Browsing by Author "Tibby, J"
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- ItemAnthropogenic acceleration of sediment accretion in lowland floodplain wetlands, Murray–Darling Basin, Australia(Elsevier, 2009-07-01) Gell, PA; Fluin, J; Tibby, J; Hancock, G; Harrison, JJ; Zawadzki, A; Haynes, D; Khanum, SI; Little, F; Walsh, BOver the last decade there has been a deliberate focus on the application of paleolimnological research to address issues of sediment flux and water quality change in the wetlands of the Murray–Darling Basin of Australia. This paper reports on the research outcomes on cores collected from sixteen wetlands along the Murrumbidgee–Murray River continuum. In all sixteen wetlands radiometric techniques and exotic pollen biomarkers were used to establish sedimentation rates from the collected cores. Fossil diatom assemblages were used to identify water source and quality changes to the wetlands. The sedimentation rates of all wetlands accelerated after European settlement, as little as two-fold, and as much as eighty times the mean rate through the Late Holocene. Some wetlands completely infilled through the Holocene, while others have rapidly progressed towards a terrestrial state due to accelerated accretion rates. Increasing wetland salinity and turbidity commenced within decades of settlement, contributing to sediment inputs. The sedimentation rate was observed to slow after river regulation in one wetland, but has accelerated recently in others. The complex history of flooding and drying, and wetland salinisation and eutrophication, influence the reliability of models used to establish recent, fine-resolution chronologies with confidence and the capacity to attribute causes to documented effects. © 2009 Elsevier B.V
- ItemThe application of pollen radiocarbon dating and bayesian age-depth modeling for developing robust geochronological frameworks of wetland archives(Cambridge University Press for the Arizona Board of Regents on behalf of the University of Arizona, 2022-04-27) Cadd, HR; Sherborne-Higgins, B; Becerra-Valdivia, L; Tibby, J; Barr, C; Forbes, MS; Cohen, TJ; Tyler, JJ; Vandergoes, MJ; Francke, A; Lewis, RJ; Jacobsen, GE; Marjo, CE; Turney, CSM; Arnold, LJWetland sediments are valuable archives of environmental change but can be challenging to date. Terrestrial macrofossils are often sparse, resulting in radiocarbon (14C) dating of less desirable organic fractions. An alternative approach for capturing changes in atmospheric 14C is the use of terrestrial microfossils. We 14C date pollen microfossils from two Australian wetland sediment sequences and compare these to ages from other sediment fractions (n = 56). For the Holocene Lake Werri Berri record, pollen 14C ages are consistent with 14C ages on bulk sediment and humic acids (n = 14), whilst Stable Polycyclic Aromatic Carbon (SPAC) 14C ages (n = 4) are significantly younger. For Welsby Lagoon, pollen concentrate 14C ages (n = 21) provide a stratigraphically coherent sequence back to 50 ka BP. 14C ages from humic acid and >100 µm fractions (n = 13) are inconsistent, and often substantially younger than pollen ages. Our comparison of Bayesian age-depth models, developed in Oxcal, Bacon and Undatable, highlight the strengths and weaknesses of the different programs for straightforward and more complex chrono-stratigraphic records. All models display broad similarities but differences in modeled age-uncertainty, particularly when age constraints are sparse. Intensive dating of wetland sequences improves the identification of outliers and generation of robust age models, regardless of program used. © The Author(s), 2022. Published by Cambridge University Press for the Arizona Board of Regents on behalf of the University of Arizona
