Browsing by Author "Kershaw, AP"

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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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    High-resolution record of vegetation and climate through the last glacial cycle from Caledonia Fen, southeastern highlands of Australia.
    (Wiley-Blackwell, 2007-07) Kershaw, AP; McKenzie, GM; Porch, N; Roberts, RG; Brown, J; Heijnis, H; Orr, ML; Jacobsen, GE; Newallt, PR
    A blocked tributary has provided a rare site of long-term sediment accumulation in montane southeastern Australia. This site has yielded a continuous, detailed pollen record through the last ca. 140000 years and revealed marked vegetation and environmental changes at orbital to sub-millennial scales. Radiocarbon and optically stimulated luminescence (OSL, or optical) ages provide some chronological control for the last ca. 70 000 years. Most of the sediment is inorganic but with well preserved pollen that accumulated under unproductive and probably largely ice-covered lake conditions. The lake was surrounded by low-growing plants with an alpine character. Exceptions include three discrete periods of high organic sedimentation in the basin and forest development in the surrounding catchment. The two major periods of forest expansion are related to the last interglacial and the Holocene, with the third, shorter period considered to represent an interstadial in the early part of Marine Isotope Stage (MIS) 3. The latter part of the last glacial period is characterised by abrupt sub-millennial, amelioration events that may relate to documented global oscillations emanating from the North Atlantic. There are systematic changes through the record that can be partly attributed to basin infilling but the progressive reduction and regional extinction of some plant taxa is attributed to along-term trend towards climatic drying. © 2007, Wiley-Blackwell.
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    Integration of ice-core, marine and terrestrial records for the Australian Last Glacial Maximum and Termination: a contribution from the OZ INTIMATE group
    (Wiley, 2006-10) Turney, CSM; Haberle, SG; Fink, D; Kershaw, AP; Barbetti, M; Barrows, TT; Black, M; Cohen, TJ; Corrège, T; Hesse, PP; Hua, Q; Johnston, R; Morgan, VI; Moss, PT; Nanson, GC; van Ommen, TD; Rule, S; Williams, NJ; Zhao, JX; D'Costa, D; Feng, YX; Gagan, MK; Mooney, SD; Xia, Q
    The degree to which Southern Hemisphere climatic changes during the end of the last glacial period and early Holocene (30-8 ka) were influenced or initiated by events occurring in the high latitudes of the Northern Hemisphere is a complex issue. There is conflicting evidence for the degree of hemispheric ‘teleconnection’ and an unresolved debate as to the principle forcing mechanism(s). The available hypotheses are difficult to test robustly, however, because the few detailed palaeoclimatic records in the Southern Hemisphere are widely dispersed and lack duplication. Here we present climatic and environmental reconstructions from across Australia, a key region of the Southern Hemisphere because of the range of environments it covers and the potentially important role regional atmospheric and oceanic controls play in global climate change. We identify a general scheme of events for the end of the last glacial period and early Holocene but a detailed reconstruction proved problematic. Significant progress in climate quantification and geochronological control is now urgently required to robustly investigate change through this period. © 2006 John Wiley & Sons, Ltd.