Browsing by Author "Tyler, JJ"

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    A 1000-year isotope-based record of climate variability inferred from the sediments of Lake Yukidori, East Antarctica
    (Australasian Quaternary Association Inc., 2022-01-06) Toben, L; Rudd, R; Jacobsen, GE; Tyler, JJ
    Anthropogenic contributors to global warming are extensively altering climate and ice melt patterns in the polar regions. The Antarctic ice sheet is responsible for aspects of global climate regulation. It is vital to construct a comprehensive model of historical climate fluctuations and their consequences in the region, to effectively predict future scenarios under the current climate regime. To supplement detailed ice core records, Antarctic coastal lake sediments are a valuable paleoclimate and hydrological proxy, providing alternative indicators of environmental and climatic changes in ice-free areas. Here, we analysed a sediment core from Lake Yukidori on the Langhovde Peninsula of East Antarctica. The Yukidori sediments consist of organic rich sediments, mostly derived from aquatic mosses which grow on the lake floor. The lake itself is freely drained and freshwater, receiving water from snowmelt in a relatively small, mountainous catchment. Bulk sediment carbon and nitrogen concentration and carbon, nitrogen and oxygen stable isotope ratios were used to infer changes in lake primary productivity and the oxygen isotope composition of precipitation over the last 1000 years. The 18O/16O data exhibit marked centennial-scale variability and no marked change in the recent, post-industrial period. 15N/14N data, by contrast, suggest a notable increase in lake primary productivity in the last century, possibly a result of an increase in the seasonal ice-free period. Further work is needed to improve the chronology of the recent sediments at Lake Yukidori, and to validate these proxies in this remote environment.
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    The 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, LJ
    Wetland 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
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    Changes in hydrology and carbon cycling following Late Holocene deforestation in a New Zealand lake catchment
    (European Geosciences Union (EGU), 2018-04-13) Woodward, CA; Hua, Q; Tyler, JJ; Meredith, KT; Moss, PT; Gadd, PS; Zawadzki, AW
    New Zealand was one of the last major land masses to be impacted by humans, with two waves of settlement occurring in the last 800 years. Polynesian (Maori) settlers arrived in New Zealand ca. 1250 A.D., while major European settlement occurred after 1840 A.D. A major impact of both phases of settlement was clearance of indigenous forest. An increasing number of pollen and macroscopic charcoal records reveal the timing and extent of past forest clearance in New Zealand. Only a few records explore the wider implications of this land use change in terms of catchment biogeochemical cycles and aquatic ecosystem functioning. We used multiple proxies from a lake sediment core from a cleared catchment to explore changes in catchment hydrology and carbon cycling after forest clearance. One of the most interesting findings emerged from paired radiocarbon dates on terrestrial targets (e.g. leaves and charcoal) and seeds from the aquatic plant Myriophyllum. The offset between terrestrial and aquatic radiocarbon ages increased to 1000 years and then decreased to 100 years within three centuries of local Maori forest clearance. There was a further increase in the radiocarbon age offset to 1500 radiocarbon years within decades of the start of the European forest clearance. We argue that the offset between terrestrial and aquatic radiocarbon ages results from an increased contribution of old dissolved inorganic carbon from groundwater to the lake after forest clearance. Forest clearance reduced evapotranspiration, increased aquifer recharge and increased the contribution of groundwater to the lake. This interpretation is supported by a major increase in the δ 13C of Myriophyllum seeds following Maori deforestation. At the time of abstract submission the results are pending for δ 18O analysis on Myriophyllum seeds and aquatic insects. This will provide a further test for changes in catchment hydrology following deforestation. Reviews of catchment impacts on hydrology and carbon cycling have shown an increased catchment water yield and flux of old carbon in disturbed catchments. Our study provides one of the most comprehensive records of forest clearance and provides valuable insights into the causal mechanisms and consequences of these changes. © Author(s) 2018. CC Attribution 4.0 license.
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    Climate 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, AW; Jacobsen, GE
    Climates 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.