- ItemChanging fluxes of sediments and salts as recorded in lower River Murray wetlands, Australia(International Association of Hydrological Sciences (IAHS), 2006-07-06) Gell, PA; Fluin, J; Tibby, J; Haynes, D; Khanum, SI; Walsh, B; Hancock, G; Harrison, JJ; Zawadzki, A; Little, FThe River Murray basin, Australia’s largest, has been significantly impacted by changed flow regimes and increased fluxes of salts and sediments since settlement in the 1840s. The river’s flood plain hosts an array of cut-off meanders, levee lakes and basin depression lakes that archive historical changes. Pre-European sedimentation rates are typically approx. 0.1–1 mm year-1, while those in the period after European arrival are typically 10 to 30 fold greater. This increased sedimentation corresponds to a shift in wetland trophic state from submerged macrophytes in clear waters to phytoplankton dominated, turbid systems. There is evidence for a decline in sedimentation in some natural wetlands after river regulation from the 1920s, but with the maintenance of the phytoplankton state. Fossil diatom assemblages reveal that, while some wetlands had saline episodes before settlement, others became saline after, and as early as the 1880s. The oxidation of sulphurous salts deposited after regulation has induced hyperacidity in a number of wetlands in recent years. While these wetlands are rightly perceived as being heavily impacted, other, once open water systems, that have infilled and now support rich macrophyte beds, are used as interpretive sites. The rate of filling, however, suggests that the lifespan of these wetlands is short. The rate of wetland loss through such increased infilling is unlikely to be matched by future scouring as regulation has eliminated middle order floods from the lower catchment. © 2006 IAHS Press
- ItemClimate variability in south-eastern Australia over the last 1500 years inferred from the high-resolution diatom records of two crater lakes(Pergamon-Elsevier Science Ltd, 2014-07-01) Barr, C; Tibby, J; Gell, PA; Tyler, JJ; Zawadzki, A; Jacobsen, GEClimates of the last two millennia have been the focus of numerous studies due to the availability of high-resolution palaeoclimate records and the occurrence of divergent periods of climate, commonly referred to as the 'Medieval Climatic Anomaly' and The Little Ice Age'. The majority of these studies are centred in the Northern Hemisphere and, in comparison, the Southern Hemisphere is relatively understudied. In Australia, there are few high-resolution, palaeoclimate studies spanning a millennium or more and, consequently, knowledge of long-term natural climate variability is limited for much of the continent. South-eastern Australia, which recently experienced a severe, decade-long drought, is one such region. Results are presented of investigations from two crater lakes in the south-east of mainland Australia. Fluctuations in lake-water conductivity, a proxy for effective moisture, are reconstructed at sub-decadal resolution over the past 1500 years using a statistically robust, diatom-conductivity transfer function. These data are interpreted in conjunction with diatom autecology. The records display coherent patterns of change at centennial scale, signifying that both lakes responded to regional-scale climate forcing, though the nature of that response varied between sites due to differing lake morphometry. Both sites provide evidence for a multi-decadal drought, commencing ca 650 AD, and a period of variable climate between ca 850 and 1400 AD. From ca 1400-1880 AD, coincident with the timing of the 'Little Ice Age', climates of the region are characterised by high effective moisture and a marked reduction in interdecadal variability. The records provide context for climates of the historical period and reveal the potential for more extreme droughts and more variable climate than that experienced since European settlement of the region ca 170 years ago. © 2014, Elsevier Ltd.
- ItemClimates 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, GERecords 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
- ItemComparing interglacials in eastern Australia: a multi-proxy investigation of a new sedimentary record(Elsevier, 2021-01-01) Forbes, MS; Cohen, TJ; Jacobs, Z; Marx, SK; Barber, E; Dodson, JR; Zamora, A; Cadd, HR; Franke, A; Constantine, M; Mooney, SD; Short, J; Tibby, J; Parker, A; Cendón, DI; Peterson, MA; Tyler, JJ; Swallow, E; Haines, HA; Gadd, PS; Woodward, CAThe widespread formation of organic rich sediments in south-east Australia during the Holocene (Marine Isotope Stage [MIS] 1) reflects the return of wetter and warmer climates following the Last Glacial Maximum (LGM). Yet, little is known about whether a similar event occurred in the region during the previous interglacial (MIS 5e). A 6.8 m sediment core (#LC2) from the now ephemeral Lake Couridjah, Greater Blue Mountains World