Browsing by Author "Dux, F"

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    A high-resolution record of south-eastern Australian hydroclimate between 30,000 - 10,000 years ago: toward a better understanding of the Australian LGM
    (International Union for Quaternary Research (INQUA), 2019-07-29) Falster, G; Tyler, JJ; Grant, K; Tibby, J; Turney, C; Löhr, S; Jacobsen, GE; Kershaw, AP; Kluge, T; Drysdale, RN; Dux, F
    Global climate variability during the late Quaternary is commonly framed in terms of the ‘bipolar seesaw’ pattern of asynchronous temperature variations in the northern and southern polar latitudes. However, the terrestrial hydrological response to this pattern in south-eastern Australia is not fully understood, as continuous, high-resolution, well-dated proxy records for the hydrological cycle in the region are sparse. Here we present a well-dated, highly resolved record of moisture balance spanning 30000 – 10000 calendar years before present (30 – 10 ka BP), based on x-ray fluorescence and organic carbon isotope (δ13COM) measurements of a sedimentary sequence from Lake Surprise in south-eastern Australia. The data provide a locally coherent record of the hydrological cycle (Fig. 2). Elevated Si (reflecting windblown quartz and clays), and relatively high δ13COM, indicate an extended period of relative aridity between 28 – 17.5 ka BP, interrupted by millennial-scale episodes of decreased Si and δ13COM­, suggesting increased moisture balance. Peak aridity was reached between 21 and 17.5 ka BP, possibly representing the expression of the global Last Glacial Maximum. This was followed by a rapid deglacial shift to low Si and δ13COM at 17.5 ka BP, indicative of wetter conditions. We find that these changes are broadly coeval with similarly high-resolution records from south-eastern Australia and New Zealand. We also supplement our high-resolution record with discrete clumped isotope measurements on freshwater gastropods from Blanche Cave, also in south-eastern Australia. Temperatures either side of the Last Glacial Maximum were slightly cooler than those of the modern day, with the hint of a decrease from 40 to 30 ka BP. We did not find gastropods within the 28-17.5 ka BP interval in this cave, but identify this as a period for urgent attention. Together, our analyses suggest that drivers of the regional hydrological cycle have varied on multi-millennial time scales, in response to major shifts in global atmosphere-ocean dynamics during the last glacial-interglacial transition. Southern Ocean processes were the dominant control on hydroclimate during glacial times, via a strong influence of cold sea surface temperatures on moisture uptake and delivery onshore. Following the last deglaciation, the southward migration of cold Southern Ocean fronts likely resulted in the establishment of conditions more like those of the present day. These conclusions will be tested in future work, focused on quantitative rainfall estimates from clumped isotope of land snail shells. Figure 1. Selected data from the Lake Surprise record: a) Bulk sediment carbon isotope ratios (δ13COM), interpreted to reflect plant moisture stress; b) First principal component (PC1) of the calibrated scanning XRF dataset, interpreted to reflect aeolian deposition of Si. Arrows indicate periods of increased effective moisture within the relatively arid LGM. Triangles denote 14C age control points.