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    Clumped isotope analysis of Central Australian carbonates: a potential palaeoclimate proxy for Australia’s arid interior
    (American Geophysical Union (AGU), 2022-12-13) Nixon, F; Tyler, JJ; Priestley, SC; Cohen, TJ; Klaebe, RM; Crossey, LJ; Karlstrom, KE; Polak, VJ; Asmerom, Y; Love, AJ; Hua, Q; Wade, B; Pollard, T; Drysdale, RN; Hall, PA
    Quantitative records of past temperature variability in arid environments are crucial for validating climate models and their ability to capture the full range of the Earth’s climatic regions. However, arid zone temperature reconstructions are rare, particularly in the Southern Hemisphere, including Australia. The clumped isotope thermometer provides a novel approach to potentially address this demand by allowing the estimation of carbonate precipitation temperature independent of environmental water isotopic composition. Two types of carbonate materials offer potential for clumped isotope temperature reconstructions in arid central Australia: fossil mollusk shells deposited within the shoreline sediments of now dry lakes, and tufa deposits formed in mound springs fed by continuous discharge of Great Artesian Basin groundwater. Here we present preliminary clumped isotope analyses from tufa and shell samples from central Australia. We also discuss the use of micro-XRF scanning and XRD to evaluate sample suitability for both clumped isotope analysis and U-series dating. Air temperatures inferred from tufa Δ47 measurements suggest mean annual air temperatures (MAAT) ~5°C cooler than present between 12-9 ka, which supports palaeoclimate model based estimates for central Australia. Average air temperatures inferred from mollusk shells indicate MAAT at least 15°C cooler than present during 70-35 ka, suggesting a larger MAAT reduction than previously estimated. Carbonate δ18O appears to have been largely driven by changes in environmental water δ18O for lakes but not for mound springs, reflecting different hydrological controls on the two water sources. Agreement between temperatures and palaeoclimate models suggest clumped isotope analysis may function as a valuable quantitative palaeotemperature proxy in central Australia. Analysis of additional tufa and shell samples along with an investigation of the genesis of different tufa is ongoing.
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    Clumped isotope analysis of central Australian carbonates: a potential palaeoclimate proxy for Australia’s arid interior
    (Australasian Quaternary Association Inc., 2022-12-06) Nixon, F; Tyler, JJ; Priestley, SC; Cohen, TJ; Klaebe, RM; Crossey, L; Karlstrom, KE; Polyak, V; Asmerom, Y; Love, AJ; Hua, Q; Wade, B; Pollard, T; Drysdale, R; Hall, PA
    Quantitative records of past temperature variability in arid environments are crucial for validating climate models and their ability to capture the full range of the Earth’s climatic regions. However, arid zone temperature reconstructions are rare, particularly in the Southern Hemisphere, including Australia. The clumped isotope thermometer provides a novel approach to potentially address this demand by allowing the estimation of carbonate precipitation temperature independent of environmental water isotopic composition. Two types of carbonate materials offer potential for clumped isotope temperature reconstructions in arid central Australia: fossil mollusk shells deposited within the shoreline sediments of now dry lakes, and tufa deposits formed in mound springs fed by continuous discharge of Great Artesian Basin groundwater. Here we present preliminary clumped isotope analyses from tufa and shell samples from central Australia. We also discuss the use of micro-XRF scanning and XRD to evaluate sample suitability for both clumped isotope analysis and U-series dating. Air temperatures inferred from tufa Δ47 measurements suggest mean annual air temperatures (MAAT) ~5°C cooler than present between 12-9 ka, which supports palaeoclimate model based estimates for central Australia. Average air temperatures inferred from mollusk shells indicate MAAT at least 15°C cooler than present during 70-35 ka, suggesting a larger MAAT reduction than previously estimated. Carbonate δ18O appears to have been largely driven by changes in environmental water δ18O for lakes but not for mound springs, reflecting different hydrological controls on the two water sources. Agreement between temperatures and palaeoclimate models suggest clumped isotope analysis may function as a valuable quantitative palaeotemperature proxy in central Australia. Analysis of additional tufa and shell samples along with an investigation of the genesis of different tufa is ongoing.