Heritage Area, Australia, provides insight into this question. Organic rich sediments associated with both MIS 1 and 5e are identified using 14C and optically stimulated luminescence (OSL) dating techniques. Also apparent are less organic sedimentary units representing MIS 6, 5d and 2 and a large depositional hiatus. Sediment δ13C values (−34 to −26‰) suggests that C3 vegetation dominates the organic matter source through the entire sequence. The pollen record highlights the prevalence of sclerophyll trees and shrubs, with local hydrological changes driving variations in the abundance of aquatic and lake-margin species. The upper Holocene sediment (0–1.7 m) is rich in organic matter, including high concentrations of total organic carbon (TOC; 20–40%), fine charcoal and macrophyte remains. These sediments are also characterised by a large proportion of epiphytic diatoms and a substantial biogenic component (chironomids and midges). These attributes, combined with low δ13C and δ15N values, and C:N ratios of approximately 20, indicate a stable peat system in a swamp like setting, under the modern/Holocene climate. In comparison, the lower organic rich unit (MIS 5e-d) has less TOC (5–10%), is relatively higher in δ13C and δ15N, and is devoid of macrophyte remains and biogenic material. Characterisation of the organic matter pool using 13C-NMR spectroscopy identified a strong decomposition signal in the MIS 5e organic sediments relative to MIS 1. Thus the observed shifts in δ13C, δ15N and C:N data between the two periods reflects changes in the organic matter pool, driven by decompositional processes, rather than environmental conditions. Despite this, high proportions of aquatic pollen taxa and planktonic diatoms in the MIS 5e–d deposits, and their absence in the Holocene indicates that last interglacial Lake Couridjah was deeper and, or, had more permanent water, than the current one. ©2020 Elsevier Ltd.
- ItemA detailed study of Holocene climate variability in south-east Australia based on cellulose inferred lake water isotopes and monitoring and modelling approach at Lake Surprise, western Victoria.(Australasian Quaternary Association Inc., 2022-12-06) Dharmarathma, A; Tyler, JJ; Tibby, J; Barr, C; Cadd, HR; Ankor, MJ; Jones, MD; Tadros, CV; Hua, Q; Child, DP; Zawadzki, A; Hotchkis, MAC; Gadd, PS; Klaeb, RM; Hall, TDuring the Holocene, southeast Australia experienced intense climate conditions including extended droughts. However, knowledge of the frequency and intensity of such episodes is restricted due to the scarcity of quantitative, high-resolution climate records from the region. Where conditions are possible, oxygen isotopes preserved in lake sediments are a useful tool for retracing the past climatic and environment. Here we present a well-dated, highly resolved Holocene record based on δ18O values of aquatic cellulose, alongside organic carbon isotopes and carbon/nitrogen ratios from sediments at Lake Surprise in western Victoria. Our interpretation of the palaeo-data is supported by both monitoring of water and sediment accumulation and lake isotope mass balance modelling to track the modern hydrology of the lake. The lake is highly groundwater dependant alongside its evaporative enrichment of major ions and stable isotopes. The cellulose record indicates a trend of gradually increasing aridity towards the present day, with notable extreme wet periods prevailing from 10900 – 10000, 7600 – 7000 and 5600 – 4500 cal yr BP. the lake represent a significant climate transition to towards aridity at 4500 cal yr BP and remained consistent over the last 4000 years, along with the driest period recorded from 2000 – 1550 cal yr BP. while our record is consistent with other studies from western Victoria, we demonstrate a strong coherence with SWW variability suggesting that the southern Ocean processes were the dominant controls of Holocene climate change at least over the study area. Further, we suggest an increasing influence of ENSO and IOD during the last two millennia. Our record also agrees with the pattern of variation in solar forcing to some extent which may symbolize a connection to proxy data and climate drivers. However, detailed analyses focused on solar activity and climate modes are required to understand teleconnections among these climate drivers and their mechanisms.
