Browsing by Author "Marshall, JC"

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    Climates of the last three interglacials in subtropical eastern Australia inferred from wetland sediment geochemistry
    (Elsevier, 2020-01-15) Kemp, CW; Tibby, J; Arnold, LJ; Barr, C; Gadd, PS; Marshall, JC; McGregor, GB; Jacobsen, GE
    Records of Australian climate during Marine Isotope Stages 5 and 7 (130–71 and 243–191 ka) are rare, preventing detailed assessments of long-term climate, drivers and ecological responses across the continent over glacial-interglacial timescales. This study presents a geochemistry-based palaeoclimate record from Fern Gully Lagoon on North Stradbroke Island (also known as Minjerribah) in subtropical eastern Australia, which records climates in MIS 7a–c, MIS 5 and much of the Holocene, in addition to MIS 4 (71–57 ka), and parts of MIS 6, MIS 3 and MIS 2 (191–130, 57–29 and 29–14 ka). Indicators of inorganic sedimentation from a 9.5 m sediment core – focussed on high-resolution estimates of sediment geochemistry supported by x-radiography, inorganic content and magnetic susceptibility – were combined with a chronology consisting of six radiocarbon (14C) and thirteen single-grain optically stimulated luminescence (OSL) ages. Hiatuses occurred at ~178–153 ka, ~36–21 ka and ~7–2 ka and likely result from the wetland drying. Low values of locally sourced aeolian materials indicate a wet MIS 7a–c and early MIS 6 before a relatively dry MIS 5. Inorganic flux during the Holocene was up to four times greater than during MIS 5, consistent with long-term interglacial drying observed in other regions, most notably in central Australia. This study highlights the importance of employing a combination of multiple dating approaches and calibrated geochemical proxies to derive climate reconstructions and to identify depositional complexities in organic-rich wetland records. © 2020 Elsevier B.V
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    Holocene El Niño–Southern Oscillation variability reflected in subtropical Australian precipitation
    (Springer Nature, 2019-02-07) Barr, C; Tibby, J; Leng, MJ; Tyler, JJ; Henderson, ACG; Overpeck, JT; Simpson, GL; Cole, JE; Phipps, SJ; Marshall, JC; McGregor, GB; Hua, Q; McRobie, FH
    The La Niña and El Niño phases of the El Niño-Southern Oscillation (ENSO) have major impacts on regional rainfall patterns around the globe, with substantial environmental, societal and economic implications. Long-term perspectives on ENSO behaviour, under changing background conditions, are essential to anticipating how ENSO phases may respond under future climate scenarios. Here, we derive a 7700-year, quantitative precipitation record using carbon isotope ratios from a single species of leaf preserved in lake sediments from subtropical eastern Australia. We find a generally wet (more La Niña-like) mid-Holocene that shifted towards drier and more variable climates after 3200 cal. yr BP, primarily driven by increasing frequency and strength of the El Niño phase. Climate model simulations implicate a progressive orbitally-driven weakening of the Pacific Walker Circulation as contributing to this change. At centennial scales, high rainfall characterised the Little Ice Age (~1450–1850 CE) in subtropical eastern Australia, contrasting with oceanic proxies that suggest El Niño-like conditions prevail during this period. Our data provide a new western Pacific perspective on Holocene ENSO variability and highlight the need to address ENSO reconstruction with a geographically diverse network of sites to characterise how both ENSO, and its impacts, vary in a changing climate. © The Author(s) 2019, corrected publication 2021
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    Holocene sediment records from World Heritage-listed K'gari/Fraser Island lakes (subtropical eastern Australia) highlight their sensitivity to drying
    (International Union for Quaternary Research (INQUA), 2019-07-30) Tibby, J; Barr, C; McInerney, F; Murphy, C; Raven, M; Leng, MJ; Tyler, JJ; Marshall, JC; McGregor, GB; Gadd, PS
    Lakes are some of the most biodiverse, yet vulnerable, ecosystems on the planet. In Australia, the driest inhabited continent on earth, permanent lakes are relatively rare. By contrast, K'gari or Fraser Island, the largest sand island in the world, has a large number of permanent lakes and represents one of the few lake districts on the continent. The lakes of K'gari/Fraser island are remarkable because many are perched above the regional water table where an impermeable layer separates them from the sand below. They are one of the reasons why the island is listed as a UNESCO World Heritage site. Holocene sediment sequences have now been analysed from at least six lakes on K'gari/Fraser Island. It appears that there was marked aridity on the island from c. 8000 to 5000 ka BP. Some lakes dried completely at a time previously thought to be characterised by humid climates in the Australian subtropics. Interestingly, in some sequences there is little to no physical evidence of drying which is recorded as a hiatus in the accumulation of highly organic, acidic, lake sediments. The mid-Holocene dry phase recorded on K'gari/Fraser Island contrasts with evidence from North Stradbroke Island, a similar sand island which also has perched lakes, approximately 150 km to the south. As a result, there is strong potential to infer the Holocene regional climatology of the Australian subtropics at small spatial scales from these records. Lastly, our study highlights a largely unrecognised vulnerability of lakes on K’gari to drying and indicates a need to better understand their hydrology and response to projected future climate change. © The Authors.