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    Clumped isotope analysis of central Australian carbonates: a potential palaeoclimate proxy for Australia’s arid interior
    (Australasian Quaternary Association Inc., 2022-12-06) Nixon, F; Tyler, JJ; Priestley, SC; Cohen, TJ; Klaebe, RM; Crossey, LJ; Karlstrom, KE; Polyak, VJ; Asmerom, Y; Love, A; Hua, Q; Wade, B; Pollard, T; Drysdale, RN; Hall, PA
    Quantitative records of past temperature variability in arid environments are crucial for validating climate models and their ability to capture the full range of the Earth’s climatic regions. However, arid zone temperature reconstructions are rare, particularly in the Southern Hemisphere, including Australia. The clumped isotope thermometer provides a novel approach to potentially address this demand by allowing the estimation of carbonate precipitation temperature independent of environmental water isotopic composition. Two types of carbonate materials offer potential for clumped isotope temperature reconstructions in arid central Australia: fossil mollusk shells deposited within the shoreline sediments of now dry lakes, and tufa deposits formed in mound springs fed by continuous discharge of Great Artesian Basin groundwater. Here we present preliminary clumped isotope analyses from tufa and shell samples from central Australia. We also discuss the use of micro-XRF scanning and XRD to evaluate sample suitability for both clumped isotope analysis and U-series dating. Air temperatures inferred from tufa Δ47 measurements suggest mean annual air temperatures (MAAT) ~5°C cooler than present between 12-9 ka, which supports palaeoclimate model based estimates for central Australia. Average air temperatures inferred from mollusk shells indicate MAAT at least 15°C cooler than present during 70-35 ka, suggesting a larger MAAT reduction than previously estimated. Carbonate δ18O appears to have been largely driven by changes in environmental water δ18O for lakes but not for mound springs, reflecting different hydrological controls on the two water sources. Agreement between temperatures and palaeoclimate models suggest clumped isotope analysis may function as a valuable quantitative palaeotemperature proxy in central Australia. Analysis of additional tufa and shell samples along with an investigation of the genesis of different tufa is ongoing.
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    Coherent patterns of environmental change at multiple organic spring sites in northwest Australia: evidence of Indonesian-Australian summer monsoon variability over the last 14,500 years
    (Elsevier, 2018-09-15) Field, E; Tyler, JJ; Gadd, PS; Moss, PT; McGowan, HA; Marx, SK
    At present, knowledge of late Quaternary variability of the Indonesian-Australian summer monsoon in the Australian tropics is limited. Organic spring deposits, which occur throughout the Kimberley region of northwest Australia, are valuable archives that contain records spanning the past ∼14,500 years. In this study we compare multiple proxies from three organic springs. Principal Components Analyses demonstrates similar patterns of change in the elemental and non-pollen palynomorph (NPP) datasets between the springs, implying regional drivers are responsible for changes in these proxies. By comparison, the pollen records differ between each of the springs, with the assemblage at each thought to be influenced by spring recharge and evolution rather than climate variability. In order to empirically and objectively assess the synchronicity of changes, we applied Monte Carlo empirical orthogonal function (MCEOF) analysis to one variable in each μXRF and NPP dataset (Si/Ti ratios and Pseudoschizaea accumulation rates, as these proxies are expected to reflect hydrological conditions in springs) to assess regional patterns of change in site moisture. This analysis revealed periods of increased monsoonal precipitation from ∼14,500–7500 cal. yr BP corresponding with deglacial sea level rise, high orbital tilt coupled with warmer sea surface temperatures, and with possible links to a southward migration of the Inter Tropical Convergence Zone (ITCZ) during the Younger Dryas. Monsoonal precipitation was reduced from 7500 cal. yr BP coinciding with the culmination of deglacial sea level rise and a possible northward shift in the mean position of the ITCZ, in addition to between 2600 and 1000 cal. yr BP corresponding with increased moderate-to-strong ENSO events. ©2018 Elsevier Ltd
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    Comparing 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, CA
    The 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.
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    A 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, AW; Hotchkis, MAC; Gadd, PS; Klaeb, RM; Hall, T
    During 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.
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    Development of an autonomous, monthly and daily, rainfall sampler for isotope research
    (Elsevier B. V., 2019-08) Ankor, MJ; Tyler, JJ; Hughes, CE
    An autonomous, low cost (
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    Ecology and climate sensitivity of a groundwater-fed lake on subtropical North Stradbroke Island (Minjerribah), Queensland, Australia over the last 7500 years
    (Springer Nature, 2022-01) Maxson, C; Tibby, J; Barr, C; Tyler, JJ; Leng, MJ; Lomax, B; Marshall, J; McGregor, G; Schulz, C; Cadd, H; Jacobsen, GE
    Lake sediments are important archives of past climate variability and lake responses to climate. In order to accurately infer past climates, it is necessary to understand, and account for, the ecological processes that affect the record of indicators preserved in lake sediment. This is particularly the case with respect to the concentration of carbon and nitrogen (TOC, TN, and calculated C:N), and the stable isotope composition of organic matter preserved in lake sediments. These are common, yet ambiguous, tracers of environmental change. Ideally, palaeoenvironmental reconstructions using the concentration and isotope composition of organic matter should be grounded in a detailed understanding of the sources of the organic material. This study documents the history and evolution of Blue Lake, an environmentally and culturally important oligotrophic, groundwater window lake on North Stradbroke Island, Queensland, Australia. We utilise organic matter δ13C, TOC, TN, and C:N from a 2.4 m sediment core with a basal age of 7.5 cal kyr BP, to investigate changing organic matter sources as a measure of the climate sensitivity of Blue Lake. This interpretation is supported by data from contemporary algae, aquatic and terrestrial plants, and catchment soils. We show that lake nutrient dynamics drove an increase in algal biomass at 4.2 cal kyr BP. This change coincides with a widely documented intensification of the El Niño-Southern Oscillation, which we infer to have influenced lake nutrient concentrations by reducing groundwater throughflow. Climatic changes resulted in marked changes in lake primary productivity, despite relatively little turnover of the lake diatom flora and catchment vegetation. This suggests that south-east Queensland dune lakes are sensitive to climate changes and helps to refine past and future palaeoclimate research using sediments from these lakes. It also indicates that increased nutrient concentrations in Blue Lake may result from projected changes in 21st Century climate. © 2024 Springer Nature.