- ItemA fine-resolution reconstruction of climatic variability in southeastern Australia over the last 1500 years(18th INQUA Congress, 2011-07-21) Barr, C; Tibby, J; Gell, PA; Jacobsen, GE; Zawadzki, AHigh-resolution palaeoclimate records extend knowledge of long- and short-term climatic variability beyond the limit of instrumental data. However, to date, no millennial-length, sub-decadal resolution climate records have been produced from mainland Australia. In part, this is due to the absence of suitable archives of proxies amenable to high-resolution analysis. Here, we present a study of two crater lakes in western Victoria, southeastern Australia. A diatom-conductivity transfer function was developed specifically for application to oligosaline and mesosaline lakes, such as the two study sites; Lake Elingamite and Lake Surprise. A sub-decadal resolution sampling regime was undertaken and results demonstrate that over the past 1500 years, both lakes responded to a common regional-scale climate signal. Reconstructed conductivity, a proxy for moisture balance, indicates distinct periods of contrasting climates. Both lakes record evidence of a severe, and prolonged, dry phase centered around AD 700, which was more extreme than any subsequent drought. Between ca. AD 900 and 1500, the climate was highly variable, with substantial fluctuations in effective moisture. Thereafter, a period of positive moisture balance is evident from ca. AD 1500-1850, with a marked reduction in the amplitude of variability. Correlations with studies from further afield suggest that ENSO, and possibly the Indian Ocean Dipole, are the key drivers of the observed shifts in moisture balance. These records constitute the first high-resolution evidence of centennial- and decadal-scale climatic variability over the last 1500 years from mainland Australia. This enables a recent major drought to be viewed in an historical context for the first time and provides insight into past climate regimes across southeastern Australia in general, and western Victoria in particular.Copyright (c) 2011 INQUA 18
- ItemFire and ecosystem change on Kangaroo Island, South Australia, over the past 5,000 years(2021-07-08) Duxbury, LC; Tyler, JJ; Ambrecht, LH; Francke, A; Cadd, HR; Law, WB; Zawadzki, A; Child, DP; Gadd, PS; Jacobsen, GE; Tibby, J; Mitchell, KJFire has long been a familiar and important part of Australian landscapes. However, anthropogenic climate change has heralded major shifts in fire regimes, negatively impacting ecosystems. These effects are expected to worsen in coming years, but there remain difficulties with projecting fire regime trajectories and their environmental impacts, in part due to a lack of data on centennial to millennial timescales. Uncertainties remain concerning the independent effects of climate and human impact on bushfires, and the long term impacts of fire on both terrestrial and aquatic ecosystems. This study aims to address these uncertainties by returning to Lashmars Lagoon, Kangaroo Island, a site of pioneering palaeoenvironmental research in South Australia. Kangaroo Island presents a fascinating case study, due to the putative abandonment of the island by ancient Aboriginal populations 2,450 ± 300 cal yrs BP. As such, it represents a unique opportunity to study the impact of cessation of Aboriginal management practices on ecosystems prior to European invasion. We collected sediment cores from Lashmars Lagoon, which we estimate to span the past 5,000 years. We are combining multiple palaeoecological and geochemical proxies to infer both fire and hydroclimate variability, augmented by an age model based on Pb-210, Pu isotopic profiling and C-14 dating. We will also analyse sedimentary ancient DNA (sedaDNA), which we hope will provide novel insights into the occurrence of taxa not usually detected through conventional palaeoecology. Our aim is to provide insights into the drivers of palaeofire and ecosystem response to changing fire regimes, with relevance to contemporary bushfire predictability and environmental management. For this conference, we will present preliminary data with a particular focus on the recent historical period. The potential and challenges of using lake sedaDNA in an Australian context will also be discussed. © The Authors.
- ItemA 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, FGlobal 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.