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    Partitioning of Mg, Sr, Ba and U into a subaqueous calcite speleothem
    (Elsevier, 2019-11-01) Drysdale, RN; Zanchetta, G; Baneschi, I; Guidi, M; Isola, I; Couchoud, I; Piccini, L; Greig, A; Wong, HKY; Woodhead, JD; Regattieri, E; Corrick, E; Paul, B; Spötl, C; Denson, E; Gordon, J; Jaillet, S; Dux, F; Hellstrom, JC
    The trace-element geochemistry of speleothems is becoming increasingly used for reconstructing palaeoclimate, with a particular emphasis on elements whose concentrations vary according to hydrological conditions at the cave site (e.g. Mg, Sr, Ba and U). An important step in interpreting trace-element abundances is understanding the underlying processes of their incorporation. This includes quantifying the fractionation between the solution and speleothem carbonate via partition coefficients (where the partitioning (D) of element X (DX) is the molar ratio [X/Ca] in the calcite divided by the molar ratio [X/Ca] in the parent water) and evaluating the degree of spatial variability across time-constant speleothem layers. Previous studies of how these elements are incorporated into speleothems have focused primarily on stalagmites and their source waters in natural cave settings, or have used synthetic solutions under cave-analogue laboratory conditions to produce similar dripstones. However, dripstones are not the only speleothem types capable of yielding useful palaeoclimate information. In this study, we investigate the incorporation of Mg, Sr, Ba and U into a subaqueous calcite speleothem (CD3) growing in a natural cave pool in Italy. Pool-water measurements extending back 15 years reveal a remarkably stable geochemical environment owing to the deep cave setting, enabling the calculation of precise solution [X/Ca]. We determine the trace element variability of ‘modern’ subaqueous calcite from a drill core taken through CD3 to derive DMg, DSr, DBa and DU then compare these with published cave, cave-analogue and seawater-analogue studies. The DMg for CD3 is anomalously high (0.042 ± 0.002) compared to previous estimates at similar temperatures (∼8 °C). The DSr (0.100 ± 0.007) is similar to previously reported values, but data from this study as well as those from Tremaine and Froelich (2013) and Day and Henderson (2013) suggest that [Na/Sr] might play an important role in Sr incorporation through the potential for Na to outcompete Sr for calcite non-lattice sites. DBa in CD3 (0.086 ± 0.008) is similar to values derived by Day and Henderson (2013) under cave-analogue conditions, whilst DU (0.013 ± 0.002) is almost an order of magnitude lower, possibly due to the unusually slow speleothem growth rates (<1 μm a−1), which could expose the crystal surfaces to leaching of uranyl carbonate. Finally, laser-ablation ICP-MS analysis of the upper 7 μm of CD3, regarded as ‘modern’ for the purposes of this study, reveals considerable heterogeneity, particularly for Sr, Ba and U, which is potentially indicative of compositional zoning. This reinforces the need to conduct 2D mapping and/or multiple laser passes to capture the range of time-equivalent elemental variations prior to palaeoclimate interpretation. © 2019 Elsevier Ltd
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    Radiometrically dated speleothem records of Terminations IV and V and linkages to the North Atlantic
    (International Union for Quaternary Research (INQUA), 2019-07-28) Pollard, T; Drysdale, RN; Woodhead, JD; Edwards, RL; Hellstrom, JC; Cheng, H; Dux, F; Daëron, M; Li, XL; Wong, HKY; Couchoud, I; Regattieri, E; Zanchetta, G; Isola, I
    Paleoclimate archives tied to accurate and precise chronologies are crucial for developing a dynamical understanding of the causes and nature of Quaternary glacial terminations [1]. While numerous well-dated archives provide good chronological control through Terminations I and II, there is presently a lack of well-dated records spanning earlier terminations. A notable exception to this is a suite of remarkably well-dated Chinese speleothems that have been used to date the commencement of each termination over the past 640 kyr [2,3]. This has been achieved by correlating weak Asian Monsoon anomalies as captured by speleothem oxygen isotope signals with terminal Heinrich events in the North Atlantic. While this approach is well-suited to testing orbital hypothesis by comparing the timing of termination commencement with insolation metrics, it only provides precise age control at the beginning of each termination. This precludes assessment of the progression of climatic changes over the full course of the termination, and the timing at which full interglacial conditions are reached. Here we present a composite speleothem record spanning glacial terminations IV and V from the Antro del Corchia cave system located on the western coast of central Italy. This record is anchored to a uranium-thorium based chronology and contains numerous proxies representing both local and regional climate, including Δ47-based temperature data derived from a pool carbonate formed under very slow degassing conditions. By taking advantage of established links between speleothem proxies from this cave site and marine proxies from the North Atlantic, we fix the marine sediment data to a radiometric age scale. This allows us to constrain the timing of ocean circulation and SST changes occurring in the North Atlantic throughout the duration of Terminations IV and V, and compare these with terrestrial temperatures in central Italy. © The Authors.