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    The evolution of Thirlmere lakes: a long-term sedimentary record of climate and fire dynamics in the Sydney Basin
    (Australasian Quaternary Association Inc., 2018-12-10) Cohen, TJ; Marx, SK; Barber, E; Forbes, MS; Gadd, PS; Tyler, JJ; Haines, HA; Woodward, C; Zamora, A; Mooney, SD; Constantine, M
    The Thirlmere lakes are located 40 km from the coast and are at ~300 m elevation and fall within the Greater Blue Mountains World Heritage area. The series of five lakes sit within a narrow and sinuous former river valley within the Hawkesbury sandstone with surrounding dry sclerophyll forest. Recent declines in water levels have prompted the NSW Office of Environment and Heritage to fund research about the history of Thirlmere lakes, the sub-surface characteristics and the potential frequency of past drying. This research builds on some existing work and has highlighted the extraordinary potential for the region for a long-term archive for palaeoenvironmental research.To date we have taken multiple vibracores across three lakes to depths of 7 m and we have supplemented this with some preliminary deep drilling to depths of 14 m. Our initial chronology is based on radiocarbon and OSL and we have employed a raft of geochemical and palaeoecological techniques to investigate changes through time. The lakes contain excellent organic preservation with deposition of the ‘modern’ peat environments commencing ~11 ka across two of the lakes investigated. This phase is represented by the upper 2 -3 m of organic rich peat (50% TOC). The underlying sediments are a mix of weakly bedded organic clays and oxidised clay facies that represent lake-wide drying intervals, a sequence that is repeated down profile. All five lakes are separated by alluvial sills that are comprised of medium to well-sorted sands, interbedded with organic ‘marker’ horizons that indicate these separate lakes were once joined, prior to the Last Glacial Maximum. The sandy sills that separate the lakes are derived from tributary alluvial fans accumulating progressively over the Holocene and effectively blocking and separating the lakes into their current configuration. This paper provides a preliminary overview of the chrono-stratigraphic history of Thirlmere lakes. © The Authors
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    Fire 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, AW; Child, DP; Gadd, PS; Jacobsen, GE; Tibby, J; Mitchell, KJ
    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. 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.
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    First Holocene cryptotephras in mainland Australia reported from sediments at Lake Keilambete, Victoria, Australia
    (Elsevier, 2017-05) Smith, RE; Tyler, JJ; Reeves, JM; Blockley, S; Jacobsen, GE
    We report the first observations of Holocene cryptotephra deposits in lacustrine sediments from mainland Australia. All counts of cryptotephra shards are presented, but we focus on two prominent peaks of dark coloured glass shards representing distinct cryptotephras within the sediments of Lake Keilambete, Victoria, southeast Australia. These two basaltic cryptotephras, aged 4589-3826 cal BP and 7149-5897 cal BP, may have derived from eruptions of Mts Gambier or Schank, South Australia. In addition, colourless shards, most likely of silicic composition and therefore unlikely to emanate from an Australian volcano were observed, suggesting a distant volcanic source beyond Australia. The presence of both the ‘local’ basaltic shards and the distal silicic shards highlights the potential to identify isochronous marker horizons in southern Australian sediments, thus potentially enabling a long-term goal of establishing a novel chronostratigraphic tool based on a cryptotephra network. © 2016 Elsevier B.V.
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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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    Holocene 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; Zawadzki, AW; Hotchkis, MAC; Zolitschka, B
    South 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.
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    Holocene 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, AW; Hotchkis, MAC; Zolitschka, B; Cadd, HR
    During 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.
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    Holocene 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, AW; Child, DP; Gadd, PS; Jacobsen, GE; Tibby, J; Mitchell, K
    Introduction 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
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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