- ItemHolocene climate variability in south east Australia; inferred from oxygen isotopes in sedimentary cellulose at Lake Surprise, Victoria(European General Assembly, 2022-05-23) Dharmarathna, A; Tyler, JJ; Barr, C; Tibby, J; Jones, MD; Anjor, MJ; Cadd, HR; Gadd, PS; Hua, Q; Child, DP; Zawadski, A; Hotchkis, MAC; Zolitschka, BSouth east Australia experienced periods of multi-year droughts particularly within the last 2 millennia. However, given the limited evidence from smaller number of sites and scarcity of quantitative, high-resolution climate records, it is largely unknown whether these droughts are a feature of climate through the Holocene and the extent to which they are experienced throughout the region. Where conditions are suitable, oxygen isotopes preserved in lake sediments are a useful tool for reconstructing past climate and environmental conditions. Here, we present preliminary results of a Holocene length record from Lake Surprise in western Victoria, from which we analysed δ18O of aquatic cellulose as a proxy for lake-water δ18O, complemented by organic carbon/nitrogen ratios, organic carbon isotopes and XRF (ITRAX) inferred elemental composition. Our interpretation of the palaeo-data is supported by ~3 monthly monitoring of water and sediment geochemistry to track the modern hydrology of the lake. Our preliminary results show a strong positive correlation between precipitation and sedimentary calcium (carbonate deposition) over the last 150 years, likely linked to changes in primary productivity. The aquatic cellulose δ18O record through Holocene is also correlated with carbonate concentration, reinforcing our interpretation of CaCO3 deposition in the lake during wet periods. The cellulose δ18O record indicates a trend of gradually increasing aridity from early to late Holocene, with a notable extremely dry phase over the last 2 ka. Comparison of the cellulose δ18O record with high-resolution Holocene climate records indicates that multiple climate drivers such as ENSO intensification and Antarctic warming are strongly linked to increasing aridity of the region. Further work will focus on both increasing the resolution of the record to better identify the frequency and duration of key events and on quantifying natural hydroclimate variability, particularly via lake hydrologic modelling to better constrain the paleoclimate record. © Author(s) 2022. Creative Commons Attribution 4.0 Licence.
- ItemHolocene climate variability in south-eastern Australia; inferred from oxygen isotopes in sedimentary cellulose at Lake Surprise, Victoria(Australasian Quaternary Association (AQUA), 2021-07-08) Dharmarathna, A; Tyler, JJ; Barr, C; Tibby, J; Jones, MD; Ankor, MJ; Gadd, PS; Hua, Q; Child, DP; Zawadzki, A; Hotchkis, MAC; Zolitschka, B; Cadd, HRDuring the Holocene, south-eastern Australia experienced periods of multi-year drought. However, the scarcity of quantitative, high-resolution climate records from the region means understanding of the frequency and intensity of such events is limited. Where conditions are suitable, oxygen isotopes preserved in lake sediments are a useful tool for reconstructing past climate and environmental conditions. Here, we present preliminary results from a ca. 8700 ka record from Lake Surprise in western Victoria, from which we analysed δ18O of aquatic cellulose, alongside organic carbon/nitrogen ratios, organic carbon isotopes and XRF (ITRAX) inferred elemental composition. Our interpretation of the palaeo- data is supported by ~3 monthly monitoring of water and sediment geochemistry to track the modern hydrology of the lake. Our preliminary results show a strong positive correlation between meteorological precipitation data and sedimentary calcium (carbonate deposition) over the last 150 years, likely linked to changes in primary productivity. As a proxy for lake-water δ18O, the aquatic cellulose δ18O record is also correlated with carbonate concentration, reinforcing our interpretation of CaCO3 deposition in the lake during wet periods. The cellulose δ18O record indicates a trend of gradually increasing aridity over the last 8 ka, with a notable extremely wet period ca. 7.5–7 ka and a dry period ca 2–1.5 ka. Further work will focus on increasing the resolution of the data to better identify the frequency and duration of key events and quantifying natural hydroclimatic variability, alongside continued geochemical monitoring and modelling to better constrain the interpretation of the palaeoclimate record.
