemisphere-wide fire and hydroclimatic trends over the past 2400 years

Millennial-scale latitudinal shifts in the southern westerly winds (SWW) drive changes in Southern Ocean upwelling, leading to changes in atmospheric CO2 levels, thereby affecting the global climate and carbon cycle. Our aim here is to understand whether century-scale shifts in the SWW also drive changes in atmospheric CO2 content. We report new multiproxy lake sediment data from southwest Tasmania, Australia, that show centennial-scale changes in vegetation and fire activity over the past 2400 yr. We compare our results with existing data from southern South America and reveal synchronous and in-phase centennial-scale trends in vegetation and fire activity between southwest Tasmania and southern South America over the past 2400 yr. Interannual to centennial-scale rainfall anomalies and fire activity in both these regions are significantly correlated with shifts in the SWW associated with the Southern Annular Mode (SAM; atmospheric variability of the Southern Hemisphere). Thus, we interpret the centennial-scale trends we have identified as reflecting century-scale SAM-like shifts in the SWW over the past 2400 yr. We identify covariance between our inferred century-scale shifts in the SWW and Antarctic ice core CO2 values, demonstrating that the SWW-CO2 relationship operating at a millennial scale also operates at a centennial scale through the past 2400 yr. Our results indicate a possible westerly-driven modulation of recent increases in global atmospheric CO2 content that could potentially exacerbate current greenhouse gas–related warming.

Using X-ray fluorescence core scanning to assess acid sulfate soils

During the formation of acid sulfate soils (ASS), several chemical elements in the sediment are mobilised. These elements are removed from the sediment or become enriched as precipitates in distinct horizons. The stratigraphic depth in which these precipitates accumulate is element-specific and is located either within the oxidised or in a transitional zonebetweentheoxidisedandthereducedzone.AimofthisstudyistodemonstratehowX-ray fluorescencecorescanning, together with detailed sediment descriptions, can be used to perform an initial assessment of these different zones in ASS in a fast and cost-effective manner. We measured the chemical element signatures of K, Fe, Pb, Sr, Zn, Ni, Y, Mn and Ca in two sediment cores from Western Australia where ASS are suspected to occur. The oxidised zone in both cores is characterised by the occurrence of jarosite, which is indicated by pale straw yellow mottling and synchronous peaks in Fe/ Ti, K/Ti, Pb/Ti and Sr/Ti, and of other secondary Fe-oxides, which are indicated by reddish mottling and synchronous peaks in Fe/Ti and Pb/Ti. The transition zone into reduced material is marked by synchronous peaks in Zn/Ti, Ni/Ti, Y/Ti and Mn/Ti. Based on these characteristic signatures, we broadly estimated the depth of the oxidised and the transitional zone at both sites.