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    A Holocene subtropical hydroclimate reconstruction from Karboora (Blue Lake), Minjerribah, Queensland
    (Australasian Quaternary Association Inc., 2022-12-06) Maxson, C; Tibby, J; Tyler, JJ; Marshall, JC; McGregor, G; Schulz, C; Jacobsen, GE; Klaebe, R
    Holocene palaeoclimatology provides insights into the climate system, with particular relevance to the next century. This is especially true in sub-tropical Australia due to the under representation of the region in Holocene climate studies. Karboora (Blue Lake), on Minjerribah (North Stradbroke Island), Queensland, Australia is a groundwater window lake of major ecological and cultural significance. The lake’s strong connection with the regional aquifer underpins lake level stability, rendering Blue Lake sediments an ideal tracer of subtle changes in climate. Here, we report a new 5,500-year oxygen isotope record from biogenic (diatom) silica (δ18OBSi) that records variations in rainfall resulting from changes in Pacific atmospheric circulation. These interpretations are supported by modern monitoring over a 20 month period, including the δ18O of lake water, rain water, plant cellulose, and biogenic silica. We link rain δ18O to changes in El Niño Southern Oscillation (ENSO) phases, with phases showing distinct isotopic change that may be linked to tropical or extratropical sources of rainfall. On these grounds, we infer a dominance of extratropical rainfall from 5.5 kyr BP to 3.5 kyr BP, a period of transition from 3.5 kyr BP to 2.5 kyr BP dominated by neither tropical or extratropical rainfall, then a shift to tropically sourced rain from 2.5 kyr BP to the present. The early record (5.5 kyr BP – 3.5 kyr BP) most likely reflects a suppression of summer rainfall caused by a weakened ENSO. This is most likely linked to higher northern hemisphere insolation causing a northward shift in the intertropical convergence zone and westerly wind belt which in turn affected synoptic systems in the Coral and Tasman Seas. The increasing variability in the late record (3.5 kyr BP to present) most likely represents an increase in summer rainfall driven by the intensification of ENSO in the late Holocene.
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    Independent Bayesian age modelling in subtropical wetlands to assess the influence of global climate drivers across Australia
    (Australasiain Quaternary Association Inc, 2018-12-10) Lewis, RJ; Tibby, J; Arnold, LJ; Barr, C; Marshall, JC; McGregor, GB; Gadd, PS
    Rigorously dated, continuous sedimentological records capturing multiple glacial/interglacial cycles are important for evaluating the magnitude and range of drivers influencing ecosystem change in Australia. Multi-proxy palaeoenvironmental reconstructions are commonly used to identify changes in long-term environmental conditions, particularly when exploring the climatic backdrop to Australia’s large scale faunal extinctions. However, interpretations of these records may not be straightforward as local and regional climate signals are often mixed in proxy records. In order to evaluate whether improved temporal constraint can help with differentiating such convoluted signals, thereby increasing the confidence placed in the role of teleconnections across the Southern Hemisphere, we present a comprehensively dated 12.7 m (basal age ~130 ka) wetland core consisting of 21 optically stimulated luminescence and seven radiocarbon ages from North Stradbroke Island. The amalgamation of stratigraphic information and independent age constraints within a Bayesian framework, highlights the complex depositional history of Welsby Lagoon between late MIS 5 and MIS 2. ITRAX core scanning data reveals fluctuations in elemental abundance through time, in particular the decrease in the amount of aeolian sediment following MIS 3. Variability is attributed to regional environmental regime changes controlled by global drivers, including Heinrich events, and the influence of moisture across mainland Australia. The comprehensive dating approach undertaken at Welsby Lagoon highlights the role that the terrestrial palaeoenvironmental records of North Stradbroke Island can play in assessing long-term climate drivers across continental Australia, without relying exclusively on isotopic tuning of remote (ice core or marine) records. © The Authors
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    Insights into subtropical Australian aridity from Welsby Lagoon, North Stradbroke Island, over the past 80,000 years
    (Elsevier, 2020-04-15) Lewis, RJ; Tibby, J; Arnold, LJ; Barr, C; Marshall, JC; McGregor, GB; Gadd, PS; Yokoyama, Y
    Terrestrial sedimentary archives that record environmental responses to climate over the last glacial cycle are underrepresented in subtropical Australia. Limited spatial and temporal palaeoenvironmental record coverage across large parts of eastern Australia contribute to uncertainty regarding the relationship between long-term climate change and palaeoecological turnover; including the extinction of Australian megafauna during the late Pleistocene. This study presents a new, high-resolution, calibrated geochemical record and numerical dating framework from Welsby Lagoon, a wetland from North Stradbroke Island that records key periods of late Pleistocene environmental change. Single-grain optically stimulated luminescence and radiocarbon dating are integrated into a Bayesian age-depth model for the sedimentary sequence spanning Marine Isotope Stage (MIS) 5 to the present. Scanning micro X-ray fluorescence (XRF) and bulk sediment XRF assays are used to infer past dust dynamics, with changes in the abundance of silica and potassium interpreted as proxies for aridity across local and regional sources. Variations in dust flux were contemporaneous with hydrological change, concordant with changes in vegetation cover on the island and, relate to deflation events at major dust source regions on the Australian continent. The Welsby Lagoon record supports the notion of a variable MIS4 within which an increased dust flux (71–67 ka), may be indicative of drier climate. Additionally, the record also shows a lower dust flux through the Last Glacial Maximum (LGM) than is evident in other Australian aeolian records. However, this low LGM flux is attributed to the wetland’s evolution, rather than a reduction in total dust flux. ©2020 Elsevier Ltd