- ItemHolocene climate, fire and ecosystem change on Kangaroo Island, South Australia(Australian Nuclear Science and Technology Organisation, 2021-11-17) Duxbury, LC; Tyler, JJ; Armbrecht, L; Francke, A; Cadd, HR; Law, WB; Zawadzki, A; Child, DP; Gadd, PS; Jacobsen, GE; Tibby, J; Mitchell, KIntroduction Fire has long been a familiar and important part of Australian landscapes. However, anthropogenic climate change has heralded major shifts in fire regimes, negatively impacting ecosystems. These effects are expected to worsen in coming years, but there remain difficulties with projecting fire regime trajectories and their environmental impacts, in part due to a lack of data on centennial to millennial timescales. Uncertainties remain concerning the independent effects of climate and human impact on bushfires, and the long term impacts of fire on both terrestrial and aquatic ecosystems. Aims This study aims to address these uncertainties by returning to Lashmars Lagoon, Kangaroo Island, a site of pioneering palaeoenvironmental research in South Australia that has been overlooked in recent decades. Kangaroo Island presents a fascinating case study, due to the putative abandonment of the island by ancient Aboriginal populations ~ 2,500 years ago. As such, it represents a unique opportunity to study the impact of cessation of Aboriginal management practices on ecosystems prior to European invasion. Methods We collected a ~ 7.5 metre long sediment core from Lashmars Lagoon, which we expected, from the work of previous studies, to span the past 5,000 years. We are combining multiple traditional and novel palaeoecological and geochemical proxies to infer both fire, catchment and ecosystem variability, augmented by an age model based on Pb-210, Pu isotopic profiling and C-14 dating. Results Our preliminary age model determined our core to span the past ~ 7,000 years, an adjustment to previous estimates. Our model is based on the radiocarbon dating of 6 plant macrofossils, 2 pollen samples and 1 shell. The pollen dates concur well with the plant macrofossils. The shell demonstrates an older age than the other samples from a similar horizon, a 'reservoir effect' that is expected from the integration of older carbon into the sample. The model also integrates 15 Pb-210 dates from the uppermost 30 cm, verified by the establishment of a nuclear bomb testing peak from Pu isotopic profiling. The broad peak detected in the Pu profile is also worthwhile of mention. Further interrogation of this phenomenon could be useful to infer certain processes the uppermost sediments, such as bioturbation, lateral leaching of Pu in the sediment or disturbance from the coring process. Overall, the age model indicates a constant rate of sedimentation approximately 1 mm/yr across the entire length of the, a somewhat surprising result given the considerable variation in sedimentology. Conclusions The development of a robust age model is integral to the interpretation of environmental, geochemical and climatic proxies at Lashmars Lagoon, South Australia. Importantly, the better constraint of our age model improves certainty around the timing of the human exodus from Kangaroo Island and the resultant discontinuation of Indigenous fire management. © The Authors
- ItemHolocene 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, FHThe 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
- ItemHolocene 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, PSLakes 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.
- ItemA Holocene subtropical hydroclimate reconstruction from Karboora (Blue Lake), Minjerribah, Queensland(Australasian Quaternary Association, 2022-12-06) Maxson, C; Tibby, J; Tyler, JJ; Marshall, J; McGregor, G; Schulz, C; Jacobsen, GE; Klaebe, RMHolocene 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.
- ItemA 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, RHolocene 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.
- ItemHolocene ‘megadroughts’ in south-eastern Australia: deciphering regional patterns from lake sediment archives(European Geosciences Union (EGU), 2020-05-04) Tyler, JJ; Barr, C; Tibby, J; Dhar, A; Andrew, C; Dean, C; Gadd, PS; Zawadzki, A; Child, DP; Jacobsen, GEDocumenting and understanding centennial scale hydroclimatic variability in Australia is significant both to global climate science and to regional efforts to predict and manage water resources. In particular, multidecadal to centennial periods of low rainfall – ‘megadroughts’ – have been observed in semi-arid climates worldwide, however they are poorly constrained in Australia. Here, we bring together multiple, sub-decadally resolved records of hydrological change inferred from lake sediments in western Victoria, Australia. Our analyses incorporate new elemental (ITRAX μXRF) and stable isotope (oxygen, carbon isotopes) geochemical data from West Basin and Lake Surprise, both augmented by high quality radiometric chronologies based on radiocarbon, 210Pb and 239/240Pu analyses. Collectively, the records document a transition towards a more arid and variable climate since the mid-late Holocene, which is comparable to reports of an intensification of the El Nino Southern Oscillation (ENSO) through this period. Furthermore, during the last 2000 years, the records exhibit marked periods of reduced effective moisture which contrast with records of Australian hydroclimate inferred from distal archives, as well those predicted by climate model hindcasts. Our analyses indicate that megadroughts are a natural phenomenon in southeastern Australia, requiring greater attention in efforts to predict and mitigate future climatic change. © Author(s) 2021 Creative Commons Attribution 4.0 License.
- ItemIndependent 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, PSRigorously 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
- ItemInsights 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, YTerrestrial 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